Faculty Research Interests
|Michael Chopp |
|George Martins |
|Gopalan Srinivasan |
Ph.D., New York University
- Development and Treatment of Stroke
- Applications of MRI in Biomedical Areas
In support of his research, Prof. Chopp received major grants from the NIH to HFH. A significant fraction of OU pre-doctoral students work in his laboratory. The focus of Prof. Chopp's research is the development of treatments for stroke. His goal is to salvage affected brain tissue. He and his group have recently identified novel death pathways of brain cells after stroke. After the onset of a stroke, brain cells undergo self-destruction, a form of programmed cell death. This suicidal process is programmed by genetic alterations.
They have identified proteins and genes responsible for the promotion of this form of cell death. With this knowledge, they may be able to intervene to inhibit this process. Prof. Chopp and his group have recently identified methods to induce the production of new brain cells. This discovery may yield important therapeutic benefits for a broad range of neurological injuries and degenerative diseases. They have also found that after a stroke secondary events contribute to the growth of the dead tissue. A major contributing factor to this secondary injury is the influx of white blood cells into the region of damage. They have identified the signaling molecules that target these cells to the site of injury and have blocked the function of these molecules. Their data indicate that using this therapeutic approach the amount of injured brain tissue is decreased by a factor of two and that they can significantly reduce damage from stroke. Prof. Chopp and his group have also developed novel imaging methods using MRI that permit the non-invasive evaluation of the health status of brain tissue. These techniques allow them to identify whether brain cells are simply affected and compromised by the stroke, are in the process of dying, or are already dead.
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Ph.D., University of Toronto
Phone: (248) 370-3424
Office: 186H Mathematics and Science Center
- Non-Equilibrium Statistical Mechanics
- Phase Separation and Pattern Formation
- Computational Condensed Matter Physics
The research of Prof. Elder is devoted to understanding the complex structures or patterns that emerge in non-equilibrium phenomena. Such patterns are ubiquitous in nature, from double helix structures in DNA to the beautiful array of snowflake shapes. More importantly these patterns often control key material properties and biological functions. Unlocking the enormous potential of such structures lies in the ability to make efficient predictions. Unfortunately this task is complicated by the complexity of interactions between various system components. For this reason computational modeling has proved to be an invaluable tool. The bulk of Elder's research has been devoted to the development of methods to model non-equilibrium phenomena in materials physics. This research has included studies of spinodal decomposition, Ostwald ripening, eutectic solidification, order/disorder transitions and amorphous/crystal transitions, Rayleigh-Benard convection, flame front propagation explosive crystallization, the decay of supercurrents in superconducting rings, the motion of charge density waves, the absorption of liquids by random media (or imbibition) and phase separation in fluids.
More recently Prof. Elder has worked on the development a phase field model method that resolves microscopic length scales on mesoscopic times scales. This differs from traditional atomic or molecular (MD) approaches that are limited by the atomic time (femto seconds) and length (nanometers) scales. It also differs from standard phase field methods that describe mesoscopic scales which cannot describe microscopic details and are often limited to overly simplified descriptions. The advantage of this new 'phase field crystal' method is that it naturally incorporates the physics contained at the microscopic level on time scales many orders of magnitude larger than traditional atomic methods. It is not twice or ten times faster than conventional MD (this level of speed can be achieved by incremental improvements in computational power and algorithms) but can be millions or billions times faster. Prof. Elder and collaborators have used this method to conduct large scale numerical simulations of a variety of technologically important processes or phenomena including, epitaxial growth, the strength of nano-crystalline materials, spinodal age hardening and dislocation climb, glide and annihilation.
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Ph.D., University of Chicago
Phone: (248) 370-3411
Office: 186J Mathematics and Science Center
- General Relativity
Prof. Garfinkle's research is in numerical relativity: the use of computer simulations to study the properties of strong gravitational fields. Much of his recent research has been on (i) properties of singularities (ii) critical gravitational collapse and (iii) cosmic censorship.
Singularities occur in the centers of black holes and at the big bang at the beginning of the universe. These singularities are described by the Einstein field equations. While these equations are quite complicated, it has long been conjectured that some terms in the equations become dominant near a singularity and that as a consequence the approach to the singularity becomes simple. To test this conjecture, Prof. Garfinkle has performed computer simulations of the approach to the singularity. At first these simulations (done in collaboration with Prof. Beverly Berger) were of spacetimes with symmetry. However, recently Prof. Garfinkle has simulated the general situation of spacetimes with no symmetry (Phys. Rev. Lett. 93, 161101 (2004)). The results support the so called BKL conjecture that the approach to the singularity is locally homogeneous and oscillatory.
Critical gravitational collapse refers to the scaling properties of gravitational collapse at and near the threshold of black hole formation. These properties are analogous to those of phase transitions in condensed matter physics and include (i) a power law relation between the mass of the black hole formed and the nearness to the black hole formation threshold and (ii) a self similarity of the "critical solution" that is exactly at the threshold of black hole formation. These phenomena were found by Choptuik in numerical simulations of the collapse of a self-gravitating scalar field. Prof. Garfinkle has investigated many aspects of these phenomena. These include: (i) Scaling of tidal force for systems that just barely fail to form a black hole. (ii) critical gravitational collapse in spacetime dimensions other than four. (iii) closed form solutions describing critical gravitational collapse. (iv) critical gravitational collapse of a massive vector field. (v) an analog of critical gravitational collapse in Ricci flow.
Cosmic censorship is the question of whether the singularities that form in gravitational collapse are hidden inside black holes. There are exceptional cases where singularities are naked (i.e. not hidden inside black holes). These include the critical solution of critical gravitational collapse. However, it is thought (but not yet proved or disproved) that generic singularities are hidden inside black holes. Recently Prof. Garfinkle performed numerical simulations of the gravitational collapse of a scalar field with negative potential energy. This system had been proposed as a counterexample to cosmic censorship. However, the result of Prof. Garfinkle's simulations is that the singularity is hidden inside a black hole.
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Ph.D., Hebrew University of Jerusalem, Israel
Phone: (248) 370-3412
Office: 272 Hannah Hall
- Modeling of collective behavior in biological systems (growth of malignant brain tumors, wound healing)
- Statistical physics far from equilibrium
- Pattern formation and nonlinear dynamics
- Driven granular gases, instabilities in granular flows
Biological physics. During the recent years, the newly developing field of biological physics has experienced a tremendous growth. The overall goal of Dr. Khain’s research is to identify and describe basic physical mechanisms which govern complex biological processes. He investigates the collective behavior of a large number of living cells. Biological multicellular systems are an exciting example of stochastic non-equilibrium systems. They exhibit numerous physically interesting and biologically important collective phenomena, ranging from wound healing to tumor growth. Dr. Khain’s primary goal is to model the growth of malignant brain tumors, which can not be treated by current therapies. He takes a physical approach, which consists in formulating minimalist models with a small number of parameters, in order to determine the role of basic biological processes, such as cell proliferation, cell motility, cell-cell adhesion, etc., in growth patterns of brain tumors. Dr. Khain investigates these problems using both continuum modeling of basic biological processes on the multi-cellular level (reaction-diffusion equations) and discrete stochastic modeling of cells on a lattice.
Physics of granular matter. Granular materials are ubiquitous in nature and of great importance in industry. Recently, granular matter (matter composed of macroscopic particles interacting dissipatively) attracted significant attention of physicists, since it presents a fascinating example of intrinsically non-equilibrium systems. Fluidized granular media exhibit a variety of symmetry-breaking instabilities and pattern-formation phenomena. The understanding these instabilities is necessary for the development of quantitative models of granular flow, which have various industrial applications. Dr. Khain’s research focuses on driven granular gases, as well as on phase separation in a dense shear granular flow. Currently he investigates the challenging problem of rapid dense shear flows. It is known that transport coefficients of hard sphere fluid diverge at the density of dense close packing. However, there is recent evidence that the coefficient of shear viscosity diverges at a lower density than other constitutive relations. This may result in a coexistence of “solid-like” and “fluid-like” layers in dense shear flow, resembling the most intriguing problem of shear-band formation. Dr. Khain investigates these problems employing granular hydrodynamics and comparing the theoretical predictions in a series of molecular dynamics simulations.
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Phone: (248) 370-3417
Office: 174 Hannah Hall
- Numerical Methods Applied to Strongly Correlated Electrons
Dr. Martins's research interests are in the area of strongly correlated electrons. In colaboration with research groups in the United States, Europe and Brazil, he has been applying different numerical techniques to probe and understand the properties of strongly correlated electronic systems. 'Strongly correlated condensed matter' is truly a vast area and there are a variety of different computational techniques that can be applied to obtain understanding of their multi-faceted behavior. Dr. Martins has concentrated for now on Exact Diagonalization Methods as a tool to gain understanding of nano structures, High- Tc cuprates, ladders and spin chains and more recently frustrated spin systems.
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Ph.D., Instituto Balseiro, Bariloche, Argentina
Phone: (248) 370-3422
Office: 164 Hannah Hall
View "Walk on Water" demonstration
- Electron transport at low temperatures
- Quantum fluctuations
Many electron properties in two layer systems. In 1992, together with G. D. Mahan, Dr. Rojo discovered the effect of non-dissipative drag (NDD) on superconductors and mesoscopic systems. He plans to continue this line of research, exploring various applications of this fascinating effect. Dr. Rojo's work in this area has stimulated significant experimental and theoretical activity. NDD results from the coupling of the zero point charge fluctuations between two systems with no tunneling from one to the other. Dr. Rojo has discussed and summarized its current status and its relation with the dissipative current drag in his recent review article. In collaboration with his graduate student Joe Baker he has studied both analytically and by two different numerical methods the effect of disorder on NDD in order to make contact with experiments. A related effect that has bearing on the coupling between non-tunneling systems is the eddy current coupling between a superconductor and a normal, highly conducting system. He is involved in an ongoing collaboration with the experimental group of C. Thomsen and A. Goñi at the Technische Universität in Berlin, where the effect was observed for the first time in the InSb/GaAs system. The experimental results are in quantitative agreement with Dr. Rojo's theoretical predictions. He is seeking external funding to strengthen the collaboration in which further ramifications of this very interesting and significant effect will be explored.
Squeezing and control of quantum noise. Another project that has been particularly successful since Dr. Rojo's arrival at Michigan was his work on phonon squeezing, a field that falls within his interest in zero point fluctuations. In preliminary calculations he had identified the mechanism of pulses acting on harmonic systems as a means of producing squeezing. For the case of phonons the effect corresponds to a time modulation of the amplitude of the zero point fluctuations in the atomic positions within the solid. Dr. Rojo started collaboration with R. Merlin’s group, who measured the effect using ultra fast optical pulses. The experiment constituted the first observation of the squeezing effect in condensed matter, and could have exciting future applications in device physics and in several areas where, in general, a “stroboscopic” control over the quantum noise might be necessary. A very important question to be addressed in the future is: what other excitations can be squeezed in condensed matter, and what are the possible applications? Part of Dr. Rojo's future research effort will be devoted to answering these questions.
Role of confinement in high temperature superconductivity. Before arriving in Michigan Dr. Rojo did some important work on high temperature superconductors. Since his arrival he has continued working on some problems within this field. With his former graduate student Mathew Reilly, Dr. Rojo solved the two-magnon Raman scattering problem, showing that some recent experiments can be understood using a spin-phonon model without disorder in the non-adiabatic approximation. The study of High Tc superconductors has motivated an intense study of spin systems and Heisenberg, e.g. spin ladders, where the issue of a gapless versus gapped spectrum of excitations is the subject of experimental and theoretical study. He contributed to that subfield by providing a proof, extending the Lieb-Mattis theorem, that spin ladders with an odd number of legs are gapless. His recent work on confinement on c-axis transport addresses the fundamental issue of whether correlations can give rise to a “confined” phase in which transport is coherent in two spatial directions, and incoherent in the third. This is an unresolved many-body problem, the detailed study of which originates in P. W. Anderson’s conjecture that the ideas and paradigms of one-dimensional non-Fermi liquids can be extended to two and three-dimensional systems. In collaboration with C. Balseiro from Bariloche (Argentina) Dr. Rojo considered the strongly correlated anisotropic system, proposed and solved a model using a new slave-fermion scheme, and showed that a confinement transition emerges naturally from the solution. This collaboration is funded by the National Science Foundation through its international program, and has proven very fruitful. The researchers have also approached two other significant problems within High Tc superconductivity: the effect of disorder on d-wave pairing, and the problem of resistance at the melting point of a vortex lattice. Dr. Rojo plans to continue studying the issue of confinement. This will be the subject of the Ph.D. thesis of a graduate student in Bariloche who is studying finite anisotropic systems using the Lanczos method.
Bose-Einstein condensation. The field of Bose-Einstein condensation is one of the most exciting problems in physics. Due to its observation in supercooled atomic systems, the problem combines knowledge from condensed matter and atomic physics. For example, a condensate can be produced of Rb atoms in two internal states, which invites analogies with anisotropic magnetic systems. Dr. Rojo has proven an interesting theorem that establishes the regimes of phase separation for these kind of condensates. Also, in collaboration with P. Berman (Atomic Physics) at the University of Michigan, he studied the so-called Talbot oscillations, already well known for independent atoms, and their modification in the presence of a Bose-Einstein condensate. The goal was to understand the effects that atom-atom interactions will have on the Talbot oscillations. Since the atom-atom interaction makes the problem an unsolved many-body problem, one has to resort to approximations. To approach this problem I have proposed a simplified version that can be solved exactly. The simplification consists of treating the problem in one dimension, and mapping strongly interacting (hard-core) bosons to free fermions. This trick, originally introduced by M. Girardeaux, can be proven to work in this case and we describe the interplay of collision and quantum coherence in an exact framework. Dr. Rojo's work has already attracted some attention and has motivated interesting extensions.
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Bradley J. Roth
Phone: (248) 370-4871
Office: 166 Hannah Hall
- Biological Physics
- Computational Physics
Electrical Stimulation of Cardiac Tissue. Heart disease is the leading cause of death in the United States. Yet, decades of cardiology research has not resolved many questions about the mechanisms of electrical stimulation of cardiac tissue. The goal is to use mathematical modeling and computer simulations to resolve some of these questions. In particular, Prof. Roth studies how the anisotropy of cardiac tissue influences the distribution of transmembrane potential in cardiac tissue during stimulation.
Spiral Waves in the Heart. Many cardiac arrhythmias are thought to be caused by spiral waves of electrical activity. The core, or tip, of such a spiral wave may be stationary, or it may meander through the tissue in a complicated pattern. Prof. Roth is trying to understand how the anisotropy of cardiac tissue influences the pattern of meander. This topic is important, because it may affect how a non-lifethreatening fast heart beat (a ventricular tachycardia) may degrade into lethal ventricular fibrillation.
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Ph.D., St.Petersburg Tech Univ, Russia
Phone: (248) 370-3401
Office: 186G Mathematics and Science Center
- Linear and nonlinear magnetization dynamics
- Microwave signal processing
The research interests of Prof. Andrei Slavin are in the linear and nonlinear magnetization dynamics in magnetic micro- and nano-structures. He is doing theoretical research on the spectra of microwave spin-wave modes confined in magnetic nano-structures and array of magnetic nano-elements. In particular, he is working on the self-localized nonlinear eigenmodes of magnetic nano-structures and on the linear and nonlinear dynamics of magnetic vortices.
Another important topic of his research is spin-transfer-torque effect in magnetic nano-structures and development of microwave oscillators based on this effect. He is working on the development of a comprehensive theoretical model describing current-induced magnetization dynamics (both deterministic and stochastic) in magnetic nano-pillars and nano-contacts.
Prof. Slavin is also working on parametric nonlinear processes in magnetic films including Bose-Einstein condensation (BEC) of magnons under the influence of parametric pumping at a room temperature and storage and parametrically induced recovery of microwave signals in magnetic films.
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Ph.D., Indian Inst.Tech., Bombay, India
Phone: (248) 370-3419
Office: 186F Mathematics and Science Center
- Thin film magnetism
- Ferromagnetic resonance
Prof. Srinivasan is involved in the physics and applications of the magnetoelectric interaction phenomena in multiferroics. Studies are performed on such interactions in ferromagnetic -ferroelectric composites over a wide frequency, from 1 Hz to 110 GHz. The composites are potentially useful for sensors, transducers, miniature antennas and microwave devices. The research is supported by grants from NSF and DoD.
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Visiting Assistant Professor
Ph.D., Wayne State University, Detroit, MI
Phone: (248) 370-3409
Office: 172 Hannah Hall
- Multi-scale inclusive approach to physics phenomena relevant to proton/ion-beam cancer therapy
Dr. Surdutovich has joined the Department of Physics in January 2008. His research interests lie in the field of proton- and ion-beam therapies, which are becoming more and more accepted treatments for malignant tumors. Protons and ions are more advantageous projectiles than the now common photons because they may cause less damage to the regions surrounding tumors and thus induce fewer side effects. This is especially important if the side effects are crucial for the patient's quality of life. As a physicist, Dr. Surdutovich is interested in developing a multiscale inclusive approach that would allow a thorough calculation of the efficiency of DNA damage in proton/ion-beam cancer therapy. This method is based on the analysis of different physical, chemical and biochemical phenomena that take place during irradiation by ions. Each phenomenon determines pertinent distances, times, and energies and contribute to the inclusive model of the therapy. This will eventually lead to rigorous calculation of beam energies, dosages, energy deposition rate, and other characteristics of proton/ion-beam therapy.
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- High pressure physics
Pressure along with temperature and chemical composition defines the state of matter. High pressure could decrease the distance among atoms, shorten the chemical bonds, and distort the electron orbitals. Beyond a certain pressure point, materials may reach a new state of equilibrium and transit into a phase with distinctive atomic arrangement and crystal structure exhibiting properties quite different from that stable phase at ambient conditions. For example, under high pressure soft and black graphite transforms into a superhard and light-transparent diamond. With the rapid development of technology (high pressure generation apparatus, synchrotron X-ray, Raman), high-pressure technique has become a prevalent and important tool for exploring the unique nature of matter in solid, liquid, or gaseous state under extreme conditions.
The most popular apparatus for the generation of high pressure is a small vise-like device called diamond anvil cell, consisting of two opposite diamonds with tiny tips. Pressing two anvils, between which the sample is located, can create pressure as high as that in the earth’s core (~360 GPa). Because of diamond’s transparency over a broad frequency of electromagnetic radiations (X-ray, Raman, visible light, etc.), we can do the in-situ measurements by integrating diamond anvil cell with characterization facilities (Synchrotron X-ray, Raman spectroscope, and so on)
By taking advantage of high-pressure technique, Dr. Wang’s research focuses on the study of material’s optical property, elasticity, plasticity, phase stability, chemical reactivity, and microstructure evolution (defects, grain size, and grain boundaries), as well as the synthesis of new materials under pressure conditions.
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- NMR microscopic imaging (?MRI)
- Polarized light microscopy (PLM)
- Fourier-transform infrared imaging (FTIRI)
- Detection of osteoarthritis at its early stages
- Applications of micro-imaging in biomedical areas
Quantitative Microscopic Imaging of Biological Tissues. Prof. Xia's major research effort has been concentrated on multidisciplinary microscopic imaging study of articular cartilage. As we know, osteoarthritis is a common disease affecting 33% of the US population (CDC Report, Oct 24, 2002); and cartilage degradation is an early event that occurs in this disease. Microscopic imaging may offer a way to provide early diagnosis of this disease. His cartilage research, continuously supported by the National Institutes of Health (NIH) since January 1999, is currently funded by two R01 grants from NIH.
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