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At least 451 records · Page 25

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DOE OSTI2025

Soil oxygen dynamics: a key mediator of tile drainage impacts on coupled hydrological, biogeochemical, and crop systems

Tile drainage removes excess water and is an essential, widely adopted management practice to enhance crop productivity in the US Midwest and throughout the world. Tile drainage has been shown to significantly change hydrological and biogeochemical cycles by lowering the water table and reducing the residence time of soil water, although examining the complex interactions and feedbacks in an integrated hydrology–biogeochemistry–crop system remains elusive. Oxygen dynamics are critical to unraveling these interactions and have been ignored or oversimplified in existing models. Understanding these impacts is essential, particularly so because tile drainage has been highlighted as an adaptation under projected wetter springs and drier summers in the changing climate in the US Midwest. We used the ecosys model that uniquely incorporates first-principle soil oxygen dynamics and crop oxygen uptake mechanisms to quantify the impacts of tile drainage on hydrological and biogeochemical cycles and crop growth in corn–soybean rotation fields. The model was validated with data from a multi-treatment, multi-year experiment in Washington, IA. The relative root mean square error (rRMSE) for the corn and soybean yield in validation is 5.66 % and 12.57 %, respectively. The Pearson coefficient (r) of the monthly tile flow during the growing season is 0.78. Plant oxygen stress turns out as an emergent property of the equilibrium between the soil oxygen supply and biological demand. The impact of tile drainage on the system is achieved through a series of coupled feedback mechanisms. The model results show that tile drainage reduces the soil water content and enhances soil oxygenation. It additionally increases the subsurface discharge and elevates inorganic nitrogen leaching, with seasonal variations influenced by climate and crop phenology. The improved aerobic condition alleviates crop oxygen stress during wet springs, thereby promoting crop root growth during the early growth stage. The development of greater root density, in turn, mitigates water stress during dry summers, leading to an overall increase in the crop yield by ∼6 %. These functions indicate the potential of tile drainage in bolstering crop resilience to climate change and the use of this modeling tool for large-scale assessments of tile drainage. The model reveals the underlying causal mechanisms that drive the agroecosystem response to drainage on the coupled hydrology, biogeochemistry, and crop system dynamics.

60 APPLIED LIFE SCIENCES↗

NASA NTRS1974

A three parameter analytic phase function for multiple scattering calculations

A simple procedure was developed to fit the first three moments of an actual phase function with a three parameter analytic phase function. The exact Legendre Polynomial decomposition of this function is, suitable for multiple scattering calculations. The use of this function is expected to yield excellent flux values at all depths within a medium. Since it is capable of reproducing the glory, it can be used in synthetic spectra computations from planetary atmospheres. Accurate asymptotic radiance values can also be achieved as long as the single scattering albedo omega sub 0 is greater than or equal to 0.9.

Kattawar, G. W.↗

NASA NTRS1975

Comparison of sonic boom minimization results in real and isothermal atmospheres

The method of Seebass and George (1972, 1974) for minimizing certain features of the pressure signature and yielding the corresponding F function and equivalent area distribution A in an isothermal atmosphere is modified to provide the same capability for a real atmosphere. The appropriate equations of George and Plotkin (1969) describing horizontal advance, ray tube area, and signature propagation are used.

Darden, C. M.↗

NASA NTRS1975

Fully unsteady subsonic and supersonic potential aerodynamics for complex aircraft configurations with applications to flutter

A general formulation is presented for the analysis of steady and unsteady, subsonic and supersonic aerodynamics for complex aircraft configurations. The theoretical formulation, the numerical procedure, the description of the program SOUSSA (steady, oscillatory and unsteady, subsonic and supersonic aerodynamics) and numerical results are included. In particular, generalized forces for fully unsteady (complex frequency) aerodynamics for a wing-body configuration, AGARD wing-tail interference in both subsonic and supersonic flows as well as flutter analysis results are included. The theoretical formulation is based upon an integral equation, which includes completely arbitrary motion. Steady and oscillatory aerodynamic flows are considered. Here small-amplitude, fully transient response in the time domain is considered. This yields the aerodynamic transfer function (Laplace transform of the fully unsteady operator) for frequency domain analysis. This is particularly convenient for the linear systems analysis of the whole aircraft.

Tseng, K.↗

NASA NTRS1977

Integrated circuit process and design rule evaluation techniques

A technique is described for determining the applicability of a particular process for the fabrication of large-scale integrated (LSI) circuits. Test arrays were developed to isolate various critical processing steps in a fabrication sequence and a statistical evaluation of these steps was carried out that related yield or success in achieving a desired result to the number of times the results were attempted. It was found that, in general, yield is a sensitive function of physical dimensions as is the packing density of a particular array. It is, therefore, possible to generate an optimum set of physical dimensions or design rules that maximize the expected number of working circuits on a wafer.

Ipri, A. C.↗

NASA NTRS1980

Intercommunications in Real Time, Redundant, Distributed Computer System

An investigation into the applicability of fiber optic communication techniques to real time avionic control systems, in particular the total automatic flight control system used for the VSTOL aircraft is presented. The system consists of spatially distributed microprocessors. The overall control function is partitioned to yield a unidirectional data flow between the processing elements (PE). System reliability is enhanced by the use of triple redundancy. Some general overall system specifications are listed here to provide the necessary background for the requirements of the communications system.

Zanger, H.↗

NASA NTRS1983

Core level excitation of simple gases

The ionization of simple gases by electron bombardment exhibits distinct resonances at electron energies slightly below the core level binding energies of the atomic constituents of the gas. A vacancy in an inner shell of the atom may recombine by a radiationless Auger process, thus leaving the molecule in a singly or higher ionized state. These ions are easily collected and the threshold resonances for excitation are evident in the second derivative of the ion yield plotted as a function of the energy of the electron beam. By using a mixture of gases, such as CO and CO2, it is possible to measure relative chemical shifts of the C and O 1s thresholds. In this case the C 1s threshold is 3.9 eV lower in CO than in CO2, and the O 1s threshold is 2.7 eV lower in CO than in CO2. The feasibility of constructing a simple analyzer based on this technique will be discussed to supplement conventional mass spectrometer analysis of gas composition.

Zhang, A.↗

NASA NTRS1985

Processing of Image Data by Integrated Circuits

Sensors combined with logic and memory circuitry. Cross-correlation of two inputs accomplished by transversal filter. Position of image taken to point where image and template data yield maximum value correlation function. Circuit used for controlling robots, medical-image analysis, automatic vehicle guidance, and precise pointing of scientific cameras.

Armstrong, R. W.↗

NASA NTRS1988

Extended fine structures in the electron energy loss spectrum of InAs

The possibility of using electron energy loss fine structure (EELFS) for the characterization of thin pseudomorphic quantum wells of InAs and GaAs(100) is investigated. It is shown that the EELFS technique can yield reliable radial distribution functions for bulk InAs, provided beam-induced sample degradation is controlled stringently. Additional improvements in the data collection procedures, including better control of the sample condition, are required as well as more detailed work on separating contributions from multiple edges in the data analysis.

Schowengerdt, F. D.↗

NASA NTRS1989

Vibrational relaxation of OH (X 2Pi sub i, v = 2)

A two-laser pump-and-probe technique is used to determine vibrational relaxation rates for the v = 2 level of the X 2Pi sub i state of the OH radical. In the present method, the time delay between the lasers is scanned at a given collider pressure, producing exponential decay whose rate as a function of collider pressure yields the rate constant. With the exception of ammonia, the values obtained are two to three orders of magnitude smaller than those found for relaxation of v = 1 in the A 2Sigma(+) excited state of OH.

Rensberger, Karen J.↗

NASA NTRS1989

Sonic-point capturing

A prototype scheme that produces perfectly smooth transonic solutions to nozzle-flow problems is derived and tested. The basic upwind scheme is described as well as satisfying the entropy condition, treatment of the source term, and numerical verification. The analysis yielded a numerical flux function for use near a sonic point, which is based on a full model of a transonic expansion wave, and a matched treatment for the source term.

Van Leer, Bram↗

NASA NTRS1990

Active control of the forced and transient response of a finite beam

Structural vibrations from a point force are modelled on a finite beam. This research explores the theoretical limit on controlling beam vibrations utilizing another point source as an active controller. Three different types of excitation are considered, harmonic, random, and transient. For harmonic excitation, control over the entire beam length is possible only when the excitation frequency is near a resonant frequency of the beam. Control over a subregion may be obtained even between resonant frequencies at the cost of increasing the vibration outside of the control region. For random excitation, integrating the expected value of the displacement squared over the required interval, is shown to yield the identical cost function as obtained by integrating the cost function for harmonic excitation over all excitation frequencies. As a result, it is always possible to reduce the cost function for random excitation whether controlling the entire beam or just a subregion, without ever increasing the vibration outside the region in which control is desired. The last type of excitation considered is a single, transient pulse. The form of the controller is specified as either one or two delayed pulses, thus constraining the controller to be casual. The best possible control is examined while varying the region of control and the controller location. It is found that control is always possible using either one or two control pulses.

Post, John T.↗

NASA NTRS1991

Atomic oxygen interactions with FEP Teflon and silicones on LDEF

The Long Duration Exposure Facility (LDEF) spacecraft represents the first controlled unidirectional exposure of high-fluence atomic oxygen on fluorinated ethylene propylene (FEP Teflon) and silicones. The atomic oxygen erosion yield for FEP Teflon was found to be significantly in excess of previous low fluence orbital data and is an order of magnitude below that of polyimide Kapton. LDEF FEP Teflon erosion yield data as a function of angle of attack is presented. Atomic oxygen interaction with silicon polymers results in crazing of the silicones as well as deposition of dark contaminant oxidation products on adjoining surfaces. Documentation of results and possible mechanistic explanations are presented.

Banks, Bruce A.↗

NASA NTRS1992

Flexural analysis of uplifted rift flanks on Venus

Knowledge of the thermal structure of a planet is vital to a thorough understanding of its general scheme of tectonics. Since no direct measurements of heat flow or thermal gradient are available for Venus, most estimates have been derived from theoretical considerations or by analog with the Earth. The flexural response of the lithosphere to applied loads is sensitive to regional thermal structure. Under the assumption that the yield strength as a function of depth can be specified, the temperature gradient can be inferred from the effective elastic plate thickness. Previous estimates of the effective elastic plate thickness of Venus range from 11-18 km for the foredeep north of Uorsar Rupes to 30-60 km for the annular troughs around several coronae. Thermal gradients inferred for these regions are 14-23 K km(exp -1) and 4-9 K km(exp -1) respectively. In this study, we apply the same techniques to investigate the uplifted flanks of an extensional rift. Hypotheses for the origin of uplifted rift flanks on Earth include lateral transport of heat from the center of the rift, vertical transport of heat by small-scale convection, differential thinning of the lithosphere, dynamical uplift, and isostatic response to mechanical uploading of the lithosphere. The 1st hypothesis is considered the dominant contributor to terrestrial rift flanks lacking evidence for volcanic activity, particularly for rift structures that are no longer active. In this study, we model the uplifted flanks of a venusian rift as the flexural response to a vertical end load.

Evans, Susan A.↗

NASA NTRS1992

Comparative study of the dissociation energies of Ni2 and Ni2(+)

Computations at the internally contracted averaged coupled-pair-functional level of theory yield a dissociation energy (Do) for Ni2(+) that is 0.17 eV larger than that of Ni2. This finding is consistent with the collision-induced dissociation experiments of Lian, Su, and Armentrout, but rules out the results from the resonant two-photon dissociation experiments of Lessen and Brucat, which predict that the Do value of Ni2(+) is about 1 eV larger than that of Ni2.

Bauschlicher, Charles W., Jr.↗

NASA NTRS1993

An approach to estimate the areal rain-rate distribution from spaceborne radar by the use of multiple thresholds

Estimates of rain rate derived from a spaceborne weather radar will be most reliable over an intermediate range of values. In forming an area average of the rain rate, an alternative to the averaging of the high-resolution estimates, irrespective of their individual accuracies, is a multiple threshold approach. The method is based on the fact that the fractional area above a particular rain-rate threshold R(j) is related to the cumulative distribution of rain rates evaluated at R(j). Varying the threshold over the effective dynamic range of the radar yields the cumulative distribution function over this range. To obtain the distribution at all rain rates, a lognormal or gamma test function is selected such that the mean-square error between the test function and the measured values is minimized. Once the unknown parameters are determined, the first-order statistics of the areawide rain-rate distribution can be found. Tests of the method with data from the SPANDAR radar provide comparisons between it and the single threshold and the direct averaging approaches.

Meneghini, R.↗

NASA NTRS1993

Vectorization and parallelization of the finite strip method for dynamic Mindlin plate problems

The finite strip method is a semi-analytical finite element process which allows for a discrete analysis of certain types of physical problems by discretizing the domain of the problem into finite strips. This method decomposes a single large problem into m smaller independent subproblems when m harmonic functions are employed, thus yielding natural parallelism at a very high level. In this paper we address vectorization and parallelization strategies for the dynamic analysis of simply-supported Mindlin plate bending problems and show how to prevent potential conflicts in memory access during the assemblage process. The vector and parallel implementations of this method and the performance results of a test problem under scalar, vector, and vector-concurrent execution modes on the Alliant FX/80 are also presented.

Chen, Hsin-Chu↗

NASA NTRS1995

Measurements of the millimeter-wave spectrum of interstellar dust emission

We report measurements of the differential brightness of interstellar dust emission near the Galactic plane and at high Galactic latitudes. The data were obtained as part of a program to measure anisotropy in the cosmic microwave background (CMB). The measurements were made with a 0.5 deg beam size and a 1.3 deg sinusoidal chop, in broad bands (Delta nu/nu approximately 0.3) centered near frequencies of 6, 9, and 12 cm(exp -1). A measurement made toward the Galactic plane, at longitude 1 = 23.7 deg, is compared with the contrast observed in the 100 micrometers IRAS data. Assuming the dust emission has a brightness I(sub nu) proportional to nu(sup n)B(sub nu)(T(sub d)), where B(sub nu) is the Planck function, a best fit yields n = 1.6 +/- 0.4, T(sub d) = 24 +/- 5 K. In a region near the star mu Pegasi (mu PEG l = 91 deg, b = -31 deg), the comparison of our data with the 100 micrometers IRAS data yields n = 1.4 +/- 0.4, and T(sub d) = 18 +/- 3 K. In a second region near the star gamma Ursa Minoris (GUM l = 108 deg, b = 41 deg), an upper limit is placed on contrast in dust emission. This upper limit is consistent with spectrum measured at mu PEG and the IRAS 100 micrometer emission contrast at GUM, which is approximately 8 times lower than mu PEG.

Fischer, M. L.↗