1,215 research outputs found
Fast generation of quantum dynamics data using a GPU implementation of the time-dependent Schrodinger equation
Efficient methods for generating samples of wave packet trajectories are
needed to build machine learning models for quantum dynamics. However,
simulating such data by direct integration of the time-dependent Schrodinger
equation can be demanding, especially when multiple spatial dimensions and
realistic potentials are involved. In this paper, we present a graphics
processor unit (GPU) implementation of the finite-difference time-domain (FDTD)
method for simulating the time-dependent Schrodinger equation. The performance
of our implementation is characterized in detail by simulating electron
diffraction from realistic material surfaces. On our hardware, our GPU
implementation achieves a roughly 350 times performance increase compared to a
serial CPU implementation. The suitability of our implementation for generating
samples of quantum dynamics data is also demonstrated by performing electron
diffraction simulations from multiple configurations of an organic thin film.
By studying how the structure of the data converges with sample sizes, we
acquire insights into the sample sizes required for machine learning purposes.Comment: 20 pages, 7 figures, 1 table. In preparation for submission to a
journa
Evaluation of incipient cavitation erosion for pipe wall at downstream of an orifice
Cavitation induced vibration and the consequent erosion of pipes are the potential damaging factors in the piping systems. In order to prevent such trouble, it is preferable to develop a detection method for cavitation occurrence. Especially, in power plants, it is necessary to detect cavitation from the outside of the piping during operation. In this paper, in order to evaluate incipience of cavitation erosion, we carried out cavitation erosion experiments using aluminium specimens and we measured impulsive force induced by cavitation bubbles collapse using impact force detectors. In the cavitation erosion experiments, the incipient cavitation numbers, where cavitation erosion pits occured, were 0.8 at 50mm and 75mm downstream from the orifice and 0.7 at 100mm downstream. At those cavitation numbers, the states of cavitation was in a developed state or nearly so. In the measurements of impulsive force, the cavitation number, where impulsive force began to increase, was almost with the same as cavitation numbers at the occurrence of erosion pits.http://deepblue.lib.umich.edu/bitstream/2027.42/84261/1/CAV2009-final64.pd
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
Measuring Cosmic Defect Correlations in Liquid Crystals
From the theory of topological defect formation proposed for the early
universe, the so called Kibble mechanism, it follows that the density
correlation functions of defects and anti-defects in a given system should be
completely determined in terms of a single length scale , the relevant
domain size. Thus, when lengths are expressed in units of , these
distributions should show universal behavior, depending only on the symmetry of
the order parameter, and space dimensions. We have verified this prediction by
analyzing the distributions of defects/anti-defects formed in the
isotropic-nematic phase transition in a thin layer of nematic liquid crystals.
Our experimental results confirm this prediction and are in reasonable
agreement with the results of numerical simulations.Comment: 15 pages, 4 figures, minor changes, few new references adde
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
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
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