73,967 research outputs found
Influence of structure and material research on advanced launch systems' weight, performance, and cost Summary report, May 25, 1965 - Jun. 30, 1967
Influence of structure and materials research on weight, performance, and cost of advanced launch vehicle system
A.E.S. Circular, No. 39
During 1979 and 1980, soil fertility research was conducted at two locations in the Delta
Clearwater area. One of the test sites, Lee F ett’s Farm, was cleared in the mid-1950s and has been in production for about 25 years. The other test site is situated on a tract of newly cleared
land owned by Dennis Green. The new lands site was cleared by the traditional berm-pile method during the winter of 1978-79. This method removes much of the moss layer, and in some cases,
part o f the topsoil. Land cleared by this procedure is lower in natural fertility, but has the advantage
of enabling the farmer to plant a crop the first summer after clearing.
In this publication, progress reports are given for several research projects involving fertilizer use and rates of application.Introduction -- Weather Summary for the 1979 and 1980 Growing Season: Table 1: Climatic Data for Delta Junction During the 1979 and 1980 Growing Season -- Response of Barley to Nitrogen and Phosphorus Fertilizer Applications on New Land:
Table 2: Response of Barley to Nitrogen and Phosphorus Fertilizers on New Land
in the Delta-Clearwater Area of Alaska -- Variety-Fertilizer Interactions of Barley Grown on Newly Cleared Land: Table 3: Variety-Fertilizer Interactions of Barley Grown on New Land in the Delta-Clearwater Area of Alaska -- Response of Barley and Rapeseed to Sulfur Fertilization: Table 4: Response of Barley to Sulfur Fertilization When Grown Under
Different Crop Rotations; Table 5: Response of Sulfur Fertilization When Grown Under Different Crop Rotation
Alternative Adaptive Filter Structures for Improved Radio Frequency Interference Cancellation in Radio Astronomy
In radio astronomy, reference signals from auxiliary antennas that receive
only the radio frequency interference (RFI) can be modified to model the RFI
environment at the astronomy receivers. The RFI can then be canceled from the
astronomy signal paths. However, astronomers typically only require signal
statistics. If the RFI statistics are changing slowly, the cancellation can be
applied to the signal correlations at a much lower rate than is required for
standard adaptive filters. In this paper we describe five canceler setups;
precorrelation and postcorrelation cancelers that use one or two reference
signals in different ways. The theoretical residual RFI and added noise levels
are examined and are demonstrated using microwave television RFI at the
Australia Telescope Compact Array. The RFI is attenuated to below the system
noise, a reduction of at least 20 dB. While dual-reference cancelers add more
reference noise than single-reference cancelers, this noise is zero-mean and
only adds to the system noise, decreasing the sensitivity. The residual RFI
that remains in the output of single-reference cancelers (but not
dual-reference cancelers) sets a nonzero noise floor that does not act like
random system noise and may limit the achievable sensitivity. Thus,
dual-reference cancelers often result in superior cancellation. Dual-reference
precorrelation cancelers require a double-canceler setup to be useful and to
give equivalent results to dual-reference postcorrelation cancelers.Comment: 11 pages created using emulateap
Terahertz magneto-spectroscopy of transient plasmas in semiconductors
Using synchronized near-infrared (NIR) and terahertz (THz) lasers, we have
performed picosecond time-resolved THz spectroscopy of transient carriers in
semiconductors. Specifically, we measured the temporal evolution of THz
transmission and reflectivity after NIR excitation. We systematically
investigated transient carrier relaxation in GaAs and InSb with varying NIR
intensities and magnetic fields. Using this information, we were able to
determine the evolution of the THz absorption to study the dynamics of
photocreated carriers. We developed a theory based on a Drude conductivity with
time-dependent density and density-dependent scattering lifetime, which
successfully reproduced the observed plasma dynamics. Detailed comparison
between experimental and theoretical results revealed a linear dependence of
the scattering frequency on density, which suggests that electron-electron
scattering is the dominant scattering mechanism for determining the scattering
time. In InSb, plasma dynamics was dramatically modified by the application of
a magnetic field, showing rich magneto-reflection spectra, while GaAs did not
show any significant magnetic field dependence. We attribute this to the small
effective masses of the carriers in InSb compared to GaAs, which made the
plasma, cyclotron, and photon energies all comparable in the density, magnetic
field, and wavelength ranges of the current study.Comment: 8 pages, 9 figures, submitted to Phys. Rev.
Halide Adsorption on Single-crystal Silver Substrates: Dynamic Simulations and ab-initio Density-functional Theory
We investigate the static and dynamic behaviors of a Br adlayer
electrochemically deposited onto single-crystal Ag(100) using an off-lattice
model of the adlayer. Unlike previous studies using a lattice-gas model, the
off-lattice model allows adparticles to be located at any position within a
two-dimensional approximation to the substrate. Interactions with the substrate
are approximated by a corrugation potential. Using Density Functional Theory
(DFT) to calculate surface binding energies, a sinusoidal approximation to the
corrugation potential is constructed. A variety of techniques, including Monte
Carlo and Langevin simulations, are used to study the behavior of the adlayer.
The lateral root-mean-square (rms) deviation of the adparticles from the
binding sites is presented along with equilibrium coverage isotherms, and the
thermally activated Arrhenius barrier-hopping model used in previous dynamic
Monte Carlo simulations is tested.Comment: 30 pages, 9 figures, 3 tables, to appear in Faraday Discussion
Advanced expander test bed program
The Advanced Expander Test Bed (AETB) is a key element in NASA's Chemical Transfer Propulsion Program for development and demonstration of expander cycle oxygen/hydrogen engine technology component technology for the next space engine. The AETB will be used to validate the high-pressure expander cycle concept, investigate system interactions, and conduct investigations of advanced missions focused components and new health monitoring techniques. The split-expander cycle AETB will operate at combustion chamber pressures up to 1200 psia with propellant flow rates equivalent to 20,000 lbf vacuum thrust
Transmission Efficiency Measurements and Correlations with Physical Characteristics of the Lubricant
Data from helicopter transmission efficiency tests were compared to physical properties of the eleven lubricants used in those tests. The tests were conducted with the OH-58 helicopter main rotor transmission. Efficiencies ranged from 98.3 to 98.8 percent. The data was examined for correlation of physical properties with efficiency. There was a reasonable correlation of efficiency with absolute viscosity if the viscosity was first corrected for temperature and pressure in the lubricated contact. Between lubricants, efficiency did not correlate well with viscosity at atmospheric pressure. Between lubricants, efficiency did not correlate well with calculated lubricant film forming capacity. Bench type sliding friction and wear measurements could not be correlated to transmission efficiency and component wear
A Content Analysis of Youth Internet Safety Programs: Are Effective Prevention Strategies Being Used?
ABSTRACT: Almost half of youth in the U.S. report receiving internet safety education (ISE) in their schools. Unfortunately, we know little about what educational messages make a difference in problems such as cyberbullying, sexting, or online predators. To consider directions for improving effectiveness, a content analysis was conducted on materials from four ISE programs. Results indicate that ISE programs are mostly not incorporating proven educational strategies. Common ISE messages have proliferated without a clear rationale for why they would be effective. It is recommended that program developers and other stakeholders reconsider ISE messages, improve educational strategies, and participate in evaluation. The field must also consider whether ISE messages would be better delivered through broader youth safety prevention programs versus stand-alone lessons
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