Shock wave induced vaporization of porous solids

Strong shock waves generated by hypervelocity impact can induce vaporization in solid materials. To pursue knowledge of the chemical species in the shock-induced vapors, one needs to design experiments that will drive the system to such thermodynamic states that sufficient vapor can be generated for investigation. It is common to use porous media to reach high entropy, vaporized states in impact experiments. We extended calculations by Ahrens [J. Appl. Phys. 43, 2443 (1972)] and Ahrens and O'Keefe [The Moon 4, 214 (1972)] to higher distentions (up to five) and improved their method with a different impedance match calculation scheme and augmented their model with recent thermodynamic and Hugoniot data of metals, minerals, and polymers. Although we reconfirmed the competing effects reported in the previous studies: (1) increase of entropy production and (2) decrease of impedance match, when impacting materials with increasing distentions, our calculations did not exhibit optimal entropy-generating distention. For different materials, very different impact velocities are needed to initiate vaporization. For aluminum at distention (m)<2.2, a minimum impact velocity of 2.7 km/s is required using tungsten projectile. For ionic solids such as NaCl at distention <2.2, 2.5 km/s is needed. For carbonate and sulfate minerals, the minimum impact velocities are much lower, ranging from less than 1 to 1.5 km/s

Centerscope

Centerscope, formerly Scope, was published by the Boston University Medical Center "to communicate the concern of the Medical Center for the development and maintenance of improved health care in contemporary society.

Ne II Observations of Gas Motions in Compact and Ultracompact H II Regions

We present high spatial and spectral resolution observations of 16 Galactic compact and ultracompact H II regions in the [Ne II] 12.8 mu m fine-structure line. The small thermal width of the neon line and the high dynamic range of the maps provide an unprecedented view of the kinematics of compact and ultracompact H II regions. These observations solidify an emerging picture of the structure of ultracompact H II regions suggested in our earlier studies of G29.96-0.02 and Mon R2 IRS 1; systematic surface flows, rather than turbulence or bulk expansion, dominate the gas motions in the H II regions. The observations show that almost all of the sources have significant (5-20 km s(-1)) velocity gradients and that most of the sources are limb-brightened. In many cases, the velocity pattern implies tangential flow along a dense shell of ionized gas. None of the observed sources clearly fits into the categories of filled expanding spheres, expanding shells, filled blister flows, or cometary H II regions formed by rapidly moving stars. Instead, the kinematics and morphologies of most of the sources lead to a picture of H II regions confined to the edges of cavities created by stellar wind ram pressure and flowing along the cavity surfaces. In sources where the radio continuum and [Ne II] morphologies agree, the majority of the ionic emission is blueshifted relative to nearby molecular gas. This is consistent with sources lying on the near side of their natal clouds being less affected by extinction and with gas motions being predominantly outward, as is expected for pressure-driven flows.NSF AST-0607312, NSF-0708074SOFIA USRA8500-98-008NYSTAR Faculty Development ProgramNASA NNG 04-GG92G, CAN-NCC5-679Lunar and Planetary InstituteAstronom

Long-range electron transfer in structurally engineered pentaammineruthenium (histidine-62) cytochrome c

In many biological processes, long-range electron transfer (ET) plays a key role. When the three-dimensional structures of proteins are accurately known, use of modified proteins and protein-protein complexes provides an experimental approach to study ET rates between two metal centers. For Ru(His)- modified proteins, the introduction of histidine residues at any desired surface location by site-directed mutagenesis opens the way for systematic investigations of ET pathways

Equation of state of forsterite

Shock wave data for pure forsterite with initial bulk densities of 2.6 and 3.1 g/cm^3 are obtained to 0.370 Mb by impacting series of specimens with tungsten alloy plates that are launched at speeds of up to 2.3 km/sec with a high-performance propellant gun. The onset of a shock-induced phase change, probably corresponding to the forsterite-‘post spinel’ phase change is observed at 0.280±0.025 Mb. Because of the low shock temperatures, the transition is believed to be limited by the reaction rate and this pressure value should be taken only as an upper limit. Adiabats derived from the Hugoniot data for the forsterite phase are fit to the two-parameter finite strain Birch-Murnaghan equation and to two simple ionic equations of state. The Birch-Murnaghan form of the equation of state gives a zero-pressure bulk modulus (1.29 Mb) that agrees more closely with the ultrasonic data than the modulus obtained from the ionic equations of state. An unusual relaxation effect, in which the elastic shock precursor velocity varies from 5.8 to 9.5 km/sec, is also observed. The characteristic time of the relaxation process appears to be less than 1 μsec

Machine Learning Stock Market Prediction Studies: Review and Research Directions

Stock market investment strategies are complex and rely on an evaluation of vast amounts of data. In recent years, machine learning techniques have increasingly been examined to assess whether they can improve market forecasting when compared with traditional approaches. The objective for this study is to identify directions for future machine learning stock market prediction research based upon a review of current literature. A systematic literature review methodology is used to identify relevant peer-reviewed journal articles from the past twenty years and categorize studies that have similar methods and contexts. Four categories emerge: artificial neural network studies, support vector machine studies, studies using genetic algorithms combined with other techniques, and studies using hybrid or other artificial intelligence approaches. Studies in each category are reviewed to identify common findings, unique findings, limitations, and areas that need further investigation. The final section provides overall conclusions and directions for future research