Mixed Mimetic Spectral Element Method for Stokes Flow: A Pointwise Divergence-Free Solution Abstract. In this paper we apply the recently developed mimetic discretization method to the mixed formulation of the Stokes problem in terms of vorticity, velocity and pressure. The mimetic discretization presented in this paper and in [50] is a higher-order method for curvilinear quadrilaterals and hexahedrals. Fundamental is the underlying structure of oriented geometric objects, the relation between these objects through the boundary operator and how this defines the exterior derivative, representing the grad, curl and div, through the generalized Stokes theorem. The mimetic method presented here uses the language of differential k-forms with kcochains as their discrete counterpart, and the relations between them in terms of the mimetic operators: reduction, reconstruction and projection. The reconstruction consists of the recently developed mimetic spectral interpolation functions. The most important result of the mimetic framework is the commutation between differentiation at the continuous level with that on the finite dimensional and discrete level. As a result operators like gradient, curl and divergence are discretized exactly. For Stokes flow, this implies a pointwise divergence-free solution. This is confirmed using a set of test cases on both Cartesian and curvilinear meshes. It will be shown that the method converges optimally for all admissible boundary conditions. We consider Stokes flow, which models a viscous, incompressible fluid flow in which the inertial forces are negligible with respect to the viscous forces, i.e. when the Reynolds number is very small, Re 1. Since Re = U L/ν, small Reynolds numbers appear when either considering extremely small length scales, when dealing with a very viscous liquid or when one treats slow flows. Despite the simple appearance of Stokes flow model, there exists a large number of numerical methods to simulate Stokes flow. They all reduce to two classes of either circumventing the LadyshenskayaBabuška-Brezzi (LBB) stability condition or satisfying this condition, [35] . The first class can roughly be split into two subclasses, one is the group of stabilized methods, see e.g. [11, 43] and the references therein, the other the group of least-squares methods, see e.g. [13, 46] .. The class that satisfies the LBB condition is the group of compatible methods. In compatible methods discrete vector spaces are constructed such that they satisfy the discrete LBB condition. Best known are the curl conforming Nédélec [55] and divergence conforming Raviart-Thomas [64] and Brezzi-Douglas-Marini [21] spaces. A subclass of compatible methods consists of mimetic methods. Mimetic methods do not solely search for appropriate vector spaces, but try to mimic structures and symmetries of the continuous problem, see [14, 20, 50, 52, 57, 70, 71] . As a consequence of this mimicking, mimetic methods automatically preserve structures of the continuous formulation.. At the heart of the mimetic method we present is the generalized Stokes theorem, which couples the exterior derivative to the boundary operator. In vector calculus this theorem is equivalent to the classical Newton-Leibnitz, Stokes circulation and Gauss divergence theorems. These wellknown theorems relate the vector operators grad, curl and div to the restriction to the boundary of a manifold. Therefore, obeying geometry and orientation will result in satisfying exactly the mentioned theorems, and consequently performing the vector operators exactly in a finite dimensional setting. This is indeed what we are looking for and what our mimetic method has in common with finite volume methods, [41, 70] . In a three dimensional space we distinguish between four types of submanifolds, that is, points, lines, surfaces and volumes, and two types of orientation, namely, outer-and inner-orientation. The inner and outer orientations can be seen as generalizations of the concept of tangential and normal in vector calculus, respectively. This geometric structure will form the backbone of the mimetic method to be discussed in this paper. It will reappear throughout the paper in various guises. Examples of submanifolds in R 3 are shown in Figure 1 together with the action of the boundary operator.

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Integrated design in a service marketplace This paper presents a service marketplace vision for enterprise-wide integrated design modeling. In this environment, expert participants and product development organizations are empowered to publish their geometric design, CAE, manufacturing, or marketing capabilities as live services that are operable over the Internet. These services are made available through a service marketplace. Product developers, small or large, can subscribe to and flexibly inter-relate these services to embody a distributed product development organization, while simultaneously creating system models that allow the prediction and analysis of integrated product performance. It is hypothesized that product development services will become commodities, much like many component-level products are today. It will be possible to rapidly interchange equivalent design service providers so that the development of the product and the definition of the product development organization become part of the same process. Computer-aided design tools will evolve to facilitate the publishing of live design services. A research prototype system called DOME is used to illustrate the concept and a pilot study with Ford Motor Company is used in a preliminary assessment of the vision. Predicting overall product and enterprise performance during development phases is becoming increasingly important as companies seek to produce better products with fewer resources. Interaction with our industrial partners (CIPD, 1999) suggests primary objectives include reducing time-to-market and costly design, build, test and refine cycles, while simultaneously increasing the breadth of knowledge that can be applied to solving a problem and considering more design alternatives. In recent years CAD has made the transition beyond geometry to include tightly linked CAE, revision management and BOM (Bill of Materials) capabilities, and more recently parametric optimization.. 1 However, even this scope is limited in comparison to an enterprise-wide modeling viewpoint.. This paperÕs vision is a product development environment where digital representations of products and associated organizational infrastructure such as design, manufacturing, marketing, distribution, and support can be readily evaluated against corporate, customer, market, and policy objectives. Expert participants and organizations publish their geometric design, CAE, manufacturing, or marketing capabilities as live services that are operable over the Internet. These product development services are made available through a service marketplace. Product developers, small or large, can flexibly subscribe to and inter-relate services through appropriate computer-mediated interactions, building service network models that embody the capabilities of a product development organization.. Such models will allow the mathematical prediction, simulation, and visualization of product performance. Additionally, it will be possible to dynamically analyze the structure and performance of the service network (or product development organization) in real time. Tools will be introduced to facilitate the rapid elucidation and evaluation of tradeoffs across the product development organization. Product development services will become commodities, much like many component-level products are today. As a result, it will be possible to rapidly interchange equivalent design service providers so that the design of the product and the organization become part of the same process. In short, the design service marketplace provides a virtual environment for the integrated development of new products. Product development firms will compete on their ability to identify new product opportunities, to develop product system models and organizations leveraging appropriate service providers, and to embody and publish new product development services. This is consistent with views such as the once and future craftsperson described by Lester Alberthal (Albethal, 1998) and in work by Wellman (Wellman, 1994) . In this paradigm, highly responsive modeling and simulation systems move customers and suppliers closer together, allowing the rapid creation, validation, and delivery of products that closely match individual preferences. The modeling systems facilitate the exploration of how various objectives can be achieved. This paper illustrates three key elements of this vision: providing design participants with the ability to publish live services; creating a service marketplace that allows for the synthesis and seamless inter-relation of services to create integrated product models; and the introduction of tools that facilitate the rapid elucidation and evaluation of tradeoffs.. An overview of integrated modeling challenges and approaches is first provided, and then the design service marketplace is demonstrated using a prototype implementation of the concept called DOME (Distributed Object-based Modeling Environment). Architectural elements of the DOME prototype are provided in overview, and then a research and development deployment of the concept, in application to a door glass system at Ford Motor Company, is described.

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The complexity of dissociation set problems in graphs Abstract: A subset of vertices in a graph is called a dissociation set if it induces a subgraph with vertex degree at most 1. A dissociation set D is maximal if no other dissociation set contains D. The complexity of finding a dissociation set of maximum size in line graphs and finding a maximal dissociation set of minimum size in general graphs is considered. Dissociation set problems in graphs find applications in telecommunications and scheduling. The maximum dissociation set problem can be viewed as a generalization both of the maximum induced matching problem which is important in connection with applications to secure communication channels (Golumbic and Lewenstein, 2000) and to the maximum independent set problem which finds applications in manufacturing for production planning and facility location (Haynes et al., 1998) .. Let G be a graph with the vertex set ) (G V V = and the edge set ) (G E E = . For a subset of vertices ) (G V X ⊆ , the subgraph of G induced by X is denoted by G(X). As usual ) (x N G , or simply N(x) , denotes the neighborhood of a vertex V x ∈ , i.e., the set of all vertices that are adjacent to x in G. The degree of x is defined as | ). The maximum vertex degree of G is denoted by ) (G Δ .. is called a dissociation set if it induces a subgraph with a vertex degree at most 1, i.e., 1 )) . The MAXIMUM DISSOCIATION SET problem has been introduced by Yannakakis (1981) and was shown to be NPcomplete for the class of bipartite graphs. Boliac et al., (2004) strengthen the result of Yannakakis by showing that the problem is NP-complete for bipartite graphs with maximum degree 3 and 4 C -free bipartite graphs. It is also known that the problem is NP-complete for planar graphs, see Papadimitriou and Yannakakis (1982) . As mentioned above, dissociation set problems are connected with the well-known independent set and induced matching problems. For a graph G, a subset. vertices is called an independent set if no two vertices in S are adjacent. In other words, the degrees of all vertices of the subgraph of G induced by S are equal to 0, i.e., the subgraph is 0-regular. The maximum cardinality of an independent set of G is the independence number, and it is denoted by. of edges is called an induced matching if (i) set M is a matching in G (a set of pairwise non-adjacent edges) and (ii) there is no edge in. connecting two edges of M.. In other words, the degrees of all vertices of the subgraph of G induced by the end-vertices of edges of M are equal to 1, i.e., the subgraph is 1-regular. The maximum cardinality of an induced matching of G is the induced matching number, and it is denoted by ) (G Σ . Brandstädt et al., (1999) .. Below it is shown that the MAXIMUM DISSOCIATION SET problem is NP-complete for line graphs and therefore for claw-free graphs. . It is well known that this problem is NP-complete for any fixed H that contains a connected component of three or more vertices (Kirkpatrick and Hell, 1978) , see also Garey and Johnson (1979) . This theorem can be strengthened (Theorem 2) using the following results. Orlovich et al., (2008) prove that PARTITION INTO SUBGRAPHS ISOMORPHIC TO 3 P is an NP-complete problem for planar bipartite graphs of maximum degree 4 in which every vertex of degree 4 is a cut-vertex.

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Many Distances in Planar Graphs We show how to compute in O(n 4/3 log 1/3 n + n 2/3 k 2/3 log n) time the distance between k given pairs of vertices of a planar graph G with n vertices. This improves previous results whenever (n/ log n) 5/6 ≤ k ≤ n 2 / log 6 n. As an application, we speed up previous algorithms for computing the dilation of geometric planar graphs. We have presented data structures and algorithms for computing distances in planar graphs with non-negative edge-lengths. The algorithms and data structures can easily be extended to directed planar graphs. They also extend to directed planar graphs with negative and positive weights, assuming that there are no cycles of negative length. For this, we just convert the problem to a problem involving positive weights by computing all the distances from an arbitrary source in O(n log 2 n) time and then defining a feasible price function; see [14] or [8] .. The main open problem concerns the complexity of the many distances problem. In particular, can it be solved in roughly O(n + k) time? Near-linear time answers are known only when k = O( √ n) or k = (n 2 ). A first approach towards this problem may be to consider the problem of computing the pairwise distances between a set of k vertices in a planar graph. Currently, the best result when k = ( √ n) is achieved by reducing it to the problem of computing (k 2 ) = (n) distances.

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A Generalization of Nash Bargaining and Proportional Fairness to Log-Convex Utility Sets With Power Constraints Abstract-Many solutions and concepts in resource allocation and game theory rely on the assumption of a convex utility set. In this paper, we show that the less restrictive assumption of a logarithmic "hidden" convexity is sometimes sufficient. We consider the problems of Nash bargaining and proportional fairness, which are closely related. We extend the Nash bargaining framework to a broader family of log-convex sets. We then focus on the set of feasible signal-to-interference-plus-noise ratios (SINRs), for the cases of individual power constraints and a sum power constraint. Under the assumption of log-convex interference functions, we show how Pareto optimality of boundary points depends on the interference coupling between the users. Finally, we provide necessary and sufficient conditions for strict log-convexity of the feasible SINR region. In this paper we have analyzed log-convex utility regions, resulting from different assumptions and power constraints and interference coupling. This "hidden convexity" is useful for developing resource allocation strategies that operate on the boundary of the region. As an example, we have analyzed the Nash bargaining problem. We have shown that the properties of the classical Nash bargaining solution are preserved for certain nonconvex utility sets. This paper provides a theoretical basis for exploiting log-convexity in interference-coupled multiuser networks and extends previous results in [4] .. The results are potentially useful for different kinds of resource allocation problems. Nash bargaining is just one possible operating point. Other types of fairness can be studied in future work.

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On Stabilization of Gradient-Based Training Strategies for Computationally Intelligent Systems Abstract-This paper develops a novel training methodology for computationally intelligent systems utilizing gradient information in parameter updating. The devised scheme uses the first-order dynamic model of the training procedure and applies the variable structure systems approach to control the training dynamics. This results in an optimal selection of the learning rate, which is continually updated as prescribed by the adopted strategy. The parameter update rule is then mixed with the conventional error backpropagation method in a weighted average. The paper presents an analysis of the imposed dynamics, which is the response of the training dynamics driven solely by the inputs designed by variable structure control approach. The analysis continues with the global stability proof of the mixed training methodology and the restrictions on the design parameters. The simulation studies presented are focused on the advantages of the proposed scheme with regards to the compensation of the adverse effects of the environmental disturbances and its capability to alleviate the inherently nonlinear behavior of the system under investigation. The performance of the scheme is compared with that of a conventional backpropagation. It is observed that the method presented is robust under noisy observations and time varying parameters due to the integration of gradient descent technique with variable structure systems methodology. In the application example studied, control of a two degrees of freedom direct-drive robotic manipulator is considered. A standard fuzzy system is chosen as the controller in which the adaptation is carried out only on the defuzzifier parameters. One of the major problems in applications of gradient-based training strategies is the lack of stabilizing forces to prevent the adjustable parameters to grow unboundedly. This aspect of training without safety conditions constitutes a barrier between the theoretical developments and industrial applications whose prime concern is stability and robustness. The application examples utilizing the gradient information in training have, therefore, used the methods of computational intelligence, which are typically trained off-line with a priori data. In this paper, we propose a generalized method for creating stabilizing forces on the training dynamics of computationally intelligent systems, more specifically the typical forms of which are artificial neural networks, fuzzy inference systems, or systems capable of learning and generalizing knowledge.. The proposed method is based on the integration of EBP strategy with VSS technique to benefit from the robustness property of VSS approach as well as the cost minimizing property of the EBP method. An analytical study of the conditions of stability in the parameter change space is presented. Since the extracted forms of the components and are mutually independent, the performance of the algorithm depends on the compatibility between the design objectives. More specifically, the applications entailing continuous evolution on the adjustable parameters can adversely be affected from the VSS based component as it enforces the parameters to converge.. Simulation studies carried out aim to compare the performance of the proposed scheme with that obtained with pure EBP technique. For this purpose, a standard fuzzy system is used as the computationally intelligent architecture and the adaptation is performed on the parameters of the defuzzifier. The task assigned to the fuzzy system is the control of a two degrees of freedom direct drive manipulator. Despite the representational simplicity of the plant, the existence of a considerable amount of observation noise corrupting the state variables and time-varying payload mass make the problem challenging for conventional learning schemes.. The comparison strongly recommends the use of the algorithm for the applications requiring on-line tuning of the parameters, stability in the parametric displacement space and insensitivity to environmental disturbances.

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Model-driven automation for simulation-based functional verification Developing testbenches for dynamic functional verification of hardware designs is a software-intensive process that lies on the critical path of electronic system design. The increasing capabilities of electronic components is contributing to the construction of complex verification environments that are increasingly difficult to understand, maintain, extend, and reuse across projects. Model-driven software engineering addresses issues of complexity, productivity, and code quality through the use of high-level system models and subsequent automatic transformations. Reasoning about verification testbench decomposition becomes simpler at higher levels of abstraction. In particular, the aspect-oriented paradigm, when applied at the model level, can minimize the overlap in functionality between modules, improving maintainability and reusability. This article presents an aspect-oriented model-driven engineering process and toolset for the development of hardware verification testbenches. We illustrate how this process and toolset supports modularized design and automatic transformation to verification environment-specific models and source code through an industry case study. Advances in design automation and semiconductor manufacturing have resulted in the potential to build increasingly complex electronic systems that consequently are difficult to develop and test. The development process is constrained by a need to test early because of the increased cost of correcting faults after hardware has gone into production [Murphy 2010] .. Verification can be performed using either formal verification tools or through simulation with functional verification testbenches. The most widely used approach is dynamic and simulation-based, where random or directed stimulus is applied to the design by a testbench and a set of assertions are used to check the resulting behavior for conformance with the specification. Figure 1 illustrates a typical hardware development process with verification being performed on the design before the fabrication phase begins [Hamid 2010; Wang et al. 2009] . Simulation-based functional verification consists of developing a testbench and set of testcases. Typically, testbenches perform the following tasks:. -instantiate the Design Under Test (DUT), -stimulate the DUT by injecting stimuli, -collect output results and optionally compare them to expected results.. Functional verification testbenches are typically written in domain-specific verification languages such as VHDL, Verilog, e, or OpenVera [Bunker et al. 2004; Engel and Spinczyk 2008] , but may also include external data files or C routines [Yogesh et al. 2009; Bergeron 2003 ]. The development of these testbenches is a software-intensive process that has been reported by Bergeron to consume 70% of the total development time [Bergeron 2003 ], while in 2007, Li et al. asserted that up to 80% of design costs in many circuit design projects are due to verification [Li et al. 2007] .. The large proportion of design time consumed puts verification on the critical path of a design process that is increasing in complexity and cost [Grose 2010 ]. In addition, the majority of design flaws are functional or logic-related (78% and increasing) and current design processes and tools are achieving a first silicon success of only 28% with a downward trend [Foster 2010] .. As systems become more complex, industry demands that verification engineers complete exponentially more complex verification projects in shorter time periods. In electronic systems design, this problem is commonly referred to as the "productivity gap". As complexity grows, the productivity gap is the difference between hardware capacity and engineering output [Cadence Design Systems, Inc. 2010 ]. With such a large proportion of design time spent on verification, reducing the productivity gap requires verification engineers to shorten the development time without compromising quality. As functional verification is largely a software engineering task we can turn to the accepted software engineering approaches of increasing productivity by: (1) increasing verification component reuse; and (2) working at higher levels of abstraction.. There have been a number of recent efforts to address the problem of reusability in functional hardware verification [Verisity Design Inc. 2005; OVM World 2007] .. However, reusing verification IP is challenging, not least because of incompatible methodologies from single vendors targeting single verification environments, poorly documented verification components, and a need to customize verification components provided by third parties. In addition, many verification components have evolved over years, developed by different teams at different sites, with many layers of new functionality added over a period of time, with knowledge lost along the way through incomplete documentation [Galpin et al. 2009 ].. The second approach to increasing productivity is to work at higher levels of abstraction where reusing components is made simpler by hiding implementation detail. This approach has been used to enhance the productivity of electronic systems designers by allowing them describe an object (for example, a logic gate made of transistors) using a model where some low-level details are ignored. By applying this approach, digital electronic design went from drawing layouts, to transistor schematics and logic gate netlists, to today's Register Transfer Level (RTL) descriptions [Zurawski 2004 ]. Similarly, verification engineers have used hardware environments that have evolved from low-level C libraries to aspect-and object-oriented domain-specific languages for the verification of RTL designs. These environments have built-in support for functional coverage measurement, constrained random generation, and other verification-specific functionality. However, tool support remains limited, and the volume and complexity of code is increasing.. Model-Driven Engineering (MDE) is a design approach where systems are specified as models 1 . Depending on the level of abstraction of the model, code can be generated ranging from system skeletons to complete, deployable products. MDE raises the level of abstraction at which developers work, promising improved quality and increased productivity through automation [Yusuf et al. 2006] . Companies such as Thales perceive the benefits as (among others) improved productivity, ease of reuse, and independence from technology changes [Koudri et al. 2009 ]. In the automotive electronics domain specifically, the architecture is evolving along the model-driven route, with companies like Telelogic producing an Autosar model-driven development environment based on UML and SysML, and TNI Software producing Autosar Eclipse/EMF-based tools for model transformation centered on AADL (Architecture and Analysis Definition Language) [Bézivin et al. 2010] . However, to date, the design of verification testbenches has benefited little from the use of model-driven engineering [Shokry and Hinchey 2009] .. This article presents an MDE process and toolset that supports modularized development of hardware verification testbenches. Our model-driven development process and toolset includes: a metamodel that facilitates the design of verification testbenches at a higher level of abstraction using a well-accepted set of verification concepts; a model transformation tool that decreases the level of abstraction to produce an aspectoriented model containing enough details for automatic generation of an executable testbench; a metamodel facilitating the definition of models capturing the full set of concepts from the e hardware verification language; and a code synthesis tool that performs template-based e code generation. In addition, tools have been developed for the eclipse development environment that parse e code to calculate software metrics or generate UML models.. The rest of this article is structured as follows. Section 2 summarizes related work. Section 3 provides a background to aspect-oriented modularization and model-driven engineering. Section 4 describes a formative study that analyses how the challenges identified are manifesting themselves as difficulties in maintaining existing hardware verification testbench code. Section 5 describes our model-driven approach to the development of testbench environments for functional verification. Section 6 presents the results of the application of the approach to four case studies. Section 7 concludes the article. We have presented a novel model-driven engineering process and toolset that supports modularized development of hardware verification testbenches. Our process tackles the technical challenge of complexity which limits the reusability of testbenches as evidenced through an empirical analysis of testbench source code. Our toolset incorporates a new metamodel that facilitates the design of verification testbenches using high-level verification concepts, a model transformation tool that decreases the level of abstraction to produce an aspect-oriented source-code-level model of a testbench, a metamodel facilitating the modeling of the e hardware verification language, and a code synthesis tool.. We demonstrated through case studies that our model-driven development process and tools can have a positive impact on system modularity when applied to the reimplementation of an industry testbench. Through our modeling languages and transformation, we have facilitated the separation of functional verification concerns at design time that would have otherwise resulted in scattering and tangling in the testbench. These aspect-oriented techniques have been shown to improve the comprehensibility and reusability of testbenches, thereby reducing development time. The case studies presented before demonstrate that in some cases, our approach can result in a better modularized testbench that will, in turn, be easier to maintain and reuse. This has been achieved without needing to introduce verification engineers to aspect-oriented analysis and design by transforming an object-oriented platformindependent testbench model into an aspect-oriented model based on the naturally crosscutting nature of verification components such as coverage, logging, checking, etc. [Engel and Spinczyk 2008] .. The case studies indicate that the biggest improvements are found in testbenches that are designed with little or no concern-based modularization (Case Studies 1 and 3). These testbenches typically contain a proportionately large number of structs and modules with a scattering of behavior throughout the testbench. By refactoring these testbenches using our aspect-oriented approach, it is possible to reduce the number of modules and structs, which in turn helps to decrease coupling and complexity in the testbench.. However, testbenches that are designed with a more concern-based approach, such as those in Case Studies 2 and 4, do not benefit from our approach to the same extent. In these cases traditionally crosscutting behavior will be modularized to a large degree, limiting the benefit of the approach outlined here. Of course, even in these cases, the development process can benefit from the higher level of abstraction that can be supported with models.. As a result of these studies, it would be interesting to explore the boundaries around which it is beneficial for companies to engage in this process. Given that our results show mixed benefits, we advise that the goals for changing an established approach should be carefully considered, and the potential benefits of either improved reuse or modeling with abstractions and using transformations are assessed. From our point of view as researchers, we would like to be in a position to more scientifically define a set of heuristics to aid in this process.. The design of a platform-specific model for the e verification language introduces familiar verification constructs into the MDE process, making it easier for verification engineers to adopt modeling as part of their development process. The ability to automatically synthesize code and reverse engineer code back into UML allows engineers to refactor and elaborate source code without reducing the value of the models.. However, our current model-driven engineering process has a number of limitations that will provide the focus of our future work. Firstly, limited behavior is generated as part of the case studies undertaken during our evaluation process. The focus of the work was on investigating structural improvements through modularization. To be fully functional, the model needs to be extended to place more behavioral elements within the relevant structures. Secondly, our approach models a single testcase as a collection of constraints, however, we do not use Object Constraint Language (OCL) [OMG 2011a ] as part of this modeling. OCL is a key component of the OMG standard for transforming models and its set of formal constraints and object query expressions would provide a more standardized approach to define these constraints than employed in our approach.. Finally, our initial research question was to investigate a profile specific for hardware verification and we focused our efforts on the e language. We would now like to more formally attach this work to the OMG's testing standard by investigating our profile as an extension of the UML Testing Profile (UTP). This would more closely align our work with the testing standards. Modeling Embedded Systems. There have been several projects that applied UML to the modeling of embedded systems using UML profiles, which provide a means of extending UML for a target application domain. Embedded systems have been modeled at the system level through UML profiles that extended the UML semantics to support the specification of system-on-chip designs [Ben Atitallah et al. 2007; Pimentel 2008; Robert and Perrier 2010] . Riccobene et al. have presented a development environment for the hardware/software codesign of embedded systems based on UML and SystemC [Riccobene et al. 2009 ]. The approach supports graphical specification of SystemC designs in UML and generation of SystemC code from the UML models. Other projects extended the standard UML with profiles supporting embedded systems concepts [Mura et al. 2008; Pampagnin et al. 2008] .. Modeling Hardware Specification and Verification. Other work targeted hardware definition and verification languages. Thompson and Williamson used standard UML class diagrams to generate code stubs for the verification language, Vera, using UML to C++ code synthesis [Thompson and Williamson 2002] . The code skeletons are modified by hand to remove C++-specific artifacts and have their behavior inserted. McUmber and Cheng also make use of UML class and state diagrams to specify both structure and behavior [McUmber and Cheng 1999] . In their case, VHDL specifications are generated by applying a set of rules for mapping from UML to VHDL. The UML to SystemVerilog synthesis proposed by Li et al. extends UML with a profile supporting the modeling of real-time systems and informally specifying verification assertions at the model level [Li et al. 2007 ]. UML state diagrams are then transformed using an intermediate XMI representation to SystemVerilog code. Other tools have applied OMG's MDA approach to hardware description and verification languages [Rouxel et al. 2005; Coyle and Thornton 2005; Bunse et al. 2007; Porter et al. 2009; Ben Atitallah et al. 2007] .. These early examples of modeling hardware definition and verification languages fail to hide implementation details from the model level. They do, however, increase the level of automation and facilitate the specification and transformation of models at multiple levels of detail. The value in providing models of hardware verification environments was demonstrated by Gluska and Libis in the development of their pre-RTL model for verification [Gluska and Libis 2009] . They identified verification as being on the critical path of hardware development and demonstrated how abstract modeling of designs can shorten the verification process and enhance the effective use of coverage and formal verification techniques. However, the modeling approach taken was textual and did not consider reusability or modularity.. Modeling Multiprocessor Systems. Oliveira et al. describe a model-driven approach for MPSoC design space exploration that focuses on addressing the issue of reasoning about complex multiprocessor systems [Oliveira et al. 2007 ]. The tool supports a UML-based approach to design space exploration and an automatic multiobjective design space estimation mechanism. Support for model transformation is provided following the exploration phase of the development cycle, although it is unclear whether automated support for code generation is provided.. Modeling Verification Testbenches. The TestBencher Pro graphical code generator by SynaptiCAD Inc., inspired by model-driven engineering's platform-independent models, provides a means to model verification testbenches independent of the verification language in use [SynaptiCAD 2010 Aspect-Oriented Modeling. These examples of model-driven engineering approaches reduce design complexity by raising the level of abstraction at which engineers work. However, simply raising the level of abstraction does not necessarily result in improved comprehensibility and reusability. These properties are often determined by how well concerns are modularized in the design. Aspect-oriented design has been proposed as a better modularization for cross cutting concerns in embedded systems [Driver et al. 2010; Loukil et al. 2010] .. There has been some work in aspect-oriented and model-driven engineering of embedded systems [Afonso et al. 2008; Wehrmeister et al. 2007; Bergeron 2003; Gérard et al. 2005; Gomes et al. 2009; Diaz-Herrera et al. 2002] . However, these approaches cannot be directly applied to functional verification as hardware verification languages incorporate constructs that do not appear in general-purpose high-level languages (like C++ or Java).. In general, related work provides modeling constructs for related domains such as embedded systems, hardware specification, or multiprocessor systems, but not hardware verification testbenches. They also provide for aspect separation at the model level, but again, do not support hardware verification. This article provides both with an approach to managing the increasing complexity of hardware verification testbenches through the application of an aspect-oriented modularization at the model level. This approach is supported by a model-driven engineering process, a set of modeling languages, model transformations, and tools. The modeling approach described in this article draws on aspect-oriented and MDE techniques. Here, we present a brief introduction to these concepts.

O O O O O B O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O B O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O B B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O B O O O O B O O O O O O O O O B O O O B O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B 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O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O B O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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Feedback in the Non-Asymptotic Regime Abstract-Without feedback, the backoff from capacity due to non-asymptotic blocklength can be quite substantial for blocklengths and error probabilities of interest in many practical applications. In this paper, novel achievability bounds are used to demonstrate that in the non-asymptotic regime, the maximal achievable rate improves dramatically thanks to variable-length coding and feedback. For example, for the binary symmetric channel with capacity 1=2 the blocklength required to achieve 90% of the capacity is smaller than 200, compared to at least 3100 for the best fixed-blocklength code (even with noiseless feedback). Virtually all the advantages of noiseless feedback are shown to be achievable, even if the feedback link is used only to send a single signal informing the encoder to terminate the transmission (stop-feedback). It is demonstrated that the non-asymptotic behavior of the fundamental limit depends crucially on the particular model chosen for the "end-of-packet" control signal. Fixed-blocklength codes and related questions concerning communicating with a guaranteed delay are discussed, in which situation feedback is demonstrated to be almost useless even non-asymptotically. We have demonstrated that by allowing variable length, even a modicum of feedback is enough to considerably speed up convergence to capacity. For illustration purposes we can see in Fig. 2 that we have constructed a stop-feedback code, that achieves, for example, 90% of the capacity of the BSC with crossover probability and probability of error at blocklength 200; see Fig. 2 . In contrast, to obtain the same performance with fixed-blocklength codes requires a blocklength of at least 3100 even if full noiseless feedback is available at the transmitter. This practical benefit of feedback opens the possibility of utilizing the full capacity of the link without the complexity required to implement coding of very long data packets.. A major ingredient of the achievability bounds in this paper is the idea of terminating early on favorable noise realizations. Although, we have applied this idea to the codes with codewords with unbounded durations, it is clear that without any significant effect on probability of error we could also assume that the transmission forcibly terminates after a time which is a few times the average blocklength . Consequently, it can be shown that any point on the achievability curve of Fig. 2 can be realized by pairing some linear block code with the stopping rule (35). In other words, even traditional fixed-blocklength linear codes can be decoded with significantly less (average) delay if -. used in the variable-length setting. It is important, thus, to investigate whether traditionally good codes (such as low-density parity-check (LDPC) codes) are also competitive in this setting. Theoretically, the benefit of feedback is manifested by the absence of the term in the expansions (16) and (17), whereas this term is crucial to determine the non-asymptotic performance without feedback. Equivalently, we have demonstrated that for variable-length codes with feedback the channel dispersion is zero. To intuitively explain this phenomenon, we note that without feedback the main effect governing the behavior was the stochastic variation of information density around its mean, which is tightly characterized by the central limit theorem. In the variable-length setup with feedback, the main idea is that of Wald-like stopping once the information density of some message is large enough. Therefore, there is virtually no stochastic variation (besides a negligible overshoot) and this explains the absence of any references to the central limit theorem.. We have also analyzed a modification of the coding problem by introducing a termination symbol (VLFT codes), which is motivated in many practical situations in which control signals are sent over a highly reliable upper layer. We have shown that in this setup, in addition to the absence of term, the principal new effect is that the zero-error capacity increases to the full Shannon capacity of the channel. Although availability of a "use-once" termination symbol is immaterial asymptotically, the transient behavior is significantly improved. Analytically, this effect is predicted by the absence of not only the term but also of the term in the achievability bound (156). Furthermore, our codes with termination have a particularly convenient structure: the encoder uses the feedback link only to choose the time when to stop the transmission (by sending the termination symbol), and otherwise simply sends a fixed message-dependent codeword. The codes with such structure have been called fixed-to-variable (FV), or fountain, codes in [19] . Thus, in short, we have demonstrated that fountain codes can achieve 90% of the capacity of the BSC with crossover probability at average blocklength and with zero probability of error. Practically, of course, "zero-error" should be understood as the reliability being essentially the probability with which the termination symbol is correctly detected.. Finally, we have discussed some questions regarding communication of real-time data. We have demonstrated that constraints on the excess delay nullify the advantage of feedback (and variable length), i.e., the improvement in performance of the best feedback code can be marginal at best compared to non-feedback, fixed-blocklength codes. This is in sharp contrast with the results of the previous sections.

B O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O


A CMOS elliptic low-pass switched capacitor ladder filter for video communication using bilinear implementation This paper presents an approach to design of a high frequency switched capacitor filters for video communication networks. In the case of low OSR, using common methods reduces the SNDR and accuracy of the filter. Bilinear implementation techniques are applied to an untried fifth-order elliptic SC filter, and are simulated in a 0.35µm CMOS technology. Cutoff frequency of the filter is 3.6MHz and with bilinear implementation, we achieve 72dB SFDR, 62dB THD and stop band attenuation greater than30dB. All the capacitors are scaled down in order to reduce the settling time of the amplifiers. The circuit operates with +3V supply and typically dissipates 15 mw when sampled at 18MHz and has full swing about 1.8V. Switched capacitor (SC) filters have proven their high quality and simplicity. They are now considered as one of the most successful techniques in the making of analog filters in the form of integrated circuits. This success has been obtained entirely in the audio range. Many techniques are available for the exact synthesis of these filters and many circuit techniques exist for single ended and differential filters. Unfortunately, this success has not been extended to high-frequency (HF) applications. At high frequency, many problems have to be studied and solved. The HF application of these filters is very important especially in the design of integrated communication systems.. This work has met the video communication filter specification. Therefore it provides a very interesting solution to the design of integrated filters in this range with small area and low power consumption. In this case, a low sampling frequency can be chosen as there is no anti-aliasing filter in the receiver section and the smoothing filter is assured by the monitor set [1] . A filter with this specification has been implemented on a chip by Tawfik and Sen [1] with loss-less discrete transformation. They used Leapfrog equations that simplify assigning the capacitors values and used five OTAs for a 5 th order filter. The drawback of this method is its single-ended realization, and fully differential realization has some crucial restrictions [1] - [8] . Consequently noise and even harmonics magnitude at the output of these kinds of filters is substantially large. Caniv and Gabriel in [9] established a new method using parallel and series combination of the all-pass filters. This method is insensitive to OTA DC-gain and the existence of all-pass filters permits direct implementation in the z-domain. However extracting the capacitance value is very difficult and a large number of OTA's are required (for example a 5 th order filters needs 9 OTA and some buffers). Also single-ended realization is necessary.. In this paper we used bilinear transformation in order to realize a fully differential switched capacitor filter. Bilinear transform is more precise than loss-less discrete transform especially in low OSR schemes. Therefore resultant transfer function in the zdomain is compatible with its ideal transfer function in s-domain. On the other hand, using a fully differential structure reduces noise and even harmonics magnitudes. Also, the required number of OTAs is equal to the filter degree. In section 2 SC implantation based on passive circuit is explained. OTA structure and its specifications are briefly clarified in section 3. Finally simulation results of the proposed switched capacitor filter is presented in section 4. We have proposed a fifth order switched capacitor ladder filter with a cutoff frequency of 3.6 MHz and 18 MHz sampling frequency. Design techniques for this filter were also given, such as low sampling frequency, a bilinear transform implementation scheme and an exact synthesis algorithm. We have demonstrated that when bilinear transform and fully differential concept are taken in account, a very precise and linear filter is achieved.

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Can agents measure up? A comparative study of an agent-based and on-line optimization approach for a drayage problem with uncertainty Experiments studying the behavior of agent based methods over varying levels of uncertainty in comparison to traditional optimization methods are generally absent from the literature. In this paper we apply two structurally distinct solution approaches, an on-line optimization and an agent based approach, to a drayage problem with time windows under two types of uncertainty. Both solution approaches are able to respond to dynamic events. The on-line optimization approach utilizes a mixed integer program to obtain a feasible route at 30-second intervals. The second solution approach deploys agents that engage in auctions to satisfy their own objectives based on the information they perceive and maintain locally. Our results reveal that the agent-based system can out perform the online optimization when service time duration is highly uncertain. The on-line optimization approach, on the other hand, performs competitively with the agent-based system under conditions of job arrival uncertainty. When both moderate service time and job arrival uncertainties are combined, the agent system outperforms the on-line optimization; however, in the case of extremely high combined uncertainty, the on-line optimization outperforms the agent-based approach. Total maritime container traffic grew to approximately 417 million twenty foot equivalent units (TEUs) in 2006 (BTS, 2007 . This phenomenal growth of containerized freight, since the container's introduction in 1956, has led to similar growth in the drayage industry. Drayage commonly refers to the transport of containerized cargo to and from port or rail terminals and inland locations. Unfortunately, the drayage portion of a door-to-door container move tends to be the most costly part of the move. Morlok and Spasovic (1994) indicate that up to 40% of the cost for a 900 mile container move can be attributed to the 50 mile drayage portion of the move. There are a variety of reasons for this disproportionate assignment of costs, including a great deal of uncertainty at the interface of modes. For example, trucks moving containers to and from a port terminal are often uncertain about the time a designated container will become available due to disruptions in the physical and administrative processes involving, among others, the shipping line, stevedore, and customs. In order to generate a profitable route for multiple containers, in one day, the drayage industry must adopt planning systems that can anticipate such uncertainty. This paper compares two structurally different planning approaches for drayage operations in an uncertain environment.. Agent-based solutions have been shown to perform well in uncertain domains (Fischer et al., 1995) . That is, in domains where the problem is continually evolving. The key objective of this paper is to study the performance of an agent-based solution and an on-line optimization approach with respect to handling uncertainty in the context of a drayage company at the Port of Rotterdam, the Netherlands. In our case, a container transport company with a fleet of 40 vehicles must pick up containers from terminals at the Port of Rotterdam, transport the containers to a customer location in the hinterland arriving within a given time window, wait with the container until it is loaded or unloaded, and then return the full or empty container to another port terminal.. Given this method of operations, the problem may be described, in a static manner, as a pick-up and delivery problem with time windows (PDPTW). Reality, however, reminds us that this problem is anything but static and as such we study this problem in an on-line context taking into account two types of uncertainty -service time uncertainty and job arrival uncertainty. Job arrival uncertainty is the most basic type of uncertainty, as a job cannot be planned for or served until it is made known to the planning system. Furthermore, while the presence of a job may be known in advance, the amount of time required to pick it up from the terminal, service it at the customer location, and process it at the return terminal can be highly variable.. The remainder of this document describes the foundational literature on the PDPTW under conditions of uncertainty as solved by both optimization-based and agent-based solution approaches (Section 2). In Section 3, we provide a detailed description of our experimental design including a description of the solution approaches, the data used, and the two types of uncertainty examined. Results, on the performance of both systems across several scenarios of varying service time and job arrival uncertainty, appear in Section 4. A discussion of these results and suggestions for future research conclude this article. Returning to the question raised in our title -can agents measure up? From the results presented here, we are safe to say: yes, but that is not the end of the story. Not only do the agents perform competitively in comparison to the on-line optimization approach on the spatially realistic drayage case, but they also demonstrate a certain number of strengths in handling uncertainty.. These strengths are most obvious in the experiments focused on service time uncertainty. In both independent (S * ) and dependent (Sd * ) cases the agents consistently yield lower routing costs when the variation in service times is greater than 10 minutes. We attribute this advantage to the limitations of the heuristics agents use to compute a solution. These heuristics provide sub-optimal results when faced with a static problem. In a series of problems however, being suboptimal in the beginning means having more trucks on the move, yielding more options to accommodate changes.. There are, on the other hand, settings in which the on-line optimization approach gives significantly better results. In particular, in settings where job arrival uncertainty is a dominant feature. Admittedly, this is not surprising, as job arrival uncertainty is the type of uncertainty most commonly studied in the literature and the type of uncertainty the on-line optimization approach was truly calibrated for.. Given these findings, one might ask the question: "how much are these differences attributable to the centralized versus decentralized nature of the systems as opposed to the optimization versus heuristic characteristics of the approaches?" We begin to answer this question by noting that the comparison between the two approaches is a comparison of heuristics. While the on-line optimization has the opportunity to find an optimal solution, it more often finds only a good feasible solution within each 30-second interval. As such, neither system can claim to produce an optimal solution. Nevertheless, we cannot, so easily, disentangle the centralization/decentralization and heuristic/optimization facets of each approach. The near optimal solutions put forth by the on-line optimization are highly dependent on the centralization of all problem data; the agility exhibited by the decentralized agents is dependent on fast running heuristics.. As the on-line optimization operates by batching all system information at 30-second intervals, it is also forced to batch routing decisions in the same intervals. This process of centralizing information, and using all this information in making job assignment as well as rejection decisions yields assignments that may later turn out to be late, because service times may vary. On the other hand, when service times are static, this approach yields assignments that very effectively balance empty distance against job rejection.. In contrast, the agents, simulated in an individualized manner, are not dependent on batched decisions made every 30-seconds. They can react at any time, but they have a limited view. The individualized outlook implies that the truck agents do not recognize the cost of a rejected container. The container agents, in turn, are the victims of the trucks' inefficiency (or service time variability). This yields a high level of rejected jobs, but a minimal level of lateness when service time uncertainty is high. However, when job arrival uncertainty is the only source of uncertainty, the agents lack the ability to globally weigh routing costs against rejection penalties.. The advantage of a global perspective, regarding the ability to balance empty distance against rejection costs, is supported by our results. Paired t-tests, comparing only the combined costs of empty distance and rejection penalties (leaving out lateness), reveal a significant difference in these mean costs for all service time uncertainty scenarios; and for all, but the R 100 , job arrival uncertainty scenarios. Alternately, the combined service time and job arrival uncertainty scenarios show a significant difference only in the most uncertain case (R 50 S 14400 ). These results lead us to the following conclusion, when the on-line optimization approach performed better, it was by capitalizing on the optimal (or near optimal) balance between routing and rejection costs. In cases the agents performed better, their flexibility provided by their distributed nature was the competitive advantage.. Aside from the observable and quantifiable results presented in this comparative study, we would be remiss if we did not highlight a few qualitative differences between agent-based and on-line optimization approaches for vehicle routing. Agents permit modeling a complex system in a rather "ergonomic" way. That is in a way that closely mirrors the problem being solved. This feature of agent-based systems can make them especially appealing to the lay-person. Thus, when we consider the real-world environment of a drayage company, it is easy to imagine a dispatcher embracing a solution approach that directly maps onto their existing operations. Additionally, in a competitive environment, where sharing of sensitive information is an issue, the distributed agent model may be advantageous.. On the other hand, agent technology is new. New technology often represents a risky choice. In contrast, many existing decision support systems depend on optimization techniques. Furthermore, there is a perception that optimization and operations research represents a technique with years of scientific research underpinning it. Additionally, the management level of logistics companies often prefers to specify their goals for the company as encapsulated in an objective function. The notion of emergent behavior or autonomous fulfillment of local goals may appear threatening to those that must select and invest in a new decision support system. Given both the quantitative and qualitative advantages and disadvantages of both approaches, the future of this research lays in the investigation of how ideas from an agent-based approach can be used in an on-line approach, and vice versa. We expect that a hybrid approach with the ability to exhibit the right behavior depending on the current situation is ultimately the best way of dealing with uncertainty. Furthermore, the agent-based approach can itself be augmented to include learning. In this paper we describe agents that do not make any effort to adjust their behavior based on what they have seen before. One may conjecture that some of the global state could be inferred from past experiences, and that agents with limited information could benefit from learning. An interesting challenge, for future research, would be to find the conditions in which agents can learn and adapt to uncertainties in comparison to a centralized system based on stochastic programming.. In order to find the exact conditions under which one approach outperforms the other, and to understand the fundamental reasons for that behavior, further experiments are required. Not only should we study more general vehicle routing problems (using standard datasets such as the Solomon benchmark sets (Solomon, 1987) ), we should also study other sources of uncertainty, such as travel time uncertainty (to see if this indeed shows similar behavior to the dependent service times considered in this paper) and truck break downs. Furthermore, as instances grow larger, the effect of limited time and/or memory may influence performance drastically, and should thus be carefully taken into consideration. Finally, we would like to see a similar study focused on a comparison of agents with stochastic approaches. We believe the set-up of the experiments in this paper, as well as the results presented, support performing these future experiments. The basis on which both methods are compared across all datasets is total routing cost. Specifically, total routing cost, as defined here, is the sum of the amount of time spent traveling empty, the penalty affiliated with rejecting loads, and the amount of time incurred from delivering jobs outside their appointed time windows. Note, in the design of both systems only time spent traveling empty and job rejection penalties are considered explicitly. Late penalties are a by-product of service time variability in an on-line setting.. To demonstrate the effect of this design consideration, the results are presented in two formats. The tables presented in the following subsections include the mean and standard errors of the total routing costs, while the graphs illustrate the split of these mean total costs across their three component costs. As noted in the introduction, at the heart of this research is a case study in drayage. This case can be described in operations research terms as a truckload pick-up and delivery problem with time-windows (PDPTW). In the PDPTW, a fleet of vehicles, capable of carrying only one job at a time, must pick up a job from one location and drop it off at another location within a specified time period. Finding the assignment of jobs to trucks that minimizes costs (in the form of total distance, empty distance, or operating costs) is the solution goal. Recently, the literature has seen a burst of survey papers on the topic of pick-up and delivery problems. These papers collectively detail the basic problem while classifying the multiple variants (Berbeglia et al., 2007; Parragh et al., 2008a,b; Gribkovskaia and Laporte, 2008; Cordeau et al., 2008) . Using the classification scheme of Berbeglia et al. (2007) our problem may be more specifically described as a one-to-one pick-up and delivery problem with time windows and multiple unit-load vehicles.. While it is easiest to describe and classify these problems in a static manner, these problems may in reality be studied from either a static or dynamic perspective (Ghiani et al., 2003) . Static vehicle routing problems (VRPs) assume that all relevant problem information or input data is known ahead of time and may be exploited in the solution process. On the other hand, the input data for dynamic (also known as on-line (Jaillet and Wagner, 2006) or real-time (Yang et al., 1999) ) VRPs is revealed over time and solution mechanisms are designed to react and evolve accordingly. In this regard there is little time to plan for or optimize decisions -there is only time to react. Given this reactive nature of on-line solution mechanisms, one could argue that all on-line algorithms are in effect heuristics -solution mechanisms designed to yield a good feasible solution rapidly.. Dynamism, also referred to as uncertainty, can have different sources. The type of uncertainty classically studied in vehicle routing is new job arrival. Other types of uncertainty, often studied in the related field of scheduling, include variable activity durations or variable resource failures. A recent review of dynamism in the field of scheduling was published by Herroelen and Leus (2005) . For our study, we focus on two types of uncertainty -variable service times and job arrivals revealed over time.. To summarize the position of our work in the literature, we examine two structurally distinct solution approaches-an optimization-based solution approach and an agent-based solution approach -to the dynamic truckload pick-up and delivery problem with time windows under two types of uncertainty. The structurally differentiating feature of the two solution approaches is the level of control -centralized versus decentralized. Specifically, an optimization-based solution approach, focusing on a single objective and using full system information, exemplifies centralized control. In comparison, agents, optimizing their own unique objectives using information they perceive and maintain locally, exemplify decentralized control. The following two subsections describe in greater detail both optimization-based and agent-based approaches to the Dynamic Vehicle Routing Problem (DVRP).

O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I I I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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O O O O O O O O O O O O O O O O O O O O B I I I I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O