27,232 research outputs found
Unified model of loop quantum gravity and matter
We reconsider the unified model of gravitation and Yang--Mills interactions
proposed by Chakraborty and Peld\'an, in the light of recent formal
developments in loop quantum gravity. In particular, we show that one can
promote the Hamiltonian constraint of the unified model to a well defined
anomaly-free quantum operator using the techniques introduced by Thiemann, at
least for the Euclidean theory. The Lorentzian version of the model can be
consistently constructed, but at the moment appears to yield a correct weak
field theory only under restrictive assumptions, and its quantization appears
problematic.Comment: 4 pages, dedicated to Michael P. Ryan on the occasion of his sixtieth
birthda
Simulating quantum effects of cosmological expansion using a static ion trap
We propose a new experimental testbed that uses ions in the collective ground
state of a static trap for studying the analog of quantum-field effects in
cosmological spacetimes, including the Gibbons-Hawking effect for a single
detector in de Sitter spacetime, as well as the possibility of modeling
inflationary structure formation and the entanglement signature of de Sitter
spacetime. To date, proposals for using trapped ions in analog gravity
experiments have simulated the effect of gravity on the field modes by directly
manipulating the ions' motion. In contrast, by associating laboratory time with
conformal time in the simulated universe, we can encode the full effect of
curvature in the modulation of the laser used to couple the ions' vibrational
motion and electronic states. This model simplifies the experimental
requirements for modeling the analog of an expanding universe using trapped
ions and enlarges the validity of the ion-trap analogy to a wide range of
interesting cases.Comment: (v2) revisions based on referee comments, figure added for clarity;
(v1) 17 pages, no figure
Ratchet Cellular Automata for Colloids in Dynamic Traps
We numerically investigate the transport of kinks in a ratchet cellular
automata geometry for colloids interacting with dynamical traps. We find that
thermal effects can enhance the transport efficiency in agreement with recent
experiments. At high temperatures we observe the creation and annihilation of
thermally induced kinks that degrade the signal transmission. We consider both
the deterministic and stochastic cases and show how the trap geometry can be
adjusted to switch between these two cases. The operation of the dynamical trap
geometry can be achieved with the adjustment of fewer parameters than ratchet
cellular automata constructed using static traps.Comment: 7 pages, 5 postscript figure
Continuous data assimilation with blurred-in-time measurements of the surface quasi-geostrophic equation
An intrinsic property of almost any physical measuring device is that it
makes observations which are slightly blurred in time. We consider a
nudging-based approach for data assimilation that constructs an approximate
solution based on a feedback control mechanism that is designed to account for
observations that have been blurred by a moving time average. Analysis of this
nudging model in the context of the subcritical surface quasi-geostrophic
equation shows, provided the time-averaging window is sufficiently small and
the resolution of the observations sufficiently fine, that the approximating
solution converges exponentially fast to the observed solution over time. In
particular, we demonstrate that observational data with a small blur in time
possess no significant obstructions to data assimilation provided that the
nudging properly takes the time averaging into account. Two key ingredients in
our analysis are additional boundedness properties for the relevant interpolant
observation operators and a non-local Gronwall inequality.Comment: 44 page
Plasma Sterilization Technology for Spacecraft Applications
The application of plasma gas technology to sterilization and decontamination of spacecraft components is considered. Areas investigated include: effective sterilizing ranges of four separate gases; lethal constituents of a plasma environment; effectiveness of plasma against a diverse group of microorganisms; penetrating efficiency of plasmas for sterilization; and compatibility of spacecraft materials with plasma environments. Results demonstrated that plasma gas, specifically helium plasma, is a highly effective sterilant and is compatible with spacecraft materials
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