检索结果-南通市图书馆

Effects of Topography and Land use on Woody Plant Species Composition and Beta Diversity in an Arid Trans-Himalayan Landscape, Nepal

引用

Journal of Mountain Science 2014年第5期11卷 1112-1122页

作者： Shishir PAUDEL ole r vetaas Natural resources Ecology and Management Oklahoma State UniversityStillwater OK 74078 USA Department of Geography University of BergenPost Box 7800 N-5020 Bergen Norway

Distribution patterns of plant species are believed to be impacted by small-scale habitat heterogeneity. However, there have been few comparative studies examining how woody vegetation composition and diversity varies with aspects of different orientations in the Trans-Himalayan region at a local scale. Here, we examined the effects of incoming solar radiation on variation in woody species composition and compared the diversity between the northeast- and southwest-facing slopes in a Trans-Himalayan valley of Nepal. We also examined the implicit interactions between slope orientation and land use in determining the compositional variations between the slopes. We selected two pairs of northeast- and southwest-facing slopes where the first pair has a similar land use and differs in exposure only(Pisang site) while the other pair has clear differences in land use in addition to slope exposure(Braka site). In each site, we sampled 72 plots(36 on each slope) in which the presence and absence of woody species, environmental variables, and disturbance were recorded. Correspondence Analysis(CA) results suggested that the woody species composition significantly varied between northeast- and southwest-facing slopes at both sites, and was significantly correlated with measured environmental variables such as radiation index, altitude, and canopy openness. In the Braka site,mean alpha diversity was significantly higher on southwest-facing slopes. In contrast, beta diversity and gamma diversity were greater on northeast-facing slopes at both sites. Our results suggest that topographic variables(e.g., radiation index) affect species composition between the slopes, likely due to their influence on small scale abiotic environmental variables. However, the effects of land use, such as livestock browsing/grazing may interact with the effects of slope exposure, effectively reducing differences in species composition within slopes but enhancing the differences in beta diversity between

关键词： Correspondence analysis Diversity Environmental gradients Himalaya Land use Topographic aspect Woody vegetation

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

Microtopography driven plant species composition in alpine region: a fine-scale study from Southern Norway

引用

Journal of Mountain Science 2020年第3期17卷 542-555页

作者： BHATTArAI Prakash BHATTA Kuber Prasad ZHANG Yang-jian vetaas ole reidar Key Laboratory of Ecosystem Network Observation and Modelling Institute of Geographic Sciences and Natural Resources ResearchBeijing 100101China University of Chinese Academy of Sciences Beijing 100049China Department of Biological Sciences University of BergenBergenN-5020Norway Department of Geography University of BergenBergenN-5020Norway

This study explores the relationship between the species composition of lichen and vascular plant species with microtopography at fine scale. We conducted our study in Hardengervidda National Park, Norway. Specifically, we aim to test whether the species richness of different plant lifeforms peaks at middle of the microtopography gradient, and then explain the observed patterns with an aid of snow cover gradient along microtopography and snow cover. We sampled 69 species of vascular plants and lichens in 151 plots of 4 m^2 along 23 transects during summer on Tronsbu, Sandhaug and Besso. Detrended correspondence analysis(DCA) was performed to explore how microtopographical gradient was related to the variation in the species composition. One-way ANOVA was performed to test the microtopographic variability in species ***, generalized linear model(GLM) was used to reveal species richness patterns along the snow cover gradient. The first axis in DCA represents the complex gradient from snow free ridge to wet snowbed habitats and the second axis represents a gradient from acidic to calcareous sites. Lichen’s species richness is greater in ridge than in snowbeds, while all other life forms follow the opposite trend. Species richness for total plant species, vascular plant species and herbaceous plant species increased with increase in weighted average snow indicator value(WASI), whilst species richness for lichen species declined substantially towards the maximum WASI value. In contrast, species richness for dwarf shrub species showed a unimodal relationship with WASI. This study shows that liquid water availability provides a good potential explanation for species composition and richness in mountains, which is controlled by snow cover and prevalent wind direction.

关键词： Species richness Water energy dynamics hypothesis Weighted average snow indicator value Microtopography Ordination

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

Ecological Consequences of Land Use Change: Forest Structure and regeneration across the Forest-grassland Ecotone in Mountain Pastures in Nepal

引用

Journal of Mountain Science 2014年第4期11卷 838-849页

作者： Lila Nath SHArMA ole reidar vetaas ram Prasad CHAUDHArY Inger Elisabeth MrEN Department of Geography University of Bergen Bergen 5020 Norway research Centre for Applied Science and Technology and Central Department of Botany Tribhuvan UniversityKathmandu 977 Nepal

The ecotone, the spatial transition zone between two vegetation communities, is claimed to have more species than the adjoining communities. However, empirical studies do not always confirm higher richness at the ecotone. The ecotone position and structure are dynamic over time and space and it is driven by the changes in climate, land use or their interaction. In this context, we assessed the forest- grassland ecotone of temperate mountains in central Nepal by i） comparing species composition and richness across the ecotone, ii） analyzing if the forestgrassland ecotone is shifting towards the grassland center by colonizing them with trees, and iii） discussing the consequence of changed disturbance regime in the dynamics of this ecotone and the surrounding grasslands. We analyzed vegetation data sampled from belt transects laid across the forest- grassland ecotone in semi-natural grassland patches. Vegetation data consisting of species richness and composition, and size structure and regeneration of the two most dominant tree species, namely rhododendron arboreum and Abies spectabilis, from the transects, were used to analyze the trend of the forest-grassland ecotone. Forest and grasslands were different in terms of floristic composition and diversity. Vascular plant speciesrichness linearly increased while moving from forest interior to grassland center. Spatial pattern of tree size structure and regeneration infers that forest boundary is advancing towards the grasslands at the expense of the grassland area, and tree establishment in the grasslands is part of a suceessional process. Temporally, tree establishment in grasslands started following the gradual decline in disturbance. We argue that local processes in terms of changed land use may best explain the phenomenon of ecotone shift and consequent forest expansion in these grasslands. We underpin the need for further research on the mechanism, rate and spatial extent of ecotone shift by using advaneed tools to

关键词： Ecotone shift Grasslands Forest Landuse change rhododendron

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

Weighted average regression and environmental calibration as a tool for quantifying climate-driven changes in vegetation

引用

Journal of Plant Ecology 2019年第3期12卷 787-789页

作者： Kuber Prasad Bhatta Harry John Betteley Birks John-Arvid Grytnes ole reidar vetaas Department of Geography University of Bergen Bergen Norway Correspondence address. Department of Geography University of Bergen PO Box 7802 5020 Bergen Norway. Tel: +47-93425064 E-mail: kuber.bhatta@uib.no Department of Biological Sciences University of Bergen Bergen Norway Department of Biological Sciences University of Bergen Bergen Norway

J Plant Ecol 2018 doi:10.1093/jpe/rty039 The authors wish to report the following error in the data ana-lysis in this paper that ***(Department of Biological Sciences,University of Bergen)has drawn to our attention after detailed scrutiny of our r *** error is that we accidentally derived the bootstrap es-timates of rMSEP,r2,mean and maximum bias,and skill of the training-set data twice,once in the weighted averaging regression analysis of the training sets themselves and once in the analysis of the‘reconstruction data-sets’.

关键词： error averaging regression

来源：

维普期刊数据库

维普期刊数据库评论

在线全文

学校读者我要写书评

暂无评论

Manufacturing tolerant topology optimization

引用

Acta Mechanica Sinica 2009年第2期25卷 227-239页

作者： ole Sigmund Department

In this paper we present an extension of the topology optimization method to include uncertainties during the fabrication of macro, micro and nano structures. More specifically, we consider devices that are manufactured using processes which may result in （uniformly） too thin （eroded） or too thick （dilated） structures compared to the intended topology. Examples are MEMS devices manufactured using etching processes, nano-devices manufactured using e-beam lithography or laser micro-machining and macro structures manufactured using milling processes. In the suggested robust topology optimization approach, under- and over-etching is modelled by image processing-based ＂erode＂ and ＂dilate＂ operators and the optimization problem is formulated as a worst case design problem. Applications of the method to the design of macro structures for minimum compliance and micro compliant mechanisms show that the method provides manufacturing tolerant designs with little decrease in performance. As a positive side effect the robust design formulation also eliminates the longstanding problem of one-node connected hinges in compliant mechanism design using topology optimization.

关键词： Topology optimization robust designCompliant mechanisms Manufacturing constraints

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

Mechanisms of species divergence through visual adaptation and sexual selection:Perspectives from a cichlid model system

引用

Current Zoology 2010年第3期56卷 285-299页

作者： Martine E.MAAN ole SEEHAUSEN Institute of Ecology & Evolution University of Bern Eawag Centre of Ecology Evolution and Biogeochemistry(CEEB)

The theory of ecological speciation suggests that assortative mating evolves most easily when mating preferences aredirectly linked to ecological traits that are subject to divergent selection. Sensory adaptation can play a major role in this process,because selective mating is often mediated by sexual signals: bright colours, complex song, pheromone blends and so on. Whendivergent sensory adaptation affects the perception of such signals, mating patterns may change as an immediate ***, mating preferences can diverge as a result of indirect effects: assortative mating may be promoted by selectionagainst intermediate phenotypes that are maladapted to their (sensory) environment. For Lake Victoria cichlids, the visual environmentconstitutes an important selective force that is heterogeneous across geographical and water depth gradients. We investigatethe direct and indirect effects of this heterogeneity on the evolution of female preferences for alternative male nuptial colours(red and blue) in the genus Pundamilia. Here, we review the current evidence for divergent sensory drive in this system, extractgeneral principles, and discuss future perspectives [Current Zoology 56 (3): 285-299, 2010].

关键词： Cichlid Sexual selection Species divergence Visual adaptation

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

Topology optimization of 3D shell structures with porous infill

引用

Acta Mechanica Sinica 2017年第4期33卷 778-791页

作者： Anders Clausen Erik Andreassen ole Sigmund Department of Mechanical Engineering Solid MechanicsTechnical University of Denmark 2800 Lyngby Denmark

This paper presents a 3D topology optimization approach for designing shell structures with a porous or void interior. It is shown that the resulting structures are significantly more robust towards load perturbations than completely solid structures optimized under the same conditions. The study indicates that the potential benefit of using porous structures is higher for lower total volume *** to earlier work dealing with 2D topology optimization, we found several new effects in 3D problems. Most notably, the opportunity for designing closed shells significantly improves the performance of porous structures due to the sandwich effect. Furthermore, the paper introduces improved filter boundary conditions to ensure a completely uniform coating thickness at the design domain boundary.

关键词： porous shells topology interior perturbations opportunity dealing earlier stiffness struc

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

The First-Quantized Theory of Photons

引用

Chinese Physics Letters 2007年第2期24卷 418-420页

作者：王智勇熊彩东 Keller ole School of Physical Electronics University of Electronic Science and Technology of China Chengdu 610054 Institute of Physics Aalborg Universlty Pontoppldanstrcede 103 DK-9220 Aalborgest Denmark

In near-field optics and optical tunnelling theory, photon wave mechanics, i.e. the first-quantized theory of photons, allows us to address the spatial field localization problem in a flexible manner which links smoothly to classical electromagnetics. We develop photon wave mechanics in a rigorous and unified way, based on which field quantization is obtained in a new way.

关键词： WAVE-FUNCTION LOCALIZATION

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

Design and development of guide vane cascade for a low speed number Francis turbine

引用

Journal of Hydrodynamics 2016年第4期28卷 676-689页

作者： Biraj Singh THAPA Chirag TrIVEDI ole Gunnar DAHLHAUG Department of Energy and Process Engineering Norwegian University of Science and Technology

Guide vane cascade of a low speed number Francis turbine is developed for the experimental investigations. The test setup is able to produce similar velocity distributions at the runner inlet as that of a reference prototype turbine. Standard analytical methods are used to design the reference turbine. Periodic walls of flow channel between guide vanes are identified as the starting profile for the boundary of the cascade. Two alternative designs with three guide vanes and two guide vanes, without runner, are studied. A new approach, for the hydraulic design and optimization of the cascade test setup layout, is proposed and investigated in details. CFD based optimization methods are used to define the final layout of the test setup. The optimum design is developed as a test setup and experimental validation is done with PIV methods. The optimized design of cascade with one guide vane between two flow channels is found to produce similar flow conditions to that in the runner inlet of a low speed number Francis turbine.

关键词： guide vanes Francis turbine cascade optimization CFD PIV

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

Umamification of food facilitates the green transition

引用

Soil Ecology Letters 2023年第1期5卷 1-3页

作者： ole G.Mouritsen Department of Food Science Taste forLifeDesign and Consumer BehaviorUniversity of Copenhagen26 RolighedsvejDK-1958 FrederiksbergDenmark

The planet is facing a global climate *** have urgently to be taken to alleviate the consequences by diminishing emission of greenhouse gases,cutting fossil energy consumption,and implementing sustainable uses of the world's *** responsible for more than one third of the stressors on the climate,the global food production systems and our eating behavior must change dramatically(Vermeulen et al.,2012).

关键词： planet consequences gases

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：