1,845 research outputs found
Generalized Second Law of Black Hole Thermodynamics and Quantum Information Theory
We propose a quantum version of a gedanken experiment which supports the
generalized second law of black hole thermodynamics. A quantum measurement of
particles in the region outside of the event horizon decreases the entropy of
the outside matter due to the entanglement of the inside and outside particle
states. This decrease is compensated, however, by the increase in the detector
entropy. If the detector is conditionally dropped into the black hole depending
on the experimental outcome, the decrease of the matter entropy is more than
compensated by the increase of the black hole entropy via the increase of the
black hole mass which is ultimately attributed to the work done by the
measurement.Comment: 5 pages, RevTex, submitted to PR
Using a Dynamic Model to Simulate the Heuristic Evaluation of Usability
Among usability inspection methods, heuristic evaluation, or expert
evaluation, is considered the most used and well-known usability evaluation
method. The number of evaluators and their expertise are essential aspects that
affect the quality of the evaluation, the cost that its application generates, and
the time that it is necessary to spend. This paper presents a dynamic simulation
model to analyze how different configurations of evaluator team have an effect
upon the results of the heuristic evaluation method. One of the main advantages
of using a dynamic simulation model is the possibility of trying out different
decisions before carrying them out, and change them during the simulation of
the evaluation process.Ministerio de Educación y Ciencia QSimTest TIN2007-67843-C06 03Ministerio de Educación y Ciencia TIN2007-67843-C06-0
Lorentz invariance of effective strings
Starting from a Poincar\'e invariant field theory of a real scalar field with
interactions governed by a double-well potential in 2+1 dimensions, the Lorentz
representation induced on the collective coordinates describing low-energy
excitations about an effective string background is derived. In this
representation, Lorentz transformations are given in terms of an infinite
series, in powers of derivatives along the worldsheet. Transformations that act
on the direction transverse to the string worldsheet involve a universal
dimension term. As a consequence, Lorentz invariance holds in this theory
of long effective strings due to cancellations in the action between irrelevant
terms and the dimension two term that describes free massless scalar fields in
two dimensions. (in plain tex, no macropackages necessary)Comment: 9 page
On the Number of Unbordered Factors
We illustrate a general technique for enumerating factors of k-automatic
sequences by proving a conjecture on the number f(n) of unbordered factors of
the Thue-Morse sequence. We show that f(n) = 4 and that f(n) = n
infinitely often. We also give examples of automatic sequences having exactly 2
unbordered factors of every length
Monopole clusters, Z(2) vortices and confinement in SU(2)
We extend our previous study of magnetic monopole currents in the maximally
Abelian gauge [hep-lat/9712003] to larger lattices at small lattice spacings
(20^4 at beta = 2.5 and 32^4 at beta = 2.5115). We confirm that at these weak
couplings there continues to be one monopole cluster that is very much longer
than the rest and that the string tension, K, is entirely due to it. The
remaining clusters are compact objects whose population as a function of radius
follows a power law that deviates from the scale invariant form, but much too
weakly to suggest a link with the analytically calculable size distribution of
small instantons. We also search for traces of Z(2) vortices in the Abelian
projected fields; either as closed loops of `magnetic' flux or through
appropriate correlations amongst the monopoles. We find, by direct calculation,
that there is no confining condensate of such flux loops. We also find, through
the calculation of doubly charged Wilson loops within the monopole fields, that
there is no suppression of the q=2 effective string tension out to at distances
of at least r ~ 1.6/sqrt{K}, suggesting that if there are any vortices they are
not encoded in the monopole fields.Comment: 26 pages of LaTeX and PostScript figure
Understanding Experimental Economics
Experiments have become a well-established methodological tool in economics. e development of experi- mental economics and the diversi cation of experimental methods have equipped economists with new and powerful means of scienti c investigation. eir worth is readily demonstrated in the exciting and promising results they have produced, and will continue to produce. Against the background of this success story, our selective discussion critically highlights four important aspects of experimentation in economics. We concen- trate on the role and importance of material incentives, potentially confounding experimenter demand e ects and strategies to minimise these, the no deception rule as well as the issue of external validity.
Performance comparison of 40 Gb/s ULH transmissions using CSRZ-ASK or CSRZ-DPSK modulation formats on Ultra Wave™ fiber
In this work we present extensive comparisons between numerical modelling and experimental measurements of the transmission performance of either CSRZ-ASK or CSRZ-DPSK modulation formats for 40-Gb/s WDM ULH systems on UltraWave™ fiber spans with all-Raman amplification. We numerically optimised the amplification and the signal format parameters for both CSRZ-DPSK and CSRZ-ASK formats. Numerical and experimental results show that, in a properly optimized transmission link, the DPSK format permits to double the transmission distance (for a given BER level) with respect to the ASK format, while keeping a substantial OSNR margin (on ASK modulation) after the propagation in the fiber line. Our comparison between numerical and experimental results permits to identify what is the most suitable BER estimator in assessing the transmission performance when using the DPSK format. © 2007 Optical Society of America
Dynamical measure and field theory models free of the cosmological constant problem
Summary of abstract Field theory models including gauge theories with SSB are
presented where the energy density of the true vacuum state (TVS) is zero
without fine tuning. The above models are constructed in the gravitational
theory where a measure of integration \Phi in the action is not necessarily
\sqrt{-g} but it is determined dynamically through additional degrees of
freedom. The ratio \Phi/\sqrt{-g} is a scalar field which can be solved in
terms of the matter degrees of freedom due to the existence of a constraint. We
study a few explicit field theory models where it is possible to combine the
solution of the cosmological constant problem with: 1) possibility for
inflationary scenario for the early universe; 2) spontaneously broken gauge
unified theories (including fermions). The models are free from the well known
problem of the usual scalar-tensor theories in what is concerned with the
classical GR tests. The only difference of the field equations in the Einstein
frame from the canonical equations of the selfconsistent system of Einstein's
gravity and matter fields, is the appearance of the effective scalar field
potential which vanishes in TVS without fine tuning.Comment: Extended version of the contribution to the fourth Alexander
Friedmann International Seminar on Gravitation and Cosmology; accepted for
publication in Phys. Rev. D; 31 page
Black Hole Evaporation in the Presence of a Short Distance Cutoff
A derivation of the Hawking effect is given which avoids reference to field
modes above some cutoff frequency in the free-fall frame
of the black hole. To avoid reference to arbitrarily high frequencies, it is
necessary to impose a boundary condition on the quantum field in a timelike
region near the horizon, rather than on a (spacelike) Cauchy surface either
outside the horizon or at early times before the horizon forms. Due to the
nature of the horizon as an infinite redshift surface, the correct boundary
condition at late times outside the horizon cannot be deduced, within the
confines of a theory that applies only below the cutoff, from initial
conditions prior to the formation of the hole. A boundary condition is
formulated which leads to the Hawking effect in a cutoff theory. It is argued
that it is possible the boundary condition is {\it not} satisfied, so that the
spectrum of black hole radiation may be significantly different from that
predicted by Hawking, even without the back-reaction near the horizon becoming
of order unity relative to the curvature.Comment: 35 pages, plain LaTeX, UMDGR93-32, NSF-ITP-93-2
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