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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
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NASA NTRS2011

Results from Numerical General Relativity

For several years numerical simulations have been revealing the details of general relativity's predictions for the dynamical interactions of merging black holes. I will review what has been learned of the rich phenomenology of these mergers and the resulting gravitational wave signatures. These wave forms provide a potentially observable record of the powerful astronomical events, a central target of gravitational wave astronomy. Asymmetric radiation can produce a thrust on the system which may accelerate the single black hole resulting from the merger to high relative velocity.

Baker, John G.↗
NASA NTRS2012

An Assessment of the Surface Longwave Direct Radiative Effect of Airborne Dust in Zhangye China During the Asian Monsoon Year Field Experiment (2008)

Tiny suspensions of solid particles or liquid droplets, called aerosols, hover in earth's atmosphere and can be found over just about anywhere including oceans, deserts, vegetated areas, and other global regions. Aerosols come in a variety of sizes, shapes, and compositions which depend on such factors as their origin and how long they have been in the atmosphere (i.e., their residence time). Some of the more common types of aerosols include mineral dust and sea salt which get lifted from the desert and ocean surfaces, respectively by mechanical forces such as strong winds. Depending on their size, aerosols will either fall out gravitationally, as in the case of larger particles, or will remain resident in the atmosphere where they can undergo further change through interactions with other aerosols and cloud particles. Not only do aerosols affect air quality where they pose a health risk, they can also perturb the distribution of radiation in the earth-atmosphere system which can inevitably lead to changes in our climate. One aerosol that has been in the forefront of many recent studies, particularly those examining its radiative effects, is mineral dust. The large spatial coverage of desert source regions and the fact that dust can radiatively interact with such a large part of the electromagnetic spectrum due to its range in particle size, makes it an important aerosol to study. Dust can directly scatter and absorb solar and infrared radiation which can subsequently alter the amount of radiation that would otherwise be present in the absence of dust at any level of the atmosphere like the surface. This is known as radiative forcing. At the surface dust can block incoming solar energy, however at infrared wavelengths, dust acts to partially compensate the solar losses. Evaluating the solar radiative effect of dust aerosols is relatively straightforward due in part to the relatively large signal-to-noise ratio in the measurements. At infrared wavelengths, on the other hand, the effect is rather difficult to ascertain since the measured dust signal level is on the same order as the instrumental uncertainties. Although the radiative impact of dust is much smaller in the infrared, it can still have a noticeable influence on the distribution of energy in the Earth-atmosphere system. This is mainly attributed to the strong light-absorptive properties commonly found in many earth minerals.

Hansell, Richard A.↗
NASA NTRS1992

Two-component gravitating systems and the red giant-like structure

The present study investigates the equilibria and evolution of gravitating systems composed of two components by approximating their equations of states to polytropes. The structures are explored in hydrostatic equilibrium systematically under the condition that two components interact with each other only through gravity. The systems are found to be characterized by four parameters, the ratio of central densities and the ratio of central thermal energies per unit mass, and the polytropic indices of two components. If the central density is much higher, the structure is little affected by the presence of the other component. If the difference in the central thermal energies is smaller than specified by beta-cri, the system adopts an equilibrium configuration for any mass ratio. Two-component systems necessarily evolve to have the red giantlike structure if one component suffers cooling faster than the other. It is concluded that the red giant structure is a general characteristic of gravitating systems for which there is an appropriate mechanism to decouple the constituent into the hotter and cooler components.

Fujimoto, Masayuki Y.↗
NASA NTRSDate not supplied

Lunar Regolith Trajectories as a Result of Plume Surface Interactions

Lunar regolith is ejected from the impingement points of descent engine plumes. Such particles pose potential risks to surface operations, sites of scientific and historical interest, and orbiting spacecraft. Consequently, determining the resultant trajectories of these particles is necessary in order to estimate and mitigate risk. Here we present the ranges, impact latitudes, times of flight, and maximum altitudes for particles accelerated by a plume surface interaction at the lunar south pole. Using launch angles determined from observations and simulations, and for velocities <1:6 km/s, particles pose little risk. However, above 1:6 km/s the risks increase, and the results become highly sensitive to the initial angle. In addition, gravitational and non-gravitational processes will introduce perturbations to high-velocity trajectories resulting in a reduction in precision. Therefore, while local topography or artificial berms may mitigate trajectories with low initial angles, it remains important to place tight constraints on the potential launch angles of particles accelerated by plume surface interactions through simulations and experimentation. If these angles are indeed constrained to within a few degrees of the horizon, the risks posed by accelerated regolith particles at any velocity will be minimal.

Daniel Batcheldor↗
NASA NTRS1988

A general model for Io's neutral gas clouds. I - Mathematical description

A general mathematical formalism for calculating the physical properties of any of Io's neutral gas clouds (Na, K, O, S, SO2) is presented. The dynamical effects of both the gravitational fields of Io and Jupiter and solar radiation pressure are included, in addition to the many complex space- and time-dependent interactions that occur between the neutral clouds and the plasma torus. The importance of this new model in studying both the plasma conditions prevalent in the inner planetary magnetosphere and the nature of Io's local atmosphere is discussed. A numerical method for evaluating the physical properties of the neutral clouds using the new model is described.

Smyth, W. H.↗
NASA NTRS1994

Some considerations on velocity vector accuracy in dust trajectory analysis

The relative contributions of comets and asteroids to the reservoir of dust in the interplanetary medium is not known. There are direct observations of dust released from comets and there is evidence to associate the IRAS dust bands with possible collisions of asteroids in the main belt. A means towards sorting out the parent sources has been proposed in the establishment of a dust collector in orbit about the Earth. The purpose of such a facility would be to collect not only cosmic dust particles intact but also the state vectors, as they arrive at the detector, the idea being that one may combine analytical laboratory analysis of the physics and chemistry of the captured particles with orbital data in order to help distinguish between bodies and identify parent bodies. The theoretical study of dust particle orbits in the solar system takes on greatly more importance if we use collected trajectory data. The orbital motion of dust when radiation and forces alone are acting is well understood. When gravitational forces due to the planets are included, the motion can become quite complex. In order to characterize the orbits of particles as they crossed the Earth's orbits, a study of the long-time dust orbital evolution was undertaken. We have considered various parameters associated with these dust orbits to see if one may in a general way discriminate between particles evolved from comets and asteroids. We proceed in this study as we have done previously. That is, we considered the dust particles as ideal black bodies, of density 1 gm/cc, spherical, with radii 10-100 microns. Particles of this size are affected by radiation forces, photon pressure, and Poynting-Robertson drag. Account was also taken of solar wind drag, which amounts to about 30 percent of the Poynting-Robertson drag negligible. The gravitational forces due to the planets are included, unlike in our previous study; the planetary orbits are those of true n-body interaction so that the possibility of secular resonance is included. Our method was to calculate explicitly by a numerical procedure the orbits of dust particles after they left their parent bodies. The motion is determined numerically with the implicit Runge-Kutta integrator using Gauss-Radau spacings.

Jackson, A. A.↗
NASA NTRS2019

Search for Eccentric Binary Black Hole Mergers with Advanced LIGO and Advanced Virgo during Their First and Second Observing Runs

When formed through dynamical interactions, stellar-mass binary black holes (BBHs) may retain eccentric orbits (e > 0.1 at 10 Hz) detectable by ground-based gravitational-wave detectors. Eccentricity can therefore be used to differentiate dynamically formed binaries from isolated BBH mergers. Current template-based gravitational-wave searches do not use waveform models associated with eccentric orbits, rendering the search less efficient for eccentric binary systems. Here we present the results of a search for BBH mergers that inspiral in eccentric orbits using data from the first and second observing runs (O1 and O2) of Advanced LIGO and Advanced Virgo. We carried out the search with the coherent WaveBurst algorithm, which uses minimal assumptions on the signal morphology and does not rely on binary waveform templates. We show that it is sensitive to binary mergers with a detection range that is weakly dependent on eccentricity for all bound systems. Our search did not identify any new binary merger candidates. We interpret these results in light of eccentric binary formation models. We rule out formation channels with rates ≳100 Gpc−3 yr−1 for e > 0.1, assuming a black hole mass spectrum with a power-law index ≲2.

B. P. Abbott↗
NASA NTRS1973

Comets and the formation of planets

Morphological study of the physical and dynamical processes of planet formation, with emphasis on the role of comet nuclei. A consistent model proposes the formation of comets and planets in preplanetary rings of the residual solar nebula, with subsequent ejection, chiefly by Jupiter, of the comets to Oort's (1950) sphere. Physically, dynamically, or statistically evaluated items include: (1) the total number and mass of comets in Oort's cloud; (2) reevaluation of the diameters and masses of comet nuclei; (3) the processes of nucleation from gravitational and 'Boltzmann' instabilities of gaseous media to agglomerations of particulate matter; and (4) the statistical-dynamical conditions and time scales of orbital interaction of comets with the planets and the consequences of disintegration.

Opik, E. J.↗
NASA NTRS1996

Kuiper Belt Dust Grains as a Source of Interplanetary Dust Particles

The recent discovery of the so-called Kuiper belt objects has prompted the idea that these objects produce dust grains that may contribute significantly to the interplanetary dust population. In this paper, the orbital evolution of dust grains, of diameters 1 to 9 microns, that originate in the region of the Kuiper belt is studied by means of direct numerical integration. Gravitational forces of the Sun and planets, solar radiation pressure, as well as Poynting-Robertson drag and solar wind drag are included. The interactions between charged dust grains and solar magnetic field are not considered in the model. Because of the effects of drag forces, small dust grains will spiral toward the Sun once they are released from their large parent bodies. This motion leads dust grains to pass by planets as well as encounter numerous mean motion resonances associated with planets. Our results show that about 80% of the Kuiper belt grains are ejected from the Solar System by the giant planets, while the remaining 20% of the grains evolve all the way to the Sun. Surprisingly, the latter dust grains have small orbital eccentricities and inclinations when they cross the orbit of the Earth. This makes them behave more like asteroidal than cometary-type dust particles. This also enhances their chances of being captured by the Earth and makes them a possible source of the collected interplanetary dust particles; in particular, they represent a possible source that brings primitive/organic materials from the outer Solar System to the Earth. When collisions with interstellar dust grains are considered, however, Kuiper belt dust grains around 9 microns appear likely to be collisionally shattered before they can evolve toward the inner part of the Solar System. The collision destruction can be applied to Kuiper belt grains up to about 50 microns. Therefore, Kuiper belt dust grains within this range may not be a significant part of the interplanetary dust complex in the inner Solar System.

Liou, Jer-Chyi↗
NASA NTRS1993

Cytoskeleton-amyloplast interactions in sweet clover

The distribution of organelles within columella cells of sweet clover was examined by transmission electron microscopy following growth under static or clinorotating conditions. A developmentally conditioned polarity was observed, with a proximal location of the nucleus and a distal accumulation of the endoplasmic reticulum. This polarity was insensitive to clinorotation. In contrast, clinorotation altered the location of amyloplasts. Application of cytoskeletal poisons (colchicine, cytochalasin D, taxol, and phalloidin), especially during clinorotation, had interesting effects on the maintenance of columella cell polarity, with a profound effect on the extent, location, and structure of the endoplasmic reticulum. The site of cytoskeletal interactions with sedimenting amyloplasts is thought to be the amyloplast envelope. An envelope fraction, having over 17 polypeptides, was isolated using immobilized antibody technology, and will provide a means of assessing the role of specific peptides in cytoskeleton/amyloplast interactions.

Non-NASA Center↗
NASA NTRS2001

An active role of the amyloplasts and nuclei of root statocytes in graviperception

Three main phases are discerned in the gravitropic reaction: perception of a gravitational stimulus, its transduction, and fixation of the reaction resulting in bending of an organ. According to the starch-statolith hypothesis of Nemec and Haberlandt, amyloplasts in the structurally and functionally specialized graviperceptive cells (statocytes) sediment in the direction of a gravitational vector in the distal part of a cell while a nucleus is in the proximal one. If amyloplasts appear to act as gravity sensors, the receptors, which interact with sedimented amyloplasts, and next signaling are still unclear. An analysis of the structural-functional organization of cells in different root cap layers of such higher plants as pea, Arabidopsis thaliana, and Brassica rapa grown under 1 g, on the clinostats, and in microgravity, allows us to support the hypothesis that amyloplasts function as statoliths in statocytes, but they may not be only the passive statolithic mass. We propose that amyloplasts fulfill a more complex function by interacting with a receptor, which is a nucleus, in transduction of some signal to it. Gravity-induced statolith movement in certain order leads to a new functional connection between gravity susceptors--amyloplasts and a receptor--a nucleus receiving some signal presumedly of a mechanical or biochemical nature from the amyloplasts. During gravitropism, sugar signaling could induce expression of genes encoding auxin transport proteins in a nucleus giving the nucleus an intermediate role in signal trunsduction following perception. c 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

short duration↗
NASA NTRS1993

Analysis of the effects of mean local node-crossing time on the evolution of Sun-synchronous orbits

An investigation of the effect of mean local node-crossing time on the evolution of Sun-synchronous orbits was undertaken during Phase-A orbit analysis for the National Oceanic and Atmospheric Administration (NOAA) O,P,Q environmental spacecraft. That analysis added to the growing body of evidence that individual Sun-synchronous missions, at differing node-crossing times, experience nodal drift rates that can differ in both magnitude and direction. A Sun-synchronous orbit is obtained by means of a nodal drift rate approximating the 0.9856-degree-per-day apparent precession of the position of the mean Sun. This drift rate is achieved through the interaction of the orbital semimajor axis and inclination in Earth's geopotential field. Influencing perturbations include atmospheric drag and, most important, the effects of solar gravitation on inclination. The present analysis examines a series of Sun-synchronous orbits with mean local node-crossing times at 1-hour intervals from 6 a.m. to 6 p.m. It considers the fixed geometry of each orbital plane with respect to both the Sun and the diurnal atmospheric bulge, then analyzes the influence of these features upon the evolution of the semimajor axix and inclination and thus upon the rate of the nodal drift in the course of 1 year.

Jordan, P.↗
NASA NTRS1992

Tidal interactions of inspiraling compact binaries

We discuss the tidal interaction in neutron star-neutron star and neutron star-black hole binaries and argue that they will not be tidally locked during the gravitational inspiral. More specifically, we show that, for inspiraling neutron stars of mass greater than about 1.2 solar mass, the shortest possible tidal synchronization time exceeds the gravitational decay time, so that the neutron star cannot be tidally locked prior to tidal disruption, regardless of its internal viscosity. For smaller mass neutron stars, an implausibly large kinematic viscosity - nearly the speed of light times the stellar radius - is required for tidal locking. We also argue that the mass transfer which occurs when the neutron star reaches the tidal radius will be unstable in neutron star-black hole binaries, and the instability will destroy the neutron star in a few orbital periods. The implications of our work for the detection of these sources by LIGO and other gravitational wave observatories and for the gamma-ray burst scenarios of Paczynski (1986, 1991) are discussed.

Bildsten, Lars↗
NASA NTRS1994

Excitation of neutron star normal modes during binary inspiral

As a compact binary inspirals due to the emission of gravitational waves, its orbital period decreases continuously down to approximately 1 ms, its value at coalescence. During the last part of the inspiral, the two stars are close together, and their tidal interactions become strong. Neutron stars have many normal modes (core g-modes, crustal discontinuity modes, shear modes, etc.) whose periods lie in the range (approximately several ms) swept by the orbital period. Some of these modes are resonantly excited by the tidal force. The amount of energy a mode absorbs is proportional to the square of the overlap integral between its displacement field and the tidal force field. For all modes of interest, this overlap is poor, resulting in relatively weak excitation. For the best case, the absorbed energy is only a small fraction (approximately 10(exp -6)) of the orbital energy, so the orbital phase shift is too weak to be detected by observations of the gravitational wave signal emitted by the inspiraling binary. However, with displacement amplitudes of excited quadrupole modes ranging up to 0.5% of the stellar radius, the possibility of a detectable electromagnetic signature cannot be dismissed. Both the periods of the modes and the energy they absorb depend quite strongly on the internal structure of the star. Their observation could shed light on the correct high-density equation of state.

Reisenegger, Andreas↗
NASA NTRS1997

Gravity, light and plant form

Plants have evolved highly sensitive and selective mechanisms that detect and respond to various aspects of their environment. As a plant develops, it integrates the environmental information perceived by all of its sensory systems and adapts its growth to the prevailing environmental conditions. Light is of critical importance because plants depend on it for energy and, thus, survival. The quantity, quality and direction of light are perceived by several different photosensory systems that together regulate nearly all stages of plant development, presumably in order to maintain photosynthetic efficiency. Gravity provides an almost constant stimulus that is the source of critical spatial information about its surroundings and provides important cues for orientating plant growth. Gravity plays a particularly important role during the early stages of seedling growth by stimulating a negative gravitropic response in the primary shoot that orientates it towards the source of light, and a positive gravitropic response in the primary root that causes it to grow down into the soil, providing support and nutrient acquisition. Gravity also influences plant form during later stages of development through its effect on lateral organs and supporting structures. Thus, the final form of a plant depends on the cumulative effects of light, gravity and other environmental sensory inputs on endogenous developmental programs. This article is focused on developmental interactions modulated by light and gravity.

NASA Discipline Plant Biology↗
NASA NTRS2003

Application of Core Dynamics Modeling to Core-Mantle Interactions

Observations have demonstrated that length of day (LOD) variation on decadal time scales results from exchange of axial angular momentum between the solid mantle and the core. There are in general four core-mantle interaction mechanisms that couple the core and the mantle. Of which, three have been suggested likely the dominant coupling mechanism for the decadal core-mantle angular momentum exchange, namely, gravitational core-mantle coupling arising from density anomalies in the mantle and in the core (including the inner core), the electromagnetic coupling arising from Lorentz force in the electrically conducting lower mantle (e.g. D-layer), and the topographic coupling arising from non-hydrostatic pressure acting on the core-mantle boundary (CMB) topography. In the past decades, most effort has been on estimating the coupling torques from surface geomagnetic observations (kinematic approach), which has provided insights on the core dynamical processes. In the meantime, it also creates questions and concerns on approximations in the studies that may invalidate the corresponding conclusions. The most serious problem is perhaps the approximations that are inconsistent with dynamical processes in the core, such as inconsistencies between the core surface flow beneath the CMB and the CMB topography, and that between the D-layer electric conductivity and the approximations on toroidal field at the CMB. These inconsistencies can only be addressed with numerical core dynamics modeling. In the past few years, we applied our MoSST (Modular, Scalable, Self-consistent and Three-dimensional) core dynamics model to study core-mantle interactions together with geodynamo simulation, aiming at assessing the effect of the dynamical inconsistencies in the kinematic studies on core-mantle coupling torques. We focus on topographic and electromagnetic core-mantle couplings and find that, for the topographic coupling, the consistency between the core flow and the CMB topography is critical for correct evaluation of the coupling torque.

Kuang, Weijia↗
NASA NTRS1987

Thermocapillary migration of a gas bubble in an arbitrary direction with respect to a plane surface

The thermocapillary migration of a gas bubble in an unbounded fluid in the presence of a neighboring rigid plane surface is considered in the limit of negligible Reynolds and Marangoni numbers. Results are given for a scalar interaction parameter defined as the ratio of the speed of the bubble in the presence of the plane surface to the speed in its absence. It is suggested that the weaker interaction effects noted for the case of thermocapillary migration relative to the case of motion due to a body force such as that caused by a gravitational field is attributable to the more rapid decay, away from the bubble, of the disturbance velocity and temperature gradient fields. The surface is found to exert the greatest influence in the case of motion normal to it, and the weakest influence in the case of parallel motion.

Meyyappan, M.↗
NASA NTRS1990

Astrophysics from the moon; Proceedings of the Workshop, Annapolis, MD, Feb. 5-7, 1990

The present conference on astrophysics from the moon encompasses the study of the Galaxy, external planetary systems, solar physics, stars and stellar evolution, the frontiers of Galactic, extragalactic, and cosmological astronomy, an introduction to lunar-based astronomy, concepts for lunar observatories including high-energy observatories, solar observatories, and observatories for particle astrophysics and gravitational studies. Specific issues addressed include the dynamics of Jovian atmospheres, planetary magnetospheres, flare physics, exobiology and SETI from the lunar farside, and the study of interactive stars, star formation, H II regions in absorption at low frequencies, and normal galaxies. Also addressed are the potential lunar investigation of quasars, the formation epoch, and the large-scale structure of the universe, and observational issues related to X-ray large arrays, optical interferometers, VLF radio astronomy, a UV-solar reflecting coronagraph, and a heavy-nucleus detector.

Mumma, Michael J.↗