Linear current instability in loop prominences     

Y. H. Tang  C. Fang  L. S. Cui 《Solar physics》1995,158(1):71-80

By use of the dispersion equation given by Song, Wu, and Dryer (1987) for a cylinder plasma with mass motion and gravity included, we investigate the linear current instabilities developed in loop prominences. The results indicate that the mode of linear instability depends mainly on whetherv _s ² > or not, wherev _s is the sonic velocity at heightz, =GM/(R +z) is the gravity potential,G the gravitational constant,M andR the mass and the radius of the Sun respectively. Ifv _s ² > , then the sausage instability will be dominant. Otherwise, the kink instability will be more important. A possible explanation of knot structure, which appears sometimes in solar loop prominences has been given.  相似文献   

The research of phosphorus of Xiangxi River nearby the Three Gorges, China     

Chang-Ying Fu  Tao Fang  Nan Sheng Deng 《Environmental Geology》2006,49(6):923-928

The Xiangxi River is the first middling tributary of the Changjiang River near the Three Gorges Dam. The River is subject to phosphorus pollution mainly from industrial wastewater. As the water quality of the Xiangxi River could directly influence the water quality of the Three Gorges Reservoir, the research on phosphorus levels and its change in the sediment profile of the Xiangxi River could provide useful information in the dynamic changes in the system, thereby offering options for mitigative measures. Water and sediment samples from lower reaches of Xiangxi River were collected and the different forms of phosphorus in sediments of the Xiangxi River were studied. The concentrations of total phosphorus in sediment ranged from 757.67 to 1438.54 mg/kg. Inorganic phosphorus concentrations ranged from 684.63 to 1055.58 mg/kg. Phosphorus contamination was serious in some parts of the Xiangxi River. With an average concentration of 635.17 mg/kg, calcium-bound phosphorus is the main form among different inorganic phosphorus forms. Labile phosphorus and iron/aluminum-bound phosphorus measured 3.40, 0.05and 35.28 mg/kg, respectively. The mobilization potential of phosphorus of sediments was studied through adsorption and release experiments. The equilibrium concentration of phosphorus adsorption and release was around 0.1 mg/L. The initial concentrations of phosphorus in the overlying water and the sediments have obvious effect on phosphorus mobilization potential. In addition, the release rate of phosphorus in sediment increased with water depth.  相似文献   

金沙江干热河谷区土壤侵蚀危险度评价——以云南元谋为例     

周红艺  熊东红杨忠 《山地学报》2006,24(B10):52-56

利用空间主成分分析方法，选取降水、坡度、植被、土地利用、土壤类型、人口、高程等作为评价指标，建立空间主成分评价模型Pi=0．78X1＋0．06X2＋0．05X3＋0．04X4，将研究区分为无险型、轻险型、危险型、强险型和极险型五种类型，较为准确地得到了危险度综合评价结果。因此，空间主成分分析模型，在土壤侵蚀危险程度评价方面的应用较为成功，是一种科学有效的研究方法。  相似文献   

Mongolian gerbils and Daurian pikas responded differently to changes in precipitation in the Inner Mongolian grasslands     

G. Wang  W. Zhong 《Journal of Arid Environments》2006,66(4):648-656

Mongolian gerbils (Meriones unguiculatus) and Daurian pikas (Ochotona dauurica) are two key small mammal species in the Inner Mongolian grasslands, China. Mongolian gerbils displayed density-dependent population growth, but the time lag of density dependence was short and within season. The spring–autumn population growth rate was inversely related to population density in Mongolian gerbils of the Erdos desert grasslands. The autumn–spring population growth rate of Mongolian gerbils was inversely related to winter precipitation. Precipitation had stronger effects on the population growth of gerbils during the non-breeding season. The monthly population growth rate of Daurian pikas was positively related to the monthly precipitation and was inversely related to population density in central Inner Mongolia. Daurian pikas select habitats with tall plants. Increased precipitation enhances plant production and increases the height of plants in arid and semi-arid regions. This enhancement of plant height might increase the population growth of Daurian pikas. Mongolian gerbils live in short grasslands. Increased winter precipitation might result in higher winter mortality of Mongolia gerbils, or taller plants might supress gerbil population growth in wet years. Therefore, responses of small mammal species to changes in precipitation depend on the life history of small mammals and changes in vegetation induced by climatic changes.  相似文献   

青藏高原清水河多年冻土区铁路路基沉降变形特征研究   总被引：3，自引：1，他引：3  

李忠  徐文明  陈明长 《工程地质学报》2006,14(6):824-829

通过埋设在青藏铁路路基中两个断面内的6条沉降观测管3 a来的地基沉降变形资料,研究了高原多年冻土区铁路路基的沉降变形特征,分析了填筑铁路路基对下伏多年冻土融化变形的影响。研究表明,由于受到填筑路基时赋存在路基填料内的热量的影响,铁路路基下伏多年冻土上限在施工初期会有一个明显的下移沉降,铁路路基也随之有一个较大幅度的工后下沉变动,随着时间的推移,路基下降速率会逐渐下降,但在短时间内不会停止下来,而且由于太阳辐射和路基边坡形状的影响,路基向阳面与背阴面的变形有较大的差别,且在近南北向展布的路基上表现最为明显。  相似文献   

西北地区的自然环境类型   总被引：3，自引：0，他引：3  

何芳  李英  徐友宁  张江华  陈社斌 《西北地质》2005,38(3):93-99

自然环境区划是国土规划的重要基础，是自然环境综合特征的基本反映.以西北地区的气候分区、地貌分区、植被分区（生态分区）为基础，将西北地区的自然环境类型划分为5个自然分区：阿尔泰-准噶尔区，塔克拉玛干-毛乌素沙漠区，青藏高原东北缘区，黄土高原区，秦巴山地与汉水谷地区.这5个区有完全不同的自然环境特征和资源优势特征，因而开发对策和环境对策是不同的，应予以分别对待.正确认识各区的自然环境特征，才能实现西北地区社会经济及环境的可持续发展。  相似文献   

石太线下行K135滑坡特征与成因分析     

曹金亮  魏放  韩颖 《中国地质灾害与防治学报》2005,16(1):49-52

滑坡位于石太线下行K135路段右侧偏西，平面上呈近似椭圆形，由原有老滑坡复活而形成。根据滑坡勘察，滑坡所处地貌单元属侵蚀剥蚀低中山区，滑坡区地层组成为第四系松散堆积物下伏晚古生代二叠系石千峰组泥岩、砂岩互层。在分析滑坡几何特征、地质构造特征、水文地质条件及滑坡变形破坏特征的基础上，探讨了滑坡的成因，认为老滑坡的成因以自然形成为主，新滑坡则发育并活动于老滑坡堆积物中，因某部门在老滑坡体前缘修建收费站，进行了大面积不适当的工程开挖，形成临空面，加之降雨的作用降低了土体的粘聚力及抗剪强度，在上覆岩土体的重力作用下形成新滑坡。老滑坡为巨型厚层滑坡，属于自然滑坡，新滑坡为大型中层滑坡，属于工程滑坡。  相似文献   

胶北晚中生代煌斑岩的岩石地球化学特征及其成因研究   总被引：16，自引：5，他引：16  

刘燊胡瑞忠赵军红  冯彩霞钟宏曹建劲史丹妮 《岩石学报》2005,21(3):947-958

胶北煌斑岩分别采自龙口、烟台和威海地区，包括拉辉煌斑岩、斜闪正煌岩和角闪煌斑岩，煌斑岩K—Ar全岩年龄变化于89．3～169．5Ma，为晚中生代岩浆活动的产物。在岩石化学组成上，SiO2=42．02％～54．95％，以钙碱性系列为主．岩石以富集大离子亲石元素（LILE）（Ba，U，K，Th）和LREE，亏损高场强元素（HFSE）（Nb，Ta和Ti）为特征，Mg^#=33．9～53．9，Eu／Eu^＊=0．71～0．89，^87Sr／^86Sr初始比值0．707642～0．709791，εNd（t）为-17．6～-10．4，^206Pb／^204Pb=37．588～38．431，^207Pb／^204Pb=15．423～15．531，^206Pb／^204Pb=17．204～18．179。表明煌斑岩源自俯冲陆壳（扬子下地壳）在地幔源区发生交代作用时形成的富集型地幔的部分熔融体．考虑到煌斑岩具有大陆边缘弧玄武岩的特征，我们认为煌斑岩在成因上同样与古大洋板块的俯冲作用有关，为碰撞后弧岩浆作用形成的脉岩。  相似文献   

青海气候条件对牧草再生性影响的研究   总被引：2，自引：0，他引：2  

祁如英  汪青春  陈芳 《气象》2005,31(5):21-25

选取1994～2001年河南、甘德两站牧草再生草资料及同期气象资料，通过分析同一地区不同时期及同一时期不同地区气候条件对牧草再生性的影响，建立了牧草再生草产量气候模式，讨论了再生草增、减产的气候条件。研究得出：同一地区不同时期和同一时期不同地区因气候条件不同，割草不一定能增产。  相似文献   

冬小麦夏玉米土壤水分预报及优化灌溉模型          下载免费PDF全文

邓天宏方文松  付祥军刘荣花 《气象科技》2005,33(1):68-72

利用土壤水分平衡方程，结合河南省冬小麦和夏玉米的生长规律和1994～2000年冬小麦、夏玉米田实测土壤湿度资料，建立了河南省冬小麦、夏玉米土壤水分预报及优化灌溉的计算机模型。用1998～1999年郑州市麦田实测土壤湿度资料验证该模型模拟结果，未来10、20、30天土壤湿度相对误差分别为-7．3％～7．7％、-8．3％～6．8％、-7．6％～7．7％，表明利用该模型，可以较为准确地预报未来1个月的土壤水分变化，并可根据小麦、玉米不同发育期特点，给出以最高产量和最佳经济效益为目标的灌溉建议。  相似文献