Improving the toughness of refractory compounds

Composition and processing studies were conducted on silicon nitride and silicon carbide materials. Charpy mode impact testing to 2415 F established the effectiveness of higher purity silicon nitride powder sources in reducing the scatter of measurements and in improving short time bend strengths as well as bend stress rupture properties. Stabilized zirconia additions in particular were observed to dramatically enhance low and high temperature bend strengths and stress rupture properties for all grades of silicon nitride powder. Silicon carbide samples showed relatively poor impact resistance, although the maxima in stress rupture behavior was exhibited by this material

Class of near-perfect coded apertures

Coded aperture imaging of gamma ray sources has long promised an improvement in the sensitivity of various detector systems. The promise has remained largely unfulfilled, however, for either one of two reasons. First, the encoding/decoding method produces artifacts, which even in the absence of quantum noise, restrict the quality of the reconstructed image. This is true of most correlation-type methods. Second, if the decoding procedure is of the deconvolution variety, small terms in the transfer function of the aperture can lead to excessive noise in the reconstructed image. It is proposed to circumvent both of these problems by use of a uniformly redundant array (URA) as the coded aperture in conjunction with a special correlation decoding method

Cratering in low-density targets

Cratering in low density targets, and comparisons of various hypervelocity projectile-target combination

The mass and dynamical state of Abell 2218

Abell 2218 is one of a handful of clusters in which X-ray and lensing analyses of the cluster mass are in strong disagreement. It is also a system for which X-ray data and radio measurements of the Sunyaev-Zel'dovich decrement have been combined in an attempt to constrain the Hubble constant. However, in the absence of reliable information on the temperature structure of the intracluster gas, most analyses have been carried out under the assumption of isothermality. We combine X-ray data from the ROSAT PSPC and the ASCA GIS instruments, enabling us to fit non-isothermal models, and investigate the impact that this has on the X-ray derived mass and the predicted Sunyaev-Zel'dovich effect. We find that a strongly non-isothermal model for the intracluster gas, which implies a central cusp in the cluster mass distribution, is consistent with the available X-ray data and compatible with the lensing results. At r<1 arcmin, there is strong evidence to suggest that the cluster departs from a simple relaxed model. We analyse the dynamics of the galaxies and find that the central galaxy velocity dispersion is too high to allow a physical solution for the galaxy orbits. The quality of the radio and X-ray data do not at present allow very restrictive constraints to be placed on H_0. It is apparent that earlier analyses have under-estimated the uncertainties involved. However, values greater than 50 km/s/Mpc are preferred when lensing constraints are taken into account.Comment: 16 pages, 9 postscript figures, accepted for publication in MNRA

Precise control of flexible manipulators

The design and experimental testing of end point position controllers for a very flexible one link lightweight manipulator are summarized. The latest upgraded version of the experimental set up, and the basic differences between conventional joint angle feedback and end point position feedback are described. A general procedure for application of modern control methods to the problem is outlined. The relationship between weighting parameters and the bandwidth and control stiffness of the resulting end point position closed loop system is shown. It is found that joint rate angle feedback in addition to the primary end point position sensor is essential for adequate disturbance rejection capability of the closed loop system. The use of a low order multivariable compensator design computer code; called Sandy is documented. A solution to the problem of control mode switching between position sensor sets is outlined. The proof of concept for endpoint position feedback for a one link flexible manipulator was demonstrated. The bandwidth obtained with the experimental end point position controller is about twice as fast as the beam's first natural cantilevered frequency, and comes within a factor of four of the absolute physical speed limit imposed by the wave propagation time of the beam

Where California Went Wrong with the Amazon Tax: Application of Due Process and Commerce Clause Jurisprudence to State Use Tax Collection Requirements Imposed on Out-of-State Internet Retailers

California recently enacted legislation that aims to collect revenue from a novel source: out-of-state internet retailers. The statute achieves this goal by imposing greater responsibilities for collection of use taxes on these retailers. While the State\u27s objective is laudable, the new law missed the mark from the start. The use tax collection law makes an exception for out-of-state online retailers that engage in their business through Google, Inc., an internet business having an obvious California nexus. This Note analyzes long-standing and recent case authority and legislative policy to provide an alternative that will better meet the State\u27s needs

Reconciling Brady and Pitchess: Association for Los Angeles Deputy Sheriffs v. Superior Court, and the Future of Brady Lists

In 2014, the Los Angeles County Sherriff’s Department (LASD) joined a growing number of law enforcement agencies utilizing “Brady lists”; a system by which prosecutorial agencies are notified of potential Brady/Giglio material in a police officer’s personnel file. These lists enable prosecutors to comply with their constitutional Brady disclosure obligations—to turn over all evidence material to guilt or punishment, including impeachment material. However, in 1978 California made the contents of police officer personnel files confidential with the passage of the Pitchess statutes. Since that time, California courts have wrestled with the extent of allowable disclosure under the Pitchess statutes, including whether disclosure of an officer’s name would violate Pitchess confidentiality. Following a legal challenge to the LASD “Brady list” policy by the union representing Los Angeles deputy sheriffs (ALADS), the California Court of Appeal for the Second District held that Pitchess confidentiality prevented the disclosure of names on a “Brady list” to prosecutors. This decision has, for a time, threatened the continued use of Brady lists in California and increased the potential for Brady violations by California prosecutors. The California Supreme Court has since granted review of the case. In light of the Court’s recent promulgation of new rules mandating broad disclosure by prosecutorial agencies—as well as revelations of prosecutorial misconduct within district attorney offices throughout California — the California Supreme Court should preserve the use of “Brady lists.” Disclosure of officer names to members of the prosecutorial team can, and should be, distinguished from the previously established limitations on disclosure to news outlets via California Public Records Act requests. Additionally, California should look to the federal system to craft a policy mandating disclosure by officers themselves, to allow for robust Brady disclosure while preserving Pitchess protections