706 research outputs found
Magnetic moment of welded HTS samples: dependence on the current flowing through the welds
We present a method to calculate the magnetic moments of the high-temperature
superconducting (HTS) samples which consist of a few welded HTS parts. The
approach is generalized for the samples of various geometrical shapes and an
arbitrary number of welds. The obtained relations between the sample moment and
the density of critical current, which flows through the welds, allow to use
the magnetization loops for a quantitative characterization of the weld quality
in a wide range of temperatures and/or magnetic fields.Comment: RevTeX4, 4 pages, 2 figures. Submitted to Supercond. Sci. Techno
Selective excitation of metastable atomic states by femto- and attosecond laser pulses
The possibility of achieving highly selective excitation of low metastable
states of hydrogen and helium atoms by using short laser pulses with reasonable
parameters is demonstrated theoretically. Interactions of atoms with the laser
field are studied by solving the close-coupling equations without
discretization. The parameters of laser pulses are calculated using different
kinds of optimization procedures. For the excitation durations of hundreds of
femtoseconds direct optimization of the parameters of one and two laser pulses
with Gaussian envelopes is used to introduce a number of simple schemes of
selective excitation. To treat the case of shorter excitation durations,
optimal control theory is used and the calculated optimal fields are
approximated by sequences of pulses with reasonable shapes. A new way to
achieve selective excitation of metastable atomic states by using sequences of
attosecond pulses is introduced.Comment: To be published in Phys. Rev. A, 10 pages, 3 figure
Fluctuations and defect-defect correlations in the ordering kinetics of the O(2) model
The theory of phase ordering kinetics for the O(2) model using the gaussian
auxiliary field approach is reexamined from two points of view. The effects of
fluctuations about the ordering field are included and we organize the theory
such that the auxiliary field correlation function is analytic in the
short-scaled distance (x) expansion. These two points are connected and we find
in the refined theory that the divergence at the origin in the defect-defect
correlation function obtained in the original theory is removed.
Modifications to the order-parameter autocorrelation exponent are
computed.Comment: 29 pages, REVTeX, to be published in Phys. Rev. E. Minor
grammatical/syntax changes from the origina
Molecular Clouds associated with the Type Ia SNR N103B in the Large Magellanic Cloud
N103B is a Type Ia supernova remnant (SNR) in the Large Magellanic Cloud
(LMC). We carried out new CO( = 3-2) and CO( = 1-0)
observations using ASTE and ALMA. We have confirmed the existence of a giant
molecular cloud (GMC) at 245 km s towards the
southeast of the SNR using ASTE CO( = 3-2) data at an angular
resolution of 25 (6 pc in the LMC). Using the ALMA CO(
= 1-0) data, we have spatially resolved CO clouds along the southeastern edge
of the SNR with an angular resolution of 1.8 (0.4 pc in the
LMC). The molecular clouds show an expanding gas motion in the
position-velocity diagram with an expansion velocity of km s.
The spatial extent of the expanding shell is roughly similar to that of the
SNR. We also find tiny molecular clumps in the directions of optical nebula
knots. We present a possible scenario that N103B exploded in the wind-bubble
formed by the accretion winds from the progenitor system, and is now
interacting with the dense gas wall. This is consistent with a
single-degenerate scenario.Comment: 12 pages, 1 table, 8 figures, accepted for publication in The
Astrophysical Journal (ApJ
ALMA CO Observations of Supernova Remnant N63A in the Large Magellanic Cloud: Discovery of Dense Molecular Clouds Embedded within Shock-Ionized and Photoionized Nebulae
We carried out new CO( = 1-0, 3-2) observations of a N63A supernova
remnant (SNR) from the LMC using ALMA and ASTE. We find three giant molecular
clouds toward the northeast, east, and near the center of the SNR. Using the
ALMA data, we spatially resolved clumpy molecular clouds embedded within the
optical nebulae in both the shock-ionized and photoionized lobes discovered by
previous H and [S II] observations. The total mass of the molecular
clouds is for the shock-ionized region and
for the photoionized region. Spatially resolved X-ray spectroscopy
reveals that the absorbing column densities toward the molecular clouds are
- cm, which are - times less
than the averaged interstellar proton column densities for each region. This
means that the X-rays are produced not only behind the molecular clouds, but
also in front of them. We conclude that the dense molecular clouds have been
completely engulfed by the shock waves, but have still survived erosion owing
to their high-density and short interacting time. The X-ray spectrum toward the
gas clumps is well explained by an absorbed power-law or high-temperature
plasma models in addition to the thermal plasma components, implying that the
shock-cloud interaction is efficiently working for both the cases through the
shock ionization and magnetic field amplification. If the hadronic gamma-ray is
dominant in the GeV band, the total energy of cosmic-ray protons is calculated
to be - erg with the estimated ISM proton density
of cm, containing both the shock-ionized gas and
neutral atomic hydrogen.Comment: 18 pages, 4 tables, 8 figures, accepted for publication in The
Astrophysical Journal (ApJ
Vortex annihilation in the ordering kinetics of the O(2) model
The vortex-vortex and vortex-antivortex correlation functions are determined
for the two-dimensional O(2) model undergoing phase ordering. We find
reasonably good agreement with simulation results for the vortex-vortex
correlation function where there is a short-scaled distance depletion zone due
to the repulsion of like-signed vortices. The vortex-antivortex correlation
function agrees well with simulation results for intermediate and long-scaled
distances. At short-scaled distances the simulations show a depletion zone not
seen in the theory.Comment: 28 pages, REVTeX, submitted to Phys. Rev.
Ohta-Jasnow-Kawasaki Approximation for Nonconserved Coarsening under Shear
We analytically study coarsening dynamics in a system with nonconserved
scalar order parameter, when a uniform time-independent shear flow is present.
We use an anisotropic version of the Ohta-Jasnow-Kawasaki approximation to
calculate the growth exponents in two and three dimensions: for d=3 the
exponents we find are the same as expected on the basis of simple scaling
arguments, that is 3/2 in the flow direction and 1/2 in all the other
directions, while for d=2 we find an unusual behavior, in that the domains
experience an unlimited narrowing for very large times and a nontrivial
dynamical scaling appears. In addition, we consider the case where an
oscillatory shear is applied to a two-dimensional system, finding in this case
a standard t^1/2 growth, modulated by periodic oscillations. We support our
two-dimensional results by means of numerical simulations and we propose to
test our predictions by experiments on twisted nematic liquid crystals.Comment: 25 RevTeX pages, 7 EPS figures. To be published in Phys. Rev.
Atrial natriuretic peptide and three-dimensional echocardiography after transcatheter closure of atrial septal defect
<p>Abstract</p> <p>Background</p> <p>Atrial septal defect (ASD) accounts for 10% of all congenital heart lesions and represent the third most congenital cardiac defect seen in adults. Atrial natriuretic peptide (ANP) is an important regulator of the sodium and volume homeostasis. This study was designed to investigate the changes in plasma ANP concentrations and three-dimensional echocardiography (3DE) measurements of cardiac volume in patients with ASD during transcatheter closure of defect.</p> <p>Methods</p> <p>Plasma ANP concentrations and transthoracic 3DE measurements of right ventricular volume were performed in 46 patients with ASD before closure, and at 3 days after closure. 22 healthy subjects matched for age, sex served as control subjects.</p> <p>Results</p> <p>The 46 patients (20 men, 26 women; mean age 26.32 ± 13.28, range 6 to 63 years) were diagnosed to secundum ASD (the stretched diameters of ASD were from 9~36(25.34 ± 7.80 mm), and had been successfully placed Amplatzer septal occluder (the sizes of occluder were from 11 to 40 mm). The results showed that compared with control subjects, plasma ANP concentrations were elevated in patients with ASD. Plasma ANP concentrations positively correlated significantly with pulmonary artery pressure (PAP) (r = 0.74, <it>p </it>< 0.05) and 3DE measurements of cardiac volumes (right ventricular end-diastolic (r = 0.50, <it>p </it>< 0.05) and end-systolic volume (r = 0.50, <it>p </it>< 0.05) and negatively correlated with RVEF (r = -0.38, <it>p </it>< 0.05). Transthoracic 3DE measurements of right ventricular volume and plasma ANP concentrations decreased significantly at 3 days after closure (<it>p </it>< 0.05) compared with it before closure.</p> <p>Conclusion</p> <p>Plasma ANP concentrations were markedly elevated in patients with pulmonary arterial hypertension and right ventricular volume overload and decreased significantly after closure of ASD. This study suggested that ANP may help to identify patients with ASD complicated by pulmonary arterial hypertension and right ventricular volume overload that demanded early intervention and may become effective marker for evaluating changes in cardiac load after transcatheter ASD closure.</p
Dynamical Scaling: the Two-Dimensional XY Model Following a Quench
To sensitively test scaling in the 2D XY model quenched from
high-temperatures into the ordered phase, we study the difference between
measured correlations and the (scaling) results of a Gaussian-closure
approximation. We also directly compare various length-scales. All of our
results are consistent with dynamical scaling and an asymptotic growth law , though with a time-scale that depends on the
length-scale in question. We then reconstruct correlations from the
minimal-energy configuration consistent with the vortex positions, and find
them significantly different from the ``natural'' correlations --- though both
scale with . This indicates that both topological (vortex) and
non-topological (``spin-wave'') contributions to correlations are relevant
arbitrarily late after the quench. We also present a consistent definition of
dynamical scaling applicable more generally, and emphasize how to generalize
our approach to other quenched systems where dynamical scaling is in question.
Our approach directly applies to planar liquid-crystal systems.Comment: 10 pages, 10 figure
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