Hard X-ray spectrum of Mkn 421 during the active phase

Spectral measurement of Mkn 421 were made in the hard X-ray energy band of 20–200 keV using a high sensitivity, large area scintillation counter telescope on November 21, 2000 and these coincided with the onset of an active X-ray phase as seen in the ASM counting rates on board RXTE. The observed spectrum can not be fitted to a single power law similar to the PDS data of BeppoSAX. The data can be fitted both by a two component power-law function or a combination of an exponential function with a power law component at the high energies above 80 keV. We identify these components with those arising from the synchrotron self compton and the high energy power-law tail arising from the upgrading of the thermal photons due to multiple Compton scattering a la Cyg X-1. A comparison with the earlier data clearly suggests a spectral variability in the hard X-ray spectrum of the source. We propose a continuously flaring geometry for the source as the underlying mechanism for energy release.     

Dahmani,a highly oxidised LL6 chondrite bearing Ni-rich taenite

Abstract Dahmani is a shocked LL6 fragmental breccia. According to the composition of the silicates (olivine Fa_30,32.6, orthopyroxene Fs_24.5–26.3) and of the metal (a 60% Ni taenite) it is one of the most oxidised known.     

Planetary cratering 1. The question of multiple impactor populations: Lunar evidence

Abstract— This paper addresses several current issues related to use of craters in interpreting planetary surface histories. The primary goal is to test the widely adopted hypothesis of multiple populations of impactors at different times or places in the Solar System. New data presented here revise a “lunar highland” crater diameter distribution that has been widely used as evidence of an early distinct population of impactors. This curve, which has a depression of the size distribution at mid-sizes, does not, in fact, represent the lunar highlands generally. I show that it is associated with regions of intercrater plains. The more extensive the obliteration by intercrater plains, the deeper the depression. Modeling indicates that the depression of the curve is caused by the obliteration process itself. The oldest, most cratered regions of lunar highlands do not show the depression. These findings call into question earlier interpretations of multiple populations of impactors in the Solar System and of a distinctive primordial population. The present work is consistent, instead, with (1) a relatively uniform size distribution of interplanetary impactors, of mixed origins, back to 4 Ga ago and throughout the sampled Solar System; (2) fragmentation as the process that produced that size distribution; (3) saturation equilibrium on the most heavily cratered surfaces; and (4) differences in structure in the size distribution caused not by distinct impactor populations but by episodes of endogenic obliteration. If accepted, these results would modify some studies of solar system evolution, including assertions of two to five distinct populations of impactors, assumptions of lack of saturation equilibrium, and identifications of specific heliocentric or planetocentric sources for impactors within outer planet satellite systems.     

Time-dependent scattering and transmission function in an anisotropic two-layered atmosphere

In this paper we consider the time-dependent diffuse reflection and transmission problems for a homogeneous anisotropically-scattering atmosphere of finite optical depth and solve it by the principle of invariance. Also we consider the time-dependent diffuse reflection and transmission of parallel rays by a slab consisting of two anisotropic homogeneous layers, whose scattering and transmission properties are known. It is shown how to express the time-dependent reflected and transmitted intensities in terms of their components. In a manner similar to that given by Tsujita (1968), we assumed that the upward-directed intensities of radiation at the boundary of the two layers are expressed by the sum of products of some auxiliary functions depending on only one argument. Then, after some analytical manipulations, three groups of systems of simultaneous integral equations governing the auxiliary functions are obtained.     

Evolution of short period meteoroid streams

The dynamical evolution of meteoroid streams associated with cornets Encke, Halley, Machholz 1986 VIII and asteroid Phaethon is discussed. It is shown that the planetary perturbations can greatly increase the streams thickness and each stream may produce several couples of meteor showers active in different seasons of the year. The theoretical and observed data are in a satisfactory accordance.     

Searching for Planetary Eclipses in Open Clusters: NGC 7086

In an attempt to discover planetary eclipses, we observed the open cluster NGC 7086. On one night we observed the cluster and standard stars through the B and V filters, enabling us to make a colour-magnitude diagram. Plots of the differential magnitudes were inspected for variability, but no planetary eclipses were found. New variable stars were discovered and their light curves show some of them to be eclipsing binary stars. The location on the colour-magnitude diagram of some of the variable stars is consistent with cluster membership.     

A micromechanical finite element model for linear and damage‐coupled viscoelastic behaviour of asphalt mixture

This study presents a finite element (FE) micromechanical modelling approach for the simulation of linear and damage‐coupled viscoelastic behaviour of asphalt mixture. Asphalt mixture is a composite material of graded aggregates bound with mastic (asphalt and fine aggregates). The microstructural model of asphalt mixture incorporates an equivalent lattice network structure whereby intergranular load transfer is simulated through an effective asphalt mastic zone. The finite element model integrates the ABAQUS user material subroutine with continuum elements for the effective asphalt mastic and rigid body elements for each aggregate. A unified approach is proposed using Schapery non‐linear viscoelastic model for the rate‐independent and rate‐dependent damage behaviour. A finite element incremental algorithm with a recursive relationship for three‐dimensional (3D) linear and damage‐coupled viscoelastic behaviour is developed. This algorithm is used in a 3D user‐defined material model for the asphalt mastic to predict global linear and damage‐coupled viscoelastic behaviour of asphalt mixture. For linear viscoelastic study, the creep stiffnesses of mastic and asphalt mixture at different temperatures are measured in laboratory. A regression‐fitting method is employed to calibrate generalized Maxwell models with Prony series and generate master stiffness curves for mastic and asphalt mixture. A computational model is developed with image analysis of sectioned surface of a test specimen. The viscoelastic prediction of mixture creep stiffness with the calibrated mastic material parameters is compared with mixture master stiffness curve over a reduced time period. In regard to damage‐coupled viscoelastic behaviour, cyclic loading responses of linear and rate‐independent damage‐coupled viscoelastic materials are compared. Effects of particular microstructure parameters on the rate‐independent damage‐coupled viscoelastic behaviour are also investigated with finite element simulations of asphalt numerical samples. Further study describes loading rate effects on the asphalt viscoelastic properties and rate‐dependent damage behaviour. Copyright © 2006 John Wiley & Sons, Ltd.