2,672 research outputs found
Phospholipid distribution in the cytoplasmic membrane of Gram-negative bacteria is highly asymmetric, dynamic, and cell shape-dependent
Supercurrent fluctuations in short filaments
We evaluate the average and the standard deviation of the supercurrent in
superconducting nanobridges, as functions of the temperature and the phase
difference, in an equilibrium situation. We also evaluate the autocorrelation
of the supercurrent as a function of the elapsed time. The behavior of
supercurrent fluctuations is qualitatively different from from that of the
normal current: they depend on the phase difference, have a different
temperature dependence, and for appropriate range their standard deviation is
independent of the probing time. We considered two radically different
filaments and obtained very similar results for both. Fluctuations of the
supercurrent can in principle be measured
Microbial Volatile Organic Compound (VOC)-Driven Dissolution and Surface Modification of Phosphorus-Containing Soil Minerals for Plant Nutrition: An Indirect Route for VOC-Based Plant-Microbe Communications
Thermal fluctuations in moderately damped Josephson junctions: Multiple escape and retrapping, switching- and return-current distributions and hysteresis
A crossover at a temperature T* in the temperature dependence of the width s
of the distribution of switching currents of moderately damped Josephson
junctions has been reported in a number of recent publications, with positive
ds/dT and IV characteristics associated with underdamped behaviour for lower
temperatures T<T*, and negative ds/dT and IV characteristics resembling
overdamped behaviour for higher temperatures T>T*. We have investigated in
detail the behaviour of Josephson junctions around the temperature T* by using
Monte Carlo simulations including retrapping from the running state into the
supercurrent state as given by the model of Ben-Jacob et al. We develop
discussion of the important role of multiple escape and retrapping events in
the moderate-damping regime, in particular considering the behaviour in the
region close to T*. We show that the behaviour is more fully understood by
considering two crossover temperatures, and that the shape of the distribution
and s(T) around T*, as well as at lower T<T*, are largely determined by the
shape of the conventional thermally activated switching distribution. We show
that the characteristic temperatures T* are not unique for a particular
Josephson junction, but have some dependence on the ramp rate of the applied
bias current. We also consider hysteresis in moderately damped Josephson
junctions and discuss the less commonly measured distribution of return
currents for a decreasing current ramp. We find that some hysteresis should be
expected to persist above T* and we highlight the importance, even well below
T*, of accounting properly for thermal fluctuations when determining the
damping parameter Q.Comment: Accepted for publication in PR
The Geant4 Hadronic Verification Suite for the Cascade Energy Range
A Geant4 hadronic process verification suite has been designed to test and
optimize Geant4 hadronic models in the cascade energy range. It focuses on
quantities relevant to the LHC radiation environment and spallation source
targets. The general structure of the suite is presented, including the user
interface, stages of verification, management of experimental data, event
generation, and comparison of results to data. Verification results for the
newly released Binary cascade and Bertini cascade models are presented.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 5 pages, LaTeX, 3 eps figures. PSN
MOMT00
Gate-controlled superconductivity in diffusive multiwalled carbon nanotube
We have investigated electrical transport in a diffusive multiwalled carbon
nanotube contacted using superconducting leads made of Al/Ti sandwich
structure. We find proximity-induced superconductivity with measured critical
currents up to I_cm = 1.3 nA, tunable by gate voltage down to 10 pA. The
supercurrent branch displays a finite zero bias resistance which varies as R_0
proportional to I_cm^-alpha with alpha=0.74. Using IV-characteristics of
junctions with phase diffusion, a good agreement is obtained with Josephson
coupling energy in the long, diffusive junction model of A.D Zaikin and G.F.
Zharkov (Sov. J. Low Temp. Phys. 7, 184 (1981)).Comment: 5 pages, 4 figure
Computation of the asymptotic states of modulated open quantum systems with a numerically exact realization of the quantum trajectory method
Quantum systems out of equilibrium are presently a subject of active
research, both in theoretical and experimental domains. In this work we
consider time-periodically modulated quantum systems which are in contact with
a stationary environment. Within the framework of a quantum master equation,
the asymptotic states of such systems are described by time-periodic density
operators. Resolution of these operators constitutes a non-trivial
computational task. To go beyond the current size limits, we use the quantum
trajectory method which unravels master equation for the density operator into
a set of stochastic processes for wave functions. The asymptotic density matrix
is calculated by performing a statistical sampling over the ensemble of quantum
trajectories, preceded by a long transient propagation. We follow the ideology
of event-driven programming and construct a new algorithmic realization of the
method. The algorithm is computationally efficient, allowing for long 'leaps'
forward in time, and is numerically exact in the sense that, being given the
list of uniformly distributed (on the unit interval) random numbers, , one could propagate a quantum trajectory (with 's
as norm thresholds) in a numerically exact way. %Since the quantum trajectory
method falls into the class of standard sampling problems, performance of the
algorithm %can be substantially improved by implementing it on a computer
cluster. By using a scalable -particle quantum model, we demonstrate that
the algorithm allows us to resolve the asymptotic density operator of the model
system with states on a regular-size computer cluster, thus reaching
the scale on which numerical studies of modulated Hamiltonian systems are
currently performed
Lyapunov exponents of quantum trajectories beyond continuous measurements
Quantum systems interacting with their environments can exhibit complex
non-equilibrium states that are tempting to be interpreted as quantum analogs
of chaotic attractors. Yet, despite many attempts, the toolbox for quantifying
dissipative quantum chaos remains very limited. In particular, quantum
generalizations of Lyapunov exponent, the main quantifier of classical chaos,
are established only within the framework of continuous measurements. We
propose an alternative generalization which is based on the unraveling of a
quantum master equation into an ensemble of so-called 'quantum jump'
trajectories. These trajectories are not only a theoretical tool but a part of
the experimental reality in the case of quantum optics. We illustrate the idea
by using a periodically modulated open quantum dimer and uncover the transition
to quantum chaos matched by the period-doubling route in the classical limit.Comment: 5 pages, 4 figure
Evidence of Josephson-coupled superconducting regions at the interfaces of Highly Oriented Pyrolytic Graphite
Transport properties of a few hundreds of nanometers thick (in the graphene
plane direction) lamellae of highly oriented pyrolytic graphite (HOPG) have
been investigated. Current-Voltage characteristics as well as the temperature
dependence of the voltage at different fixed input currents provide evidence
for Josephson-coupled superconducting regions embedded in the internal
two-dimensional interfaces, reaching zero resistance at low enough
temperatures. The overall behavior indicates the existence of superconducting
regions with critical temperatures above 100 K at the internal interfaces of
oriented pyrolytic graphite.Comment: 6 Figures, 5 page
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