Fall 2015 Seminars
All Physics Seminars are held in S-3-126 at 1pm on Thursday, unless otherwise noted.
Tuesday, Sep 8, 1:00pm
CSIRO Manufacturing, Australia
Acoustics, Optics and Superconductivity Activities at CSIRO Sydney, Australia
The CSIRO Lindfield site in Sydney, Australia has been involved with an array of projects in the areas of acoustics, optics and superconductivity. These have included producing optics for the original LIGO (Interferometric Gravitational-Wave Observatory) and coatings for Advanced LIGO projects, working with the NASA Armstrong Flight Research Center on a heat shield embedded with Fibre Bragg-gratings and acoustics sensors, an etalon for the Solar Orbiter mission and HTS SQUID (High-temperature superconducting quantum interference device) based magnetometers and gradiometers. In this talk, it will be my pleasure to discuss:
* Interferometric detection of gravity waves and the optics we constructed for the LIGO project.
* Fabry-Pérot etalons. An optical filter which can be constructed to tune with high finesse to a particular wavelength using temperature and voltage. The etalon for the Solar Orbiter mission will be presented as an example.
* High- temperature SQUID magnetometers and gradiometers and their application to geophysical exploration (LANDTEM) and magnetic anomaly detection with examples illustrated from the MAGSAFE, airborne submarine detection and OceanMAG, underwater magnetic sensing projects.
* The NASA Thermal Protection Shield and its use of Fibre Bragg-gratings, Optical Frequency Domain Reflectometry and PVDF (polyvinylidene fluoride) PZT based acoustic sensors to detect and assess damage to the TPS in flight.
Thursday, Sep 17, 1:00pm
Traveling-Wave MRI at Ultra-High Magnetic Fields
In conventional magnetic resonance imaging (MRI) near-field RF coils are used as the only excitation method to obtain images of subjects in clinical and research environments. At high-field strength (exceeding 4Tesla), the propagation wave vector of the excitation field can no longer be ignored as the wavelength becomes comparable than the imaging volume, particularly if the medium dielectric constant is large. As ultra-high field MRI scanners are becoming widely available, it is essential to study the associated far-field effects and develop more efficient methods of spin excitation for MRI. In my talk, I show our latest developments in ultra-high field imaging based on a specially designed traveling-wave transmission system that allows RF wave propagation at ultra-high field NMR systems (7 T, 16.4 T, 21 T). The main implications of our research efforts include a gain in the size of the imaging field of view, as well as a possibility for the robust manipulation of the rf field profile.
Thursday, Sep 24, 1:00pm
Princeton Plasma Physics Laboratory, Princeton University
Quantumlike physics in classical plasmas
Dynamics of classical plasmas is essentially determined by collective oscillations, or waves, mediated by long-range electromagnetic (EM) interactions. The standard approach to studying these waves is to use Maxwell's equations for EM fields. But plasma waves are more than just EM fields; they can be viewed as dynamical objects with distinct properties that allow for an axiomatic variational theory. Using nothing but the definition of a classical wave, this theory leads to the identification of the wave most natural characteristic, the (classically normalized) "photon state function", and the corresponding quantumlike Lagrangian of a wave, or "photon", in a general dispersive medium.
Establishing the general quantitative analogy between the dynamics of classical dispersive waves and particles significantly simplifies calculations of many EM effects in plasmas and suggests new ways of manipulating plasma waves. Some examples will be presented, which include calculations of the wave canonical and kinetic energy-momenta, ponderomotive (dipole) forces on photons and their impact on the dispersion of the ambient medium, nonlinear autoresonant acceleration of classical waves, and extensions of geometrical optics. In particular, it will be shown that linear nondissipative EM waves can be viewed as generalized Dirac particles; hence they experience polarization-driven bending of ray trajectories and polarization dynamics that can be interpreted as the precession of the wave "spin". The same theory also yields, as a spinoff, a fully Lagrangian point-particle model of the actual Dirac electron. The well known Bargmann-Michel-Telegdi theory is hence naturally restated in a conservative variational form, and a relativistic ponderomotive Hamiltonian of the Dirac electron (with spin effects included) is derived.
Thursday, Oct 1, 1:00pm
Superheated integrability and multisoliton survival through scattering off barriers
A true soliton is a solitary wave---an isolated wave that maintains its shape due to a balancing of dispersion and nonlinear attraction---with a key additional property: when a soliton collides with another local disturbance in the same medium, and, in particular, with another soliton, then asymptotically far from the collision, the soliton will regain its exact initial shape and velocity. It is this maintaining of identity through collisions that is the observable signature of integrability of the underlying nonlinear system, of the presence of infinitely many "higher" conservation laws. But then, if solitons meet on top of a strong integrability-breaking barrier, one would expect the solitons to undergo some process consistent with energy conservation but not with higher conservation laws, such as the larger soliton cannibalizing the smaller one. However, here we show that when a strongly-coupled "breather" of the integrable nonlinear Schrodinger equation is scattered off a strong barrier, the solitons constituting the breather separate but survive the collision: as we launch a breather with a fixed impact speed at barriers of lower and lower height, at first all constituent solitons are fully reflected; then, at a critical barrier height, the smallest soliton gets to be fully transmitted, while the other ones are still fully reflected. This persists as the barrier is lowered some more until, at another critical height, the second smallest soliton begins to be fully transmitted as well, etc., resulting in a staircase-like transmission plot, with quantized plateaus. We show how this effect makes tangible the inverse scattering transform: the powerful, but otherwise physically opaque mathematical formalism for solving completely integrable partial differential equations. Furthermore, if such collisions can be realized experimentally in ultracold Bose gases, they could become a basis of improved atom interferometers.
Thursday, Oct 8, 1:00pm
Rosemary L. Smith
Dept of Electrical and Computer Engineering
MicroInstruments and Systems Laboratory
University of Maine
Micro and Nano Engineering of Biomedical Microdevices
Micro and nano fabrication technologies enable the engineering of sophisticated structures and devices that are on the same geometric scale as molecules and cells. Application to research and analysis provides the user with new and unique measurement, modification and manipulation capabilities. Instruments for the study of cell biology, single molecule sensors, targeted drug delivery particles, and single cell analyses have been realized. Gradually, these devices and instruments are transitioning from the research lab to commercial development and the consumer market. This talk will present the design, fabrication and application of several example biomedical micro and nanodevices recently demonstrated by Dr. Smith and her colleagues, including transdermal microneedle arrays, a nanopore DNA sensor and a cells-on-chip microfluidic instrument. Important engineering issues, such as choice of materials and methods, assembly and packaging in order to interface resulting devices with traditional instrumentation and the end user, will be discussed.
Rosemary L. Smith is Professor of Electrical & Computer Engineering, and a Cooperating Professor in the Chemical and Biological Engineering Department at the University of Maine in Orono, Maine. She holds a Bachelor of Science degree in Electrical Engineering from the University of Rhode Island and a Doctorate of Philosophy (PhD) in Bioengineering from the University of Utah. She is an active member of the Graduate School for Biomedical Sciences and Engineering at UMaine, serving as a member of the curriculum committee and engineering student mentor. Her research activities involve the application of micro and nano technologies to biomedical sensors, devices and microsystems. She is Co-director of the MicroInstruments and Systems Laboratory at UMaine, Associate Editor for the journal Biomedical Microdevices, and co-Chair of the newly formed Northern New England IEEE Chapter of the Engineering in Medicine and Biology Society. She has co-authored over 165 journal articles and conference proceedings papers and ten US Patents. Professor Smith has developed and taught courses at both the undergraduate and graduate level in biomedical microsystems engineering, integrated circuit manufacturing, semiconductor device physics and nanotechnology.
Thursday, Oct 15, 1:00pm
Spatial Extent of Branching Brownian Motion
One dimensional Branching Brownian Motion begins with a single particle at the origin and at each subsequent time step particles either diffuse, split into two (with a rate b), or die (with a rate d). Depending on the relative rates of birth and death, the process is either explosive (b > d), critical (b = d), or eventually dies (b < d). We investigate the joint statistics of the rightmost and leftmost visited sites by such a process (Xmax and -Xmin respectively) up to a time t. This is an interesting instance of extreme value statistics of correlated random variables. In the b > d regime Xmax and Xmin increase with a finite velocity and eventually become uncorrelated. In the b <= d regimes the individual and joint distributions of Xmax and Xmin become stationary at large times. We derive exact results for this stationary joint distribution and use it to construct the stationary distribution of the spatial extent s = Xmax - Xmin. This distribution has a non-trivial power law tail ~1/s^3 for large s in the critical case and is exponential for b < d. Our exact results demonstrate that the correlations between Xmax and Xmin persist even in the stationary state. These results have possible applications to the spread of epidemics in animal populations.
Thursday, Oct 22, 1:00pm
Pollockian Mechanics: Painting with Viscous Jets
Beginning around 1945, American Abstract Expressionist painter Jackson Pollock invented and perfected a new artistic technique based on pouring and dripping liquid pigment onto a canvas stretched horizontally on the floor. Long recognized as important and influential by art historians, Pollock's works have also been studied as complex webs. But although the artist manipulated gravitational flows to achieve his aims, the fluid dynamical aspects of his process remained largely unexplored. I will discuss Pollockian Mechanics—the physics of lifting paint by viscous adhesion and dispensing it in free jets—focusing on the role of fluid instability. This technique will be contrasted with flows of pigment employed by other artists. I will conclude with comments on the scaling regularities of the poured patterns and their affinity to the "geometry of nature."
Thursday, Oct 29, 1:00pm
Fluctuations of ions in ion atmosphere modulate RNA dynamics
We have developed** a model to investigate the excess ion atmosphere around an irregular RNA structure in aqueous solution containing MgCl2 and KCl under physiological ionic strength. We couple the electrostatics to a structure based coarse-grained model, and probe native basin fluctuations by molecular dynamics simulations. The structure based model is designed to capture the dynamics of outer sphere Mg2+ population, and one can sample the partially unfolded conformational ensembles. Condensation of K+ and Cl- is described implicitly, while Mg2+ ions explicitly. The model takes into account electrostatic heterogeneity of phosphates, electrostatic and mixing free energy of the screening ions, and enforces ion accessibility near the RNA. A key idea is to make monovalent cation condensation a dynamical variable that depends on the atomic coordinates, and calculated from first principles. Our predictions for the excess ion atmosphere and Mg2+-RNA interactions in adenine riboswitch, a 58 nucleotide ribosomal fragment, and beet western yellow virus pseudoknot, are in good agreement with experimental data of over 7.5 fold [KCl] and several decades of [MgCl2].
** in collaboration with R. Hayes, J. Noel, P. Whitford, S. Hennelly, J. Onuchic, K. Sanbonmatsu. UM acknowledges a John Simon Guggenheim Memorial Foundation fellowship.
Thursday, Nov 5, 1:00pm
Temporary yet fatal: metastable electronic states as a gateway for electron-attachment induced chemistry
Electronic states metastable with respect to electron ejection are ubiquitous in highly energetic environment, chemical, and biological systems, and often lead to chemical destruction. Prediction of the energetics and lifetimes of the metastable states, resonances, is crucial for understanding the processes of electron capture and the resulting chemical conversion. In this talk I will give a general introduction to the phenomenon of metastable states and to the theoretical tools for treatment of resonances. Specifically, the focus will be on non-Hermitian quantum mechanics approaches for calculating energies and lifetimes of metastable electronic states from the first principles . Non-Hermitian formalisms allow one to exploit quantum chemistry methods developed for conventional bound electronic states for treatment of resonances, which belong to continuous spectrum. I will also discuss the role of the metastable states in chemical and biological processes. In particular, I will present the result of our recent computational studies of electronic structure para-benzoquinone, prototypical biological electron acceptor, and highlight the role of resonances in electron capture by the molecule .
1. D. Zuev, T.-C. Jagau, K.B. Bravaya, E. Epifanovsky, Y. Shao, E. Sundstrom, M. Head-Gordon, and A.I. Krylov. Complex absorbing potentials within eom-cc family of methods: Theory, implementation, and benchmarks. J. Chem. Phys., 141:024102, 2014.
2. A.A. Kunitsa and K.B. Bravaya; First-principles calculations of the energy and width of the 2Au shape resonance in p-benzoquinone, a gateway state for electron transfer. J. Phys. Chem. Lett., 6:1053-1058, 2015.
Thursday, Nov 12, 1:00pm
Information, Computation, and Thermodynamics in Cells
Cells live in complex and dynamic environments. Adapting to changing environments often requires cells to perform complex information processing, and cells have developed elaborate signaling networks to accomplish this feat. These biochemical networks are ubiquitous in biology. They range from naturally occurring biochemical networks in bacteria and higher organisms, to sophisticated synthetic cellular circuits that rewire cells to perform complex computations in response to specific inputs. The tremendous advances in our ability to understand and manipulate cellular information processing networks raise fundamental questions about the physics of information processing in living systems. I will discuss recent work in this direction trying to understand the fundamental constraints placed by (nonequilibrium) thermodynamics on the ability of cellular circuits to process information and perform computations.
Thursday, Nov 19, 1:00pm
Thermodynamics, Fluid Dynamics, and Jupiter's Great Red Spot
Motivated by the longevity of large scale vortex structures in planetary atmospheres, most notably Jupiter's Great Red Spot, I will show how one can derive these as inhomogeneous equilibrium structures, at least in idealized models, by applying statistical mechanics to the fluid equations. The treatment produces an exact set of variational equations, with a very rich structure generated by the infinite number of conservation laws present in these equations. Of course, real atmospheres contain forcing and dissipation that violate such idealized treatments, but I argue that if these are not too strong, their balance will produce steady states that compare favorably to the thermodynamic predictions.
Thursday, Nov 26, 1:00pm
Thursday, Dec 3, 1:00pm
Nonlinear dynamics of heart rhythm disorders
Thursday, Dec 10, 1:00pm
Nonlocality in Quantum Physics? A Testbed Case for Qbism