496 research outputs found
Quantum sealed-bid auction using a modified scheme for multiparty circular quantum key agreement
A feasible, secure and collusion-attack-free quantum sealed-bid auction
protocol is proposed using a modified scheme for multi-party circular quantum
key agreement. In the proposed protocol, the set of all () bidders is
grouped in to subsets (sub-circles) in such a way that only the initiator
(who prepares the quantum state to be distributed for a particular round of
communication and acts as the receiver in that round) is a member of all the
subsets (sub-circles) prepared for a particular round, while any other bidder
is part of only a single subset. All bidders and auctioneer initiate one
round of communication, and each of them prepares copies of a
-partite entangled state (one for each sub-circle), where
. The efficiency and security\textcolor{blue}{{} }of the
proposed protocol are critically analyzed. It is shown that the proposed
protocol is free from the collusion attacks that are possible on the existing
schemes of quantum sealed-bid auction. Further, it is observed that the
security against collusion attack increases with the increase in , but that
reduces the complexity (number of entangled qubits in each entangled state) of
the entangled states to be used and that makes the scheme scalable and
implementable with the available technologies. The additional security and
scalability is shown to arise due to the use of a circular structure in place
of a complete-graph or tree-type structure used earlier.Comment: 10 pages, 2 figure
Which verification qubits perform best for secure communication in noisy channel?
In secure quantum communication protocols, a set of single qubits prepared
using 2 or more mutually unbiased bases or a set of -qubit ()
entangled states of a particular form are usually used to form a verification
string which is subsequently used to detect traces of eavesdropping. The qubits
that form a verification string are referred to as decoy qubits, and there
exists a large set of different quantum states that can be used as decoy
qubits. In the absence of noise, any choice of decoy qubits provides equivalent
security. In this paper, we examine such equivalence for noisy environment
(e.g., in amplitude damping, phase damping, collective dephasing and collective
rotation noise channels) by comparing the decoy-qubit assisted schemes of
secure quantum communication that use single qubit states as decoy qubits with
the schemes that use entangled states as decoy qubits. Our study reveals that
the single qubit assisted scheme perform better in some noisy environments,
while some entangled qubits assisted schemes perform better in other noisy
environments. Specifically, single qubits assisted schemes perform better in
amplitude damping and phase damping noisy channels, whereas a few
Bell-state-based decoy schemes are found to perform better in the presence of
the collective noise. Thus, if the kind of noise present in a communication
channel (i.e., the characteristics of the channel) is known or measured, then
the present study can provide the best choice of decoy qubits required for
implementation of schemes of secure quantum communication through that channel.Comment: 11 pages, 4 figure
Symmetry Breaking for Rho Meson in Neutron Matter
Qualitative changes in the collective excitation spectra of the -meson
triplet in neutron matter is studied, with particular emphasis on the breaking
of the discrete symmetry. The appearance of additional
branches in the dispersion characteristics, the mass splitting among the charge
states, the splitting between longitudinal and transverse modes of the
mesons and the appearance of `island' modes (or loops) in the
time-like region are some of the features that are exposed.Comment: Plain LaTeX fil
Matter induced rho-omega mixing
A novel mechanism for mixing induced by neutron-proton
asymmetry in nuclear matter is uncovered and the variation of the mixing angle
with the extent of asymmetry is presented.Comment: Contains two postscript figures in the uuencoded fil
Cerebral metabolism in major depressive disorder:A voxel-based meta-analysis of positron emission tomography studies
BACKGROUND: Major depressive disorder (MDD) is a common mental illness with high lifetime prevalence close to 20%. Positron emission tomography (PET) studies have reported decreased prefrontal, insular and limbic cerebral glucose metabolism in depressed patients compared with healthy controls. However, the literature has not always been consistent. To evaluate current evidence from PET studies, we conducted a voxel-based meta-analysis of cerebral metabolism in MDD. METHOD: Data were collected from databases including PubMed and Web of Science, with the last report up to April 2013. Voxel-based meta-analyses were performed using the revised activation likelihood estimation (ALE) software. RESULTS: Ten whole-brain-based FDG-PET studies in MDD were included in the meta-analysis, comprising 188 MDD patients and 169 healthy controls. ALE analyses showed the brain metabolism in bilateral insula, left lentiform nucleus putamen and extra-nuclear, right caudate and cingulate gyrus were significantly decreased. However, the brain activity in right thalamus pulvinar and declive of posterior lobe, left culmen of vermis in anterior lobe were significantly increased in MDD patients. CONCLUSION: Our meta-analysis demonstrates the specific brain regions where possible dysfunctions are more consistently reported in MDD patients. Altered metabolism in insula, limbic system, basal ganglia, thalamus, and cerebellum and thus these regions are likely to play a key role in the pathophysiology of depression
Distinctive visual tasks for characterizing mild cognitive impairment and dementia using oculomotor behavior
IntroductionOne’s eye movement (in response to visual tasks) provides a unique window into the cognitive processes and higher-order cognitive functions that become adversely affected in cases with cognitive decline, such as those mild cognitive impairment (MCI) and dementia. MCI is a transitional stage between normal aging and dementia.MethodsIn the current work, we have focused on identifying visual tasks (such as horizontal and vertical Pro-saccade, Anti-saccade and Memory Guided Fixation tasks) that can differentiate individuals with MCI and dementia from their cognitively unimpaired healthy aging counterparts based on oculomotor Performance indices. In an attempt to identify the optimal combination of visual tasks that can be used to differentiate the participant groups, clustering was performed using the oculomotor Performance indices.ResultsResults of our study with a group of 60 cognitively unimpaired healthy aging individuals, a group with 60 individuals with MCI and a group with 60 individuals with dementia indicate that the horizontal and vertical Anti-saccade tasks provided the optimal combination that could differentiate individuals with MCI and dementia from their cognitively unimpaired healthy aging counterparts with clustering accuracy of ∼92% based on the saccade latencies. Also, the saccade latencies during both of these Anti-saccade tasks were found to strongly correlate with the Neuropsychological test scores.DiscussionThis suggests that the Anti-saccade tasks can hold promise in clinical practice for professionals working with individuals with MCI and dementia
Volumetric, relaxometric and diffusometric correlates of psychotic experiences in a non-clinical sample of young adults
BackgroundGrey matter (GM) abnormalities are robust features of schizophrenia and of people at ultra high-risk for psychosis. However the extent to which neuroanatomical alterations are evident in non-clinical subjects with isolated psychotic experiences is less clear.MethodsIndividuals (mean age 20 years) with (n = 123) or without (n = 125) psychotic experiences (PEs) were identified from a population-based cohort. All underwent T1-weighted structural, diffusion and quantitative T1 relaxometry MRI, to characterise GM macrostructure, microstructure and myelination respectively. Differences in quantitative GM structure were assessed using voxel-based morphometry (VBM). Binary and ordinal models of PEs were tested. Correlations between socioeconomic and other risk factors for psychosis with cortical GM measures were also computed.ResultsGM volume in the left supra-marginal gyrus was reduced in individuals with PEs relative to those with no PEs. The greater the severity of PEs, the greater the reduction in T1 relaxation rate (R1) across left temporoparietal and right pre-frontal cortices. In these regions, R1 was positively correlated with maternal education and inversely correlated with general psychopathology.ConclusionsPEs in non-clinical subjects were associated with regional reductions in grey-matter volume reduction and T1 relaxation rate. The alterations in T1 relaxation rate were also linked to the level of general psychopathology. Follow up of these subjects should clarify whether these alterations predict the later development of an ultra high-risk state or a psychotic disorder
Tensor Coupling and Vector Mesons in Dense Nuclear Matter
The effects of magnetic interaction between vector mesons and nucleons on the
propagation (mass and width) of the -meson in particular moving through
very dense nuclear matter is studied and the modifications, qualitative and
quantitative, due to the relevant collective modes (zero-sound and plasma
frequencies) of the medium discussed. It is shown that the -mesons
produced in high-energy nuclear collisions will be longitudinally polarized in
the region of sufficiently dense nuclear matter, in the presence of such an
interaction.Comment: Plain Latex file. Three figures, not appended, may be obtained on
request to [email protected]
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