2,050 research outputs found
Glauber - Gribov approach for DIS on nuclei in N=4 SYM
In this paper the Glauber-Gribov approach for deep-inelastic scattering (DIS)
with nuclei is developed in N=4 SYM. It is shown that the amplitude displays
the same general properties, such as geometrical scaling, as is the case in the
high density QCD approach. We found that the quantum effects leading to the
graviton reggeization, give rise to an imaginary part of the nucleon amplitude,
which makes the DIS in N=4 SYM almost identical to the one expected in high
density QCD. We concluded that the impact parameter dependence of the nucleon
amplitude is very essential for N=4 SYM, and the entire kinematic region can be
divided into three regions which are discussed in the paper. We revisited the
dipole description for DIS and proposed a new renormalized Lagrangian for the
shock wave formalism which reproduces the Glauber-Gribov approach in a certain
kinematic region. However the saturation momentum turns out to be independent
of energy, as it has been discussed by Albacete, Kovchegov and Taliotis. We
discuss the physical meaning of such a saturation momentum and argue
that one can consider only within the shock wave approximation.Comment: 40pp.,9 figures in eps file
Superconductors with Magnetic Impurities: Instantons and Sub-gap States
When subject to a weak magnetic impurity potential, the order parameter and
quasi-particle energy gap of a bulk singlet superconductor are suppressed.
According to the conventional mean-field theory of Abrikosov and Gor'kov, the
integrity of the energy gap is maintained up to a critical concentration of
magnetic impurities. In this paper, a field theoretic approach is developed to
critically analyze the validity of the mean field theory. Using the
supersymmetry technique we find a spatially homogeneous saddle-point that
reproduces the Abrikosov-Gor'kov theory, and identify instanton contributions
to the density of states that render the quasi-particle energy gap soft at any
non-zero magnetic impurity concentration. The sub-gap states are associated
with supersymmetry broken field configurations of the action. An analysis of
fluctuations around these configurations shows how the underlying supersymmetry
of the action is restored by zero modes. An estimate of the density of states
is given for all dimensionalities. To illustrate the universality of the
present scheme we apply the same method to study `gap fluctuations' in a normal
quantum dot coupled to a superconducting terminal. Using the same instanton
approach, we recover the universal result recently proposed by Vavilov et al.
Finally, we emphasize the universality of the present scheme for the
description of gap fluctuations in d-dimensional superconducting/normal
structures.Comment: 18 pages, 9 eps figure
Calorimetric readout of a superconducting proximity-effect thermometer
A proximity-effect thermometer measures the temperature dependent critical
supercurrent in a long superconductor - normal metal - superconductor (SNS)
Josephson junction. Typically, the transition from the superconducting to the
normal state is detected by monitoring the appearance of a voltage across the
junction. We describe a new approach to detect the transition based on the
temperature increase in the resistive state due to Joule heating. Our method
increases the sensitivity and is especially applicable for temperatures below
about 300 mK.Comment: 10 pages, 5 figures. To appear in the proceedings of the Conference
on Micro- and Nanocryogenics (LT25 satellite) organized in Espoo, Finland
(2008
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
Near-optimal mean value estimates for multidimensional Weyl sums
We obtain sharp estimates for multidimensional generalisations of
Vinogradov's mean value theorem for arbitrary translation-dilation invariant
systems, achieving constraints on the number of variables approaching those
conjectured to be the best possible. Several applications of our bounds are
discussed
An NMR-based nanostructure switch for quantum logic
We propose a nanostructure switch based on nuclear magnetic resonance (NMR)
which offers reliable quantum gate operation, an essential ingredient for
building a quantum computer. The nuclear resonance is controlled by the magic
number transitions of a few-electron quantum dot in an external magnetic field.Comment: 4 pages, 2 separate PostScript figures. Minor changes included. One
reference adde
Finite element simulation of three-dimensional free-surface flow problems
An adaptive finite element algorithm is described for the stable solution of three-dimensional free-surface-flow problems based primarily on the use of node movement. The algorithm also includes a discrete remeshing procedure which enhances its accuracy and robustness. The spatial discretisation allows an isoparametric piecewise-quadratic approximation of the domain geometry for accurate resolution of the curved free surface.
The technique is illustrated through an implementation for surface-tension-dominated viscous flows modelled in terms of the Stokes equations with suitable boundary conditions on the deforming free surface. Two three-dimensional test problems are used to demonstrate the performance of the method: a liquid bridge problem and the formation of a fluid droplet
Prolactin
During an oral glucose tolerance test (OGTT) glucose and insulin levels were measured in 26 patients with prolactin-producing pituitary tumours without growth hormone excess. Basal glucose and insulin levels did not differ from the values of an age-matched control group. After glucose load the hyperprolactinaemic patients showed a decrease in glucose tolerance and a hyperinsulinaemia. Bromocriptine (CB 154), which suppressed PRL, improved glucose tolerance and decreased insulin towards normal in a second OGTT. — Human PRL or CB 154 had no significant influence on insulin release due to glucose in the perfused rat pancreas. — These findings suggest a diabetogenic effect of PRL. CB 154 might be a useful drug in improving glucose utilization in hormone-active pituitary tumours
Spin-polarized Tunneling in Hybrid Metal-Semiconductor Magnetic Tunnel Junctions
We demonstrate efficient spin-polarized tunneling between a ferromagnetic
metal and a ferromagnetic semiconductor with highly mismatched conductivities.
This is indicated by a large tunneling magnetoresistance (up to 30%) at low
temperatures in epitaxial magnetic tunnel junctions composed of a ferromagnetic
metal (MnAs) and a ferromagnetic semiconductor (GaMnAs) separated by a
nonmagnetic semiconductor (AlAs). Analysis of the current-voltage
characteristics yields detailed information about the asymmetric tunnel
barrier. The low temperature conductance-voltage characteristics show a zero
bias anomaly and a V^1/2 dependence of the conductance, indicating a
correlation gap in the density of states of GaMnAs. These experiments suggest
that MnAs/AlAs heterostructures offer well characterized tunnel junctions for
high efficiency spin injection into GaAs.Comment: 14 pages, submitted to Phys. Rev.
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