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At least 217 records · Page 12

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NASA NTRS1984

Failure of vincristine induce twinning

Mammalian ova do not contain axes of symmetry from which are derived embryonic axes of symmetry. Mammalian axis determination is an early embryologic event occurring at about the time that monozygous twinning in mice. (Kaufma MH & O'Shea KS, 1978, Nature 276:707) and an attempt was made to reproduce their work in several strains of mice. Over 3200 embryos were examined without any twins being found. To rule out the possibility that vincristine caused twinning plus some lethal malformation (with subsequent resorption of the embryo) the embryos were examined 36-60 hours after vincristine treatment.

Binder, M.↗

NASA NTRS1983

Geometry of spinor regularization

The Kustaanheimo theory of spinor regularization is given a new formulation in terms of geometric algebra. The Kustaanheimo-Stiefel matrix and its subsidiary condition are put in a spinor form directly related to the geometry of the orbit in physical space. A physically significant alternative to the KS subsidiary condition is discussed. Derivations are carried out without using coordinates.

Hestenes, D.↗

NASA NTRS1984

The Brownell and Ness County (1894) L6 chondrites - Further sorting-out of Ness County meteorites

Brownell is a new moderately shocked L6 chondrite from Ness County, KS, that is petrologically distinct from the other L6 chondrites from Ness County. These latter meteorites, Wellmanville, Franklinville, and Ness County (1894), are very similar in their olivine and low-Ca pyroxene compositional distributions, kamacite Co contents, modal abundances of metallic Fe, Ni, and presence of martensitic metallic Fe, Ni (about 14 wt pct Ni). However, their silicates indicate that they have been shocked to different extents. It is suggested that all three probably represent a single heterogeneously-shocked L6 fragmental breccia that fell over a large area over 30 km in length.

Rubin, A. E.↗

NASA NTRS1986

Relation between microstructural heterogeneous surface layer and nitrogen pressure during sintering in Si3N4-Ml2O3 ceramics

The effects of N2 pressure (0.1 to 50 MPa) during sintering on the thickness of the microstructurally heterogeneous layer (MHL) formed near the surface of the compact, transverse-rupture strength, were investigated for Si3N4-(10 to 20) mol % MgO-5.5 mol % Al2O3 ceramics. The sintering temperature and time were 1973 K and 3.6 ks, respectively. The N2 gas was introduced into the furnace at about 1273 K. When the compacts were sintered under a certain N2 pressure, for example, about 20 and 7 MPa for 10 and 15 mol% MgO, respectively, the evolutions of N and Si were suppressed. The thickness of the MHL became very small and at the same time the strength of the surface layer of the compact (which was normally less than that of the inside in the case of 0.1 MPa) became nearly the same value as that of the inside. At higher pressure, the strength of both surface layer and the inside decreased considerably. Some discussion was made on these results.

Hayashi, K.↗

NASA NTRS1988

Fully-coupled analysis of jet mixing problems. Three-dimensional PNS model, SCIP3D

Numerical procedures formulated for the analysis of 3D jet mixing problems, as incorporated in the computer model, SCIP3D, are described. The overall methodology closely parallels that developed in the earlier 2D axisymmetric jet mixing model, SCIPVIS. SCIP3D integrates the 3D parabolized Navier-Stokes (PNS) jet mixing equations, cast in mapped cartesian or cylindrical coordinates, employing the explicit MacCormack Algorithm. A pressure split variant of this algorithm is employed in subsonic regions with a sublayer approximation utilized for treating the streamwise pressure component. SCIP3D contains both the ks and kW turbulence models, and employs a two component mixture approach to treat jet exhausts of arbitrary composition. Specialized grid procedures are used to adjust the grid growth in accordance with the growth of the jet, including a hybrid cartesian/cylindrical grid procedure for rectangular jets which moves the hybrid coordinate origin towards the flow origin as the jet transitions from a rectangular to circular shape. Numerous calculations are presented for rectangular mixing problems, as well as for a variety of basic unit problems exhibiting overall capabilities of SCIP3D.

Wolf, D. E.↗

NASA NTRS1991

An integrated control/structure design method using multi-objective optimization

The benefits are demonstrated of a multiobjective optimization based control structure integrated design methodology. An application of the proposed CSI methodology to the integrated design of the Spacecraft COntrol Lab Experiment (SCOLE) configuration is presented. Integrated design resulted in reducing both the control performance measure and the mass. Thus, better overall performance is achieved through integrated design optimization. The mutliobjective optimization approach used provides Pareto optimal solutions by unconstrained minimization of a differentiable KS function. Furthermore, adjusting the parameters gives insight into the trade-offs involved between different objectives.

Gupta, Sandeep↗

NASA NTRS1990

Quasilinear saturation of forced current sheet tearing modes

Numerical studies of tearing modes in a nearly singular forced current sheet equilibrium (Liewer and Payne, 1990) show that the modes saturate quasilinearly when the width of the magnetic island formed by the reconnection is on the order of several times the linear mode width which scales as approximately (kS) exp -2/5, where S is the Lundquist number and k is the wavenumber. The modes saturate quasilinearly by flattening the current profile, converting magnetic energy into plasma energy. The longer wavelength modes, which saturate at higher levels, release the most energy. These modes may, nonlinearly, play a role in coronal heating when sharp current sheets form as a result of global magnetic stresses.

Liewer, Paulett C.↗

NASA NTRS1990

Net radiation, sensible and latent heat flux densities on slopes computed by the energy balance method

Energy balance components obtained over five grass-covered sloping surfaces near Manhattan, KS, using the Bowen ratio energy balance technique with the instruments mounted horizontally were compared with calculated values when the instruments were mounted parallel to the surfaces. Hourly values of the components changed when the instruments were parallel to the surfaces. The changes were larger at low solar angles (spring and fall) and on steeper slopes. An area average of daylight totals, assuming that all aspects were equally represented, changed only 0.1 percent on June 6 and 2.3 percent on October 11. The calculations, extended to steeper slopes, indicated small changes in the daylight totals for slopes of less than 10 deg.

Fritschen, Leo↗

NASA NTRS1991

Future missions studies: Combining Schatten's solar activity prediction model with a chaotic prediction model

K. Schatten (1991) recently developed a method for combining his prediction model with our chaotic model. The philosophy behind this combined model and his method of combination is explained. Because the Schatten solar prediction model (KS) uses a dynamo to mimic solar dynamics, accurate prediction is limited to long-term solar behavior (10 to 20 years). The Chaotic prediction model (SA) uses the recently developed techniques of nonlinear dynamics to predict solar activity. It can be used to predict activity only up to the horizon. In theory, the chaotic prediction should be several orders of magnitude better than statistical predictions up to that horizon; beyond the horizon, chaotic predictions would theoretically be just as good as statistical predictions. Therefore, chaos theory puts a fundamental limit on predictability.

Ashrafi, S.↗

NASA NTRS1991

The coronal dividing line in the Rosat X-ray All-Sky Survey

Rosat All-Sky Survey soft X-ray observations of nearly 1000 bright single evolved stars of spectral types G, K, and M in the vicinity of the dividing line proposed by Linsky and Haisch (1979) are reported. Most observations consist of upper limits in the 0.1-2.0-keV band distributed between 604 stellar targes of spectral type K3 or earlier and 264 stellar targets of spectral type K4 or later. Of the 65 Rosat detections, only one involves an apparently single star of spectral type later than K3: HR 4289 (K5 III). A clear dichotomy exists between coronal and noncoronal stars of luminosity classes II, III, and IV at approximately spectral type Ke. The extremely low upper limit for the archetypal 'noncoronal' red giant, Arcturus, less than 3 x 24 exp 25 ergs/s achieved by Rosat during an 18.6-ks targeted observations by Ayres et al. (1991) indicates a very steep decline at the coronal dividing line.

Haisch, Bernhard↗

NASA NTRS1993

ROSAT investigation of flaring and activity on Prox Cen

The objective of this program was to investigate with high sensitivity the low-level flare activity which may underlie coronal heating. This was done. The ROSAT observations of Prox Cen were scheduled for 50 ks spread out from 26 Feb. - 10 Mar. 1992. Unfortunately because of spacecraft problems many of these pointings turned out to contain no useful data or extremely truncated valid data sets. Considerable time was spent trying to determine which of the data would be scientifically useful and which would not. Fortunately, several developments took place to augment the original data in such a way that the scientific goal of advancing the study of flaring and variability was able to be achieved after all. These are as follows: (1) a second round of ROSAT observations was carried out in Feb. 1993 which only came to the attention of the PI in Apr. 1993 when a new data tape arrived; (2) simultaneous IUE observations were requested and obtained; (3) data from the UK WFC are available via the collaboration with Dr. G. Bromage; and (4) the 'cleaned-up' original data set was found to include one major flare and 2 moderate flares. Because of the problems with the original data set, the unexpected acquisition of new data only two months ago, and the availability of IUE and WFC data, an article on Prox Cen for publication is not ready at this time. Such an article is being developed and can be completed as part of ongoing ROSAT research efforts on stellar coronae and flaring.

Haisch, Bernhard↗

NASA NTRS1993

A giant X-ray flare on Lambda Eridani (B2e)

A 30 ks observation with the ROSAT PSPC distributed over 39 hr shows that the putatively single, mild B2e star Lambda Eri emits at most times a soft X-ray flux at a rate and temperature consistent with other B stars. However, during the middle of our observations, this star's X-ray flux increased by a factor of 6 before returning to the basal level. This brightening, due entirely to photon energies of 0.7 keV or greater, can be fitted well to a Raymond-Smith temperature parameter of 14 MK and luminosity 4 x 10 exp 31 ergs/s; these are characteristics of giant stellar flares. With an estimated duration of about 50,000 s, this event is arguably the strongest X-ray flare yet observed. We consider several possible scenarios for the site of the flare, including several with an active cool secondary or degenerate companion. We find that IUE and optical spectra do not support a binary picture and that it is most probable that the flare site is on or related to Lambda Eri itself. This supports other evidence for violent magnetic activity on some B-type stars.

Smith, Myron A.↗

NASA NTRS1993

Angular momentum regulation in low-mass young stars surrounded by accretion disks

From study of a sample of 34 T Tauri stars with photometrically derived rotation periods and spectral types later than KS, we find that the observed periods appear to be related to the presence or absence of an accretion disk. Those stars which we infer to be surrounded by accretion disks have rotation periods P(rot) over 4 days with a most probable P(rot) of about 8.5 days, while those stars which lack accretion disk signatures cover a wide range of P(rot) from 1.5 to 16 days, including a significant number of objects with P(rot) less than 4 days. This suggests the possibility that the 'initial' angular momentum of a star is not established until it dissipates its circumstellar accretion disk. During the disk accretion phase, the stellar angular velocity appears to be regulated at a low value, countering the tendency of the star to spin up both from contraction toward the main sequence and from the accretion of inner disk material of high specific angular momentum. When the accretion disk is dissipated, this regulation mechanism will cease to function. At this point, the star is no longer maintained at a low angular velocity, but is 'free' to conserve its angular momentum, and thus to increase its angular velocity in response to contraction and changes in moment of inertia. This hypothesis, combined with a spread in disk dispersal time scales, provides a context for explaining the observed distribution of stellar rotational velocities for stars on the ZAMS in young clusters.

Edwards, Suzan↗

NASA NTRS1993

The 5-6 December 1991 FIRE IFO 2 jet stream cirrus case study: The influence of volcanic aerosols

In presenting an overview of the cirrus clouds comprehensively studied by ground-based and airborne sensors from Coffeyville, KS, during the 5-6 Dec. 1992 Project FIRE (First International Satellite Cloud Climatology Project Regional Experiment) IFO II case study period, evidence is provided that volcanic aerosols from the June 1991 Pinatubo eruptions significantly influenced the formation and maintenance of the cirrus. Following the local appearance of a spur of stratospheric volcanic debris from the subtropics, a series of jet streaks subsequently conditioned the troposphere through tropopause foldings with sulfur-based particles that became effective cirrus cloud-forming nuclei. Aerosol and ozone measurements suggest a complicated history of stratospheric-tropospheric exchanges embedded within the upper level flow, and cirrus cloud formation was noted to occur locally at the boundaries of stratospheric aerosol-enriched layers that became humidified through diffusion, precipitation, or advective processes. Apparent cirrus cloud alterations include abnormally high ice crystal concentrations (up to approximately 600 l(sup -1), small but complex radial ice crystal types, and relatively large haze particles in cirrus uncinus cell heads at temperatures between -40 to -50 C. Implications for volcanic-cirrus cloud climate effects, and usual (non-volcanic aerosol) jet stream cirrus cloud formation are discussed.

Sassen, Kenneth↗

NASA NTRS1994

An algorithm for solving the system-level problem in multilevel optimization

A multilevel optimization approach which is applicable to nonhierarchic coupled systems is presented. The approach includes a general treatment of design (or behavior) constraints and coupling constraints at the discipline level through the use of norms. Three different types of norms are examined: the max norm, the Kreisselmeier-Steinhauser (KS) norm, and the 1(sub p) norm. The max norm is recommended. The approach is demonstrated on a class of hub frame structures which simulate multidisciplinary systems. The max norm is shown to produce system-level constraint functions which are non-smooth. A cutting-plane algorithm is presented which adequately deals with the resulting corners in the constraint functions. The algorithm is tested on hub frames with increasing number of members (which simulate disciplines), and the results are summarized.

Balling, R. J.↗

NASA NTRS1994

NASA Goddard Earth Sciences Graduate Student Program

The evolution of synoptic-scale dynamics associated with a middle and upper tropospheric cloud event that occurred on 26 November 1991 is examined. The case under consideration occurred during the FIRE CIRRUS-II Intensive Field Observing Period held in Coffeyville, KS during Nov. and Dec., 1991. Using data from the wind profiler demonstration network and a temporally and spatially augmented radiosonde array, emphasis is given to explaining the evolution of the kinematically-derived ageostrophic vertical circulations and correlating the circulation with the forcing of an extensively sampled cloud field. This is facilitated by decomposing the horizontal divergence into its component parts through a natural coordinate representation of the flow. Ageostrophic vertical circulations are inferred and compared to the circulation forcing arising from geostrophic confluence and shearing deformation derived from the Sawyer-Eliassen Equation. It is found that a thermodynamically indirect vertical circulation existed in association with a jet streak exit region. The circulation was displaced to the cyclonic side of the jet axis due to the orientation of the jet exit between a deepening diffluent trough and building ridge. The cloud line formed in the ascending branch of the vertical circulation with the most concentrated cloud development occurring in conjunction with the maximum large-scale vertical motion. The relationship between the large scale dynamics and the parameterization of middle and upper tropospheric clouds in large-scale models is discussed and an example of ice water contents derived from a parameterization forced by the diagnosed vertical motions and observed water vapor contents is presented.

Ackerman, Thomas P.↗

NASA NTRS1994

Extended field observations of cirrus clouds using a ground-based cloud observing system

Ackerman, Thomas P.↗

NASA NTRS1995

Prepsolv (TM): The optimum alternative to 1,1,1-trichloroethane and methyl ethyl ketone for hand-wipe cleaning of aerospace materials

Engineers at Hercules Aerospace, a rocket motor manufacturer in Utah, have worked closely with chemists at Glidco Organics to study the feasibility of using terpenes for zero-residue wipe cleaning. The result of this work is a technological breakthrough, in which the barrier to ultra-low non-volatile residue formation has been broken. After 2 years of development and testing, SCM Glidco Organics has announced the availability of Glidsafe(registered trademark) Prepsolv(TM): a state-of-the-art ultra-low residue terpene wipe cleaning agent that does not require rinsing. Prepsolv(TM) can successfully be used in simple hand-wipe cleaning processes without fear of leaving surface residues. Industry testing has confirmed that Prepsolv(TM) is not only highly effective, but can even be less expensive to use than traditional cleaning solvents like methyl chloroform. This paper addresses the features and benefits of Prepsolv(TM), and presents performance and material compatibility data that characterizes this unique cleaning agent. Since its commercialization, Hercules Aerospace has chosen Prepsolv(TM) as the optimum cleaning agent to replace ozone-depleting solvents in their weapons factory in Magna, UT. Likewise, Boeing has approved Prepsolv(TM) for cleaning components in the manufacture of commercial aircraft at their facilities in Seattle, WA and Wichita, KS. Additional approvals are forthcoming for this uniquely safe and effective solvent.

Gallagher, R. Scott↗