X-ray transient sources

The galactic distribution and physical nature of X-ray transient sources is investigated. Two types of transients are considered. The observational data on 41 X-ray transient sources are given, and the average parameters of hard and soft X-ray transients are estimated.     

Mantle(?) xenoliths in the carbonatites of northern Transbaikalia

The composition and nature of high-Cr minerals in lithic clasts from the carbonatites of the Veseloe occurrence, northern Transbaikalia, were considered. In order to determine their source, the Cr-bearing phases were compared with chromite, magnetite, and rutile from ultrabasic rocks, mantle xenoliths, and eclogites. It was suggested that the xenoclasts studied were formed at great depths, whereas the carbonatites were directly derived from the mantle rather than formed by the crustal differentiation of a silicate-carbonate melt.     

Power spectrum of brightness temperature fluctuations derived from solar eclipse observations at 2.8 GHz

In this paper we report on the MEM power spectrum analysis of brightness temperature fluctuations observed at 2.8 GHz during the total solar eclipse of 16 February 1980. The observed periodicities range from 3.5 min to 64 min. These periodicities may arise due to spatial and/or temporal variations in the solar radio emission. The observed periodicities imply presence of scale sizes ranging from 70,000 to 600,000 km assuming that the brightness fluctuations arise because of spatial variation only. On the other hand, if these fluctuations are due to temporal variation, the observed periodicities correspond well to predicted modes of solar global oscillations.     

The collision singularity in a perturbed two-body problem

It is shown that, in the neighborhood of a collision singularity, the motion in a perturbed two-body problem \(\ddot r = - \mu r^{ - 3} r + P\) , whereP remains bounded, has the same basic properties as the motion in the neighborhood of a collision in the unperturbed two-body problemP=0.     

Evidence for focused hot fluid flow within the Britannia Field, offshore Scotland, UK

Fluid inclusion and scanning electron microscope‐cathodoluminescence evidence indicates focused hot, saline, diagenetic fluid flow within the Eastern Flank of the Britannia Field, offshore Scotland, UK. The fluid was sourced from the Andrew Salt Dome, 10 km to the east. The fluids, which promoted quartz cementation of the upper zones within the field, were up to ～30°C hotter and had salinities up to ～10 wt% NaCl equivalent higher than fluids from lower in the reservoir section. During diagenesis hot saline fluids migrated westwards as part of a radiating ‘diagenetic front’ from the Andrew Salt Dome. Structural dip associated with the Eastern Flank of the Fladen Ground Spur impeded the westward movement of the diagenetic fluid. The quartz cements from the upper and lower reservoir zones can be distinguished by morphology. In the upper zones the quartz cements have well‐developed macro‐crystalline zoning and heterogeneous luminescence across the grain. In the lower zones, the cements are much less developed, unzoned and very weakly luminescent. The diagenetic fluids were primarily focused into Zone 45 within the upper reservoir. Furthermore, within the Main Platform Area the most prolific producing zone is Zone 45, indicating the importance of this interval as a permeable flow unit during both diagenetic and production timescales. Within the Eastern Flank, the quartz overgrowths have a major impact on reservoir permeability and thus well productivity. The overgrowths are most extensive in the originally clean sandstones with low clay content. Clay in optimum volumes (5–10%) can inhibit nucleation of the damaging quartz overgrowths without having a detrimental effect on pore connectivity. These observations provide a predictive concept for use in the search for relative reservoir sweetspots within the degraded Eastern Flank.     

Electron paramagnetic resonance,optical absorption,and magnetic circular dichroism studies of the CO 3 − molecular-ion in irradiated natural beryl

Room temperature X-irradiation of some natural beryls produced several new absorption lines in the electron paramagnetic resonance (EPR) spectrum, a known series of optical absorption lines in the 500–700 nm range, and a shift of the absorption edge to lower energies. Several of the new EPR lines and part of the irradiation-induced shift of the absorption edge disappeared after a few days at room temperature, and were not examined in detail. However, three of the paramagnetic centres responsible for the new EPR lines were stable at room temperature and two of these have previously been identified as atomic hydrogen and the methyl radical, CH₃. These species were stable to ～150 and ～450°C respectively. The third stable species, hitherto unreported, showed a single-line EPR spectrum of axial symmetry, with g∥=2.0051 and g⊥=2.0152. This spectrum was found to be intensity-correlated with the series of optical bands in the 500–700 nm range, after thermal bleaching at 175°C. The EPR and optical spectra are therefore assigned to the same species. It is argued that this species is the CO ₃ ^? molecular ion, located in the widest part of the structural channel and aligned with the plane of the molecule perpendicular to the c axis. The EPR spectrum is consistent with a ² A′₂ ground state of a CO ₃ ^? molecule with trigonal symmetry, and this requires that the optical transition has a ² A′₂ → ² E′ character. Most of the features in the optical spectrum can be assigned to coupling of a totally symmetric mode of frequency ～1020 cm^?1 onto a zero-phonon line at 14,490 cm^?1 and a second weaker line at 16,020 cm^?1. However, both of these two fundamental lines are structured, and the two components show strong temperature-dependent derivative-shaped magnetic circular dichroism (MCD). Furthermore, the overall sign of the MCD for the line at 16,020 cm^?1 is opposite to that at 14,490 cm^?1. The separation (～120 cm^?1) of the two components of the 14,490 cm^?1 line is much larger than that expected from spin-orbit interaction, and the origin of this splitting is not yet understood.     

Non-Linear Elasto-Plastic Behaviour of Lacustrine Clay

The paper presents the experimental investigation and analysis of the non-linear elasto-plastic stress–strain behaviour of normally consolidated lacustrine clay. Drained triaxial stress path tests were performed on natural block samples of Swiss lacustrine clay. Data were analysed using plasticity theory and the shape and extent of kinematic yield and bounding surfaces were determined and found to be elliptical but not congruent. Cross-anisotropic elasticity was used to quantify elastic strains to permit plastic strain increment vectors and hence a plastic potential surface to be defined.     

Structural characteristics of zooplankton of the Shardarinskoe Reservoir and their use in water quality assessment

Data on the Shardarinskoe Reservoir are used to assess the indicator role of zooplankton community under unstable hydrological regime. The structural characteristics of zooplankton featured significant seasonal variations. The averaged indices characterized reservoir water quality at the level of mesotrophic and eutrophic water bodies. The possible use of cyclopidas to characterize toxic pollution of water is discussed.