4,836 research outputs found
Constraints on the mass of a habitable planet with water of nebular origin
From an astrobiological point of view, special attention has been paid to the
probability of habitable planets in extrasolar systems. The purpose of this
study is to constrain a possible range of the mass of a terrestrial planet that
can get water. We focus on the process of water production through oxidation of
the atmospheric hydrogen--the nebular gas having been attracted
gravitationally--by oxide available at the planetary surface. For the water
production to work well on a planet, a sufficient amount of hydrogen and enough
high temperature to melt the planetary surface are needed. We have simulated
the structure of the atmosphere that connects with the protoplanetary nebula
for wide ranges of heat flux, opacity, and density of the nebular gas. We have
found both requirements are fulfilled for an Earth-mass planet for wide ranges
of the parameters. We have also found the surface temperature of planets of <=
0.3 Earth masses is lower than the melting temperature of silicate (~ 1500K).
On the other hand, a planet of more than several Earth masses becomes a gas
giant planet through runaway accretion of the nebular gas.Comment: 25 pages, 8 figures, to appear in the 01 September 2006 issue of Ap
XMM-Newton Observation of the Northwest Radio Relic Region in Abell 3667
Abell 3667 is the archetype of a merging cluster with radio relics. The NW
radio relic is the brightest cluster relic or halo known, and is believed to be
due to a strong merger shock. We have observed the NW relic for 40 ksec of net
XMM time. We observe a global decline of temperature across the relic from 6 to
1 keV, similar to the Suzaku results. Our new observations reveal a sharp
change of both temperature and surface brightness near the position of the
relic. The increased X-ray emission on the relic can be equivalently well
described by either a thermal or nonthermal spectral model. The parameters of
the thermal model are consistent with a Mach number M~2 shock and a shock speed
of ~1200 km s^-1. The energy content of the relativistic particles in the radio
relic can be explained if they are (re)-accelerated by the shock with an
efficiency of ~0.2%. Comparing the limit on the inverse Compton X-ray emission
with the measured radio synchrotron emission, we set a lower limit to the
magnetic field in the relic of 3 muG. If the emission from the relic is
non-thermal, this lower limit is in fact the required magnetic field.Comment: 11 pages, ApJ in pres
3-D inelastic analysis methods for hot section components (base program)
A 3-D inelastic analysis methods program consists of a series of computer codes embodying a progression of mathematical models (mechanics of materials, special finite element, boundary element) for streamlined analysis of combustor liners, turbine blades, and turbine vanes. These models address the effects of high temperatures and thermal/mechanical loadings on the local (stress/strain) and global (dynamics, buckling) structural behavior of the three selected components. These models are used to solve 3-D inelastic problems using linear approximations in the sense that stresses/strains and temperatures in generic modeling regions are linear functions of the spatial coordinates, and solution increments for load, temperature and/or time are extrapolated linearly from previous information. Three linear formulation computer codes, referred to as MOMM (Mechanics of Materials Model), MHOST (MARC-Hot Section Technology), and BEST (Boundary Element Stress Technology), were developed and are described
On 3-D inelastic analysis methods for hot section components (base program)
A 3-D Inelastic Analysis Method program is described. This program consists of a series of new computer codes embodying a progression of mathematical models (mechanics of materials, special finite element, boundary element) for streamlined analysis of: (1) combustor liners, (2) turbine blades, and (3) turbine vanes. These models address the effects of high temperatures and thermal/mechanical loadings on the local (stress/strain)and global (dynamics, buckling) structural behavior of the three selected components. Three computer codes, referred to as MOMM (Mechanics of Materials Model), MHOST (Marc-Hot Section Technology), and BEST (Boundary Element Stress Technology), have been developed and are briefly described in this report
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