2,263 research outputs found
The Coherence of Primordial Fluctuations Produced During Inflation
The behaviour of quantum metric perturbations produced during inflation is
considered at the stage after the second Hubble radius crossing. It is shown
that the classical correlation between amplitude and momentum of a perturbation
mode, previously shown to emerge in the course of an effective
quantum-to-classical transition, is maintained for a sufficiently long time,
and we present the explicit form in which it takes place using the Wigner
function. We further show with a simple diffraction experiment that quantum
interference, non-expressible in terms of a classical stochastic description of
the perturbations, is essentially suppressed. Rescattering of the perturbations
leads to a comparatively slow decay of this correlation and to a complete
stochastization of the system.Comment: LaTeX (7 pages
Quantum cosmology with big-brake singularity
We investigate a cosmological model with a big-brake singularity in the
future: while the first time derivative of the scale factor goes to zero, its
second time derivative tends to minus infinity. Although we also discuss the
classical version of the model in some detail, our main interest lies in its
quantization. We formulate the Wheeler-DeWitt equation and derive solutions
describing wave packets. We show that all such solutions vanish in the region
of the classical singularity, a behaviour which we interpret as singularity
avoidance. We then discuss the same situation in loop quantum cosmology. While
this leads to a different factor ordering, the singularity is there avoided,
too.Comment: 24 pages, 7 figures, figures improved, references added, conceptual
clarifications include
Hawking radiation from the quantum Lemaitre-Tolman-Bondi model
In an earlier paper, we obtained exact solutions of the Wheeler-DeWitt
equation for the Lemaitre-Tolman-Bondi (LTB) model of gravitational collapse,
employing a lattice regularization. In this paper, we derive Hawking radiation
in non-marginally bound models from our exact solutions. We show that a
non-vanishing energy function does not spoil the (approximate) Planck spectrum
near the horizon. We can also reliably compute corrections to the Bogoliubov
coefficient because our solutions are exact. The corrections are obtained by
going beyond the near horizon region and are shown to introduce additional
greybody factors, which modify the black body spectrum of radiation from the
black hole.Comment: 14 page
Wavelet transform based new interpolation technique for satellite image resolution enhancement
In this research paper, we propose a new interpolation technique based on the Stationary Wavelet Transform (SWT) and iterative back projection (IBP) for satellite images. Firstly the low resolution image is interpolated by using bicubic interpolation and then decomposed into different subband images by SWT. Each subband is decimated to four lower low resolution images. The four low resolution images are interpolated and registered by using bicubic interpolation and IBP respectively. Inverse SWT (ISWT) is used to generate a Super-resolved output image. The proposed interpolation technique has been tested on several remote sensing images. The quantitative PSNR and SSIM results as well as the visual results show the superiority of the proposed interpolation technique over the other interpolation and image resolution enhancement techniques. For one of the images the PSNR of the proposed method has achieved 3.84dB, 2.11dB, and 1.1dB more improvements than bicubic interpolation, Irani and Peleg technique, and Wavlet Zero Padding technique respectively
Geologic Hazards in Kentucky
Geologic data were derived from the Kentucky Geological Survey-U.S. Geological Survey areal geologic mapping project. Nearly 190 geologists mapped the geology of Kentucky from 1960 to 1978. KGS geologists converted the resulting 707 geologic quadrangle maps into digital format at part of the STATEMAP component of the National Cooperative Geologic Mapping Program of the United States Geological Survey
On rationality of nonnegative matrix factorization
Nonnegative matrix factorization (NMF) is the problem of decomposing a given nonnegative n × m matrix M into a product of a nonnegative n × d matrix W and a nonnegative d × m matrix H. NMF has a wide variety of applications, including bioinformatics, chemometrics, communication complexity, machine learning, polyhedral combinatorics, among many others. A longstanding open question, posed by Cohen and Rothblum in 1993, is whether every rational matrix M has an NMF with minimal d whose factors W and H are also rational. We answer this question negatively, by exhibiting a matrix M for which W and H require irrational entries.
As an application of this result, we show that state minimization of labeled Markov chains can require the introduction of irrational transition probabilities.
We complement these irrationality results with an NP- complete version of NMF for which rational numbers suffice
Recommended from our members
Multiple roles for FGF-3 during cranial nerve development in the chicken
FGF-3 has been implicated in the development of the hindbrain and otocyst in vertebrate embryos. Since the chicken embryo offers a favourable system in which to study the development of these structures, we have isolated and characterised cDNAs for chicken Fgf-3 and determined its pattern of expression in chick embryos from stage 3 (primitive streak) to stage 25 (early organogenesis). Within the developing cranial neural tube, Fgf-3 exhibits dynamic spatial and temporal expression. During extension of the head process, RNA is detected in the midline of the developing neural plate. In neurulating embryos, transcripts are observed initially in rhombomeres 4 and 5 of the hindbrain and later, in rhombomere 6. During hindbrain development, expression is lost from these rhombomeres, but becomes restricted to rhombomere boundaries, providing an intracellular marker which distinguishes a population of cells within boundary regions. Fgf-3 expression is elevated in ventral and medial boundary regions and is greatly reduced in dorsal parts. Studies of regenerating rhombomere boundaries show that Fgf-3 expression is induced in reforming boundaries when even-numbered rhombomere tissue is grafted next to odd, but not when like is juxtaposed to like. Fgf-3 disappears from boundary regions just prior to the loss of the morphological boundaries suggesting a boundary-associated function. Other sites of expression have also been identified. At early stages of development Fgf-3 is expressed in the epiblast and mesendoderm of the primitive streak, in mesoderm lateral to the streak and in Hensen's node. In older embryos transcripts are detected in the endoderm of the pharyngeal pouches, the ectoderm of the second and third pharyngeal arches and the stomodeum. Expression was also detected in the segmental plate and in the posterior half of the three most-recently generated somites
Exact positivity of the Wigner and P-functions of a Markovian open system
We discuss the case of a Markovian master equation for an open system, as it
is frequently found from environmental decoherence. We prove two theorems for
the evolution of the quantum state. The first one states that for a generic
initial state the corresponding Wigner function becomes strictly positive after
a finite time has elapsed. The second one states that also the P-function
becomes exactly positive after a decoherence time of the same order. Therefore
the density matrix becomes exactly decomposable into a mixture of Gaussian
pointer states.Comment: 11 pages, references added, typo corrected, to appear in J. Phys.
Generalized Geologic Map for Land-Use Planning: Carroll County, Kentucky
This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock
Generalized Geologic Map for Land-Use Planning: Kenton County, Kentucky
This map is not intended to be used for selecting individual sites. Its purpose is to inform land-use planners, government officials, and the public in a general way about geologic bedrock conditions that affect the selection of sites for various purposes. The properties of thick soils may supercede those of the underlying bedrock and should be considered on a site-to-site basis. At any site, it is important to understand the characteristics of both the soils and the underlying rock
- …