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种群动态

种群动态

Chemical forms and extractability of iron in sediments of three contrasting lakes of China and UK

作者： m.e.·所罗门(m.e. Solomon)

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Journal of environmental Sciences 2003年第6期15卷 728-733页

作者： Gibson C.e.,Stewart B.m. Key Laboratory of Terrestrial ecological Process Institute of Applied ecology Chinese Academy of Sciences Department of Agricultural and environmental Science Queen's University Belfast Shenyang 110016 China Newforge Lane Belfast BT9 5PX UK

Iron is a limiting factor for the eutrophication of lakes, especially those lakes that are enriched with phosphorus. extractability of iron in sediments of West Lake and Taihu Lake in China and Lower Lough erne in Northern Ireland of UK was comparatively investigated on the basis of analysing chemical forms of iron using different extractants. It was shown that extractable iron in sediments of the lakes was greatly different using various extractants. Reactive iron or easily released iron such as “active" iron oxides, total free iron oxide and water-soluble iron was not high, only accounting for 0.01%—0.15% of total iron. The efficiency of the extractants for exchangeable iron was decreased in the sequence 0.1 mol/L HCl DTPA+TeA mixed solution > 1 mol/L NH 4OAc > 0.5 mol/L mgCl 2 = 0.5 mol/L CaCl 2. It seems that the complexion of iron by organic matter was not strong because the concentration of organically bound iron was significantly lower than the concentration it was forecasted. extractable iron is not entirely consistent with or dependent on total iron in lake sediments. To a certain extent, phosphate can inhibit the release of iron in sediments of the lakes. The selection of extractants is thus the first key step to evaluate bioavailability of iron in lake sediments.

关键词： iron chemical form extractability lake sediment eutrophication

erlang mixture distribution with application on COVID-19 cases in egypt

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International Journal of Biomathematics 2021年第3期14卷 203-220页

作者： m.m.e.Abd el-monsef Faculty of Science Tanta University Al-Geish StreetTantaGharbiaEgypt

In this paper,a finite mixture of m-Brlang distributions is *** moments,shape characteristics and parameter estimates of the proposed model are also *** proposed mixture has the property that it has a bounded hazard function.A special case of the mixed erlang distribution is introduced and *** addition,a predictive technique is introduced to estimate the needed num.e. of mixture components to fit a certain data.A real data concerning the confirmed COVID-19 cases in egypt is introduced to utilize the predictive estimation *** more real datasets are used to examine the flexibility of the proposed model.

关键词： erlang distribution mixture distribution goodness-of-fit test COVID-19

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耗水量与灌溉需水量

耗水量与灌溉需水量

Dipole (hyper)polarizabilities of neutral silver clusters

作者： m.e.·詹森(m.e. Jensen)

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Chinese Physics B 2016年第12期25卷 217-222页

作者： Francisco e Jorge Luiz G m de macedo Departarnento de Fisica Universidade Fedoral do Espirito Santo 29060-900 Vitoria Brazil Unidade Academica de Fisica Universidade Federal de Campina Grande 58429-900 Campina Grande Brazil Faculdade de Biotecnologia ICB Universidade Federal do Para 66075-110 Belem Brazil

At the Douglas-Kroll-Hess （DKI4） level, the B3PW91 functional along with the all-eleclron relativistic basis sets of valence triple and quadruple zeta qualities are used to determine the structure, stability, and electronic properties of the small silver clusters （Agn, n ≤ 7）. The results presented in this study are in good agreement with the experimental data and theoretical values obtained at a higher level of theory from the literature. Static polarizability and hyperpolarizability are also reported. It is verified that the mean dipole polarizability per atom.e.hibits an odd-even oscillation and that the polarizability anisotropy is directly related to the cluster shape. In this article, the first study of hyperpolarizabilities of small silver clusters is presented. except for the monomer, the second hyperpolarizabilities of the silver clusters are significantly larger than those of the copper clusters.

关键词： B3PW91 functional all-electron basis sets non-relativistic and DKH2 calculations silver clusters,dipole (hyper)polarizabilities

The effect of fractional therm.e.asticity on a two-dimensional problem of a mode I crack in a rotating fiber-reinforced therm.e.astic medium

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Chinese Physics B 2013年第10期22卷 575-582页

作者： Ahmed e.Abouelregal Ashraf m.Zenkour Department of mathematics Faculty of ScienceMansoura University Department of mathematics Faculty of ScienceKing Abdulaziz University Department of mathematics College of Science and ArtsUniversity of Aljouf Department of mathematics Faculty of ScienceKafrelsheikh University

This article is concerned with the effect of rotation on the general model of the equations of the generalized therm.e. lasticity for a homogeneous isotropic elastic half-space solid, whose surface is subjected to a mode-I crack problem. The fractional order theory of therm.e.asticity is used to obtain the analytical solutions for displacement components, force stresses, and tem.e.ature. The boundary of the crack is subjected to a prescribed stress distribution and tem.e.ature. The normal mode analysis technique is used to solve the resulting non-dimensional coupled governing equations of the problem. The variations of the considered variables with the horizontal distance are illustrated graphically. Some particular cases are also discussed in the context of the problem. effects of the fractional parameter, reinforcement, and rotation on the varia- tions of different field quantities inside the elastic medium are analyzed graphically. Comparisons are made between the results in the presence and those in the absence of fiber-reinforcing, rotating and fractional parameters.

关键词： fiber-reinforced mode-I crack fractional order therm.e.asticity theory rotating medium normalmode analysis

effects of the partial replacement of La by m(m=Ce,Ca and Sr) in La_(2-x)m_xCuO_4 perovskites on catalysis of the water-gas shift reaction

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Journal of Natural Gas Chemistry 2010年第6期19卷 567-574页

作者： S.S.maluf e.m.Assaf Institute de Química de So Carlos Universidade de So PauloAv.Trabalhador Socarlense400 So CarlosSP 13560-970Brazil

The performance of La2-x m x CuO4 perovskites （where m=Ce,Ca or Sr） as catalysts for the water-gas shift reaction was investigated at 290℃ and 360℃.The catalysts were characterized by eDS,XRD,N2 adsorption-desorption,XPS and *** XRD results showed that all the perovskites exhibited a single phase （the presence of perovskite structure）,suggesting the incorporation of metals in the perovskite *** XPS and XANeS results showed the presence of Cu2＋ on the *** perovskites that exhibited the best catalytic performance were La 2 x Ce x CuO 4 perovskites,with CO conversions of 85% 90%.moreover,these perovskites have higher surface areas and larger amounts of Cu on the *** Ce has a higher filled energy level than the other metals,increasing the energy of the valence band of Ce and providing more electrons for the ***,the La1.80Ca0.20CuO4 perovskite showed a good catalytic performance.

关键词： perovskites water-gas shift reaction lanthanum copper calcium cerium strontium

exploring tree diversity and stand structure of savanna woodlands in southeastern Sudan

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Journal of Arid Land 2020年第4期12卷 609-617页

作者： Ahmed m m HASOBA Ahmed A H SIDDIG Yousif e YAGOUB Faculty of Forest Sciences and Technology University of GeziraMadani 22212Sudan Faculty of Forestry University of KhartoumKhartoum North 13314Sudan Department of environmental Conservation University of Massachusetts AmherstAmherst 01003USA

Savanna woodlands in Sudan host great biodiversity, provide a plethora of ecosystem goods and services to local communities, and sustain numerous ecological functions. Although the importance of the Acacia trees in these areas is well known, up-to-date information about these woodlands' diversity is limited and changes in their woody vegetation composition, density, diversity and relative frequency are not monitored over time. This study explored tree diversity and stand stage structure in Nuara Reserved Forest, a typical savanna woodland ecosystem in southeastern Sudan. A total of 638 circular sample plots(1000 m^2 for each) were established using a systematic sampling grid method. The distance between plots was 200 m. In each plot, all living trees with diameter at breast height(DBH) ≥5.00 cm were identified and counted, and their DBH values were recorded. From these data, tree composition, diversity, density and stage structure were assessed. There were 12,259 individual trees representing four species(Acacia seyal, Balanites aegyptiaca, Acacia Senegal and Acacia mellifera) that belong to two families. The dominant species was Acacia seyal. Average tree density was 191 trees/hm^2 and the Shannon-Weiner index for trees diversity was 0.204. Overall, young trees comprised 86.30% of the forest. The state of tree richness and density in the study area was low compared to other similar environments in the region and around the world. We recom.e.ded adoption of a proper management system that includes monitoring of woody vegetation diversity in this forest, and management actions to enhance tree diversity and sustain ecosystem services to local communities. In addition to care for the dominant Acacia seyal stands, more attention and conservation should be devoted to reestablishing Acacia senegal and Acacia mellifera trees because of their high ecological and economic values for local communities.

关键词： species diversity stand structure savanna woodland ecosystem forest monitoring forest management ecosystem services Nuara Reserved Forest

Impurity effects on electrical conductivity of doped bilayer graphene in the presence of a bias voltage

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Chinese Physics B 2016年第7期25卷 316-323页

作者： e Lotfi H Rezania B Arghavaninia m Yarmohammadi Department of Physics Sanandaj Branch Islamic Azad University Department of Physics Razi University Department of Physics Kermanshah Branch Islamic Azad University Young researchers and elite Club Kermanshah Branch Islamic Azad University

We address the electrical conductivity of bilayer graphene as a function of tem.e.ature, impurity concentration, and scattering strength in the presence of a finite bias voltage at finite doping, beginning with a description of the tight-binding model using the linear response theory and Green＇s function approach. Our results show a linear behavior at high doping for the case of high bias voltage. The effects of electron doping on the electrical conductivity have been studied via changing the electronic chemical potential. We also discuss and analyze how the bias voltage affects the tem.e.ature behavior of the electrical conductivity. Finally, we study the behavior of the electrical conductivity as a function of the impurity concentration and scattering strength for different bias voltages and chemical potentials respectively. The electrical conductivity is found to be monotonically decreasing with impurity scattering strength due to the increased scattering among electrons at higher impurity scattering strength.

关键词： bilayer graphene Green's function electrical conductivity