7,667 research outputs found
Haptic Interface for Center of Workspace Interaction
We build upon a new interaction style for 3D interfaces, called the center of workspace interaction. This style of interaction is defined with respect to a central fixed point in 3D space, conceptually within arm\u27s length of the user. For demonstration, we show a haptically enabled fish tank VR that utilizes a set of interaction widgets to support rapid navigation within a large virtual space. The fish tank VR refers to the creation of a small but high quality virtual reality that combines a number of technologies, such as head-tracking and stereo glasses, to their mutual advantag
Rogue decoherence in the formation of a macroscopic atom-molecule superposition
We theoretically examine two-color photoassociation of a Bose-Einstein
condensate, focusing on the role of rogue decoherence in the formation of
macroscopic atom-molecule superpositions. Rogue dissociation occurs when two
zero-momentum condensate atoms are photoassociated into a molecule, which then
dissociates into a pair of atoms of equal-and-opposite momentum, instead of
dissociating back to the zero-momentum condensate. As a source of decoherence
that may damp quantum correlations in the condensates, rogue dissociation is an
obstacle to the formation of a macroscopic atom-molecule superposition. We
study rogue decoherence in a setup which, without decoherence, yields a
macroscopic atom-molecule superposition, and find that the most favorable
conditions for said superposition are a density ~ 1e12 atoms per cc and
temperature ~ 1e-10.Comment: 10 pages, 4 figures, 46+ references; submitted to PR
Sonoluminescence and the QED vacuum
In this talk I shall describe an extension of the quantum-vacuum approach to
sonoluminescence proposed several years ago by J.Schwinger. We shall first
consider a model calculation based on Bogolubov coefficients relating the QED
vacuum in the presence of an expanded bubble to that in the presence of a
collapsed bubble. In this way we shall derive an estimate for the spectrum and
total energy emitted. This latter will be shown to be proportional to the
volume of space over which the refractive index changes, as Schwinger
predicted. After this preliminary check we shall deal with the physical
constraints that any viable dynamical model for SL has to satisfy in order to
fit the experimental data. We shall emphasize the importance of the timescale
of the change in refractive index. This discussion will led us to propose a
somewhat different version of dynamical Casimir effect in which the change in
volume of the bubble is no longer the only source for the change in the
refractive index.Comment: 15 pages, 1 figure, uses sprocl.sty. Talk at the 4th Workshop on
Quantum Field Theory Under the Influence of External Conditions, Leipzig,
14-18 September, 199
Structural Evidence for the Tetrameric Assembly of Chemokine CCL11 and the Glycosaminoglycan Arixtra™.
Understanding chemokine interactions with glycosaminoglycans (GAG) is critical as these interactions have been linked to a number of inflammatory medical conditions, such as arthritis and asthma. To better characterize in vivo protein function, comprehensive knowledge of multimeric species, formed by chemokines under native conditions, is necessary. Herein is the first report of a tetrameric assembly of the human chemokine CCL11, which was shown bound to the GAG Arixtra™. Isothermal titration calorimetry data indicated that CCL11 interacts with Arixtra, and ion mobility mass spectrometry (IM-MS) was used to identify ions corresponding to the CCL11 tetrameric species bound to Arixtra. Collisional cross sections (CCS) of the CCL11 tetramer-Arixtra noncovalent complex were compared to theoretical CCS values calculated using a preliminary structure of the complex deduced using X-ray crystallography. Experimental CCS values were in agreement with theoretical values, strengthening the IM-MS evidence for the formation of the noncovalent complex. Tandem mass spectrometry data of the complex indicated that the tetramer-GAG complex dissociates into a monomer and a trimer-GAG species, suggesting that two CC-like dimers are bridged by Arixtra. As development of chemokine inhibitors is of utmost importance to treatment of medical inflammatory conditions, these results provide vital insights into chemokine-GAG interactions
Naturalness in emergent spacetime
Effective field theories (EFTs) have been widely used as a framework in order
to place constraints on the Planck suppressed Lorentz violations predicted by
various models of quantum gravity. There are however technical problems in the
EFT framework when it comes to ensuring that small Lorentz violations remain
small -- this is the essence of the "naturalness" problem. Herein we present an
"emergent" space-time model, based on the "analogue gravity'' programme, by
investigating a specific condensed-matter system that is in principle capable
of simulating the salient features of an EFT framework with Lorentz violations.
Specifically, we consider the class of two-component BECs subject to
laser-induced transitions between the components, and we show that this model
is an example for Lorentz invariance violation due to ultraviolet physics.
Furthermore our model explicitly avoids the "naturalness problem", and makes
specific suggestions regarding how to construct a physically reasonable quantum
gravity phenomenology.Comment: V1:4 pages, revtex4; V2: slight changes in title, presentation, and
conclusions. This version to appear in Physical Review Letter
Kinetic energy release in electron-induced decay reactions of molecular ions: C3H8+ and C3H7+
We have measured the kinetic energy release (KER) distributions for electron-induced dissociation of mass-selected molecular parent and fragment ions of propane. They are compared with distributions determined for spontaneous (metastable) dissociation. The average KER for induced dissociation of C3H8+ into C3H7+ is 13.2 +/- 1.2 meV, about 42% larger than for the spontaneous reaction. This large difference is attributed to the dramatically reduced time at which the induced reaction can be sampled. In contrast, the KER for dissociation of C3H7+ into C3H5+, which is characterized by a large reverse activation energy, is hardly affected by the experimental time scale. (C) 2000 American Institute of Physics. [S0021-9606(00)00826-6]
- …