4,577 research outputs found
Response of finite-time particle detectors in non-inertial frames and curved spacetime
The response of the Unruh-DeWitt type monopole detectors which were coupled
to the quantum field only for a finite proper time interval is studied for
inertial and accelerated trajectories, in the Minkowski vacuum in (3+1)
dimensions. Such a detector will respond even while on an inertial trajctory
due to the transient effects. Further the response will also depend on the
manner in which the detector is switched on and off. We consider the response
in the case of smooth as well as abrupt switching of the detector. The former
case is achieved with the aid of smooth window functions whose width, ,
determines the effective time scale for which the detector is coupled to the
field. We obtain a general formula for the response of the detector when a
window function is specified, and work out the response in detail for the case
of gaussian and exponential window functions. A detailed discussion of both and limits are given and several
subtlities in the limiting procedure are clarified. The analysis is extended
for detector responses in Schwarzschild and de-Sitter spacetimes in (1+1)
dimensions.Comment: 29 pages, normal TeX, figures appended as postscript file, IUCAA
Preprint # 23/9
Preparation of pigments for space-stable thermal control coatings Interim summary report, 1 Jun. 1968 - 30 Apr. 1969
Control of vapor phase reaction kinetics to produce pigments by homogeneous nucleatio
Spontaneous excitation of an accelerated multilevel atom in dipole coupling to the derivative of a scalar field
We study the spontaneous excitation of an accelerated multilevel atom in
dipole coupling to the derivative of a massless quantum scalar field and
separately calculate the contributions of the vacuum fluctuation and radiation
reaction to the rate of change of the mean atomic energy of the atom. It is
found that, in contrast to the case where a monopole like interaction between
the atom and the field is assumed, there appear extra corrections proportional
to the acceleration squared, in addition to corrections which can be viewed as
a result of an ambient thermal bath at the Unruh temperature, as compared with
the inertial case, and the acceleration induced correction terms show
anisotropy with the contribution from longitudinal polarization being four
times that from the transverse polarization for isotropically polarized
accelerated atoms. Our results suggest that the effect of acceleration on the
rate of change of the mean atomic energy is dependent not only on the quantum
field to which the atom is coupled, but also on the type of the interaction
even if the same quantum scalar field is considered.Comment: 11 pages, no figure
Interpolating between the Bose-Einstein and the Fermi-Dirac distributions in odd dimensions
We consider the response of a uniformly accelerated monopole detector that is
coupled to a superposition of an odd and an even power of a quantized, massless
scalar field in flat spacetime in arbitrary dimensions. We show that, when the
field is assumed to be in the Minkowski vacuum, the response of the detector is
characterized by a Bose-Einstein factor in even spacetime dimensions, whereas a
Bose-Einstein as well as a Fermi-Dirac factor appear in the detector response
when the dimension of spacetime is odd. Moreover, we find that, it is possible
to interpolate between the Bose-Einstein and the Fermi-Dirac distributions in
odd spacetime dimensions by suitably adjusting the relative strengths of the
detector's coupling to the odd and the even powers of the scalar field. We
point out that the response of the detector is always thermal and we, finally,
close by stressing the apparent nature of the appearance of the Fermi-Dirac
factor in the detector response.Comment: RevTeX, 7 page
Second large-scale Monte Carlo study for the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) represents the next generation of ground
based instruments for Very High Energy gamma-ray astronomy. It is expected to
improve on the sensitivity of current instruments by an order of magnitude and
provide energy coverage from 20 GeV to more than 200 TeV. In order to achieve
these ambitious goals Monte Carlo (MC) simulations play a crucial role, guiding
the design of CTA. Here, results of the second large-scale MC production are
reported, providing a realistic estimation of feasible array candidates for
both Northern and Sourthern Hemisphere sites performance, placing CTA
capabilities into the context of the current generation of High Energy
-ray detectors.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
Quantitative multi-objective verification for probabilistic systems
We present a verification framework for analysing multiple quantitative objectives of systems that exhibit both nondeterministic and stochastic behaviour. These systems are modelled as probabilistic automata, enriched with cost or reward structures that capture, for example, energy usage or performance metrics. Quantitative properties of these models are expressed in a specification language that incorporates probabilistic safety and liveness properties, expected total cost or reward, and supports multiple objectives of these types. We propose and implement an efficient verification framework for such properties and then present two distinct applications of it: firstly, controller synthesis subject to multiple quantitative objectives; and, secondly, quantitative compositional verification. The practical applicability of both approaches is illustrated with experimental results from several large case studies
Novel self-assembled morphologies from isotropic interactions
We present results from particle simulations with isotropic medium range
interactions in two dimensions. At low temperature novel types of aggregated
structures appear. We show that these structures can be explained by
spontaneous symmetry breaking in analytic solutions to an adaptation of the
spherical spin model. We predict the critical particle number where the
symmetry breaking occurs and show that the resulting phase diagram agrees well
with results from particle simulations.Comment: 4 pages, 4 figure
Revisiting loss-specific training of filter-based MRFs for image restoration
It is now well known that Markov random fields (MRFs) are particularly
effective for modeling image priors in low-level vision. Recent years have seen
the emergence of two main approaches for learning the parameters in MRFs: (1)
probabilistic learning using sampling-based algorithms and (2) loss-specific
training based on MAP estimate. After investigating existing training
approaches, it turns out that the performance of the loss-specific training has
been significantly underestimated in existing work. In this paper, we revisit
this approach and use techniques from bi-level optimization to solve it. We
show that we can get a substantial gain in the final performance by solving the
lower-level problem in the bi-level framework with high accuracy using our
newly proposed algorithm. As a result, our trained model is on par with highly
specialized image denoising algorithms and clearly outperforms
probabilistically trained MRF models. Our findings suggest that for the
loss-specific training scheme, solving the lower-level problem with higher
accuracy is beneficial. Our trained model comes along with the additional
advantage, that inference is extremely efficient. Our GPU-based implementation
takes less than 1s to produce state-of-the-art performance.Comment: 10 pages, 2 figures, appear at 35th German Conference, GCPR 2013,
Saarbr\"ucken, Germany, September 3-6, 2013. Proceeding
Monte Carlo Performance Studies of Candidate Sites for the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is the next-generation gamma-ray
observatory with sensitivity in the energy range from 20 GeV to beyond 300 TeV.
CTA is proposed to consist of two arrays of 40-100 imaging atmospheric
Cherenkov telescopes, with one site located in each of the Northern and
Southern Hemispheres. The evaluation process for the candidate sites for CTA is
supported by detailed Monte Carlo simulations, which take different attributes
like site altitude and geomagnetic field configuration into account. In this
contribution we present the comparison of the sensitivity and performance of
the different CTA site candidates for the measurement of very-high energy gamma
rays.Comment: In Proceedings of the 34th International Cosmic Ray Conference
(ICRC2015), The Hague, The Netherlands. All CTA contributions at
arXiv:1508.0589
- âŠ