LaCNS Seminars Fall 2018 

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Hang Chi photo1) Monday, August 20, 3:00 pm, 1008B Digital Media Center

Dr. Hang Chi (Research Fellow, University of Michigan), host Rongying Jin

"Transport properties of novel thermoelectric chalcogenides"

Abstract: Thermoelectric materials can recover waste industrial heat and convert it to electricity as well as provide efficient local cooling of electronic devices. We first demonstrate that the efficiency (determined by the dimensionless figure-of-merit ZT) of such environmentally responsible and exceptionally reliable solid-state energy conversion can be enhanced through electronic band engineering in Mn-doped SnTe. Moreover, using thin film configurations, systematic study in Bi2Te3-based molecular beam epitaxial (MBE) films grown on sapphire (0001) and/or BaF2 (111) substrates, has revealed that the peak of phonon-drag thermopower can be tuned by the choice of substrates with different Debye temperatures. Finally, ZrTe5, known for large thermopower at cryogenic temperatures, has recently been revisited as a potential topological platform, hosting a highly anisotropic three-dimensional Dirac band. Transport measurements suggest the long-debated anomalous resistivity peak could be associated with a Lifshitz transition in the Dirac band. Such Lifshitz transition is readily controllable by means of doping. The anomaly peak temperature monotonically increases with the chemical potential, serving as an effective knob for fine tuning transport properties in pentatelluride-based Dirac semimetals.

 

Ahmad Us Saleheen2) Monday, August 27, 3:00 pm, 1008B Digital Media Center

Ahmad Us Saleheen (PhD candidate, Department of Physics & Astronomy, Louisiana State University), host Rongying Jin

"Magnetocaloric and barocaloric effects in (MnNiSi)1-x(FeCoGe)x"

Abstract: Solid-state caloric effects, such as the magnetocaloric (MCE) and barocaloric (BCE) effects, may be utilized in future cooling technologies that are more efficient and environment-friendly. Large caloric effects often occur near phase transitions, especially near coupled first-order magnetostructural transitions (MST), and are initiated by external parameters, such as magnetic field or hydrostatic pressure. In this talk, the effects of pressure, temperature, and magnetic field on the phase transitions and associated caloric effects in a MnNiSi-based system will be discussed. MnNiSi undergoes a structural transition at about 1200 K, and a magnetic transition at TC = 662 K. Tuning these two transitions so that they coincide in temperature, produced a coupled MST which, in this case, was achieved through an isostructural alloying of MnNiSi with FeCoGe. The resulting coupled MST gave rise to a large conventional MCE near room temperature. Moreover, the MST was found to be extremely sensitive to applied hydrostatic pressure, which shifts the transition towards lower temperature at a rate of -7.5 K/kbar. Conversely, an applied magnetic field shifts the transition towards higher temperature. The strong pressure dependence along with a large volume change during the MST suggested the possibility of pressure-induced barocaloric effect (BCE) in this material. Subsequently, a large inverse BCE (i.e., the temperature decreases with increasing pressure) was observed through pressure-dependent calorimetric measurements. Through a purpose-built experimental setup, the temperature change due to the BCE was also measured directly, which was about -4.3 K for P = 2.5 kbar near room temperature. Since this material shows multiple caloric effects (MCE and BCE) at the same phase transition, it is considered to be a multicaloric material.


Michalis Charilaou3) Monday, October 1, 3:00 pm, 1008B Digital Media Center

Dr. Michalis Charilaou (Assistant Professor, University of Louisiana at Lafayette), host John DiTusa   

Title: TBA

Abstract: TBA

  

 

Despina Louca photo

4) Monday, October 8, 3:00 pm, 1008B Digital Media Center

Dr. Despina Louca (Professor, Experimental Condensed Matter Physics, University of Virginia), host Ilya Vekhter

Title: TBA

Abstract: TBA

 


Lilo Pozzo photo5) Monday, October 15, 3:00 pm, 1008B Digital Media Center

Dr. Lilo Pozzo (The Weyerhaeuser Endowed Associate Professor of Chemical Engineering, University of Washington), host Bhuvnesh Bharti

"Structure and Dynamics of Conjugated Polymers from Neutron Scattering and MD Simulations"

Abstract: Conjugated polymer films, nanofibers, and networks can be ideal materials for the design of efficient photovoltaic devices, batteries, thermoelectric cells, light emitting diodes and many emerging energy technologies. It is also recognized that the structure and dynamics of organic semiconductor materials correlates strongly with large changes in optical, electronic and mechanical properties so that their control and manipulation is essential to advancing the field. This presentation outlines the use of neutron scattering techniques in the development of structure-property relationships for conjugated polymer nanomaterials. It also highlights recent results on the use of neutron and x-ray scattering techniques for improvements in molecular simulation force fields specifically produced for conjugated polymers. Quasi-elastic neutron scattering (QENS) experiments are used along with computationally efficient MD simulations to understand the nature of important nanoscale motions. X-ray and polarized neutron diffraction are also used to correlate experimental and model-generated polymer structures. QENS validation of MD force fields presents a unique opportunity to increase the accuracy of highly uncertain parameters used in simulation of conjugated polymers and other complex macromolecules. These parameters are currently estimated from quantum mechanical calculations such as density functional theory but, unlike many force fields for small molecules, they are not parameterized to available experimental data. Moreover, high variability is observed in parameters for the small number of force fields that have been proposed in the literature.

  

Sunil Sinha6) Monday, October 22, 3:00 pm, 1008B Digital Media Center

Dr. Sunil Sinha (Distinguished Professor of Physics, University of California San Diego), host Gerald Schneider

"Studies of Dynamics of Soft Matter using Coherent X-Ray Scattering"

Abstract: The dynamics of thin polymer films can be probed by studying the relaxation of surface capillary wave fluctuations using the technique of X-ray Photon Correlation Spectroscopy. This is the X-ray analog of Dynamical Light Scattering and utilizes beams of coherent X-rays available from modern synchrotron X-ray sources. We shall review the method and some of the results obtained, including the limits of validity of simple hydrodynamic fluid theory, the behavior of very thin polymer films, what happens as the glass transition is approached, and the study of the entangled dynamics of nanoparticles inserted into polymer films. We will also briefly discuss some recent applications of Soft X-Ray Resonant Magnetic Scattering to study phase transitions in frustrated spin systems.

 

7) Tuesday, October 23, TBA

Dr. Sunil Sinha (Distinguished Professor of Physics, University of California San Diego), host Gerald Schneider                                    

Title: TBA

Abstract: TBA

 


Kunlun Hong8) Monday, October 29, 3:00 pm, 1008B Digital Media Center   

Dr. Kunlun Hong (Senior Research Staff, Oak Ridge National Laboratory), host Gerald Schneider

Title: TBA

Abstract: TBA

 

 


Susan Krueger9) Monday, November 5, 3:00 pm, 1008B Digital Media Center

Dr. Susan Krueger (Research Physicist, NIST Center for Neutron Research), host Gerald Schneider

"Structure and Function of Biological Macromolecules in Solution: The Unique Role of Small-Angle Neutron Scattering"

Abstract: Small-angle neutron scattering (SANS) is a useful tool for investigating the structure of complex biological macromolecules in solution.  Neutrons are sensitive to the positions of the light elements such as hydrogen, carbon, nitrogen and oxygen, which are of central importance to all biological systems.  They are also sensitive to different isotopes, especially hydrogen and deuterium.  SANS takes advantage of these properties to provide unique insight into macromolecular structure and function through a technique known as contrast variation.  The scattering from one component in a biological complex can be separated from that of the others, providing unique structural information about each component individually, as it is interacting with the others in the complex.  The concept of SANS from biological macromolecules in the dilute limit will be introduced, focusing on the use of deuterium labeling, contrast variation and all-atom structure modeling to determine the structure of the individual components in protein-nucleic acid, protein-lipid and protein-protein complexes.  More advanced topics such as concentrated solutions and extreme environmental conditions will also be mentioned.

  

John Katsaras photo10) Monday, November 12, 3:00 pm, 1008B Digital Media Center

Dr. John Katsaras (Senior Scientist, ORNL Large Scale Structures Neutron Sciences Directorate)

"Static and Dynamic Neutron Scattering Studies of Biologically Relevant Membranes"

Abstract: Biomembranes are the active boundary between cells and their surroundings. They are sophisticated and dynamic machines that perform a diverse array of functions, including selective transport, localization, communication and recognition, to name a few. It is also widely accepted that the plasma membrane is laterally heterogeneous containing nanoscopic regions enriched in certain types of lipids, which have different physical properties from the surrounding lipids. These functional lipid domains in biology are commonly referred to as “rafts”. Rafts have been implicated in a wide range of cellular functions, including signal transduction, drug uptake, and interactions with pathogens. In recent years, we have used small angle neutron scattering (SANS) and neutron spin echo (NSE) to study nanoscopic lipid domains in model membrane systems [1-3] and more recently, in the Gram-positive bacterium Bacillus subtilis in which the first ever observation of lipid domains was made [4]. The seminar will conclude with future directions of potential interest to biophysicists and biologists.

[1] F. A. Heberle, R. S. Petruzielo, J. Pan, P. Drazba, N. Kučerka, R. F. Standaert, G. W. Feigenson, J. Katsaras, J. Am. Chem. Soc. 135, 6853 (2013).
[2] F. A. Heberle, M. Doktorova, S.-L. Goh, R. F. Standaert, J. Katsaras, G. W. Feigenson, J. Am. Chem. Soc. 135, 14932 (2013).
[3] J. D. Nickels et al., J. Am. Chem. Soc. 137, 15772 (2015).
[4] J. D. Nickels et al., PLoS Biology 15, e2002214 (2017).
 
 

                                       11) Monday, November 19, 3:00 pm, 1008B Digital Media Center

                                       Dr. Markus Bleuel (NIST Center for Neutron Research), host Gerald Schneider

                                       Title: TBA

                                       Abstract: TBA

 


John Singleton12) Monday, November 26, 3:00 pm, 1008B Digital Media Center

Dr. John Singleton (Los Alamos National Laboratory/National High Magnetic Field Laboratory), host John DiTusa

Title: TBA

Abstract: TBA

  

Jeremy Smith photo13) Friday, November 30, 12:30 pm, 215 Williams Hall

Dr. Jeremy Smith (Director, ORNL Center for Molecular Biophysics)

Title: TBA

Abstract: TBA

 

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