557 research outputs found
Dynamics of the superconducting condensate in the presence of a magnetic field. Channelling of vortices in superconducting strips at high currents
On the basis of the time-dependent Ginzburg-Landau equation we studied the
dynamics of the superconducting condensate in a wide two-dimensional sample in
the presence of a perpendicular magnetic field and applied current. We could
identify two critical currents: the current at which the pure superconducting
state becomes unstable ( \cite{self1}) and the current at which the
system transits from the resistive state to the superconducting state
(). The current decreases monotonically with external
magnetic field, while exhibits a maximum at . For sufficient
large magnetic fields the hysteresis disappears and . In
this high magnetic field region and for currents close to the voltage
appears as a result of the motion of separate vortices. With increasing current
the moving vortices form 'channels' with suppressed order parameter along which
the vortices can move very fast. This leads to a sharp increase of the voltage.
These 'channels' resemble in some respect the phase slip lines which occur at
zero magnetic field.Comment: 5 pages, 4 figures, Proceedings of Third European Conference on
Vortex Matter in Superconductor
Regulator constants and the parity conjecture
The p-parity conjecture for twists of elliptic curves relates multiplicities
of Artin representations in p-infinity Selmer groups to root numbers. In this
paper we prove this conjecture for a class of such twists. For example, if E/Q
is semistable at 2 and 3, K/Q is abelian and K^\infty is its maximal pro-p
extension, then the p-parity conjecture holds for twists of E by all orthogonal
Artin representations of Gal(K^\infty/Q). We also give analogous results when
K/Q is non-abelian, the base field is not Q and E is replaced by an abelian
variety. The heart of the paper is a study of relations between permutation
representations of finite groups, their "regulator constants", and
compatibility between local root numbers and local Tamagawa numbers of abelian
varieties in such relations.Comment: 50 pages; minor corrections; final version, to appear in Invent. Mat
ac-Field-Controlled Anderson Localization in Disordered Semiconductor Superlattices
An ac field, tuned exactly to resonance with the Stark ladder in an ideal
tight binding lattice under strong dc bias, counteracts Wannier-Stark
localization and leads to the emergence of extended Floquet states. If there is
random disorder, these states localize. The localization lengths depend
non-monotonically on the ac field amplitude and become essentially zero at
certain parameters. This effect is of possible relevance for characterizing the
quality of superlattice samples, and for performing experiments on Anderson
localization in systems with well-defined disorder.Comment: 10 pages, Latex; figures available on request from [email protected]
The Similarity Hypothesis in General Relativity
Self-similar models are important in general relativity and other fundamental
theories. In this paper we shall discuss the ``similarity hypothesis'', which
asserts that under a variety of physical circumstances solutions of these
theories will naturally evolve to a self-similar form. We will find there is
good evidence for this in the context of both spatially homogenous and
inhomogeneous cosmological models, although in some cases the self-similar
model is only an intermediate attractor. There are also a wide variety of
situations, including critical pheneomena, in which spherically symmetric
models tend towards self-similarity. However, this does not happen in all cases
and it is it is important to understand the prerequisites for the conjecture.Comment: to be submitted to Gen. Rel. Gra
On the statistical significance of the conductance quantization
Recent experiments on atomic-scale metallic contacts have shown that the
quantization of the conductance appears clearly only after the average of the
experimental results. Motivated by these results we have analyzed a simplified
model system in which a narrow neck is randomly coupled to wide ideal leads,
both in absence and presence of time reversal invariance. Based on Random
Matrix Theory we study analytically the probability distribution for the
conductance of such system. As the width of the leads increases the
distribution for the conductance becomes sharply peaked close to an integer
multiple of the quantum of conductance. Our results suggest a possible
statistical origin of conductance quantization in atomic-scale metallic
contacts.Comment: 4 pages, Tex and 3 figures. To be published in PR
Modelling caregiving interactions during stress
Few studies describing caregiver stress and coping have focused on the effects of informal caregiving for depressed care recipients.The major purpose of this paper was to investigate the dynamics of the informal care support and receipt interactions among caregivers and care recipients using a computational modelling approach.Important concepts in coping skills, strong ties support networks and stress buffering studies were used as a basis for the model design and verification.Simulation experiments for several cases pointed out that the model is able to reproduce interaction among strong tie network members during stress.In addition, the possible equillibria of the model have been determined, and the model has been automatically verified against expected overall properties
Modelling caregiving interactions during stress
Few studies describing caregiver stress and coping have focused on the effects of informal caregiving for depressed care recipients.The major purpose of this paper was to investigate the dynamics of the informal care support and receipt interactions among caregivers and care recipients using a computational modelling approach.Important concepts in coping skills, strong ties support networks and stress buffering studies were used as a basis for the model design and verification.Simulation experiments for several cases pointed out that the model is able to reproduce interaction among strong tie network members during stress.In addition, the possible equillibria of the model have been determined, and the model has been automatically verified against expected overall properties
Determination of the Strange Quark Content of the Nucleon from a Next-to-Leading-Order QCD Analysis of Neutrino Charm Production
We present the first next-to-leading-order QCD analysis of neutrino charm
production, using a sample of 6090 - and -induced
opposite-sign dimuon events observed in the CCFR detector at the Fermilab
Tevatron. We find that the nucleon strange quark content is suppressed with
respect to the non-strange sea quarks by a factor \kappa = 0.477 \:
^{+\:0.063}_{-\:0.053}, where the error includes statistical, systematic and
QCD scale uncertainties. In contrast to previous leading order analyses, we
find that the strange sea -dependence is similar to that of the non-strange
sea, and that the measured charm quark mass, , is larger and consistent with that determined in other processes.
Further analysis finds that the difference in -distributions between
and is small. A measurement of the Cabibbo-Kobayashi-Maskawa
matrix element is also presented.
uufile containing compressed postscript files of five Figures is appended at
the end of the LaTeX source.Comment: Nevis R#150
Maintenance and refurbishment planning for a group of bridges
During the service, highway overpasses are exposed to various deterioration processes. The rate of these unavoidable processes depends on intensity of usage, weather influences and maintenance level. If maintenance works are not planned and executed in an adequate manner, the performance of the structures under consideration reduces. Planning an optimum set of intervention measures on the level of a group of structures is a complex task that is often left to subjective, partial decisions of managers that have to take int the account also financial limitations.\ud
A group of 27 highway overpasses, spanning over the highway section under consideration, was analysed. A multi-criteria model for the selection of bridges that should have priority in the refurbishment process was developed. Condition rating data were collected from the periodic check\ud
reports and and structured appropriately. Key criteria that need to be taken into the account were identified: condition ration of the whole structure, age of the pass, possibility of joining the works on a string of passes, indirect cost influence, refurbishment cost for a structure and deterioraton rate of the structure. Relative importance among these citeria was determined by using Analytical Hierarchy Method (AHP). On this basis, a multi-criteria model to be used for the selection of a set of structures\ud
that have refurbishment priority in the case of limited financial contribution was developed. Refurbishment priority was identified for a group of structures that have, as a whole, a maximum overall benefit with respect to the selected criteria and their relative importance. Further, the analysis of the influence of the financial constraint magnitude upon the selection of structures to be repaired and the accompanying benefits ( that can facilitate the decision of the decision-makers' side) was carried out. The obtained results show that the proposed model can serve as an efficient tool used in rational selection of group of structures yielding the maximum overall benefit, and in analysis of possibilitie that lead to additional benefit with minimum financial input
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