榆林25窟一佛八菩萨图研究

在吐蕃统治敦煌时期所开凿的洞窟中,榆林25窟是相对较特殊的一个,窟内南北两壁的观无量寿经变与弥勒经变延续了盛唐洞窟中经变画的构图、风格,而正壁残存的一佛八菩萨图在造像样式上与窟内其他图像则有一定的差别。从正壁残存的主尊、菩萨名号题记中可以发现,唐代不空译《八大菩萨曼荼罗经》能够与之相对应,但是该经对八大菩萨身形的描述与榆林25窟的图像有一定差别。此图像与藏经洞中的部分绢画具有类似的风格特征,其中一部分有藏文题记,表明它们与居住在敦煌的吐蕃信众有密切的关系,而藏经洞中发现的藏文抄写的《八大菩萨曼拏罗经》可以证明此地的吐蕃信众确实信奉这一经典。一佛八菩萨的图像在吐蕃本土拉萨及青海地区屡有发现,其中西藏昌都与青海玉树的两处摩崖石刻由高僧益西央开凿,年代均在九世纪初,这些遗迹说明一佛八菩萨图像在吐蕃本土的流传情况。在这几处图像与榆林25窟的一佛八菩萨的比较中可以发现,吐蕃流行的八大菩萨图样并不十分固定,但其构图和风格是基本接近的,而榆林25窟所采用的图像可能来源于吐蕃地区。     

Are rocks still water‐wet in the presence of dense CO2 or H2S?

The various modes of acid gas storage in aquifers, namely structural, residual, and local capillary trapping, are effective only if the rock remains water‐wet. This paper reports an evaluation, by means of the captive‐bubble method, of the water‐wet character in presence of dense acid gases (CO₂, H₂S) of typical rock‐forming minerals such as mica, quartz, calcite, and of a carbonate‐rich rock sampled from the caprock of a CO₂ storage reservoir in the South‐West of France. The method, which is improved from that previously implemented with similar systems by Chiquet et al. (Geofluids 2007; 7 : 112), allows the advancing and receding contact angles, as well as the adhesion behavior of the acid gas on the mineral substrate, to be evaluated over a large range of temperatures (up to 140°C), pressures (up to 150 bar), and brine salinities (up to NaCl saturation) representative of various geological storage conditions. The water‐receding (or gas‐advancing) angle that controls structural and local capillary trapping is observed to be not significantly altered in the presence of dense CO₂ or H₂S. In contrast, some alteration of the water‐advancing (or gas‐receding) angle involved in residual trapping is observed, along with acid gas adhesion, particularly on mica. A spectacular wettability reversal is even observed with mica and liquid H₂S. These results complement other recent observations on similar systems and present analogies with the wetting behavior of crude oil/brine/mineral systems, which has been thoroughly studied over the past decades. An insight is given into the interfacial forces that govern wettability in acid gas‐bearing aquifers, and the consequences for acid gas geological storage are discussed along with open questions for future work.     

北京延庆西屯墓地出土汉代铜器的科学分析

延庆西屯墓地出土的汉代铜器对于了解北京地区汉代铜器文化特征、制作技术以及与周边地区的相互关系,具有十分重要的意义。为进一步揭示该批铜器包含的科学信息,本文对其进行了科学分析检测。结果显示,西屯墓地出土铜器的材质以铜锡铅三元合金为主,仅两件铜盆检测为铜铅二元合金、一件铜带钩为铜锡铅砷四元合金,且三类材质的合金化程度较低。除铜镜外,铜器的合金成分与器物类型之间没有明显关系,可见其青铜技术逐步衰退。多数铜器为铸造而成,根据器物的需要,还在局部采用热锻、热锻后冷加工等加工方式,说明当时的工匠已经能够根据需要应用相关技术。     

Fluid dynamics and fluid‐structural relationships in the Red Lake mine trend,Red Lake greenstone belt,Ontario, Canada

The Red Lake mine trend, a deformation zone in the Archean Red Lake greenstone belt that hosts the world‐class Campbell‐Red Lake gold deposit, is characterized by abundant foliation‐parallel iron‐carbonate ± quartz veins with banded colloform‐crustiform structures and cockade breccias overprinted by silicification and gold mineralization. There is an apparent incompatibility between the cavity‐fill structures of the veins and breccias (typically developed at shallow crustal depths) and the upper greenschist to lower amphibole facies metamorphic conditions recorded in the host rocks (indicating relatively deep environments). This, together with the development of veins along the foliation plane, represents an enigmatic problem that may be related to the interplay between fluid dynamics and stress field. We approach this problem through systematic study of fluid inclusion planes (FIPs) in the vein minerals, including the orientations of the FIPs and the pressure–temperature conditions inferred from fluid inclusion microthermometry. We find that fluid inclusions in the main stage vein minerals (pregold mineralization ankerite and quartz and syn‐ore quartz) are predominantly carbonic without a visible aqueous phase, whereas many inclusions in the postore stage contain an aqueous phase. Most FIPs are subvertical, and many are subparallel to the foliation. High fluid pressure coupled with the high wetting angles of the water‐poor, carbonic fluids may have been responsible for the abundance of brittle deformation features. The development of subvertical FIPs is interpreted to indicate episodic switching of the maximum principal compressive stress (σ₁) from subhorizontal (perpendicular to the foliation) to subvertical (parallel to the foliation) orientation. The subvertical σ₁ is favorable for the formation of foliation‐parallel veins, as fractures are preferentially opened along the foliation in such a stress regime, the origin of which may be linked to the fluid source.     

Approximate Methods for Estimating Hysteretic Energy Demand on Plan-Asymmetric Buildings

The first step in a hysteretic energy-based design approach of performance-based design is the estimation of hysteretic energy demand in the structure. A nonlinear response-history analysis of the multi-degree of freedom model gives an accurate estimation, but it is not suitable for adopting in design. Two alternative methods, based on the concepts of modal pushover analysis (MPA) and 2D-MPA, are proposed in this article for uniaxial plan-asymmetric structures. Application studies show that both methods are efficient. While the 2D-MPA-based method is more accurate, the MPA-based method is more suitable for design adoption. Significant conclusions are given for prospective application of these methods.     

Numerical Evaluation of Topographic Effects at the Nicastro Ridge in Southern Italy

Numerical site response analyses were carried out on the Nicastro ridge in Southern Italy in order to investigate topographic effects. First, the analyses were carried out on a simplified model by employing simple artificial signals, in order to get preliminary physical insights into the two-dimensional phenomena involved. Then, numerical analyses were carried out on a more realistic heterogeneous subsoil model developed on the basis of geotechnical and geophysical investigations. Real accelerograms were selected for these analyses. Particular attention was devoted to separating topographic from stratigraphic amplification. Finally, the topographic amplification factors were compared with literature data and Eurocode 8 recommendations.     

DAUGHTER DISCRIMINATION AND FUTURE SEX RATIO AT BIRTH IN INDIA

This paper examines recent trends in sex ratio at birth in all the major states of India, based on three rounds of the National Family Health Survey. It finds evidence of an increase in the ratio, particularly at the second-order birth among women having a first daughter in many states in the northwestern region of the country. Also, there are signs of daughter aversion emerging in Odisha, an eastern state. Based on parity progression ratios and the trend in sex selection, an attempt is made to estimate the peak of sex ratio at birth in India. With moderate intensification in sex selection in the northwestern region, sex ratio at birth is expected to reach a peak of 117–119 males per 100 females around the period 2021–2026. If, in addition, sex selection spreads further in the southeastern region, the sex ratio at birth in India could even increase to a level of 124.