Eric Sembrat's Test Bonanza

In ordinary solids, acoustic shocks are extreme mechanical phenomena: they occur when rigid materials are subjected to violent impacts. But in soft materials things are different. Granular media, foams and polymer networks can all be prepared in a state of vanishing rigidity in which even the tiniest perturbation elicits an extreme mechanical response. When that happens these materials are not just soft, they have become fragile.

In this talk, we present simulations in which two-dimensional jammed granular packings are dynamically compressed, and demonstrate that the elementary excitations are strongly nonlinear shocks, rather than ordinary phonons. We capture the full dependence of the shock speed on pressure and impact intensity by a surprisingly simple analytical model.

We also discuss shear shocks within a simplified viscoelastic model of nearly-isostatic random networks comprised of harmonic springs. In this case, anharmonicity does not originate locally from nonlinear interactions between particles, as in granular media. Instead, it emerges from the global architecture of the network. As a result, the diverging width of the shear shocks bears a nonlinear signature of the diverging isostatic length associated with the loss of rigidity in these floppy networks.

The detection of gravitational waves from the inspiral of a neutron star or stellar-mass black hole into an intermediate-mass black hole (IMBH) promises an entirely new look at strong field gravitational physics. Gravitational waves from these intermediate-mass-ratio inspirals (IMRIs), systems with mass ratios from 10:1 to 100:1, may be detectable at rates of up to a few tens per year and will encode a signature of the central body's spacetime. Direct observation of the spacetime will allow us to use the "no-hair" theorem of general relativity to determine if the IMBH is a Kerr black hole (or some more exotic object, e.g. a boson star). In this talk, I will discuss the prospects for constraining the central body's mass-quadrupole moment in Advanced LIGO, and the potential to detect large, non-Kerr compact objects. I will also discuss the current status of LIGO, and prospects for parameter estimation in the advanced detector era, including the results of a recent blind injection challenge.

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EN-US;mso-bidi-language:AR-SA">Over the last several years the field of ferroelectric and multiferroic oxides has been experiencing a significant revival. This is largely due to recent experimental advances allowing characterization of their functional properties down to the nano- and atomic scale. Specifically, Piezoresponse Force Microscopy (PFM) proved to be an indispensable tool for high-resolution characterization of ferroelectrics. Although, the standard implementation of this technique has been around for almost 15 years, recent years have witnessed the development of advanced modes of PFM such as resonance-enhanced PFM, stroboscopic PFM, switching spectroscopy PFM and so on. This lecture will focus on application of the advanced PFM modes to investigation of the dynamic switching and electronic properties of ferroelectric nanostructures. This will include critical polarization behavior in single-crystalline mso-bidi-font-family:Times-Roman;mso-ansi-language:EN-US;mso-fareast-language:
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mso-bidi-language:AR-SA">he structural disorder effect on domain switching dynamics in ferroelectric polymers will be discussed as well.

Joseph Ford saw beauty in "Chaos" and the potential for ``villainous chaos" to be used in a constructive manner. His ideas have proved prescient. The talk will focus mainly on how chaotic dynamics may have played a key constructive -- rather than destructive -- role in shaping certain features of the Kuiper belt: in particular, the formation and properties of binary objects in the transneptunian part of the Solar System. Kuiper belt binaries stand out from other known binary objects in having a range of peculiar orbital and physical properties which may, actually, be the fingerprint of chaos in the primordial Kuiper belt. Understanding how these remote binaries formed may shed light on the formation and evolution of the Solar System itself.

Advances in microscopy have enabled measurements in living cells, but there is a wealth of biologically relevant dynamical information contained in experimental data that has not been utilized.  Existing analysis methods either coarse grain too much or cannot overcome some technical challenges inherent to in vivo measurements. The importance of more fully utilizing information “hidden” in noisy 3D in vivo measurements will be emphasized in several problems.  In this talk, I demonstrate how recent advances in time series analysis can be used to estimate stochastic differential equations (SDEs) and construct hypothesis tests checking the consistency of a fitted model with a single experimental trajectory. The inferred SDE parameters change in a statistically significant fashion over the lifetime of a single trajectory, so methods capable of rigorous statistical inference checking all SDE model (and measurement noise) assumptions using only one time series are valuable.   Analyzing a single trajectory is important for quantitatively identifying heterogeneity in noisy complex systems.  The methods discussed offer new tools for quantitatively probing molecular traffic in the cytoplasm and also enable new discoveries. Although the results presented are centered around the analysis of experimental  mRNA in live yeast cells (Saccharomyces Cerevisiae), the work is also relevant to tracking groups of particles in crowded, noisy, complex environments.

The development of the technology for trapping atoms in the vacuum and cooling them to ultralow temperatures has opened up the exciting new field of cold atom physics.  This field provides a new domain of applications for local quantum field theory, an approach whose previous applications have been primarily in high energy particle physics and have involved energy scales that are more than 20 orders of magnitude higher.  I will describe a systematic approximation method for quantum field theory called Effective Field Theory that has proved to be a powerful framework for addressing many important problems in ultracold atoms.

Topological states of matter have quantum entangled ground states characterized by topological quantum numbers rather than symmetry
breaking. Inspired by the discovery of topological insulators, I describe recent progress in finding a variety of new classes of topological materials
in semiconductors and superconductors. Potential applications in electronics and quantum computation will be briefly discussed.

We present a Hamiltonian derivation of a class of reduced models in plasma physics obtained by imposing dynamical constraints on a parent Hamiltonian model. We will consider MHD equations and Maxwell-Vlasov equations as parent models. It is shown that the Poisson bracket associated with these reduced models is the Dirac bracket obtained from the Poisson bracket of the parent model.

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When sufficiently charged, the interface between a conducting liquid and an insulator (vacuum, gas, liquid) becomes unstable and forms sharp conical tips (Taylor cones) which inject liquid into the insulator. This injection most often takes the form of a micro-jet issuing from the tip of the Taylor cone. The physics of this cone-jet is approximately understood. In particular, the larger the electrical conductivity K of the liquid and the smaller its flow rate Q pushed through the cone-jet, the smaller the jet radius R. However, the process of jet shrinking with increasing K does not go forever. When K reaches values in the range of 1 S/m, R may become as small as 5 nm. This leads to electric fields strong enough for ions dissolved in the liquid conductor to be field-evaporated through the interface, resulting in a mixed regime with simultaneous ejection of ions and drops. An extreme behavior when only ions and no drops are formed has been known for decades in the case of positively charged liquid metals exposed to vacuum. The subject of our enquiry is whether a transition takes place between the convex drop-emitting cone-jet and the presumably concave tip emitting ions alone. We have studied this presumed transition under a variety of circumstances It is better probed with electrolytes than with liquid metals, as the latter have conductivities many orders of magnitude higher than the transitional range K~1 S/m. It is not readily studied when either a liquid metal or an electrolyte is surrounded by a gas because the evaporated ions produce electrical breakdown turning the insulating gas into a conductor. One line of research therefore involves the study (by time of flight mass spectrometry) of highly conducting electrolytes (including molten salts or ionic liquids) in a vacuum. In another approach we substitute the gas by a dielectric liquid, and explore whether or not ions or nanodrops are injected into an insulating liquid.  Although the dielectric liquid alters drastically the situation through space charge effects limiting the current, we observe the production of nanodrops in the 5-10 nm size range, as well as ion injection. The purely ionic regime has been encountered with ionic liquids in vacuum, but not yet in insulating liquids.

Superfluidity is a fascinating emergent phenomenon not only because matters are transported without energy dissipation but fundamentally it is a macroscopic manifestation of the quantum state of microscopic particles. Superfluidity was discovered in quantum liquids like liquid helium and most recently in ultra cold atomic gas Bose condensate. However the experimental evidence of the existence of superfluid state in the crystalline solid (“supersolid”) has been elusive in spite of a theoretical prediction more than 40 years ago [1]. The discovery of Non Classical Rotational Inertial (NCRI) in the solid ⁴He with torsional oscillator (TO) technique [2] ignited renewed interest in solid helium. Further studies indicate multiple possible origins of NCRI. In this presentation, I will give a concise introduction about the progress in the search for “supersolid”. I will also discuss our NMR experiments on dilute solid solution of ³He in ⁴He. We observed isotopic phase separation in all the samples we studied. We detected a significant change in the spin lattice relaxation time (T₁) in the regime where NCRI was reported, which suggests an abnormal dynamics of ³He atoms near the Larmor frequency. A phenomenological model of thermally activated relaxation is proposed to describe this anomaly.

[1] A. F. Andreev and I. M. Lifshits, JEPT 29, 1107 (1969)

[2] E. Kim and M. H. W. Chan, Nature 427, 225 (2004); Science 305, 1941 (2004)