藏北牧区牲畜掉膘期温度变化特征          下载免费PDF全文

杜军  胡军  廖健  拉巴  杨勇 《气候变化研究进展》2008,4(01):26-31

利用西藏那曲地区1971-2005年日平均气温≤-5℃的初终日、持续时间及期间的负积温、平均气温、最高气温、最低气温等资料,采用气候倾向率等方法分析了近35 a来藏北牧区牲畜掉膘期及期间温度要素的变化趋势和异常年份。结果表明：藏北各牧区牲畜掉膘期开始日均呈现推迟趋势,平均推迟2.1～4.9 d/10 a;终日变化不显著;掉膘期持续时间均呈现缩短趋势。掉膘期间各牧区平均气温呈升高趋势,≤-5℃的负积温为减少趋势。掉膘期持续时间年代际变化呈明显的下降趋势,20世纪90年代掉膘持续时间短,有利于牧业生产。  相似文献   

降水时间随机性对月总降水量的影响          下载免费PDF全文

苏京志 《大气科学学报》2019,42(1):109-116

降水量在时间分布上呈现较大的随机性,极端降水事件尤为如此。受此影响,月初(月末) 1～5 d之内的累积降水量很可能会超过当月总降水量的50%乃至更多。对1961—2017年中国2 400多站点资料统计分析结果发现,月初(月末) 1～5 d累积降水量对当月总降水量显著影响事件的出现频次,在季节和空间分布上都有鲜明特征。主要包括:1)月初累积降水量对秋冬季中各月的总降水量影响更大,月末累积降水量对1—4月的月总降水量影响较大。2)受月初累积降水量的影响,显著站点数在某些年份的某些月份出现极大值;受单次事件显著影响的站点数占全国总站点数的30%～50%,此即对应着一次全国大范围的极端降水事件。3)受月初(月末)累积降水量显著影响的站点空间分布随季节变化呈现出明显空间集聚特征。  相似文献   

不同温度培养下莕菜(Nymphoides peltata)生长与光合作用特征   总被引：1，自引：0，他引：1  

施娴  陈开宁  黄蔚  杨鑫 《湖泊科学》2013,25(4):545-550

以太湖东山与西山之间水域的莕菜根茎为实验材料,在室内分别进行3种温度(28、30、32℃)处理,利用Li-6400便携式光合作用测量系统,分别测定3种温度处理下莕菜的光响应曲线和CO2响应曲线,并且利用非直角双曲线法进行拟合,得到相关参数.结果表明,3种温度下,莕菜的光合能力大小顺序表现为30℃>32℃>28℃,羧化效率为32℃>30℃>28℃,蒸腾速率、气孔导度均为30℃>28℃>32℃;28、30和32℃下的单位叶片生物量分别为0.0019±0.0002、0.0021±0.0003、0.0020±0.0003 g(DW)/cm2,叶片及其单位面积生物量为30℃>28℃>32℃,但差异不显著;30℃下的根、茎干重显著高于另外2个温度下的.在低于30℃的温度条件下,随着温度的升高,莕菜的光合能力均明显升高,促进了植物的生长;而当温度超过30℃后,光合作用效率降低,植物的生长则受到抑制.在适宜温度范围内(<30℃),小幅度的升温(2℃)产生了显著的积温效应(200℃.d),促进了莕菜的生长.因此推断,1998 2006年太湖地区平均气温升高约1.0℃的现象对近年来太湖莕菜的大面积扩张可能具有促进作用.  相似文献   

CHARACTERISTICS AND FORMATION MECHANISM OF LARGE ROCK AVALANCHES TRIGGERED BY THE LUDIAN M_S6.5 EARTHQUAKE AT HONGSHIYAN AND GANJIAZHAI          下载免费PDF全文

CHANG Zu-feng  CHANG Hao  YANG Sheng-yong  CHEN Gang  LI Jian-lin 《地震地质》2017,39(5):1030-1047

The 3 August 2014 Ludian, Yunnan M_S6.5 earthquake has spawned more than 1, 000 landslides which are from several tens to several millions and over ten millions of cubic meters in volumes. Among them, the Hongshiya and Ganjiazai landslides are the biggest two with volumes over 1 000×10⁴m³. The Hongshiya and Ganjiazai landslides are two typical landslides, the former belongs to tremendous rock avalanche, and the latter belongs to unconsolidated werthering deposit landslide developed in concave mountain slope. Based on field investigations, causes and formation mechanism of the two landslides are discussed in this study. The neotectonic movement in the area maintains sustainable uplifting violently all the time since Cenozoic. The landform process accompanied with the regional tectonic uplifting is the violent downward erosion along the Jinshajiang River and its tributary, forming landforms of high mountains and canyons, deeply cut valleys, with great height difference. The regional seismo-tectonics situation suggests that:Ludian earthquake region is situated on the southern frontier boundary of Daliangshan secondary active block, and is seismically the strongest active area with one earthquake of magnitude greater than M5.0 occurring every 6 years. Frequent and strong seismicity produces accumulated effects on the ground rock to gradually lower the mechanical strength of slopes and their stability, which is the basis condition to generate large-scale collapse and landslide at Hongshiyan and Ganjiazhai. The occurring of Hongshiyan special large rock avalanche is associated with the large terrain height difference, steep slope, soft interlayer structure and unloading fissures and high-angle joints. The formation mechanism of Hongshiyan rock avalanche may have three stages as follows:Stage 1, when P wave arriving, under the situation of free surface, rocks shake violently, the pre-existent joints(in red)parallel to and normal to the river and unloading cracks are opened and connected. Stage 2, on the basis of the first stage, when S wave arriving, the ground movement aggravates. Joints(in green)along beds develop further, resulting in rock masses intersecting each other. Stage 3, rock masses lose stability, sliding downward, collapsing, and moving over a short distance along the sliding surface to the inside of the valley, blocking the river to form the dammed lake. The special large landslide at Ganjiazhai is a weathering layer landslide occurring in the middle-lower of a large concave slope. Its formation process may have two stages as follows:Firstly, under strong ground shaking and gravity, the ground rock-soil body around moves and assembles to the lower of the central axis of the large concave slope, which suffers the largest earthquake inertia force and firstly yields plastic damage to generate compression-expansion deformation, because of the largest water content and volume-weight within the loose soil of it. Secondly, in view of the steep slope, along with the compression, the plastic deformation area enlarges further in the lower of slope, giving rise to a tensional stress area along the middle of the slope. As soon as the tensional stress exceeds the tensile strength of the weathering layer, a tensional fracture will occur and the landslide rolls away immediately making use of momentum. This two large landslides are the basic typical ones triggered by the M_S6.5 Ludian earthquake, and their causes and mechanism have a certain popular implication for the landslides occurring in this earthquake region.  相似文献   

鲁北平原地面沉降现状与机理分析          下载免费PDF全文

段晓飞  孙晓晓  杨亚宾  刘毅 《山东国土资源》2018,34(10)

该文详细论述了鲁北地区水文地质条件、工程地质条件。以多期水准测量数据为基础,以校验后的多年insar解译数据辅助,获取了鲁北地区地面沉降速率及多年累积地面沉降量。结果表明,鲁北平原年沉降速率大于50mm/a的地区面积502.73km~2,区内存在2个显著的沉降中心,一个位于德州市城区西北部张庄,地面累积沉降量超过1.3m,一个位于广饶县县城东北部,多年地面累积沉降量达1.605m,200mm沉降等值线圈闭面积14 904km~2,占鲁北平原区面积的34.34%。分析了鲁北平原地区地面沉降机理,建立了地面沉降与地下水水位相关关系,并针对现状问题提出了防治措施与建议。  相似文献   

台风对海上风电单桩基础累积变形影响试验研究          下载免费PDF全文

芦直跃  马宏旺  李玉韬  陈琛  杨峻 《海洋技术学报》2019,38(6):75-82

文中主要采用小比尺模型试验,研究了台风对海上风电单桩基础累积变形的影响。通过在模型槽中进行桩的水平静力和循环加载试验,得到了不同工况下桩的累积转角与循环加载次数之间的关系曲线。随后对曲线进行分析,拟合出无台风工况下累积转角的计算公式,然后运用叠加法,得出了有台风工况下累积转角的计算公式。试验结果表明,单独作用一种循环荷载时,桩的累积转角是循环次数的幂函数。台风引起的大幅值循环荷载会导致转角的陡升,且增加幅度与小幅值循环荷载的幅值负相关。当将台风荷载设置在加载过程的开头时,对于疲劳设计工况,台风荷载产生的累积转角占总的累积转角的99%以上,因而可以忽略小幅值循环荷载产生的累积转角,直接用台风荷载产生的累积转角代表桩的长期累积转角,实现简化设计。  相似文献   

河流过程的累积现象和随机模型     

景唤  钟德钰  张红武  石旭芳  王彦君 《地理学报》2020,75(5):1079-1094

累积现象普遍存在于河流过程中,准确考虑前期水沙条件的累积影响对冲积河流河床演变规律的研究至关重要。为揭示累积现象的物理实质,本文对国内外多条典型冲积河流上枢纽修建后其上下游河道冲淤实测资料进行了分析。定义水沙条件变化为外部扰动,并假定其发生概率符合泊松分布及单个扰动引发的系统反馈强度随时间呈指数衰减。本文运用统计力学中的随机理论给出了冲积河流外部扰动诱发的内部反馈随时间的累积过程及其时空间演进的数学描述和理论模型,并将其应用于枢纽修建后其上下游河道形态时空调整过程的模拟。结果发现,从时间上看,断面垂向、横向及全河段的冲淤调整速率早期较快,之后迅速减缓,河床累积冲刷深度、河宽及河段累积淤积量随时间不断增大直至平衡,表现出典型的累积特性;从空间上看,坝下河段冲刷强度沿程非线性衰减直至消失,这种空间分布上的不平衡是外部扰动引发的系统反馈在空间传播的同时随时间衰减的综合结果,是河流过程累积特性的另一外在表现。模型应用结果表明,河道垂向、横向、纵向及全河段的时空冲淤调整过程均可用归一化公式来描述,计算值与实测值符合较好,相关系数R ²达0.92、0.93、0.76和0.95。本文模型同时考虑了河流过程的累积特性和系统反馈的空间传播特性,可为定量描述扰动后非平衡态河道的时空调整过程提供理论依据和新的计算方法。  相似文献   

渔港港内作业水域泊稳条件的研究     

奕曙光  王云天  孟宪钦 《海洋工程》1999,17(3)

就渔港港内作业水域泊稳条件研究课题查阅了国内外有关资料,走访了多年从事渔港建设、管理的专家,并选择了两条代表性船型,进行了不同边界、不同载态情况下的模型试验及分析。试验与调查结果符合良好,在此基础上给出了１００～６００ＨＰ渔船装卸作业允许波高的近似计算公式。  相似文献   

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刘志平  何秀凤 《大地测量与地球动力学》2008,28(1):41-44

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The Newly Discovered Super-Large Wulashan-Hademengou Gold Metallogenic Belt in Inner Mongolia,China Has Gold Reserves of Over 100 Tons     

HAO Ziguo  ;FEI Hongcai  ;HAO Qingqing  ;Susan TURNER 《《地质学报》英文版》2014,88(4):1332-1333

正The Wulashan-Hademengou gold ore district in Baotou city,Inner Mongolia,is a further newly discovered super-large gold metallogenic belt in northern China.The accumulated proven gold metal amount is 84.46 t,with an average grade of3.53 g/t and a gold metal amount of 63.16 t,with an average grade of 3.30 g/t.The potential reserves are over 100 t.  相似文献