554 research outputs found
Effect of ferromagnetic film thickness on magnetoresistance of thin-film superconductor-ferromagnet hybrids
We study the influence of the thickness Df of the plain ferromagnetic (F)
film on the electrical resistance of the flux-coupled hybrids, consisting of
superconducting (S) Al film and multilayer [Co/Pt] F film with out-of-plain
magnetization. The behavior of such hybrids at high and low temperatures is
found to be different: the nucleation of superconductivity at high temperatures
is governed mainly by the typical lateral dimensions of the magnetic domains,
while low temperature properties are determined by topology of the magnetic
template. We show that an increase in the Df value leads to a broadening of the
field- and temperature intervals where non-monotonous dependence of the
superconducting critical temperature Tc on the applied magnetic field H is
observed (for demagnetized F films). Further increase in the Df value results
in a global suppression of superconductivity. Thus, we determined an optimal
thickness, when the non-monotonous dependence Tc(H) can be observed in rather
broad T and H range, what can be interesting for further studies of the
localized superconductivity in planar Al-based S/F hybrids and for development
of the devices which can exploit the localized superconductivity.Comment: 10 pages, 9 figure
Transillumination imaging through scattering media by use of photorefractive polymers
We demonstrate the use of a near-infrared-sensitive photorefractive polymer with high efficiency for imaging through scattering media, using an all-optical holographic time gate. Imaging through nine scattering mean free paths is performed at 800 nm with a mode-locked continuous-wave Ti:sapphire laser
Sonoluminescence and collapse dynamics of multielectron bubbles in helium
Multielectron bubbles (MEBs) differ from gas-filled bubbles in that it is the
Coulomb repulsion of a nanometer thin layer of electrons that forces the bubble
open rather than the pressure of an enclosed gas. We analyze the implosion of
MEBs subjected to a pressure step, and find that despite the difference in the
underlying processes the collapse dynamics is similar to that of gas-filled
bubbles. When the MEB collapses, the electrons inside it undergo strong
accelerations, leading to the emission of radiation. This type of
sonoluminescence does not involve heating and ionisation of any gas inside the
bubble. We investigate the conditions necessary to obtain sonoluminescence from
multielectron bubbles and calculate the power spectrum of the emitted
radiation.Comment: 6 figure
Marcinkiewicz-type law of large numbers for double arrays
Chatterji strengthened version of a theorem for martingales which is a generalization of a theorem of Marcinkiewicz proving that if Xn is a sequence of independent, identically distributed random variables with E|X n|p < ∞, 0 < p < 2 and EX1 = 0 if 1 ≤ p ≤ 2, then n-1/p ∑i=1 n → 0 a.s. and in Lp. In this paper, we prove a version of law of large numbers for double arrays. If {Xij} is a double sequence of random variables with E|X11|p log+ |X 11|p < ∞, 0 < p < 2, then lim mVn→∞ ∑i=1 m ∑ j=1 n (Xij-aij/(mn)1/p = 0 a.s. and in Lp, where aij = 0 if 0 < p < 1, and a ij = E[Xij|Fij] if 1 ≤ p ≤ 2, which is a generalization of Etemadi's Marcinkiewicz-type SLLN for double arrays. This also generalize earlier results of Smythe, and Gut for double arrays of i.i.d. r.v's
Stability of multi-electron bubbles in liquid helium
The stability of multi-electron bubbles in liquid helium is investigated
theoretically. We find that multi-electron bubbles are unstable against fission
whenever the pressure is positive. It is shown that for moving bubbles the
Bernoulli effect can result in a range of pressures over which the bubbles are
stable.Comment: 7 pages, 5 figure
Charged-Surface Instability Development in Liquid Helium; Exact Solutions
The nonlinear dynamics of charged-surface instability development was
investigated for liquid helium far above the critical point. It is found that,
if the surface charge completely screens the field above the surface, the
equations of three-dimensional (3D) potential motion of a fluid are reduced to
the well-known equations describing the 3D Laplacian growth process. The
integrability of these equations in 2D geometry allows the analytic description
of the free-surface evolution up to the formation of cuspidal singularities at
the surface.Comment: latex, 5 pages, no figure
Effects of kinked linear defects on planar flux line arrays
In the hard core limit, interacting vortices in planar type II
superconductors can be modeled as non-interacting one dimensional fermions
propagating in imaginary time. We use this analogy to derive analytical
expressions for the probability density and imaginary current of vortex lines
interacting with an isolated bent line defect and to understand the pinning
properties of such systems. When there is an abrupt change of the direction of
the pinning defect, we find a sinusoidal modulation of the vortex density in
directions both parallel and perpendicular to the defect.Comment: 13 figure
A note on complete convergence for arrays
We extend and generalize some recent results on complete convergence for independent non-identically distributed random variables (cf. Duncan and Szynal, 1984; Gut, 1992; Hu et al., 1989). In the main result no assumptions are made concerning the existence of expected values or absolute moments of the random variables. Some well-known results from the literature can be easily obtained from our theorem. © 1998 Elsevier Science B.V. All rights reserved
State of charge and state of health assessment of viologens in aqueous-organic redox-flow electrolytes using in situ IR spectroscopy and multivariate curve resolution
Aqueous-organic redox flow batteries (RFBs) have gained considerable interest in recent years, given their potential for an economically viable energy storage at large scale. This, however, strongly depends on both the robustness of the underlying electrolyte chemistry against molecular decomposition reactions as well as the device's operation. With regard to this, the presented study focuses on the use of in situ IR spectroscopy in combination with a multivariate curve resolution approach to gain insight into both the molecular structures of the active materials present within the electrolyte as well as crucial electrolyte state parameters, represented by the electrolyte's state of charge (SOC) and state of health (SOH). To demonstrate the general applicability of the approach, methyl viologen (MV) and bis(3-trimethylammonium)propyl viologen (BTMAPV) are chosen, as viologens are frequently used as negolytes in aqueous-organic RFBs. The study's findings highlight the impact of in situ spectroscopy and spectral deconvolution tools on the precision of the obtainable SOC and SOH values. Furthermore, the study indicates the occurrence of multiple viologen dimers, which possibly influence the electrolyte lifetime and charging characteristics
Amplification of Fluctuations in Unstable Systems with Disorder
We study the early-stage kinetics of thermodynamically unstable systems with
quenched disorder. We show analytically that the growth of initial fluctuations
is amplified by the presence of disorder. This is confirmed by numerical
simulations of morphological phase separation (MPS) in thin liquid films and
spinodal decomposition (SD) in binary mixtures. We also discuss the
experimental implications of our results.Comment: 15 pages, 4 figure
- …