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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Filament disappearances

The phenomenon of the sudden filament disappearance (Disparition Brusque) is a familiar one to observers at H alpha telescopes. Nevertherless, the importance in Disparition Brusques (DB) continues to grow for several reasons which are cited in the discussion. It is reported that there seems to be more interest on building and maintain filaments than in destroying them. As a consequence, this sub-group is smaller than most of the others. All the same, progress in this area of filament disapperences seems steady and assured. The importance and interest in DBs is discussed and future directions are indicated.

Wagner, William J.↗
NASA NTRS1986

Interplanetary shocks preceded by solar filament eruptions

The solar and interplanetary characteristics of six interplanetary shock and energetic particle events associated with the eruptions of solar filaments lying outside active regions are discussed. The events are characterized by the familiar double-ribbon H-alpha brightenings observed with large flares, but only very weak soft X-ray and microwave bursts. Both impulsive phases and metric type II bursts are absent in all six events. The energetic particles observed near the earth appear to be accelerated predominantly in the interplanetary shocks. The interplanetary shock speeds are lower and the longitudinal extents considerably less than those of flare-associated shocks. Three of the events were associated with unusual enhancements of singly-ionized helium in the solar wind following the shocks. These enhancements appear to be direct detections of the cool filament material expelled from the corona. It is suggested that these events are part of a spectrum of solar eruptive events which include both weaker events and the large flares. Despite their unimpressive and unreported solar signatures, the quiescent filament eruptions can result in substantial space and geophysical disturbances.

Cane, H. V.↗
NASA NTRS1987

A method for overcoming the velocity space filamentation problem in collisionless plasma model solutions

The solution of filtered Vlasov-Maxwell equations, rather than the Vlasov-Maxwell equations themselves, is shown to ameliorate the velocity space filamentation problem in collisionless plasma models. Exact field solutions and filtered velocity distribution functions are obtained without introducing errors. Proper selection of the filter width is demonstrated to inhibit development of velocity space filamentation and, it is conjectured, position space filamentation. The results of sample calculations of both filtered and nonfiltered field solutions illustrate a high degree of agreement between both solutions, with significant savings in computational time and memory requirements with the filtered solutions.

Klimas, Alexander J.↗
NASA NTRS1987

Dynamics of solar filaments. V - Oscillations in the H-alpha and 1548 A C IV lines

The Multichannel Subtractive Double Pass (MSDP) Spectrograph operating in the Meudon solar tower and the Ultraviolet Spectrometer and Polarimeter (UVSP) aboard the Solar Maximum Mission (SMM) satellite are used to analyze, by Fourier transform technique, time sequence observations of filaments in both the H-alpha line and in the 1548 A C IV line. The H-alpha data confirm previous findings that there are no oscillations at the location of the filament in the observed range 1-10 mHz. In the C IV line, power is observed in some parts of the filament where a steady velocity gradient is present, e.g. in the footpoints. The energy is probably due to convection motions rather than pressure oscillations.

Malherbe, J. M.↗
NASA NTRS1988

Diamond film by hot filament CVD method

Diamond synthesis by the hot filament CVD method is discussed. A hot filament decomposes gas mixtures and oxygen containing organic compounds such as alcohols. which are carbon sources. The resulting thin films, growth mechanisms, and characteristics and problems associated with the hot filament CVD method are analyzed and evaluated.

Hirose, Y.↗
NASA NTRS1988

Interaction and merging of vortex filaments

The asymptotic solutions of Navier-Stokes equations for vortex filaments of finite strength with small effective vortical cores are summarized with special emphasis placed on the physical meaning and the practical limit to the applicability of the asymptotic solution. Finite-difference solutions of Navier-Stokes equations for the marging of the filament(s) are described with a focus on the development of the approximate boundary conditions for the computational domain. An efficiency study employing a model problem is used to assess the advantages of the present approximate boundary condition method over previously used techniques. Applications of the present method are presented for the motion and decay of a 3:1 elliptic vortex ring, and for the merging process of a pair of coaxial vortex rings. A numerical procedure for the problem of local merging of vortex filaments, which requires the asymptotic analysis as well as the numerical Navier-Stokes solver, is also presented.

Liu, C. H.↗
NASA NTRS1988

Filamentation instability of large-amplitude Alfven waves

An instability that leads to the filamentation of large-amplitude Alfven waves and gives rise to purely growing density and magnetic field fluctuations is studied. The dispersion relation of the instability is derived, from which the threshold conditions and the growth rates of the instability are analyzed quantitatively for applications to the solar wind plasma. Their dependence on the filamentation spectrum, the plasma beta, and the pump frequency and intensity was examined for both right-hand and left-hand circularly polarized Alfven waves. The excitation of filamentation instability for certain cases of interest is discussed and compared with that of the parametric decay and modulation instability. The relevance of the proposed instability to some observations is discussed.

Kuo, S. P.↗
NASA NTRS1988

The vertical structure of arch filament systems in solar emerging flux regions

The paper studies the vertical velocity of arch filaments in emerging flux regions by measuring their proper motion near the limb in H-alpha filtergrams and their radial velocity near the disk center in H-alpha spectrograms. Both show that arch filaments rise at a velocity between 10 and 15 km/s. The possible mechanisms producing this high velocity are discussed. None of them is satifactory, but it appears that the unloading of the arches by outflow must play a role. From the strength of H-alpha emission and D3 absorption, the temperature of arch filaments is estimated at 6000-15,000 K and the density at 10 to the 11th-12th/cu cm.

Chou, Dean-Yi↗
NASA NTRS1988

Spur-type instability observed on numerically simulated vortex filaments

An instability observed on vortex filaments during numerical simulations of the three-dimensional, time-dependent dynamics of vortex wakes is studied to determine when and why it occurs. It is concluded that the observed instability is a consequence of the use of straight-line vortex segments of finite length to model continuously curving vortex filaments. The instability appears to occur only when the link length is a sizable fraction of the vortex span and, therefore, is not expected in an experiment. Guidelines are then given that help avoid numerical instabilities when vortex filaments are used in flow simulations.

Rossow, Vernon J.↗
NASA NTRS1989

Microwave evidence for large-scale changes associated with a filament eruption

VLA observations at 6 and 20 cm wavelengths taken on August 3, 1985 are presented, showing an eruptive filament event in which microwave emission originated in two widely separated regions during the disintegration of the filament. The amount of heat required for the enhancement is estimated. Near-simultaneous changes in intensity and polarization were observed in the western components of the northern and southern regions. It is suggested that large-scale magnetic interconnections permitted the two regions to respond similarly to an external energy or mass source involved in the disruption of the filament.

Kundu, M. R.↗
NASA NTRS1990

Hot filament technique for measuring the thermal conductivity of molten lithium fluoride

Molten salts, such as lithium fluoride, are attractive candidates for thermal energy storage in solar dynamic space power systems because of their high latent heat of fusion. However, these same salts have poor thermal conductivities which inhibit the transfer of heat into the solid phase and out of the liquid phase. One concept for improving the thermal conductivity of the thermal energy storage system is to add a conductive filler material to the molten salt. High thermal conductivity pitch-based graphite fibers are being considered for this application. Although there is some information available on the thermal conductivity of lithium fluoride solid, there is very little information on lithium fluoride liquid, and no information on molten salt graphite fiber composites. This paper describes a hot filament technique for determining the thermal conductivity of molten salts. The hot filament technique was used to find the thermal conductivity of molten lithium fluoride at 930 C, and the thermal conductivity values ranged from 1.2 to 1.6 W/mK. These values are comparable to the slightly larger value of 5.0 W/mK for lithium fluoride solid. In addition, two molten salt graphite fiber composites were characterized with the hot filament technique and these results are also presented.

Jaworske, Donald A.↗
NASA NTRS1989

On the mechanics of filament winding. I - A generalized model

In this paper the filament winding process was analyzed to relate process variables to structural parameters. An analytical model has been developed for a filament wound preform by determining the necessary geometric and kinematic conditions. An equation of motion of winding was developed to predict layer by layer geometry using the mandrel shape as the initial boundary condition. This model provides the laws of motion of the traverse stroke relative to the mandrel to ensure that the filament laydown is of the predetermined geodesic path over the mandrel, that the winding density is distributed over the mandrel in the prearranged manner, and that the winding build is being formed to reproduce the preassigned shape or contour of the preform. From this analysis, the winding process parameters can be controlled accordingly to produce any given shape. The analytical model was used to produce computer simulation of the winding process. The dynamic simulation of the winding process visualizes and inspects the layer by layer path of the tow and provides process variables required to produce preforms of optimum structural parameters.

Hamouda, Hechmi↗
NASA NTRS1992

Making Crystal Filaments From Extruded Ceramic Rods

New process produces single-crystal fibers of ceramic or metal at lower cost. Single-crystal filament drawn from tip of extruded polycrystalline rod. Extrusion produces longer rods from which longer fibers drawn. Potentially feeds single fiber drawing process directly. Continuous filaments made, and material not subjected to contamination from storage and transfer to drawing machine. Filaments used as reinforcing fibers in composite materials.

Westfall, Leonard J.↗
NASA NTRS1991

Filament disappearances and associated shocks of May 1979

In late May 1979 a shock was seen at each of two locations separated by about 90 deg in heliolongitude and at about the same time. A shock was detected near the earth, and a shock was detected at Helios 1 when it was off the sun's west limb. Some authors have considered that these shocks were part of the same event, which originated with a filament disappearance near 65 deg W. The paper discusses the observations which show that a large complex filament, extending from 20 deg to 70 deg W, disappeared in several places, probably generating more than one shock. The shock detected near earth was probably associated with a filament section which disappeared near the central meridian. If this is the case, then the interplanetary scintillation observations of this time period can be explained without invoking highly anisotropic shock propagation.

Cane, H. V.↗
NASA NTRS1992

X-ray-emitting filaments in the cooling flow cluster A2029

High-resolution X-ray observations of the cluster A2029 are presented which confirm the presence of a cooling flow, despite the lack of optical line emission or evidence for recent star formation. The cooling rate and radius are about 370 solar mass/yr and 230 kpc, respectively. Emission from the inner cooling flow is dominated by a number of X-ray-emitting filaments. This may be the first case where such inhomogeneities are clearly resolved. The filaments are theorized to be supported in part by magnetic fields and may be connected with the filaments of very strong Faraday rotation seen in several nearly cooling flows.

Sarazin, Craig L.↗
NASA NTRS1993

System Applies Polymer Powder To Filament Tow

Polymer powder applied uniformly and in continuous manner. Powder-coating system applies dry polymer powder to continuous fiber tow. Unique filament-spreading technique, combined with precise control of tension on fibers in system, ensures uniform application of polymer powder to web of spread filaments. Fiber tows impregnated with dry polymer powders ("towpregs") produced for preform-weaving and composite-material-molding applications. System and process valuable to prepreg industry, for production of flexible filament-windable tows and high-temperature polymer prepregs.

Baucom, Robert M.↗
NASA NTRS1992

The structure of the coronal soft X-ray source associated with the dark filament disappearance of 1991 September 28 using the Yohkoh Soft X-ray Telescope

The structure of the coronal soft X-ray source associated with the dark filament disappearance on September 28, 1991, observed with the Soft X-ray Telescope, is examined as a possible example of the 'eruption-reconnection' model of filament disappearance. The results suggest, however, that this model may not fit. There is a strong possibility that much of the dark filament mass remains in the heated unwinding axial field.

Mcallister, Alan↗
NASA NTRS1993

Influence of local fiber undulations on the global buckling behavior of filament-wound cylinders

The predicted compressive stiffness and buckling strength of filament-wound cylinders using classical lamination theory is significantly higher than those observed experimentally. This discrepancy is partially influenced by the variation of mechanical properties in the region of fiber undulations. These regions are localized geometric defects intrinsic to the filament-winding, weaving, and braiding processes. In the present work, the average mechanical properties of the fiber undulation region are quantified using modified models of woven-fabric composites to account for the 3-dimensional effects. The mechanical properties thus determined can be incorporated as local element properties into global finite-element models. Preliminary results from large-displacement analyses of filament-wound cylinders are relatively more accurate when fiber undulations are accounted for.

Jensen, D. W.↗