Condensed Matter & Biological Physics SeminarCondensed Matter & Biological Physics Seminar| Date | Speaker | Affiliation | Title | Host |
|---|---|---|---|---|
| September 3rd | Prof. Veit Elser | Cornell | Phase retrieval with atoms, bits, and pixels | Bowick |
| Special time: 1pm Imagine a microscope that reveals the structure of a small object through the diffraction pattern it produces. Can one interpret this data and perhaps even use it to reconstruct the object? In this talk I will demonstrate that in a variety of situations this is indeed possible. The technique involves an iterative algorithm that in effect "retrieves" the unknown phases in the diffraction pattern. | ||||
| September 10th | Dr. Valerii Vinokur | Argonne National Laboratory | Transport properties of granular materials | Marchetti |
| We investigate transport in a granular metallic system at large tunneling conductance gT between the grains. We show that at low temperatures, T<gTd, where d is the mean energy level spacing in a single grain, the coherent electron motion at large distances dominates the physics, contrary to the high-temperature behavior where conductivity is controlled by the scales of the order of the grain size. In three dimensions we predict the metal-insulator transition at the bare tunneling conductance gC=(1/6p)ln(EC/d), where EC is the charging energy of a single grain. Corrections to the density of states of granular metals due to the electron-electron interaction are found. | ||||
| September 17th | Michael Defeo and Maxim Marchevsky | Syracuse University | Magnetic domains in garnets: structures, defects, dynamics and resonance | |
| Research in ferromagnetic garnets and their technologically useful magnetic and optical properties has been active for several decades. In thin garnet films with perpendicular anisotropy magnetic domains arrange in a variety of unique configurations and exhibit peculiar magnetization dynamics. Among different known domain structures, the labyrinthine state, where structural disorder and order coexist, is of particular interest. We use Scanning Hall Microscope / Susceptometer to examine formation of the labyrinthine domain state and to image its local magnetic dynamics when the external field is varied. A.c. modulation of the applied magnetic field results in the non-uniform domain wall vibrations, with response maxima at localized at the "topological defects" in the domain patterns. Driving the domain structures with a "noisy" external field reveals local stochastic amplification of the domain response around the "loops" of the labyrinthine domain structure. We will discuss possible causes of the observed phenomena and show results of the most recent experiments. | ||||
| September 24th | Dr. A.J. Rader | University of Pittsburgh | Protein Folding Predictions from Network Models | Meinke |
| The elusive protein folding problem is considered by rigidity analysis of native state structures using the FIRST software.
A constraint network model is created for a set of structurally diverse
proteins representing covalent bonds and non-covalent interactions from
which rigid and flexible regions are calculated. Unfolding by thermal
denaturation is simulated by breaking the hydrogen bonds and salt bridges
according to their relative strength. This reduces the mean atomic
coordination, |
||||
| Wednesday, September 29, 11am | Prof. Paul Goldbart | UIUC | Quantifying Quantum Entanglement in Few- and Many-Body Settings | Marchetti |
| No longer only a mysterious curiosity of the quantum realm, the entanglement of quantum systems is now regarded as a central enabling resource for quantum technologies, such as teleportation, cryptography and, potentially, computing. This brings to the foreground the task of characterizing entanglement in quantum systems. In this seminar I shall describe a simple, global measure of entanglement that is rooted in the familar ground of the Hartree approximation, and has precursors in the works of Shimony and of Barnum and Linden. I shall show how this measure yields results for the entanglement of quantum systems in a variety of settings involving pure and mixed quantum states, and ranging from two to several to many parties. I shall conclude by examining entanglement in the setting of quantum phase transitions, illustrating this issue via results from certain exactly solvable many-body systems. | ||||
| October 1st | ||||
| October 8th | Prof. Michael Wigler | Cold Spring Harbor Laboratory | Mathematical problems related to data analysis of copy number variation in humans; relation of copy number variation to disease | Bowick |
Microarray hybridization is a versatile tool widely used for gathering information about transcriptional states. We have used representational genomic approaches combined with microarray hybridization to analyze the structure and content of genomes. A representation is a pseudo random sampling of the genome. When hybridized to a microarray, we gather information about the copy number of genes in genomes. We have used this method to analyze the content of cancer cells, but also to analyze the difference between "normal" people and between normal people and people with various genetic diseases. There is a surprising variation in the genome of normal people, and certain variations may correlate with various diseases. In addition to describing the biological relevance of our approach, I will discuss the algorithms for probe design, image analysis routines, and the mathematical and statistical analysis of the microarray data. Many, but not all, of these problems have been solved. I will describe the solved problems (string matching algorithms for probe design, transformations of the plane for image analysis, hidden Markov models for interpreting single experiments) and the outstanding problem of interpreting large series of experiments. |
||||
| October 15th | Vincenzo Vitelli | Harvard University | Defect textures in thin films on a curved surface | Bowick |
| The physics of topological defects on curved surfaces plays an increasingly significant role in the engineering of devices based on coated interfaces. Furthermore, the effects induced by a curved substrate on the distribution of defects are not fully understood even in well studied systems such as thin superfluid or superconducting films. In this talk, I discuss simple continuum generalizations of the plane XY model to frozen surfaces of varying curvature to gain a broad understanding of the interaction between topological defects and curvature. | ||||
| October 22nd | Prof. Sahraoui Chaïeb | UIUC | Conformations in Lipid Membranes: from the Golgi to Glassy Wrinkling | Bowick |
| The golgi is a tube like structure, made of a lipid membrane, that serves as receiving-shipping room of the cell. The transport is achieved via some kind of instability of the tube into a string of beads and the pinch off is the mean by which the molecules and nutrients are transported within the cell. On the other hand, when disorder is introduced in a lipid membrane a new phase appears which we call the wrinkling phase due to its frozen state. I will describe how we can model both phenomenon using experimental techniques and theoretical means. | ||||
| October 29th | ||||
| November 5th | Dr. Charles Reichhardt | Los Alamos | Crystallization, Melting, and Jamming in Colloidal Systems with External Fields | Marchetti |
| Special time: 1pm. An important motivation for studying soft matter systems such as colloids or granular materials is that, in these systems, the microscopic details of phenomena such as crystallization or glass transitions can be accessed directly, offering new insights into similar processes that occur on the atomic or molecular scale. Here we study the statics and dynamics of colloids interacting with an external field applied either locally or globally. In the presence of an applied periodic substrate, we find a variety of novel crystalline states with interesting multi-stage melting transitions, including a new phase that we term a colloidal molecular crystal. We also consider a single colloid driven through a disordered assembly. For hard sphere interactions, we find evidence for a continuous phase transition into a "jammed state" where the system acts as a solid. We discuss the implications of the jammed state for the glass transition in light of the recently proposed jamming phase diagram of Nagel and Liu. For softer interactions, we find that the particle moves by creating a fracture zone and that scaling in the velocity force characteristics occurs, similar to that observed in other systems which exhibit plastic depinning. | ||||
| Wednesday, November 10, 4pm | Prof. Mark Newman | University of Michigan | Using physics methods to solve non-physics problems | Middleton |
| Methods developed to solve problems in physics can often be of use in other fields as well, and these days there are many opportunities for physicists to apply their knowledge in new areas. In this talk, I will present three short case studies of applications of physics methods to non-physics problems in cartography, political science, and information theory, respectively. The first example is an application of Fourier-space methods to the construction of map projections, the second an analysis of US congressional voting records using principal components, and the third a study of optimal encoding in radio transmissions. As an amusing corollary of the latter, we argue that the people who spend their lives watching the sky for radio messages from extraterrestrials are wasting their time; regardless of whether anything is out there, their efforts are doomed to failure by the law of maximum entropy. | ||||
| November 12th | Prof. S. G. Rajeev | University of Rochester | A model for Two Dimensional Turbulence Based on Random Matrix Theory | Bowick |
| We will present a model for turbulence of incompressible flow in two dimensions. Random matrix theory can be used to get a formula for the turbulence entropy of such a flow as a function of vorticity. The vortex distribution that maximizes the entropy can be determined analytically. When two vortices merge to form a larger vortex, the entropy increases. (The opposite is believed to be true in three dimensional flow.)This might explain the observed phenomenon of `reverse cascade' in two dimensional flow. Based on joint work with Savitri Iyer, arXiv:physics/0206083. | ||||
| November 19th | ||||
| November 26th | Thanksgiving | |||
| December 3rd | Prof. Dave Drabold | Ohio University | Novel methods for first principles modeling of glasses | Schiff |
| In this talk, I discuss novel approaches to first principles modeling of glasses. Recently, we have explored two methods to form models of binary glasses that offer significant computational advantage and enable inclusion of a priori information about structure from experiments or other considerations. For glassy SiO2 and some other IV-VI binary glasses, we find that decoration of bond centers of a good quality tetrahedral amorphous network followed by rescaling and relaxation leads to a highly realistic and large (648 atom) ab initio model of silica and other glasses. The problem of "freezing in" too much disorder from the liquid state, familiar from quench from melt simulations, appears to be ameliorated. Next, we show that Reverse Monte Carlo (RMC) may be used to produce chemically and topologically realistic models if appropriate constraints are employed in addition to forcing models to agree with diffraction measurements. The method has a high degree of flexibility that enables us to include information from Fluctuation Electron Microscopy (FEM) experiments, which have recently shown that some samples of a-Si:H exhibit medium range order. We have successfully fit diffraction and FEM data and thus formed models reproducing the experimental MRO. It seems unlikely that melt quench or continuous random network models would reproduce such complex ordering. By adopting an information theoretic viewpoint, we have merged RMC with first principles simulation to build models which simultaneously reproduce experimental data and are a minimum energy configuration of a density functional prescription for interatomic interactions. The method is applied to a 648 atom model of g-GeSe2 and produces an essentially perfect neutron static structure factor (including first sharp diffraction peak), electronic density of states and vibrational spectrum. | ||||
| Date | Speaker | Affiliation | Title | Host |
|---|---|---|---|---|
| January 21st | Dr. Benny Davidovitch | Harvard University | Continuum approach in studying nano-scale surface phenomena | Marchetti |
| Interfacial phenomena play a crucial role in systems composed of small particles. When the size of such particles is in the nano-scale regime, the validity of classical interfacial theory is naturally questioned. In some cases, the theory must be modified in order to reach quantitative agreement with experiments and simulations. In this talk, I will present two examples of such systems. The first one is a dip-pen, used to print on solid surfaces in humid environment. The second example is a colloidal gel, made a of non-silica beads. In both cases, surface energies govern various physical properties, such as gel strength and size of condensed liquid drops. Problems and subtleties in applying continuum surface theories in the nano-regime will be demonstrated through these examples. | ||||
| January 28th | Dr. Brian DiDonna | University of Minnesota | Elasticity of inhomogeneous materials: relaxing the affine assumption | Marchetti |
| There has recently been a surge of interest in the rheology of inhomogenous materials such as foams, granular materials, and biopolymer networks. The elastic response of such materials is strongly affected by non-uniformities in the displacement field at intermediate length scales. I will present a general framework for the non-uniform, or "non-affine" component of a material's response to externally applied stresses. This framework succeeds in separating the microscopic elasticity of material sub-blocks from macroscopic structural effects. | ||||
| February 4th | ||||
| Wednesday, February 9, 11am | Dr. Roya Zandi | University of California, Los Angeles | Casimir forces, surface fluctuations, and thinning of superfluid films | Marchetti |
| February 11th | Prof. Larry Liebovitch | Florida Atlantic University | Modeling Epidemics and the Spread of Infectious Disease | Foster |
| An introduction to the models and their dynamics that describe the spread of infectious disease. We use "patches" with different infectious parameters and the movement of people between them to determine how an epidemic depends on local conditions and the geographic gradients of the infectious parameters. This approach is useful in understanding what happens when two populations are suddenly exposed to each other and when an epidemic spreads out from a geographic center. Reference: Liebovitch and Schwartz, Migration induced epidemics: dynamics of flux-based multipatch models, Physics Letters A332:256-267 www.ccs.fau.edu/~liebovitch/patchPLA.pdf. | ||||
| February 18th | ||||
| February 25th | Dr. Xiangjun (Sean) Xing | University of Illinois, Urbana-Champaign | Scaling of entropic shear rigidity | Marchetti |
| The scaling of shear modulus of rubbers and gels near the vulcanization/gelation transition has been studied for more than twenty years, via different approaches. Experimental as well show that study of rubbery systems needs two statistical ensembles: the preparation ensemble and the measurement ensemble. The vulcanization theory provides a natural frame-work for understanding of these systems. I will also show the physics of rubber elasticity depends on the repulsive interactions between neighboring particles. Using field theory and renormalization group transformation, we find that there are two universality classes for the shear modulus scaling: phantom systems and incompressible systems. The corresponding exponents of shear modulus agree with the conjecture of de Gennes as well as that of Daoud and Coniglio respectively. | ||||
| March 4th | ||||
| March 11th | ||||
| March 18th | Spring Break | |||
| March 25th | APS March Meeting | |||
| April 1st | Dr. David Hubel | Harvard University | Vision and Brain: Possible Physiological Basis for Some Common Illusions | |
| Special Announcement Sixth Distinguished Lecture in Vision at Upstate Medical University (2231 Weiskotten Hall). For an autobiography of the speaker, please visit http://nobelprize.org/medicine/laureates/1981/hubel-autobio.html. | ||||
| April 8th | Dr. Frank Wilhelm | Ludwig-Maximilians University, Munich | Quantum coherence in superconducting circuits | Plourde |
| Superconducting quantum circuits containing Josephson junctions can be used for designing quantum electrodynamical circuits, such as quantum bits and cavities. Thus, collective states of the systems which involve a macroscopic number of particles behave as if they were mere two-level atoms. I will outline how to design such systems and how to use the unique flexibility of microfabrication to reach an exquisite degree of control, in particular a switchable qubit-qubit interaction. I will introduce a model for the decoherence, which allows to determine dephasing and relaxation rates within conventional techniques. A more subtle analysis based on an exact solution clarifies the previously unexplained loss of fringe visibility seen in most experiments. Finally, will show how by applying optimum quantum control theory known from NMR and femtochemistry, high-fidelity time-optimal realizations of the controlled not quantum logic gate may be achieved within present-day experimental technology. The models and techniques presented can also be applied to other systems. | ||||
| April 15th | Prof. Dmitrii Makarov | University of Texas, Austin | Unfolding proteins with mechanical forces: Pulling and squeezing molecules using computer simulations | Movileanu |
| Proteins that perform “load bearing” functions in living organisms are often unique materials that display a combination of strength and toughness unmatched by any artificial materials. Their unique mechanical properties are believed to be related to the ability of certain protein domains to resist unfolding by mechanical forces. Mechanical pulling has also been implicated as the mechanism by which proteins are denatured and translocated to enable their subsequent degradation by ATP dependent proteases. In this talk, I will report on our group's theoretical and computational studies of protein domains under mechanical tension. I will describe our recent studies of the “topological optimization problem”, which have identified protein folds with topology that leads to maximum mechanical resistance. I will further report on our simulations of the protein translocation through pores and compare the mechanisms of chemical/thermal denaturation, mechanical unfolding, and translocation-induced unfolding. | ||||
| April 22nd | Dr. Mary Beth Hatten | Rockefeller University | Spring Distinguished Lecture, Syracuse Neuroscience Organization (SNO) | |
| Special Announcement Location and time to be announced. For more information, please visit http://sno.syr.edu. | ||||
| April 29th | Prof. Gino Cingolani | SUNY Upstate Medical University | Cellular trafficking: from genes to atoms | Marchetti |