地理信息系统中自然语言查询的分词处理与应用   总被引：4，自引：3，他引：1  

吴静  蔡砥  王铮 《地球信息科学学报》2005,7(3):67-71

随着地理信息系统应用的不断发展,本文提出了在地理信息系统中对基于受限自然语言的查询语句进行分词处理的方法--首字扩词分词法。该分词方法在汲取正向最大匹配分词方法的核心思想--长词优先原则。为了缩小匹配范围,提高匹配效率,该方法首先根据查询自然语言的首字对词汇库的记录进行筛选,得到以该首字开头的词汇库子集;然后再按照长词优先原则把原查询语句与词汇库子集进行匹配,切分查询语句。通过比较,该方法比正向最大匹配方法具有较小的时间复杂度。同时,采用DELPHI编程语言在计算机上得到了实现。  相似文献   

MAGNETIC RECONNECTION IN MULTIPLE HELIOSPHERIC CURRENT SHEETS     

Wang  S.  Liu  Y. F.  Zheng  H. N. 《Solar physics》1997,173(2):409-426

Satellite observations of the heliospheric current sheet indicate that the internal structure of sector boundaries is a very complex structure with many directional discontinuities in the magnetic field. This implies that the heliospheric current sheet is not a single surface but a constantly changing layer with a varying number of current sheets. In this paper, we investigate magnetic reconnection caused by the resistive tearing mode instability in non-periodic multiple current sheets by using two-dimensional magnetohydrodynamic simulation. The results show that it is complex unsteady magnetic reconnection. Accompanying the nonlinear development of the tearing mode, the width of each magnetic island in multiple current sheets increases with time, and this leads to new magnetic reconnection. At the same time, the width of each current sheet increases, and the current intensity decreases gradually. Finally, the reverse current disappears, and a big magnetic island is formed in the central region. This process is faster when the separation between the current sheets is smaller. We suggest that the occurrence of multiple directional discontinuities observed at sector boundary crossings in the heliosphere may be associated with the magnetic islands and plasmoids caused by magnetic reconnection in multiple current sheets.  相似文献   

我国历史时期冷暖年代的干旱型   总被引：12，自引：2，他引：10  

郑斯中 《地理研究》1983,2(4):32-40

中国历史时期的旱涝变化与冷暖变化是有联系的。冷的年代,我国的气候是西干东湿,而暖的年代则是西湿东干。  相似文献   

A fisheries study on the sectional circulation in the East China Sea     

Zheng Jianyuan 《中国海洋湖沼学报》1989,7(3):196-210

Surveys since 1959 showed that the dynamic basis of the East China Sea sectional circulation is the nearshore seawater horizontal divergence caused by wind on the surface compensated by Kuroshio subsurface water convergence caused by meridional current in the lower layer. Fish always tend to migrate along certain routes or stay in certain areas favorable for development of eggs, survival of larvae and living of adults. The movement of water masses supplies a very important driving force for marine animals migrating long distance. The lower part of the sectional circulation formed by the subsurface water of Kuroshio is not suitable for the aggregation of fish because of its lack of oxygen, and has therefore a driving influence on demersal fishes. This study of the sectional circulation influence on the distributions of some commercially important species in the East China Sea reveals a close relationship between the circulation and the movement of fish schools. The principal factors influencing zonal vertical circulation are the meridional vector of the Kuroshio lower layer and atmospheric circulation, referning here mainly to the subtropical high pressure in the Asia-Pacific area that causes surface divergence and lifts subsurface water from the bottom to the surface at the nearshore area. Some simple methods for estimating the intensity of the sectional circulation are, introduced for fishery forecasts and operations.  相似文献   

东昆仑区域构造的发展演化   总被引：1，自引：0，他引：1  

郑健康 《青海国土经略》1992,(1)

本文主要依据东昆仑地区的超镁铁岩,玄武岩和花岗岩类岩石的岩石化学、稀土元素、痕量元素及同位素测年等测试成果,结合孢粉及生物化石特征,并综合有关地质构造与地球物理资料,认为至少在中元古代昆仑洋壳即已形成,并在此基础上探讨了东昆仑区域构造的发展演化特征。  相似文献   

Sulphur isotopic fractionation between sulphate and sulphide in hydrothermal ore deposits: disequilibrium vs equilibrium processes     

Yong-Fei Zheng 《地学学报》1991,3(5):510-516

Correlative fractionation relationships of sulphur isotope data for coexisting sulphate and sulphide pairs from hydrothermal ore deposits on δ³⁸S versus Δ³⁴S diagrams are deciphered theoretically. Taking into account dissolved H₂S and SO₄^2- in hydrothermal fluids during precipitation of both sulphate and sulphide minerals, a 4-species closed system is suggested for describing the conservation of mass among all sulphur-bearing species on the δ-Δ diagrams. The covariation in the δ³⁴S values of both sulphate and sulphide is ascribed to isotopic exchange between oxidized and reduced sulphur species during mineral precipitation. The isotopic exchange could be a thermodynamic process due to simple cooling of high temperature fluids, which results in an equilibrium fractionation, or a kinetic process due to mixing of two sulphur reservoirs, which leads to a disequilibrium fractionation. The δ³⁴S value of total sulphur in a hydrothermal system could change due to the precipitation of minerals, or due to the escape of H₂S and/or SO₄^2-. Sulphur isotope data for anhydrite and pyrite pairs from the Luohe porphyrite iron deposit in the Yangtze River Valley is used to illustrate the mixing responsible for the disequilibrium fractionation.  相似文献   

聂尔库组植物化石新材料及其地层意义     

郑少林  张武 《国土资源》1989,(1)

聂尔库组分布于辽宁东北部新宾县南杂木一带的苏子河盆地,为一套河湖相砂页岩沉积。该组含有较丰富的动、植物化石,但由于系统采集和研究不够,自建组以来,在地层时代和对比方面迄今仍是众说纷云。作者通过系统采集,共获植物亿石12属13种,化石组合面貌与英国威尔登植物群可以比较;与辽西的海州组、辽北—吉中营城组、黑龙江东部的穆棱组植物组合亦很相似,其时代大体相当于早白垩世尼殴克姆晚期。文中对我国首次发现的属种作了描述。  相似文献   

招远、莱州地区金矿床黄铁矿的标型特征及黄铁矿中金的赋存状态          下载免费PDF全文

郑若惠  杜心君 《山东国土资源》1989,5(1):73-87

招远、莱州地区金矿床黄铁矿的标型特征及黄铁矿中金的赋存状态的研究,采用了化学成分分析、电子探针成分分析、透射电镜分析、物相分析、晶胞参数测定、热电系数测定、比重硬度测定、粒度测定等多种物理化学手段。初步探讨了黄铁矿与金矿成矿的关系,并归纳出以下特征,可作为找矿标志:一是裂隙发育,结构疏松不规则的碎块状及五角十二面体、八面体、立方体黄铁矿含金高,与金关系密切。二是金矿中黄铁矿热电系数为正值,热电场为空穴型及电子—空穴型两种。三是金矿中黄铁矿晶胞参数大、比重低、硬度低、反射率低者含金量高。四是黄铁矿的主要成分S、Fe偏低,杂质元素Au、Ag、As、Sb、Bi、Co、Ni等微量元素较高,是含金黄铁矿成分特征。五是在金矿中黄铁矿是主要载金矿物,有80％以上的金与黄铁矿有关。查明金主要呈独立矿物赋存在黄铁矿中。另外在黄铁矿中还有可能存在微量固溶体金。  相似文献   

尼罗罗非鱼(Oreochromis niloticus Linn)胃酸的PH值,周日变化及其在消化兰藻中的作用     

吉滨河  周路  曾纪财 《广东海洋大学学报》1989,(Z1)

通过测定喂食水华微囊藻的尼罗罗非鱼胃PH值、不同颜色粪便的叶綠素/脱镁叶綠素比例,发现尼罗罗非鱼具有一个与摄食相关的胃酸分泌周期。摄食旺期胃平均PH值为1.47,最低值为0.8。停食后PH值升高,最大值为6.0。用不同浓度的盐酸处理水华微囊藻和对不同颜色粪便的营养分析结果表明,高浓度的胃酸(PH<2)溶解了水华微囊藻细胞壁,为肠消化酶对细胞内含物进行消化创造了先决条件。  相似文献   

Organochlorines and dioxin-like compounds in green-lipped mussels Perna viridis from Hong Kong mariculture zones     

So MK  Zhang X  Giesy JP  Fung CN  Fong HW  Zheng J  Kramer MJ  Yoo H  Lam PK 《Marine pollution bulletin》2005,51(8-12):677-687

Concentrations of persistent organic pollutants including polychlorinated biphenyls (PCBs), organochlorine (OC) pesticides and dioxin-like compounds were measured in green-lipped mussels, Perna viridis, collected from seven mariculture zones in Hong Kong between September and October in 2002 in order to evaluate the status, spatial distribution and potential sources of pollution in these areas. Concentrations ranged from 300 to 4400 ng/g lipid weight for total OCs and 170–1000 ng/g lipid weight for total PCBs (based on 28 congeners). Relatively smaller DDT concentrations in mussels compared with previous studies suggest reduced discharges of DDTs from nearby regions into Hong Kong waters. Detection of a mixture of HCH isomers in the mussels indicated that Hong Kong waters were predominantly contaminated by technical HCHs rather than lindane. Mussel samples from all sampling locations elicited significant dioxin-like activity in the H4IIE-luc bioassay. The greatest magnitude of dioxin-like response (39 pg TEQ/g wet wt.) was detected in mussels from Ma Wan in the western waters of Hong Kong, which is strongly influenced by the Pearl River discharge. Human health risk assessment was undertaken to evaluate potential risks associated with the consumption of the green-lipped mussels. Risk quotient (RQ) for dioxin-like compounds was greater than unity suggesting that adverse health effects may be associated with high mussel consumption.  相似文献