Designing and evaluating the tabletop game experience for senior citizens Al Mahmud, A.; Mubin, O.; Shahid, S.; Martens, J. (Vol. 358,. Lund, Sweden: ACM.Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.-Users may download and print one copy of any publication from the public portal for the purpose of private study or research -You may not further distribute the material or use it for any profit-making activity or commercial gain -You may freely distribute the URL identifying the publication in the public portalIf you believe that this document breaches copyright, please contact us providing details, and we will remove access to the work immediately and investigate your claim. In this paper, we report on the design and evaluation of a tabletop game especially created for senior citizens. The game is intended to provide leisure and fun and is played with four players on an augmented tabletop. It evolved from existing games and rules that are popular and familiar amongst senior citizens. Several aspects that are part of the gaming experience, such as immersion, flow, affect and, challenge, were assessed experimentally. The gaming experience was measured relatively by subjectively comparing user reactions across two sessions, one using a conventional board game and another using a digital tabletop version of the same game. Our results indicate that senior citizens found the tabletop version of the game to be more immersive and absorbing. We also discuss some implications to tabletop game design that can be deduced from the qualitative feedback provided by our participants. Gaming is widely experienced as a means for social interaction and enjoyment, and playing games can help to improve the quality of life, especially for the elderly who have ample leisure time. Elderly people today mostly play low-tech games such as card games. They seem to be less inclined towards computer games than younger people are. Some contributing factors to this difference are obviously that they are less familiar with the games being offered and more afraid of the complexity involved in installing and playing the games. Another factor may however be that existing computer games simply deviate too much from the games that are familiar to the elderly, and that current games insufficiently take into account their real needs (or wishes). Therefore, in this paper, rather than designing a completely new game, we concentrate on augmenting a familiar game. This seems like the most straightforward way of establishing whether or not elderly people could be interested in computer games.. Increasingly, researchers are now focusing on designing social games, for example in [8] , where several players can be involved in a co-located and collaborative way. Augmented tabletop gaming is one possible approach to allowing more players to participate and enjoy the flavor of traditional board games in a new setting. Combining board games with the rich media that are typically used within computer games, such as audio and computer graphics, allows to create new experiences. The game environment can also be made more challenging and more engaging by adapting dynamically to the game situation. Tangible interaction is a strong point of traditional board games and it helps to provide an enjoyable user experience for players. It can be incorporated in tabletop games by augmenting physical game elements with digital functionality. There are few examples of computer games that were especially developed for the elderly. One exception is a video game used for therapy, i.e., to help improve social and educational skills (see [7] for a detailed treatment). Although such games have obvious (functional) merits, they also have (social and usability) deficits that may influence end-user acceptance. For instance, PC games do not allow for personal face to face contact, an aspect that is crucial in traditional games. The complexity of the interfaces to many existing computer games may also create a threshold for their widespread acceptance. Elderly people are likely to be more sensitive then most to such aspects, so that they might also profit more from alternative approaches such as tangible interaction, on augmented tabletop surfaces.. Though there are a lot of games available today for children and adults, not much attention has been devoted up to now to games for senior citizens, especially not in the area of augmented tabletop gaming. One notable exception is 'SharePic', an Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee application aimed at elderly for sharing digital photographs [3] . Examples of tangible tabletop games not aimed at elderly users are Weathergods [4] and Tankwar [9] . The aim of the project that we report here is to unveil some of the potential in designing senior-friendly tabletop games, where seniors are in the age range of 65-75 years. In our research, we have compared both digital and static version of a tabletop game with the elderly. The former was generally rated to be as more immersive and engaging by the participants. In addition, our study reveals two important findings. Firstly, the game playing experience of the elderly can be enhanced by digital tabletop games, as technology is latent in them and hence dynamic game behavior can be incorporated, leading to easy interaction. Secondly, adaptive multimedia plays an important role when designing an engaging and enjoyable tabletop game for the elderly. As a direct and logical extension of our current research we will carry out further game evaluations with more participants in a longitudinal manner. It may well be the case that the results related to immersion and flow would be different when the elderly play the same game multiple times for a longer period.

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New bounds for the Marcum Q-function Abstract-New


Isotone optimization in r: Pool-adjacent-violators algorithm (pava) and active set methods In this paper we give a general framework for isotone optimization. First we discuss a generalized version of the pool-adjacent-violators algorithm (PAVA) to minimize a separable convex function with simple chain constraints. Besides of general convex functions we extend existing PAVA implementations in terms of observation weights, approaches for tie handling, and responses from repeated measurement designs. Since isotone optimization problems can be formulated as convex programming problems with linear constraints we then develop a primal active set method to solve such problem. This methodology is applied on specific loss functions relevant in statistics. Both approaches are implemented in the R package isotone. After a historical outline we presented the theory and the algorithmical descriptions of approaches for solving isotone optimization problems: PAVA and active set. We started with the classical representation of the monotone LS regression problem with simple chain constraints and extended it to general convex programming problems with linear inequality constraints. This leads to a general isotone optimization framework that is implemented in the R package isotone. Applications on real and simulated data sets were shown.. One option for the extension of the PAVA algorithm is to allow for multiple predictors. This approach is elaborated in Burdakov et al. (2004) .. Of course, the field of convex analysis is rather extensive and our activeSet() function covers only a certain fraction (cf. Boyd and Vandenberghe 2004 ). Since we use optim() in the fSolver() function this may cause troubles for non-differentiable convex functions. Therefore, a replacement of this optimizer would facilitate the optimization of such nondifferentiable problems. In addition, for a target f (x) we allow for one particular type of solver s(x) only, that is, the target function is separable but the components must be of the same type. This could be extended in terms of different solvers for one particular optimization problem.

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


Compositional analysis for linear control systems The complexity of physical and engineering systems, both in terms of the governing physical phenomena and the number of subprocesses involved, is mirrored in ever more complex mathematical models. While the demand for precise models is indisputable, the analysis of such system models remains challenging. Adopting techniques from computer science makes available a framework for compositional analysis of interconnected control systems. Simulation relations relate process models with their specifications thus checking whether the derived model behaves as desired. Based on that, compositional and assume-guarantee reasoning rules decompose the actual verification task into several subtasks that can be checked with less computational effort. Thus, modularly composed system models can be treated with modular analysis techniques. In this paper, we want to give an overview of how these concepts can be applied to analyze linear continuous-time systems (LTI). Motivated by the underlying physics, we introduce a general type of interconnection that can also be interpreted as a feedback control configuration in the spirit of decentralized control. Additionally, parallel composition of LTI systems is discussed with special emphasis on decomposition strategies for a given specification. The proposed methodology could be extended further to classes of hybrid systems where compositional analysis techniques are of particular interest. In formal verification, the curse of dimensionality forms an obstacle to efficiently check properties of programs involving concurrent processes. Interaction between these concurrent processes leads immediately to combinatorial explosion in terms of the size of the state space. As a result, straightforward approaches to formal verification such as simulating all possible executions of a program usually fail. More structured techniques are needed instead to deal with the inherent complexity. One important development was the introduction of simulation relations by Milner [10] . Expressing both the program to be verified and the property to be checked in the same language -in the area of verification mostly as labeled transition systems -and then relating them by constructing a simulation relation ensures that the given system behavior matches the desired specification. To reduce the complex verification task for the overall system, compositional analysis techniques can be employed. The main idea of compositional reasoning is to decompose proof obligations for the whole interconnected system into obligations for components which computationally are more efficiently solvable. Complementary to compositionality is the idea of assume-guarantee reasoning which can be used when properties of individual components can not be verified directly ( [11] ). The key principle is to restrict the behavior of a subsystem to a specific environment by interconnecting it with a subsystem representing parts of the specification. Splitting the global proof obligation into several steps for restricted components, it is possible to guarantee the original verification goal yet with reduced efforts. Both for labeled transition systems and hybrid systems, there have been applications of compositional and assume-guarantee reasoning in recent years, see e.g. [4] and [5] . Encouraged by these advances in the area of computer science, compositional analysis techniques could play an important role for the analysis of control systems as well. In fact, models of engineering systems have similar features as models of concurrent processes. Firstly, the number of state components is large in several applications, e.g. for chemical plants, mechatronic or embedded systems ( [3] ). Secondly, interaction between subprocesses is characteristic for various control problems such as decentralized control where a global control target is solved by the interplay of local controllers and plant subsystems. The goal of this work is to make compositional techniques applicable to analyze linear continuous-time systems. As a first step, simulation relations for dynamical systems have been introduced, see in particular [1] , [12] and [14] . Besides using them to verify properties of implemented process mod-els, simulation relations can also serve as a tool to abstract a given model with a lower dimensional one. This idea was brought forward in [13] as a means to reduce the complexity of interconnected system models. Abstractions provide a conservative approximation of the given system model so that properties can be checked reliably on a higher level. A two-sided version of simulations, bisimulation relations, has been studied extensively in [12] for both labeled transition systems and continuous-time control systems stressing the link between formal verification and control theory. Moreover, the idea of compositional reasoning has recently been investigated for feedback interconnections of linear ( [7] ) and hybrid systems ( [6] ). This paper generalizes and extends the proposed methodology by considering two different types of interconnection for linear continuous-time systems. Motivated by many physical applications, a feedback type of interconnection is studied first where the external variables are equated. A methodology for compositional and assumeguarantee reasoning is developed and illustrated with an example from circuit analysis. Second, parallel composition is introduced as an alternative but equally relevant interconnection for control systems. We focus on decomposition strategies for a given global specification, i.e. how to arrive at an interconnection of local specifications that can then be used for compositional and assume-guarantee reasoning. We conclude by giving an outlook as to possible further directions of research.

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


J2EE server scalability through EJB replication With the development of Internet-based business, Web applications are becoming increasingly complex. The J2EE specification aims at enabling the design of such web application servers. These servers have to ensure scalability and availability of the supported applications. Scalibility can be achieved using replication techniques or partitionning techniques. The aim of this paper is to compare these approaches. In a J2EE web application server, one important component is the EJB tier. In this context, the JOnAS web application server provides an example of EJB replication system called CMI (Cluster Method Invocation). In a first step, this paper presents a performance evaluation of CMI. It then introduces incrementally an alternative scheme based on partitionning and shows the performance benefits compared to CMI. The J2EE specification [14] aims at enabling the design of complex web application servers, structured in several tiers. A J2EE application server is generally composed of four tiers which can execute on different machines, as illustrated in Figure 1 :. The web tier executes client requests (e.g. Apache [16] ): a reference to a static web page is resolved by the web server , a reference to a dynamic page is forwarded to the Servlet tier.. The Servlet tier (e.g. Tomcat [5] ) generates a web page on the fly (the creation of the web page is dynamic), from data which can be requested to the EJB tier.. The EJB tier (e.g. JOnAS [6] ) includes the functional code of the application which computes the data requested by the Servlet tier. The EJB server interacts with a database server which manages the persistent data of the application.. The database tier (e.g. MySQL [11] ) which manages persistent data. The J2EE specification allows designing multi-tiers application servers. A J2EE server is generally composed of four tiers, each being executed on a separate machine: a Web server tier, a Servlet server tier, an EJB server tier and a database server tier. The growth of the load that these servers (in terms of number of requests) may have to face raises the issue of the scalability of J2EE architectures.. The widely adopted approach consists in replicating the different tiers of the J2EE server, the unit of replication being the tier server as a whole. This approach has the advantage to manage replicas uniformly (the clones are not distinguished), which simplifies the routing of the requests (any replica can treat any request). However, the difficult issue raised by this approach is consistency management of state of a tier server when this state can be modified, which is the case for the EJB server. CMI is the solution of the JOnAS EJB server; CMI ensures consistency by synchronizing the replicas through the database tier (it forces propagation of accesses to the database), but it requires caching in JOnAS to be disabled.. In the context of a clusterized J2EE architecture, we compared the performance of a J2EE server with a single EJB server (with cache enabled) and with an EJB server replicated with CMI (with cache disabled). We observed and analyzed the benefits from using CMI. We then introduced a solution based on bean partitioning, which aims at improving the performance of CMI, by enabling EJB server replication and caching. The evaluation showed that this solution performs poorer than CMI, but our analysis allowed designing a hybrid solution between CMI and partitioning. In this hybrid solution, read-only beans are replicated with CMI (and can be cached) and writable beans are partitioned (a single copy is managed and can be cached). This solution improves the throughput of the J2EE server by 20-30% compared to CMI.. We are pursuing this work following two-directions:. We wish to evaluate the strategies presented in this paper with a greater number of nodes and to study different partitioning policies, especially by beans instead of by factories.. We are currently implementing facilities to dynamically adjust the number of server replicas according to the load that each tier has to face. Resource replication (at any level: disk, process, machine, etc.) has been much more studied in the purpose to provide fault tolerance than in the goal to provide scalability. However, fault tolerance and scalability are tightly coupled (especially in distributed systems) and often considered together, as illustrated by the definition of the performability metric [10] . Replication mechanisms introduced for fault tolerance often improve scalability (as a side effect). For instance, RAID-1 hard disks replication [12] tolerates a disk crash but also improve the performance of the overall persistent storage. This observation has motivated the C-JDBC project [2] whose objective is to provide scalability for relational database systems which enforcing their fault tolerance. C-JDBC exploits the principles of RAID to replicate a database on several machines and to maintain its consistency.. Resource replication allows obtaining scalability in two cases:. The replicas are idempotent and the treatment of requests is not replicated (requests are distributed among replicas and their treatment always takes place on one server).. The treatment of requests is replicated on several servers and the replicas are not necessarily idempotent.. For example, the active replication model and primary-backup replication model were designed to ensure fault tolerance, but they don't provide scalability [4] .. Replication of stateless servers has been explored, especially for static web pages servers. Web servers can be replicated and requests distributed between replicas with a Round-Robin DNS or a L4 switch [7] [13] . In the case of a statefull server, state consistency is the important issue; current solutions rely either on (i) broadcast of the state (or of updates) to the replicas [5] [8] using group communication protocols (multicast IP, JGroup, etc.) or (ii) externalization of the state on a transactional support shared by all the replicas [6] ; the choice of this transactional support is key to performance [3] , but the most common choice (and inefficient) is to use a database system. Other solutions are considering replication in volatile memory in order to improve the management of this state [9] .. Our hybrid solution is an alternative which consists in partitioning the state between a set of servers; therefore the state is distributed, but not replicated, which prevents the overhead due to consistency management. Fault tolerance is provided by the underlying transactional database system.

B O B O B 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 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 B O O O O O O O O B O O O O O O O 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 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 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 B 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 B 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 B O B 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 O O O O O O O O O O O O O O O O O O O O O O O O O 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 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 B O O O O O O O B O O O O B 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 B 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 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 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 B 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 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 O O O O 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 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 B O O O B O O O O O O O O O O O B 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 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


Continuous input nonlocal games We present three nonlocal games for a two-player team, in which the inputs the players receive are continuous. In addition, the inputs are not constrained by a "promise". The games therefore admit a simple set of rules. It can be shown that in the first two games a quantum advantage obtains. We conjecture that this is true for the third game as well.The nonlocal nature of quantum mechanics [1, 2, 3] has recently been highlighted in a number of games [4, 5, 6, 7, 8, 9, 10] . Termed nonlocal [9] , these are joint tasks for a team composed of several remote players. Each of the players is assigned by a verifier an input generated according to some joint probability distribution. The players must then send an output to the verifier, who carries a truth table dictating for each combination of inputs, which combinations of outputs result in a win. The players may coordinate a joint strategy prior to receiving their input, but cannot communicate with one another subsequently. A team sharing quantum correlations (entanglement) is said to employ a "quantum" strategy, while a team restricted to sharing classical correlations is said to employ a "classical" strategy.In previously introduced nonlocal games the input set is discrete and finite. In contrast, in the games we present the input is continuous. Moreover, most nonlocal games include a "promise" regarding the allowed input combinations. This means that if n i is the number of inputs that may be assigned to player i, then the total number of input combinations that may simultaneously be assigned, n, satisfies n < i n i . This restriction is especially tailored to guarantee a maximum advantage for quantum strategies over classical ones, and can make the rules of the game complex. In the games we present there is no such promise. The joint probability distribution governing the assignment of inputs is uniform, and the rules are simple. Nevertheless, a non-negligible quantum advantage obtains.In the first game two remote players A and B receive a uniformly generated input a ∈ [0, 1] and b ∈ [0, 1], respectively. Following this, each of the players sends a classical bit representing an output o i ∈ {1, −1} (i = A, B) to the verifier. The game is considered to have been won ifThe game, therefore, amounts to the problem of returning a positive (negative) product of outputs when the sum of the inputs is less than (greater than or equal to) 1. In the following we show that a team employing a quan- of the total area of the square.tum strategy can achieve a higher probability for winning the game than a team restricted to classical strategies. We begin by presenting the optimal classical strategy. It is easy to show that it is deterministic, i.e. the output is a single-valued function of the input, and is given for example byThe winning probability then equals 75% (see Fig. 1 ). This can be proven rigorously by translating the game into a Bell inequality for an infinite number of measurement settings. Indeed, the inequality obtains as the continuum limit of a family of Bell inequalities first discovered by Gisin [11]. For details see [12] .In the quantum strategy we present the players share a two qubit singlet state

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Dependability evaluation of an air traffic control computing system Abstract The French Air Traffic Control (ATC) is based on an automated system (the CAUTRA), implemented on a distributed fault-tolerant computing system composed of five Regional en-route air traffic Control Centers (RCC) and one Centralized Operating Center (COC), connected through a dedicated telecommunication network. The same computer architecture is implemented in each RCC. The CAUTRA design has been in a continuous evolution during the last few years in order to face the growth of air traffic volume, to improve the dependability of the CAUTRA and to include additional functionality to the controller. The defini-* Nicolae Fota was at LAAS-CNRS when this work was performed.. tion of the new CAUTRA architecture is supported by quantitative evaluation techniques. In this context, our work focuses on the analysis and evaluation of the impact of CAUTRA failures on the service delivered to the controller to ensure air traffic safety.. The analysis and evaluation of this impact has been performed in three successive phases. The first one, aimed at a preliminary Failure Modes Effects and Criticality Analysis of the CAUTRA, led us to define five levels of ATC service degradation and to identify the main subsystems providing vital services for air traffic safety. The second phase focused on the dependability modeling and evaluation of each of these subsystems. The third phase was devoted to the combination of the dependability measures evaluated for each subsystem to: 1) obtain global measures for each service degradation level, 2) analyze the contribution of each subsystem to these degradation levels, and 3) identify improvement areas of the CAUTRA architecture to reduce the effects of failures. In this paper, we outline the results of the first phase, then we focus on the RCC system (one part of the second phase).. The complexity of the RCC and COC systems, and the necessity for a detailed modeling of failure and recovery scenarios (to evaluate the system with respect to different levels of degradation) lead to handle a large set of failure and recovery assumptions of a system constituted of components having multiple interactions. State-of-the-art modeling techniques are difficult to use in this context if they are not supported by a systematic and structured modeling approach. In [9] , we presented a modeling approach based on stochastic Petri nets that assists the users in the construction and validation of complex dependability models of several thousands of Markov states. The system is modeled as a set of modules interconnected via coupling mechanisms. The model is constructed in successive steps according to an incremental approach. Each step integrates the failure and recovery assumptions of an additional component and updates the model built in the previous step by accounting for the impact of the new component on the behavior of those already considered by the model. Construction guidelines are defined to assist the users in the modeling process. In this paper, we illustrate the application of the approach defined in [9] to a real complex system, the RCC. The system model is composed of seventeen modules with multiple interactions between them. A number of possible configurations of the RCC architecture are discussed and evaluated. The results show that the distribution of the software replicas on the hardware, the communication between them and the software reliability of the most critical replicas are the most critical parameters that need to be monitored during the design.. This paper is composed of seven sections. Section 2 positions our work with respect to the state-of-the art. Section 3 presents the CAUTRA, the service degradation levels and the RCC architecture. Section 4 summarizes the modeling approach used to describe the RCC behavior and evaluate its dependability measures. The RCC modeling assumptions and the corresponding model are presented in Section 5, while Section 6 comments the results. Finally, Section 7 concludes the paper. This paper summarizes the results of a case study dealing with the analysis and evaluation of the impact of CAUTRA failures on air traffic safety and presents some results of the analysis. The effects of these failures on the service delivered to the controllers to ensure traffic safety are grouped into five degradation levels. To be able to evaluate the system dependability with respect to these levels and to master the model complexity, we have applied a GSPN-based modeling approach presented in [9] which consists in modeling the system as a set of modules interconnected via coupling mechanisms describing interactions between components. The model is constructed in several steps following an incremental approach. Each step integrates the failure and recovery assumptions of an additional component and updates the model obtained in the previous step by modeling the impact of the new component on the behavior of those already considered by the model.. Thanks to this approach, we were able to build and validate complex models of several thousands of Markov states for the CAUTRA. The results allowed us to analyze several configurations of the CAUTRA architecture and to identify improvement areas to reduce the impact of CAUTRA failures on air traffic safety. The architecture was modeled at a level of detail that made it possible to assess the impact of software and hardware failures, considering different levels of service degradation. Sensitivity analyses with respect to dependability parameters were also performed. Only some results concerning the RCC subsystem could be discussed in the paper. They show that the main variation in dependability measures is related to 1) communication failures between Radar Data processing and Flight Plan processing replicas, and 2) software failure rate of Radar Data processing replicas. previous study we have done on a former architecture of the CAUTRA where only service unavailability was analyzed without considering different levels of service degradation [18] . Moreover, the measures derived from our models compare well with those observed on the CAUTRA system which is currently in operation.. On one hand, our study allowed us to provide feedback to the CAUTRA development and operation teams. On the other hand, it gave us the opportunity to experiment the applicability of the modeling approach presented in [9] to a complex real-life system. One possible extension of this work is to analyze the impact of CAUTRA failures on air traffic performance. Indeed, the occurrence of CAUTRA failures leads, in some situations, to air traffic limitations and delays. The same modeling framework could be used by including reward parameters characterizing performance degradation for different failure and recovery scenarios. Using the Markov chain generated at the final step of the incremental modeling approach (i.e., step 18), measures UA(X) and W(X) -defined in Section 2 related to the failure modes X identified in Table 2 -have been evaluated. These measures allow comparison of different fault tolerance strategies of the RCC system as well as the comparison of various strategies for FP and RD replicas distribution on the DG computers (i.e., the configuration strategies), to identify an optimal solution.. Sensitivity analyses with respect to the most significant reliability parameters (considering different parameter values) are then performed for the optimal architecture, to identify: 1) the components which reliability improvement have the most important impact on air traffic safety or 2) the parameters on which operational reliability data collection should focus in the future. For the evaluation purpose, the hardware reliability parameters were obtained from the equipment providers, while some of the software reliability data items were collected during the RCC operation . When the numerical values of the parameters were not available, they have been evaluated using data available on similar systems [4, 15, 19] . The uncertainty was accounted for by performing sensitivity analysis with respect to the main reliability parameters.. We illustrate the RCC system evaluation results by presenting the influence of configuration strategies and the impact of the RD fault tolerance strategies on the RCC measures. Additionally, we give an example of result concerning the CAUTRA, showing the influence of RCC system configuration strategies on the global measures. Several papers dealt with ATC systems dependability. Papers [1, 2, 6] focus on the specification and the design of fault tolerance procedures, while the work presented in [12, 23] addresses the qualitative evaluation of ATC system dependability. Most of the papers dealing with the modeling and quantitative evaluation of ATC architectures can be found in our previous work on the CAUTRA system. The work presented in [11] is devoted to the dependability of the COC. Our earlier work presented in [18] dealt with former architectures of the RCC where the only dependability measure considered was availability without taking into account different levels of service degradation. The work presented in this paper, and related to RCC, considers a new generation of the RCC and refines the dependability measures to account for several service degradation levels. To evaluate these dependability measures, we used the incremental and modular modeling approach based on Stochastic Petri Nets (SPN) which is summarized in [9] . In that paper, guidelines are presented to assist the user in the construction and validation of complex dependability models. Petri nets are well suited to model the interactions between hardware and software components resulting from the occurrence of failure and recovery events. Other approaches for system dependability evaluation are also available, either based on analytical modeling (e.g. [7, 20] ) or on simulation (e.g., [13] ). The discussion about which one is the best is out of the scope of this paper. A review of some these methods can be found in [21] .. Considering the modular construction of quantitative evaluation models, several methods have been proposed, either based on SPNs or their offspring's (see e.g. [17, 22] ) or based on Markov chains [14] . Other techniques based on SPN decomposition are also proposed, e.g., in [5] . Some of these methods are efficient when the sub-models are loosely coupled, others become hard to implement when interactions are too complex. For the dependability modeling of fault-tolerant systems, multiple and complex interactions between system components have to be explicitly considered because of the dependencies induced by component failures and repairs. When the number of components is not very high and the number of interactions is limited, the model can be obtained by composition of the component models with their interactions as in [17, 22] . When these numbers increase, alternative approaches, such as the incremental approach proposed in [9] , are needed to handle progressively the complexity of the resulting model. The main principles of this method are summarized in Section 4, and its application in the context of the CAUTRA is illustrated in Section 5.2.

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One-Pass Wavelet Decompositions of Data Streams Abstract-We present techniques for computing small space representations of massive data streams. These are inspired by traditional wavelet-based approximations that consist of specific linear projections of the underlying data. We present general "sketch"-based methods for capturing various linear projections and use them to provide pointwise and rangesum estimation of data streams. These methods use small amounts of space and per-item time while streaming through the data and provide accurate representation as our experiments with real data streams show. S ITUATIONS abound in which data arrives and is processed in a stream. For example, network service providers collect logs of network usage (telephone calls, IP flows, etc.) in great detail from switches and routers into data processing centers and use them for trend-related analysis. In most cases, not all detail history can be accumulated and stored in online databases; often past data is archived and access to it is very expensive. Hence, it is highly desirable to have an approximate, but reasonably accurate, representation of the data stream that can be stored in a small amount of space. However, unlike typical selectivity estimation scenarios where such summary data structures are used, it is not realistic to make several passes over the data in the streaming setting. It is crucial that the summary representation be computed on the stream directly, i.e., in one pass.. Consider the following application scenario that arises in telecommunications network monitoring. Switches in telecommunications networks handle a tremendous number of connections every minute. Typically, for each call it handles, a switch generates a record (known as a Call Detail Record or CDR). These get written when calls complete and, when buffers get full, switches dump them into a central or distributed data processing facility. Eventually, these records flow through the system and get channeled into centers for billing, network operations, etc. However, for many mission-critical tasks such as fraud, security, and performance monitoring, telecommunications companies need rapid access to the CDRs to perform trendrelated analysis such as: What is the total number of outgoing calls from a telephone number? What is the total traffic at an npa-nxx (the first six digits of a telephone number) in the past two hours? Is the outgoing calling pattern of a telephone number unusual? Can a signature be maintained of user profiles? All of these queries need to be answered on the stream since trend analyses are urgent (the sooner a fraud is detected, the sooner it gets stopped). Similar issues arise in monitoring Internet network elements such as routers and Web servers where traffic is potentially far more voluminous.. The need for processing data streams is beginning to be understood and, consequently, there is effort underway in the data mining [11] , database, and algorithms communities to address the outstanding problems that arise. Within the database community, it is understood that "...Today's database systems and data processing algorithms (e.g., data mining) are ill-equipped to handle data streams effectively, and many aspects of data management and processing need to be reconsidered in the presence of data streams.". 1 In this paper, we address a fundamental problem that arises in data streaming scenarios, namely, to what extent can the data streams be summarized in a small amount of space so that accurate estimates can be provided for basic aggregate queries on the underlying signal. While small space data summarization has been studied in the database community recently, data streaming applications present novel issues, chiefly, first, the ability to summarize accurately the signal in one pass, rather than over multiple passes and, second, the massive scale of the updates to the underlying signal over time.. In Section 2, we discuss related work, while in Section 3 we present different data models and formats for data stream applications. In Section 4, we provide the necessary background on wavelet computations. In Section 5, we address some of the theoretical issues in designing algorithms for wavelet computations in data streams. In Section 6, we present our approach, together with provable results and address the implementation issues that arise in our sketch-based methods. In Section 7, we present experiments with real data, while in Section 8 we present concluding remarks. Streaming or one-pass algorithms have been studied in different areas. In algorithms, streaming models have been studied in [3] , [13] , [14] , [25] , [24] , where methods have been developed for comparing data streams under various L p distances or clustering them. Within the database community, one-pass algorithms have been designed for obtaining median, quantiles, and other order statistics [1] , [30] , [19] , correlated aggregate queries [16] , mining [15] , [9] , etc.. Recently, there is an effort to study the general principles behind continuous queries over data streams in the database community (e.g., [4] , [29] ); this is different from our approach here of supporting ad hoc estimates over the distribution. The problem of summarizing a data stream to provide point and range estimates was first considered in the conference version of this article [22] . Dobra et al. [10] build on the idea of using sketches to answer complex multijoin aggregate queries over multiple data streams. A sketch-based architecture for collecting and processing distributed network measurements is discussed in [20] .. Many techniques have been devised in databases for small space approximations in the context of selectivity estimation: sampling techniques [23] , [35] , histograms [34] , wavelet methods [31] , [5] , etc. Much of this work is for static data sets and they do not provide strict performance guarantees in a streaming scenario. Sampling methods do work for the dynamic case when input is read over time, but they do not directly yield any performance bounds for linear projections that generate wavelet coefficients. Randomized algorithms have been studied in [18] for dynamically maintaining V -Opt histograms and in [26] for multidimensional histogram maintenance.. Recently, the problem of maintaining wavelet transforms as data dynamically changes was considered in [32] ; in contrast to the problem of maintaining traditional histograms, maintaining wavelet transforms requires tracking significant wavelet coefficients over time, a nontrivial task as the authors argue. When a data item changes in value, many coefficients may get affected and the set of significant coefficients could change rather dramatically (as is revealed from our experiments). Conceptually, maintaining the set of significant transform values is somewhat similar to the problem of maintaining bestseller items where the goal is to maintain the top-k selling items as sales continue, but could be significantly harder depending upon the transformation. The main difficulty in the hot lists (a special case of what is known as iceberg queries [12] ) is in detecting which infrequent values become significantly frequent as data items accumulate, using small amount of space. The authors in [27] propose maintaining a fixed set of transform coefficients over time. The authors in [32] propose a sophisticated probabilistic counting technique. In either case, no provable results are known on how effective these methods are in tracking the significant coefficients.. In addition to the wavelet-based methods, the authors in [27] attempted to maintain the significant Discrete Cosine transform values over time. In [17] , nonadaptive sampling is used for finding a small-space Fourier representation, such that the sum-squares-error of the representation is within the factor ð1 þ Þ of best possible error. For the experiments, we used traces from AT&T's call detail data for a period of one week. The data set describes a certain type of long-distance calls, aggregated at the npanxx level. The stream is in the unordered cash-register format and contains 511,033,795 values. The npa-nxx value corresponds to the originating number. We present an analysis of the batch method of answering queries (including several heuristics presented in the previous section) and a comparison of the online methods (both direct point and wavelet estimates). We further explore the improvements we obtain by using adaptive greedy pursuit.

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


Task mapping and priority assignment for soft real-time applications under deadline miss ratio constraints Both analysis and design optimisation of real-time systems has predominantly concentrated on considering hard real-time constraints. For a large class of applications, however, this is both unrealistic and leads to unnecessarily expensive implementations. This paper addresses the problem of task priority assignment and task mapping in the context of multiprocessor applications with stochastic execution times and in the presence of constraints on the percentage of missed deadlines. We propose a design space exploration strategy together with a fast method for system performance analysis. Experiments emphasize the efficiency of the proposed analysis method and optimisation heuristic in generating high-quality implementations of soft real-time systems with stochastic task execution times and constraints on deadline miss ratios. Manolache, S., Eles, P., and Peng, Z. 2008. Task mapping and priority assignment for soft realtime applications under deadline miss ratio constraints. For the large majority of applications, if not all, the task execution times are not fixed, but vary from one activation of the task to the other. This variability may be caused by application-dependent factors (data-dependent loops and branches) [Hughes et al. 2001] , architectural factors (unpredictable cache Authors' addresses: Sorin Manolache, Petru Eles, and Zebo Peng, Linköping University, Sweden. Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or direct commercial advantage and that copies show this notice on the first page or initial screen of a display along with the full citation. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, to redistribute to lists, or to use any component of this work in other works requires prior specific permission and/or a fee. Permissions may be requested from Publications Dept., ACM, Inc., 2 Penn Plaza, Suite 701, New York, NY 10121-0701 USA, fax +1 (212) 869-0481, or permissions@acm.org. and pipeline behavior, dynamic branch predictors), or environment-dependent factors (network load, for example). In the case of safety-critical applications (avionics, automotive, medicine, and nuclear plant control systems), the designers have to deal with the worst-case scenario, in particular, with worst-case task execution times (WCET). An impressive amount of research results, both for analyzing and designing these systems has been published [Buttazzo 1997 ].. Designing the system based on the worst-case execution times (WCET) guarantees that no timing requirement is broken. However, for large classes of applications, the soft real-time systems, breaking a timing requirement, though not desirable, is tolerated provided that this happens with a sufficiently low probability. Typical applications are, for example, telecommunications, multimedia applications like MPEG and JPEG, and audio encoding. Thus, for example, Ng et al. report that 1-4 B-frames out of a group-of-pictures (a group of 12 frames ordered as IBBPBBPBBPBB, where I, B, and P are frame types defined by the MPEG standard) may be lost in an MPEG decoding without compromising the required QoS [Ng et al. 2002] . While in the case of safety critical systems, the designers stress safety at the expense of product cost, in the case of soft real-time systems, cost reduction can be a strong incentive for using cheap architectures.. While in hard real-time analysis the tasks are assumed to execute for the amount of time that leads to the worst-case scenario, in soft real-time analysis task execution time probability distributions are preferred in order to be able to determine execution time combinations and their likelihoods. These distributions can be extracted from performance models [van Gemund 1996] by means of analytic methods or simulation, and profiling [van Gemund 2003b; Gautama and van Gemund 2000; Gautama 1998 ]. Obviously, the worst-case task execution time model is a particular case of such a stochastic one.. Let us consider a cheap processor and a task that runs on it. The probability density function of the task execution time (ETPDF) on the cheap processor is depicted in Figure 1a . If the imposed deadline of the task is t, as shown in the figure, then the cheap processor cannot guarantee that the task will always meet its deadline, as the WCET of the task exceeds the deadline. If no deadline misses were tolerated, a faster and more expensive processor would be needed. The ETPDF of the task on the faster processor is depicted in Figure 1b . In this case, the more expensive processor guarantees that no deadlines are missed. However, if a miss deadline ratio of, at most, 15% is tolerated, then even the cheaper processor would suffice. The problem of finding the deadline miss ratios, given a hardware platform and an application, is not trivial and has attracted relatively recent research work both for mono [Tia et al. 1995; Lehoczky 1996; Sun et al. 1997; Zhou et al. 1999; Gardner 1999; Gardner and Liu 1999; Hu et al. 2001; Manolache et al. 2001 Manolache et al. , 2004b Díaz et al. 2002; Burns et al. 2003 ] and for multiprocessor systems [Lehoczky 1997; Kalavade and Moghé 1998; Nissanke et al. 2002; Manolache et al. 2002 Manolache et al. , 2004a van Gemund 2003a] .. This work addresses the complementary problem: given a multiprocessor hardware architecture and a functionality as a set of task graphs, find a task mapping and priority assignment such that the deadline miss ratios satisfy imposed constraints.. A naïve approach to this problem would be to optimize the system based on fixed execution time models (average, median, worst case execution time, etc.) and to hope that the resulting designs would be optimal or close to optimal from the point of view of the percentage of missed deadlines. The following example illustrates the pitfalls of such an approach and emphasizes the need for an optimisation technique, which considers the stochastic execution times. Let us consider the application in Figure 2a . The circles denote the tasks and their shades denote the processors they are mapped onto. The marked edges show the interprocessor communication. The arrows between the tasks indicate their data dependencies. All the tasks have period 20 and the deadline of the task graph is 18. Tasks t 1 , t 2 , t 3 , and t 4 have constant execution times of 1, 6, 7, and 8, respectively. Task t 5 has a variable execution time whose probability is uniformly distributed between 0 and 12. Hence, the average (expected) execution time of task t 5 is 6. The interprocessor communication takes 1 time unit per message. Let us consider the two mapping alternatives depicted in Figure 2a and 2b, respectively. The two Gantt diagrams in Figure 3a and 3b depict the execution scenarios corresponding to the two considered mappings if the execution of task t 5 took the expected amount of time, that is 6. The shaded rectangles depict the probabilistic execution of t 5 . A mapping strategy based on the average execution times would select the mapping in Figure 2a as it leads to a shorter response time (15 compared to 17). However, in this case, the worst-case execution time of the task graph is 21. The deadline miss ratio of the task graph is 3/12 = 25%. If we took into consideration the stochastic nature of the execution time of task t 5 , we would prefer the second mapping alternative, because of the better deadline miss ratio of 1/12 = 8.33%. If we considered worst-case response times, instead of average ones, then we would chose the second mapping alternative, the same as the stochastic approach. However, approaches based on worst-case execution times can be dismissed by means of very simple counterexamples. Let us consider a task τ , which can be mapped on processor P 1 , or on processor P 2 . P 1 is a fast processor with a very deep pipeline. Because of its pipeline depth, mispredictions of target addresses of conditional jumps, though rare, are severely penalized. If τ is mapped on P 1 , its ETPDF is shown in Figure 4a . The long and flat density tail corresponds to the rare, but expensive, jump target address misprediction. If τ is mapped on processor P 2 , its ETPDF is shown in Figure 4b . Processor P 2 is slower with a shorter pipeline. The WCET of task τ on processor P 2 is smaller than the WCET if τ ran on processor P 1 . Therefore, a design space exploration tool based on the WCET would map task τ on P 2 . However, as Figure 4 shows, the deadline miss ratio in this case is larger than if task τ was mapped on processor P 1 .. The remainder of the paper is structured as follows. The next section presents some of the related work in the area and underlines our contribution. Section 3 introduces our system model and gives the problem formulation. Section 4 presents the design space exploration strategy detailing the neighborhood restriction heuristic. Section 5 describes the fast approximate method for system analysis. Section 6 presents a set of experiments we conducted in order to evaluate and demonstrate the efficiency of the proposed heuristic. Finally, Section 7 draws conclusions. In this paper, we addressed the problem of design optimization of soft realtime systems with stochastic task execution times under deadline miss ratio constraints. The contribution is threefold. First, we have shown that methods considering fixed execution time models are unsuited for this problem. Second, we presented a design space exploration strategy based on tabu search for task mapping and priority assignment. Third, we introduced a fast and approximate analysis for guiding the design space exploration. Experiments demonstrated the efficiency of the proposed approach. This section presents our analysis algorithm that is used for evaluation of the cost function that is driving the design space exploration. The first part of the section discusses the deduction of the algorithm itself, while the second part presents some considerations on the approximations that were made and their impact regarding the accuracy.

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


Articulated mesh animation from multi-view silhouettes The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters.Details in mesh animations are difficult to generate but they have great impact on visual quality. In this work, we demonstrate a practical software system for capturing such details from multi-view video recordings. Given a stream of synchronized video images that record a human performance from multiple viewpoints and an articulated template of the performer, our system captures the motion of both the skeleton and the shape. The output mesh animation is enhanced with the details observed in the image silhouettes. For example, a performance in casual loose-fitting clothes will generate mesh animations with flowing garment motions. We accomplish this with a fast pose tracking method followed by nonrigid deformation of the template to fit the silhouettes. The entire process takes less than sixteen seconds per frame and requires no markers or texture cues. Captured meshes are in full correspondence making them readily usable for editing operations including texturing, deformation transfer, and deformation model learning. Meshes are most often animated by hand using keyframing and procedural deformations. Adding detail with this approach is tedious because it requires setting more than a hundred parameters. As a result, most animated characters appear to wear skin-tight garments that move stiffly without flowing. Procedural approaches that take physics into account can generate these details with more ease and efficiency but they are difficult to control when the goal is to match a particular motion or performance.. In this paper, we pursue a complementary direction to create detailed mesh animations through observation rather than simulation. Motion capture of moving meshes provides an alternative to efficient generation of detailed animations. The potential value of this approach is readily apparent in the success of motion capture for skeletal animation. There, observed motions of the skeleton are edited, transformed, interpolated, and recomposed to produce new high-quality animations. The relative simplicity of that approach has already taken root in the film industry where recorded motions are often used instead of more traditional animation techniques. What current motion capture lacks, however, is the ability to efficiently acquire both the internal skeleton and the external shape. A multi-view studio provides a set of synchronized high-definition silhouette videos by recording a performance from several angles using multiple calibrated cameras. Our software pipeline, shown in Figure 3 , also uses a template mesh rigged with a skeleton that matches the physical dimensions of the performer: the skeleton is positioned within the template mesh and each vertex is assigned a weight that is used to deform the template with linear blend skinning (LBS). Our software outputs a sequence of joint configurations and vertex positions to represent the pose and shape of the performer in every frame of the multi-view sequence.. The software pipeline proceeds in two stages: skeleton tracking Silhouettes Template Visual Hull LBS Shape Estimate Edits Figure 3 : From left to right, our system starts with a stream of silhouette videos and a rigged template mesh. At every frame, it fits the skeleton to the visual hull, deforms the template using linear blend skinning (LBS), and adjusts the deformed template to fit the silhouettes. The user can then easily edit the geometry or texture of the entire motion.. and surface refinement. In the first stage (Section 2), the system optimizes the fit of the skeleton to the visual hull at each time step.. The system tracks most simple motions automatically, but may fail on very complex motions. In such cases an easy manual intervention can be used to correct the skeleton. In the second stage (Section 3), our system deforms the template according to the skeleton and adjusts its surface to better match the silhouettes. Our approach demonstrates that by taking advantage of geometric information in the silhouettes, we can obtain detailed mesh animations with full correspondence and correct topology. The output mesh animations are suitable for editing with methods such as texturing and deformation transfer. The key insight is to use skeletal pose estimation for gross deformation followed by iterative nonrigid shape matching to fit the image data. Moreover, an interactive mechanism for correcting occasional pose estimation mistakes allowed us to obtain high-quality tracking of complex sequences with little effort. Our results show that silhouettes alone can convey rich and complex visual details despite inaccuracies away from the contours.. Because our method only relies on silhouettes, it is completely immune to color noise, lighting, and color calibration problems. However, this reliance leads to two limitations. First, our method cannot reproduce the surface accurately away from the contours: it has to rely on the template to interpolate geometric information. This is especially problematic for unarticulated objects such as long scarves, faces, or flowing hair. Using color information in a manner that does not sacrifice robustness would improve their reconstruction. Second, our method is sensitive to errors in the silhouettes, and will produce incorrect geometry when visual hulls are noisy. However, this is not a serious problem in a studio setting where chroma-keying methods can be used to obtain clean silhouettes.. We found that the quality of the output animation strongly depends on the quality of the template. While a space-carved template can convey the character of the motion convincingly, the final appearance is much better for templates with accurate and highresolution detail, such as those obtained with a laser scanner. Additionally, pose estimation is sensitive to the accuracy of the template skeleton proportions and degrees of freedom. Fine-tuning the skeleton is currently a manual task, but it may be possible to extract an improved skeleton automatically from our output sequences and use it to improve tracking of the same performer.. Another issue we have not completely addressed is texture sliding, which is still occasionally visible despite bilateral filtering. We believe that this problem traces back to temporally inconsistent ray constraints used in shape estimation. A possible remedy is to permit motions of a constrained point within the tangent plane of the silhouette cone. This would allow more natural configurations of the mesh and the resulting optimization procedure would still be efficient to solve.. An interesting application of our results would be to learn a model of shape motion that takes clothing and dynamics into account. Such a model could simplify mesh animation from skeletal motion capture data and retain the details acquired during performance. Another possible future direction would be to provide an interface to edit and clean up the output mesh sequences, similar to our user interface for pose correction. Standard mesh editing techniques are not well suited for this purpose because they do not account for temporal consistency. An integrated mesh-editing framework could take advantage of the video data to assist the user and improve reconstruction.. Because future research can greatly benefit from a large volume of data, we have built a studio that will enable us to capture more performances, including multiple people interacting, animals, and props. We hope that we can support further improvement of mesh capture and processing techniques by acquiring a large data set and sharing it with other researchers. We tested our method on eleven sequences with five subjects captured in two different studios. The accompanying video demonstrates the ability of our method to produce meshes that capture fine motion details for very fast and challenging motions. Figure 8 shows reconstructed shapes from five of these sequences. We evaluate our algorithm according to several criteria: computation efficiency, the amount of user interaction needed, and robustness to parameter changes. We demonstrate the utility of our resulting meshes by applying a static texture and a geometric deformation to some sequences. Traditional motion capture estimates skeleton motion using information from markers or sensors on the body. While these systems are accurate, they still require manual adjustments to clean up recorded data. Furthermore, recording requires skin-tight garments to ensure that markers move rigidly with the corresponding limb. Markerless motion capture addresses these limitations by estimating pose directly from multi-view video [Ménier et al. 2006; Cheung et al. 2005; Theobalt et al. 2002; de Aguiar et al. 2004 ]. However, these methods are less reliable when limbs are not clearly distinguishable (e.g., when arms are close to the body). Manual clean-up is often necessary, but the above methods do not discuss ways to assist in this process.. Pose estimation does not capture the fine detail on the surface of the shape. Richer templates with more degrees of freedom can capture time-varying geometric detail better. Sand et al. [2003] capture some of those effects with silhouette-bounded needles radiating from each bone, without maintaining frame-to-frame correspondence. Park and Hodgins [2006] improve on these results to record detailed bulging and jiggling using a traditional motioncapture system with many markers. Other researchers have shown how to design patterns that can be printed on clothing to enable highly detailed estimation of garment motion [Scholz et al. 2005; White et al. 2007 ]. Markers, either attached or printed, make it less convenient to record arbitrary human performances in casual clothing. Purely vision-based techniques rely on texture cues to track motion of a few carefully selected points [de Aguiar et al. 2007b; de Aguiar et al. 2007a ]. These approaches are not as reliable on fast motions, especially when there are few textures cues (e.g., pants in Figure 1 ).. The multi-view stereo literature provides a powerful collection of tools for recovering a single static mesh [Seitz et al. 2006 ]. Some of the best methods produce extremely accurate results but they are computationally expensive, requiring an hour of computation or more for a single frame [Hornung and Kobbelt 2006; Furukawa and Ponce 2006; Esteban and Schmitt 2004] . Faster carving methods sacrifice quality but capture meshes at speeds more practical for processing video streams [Rander et al. 1997; Starck and Hilton 2007; Goldlücke et al. 2007 ]. These methods do not make assumptions about the observed deformations and geometry, allowing them to capture arbitrary deforming surfaces, not just articulated characters. They, however, do not always reconstruct the Template-based Static carving topology correctly and produce uncorresponded results ( Figure 2 ). Our approach is much faster and it generates mesh animations with frame-to-frame vertex correspondence. Our approach maintains correspondence by matching a single mesh template to every frame in the sequence. Using a template mesh leads to faster algorithms and allows interpolation of regions where data is unavailable. Articulated templates are often used to improve pose tracking, but they do not deform to capture details in the video [Carranza et al. 2003; Theobalt et al. 2007; Cheung et al. 2005; Anguelov et al. 2005; Corazza et al. 2006; Balan et al. 2007] . A template based on implicit surfaces [Plänkers and Fua 2001] can capture time-varying detail, but does not produce corresponded meshes. To learn a skinning model, Allen et al. [2002] obtain corresponded shapes for different poses by matching a subdivision surface template to range data.. Our processing pipeline is most similar to the work of de Aguiar and colleagues [2005] who also estimate the skeleton configuration before deforming the template mesh to match the data. Both approaches use Laplacian coordinates to preserve mesh detail while satisfying silhouette constraints (their method also uses texture constraints). A critical difference is that they sample the mesh and drive the samples towards the visual hull, while we sample the contours and pull only the closest mesh points to our samples. Because most of the correct surface is not on the visual hull, their method tends to distort the shape and needs strong regularization as well as reliable texture cues. In contrast, we only pull those vertices to the visual hull that are likely to be on it and can therefore match the contours more closely. Hence, our method performs significantly better on images with poor texture cues and strong silhouette cues. Additionally, our method is over an order of magnitude faster, which allowed us to develop an interactive user interface to assist pose correction. These differences enable us to capture mesh animations even for fast and complex human motions. We have data sets from two different sources. In both cases the setup consists of a ring of eight cameras looking down at the performer. The first data set was provided by Starck and Hilton [2007] . Their video streams are recorded at 25 FPS at 1920 by 1080 pixel resolution. The second source was our studio where we capture video at 1600 by 1200 resolution also at 25 FPS. We calibrated our cameras using an LED and software by Svoboda et al. [2005] . The template mesh may be obtained by various means, such as 3D scanning [Levoy et al. 2000 ], static multi-view stereo of a single frame [Seitz et al. 2006 ], or manual modeling (as in [Park and Hodgins 2006] ). For the Starck and Hilton data set, we use a good frame obtained by their multi-view stereo method [2007] as the template. For our data sets we use a 3D scan of the performer (see Figure 8 ) obtained with a Cyberware scanner. Each template mesh was decimated to 10,000 vertices.. We manually built 40-DOF skeletons to fit the dimensions of each performer and embedded them within the template meshes (Figure 3, left) . We attached each mesh to its skeleton with linear blend skinning using weights generated with Pinocchio [ Baran and Popović 2007] .

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 B 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 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 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 O O O O O O O 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 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 B 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 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


A lack-of-fit test for quantile regression models with high-dimensional covariates We propose a new lack-of-fit test for quantile regression models that is suitable even with high-dimensional covariates. The test is based on the cumulative sum of residuals with respect to unidimensional linear projections of the covariates. The test adapts concepts proposed by Escanciano (Econometric Theory, 22, 2006) to cope with many covariates to the test proposed by He and Zhu (Journal of the American Statistical Association, 98, 2003). To approximate the critical values of the test, a wild bootstrap mechanism is used, similar to that proposed by Feng et al. (Biometrika, 98, 2011). An extensive simulation study was undertaken that shows the good performance of the new test, particularly when the dimension of the covariate is high. The test can also be applied and performs well under heteroscedastic regression models. The test is illustrated with real data about the economic growth of 161 countries. Let us consider a regression setting where a quantile of the response variable of interest, Y , is expressed as a function of a vector of explanatory variables, X. The resulting regression model can then be denoted by Y = g(X) + ε where g represents the quantile regression function; and the error, ε, has a conditional τ -quantile equal to zero, P (ε < 0|X = x) = τ for almost all x. Quantile regression models have been receiving increased attention in the literature, due to their flexibility for general error distributions and because they provide a more detailed description of the conditional distribution of the response, compared to classical mean regression. Koenker and Bassett (1978) can be considered as the seminal work on the estimation of linear quantile regression models. The main concept is to exploit that the τ -quantile, g, of a variable minimizes the expectation,. where ρ τ (r) = τ rI(r > 0) + (τ − 1)rI(r < 0), and I(·) denotes the indicator function of an event. Estimation of quantile models is obtained by minimizing the sum of penalized residuals, similarly to the sum of squares in the case of mean regression. That is, given a sample of independent observations, (X 1 , Y 1 ), . . . , (X n , Y n ), the coefficients of a linear model, g(x) = x θ (x denotes the transpose of x), are estimated as the minimizers of. The same criterion can be applied to estimate general parametric models, where the regression function is of the type g(·, θ) and θ is a parameter to be estimated, and even to nonparametric estimation of the quantile regression function. See Koenker (2005) for a complete review on quantile regression methods.. We focus on the problem of testing a parametric model of quantile regression. That is, a test of the null hypothesis. versus a nonparametric alternative. This problem was addressed by He and Zhu (2003) , who based their test on the process. where ψ(r) = τ I(r > 0) + (τ − 1)I(r < 0) is the derivative of ρ τ ,ġ(x, θ) = ∂ ∂θ g(x, θ), and θ is an estimator of θ. This is an extension to the quantile regression setting of the cumsum process considered by Stute (1997) in the mean regression setting. Zheng (1998) proposed a U-statistic of the quantities ψ(Y i − g(X i , θ)) with smoothing kernel weights, thereby extending the test of Zheng (1996) to quantile models. Other specification tests for quantile regression models can be found in Horowitz and Spokoiny (2002) , Whang (2006) , Otsu (2008) , Escanciano and Velasco (2010) , and Escanciano and Goh (2014) , among others.. It is well-known that a high (or even moderate) dimension of the covariate can affect the performance of the specification tests. This problem has been addressed by several authors in the mean regression setting, where modified tests have been proposed with better properties for multiple covariates. In particular, Escanciano (2006) applied a cumsum test to one-dimensional projections of the covariates, Lavergne and Patilea (2008) considered similar one-dimensional projections for a Zheng type test, and Stute et al. (2008) based their test on the residual empirical process marked by proper functions of the regressors.. Little can be found in the literature for lack-of-fit testing adapted to multidimensional covariates in the framework of quantile regression. Wilcox (2008) used a He and Zhu type test and defined some ranks over the covariate. This proposal has the virtue of simplicity but does not provide an omnibus test, i.e., it is not consistent for all alternatives.. We propose and study a lack-of-fit test for parametric models of quantile regression, with good properties for multidimensional covariates and consistent for all alternatives. In Section 2 we present the new He and Zhu type test calculated on one-dimensional projections of the covariates. A bootstrap method is also proposed to approximate the critical values of the test. Section 3 contains a simulation study where the performance of the test is studied under homoand heteroscedastic models, with different error distributions and with increasing dimension of the covariate. We compare the proposed test with a He and Zhu test. In Section 4 the test is applied to real data, and we provide some concluding remarks and extensions in Section 5.. 2 The proposed method

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