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At least 127 records · Page 7

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NASA NTRS1971

Photographic Remote Sensing of Sick Citrus Trees

Remote sensing with infrared color aerial photography (Kodak Ektachrome Infrared Aero 8443 film) for detecting citrus tree anomalies is described. Illustrations and discussions are given for detecting nutrient toxicity symptoms, for detecting foot rot and sooty mold fungal diseases, and for distinguishing among citrus species. Also, the influence of internal leaf structure on light reflectance, transmittance, and absorptance are considered; and physiological and environmental factors that affect citrus leaf light reflectance are reviewed briefly and illustrated.

Gausman, H. W.↗

NASA NTRS1975

Use of remote sensing in agriculture

The remote sensing studies of (a) cultivated peanut areas in Southeastern Virginia; (b) studies at the Virginia Truck and Ornamentals Research Station near Painter, Virginia, the Eastern Virginia Research Station near Warsaw, Virginia, the Tidewater Research and Continuing Education Center near Suffolk, Virginia, and the Southern Piedmont Research and Continuing Education Center Blackstone, Virginia; and (c) land use classification studies at Virginia Beach, Virginia are presented. The practical feasibility of using false color infrared imagery to detect and determine the areal extent of peanut disease infestation of Cylindrocladium black rot and Sclerotinia blight is demonstrated. These diseases pose a severe hazard to this major agricultural food commodity. The value of remote sensing technology in terrain analyses and land use classification of diverse land areas is also investigated. Continued refinement of spectral signatures of major agronomic crops and documentation of pertinent environmental variables have provided a data base for the generation of an agricultural-environmental prediction model.

Pettry, D. E.↗

NASA NTRS1977

Study of coatings for improved fire and decay resistance of mine timbers

The purpose of this program was to find a fire- and rot-retardant polymer/fungicide reaction product for coating mine timbers. Fire-retardant polymers were screened as films and coatings on fir wood. Curable polyimide appeared to be flame retardant and evolved a minimum of fumes when exposed to a flame. Several organic and metal, low toxicity, fungicides were reacted with the polyimide in-situ on the wood. These coated samples were screened for fungus resistance. All formulations rated well - even the polyimide film without additives was fungicidal. The fir wood control itself resisted internal damage during the ten weeks of fungus exposure. A more severe test for fungus resistance will be required.

Baum, B.↗

NASA NTRS1979

The use of wood for wind turbine blade construction

The interrelationships between moisture and wood, conditions for dry rot spore activity, the protection of wood fibers from moisture, wood resin composites, wood laminating, quality control, and the mechanical properties of wood are discussed. The laminated veneer and the bonded sawn stock fabrication techniques, used in the construction of a turbine blade with a monocoque 'D' section forming the leading edge and a built up trailing edge section, are described. A 20 foot root end sample complete with 24 bonded-in studs was successfully subjected to large onetime loads in both the flatwise and edgewise directions, and to fatigue tests. Results indicate that wood is both a viable and advantageous material for use in wind turbine blades. The basic material is reasonably priced, domestically available, ecologically sound, and easily fabricated with low energy consumption.

Gougeon, M.↗

NASA NTRS1979

Interstellar methyl mercaptan

Methyl mercaptan (CH3SH) has been identified in Sgr B2 from observations of six lines in its millimeter-wave spectrum. The CH3SH rotational temperature and column density in Sgr B2 are T(rot) = 9 plus or minus 3 K and N = 1.5 plus or minus 0.2 x 10 to the 14th per sq cm, respectively. The CH3SH/CH3OH ratio is apparently not greatly different from the cosmic S/O ratio.

Linke, R. A.↗

NASA NTRS1981

General description and operation of the agro-environmental system: Crop management modeling

Input for a data management system to provide farmers with information to improve crop management practices in Virginia requires monitoring of control crops at field stations, crop surveys derived from remotely sensed aircraft data, meteorological data from synchronous satellites, and details of local agricultural conditions. Presently models are under development for determining pest problems, water balance in the soil, stages of plant maturity, and optimum planting date. The status of the Cerospora leafspot model for peanut crop management is considered. Other models under development planned relate to Cylindtocladium Blackrot and Sclerotinia blight of peanuts, cyst nematode (Globerdena solanacearum) of tobacco, and red crown rot of soybeans. A software for program for estimating precipitation and solar radiation on a statewise basis is also being developed.

Gross, E.↗

NASA NTRS1984

The detection of interstellar methylcyanoacetylene

A new interstellar molecule, methylcyanoacetylene (CH3C3N), has been detected in the molecular cloud TMC-1. The J = 8 to 7, J = 7 to 6, J = 6 to 5, and J = 5 to 4 transitions have been observed. For the first three of these, both the K = 0 and K = 1 components are present, while for J = 5 to 4, only the K = 0 line has been detected. The observed frequencies were calculated by assuming a value of radial velocity V(LSR) = 5.8 km/s for TMC-1, typical of other molecules in the cloud. All observed frequencies are within 10 kHz of the calculated frequencies, which are based on the 1982 laboratory constants of Moises et al. (1982), so the identification is secure. The lines are broadened by hyperfine splitting, and the J = 5 to 4, K = 0 transition shows incipient resolution into three hyperfine components. The rotational temperature determined from these observations is quite low, with T(rot) in the range from 2.7 to 4 K. The total column density is approximately 5 x 10 to the 12th per sq cm.

Broten, N. W.↗

NASA NTRS1983

Observations of magnetic fields on late-type stars

The 'Robinson' method for measuring magnetic fields on solarand late-type stars is reviewed. The results of such measurements for a sample of 29 G and K main-sequence stars are presented. The area covering-factors of magnetic regions are greater in the K dwarfs than in the G dwarfs, but no spectral-type dependence is found for the field strengths, contrary to expectations of some flux-tube models. The dependence of Ca II H and K emission on magnetic fields and T(eff) is consistent with theoretical expections for 'slow-mode' mhd wave-generation rates, but inconsistent with those of other mhd modes. Coronal soft X-ray fluxes correlate well with the magnetic fields, and it is argued that Alfven waves are the likely energy-transport mechanism. Surface magnetic fluxes vary with rotation as V(0.5-1.0 rot) depending on spectral type.

Marcy, G. W.↗

NASA NTRS1985

Io: Mountains and crustal extension

It is argued that there is good reason to conclude that mountains on Io, like those on Earth, are subject to growth and decay. The decay of mountains will be assisted by the ability of SO sub 2 to rot silicate rock and by explosive escape of sub-surface SO sub 2 from aquifers (Haemus Mons is seen to be covered by bright material, presumably fallout from a SO sub 2 rich plume which had been active on the mountain flanks). On the west side of the massif at 10 degrees S, 270 degrees W a rugged surface consists of long ridges running perpendicular to the downslope direction, suggesting tectonic denudation with crustal blocks sliding down the mountain flank. Tectonic denudation may be assisted, as in the case of the Bearpaw Mountains, Montana by overloading mountain flanks with volcanic products. The surfaces of some massifs exhibit a well developed, enigmatic corrugated terrain, consisting of complex ridge systems. Ridges may bifurcate, anastomose to form closed depressions and form concentric loops. Taken together, observations of morphology, heat flux, surface deposits and styles of volcanism may point to the existence of lithosphere domains with distinct compositions and tectonic regimes.

Heath, M. J.↗

NASA NTRS1986

Multifrequency passive microwave observations of first-year sea ice grown in a tank

Microwave brightness temperatures of new, young, and optically opaque sea ice grown in a large tank were obtained in the course of a joint microwave experiment at CRREL in Hanover, NH, during the winters of 1983-1984 and 1984-1985. Dual-polarized observations were taken at frequencies of 10, 18, 37, and 90 GHz over a range of incidence angles, and the concurrent temperature and ice thickness were obtained. Emissivity and degree of polarization were observed in detail during the early stages of ice growth and variations were found indicating that the ice became optically opaque at 10 GHz for ice thickness between 30 and 50 mm. Cluster plots of the data show six distinguishable surface types: optically opaque bare ice, thin ice (less than 15 mm), roughened ice, ridged ice, rotting wet ice, and open water.

Grenfell, T. C.↗

NASA NTRS1987

A flash spectrum of Cl I, C I, N I, and Ni II absorption in 31 Cygni: A direct observation of the reversing layer

In the process of surveying IUE observations of the zeta Aurigae binary system 31 Cygni for evidence of a shock, the presence of narrow low temperature lines Cl I, C I, N I, and Ni II has been discovered. These lines cannot be due to the local interstellar medium, since they appear only in one of the 16 high resolution, short wavelength observations made of this system. The phase of their appearance is theta = 0.017, approximately two months after egress of the blue dwarf component from eclipse behind the cool supergiant. Such lines might be produced by the shining of the hot dwarf companion's continuum through the edge of the supergiant's reversing layer or through a condensation in the supergiant atmosphere. If the former is the case, then the height of the reversing layer may be estimated from this observation. The radial velocities and equivalent widths of ten of these lines have been measured and the former is found to be -8.2 +/- 0.5 km/sec, precisely equal to the radial velocity of the system center of mass. This places a strict upper limit on the rotational velocity of the supergiant: V sub rot less than 2 km/s to better than 3 sigma.

Ahmad, Imad A.↗

NASA NTRS1989

X-ray emission from O-type stars - Parameters which affect it

As a result of previous analyses of the X-ray fluxes of O-type stars, it has been established that, surprisingly, there is no correlation between X-ray flux and such basic parameters as M, R, v(rot), T(eff), mass accretion rate v(infinity), L(w) = mass accretion rate v(infinity), and wind energy. In this paper, other factors influencing the X-ray flux of the hottest stars are sought. As a result of the present analysis, it is found that stars embedded in dense clouds are often X-ray brighter, runaway stars are fainter in X-rays, massive binaries emit more X-rays than single stars, and radio-bright stars are also more active in X-rays. All these correlations lead to the conclusion that the stellar environment and the interaction of the stellar wind with circumstellar matter (possible remnants of protostellar clouds) play a dominant role in the production of the X-ray flux.

Chlebowski, T.↗

NASA NTRS1990

Spiral structure of M51: Streaming motions across the spiral arms

The atomic hydrogen (HI) and the H alpha emission line in the grand-design spiral galaxy M51 have been observed with the Westerbork Synthesis Radio Telescope and the Taurus Fabry-Perot imaging spectrometer, respectively. Across the inner spiral arms significant tangential and radial velocity gradients are detected in the H alpha emission after subtraction of the axi-symmetric component of the velocity field. The shift is positive on the inside and negative on the outside of the northern arm. Across the southern arm this situation is reversed. The direction of the shifts is such that the material is moving inward and faster compared to circular rotation in both arms, consistent with the velocity perturbations predicted by spiral density wave models for gas downstream of a spiral shock. The observed shifts amount to 20 to 30 km (s-1), corresponding to streaming motions of 60 to 90 km (s-1) in the plane of the disk (inclination angle 20 degrees). Comparable velocity gradients have also been observed by Vogel et al. in the CO emission from the inner northern arm of M51. The streaming motions in M51 are about 2 to 3 times as large as the ones found in HI by Rots in M81, and successfully modelled by Visser with a self-consistent density wave model. Researchers have not been able to detect conclusively streaming motions in the HI emission from the arms, perhaps due to the relatively poor angular resolution (approx. 15 seconds) of the HI observations.

Tilanus, R. P. J.↗

NASA NTRS1990

Runway Exit Designs for Capacity Improvement Demonstrations. Phase 1: Algorithm Development

A description and results are presented of a study to locate and design rapid runway exits under realistic airport conditions. The study developed a PC-based computer simulation-optimization program called REDIM (runway exit design interactive model) to help future airport designers and planners to locate optimal exits under various airport conditions. The model addresses three sets of problems typically arising during runway exit design evaluations. These are the evaluations of existing runway configurations, addition of new rapid runway turnoffs, and the design of new runway facilities. The model is highly interactive and allows a quick estimation of the expected value of runway occupancy time. Aircraft populations and airport environmental conditions are among the multiple inputs to the model to execute a viable runway location and geometric design solution. The results presented suggest that possible reductions on runway occupancy time (ROT) can be achieved with the use of optimally tailored rapid runway designs for a given aircraft population. Reductions of up to 9 to 6 seconds are possible with the implementation of 30 m/sec variable geometry exits.

Trani, A. A.↗

NASA NTRS1991

Rotation and emission lines in stars and accretion disks

In the accretion disks of quiescent dwarf novae, Doppler mapping studies reveal that Balmer emission lines increase sharply toward the center of the disk, with surface brightnesses scaling roughly as R exp -3/2 varies as Omega(Kep). Similarly, among chromospherically active stars the H-alpha and Ca II H and K emission cores are stronger in the more rapidly rotating stars, with surface brightnesses scaling again roughly as Omega(rot). Since in both cases the emission lines scale linearly with the rotation frequency, it is proposed that the mechanism powering the emission lines in quiescent accretion disks is the same as that in chromospherically active stars, namely, the emergence of magnetic flux generated by the action of a dynamo, and its interaction with the atmosphere. If this empirical connection between disks and stars is in fact due to magnetic dynamos, the range of rotation rates available for testing dynamo theories expands from a factor of 1000 to 10 to the 7th.

Horne, Keith↗

NASA NTRS1992

Soluble species in the Arctic summer troposphere - Acidic gases, aerosols, and precipitation

The large-scale spatial distribution from 0.15-to 6 km altitude in the North American Arctic troposphere of several soluble acidic gases and major aerosol species during the summertime is reported. The distribution is found to be compositionally consistent on a large spatial scale. The summertime troposphere is an acidic environment, with HCOOH and CH3COOH the principal acidic gases while acidic sulfate aerosols dominate the particulate phase. There appears to be a surface source of NH3 over the pack ice which may originate from decay of dead marine organisms on the ice surface, evolution from surface ocean waters in open ice leads, or release from rotting sea ice. At low altitude over the pack ice this NH34 appears to partially neutralize aerosol acidity. Over sub-Arctic tundra in southeastern Alaska, inputs of marine biogenic sulfur from the Bering Sea appear to be an important source of boundary layer aerosol SO4(2-). The rainwater acidity over the tundra is typical of remote regions.

Talbot, R. W.↗

NASA NTRS1995

Guidance and control requirements for high-speed Rollout and Turnoff (ROTO)

This report defines the initial requirements for designing a research high-speed rollout and turnoff (ROTO) guidance and control system applicable to transport class aircraft whose purpose is to reduce the average runway occupancy time (ROT) for aircraft operations. The requirements will be used to develop a ROTO system for both automatic and manual piloted operation under normal and reduced visibility conditions. Requirements were determined for nose wheel/rudder steering, braking/reverse thrust, and the navigation system with the aid of a non-real time, three degree-of-freedom MD-11 simulation program incorporating airframe and gear dynamics. The requirements were developed for speeds up to 70 knots using 30 ft exit geometries under dry and wet surface conditions. The requirements were generated under the assumptions that the aircraft landing system meets the current Category III touchdown dispersion requirements and that aircraft interarrival spacing is 2 nautical miles. This effort determined that auto-asymmetric braking is needed to assist steering for aft center-of-gravity aircraft. This report shows various time-history plots of the aircraft performance for the ROTO operation. This effort also investigated the state-of-the-art in the measurement of the runway coefficient of friction for various runway conditions.

Goldthorpe, Steve H.↗

NASA NTRS1994

Two-fluid simulations of galaxy formation

We investigate the formation of galaxies and larger structure with a simulation modeling two gravitationally coupled fluids representing dark matter and baryons. The baryon gas dynamics are calculated with a smoothed particle hydrodynamics (SPH) method, and the physics modeled includes thermal pressure, shock heating, and radiative cooling. We simulate a 16 Mpc periodic cube with 64(exp 3) particles in each fluid and 10% baryon mass fraction. We confirm, for the first time experimentally, disk formation as a natural consequence of hierarchical clustering in a large-scale cosmological environment. The majority of isolated galaxies exhibit centrifugally supported disks. A power-law relation between cold baryonic mass and maximum rotation velocity is found, M varies as nu(sub rot)(exp alpha) with alpha = 2.5 after correcting for differential numerical resolution. Both the spatial and velocity distributions of the simulated galaxies are biased with respect to the dark matter. A counts-in-cells analysis indicates that an unphysical degree of merging in the central cluster is likely responsible for the antibias signal in the correlation function. A robust, scale-dependent velocity bias is measured. The ratio of galaxy to dark matter pairwise velocity dispersions on a scale of 1 Mpc is 0.7. The amplitude is only mildly dependent on redshift or mass cutoff and scales with separation as r(exp 0.2). The degree to which these results depend on numerical parameters is discussed. Mass resolution plays a key role in controlling the resulting fraction of cold, dense baryons. The mass fraction associated with galaxies decreases by a factor of approximately greater than 3 when the mass per particle is increased by a factor 8. Photoionization and energy input from supernova will have to be included to determine more carefully the fraction of highly dissipated material and the characteristics of the stellar component of galaxies.

Evrard, August E.↗