947 research outputs found
Melting of regular and decoupled vortex lattices in BSCCO crystals
The angular dependence of the first-order phase transition (FOT) in the
vortex lattice in BiSrCaCuO crystals was investigated
by a low frequency AC shielding technique (with the AC field ), in
which the static-field component parallel to - () was varied with
the in-plane field held constant. The linear decrease of the
FOT field with increasing ends at a
temperature--dependent critical value of . A new transition,
marked by the abrupt drop of the -plane shielding current, appears at this
point. We draw a new phase diagram with and field
components as coordinates; this features at least two distinct regions in the
vortex solid phase, that are determined by the different interplay between the
pancake vortex-- and Josephson vortex lattice.Comment: 2 pages, 2 figures Paper submitted to the conference proceedings of
M2S-2000 Houston, T
The Ginzburg-Landau theory in application
A numerical approach to Ginzburg-Landau (GL) theory is demonstrated and we
review its applications to several examples of current interest in the research
on superconductivity. This analysis also shows the applicability of the
two-dimensional approach to thin superconductors and the re-defined effective
GL parameter kappa. For two-gap superconductors, the conveniently written GL
equations directly show that the magnetic behavior of the sample depends not
just on the GL parameter of two bands, but also on the ratio of respective
coherence lengths.Comment: To be published in Physica C, VORTEX VI Conference Proceeding
Breakdown by a magnetic field of the superconducting fluctuations in the normal state: A simple phenomenological explanation
We first summarize our recent observations, through magnetization
measurements in different low-Tc superconductors, of a rather sharp
disappearance of the superconducting fluctuations in the normal state when the
magnetic field approaches Hc2(0), the upper critical field extrapolated to
T=0K. We propose that a crude phenomenological description of the observed
effects may be obtained if the quantum limits associated with the uncertainty
principle are introduced in the Gaussian-Ginzburg-Landau description of the
fluctuation-induced magnetization.Comment: LaTeX, 8 pages, including 2 eps figures. Proceedings of SNS'04,
Sitges, Spai
Boson expansion methods applied to a two-level model in the study of multiple giant resonances
We apply boson expansion methods to an extended Lipkin-Meshkov-Glick model
including anharmonicities in analogy with previous microscopic calculations. We
study the effects of different approximations present in these calculations,
among which the truncation of the hamiltonian and of the space, in connection
with the study of the properties of two-phonon and three-phonon states. By
comparing the approximate results on the spectrum with the exact ones we
conclude that the approximations made in the microscopic calculations on
two-phonon states are well justified. We find also that a good agreement with
the exact results for the three-phonon state is obtained by using a bosonic
hamiltonian truncated at the fourth order. This result makes us confident that
such approximation can be used in realistic calculations, thus allowing a
theoretical study of triple excitations of giant resonances.Comment: 12 pages, 2 figures, Latex with epsfig.st
Production of Neutron-rich Heavy Residues and the Freeze-out Temperature in the Fragmentation of Relativistic 238U Projectiles Determined by the Isospin Thermometer
Isotope yields of heavy residues produced in collisions of 238U with lead at
1AGeV show indications for a simultaneous break-up process. From the average
N-over-Z ratio of the final residues up to Z = 70, the average limiting
temperature of the break-up configuration at freeze out was determined to T
approximately 5 MeV using the isospin-thermometer method. Consequences for the
understanding of other phenomena in highly excited nuclear systems are
discussed.Comment: 22 pages, 9 figures, accepted by Nucl. Phys.
From Greenland to Canada in Ten Days: Tracks of Bowhead Whales, Balaena mysticetus, across Baffin Bay
Five bowhead whales (Balaena mysticetus) were instrumented with satellite transmitters in northwestern Disko Bay, West Greenland, in May 2001. Best results were obtained when tags were deployed with a pole rather than a pneumatic gun. At least three of the tagged whales remained in the northwestern part of the bay for one to two weeks after tagging. A male and a female whale moved from Disko Bay to northern Canada. They left Disko Bay 11 days apart and took different routes across Baffin Bay to the southern part of the North Water polynya, just east of the entrance to Lancaster Sound. The whales crossed the central part of Baffin Bay relatively rapidly (travel time of 9-10 days, 3.1 and 4.5 km/h). Dive behaviour of one whale was monitored and showed changes in dive depths, dive rates, and surfacing times in different localities, indicating behavioural changes probably related to feeding. The whales were presumably feeding in both Disko Bay in May and in the southern part of the North Water (southeast of Bylot Island) in June. This study confirms whalers' observations that bowhead whales move between West Greenland and the east coast of Baffin Island.En mai 2001, cinq baleines boréales (Balaena mysticetus) ont été équipées d'émetteurs spatiaux dans le nord-ouest de la baie de Disko (Groenland occidental). Les meilleurs résultats ont été obtenus lorsque les marqueurs ont été apposés avec une perche plutôt qu'avec un fusil à air comprimé. Au moins trois des baleines marquées sont restées dans la partie nord-ouest de la baie pendant une à deux semaines après le marquage. Deux individus, un mâle et une femelle, se sont déplacés de la baie de Disko au nord du Canada. Ils ont quitté la baie à 11 jours d'écart et ont emprunté des trajets différents pour traverser la baie de Baffin et rejoindre la partie méridionale de la polynie de l'Eau du Nord, située juste à l'est de l'entrée du détroit de Lancaster. Les baleines ont traversé la partie centrale de la baie de Baffin assez vite (en 9 et 10 jours, soit 3,1 et 4,5 km/h). On a suivi le comportement de plongée d'une baleine, qui a montré des changements dans la profondeur des plongées, leur fréquence et le temps en surface à divers endroits, révélant des modifications du comportement probablement associées au nourrissage. On suppose que les baleines s'alimentaient dans la baie de Disko en mai aussi bien que dans la partie méridionale de l'Eau du Nord (au sud-est de l'île Bylot) en juin. Cette étude confirme les observations des baleiniers à l'effet que les baleines boréales se déplacent entre l'ouest du Groenland et la côte est de l'île de Baffin
Surface passivation of silicon solar cells using industrially relevant Al2O3 deposition techniques
The next generation of industrial silicon solar cells aims at efficiencies of 20% and above. To achieve this goal using ever-thinner silicon wafers, a highly effective surface passivation of the cell front and rear is required. In the past, finding a suitable dielectric layer providing a high-quality rear passivation has been a major challenge. Aluminium oxide (Al2O3) grown by atomic layer deposition (ALD) has only recently turned out to be a nearly perfect candidate for such a dielectric. However, conventional ALD is limited to deposition rates well below 2nm/min, which is incompatible with industrial solar cell production. This paper assesses the passivation quality provided by three different industrially relevant techniques for the deposition of Al2O3 layers, namely high-rate spatial ALD, plasma-enhanced chemical vapour deposition (PECVD) and reactive sputtering
Electromagnetic transitions of the helium atom in superstrong magnetic fields
We investigate the electromagnetic transition probabilities for the helium
atom embedded in a superstrong magnetic field taking into account the finite
nuclear mass. We address the regime \gamma=100-10000 a.u. studying several
excited states for each symmetry, i.e. for the magnetic quantum numbers
0,-1,-2,-3, positive and negative z parity and singlet and triplet symmetry.
The oscillator strengths as a function of the magnetic field, and in particular
the influence of the finite nuclear mass on the oscillator strengths are shown
and analyzed.Comment: 10 pages, 8 figure
Phase Transitions in Isolated Vortex Chains
In very anisotropic layered superconductors (e.g. BiSrCaCuO)
a tilted magnetic field can penetrate as two co-existing lattices of vortices
parallel and perpendicular to the layers. At low out-of-plane fields the
perpendicular vortices form a set of isolated vortex chains, which have
recently been observed in detail with scanning Hall-probe measurements. We
present calculations that show a very delicate stability of this isolated-chain
state. As the vortex density increases along the chain there is a first-order
transition to a buckled chain, and then the chain will expel vortices in a
continuous transition to a composite-chain state. At low densities there is an
instability towards clustering, due to a long-range attraction between the
vortices on the chain, and at very low densities it becomes energetically
favorable to form a tilted chain, which may explain the sudden disappearance of
vortices along the chains seen in recent experiments.Comment: 9 pages, 10 figure
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