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531.
本文介绍了ScS波的传播路径及走时曲线,选用图象说明ScS波震相的运动学和动力学的主要特征.并利用ScS波震相测定沈阳地震台单台记录的八个远震震源深度,通过对ScS波、pP波和sP波在远震地震图中进行比较分析,结果表明:所得到震源深度误差都在±30Km范围内,达到所要求的精度范围,提高了单台测定震相精度,因此用ScS波震相测定远震深度是一种测定震源深度行之有效的辅助方法. 相似文献
532.
Abstract Nowadays the rising of opportunity cost of farm labor comes to the forefront of attention in China. In order to understand its impact on agricultural land-use structure, a theoretical framework of household economics is formulated drawn on Low’s model. Under the theoretical framework, the impact of the rising opportunity cost of on-farm on cropping structure is deduced in theory. And then, using statistic and survey data, taking mountain area of southern Ningxia as an example, the theoretical assumes are verified. The results show that the rise of opportunity cost of farm labor leads to less diversified cropping structure. 相似文献
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536.
电子设备、仪器的广泛使用产生的电磁辐射已成为当今的重要污染之一。电磁辐射分为天然和人为两种,严重危害和影响着人类的生活和生产。人们要重视电磁辐射,从行政、科学技术、个人生活方面加强对电磁辐射的防范。 相似文献
537.
M. Gharebaghi R.M.A. Irons L. Ma M. Pourkashanian A. Pranzitelli 《International Journal of Greenhouse Gas Control》2011
Oxy-fuel combustion is considered as one of the most promising technologies for carbon capture and storage (CCS). In this study, a commercial computational fluid dynamics (CFD) code has been employed for the simulation of an air-fired coal combustion and an oxy-fired coal combustion with recycled flue gas in a 1 MWth combustion test facility. Reynolds–averaged Navier–Stokes (RANS) solutions have been obtained for both cases. Results indicate that the CFD code with existing physical sub-models can provide a reasonable prediction for the air-fired combustion. However, the prediction for the oxy-fired case has not been as satisfactory as expected. In order to assess the impact of the turbulence treatment in CFD on the predictions, large eddy simulation (LES) has been performed for oxy-fired case and compared with the results from the RANS simulation and the available experimental data. Although the results suggest that LES can provide a more realistic prediction of the shape and the physical properties of the flame, there has not been significant improvement in the prediction of the temperature. In addition, the complexity of the problem requires more detailed experimental data for the validation of the LES. In order to improve the validity of numerical simulations for design purposes, further modelling improvements for oxy-coal combustion that are necessary for more accurate predictions are addressed. Based on this study, it is envisaged that the complexity in the oxy-coal combustion process requires more detailed analyses of the available physical sub-models. 相似文献
538.
类二噁英多氯联苯生殖毒性的研究进展 总被引:1,自引:0,他引:1
类二噁英多氯联苯(DlPCBs)作为典型的环境内分泌干扰物,会干扰接触个体或其后代的内分泌功能,破坏机体的神经系统、免疫系统,尤其对生殖系统的影响最为明显,比如对生殖器官的形态与功能、生殖内分泌、原始生殖细胞及其受精和早期胚胎发育等产生严重影响,最终导致各种生殖系统疾病的发生。DlPCBs的蓄积性及半挥发性使其在环境中分布广泛,半衰期长的特点使其将对动物及人类的生存和健康造成难以想象的影响。本文综述了DlPCBs的分类与构成、一般性质、生殖毒性以及其可能的致病机理,并对DlPCBs生殖毒性机理研究的重点方向进行了展望。 相似文献
539.
Jinyu Sun Xuhui Wang Anping Chen Yuecun Ma Mengdi Cui Shilong Piao 《Environmental monitoring and assessment》2011,179(1-4):1-14
How urban vegetation was influenced by three decades of intensive urbanization in China is of great interest but rarely studied. In this paper, we used satellite derived Normalized Difference Vegetation Index (NDVI) and socioeconomic data to evaluate effects of urbanization on vegetation cover in China??s 117 metropolises over the last three decades. Our results suggest that current urbanization has caused deterioration of urban vegetation across most cities in China, particularly in East China. At the national scale, average urban area NDVI (NDVIu) significantly decreased during the last three decades (P?<?0.01), and two distinct periods with different trends can be identified, 1982?C1990 and 1990?C2006. NDVIu did not show statistically significant trend before 1990 but decrease remarkably after 1990 (P?<?0.01). Different regions also showed difference in the timing of NDVIu turning point. The year when NDVIu started to decline significantly for Central China and East China was 1987 and 1990, respectively, while NDVIu in West China remained relatively constant until 1998. NDVIu changes in the Yangtze River Delta and the Pearl River Delta, two regions which has been undergoing the most rapid urbanization in China, also show different characteristics. The Pearl River Delta experienced a rapid decline in NDVIu from the early 1980s to the mid-1990s; while in the Yangtze River Delta, NDVIu did not decline significantly until the early 1990s. Such different patterns of NDVIu changes are closely linked with policy-oriented difference in urbanization dynamics of these regions, which highlights the importance of implementing a sustainable urban development policy. 相似文献
540.
Pawlaczyk-?uszczyńska M Dudarewicz A Zamojska M Sliwinska-Kowalska M 《International journal of occupational safety and ergonomics》2011,17(3):255-269
This study aimed to assess exposure to sound and the risk of noise-induced hearing loss (NIHL) in orchestral musicians. Sound pressure level was measured in 1 opera and 3 symphony orchestras; questionnaires were filled in. On the basis of that data, the risk of NIHL was assessed according to Standard No. ISO 1999:1990. Classical orchestral musicians are usually exposed to sound at equivalent continuous A-weighted sound pressure levels of 81?90 dB (10th?90th percentiles), for 20?45 h (10th?90th percentiles) per week. Occupational exposure to such sound levels over 40 years of employment might cause hearing loss (expressed as a mean hearing threshold level at 2, 3, 4 kHz exceeding 35 dB) of up to 26%. Playing the horn, trumpet, tuba and percussion carries the highest risk (over 20%). 相似文献