3,428 research outputs found
Black holes, quantum information, and unitary evolution
The unitary crisis for black holes indicates an apparent need to modify local
quantum field theory. This paper explores the idea that quantum mechanics and
in particular unitarity are fundamental principles, but at the price of
familiar locality. Thus, one should seek to parameterize unitary evolution,
extending the field theory description of black holes, such that their quantum
information is transferred to the external state. This discussion is set in a
broader framework of unitary evolution acting on Hilbert spaces comprising
subsystems. Here, various constraints can be placed on the dynamics, based on
quantum information-theoretic and other general physical considerations, and
one can seek to describe dynamics with "minimal" departure from field theory.
While usual spacetime locality may not be a precise concept in quantum gravity,
approximate locality seems an important ingredient in physics. In such a
Hilbert space approach an apparently "coarser" form of localization can be
described in terms of tensor decompositions of the Hilbert space of the
complete system. This suggests a general framework in which to seek a
consistent description of quantum gravity, and approximate emergence of
spacetime. Other possible aspects of such a framework -- in particular
symmetries -- are briefly discussed.Comment: 39 pages, 5 figures. v2: refs added, very minor clarifications v3:
few small changes to agree with published version v4: corrected sign in eq.
3.3
Panels illuminated by edge-lighted lens technique
Electroluminescent lamps used to edge-light a specially ground lens provide nonglare, reduced eye strain panel illumination. There is no noticeable falloff in brightness along the lens edge. Light intensity diminishes toward the lens center. A slight halo, observed along the lens edge, has no detrimental effect
Vehicles Recognition Using Fuzzy Descriptors of Image Segments
In this paper a vision-based vehicles recognition method is presented.
Proposed method uses fuzzy description of image segments for automatic
recognition of vehicles recorded in image data. The description takes into
account selected geometrical properties and shape coefficients determined for
segments of reference image (vehicle model). The proposed method was
implemented using reasoning system with fuzzy rules. A vehicles recognition
algorithm was developed based on the fuzzy rules describing shape and
arrangement of the image segments that correspond to visible parts of a
vehicle. An extension of the algorithm with set of fuzzy rules defined for
different reference images (and various vehicle shapes) enables vehicles
classification in traffic scenes. The devised method is suitable for
application in video sensors for road traffic control and surveillance systems.Comment: The final publication is available at http://www.springerlink.co
Derivation of phenomenological expressions for transition matrix elements for electron-phonon scattering
In the literature on electron-phonon scatterings very often a
phenomenological expression for the transition matrix element is used which was
derived in the textbooks of Ashcroft/Mermin and of Czycholl. There are various
steps in the derivation of this expression. In the textbooks in part different
arguments have been used in these steps, but the final result is the same. In
the present paper again slightly different arguments are used which motivate
the procedure in a more intuitive way. Furthermore, we generalize the
phenomenological expression to describe the dependence of the matrix elements
on the spin state of the initial and final electron state
Quantum information transfer and models for black hole mechanics
General features of information transfer between quantum subsystems, via
unitary evolution, are investigated, with applications to the problem of
information transfer from a black hole to its surroundings. A particularly
direct form of quantum information transfer is "subspace transfer," which can
be characterized by saturation of a subadditivity inequality. We also describe
more general unitary quantum information transfer, and categorize different
models for black hole evolution. Evolution that only creates paired excitations
inside/outside the black hole is shown not to extract information, but
information-transferring models exist both in the "saturating" and
"non-saturating" category. The former more closely capture thermodynamic
behavior; the latter generically have enhanced energy flux, beyond that of
Hawking.Comment: 31 pages, harvmac. v2: nomenclature change, minor added explanation.
v3: small corrections/rewordings; improved figure; version to match
publication in PR
Nickel hydrogen low Earth orbit test program update and status
The current status of nickel-hydrogen (NiH2) testing ongong at NWSC, Crane In, and The Aerospace Corporation, El Segundo, Ca are described. The objective of this testing is to develop a database for NiH2 battery use in Low Earth Orbit (LEO) and support applications in Medium Altitude Orbit (MAO). Individual pressure vessel-type cells are being tested. A minimum of 200 cells (3.5 in diameter and 4.5 in diameter) are included in the test, from four U.S. vendors. As of this date (Nov. 18, 1986) approximately 60 cells have completed preliminary testing (acceptance, characterization, and environmental testing) and have gone into life cycling
Causality and dispersion relations and the role of the S-matrix in the ongoing research
The adaptation of the Kramers-Kronig dispersion relations to the causal
localization structure of QFT led to an important project in particle physics,
the only one with a successful closure. The same cannot be said about the
subsequent attempts to formulate particle physics as a pure S-matrix project.
The feasibility of a pure S-matrix approach are critically analyzed and their
serious shortcomings are highlighted. Whereas the conceptual/mathematical
demands of renormalized perturbation theory are modest and misunderstandings
could easily be corrected, the correct understanding about the origin of the
crossing property requires the use of the mathematical theory of modular
localization and its relation to the thermal KMS condition. These new concepts,
which combine localization, vacuum polarization and thermal properties under
the roof of modular theory, will be explained and their potential use in a new
constructive (nonperturbative) approach to QFT will be indicated. The S-matrix
still plays a predominant role but, different from Heisenberg's and
Mandelstam's proposals, the new project is not a pure S-matrix approach. The
S-matrix plays a new role as a "relative modular invariant"..Comment: 47 pages expansion of arguments and addition of references,
corrections of misprints and bad formulation
Wightman Functions' Behaviour on the Event Horizon of an Extremal Reissner-Nordstr\"om Black Hole
A weaker Haag, Narnhofer and Stein prescription as well as a weaker Hessling
Quantum Equivalence Principle for the behaviour of thermal Wightman functions
on an event horizon are analysed in the case of an extremal
Reissner-Nordstr\"{o}m black hole in the limit of a large mass. In order to
avoid the degeneracy of the metric in the stationary coordinates on the
horizon, a method is introduced which employs the invariant length of geodesics
which pass the horizon. First the method is checked for a massless scalar field
on the event horizon of the Rindler wedge, extending the original procedure of
Haag, Narnhofer and Stein onto the {\em whole horizon} and recovering the same
results found by Hessling. Afterwards the HNS prescription and Hessling's
prescription for a massless scalar field are analysed on the whole horizon of
an extremal Reissner-Nordstr\"{o}m black hole in the limit of a large mass. It
is proved that the weak form of the HNS prescription is satisfyed for all the
finite values of the temperature of the KMS states, i.e., this principle does
not determine any Hawking temperature. It is found that the
Reissner-Nordstr\"{o}m vacuum, i.e., does satisfy the weak HNS
prescription and it is the only state which satisfies weak Hessling's
prescription, too. Finally, it is suggested that all the previously obtained
results should be valid dropping the requirements of a massless field and of a
large mass black hole.Comment: 27 pages, standard LaTex, no figures, final version containing the
results following from Hessling's principle as they appeared in the other
paper gr-qc/9510016, minor changes in the text and in references, it will
appear on Class. Quant. Gra
Probability distributions of smeared quantum stress tensors
We obtain in closed form the probability distribution for individual
measurements of the stress-energy tensor of two-dimensional conformal field
theory in the vacuum state, smeared in time against a Gaussian test function.
The result is a shifted Gamma distribution with the shift given by the
previously known optimal quantum inequality bound. For small values of the
central charge it is overwhelmingly likely that individual measurements of the
sampled energy density in the vacuum give negative results. For the case of a
single massless scalar field, the probability of finding a negative value is
84%. We also report on computations for four-dimensional massless scalar fields
showing that the probability distribution of the smeared square field is also a
shifted Gamma distribution, but that the distribution of the energy density is
not.Comment: 9 pages, 1 figure. Minor edits implemente
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