Direct detection of the secondary spectrum of the interacting eclipsing binary TX UMa

Eclipsing binary TX UMa was observed with the D.A.O. high-dispersion spectrographs in 1969–1970, with emphasis on the detailed coverage of the primary minimum. One spectrum was taken exclusively within totality, thus exhibiting an uncontaminated spectrum of the secondary component. This leads to spectral reclassification of the secondary (F6 IV). The narrowing of the line profile of the H-line in totality is interpreted in terms of synchronous rotation of the secondary (v sini80 km s^–1) while the primary rotates faster (v sini130 km s^–1) than synchronously (v sini50 km s^–1). Although the secondary does not fill in its Roche lobe fully, the system exhibits pronounced indications of rather strong physical interaction. This is now supported also by the profound changes of the line profiles of the H-line with phase.     

Particle-Velocity-Field Difference Smoothing for Coherent Source Localization in Spatially Nonuniform Noise

This communication considers the problem of estimating 2-D directions of arrival (DOAs) of multiple coherent signals under spatially nonuniform noise (spatially inhomogeneous temporary white noise) using an array of vector hydrophones. A novel preprocessing method called particle-velocity-field difference smoothing (PVFDS) is proposed. The key idea underlying the PVFDS is to remove the spatially nonuniform noise by using the matrix difference of pairs of particle-velocity data correlation matrices, and to decorrelate the coherent signals by summing these difference correlation matrices. Unlike most of other existing preprocessing techniques, such as spatial smoothing and forward–backward averaging, the PVFDS processing does not decrease the array aperture. For arbitrary array geometries, the PVFDS can resolve up to four coherent signals, and for centro–symmetric arrays, forward–backward averaging can double this number to eight. Monte Carlo simulations illustrate that the PVFDS-based eigenstructure algorithms can offer better performance than the particle-velocity-field smoothing (PVFS)-based counterparts.      

Simulation of hydraulic fracture propagation near a natural fracture using virtual multidimensional internal bonds

A virtual multidimensional internal bond (VMIB) model developed to simulate the propagation of hydraulic fractures using the finite‐element method is formulated within the framework of the virtual internal bond theory (VIB) that considers a solid as randomized material particles in the micro scale, and derives the macro constitutive relation from the cohesive law between the material particles with an implicit fracture criterion. Hydraulic pressure is applied using a new scheme that enables simulation of hydraulically driven cracks. When the model is applied to study hydraulic fracture propagation in the presence of a natural fracture, the results show the method to be very effective. It shows that although the in situ stress ratio is the dominant factor governing the propagation direction, a natural fault can also strongly influence the hydraulic fracture behavior. This influence is conditioned by the shear stiffness of the fault and the distance to the original hydraulic fracture. The model results show that when the fault is strong in shear, its impact on hydraulic fracture trajectory is weak and the hydraulic fracture will likely penetrate the fault. For a weak fault, however, the fracture tends to be arrested at the natural fault. The distance between the fault and the hydraulic fracture is also important; the fault influence increases with decreasing distance. The VMIB does not require selection of a fracture criterion and remeshing when the fracture propagates. Therefore, it is advantageous for modeling fracture initiation and propagation in naturally fractured rock. Copyright © 2010 John Wiley & Sons, Ltd.     

Shift trend and step changes for runoff time series in the Shiyang River basin,northwest China

Shift trend and step changes were detected for runoff time series in the Shiyang River basin, one of the inland river basins in north‐west China. Annual runoff data from eight tributaries as well as both annual and monthly runoff from the mainstream from 1958 to 2003 were used. Seven statistical test methods were employed to identify the shift trends and step changes in the study. Mann–Kendall test, Spearman's Rho test, linear regression and Hurst exponent were used to detect past and future shift trends for runoff time series, while the distributed‐free CUSUM test, cumulative deviations and the Worsley likelihood ratio test were used to detect step changes for the same time series. Results showed that the annual runoff from Zamu, Huangyang and Gulang rivers, as well as both annual and monthly runoff from the mainstream, show statistically significant decreasing trends. Future tendency of runoff for both tributaries and mainstream were consistent with that from 1958 to 2003. Step changes probably occurred in 1961 for the runoff from Huangyang, Gulang and Dajing rivers according to the Worsley likelihood ratio test, but no similar results were found using the other two test methods. Three change points (1979, 1974 and 1973) were detected for the mainstream using different methods. These change points were close to the years that reservoirs started to be operated. Both climate change and human activities, especially the latter, contributed to the decreasing runoff in the study area. Between 21% and 79% of the reduction in runoff from the mainstream was due to the impact of human activities during the past few decades. Copyright © 2008 John Wiley & Sons, Ltd.     

Characteristics and distribution of clay minerals and their effects on reservoir quality: Huagang Formation in the Xihu Sag,East China Sea Basin

Abstract

The characteristics and distribution of clay minerals and their effects on reservoir quality in the Huagang sandstones in the Xihu Sag, East China Sea Basin were studied by using X-ray diffraction, casting thin-sections, scanning electron microscopy, electron microprobe analysis, fluid inclusion analysis, constant-rate mercury injection and nuclear magnetic resonance. Clay minerals consist of kaolinite, chlorite, illite and illite–smectite mixed layer (I/S); kaolinite forms from dissolved feldspars, chlorite occurs as clay coatings that are transformed from clay precursors owing to the flocculation of suspended detrital clays or the crystallisation of pore fluids, and illite forms from the illitisation of detrital smectite, authigenic kaolinite and K-feldspars. Clay distribution is controlled by sedimentary environments, burial history and lithologies. Typical reservoirs in the western sub-sag are thin and developed in braided river facies at relatively shallow burial depths with clays dominated by kaolinite. However, typical reservoirs in the central inversion tectonic zone are thicker and developed in a braided delta front facies at deeper burial depths with clays mainly consisting of chlorite, illite and I/S. High-quality reservoirs are characterised by coarse granularity, high quartz content and low clay content with widespread development of chlorite coatings that inhibit quartz cements at low temperatures. At higher temperatures, the high-quality reservoirs develop more pores providing growth space for quartz cements and result in the coexistence of chlorite coatings and quartz cements. The high-quality reservoirs are controlled by their lithological characteristics rather than chlorite coatings. Illite and I/S clays create severe damage to reservoirs by reducing the size and connectivity of pore-throats.     

Long‐term trend analysis for major climate variables in the Yellow River basin*

Some previous studies have shown that drying‐up of the lower Yellow River resulted from decreasing precipitation and excessive industrial and agricultural consumption of water from the middle and downstream regions of the Yellow River. On the basis of average air temperature, precipitation, and pan evaporation data from nearly 80 gauging stations in the Yellow River basin, the monotonic trends of major climate variables over the past several decades are analysed. The analysis was mainly made for 12 months and the annual means. The isograms for annual and typical months are given in the paper. The result shows that the average temperature in the study area exhibits an increasing trend, mainly because of the increase of temperature in December, January and February. The largest trend is shown in December and the smallest is in August. There are 65 of 77 stations exhibiting a downward trend for annual precipitation. In all seasons except summer, there is a similar trend in the upstream region of the Yellow River, south of latitude 35°N. It is interesting to note that the pan evaporation has decreased in most areas of the Yellow River basin during the past several decades. April and July showed the greatest magnitude of slope, and the area from Sanmenxia to Huayuankou as well as the Yiluo River basin exhibited the strongest declining trend. The conclusion is that the decreasing pan evaporation results from complex changes of air temperature, relative humidity, solar radiation, and wind speed, and both climate change and human activities have affected the flow regime of the Yellow River during the past several decades. Copyright © 2007 John Wiley & Sons, Ltd.     

Investigation on strength and stability of jointed rock mass using three‐dimensional numerical manifold method

This paper proposes a numerical model for jointed rock masses within the 3‐D numerical manifold method (NMM) framework equipped with a customized contact algorithm. The strength of rock sample containing a few sets of discontinuities is first investigated. The results of models with simple geometries are compared with the available analytical solutions to verify the developed computer code, whereas models with complex geometries are simulated to better understand the fundamental behavior and failure mechanism of jointed rock mass. Furthermore, the stability of jointed rock mass in an underground excavation is studied, where rock failure process is determined by the 3‐D NMM simulation. The simulation results provide valuable guidance on excavation process design and stabilization design in rock engineering practice. Copyright © 2012 John Wiley & Sons, Ltd.     

Isotopes and geochemistry in a managed aquifer recharge scheme: a case study of fresh water injection at the Damascus University Campus,Syria

A combination of stable isotopes (¹⁸O and ²H) and hydrochemistry has been applied to investigate storage processes in relation to aquifer storage and recovery (ASR) of the shallow alluvial Quaternary aquifer in Damascus basin. The stored water, entirely taken from the Figeh springs during flood periods, was injected in a single well having a brackish groundwater. Water samples were collected from four observation wells drilled in the Damascus University Campus (DUC) site during a 3‐year period (2006–2008). The injectant water, which deviates in its chemical and isotopic signatures from that of the ambient groundwater, shows that the stored water plume remains within close proximity to the injection well (IW) (<≈ 100 m). Thus, only two wells (W13 and W14) located at a distance less than 80 m from the injection point were affected by this injection. The observation wells located at longer distances from the IW (≈145 m and ≈ 600 m for wells W15 and WHz, respectively) were completely unaffected by the injection. Although most of the chemical and isotopic parameters usefully reflected the mixing process that occurs between the injectant water and ambient groundwater, the stable isotope (¹⁸O) and chloride (Cl⁻) were the most sensitive parameters that quickly reflect this signature. Using a simple mass balance, the calculated proportion of injectant water reaching the well W13 was in the range of 50–90%. This proportion was even lower (30–55%) in the case of well W14. Although the drought event prevailing during this study did not much help to inject further amounts of water, higher than the injected volume (0·2416 M m³) and also not favourable to better evaluate the fate and subsurface hydrological processes, these findings offer encouragement to continue the ASR activities, as an alternative way for better management of water resources in this basin facing intensive problems. Copyright © 2010 John Wiley & Sons, Ltd.