2,051 research outputs found
Subnormalized states and trace-nonincreasing maps
We investigate the set of completely positive, trace-nonincreasing linear
maps acting on the set M_N of mixed quantum states of size N. Extremal point of
this set of maps are characterized and its volume with respect to the
Hilbert-Schmidt (Euclidean) measure is computed explicitly for an arbitrary N.
The spectra of partially reduced rescaled dynamical matrices associated with
trace-nonincreasing completely positive maps belong to the N-cube inscribed in
the set of subnormalized states of size N. As a by-product we derive the
measure in M_N induced by partial trace of mixed quantum states distributed
uniformly with respect to HS-measure in .Comment: LaTeX, 21 pages, 4 Encapsuled PostScript figures, 1 tabl
A Lemaitre-Tolman-Bondi cosmological wormhole
We present a new analytical solution of the Einstein field equations
describing a wormhole shell of zero thickness joining two
Lema{\i}tre-Tolman-Bondi universes, with no radial accretion. The material on
the shell satisfies the energy conditions and, at late times, the shell becomes
comoving with the dust-dominated cosmic substratum.Comment: 5 pages, latex, no figures, to appear in Phys. Rev.
Security Proof for Quantum Key Distribution Using Qudit Systems
We provide security bounds against coherent attacks for two families of
quantum key distribution protocols that use -dimensional quantum systems. In
the asymptotic regime, both the secret key rate for fixed noise and the
robustness to noise increase with . The finite-key corrections are found to
be almost insensitive to .Comment: 5 pages, 1 figure, version 3 corrects equations (9) and (11), and
slightly modifies the figure to reflect the change to equation (11
Reentrant behavior of the phase stiffness in Josephson junction arrays
The phase diagram of a 2D Josephson junction array with large substrate
resistance, described by a quantum XY model, is studied by means of Fourier
path-integral Monte Carlo. A genuine Berezinskii-Kosterlitz-Thouless transition
is found up to a threshold value g* of the quantum coupling, beyond which no
phase coherence is established. Slightly below g* the phase stiffness shows a
reentrant behavior with temperature, in connection with a low-temperature
disappearance of the superconducting phase, driven by strong nonlinear quantum
fluctuations.Comment: 4 pages, 7 figures, to appear in Phys.Rev.Let
Detection and correction of the misplacement error in THz Spectroscopy by application of singly subtractive Kramers-Kronig relations
In THz reflection spectroscopy the complex permittivity of an opaque medium
is determined on the basis of the amplitude and of the phase of the reflected
wave. There is usually a problem of phase error due to misplacement of the
reference sample. Such experimental error brings inconsistency between phase
and amplitude invoked by the causality principle. We propose a rigorous method
to solve this relevant experimental problem by using an optimization method
based upon singly subtractive Kramers-Kronig relations. The applicability of
the method is demonstrated for measured data on an n-type undoped (100) InAs
wafer in the spectral range from 0.5 up to 2.5 THz.Comment: 16 pages, 5 figure
The SOD2 C47T polymorphism influences NAFLD fibrosis severity: evidence from case-control and intra-familial allele association studies.
AIMS:
Non-alcoholic fatty liver disease (NAFLD) is a complex disease trait where genetic variations and environment interact to determine disease progression. The association of PNPLA3 with advanced disease has been consistently demonstrated but many other modifier genes remain unidentified. In NAFLD, increased fatty acid oxidation produces high levels of reactive oxygen species. Manganese-dependent superoxide dismutase (MnSOD), encoded by the SOD2 gene, plays an important role in protecting cells from oxidative stress. A common non-synonymous polymorphism in SOD2 (C47T; rs4880) is associated with decreased MnSOD mitochondrial targeting and activity making it a good candidate modifier of NAFLD severity.
METHODS:
The relevance of the SOD2 C47T polymorphism to fibrotic NAFLD was assessed by two complementary approaches: we sought preferential transmission of alleles from parents to affected children in 71 family trios and adopted a case-control approach to compare genotype frequencies in a cohort of 502 European NAFLD patients.
RESULTS:
In the family study, 55 families were informative. The T allele was transmitted on 47/76 (62%) possible occasions whereas the C allele was transmitted on only 29/76 (38%) occasions, p=0.038. In the case control study, the presence of advanced fibrosis (stage>1) increased with the number of T alleles, p=0.008 for trend. Multivariate analysis showed susceptibility to advanced fibrotic disease was determined by SOD2 genotype (OR 1.56 (95% CI 1.09-2.25), p=0.014), PNPLA3 genotype (p=0.041), type 2 diabetes mellitus (p=0.009) and histological severity of NASH (p=2.0×10(-16)).
CONCLUSIONS:
Carriage of the SOD2 C47T polymorphism is associated with more advanced fibrosis in NASH
The GP Tests of Competence assessment: which part best predicts fitness to practise decisions?
BACKGROUND:
The General Medical Council (GMC) conducts Tests of Competence (ToC) for doctors referred for Fitness to Practise (FtP) issues. GPs take a single best answer knowledge test, an Objective Structured Clinical Examination (OSCE), and a Simulated Surgery (SimSurg) assessment which is a simulated GP consultation. The aim of this study was to examine the similarities between OSCEs and SimSurg to determine whether each assessment contributed something unique to GP ToCs.
METHODS:
A mixed methods approach was used. Data were collated on 153 GPs who were required to undertake a ToC as a part of being investigated for FtP issues between February 2010 and October 2016. Using correlation analysis, we examined to what degree performance on the knowledge test, OSCE, and SimSurg related to case examiner recommendations and FtP outcomes, including the unique predictive power of these three assessments. The outcome measures were case examiner recommendations (i) not fit to practise; ii) fit to practise on a limited basis; or iii) fit to practise) as well as FtP outcomes (i) erased/removed from the register; ii) having restrictions/conditions; or iii) be in good standing).
For the qualitative component, 45 GP assessors were asked to rate whether they assess the same competencies and which assessment provides better feedback about candidates.
RESULTS:
There was significant overlap between OSCEs and SimSurg, p < 0.001. SimSurg had additional predictive power in the presence of OSCEs and the knowledge test (p = 0.030) in distinguishing doctors from different FtP categories, while OSCEs did not (p = 0.080). Both the OSCEs (p = 0.004) and SimSurg (p < 0.001) had significant negative correlations with case examiner recommendations when accounting for the effects of the other two assessments.
Inductive thematic analysis of the responses to the questionnaire showed that assessors perceived OSCEs to be better suited to target specific knowledge and skills. SimSurg was thought to produce a more global picture as the scenarios more accurately portray a patient consultation.
CONCLUSION:
While all three assessments are strong predictors of both case examiner recommendations and FtP outcomes, our findings suggest that the efficiency of GP ToCs can be improved by removing some of this overlapping content
Polymer Quantum Dynamics of the Taub Universe
Within the framework of non-standard (Weyl) representations of the canonical
commutation relations, we investigate the polymer quantization of the Taub
cosmological model. The Taub model is analyzed within the Arnowitt-Deser-Misner
reduction of its dynamics, by which a time variable arises. While the energy
variable and its conjugate momentum are treated as ordinary Heisenberg
operators, the anisotropy variable and its conjugate momentum are represented
by the polymer technique. The model is analyzed at both classical and quantum
level. As a result, classical trajectories flatten with respect to the
potential wall, and the cosmological singularity is not probabilistically
removed. In fact, the dynamics of the wave packets is characterized by an
interference phenomenon, which, however, is not able to stop the evolution
towards the classical singularity.Comment: 12 pages, 6 figures; published versio
Nonlocality tests enhanced by a third observer
We consider Bell tests involving bipartite states shared between three
parties. We show that the simple inclusion of a third part may greatly simplify
the measurement scenario (in terms of the number of measurement settings per
part) and allows the identification of previously unknown nonlocal resources.Comment: 4 pags, 4 figs. v2: fig 3 corrected. V3: refs corrected. Close to
published versio
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