134,426 research outputs found
Nonuniversal Effects in the Homogeneous Bose Gas
Effective field theory predicts that the leading nonuniversal effects in the
homogeneous Bose gas arise from the effective range for S-wave scattering and
from an effective three-body contact interaction. We calculate the leading
nonuniversal contributions to the energy density and condensate fraction and
compare the predictions with results from diffusion Monte Carlo calculations by
Giorgini, Boronat, and Casulleras. We give a crude determination of the
strength of the three-body contact interaction for various model potentials.
Accurate determinations could be obtained from diffusion Monte Carlo
calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te
Calibration and Irradiation Study of the BGO Background Monitor for the BEAST II Experiment
Beam commissioning of the SuperKEKB collider began in 2016. The Beam Exorcism
for A STable experiment II (BEAST II) project is particularly designed to
measure the beam backgrounds around the interaction point of the SuperKEKB
collider for the Belle II experiment. We develop a system using bismuth
germanium oxide (BGO) crystals with optical fibers connecting to a multianode
photomultiplier tube (MAPMT) and a field-programmable gate array (FPGA)
embedded readout board for monitoring the real-time beam backgrounds in BEAST
II. The overall radiation sensitivity of this system is estimated to be
Gy/ADU (analog-to-digital unit) with the standard
10 m fibers for transmission and the MAPMT operating at 700 V. Our -ray
irradiation study of the BGO system shows that the exposure of BGO crystals to
Co -ray doses of 1 krad has led to immediate light output
reductions of 25--40%, and the light outputs further drop by 30--45% after the
crystals receive doses of 2--4 krad. Our findings agree with those of the
previous studies on the radiation hard (RH) BGO crystals grown by the low
thermal gradient Czochralski (LTG Cz) technology. The absolute dose from the
BGO system is also consistent with the simulation, and is estimated to be about
1.18 times the equivalent dose. These results prove that the BGO system is able
to monitor the background dose rate in real time under extreme high radiation
conditions. This study concludes that the BGO system is reliable for the beam
background study in BEAST II
Post-Oligarchic Evolution of Protoplanetary Embryos and the Stability of Planetary Systems
We investigate the orbit-crossing time (T_c) of protoplanet systems both with
and without a gas-disk background. The protoplanets are initially with equal
masses and separation (EMS systems) scaled by their mutual Hill's radii. In a
gas-free environment, we find log (T_c/yr) = A+B \log (k_0/2.3). Through a
simple analytical approach, we demonstrate that the evolution of the velocity
dispersion in an EMS system follows a random walk. The stochastic nature of
random-walk diffusion leads to (i) an increasing average eccentricity ~
t^1/2, where t is the time; (ii) Rayleigh-distributed eccentricities
(P(e,t)=e/\sigma^2 \exp(-e^2/(2\sigma^2)) of the protoplanets; (iii) a
power-law dependence of T_c on planetary separation. As evidence for the
chaotic diffusion, the observed eccentricities of known extra solar planets can
be approximated by a Rayleigh distribution. We evaluate the isolation masses of
the embryos, which determine the probability of gas giant formation, as a
function of the dust and gas surface densities.Comment: 15 pages, 13 figures (2 color ones), accepted for publication in Ap
Observation of strong electron dephasing in disordered CuGeAu thin films
We report the observation of strong electron dephasing in a series of
disordered CuGeAu thin films. A very short electron dephasing
time possessing very weak temperature dependence around 6 K, followed by an
upturn with further decrease in temperature below 4 K, is found. The upturn is
progressively more pronounced in more disordered samples. Moreover, a ln
dependent, but high-magnetic-field-insensitive, resistance rise persisting from
above 10 K down to 30 mK is observed in the films. These results suggest a
nonmagnetic dephasing process which is stronger than any known mechanism and
may originate from the coupling of conduction electrons to dynamic defects.Comment: to appear in Phys. Rev. Let
Profile control charts based on nonparametric -1 regression methods
Classical statistical process control often relies on univariate
characteristics. In many contemporary applications, however, the quality of
products must be characterized by some functional relation between a response
variable and its explanatory variables. Monitoring such functional profiles has
been a rapidly growing field due to increasing demands. This paper develops a
novel nonparametric -1 location-scale model to screen the shapes of
profiles. The model is built on three basic elements: location shifts, local
shape distortions, and overall shape deviations, which are quantified by three
individual metrics. The proposed approach is applied to the previously analyzed
vertical density profile data, leading to some interesting insights.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS501 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Uniform fractional factorial designs
The minimum aberration criterion has been frequently used in the selection of
fractional factorial designs with nominal factors. For designs with
quantitative factors, however, level permutation of factors could alter their
geometrical structures and statistical properties. In this paper uniformity is
used to further distinguish fractional factorial designs, besides the minimum
aberration criterion. We show that minimum aberration designs have low
discrepancies on average. An efficient method for constructing uniform minimum
aberration designs is proposed and optimal designs with 27 and 81 runs are
obtained for practical use. These designs have good uniformity and are
effective for studying quantitative factors.Comment: Published in at http://dx.doi.org/10.1214/12-AOS987 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
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