9,640 research outputs found
Theoretical Determination of the Boundary of the Geomagnetic Field in a Steady Solar Wind
Theoretical determination of the boundary of the geomagnetic field in a steady solar win
A GPU based real-time software correlation system for the Murchison Widefield Array prototype
Modern graphics processing units (GPUs) are inexpensive commodity hardware
that offer Tflop/s theoretical computing capacity. GPUs are well suited to many
compute-intensive tasks including digital signal processing.
We describe the implementation and performance of a GPU-based digital
correlator for radio astronomy. The correlator is implemented using the NVIDIA
CUDA development environment. We evaluate three design options on two
generations of NVIDIA hardware. The different designs utilize the internal
registers, shared memory and multiprocessors in different ways. We find that
optimal performance is achieved with the design that minimizes global memory
reads on recent generations of hardware.
The GPU-based correlator outperforms a single-threaded CPU equivalent by a
factor of 60 for a 32 antenna array, and runs on commodity PC hardware. The
extra compute capability provided by the GPU maximises the correlation
capability of a PC while retaining the fast development time associated with
using standard hardware, networking and programming languages. In this way, a
GPU-based correlation system represents a middle ground in design space between
high performance, custom built hardware and pure CPU-based software
correlation.
The correlator was deployed at the Murchison Widefield Array 32 antenna
prototype system where it ran in real-time for extended periods. We briefly
describe the data capture, streaming and correlation system for the prototype
array.Comment: 11 pages, to appear in PAS
Containerless low gravity processing of glass forming and immiscible alloys
Under normal one-g conditions immiscible alloys segregate extensively during solidification due to sedimentation of the more dense of the immiscible liquid phases. Immiscible (hypermonotectic) gold-rhodium alloys were processed in the 100 meter drop tube under low gravity, containerless conditions to determine the feasibility of producing dispersed structures. Three alloy compositions were utilized. Alloys containing 10 percent by volume of the gold-rich hypermonotectic phase exhibited a tendency for the gold-rich liquid to wet the outer surface of the samples. This wetting tendency led to extensive segregation in several cases. Alloys containing 80 and 90 percent by volume of the gold-rich phase possessed completely different microstructures from the 10 percent samples when processed under low-g, containerless conditions. Several samples exhibited microstructures consisting of well dispersed 2 to 3 microns diameter rhodium-rich spheres in a gold-rich matrix
Lifetime cost effectiveness of simvastatin in a range of risk groups and age groups derived from a randomised trial of 20,536 people
<i>Objectives</i>: To evaluate the cost effectiveness of 40 mg simvastatin daily continued for life in people of different ages with differing risks of vascular disease.
Design A model developed from a randomised trial was used to estimate lifetime risks of vascular events and costs of treatment and hospital admissions in the United Kingdom.
<i>Setting</i>: 69 hospitals in the UK.
<i>Participants</i>: 20 536 men and women (aged 40-80) with coronary disease, other occlusive arterial disease, or diabetes.
<i>Interventions</i>: 40 mg simvastatin daily versus placebo for an average of 5 years.
<i>Main</i> <i>outcome</i> <i>measures</i>: Cost effectiveness of 40 mg simvastatin daily expressed as additional cost per life year gained. Major vascular event defined as non-fatal myocardial infarction or death from coronary disease, any stroke, or revascularisation procedure. Results were extrapolated to younger and older age groups at lower risk of vascular disease than were studied directly, as well as to lifetime treatment.
<i>Results</i>: At the April 2005 UK price of £4.87 (€7; $9) per 28 day pack of generic 40 mg simvastatin, lifetime treatment was cost saving in most age groups and vascular disease risk groups studied directly. Gains in life expectancy and cost savings decreased with increasing age and with decreasing risk of vascular disease. People aged 40-49 with 5 year risks of major vascular events of 42% and 12% at start of treatment gained 2.49 and 1.67 life years, respectively. Treatment with statins remained cost saving or cost less than £2500 per life year gained in people as young as 35 years or as old as 85 with 5 year risks of a major vascular event as low as 5% at the start of treatment.
<i>Conclusions</i>: Treatment with statins is cost effective in a wider population than is routinely treated at present
Spin detection at elevated temperatures using a driven double quantum dot
We consider a double quantum dot in the Pauli blockade regime interacting
with a nearby single spin. We show that under microwave irradiation the average
electron occupations of the dots exhibit resonances that are sensitive to the
state of the nearby spin. The system thus acts as a spin meter for the nearby
spin. We investigate the conditions for a non-demolition read-out of the spin
and find that the meter works at temperatures comparable to the dot charging
energy and sensitivity is mainly limited by the intradot spin relaxation.Comment: 8 pages, 6 figure
Contextual planning for NASA - A second workbook of alternative future environments for mission analysis, volume 1 Interim report
Contextural planning for selecting alternate NASA program
Subtraction of Bright Point Sources from Synthesis Images of the Epoch of Reionization
Bright point sources associated with extragalactic AGN and radio galaxies are
an important foreground for low frequency radio experiments aimed at detecting
the redshifted 21cm emission from neutral hydrogen during the epoch of
reionization. The frequency dependence of the synthesized beam implies that the
sidelobes of these sources will move across the field of view as a function of
observing frequency, hence frustrating line-of-sight foreground subtraction
techniques. We describe a method for subtracting these point sources from dirty
maps produced by an instrument such as the MWA. This technique combines matched
filters with an iterative centroiding scheme to locate and characterize point
sources in the presence of a diffuse background. Simulations show that this
technique can improve the dynamic range of EOR maps by 2-3 orders of magnitude.Comment: 11 pages, 8 figures, 1 table, submitted to PAS
Exact semi-relativistic model for ionization of atomic hydrogen by electron impact
We present a semi-relativistic model for the description of the ionization
process of atomic hydrogen by electron impact in the first Born approximation
by using the Darwin wave function to describe the bound state of atomic
hydrogen and the Sommerfeld-Maue wave function to describe the ejected
electron. This model, accurate to first order in in the relativistic
correction, shows that, even at low kinetic energies of the incident electron,
spin effects are small but not negligible. These effects become noticeable with
increasing incident electron energies. All analytical calculations are exact
and our semi-relativistic results are compared with the results obtained in the
non relativistic Coulomb Born Approximation both for the coplanar asymmetric
and the binary coplanar geometries.Comment: 8 pages, 6 figures, Revte
Trauma histories among justice-involved youth: findings from the National Child Traumatic Stress Network.
BackgroundUp to 90% of justice-involved youth report exposure to some type of traumatic event. On average, 70% of youth meet criteria for a mental health disorder with approximately 30% of youth meeting criteria for post-traumatic stress disorder (PTSD). Justice-involved youth are also at risk for substance use and academic problems, and child welfare involvement. Yet, less is known about the details of their trauma histories, and associations among trauma details, mental health problems, and associated risk factors.ObjectiveThis study describes detailed trauma histories, mental health problems, and associated risk factors (i.e., academic problems, substance/alcohol use, and concurrent child welfare involvement) among adolescents with recent involvement in the juvenile justice system.MethodThe National Child Traumatic Stress Network Core Data Set (NCTSN-CDS) is used to address these aims, among which 658 adolescents report recent involvement in the juvenile justice system as indexed by being detained or under community supervision by the juvenile court.ResultsAge of onset of trauma exposure was within the first 5 years of life for 62% of youth and approximately one-third of youth report exposure to multiple or co-occurring trauma types each year into adolescence. Mental health problems are prevalent with 23.6% of youth meeting criteria for PTSD, 66.1% in the clinical range for externalizing problems, and 45.5% in the clinical range for internalizing problems. Early age of onset of trauma exposure was differentially associated with mental health problems and related risk factors among males and females.ConclusionsThe results indicate that justice-involved youth report high rates of trauma exposure and that this trauma typically begins early in life, is often in multiple contexts, and persists over time. Findings provide support for establishing trauma-informed juvenile justice systems that can respond to the needs of traumatized youth
Simulation of phosphorus implantation into silicon with a single-parameter electronic stopping power model
We simulate dopant profiles for phosphorus implantation into silicon using a
new model for electronic stopping power. In this model, the electronic stopping
power is factorized into a globally averaged effective charge Z1*, and a local
charge density dependent electronic stopping power for a proton. There is only
a single adjustable parameter in the model, namely the one electron radius rs0
which controls Z1*. By fine tuning this parameter, we obtain excellent
agreement between simulated dopant profiles and the SIMS data over a wide range
of energies for the channeling case. Our work provides a further example of
implant species, in addition to boron and arsenic, to verify the validity of
the electronic stopping power model and to illustrate its generality for
studies of physical processes involving electronic stopping.Comment: 11 pages, 7 figures. See http://bifrost.lanl.gov/~reed
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