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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Contactless Growth of ZnSe Single Crystals by Physical Vapor Transport

ZnSe crystals were grown by self-seeded physical vapor transport (PVT) technique in the horizontal configuration. The source materials were heat treated by H2 reduction to remove the oxide followed by baking under dynamic vacuum to adjust the source composition toward that of congruent sublimation. Contactless growth of ZnSe single crystals have been performed consistently using three different source materials. The crystals grew away from the wall during the later stage of the growth with large (110) facets tend to align parallel to the gravity direction. The Scanning Electron Micrography (SEM) micrographs and the Atomic Force Microscope (AFM) images showed that large (110) terraces and steps dominate the as-grown facets. The measured residual gas pressures in the processed ampoules agree well among various source materials and the major components were CO and H2. No preferred growth direction was found. The one-dimensional diffusion model on the mass flux of a multi-species PVT system was employed to analyze the conditions for contactless growth. The calculated thermal profile for supersaturation is very close to the thermal profile measured inside the empty furnace bore in the region of contactless growth. The effects of convective flows in the vapor phase inside the ampoule on the growth processes are discussed.

Su, Ching-Hua↗
NASA NTRS2004

Kinetic Roughening and Energetics of Tetragonal Lysozyme Crystal Growth: A Preliminary Atomic Force Microscopy Investigation

We examined particulars of crystal growth from measurements obtained at both microscopic and molecular levels. The crystal growth measurements performed at the microscopic level are well characterized by a model that balances the flux of macromolecules towards the crystal surface with the flux of the crystal surface. Numerical evaluation of model with measurements of crystal growth, in time, provided accurate estimates for the average growth velocities. Growth velocities thus obtained were also interpreted using well-established phenomenological theories. Moreover, we find that microscopic measurements of growth velocity measurements obtained as a function of temperature best characterizes changes in crystal growth modes, when present. We also examined the possibility of detecting a change in crystal growth modes at the molecular level using atomic force microscopy, AFM. From preliminary AFM measurements performed at various supersaturations, we find that magnitude of surface height fluctuations, h(x), increases with supersaturation. Further examination of surface height fluctuations using methods established for fluctuation spectroscopy also enabled the discovery of the existence of a characteristic length, c, which may possibly determine the mode of crystal growth. Although the results are preliminary, we establish the non- critical divergence of 5 and the root-mean-square (rms) magnitude of height-height fluctuations as the kinetic roughening transition temperatures are approached. Moreover, we also examine approximate models for interpreting the non-critical behavior of both 6 and rms magnitude of height-height fluctuations, as the solution supersaturation is increased towards the kinetic roughening supersaturation.

Gorti, Sridhar↗
NASA NTRS1983

Doubly diffusive magnetic buoyancy instability in the solar interior

An investigation of the buoyancy of diffuse magnetic fields has shown that in the presence of rotation, static equilibrium configurations of the toroidal magnetic field and ambient plasma can exist. In that case, the escape of toroidal magnetic flux from the solar interior may be determined by the growth of instabilities which the equilibrium configuration may be subject to. In connection with the present investigation, it is assumed that in the region of toroidal magnetic flux amplification, the magnetic field has not as yet filamented into flux ropes, and is therefore 'diffuse'. A study is conducted of the MHD stability of an electrically conducting and differentially rotating gas in the presence of a toroidal magnetic field, an external constant gravitational field, and radiance pressure. The full dispersion relation for the magnetic buoyancy problem is developed, and the solutions of the dispersion relation are discussed.

Schmitt, J. H. M. M.↗
NASA NTRS2017

The Regional Influence of the Arctic Oscillation and Arctic Dipole on the Wintertime Arctic Surface Radiation Budget and Sea Ice Growth

An analysis of 2000-2015 monthly Clouds and the Earth's Radiant Energy System-Energy Balanced and Filled (CERES-EBAF) and Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA2) data reveals statistically significant fall and wintertime relationships between Arctic surface longwave (LW) radiative flux anomalies and the Arctic Oscillation (AO) and Arctic Dipole (AD). Signifying a substantial regional imprint, a negative AD index corresponds with positive downwelling clear-sky LW flux anomalies (greater than10W m(exp -2)) north of western Eurasia (0 deg E-120 deg E) and reduced sea ice growth in the Barents and Kara Seas in November-February. Conversely, a positive AO index coincides with negative clear-sky LW flux anomalies and minimal sea ice growth change in October-November across the Arctic. Increased (decreased) atmospheric temperature and water vapor coincide with the largest positive (negative) clear-sky flux anomalies. Positive surface LW cloud radiative effect anomalies also accompany the negative AD index in December-February. The results highlight a potential pathway by which Arctic atmospheric variability influences the regional surface radiation budget over areas of Arctic sea ice growth.

Hegyi, Bradley M.↗
NASA NTRS2004

Optimizing environmental conditions for mass application of mechano-dwarfing stimuli to Arabidopsis

Obtaining uniform mechano-dwarfing of Arabidopsis thaliana (L.) Heynh. seedlings within dense plantings is problematic. Alternative forms of mechano-stimulation were applied to seedlings in effort to obtain uniform growth reduction compared with undisturbed controls in both greenhouse and controlled growth environments. Arabidopsis grown under low photosynthetic photon flux (PPF) artificial light grew upright with limited leaf expansion, which enhanced mechano-responsiveness compared to that of rosette-growing plants under filtered sunlight or high PPF artificial light. Hypocotyls of seedlings grown at PPFs > 60 micromoles m-2 s-1 elongated less and had 6% less sensitivity to mechanical stress than seedlings grown at PPFs < 60 micromoles m-2 s-1. Fluorescent lamps alone (F) or fluorescent plus incandescent (F+I) lamps were compared for seedling responses to mechanical stress. Under F lighting, hypocotyl elongation was reduced 25% to 40% by twice-daily brush or plate treatments, and brushed seedlings exhibited more growth reduction than did plate treatments. Seedlings grown under F+I lamps exhibited similar stress-induced growth reduction compared to seedlings grown under F only, but stressed F+I seedlings lodged to a greater extent due to excessive hypocotyl elongation. Temperature-response studies using standardized F-only lighting indicated increased hypocotyl elongation but decreased leaf expansion, and decreased mechano-responsivity to brushing over the temperature range from 20 to 28 degrees C. Daylength studies indicated similar degrees of mechano-inhibition of hypocotyl elongation over the daylength range of 12, 16, 20, and 24 hours, whereas fresh weight of stressed seedling shoots declined compared to controls. A combination of environmental growth parameters that give repeatable, visual mechanical dwarfing of Arabidopsis include low-PPF fluorescent lighting from 55 to 60 micromoles m-2 s-1, ambient temperatures from 22 to 25 degrees C, and twice-daily brush treatments.

NASA Discipline Life Support Systems↗
NASA NTRS2009

Simulating the Effects of Irrigation over the U.S. in a Land Surface Model Based on Satellite Derived Agricultural Data

A novel method is introduced for integrating satellite derived irrigation data and high-resolution crop type information into a land surface model (LSM). The objective is to improve the simulation of land surface states and fluxes through better representation of agricultural land use. Ultimately, this scheme could enable numerical weather prediction (NWP) models to capture land-atmosphere feedbacks in managed lands more accurately and thus improve forecast skill. Here we show that application of the new irrigation scheme over the continental US significantly influences the surface water and energy balances by modulating the partitioning of water between the surface and the atmosphere. In our experiment, irrigation caused a 12% increase in evapotranspiration (QLE) and an equivalent reduction in the sensible heat flux (QH) averaged over all irrigated areas in the continental US during the 2003 growing season. Local effects were more extreme: irrigation shifted more than 100 W/m from QH to QLE in many locations in California, eastern Idaho, southern Washington, and southern Colorado during peak crop growth. In these cases, the changes in ground heat flux (QG), net radiation (RNET), evapotranspiration (ET), runoff (R), and soil moisture (SM) were more than 3 W/m(sup 2), 20 W/m(sup 2), 5 mm/day, 0.3 mm/day, and 100 mm, respectively. These results are highly relevant to continental- to global-scale water and energy cycle studies that, to date, have struggled to quantify the effects of agricultural management practices such as irrigation. Based on the results presented here, we expect that better representation of managed lands will lead to improved weather and climate forecasting skill when the new irrigation scheme is incorporated into NWP models such as NOAA's Global Forecast System (GFS).

Ozdogan, Mutlu↗
NASA NTRS1986

An engineering analysis of a closed cycle plant growth module

The SOLGEM model is a numerical engineering model which solves the flow and energy balance equations for the air flowing through a growing environment, assuming quasi-steady state conditions within the system. SOLGEM provides a dynamic simulation of the controlled environment system in that the temperature and flow conditions of the growing environment are estimated on an hourly basis in response to the weather data and the plant growth parameters. The flow energy balance considers the incident solar flux; incoming air temperature, humidity, and flow rate; heat exchange with the roof and floor; and heat and moisture exchange with the plants. A plant transpiration subroutine was developed based plant growth research facility, intended for the study of bioregenerative life support theories. The results of a performance analysis of the plant growth module are given. The estimated energy requirements of the module components and the total energy are given.

Stickford, G. H., Jr.↗
NASA NTRS2000

Protein Crystal Growth Dynamics and Impurity Incorporation

The general concepts and theories of crystal growth are proven to work for biomolecular crystallization. This allowed us to extract basic parameters controlling growth kinetics - free surface energy, alpha, and kinetic coefficient, beta, for steps. Surface energy per molecular site in thermal units, alpha(omega)(sup 2/3)/kT approx. = 1, is close to the one for inorganic crystals in solution (omega is the specific molecular volume, T is the temperature). Entropic restrictions on incorporation of biomolecules into the lattice reduce the incorporation rate, beta, by a factor of 10(exp 2) - 10(exp 3) relative to inorganic crystals. A dehydration barrier of approx. 18kcal/mol may explain approx. 10(exp -6) times difference between frequencies of adding a molecule to the lattice and Brownian attempts to do so. The latter was obtained from AFM measurements of step and kink growth rates on orthorhombic lysozyme. Protein and many inorganic crystals typically do not belong to the Kossel type, thus requiring a theory to account for inequivalent molecular positions within its unit cell. Orthorhombic lysozyme will serve as an example of how to develop such a theory. Factors deteriorating crystal quality - stress and strain, mosaicity, molecular disorder - will be reviewed with emphasis on impurities. Dimers in ferritin and lysozyme and acetylated lysozyme, are microheterogeneous i.e. nearly isomorphic impurities that are shown to be preferentially trapped by tetragonal lysozyme and ferritin crystals, respectively. The distribution coefficient, K defined as a ratio of the (impurity/protein) ratios in crystal and in solution is a measure of trapping. For acetylated lysoyzme, K = 2.15 or, 3.42 for differently acetylated forms, is independent of both the impurity and the crystallizing protein concentration. The reason is that impurity flux to the surface is constant while the growth rate rises with supersaturation. About 3 times lower dimer concentration in space grown ferritin and lysozyme crystals might be examples explaining higher quality of the space grown protein crystal. Depletion of solution with respect to isomorphic impurities around a growing crystal may be K times deeper than with respect to the crystallizing protein.

Chernov, Alex A.↗
NASA NTRS2016

Modeling Antarctic Subglacial Lake Filling and Drainage Cycles

The growth and drainage of active subglacial lakes in Antarctica has previously been inferred from analysis of ice surface altimetry data. We use a subglacial hydrology model applied to a synthetic Antarctic ice stream to examine internal controls on the filling and drainage of subglacial lakes. Our model outputs suggest that the highly constricted subglacial environment of our idealized ice stream, combined with relatively high rates of water flow funneled from a large catchment, can combine to create a system exhibiting slow-moving pressure waves. Over a period of years, the accumulation of water in the ice stream onset region results in a buildup of pressure creating temporary channels, which then evacuate the excess water. This increased flux of water beneath the ice stream drives lake growth. As the water body builds up, it steepens the hydraulic gradient out of the overdeepened lake basin and allows greater flux. Eventually this flux is large enough to melt channels that cause the lake to drain. Lake drainage also depends on the internal hydrological development in the wider system and therefore does not directly correspond to a particular water volume or depth. This creates a highly temporally and spatially variable system, which is of interest for assessing the importance of subglacial lakes in ice stream hydrology and dynamics.

drainage↗
NASA NTRS2012

Examples of Level Products Possible from Existing Assets

How do patterns of human environmental and infectious diseases respond to leading environmental changes, particularly to urban growth and change and the associated impacts of urbanization? We use HyspIRI high spatial resolution, multispectral, and multitemporal TIR data to track energy balance and energy flux characteristics for changing land covers/land uses through time to provide synoptic views of impacts on surface energy fluxes, emissivity and temperature and HyspIRI data in conjunction with spatial growth models to project land cover/land use changes in the future to assess impacts on natural and human ecosystems. We use multispectral thermal IR land cover maps at a high spatial resolution (60m) on a weekly basis for long-term validation of surface energy responses and changes in emissivity and integration of HyspIRI TIR data with spatial modeling to assess changes in land cover/land use through time and subsequent changes in thermal energy responses

Quattrochi, Dale A.↗
NASA NTRS1992

Mass-Transport Properties In Growth Of Crystals From Vapors

Brief report summarizes results of experimental and theoretical studies of mass-transport properties of GeSe/Gel4 and Hg0.8Cd0.2Te systems in connection with growth of crystals in closed ampoules. Primary emphasis in studies was on thermochemical analyses, on development of mathematical models to predict diffusion-limited mass transport, and on comparison of theoretically predicted with experimental fluxes. Results applied to design, preparation, performance, and analysis of crystal-growth experiments of semiconducting materials on Earth and in outer space. Model extended to predict mass flux and overall composition of transport products of Hg0.8Cd0.2Te transport system.

Wiedemeier, H.↗
NASA NTRS1987

The effect of V2O5 on the growth and properties of Bi-YIG

The effect of V2O5 additions to PbO-Bi2O3 flux was investigated with respect to the properties of Bi-YIG epitaxial films for magnetic bubble devices. The Bi content of the films (including an estimated 10 percent Pt(2+) were calculated from Faraday rotation measurements. For films grown at constant supercooling, the Bi content increased by 60 percent as the V2O5 content of the flux was increased from 0 to 9 mol pct. Lattice constant data were shown to agree with measured Bi and Ca-Si contents. The growth-induced magnetic anisotropy increased proportionally to the Bi content and could be fairly represented by a model; however, the coefficients of the model vary widely between data sets for different melt compositions.

Luther, L. C.↗
NASA NTRS1982

The coronal field lines of an evolving bipolar magnetic region

A simple potential field model is presented to illustrate that loops of magnetic flux rise upward through the corona during the relatively short growth phase of a bipolar magnetic region but contract back to the sun's surface during the much longer decay phase of the photospheric region. To reconcile this behavior with the unidirectional, solar-wind-driven convection of flux outward from the sun, one must postulate the existence of an X-type neutral line in the middle corona where open field lines can be converted back to closed ones.

Sheeley, N. R., Jr.↗
NASA NTRS1983

Dependence of 50-keV upstream ion events at IMP 7 and 8 upon magnetic field bow shock geometry

Results are presented for a statistical study of four years (1972-1976) of IMP 7 and 8 observations at approximately 40 R(E) of 50-200 keV upstream ion events measured with the Energetic Particle Experiment. A monotonic increase in the probability of observing upstream particle events is found with a decrease in the angle (theta-Bn) between the interplanetary magnetic field (IMF) and the local shock normal at the point where the IMF intersects the bow shock, independent of the length of time of bow shock connections exceeding approximately 10 min. Approximately equal probabilities are found for observing an event above a given flux from any portion of the bow shock with the same value of theta-Bn, a growth time of the 50-200 keV events of approximately 10 min, a maximum attainable flux of approximately 25,000/sq cm s sr, and a positive correlation between the probability of exceeding a given flux and the 3 hr Kp index. It is concluded that the local structure of the bow shock in the immediate vicinity of the field line connection is the dominant influence in the generation process of energetic upstream particle events and that wave-particle interactions produce a self-throttling mechanism that limits the maximum flux of ions escaping the upstream foreshock.

Mitchell, D. G.↗
NASA NTRS1985

Evidence for submergencew of magnetic flux in a growing active region

In NOAA Active Region 2372 (April 1980), 4 x 10 to the 20th power maxwell of magnetic flux concentrated within a 30" circular area disappeared overnight. Vector magnetograms show that all components of the magnetic field weakened together. If the field had weakened through diffusion or fluid flow, 80% of the original flux would still have been detected by the magnetograph within a suitably enlarged area. In fact there was at least a threefold decrease in detected flux. Evidently, magnetic field was removed from the photosphere. Since the disappearing flux was located in a region of low magnetic shear and low activity, it is unlikely that the field dissipated through reconnection. The most likely possibility is that flux submerged. Observations suggest that even in the growth phase of active regions, submergence is a strong process comparable in magnitude to emergence.

Rabin, D. M.↗
NASA NTRS1985

The observed life cycle of a baroclinic instability

Medium-scale waves (zonal wavenumbers 4-7) frequently dominate Southern Hemisphere summer circulation patterns. Randel and Stanford have studied the dynamics of these features, demonstrating that the medium-scale waves result from baroclinic excitation and exhibit well-defined life cycles. This study details the evolution of the medium-scale waves during a particular life cycle. The specific case chosen exhibits a high degree of zonal symmetry, prompting study based upon zonally averaged diagnostics. An analysis of the medium-scale wave energetics reveals a well-defined life cycle of baroclinic growth, maturity, and barotropic decay. Eliassen-Palm flux diagrams detail the daily wave structure and its interaction with the zonally-averaged flow.

Randel, W. J.↗
NASA NTRS1983

Enhancement of lettuce yield by manipulation of light and nitrogen nutrition

Several levels of photosynthetic photon flux density (PPFD) were tested for effects on growth of 4 cultivars of lettuce (Lactuca sativa L.) under controlled-environment conditions. Growth of 'Salad Bowl', 'Bibb', and 'Ruby' was greater at 932 micromoles s-1 m-2 than at < or = 644 micromoles s-1 m-2 under a 16-hour photoperiod. Thirty mM NO3- or 5 mM NH4+ + 25 mM NO3- increased leaf dry weight while reducing leaf chlorosis in 'Salad Bowl' and 'Grand Rapids' relative to that with 15 mM NO3-, and reduced leaf purpling in 'Bibb' and 'Ruby' with little or no effect on yield. Continuous illumination with 455 or 918 micromoles s-1 m-2 stimulated yield of 'Salad Bowl' and 'Bibb' when 30 mM N as NH4+ + NO3- was used relative to that with 15 mM NO3-.

Nitrogen/metabolism↗
NASA NTRS2018

Evaluation of a Thermodynamic Ice Crystal Icing Model Using Experimental Ice Accretion Data

This paper presents the evaluation of a thermodynamic ice crystal icing model, previously presented to describe the possible mechanisms of icing within the core of a turbofan jet engine. It has been proposed that there are two types of distinct ice accretions based on a surface energy balance: freeze-dominated icing and melt-dominated icing. In the former, ice accretion occurs where a freeze fraction (0 to 1) of melted ice crystals freezes on a surface, along with the existing ice of the impinging water and ice mass. This freeze-dominated icing is characterized by having strong adhesion to the surface. In the latter, icing occurs from accumulated unmelted ice on a surface, where a melt fraction (0 to 1) dictates the amount of unmelted impinged ice. This melt-dominated icing is characterized by weakly bonded surface adhesion. The experimentally observed ice growth rates suggest that only a small fraction of the impinging ice remains on the surface, implying a mass loss mechanism such as splash, runback, bounce, or erosion. This mass loss parameter must be determined in conjunction with the fraction of freezing liquid water or fraction of melting ice on an icing surface. This loss parameter, however, along with the freeze and melt fraction, are the only experimental parameters that are currently not measured directly. Using reported icing growth rates from published ice crystal icing experiments, a methodology is proposed to determine these unknown parameters. This work takes reported ice accretion data from tests conducted by the National Aeronautics and Space Administration (NASA) in 2016 and tests NASA collaborated on with the National Research Council (NRC) of Canada in 2012 that examined the fundamental physics of ice crystal icing. Those research efforts sought to generate icing conditions representative of those that occur inside a jet engine when ingesting ice crystals. This paper presents the fundamental equations of the thermodynamic model, the methodology used to determine the aforementioned unknown icing parameters, and results from model evaluation using experimental data. In addition, this paper builds on the previously proposed model by adding a transient conduction term to explain ice growth behavior at the onset of experimental tests that was observed to be different from steady-state ice growth that occurred later in the test run.With the addition of this energy term, this becomes a quasi-steady model. A key finding from this work suggests that mass loss fractions can exceed 0.90 for steady ice growth periods. In addition, due to conductive heat fluxes when using a warmer-than-freezing airfoil, lower mass loss fraction values were calculated during the initial transient period.

Ice-Crystal Ice Accretion↗