10,573 research outputs found
The Binary Second Sequence in Cluster Colour--Magnitude Diagrams
We show how the second sequence seen lying above the main sequence in cluster
colour magnitude diagrams results from binaries with a large range of mass
ratios and not just from those with equal masses. We conclude that the presence
of a densely populated second sequence, with only sparse filling in between it
and the single star main sequence, does not necessarily imply that binary mass
ratios are close to unity.Comment: Accepted to MNRAS. 5 Pages including 3 figure
Effects of Low pH on Lactate Dehydrogenase Kinetics of Diving and Nondiving Reptiles
The properties of lactate dehydrogenase were examined in two snake species, Nerodia rhombifera and Elaphe obsoleta, and a turtle species, Pseudemys scripta. Our purpose was to compare the LDH activity of reptiles with limited anaerobic capabilities with that of the well established diver Pseudemys. The Michaelis-Menten kinetics of LDH and its susceptibility to inhibition by elevated pyruvate concentrations were investigated in the brain and heart of the three species. All tissue incubations and enzyme activity determinations were done at a pH of 7.0 in order to stimulate a diving blood pH in the three species. In both tissues the LDH activity of the snakes was higher than that of Pseudemys at pyruvate concentrations ranging between .03 mM and .50 mM. The Km values of the snakes were lower than those of Pseudemys, suggesting a greater enzyme-substrate affinity in the snake tissues. The Vmax values were higher in the snake tissues indicating a faster conversion of substrate to product. Heart LDH activity was reduced to an equal extent by high pyruvate concentrations in each of the three species. Elaphe brain LDH was most susceptible to pyruvate inhibition, but Nerodia and Pseudemys brain LDH were inhibited to an equal extent. The results indicate that the kinetic behavior of brain and heart LDH of the three species is similar at a pH of 7.4 and a pH of 7.0. The results also suggest that the LDH of Pseudemys is no better adapted to withstand anaerobic conditions than that of Nerodia or Elaphe at a pH of 7.0
Application of biological filters in water treatment systems
Silver chloride placed on or close to barrier kills bacteria as they arrive. Dead bacteria accumulate linearly, whereas previously, live bacteria accumulated exponentially. During continuous 30-day tests, no bacteriological contamination was found downstream of filters with silver chloride added
Chandra astrometry sets a tight upper limit to the proper motion of SGR 1900+14
The soft gamma-ray repeater (SGR) SGR 1900+14 lies a few arcminutes outside
the edge of the shell supernova remnant (SNR) G42.8+0.6. A physical association
between the two systems has been proposed - for this and other SGR-SNR pairs -
based on the expectation of high space velocities for SGRs in the framework of
the magnetar model. The large angular separation between the SGR and the SNR
center, coupled with the young age of the system, suggest a test of the
association with a proper motion measurement. We used a set of three
Chandra/ACIS observations of the field spanning 5 years to perform accurate
relative astrometry in order to measure the possible angular displacement of
the SGR as a function of time. Our investigation sets a 3-sigma upper limit of
70 mas/yr to the overall proper motion of the SGR. Such a value argues against
an association of SGR 1900+14 with G42.8+0.6 and adds further support to the
mounting evidence for an origin of the SGR within a nearby, compact cluster of
massive stars.Comment: Accepted for publication in The Astrophysical Journal. 4 pages in
emulate-apj styl
The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs
Between 1996 July and 2002 April, one or more spacecraft of the
interplanetary network detected 787 cosmic gamma-ray bursts that were also
detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera
experiments aboard the BeppoSAX spacecraft. During this period, the network
consisted of up to six spacecraft, and using triangulation, the localizations
of 475 bursts were obtained. We present the localization data for these events.Comment: 89 pages, 3 figures. Submitted to the Astrophysical Journal
Supplement Serie
Potable water bactericide agent development
The results are summarized of the work performed for the development and evaluation of a bactericide agent/system concept capable of being used in the space shuttle potable water system. The concept selected for evaluation doses fuel cell water with silver ions before the water is stored and used, by passing this water through columns packed with silver chloride and silver bromide particles, respectively. Four simulated space shuttle potable water system tests, each of seven days duration, were performed to demonstrate that this concept is capable of delivering sterile water even though 3 + or - 1 x 10 to the 9th power Type IIIa or Pseudomonas aeruginosa bacteria, two types which have been found in the Apollo potable water system, are purposely injected into the system each day. This result, coupled with the fact that silver ions do not have to be periodically added to the stored water, indicates that this concept is superior to the chlorine and iodine techniques used on Apollo
Feasibility study of an Integrated Program for Aerospace-vehicle Design (IPAD) system. Volume 1: Summary
An overview is provided of the Ipad System, including its goals and objectives, organization, capabilities and future usefulness. The systems implementation is also presented with operational cost summaries
Public Health Workforce Shortages Imperil Nation's Health
Examines from a community-based perspective the scope of the shortages in the public health workforce; contributing factors such as inadequate funding, salaries, and benefits; and strategies for training, recruiting, and retaining public health workers
Evolution of binary stars and the effect of tides on binary populations
We present a rapid binary evolution algorithm that enables modelling of even
the most complex binary systems. In addition to all aspects of single star
evolution, features such as mass transfer, mass accretion, common-envelope
evolution, collisions, supernova kicks and angular momentum loss mechanisms are
included. In particular, circularization and synchronization of the orbit by
tidal interactions are calculated for convective, radiative and degenerate
damping mechanisms. We use this algorithm to study the formation and evolution
of various binary systems. We also investigate the effect that tidal friction
has on the outcome of binary evolution. Using the rapid binary code, we
generate a series of large binary populations and evaluate the formation rate
of interesting individual species and events. By comparing the results for
populations with and without tidal friction we quantify the hitherto ignored
systematic effect of tides and show that modelling of tidal evolution in binary
systems is necessary in order to draw accurate conclusions from population
synthesis work. Tidal synchronism is important but because orbits generally
circularize before Roche-lobe overflow the outcome of the interactions of
systems with the same semi-latus rectum is almost independent of eccentricity.
It is not necessary to include a distribution of eccentricities in population
synthesis of interacting binaries, however, the initial separations should be
distributed according to the observed distribution of semi-latera recta rather
than periods or semi-major axes.Comment: 36 pages, 12 figures, to be published in the Monthly Notices of the
Royal Astronomical Societ
Dynamical Interactions Make Hot Jupiters in Open Star Clusters
Explaining the origin and evolution of exoplanetary "hot Jupiters" remains a
significant challenge. One possible mechanism for their production is
planet-planet interactions, which produces hot Jupiters from planets born far
from their host stars but near their dynamical stability limits. In the much
more likely case of planets born far from their dynamical stability limits, can
hot Jupiters can be formed in star clusters? Our N-body simulations of
planetary systems inside star clusters answer this question in the affirmative,
and show that hot Jupiter formation is not a rare event. We detail three case
studies of the dynamics-induced births of hot Jupiters on highly eccentric
orbits that can only occur inside star clusters. The hot Jupiters' orbits bear
remarkable similarities to those of some of the most extreme exoplanets known:
HAT-P-32 b, HAT-P-2 b, HD 80606 b and GJ 876 d. If stellar perturbations formed
these hot Jupiters then our simulations predict that these very hot, inner
planets are often accompanied by much more distant gas giants in highly
eccentric orbits.Comment: 18 pages, 4 figure
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