4,542 research outputs found
Chaotic dynamics of superconductor vortices in the plastic phase
We present numerical simulation results of driven vortex lattices in presence
of random disorder at zero temperature. We show that the plastic dynamics is
readily understood in the framework of chaos theory. Intermittency "routes to
chaos" have been clearly identified, and positive Lyapunov exponents and
broad-band noise, both characteristic of chaos, are found to coincide with the
differential resistance peak. Furthermore, the fractal dimension of the strange
attractor reveals that the chaotic dynamics of vortices is low-dimensional.Comment: 5 pages, 3 figures Accepted for publication in Physical Review
Letter
Driven flux-line lattices in the presence of weak random columnar disorder: Finite-temperature behavior and dynamical melting of moving Bose glass
We use 3D numerical simulations to explore the phase diagram of driven flux
line lattices in presence of weak random columnar disorder at finite
temperature and high driving force. We show that the moving Bose glass phase
exists in a large range of temperature, up to its melting into a moving vortex
liquid. It is also remarkably stable upon increasing velocity : the dynamical
transition to the correlated moving glass expected at a critical velocity is
not found at any velocity accessible to our simulations. Furthermore, we show
the existence of an effective static tin roof pinning potential in the
direction transverse to motion, which originates from both the transverse
periodicity of the moving lattice and the localization effect due to correlated
disorder. Using a simple model of a single elastic line in such a periodic
potential, we obtain a good description of the transverse field penetration at
surfaces as a function of thickness in the moving Bose glass phase.Comment: 5 pages, 4 figures, New title and minor changes in text and figures.
Accepted for publication in Physical Review
Scalar leptoquarks and the rare B meson decays
We study some rare decays of meson involving the quark level transition
in the scalar leptoquark model. We constrain the
leptoquark parameter space using the recently measured branching ratios of
processes. Using such parameters, we obtain the
branching ratios, direct CP violation parameters and isospin asymmetries in and processes. We also obtain the
branching ratios for some lepton flavour violating decays .
We find that the various anomalies associated with the isospin asymmetries of
process can be explained in the scalar leptoquark model.Comment: 28 pages, 7 figures. typos corrected, to appear in Phys. Rev.
Sputtered gold mask for deep chemical etching of silicon
Sputtered mask resists chemical attack from acid and has adherence to withstand prolonged submergence in etch solution without lifting from silicon surface. Even under prolonged etch conditions with significant undercutting, gold mask maintained excellent adhesion to silicon surface and imperviousness to acid
Environmental Dependence of Masses and Coupling Constants
We construct a class of scalar field models coupled to matter that lead to
the dependence of masses and coupling constants on the ambient matter density.
Such models predict a deviation of couplings measured on the Earth from values
determined in low-density astrophysical environments, but do not necessarily
require the evolution of coupling constants with the redshift in the recent
cosmological past. Additional laboratory and astrophysical tests of \Delta
\alpha and \Delta(m_p/m_e) as functions of the ambient matter density are
warranted.Comment: 20 pages, no figures, references added, minor editorial change
Critical behavior of plastic depinning of vortex lattices in two dimensions: Molecular dynamics simulations
Using molecular dynamics simulations, we report a study of the dynamics of
two-dimensional vortex lattices driven over a disordered medium. In strong
disorder, when topological order is lost, we show that the depinning transition
is analogous to a second order critical transition: the velocity-force response
at the onset of motion is continuous and characterized by critical exponents.
Combining studies at zero and nonzero temperature and using a scaling analysis,
two critical expo- nents are evaluated. We find v\sim (F-F_c)^\beta with
\beta=1.3\pm0.1 at T=0 and F>F_c, and v\sim T^{1/\delta} with
\delta^{-1}=0.75\pm0.1 at F=F_c, where F_c is the critical driving force at
which the lattice goes from a pinned state to a sliding one. Both critical
exponents and the scaling function are found to exhibit universality with
regard to the pinning strength and different disorder realizations.
Furthermore, the dynamics is shown to be chaotic in the whole critical region.Comment: 8 pages, 6 figure
High-Energy Constraints on the Direct Detection of MSSM Neutralinos
The requirement that the MSSM remain an acceptable effective field theory up
to energies beyond the weak scale constrains the sparticle spectrum, and hence
the permissible ranges of cold dark matter neutralino-proton cross sections.
Specifically, squarks are generally much heavier than sleptons if no tachyons
are to appear before the GUT scale ~10^16 GeV, or even before 10 TeV. We
display explicitly the allowed ranges of effective squark and slepton masses at
the weak scale, and the cross-section ranges allowed if the MSSM is to remain
valid without tachyons up to 10 TeV or the GUT scale. The allowed areas in the
cross section-mass plane for both spin-independent and spin-dependent
scattering are significantly smaller than would be allowed if the MSSM were
required to be valid only around the weak scale. In addition to a reduction in
the maximum cross section, the upper limit on the neutralino mass is greatly
reduced when tachyons are avoided, particularly for smaller values of the
squark masses.Comment: 22 pages, 22 figure
SCRIPTKELL : a tool for measuring cognitive effort and time processing in writing and other complex cognitive activities
We present SCRIPTKELL, a computer-assisted experimental tool that makes it possible to measure the time and cognitive effort allocated to the subprocesses of writing and other cognitive activities, SCRIPTKELL was designed to easily use and modulate Kellogg's (1986) triple-task procedure,.which consists of a combination of three tasks: a writing task (or another task), a reaction time task (auditory signal detection), and a directed retrospection task (after each signal detection during writing). We demonstrate how this tool can be used to address several novel empirical and theoretical issues. In sum, SCRIPTKELL should facilitate the flexible realization of experimental designs and the investigation of critical issues concerning the functional characteristics of complex cognitive activities
Chaos and plasticity in superconductor vortices: a low-dimensional dynamics
We present new results of numerical simulations for driven vortex lattices in
presence of random disorder at zero temperature. We show that the plastic
dynamics of vortices display dissipative chaos. Intermittency "routes to chaos"
have been clearly identified below the differential resistance peak. The peak
region is characterized by positive Lyapunov exponents characteristic of chaos,
and low frequency broad-band noise. Furthermore we find a low fractal dimension
of the strange attractor, which suggests that only a few dynamical variables
are sufficient to model the complex plastic dynamics of vortices.Comment: 8 pages, 6 figures, accepted for publication in The Physical Review
Solitons and Vertex Operators in Twisted Affine Toda Field Theories
Affine Toda field theories in two dimensions constitute families of
integrable, relativistically invariant field theories in correspondence with
the affine Kac-Moody algebras. The particles which are the quantum excitations
of the fields display interesting patterns in their masses and coupling and
which have recently been shown to extend to the classical soliton solutions
arising when the couplings are imaginary. Here these results are extended from
the untwisted to the twisted algebras. The new soliton solutions and their
masses are found by a folding procedure which can be applied to the affine
Kac-Moody algebras themselves to provide new insights into their structures.
The relevant foldings are related to inner automorphisms of the associated
finite dimensional Lie group which are calculated explicitly and related to
what is known as the twisted Coxeter element. The fact that the twisted affine
Kac-Moody algebras possess vertex operator constructions emerges naturally and
is relevant to the soliton solutions.Comment: 27 pages (harvmac) + 3 figures (LaTex) at the end of the file,
Swansea SWAT/93-94/1
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