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MANY-SERVER QUEUES WITH CUSTOMER ABANDONMENT:A SURVEY OF DIFFUSION AND FLUID APPROXIMATIONS

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j.urnal of Systems Science and Systems Eng.neering 2012年第1期21卷 1-36页

作者： j. g. DAI Shuang.hi HE H. Milton Stewart School of Industrial and Systems Eng.neering Georgia Institute of Technology Atlanta GA 30332 USA. Department of Industrial and Systems Eng.neering National University of Singapore Singapore 11757

The performance of a call center is sensitive to customer abandonment. In this survey paper, we focus on g.g./n ＋ g. parallel-server queues that serve as a building.block to model call center operations. Such a queue has a g.neral arrival process （the g.）, independent and identically distributed （iid） service times with a g.neral distribution （the first g. ）, and iid patience times with a g.neral distribution （the ＋g.）. Following.the square-root safety staffing.rule, this queue can be operated in the quality- and efficiency-driven （QED） reg.me, which is characterized by larg. customer volume, the waiting.times being.a fraction of the service times, only a small fraction of customers abandoning.the system, and hig. server utilization. Operational efficiency is the central targ.t in a system whose staffing.costs dominate other expenses. If a moderate fraction of customer abandonment is allowed, such a system should be operated in an overloaded reg.me known as the efficiency-driven （ED） reg.me. We survey recent results on the many-server queues that are operated in the QED and ED reg.mes. These results include the performance insensitivity to patience time distributions and diffusion and fluid approximate models as practical tools for performance analysis.

关键词： Heavy traffic square-root safety staffing quality- and efficiency-driven reg.me efficiency-driven reg.me piecewise OU process

Two-dimensional numerical alg.rithm for water quality modeling.in the topog.aphically complicated river

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j.urnal of Environmental Sciences 2000年第4期12卷 469-473页

作者： Zeng. g. j.ang. Y. g.o, H. Huang. g.g.-H. Environmental Protection Institute Human University Hunan 410082 China

In this paper, a two-dimensional numerical calculation alg.rithm for the water quality modeling.in the Heng.ang.City section of the Xiang.0}ang.River is researched considering.the effect of the Dayuandu navig.tional key proj.ct. The research river is winding.and has two branches resulted from an isle. The numerical calculation alg.rithm for the water quality modeling.is set up on the basis of applying.topog.aphic map of the river course and the finite element method. The calculation result for the water quality modeling.includes the concentration fields for various pollutants. The numerical calculation alg.rithm for the water quality modeling.set up in this paper can be applied to shallow river with similar topog.aphically complicated river course.

关键词： Alg.rithms Finite element method River pollution Rivers

Effects of particle size and concentration on bubble coalescence and froth formation in a slurry bubble column

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Particuolog. 2018年第1期16卷 82-95页

作者： A.R. Sarhan j. Naser g. Brooks Department of Mechanical and Product Desig. Eng.neering Swinburne University of Technology Hawthorn Victoria 3122 Australia Department of Mechanical Eng.neering University ofAnbar Ramadi Anbar 31001 lraq

A new approach for simulating.the formation of a froth layer in a slurry bubble column is proposed. Froth is considered a separate phase, comprised of a mixture of g.s, liquid, and solid. The simulation was carried out using.commercial flow simulation software （FIRE v2014） for particle sizes of 60-150 μm at solid concentrations of 0-40vol%, and superficial g.s velocities of 0.02-0.034m/s in a slurry bubble column with a hydraulic diameter of 0.2 m and heig.t of 1.2 m. Modelling.calculations were conducted using.a Eulerian-Eulerian multiphase approach with k-ε turbulence. The population balance equations for bubble breakup, bubble coalescence rate, and the interfacial exchang. of mass and momentum were included in the computational fluid dynamics code by writing.subroutines in Fortran to track the number density of different bubble sizes. Flow structure, radial g.s holdup, and Sauter mean bubble diameter distributions at different column heig.ts were predicted in the pulp zone, while froth volume fraction and density were predicted in the froth zone. The model was validated using.available experimental data, and the predicted and experimental results showed reasonable ag.eement. To demonstrate the effect of increasing.solid concentration on the coalescence rate, a solid-effect multiplier in the coalescence effi- ciency equation was used. The solid-effect multiplier decreased with increasing.slurry concentration, causing.an increase in bubble coalescence efficiency. A slig.t decrease in the coalescence efficiency was also observed owing.to increasing.particle size, which led to a decrease in Sauter mean bubble diam- eter. The froth volume fraction increased with solid concentration. These results provide an improved understanding.of the dynamics of slurry bubble reactors in the presence of hydrophilic particles.

关键词： Computational fluid dynamics Slurry concentration g.s holdup Particle size Froth Coalescence efficiency

The Virtual g.oscience Workbench, Vg.: Open Source tools for discontinuous systems

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Particuolog. 2010年第2期8卷 100-105页

作者： A. Munj.za j. Xiang.X. g.rcia j.P. Latham g.g. Schiava D'Albano N.W.M. j.hn Department of Eng.neering Queen Mary London University London UK Department of Earth Science and Eng.neering Imperial College London UK

In 1989 work beg.n on merg.ng.finite and discrete elements. During.1990 alg.rithmic solutions for the new combined method were developed, tog.ther with a C-based implementation known as the Y code. In 2004 these developments and implementations were published as a textbook. Queen Mary University of London ~QMUL） and Imperial Colleg. are currently eng.g.d in a research proj.ct to make Y codes in both 2D and 3D available in Open Source format and with mainly g.oscience problems in mind. The result is a set of Open Source tools for g.oscience （Vg.）, key components of which are summarised in this paper, tog.ther with illustrative rang. of simulation results. 2009 Chinese Society of Particuolog. and Institute of Process Eng.neering. Chinese Academy of Sciences. Published by Elsevier B.V. All rig.ts reserved.

关键词： Combined finite-discrete elementWorkbenchModelling.eoscience

;oxicity models of metal mixtures established on the basis o ＂additivity＂ and ＂interactions＂

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Frontiers of Environmental Science & Eng.neering 2017年第2期11卷 11-23页

作者： Yang.Liu Martina g. Vij.er Bo Pan Willie j. g. M. Peij.enburg Faculty of Environmental Science and Eng.neering Kunming University of Science and Technology Kunming 650500 China Institute of Environmental Sciences (CML) Leiden University Leiden 2300 RA The Netherlands National Institute of Public Health and the Environment (RIVM) Center for Safety of Substances and Products Bilthoven 3720 BA The Netherlands

Observed effects of metal mixtures on animals and plants often differ from the estimates, which are commonly calculated by adding.up the biolog.cal responses of individual metals. This difference from additivity is commonly referred to as being.a consequence of specific interactions between metals. The science of how to quantify metal interactions and whether to include them in risk assessment models is in its infancy. This review summarizes the existing.predictive tools for evaluating.the combined toxicity of metals present in mixtures and indicates the advantag.s and disadvantag.s of each method. We intend to provide eco-toxicolog.sts with backg.ound information on how to make g.od use of the tools and how to advance the methods for assessing.toxicity of metal mixtures, It is concluded that statistically sig.ificant deviations from additivity are not necessarily biolog.cally relevant. Incorporation of interactions between metals in a model does not on forehand mean that the model is more accurate than a model developed based on additivity only. It is recommended to first use a relatively simple method for effect prediction of uninvestig.ted metal mixtures. To improve the reliability of toxicity modeling.for metal mixtures, further efforts should focus on balancing.the relationship between the sig.ificance of statistics and the biolog.cal meaning. and unraveling.the toxicity mechanisms of metals and their mixtures.

关键词： Metal Mixtures Toxicity Additivity Modeling Interactions

Investig.tion on 3Dt wake flow structures of swimming.bionic fish

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Acta Mechanica Sinica 2012年第5期28卷 1494-1508页

作者： g.-X.Shen g.-K.Tan g.-j.Lai Fluid Mechanics Institute Beihang University

A bionic experimental platform was desig.ed for the purpose of investig.ting.time accurate three-dimensional flow field, using.dig.tal particle imag. velocimetry （DSPIV）. The wake behind the flapping.trail of a robotic fish model was studied at hig. spatial resolution. The study was performed in a water channel. A robot fish model was desig.ed and built. The model was fixed onto a rig.d support frame- work using.a cable-supporting.method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two deg.ees of freedom, mainly in carang.form mode, by driving.its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a trans- lational manner, measuring.velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing.reconstruction of phase averag. flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including.＂reverse hairpin vortex＂ and ＂reverse Karman S-H vortex ring.＂, allowing.insig.t into physics of this complex flow.

关键词： Fish swimming 3D flow structure Unsteadyhydrodynamics DSPIV measurement - Vortex ring

Conservation laws for energ. and momentum in curved spaces

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j.urnal of Zhej.ang.University-Science A(Applied Physics & Eng.neering. 2007年第4期8卷 665-668页

作者： LóPEZ-BONILLA j. MORALES j. OVANDO g. Section of Postg.aduate Studies and Research Superior School of Mechanical and Electrical EngineeringNational Polytechnic InstituteCP 07738Mexico Division of Basic Sciences and Eng.neering Autonomous Metropolitan UniversityCP 02200Mexico

In arbitrary Riemannian 4-spaces, continuity equations are constructed which could be interpreted as conservation laws for the energ. and momentum of the g.avitational field. Special attention is g.ven to g.neral relativity to obtain, of natural manner, the pseudotensors of Einstein, Landau-Lifshitz, Moeller, g.ldberg.and Stachel, and also the conservation equations of Komar, Trautman, DuPlessis and Moss.

关键词： Noether theorem Lag.ang.ans in curved spaces Energ. and momentum in Riemannian spaces Rund-Lovelock identities

Does erectile dysfunction drug.use contribute to risky sexual behavior？

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Asian j.urnal of Androlog. 2010年第5期12卷 626-627页

作者： Wayne j. g. Hellstrom Tulane University Health Sciences Center New Orleans LA 70112 USA

Erectile dysfunction （ED） is a common sexual problem affecting.up to one-third of men throug.out their lives. According.to the Massachusetts Male Ag.ng.Study （MMAS）, ED affects an estimated 52% of men between the ag.s of 40 and 70. With the approval of sildenafil （USA in March 1998）, the first phosphodiesterase type 5 （PDE-5） inhibitor to be made available for treatment of ED, and the subsequent approval of vardenafil （USA in Aug.st 2003） and tadalafil （USA in November 2003）, the PDE-5 inhibitor class of drug. has rapidly become the first-line therapy for ED of varying.etiolog.es and severities.

关键词： Elderly Silver USA Ag.ng Men

Deformations of surface and rock mass in salt mines of Southern Poland

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中国有色金属学会会刊：英文版 2005年第S1期15卷 310-314页

作者： j..Szewczyk g. Kortas StanisΙaw Staszic Ag.-University of Science and Technolog. CracowPolandInstitute of Rock Mass Mechanics PAN-Polish Academy of Science CracowPoland

The existing.salt mines “Wieliczka”and“Bochnia”, where the exploitation of rock salt wasg.ing.on since 14th century ,have recently finishedtheir mining.activities .Inthe rock mass ,however ,old working. *** are ofteninaccessibleand not inventoried properly . Clamping.of suchworking. causes deformations in the rock mass it-self and onthe surface of the area .The specifics ofphysical properties of salt rock mass and also theapplied exploitation systemsinfluence the course ofthe deformation process ....

关键词： rock Deformations of surface and rock mass in salt mines of Southern Poland