A method for testing the distinctness of clusters: A test of the disjunction of two clusters in Euclidean space as measured by their overlap     

P. H. A. Sneath 《Mathematical Geology》1977,9(2):123-143

A method is described for testing the distinctness of two clusters in Euclidean space. One first calculates the projections, q,of the N₁ and N₂ members of the clusters onto the line joining the cluster centroids. From the distributions of qan index of disjunction, W,is calculated, which corresponds to an index of overlap, V_G.The quantity W√(N₁+N₂)is distributed as noncentral tsubject to assumptions on the multivariate normal distribution of the clusters. This allows a test of whether the observed disjunction is significantly greater than a chosen figure, which is equivalent to testing whether the overlap of the clusters is significantly less than a corresponding value of V_G.Two clusters that appear distinct may be produced simply by the partitioning of a homogeneous swarm into two contiguous regions. Provided that the clusters form a dichotomy in a dendrogram, and that the clustering method yields geometrically convex clusters, a conservative test of this situation can be derived by determining the excess of Wover the value expected for a rectangular distribution.  相似文献   

甘肃河西山地土壤系统分类   总被引：2，自引：0，他引：2  

齐善忠  肖洪浪  罗芳 《山地学报》2003,21(6):763-774

根据中国土壤系统分类检索(第三版)，以甘肃河西地区土壤野外调查、室内分析数据和已有的土壤资源研究资料，在原有土壤系统分类的基础上，对河西地区山地土壤系统分类进行比较全面的归纳、概括和总结。结果表明，河西地区山地土壤分为5个土纲(干旱土、钙层土、半淋溶土、雏形土和新成土)，8个亚纲，10个土类和26个亚类。  相似文献   

What makes territory important: tangible and intangible dimensions     

Daniel J. Dzurek 《GeoJournal》2005,64(4):263-274

Conflicts over territory have resulted in innumerable wars and other violent incidents, but the reasons that some territory is more highly valued or volatile than other areas may not be obvious. This paper demonstrates a taxonomy for analyzing international territorial disputes that seeks to capture their tangible and symbolic dimensions and to weigh them as the international community might. Twenty-six territorial disputes, including offshore areas and separatist issues, were examined and scored according to 15 criteria for objective prominence and 7 criteria related to how a country might view the dispute in terms of its national interest. The taxonomy used Saaty’s Analytic Hierarchy Process to identify tangible and intangible properties, measure their interrelations, and produce intermediate and overall ranks. Each dispute was evaluated for prominence by examining intensifying (symbolic) factors, measures of magnitude, and characteristics that retard resolution. The magnitude of a dispute was judged to contribute the most to overall prominence, having twice the weight of the other two factors. The top five disputes in terms of prominence were the Kurdish issue, Kashmir, Tibet, Nagorno-Karabakh, and Xinjiang. The second hierarchy evaluated the disputes from the perspective of an international actor, in this case the United States. When judged by U.S. national interest, the most important factors were the deployment of U.S. forces in the claimant countries and if one of the claimants were a U.S. ally. Finally, the results from the two hierarchies were compared.  相似文献   

Two New Species of Eretmophyllum (Ginkgoales) from the Jurassic of Eastern Siberia     

Andrey FROLOV  Irina MASHCHUK 《《地质学报》英文版》2023,97(4):1014-1025

Two new species of Eretmophyllum Thomas are described from the lower (Toarcian) and upper (Aalenian) Prisayan Formation of the Irkutsk Basin, Eastern Siberia, Russia based on distinct morphological and cuticular features of the leaves that distinguish them from other species of the genus. Eretmophyllum polypapillosum sp. nov. is characterized by the presence of 2–3 papillae on the lower and upper epidermis of ordinary cells. Taphonomically, the leaf burials of E. polypapillosum sp. nov. indicate that it preferred mesophilic forests developed on river terraces and/or low watersheds. Eretmophyllum yershowskiensis sp. nov. is represented exclusively by leaf cuticles extracted by coal maceration, and it probably inhabited the low banks of peat bogs. The presence of the genus Eretmophyllum in the Early Jurassic of France and Eastern Siberia shows that it was already widespread in the territory of Eurasia, distributed from Western Europe to Eastern Siberia. This indicates the possible existence of Eretmophyllum species elsewhere in the Early Jurassic such as Central Asia and Northwest China.  相似文献   

The Status of the Twaite Shad, Alosa agone, in Italy and the Western Balkans     

Pier Giorgio Bianco 《Marine Ecology》2002,23(S1):51-64

Abstract. The twaite shad, Alosa agone , is still quite common in Italy and the western Balkans, but locally is endangered or extinct. Two eco-phenotypes are recognized: the migratory'Cheppia'or'Laccia'and the landlocked'Agone'. The two forms have never been in contact, at least in Italy. The migratory form is more endangered since barriers and dams prevent it from reaching upstream spawning grounds. A few reproductive communities are documented, e. g. in the Po River in Italy and Neretva River in Croatia. Resident stocks have increased to substantial populations in the large lakes of Italy, especially in the last ten years, probably as a result of improved water quality. The landlocked form from northern Italy was successfully introduced into lakes of central Italy about 75 years ago. In Sardinia a population derived from the migratory form was established about 80 years ago in the artificial Lake Omodeo. In Croatia the'Cheppia'seems to live only in the lower course of the Neretva River. In Montenegro,'Cheppia'and'Agone'live in sympatry in Lake Skadar, but a dam built in 1960 caused a strong decline of both forms. The twaite shad is a very variable species, able to modify its morphology and biology according to its adaptation to freshwater or marine biotopes. In the Mediterranean area, only one taxon should be then recognized, Alosa agone (Scopoli, 1786). This will replace Alosa fallax (Lacépède, 1803), a taxon described from the Atlantic drainage area which seems to be distinct from Mediterranean populations. A survey of the distribution of reproductive communities of the migrating form in the Mediterranean area must be carried out.  相似文献   

中国球毛藻属Sphaerotrichia Kylin (Chordariales，Phaeophyta)的分类研究     

丁兰平  陆保仁  黄冰心  曾呈奎 《海洋科学集刊》2003,(45):185-191

瑞典藻类学家Kyin(1940)在研究索藻目Chordariales的过程中建立了球毛藻属Sphaerotrichia Kylin，模式种为Sphaerotrichia divaricata (Agardh) Kylin。Kylin(1940)在该属中建立了两个种，即S.divaricata(Ag.)Kyin和S.japonica Kylin，前一种分布于大西洋，原名为Chordaria divaricata A.，后一种分布于西太平洋。 日本藻类学家Inagaki(1954)在《Contributions to the Knowledge of the Chordariales from Japan Ⅰ)一文中，报道了日本的叉状球毛藻S.divaricata(Ag.) Kylin及其变型。前苏联藻类学家研究了部分大西洋和太平洋的球毛藻属Sphaerotrichia标本后将其划分为三种，即S.divaricata(Ag.) Kylin、S.firma(Gepp.)A. Zinova、S.dissessa(S.et G.)A.Zinova，她认为S.divaricata是大西洋的种，而S.firma和S.dissessa为太平洋的种。其中，中国有S.firma和S.dissessa。 Lu Bao ren等(1983)(C.K. Tseng edit.)在《Common Seaweeds of China》中报道了产于中国的硬球毛藻S.firma。 球毛藻属Spherotrichia是 Kylin(1940)从索藻属Chordaria中分离出来的一个新属。其与索藻属Chordaria的主要区别在于前者的中央轴单管状且同化丝顶细胞膨大。目前，世界上球毛藻属 Sphaerotrichia Kylin有6个种。而中国的球毛藻属经过本文作者的研究后确定为三个种，即硬球毛藻Sphaerotrichia firma(Gepp.)A. Zinova、黄海球毛藻S.huanghaiensis Ding et Lu和日本球毛藻S.japonica Kylin。其中，日本球毛藻S.japonica Kylin为中国的新记录。  相似文献   

浙江南麂列岛有节珊瑚藻(红藻门Rhodophyta)的分类研究     

陈彦伟  姜晶晶  丁兰平  黄冰心  陈万东  林利 《海洋与湖沼》2020,51(1):163-175

利用冷冻切片技术,通过形态学和解剖学方法,对采自我国东海沿岸浙江南麂列岛的大型海洋红藻珊瑚藻目(Corallinales)的有节类群进行了分类学研究。经鉴定,共发现珊瑚藻目有节类群2属5种,分别为珊瑚藻科Corallinaceae叉节藻亚科Amphiroideae叉节藻属Amphiroa的带形叉节藻A.beauvoisii;珊瑚藻亚科Corallinoideae珊瑚藻属Corallina的鳞形珊瑚藻C.confusa、粗枝珊瑚藻C.crassisima、珊瑚藻C.officinalis和小珊瑚藻C.pilulifera。通过较为清晰的解剖学特征图片,对该5种有节珊瑚藻外部形态和内部特征进行了详细的比较与描述。结合近年来国际上有关上述部分物种的分类地位变化,对我国现存的带形叉节藻A.zanata、粗扁节藻Bossiella cretacea和大边孢藻Marginisporum crassissimum的归并问题展开了详细分析与讨论,以期促进对珊瑚藻目海藻分类学有更加深入的理解。  相似文献   

湛江徐闻西海岸柳珊瑚的物种多样性和分布研究   总被引：3，自引：0，他引：3  

黄晖  李秀保  何建国  邹仁林 《热带海洋学报》2007,26(1):60-67

2004年8月对湛江徐闻西海岸柳珊瑚资源进行调查,共采得柳珊瑚16种,分别属于7科14属;基本查清该海区柳珊瑚的分布状况。根据柳珊瑚群体颜色及骨针的形态学特征,系统阐述徐闻西海岸柳珊瑚的系统分类关系,第一次系统研究了徐闻柳珊瑚的资源状况。结合国际上最新的柳珊瑚分类系统,对国内原有的形态分类系统作出了更新和改进,这将有助于国际上认同和了解中国柳珊瑚资源情况。研究发现了1个新记录科、4个新记录属和1个新记录种。等柳珊瑚科Parisididae为新记录科,Parisis、Paraplexaura、Villogorgia、Dichotella为新记录属,鞭柳珊瑚Ellisella maculataStuder,1878,为新记录种。  相似文献   

海湾扇贝(Argopecten irradians)附着基异养细菌区系初探   总被引：1，自引：0，他引：1  

李筠  生菊  纪伟尚  徐怀恕 《中国海洋大学学报(自然科学版)》2001,31(1):69-74

从海湾扇贝附着基上分离出61株异养细菌，对其进行80项生理生化特征测定，以数值分类法进行分析。鉴定结果表明，海湾扇贝附着基上异养菌属于假单胞菌(Pseudomonas)、气单胞菌(Aeromonas)、弧菌(Vibrio)、芽孢杆菌(Bacillus)和产碱杆菌(Alcaligenes)。扇贝幼虫附着前附着的细菌主要为芽孢杆菌与假单胞菌，扇贝幼虫附着后气单胞菌成为优势，弧菌数量明显增加，与假单胞菌数量相当。  相似文献   

Studies on the species composition and biodiversity of free-living marine nematodes in the southern Huanghai Sea   总被引：1，自引：0，他引：1  

HUANG Yong  ZHANG Zhinan  LIU Xiaoshou  ZHANG Yan 《海洋学报(英文版)》2006,25(2):87-98

1 IntroductionThe conservation, persistentuse and basic re-search ofbiodiversity are increasingly becom ing oneofthe centraltopics concerned by internationalaca-dem iccirclesandothergroupsdueto itshugevaluetom ankind living and suffered seriousthreats. Fr…  相似文献