3,983 research outputs found
How typical is the Coma cluster?
Coma is frequently used as the archetype z~0 galaxy cluster to compare higher
redshift work against. It is not clear, however, how representative the Coma
cluster is for galaxy clusters of its mass or X-ray luminosity, and
significantly: recent works have suggested that the galaxy population of Coma
may be in some ways anomolous. In this work, we present a comparison of Coma to
an X-ray selected control sample of clusters. We show that although Coma is
typical against the control sample in terms of its internal kinematics
(substructure and velocity dispersion profile), it has a significantly high
(~3sigma) X-ray temperature set against clusters of comparable mass. By
de-redshifting our control sample cluster galaxies star-formation rates using a
fit to the galaxy main sequence evolution at z < 0.1, we determine that the
typical star-formation rate of Coma galaxies as a function of mass is higher
than for galaxies in our control sample at a confidence level of > 99 per cent.
One way to alleviate this discrepency and bring Coma in-line with the control
sample would be to have the distance to Coma to be slightly lower, perhaps
through a non-negligible peculiar velocity with respect to the Hubble
expansion, but we do not regard this as likely given precision measurements
using a variety of approaches. Therefore in summary, we urge caution in using
Coma as a z~0 baseline cluster in galaxy evolution studies.Comment: accepted for publication in MNRA
Input guide for computer programs to generate thermodynamic data for air and Freon CF4
FORTRAN computer programs were developed to calculate the thermodynamic properties of Freon 14 and air for isentropic expansion from given plenum conditions. Thermodynamic properties for air are calculated with equations derived from the Beattie-Bridgeman nonstandard equation of state and, for Freon 14, with equations derived from the Redlich-Quang nonstandard equation of state. These two gases are used in scale model testing of model rocket nozzle flow fields which requires simulation of the prototype plume shape with a cold flow test approach. Utility of the computer programs for use in analytical prediction of flow fields is enhanced by arranging card or tape output of the data in a format compatible with a method-of-characteristics computer program
Assessment of analytical and experimental techniques utilized in conducting plume technology tests 575 and 593
Since exhaust plumes affect vehicle base environment (pressure and heat loads) and the orbiter vehicle aerodynamic control surface effectiveness, an intensive program involving detailed analytical and experimental investigations of the exhaust plume/vehicle interaction was undertaken as a pertinent part of the overall space shuttle development program. The program, called the Plume Technology program, has as its objective the determination of the criteria for simulating rocket engine (in particular, space shuttle propulsion system) plume-induced aerodynamic effects in a wind tunnel environment. The comprehensive experimental program was conducted using test facilities at NASA's Marshall Space Flight Center and Ames Research Center. A post-test examination of some of the experimental results obtained from NASA-MSFC's 14 x 14-inch trisonic wind tunnel is presented. A description is given of the test facility, simulant gas supply system, nozzle hardware, test procedure and test matrix. Analysis of exhaust plume flow fields and comparison of analytical and experimental exhaust plume data are presented
Analysis of SRM model nozzle calibration test data in support of IA12B, IA12C and IA36 space shuttle launch vehicle aerodynamics tests
Variations of nozzle performance characteristics of the model nozzles used in the Space Shuttle IA12B, IA12C, IA36 power-on launch vehicle test series are shown by comparison between experimental and analytical data. The experimental data are nozzle wall pressure distributions and schlieren photographs of the exhaust plume shapes. The exhaust plume shapes were simulated experimentally with cold flow while the analytical data were generated using a method-of-characteristics solution. Exhaust plume boundaries, boundary shockwave locations and nozzle wall pressure measurements calculated analytically agree favorably with the experimental data from the IA12C and IA36 test series. For the IA12B test series condensation was suspected in the exhaust plumes at the higher pressure ratios required to simulate the prototype plume shapes. Nozzle calibration tests for the series were conducted at pressure ratios where condensation either did not occur or if present did not produce a noticeable effect on the plume shapes. However, at the pressure ratios required in the power-on launch vehicle tests condensation probably occurs and could significantly affect the exhaust plume shapes
Study of high altitude plume impingement
Computer program has been developed as analytical tool to predict severity of effects of exhaust of rocket engines on adjacent spacecraft surfaces. Program computes forces, moments, pressures, and heating rates on surfaces immersed in or subjected to exhaust plume environments. Predictions will be useful in design of systems where such problems are anticipated
Playing the odds in clinical decision making: lessons from berry aneurysms undetected by magnetic resonance angiography
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Welcome back, Polaris the Cepheid
For about 100 years the amplitude of the 4-day pulsation in Polaris has
decreased. We present new results showing a significant increase in the
amplitude based on 4.5 years of continuous monitoring from the ground and with
two satellite missions.Comment: 5 pages; to appear in the proceedings of the "Cool Stars 15" workshop
held at St Andrews, U
Demographic characteristics of exploited tropical lutjanids: a comparative analysis
Demographic parameters from seven exploited coral reef lutjanid species were compared as a case study of the implications of intrafamily variation in life histories for
multispecies harvest management. Modal lengths varied by 4 cm among four species (Lutjanus fulviflamma, L. vitta, L. carponotatus, L. adetii), which were at least 6 cm smaller than the modal lengths of the largest species (L. gibbus, Symphorus nematophorus, Aprion virescens). Modal ages, indicating ages of full selection to fishing gear, were 10 years or less for all species, but maximum ages ranged from
12 (L. gibbus) to 36 years (S. nematophorus). Each species had a unique growth pattern, with differences in length-at-age and mean asymptotic fork length (L∞), but smaller species generally grew fast during the first 1–2 years of life and larger species grew more slowly over a longer period. Total mortality rates varied among species; L. gibbus had the highest mortality and L. fulviflamma, the
lowest mortality. The variability in life history strategies of these tropical lutjanids makes generalizations about lutjanid life histories difficult, but the fact that all seven had characteristics that would make them particularly vulnerable to fishing indicates that
harvest of tropical lutjanids should be managed with caution
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