308 research outputs found
Short-Range Interactions and Scaling Near Integer Quantum Hall Transitions
We study the influence of short-range electron-electron interactions on
scaling behavior near the integer quantum Hall plateau transitions. Short-range
interactions are known to be irrelevant at the renormalization group fixed
point which represents the transition in the non-interacting system. We find,
nevertheless, that transport properties change discontinuously when
interactions are introduced. Most importantly, in the thermodynamic limit the
conductivity at finite temperature is zero without interactions, but non-zero
in the presence of arbitrarily weak interactions. In addition, scaling as a
function of frequency, , and temperature, , is determined by the
scaling variable (where is the exponent for the temperature
dependence of the inelastic scattering rate) and not by , as it would
be at a conventional quantum phase transition described by an interacting fixed
point. We express the inelastic exponent, , and the thermal exponent, ,
in terms of the scaling dimension, , of the interaction strength
and the dynamical exponent (which has the value ), obtaining
and .Comment: 9 pages, 4 figures, submitted to Physical Review
What Can Be Learned with an Iodine Solar-Neutrino Detector?
We study the potential benefits of an iodine-based solar-neutrino detector
for testing hypotheses that involve neutrino oscillations. We argue that such a
detector will have a good chance of distinguishing the two allowed regions of
-- parameter space if neutrino conversion is
occurring in the sun. It should also be able to detect seasonal variations in
the signal due to vacuum oscillations and might be sensitive enough to detect
day/night variations due to MSW transitions in the earth. Although it would
need to be calibrated, a working iodine detector could be completed before more
ambitious projects that seek to accomplish the same things.Comment: 8 pages, RevTex, 2 uuencoded figures, submittted to Phys. Rev.
Teacher Ratings of Children's Behavior Problems and Functional Impairment Across Gender and Ethnicity:Construct Equivalence of the Strengths and Difficulties Questionnaire
The present study examined construct equivalence of the teacher Strengths and Difficulties Questionnaire and compared mean scores in an ethnically diverse sample of children living in the Netherlands. Elementary schoolteachers completed the Strengths and Difficulties Questionnaire for 2,185 children aged 6 to 10 years of the four largest ethnic groups in the Netherlands, namely native Dutch (n = 684) and Moroccan (n = 702), Turkish (n = 434), and Surinamese (n = 365) immigrant children. Multigroup confirmatory factor analysis suggested the factor structure of the Strengths and Difficulties Questionnaire to be invariant across children's ethnicity and gender. Additionally, the factor structure appeared to be similar for Dutch and Surinamese teachers. However, mean scores on emotional problems, hyperactivity, conduct problems, prosocial behavior, and impairment varied significantly according to ethnicity and gender. Mean scores on peer problems differed significantly for boys and girls, but not across ethnicity. Whether mean differences reflect a method bias or actual differences in classroom behaviors is discussed and needs further research
Multiple Interactions and the Structure of Beam Remnants
Recent experimental data have established some of the basic features of
multiple interactions in hadron-hadron collisions. The emphasis is therefore
now shifting, to one of exploring more detailed aspects. Starting from a brief
review of the current situation, a next-generation model is developed, wherein
a detailed account is given of correlated flavour, colour, longitudinal and
transverse momentum distributions, encompassing both the partons initiating
perturbative interactions and the partons left in the beam remnants. Some of
the main features are illustrated for the Tevatron and the LHC.Comment: 69pp, 33 figure
Acoustic Mapping Velocimetry (AMV) for in-situ bedload transport estimation
Despite the importance of sediment transport processes in large rivers, the measurement of sed-iment transport rate in the in-situ, especially bedload, is difficult, costly and time consuming using conven-tional methods. In this paper, a novel indirect bedload estimation methodology is presented that is based on the Acoustic Mapping Velocimetry (AMV). AMV is a combination of acoustic and imaging techniques that provides 2D bedform velocity maps. As such, it can only be used if bedload is represented by bedform migra-tion. This paper illustrates the applicability of the bedload estimation method using as test case a section of the Ohio River in the United States. Repeated measurements of the bathymetry provided by multi-beam echo sounder serve as input data for AMV. Cross-sectional distributions of bedload transport rates obtained with AMV are compared with the estimates provided by another non-intrusive technique, ISSDOTv2, developed by the US Army Corps of Engineers. The good agreement between the results with the two different methods is encouraging and suggests further field tests covering a wider range of hydro-morphological situations
Supernova Observation Via Neutrino-Nucleus Elastic Scattering in the CLEAN Detector
Development of large mass detectors for low-energy neutrinos and dark matter
may allow supernova detection via neutrino-nucleus elastic scattering. An
elastic-scattering detector could observe a few, or more, events per ton for a
galactic supernova at 10 kpc ( m). This large yield, a
factor of at least 20 greater than that for existing light-water detectors,
arises because of the very large coherent cross section and the sensitivity to
all flavors of neutrinos and antineutrinos. An elastic scattering detector can
provide important information on the flux and spectrum of and
from supernovae. We consider many detectors and a range of target
materials from He to Pb. Monte Carlo simulations of low-energy
backgrounds are presented for the liquid-neon-based Cryogenic Low Energy
Astrophysics with Noble gases (CLEAN) detector. The simulated background is
much smaller than the expected signal from a galactic supernova.Comment: 10 pages, 5 figures, submitted to Phys. Rev.
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
The exposure of the hybrid detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a detector for ultra-high energy cosmic rays.
It consists of a surface array to measure secondary particles at ground level
and a fluorescence detector to measure the development of air showers in the
atmosphere above the array. The "hybrid" detection mode combines the
information from the two subsystems. We describe the determination of the
hybrid exposure for events observed by the fluorescence telescopes in
coincidence with at least one water-Cherenkov detector of the surface array. A
detailed knowledge of the time dependence of the detection operations is
crucial for an accurate evaluation of the exposure. We discuss the relevance of
monitoring data collected during operations, such as the status of the
fluorescence detector, background light and atmospheric conditions, that are
used in both simulation and reconstruction.Comment: Paper accepted by Astroparticle Physic
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
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