首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 78 毫秒
1.
解剖了一条出现腹泻等症状、经治疗无效死亡的海豚 ,发现肺、肝、脾、胃等均有病变 ,从病变组织器官中分离到 7株细菌 ,通过菌株的形态、染色特征、生化特性、血清学鉴定 ,发现其中 5株菌株为大肠艾希氏菌 O8血清型 ,另 2株分别为普通变形杆菌和奇异变形杆菌。动物试验表明 ,大肠埃希氏菌和变形杆菌是海豚发病的致病菌。 7个菌株均对菌必治和先锋噻肟高敏 ,对氯霉素、链霉素、痢特灵等中敏 ,对青霉素 G、氨苄青霉素等耐药  相似文献   

2.
The study aimed to assess the response of ep- and hemiedaphic Collembola communities (activity, richness, community structure) to a disturbance, the subsequent management regime and to the season (summer, winter) in a High Tatra Mountainsspruce forest destroyed by a windstorm. Fire and clear-cut resulted in an initial increase in the activity of Collembola inhabiting open areas, opportunistic or generalist species, while forest specialists diminished in numbers or disappeared. Our results indicated that treatment with non-extracted fallen trees (NEX) provided a better chance for forest species to survive compared with their survival in open habitats of extracted (EXT) and wildfire (FIR) treatments. Great species’ potential of NEX treatment was indicated by Chao2 estimator and activity/species rarefaction curves. Communities of NEX treatment were more similar to the reference (REF) treatment, documented by ordination and cluster analyses. Thus, leaving fallen timber after a windthrow to natural process of succession is suitable for survival of forest species and maintenance of diversity in forests restoration than timber extraction. Community structure in wildfire (FIR) stands was the most dissimilar to the other treatments. Most of the species trapped in this treatment belonged to hemiedaphic life forms, while the activity of larger epedaphic species diminished. In contrast, the highest number of trapped Collembola in EXT treatment was connected with the larger-bodied epigeic species with fast dispersal ability. The trapping period affected both the number of individuals and species richness; Collembola activity and species diversity in the individual treatments were lower in winter compared with the summer period. Several species increased activity during the winter period, namelyFolsomia penicula, Friesea mirabilis, F. truncata,Hypogastrura socialisand Protaphorura aurantiaca.  相似文献   

3.
建设和谐图书馆是一项长期的战略任务,馆员的审美精神对于和谐图书馆建设意义深远。阐述审美精神的内涵和基本特征,分析审美精神与图书馆精神的关系,探讨了高校图书馆馆员审美精神对和谐图书馆建设的意义,指出培育馆员审美精神的基本途径。  相似文献   

4.
为对日长年际变化进行更细致分析,利用标准Morlet小波变换方法,从日长变化序列中识别和提取出6个主要的年际信号,周期分别为2.3 a(2.4 a)、3.3 a、3.7 a、4.8 a、6.1 a和8.1 a,并基于信号的时域提取结果,计算获得相应信号的平均振幅,依次为0.08 ms、0.05 ms、0.05 ms、0.07 ms、0.10 ms和0.07 ms。仿照提取出的6个日长年际信号,对大气角动量序列中相应的信号进行提取,并对两者进行相关性分析。结果显示,大气和日长对应的4个高频年际信号(2.3 a(2.4 a)、3.3 a、3.7 a和4.8 a信号)存在强相关,相关系数分别为0.99、0.93、0.99和0.91,且大气的激发贡献率依次为99.7%、63.1%、94.7%和69.3%,表明日长2.3 a(2.4 a)和3.7 a信号几乎完全可由大气解释,而大气也为其余2个日长信号的主要激发源;大气6.0 a、8.5 a信号与日长对应的6.1 a、8.1 a信号不相关或弱相关,相关系数分别为-0.11和-0.56。  相似文献   

5.
Climatic change and human activities of northeastern sahara in Holocene   总被引:1,自引:0,他引:1  
GeologicalrecordsrevealedthattheHoloceneenvironmentshadexperienceddrasticchanges,whichwascloselyrelatedtohumanevolutionandfin...  相似文献   

6.
Relative dispersion ratio(RDR) can be used to quantify the deviation behavior of a water parcel's trajectory caused by a disturbance in a hydrodynamic system. It can be calculated by using a standard method for determining relative dispersion(RD),which accounts for the growth of the deviation of a cluster of particles from a specific initial time. However, the standard method for computing RD is time consuming. It involves numerous computations on tracing many water parcels. In this study, a new method based on the adjoint method is proposed to acquire a series of RDR fields in one round of tracing. Through this method,the continuous variation in the RDR corresponding to a time series of the disturbance time t can be obtained. The consistency and efficiency of the new method are compared with those of the standard method by applying it to a double-gyre flow and an unsteady Arnold-Beltrami-Childress flow field. Results show that the two methods have good consistency in a finite time span. The new method has a notable speedup for evaluating the RDR at multiple t.  相似文献   

7.
Seismic wave modeling is a cornerstone of geophysical data acquisition, processing, and interpretation, for which finite-difference methods are often applied. In this paper, we extend the velocity-pressure formulation of the acoustic wave equation to marine seismic modeling using the staggered-grid finite-difference method. The scheme is developed using a fourth-order spatial and a second-order temporal operator. Then, we define a stability coefficient (SC) and calculate its maximum value under the stability condition. Based on the dispersion relationship, we conduct a detailed dispersion analysis for submarine sediments in terms of the phase and group velocity over a range of angles, stability coefficients, and orders. We also compare the numerical solution with the exact solution for a P-wave line source in a homogeneous submarine model. Additionally, the numerical results determined by a Marmousi2 model with a rugged seafloor indicate that this method is sufficient for modeling complex submarine structures.  相似文献   

8.
在群舞创作中,舞蹈构图就是舞蹈演员与整个舞台空间的静止画面,"静止"是舞蹈构图的表现形式,"流动"是舞蹈调度的表现形式,作为舞蹈构图与构图的必要连接,在营造舞蹈情境和增强形式美上起到了补充作用。舞蹈调度是变换舞蹈构图的一种过程,舞蹈构图是调度过程的某一个停顿和结果。二者相辅相成,不断进行连接和变化,为表现舞蹈作品的主题,交代环境情节和塑造舞蹈形象而发挥其特有的作用。  相似文献   

9.
Chronology establishment and dating data analyses on lacustrine deposits in northeastern Sahara show that vast fresh lakes existed over there between 9900–2400 a B. P. Especially, great continuous lakes developed and got their maximum extent during the period from 9800 a B. P. to 6450 a B. P. From 6000 a B. P. to 3600 a B. P., the evolution of the lakes experienced a new stage with a property of drastic fluctuations and a periodicity of 600 years, which was the response to the climatic environment changes. On the aspect of the relation between natural environment and the human, the warm-humid period in the Holocene was not only a very important time for human development and evolution, but also was a moment for human reproduction and division. On the other hand, this warm-humid period was also a distinguished time to natural environment changes, the accumulation of the strong weathered debris and fine materials formed the basements for the formation of the Sahara Desert. Supported by the National Natural Science Foundation of China, German Research Foundation and Gansu Provincial Natural Science Foundation.  相似文献   

10.
中国民俗中对婴儿体貌的审美是以婴儿的生理特征为基础,认为身体白胖、脸庞丰满、额部高宽、头部圆大是形成婴儿体貌美的因素。这种婴儿的体貌美是一种趋向变形、夸张的美,是融合优美和滑稽美的审美形态。也是一种象征意义的美,具有深厚的中国民俗文化意蕴。反映了中国人特有的追求平安、健康的在世理想,以及特殊的求福、祈福文化和审美心理。  相似文献   

11.
电影不仅是作为一种艺术品,同时也是作为一种商品存在,而电影片名就好比是电影的一件外衣,因此,确切地翻译电影片名非常重要。电影片名的翻译技巧有很多,同时影响电影片名的翻译的因素也有很多。因此,在翻译电影片名时要从各方面因素考虑,从而选择恰当的翻译技巧,使得译名不仅能够从意义上忠实于源名,涵盖电影的内容,同时在形式上做到简练并具有吸引力。  相似文献   

12.
To study the bubble plume’s seismic response characteristics, the model of a plume water body has been built in this article using the bubble-contained medium acoustic velocity model and the stochastic medium theory based on an analysis of both the acoustic characteristics of a bubble-contained water body and the actual features of a plume. The finite difference method is used for forward modelling, and the single-shot seismic record exhibits the characteristics of a scattered wave field generated by a plume. A meaningful conclusion is obtained by extracting seismic attributes from the pre-stack shot gather record of a plume. The values of the amplitude-related seismic attributes increase greatly as the bubble content goes up, and changes in bubble radius will not cause seismic attributes to change, which is primarily observed because the bubble content has a strong impact on the plume’s acoustic velocity, while the bubble radius has a weak impact on the acoustic velocity. The above conclusion provides a theoretical reference for identifying hydrate plumes using seismic methods and contributes to further study on hydrate decomposition and migration, as well as on distribution of the methane bubble in seawater.  相似文献   

13.
Reviving Ancient Water Tunnels in the Desert-Digging for Gold?   总被引:3,自引:0,他引:3  
The water shortage in the Middle East is a well-known problem. The introduction of diesel operated pumps for irrigation has caused a severe drop in groundwater levels. At the same time the demand for groundwater is growing to alarming proportions. Alternative ways of groundwater supply and management need to be found to halt social and economical disaster in the future. Why not look at history? Qanats are subterranean tunnels ancient civilizations built to access groundwater. The technique is a sustainable method of groundwater extraction. Throughout the Middle East some settlements still make use of these ancient systems. In the summer of 2000, a community rehabilitation of a qanat was executed International Center for Areas (ICARDA) and with support from the Agricultural Research in Dry international donors. The renovation served as a pilot community intervention within a participatory action research project aimed at evaluating the use of qanats in Syria. In a second stage of the project, the pilot was scaled up to a nation-wide survey of Syrian qanats in 2001. This resulted in qanat renovations on other sites executed in 2oo2 and 2oo3 with further international support. This paper compares the first pilot renovation with a recent qanat renovation that took place in Qarah, Syria.  相似文献   

14.
通过对几种重力场插值算法的研究指出,重力场高频区域往往存在较大的插值误差,若能在高频区域补充测点,则可以较小的代价,达到提高插值精度的目的。利用小波分析可感知重力场空间频率信息的特点,提出以一定分辨率重力基准图的小波细节信息为转移概率,由随机采样方案在重力场高频区域增加测点,从而有效提高插值精度的策略。与均匀分布测点的方案对比可知,在插值精度提升程度大致相同的情况下,该策略所需的测点数较少,插值误差的极值较小,效率较高。  相似文献   

15.
A framework is proposed to characterize and forecast the displacement trends of slow-moving landslides, defined as the reactivation stage of phenomena in rocks or fine-grained soils, with movements localized along one or several existing shear surfaces. The framework is developed based on a thorough analysis of the scientific literature and with reference to significant reported case studies for which a consistent dataset of continuous displacement measurements is available. Three distinct trends of movement are defined to characterize the kinematic behavior of the active stages of slow-moving landslides in a velocity-time plot: a linear trend-type I, which is appropriate for stationary phenomena; a convex shaped trend-type II, which is associated with rapid increases in pore water pressure due to rainfall, followed by a slow decrease in the groundwater level with time; and a concave shaped trend-type III, which denotes a non-stationary process related to the presence of new boundary conditions such as those associated with the development of a newly formed local slip surface that connects with the main existing slip surface. Within the proposed framework, a model is developed to forecast future displacements for active stages of trend-type II based on displacement measurements at the beginning of the stage. The proposed model is validated by application to two case studies.  相似文献   

16.
在对牛顿经典力学和爱因斯坦相对论对空间时间概念阐述的基础上,指出由于地壳运动是个宏观低速现象,因此完全可采用牛顿力学描述地壳质点在空间的位置以及在外力作用下该位置是如何随时间改变的,决定了必须选择一个不作加速度运动的参照系,才能正确使用牛顿定律对地壳运动进行正确的描述.因此满足牛顿惯性定律的参照系为地壳运动分析使用的坐...  相似文献   

17.
A number of different lahars have been recognized from a systematic survey of a mapping project. The high setting temporamre feature of the deposits indicates a relationship between the lahar and the Millennium eruption event of Tianchi Volcano. The lahars caused a dramatic disaster. Recognize of the huge avalanche scars and deposits around Tianchi Volcano imply another highly destructive hazard. Three types of different texture of the avalanche deposits have been recognized. There was often magma mixing processes during the Millennium eruption of Tianchi Volcano, indicating a mixing and co-eruption regime of the eruption.  相似文献   

18.
排山楼异常是一个由Au,Ag,Sb和Hg等元素组成的低缓组合异常,金元素离散程度大,分布不均匀。伽玛能谱测量钾含量结果表明;钾的增高与降低同高背景中磁场的变化相吻合.异常曲线形态呈“马鞍形”特征,这一地球物理场可作为排山搂金矿地球物理模型,同时亦是在该区寻找同类金矿的找矿标志。  相似文献   

19.
Rossby waves with linear topography in barotropic fluids   总被引:1,自引:0,他引:1  
Rossby waves are the most important waves in the atmosphere and ocean, and are parts of a large-scale system in fluid. The theory and observation show that, they satisfy quasi-geostrophic and quasi-static equilibrium approximations. In this paper, solitary Rossby waves induced by linear topography in barotropic fluids with a shear flow are studied. In order to simplify the problem, the topography is taken as a linear function of latitude variable y, then employing a weakly nonlinear method and a perturbation method, a KdV (Korteweg-de Vries) equation describing evolution of the amplitude of solitary Rossby waves induced by linear topography is derived. The results show that the variation of linear topography can induce the solitary Rossby waves in barotropic fluids with a shear flow, and extend the classical geophysical theory of fluid dynamics.  相似文献   

20.
在地理空间知识的表达中,通常以文本方式描述位置。除了常见的地名以及地址外,许多陈述根据与参照地物的空间关系来表达一个目标地物的位置。由于一个空间陈述只是粗略描述了目标对象的位置,因此具有不确定性。在基于空间陈述的定位问题中,不确定性包括4个层次,分别对应于陈述、参照对象、空间关系和目标对象。这4个层次的不确定性适合于不同的建模方式,如概率方法、模糊集方法,以及证据理论方法等。本文采用不确定性场的概念,对点状目标地物的分布进行了探讨,并利用贝叶斯定理证明了对于给定的空间陈述,其不确定性场分布与做出该陈述概率,以及相应空间关系的模糊性之间的联系,该结论可用于指导不确定性场的建立。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号