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All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Simple dynamical models of Neptune's Great Dark Spot

The large amplitude oscillations of the shape of Neptune's Great Dark Spot are well reproduced by simple dynamical models of an isolated vortex embedded in a background shear flow. From the time series of the aspect ratio and inclination of the vortex values are estimated for the background shear and the mean vorticity of the Great Dark Spot, and a lower bound is placed on the value of the Rossby deformation radius. These models imply the existence of a planetary-scale zone of deterministic chaotic advection in the atmosphere of Neptune.

Polivani, L. M.↗
NASA NTRS1986

Simple methods of exploiting the underlying structure of rule-based systems

Much recent work in the field of expert systems research has aimed at exploiting the underlying structures of the rule base for reasons of analysis. Such techniques as Petri-nets and GAGs have been proposed as representational structures that will allow complete analysis. Much has been made of proving isomorphisms between the rule bases and the mechanisms, and in examining the theoretical power of this analysis. In this paper we describe some early work in a new system which has much simpler (and thus, one hopes, more easily achieved) aims and less formality. The technique being examined is a very simple one: OPS5 programs are analyzed in a purely syntactic way and a FSA description is generated. In this paper we describe the technique and some user interface tools which exploit this structure.

Hendler, James↗
NASA NTRS1991

Analysis Of Turbulence In A Simple Shear Flow

Report presents analysis of turbulence in simple shear flow. In mathematical model used in study, turbulence considered to arise from growth of small fluctuations in initially unstable plane Poiseuille flow. Invoking principle of stabilization, fluctuations in velocity, therefore, Reynolds stresses, considered to grow until new stable state approached. Principle enables one to find Reynolds stresses and mean velocity of turbulent flow arising from initial plane Poiseulle flow.

Zak, Michail A.↗
NASA NTRS1990

Evidence against a simple two-component model for the far-infrared emission from galaxies

Two of the first Infrared Astronomy Satellite (IRAS) results were that galaxies have a wide range of values for the ratio of 60 micron to 100 micron flux density (0.2 less than or equal to S sub 60/S sub 100 less than or equal to 1.0) and that this ratio is correlated with L sub fir, L sub b, L sub fir being the total far-infrared luminosity and L sub b being the luminosity at visible wavelengths (de Jong et al. 1984; Soifer et al. 1984). From these results arose the following simple model for the far-infrared emission from galaxies (de Jong et al. 1984), which has remained the standard model ever since. In this model, the far-infrared emission comes from two dust components: warm dust (T approx. equals 50 K) intermingled with, and heated by, young massive OB stars in molecular clouds and HII regions, and colder dust (T approx. equals 20 K) associated with the diffuse atomic hydrogen in the interstellar medium and heated by the general interstellar radiation field. As the number of young stars in a galaxy increases, S sub 60/S sub 100 increases, because there is a greater proportion of warm dust, and so does L sub fir/L sub b, because most of the radiation from the young stars is absorbed by the dust, leading to a swifter increase in far-infrared emission than in visible light. Although this model explains the basic IRAS results, it is inelegant. It uses two free parameters to fit two data (the 60 and 100 micron flux densities)-and there are now several observations that contradict it. Despite these major problems with the two-component model, it is not clear what should be put in its place. When considering possible models for the far-infrared emission from galaxies, the observational evidence for our own galaxy must be considered. Researchers suspect that the study by Boulanger and Perault (1988) of the far-infrared properties of the local interstellar medium may be particularly relevant. They showed that molecular clouds are leaky - that most of the light from OB stars in molecular clouds does not heat the dust in the clouds, but instead leaks out. The consequence of this is that that while most of the far-infrared emission from the solar neighborhood is from dust associated with diffuse HI, this dust is mostly heated by young stars.

Eales, Stephen A.↗
NASA NTRS1990

Computation of thermochemical nonequilibrium flows around a simple and a double ellipse

The nonequilibrium viscous reactive flows over a simple and a double ellipse at a 30 degree angle of attack were computed. The geometry and the free stream conditions are given by INRIA/GAMNI/SMAI workshop test cases 6.2-2 and 6.2-4. The governing Navier-Stokes equations coupled with thermochemical nonequilibrium processes are solved numerically using a fully coupled, implicit, finite volume technique with a dynamically adaptive grid. The nonequilibrium gas model and the numerical method used in the calculations are briefly described.

Gokcen, Tahir↗
NASA NTRS1991

A simple, analytical, axisymmetric microburst model for downdraft estimation

A simple analytical microburst model was developed for use in estimating vertical winds from horizontal wind measurements. It is an axisymmetric, steady state model that uses shaping functions to satisfy the mass continuity equation and simulate boundary layer effects. The model is defined through four model variables: the radius and altitude of the maximum horizontal wind, a shaping function variable, and a scale factor. The model closely agrees with a high fidelity analytical model and measured data, particularily in the radial direction and at lower altitudes. At higher altitudes, the model tends to overestimate the wind magnitude relative to the measured data.

Vicroy, Dan D.↗
NASA NTRS1991

A simple test for thermomechanical evaluation of ceramic fibers

A simple bend stress relaxation (BSR) test was developed to measure the creep related properties of ceramic fibers and whiskers. The test was applied to a variety of commercial and developmental Si based fibers to demonstrate capabilities and to evaluate the relative creep resistance of the fibers at 1200 to 1400 C. The implications of these results and the advantages of the BSR test over typical tensile creep tests are discussed.

Morscher, Gregory N.↗
NASA NTRS1991

Atmospheric water vapor transport: Estimation of continental precipitation recycling and parameterization of a simple climate model

The advective transport of atmospheric water vapor and its role in global hydrology and the water balance of continental regions are discussed and explored. The data set consists of ten years of global wind and humidity observations interpolated onto a regular grid by objective analysis. Atmospheric water vapor fluxes across the boundaries of selected continental regions are displayed graphically. The water vapor flux data are used to investigate the sources of continental precipitation. The total amount of water that precipitates on large continental regions is supplied by two mechanisms: (1) advection from surrounding areas external to the region; and (2) evaporation and transpiration from the land surface recycling of precipitation over the continental area. The degree to which regional precipitation is supplied by recycled moisture is a potentially significant climate feedback mechanism and land surface-atmosphere interaction, which may contribute to the persistence and intensification of droughts. A simplified model of the atmospheric moisture over continents and simultaneous estimates of regional precipitation are employed to estimate, for several large continental regions, the fraction of precipitation that is locally derived. In a separate, but related, study estimates of ocean to land water vapor transport are used to parameterize an existing simple climate model, containing both land and ocean surfaces, that is intended to mimic the dynamics of continental climates.

Brubaker, Kaye L.↗
NASA NTRS1990

Recognition of simple visual images using a sparse distributed memory: Some implementations and experiments

Previously, a method was described of representing a class of simple visual images so that they could be used with a Sparse Distributed Memory (SDM). Herein, two possible implementations are described of a SDM, for which these images, suitably encoded, will serve both as addresses to the memory and as data to be stored in the memory. A key feature of both implementations is that a pattern that is represented as an unordered set with a variable number of members can be used as an address to the memory. In the 1st model, an image is encoded as a 9072 bit string to be used as a read or write address; the bit string may also be used as data to be stored in the memory. Another representation, in which an image is encoded as a 256 bit string, may be used with either model as data to be stored in the memory, but not as an address. In the 2nd model, an image is not represented as a vector of fixed length to be used as an address. Instead, a rule is given for determining which memory locations are to be activated in response to an encoded image. This activation rule treats the pieces of an image as an unordered set. With this model, the memory can be simulated, based on a method of computing the approximate result of a read operation.

Jaeckel, Louis A.↗
NASA NTRS1990

A simple inertial model for Neptune's zonal circulation

Voyager imaging observations of zonal cloud-tracked winds on Neptune revealed a strongly subrotational equatorial jet with a speed approaching 500 m/s and generally decreasing retrograde motion toward the poles. The wind data are interpreted with a speculative but revealingly simple model based on steady gradient flow balance and an assumed global homogenization of potential vorticity for shallow layer motion. The prescribed model flow profile relates the equatorial velocity to the mid-latitude shear, in reasonable agreement with the available data, and implies a global horizontal deformation scale L(D) of about 3000 km.

Allison, Michael↗
NASA NTRS1991

A simple method for correcting spatially resolved solar intensity oscillation observations for variations in scattered light

A measurement of the intensity distribution in an image of the solar disk will be corrupted by a spatial redistribution of the light that is caused by the earth's atmosphere and the observing instrument. A simple correction method is introduced here that is applicable for solar p-mode intensity observations obtained over a period of time in which there is a significant change in the scattering component of the point spread function. The method circumvents the problems incurred with an accurate determination of the spatial point spread function and its subsequent deconvolution from the observations. The method only corrects the spherical harmonic coefficients that represent the spatial frequencies present in the image and does not correct the image itself.

Jefferies, S. M.↗
NASA NTRS1991

A simple parameterization of ozone infrared absorption for atmospheric heating rate calculations

A simple parameterization of ozone absorption in the 9.6-micron region which is suitable for two- and three-dimensional stratospheric and tropospheric models is presented. The band is divided into two parts, a brand center region and a band wing region, grouping together regions for which the temperature dependence of absorption is similar. Each of the two regions is modeled with a function having the form of the Goody random model, with pressure and temperature dependent band parameters chosen by empirically fitting line-by-line equivalent widths for pressures between 0.25 and 1000 mbar and ozone absorber amounts between 1.0 x 10 to the -7th and 1.0 cm atm. The model has been applied to calculations of atmospheric heating rates using an absorber amount weighted mean pressure and temperature along the inhomogeneous paths necessary for flux computations. In the stratosphere, maximum errors in the heating rates relative to line-by-line calculations are 0.1 K/d, or 5 percent of the peak cooling at the stratopause. In the troposphere the errors are at most 0.005 K/d.

Rosenfield, Joan E.↗
NASA NTRS1991

A simple recipe for modeling reaction-rate in flows with turbulent-combustion

A computationally viable scheme to account for chemical reaction in turbulent flows is presented. The multivariate beta-pdf model for multiple scalar mixing forms the basis of this scheme. Using the model scalar joint pdf and a general form of the instantaneous reaction-rate, the unclosed chemical reaction terms are expressed as simple functions of scalar means and the turbulent scalar energy. The calculation procedure requires that the mean scalar equations and only one other transport equation - for the turbulent scalar energy - be solved.

Girimaji, Sharath S.↗
NASA NTRS1991

A simple electrical-mechanical model of the heart applied to the study of electrical-mechanical alternans

Recent evidence has shown that a subtle alternation in the surface ECG (electrical alternans) may be correlated with the susceptibility to ventricular fibrillation. In the present work, the author presents evidence that a mechanical alternation in the heartbeat (mechanical alternans) generally accompanies electrical alternans. A simple finite-element computer model which emulates both the electrical and the mechanical activity of the heart is presented. A pilot animal study is also reported. The computer model and the animal study both found that (1) there exists a regime of combined electrical-mechanical alternans during the transition from a normal rhythm towards a fibrillatory rhythm, (2) the detected degree of alternation is correlated with the relative instability of the rhythm, and (3) the electrical and mechanical alternans may result from a dispersion in local electrical properties leading to a spatial-temporal alternation in the electrical conduction process.

Clancy, Edward A.↗
NASA NTRS1990

A simple low-cost array on the lunar near-side for the early lunar expeditions

A concept of a simple, low-cost array on the lunar near-side is discussed. The concept includes 19 stations laid in a T, with three arms each 36 km long, and separated by 6 km. Each station consists of two 10-m-long orthogonal dipoles, each feeding a receiver of a commercial pocket digital shortwave radio type, and a 3-m spring-loaded mast with a small UHF array at the top for receiving the timing signals and tuning commmands and for sending out the digitized data streams. Each station has 0.25 square meters of solar arrays and 20 kg of lithium batteries. At the array center there is either a digital correlator for processing the signals from each antenna pair to compact the data into a 32-kb/sec channel or a 10-cm telescope for sending back raw data to earth.

Kuiper, T. B. H.↗
NASA NTRS1992

Simple Schlieren Light Meter

Simple light-meter circuit used to position knife edge of schlieren optical system to block exactly half light. Enables operator to check quickly position of knife edge between tunnel runs to ascertain whether or not in alignment. Permanent measuring system made part of each schlieren system. If placed in unused area of image plane, or in monitoring beam from mirror knife edge, provides real-time assessment of alignment of schlieren system.

Rhodes, David B.↗
NASA NTRS1991

Gradational evolution of young, simple impact craters on the Earth

From these three craters, a first order gradational evolutionary sequence can be proposed. As crater rims are reduced by backwasting and downwasting through fluvial and mass wasting processes, craters are enlarged by approx. 10 pct. Enlargement of drainages inside the crater eventually forms rim breaches, thereby capturing headward portions of exterior drainages. At the same time, the relative importance of gradational processes may reverse on the ejecta: aeolian activity may supersede fluvial incisement and fan formation at late stages of modification. Despite actual high drainage densities on the crater exterior during early stages of gradation, the subtle scale of these systems results in low density estimates from air photos and satellite images. Because signatures developed on surfaces around all three craters appear to be mostly gradient dependent, they may not be unique to simple crater morphologies. Similar signatures may develop on portions of complex craters as well; however, important differences may also occur.

Grant, J. A.↗