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Physics

 


Ruga Mechanics of Folding Atomic-Layer Nanostructures.

Professor Kyung-Suk Kim,

Institute of Molecular and Nanoscale Innovation, Brown University.
 

Monday, October 20, 2014, 3:00-4:00pm (Refreshments will be served at 2:30).

<Special Location!!>  271 Batcheller Technology Center

When one folds a thin solid film that is only a few atoms thick, such as graphene, the film properties can be controlled for various functions. For example, a simple compression of the folded film can change optical, electrical, wetting and adhesion characteristics of the film, and can be used for making multifunctional materials such as transparent electric circuits, self-cleaning surfaces, oil-spill cleaning cloths and self-adjusting friction grips. Such atomic-layer nanostructures can be folded and self-organized by nonlinear large deformation of soft material substrates. In particular, nano science and technology has enabled us to explore new functional properties of hierarchically ruga-structured materials through folding or wrapping thin atomic-layer structures with nanometer scale features. The Latin word ruga means a state of a “large-amplitude” wrinkle, crease, fold or ridge to form various 1-D or 2-D patterns. As multi-scale surface morphologies of rugae determine effective properties such as wetting, adhesion, friction, flexoelectric and optoelectronic properties, ruga state control is considered as a viable method for real-time regulation of effective material properties. It is found that graded or layered elastic properties of the substrate can provide diverse bifurcation paths of the attached atomic-layer deformation under lateral compression, producing various atomic-layer ruga states. Nonlinear mechanics of soft-material substrate enables us to construct ruga-phase diagrams. As an example, a mathematical analysis of sequential bifurcation processes of hyper-elastic neo-Hookean substrates is used to construct generic ruga-phase diagrams. When an atomically layered structure such as multi-layer graphene is folded by ruga control, nano-scale crinkles are generated. In general, nano-scale crinkle ridges are invisible to conventional AFM due to its peculiar flexoelectric properties. Here, a new invention of “Dual-Tip AFM Interferometer” (DT-AFMI) will be introduced, which makes the invisible visible. The DT-AFMI image reveals that the crinkle ridge of a multi-layer graphene has its ridge width less than 1.8nm. The nano-crinkle ridges have strong flexoelectric characteristics, and the crinkle ridge networks of the top graphene layer exhibit high molecular adsorptivity. Potential applications of such high molecular adsorptivity localized along the nano-ridges will be discussed as well.

For more information, contact Erik K. Hobbie, 701-231-6103, erik.hobbie [at] ndsu [dot] edu

Ab initio electron dynamics at metal–semiconductor nano-interfaces.

Dr. Dmitri Kilin

Assistant Professor of Chemistry, University of South Dakota
 

FRIDAY, September 26, 2014, 3:00-4:00pm (Refreshments will be served at 2:30).

221 South Engineering

Photo-induced charge transfer at the interface of two materials is a fundamental process in (i) photovoltaic and (ii) photocatalytic applications. The photo-induced time-dependent electron dynamics are computed for different interfaces by a combination of ab initio electronic structure and time-dependent density matrix methodology. A dissipative equation of motion for the reduced density matrix for electronic degrees of freedom is used to study the phonon-induced relaxation of hot electrons in the simulated systems. Non-adiabatic couplings between electronic orbitals are computed on-the-fly along nuclear trajectories. Equations are solved in a basis set of orbitals generated ab initio from a density functional.[1] For an application to photovoltaic effect, one explores light-induced electric current in a model of a simplified photovoltaic cell composed of a Si nano-crystal co-doped with p-and n- type doping, interfacing with Au electrodes. Charge carrier dynamics induced by selected photo-excitations show that hole relaxation in energy and in space is much faster than electron relaxation. Use of the continuity equation for electric current allows to identify substantial local currents at the Si/Au interfaces and small overall net charge transfer across the slab. [2] For an application to photocatalytic water splitting, charge transfer dynamics is explored at the interface of supported metal nanocluster and liquid water. The metal cluster introduces new states into the band gap of semiconductor TiO2 surface, narrows the band gap of TiO2, and enhances the absorption strength. The H2O adsorption significantly enhances the intensity of photon absorption, which is due to the formation of metal−oxygen (water) coordination bonds at the interfaces. The metal cluster promotes the dissociation of water, facilitates charge transfer, and increases the relaxation rates of holes and electrons. [3] Reported results help in understanding basic photophysical and protochemical processes contributing to harvesting solar energy by photovoltaics and photoelectrochemical water splitting.

1. Huang, S.; Kilin, D. S., Charge Transfer, Luminescence, and Phonon Bottleneck in TiO2 Nanowires Computed by Eigenvectors of Liouville Superoperator. J. Chem. Theor. Computation 2014, 10 (9), 3996-4005.

2. Han, Y.; Micha, D.; Kilin, D., Ab initio study of the photocurrent at the Au/Si metal semiconductor nano-interface. Mol. Phys. 2014, in print, DOI: 10.1080/00268976.2014.944598.

3. Huang, S.; Inerbaev, T. M.; Kilin, D. S., Excited state dynamics of Ru10 cluster interfacing anatase TiO2(101) surface and liquid water. J. Phys. Chem. Lett. 2014, 5, 2823–2829.

Spring 2014 Seminars

Date

Title

Author

January 20, 2014

Martin Luther King Jr. Day

January 27, 2014

A Tale of Two Colloids: Order and Disorder on a Soft Substrate.

Andrew B. Croll

February 3, 2014

Molecular Simulation of Physical Aging in Ultrathin Polymer Films

Qiyun Tang

February 10, 2014

Multiple Exciton Generation in Nanometer-sized Silicon Nanoparticles

Andrei Kryjevski

February 17, 2014

President's Day

February 24, 2014

PreAPS Blitz.

Bekele, Damith, others!

March 3, 2014

APS March Meeting

March 10, 2014

MacKenzie Steltzer

March 17, 2014

Spring Break

March 24, 2014

Determination of pK Values of Ionizable Residues in Pentapeptides and in SNase protein.

Guilherme Volpe Bossa

March 31, 2014

April 7, 2014

Following molecules out of equilibrium: From the formation of nanoparticles to the complex behavior of strongly driven systems.

Jerome Delhommelle

April 14, 2014

Coherent Raman Standoff Detection with Shaped Femtosecond Pulses

Marshall Bremer

April 21, 2014

Holiday

April 28, 2014

Answer First: Applying the heuristic-analytic theory of reasoning to examine student intuitive thinking in the context of physics

Mila Kryjevskaia

May 5, 2014

Hyperspectral Imaging: Optical System Design Considerations for an orbiting imaging Fourier Transform Spectrometer

Bruce Rafert

May 12, 2014

Excitons in Nanoscale Semiconductor Structures from the Bethe-Salpeter Equation

Deyan Mihaylov

May 19, 2014

Bacterial Adhesion on Material Surfaces

Klemen Bohinc

 

 

Bacterial Adhesion on Material Surfaces.

Dr. Klemen Bohinc

Faculty of Health Sciences, University of Ljublijana, Slovenia
 

Monday, May 19, 2014, 3:30-4:30pm (Refreshments will be served at 3:00).

221 South Engineering

Bacterial adhesion can be controlled by different material surface characteristics like surface roughness, on which we concentrate in our study. Different glass surfaces were prepared by polishing the glass plates with different gradations. The corresponding surface roughness was controlled by atomic force microscope and profilometer.  The rate of adhered bacteria on glass surfaces was determined with spectrophotometer and scanning electron microscopy. Our results showed that the rate of adhered bacteria increases with increasing surface roughness. The increased adhesion of bacteria on more rough surfaces is the interplay between the increasing effective surface and increasing number of defects on the surface.

Excitions in Nanoscale Semiconductor Structures from the Bethe-Salpeter Equation.

Deyan Mihaylov

Department of Physics, North Dakota State University
 

Monday, May 12, 2014, 3:00-4:00pm

221 South Engineering

Deyan is a graduate student working with Andrei Kryjevski

 

Excitons are bound states of electrons and holes held together by Coulomb attraction. In semiconductor nanoparticles of size comparable to or smaller than the Exciton-Bohr radius excitons have significant effect on the density of states of the system. The standard way of calculating energies and wave functions of excitons is to solve the Bethe Salpeter equation (BSE) in the basis of Kohn-Sham (KS) orbitals and energies, the output of Density Functional Theory. In this work, we derive BSE using basic tools of many body quantum mechanics. Namely, we compute the matrix of the full, interacting Hamiltonian in the basis of electron-hole KS states, and, in particular, derive direct and exchange Coulomb terms present in the standard BSE. The method is then applied to calculating energies and wave functions of low energy excitons in a nm-sized Hydrogenated crystalline Silicon quantum dot.

 

Spectroscopic Studies of the Jovian Magnetosphere and the Atmospheres of the Galilean Satellites with Voyager, Cassini and Hubble Space Telescope.

Dr. Darrell Strobel

Departments of Earth & Planetary Sciences and Physics & Astronomy, The Johns Hopkins University
 

Wednesday, April 30, 2014, 3:00-4:00pm (Refreshments will be served at 2:30).

Special Location - 271 Batcheller Technology Center

 

This talk will review remote sensing measurements of the Jovian system with ultraviolet spectrometers over the past 35 years which led to the discovery of the Io plasma torus in the inner Jovian magnetosphere, molecular oxygen atmospheres of Europa, Ganymede, and now Callisto, auroras on Io, Europa, and Ganymede, and water vapor plumes from Europa.  These discoveries were made as a Co-Investigator and Science Team Leader on the Voyager Ultraviolet Spectrometer Experiment, a key member of the Hopkins UV team using IUE and Hubble Space Telescope and as an interdisciplinary scientist on the Cassini Mission.

Answer First: Applying the heuristic-analytic theory of reasoning to examine student intuitive thinking in the context of physics.

Dr. Mila Kryjevskaia

Dept. Physics, North Dakota State University
 

Monday, April 28, 2014, 3:30-4:30pm

221 South Engineering

It is a common expectation that, after instruction, students will consciously and systematically construct chains of reasoning that start from established scientific principles and lead to well-justified predictions.  When student performance on course exams does not reveal such patterns, it is often assumed that students either do not possess a suitable understanding of the relevant physics or are unable to construct such inferential reasoning chains due to deficiencies in reasoning abilities.  Psychological research, however, suggests that in many cases thinking processes are strikingly different from those outlined above.  Dual-process theories suggest that there are two distinct processes involved in many cognitive tasks.  Process 1 supports reasoning that is quick, intuitive, and automatic, while Process 2 is slow, rule-based, analytical, and reflective.  In this project, we will apply the extended heuristic-analytic theory of reasoning proposed by Evans, which was specifically designed to explain a particularly puzzling phenomenon related to reasoning:  logical competence demonstrated on one task is often not exhibited in the performance of another related task.  Indeed, student often rely on a variety of intuitive (often erroneous) reasoning strategies even though they possess the knowledge and skills necessary to arrive at a correct answer.  In this study, we developed a methodology that allowed for the disentanglement of student conceptual understanding and reasoning approaches.  We then applied the heuristic-analytic theory of reasoning in order to account for, in a mechanistic fashion, the observed inconsistencies in student responses.  Data from introductory calculus-based physics courses will be presented and implications for instruction will be discussed.

CANCELLED!


Imaging of Complex Biological Systems at the Sub-Cellular, Cellular and Multicellular Levels

Dr. Alexander Khmaladze

University of Michigan
 

tuesday, April 15, 2014, 3:00-4:00pm (Refreshments will be served at 2:45).

Special Location - 271 Batcheller Technology Center

 

Non-invasive nature of optical microscopy enables researchers to study a great variety of materials under conditions approaching or similar to their "natural" environment. This is especially relevant to live biological specimens, which can be studied both in-vitro and in-vivo, providing a unique insight into the dynamic processes occurring in the live organisms. In recent years, the emphasis has been shifting towards the technologies that combine several different imaging techniques to study a particular system. Each technique then allows measuring a partially overlapping set of parameters, leading to deeper understanding of the processes occurring within that system. This talk presents several imaging and spectroscopic techniques, namely dual-wavelength digital holographic microscopy, hyperspectral coherent anti-Stokes Raman imaging and spontaneous Raman spectroscopy. I will show how these techniques proved to be useful to answer specific questions, and also how they can be applied to solve a wide range of problems in physics, chemistry, biology and medicine. Moreover, by combining them, a single objective, such as a comprehensive study nanoparticles entry into cells and tissues, can be achieved. Due to interdisciplinary nature of these research topics, they are particularly well suited for involving researchers with various scientific backgrounds and interests. This research also provides rich opportunities for students to explore and gain knowledge in optical design, software programming, mathematics and nano-biology.

Coherent Raman Standoff Detection with Shaped Femtosecond Pulses

Marshall Bremer

Applied Physicist, Appareo Systems.
 

Monday, April 14, 2014, 3:30-4:30pm, 221 South Engineering

Standoff detection of explosives in order to protect public spaces is extremely challenging. Explosives generally have very low vapor pressures, limiting the effectiveness of air sampling and promoting research into optical methods to detect thin residues or micro-particles on surfaces as indicators of concealed danger. With excellent chemical specificity, Raman spectroscopy is capable of detecting particular compounds within the chemically complex background manifest in everyday surfaces, but the weak signal of the spontaneous process prohibits quickly detecting such small quantities.

I will discuss my graduate work at Michigan State University in which stimulated Raman scattering was used to quickly detect and image trace quantities of explosives in a standoff configuration.1 Stimulated Raman microscopy techniques generally employ two synchronized laser pulses and wavelength scanning to tune to the appropriate vibrational frequency.  Our approach uses a single femtosecond laser and pulse shaper to selectively excite a particular transition with the broad bandwidth. The transition is detected by simultaneously measuring stimulated Raman gain and loss using the diffusely reflected laser light from a single pulse. I will present images showing detection of single microcrystals of NH4NO3 on a variety of real world surfaces using a few laser shots and collecting the strong signal at ten meters.

1. Bremer, M. T. & Dantus, M. Standoff explosives trace detection and imaging by selective stimulated Raman scattering. Appl. Phys. Lett. 103, 061119–061119–5 (2013).

Macromolecules on Lipid Membranes: Brownian Motion, Conformational Dynamics, and Local Perturbations

Dr. Eugene Petrov

Max Planck Institute of Biochemistry, Department of Cellular and Molecular Biophysics, Martinsried, Germany
 

Tuesday, April 8, 2014, 3:30-4:30pm (Refreshments will be served at 3:15).

Special Location - 271 Batcheller Technology Center

 

Interaction of polymer molecules and colloidal particles with lipid membranes is one of the important problems of the modern bio-inspired soft matter physics. Its understanding provides an insight into mechanisms of interaction of biological macromolecules with cell membranes. What is the effect of the lipid membrane on the conformational dynamics and Brownian motion of membrane-bound polymer molecules? How lipid diffusion and phase separation in the membrane are affected by local perturbations induced by macromolecules? In my talk I will address these and other related questions using my recent results for model membrane systems and macromolecular structures including DNA, DNA origami, fd-virus, and artificial FtsZ-based membrane cortex. Experimental results obtained using fluorescence video-microscopy, fluorescence correlation spectroscopy, and single-particle tracking will be compared with Monte Carlo simulations and theoretical models. I will discuss implications for understanding important biological issues such as anomalous diffusion in cell membranes, effect of the membrane cytoskeleton on cold-shock resistance of organisms, and spontaneous DNA uptake by living cells

Directed Assembly of Colloidal Particles at Liquid Crystal Interfaces

Dr. Mohamed Gharbi

University of Pennsylvania
 

Monday, March 31, 2014, 3:00-4:00pm (Refreshments will be served at 2:45).

Special Location - 271 Batcheller Technology Center

 

Colloidal particles organize spontaneously at fluid interfaces owing to a variety of interactions to form well-organized structures that can be exploited to synthesize advanced materials. While the physics of colloidal assembly at isotropic interfaces is well understood, the mechanisms that govern interactions between particles at complex fluid interfaces are not yet clearly established. In particular, nematic and smectic liquid crystal materials offer important degrees of freedom that can be used to direct particles into new structures. In this work, I report the behavior of solid micrometric beads with homeotropic anchoring confined at interfaces of liquid crystal films. First, I will detail the behavior of spherical solid particles at planar nematic liquid crystal (NLC) interfaces. Subsequently, I will report the behavior of particles at more complex NLC interfaces. I will review how the competition between anchoring conditions, liquid crystal elasticity, and topology of curved surfaces is responsible for the formation of new ordered structures in a self-assembly process. Second, I will report the behavior of silica beads confined at interfaces of thin smectic films. I study the interactions and self-assembly of these particles in both supported and free standing films. When particles are captured in thin membranes, they induce distortions of the smectic interface to satisfy wetting properties at particle boundaries, leading to capillary interactions. These forces compete with elastic ones induced by the distortion of the smectic layers. The resulting potential drives assembly of the spheres into new different structures. Recent progress in understanding the mechanism of particle self-organization is presented.

Single Molecule Bioelectronics

Dr. Yongki Choi

Department of Physics and Astronomy, University of California Irvine.
 

Thursday, March 27, 2014, 3:30-4:30pm (Refreshments will be served at 3:15).

Special Location - 271 Batcheller Technology Center

 

Nanoscale electronic devices like field-effect transistors have long promised to provide sensitive, label-free detection of biomolecules.  In particular, single-walled carbon nanotubes have the requisite sensitivity to detect single molecule events, and have sufficient bandwidth to directly monitor single molecule dynamics in real time.  Our recent work has demonstrated this premise by monitoring the dynamic, single-molecule processivity of three different enzymes: lysozyme, protein Kinase A, and DNA polymerase I.  With all three enzymes, single molecules were electronically monitored for 10 or more minutes, allowing us to directly observe rare transitions to chemically inactive and hyperactive protein conformations.  The high bandwidth of the nanotube transistors further allow every individual chemical event to be clearly resolved, providing excellent statistics from tens of thousands of turnovers by a single enzyme. Besides establishing values for processivity and turnover rates, the measurements reveal variability, dynamic disorder, and the existence of intermediate states.  Initial success with the three enzymes indicates the generality and attractiveness of the nanotube devices as a new tool to complement existing single molecule techniques.  Furthermore, our focused research on transduction mechanisms provides the design rules necessary to further generalize this architecture.

Determination of pK Values of Ionizable Residues in Pentapeptides and SNase Protein

Guilherme Volpe Bossa

Department of Physics, NDSU
 

Monday, March 24, 2014, 3:30-4:30pm.

South Engineering, Rm 221

 pK is a parameter related with the ionization process of ionizable groups, as amine and hydroxyl. The determination of amino acids pK values in an electrolytic solution is crucial to understand the dynamics of various biological processes as, for example, adsorption of peptides and their interactions with enzymes active site. In this work we developed a mean-field model to calculate the mean electrostatic potential on amino acids surface. Such potential, which takes into account the contributions exerted by neighboring groups and ions in solution, is responsible for determine the pK value of each residue. The proposed model is applied to amino acids Asp, Glu, Lys, His, Tyr and Cys. Since the results were consistent with those reported in experimental works, our model was extended and applied to the computation of pK in Gly and Ala pentapeptides and of ionizable residues of Staphylococcal Nuclease (SNase) protein. In this last case, we used an approach similar to the first-neighbors approximation and the results shown good agreement with other theoretical works. These facts and the tiny computational cost involved points to a promising applicability of the suggested approach to modeling force fields.

 

 

Revealing Protein Dynamics by Integrating Molecular Dynamics Simulations with Neutron Scattering Experiments

Dr. Liang Hong

Center for Molecular Biophysics, Oak Ridge National Laboratory, Oak Ridge, TN 37831
 

Wednesday, March 19, 2014, 3:00-4:00pm (Refreshments will be served at 2:45).

Special Location - 271 Batcheller Technology Center

 

Protein, the engine of life, carries out most functions in living things on the earth through characteristic modulation of its three-dimensional structure over time. Understanding the microscopic nature of the protein internal motion and its connection to the function and structure of the biomolecule is a central topic in biophysics, and of great practical importance for drug design, study of diseases, and the development of renewable energy, etc. Under physiological conditions, protein exhibits a complex dynamics landscape, i.e., a variety of diffusive and conformational motions occur on similar time and length scales. This variety renders difficult the derivation of a simplified description of protein internal motions in terms of a small number of distinct, additive components. This difficulty is overcome by our work using a combined approach of Molecular Dynamics (MD) simulations and the state-of-the-art Neutron Scattering experiments. Our approach enables quantitative characterization of distinct protein motions, furnishing an in-depth understanding of the connection between protein structure, dynamics, energy landscape and function.

Investigating student understanding of electric circuits:  New insights from introductory physics and upper-division analog electronics

MacKenzie R. Stetzer

Department of Physics and Astronomy,University of Maine

 

Monday, Mar. 10, 3:30-4:30pm
South Engineering 221

REFRESHMENTS AT 3:15!!

 

In recent years, large-scale undergraduate course transformation efforts have become an increasingly visible response to a well-documented need for improved STEM instruction at all levels.  The role that research-validated instructional materials play in such transformations, however, is sometimes overlooked.  As the focus of these efforts shifts from introductory to upper-division courses, there is an increasing need for the kind of in-depth studies of student understanding that may inform the development of effective instructional materials.  In this talk, I present examples from an ongoing, multi-year, multi-institutional investigation of student understanding of electric circuits and analog electronics.  The insights drawn from work conducted in both introductory and upper-division courses continue to guide efforts to minimize the disconnect between what we teach and what students learn in junior-level laboratory courses in analog electronics.

Multipole Excition Generation in Nanometer-Sized Silicon Nanoparticles 

Andrei Kryjevski

Department of Physics, NDSU

Monday, Feb. 10, 3:30-4:30pm
South Engineering 221


In a semiconductor absorption of an energetic photon with energy exceeding twice the bandgap results in a creation of an energetic electron-hole pair (or an exciton, to be more precise). Typically, this excess energy is lost to heat due to phonon emission. An alternative path for the time evolution of an energetic exciton is the carrier multiplication (CM), or multiple exciton generation (MEG) mechanism, where two (or more) electron-hole pairs (excitons) are created from one absorbed photon. This mechanism is expected to be appreciable in nano-structures since electrostatic electron interactions here are enhanced by the spatial confinement. So, in nanoparticles it may be possible to channel the excess photon energy into creation of an additional electron-hole pair instead of being lost to heat. This is one reason why nano-material based photovoltaic devices are hoped to exceed the Shockley–Queisser efficiency limit of about 30%. In this talk, we will discuss MEG calculations in several semiconductor nanosystems. The calculations are based on Density Functional Theory (DFT) combined with the many body perturbation theory. Hydrogen-passivated Si29H36 quantum dots (QDs) with crystalline and amorphous core structures, the quasi one dimensional (1-D) arrays constructed from these QDs, as well as crystalline and amorphous Si nanowires have been studied. Amorphous Si nanostructures are predicted to have more effective carrier multiplication. Also, we will discuss our ongoing work on the carrier energy loss due to phonon emission. The ultimate goal of this project is to make predictions of efficiency of both MEG and electron energy loss to heat in the same nanoparticle. This should help in selecting nanomaterials suitable for photovotaic applications.

Molecular Simulation of Physical Aging in Ultrathin Polymer Film

Qiyun Tang

Post. Doc., Department of Physics, NDSU

Monday, Feb. 03, 3:30-4:30pm
South Engineering 221

Physical aging in glassy polymer films has attracted much attention in the past decades due to their strong correlation with the lifetime of polymer-based nano-devices. In the past years, many simulations were performed to understand the physical aging of bulk polymers while little attention was focused on the aging of ultrathin polymer films. Here we performed a Monte Carlo simulation by introducing the vacancy diffusion and vanishing mechanisms to investigate the physical aging of ultrathin polymer films. The obtained results are consistent with that observed in experiments, such as the linear increase of the local average density of segments with the logarithm of time, and the responses of aging rates to temperatures. Especially, at the extremely small thickness, the accelerated physical aging commonly observed experimentally in thin polymer films slows down, and the phenomenon is suppressed in the case of low molecular-weight ultrathin films. This anomalous behavior can be attributed to an inversed vacancy diffusion process caused by the sliding motion of chain molecules between the two free surface layers in free-standing polymer films. More interestingly, we verify that the average length of short chain-fragments defines a critical film thickness and demonstrate the existence of a new confinement effect at the nanoscale. The outlined approach could indeed provide new insights from the molecular levels to understand the physical aging of ultrathin films, and can be easily extended to unveil the correlations between the structure and dynamics in ultrathin polymer films with complex architectures.

A Tale of Two Colloids: Order and Disorder on a Soft Substrate

Andrew B. Croll

Department of Physics, NDSU

Monday, Jan 27, 3:30-4:30pm
South Engineering 314

The buckling of thin films has recently received considerable attention in both the materials and the continuum elasticity communities.  To the former, elastic instabilities form a platform for the mechanical measurement of material properties under increasing degrees of confinement.  To the latter, instabilities represent a testing ground for advanced elastic theory.  Buckling is also of considerable importance in the evolution of granular systems, which often show deformations that resemble those of continua.  Previously, we documented several differences between continuum theory and discrete elasticity in a discrete model of a thin film experimentally constructed from a well ordered (hexagonally packed) layer of colloid scale particles.  Here we consider how the structure of the 2D layer influences the buckling process.  In particular, we examine the details of how a complex, disordered (glassy) 2D layer resting on soft foundations responds to in-plane compressive stress.  We show how the fundamental buckling lengthscale remains identical to that of ordered layers, despite considerable heterogeneity in the motion of the particles.

Fall 2013 Seminars

Date

Title

Author

August 26, 2013

Membrane-Macromolecule Interactions: A Physical View on Complex Systems

Dr. Miha Fošnarič

September 2, 2013

Labor Day

September 9, 2013

Modelling Fluctuations in Computer Simulations

Dr. Alexander Wagner

September 16, 2013

Skyrmion wormholes and Skyrmion Black Holes

Dr. Terry Pilling

September 23, 2013

Local fluctuations in the lattice Boltzmann method

Goetz Kaehler

September 30, 2013

Drying of Colloidal Suspensions

Dr. Alexander Wagner

October 7, 2013

Using a lens of resources and framing to make sense of students' ideas about matrix multiplication

Dr. Warren Christensen

October 14, 2013

(Comprehensive Exam) Production of a thin solar cell using Si6H12 and type-sorted carbon nanotubes

Matthew Semler

October 21, 2013

Student difficulties measuring distances in terms of wavelength: Lack of basic skills or failure to transfer?

Dr. Mila Kryjevskaia

October 28, 2013

Nanoscale Carbon and Silicon at the Hard-Soft Interface

Dr. Erik Hobbie

November 4, 2013

Including Water-Mediated Effective Interactions into Electrolyte Mean-Field Models

Dr. Sylvio May

November 11, 2013

Veterans Day

November 18, 2013

Quantitative Kinetic Theory of Self-Propelled Particles

Dr. Thomas Ihle

November 25, 2013

Hydration and Screening in Ionic Mixtures: Multiscale Modeling

Dr. Alan Denton

December 2, 2013

December 9, 2013

(Comprehensive Exam)

John Harris

December 16, 2013

Dr. Andrei Kryjevski


Hydration and Screening in Ionic Mixtures: Multiscale Modeling

Alan Denton

Department of Physics, NDSU

Monday, November 25, 3:30-4:30pm
South Engineering 314

Ionic mixtures have long been a focus of soft matter research, owing to both their rich variety of interparticle forces and their diverse applications, from batteries to biology. On length scales > 1 nm, electrostatic forces dominate and can stabilize colloidal suspensions and polyelectrolyte solutions, with practical importance for foods and pharmaceuticals. On shorter length scales, non-electrostatic forces (e.g., due to hydration of ions) become relevant and entail ion-specific effects, such as the classic Hofmeister series, which classifies ions according to their ability to salt out or salt in proteins. The physical mechanism by which a solvent (water) mediates effective ion-ion interactions, however, is still poorly understood. In modeling such complex mixtures, multiscale approaches often prove essential to surmount computational challenges posed by broad length and time scales. I will outline our recent efforts to derive from perturbation theory a coarse-grained model of ions interacting via both long-range Coulomb and short-range solvent-induced forces. By inputting effective interactions into molecular simulations, we explore ion-specific properties of electrolyte solutions

Quantitative kinetic theory of self-propelled particles

Thomas Ihle

Department of Physics, NDSU


Monday, November 18, 3:30-4:30pm
South Engineering 318 (note the room change)



The Vicsek-model [1] for self-propelled agents such as birds, fish or bacteria, where agents try to align with their neighbors, is considered. Starting from a Markov chain in phase space and assuming Molecular Chaos I derive a kinetic equation for the evolution of the one-particle density [2]. This equation is solved numerically by a novel Lattice-Boltzmann-like algorithm which relies on about 1000 microscopic velocities [3]. Steep soliton-like invasion waves are observed. It is shown that these waves change the order of the phase transition to collective motion from continuous to discontinuous. For large particle speeds, the shapes of the waves agree quantitatively with agent-based simulations. Attempts to go beyond the mean-field assumption of Molecular Chaos and to include correlation effects are also discussed.

[1] T. Vicsek et al, Phys. Rev. Lett. 75 (1995) 1226.
[2] T. Ihle, Phys. Rev. E 83 (2011) 030901.
[3] T. Ihle, Phys. Rev. E 88 (2013) 040303.

Including Water-Mediated Effective Interactions into Electrolyte Mean-Field Models

Sylvio May

Department of Physics, NDSU

Monday, November 4, 3:30-4:30pm
South Engineering 118 (note the room change)

This talk gives an introduction to ion specific effects in electrolyte solutions, including the Hofmeister effect, and then discusses a systematic method to include non-electrostatic interactions into the (mean-field) Poisson-Boltzmann model. These non-electrostatic interactions account for the influence of the aqueous solvent (beyond merely providing a background dielectric constant). We will employ a separate field to account for the presence of Yukawa-like interactions in addition to the Coulomb potential. Extensions to more realistic oscillating Yukawa-like interactions are briefly sketched.

Nanoscale Carbon and Silicon at the Hard-Soft Interface

Erik Hobbie

Department of Physics, NDSU

 

Monday (Oct 28) 3:30-4:30pm
South Engineering 118 (note the room change)

Leveraging ‘soft matter’ at the nanoscale to simplify materials processing and improve material performance is becoming a reality, with potentially profound implications for a number of emerging technologies. A critical element of this is the manipulation and assembly of colloidal nanoparticles of exceptional purity through fluid-phase processing, and many of the current approaches for this are being drawn from polymer science. Aspects of our experimental research on single-wall carbon nanotubes and nanocrystalline silicon will be presented in this context, with an emphasis on applications related to flexible electronics and photoluminescent spectroscopic imaging.

Student difficulties measuring distances in terms of wavelength: Lack of basic skills or failure to transfer?

Mila Kryjevskaia

Department of Physics, NDSU

Monday, October 21, 3:30-4:30pm
South Engineering 221

We will discuss  student reasoning on problems involving two-source and thin-film interference. In both cases, interference arises from differences in the path lengths traveled by two waves. We found that some students (up to 40% on certain questions) had difficulty with a task that is fundamental to understanding these phenomena: expressing a physical distance, such as the separation between two sources, in terms of the wavelength of a periodic wave. We administered a series of questions to try to identify factors that influence student performance. We concluded that most incorrect responses stemmed from erroneous judgment about the type of reasoning required, not an inability to do said reasoning. A number of students do not seem to treat the spacing of moving wave fronts as analogous to immutable measurement tools (e.g., rulers).

Production of a thin solar cell using Si6H12 and type-sorted carbon nanotubes

Matthew Semler

Department of Physics, NDSU

 

Monday, October 14, 3:30-4:30pm
South Engineering 221

This talk is part of Matt's comprehensive examination.


Thin film silicon has primarily been made by depositing amorphous silicon (a-Si) via plasma enhanced chemical vapor deposition (PECVD), which is energy intensive.  A decade ago, NDSU formulated a novel technique to produce a silane solution, cyclohexasilane (CHS), that can be spin-cast onto a substrate, producing an a-Si film.  Using a pulsed laser, we have crystallized these a-Si films, producing polycrystalline silicon films.  In this presentation, I will discuss laser crystallization of a-Si and its potential use in solar cells, as well as other research I have thus far completed in fulfillment of my graduate comprehensive presentation.

Using a lens of Resources and Framing to make sense of students' ideas about matrix multiplication

Warren Christensen

Department of Physics, NDSU

 

Monday October 7, 3:30-4:30pm

South Engineering 221

In principle, a student who has completed both Linear Algebra and Quantum Mechanics should have a wealth of conceptual and procedural knowledge that has been attained from both mathematics and physics classes.  However in practice, it seems that many students come into our physics courses with an apparent lack of skills that we know were taught in math courses. This investigation casts light on students' thinking about matrix multiplication and how their thinking appears to be influenced by their framing of the problem as either a mathematics or physics question. We use the framework of Framing and Resources to describe a single student's thinking during an interview. Using an interview protocol written by mathematicians from a study in Mathematics Education, we explicitly probed mathematical thinking, and investigated if (and when) students attempted to relate mathematical problems to physics. Using lexicon analysis, we find students seem to shift from a "mathematical frame" to a "physics frame" and back again, but struggle to successfully transfer concepts between those frames. I will highlight the markers for these frame shifts and explore the potential instructional consequences of this work.

Drying of colloidal suspensions

Alexander Wagner

Department of Physics, NDSU

 

Monday, September 30,  3:30-4:30pm

South Engineering 221


This will be an interactive research talk where I report on recent simulations of evaporation or colloid laden drops. The research is driven by interesting experimental results by Erik Hobbie et al. in our department. I will show some results of my numerical investigations which show the effect of hydrodynamics and of Marangoni flows.

Local fluctuations in the lattice Boltzmann method

Goetz Kaehler

Department of Physics, NDSU

 

Monday, September 23, 3:30-4:30pm

South Engineering 221

 


The implementation of thermal fluctuations in lattice Boltzmann methods has been an active research topic in the last ten years. While implementations at high number density have been used successfully, even in some cases of non-ideal systems, examples at low number density still exhibit significant problems. It has been shown shown earlier that it is possible to largely avoid Galilean invariance violations by implementing a locally velocity dependent set of transforms to moment space. Recent calculations indicate that at low number densities the locality of the BGK collision operator leads to results different in nature than those obtained from Langevin theory. In this presentation I will discuss, in detail, our most recent results in obtaining a closed fluctuation dissipation theorem.

Skyrmion wormholes and Skyrmion black holes

Terry Pilling

Department of Physics, NDSU

 

Monday, Sept 16 3:30-4:30pm

South Engineering 221, NDSU

 

Skyrmions are soliton solutions to the non-linear sigma model lagrangian with a `Skyrme term'. The Skyrme model originated in the early 1960's as an attempt to model nucleons as solitons in a meson background field with the conserved topological charge identified as the baryon number. 

In 1983 Witten showed that the Skyrme model constitutes a low energy effective field theory of QCD and it is expected that the Skyrme model will give access to non-perturbative phenomena to which perturbative QCD is not accesible. There are a number of groups, most notably that of Nick Manton at DAMTP in Cambridge who are still working on the Skyrme model of nuclear physics and low energy QCD. 

In 2008, Manton, Diakonov, and I began studying the coupling Skyrmions to gravity to explore some previously discovered properties such as violations of the `no-hair' conjecture. Dmitiri Diakonov, until he passed away last year, was the Deputy Director, and the head of the Theory group, at the Petersburg Nuclear Physics Institute in Russia. 

After Diakonov passed away, I sent all of my calculations and computer code on skyrmion black holes to his students at PNPI and began instead to try and construct a Morris-Thorne wormhole with a skyrmion matter source in the hope that the conserved topological SU(2) charge would prevent the usual collapse and allow one to form a stable, traversable, wormhole needing only a vanishing amount of negative energy.

Membrane-Macromolecule Interactions: A Physical View on Complex Systems

Dr. Miha Fošnarič

Laboratory of Biophysics, Faculty of Electrical Engineering, University of Ljubljana

 

Monday, August 26th at 3:30 p.m.
South Engineering 221, NDSU
Refreshments at 3:00 p.m. in SE 216

After an introduction in the physical perspective of biological systems, we will present three examples of modelling membrane-macromolecule interactions: the influence of rigid membrane inclusion on membrane elasticity [1]; vesicle wrapping of a charged colloid [2]; and vesicle accommodation of a linear semi-flexible polymer [3]. Phenomenological modelling and Monte-Carlo simulations will be discussed. Most of the talk will be relatively general, suitable for graduate and undergraduate students interested in biophysics and complex systems. 

[1] M. Fošnarič, A. Iglič, S. May: Influence of rigid inclusions on the bending elasticity of a lipid membrane, Phys. Rev. E, 2006. 

[2] M. Fošnarič, A. Iglič, D.M. Kroll, S. May: Monte Carlo simulations of complex formation between a mixed fluid vesicle and a charged colloid, J. Chem. Phys., 2009. 

[3] M. Fošnarič, A. Iglič, D. M. Kroll, S. May: Monte Carlo simulations of a polymer confined within a fluid vesicle, Soft Matter, 2013.

Phospholipids are where and do what?

Dr. Edgar E. Kooijman

Department of Biological Sciences, Kent State University


Tuesday, July 09 at 2:00 p.m.
South Engineering 221, NDSU
Refreshments at 1:45 p.m. in SE 216

Phospholipids are everywhere; from the biological membranes surrounding cells and intracellular organelles to the phospholipid monolayer in your lungs and the monolayer surrounding VLDL/LDL and intracellular lipid droplets. In this talk I will introduce two distinct lines of research carried out in my lab. The first of these lines is concerned with how
specific phospholipid species (might) function in biological membranes.  The goal of this work is to characterize the physicochemical properties of these lipids such as their effective molecular shape and ionization  properties. As an example I will discuss some recent results on a lipid primarily found in plant membranes that is involved in stress (e.g. salinity and drought) signaling.


The second line of research concerns the structure of intracellular lipid droplets. Specifically, we are interested in how a subset of LD binding proteins interacts with the phospholipid monolayer covering the neutral lipid core. In the talk I will introduce the structure of these intracellular "organelles" and then discuss some monolayer data on a model protein that actually functions in protein transport in insects.  For both lines I will discuss why these projects are interesting and why you should care about them.

Liposomes loaded with a lipophilic drug: Is there a transfer of the drug to blood components before the liposome is reaching its target and is this behaviour good or bad?

Dr. Alfred Fahr

Department of Pharmaseutical Technology, Friedrich-Schiller University Jena, Jena, Germany

 

Wednesday, March 13th at 4:00 p.m.
South Engineering 221, NDSU
Refreshments at 3:30 p.m. in SE 216

We have incorporated the very lipophilic photosensitizer temoporfin into liposomes of varying membrane composition, cholesterol content, vesicle size and life-prolonging liposome modifications.  We measured the resulting pharmacokinetic profile of the liposomal carrier and the incorporated temoporfin in a rat model. A novel pharmacokinetic model allowed distinguishing between temoporfin eliminated together with the liposomal carrier and temoporfin that is first transferred to other blood components (e. g. plasma proteins) before being eliminated from the blood. Our analysis using this model demonstrates that a fraction of temoporfin is released from the liposomes prior to being eliminated from the blood. In case of unmodified liposomes this temoporfin release was observed to increase with decreasing bilayer fluidity, indicating an accelerated temoporfin transfer from gel-phase liposomes to e.g. plasma proteins. This was predicted by earlier in vitro experiments using a liposome-liposome transfer system. The advantages of such a “leaky” carrier system for therapy will be discussed.

Monte Carlo simulations of a polymer confined within a fluid vesicle

Dr. Sylvio May

Department of Physics, North Dakota State University, Fargo, North Dakota, United States

 

Monday, January 28th at 3:30 p.m.
South Engineering 221, NDSU

Monte Carlo simulations are employed to study a fluid vesicle that contains a single worm-like polymer chain. We vary the degree of polymer confinement in our simulations by increasing the persistence length of the polymer. The vesicle is represented by a randomly triangulated self-avoiding network that can undergo bending deformations. Upon increasing the persistence length of the polymer beyond the size of the vesicle, we observe a transition of the polymer from an isotropic disordered random conformation to an ordered toroidal coil. Concomitantly, the vesicle adopts an oblate shape to allow for some expansion of the polymer coil inside the vesicle. It is convenient to characterize both polymer and vesicle in terms of the asphericity, a quantity derived from the gyration tensor. At the onset of the polymer's ordering transition, the asphericity passes through a minimum for both polymer and vesicle. The increase in vesicle asphericity for a semi-flexible polymer can be understood in terms of ground state energy calculations, either for a simplified representation of the vesicle shape (we specifically discuss a disk shape with a semi-toroidal rim) or involving a full vesicle shape optimization. The asphericity of the polymer's coil results from conformational fluctuations and can be rationalized using Odijk's deflection length of strongly curved semi-flexible polymers.

Dynamics of Microstructural Transitions in Block Copolymer Melts

Dr. Robert Wickham

Department of Physics, University of Guelph, Guelph, Ontario, Canada

Monday, January 21st at 3:30 p.m.
South Engineering 221, NDSU
Refreshments at 3:00 p.m. in SE 216

Soft materials are dynamical by nature and the study of the dynamics of soft materials is an exciting, rich area of current interest. During macromolecular self-assembly, as occurs in block copolymers, long structural relaxation timescales due to collective molecular motion are often seen. How microstructure influences the dynamics, the existence and lifetime of metastable states, and the dynamics of long-lived non-equilibrium structures are all poorly-understood issues. Our large-scale dynamical simulations address these questions in the context of the nucleation of one microstructured phase out of another in a block copolymer melt. Specifically, we simulate the model-B dynamics of the conserved monomer density driven by a Landau-Brazovskii free-energy, which is appropriate for diblock copolymer melts. I will discuss our simulations of nucleation at the cylinder-to-lamellar transition, and our recent study of the kinetics of crystallization of the body-centered cubic phase of spherical micelles from disorder.

Volumetric Investigations of Biological Macromolecules and Colloidal Particles: Where Thermodynamics Meet Structure

Dr. Heiko Heerklotz

Faculty of Pharmacy, University of Toronto, Toronto, Ontario, Canada

Wednesday, January 16th at 3:30 p.m.
South Engineering 221, NDSU
Refreshments at 3:00 p.m. in SE 216

Biological macromolecules and colloidal aggregates such as micelles, liposomes, etc. in aqueous dispersion exhibit a relatively large interface to the water. Structural changes of these particles change their particle volume due to variations of (i) their internal packing (i.e. the void volume between the atoms) and (ii) their hydration (altered packing of water at the interface). The relatively new method of pressure perturbation calorimetry (PPC) permits one to measure thermotropic changes in partial volume and expansivity at a new level of precision and convenience. The talk presents PPC experiments to study the unfolding of globular proteins, DNA helicies and tetraplexes, the melting of lipids, self-association of surfactants, and micellar shape transitions. The overall aim is to better dissect packing and hydration effects and utilize the structural and thermodynamic information from volumetric experiments to its full capacity.


All are welcome!

Advances in Surface Plasmon Resonance Imaging Enable Quantitative Measurement of Laterally Heterogeneous Coatings of Nanoscale Thickness

Dr. Adam Raegen

Department of Physics, University of Guelph, Guelph, Ontario, Canada

Monday, January 14th at 3:30 p.m.
South Engineering 221, NDSU
Refreshments at 3:00 p.m. in SE 216

The Surface Plasmon Resonance (SPR) phenomenon is routinely exploited to qualitatively probe changes to the optical properties of nanoscale coatings on thin metallic surfaces, for use in probes and sensors. Unfortunately, extracting truly quantitative information is usually limited to a select few cases -- uniform absorption/desorption of small biomolecules and films, in which a continuous ``slab'' model is a good approximation. I will present advancements in the SPR technique that expand the number of cases for which the technique can provide meaningful results. Use of a custom, angle-scanning SPR imaging system, together with a refined data analysis method, allow for quantitative kinetic measurements of laterally heterogeneous systems. I will first demonstrate the directionally heterogeneous nature of the SPR phenomenon using a directionally ordered sample, then show how this allows for the calculation of the average coverage of a heterogeneous sample. Finally, the degradation of cellulose microfibrils and bundles of microfibrils due to the action of cellulolytic enzymes will be presented as an excellent example of the capabilities of the SPR imaging system.


All are welcome!

Stabilizing Nanotube Films with Thin Polymer Layers

Matthew Semler

Department of Physics, North Dakota State University, Fargo, North Dakota, United States

Monday, December 3rd at 3:30 p.m.
South Engineering 221, NDSU

Thin membranes of single-wall carbon nanotubes (SWCNTs) on elastic polymer substrates show considerable promise for flexible electronics applications, but the modulus and conductivity of these films decrease dramatically in response to applied strains. This softening arises from the strong van der Waals interactions between contacted nanotubes, which favor the parallel coarsening of SWCNT bundles in response to even very small external forces. By capping the SWCNT membranes with a thin layer of glassy polymer, we demonstrate a dramatic improvement in the mechanical response of the strained films. We link this behavior to the stabilizing influence of excluded-volume interactions mediated by the glassy polymer layer.


All are welcome!

Endeavors in Photovoltaic Design using Chemically Functionalized Single-wall Carbon Nanotubes

John Harris

Department of Physics, North Dakota State University, Fargo, North Dakota, United States

Monday, November 26th at 3:30 p.m.
South Engineering 221, NDSU

The coupling between mechanical flexibility and electronic performance is evaluated for thin coatings of electronically type-sorted metallic and semiconducting single-wall carbon nanotubes (SWCNTs) deposited on both soft-polymer and noncompliant supports. The microstructure, transparency, and electronic properties of the films are independently characterized using both optical and electron microscopy, as well as optical-absorption and impedance spectroscopy. Uniaxial and cyclic compression experiments suggest that thin films made from metallic SWCNTs show better durability as flexible transparent conductive coatings, which we attribute to a combination of superior mechanical performance and higher interfacial conductivity. In current research we investigate the use of both electronically type-sorted and chirality-sorted semiconducting films as the chemically functionalized p-type layer in photovoltaic pn-junctions on crystalline silica.


All are welcome!

Block Copolymer Emulsion Drops

Dr. Andrew B. Croll

Department of Physics, North Dakota State University, Fargo, North Dakota, United States

Monday, November 19th at 3:30 p.m.
South Engineering 221, NDSU

Diblock copolymers form an interesting class of synthetic surfactant molecules, finding uses ranging from compatibilizing polymer blends (alloys) to drug delivery schemes.  Remarkably, aside from analogy to small molecular surfactants, little has been done to understand (and exploit) many of the unique properties of block copolymers at fluid interfaces.  Here we present some of the results of our ongoing studies of the polystyrene-polyethylene oxide (PS-PEO) system in water/toluene emulsions.  In particular, we focus on using buoyancy as a convenient experimental handle on the system.  We show a simple and very sensitive measurement of the surface tension, some observations of adhesive properties as well as some unique hydrodynamic instability.


All are welcome!

Coarse-grained modeling of mixtures of charged macroions

Dr. Jun Kyung Chung

Department of Physics, North Dakota State University, Fargo, North Dakota, United States

Monday, November 5th at 3:30 p.m.
South Engineering 221, NDSU

In suspensions of charged macroions, such as charge-stabilized colloids and polyelectrolyte microgels, the electrostatic interactions between macroions are relatively easily controlled by changing the sizes and charges of the macroions, as well as the concentration of salt.  This tunability of interactions can be exploited to stabilize various structures that self-assemble under appropriate conditions. In this talk, a statistical mechanical coarse-graining approach to modeling mixtures of charged spherical macroions will be discussed and results presented for effective electrostatic interactions in binary mixtures of charged colloids and microgels.  Finally, applications to charge renormalization, structure, and phase behavior of charged colloidal mixtures will be discussed.


All are welcome!

On mathematical modeling of biological evolution

Dr. Artem Novozhilov

Department of Mathematics, North Dakota State University, Fargo, North Dakota, United States

Monday, October 29th at 4:00 p.m.
South Engineering 221, NDSU

In my talk I will give an introduction to the mathematical approaches to model biological evolution. In particular, I will formulate the celebrated Eigen's quasispecies model and state the basic results concerning the quasispecies concept and the error threshold. A number of results in this area were discovered and rediscovered by physicists using methods of statistical physics. I will conclude my presentation with a discussion of open problems.
All are welcome!


All are welcome!

From Colloids and Nanoparticles to Quantum Computers

Dr. Alan Denton

North Dakota State University, Fargo, North Dakota, United States

Monday, October 22nd at 3:30 p.m.
South Engineering 221, NDSU


When sufficiently concentrated, colloidal particles, suspended by Brownian motion in a solvent, may self-assemble into crystals with lattice constants comparable to wavelengths of visible light. Colloidal crystals can serve as templates for fabricating "inverse opals" -- highly porous materials, whose micron-sized cavities affect the propagation of (and can even trap) light.  This year's Nobel Prize in Physics was awarded for fundamental research on controlling trapped photons and ions while preserving their quantum states.  Colloidal  crystals may provide the delicate matrix needed to enable potential applications to quantum computers.  Mixing colloids with nanoparticles, and independently varying concentrations, size and charge ratios, vastly expands the possibilities for tuning interparticle forces and stabilizing new crystal structures.  In modeling such complex materials, multiscale methods often prove essential to surmount computational challenges posed by multiple length and time scales.  I will summarize our recent efforts to develop a hierarchical approach to modeling effective interactions, with the goal of predicting structural and thermodynamic properties of colloidal and other soft materials. 

All are welcome!

Optical Studies of Graphite at High Magnetic Field

Dr. Tung, Li-Chun Richard

University of North Dakota, Grand Forks, North Dakota; National High Magnetic Field Laboratory-FSU, Tallahassee, Florida, USA

Monday, October 15th at 3:30 p.m.
South Engineering 221, NDSU

Graphite, the parent compound of graphene, contains the characteristics of both monolayer and bilayer graphene. The massless holes at graphite's H-point behave like Dirac fermions in monolayer graphene, while the massive electrons at the K-point behave like Schrodinger fermions in bilayer graphene but with an adjusted interlayer coupling constant. Understanding graphite helps to learn more about the nature of monolayer, bilayer and multilayer graphene, while the later two hold promise for commercial applications. Using the magneto-reflectance study, we determine the tight-binding band parameters from the SWM band theory. Moreover, the result implies that not only should the H-point fermions regarded as massless relativistic particles, the K-point fermions can also be regarded as massive relativistic particles at magnetic field. As a result, graphite may be an excellent platform to study some phenomena which were considered inaccessible in a laboratory setting. In the magneto-transmittance study, the electron-phonon couplings between H-point fermions and two zone boundary phonon modes are manifested as two kinds of resonant phenomena. We discovered a strong anticrossing resonance due to the interactions between the large momentum K-point phonons and the H-point Dirac-like fermions, as well as a Fano resonance, resulting from the coupling of the -point phonons with the cyclotron resonance of charged carriers. The uniqueness and implication of these resonances will be discussed.

 

All are welcome!

Preliminary investigation of instructor effects on gender gap in introductory physics

Kimberly Kreutzer

Graduate Student, North Dakota State University, Fargo, North Dakota, United States

Monday, October 8th at 3:30 p.m.
South Engineering 221, NDSU

Gender differences in student learning in the introductory, calculus-based electricity and magnetism course were assessed by administering the Conceptual Survey of Electricity and Magnetism pre- and postcourse. As expected, male students outgained females in traditionally taught sections as well as sections that incorporated interactive engagement (IE) techniques. In two of the IE course sections, however, the gains of female students were comparable to those of male students. Classroom observations of the course sections involved were made over an extended period. In this paper, we characterize the observed instructor-student interactions using a framework from educational psychology referred to as wise schooling. Results suggest that instructor practices affect differential learning, and that wise schooling techniques may constitute an effective strategy for promoting gender equity in the physics classroom. 


All are welcome!

Evaporation of Colloidal suspensions

Dr. Alexander Wagner

North Dakota State University, Fargo, North Dakota, United States

Monday, September 17th at 3:30 p.m.
South Engineering 221, NDSU

When a drop of colloidal suspension evaporates we usually find that a large portion of the colloids is deposited at the edges of the drop, which we are all familiar with because this is also known as the coffee ring effect. The underlying reason for this deposition is that the edges of the drop is pinned and this causes a hydrodynamic flow of material towards the edges which drags the small particles towards the edge of the drop.

A separate phenomenon is that suspended particles typically like to aggregate at an interface. The timescale for this is related to the time it takes a particle undergoing Brownian motion to reach the interface. Once the interface is coated with particles, this will reduce the evaporation from the covered surface. This raises the possibility that a particle suspension where a noticeable fraction of the surface is covered with particles near the edges will show a much reduced hydrodynamic flow and thereby a reduction of deposition of particles at the rim of the drop.

In this talk we will analyze the effects of evaporation and present our analytical predictions of the difference in evaporation rates as a function of the covering of the surface with particles and validate our analytical predictions with numerical simulations and speculate on the feasibility of utilizing this mechanism to generate (more) uniform particle distributions as a result of the evaporation process.

 

All are welcome!

Thermal fluctuations of lipid bilayers

Dr. Miha Fošnarič

Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia

Monday, September 10th at 3:30 p.m.
South Engineering 221, NDSU

Lipid bilayers are a few nanometers thin sheets that form the basis of biological membranes. Due to their softness lipid bilayers are subject to thermal fluctuations. In the seminar we will present an experimental method for direct measurement of their bending elasticity through the analysis of thermally induced shape fluctuations of lipid vesicles. Theoretical and experimental aspects of the method will be addressed and the connection with Monte-Carlo simulations, where the stochastic Metropolis-Hastings algorithm allows us to sample thermal fluctuations of a system in thermodynamical equilibrium, will be  discussed.

 

All are welcome!

Ionic driven assembly of membranes: Surprising findings in shell shape and composition

Dr. Monica Olvera de la Cruz

Lawyer Taylor Professor, Materials Science & Engineering, Chemical & Biological Engineering and Chemistry, Northwestern University, Evanston, Illinois, United States

Wednesday, May 2nd at 3:30 p.m.
FLC 124, NDSU
Refreshments at 3:00 p.m. in SE 216

Large viral shells or fullerenes exhibit molecular crystalline structures with icosahedral shapes. Other faceted shapes, including Platonic and Archimedean geometries, arise spontaneously in shells formed by more than one component (1). We describe buckling of a crystalline shell with two co-existing elastic components into various polyhedra. Our work explains the principles to design hollow polyhedra and the existence of regular and irregular polyhedral shells observed in organelles and in halophilic organisms wall envelopes, as well as viral capsids made of various proteins. We provide experimental evidence of the spontaneous buckling phenomena in shells made of mixtures of cationic and anionic amphiphiles  (2), where their co-assembly is driven by electrostatics, which orders the assembly into faceted ionic structures with various crystalline domains. These shells are stable at high monovalent salt concentrations. Their crystalline structure and shape, however, are modified by the pH value of the solution. Our work provides guidelines for the fabrication of robust nanocontainers with specific shapes and may aid to elucidate paradigms that relate shape and composition of cellular shells.

(1) G. Vernizzi, R. Sknepnek, and M. Olvera de la Cruz "Platonic and Archimedean geometries in multi-component elastic membranes" Proc. Natl.Acad. Sci. USA, 118, 4292–4296 (2011).

(2) M. A. Greenfield, L. C. Palmer, G. Vernizzi, M. Olvera de la Cruz, and S. I. Stupp “Buckled Membranes in Mixed-Valence Ionic Amphiphile Vesicles” J. Am. Chem. Soc., 131, 12030–12031 (2009).

 

All are welcome!

Correlated electron dynamics in QD sensitized solar cells

Dr. Yuri Dahnovski

Department of Physics and Astronomy, University of Wyoming, Laramie, Wyoming, United States

Wednesday, April 25th at 4:00 p.m.
South Engineering 221, NDSU
Refreshments at 3:30 p.m. in SE 216

Photoelectron current and nonlinear optical effects are considered in terms of quantum correlation functions, i.e., nonequilibrium Green's functions (NEGFs). In this approach photoelectric current is expressed in terms of NEGFs. To find NEFs we numerically solve two-time Kadanoff-Baym equations for a model system where electron correlation is due to the e-e interaction between QD and semiconductor electrons. The results are compared with the results obtained from the often used approximation based on the Markovian rate equations for a density matrix. The found discrepancy appeared to be up to one order of magnitude. Nonlinear optical effects for a pump-probe experiments are theoretically studied for the same system. We have found that nonlinear polarization can differ by a factor of five for current states ( the current is on) and for isolated QD (the current is off). There is a discrepancy between the Kadanoff-Baym and Markovian approaches either.

 

All are welcome!

Innovation as a Core Competency at 3M From Sandpaper Company to 'Playground for Scientists'

Dr. Bret Ludwig

Communications Manager, 3M Innovation Center, St. Paul, Minnesota, United States

Thursday, April 12th at 3:30 p.m.
FLC 124, NDSU
Refreshments at 3:00 p.m. in SE 216

3M is famous for its innovations - ranging from the world's first masking and transparent tapes to the latest in high tension power lines and plastic films that achieve 99% reflectance of the visible spectrum by packing hundreds of layers into a 50 micron thickness. More important to 3M than these individual technological advances is the culture of open innovation that made these and thousands of other advances possible. This talk will cover some of the 'how' behind 3M's reputation for innovation and some of the history that enabled a sandpaper company to evolve into a world leader in dozens of technologies, now employing more than 10,000 technical employees worldwide and spending $1.6 billion on R&D in 2011. A good deal of time will be spent on the Tech Forum, the organization of technical employees that keeps everyone in 39 labs talking to each other so silos can't form and technologies flow freely between businesses. The speaker will also share a story of his own experience with an adhesion challenge in a corporate product development lab. Come hear the not-always-fun story, complete with instances of 'old-timers' saying, "We've tried that; it doesn't work." and a 'simple' addition that worked in hundreds of lab experiments but failed totally in its first two tries in the factory.

 

All are welcome!

Ultracold Atoms in Optical Lattices: the Quest for Antiferromagnetism

Dr. Yen Lee Loh

Physics Department, University of North Dakota, Grand Forks, North Dakota, United States

Wednesday, April 4th at 4:00 p.m.
South Engineering 221, NDSU
Refreshments at 3:30 p.m. in SE 216

Recent advances have made it possible to prepare clouds of atoms at temperatures of about 0.0000000004 Kelvin – less than a billionth of a degree above absolute zero.  At such low temperatures the atoms reveal their quantum mechanical wave nature, marching in lockstep to produce novel phases of matter.  The density, composition, disorder, interactions, and lattice potential can be all be controlled independently using lasers and magnetic fields.  Ultracold atomic gases hold great promise for precision measurement (clocks), quantum computing, and the emulation of condensed matter systems such as the Fermi Hubbard model, which may apply to high-temperature superconductors.

The Fermi Hubbard model has now been realized using potassium-40 atoms in optical lattices.  However, the average entropy is rather high (S/N ≈ 1 kB/atom).  Our quantum Monte Carlo simulations suggest that antiferromagnetic order begins to develop below S/N ≈ 0.65 kB/atom, which may be achievable with current techniques.  However, lower entropies are required for robust antiferromagnetism.  I have proposed a way to attain very low temperatures and entropies (≾ 0.03 kB/atom) by trapping fermions in a corral formed from another species of atoms.  This Fermi system can then be evolved into an antiferromagnet by morphing the lattice into a set of double wells, quasi-adiabatically.  Quantum dynamics simulations have, so far, given promising results.

[1] Thereza Paiva, Yen Lee Loh, Mohit Randeria, Richard T. Scalettar, and Nandini Trivedi, “ Fermions in 3D optical lattices: Cooling protocol to obtain antiferromagnetism,” Phys. Rev. Lett. 107, 086401 (2011)
[2] Yen Lee Loh, “Proposal for achieving very low entropies in optical lattice systems,” arxiv:1108.0628
All are welcome!

 

All are welcome!

Exploring the interface between physics and biology: from a traffic model to protein synthesis and beyond

Dr. JiaJia Dong

Physics Department, Hamline University, St. Paul, Minnesota, United States

Thursday, March 29th at 3:30 p.m.
South Engineering 221, NDSU

Statistical mechanics (SM) for systems in thermal equilibrium, founded over a century ago, forms part of the current physics core curriculum. However, like most homework problems do not directly apply to real situations, textbook equilibrium SM falls short of characterization of systems in non-equilibrium (NE), such as biological systems. An overarching theoretical framework of NESM remains elusive and has been attracting increasing interest from physicists.

In this talk, I first contrast the key features of NESM with the familiar ESM. To illustrate how tools developed in NESM help untangle the complex biological process, we then zoom in on modeling protein synthesis in bacteria through a particle transport model (the totally asymmetric simple exclusion process, or TASEP). We discuss the quantitative effect of different elongation rates, associated with different codons, on the overall protein production rate. We conclude with some ongoing projects and open questions that nestle on the interface of physics and biology to set the stage for further investigation in this field.

 

All are welcome!

Phases and Phase Transitions of Block Copolymers

Dr. An-Chang Shi

Physics Department, McMaster University, Hamilton, Ontario, Canada

Monday, March 12th at 3:00 p.m.
(Refreshments at 2:45 p.m. in SE 216.)
South Engineering 221, NDSU

Spontaneous formation of ordered structures from amphiphilic molecules has attracted tremendous attention in the last decades.  Among the many different amphiphilic systems, block copolymers, with their rich phase behavior and ordering transitions, have become a paradigm for the study of structural self-assembly in soft materials.  Understanding the structures and phase transitions in block copolymers has been one of the most active research areas in polymer science in the past two decades. Theoretical studies of block copolymers focuses on their phase behavior and the phase transition pathways between different ordered phases.  I will present a strategy to discover complex ordered phases of block copolymers and a method to construct phase transition pathways connecting different ordered phases.  Applications of these methods will be illustrated by the phase behavior of ABC triblock copolymers and the phase transition pathways of AB diblock copolymers.

 

Cosponsored by the Department of Coatings and Polymeric Materials, with support from the NDSU Cooperative Sponsorship Committee.

 

All are welcome!

Spatial reasoning, a potential roadblock to conceptual understanding of waves

Dr. Mila Kryjevskaia

Physics Department, North Dakota State University, Fargo, North Dakota, United States

Wednesday, February 22nd at 4:00 p.m.

As a part of a multi-year investigation of student understanding of mechanical wave in introductory courses, a set of tutorials on wave behavior at a boundary has been developed.  However, even after the targeted instruction many students still are not able to systematically analyze complex unfamiliar situations. We hypothesized that poor performance on some post-tests may be attributable to difficulties in visualizing and reasoning spatially about transformations in the shape of a spring that occur over time as a complex pulse reflects from a boundary.  We probed the extent to which student performance hinges on their ability to visualize and reason spatially by examining the degree of association between student performance on the post-tests and on a spatial visualization test - paper folding test.

 

All are welcome!

Kinetic theory for systems of self-propelled particles

Dr. Yen-Liang Chou

Physics Department, North Dakota State University, Fargo, North Dakota, United States

Wednesday, February 15th at 4:00 p.m.

Models of self-driven particles similar to the Vicsek model [Phys. Rev. Lett. 75 (1995) 1226] are studied by means of kinetic theory. In these non-equilibrium models, particles try to align their travel directions with the average direction of their neighbors. At strong alignment a global flocking state forms. The alignment is defined by a stochastic rule, not by a Hamiltonian. The corresponding interactions are non-additive and are typically of genuine multi-body nature. The theory [1] is based on a Master equation in 3N-dimensional phase space, which is made tractable by means of the molecular chaos approximation. The phase diagram for the transition to collective motion is calculated and compared to direct numerical simulations. A stability analysis of a homogeneous ordered state is performed, which reveals a long wave length insta- bility for some of the considered models. The mean-field calculations of one of the models show a tricritical point where the flocking transition changes its character from continuous to discontinuous.

[1] T. Ihle, Phys. Rev. E 83 (2011) 030901

 

All are welcome!

Buckling in a Particle Film

Dr. Andrew Croll

Physics Department, North Dakota State University, Fargo, North Dakota, United States

Wednesday, February 1st at 4:00 p.m.

When a thin rigid plate is adhered to a soft substrate and compressed, the plate will buckle out of plane to accommodate the applied stress. The out of plane buckling results in a sinusoidal topography (wrinkles) due to the interplay of rubber stretching and film bending. When the plate is replaced by a collection of closely packed particles similar phenomena results – the positions of the particles move out of plane and follow a roughly sinusoidal curve. Due to the similarity of the end state of each system, the same continuum theory is often applied to model both films. Here, we use a carefully constructed experimental system consisting of micron-scale polymer and silica spheres on a PDMS elastomer substrate to demonstrate the physical differences between a continuum plate and a discrete set of particles.  In particular, because we can easily track the position of each particle in three dimensions with confocal microscopy, we have access to all aspects of the particles motion. We note that the wrinkling is independent of particle modulus, and highly dependent on particle packing. This leads us to suggest that the underlying physics is granular (and not continuum) in nature. This result may have implications in biology, where elastic continua are often made of discrete building blocks (e.g. cells).

 

All are welcome!

Selective Partitioning of Cholesterol and Drugs into Liposomes of Varying Size

Dr. Sylvio May

Physics Department, North Dakota State University, Fargo, North Dakota, United States

Wednesday, January 25th at 4:00 p.m.

The bending stiffness of a lipid bilayer generally depends on the presence of membrane additives such as sterols, cosurfactants, peptides, and drugs. As a consequence, the partitioning of such membrane additives into liposomes becomes selective with respect to liposome size; i.e., membrane rigidification depletes the membrane additives in the smaller (more strongly curved) liposomes. We have measured this liposome size-selective partitioning for two membrane additives, namely cholesterol and the porphyrin-based photosensitizer temoporfin, using asymmetrical flow field-flow fractionation (AF4) of liposomes and radioactive labeling of the membrane additive and lipid. The method yields either the molar cholesterol-to-lipid or the temoporfin-to-lipid ratio as a function of liposome size, from which we calculate the corresponding change of the membrane bending stiffness. For small unilamellar fluid liposomes composed of palmitoyloleoylphosphocholine (POPC) and palmitoyloleoylphosphoglycerol (POPG), we find that cholesterol rigidifies the host membrane in a manner consistent with previous findings. In contrast, temoporfin softens this membrane. Partitioning results for gel-phase liposomes composed of dipalmitoylphosphocholine (DPPC) and dipalmitoylphosphoglycerol (DPPG) are also curvature-sensitive but cannot be interpreted on the basis of the bending stiffness alone.

 

All are welcome!

How quantum and thermal physics can be used to improve fuel cells

Dr. Ananda Shastri

Physics Department, Minnesota State University Moorhead, Moorhead, Minnesota, United States

Thursday, October 27th at 2:00 p.m.

Undergraduates in the Solid State Nuclear Magnetic Resonance (NMR) Research Group at Minnesota State University Moorhead are currently studying a series of materials that have potential application as proton exchange membranes in hydrogen-oxygen fuel cells. These solids, called sodium thio-hydroxogermanates, are electronic insulators but allow hydrogen ions to diffuse through them with a mobility comparable to that of liquids! Using NMR, and principles of quantum and thermal physics, we will illustrate how fundamental physical principles allow data to be interpreted. We present arguments that the hydrogen dynamics involves coordinated water rotation and jump across hydrogen bonds within the material.  Understanding how the hydrogen dynamics depends on chemical composition could lead to improvements in fuel cells.

 

All are welcome!

Employing Simple Optical Methods to Study Daphnia magna Movement

Dr. Matthew L. Beckman

Biology Department, Augsburg College, Minneapolis, Minnesota, United States

Thursday, October 27th at 2:35 p.m.

Daphnia magna (D.magna) is a freshwater crustacean that is an emerging model organism in biological research. Historically, this organism has been studied by ecologists and environmental toxicologists. Our work is focused on studies of the neural mechanism of movement in Daphnia magna. We have developed low-cost methods utilizing custom-made recording chambers, video-rate cameras, and a variety of free and commercial software to record and analyze Daphnia movement. We are using these methods to study the effects of drugs which perturb the dopaminergic nervous system, a neurotransmitter system involved in movement in many organisms. Data will be presented on three primary areas of this work. First, I will show that two dimensional swimming behavior of Daphnia magna can be reliably quantified using a multi-well chamber amenable to drug-screening studies. Using these imaging methods we have quantified the effect of drugs that perturb the dopamine nervous system in Daphnia. Second, I will describe experiments aimed at recording and modeling Daphnia swimming in three dimensions. This work involves labeling the daphnids with fluorescent quantum dots followed by imaging the animal’s trajectory over time. Preliminary experiments utilizing this quantum dot labeling method have enabled us to track the movement of fluorescent daphnids freely swimming in a 3D chamber. Finally, I will describe our efforts to clone and characterize genes involved in dopamine neuron function. The complete genome sequence of Daphnia pulex, a relative of Daphnia magna, was recently reported giving us access to genomic sequence information. Using bioinformatics tools to design DNA primers and a polymerase chain reaction (PCR) cloning strategy we have retained a partial clone of a dopamine decarboxylase gene from Daphnia magna.  We intend to use these molecular tools to identify dopamine neurons using microscopic fluorescent in situ hybridization methods. Taken together, these studies are beginning to shed light new light on Daphnia movement.

 

All are welcome!

In vitro measurement of drug transfer between liposomal membranes

Kathrin Kaeß

Department of Pharmaceutical Technology, Friedrich-Schiller-Universität Jena, Germany

Thursday, October 27th at 3:10 p.m.

An investigation of the transfer kinetics of drugs from different liposomal formulations to their targets is inevitable for a successful development and optimization of liposomal drug delivery systems. Therefore, during the last years a lot of efforts have been made for the establishment of methods allowing the in vitro measurement of drug transfer from donor to acceptor vesicles [1]. A simple and fast technique is represented by fluorescence spectroscopy, which is based on excitation of fluorophores and following detection of emission light.  Within my prospective work the transfer kinetics of the lipophilic fluorescent photosensitizer 5,10,15,20-tetrakis(m-hydroxyphenyl)chlorine (mTHPC, Foscan®) between liposomal membranes will be investigated by using the so called fluorescence dequenching effect. For this purpose different drug-loaded liposomes (donor vesicles) as well as empty liposomes (acceptor vesicles) are prepared, whereby the latter serve as a model for biological membranes. The mTHPC concentration of donor liposomes is chosen in such a way, that the fluorescence intensity of the drug is self-quenched. Hence, the temporally transfer of the drug to acceptor liposomes can be analyzed via an increase in fluorescence intensity [2].

References

[1]

Hefesha, H., Loew, S., Liu, X., May, S., Fahr, A.: Transfer mechanism of temoporfin between liposomal membranes. J. Control. Release, 2011. doi:10.1016/j.jconrel.2010.09.021

[2]

Zhu, X.: Transfer of lipophilic drugs between liposomal membranes by using the ion-exchange micro-column technique and the fluorescence dequenching effect. Dissertation, 2008.  http://d-nb.info/993360122/34 (accessed: 22.03.2011)

 

All are welcome!

Rethinking Physics for Biologists: Considering Value Added

E. F. “Joe” Redish

Department of Physics, University of Maryland, College Park, Maryland, United States

Thursday, October 6th at 4:00 p.m.
(Refreshments at 5:00 p.m.)
South Engineering 116, NDSU

Over the past decade, biology and pre-health care students have grown into the largest population served by physics service courses.  With the recent explosion of high-tech biology and medicine, both the character of the students in this class and their educational needs have changed dramatically from when the current course was designed decades ago.  What can physics departments do to provide a better education for our students from biology? In order to answer this question, we have to understand not only the physics required but also the context and needs of the students.

The Discipline-Based Education Research Groups in Physics and Biology (PERG/BERG) at the University of Maryland have been studying this question for a decade. We have developed an understanding of the context and needs of biology students both through extensive observations (interviews, surveys, quizzes, exams, and videotaped observations of labs and tutorials) and through detailed negotiations with biology faculty. In this talk, I will discuss some of our previous reforms, our insights into interdisciplinary challenges, and our current work on developing a new biology-oriented introductory physics class.

References

E. F. Redish and D. Hammer, “Reinventing College Physics for Biologists: Explicating an Epistemological Curriculum,” Am. J. Phys., 77, 629-642 (2009). [http://arxiv.org/abs/0807.4436]

“Collaboration seeks to create interdisciplinary undergraduate curriculum”, www.hhmi.org/news/ nexus20110608.html

(Seminar Announcement.)

 

All are welcome!

Application of block copolymer patterning to magnetic materials

Dr. Andrew Baruth

Department of Chemical Engineering and Materials Science, University of Minnesota - Minneapolis, Minneapolis, Minnesota, United States

Wednesday, March 30th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

Block copolymers are comprised of two or more homopolymer subunits linked by a covalent bond, yet their mutual immiscibility results in microphase separation leading to the formation of useful periodic nanostructures (spheres, cylinders, lamellar, etc). Nanolithographic techniques based on self-assembled block copolymer templates offer exceptional potential for fabrication of large-area nanostructure arrays. Applying these techniques to magnetic materials will allow for the study of fundamental magnetic properties at the nanometer scale. In addition, the block copolymer approach to nanolithography has huge implications for the progress of bit-patterned magnetic recording media for ultra high-density storage (>1Tb/in^2). In the case of pattern transfer, the production of well-ordered, extremely small (<50nm) features, has been plagued with complications. In this presentation I will describe these issues and report our recent approaches to overcoming these problems. The process we developed can be summarized as an overfill/planarize/etch-back scheme, exploiting the large Ar ion beam etch rate contrast between polymers and typical metals. The process is demonstrated via formation of a large-area array of 24 1.5 nm diameter Ni80Fe20 nanodots (~0.4 x 10^12 dots/in^2) with exceptional long-range, hexagonally-close-packed order. Extensive microscopy, magnetometry, and electrical measurements provide detailed characterization of the pattern formation and fidelity. We argue that this generic approach can be applied to a wide variety of materials and is scalable to even smaller feature sizes. This work is funded by the NSF MRSEC.

 

All are welcome!

Applications of non-equilibrium work theorems in computational biophysics

Dr. Bruno Tomberli

Department of Physics and Astronomy, Brandon University, Brandon, Manitoba, Canada

Wednesday, March 9th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

Recent theoretical advances in statistical mechanics have enabled difficult yet informative free energy calculations to be carried out for complex biological systems using molecular dynamics simulations. An intuitive explanation of the important aspects of the theory will be used to introduce some recent generalizations made by my group. Results we have obtained from the application of these techniques to several systems (NaCl disassociation, stretching energy of a short peptide, penetration of a trace amine through a neuronal membrane) will be presented and compared to experimental results.

 

All are welcome!

Seeing is believing: A blend of STM Studies

Dr. Nuri Oncel

Department of Physics and Astrophysics, University of North Dakota, Grand Forks, North Dakota, USA

Thursday, March 3rd at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

Moore’s law predicts that the number of transistors on an integrated circuit doubles every eighteen months. This is possible only if the size of individual components can be continually reduced in a cost effective way. The most commonly used approach to build the components of an integrated circuit is the top-down approach, where externally-controlled devices, such as conventional lithographic techniques, are used to shape materials into the desired forms. This approach is reaching fundamental (diffraction) size limits, and is not useful for the precise positioning and interconnecting of molecular sized components. Therefore the second approach, a so called bottom-up approach, which utilizes the concepts of self-assembly and molecular recognition of individual molecules to build such devices, may facilitate the field of molecular electronics. Scanning tunneling microscopy/spectroscopy (STM/STS) is a unique technique with enough resolution to study the physical and chemical properties of surfaces and interfaces in molecular electronic devices. I will present STM/STS studies of various self-assembled molecular films and nano-structured Pt modified Ge(001) surfaces, relevant to the design and
implementation of molecular electronic devices.

 

All are welcome!

From Stiff Polymers to Cell Mechanics

Dr. Jens Glaser

Department of Physics, Leipzig University and Department of Chemical Engineering, University of Minnesota, Minneapolis, Minnesota, USA

Wednesday, February 9th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

The mechanical performance of living cells relies on the remarkable (visco)elastic properties of the cytoskeleton which consists of a dense meshwork of semiflexible protein filaments. I will discuss minimal theoretical descriptions of those networks, starting from the wormlike chain model for a single polymer. The first part of my talk concerns entangled solutions of semiflexible polymers, where interactions between impenetrable neighboring chains lead to the chains being confined into effective tube-like cages. One can calculate the average tube diameter using a Binary Collision approximation (BCA). I will show that within a systematic generalization of the BCA (the ”segment-fluid” model) it is possible to calculate not only the mean value of the tube radius R but also the distribution function P(R) of the tube radius [1]. In the second part, I will discuss the dynamics of entangled polymers by means of a phenomenological model for sticky polymer solutions, the ”glassy wormlike chain” The predictions of this model are compared to in-vitro and in-vivo experimental data.

[1] J. Glaser et al., Phys. Rev. Lett., 105 (2010) 037801

 

 Sponsored by NDSU Geosciences and Physics Department, and by the Cooperative Sponsorship program

 

All are welcome!

Simulations of phonon-mediated dynamics in quantum dots

Dr. Svetlana V. Kilina

Department of Chemistry, North Dakota State University, Fargo, North Dakota, USA

Monday, December 6th at 4:00 p.m.
South Engineering 221, NDSU

Nanotechnology represents a nexus of materials science, chemistry, physics, and engineering and is vital for the development of revolutionary applications ranging from electronics and photovoltaics to medicine. However, before advances in next generation technologies can come to fruition, understanding and control of the structure-property relationship of nanomaterials are required. Computational predictions based on atomistic modeling could provide valuable insight into these issues. In this talk, I first briefly overview the quantum-chemical approaches that we use to describe morphologies, optoelectronic properties, and photoexcited dynamics in novel nano-structured materials, such as semiconductor quantum dots (QDs). Based on these methods, we simulate phonon-assisted dynamics in ligated CdSe QDs with an ultimate goal to understand the role of surface ligands in fast relaxation of photoexcitation in QDs. Our simulations reveal that ligands passivating the QD surface introduce many hybridized states, which electronic density is spread over the QD and ligand atoms. Hybridized orbitals increase the overall electron-phonon couplings through their strong interaction both with the high frequency vibrations of the ligands and low energy phonons of the QD, thus, open new channels for relaxation. These results open a new prospective for understanding of fast energy relaxation mechanisms in QDs – a topic of general interest due to the recent focus on QD-based solar cells, light-emitting diodes, field-effect transistor, etc.

 

All are welcome!

Computational modeling of physical and chemical properties of nanostructured silicon surfaces for electronics and photovoltaics

Dr. Dmitri S. Kilin

Department of Chemistry, University of South Dakota, Vermillion, South Dakota, USA

Monday, November 15th at 4:00 p.m.

(Refreshments at 3:45 p.m. in SE216.)

South Engineering 221, NDSU

 

A new method combining ab initio electronic structure and density matrix approaches has been developed to simulate photo-excited dynamics in silicon-based energy materials. The interaction of electrons with thermalized lattice vibrations provides the dissipative terms in the equation of motion (EOM) for the reduced density matrix of the silicon surface and describes line broadening of optical excitations, dephasing, and population relaxation from the photoexcited state towards thermalized electronic state. The steady state solutions of the EOM in a basis of Kohn-Sham orbitals provide the electronic charge density for excited states responsible for the induction of a photovoltage at the surfaces [1], while time dependent solutions of the EOM provide rates for carrier relaxation induced by lattice vibrations [2]. Our simulations predict that absorption and photovoltage spectra of the silicon surfaces are drastically affected by presence of adsorbates on the surface or by p- or n- doping. The results obtained by our atomistic approach provide insight on trends relevant to the absorption of near IR, visible, and near UV light, which is of interest in measurements of photovoltages and in the utilization of solar energy.


 

All are welcome!

The Casimir effect in rectangular geometries

Dr. Luis Manzoni

Department of Physics, Concordia College, Moorhead, Minnesota USA

Wednesday, October 13th at 4:00 p.m.

(Refreshments at 3:45 p.m. in SE216.)

South Engineering 221, NDSU

 

The name Casimir effect is generally applied to a number of phenomena associated with the change in the zero-point energy of a quantized field due to the presence of external constraints. The simplest of such effects, and the one originally predicted by Casimir, is the force between two uncharged conducting parallel plates in vacuum. After introducing some of the basic concepts of the field we will discuss the difficulties of dealing with the Casimir effect in rectangular geometries and present some recent results for the double piston geometry.

 

All are welcome!

Wrinkles, Stress and Localization in Thin Block Copolymer Films

Dr. Andrew B. Croll

Department of Physics, North Dakota State University, Fargo, North Dakota, USA

Thursday, September 16th at 4:15 p.m.
South Engineering 221, NDSU

One of the most interesting and simple examples of pattern formation in Nature can be found as one squeezes together tissue on an arm – a set of equally spaced bends appear in the skin; it wrinkles! In fact any system that is composed of a rigid layer (here the skin) on a much softer substrate (the tissue below the skin) and placed under compressive stress will show the same behavior. The simple sinusoidal wrinkle pattern, however, can break down and the stress which is spread evenly throughout the pattern can localize – in other words the system can be pushed to failure. Here I show how localization can occur due to an appropriately chosen perturbation, notably at a vanishingly small applied stress. I will then show how the stresses present in the wrinkled film itself have, in fact, already broken the energetic symmetry. This effect is most dramatically realized when a disordered block copolymer film is wrinkled and then allowed to microphase separate. This experiment show how a macroscopic stimulus (the applied stress) is easily translated into local variations in molecular mobility.

 

All are welcome!

Iron Oxide Nanoparticles: Synthesis, Properties, And Biomedical Applications

Dr. Kevin J. Landmark

Department of Physics, Augsburg College, Minneapolis, Minnesota, USA

Thursday, September 16th at 3:15 p.m.
South Engineering 221, NDSU

Although various organisms have long been able to biochemically produce uniform crystalline magnetic nanoparticles and leverage their unique properties, laboratory syntheses and applications of such particles are relatively recent developments. Scientists have devised synthetic schemes to generate batches of magnetic nanoparticles with very narrow size distributions and exceptional magnetic properties using precursors containing transition metals. Particles composed of nickel, cobalt, and their oxides generally have more favorable magnetic characteristics than particles of comparable size made of iron and its oxides. However, the toxicity of nickel and cobalt and the instability of pristine transition metal nanoparticles, make iron oxide-based materials a better choice for biomedical applications such as hyperthermia, targeting therapeutics, and MRI contrast agents.

 

All are welcome!

Single-molecule diffusion and conformational studies of MHC Class I proteins in fribroblast cells

Dr. Ahmed A. Heikal

Department of Chemistry and Biochemistry, and Department of Pharmaceutical Sciences, University of Minnesota, Duluth, USA

Thursday, February 4th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

 

Major histocompatability complex (MHC) class I proteins present pathogen peptides to effector T lymphocytes to trigger the destruction of infected cells.  The assembly of MHC I proteins in the endoplasmic reticulum (ER) involves their binding to a number of ER chaperones and accessory proteins, which supply the proteasome-generated peptides in the cytosol to the nascent MHC I.  Peptide-loaded MHC I proteins then dissociate from transporter associated with antigen processing (TAP) complex.  The mechanisms by which MHC proteins are transiently retained in the ER are not understood.  Conventaional biochemical analyses are inherently incapable of characterizing the association dynamics of MHC I with the TAP complex.  In the contribution, I will present our recent single-molecule studies of GFP-encoded MHC I diffusion in living mouse fibroblast cells.  Using multimodal and noninvasiv fluorescence micro-spectroscopy methods, we also quantified the intracellular distribution, lateral heterogeneity, and conformational dynamics of MHC I proteins in living cells under different conditions of proteasome inhibition and peptide loading.

 (Seminar Announcement)

 

All are welcome!

Simulations of Membrane Fusion and the Role of Different Lipids

Dr. Mark Stevens

Center for Integrated Nano-Technologies, Sandia National Laboratories, Albuquerque, New Mexico, USA

Wednesday, January 27th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 120, NDSU

 

Abstract: We have performed molecular dynamics simulations of vesicle fusion using coarse-grained lipid models. Using the weighted histogram method, we calculate the free energy barrier for two vesicles to come into contact and the initial fusion event to occur, i.e. mixing of lipids between the two outer leaflets. The structural dynamics of the initial fusion event is imaged and connected to the free energy differences. These calculations have been performed for four different vesicles. The lipids in the four vesicle types are DPPC, DOPC, a 3:1 mixture of DPPC/DPPE and an asymmetric lipid tail system in which one tail length was reduced to half the length. We find the free energy barrier to be about the same magnitude for all except the system with asymmetric tail lengths. In addition, the free energy curves can be overlaid on a single curve by plotting versus the surface separation. The asymmetric tailed system has a barrier about 3 times larger than the others. Examination of the initial lipid mixing shows that the initial lipids crossing from one vesicle to another often have splayed tails, and the tails span the gap between the two vesicles. Thus the splayed lipid provides the initial connection between the vesicles that then promotes successive lipids to cross between the vesicles leading to fusion of the outer leaflets and ultimately full fusion. The reason for the asymmetric tail system having a larger barrier is that the asymmetric tail requires a smaller separation for fusion, because its shorter tail can only span a smaller gap. Consequently, this system must go further up the free energy curve (i.e. more water must be removed from between the vesicles and more deformation). We compare our results with experimental data, but since our vesicle size is very small, direct comparison is not possible, but there are interesting issues that arise.

 (Seminar Announcement)

 

All are welcome!

Chemomechanical coupling and multiscale motility of molecular motors

Dr. Reinhard Lipowsky

Director of the Department of Theory & Bio-Systems, Max-Planck Institute of Colloids and Interfaces, Potsdam, Germany

Wednesday, December 9th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

 

All eukaryotic cells including those of our body contain a large variety of molecular machines that convert the chemical energy released from nucleotide hydrolysis into mechanical work. This talk will focus on cytoskeletal motors which walk with two motor heads and have been intensely studied by single molecule experiments. One such motor is conventional kinesin, for which each motor head contains a single domain for ATP binding and hydrolysis. Our theory for these motors starts with a network representation based on the different nucleotide states of the motor heads. The properties of single motors are then used to describe the cooperative behavior of many motors. The latter behavior includes uni-directional and bi-directional transport of cargo particles by small teams of motors as well as pattern formation and phase transitions in motor traffic.

 (Seminar Announcement)

Supported by the Departments of Physics, Mechanical Engineering, Coatings & Polymeric Materials, and the Cooperative Sponsorship Committee.

 

 

 

 

All are welcome!

Unveiling Dark Energy - An Accelerating Universe

Dr. Wayne Barkhouse

Department of Physics and Astrophysics, University of North Dakota, Grand Forks, North Dakota, USA

Wednesday, December 2nd at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

 

In 1998, two independent teams of astronomers announced that the Universe was in a period of accelerated expansion. This unexpected discovery signifies either a breakdown in our understanding of gravity on large scales or the existence of an ”anti-gravitational” force (dark energy) that permeates the Universe.
Due to the potential paradigm shift in our understanding of physics at a fundamental level, major funding sources (i.e., NASA, DOE, and NSF) have expressed interest in supporting research initiatives that seek to uncover the nature of dark energy. One of these projects, the Dark Energy Survey (DES), will observe 5000 square degrees of the southern hemisphere using a new wide-field imaging camera mounted on a 4-meter telescope in Chile. The DES will allow astronomers to characterize dark energy with high precision and provide important observational constraints on its nature. As a member of the DES, I will describe how this project will help to shed light on dark energy.

 (Seminar Announcement)

 

All are welcome!

Molecular Simulation of Self-Assembly on the Nanoscale

Dr. Jerome Delhommelle

Department of Chemistry, University of North Dakota, Grand Forks, North Dakota, USA

Wednesday, November 18th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

 

We review recent work on the molecular simulation of the crystallization process.  The aim of this work is to obtain a complete understanding of the molecular mechanisms underlying crystal nucleation and growth, and, in particular, to shed light on the polymorph selection process.  For this purpose, we carry out three different types of molecular simulation: (i) to determine the phase diagram of the simulated system, (ii) to simulate the crystal nucleation event and (iii) to gain a direct access to the crystal growth mechanism.  We present results obtained on a variety of systems, ranging from model systems to colloidal systems and metal nanopoarticles and discuss new leads to improve the accuracy of simulation methods for the determination of phase diagrams.

 

 (Seminar Announcement)

 

All are welcome!

Mathematical Models of Dielectric Breakdown and Polycrystal Plasticity

Dr. Marian Bocea

Department of Mathematics, North Dakota State University, Fargo, North Dakota, USA

Wednesday, November 4th at 4:00 p.m.
South Engineering 221, NDSU

 

I will discuss several models of (first-failure) dielectric breakdown and polycrystal plasticity, with a focus on their mathematical derivation from more flexible power-law models via Γ-convergence, and on the characterization of the effective yield sets by means of variational principles associated to the limiting supremal functionals. This is based on joint with with Enzo Nesi (Universita di Roma, "La Sapienza"), and with Cristina Popovici (NDSU).

 

 (Seminar Announcement)

 

All are welcome!

Wrinkling and Strain Softening in Nanotube Membranes

Dr. Erik K. Hobbie

Department of Physics, Department of Coatings and Polymeric Materials, North Dakota State University, Fargo, North Dakota, USA

Thursday, October 8th at 4:15 p.m.
South Engineering 221, NDSU

The ability of an applied strain to distort the nanoscale structure of thin polymer films has profound scientific and technological implications. The mechanical characteristics of such membranes are dictated by the arrangement and strength of molecular contacts, and structural changes at these small length scales can have a significant impact on film performance. Membranes comprised of single-wall carbon nanotubes (SWNTs) represent an intriguing example of this. The mechanical properties of the individual SWNTs can be outstanding while their high aspect ratio enables 2D network formation at remarkably low surface density. The mechanics of inter-SWNT contacts, however, can ultimately limit the response of the film. Recent advances in the separation of nanotubes by length and type make ultra-pure SWNT membranes a reality, creating the need to better understand the deformation mechanics of this technologically important class of film. I will describe our recent work on measuring the microscale wrinkling of thin SWNT films under compressive strains and demonstrate how existing models fail to capture the essential physics occurring at the nanoscale.

 

All are welcome!

Modeling and Simulation of the Behavior of Heat-Shrinkable Thin Films

Dr. Pavel Belik

Department of Mathematics, Augsburg College, Minneapolis, Minnesota, USA

Thursday, October 8th at 3:15 p.m.
South Engineering 221, NDSU

In this talk we will discuss mathematical modeling and computer simulation, and illustrate their power in understanding and predicting the behavior of polyester thin films when subjected to heat treatment. The motivation of this problem comes from applying thin transparent films on car windshields. Experimental data will be discussed, a mathematical model will be developed, and numerical results will be presented that predict how such films might deform when heated.

 

All are welcome!

Monte Carlo simulations of complex formation between a mixed fluid vesicle and a charged colloid

Dr. Miha Fosnaric

Faculty of Electrical Engineering, University of Ljubljana, Slovenia

Wednesday, August 26th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE216.)
South Engineering 221, NDSU

 

Monte Carlo simulations are employed to investigate the ability of a charged fluid-like vesicle to adhere to and encapsulate an oppositely charged spherical colloidal particle. The vesicle contains mobile charges that interact with the colloid and among themselves through a screened electrostatic potential. Both migration of charges on the vesicle surface and elastic deformations of the vesicle contribute to the optimization of the vesicle-colloid interaction. Our Monte Carlo simulations reveal a discontinuous wrapping transition of the colloid as a function of the number of charges on the vesicle. Upon reducing the bending stiffness of the vesicle, the transition terminates in a critical point. At large electrostatic screening length we find a re-entrant wrapping-unwrapping behavior upon increasing the total number of charges on the vesicle. We present a simple phenomenological model that qualitatively captures some features of the wrapping transition.

 

 

 

(Seminar Announcement)

 

 

All are welcome!

Block Copolymer Droplets, Thin Films, and Wrinkles

Dr. Andrew B. Croll

Department of Polymer Science and Engineering, University of Massachusetts Amherst, Massachusetts, United States

Wednesday, July 15th at 11:00 a.m.
(Refreshments at 10:45 a.m. in SE216.)
South Engineering 221, NDSU

 

Block copolymers are long chain molecules made of segments of more than one polymer variety covalently joined together. This molecular architecture leads to many technologically important phenomena which are useful in applications that range from the semiconductor to the commodity polymer industries. Many of the most important properties of these systems result from the nanoscopic structures that form due to the chemical incompatibility of the blocks. In this talk I will present our progress towards a more detailed understanding of the physics of these systems. I will focus on the simplest system, that of symmetric diblock copolymers (where the chain consists of two distinct blocks of equal size) in a variety of different experimental confining geometries. I will show how the micro-phase separated structures lead to conically shaped fluid droplets, how the thin film geometry can be adapted into a very simple measurement of the Flory-Huggins interaction parameter and how the structured surface of a thin film can be used to drive a simple wrinkle into a state of stress localization.

 

 

(Seminar Announcement)

 

 

All are welcome!

Phase separation in binary fluids with varying temperature

Dr. Guiseppe Gonnella

Dipartimento di Fisica, Università degli Studi di Bari, Italy

Wednesday, May 27th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE218.)
South Engineering 221, NDSU

 

A hybrid Lattice Boltzmann method is used to simulate binary fluids where also the temperature evolves following its dynamical equation.  The system is quenched by contact with cold walls at temperatures below the critical value and different morphologies are observed for different thermal diffusivities and viscosities.  Lamellar patterns are favoured at high viscosity and with slight asymmeteric concentrations.

 

 

Sponsored by NDSU Geosciences and Physics Department, the Department of Coatings and Polymeric Materials, and by the Cooperative Sponsorship program.

 

All are welcome!

 

 

Soft Materials on the Nanoscale

Dr. James Forrest*

Department of Physics and Astronomy, Waterloo Institute for Nanotechology, University of Waterloo, Waterloo, Iowa, United States

Friday, April 17th at 1:30 p.m.
EML 370, NDSU

 

There is little doubt that nanotechnology, the exploitation of nanometer sized entities in technology, is among the most rapidly expanding areas of materials science and technology.  It is also true that our understanding of such objects or of bulk materials on the same nm scale has not expanded at the same rate, and that knowledge of bulk material properties does not necessarily lead to reasonable predictions of the properties on the nanoscale. It is crucial to increase our understanding of how materials behave on the nm scale to provide a strong underpinning for emerging nanotechnologies. In this talk I will give two recent examples we have studied showing how soft materials in the “nanoworld” behave very differently than we may have guessed. Both of these examples have immediate technological implications.  The first example is the properties of the first few nm of a glassy polymer surface- a problem highly relevant for some recent proposals for high density information storage.  While this question has been hotly debated for about 15 years, only recently has a clear picture emerged.  We have shown that for glassy polymer systems there is strong evidence for a surface layer that in many ways behaves like a liquid (rather than a softer solid). We have also provided bounds on the length scale of this near surface effect.  The second example involves the interaction of proteins with nanoparticles.  This interaction is fundamental in the rapidly growing area of nanobiosensing, and in understanding potential toxicity of nanoparticles. We have shown that the adsorption of protein, as well as both reversible and irreversible structural changes of proteins on nanoparticles are surprisingly sensitive to the size of the nanoparticle. These examples highlight the importance of having basic knowledge keep pace with technological developments on the nanoscale. Finally, I will discuss how the Materials Science and Nanotechnology graduate program at NDSU can be a prominent player on the national and perhaps international stage in advancing nanotechnology and nanoscience particularly, but not exclusively, in areas traditionally denoted as soft materials.

 

 

 

* Dr. Forrest is a candidate for the position of Director of the Graduate Program in Materials and Nanotechnology.

 

 

All are welcome!

Joining of Nano-building Blocks and Fabrication of Nanojoints

Prof. Mustafa Yavuz*

Waterloo Institute of Techology, University of Waterloo, Waterloo, Iowa, United States

Monday, April 13th at 1:00 p.m.
Reimers Conference Room, Alumni Center, NDSU

 

To realize electronic applications of carbon nanotubes, such as quantum wires, ballistic conductors, microchip interconnects and transistors, reproducible fabrication of joints between individual nano-tubes and -electrodes has been identified as a major impediment. Previous studies have shown that electrically conductive connection between nano building blocks is not straightforward. Instead of desired ohmic contacts, tunnel junctions or weak links of a high contact resistance typically at 200 kΩ for contact regimes on the order of 1 nm2, are often generated. Obviously, the gap-sensitive contact resistance makes it difficult to join nano building blocks with repeatable performance in nano-devices [1, 2]. 

 

 

 

[1] W. Wu, A. Hu, X. Li, J.Q. Wei, K.L. Wang, M. Yavuz  and N. Zhou, “Vacuum Brazing of Carbon Nano Tube Bundles”, Materials Letter (Elsevier), vol. 62, pp. 4486-4488, 2008.

[2] S. Sahin, M. Yavuz and N. Zhou, Handbook of Microjoining and Nanojoining, “Chapter 18:

Introduction to Nanojoining”, 70 pages, editor: N. Zhou, Woodhead Publishing Ltd., 2007. 

 

 

 

* Professor Yavuz is a candidate for the position of Director of the Graduate Program in Materials and Nanotechnology.

 

 

All are welcome!

Interaction of Biological Molecules with Nanostructures: The Hybrid DNA-Nanostructure System

Dr. Ravindra Pandey*

Department of Physics, Michigan Technology University, Houghton, Michigan, United States

Wednesday, April 8th at 1:30 p.m.
Reimers Conference Room, Alumni Center, NDSU

 

The combination of biological molecules and nanostructures offers exciting possibilities for the design of new applications. In particular, DNA and RNA, two classes of extremely versatile bio-polymers may be connected non-covalently to carbon nanotubes to form a novel hybrid system with a number of interesting properties.

In this talk, we present the results of our first-principles study of the interaction of nucleic acid bases with a metallic carbon nanotube as a significant step towards an understanding of the fundamental physics and the mechanism of this sequence-dependent interaction of ssDNA with CNTs.

The second part of the talk will describe the results of calculations on the functionalized nanopore-embedded gold electrodes with the aim of improving nanopore-based DNA sequencing method.  The results of our study indicate that our proposed scheme could allow DNA sequencing with a robust and reliable yield, producing current signals that differ by at least one order of magnitude for the different bases.  Hydrogen bonds formed between the molecular probe and target bases appear to stabilize the scanned DNA unit against thermal fluctuations and thus greatly reduce noise in the current signal.

(in collaboration with  groups at Trinity College, Uppsala University, and Army Research Lab)

 

 

* Dr. Pandey is a candidate for the position of Director of the Graduate Program in Materials and Nanotechnology.

 

 

All are welcome!

Engineering New Materials from Polymers and Nanoparticles

Dr. Erik K. Hobbie*

National Institute of Standards and Technology, Gaithersburg, Maryland, United States

Wednesday, March 25th at 10:00 a.m.
Reimers Conference Room, Alumni Center, NDSU

 

 

Hybrid soft materials composed of polymers and synthetic nanoparticles represent a simple paradigm that lies at the core of a number of current trends in nanotechnology. Examples range from polymer nanocomposites and organic photovoltaic devices to biochemical sensors and the potentially toxic interaction of nanoparticles with living biological cells. I will discuss some of these examples from the perspective of our recent and current work on the dispersion, purification and self-assembly of single-wall carbon nanotubes using biological polymers and surfactants, and I will outline my vision for extending this effort to other types of nanoparticles that show particular promise for emerging applications in energy, medicine and biotechnology.

 

 

 

* Dr. Hobbie is a candidate for the position of Director of the Graduate Program in Materials and Nanotechnology.

 

 

All are welcome!

 

 

Biophysical Properties and Applications of Cholesterol in Lipid Membranes

Dr. Benjamin Stottrup

Department of Physics, Augsburg College, Minneapolis, Minnesota, United States

Thursday, March 12th at 2:00 p.m.
(Refreshments at 1:45 p.m. in SE 216)
South Engineering 221, NDSU

 

 

The plasma cell membrane is a dynamic biological structure which separates the cell from its surroundings, localizes proteins at an interface, and plays an active role in many cellular processes.  The multi-functionality of the membrane is provided by a diverse array of molecules.  For example, in the presence of water, amphiphilic molecules called lipids self-assemble into bilayers which provide a structural backbone for the membrane.  Of these lipids, cholesterol has been identified as unique.  I will describe work in my lab to understand how structural features of the cholesterol molecule confer important biophysical properties to the lipid membrane.  Two areas of focus will be on the transbilayer diffusion rates for phospholipids in the presence of sterols and line tension measurements between coexisting liquid phases.  Materials scientists and engineers seek to exploit the biophysical properties of these systems in the development of biomimetic surfaces and drug delivery systems. Potential applications of this work as a tool in biotechnology, experimental techniques, and future research directions will be described.

 

 

 

 

All are welcome!

Investigations into Student Understanding of Thermal Physics

Dr. Warren Christensen*

Department of Physics and Astronomy, University of Maine, United States

Wednesday, February 11th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE 216)
South Engineering 221, NDSU

 

This talk will highlight some of my work with students' understanding of entropy and the second law of thermodynamics in the introductory and upper-level courses in physics.  The research has led to the development of several pieces of curriculum.  Additionally, I will present evidence of similar confusion among students in an introductory chemistry course, and lay out the future plans for this investigation.


* Dr. Christensen is a candidate for a faculty position in the Department of Physics and the School of Education.

 

 

 

All are welcome!

Self assembled Polymer Nanocomposites in Solution: The example of Pluronic systems

Dr. Alex Travesset

Iowa State University and Ames Lab, Ames, Iowa, United States

Wednesday, January 21st at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE 216)
South Engineering 221, NDSU

 

The phase diagram of soluble non-ionic polymers in aqueous solutions containing hydrophobic monomers is amazingly rich. A prototypical example is provided by Pluronic polymers, consisting of symmetric triblocks of Polyethylene oxide and Polypropilene oxyde, which display a miriad of phases, both liquid crystalline or crystalline. I will present a general approach to map the phase diagram of non-ionic multiblock polymers from coarse-grained molecular dynamics simulations and theory. As a concrete example, I will discuss the self-assembly of micellar crystals with cubic symmetry in pluronic systems and general strategies for the design of nanocomposites materials from multiblock copolymers in solution. I will show that when inorganic particles or nanoparticles are added, functionalization, that is, attaching functional groups at the two polymer ends with specific affinity for the inorganic phase, provides a robust and versatile strategy to create composite materials where self-assembled inorganic crystals follow a bewildering ordered phases inherited from the polymeric matrix.

 

 

Sponsored by NDSU Geosciences and Physics Department, the Department of Coatings and Polymeric Materials, and by the Cooperative Sponsorship program.

 

 

 

 

 

All are welcome!

"A naturally-occurring replication protein homolog that prevents cell proliferation"

Dr. Stuart J. Haring

North Dakota State University, Fargo, North Dakota, United States

Wednesday, November 19th at 4:00 p.m.
South Engineering 221, NDSU

 

It is essential for cells to duplicate their genetic information with high fidelity and to preserve the integrity of the genome in order to proliferate and develop properly.  One of the key factors in the duplication and maintenance of DNA is the eukaryotic single-strand DNA (ssDNA) bindingprotein complex, Replication Protein A (RPA).  This complex was originally isolated as a factor essential for eukaryotic DNA replication and is present in all eukaryotes examined.

The major biochemical activity of RPA is to bind and protect ssDNA; however, it is becoming clear that the importance of this complex lies beyond its interactions with DNA.  A novel RPA subunit homolog, called RPA4, has been identified in human cells.  We have demonstrated that the RPA4 subunit can participate in the formation of an alternative RPA complex that interacts with ssDNA.  I will present data showing that the alternative RPA prevents cell proliferation through a number of mechanisms and may directly influence whether or not a cell is proliferating or quiescent.

 

 

 

All are welcome!

"The Electrochemical Assessment of Coatings"

Dr. Victoria Gelling

North Dakota State University, Fargo, North Dakota, United States

Monday, November 3rd at 2:00 p.m.
South Engineering 221, NDSU

 

Historically, the assessment of corrosion and coating degradation has been primarily a visual science.  This lends itself to estimates of durability that tend to be qualitative in nature with the results varying depending on the person performing the assessment.  In order to overcome these inherent difficulties, the use of electrochemical techniques to investigate the durability, degradation, and subsequent corrosion of the substrate are becoming widely used.

Electrochemical techniques allow for the determination of changes in coating properties, which often occur prior to visual changes.  Current electrochemical techniques, such as electrochemical impedance spectroscopy (EIS), provide one with information that is far superior to the historical visual assessments alone.  Now, small changes in capacitance and resistance of a coating sample can be monitored via EIS.  These changes can be followed by using circuit modeling to extract further information from the EIS results.  EIS characterization of coated substrates degradation may allow for the extraction of a service life prediction of a coating.  In the talk, the use of electrochemical techniques, will be introduced with recent results from the research group given as examples.

 

 

All are welcome!

"Lie groups and matrix generating functions"

Dr. William Schwalm

University of North Dakota, Grand Forks, North Dakota, United States

Wednesday, October 22nd at 4:00 p.m.
South Engineering 221, NDSU

 

A familiar generating function is the one giving Legendre polynomials as coefficients in a series expansion.  The point of it is that it facilitates efficient calculations.  Similarly, one would like generating functions for the eigenstates of other Hermitian eigenvalue problems that arise in quantum mechanics, electromagnetism or continuum dynamics.  A tool for this is Weisner's method, which utilizes the problem's symmetry algebra.  To illustrate the idea, first standard generating functions the Bessel functions and the one dimensional quantum oscillator are found.  A Lie group is introduced as a kind of Taylor series expansion.  Then the construction of a generating function for mutual eigenstates of the isotropic 3D oscillator and angular momentum is outlined.  As application, these are used to analyze several interesting problems in quantum mechanics and radiation theory.

 

 

All are welcome!

"Thermodynamically consistent lattice Boltzmann simulations of multiphase and multicomponent systems"

 

Dr. Alexander Wagner

North Dakota State University, Fargo, North Dakota, United States

Wednesday, October 8th at 4:00 p.m.
South Engineering 221, NDSU

 

In this talk I present some recent results for the implementation of multiphase and multicomponent systems.  I will briefly review existing methods for implementing non-ideal fluid mixtures and point out their shortcomings.  In the second part of the talk I will then present one-dimensional implementations which are thermodynamically consistent.

 

All are welcome!

"Self-consistent field theory of polyelectrolytes and application on gene delivery"

Dr. Shuang Yang

North Dakota State University, Fargo, North Dakota, United States

Wednesday, September 24th at 4:00 p.m.
South Engineering 221, NDSU

 

Self-consistent field theory (SCFT) of polyelectrolyte systems will be introduced.  In this theory, one approximates the ensemble of interacting polymers by a system of non-interacting polymer chains in an effective potential field.  The field depends in a self-consistent manner on the density profile and determines the conformation of polymer chains.  SCFT provides a powerful tool in describing polymer interfaces and self-assembly of block copolymers.  Based on the above theory, we investigated the release of cationic polymer-DNA complexes from the endosome, which is an important issue in gene delivery in a cell

 

All are welcome!

"Dark Entropy"

Dr. Terry Pilling

North Dakota State University, Fargo, North Dakota, United States

Wednesday, September 10th at 4:00 p.m.
South Engineering 221, NDSU

 

We examine the consequences of a universe with a non-constant cosmological term in Einstein's equations and find that the Bianchi identities reduce to the first law of thermodynamics when the cosmological term is identified as being proportional to the entropy density of the universe.  This means that gravitating dark energy can be viewed as entropy, but more, the holographic principle, along with the known expansion of the universe leads to a cosmic repulsion that also grows with time.  Direct implications of this result are calculated and shown to be in good accord with recent observational data

 

All are welcome!

"Lattice-Boltzmann simulations and analytical results for Phase-separation in Lipid Bilayers"

Waipot Ngamsaad

Mahidol University, Bangkok, Thailand

Wednesday, August 27th at 4:00 p.m.
(Refreshments at 3:45 p.m. in SE 216)
South Engineering 221, NDSU

 

Many lipid bilayers will undergo phase-separation. It is believed that this
phase-separation may play significant roles in cell membranes. For sup-
ported lipid bilayers, the effect of substrate-induced immobilization of the
lower monolayer is important. It has been observed that lipid domains
in two leaves can be in or out of registration depending on the friction
between the lower monolayer and the substrate. We model the supported
lipid bilayers as two two-dimensional binary fluids that are coupled through
a simple interaction term as well as friction terms between each other and
the substrate. We developed a lattice-Boltzmann method (LBM) to numer-
ically investigate this model. In our simulations we found several dynamic
regimes for domain coarsening, including diffusive coarsening in the lower
monolayer, hydrodynamic coarsening in the upper monolayer and arrested
growth in the upper monolayer due to the coupling interaction. By sim-
plifying the membrane morphology patterns, we are able to find analytical
solutions for the arrested length-scale of domains in the upper monolayer.
Our simulation results support extending to more complex situations.

(Seminar Announcement)

All are welcome!


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Published by Department of Physics

Last Updated: Tuesday, October 21, 2014 12:37:48 PM