17,793 research outputs found
A full quantal theory of one-neutron halo breakup reactions
We present a theory of one-neutron halo breakup reactions within the
framework of post-form distorted wave Born approximation wherein pure Coulomb,
pure nuclear and their interference terms are treated consistently in a single
setup. This formalism is used to study the breakup of one-neutron halo nucleus
11Be on several targets of different masses. We investigate the role played by
the pure Coulomb, pure nuclear and the Coulomb-nuclear interference terms by
calculating several reaction observables. The Coulomb-nuclear interference
terms are found to be important for more exclusive observables.Comment: 22 pages latex, 9 figures, submitted to Phy. Rev.
Entropy and temperature of black holes in a gravity's rainbow
The linear relation between the entropy and area of a black hole can be
derived from the Heisenberg principle, the energy-momentum dispersion relation
of special relativity, and general considerations about black holes. There
exist results in quantum gravity and related contexts suggesting the
modification of the usual dispersion relation and uncertainty principle. One of
these contexts is the gravity's rainbow formalism. We analyze the consequences
of such a modification for black hole thermodynamics from the perspective of
two distinct rainbow realizations built from doubly special relativity. One is
the proposal of Magueijo and Smolin and the other is based on a canonical
implementation of doubly special relativity put forward recently by the
authors. In these scenarios, we obtain modified expressions for the entropy and
temperature of black holes. We show that, for a family of doubly special
relativity theories satisfying certain properties, the temperature can vanish
in the limit of zero black hole mass. For the Magueijo and Smolin proposal,
this is only possible for some restricted class of models with bounded energy
and unbounded momentum. With the proposal of a canonical implementation, on the
other hand, the temperature may vanish for more general theories; in
particular, the momentum may also be bounded, with bounded or unbounded energy.
This opens new possibilities for the outcome of black hole evaporation in the
framework of a gravity's rainbow.Comment: 11 pages, 2 new references added, version accepted for publication in
Physical Review
Testing Convolutional Neural Networks for finding strong gravitational lenses in KiDS
Convolutional Neural Networks (ConvNets) are one of the most promising
methods for identifying strong gravitational lens candidates in survey data. We
present two ConvNet lens-finders which we have trained with a dataset composed
of real galaxies from the Kilo Degree Survey (KiDS) and simulated lensed
sources. One ConvNet is trained with single \textit{r}-band galaxy images,
hence basing the classification mostly on the morphology. While the other
ConvNet is trained on \textit{g-r-i} composite images, relying mostly on
colours and morphology. We have tested the ConvNet lens-finders on a sample of
21789 Luminous Red Galaxies (LRGs) selected from KiDS and we have analyzed and
compared the results with our previous ConvNet lens-finder on the same sample.
The new lens-finders achieve a higher accuracy and completeness in identifying
gravitational lens candidates, especially the single-band ConvNet. Our analysis
indicates that this is mainly due to improved simulations of the lensed
sources. In particular, the single-band ConvNet can select a sample of lens
candidates with purity, retrieving 3 out of 4 of the confirmed
gravitational lenses in the LRG sample. With this particular setup and limited
human intervention, it will be possible to retrieve, in future surveys such as
Euclid, a sample of lenses exceeding in size the total number of currently
known gravitational lenses.Comment: 16 pages, 10 figures. Accepted for publication in MNRA
Finding Strong Gravitational Lenses in the Kilo Degree Survey with Convolutional Neural Networks
The volume of data that will be produced by new-generation surveys requires
automatic classification methods to select and analyze sources. Indeed, this is
the case for the search for strong gravitational lenses, where the population
of the detectable lensed sources is only a very small fraction of the full
source population. We apply for the first time a morphological classification
method based on a Convolutional Neural Network (CNN) for recognizing strong
gravitational lenses in square degrees of the Kilo Degree Survey (KiDS),
one of the current-generation optical wide surveys. The CNN is currently
optimized to recognize lenses with Einstein radii arcsec, about
twice the -band seeing in KiDS. In a sample of colour-magnitude
selected Luminous Red Galaxies (LRG), of which three are known lenses, the CNN
retrieves 761 strong-lens candidates and correctly classifies two out of three
of the known lenses. The misclassified lens has an Einstein radius below the
range on which the algorithm is trained. We down-select the most reliable 56
candidates by a joint visual inspection. This final sample is presented and
discussed. A conservative estimate based on our results shows that with our
proposed method it should be possible to find massive LRG-galaxy
lenses at z\lsim 0.4 in KiDS when completed. In the most optimistic scenario
this number can grow considerably (to maximally 2400 lenses), when
widening the colour-magnitude selection and training the CNN to recognize
smaller image-separation lens systems.Comment: 24 pages, 17 figures. Published in MNRA
Dynamics of Shock Probes in Driven Diffusive Systems
We study the dynamics of shock-tracking probe particles in driven diffusive
systems and also in equilibrium systems. In a driven system, they induce a
diverging timescale that marks the crossover between a passive scalar regime at
early times and a diffusive regime at late times; a scaling form characterises
this crossover. Introduction of probes into an equilibrium system gives rise to
a system-wide density gradient, and the presence of even a single probe can be
felt across the entire system.Comment: Accepted in Journal of Statistical Mechanics: Theory and Experimen
Erosion - Deposition in Hooghly Estuary
An attempt has been made to give an overall idea of erosion-deposition at theBalari-Haldia-Gangra reach of the Hooghly estuary in India. The sediment transport relationships developed by van Rijn and AcKers- White have been tried. Calculation of bed-load transport has beenmade based on'bed material sizes, flow conditions, depth and width of the channels, during 1993-97 Comparison of the results indicates the discrepancies between calculated and observed quantum of deposition/erosion to the extent of 0.6 to 0 :8 times in case ofvan Rijn ' sequation and 0.8 to 1.8 times incase of Ackers-White's model. Results sugges that the Haldia-Balari channel is deteriorating due toaccumulation of sediment
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