检索结果-南通市图书馆

Single Charged Particle Motion in a Flat Surface with Static Electromagnetic Field and Quantum Hall Effect

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Modern Physics 2022年第11期13卷 1324-1330页

作者： Gustavo V. lópez Jorge A. lizarraga Departamento de Física Universidad de Guadalajara Guadalajara México

Taking into account the non separable solution for the quantum problem of the motion of a charged particle in a flat surface of lengths lx and ly with transversal static magnetic field B and longitudinal static electric field E, the quantum current, the transverse (Hall) and longitudinal resistivities are calculated for the state n = 0 and j = 0. We found that the transverse resistivity is proportional to an integer number, due to the quantization of the magnetic flux, and longitudinal resistivity can be zero for times t >> lxB/cE. In addition, using a modified periodicity of the solution, a modified quantization of the magnetic flux is found which allows to have IQHE and FQHE of any filling factor of the form v = k/l, with k, l ∈Z.

关键词： landau’s Gauge Quantum Hall Effect Degeneration

Costate mapping for indirect trajectory optimization

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Astrodynamics 2021年第4期5卷 359-371页

作者： Ehsan Taheri Vishala Arya John l.Junkins Department of Aerospace Engineering Auburn UniversityAuburnAL 36849USA Department of Aerospace Engineering Texas A&M UniversityCollege StationTX 77843-3141USA

Numerical solutions of optimal control problems are influenced by the appropriate choice of *** proposed method based on the variational approach to map costates between sets of coordinates and/or elements is suitable for solving optimal control problems using the indirect formalism of optimal control *** Jacobian of the nonlinear map between any two sets of coordinates and elements is a key component of costate vector mapping theory.A new solution for the class of planar,free-terminal-time,minimum-time,orbit rendezvous maneuvers is also *** accuracy of the costate mapping is verified,and its utility is demonstrated by solving minimum-time and minimum-fuel spacecraft trajectory optimization problems.

关键词： indirect optimization spacecraft trajectory optimization optimal control theory minimum time minimum fuel interplanetary Earth-centered low thrust

THE EFFECT OF BORON AND CARBON ADDITION ON WElDABIlITY OF DS TMS-75 SUPERAllOY

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Metallurgica Sinica(English letters) 2005年第1期18卷 24-32页

作者： M.C. Chaturvedi N.l. Richards Department of Mechanical and Industrial Engineering University of Manitoba Winnipeg Manitoba R3T 5V6 CanadaDepartment of Mechanical and Industrial Engineering University of Manitoba Winnipeg Manitoba R3T 5V6 Canada

Four alloys TMS-75 (Base), Base+B, Base+C and TMD-103 (Base+B+C) with varying levels of B, C were directionally solidified (DS), and their weldability was investigated by bead-on-plate electron beam welding. It was found that cracking occurred in the weld-metal, as well as in the heat affected zone (HAZ). Both γ/γ' and/or γ/carbide eutectic contributed to the weld-metal cracking, and the γ/γ' eutectic was found to be mainly responsible for cracking in HAZ. However, constitutional liquation of carbides seems to have made some contribution also. The B addition had a detrimental effect on HAZ cracking susceptibility, while C addition improved it appreciably even in the presence of B. In addition, no obvious differences were observed in cracking susceptibility of weld-metal in the four alloys. The cracking modes and mechanisms underlying the effect of B and C addition on weldability could be explained on the basis of microstructures of the four alloys.

关键词： Ni-based superalloy low melting point constituents liquation cracking

NONlOCAl CROWD DYNAMICS MODElS FOR SEVERAl POPUlATIONS

在线全文

学校读者我要写书评

暂无评论

Acta Mathematica Scientia 2012年第1期32卷 177-196页

作者： Rinaldo M.Colombo Magali lcureux-Mercier Department of Mathematics Brescia University Department of Mathematics TechnionIsrael Institute of Technology

This paper develops the basic analytical theory related to some recently intro- duced crowd dynamics models. Where well posedness was known only locally in time, it is here extended to all of R＋. The results on the stability with respect to the equations are improved. Moreover, here the case of several populations is considered, obtaining the well posedness of systems of multi-D non-local conservation laws. The basic analytical tools are provided by the classical Kruzkov theory of scalar conservation laws in several space dimensions.

关键词： hyperbolic conservation laws nonlocal flow pedestrian traffic

Effect of Composts,lime and Diammonium Phosphate on the Phytoavailability of Heavy Metals in a Copper Mine Tailing Soil

在线全文

学校读者我要写书评

暂无评论

Pedosphere 2009年第5期19卷 631-641页

作者： M.J.KHAN D.l.JONES Department of Soil and Environmental Sciences NWFP Agricultural UniversityPeshawar(Pakistan) School of Agricultural and Forest Sciences University of WalesBangorGwynedd LL57 2UW(UK)

Soil samples from a historic copper mine tailing site at the Parys Mountain,North Wales(UK) were amended with green waste compost(GC),GC+30% sewage sludge(GCS),lime and diammonium phosphate(DAP),to determine the effect of amendments on DTPA-and Ca(NO3)2-extractable metals in the mine tailing and on the phytoavailability of heavy metals by a lettuce(lactuca sativa l.).Both compost were added at the rate of 10% by weight,lime was added as calcium carbonate equivalent(pH = 7) and DAP at a 2300 mg kg-1 soil *** experiment was arranged in randomised complete design with three replicates in pots under control *** of lime resulted in the largest reduction in metal extractability with DTPA and Ca(NO3)2 and phytoavailability of Cu,Fe and Zn while DAP was effective in lowering Pb extractability and *** exception of Zn,all other metals extracted decreased with time after amendment *** distribution of heavy metals between and within the four procedures of potentially bioavailable sequential extraction(PBASE) varied significantly(P lationships were noted between the metals extracted with PBASE SE1 and Cu,Pb(P lts indicate that addition of lime is sufficient to restore the vegetative cover to a high metal mine waste while DAP is good for stabilizing Pb,but its detrimental role on plant growth and the risk associated with presence of N in DAP(through N leaching) may restrict its chances for remediation of contaminated sites.

关键词：铜矿尾矿磷酸二铵重金属堆肥土壤石灰

Grasshoppers （Orthoptera： Acrididae） select vegetation patches in local-scale responses to foliar nitrogen but not phosphorus in native grassland

在线全文

学校读者我要写书评

暂无评论

Insect Science 2011年第5期18卷 533-540页

作者： Viviana loaiza Jayne l. Jonas Anthony Joern Division of Biology Kansas State University Manhattan Kansas USA

Key elements such as nitrogen （N） and phosphorus （P） are often limiting relative to the nutritional needs of herbivores that feed on them. While N often limits insect herbivores in natural terrestrial ecosystems, the effect of P is poorly studied in the field, even though compelling hypotheses from the ecological stoichiometry literature predict its importance. We evaluated small-scale spatial distributions of, and herbivory by, grasshoppers among neighboring plots that vary in foliar-N and -P in tallgrass prairie. Grasshopper densities were 67% greater in N-fertilized plots but detected no effect to grasshopper densities from P-fertilizer. leaf damage to the dominant grass Andropogon gerardii was 32% greater in N-fertilized plots, but no response to foliar-P was detected. Herbivore damage to a common forb, goldenrod （Solidago missouriensis）, was not strongly linked by fertilizer treatments, although there was increased leaf damage in N-fertilizer treatments when no P was applied （a significant N ~ P interaction）. Under field conditions at local scales, we conclude that spatially heterogeneous distributions of grasshoppers are primarily affected by foliar-N in host plants with little evidence that P-levels contribute to the spatial patterns.

关键词： Andropogon gerardii ecological stoichiometry insect herbivory Konza Prairie N-P fertilization experiment Solidago rnissouriensis

Potential influence of wildfire in modulating climate-induced forest redistribution in a central Rocky Mountain landscape

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Ecological Processes 2017年第1期6卷 52-68页

作者： John l.Campbell Douglas J.Shinneman Department of Forest Ecosystems and Society Oregon State UniversityCorvallisORUSA U.S.Geological Survey Forest and Rangeland Ecosystem Science CenterBoiseIDUSA.

Introduction:Climate change is expected to impose significant tension on the geographic distribution of tree ***,tree species range shifts may be delayed by their long life spans,capacity to withstand long periods of physiological stress,and dispersal *** could theoretically break this biological inertia by killing forest canopies and facilitating species redistribution under changing *** investigated the capacity of wildfire to modulate climate-induced tree redistribution across a montane landscape in the central Rocky Mountains under three climate scenarios(contemporary and two warmer future climates)and three wildfire scenarios(representing historical,suppressed,and future fire regimes).Methods:Distributions of four common tree species were projected over 90 years by pairing a climate niche model with a forest landscape simulation model that simulates species dispersal,establishment,and mortality under alternative disturbance regimes and climate ***:Three species(Douglas-fir,lodgepole pine,subalpine fir)declined in abundance over time,due to climate-driven contraction in area suitable for establishment,while one species(ponderosa pine)was unable to exploit climate-driven expansion of area suitable for *** fire frequency accelerated declines in area occupied by Douglas-fir,lodgepole pine,and subalpine fir,and it maintained local abundance but not range expansion of ponderosa ***:Wildfire may play a larger role in eliminating these conifer species along trailing edges of their distributions than facilitating establishment along leading edges,in part due to dispersal limitations and interspecific competition,and future populations may increasingly depend on persistence in locations unfavorable for their establishment.

关键词： Forest disturbance Wildfire Climate change Central Rocky Mountains Climate niche Species migration Species distribution

Existence and Uniqueness of Fixed Point in Partially Ordered Sets and Applications to Ordinary Differential Equations

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mathematica Sinica,English Series 2007年第12期23卷 2205-2212页

作者： Juan J.NIETO RosanaRODRGUEZ-lPEZ Departamento de Análisis Matemático Facultad de MatemáticasUniversidad de Santiago de Compostela

We prove some fixed point theorems in partially ordered sets, providing an extension of the Banach contractive mapping theorem. Having studied previously the nondecreasing case, we consider in this paper nonincreasing mappings as well as non monotone mappings. We also present some applications to first-order ordinary differential equations with periodic boundary conditions, proving the existence of a unique solution admitting the existence of a lower solution.

关键词： fixed point partially ordered set first-order differential equation lower and upper solutions

Global evolution of Equidae and Gomphotheriidae from South America

在线全文

学校读者我要写书评

暂无评论

Integrative Zoology 2014年第4期9卷 434-443页

作者： Josél.PRADO María T.AlBERDI INCUAPA CONICET-UNICENNational University of Central Buenos Aires ProvinceOlavarríaArgentina Department of Paleobiology Museo Nacional de Ciencias NaturalesCSICMadridSpain

The contemporary South American mammalian communities were determined by the emergence of the Isthmus of Panama and by the profound climatic oscillations during the *** and gomphotheres were 2 very conspicuous groups of immigrant mammals from North America that arrived in South America during the *** present study compiles updated data on the phylogeny,systematics and ecology of both groups in South *** horses in South America are represented by 2 genera,Hippidion and Equus,as are the gomphotheres,represented by Cuvieronius and *** genera of horses include small(Hippidion devillei,***,*** and ***)and large forms(Equus neogeus and ***),which dispersed into South America using 2 different *** possible model for this dispersion indicates that the small forms used the Andes corridor,while larger horses dispersed through the eastern route and through some coastal *** the case of gomphotheres,Cuvieronius and Stegomastodon reached South America in 2 independent dispersal events,and Cuvieronius dispersed across the Andean corridor,while large Stegomastodon spread along the eastern *** and gomphotheres present values ofδ^(13)C from woodlands to C4 grass*** present lower values ofδ^(13)C than Equus in the late Pleistocene,whereas the gomphotheres diverge from value ofδ^(18)O,reflecting that Cuvieronius inhabited the Andean corridor and Stegomastodon dispersed through eastern *** gomphothere and horse species recorded in South America became extinct around the time that humans arrived.

关键词： Equidae Gomphotheriidae Plio-Pleistocene South America