Bianchi type-VI0 cosmological model in the general scalar-tensor theory of gravitation

The exact Bianchi type-VI₀ stiff-fluid cosmological model is obtained in the Nordtvedt-Barker general scalar-tensor theory of gravitation. Some properties of the model are discussed.     

Joint Russian-American hydrogeological-geochemical studies of the Karachai-Mishelyak system, South Urals, Russia

 In September 1994, a Russian-American team conducted hydrogeological, geochemical, geophysical, and radiometric measurements in the territory of the Mayak Production Association, Russia. The primary purpose of these operations was to examine the frontal area of a radioelement- and nitrate-laden groundwater plume moving from the disposal site, Lake Karachai, toward the Mishelyak River. Activities encompassed (1) isolation of hydrologic intervals in two wells and production of water from these intervals, to compare isolated versus open-well sampling methods and to determine hydraulic transmissivities of the aquifer(s); (2) surface and soil-water sampling, accompanying radiometric measurements and subsequent chemical analyses; and (3) electrical resistivity profiling in areas of expected contrasting resistivity. Preliminary results indicate that (1) ⁶⁰Co, ¹³⁷Cs, and ⁹⁰Sr are present in small concentrations (∼0.1% of permissible levels) in water of the Mishelyak River; (2) analyses of water samples collected by a downhole sampler and of water produced from packed-off intervals agree within limits of laboratory accuracy, attesting to the efficacy of the sampling methods presently used by the Russian workers; (3) considerable differences in contaminant concentrations exist between nearby wells, supporting the concept that the plume from Lake Karachai toward the Mishelyak River is controlled by steeply dipping fractures and shear zones; and (4) strong contrasts occur between the electrical resistivities of soil and bedrock. Further collaborative work is strongly recommended and should include more detailed isolation of intervals in wells by multi-packer installations, to better determine the geochemical and hydrological characteristics of the Karachai-Mishelyak system; deployment of a broader soil water and soil sampling array; a more detailed examination of the distribution and concentration of radionuclides by high-resolution field gamma spectrometry; and a detailing of the area's electrical resistivity setting, using a mobile electromagnetic measurement system. Received: 22 January 1996 · Accepted: 1 April 1996     

EPR evidence for maghemitization of magnetite in a tropical soil

Electron paramagnetic spectroscopy (EPR) was used in combination with standard rock magnetic methods to study magnetic minerals in a tropical soil. The susceptibility and hysteresis measurements showed magnetite grains with a Curie temperature near 850 K as the dominant magnetic remanence carriers in the soil. A minor Ti content in the magnetite was found by energy dispersive X-ray analysis. In order to get insight into the weathering status of the magnetite, different chemical treatments, including oxalate and citrate–bicarbonate–dithionite (CBD) extraction, were applied to the soil samples. The hysteretic properties exhibited no significant differences between the untreated and the CBD or oxalate treated samples. By contrast, the comparison of the EPR spectra revealed a significant broadening of the linewidth (δB) and a shift of the g -values ( g _eff) to lower fields after the CBD treatment. Furthermore, the spectral parameters g _eff and δB exhibited an angular dependence. At low temperature, the CBD treated samples showed a jump in δB between 120 and 100 K, the temperature range characteristic for the Verwey transition in magnetite. The changes in the spectral properties after the CBD treatment, which dissolves ferric oxides, were attributed to the removal of maghemite formed by the oxidation of magnetite, that is, during the maghemitization of the magnetite grains.     

河南省义马县中侏罗统义马组兽脚类恐龙足印化石的发现及其意义

本文记述了河南省义马县中侏罗世地层中首次发现的大型兽脚类恐龙足印。该足印虽然与发现于下—中侏罗统的张北足印类似,但是又不完全相同,从而命名为该属的一新种:徐氏张北足印(新足迹种):Changpeipus xuianainchnosp. nov.。它具有以下特征:足印的长度与宽度的比率约为1.9,第Ⅱ趾长度稍短于第Ⅳ趾的长度;第Ⅱ和第Ⅲ趾之间的夹角约为25°;第Ⅲ和第Ⅳ趾之间的夹角约为32°,足印的后部具有蹠骨所留下的印痕。徐氏张北足印的发现,不仅为我国中侏罗世恐龙足印增加了新的成员,而且为将来在该地区中侏罗世的地层中发现大型兽脚类恐龙骨骼化石提供确凿的依据。     

Origin of high field strength element enrichment in volcanic arcs: Geochemical evidence from the Sulu Arc, southern Philippines

Lavas from the Sulu Arc, southern Philippines, exhibit an enrichment in high field strength elements (HFSE) that represents a departure from the typical volcanic arc geochemical signature. It has been postulated that this relative enrichment arises from metasomatism of mantle wedge peridotites by melts derived from the subducting oceanic lithosphere, through formation of amphibole which subsequently breaks down and enriches the mantle source of parental arc magmas in HFSE. Divergent chemical and isotopic characteristics between Sulu Arc HFSE-enriched lavas and the Sulu Sea crust being subducted—the presumed source of slab-derived melts—render it unlikely, however, that HFSE enrichment arises from the influence of such melts. New geochemical data suggest that the varying degrees of HFSE enrichment in Sulu Arc lavas are instead the result of variable amounts of mixing between enriched and depleted mantle end-components—the sources of South China Sea intraplate lavas and Sulu seafloor basalts, respectively—within a compositionally heterogeneous mantle wedge.     

Simulation of rain-bearing summer monsoon systems along the west coast of India by use of ARMEX re-analysis

Re-analysis, using surface, upper-air, and satellite observations specially collected during the Arabian Sea Monsoon Experiment-I (ARMEX-I), has been performed with a global data assimilation system at T-80/L18 resolution. Re-analysis was performed for the entire ARMEX-I period (15th June–16th August 2002). In this paper we discuss the results based on re-analysis and subsequent forecasts for two successive intensive observation periods associated with heavy rainfall along the west coast of India during 2–12 August, 2002. Results indicate that the re-analysed fields can bring out better synoptic features, for example troughs along the west coast and mid tropospheric circulation over the Arabian Sea. Simulated rainfall distribution using re-analysis as initial condition also matches observed rainfall better than data from the initial analysis.     

Sea-breeze-initiated rainfall over the east coast of India during the Indian southwest monsoon

Sea-breeze-initiated convection and precipitation have been investigated along the east coast of India during the Indian southwest monsoon season. Sea-breeze circulation was observed on approximately 70–80% of days during the summer months (June–August) along the Chennai coast. Average sea-breeze wind speeds are greater at rural locations than in the urban region of Chennai. Sea-breeze circulation was shown to be the dominant mechanism initiating rainfall during the Indian southwest monsoon season. Approximately 80% of the total rainfall observed during the southwest monsoon over Chennai is directly related to convection initiated by sea-breeze circulation.