1,420 research outputs found
Vortex matter in mesoscopic superconductors
Superconducting mesoscopic devices in magnetic fields present novel
properties which can only be accounted for by both the quantum confinement of
the Cooper pairs and by the interaction between the magnetic-field-induced
vortices. Sub-micrometer disks, much the same as their semiconductor
counterparts known as quantum dots, are being subject to experimental
investigation by measuring their conducting properties and, more recently,
their magnetization by using state-of-the-art ballistic Hall magnetometry. In
this work I review the main results obtained in these two types of experiments
as well as the current theoretical developments which are contributing to our
understanding of the superconducting condensate in these systems.Comment: 16 pages, 4 figures. Invited presentation at the 13th International
Conference on High Magnetic Fields in Semiconductor Physics to appear in
Physica
Glucocorticoids, vitamin D and bone : a pathophysiologic and therapeutic study of glucocorticoid-induced bone disease
Mooser's report ( 1921) of a patient with osteoporosis and obesity is one of the first
descriptions of endogenous hypercortisolism. Later Cushing (1932) described the
syndrome as a clinical entity and Albright et al. (1941) reported 9 patients who at
autopsy all appeared to have sustained a severe degree of cortical and trabecular
bone loss. In 1949 glucocorticoids (GC) became available as therapeutic agents. in
addition to their favourable antiinflammatory action deleterious side effects (e.g.
on bone mass) have become apparent (Kjellstrand, 1975).
A diminished bone mass, measured as trabecular bone volume of iliac crest
biopsies (Birkenhager et al., 1967) or by total body Ca with neutron activation
analysis (Aloia et al., 1974), is a typical hallmark in patients with endogenous
hypercortisolism. The impact of exogenous GC excess on bone mass is more
difficult to evaluate. In the quantification of the amount of bone in such patients
by several techniques one has to take into account not only the physiological age
related bone loss (see Chapter II), but also the underlying disease for which GC are
prescribed. This is illustrated by Stresemann & Krokowski ( 1967) who found signs
of a decreased bone mineral content on X-rays of the vertebral column (using a
quantitative measurement technique) in 32% of patients treated with varying
doses of GC for chronic obstructive lung disease, but similar signs were observed
in an equal percentage of patients who never had used steroids. However, Adinof
& Hollister (1983) described a significant loss of trabecular bone mass at the
metaphysis of the radius with single photonabsorptiometry only in asthmatic
subjects on long-term daily steroids. Measurement of total body Ca with neutron
activation analysis showed lower values in patients with rheumatoid arthritis
treated with non steroidal antiinflammatory drugs than controls, but even lower
values in rheumatic patients treated with steroids (Reid et a!., 1982). Similar
findings were reported by Hahn et al. (J 973) with photonabsortiometry of the
metaphyseal mass of the forearm. The decreased mineral content was correlated
with the duration of GC therap
Cerium anomalies in lateritic profiles
L'étude minéralogique et géochimique des terres rares permet de définir le comportement du cérium dans 4 profils latéritiques du Camerou
An augmented Lagrangian decomposition method for quasi-separable problems in MDO
Several decomposition methods have been proposed for the distributed optimal design of quasi-separable problems encountered in Multidisciplinary Design Optimization (MDO). Some of these methods are known to have numerical convergence difficulties that can be explained theoretically. We propose a new decomposition algorithm for quasi-separable MDO problems. In particular, we propose a decomposed problem formulation based on the augmented Lagrangian penalty function and the block coordinate descent algorithm. The proposed solution algorithm consists of inner and outer loops. In the outer loop, the augmented Lagrangian penalty parameters are updated. In the inner loop, our method alternates between solving an optimization master problem, and solving disciplinary optimization subproblems. The coordinating master problem can be solved analytically; the disciplinary subproblems can be solved using commonly available gradient-based optimization algorithms. The augmented Lagrangian decomposition method is derived such that existing proofs can be used to show convergence of the decomposition algorithm to KKT points of the original problem under mild assumptions. We investigate the numerical performance of the proposed method on two example problems. I
From GHz to mHz: A Multiwavelength Study of the Acoustically Active 14 August 2004 M7.4 Solar Flare
We carried out an electromagnetic acoustic analysis of the solar flare of 14
August 2004 in active region AR10656 from the radio to the hard X-ray spectrum.
The flare was a GOES soft X-ray class M7.4 and produced a detectable sun quake,
confirming earlier inferences that relatively low-energy flares may be able to
generate sun quakes. We introduce the hypothesis that the seismicity of the
active region is closely related to the heights of coronal magnetic loops that
conduct high-energy particles from the flare. In the case of relatively short
magnetic loops, chromospheric evaporation populates the loop interior with
ionized gas relatively rapidly, expediting the scattering of remaining trapped
high-energy electrons into the magnetic loss cone and their rapid precipitation
into the chromosphere. This increases both the intensity and suddenness of the
chromospheric heating, satisfying the basic conditions for an acoustic emission
that penetrates into the solar interior.Comment: Accepted in Solar Physic
Strange particle production at RHIC in a single-freeze-out model
Strange particle ratios and pT-spectra are calculated in a thermal model with
single freeze-out, previously used successfully to describe non-strange
particle production at RHIC. The model and the recently released data for phi,
Lambda, anti-Lambda, and K*(892) are in very satisfactory agreement, showing
that the thermal approach can be used to describe the strangeness production at
RHIC.Comment: We have added the comparison of the model predictions to the newly
released Lambda and K*(892) pT-spectra from STA
Properties of Flares-Generated Seismic Waves on the Sun
The solar seismic waves excited by solar flares (``sunquakes'') are observed
as circular expanding waves on the Sun's surface. The first sunquake was
observed for a flare of July 9, 1996, from the Solar and Heliospheric
Observatory (SOHO) space mission. However, when the new solar cycle started in
1997, the observations of solar flares from SOHO did not show the seismic
waves, similar to the 1996 event, even for large X-class flares during the
solar maximum in 2000-2002. The first evidence of the seismic flare signal in
this solar cycle was obtained for the 2003 ``Halloween'' events, through
acoustic ``egression power'' by Donea and Lindsey. After these several other
strong sunquakes have been observed. Here, I present a detailed analysis of the
basic properties of the helioseismic waves generated by three solar flares in
2003-2005. For two of these flares, X17 flare of October 28, 2003, and X1.2
flare of January 15, 2005, the helioseismology observations are compared with
simultaneous observations of flare X-ray fluxes measured from the RHESSI
satellite. These observations show a close association between the flare
seismic waves and the hard X-ray source, indicating that high-energy electrons
accelerated during the flare impulsive phase produced strong compression waves
in the photosphere, causing the sunquake. The results also reveal new physical
properties such as strong anisotropy of the seismic waves, the amplitude of
which varies significantly with the direction of propagation. The waves travel
through surrounding sunspot regions to large distances, up to 120 Mm, without
significant decay. These observations open new perspectives for helioseismic
diagnostics of flaring active regions on the Sun and for understanding the
mechanisms of the energy release and transport in solar flares.Comment: 12 pages, 4 figures, submitted to Ap
Type IIB Flux Vacua from M-theory via F-theory
We study in detail some aspects of duality between type IIB and M-theory. We
focus on the duality between type IIB string theory on K3 x T^2/Z_2 orientifold
and M-theory on K3 x K3, in the F-theory limit. We give the explicit map
between the fields and in particular between the moduli of compactification,
studying their behavior under the F-theory limit. Turning on fluxes generates a
potential for the moduli both in type IIB and in M-theory. We verify that the
type IIB analysis gives the same results of the F-theory analysis. In
particular, we check that the two potentials match.Comment: 24 pages; reference correcte
Asymptotes in SU(2) Recoupling Theory: Wigner Matrices, Symbols, and Character Localization
In this paper we employ a novel technique combining the Euler Maclaurin
formula with the saddle point approximation method to obtain the asymptotic
behavior (in the limit of large representation index ) of generic Wigner
matrix elements . We use this result to derive asymptotic
formulae for the character of an SU(2) group element and for
Wigner's symbol. Surprisingly, given that we perform five successive
layers of approximations, the asymptotic formula we obtain for is
in fact exact. This result provides a non trivial example of a
Duistermaat-Heckman like localization property for discrete sums.Comment: 36 pages, 3 figure
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