10,857 research outputs found
Long term frequency stability analysis of the GPS NAVSTAR 6 Cesium clock
Time domain measurements, taken between the NAVSTAR 6 Spacecraft Vehicle (SV) and the Vandenberg Global Positioning System (GPS) Monitor Site, by a pseudo random noise receiver, were collected over an extended period of time and analyzed to estimate the long term frequency stability of the NAVSTAR 6 onboard frequency standard, referenced to the Vandenberg MS frequency standard. The technique employed separates the clock offset from the composite signal by first applying corrections for equipment delays, ionospheric delay, tropospheric delay, Earth rotation and the relativistic effect. The data are edited and smoothed using the predicted SV ephemeris to calculate the geometric delay. Then all available passes from each of the four GPS monitor stations, are collected at 1-week intervals and used to calculate the NAVSTAR orbital elements. The procedure is then completed by subtracting the corrections and the geometric delay, using the final orbital elements, from the composite signal, thus leaving the clock offset and random error
Booster propulsion/vehicle impact study, 2
This is the final report in a study examining the impact of launch vehicles for various boost propulsion design options. These options included: differing boost phase engines using different combinations of fuels and coolants to include RP-1, methane, propane (subcooled and normal boiling point), and hydrogen; variable and high mixture ratio hydrogen engines; translating nozzles on boost phase engines; and cross feeding propellants from the booster to second stage. Vehicles examined included a fully reusable two stage cargo vehicle and a single stage to orbit vehicle. The use of subcooled propane as a fuel generated vehicles with the lowest total vehicle dry mass. Engines with hydrogen cooling generated only slight mass reductions from the reference, all-hydrogen vehicle. Cross feeding propellants generated the most significant mass reductions from the reference two stage vehicle. The use of high mixture ratio or variable mixture ratio hydrogen engines in the boost phase of flight resulted in vehicles with total dry mass 20 percent greater than the reference hydrogen vehicle. Translating nozzles for boost phase engines generated a heavier vehicle. Also examined were the design impacts on the vehicle and ground support subsystems when subcooled propane is used as a fuel. The most significant cost difference between facilities to handle normal boiling point versus subcooled propane is 5 million dollars. Vehicle cost differences were negligible. A significant technical challenge exists for properly conditioning the vehicle propellant on the ground and in flight when subcooled propane is used as fuel
Utilization of ERTS-1 data in North Carolina
The author has identified the following significant results. ERTS-1 imagery has been used to study forested wetlands, dynamic processes off Coastal North Carolina, and land use patterns in the Wilmington, North Carolina area. The thrust of the investigation is still involvement of state and regional agencies in the use of ERTS-1 imagery in solving some of their day-to-day problems
The Rachel Carson Letters and the Making of Silent Spring
Environment, conservation, green, and kindred movements look back to Rachel Carson’s 1962 book Silent Spring as a milestone. The impact of the book, including on government, industry, and civil society, was immediate and substantial, and has been extensively described; however, the provenance of the book has been less thoroughly examined. Using Carson’s personal correspondence, this paper reveals that the primary source for Carson’s book was the extensive evidence and contacts compiled by two biodynamic farmers, Marjorie Spock and Mary T. Richards, of Long Island, New York. Their evidence was compiled for a suite of legal actions (1957-1960) against the U.S. Government and that contested the aerial spraying of dichlorodiphenyltrichloroethane (DDT). During Rudolf Steiner’s lifetime, Spock and Richards both studied at Steiner’s Goetheanum, the headquarters of Anthroposophy, located in Dornach, Switzerland. Spock and Richards were prominent U.S. anthroposophists, and established a biodynamic farm under the tutelage of the leading biodynamics exponent of the time, Dr. Ehrenfried Pfeiffer. When their property was under threat from a government program of DDT spraying, they brought their case, eventually lost it, in the process spent US$100,000, and compiled the evidence that they then shared with Carson, who used it, and their extensive contacts and the trial transcripts, as the primary input for Silent Spring. Carson attributed to Spock, Richards, and Pfeiffer, no credit whatsoever in her book. As a consequence, the organics movement has not received the recognition, that is its due, as the primary impulse for Silent Spring, and it is, itself, unaware of this provenance
Apollo experience report: Development of the extravehicular mobility unit
The development and performance history of the Apollo extravehicular mobility unit and its major subsystems is described. The three major subsystems, the pressure garment assembly, the portable life-support system, and the oxygen purge system, are defined and described in detail as is the evolutionary process that culminated in each major subsystem component. Descriptions of ground-support equipment and the qualification testing process for component hardware are also presented
Second-generation PLINK: rising to the challenge of larger and richer datasets
PLINK 1 is a widely used open-source C/C++ toolset for genome-wide
association studies (GWAS) and research in population genetics. However, the
steady accumulation of data from imputation and whole-genome sequencing studies
has exposed a strong need for even faster and more scalable implementations of
key functions. In addition, GWAS and population-genetic data now frequently
contain probabilistic calls, phase information, and/or multiallelic variants,
none of which can be represented by PLINK 1's primary data format.
To address these issues, we are developing a second-generation codebase for
PLINK. The first major release from this codebase, PLINK 1.9, introduces
extensive use of bit-level parallelism, O(sqrt(n))-time/constant-space
Hardy-Weinberg equilibrium and Fisher's exact tests, and many other algorithmic
improvements. In combination, these changes accelerate most operations by 1-4
orders of magnitude, and allow the program to handle datasets too large to fit
in RAM. This will be followed by PLINK 2.0, which will introduce (a) a new data
format capable of efficiently representing probabilities, phase, and
multiallelic variants, and (b) extensions of many functions to account for the
new types of information.
The second-generation versions of PLINK will offer dramatic improvements in
performance and compatibility. For the first time, users without access to
high-end computing resources can perform several essential analyses of the
feature-rich and very large genetic datasets coming into use.Comment: 2 figures, 1 additional fil
Leaving the Gang: A Review and Thoughts on Future Research
Researchers have examined aspects of gangs and their members for almost a century. This work, however, focuses primarily on youth prior to joining as well as during gang involvement. While comparatively less is known about the leaving processes, work in this area has been increasing in recent years. This chapter will discuss the growing body of research on the processes associated with leaving the gang. Specifically, it will review difficulties associated with defining gang desistance, theoretical perspectives on desistance, variations in motives, methods, and consequences of leaving, barriers to desistance, as well as make recommendations for policy and future research
The Structure of Nuclear Star Clusters in Nearby Late-type Spiral Galaxies from Hubble Space Telescope Wide Field Camera 3 Imaging
We obtained Hubble Space Telescope/Wide Field Camera 3 imaging of a sample of
ten of the nearest and brightest nuclear clusters residing in late-type spiral
galaxies, in seven bands that span the near-ultraviolet to the near-infrared.
Structural properties of the clusters were measured by fitting two-dimensional
surface brightness profiles to the images using GALFIT. The clusters exhibit a
wide range of structural properties. For six of the ten clusters in our sample,
we find changes in the effective radius with wavelength, suggesting radially
varying stellar populations. In four of the objects, the effective radius
increases with wavelength, indicating the presence of a younger population
which is more concentrated than the bulk of the stars in the cluster. However,
we find a general decrease in effective radius with wavelength in two of the
objects in our sample, which may indicate extended, circumnuclear star
formation. We also find a general trend of increasing roundness of the clusters
at longer wavelengths, as well as a correlation between the axis ratios of the
NCs and their host galaxies. These observations indicate that blue disks
aligned with the host galaxy plane are a common feature of nuclear clusters in
late-type galaxies, but are difficult to detect in galaxies that are close to
face-on. In color-color diagrams spanning the near-UV through the near-IR, most
of the clusters lie far from single-burst evolutionary tracks, showing evidence
for multi-age populations. Most of the clusters have integrated colors
consistent with a mix of an old population (> 1 Gyr) and a young population
(~100-300 Myr). The wide wavelength coverage of our data provides a sensitivity
to populations with a mix of ages that would not be possible to achieve with
imaging in optical bands only.Comment: Corrected a typo in author name and affiliation for MC and corrected
a typo in the conclusio
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