Effects of real-time thermal aging on graphite/polyimide composites

As part of a program to evaluate high-temperature advanced composites for use on supersonic cruise transport aircraft, two graphite/polyimide composites have been aged at elevated temperatures for times up to 5.7 years. Work on the first, HT-S/710 graphite/polyimide, was started in 1974. Evaluation of the second polyimide, Celion 6000/LARC-160, began in 1980. Baseline properties are presented, including unnotched and notched tensile data as a function of temperature, compression, flexure, shear, and constant-amplitude fatigue data at R = 0.1 and R = -1. Tensile specimens were aged in ovens where pressure and aging temperatures were controlled for various times up to and including 50,000 hours. Changes in tensile strength were determined and plotted as a function of aging time. The HT-S/710 composite aged at 450 F and 550 F if compared to the Celion 6000/LARC-160 composite aged at 350 F and 450 F. After tensile testing, many of the thermal aging specimens were examined using a scanning electron microscope. Results of these studies are presented, and changes in properties and degradation mechanisms during high-temperature aging are discussed and illustrated using metallographic techniques

The Supply Side of Innovation: H-1B Visa Reforms and US Ethnic Invention

This study evaluates the impact of high-skilled immigrants on US technology formation. Specifically, we use reduced-form specifications that exploit large changes in the H-1B visa program. Fluctuations in H-1B admissions levels significantly influence the rate of Indian and Chinese patenting in cities and firms dependent upon the program relative to their peers. Most specifications find weak crowding-in effects or no effect at all for native patenting. Total invention increases with higher admission levels primarily through the direct contributions of ethnic inventors.Innovation, Research and Development, Patents, Scientists, Engineers, Inventors, H-1B, Immigration, Ethnicity, India, China, Endogenous Growth.

Rural Zoning for Economic Development

Rural zoning for economic development defines rural zoning, the planning process, suggested citizens for planning committees, tools needed, and legal steps for rural zoning in South Dakota

Social and Economic Impact of the Pollock-Herreid Irrigation Unit

Development of the Pollock-Herreid Irrigation Unit in Campbell County would create a stable agricultural economy and tend to inspire a feeling of security among the people of the area. This security is not, in itself, measurable in dollars. It is possible however to predict, with reasonable accuracy, what changes will gradually take place after the Pollock-Herreid Unit is in operation and to predict what these changes will mean to the dollar value of the economy. The changes that take place, in turn, contribute to stability and greater security. The estimated changes outlined in this publication are based on what has happened in other projects under similar conditions

Some problems associated with large scale galactic structure

The distribution and motions of both neutral and ionized hydrogen can be studied throughout the Galaxy by radio methods. The neutral hydrogen is observed through the 21-cm hyperfine transition line; the continuity of many prominent features indicates that we are seeing the galactic spiral pattern, but it is difficult to locate the spiral arms in space because we are restricted to kinematic distance estimates for the hydrogen.Asociación Argentina de Astronomí

The high velocity hydrogen clouds considered as satellites of the galaxy

The high-velocity hydrogen clouds at high latitudes have been widely discussed as material falling into the galactic disk from outside. The observed velocities show strong effects arising from the galactic rotation at the Sun's position. When this rotation is removed, the residual velocities are compatible with the clouds being in highly eccentric orbits around the Galaxy at distances of the order of 50 kpc. We propose new observations which may help to decide between galactic and extra-galactic interpretations.Asociación Argentina de Astronomí

Some problems associated with large scale galactic structure

The distribution and motions of both neutral and ionized hydrogen can be studied throughout the Galaxy by radio methods. The neutral hydrogen is observed through the 21-cm hyperfine transition line; the continuity of many prominent features indicates that we are seeing the galactic spiral pattern, but it is difficult to locate the spiral arms in space because we are restricted to kinematic distance estimates for the hydrogen.Asociación Argentina de Astronomí

Some problems associated with large scale galactic structure

The distribution and motions of both neutral and ionized hydrogen can be studied throughout the Galaxy by radio methods. The neutral hydrogen is observed through the 21-cm hyperfine transition line; the continuity of many prominent features indicates that we are seeing the galactic spiral pattern, but it is difficult to locate the spiral arms in space because we are restricted to kinematic distance estimates for the hydrogen.Asociación Argentina de Astronomí

The high velocity hydrogen clouds considered as satellites of the galaxy

The high-velocity hydrogen clouds at high latitudes have been widely discussed as material falling into the galactic disk from outside. The observed velocities show strong effects arising from the galactic rotation at the Sun's position. When this rotation is removed, the residual velocities are compatible with the clouds being in highly eccentric orbits around the Galaxy at distances of the order of 50 kpc. We propose new observations which may help to decide between galactic and extra-galactic interpretations.Asociación Argentina de Astronomí