4,811 research outputs found
Positioning and clock synchronization through entanglement
A method is proposed to employ entangled and squeezed light for determining
the position of a party and for synchronizing distant clocks. An accuracy gain
over analogous protocols that employ classical resources is demonstrated and a
quantum-cryptographic positioning application is given, which allows only
trusted parties to learn the position of whatever must be localized. The
presence of a lossy channel and imperfect photodetection is considered. The
advantages in using partially entangled states is discussed.Comment: Revised version. 9 pages, 6 figure
Conditional probabilities in quantum theory, and the tunneling time controversy
It is argued that there is a sensible way to define conditional probabilities
in quantum mechanics, assuming only Bayes's theorem and standard quantum
theory. These probabilities are equivalent to the ``weak measurement''
predictions due to Aharonov {\it et al.}, and hence describe the outcomes of
real measurements made on subensembles. In particular, this approach is used to
address the question of the history of a particle which has tunnelled across a
barrier. A {\it gedankenexperiment} is presented to demonstrate the physically
testable implications of the results of these calculations, along with graphs
of the time-evolution of the conditional probability distribution for a
tunneling particle and for one undergoing allowed transmission. Numerical
results are also presented for the effects of loss in a bandgap medium on
transmission and on reflection, as a function of the position of the lossy
region; such loss should provide a feasible, though indirect, test of the
present conclusions. It is argued that the effects of loss on the pulse {\it
delay time} are related to the imaginary value of the momentum of a tunneling
particle, and it is suggested that this might help explain a small discrepancy
in an earlier experiment.Comment: 11 pages, latex, 4 postscript figures separate (one w/ 3 parts
Heavy Ion Physics at the LHC with the ATLAS Detector
The ATLAS detector at CERN will provide a high-resolution
longitudinally-segmented calorimeter and precision tracking for the upcoming
study of heavy ion collisions at the LHC (sqrt(s_NN)=5520 GeV). The calorimeter
covers |eta|<5 with both electromagnetic and hadronic sections, while the inner
detector spectrometer covers |eta|<2.5. ATLAS will study a full range of
observables necessary to characterize the hot and dense matter formed at the
LHC. Global measurements (particle multiplicities, collective flow) will
provide access into its thermodynamic and hydrodynamic properties. Measuring
complete jets out to 100's of GeV will allow detailed studies of energy loss
and its effect on jets. Quarkonia will provide a handle on deconfinement
mechanisms. ATLAS will also study the structure of the nucleon and nucleus
using forward physics probes and ultraperipheral collisions, both enabled by
segmented Zero Degree Calorimeters.Comment: 9 pages, 8 figures, submitted to the Proceedings of Quark Matter
2006, Shanghai, China, November 14-20, 200
System-size dependence
The final state in The final state in heavy-ion collisions has a higher
degree of strangeness saturation than the one produced in collisions between
elementary particles like p-p or p-. A systematic analysis of this
phenomenon is made for C-C, Si-Si and Pb-Pb collisions at the CERN SPS collider
and for collisions at RHIC and at AGS energies. Strangeness saturation
is shown to increase smoothly with the number of participants at AGS, CERN and
RHIC energies.Comment: 5 pages, 5 figures, presented at SQM2003 conferenc
Simple models of the chemical field around swimming plankton
Background. Cervical cancer is the fourth most common cancer in women, and we recently reported human leukocyte antigen (HLA) alleles showing strong associations with cervical neoplasia risk and protection. HLA ligands are recognized by killer immunoglobulin-like receptors (KIRs) expressed on a range of immune cell subsets, governing their proinflammatory activity. We hypothesized that the inheritance of particular HLA-KIR combinations would increase cervical neoplasia risk. Methods. Here, we used HLA and KIR dosages imputed from single-nucleotide polymorphism genotype data from 2143 cervical neoplasia cases and 13 858 healthy controls of European decent. Results. The following 4 novel HLA alleles were identified in association with cervical neoplasia, owing to their linkage disequilibrium with known cervical neoplasia-associated HLA-DRB1 alleles: HLA-DRB3*9901 (odds ratio [OR], 1.24; P = 2.49 Ă 10â9), HLA-DRB5*0101 (OR, 1.29; P = 2.26 Ă 10â8), HLA-DRB5*9901 (OR, 0.77; P = 1.90 Ă 10â9), and HLA-DRB3*0301 (OR, 0.63; P = 4.06 Ă 10â5). We also found that homozygosity of HLA-C1 group alleles is a protective factor for human papillomavirus type 16 (HPV16)-related cervical neoplasia (C1/C1; OR, 0.79; P = .005). This protective association was restricted to carriers of either KIR2DL2 (OR, 0.67; P = .00045) or KIR2DS2 (OR, 0.69; P = .0006). Conclusions. Our findings suggest that HLA-C1 group alleles play a role in protecting against HPV16-related cervical neoplasia, mainly through a KIR-mediated mechanism
Transverse Fresnel-Fizeau drag effects in strongly dispersive media
A light beam normally incident upon an uniformly moving dielectric medium is
in general subject to bendings due to a transverse Fresnel-Fizeau light drag
effect. In conventional dielectrics, the magnitude of this bending effect is
very small and hard to detect. Yet, it can be dramatically enhanced in strongly
dispersive media where slow group velocities in the m/s range have been
recently observed taking advantage of the electromagnetically induced
transparency (EIT) effect. In addition to the usual downstream drag that takes
place for positive group velocities, we predict a significant anomalous
upstream drag to occur for small and negative group velocities. Furthermore,
for sufficiently fast speeds of the medium, higher order dispersion terms are
found to play an important role and to be responsible for peculiar effects such
as light propagation along curved paths and the restoration of the spatial
coherence of an incident noisy beam. The physics underlying this new class of
slow-light effects is thoroughly discussed
How much time does a tunneling particle spend in the barrier region?
The question in the title may be answered by considering the outcome of a
``weak measurement'' in the sense of Aharonov et al. Various properties of the
resulting time are discussed, including its close relation to the Larmor times.
It is a universal description of a broad class of measurement interactions, and
its physical implications are unambiguous.Comment: 5 pages; no figure
Strictly and asymptotically scale-invariant probabilistic models of correlated binary random variables having {\em q}--Gaussians as limiting distributions
In order to physically enlighten the relationship between {\it
--independence} and {\it scale-invariance}, we introduce three types of
asymptotically scale-invariant probabilistic models with binary random
variables, namely (i) a family, characterized by an index ,
unifying the Leibnitz triangle () and the case of independent variables
(); (ii) two slightly different discretizations of
--Gaussians; (iii) a special family, characterized by the parameter ,
which generalizes the usual case of independent variables (recovered for
). Models (i) and (iii) are in fact strictly scale-invariant. For
models (i), we analytically show that the probability
distribution is a --Gaussian with . Models (ii) approach
--Gaussians by construction, and we numerically show that they do so with
asymptotic scale-invariance. Models (iii), like two other strictly
scale-invariant models recently discussed by Hilhorst and Schehr (2007),
approach instead limiting distributions which are {\it not} --Gaussians. The
scenario which emerges is that asymptotic (or even strict) scale-invariance is
not sufficient but it might be necessary for having strict (or asymptotic)
--independence, which, in turn, mandates --Gaussian attractors.Comment: The present version is accepted for publication in JSTA
Search for corannulene (C20H10) in the Red Rectangle
Polycyclic Aromatic Hydrocarbons (PAHs) are widely accepted as the carriers of the Aromatic Infrared Bands (AIBs), but an unambiguous identification of any specific interstellar PAH is still missing. For polar PAHs, pure rotational transitions can be used as spectral fingerprints for identification. Combining dedicated experiments, detailed simulations and observations, we explore d the mm wavelength domain to search for specific rotational transitions of corannulene (C20H10). We performed high-resolution spectroscopic measurements and a simulation of the emission spectrum of ultraviolet-excited C20H10 in the environment of the Red Rectangle (RR), calculating its synthetic rotational spectrum. Based on these results, we conducted a first observational campaign at the IRAM 30-m telescope towards this source to search for several high-J rotational transitions of C20H10. The laboratory detection of the J = 112 â 111 transition of corannulene showed that no centrifugal splitting is present up to this line. Observations with the IRAM 30-m telescope towards the RR do not show any corannulene emission at any of the observed frequencies, down to a rms noise level of Tmb= 8 mK for the J =135 â 134 transition at 137.615 GHz. Comparing the noise level with the synthetic spectrum, we are able to estimate an upper limit to the fraction of carbon locked in corannulene of about 1.0 Ă 10â5 relative to the total abundance of carbon in PAHs. The sensitivity achieved in this work shows that radio spectroscopy can be a powerful tool to search for polar PAHs. We compare this upper limit with models for the PAH size distribution, emphasizing that small PAHs are much less abundant than predicted. We show that this cannot be explained by destruction but is more likely related to the chemistry of their formation in the environment of the R
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