4,477 research outputs found
Attitude determination of the spin-stabilized Project Scanner spacecraft
Attitude determination of spin-stabilized spacecraft using star mapping techniqu
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
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
Identifying Nearby UHECR Accelerators using UHE (and VHE) Photons
Ultra-high energy photons (UHE, E > 10^19 eV) are inevitably produced during
the propagation of 10^20 eV protons in extragalactic space. Their short
interaction lengths (<20 Mpc) at these energies, combined with the impressive
sensitivity of the Pierre Auger Observatory detector to these particles, makes
them an ideal probe of nearby ultra-high-energy cosmic ray (UHECR) sources. We
here discuss the particular case of photons from a single nearby (within 30
Mpc) source in light of the possibility that such an object might be
responsible for several of the UHECR events published by the Auger
collaboration. We demonstrate that the photon signal accompanying a cluster of
a few > 6x10^19 eV UHECRs from such a source should be detectable by Auger in
the near future. The detection of these photons would also be a signature of a
light composition of the UHECRs from the nearby source.Comment: 4 pages, 2 figures, accepted for publication in PR
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
ShapeCodes: Self-Supervised Feature Learning by Lifting Views to Viewgrids
We introduce an unsupervised feature learning approach that embeds 3D shape
information into a single-view image representation. The main idea is a
self-supervised training objective that, given only a single 2D image, requires
all unseen views of the object to be predictable from learned features. We
implement this idea as an encoder-decoder convolutional neural network. The
network maps an input image of an unknown category and unknown viewpoint to a
latent space, from which a deconvolutional decoder can best "lift" the image to
its complete viewgrid showing the object from all viewing angles. Our
class-agnostic training procedure encourages the representation to capture
fundamental shape primitives and semantic regularities in a data-driven
manner---without manual semantic labels. Our results on two widely-used shape
datasets show 1) our approach successfully learns to perform "mental rotation"
even for objects unseen during training, and 2) the learned latent space is a
powerful representation for object recognition, outperforming several existing
unsupervised feature learning methods.Comment: To appear at ECCV 201
Evidence for shape coexistence in Mo
A angular correlation experiment has been performed to
investigate the low-energy states of the nucleus Mo. The new data,
including spin assignments, multipole mixing ratios and lifetimes reveal
evidence for shape coexistence and mixing in Mo, arising from a proton
intruder configuration. This result is reproduced by a theoretical calculation
within the proton-neutron interacting boson model with configuration mixing,
based on microscopic energy density functional theory. The microscopic
calculation indicates the importance of the proton particle-hole excitation
across the Z=40 sub-shell closure and the subsequent mixing between spherical
vibrational and the -soft equilibrium shapes in Mo.Comment: 6 pages, 5 figures, 3 tables; published in Phys. Rev.
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