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Seasonal variations in the Earth's gravitational field are investigated through the analyis of LAGEOS I satellite laser ranging measurements and are compared with those produced by atmospheric mass redistribution as inferred from global surface pressure date from the National Centers for Environmental Prediction (NCEP) reanalyses.
We study properties of boson stars consisting of ultra-light scalar dark matter with repulsive self-interactions. We investigate the origin of the maximum mass of spherically symmetric stable stars which emerges only when solving the full equations of motion in curved space-time, but not when solving the approximated Schrödinger-Newton equations. When the repulsion is weak, the backreaction of the curvature on the scalars acts as an additional source of attraction and can overcome the repulsion, resulting in a maximum star mass and compactness. We also point out that the potential in a UV completed particle physics model of light scalar dark matter is generally more complicated than the widely used φ 4 interaction. Additional interactions beyond φ 4 in the potential can dramatically change the properties of boson stars as well as modify the prospect of LIGO gravitational wave detection for binary mergers of boson stars.
Free fall in an external static gravitational field of a composite test body consisting of electromagnetically interacting charged particles is analyzed using the TH-epsilon-mu formalism developed by Lightman and Lee (1973). The Lightman and Lee calculation that was carried out to 'post-Coulombian' order is extended to 'post-post-Coulombian' order, and violations of the weak equivalence principle are found which result from the magnetostatic self-energy of the test body. The current generation of Eotvos experiments is shown to test the cited formalism at first order in the external gravitational potential to an accuracy of 4 by 10 to the -10th power for electrostatic energies and 6 by 10 to the -6th power for magnetostatic energies. It is concluded that although the formalism can be tested to an accuracy of 0.04 for electrostatic energies at second order in the gravitational potential, a significant second-order test for magnetostatic energies would require Eotvos experiments accurate to better than one part in 10 to the 15th power.
A vehicle simulation is surface-interacting if the state of the vehicle (position, velocity, and acceleration) relative to the surface is important. Surface-interacting simulations perform ascent, entry, descent, landing, surface travel, or atmospheric flight. Modeling of gravity is an influential environmental factor for surface-interacting simulations. Gravity is the free-fall acceleration observed from a world-fixed frame that rotates with the world. Thus, gravity is the sum of gravitation and the centrifugal acceleration due to the world s rotation. In surface-interacting simulations, the fidelity of gravity at heights above the surface is more significant than gravity fidelity at locations in inertial space. A surface-interacting simulation cannot treat the gravity model separately from the world model, which simulates the motion and shape of the world. The world model's simulation of the world's rotation, or lack thereof, produces the centrifugal acceleration component of gravity. The world model s reproduction of the world's shape will produce different positions relative to the world center for a given height above the surface. These differences produce variations in the gravitation component of gravity. This paper examines the actual performance of world and gravity/gravitation pairs in a simulation using the Earth.
The capability of ultrasonic levitators operating in air to perform density measurements has been demonstrated. The remote determination of the density of ordinary liquids as well as low density solid metals can be carried out using levitated samples with size on the order of a few millimeters and at a frequency of 20 kHz. Two basic methods may be used. The first one is derived from a previously known technique developed for acoustic levitation in liquid media, and is based on the static equilibrium position of levitated samples in the earth's gravitational field. The second approach relies on the dynamic interaction between a levitated sample and the acoustic field. The first technique appears more accurate (1 percent uncertainty), but the latter method is directly applicable to a near gravity-free environment such as that found in space.
The oscillating mass 2(exp l)-pole moment, M(sub nl), of a star in a given (normalized) oscillation mode determines the energy that can be absorbed by the mode in a tidal interaction and the power radiated by the mode in gravitational waves, both of which are proportional to (absolute value of M(sub nl))(exp 2). The coefficients in the expansion of the vector fields del(r(exp l)Y(sub lm)(theta, phi)) in terms of the displacement fields of modes of given l and m are proportional to M(sub nl). This expansion leads to a sum rule sum over n(absolute value of M(sub nl))(exp 2) = constant. For stars of weak to moderate central condensation (such as neutron stars), the f-mode is well approximated by the vector field being expanded, and therefore it takes the lion's share of the sum. Thus the multipole moments of all other modes must be small. In there numerical evaluation, it is necessary to know the shape of the eigenfunctions quite precisly, since a small f-mode contamination can significantly increase the obtained values. This contamination occurs in some `hybrid' numerical computations of neutron star oscillations with relativistic equilibrium stars and Newtonian dynamics (e.g., McDermott et al. 1988). In this case, it is due to a slight inconsistency in the models and leads to a large overestimate of the power radiated in gravitational waves by modes other than the f-mode, although their oscillation periods are nearly unaffected.
Granular materials exhibit a rich variety of dynamical behavior, much of which is poorly understood. Fractal-like stress chains, convection, a variety of wave dynamics, including waves which resemble capillary waves, l/f noise, and fractional Brownian motion provide examples. Work beginning at Duke will focus on gravity driven convection, mixing and gravitational collapse. Although granular materials consist of collections of interacting particles, there are important differences between the dynamics of a collections of grains and the dynamics of a collections of molecules. In particular, the ergodic hypothesis is generally invalid for granular materials, so that ordinary statistical physics does not apply. In the absence of a steady energy input, granular materials undergo a rapid collapse which is strongly influenced by the presence of gravity. Fluctuations on laboratory scales in such quantities as the stress can be very large-as much as an order of magnitude greater than the mean.
The gravity receptor organs of gastropod molluscs, such as Aplysia californica, are bilateral paired statocysts, which contain dense statoconia within a fluid-filled cyst. Gravitational forces on the statoconia are sensed through their interaction with ciliated mechanoreceptor cells in the wall of the cyst. Larval Aplysia contain a single statolith within each statocyst; when the animals grow to a critical size, they begin producing multiple statoconia, a process that continues throughout life. The number of statoconia is highly correlated with animal weight but poorly correlated with age, indicating that stone production is related to total metabolism. The single statolith has an amorphous internal structure whereas the multiple statoconia have calcification deposited on concentric layers of membrane or matrix protein. The statolith appears to be produced within the cyst lumen but the multiple statoconia are produced within supporting cells between the receptor cells. Large adult animals have statoconia larger than those in early post-metamorphic animals which have just started producing multiple stones. The maximum statocyst diameter at which the receptor-cell cilia can suspend the statolith in the center of the cyst lumen is 45 micrometers; production of multiple stones begins when the cyst reaches this size. The mechanisms by which statoconia production is initiated and controlled are discussed.
The macromolecules comprising the cytoskeleton and extracellular matrix of cells may be sensitive to gravitation. Since early development of organs depends on dynamic interactions across cell surfaces, altered gravity may disturb development. We investigated this possibility for heart development. Previous studies showed that the extracellular matrix glycoprotein fibronectin (Fn) is necessary for normal heart development. We cultured precardiac tissue explants in a high aspect ratio bioreactor vessel (HARV) to simulate microgravity. We observed tissue morphology, contraction, and Fn distribution by immunolocalization in HARV rotated and control (lxg) explants, cultured 18 hr. We also measured Fn amount by immunoassay. Explants in HARV were rotated at 6 rpm to achieve continuous freefall. Thirty-five of 37 control, but only 1 of 37 matched rotated explants exhibited contractions. Tissue architecture was identical. Immunolocalization of Fn showed remarkable differences which may be related to the development of contractions. The Fn staining in the HARV explants was less intense in all areas. Areas of linear staining along epithelia were present but shorter, and there was less intercellular staining in both mesenchymal tissue and myocardium. Initial immunoassay results of 5 matched pairs of explants showed a 22% reduction in total tissue Fn in the HARV rotated samples. Our results indicate that altered gravity in the HARV reduced the amount and distribution of Fn, as assessed by two independent criteria. This was correlated with a reduction in the development of contractile activity.
Astronauts experience disturbances in sensorimotor function following their return to Earth due to adaptive responses that occur during exposure to the microgravity conditions of space flight. As part of the Crew Exploration Vehicle design requirements, the crewmember adapted to the microgravity state may need to egress the vehicle within a few minutes for safety and operational reasons in various sea state conditions following a water landing. The act of emergency egress includes and is not limited to rapid motor control tasks (including both fine motor such as object manipulation and gross motor such as opening a hatch) and visual acuity tasks while maintaining spatial orientation and postural stability in time to escape safely. Exposure to even low frequency motions (0.2-2.0 Hz) induced by sea conditions surrounding a vessel can cause significant fine and gross motor control problems affecting critical functions. These motion frequencies coupled with the varying sea state conditions (frequencies ranging from 0.125-0.5 Hz) cause performance deficits by affecting the efficacy of motor and visual acuity dependent skills in tasks critical to emergency egress activities such as visual monitoring of displays, actuating discrete controls, operating auxiliary equipment and communicating with Mission Control and recovery teams. Thus, during exploration class missions the sensorimotor disturbances due to the crewmember's adaptation to microgravity may lead to disruption in the ability to maintain postural stability and perform functional egress tasks during the initial introduction to the Earth's gravitational environment. At present, the functional implication of the interactions between a debilitated crewmember during readaptation to Earth s gravity and the environmental constraints imposed by a water landing scenario is not defined and no operational countermeasure has been implemented to mitigate this risk. Stochastic resonance (SR) is a mechanism whereby noise can assist and hence enhance the response of neural systems to relevant, subthreshold sensory signals. Application of subthreshold stochastic resonance noise coupled to sensory input either through the proprioceptive, visual or vestibular sensory systems, has been shown to improve motor function. Crew members who have adapted to microgravity have acquired new sensorimotor strategies that take time to discard. We hypothesize that detection of time-critical subthreshold sensory signals will play a crucial role in improving strategic responses and thus the rate of skill re-acquisition will be faster, leading to faster recovery of function during their re-adaptation to Earth G. Therefore, we expect the use of stochastic resonance mechanisms will enhance the acquisition of new strategic abilities. This process should ensure rapid restoration of functional egress capabilities during the initial return to Earth G after prolonged space flight. Therefore, the overall goals of this project are to investigate performance of motor and visual tasks during varying sea state conditions and develop a countermeasure based on stochastic resonance that could be implemented to enhance sensorimotor capabilities with the aim of facilitating rapid adaptation to Earth s gravity, allowing rapid CEV egress on water in varying sea states following long-duration space flight.
Compact groups, with their high number densities, small velocity dispersions, and an interstellar medium that has not been fully processed, provide a local analog to conditions of galaxy interactions in the earlier universe. The frequent and prolonged gravitational encounters that occur in compact groups affect the evolution of the constituent galaxies in a myriad of ways, for example, gas processing and star formation. Recently, a statistically significant "gap" has been discovered in the mid-infrared (MIR: 3.6-8 μm) IRAC color space of compact group galaxies. This gap is not seen in field samples and is a new example of how the compact group environment may affect the evolution of member galaxies. In order to investigate the origin and nature of this gap, we have compiled a larger sample of 37 compact groups in addition to the original 12 groups studied by Johnson et al. (yielding 174 individual galaxies with reliable MIR photometry). We find that a statistically significant deficit of galaxies in this gap region of IRAC color space is persistent in the full sample, lending support to the hypothesis that the compact group environment inhibits moderate specific star formation rates. Using this expanded sample, we have more fully characterized the distribution of galaxies in this color space and quantified the low-density region more fully with respect to MIR bluer and MIR redder colors. We note a curvature in the color-space distribution, which is fully consistent with increasing dust temperature as the activity in a galaxy increases. This full sample of 49 compact groups allows us to subdivide the data according to physical properties of the groups. An analysis of these subsamples indicates that neither projected physical diameter nor density shows a trend in color space within the values represented by this sample. We hypothesize that the apparent lack of a trend is due to the relatively small range of properties in this sample, whose groups have already been pre-selected to be compact and dense. Thus, the relative influence of stochastic effects (such as the particular distribution and amount of star formation in individual galaxies) becomes dominant. We analyze spectral energy distributions of member galaxies as a function of their location in color space and find that galaxies in different regions of MIR color space contain dust with varying temperatures and/or polycyclic aromatic hydrocarbon emission.
On the basis of almost universally held assumptions concerning the formation of the planets and the isolation of the solar system from outside influences it follows rather plausibly that all terrestrial planets pass in principle through seven stages. The processes involved include the solidification of grains from gas in the condensation stage, planetesimal interactions, and formation processes. Vigorous convection processes lead to the gravitational separation of iron and the outgassing of oceans. Other stages are related to plate tectonics and terminal volcanism. The ultimate stage of quiescence is characterized by a thick lithosphere and no volcanism.
A general theory of the rotation of solid bodies in the solar system leads to the following conclusions: No special initial conditions on the primordial rotation states of most tidally evolved bodies are necessary to account for their present rotation. The possible exception is the rotation of Venus, which must have been initially retrograde unless a liquid core-solid mantle interaction or an accelerating atmospheric tide could dominate the ordinary gravitational tides. Tides eventually drive all bodies in precessing orbits to 'Cassini states', where the spin vector, normal to the orbit and normal to the invariable plane remain coplanar as the first two precess about the latter. The constant obliquity in this configuration, together with the lowest order gravitational harmonics and the amplitude of the physical libration allows the determination of the central condensation and the extent of a liquid-core for Mercury. Criteria for the existence of observable amplitudes of the free wobble, free precession and libration of the moon are established which do not exclude current, non-zero values.
The wide variety of optical appearances observed in spiral galaxies has encouraged the growth of two theoretical approaches to explain the spiral patterns exhibited by such young objects as OB associations, giant H II regions, and dark dust lanes. These approaches are related to the density wave theory of spiral structure and 'stochastic, self-propagating star formation'. Levinson and Roberts (1981) tried to reconcile these two theoretical approaches, and considered a disk filled with discrete gas clouds. The present investigation is concerned with refinements and extensions of the model of Levinson and Roberts. Attention is given to gravitational forces and dynamical propagation, cloud-cloud collisions, supernova interactions, computational models, a theory concerning the interactions of the gas cloud and stellar association systems, the time evolution of the gas cloud-stellar association systems, and aspects of collisionally triggered star formation.
Radio continuum observations have shown a chain of blobs of emission leading from SgrA* to a small cavity which is located in one of the ionized gas streamers (the Bar) that orbit SgrA* and which is associated with hot gas. Further high-resolution radio images are presented here which show that the blobs are connected to SgrA* by a ridge of emission. It is suggested that the blobs are formed by the interaction of stellar winds from the IRS16 cluster with the gravitational potential of SgrA*. The hot gas then results from the dissipation of the kinetic energy of the blobs as they collide with the orbiting ionized streamer. These collisions are of dynamical significance for the motion of the Bar around the Galactic Center, and there should be detectable variability in the structure on a timescale of 10 yrs.
The cosmic neutrino background is expected to consist of relic neutrinos from the big bang, of neutrinos produced during nuclear burning in stars, of neutrinos released by gravitational stellar collapse, and of neutrinos produced by cosmic ray interactions with matter and radiation in the interstellar and intergalactic medium. Formation of baryonic dark matter in the early universe, matter-antimatter annihilation in a baryonic symmetric universe, and dark matter annihilation could have also contributed significantly to the cosmic neutrino background. The purpose of this paper is to review the properties of these cosmic neutrino backgrounds, the indirect evidence for their existence, and the prospects for their detection.
Lunar dust is a ubiquitous phenomenon which must be explicitly addressed during upcoming human lunar exploration missions. Near term plans to revisit the moon as a stepping stone for further exploration of Mars, and beyond, places a primary emphasis on characterization and mitigation of lunar dust. Comprised of regolith particles ranging in size from tens of nanometers to microns, lunar dust is a manifestation of the complex interaction of the lunar soil with multiple mechanical, electrical, and gravitational effects. The environmental and anthropogenic factors effecting the perturbation, transport, and deposition of lunar dust must be studied in order to mitigate it's potentially harmful effects on exploration systems. The same hold true for assessing the risk it may pose for toxicological health problems if inhaled. This paper presents the current perspective and implementation of dust knowledge management and integration, and mitigation technology development activities within NASA's Exploration Technology Development Program. This work is presented within the context of the Constellation Program's Integrated Lunar Dust Management Strategy. This work further outlines the scientific basis for lunar dust behavior, it's characteristics and potential effects, and surveys several potential strategies for its control and mitigation both for lunar surface operations and within the working volumes of a lunar outpost. The paper also presents a perspective on lessons learned from Apollo and forensics engineering studies of Apollo hardware.
NASA s plans for implementing the Vision for Space Exploration include returning to the moon as a stepping stone for further exploration of Mars, and beyond. Dust on the lunar surface has a ubiquitous presence which must be explicitly addressed during upcoming human lunar exploration missions. While the operational challenges attributable to dust during the Apollo missions did not prove critical, the comparatively long duration of impending missions presents a different challenge. Near term plans to revisit the moon places a primary emphasis on characterization and mitigation of lunar dust. Comprised of regolith particles ranging in size from tens of nanometers to microns, lunar dust is a manifestation of the complex interaction of the lunar soil with multiple mechanical, electrical, and gravitational effects. The environmental and anthropogenic factors effecting the perturbation, transport, and deposition of lunar dust must be studied in order to mitigate it s potentially harmful effects on exploration systems. This paper presents the current perspective and implementation of dust knowledge management and integration, and mitigation technology development activities within NASA s Exploration Technology Development Program. This work is presented within the context of the Constellation Program s Integrated Lunar Dust Management Strategy. The Lunar Dust Mitigation Technology Development project has been implemented within the ETDP. Project scope and plans will be presented, along with a a perspective on lessons learned from Apollo and forensics engineering studies of Apollo hardware. This paper further outlines the scientific basis for lunar dust behavior, it s characteristics and potential effects, and surveys several potential strategies for its control and mitigation both for lunar surface operations and within the working volumes of a lunar outpost.