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At least 919 records · Page 51

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NASA NTRS1975

Wheat productivity estimates using LANDSAT data

The author has identified the following significant results. The electro-optical leaf area meter was the most accurate of the approaches tested on harvested wheat samples, but it is very time consuming. It was decided to infer leaf area from dry weight biomass after establishing a relationship between dry weight biomass and area as measured by the leaf area meter. There is a good correlation between leaf area as measured by the meter and dry leaf biomass. There is a less consistent relationship between stem area and stem biomass.

Nalepka, R. F.↗

NASA NTRS1976

Diffraction of a shock wave by a compression corner; regular and single Mach reflection

The two dimensional, time dependent Euler equations which govern the flow field resulting from the injection of a planar shock with a compression corner are solved with initial conditions that result in either regular reflection or single Mach reflection of the incident planar shock. The Euler equations which are hyperbolic are transformed to include the self similarity of the problem. A normalization procedure is employed to align the reflected shock and the Mach stem as computational boundaries to implement the shock fitting procedure. A special floating fitting scheme is developed in conjunction with the method of characteristics to fit the slip surface. The reflected shock, the Mach stem, and the slip surface are all treated as harp discontinuities, thus, resulting in a more accurate description of the inviscid flow field. The resulting numerical solutions are compared with available experimental data and existing first-order, shock-capturing numerical solutions.

Vijayashankar, V. S.↗

NASA NTRS1976

The development of a positive isolation disconnect

Conceptual design and developmental testing were conducted to determine the feasibility of a highly reliable, positive isolation disconnect (PID) for potential inflight maintenance of Shuttle environmental control/life support system subsystems. The PID design consists of two coupled valves, each capable of fluid isolation through the use of individually operated opposing poppets. An integral level clamping mechanism couples the two valves and locks the bodies together. The coupling lever is locked in position by turning the valve stems that have foolproof caps. The stem shaft has an integral cam that turns inside a yoke to open the poppet to permit fluid flow. Results of 5000 life cycle tests, hydraulic lock test, leakage tests, and pressure drop tests are included.

Rosener, A. A.↗

NASA NTRS1976

Stratigraphy in Apollo 16 drill section 60002

Contacts in drill stem 60002 which indicate layers at least several centimeters thick and with one firm age of about 2.5 x 10 to the 7th yr are observed on the basis of characteristic patterns of track density variation with depth from the contact. The patterns can be observed primarily because the drill stem has a large immature component (path II soils).

Blanford, G. E.↗

NASA NTRS1980

Dynamics of change of lipid and monoamine metabolisms and the blood coagulation system during experimental atherosclerosis caused by restriction of movement

Shifts in lipid, catecholamine, and blood coagulation systems following various periods (1, 2, 3, and 4 months) of experimentally induced atherosclerosis were studied. The same indices were studied in the tissues of the myocardium, liver, and brain stem-reticular formation after decapitation of the animals at the end of the experiment. Periodic motion restriction caused an increase in blood beta-lipoproteins in the rabbits at the beginning of the experiment. An increase in general cholesterol content and a decrease in the lecithincholesterol index were established at the end of the experiment. Myocardial beta-lipoprotein and brain stem reticular formation general cholesterol contents were elevated; catecholamine content was increased at the end of the experiment. In the initial months, free adrenaline basically increased, while in later months blood adrenaline decreased and blood noradrenaline increased.

Gvishiani, G. S.↗

NASA NTRS1983

Late skin damage in rabbits and monkeys after exposure to particulate radiations

Preliminary results are reported of experiments on the late effects of exposure to particulate radiations on stem cell populations. Skin biopsies were taken from the ears of rabbits irradiated 2-5 years previously with 530 MeV/amu Ar ions (LET 90 keV/micron), or 365 MeV/amu Ne ions (LET 35 keV micron), and from the chests and inner thighs of rhesus monkeys irradiated 16-18 years previously with 32-MeV protons (LET about 1.2 keV/micron). Skin fibroblast cultures obtained from the biopsy samples in rabbits were observed to undergo dose-dependent decreases in in vitro life span, with estimated survival curves showing the effects of Ar-ion irradiation to be more severe than those of Ne-ion irradiation. In addition, the healing of the biopsy wound was observed to become slower as radiation dose increased. In the monkey, radiation reduced the average number of fibroblasts at the time of cessation of growth in culture. Results thus demonstrate the capacity of skin sampling to reveal stem cell destruction, and have important implications for astronauts and other persons at risk of particle exposure with regard to healing responses to trauma or surgery.

Bergtold, D. S.↗

NASA NTRS1984

Interactions of light and gravity on growth, orientation, and lignin biosynthesis in mung beans

Mung beans (Vigna radiata L.) seedlings grown on the third Space Transport Mission (STS-3) showed marked orientation problems (some of the stems elongated horizontally and many of the roots were growing upward) and had a lower lignin content than the ground based controls. This research was initiated to determine if the atypical growth characteristics of mung beans grown in microgravity could be simulated using horizontal clinostats. Most of the effort focused on the design, construction and testing of the clinostats. In order to closely approximate the growth conditions of the plants grown in the plant growth unit on STS-3, cylindrical lexan minichambers were constructed. Results showed that plants grown using these clinostats in the horizontal position exhibit similar growth characteristics to the plants grown on STS-3 (disorientation of both stems and roots), while the vertical stationary and vertical rotating controls exhibit normal growth.

Jahns, G. C.↗

NASA NTRS1984

Isolation and characterization of beta-glucan synthase: A potential biochemical regulator of gravistimulated differential cell wall loosening

In plants, gravity stimulates differential growth in the upper and lower halves of horizontally oriented organs. Auxin regulation of cell wall loosening and elongation is the basis for most models of this phenomenon. Auxin treatment of pea stem tissue rapidly increases the activity of Golgi-localized Beta-1,4-glucan synthase, an enzyme involved in biosynthesis of wall xyloglucan which apparently constitutes the substrate for the wall loosening process. The primary objective is to determine if auxin induces de novo formation of Golgi glucan synthase and increases the level of this glucan synthase mRNA. This shall be accomplished by (a) preparation of a monoclonal antibody to the synthase, (b) isolation, and characterization of the glucan synthase, and (c) examination for cross reactivity between the antibody and translation products of auxin induced mRNAs in pea tissue. The antibody will also be used to localize the glucan synthase in upper and lower halves of pea stem tissue before, during and after the response to gravity.

Kuzmanoff, K. M.↗

NASA NTRS1983

Observations on the connectivity of the parvicellular reticular formation with respect to a vomiting center

The intrinsic and extrinsic connections of the parvicellular reticular formation (PCRF) that have been demonstrated by fiber degeneration studies and studied by more recently introduced horseradish peroxidase retrograde cell labeling are reviewed in an attempt to delimit the connectivity of the region in the PCRF where electrical stimulation produced emesis. Evidence is presented that certain specific functional subdivisions in PCRF such as the salivatory nuclei and the cells which give rise to the vestibular efferent projections can be delimited. An attempt is made to differentiate the sources of brain stem afferent connections with the nucleus of the tractus solitarius, the vagal nucleus and the nucleus ambiguus complex. The literature bearing on the histochemistry of the brain stem is reviewed in a search for clues to possible unique histo- or immunochemical cytological subdivisions in the parvicellular reticular formation.

Mehler, W. R.↗

NASA NTRS1984

Thermoelastic limit cycling of zippered cross section spacecraft booms

The phenomenon of thermal flutter of open cross section storable tubular extendible member (STEM) spacecraft booms was first observed in OGO IV and subsequently on a number of other satellites. Theoretical work ultimately ascribed the anomalous, undamped oscillations to the low torsional rigidity of the open section booms. This was confirmed when 'zippered' cross section booms, with substantially higher torsional rigidity, were later flown without exhibiting thermal flutter. However, zippered STEM booms generally have sizeable torsional backlash zones. It is shown here that small amplitude thermoelastic limit cycling within this backlash zone is theoretically possible and is the likely explanation for undamped oscillations recorded on Voyager 1 and 2 in the early stages of the Voyager mission.

Laskin, R. A.↗

NASA NTRS1984

The development of a microprocessor-controlled linearly-actuated valve assembly

The development of a proportional fluid control valve assembly is presented. This electromechanical system is needed for space applications to replace the current proportional flow controllers. The flow is controlled by a microprocessor system that monitors the control parameters of upstream pressure and requested volumetric flow rate. The microprocessor achieves the proper valve stem displacement by means of a digital linear actuator. A linear displacement sensor is used to measure the valve stem position. This displacement is monitored by the microprocessor system as a feedback signal to close the control loop. With an upstream pressure between 15 and 47 psig, the developed system operates between 779 standard CU cm/sec (SCCS) and 1543 SCCS.

Wall, R. H.↗

NASA NTRS1984

Slow opening valve

A valve control is described having a valve body with an actuator stem and a rotating handle connected to the actuator stem by a differential drive mechanism which, during uniform movement of the handle in one direction, initially opens the valve at a relatively slow rate and, thereafter, complete the valve movement at a substantially faster rate. A series of stop rings are received about the body in frictional abutting relationship and serially rotated by the handle to uniformly resist handle movement independently of the extent of handle movement.

Drapeau, D. F.↗

NASA NTRS1986

Characterization of vegetation by microwave and optical remote sensing

Two series of carefully controlled experiments were conducted. First, plots of important crops (corn, soybeans, and sorghum), prairie grasses (big bluestem, switchgrass, tal fescue, orchardgrass, bromegrass), and forage legumes (alfalfa, red clover, and crown vetch) were manipulated to produce wide ranges of phytomass, leaf area index, and canopy architecture. Second, coniferous forest canopies were simulated using small balsam fir trees grown in large pots of soil and arranged systematically on a large (5 m) platform. Rotating the platform produced many new canopies for frequency and spatial averaging of the backscatter signal. In both series of experiments, backscatter of 5.0 GHz (C-Band) was measured as a function of view angle and polarization. Biophysical measurements included leaf area index, fresh and dry phytomass, water content of canopy elements, canopy height, and soil roughness and moisture content. For a subset of the above plots, additional measurements were acquired to exercise microwave backscatter models. These measurements included size and shape of leaves, stems, and fruit and the probability density function of leaf and stem angles. The relationships of the backscattering coefficients and the biophysical properties of the canopies were evaluated using statistical correlations, analysis of variance, and regression analysis. Results from the corn density and balsam fir experiments are discussed and analyses of data from the other experiments are summarized.

Daughtry, C. S. T.↗

NASA NTRS1986

Simulation model for plant growth in controlled environment systems

The role of the mathematical model is to relate the individual processes to environmental conditions and the behavior of the whole plant. Using the controlled-environment facilities of the phytotron at North Carolina State University for experimentation at the whole-plant level and methods for handling complex models, researchers developed a plant growth model to describe the relationships between hierarchial levels of the crop production system. The fundamental processes that are considered are: (1) interception of photosynthetically active radiation by leaves, (2) absorption of photosynthetically active radiation, (3) photosynthetic transformation of absorbed radiation into chemical energy of carbon bonding in solube carbohydrates in the leaves, (4) translocation between carbohydrate pools in leaves, stems, and roots, (5) flow of energy from carbohydrate pools for respiration, (6) flow from carbohydrate pools for growth, and (7) aging of tissues. These processes are described at the level of organ structure and of elementary function processes. The driving variables of incident photosynthetically active radiation and ambient temperature as inputs pertain to characterization at the whole-plant level. The output of the model is accumulated dry matter partitioned among leaves, stems, and roots; thus, the elementary processes clearly operate under the constraints of the plant structure which is itself the output of the model.

Raper, C. D., Jr.↗

NASA NTRS1986

Potato leaf explants as a spaceflight plant test system

The use of explant tissues or organs may circumvent limitations facing whole-plant experimentation during spaceflight. In the case of potato, a crop currently being studied for application to bioregenerative life support systems, excised leaves and their subtended axillary buds can be used to test a variety of stem growth and development phases ranging from tubers through stolons (horizontal stems) to upright leafy shoots. The leaves can be fit well into small-volume test packages and sustained under relatively low irradiance levels using light-weight growing media. Tubers formed on potato leaf cuttings can yield up from 0.5 to 1.0 g fresh mass 10 days after excision and up to 2.0 g or more, 14 days from excision.

Wheeler, R. M.↗

NASA NTRS1985

Characterization of carbon fibers and fiber-matrix adhesion in composites

The effect of fiber/matrix interactions on the mechanical properties of thermoplastic carbon fiber composites was determined. The experimental approach was a multi-faceted one involving the following areas: characterization of the surface of carbon fibers using X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and scanning transmission electron microcopy (STEM); determination of the functional groups on carbon fiber surfaces using an elemental tagging scheme - derivatization; determination of the polar and dispersion contribution to the surface energy of carbon fibers by measuring wetting forces in a series of liquids having known polar and dispersion components; and study of the interaction of thermoplastic polymers with carbon surfaces by solution adsorption, STEM and fiber critical length.

Wightman, J. P.↗

NASA NTRS1986

Microwave backscattering from an anisotropic soybean canopy

Electromagnetic backscattering from a soybean canopy is modeled in the L band region of the spectrum. Mature soybean plants are taken as an ensemble of leaves and stems which are represented by lossy dielectric disks and rods respectively. Field data indicated that leaves and stems are not distributed uniformly in the azimuth coordinate. The plant has a tendency to grow out into the area between the rows. The effects on backscattered radar waves was computed by the distorted Born approximation. Results for look directions along the rows and perpendicular to the rows show that only a modest difference occurs in the L band frequency range. The use of another nonuniform distribution, different from those observed experimentally, results in a significant effect due to vegetation asymmetry.

Lang, R. H.↗

NASA NTRS1987

Surface characterization in composite and titanium bonding: Carbon fiber surface treatments for improved adhesion to thermoplastic polymers

The effect of anodization in NaOH, H2SO4, and amine salts on the surface chemistry of carbon fibers was examined by X-ray photoelectron spectroscopy (XPS). The surfaces of carbon fibers after anodization in NaOH and H2SO4 were examined by scanning transmission electron microscopy (STEM), angular dependent XPS, UV absorption spectroscopy of the anodization bath, secondary ion mass spectrometry, and polar/dispersive surface energy analysis. Hercules AS-4, Dexter Hysol XAS, and Union Carbide T-300 fibers were examined by STEM, angular dependent XPS, and breaking strength measurement before and after commercial surface treatment. Oxygen and nitrogen were added to the fiber surfaces by anodization in amine salts. Analysis of the plasmon peak in the carbon 1s signal indicated that H2SO4 anodization affected the morphological structure of the carbon fiber surface. The work of adhesion of carbon fibers to thermoplastic resins was calculated using the geometric mean relationship. A correlation was observed between the dispersive component of the work of adhesion and the interfacial adhesion.

Devilbiss, T. A.↗