Energy balance of simple elastodynamic sources

Complete relations are derived for energy and energy flux of elastic waves generated by an isotropic and double-couple source in a perfectly elastic, homogeneous, isotropic, and unbounded medium. In the energy balance of elastodynamic sources near-field waves play an essential role, transforming static energy into wave energy, andvice versa. For explosive and dislocation sources, the sources surface radiates a positive wave energy that is partially distributed to the medium transforming into static energy. For implosive and antidislocation sources, the source surface generates elastic waves, but it does not necessarily imply that it also radiates a positive wave energy. The energy transported by waves can originate in gradual transformation of the static-to-wave energy during propagation of waves through a stressed medium.On leave from Geophysical Institute, Czech Academy of Sciences, Boní II/1401, 41 31, Praha 4 Czech Republic     

Textural segmentation of digital rock images into bedding units using texture energy and cluster labels

The texture of digital rock images, as recorded, for instance, with borehole imaging devices, is shown to reflect different bedding types. Textural segmentation of borehole images, therefore, subdivides the recorded sequence into bedding units. We show that a textural segmentation algorithm based on the concept of texture energy achieves good results when compared with synthetic as well as real data in which petroleum geologists have performed zonations on cores. Texture energy involves filtering of the original image with a set of texture sensitive masks. The filtering is done as a finite convolution over the size of the masks. On the resulting images the variance is computed over a relatively large sliding window, which, in its practical implementation, covers the full width of the image. The resulting nine one-dimensional curves are then clustered hierarchically into a user-determined number of image texture or lithological bedding classes. Principal component analysis previous to clustering can be used to reduce redundancy in the data. A recurring and relatively ill-defined problem in this field are macro-textures, i.e., the cyclic interbedding of two or more bedding types. We show that sliding Fourier transforms and variable mask scale can successfully address the zonation of macro-textures. In general, the method gives best results with mask sizes equivalent to 2–4 centimeters, reflecting the length scale at which the investigated geological bedding seems to have its highest variation.     

清代地理学家魏源及其《海国图志》──纪念魏源诞生200周年

本文阐述我国清代中期思想家、地理学家魏源的思想及共《海国图志》的特点及历史意义。     

碳中和目标下关键矿产在清洁能源转型中的作用、供需分析及其建议

在"碳中和"目标的驱动下，全球能源系统向清洁化、低碳化甚至无碳化发展已是大势所趋。针对向清洁能源转型的需求，采用了统计对比、分类汇总、综合分析等方法，分析研究了关键矿产在电池、电网、低碳发电和氢能等行业中的作用和需求。结合当前关键矿产产量的地理集中度高、项目开发周期长、资源质量下降等矿产供应和投资计划不能满足清洁能源转型的需求等问题，提出确保关键矿产多样性供应，推动价值链各环节的技术创新，扩大回收利用，增强供应链弹性和市场透明度，将更高的环境、社会和治理标准纳入主流程及加强生产者和消费者之间的国际合作等建议。     

A search for ultra-high energy counterparts to gamma-ray bursts

A small air shower array operating over many years has been used to search for ultra-high energy (UHE) gamma radiation ( 50 TeV) associated with gamma-ray bursts (GRBs) detected by the BATSE instrument on the Compton Gamma-Ray Observatory (CGRO). Upper limits for a one minute interval after each burst are presented for seven GRBs located with zenith angles < 20°. A 4.3 excess over background was observed between 10 and 20 minutes following the onset of a GRB on 11 May 1991. The confidence level that this is due to a real effect and not a background fluctuation is 99.8%. If this effect is real then cosmological models are excluded for this burst because of absorption of UHE gamma rays by the intergalactic radiation fields.     

《干旱区地理》的引文统计分析

本文使用文献计量学中的引文分析方法,以《干旱区地理》为调查样本进行了统计分析。《干旱地理》１９８５－１９９４年共版４３期,刊登论文５５８篇,其中附有引文的论文４３６篇,引文２７６６条。     

War and the commons: Assessing the changing politics of violence, access and entitlements in Sri Lanka

There are two antagonistic, but equally influential traditions in the study of the nexus between resource use and violent conflict. One works through a Malthusian frame linking resource scarcity with violence, the other school of thought establishes a nexus between resource abundance and the incentives to use violence for rent monopolisation in a political economy of war or markets of violence. The tacit essentialism inherent in both schools of thought has increasingly come under critical scrutiny by geographers and anthropologists. To escape such essentialism requires a more detailed study of the dynamism of the political economy of (civil) war and its spatial dynamics, the political geographies of violence. In this paper, we study endowments and entitlements of people depending on common-pool or open-access resources in war-affected areas of Sri Lanka. Rural spaces in the war-affected areas became both a strategic retreat for fighters and an important common-pool resource on which a large part of the rural populace depended for their survival. Our research illustrates how the political geographies of war affect access regimes and entitlements to common-pool resources and thereby confine the livelihood opportunities of resource users. These dynamics of the political economy of war cross different scales and go beyond simple place-based struggles, for they are rooted in broader spatial dynamics of warfare creating place-space tensions in the sense that spatial dynamics of military control impinge changing access regimes upon specific places.     

Some breakage characteristics of ultra-fine wet grinding with a centrifugal mill

A centrifugal mill is a high-power intensity media mill that can be used for ultra-fine grinding, employing centrifugal forces generated by gyration of the axis of the mill tube in a circle. The mill charge motion is quite different depending on the ratio of the gyration diameter to the mill diameter (G / D ratio), varying from a motion similar to that of a conventional tumbling media mill to that of a vibration mill. In this study, a centrifugal mill was constructed with an arrangement where the gyration diameter could be readily adjusted. The batch grinding characteristics of three different minerals (limestone, talc and illite) in water with dispersing agent were investigated at various G / D ratios. It was found that the optimum G / D ratio in terms of the specific energy consumption to give a desired fineness of product was different for the three minerals. This was due to their different reactions to the breakage mechanisms provided by the mill charge motion at varying G / D ratios. The size distributions became progressively narrower at increased grinding times, and particles finer than about 0.1 μm were not detected even for prolonged grinding times. Measurement of specific surface areas indicated that this was not due to an artifact of the size measurements by laser diffractometry. This implies that there is a limitation in which particles finer than 0.1 μm are not produced under the conditions tested in this type of mill, but further investigation is needed for experimental verification of this limit of comminution.     

On the role of heat flow, lithosphere thickness and lithosphere density on gravitational potential stresses

Gravitational potential stresses (GPSt) are known to play a first-order role in the state of stress of the Earth's lithosphere. Previous studies focussed mainly on crust elevation and structure and little attention has been paid to modelling GPSt using realistic lithospheric structures. The aim of the present contribution is to quantify gravitational potential energies and stresses associated with stable lithospheric domains. In order to model realistic lithosphere structures, a wide variety of data are considered: surface heat flow, chemical depletion of mantle lithosphere, crustal thickness and elevation. A numerical method is presented which involves classical steady-state heat equations to derive lithosphere thickness, geotherm and density distribution, but additionally requires the studied lithosphere to be isostatically compensated at its base. The impact of varying surface and crustal heat flow, topography, Moho depth and crust density on the signs and magnitudes of predicted GPSt is systematically explored. In clear contrast with what is assumed in most previous studies, modelling results show that the density structure of the mantle lithosphere has a significant impact on the value of the predicted GPSt, in particular in the case of thick lithospheres. Using independent information from the literature, the method was applied to get insights in the state of stress of continental domains with contrasting tectono-thermal ages. The modelling results suggest that in the absence of tectonic stresses Phanerozoic and Proterozoic lithospheres are spontaneously submitted to compression whereas Archean lithospheres are in a neutral to slightly tensile stress state. These findings are in general in good agreement with global stress measurements and observed geoid undulations.     

中国能源安全与南海开发

二十一世纪是海洋经济时代。随着我国经济的发展,能源问题日益突出。由于我国陆上石油资源日益枯竭,海上石油开发成为我国能源的战略重点。南海陆架新生代地层厚约2000～3000m。第三纪沉积有海相、陆相及海陆交互相,具有良好的生油和储油岩系。南海扼海上要冲-马六甲海峡,南海航线是我国能源的海上生命线,具有不可替代的战略地位。我国南海资源和海域主权遭受到极大的侵犯。发展深海油气的勘探和开发技术,开发我国的南海深水石油资源,维护我国海域主权已经刻不容缓。优先进行南海石油开发是破解我国石油能源困局的必选战略。