P‐wave transmission across fractures with nonlinear deformational behaviour     

X. B. Zhao  J. Zhao  J. G. Cai 《国际地质力学数值与分析法杂志》2006,30(11):1097-1112

Stress wave attenuation across fractured rock masses is a great concern of underground structure safety. When the wave amplitude is large, fractures experience nonlinear deformation during the wave propagation. This paper presents a study on normal transmission of P‐wave across parallel fractures with nonlinear deformational behaviour (static Barton–Bandis model). The results show that the magnitude of transmission coefficient is a function of incident wave amplitude, nondimensional fracture spacing and number of fractures. Two important indices of nondimensional fracture spacing are identified, and they divide the area of nondimensional fracture spacing into three parts (individual fracture area, transition area and small spacing area). In the different areas, the magnitude of transmission coefficient has different trends with nondimensional fracture spacing and number of fractures. In addition, the study reveals that under some circumstances, the magnitude of transmission coefficient increases with increasing number of fractures, and is larger than 1. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

GPS/LEO掩星观测的变分同化技术   总被引：6，自引：0，他引：6  

刘敏  郭鹏 《天文学进展》2006,24(1):27-42

在简单介绍GPS/LEO掩星探测大气的发展历史和科学意义之后,详细阐述了反演的基本原理;分析了标准反演中存在的问题,并说明一维变分同化(1DVAR)在反演方法中的重要性;给出了一维变分同化中价值函数的求解,以及各种同化因子;简单介绍了对当前气象学中普遍使用的四维变分同化(4DVAR);重点讨论了各种同化方法,以及使用各种同化因子的优缺点。最后,通过CHAMP卫星的观测实例分析,验证了GPS数据在数值天气预报(NWP)中的作用,以及相对于标准反演法一维变分对气象要素的改进。  相似文献   

Observational evidence for solar coronal decimetric radio pulsations with very short periods     

Xie Rui-xiang  Wang Min  Shi Shuo-biao  Xu Chun  Li Wei-hua  Yan Yi-hua 《Chinese Astronomy and Astrophysics》2003,27(4):426-434

Using the decimetric (700–1500 MHz) radio spectrometer and the synchronous observational system with high temporal resolution at four frequencies (1420, 2130, 2840 and 4260 MHz) of Yunnan Observatory, two rare events were observed on 2001 June 24 and 1990 July 30. The former was a small radio burst exhibiting pulsations with short periods (about 29, 40 and 100 ms) in the impulsive phase. The latter was a large radio burst, which at 2840 MHz produced radio pulsations with period of about 30 ms. This paper focuses on pulsations with very short periods in the range of 29–40 ms. The mechanism of generation of such pulsations may be modulation of radio radiation by the periodic trains of whistler packets originating in unstable regions of the corona. Alternatively, these pulsations can be attributed to wave-wave non-linear interactions of electrostatic upper hybrid waves driven by beams of precipitating electrons in flaring loops.  相似文献   

CARBON DYNAMICS OF WETLAND IN THE SANJIANG PLAIN   总被引：2，自引：0，他引：2  

SONG Chang-chun    WANG Yi-yong  WANG Yue-si  YAN Bai-xing WANG De-xuan  ZHAO Zhi-chun  LOU Yan-jing 《中国地理科学(英文版)》2003,13(3):228-231

1INTRODUCTIONWetlandsplayanimportant roleintheprocessofcar-bonstorage.Thetotalcarbonstoredindifferentkindsofwetlandsisabout15%-35%ofthetotalcarboninthegloballandsoils(POSTetal.,1982;GORHAM,1991).Inaddition,wetlandsaresignificantnaturalsources fortheatmospheric CH4 (MOORE,1994).It isestimatedthatabout110×1012gCH4 originates fromanaerobicdecompositioninthenaturalwetlands,CH4 emission fromthenaturalwetlandsis15%-30%oftheglobalCH4 emission andtheCH4 emission from thepeat land at hi…  相似文献   

疏散星团的最新研究进展     

俎中良  赵君亮 《天文学进展》2003,21(2):152-162

疏散星团在天文学和天体物理学研究中有着多方面的重要性。近年来在观测和理论工作上都取得了显著的进展。综述了疏散星团的研究现状，对成员判别、基本参数确定、团与恒星的演化、团的结构和动力学进行了详细评述。  相似文献   

成团天体系统成员概率计算的有效性问题     

邵正义  赵君亮 《天文学报》1996,37(4):377-386

本文提出了一个普适的衡量成团天体系统成员概率计算结果的有效性指数：Ｅ＝１－ＮΣ｛Ｐ（ｉ）［１－Ｐ（ｉ）］｝／ΣＰ（ｉ）Σ［１－Ｐ（ｉ）］｝，并以此对以Ｓａｎｄｅｒｓ方法为基础的各种成员确定模型的有效性进行了分析．从总体上说，运动学资料（自行、视向速度等）是一类有效的观测判据．  相似文献   

Models of CN and C₂ comae for comet Tago-Sato-Kosaka and comet bennett     

Zhong-wei Hu  Shu-dong Chen  Jiang-nan Zhao 《Chinese Astronomy and Astrophysics》1985,9(1):86-90

Based on the CN and C₂ comae isophotes for two comets (1961 IX and 1970 16) given by Rahe et al. and the relevant theory of physical chemistry, we have deduced the distributions of the CN and C₂ modecules in the coma, their scale heights and mean lifetimes. The results favour the viewpoint that HCN is the parent of CN, and that C₂H₂ is the parent of C₂.  相似文献   

Method for evaluating the degrees of land use sustainability of mountainous county and its application in Yunnan Province,China   总被引：4，自引：1，他引：3  

Zisheng Yang  Yansui Liu  Wenxing Tao  Jingjing Xu  Qiaogui Zhao 《山地科学学报》2008,5(2):98-112

The evaluation of sustainable land use is the key issue in the field of studying the sustainable land utilization. In general analysis, the sustainable land use is evaluated respectively from its ecological sustainability, economic sustainability and social sustainability in China and other countries in recent years. Although this evaluation is an important work, it seems insufficient and hard to comprehensively reflect the whole degree of land use sustainability. Thus, to make up this deficiency, this paper brings forward the evaluation indexes, which make it possible to quantitatively reflect the whole degree of land use sustainability, namely, the concept of ＂degrees of overall land use sustainability＂ （Dos）, and research and measurement development of the method of and calculation in Dos. Taking the evaluation of the degree of land use sustainability in county regions of Yunnan Province as the actual example for analysis, results are basically as follows：
1） The degree of land use sustainability （Dos） is the ration index to organically and systematically integrate the degree of ecological friendliness （DeF）, the degree of economic viability （Dev） and the degree of social acceptability （Dsa）, able to comprehensively reflect the whole sustainability degree of regional land use
2） Based on the value of Dos, the grading system and standard for the sustainability of land use may be established and totally divided into five grades, namely, the high-degree sustainability, middle-degree sustainability, low-degree sustainability, conditional sustainability and non-sustainability. Meanwhile, the standard for distinguishing sustainability grades has also been confirmed so as to determine the nature of sustainability degrees in different grades. This makes the possibility for the combination of nature determination with ration in research result and provides with the scientific guideline and decision-making gist for better implementation of sustainable land use strategy.
3） The pract  相似文献   

太阳系自然卫星运动的稳定区域     

刘林  赵长印 《紫金山天文台台刊》1993,12(1):37-44

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第一代恒星的观测和研究进展     

陆烨  赵刚  梁艳春 《天文学进展》2001,19(4):470-476

第一代恒星（星族Ⅲ恒星）标志着宇宙从暗物质时代到现在已知的宇宙的转折点。目前对第一代恒星（星族Ⅲ恒星）的观测结果表明，在银河系中还没有发现零金属丰度的恒星，金属丰度[Fe/H]≤-2.5的恒星极少。由于近几年的BPS巡天，银河系中已知的极端贫金属丰度的恒星数目大大增多。目前，可探测到的极端贫金属星的金属丰度[Fe/H]最低约为－4．1。金属丰度在－4到－3之间的恒星大约有100多颗，这些恒星的运动学特性非常类似于其它晕星。然而还没有发现第一代恒星，或金属丰度[Fe/H]≤-5的恒星。关于第一代恒星的形成过程、初始质量函数以及存在于银河系的什么地方，都还没有任何直接的证据。但第一代恒星确实存在。第一代恒星这个谜一般的实体，向观测和理论天文学家提出了巨大挑战。为探测和预言银河系中的第一代恒星，天文学家提出了许多观测方案和理论模型。对有关第一代恒星在观测和理论研究上的进展进行了综述。  相似文献