9,445 research outputs found
Shuttle active thermal control system development testing. Volume 2: Modular radiator system tests
Tests were designed to investigate the validity of the "modular" approach to space radiator system design for space shuttle and future applications by gathering performance data on various systems comprised of different numbers of identical panels, subject to nominal and extreme heat loads and environments. Both one-sided and two-sided radiation was tested, and engineering data was gathered on simulated low a/e coatings and system response to changes in outlet temperature control point. The results of the testing showed system stability throughout nominal orbital transients, unrealistically skewed environments, freeze-thaw transients, and rapid changes in outlet temperature control point. Various alternative panel plumbing arrangements were tested with no significant changes in performance being observed. With the MRS panels arranged to represent the shuttle baseline system, a maximum heat rejection of 76,600 Btu/hr was obtained in segmented tests under the expected worst case design environments. Testing of an alternate smaller two-sided radiation configuration yielded a maximum heat rejection of 52,931 Btu/hr under the maximum design environments
Stability of Coalescence Hidden variable Fractal Interpolation Surfaces
In the present paper, the stability of Coalescence Hidden variable Fractal
Interpolation Surfaces(CHFIS) is established. The estimates on error in
approximation of the data generating function by CHFIS are found when there is
a perturbation in independent, dependent and hidden variables. It is proved
that any small perturbation in any of the variables of generalized
interpolation data results in only small perturbation of CHFIS. Our results are
likely to be useful in investigations of texture of surfaces arising from the
simulation of surfaces of rocks, sea surfaces, clouds and similar natural
objects wherein the generating function depends on more than one variable
A statistical test of emission from unresolved point sources
We describe a simple test of the spatial uniformity of an ensemble of
discrete events. Given an estimate for the point source luminosity function and
an instrumental point spread function (PSF), a robust upper bound on the
fractional point source contribution to a diffuse signal can be found. We
verify with Monte Carlo tests that the statistic has advantages over the
two-point correlation function for this purpose, and derive analytic estimates
of the statistic's mean and variance as a function of the point source
contribution. As a case study, we apply this statistic to recent gamma-ray data
from the Fermi Large Area Telescope (LAT), and demonstrate that at energies
above 10 GeV, the contribution of unresolved point sources to the diffuse
emission is small in the region relevant for study of the WMAP Haze.Comment: 11 pages, 7 figures. Final version, accepted by Mon. Not. R. Astron.
Soc. The definitive version is available at www.blackwell-synergy.com
Pre-discovery observations of CoRoT-1b and CoRoT-2b with the BEST survey
The BEST wide-angle telescope installed at the Observatoire de Haute-Provence
and operated in remote control from Berlin by the Institut fuer
Planetenforschung, DLR, has observed the CoRoT target fields prior to the
mission. The resulting archive of stellar photometric lightcurves is used to
search for deep transit events announced during CoRoT's alarm-mode to aid in
fast photometric confirmation of these events. The "initial run" field of CoRoT
(IRa01) has been observed with BEST in November and December 2006 for 12
nights. The first "long run" field (LRc01) was observed from June to September
2005 for 35 nights. After standard CCD data reduction, aperture photometry has
been performed using the ISIS image subtraction method. About 30,000
lightcurves were obtained in each field. Transits of the first detected planets
by the CoRoT mission, CoRoT-1b and CoRoT-2b, were found in archived data of the
BEST survey and their lightcurves are presented here. Such detections provide
useful information at the early stage of the organization of follow-up
observations of satellite alarm-mode planet candidates. In addition, no period
change was found over ~4 years between the first BEST observation and last
available transit observations.Comment: AJ, accepte
Parallel Algorithm and Dynamic Exponent for Diffusion-limited Aggregation
A parallel algorithm for ``diffusion-limited aggregation'' (DLA) is described
and analyzed from the perspective of computational complexity. The dynamic
exponent z of the algorithm is defined with respect to the probabilistic
parallel random-access machine (PRAM) model of parallel computation according
to , where L is the cluster size, T is the running time, and the
algorithm uses a number of processors polynomial in L\@. It is argued that
z=D-D_2/2, where D is the fractal dimension and D_2 is the second generalized
dimension. Simulations of DLA are carried out to measure D_2 and to test
scaling assumptions employed in the complexity analysis of the parallel
algorithm. It is plausible that the parallel algorithm attains the minimum
possible value of the dynamic exponent in which case z characterizes the
intrinsic history dependence of DLA.Comment: 24 pages Revtex and 2 figures. A major improvement to the algorithm
and smaller dynamic exponent in this versio
Quantitative Analysis of the Publishing Landscape in High-Energy Physics
World-wide collaboration in high-energy physics (HEP) is a tradition which
dates back several decades, with scientific publications mostly coauthored by
scientists from different countries. This coauthorship phenomenon makes it
difficult to identify precisely the ``share'' of each country in HEP scientific
production. One year's worth of HEP scientific articles published in
peer-reviewed journals is analysed and their authors are uniquely assigned to
countries. This method allows the first correct estimation on a ``pro rata''
basis of the share of HEP scientific publishing among several countries and
institutions. The results provide an interesting insight into the geographical
collaborative patterns of the HEP community. The HEP publishing landscape is
further analysed to provide information on the journals favoured by the HEP
community and on the geographical variation of their author bases. These
results provide quantitative input to the ongoing debate on the possible
transition of HEP publishing to an Open Access model.Comment: For a better on-screen viewing experience this paper can also be
obtained at:
http://doc.cern.ch/archive/electronic/cern/preprints/open/open-2006-065.pd
Publishing in face of the COVID-19 pandemic
Doctors around the world are desperately looking for guidance to enable them to better manage their COVID-19 patients..
Towards a modeling of the time dependence of contact area between solid bodies
I present a simple model of the time dependence of the contact area between
solid bodies, assuming either a totally uncorrelated surface topography, or a
self affine surface roughness. The existence of relaxation effects (that I
incorporate using a recently proposed model) produces the time increase of the
contact area towards an asymptotic value that can be much smaller than
the nominal contact area. For an uncorrelated surface topography, the time
evolution of is numerically found to be well fitted by expressions of
the form [, where the exponent depends on
the normal load as , with close to 0.5. In
particular, when the contact area is much lower than the nominal area I obtain
, i.e., a logarithmic time increase of the
contact area, in accordance with experimental observations. The logarithmic
increase for low loads is also obtained analytically in this case. For the more
realistic case of self affine surfaces, the results are qualitatively similar.Comment: 18 pages, 9 figure
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