Fracture spacing during hydro‐fracturing of cap‐rocks

Layered low permeability rock units, like shales, represent seals or ‘cap‐rocks’ in a variety of geological settings. A continuous increase in the fluid pressure gradients across a virtually impermeable rock layer will ultimately lead to hydro‐fracturing. Depending on the boundary conditions, such fracturing may lead to the formation of a set of sub‐parallel cracks oriented more or less perpendicular to the cap‐rock layer. In this article, we propose a new numerical model that describes interactions between multiple cross‐cutting fractures in an elastic low permeability rock layer. The width of each fracture and the spacing between them are modeled as a force balance between the fluid pressure and the elastic forces in the cap‐rock and between each fracture. The model indicates that the system of fractures evolves toward a spatially periodic steady‐state distribution with a fixed fracture spacing and aperture. The results are similar for incompressible and compressible fluids. The steady‐state conditions depend on only two dimensionless parameters, and the fracture spacing is only weakly dependent on the cap‐rock thickness. This is in contrast to fracturing produced by simple extension of an elastic rock layer beyond the fracture strength, in which case fracture spacing is proportional to layer thickness.     

中国共产党领导民族振兴的90年

中国共产党的90年,是领导中华民族重新崛起进而走向伟大振兴的90年。大体看来,前28年侧重于民族独立和民族解放,为民族振兴大业创造政治前提;中30年侧重于在中国实践马克思、恩格斯社会主义建设模式;近32年侧重于探索中国特色的社会主义发展模式并形成体现中西文化结合的中国特色社会主义的完善形态。     

第二轮《江苏省志》文化部类编纂的粗浅思考

第二轮《江苏省志》文化部类编纂期间,江苏文化领域随着文化地位的提升、文化产业的兴起和文化观念的变迁,这一领域发生了巨大变化。文化软实力地位的提高,也要求第二轮志书编纂要给文化部类更多的关注。第二轮《江苏省志》在与首轮的过渡和衔接方面,着力抓了以下三方面的工作：1．篇目设置上体现传承性和创新性;2．内容记述上体现专业性与地域性;3．内涵外延上体现深刻性和趋向性。     

Comment on ‘Did China Import Metals from Africa in the Bronze Age?’

Lead isotope compositions provide a direct means of assessing provenance. The lead contents in bronzes cannot be used to argue against lead isotopes. Any claim for the origin of the source material for the origin of Yin‐Shang bronzes must satisfy the measured lead isotope compositions. Thus far, only southern African sources are found to meet this criteria.     

The Colonization of the Russian Barents Sea Coast (Mid-19th to Early 20th Century): Two Approaches to the Economic Development of the Area

This article deals with the early colonization of the Russian Barents Sea Coast (the so-called Murman Coast) in the middle of the 19th and early 20th century. It focuses mainly on the household economy and economic adaptation in the area by groups of Finnish, Russian, Karelian, Norwegian and Sami colonists. The opening up of the new territory by the colonists resulted partly in the employment of traditional methods of using natural resources and partly in the culture of these groups being transformed. Based on this, two different patterns of using natural resources were singled out within the ethnic groups that settled on the Murman Coast (western and eastern). These patterns were more suited to the new living conditions in each of the respective areas, and became the basis for different trends in the economic development of the Murman Coast.     

Bioarchaeological Investigation of Possible Gunshot Wounds in 18th Century Human Skeletons from Korea

Notwithstanding the relative abundance of bioarchaeological evidence of pre‐20th century gunshot wounds discovered at European and American archaeological sites, similar findings in East Asian countries have been very rare. In this study, we report evidence of possible gunshot wounds sustained by two individuals buried in Joseon tombs of Korea. The shapes of the trauma seemed to indicate low‐velocity projectiles, most likely musket balls. To our knowledge, this is the first bioarchaeological report specifically concerning possible gunshot‐wound evidence in East Asian skeletons recovered from archaeological fields. Copyright © 2011 John Wiley & Sons, Ltd.     

A PROCEDURE FOR ESTIMATING INPUT ENERGY SPECTRA FOR SEISMIC DESIGN

In this paper, the damage potential of an earthquake ground motion is evaluated in terms of the total power of the acceleration of the ground motion. By assuming an appropriate spectral shape for the input energy spectrum, and using the well-known Parseval theorem for evaluating the total power of a random signal, the peak amplification factor for the equivalent input energy velocity spectrum can be determined. It is shown that the peak amplification factor for the input energy spectrum depends on the peak-ground-acceleration to peak-ground-velocity ratio and duration of the strong motion phase of the ground motion. Values for the equivalent input energy velocity amplification factor vary from about 2 to 10 for most of the recorded ground motions used in this study. Although a considerable scatter of data is observed in this study, the peak amplification factor predicted by the Fourier amplitude spectrum of the ground acceleration provides a fairly good estimate of the mean value of the peak input energy compared to that determined from inelastic dynamic time history analyses, particularly for systems with high damping and low lateral strength. The peak amplification factor derived in this paper provides a more consistent approach for estimation of seismic demand when compared to an earlier empirical expression used for the formulation of duration-dependent inelastic seismic design spectra, even though only a slight difference in the required lateral strength results from the use of the new formula.     

MODELLING OF STRUCTURAL ACCELERATIONS AND APPLICATION TO CONTROLLER DESIGN

In this paper a method for the identification of simplified linear models for building structures is applied to the case when acceleration, rather than displacement, is measured. A frame from benchmark structural controller studies is simulated, and from the input-output data of these simulations, simplified models for the acceleration response of the frame are obtained that have far fewer degrees of freedom. One of these simplified models is used to design a controller, which is tested using an evaluation model from the benchmark controller studies and found to be effective.