27 research outputs found
Two decades of pulsar timing of Vela
Pulsar timing at the Mt Pleasant observatory has focused on Vela, which can
be tracked for 18 hours of the day. These nearly continuous timing records
extend over 24 years allowing a greater insight into details of timing noise,
micro glitches and other more exotic effects. In particular we report the
glitch parameters of the 2004 event, along with the reconfirmation that the
spin up for the Vela pulsar occurs instantaneously to the accuracy of the data.
This places a lower limit of about 30 seconds for the acceleration of the
pulsar to the new rotational frequency. We also confirm of the low braking
index for Vela, and the continued fall in the DM for this pulsar.Comment: Isolated Neutron Stars conference, London, April 24-28 200
Spectral method for the time-dependent Gross-Pitaevskii equation with a harmonic trap
We study the numerical resolution of the time-dependent Gross-Pitaevskii
equation, a non-linear Schroedinger equation used to simulate the dynamics of
Bose-Einstein condensates. Considering condensates trapped in harmonic
potentials, we present an efficient algorithm by making use of a spectral
Galerkin method, using a basis set of harmonic oscillator functions, and the
Gauss-Hermite quadrature. We apply this algorithm to the simulation of
condensate breathing and scissors modes.Comment: 23 pages, 5 figure
Tractable non-local correlation density functionals for flat surfaces and slabs
A systematic approach for the construction of a density functional for van
der Waals interactions that also accounts for saturation effects is described,
i.e. one that is applicable at short distances. A very efficient method to
calculate the resulting expressions in the case of flat surfaces, a method
leading to an order reduction in computational complexity, is presented.
Results for the interaction of two parallel jellium slabs are shown to agree
with those of a recent RPA calculation (J.F. Dobson and J. Wang, Phys. Rev.
Lett. 82, 2123 1999). The method is easy to use; its input consists of the
electron density of the system, and we show that it can be successfully
approximated by the electron densities of the interacting fragments. Results
for the surface correlation energy of jellium compare very well with those of
other studies. The correlation-interaction energy between two parallel jellia
is calculated for all separations d, and substantial saturation effects are
predicted.Comment: 10 pages, 6 figure
Performance of novel VUV-sensitive Silicon Photo-Multipliers for nEXO
Liquid xenon time projection chambers are promising detectors to search for
neutrinoless double beta decay (0), due to their response
uniformity, monolithic sensitive volume, scalability to large target masses,
and suitability for extremely low background operations. The nEXO collaboration
has designed a tonne-scale time projection chamber that aims to search for
0 of \ce{^{136}Xe} with projected half-life sensitivity of
~yr. To reach this sensitivity, the design goal for nEXO is
1\% energy resolution at the decay -value (~keV).
Reaching this resolution requires the efficient collection of both the
ionization and scintillation produced in the detector. The nEXO design employs
Silicon Photo-Multipliers (SiPMs) to detect the vacuum ultra-violet, 175 nm
scintillation light of liquid xenon. This paper reports on the characterization
of the newest vacuum ultra-violet sensitive Fondazione Bruno Kessler VUVHD3
SiPMs specifically designed for nEXO, as well as new measurements on new test
samples of previously characterised Hamamatsu VUV4 Multi Pixel Photon Counters
(MPPCs). Various SiPM and MPPC parameters, such as dark noise, gain, direct
crosstalk, correlated avalanches and photon detection efficiency were measured
as a function of the applied over voltage and wavelength at liquid xenon
temperature (163~K). The results from this study are used to provide updated
estimates of the achievable energy resolution at the decay -value for the
nEXO design
Genetics of restless legs syndrome.
At the outset of genetic studies in restless legs syndrome (RLS), the disorder was assumed to be a classical monogenic disorder that runs in families. However, years of family studies did not reveal any causally-related genes or genetic variants. The advent of high-throughput genotyping technology led to a change; genome-wide association studies in large case-control samples became feasible, which led to the identification of first genetic risk variants for RLS. Variants detected by this approach are common ones, which that individually confer only a minor increase in risk of disease. Overall, the currently known risk variants in six genomic loci account for only a small proportion of the genetically determined susceptibility to RLS. Additional risk loci and individual variants remain to be discovered. First studies indicate that rare genetic variants are also important contributors in RLS. These are expected to have a larger impact on the phenotype and may thus prove to be excellent candidates for functional studies and, in the long-term, targets for developing therapeutics or preventive measures. To enable their discovery, large-scale studies including tens of thousands of affected individuals may be needed. Next-generation sequencing technologies such as whole exome or whole genome sequencing will be essential for this endeavor. Even though the number of known risk variants is still limited, they have been indispensable in terms of deciphering the underlying pathophysiology of RLS, providing the molecular starting points for animal models and in vitro studies to understand disease mechanisms. In addition, genetic risk variants can be valuable tools for disentangling the phenotypic complexity observed in RLS. Testing RLS risk variants for associations with periodic limb movements (PLMs) identified a significant role of some of the variants and suggested PLMs as an endophenotype in RLS. Further advances in genetics research in RLS will be driven by large-scale sequencing projects and the identification of additional common, but also rarer risk variants with larger effects on disease risk. Another uncharted territory in RLS research epigenetic effect on gene activity. Overall, genetic studies continue to hold great potential for understanding biology of the disease
Low Elevation Transmission Measurements at EOPACE Part I: Molecular and Aerosol Effects
An analysis is presented showing the effects of molecules and aerosols on atmospheric transmission data obtained during the Electro-Optical Propagation Assessment in Coastal Environments (EOPACE) campaign carried out in San Diego during March and April, 1996. Mid wave infrared transmission was measured over San Diego Bay along a 14.9 km path and a 7.0 km path at heights less than 4 meters above the water. Simultaneous meteorological measurements were obtained from two buoys placed at the mid-points of each path. An aerosol spectrometer was used to measure the aerosol size distribution over each transmission path. Data were analyzed with MODTRAN and Mie theory. The conclusion of this and the next two papers is that low altitude infrared transmission is a complex phenomenon whose mean value may be controlled either by molecular absorption, aerosol scattering, or refractive focusing, and whose fluctuating value is controlled by scintillation. ©2005 Copyright SPIE - The International Society for Optical Engineering