4,876 research outputs found
Existence Criterion of Genuine Tripartite Entanglement
In this paper, an intuitive mathematical formulation is provided to
generalize the residual entanglement for tripartite systems of qubits [Phys.
Rev. A 61, 052306 (2000)] to the tripartite systems in higher dimension. The
spirit lies in the tensor treatment of tripartite pure states [Phys. Rev. A 72,
022333 (2005)]. A distinct characteristic of the present generalization is that
the formulation for higher dimensional systems is invariant under permutation
of the subsystems, hence is employed as a criterion to test the existence of
genuine tripartite entanglement. Furthermore, the formulation for pure states
can be conveniently extended to the case of mixed states by utilizing the
Kronecker product approximate technique. As applications, we give the analytic
approximation of the criterion for weakly mixed tripartite quantum states and
consider the existence of genuine tripartite entanglement of some weakly mixed
states.Comment: 6 pages, 2 figure
Quantum Computing with Continuous-Variable Clusters
Continuous-variable cluster states offer a potentially promising method of
implementing a quantum computer. This paper extends and further refines
theoretical foundations and protocols for experimental implementation. We give
a cluster-state implementation of the cubic phase gate through photon
detection, which, together with homodyne detection, facilitates universal
quantum computation. In addition, we characterize the offline squeezed
resources required to generate an arbitrary graph state through passive linear
optics. Most significantly, we prove that there are universal states for which
the offline squeezing per mode does not increase with the size of the cluster.
Simple representations of continuous-variable graph states are introduced to
analyze graph state transformations under measurement and the existence of
universal continuous-variable resource states.Comment: 17 pages, 5 figure
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Sex differences in the influence of body mass index on anatomical architecture of brain networks.
Background/objectivesThe brain has a central role in regulating ingestive behavior in obesity. Analogous to addiction behaviors, an imbalance in the processing of rewarding and salient stimuli results in maladaptive eating behaviors that override homeostatic needs. We performed network analysis based on graph theory to examine the association between body mass index (BMI) and network measures of integrity, information flow and global communication (centrality) in reward, salience and sensorimotor regions and to identify sex-related differences in these parameters.Subjects/methodsStructural and diffusion tensor imaging were obtained in a sample of 124 individuals (61 males and 63 females). Graph theory was applied to calculate anatomical network properties (centrality) for regions of the reward, salience and sensorimotor networks. General linear models with linear contrasts were performed to test for BMI and sex-related differences in measures of centrality, while controlling for age.ResultsIn both males and females, individuals with high BMI (obese and overweight) had greater anatomical centrality (greater connectivity) of reward (putamen) and salience (anterior insula) network regions. Sex differences were observed both in individuals with normal and elevated BMI. In individuals with high BMI, females compared to males showed greater centrality in reward (amygdala, hippocampus and nucleus accumbens) and salience (anterior mid-cingulate cortex) regions, while males compared to females had greater centrality in reward (putamen) and sensorimotor (posterior insula) regions.ConclusionsIn individuals with increased BMI, reward, salience and sensorimotor network regions are susceptible to topological restructuring in a sex-related manner. These findings highlight the influence of these regions on integrative processing of food-related stimuli and increased ingestive behavior in obesity, or in the influence of hedonic ingestion on brain topological restructuring. The observed sex differences emphasize the importance of considering sex differences in obesity pathophysiology
Two pressure-induced structural phase transitions in TiOCl
We studied the crystal structure of TiOCl up to pressures of =25~GPa at
room temperature by x-ray powder diffraction measurements. Two pressure-induced
structural phase transitions are observed: At 15~GPa emerges
an 22 superstructure with -axis unique monoclinic
symmetry (space group P2/). At 22~GPa all lattice
parameters of the monoclinic phase show a pronounced anomaly. A fraction of the
sample persists in the ambient orthorhombic phase (space group ) over the
whole pressure range.Comment: 5 pages, 5 figures; accepted for publication in Phys. Rev.
Psychosis and relapse in bipolar disorder are related to GRM3, DAOA, and GRIN2B genotype
Objective:Â Â Key Words: Manic-Depressive Psychosis; Glutamate; GRIN2B receptor; mGluR3; G72 protein; HumanDysfunction in glutamate signalling is thought to play a role in the pathophysiology of bipolar disorder (BD). There is evidence of associations between single nucleotide polymorphisms (SNPs) in GRM3, GRIN2B, and DAOA genes and the diagnosis of BD. In this pilot study, we investigated the frequency of SNP variants in these 3 genes within South African population groups, and assessed interactions between genes and phenotypes of BD disease severity. Method: Multiplex SNaPshotTM PCR was used to genotype 191 case and 188 control samples. Cases comprised of 191 individuals in a South African cohort of mixed ancestry and Caucasians, with BD Type 1. Phenotypes of BD disease severity were: age of onset, number of illness episodes, number of hospitalisations for depression or mania and history of psychotic symptoms. Results: There were no significant difference in SNP allele frequencies between cases and controls. In the case-only analysis, the GRM3 rs6465084 heterozygote was associated with a 4-fold increased risk of lifetime history of psychotic symptoms, and the specific variants within the gene pair, DAOA and GRIN2B, had a significant interaction with the number of hospitalisations for mania, with lowest admission rates associated with both pairs of ancestral alleles. Conclusion: In BD, variations in glutamatergic genes may influence phenotypes related to the severity of illness. Speculatively, newly derived genes associated with various evolutionary advantages, may also increase the risk for more severe BD. These preliminary findings deserve validation in a larger cohort
Selecting a single orientation for millimeter sized graphene sheets
We have used Low Energy Electron Microscopy (LEEM) and Photo Emission
Electron Microscopy (PEEM) to study and improve the quality of graphene films
grown on Ir(111) using chemical vapor deposition (CVD). CVD at elevated
temperature already yields graphene sheets that are uniform and of monatomic
thickness. Besides domains that are aligned with respect to the substrate,
other rotational variants grow. Cyclic growth exploiting the faster growth and
etch rates of the rotational variants, yields films that are 99 % composed of
aligned domains. Precovering the substrate with a high density of graphene
nuclei prior to CVD yields pure films of aligned domains extending over
millimeters. Such films can be used to prepare cluster-graphene hybrid
materials for catalysis or nanomagnetism and can potentially be combined with
lift-off techniques to yield high-quality, graphene based electronic devices
Pressure-induced metallization and structural phase transition of the Mott-Hubbard insulator TiOBr
We investigated the pressure-dependent optical response of the
low-dimensional Mott-Hubbard insulator TiOBr by transmittance and reflectance
measurements in the infrared and visible frequency range. A suppression of the
transmittance above a critical pressure and a concomitant increase of the
reflectance are observed, suggesting a pressure-induced metallization of TiOBr.
The metallic phase of TiOBr at high pressure is confirmed by the presence of
additional excitations extending down to the far-infrared range. The
pressure-induced metallization coincides with a structural phase transition,
according to the results of x-ray powder diffraction experiments under
pressure.Comment: 4 pages, 3 figure
Dynamical approach to the Casimir effect
Casimir forces can appear between intrusions placed in different media driven
by several fluctuation mechanisms, either in equilibrium or out of it. Herein,
we develop a general formalism to obtain such forces from the dynamical
equations of the fluctuating medium, the statistical properties of the driving
noise, and the boundary conditions of the intrusions (which simulate the
interaction between the intrusions and the medium). As a result, an explicit
formula for the Casimir force over the intrusions is derived. This formalism
contains the thermal Casimir effect as a particular limit and generalizes the
study of the Casimir effect to such systems through their dynamical equations,
with no appeal to their Hamiltonian, if any exists. In particular, we study the
Casimir force between two infinite parallel plates with Dirichlet or Neumann
boundary conditions, immersed in several media with finite correlation lengths
(reaction--diffusion system, liquid crystals, and two coupled fields with
non-Hermitian evolution equations). The driving Gaussian noises have vanishing
or finite spatial or temporal correlation lengths; in the first case,
equilibrium is reobtained and finite correlations produce nonequilibrium
dynamics. The results obtained show that, generally, nonequilibrium dynamics
leads to Casimir forces, whereas Casimir forces are obtained in equilibrium
dynamics if the stress tensor is anisotropic.Comment: 12 pages, 1 figur
Concepts for increasing gentamicin release from handmade bone cement beads
Background and purpose Commercial gentamicin-loaded bone cement beads (Septopal) constitute an effective delivery system for local antibiotic therapy. These beads are not available in all parts of the world, and are too expensive for frequent use in others. Thus, orthopedic surgeons worldwide make antibiotic-loaded beads themselves. However, these beads are usually not as effective as the commercial beads because of inadequate release kinetics. Our purpose was to develop a simple, cheap, and effective formulation to prepare gentamicin-loaded beads with release properties and antibacterial efficacy similar to the commercially ones. Methods Acrylic beads were prepared with variable monomer content: 100% (500 μL/g polymer), 75%, and 50% to increase gentamicin release through creation of a less dense polymer matrix. Using the optimal monomer content, different gel-forming polymeric fillers were added to enhance the permeation of fluids into the beads. Polyvinylpyrrolidone (PVP) 17 was selected as a suitable filler; its concentration was varied and the antibiotic release and antibacterial efficacy of these beads were compared with the corresponding properties of the commercial ones. Results Gentamicin release rate and the extent of release from beads prepared with 50% monomer increased when the PVP17 content was increased. Beads with 15 w/w% PVP17 released 87% of their antibiotic content. This is substantially more than the gentamicin release from Septopal beads (59%). Acrylic beads with 15 w/w% PVP17 reduced bacterial growth by up to 93%, which is similar to the antibacterial properties of the commercial ones. Interpretation A simple, cheap, and effective formulation and preparation process has been described for hand-made gentamicin-releasing acrylic beads, with better release kinetics and with antibacterial efficacy similar to that of the commercial ones
H_2 Emission From Disks Around Herbig Ae and T Tauri Stars
We present the initial results of a deep ISO-SWS survey
for the low J pure rotational emission lines of H2
toward a number of Herbig Ae and T Tauri stars.
The objects are selected to be as isolated as possible
from molecular clouds, with a spectral energy distribution
characteristic of a circumstellar disk. For most
of them the presence of a disk has been established
directly by millimeter interferometry. The S (1) line is
detected in most sources with a peak flux of 0.3-1 Jy.
The S(0) line is definitely seen in 2 objects: GG Tau
and HD 163296. The observations suggest the presence
of "warm" gas at T_(kin) ≈ 100 K with a mass of a
few % of the total gas+ dust mass, derived assuming
a gas-to-dust ratio of 100:1. The S(1) peak flux does
not show a strong correlation with spectral type of
the central star or continuum flux at 1.3 millimeter.
Possible origins for the warm gas seen in H_2 are discussed,
and comparisons with model calculations are
made
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