2,817 research outputs found
Generalized quantum measurements and local realism
The structure of a local hidden variable model for experiments involving
sequences of measurements rigorously is analyzed. Constraints imposed by local
realism on the conditional probabilities of the outcomes of such measurement
schemes are explicitly derived. The violation of local realism in the case of
``hidden nonlocality'' is illustrated by an operational example.Comment: Revtex, 12 pages; Some modifications of introduction has been made; a
note stating that part of results had been obtained earlier by other authors,
has been added; one postscript figure available at request from
[email protected]
Purification of Noisy Entanglement and Faithful Teleportation via Noisy Channels
Two separated observers, by applying local operations to a supply of
not-too-impure entangled states ({\em e.g.} singlets shared through a noisy
channel), can prepare a smaller number of entangled pairs of arbitrarily high
purity ({\em e.g.} near-perfect singlets). These can then be used to faithfully
teleport unknown quantum states from one observer to the other, thereby
achieving faithful transfrom one observer to the other, thereby achieving
faithful transmission of quantum information through a noisy channel. We give
upper and lower bounds on the yield of pure singlets ()
distillable from mixed states , showing if
\bra{\Psi^-}M\ket{\Psi^-}>\half.Comment: 4 pages (revtex) plus 1 figure (postscript). See also
http://vesta.physics.ucla.edu/~smolin/ . Replaced to correct interchanged
and near top of column 2, page
Flood risk assessment due to cyclone-induced dike breaching in coastal areas of Bangladesh
Bangladesh, one of the most disaster-prone countries in the world, has a
dynamic delta with 123 polders protected by earthen dikes. Cyclone-induced
storm surges cause severe damage to these polders by overtopping and
breaching the dikes. A total of 19 major tropical storms have hit the coast in the last
50 years, and the storm frequency is likely to increase due to climate change.
The present paper presents an investigation of the inundation pattern in a
protected area behind dikes due to floods caused by storm surges and
identifies possible critical locations of dike breaches. Polder 48 in the
coastal region, also known as Kuakata, was selected as the study area. A
HEC-RAS 1-D–2-D hydrodynamic model was developed to simulate inundation of the polder under different scenarios. Scenarios were developed by considering
tidal variations, the angle of the cyclone at landfall, possible dike breach
locations and sea level rise due to climate change according to the Fifth
Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC).
A storm surge for a cyclone event with a 1-in-25-year return period was considered
for all the scenarios. The primary objective of this research was to present
a methodology for identifying the critical location of dike breaching,
generating a flood risk map (FRM) and a probabilistic flood map (PFM) for the
breaching of dikes during a cyclone. The critical location of the dike breach
among the chosen possible locations was identified by comparing the
inundation extent and damage due to flooding corresponding to the developed
scenarios. A FRM corresponding to the breaching in the
critical location was developed, which indicated that settlements adjacent to
the canals in the polders were exposed to higher risk. A PFM was developed using the simulation results corresponding to the
developed scenarios, which was used to recommend the need of appropriate land
use zoning to minimize the vulnerability to flooding. The developed
hydrodynamic model can be used to forecast inundation, to identify critical
locations of the dike requiring maintenance and to study the effect of
climate change on flood inundation in the study area.
The frequency and intensity of the cyclones around the world are likely to
increase due to climate change, which will require resource-intensive
improvement of existing or new protection structures for the deltas. The identification and prioritization of the maintenance of critical locations of dike
breaching can potentially prevent a disaster. The use of non-structural tools such as
land use zoning with the help of flood risk maps and probabilistic flood
maps has the potential to reduce risk and damage. The method presented in
this research can potentially be utilized for deltas around the world to
reduce vulnerability and flood risk due to dike breaching caused by cyclone-induced storm surge.</p
Sufficient conditions for three-particle entanglement and their tests in recent experiments
We point out a loophole problem in some recent experimental claims to produce
three-particle entanglement. The problem consists in the question whether
mixtures of two-particle entangled states might suffice to explain the
experimental data.
In an attempt to close this loophole, we review two sufficient conditions
that distinguish between N-particle states in which all N particles are
entangled to each other and states in which only M particles are entangled
(with M<N). It is shown that three recent experiments to obtain three-particle
entangled states (Bouwmeester et al., Pan et al., and Rauschenbeutel et al.) do
not meet these conditions. We conclude that the question whether these
experiments provide confirmation of three-particle entanglement remains
unresolved. We also propose modifications of the experiments that would make
such confirmation feasible.Comment: 16 page
On the Optimization of Broad-Band Photometry for Galaxy Evolution Studies
We have derived the uncertainties to be expected in the derivation of galaxy
physical properties (star formation history, age, metallicity, reddening) when
comparing broad-band photometry to the predictions of evolutionary synthesis
models. We have obtained synthetic colors for a large sample (9000) of
artificial galaxies assuming different star formation histories, ages,
metallicities, reddening values, and redshifts. The colors derived have been
perturbed by adopting different observing errors, and compared back to the
evolutionary synthesis models grouped in different sets. The comparison has
been performed using a combination of Monte Carlo simulations, a Maximum
Likelihood Estimator and Principal Component Analysis. After comparing the
input and derived output values we have been able to compute the uncertainties
and covariant degeneracies between the galaxy physical properties as function
of (1) the set of observables available, (2) the observing errors, and (3) the
galaxy properties themselves. In this work we have considered different sets of
observables, some of them including the standard Johnson/Cousins (UBVRI) and
Sloan Digital Sky Survey (SDSS) bands in the optical, the 2 Micron All Sky
Survey (2MASS) bands in the near-infrared, and the Galaxy Evolution Explorer
(GALEX) bands in the UV, at three different redshifts, z=0.0, 0.7, and 1.4.
This study is intended to represent a basic tool for the design of future
projects on galaxy evolution, allowing an estimate of the optimal band-pass
combinations and signal-to-noise ratios required for a given scientific
objective.Comment: 20 pages, 9 postscript figures, 3 tables, accepted for publication in
A
Motional effects on the efficiency of excitation transfer
Energy transfer plays a vital role in many natural and technological
processes. In this work, we study the effects of mechanical motion on the
excitation transfer through a chain of interacting molecules with application
to biological scenarios of transfer processes. Our investigation demonstrates
that, for various types of mechanical oscillations, the transfer efficiency is
significantly enhanced over that of comparable static configurations. This
enhancement is a genuine quantum signature, and requires the collaborative
interplay between the quantum-coherent evolution of the excitation and the
mechanical motion of the molecules; it has no analogue in the classical
incoherent energy transfer. This effect may not only occur naturally, but it
could be exploited in artificially designed systems to optimize transport
processes. As an application, we discuss a simple and hence robust control
technique.Comment: 25 pages, 11 figures; completely revised; version accepted for
publicatio
Diffusion Limited Aggregation with Power-Law Pinning
Using stochastic conformal mapping techniques we study the patterns emerging
from Laplacian growth with a power-law decaying threshold for growth
(where is the radius of the particle cluster). For
the growth pattern is in the same universality class as diffusion
limited aggregation (DLA) growth, while for the resulting patterns
have a lower fractal dimension than a DLA cluster due to the
enhancement of growth at the hot tips of the developing pattern. Our results
indicate that a pinning transition occurs at , significantly
smaller than might be expected from the lower bound
of multifractal spectrum of DLA. This limiting case shows that the most
singular tips in the pruned cluster now correspond to those expected for a
purely one-dimensional line. Using multifractal analysis, analytic expressions
are established for both close to the breakdown of DLA universality
class, i.e., , and close to the pinning transition, i.e.,
.Comment: 5 pages, e figures, submitted to Phys. Rev.
Melodic Intonation Therapy for aphasia: A multi-level meta-analysis of randomized controlled trials and individual participant data
Melodic Intonation Therapy (MIT) is a prominent rehabilitation program for individuals with post-stroke aphasia. Our meta-analysis investigated the efficacy of MIT while considering quality of outcomes, experimental design, influence of spontaneous recovery, MIT protocol variant, and level of generalization. Extensive literature search identified 606 studies in major databases and trial registers; of those, 22 studies-overall 129 participants-met all eligibility criteria. Multi-level mixed- and random-effects models served to separately meta-analyze randomized controlled trial (RCT) and non-RCT data. RCT evidence on validated outcomes revealed a small-to-moderate standardized effect in noncommunicative language expression for MIT-with substantial uncertainty. Unvalidated outcomes attenuated MIT's effect size compared to validated tests. MIT's effect size was 5.7 times larger for non-RCT data compared to RCT data (g̅case report = 2.01 vs. g̅RCT = 0.35 for validated Non-Communicative Language Expression measures). Effect size for non-RCT data decreased with number of months post-stroke, suggesting confound through spontaneous recovery. Deviation from the original MIT protocol did not systematically alter benefit from treatment. Progress on validated tests arose mainly from gains in repetition tasks rather than other domains of verbal expression, such as everyday communication ability. Our results confirm the promising role of MIT in improving trained and untrained performance on unvalidated outcomes, alongside validated repetition tasks, and highlight possible limitations in promoting everyday communication ability
Counterfactual entanglement and nonlocal correlations in separable states
It is shown that the outcomes of measurements on systems in separable mixed
states can be partitioned, via subsequent measurements on a disentangled
extraneous system, into subensembles that display the statistics of entangled
states. This motivates the introduction of the concept of "counterfactual"
entanglement, which can be associated with all separable mixed states including
those that are factorable. This type of entanglement gives rise to a new kind
of postselection-induced Bell inequality violation. The significance of
counterfactual entanglement, and its physical implications, are assessed
- …