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NASA NTRS1989

Communication requirements of sparse Cholesky factorization with nested dissection ordering

Load distribution schemes for minimizing the communication requirements of the Cholesky factorization of dense and sparse, symmetric, positive definite matrices on multiprocessor systems are presented. The total data traffic in factoring an n x n sparse symmetric positive definite matrix representing an n-vertex regular two-dimensional grid graph using n exp alpha, alpha not greater than 1, processors are shown to be O(n exp 1 + alpha/2). It is O(n), when n exp alpha, alpha not smaller than 1, processors are used. Under the conditions of uniform load distribution, these results are shown to be asymptotically optimal.

Naik, Vijay K.↗

NASA NTRS1994

Summertime distribution and relations of reactive odd nitrogen species and NO(y) in the troposphere over Canada

We report here large-scale features of the distribution of NO(x), HNO3, PAN, particle NO3, and NO(y) in the troposphere from 0.15 to 6 km altitude over central Canada. These measurements were conducted in July - August 1990 from the NASA Wallops Electra aircraft as part of the joint United States-Canadian Arctic Boundary Layer Expedition (ABLE) 3B-Northern Wetlands Study. Our findings show that this region is generally NO(x) limited, with NO(x) mixing ratios typically 20-30 parts per trillion by volume (pptv). We found little direct evidence for anthropogenic enhancement of mixing ratios of reactive odd nitrogen species and NO(y) above those in 'background' air. Instead, it appears that enhancements in the mixing ratios of these species were primarily due to emissions from several day old or CO-rich-NO(x)-poor smoldering local biomass-burning fires. NO(x) mixing ratios in biomass-burning impacted air masses were usually less than 50 pptv, but those of HNO3 and PAN were typically 100-300 pptv representing a twofold-threefold enhancement over 'background' air. During our study period, inputs of what appeared to be aged tropical air were a major factor influencing the distribution of reactive odd nitrogen in the midtroposphere over northeastern North America. These air masses were quite depleted in NO(y) (generally less than 150 pptv), and a frequent summertime occurrence of such air masses over this region would imply a significant influence on the reactive odd nitrogen budget. Our findings show that the chemical composition of aged air masses over subarctic Canada and those documented in the Arctic during ABLE 3A have strikingly similar chemistries, suggesting large-scale connection between the air masses influencing these regions.

Talbot, R. W.↗

NASA NTRS1997

Airborne Measurements of NO, NO2, and NO(y) as Related to NASA's Pacific Exploratory Mission

The Tropospheric Trace Gas and Airborne Measurements Group's (TTGAMG) efforts on NASA GTE (Global Tropospheric Experiment) PEM (Pacific Exploratory Mission) West A & B field campaign primarily involved the acquisition of NO, NO2 and NO(y) measurements, as well as the subsequent analysis and interpretation of the data base obtained during the PEM West field campaign. These investigations focused on the distribution of trace gases, sources and sinks of ozone, ozone producing precursors with a heavy emphasize on ozone's photochemical state, and the partitioning of the molecules within the NO(y) family over the north western Pacific Ocean. The two components of PEM West were focused on observing air masses as they reached the Asian Continent (PEM West A) or as the air mass departed the Asian Continent (PEM West B). NO(x) concentrations play a pivotal role in controlling the photochemical lifetime of ozone in these environments, and understanding the NO(x) species partitioning is paramount. The transport of NO(x) into the regions, in the form of longer lived NO(y) family members, was examined in relation to the comparison of natural occurring sources of NO(x) (i.e., lightning and stratosphere/troposphere exchange) to those produced as a result of anthropogenic activity (i.e., biomass burning and aircraft emissions). The TTGAMG's measurements of NOx and NO(y), in conjunction with other investigators' measurements of PAN (H. B. Singh's group) and HNO3 (R. W. Talbot's group), have been used to assess the total reactive odd nitrogen levels over the study regions, the partitioning of the reactive odd nitrogen species in their various forms, and the usefulness of the NO, measurement and its measurement technique. The TTGAMG's primary PEM West objectives were the characterization of the factors controlling the distribution and fate of reactive odd nitrogen compounds over the western Pacific Ocean and an analysis of the concentration of various trace gases in the troposphere as the air mass aged by both dynamical mixing and photochemical processes in the troposphere.

Sandholm, Scott↗

NASA NTRS1968

Synchrotron radiation from electrons in helical orbits

Correction factors for spectral distribution and frequency range of radiating synchrotron electron motion

Sakurai, K.↗

NASA NTRS1975

Stress analysis of ribbon parachutes

An analytical method has been developed for determining the internal load distribution for ribbon parachutes subjected to known riser and aerodynamic forces. Finite elements with non-linear elastic properties represent the parachute structure. This method is an extension of the analysis previously developed by the authors and implemented in the digital computer program CANO. The present analysis accounts for the effect of vertical ribbons in the solution for canopy shape and stress distribution. Parametric results are presented which relate the canopy stress distribution to such factors as vertical ribbon strength, number of gores, and gore shape in a ribbon parachute.

Reynolds, D. T.↗

NASA NTRS1976

Agricultural resources investigations in northern Italy and southern France (Agreste Project)

The author has identified the following significant results. The vegetation structure of rice was investigated and interpreted in dynamic terms as a significant factor governing the distribution of solar energy thoughout the canopy and therefore conditions the final yield. Radiometric characteristics of rice culture were described for various stages of development in relation to the vegetation structure in an attempt to establish correlations between data of total biomass and of grain yield. Qualitative classification results were encouraging although the discrimination achieved was far from complete.

Source record↗

NASA NTRS1986

Thermodynamic evaluation of transonic compressor rotors using the finite volume approach

A method was developed which calculates two-dimensional, transonic, viscous flow in ducts. The finite volume, time marching formulation is used to obtain steady flow solutions of the Reynolds-averaged form of the Navier Stokes equations. The entire calculation is performed in the physical domain. The method is currently limited to the calculation of attached flows. The features of the current method can be summarized as follows. Control volumes are chosen so that smoothing of flow properties, typically required for stability, is now needed. Different time steps are used in the different governing equations to improve the convergence speed of the viscous calculations. A new pressure interpolation scheme is introduced which improves the shock capturing ability of the method. A multi-volume method for pressure changes in the boundary layer allows calculations which use very long and thin control volumes. A special discretization technique is also used to stabilize these calculations. A special formulation of the energy equation is used to provide improved transient behavior of solutions which use the full energy equation. The method is then compared with a wide variety of test cases. The freestream Mach numbers range from 0.075 to 2.8 in the calculations. Transonic viscous flow in a converging diverging nozzle is calculated with the method; the Mach number upstream of the shock is approximately 1.25. The agreement between the calculated and measured shock strength and total pressure losses is good. Essentially incompressible turbulent boundary layer flow in a adverse pressure gradient is calculated and the computed distribution of mean velocity and shear stress are in good agreement with the measurements. At the other end of the Mach number range, a flat plate turbulent boundary layer with a freestream Mach number of 2.8 is calculated using the full energy equation; the computed total temperature distribution and recovery factor agree well with the measurements when a variable Prandtl number is used through the boundary layer.

Nicholson, S.↗

NASA NTRS1986

Explicit finite-volume time-marching calculations of total temperature distributions in turbulent flow

A method was developed which calculates two-dimensional, transonic, viscous flow in ducts. The finite volume, time-marching formulation is used to obtain steady flow solutions of the Reynolds-averaged form of the Navier-Stokes equations. The entire calculation is performed in the physical domain. This paper investigates the introduction of a new formulation of the energy equation which gives improved transient behavior as the calculation converges. The effect of variable Prandtl number on the temperature distribution through the boundary layer is also investigated. A turbulent boundary layer in an adverse pressure gradient (M = 0.55) is used to demonstrate the improved transient temperature distribution obtained when the new formulation of the energy equation is used. A flat plate turbulent boundary layer with a supersonic free-stream Mach number of 2.8 is used to investigate the effect of Prandtl number on the distribution of properties through the boundary layer. The computed total temperature distribution and recovery factor agree well with the measurements when a variable Prandtl number is used through the boundary layer.

Nicholson, Stephen↗

NASA NTRS1987

Explicit finite-volume time-marching calculations of total temperature distributions in turbulent flow

Nicholson, Stephen↗

NASA NTRS1988

Separation processes in monotectic systems

Low-gravity work is reviewed and various factors influencing phase distribution are analyzed. The behavior of miscibility gap type materials in low gravity is studied. The nature of the attraction between the solution and the container or surface affects the volume of the minority phase available to form dispersed droplets as well as the extent of undercooling of the monotectic reaction.

Facemire, Barbara R.↗

NASA NTRS1989

Small scale patches of suspended matter and phytoplankton in the Elbe River estuary, German Bight and tidal flats

Landsat 5 TM measurements are found suitable for study of small scale features in coastal waters; three independent factors, namely suspended matter concentration, atmospheric scattering, and sea-surface temperature, were extracted from all seven TM channels on the basis of factor analysis. The distribution of suspended matter in near-surface water layer and sea surface temperature is observable with a spatial resolution of at least 120 x 120 sq m. The high correlation between water depth and suspended matter distribution established by ship-gathered data supports the presently hypothesized control by bottom topography and wind-modified tidal currents of eddy and front formation.

Doerffer, R.↗

NASA NTRS1990

Satellite ocean color studies of Antarctic ice edges in summer and autumn

Large areas of elevated phytoplanton pigment concentration were observed using CZCS satellite data in the Weddell Sea marginal ice zone and adjacent regions during the austral summer-autumn transition. Pigment values higher in the south than in the north indicate that, besides the irradiance, there are other factors controlling spatial distributions of the phytoplankton pigment concentrations at this time. Low pigment concentrations (as in observations near the Greenwich meridian) may result from turbulent oceanic and atmospheric forcings during the early stage of sea ice development. The data indicate that the phytoplankton blooms are not only characteristic of the spring/summer period, but also extend into the austral autumn and may contribute significantly to regional productivity.

Comiso, J. C.↗

NASA NTRS1993

The Ca II emission lines of SN 1987A

We study the evolution of the forbidden Ca II 7300 A and Ca II 8600 A emission lines in the spectrum SN 1987A. We can explain the observations with a model in which (1) the lines come from about 1.7 x 10 exp -4 solar mass of calcium distributed with filling factor about 0.1 in a sphere expanding with velocity 2500 km/s; (2) the electron number density is given by 4 x 10 exp 9/cu cm/(t/100d)-cubed; (3) the gas temperature decreases from T roughly 6400 K at 200 days to T roughly 3900 K at 500 days; and (4) ultraviolet pumping in the Ca II 3934 A, 3969 A (K, H) lines is required to explain the line ratios for t greater than about 350 days. The mass of calcium in our model is consistent with the LMC abundance of calcium in about 5 solar mass of hydrogen in the inner envelope of SN 1987A. If more calcium is produced by supernova nucleosynthesis, it must be in dense clumps that are too cool to emit the forbidden Ca II 7300 A and Ca II 8600 A lines.

Li, Hongwei↗

NASA NTRS1956

Investigation of Local Heat-transfer and Pressure Drag Characteristics of a Yawed Circular Cylinder at Supersonic Speeds

Local heat-transfer coefficients, temperature recovery factors, and pressure distributions were measured on the front side of a circular cylinder at a nominal Mach number of 3.9 over a range of free-stream Reynolds numbers from 2.1 x 10 to the 3rd power to 6.7 x 10 to the 3rd power and yaw angles from zero degrees to 44 degrees. Yawing the cylinder reduced the heat-transfer coefficients and the pressure drag coefficients. The amount of reduction may be predicted by a theory presented herein.

Goodwin, Glen↗

NASA NTRS1994

Probability techniques for reliability analysis of composite materials

Traditional design approaches for composite materials have employed deterministic criteria for failure analysis. New approaches are required to predict the reliability of composite structures since strengths and stresses may be random variables. This report will examine and compare methods used to evaluate the reliability of composite laminae. The two types of methods that will be evaluated are fast probability integration (FPI) methods and Monte Carlo methods. In these methods, reliability is formulated as the probability that an explicit function of random variables is less than a given constant. Using failure criteria developed for composite materials, a function of design variables can be generated which defines a 'failure surface' in probability space. A number of methods are available to evaluate the integration over the probability space bounded by this surface; this integration delivers the required reliability. The methods which will be evaluated are: the first order, second moment FPI methods; second order, second moment FPI methods; the simple Monte Carlo; and an advanced Monte Carlo technique which utilizes importance sampling. The methods are compared for accuracy, efficiency, and for the conservativism of the reliability estimation. The methodology involved in determining the sensitivity of the reliability estimate to the design variables (strength distributions) and importance factors is also presented.

Wetherhold, Robert C.↗

NASA NTRS1993

Solar cycle variation of interplanetary disturbances observed as Doppler scintillation transients

Interplanetary disturbances characterized by plasma that is more turbulence and/or moves faster than the background solar wind are readily defected as transients in Doppler scintillation measurements of the near-Sun solar wind. Systematic analysis of over 23,000 hours of Pioneer Venus Orbiter Doppler measurements obtained inside 0.5 AU during 1979-1987 have made it possible for the first time to investigate the frequency of occurrence of Doppler scintillation transients under solar minimum conditions and to determine its dependence on solar cycle. On the basis of a total of 142 transients, Doppler scintillation transient rates vary from a high of 0.22 in 1979 (one every 4.6 days) to a low of 0.077 transients/d in 1986 (one every 13 days), a decrease by almost a factor of 3 from solar maximum to solar minimum. This solar cycle variation, the strongest yet of any solar wind Doppler scintillation property, is highly correlated with both solar activity characterized by sunspot number and the coronal mass ejection rates deduced from Solswind and Solar Maximum Mission (SMM) coronagraph observations. These results indicate that coronal mass ejections and Doppler scintillation transients are closely related not just during solar maximum, as occasional individual comparisons have shown in the past, but throughout the entire solar cycle, and strengthen the notation that the Doppler scintillation and optical transients are different manifestations of the same physical phenomenon. The magnitudes of the transients, as described by the ratio of peak to pretransient scintillation levels (EF for enhancement factor), and their distribution iwth heliocentric distance also vary with solar cycle. While EF tends to diminish with increasing heliocentric distance during high solar activity, it is more evenly distributed during low solar activity. EF is also lower during solar minimum, as 13% of the transients during solar maximum have values exceeding 23, the highest EF observed during solar minimum. These results are consistent with the fact that occasional major fast-moving interplanetary shocks that are observed during solar maximum are very rate during solar minimum.

Woo, Richard↗

NASA NTRS1995

Spaceflight and immune responses of rhesus monkeys

The effects of restraint on immunological parameters was determined in an 18 day ARRT (adult rhesus restraint test). The monkeys were restrained for 18 days in the experimental station for the orbiting primate (ESOP), the chair of choice for Space Shuttle experiments. Several immunological parameters were determined using peripheral blood, bone marrow, and lymph node specimens from the monkeys. The parameters included: response of bone marrow cells to GM-CSF (granulocyte-macrophage colony stimulating factor), leukocyte subset distribution, and production of IFN-a (interferon-alpha) and IFN-gamma (interferon-gamma). The only parameter changed after 18 days of restraint was the percentage of CD8+ T cells. No other immunological parameters showed changes due to restraint. Handling and changes in housing prior to the restraint period did apparently result in some restraint-independent immunological changes. Handling must be kept to a minimum and the animals allowed time to recover prior to flight. All experiments must be carefully controlled. Restraint does not appear to be a major issue regarding the effects of space flight on immune responses.

Sonnenfeld, Gerald↗

NASA NTRS1996

Theoretical and global scale model studies of the atmospheric sulfur/aerosol system

The primary focus during the third-phase of our on-going multi-year research effort has been on 3 activities. These are: (1) a global-scale model study of the anthropogenic component of the tropospheric sulfur cycle; (2) process-scale model studies of the factors influencing the distribution of aerosols in the remote marine atmosphere; and (3) an investigation of the mechanism of the OH-initiated oxidation of DMS in the remote marine boundary layer. In this paper, we describe in more detail our research activities in each of these areas. A major portion of our activities during the fourth and final phase of this project will involve the preparation and submission of manuscripts describing the results from our model studies of marine boundary-layer aerosols and DMS-oxidation mechanisms.

Kasibhatla, Prasad↗