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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Solar wind protons - Three-dimensional velocity distributions and derived plasma parameters measured between 0.3 and 1 AU

Such nonthermal features as temperature anisotropies, heat fluxes, and proton double streams have been observed by a Helios solar probe survey of solar wind three-dimensional proton velocity distributions between 0.3 and 1 AU. It is found that a strong anisotropy in the core of proton distributions, with a temperature that is larger perpendicular rather than parallel to the magnetic field, is a persistent feature of high-speed streams, becoming most pronounced in the perihelion, or about 0.3 AU. Isotropic distributions have been detected only close to, and at, magnetic sector boundaries, and the flattest radial temperature profiles are found in high-speed streams. These observations indicate that local heating or proton heat conduction occurs in the solar wind.

Marsch, E.↗
NASA NTRS1995

The microscopic state of the solar wind: Links between composition, velocity distributions, waves and turbulence

An overview is given of the microscopic state of the solar wind with emphasis on recent Ulysses high-latitude observations and previous Helios in-ecliptic observations. The possible links between composition, ionization state. velocity distribution functions of electrons, protons and heavy ions. kinetic plasma waves and MHD-scale turbulence are elaborated. Emphasis is placed on a connection of interplanetary kinetic-scale phenomena with their generating microscopic processes in the corona. The fast streams seem to consist of mesoscale pressure-balanced plasma filaments and magnetic flux tubes, reminiscent of the supergranular-size structures building the open corona, from which copious Alfven waves emanate. The wind from the magnetically structured and active corona shows developed compressive turbulence and considerable abundance and ionization state variations. Some modelling attempts to explain the observed element fractionation are briefly reviewed. The causes of the nonthermal particle features. such as proton-ion differential streaming, ion beams. temperature anisotropies, and skewed distributions associated with collisionless heat conduction, are ultimately to be searched in the fact, that the corona is never quiescent but fundamentally variable in space and time. Consequently, the radial evolution of the internal state of the wind resembles at all latitudes a complicated relaxation process, in the course of which the free (in comparison with LTE conditions) particle kinetic energy is converted into plasma waves and MHD turbulence on a wide range of scales. This leads to intermittent wave-particle interactions and unsteady anomalous transport, mixed with the weak effects of the rare Coulomb collisions. Spherical expansion and large-scale inhomogeneity forces the wind to attain microscopically a complex internal state of dynamic statistical equilibrium.

Marsch, E.↗
NASA NTRS1993

Asteroid collisions: Target size effects and resultant velocity distributions

To study the dynamic fragmentation of rock to simulate asteroid collisions, we use a 2-D, continuum damage numerical hydrocode which models two-body impacts. This hydrocode monitors stress wave propagation and interaction within the target body, and includes a physical model for the formation and growth of cracks in rock. With this algorithm we have successfully reproduced fragment size distributions and mean ejecta speeds from laboratory impact experiments using basalt, and weak and strong mortar as target materials. Using the hydrocode, we have determined that the energy needed to fracture a body has a much stronger dependence on target size than predicted from most scaling theories. In addition, velocity distributions obtained indicate that mean ejecta speeds resulting from large-body collisions do not exceed escape velocities.

Ryan, Eileen V.↗
NASA NTRS1927

Determining the velocity distribution in the boundary layer of an airfoil fitted with a rotary cylinder

In the closer investigation of the results obtained from a wing model with a rotary cylinder mounted in its leading edge (NACA TM's 307 and 354), the velocity distribution in the vicinity of the surface of the model was determined by a hot-wire anemometer. The results confirmed the belief that the rotary cylinder had considerable effect on the air flow, but demonstrated the fact that the direct influence of the cylinder is confined to a very thin layer in immediate proximity to the surface.

CYLINDERS, ROTATING↗
NASA NTRS2010

Solar Wind Halo Formation by the Scattering of the Strahl via Direct Cluster/PEACE Observations of the 3D Velocity Distribution Function

It has been suggested by a number of authors that the solar wind electron halo can be formed by the scattering of the strahl. On frequent occasions we have observed in electron angular skymaps (Phi/Theta-plots) of the electron 3D velocity distribution functions) a bursty-filament of particles connecting the strahl to the solar wind core-halo. These are seen over a very limited energy range. When the magnetic field is well off the nominal solar wind flow direction such filaments are inconsistent with any local forces and are probably the result of strong scattering. Furthermore, observations indicates that the strahl component is frequently and significantly anisotropic (Tper/Tpal approx.2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism. The empirical observational evidence between the halo and the strahl suggests that the strahl population may be, at least in part, the source of the halo component.

Figueroa-Vinas, Adolfo↗
NASA NTRS1983

Electron velocity distributions near the earth's bow shock

New information is presented on the general characteristics of electron distribution functions upstream, within, and downstream of the earth's bow shock, thereby providing new insights into the instabilities in collisionless shocks. The results presented are from a survey of electron velocity distributions measured near the earth's bow shock between October 1977 and December 1978 using the Los Alamos/Garching plasma instrumentation aboard ISEE 2. A wide variety of distribution shapes is found within the different plasma regions in close proximity to the bow shock. It is found that these shapes can be classified into general types that are characteristic of three different plasma regions, namely the upstream region or electron foreshock, the shock proper where most of the heating occurs, and the downstream region or the magnetosheath. Evidence is provided that field-aligned, rather than cross-field, instabilities are the major source of electron dissipation in the earth's bow shock.

Feldman, W. C.↗
NASA NTRS1980

Observations of the velocity distribution of solar wind ions

Measurements made by the Isee 3 ion composition experiment have been used to determine the kinetic temperatures of 3He(++), 4He(++), 16O(6+), and 16O(7+) in the solar wind. It is found that these temperatures generally obey the relation that T(i)/m(i) equals const, but fluctuations, some of which are caused by dynamical effects in the flow, are observed. The temperature of oxygen sometimes rises above 10 K, which is very strong evidence for heating outside the collisional region of the corona. The tendency toward equal temperatures per nucleon occurs everywhere where collisions are unimportant, suggesting that the temperatures are set up close to the sun rather than elsewhere in the interplanetary medium. The velocity distribution function of helium is observed to be non-Maxwellian, with a pronounced high velocity tail.

Ogilvie, K. W.↗
NASA NTRS1993

Determination of cosmic bodies size-velocity distribution by observation of current impacts on Mars

Collisions of cosmic bodies with terrestrial planets involve many physical processes such as deceleration and ablation during their flight through an atmosphere, the impact at a surface accompanied by cratering, melting and evaporation of surface material, generation of shock waves, etc. If body velocity is high enough then a thermal radiation is very important. All these processes on Mars proceed differently than on the other planets because of the low density of its atmosphere. In particular, this leads to the fact that smaller bodies of sizes of the order of 0.1-10 m strike the planet surface without being decelerated and perform some effects which may be detected by equipment placed on a board of artificial satellites, by a network of stations at the surface of Mars and even from the Earth. These observations can be used to determine size-velocity distribution of such bodies in the Solar System. Numerical simulation of the impacts at the surface of Mars have been carried out using two-dimensional gas dynamic code with detailed consideration of the thermal radiative transfer. This work is an extension of our previous paper. We have expanded a range of projectile sizes up to r sub 0 = 100 m. For such a large-scale body, the initial stage of the impact, involving crate ring and ejection of surface material, is very important. Thus, these effects have been taken into account.

Nemchinov, I. V.↗
NASA NTRS1989

The velocity distributions of cometary protons picked up by the solar wind

Velocity space distributions of picked up cometary protons were measured by the ion mass spectrometer on the Giotto spacecraft upstream of the Halley bow shock. Large pitch angle anisotropies were observed at all distances greater than 1.2 x 10 to the 6th km from the comet. As expected, pitch angle diffusion was much more rapid than energy diffusion. When the field was quasi-parallel to the solar wind velocity vector, it was possible to discern the effect of pitch angle scattering by sunward propagating, field-aligned hydromagnetic waves, but there is evidence for other scattering modes as well. For quasi-perpendicular geometries, the pitch angle distribution was very asymmetric with phase space density peaks near pitch angles of 180 deg. It is suggested that the asymmetric pitch angle distribution may be caused by global rather than local wave-particle interactions. Just outside the shock, the pitch angle distribution was nearly isotropic and the radius of the pickup shell increased significantly.

Neugebauer, M.↗
NASA NTRS1981

Mass flow velocity distribution in the solar chromosphere

A study of chromospheric lines (those of Si-II and Si-III) was made using the data from high resolution telescope and spectrograph (HRTS). The optically thick line profiles such as lambda 1206 due to Si-III and lambda 1265 and lambda 1533 due to Si-II were to be investigated in detail using the techniques of spectrum synthesis in an attempt to model the mass flow velocity distribution in the region of the solar atmosphere.

Tripp, D. A.↗
NASA NTRS1979

The velocity distribution of interstellar titanium toward Zeta Persei

Observations of the interstellar 3384-A line of Ti II toward Zeta Persei are reported at a resolution of 1.4 km/s. This resolution exceeds by a factor of almost 3 that used in any previous observations of ions that are dominant stages of ionization in H I regions. Toward Zeta Per, two resolved line components of Ti II having widths generally comparable to those of the corresponding line components of trace ions K I, Ca II, and Na I are seen. For any other ions along this line of sight which have velocity distributions similar to that observed for Ti II, the critical equivalent width above which line saturation must be significant therefore does not exceed 14 mA for ultraviolet lines lying near 1200 A.

Hobbs, L. M.↗
NASA NTRS1992

High-resolution observations of the spatial and velocity distribution of cometary hydrogen

We have obtained high velocity and spatial resolution long-slit H alpha spectra of comets Austin (1989c1) and Levy (1990c). Spectra of both comets clearly show the existence of a low velocity thermalized component of hydrogen gas. The amount of slow hydrogen is estimated for comet Austin. The Levy spectrum shows an unusual high-velocity spatially-confined blob of hydrogen emission of unknown origin.

Brown, Michael E.↗