12,496 research outputs found
Radar exploration of Venus
Spacecraft radar systems for exploration of Venu
Experimental investigation of hypersonic buzz on a high cross-range shuttle configuration
A wind tunnel investigation has been conducted to determine the nature of an unsteady hypersonic flow phenomenon, often referred to as hypersonic buzz, on a 1:100 scale model representative of a high cross-range shuttle configuration. The tests, conducted in helium at a nominal Mach number of 17.5, were specifically directed at obtaining a better understanding of the character of the hypersonic flow field in the vicinity of a deflected control surface. Power spectral densities and root mean squared values of surface pressure fluctuations are presented along with observations made from high speed motion pictures, schlieren and oil flow photographs. Flap deflections of 0, 20, 30, 35, 40 and 60 deg were tested at various angles of attack from 0 deg to 37 deg. It is quite clear from these tests that, under certain conditions, extremely unstable hypersonic flow patterns are formed
Buneman instability in a magnetized current-carrying plasma with velocity shear
Buneman instability is often driven in magnetic reconnection. Understanding
how velocity shear in the beams driving the Buneman instability affects the
growth and saturation of waves is relevant to turbulence, heating, and
diffusion in magnetic reconnection. Using a Mathieu-equation analysis for weak
cosine velocity shear together with Vlasov simulations, the effects of shear on
the kinetic Buneman instability are studied in a plasma consisting of strongly
magnetized electrons and cold unmagnetized ions. In the linearly unstable
phase, shear enhances the coupling between oblique waves and the sheared
electron beam, resulting in a wider range of unstable eigenmodes with common
lower growth rates. The wave couplings generate new features of the electric
fields in space, which can persist into the nonlinear phase when electron holes
form. Lower hybrid instabilities simultaneously occur at
with a much lower growth
rate, and are not affected by the velocity shear.Comment: Accepted by Physics of Plasm
Evaluation of the cardiovascular system during various circulatory stresses Progress report, 1 Sep. 1968 - 1 May 1969
Cardiac response to chemotherapy after myocardial infraction and diagnostic methods of heart disease in man and animal
A computer program for the calculation of laminar and turbulent boundary layer flows
The results are presented of a study to produce a computer program to calculate laminar and turbulent boundary layer flows. The program is capable of calculating the following types of flow: (1) incompressible or compressible, (2) two dimensional or axisymmetric, and (3) flows with significant transverse curvature. Also, the program can handle a large variety of boundary conditions, such as blowing or suction, arbitrary temperature distributions and arbitrary wall heat fluxes. The program has been specialized to the calculation of equilibrium air flows and all of the thermodynamic and transport properties used are for air. For the turbulent transport properties, the eddy viscosity approach has been used. Although the eddy viscosity models are semi-empirical, the model employed in the program has corrections for pressure gradients, suction and blowing and compressibility. The basic method of approach is to put the equations of motion into a finite difference form and then solve them by use of a digital computer. The program is written in FORTRAN 4 and requires small amounts of computer time on most scientific machines. For example, most laminar flows can be calculated in less than one minute of machine time, while turbulent flows usually require three or four minutes
High powered arc electrodes
Nonconsumable metal electric arc electrodes are described capable of being operated in a variety of gases at various pressures, current, and powers. The cathode has a circular annulus tip to spread the emission area for improved cooling
Image Processing for Cartographic Applications
The goal of classifying objects of cartographic interest in aerial photographs was approached using techniques from pattern recognition and image processing. Bridge and airport images were chosen as the initial objects of interest and segments of photographs containing them were digitized for the data base. Edge-detection and Hough transform algorithms identified structures as candidate bridges; additional decision logic (using global contrast and other attributes) further reduced the set. Results indicate the feasibility and low computational cost of the approach
Simulation studies of improved sounding systems
Two instrument designs for indirect satellite sounding of the atmosphere in the infrared are represented by the High Resolution Infra-Red Sounder, Model 2 (HIRS-2) and by the Advanced Meteorological Temperature Sounder (AMTS). The relative capabilities of the two instruments were tested by simulating satellite measurements from a group of temperature soundings, allowing the two participants to retrieve the temperature profiles from the simulated data, and comparing the results with the original temperature profiles. Four data sets were produced from radiosondes data extrapolated to a suitable altitude, representing continents and oceans, between 30S and 30N. From the information available, temperature profiles were retrieved by two different methods, statistical regression and inversion of the radiative transfer equation. Results show the consequence of greater spectral purity, concomitant increase in the number of spectral intervals, and the better spatial resolution in partly clouded areas. At the same time, the limitation of the HIRS-2 without its companion instrument leads to some results which should be ignored in comparing the two instruments. A clear superiority of AMTS results is shown
Color Magnetic Corrections to Quark Model Valence Distributions
We calculate order color magnetic corrections to the valence quark
distributions of the proton using the Los Alamos Model Potential wavefunctions.
The spin-spin interaction breaks the model SU(4) symmetry, providing a natural
mechanism for the difference between the up and down distributions. For a value
of sufficient to produce the mass splitting, we find up
and down quark distributions in reasonable agreement with experiment.Comment: 25 Pages, LA-UR-93-132
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