16,160 research outputs found
Six-degree-of-freedom program to optimize simulated trajectories (6D POST). Volume 1: Formulation manual
The basic equations and models used in a computer program (6D POST) to optimize simulated trajectories with six degrees of freedom were documented. The 6D POST program was conceived as a direct extension of the program POST, which dealt with point masses, and considers the general motion of a rigid body with six degrees of freedom. It may be used to solve a wide variety of atmospheric flight mechanics and orbital transfer problems for powered or unpowered vehicles operating near a rotating oblate planet. Its principal features are: an easy to use NAMELIST type input procedure, an integrated set of Flight Control System (FCS) modules, and a general-purpose discrete parameter targeting and optimization capability. It was written in FORTRAN 4 for the CDC 6000 series computers
Study of extraterrestrial disposal of radioactive wastes. Part 1: Space transportation and destination considerations for extraterrestrial disposal of radioactive wastes
A feasibility study of extraterrestrial disposal of radioactive waste is reported. This report covers the initial work done on only one part of the NASA study, that evaluates and compares possible space destinations and space transportation systems. The currently planned space shuttle was found to be more cost effective than current expendable launch vehicles by about a factor of 2. The space shuttle requires a third stage to perform the waste disposal missions. Depending on the particular mission, this third stage could be either a reusable space tug or an expendable stage such as a Centaur
Capabilities and applications of the Program to Optimize Simulated Trajectories (POST). Program summary document
The capabilities and applications of the three-degree-of-freedom (3DOF) version and the six-degree-of-freedom (6DOF) version of the Program to Optimize Simulated Trajectories (POST) are summarized. The document supplements the detailed program manuals by providing additional information that motivates and clarifies basic capabilities, input procedures, applications and computer requirements of these programs. The information will enable prospective users to evaluate the programs, and to determine if they are applicable to their problems. Enough information is given to enable managerial personnel to evaluate the capabilities of the programs and describes the POST structure, formulation, input and output procedures, sample cases, and computer requirements. The report also provides answers to basic questions concerning planet and vehicle modeling, simulation accuracy, optimization capabilities, and general input rules. Several sample cases are presented
Age at quitting smoking as a predictor of risk of cardiovascular disease incidence independent of smoking status, time since quitting and pack-years
BACKGROUND Risk prediction for CVD events has been shown to vary according to current smoking status, pack-years smoked over a lifetime, time since quitting and age at quitting. The latter two are closely and inversely related. It is not known whether the age at which one quits smoking is an additional important predictor of CVD events. The aim of this study was to determine whether the risk of CVD events varied according to age at quitting after taking into account current smoking status, lifetime pack-years smoked and time since quitting. FINDINGS We used the Cox proportional hazards model to evaluate the risk of developing a first CVD event for a cohort of participants in the Framingham Offspring Heart Study who attended the fourth examination between ages 30 and 74 years and were free of CVD. Those who quit before the median age of 37 years had a risk of CVD incidence similar to those who were never smokers. The incorporation of age at quitting in the smoking variable resulted in better prediction than the model which had a simple current smoker/non-smoker measure and the one that incorporated both time since quitting and pack-years. These models demonstrated good discrimination, calibration and global fit. The risk among those quitting more than 5 years prior to the baseline exam and those whose age at quitting was prior to 44 years was similar to the risk among never smokers. However, the risk among those quitting less than 5 years prior to the baseline exam and those who continued to smoke until 44 years of age (or beyond) was two and a half times higher than that of never smokers. CONCLUSIONS Age at quitting improves the prediction of risk of CVD incidence even after other smoking measures are taken into account. The clinical benefit of adding age at quitting to the model with other smoking measures may be greater than the associated costs. Thus, age at quitting should be considered in addition to smoking status, time since quitting and pack-years when counselling individuals about their cardiovascular risk.This research was supported by an NHMRC health services
research grant (no. 465130), an NHMRC/NHF PhD scholarship and a
Vichealth Fellowship
Golabi-Ito-Hall syndrome results from a missense mutation in the WW domain of the PQBP1 gene
Background: Golabi, Ito, and Hall reported a family with X linked mental retardation (XLMR), microcephaly, postnatal growth deficiency, and other anomalies, including atrial septal defect, in 1984.Methods: This family was restudied as part of our ongoing study of XLMR, but significant linkage to X chromosome markers could not be found. Extreme short stature and microcephaly as well as other new clinical findings were observed. Mutations in the polyglutamine tract binding protein 1 gene (PQBP1) have recently been reported in four XLMR disorders (Renpenning, Hamel cerebro-palato-cardiac, Sutherland-Haan, and Porteous syndromes) as well as in several other families. The clinical similarity of our family to these patients with mutations in PQBP1, particularly the presence of microcephaly, short stature, and atrial septal defect, prompted examination of this gene.Results: A missense mutation in PQBP1 was identified which changed the conserved tyrosine residue in the WW domain at position 65 to a cysteine (p.Y65C).Conclusions: This is the first missense mutation identified in PQBP1 and the first mutation in the WW domain of the gene. The WW domain has been shown to play an important role in the regulation of transcription by interacting with the PPxY motif found in transcription factors. The p.Y65C mutation may affect the proper functioning of the PQBP1 protein as a transcriptional co-activator
Program to Optimize Simulated Trajectories (POST). Volume 1: Formulation manual
A general purpose FORTRAN program for simulating and optimizing point mass trajectories (POST) of aerospace vehicles is described. The equations and the numerical techniques used in the program are documented. Topics discussed include: coordinate systems, planet model, trajectory simulation, auxiliary calculations, and targeting and optimization
Hydromagnetic constraints on deep zonal flow in the giant planets
The observed zonal flows of the giant planets will, if they penetrate below the visible atmosphere, interact
significantly with the planetary magnetic field outside the metallized core. The appropriate measure of this
interaction is the Chandrasekhar number Q = H^2 /4πρνα^2 λ (H = radial component of the magnetic field,
ν = eddy viscosity, λ = magnetic diffusivity, α^-1 = length scale on which λ varies); at depths where Q ≳ 1, the velocity will be forced to oscillate on a small length scale or decay to zero. We estimate the conductivity due
to semiconduction in H_2 (Jupiter, Saturn) and ionization in H_(2)0 (Uranus, Neptune) as a function of depth;
the value λ ≈ 10^10 cm^2 s^-1 needed for Q = 1 is readily obtained well outside the metallic core (where A ≈ 10^2
cm^2 s^-1). These assertions are quantified by a simple model of the equatorial zonal jet in which the flow is assumed uniform on cylinders concentric with the spin axis, and viscous and magnetic torques on each cylinder are
balanced. We solve this "Taylor constraint" simultaneously with the dynamo equation to obtain the velocity and magnetic field in the equatorial plane. With this model we reproduce the widely differing jet widths of Jupiter and Saturn (though not the flow at very high or low latitudes) using v = 2500 cm^2 s^-1, consistent with the requirement that viscous dissipation not exceed the specific luminosity. A model Uranian jet consistent with the limited Voyager data can also be constructed, with appropriately smaller v, but only if one assumes a two-layer interior. We tentatively predict a wide Neptunian jet. For Saturn (but not Jupiter or Uranus) the model has a large magnetic Reynolds number where Q = 1 and hence exhibits substantial axisymmetrization of the field in the equatorial plane. This effect may or may not
persist at higher latitudes. The one-dimensional model presented is only a first step. Variation of the velocity
and magnetic field parallel to the spin axis must be modeled in order to answer several important questions,
including: (1) What is the behavior of flows at high latitudes, whose Taylor cylinders are interrupted by the
region with Q > 1? (2) To what extent is differential rotation in the envelope responsible for the spinaxisymmetry
of Saturn's magnetic field
The Non-Trivial Effective Potential of the `Trivial' lambda Phi^4 Theory: A Lattice Test
The strong evidence for the `triviality' of (lambda Phi^4)_4 theory is not
incompatible with spontaneous symmetry breaking. Indeed, for a `trivial' theory
the effective potential should be given exactly by the classical potential plus
the free-field zero-point energy of the shifted field; i.e., by the one-loop
effective potential. When this is renormalized in a simple, but nonperturbative
way, one finds, self-consistently, that the shifted field does become
non-interacting in the continuum limit. For a classically scale-invariant (CSI)
lambda Phi^4 theory one finds m_h^2 = 8 pi^2 v^2, predicting a 2.2 TeV Higgs
boson. Here we extend our earlier work in three ways: (i) we discuss the
analogy with the hard-sphere Bose gas; (ii) we extend the analysis from the CSI
case to the general case; and (iii) we propose a test of the predicted shape of
the effective potential that could be tested in a lattice simulation.Comment: 22 pages, LaTeX, DE-FG05-92ER40717-
Concept design and alternate arrangements of orbiter mid-deck habitability features
The evaluations and recommendations for habitability features in the space shuttle orbiter mid-deck are summarized. The orbiter mission plans, the mid-deck dimensions and baseline arrangements along with crew compliments and typical activities were defined. Female and male anthropometric data based on zero-g operations were also defined. Evaluations of baseline and alternate feasible concepts provided several recommendations which are discussed
New Analysis Indicates No Thermal Inversion in the Atmosphere of HD 209458b
An important focus of exoplanet research is the determination of the
atmospheric temperature structure of strongly irradiated gas giant planets, or
hot Jupiters. HD 209458b is the prototypical exoplanet for atmospheric thermal
inversions, but this assertion does not take into account recently obtained
data or newer data reduction techniques. We re-examine this claim by
investigating all publicly available Spitzer Space Telescope secondary-eclipse
photometric data of HD 209458b and performing a self-consistent analysis. We
employ data reduction techniques that minimize stellar centroid variations,
apply sophisticated models to known Spitzer systematics, and account for
time-correlated noise in the data. We derive new secondary-eclipse depths of
0.119 +/- 0.007%, 0.123 +/- 0.006%, 0.134 +/- 0.035%, and 0.215 +/- 0.008% in
the 3.6, 4.5, 5.8, and 8.0 micron bandpasses, respectively. We feed these
results into a Bayesian atmospheric retrieval analysis and determine that it is
unnecessary to invoke a thermal inversion to explain our secondary-eclipse
depths. The data are well-fitted by a temperature model that decreases
monotonically between pressure levels of 1 and 0.01 bars. We conclude that
there is no evidence for a thermal inversion in the atmosphere of HD 209458b.Comment: 8 pages, 5 figures; accepted for publication in Ap
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