Meta-Heuristics for the Design of a Demand-Responsive Transit Line
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The Majestic and Unique OstrichThe ostrich is a fascinating and unique bird that stands out in the animal kingdom due to its impressive size,speed,and distinctive features. Native to Africa,the ostrich is the largest and heaviest living bird,and it has adapted remarkably well to its environment.This essay will explore the characteristics,behavior,habitat,ecological importance,and interactions of ostriches with humans.Characteristics of OstrichesOstriches possess several distinctive features that make them easily recognizable:Physical Appearance:Ostriches are large,flightless birds with long necks, powerful legs,and a small head.Adult males can reach heights of up to9 feet(2.7meters)and weigh between220to350pounds(100to160 kilograms).Females are slightly smaller.Their plumage is predominantly black and white in males and brownish-gray in females,providing camouflage in their natural habitat.Legs and Feet:Ostriches have strong,muscular legs that are adapted for running.They have two toes on each foot,with the larger toe bearing a sharp claw that can be used for defense.Their legs are capable of delivering powerful kicks,which can deter predators.Eyes and Vision:Ostriches have large eyes,which are the largest of any land animal,measuring up to2inches(5centimeters)in diameter.Their keen eyesight allows them to spot predators from a distance,giving them ample time to flee.Feathers and Wings:Although ostriches cannot fly,they have large wings that they use for balance while running and for display during courtship rituals.Their feathers are soft and fluffy,providing insulation and protection from the harsh sun.Behavior and AdaptationsOstriches exhibit a range of behaviors and adaptations that help them survive in their environments:Running Speed:Ostriches are the fastest running birds,capable of reaching speeds of up to45miles per hour(72kilometers per hour). Their long legs and powerful muscles enable them to cover great distances quickly,helping them escape predators and travel between feeding areas.Diet:Ostriches are omnivores,feeding on a variety of plant materials, including seeds,leaves,and fruits,as well as insects and small vertebrates.They have a unique digestive system that includes a large, muscular stomach called a gizzard,which grinds up food with the help of swallowed stones.Reproduction:During the breeding season,male ostriches perform elaborate courtship displays to attract females.These displays include dancing,feather fluffing,and vocalizations.Once a pair has mated,the female lays her eggs in a communal nest,which is a shallow depression in the ground.Multiple females may lay their eggs in the same nest,with the dominant female's eggs placed in the center.Both males and females take turns incubating the eggs.Social Structure:Ostriches are social animals that often live in groups called flocks.These flocks can range in size from a few individuals to several dozen.Living in groups provides protection from predators,as there are more eyes to keep watch and more individuals to deter threats.Habitat and DistributionOstriches are highly adaptable and can be found in a variety of habitats across Africa:Savannas and Grasslands:Ostriches are commonly found in open savannas and grasslands,where they have access to abundant food sources and can easily spot predators.These environments provide the space needed for their large size and running capabilities.Deserts and Semi-Arid Regions:Ostriches are also well-adapted to arid and semi-arid regions,such as the Sahara Desert.They can tolerate high temperatures and have physiological adaptations that allow them to conserve water and survive in harsh conditions.Woodlands and Shrublands:In some areas,ostriches inhabit woodlands and shrublands,where they find shelter and food among the trees and bushes.These environments offer protection from the sun and predators.Ecological ImportanceOstriches play several important roles in their ecosystems:Seed Dispersal:As they forage on a variety of plant materials,ostriches help disperse seeds through their droppings.This contributes to the regeneration and spread of plant species,promoting biodiversity and ecosystem health.Prey Species:Although adult ostriches have few natural predators due to their size and speed,their eggs and chicks are vulnerable to predation by animals such as jackals,hyenas,and birds of prey.This predation pressure helps regulate ostrich populations and maintain ecological balance.Grazing and Vegetation Management:By feeding on grasses and other vegetation,ostriches help manage plant growth and prevent overgrowth.This grazing activity can benefit other herbivores and contribute to the overall health of the ecosystem.Interactions with HumansOstriches have a range of interactions with humans,both positive and negative:Farming and Domestication:Ostriches have been farmed and domesticated for their feathers,meat,and leather.Ostrich farming is a significant industry in some parts of the world,providing economic benefits and sustainable livelihoods.Ostrich meat is lean and high in protein,while their feathers are used in fashion and decoration.Tourism and Wildlife Viewing:Ostriches are a popular attraction for tourists and wildlife enthusiasts.Safaris and wildlife reserves often include opportunities to observe ostriches in their natural habitat, contributing to eco-tourism and conservation awareness.Cultural Significance:Ostriches hold cultural significance in many African societies,symbolizing speed,strength,and beauty.They appear in folklore,art,and traditional ceremonies,reflecting their importance in local cultures.Conservation Challenges:While ostrich populations are generally stable, they face threats from habitat loss,hunting,and human-wildlife conflict. Conservation efforts focus on protecting their habitats,regulating hunting,and promoting sustainable farming practices.ConclusionOstriches are remarkable creatures that play important roles in their ecosystems and have a variety of interactions with humans.Their unique characteristics,behaviors,and adaptations make them fascinatingsubjects of study and appreciation.Understanding and appreciating ostriches can lead to greater awareness of the importance of biodiversity and the need to protect and conserve our natural environments.By fostering a deeper connection to the natural world and recognizing the ecological significance of even the most unique creatures,we can work towards a more sustainable and harmonious relationship with the environment.Protecting ostriches and their habitats is essential for maintaining the health and balance of ecosystems and ensuring the continued survival of these majestic and unique birds.。
计算机领域国际会议分类排名现在的会议非常多,在投文章前,大家可以先看看会议的权威性、前几届的录用率,这样首先对自己的文章能不能中有个大概的心理底线。
权威与否可以和同行的同学沟通、或者看录用文章的水平、或者自己平时阅读文献的时候的慢慢累及。
原来有人做过一个国际会议的排名,如下.sg/home/assourav/crank.htm其中的很多会议我们都非常熟悉的。
但是这个排名是大概2000的时候做的,后来没有更新,所以像ISWC 这个会议在其中就看不到。
但是很多悠久的会议上面都有的,如www,SIGIR,VLDB,EMLC,ICTAI这些等等。
这些东西可以作为一个参考。
现在很多学校的同学毕业都要有检索的要求了。
因此很多不在SCI,EI检索范围内的会议投了可能对毕业无用,所以投之前最好查查会议是不是被SCI,EI检索的。
当然这也不绝对,如Web领域最权威的WWW的全文就只是ISTP检索,而不是SCI,EI检索的(可能是ACM出版的原因吧?)。
罗嗦了这么多!祝愿大家能在好的会议上发PAPER,能被SCI,EI检索。
---------------附,会议排名(from .sg/home/assourav/crank.htm)Computer Science Conference RankingsSome conferences accept multiple categories of papers. The rankings below are for the mos t prestigious category of paper at a given conference. All other categories should be treat ed as "unranked".AREA: DatabasesRank 1:SIGMOD: ACM SIGMOD Conf on Management of DataPODS: ACM SIGMOD Conf on Principles of DB SystemsVLDB: Very Large Data BasesICDE: Intl Conf on Data EngineeringICDT: Intl Conf on Database TheoryRank 2:SSD: Intl Symp on Large Spatial DatabasesDEXA: Database and Expert System ApplicationsFODO: Intl Conf on Foundation on Data OrganizationEDBT: Extending DB TechnologyDOOD: Deductive and Object-Oriented DatabasesDASFAA: Database Systems for Advanced ApplicationsCIKM: Intl. Conf on Information and Knowledge ManagementSSDBM: Intl Conf on Scientific and Statistical DB MgmtCoopIS - Conference on Cooperative Information SystemsER - Intl Conf on Conceptual Modeling (ER)Rank 3:COMAD: Intl Conf on Management of DataBNCOD: British National Conference on DatabasesADC: Australasian Database ConferenceADBIS: Symposium on Advances in DB and Information SystemsDaWaK - Data Warehousing and Knowledge DiscoveryRIDE WorkshopIFIP-DS: IFIP-DS ConferenceIFIP-DBSEC - IFIP Workshop on Database SecurityNGDB: Intl Symp on Next Generation DB Systems and AppsADTI: Intl Symp on Advanced DB Technologies and Integration FEWFDB: Far East Workshop on Future DB SystemsMDM - Int. Conf. on Mobile Data Access/Management (MDA/MDM)ICDM - IEEE International Conference on Data MiningVDB - Visual Database SystemsIDEAS - International Database Engineering and Application Symposium Others:ARTDB - Active and Real-Time Database SystemsCODAS: Intl Symp on Cooperative DB Systems for Adv AppsDBPL - Workshop on Database Programming LanguagesEFIS/EFDBS - Engineering Federated Information (Database) Systems KRDB - Knowledge Representation Meets DatabasesNDB - National Database Conference (China)NLDB - Applications of Natural Language to Data BasesFQAS - Flexible Query-Answering SystemsIDC(W) - International Database Conference (HK CS)RTDB - Workshop on Real-Time DatabasesSBBD: Brazilian Symposium on DatabasesWebDB - International Workshop on the Web and DatabasesWAIM: Interational Conference on Web Age Information ManagementDASWIS - Data Semantics in Web Information SystemsDMDW - Design and Management of Data WarehousesDOLAP - International Workshop on Data Warehousing and OLAPDMKD - Workshop on Research Issues in Data Mining and Knowledge DiscoveryKDEX - Knowledge and Data Engineering Exchange WorkshopNRDM - Workshop on Network-Related Data ManagementMobiDE - Workshop on Data Engineering for Wireless and Mobile AccessMDDS - Mobility in Databases and Distributed SystemsMEWS - Mining for Enhanced Web SearchTAKMA - Theory and Applications of Knowledge MAnagementWIDM: International Workshop on Web Information and Data ManagementW2GIS - International Workshop on Web and Wireless Geographical Information Systems CDB - Constraint Databases and ApplicationsDTVE - Workshop on Database Technology for Virtual EnterprisesIWDOM - International Workshop on Distributed Object ManagementOODBS - Workshop on Object-Oriented Database SystemsPDIS: Parallel and Distributed Information SystemsAREA: Artificial Intelligence and Related SubjectsRank 1:AAAI: American Association for AI National ConferenceCVPR: IEEE Conf on Comp Vision and Pattern RecognitionIJCAI: Intl Joint Conf on AIICCV: Intl Conf on Computer VisionICML: Intl Conf on Machine LearningKDD: Knowledge Discovery and Data MiningKR: Intl Conf on Principles of KR & ReasoningNIPS: Neural Information Processing SystemsUAI: Conference on Uncertainty in AIAAMAS: Intl Conf on Autonomous Agents and Multi-Agent Systems (past: ICAA)ACL: Annual Meeting of the ACL (Association of Computational Linguistics)Rank 2:NAACL: North American Chapter of the ACLAID: Intl Conf on AI in DesignAI-ED: World Conference on AI in EducationCAIP: Inttl Conf on Comp. Analysis of Images and PatternsCSSAC: Cognitive Science Society Annual ConferenceECCV: European Conference on Computer VisionEAI: European Conf on AIEML: European Conf on Machine LearningGECCO: Genetic and Evolutionary Computation Conference (used to be GP)IAAI: Innovative Applications in AIICIP: Intl Conf on Image ProcessingICNN/IJCNN: Intl (Joint) Conference on Neural NetworksICPR: Intl Conf on Pattern RecognitionICDAR: International Conference on Document Analysis and RecognitionICTAI: IEEE conference on Tools with AIAMAI: Artificial Intelligence and MathsDAS: International Workshop on Document Analysis SystemsWACV: IEEE Workshop on Apps of Computer VisionCOLING: International Conference on Computational LiguisticsEMNLP: Empirical Methods in Natural Language ProcessingEACL: Annual Meeting of European Association Computational LingusticsCoNLL: Conference on Natural Language LearningDocEng: ACM Symposium on Document EngineeringIEEE/WIC International Joint Conf on Web Intelligence and Intelligent Agent Technology Rank 3:PRICAI: Pacific Rim Intl Conf on AIAAI: Australian National Conf on AIACCV: Asian Conference on Computer VisionAI*IA: Congress of the Italian Assoc for AIANNIE: Artificial Neural Networks in EngineeringANZIIS: Australian/NZ Conf on Intelligent Inf. SystemsCAIA: Conf on AI for ApplicationsCAAI: Canadian Artificial Intelligence ConferenceASADM: Chicago ASA Data Mining Conf: A Hard Look at DMEPIA: Portuguese Conference on Artificial IntelligenceFCKAML: French Conf on Know. Acquisition & Machine LearningICANN: International Conf on Artificial Neural NetworksICCB: International Conference on Case-Based ReasoningICGA: International Conference on Genetic AlgorithmsICONIP: Intl Conf on Neural Information ProcessingIEA/AIE: Intl Conf on Ind. & Eng. Apps of AI & Expert SysICMS: International Conference on Multiagent SystemsICPS: International conference on Planning SystemsIWANN: Intl Work-Conf on Art & Natural Neural NetworksPACES: Pacific Asian Conference on Expert SystemsSCAI: Scandinavian Conference on Artifical IntelligenceSPICIS: Singapore Intl Conf on Intelligent SystemPAKDD: Pacific-Asia Conf on Know. Discovery & Data MiningSMC: IEEE Intl Conf on Systems, Man and CyberneticsPAKDDM: Practical App of Knowledge Discovery & Data MiningWCNN: The World Congress on Neural NetworksWCES: World Congress on Expert SystemsASC: Intl Conf on AI and Soft ComputingPACLIC: Pacific Asia Conference on Language, Information and ComputationICCC: International Conference on Chinese ComputingICADL: International Conference on Asian Digital LibrariesRANLP: Recent Advances in Natural Language ProcessingNLPRS: Natural Language Pacific Rim SymposiumMeta-Heuristics International ConferenceRank 3:ICRA: IEEE Intl Conf on Robotics and AutomationNNSP: Neural Networks for Signal ProcessingICASSP: IEEE Intl Conf on Acoustics, Speech and SPGCCCE: Global Chinese Conference on Computers in EducationICAI: Intl Conf on Artificial IntelligenceAEN: IASTED Intl Conf on AI, Exp Sys & Neural NetworksWMSCI: World Multiconfs on Sys, Cybernetics & InformaticsLREC: Language Resources and Evaluation ConferenceAIMSA: Artificial Intelligence: Methodology, Systems, ApplicationsAISC: Artificial Intelligence and Symbolic ComputationCIA: Cooperative Information AgentsInternational Conference on Computational Intelligence for Modelling, Control and Automation Pattern MatchingECAL: European Conference on Artificial LifeEKAW: Knowledge Acquisition, Modeling and ManagementEMMCVPR: Energy Minimization Methods in Computer Vision and Pattern RecognitionEuroGP: European Conference on Genetic ProgrammingFoIKS: Foundations of Information and Knowledge SystemsIAWTIC: International Conference on Intelligent Agents, Web Technologies and Internet Commer ceICAIL: International Conference on Artificial Intelligence and LawSMIS: International Syposium on Methodologies for Intelligent SystemsIS&N: Intelligence and Services in NetworksJELIA: Logics in Artificial IntelligenceKI: German Conference on Artificial IntelligenceKRDB: Knowledge Representation Meets DatabasesMAAMAW: Modelling Autonomous Agents in a Multi-Agent WorldNC: ICSC Symposium on Neural ComputationPKDD: Principles of Data Mining and Knowledge DiscoverySBIA: Brazilian Symposium on Artificial IntelligenceScale-Space: Scale-Space Theories in Computer VisionXPS: Knowledge-Based SystemsI2CS: Innovative Internet Computing SystemsTARK: Theoretical Aspects of Rationality and Knowledge MeetingMKM: International Workshop on Mathematical Knowledge ManagementACIVS: International Conference on Advanced Concepts For Intelligent Vision Systems ATAL: Agent Theories, Architectures, and LanguagesLACL: International Conference on Logical Aspects of Computational LinguisticsAREA: Hardware and ArchitectureRank 1:ASPLOS: Architectural Support for Prog Lang and OSISCA: ACM/IEEE Symp on Computer ArchitectureICCAD: Intl Conf on Computer-Aided DesignDAC: Design Automation ConfMICRO: Intl Symp on MicroarchitectureHPCA: IEEE Symp on High-Perf Comp ArchitectureRank 2:FCCM: IEEE Symposium on Field Programmable Custom Computing MachinesSUPER: ACM/IEEE Supercomputing ConferenceICS: Intl Conf on SupercomputingISSCC: IEEE Intl Solid-State Circuits ConfHCS: Hot Chips SympVLSI: IEEE Symp VLSI CircuitsCODES+ISSS: Intl Conf on Hardware/Software Codesign & System SynthesisDATE: IEEE/ACM Design, Automation & Test in Europe ConferenceFPL: Field-Programmable Logic and ApplicationsCASES: International Conference on Compilers, Architecture, and Synthesis for Embedded Syste msRank 3:ICA3PP: Algs and Archs for Parall ProcEuroMICRO: New Frontiers of Information TechnologyACS: Australian Supercomputing ConfISC: Information Security ConferenceUnranked:Advanced Research in VLSIInternational Symposium on System SynthesisInternational Symposium on Computer DesignInternational Symposium on Circuits and SystemsAsia Pacific Design Automation ConferenceInternational Symposium on Physical DesignInternational Conference on VLSI DesignCANPC: Communication, Architecture, and Applications for Network-Based Parallel Computing CHARME: Conference on Correct Hardware Design and Verification MethodsCHES: Cryptographic Hardware and Embedded SystemsNDSS: Network and Distributed System Security SymposiumNOSA: Nordic Symposium on Software ArchitectureACAC: Australasian Computer Architecture ConferenceCSCC: WSES/IEEE world multiconference on Circuits, Systems, Communications & Computers ICN: IEEE International Conference on Networking Topology in Computer Science ConferenceAREA: Applications and MediaRank 1:I3DG: ACM-SIGRAPH Interactive 3D GraphicsSIGGRAPH: ACM SIGGRAPH ConferenceACM-MM: ACM Multimedia ConferenceDCC: Data Compression ConfSIGMETRICS: ACM Conf on Meas. & Modelling of Comp SysSIGIR: ACM SIGIR Conf on Information RetrievalPECCS: IFIP Intl Conf on Perf Eval of Comp \& Comm Sys WWW: World-Wide Web ConferenceRank 2:IEEE VisualizationEUROGRAPH: European Graphics ConferenceCGI: Computer Graphics InternationalCANIM: Computer AnimationPG: Pacific GraphicsICME: Intl Conf on MMedia & ExpoNOSSDAV: Network and OS Support for Digital A/VPADS: ACM/IEEE/SCS Workshop on Parallel \& Dist Simulation WSC: Winter Simulation ConferenceASS: IEEE Annual Simulation SymposiumMASCOTS: Symp Model Analysis \& Sim of Comp \& Telecom Sys PT: Perf Tools - Intl Conf on Model Tech \& Tools for CPE NetStore: Network Storage SymposiumMMCN: ACM/SPIE Multimedia Computing and NetworkingJCDL: Joint Conference on Digital LibrariesRank 3:ACM-HPC: ACM Hypertext ConfMMM: Multimedia ModellingDSS: Distributed Simulation SymposiumSCSC: Summer Computer Simulation ConferenceWCSS: World Congress on Systems SimulationESS: European Simulation SymposiumESM: European Simulation MulticonferenceHPCN: High-Performance Computing and NetworkingGeometry Modeling and ProcessingWISEDS-RT: Distributed Simulation and Real-time Applications IEEE Intl Wshop on Dist Int Simul and Real-Time Applications ECIR: European Colloquium on Information RetrievalEd-MediaIMSA: Intl Conf on Internet and MMedia SysUn-ranked:DVAT: IS\&T/SPIE Conf on Dig Video Compression Alg \& TechMME: IEEE Intl Conf. on Multimedia in EducationICMSO: Intl Conf on Modelling, Simulation and OptimisationICMS: IASTED Intl Conf on Modelling and SimulationCOTIM: Conference on Telecommunications and Information MarketsDOA: International Symposium on Distributed Objects and ApplicationsECMAST: European Conference on Multimedia Applications, Services and TechniquesGIS: Workshop on Advances in Geographic Information SystemsIDA: Intelligent Data AnalysisIDMS: Interactive Distributed Multimedia Systems and Telecommunication ServicesIUI: Intelligent User InterfacesMIS: Workshop on Multimedia Information SystemsWECWIS: Workshop on Advanced Issues of E-Commerce and Web/based Information Systems WIDM: Web Information and Data ManagementWOWMOM: Workshop on Wireless Mobile MultimediaWSCG: International Conference in Central Europe on Computer Graphics and Visualization LDTA: Workshop on Language Descriptions, Tools and ApplicationsIPDPSWPIM: International Workshop on Parallel and Distributed Computing Issues in Wireless N etworks and Mobile ComputingIWST: International Workshop on Scheduling and TelecommunicationsAPDCM: Workshop on Advances in Parallel and Distributed Computational ModelsCIMA: International ICSC Congress on Computational Intelligence: Methods and Applications FLA: Fuzzy Logic and Applications MeetingICACSD: International Conference on Application of Concurrency to System DesignICATPN: International conference on application and theory of Petri netsAICCSA: ACS International Conference on Computer Systems and ApplicationsCAGD: International Symposium of Computer Aided Geometric DesignSpanish Symposium on Pattern Recognition and Image AnalysisInternational Workshop on Cluster Infrastructure for Web Server and E-Commerce Applications WSES ISA: Information Science And Applications ConferenceCHT: International Symposium on Advances in Computational Heat TransferIMACS: International Conference on Applications of Computer AlgebraVIPromCom: International Symposium on Video Processing and Multimedia Communications PDMPR: International Workshop on Parallel and Distributed Multimedia Processing & Retrieval International Symposium On Computational And Applied PdesPDCAT: International Conference on Parallel and Distributed Computing, Applications, and Tec hniquesBiennial Computational Techniques and Applications ConferenceSymposium on Advanced Computing in Financial MarketsWCCE: World Conference on Computers in EducationITCOM: SPIE's International Symposium on The Convergence of Information Technologies and Com municationsConference on Commercial Applications for High-Performance ComputingMSA: Metacomputing Systems and Applications WorkshopWPMC : International Symposium on Wireless Personal Multimedia Communications WSC: Online World Conference on Soft Computing in Industrial Applications HERCMA: Hellenic European Research on Computer Mathematics and its Applications PARA: Workshop on Applied Parallel ComputingInternational Computer Science Conference: Active Media TechnologyIW-MMDBMS - Int. Workshop on Multi-Media Data Base Management SystemsAREA: System TechnologyRank 1:SIGCOMM: ACM Conf on Comm Architectures, Protocols & AppsINFOCOM: Annual Joint Conf IEEE Comp & Comm SocSPAA: Symp on Parallel Algms and ArchitecturePODC: ACM Symp on Principles of Distributed ComputingPPoPP: Principles and Practice of Parallel ProgrammingRTSS: Real Time Systems SympSOSP: ACM SIGOPS Symp on OS PrinciplesSOSDI: Usenix Symp on OS Design and ImplementationCCS: ACM Conf on Comp and Communications SecurityIEEE Symposium on Security and PrivacyMOBICOM: ACM Intl Conf on Mobile Computing and NetworkingUSENIX Conf on Internet Tech and SysICNP: Intl Conf on Network ProtocolsPACT: Intl Conf on Parallel Arch and Compil TechRTAS: IEEE Real-Time and Embedded Technology and Applications Symposium ICDCS: IEEE Intl Conf on Distributed Comp SystemsRank 2:CC: Compiler ConstructionIPDPS: Intl Parallel and Dist Processing SympIC3N: Intl Conf on Comp Comm and NetworksICPP: Intl Conf on Parallel ProcessingSRDS: Symp on Reliable Distributed SystemsMPPOI: Massively Par Proc Using Opt InterconnsASAP: Intl Conf on Apps for Specific Array ProcessorsEuro-Par: European Conf. on Parallel ComputingFast Software EncryptionUsenix Security SymposiumEuropean Symposium on Research in Computer SecurityWCW: Web Caching WorkshopLCN: IEEE Annual Conference on Local Computer NetworksIPCCC: IEEE Intl Phoenix Conf on Comp & CommunicationsCCC: Cluster Computing ConferenceICC: Intl Conf on CommWCNC: IEEE Wireless Communications and Networking ConferenceCSFW: IEEE Computer Security Foundations WorkshopRank 3:MPCS: Intl. Conf. on Massively Parallel Computing SystemsGLOBECOM: Global CommICCC: Intl Conf on Comp CommunicationNOMS: IEEE Network Operations and Management SympCONPAR: Intl Conf on Vector and Parallel ProcessingVAPP: Vector and Parallel ProcessingICPADS: Intl Conf. on Parallel and Distributed SystemsPublic Key CryptosystemsAnnual Workshop on Selected Areas in CryptographyAustralasia Conference on Information Security and PrivacyInt. Conf on Inofrm and Comm. SecurityFinancial CryptographyWorkshop on Information HidingSmart Card Research and Advanced Application ConferenceICON: Intl Conf on NetworksNCC: Nat Conf CommIN: IEEE Intell Network WorkshopSoftcomm: Conf on Software in Tcomms and Comp NetworksINET: Internet Society ConfWorkshop on Security and Privacy in E-commerceUn-ranked:PARCO: Parallel ComputingSE: Intl Conf on Systems Engineering (**)PDSECA: workshop on Parallel and Distributed Scientific and Engineering Computing with Appli cationsCACS: Computer Audit, Control and Security ConferenceSREIS: Symposium on Requirements Engineering for Information SecuritySAFECOMP: International Conference on Computer Safety, Reliability and SecurityIREJVM: Workshop on Intermediate Representation Engineering for the Java Virtual Machine EC: ACM Conference on Electronic CommerceEWSPT: European Workshop on Software Process TechnologyHotOS: Workshop on Hot Topics in Operating SystemsHPTS: High Performance Transaction SystemsHybrid SystemsICEIS: International Conference on Enterprise Information SystemsIOPADS: I/O in Parallel and Distributed SystemsIRREGULAR: Workshop on Parallel Algorithms for Irregularly Structured ProblemsKiVS: Kommunikation in Verteilten SystemenLCR: Languages, Compilers, and Run-Time Systems for Scalable ComputersMCS: Multiple Classifier SystemsMSS: Symposium on Mass Storage SystemsNGITS: Next Generation Information Technologies and SystemsOOIS: Object Oriented Information SystemsSCM: System Configuration ManagementSecurity Protocols WorkshopSIGOPS European WorkshopSPDP: Symposium on Parallel and Distributed ProcessingTreDS: Trends in Distributed SystemsUSENIX Technical ConferenceVISUAL: Visual Information and Information SystemsFoDS: Foundations of Distributed Systems: Design and Verification of Protocols conference RV: Post-CAV Workshop on Runtime VerificationICAIS: International ICSC-NAISO Congress on Autonomous Intelligent SystemsITiCSE: Conference on Integrating Technology into Computer Science EducationCSCS: CyberSystems and Computer Science ConferenceAUIC: Australasian User Interface ConferenceITI: Meeting of Researchers in Computer Science, Information Systems Research & Statistics European Conference on Parallel ProcessingRODLICS: Wses International Conference on Robotics, Distance Learning & Intelligent Communic ation SystemsInternational Conference On Multimedia, Internet & Video TechnologiesPaCT: Parallel Computing Technologies workshopPPAM: International Conference on Parallel Processing and Applied MathematicsInternational Conference On Information Networks, Systems And TechnologiesAmiRE: Conference on Autonomous Minirobots for Research and EdutainmentDSN: The International Conference on Dependable Systems and NetworksIHW: Information Hiding WorkshopGTVMT: International Workshop on Graph Transformation and Visual Modeling Techniques AREA: Programming Languages and Software EngineeringRank 1:POPL: ACM-SIGACT Symp on Principles of Prog LangsPLDI: ACM-SIGPLAN Symp on Prog Lang Design & ImplOOPSLA: OO Prog Systems, Langs and ApplicationsICFP: Intl Conf on Function ProgrammingJICSLP/ICLP/ILPS: (Joint) Intl Conf/Symp on Logic ProgICSE: Intl Conf on Software EngineeringFSE: ACM Conf on the Foundations of Software Engineering (inc: ESEC-FSE) FM/FME: Formal Methods, World Congress/EuropeCAV: Computer Aided VerificationRank 2:CP: Intl Conf on Principles & Practice of Constraint ProgTACAS: Tools and Algos for the Const and An of SystemsESOP: European Conf on ProgrammingICCL: IEEE Intl Conf on Computer LanguagesPEPM: Symp on Partial Evalutation and Prog ManipulationSAS: Static Analysis SymposiumRTA: Rewriting Techniques and ApplicationsIWSSD: Intl Workshop on S/W Spec & DesignCAiSE: Intl Conf on Advanced Info System EngineeringSSR: ACM SIGSOFT Working Conf on Software ReusabilitySEKE: Intl Conf on S/E and Knowledge EngineeringICSR: IEEE Intl Conf on Software ReuseASE: Automated Software Engineering ConferencePADL: Practical Aspects of Declarative LanguagesISRE: Requirements EngineeringICECCS: IEEE Intl Conf on Eng. of Complex Computer SystemsIEEE Intl Conf on Formal Engineering MethodsIntl Conf on Integrated Formal MethodsFOSSACS: Foundations of Software Science and Comp StructAPLAS: Asian Symposium on Programming Languages and SystemsMPC: Mathematics of Program ConstructionECOOP: European Conference on Object-Oriented ProgrammingICSM: Intl. Conf on Software MaintenanceHASKELL - Haskell WorkshopRank 3:FASE: Fund Appr to Soft EngAPSEC: Asia-Pacific S/E ConfPAP/PACT: Practical Aspects of PROLOG/Constraint TechALP: Intl Conf on Algebraic and Logic ProgrammingPLILP: Prog, Lang Implentation & Logic ProgrammingLOPSTR: Intl Workshop on Logic Prog Synthesis & TransfICCC: Intl Conf on Compiler ConstructionCOMPSAC: Intl. Computer S/W and Applications ConfTAPSOFT: Intl Joint Conf on Theory & Pract of S/W DevWCRE: SIGSOFT Working Conf on Reverse EngineeringAQSDT: Symp on Assessment of Quality S/W Dev ToolsIFIP Intl Conf on Open Distributed ProcessingIntl Conf of Z UsersIFIP Joint Int'l Conference on Formal Description Techniques and Protocol Specification, Tes ting, And VerificationPSI (Ershov conference)UML: International Conference on the Unified Modeling LanguageUn-ranked:Australian Software Engineering ConferenceIEEE Int. W'shop on Object-oriented Real-time Dependable Sys. (WORDS)IEEE International Symposium on High Assurance Systems EngineeringThe Northern Formal Methods WorkshopsFormal Methods PacificInt. Workshop on Formal Methods for Industrial Critical SystemsJFPLC - International French Speaking Conference on Logic and Constraint ProgrammingL&L - Workshop on Logic and LearningSFP - Scottish Functional Programming WorkshopLCCS - International Workshop on Logic and Complexity in Computer ScienceVLFM - Visual Languages and Formal MethodsNASA LaRC Formal Methods WorkshopPASTE: Workshop on Program Analysis For Software Tools and EngineeringTLCA: Typed Lambda Calculus and ApplicationsFATES - A Satellite workshop on Formal Approaches to Testing of SoftwareWorkshop On Java For High-Performance ComputingDSLSE - Domain-Specific Languages for Software EngineeringFTJP - Workshop on Formal Techniques for Java ProgramsWFLP - International Workshop on Functional and (Constraint) Logic ProgrammingFOOL - International Workshop on Foundations of Object-Oriented LanguagesSREIS - Symposium on Requirements Engineering for Information SecurityHLPP - International workshop on High-level parallel programming and applicationsINAP - International Conference on Applications of PrologMPOOL - Workshop on Multiparadigm Programming with OO LanguagesPADO - Symposium on Programs as Data ObjectsTOOLS: Int'l Conf Technology of Object-Oriented Languages and SystemsAustralasian Conference on Parallel And Real-Time SystemsPASTE: Workshop on Program Analysis For Software Tools and EngineeringAvoCS: Workshop on Automated Verification of Critical SystemsSPIN: Workshop on Model Checking of SoftwareFemSys: Workshop on Formal Design of Safety Critical Embedded SystemsAda-EuropePPDP: Principles and Practice of Declarative ProgrammingAPL ConferenceASM: Workshops on Abstract State MachinesCOORDINATION: Coordination Models and LanguagesDocEng: ACM Symposium on Document EngineeringDSV-IS: Design, Specification, and Verification of Interactive SystemsFMCAD: Formal Methods in Computer-Aided DesignFMLDO: Workshop on Foundations of Models and Languages for Data and ObjectsIFL: Implementation of Functional LanguagesILP: International Workshop on Inductive Logic ProgrammingISSTA: International Symposium on Software Testing and AnalysisITC: International Test ConferenceIWFM: Irish Workshop in Formal MethodsJava GrandeLP: Logic Programming: Japanese ConferenceLPAR: Logic Programming and Automated ReasoningLPE: Workshop on Logic Programming EnvironmentsLPNMR: Logic Programming and Non-monotonic ReasoningPJW: Workshop on Persistence and JavaRCLP: Russian Conference on Logic ProgrammingSTEP: Software Technology and Engineering PracticeTestCom: IFIP International Conference on Testing of Communicating SystemsVL: Visual LanguagesFMPPTA: Workshop on Formal Methods for Parallel Programming Theory and Applications WRS: International Workshop on Reduction Strategies in Rewriting and Programming FATES: A Satellite workshop on Formal Approaches to Testing of Software FORMALWARE: Meeting on Formalware Engineering: Formal Methods for Engineering Software DRE: conference Data Reverse EngineeringSTAREAST: Software Testing Analysis & Review ConferenceConference on Applied Mathematics and Scientific ComputingInternational Testing Computer Software ConferenceLinux Showcase & ConferenceFLOPS: International Symposum on Functional and Logic ProgrammingGCSE: International Conference on Generative and Component-Based Software Engineering JOSES: Java Optimization Strategies for Embedded Systems。
专利名称:Automated method and system for theevaluation of disease and registrationaccuracy in the subtraction of temporallysequential medical images发明人:Heber MacMahon,Samuel G. Armato申请号:US10721827申请日:20031126公开号:US20050111718A1公开日:20050526专利内容由知识产权出版社提供专利附图:摘要:An apparatus, method and computer program product for performingcomputer aided diagnosis on temporal subtraction images of objects. A mode of a gray-level histogram is identified, and a gray-level threshold is established at a predefined fraction of this modal value. All pixels with gray levels below this threshold that lie within the lung regions of the temporal subtraction image remain “on,” while all other pixels are set to zero. Area and circularity requirements are imposed to eliminate false-positive regions. Areas of pathologic change identified in this manner may be presented as outlines in the subtraction image or as highlighted regions in the original radiographic image so that, in effect, temporal subtraction becomes a “background” process for computer-aided diagnosis. The present invention is also directed to method, apparatus, and computer program product for performing temporal subtraction on energy subtraction images, with or without subsequent computer aided diagnosis, of objects.申请人:Heber MacMahon,Samuel G. Armato地址:Chicago IL US,Downers Grove IL US国籍:US,US更多信息请下载全文后查看。
Metaphysics形而上学I. IntroductionMetaphysics, branch of philosophy concerned with the nature of ultimate reality. Metaphysics is customarily divided into ontology, which deals with the question of how many fundamentally distinct sorts of entities compose the universe, and metaphysics proper, which is concerned with describing the most general traits of reality. These general traits together define reality and would presumably characterize any universe whatever. Because these traits are not peculiar to this universe, but are common to all possible universes, metaphysics may be conducted at the highest level of abstraction. Ontology, by contrast, because it investigates the ultimate divisions within this universe, is more closely related to the physical world of human experience.The term metaphysics is believed to have originated in Rome about 70 bc, with the Greek Peripatetic philosopher Andronicus of Rhodes (flourished 1st century bc) in his edition of the works of Aristotle. In the arrangement of Aristotle's works by Andronicus, the treatise originally called First Philosophy, or Theology, followed the treatise Physics. Hence, the First Philosophy came to be known as meta (ta) physica, or “following (the) Physics,” later shortened to Metaphysics. The word took on the connotation, in popular usage, of matters transcending material reality. In the philosophic sense, however, particularly as opposed to the use of the word by occultists, metaphysics applies to all reality and is distinguished from other formsof inquiry by its generality.The subjects treated in Aristotle's Metaphysics (substance, causality, the nature of being, and the existence of God) fixed the content of metaphysical speculation for centuries. Among the medieval Scholastic philosophers, metaphysics was known as the “transphysical science” on the assumption that, by means of it, the scholar philosophically could make the transition from the physical world to a world beyond sense perception. The 13th-century Scholastic philosopher and theologian St. Thomas Aquinas declared that the cognition of God, through a causal study of finite sensible beings, was the aim of metaphysics. With the rise of scientific study in the 16th century the reconciliation of science and faith in God became an increasingly important problem.II Metaphysics Before Kant康德(德国哲学家, 1724-1805, 古典唯心主义的创始人)Before the time of the German philosopher Immanuel Kant metaphysics was characterized by a tendency to construct theories on the basis of a priori knowledge, that is, knowledge derived from reason alone, in contradistinction to a posteriori knowledge, which is gained by reference to the facts of experience. From a priori knowledge were deduced general propositions that were held to be true of all things. The method of inquiry based on a priori principles is known as rationalistic. This method may be subdivided into monism, which holds that the universe is made up of a single fundamental substance; dualism, the belief in two such substances; and pluralism,which proposes the existence of many fundamental substances.The monists, agreeing that only one basic substance exists, differ in their descriptions of its principal characteristics. Thus, in idealistic monism the substance is believed to be purely mental; in materialistic monism it is held to be purely physical, and in neutral monism it is considered neither exclusively mental nor solely physical. The idealistic position was held by the Irish philosopher George Berkeley, the materialistic by the English philosopher Thomas Hobbes, and the neutral by the Dutch philosopher Baruch Spinoza. The latter expounded a pantheistic view of reality in which the universe is identical with God and everything contains God's substance. See Idealism; Materialism; Pantheism.The most famous exponent of dualism was the French philosopher René Descartes, who maintained that body and mind are radically different entities and that they are the only fundamental substances in the universe. Dualism, however, does not show how these basic entities are connected.In the work of the German philosopher Gottfried Wilhelm Leibniz, the universe is held to consist of an infinite number of distinct substances, or monads. This view is pluralistic in the sense that it proposes the existence of many separate entities, and it is monistic in its assertion that each monad reflects within itself the entire universe.Other philosophers have held that knowledge of reality is not derived from a priori principles, but is obtained only from experience. This type of metaphysics is called empiricism. Still another school ofphilosophy has maintained that, although an ultimate reality does exist, it is altogether inaccessible to human knowledge, which is necessarily subjective because it is confined to states of mind. Knowledge is therefore not a representation of external reality, but merely a reflection of human perceptions. This view is known as skepticism or agnosticism in respect to the soul and the reality of God.III The Metaphysics of KantSeveral major viewpoints were combined in the work of Kant, who developed a distinctive critical philosophy called transcendentalism. His philosophy is agnostic in that it denies the possibility of a strict knowledge of ultimate reality; it is empirical in that it affirms that all knowledge arises from experience and is true of objects of actual and possible experience; and it is rationalistic in that it maintains the a priori character of the structural principles of this empirical knowledge.These principles are held to be necessary and universal in their application to experience, for in Kant's view the mind furnishes the archetypal forms and categories (space, time, causality, substance, and relation) to its sensations, and these categories are logically anterior to experience, although manifested only in experience. Their logical anteriority to experience makes these categories or structural principles transcendental; they transcend all experience, both actual and possible. Although these principles determine all experience, they do not in any way affect the nature of things in themselves. The knowledge of which these principles are the necessary conditions must not be considered, therefore, as constituting a revelation ofthings as they are in themselves. This knowledge concerns things only insofar as they appear to human perception or as they can be apprehended by the senses. The argument by which Kant sought to fix the limits of human knowledge within the framework of experience and to demonstrate the inability of the human mind to penetrate beyond experience strictly by knowledge to the realm of ultimate reality constitutes the critical feature of his philosophy, giving the key word to the titles of his three leading treatises, Critique of Pure Reason, Critique of Practical Reason, and Critique of Judgment. In the system propounded in these works, Kant sought also to reconcile science and religion in a world of two levels, comprising noumena, objects conceived by reason although not perceived by the senses, and phenomena, things as they appear to the senses and are accessible to material study. He maintained that, because God, freedom, and human immortality are noumenal realities, these concepts are understood through moral faith rather than through scientific knowledge. With the continuous development of science, the expansion of metaphysics to include scientific knowledge and methods became one of the major objectives of metaphysicians.IV Metaphysics Since KantSome of Kant's most distinguished followers, notably Johann Gottlieb Fichte, Friedrich Schelling, Georg Wilhelm Friedrich Hegel, and Friedrich Schleiermacher, negated Kant's criticism in their elaborations of his transcendental metaphysics by denying the Kantian conception of the thing-in-itself. They thus developed anabsolute idealism in opposition to Kant's critical transcendentalism.Since the formation of the hypothesis of absolute idealism, the development of metaphysics has resulted in as many types of metaphysical theory as existed in pre-Kantian philosophy, despite Kant's contention that he had fixed definitely the limits of philosophical speculation. Notable among these later metaphysical theories are radical empiricism, or pragmatism, a native American form of metaphysics expounded by Charles Sanders Peirce, developed by William James, and adapted as instrumentalism by John Dewey; voluntarism, the foremost exponents of which are the German philosopher Arthur Schopenhauer and the American philosopher Josiah Royce; phenomenalism, as it is exemplified in the writings of the French philosopher Auguste Comte and the British philosopher Herbert Spencer; emergent evolution, or creative evolution, originated by the French philosopher Henri Bergson; and the philosophy of the organism, elaborated by the British mathematician and philosopher Alfred North Whitehead. The salient doctrines of pragmatism are that the chief function of thought is to guide action, that the meaning of concepts is to be sought in their practical applications, and that truth should be tested by the practical effects of belief; according to instrumentalism, ideas are instruments of action, and their truth is determined by their role in human experience. In the theory of voluntarism the will is postulated as the supreme manifestation of reality. The exponents of phenomenalism, who are sometimes called positivists, contend that everything can be analyzed in terms of actualor possible occurrences, or phenomena, and that anything that cannot be analyzed in this manner cannot be understood. In emergent or creative evolution, the evolutionary process is characterized as spontaneous and unpredictable rather than mechanistically determined. The philosophy of the organism combines an evolutionary stress on constant process with a metaphysical theory of God, the eternal objects, and creativity.V Contemporary DevelopmentsIn the 20th century the validity of metaphysical thinking has been disputed by the logical positivists (see Analytic and Linguistic Philosophy; Positivism) and by the so-called dialectical materialism of the Marxists. The basic principle maintained by the logical positivists is the verifiability theory of meaning. According to this theory a sentence has factual meaning only if it meets the test of observation. Logical positivists argue that metaphysical expressions such as “Nothing exists except material particles” and “Everything is part of one all-encompassing spirit” cannot be tested empirically. Therefore, according to the verifiability theory of meaning, these expressions have no factual cognitive meaning, although they can have an emotive meaning relevant to human hopes and feelings.The dialectical materialists assert that the mind is conditioned by and reflects material reality. Therefore, speculations that conceive of constructs of the mind as having any other than material reality are themselves unreal and can result only in delusion. To these assertions metaphysicians reply by denying the adequacy of the verifiabilitytheory of meaning and of material perception as the standard of reality.Both logical positivism and dialectical materialism, they argue, conceal metaphysical assumptions, for example, that everything is observable or at least connected with something observable and that the mind has no distinctive life of its own. In the philosophical movement known as existentialism, thinkers have contended that the questions of the nature of being and of the individual's relationship to it are extremely important and meaningful in terms of human life. The investigation of these questions is therefore considered valid whether or not its results can be verified objectively.Since the 1950s the problems of systematic analytical metaphysics have been studied in Britain by Stuart Newton Hampshire and Peter Frederick Strawson, the former concerned, in the manner of Spinoza, with the relationship between thought and action, and the latter, in the manner of Kant, with describing the major categories of experience as they are embedded in language. In the U.S. metaphysics has been pursued much in the spirit of positivism by Wilfred Stalker Sellars and Willard Van Orman Quine. Sellars has sought to express metaphysical questions in linguistic terms, and Quine has attempted to determine whether the structure of language commits the philosopher to asserting the existence of any entities whatever and, if so, what kind. In these new formulations the issues of metaphysics and ontology remain vital.。
HETEROGENEOUS COMPUTINGShoukat Ali, Tracy D. Braun, Howard Jay Siegel, and Anthony A. MaciejewskiSchool of Electrical and Computer Engineering, Purdue UniversityHeterogeneous computing is a set of techniques enabling the use of diverse computational capabilities for the execution of a meta-task [2, 4, 7]. A meta-task is an arbitrary collection of independent (non-communicating) tasks with a variety of computational needs, which are to be executed during a given interval of time (e.g., a day). Some tasks may be decomposable into one or more communicating subtasks (subtasks may, in turn, have diverse computational needs). There are many types of heterogeneous computing systems [2]. This article focuses on mixed-machine systems, where a heterogeneous suite of independent machines is interconnected by high-speed links to function as a meta-computer (see Meta-Computer) or as part of a computational grid(see Computational Grid) [3]. The user of a heterogeneous suite has the illusion of working on a single virtual machine.Research in the field of heterogeneous computing is motivated by the fact that high performance machines vary in capability and, hence, suitability for different types of tasks and subtasks. Examples of such machine architectures include large distributed shared memory machines (e.g., an SGI 2800), distributed memory multiprocessors (e.g., an IBM SP2), and small shared memory machines (e.g., a Sun Enterprise 3000 Server). Furthermore, two implementations of a given machine type may vary in CPU speed, cache memory size and structure, I/O bandwidth, etc. With the recent advances in high-speed digital communications, it has become possible to use collections of different machines in concert to execute large meta-tasks whose tasks and subtasks have diverse computational needs.The goal of heterogeneous computing is to assign these tasks and subtasks to machines and schedule their execution to optimize some performance measure. This measure may be as simple as the execution time of the meta-task. The measure may be more complex and be a mathematical function of various factors such as the weighted priorities of tasks, deadlines for task execution, security requirements, and quality of service (QoS) needs (see QoS). The process of assigning (matching) tasks/subtasks to machines and scheduling their execution is called mapping.A hypothetical example task with four subtasks that are best suited for different machine architectures is shown in Figure 1. The example task executes for 100 time units on a typical workstation. The task consists of four subtasks: the first (S1) is best suited to execute on a large cluster of PCs (e.g., a Beowulf Cluster), the second (S2) is best suited to execute on a distributed memory multiprocessor, the third (S3) is best suited to execute on a distributed shared memory machine, and the fourth (S4) is best suited to execute on a small shared memory machine.Executing the whole task on a large cluster may improve the execution time of the first subtask from 25 to 0.3 time units, and those of the other subtasks to varying extents. The overall execution time improvement may only be about a factor of five because other subtasks are not well suited for execution on a cluster (e.g., due to the need for inter-processor communication). However, using four different machines that match the computational requirements for each of the individual subtasks can result in an overall execution time that is better than the execution time on the workstation by a factor of over 50. For communicating subtasks, inter-machine data transfers need to be performed when multiple machines are used. Hence, data transfer overhead has to be considered as part of the overall execution time on the heterogeneous computing suite whereas there is no such overhead when the entire task is executed on a single workstation.This is a simplified example. Actual tasks may consist of a large number of subtasks with a much more complex inter-subtask communications structure. Also, the sharing of the machines by all the tasks in the meta-task must be considered when mapping.MappingFinding a mapping for tasks that optimizes some performance measure is, in general, an NP-complete problem. For example, consider mapping 30 tasks onto five machines. This means that there are 530 possible mappings. Even if it took only one nanosecond to evaluate each mapping, an exhaustive search to find the best mapping would require 530 nanoseconds > 1000 years! Therefore, it is necessary to have heuristics to find near-optimal mappings without using an exhaustive search. Factors that impact mapping decisions include: (1) match of the task computational requirements to the machine capabilities, (2) overhead for the inter-machine communication of code and data (initial and generated), (3) expected machine load and network congestion, and (4) inter-subtask precedence constraints.There are many different types of heuristics for mapping tasks to the machines in a heterogeneous computing suite. In static mapping heuristics [1], the mapping decisions are made off-line before the execution of the meta-task. A staticmapping heuristic is employed if (1) the tasks that comprise the meta-task are known a priori , (2) predictions about the available heterogeneous computing resources are likely to be accurate, and (3) the estimated expected execution time of each task on each machine in the suite is known reasonably accurately. Static mapping heuristics can be used for planning the “next day’s work” on a heterogeneous computing system.Figure 1. Hypothetical example (based on [4]) of the advantage of using a heterogeneous computing suite of machines. The number underneath each bar indicates execution time. For the suite, each subtask execution time includes the overhead to receive data. Not drawn to scale.In dynamic mapping heuristics [6], the mapping decisions are made on-line during the execution of the meta-task. Dynamic approaches to mapping are needed if any of the following are unpredictable: (1) arrival times of the tasks, (2) machines available in the heterogeneous computing system (some machines in the suite may go off-line and new machines may come on-line), and (3) expected execution times of the tasks on the machines. While a static mapper considers the entire meta-task to be executed (e.g., the next day) when making decisions, a dynamic mapper has only information about tasks that have already arrived for execution. Furthermore, because a dynamic mapper operates on-line, it must make decisions much faster than an off-line static mapper. Consequently, dynamic mapping heuristics often use feedback from the heterogeneous computing system (while tasks are executing) to improve any “bad” mapping decisions.A semi-static mapping heuristic [8] can be used for an iterative task whose subtask execution times will change from iteration to iteration based on the input data. A semi-static methodology observes, from one iteration to another, the effects of the changing characteristics of the task's input data, called dynamic parameters, on the task's execution time. The off-line phase uses a static mapping algorithm to generate high quality mappings for a sampling of values for the dynamic parameters a priori. During the on-line phase, the actual dynamic parameters are observed and a new mapping for the subtasks may be selected from the precomputed off-line mappings. Automatic Heterogeneous ComputingOne of the long-term goals of heterogeneous computing research is to develop software environments that will automatically map and execute tasks expressed in a machine-independent high-level language. Such an environment will facilitate the use of heterogeneous computing suite by increasing portability, because the programmer need not be concerned with the composition of the heterogeneous computing suite, and increasing the possibility of deriving better mappings than the user can derive with ad hoc methods. Thus, it will improve the performance of and encourage the use of heterogeneous computing. While no such environment exists today, many researchers are working to develop one. A conceptual model for such an environment using a dedicated heterogeneous computing suite of machines is described in Figure 2, and consists of four stages.Stage 1 uses information about the type of tasks in the meta-task and machines in the heterogeneous computing suite to generate a set of parameters relevant to both the computational characteristics of tasks and the architectural features of machines. The system then derives categories for computational requirements and categories for machine capabilities from this set of parameters.Stage 2 consists of two components: task profiling and analytical benchmarking. Task profiling (see Task Profiling) decomposes each task of the meta-task into subtasks, where each subtask is computationally homogeneous. The computational requirements of each subtask are quantified by profiling the code and data. Analytical benchmarkingexecution on a cluster(see Analytical Benchmarking) quantifies how effectively each available machine in the suite performs on each type of computational requirement.The information available from stage 2 is used by stage 3 to derive the estimated execution time of each subtask on each machine in the heterogeneous computing suite, along with the associated inter-machine communication overheads. These statically derived results are then incorporated with initial values for machine ready times, inter-machine network delays, and status parameters (e.g., machine/network faults) to perform the mapping of subtasks to machines based on a given performance metric. The result is an assignment of subtasks to machines and an execution schedule. The process as described corresponds to a static mapping.The subtasks are executed in stage 4. If dynamic mapping is employed, the subtask completion times and loading/status of the machines/network are monitored (shown in dashed lines in Figure 2). The monitoring process is necessary because the actual computation times and data transfer times may be input-data dependent and deviate considerably from the static estimates. This information may be used to re-invoke the mapping of stage 3 to improve the machine assignment and execution schedule.Figure 2. Model for integrating the software support needed for automating the use of heterogeneous computing systems (based on [7]). Ovals indicate information and rectangles indicate action.1 2 3 4Environments and ApplicationsExamples of heterogeneous computing environments are: (1) the Purdue University Network Computing Hubs, a wide area network computing system which can be used to run a selection of software tools via a World Wide Web browser [5]; (2) NetSolve, a client-server system with geographically distributed servers that can be accessed from a variety of interfaces, including MATLAB, shell scripts, C, and FORTRAN [3]; and (3) the Globus meta-computing infrastructure toolkit, a set of low-level mechanisms that can be built upon to develop higher level heterogeneous computing services [3].Example applications that have demonstrated the usefulness of heterogeneous computing include: (1) a three-dimensional simulation of mixing and turbulent convection at the Minnesota Supercomputer Center [7]; (2) the shipboard anti-air warfare program (HiPer-D) used at the Naval Surface Warfare Center for threat detection, target engagement, and missile guidance; and (3) a simulation of colliding galaxies performed by solving large n-body dynamics problems and large gas dynamics problems at the National Center for Supercomputing Applications [7]. Open Problems in Heterogeneous ComputingHeterogeneous computing is a relatively new research area for the computer field. Interest in such systems continues to grow both in the research community and in the user community. The realization of the automatic heterogeneous computing environment envisioned in Figure 2 requires further research in many areas. Machine-independent languages with user-specified directives are needed to (1) allow compilation of a given task into efficient code for any machine in the suite, (2) aid in decomposing tasks into subtasks, and (3) facilitate determination of subtask computational requirements. Moreover, methods must be refined for measuring the loading and status of the machines in the heterogeneous computing suite and the network, and for estimating the subtask completion times. Also, the uncertainty present in the estimated parameter values, such as subtask completion times, should be taken into consideration in determining the mappings. Other research areas are (1) developing communication protocols for reliable, low overhead data transmission over heterogeneous networks with given QoS requirements, (2) devising debugging tools that can be used transparently across the suite of machines, and (3) formulating algorithms for task migration between heterogeneous machines, using task migration for fault tolerance or load re-balancing. Acknowledgment: This work was supported by the DARPA/ITO Quorum Program through the Office of Naval Research under Grant No. N00014-00-1-0599.References[1] T. D. Braun, H. J. Siegel, N. Beck, L. L. Boloni, M. Maheswaran, A. I. Reuther, J. P. Robertson, M. D. Theys, B. Yao, D. Hensgen, and R. F. Freund, A Comparison of Eleven Static Heuristics for Mapping a Class of Independent Tasks onto Heterogeneous Distributed Computing Systems, Journal of Parallel and Distributed Computing, 61(6), 810-837, 2001.[2] M. M. Eshaghian (ed.), Heterogeneous Computing, Artech House, Norwood, MA, 1996.[3] I. Foster and C. Kesselman (eds.), The Grid: Blueprint for a New Computing Infrastructure, Morgan Kaufmann, San Francisco, CA, 1999.[4] R. F. Freund and H. J. Siegel (guest eds.), Special Issue on Heterogeneous Processing, IEEE Computer, 26(6), 1993.[5] N. H. Kapadia and J. A. B. Fortes, PUNCH: An Architecture for Web-Enabled Wide-Area Network-Computing, Cluster Computing: The Journal of Networks, Software Tools and Applications, Special Issue on High Performance Distributed Computing, 2(2), 153-164, 1999.[6] M. Maheswaran, S. Ali, H. J. Siegel, D. Hensgen, and R. F. Freund, Dynamic Mapping of a Class of Independent Tasks onto Heterogeneous Computing Systems, Journal of Parallel and Distributed Computing, Special Issue on Software Support for Distributed Computing, 59(2), 107-131, 1999.[7] M. Maheswaran, T. D. Braun, and H. J. Siegel, “Heterogeneous Distributed Computing,” in Encyclopedia of Electrical and Electronics Engineering, Vol. 8, J. G. Webster, ed., John Wiley, New York, NY, 1999, pp. 679-690. [8] M. D. Theys, T. D. Braun, Y.-K. Kwok, H. J. Siegel, and A. A. Maciejewski, “Mapping of Tasks onto Distributed Heterogeneous Computing Systems Using a Genetic Algorithm Approach,” in Solutions to Parallel and Distributed Computing Problems: Lessons from Biological Sciences, A. Y. Zomaya, ed., John Wiley & Sons, New York, NY, 2001, pp. 135-178.Cross Reference:Analytical Benchmarking see Heterogeneous Computing.Computational Grid see Heterogeneous Computing.Meta-Computer see Heterogeneous Computing.Meta-Task see Heterogeneous Computing.Task Profiling see Heterogeneous Computing.Dictionary Terms:Analytical BenchmarkingAnalytical benchmarking of a given computing machine provides a measure of performance of the machine on each of the different code types that may be present in a given source program. The performance of a particular code type on a specific kind of resource is a multi-variable function. Some of the variables of such a function may be: the quality of service requirements of the application program (e.g., data precision), the size of the data set to be processed, the algorithm to be applied, programmer and compiler efforts to optimize the program, and the operating system and architecture of the machine that will execute the specific code type. (See Heterogeneous Computing.) Computational GridA developing area of research and technology seeking to connect regional and national computational resources in a transparent fashion, thus transforming any computer connected to the grid into part of a new class of supercomputer. The implied analogy is with an electric power grid. If access to advanced computational capabilities and accessories became as ubiquitous and dependable as an electric power grid, the impact on society would be dramatic. (See Heterogeneous Computing.)Meta-ComputerA system framework that utilizes the resources of many different computers connected via a network to cooperate on solving a problem. In general, this allows the problem to be solved much more quickly than would be possible using a single computer. Meta-computers usually consist of heterogeneous, distributed elements, and operate in a coarse-grained fashion. A meta-computer would be a more localized component of a larger computational grid. (See Heterogeneous Computing.)QoSQoS (Quality of Service) is an aggregate function of many different system characteristics used to represent the overall performance of a system. The components in the function, and the computation of the function itself, vary widely (i.e., QoS means many different things to many different people). Sample components of a QoS measure could include task deadlines, data precision, image color range, video jitter, network bandwidth, bit error rate, and end-to-end latency. (See Heterogeneous Computing.)Task ProfilingTask profiling of a given source program specifies types of computations that are present in the source program by decomposing it into code blocks based on computational requirements of the blocks. The set of computation types defined depends on the architectural features of the machines available for executing the source program or its subprograms, and on both the application task code and the types and sizes of data sets it is to process. (See Heterogeneous Computing.)。
M e t a分析的思想及步骤Meta分析的前身源于Fisher1920年“合并P值”的思想,1955年由Beecher首次提出初步的概念,1976年心理学家Glass进一步按照其思想发展为“合并统计量”,称之为Meta分析;1979年英国临床流行病学家ArchieCochrane提出系统评价systematicreview,SR的概念,并发表了激素治疗早产孕妇降低新生儿死亡率随机对照试验的系统评价,对循证医学的发展起了举足轻重的作用;Meta分析国内翻译为“荟萃分析”,定义是“Thestatisticalanalysisoflargecollectionofanalysisresultsfromindividual studiesforthepurposeofintegratingthefindings.”亦即“对具备特定条件的、同课题的诸多研究结果进行综合的一类统计方法;”Meta从字源来说据考证有“Metalogic:abranchofanalyticphilosophythatdealswiththecriticalexaminationofthebasic conceptsoflogic”;“Metamathematics:thephilosophyofmathematics,especially,thelogicalsyntaxofmathematics.”其中最简洁并且一语中的的是Metascience::atheoryorscienceofscience,atheoryconcernedwiththeinvestigationanalysisor descriptionoftheoryitself.”意为一种科学中的科学或理论,一种对原理本身进行调查、分析和描述的原理;Meta分析有广义和狭义两种概念:前者指的是一个科学的临床研究活动,指全面收集所有相关研究并逐个进行严格评价和分析,再用定量合成的方法对资料进行统计学处理得出综合结论的整个过程;后者仅仅是一种单纯的定量合成的统计学方法;目前国内外文献中以广义的概念应用更为普遍,系统评价常和Meta分析交叉使用,当系统评价采用了定量合成的方法对资料进行统计学处理时即称为Meta-分;因此,系统评价可以采用Meta-分析quantitativesystematicreview 定量系统评价,也可以不采用Meta-分析non-quantitativesystematicreview,定性系统评价;参照Cochrane协作网系统评价工作手册CochraneReviewers’Handbook制定的统一标准; Meta分析的基本步骤如下:1明确简洁地提出需要解决的问题;2制定检索策略,全面广泛地收集随机对照试验;3确定纳入和排除标准,剔除不符合要求的文献;4资料选择和提取;5各试验的质量评估和特征描述;6统计学处理;a.异质性检验齐性检验;b.统计合并效应量加权合并,计算效应尺度及95%的置信区间并进行统计推断; c.图示单个试验的结果和合并后的结果;d.敏感性分析;e.通过“失安全数”的计算或采用“倒漏斗图”了解潜在的发表偏倚;7结果解释、作出结论及评价;8维护和更新资料;临床医生只需要知道Meta分析的基本思想,具体的统计学方法让统计学家研究,让统计学软件帮我们完成;ReviewManagerRevMan是Cochrane协作网提供给评价者准备和维护更新Cochrane系统评价而设计的软件,也可以说是专门为临床医生度身订做,用于完成Meta分析的软件,它不仅可以协助我们完成Meta分析的计算过程,还可以帮助我们了解Meta分析的架构并学习系统评价的分析方法,最后把完成的系统评价制作成易于通过电子转换的文件以标准统一的格式发送到Cochrane系统评价资料库TheCochraneDatabaseofSystematicReviews,CDSR,便于电子出版和日后更新;充分利用RevMan软件对初次从事系统评价的人员获得方法学上的指导有很大的裨益;系统评价有多种类型,如病因研究、诊断性试验的评价、预后及流行病学研究等;Cochrane系统评价目前主要限于随机对照试验;非随机对照试验的系统评价方法学还处于不太完善的阶段,需要进行更多的相关研究;诊断试验的Meta分析方法与一般的随机对照试验Meta分析不同,需要同时考虑敏感性与特异性,采用综合接受者工作特征summaryreceiveroperatingcharacteristiccurve,SROC的分析,但RevMan4.2未提供Meta分析的完整步骤,根据个人的体会,结合战友的经验总结而成,meta的精髓就是对文献的二次加工和定量合成,所以这个总结也算是对战友经验的meta分析吧;一、选题和立题一形成需要解决的临床问题:系统评价可以解决下列临床问题:1.病因学和危险因素研究;2.治疗手段的有效性研究;3.诊断方法评价;4.预后估计;5.病人费用和效益分析等;进行系统评价的最初阶段就应对要解决的问题进行精确描述,包括人群类型疾病确切分型、分期、治疗手段或暴露因素的种类、预期结果等,合理选择进行评价的指标;二指标的选择直接影响文献检索的准确性和敏感性,关系到制定检索策略;三制定纳入排除标准;二、文献检索一检索策略的制定这是关键,要求查全和查准;推荐Mesh联合freeword检索;二文献检索,获取摘要和全文国内的有维普全文VIP,CNKI,万方数据库,外文的有medline,SD,OVID等;三文献管理强烈推荐使用endnote,procite,noteexpress等文献管理软件进行检索和管理文献;查找文献全文的途径:在这里,讲一下找文献的过程,以请后来的战友们参考不包括网上有电子全文的:1.查找免费全文:1在pubmedcenter中看有无免费全文;有的时候虽然没有显示freefulltext,但是点击进去看全文链接也有提供免费全文的;我就碰到几次;2在google中搜一下;少数情况下,NCBI没有提供全文的,google有可能会找到,使用“学术搜索”;本人虽然没能在google中找到一篇所需的文献,但发现了一篇非常重要的综述,里面包含了所有我需要的文献当然不是数据,但起码提供了一个信息,所需要的文献也就这么多了,因为老外的综述也只包含了这么多的内容;这样,到底找多少文献,找什么文献,心里就更有底了;3免费医学全文杂志网站;;提供很过超过收费期的免费全文;2.图书馆查馆藏目录:包括到本校的,当然方便,使用pubmed的linkout看文献收录的数据库,就知道本校的是否有全文;其它国内高校象复旦、北大、清华等医学院的全文数据库都很全,基本上都有权限;上海的就有华东地区联目、查国内各医学院校的图书馆联目;这里给出几个:1中国高等院校医药图书馆协会的地址:,进入左侧的“现刊联目”,可以看到有“现刊联目查询”和“过刊联目查询”,当然,查询结果不可全信,里面有许多错误;本人最难找的两篇文章全部给出了错误的信息后来电话联系证实的;2再给出两个比较好的图书馆索要文献的email地址有偿服务,但可以先提供文献,后汇钱,当然做为我们,一定要讲信誉吆;一是解放军医学图书馆信息部:,电话:;3二是复旦大学医科图书馆原上医:i,联系人,周月琴,王蔚之,郑荣,电话,,需下载文献传递申请表;其他的图书馆要么要求先交开户费,比如协和500元,要么嫌麻烦,虽然网上讲过可提供有偿服务,在这里我就不一一列出了;3.请DXY战友帮忙,在馆藏文献互助站中发帖,注意格式正确,最好提供linkout的多个数据库的全文链接,此时为帮助的人着想,就是帮助自己;自己也同时帮助别人查文献,一来互相帮助,我为人人,人人为我;二则通过帮助别人可以积分,同时学会如何发帖和下载全文,我就感觉通过帮助别人收获很大,自己积分越高,获助的速度和机会也就相应增加;现在不少免费的网络空间我常用爱存,比发邮件简便很多;所以如果你求助以后,要及时去“我的论坛”中查看帖子,有的很快就把下载链接发过来了,不要一味只看邮箱;4.实在不行,给作者发email;这里给出一个查作者email的方法,先在NCBI中查出原文献作者的所有文章,注意不要只限于第一作者,display,abstract,并尽可能显示多的篇数,100,200,500;然后在网页内查找“”,一般在前的字母会与人名有些地方相似;再根据地址来确定是否是同一作者;5.查找杂志的网址,给主编发信求取全文;这里我就不讲查找的方法了,DXY中有许多帖子;我的一篇全文就是这样得到的;6.向国外大学里的朋友求助;国外大学的图书馆一般会通过馆际互借来查找非馆藏文献,且获得率非常高;我的三篇文献是通过这一途径得到的;如果还是找不到,那就……我也没辙了,还有朋友如有其他的方法,不妨来这里交流;难度不小吧,比起做实验来如何三、对文献的质量评价和数据收集一研究的质量评价对某一试验研究的质量评价主要是评价试验结果是否有效,结果是什么该结果是否适用于当地人群;下面一系列问题可以帮助研究者进行系统的质量评价:①该研究的试验设计是否明确,包括研究人群、治疗手段和结果判定方法;②试验对象是否随机分组;③病人的随访率是否理想及每组病人是否经过统计分析;④受试对象、研究人员及其它研究参与者是否在研究过程中实行“盲法”;⑤各组病人的年龄、性别、职业等是否相似;⑥除进行研究的治疗手段不同外,其它的治疗是否一致;⑦治疗作用大小;⑧治疗效果的评价是否准确;⑨试验结果是否适用于当地的人群,种族差异是否影响试验结果;⑩是否描述了所有重要的治疗结果;治疗取得的效益是否超过了治疗的危险性和费用;系统评价者应根据上述标准进行判断,不满足标准的文献应剔除或区别对待数据合并方法不同,以保证系统评价的有效性;二、数据收集研究者应设计一个适合本研究的数据收集表格;许多电子表格制作软件如Excel、Access,和数据库系统软件如FoxPro等,可以用于表格的制作;表格中应包括分组情况、每组样本数和研究效应的测量指标;根据研究目的不同,测量指标可以是率差、比数odds、相对危险度relativerisk,包括RR和OR;各研究间作用测量指标不一致,需转化为统一指标;常用的统一指标是作用大小EffectSize,ES,ES是两比较组间作用差值除以对照组或合并组的标准差;ES无单位是其优点;三、数据分析系统评价过程中,对上述数据进行定量统计合并的流行病学方法称为Meta分析Metaanalysis;Meta意思是morecomprehensive,即更加全面综合;通过Meta分析可以达到以下目的:1.提高统计检验效能;2.评价结果一致性,解决单个研究间的矛盾;3.改进对作用效应的估计;4.解决以往单个研究未明确的新问题;统计分析的指标一、异质性检验1.检验原理:meta分析的原理首先是假定各个不同研究都是来自非同一个总体H0:各个不同样本来自不同总体,存在异质性,备择假设H1,如果p>0.1,拒绝H0,接受H1,,即来自同一总体这样就要求不同研究间的统计量应该接近总体参数真实值,所以各个不同文献研究结果是比较接近,就是要符合同质性,这时候将所有文献的效应值合并可以采用固定效应模型的有些算法,如倒方差法,mantelhaenszel法,peto法等.2.分类:异质性检验,包括三个方面:临床异质性,统计学异质性和方法学异质性,作meta分析首先应当保证临床同质性,比如研究的设计类型、实验目的、干预措施等相同,否则就要进入亚组分析,或者取消合并,在满足临床同质性的前提下非常重要,不能一味追求统计学同质性,首先考虑专业和临床同质性,我们进一步观测统计学同质性;临床异质性较大时不能行meta分析,随机效应模型也不行.只能行描述性系统综述systemicreviews,SR或分成亚组消除临床异质性.解决临床异质后再考虑统计学异质性的问题.如果各个文献研究间结果不存在异质性p>0.1,选用固定效应模型fixedmodel,这时其实选用随即效应模型的结果与固定效应模型相同;如果不符合同质性要求,即异质性检验有显着性意义p<0.1,这时候固定效应模型的算法来合并效应值就是有偏倚,合并效应值会偏离真实值.所以,异质性存在时候要求采用随机模型,主要是矫正合并效应值的算法,使得结果更加接近无偏估计,即结果更为准确.此外,这里要说明的是,采用的模型不同,和合并效应值的方法不同,都会导致异质性检验P值存在变动,这个可以从算法原理上证明,不过P值变动不会很大,一般在小数点后第三位的改变.异质性检验的Q值在固定模型中采用倒方差法和Mantel-haenszel法中也会不同;随机效应模型是不需要假定各个研究来自同一个总体为前提,本来就是对总体参数的近似无偏估计,这个与固定模型不一样必须要同质为基础,所以随机模型来作异质性检验简直是“画蛇添足”,无奈之举因此,随机模型异质性检验是否有统计学意义都是可以用,而固定模型必须要求无异质性;可以证明和实践,如果无异质性存在的时候,随机模型退化为固定,即固定模型的结果于随机模型的合并效应值是相等的具体见下图:目前,国内外对meta分析存在异质性,尤其是异质性检验P值很小的时候具体范围我不清楚,是0.05~0.1吗请版主补充,学术界有着不同的争论,很多人认为这个时候做meta分析是没有意义,相当于合并了一些来自不同总体的统计结果,也有人认为,这些异质性的存在可能是由于文献发表的时间,研究的分组,研究对象的特征等因素引起,只要采用亚组分析或meta回归分析可以将异质性进行控制或解释,还是可以进行meta分析,至少运用随机效应模型可以相对无偏的估计总体.这里要强调的是,异质性检验P值较小时候,最好能对异质性来源进行分析和说明;合理进行解释,同时进行亚组分析,相当于分层分析,消除混杂因素造成的偏倚bias;3.衡量异质性的指标一个有用的定量衡量异质性的指标是I2,I2=Q–df/Qx100%,此处的Q是卡方检验的统计值,df是其自由度Higgins2003,Higgins2002;这个I2值代表了由于异质性而不是抽样误差机会导致的效应占总效应估计值的百分率;I2值大于50%时,可以认为有明显的异质性;参考二、敏感性分析:1.敏感性分析的含义:改变纳入标准特别是尚有争议的研究、排除低质量的研究、采用不同统计方法/模型分析同一资料等,观察合并指标如OR,RR的变化,如果排除某篇文献对合并RR有明显影响,即认为该文献对合并RR敏感,反之则不敏感,如果文献之间来自同一总体,即不存在异质性,那么文献的敏感性就低,因而敏感性是衡量文献质量纳入和排除文献的证据和异质性的重要指标;敏感性分析主要针对研究特征或类型如方法学质量,通过排除某些低质量的研究、或非盲法研究探讨对总效应的影响;王吉耀第二版P76中“排除某些低质量的研究,再评价,然后前后对比,探讨剔除的试验与该类研究特征或类型对总效应的影响”;王家良第一版八年制P66、154敏感性分析是从文献的质量上来归类,亚组分析主要从文献里分组病例特征分类;敏感性分析是排除低质量研究后的meta分析,或者纳入排除研究后的meta分析;亚组分析是根据纳入研究的病人特点适当的进行分层,过多的分层和过少的分层都是不好的;例如在排除某个低质量研究后,重新估计合并效应量,并与未排除前的Meta分析结果进行比较,探讨该研究对合并效应量影响程度及结果稳健性;若排除后结果未发生大的变化,说明敏感性低,结果较为稳健可信;相反,若排除后得到差别较大甚至截然相反结论,说明敏感性较高,结果的稳健性较低,在解释结果和下结论的时候应非常慎重,提示存在与干预措施效果相关的、重要的、潜在的偏倚因素,需进一步明确争议的来源;2.衡量方法和措施其实常用的就是选择不同的统计模型或进行亚组分析,并探讨可能的偏倚来源,慎重下结论;亚组分析通常是指针对研究对象的某一特征如性别、年龄或疾病的亚型等进行的分析,以探讨这些因素对总效应的影响及影响程度;而敏感性分析主要针对研究特征或类型如方法学质量,通过排除某些低质量的研究、或非盲法的研究以探讨对总效应的影响;建议可以看参考王吉耀主编,科学出版社出版的循证医学与临床实践;敏感性分析只有纳入可能低质量文献时才作,请先保证纳入文献的质量纳入文献的质量评价方法,如果是RCT,可选用JADAD评分;如果病因学研究,我认为使用敏感性分析是评价文献质量前提是符合纳入标准的较为可行的方法;敏感性分析是分析异质性的一种间接方法;有些系统评价在进行异质性检验时发现没有异质性,这时还需不需要作敏感性分析我的看法是需要,因为我觉得异质性也是可以互相抵消的,有时候作出来没有异质性,但经过敏感性分析之后,结果就会有变化;三对入选文献进行偏倚估计发表偏倚publicationbias评估包括作漏斗图,和对漏斗图的对称性作检验;可以用stata软件进行egger检验;人是活的,软件是死的,临床是相对的,统计学是绝对的;四、总结:一结果的解释Meta-分析结果除要考虑是否有统计学意义外,还应结合专业知识判断结果有无临床意义;若结果仅有统计学意义,但合并效应量小于最小的有临床意义的差值时,结果不可取;若合并效应量有临床意义,但无统计学意义时,不能定论,需进一步收集资料;不能推荐没有Meta-分析证据支持的建议;在无肯定性结论时,应注意区别两种情况,是证据不充分而不能定论,还是有证据表明确实无效;二结果的推论Meta-分析的结果的外部真实性如何在推广应用时,应结合该Meta-分析的文献纳入/排除标准,考虑其样本的代表性如何,特别应注意研究对象特征及生物学或文化变异、研究场所、干预措施及研究对象的依从性、有无辅助治疗等方面是否与自己的具体条件一致;理想的Meta-分析应纳入当前所有相关的、高质量的同质研究,无发表性偏倚,并采用合适的模型和正确统计方法;三系统评价的完善与应用系统评价完成后,还需要在实际工作中不断完善,包括:①接受临床实践的检验和临床医师的评价;②接受成本效益评价;③关注新出现的临床研究,要及时对系统评价进行重新评价;临床医师只有掌握了系统评价的方法,才能为本专业的各种临床问题提供证据,循证医学才能够顺利发展;。
Unit 5Section ASoftware Design (软件设计)Design is defined in [IEEE610.12-90] as both “the process of defining the architecture,components, interfaces, and other characteristics of a system or component ” and “the result of that process.” Viewed as a process, software design is the software engineering life cycle activity in which software requirements are analyzed in order to produce a description of the software ’s internal structure that will serve as the basis for itsconstruction. More precisely, a software design (the result) must describe the software architecture -- that is how software is decomposed and organized into components -- and the interfaces between those components. It must also describe the components at a level of detail that enable their construction. Software design plays an important role indeveloping software: it allows software engineers to produce various models that form a kind of blueprint of the solution to be implemented. We can analyze and evaluate these models to determine whether or not they will allow us to fulfill the variousrequirements. We can also examine and evaluate various alternative solutions and trade-offs . Finally, we can use the resulting models to plan thesubsequent development activities, in addition to using them as input and the starting point of construction and testing.In a standard listing of software life cycleprocessed such as IEEE/EIA 12207 Software Life Cycle Processes [IEEE 12207.0-96], software design consists of two activities that fit between software requirements analysis and software construction:Software architectural design (sometimes called top level design): describing software ’s top-level structure and organization and identifying the various components.Software detailed design: describing eachcomponent sufficiently to allow for its construction.General StrategiesSoftware often-cited examples of general strategies useful in the design process aredivide-and-conquer and stepwise refinement,top-down vs. bottom-up strategies, data abstraction and information hiding, use of heuristics, use of patterns and pattern languages, use of an iterative and incremental approach.Function-Oriented (Structured) DesignThis is one of the classical methods of software design, where decomposition centers on identifying the major software functions and then elaborating and refining them in a top-down manner. Structured design is generally used after structured analysis, thus producing, among other things, data flow diagrams and associated process descriptions. Researchers have proposed various strategies (for example, transformation analysis, transaction analysis) and heuristics (for example, fan-in/fan-out, scope of effect vs. scope of control) to transform a DFD into a software architecture generally represented as a structure chart.Object-Oriented DesignNumerous software design methods based on objects have been proposed. The field has evolved from the early object-based design of the mid-1980s (noun=object; verb=method; adjective=attribute) through OO design, where inheritance and polymorphism play a key role, to the field of component-based design, where meta-information can be defined and accessed (through reflection, for example). Although OO design’s roots stem fromthe concept of data abstraction, responsibility-driven design has also been proposed as an alternative approach to OO design.Data-Structure-Centered DesignData-structure-centered design (for example, Jackson, Warnier-Orr) starts from the data structures a program manipulates rather than from the function it performs. The software engineer first describes the input and output data structures (using Jackson’s structure diagrams, for instance) andthen develops the program ’s control structure based on these data structure diagrams. Various heuristics have been proposed to deal with special cases -- for example, when there is a mismatch between the input and output structures.Component-Based Design (CBD)A software component is an independent unit, having well-defined interfaces and dependencies that can be composed and deployed independently, Component-based design addresses issues related to providing, developing, and integrating such components in order to improve reuse .Other MethodsOther interesting but less mainstreamapproaches also exist: formal and rigorous methodand transformational methods.。
2023年度军队文职人员公开招录《英语语言文学》高频考题汇编(含答案) 学校:________ 班级:________ 姓名:________ 考号:________一、单选题(55题)1.The computer center,( )last year,is very popular among the students in this school.A.openB.openingC.having openedD.opened2.( ),he does get annoyed with her sometimes.A.Although much he likes herB.Much although he likes herC.As he likes her muchD.Much as he likes her3.I just wonder( )that makes him so excited.A.why it doesB.what he doesC.how it isD.what it is4.Australia has several different climatic regions,from warm to( )and tropical.A.temperateB.subtropicalC.humidD.continental5.The fifth-generation computers,with artificial intelligence,( )and perfected now.A.developedB.have developedC.are being developedD.will have been developed6.Which kind of animal is not the executive of Australia?( )A.EmuB.KiwiC.Duck-billed platypusD.Kangaroo7.The criterion used in IC analysis is ( )A.transformationB.conjoiningC.groupingD.substitutability8.John is reading an interesting book on evolution theory which was written by Charles Darwin,who was a British naturalist who developed a theory of evolution based on natural selection.What design feature of language is reflected in the example?( )A.CreativityB.ArbitrarinessC.DisplacementD.Duality9.Her mother is one of the representatives of( )feminism.A.vitalB.fundamentalC.radicalD.basic10.According to the maxim of ( ) suggested by Grice,one should speak truthfully.A.qualityB.mannerC.relationD.quantity11.Which of the following statements about American education is wrong?( )A.Elementary and secondary education is free and compulsoryB.More public collges,universities than private onesC.Private school fnancially supported by religious,nonreligious and private organizations,individualsD.Credits taken at community colleges are normally applicable to requirement for a four-year bachelor’s degree12.The Anglo-Saxons brought( )religion to Britain.A.ChristianB.DruidC.Roman CatholicD.Teutonic13.The Hundred Year’s War lasted from 1337 to 1453 between Britain and( )A.the USB.FranceC.CanadaD.Australia14.In the Canadian parliamentary system,( )holds the highest position.A.free morphemeB.The PresidentC.The Governor GeneralD.The Prime Minister15.-It was an interesting exhibition,wasn′t it?-No,it was very uninteresting.Which maxim of the Politeness Principle that above example violates?( )A.The tact maximB.The modesty maximC.The agreement maximD.The sympathy maxim16.In which day is Halloween celebrated?( )A.5 NovemberB.31 OctoberC.17 MarchD.25 December17.The Cooperative Principle is proposed by ( ).A.SaussureB.GriceC.ChomskyD.Leech18.The captain and his crews depended on the( )of navigation- the compass for orientation.A.instrumentB.deviceC.applianceD.equipment19.The heart is( )intelligent than the stomach,for they are both controlled by the brain.A.not soB.not muchC.much moreD.no more20.I don’t think it advisable that Tim( )to the job since he has no experience.A.is assignedB.will be assignedC.be assignedD.has been assigned21.Agressive courage and determination,and( )spirit is inevitable for rapid social development.A.innovativeB.freshC.novelD.original22.“X buys something from Y” and“Y sells something to X” are in a relation of ( )A.hyponymyB.gradable antonymyplementary antonymyD.converse antonymy23.Neither of the young men who had applied for a position in the university _____.A.has been acceptedB.have been acceptedC.was acceptedD.were accepted24.( ) is regarded as the“father of American literature”A.James Fenimore CooperB.Ralph Waldo EmersonC.Thomas JeffersonD.Washington Irving25.The National Day of Canada is( )A.July 1stB.June 1stC.October 1stD.July 3rd26.Although the teacher has explained to us,the meaning of the article is still( )to me.A.faintB.obscureC.ambiguousD.vague27.The passengers in missing airplane were( )dead after several months of search.A.rectifiedB.testifiedC.certifiedD.verified28.Jane Austen wrote all the following novels EXCEPT ( )A.Sense and SensibilityB.FrankensteinC.Pride and PrejudiceD.Emma29.Year-end bonus will be( )according to individual contribution.A.detachedB.apportionedC.separatedD.allocated30.( ) is the first African-American winner of the Nobel Prize for Literature.A.Ralph EllisonB.Toni MorrisonC.Richard WrightD.James Baldwin31.In an effort to( )culture shocks,I think it is necessary to know something about the nature of culture.A.get offB.get byC.get throughD.get over32.The Great Charter was signed in( )and had( )clauses.A.1251,63B.1251,73C.1215,63D.1215,7333.The semantic components of the word“gentleman” can be expressed as ( )A.+animate,+male,+human,+adultB.+animate,-male,+human,+adultC.+animate,+male,-human,+adultD.+animate,+male,+human,-adult34.Of the following writers,( )is NOT a Nobel Prize Winner.A.Samuel BeckettB.James JoyceC.John GalsworthyD.William Butler Yeats35.The fans did not think( )of him because they know how poorly he was.A.highB.highlyC.badD.badly36.-Would you mind telling me your address?-Somewhere in the southern of Handan.Which maxim of the Cooperative Principle that above example violates?( )A.The maxim of qualityB.The maxim of relationC.The maxim of quantityD.The maxim of manner37.Lexical ambiguity arises from polysemy or ( ) which cannot be determined by the context.A.homonymyB.antonymyC.meronymyD.synonymy38.My son failed to come back last night.This morming the police came to our house and( )my worst fears that he was injured in a car accident.A.advocatedB.confirmedC.promisedD.insured39.The scents of the flowers were( )to us by the breeze.A.interceptedB.detestedC.saturatedD.wafted40.( ) is the defining properties of units like number,gender,case.A.Parts of speechB.Word classesC.Grammatical categoriesD.Functions of words41.( ) was honored as“the Father of English PoetryA.William LanglandB.Sir Thomas MarloryC.Geoffrey ChaucerD.Bede42.What is the construction of the sentence “The boy smiled”?( )A.ExocentricB.EndocentricC.CoordinateD.Subordinate43.The suspect made a pretty( )description of his process of committing a crime in his confession.A.dimB.faintC.obscureD.vague44.Of the fifty states,the smallest state in America is( )A.Rhode IslandB.VirginiaC.TexasD.Montana45.Typical of the grassland dwellers of the continent( ),or pronghorn.A.it is the American antelopeB.the American antelope isC.is the American antelopeD.the American antelope46.The( )nature of the plant is very different from others for its growth and distribution depend on its host completely.A.specificB.peculiarC.extraordinaryD.particular47.When did the Australian Constitution take effect?( )A.1 January,1900B.1 January,1901C.26 January,1801D.26 January,180048.What is the ranking of Canada in the world by land area?( )A.FirstB.SecondC.ThirdD.Fourth49.( ),domesticated grapes grow in clusters,range in color from pale green to black,and contain sugar in varying quantities.A.Their botanical classification as berriesB.Although their botanical classification as berriesC.Because berries being their botanical classificationD.Classified botanically as berries50.The bomb destroyed a police station and damaged a church( )A.badlyB.badC.worseD.mostly51.( ) is NOT included in the modernist groupA.Oscar WildeB.Virginia WoolfC.William Butler YeatsD.T.S.Eliot52.The old man has developed a( )headache which cannot be cured in a short time.A.perpetualB.permanentC.chronicD.sustained53.Bloomfield introduced the IC analysis,whose full name is ( ) Analysis.A.Internal ComponentB.Innate CapacityC.Internal ConstituentD.Immediate Constituents54.He copied other people’s ideas in writing his new book,which is a kind of copywrite( )A.offenceB.violationC.crimeD.sin55.Which of the following sounds does not belong to the allomorphs of the English plural morpheme?( )A.[s]B.[iz]C.[ai]D.[is]参考答案1.D2.D3.D4.B澳大利亚的气候,因其地域广阔,所以呈多样化。
第41卷第3期2024年3月控制理论与应用Control Theory&ApplicationsV ol.41No.3Mar.2024基于强化学习的多技能项目调度算法胡振涛1,崔南方1†,胡雪君2,雷晓琪1(1.华中科技大学管理学院,湖北武汉430074;2.湖南大学工商管理学院,湖南长沙410082)摘要:多技能项目调度存在组合爆炸的现象,其问题复杂度远超传统的单技能项目调度,启发式算法和元启发式算法在求解多技能项目调度问题时也各有缺陷.为此,根据项目调度的特点和强化学习的算法逻辑,本文设计了基于强化学习的多技能项目调度算法.首先,将多技能项目调度过程建模为符合马尔科夫性质的序贯决策过程,并依据决策过程设计了双智能体机制.而后,通过状态整合和行动分解,降低了价值函数的学习难度.最后,为进一步提高算法性能,针对资源的多技能特性,设计了技能归并法,显著降低了资源分配算法的时间复杂度.与启发式算法的对比实验显示,本文所设计的强化学习算法求解性能更高,与元启发式算法的对比实验表明,该算法稳定性更强,且求解速度更快.关键词:多技能资源;项目调度;智能算法;强化学习;并行调度引用格式:胡振涛,崔南方,胡雪君,等.基于强化学习的多技能项目调度算法.控制理论与应用,2024,41(3):502–511DOI:10.7641/CTA.2023.20566Reinforcement learning-based algorithm formulti-skill project scheduling problemHU Zhen-tao1,CUI Nan-fang1†,HU Xue-jun2,LEI Xiao-qi1(1.School of Management,Huazhong University of Science and Technology,Wuhan Hubei430074,China;2.Business School,Hunan University,Changsha Hunan410082,China)Abstract:Combinatorial explosion is a common phenomenon in multi-skill project scheduling,which leads to higher complexity in multi-skill project scheduling problem(MSPSP)than in traditional single-skill project scheduling problem. Heuristics and meta-heuristics have disadvantages in solving MSPSP.Therefore,based on the characteristics of project scheduling and the algorithmic logic of reinforcement learning,a multi-skilled project scheduling algorithm based on re-inforcement learning is designed in this paper.Firstly,the multi-skill project scheduling process is modeled as a Markov decision process(MDP).Then,a double-agent mechanism is proposed,and state integration method and action decom-position method are designed to reduce the complexity of value function learning.Finally,skills conflation algorithm is developed to reduce the time complexity of allocating resources in parative experiments between the proposed RL algorithm and heuristics show that the reinforcement learning(RL)has better performance,and experiments between the proposed RL algorithm and meta-heuristics show that the RL has higher stability and shorter running time.Key words:multi-skill resource;project scheduling;intelligence algorithm;reinforcement learning;PSGSCitation:HU Zhentao,CUI Nanfang,HU Xuejun,et al.Reinforcement learning-based algorithm for multi-skill project scheduling problem.Control Theory&Applications,2024,41(3):502–5111引言现代项目中存在着一类多技能资源,如R&D行业的多技能研发人员、工程项目中的多功能作业车等[1].这使得多技能项目调度问题(multi-skilled project sch-eduling problem,MSPSP)[2]成为近年来学者们关注的热点.在项目调度研究领域,资源的指派是最重要的研究内容之一,它不仅能影响项目的工期,还能影响调度计划的鲁棒性[3]、项目产品的质量[4]等.与传统的资源受限项目调度问题(resource constrained pro-ject scheduling problem,RCPSP)相比,MSPSP中资源的多技能特征增加了资源指派的难度,因为在多技能项目调度中,在为活动指派资源的同时,还要为资源收稿日期:2022−06−27;录用日期:2023−06−10.†通信作者.E-mail:***************;Tel.:+86150****7933.本文责任编委:周平.国家自然科学基金项目(71971094,71701067,72071075),湖南省自然科学基金项目(2019JJ50039)资助.Supported by the National Natural Science Foundation of China(71971094,71701067,72071075)and the Natural Science Foundation of Hunan Province(2019JJ50039).第3期胡振涛等:基于强化学习的多技能项目调度算法503指派技能,问题的维度增加,求解难度也更大.MSPSP属于NP难问题[5].作为组合优化问题, MSPSP中活动、技能和资源间可能出现组合爆炸.精确求解算法只能求解规模极小的算例[6].因此更多的研究集中于启发式和元启发式算法.如Almeida等[7–8]和胡振涛等[9]根据多技能资源的特征分别设计了基于静态资源权重和基于动态资源权重的启发式方法. Laszczyk等[10]、Javanmard等[11]和Tabrizi等[12]则设计了遗传算法予以求解,此外禁忌搜索[13]、蚁群算法[14]、差分进化算法[15]等也常被用于求解MSPSP.然而启发式算法往往需要根据项目特征设计规则或参数,导致算法迁移性较差.元启发式算法虽然通用性较强,但在求解大规模项目案例时常需要很长的时间才能求得满意解.此外,由于这些算法涉及的参数较多,加之项目调度问题自身的复杂性,算法的设计和使用常需要较深的专业知识辅助[16].机器学习作为近些年的热点研究对象,被广泛应用于计算机视觉、自然语言处理等领域.强化学习作为机器学习的方法论之一,具有参数少、迁移性强等优点,且在求解组合优化问题方面也有了显著的成果,如围棋游戏问题[17]、车间调度问题[18]、旅行商问题[19]等.而项目调度过程很容易建模为马尔科夫决策过程,这为应用强化学习算法提供了条件.此外,项目调度模型往往是明确的,如工序约束、资源约束和时间约束等,这为强化学习的采样提供了便利.如Sal-lam等[20]针对单技能项目调度问题,考虑了差分进化和布谷鸟算法,并以强化学习作为算法优选技术,在进化过程中从两个算法中选择其一;Sung等[21]针对存在活动反复的单技能项目中的资源分配问题,设计了强化学习算法.此外,Gai等[22]和Mao等[23]也将强化学习算法应用于求解项目调度中的资源分配问题.从现有文献看,项目调度问题应用强化学习的研究主要集中在近几年,且研究成果不多,尤其是针对多技能项目调度问题,尚未发现有深入的研究.基于此,以下第2部分构建了多技能项目调度问题的数学模型;第3部分在介绍强化学习算法和项目调度问题的基础上,针对工期最短的MSPSP设计了基于强化学习的求解算法;第4部分为数值实验及结果分析;第5部分总结了研究内容并提出了下一步的研究方向.2问题建模项目网络采用节点式(AON)表示,共包含n个活动节点,其中起始节点1和终止节点n代表虚活动;活动之间存在工序约束;以G=(V,E)表示项目网络,其中V={1,···,i,j,···n}表示活动集合,E为有向弧,表示活动的工序约束;活动i的工期是为d i,对技能l的需求量为TF il;资源具备多技能,R={1,···,k,···,K}表示资源集合,资源总量为K,RF kl表示资源的技能禀赋,当资源k可执行技能l时RF kl=1,否则RF kl=0;F={1,···,l,···,L}表示技能集合,技能种类为L.在以项目工期最短为目标函数的MSPSP模型中,决策变量有两个,即活动的开始时间S i,以及活动的资源分配x kli,当x kli=1时,表示资源k以技能l的形式被分配到活动i中去.相应的模型如下:min S n,(1)s.t.S i+d i S j,∀j,∀i∈P j,(2) x kli(RF kl−1)=0,∀k,∀l,∀i,(3)∑k∈Rx kli=TF il,∀i,∀l,(4)∑l∈Fx kli 1,∀k,∀i,(5)q ij+q ji 1,∀i,∀j,(6)∑l∈Fx kli+∑l∈Fx klj q ij+q ji+1,∀i,∀j,∀k,(7)S i∈T,q ij∈{0,1},x kli∈{0,1},∀i,∀j,∀k,∀l,(8)其中:式(1)表示目标函数;式(2)表示工序约束,其中P j表示活动j的紧前活动集合;式(3)表示资源只可执行其所掌握的技能;式(4)表示各活动的技能需求必须得到满足,且不会被分配到过多的资源;式(5)表示资源在一个活动中最多只能执行一种技能;式(6)表示两个活动不可互为前序,其中当活动i在活动j开始之前已完工时q ij=1,否则q ij=0;式(7)表示并行的活动不可使用同一资源;式(8)表示决策变量的可行域,T∈{0,1,···,t,···}表示时间点集合.3算法设计采用不同算法求解项目调度问题时,需要根据相应的算法逻辑解构问题,如基于规则的启发式算法需要根据规则解析项目的特征参数,元启发式算法在编码和解码时需要耦合项目的调度过程.以下将结合强化学习的算法逻辑,根据算法思想解构多技能项目调度过程,设计基于强化学习的多技能项目调度算法(reinforcement learning-based parallel scheduling algo-rithm for multi-skill project,RLP).在强化学习(reinforcement learning,RL)中,智能体(Agent)在环境(Environment)中处于不同状态(Sta-te)时,根据不同策略(Policy),尝试各种行动(Action),并被环境回馈以不同的奖励(Reward),一次“状态–行动–获得奖励–新状态–新行动–···”的过程,称为一个回合(Episode).主要过程如图1所示.504控制理论与应用第41卷⣦ 图1强化学习过程Fig.1Process of RL强化学习将问题建模为马尔科夫决策过程(mar-kov decision process,MDP),可用一个四元组表示,即MDP ={State ,Action ,P (a |s ),R (a |s )},元组内分别代表状态空间、行动空间、状态转移概率和回报函数.其中状态指的是智能体每次决策时所处的状态,具体到项目调度问题中,是每次决策时的活动、资源或其他项目要素的状态,状态信息越全面,价值函数便越精确,同时其值空间也越大;行动是智能体每次迭代时所做的决策,在项目调度问题中,背景和目标函数的不同,行动的内容也不同;强化学习的最终目的是通过更新价值函数获得一个最优策略使得整个事件的总回报(Return)最高,这里的回报即是所求解问题的目标函数.价值函数需要考虑的因素有两个:奖励和回报.奖励一般指即时奖励,是在一步行动后所获得的收益.回报一般指长期收益,是完成一个MDP 的收益和后续行动的奖励之和.在项目调度问题中,奖励和回报与目标函数有关,以工期最短为目标,则奖励和回报便和项目工期大小负相关.3.1基于并行调度的MDP 模型项目调度的本质是活动排程和资源分配.并行调度(parallel scheduling generation scheme,PSGS)和串行调度(serial scheduling generation scheme,SSGS)作为两种最常见的项目调度计划生成方式[20],都是通过迭代将项目活动一一加入到调度计划之中,是一种严格的MDP,这为项目调度问题应用强化学习算法提供了条件.引入一个多技能项目案例,项目网络及活动参数如图2(a)所示,资源数量为4,技能数量为3,资源技能矩阵为[010;101;101;100].图2(b)–(f)表示该项目调度过程中的甘特图,坐标系内的方块表示加入调度计划的活动,虚框内的方块表示未加入调度计划的活动.可以看出,该项目的调度过程是一个包含5个状态、4个行动的MDP,其中状态表示当前排程状况,行动表示从未排程活动中选择一个加入调度计划.如图2(b),state1表示当前状态尚未有活动加入排程,action1表示当前选择了活动2加入排程,达到新的状态state2,即图2(c).依照这种方式,直至所有活动加入排程,并达到state5,调度结束.PSGS 随时间迭代[24],在每个决策时点t ,从当前不违背工序及资源约束的活动集V s t 中选择活动加入排程,直至调度完成.用V c t 表示在时点t 已排程的活动,用V u t 表示在时点t 未加入排程的活动,可知V c t ∪V u t =V,V s t ⊆V u t ,∀t.(9)(b) ⭈⢩ 1(a) 亩ⴞ㖁㔌 ⍫ 313233343333333333333333(c) ⭈⢩ 2(d) ⭈⢩ 3(e) ⭈⢩ 4(f) ⭈⢩ 5图2项目调度的MDP 过程Fig.2MDP of project scheduling第3期胡振涛等:基于强化学习的多技能项目调度算法505从PSGS 的角度,项目调度过程是包含n −1个状态和n −2个行动的MDP.在时点t ,其完备的状态空间是V c t 及其内活动和资源的详细排程,即State(t )={{i |i ∈V c t },{S i |i ∈V c t },{R i |R i ={k |x kli =1,l ∈F },i ∈V c t }}.(10)在决策时点t ,行动是从V s t 中选择一个活动加入V c t 并为之分配资源,以R tj 表示在时点t 活动j 的一个可行的资源方案,则时点t 完备的行动空间是为Action(t )={{j |j ∈V s t },{R tj |j ∈V s t }}.(11)在每个回合内,所选活动的开始时间便是当前决策时点,这降低了行动空间的维度,此时的行动空间可以用式(11)的二元组表示.尽管如此,结合式(10)–(11)可以看出,二者仍极易产生组合爆炸.尤其是在MSPSP 中,一个活动往往有很多种可满足其技能需求的资源分配方案,这导致式(11)中{R tj |j ∈V s t }元素过多,使得状态与行动作为组合之后的再组合,其规模将呈现指数级增长.过于庞大的状态和行动空间会导致强化学习算法很难在较短的时间内训练出一个满意的价值函数,为此,设计双智能体机制,以降低多技能项目调度过程中的状态行动空间.3.2双智能体机制由式(11)可知在项目调度的MDP 中,一步行动包含了活动选择和资源分配,为简化行动内容,设计双智能体,见图3.其中Agent1用以指导活动选择,即式(11)二元组的第1项,Agent2指导资源分配,即式(11)二元组的第2项.3333(b)(c)3333图3双智能体机制Fig.3Mechanism of two agents3.2.1Agent1状态及行动定义在学习过程中,需要根据状态State1做出行动Act-ion1.首先分析状态空间State1,针对式(10)三元组的第1项,由式(9)知V c t 和V u t 关于V 互补,以V u t 代替V c t 表示State1不会丢失信息.更进一步地,在V u t 中,当前回合内行动所需要主要的信息是V s t .为了尽可能保留信息,提取已排程活动的个数信息且用V s t 代替已排活动具体内容,式(10)中第1项便转化为{|V c t |,V s t }.针对式(10)三元组的第2项,每次迭代内决策时点t 已为确定值,V c t 内活动的开始时间对当前选择哪个活动加入排程这一行动的影响较小,因此将之省略.针对式(10)三元组的第3项,影响决策最主要的因素是当前剩余资源,用当前剩余资源数量表示.综上,状态空间State1可整合为State1={|V c t |,V s t ,|R at |}.(12)再分析行动空间Action1,Agent1只考虑活动选择,即从V s t 中选择一个活动j 加入排程.其行动空间为Action1={j |j ∈V s t }.(13)可以看出,状态空间State1虽然也是三元组的形式,但是其第1项和第2项都是仅含一个元素的数组,这大大降低了状态空间的规模.而Action1的规模则等于|V s t |,即当前可开始活动的数量.3.2.2Agent2状态及行动定义在学习过程中,需要根据状态State2做出行动Ac-tion2.首先分析状态空间State2,在Agent1根据State1做出Action1后,达到新的状态State2,此时完备的状态需要明确已排活动所用资源及资源的使用时间,而Agent2只负责为Agent1所选活动分配资源,因此对Action2而言,最重要的状态信息是Action1所选择的活动j ,故状态空间State2省略为506控制理论与应用第41卷State2={j }.(14)再分析行动Action2,行动内容是为活动j 分配资源,行动的规模是在当前可用资源约束下,活动j 可行的资源分配方案个数.Action2={R tj }.(15)双智能体机制将调度中的每一步分为两个阶段,用State1和State2表示状态,既能降低状态的规模,也可以最大程度地保留调度过程中的主要信息.此外,Action1和Action2的规模分别等于V s t 内活动的数量和活动j 可行的资源分配方案数量.行动规模为二者之和,而不再是二者之积,这降低了价值函数的维度.以图3为例,当t =2,V c t ={2,4},V u t ={3,5},V s t ={3},则State1={2,{3},1},Action1={3},State2={3},Action2={{R 4}}.3.3价值函数以项目工期最短为目标的MSPSP 属于稀疏回报问题,本文的RLP 算法不考虑即时奖励,使智能体尽可能地搜索全局最优解.以Deadline 表示项目的工期期限,D S 表示当前调度事件S 的工期,最终回报为Reward =Deadline −D S .(16)强化Q 学习算法采用一个表格直观地表示价值函数.本文参考这种形式,针对Agent1和Agent2,设计了表Q aa 和Q ar ,其中Q aa 对应State1,Action1,Q ar 对应State2,Action2,Q 表的格式如图4所示.State1Action1O{0 1 10}{1 2 4 10}{2 3 4 5}2BB 㺘12ĂĂĂState2Action2,{1}{2}{O }12ĂĂĂ2BS 㺘图4Q aa 表与Q ar 表Fig.4Q aa and Q arQ aa 的行数可变,列数为n +1.第1列表示状态State1,第2到n +1列表示Action1.其中State1数组的第1个数值表示该状态下已排程活动数,最后一个数值表示该状态下可使用的资源数,中间数值表示当前可加入排程的活动.在调度过程中会不断产生新的状态State1,这些状态被不重复地列在Q aa 表第1列,因此Q aa 表的行是随着调度事件的产生不断增多的.而无论面临怎样的状态,Action1都是选择一个活动加入排程,即Action1的选择规模为活动数量n ,因此Q aa 表的列包括一个状态列及n 个行动列.Q ar 的行数为n ,列数为K +1.第1列表示状态State2,第2到K +1列表示行动Action2.在调度过程中,State2是Action1所选的活动,规模为项目活动数量n ,因此Q ar 表有n 行.而所选活动所能使用的最大资源数量是项目中的资源总数K ,即Q ar 表包括一个状态列和K 个行动列.3.4算法流程以PSGS 的角度看,以项目工期最短为目标的MSPSP,状态转移概率是已知且等于1的,然而其每一步的行动奖励是非即时且不确定的,即RLP 算法是Model-free 的,需要不断产生调度计划以供智能体采样,更新各状态行动的价值函数,基于此,算法流程包括两部分:调度(采样)过程和学习过程,见图5所示.图5RLP 算法流程Fig.5RLP algorithm flow chart第3期胡振涛等:基于强化学习的多技能项目调度算法507 3.4.1调度过程调度过程以PSGS为框架,随着决策时点t迭代,活动从V st 依次被加入V ct,直至完成调度.RLP采用Off-policy的方式以ε的概率随机选择,以1−ε的概率贪婪选择,其中ε∈[0,1].随机选择时,决策不参考任何经验信息,完全随机地选择活动和资源.贪婪选择时,根据Q表做出决策.其中Action1的贪婪决策过程为:根据当前调度进度,确定State1=state1,根据state1查询Q aa表决定Action1={j}.由于Q aa表中的状态空间初期并不完备,查询Q aa表时可能面临以下两种情况:第1种情况,在Q aa表中可以找到与state1一致的状态,即该状态曾被采样过.此时只需要找到对应行,从该行中选择Q值最大的活动j进入state2即可.第2种情况,在Q aa表中不存在与state1一致的状态,此时统计MDP下一步各个状态的最优价值: v(state1′)=max Q(state1′,action1′).而后根据v(state1′)选择最优价值最大的状态state1′,并将之与当前状态state1对比,选择一个在state1′中已排程而在state1中未排程的活动j作为Action1进入state2即可.采用这种方式的原因是:即便Q aa表中尚未有与state1完全一致的状态,也可以通过将当前状态向最优状态靠近的方式,进行贪婪寻优.Action2则相对简单,由State2={j},查询Q ar表中的第j行,根据当前可用资源R at剔除不可用资源,并根据活动j的技能需求,列出剩余资源的所有组合,从中选择Q值之和最大的资源组合分配给活动j,即可完成Action2进入最终状态state3.3.4.2学习过程RLP的学习过程是智能体不断从调度计划中汲取经验更新价值函数的过程.它以MC-update法作为价值函数更新方式,即在调度计划生成的过程中暂停学习过程,在调度计划生成过程结束后,再根据调度计划的工期更新Q表.首先,分析Agent1,与调度过程相似,在更新Q值时可能面临以下两种情况:第1种情况,在表中可以找到与state1一致的状态,此时直接更新对应Q值:Q aa(state1,action1)←Q aa(state1,action1)+ (1/N visit)·(Reward−Q aa(state1,action1)),(17)其中N visit是当前访问Q表中Q aa(state1,action1)位置的次数,Reward可根据式(16)获得.第2种情况,找不到与state1一致的状态,则增加Q aa表的长度,将state1及以下Q值直接加入表中: Q aa(state1,action1)←Reward.(18) Agent2的Q表是完备的,在表中一定能找到与sta-te2完全一致的状态,其更新方式为Q ar(state2,action2)←Q ar(state2,action2)+ (1/N visit)·(Reward−Q ar(state2,action2)).(19) 3.5算法优化3.5.1调度过程优化在MSPSP中,根据当前可用资源求解可开始活动集V st是一个难点,在单技能RCPSP,只需要对比资源需求数量和资源供给数量即可,而在MSPSP中,即便资源数量足够,活动也不一定可以开始.该问题可描述为:如何判断当前可用资源R at能否满足活动集V st 内所有活动的技能需求.整理V st的技能需求,对其内活动的技能需求求和,用TF stl表示V st内活动对技能l的需求量,则TF stl=∑i∈V stTF il,∀l.(20)整理资源的技能供给,由于在同一时刻每个资源只能被使用一次,尽管资源具备多技能,这些技能也是互斥的,因此有以下约束:x kli∈{0,1},∀k∈R a t,∀i∈V s t,∀l,(21)∑i∈V st∑l∈Fx kli 1,∀k∈R a t,∀l.(22)V st内活动在当前时点t可以同时开始的充要条件是:R at中资源的技能供给不少于V st的技能需求,即∑k∈R at∑i∈V stx kli TF s tl,∀l∈F.(23)因此以x kli为未知数,只需判断方程组(20)–(23)是否有解,即可判断V st是否可行.然而该方程组是0–1型线性整数规划问题,属于NP难问题.对此本文提出技能归并法,算法伪代码见表1.表1算法1:技能归并法Table1Algorithm1:Skills conflation algorithm输入:V s t,TF s tl,R a t,RF输出:Feasb,在当前资源约束下V s t可行时=11Feasb←1;2for z=1→L do3SkillComb z←从{1,2,···,L}中选出z个技能的所有组合;4for h=1→C z L do5Fs h←SkillComb z中的第h个技能组合;6supply←|{k|k∈R a t,∑l∈Fs hRF kl=0}|;7demand←∑i∈V s t∑l∈Fs hTF il;8if supply<demand then9Feasb←0;return10end if11end for12end for13return Feasb508控制理论与应用第41卷算法第3行列出了要归并的z 个技能的所有组合,第4–11行检验归并后的技能能否被当前资源满足,以supply 和demand 表示技能归并后的资源供给和活动需求.在过程中一旦出现供给不足则跳出所有循环,Feasb =0.若能通过所有组合的检验,则V s t 可行,Feasb =1.技能归并法的合理性来源于以下命题:命题若归并任意数量任意组合的技能后,R at 对所归并技能的供给数量,都不少于V s t 对所归并技能的需求数量,则至少存在一个资源分配方案,使得V s t 内的所有技能需求能被R at 满足.命题1Z 若对V s t ,资源R at 不存在可行的分配方案,则至少存在一个归并的技能组合,使得R at 对所归并技能的供给数量少于V s t 对所归并技能的需求数量,即使得supply <demand .可以看出命题1Z 为命题1的逆否命题,以下证明命题1Z.证资源R at 不满足V s t 有以下3种情况.第1种情况是,资源的总数量不足,即|R at |<∑i ∈V s t ∑l ∈FTF il .(24)式(24)不等号左侧为可用资源总量,它等于归并所有技能(即z =L )为一个技能后,资源对所归并技能的供给supply .同理,不等号右侧等于归并L 个技能后,活动对所归并技能的需求demand .因此式(24)等价于supply <demand ,符合命题1Z.第2种情况,资源总量足够,但是在某一个或几个技能上的数量不足,即∃l ∈F,∑k ∈R a tRF kl <∑i ∈V st TF il .(25)式(25)不等号左侧等于归并单个技能(即z =1)为一个技能后,资源对所归并技能的供给supply .同理,不等号右侧等于归并单个技能后活动的需求demand .因此式(25)等价于supply <demand ,符合命题1Z.第3种情况,可用资源总量足够,在每个技能上的资源量也足够,但是不存在可行的资源分配方案使所有技能需求被同时满足.出现这种情况的原因是资源技能的排他性,即一个资源虽然同时具备多项技能,但同一个时刻它只能执行一个技能.此时V s t 不可行的原因是技能之间存在抢夺资源的情况.分析两个技能l 和m 间抢夺资源的情况.首先,从R a t 中选出具备技能l 而不具备技能m 的资源R alt,具备技能m 而不具备技能l 的资源R amt,以及同时具备二者的资源R almt.将R al t 全部分配给技能l 的需求,将R am t 全部分配给技能m 的需求,技能l 和m 的需求至少仍有一个未得到满足,且剩余可分配的资源R almt无论如何分配,都不能使二者被同时满足,即两个技能需求的差额之和,大于R almt 的数量,即∑i ∈V st TF il −|R al t |+∑i ∈V st TF im −|R am t |>|R almt |,等价于|R al t |+|R am t |+|R alm t |<∑i ∈V st TF il +∑i ∈V st TF im .(26)式(26)不等号左侧等于归并l 和m 为一个技能,资源对所归并技能的供给supply .不等号右侧等于归并l 和m 后活动的需求demand .因此式(26)等价于supply <demand ,符合命题1Z.类似地,当出现两个以上的技能抢夺资源时,可推导出同样的结论.综合以上3种情况和式(24)–(26),命题1Z 得证,作为其逆否命题,命题1得证.证毕.由算法流程可知,技能归并法的时间复杂度为O(L ∑z =1C zL)=O(2L ).针对这一问题,文献[7–8]和文献[9]分别采用了最小费用最大流和二分图最大匹配法予以求解.在这两种方法中,该问题所对应的顶点包含活动的技能需求顶点和资源的技能供给顶点,顶点数量N =∑i ∈V s t ∑l ∈FTF il +|R at |,文献中Dijkstra 算法的时间复杂度为O(N 2),Hungarian 算法的时间复杂度为O(N 3).针对一个项目而言,技能种类L 是一定的,且往往不会太多,如文献[7–9]的项目算例库中最多技能种类为L =4.而在调度过程中,活动需求和资源供给往往是较多的,文献[7–9]中最多资源数量为25.对比可知,当面临技能种类较少的项目时,技能归并法的时间复杂度远小于其他算法.3.5.2学习过程优化针对Agent1,在每次迭代时,它需要根据当前访问次数更新Q 值,为此,设计了辅助表M aa ,其规模与Q aa 表相同,M aa (state1,action1)中数值的含义是:当前访问Q aa (state1,action1)位置的次数N visit .同样地,针对Agent2,设计了辅助表M ar ,其大小与Q ar 表相同,M ar (state2,action2)值的含义是:当前访问Q ar (state2,action2)位置的次数N visit .4实验与分析4.1实验设计为验证RLP 算法,设计了单项目算例实验和项目算例集实验.相关程序用Matlab R2017a 编写,测试平台为Windows 10操作系统,处理器为Intel(R)Core (T M)i7-6700CPU @3.40GHz.4.1.1单项目算例实验设计在实验对象方面,采用如下项目案例.图6是一个包含30个实活动的项目,拥有10个多技能资源,4项技能,其网络图及活动信息标注在图中,资源技能矩阵。
时间修辞与亚洲书写:《东方志》的政治宇宙学* #Time Rhetoric and Asia Writing:The Political Cosmology in The Suma Oriental of Tomé Pires 周云龙 福建师范大学ZHOU Yunlong Fujian Normal University*************************Abstract: The Suma Oriental of Tomé Pires : An Account of the East , from theRed Sea to Japan , Written in Malacca and India in 1512–1515 is an official reportby Tomé Pires who was sent as an ambassador to Asia in the early sixteenthcentury. This report partly represents the knowledge of Asia before Europe enteredthe Indian Ocean international trade system. There are two series of time: universaltime shared between the narrator and Manuel I and the Asia-Indian Ocean timesealed by the former. The Suma Oriental records the conversation of a Christianreporting his traveling in Asia and providing secular knowledge about manydifferent areas to Manuel I. This scene secularizes the sacred time as “universalizingtime.” The narrator in The Suma Oriental seems to travel not only in spaces, but alsoin time and ideas. With the narrator’s traveling, the secular knowledge of Asia isaccumulated and Europe is gradually modernized. The exotic traveling becomes asecular pilgrimage. In fact, the present tense that is used to represent Asia has nevershared the same significance with the “universalizing time” which is owned by thenarrator and the Manuel I, but imprisons Asia by the time preservative. In otherwords, Asia represented in The Suma Oriental relies on the spatialized-time rhetoric.This time rhetoric separates the narrator from Asian spectacle and distributes andresettles the exotic knowledge in a Foucauldian tableau. Then, the cultural distanceand ranks between Europe and Asia are produced, and the spatialized-timesignificance is foregrounded. This time rhetoric sets a non-synchronicity relationbetween Asia and Europe and freezes Asia in the narrating as the reference ofEuropean time and space. The political cosmology in The Suma Oriental is ametaphor of the producing mechanism of exotic knowledge and world awareness inearly modern Europe.Keywords: Tomé Pires; spatialized time; Asia writing; Indian Ocean;Portugal* 投稿日期 Submitted Date: Nov. 9, 2020;接受刊登日期 Accepted Date: Jan. 4, 2021.# 本文系国家社会科学基金一般项目“地理大发现时代欧洲游记中的亚洲形象研究”(项目编号:15BWW011)阶段性成果。
2008年国外马克思主义著作索引(英文)吕增奎编译1.《马克思主义与犯罪学:批评与手段》Marxism and Criminological Theory:A Critique and a Toolkit / Mark Cowling. New York: PalgraveMacmillan, 2008.2.《马克思主义、社会主义与印度政治》Marxism, Socialism, Indian Politics / Randhir Singh. Delhi: Aakar Books, 2008.3.《从马克思主义到后马克思主义》From Marxism to Post-Marxism / G?ran Therborn. London London: Verso Books, 2008.4.《俄国的马克思主义:1879-1906年的主要文献》Marxism in Russia: Key Documents 1879-1906 / ed. Neil Harding, tr. Richard Taylor. NewYork: Cambridge University Press, 2008.5. 《西班牙的马克思主义对苏联共产主义:西班牙内战期间的马克思主义统一工人党》Spanish Marxism versus Soviet Communism: A History of the P.O.U.M.in the Spanish Civil War / Victor Alba and Stephen Schwartz. Transaction Books, 2008.6.《后马克思主义与政治:巴西劳工党研究》Post-Marxism and Politics: The Case of the Brazilian Workers’ Party / Carlos Pessoa. VDM Verlag, 2008.7. 《马克思主义、批评、对话》Marxism, Criticism, Dialogue / Terrence Hawkes.Routledge, 2008.8. 《马克思主义、法西斯主义与极权主义:激进主义思想史上的三个篇章》Marxism, Fascism, and Totalitarianism: Chapters in the Intellectual History of Radicalism / A. James Gregor. Stanford University Press, 2008.9. 《苏联的马克思主义与自然科学:1917-1932年》Soviet Marxism and NaturalScience: 1917-1932 / David Joravsky. Routledge, 2008.10.《世界劳工协会与萨帕塔:关于无政府主义、马克思主义和激进历史的对话》Wobblies and Zapatistas: Conversations on Anarchism, Marxism andRadical History / Staughton Lynd and Andrej Grubacic. PM Press, 2008.11.《马克思主义与阶级分析》Marxism and Class Analysis / AndreBeteille. Oxford University Press, USA, 2008.12.《乌托邦主义与马克思主义》Utopianism and Marxism, Second Updated Edition/ Vincent Geoghegan. Peter Lang Publishing, 2008.13. 《霸权与教育:重访葛兰西、后马克思主义与激进民主》(Hegemony andEducation: Gramsci, Post-Marxism, and Radical Democracy Revisited / DebSandra Bloodworth. Melbourne: Socialist Alternative, 2008.28.《伦理的马克思主义:解放的绝对命令》Ethical Marxism: The CategoricalImperative of Liberation / Bill Martin. Chicago, Ill.: Open Court, 2008.29.《马克思主义与环境危机》Marxism and Environmental Crises / DavidLayfield. Arena Books Ltd, 2008.30.《曼海姆与匈牙利的马克思主义》Mannheim and Hungarian Marxism / JosephGabel. Somerset, N.J. : Transaction, 2008.31.《马克思主义、政治与文化》Marxism, Politics and Culture / GregorBenton. London: Routledge, 2008.32.《早期萨特与马克思主义》The Early Sartre and Marxism / Sam Coombes. NewYork, NY. : Wien Lang, 2008.33.《东方的马克思主义和其他论文集》Eastern Marxism and Other Essays / S.N. Nagarajan, T. G.. Jacob, and P. Bandhu. Ootacamund: Odyssey, 2008.34.《马克思主义与教育理论》Marxism and Educational Theory: Origins andIssues / Mike Cole. London: Routledge, 2008.35.《马克思主义与科学社会主义:从恩格斯到阿尔都塞》Marxism & ScientificSocialism: From Engels to Althusser / Paul Thomas. 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Meta-Heuristics for the Design of aDemand-Responsive Transit Line Teodor Gabriel Crainic∗Federico Malucelli†Maddalena Nonato‡∗D´e partement de management et technologie,Universit´e du Qu´e bec`a Montr´e al andCentre de recherche sur les transports,Universit´e de Montr´e alEmail:theo@crt.umontreal.ca†Dipartimento di Elettronica e InformazionePolitecnico di MilanoEmail:malucell@elet.polimi.it‡Dipartimento di Ingegneria Elettronica e dell’InformazioneUniversit`a di PerugiaEmail:nonato@istel.ing.unipg.it1IntroductionTraditional public transport is evolving towards moreflexible services and operation modes in order to better serve the needs of the population,capture additional demand,and increase its profitability.The transportation system that we study integrates traditional bus transportation and on-demand services. Demand-responsive lines provide a classical,scheduled,transportation service among a limited number of specific points.Such compulsory stops are locations where a demand for transportation may be naturally assumed to be present:stops of express lines,rail or subway stations,or any other points which must be serviced according to the policies of the local transit authority.The vehicle is allowed to transit by each compulsory stop during a time window.Beside the compulsory stops,a set of optional stops to be activated on demand is available to users.Between each pair of consecutive compulsory stops a set of optional stops is defined,which can be served by the vehicle on its way from a compulsory stop to the next.A user issues a service request specifying the pick up and drop offstops.In the absence of requests involving optional stops,the vehicle travels along the shortest path on the network within each pair of consecutive compulsory stops.The acceptance of a request implies the rerouting of the vehicle for that part of route involving the optional stop(s)related to the request.The detour may cause a delay of the transit time at the following stops.Such a Demand Adaptive System(das)represents a good compromise between an expensive personalized service that precisely fulfills individual requests, and the cheap alternative supplied by the traditional public transport,that usually does not provide transportation along individual itineraries.It is a system that may well address the needs of relatively low demand areas(e.g.,North American city suburbs)or periods(e.g.,non-rush hours,evenings,week ends,etc.).The scheduling of one occurrence of a demand-adaptive line constitutes a major building block for more comprehensive das models where a large number of one-time-one-line sub-problems have to be solved repeatedly[2,3].In this case,a single line circuit is traversed once by a single vehicle and the most profitable subset of requests that can be feasibly served must be selected.Once a request has been accepted,the user must be boarded and alighted exactly at the desired stops.Called das1,the model yields a mixed-integer formulation that is NP-Hard and that,for realistic dimensions,cannot bePorto,Portugal,July16-20,2001addressed by exact methods within acceptable computing times.Moreover,there are significant differ-ences in problem and model structure between das and classical dial-a-ride problems [6].Consequently,the straightforward application of well-known vehicle routing problem algorithms does not appear as a viable resolution approach,and the challenge is to devise new approaches that,based on innovative as well as classical methodologies,exploit the problem structure and solve das1formulations efficiently.We developed,tested,and compared several solution strategies for the das1formulation that belong to two general meta-heuristic classes:memory-enhanced greedy randomized multi-start constructive procedures and tabu search methods [1].For the former,we developed a framework where short and long term memories enhance the search.For the later,we studied several neighbourhood-move strategies.We also brought together the two solution approaches to yield hybrid meta-heuristics that aim to capitalize on the respective strengths of each.In the presentation we will briefly describe the das1problem and formulation,introduce the elements common to all search strategies (neighbourhoods,memories,evaluation functions,etc.),describe the constructive grasp -based heuristics,the improving tabu search meta-heuristics,and the three hybrid strategies,present and discuss the performance and comparative experimental results.We will conclude with a number of perspectives for future developments.2Problem Definition and FormulationConsider a line structured as a circuit,served by a single vehicle,starting and ending its tour at the same terminal.Along the tour,the vehicle traverses a sequence H ={f 1,f 2,...,f n +1}of n +1compulsory stops according to a given order,where the terminal is the first (f 1)and the last (f n +1=f 1)element of the sequence.A time window [a h ,b h ]is defined for each stop f h .A set F h of optional stops is associated to each pair of consecutive compulsory stops f h ,f h +1 .Sets F h are mutually disjoint.For any pair f h ,f h +1 ,one can define a directed graph G h =(N h ,A h ),such that N h =F h {f h ,f h +1}is the stop set and A h ⊆N h ×N h is the set of arcs connecting the stops.We refer to G h as the segment h .G =(N,A )is the whole graph,where G = h G h .The travel time τij and cost c ij ,(i,j )∈A ,are given and positive.Travel time τij represents the duration of the shortest path from i to j and takes into account the time needed for stopping at i .Denote by P h the set of paths in G h from f h to f h +1.The vehicle itinerary in segment h is a path p ∈P h whose travel time τ(p )and cost c (p )is given by the sum of the travel times and costs of its arcs,respectively.The sequence of paths defined for each segment forms a tour q ∈Q .Denote by R the request set ,where request r ∈R is defined as a pair s (r ),d (r ) of boarding and alighting stops.Let h (s (r ))and h (d (r ))denote the boarding and alighting segments,respectively.We assume s (r )and d (r )do not belong to the same segment.Let R (q )⊆R be the set of requests satisfied by tour q ∈Q .A benefit u (r )≥0is associated with each request r ∈R .The global benefit u (q )of tour q is u (q )= r ∈R (q )u (r ),while its global cost c (q )is given by the sum of the costs of its paths.Then,the main objective of the das1model is to select the requests to be served and find a maximum-profit(benefit -cost)feasible tour q ∗∈Q .The decision variables are:z h p =1if path p ∈P h is chosen (0,otherwise);y r =1if request r is satisfied (0,otherwise);t h :the starting time of the vehicle from f h .A path-based mathematical formulation of the das1model may then be written as:max Z (y,z )=r ∈R u (r )y r −n h =1 p ∈P h c (p )z h p (1)s.t.y r ≤ p ∈P h δs (r ),p z h p and y r ≤ p ∈P h δd (r ),p z h p ,∀r ∈R (2) p ∈P h z h p =1,h =1,...,n −1(3)t h +p ∈P h τ(p )z h p ≤t h +1,h =1,...,n −1,and t n + p ∈P n τ(p )z n p ≤b n +1(4)a h ≤t h ≤b h h =1,...,n(5)y r ∈{0,1},∀r ∈R,and z h p ∈{0,1}∀p ∈P h ,h =1,...,n(6)Porto,Portugal,July 16-20,2001whereδs(r),p(δd(r),p)is a constant that equals1if s(r)(d(r))is a node served by path p(0,otherwise)∀p∈P,∀r∈R.A request r is served if and only if the vehicle passes by both its boarding s(r)and alighting d(r)stops.The tour is then request-feasible with respect to request r.Constraints(2)are typical network design linking constraints.They enforce the request-feasibility of the tour by linking the path choice to the requests served by the tour and coupling boarding and alighting stops for each request.Constraints(3)impose the selection of one path for each segment,while constraints(4)and (5)state the requirement that the selected paths form a time-feasible tour.3Path-based Meta-heuristicsTwo meta-heuristic approaches are discussed in this paper,memory-enhanced randomized multi-trial heuristics and tabu search procedures.The former belongs to the constructive class of meta-heuristics and it raises the issue whether and how it is possible to define a measure of the potential benefit of a path in a framework where only a partial solution is known.This leads to the to the need to add long term memories to initial the grasp-like[4]procedure.The later is a classical tabu search heuristic [5]based on the use of memory as a mean of recognizing good solutions and using history on“good”solution attributes to guide the search.Both meta-heuristics make use of a pool of paths P =hPh,Ph⊆P h,where P h corresponds tothe set of paths already generated for segment h.The pool of paths evolves dynamically during the search:new paths are added to the pool,others are modified,some may be discarded.Changes in the path set occur due to generation of paths by node deletion or insertion,extraction of sub-paths from time-infeasible paths,path optimization by node reordering,path deletion due to pool overflow.Both procedures are built around a local search phase that iteratively attempts to improve a current solution and build a maximum profit tour by swapping paths in and out of a tour.Starting from a feasible solution,at each step,the best path in P with respect to q for a given segment h is selected according to an evaluation function:the score.The path swapping operation thus represents the fundamental move of the path-based meta-heuristics we introduce.Then,the neighbourhood of the current solution q is the set of all time-feasible tours which can be obtained by way of a single path swap move,while the pool P defines the restricted neighbourhood on which swaps are actually evaluated and performed. The basic memory-enhanced,randomized,multi-trial greedy heuristic iterates as follows:1.Outer loop:Perform max iter macro-iterations.At each macro-iteration,a feasible tour isconstructed by performing(at most)n successful swap moves,one for each segment(the segment loop).At the end of the macro-iteration,a local improvement of the current tour is performed by re-ordering the nodes of the selected paths and by inserting new nodes according to a specific priority function.2.Segment loop:Randomly select a segment not yet examined and identify the best path in thepool to be swapped with the basic path such that the tour continues to be time-feasible(the path loop).Following the move,sure orphan requests and profitless nodes are dropped and the pool is updated by inserting the new paths generated during the path loop.3.Path loop:All paths in the pool for the given segment are evaluated and sorted according tothe score function.Paths are then examined in decreasing score order until either a time-feasible swap is found or all paths are examined.Path reduction is applied to each path in the pool that does not offer a time-feasible swap.The method has been enhanced with a number of additional features that allow the development of a meaningful and computationally-tractable score function.In particular,we try to build up knowledge on the potential performance of each path and node based on the solutions which have been visited previously during the search process.This is naturally implemented by way of long-term frequency andPorto,Portugal,July16-20,2001recency memories.The main idea is to approximate the value of a path by estimating the potential revenue that may be gained by the satisfaction of requests boarding or alighting at the nodes of the path.This estimation is to be carried out by evaluating the probabilities of satisfying requests based on the record of the outcome of the previous macro-iterations.The score function is further enriched by a number of randomization terms that impact the relative evaluations of nodes and paths.Moreover, memories are introduced to record,on the one hand,the long-term evolution of the solution values generated by the constructive heuristic and,on the other hand,the performance of nodes and paths in the most recent macro-iterations.The information gathered in these memories is then combined to the randomization factors to further bias the node and path revenues and,thus,the selection process of the constructive meta-heuristic.The tabu search family of algorithms we developed makes use of the concepts-neighborhoods and moves,evaluation mechanisms,solution enhancement methods,and pool management strategies-im-plemented in the memory-enhanced multi-trial procedure,as well as of the learning capabilities of tabu search to efficiently guide the search towards not yet explored zones of the solution space.The basic tabu search procedure follows the classical form:1.A Neighbourhood Search(the“local”search phase)is performed until a given number ofunimproving consecutive iterations are observed.At each iteration,a segment isfirst selected.The non-tabu path in the pool that ensures the best swap with the path currently in the segment is then identified,the move is implemented,the tour is cleaned(orphan requests and profitless nodes are dropped)and mended(new requests are added),the memories and best solutions are updated.2.If the local best solution has been improved during the last Neighbourhood Search phase,anIntensification phase is performed to attempt to further improve it.The basic principle is to “lock”in the solution the elements that appeared most often in the best local solution and to return to the local search component.3.If the local best solution has not been improved during the last Neighbourhood Search phase,weDiversify the search.In this phase,a number of paths that have most often appeared in the best global tour are swapped out of the solution and a tabu tag forbids their re-entry for a number of iterations;This constructs the set D.A new Neighbourhood Search phase is initiated from the resulting tour.Other that the memories required to compute the node potentials,three memories are defined to guide the search through these three neighbourhoods:a short term path tabu memory,a long term path frequency(in the best global tour)memory,and an medium term request frequency(number of iterations in the best local tour)memory in the current Neighborhood Search phase.Four variants of this basic framework have been defined and tested.The variants differ according to the particular score used to evaluate moves(exact or probabilistic),the mending procedure used to re-insert requests and node in the tour,and the strategy used to select the new tour between the solutions yielded by the swap and mending operations.Three hybrid structures have been defined combining the two preceding meta-heuristics:1.Consecutive.It corresponds to a simple juxtaposition of the two procedures with an equal shareof the total computation effort.The procedure starts with the multi-trial constructive heuristic, which is stopped after half the specified number of iterations or computing time.The tabu search procedure starts from the best solution identified during the constructive phase and continues for the other half of the total computing effort.The idea behind this basic approach is to stop the somewhat random search of the constructive search and attempt to improve from the best solution found.2.G TS Postopt.This procedure implements the multi-trial heuristic but the solution found ateach iteration is improved by using the tabu search meta-heuristic.Porto,Portugal,July16-20,20013.TS G Div.The Tabu Search procedure is run with one iteration of the construction procedureas diversification scheme.The idea behind this approach is that diversifying the search is oftena critical success factor is meta-heuristic search.The strategy does not correspond to a randomre-start procedure since all long-term memories are kept and used.In the three approaches,the pool constitutes a common resource,shared and enriched by each algo-rithm.Similarly,all memories are updated and kept from phase to phase to ensure the long term learning capabilities of the composite procedure.Each structure may yield four hybrids according to the particular tabu search variant used.The procedures are designed to require similar computational efforts to ensure meaningful comparisons. Calibration and experimentation have been performed on sets of problems derived from actual transit lines from one Canadian and one European parisons to results obtained by using standard software tools are also presented.References[1]Crainic T.G.,Malucelli F.,Nonato M.,Guertin F.,Meta-heuristics for a Class of Demand-adaptiveTransit Systems,Publication,Centre for Research on Transportation,Universit´e de Montr´e al,2001.[2]Malucelli F.,Nonato M.,Crainic T.G.,Guertin F.,Adaptive Memory Programming for a Class ofDemand-Responsive Transit Systems,Proceedings CASPT2000-8th International Con-ference on Computed Aided Scheduling of Public Transport,Berlin,Germany,June21-23, 2000,to appear.[3]Crainic T.G.,Malucelli F.,Nonato M.,A Demand Responsive Feeder Bus System,CD-ROM of7th World Congress on Intelligent Transport Systems,Torino,Italia.[4]Feo,T.A.,Resende,M.G.C.,Greedy Randomized Adaptive Search Procedures,Journal of GlobalOptimization6(2),109-133,1995.[5]Glover,F.,Laguna,M.,Tabu Search,Kluwer,Norwell,MA,1997.[6]Malucelli,F.,Nonato,M.,Pallottino,S.,Some proposals onflexible transit,in T.Ciriani et al.(eds.),Operations Research in Industry,McMillian(1999).Porto,Portugal,July16-20,2001。