Effect of particle acceleration process on the flare characteristics of blazars

Following the kinetic equation approach, we study the flare processes in blazars in the optical-to-X-ray region, considering energy dependent acceleration time-scale of electrons and synchrotron and adiabatic cooling as their dominant energy loss processes.     

Eastern Aphrodite Terra on Venus: Characteristics,structure, and mode of origin

Eastern Aphrodite Terra and Western Aphrodite form an altimetrically prominent 14,000 km long part of the equatorial highlands on Venus. Several parallel linear discontinuities striking northwest across the general east-west regional strike of the highlands are mapped in the altimetric and radar image data of Eastern Aphrodite and identified on the basis of abrupt termination of rift-like central chasma, offset and segmentation of the center of the highlands, and radar image discontinuities in the lowlands to the north. These characteristics are similar to those of linear discontinuities previously mapped in Western Aphrodite in terms of length, orientation, and influence on the central highlands and adjacent lowlands.Altimetric profiles in directions parallel to the discontinuities are regionally symmetric, more ridge-like in Eastern Aphrodite compared to the plateau-dominated form of topography in Western Aphrodite, and are characterized by alternating paired ridge-and-trough forms near their crests and on their flanks. By mapping the center of symmetry in multiple profiles, the prominent segmentation of the highland is shown to be imparted by an offset of the regional symmetry along the mapped discontinuities. These characteristics are morphologically similar to several of the large-scale characteristics of divergent plate boundaries of Earth, including mid-ocean rise crests and rifts, offset at fracture zones and transform faults, and symmetric thermal boundary layer topography.The altitude of the surface in profiles parallel to the discontinuities decreases as the square root of distance from the symmetry axes and with a slope similar to that predicted for thermal boundary layer topography associated with rates of divergence on Venus of ~ 1 ± 0.5 cm/yr. In order to test the hypothesis that the linear discontinuities are analogous to fracture zones, the predicted altitude of the surface at great distance from the centers of symmetry of the central highland and in directions across the discontinuities was calculated on the basis of a thermal boundary layer topography model with offset of altimetric symmetry at each discontinuity. Similarity of observed Arecibo high-resolution altimetric profiles across the discontinuities with that calculated for thermal boundary layer topography offset by transform faults reveals that in terms of the sense and magnitude of regional steps in altimetry across discontinuities and the altitude of the surface, Eastern Aphrodite is similar to the known characteristics of crustal spreading at divergent boundaries. The plateau-like form of Western Aphrodite and the ridge-like form of Eastern Aphrodite are analogous respectively to the difference between areas of anomalous (Iceland) and normal crustal production along rise crests on Earth. Estimates of volumetric differences in crustal production in the environment of Venus and as it would be influenced by differences in mantle temperature beneath Western and Eastern Aphrodite imply that Eastern Aphrodite represents normal crustal production. On this basis, Western Aphrodite may be characterized by a mantle temperature that is warmer than the mantle beneath Eastern Aphrodite Terra, perhaps in association with deep convective mantle upwelling.'Geology and Tectonics of Venus', special issue edited by Alexander T. Basilevsky (USSR Acad. of Sci., Moscow), James W. Head (Brown University, Providence), Gordon H. Pettengill (MIT. Cambridge, Massachusetts) and R. S. Saunders (J.P.L., Pasadena).     

Stray-light measurements at the Observatorio del Teide

A new procedure to separate the instrumental and atmospheric components of stray light is presented. It is based on the dependence of the aureole's atmospheric component on the air mass and is applied to measurements taken with the Vacuum Newton Telescope (VNT) at the Observatorio del Teide (Tenerife). The resulting instrumental part is independent of the air mass.The variation of both components with wavelength is also studied. The instrumental component shows no dependence on wavelength, in contrast to the atmospheric one which is greater in the blue than in the red.It is concluded that observations with air masses larger than two will probably be strongly affected by stray light.     

Spectrophotometry of comet Levy (1990c)

Two spectrophotometric scans of comet Levy (1990c) have been analysed to estimate Haser model column densities and production rates of CN andC ₂ molecules.     

Finite-element analysis of time-dependent large-deformation problems

An updated Lagrangian finite-element formulation has been developed for time-dependent problems of soil consolidation involving finite deformations. Large plastic strains as well as rotations occur in such problems and nominal stress measures are introduced in the formulation to redefine stresses. This leads to corrective terms for equilibrium and yield violations in addition to geometric stiffening terms in the governing integral equations. The soil is considered to be either a linear elastic or an elastoplastic, critical-state material. Some simple numerical examples are studied to validate the formulation, followed by a detailed analysis of the problem of penetration of a pile into soil. The results of this problem are viewed with emphasis on the physical interpretation and practical significance.     

SHRIMP U–Pb ages of diagenetic and hydrothermal xenotime from the Archaean Witwatersrand Supergroup of South Africa

SHRIMP dating of xenotime overgrowths on detrital zircon grains can constrain maximum durations since diagenesis and therefore provide minimum dates of sediment deposition. Thus, xenotime dating has significant economic application to Precambrian sediment-hosted ore deposits, such as Witwatersrand Au–U, for which there are no precise depositional ages. The growth history of xenotime in the Witwatersrand Supergroup is texturally complex, with several phases evident. The oldest authigenic xenotime ²⁰⁷Pb/²⁰⁶Pb age obtained in sandstone underlying the Vaal Reef is 2764 ± 5 Myr (1 σ), and most likely represents a mixture of diagenetic and hydrothermal growth. Nevertheless, this represents the oldest authigenic mineral age yet recorded in the sequence and provides a minimum age of deposition. Other xenotime data record a spread of ages that correspond to numerous post-diagenetic thermotectonic events (including a Ventersdorp event at ≈ 2720 Ma) up to the ≈2020 Ma Vredefort event.     

The mass ratio of Nova Muscae 1991

We report intermediate resolution H spectroscopy of the black hole candidate Nova Muscae 1991 during quiescence. We classify the companion star as a K3-K4V which contributes 85±6 percent to the total flux from the binary. The photospheric absorption lines are broadened by 106±13 kms⁻¹ with respect to template field stars, leading to a system mass ratio of q =M₁/M₂ = 7.8_−2.0^+3.4. Doppler imaging of the H line shows strong emission coming from the secondary star (EW=3.1±0.6Å) which we associate with chromospheric activity. However, the hot-spot is not detected and this may indicate a lower mass transfer rate than in other X-ray transients of comparable orbital periods. The surface brightness distribution of the accretion disk in H follows a relation I∝R^−1.1, less steep than typically observed in cataclysmic variables. Updated system parameters are also presented.