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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Are Methanol-Derived Foliar Methyl Acetate Emissions a Tracer of Acetate-Mediated Drought Survival in Plants?

Upregulation of acetate fermentation in plants has recently been described as an evolutionarily conserved drought survival strategy, with the amount of acetate produced directly correlating to survival. However, destructive measurements are required to evaluate acetate-linked drought responses, limiting the temporal and spatial scales that can be studied. Here, 13C-labeling studies with poplar (Populus trichocarpa) branches confirmed that methyl acetate is produced in plants from the acetate-linked acetylation of methanol. Methyl acetate emissions from detached leaves were strongly stimulated during desiccation, with total emissions decreasing with the leaf developmental stage. In addition, diurnal methyl acetate emissions from whole physiologically active poplar branches increased as a function of temperature, and light-dark transitions resulted in significant emission bursts lasting several hours. During experimental drought treatments of potted poplar saplings, light-dark methyl acetate emission bursts were eliminated while strong enhancements in methyl acetate emissions lasting > 6 days were observed with their initiation coinciding with the suppression of transpiration and photosynthesis. The results suggest that methyl acetate emissions represent a novel non-invasive tracer of acetate-mediated temperature and drought survival response in plants. The findings may have important implications for the future understanding of acetate-mediated drought responses to transcription, cellular metabolism, and hormone signaling, as well as its associated changes in carbon cycling and water use from individual plants to whole ecosystems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Impacts of land use change and elevated CO 2 on the interannual variations and seasonal cycles of gross primary productivity in China

Climate change, rising CO 2 concentration, and landuse and land cover change (LULCC) are primary driving forces for terrestrialgross primary productivity (GPP), but their impacts on the temporal changesin GPP are uncertain. In this study, the effects of the three main factorson the interannual variation (IAV) and seasonal cycle amplitude (SCA) of GPPin China were investigated using 12 terrestrial biosphere models from theMulti-scale Synthesis and Terrestrial Model Intercomparison Project. Thesimulated ensemble mean value of China's GPP between 1981 and 2010, drivenby common climate forcing, LULCC and CO 2 data, was found to be7.4±1.8 Pg C yr -1 . In general, climate was the dominant controlfactor of the annual trends, IAV and seasonality of China's GPP. Theoverall rising CO2 led to enhanced plant photosynthesis, thusincreasing annual mean and IAV of China's total GPP, especially innortheastern and southern China, where vegetation is dense. LULCC decreasedthe IAV of China's total GPP by ~7%, whereas rising CO 2 induced an increase of 8 %. Compared to climate change andelevated CO 2 , LULCC showed less contributions to GPP's temporalvariation, and its impact acted locally, mainly in southwestern China.Furthermore, this study also examined subregional contributions to thetemporal changes in China's total GPP. Southern and southeastern Chinashowed higher contributions to China's annual GPP, whereas southwestern andcentral parts of China explained larger fractions of the IAV in China's GPP.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1982

Variations in atmospheric angular momentum and the length of day

Six years of twice daily global analyses were used to create and study a lengthy time series of high temporal resolution angular momentum values. Changes in these atmospheric values were compared to independently determined charges in the rotation rate of the solid Earth. Finally, the atmospheric data was examined in more detail to determine the time and space scales on which variations in momentum occur within the atmosphere and which regions are contributing most to the changes found in the global integral. The data and techniques used to derive the time series of momentum values are described.

Rosen, R. D.↗
NASA NTRS1983

Thermal and suprathermal protons and alpha particles in the earth's plasma sheet

Detailed proton energy spectra in the quasi-stable distant plasma sheet over the energy range from approximately 13 keV to approximately 130 keV are presented. These spectra are compared with spectra of simultaneously measured alpha particles in the energy range from approximately 30 keV/Q to approximately 130 keV/Q. The proton spectra are then extended into the higher energy range up to approximately 1 MeV, thereby supplementing the study of Sarris et al. (1981). The temporal behavior of the spectra in the higher energy range is discussed. It is found that below about 16 keV the proton spectra can be represented by a Maxwellian distribution; above this level, a suprathermal tail is found that cannot be represented by a single power law.

Ipavich, F. M.↗
NASA NTRS1983

Field investigation of techniques for remote laser sensing of oceanographic parameters

A laser fluorosensor, previously studied in the laboratory, was deployed at a pier in lower Chesapeake Bay for field testing. A Q-switched Nd:YAG laser doubled to 532 nm in conjunction with a gated optical multichannel analyzer (OMA) allow spectra with high signal-to-noise ratios to be recorded in full daylight at a distance of 20 m. As a test of the system a study was conducted of the spatial and temporal variations of the phytopigments phycoerythrin and chlorophyll. The phycoerythrin feature was resolved into two components, one attributable to cyanophytes and the other to cryptophytes. A comparison was also made with spectra obtained by the NASA airborne oceanographic lidar (AOL).

Houghton, W. M.↗
NASA NTRS1983

Variations in atmospheric angular momentum on global and regional scales and the length of day

It is pointed out that a fundamental measure of the dynamic state of the atmosphere is its angular momentum about the polar axis relative to the earth. Hide et al. (1980) demonstrated the potential which now exists for studying high frequency changes in atmospheric angular momentum by using the global grid point analyses produced by the British Meteorological Office and by the U.S. National Meteorological Center (NMC) for the same 4-month period. The present investigation is concerned with an extension of the work of Hide et al. by using six years (1976-1981) of NMC twice-daily global analyses to create and study a lengthy time series of high temporal resolution angular momentum values. Changes in these atmospheric values are compared with independently determined changes in the rotation rate of the solid earth. The atmospheric data are examined in more detail to determine the time and space scales on which variations in momentum occur within the atmosphere and the regions which contribute most to the changes found in the global integral.

Rosen, R. D.↗
NASA NTRS1985

Atmospheric Emission Photometric Imaging (AEPI)

The atmospheric emission photometric imaging (AEPI) consists of a dual channel, low light level video system with a filter wheel to isolate the emissions of interest, mounted on a stabilized, two axis gimbal system for pointing and control. The objectives are to produce images of various atmospheric emissions to: investigate ionospheric transport processes; observe induced emissions from artificial particle injection; measure electron impact cross sections of atmospheric species; study natural aurora at high spatial and temporal resolutions and in the ultraviolet.

Roberts, W. T.↗
NASA NTRS1984

Accuracy of diagnostic heat and moisture budgets using SESAME-79 field data as revealed by observing system simulation experiments

Observing system simulation experiments are used to investigate the accuracy of diagnostic heat and moisture budgets which employ the AVE-SESAME 1979 data. The time-including, four-dimensional data set of a mesoscale model is used to simulate rawinsonde observations from AVE-SESAME 1979. The 5 C/day (heat budget) and 2 g/kg per day (moisture budget) magnitudes of error obtained indicate difficulties in the diagnosis of the heating rate in weak convective systems. The influences exerted by observational frequency, objective analysis, observational density, vertical interpolation, and observational errors on the budget are also studied, and it is found that the temporal and spatial resolution of the SESAME regional network is marginal for diagnosing convective effects on a horizontal time scale of 550 x 550 km.

Kuo, Y.-H.↗
NASA NTRS1986

Atmospheric Emission Photometric Imaging (AEPI)

The atmospheric emission photometric imaging (AEPI) consists of a dual channel, low light level video system with a filter wheel to isolate the emissions of interest, mounted on a stabilized, two axis gimbal system for pointing and control. The objectives are to produce images of various atmospheric emissions to: investigate ionospheric transport processes; observe induced emissions from artificial particle injection; measure electron impact cross sections of atmospheric species; study natural aurora at high spatial and temporal resolutions and in the ultraviolet.

Roberts, B.↗
NASA NTRS1986

Mass loading of the Earth's magnetosphere by micron size lunar ejecta. 2: Ejecta dynamics and enhanced lifetimes in the Earth's magnetosphere

Extensive studies were conducted concerning the indivdual mass, temporal and positional distribution of micron and submicron lunar ejecta existing in the Earth-Moon gravitational sphere of influence. Initial results show a direct correlation between the position of the Moon, relative to the Earth, and the percentage of lunar ejecta leaving the Moon and intercepting the magnetosphere of the Earth at the magnetopause surface. It is seen that the Lorentz Force dominates all other forces, thus suggesting that submicron dust particles might possibly be magnetically trapped in the well known radiation zones.

Alexander, W. M.↗
NASA NTRS1987

Simulation of amplitude-modulated circularly polarized Alfven waves for beta less than one

The nonlinear properties of the amplitude-modulated circularly polarized Alfven wave are studied for beta less than one. The temporal behavior of the wave packet of the electromagnetic hybrid simulation is compared with a numerical solution of the derivative nonlinear Schroedinger (DNLS) equation. It is shown that the left-hand-polarized mode evolves into a shocklike structure due to the modulational instability. However, both cyclotron damping and a snowplow effect near the steepened wave packet suppress its further steepening, contrary to the predictions of the DNLS equation. For the right-hand mode, formation of the shock does not take place, and the initial time development is well described by the DNLS equation. The daughter Alfven wave and ion acoustic waves are excited due to the decay instability at a later time. Heating or acceleration of the particles takes place for both left- and right-hand waves. Energy transfer from the wave to the particles occurs effectively when substantial modulation in the wave amplitude is present.

Machida, S.↗
NASA NTRS1989

Temporal stability of multiple-cell vortices

The temporal stability of multiple cell vortices is studied with a staggered Chebyshev spectral collocation technique. It is shown that cell multiplicity in the vortex core has a drastic effect on the stability characteristics. While validating the spectral collocation algorithm, two new viscous modes of instability for Batchelor's (1964) vortex were found. These modes are discussed in detail.

Khorrami, M. R.↗
NASA NTRS1990

The temporal development of hollow cathode discharges

The temporal development of hollow cathode discharges was studied by means of electrical and optical diagnostic techniques. The results indicate that the discharge develops in two stages. The initial breakdown occurs along the longest straight path of the system, i.e., from the anode to the bottom of the cathode hole. This predischarge is confined to a narrow filament along the axis and carries a current of up to hundreds of milliamperes. The resulting distortion of the electric field in the cathode hole is assumed to cause a radial breakdown from the filamentary plasma on the axis to the edge of the cathode hole. After this second breakdown, an increase in current by more than three orders of magnitude is observed. Measurements with axial magnetic fields support the two-stage model.

Ngo, Mai T.↗
NASA NTRS1992

High level cognitive information processing in neural networks

Two related research efforts were addressed: (1) high-level connectionist cognitive modeling; and (2) local neural circuit modeling. The goals of the first effort were to develop connectionist models of high-level cognitive processes such as problem solving or natural language understanding, and to understand the computational requirements of such models. The goals of the second effort were to develop biologically-realistic model of local neural circuits, and to understand the computational behavior of such models. In keeping with the nature of NASA's Innovative Research Program, all the work conducted under the grant was highly innovative. For instance, the following ideas, all summarized, are contributions to the study of connectionist/neural networks: (1) the temporal-winner-take-all, relative-position encoding, and pattern-similarity association techniques; (2) the importation of logical combinators into connection; (3) the use of analogy-based reasoning as a bridge across the gap between the traditional symbolic paradigm and the connectionist paradigm; and (4) the application of connectionism to the domain of belief representation/reasoning. The work on local neural circuit modeling also departs significantly from the work of related researchers. In particular, its concentration on low-level neural phenomena that could support high-level cognitive processing is unusual within the area of biological local circuit modeling, and also serves to expand the horizons of the artificial neural net field.

Barnden, John A.↗
NASA NTRS1951

On the recording of turbulent longitudinal and transverse fluctuations

A thorough understanding of the turbulent flow movements cannot be arrived at from investigations of the temporal mean values of the flows alone. Study of the fluctuation phenomena themselves is indispensable. Thus turbulence research entered a new promising stage when investigators started performing fluctuation measurements and basing theories on those measurements. The investigations of fluctuations carried out so far refer almost exclusively to the so-called isotropic turbulence. It represents a damping phenomenon; it is the simplest type of turbulence where merely the longitudinal fluctuations need to be measured. However, it is precisely nonisotropic turbulence which involves the most essential problem of the turbulent exchange movement and the turbulent apparent friction. Investigation of nonisotropic turbulence requires measurement of longitudinal and transverse fluctuations.

TURBULENCE MEASURING APPARATUS, HOT-WIRE↗
NASA NTRS1993

A Regional Analysis of Cloudy Mean Spherical Albedo over the Marine Stratocumulus Region and the Tropical Atlantic Ocean

Since clouds are the largest variable in Earth's radiation budget, it is critical to determine both the spatial and temporal characteristics of their radiative properties. This study examines the relationships between cloud properties and cloud fraction in order to supplement grid scale parameterizations. The satellite data used in this study is from three hourly ISCCP (International Satellite Cloud Climatology Project) and monthly ERBE (Earth Radiation Budget Experiment) data on a 2.50 x 2.50 latitude-longitude grid. Mean cloud spherical albedo, the mean optical depth distribution and cloud fraction are examined and compared off the coast of California and the mid-tropical Atlantic for July 1987 and 1988. Individual grid boxes and spatial averages over several grid boxes are correlated to Coakleys (1991) theory of reflection for uniform and broken layered cloud and to Kedem, et al.(1990) findings that rainfall volume and fractional area of rain in convective systems is linear. Kedem's hypothesis can be expressed in terms of cloud properties. That is, the total volume of liquid in a box is a linear function of cloud fraction. Results for the marine stratocumulus regime indicate that albedo is often invariant for cloud fractions of 20% to 80%. Coakley's satellite model of small and large clouds with cores (1 km) and edges (100 in) is consistent with this observation. The cores maintain high liquid water concentrations and large droplets while the edges contain low liquid water concentrations and small droplets. Large clouds are just a collection of cores. The mean optical depth (TAU) distributions support the above observation with TAU values of 3.55 to 9.38 favored across all cloud fractions. From these results, a method based upon Kedem, et al. theory is proposed to separate the cloud fraction and liquid water path (LWP) calculations in a general circulation model (GCM). In terms of spatial averaging, a linear relationship between albedo and cloud fraction is observed. For tropical locations outside the Intertropical Convergence Zone (ITCZ), results of cloud fraction and albedo spatial averaging followed that of the stratus boxes containing few overcast scenes. Both the ideas of Coakley and Kedem, et al. apply. Within the ITCZ, the grid boxes tended to have the same statistical properties as stratus boxes containing many overcast scenes. Because different dynamical forcing mechanisms are present, it is difficult to devise a method for determining subgrid scale variations. Neither of the theories proposed by Kedem, et al. or Coakley works well for the boxes with numerous overcast scenes.

Ginger, Kathryn M.↗
NASA NTRS1997

Radar Monitoring of Wetlands for Malaria Control

Malaria is the most important vector-borne tropical disease (Collins and Paskewitz, 1995) and there is no simple and universally applicable form of vector control. While new methods such as malaria vaccine or genetic manipulation of mosquitoes are being explored in the laboratories, the need for more field research on malaria transmission remains very strong. For the foreseeable future many malaria programs must focus on controlling the vector, the anopheline mosquito, often under the specter of shrinking budgets. Therefore information on which human populations are at the greatest risk is especially valuable when allocating scarce resources. The goal of the Radar Monitoring of Wetlands for Malaria Control Project is to demonstrate the feasibility of using Radarsat or other comparable satellite radar imaging systems to determine where and when human populations are at greatest risk for contracting malaria. The study area is northern Belize, a region with abundant wetlands and a potentially serious malaria problem. A key aspect of this study is the analysis of multi-temporal satellite imagery to track seasonal flooding of anopheline mosquito breeding sites. Radarsat images of the test site in Belize have been acquired one to three times a month over the last year, however,, to date only one processed image has been received from the Alaska SAR Facility for analysis. Therefore analysis at this stage is focussed on determining the radar backscatter characteristics of known anopheline breeding sites, with future work to be dedicated toward seasonal changes.

Pope, Kevin O.↗