On crosswell diffusive time-domain electromagnetic tomography

We investigate the reconstruction of a conductive target using crosswell time-domain electromagnetic tomography in the diffusive limit. The work is a natural extension of our ongoing research in the modification of time-domain methods for the rugged marine mid-ocean-ridge environment, an environment characterized by extreme topography and pronounced variations in crustal conductivity on all scales. We have proved both in theory and in practice that 'traveltime', the time taken for an electromagnetic signal to be identified at a receiver following a change of current in the transmitter, is an excellent, robust estimator of average conductivity on a path between transmitter and receiver. A simple estimate of the traveltime for a parallel electric dipole-dipole system is the time at which the derivative of the electric field with respect to logarithmic time at the receiver reaches its maximum. We have derived the fundamental relationship between the traveltime and the conductivity of the medium for a uniform whole-space. We have applied the concept of the traveltime inversion to the related crosswell problem and demonstrated reconstructions of finite targets based on tomographic analyses. Results show that the crosswell time-domain electromagnetic tomography can supply useful information, such as the location and shape of a conductive target.     

Notes Light and electron microscopic study on Lymphocystis of cage cultured kelp bass, Epinethelus moara (Temminck et Schlegel)

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First measurements from a deep-tow transient electromagnetic sounding system

An electromagnetic sounding system has been developed to map the shallow electrical conductivity structure of the deep sea floor. The instrument consists of a magnetic source and several colinear magnetic receivers forming an array which is towed along the seafloor. The source generates a time varying magnetic field; the shape of the resulting magnetic field waveform at the receivers depends on the electrical conductivity below the seafloor between the receivers and the source. The instrument can be towed systematically over a study area under acoustic transponder or GPS navigation to construct a map of the electrical conductivity. Towing speeds of greater than 1 m s^–1 (2 knots) can be achieved without adversely effecting data quality. The instrument is sufficiently robust to survive continual contact with thinly sedimented, abrasive basalt. We present the first results from a deployment in August, 1990 near the Cleft Segment of the Juan de Fuca Ridge along an 8 km track to the west of the spreading center. Unforeseen problems with the instrument restricted the utility of the measurements for constructing detailed vertical conductivity profiles, but the measurements were adequate to determine an average conductivity in the upper 25 m, at more than 70 stations. The conductivity was found to vary from 0.1 to 0.4 S/m along the track.     

中国东南部异常降水型变化特征及其与赤道东太平洋海面温度的关系

采用主分量分析法（PCA）对中国东南部（105°—122°E，19°—33°N）90个测站（除台湾省外）1954—1989年逐年1，4，7，10月降水量标准化资料进行分解，得到各种异常降水型及相应的时变序列；对最为典型的3种异常降水型的空间分布特点、时变特征、逐年分型情况进行了分析，并探讨了各月各异常降水型变化与赤道东太平洋海面温度变化间的可能关系及它们在厄尔尼诺年份（或次年）的一些特点和规律。     

Response of the low-frequency fluctuations of sea level to atmospheric forcing along the coasts of the Huanghai Sea and the East China Sea

In this paper, the low-frequency fluctuations of sea level and their relationship to atmospheric forcing along the coasts of the Huanghai Sea and the East China Sea are studied. Spectrum analyses are made for the time series of daily mean sea level, atmospheric pressure and wind stress at seven coastal stations. It is found that at all the stations, the main part of the energy of the sea level fluctuations, within the (2-60)-day period, is concentrated on the (12-60)-day period band and that an obvious spectral peak appears at the 3-day period. Along the coast of the Huanghai Sea, variations in the sea level are greater in winter than in summer. In winter, along the coasts of the Huanghai Sea and the East China Sea there is a kind of sea level fluctuations propagating southwards. Among the many factors causing sea level variation, the most obvious one is atmospheric pressure, followed next by the alongshore wind stress.     

利用门限自回归建模和样条函数拟合方法研究甘肃东南部地区地震活动特征

本文应用数学门限自回归模型和样条函数,研究了甘肃东南部的地震活动特征。结论如下:(1)甘肃东南部的地震活动具有"准周期"现象,本世纪以来已经历了三个"准周期",目前,处于第三活动期。(2)1900年以来的地震活动处于较低的水平,大多数地震的震级为5-6级。根据本文的研究,下一次地震的震级约为5级左右,目前发震的概率为0.74.(3)震级大于4.7级地震的空间分布图象与数字模拟实验结果一致。     

中国城市土地有偿使用的回顾与展望

作者首先对中国城市土地使用的各个阶段作了历史回顾。50年代初,中国土地使用是有偿的;1954年开始则施行行政划拨、无偿使用;80年代,在改革开放的形势下,我国沿海的部份城市率先进行了土地有偿使用的改革和实践,建立各级土地管理机构,修改及制订有关法规。文章着重阐述了自80年代开始的部份城市土地有偿使用改革的内容、办法、难点和问题。同时,对我国土地有偿使用改革的发展趋势进行了评述,认为,土地使用的两种体制将继续并存。为提高土地有偿使用的科学性,作者还详细介绍了一种土地经济评价方法——多因素叠加法。     

危险气体泄漏突发事件的应急措施探讨

本文根据近几年重庆市处置危险气体泄漏突发事件的经验,探讨了应对危险气体泄漏突发事件时应采取的对策和措施,提出了应对危险气体泄漏突发事件应建立综合性的危险气体泄漏突发公共事件应急管理常设机构、明确危险气体泄漏突发公共事件应急决策的职责权限关系、建立危险气体泄漏突发公共事件应急决策的专家咨询机制、建立有效的危险气体泄漏灾害信息系统、重视危险气体泄漏灾害应急管理中媒体的传播作用、建立健全危险气体污染气象应急预警服务系统、加强应对危险气体泄漏突发事件的能力建设等主要对策和措施。     

区域可持续发展综合集成研讨厅体系研究*

区域可持续发展研究与决策是一个复杂的大成智慧工程问题。文章结合系统科学近今发展成果,提出区域可持续发展综合集成研讨厅体系的基本框架。该框架集计算机技术、决策技术、系统工程技术于一体,强调把人的思维和思维的成果、人的知识、智慧以及各种资料信息集成起来。并讨论了区域可持续发展研讨厅的定义,分析了研讨厅的功能机制、网络体系及支撑技术。     

自组织临界现象在地震空间演化特征上的应用研究

将自组织临界现象理论在地震预报领域作深入的应用研究,根据各量的物理含义重新讨论了在地震科学中的应用,并用重整化群方法对强震前中小地震强现象的临界点问题进行研究。