Eric Sembrat's Test Bonanza

Animals move with a level of grace, speed, and agility that, as of yet, eludes our best  attempts at robotic mimicry.  In this talk we will discuss the modeling and dynamics of rapid vertical ascension and review some recent efforts at instantiating these results into climbing robots.
 

Matter placed in a strong magnetic field provides a fascinating laboratory in which to study exotic quantum phenomena in a highly controllable manner.  This talk will summarize our recent findings of novel magnetic properties of carbon nanotubes, graphene, and graphite, probed via high-field magneto-optical spectroscopy.  A magnetic field applied parallel to a nanotube introduces an Aharonov-Bohm phase to the electronic wave function, which leads to band gap oscillations, magnetic brightening of dark excitons, and extremely large magnetic susceptibility anisotropy.  In graphene, a magnetic field applied perpendicular to the layer results in Landau quantization with non-equal spacings; we highlight a novel situation where electron cyclotron resonance appears in the magnetic quantum limit even though the sample is p-type.  Finally, for graphite, we observe strongly temperature-dependent, asymmetric spectral lines in electronic Raman spectra in magnetic fields up to 45 T applied along the c-axis.  The magnetic field quantizes the in-plane motion while the out-of-plane motion remains free, effectively reducing the system dimension from three to one.  Optically created electron-hole pairs interact with, or “shake up,” the one-dimensional Fermi sea in the lowest Landau subbands, resulting in Fermi-edge singularities.

The standard model of cosmology suggests that the universe started with a phase of very high density, described by general relativity as a singularity. Quantum gravity attempts to resolve the singularity by a more fundamental, microscopic theory whose equations remain valid and could tell us what happened at or even before the big bang. This talk reviews one approach, loop quantum gravity, and discusses several surprising new results that shed light on the structure of quantum space-time, with implications for mathematical modeling and conceptual questions in
cosmology.

The ATLAS Experiment at the Large Hadron Collider with its sister experiment CMS reported a discovery last summer of a new boson which is consistent with the Standard Model Higgs boson.  The Higgs particle has been searched for decades. It is the final jewel in the Standard Model of particle physics, a crowning achievement of 20th century science that gives a powerful understanding of fundamental particles and their interactions. In the Standard Model, the Higgs is the quantum of a field that accounts for the masses of those particles.  We will describe the apparatus, the data and other searches.

The mechanisms governing the transfer of pathogens between infected and non-infected members of a population  are critical in  shaping the outcome of an  epidemic.  This is true whether one considers human,  animal or plant populations.  Despite major efforts aimed at the mathematical modeling and mitigation of infectious diseases, the fundamental mechanisms of pathogen spreading for most infectious diseases remain poorly understood.  I present here the results of  combined theoretical and experimental studies of the role of fluid dynamics and fragmentation in disease transmission.

Most organisms live in aqueous environments and propel themselves by swimming. A large subclass is micro-organisms that have slender rod-like shapes, e.g. sperm. These organisms propel themselves using undulations that follow certain waveforms depending on the type of desired motion. At these small lengths scales and slow velocities, water behaves as a viscous fluid: the Reynolds number is small and Resistive Force Theory is a good approximation. Recently RFT has been extended to non-traditional types of fluids, such as dense granular matter, in order to model sand-swimming of undulating animals and robots.

The optimal planar undulatory strategy for a swimming filament in a viscous fluid is the sawtooth waveform, which was identified by Lighthill. Although this result was intended for infinite-length filaments, it also is applicable to finite-length filaments where the number of undulations is large, $U \gtrsim 10$. However the sawtooth's sharp kinks limits the applicability of Lighthill's result in nature and engineering applications, and thus we consider planar waveforms which have constrained curvatures, $| {\mathcal C} | \le {\mathcal C}_\mathrm{max}$. This naturally leads to the dimensionless number, $N = {\mathcal C}_\mathrm{max} S/(2\pi)$, which we call the winding number. 

We find that a piece-wise constant curvature function is optimal, which we determine for a range of winding numbers. These results for viscous fluids also transfer to sand-swimming, albeit the optimal choice for parameters is different.

The control of quantum systems is limited by unwanted interactions with the environment and uncertainties in the applied control fields.  For ions these uncertainties include unwanted fluctuations in the intensity and the frequency of the electromagnetic field used to control the qubit. For unknown but static errors on the time scale of the experiment, compensating composite pulses sequences can be used to minimize the effect of these errors. In this talk, I will describe the general method of compensating composite pulse sequences for single qubit and multi-qubit systems. I will then discuss two experiments performed in collaboration with GTRI using composite pulse sequences. The first experiment uses known pulse sequences to effectively reduce the spatial variation in a microwave field. The second experiment tests a family of narrowband composite pulse sequences that we have developed. Narrowband pulse sequences can improve ion addressing in a chain by minimizing the effective rotation on neighboring ions.  The new pulse sequences are an improvement in both sequence time and cross talk minimization.
 

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.

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.

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.