Eric Sembrat's Test Bonanza

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Condensed matter physics in the 20th Century was developed mostly for crystalline solids, and we know so little about the physics of liquids and glasses.  We do not even know how to describe the structure of these amorphous matters to discuss the structure-properties relationship, even though liquids and glasses are so important to everyday life.  This is because liquids and glasses are condensed matter with high density in which atoms are strongly correlated to each other.  Any theoretical effort runs into a thick barrier of many-body interactions.  To circumvent this difficulty the dynamics of a liquid is described usually by the continuum hydrodynamic theories with non-linear extension.  An alternative approach is to use the molecular dynamics (MD) simulation, taking advantage of recent progress in computing power.  However, MD simulations tend to leave us in a deluge of numbers, without a physical idea.  Our effort focused on breaking this conundrum by developing new concepts, using MD as a tool to shape the concept.  We introduced the idea of local topology of atomic connectivity, expressed in terms of the atomic level stresses.  We show that the macroscopic dynamics of a liquid and glass is directly connected to the local atomic dynamics in the form of topological excitations.  Characterization of these excitations leads to a better understanding of the glass transition and mechanical failure of a glass.

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This review of the US fusion research program has two parts.  The first part (after a brief primer on fusion) surveys the plasma and fusion research issues that dominate the present US program.  The second part discusses in more detail two specific topics---the fusion-fission hybrid and the possibility of thermal equilibrium confinement---in more detail. The review assumes very little prior knowledge of plasma physics or fusion research.

 

 

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I will present some recent results from our Lab on the mechanical response of complex-shaped shells subject to loading and in different mechanical environments (with or without an in-out pressure difference). A powerful aspect of our experimental approach is that the geometry and material properties of our shells can be accurately custom-controlled using digital rapid prototyping techniques. First, we focus on the linear response of non-spherical shells under indentation to explore the new concept of geometry-induced rigidity. Despite the complex geometries, we find a remarkable predictive description. Moreover, we investigate universal modes of localization under large displacements. Finally, I will introduce a new class of micro-structured shells, the Buckliball, which undergo a structural transformation induced by buckling under pressure loading. The common underlying feature in these various problems is the prominence of geometry in dictating the mechanical response in thin elastic shells.

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Directed cell motility is a process whereby the motility machinery of the cell (involving the interaction of actin with myosin) is organized spatially so as to cause directed motion. In Dictyostelium, this occurs as the cell responds to cAMP gradients during the aggregation process. In keratocytes, the cell spontaneously polarizes itself (without external cues). This talk will focus on spatially extended modeling of both the signaling system which encodes the directional information and the downstream mechanical response and the comparison of these models to detailed experimental studies of both of these systems.

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I will discuss some recent computer simulations of three different systems; nematic shells, sticky colloidal particles on surfaces and the bulk phases of liquid crystalline bolaamphiphiles. For nematic shells, a layer of liquid crystal is used to coat a microscopic particle. In this geometry, defects necessarily occur – the system is frustrated so that the director profile and local orientational ordering is not constant everywhere. We examine the interactions between the defects for a number of different types and shapes of particles and other cavities. I will also discuss sticky colloids on a flat surface. We will observe how different phases (or different shaped 'nets') can be templated onto the surface by minor modifications to the size and interactions of the sticky patches. Finally, we will examine the bulk phases of liquid crystalline bolaamphiphiles. These are unusual liquid crystals, with long side chains off a relatively rigid rod that form unusual columnar phases. They differ from conventional liquid crystal columnar phases in that the columns are aliphatic with aromatic walls, rather than aromatic columns with aliphatic walls. We examine how frustration in these systems can lead to novel phases, with unit cells significantly larger than single molecules.

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We have performed absorption imaging of a single atom for the first time [1]. A trapped Yb+ atomic ion scatters light out of an illumination beam tuned to atomic resonance at 369.5 nm. When the beam is reimaged onto a CCD camera, we observe an absorption image of 440 nm diameter and 5% contrast. The absorption contrast is investigated as a function of laser intensity and detuning, and closely conforms to the limits imposed by simple quantum theory and known properties of our imaging system. Defocused absorption images provide spatial interferograms of the scattered light, permitting accurate retrieval of the amplitude and phase of the scattered wave. We measure a phase shift of >1 radian in the scattered light as a function of laser detuning, which may be useful in quantum information protocols. The interferograms point to the possibility of observing the focusing of light by a single atom.

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color:black;mso-themecolor:text1">Our group is applying the techniques of modern atomic physics to the system of diatomic molecules.  Molecules are more complex than atoms because of their vibrational and rotational degrees of freedom, and this makes them difficult to control.  However, we have identified a variety of simple principles that allow us to make use of these "new" properties to provide powerful types of leverage on a broad range of problems.  These span fields all the way from particle physics to quantum computation to chemical physics. This talk will give an overview of the field, along with some specific examples of our recent work. These include the first-ever laser cooling of a molecule, and the search for the CP-violating electric dipole moment of the electron.

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Calibri;mso-fareast-theme-font:minor-latin;mso-hansi-theme-font:minor-latin;
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ecent cold atom researches are reaching out far beyond the realm that was conventionally viewed as atomic physics. Many long standing issues in other physics disciplines or in Gedanken-experiments are nowadays common targets of cold atom physicists. Two prominent examples will be outlined in this talk: BEC-BCS crossover and Efimov physics. Here, cold atoms are employed to emulate electrons in superconductors, and nucleons in nuclear reactions, respectively.

The ability to emulate exotic or thought systems using cold atoms stems from the precisely determined, simple, and tunable interaction properties of cold atoms. New experimental tools have also been devised toward an ultimate goal: a complete control and a complete characterization of a few- or many-body quantum system. We are tantalizingly close to this major milestone, and will soon open new venues to explore new quantum phenomena that may (or may not!) exist in scientists’ dreams.

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Here I present our experimental work synthesizing static gauge fields for ultracold neutral atoms (bosonic and fermionic alkali atoms).  I will discuss this gauge field in the language of spin-orbit coupling where it consists of an equal sum of Rashba and Dresselhaus couplings. In experiment, we couple two internal states of our alkali atoms with a pair of ``Raman'' lasers and load our degenerate quantum gas into the resulting adiabatic eigenstates.

For a Bose gas, a function of the Raman laser strength, a new exchange-driven interaction between the two dressed spins develops, which drives a (quantum) phase transition from a state where the two dressed spin states spatially mix, to one where they phase separate.   Going beyond this simple modification to the spin-dependent interaction, we show that in the limit of large laser intensity, the particles act as free atoms, but interact with contributions from higher even partial waves.

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