224 research outputs found
On the Origin of Traveling Pulses in Bistable Systems
The interaction between a pair of Bloch fronts forming a traveling domain in
a bistable medium is studied. A parameter range beyond the nonequilibrium
Ising-Bloch bifurcation is found where traveling domains collapse. Only beyond
a second threshold the repulsive front interactions become strong enough to
balance attractive interactions and asymmetries in front speeds, and form
stable traveling pulses. The analysis is carried out for the forced complex
Ginzburg-Landau equation. Similar qualitative behavior is found in the bistable
FitzHugh-Nagumo model.Comment: 5 pages, RevTeX. Aric Hagberg: http://t7.lanl.gov/People/Aric/; Ehud
Meron:http://www.bgu.ac.il/BIDR/research/staff/meron.htm
Multistable Pulse-like Solutions in a Parametrically Driven Ginzburg-Landau Equation
It is well known that pulse-like solutions of the cubic complex
Ginzburg-Landau equation are unstable but can be stabilised by the addition of
quintic terms. In this paper we explore an alternative mechanism where the role
of the stabilising agent is played by the parametric driver. Our analysis is
based on the numerical continuation of solutions in one of the parameters of
the Ginzburg-Landau equation (the diffusion coefficient ), starting from the
nonlinear Schr\"odinger limit (for which ). The continuation generates,
recursively, a sequence of coexisting stable solutions with increasing number
of humps. The sequence "converges" to a long pulse which can be interpreted as
a bound state of two fronts with opposite polarities.Comment: 13 pages, 6 figures; to appear in PR
Grain boundary pinning and glassy dynamics in stripe phases
We study numerically and analytically the coarsening of stripe phases in two
spatial dimensions, and show that transient configurations do not achieve long
ranged orientational order but rather evolve into glassy configurations with
very slow dynamics. In the absence of thermal fluctuations, defects such as
grain boundaries become pinned in an effective periodic potential that is
induced by the underlying periodicity of the stripe pattern itself. Pinning
arises without quenched disorder from the non-adiabatic coupling between the
slowly varying envelope of the order parameter around a defect, and its fast
variation over the stripe wavelength. The characteristic size of ordered
domains asymptotes to a finite value $R_g \sim \lambda_0\
\epsilon^{-1/2}\exp(|a|/\sqrt{\epsilon})\epsilon\ll 1\lambda_0a$ a constant of order unity. Random fluctuations allow defect motion to
resume until a new characteristic scale is reached, function of the intensity
of the fluctuations. We finally discuss the relationship between defect pinning
and the coarsening laws obtained in the intermediate time regime.Comment: 17 pages, 8 figures. Corrected version with one new figur
Controlled transport of solitons and bubbles using external perturbations
We investigate generalized soliton-bearing systems in the presence of
external perturbations. We show the possibility of the transport of solitons
using external waves, provided the waveform and its velocity satisfy certain
conditions. We also investigate the stabilization and transport of bubbles
using external perturbations in 3D-systems. We also present the results of real
experiments with laser-induced vapor bubbles in liquids.Comment: 26 pages, 24 figure
Modulation of Localized States in Electroconvection
We report on the effects of temporal modulation of the driving force on a
particular class of localized states, known as worms, that have been observed
in electroconvection in nematic liquid crystals. The worms consist of the
superposition of traveling waves and have been observed to have unique, small
widths, but to vary in length. The transition from the pure conduction state to
worms occurs via a backward bifurcation. A possible explanation of the
formation of the worms has been given in terms of coupled amplitude equations.
Because the worms consist of the superposition of traveling waves, temporal
modulation of the control parameter is a useful probe of the dynamics of the
system. We observe that temporal modulation increases the average length of the
worms and stabilizes worms below the transition point in the absence of
modulation.Comment: 4 pages, 4 figure
Control of Rayleigh-Taylor instability by vertical vibration in large aspect ratio containers
We consider a horizontal heavy fluid layer supported by a light, immiscible one in a wide (as compared to depth) container, which is vertically vibrated intending to counterbalance the Rayleigh-Taylor instability of the flat, rigid-body vibrating state. In the simplest case when the density and viscosity of the lighter fluid are small compared to their counterparts in the heavier fluid, we apply a long wave, weakly nonlinear analysis that yields a generalized Cahn-Hilliard equation for the evolution of the fluid interface. This equation shows that the stabilizing effect of vibration is like that of surface tension, and is used to analyze the linear stability of the flat state, the local bifurcation at the instability threshold and some global existence and stability properties concerning the steady states without dry spots. The analysis is extended to two cases of practical interest. Namely, (a) the viscosity of one of the fluids is much smaller than that of the other one, and (b) the densities and viscosities of both fluids are quite close to each other
Combustion- and friction-derived magnetic air pollution nanoparticles in human hearts
Air pollution is a risk factor for cardiovascular and Alzheimer's disease (AD). Iron-rich, strongly magnetic, combustion- and friction-derived nanoparticles (CFDNPs) are abundant in particulate air pollution. Metropolitan Mexico City (MMC) young residents have abundant brain CFDNPs associated with AD pathology. We aimed to identify if magnetic CFDNPs are present in urbanites' hearts and associated with cell damage. We used magnetic analysis and transmission electron microscopy (TEM) to identify heart CFDNPs and measured oxidative stress (cellular prion protein, PrPC), and endoplasmic reticulum (ER) stress (glucose regulated protein, GRP78) in 72 subjects age 23.8 ± 9.4y: 63 MMC residents, with Alzheimer Continuum vs 9 controls. Magnetite/maghemite nanoparticles displaying the typical rounded crystal morphologies and fused surface textures of CFDNPs were more abundant in MMC residents' hearts. NPs, ∼2–10 × more abundant in exposed vs controls, were present inside mitochondria in ventricular cardiomyocytes, in ER, at mitochondria-ER contact sites (MERCs), intercalated disks, endothelial and mast cells. Erythrocytes were identified transferring ‘hitchhiking’ NPs to activated endothelium. Magnetic CFDNP concentrations and particle numbers ranged from 0.2 to 1.7 μg/g and ∼2 to 22 × 109/g, respectively. Co-occurring with cardiomyocyte NPs were abnormal mitochondria and MERCs, dilated ER, and lipofuscin. MMC residents had strong left ventricular PrPC and bi-ventricular GRP78 up-regulation. The health impact of up to ∼22 billion magnetic NPs/g of ventricular tissue are likely reflecting the combination of surface charge, ferrimagnetism, and redox activity, and includes their potential for disruption of the heart's electrical impulse pathways, hyperthermia and alignment and/or rotation in response to magnetic fields. Exposure to solid NPs appears to be directly associated with early and significant cardiac damage. Identification of strongly magnetic CFDNPs in the hearts of children and young adults provides an important novel layer of information for understanding CVD pathogenesis emphasizing the urgent need for prioritization of particulate air pollution control
Colossal dielectric constants in transition-metal oxides
Many transition-metal oxides show very large ("colossal") magnitudes of the
dielectric constant and thus have immense potential for applications in modern
microelectronics and for the development of new capacitance-based
energy-storage devices. In the present work, we thoroughly discuss the
mechanisms that can lead to colossal values of the dielectric constant,
especially emphasising effects generated by external and internal interfaces,
including electronic phase separation. In addition, we provide a detailed
overview and discussion of the dielectric properties of CaCu3Ti4O12 and related
systems, which is today's most investigated material with colossal dielectric
constant. Also a variety of further transition-metal oxides with large
dielectric constants are treated in detail, among them the system La2-xSrxNiO4
where electronic phase separation may play a role in the generation of a
colossal dielectric constant.Comment: 31 pages, 18 figures, submitted to Eur. Phys. J. for publication in
the Special Topics volume "Cooperative Phenomena in Solids: Metal-Insulator
Transitions and Ordering of Microscopic Degrees of Freedom
D* Production in Deep Inelastic Scattering at HERA
This paper presents measurements of D^{*\pm} production in deep inelastic
scattering from collisions between 27.5 GeV positrons and 820 GeV protons. The
data have been taken with the ZEUS detector at HERA. The decay channel
(+ c.c.) has been used in the study. The
cross section for inclusive D^{*\pm} production with
and is 5.3 \pms 1.0 \pms 0.8 nb in the kinematic region
{ GeV and }. Differential cross
sections as functions of p_T(D^{*\pm}), and are
compared with next-to-leading order QCD calculations based on the photon-gluon
fusion production mechanism. After an extrapolation of the cross section to the
full kinematic region in p_T(D^{*\pm}) and (D^{*\pm}), the charm
contribution to the proton structure function is
determined for Bjorken between 2 10 and 5 10.Comment: 17 pages including 4 figure
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