718 research outputs found
Crop-phenology and LANDSAT-based irrigated lands inventory in the high plains
Optimal LANDSAT image dates for 1980 were identified based on the weekly crop-weather reports for Colorado, New Mexico, South Dakota, Texas, Oklahoma, Kansas, Nebraska, and Wyoming. The 1979 agricultural statistics data were entered into computer files and a revised questionnaire was developed and mailed to ASCS county agents. A set of computer programs was developed to allow the preparation of computer-assisted graphic displays of much of the collected data
Crop phenology and LANDSAT-based irrigated lands inventory in the high plains
The activity concentrated on identifying crop and irrigation data sources for the eight states within the High Plains Aquifer and making contacts concerning the nature of these data. A mail questionnaire was developed to gather specific data not routinely reported through standard data collection channels. Input/output routines were designed for High Plains crop and irrigation data and initial statistical data on crops were input to computer files
Modeling pN2 through Geological Time: Implications for Planetary Climates and Atmospheric Biosignatures
Nitrogen is a major nutrient for all life on Earth and could plausibly play a
similar role in extraterrestrial biospheres. The major reservoir of nitrogen at
Earth's surface is atmospheric N2, but recent studies have proposed that the
size of this reservoir may have fluctuated significantly over the course of
Earth's history with particularly low levels in the Neoarchean - presumably as
a result of biological activity. We used a biogeochemical box model to test
which conditions are necessary to cause large swings in atmospheric N2
pressure. Parameters for our model are constrained by observations of modern
Earth and reconstructions of biomass burial and oxidative weathering in deep
time. A 1-D climate model was used to model potential effects on atmospheric
climate. In a second set of tests, we perturbed our box model to investigate
which parameters have the greatest impact on the evolution of atmospheric pN2
and consider possible implications for nitrogen cycling on other planets. Our
results suggest that (a) a high rate of biomass burial would have been needed
in the Archean to draw down atmospheric pN2 to less than half modern levels,
(b) the resulting effect on temperature could probably have been compensated by
increasing solar luminosity and a mild increase in pCO2, and (c) atmospheric
oxygenation could have initiated a stepwise pN2 rebound through oxidative
weathering. In general, life appears to be necessary for significant
atmospheric pN2 swings on Earth-like planets. Our results further support the
idea that an exoplanetary atmosphere rich in both N2 and O2 is a signature of
an oxygen-producing biosphere.Comment: 33 pages, 11 figures, 2 tables (includes appendix), published in
Astrobiolog
The power induced effects module: A FORTRAN code which estimates lift increments due to power induced effects for V/STOL flight
A user friendly FORTRAN code that can be used for preliminary design of V/STOL aircraft is described. The program estimates lift increments, due to power induced effects, encountered by aircraft in V/STOL flight. These lift increments are calculated using empirical relations developed from wind tunnel tests and are due to suckdown, fountain, ground vortex, jet wake, and the reaction control system. The code can be used as a preliminary design tool along with NASA Ames' Aircraft Synthesis design code or as a stand-alone program for V/STOL aircraft designers. The Power Induced Effects (PIE) module was validated using experimental data and data computed from lift increment routines. Results are presented for many flat plate models along with the McDonnell Aircraft Company's MFVT (mixed flow vectored thrust) V/STOL preliminary design and a 15 percent scale model of the YAV-8B Harrier V/STOL aircraft. Trends and magnitudes of lift increments versus aircraft height above the ground were predicted well by the PIE module. The code also provided good predictions of the magnitudes of lift increments versus aircraft forward velocity. More experimental results are needed to determine how well the code predicts lift increments as they vary with jet deflection angle and angle of attack. The FORTRAN code is provided in the appendix
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Dynamic rock fragmentation: oil shale applications
Explosive rock fragmentation techniques used in many resource recovery operations have in the past relied heavily upon traditions of field experience for their design. As these resources, notably energy resources, become less accessible, it becomes increasingly important that fragmentation techniques be optimized and that methods be developed to effectively evaluate new or modified explosive deployment schemes. Computational procedures have significant potential in these areas, but practical applications must be preceded by a thorough understanding of the rock fracture phenomenon and the development of physically sound computational models. This paper presents some of the important features of a rock fragmentation model that was developed as part of a program directed at the preparation of subterranean beds for in situ processing of oil shale. The model, which has been implemented in a two-dimensional Lagrangian wavecode, employs a continuum damage concept to quantify the degree of fracturing and takes into account experimental observations that fracture strength and fragment dimensions depend on tensile strain rates. The basic premises of the model are considered in the paper as well as some comparisons between calculated results and observations from blasting experiments
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Towards assessing the violence of reaction during cookoff of confined energetic materials
An analysis of post-ignition events in a variable confinement cookoff test (VCCT) geometry is presented aimed toward predicting the level of violence during cookoff of confined thermally-degraded energetic materials. This study focuses on the dynamic events following thermal initiation whereby accelerated combustion interacts with confinement. Numerical simulations, based on a model of reactive multiphase mixtures, indicate that the response of energetic material is highly dependent upon thermal/mechanical damage states prior to ignition. These damaged states affect the rate of pressurization, dynamic compaction behavior and subsequent growth to detonation. Variations of the specific surface area and porosity produced by decomposition of the energetic material causes different responses ranging from pressure burst to detonation. Calculated stress histories are used in estimating breakup of the VCCT confinement based on Grady-Kipp fragmentation theory
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Comparison of calculated and experimental results of fragmenting cylinder experiments
The Grady-Kipp fragmentation model provides a physically based method for determining the fracture and breakup of materials under high loading rates. Recently, this model has been implemented into the CTH Shock Physics Code and has been used to simulate several published experiments. Materials studied in this paper are AerMet 100 steel and a 90% tungsten alloy. The experimental geometry consists of a right circular cylinder filled with an explosive main charge that is initiated at its center. The sudden expansion of the resulting detonation products causes fracture of the cylinder. Strain rates seen in the cylinder are on the order of 10{sup 4} s{sup {minus}1}. The average fragment sizes calculated with the Grady-Kipp fragmentation model successfully replicate the mean fragment size obtained from the experimental fragment distribution. When Poisson statistics are applied to the calculated local average fragment sizes, good correlation is also observed with the shape of the experimental cumulative fragment distribution. The experimental fragmentation results, CTH numerical simulations, and correlation of these numerical results with the experimental data are described
Frequency of false-positive FISH 1p/19q codeletion in adult diffuse astrocytic gliomas
Oligodendroglioma is genetically defined by concomitant IDH (IDH1/IDH2) mutation and whole-arm 1p/19q codeletion. Codeletion of 1p/19q traditionally evaluated by fluorescence in situ hybridization (FISH) cannot distinguish partial from whole-arm 1p/19q codeletion. Partial 1p/19q codeletion called positive by FISH is diagnostically a "false-positive" result. Chromosomal microarray (CMA) discriminates partial from whole-arm 1p/19q codeletion. Herein, we aimed to estimate the frequency of partial 1p/19q codeletion that would lead to a false-positive FISH result
Energetic and spatial bonding properties from angular distributions of ultraviolet photoelectrons: application to the GaAs(110) surface
Angle-resolved ultraviolet photoemission spectra are interpreted by combining
the energetics and spatial properties of the contributing states. One-step
calculations are in excellent agreement with new azimuthal experimental data
for GaAs(110). Strong variations caused by the dispersion of the surface bands
permit an accurate mapping of the electronic structure. The delocalization of
the valence states is discussed analogous to photoelectron diffraction. The
spatial origin of the electrons is determined, and found to be strongly energy
dependent, with uv excitation probing the bonding region.Comment: 5 pages, 3 figures, submitted for publicatio
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