Eric Sembrat's Test Bonanza

Gravitational waves sap orbital angular momentum and energy from a black hole--neutron star (BH-NS) binary, driving it to inspiral and merge. In the violence of merger, the NS may tidally disrupt and form a hot accretion disk with the collimated magnetic fields necessary to launch jets, providing the central engine for one of the most energetic phenomena in the Universe: a gamma-ray burst (GRB). We assess the feasibility of this scenario with numerical relativity simulations of magnetized BH-NS binary mergers, seeding the NS with magnetic fields and exploring their effects on the remnant disk and the gravitational waves. We find that the gravitational waves are likely to be detectable by Advanced LIGO if the merger occurs within ~100Mpc, though the effects of magnetic fields on the waveforms are likely negligible. Further, we find that a GRB central engine may form if large-scale poloidal magnetic fields anchored in the disk are accreted onto the BH after the NS disrupts.

I will review ideas that may be useful in identifying electromagnetic (EM) emission from supermassive black hole (SMBH) binaries. In particular, any detectable EM emission is likely to be time-variable, which should aid in its identification. I will discuss four possibilities for such variable emission: (i) roughly periodic signals due to the orbital motion prior to coalescence, (ii) a transient pre-cursor caused by the gas trapped inside the binary's orbit, and transients "after-glows" produced by (iii) post-merger gas accretion and (iv) by merger-induced shocks in a circumbinary disk. I will argue that these time-variable EM signatures may be used to identify unique counterparts of gravitational wave sources expected to be detected by (e)LISA and by Pulsar Timing Arrays. I will also highlight the extra science that will be enabled if an EM counterpart is found, such as constraints on SMBH accretion physics, cosmology, and gravitational physics.

Following Yogi Berra's advice, I will use high-speed video clips to highlight some of the interesting physics underlying the game of baseball.  The talk will focus on two broad aspects of the game:  the physics of the baseball-bat collision and the flight of the baseball through the air. I will investigate some very practical questions and show how a  physicist goes about trying to answer these question.  Some examples:  what is the "sweet spot" of a bat; how does the batter's grip affect the batted ball; why does aluminum outperform wood; how determines how far a fly travels; how much does a curve ball break; and why is Mariano Rivera such a great pitcher.  My talk should have something for everybody, whether your interest is baseball, physics, or the connection between them.

Movement is a defining feature of animals. They have evolved diverse locomotor strategies, demonstrating remarkable stability and maneuverability in complex environments. To accomplish this, an animal’s nervous system acquires, processes and acts upon information. Yet to do so, the nervous system must interface with the animal’s environment through the physics of sensors and actuators. Using a series of vignettes from running and flying insects, I will show how the intersection of neurons, muscles and mechanics leads to an understanding of 1) muscle multifunctionality, 2) physiological tuning of motor control strategies, and 3) maneuverability at the extremes of sensing and movement. A common feature throughout is that the timing of neural control during the periodic dynamics of locomotion is a critical determinant of the response. In each case the animal’s neuromechanical strategy is tuned for the stability or maneuverability demands of the task rather than for maximizing absolute power or performance in all situations.  By leveraging the tools of physics and engineering to probe biological systems, we can converge on neuromechanical principles that underlie an integrative science of biology movement.

Understanding the locomotion of animals and robots can be a challenging problem, involving nonlinear dynamics and the coordination of many degrees of freedom. Geometric mechanics offers a vocabulary for discussing these dynamics in terms of lengths, areas, and curvatures. In particular, a tool called the *Lie bracket* combines these geometric concepts to describe the effects of cyclic changes in the locomotor's shape, such as the gaits used by walking or crawling systems.

In this talk, I will introduce some basic principles of geometric mechanics, and show how they provide insight into the locomotion of undulating systems (such as snakes and micro-organisms). I will then discuss my work on how coordinate representations affect the information provided by the geometric structures, and show that the choice of coordinates for a given system can be optimized in a simple, fundamental manner. Finally, I will demonstrate that the geometric techniques are useful beyond the "clean" ideal systems on which they have traditionally been developed, and can provide insight into the motion of systems with considerably more complex dynamics, such as locomotors in granular media.

Bio:
Ross L. Hatton is an Assistant Professor of Mechanical Engineering at Oregon State University. He received PhD and MS degrees in Mechanical Engineering from Carnegie Mellon University, following an SB in the same from Massachusetts Institute of Technology. His research focuses on understanding the fundamental mechanics of locomotion and on finding abstractions that facilitate human control of unconventional locomotors.

PLEASE NOTE: This is a WEBINAR

We investigate the effect of anharmonicity and interactions on the dynamics of an initially Gaussian wavepacket in a weakly anharmonic potential. We find that repeated perturbations can create revivals, echoes, and revival-echoes, with properties that can be controlled via the strength and symmetry of the perturbations.  We also find that depending on the strength and sign of interactions and anharmonicity, the quantum state can be either localized or delocalized in the potential. We formulate a classical model of this phenomenon and compare it to quantum simulations done for a self-consistent potential given by the Gross-Pitaevskii Equation.

From the earliest days of the field of quantum information, trapped atomic ions have had great potential as qubits. Trapped-ion experiments have separately demonstrated the individual ingredients believed necessary for scalable quantum information processing, and, for small numbers of ions, many of these ingredients have been combined within the same experimental system. The central challenge going forward is to enlarge these systems, so that many more qubits can be controlled at a much higher level of accuracy. This will require advances in ion trap materials and designs; a higher level of integration between traps, optics, and control systems; and a greater degree of automation in the experiments. I will discuss work in several of these areas, including the coupling of ions in separate traps, a record-high fidelity single qubit gate, and recent progress in microfabricated ion trap technologies.

Entropy can order shapes into complex structures, even in the absence of explicit attractive forces. As such, shape is important in the self assembly and crystallization of colloids, nanoparticles, proteins and viruses, and in the packing of granular matter.  Using computer simulations of nearly 200 different hard polyhedra, including families of tetrahedra, we demonstrate the emergence of entropic bonds and show how simple measures of building block shape and local order in fluid phases can predict crystals and quasicrystals, liquid crystals, rotator crystals, and glasses.  From these findings, we propose design rules for entropically patchy particles.

Why does a piano sound like a piano? A similar question can be asked of virtually all musical instruments. A particular note, such as middle C, can be produced by a piano, a violin, and a clarinet.  Yet, it is easy for even a musically untrained listener to distinguish between these instruments.  One would like to understand why the sound of the “same” note depends greatly on the instrument.  In particular, we would like to understand what aspects of the piano are most critical in producing its musical tones.  The questions we will address in the talk include:

• Who invented the piano and why?
• Why does the piano have 88 keys and not more or fewer?
• How and why is the tone color of a loud note different from that of a soft note, and why is this important?
• Why are the bass strings on a piano made by wrapping a coil of wire around a central wire core?
• A piano tone is the sum of components that can be described by sine waves. The frequencies of these sine waves deviate a small amount from a simple harmonic series. What is the source of these deviations and why are they important?

After we have addressed all of these questions, we’ll be able to understand why a piano sounds like a piano.

A triumph of contemporary physics is the highly successful description of the most fundamental constituents of Nature and their excitations. Recent theories of “topological insulators” [1,2] have shown that in the complex and emergent world of condensed matter physics, one can engineer the interplay between fundamental symmetries, band structure and spin-orbit coupling to create novel energy-spin-momentum relationships for band electrons and to yield effective realizations of exotic particles predicted but yet unobserved in Nature.  This Colloquium will describe the experimental routes we are pursuing in this context to build "detectors" for such particles, by coupling the surface states of a topological insulator with the gauge symmetry breaking effects of superconductivity [3] and the time-reversal symmetry breaking effect of magnetism [4.5].
1. M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010).
2. Xiao -Liang Qi and Shou-Cheng. Zhang, Rev. Mod. Phys. 83, 1057 (2011).
3. Duming Zhang et al., Phys. Rev. B 84, 165120 (2011).
4. Su-Yang Xu et al., Nature Physics 8, 616 (2012).
5. Duming Zhang et al., arxiv: 1206.2908.