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Description of a method for the preparation of A-15 superconducting films by cosputtering. This method is useful for the study of both alloying effects and crystal structure stability determinations. Measurements in the A-15 systems Nb3Al, Nb3Al sub .75 Ge sub .25, and V3Si prepared by this method are presented. In addition a new method for the preparation of V3Si by 'reactive diffusion' is presented.
A review is given of our present knowledge of the Martian atmosphere with special emphasis on the results obtained by the Mariner 4, 6 and 7 fly-bys. The Viking Project offers the first opportunity for in situ measurements which should resolve many questions left open by previous work. A description is given of the neutral gas mass spectrometer and retarding potential analyzer experiments to be performed as the lander enters the upper atmosphere and the experiments planned for determining atmospheric structure as the lander approaches the surface of the planet.
Finite-difference calculations have been carried out to determine the structure of finite-amplitude thermal convection within a self-gravitating fluid sphere with uniform heat release. For a fixed-surface boundary condition, single-cell convection breaks up into double-cell convection at a Rayleigh number of 30,000, at a Rayleigh number of 500,000 four-cell convection is observed. With a free-surface boundary condition only single cell convection is obtained up to a Rayleigh number of 5,000,000.
Extensive numerical calculations have been carried out to determine the structure of the primitive solar nebula. The resulting structure shows a dominance of the radial pressure gradient near the center, and a dominance of the centrifugal forces throughout most of the outer region. Thermal convection and Eddington-Sweet circulation currents can be expected to cause a rapid dissipation of the disk, requiring only a few centuries. It is therefore postulated that the planets were formed in an exceedingly hot initial state due to their rapid rates of accumulation. Beyond one or two astronomical units from the center, the original interstellar grains should not be completely destroyed during the formation of the disk, and these will form the nuclei for subsequent chemical condensations and chemical accumulation. Inside this distance, nucleation of condensed materials must occur within the nebular gases.
Surface research tools such as LEED, Auger emission spectroscopy analysis, and field ion microscopy are discussed. Examples of their use in studying adhesion, friction, wear, and lubrication presented. These tools have provided considerable insight into the basic nature of solid surface interactions. The transfer of metals from one surface to another at the atomic level has been observed and studied with each of these devices. The field ion microscope has been used to study polymer-metal interactions and Auger analysis to study the mechanism of polymer adhesion to metals. LEED and Auger analysis have identified surface segregation of alloying elements and indicated the influence of these elements in metallic adhesion. LEED and Auger analysis have assisted in adsorption studies in determining the structural arrangement and quantity of adsorbed species present in making an understanding of the influence of these species on adhesion possible. These devices are assisting in the furtherance of understanding of the fundamental mechanism involved in the adhesion, friction, wear, and lubrication processes.
When high energy protons from solar proton events or trapped radiation belts impinge on spacecraft structures, secondary particles are emitted. The most pernicious secondaries, from either a biological or physical standpoint, are the cascade and evaporation neutrons because of their reaction with matter leading to radioactive materials in the spacecraft structures. Empirically determined cascade and evaporation neutron emission spectra for protons of energy between 20 and 500 MeV incident on all materials at or above carbon in mass number are presented.
Apollo 17 seismic data are interpreted to determine the structure of the lunar crust to a depth of several kilometers. Seismic velocity increases in a marked stepwise manner beneath the Taurus-Littrow region at the Apollo 17 site. A thickness of about 1200 meters is indicated for the infilling mare basalts at Taurus-Littrow. The apparent velocity is high (about 4 kilometers per second) in the material immediately underlying the basalts.
Parameters for a lumped linear model approximating a distributed elastic structure are determined from dynamic test data comprised of several mode shapes and frequencies. Measurement errors, nonlinear response, and nonmeasurable quantities such as mode slope components are accommodated. Some mass and stiffness parameters may be known accurately, whereas the remainder are to be estimated. The method entails minimizing a quadratic function of the difference between corresponding modes and frequencies of the theoretical model and the test specimen. This technique was applied to some actual vibration test data, and the special techniques that are required to overcome convergence problems are described.
The lubricating properties of some benzyl and benzene structures were determined by using 304 stainless steel surfaces strained to various hardness. Friction coefficients and wear track widths were measured with a Bowden-Leben type friction apparatus by using a pin-on-disk specimen configuration. Results obtained indicate that benzyl monosulfide, dibenzyl disulfide, and benzyl alcohol resulted in the lowest friction coefficients for 304 stainless steel, while benzyl ether provided the least surface protection and gave the highest friction. Strainhardening of the 304 stainless steel prior to sliding resulted in reduced friction in dry sliding. With benzyl monosulfide, dibenzyl disulfide, and benzyl alcohol changes in 304 stainless steel hardness had no effect upon friction behavior.
Questions of lunar bulk chemistry are being considered, giving attention to the depletion of the moon in iron and compounds more volatile than iron. Currently four seismic stations are operating on the moon to provide data for the study of the lunar interior. The travel times of seismic waves generated by artificial impacts have been used to determine the structure of the outer 150 km of the moon. New evidence fails to resolve the controversy whether the lunar interior is hot or cold. A schematic cross section of the moon is presented and problems concerning the origin of the moon are considered.
In the theoretical approach to model-atmosphere construction, all opacities are computed theoretically and the temperature-pressure structure is determined by conservation of energy. Until recently, this has not been a very useful method for later type stars, because the line opacity was both poorly known and difficult to calculate. However, methods have now been developed that are capable of representing the line opacity well enough for construction of realistic models. A preliminary theoretical solar model is presented that produces closer agreement with observation than has been heretofore possible. The qualitative advantages and shortcomings of this model are discussued and projected improvements are outlined.
Model is generated from description of element connections involved in complete arc network, list of corresponding circuit element values, description of circuit current excitation, and list of out-puts desired. Waveform of current is determined by structure of capacitor storage system, driver geometry, and preset driver conditions.
An analytical method and a design procedure to develop flanged separable pipe connectors are discussed. A previously established algorithm is the basis for calculating low profile flanges. The characteristics and advantages of the low profile flange are analyzed. The use of aluminum, titanium, and plastics for flange materials is described. Mathematical models are developed to show the mechanical properties of various flange configurations. A computer program for determining the structural stability of the flanges is described.
The papers consider the origin and evolution of the lunar regolith utilizing data obtained during American and Soviet manned and unmanned lunar missions as well as surface and orbital observations, photography, sample collections, and experimental studies. Topics include the transport and emplacement of crater and basin deposits, development of the mare regolith, the shallow lunar structure as determined from the passive seismic experiment, horizontal transport of the regolith, the origin of the exotic component and KREEP-rich materials, the influx of interplanetary materials onto the moon, stratification in the lunar regolith, catastrophic rupture of lunar rocks, cosmic-ray exposure ages of surface features, breccia formation by sintering and crystallization, evolution of the lunar soil, and effects of maturation on the reflectance of the regolith. Individual items are announced in this issue.
Two computational procedures for analyzing complex structural systems for their natural modes and frequencies of vibration are presented. Both procedures are based on a substructures methodology and both employ the finite-element stiffness method to model the constituent substructures. The first procedure is a direct method based on solving the eigenvalue problem associated with a finite-element representation of the complete structure. The second procedure is a component-mode synthesis scheme in which the vibration modes of the complete structure are synthesized from modes of substructures into which the structure is divided. The analytical basis of the methods contains a combination of features which enhance the generality of the procedures. The computational procedures exhibit a unique utilitarian character with respect to the versatility, computational convenience, and ease of computer implementation. The computational procedures were implemented in two special-purpose computer programs. The results of the application of these programs to several structural configurations are shown and comparisons are made with experiment.
Two parameters, side on overpressure and side on impulse loads, and their application to the determination of structural damage to buildings and vehicles in the vicinity of an explosion are investigated. Special consideration was given to what constitutes damage and what level of damage is acceptable. Solutions were sorted through the examination of glass breakage, curve fit to bomb damage, overturning of marginal structures (buses, trucks, mobile homes) subject to toppling, and initiation of yielding in either beam or plate structural components. Three different empirical pressure versus impulse diagrams were presented - the first is for minor structural damage involving wrenched joints and partitions, the second is for major damage structural damage with load bearing members at least partially destroyed, and the third is for 50% to 75% of the building demolished. General guidelines were obtained from the results when the accurate structural details are unknown.
Results from a seminar on the role of solar magnetic fields in determining the structure of the corona and interplanetary medium are presented. Some topics considered are: (1) polar regions of the sun which have identical magnetic configurations but display a vastly different appearance in the corona, (2) the influence of latitude on coronal and interplanetary microstructure, and (3) the role of the corona in contributing to the solar wind. It is proposed that an out-of-the-ecliptic solar probe mission would provide needed information on the above topics, and the study of solar activity in general.
Several current problems concerning the overall distribution of hydrogen in the galaxy are discussed in general terms. These problems include the degree of saturation characterizing low-latitude emission observations of HI, and the optical-depth corrections to the derived column and volume densities; the amount of fine-scale velocity and spatial structure diluted by the instrumental limitations of the presently available surveys; and the general problem of detailed mapping of the HI in the galaxy. Comparison is made between the distribution of HI and that of CO and several other galactic tracers. The galactic disk as defined by atomic hydrogen has a diameter fully twice as large as that defined by the ionized and molecular states of hydrogen, as well as by other molecules, supernova remnants, pulsars, gamma radiation, synchroton radiation, and the youngest stars. It is also less confined to the galactic equator than most of the other constituents. The degree of small-scale structure apparent in the molecular observations is much greater than in the HI observations. Parameters describing the small-scale structure were determined using Monte Carlo techniques to simulate the observations.