998 research outputs found
Small-World Networks: Links with long-tailed distributions
Small-world networks (SWN), obtained by randomly adding to a regular
structure additional links (AL), are of current interest. In this article we
explore (based on physical models) a new variant of SWN, in which the
probability of realizing an AL depends on the chemical distance between the
connected sites. We assume a power-law probability distribution and study
random walkers on the network, focussing especially on their probability of
being at the origin. We connect the results to L\'evy Flights, which follow
from a mean field variant of our model.Comment: 11 pages, 4 figures, to appear in Phys.Rev.
Correlation effects in a simple model of small-world network
We analyze the effect of correlations in a simple model of small world
network by obtaining exact analytical expressions for the distribution of
shortest paths in the network. We enter correlations into a simple model with a
distinguished site, by taking the random connections to this site from an Ising
distribution. Our method shows how the transfer matrix technique can be used in
the new context of small world networks.Comment: 10 pages, 3 figure
Parity lifetime of bound states in a proximitized semiconductor nanowire
Quasiparticle excitations can compromise the performance of superconducting
devices, causing high frequency dissipation, decoherence in Josephson qubits,
and braiding errors in proposed Majorana-based topological quantum computers.
Quasiparticle dynamics have been studied in detail in metallic superconductors
but remain relatively unexplored in semiconductor-superconductor structures,
which are now being intensely pursued in the context of topological
superconductivity. To this end, we introduce a new physical system comprised of
a gate-confined semiconductor nanowire with an epitaxially grown superconductor
layer, yielding an isolated, proximitized nanowire segment. We identify
Andreev-like bound states in the semiconductor via bias spectroscopy, determine
the characteristic temperatures and magnetic fields for quasiparticle
excitations, and extract a parity lifetime (poisoning time) of the bound state
in the semiconductor exceeding 10 ms.Comment: text and supplementary information combine
Transport signatures of quasiparticle poisoning in a Majorana island
We investigate effects of quasiparticle poisoning in a Majorana island with
strong tunnel coupling to normal-metal leads. In addition to the main Coulomb
blockade diamonds, "shadow" diamonds appear, shifted by 1e in gate voltage,
consistent with transport through an excited (poisoned) state of the island.
Comparison to a simple model yields an estimate of parity lifetime for the
strongly coupled island (~ 1 {\mu}s) and sets a bound for a weakly coupled
island (> 10 {\mu}s). Fluctuations in the gate-voltage spacing of Coulomb peaks
at high field, reflecting Majorana hybridization, are enhanced by the reduced
lever arm at strong coupling. In energy units, fluctuations are consistent with
previous measurements.Comment: includes supplementary materia
Fractional Kinetics for Relaxation and Superdiffusion in Magnetic Field
We propose fractional Fokker-Planck equation for the kinetic description of
relaxation and superdiffusion processes in constant magnetic and random
electric fields. We assume that the random electric field acting on a test
charged particle is isotropic and possesses non-Gaussian Levy stable
statistics. These assumptions provide us with a straightforward possibility to
consider formation of anomalous stationary states and superdiffusion processes,
both properties are inherent to strongly non-equilibrium plasmas of solar
systems and thermonuclear devices. We solve fractional kinetic equations, study
the properties of the solution, and compare analytical results with those of
numerical simulation based on the solution of the Langevin equations with the
noise source having Levy stable probability density. We found, in particular,
that the stationary states are essentially non-Maxwellian ones and, at the
diffusion stage of relaxation, the characteristic displacement of a particle
grows superdiffusively with time and is inversely proportional to the magnetic
field.Comment: 15 pages, LaTeX, 5 figures PostScrip
Flow Properties of Tailored Net-Shape Thermoplastic Composite Preforms
A novel thermoplastic programmable preforming process, TP-P4, has been used to manufacture preforms for non-isothermal compression molding. Commingled glass and polypropylene yarns are deposited by robot onto a vacuum screen, followed by a heat-setting operation to stabilize the as-placed yarns for subsequent handling. After an optional additional preconsolidation stage, the preforms are molded by preheating and subsequent press forming in a shear edge tool. The in- and out-of-plane flow capabilities of the material were investigated, and compared to those of 40 wt% Glass Mat Thermoplastics (GMTs). Although the TP-P4 material has a fiber fraction of 60 wt%, the material could be processed to fill 77mm deep ribs with a thickness of 3mm, indicative of complex part production. The pressure requirements for out-of-plane flow were shown to depend on the fiber length and fiber alignment. Segregation phenomena were found to be less severe with TP-P4 than with GMT materia
The effect of color type on early wound healing in farmed mink (Neovison vison)
Abstract Background Individual differences of mink, including color type, are speculated to affect the course of wound healing, thereby impacting wound assessment and management on the farms, as well as the assessment of wounds in forensic cases. In this study, we examined the effect of color type on early wound healing in farmed mink. Full thickness excisional wounds (2 × 2 cm) were made on the back in 18 mink of the color types Brown, Silverblue and Blue Iris. Gross and microscopic pathology of the wounds was evaluated 2 days post-wounding together with degree of wound size reduction, presence of bacteria and blood analyses. Results Pathological examination on day 2 showed the greatest mean wound size reduction in Brown mink (11.0%) followed by Blue Iris (7.9%) and Silverblue (1.6%). Bacteria were cultured from all wounds, and predominantly Staphylococcus species were recovered in mixed or pure culture. Histopathology from day 2 wounds showed a scab overlying necrotic wound edges, which were separated from underlying vital tissue by a demarcation zone rich in polymorphonuclear leukocytes. Fibroblasts and plump endothelial cells were more numerous in the deeper tissues. Complete blood count parameters were within normal ranges in most cases, however, the mink showed mildly to markedly decreased hematocrit and six mink of the color types Silverblue and Blue Iris showed moderately elevated numbers of circulating segmented neutrophils on day 2. There was a marked increase in concentration of serum amyloid A from day 0 to day 2 in all color types. Conclusions We have described differences in early wound healing between mink of the color types Brown, Silverblue and Blue Iris by use of an experimental wound model in farmed mink. The most pronounced difference pertained to the degree of wound size reduction which was greatest in Brown mink, followed by Blue Iris and Silverblue, respectively
Metformin use and early lactate levels in critically ill patients according to chronic and acute renal impairment
Superconductivity enhanced conductance fluctuations in few layer graphene nanoribbons
We investigate the mesoscopic disorder induced rms conductance variance
in a few layer graphene nanoribbon (FGNR) contacted by two
superconducting (S) Ti/Al contacts. By sweeping the back-gate voltage, we
observe pronounced conductance fluctuations superimposed on a linear background
of the two terminal conductance G. The linear gate-voltage induced response can
be modeled by a set of inter-layer and intra-layer capacitances.
depends on temperature T and source-drain voltage .
increases with decreasing T and . When lowering , a
pronounced cross-over at a voltage corresponding to the superconducting energy
gap is observed. For |V_{sd}|\ltequiv \Delta the fluctuations are
markedly enhanced. Expressed in the conductance variance of one
graphene-superconducutor (G-S) interface, values of 0.58 e^2/h are obtained at
the base temperature of 230 mK. The conductance variance in the sub-gap region
are larger by up to a factor of 1.4-1.8 compared to the normal state. The
observed strong enhancement is due to phase coherent charge transfer caused by
Andreev reflection at the nanoribbon-superconductor interface.Comment: 15 pages, 5 figure
Rapid Processing of Net-Shape Thermoplastic Planar-Random Composite Preforms
A novel thermoplastic composite preforming and moulding process is investigated to target cost issues in textile composite processing associated with trim waste, and the limited mechanical properties of current bulk flow-moulding composites. The thermoplastic programmable powdered preforming process (TP-P4) uses commingled glass and polypropylene yarns, which are cut to length before air assisted deposition onto a vacuum screen, enabling local preform areal weight tailoring. The as-placed fibres are heat-set for improved handling before an optional preconsolidation stage. The preforms are then preheated and press formed to obtain the final part. The process stages are examined to optimize part quality and throughput versus processing parameters. A viable processing route is proposed with typical cycle times below 40s (for a plate 0.5 × 0.5m2, weighing 2kg), enabling high production capacity from one line. The mechanical performance is shown to surpass that of 40wt.% GMT and has properties equivalent to those of 40wt.% GMTex at both 20°C and 80°
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