1,626 research outputs found
Small-World Rouse Networks as models of cross-linked polymers
We use the recently introduced small-world networks (SWN) to model
cross-linked polymers, as an extension of the linear Rouse-chain. We study the
SWN-dynamics under the influence of external forces. Our focus is on the
structurally and thermally averaged SWN stretching, which we determine both
numerically and analytically using a psudo-gap ansatz for the SWN-density of
states. The SWN stretching is related to the probability of a random-walker to
return to its origin on the SWN. We compare our results to the corresponding
ones for Cayley trees.Comment: 14 pages, 4 figures. Preprint version, submitted to JC
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
Synchronization Landscapes in Small-World-Connected Computer Networks
Motivated by a synchronization problem in distributed computing we studied a
simple growth model on regular and small-world networks, embedded in one and
two-dimensions. We find that the synchronization landscape (corresponding to
the progress of the individual processors) exhibits Kardar-Parisi-Zhang-like
kinetic roughening on regular networks with short-range communication links.
Although the processors, on average, progress at a nonzero rate, their spread
(the width of the synchronization landscape) diverges with the number of nodes
(desynchronized state) hindering efficient data management. When random
communication links are added on top of the one and two-dimensional regular
networks (resulting in a small-world network), large fluctuations in the
synchronization landscape are suppressed and the width approaches a finite
value in the large system-size limit (synchronized state). In the resulting
synchronization scheme, the processors make close-to-uniform progress with a
nonzero rate without global intervention. We obtain our results by ``simulating
the simulations", based on the exact algorithmic rules, supported by
coarse-grained arguments.Comment: 20 pages, 22 figure
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
Phase transitions in a network with range dependent connection probability
We consider a one-dimensional network in which the nodes at Euclidean
distance can have long range connections with a probabilty in addition to nearest neighbour connections. This system has been
shown to exhibit small world behaviour for above which its
behaviour is like a regular lattice. From the study of the clustering
coefficients, we show that there is a transition to a random network at . The finite size scaling analysis of the clustering coefficients obtained
from numerical simulations indicate that a continuous phase transition occurs
at this point. Using these results, we find that the two transitions occurring
in this network can be detected in any dimension by the behaviour of a single
quantity, the average bond length. The phase transitions in all dimensions are
non-trivial in nature.Comment: 4 pages, revtex4, submitted to Physical Review
Functional characterization of the vertebrate primary ureter: Structure and ion transport mechanisms of the pronephric duct in axolotl larvae (Amphibia)
<p>Abstract</p> <p>Background</p> <p>Three kidney systems appear during vertebrate development: the pronephroi, mesonephroi and metanephroi. The pronephric duct is the first or primary ureter of these kidney systems. Its role as a key player in the induction of nephrogenic mesenchyme is well established. Here we investigate whether the duct is involved in urine modification using larvae of the freshwater amphibian <it>Ambystoma mexicanum </it>(axolotl) as model.</p> <p>Results</p> <p>We investigated structural as well as physiological properties of the pronephric duct. The key elements of our methodology were: using histology, light and transmission electron microscopy as well as confocal laser scanning microscopy on fixed tissue and applying the microperfusion technique on isolated pronephric ducts in combination with single cell microelectrode impalements. Our data show that the fully differentiated pronephric duct is composed of a single layered epithelium consisting of one cell type comparable to the principal cell of the renal collecting duct system. The cells are characterized by a prominent basolateral labyrinth and a relatively smooth apical surface with one central cilium. Cellular impalements demonstrate the presence of apical Na<sup>+ </sup>and K<sup>+ </sup>conductances, as well as a large K<sup>+ </sup>conductance in the basolateral cell membrane. Immunolabeling experiments indicate heavy expression of Na<sup>+</sup>/K<sup>+</sup>-ATPase in the basolateral labyrinth.</p> <p>Conclusions</p> <p>We propose that the pronephric duct is important for the subsequent modification of urine produced by the pronephros. Our results indicate that it reabsorbs sodium and secretes potassium via channels present in the apical cell membrane with the driving force for ion movement provided by the Na<sup>+</sup>/K<sup>+ </sup>pump. This is to our knowledge the first characterization of the pronephric duct, the precursor of the collecting duct system, which provides a model of cell structure and basic mechanisms for ion transport. Such information may be important in understanding the evolution of vertebrate kidney systems and human diseases associated with congenital malformations.</p
Childhood motor performance is increased by participation in organized sport: the CHAMPS Study-DK
Evidence suggests that motor performance in children is declining globally. We tested whether participation in organized sport is associated with motor performance, and estimate the effect of 30 months participation in organized sport on motor performance. Study participants were 1067 primary school students, enrolled in the Danish Childhood Health, Activity, and Motor Performance School study. Participation in organized sport was reported via text messaging. Coordination-related motor performance composite, fitness-related motor performance composite, and total motor performance composite were calculated. Data were analyzed using Generalized Estimating Equations. Participation in organized sport was positively associated with motor performance (all composites) in models that did and did not control for baseline motor performance. For models that did not control for baseline motor performance, this equated to 2–6% increases in motor performance per weekly sport session; for models that did control for baseline motor performance, this equated to 1–5% increases in motor performance per weekly sport session. Positive associations between participation in organized sport and motor performance identify participation in organized sport as a way to improve motor performance in children. These results might provide the basis to determine whether participation in organized sport could be beneficial for children with developmental movement disorders
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