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At least 577 records · Page 32

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NASA NTRS1975

Computer-developed construction of analytic expressions for the coordinates and partial derivatives of Jupiter's Galilean satellites

A method for improving Sampson's (1910, 1912, 1921) original work in developing series expressions for accurate coordinates of the Galilean satellites is discussed. The method, which utilizes computer-based algebraic manipulation software, was developed to reconstruct Sampson's theory, remove existing errors, introduce neglected effects, and provide analytic expressions for the coordinates as well as for the partial derivatives with respect to orbital parameters, Jupiter's mass and oblateness, the satellite masses, and Jupiter's pole and rotation period. The software system, capable of handling Poisson series with up to 73 polynomial variables and 28 trigonometric arguments, is described. The preliminary solution is presented, and procedures are outlined for calculating perturbations and eliminating auxiliary parameters.

Lieske, J. H.↗

NASA NTRS1977

Expressions for the precession quantities based upon the IAU /1976/ system of astronomical constants

The structure of the expressions usually employed in calculating the effects of precession is examined, and a method is outlined for revising the expressions to account for changes in the fundamental astronomical constants. It is shown that the basic set of parameters, upon which depend the lengthy polynomials for computing the mean obliquity of data and the elements of the precession matrix, consists of the mean obliquity, the speed of general precession in longitude at a fixed epoch, and the system of planetary masses. Special attention is given to the motion of the ecliptic pole, formulations for a basic epoch as well as an arbitrary epoch, and ecliptic motion relative to the basic epoch. Numerical precession quantities at epoch J2000.0 (JED 2451545.0) are presented which result from the revision of astronomical constants adopted at the XVI General Assembly of the IAU.

Lieske, J. H.↗

NASA NTRS1984

Expressions to determine temperatures and emission measures for solar X-ray events from GOES measurements

Expressions which give the effective color temperatures and corresponding emission measures for solar X-ray events observed with instruments onboard any of the GOES satellites are developed. Theoretical spectra were used to simulate the solar X-ray input at a variety of plasma temperatures. These spectra were folded through the wavelength dependent transfer functions for the two GOES detectors. The resulting detector responses and their ratio as a function of plasma temperature were then fit with simple analytic curves. Over the entire range between 5 and 30 million degrees, these fits reproduce the calculated color temperatures within 2% and the calculated emission measures within 5%. With the theoretical spectra, similar expressions for any pair of broadband X-ray detectors whose sensitivities are limited to wavelengths between 0.2 and 100 A are calculable.

Thomas, R. J.↗

NASA NTRS1984

Temperature-dependent reaction-rate expression for oxygen recombination at Shuttle entry conditions

A temperature-dependent oxygen surface reaction-rate coefficient has been determined from experimental STS-2 heating and wall temperature data at altitudes of 77.91 km, 74.98 km, and 71.29 km. The coefficient is presented in an Arrhenius form and is shown to be less temperature dependent than previous results. Finite-rate viscous-shock-layer heating rates based on this present expression have been compared with predicted heating rates using the previous rate coefficients and with experimental heating data obtained over an extensive range of STS-2 and STS-3 entry conditions. A substantial improvement is obtained in comparison of experimental data and predicted heating rates using the present oxygen reaction-rate expression.

Zoby, E. V.↗

NASA NTRS1985

Expressions to determine temperatures and emission measures for solar X-ray events from GOES measurements

Expressions which give the effective color temperatures and corresponding emission measures for solar X-ray events observed with instruments onboard any of the GOES satellites are developed. Theoretical spectra were used to simulate the solar X-ray input at a variety of plasma temperatures. These spectra were folded through the wavelength dependent transfer functions for the two GOES detectors. The resulting detector responses and their ratio as a function of plasma temperature were then fit with simple analytic curves. Over the entire range between 5 and 30 million degrees, these fits reproduce the calculated color temperatures within 2 percent and the calculated emission measures within 5 percent. With the theoretical spectra, similar expressions for any pair of broadband X-ray detectors whose sensitivities are limited to wavelengths between 0.2 and 100 A are calculable.

Thomas, R. J.↗

NASA NTRS1985

Wide-range displacement expressions for standard fracture mechanics specimens

Wide-range algebraic expressions for the displacement of cracked fracture mechanics specimens are developed. For each specimen two equations are given: one for the displacement as a function of crack length, the other for crack length as a function of displacement. All the specimens that appear in ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399) are represented in addition to the crack mouth displacement for a pure bending specimen. For the compact tension sample and the disk-shaped compact tension sample, the displacement at the crack mouth and at the load line are both considered. Only the crack mouth displacements for the arc-shaped tension samples are presented. The agreement between the displacements or crack lengths predicted by the various equations and the corresponding numerical data from which they were developed are nominally about 3 percent or better. These expressions should be useful in all types of fracture testing including fracture toughness, K-resistance, and fatigue crack growth.

Kapp, J. A.↗

NASA NTRS1988

Directed band ratioing for the retention of perceptually-independent topographic expression in chromaticity-enhanced imagery

A band ratioing method is developed which directs the retention of topographic expression and albedo information so that they remain depicted as prominent variations in image intensity. Band data are adjusted so that ratio values for each surface material coherently increase with increasing pixel bispectral radiance for all three ratios of the color composite. The retained topographic expression and albedo information do not significantly distort the ratio-enhanced band-variant reflectance information, and the resultant images are similar to chromaticity-enhanced band composite images, but require only simple arithmetic processing steps.

Crippen, Robert E.↗

NASA NTRS1990

Evaluation of expressions involving higher order derivations

The local geometric properties of a nonlinear control system defined by vector fields E(sub 1),..., E(sub M) are determined by the algebraic properties of the iterated Lie brackets of the E(sub j)'s. The problem of rewriting expressions is examined involving the E(sub j)'s in terms of the D(sub mu)'s in such a way as to handle effectively any cancellation occurring due to commuting of the D(sub mu)'s. A data structure is introduced which allows us to organize the computation to take advantage of the symmetries in the expression and reduce the operation count.

Grossman, Robert↗

NASA NTRS1990

Optimal expression evaluation for data parallel architectures

A data parallel machine represents an array or other composite data structure by allocating one processor per data item. A pointwise operation can be performed between two such arrays in unit time, provided their corresponding elements are allocated in the same processors. If the arrays are not aligned in this fashion, the cost of moving one or both of them is part of the cost of operation. The choice of where to perform the operation then affects this cost. If an expression with several operands is to be evaluated, there may be many choices of where to perform the intermediate operations. An efficient algorithm is given to find the minimum cost way to evaluate an expression, for several different data parallel architectures. The algorithm applies to any architecture in which the metric describing the cost of moving an array has a property called robustness. This encompasses most of the common data parallel communication architectures, including meshes of arbitrary dimension and hypercubes.

Gilbert, J. R.↗

NASA NTRS1991

Optimal expression evaluation for data parallel architectures

A data parallel machine represents an array or other composits data structure by allocating one processor per data item. A pointwise operation can be performed between two such arrays in unit time, provided their corresponding elements are allocated in the same processors. If the arrays are not aligned in this fashion, the cost of moving one or both of them is part of the cost of operation. The choice of where to perform the operation then affects this cost. If an expression with several operands is to be evaluated, there may be many choices of where to perform the intermediate operations. An efficient algorithm is given to find the minimum cost way to evaluate an expression, for several different data parallel architectures. The algorithm applies to any architecture in which the metric describing the cost of moving an array has a property called robustness. This encompasses most of the common data parallel communication architectures, including meshes of arbitrary dimension and hypercubes.

Gilbert, John R.↗

NASA NTRS1990

Optimal expression evaluation for data parallel architectures

A data parallel machine represents an array or other composite data structure by allocating one processor (at least conceptually) per data item. A pointwise operation can be performed between two such arrays in unit time, provided their corresponding elements are allocated in the same processors. If the arrays are not aligned in this fashion, the cost of moving one or both of them is part of the cost of the operation. The choice of where to perform the operation then affects this cost. If an expression with several operands is to be evaluated, there may be many choices of where to perform the intermediate operations. An efficient algorithm is given to find the minimum-cost way to evaluate an expression, for several different data parallel architectures. This algorithm applies to any architecture in which the metric describing the cost of moving an array is robust. This encompasses most of the common data parallel communication architectures, including meshes of arbitrary dimension and hypercubes. Remarks are made on several variations of the problem, some of which are solved and some of which remain open.

Gilbert, John R.↗

NASA NTRS1996

The Favre-Reynolds Average Distinction and a Consistent Gradient Transport Expression for the Dissipation

Two equation and higher order closures for compressible turbulence fail to capture the compressible wall layers' log scaling. Accounting for the distinction between Favre and Reynolds averaged variables in the compressible moment equations indicate that turbulent transport expressions obtained using the 'variable density approximation' are in error. The error is related to the enstrophy, a Reynolds averaged variable appearing in the equation for the Favre averaged k; recognizing this fact an expression for the transport of dissipation consistent with simple mixing length arguments is obtained. Within the (limited) context of a gradient transport hypothesis a rational form for the turbulent transport of the dissipation is found. Modestly better agreement with the well established compressible Van Driest log scaling is found in k - epsilon calculation.

Ristorcelli, J. R.↗

NASA NTRS1996

In Vitro Interleukin-1 and 2 Production and Interleukin 2 Receptor Expression in the Rhesus Monkey

Anti-human monoclonal antibodies were used to detect and quantify interleukins-1 and 2 and interleukin-2 receptor expression in peripheral blood mononuclear cells from a rhesus monkey. Interleukin-1 production could be induced by phorbol esters (PMA) and was potentiated by phytohemagglutinin (PHA). Interleukin-2 secretion could also be induced by the combination of PHA and PMA, but only weakly with PHA alone. Interleukin-2 receptor expression was present in a subpopulation of unstimulated lymphocytes and could be enhanced by PHA or PMA. These data show once again that the rhesus monkey immune system is cross-reactive with the human one and that rhesus macaque could be a good model to study interleukin therapy.

Schmitt, Didier A.↗

NASA NTRS1997

Kuiper Belt Objects Along the Pluto-Express Path

The science objective of this work is to identify objects in the Kuiper Belt which will, in the 5 years following Pluto encounter, be close to the flight path of NASA's Pluto Express. Our hope is that we will find a Kuiper Belt object or objects close enough that a spacecraft flyby will be possible. If we find a suitable object, the science yield of Pluto Express will be substantially enhanced. The density of objects in the Kuiper Belt is such that we are reasonably likely to find an object close enough to the flight path that on-board gas thrusters can effect a close encounter.

Jewitt, David↗

NASA NTRS1998

Central Renin Injections: Effects on Drinking and Expression of Immediate Early Genes

This study investigated the drinking response and the expression of Fos- and Egr-1-immunoreactivity (Fos-ir, Egr-1-ir) in the brain induced by endogenous angiotensin generated by intracerebroventricular (i.c.v.) injection of renin. Renin induced Fos-ir in the subformical organ (SFO), median preoptic (MnPO), supraoptic and paraventricular nuclei (SON and PVN), area postrema (AP), nuclei of the solitary tract (NTS) and lateral parabrachial nuclei (LPBN). Renin-induced Egr-1-ir exhibited a similar pattern of distribution as that observed for Fos-ir. The dose of i.c.v. renin that induced expression of immediate early gene (IEG) product immunoreactivity also produced vigorous drinking. When renin-injected rats were pretreated with captopril, an angiotensin converting enzyme inhibitor, drinking was blocked. With the same captopril pretreatment, both Fos- and Egr-1-ir in the SFO, MnPO, SON, PVN, AP and LPBN were also significantly reduced.

Xu, Zhice↗

NASA NTRS1999

The Effects of Orbital Spaceflight on Human Osteoblastic Cell Physiology and Gene Expression

The purpose of the proposed study is to establish whether changes in gravitational loading have a direct effect on osteoblasts to regulate TGF-6 expression. The effects of spaceflight and reloading on TGF-B MRNA and peptide levels will be studied in a newly developed line of immortalized human fetal osteoblasts (HFOB) transfected with an SV-40 temperature dependent mutant to generate proliferating, undifferentiated hFOB cells at 33-34 C and a non-proliferating, differentiated HFOB cells at 37-39'C. Unlike previous cell culture models, HFOB cells have unlimited proliferative capacity yet can be precisely regulated to differentiate into mature cells which express mature osteoblast function. If isolated osteoblasts respond to changes in mechanical loading in a manner similar to their response in animals, the cell system could provide a powerful model to investigate the signal transduction pathway for gravitational loading.

Turner, R. T.↗

NASA NTRS1999

Myosin Heavy Chain Gene Expression in Developing Neonatal Skeletal Muscle: Involvement of the Nerve, Gravity, and Thyroid State

The myosin heavy chain (MHC) gene family encodes at least six MHC proteins (herein designated as neonatal, embryonic, slow type I (beta), and fast IIa, IIx, and IIb) that are expressed in skeletal muscle in a muscle-specific and developmentally-regulated fashion. At birth, both antigravity (e.g. soleus) and locomotor (e.g., plantaris) skeletal muscles are undifferentiated relative to the adult MHC phenotype such that the neonatal and embryonic MHC isoforms account for 80 - 90% of the MHC pool in a fast locomotor muscle; whereas, the embryonic and slow, type I isoforms account for approx. 90% of the pool in a typical antigravity muscle. The goal of this study was to investigate the role of an intact nerve, gravity and thyroid hormone (T3), as well as certain interactions of these interventions, on MHC gene expression in developing neonatal skeletal muscles of rodents.

Baldwin, K. M.↗

NASA NTRS1999

Kuiper Belt Objects Along the Pluto Express Path

The objective of this proposal was to mount a ground-based search for Kuiper Belt objects near the trajectory of the NASA Pluto Express spacecraft. The high density of Kuiper Belt objects established from work on Mauna Kea makes it probable that one or more bodies can be visited by Pluto Express after its encounter with Pluto. The work was funded during its first year through NASA HQ. The second year was funded through Goddard. The third year was never funded.

Jewitt, David↗