3,954 research outputs found
Reformulation of the Stochastic Potential Switching Algorithm and a Generalized Fourtuin-Kasteleyn Representation
A new formulation of the stochastic potential switching algorithm is
presented. This reformulation naturally leads us to a generalized
Fourtuin-Kasteleyn representation of the partition function Z. A formula for
internal energy E and that of heat capacity C are derived from derivatives of
the partition function. We also derive a formula for the exchange probability
in the replica exchange Monte Carlo method. By combining the formulae with the
Stochastic Cutoff method, we can greatly reduce the computational time to
perform internal energy and heat capacity measurements and the replica exchange
Monte Carlo method in long-range interacting systems. Numerical simulations in
three dimensional magnetic dipolar systems show the validity and efficiency of
the method.Comment: 11 pages, 6 figures, to appear in PR
Continuous loading of S calcium atoms into an optical dipole trap
We demonstrate an efficient scheme for continuous trap loading based upon
spatially selective optical pumping. We discuss the case of S
calcium atoms in an optical dipole trap (ODT), however, similar strategies
should be applicable to a wide range of atomic species. Our starting point is a
reservoir of moderately cold (K) metastable
P-atoms prepared by means of a magneto-optic trap (triplet-MOT). A
focused 532 nm laser beam produces a strongly elongated optical potential for
S-atoms with up to 350 K well depth. A weak focused laser beam
at 430 nm, carefully superimposed upon the ODT beam, selectively pumps the
P-atoms inside the capture volume to the singlet state, where they
are confined by the ODT. The triplet-MOT perpetually refills the capture volume
with P-atoms thus providing a continuous stream of cold atoms into
the ODT at a rate of s. Limited by evaporation loss, in 200 ms we
typically load atoms with an initial radial temperature of 85
K. After terminating the loading we observe evaporation during 50 ms
leaving us with atoms at radial temperatures close to 40 K and a
peak phase space density of . We point out that a
comparable scheme could be employed to load a dipole trap with
P-atoms.Comment: 4 pages, 4 figure
Liveness-Based Garbage Collection for Lazy Languages
We consider the problem of reducing the memory required to run lazy
first-order functional programs. Our approach is to analyze programs for
liveness of heap-allocated data. The result of the analysis is used to preserve
only live data---a subset of reachable data---during garbage collection. The
result is an increase in the garbage reclaimed and a reduction in the peak
memory requirement of programs. While this technique has already been shown to
yield benefits for eager first-order languages, the lack of a statically
determinable execution order and the presence of closures pose new challenges
for lazy languages. These require changes both in the liveness analysis itself
and in the design of the garbage collector.
To show the effectiveness of our method, we implemented a copying collector
that uses the results of the liveness analysis to preserve live objects, both
evaluated (i.e., in WHNF) and closures. Our experiments confirm that for
programs running with a liveness-based garbage collector, there is a
significant decrease in peak memory requirements. In addition, a sizable
reduction in the number of collections ensures that in spite of using a more
complex garbage collector, the execution times of programs running with
liveness and reachability-based collectors remain comparable
Immobilized photocatalyst on stainless steel woven meshes assuring efficient light distribution in a solar reactor
An immobilized TiO<sub>2</sub> photocatalyst with a high specific surface area was
prepared on stainless steel woven meshes in order to be used packed in layers
for water purification. Immobilization of such a complex shape needs a
special coating technique. For this purpose, dip coating and electrophoretic
deposition (EPD) techniques were used. The EPD technique gave the TiO<sub>2</sub>
coating films a better homogeneity and adhesion, fewer cracks, and a higher
<sup>·</sup>OH formation than the dip coating technique. The woven mesh
structure packed in layers guaranteed an efficient light-penetration in water
treatment reactor. A simple equation model was used to describe the
distribution of light through the mesh layers in the presence of absorbing
medium (e.g., colored water with humic acids). Maximum three or four coated
meshes were enough to harvest the solar UV light from 300 nm to 400 nm with
a high penetration efficiency. The separation distance between the mesh
layers played an important role in the efficiency of solar light penetration
through the coated mesh layers, especially in case of colored water
contaminated with high concentrations of humic acid
The Diffusion of Humans and Cultures in the Course of the Spread of Farming
The most profound change in the relationship between humans and their
environment was the introduction of agriculture and pastoralism. [....] For an
understanding of the expansion process, it appears appropriate to apply a
diffusive model. Broadly, these numerical modeling approaches can be catego-
rized in correlative, continuous and discrete. Common to all approaches is the
comparison to collections of radiocarbon data that show the apparent wave of
advance of the transition to farming. However, these data sets differ in entry
density and data quality. Often they disregard local and regional specifics and
research gaps, or dating uncertainties. Thus, most of these data bases may only
be used on a very general, broad scale. One of the pitfalls of using
irregularly spaced or irregularly documented radiocarbon data becomes evident
from the map generated by Fort (this volume, Chapter 16): while the general
east-west and south-north trends become evident, some areas appear as having
undergone anomalously early transitions to farming. This may be due to faulty
entries into the data base or regional problems with radiocarbon dating, if not
unnoticed or undocumented laboratory mistakes.Comment: 20 pages, 5 figures, submitted to Diffusive Spreading in Nature,
Technology and Society, edited by Armin Bunde, J\"urgen Caro, J\"org
K\"arger, Gero Vogl, Chapter 1
Systematic effects from an ambient-temperature, continuously-rotating half-wave plate
We present an evaluation of systematic effects associated with a
continuously-rotating, ambient-temperature half-wave plate (HWP) based on two
seasons of data from the Atacama B-Mode Search (ABS) experiment located in the
Atacama Desert of Chile. The ABS experiment is a microwave telescope sensitive
at 145 GHz. Here we present our in-field evaluation of celestial (CMB plus
galactic foreground) temperature-to-polarization leakage. We decompose the
leakage into scalar, dipole, and quadrupole leakage terms. We report a scalar
leakage of ~0.01%, consistent with model expectations and an order of magnitude
smaller than other CMB experiments have reported. No significant dipole or
quadrupole terms are detected; we constrain each to be <0.07% (95% confidence),
limited by statistical uncertainty in our measurement. Dipole and quadrupole
leakage at this level lead to systematic error on r<0.01 before any mitigation
due to scan cross-linking or boresight rotation. The measured scalar leakage
and the theoretical level of dipole and quadrupole leakage produce systematic
error of r<0.001 for the ABS survey and focal-plane layout before any data
correction such as so-called deprojection. This demonstrates that ABS achieves
significant beam systematic error mitigation from its HWP and shows the promise
of continuously-rotating HWPs for future experiments.Comment: 11 pages, 8 figures; revision to submitted version, Fig. 5 and Eqs.
(14) and (15) corrected; added Fig. 9 and description, text revisions for
clarification, Fig. 5 revised for better calibration, corrected labeling
errors and plotting bugs in Fig. 3, 4, and Eq. (14) and (15
Characterizing Atacama B-mode Search Detectors with a Half-Wave Plate
The Atacama B-Mode Search (ABS) instrument is a cryogenic (10 K)
crossed-Dragone telescope located at an elevation of 5190 m in the Atacama
Desert in Chile that observed for three seasons between February 2012 and
October 2014. ABS observed the Cosmic Microwave Background (CMB) at large
angular scales () to limit the B-mode polarization spectrum around
the primordial B-mode peak from inflationary gravity waves at .
The ABS focal plane consists of 480 transition-edge sensor (TES) bolometers.
They are coupled to orthogonal polarizations from a planar ortho-mode
transducer (OMT) and observe at 145 GHz. ABS employs an ambient-temperature,
rapidly rotating half-wave plate (HWP) to mitigate systematic effects and move
the signal band away from atmospheric noise, allowing for the recovery of
large angular scales. We discuss how the signal at the second harmonic of the
HWP rotation frequency can be used for data selection and for monitoring the
detector responsivities.Comment: 7 pages, 3 figures, conference proceedings submitted to the Journal
of Low Temperature Detector
Modulation of CMB polarization with a warm rapidly-rotating half-wave plate on the Atacama B-Mode Search (ABS) instrument
We evaluate the modulation of Cosmic Microwave Background (CMB) polarization
using a rapidly-rotating, half-wave plate (HWP) on the Atacama B-Mode Search
(ABS). After demodulating the time-ordered-data (TOD), we find a significant
reduction of atmospheric fluctuations. The demodulated TOD is stable on time
scales of 500-1000 seconds, corresponding to frequencies of 1-2 mHz. This
facilitates recovery of cosmological information at large angular scales, which
are typically available only from balloon-borne or satellite experiments. This
technique also achieves a sensitive measurement of celestial polarization
without differencing the TOD of paired detectors sensitive to two orthogonal
linear polarizations. This is the first demonstration of the ability to remove
atmospheric contamination at these levels from a ground-based platform using a
rapidly-rotating HWP.Comment: 8 pages, 8 figures, Published in RSI under the title "Modulation of
cosmic microwave background polarization with a warm rapidly rotating
half-wave plate on the Atacama B-Mode Search instrument.
Odd Parity and Line Nodes in Heavy Fermion Superconductors
Group theory arguments have demonstrated that a general odd parity order
parameter cannot have line nodes in the presence of spin-orbit coupling. In
this paper, it is shown that these arguments do not hold on the
zone face of a hexagonal close packed lattice. In particular, three of the six
odd parity representations vanish identically on this face. This has potential
relevance to the heavy fermion superconductor .Comment: 5 pages, revte
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