10,368 research outputs found
Results of transonic wind tunnel tests on an 0.015-scale space shuttle mated vehicle model (67-ots) in the LaRC 8 foot TPT (IA41)
Wind tunnel tests were conducted to obtain aerodynamic force data for Mach numbers from 0.60 to 1.20. Data were obtained for an alpha range of -10 deg to +10 deg (beta = 0 deg beta = 5 deg) and beta range of -10 deg to +10 deg (alpha = 0 deg). Longitudinal and lateral-directional stability and control data were obtained for tank alone, tank plus SRB's, tank plus Orbiter, and mated configuration of tank + Orbiter + SRB's. Also, single-component rudder hinge moment data were obtained at rudder deflections of 0 and -20 deg for each Mach number tested. Plots of aerodynamic coefficients vs. Mach number are presented, using data from both test IA41 and tests LRC-UPWT-1056, 1073 (IA42A/B) for Mach numbers of 1.60 to 4.63. The model tested in IA42A/B was the same model as tested in IA41
Design reliability goal developed from small sample
Sampling distributions, constructed by Monte Carlo simulation are used in hardware development to establish a design reliability goal, to place a confidence coefficient on reliability estimates, and to determine whether sample stress/strength data demonstrate a specified reliability at a specified confidence level
Evolutionary Models of Super-Earths and Mini-Neptunes Incorporating Cooling and Mass Loss
We construct models of the structural evolution of super-Earth- and
mini-Neptune-type exoplanets with hydrogen-helium envelopes, incorporating
radiative cooling and XUV-driven mass loss. We conduct a parameter study of
these models, focusing on initial mass, radius, and envelope mass fractions, as
well as orbital distance, metallicity, and the specific prescription for mass
loss. From these calculations, we investigate how the observed masses and radii
of exoplanets today relate to the distribution of their initial conditions.
Orbital distance and initial envelope mass fraction are the most important
factors determining planetary evolution, particular radius evolution. Initial
mass also becomes important below a "turnoff mass," which varies with orbital
distance, with mass-radius curves being approximately flat for higher masses.
Initial radius is the least important parameter we study, with very little
difference between the hot start and cold start limits after an age of 100 Myr.
Model sets with no mass loss fail to produce results consistent with
observations, but a plausible range of mass loss scenarios is allowed. In
addition, we present scenarios for the formation of the Kepler-11 planets. Our
best fit to observations Kepler-11b and Kepler-11c involves formation beyond
the snow line, after which they moved inward, circularized, and underwent a
reduced degree mass loss.Comment: 17 pages, 18 figures, 1 table, Accepted to Ap
Wind tunnel test 0A113 of the 0.010-scale space shuttle orbiter model 51-0 in the calspan hypersonic shock tunnel (48-inch leg)
Results are presented of wind tunnel test conducted Hypersonic Shock Tunnel using a 0.010-scale 140A/B configuration orbiter model designated 51-0. The test objectives were: (1) to obtain force and moment data at various Mach numbers and Reynolds numbers from which viscous interaction effects on stability and control may be determined. (1) To provide flow visualization data from which the effects of control surface separation may be evaluated. and (3) To obtain pressure data in conjunction with force and moment data to assist in analyzing viscous interaction and flow separation effects. Data were obtained at angles-of-attack of 20 deg, 30 deg, 40 deg, and 50 deg. The Mach number range covered was from 10 to 16 and the viscous interaction parameter range was from 0.01 to 0.06
Summary of Discussion Question 4: Energy Expandability of a Linear Collider
We report on Discussion Question 4, in Sub-group 1 (`TeV-class') of the
Snowmass Working Group E3: `Experimental Approaches: Linear Colliders', which
addresses the energy expandability of a linear collider. We first synthesize
discussions of the energy reach of the hardware of the 500 GeV designs for
TESLA and NLC/JLC. Next, we review plans for increasing the energy to 800-1000
GeV. We then look at options for expanding the energies to 1500 GeV and sketch
the two-beam accelerator approach to achieving multi-TeV energies.Comment: Presented at Snowmass 2001 (6 pages, 2 figures
An Information-Theoretic Approach to Optimize JWST Observations and Retrievals of Transiting Exoplanet Atmospheres
We provide an example of an analysis to explore the optimization of
observations of transiting hot jupiters with JWST to characterize their
atmospheres, based on a simple three-parameter forward model. We construct
expansive forward model sets for eleven hot jupiters, ten of which are
relatively well-characterized, exploring a range of parameters such as
equilibrium temperature and metallicity, as well as considering host stars over
a wide range in brightness. We compute posterior distributions of our model
parameters for each planet with all of the available JWST spectroscopic modes
and several programs of combined observations and compute their effectiveness
using the metric of estimated mutual information per degree of freedom. From
these simulations, clear trends emerge that provide guidelines for designing a
JWST observing program. We demonstrate that these guidelines apply over a wide
range of planet parameters and target brightnesses for our simple forward
model.Comment: Accepted to ApJ, 25 pages, 14 figures, 8 table
Axions and SN1987A
The effect of free-streaming axion emission on numerical models for the cooling of the newly born neutron star associated with SN1987A is considered. It is found that for an axion mass of greater than approximately 10 to the -3 eV, axion emission shortens the duration of the expected neutrino burst so significantly that it would be inconsistent with the neutrino observations made by the Kamiokande II and Irvine-Michigan-Brookhaven detectors. However, the possibility has not been investigated that axion trapping (which should occur for masses greater than or equal to 0.02 eV) sufficiently reduces axion emission so that axion masses greater than approximately 2 eV would be consistent with the neutrino observations
Mass-Radius Relations and Core-Envelope Decompositions of Super-Earths and Sub-Neptunes
Many exoplanets have been discovered with radii of 1-4 Earth radii, between
that of Earth and Neptune. A number of these are known to have densities
consistent with solid compositions, while others are "sub-Neptunes" likely to
have significant hydrogen-helium envelopes. Future surveys will no doubt
significantly expand these populations. In order to understand how the measured
masses and radii of such planets can inform their structures and compositions,
we construct models both for solid layered planets and for planets with solid
cores and gaseous envelopes, exploring a range of core masses, hydrogen-helium
envelope masses, and associated envelope entropies. For planets in the
super-Earth/sub-Neptune regime for which both radius and mass are measured, we
estimate how each is partitioned into a solid core and gaseous envelope,
associating a specific core mass and envelope mass with a given exoplanet. We
perform this decomposition for both "Earth-like" rock-iron cores and pure ice
cores, and find that the necessary gaseous envelope masses for this important
sub-class of exoplanets must range very widely from zero to many Earth masses,
even for a given core mass. This result bears importantly on exoplanet
formation and envelope evaporation processes.Comment: 26 pages, 21 figures, 16 tables, accepted to Ap
Many-Body Corrections to Charged-Current Neutrino Absorption Rates in Nuclear Matter
Including nucleon--nucleon correlations due to both Fermi statistics and
nuclear forces, we have developed a general formalism for calculating the
charged--current neutrino--nucleon absorption rates in nuclear matter. We find
that at one half nuclear density many--body effects alone suppress the rates by
a factor of two and that the suppression factors increase to 5 at
g cm. The associated increase in the neutrino--matter
mean--free--paths parallels that found for neutral--current interactions and
opens up interesting possibilities in the context of the delayed supernova
mechanism and protoneutron star cooling.Comment: 11 pages, APS REVTeX format, 1 PostScript figure, uuencoded
compressed, and tarred, submitted to Physical Review Letter
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