VCU Department of Physics Colloquia: Spring 2020

 

Friday, January 17 2020

There is no Colloquium Today

 

VCU Department of Physics Colloquia: Fall 2019

DNA for Data Storage: A Literature Review

Graeme Murray 

Virginia Commonwealth University

Friday, December 6 at 4:00 pm in 701 W. Grace St., Room 2310

Digital data production is exponential increasing and outpacing the growth of mainstream storage devices such as hard disks. This demand has led to major investments in data centers on the order of billions of dollars in the Richmond area alone. As production of data is only set to increase there is demand for better storage devices. DNA has some promising properties when it comes for digital data storage owing to its extreme density, evolutionarily optimized replication machinery, and high durability. While synthesis and sequencing are still expensive, improvements have exceeded Moore’s law and continued demand for decreased costs is driven by the medical industry. In this talk, I will discuss topics from basic principles of DNA replication to the latest techniques for storing data in DNA which utilize techniques developed for mobile broadcasting to optimize storage density.   

3D Printed Neural Regeneration Devices

Prof. Daeha Joung

Department of Physics 

Virginia Commonwealth University

Friday, November 22 at 4:00 pm in 701 W. Grace St., Room 2310

Biological structures ranging in size from molecules to organelles, cells, organs, tissues, and the human body are exquisitely structured in three-dimensions (3D). In order to mimic, sense, or to interface functional devices with biological ones, there is a need to create 3D, artificially structured materials or 3D, heterogeneously integrated, functional devices (from nano- to macro- scales). Existing conventional fabrication/assembly technologies have facilitated the representation of 2D networks of interface-active devices or platforms with biology, but the technology is impeded in its application to complex 3D geometries that require hierarchical precision and multi-material heterogeneity. The solutions generally require fundamental, conceptual advances in materials science and engineering. Our approach is to use 3D printing, which is an additive manufacturing technology that permits the manufacturing of complex multi-(bio)material, multi-scale, and/or multi-functional 3D devices. In this talk, we will discuss the application of 3D printing to neural regeneration devices and how this approach benefits nervous system tissue engineering.

References:
[1] D. Joung et al., “3D Printed Neural Regeneration Devices.” Adv. Funct. Mater. 29, 1906237 (2019).
[2] D. Joung et al., “3D Printed Stem-Cell Derived Neural Progenitors Generate Spinal Cord Scaffolds.”
Adv. Funct. Mater. 28, 1801850 (2018).

No Physics Colloquium for Friday Nov. 15.

 

 

Molecular Magnets for Spectroscopic Sensing of Chemical Reactions and Qubits

Prof. Mark R. Pederson,

Department of Physics 

University of Texas – El Paso

Friday, November 8 at 4:00 pm in 701 W. Grace St., Room 2310

 Early experimental investigations on spin-carrying metal centers, initially aimed at understanding how nature converts water to hydrogen and fixes nitrogen, formed the basis for the field of molecular magnetism 25 years ago. Shortly thereafter such molecules were postulated to be potentially realistic physical manifestations of spin-based qubits for quantum computers [1]. In this talk I will discuss computational and theoretical challenges associated with the accurate quantum-mechanical computational description of these systems and discuss two recent computer experiments that respectively: (A) show how a low-energy quantum-sensing technique can be used to deduce the chemical splitting of water into hydroxyl and hydrogen molecules [2] and (B) demonstrate how computational density-functional-based methods can be used to accurately determine the properties and complexities of putative molecular magnetic qubits that are composed of a perfect triangle of half-integer spin metal ions[3,4]. Connections to recent experimental publications will be made.

   The Mn 12 O 12 (COOR) 16 (HOH) 4 molecule, with S 4 symmetry, has four of everything. Our recent calculations find that this system readily accepts four excess electrons at the cost of only 0.32 eV in vacuum. This molecule exhibits a macro-spin with S=10. It has received significant past interest due to the experimental  observations and theoretically confirmed process of quantum tunneling of magnetization (QTM). Here, we show that the spectroscopic signatures associates with QTM are extremely sensitive to the presence of the four HOH terminators (e.g. 4 waters vs. 2H 2 and 2OH) and to the number of added electrons (0 vs. 4). Our calculations suggest that QTM can be used as an ultra-low-energy non-destructive observation of water decomposition in a molecule with a core Mn 4 O 4 unit that bears a striking similarity to the reaction center in the oxygen evolving complex. See Ref. 1.   Recently, Boudalis et al have experimentally observed the magneto-electric effect in a chiral Fe 3 O(NC 5 H 5 ) 3 (O 2 CC 6 H 5 ) 6 molecule [5] and have noted further that this is the first possible spin-electric system based upon spin 5/2 metal centers. Our results [3], using standard density-functional methods, show that the spin-electric behavior of this molecule could be even more interesting as there are energetically competitive reference states with high and low local spins (S=5/2 vs. S=1/2) on the Fe 3+ ions. We provide predictions of magnetic and x-ray spectroscopies to deduce the presence of both states. Possible uses for low-temperature quantum sensing of fields and pressure variations are suggested. Recent efforts at improving standard approximations of density-functional theory using a new version of self-interaction-corrected DFT will be discussed within the context of this work [2,6].

[1] B. Georgeot and F. Mila, Chirality of triangular antiferromagnetic clusters as a qubit, Phys. Rev. Lett. 104, 200502 (2010).

[2] J. Batool, T. Hahn and M.R. Pederson, Magnetic Signatures of Hydroxyl and Water Terminated
Neutral and Tetra-anionic Mn 12 -Acetate, J. Comput. Chem. 25, 2301-2308 (2019).

[3]M. F. Islam, J. F. Nossa, C. M. Canali and M. Pederson, First-principles study of spin-electric coupling
in a Cu 3 single molecular magnet, Phys. Rev. B 82 155446 (2010).

[4]A. I. Johnson, M. F. Islam, C. M. Canali and M. R. Pederson, A Multiferroic molecular magnetic qubit,
Submitted to J. Chem. Phys. (https://arxiv.org/abs/1909.08803).

[5]A. K. Boudalis, J. Robert & P. Turek, 1 st demonstration of magnetoelectric coupling in a polynuclear
molecular nanomagnet via EPR studies Fe 3 O(O 2 CPh) 6 (Py) 3 ClO 4 , Chem. Eur. J 24 14896-14900 (2018).

[6] M.R. Pederson, A Ruzsinszky and J. P. Perdew, Communication: Self-Interaction Correction with
Unitary Invariance in Density Functional Theory, J. of Chem. Phys., 140, 121103 (2014).

 

Computational research of materials for nanoscale semiconductors and Li-ion battery applications

Prof. Xihong Peng

Department of Physics 

Arizona State University

Friday, November 1 at 4:00 pm in 701 W. Grace St., Room 2310

 First-principles electronic structure calculations are applicable to solve problems across multi-fields and play an essential role in modern scientific research. In this talk, I will outline the computational work in our group in two areas, nanoscale semiconductors and new materials as anode in Li-ion batteries. Semiconductor nanostructures have attracted extensive research efforts in the past decades due to potential applications in nanotechnology. We have studied how size,
surface/edge passivation and mechanical strain affect the properties of nano-semiconductors and obtained a picture on the interplay of size, passivation and strain on their electronic properties. Li-ion batteries are widely used as power devices and current typical anode is graphite. Other group IV elements such as Si has been considered as an alternative anode due to its higher energy capacity. However, bulk Si undergoes large volume change during lithiation. New materials such as clathrates - open framework structures attract research interests. We studied the clathrates as potential anode in Li-ion batteries via close collaborations with experimentalists.

 

 

Comparison of the structure function F2 as measured by charged
lepton and neutrino scattering from iron targets

Prof. Narbe Kalantarians

Jefferson Laboratory and Virginia Union University

Friday, October 25 at 4:00 pm in 701 W. Grace St., Room 2310

 The F2 structure function characterizes the quark composition of nucleons and nuclei. This information is obtained by deeply inelastic scattering. In this analysis, world data for the structure function F2 for Iron from charged lepton and neutrino scattering experiments are compared. The observations cleanly underscore previously observed hints of a difference in the behavior of the data between charged lepton and neutrino scattering, notably in the anti-shadowing region where the Bjorken scaling variable x is below 0.15. The charged lepton data appear to undergo shadowing/anti-shadowing whereas the neutrino data seem to exhibit no nuclear effects. Moreover, we find very good agreement between the different types of probes in the x region above 0.15. Details and results of the data comparison will be shown in this talk.

 

Gene Clustering Drives Transcriptional Coherence of Disparate biological Pathways

Prof. Richard Joh

Department of Physics 

Virginia Commonwealth University

Friday, October 11 at 4:00 pm in 701 W. Grace St., Room 2310

 The establishment of distinct transcriptional states in response to developmental or environmental cues is critical for survival. This involves the concordant or discordant transcriptional regulation of several distinct biological pathways, often involving thousands of genes, which together enhance survival. How these system-level changes to transcriptomes are coordinated is an understudied problem in eukaryotic biology. Here, using computational approaches in eukaryotes ranging from yeast to human, we report that this transcriptional coordination is in part achieved by the genic proximity of the regulatory nodes of disparate biological pathways whose co-regulation drives the transcriptional coherence of their respective pathways. Overall, our data identify conserved and species-specific transcriptional co-regulation of hundreds of different biological pathway pairs and suggest that genomic clustering of regulatory nodes such as transcription factors coordinate the expression of thousands of genes, creating tunable regulons in eukaryotes. 

 

 

The Past, Present, and Future of Quantum Chemistry

Prof. Ka Un Lao

Department of Chemistry

Virginia Commonwealth University

Friday, October 4 at 4:00 pm in 701 W. Grace St., Room 2310

 The Lao group is a computational/theoretical group that focuses on developing and applying new electronic structure models and algorithms based on quantum mechanics, combining concepts and techniques from chemistry, physics, mathematics, and computer science, to study molecules, clusters, and condensed phase systems, ranging from chemistry to biochemistry and materials science. 

One particular area of emphasis is the accurate and efficient calculation of intermolecular interactions, which is a challenging problem for electronic structure theory. Our research goal is to develop fast and accurate approaches for gaining a
fundamental understanding of the factors governing the drug binding and molecular materials packing in order to provide a basis for the development of new drug binding molecules and functionalized molecular materials. 

 Furthermore, adapting the methodology we are going to develop to the rapid evolution of machine-learning techniques offers a unique opportunity to generate new noncovalent molecular electronics and drug molecules through large-scale computational screening and design since the combination of different strategies to functionalize molecules is seemingly infinite.

 

 

 Perspectives on processing magnetocaloric transition-metal borides for solid state cooling applications

Prof. Radhika Barua 

College of Engineering,

Virginia Commonwealth University

Friday, September 27 at 4:00 pm in 701 W. Grace St., Room 2310

 

In the United States, residential and commercial buildings currently account for 72% of the nation's electricity use and 40% of carbon dioxide (CO2) emissions annually, 15% of which originates from air conditioning and refrigeration systems. Novel cooling technologies are required to minimize global energy consumption and environmental impact. To this end, solid state magnetic cooling devices enabled with the “magnetocaloric” class of functional materials are attractive as they allow complete elimination of conventional high-global warming potential (GWP) refrigerants and have the potential for efficiency improvements of up to 25% over conventional vapor compression systems, which is equivalent to 60% of Carnot efficiency

 Within this context, this talk will address the major principles guiding the development of magnetocaloric transition-metal borides for active magnetic regenerator (AMR) magnetic cooling devices.  Specific attention will be given to current research efforts for processing AlFe2B2 – a rare-earth-free intermetallic alloy that exhibits an appreciable magnetocaloric response corresponding to an adiabatic temperature change of 2.2 K and magnetic entropy change of 4.4 J/kgK at an applied magnetic field of 2 T. Computational and experimental results will be presented to demonstrate that spin-orbit coupling in the layered orthorhombic AlFe2B2 crystal structure results in an anisotropic magnetocrystalline energy, thus producing an associated anisotropic magnetofunctional response. Further, the influence of compositional variation on the magnetic properties of AlFe2B2 will be discussed.



 

Prof. John Hackett

Department of Physiology and Biophysics and

The Massey Cancer Center

Virginia Commonwealth University

Friday, September 20 at 4:00 pm in 701 W. Grace St., Room 2310

  Cytochrome P450 19A1 (CYP19A1, aromatase) required for the synthesis of estrogens from androgens, is among the key targets for treatment of estrogen-dependent cancers. It is representative of other steroidogenic CYPs (i.e. 11A1 ,11B2, 17A1, 51) insofar as it also catalyzes a sequential oxidation and shares structural features at the putative substrate recognition interface. It is one of the few enzymes known to construct an aromatic ring with a controversial mechanism. How steroidogenic CYPs, including CYP19A1, recognize, and in some cases discriminate between very similar substrates remain salient unanswered questions in the field. Little effort has been made to elucidate substrate recognition and discrimination mechanisms of the highly-selective endobiotic-metabolizing CYPs. This colloquium will provide an update on the current state of knowledge of the CYP19A1 catalytic mechanism and summarize our recent efforts to integrate experimental and computational approaches to glean novel insight into the functional dynamics of CYP19A1 in a native-like membrane.

 

Pool and Flow Boiling Heat Transfer in Variable Gravity Environments

Dr Jungho Kim

Department of Mechanical Engineering

University of Maryland

Friday, September 13 at 4:00 pm in 701 W. Grace St., Room 2310

Knowledge of how gravity affects two-phase heat transfer is critical to the design of equipment (e.g., heat exchangers and nuclear reactors) that will be operated in variable gravity environments (high-g, low-g, lunar, and Martian-g). Relatively little is known about boiling mechanisms in these environments since data from long duration microgravity environments are limited due to high cost and limited flight opportunities. Although a few studies have been performed under high quality microgravity environments on board orbital platforms, most low gravity boiling research has been obtained using drop towers, aircraft, and sounding rockets. The relatively large g-jitter and/or the short periods of microgravity duration of these studies has resulted in confusion about the heat transfer mechanisms. The results of a recent International Space Station experiment the clarifies gravity effects on pool boiling mechanisms will be presented along with a model that can be used to scale boiling data. Recent investigations into flow boiling using temperature sensitive paints will also be discussed.

 

The September 6 Colloquia Has been Cancelled!

From Fundamental Nuclear Physics to Cancer Instrumentation: Science at Jefferson Lab

Dr. Cynthia Keppel,

Hall Leader

Jefferson Lab

Friday, September 6 at 4:00 pm in 701 W. Grace St., Room 2310

The Thomas Jefferson National Accelerator Facility (Jefferson Lab) underwent a major upgrade, doubling the beam energy to 12 GeV and substantially upgrading the associated experimental equipment. Experiments leveraging this upgrade have been underway for almost two years now, with many new results recently becoming available. An overview of the laboratory and some first data will be presented. In addition, focus will be given to applications of detector technology from the fundamental nuclear physics program to medical instrumentation.  

 

 

Meeting the Faculty

Friday, August 30 at 4:00 pm in 701 W. Grace St., Room 2310