Gravitational coagulation of charged cloud drops in turbulent flow

Summary Gravitational coagulation of particles in turbulent flow is investigated with respect to the electrostatic forces. As turbulence mixes particle trajectories at large distances, its account reduces the consideration of drawing particles together till some definite distance. Taking into account hydrodynamical forces of interaction, series converging faster thanHocking's one and their more exact values are obtained. For electrostatic forces series with better convergence are also obtained. Equations of moment were solved numerically on electronic computer BESM-2. Results of collection efficiency computation are given.     

Annual precipitation since 515 BC reconstructed from living and fossil juniper growth of northeastern Qinghai Province, China

Annual precipitation for the last 2,500 years was reconstructed for northeastern Qinghai from living and archaeological juniper trees. A dominant feature of the precipitation of this area is a high degree of variability in mean rainfall at annual, decadal, and centennial scales, with many wet and dry periods that are corroborated by other paleoclimatic indicators. Reconstructed values of annual precipitation vary mostly from 100 to 300 mm and thus are no different from the modern instrumental record in Dulan. However, relatively dry years with below-average precipitation occurred more frequently in the past than in the present. Periods of relatively dry years occurred during 74–25 BC, AD 51–375, 426–500, 526–575, 626–700, 1100–1225, 1251–1325, 1451–1525, 1651–1750 and 1801–1825. Periods with a relatively wet climate occurred during AD 376–425, 576–625, 951–1050, 1351–1375, 1551–1600 and the present. This variability is probably related to latitudinal positions of winter frontal storms. Another key feature of precipitation in this area is an apparently direct relationship between interannual variability in rainfall with temperature, whereby increased warming in the future might lead to increased flooding and droughts. Such increased climatic variability might then impact human societies of the area, much as the climate has done for the past 2,500 years.     

Post-mortem transport of freshwater mollusc shells in the northern Caspian Sea: A cautionary note on the implications for palaeoecological reconstructions

Fossils of stenohaline taxa are frequently used in palaeoecological and archaeological investigations to indicate the former position of deltas or the occurrence of freshwater conditions. However, the post-mortem transport of freshwater mollusc shells from deltaic and other areas can complicate interpretation of fossil assemblages. We present an example from the north Caspian Sea that shows that failure to consider these taphonomic processes can lead to erroneous conclusions.     

Geochemical features of the ore-bearing medium in uranium deposits in the Khiagda ore field

The Neogene uranium deposits of the Khiagda ore field (KOF) belong to the paleovalley variety of the hydrogene type and differ from other deposits of this genetic type in the geological and geochemical localization conditions. The contemporary hydrogeochemical setting and microbiological composition of ore-bearing medium are discussed. The redox potential of the medium (Eh is as low as–400 mV) is much lower than those established at other hydrogenic deposits, both ancient Late Mesozoic and young Late Alpine, studied with the same methods in Russia, Uzbekistan, and southern Kazakhstan. The pH of subsurface water (6.86–8.13) differs in significant fluctuations both between neighboring deposits and within individual ore lodes. Hydrogen-forming and denitrifying bacteria are predominant in microbiological populations, whereas sulfate-reducing bacteria are low-active. The consideration of these factors allowed us to describe the mechanism of uranium ore conservation as resulting from the development of the cryolithic zone, which isolates ore lodes from the effect of the external medium. Carbonated water supplied from the basement along fault zones also participates in the formation of the present-day hydrogeochemical setting. Based on the features of the ore-bearing medium, we propose a method of borehole in situ acid leaching to increase the efficiency of mining in the Khiagda ore field.     

An approach to large-scale field stress determination

The construction of stable structures in rock masses requires knowledge of the in situ stresses at the scale of excavations. However, the measurements obtained by the conventional overcoring technique are related to a small scale (centimetres). To extrapolate them to the scales of interest to rock mechanics (from meters to kilometres) requires a large number of individual stress measurements, followed by statistical analysis to avoid a considerable scatter of the measured values. In this paper, a method is proposed based on (a) large-scale surface stress and modulus measurements using the cylindrical jack method complemented by a special measuring scheme and then (b) back analysis for a given excavation shape. The method allows the simultaneous reconstruction of the stress components at the scale of excavation. A numerical simulation for a cylindrical excavation in an isotropic rock mass demonstrates the high accuracy and robustness of the method. The presence of a fractured zone surrounding the excavation can hamper the stress reconstruction, hence special measures should be taken to conduct the measurements in competent rock.     

Surface abundances of light elements for a large sample of early B-type stars – I. Spectral observations of 123 stars; measurements of hydrogen and helium lines; infrared photometry

High-resolution spectral observations of 123 B0–B5 stars in the main sequence evolutionary phase were obtained at two observatories, namely the McDonald Observatory (McDO) and the Crimean Astrophysical Observatory (CrAO). Accurate equivalent widths W of two Balmer lines, H β and H γ , and ten He  i lines were obtained for all the stars, as well as of the He  ii   λ 4686 line for the hottest ones. A careful analysis of the measured equivalent widths was performed. It is shown that there is a very good agreement between the W values derived from the McDO and CrAO spectra for 14 common stars. A comparison with published data leads to the conclusion that the W values measured earlier by some authors for strong He  i lines are very likely to be underestimated. Infrared photometric observations in the J , H , and K bands were performed for 70 programme stars. All these data will be used in other papers: in particular for the T _eff and log  g determination and for the He, C, N and O abundance analyses.     

A new regard on the tectonic map of the Arabian–African region inferred from the satellite gravity analysis

Satellite gravimetry is a powerful and reliable tool for regional tectono-geodynamic zonation. The studied region contains intricate geodynamical features (high seismological indicators, active rift systems and collision processes), richest structural arrangement (existence of mosaic blocks of oceanic and continental Earth’s crust of various age), and a number of high-amplitude gravity anomalies and complex magnetic pattern. The most hydrocarbon reserves of the world and other important economic deposits occur in this region. Comprehensive analysis of satellite gravity data with application of different approaches was used to develop a sequence of maps specifying crucial properties of the region deep structure. Careful examination of numerous geological sources and their combined examination with satellite gravity (main), magnetic, GPS, seismic, seismological and some other geophysical data enabled to develop a new tectonic map of the Arabian–African region. Integrated analysis of series of gravity map transformations and certain geological indicators allowed to reveal significant geodynamic features of the region.