3,737 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
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
Stochastic Cutoff Method for Long-Range Interacting Systems
A new Monte-Carlo method for long-range interacting systems is presented.
This method consists of eliminating interactions stochastically with the
detailed balance condition satisfied. When a pairwise interaction of a
-particle system decreases with the distance as ,
computational time per one Monte Carlo step is for
and for , where is the spatial
dimension. We apply the method to a two-dimensional magnetic dipolar system.
The method enables us to treat a huge system of spins with reasonable
computational time, and reproduces a circular order originated from long-range
dipolar interactions.Comment: 18 pages, 9 figures, 1 figure and 1 reference are adde
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.
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
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
A new measurement of K+(e4) decay and the s-wave pi-pi-scattering length a00
A sample of 400000 events from the decay K+->pi+pi-e+nu(e)(K(e4)) has been
collected in experiment E865 at the Brookhaven AGS. The analysis of these data
yields new measurements of the K(e4) branching ratio
(4.11+-0.01+-0.11)*10**(-5)), the s-wave pi-pi scattering length
a00=0.228+-0.012+-0.003, and the form factors F, G, and H of the hadronic
current and their dependence on the invariant pi-pi mass
First observation of the decay K+ -> e+ nu mu+ mu-
Experiment 865 at the Brookhaven AGS has observed the decay K^+ -> e^+ nu
mu^+ mu^-. The branching ratio extracted is (1.72 +/- 0.37(stat) +/- 0.17(syst)
+/- 0.19(model)) x 10^{-8} where the third term in the error results from the
use of a model to extrapolate into a kinematic region dominated by background.Comment: 4 pages, 6 figures, Revtex4. Correction to figure and minor text
change
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
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