检索结果-南通市图书馆

Patterns of grassland invasions by trees: insights from demographic and genetic spatial analyses

Journal of Plant Ecology 2015年第5期8卷 468-479页

作者： martin Dovčiak Richard Hrivnák Karol Ujházy dušan Gömöry State University of New York College of Environmental Science and Forestry(SUNY ESF)1 Forestry DriveSyracuseNY 13210USA Institute of Botany Slovak Academy of SciencesDúbravskácesta 9Bratislava 84523Slovakia Technical University in Zvolen Faculty of ForestryT.G.Masaryka 24Zvolen 96053Slovakia

Aims Woody invasions into grasslands have increased globally due to changing land use,climate and introduced woody species,but spatial processes generating and sustaining these invasions are not well *** gain insight into the patterns of spread of tree populations within grasslands,and to propose a full spatial analytical toolbox for studying native and non-native woody spe-cies spread when long-term data are not available,we tested if 50 years of grassland invasion in Western Carpathians by Norway spruce(Picea abies Karst.)proceeded by one of the two tradi-tionally competing hypotheses of species spread:(i)by frontier expansion,or(ii)by advanced groups established ahead of the population *** also tested whether the pattern of invasion changed over *** We analyzed the spatial demographic and genetic patterns of a Norway spruce population invading a Western Carpathian grass-land using ripley’s l(t)and genetic kinship coefficients(Fij).We mapped and genotyped spruce trees across the invasion front(from the invasion leading edge to fully colonized grassland near the source population)using three demographic classes(adults,juve-niles and seedlings)to approximate the temporal aspects of the *** studied how the spatial patterns of invasion by indi-vidual demographic classes and their genetic kinship varied among adjacent plots established at different distances from the source population(ranging from 0 to 160 m,in 40-m distance increments).Important Findings Juveniles were positively genetically related to adults on fine scales(m),suggesting that adults within the grassland acted as a seed source and accelerated early ***,adults did not act as nucleation centers for the formation of advanced juvenile ***,geneti-cally unrelated juveniles formed groups independently of *** groups were small and separate at the leading edge but they increased in size and graded into a continuous zone near the source popul

关键词： genetic spatial structure mountain meadows point pattern analysis population structure secondary succession

来源：

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Plasma and platelet serotonin levels in patients with liver cirrhosis

引用

World Journal of Gastroenterology 2007年第43期13卷 5750-5753页

作者： ■or■e m ulafi duko S mirkovi miodrag D Vukevi Jelena S Rudi Clinic of Gastroenterology and Hepatology Institute of Digestive Diseases Institute of medical Biochemistry Institute of Pulmonary Diseases Clinical Center of Serbia Medical Faculty Belgrade

AIm: To analyze the relationship between plasma and platelet serotonin levels and the degree of liver insufficiency. mETHODS: The prospective study included 30 patients with liver cirrhosis and 30 healthy controls. The degree of liver failure was assessed according to the Child-Pugh classification. Platelet and platelet poor plasma serotonin levels were determined. RESUlTS: The mean plasma serotonin level was higher in liver cirrhosis patients than in healthy subjects (215.0 ± 26.1 vs 63.1 ± 18.1 nmol/l; P mean platelet serotonin content was not significantly different in patients with liver cirrhosis compared with healthy individuals (4.8 ± 0.6; 4.2 ± 0.3 nmol/platelet; P > 0.05). Plasma serotonin levels were significantly higher in Child- Pugh grade A/B than in grade C patients (246.8 ± 35.0 vs 132.3 ± 30.7 nmol/l; P latelet serotonin content was not significantly different between Child-Pugh grade C and grade A/B (4.6 ± 0.7 vs 5.2 ± 0.8 nmol/platelet; P > 0.05). CONClUSION: Plasma serotonin levels are significantly higher in patients with cirrhosis than in the controls and represent the degree of liver insufficiency. In addition, platelet poor plasma serotonin estimation is a better marker for liver insufficiency than platelet serotonin content.

关键词： Serotonin Plasma Platelet liver cirrhosis

来源：

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

A theoretical investigation of the band alignment of type-I direct band gap dilute nitride phosphide alloy of GaN_xAs_yP_(1-x-y)/GaP quantum wells on GaP substrates

引用

Chinese Physics B 2014年第7期23卷 640-644页

作者： O l nsal B Gnül m Temiz Department of Engineering Physics University of Gaziantep

The GaP-based dilute nitride direct band gap material Ga（NAsP） is gaining importance due to the monolithic integra- tion of laser diodes on Si microprocessors. The major advantage of this newly proposed laser material system is the small lattice mismatch between GaP and Si. However, the large threshold current density of these promising laser diodes on Si substrates shows that the carrier leakage plays an important role in Ga（NAsP）/GaP QW lasers. Therefore, it is necessary to investigate the band alignment in this laser material system. In this paper, we present a theoretical investigation to optimize the band alignment of type-I direct band gap GaNxAsyP1-x-y/GaP QWs on GaP substrates. We examine the effect of nitrogen （N） concentration on the band offset ratios and band offset energies. We also provide a comparison of the band alignment of type-I direct band gap GaNxAsyP1-x-y/GaP QWs with that of the GaNxAsyP1-x-y/Al2Ga1-2P QWs on GaP substrates. Our theoretical calculations indicate that the incorporations of N into the well and AI into the barrier improve the band alignment compared to that of the GaAsP/GaP QW laser heterostructures.

关键词： quantum well band alignment carrier confinement dilute nitride phosphide alloy

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Design and numerical investigation of swirl recovery vanes for the Fokker 29 propeller

引用

Chinese Journal of Aeronautics 2014年第5期27卷 1128-1136页

作者： Wang Yangang li Qingxi G.Eitelberg l.l.m.Veldhuis m.Kotsonis School of Power and Energy Northwestern Polytechnical University School of Aerospace Engineer Delft University of Technology German-dutch Wind Tunnels

Swirl recovery vanes（SRVs） are a set of stationary vanes located downstream from a propeller, which may recover some of the residual swirl from the propeller, hoping for an improvement in both thrust and efficiency. The SRV concept design for a scaled version representing the Fokker 29 propeller is performed in this paper, which may give rise to a promotion in propulsive performance of this traditional propeller. Firstly the numerical strategy is validated from two aspects of global quantities and the local flow field of the propeller compared with experimental data, and then the exit flow together with the development of propeller wake is analyzed in *** kinds of SRV are designed with multiple circular airfoils. The numerical results show that the swirl behind the propeller is recovered significantly with model V3, which is characterized by the highest solidity along spanwise, for various working conditions, and the combination of rotor and vane produced 5.76% extra thrust at the design point. However, a lower efficiency is observed asking for a better vane design and the choice of a working point. The vane position is studied which shows that there is an optimum range for higher thrust and efficiency.

关键词： multiple circular airfoil Propellers Propulsion efficiency Swirl recovery vane Turboprop engine

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Investigation of etching method for fabricating deep through holes on ultra-high resistivity silicon

引用

Journal of Semiconductors 2017年第5期38卷 106-110页

作者： lin du Shengrui Xu Ying Wang ling lü Jincheng Zhang Yue Hao School of microelectronics Xidian University

In this paper,the etching characteristics of the ultra-high resistivity silicon（UHRS） by using the Bosch process were *** experimental results indicated that the sulfur hexafluoride flux,the temperature of the substrate,the platen power and the etching intermittence had important influence on the etching rate and the etching morphology of the *** profiles and morphologies of sidewall were characterized with scanning electron microscopy（SEm）.By using an improved three-stage Bosch process,380-μm deep through holes were fabricated on the UHRS with the average etching rate of about 3.14 μm/***,the fabrication mechanism of deep through holes on the UHRS by using the three-stage Bosch process was illustrated on the basis of the experimental results.

关键词： ultra-high resistivity silicon deep through hole three-stage etching method Bosch process

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Toward an understanding of dwell fatigue damage mechanism of bimodal Ti-6Al-4V alloys

引用

Journal of materials Science & Technology 2022年第13期108卷 244-255页

作者： l.R.Zeng l.m.lei X.m.luo G.P.Zhang Shenyang National laboratory for materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China School of mechanical Engineering Chengdu UniversityChengdu 610106China AECC Shanghai Commercial Aircraft Engine manufacturing Co. Ltd.Shanghai 201306China

Dwell fatigue effect is a long-standing problem threatening the long-term service reliability for fan blades and fan disks of an aircraft *** understand the basic mechanism of dwell fatigue damage,pure fatigue and 60 s dwell fatigue properties of bimodal Ti-6Al-4V alloys with different volume fractions of the primaryα(α_(p))phase were examined *** results showed that both pure fatigue and dwell fatigue life decreased with increasing the volume fraction of theα_(p)phase and the dwell fatigue life was lower than the pure fatigue *** quasi-in-situ test results and the quantitative characterization of damage behaviors of the local microstructure units defined by theα_(p)-secondaryα(α_(s))combination reveal that theα_(s)phase close to theα_(p)phase with extensively slip activities was gradually damaged under dwell fatigue loading,while that under pure fatigue loading was undamaged,demonstrating that the dwell loading induced the damage of theα_(s)phase,and further reduced the fatigue life.A stress relaxation-based model is proposed to describe the physical mechanism on dwell fatigue damage of the bimodal Ti-6Al-4V alloy,*** elastic deformation of theα_(s)phase caused by the strain incompatibility would be gradually transformed into plastic deformation during the dwell stage,and thus promotes fatigue *** model provides new insights into the microscopic process of stress/strain transfer between the soft and hard microstructure units under dwell fatigue loading.

关键词： Dwell effect Fatigue damage Stress relaxation Volume fraction of primaryαphase Quasi-in-situ testing

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

A Fourier Spectral moving mesh method for the Cahn-Hilliard Equation with Elasticity

引用

Communications in Computational Physics 2009年第2期5卷 582-599页

作者： W.m.Feng P.Yu S.Y.Hu Z.K.liu Q.du l.Q.Chen Department of materials Science and Engineering Pennsylvania State UniversityUniversity ParkPA 16802USA Department of mathematics Pennsylvania State UniversityUniversity ParkPA 16802USA Pacific Northwest National laboratory RichlandWA 99354USA

In recent years,Fourier spectral methods have emerged as competitive numerical methods for large-scale phase field simulations of microstructures in computational materials *** further improve their effectiveness,we recently developed a new adaptive Fourier-spectral semi-implicit method(AFSIm)for solving the phase field equation by combining an adaptive moving mesh method and the semi-implicit Fourier spectral *** this paper,we present the application of AFSIm to the Cahn-Hilliard equation with inhomogeneous,anisotropic *** implementations and test examples in both two and three dimensions are considered with a particular illustration using the well-studied example of mis-fitting particles in a solid as they approach to their equilibrium *** is shown that significant savings in memory and computational time is achieved while accurate solutions are preserved.

关键词： Phase field diffuse interface moving mesh adaptive mesh Fourier-spectral method adaptive spectral method Cahn-Hilliard equation elasticity

来源：

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Spatial-Temporal Characteristics of a Temperate-Glacier's Active-layer Temperature and Its Responses to Climate Change: A Case Study of Baishui Glacier No. 1, Southeastern Tibetan Plateau

引用

Journal of Earth Science 2014年第4期25卷 727-734页

作者： Shijin Wang Jiankuo du Yuanqing He State Key laboratory of Cryospheric Sciences Cold and Arid Regions Environmental and Engineering Research InstituteChinese Academy of Sciences

Based on the historical documents and measured data from the active-layer temperature （AlT） at A, B and C locations （4 670, 4 720 and 4 770 m a.s.l.） on Baishui Glacier No. 1, southeastern Tibetan Plateau, this paper analyzed spatial-temporal characteristics of AlT and its relationship with air temperature, and revealed the response of the active layer ice temperature towards climate change in the monitoring period. The results showed that the influence of air temperature on the active-layer ice temperature had a hysteresis characteristic on the upper of ablation zone and the lag period in- creased gradually with the altitude elevating. The decrease amplitude of AlT in the accumulation pe- riod was far below its increase magnitude in the ablation period. At the same time, the mean glacier ice temperatures at 10 m depth （T10） in A, B and C profile were obviously higher than most of glaciers previously studied. measured data also showed that the mean AlT increased by 0.24℃ in 0.5-8.5 m depth of the C profile during 28 years from July 11, 1982 to July 10, 2009.

关键词： temperate-glacier active-layer temperature temporal and spatial characteristics climate change.

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Faddeev calculations on lambda hypertriton with potentials from Gel'fand–levitan–marchenko theory

引用

Communications in Theoretical Physics 2020年第10期72卷 119-124页

作者： E F meoto m l lekala Department of Physics University of South AfricaPrivate Bag X61710 JohannesburgSouth Africa

Effective lambda-proton and lambda-neutron potentials,restored from theoretical scattering phases through Gel'fand–levitan–marchenko theory,are tested on a lambda hypertriton through three-body *** lambda hypertriton is treated as a three-body system consisting of lambda-proton,lambda-neutron and proton–neutron *** energy and root mean square radius are computed for the ground state of lambda hypertriton(Jp=12+).In coordinate space,the dynamics of the system is described using a set of coupled hyperradial equations obtained from the differential Faddeev *** solving the eigenvalue problem derived from this set of coupled hyperradial equations,the binding energy and root mean square matter radius computed are found to be-2.462 meV and 7.00 fm,*** potentials are also shown to display a satisfactory convergence behaviour.

关键词： lambda-nucleon potential lambda-proton potential lambda-neutron potential lambda hypertriton Faddeev equations hyperspherical method

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

microhabitat characteristics related to seasonal roost switching:implications from a threatened and introduced cockatoo species in an urban landscape

引用

Avian Research 2021年第3期12卷 317-326页

作者： Sifeng Wang l.m.Chu School of life Sciences The Chinese University of Hong KongShatinNTHong Kong SARChina

Background:Communal roosting is a common avian social behaviour,which potentially provides foraging benefits,predation avoidance or thermoregulation in *** identify the crucial environmental factors associated with roost site selection,most studies have focused on the comparison of physical characteristics between roosts and ***,the differences among roosts have usually been neglected and the causes of roost switching have seldom been ***:To explore the variations among roost sites and assess the most influential environmental factors related to seasonal roost switching,we conducted a 105-day observation on an introduced population of critically endan-gered Yellow-crested Cockatoo(Cacatua sulphurea)in an urban environment in Hong Kong from 2014 to *** identified seven roost sites that were occupied in different seasons and then measured their microhabitat character-istics in terms of land use types,human disturbance and microclimate *** quantify these differences,we used Pearson’s chi-squared test,partial least squares determinant analysis(PlS-DA)and one-way repeated measures ANOVA,***:Our results distinguished roost sites occupied in three seasons,***,summer and winter roosts,using several microhabitat *** land use types were significantly associated with roosts,where spring roosts were usually located in tree-dominated areas,which are the major feeding *** discriminant analysis on human disturbance variables indicated that summer roosts were positively associated with night *** microhabitat temperatures of winter roosts were significantly higher than those of most other roosts on cold ***:The results highlighted significant variations among roosts,and seasonal roost switching was likely driven by specific microhabitat characteristics of each roost site,such as *** also helps us understand the behavioural adaptation of birds to

关键词： Communal roosting Human disturbance land use microclimate Seasonal variation

来源：

维普期刊数据库

同方期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

欢迎您,

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案：

请选择收藏分类：

通借通还

欢迎您,

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

在线全文

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：