江西省修水县地质灾害及减灾防灾措施探讨     

楼法生 《江西地质》1998,12(4):291-294

崩塌、滑坡、山洪、山坡型泥石流为修水县主要地质灾害类型。通过对地质灾害形成条件的分析,进而提出防灾减灾措施  相似文献   

近百年齐齐哈尔市的气温变化   总被引：6，自引：0，他引：6  

娄德君  孙卫国  李治民 《气象》2004,30(12):65-67

通过对齐齐哈尔市近百年来气温变化的多时间尺度结构和局部化特征的分析，得出齐齐哈尔市的气温不仅存在准2a、4a、4～6a和8a左右的年际尺度的周期性变化，也存在40～60a的年代际尺度的周期性变化；而且具有明显的突变特征，40～60a尺度的冷暖交替分别出现在1924、1955和1989年。  相似文献   

Physical properties of white-light flares derived from their center-to-limb distribution     

Donald F. Neidig  Philip H. Wiborg  Lou B. Gilliam 《Solar physics》1993,144(1):169-194

We compare the observed center-to-limb distribution of 86 white-light flares (WLFs) with calculated distributions derived from five flare models, each covering different heights, temperatures, and densities in the solar atmosphere. Considering the limited statistics and the possibility of selection effects in reporting WLFs, the following results may be considered tentative: (1) WLFs cannot be modeledsolely by high-altitude optically thin sources, by optically thin chromospheric sources, or by photospheric sources located less than 150 km above the ₅₀₀₀ = 1 level; (2) middle photospheric sources extending somewhat higher than 150 km provide the best fit to the observed center-to-limb distribution, and (3) middle photospheric sources not exceeding 150 km altitude combined with chromospheric or higher-altitude sources are acceptable. An important feature of this work is that the methods used in the analysis are entirely independent of spectral analysis; yet spectral analysis has provided evidence for both photospheric and chromospheric components in WLFs.Operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. Partial support for the National Solar Observatory is provided by the USAF under a Memorandum of Understanding with the NSF.  相似文献   

海洋测量船激光码头标校的论证与试验     

陈一飞 《测绘学院学报》1990,(1)

本文简要介绍激光码头标校方案,采用电子全站仪的极坐标法测定激光束首尾两点的坐标,来解算惯性导航平面倾角(θ、ψ)和航向角κ。文中对DIOR 3002测距仪无反光镜合作时的测距精度、电子全站仪的定点精度、电子全站仪之间同步测量、数据自动传输等作了详细的试验,得出了适合于激光码头标校最佳测量条件,为激光码头标校部分代替船坞标校提供了论证基础。  相似文献   

Obduction-type granites within the NE Jiangxi Ophiolite: Implications for the final amalgamation between the Yangtze and Cathaysia Blocks   总被引：7，自引：0，他引：7  

Wu-Xian Li  Xian-Hua Li  Zheng-Xiang Li  Fa-Sheng Lou 《Gondwana Research》2008,13(3):288-301

Leucogranitic lenses are found within the Xiwan ophiolitic mélange in northeastern Jiangxi Province, South China. The leucogranites occur exclusively within the serpentinized peridotite unit of the ophiolite suite. SHRIMP U–Pb zircon dating results indicate that these granites were formed at 880 ± 19 Ma, and were overprinted by an Indosinian tectono-thermal event at ~ 230 Ma. The leucogranites are peraluminous (A/CNK = 1.0–1.24), characterized by high Al₂O₃ (14–18.33%) and Na₂O (6.5–10%) and clearly low εNd(T) values of 0.8 to − 3.9 compared with the other rock units of the ophiolite suite. On the basis of their REE characters, the leucogranites can be divided into three groups. Group I leucogranites show the most fractionated LREE-enrichment patterns (with La_N/Yb_N and La_N/Sm_N ratios of 30.1–75.0 and 2.3–3.9, respectively). Group II leucogranites have moderately fractionated LREE-enrichment patterns (with La_N/Yb_N and La_N/Sm_N ratios of 13.1–26.5 and 0.8–1.9, respectively). Group III leucogranites are characterized by obviously low total REE contents and flat REE patterns with significant positive Eu anomalies, probably due to small degrees of partial melting. All these leucogranites were likely formed by partial melting of sedimentary rocks from a marginal basin at the Yangtze side of the orogen, beneath a major thrust fault during the obduction of the ophiolite onto the continental crust. They are broadly similar to obduction-related granites within ophiolites identified in many places worldwide. Identification of the ca. 880 Ma obduction-type granites in the NE Jiangxi ophiolite provides a petrological constraint on the timing of the ophiolite obduction onto the continental crust. In combination with the termination of the Shuangxiwu arc magmatism at ca. 890 Ma, we interpret that the close of the Neoproterozoic back-arc basin and the termination of the continental amalgamation between the Yangtze and Cathaysia Blocks occurred at ca. 880 Ma.  相似文献   

入户盗窃犯罪的时空分布热点及其机理研究——以A市CP区警情分析为例     

付逸飞 《世界地理研究》2021,30(5):1005-1014

采用核密度估计和Aoristic analysis等方法分析了2015年A市CP区入户盗窃警情的时空分布热点,并通过热点矩阵分类进一步对热点内的犯罪时空分布格局及其内在犯罪机理进行分析。结果显示：CP区共有3个犯罪热点区域和2个集中时段;3个热点区域分别为时间集中-空间聚集型、时间集中-空间分散型、时间集中-空间热点型;同时,影响入户盗窃犯罪的机理在于犯罪主体关联要素、犯罪客体关联要素、犯罪环境关联要素在时空上的密切耦合,共同影响入户盗窃犯罪活动的形成;提示在预防及控制犯罪“热点”中,需要采取更有针对性的防范措施和对策。  相似文献   

Adjustment of flood discharge capacity with varying boundary conditions in a braided reach of the Lower Yellow River     

CHENG Yifei  XIA Junqiang  ZHOU Meirong  DENG Shanshan  LI Zhiwei 《地理学报(英文版)》2021,31(11):1615-1632

It is of necessity to investigate the adjustment of flood discharge capacity in the Lower Yellow River(LYR) because of its profound importance in sediment transport and flood control decision-making, and additionally its magnitude is influenced by the channel and upstream boundary conditions, which have significantly varied with the ongoing implementation of soil and water conservation measures in the Loess Plateau and the operation of the Xiaolangdi Reservoir. The braided reach between two hydrometric stations of Huayuankou and Gaocun in the LYR was selected as the study area. Different parameters in the study reach during the period 1986–2015 were calculated, covering bankfull discharge(the indicator of flood discharge capacity), the pre-flood geomorphic coefficient(the indicator of channel boundary condition), and the previous five-year average fluvial erosion intensity during flood seasons(the indicator of incoming flow and sediment regime). Functional linkages at scales of section and reach were then developed respectively to quantitatively demonstrate the integrated effects of channel and upstream boundary conditions on the flood discharge capacity.Results show that:(1) the reach-scale bankfull discharge in the pre-dam stage(1986–1999)decreased rapidly by 50%, accompanied with severe channel aggradation and main-channel shrinkage. It recovered gradually as the geometry of main channel became narrower and deeper in the post-dam stage, with the geomorphic coefficient continuously reducing to less than 15 m-1/2.(2) The response of bankfull discharge to the channel and upstream boundary conditions varied at scales of section and reach, and consequently the determination coefficients differed for the comprehensive equations, with a smallest value at the Jiahetan station and a highest value(0.91) at reach scale. Generally, the verified results calculated using the comprehensive equations agreed well with the corresponding measured values in 2014–2015.(3) The effect of channel boundary condition was more prominent than that of upstream boundary condition on the adjustment of bankfull discharge at the Jiahetan station and the braided reach, which was proved by a larger improvement in determination coefficients for the comprehensive equations and a better performance of geomorphic coefficient on the increase of bankfull discharge.  相似文献   

草地贪夜蛾在江苏地区的发生特征及主要影响因素          下载免费PDF全文

徐敏  张海波  徐忆菲  郭安红  杨荣明  高苹 《气象科学》2023,43(6):790-797

基于2019—2022年江苏草地贪夜蛾虫情监测资料，分析了草地贪夜蛾的时空发生特征及其影响因素。结果表明：草地贪夜蛾发生区域主要集中在淮河以南地区，东部沿海的盐城和南通两地为重发区，2020年是近4 a来重发面积最大的年份；草地贪夜蛾在江苏主要危害玉米，春玉米、常规夏玉米、迟播夏玉米上均有发生，其中迟播夏玉米发生程度最重，多为集中连片发生，最高百株虫量在54.7~125.6头，最高被害株率均在93.0%以上；成虫迁入江苏的时段主要是5—9月，其中6—7月为成虫迁入峰期；草地贪夜蛾重发区、迁入峰期等与玉米种植情况、迁飞规律、大气环流、气象条件等因素密切相关。可为精准制定防控策略和监测预警提供科学依据。  相似文献   

IERS1996规范在参考系方面的改进   总被引：2，自引：0，他引：2  

夏一飞  萧耐园 《天文学进展》1999,17(2):104-112

对ＩＥＲＳ１９９６规范中有关参考系方面作了简单而系统的介绍，重点叙述了与ＩＥＲＳ１９９２标准相比ＩＥＲＳ１９９６规范在参考系方面的主要改进：天球参考架中的基本源从５７颗增加到２３６颗；动力学参考架采用ＪＰＬ ＤＥ４０３／ＬＥ４０３历表代替ＤＥ２００／ＬＥ２００历表；采用ＮＵＶＥＬ ＮＮＲ－１Ａ板块运动模型代替ＮＵＶＥＬ ＮＮＲ－１模型；变更了９个基本常数值；给出了天极坐标的观测和理论间差的经验模型  相似文献   

Self-similar dynamics of a magnetized polytropic gas     

Wei-Gang Wang  Yu-Qing Lou 《Astrophysics and Space Science》2007,311(4):363-400

In broad astrophysical contexts of large-scale gravitational collapses and outflows and as a basis for various further astrophysical applications, we formulate and investigate a theoretical problem of self-similar magnetohydrodynamics (MHD) for a non-rotating polytropic gas of quasi-spherical symmetry permeated by a completely random magnetic field. Within this framework, we derive two coupled nonlinear MHD ordinary differential equations (ODEs), examine properties of the magnetosonic critical curve, obtain various asymptotic and global semi-complete similarity MHD solutions, and qualify the applicability of our results. Unique to a magnetized gas cloud, a novel asymptotic MHD solution for a collapsing core is established. Physically, the similarity MHD inflow towards the central dense core proceeds in characteristic manners before the gas material eventually encounters a strong radiating MHD shock upon impact onto the central compact object. Sufficiently far away from the central core region enshrouded by such an MHD shock, we derive regular asymptotic behaviours. We study asymptotic solution behaviours in the vicinity of the magnetosonic critical curve and determine smooth MHD eigensolutions across this curve. Numerically, we construct global semi-complete similarity MHD solutions that cross the magnetosonic critical curve zero, one, and two times. For comparison, counterpart solutions in the case of an isothermal unmagnetized and magnetized gas flows are demonstrated in the present MHD framework at nearly isothermal and weakly magnetized conditions. For a polytropic index γ=1.25 or a strong magnetic field, different solution behaviours emerge. With a strong magnetic field, there exist semi-complete similarity solutions crossing the magnetosonic critical curve only once, and the MHD counterpart of expansion-wave collapse solution disappears. Also in the polytropic case of γ=1.25, we no longer observe the trend in the speed-density phase diagram of finding infinitely many matches to establish global MHD solutions that cross the magnetosonic critical curve twice.   相似文献