28,914 research outputs found
HI 21cm observations of the PG1216+069 sub-DLy-alpha absorber field at z=0.00632
The Westerbork Synthesis Radio Telescope finds a weak 21cm line emission
feature at the coordinates (RA-Dec-velocity) of the sub-Damped Lyman-alpha
absorber observed at z_abs=0.00632 in the spectrum of PG1216+069. The emission
feature, WSRT-J121921+0639, lies within 30" of the quasar sightline, is
detected at 99.8% (3 sigma) confidence level, has M_HI between 5 and 15x10^6
M_solar, and has velocity spread between 20 and 60 km/s. Other HI emitters in
the field include VCC297 at a projected distance of 86/h_75 kpc and a
previously unreported HI cloud, WSRT-J121919+0624 at 112/h_75 kpc with M_HI ~
3x10^8 M_solar. The optically identified, foreground galaxy that is closest to
the quasar sightline appears to be VCC339 (~L*/25) at 29/h_75 kpc and velocity
offset 292 km/s . A low surface brightness galaxy with the HI mass of the
sub-DLA absorber WSRT-J121921+0639 would likely have m_B ~ 17, and its diffuse
optical emission would need to compete with the light of both the background
QSO and a brighter foreground star ~10" from the QSO sight line.Comment: 10 pages, 2 figures, accepted for publication in ApJLet
Unleashing the Power of Distributed CPU/GPU Architectures: Massive Astronomical Data Analysis and Visualization case study
Upcoming and future astronomy research facilities will systematically
generate terabyte-sized data sets moving astronomy into the Petascale data era.
While such facilities will provide astronomers with unprecedented levels of
accuracy and coverage, the increases in dataset size and dimensionality will
pose serious computational challenges for many current astronomy data analysis
and visualization tools. With such data sizes, even simple data analysis tasks
(e.g. calculating a histogram or computing data minimum/maximum) may not be
achievable without access to a supercomputing facility.
To effectively handle such dataset sizes, which exceed today's single machine
memory and processing limits, we present a framework that exploits the
distributed power of GPUs and many-core CPUs, with a goal of providing data
analysis and visualizing tasks as a service for astronomers. By mixing shared
and distributed memory architectures, our framework effectively utilizes the
underlying hardware infrastructure handling both batched and real-time data
analysis and visualization tasks. Offering such functionality as a service in a
"software as a service" manner will reduce the total cost of ownership, provide
an easy to use tool to the wider astronomical community, and enable a more
optimized utilization of the underlying hardware infrastructure.Comment: 4 Pages, 1 figures, To appear in the proceedings of ADASS XXI, ed.
P.Ballester and D.Egret, ASP Conf. Serie
GPU-Based Volume Rendering of Noisy Multi-Spectral Astronomical Data
Traditional analysis techniques may not be sufficient for astronomers to make
the best use of the data sets that current and future instruments, such as the
Square Kilometre Array and its Pathfinders, will produce. By utilizing the
incredible pattern-recognition ability of the human mind, scientific
visualization provides an excellent opportunity for astronomers to gain
valuable new insight and understanding of their data, particularly when used
interactively in 3D. The goal of our work is to establish the feasibility of a
real-time 3D monitoring system for data going into the Australian SKA
Pathfinder archive.
Based on CUDA, an increasingly popular development tool, our work utilizes
the massively parallel architecture of modern graphics processing units (GPUs)
to provide astronomers with an interactive 3D volume rendering for
multi-spectral data sets. Unlike other approaches, we are targeting real time
interactive visualization of datasets larger than GPU memory while giving
special attention to data with low signal to noise ratio - two critical aspects
for astronomy that are missing from most existing scientific visualization
software packages. Our framework enables the astronomer to interact with the
geometrical representation of the data, and to control the volume rendering
process to generate a better representation of their datasets.Comment: 4 pages, 1 figure, to appear in the proceedings of ADASS XIX, Oct 4-8
2009, Sapporo, Japan (ASP Conf. Series
Vapor chamber fin studies. Operating characteristics of fin models
Operating characteristics and limits of vapor chamber fins or heat pipe
Shear thickening of cornstarch suspensions as a re-entrant jamming transition
We study the rheology of cornstarch suspensions, a dense system of
non-Brownian particles that exhibits shear thickening, i.e. a viscosity that
increases with increasing shear rate. Using MRI velocimetry we show that the
suspension has a yield stress. From classical rheology it follows that as a
function of the applied stress the suspension is first solid (yield stress),
then liquid and then solid again when it shear thickens. The onset shear rate
for thickening is found to depend on the measurement geometry: the smaller the
gap of the shear cell, the lower the shear rate at which thickening occurs.
Shear thickening can then be interpreted as the consequence of the Reynolds
dilatancy: the system under flow wants to dilate but instead undergoes a
jamming transition because it is confined, as confirmed by measurement of the
dilation of the suspension as a function of the shear rate
Safety hazards associated with the charging of lithium/sulfur dioxide cells
A continuing research program to assess the responses of spirally wound, lithium/sulfur dioxide cells to charging as functions of charging current, temperature, and cell condition prior to charging is described. Partially discharged cells that are charged at currents greater than one ampere explode with the time to explosion inversely proportional to the charging current. Cells charged at currents of less than one ampere may fail in one of several modes. The data allows an empirical prediction of when certain cells will fail given a constant charging current
Quantum Monte Carlo Simulation of the Trellis Lattice Heisenberg Model for SrCuO and CaVO
We study the spin-1/2 trellis lattice Heisenberg model, a coupled spin ladder
system, both by perturbation around the dimer limit and by quantum Monte Carlo
simulations. We discuss the influence of the inter-ladder coupling on the spin
gap and the dispersion, and present results for the temperature dependence of
the uniform susceptibility. The latter was found to be parameterized well by a
mean-field type scaling ansatz. Finally we discuss fits of experimental
measurements on SrCuO and CaVO to our results.Comment: 7 pages, 8 figure
Infrared Surface Brightness Distances to Cepheids: a comparison of Bayesian and linear-bisector calculations
We have compared the results of Bayesian statistical calculations and
linear-bisector calculations for obtaining Cepheid distances and radii by the
infrared surface brightness method. We analyzed a set of 38 Cepheids using a
Bayesian Markov Chain Monte Carlo method that had been recently studied with a
linear-bisector method. The distances obtained by the two techniques agree to
1.5 \pm 0.6% with the Bayesian distances being larger. The radii agree to 1.1%
\pm 0.7% with the Bayesian determinations again being larger. We interpret this
result as demonstrating that the two methods yield the same distances and
radii. This implies that the short distance to the LMC found in recent
linear-bisector studies of Cepheids is not caused by deficiencies in the
mathematical treatment. However, the computed uncertainties in distance and
radius for our dataset are larger in the Bayesian calculation by factors of
1.4-6.7. We give reasons to favor the Bayesian computations of the
uncertainties. The larger uncertainties can have a significant impact upon
interpretation of Cepheid distances and radii obtained from the infrared
surface brightness method.Comment: 27 pages with 9 figure
Chemical analysis of charged Li/SO(sub)2 cells
The initial focus of the program was to confirm that charging can indeed result in explosions and constitute a significant safety problem. Results of this initial effort clearly demonstrated that cells do indeed explode on charge and that charging does indeed constitute a real and severe safety problem. The results of the effort to identify the chemical reactions involved in and responsible for the observed behavior are described
- …