Eric Sembrat's Test Bonanza

Understanding the new states at the interfaces and the resulting whole behavior of the heterostructures and multilayers is a hot topic at the forefront of the fundamental research, as demonstrated by the huge number of theoretical and experimental studies published in the topmost level scientific journals. In this context, strongly electron correlated oxides are attracting an increasing attention because of their possible practical applications in the emerging field of oxide electronics [1]. With the recent advances in thin-film fabrication, controlled growth of unit-cell layers of complex oxides opened new perspectives in the study of interface effects. In fact, a wealth of microscopic phenomena may be at the work at the interface between the constituent oxides and can result in a number of novel functional properties [2]. In this seminar, I will present two particular examples of unexpected electronic and magnetic interfacial phenomena in multilayers based on complex oxides: ferromagnetism, at the interface of two antiferromagnetic insulating constituent materials [3] and superconductivity, at the interface of two insulating oxides [4]. To disentangle the role of each constituent block and disclose the mechanism giving rise to the interfacial properties, elemental sensitive spectroscopic techniques can be extremely useful. In particular, I will describe the results obtained with two state-of-art synchrotron radiation techniques, namely polarization dependent soft x-ray absorption spectroscopy and bulk sensitive hard x-ray photoelectron spectroscopy.

[1] A.P. Ramirez, Science 315, 1377 (2007); E. Dagotto, Science 318, 1076 (2007).

[2] P. Zubko et al. Annu. mso-ansi-language:EN-US">Rev. Condens. Matter. Phys. 2, 141 (2011); H. Y. Hwang et al. Nature Materials 11, 103 (2012)

[3] C. Adamo et al. Appl. mso-ansi-language:EN-US">Phys. Lett. 92, 112508 (2008); A. Bhattacharya et al. Phys. Rev. Lett. 100, 257203 (2008)

[4] EN-US;mso-fareast-language:IT">G.Balestrino et al. Phys. Rev.B 58, R8925 (1998); A. Gozar et al., Nature 455, 782-785 (2008); C. Aruta et al., Phys. mso-bidi-font-style:italic">Rev. B 78, 205120 (2008)

[5] C.Aruta et al. mso-ansi-language:EN-US">Phys. Rev. B 80, R140405 (2009)

[6] D. Di Castro et al. cond-mat arXiv:1107.2239

The workshop brings together researchers with an interest in soft materials, fluids, and biophysics to discuss their work and explore partnerships.  All participants may present a sound bite (a few minutes talk).  Registration is free, but is required.  Fill our an on-line form and send sound bite slides to alison.morain@physics.gatech.edu.

Biosketch: Dr. David Ballantyne obtained his Ph.D. in 2002 from the University of Cambridge, and has been an Assistant Professor at the
Center for Relativistic Astrophysics in the School of Physics since 2008.  His research concentrates on topics in high-energy astrophysics
with an emphasis on interpreting existing data and making predictions for future observations. His main interests are the evolution of
galaxies and their central supermassive black holes and the physics of accretion disks around both black holes and neutron stars. His work
often involves comparing computer based models with published data from X-ray, radio and/or infrared telescopes.

In this talk we will focus on the elasticity of soft filamentous networks. We will begin with the mechanical behavior of fibrin networks which
have been shown to be highly extensible in recent experiments. We believe that the high extensibility of the networks has its origins in the force induced
structural change in the proteins making up the fibrin fibers. We will present a model and experimental evidence in support of our hypothesis. In the
remainder of the talk we will describe how the quasi-harmonic approximation of statistical mechanics can be combined with the finite element method (used
in structural analysis of buildings, aeroplanes, cars and so on) to understand the entropic elasticity of semi-flexible filament networks. This technique
enables us to capture strain stiffening as well as softening due to filament buckling in networks of actin filaments.

With recent advances in experimental imaging, computational methods, and dynamics insights it is now possible to start charting out the terra incognita explored by turbulence in strongly nonlinear classical field theories, such as fluid flows. In presence of continuous symmetries these solutions sweep out 2- and higher-dimensional manifolds (group orbits) of physically equivalent states, interconnected by a web of still higher-dimensional stable/unstable manifolds, all embedded in the PDE infinite-dimensional state spaces. In order to chart such invariant manifolds, one must first quotient the symmetries, i.e. replace the dynamics on M by an equivalent, symmetry reduced flow on M/G, in which each group orbit of symmetry-related states is replaced by a single representative.

Happy news: The problem has been solved often, first by Jacobi (1846), then by Hilbert and Weyl (1921), then by Cartan (1924), then by [...], then in this week's arXiv [...]. Turns out, it's not as easy as it looks.

Still, every unhappy family is unhappy in its own way: The Hilbert's solution (invariant polynomial bases) is useless. The way we do this in quantum field theory (gauge fixing) is not right either. Currently only the "method of slices" does the job: it slices the state space by a set of hyperplanes in such a way that each group orbit manifold of symmetry-equivalent points is represented by a single point, but as slices are only local, tangent charts, an atlas comprised from a set of charts is needed to capture the flow globally. Lots of work and not a pretty sight (Nature does not like symmetries), but one is rewarded by much deeper insights into turbulent dynamics; without this atlas you will not get anywhere.

This is not a fluid dynamics talk. If you care about atomic, nuclear or celestial physics, general relativity or quantum field theory you might be interested and perhaps help us do this better.

You can take part in this seminar from wherever you are by clicking on
evo.caltech.edu/evoNext/koala.jnlp?meeting=M2MvMB2M2IDsDs9I9lDM92

The heart is an excitable system in which electrical waves normally propagate in a coordinated manner to produce an effective mechanical contraction. Rapid pacing can lead to the development of alternans, a period-doubling bifurcation in electrical response in which successive beats have long and short responses despite a constant pacing period. Alternans can develop into higher-order rhythms as well as spatiotemporally complex patterns that reflect large regions of dispersion in electrical response. These states disrupt synchrony and compromise the heart's mechanical function; indeed, alternans has been observed clinically as a precursor to dangerous arrhythmias, including ventricular fibrillation. In this talk, we will show experimental examples of alternans, describe how alternans develops using a mathematical and computational approach, and discuss the nonlinear dynamics of several possible mechanisms for alternans as well as the conditions under which they are likely to be important in initiating dangerous cardiac arrhythmias.

A neutrino detector, capable of detecting the neutrinos from the Sun’s fusion cycle, was strongly requested by the Theorists working on the Solar Model in the early 1960’s.  The Cl³⁷ → Ar³⁷ detector scheme used by Davis and Harmer at the Savannah River Experiment in the 1950’s was suggested as the basis for a scaled up Solar Neutrino Detector. The details of the design and engineering of this scale up from “Laboratory” to “Production” one mile underground at the Homestake Gold Mine in Lead, South Dakota, are discussed.   The result of the experiment, that only one third of the predicted number was detected, had unexpected consequences on the nature of neutrinos and on their theory.

The Principal Scientist on this project, Raymond Davis, Jr., won the 2002 Nobel Prize in Physics.

In an effort to address one of the grand challenges for condensed matter physics in the 21st century, namely to gain an understanding of the physics of materials which exhibit collective electronic phenomena the Advanced Photon Source, Argonne National Laboratory is developing a new intermediate-energy x-ray beamline.  This beamline, which is slated to go online in the spring of 2012, is being developed to investigate collective behavior in interacting electron systems using two distinct but complementary techniques: angle resolved photoemission spectroscopy and resonant soft x-ray scattering.  In this talk, I will discuss some of the unique capabilities being developed for the beamline and present several examples of collective behavior in interacting electron systems including electron-phonon coupling, spin and charge density waves and orbital ordering in high-temperature superconductors, transition metal oxides and graphen.

Nonlinear dynamics has the feature that it is conceptually and mathematically challenging and yet ubiquitous in its applications. Indeed, one of the appeals of the subject is the universality of some of its frameworks and results. We are attempting to take advantage of such wide applicability in order to involve an unusual range of participants in nonlinear dynamics research. This range spans from postdoctoral to K-12 students as well as teachers.

The talk will report on several projects in various depths, including Hamiltonian chaos in optical propagation, bifurcations in circadian rhythms in plants, nonlinear interaction of actuator systems, vascular dynamics, neural systems modeling, and fluid instabilities. A key arena in which novices can participate effectively is in the search for applications. A particular applied area where we are focusing is biomedicine.