Extracting nuclear transparency from p,2p-A and e,e′p-A cross sections

We study nuclear-structure effects on the transparency in high-transverse-momentum (p,2p) and (e,e′p) reactions. We show that in the eikonal-distorted-wave impulse approximation (EDWIA), even when correlations are included, one can get a factorized expression for the transparency which depends only on the average nucleon density (r) and a correlation function. A technique is developed to include correlations in a Glauber calculation, where we use a Monte Carlo method for integration over the nuclear coordinates. We compare calculations of T using the EDWIA formalism, and a continuous density, with a Monte Carlo method based on discrete nucleons.     

GaP semiconducting-to-metal transition near 220 kbar and 298°K

Resistometric measurements were made on polycrystalline GaP to pressures above 250 kbar. Reproducible resistance changes of more than four orders of magnitude were observed near 220 kbar. This transition is in excellent agreement with the prediction of the Van Vechten-Phillips dielectric theory of electronegativity in covalent systems.     

On the equation of pulsating flame fronts in solid fuel combustion

A strongly nonlinear equation describing the dynamics of pulsations in solid fuel combustion is obtained. The method consists of extending the problem via introduction of an artificial parameter into boundary conditions leading to a separation of the spatial and the temporal scales within a low-frequency region. The interface dynamics equation obtained through an asymptotic expansion is then extrapolated toward the original values of parameters. The key point in the derivation is to restore the unexpected form of the principal nonlinearity generating a strongly dissipative region near a stagnation point of the front which is responsible for the stability of pulsations. The results of a numerical simulation of the equation demonstrate strongly relaxational stable oscillations of the flame front velocity.     

Auxiliary functions of the PsbO, PsbP and PsbQ proteins of higher plant Photosystem II: a critical analysis

Numerous studies over the last 25 years have established that the extrinsic PsbO, PsbP and PsbQ proteins of Photosystem II play critically important roles in maintaining optimal manganese, calcium and chloride concentrations at the active site of Photosystem II. Chemical or genetic removal of these components induces multiple and profound defects in Photosystem II function and oxygen-evolving complex stability. Recently, a number of studies have indicated possible additional roles for these proteins within the photosystem. These include putative enzymatic activities, regulation of reaction center protein turnover, modulation of thylakoid membrane architecture, the mediation of PS II assembly/stability, and effects on the reducing side of the photosystem. In this review we will critically examine the findings which support these auxiliary functions and suggest additional lines of investigations which could clarify the nature of the functional interactions of these proteins with the photosystem.     

Variation of superparamagnetic properties with iron loading in mammalian ferritin

The average blocking temperatures of ferritin molecules containing differing amounts of iron were determined by Mossbauer spectroscopy. The results imply that the magnetic anisotropy of the ferritin core particles is a function of particle volume. By addition of⁵⁷Fe to ferritin core particles it was determined that, at a given temperature within the superpara-magnetic temperature region, the “last-in” ferric ions have average relaxation times that are shorter than those of the bulk ferric ions.     

High pressure equation of state and sound velocities to fourth order elastic constants. Application to sodium chloride to 270 kbars

Using the theory of small deformation superposed on a finite strain, we expand the strain energy to fourth order in terms of the strain invariants, and derive an athernal expression for the equation of state and the longitudinal and shear velocities of sound of a homogeneous Isotropic material to fourth order elastic constants. We evaluate reported velocity data in sodium chloride by Voronov and Grigorev to 80 kbar in terms of our formulation, to predict the equation of state to 270 kbar. Experiments performed in our laboratory (Frankel, Rich, and Homan) to 270 kbar which use ultrasonic interferometry to obtain resonance frequency intervals in the specimen were also evaluated. Both results are in good agreement with Decker's equation of state.     

High magnetic field behavior of iron impurities in chromium

Mössbauer measurements in ⁵⁷Fe in dilute FeCr alloys in external magnetic fields up to 140 kOe are presented. The magnetic hyperfine interactions are compared with results obtained by Herbert, Clark and Wilson and are discussed in terms of a model due to Housley and Dash.     

Profiling natural product biosynthesis

Natural products are a rich source of therapeutics; however, artificially reengineering the biosynthetic pathways that generate these compounds could potentially generate "designer" drugs. Last month in Chemistry & Biology, Burkart and coworkers reported their technique to track and better understand the components of these pathways.     

Compressible flow induced by the transient motion of a wavemaker

The effect of fluid compressibility on the evolution of the pressure distribution and free surface elevation, following the initiation of a horizontal motion of a vertical wavemaker, is analysed. This effect is significant even in a liquid (like water) when the time scale of the motion is very short (e.g. impulsive motions).In the leading order the present problem is analogous to that of supersonic flow about a thin wing, thus the solution is represented by means of an appropriate supersonic source distribution. Closed-form results are obtained for the case of impulsive motion (i.e. a step function velocity). The pressure field corresponds to systems of double rarefaction and double compression waves traversing the fluid domain intermittently. Following the passage of a rarefaction (compression) wave, the free surface becomes locally concave (convex). The resulting free surface profile consists of an elongating wavetrain in front of a jet riding up the vertical wall.On the compressible time-scale the pressure and velocity fields approach a steady long-time limit. This limit corresponds to the short-time incompressible flow prevailing after the attenuation of the pressure waves. The spatial nonuniformity of the asymptotic expansion in the neighbourhood of the waterline is briefly discussed.