210 research outputs found
Metastability in the BCS model
We discuss metastable states in the mean-field version of the strong coupling
BCS-model and study the evolution of a superconducting equilibrium state
subjected to a dynamical semi-group with Lindblad generator in detailed balance
w.r.t. another equilibrium state. The intermediate states are explicitly
constructed and their stability properties are derived. The notion of
metastability in this genuine quantum system, is expressed by means of
energy-entropy balance inequalities and canonical coordinates of observables
Goldstone Bosons in Josephson Junctions
For a microscopic model of a Josephson junction the normal coordinates of the
two junction Goldstone bosons are constructed and their dynamical spectrum is
computed. The explicit dependence on the phase difference of the two
superconductors is calculated
Statistics and Quantum Chaos
We use multi-time correlation functions of quantum systems to construct
random variables with statistical properties that reflect the degree of
complexity of the underlying quantum dynamics.Comment: 12 pages, LateX, no figures, restructured versio
A microscopic model for Josephson currents
A microscopic model of a Josephson junction between two superconducting
plates is proposed and analysed. For this model, the nonequilibrium steady
state of the total system is explicitly constructed and its properties are
analysed. In particular, the Josephson current is rigorously computed as a
function of the phase difference of the two plates and the typical properties
of the Josephson current are recovered
Kakutani Dichotomy on Free States
Two quasi-free states on a CAR or CCR algebra are shown to generate
quasi-equivalent representations unless they are disjoint.Comment: 12 page
Quantum macrostatistical picture of nonequilibrium steady states
We employ a quantum macrostatistical treatment of irreversible processes to
prove that, in nonequilibrium steady states, (a) the hydrodynamical observables
execute a generalised Onsager-Machlup process and (b) the spatial correlations
of these observables are generically of long range. The key assumptions behind
these results are a nonequilibrium version of Onsager's regression hypothesis,
together with certain hypotheses of chaoticity and local equilibrium for
hydrodynamical fluctuations.Comment: TeX, 13 page
Large deviations for ideal quantum systems
We consider a general d-dimensional quantum system of non-interacting
particles, with suitable statistics, in a very large (formally infinite)
container. We prove that, in equilibrium, the fluctuations in the density of
particles in a subdomain of the container are described by a large deviation
function related to the pressure of the system. That is, untypical densities
occur with a probability exponentially small in the volume of the subdomain,
with the coefficient in the exponent given by the appropriate thermodynamic
potential. Furthermore, small fluctuations satisfy the central limit theorem.Comment: 28 pages, LaTeX 2
myExperiment: Defining the Social Virtual Research Environment
The myExperiment Virtual Research Environment supports the sharing of research objects used by scientists, such as scientific workflows. For researchers it is both a social infrastructure that encourages sharing and a platform for conducting research, through familiar user interfaces. For developers it provides an open, extensible and participative environment. We describe the design, implementation and deployment of myExperiment and suggest that its four capabilities - research objects, social model, open environment and actioning research - are necessary characteristics of an effective Virtual Research Environment for e-research and open science. © 2008 IEEE
A large meteoritic event over Antarctica ca. 430 ka ago inferred from chondritic spherules from the Sør Rondane Mountains
Large airbursts, the most frequent hazardous impact events, are estimated to occur orders of magnitude more frequently than crater-forming impacts. However, finding traces of these events is impeded by the difficulty of identifying them in the recent geological record. Here, we describe condensation spherules found on top of Walnumfjellet in the Sør Rondane Mountains, Antarctica. Affinities with similar spherules found in EPICA Dome C and Dome Fuji ice cores suggest that these particles were produced during a single-asteroid impact ca. 430 thousand years (ka) ago. The lack of a confirmed crater on the Antarctic ice sheet and geochemical and 18O-poor oxygen isotope signatures allow us to hypothesize that the impact particles result from a touchdown event, in which a projectile vapor jet interacts with the Antarctic ice sheet. Numerical models support a touchdown scenario. This study has implications for the identification and inventory of large cosmic events on Earth
- …