Wavelength dependence of backscatter from rough surface
Measuring wavelength dependence of backscatter from smooth randomly rough surface using acoustic waves in water
Rouse, J. W., Jr.↗
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A model for the Centaurus X-3 phenomenon.
Description of a model for Cen X-3 according to which the X-ray emission comes from an atmosphere heated by shock waves produced by surface pulsations of a white dwarf. This model can explain the luminosity, period, and spectrum of Cen X-3. The way in which these quantities vary with pulsation period and amplitude is discussed.
Blumenthal, G. R.↗
Survey of computational methods for three-dimensional supersonic inviscid flows with shocks
Hyperbolic systems of partial differential equations governing supersonic inviscid flows are discussed and analyzed. Finite-difference analogues for integrating these systems in the interior of fluid domains are described from two points of view: a differential form approach and an integral form approach. The algorithms presented are analyzed for stability and accuracy. The concept of time splitting is discussed and supplied to these methods to achieve increased numerical efficiency. Techniques for treating conditions at the boundaries of the fluid domain and shock-wave discontinuities at surfaces within the domain are described.
Maccormack, R. W.↗
A review of the compatibility of structural materials with oxygen
Consideration of the problem of ignition and combustion of structural materials, particularly metals, which may come in contact with oxygen during its production, transport, and use. Following a review of the historical development of compatibility problems and research, a detailed account is given of compatibility testing methods aimed at detecting probable ignition sources, such as mechanical impact, electric sparks or flashes, heat, sound waves, abrasion, and surface fractures. A summary is presented of the ignition and combustion research reported in the literature, dwelling particularly on papers concerning oxygen-related accidents and the compatibility of metals with high-pressure oxygen. The relative oxygen compatibility of a number of common materials is discussed, including that of nickel and copper alloys, stainless steels, aluminum alloys, and titanium alloys. Finally, an effort is made to pinpoint research areas which would enhance understanding of the compatibility of bulk materials.
Clark, A. F.↗
Numerical solutions for supersonic corner flow
Analytical solutions for inviscid supersonic corner flows are virtually nonexistent due to the complexity of the interference geometry. In view of this, numerical solutions for swept-compressive and swept-expansive corner flows are obtained. The governing equations are written in strong conservation-law form and are solved iteratively in nonorthogonal conical coordinates by use of a second-order, shock-capturing, finite-difference technique. The computed wave structure and surface pressure distributions are compared with high Reynolds number experimental data and show very good agreement. The results clearly show that supersonic corner flow at reasonably high Reynolds numbers including the effect of sweep is dominated by the inviscid field.
Shankar, V.↗
Application of a numerically generated orthogonal coordinate system to the solution of inviscid axisymmetric supersonic flow over blunt bodies
A numerically generated orthogonal coordinate system (with the body surface and shock wave as opposite boundaries) was applied with a time asymptotic method to obtain steady flow solutions for axisymmetric inviscid flow over several blunt bodies including spheres, paraboloids, ellipsoids, hyperboloids, hemisphere cylinders, spherically blunted cones, and a body with a concavity in the stagnation region. Comparisons with experimental data and with the results of other computational methods are discussed. The numerically generated orthogonal coordinate system is described and applications of the method to complex body shapes, particularly those with concave regions, are discussed.
Hamilton, H. H., II↗
Multisensor analysis of hydrologic features in the Wind River Range, Wyoming with emphasis on the SEASAT SAR
The author has identified the following significant results. Analysis of imagery obtained over west-central Wyoming indicates that Seasat SAR has capability for hydrologic mapping. Both the L-Band (Seasat) and the X-Band (aircraft) SAR imagery were useful for observing drainage detail. Streams have bright signatures on the SAR imagery because the riparian vegetation produces a rough surface and thus high radar returns. Lakes appear relatively bright on the Seasat image presumably in response to surface ripples and waves induced by wind action. SAR imagery did not reveal snow at either the 23.5 cm (L-Band) or 2.8 cm (X-Band) wavelengths. Comparing Seasat and X-Band aircraft SAR imagery to LANDSAT RBV imagery, U-2 photography, and topographic maps of the Wind River Range, it appears that the SAR data do not seem to provide as much hydrologic information as do the other sensors in the visible and near infrared portions of the spectrum.
Foster, J. L.↗
CNO isotope production in nova outbursts
A current model of novae is presented which explains their outbursts assuming that the progenitor of a common nova is a carbon-oxygen dwarf. This white dwarf accretes H-rich material from its companion which produces strong shock waves at its surface; as the amount of accreted material increases later, its bottom ignites. The nova outburst is then triggered by CNO-Ne reactions which favor the formation of rare isotopes with proton-rich radioactive parents such as C-13, N-15, O-17, and Ne-21. The production of such nuclear species is examined in different nova models, and conclusions are drawn concerning the importance of novae in models of chemical evolution of the galaxy.
Audouze, J.↗
Kinetic theory and turbulent discontinuities
Shock tube discontinuities were used to test and extend a kinetic theory of turbulence. In shock wave and contact surface fluctuations, coherent phenomena were found which provide new support for the microscopic nonempirical approach to turbulent systems, especially those with boundary layer-like instabilities.
Johnson, J. A., III↗
The West Coast Experiment - An overview
The West Coast Experiment was conducted in the Southern California Bight during March-April 1977 for the purpose of investigating the mesoscale variability of waves, wind, and surface temperature and to demonstrate the validity and level of usefulness of airborne remote sensing techniques in the investigation of oceanographic processes. This paper presents the large-scale view of the West Coast Experiment and provides a summary of the major results.
Shemdin, O. H.↗
SEASAT views oceans and sea ice with synthetic aperture radar
Fifty-one SEASAT synthetic aperture radar (SAR) images of the oceans and sea ice are presented. Surface and internal waves, the Gulf Stream system and its rings and eddies, the eastern North Pacific, coastal phenomena, bathymetric features, atmospheric phenomena, and ship wakes are represented. Images of arctic pack and shore-fast ice are presented. The characteristics of the SEASAT SAR system and its image are described. Maps showing the area covered, and tables of key orbital information, and listing digitally processed images are provided.
Fu, L. L.↗
Ocean wind field measurement performance of the ERS-1 scatterometer
The Active Microwave Instrumentation (AMI), which will be implemented on the ERS-1, is a 5.3 GHz multipurpose radar for land surface imaging, ocean wave spectrum measurement and wind observations over oceans. The imaging and wave measurements apply Synthetic Aperture Radar (SAR) techniques, while wind field detection is performed by the Scatterometer as part of the AMI. The Scatterometer system design was developed and optimized with the aid of a performance simulator. This paper, aimed at giving an overview, is presented about the: (1) ERS-1 Scatterometer system design; (2) Error budget; and the (3) Overall calibration concept.
Hans, P.↗
Backscattering coefficient of a perturbed sinusoidal surface
A coherent model for scattering from a randomly perturbed periodic surface is developed using the Kirchhoff approximation. It is intended to model wave scattering from ground surfaces with row directions. Results are illustrated and compared with an incoherent scatter model and measured backscattering angular curves from ploughed fields.
Eom, H. J.↗
Implications of the Vega balloon results for Venus atmospheric dynamics
During the Vega Venus balloon mission, data on the thermodynamic state of the atmosphere were obtained as well as wind and cloud information. Explanations are provided for the following: (1) the large amplitude atmospheric vertical winds encountered by the Vega balloons, (2) the observed 6.5 K temperature difference consistently measured between the two Vega balloons, and (3) the apparent influence of surface topography on atmospheric motions seen by the Vega-2 balloon as it flew over mountainous terrain (known as Aphrodite). It is believed that vertical winds of the magnitude encountered by the Vega-2 balloon over Aphrodite may be the result of surface-induced gravity waves.
Young, R.↗
Intensive MHD-structures penetration in the middle atmosphere initiated in the ionospheric cusp under quiet geomagnetic conditions
In connection with the recently detected quasiperiodical magnetic disturbances in the ionospheric cusp, the penetration of compressional surface magnetohydrodynamic (MHD) waves through the middle atmosphere is modelled numerically. For the COSPAR International Reference Atmosphere (CIRA) 72 model the respective energy density flux of the disturbances in the middle atmosphere is determined. On the basis of the developed model certain conclusions are reached about the height distribution of the structures (energy losses, currents, etc.) initiated by intensive magnetic cusp disturbances.
Mateev, L. N.↗
Guided waves and defect scattering in metal matrix composite plates
Guided Rayleigh-Lamb waves in a continuous graphite fiber reinforced magnesium plate has been studied. The interest in this material arises from its high thermal stability and because it provides high strength-to-weight ratio. Previous studies have shown that for wavelengths much larger than the fiber diameters and spacing, the material can be characterized as transversely isotropic with the symmetry axis aligned with the fiber direction. Because of the high longitudinal stiffness of the graphite fibers, the material shows strong anisotropy, with very high modulus in the fiber direction. For this reason, dispersion of guided waves is strongly influenced by the deviation of the direction of propagation from the symmetry axis. Results are given for propagation in different directions and for scattering of antiplane shear waves by surface-breaking cracks and delaminations.
Datta, Subhendu K.↗
Speculation on a Solar Chronometer for Climate
Solar activity has been correlated to climatic fluctuations and has been postulated as a major factor in quasi-periodic global climatic change. However, correlations are not explanations of physical mechanisms and do not couple cause with effect. A mechanism for a chronometer for solar output variability is proposed based on relations between properties of thermonuclear fusion, nuclear magnetic moment, and nuclear magnetic resonance. A fundamental oscillation of a nucleus with a net nuclear magnetic moment (NMM) is the precession of its axis of rotation when subjected to a magnetic field. Nuclear magnetic resonance (NMR) is the preferred frequency of precession for a nucleus of a particular isotope when placed in a magnetic field of specific intensity. The NMM for those isotopes involved in the proton-proton (p-p) chain pathway for solar fusion varies from strong positive to strong negative. Individual fusion events, for hydrogen and helium isotopes which release varying amounts of energy, may be controlled by NMR frequencies. The pulses of energy from fusion events occurring at NMR frequencies in the solar interior may be transformed into pressure or gravity waves that emerge as gravity or acoustic waves at the surface. Dictated by spherical harmonics, certain wavelengths may be reinforced and reenter the solar interior to modulate the fusion process. Qualitative analysis of solar and climatic data support the interaction of the three basic components of the chronometer, magnetic activity, oscillation frequency, and solar energy output.
Perry, Charles A.↗
The use of holographic interferometry for measurements of temperature in a rectangular heat pipe
Holographic interferometry is a nonintrusive method and as such possesses considerable advantages such as not disturbing the velocity and temperature field by creating obstacles which would alter the flow field. These optical methods have disadvantages as well. Holography, as one of the interferometry methods, retains the accuracy of older methods, and at the same time eliminates the system error of participating components. The holographic interferometry consists of comparing the objective beam with the reference beam and observing the difference in lengths of optical paths, which can be observed during the propagation of the light through a medium with locally varying refractive index. Thus, change in refractive index can be observed as a family of nonintersecting surfaces in space (wave fronts). The object of the investigation was a rectangular heat pipe. The goal was to measure temperatures in the heat pipe, which yields data for computer code or model assessment. The results were obtained by calculating the temperatures by means of finite fringes.
Marn, Jure↗