The idea of combining discrete-event simulation and system dynamics has been a topic of debate in the operations research community for over a decade. Many authors have considered the potential benefits of such an approach from a methodological or practical standpoint. However, despite numerous examples of models with both discrete and continuous parameters in the computer science and engineering literature, nobody in the OR field has yet succeeded in developing a genuinely hybrid approach which truly integrates the philosophical approach and technical merits of both DES and SD in a single model. In this paper we consider some of the reasons for this and describe two practical healthcare examples of combined DES/SD models, which nevertheless fall short of the "holy grail" which has been so widely discussed in the literature over the past decade. INTRODUCTIONThe idea of combining discrete-event simulation and system dynamics has been a topic of debate for over a decade, prompted by a recognition that the division between strategic, tactical and operational decisionmaking was becoming increasingly blurred. During the 1990's there was a growing realization that because of the speed of communications and the complexity of global organizations, decisions made at one end of the operations-strategy spectrum could rapidly impact on outcomes at the other end. For example, the operational decision for a business to reduce staffing levels in its customer services call centre could impact upon the quality of service perceived by customers, which could ultimately result in lower sales, a decline in the share price and the need for a change in market positioning. It is often difficult to draw clearly-defined boundaries round any part of a large system or organization and say that the resulting subsystem can be studied in isolation. This is particularly (although not uniquely) true in healthcare organizations, where "everything affects everything else". Operations Research (OR) has historically been focused at the operational end of the spectrum, but during the 1990's new OR techniques such as Strategic Options Development and Analysis (Eden, 1989) were developed and successfully used for strategic decision-making (Dyson and O'Brien, 1998). Focusing in on simulation, these two aspects are exemplified by discrete event simulation (DES) and system dynamics (SD). DES is essentially an operational tool, designed for optimization of system performance at a very detailed level. Typically, DES is used for modeling queuing systems where stochastic variability is important. On the other hand SD is a more strategic tool, used at a much higher level for understanding overall system behavior.Over the past decade there has been considerable interest in which approach should be used and when (

A service system is an organization of the resources and processes, which interacts with the customer and produces service outcomes. Since a majority of the service systems are labor-intensive, the main resources are the service workers. Designing such service systems is nontrivial due to a large number of parameters and variations, but crucial for business decisions such as labor staffing. The most important design point of a service system is how and when service requests are assigned to service workers a.k.a. dispatching policy. This paper presents a framework for evaluation of dispatching policies in service systems. A discrete event simulation model of a service system in the data-center management domain is presented. We evaluate four dispatching policies on five real-life service systems. We observe that the simulation-based approach incorporates intricacies of service systems and allows comparative analysis of dispatching policies leading to more accurate decisions on labor staffing. INTRODUCTIONService-based economies and business models have gained significant importance. The clients and service providers exchange value through service interactions and reach service outcomes. Given the focus on the individual customer's value and the uniqueness of the customer's needs, the service providers need to meet a large variety of expectations set by the customers. This is the primary reason for the service delivery to be labor-intensive where human intervention and interaction is unavoidable. Service providers aim to maintain the quality, even in the face of unique customer expectations, by structuring their service delivery operations as service systems (SS). A SS is an organization of the resources that support and the processes that drive service interactions so that the outcomes meet customer expectations (Alter 2008;Spohrer et al. 2007;Ramaswamy and Banavar 2008). This paper focuses on the SS in the data-center management domain. However, the contributions of this paper extend to all laborintensive SS.In the domain of data-center management, the customers own data centers and other IT infrastructures supporting their business. The size, complexity, and uniqueness of the technology installations drive outsourcing of the management responsibilities to specialized service providers. The service providers manage the data-centers from remote locations called delivery centers where groups of service workers (SW) skilled in specific technology areas support corresponding service requests (SR). In each group, the processes, the people, and the customers that drive the operations of a delivery center constitute a SS. A delivery center is a system of multiple SS. This paper focuses on the problem of designing the process of routing the SRs to the right technicians (a.k.a. dispatching policy) within a SS such that certain objectives are achieved and constraints are met. What is the basis for evaluating dispatching policies? We propose that the best dispatching policy is the one that: (1) satisfies the contractual con...

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This paper presents a novel method of blind image watermarking in contourlet domain. We have used spread spectrum technique for additive watermark embedding. A correlation detector is used to detect the embedded pseudorandom sequence. The binary logo thus retrieved proves authenticity of the image. The similarity of the retrieved binary logo with the original embedded logo is veriJied using correlation technique. Post processing of the retrieved logo gives better visual effects, further aiding threshold selection for detection. We have verijied the robustness of the proposed method against dzrerent attacks including StirMark attack. The proposed method is compared with a wavelet based blind technique and the results prove that contourlet based technique gives better robustness, under similar embedding conditions.

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