检索结果-南通市图书馆

Population-size-dependent branching processes in Markovian random environments

在线全文

学校读者我要写书评

暂无评论

Chinese science Bulletin 1998年第8期43卷 635-638页

作者： WANG Hanxing 1 and DAI Yonglong 2.1. department of Mathematics, Shanghai university, Shanghai 2.1800, China 2. department of Mathematics, zhongshan university, guangzhou 51.2.5, China department of Mathematics Shanghai University Shanghai China department of Mathematics Zhongshan University Gunngzhou China

A branching model {Z n} n≥0is considered where the offspring distribution of the population’s evolution is not only dependent on the population size, but also controlled by a Markovian environmental process {ξ n} n≥0. For this model, asymptotic behaviour is studied such as limn→∞Z n and limn→∞Z n/m n in the case that the mean m k, θof the offspring distribution converges to m>1 as the population size k grows to ∞. In the case that {ξ n} n≥0is an irreducible positive recurrent Markov chain, certain extinction (i.e. P(Z n=0 for some n)=1) and noncertain extinction (i.e. P(Z n=0 for some n)<1) are studied.

关键词： Markov chains in random environments stochastic population models branching processes.

Effects of clipping on dry matter production and nutrients in the fernland of Hong Kong

在线全文

学校读者我要写书评

暂无评论

Journal of environmental sciences 1998年第1期10卷 3-14页

作者： Guan Dong sheng department of environmental {2., zhongshan university, guangzhou 51.2.5, China

The dry matter production and its nutrient amounts varied significantly with time and period from April to June was a favourable season for plant growth. Dry matter production declined significantly with clipping. Especially, repeated cutting of high frequencies for the long term had a severe effect on dry matter production. However, N, P, and K amounts in dry matter production did not significantly decline because the concentrations of N, P, and K in the plants increased with clipping. Repeated cutting for long term is a reason why net primary production has been depressed in the most of upland areas of southern China.

关键词： clipping dry matter production nutrients Dicranopteris linearis Hong Kong

THE CHARACTERISTIC OF MARINE ENVIRONMENT IN LINGDINGYANG ESTUARY

在线全文

学校读者我要写书评

暂无评论

Chinese Geographical science 2001年第2期11卷 155-162页

作者： CHEN Bing-lu1, ZHANG Yun-ni2. CHEN Xin-geng1, WANG Zhi-gang1, YANG Guang-xing1 (1.Institute of environmental science,{2., guangzhou 51.2.5, P. R. China 2. department of environmental science,{2., guangzhou 51.2.5 Institute of environmental science Zhongshan University Guangzhou P. R. China department of environmental {2. Zhongshan University Guangzhou P. R. China

Hydrologic features, load of main pollutants and current condition of water quality in Lingdingyang Estuary are discussed by references and monitoring data. Affected by topography, runoff and tide, its dynamic condition is very complicated. Different water areas have different hydrologic features. The topography under the water of Lingdingyang Estuary is higher in the northwest than that in the southeast. The shoal alternates with the deep trough within the bay .The distribution of the salinity and the contents of the mud and the main pollutants tally with the topography tendency. Change in water quality goes through four stages. Current condition of water quality is fairly good. Inorganic nitrogen is the primary pollutant, and then phosphorus. Rich in nutrition of nitrogen and phosphorus become a more and more prominent problem.

关键词： Lingdingyang Estuary hydrologic features load of pollutant water quantity

Effect of an impurity on 3-electron quantum dots in magnetic fields

在线全文

学校读者我要写书评

暂无评论

science China(Physics,Mechanics & Astronomy) 2004年第5期47卷 521-530页

作者： LIU Yimin1,2. HUANG Gangming1 & BAO Chengguang1 1. department of Physics, zhongshan university,{2., China 2. department of Physics, Shaoguan university, Shaoguan 512.05, China 1. department of Physics Zhongshan University 510275 Guangzhou China 2. department of Physics Shaoguan University 512005 Shaoguan China

The ground-state property of a 2.dimensional 3-electron quantum dot (QD) subjected to an external magnetic fieldB and affected by an impurity is studied. The impurity is located at thez-axis by a distanced from the plane of the dot. The evolution of the angular momentumL o and the spinS o of the ground state in accordance withB andd has been calculated, and the results are summarized and plotted in a (L o,S o) diagram. The spatial distribution of the electrons (the size and the geometric features) and the optical absorption have also been investigated. The (L o S o) diagram indicates thatL o andS o may jump whend and/orB vary. It was found that, due to the constraints arising from symmetry, each symmetric geometry is accessible only to a specific group of states having specificL o andS o.

关键词： quantum dot, ground state, charged impurity, magnetic field.

Variation of the Fe/Mn ratio of ferromanganese crusts from the Central North Pacific: implication for paleoclimate changes

在线全文

学校读者我要写书评

暂无评论

Progress in Natural science:Materials International 2005年第6期15卷 530-537页

作者： LU Zunli1**, LING Hongfei1*, ZHOU Feng1, JIANG Shaoyong1, CHEN Xiaoming1 and ZHOU Huaiyang2.1. State Key Laboratory for Mineral Deposits Research, department of Earth sciences, Nanjing {2., Nanjing 2.0093, China 2. guangzhou Institute of Geochemistry, Chinese Academy of sciences, guangzhou 510640, China)department of Earth & environmental science, {2. of Rochester State Key Laboratory for Mineral Deposits Research Department of Earth Sciences Nanjing University Nanjing 210093 China department of Earth & environmental {2. University of Rochester guangzhou Institute of Geochemistry Chinese Academy of Sciences Guangzhou 510640 China

Contents of Fe, Mn and other elements in four ferromanganese crusts recovered from the central North Pacific are analyzed at high depth-resolution by electron microprobe for reconstructing factors controlling their deposition. Manganese (IV) in hydrogenetic ferromanganese crusts is mainly supplied as colloidal precipitates from the Oxygen Minimum Zone (OMZ), which concentrates high amounts of dissolved Mn (II). The iron is derived from carbonate dissolution and silicate particles of eolian dust. An increase in paleoproductivity during cooler climate would potentially lead to a decrease in Mn deposition due to enlargement of the OMZ which has a “temporary storage” effect for Mn. On the other hand, not affected by the OMZ, the iron entering the Fe-Mn crust would likely increase with the eolian dust input and surface productivity at glacial stages. As a result, the increasing Fe/Mn ratio should indicate a cooling climate. This is supported by the following observations. In the profile of the past 1 Ma, the variations of Fe/Mn ratio coincide with benthic oxygen isotope fluctuation in glacial-interglacial cycles. Three episodes with high Fe/Mn ratios, approximately at 2.6, 1.8 and 0.8 Ma, are detected within the past 3 Ma and coincide with major climate transitions and cooling events. The secular evolution pattern of Fe/Mn ratio in the Cenozoic is similar to the Pb isotope evolution which is mainly controlled by eolian dust and related to climate. The Fe/Mn evolution pattern is also broadly consistent with the global deep-sea oxygen isotope records. Therefore, Fe/Mn ratio recorded in the ferromanganese crusts may be a new proxy for climate change.

关键词： Fe/Mn ratio ferromanganese crust central North Pacific paleoclimate.

Modeling the fate of paddy field pesticide in surface water and environmental risk assessment

在线全文

同方期刊数据库

学校读者我要写书评

暂无评论

Journal of environmental sciences 2000年第3期12卷 337-343页

作者： LI Shi\|yu 1, Tohru Morioka 2.(1. Institute of environmental science,{2., guangzhou 51.2.5, China. E-mail: eeslsy@*** 2.department of environmental Engineering, Osaka university, Yamada oka 2.1, Suita, Osaka 565, Japan. E- 中山大学广东广州 51 0 2 75 Osaka university 日本 Osaka 56 5

The risk of drinking water is greatly concerned because of the large amount of pesticide applied to paddy field and the contamination of drinking water sources due to the runoff. A mathematical model is developed, based on the mass balance, to predict the fate of paddy field pesticides from application, runoff and mixing in a river, taking account of the physical chemical properties and processes of volatilization, degradation, adsorption and desorption. The model is applied to a river basin in Japan to estimate the contaminant level of several popularly used pesticides at the water intakes. The health risk in drinking water induced by each pesticide concerned is estimated and evaluated by comparing with the acceptable daily intake values(ADI) and with that induced by trihalomethanes. An index to evaluate the total risk of all pesticides appearing in water is proposed. The methods for risk management are also discussed.

关键词： modeling pesticide paddy field environmental risk assessment drinking water

The Impact on environmental Kuznets Curve by Trade and Foreign Direct Investment in China

在线全文

学校读者我要写书评

暂无评论

Chinese Journal of Population,Resources and Environment 2005年第2期3卷 14-19页

作者： Yang Haisheng 1, Jia Jia 2. Zhou Yongzhang 1& Wang Shugong 1,31 Center for Earth Environment & Resources, zhongshan university, guangzhou, {2.2.Lingnan College, zhongshan university, guangzhou, {2.3 Institute of environmental science, zhongshan university, guangzhou, {2. Center for Earth Environment and Resources Zhongshan University Guangzhou 510275 China Lingnan College Zhongshan University Guangzhou 510275 China Institute of environmental science Zhongshan University Guangzhou 510275 China

Based on data of trade, foreign directinvestment (FDI), economic development andenvironmental conditions in China’s 30 provincesbetween 1990-2.02. this paper deals with the impacton environmental Kuznets Curve (EKC) of tradeand FDI in China. The results show no direct impacton EKC of trade, on the one hand. However, tradecontributes significantly to economic growth, andhas played a positive role in introducing advancedpollution prevention technology and environmentalmanagement methodology to China. Therefore, aproactive trade policy will help solve the environmentalpollution problem brought by economic growth. Onthe other hand, there is a positive correlation betweenFDI and pollutant emission, which proves that FDIdoes have some negative influence on environmentin China due to hasty introduction of foreign capitaland inadequate environmental management systemin China.

关键词： environmental economy free trade FDI environmental Kuznets Curve econometricmodel Sustainable development

Water quality modelling of Dapeng Bay, China

在线全文

学校读者我要写书评

暂无评论

Journal of environmental sciences 1989年第2期1卷 76-80页

作者： Zhan Xiaoyong Institute of environmental science,{2. university,guangzhou,China

A two-dimensional finite difference Alternating Direction Implicit (ADI) schematic numerical model to solve the vertically intergrated form of the convective-diffusion equation has been developed for description of water quality in Dapeng Bay of China. Computer software for the modelling is well designed to reduce costs of computation and storage. The results agree quite well with the observations available. Organic pollution in Dapeng Bay is discussed based on the computation and observation. environmental problems relevant to the industrial enterprises along the coast of the bay are also mentioned briefly.

关键词： quality numerical modelling Dapeng Bay organic pollution.

Solid components and acid buffering capacity of soils in South China

在线全文

学校读者我要写书评

暂无评论

Journal of environmental sciences 1998年第2期10卷 42-48页

作者： Qiu Rong liang, Wu Qing, Zhang Yun ni department of environmental {2., zhongshan university, guangzhou 51.2.5, China

The effects of soil solid components on soil sensitivity to acid deposition by sequential extraction method were studied. A multiple regression equation of soil sensitivity was set up on the basis of stepwise regression analysis. The results showed that organic matter expressed dual effects that were decided by soil original pH value and exchangeable cation composition on acid buffering reactions. The hydrolysis of activated oxides was a very important proton buffering reaction when in low pH situation. The crystalline oxides also played a role in the buffering reactions, but the role was restricted by the rate of activation of oxides. Meanwhile, the results by stepwise analysis showed that factors that had significant effect on soil acid buffering capacity were content of montmorillite, soil original pH value, Al 0, Mn 0 and CEC in decreasing order. Finally, sixteen soils were classified into four types of sensitive with single index cluster and multiple fuzzy cluster analysis respectively.

关键词： acid deposition acid buffering capacity soil sensitivity solid components.