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NASA NTRS1991

Relationships between CH4 emission, biomass, and CO2 exchange in a subtropical grassland

Methane flux was linearly correlated with plant biomass (r = 0.97, n = 6 and r = 0.95, n = 8) at two locations in a Florida Everglades Cladium marsh. One location, which had burned 4 months previously, exhibited a greater increase in methane flux as a function of biomass relative to sites at an unburned location. However, methane flux data from both sites fit a single regression (r = 0.94, n = 14) when plotted against net CO2 exchange suggesting that either methanogenesis in Everglades marl sediments is fueled by root exudation below ground, or that factors which enhance photosynthetic production and plant growth are also correlated with methane production and flux in this oligotrophic environment. The data presented are the first to show a direct relationship between spatial variability in plant biomass, net ecosystem production, and methane emission in a natural wetland.

Whiting, Gary J.↗

NASA NTRS1990

Methodology for automating software systems

Applying ITS technology to the shuttle diagnostics would not require the rigor of the Petri Net representation, however it is important in providing the animated simulated portion of the interface and the demands placed on the system to support the training aspects to have a homogeneous and consistent underlying knowledge representation. By keeping the diagnostic rule base, the hardware description, the software description, user profiles, desired behavioral knowledge, and the user interface in the same notation, it is possible to reason about the all of the properties of petri nets, on any selected portion of the simulation. This reasoning provides foundation for utilization of intelligent tutoring systems technology.

Moseley, Warren↗

NASA NTRS1991

The control network of Mars: April 1991

The modern geodetic control network of Mars was first established based on Mariner 9 images with 1-2 km/pixel resolutions and covered almost the entire Martian surface. The introduction of higher resolution (10-200 meter/pixel) Viking Orbiter images greatly improved the accuracy and density of points in the control network. Analysis of the Viking Lander radio tracking data led to more accurate measurements of Mars' rotation period, spin axis direction, and the lander coordinates relative to the inertial reference frame. The prime meridian on Mars was defined by the Geodesy/Cartography Group of the Mariner 9 Television Team as the crater Airy-0, located about 5 degrees south of the equator. The Viking 1 Lander site was identified on a high resolution Viking frame. The control point measurements form the basis of a least squares solution determined by analytical triangulation after the pixel measurements are corrected for geometric distortions and converted to millimeter coordinates in the camera focal plane. Photogrammetric strips encircling Mars at the equator and at 60 degree north south were used to strengthen the overall net and improve the accuracy of the coordinates of points. In addition, photogrammetric strips along 0, 90, 180, and 270 degrees longitude to the Viking 1 Lander site have all significantly strengthened the control network. Most recently, photogrammetric strips were added to the net along 30 degrees north latitude between 0 and 180 degrees, and along 30 degrees between 180 and 360 degrees. The Viking 1 Lander site and Airy-0 are linked through photogrammetric strips occurring along the 0 degree meridian from Airy-0 to 65 degrees north, from that point through the Viking 1 Lander site to the equator, and along the equator to 180 degrees longitude. The Viking 1 lander site is thus a well calibrated area with coordinates of points accurate to approximately 200 meters relative to the J2000 inertial coordinate system. This will be a useful calibration region for upcoming missions. The current status of the control network calculations is presented.

Davies, Merton E.↗

NASA NTRS1991

A neural network architecture for implementation of expert systems for real time monitoring

Since neural networks have the advantages of massive parallelism and simple architecture, they are good tools for implementing real time expert systems. In a rule based expert system, the antecedents of rules are in the conjunctive or disjunctive form. We constructed a multilayer feedforward type network in which neurons represent AND or OR operations of rules. Further, we developed a translator which can automatically map a given rule base into the network. Also, we proposed a new and powerful yet flexible architecture that combines the advantages of both fuzzy expert systems and neural networks. This architecture uses the fuzzy logic concepts to separate input data domains into several smaller and overlapped regions. Rule-based expert systems for time critical applications using neural networks, the automated implementation of rule-based expert systems with neural nets, and fuzzy expert systems vs. neural nets are covered.

Ramamoorthy, P. A.↗

NASA NTRS1992

Design of neural networks for classification of remotely sensed imagery

Classification accuracies of a backpropagation neural network are discussed and compared with a maximum likelihood classifier (MLC) with multivariate normal class models. We have found that, because of its nonparametric nature, the neural network outperforms the MLC in this area. In addition, we discuss techniques for constructing optimal neural nets on parallel hardware like the MasPar MP-1 currently at GSFC. Other important discussions are centered around training and classification times of the two methods, and sensitivity to the training data. Finally, we discuss future work in the area of classification and neural nets.

Chettri, Samir R.↗

NASA NTRS1992

Interactive solution-adaptive grid generation

TURBO-AD is an interactive solution-adaptive grid generation program under development. The program combines an interactive algebraic grid generation technique and a solution-adaptive grid generation technique into a single interactive solution-adaptive grid generation package. The control point form uses a sparse collection of control points to algebraically generate a field grid. This technique provides local grid control capability and is well suited to interactive work due to its speed and efficiency. A mapping from the physical domain to a parametric domain was used to improve difficulties that had been encountered near outwardly concave boundaries in the control point technique. Therefore, all grid modifications are performed on a unit square in the parametric domain, and the new adapted grid in the parametric domain is then mapped back to the physical domain. The grid adaptation is achieved by first adapting the control points to a numerical solution in the parametric domain using control sources obtained from flow properties. Then a new modified grid is generated from the adapted control net. This solution-adaptive grid generation process is efficient because the number of control points is much less than the number of grid points and the generation of a new grid from the adapted control net is an efficient algebraic process. TURBO-AD provides the user with both local and global grid controls.

Choo, Yung K.↗

NASA NTRS1992

Interactive solution-adaptive grid generation procedure

TURBO-AD is a two dimensional interactive solution adaptive grid generation program. The code uniquely combines a grid adaptation technique that uses parametric mapping with control sources and an algebraic grid generation that uses control points into a single software package. The grid adaptation is achieved by first adapting the control points to a numerical solution in the parametric domain using the control sources obtained from flow properties. Then a new grid is generated from the adapted control net using the control point formulation. The new adapted grid in the parametric domain is then mapped back to the physical domain. This solution adaptive grid generation process is efficient because the number of control points is much less than the number of grid points and the grid generation from the adapted control net is an efficient algebraic process.

Choo, Yung K.↗

NASA NTRS1992

The Mars water cycle at other epochs: History of the polar caps and layered terrain

The atmospheric water cycle at the present epoch involves summertime sublimation of water from the north polar cap, transport of water through the atmosphere, and condensation on one or both winter CO2 caps. Exchange with the regolith is important seasonally, but the water content of the atmosphere appears to be controlled by the polar caps. The net annual transport through the atmosphere, integrated over long timescales, must be the driving force behind the long-term evolution of the polar caps; clearly, this feeds back into the evolution of the layered terrain. We have investigated the behavior of the seasonal water cycle and the net integrated behavior at the pole for the last 10 exp 7 years. Our model of the water cycle includes the solar input, CO2 condensation and sublimation, and summertime water sublimation through the seasonal cycles, and incorporates the long-term variations in the orbital elements describing the Martian orbit.

Jakosky, Bruce M.↗

NASA NTRS1991

On the estimation of jet-induced fountain lift and additional suckdown in hover for two-jet configurations

Currently available methods for estimating the net suckdown induced on jet V/STOL aircraft hovering in ground effect are based on a correlation of available force data and are, therefore, limited to configurations similar to those in the data base. Experience with some of these configurations has shown that both the fountain lift and additional suckdown are overestimated but these effects cancel each other for configurations within the data base. For other configurations, these effects may not cancel and the net suckdown could be grossly overestimated or underestimated. Also, present methods do not include the prediction of the pitching moments associated with the suckdown induced in ground effect. An attempt to develop a more logically based method for estimating the fountain lift and suckdown based on the jet-induced pressures is initiated. The analysis is based primarily on the data from a related family of three two-jet configurations (all using the same jet spacing) and limited data from two other two-jet configurations. The current status of the method, which includes expressions for estimating the maximum pressure induced in the fountain regions, and the sizes of the fountain and suckdown regions is presented. Correlating factors are developed to be used with these areas and pressures to estimate the fountain lift, the suckdown, and the related pitching moment increments.

Kuhn, Richard E.↗

NASA NTRS1990

Effect of cloud cover and surface type on earth's radiation budget derived from the first year of ERBE data

One year of ERBE data is analyzed for variations in outgoing LW and absorbed solar flux. Differences in land and ocean radiation budgets as well as differences between clear-sky and total scenes, including clouds, are studied. The variation of monthly average radiative parameters is examined for February 1985 through January 1986 for selected study regions and on zonal and global scales. ERBE results show significant seasonal variations in both outgoing LW and absorbed SW flux, and a pronounced difference between oceanic and continental surfaces. The main factors determining cloud radiative forcing in a given region are solar insolation, cloud amount, cloud type, and surface properties. The strongest effects of clouds are found in the midlatitude storm tracks over the oceans. Over much of the globe, LW warming is balanced by SW cooling. The annual-global average net cloud forcing shows that clouds have a net cooling effect on the earth for the year.

Gibson, G. G.↗

NASA NTRS1990

Radiatively driven stratosphere-troposphere interactions near the tops of tropical cloud clusters

Results are presented of two numerical simulations of the mechanism involved in the dehydration of air, using the model of Churchill (1988) and Churchill and Houze (1990) which combines the water and ice physics parameterizations and IR and solar-radiation parameterization with a convective adjustment scheme in a kinematic nondynamic framework. One simulation, a cirrus cloud simulation, was to test the Danielsen (1982) hypothesis of a dehydration mechanism for the stratosphere; the other was to simulate the mesoscale updraft in order to test an alternative mechanism for 'freeze-drying' the air. The results show that the physical processes simulated in the mesoscale updraft differ from those in the thin-cirrus simulation. While in the thin-cirrus case, eddy fluxes occur in response to IR radiative destabilization, and, hence, no net transfer occurs between troposphere and stratosphere, the mesosphere updraft case has net upward mass transport into the lower stratosphere.

Churchill, Dean D.↗

NASA NTRS1991

Resonance transition radiation X-ray laser

A free electron laser is proposed using a periodic dielectric and helical magnetic field. Periodic synchronism between the electrons and the optical wave is obtained at the period of the dielectric and not at the period of the helical magnetic field. The synchronism condition and the gain of the new device are derived. The effects on the gain from dephasing and beam expansion due to elastic scattering of the electrons in the periodic medium are included in the gain calculation. Examples of the resonance transition radiation laser and klystron are given. Operation at photon energies between 2.5 and 3.5 keV with net gain up to 12 percent is feasible using high electron-beam energies of 3 and 5 GeV. Moderate (300-MeV) beam energy allows operation between 80 to 110 eV with up to 57 percent net gain using a klystron design. In both cases, rapid foil heating may limit operation to a single electron-beam pulse.

Reid, Max B.↗

NASA NTRS1991

Thermally driven diffusion of SO2 within the surface of Io

The presence of sulfur dioxide (SO2) on Io, together with the fact that the surface layer of Io has extremely high porosity, suggests the possibility of diffusion of this volatile within the surface, as well as exchange between the surface and an atmosphere. The former possibility is investigated through the development of a surface layer thermal model and subsequent calculations of the thermally driven diffusion flux of SO2 within the layer. The major factors affecting the diffusion process are the temperature and temperature gradient in the surface layer throughout the day, and the porosity and grain size in the surface layer. The results indicate that the net transport of SO2 in the near-surface region is downward into the subsurface, causing near-surface depletion of SO2. Near-surface depletion would result in a layer of reduced thermal inertia overlying the bulk of the surface, consistent with thermal eclipse observations of Io. For the present nominal model with 10-micron grains and a porosity of 85 percent, the peak net diurnal downward flux reaches nearly 0.008 g/sq cm per period.

Meade, Paul E.↗

NASA NTRS1992

Alterations in glucose and protein metabolism in animals subjected to simulated microgravity

Reduction of physical activity due to disease or environmental restraints, such as total bed rest or exposure to spaceflight, leads to atrophy of skeletal muscle and is frequently accompanied by alterations in food intake and the concentration of metabolic regulatory hormones such as insulin. Hindlimb suspension of laboratory rats, as a model for microgravity, also shows marked atrophy of gravity-dependent muscles along with a reduced gain in body weight. Suspended rats exhibit enhanced sensitivity to insulin-induced glucose uptake when compared with normal control rats and resistance to insulin action when compared with control rats matched similarly for reduced body weight gain. These changes are accompanied by decreased insulin binding and tyrosine kinase activity in soleus but not plantaris muscle, unchanged glucose uptake by perfused hindlimb and decreased sensitivity but not responsiveness to insulin-induced suppression of net proteolysis in hindlimb skeletal muscle. These findings suggest that loss of insulin sensitivity during muscle atrophy is associated with decreased insulin binding and tyrosine kinase activity in atrophied soleus muscle along with decreased sensitivity to the effects of insulin on suppressing net protein breakdown but not on enhancing glucose uptake by perfused hindlimb.

Mondon, C. E.↗

NASA NTRS1991

A grid quality manipulation system

A grid quality manipulation system is described. The elements of the system are the measures by which quality is assessed, the computer graphic display of those measures, and the local grid manipulation to provide a response to the viewed quality indication. The display is an overlaid composite where the region is first covered with colors to reflect the values of the quality indicator, the grid is then placed on top of those colors, and finally a control net is placed on top of everything. The net represents the grid in terms of the control point form of algebraic grid generation. As a control point is moved, both the grid and the colored quality measures also move. This is a real time dynamic action so that the consequences of the manipulation are continuously seen.

Lu, Ning↗

NASA NTRS1992

Global energy transports and the influence of clouds on transport requirements - A satellite analysis

This report investigates the impact of differential net radiative heating on 2D energy transports within the atmosphere ocean system and the role of clouds on this process. The 2D mean energy transports, in answer to zonal and meridional gradients in the net radiation field, show an east-west coupled dipole structure in which the Pacific acts as the major energy source and North Africa as the major energy sink. It is demonstrated that the dipole is embedded in the secondary energy transports arising mainly from the differential heating between land and oceans in the tropics in which the tropical east-west (zonal) transports are up to 30 percent of the tropical north-south (meridional) transports.

Sohn, Byung-Ju↗

NASA NTRS1992

Thermal stability during rotation in space - A scaling and numerical analysis

An analysis of thermal stability in a fluid during rotation is presented. The conditions resulting in thermal stability are examined and numerically verified. It is shown that at least one thermal field exists for any rotating fluid, with or without a gravitational background field, where convection does not occur. The numerical model used is fully nonlinear and 3D. Results are presented on the basis of both steady-state and fully transient models. The thermally stable condition is further investigated in the context of the average net acceleration and the inhomogeneous part of the acceleration field (gradient of acceleration). It is shown that in the thermally stable condition the flow that would result from the average net acceleration is equal and opposite to the flow that would result from the inhomogeneous part of the acceleration field. It is concluded that the thermally stable condition is actually a flow mode transition at Ad = 1.

Arnold, William A.↗

NASA NTRS1993

Neural-Network-Development Program

NETS, software tool for development and evaluation of neural networks, provides simulation of neural-network algorithms plus computing environment for development of such algorithms. Uses back-propagation learning method for all of networks it creates. Enables user to customize patterns of connections between layers of network. Also provides features for saving, during learning process, values of weights, providing more-precise control over learning process. Written in ANSI standard C language. Machine-independent version (MSC-21588) includes only code for command-line-interface version of NETS 3.0.

Phillips, Todd A.↗