Control of Microbial Motility
Speaker: Prof Vasily Kantsler, Research Associate, Department of Applied Mathematics and Theoretical Physics of Cambridge (UK), Assistant Professor at Skoltech
Abstract: Interactions between swimming cells and surfaces are essential to many microbiological processes, from bacterial biofilm formation to human fertilization. However, despite their fundamental importance, relatively little is known about the physical mechanisms that govern the scattering of flagellated or ciliated cells from solid surfaces. In the talk I will reveal recent advances in understanding of flagella interaction with surfaces, provide mechanisms for utilizing our knowledge about these interactions to control swimming of flagellated cells. In addition, I will describe our very recent results on sperm rheotaxis near surfaces. The key focus will be on the experimental results, supported by numerical simulation using minimal models
Soap Film Dynamics and Topological Jumps under Continuous Deformation
Speaker: Dr Keith Moffatt, Department of Applied Mathematics and Theoretical Physics University of Cambridge, UK
Abstract: Consider the dynamics of a soap-film bounded by a flexible wire (or wires) which can be continuously and slowly deformed. At each instant the soap-film is relaxed in quasi-static manner to a minimum-area (i.e. minimum-energy) state compatible with the boundary configuration. This can however pass through a critical configuration at which a topological jump is inevitable. We have studied an interesting example of this behavior: the jump of a one-sided (Mobius strip) soap-film to a two-sided film as the boundary is unfolded and untwisted from the double cover of a circle. The nature of this jump will be demonstrated and explained. More generally, dynamical systems have a natural tendency to relax through dissipative processes to a minimum-energy state, subject to any relevant constraints. An example is provided by the relaxation of a magnetic field in a perfectly conducting but viscous fluid, subject to the constraint that the magnetic field lines are frozen in the fluid. One may infer the existence of magnetostatic equilibria (and analogous steady Euler flows) of arbitrary field-line topology. In general, discontinuities (current sheets) appear during this relaxation process, and this is where reconnection of field-lines (with associated change of topology) can occur. Just as for the soap film, slow change of boundary conditions can lead to critical conditions in which such topological jumps are inevitable.
From Nano to Cosmo: Nanoscale Superconductivity Used to Detect Faint Far-Infrared Astronomical Signals
Speaker: Dr Teunis Klapwijk, Kavli Institute of Nanoscience at Delft University of Technology, Netherlands
Abstract: Superconductivity is a phenomenon, which is very well suited for interactions with far-infrared radiation. This part of the electromagnetic spectrum is very important to gather information about processes in the ‘cool universe’. It is largely masked by the absorption in the earth’s atmosphere. Superconducting devices have been developed capable of measuring the detailed chemistry of the interstellar gas using the Herschel Space telescope and more recently with the Atacama Large Millimeter Array. In considering future astronomical goals it has been recognized that there is an urgent need for multi-pixel arrays, which can advantageously be realized with superconducting resonators, which in themselves have become very important research-tools for circuit quantum electrodynamics. Meanwhile it has also been recognized that they allow the development of on-chip spectrometry at far-infrared wavelengths, which promises very compact instruments to study early galaxies in the universe.
Many-Body Physics with Quantum Gases in Disorder
Speaker: Georgy Shlyapnikov, the Laboratory of Theoretical Physics and Statistical Models, University of Paris-Sud (France) and and RQC, Moscow (Russia)
Abstract: It is commonly accepted that there are no phase transitions in one-dimensional (1D) systems at a finite temperature, because long-range correlations are destroyed by thermal fluctuations. I will demonstrate that the 1D gas of short-range interacting bosons in the presence of disorder can undergo a finite temperature phase transition between two distinct states: fluid and insulator. None of these states has long-range spatial correlations, but this is a true albeit non-conventional phase transition because transport properties are singular at the transition point. In the fluid phase the mass transport is possible, whereas in the insulator phase it is completely blocked even at finite temperatures. Thus, it is revealed how the interaction between disordered bosons influences their Anderson localization. This key question, first raised for electrons in solids, is now crucial for the studies of atomic bosons where recent experiments have demonstrated Anderson localization. I then consider weakly interacting bosons in a 1D quasiperiodic potential (Aubry-Azbel-Harper model), where all single-particle states are localized if the hopping amplitude in the primary lattice is smaller than half the amplitude of the secondary incommensurate lattice. The interparticle interaction may lead to the many-body localization-delocalization transition, and I will show the finite temperature phase diagram. Counterintuitively, in a wide temperature range an increase in temperature requires a higher interaction strength for delocalization and thus favors the insulator state. In this sense, we have an object that ”gets frozen” under an increase in temperature.
Laser Redistribution Cooling of Dense Gases
Speaker: Dr Martin Weitz, Professor of Experimental Physics, Institute of Applied Physics, University of Bonn, Germany
Abstract: Laser cooling of atomic gases via collisional redistribution of radiation is a novel cooling technique based on laser-induced transitions in a high pressure buffer gas environment. The cooled gas has a density of more than ten orders of magnitude above the typical values in Doppler cooling experiments of dilute atomic gases. In frequent collisions with noble gas atoms in the dense gas system atomic transitions are shifted into resonance with a highly red detuned laser beam, while spontaneous decay occurs close to the unperturbed transition frequency so that the ensemble is cooled. Future prospects of the cooling method include studies of supercooling beyond the homogeneous nucleation temperature and optical chillers.
Mouse Models of Cancer: Cells-of-Origin of Small Cell and Non-Small Cell Lung Cancer
Speaker: Anton Berns, Professor, Skoltech Centre for Stem Cell Research, Moscow & The Netherlands Cancer Institute, Amsterdam
Abstract: Small cell lung cancer (SCLC) is one of the most lethal human malignancies, due to its high metastatic potential and chemo-resistance upon relapse. Using the Rbf/f;p53f/f mouse model for SCLC, we found that the tumors are often composed of phenotypically different cells, characterized by mesenchymal and neuroendocrine markers. These cells often share a common origin. Crosstalk between these cells can endow the neuroendocrine component with metastatic capacity, illustrating the potential relevance of tumor cell heterogeneity in dictating functional tumor properties. Also specific genetic lesions appear to be associated with metastatic potential. Interestingly, the two cell types can also interconvert raising the question of their cell-of-origin. To investigate this in more detail, we inactivated Trp53 and Rb1 in distinct cell types in the adult lung by targeting Cre-recombinase expression to Clara, neuroendocrine, and alveolar type II cells using adenoviral vectors. We could show that neuroendocrine cells serve as the predominant although not the exclusive cell of origin of SCLC. In contrast, mutant Kras-driven adenocarcinomas (one of the NSCLC subtypes) originates primarily from alveolar type II cells. However, in LSL-mutant-Kras;p53flox/flox mice also other cell types gave effectively rise to adenomas and adenocarcinomas. Our data indicate that both cell type specific features and the nature of the oncogenic lesion(s) are critical factors in determining the tumor initiating capacity of lung (progenitor) cells. Furthermore, the cell-of-origin appears to influence the properties of the resulting tumors.
Structural Biology and X-ray Lasers
Speaker: Vadim Cherezov, Department of Integrative Structural and Computational Biology, the Scripps Research Institute, La Jolla,CA
Abstract: Recent developments of X-ray free electron lasers (XFEL) have opened up new opportunities in structural biology. XFELs produce ultra-bright (billion times more intense then synchrotron sources) and ultra-short (<50 fs) X-ray pulses allowing to collect room temperature high-resolution structural data from micron-sized protein crystals as well as to record molecular movies following protein conformational changes at femtosecond resolution. Prof. V. Cherezov from The Scripps Research Institute in La Jolla, USA will give a brief overview of the current status of structural biology research at XFELs and will describe his experience in developing new XFEL technologies for studying G protein-coupled receptors.
Early and Reliable Diagnosis of Deadly Diseases with Molecular Colonies
Speaker: Aleksander Chetverin, Institute of Protein Research, Russian Academy of Science
Abstract: Many deadly diseases, such as AIDS, cancer, and tuberculosis, are accompanied by the appearance in the patient’s body of particular nucleic acid (DNA or RNA) molecules that can serve as molecular diagnostic markers. The earlier a marker is revealed, the higher are the patient’s chances for survival and the easier can the disease be prevented from spreading. Detecting small amounts of DNA or RNA molecules is only possible after amplifying them, usually by PCR (polymerase chain reaction). However, due to limited amplification specificity, the sensitivity of even the most advanced assays is still insufficient for timely diagnosis, with the rate of false-positive and false-negative results being too high.
The problem can be overcome by carrying out the amplification reaction in a gel film, rather than in a test tube. In this format, the amplification products become entrapped in the gel matrix and accumulate around the progenitor molecule, resulting in a 2-D pattern of molecular colonies. Each colony comprises a molecular clone, the progeny of a single starting DNA or RNA template. This provides for the detection, enumeration, and analysis of single molecules present in the analyzed sample. The molecular colony format eliminates the competition from concurrently amplifying non-target nucleic acids and makes the assay digital, as the signal from a colony only needs to be detected without measuring its intensity. This greatly increases the reliability of diagnostics and permits the titer of a molecular marker to be directly determined by counting the number of specific colonies.
Algorithmic and Software Challenges when Moving Towards Exascale
Speaker: Prof Jack Dongarra, University of Tennessee, Oak Ridge National Laboratory, University of Manchester, UK
Abstract: In this talk we examine how high performance computing has changed over the last 10-year and look toward the future in terms of trends. These changes have had and will continue to have a major impact on our software. Some of the software and algorithm challenges have already been encountered, such as management of communication and memory hierarchies through a combination of compile–time and run–time techniques, but the increased scale of computation, depth of memory hierarchies, range of latencies, and increased run–time environment variability will make these problems much harder.
Dynamics of Excitons and Phonons at the Nanoscale
Speaker: Sergei Tretiak, Theoretical Division, Center for Nonlinear Studies and Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos New Mexico.
Abstract: Prediction and understanding of photoinduced processes in molecular-and nano-materials is fundamental to a myriad of technological applications, ranging from sensing, imaging, solar energy harvesting, to future optoelectronic devices. This talk will overview several applications of various quantum-chemical techniques to study excited state properties, dynamics and transport in organic molecular systems and semiconductor quantum dots. Our analysis shows intricate details of photoinduced vibronic relaxation and identifies the conformational degrees of freedom leading to ultrafast dynamics and energy transfer in conjugated polymers. Our modeling further demonstrate that chemical functionalization at low concentrations of single-walled carbon nanotubes locally alters the pi-conjugated network of the nanotube surface and leads to a spatial confinement of the electronically excited wave functions. This suggests that enhanced photo luminescent efficiency of semiconducting carbon nanotube materials can be achieved via selective chemical functionalization. Our studies of the surface ligands effects on the QDs electronic structure indicate strong surface-ligand interactions leading to formation of hybridized states. This potentially opens new relaxation channels for high energy photo excitations. Overall this theoretical modeling allows us to understand and to potentially manipulate energy transfer pathways in molecular and semiconductor nano-materials suitable for solar energy conversion.
Bose-Einstein Condensation of Magnons and Spatio-Temporal Dynamics of Magnon Condensate
Speaker: Prof Sergej Demokritov, Institute for Applied Physics, University of Muenster, Germany
Abstract: Magnons are the quanta of magnetic excitations in a magnetically ordered media. In thermal equilibrium, they can be considered as a gas of quasiparticles obeying the Bose-Einstein statistics with zero chemical potential and a temperature dependent density. We will discuss the room-temperature kinetics and thermodynamics of the magnons gas in yttrium iron garnet films driven by a microwave pumping and investigated by means of the Brillouin light scattering spectroscopy. We show that the thermalization of the driven gas results in a quasi-equilibrium state described the Bose-Einstein statistics with a non-zero chemical potential, the latter being dependent on the pumping power. For high enough pumping powers Bose-Einstein condensation (BEC) of magnons can be experimentally achieved at room temperature. Spatio-temporal kinetics of the BEC-condensate will be discussed in detail. Among others interference of two condensates, vortices, and propagating waves of the condensate density will be addressed.
Nanoelectromechanics with Spin: Effects of Resonance Scattering and Strong Electron Correlations
Speaker: Mikhail Kiselev, Research Scientist, The Abdus Salam International Centre for Theoretical Physics, Trieste, Italy
Abstract: Mikhail will discuss ideas, realizations and applications of nano-electro-mechanical devices – the systems implying a strong coupling between the electronic and mechanical degrees of freedom. In this talk he will mostly concentrate on influence of the resonance scattering (Kondo effect) and strong electron correlations on quantum transport through the mobile quantum dot devices. Mikhail will show that the study of a Kondo-NEM phenomenon provides additional (as compared with standard conductance measurements in a non-mechanical device) information on retardation effects in the formation of a many-particle cloud accompanying the Kondo tunneling. A possibility for superhigh tunability of mechanical dissipation as well as supersensitive detection of mechanical displacement is demonstrated.
Gross Impact of Slim Chances: Errors in Optical Fiber Systems
Speaker: Prof Ildar Gabitov, University of Arizona, USA and Landau Institute for Theoretical Physics, Russia
Abstract: High-speed optical fiber communications represent one of the most rapidly growing areas of the modern technology. This growth is driven by the constantly raising demand for higher bandwidth of information infrastructure. Optical fiber is a key component of modern communication infrastructure which is capable to keep up with this demand. However, there are a number of factors limiting the capacity of fiber optical networks. The noise of the optical amplifiers and spatial disorder of the fiber links caused by the inhomogeneity of fiber characteristics have a significant impact on the quality of data transmission. It will be shown that: these factors lead to fluctuations in the level of errors (BER – bit-error-rate) and probability distribution function of these fluctuations has long extended tails, which might cause outages in optical fiber systems. Theoretical results will be verified against experimental data.
Electrical Grids: Today and Tomorrow
Speaker: Misha Chertkov, Los Alamos National Lab, and Skoltech Founding Faculty Fellow
Abstract: In this talk aimed at applied mathematicians, physicists and network scientists, Professor Chertkov briefly reviews the history of electrical grids and then introduces a few of the physical, optimization and control principles and phenomena in today’s grids and those that are expected to play a major role in tomorrow’s grids.