7,143 research outputs found
NASCAP modelling of environmental-charging-induced discharges in satellites
The charging and discharging characteristics of a typical geosynchronous satellite experiencing time-varying geomagnetic substorms, in sunlight, were studied utilizing the NASA Charging Analyzer Program (NASCAP). An electric field criteria of 150,000 volts/cm to initiate discharges and transfer of 67 percent of the stored charge was used based on ground test results. The substorm characteristics were arbitrarily chosen to evaluate effects of electron temperature and particle density (which is equivalent to current density). It was found that while there is a minimum electron temperature for discharges to occur, the rate of discharges is dependent on particle density and duration times of the encounter. Hence, it is important to define the temporal variations in the substorm environments
Stellar Populations in Ten Clump-Cluster Galaxies of the Ultra Deep Field
Color-color diagrams for the clump and interclump emission in 10
clump-cluster galaxies of the Ultra Deep Field are made from B,V,i, and z
images and compared with models to determine redshifts, star formation
histories, and galaxy masses. The clump colors suggest declining star formation
over the last ~0.3 Gy, while the interclump emission is older. The clump
luminous masses are typically 6x10^8 Msun and their diameters average 1.8 kpc.
Total galaxy luminous masses average 6.5x10^10 Msun. The distribution of axial
ratios is consistent with a thick disk geometry. The ages of the clumps are
longer than their internal dynamical times by a factor of ~8, so they are
stable clusters, but the clump densities are only ~10 times the limiting tidal
densities, so they could be deformed by tidal forces. This is consistent with
the observation that some clumps have tails. The clumps could form by
gravitational instabilities in accreting disk gas, or they could be captured as
gas-rich dwarf galaxies. Support for this second possibility comes from the
high abundance of nearly identical bare clumps in the UDF field. Several
clump-clusters have disk densities that are much larger than in local disks,
suggesting they do not survive but get converted into ellipticals by
collisions.Comment: 34 pgs, including 12 figures, accepted by Astrophysical Journal for
20 July 2005 v.62
Large space system: Charged particle environment interaction technology
Large, high voltage space power systems are proposed for future space missions. These systems must operate in the charged-particle environment of space and interactions between this environment and the high voltage surfaces are possible. Ground simulation testing indicated that dielectric surfaces that usually surround biased conductors can influence these interactions. For positive voltages greater than 100 volts, it has been found that the dielectrics contribute to the current collection area. For negative voltages greater than-500 volts, the data indicates that the dielectrics contribute to discharges. A large, high-voltage power system operating in geosynchronous orbit was analyzed. Results of this analysis indicate that very strong electric fields exist in these power systems
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Promoting positive communication environments: a service evaluation.
Purpose
The purpose of this paper is to present an evaluation of a programme of training and support provided to staff, which aimed to encourage supported communication environments for people with learning disabilities.
Design/methodology/approach
Training, monitoring and support for communication, specifically augmentative and alternative communication (AAC) strategies, was provided by speech and language therapy staff to two residential services over 46 weeks. Staff and service user communications were observed pre- and post-intervention.
Findings
In one provision there was an increase in service user initiations and the use of some AAC strategies by support staff. In the other provision there was no change in service user initiations and a decrease in the range of AAC strategies used. It appears that some forms for AAC remain challenging for staff to implement.
Originality/value
This evaluation explores ways of using specialist support services to improve communication environments for people with learning difficulties. Possible reasons for differences in the outcome of the intervention are discussed. Future research into the types of communication interactions experienced by people with learning disabilities across the range of communication styles may be useful so that support staff can be better helped to provide sustained and enriched communication environments
Real time description of fission
Using the time-dependent superfluid local density approximation, the dynamics
of fission is investigated in real time from just beyond the saddle to fully
separated fragments. Simulations produced in this fully microscopic framework
can help to assess the validity of the current approaches to fission, and to
obtain estimate of fission observables. In this contribution, we concentrate on
general aspects of fission dynamics.Comment: Proceedings of the "15th Varenna Conference on Nuclear Reaction
Mechanisms," Varenna, Italy, June 201
High Redshift Candidates and the Nature of Small Galaxies in the Hubble Deep Field
We present results on two related topics: 1. A discussion of high redshift
candidates (z>4.5), and 2. A study of very small galaxies at intermediate
redshifts, both sets being detected in the region of the northern Hubble Deep
Field covered by deep NICMOS observations at 1.6 and 1.1 microns. The high
redshift candidates are just those with redshift z>4.5 as given in the recent
catalog of Thompson, Weymann and Storrie-Lombardi, while the ``small galaxy''
sample is defined to be those objects with isophotal area <= 0.2 squ. arcsec
and with photometric redshifts 1<z<4.5. Of the 19 possible high redshift
candidates listed in the Thompson et al. catalog, 11 have (nominal) photometric
redshifts less than 5.0. Of these, however, only 4 are ``robust'' in the sense
of yielding high redshifts when the fluxes are randomly perturbed with errors
comparable to the estimated measuring error in each wave band. For the 8 other
objects with nominal photometric redshifts greater than 5.0, one (WFPC2 4--473)
has a published spectroscopic redshift. Of the remaining 7, 4 are robust in the
sense indicated above. Two of these form a close pair (NIC 586 and NIC 107).
The redshift of the object having formally the highest redshift, at 6.56
(NIC118 = WFPC2 4--601), is problematic, since F606W and F814W flux are clearly
present, and the nature of this object poses a dilemma. (abridged)Comment: 44 pages, 12 figures, to appear in ApJ v591, July 10, 200
Nuclear Fission: from more phenomenology and adjusted parameters to more fundamental theory and increased predictive power
Two major recent developments in theory and computational resources created
the favorable conditions for achieving a microscopic description of nuclear
fission almost eighty years after its discovery in 1939 by Hahn and Strassmann
(1930). The first major development was in theory, the extension of the
Time-Dependent Density Functional Theory (TDDFT) to superfluid fermion systems.
The second development was in computing, the emergence of powerful enough
supercomputers capable of solving the complex systems of equations describing
the time evolution in three dimensions without any restrictions of hundreds of
strongly interacting nucleons. Even though the available nuclear energy density
functionals (NEDFs) are phenomenological still, their accuracy is improving
steadily and the prospects of being able to perform calculations of the nuclear
fission dynamics and to predict many properties of the fission fragments,
otherwise not possible to extract from experiments, are within reach, all
without making recourse anymore to uncontrollable assumptions and simplified
phenomenological models.Comment: 6 pages, account of invited talk given at FUSION17, Hobart, Tasmania,
February 20-24, 201
Morphology and Redshifts of Extremely Red Galaxies in the GOODS/CDFS deep ISAAC field
We present the photometric redshift distribution of a sample of 198 Extremely
Red Galaxies (ERGs) with Ks3.92 (Vega), selected by Roche et al.
in 50.4 sq. arcmin of the Chandra Deep Field South (CDFS). The sample has been
obtained using ISAAC-VLT and ACS-HST GOODS public data. We also show the
results of a morphological study of the 72 brightest ERGs in the z band (z<25,
AB).Comment: 2 pages, 2 figures. To appear in the proceedings of the ESO/USM/MPE
Workshop "Multiwavelength Mapping of Galaxy Formation and Evolution", Venice,
October 13-16, 200
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