988 research outputs found
Silvabase: A flexible data file management system
The need for a more flexible and efficient data file management system for mission planning in the Mission Operations Laboratory (EO) at MSFC has spawned the development of Silvabase. Silvabase is a new data file structure based on a B+ tree data structure. This data organization allows for efficient forward and backward sequential reads, random searches, and appends to existing data. It also provides random insertions and deletions with reasonable efficiency, utilization of storage space well but not at the expense of speed, and performance of these functions on a large volume of data. Mission planners required that some data be keyed and manipulated in ways not found in a commercial product. Mission planning software is currently being converted to use Silvabase in the Spacelab and Space Station Mission Planning Systems. Silvabase runs on a Digital Equipment Corporation's popular VAX/VMS computers in VAX Fortran. Silvabase has unique features involving time histories and intervals such as in operations research. Because of its flexibility and unique capabilities, Silvabase could be used in almost any government or commercial application that requires efficient reads, searches, and appends in medium to large amounts of almost any kind of data
Simulations of MHD Instabilities in Intracluster Medium Including Anisotropic Thermal Conduction
We perform a suite of simulations of cooling cores in clusters of galaxies in
order to investigate the effect of the recently discovered heat flux buoyancy
instability (HBI) on the evolution of cores. Our models follow the
3-dimensional magnetohydrodynamics (MHD) of cooling cluster cores and capture
the effects of anisotropic heat conduction along the lines of magnetic field,
but do not account for the cosmological setting of clusters or the presence of
AGN. Our model clusters can be divided into three groups according to their
final thermodynamical state: catastrophically collapsing cores, isothermal
cores, and an intermediate group whose final state is determined by the initial
configuration of magnetic field. Modeled cores that are reminiscent of real
cluster cores show evolution towards thermal collapse on a time scale which is
prolonged by a factor of ~2-10 compared with the zero-conduction cases. The
principal effect of the HBI is to re-orient field lines to be perpendicular to
the temperature gradient. Once the field has been wrapped up onto spherical
surfaces surrounding the core, the core is insulated from further conductive
heating (with the effective thermal conduction suppressed to less than 1/100th
of the Spitzer value) and proceeds to collapse. We speculate that, in real
clusters, the central AGN and possibly mergers play the role of "stirrers,"
periodically disrupting the azimuthal field structure and allowing thermal
conduction to sporadically heat the core.Comment: 16 pages, 3 tables, 17 figures, accepted to ApJ with minor revisions,
to appear in Volume 704, Oct 20, 2009 issu
Mortality of major league baseball players from Canada, Latin America, and the Caribbean
Professional baseball players have lower mortality rates than the US general population, but whether this is true of foreign-born players is not known. Using data on ballplayers from six nations, we compare mortality rates with those of US players via standardized mortality ratios. After controlling for confounders, four countries had statistically insignificant SMRs while two nations had significantly elevated SMRs. In the two nations with elevated SMRs, low average ages at death and high crime rates suggest the increased mortality may be linked to violent crime. A full understanding of the causes of disparity in mortality will require further research
The Mortality of Space Explorers
Outer space exploration poses unique risks to human survival. Here, we review the current literature on United States astronauts and Soviet and Russian cosmonauts and provide updated and original research findings. As in previous research, both astronauts and cosmonauts are shown to have reduced risk of death by natural causes, particularly from chronic diseases such as cardiovascular disease and cancer, compared with appropriately matched general populations. Simultaneously, space explorers are at increased risk of death by external forces, particularly accidents such as plane crashes and spacecraft accidents. In total, both astronauts and cosmonauts are at reduced risk of all-cause mortality in comparison to the general populations of the United States and Russia. However, in comparison to astronauts, cosmonauts have been at equal risk of accidental death, but increased risk of death by chronic disease. We conjecture that the lack of risk from chronic disease may be due to the excellent health and medical monitoring of space explorers coupled with the deliberate attempts to limit their radiation exposure levels below those that would be detrimental. The differences in the astronaut and cosmonaut mortality experiences are likely due to lifestyle factors and the background rates of mortality in the two nations
Survival, Mortality, and Life Expectancy
Cerebral palsy (CP) is a heterogenous condition, with level of disability ranging from immaterial to profound. In concert with the continuum of level of severity of disability/independent functioning, health care needs, therapies, medications, surgical interventions, costs of care, daily demands on parents and other family members, and expectations for the future in terms of education, employment, and other milestones of life all vary widely. Similarly, life expectancy in CP follows a continuum, from far lower than to potentially as high as general population life expectancy, that parallels the continuum of levels of disability. Here we review the literature documenting this, and examine the specific factors that are known to be strongly associated with mortality and longevity in CP. We also examine the evidence regarding causes of death in CP, and present some new findings related to this. Finally, we outline important methodological considerations for future research in this area
Who Ya Gonna Call? Networks of Rural School Administrators
When they need help or advice, who are rural school administrators going to call? Relationships among rural school administrators develop into networks that can affect the success of administrators and their schools. Understanding the structure and content of these networks provides insights into how resources, innovations, and communication flow both within and between rural district administrators. Based on network theory and analysis, this study examines the structure, content, and strategic implications of the administrative networks within and across six contiguous rural school districts in the Western United States. Network graphs are included, illustrating both individual district and the combined six-district rural administrator networks. While acquaintance ties and active work ties are evident both within and across districts, relationally embedded ties and greater cohesion of ties are more evident within districts than across districts. Analyses include consideration of administrative assignment, gender, and geographical location of the network structures. Strategic implications of the network structures and content are discussed
Eggshell pigment composition covaries with phylogeny but not with life history or with nesting ecology traits of British passerines
No single hypothesis is likely to explain the diversity in eggshell coloration and patterning across birds, suggesting that eggshell appearance is most likely to have evolved to fulfill many nonexclusive functions. By controlling for nonindependent phylogenetic associations between related species, we describe this diversity using museum eggshells of 71 British breeding passerine species to examine how eggshell pigment composition and concentrations vary with phylogeny and with life-history and nesting ecology traits. Across species, concentrations of biliverdin and protoporphyrin, the two main pigments found in eggshells, were strongly and positively correlated, and both pigments strongly covaried with phylogenetic relatedness. Controlling for phylogeny, cavity-nesting species laid eggs with lower protoporphyrin concentrations in the shell, while higher biliverdin concentrations were associated with thicker eggshells for species of all nest types. Overall, these relationships between eggshell pigment concentrations and the biology of passerines are similar to those previously found in nonpasserine eggs, and imply that phylogenetic dependence must be considered across the class in further explanations of the functional significance of avian eggshell coloration
Accretion onto the Supermassive Black Hole in M87
Chandra X-ray observations of the giant elliptical galaxy M87 resolve the
thermal state of the hot interstellar medium into the accretion (Bondi) radius
of its central 3 10^9 Msun black hole. We measure the X-ray gas temperature and
density profiles and calculate the Bondi accretion rate, Mdot_Bondi \sim 0.1
Msun/yr. The X-ray luminosity of the active nucleus of M87 observed with
Chandra is L_{x, 0.5-7 \keV} \sim 7 \times 10^{40}erg/s. This value is much
less than the predicted nuclear luminosity, L_{Bondi} \sim 5 \times 10^{44}
erg/s, for accretion at the Bondi rate with a canonical accretion radiative
efficiency of 10%. If the black hole in M87 accretes at this rate it must do so
at a much lower radiative efficiency than the canonical value. The
multiwavelength spectrum of the nucleus is consistent with that predicted by an
advection-dominated flow. However, as is likely, the X-ray nucleus is dominated
by jet emission then the properties of flow must be modified, possibly by
outflows. We show that the overall energetics of the system are just consistent
with the predicted Bondi nuclear power. This suggests that either most of the
accretion energy is released in the relativistic jet or that the central engine
of M87 undergoes on-off activity cycles. We show that, at present, the energy
dumped into the ISM by the jet may reduce the accretion rate onto the black
hole by a factor \propto (v_j/c_s)^{-2}, where v_j is the jet velocity and c_s
the ISM sound speed, and that this is sufficient to account for the low nuclear
luminosity.Comment: emulateapj.sty, revised version, accepted by Ap
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