1,296 research outputs found
Superconductivity-enhanced bias spectroscopy in carbon nanotube quantum dots
We study low-temperature transport through carbon nanotube quantum dots in
the Coulomb blockade regime coupled to niobium-based superconducting leads. We
observe pronounced conductance peaks at finite source-drain bias, which we
ascribe to elastic and inelastic cotunneling processes enhanced by the
coherence peaks in the density of states of the superconducting leads. The
inelastic cotunneling lines display a marked dependence on the applied gate
voltage which we relate to different tunneling-renormalizations of the two
subbands in the nanotube. Finally, we discuss the origin of an especially
pronounced sub-gap structure observed in every fourth Coulomb diamond
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
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
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
Levy flights from a continuous-time process
The Levy-flight dynamics can stem from simple random walks in a system whose
operational time (number of steps n) typically grows superlinearly with
physical time t. Thus, this processes is a kind of continuous-time random walks
(CTRW), dual to usual Scher-Montroll model, in which grows sublinearly with
t. The models in which Levy-flights emerge due to a temporal subordination let
easily discuss the response of a random walker to a weak outer force, which is
shown to be nonlinear. On the other hand, the relaxation of en ensemble of such
walkers in a harmonic potential follows a simple exponential pattern and leads
to a normal Boltzmann distribution. The mixed models, describing normal CTRW in
superlinear operational time and Levy-flights under the operational time of
subdiffusive CTRW lead to paradoxical diffusive behavior, similar to the one
found in transport on polymer chains. The relaxation to the Boltzmann
distribution in such models is slow and asymptotically follows a power-law
Raman spectroscopy and electrical properties of InAs nanowires with local oxidation enabled by substrate micro-trenches and laser irradiation
The thermal gradient along indium-arsenide nanowires was engineered by a
combination of fabricated micro- trenches in the supporting substrate and
focused laser irradiation. This allowed local control of thermally activated
oxidation reactions of the nanowire on the scale of the diffraction limit. The
locality of the oxidation was detected by micro-Raman mapping, and the results
were found consistent with numerical simulations of the temperature profile.
Applying the technique to nanowires in electrical devices the locally oxidized
nanowires remained conducting with a lower conductance as expected for an
effectively thinner conducting core
Organ-specific responses during brain death:increased aerobic metabolism in the liver and anaerobic metabolism with decreased perfusion in the kidneys
Hepatic and renal energy status prior to transplantation correlates with graft survival. However, effects of brain death (BD) on organ-specific energy status are largely unknown. We studied metabolism, perfusion, oxygen consumption, and mitochondrial function in the liver and kidneys following BD. BD was induced in mechanically-ventilated rats, inflating an epidurally-placed Fogarty-catheter, with sham-operated rats as controls. A 9.4T-preclinical MRI system measured hourly oxygen availability (BOLD-related R2*) and perfusion (T1-weighted). After 4 hrs, tissue was collected, mitochondria isolated and assessed with high-resolution respirometry. Quantitative proteomics, qPCR, and biochemistry was performed on stored tissue/plasma. Following BD, the liver increased glycolytic gene expression (Pfk-1) with decreased glycogen stores, while the kidneys increased anaerobic- (Ldha) and decreased gluconeogenic-related gene expression (Pck-1). Hepatic oxygen consumption increased, while renal perfusion decreased. ATP levels dropped in both organs while mitochondrial respiration and complex I/ATP synthase activity were unaffected. In conclusion, the liver responds to increased metabolic demands during BD, enhancing aerobic metabolism with functional mitochondria. The kidneys shift towards anaerobic energy production while renal perfusion decreases. Our findings highlight the need for an organ-specific approach to assess and optimise graft quality prior to transplantation, to optimise hepatic metabolic conditions and improve renal perfusion while supporting cellular detoxification
Evolving networks with disadvantaged long-range connections
We consider a growing network, whose growth algorithm is based on the
preferential attachment typical for scale-free constructions, but where the
long-range bonds are disadvantaged. Thus, the probability to get connected to a
site at distance is proportional to , where is a
tunable parameter of the model. We show that the properties of the networks
grown with are close to those of the genuine scale-free
construction, while for the structure of the network is vastly
different. Thus, in this regime, the node degree distribution is no more a
power law, and it is well-represented by a stretched exponential. On the other
hand, the small-world property of the growing networks is preserved at all
values of .Comment: REVTeX, 6 pages, 5 figure
Introducing Small-World Network Effect to Critical Dynamics
We analytically investigate the kinetic Gaussian model and the
one-dimensional kinetic Ising model on two typical small-world networks (SWN),
the adding-type and the rewiring-type. The general approaches and some basic
equations are systematically formulated. The rigorous investigation of the
Glauber-type kinetic Gaussian model shows the mean-field-like global influence
on the dynamic evolution of the individual spins. Accordingly a simplified
method is presented and tested, and believed to be a good choice for the
mean-field transition widely (in fact, without exception so far) observed on
SWN. It yields the evolving equation of the Kawasaki-type Gaussian model. In
the one-dimensional Ising model, the p-dependence of the critical point is
analytically obtained and the inexistence of such a threshold p_c, for a finite
temperature transition, is confirmed. The static critical exponents, gamma and
beta are in accordance with the results of the recent Monte Carlo simulations,
and also with the mean-field critical behavior of the system. We also prove
that the SWN effect does not change the dynamic critical exponent, z=2, for
this model. The observed influence of the long-range randomness on the critical
point indicates two obviously different hidden mechanisms.Comment: 30 pages, 1 ps figures, REVTEX, accepted for publication in Phys.
Rev.
- …