An experimental investigation of the effect of boundary layer refraction on the noise from a high-speed propeller

Models of supersonic propellers were previously tested for acoustics in the Lewis 8- by 6-Foot Wind Tunnel using pressure transducers mounted in the tunnel ceiling. The boundary layer on the tunnel ceiling is believed to refract some of the propeller noise away from the measurement transducers. Measurements were made on a plate installed in the wind tunnel which had a thinner boundary layer than the ceiling boundary layer. The plate was installed in two locations for comparison with tunnel ceiling noise data and with fuselage data taken on the NASA Dryden Jetstar airplane. Analysis of the data indicates that the refraction increases with: increasing boundary layer thickness; increasing free stream Mach number; increasing frequency; and decreasing sound radiation angle (toward the inlet axis). At aft radiation angles greater than about 100 deg there was little or no refraction. Comparisons with the airplane data indicated that not only is the boundary layer thickness important but also the shape of the velocity profile. Comparisons with an existing two-dimensional theory, using an idealized shear layer to approximate the boundary layer, showed that the theory and data had the same trends. Analysis of the data taken in the tunnel at two different distances from the propeller indicates a decay with distance in the wind tunnel at high Mach numbers but the decay at low Mach numbers is not as clear

Enzyme activity in terrestrial soil in relation to exploration of the Martian surface

Urease activity in soil is persistent for long periods under low water, low temperature, and sterile regimes, and it was suggested that some form of enzyme-protective mechanism exists in soil. Dublin soil was extracted by sonication in water followed by adding a mixture of salts. Urease activity is associated with the organo-mineral complex thus obtained and is resistant to the activities of proteolytic enzymes. Clay free soil organic matter prepared subsequently by filtration also exhibits urease activity which is resistant to proteolysis. Models consisting of enzymes with bentonite and lignin were found to mimic this resistance to proteolysis. A model system is presented which suggests both the origin and location of soil ureases and a reason for their persistence in nature

Great exaptations

Long interspersed nuclear elements (LINEs) are among the most successful parasitic genetic sequences in higher organisms. Recent work has discovered many instances of LINE incorporation into exons, reminding us of the hazards they pose to genes in their vicinity as well as their potential to be co-opted for the host's purposes

Sandstone Pore Aspect Ratio Spectra from Direct Observations and Velocity Inversion

Measurements of pore shapes from Scanning Electron Microscope (SEM) images for three sandstone samples (the Navajo Sandstone, the Weber Sandstone, and the Kayenta Sandstone) are compared to the aspect ratio spectra obtained from inverting laboratory velocity versus pressure data using the method of Cheng and Toksoz (1979). The results indicate that the inversion method is in very good agreement with the observations at high aspect ratios ( ex > 0.0 1). At low aspect ratios the agreement is very good for the clean Navajo Sandstone sample, but poor for the Weber and Kayenta samples which contain clay. The Navajo sample is composed chiefly of quartz with significant pressure dissolution apparent along grain contacts resulting in smooth, flat cracks between grains. The Weber and Kayenta samples have rougher crack surfaces as well as tapered pore edges, indicating that asperities ,and non-elliptical pore shapes may result in an over estimation of low aspect ratio cracks by velocity inversion. The presence of degraded feldspars may also play a role.Phillips Petroleum Fellowshi

Lithologic Cycles And Paleo Fluid Flow Channels In Old Oceanic Crust From Geophysical Logs At ODP Site 418A

Using some new processing of the multichannel sonic (MCS) log data from Site 418A, the resulting P, S, and Stoneley wave velocity estimates and apparent attenuation were integrated with the natural gamma, spectral gamma, resistivity, neutron, density, and caliper logs and core lithology information for interpretation of lithologic cycles and possible paleo fluid flow intervals. These data indicate the presence of multiple breccia or rubble zones in the lower portions of the borehole. These zones are interpreted as the last stages of eruptive cycles as described by Hyndman and Salisbury (1984). The results of permeability (packer) tests and temperature gradient measurements at Sites 395A and 504B indicate that fluid flow in the crust at those sites is localized to brecciated zones which occur below massive flow basalts. By analogy, the breccia zones interpreted at Site 418A may have acted as fluid flow channels at an earlier time. Six major paleo fluid flow zones are interpreted at Site 418A. These breccia zones have low velocities (P, S, and Stoneley), increased apparent attenuation, and an increase in gamma activity. These intervals are interpreted as permeable pathways which may have been altered by the second stage of oxidizing alteration as described by Holmes (1988). Breccia units occur just below massive basalt flow units. The massive basalt flow units are also easily identified in the MCS data. The resistivity log data suggest that each major eruptive cycle trend is made up of several smaller sub-cycles. The MCS data provides much insight into the variations in lithology in ODP boreholes. The trace energy provides a stable measure of apparent attenuation which may be related to alteration, fracturing, or permeability (if there are open fractures). Velocity estimates for P, S, and Stoneley waves provide useful information about lithologic variability if interpreted in detail.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumNational Science Foundation (U.S.) (Grant OCE-89000316

Photoinduced time-resolved electrodynamics of superconducting metals and alloys

The photoexcited state in superconducting metals and alloys was studied via pump-probe spectroscopy. A pulsed Ti:sapphire laser was used to create the non-equilibrium state and the far-infrared pulses of a synchrotron storage ring, to which the laser is synchronized, measured the changes in the material optical properties. Both the time- and frequency- dependent photoinduced spectra of Pb, Nb, NbN, Nb{0.5}Ti{0.5}N, and Pb{0.75}Bi{0.25} superconducting thin films were measured in the low-fluence regime. The time dependent data establish the regions where the relaxation rate is dominated either by the phonon escape time (phonon bottleneck effect) or by the intrinsic quasiparticle recombination time. The photoinduced spectra measure directly the reduction of the superconducting gap due to an excess number of quasiparticles created by the short laser pulses. This gap shift allows us to establish the temperature range over which the low fluence approximation is valid.Comment: 12 pages with 10 figure

Energy Partitioning and Attenuation of Guided Waves in a Radially Layered Borehole

Recently published results (Tubman et al., 1984; Baker,. 1984) indicate that synthetic full waveform acoustic logs generated in cased or damaged boreholes differ significantly from those generated in an open hole with the same formation parameters. In particular, the guided waves appear to be the most affected by such radial layering. In order to gain some understanding of these effects, the amplitude response and energy distribution of the pseudo-Rayleigh and Stoneley waves are studied for the cased and invaded borehole models. The expressions derived by Cheng et al. (1 982) are used to calculate partition coefficients (partial derivatives of phase velocity with respect to body wave velocities) for the guided wave modes. The attenuation of the guided wave can then be represented by the sum of the layer attenuation values weighted by their respective partition coefficients. The results indicate that the attenuation of the Stoneley wave is dominated by the fluid attenuation at all frequencies in fast formations, both in the open hole geometry and in the presence of casing or invaded zones. In a slow formation, the Stoneley wave attenuation becomes more sensitive to the shear wave attenuation of the formation at higher frequencies in both the open and cased hole situations. For the pseudo-Rayleigh wave, the introduction of casing reduces the effect of the fluid attenuation, while the presence of an invaded zone reduces the effect of the formation shear attenuation. Plots of the partition coefficients indicate that the casing and invasion layers are most important over a limited frequency range which is related to the thickness of the layer. Radial displacement curves illustrate the depth of penetration of the various frequency components of the pseudo-Rayleigh wave.Massachusetts Institute of Technology. Full Waveform Acoustic Logging Consortiu

Homomorphic Processing Of Acoustic Logging Data

A new processing method, which we developed for the guided waves generated during acoustic logging, accurately estimates the wavenumber when only a few seismograms are available or when the seismograms are irregularly spaced. The estimates of the attenuation coefficient are seemingly accurate when many seismograms are available but are inaccurate when only a few seismograms are available. The new method does not generate any spurious estimates as the Prony-based method does.Halliburton CompanyMassachusetts Institute of Technology. Full Waveform Acoustic Logging Consortiu

Investigation of optimization of attitude control systems, volume ii

Attitude control system optimization - computer programs, listings and subroutine

Investigation of optimization of attitude control systems, volume i

Optimization of attitude control systems by development of mathematical model and computer program for space vehicle simulatio