388 research outputs found
Einstein-Podolsky-Rosen correlations between two uniformly accelerated oscillators
We consider the quantum correlations, i.e. the entanglement, between two
systems uniformly accelerated with identical acceleration a in opposite Rindler
quadrants which have reached thermal equilibrium with the Unruh heat bath. To
this end we study an exactly soluble model consisting of two oscillators
coupled to a massless scalar field in 1+1 dimensions. We find that for some
values of the parameters the oscillators get entangled shortly after the moment
of closest approach. Because of boost invariance there are an infinite set of
pairs of positions where the oscillators are entangled. The maximal
entanglement between the oscillators is found to be approximately 1.4
entanglement bits.Comment: 11 page
Quantum Einstein-Dirac Bianchi Universes
We study the mini--superspace quantization of spatially homogeneous (Bianchi)
cosmological universes sourced by a Dirac spinor field. The quantization of the
homogeneous spinor leads to a finite-dimensional fermionic Hilbert space and
thereby to a multi-component Wheeler-DeWitt equation whose main features are:
(i) the presence of spin-dependent Morse-type potentials, and (ii) the
appearance of a q-number squared-mass term, which is of order , and which is affected by ordering ambiguities. We give the exact
quantum solution of the Bianchi type-II system (which contains both scattering
states and bound states), and discuss the main qualitative features of the
quantum dynamics of the (classically chaotic) Bianchi type-IX system. We
compare the exact quantum dynamics of fermionic cosmological billiards to
previous works that described the spinor field as being either classical or
Grassmann-valued.Comment: 50 page
Intercenter reliability and validity of the rhesus macaque GeneChip
BACKGROUND: The non-human primate (NHP) research community has been intensely interested in obtaining whole-genome expression arrays for their work. Recently, novel approaches were used to generate the DNA sequence information for a rhesus GeneChip. To test the reliability of the rhesus GeneChip across different centers, RNA was isolated from five sources: cerebral cortex, pancreas, thymus, testis, and an immortalized fibroblast cell line. Aliquots of this RNA were sent to each of three centers: Yerkes National Primate Research Center, Oregon National Primate Research Center and the University of Nebraska Medical Center. Each center labeled the samples and hybridized them with two rhesus macaque GeneChips. In addition, rhesus samples were hybridzed with human GeneChips to compare with samples hybridized with the rhesus GeneChip. RESULTS: The results indicate that center effects were minimal and the rhesus GeneChip appears highly reliable. To test the validity of the rhesus GeneChip, five of the most differentially expressed genes among tissues identified in the reliability experiments were chosen for analysis with Quantitative PCR. For all 5 genes, the qPCR and GeneChip results were in agreement with regard to differential expression between tissues. Significantly more probesets were called present when rhesus samples were hybridized with the rhesus GeneChip than when these same samples were hybridized with a human GeneChip. CONCLUSION: The rhesus GeneChip is both a reliable and a valid tool for examining gene expression and represents a significant improvement over the use of the human GeneChip for rhesus macaque gene expression studies
About maximally localized states in quantum mechanics
We analyze the emergence of a minimal length for a large class of generalized
commutation relations, preserving commutation of the position operators and
translation invariance as well as rotation invariance (in dimension higher than
one). We show that the construction of the maximally localized states based on
squeezed states generally fails. Rather, one must resort to a constrained
variational principle.Comment: accepted for publication in PR
Hawking Radiation Without Transplanckian Frequencies
In a recent work, Unruh showed that Hawking radiation is unaffected by a
truncation of free field theory at the Planck scale. His analysis was performed
numerically and based on a hydrodynamical model. In this work, by analytical
methods, the mathematical and physical origin of Unruh's result is revealed. An
alternative truncation scheme which may be more appropriate for black hole
physics is proposed and analyzed. In both schemes the thermal Hawking radiation
remains unaffected even though transplanckian energies no longer appear. The
universality of this result is explained by working in momentum space. In that
representation, in the presence of a horizon, the d'Alembertian equation
becomes a singular first order equation. In addition, the boundary conditions
corresponding to vacuum before the black hole formed are that the in--modes
contain positive momenta only. Both properties remain valid when the spectrum
is truncated and they suffice to obtain Hawking radiation.Comment: 27 pages, latex, includs 5 postscript figures, encoded using uufile
Mimimal Length Uncertainty Principle and the Transplanckian Problem of Black Hole Physics
The minimal length uncertainty principle of Kempf, Mangano and Mann (KMM), as
derived from a mutilated quantum commutator between coordinate and momentum, is
applied to describe the modes and wave packets of Hawking particles evaporated
from a black hole. The transplanckian problem is successfully confronted in
that the Hawking particle no longer hugs the horizon at arbitrarily close
distances. Rather the mode of Schwarzschild frequency deviates from
the conventional trajectory when the coordinate is given by in units of the non local distance legislated
into the uncertainty relation. Wave packets straddle the horizon and spread out
to fill the whole non local region. The charge carried by the packet (in the
sense of the amount of "stuff" carried by the Klein--Gordon field) is not
conserved in the non--local region and rapidly decreases to zero as time
decreases. Read in the forward temporal direction, the non--local region thus
is the seat of production of the Hawking particle and its partner. The KMM
model was inspired by string theory for which the mutilated commutator has been
proposed to describe an effective theory of high momentum scattering of zero
mass modes. It is here interpreted in terms of dissipation which gives rise to
the Hawking particle into a reservoir of other modes (of as yet unknown
origin). On this basis it is conjectured that the Bekenstein--Hawking entropy
finds its origin in the fluctuations of fields extending over the non local
region.Comment: 12 pages (LateX), 1 figur
An acoustic navigation system
This report describes a system for underwater acoustic
navigation developed, and in use, at the Woods Hole Oceanographic
Institution. It includes a brief discussion of the electronic
components, operation, mathematical analysis, and available computer
programs. There is a series of supplementary Technical Memoranda
containing more information on various aspects of the system. We believe that this kind of documentation is more
flexible and better meets the needs of potential users than including
all technical details in one large volume. These are not final or
definitive reports; acoustic navigation capabilities will continue
to evolve at W.H.O.I. for some time.
Acoustic navigation provides a method of tracking a ship, and an
underwater vehicle or instrument package (‘fish’), in the deep ocean.
Acoustic devices attached to the ship and fish measure the length of
time it takes a sound pulse to travel to acoustic transponders moored
on the ocean floor. If the transponder positions and the average
speed of sound are known, the ship or fish position can be found.Prepared for the Office of Naval Research
under Contracts N00014-71-C0284; NR 293-008
N00014-70-C0205; NR 263-103 and the National
Science Foundation/International Decade of
Ocean Exploration Grant GX-36024 and the
Applied Physics Laboratory of The Johns
Hopkins University Contract 372111
Leveraging human genomic information to identify nonhuman primate sequences for expression array development
BACKGROUND: Nonhuman primates (NHPs) are essential for biomedical research due to their similarities to humans. The utility of NHPs will be greatly increased by the application of genomics-based approaches such as gene expression profiling. Sequence information from the 3' end of genes is the key resource needed to create oligonucleotide expression arrays. RESULTS: We have developed the algorithms and procedures necessary to quickly acquire sequence information from the 3' end of nonhuman primate orthologs of human genes. To accomplish this, we identified terminal exons of over 15,000 human genes by aligning mRNA sequences with genomic sequence. We found the mean length of complete last exons to be approximately 1,400 bp, significantly longer than previous estimates. We designed primers to amplify genomic DNA, which included at least 300 bp of the terminal exon. We cloned and sequenced the PCR products representing over 5,500 Macaca mulatta (rhesus monkey) orthologs of human genes. This sequence information has been used to select probes for rhesus gene expression profiling. We have also tested 10 sets of primers with genomic DNA from Macaca fascicularis (Cynomolgus monkey), Papio hamadryas (Baboon), and Chlorocebus aethiops (African green monkey, vervet). The results indicate that the primers developed for this study will be useful for acquiring sequence from the 3' end of genes for other nonhuman primate species. CONCLUSION: This study demonstrates that human genomic DNA sequence can be leveraged to obtain sequence from the 3' end of NHP orthologs and that this sequence can then be used to generate NHP oligonucleotide microarrays. Affymetrix and Agilent used sequences obtained with this approach in the design of their rhesus macaque oligonucleotide microarrays
The hidden horizon and black hole unitarity
We motivate through a detailed analysis of the Hawking radiation in a
Schwarzschild background a scheme in accordance with quantum unitarity. In this
scheme the semi-classical approximation of the unitary quantum - horizonless -
black hole S-matrix leads to the conventional description of the Hawking
radiation from a classical black hole endowed with an event horizon. Unitarity
is borne out by the detailed exclusive S-matrix amplitudes. There, the fixing
of generic out-states, in addition to the in-state, yields in asymptotic
Minkowski space-time saddle-point contributions which are dominated by
Planckian metric fluctuations when approaching the Schwarzschild radius. We
argue that these prevent the corresponding macroscopic "exclusive backgrounds"
to develop an event horizon. However, if no out-state is selected, a distinct
saddle-point geometry can be defined, in which Planckian fluctuations are
tamed. Such "inclusive background" presents an event horizon and constitutes a
coarse-grained average over the aforementioned exclusive ones. The classical
event horizon appears as a coarse-grained structure, sustaining the
thermodynamic significance of the Bekenstein-Hawking entropy. This is
reminiscent of the tentative fuzzball description of extremal black holes: the
role of microstates is played here by a complete set of out-states. Although
the computations of unitary amplitudes would require a detailed theory of
quantum gravity, the proposed scheme itself, which appeals to the metric
description of gravity only in the vicinity of stationary points, does not.Comment: 29 pages, 4 figures. Typos corrected. Two footnotes added (footnotes
3 and 5
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