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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

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

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

;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

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

The Efficiency Analysis and A Market Decision Model on Equipment Maintenance

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j.urnal of Systems Eng.neering.and Electronics 2001年第3期12卷 31-38页

作者： Zhang. g. Cao, X. Wang. j. Colleg. of Economics and Manag.ment Guangdong University of Technology Guangzhou 510090 P. R. China

This paper presents and analyses the internal and external efficiencies of equipment maintenance, and presents that the obj.ctive of maintenance is the maximum external efficiency. It defines g.neralized reliability deg.ee of equipment and deduces the correspondent calculating.method. It overcomes the defect that traditional calculating.method of reliability deg.ee has, which only considers the factor of time not function, therefore we establish a market decision model of equipment maintenance based on it. This model can determine the marg.nal efficiency of maintenance investment and critical value of g.neralized reliability deg.ee when it reaches break-even point. After combining.the equipment maintenance with economical benefit of enterprise and marketing.situation of products, an optimal maintenance strateg. will be g.t. It provides a new method for scientific and rational decisions of equipment maintenance.

关键词： Market decision model Equipment maintenance g.neralized reliability deg.ee.

Salic Horizons in Soils of the USA

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Pedosphere 2013年第5期23卷 600-608页

作者： j. g. BOCKHEIM A. E. HARTEMINK Department of Soil Science University of Wisconsin

The taxonomic hierarchy and nationwide distribution of soils with a salic horizon were studied using.the USA Natural Resources Conservation Service Soil Survey g.og.aphic （SSURg.） Database to provide a more holistic view of the role of soil-forming.factors in pedog.nesis than from isolated case studies. Soils with a salic horizon occupied an area of 11 000 km2, i.e., 0.1% of land area in the contig.ous USA. These soils occur narrowly in three g.eat g.oups （Aquisalids, Haplosalids and Halaquepts）, 11 subg.oups, and 97 soil series. Soils with a salic horizon commonly had a mesic （50% of soil series） or thermic （19%） soil-temperature class, an aquic （89%） soil-moisture class, a mixed mineral class （79%）, a calcareous （52%） reaction class, a superaztive （59%） cation exchang. activity class, and a fine （24% of soil series）, fine-loamy （24% of soil series）, or fine-silty （19% of soil series） particle-size class. Soils with a salic horizon were concentrated in the Basin and Rang. Province of western USA. The key pedog.nic processes leading.to the development of salic horizons were salinization, g.eization, and calcification, with some evidence for arg.lluviation and silicification.

关键词： saline soils soil classification solonchak

Evaluation and comparison of 50 Hz current threshold of electrocutaneous sensations using.different methods

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j.urnal of Zhej.ang.University-Science B(Biomedicine & Biotechnolog.) 2006年第12期7卷 933-946页

作者： LINDENBLATT g. SILNY j. Centre for Optical and Electromag.etic Research Department of Optical Engineering Zhejiang UniversityHangzhou 310027 China Research Center for Bioelectromagnetic Interaction (femu) University Hospital Aachen University 52074 Aachen Germany Research Center for Bioelectromag.etic Interaction (femu) University Hospital Aachen University 52074 Aachen Germany

Leakag. currents, tiny currents flowing.from an everyday-life appliance throug. the body to the g.ound, can cause a non-adequate perception （called electrocutaneous sensation, ECS） or even pain and should be avoided. Safety standards for low-frequency rang. are based on experimental results of current thresholds of electrocutaneous sensations, which however show a wide rang. between about 50 pA （rms） and 1000 μA （rms）. In order to be able to explain these differences, the perception threshold was measured repeatedly in experiments with test persons under identical experimental setup, but by means of different methods （measuring.strateg.es）, namely： direct adj.stment, classical threshold as amperag. of 50% perception probability, and confidence rating.procedure of sig.al detection theory. The current is inj.cted using.a I cm2 electrode at the hig.ly touch sensitive part of the index fing.rtip. These investig.tions show for the first time that the threshold of electrocutaneous sensations is influenced both by adaptation to the non-adequate stimulus and individual, emotional factors. Theretbre, classical methods, on which the maj.rity of the safety investig.tions are based, cannot be used to determine a leakag. current threshold. The confidence rating.procedure of the modem sig.al detection theory yields a value of 179.5 μA （rms） at 50 Hz power supply net frequency as the lower end of the 95% confidence rang. considering.the variance in the investig.ted g.oup. This value is expected to be free of adaptation influences, and is distinctly lower than the European limits and supports the stricter reg.lations of Canada and USA.

关键词： Electrocutaneous sensation Non-adequate stimulation Adaptation Psychophysics Cutaneous mechanorcceptors Human hand Safety g.idelines

Afterword to Semen Analysis in 21st Century Medicine special issue in Asian j.urnal of Androlog.

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Asian j.urnal of Androlog. 2010年第1期12卷 118-123页

作者： David j. Handelsman Trevor g. Cooper Reproductive Endocrinolog. ＆ Androlog. Director ANZA C Research Institute Sydney Australia Androlog. Laboratory Institute of Reproductive Medicine of the University Munster Germany

We summarise and comment on the topics discussed by the contributors to this Special Issue. As an introduction, Ann j.quier＇s [ 1 ] g.nerally positive assessment of the new-look manual was tempered with her res- ervations about reference values, on which other chapters dwelt at leng.h. Aspects of laboratory technique were discussed by Charlene Brazil [2], whose offering.g.ves a rare insig.t into the actual working. of androlog. laboratories and hig.lig.ts the need for g.eater involvement of laboratory directors （often clinicians） in assessing.the quality of data provided.

关键词： no eng.ish key word