9,658 research outputs found
Origin of positive magnetoresistance in small-amplitude unidirectional lateral superlattices
We report quantitative analysis of positive magnetoresistance (PMR) for
unidirectional-lateral-superlattice samples with relatively small periods
(a=92-184 nm) and modulation amplitudes (V_0=0.015-0.25 meV). By comparing
observed PMR's with ones calculated using experimentally obtained mobilities,
quantum mobilities, and V_0's, it is shown that contribution from streaming
orbits (SO) accounts for only small fraction of the total PMR. For small V_0,
the limiting magnetic field B_e of SO can be identified as an inflection point
of the magnetoresistance trace. The major part of PMR is ascribed to drift
velocity arising from incompleted cyclotron orbits obstructed by scatterings.Comment: 12 pages, 9 figures, REVTe
The Pan-STARRS1 Photometric System
The Pan-STARRS1 survey is collecting multi-epoch, multi-color observations of
the sky north of declination -30 deg to unprecedented depths. These data are
being photometrically and astrometrically calibrated and will serve as a
reference for many other purposes. In this paper we present our determination
of the Pan-STARRS photometric system: gp1, rp1, ip1, zp1, yp1, and wp1. The
Pan-STARRS photometric system is fundamentally based on the HST Calspec
spectrophotometric observations, which in turn are fundamentally based on
models of white dwarf atmospheres. We define the Pan-STARRS magnitude system,
and describe in detail our measurement of the system passbands, including both
the instrumental sensitivity and atmospheric transmission functions.
Byproducts, including transformations to other photometric systems, galactic
extinction, and stellar locus are also provided. We close with a discussion of
remaining systematic errors.Comment: 39 pages, 9 figures, machine readable table of bandpasses, accepted
for publication in Ap
Development and Preliminary Application of Mathematical Models to the Weber Basin
The adoption of stream standards, whether for direct application or for the establishment of realistic effluent standards, creates a need to predict the impact of pollution loads on river water quality during critical flow periods or as the result of future user demands. Because of the complexity of aquatic systems, mathematical models are an excellent medium for bringing together the state-of-the-art knowledge from a variety of disciplines into a form which can be readily applied to practical problems. Applying a mathematical model to a river system has the added advantage of providing a structure for the systematic consideration of the many diverse aspects of water quality phenomena. This report describes the development of a river simulation model (QUAL-U) for predicting water quality and its preliminary application to the Weber River drainage basin in northeastern Utah. The model involves the numerical solution of a set of differential equations representing the aquatic system under steady state conditions. The development and use of a second model which provides the flow boundary conditions for the first model is also described. This model is a simple interactive procedure for obtaining flows at specified locations on the river system given the measured flows at other locations and typical flow ranges of headwater, diversions, surface and subsurface lateral inflows, and point loads. Previous river water quality models are reviewed and the structure of QUAL-U is presented. The economic and physical characteristics of the study area are described and the Weber River system is represented by subbasins, reaches, and computational units. Model calibration was based on water quality data collected at over eighty sampling locations in the study area during a four day period in September, 1973. Each of the sampling points was subsequently surveyed to obtain representative hydraulic characteristics for each reach of the river system. Coefficients for the mathematical equations representing hydraulic characteristics and chemical and biological reactions were estimated and adjusted during the model calibration procedure until model responses satisfactorily resembled the observed data. Results for the calibration period and also for studies involving critical low flow conditions are described and model limitations are considered. The work on which this report is based was performed for the State of Utah, Department of Social Services, Division of Health as part of a Waste Load Allocation Study on the Weber River. The scope of this project provided only for supplying the calibrated model to the client and does not include predictive runs or interpretation of management alternatives
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Spontaneous expression classification in the encrypted domain
To date, most facial expression analysis have been based on posed image databases and is carried out without being able to protect the identity of the subjects whose expressions are being recognised. In this paper, we propose and implement a system for classifying facial expressions of images in the encrypted domain based on a Paillier cryptosystem implementation of Fisher Linear Discriminant Analysis and k-nearest neighbour (FLDA + kNN). We present results of experiments carried out on a recently developed natural visible and infrared facial expression (NVIE) database of spontaneous images. To the best of our knowledge, this is the first system that will allow the recog-nition of encrypted spontaneous facial expressions by a remote server on behalf of a client
Einstein Cluster Alignments Revisited
We have examined whether the major axes of rich galaxy clusters tend to point
toward their nearest neighboring cluster. We have used the data of Ulmer,
McMillan, and Kowalski, who used position angles based on X-ray morphology. We
also studied a subset of this sample with updated positions and distances from
the MX Northern Abell Cluster Survey (for rich clusters () with well
known redshifts). A Kolmogorov-Smirnov (KS) test showed no significant signal
for nonrandom angles on any scale Mpc. However, refining the
null hypothesis with the Wilcoxon rank-sum test, we found a high confidence
signal for alignment. Confidence levels increase to a high of 99.997% as only
near neighbors which are very close are considered. We conclude there is a
strong alignment signal in the data, consistent with gravitational instability
acting on Gaussian perturbations.Comment: Minor revisions. To be published in Ap
Influence of turbulent mixing and air circulation in the lower atmosphere on fetch areas of selected WMO Global Atmosphere Watch baseline air pollution stations.
The World Meteorological Organisation (WMO) established the Global Atmosphere Watch (GAW) Programme in 1989. The scientific goals of GAW relate to investigating the role of atmospheric chemistry in global climate change, and include: understanding the complex mechanisms with respect to natural and anthropogenic atmospheric change; and improving the understanding of interactions between the atmosphere, ocean, and biosphere.American Meteorological Society; Stockholm Universit
Addendum to "Coherent radio pulses from GEANT generated electromagnetic showers in ice"
We reevaluate our published calculations of electromagnetic showers generated
by GEANT 3.21 and the radio frequency pulses they produce in ice. We are
prompted by a recent report showing that GEANT 3.21-modeled showers are
sensitive to internal settings in the electron tracking subroutine. We report
the shower and pulse characteristics obtained with different settings of GEANT
3.21 and with GEANT 4. The default setting of electron tracking in GEANT 3.21
we used in previous work speeds up the shower simulation at the cost of
information near the end of the tracks. We find that settings tracking electron
and positron to lower energy yield a more accurate calculation, a more intense
shower, and proportionately stronger radio pulses at low frequencies. At high
frequencies the relation between shower tracking algorithm and pulse spectrum
is more complex. We obtain radial distributions of shower particles and phase
distributions of pulses from 100 GeV showers that are consistent with our
published results.Comment: 4 pages, 3 figure
Electronic Structure of Three-Dimensional Superlattices Subject to Tilted Magnetic Fields
Full quantum-mechanical description of electrons moving in 3D structures with
unidirectional periodic modulation subject to tilted magnetic fields requires
an extensive numerical calculation. To understand magneto-oscillations in such
systems it is in many cases sufficient to use the quasi-classical approach, in
which the zero-magnetic-field Fermi surface is considered as a
magnetic-field-independent rigid body in k-space and periods of oscillations
are related to extremal cross-sections of the Fermi surface cut by planes
perpendicular to the magnetic-field direction. We point out cases where the
quasi-classical treatment fails and propose a simple tight-binding
fully-quantum-mechanical model of the superlattice electronic structure.Comment: 8 pages, 7 figures, RevTex, submitted to Phys. Rev.
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