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At least 397 records · Page 22

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NASA NTRS1977

Dirac cosmology

The large numbers hypothesis (LNH) linking the magnitude of large dimensionless ratios in physics (on the order of 10 to the 40th power) to cosmic time is examined. The LNH is checked against evidence on 3K background radiation of the universe and the (log N, log S)-relation for radio galaxies. Earlier criticisms of LNH by Gamow and Teller are examined, and alternative hypotheses put forth by Dicke and Carter (1974) are discussed. The discussion covers: continuous (additive or multiplicative) creation of matter, the Einstein metric and the atomic metric, and general cosmological and local astronomical implications of LNH. LNH is also viewed in relation to solar evolution and pulsar physics.

Canuto, V.↗

NASA NTRS1988

The Space Station neutral gas environment and the concomitant requirements for monitoring

At 340 km, for typical conditions, the neutral atmospheric density is several times 10E8/cc and is thus more abundant than the ionized component by several factors of 10. At that altitude, the principal series is atomic oxygen with 10 percent N2, and 1 percent He, and trace amounts of O2, H, N, NO, and Ar. The constituent densities are highly variable with local time, latitude, and geophysical indices. The physical interaction with surfaces at orbital velocity leads to large buildup of density on forward faces and great depletions in the wakes of objects. Chemical reactions lead to major modifications in constituent densities as in the case of the conversion of most colliding oxygen atoms to oxygen bearing molecules. The neutral environment about an orbiting body is thus a complex product of many variables even without a source of neutral contaminants. The addition of fluxes of gases emanating from the orbiting vehicle, as will be the case for the Space Station, with the associated physical and chemical interactions adds another level of complexity to the character of the environment and mandates a sophisticated measurement capability if the neutral environment is to be quantitatively characterized.

Carignan, George↗

NASA NTRS1974

Model atmospheres for cool stars

This report contains an extensive series of model atmospheres for cool stars having a wide range in chemical composition. Model atmospheres (temperature, pressure, density, etc.) are tabulated, along with emergent energy flux distributions, limb darkening, and information on convection for selected models. The models are calculated under the usual assumptions of hydrostatic equilibrium, constancy of total energy flux (including transport both by radiation and convection) and local thermodynamic equilibrium. Some molecular and atomic line opacity is accounted for as a straight mean. While cool star atmospheres are regimes of complicated physical conditions, and these atmospheres are necessarily approximate, they should be useful for a number of kinds of spectral and atmospheric analysis.

Johnson, H. R.↗

NASA NTRS1989

Low dielectric thermoplastic polyimide resin

NASA-Langley studies of polymer structure-property relationships have led to the development of a method for the reduction of dielectric constants in polyimides through chemical alterations of polymer backbone composition to reduce chain-chain electronic interactions, as well as through the incorporation of fluorine atoms into the polymer molecular structure. Still-greater dielectric constant reductions are obtainable by means of a physical incorporation of diamic acid additives into these low-dielectric polyimide systems; the resulting thermoplastic resins are applicable to polymer matrices for composite structural materials.

Stoakley, D. M.↗

NASA NTRS2003

[Probing Planck-scale Physics with a Ne-21/He-3 Zeeman Maser]

The Ne-21/He-3 Zeeman maser is a recently developed device which employs co-located ensembles of Ne-21 and He-3 atoms to provide sensitive differential measurements of the noble gas nuclear Zeeman splittings as a function of time, thereby greatly attenuating common-mode systematic effects such as uniform magnetic field variations. The Ne-21 maser will serve as a precision magnetometer to stabilize the system's static magnetic field, while the He-3 maser is used as a sensitive probe for violations of CPT and Lorentz symmetry by searching for small variations in the 3He maser frequency as the spatial orientation of the apparatus changes due to the rotation of the Earth (or placement on a rotating table). In the context of a general extension of the Standard Model of particle physics, the Ne-21/He-3 maser will provide the most sensitive search to date for CPT and Lorentz violation of the neutron: better than 10(exp -32) GeV, an improvement of more than an order of magnitude over past experiments. This exceptional precision will offer a rare opportunity to probe physics at the Planck scale. A future space-based Ne-21/He-3 maser or related device could provide even greater sensitivity to violations of CPT and Lorentz symmetry, and hence to Planck-scale physics, because of isolation from dominant systematic effects associated with ground-based operation, and because of access to different positions in space-time.

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NASA NTRS1995

Relativistic timescale analysis suggests lunar theory revision

The SI second of the atomic clock was calibrated to match the Ephemeris Time (ET) second in a mutual four year effort between the National Physical Laboratory (NPL) and the United States Naval Observatory (USNO). The ephemeris time is 'clocked' by observing the elapsed time it takes the Moon to cross two positions (usually occultation of stars relative to a position on Earth) and dividing that time span into the predicted seconds according to the lunar equations of motion. The last revision of the equations of motion was the Improved Lunar Ephemeris (ILE), which was based on E. W. Brown's lunar theory. Brown classically derived the lunar equations from a purely Newtonian gravity with no relativistic compensations. However, ET is very theory dependent and is affected by relativity, which was not included in the ILE. To investigate the relativistic effects, a new, noninertial metric for a gravitated, translationally accelerated and rotating reference frame has three sets of contributions, namely (1) Earth's velocity, (2) the static solar gravity field and (3) the centripetal acceleration from Earth's orbit. This last term can be characterized as a pseudogravitational acceleration. This metric predicts a time dilation calculated to be -0.787481 seconds in one year. The effect of this dilation would make the ET timescale run slower than had been originally determined. Interestingly, this value is within 2 percent of the average leap second insertion rate, which is the result of the divergence between International Atomic Time (TAI) and Earth's rotational time called Universal Time (UT or UTI). Because the predictions themselves are significant, regardless of the comparison to TAI and UT, the authors will be rederiving the lunar ephemeris model in the manner of Brown with the relativistic time dilation effects from the new metric to determine a revised, relativistic ephemeris timescale that could be used to determine UT free of leap second adjustments.

Deines, Steven D.↗

NASA NTRS1975

Resonance line transfer with partial redistribution. IV - A generalized formulation for lines with common upper states. V - The solar Ca II lines

A generalized formulation is given for treating partial redistribution effects in transfer problems in resonance lines with common upper states. The formulation allows explicitly for the possibility that several spectral lines may arise in transitions from a given upper level to several sharp lower levels, including, for example, the ground state and metastable states. Line profiles for the Ca II H and K lines have been calculated, accounting for the partial frequency coherence of scattered photons. These profiles are compared with calculations made with identical atomic and atmospheric models but assuming complete redistribution. Very significant differences between the profiles obtained using these two different physical descriptions of the scattering process are found, and it is now apparent that the assumption of complete redistribution is a serious oversimplification of the actual physical situation. The results question the validity of equating brightness temperatures observed at K(sub 1) in stellar spectra with minimum temperatures in stellar chromospheres; it appears likely that such a procedure will systematically underestimate the value of T-min.

Milkey, R. W.↗

NASA NTRS1975

Development of an economical silicon solar cell

The growth of electronically viable silicon films on inexpensive foreign substrates is studied, with the objective of creating a technology to radically reduce the overall cost of the silicon employed in photovoltaic solar energy conversion. The approach employed is to enhance crystalline ordering during film nucleation by confining arriving silicon atoms to a narrow band traveling across a substrate, i.e., the Lateral Growth Technique (LGT). The efforts have employed physical vapor deposition of silicon in a vacuum evaporator on glass and metal substrates with both slit masks and single defining edges, and subsequent chemical vapor deposition (CVD) of thicker films on these thin film structures by pyrolysis of silane at higher temperatures.

Lindmayer, J.↗

NASA NTRS1989

Spray combustion stability

The central purpose of this project is the improvement of liquid-fueled rocket motor design technology in order to assist the establishment of economical commercial access to space through the development of engines with enhanced performance and reliability. Specific research effort is focused on spray physics and associated combustion instability phenomena. Results concerning high pressure droplet gasification model, droplet turbulent dispersion model, and spray atomization model will contribute to the development of new computational tools for design of stable liquid propellant rocket engines.

Liang, Pak-Yan↗

NASA NTRS1996

Reflection Spectrum of Two Level Atoms by an Evanescent Laser Wave

An exact solution and numerical calculation of the reflection of two level atoms by atomic mirror are presented. The curve of reflection coefficient against Rabi frequency calculated shows some new features, and the physical machanism underlying is analyzed.

Tan, Weihan↗

NASA NTRS2008

Making More-Complex Molecules Using Superthermal Atom/Molecule Collisions

A method of making more-complex molecules from simpler ones has emerged as a by-product of an experimental study in outer-space atom/surface collision physics. The subject of the study was the formation of CO2 molecules as a result of impingement of O atoms at controlled kinetic energies upon cold surfaces onto which CO molecules had been adsorbed. In this study, the O/CO system served as a laboratory model, not only for the formation of CO2 but also for the formation of other compounds through impingement of rapidly moving atoms upon molecules adsorbed on such cold interstellar surfaces as those of dust grains or comets. By contributing to the formation of increasingly complex molecules, including organic ones, this study and related other studies may eventually contribute to understanding of the origins of life.

Shortt, Brian↗

NASA NTRS2018

Interstellar Mapping and Acceleration Probe (IMAP): A New NASA Mission

The Interstellar Mapping and Acceleration Probe (IMAP) is a revolutionary mission that simultaneously investigates two of the most important overarching issues in Heliophysics today: the acceleration of energetic particles and interaction of the solar wind with the local interstellar medium. While seemingly disparate, these are intimately coupled because particles accelerated in the inner heliosphere play critical roles in the outer heliospheric interaction. Selected by NASA in 2018, IMAP is planned to launch in 2024. The IMAP spacecraft is a simple sun-pointed spinner in orbit about the Sun-Earth L1 point. IMAP's ten instruments provide a complete and synergistic set of observations to simultaneously dissect the particle injection and acceleration processes at 1 AU while remotely probing the global heliospheric interaction and its response to particle populations generated by these processes. In situ at 1 AU, IMAP provides detailed observations of solar wind electrons and ions; suprathermal, pickup, and energetic ions; and the interplanetary magnetic field. For the outer heliosphere interaction, IMAP provides advanced global observations of the remote plasma and energetic ions over a broad energy range via energetic neutral atom imaging, and precise observations of interstellar neutral atoms penetrating the heliosphere. Complementary observations of interstellar dust and the ultraviolet glow of interstellar neutrals further deepen the physical understanding from IMAP. IMAP also continuously broadcasts vital real-time space weather observations. Finally, IMAP engages the broader Heliophysics community through a variety of innovative opportunities. This papersummarizes the IMAP mission at the start of Phase A development.

McComas, D. J.↗

NASA NTRS1990

Studies of the thermal and optical responses of H atoms in solid H2

It was the goal of this reserch project to model both the storage of energy in solid hydrogen in the form of atoms and the conversion of this stored energy into other forms of useful energy. The basic ideas of rocket propulsion originate in classical physics and they remain unchanged. To escape a strong gravitational field, the 'burn time' must be minimized but in negligible force fields, the burn time is unimportant and only the relative masses of rocket to fuel determine a specific exhaust velocity. It is in this latter case that low mass fuels such as hydrogen become very important. The burning of hydrogen in oxygen is a 'benchmark' fuel today providing a specific impulse of 400 seconds or better. More exotic fuels will be needed for many of the interesting explorations of the future but they still must have large energy releases per unit mass. It is in this context that propulsion based on hydrogen atom recombination receives attention and these studies will serve as engineering guides.

Gaines, James R.↗

NASA NTRS1996

Molecular Dynamics Calculations

The development of thermodynamics and statistical mechanics is very important in the history of physics, and it underlines the difficulty in dealing with systems involving many bodies, even if those bodies are identical. Macroscopic systems of atoms typically contain so many particles that it would be virtually impossible to follow the behavior of all of the particles involved. Therefore, the behavior of a complete system can only be described or predicted in statistical ways. Under a grant to the NASA Lewis Research Center, scientists at the Case Western Reserve University have been examining the use of modern computing techniques that may be able to investigate and find the behavior of complete systems that have a large number of particles by tracking each particle individually. This is the study of molecular dynamics. In contrast to Monte Carlo techniques, which incorporate uncertainty from the outset, molecular dynamics calculations are fully deterministic. Although it is still impossible to track, even on high-speed computers, each particle in a system of a trillion trillion particles, it has been found that such systems can be well simulated by calculating the trajectories of a few thousand particles. Modern computers and efficient computing strategies have been used to calculate the behavior of a few physical systems and are now being employed to study important problems such as supersonic flows in the laboratory and in space. In particular, an animated video (available in mpeg format--4.4 MB) was produced by Dr. M.J. Woo, now a National Research Council fellow at Lewis, and the G-VIS laboratory at Lewis. This video shows the behavior of supersonic shocks produced by pistons in enclosed cylinders by following exactly the behavior of thousands of particles. The major assumptions made were that the particles involved were hard spheres and that all collisions with the walls and with other particles were fully elastic. The animated video was voted one of two winning videos in a competition held at the meeting of the American Physical Society's Division of Fluid Dynamics, held in Atlanta, Georgia, in November 1994. Of great interest was the result that in every shock there were a few high-speed precursor particles racing ahead of the shock, carrying information about its impending arrival. Most recently, Dr. Woo has been applying molecular dynamics techniques to the problem of determining the drag produced by the space station truss structure as it flies through the thin residual atmosphere of low-Earth orbit. This problem is made difficult by the complex structure of the truss and by the extreme supersonic nature of the flow. A fully filled section of the truss has already been examined, and drag predictions have been made. Molecular dynamics techniques promise to make realistic drag calculations possible even for very complex partially filled truss segments flying at arbitrary angles.

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NASA NTRS1983

Science and technology results from the OSS-1 payload on the Space Shuttle

The OSS-1 Payload of nine experiments was carried on the STS-3 Space Shuttle flight in March of 1982. The OSS-1 Payload contained four instruments that evaluated specific aspects of the Orbiter's environment, including the levels of particulate, gaseous and electromagnetic emissions given off by the Orbiter, and the interactions between the Orbiter and the surrounding plasma. In addition to these environmental observations, these instruments performed scientific investigations in astronomy and in space plasma physics, including active experiments in electron beam propagation. Other experiments were in the areas of solar physics, plant growth, micrometeorite studies and the technology of actively controlled heat pipes. We present the initial results from these experiments, with some implications of these results for future operation of space experiments from the Shuttle payload bay. One major result was the unexpected discovery of a faint surface-induced optical glow created near the Shuttle surfaces by impacts of ambient atmospheric atoms and molecules.

short duration↗

NASA NTRS1979

Analysis of ultraviolet spectrophotometric data from Copernicus

Ultraviolet spectral data from the OAO 3 satellite are being used to study interstellar absorption lines and stellar and circumstellar lines in hot stars. The interstellar data are beneficial in analyzing the depletions of heavy elements from the gas phase and in elucidating how these depletions depend on physical conditions. Abundances in separate velocity components were determined from line profiles. Observations were carried out for interstellar abundances, both atomic and molecular, towards a number of stars. The better quality data are being analyzed for profile information and the lesser data are being used in curve-of-growth analyses. Molecular observations were carried out as well, N2 was sought; interstellar C2 was detected and its rotational excitation utilized to establish limits in interstellar cloud temperatures. An extensive search for H2O resulted in a tentative identification which will produce new information on chemical reaction rates. Interstellar depletions and grain properties in the rho Ophiuchi cloud, stellar wind variability, and circumstellar lines are also under study.

Snow, T. P., Jr.↗

NASA NTRS1981

Model for the circumstellar gas around alpha Orionis

Models are presented to explain the physical conditions in the circumstellar envelope surrounding the red supergiant Alpha Orionis. The models of the CO density and neutral atomic potassium density are calculated for the outer shell to reproduce simultaneously both the radio detection of CO and optical measurements of the amount of scattering by neutral potassium around Alpha Ori. CO and potassium loss rates of 7 x 10 to the 39th/sec and 8 x 10 to the 37th/sec are obtained, which imply a potassium to carbon ratio greater than that of the sun by about a factor of 25. The low carbon abundance may be attributed to extensive CNO processing, and, together with the potassium abundance, indicates a total mass loss rate of 0.000015 solar masses/year. The mass loss, mass and abundance properties of Alpha Ori suggest it to be the progenitor of a Type II supernova such as Cas A.

Jura, M.↗

NASA NTRS1984

Far-infrared Spectroscopy of Interstellar Gas

Research results of far-infrared spectroscopy with the Kuiper Airborne Observatory are discussed. Both high and intermediate resolution have been successfully employed in the detection of many new molecular and atomic lines including rotational transition of hydrides such as OH, H2O, NH3 and HCl; high J rotational transitions of CO; and the ground state fine structure transitions of atomic carbon, oxygen, singly ionized carbon and doubly ionized oxygen and nitrogen. These transitions have been used to study the physics and chemistry of clouds throughout the galaxy, in the galactic center region and in neighboring galaxies. This discussion is limited to spectroscopic studies of interstellar gas.

Phillips, T. G.↗