218 research outputs found
Symptom-severity-related brain connectivity alterations in functional movement disorders
Background Functional movement disorders, a common cause of neurological disabilities, can occur with heterogeneous motor manifestations including functional weakness. However, the underlying mechanisms related to brain function and connectivity are unknown. Objective To identify brain connectivity alterations related to functional weakness we assessed network centrality changes in a group of patients with heterogeneous motor manifestations using task-free functional MRI in combination with different network centrality approaches. Methods Task-free functional MRI was performed in 48 patients with heterogeneous motor manifestations including 28 patients showing functional weakness and 65 age- and sex-matched healthy controls. Functional connectivity differences were assessed using different network centrality approaches, i.e. global correlation, eigenvector centrality, and intrinsic connectivity. Motor symptom severity was assessed using The Simplified Functional Movement Disorders Rating Scale and correlated with network centrality. Results Comparing patients with and without functional weakness showed significant network centrality differences in the left temporoparietal junction and precuneus. Patients with functional weakness showed increased centrality in the same anatomical regions when comparing functional weakness with healthy controls. Moreover, in the same regions, patients with functional weakness showed a positive correlation between motor symptom severity and network centrality. This correlation was shown to be specific to functional weakness with an interaction analysis, confirming a significant difference between patients with and without functional weakness. Conclusions We identified the temporoparietal junction and precuneus as key regions involved in brain connectivity alterations related to functional weakness. We propose that both regions may be promising targets for phenotype-specific non-invasive brain stimulation
Quantum cryptography with finite resources: unconditional security bound for discrete-variable protocols with one-way post-processing
We derive a bound for the security of QKD with finite resources under one-way
post-processing, based on a definition of security that is composable and has
an operational meaning. While our proof relies on the assumption of collective
attacks, unconditional security follows immediately for standard protocols like
Bennett-Brassard 1984 and six-states. For single-qubit implementations of such
protocols, we find that the secret key rate becomes positive when at least
N\sim 10^5 signals are exchanged and processed. For any other discrete-variable
protocol, unconditional security can be obtained using the exponential de
Finetti theorem, but the additional overhead leads to very pessimistic
estimates
Glass transition of an epoxy resin induced by temperature, pressure and chemical conversion: a configurational entropy rationale
A comparative study is reported on the dynamics of a glass-forming epoxy
resin when the glass transition is approached through different paths: cooling,
compression, and polymerization. In particular, the influence of temperature,
pressure and chemical conversion on the dynamics has been investigated by
dielectric spectroscopy. Deep similarities are found in dynamic properties. A
unified reading of our experimental results for the structural relaxation time
is given in the framework of the Adam-Gibbs theory. The quantitative agreement
with the experimental data is remarkable, joined with physical values of the
fitting parameters. In particular, the fitting function of the isothermal
tau(P) data gives a well reasonable prediction for the molar thermal expansion
of the neat system, and the fitting function of the isobaric-isothermal tau(C)
data under step- polymerization conforms to the prediction of diverging tau at
complete conversion of the system.Comment: 16 pages, 8 figures, from the talk given at the 4th International
Discussion Meeting on Relaxations in Complex Systems (IDMRCS), Hersonissos,
Helaklion, Crete (Greece), 17-23 June 200
Neocuproine/nitrato complexes of Ni(II). Neutral and cationic species including salts with TCNQ: Preparation, chemical and spectroscopic properties and comparative structural chemistry
The cationic complex [Ni(neoc)2(NO3)]+ with NO3− (1), TCNQ− (3), or (TCNQ-TCNQ)2− (4) as counterions, and the neutral complex [Ni(neoc)([NO3]−-κ1O)([NO3]−-κ2O,O´)(H2O)] (2) can be obtained from different reactions involving Ni(II), neoc, NO3− and TCNQ. The molecular and extended crystal structure of compound 2, which displays two different coordination modes for NO3−, are compared to those of the analogous Mn, Fe and Co compounds, revealing a correlation between the coordination geometry of the nominally monodentate nitrato ligand and the covalent radius of the central metal atom. Despite the differences in molecular geometry, the extended structures of the Ni (2) and Mn compounds are similar to each other but different from those of the Fe and Co complexes, which are similar to each other. Complex 1 was further used in the preparation of a new heterospin compound [Ni(neoc)2(NO3)](TCNQ) (3), having an ionic structure with the same complex cation present in 1, accompanied by centrosymmetric anion-radicals (ARs) TCNQ•−. Through a different preparation process, complex 4, with the formula [Ni(neoc)2(NO3)]2(TCNQ-TCNQ), containing the same complex cation as in complexes 1 and 3, but now with the centrosymmetric σ-dimerized dianion (TCNQ-TCNQ)2− has been obtained. The influence of NO3−, TCNQ•− and TCNQ-TCNQ2− anions on the crystal structure of the cation [Ni(neoc)2(NO3)]+ in the compounds has been studied. All of the complexes reported here have supramolecular structures governed by hydrogen bonding systems, adding to their stability
Passive-scheme analysis for solving untrusted source problem in quantum key distribution
As a practical method, the passive scheme is useful to monitor the photon
statistics of an untrusted source in a "Plug & Play" quantum key distribution
(QKD) system. In a passive scheme, three kinds of monitor mode can be adopted:
average photon number (APN) monitor, photon number analyzer (PNA) and photon
number distribution (PND) monitor. In this paper, the security analysis is
rigorously given for APN monitor, while for PNA, the analysis including
statistical fluctuation and random noise, is addressed with a confidence level.
The results show that the PNA can achieve better performance than the APN
monitor and can asymptotically approach the theoretical limit of the PND
monitor. Also, the passive scheme with the PNA works efficiently when the
signal-to-noise ratio () is not too low and so is highly applicable to
solve the untrusted source problem in the QKD system.Comment: 8 pages, 6 figures, published versio
Homogeneous geodesics of non-unimodular Lorentzian Lie groups and naturally reductive Lorentzian spaces in dimension three
We determine, for all three-dimensional non-unimodular Lie groups equipped
with a Lorentzian metric, the set of homogeneous geodesics through a point.
Together with the results of [C] and [CM2], this leads to the full
classification of three-dimensional Lorentzian g.o. spaces and naturally
reductive spaces
Abnormal activity in the precuneus during time perception in Parkinson’s disease: An fMRI study
Background Parkinson's disease (PD) patients are deficient in time estimation. This deficit improves after dopamine (DA) treatment and it has been associated with decreased internal timekeeper speed, disruption of executive function and memory retrieval dysfunction. Methodology/Findings The aim of the present study was to explore the neurophysiologic correlates of this deficit. We performed functional magnetic resonance imaging on twelve PD patients while they were performing a time reproduction task (TRT). The TRT consisted of an encoding phase (during which visual stimuli of durations from 5s to 16.6s, varied at 8 levels were presented) and a reproduction phase (during which interval durations were reproduced by a button pressing). Patients were scanned twice, once while on their DA medication (ON condition) and once after medication withdrawal (OFF condition). Differences in Blood-Oxygenation-Level-Dependent (BOLD) signal in ON and OFF conditions were evaluated. The time course of activation in the brain areas with different BOLD signal was plotted. There were no significant differences in the behavioral results, but a trend toward overestimation of intervals ≤11.9s and underestimation of intervals ≥14.1s in the OFF condition (p<0.088). During the reproduction phase, higher activation in the precuneus was found in the ON condition (p<0.05 corrected). Time course was plotted separately for long (≥14.1s) and short (≤11.9s) intervals. Results showed that there was a significant difference only in long intervals, when activity gradually decreased in the OFF, but remained stable in the ON condition. This difference in precuneus activation was not found during random button presses in a control task. Conclusions/Significance Our results show that differences in precuneus activation during retrieval of a remembered duration may underlie some aspects of time perception deficit in PD patients. We suggest that DA medication may allow compensatory activation in the precuneus, which results in a more accurate retrieval of remembered interval duration
Passive decoy state quantum key distribution with practical light sources
Decoy states have been proven to be a very useful method for significantly
enhancing the performance of quantum key distribution systems with practical
light sources. While active modulation of the intensity of the laser pulses is
an effective way of preparing decoy states in principle, in practice passive
preparation might be desirable in some scenarios. Typical passive schemes
involve parametric down-conversion. More recently, it has been shown that phase
randomized weak coherent pulses (WCP) can also be used for the same purpose [M.
Curty {\it et al.}, Opt. Lett. {\bf 34}, 3238 (2009).] This proposal requires
only linear optics together with a simple threshold photon detector, which
shows the practical feasibility of the method. Most importantly, the resulting
secret key rate is comparable to the one delivered by an active decoy state
setup with an infinite number of decoy settings. In this paper we extend these
results, now showing specifically the analysis for other practical scenarios
with different light sources and photo-detectors. In particular, we consider
sources emitting thermal states, phase randomized WCP, and strong coherent
light in combination with several types of photo-detectors, like, for instance,
threshold photon detectors, photon number resolving detectors, and classical
photo-detectors. Our analysis includes as well the effect that detection
inefficiencies and noise in the form of dark counts shown by current threshold
detectors might have on the final secret ket rate. Moreover, we provide
estimations on the effects that statistical fluctuations due to a finite data
size can have in practical implementations.Comment: 17 pages, 14 figure
Antiferrodistortive phase transition in EuTiO3
X-ray diffraction, dynamical mechanical analysis and infrared reflectivity
studies revealed an antiferrodistortive phase transition in EuTiO3 ceramics.
Near 300K the perovskite structure changes from cubic Pm-3m to tetragonal
I4/mcm due to antiphase tilting of oxygen octahedra along the c axis (a0a0c- in
Glazer notation). The phase transition is analogous to SrTiO3. However, some
ceramics as well as single crystals of EuTiO3 show different infrared
reflectivity spectra bringing evidence of a different crystal structure. In
such samples electron diffraction revealed an incommensurate tetragonal
structure with modulation wavevector q ~ 0.38 a*. Extra phonons in samples with
modulated structure are activated in the IR spectra due to folding of the
Brillouin zone. We propose that defects like Eu3+ and oxygen vacancies strongly
influence the temperature of the phase transition to antiferrodistortive phase
as well as the tendency to incommensurate modulation in EuTiO3.Comment: PRB, in pres
Continuous Variable Quantum Cryptography using Two-Way Quantum Communication
Quantum cryptography has been recently extended to continuous variable
systems, e.g., the bosonic modes of the electromagnetic field. In particular,
several cryptographic protocols have been proposed and experimentally
implemented using bosonic modes with Gaussian statistics. Such protocols have
shown the possibility of reaching very high secret-key rates, even in the
presence of strong losses in the quantum communication channel. Despite this
robustness to loss, their security can be affected by more general attacks
where extra Gaussian noise is introduced by the eavesdropper. In this general
scenario we show a "hardware solution" for enhancing the security thresholds of
these protocols. This is possible by extending them to a two-way quantum
communication where subsequent uses of the quantum channel are suitably
combined. In the resulting two-way schemes, one of the honest parties assists
the secret encoding of the other with the chance of a non-trivial superadditive
enhancement of the security thresholds. Such results enable the extension of
quantum cryptography to more complex quantum communications.Comment: 12 pages, 7 figures, REVTe
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