Research

Featured Physics Research

Space-Time Structure

Bored by billiard ball collisions? How about collisions of space-time sheets? Saint Louis University professor Ian Redmount, Ph.D., has long been interested in the study of the structure of space-time itself.

From "space-time foam" to "colliding null sheets in Schwarzschild space-time" Redmount is imagining things that Earth-based clocks and rulers can鈥檛鈥渟ee."

Some years ago he devised a formula that applies to null sheet-collisions.

The formula is known to physicists today as the DTR relation, as it was also discovered independently by Dray and tHooft (tHooft is the 1999 co-recipient of the Nobel Prize in Physics, for contributions in subatomic physics).

More info about research in cosmology and astronomy can be found at , an electronic publication of the American Physical Society.

From Parachutes to Whales

Lunge feeding is one of several strategies employed by baleen whales to catch in only one gulp a large amount of krill and other small prey that typically swim in schools. In many ways, the water-filling process that expands the initially folded, highly-extensible and compliant buccal cavity skin shares a lot of commonalities with the unsteady fluid dynamics of parachute inflation.

Jean Potvin, Ph.D., joined forces with faculty from the University of British Columbia Zoology Department to propose a new theory of the drag force that is generated during lunge feeding.

The result is a new simulation program that computes the full trajectories of the whale and water that it is engulfing. This new tool should give biologists the means to compute the entire energy budget of this peculiar feeding strategy, a key element needed to understand why whales have evolved to be so large.

Probing the Roots of Quantum Mechanics

For many years, Thalanayar Santhanam, Ph.D., has been studying one of the root concepts of quantum mechanics - the so-called "commutation rules".

These form the basis of the well-known Uncertainty Principle of Quantum Mechanics, which specifies which physical quantities 鈥� such as position, momentum and energy 鈥� can be measured simultaneously, and which cannot. These commutation rules not only depend on the specific physical quantities, but also on the type of physical system that is being studied, i.e. individual atoms and particles, group of atoms, and so on.

Most importantly, they also depend on the type of energy spectrum that they have. Santhanam's interest has been on finding out those commutation rules that apply to systems possessing only a finite number of energy levels (in contrast to those systems that have an infinite number of levels, like ordinary atoms). With collaborators, he has come up with relationships that have attracted the attention of theoretical physicists from around the world.

Physics Research at SLU

Most of the instructors in the 麻豆传媒 Department of Physics are continuously engaged in the exploration of new ideas. The following list gives you an idea of what they are thinking about outside of the classroom. Many of the research projects led by faculty involve the participation of undergraduate students.

A close up image of a adiabatic demagnetization refrigerator

David Wisbey, Ph.D., uses the adiabatic demagnetization refrigerator (ADR), capable of reaching temperatures below 42 mK. Professor Wisbey uses this to study materials for quantum information. Quantum bits (or qubits) and microwave resonators, integral parts of a quantum computer, must be isolated from their environment in order to perform operations.

Biophysics and Biomechanics

Vijai Dixit, Ph.D.
Amina Mohammadalipour, Ph.D.
Jean Potvin, Ph.D.

Fluid Mechanics and Aerodynamics

Jean Potvin, Ph.D.

Gravity and Cosmology

Greg Comer, Ph.D.
Ian Redmount, Ph.D.

Quantum Information and Materials

Dmitry Solenov, Ph.D.
David Wisbey, Ph.D.

Superconductivity and Solid-State Physics

Irma Kuljanishvili, Ph.D.
Martin Nikolo, Ph.D.
Dmitry Solenov, Ph.D.
David Wisbey, Ph.D.

Recent Publications

Optical Direct Write of Dolan鈥揘iemeyer-Bridge Junctions for Transmon Qubits

J.T. Monroe, D. Kowsari, K. Zheng, C. Gaikwad, J. Brewster, D.S. Wisbey, K.W. Murch
Applied Physics Letters
Volume: 119 Issue: 6 Page: 062601

Abstract: We characterize highly coherent transmon qubits fabricated with a direct-write photolithography system. Multi-layer evaporation and oxidation allow us to change the critical current density by reducing the effective tunneling area and increasing the barrier thickness. Surface treatments before resist application and again before evaporation result in high-coherence devices. With optimized surface treatments, we achieve energy relaxation T1 times in excess of 80饾渿s for three dimensional transmon qubits with Josephson junction lithographic areas of 2 饾渿m.

A Two-Step Method for Transferring Single-Walled Carbon Nanotubes onto a Hydrogel Substrate

Imaninezhad, Mozhdeh; Kuljanishvili, Irma; Zustiak, Silviya Petrova
Macromolecular Bioscience
Volume: 17 Issue: 3

Abstract: Carbon nanotube (CNT)-hydrogel nanocomposites are beneficial for various biomedical applications, such as nerve regeneration, tissue engineering, sensing, or implant coatings. Still, there are impediments to developing nanocomposites, including attaining a homogeneous CNT-polymer dispersion or patterning CNTs on hydrogels. While few approaches have been reported for patterning CNTs on polymeric substrates, these methods include high temperature, high vacuum or utilize a sacrificial layer and, hence, are incompatible with hydrogels as they lead to irreversible collapse in hydrogel structure. In this study, a novel two-step method is designed to transfer CNTs onto hydrogels. First, dense CNTs are grown on quartz substrates. Subsequently, hydrogel solutions are deposited on the quartz-grown CNTs. Upon gelation, the hydrogel with transferred CNTs is peeled from the quartz. Successful transfer is confirmed by scanning electron microscopy and indirectly by cell attachment. The efficient transfer is attributed to p-interactions pregelation between the polymers in solution and the CNTs.

Bottom-up Direct Writing Approach for Controlled Fabrication of WS2/MoS2 Heterostructure Systems

Dong, Rui ; Moore, Logan ; Aripova, Nozima; Williamson, C; Schurz, Robert; Liu, Yuzi; Ocola, Leonidas E.; Kuljanishvili, Irma
RSC Advances
Volume: 6 Issue: 71 Pages: 66589-66594.

Abstract: The ability to construct heterostructures that consist of layered transition metal dichalcogenides materials (MX2) in a controlled fashion provides an attractive solution for materials design and device applications. For nanotechnology applications it is important to control the shape, geometry and precise position of the grown heterostructure assemblies on a variety of substrates. In this study, we developed a "direct writing" technique to fabricate arrays of WS2/MoS2 and MoS2/WS2/MoS2 heterostructures at predefined locations on a silicon substrate in a controlled fashion. Water based precursor inks were implemented to ensure the formation of quality heterostructure surfaces which are free of residual polymer contaminants. With this technique we demonstrate an attractive and scalable technology with unique capabilities for precise growth of dissimilar MX2 materials, layered either in a vertical or lateral arrangement.

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