Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “GRAVITATIONAL INTERACTIONS”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,009 records · Page 56
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

The effect of interacting dark energy on local measurements of the Hubble constant

In the current state of cosmology, where cosmological parameters are being measured to percent accuracy, it is essential to understand all sources of error to high precision. In this paper we present the results of a study of the local variations in the Hubble constant measured at the distance scale of the Coma Cluster, and test the validity of correcting for the peculiar velocities predicted by gravitational instability theory. The study is based on N-body simulations, and includes models featuring a coupling between dark energy and dark matter, as well as two ΛCDM simulations with different values of σ{sub 8}. It is found that the variance in the local flows is significantly larger in the coupled models, which increases the uncertainty in the local measurements of the Hubble constant in these scenarios. By comparing the results from the different simulations, it is found that most of the effect is caused by the higher value of σ{sub 8} in the coupled cosmologies, though this cannot account for all of the additional variance. Given the discrepancy between different estimates of the Hubble constant in the universe today, cosmological models causing a greater cosmic variance is something that we should be aware of.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1976

Dispersion of ensembles of non-interacting particles

The dynamics of an ensemble of noninteracting particles dispersing from a common origin and moving in a common force field with an initial distribution of momenta is analyzed using an approach where the particles are considered as a continuum described by a phase-space distribution function. General solutions are obtained for both the distribution function and the associated spatial density function. The linear case of small departures from circular orbits in an axisymmetric gravitational field is treated along with the specific case of particle dispersion from an object in a circular orbit in the same type of field. Numerical results are presented for the latter case, and consideration is given to the inverse problem of determining the initial time and velocity distribution from knowledge of the ensemble structure at a later time. Explicit results are provided for the case of an ellipsoidal distribution of initial momenta, and a numerical procedure is indicated for treating more general cases.

Heard, W. B.↗
DOE OSTI2018

Ice rule fragility via topological charge transfer in artificial colloidal ice

Artificial particle ices are model systems of constrained, interacting particles. They have been introduced theoretically to study ice-manifolds emergent from frustration, along with domain wall and grain boundary dynamics, doping, pinning-depinning, controlled transport of topological defects, avalanches, and memory effects. Recently such particle-based ices have been experimentally realized with vortices in nano-patterned superconductors or gravitationally trapped colloids. Here we demonstrate that, although these ices are generally considered equivalent to magnetic spin ices, they can access a novel spectrum of phenomenologies that are inaccessible to the latter. With experiments, theory and simulations we demonstrate that in mixed coordination geometries, entropy-driven negative monopoles spontaneously appear at a density determined by the vertex-mixture ratio. Unlike its spin-based analogue, the colloidal system displays a “fragile ice” manifold, where local energetics oppose the ice rule, which is instead enforced through conservation of the global topological charge. The fragile colloidal ice, stabilized by topology, can be spontaneously broken by topological charge transfer.

36 MATERIALS SCIENCE↗
NASA NTRS2018

A Long-Lived Neutron Star Merger Remnant in GW170817: Constraints and Clues from X-ray Observations

Multimessenger observations of GW170817 have not conclusively established whether the merger remnant is a black hole (BH) or a neutron star (NS). We show that a long-lived magnetized NS with a poloidal field B ≈ 1012 G is fully consistent with the electromagnetic dataset, when spin-down losses are dominated by gravitational wave (GW) emission. The required ellipticity ε >~ 10−5 can result from a toroidal magnetic field component much stronger than the poloidal component, a configuration expected from an NS newly formed from a merger. Abrupt magnetic dissipation of the toroidal component can lead to the appearance of X-ray flares, analogous to the one observed in gamma-ray burst (GRB) afterglows. In the X-ray afterglow of GW170817, we identify a low-significance (>~3σ) temporal feature at 155 d, consistent with a sudden reactivation of the central NS. Energy injection from the NS spin-down into the relativistic shock is negligible, and the underlying continuum is fully accounted for by a structured jet seen off-axis. Whereas radio and optical observations probe the interaction of this jet with the surrounding medium, observations at X-ray wavelengths, performed with adequate sampling, open a privileged window on to the merger remnant.

gravitational waves↗
NASA NTRS1976

Plasma in the Jovian magnetosphere

The plasma in Jupiter's ionosphere is collisionless above a certain level. In the outer magnetosphere, where the rotational force dominates the gravitational force, the collisionless plasma has a beamlike distribution and gives rise to a two-stream instability. This leads to trapping of plasma in the centrifugally dominated region of the magnetosphere. Plasma is lost through recombination. The equilibrium concentration of trapped particles is calculated by assuming a balance between trapping by wave-particle interaction and loss by recombination. The results are compared with recent observations from Pioneer 10. The observations appear to require an unexplained ion-heating mechanism.

Goertz, C. K.↗
DOE OSTI2017

A periodic table of effective field theories

We systematically explore the space of scalar effective field theories (EFTs) consistent with a Lorentz invariant and local S-matrix. To do so we define an EFT classification based on four parameters characterizing 1) the number of derivatives per interaction, 2) the soft properties of amplitudes, 3) the leading valency of the interactions, and 4) the spacetime dimension. Carving out the allowed space of EFTs, we prove that exceptional EFTs like the non-linear sigma model, Dirac-Born-Infeld theory, and the special Galileon lie precisely on the boundary of allowed theory space. Using on-shell momentum shifts and recursion relations, we prove that EFTs with arbitrarily soft behavior are forbidden and EFTs with leading valency much greater than the spacetime dimension cannot have enhanced soft behavior. We then enumerate all single scalar EFTs in d < 6 and verify that they correspond to known theories in the literature. Finally, our results suggest that the exceptional theories are the natural EFT analogs of gauge theory and gravity because they are one-parameter theories whose interactions are strictly dictated by properties of the S-matrix.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Hydrogen axion star: metallic hydrogen bound to a QCD axion BEC

As a cold dark matter candidate, the QCD axion may form Bose-Einstein condensates, called axion stars, with masses around 10 -11 M⊙ . In this paper, we point out that a brand new astrophysical object, a Hydrogen Axion Star (HAS), may well be formed by ordinary baryonic matter becoming gravitationally bound to an axion star. Here, we study the properties of the HAS and nd that the hydrogen cloud has a high pressure and temperature in the center and is likely in the liquid metallic hydrogen state. Because of the high particle number densities for both the axion star and the hydrogen cloud, the feeble interaction between axion and hydrogen can still generate enough internal power, around 10 13 W (m a /=5 meV) 4 , to make these objects luminous point sources. Furthermore, high resolution ultraviolet, optical and infrared telescopes can discover HAS via black-body radiation.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Tidal evolution of asteroidal binaries. Ruled by viscosity. Ignorant of rigidity

This is a pilot paper serving as a launching pad for study of orbital and spin evolution of binary asteroids. The rate of tidal evolution of asteroidal binaries is defined by the dynamical Love numbers k{sub l} divided by quality factors Q. Common in the literature is the (oftentimes illegitimate) approximation of the dynamical Love numbers with their static counterparts. Since the static Love numbers are, approximately, proportional to the inverse rigidity, this renders a popular fallacy that the tidal evolution rate is determined by the product of the rigidity by the quality factor: k{sub l}/Q∝1/(μQ). In reality, the dynamical Love numbers depend on the tidal frequency and all rheological parameters of the tidally perturbed body (not just rigidity). We demonstrate that in asteroidal binaries the rigidity of their components plays virtually no role in tidal friction and tidal lagging, and thereby has almost no influence on the intensity of tidal interactions (tidal torques, tidal dissipation, tidally induced changes of the orbit). A key quantity that overwhelmingly determines the tidal evolution is a product of the effective viscosity η by the tidal frequency χ. The functional form of the torque’s dependence on this product depends on who wins in the competition between viscosity and self-gravitation. Hence a quantitative criterion, to distinguish between two regimes. For higher values of ηχ, we get k{sub l}/Q∝1/(ηχ), while for lower values we obtain k{sub l}/Q∝ηχ. Our study rests on an assumption that asteroids can be treated as Maxwell bodies. Applicable to rigid rocks at low frequencies, this approximation is used here also for rubble piles, due to the lack of a better model. In the future, as we learn more about mechanics of granular mixtures in a weak gravity field, we may have to amend the tidal theory with other rheological parameters, ones that do not show up in the description of viscoelastic bodies. This line of study provides a tool to exploring the orbital history of asteroidal pairs, as well as of their final spin states.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1975

Plasma in the Jovian magnetosphere

It is shown that the plasma in Jupiter's ionosphere is collisionless above a certain level. In the outer magnetosphere, where the rotational force dominates the gravitational force, the collisionless plasma has a beam-like distribution and gives rise to a two-stream instability. This leads to trapping of plasma in the centrifugally dominated region of the magnetosphere. Plasma is lost by recombination. Equilibrium-trapped particle densities are calculated by requiring a balance between trapping by wave-particle interaction and loss by recombination. The results are compared with recent observations from Pioneer 10. It is suggested that the observations require an unexplained ion-heating mechanism. Some consequences of the model are discussed.

Goertz, C. K.↗
NASA NTRS1982

Saturn's ringlets

This paper suggests that Saturn's magnetic field is, in part, responsible for the very fine-scale radial features, or ringlets, seen in the ring-system. The planet's dipole field interacts with slight radial variations in plasma density, and the operation of an instability segregates the magnetic flux and plasma in the ring-plane into narrow alternating zones. It is suggested that this mechanism may act by itself to give rise to the inner ringlets. It is believed that at greater radial distances it amplifies gravitational resonances.

Bastin, J. A.↗
NASA NTRS1990

The spiral-compact galaxy pair AM 2208-251: Computer simulations versus observations

The system AM2208-251 is a roughly edge-on spiral extending east-west with a smaller round compact E system about 60 arcsec east of the spiral nucleus along the major axis of the spiral. Bertola, Huchtmeier, and Zeilinger (1990) have presented optical spectroscopic as well as single dish 21 cm observations of this system. Their spectroscopic data show, via emission lines lambda lambda 3727-29A, a rising rotation curve near the nucleus. These spectroscopic observations may indicate a tidal interaction in the system. In order to learn more about such pairs, the authors simulated the interaction using the computer model developed by Miller (1976 a,b, 1978) and modified by the authors (Byrd 1986, 1987, 1988). To do the simulation they need an idea of the mutual orbits of the two galaxies. Their computer model is a two-dimensional polar N-body program. It consists of a self-gravitating disk of particles, within an inert axially symmetric stabilizing halo potential. The particles are distributed in a 24(radial) by 36(azimuthal) polar grid. Self consistent calculations can be done only within the grid area. The disk is modeled with a finite Mestel disk, where all the particles initially move in circular orbits with constant tangential velocities (Mestel 1963), resulting in a flat rotation curve. The gas particles in the spiral's disk, which make up 30 percent of its mass, collide in the following manner. The number of particles in each bin of the polar grid is counted every time step. If it is greater than a given critical density, all the particles in the bin collide, obtaining in the result the same velocities, equal to the average for the bin. This process produces clumps of gas particles-the star formation sites. The authors suppress the collision in the inner part of the disk (within the circle r = 6) to represent the hole seen in the gas in the nuclear bulge of spirals. They thus avoid spurious effects due to collisions in that region. They also varied the size of the collisional bins, which did not affect their conclusions.

Klaric, Mario↗
NASA NTRS1994

Monoclonal antibodies directed against surface molecules of multicell spheroids

The objective of this project is to generate a library of monoclonial antibodies (MAbs) directed against surface molecules of tumor and transformed cells grown as multicell spheroids (MCS). These MCS are highly organized, 3-dimensional multicellular structures which exhibit many characteristics of in vivo organized tissues which are not found in conventional monolayer or suspension culture. In brief, MCS combine the relevance or organized tissues with in vitro methodology making the MCS a good model system to study the interactions of mammalian cells, and thereby provide a functional assay for surface adhesion molecules. This project also involves investigations of cell-cell interactions in a gravity-based environment. It will provide an important base of scientific information for future comparative studies on the effects of hypergravity and simulated microgravity environments on cell-cell interactions. This project also has the potential to yield important materials (e.g. cellular products) which may be useful for the diagnosis and/or treatment of certain human diseases. Moreover, this project supports the training of one undergraduate and one graduate student; thus, it will also assist in developing a pool of future scientists with research experience in gravitational biology research.

Martinez, Andrew O.↗
NASA NTRS1999

Detailed Studies on the Structure and Dynamics of Reacting Dusty Flows at Normal and Microgravity

Dusty reacting flows are of particular interest for a wide range of applications. Inert particles can alter the flammability and extinction limits of a combustible mixture. Reacting particles can release substantial amount of heat and can be used either for power generation or propulsion. Accumulation of combustible particles in air can result in explosions which, for example, can occur in grain elevators, during lumber milling and in mine galleries. Furthermore, inert particles are used as flow velocity markers in reacting flows, and their velocity is measured by non-intrusive laser diagnostic techniques. Despite their importance, dusty reacting flows have been less studied and understood compared to gas phase as well as sprays. The addition of solid particles in a flowing gas stream can lead to strong couplings between the two phases, which can be of dynamic, thermal, and chemical nature. The dynamic coupling between the two phases is caused by the inertia that causes the phases to move with different velocities. Furthermore, gravitational, thermophoretic, photophoretic, electrophoretic, diffusiophoretic, centrifugal, and magnetic forces can be exerted on the particles. In general, magnetic, electrophoretic, centrifugal, photophoretic, and diffusiophoretic can be neglected. On the other hand, thermophoretic forces, caused by steep temperature gradients, can be important. The gravitational forces are almost always present and can affect the dynamic response of large particles. Understanding and quantifying the chemical coupling between two phases is a challenging task. However, all reacting particles begin this process as inert particles, and they must be heated before they participate in the combustion process. Thus, one must first understand the interactions of inert particles in a combustion environment. The in-detail understanding of the dynamics and structure of dusty flows can be only advanced by considering simple flow geometries such as the opposed-jet, stagnation-type. In such configurations the imposed strain rate is well characterized, and the in-depth understanding of the details of the physico-chemical processes can be systematically obtained. A number of computational and experimental studies on spray and particle flows have been conducted in stagnation-type configurations. Numerically, the need for a hybrid Eulerian-Lagrangian approach has been identified by Continillo and Sirignano, and the use of such approach has allowed for the prediction of the phenomenon of droplet flow reversal. Gomez and Rosner have conducted a detailed study on the particle response in the opposed-jet configuration, and the particle thermophoretic diffusivities were determined experimentally. Sung, Law and co-workers have conducted numerical studies on the effect of strain rate and temperature gradients on the dynamics of inert particles, as a way of understanding potential errors in experimental LDV data that may arise from thermophoretic forces. This investigation is a combined experimental and numerical study on the details of reacting dusty flows. The specific tasks are: (1) Experimental determination of laminar flame speeds, and extinction strain rates of dusty flows at normal- and micro-gravity as functions of the particle type, particle initial diameter, particle initial number density, and gas phase chemical composition; (2) Detailed numerical simulation of the experiments. Results are compared with experiments and the adequacy of theoretical models is assessed; and (3) Provision of enhanced insight into the thermo-chemical coupling between the two phases.

Andac, M. Gurhan↗
NASA NTRS1993

Extracellular matrix and growth factors in branching morphogenesis

The unifying hypothesis of the NSCORT in gravitational biology postulates that the ECM and growth factors are key interrelated components of a macromolecular regulatory system. The ECM is known to be important in growth and branching morphogenesis of embryonic organs. Growth factors have been detected in the developing embryo, and often the pattern of localization is associated with areas undergoing epithelial-mesenchymal interactions. Causal relationships between these components may be of fundamental importance in control of branching morphogenesis.

Non-NASA Center↗
NASA NTRS2007

The Formation and Chronology of the PAT 91501 Impact-Melt L-Chondrite with Vesicle-Metal-Sulfide Assemblages

The L chondrite Patuxent Range (PAT) 41 91501 is an 8.5-kg unshocked, homogeneous, igneous-textured impact melt that cooled slowly compared to other meteoritic impact melts in a crater floor melt sheet or sub-crater dike. We conducted mineralogical and tomographic studies of previously unstudied mm- to cm-sized metal-sulfide-vesicle assemblages and chronologic studies of the silicate host. Metal-sulfide clasts constitute about 1 vol.%, comprise zoned taenite, troilite and pentlandite, and exhibit a consistent orientation between metal and sulfide and of metal-sulfide contacts. Vesicles make up approximately 2 vol.% and exhibit a similar orientation of long axes. Ar-39-Ar-40 measurements date the time of impact at 4.461 +/- 0.008 Gyr B.P. Cosmogenic noble gases and Be-10 and Al-2l activities suggest a pre-atmospheric radius of 40-60 cm and a cosmic ray exposure age of 25-29 Myr, similar to ages of a cluster of L chondrites. PAT 91501 dates the oldest known impact on the L chondrite parent body. The dominant vesicle-forming gas was S2 (approximately 15-20 ppm), which formed in equilibrium with impact-melted sulfides. The meteorite formed in an impact melt dike beneath a crater, as did other impact melted L chondrites, such as Chico. Cooling and solidification occurred over approximately 2 hours. During this time, approximately 90% of metal and sulfide segregated from the local melt. Remaining metal and sulfide grains oriented themselves in the local gravitational field, a feature nearly unique among meteorites. Many of these metal sulfide grains adhered to vesicles to form aggregates that may have been close to neutrally buoyant. These aggregates would have been carried upward with the residual melt, inhibiting further buoyancy-driven segregation. Although similar processes operated individually in other chondritic impact melts, their interaction produced the unique assemblage observed in PAT 91501.

Benedix, G. K.↗
DOE OSTI2015

GRB 130427A AND SN 2013cq: A MULTI-WAVELENGTH ANALYSIS OF AN INDUCED GRAVITATIONAL COLLAPSE EVENT

We performed a data analysis of the observations by the Swift, NuStar, and Fermi satellites in order to probe the induced gravitational collapse (IGC) paradigm for gamma-ray bursts (GRBs) associated with supernovae (SNe) in the terra incognita of GRB 130427A. We compare our data analysis with those in the literature. We have verified that GRB 130427A conforms to the IGC paradigm by examining the power law behavior of the luminosity in the early 10{sup 4} s of the XRT observations. This has led to the identification of the four different episodes of the binary driven hypernovae (BdHNe) and to the prediction, on 2013 May 2, of the occurrence of SN 2013cq, which was also observed in the optical band on 2013 May 13. The exceptional quality of the data has allowed the identification of novel features in Episode 3 including: (1) the confirmation and the extension of the existence of the recently discovered nested structure in the late X-ray luminosity in GRB 130427A, as well as the identification of a spiky structure at 10{sup 2} s in the cosmological rest-frame of the source; (2) a power law emission of the GeV luminosity light curve and its onset at the end of Episode 2; and (3) different Lorentz Γ factors for the emitting regions of the X-ray and GeV emissions in this Episode 3. These results make it possible to test the details of the physical and astrophysical regimes at work in the BdHNe: (1) a newly born neutron star and the supernova ejecta, originating in Episode 1; (2) a newly formed black hole originating in Episode 2; and (3) the possible interaction among these components, observable in the standard features of Episode 3.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Signatures of deconfined quark phases in binary neutron star mergers

We investigate the quark deconfinement phase transition in the context of binary neutron star (BNS) mergers. We employ a new finite-temperature composition-dependent equation of state (EOS) with a first order phase transition between hadrons and deconfined quarks to perform numerical relativity simulations of BNS mergers. Here, the softening of the EOS due to the phase transition causes the merger remnants to be more compact and to collapse to a black hole (BH) at earlier times. The phase transition is imprinted on the postmerger gravitational wave (GW) signal duration, amplitude, and peak frequency. However, this imprint is only detectable for binaries with sufficiently long-lived remnants. Moreover, the phase transition does not result in significant deviations from quasi-universal relations for the postmerger GW peak frequency. We also study the impact of the phase transition on dynamical ejecta, remnant accretion disk masses, r-process nucleosynthetic yields and associated electromagnetic (EM) counterparts. While there are differences in the EM counterparts and nucleosynthesis yields between the purely hadronic models and the models with phase transitions, these can be primarily ascribed to the difference in remnant collapse time between the two. An exception is the non-thermal afterglow caused by the interaction of the fastest component of the dynamical ejecta and the interstellar medium, which is systematically boosted in the binaries with phase transition as a consequence of the more violent merger they experience.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Cosmology of a Lorentz violating Galileon theory

We modify the scalar Einstein-aether theory by breaking the Lorentz invariance of a gravitational theory coupled to a Galileon type scalar field. This is done by introducing a Lagrange multiplier term into the action, thus ensuring that the gradient of the scalar field is time-like, with unit norm. The theory can also be considered as an extension to the mimetic dark matter theory, by adding some derivative self interactions to the action, which keeps the equation of motion at most second order in time derivatives. The cosmological implications of the model are discussed in detail. In particular, for pressure-less baryonic matter, we show that the universe experiences a late time acceleration. The cosmological implications of a special coupling between the scalar field and the trace of the energy-momentum tensor are also explored.

79 ASTRONOMY AND ASTROPHYSICS↗