Rock fracture compliance derived from time delays of elastic waves     

M. Möllhoff  C.J. Bean  P.G. Meredith 《Geophysical Prospecting》2010,58(6):1111-1122

The purpose of this study is to compare the reliability of various methods of estimating normal rock fracture compliance from elastic wave measurements. We compare ultrasonic through‐transmission laboratory measurements for a smooth fracture in a Westerly granite specimen with numerical simulations and analytical solutions. The focus is on deriving compliance from time delays. The influence of specimen and source transducer width was constrained using numerical wave simulations. We find that measured ultrasonic phase delays are better suited to estimate the fracture compliance than group delays. Using the frequency domain instead of the time domain increases the accuracy of the fracture compliance estimates. We further show that for cases where precise phase delay measurements are unavailable, employing first break times in conjunction with numerical simulations can be considered as an alternative.  相似文献   

西气东输二线某隧道南口地质安全评价研究   总被引：1，自引：0，他引：1       下载免费PDF全文

颜宇森  雷海英 《水文地质工程地质》2010,37(2):120-124

对西气东输二线工程新疆果子沟段某隧道南口进行实地调查,查明隧道工程区及其周围的自然地理、地质环境条件,同时调查隧道工程区存在的地质隐患类型、分布、规模、危险状态等因素,分析评价其对隧道施工安全的影响,最终根据地质安全评价结果,提出消除或减弱地质隐患的防治对策和建议。  相似文献   

WMN技术用于构建新型地震应急救援无线通讯平台的分析与设想   总被引：2，自引：1，他引：1  

祝恒书  宋立军  赵雯佳 《内陆地震》2008,22(3):226-233

传统的WLAN（Wireless LAN无线局域网）因为其单跳的网络特性造成了通讯瓶颈,这也使得其不能很好地满足地震应急救援通讯对效率、准确、安全等特性的要求。一种新型的无线网络形式WMN（Wireless Mesh Network无线网状网）的出现为构建下一代地震应急救援无线通讯系统提供了良好的网络基础。通过对传统地震应急救援无线平台和WMN的介绍,分析了构建新型地震应急救援无线通讯平台的技术指标和可行性,并且给出了平台搭建建议,最后对可能存在的问题以及应用前景进行了讨论。  相似文献   

Structural modulations and phase transitions in β-eucryptite: an in-situ TEM study     

H. Xu  P. J. Heaney  H. Böhm 《Physics and Chemistry of Minerals》1999,26(8):633-643

Beta-eucryptite as grown by the flux method has been investigated by in-situ cold- and hot-stage transmission electron microscopy (TEM). Using electron diffraction and dark-field TEM imaging, we found no evidence for the merohedral twinning that accompanies structural collapse at the β-to-α-quartz transition, suggesting a true hexagonal symmetry for the aluminosilicate framework of β-eucryptite. Selected-area electron diffraction (SAED) patterns exhibited a variety of incommensurate structures along the three a axes with an average modulation period of about 6.5 a. These modulated structures arise from superperiodic stacking parallel to (100) of two structural units with different Li configurations. In-situ heating experiments show that the modulated structures undergo a reversible transition to the disordered modification at elevated temperatures. This transition arises from positional order-disorder of Li ions along the main structural channels. In addition, it appears that at constant low temperature, electron beam irradiation alone can induce a sequence of transitions similar to those that are thermally induced from the ordered modification to modulated states. Received: 12 November 1998 / Revised and accepted: 31 December 1998  相似文献   

利用GPS时间传递数据修正接收机天线坐标     

郑曼黎  罗定昌 《时间频率学报》1994,(Z1)

在采用ＧＰＳ进行共视时问比对过程中，当两站位置相隔不大长（小于１０００ｋｍ）时，由于卫星轨道误差、电离层和对流层延迟修正的误差可减少至只有几纳秒，可以主为接收天线位置的误差是其主要误差来源．利用ＧＰＳ本身的时间比对数据，不必增加别的数据来源和设备，采用相对定位的方法可提高定位精度，从而提高时间比对的精度．本文利用日本（ＣＲＬ）和北京天文台（ＢＡＯ）之间五天的共视时间比对数据，对（ＢＡＯ）的天线坐标进行修正．在水平方向和高程方向的修正偏差分别为２．９ｍ和５．６ｍ．如果试验数据足够，修正６４效果会更好．  相似文献   

天然气——21世纪的能源   总被引：2，自引：1，他引：1  

史斗 《地球科学进展》1998,13(3):251-260

天然气是一种生态型能源或理想的城市能源。综述了世纪之交的全球天然气工业发展状况,包括储量的增长、输气管道的延长、液化天然气厂的发展和天然气利用技术的进步。介绍了有关国家的天然气利用法规和政策。预测了21世纪全世界天然气供需趋势。论述了为什么说天然气是21世纪的能源。指出了当前和未来全球天然气工业面临的挑战。  相似文献   

Wave energy transmission system concepts for linear generator arrays     

Karin Thorburn  Hans Bernhoff  Mats Leijon 《Ocean Engineering》2004,31(11-12):1339-1349

Wave energy is a renewable source, which has so far not been exploited widely. Many of the various schemes in the past consist of large mechanical structures, often located near the sea surface. This article presents a range of systems with point absorbers on the surface and linear generators placed on the seabed, converting the wave motion into electrical power. Electrical power components are combined in different ways to obtain solutions suitable for various conditions. Different topologies for the electrical system transmitting power to the grid are discussed. Qualitative case studies are used to exemplify system options and connection schemes.  相似文献   

Research and Application of Cosmic-ray Fast Neutron Method to Measure Soil Moisture in the Field   总被引：1，自引：0，他引：1  

Jiao Qishun  Zhu Zhongli  Liu Shaomin  Jin Rui  Du Fan 《地球科学进展》2013,28(10):1136-1143

It is very difficult to measure large region soil moisture. In recent years, measurement of surface soil moisture by the cosmic ray fast neutron probe has gradually attracted more attention. By this passive, non-invasive and intermediate scale measurement, soil moisture at a horizontal scale of around 300 m can be observed, which makes this method available to fill the gap between little scale of traditional point measurement and large scale of remote sensing in the measurement of soil moisture. In this paper, Cosmic-ray Soil Moisture Observing System (COSMOS) and Wireless Sensor Network (WSN) were used to observe field soil moisture in Zhangye Oasis. The results of the COSMOS soil moisture well reflected the variation trend of soil moisture at the field scale. There were some regular changes with the cosmic ray soil moisture during the irrigation period. Combined with irrigation data in cosmic-ray probe footprint, a bimodal change was showed in the cosmic-ray soil moisture figure during irrigation period. This was because that the order of irrigation of the three communities was different in cosmic-ray probe footprint. WSN data were used to validate this result and we found that root-mean-square error between cosmic-ray soil moisture and SoilNET average soil moisture was very large during irrigation periods because of the impact of cosmic-ray measurement theory. While root-mean-square error would decrease from 0.037 m³/m³ to 0.028 m³/m³ after we eliminated the data in irrigation period. So COSMOS can be used to measure field soil moisture under high heterogeneity condition and provide truly ground data for the validation of remote sensing  相似文献   

基于WiFi与GPS组合定位算法的无缝定位方法研究     

马燕  袁蔚林  陈秀万  许玉斌  孙华波 《地理与地理信息科学》2013,29(3)

无线局域网络(WLAN)是一种全新的无线信号传输平台,该文在总结目前无缝定位与导航技术的研究现状、分析存在的问题和发展趋势的基础上,提出了联合GPS和无线局域网络的组合定位方法,以实现室内外的无缝定位与导航.同时,在深入研究卫星导航定位和无线传感器网络定位原理与算法基础上,针对定位环境的不同,提出了无缝定位的解决方案、转换机制和切换策略,并以WiFi网与GPS组合定位算法为例,进行了详细分析和深入讨论,所用算法可以实现无GPS、少于4颗可用卫星以及GDOP值不满足定位情况下的定位,与单独WiFi网络定位算法相比,该算法可以提高定位精度.  相似文献   

地震应急现场无线通信设备与现场有线网络环境集成通信方案探讨     

段锋 《内陆地震》2010,24(2):149-154

通过对汶川8.0级地震现场工作的经验总结,提出在保障"十五"期间配备的地震应急现场技术系统可用的前提下,扩展地震应急现场设备的使用范围,对地震应急现场无线通信设备与现场有线网络环境集成通信方案进行测试和探讨,以便在复杂的现场环境下多一种通信方式选择。  相似文献