Atomic oxygen effects on candidate coatings for long-term spacecraft in low earth orbit

Candidate atomic oxygen protective coatings for long-term low Earth orbit (LEO) spacecraft were evaluated using the Los Alamos National Laboratory O-atom exposure facility. The coatings studied include Teflon, Al2O3, SiO2, and SWS-V-10, a silicon material. Preliminary results indicate that sputtered PTFE Teflon (0.1 micrometers) has a fluence lifetime of 10 to the 19th power O-atoms/cm (2), and sputtered silicon dioxide (0.1 micrometers), aluminum oxide (0.1 micrometers), and SWS-V-10, a silicone, (4 micrometers) have fluence lifetimes of 10 to the 20th power to 10 to the 21st power O-atoms/cm (2). There are large variations in fluence lifetime data for these coatings

What Is Done You Never Can Undo

https://digitalcommons.library.umaine.edu/mmb-vp/4465/thumbnail.jp

Performance and loads data from an outdoor hover test of a Lynx tail rotor

A Lynx tail rotor was tested in hover at the Outdoor Aerodynamic Research Facility at NASA Ames Research Center. The test objectives were to measure the isolated rotor performance to provide a baseline for subsequent testing, and to operate the rotor throughout the speed and collective envelope before testing in the NFAC 40- by 80-Foot Wind Tunnel. Rotor forces and blade bending moments were measured at ambient wind conditions from zero to 6.23 m/sec. The test envelope was limited to rotor speeds of 1550 to 1850 rpm and minus 13 deg to plus 20 deg of blade collective pitch. The isolated rotor performance and blade loads data are presented

X-ray line emission from the Tycho supernova remnant

The observation of the X-ray spectrum of the Tycho supernova remnant in the energy range 0.5 to 20 keV is discussed. Four significant line features in the spectrum: The K alpha lines of silicon, sulphur, and iron; and the L lines of iron are examined. Comparisons between the silicon and sulphur equivalent widths and K alpha iron line energies of Tycho and Cas A are discussed. Suggest that the X-ray emitting plasma in Tycho is further from collisional ionization equilibrium than that of Cas A

Transient and residual strains from large underground explosions

Tectonic strain readjustments associated with large underground explosions have been observed at the Nevada Test Site. The BENHAM event of December 19, 1968 produced a peak quasi-static radial strain of 1.2 × 10^(−7) at a distance of 29 km. This strain transient was followed by an exponential return to the initial state with a time constant of 13 minutes, and is interpreted as the direct elastic response of the medium to a time varying pressure in the BENHAM cavity. An upper bound on the tectonic strain release was determined to be 0.7 × 10^(−8). Using these measurements it is estimated that the permanent and quasi-static strains associated with this explosion could significantly effect local earthquake occurrences out to distances of about 15 km. The size distribution of aftershocks of this explosion resembles that seen in model experiments of brittle fracture, in which the distribution is controlled by the dimensions of inhomogeneities in the medium

Breakdown behavior in radio-frequency argon discharges

The minimum voltage required to break down a dischargeVbrk has long been known to be a strong function of the product of the neutral gas pressure and the electrode separation (pd). This paper investigates the dependence of Vbrk on pd in radio-frequency (rf) systems using experimental, computational and analytic techniques. Experimental measurements of Vbrk in an argon discharge are made for pressures in the range 1–500 mTorr and electrode separations of 2–20 cm. A particle-in-cell simulation is used to investigate a similar pd range and examine the effect of the secondary emission coefficient on the rf breakdown curve, particularly at low pd values. A zero- dimensional global (volume averaged) model is also developed to compare with experimental and simulated measurements of breakdown

Displacement of Persons by Major Public Works: Anthropological Analysis of Social and Cultural Benefits and Costs from Stream Control Measures--Phase 5

This study is concerned with social change and social impact of a major public works project on the human population required to relocate the persons being forced to sell to the Federal Government or turn over through condemnation proceedings homes, farms, and/or businesses to facilitate completion of a Federally authorized stream control measure. It is intended to test the utility of anthropological method and concept in evaluating and explicating sociocultural impact, and in addition to check hypotheses concerning importance of impact on social and economic areas of culture of the persons to be displaced, on their emigration patterns, and their cultural adaptation, and other social effects of relocation. Conclusions reached are that application of anthropological concepts and methods yield more intelligible results than sociological studies based on data generation through highly artificial questionnaire methods with attempted quantification of what are basically non-quantifiable data. This does not mean that simple counts and raw percentage comparisons are not significant to demonstrate trends, but that complex arithmetic computations are often used to imply a degree of precision that does not exist and explains nothing, Social scientists, planners, and change agents must come to realize that there are aspects of the quality of human life which must be considered which cannot be defined in numbers. The study also presents evidence for the conclusion that in forced relocation in modern rural Kentucky, and probably elsewhere, social disruption is perceived as less disastrous and threatening, therefore less tension-producing, than perceived economic ill-effects. Finally, the study suggest ways in which the action agency involved in environment-changing major works could by social science-oriented planning mitigate the social costs of its operation

The effect of bobweight and downspring on the longitudinal dynamic stability of an airplane

http://www.archive.org/details/effectofbobweigh00smitU.S. Navy (U.S.N.) author

Non-equilibrium dynamics and floral trait interactions shape extant angiosperm diversity.

Why are some traits and trait combinations exceptionally common across the tree of life, whereas others are vanishingly rare? The distribution of trait diversity across a clade at any time depends on the ancestral state of the clade, the rate at which new phenotypes evolve, the differences in speciation and extinction rates across lineages, and whether an equilibrium has been reached. Here we examine the role of transition rates, differential diversification (speciation minus extinction) and non-equilibrium dynamics on the evolutionary history of angiosperms, a clade well known for the abundance of some trait combinations and the rarity of others. Our analysis reveals that three character states (corolla present, bilateral symmetry, reduced stamen number) act synergistically as a key innovation, doubling diversification rates for lineages in which this combination occurs. However, this combination is currently less common than predicted at equilibrium because the individual characters evolve infrequently. Simulations suggest that angiosperms will remain far from the equilibrium frequencies of character states well into the future. Such non-equilibrium dynamics may be common when major innovations evolve rarely, allowing lineages with ancestral forms to persist, and even outnumber those with diversification-enhancing states, for tens of millions of years