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1.
This review article commences with a comprehensive historical review of the evolution and application of various density surfaces in atmospheric and oceanic studies. The background provides a basis for the birth of the neutral density idea. Attention is paid to the development of the neutral density surface concept from the nonlinearity of the equation of state of seawater. The definition and properties of neutral density surface are described in detail as developed from the equations of state of seawater and the buoyancy frequency when the squared buoyancy frequency N2 is zero, a neutral state of stability. In order to apply the neutral density surface to intermediate water-mass analysis, this review also describes in detail its practical oceanographic application. The mapping technique is focused for the first time on applying regularly gridded data in this review. It is reviewed how a backbone and ribs framework was designed to flesh out from a reference cast and first mapped the global neutral surfaces in the world's oceans. Several mapped neutral density surfaces are presented as examples for each world ocean. The water-mass property is analyzed in each ocean at mid-depth. The characteristics of neutral density surfaces are compared with those of potential density surfaces.  相似文献   

2.
Soil erosion and associated off-site sedimentation are threatening the sustainable use of the Three Gorges Dam.To initiate management intervention to reduce sediment yields,there is an increasing need for reliable information on soil erosion in the Three Gorges Reservoir Region(TGRR).The purpose of this study is to use 137 Cs tracing methods to construct a sediment budget for a small agricultural catchment in the TGRR.Cores were taken from a pond and from paddy fields,for 137 Cs measurements.The results show that the average sedimentation rate in the pond since 1963 is 1.50 g cm-2 yr-1 and the corresponding amount of sediment deposited is 1,553 t.The surface erosion rate for the sloping cultivated lands and the sedimentation rate in the paddy fields were estimated to be 3,770 t km-2 yr-1 and 2,600 t km-2 yr-1,respectively.Based on the estimated erosion and deposition rates,and the area of each unit,the post 1970 sediment budget for the catchment has been constructed.A sediment delivery ratio of 0.5 has been estimated for the past 42 years.The data indicate that the sloping cultivated lands are the primary sediment source areas,and that the paddy fields are deposition zones.The typical land use pattern(with the upper parts characterized by sloping cultivated land and the lower parts by paddy fields) plays an important role in reducing sediment yield from agricultural catchments in the TGRR.A 137 Cs profile for the sediment deposited in a pond is shown to provide an effective means of estimating the land surface erosion rate in the upstream catchment.  相似文献   

3.
Minke whales caught in the Yellow Sea range from 4.16 m to 8.60 m in length with an average length of 6.93 m for the female and 6.14m for the male. Sex ratio of the female is 74.3%. The pregnancy ratio of all sexually matured females is 65.8 %. The minimum size of the pregnant whale observed is 6.60 m in length. Females having a body length of more than 7 m long are all sexually matured.According to the studies on the embryos obtained from the females caught in the northern Yellow Sea, there is only one breeding season each year. Mating mostly occurs from July through September, and the length of pregnancy is ten to eleven months with the peak of calving from May through July. Most females breed one calf each time, only two cases with twins. Sex ratio of female fetus is 56.6%, and the newly born calf measures 250-270 cm in body length.  相似文献   

4.
Starfish oocytes with intact germinal vesicles (GVs) were cut along desired planes with glass needles or ligated using silk thread loops into two parts and allowed to mature in vitro, and inseminated. The experimental results showed that (1) only the parts with GVs or partial GV contents (PGVCs) cleaved, those without any GV materials did not; but nucleated and non-nucleated fragments cut from mature eggs were able to divide; (2) the development of animal parts of oocytes containing GVs or PGVGs was like that of animal fragments of matured oocytes with female pronuclei; most of them gave rise to permanent blastulae. and just a few formed ectodermal vesicles with a little primary mesenchyme; (3) a large part of vegetal fragments with GVs or PGVCs. and the vegetal parts of mature eggs without female pronuclei developed into small but normal embryos; (4) the fragments containing GVs or PGVCs obtained from the oocytes along a plane parallel to the animal-vegetal (A-V) axis developed as normally as the halve  相似文献   

5.
Magnetotelluric(MT)inversion and seismic inversion are important methods for the interpretation of subsurface exploration data,but separate inversion of MT and seismic produces ambiguous and non-unique results due to various factors.In order to achieve accurate results,the authors propose a joint inversion method of two-dimensional MT and seismic data in the frequency domain.The finite element method is used for numerical simulation of electromagnetic data in the forward modelling,and the Gauss-Newton method is used for the inversion.The 9-point-finite-difference method is used to solve the seismic wave field in the acoustic wave equation,and the inverse problem of seismic data is solved by full waveform inversion with a conjugate gradient,a simple and fast method.Cross gradient functions are used to provide constraint structure between resistivity and velocity parameters to carry out the joint inversion.The joint inversion algorithm is tested by double-rectangular model synthesis data,and the accuracy of the algorithm is verified.The results show that the joint inversion results are better than those from separate inversion.The algorithm is applied to a geophysical model of a metalliferous deposit in Jinchuan and is compared with the separate inversion results.It shows that the results obtained with joint inversion are much closer to the real model.  相似文献   

6.
The major concern of this article is to address the shortcoming and outgoing effects of the human activities on the landscape patterns and their consequences in the Sefidrood River watershed in Iran. A flow of data includes three inputs; each of them belongs to one part of three zones of a fluvial system. The three parts of the Sefidrood River fluvial system include Zone 1, a sub-watershed as degradation modeling site, Zone 2, Sefidrood Dam asdam site, and Zone 3, 17kin away from the Sefidrood River path to the Caspian Sea as ending point site. The degra-dation model in the Zone 1 provides a suitable mean for decision support system to decrease the human impacts oneach small district. The maximum number for degradation coefficient belongs to the small district with the highest physiographic density, relatively cumulative activities, and a lower figure for the habitat vulnerability. The human degradation impact were not limited to the upstream. The investigation to the Sefidrood Dam and ending point of the Sefidrood River depicts that sedimentation continues as a significant visual impact in the Sefidrood Dam reservoir and the estuary.  相似文献   

7.
A model to derive direct runoff hydrograph for an ungauged basin using the physical properties of the basin is presented. The basin is divided into grid cells and canal elements. Overland flow is generated from each grid cell of the basin by application of continuous effective rainfall of 1 mm/hr to the basin. The flow generated is routed through downstream grid cells and the canal elements using the kinematic wave approach. The travel time for direct runoff from each grid cell to the basin outlet is calculated and the S-curve is derived for the basin. The S-curve is used to derive the unit hydrograph of a given duration for the basin. The model, referred as Cell-basin model was applied to the Upper Kotmale Basin in Sri Lanka and the model predictions of direct runoff hydrographs for rainfall events agreed with the observations to a reasonable accuracy. Comparison of the unit hydrographs obtained from the model and from the conventional Snyder’s synthetic unit hydrograph using regionalized parameters assuming the basin as an ungauged basin, with the unit hydrograph derived from the observations showed that the model predicted unit hydrograph was more suitable than that obtained by Snyder’s method for Sri Lankan up country basins. Thus, the present model is a useful tool to obtain direct runoff hydrograph for ungauged basins.  相似文献   

8.
A probabilistic view of debris flow   总被引:1,自引:1,他引:0  
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9.
The Healthy China Initiative is a major health strategy being pursued by the country.To prevent and control different types of diseases as well as their complex variants,research on the spatio-temporal differentiation among and mechanisms of influence of epidemic diseases is growing worldwide.This study analyzed monthly data on the incidence of influenza by using different methods,including Moran’s I,the hotspot analysis model,concentration analysis,and correlation analysis,to determine the characteristics of spatiotemporal differentiation in the incidence of influenza across prefecture-level cities in China from 2004 to 2017,and to examine its relationship with air pollution.According to the results,the overall incidence of influenza in China exhibited a trend of increase from 2004 to 2017,with small peaks in 2009 and 2014.More cases of influenza were recorded in the first and fourth quarters of each year.Regions with higher incidences of influenza were concentrated in northwestern and northern China,and in the coastal areas of southeastern China.Over time,the distribution of regions with a higher incidence of influenza has shifted from the west to the east of the country.A significant relationship was observed between the incidence of influenza and factors related to air pollution.The contents of five air pollutants (PM_(2.5),PM_(10),SO_2,NO_2,and CO) were significantly positively correlated with the incidence of influenza,with a decreasing order of contribution to it of SO_2CONO_2PM_(2.5)PM_(10).The content of O_3 in the air was negatively correlated with the incidence of influenza.The influence of air pollution-related factors on the incidence of influenza in different regions and seasons showed minor differences.The large-scale empirical results provided here can supply a scientific basis for governmental disease control authorities to formulate strategies for regional prevention and control.  相似文献   

10.
The paper gives two examples of larger construction projects with typical stability problems. The first example is from Sakhalin Island in the Russian Far East. It is connected with a construction of oil and gas pipelines through the mountainous terrain in Makarov region. The region has an active geotectonic history and is highly affected by uncontrolled erosion and extensive landslips. Basic principles of landslide hazard mitigation are presented. The second example is from a motorway construction in Azerbaijan. This motorway leads from Baku to Russia through a seismo-tectonically active area at the toe of Caucasian mountains and in some places is situated in deep cuts at the toe of high slopes. This unsuitable routing, together with seismic activity, led to a slope stability failure of a slope affected by recent tectonic movements near the village of Devechi. Stability conditions and designed remedy measures are presented.  相似文献   

11.
The fructification of the noeggerathialean foliage Plagiozamites is very likely a cylindric strobilus based on close associations from the Early Permian Lower Shihhotse Formation of Weibei Coalfield in Shaanxi and Dengfeng Coalfield in Henan. The strobilus is articulated. Sporophylls arise from the node, with the proximal parts slightly united and with a right angle to the axis; distal parts upturned pointing upwards and nearly parallel to the axis, covering the neighboring sporophylls of the next node. A sessile sporangium is situated at the adaxial side of each sporophyll. There are 12-16 sporangia and sporophylls in each node. This type of strobilus may have been identified as some sphenophyllalean/equisetalean cones in previous study.  相似文献   

12.
Starfish oocytes with intact germinal vesicles (GVs) were cut along desired planes with glass needles or ligated using silk thread loops into two parts and allowed to mature in vitro, and inseminated. The experimental results showed that (1) only the parts with GVs or partial GV contents (PGVCs) cleaved, those without any GV materials did not; but nucleated and non-nucleated fragments cut from mature eggs were able to divide; (2) the development of animal parts of oocytes containing GVs or PGVCs was like that of animal fragments of matured oocytes with female pronuclei; most of them gave rise to permanent blastulae, and just a few formed ectodermal vesicles with a little primary mesenchyme; (3) a large part of vegetal fragments with GVs or PGVCs, and the vegetal parts of mature eggs without female pronuclei developed into small but normal embryos; (4) the fragments containing GVs or PGVCs obtained from the oocytes along a plane parallel to the animal-vegetal (A-V) axis developed as normally as the halves (with or without female pronuclei) severed from mature eggs along the same axis. Based on the data above, it was concluded that (1) the non-chromatin materials in the oocyte GVs are indispensable for successful fertilization and cleavage of starfish eggs; (2) some factor (s) located asymmetrically in the vegetal hemispheres of starfish oocytes is (are) responsible for formation of the archenteron and primary mesenchyme. It is evident from the above findings that the oocyte cytoplasm of the starfish had already regionalized before the GV break-down. Contribution No. 1722 from the Institute of Oceanology, Academia Sinica  相似文献   

13.
?????????????????????Χ??????У?????????????????????????????????????????α???? ??????????????Χ?????????????鷢????????????????????μ?????????????????????????????????? ??????????α??????????????????????????????????μ?Σ????α?????????????????μ??? ???α?????????????Σ?-????????????????????????????????μ??????α???????????????????μ?Σ????α?????????????Σ???????????????????????????Χ???????????????????Σ?ū????????????????????????ΣΣ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????  相似文献   

14.
It is unknown whether cytoplasmic determinants in goldfish eggs are asymetrically localized before maturation. In this study fully grown goldfish oocytes with intact germinal vesiles (GVs) were ligated with baby hair loops along desired planes into two parts, matured in vitro, and inseminated. Embryos developed from the animal halves with GV of oocytes ligated along the equator were unable to undergo epiboly, while those developed from the GV-containing parts of oocytes ligated along the animal-vegetal axis were able to. Also, embryos developed from the animal halves obtained from fertilized eggs could undergo epiboly. From these results, it was postulated that the goldfish's premature oocyte possessed a putative factor in the vegetal hemisphere which was responsible for epiboly of the embryonic cells. This work was supported by the NSFC and the “Climb Plan B” (PD-B6-1-1) of the Chinese Commission of Science and Technology. Contribution No. 2915 from the Institute of Oceanology, Chinese Academy of Sciences.  相似文献   

15.
根据山西煤田实际资料 ,建立了推算山西煤盆地最高古地温的数学模式 ,探讨了区内热演化史 ,提出了山西煤盆地于成煤期后 ,曾有两次大的热演化过程 ,一为印支期 ,主要是快速沉降堆积增温阶段 ;一为燕山期 ,主要表现为岩浆区域热叠加增温现象 ,煤层气相应出现两个生成高峰期  相似文献   

16.
以湖北省为研究对象,基于铁路客流的动态关系数据,采用城市网络连锁模型,以城市之间铁路客流的流动性和集聚性为研究切入点,辨析省域城市的网络关联强度和空间组织结构特征。研究表明:① 湖北省域城市网络结构初步形成,整体呈现“东强西弱,北低南高”的态势,省域“单中心”网络格局特征突出,武汉是链接鄂东、鄂中、鄂西三大区域的核心枢纽;② 中心城市指向性和地域邻近指向性特征明显,整体受省域中心城市武汉的影响较大,与之紧密联系的周边城市是构成武汉“1+8”都市圈的主体;③ 交通轴线是客流联系的主要方向,以“十堰—襄阳—荆门—武汉”、“恩施—宜昌—荆州—武汉”等城市为主体的“>”型城市带,其空间组织结构联系较为紧密,是推动湖北省经济发展和实施城镇化战略的重要载体,同时襄阳、宜昌在鄂西地区的枢纽作用日益凸显。最后基于实证研究结论,为省域空间规划的要义、趋势和取向提出了若干探讨。  相似文献   

17.
临近节点是影响矢量数据质量的关键问题.本文针对数据维度提升带来的高维信息这一特征,将要素节点升级为节点缓冲区,设计实现了基于要素节点缓冲区融合的临近节点检查方法,通过多源数据合并、要素转节点、相同节点融合、缓冲以及缓冲区融合等步骤获得要素节点缓冲区融合面,最后通过面积容差判定出临近节点所在范围.实验证明,算法通用性强,...  相似文献   

18.
收集青藏高原东北缘及其周边地区371个震源机制解数据,对该区域进行1°×1°经纬度网格的构造应力场反演。结果表明,青藏高原东北缘内缘最大主压应力以NE向为主,外缘最大主压应力由西向东呈现出顺时针旋转的特征,即最大主压应力轴由西段近NNE向转为中段NE向,再转为东段NWW向。从不同深度对青藏高原东北缘及其周边地区进行2°×2°经纬度网格的构造应力场反演。结果显示,地壳上下部分断层体系存在巨大的变化差异,产生这种差异的原因可能与地壳的挤压增厚有关。  相似文献   

19.
针对数字天顶仪,研究一种解算CCD坐标系x轴与北向之间夹角以实现定向的方法。通过对称位置两幅星图解算得到的天顶仪旋转轴的天文坐标,与已知测站点位置真值进行运算,得到相应的切平面坐标系倾斜量。结合双轴倾角仪测量的倾角计算倾角仪X敏感轴的方位角,并运用最小二乘算法解算出倾角仪的定向角,最终解算出CCD坐标系x轴方位角而实现定向。对数字天顶仪的一个工作循环采集的数据进行解算,得到的方位角标准差σ=3.06′,CCD坐标系x轴方位角满足3σ要求,可以实现定向的目的。  相似文献   

20.
径向基函数(Radial Basis Function,RBF)是一种不需对数据做任何假设,能准确逼近任意维度数据的空间插值方法。其特别适合于复杂地形的数字高程模型(Digital Elevation Model,DEM)插值重建,但随着已知点数量的增加会导致插值模型求解困难或缓慢。针对这个问题,本文基于二叉树自适应递归分块原理,采用局部最优形态参数的RBF分块插值方法进行DEM插值重建。首先,设定子区域最小点数阈值和相邻子区域的重叠率,自顶向下,对研究区域进行递归分块,构建区域分块二叉树,对二叉树叶子节点区域,采用逐点交叉验证(Leave One Out Cross Validation,LOOCV)方法求解其最优形态参数,建立局部RBF最优插值模型;然后,根据单元分解原理,采用加权平均方法对相应叶子节点区域内的待插值点高程进行加权求和,自底向上递归求解,得到待插值点最终高程值。以云南某地区DEM进行插值实验表明,采用本文方法进行DEM插值重建,稳定性较好,插值精度高。  相似文献   

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