1987-2002年辽宁中部城市群大气污染物变化特征分析   总被引：29，自引：8，他引：21  

马雁军  崔劲松  刘晓梅  张菁 《高原气象》2005,24(3):428-435

根据1987—2002年辽宁中部城市群(沈阳、鞍山、本溪、抚顺、辽阳)的主要大气污染物(TSP、PM10、SO2、NOx)的现状监测值,分析了辽宁中部城市群大气污染的现状及污染程度。结果表明：城市群的主要大气污染是TSP、PM10和SO2;冬季是城市群大气污染最严重的季节,夏季大气污染最轻;5个城市16年来TSP、PM10和SO2呈逐年下降趋势,NOx的年际变化趋势不明显;城市群大气污染最严重的城市是本溪,其次是鞍山、沈阳、抚顺、辽阳。  相似文献   

3-D Non-linear Travel-time Tomography: Imaging High Contrast Velocity Anomalies   总被引：1，自引：0，他引：1  

Chao-ying?BaiEmail author  Stewart?Greenhalgh 《Pure and Applied Geophysics》2005,162(11):2029-2049

In this paper we present an approach for 3-D travel-time tomography, which works well in reconstructing high contrast velocity anomalies in both location and strength. It uses a revised ‘irregular’ approach to the shortest-path method as the ray tracer and a damped minimum norm, and constrained least-squares CG approach as the inversion solver. In ray tracing, the advantages of the revised ‘irregular’ over the ‘regular’ approach are that the secondary nodes introduced on the cell surfaces significantly improve accuracy of computed travel times, without dramatically increasing the total number of cells and nodes; the tri-linear velocity function defined across the cell guarantees accurate ray tracing in a high velocity contrast medium; and the capacity to calculate a relatively large 3-D model, due to the fast run speed (at least one order of magnitude over the ‘regular’ approach) and less number of total nodes. The introduction of ‘soft’ and ‘hard’ bounds into the inversion process changes the conditioning and makes the solution meaningful in a physical sense. Thus the artifacts caused by noise and high velocity contrasts are substantially suppressed and the image quality is considerably improved, making the solution realistic with noisy or inconsistent travel-time data. Several numerical tests indicate that we can obtain good quality images even for high velocity contrast anomalies (say more than 20%) in the target region. This means the inversion algorithm is an efficient and effective procedure. Meanwhile, the inversion procedure is not very sensitive to the quality of the travel-time data, which is promising for practical usage.  相似文献   

A study on pathogens of Chinese prawn (Penaeus Chinensis) virus diseases     

Sun Xiu-qin  Zhang Jin-xing 《中国海洋湖沼学报》1995,13(3):284-288

This pathogenic study shows that the viral diseases of Chinese prawns (Penaeus chinensis, O'sbeck) is due to three kinds of viruses: epithelium envelope baculovirus ofPenaeus chinensis (EEBV-PC, detected by the authors in 1993), infections hypodermal and hematopoietic necrosis virus, and hepatopancreatic parvo-like virus, and that the first two viruses seem to be the main pathogens of the epidemic in the northern regions in 1993.  相似文献   

高速USB控制器的应用     

韩斌 《成都信息工程学院学报》2004,19(4):481-485

阐述了USB2.0高速总线的工作原理,并运用Cypress公司推出的USB2.0控制器CY7C68013芯片加上高速A/D转换芯片实现了高速A/D采样,为今后的USB高速应用打下了基础.  相似文献   

Dust formation in primordial Type II supernovae   总被引：1，自引：0，他引：1  

Paolo Todini  rea Ferrara 《Monthly notices of the Royal Astronomical Society》2001,325(2):726-736

We have investigated the formation of dust in the ejecta of Type II supernovae (SNe), mostly of primordial composition, to answer the question of where the first solid particles are formed in the Universe. However, we have also considered non-zero progenitor metallicity values up to Z = Z_⊙ . The calculations are based on standard nucleation theory, and the scheme has been tested for the first time on the well-studied case of SN1987A, yielding results that are in agreement with the available data. We find that: (i) the first dust grains are predominantly made of silicates, amorphous carbon (AC), magnetite and corundum; and (ii) the largest grains are the AC ones, with sizes around 300 Å, whereas the other grain types have smaller radii, around 10–20 Å . The grain size distribution depends somewhat on the thermodynamics of the ejecta expansion, and variations in the results by a factor ≈2 might occur within reasonable estimates of the relevant parameters. Also, and for the same reason, the grain size distribution is essentially unaffected by metallicity changes. The predictions on the amount of dust formed are very robust: for Z =0 , we find that SNe with masses in the range (12–35) M_⊙ produce about 0.08 M_⊙≲ M _d≲0.3 M_⊙ of dust per supernova. The above range increases by roughly three times as the metallicity is increased to solar values. We discuss the implications and the cosmological consequences of the results.  相似文献   

Soil morphology and organic matter dynamics under cheatgrass and sagebrush-steppe plant communities     

Jay B. Norton  Thomas A. Monaco  Jeanette M. Norton  Douglas A. Johnson  Thomas A. Jones 《Journal of Arid Environments》2004,57(4):445

Widespread cheatgrass (Bromus tectorum L.) invasion represents a major shift in species dominance that may alter ecosystem processes across much of the western US. To investigate differences following such conversion, soil morphology and organic matter under cheatgrass-dominated and native shrub-steppe vegetation were compared by standard soil analysis procedures at seven paired sites in Idaho and Utah. Results suggest that, following conversion to cheatgrass dominance, increased porosity and labile organic inputs enhance microbial decomposition in near-surface horizons beneath cheatgrass compared to adjacent soils under native vegetation. Enhanced decomposition could result in depletion of long-term SOM, leading to impoverished sites difficult to restore to native perennial vegetation.  相似文献   

On climate variability in Northeast of Brazil   总被引：3，自引：0，他引：3  

Vicente de Paulo Rodrigues da Silva   《Journal of Arid Environments》2004,58(4):303

The time-series (annual period and dry- and wet-season) of eight climatic variables were analysed to ascertain the existence of climate variability in Northeast of Brazil. Results indicated generally increasing trends in most of these variables (statistically significant at p<0.01 or <0.05) by Mann–Kendall test. However, relative humidity and rainfall presented decreasing behavior. The study showed that most of the stations studied are going through a process of environmental dryness. The results also suggest that the historical trends may be related to climate variability in Northeast of Brazil, which affects both semi-arid and coastal part of the region.  相似文献   

肠道病毒病毒感染的季节和年龄分布特征及其与气象条件的分析     

席林华  刘培宁 《气象科学》2001,21(3):374-378

本文利用苏州市二院和苏州中医院1990-1995年住院病例资料，研究肠道感染，病毒感染的年龄、季节分布特征及其肠道发病住院与气象要素变化的关系，以求探索一定规律、指标供防病保健对策应用。  相似文献   

江滩暴雨中尺度特征数值模拟   总被引：1，自引：4，他引：1  

徐勇  陆汉城等 《气象科学》2001,21(1):73-79

本文使用中尺度模式MM4模拟了江滩流域1991年7月6日－7月的暴雨过程，结果表明，引发此次暴雨的中尺度气施内存在中－β尺度的雨团，雨团的位置随时间的演变具有较明显的规律性，中尺度气施内存在明显的与雨区位置相对应的双涡度中心双辐合中心，其位置与预测资料的诊断分析结果较一致。  相似文献   

牡丹江市地震小区划工作中的技术思路     

方明远  程傲雪  薛仲新 《东北地震研究》2001,17(1):43-46

按照“工程场地地震安全性评价报告编写要求”，技术思路是安评报告编写的一项主要内容。如何科学、经济、合理的确定一项安评工作的技术思路是非常重要的。本文拟就牡丹江市地震小区划工作技术思路确立中的几点认识进行简略的讨论。  相似文献