A comparison of cortical and trabecular bone from C57 Black 6 mice using Raman spectroscopy

Peer reviewedPostprin

Pressure containment tests in support of the nuclear Brayton cycle heat exchanger and duct assembly /HXDA/, phase 2

Plate-fin heat exchangers for nuclear reactor Brayton cycl

Criminal Law—Right to Speedy Trial

People v. White, 2 N.Y.2d 220, 159 N.Y.S.2d 168 (1957); People v. Chirieleison, 3 N.Y.2d 170, 164 N.Y.S2d 726 (1957)

Deconstructing Internet QoS with SulksHuman

The construction of rasterization is a natural issue. In this position paper, we validate the improvement of IPv7, demonstrates the appropriate importance of artificial intelligence. We use large-scale communication to validate that replication [8, 1] can be made interactive, linear-time, and collaborative

Viscous Attenuation Of Acoustic Waves In Suspensions

A model for attenuation of acoustic waves in suspensions is proposed which includes an energy loss due to viscous fluid flow around spherical particles. The expression for the complex wavenumber is developed by considering the partial pressures acting on the solid and fluid phases of the suspension. This is shown to be equivalent to the results of the Biot theory for porous media in the limiting case where the frame moduli vanish. Unlike earlier applications of the limiting case Biot theory, however, a value for the attenuation coefficient is developed from the Stokes flow drag force on a sphere instead of attempting to apply a permeability value to a suspension. If the fluid and solid particle velocities have harmonic time dependence with angular frequency w, the attenuation in this model is proportional to w2 at low frequencies and approaches a constant value at high frequencies. The predicted attenuation is very sensitive to the radius and density of the spherical particles. Accurate modeling of observed phase velocities from suspensions of spherical polystyrene particles in water and oil and successful inversion for kaolinite properties using attenuation and velocity data from kaolinite suspensions at 100 kHz show that this viscous dissipation model is a good representation of the effects controlling the propagation of acoustic waves in these suspensions. Attenuation predictions are also compared to amplitude ratio data from an oil-polystyrene suspension. The viscous effects are shown to be significant for only a limited range of solid concentration and frequency by the reduced accuracy of the model for attenuation in a kaolinite suspension at 1 MHz.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumNational Science Foundation (U.S.). Graduate Research Fellowship Progra

Permeability Estimation From Velocity Anisotropy In Fractured Rock

Cracks in a rock mass subjected to a uniaxial stress will be preferentially closed depending on the angle between the fracture normal vectors and the direction of the applied stress. If the prestress fracture orientation distribution is isotropic, the effective elastic properties of such a material after application of the stress are then transversely isotropic due to the overall alignment of the cracks still open. Velocity measurements in multiple directions are used to invert for the probability density function describing orientations of crack normals in such a rock. This is accomplished by expanding the crack orientation distribution function into generalized spherical harmonics. The coefficients in this expansion are functions of the crack density and the crack aspect ratio distribution. The information on fracture distribution obtained from the velocity inversion allows an estimation of the anisotropic permeability of the fractured rock system. Permeability estimates are based on the number of cracks open of each aspect ratio, and the contribution of a given crack is weighted by the cosine of the angle between the crack and the direction of the applied pressure gradient. This approach yields a prediction of permeability as a function of the angle from the uniaxial stress axis. The inversion for crack orientation is applied to ultrasonic velocity measurements on Barre granite, and permeability predictions for this sample are presented. The inversion results are good and reproduce velocity measurements well, and the permeability predictions show some of the expected trends. Initial comparisons of the predictions with available permeability data, however, show deviations suggesting that further information on partial crack closure and connectivity of cracks should be included in the permeability model.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-86ER13636)National Science Foundation (U.S.). Graduate Research Fellowship Progra

Permeability Estimation From Velocity Anisotropy In Fractured Rock

Cracks in a rock mass subjected to a uniaxial stress will be preferentially closed depending on the angle between the fracture normal and the direction of the applied stress. If the prestress fracture distribution is isotropic, the effective elastic properties of such a material are then transversely isotropic due to the preferred alignment of the cracks. Velocity measurements in multiple directions are used to invert for the probability density function describing orientations of crack normals in such a rock. We suggest a means of using the results on fracture distribution from the velocity inversion to estimate the anisotropic permeability of the fracture system. This approach yields a prediction of permeability as a function of the angle from the uniaxial stress direction.Massachusetts Institute of Technology. Full Waveform Acoustic Logging ConsortiumUnited States. Dept. of Energy (Grant DE-FG02-86ERI3636)National Science Foundation (U.S.). Graduate Research Fellowship Progra

The Enrichment History of Hot Gas in Poor Galaxy Groups

We have analyzed the ASCA SIS and GIS data for seventeen groups and determined the average temperature and abundance of the hot x-ray emitting gas. For groups with gas temperatures less than 1.5 keV we find that the abundance is correlated with the gas temperature and luminosity. We have also determined the abundance of the alpha-elements and iron independently for those groups with sufficient counts. We find that for the cool groups (i.e. kT <1.5 keV) the ratio of alpha-elements to iron is ~1, about half that seen in clusters. Spectral fits with the S, Si and Fe abundances allowed to vary separately suggest the S/Fe ratio is similar to that seen in clusters while the Si/Fe ratio in groups is half the value determined for richer systems. The mass of metals per unit blue luminosity drops rapidly in groups as the temperature drops. There are two possible explanations for this decrease. One is that the star formation in groups is very different from that in rich clusters. The other explanation is that groups lose much of their enriched material via winds during the early evolution of ellipticals. If the latter is true, we find that poor groups will have contributed significantly (roughly 1/3 of the metals) to the enrichment of the intergalactic medium.Comment: 19 Pages with 2 figures, Accepted for publication in the Astrophysical Journa