3,070 research outputs found
Gauss-Codazzi thermodynamics on the timelike screen
It is a known result by Jacobson that the flux of energy-matter through a
local Rindler horizon is related with the expansion of the null generators in a
way that mirrors the first law of thermodynamics. We extend such a result to a
timelike screen of observers with finite acceleration. Since timelike curves
have more freedom than null geodesics, the construction is more involved than
Jacobson's and few geometrical constraints need to be imposed: the observers'
acceleration has to be constant in time and everywhere orthogonal to the
screen. Moreover, at any given time, the extrinsic curvature of the screen has
to be flat. The latter requirement can be weakened by asking that the extrinsic
curvature, if present at the beginning, evolves in time like on a cone and just
rescales proportionally to the expansion.Comment: 8+1 pages, final versio
Wind sensitivity studies of a non-return wind tunnel with a 216- by 432-mm (8.5- by 17.0-inches) test section, phase 2
The refinement of inlet and exit treatments were studied which would minimize the effect of external wind on the test-section flow quality of a nonreturn wind tunnel. The investigation was conducted in the Ames Research Center 40- by 80-foot Wind Tunnel which served as the wind source. Several inlets and two exits were tested at wind directions ranging from 0 to 180 degrees and at wind-to-test-section velocity ratios from zero to somewhat greater than one. For the best inlet configuration the flow quality was good, with a velocity deviation in each of the three component directions generally less. The loss in total pressure due to the inlet treatment was low: about 0.035 of the test-section dynamic pressure for the no-wind case
Wind sensitivity studies of a non-return wind tunnel, with a 216- by 432-mm (8.5- by 17.0-inch) test section, phase 1
The study to develop inlet and exit treatments which would minimize the effect of external wind on the test-section flow quality of a nonreturn wind tunnel is reported. The investigation was conducted in the Ames Research Center 40- by 80-Foot Wind Tunnel which served as the wind source. Several inlets and two exits were tested at wind directions ranging from 0 to 180 degrees and at wind-to-test-section velocity ratios between zero and one. For the best inlet configuration the flow quality was good, with a velocity deviation in each of the three directions generally less than 1/2 knot (0.26 m/sec) for wind velocities of 15 knots (7.7 m/sec) or less. The loss in total pressure due to the inlet treatment was low: about 0.03 of the test-section dynamic pressure
Sub-eV scalar dark matter through the super-renormalizable Higgs portal
The Higgs portal of the Standard Model provides the opportunity for coupling
to a very light scalar field via the super-renormalizable operator
. This allows for the existence of a very light scalar dark
matter that has coherent interaction with the Standard Model particles and yet
has its mass protected against radiative corrections. We analyze ensuing
constraints from the fifth-force measurements, along with the cosmological
requirements. We find that the detectable level of the fifth-force can be
achieved in models with low inflationary scales, and certain amount of
fine-tuning in the initial deviation of from its minimum.Comment: 6 pages, 3 figures. References added in the revised version
Phase Estimation With Interfering Bose-Condensed Atomic Clouds
We investigate how to estimate from atom-position measurements the relative
phase of two Bose-Einstein condensates released from a double-well potential.
We demonstrate that the phase estimation sensitivity via the fit of the average
density to the interference pattern is fundamentally bounded by shot noise.
This bound can be overcome by estimating the phase from the measurement of
(or higher) correlation function. The optimal estimation strategy
requires the measurement of the -th order correlation function. We also
demonstrate that a second estimation method -- based on the detection of the
center of mass of the interference pattern -- provides sub shot-noise
sensitivity. Yet, the implementation of both protocols might be experimentally
challenging.Comment: 4 pages, 2 figure
Energy transfer in nonlinear network models of proteins
We investigate how nonlinearity and topological disorder affect the energy
relaxation of local kicks in coarse-grained network models of proteins. We find
that nonlinearity promotes long-range, coherent transfer of substantial energy
to specific, functional sites, while depressing transfer to generic locations.
Remarkably, transfer can be mediated by the self-localization of discrete
breathers at distant locations from the kick, acting as efficient
energy-accumulating centers.Comment: 4 pages, 3 figure
Slow energy relaxation of macromolecules and nano-clusters in solution
Many systems in the realm of nanophysics from both the living and inorganic
world display slow relaxation kinetics of energy fluctuations. In this paper we
propose a general explanation for such phenomenon, based on the effects of
interactions with the solvent. Within a simple harmonic model of the system
fluctuations, we demonstrate that the inhomogeneity of coupling to the solvent
of the bulk and surface atoms suffices to generate a complex spectrum of decay
rates. We show for Myoglobin and for a metal nano-cluster that the result is a
complex, non-exponential relaxation dynamics.Comment: 5 pages, 3 figure
Aharonov-Bohm oscillations of a tunable quantum ring
With an atomic force microscope a ring geometry with self-aligned in-plane
gates was directly written into a GaAs/AlGaAs-heterostructure. Transport
measurements in the open regime show only one transmitting mode and
Aharonov-Bohm oscillations with more than 50% modulation are observed in the
conductance. The tuning via in-plane gates allows to study the Aharonov-Bohm
effect in the whole range from the open ring to the Coulomb-blockade regime.Comment: 3 pages, 3 figure
Equilibrium cluster phases and low-density arrested disordered states: The role of short-range attraction and long-range repulsion
We study a model in which particles interact with short-ranged attractive and
long-ranged repulsive interactions, in an attempt to model the equilibrium
cluster phase recently discovered in sterically stabilized colloidal systems in
the presence of depletion interactions. At low packing fraction particles form
stable equilibrium clusters which act as building blocks of a cluster fluid. We
study the possibility that cluster fluids generate a low-density disordered
arrested phase, a gel, via a glass transition driven by the repulsive
interaction. In this model the gel formation is formally described with the
same physics of the glass formation.Comment: RevTeX4, 4 pages, 4 eps figure
Collective excitations and supersolid behavior of bosonic atoms inside two crossed optical cavities
We discuss the nature of symmetry breaking and the associated collective excitations for a system of bosons coupled to the electromagnetic field of two optical cavities. For the specific configuration realized in a recent experiment at ETH [1, 2], we show that, in absence of direct intercavity scattering and for parameters chosen such that the atoms couple symmetrically to both cavities, the system possesses an approximate U(1) symmetry which holds asymptotically for vanishing cavity field intensity. It corresponds to the invariance with respect to redistributing the total intensity between the two cavities. The spontaneous breaking of this symmetry gives rise to a broken continuous translation-invariance for the atoms, creating a supersolid-like order in the presence of a Bose–Einstein condensate. In particular, we show that atom-mediated scattering between the two cavities, which favors the state with equal light intensities and reduces the symmetry to , gives rise to a finite value of the effective Goldstone mass. For strong atom driving, this low energy mode is clearly separated from an effective Higgs excitation associated with changes of the total intensity I. In addition, we compute the spectral distribution of the cavity light field and show that both the Higgs and Goldstone mode acquire a finite lifetime due to Landau damping at non-zero temperature
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