Atomic Congestion Games: Fast, Myopic and Concurrent

We study here the effect of concurrent greedy moves of players in atomic congestion games where n selfish agents (players) wish to select a resource each (out of m resources) so that her selfish delay there is not much. The problem of “maintaining” global progress while allowing concurrent play is exactly what is examined and answered here. We examine two orthogonal settings: (i) A game where the players decide their moves without global information, each acting “freely” by sampling resources randomly and locally deciding to migrate (if the new resource is better) via a random experiment. Here, the resources can have quite arbitrary latency that is load dependent. (ii) An “organised” setting where the players are pre-partitioned into selfish groups (coalitions) and where each coalition does an improving coalitional move. Our work considers concurrent selfish play for arbitrary latencies for the first time. Also, this is the first time where fast coalitional convergence to an approximate equilibrium is shown.     

Weak Updates and Separation Logic

Separation logic provides a simple but powerful technique for reasoning about low-level imperative programs that use shared data structures. Unfortunately, separation logic supports only “strong updates,” in which mutation to a heap location is safe only if a unique reference is owned. This limits the applicability of separation logic when reasoning about the interaction between many high-level languages (e.g., ML, Java, C#) and low-level ones since the high-level languages do not support strong updates. Instead, they adopt the discipline of “weak updates,” in which there is a global “heap type” to enforce the invariant of type-preserving heap updates. We present SL ^w , a logic that extends separation logic with reference types and elegantly reasons about the interaction between strong and weak updates. We describe a semantic framework for reference types, which is used to prove the soundness of SL ^w . Finally, we show how to extend SL ^w with concurrency.     

Generic prognosis model for proactive maintenance decision support: application to pre-industrial e-maintenance test bed

Proactivity in maintenance, which is mainly materialized by degradation-based anticipation, becomes essential to avoid failure situation with negative impact on product and/or system conditions. It leads to make emerging the E-maintenance philosophy to move from “fail and fix” maintenance practices to “predict and prevent” strategies. Within these new strategies, the anticipation action is fully supported by prognosis business process. Indeed it analyses the degradation impact on the component itself but also on the global performances of the production system in order to predict future failures of the system and investigate (future maintenance) actions. However, only few research works focuses on generic and scalable prognostic approach. Existing methods are generally restricted on component view and for solving the failure prediction issue. Consequently, the contribution presented in this paper aims at developing a global formalization of the generic prognosis business process. This generic process can be used after, from an instantiation procedure, to develop specific prognosis processes related to particular application such as shown in this paper with the case of E-maintenance platform developed within DYNAMITE Project.     

Facial expression recognition of a speaker using front-view face judgment, vowel judgment, and thermal image processing

For facial expression recognition, we selected three images: (i) just before speaking, (ii) speaking the first vowel, and (iii) speaking the last vowel in an utterance. In this study, as a pre-processing module, we added a judgment function to distinguish a front-view face for facial expression recognition. A frame of the front-view face in a dynamic image is selected by estimating the face direction. The judgment function measures four feature parameters using thermal image processing, and selects the thermal images that have all the values of the feature parameters within limited ranges which were decided on the basis of training thermal images of front-view faces. As an initial investigation, we adopted the utterance of the Japanese name “Taro,” which is semantically neutral. The mean judgment accuracy of the front-view face was 99.5% for six subjects who changed their face direction freely. Using the proposed method, the facial expressions of six subjects were distinguishable with 84.0% accuracy when they exhibited one of the intentional facial expressions of “angry,” “happy,” “neutral,” “sad,” and “surprised.” We expect the proposed method to be applicable for recognizing facial expressions in daily conversation.     

Handling Communication Restrictions and Team Formation in Congestion Games

There are many domains in which a multi-agent system needs to maximize a “system utility” function which rates the performance of the entire system, while subject to communication restrictions among the agents. Such communication restrictions make it difficult for agents that take actions to optimize their own “private” utilities to also help optimize the system utility. In this article we show how previously introduced utilities that promote coordination among agents can be modified to be effective in domains with communication restrictions. The modified utilities provide performance improvements of up to 75 over previously used utilities in congestion games (i.e., games where the system utility depends solely on the number of agents choosing a particular action). In addition, we show that in the presence of severe communication restrictions, team formation for the purpose of information sharing among agents leads to an additional 25 improvement in system utility. Finally, we show that agents’ private utilities and team sizes can be manipulated to form the best compromise between how “aligned” an agent’s utility is with the system utility and how easily an agent can learn that utility.     

Physical Limits on Self-Replication Processes

Using few very general axioms which should be satisfied by any reasonable theory consistent with the Second Law of Thermodynamics we argue that: a) “no-cloning theorem” is meaningful for a very general theoretical scheme including both quantum and classical models, b) in order to describe self-replication, Wigner’s “cloning” process should be replaced by a more general “broadcasting”, c) “separation of species” is possible only in a non-homogeneous environment, d) “parent” and “offspring” must be strongly correlated. Motivated by the existing results on broadcasting which show that only classical information can self-replicate perfectly we discuss briefly a classical toy model with “quantum features” — overlapping pure states and “entangled states” for composite systems.     

Coach planning with opponent models for distributed execution

In multi-agent domains, the generation and coordinated execution of plans in the presence of adversaries is a significant challenge. In our research, a special “coach” agent works with a team of distributed agents. The coach has a global view of the world, but has no actions other than occasionally communicating with the team over a limited bandwidth channel. Our coach is given a set of predefined opponent models which predict future states of the world caused by the opponents’ actions. The coach observes the world state changes resulting from the execution of its team and opponents and selects the best matched opponent model based on its observations. The coach uses the recognized opponent model to predict the behavior of the opponent. Upon opportunities to communicate, the coach generates a plan for the team, using the predictions of the opponent model. The centralized coach generates a plan for distributed execution. We introduce (i) the probabilistic representation and recognition algorithm for the opponent models; (ii) a multi-agent plan representation, Multi-Agent Simple Temporal Networks; and (iii) a plan execution algorithm that allows the robust distributed execution in the presence of noisy perception and actions. The complete approach is implemented in a complex simulated robot soccer environment. We present the contributions as developed in this domain, carefully highlighting their generality along with a series of experiments validating the effectiveness of our coach approach.     

Coordination in hospitals: organized or emergent process?

Hospitals have become more and more complex organizations that require increasing degrees of vertical, lateral and longitudinal coordination among their staff. As organizations, hospitals positively organize the coordination between the activities of its different agents, as well as the associated communication between them. The overall goal is to construct a “common ground” between the agents about the work process. In order to achieve this, a series of management tools are called upon. However these coordination mechanisms may fail. In the case analyzed, the agents seem to organize their behavior through direct and local individual interactions with their work environment, rather than through a global representation of the work. The case study demonstrates that intentionally organized coordination mechanisms interact with, and may be superseded by, the “emergence-through use” of coordination mechanisms in real time. These two mechanisms are clearly embedded at work, and can both be beneficial in promoting coordination in large scale systems.     

Facial expression recognition of a speaker using vowel judgment and thermal image processing

We have previously developed a method for the recognition of the facial expression of a speaker. For facial expression recognition, we previously selected three images: (i) just before speaking, (ii) speaking the first vowel, and (iii) speaking the last vowel in an utterance. By using the speech recognition system named Julius, thermal static images are saved at the timed positions of just before speaking, and when just speaking the phonemes of the first and last vowels. To implement our method, we recorded three subjects who spoke 25 Japanese first names which provided all combinations of the first and last vowels. These recordings were used to prepare first the training data and then the test data. Julius sometimes makes a mistake in recognizing the first and/or last vowel (s). For example, /a/ for the first vowel is sometimes misrecognized as /i/. In the training data, we corrected this misrecognition. However, the correction cannot be carried out in the test data. In the implementation of our method, the facial expressions of the three subjects were distinguished with a mean accuracy of 79.8% when they exhibited one of the intentional facial expressions of “angry,” “happy,” “neutral,” “sad,” and “surprised.” The mean accuracy of the speech recognition of vowels by Julius was 84.1%.     

Foundations of distributed interaction systems

There are numerous applications where a variety of human and software participants interactively pursue a given task (play a game, engage in a simulation, etc.). In this paper, we define a basic architecture for a distributed, interactive system (DIS for short). We then formally define a mathematical construct called a DIS abstraction that provides a theoretical basis for a software platform for building distributed interactive systems. Our framework provides a language for building multiagent applications where each agent has its own behaviors and where the behavior of the multiagent application as a whole is governed by one or more “master” agents. Agents in such a multiagent application may compete for resources, may attempt to take actions based on incorrect beliefs, may attempt to take actions that conflict with actions being concurrently attempted by other agents, and so on. Master agents mediate such conflicts. Our language for building agents (ordinary and master) depends critically on a notion called a “generalized constraint” that we define. All agents attempt to optimize an objective function while satisfying such generalized constraints that the agent is bound to preserve. We develop several algorithms to determine how an agent satisfies its generalized constraints in response to events in the multiagent application. We experimentally evaluate these algorithms in an attempt to understand their advantages and disadvantages. This revised version was published online in June 2006 with corrections to the Cover Date.     

Matters of (Meta-) Modeling

With the recent trend to model driven engineering a common understanding of basic notions such as “model” and “metamodel” becomes a pivotal issue. Even though these notions have been in widespread use for quite a while, there is still little consensus about when exactly it is appropriate to use them. The aim of this article is to start establishing a consensus about generally acceptable terminology. Its main contributions are the distinction between two fundamentally different kinds of model roles, i.e. “token model” versus “type model” (The terms “type” and “token” have been introduced by C.S. Peirce, 1839–1914.), a formal notion of “metaness”, and the consideration of “generalization” as yet another basic relationship between models. In particular, the recognition of the fundamental difference between the above mentioned two kinds of model roles is crucial in order to enable communication among the model driven engineering community that is free of both unnoticed misunderstandings and unnecessary disagreement.     

Comparison of human face matching behavior and computational image similarity measure

Computational similarity measures have been evaluated in a variety of ways, but few of the validated computational measures are based on a high-level, cognitive criterion of objective similarity. In this paper, we evaluate two popular objective similarity measures by comparing them with face matching performance in human observers. The results suggest that these measures are still limited in predicting human behavior, especially in rejection behavior, but objective measure taking advantage of global and local face characteristics may improve the prediction. It is also suggested that human may set different criterions for “hit” and “rejection” and this may provide implications for biologically-inspired computational systems. Supported by the National Basic Research Program of China (Grant No. 2006CB303101), the National Natural Science Foundation of China (Grant Nos. 60433030, 30600182 and 30500157), and the Royal Society     

Detecting global predicates in distributed systems with clocks

Summary. This paper proposes a framework for detecting global state predicates in systems of processes with approximately-synchronized real-time clocks. Timestamps from these clocks are used to define two orderings on events: “definitely occurred before” and “possibly occurred before”. These orderings lead naturally to definitions of 3 distinct detection modalities, i.e., 3 meanings of “predicate held during a computation”, namely: (“ possibly held”), (“ definitely held”), and (“ definitely held in a specific global state”). This paper defines these modalities and gives efficient algorithms for detecting them. The algorithms are based on algorithms of Garg and Waldecker, Alagar and Venkatesan, Cooper and Marzullo, and Fromentin and Raynal. Complexity analysis shows that under reasonable assumptions, these real-time-clock-based detection algorithms are less expensive than detection algorithms based on Lamport's happened-before ordering. Sample applications are given to illustrate the benefits of this approach. Received: January 1999 / Accepted: November 1999     

Black hole masking and black hole thermodynamics

Masking of black holes means that, for given total mass and Hawking temperatures, these data may correspond to either a “pure” black hole or a black hole of smaller mass surrounded by a massive shell. It is shown that there is a one-to one correspondence between this phenomenon and thermodynamics of a black hole in a finite size cavity: masking of black holes is possible if and only if there exists at least one locally unstable black hole solution in the corresponding canonical ensemble.     

The Stable Roommates Problem with Choice Functions

The stable marriage theorem of Gale and Shapley states that for n men and n women there always exists a stable marriage scheme, that is, a set of marriages such that no man and woman mutually prefer one another to their partners. The stable marriage theorem was generalized in two directions: the stable roommates problem is the “one-sided” version, where any two agents on the market can form a partnership. The generalization by Kelso and Crawford is in the “two-sided” model, but on one side of the market agents have a so-called substitutable choice function, and stability is interpreted in a natural way. It turned out that even if both sides of the market have substitutable choice functions, there still exists a stable assignment. The latter version contains the “many-to-many” model where up to a personal quota, polygamy is allowed for both men and women in the two-sided market.     

“Those found responsible have been sacked”: some observations on the usefulness of error

Erik Hollnagel’s body of work in the past three decades has molded much of the current research approach to system safety, particularly notions of “error”. Hollnagel regards “error” as a dead-end and avoids using the term. This position is consistent with Rasmussen’s claim that there is no scientifically stable category of human performance that can be described as “error”. While this systems view is undoubtedly correct, “error” persists. Organizations, especially formal business, political, and regulatory structures, use “error” as if it were a stable category of human performance. They apply the term to performances associated with undesired outcomes, tabulate occurrences of “error”, and justify control and sanctions through “error”. Although a compelling argument can be made for Hollnagel’s view, it is clear that notions of “error” are socially and organizationally productive. The persistence of “error” in management and regulatory circles reflects its value as a means for social control.     

Layered hidden Markov models for real-time daily activity monitoring using body sensor networks

This paper presents an inferring and training architecture for long-term and continuous daily activity monitoring using a wearable body sensor network. Energy efficiency and system adaptivity to wearers are two of the most important requirements of a body sensor network. This paper discusses a two-layered hidden Markov model (HMM) architecture for in-network data processing to achieve energy efficiency and model individualization. The bottom-layer HMM is used to process sensory data locally at each wireless sensor node to significantly reduce data transmissions. The top-layer HMM is utilized to find the activity sequence from the result of the local processing. This approach is energy efficient in that only the results of the decoding procedure in each node need to be transmitted rather than raw sensing data. Therefore, the volume of data are significantly reduced. When the algorithm is applied in online monitoring systems, the results of local processing are transmitted only upon hidden state changes. The top-layer processing uses “old data” of one sensor node when it does not receive a “new” result sequence of the local processing from that sensor node. The adaption to various wearers is also discussed, and the robustness of this classification system is depicted. Experiments of 19 activity sequences to be classified are taken by 5 subjects to evaluate the performance of this system.     

Periodic Plus Smooth Image Decomposition

When the Discrete Fourier Transform of an image is computed, the image is implicitly assumed to be periodic. Since there is no reason for opposite borders to be alike, the “periodic” image generally presents strong discontinuities across the frame border. These edge effects cause several artifacts in the Fourier Transform, in particular a well-known “cross” structure made of high energy coefficients along the axes, which can have strong consequences on image processing or image analysis techniques based on the image spectrum (including interpolation, texture analysis, image quality assessment, etc.). In this paper, we show that an image can be decomposed into a sum of a “periodic component” and a “smooth component”, which brings a simple and computationally efficient answer to this problem. We discuss the interest of such a decomposition on several applications.     

Design and analysis of a video-on-demand server

The availability of high-speed networks, fast computers and improved storage technology is stimulating interest in the development of video on-demand services that provide facilities similar to a video cassette player (VCP). In this paper, we present a design of a video-on-demand (VOD) server, capable of supporting a large number of video requests with complete functionality of a remote control (as used in VCPs), for each request. In the proposed design, we have used an interleaved storage method with constrained allocation of video and audio blocks on the disk to provide continuous retrieval. Our storage scheme interleaves a movie with itself (while satisfying the constraints on video and audio block allocation. This approach minimizes the starting delay and the buffer requirement at the user end, while ensuring a jitter-free display for every request. In order to minimize the starting delay and to support more non-concurrent requests, we have proposed the use of multiple disks for the same movie. Since a disk needs to hold only one movie, an array of inexpensive disks can be used, which reduces the overall cost of the proposed system. A scheme supported by our disk storage method to provide all the functions of a remote control such as “fast-forwarding”, “rewinding” (with play “on” or “off”), “pause” and “play” has also been discussed. This scheme handles a user request independent of others and satisfies it without degrading the quality of service to other users. The server design presented in this paper achieves the multiple goals of high disk utilization, global buffer optimization, cost-effectiveness and high-quality service to the users.     

Individual and Social Learning

We use adaptive models to understand the dynamics that lead to efficient and fair outcomes in a repeated Battle of the Sexes game. Human subjects appear to easily recognize the possibility of a coordinated alternation of actions as a mean to generate an efficient and fair outcome. Yet such typical learning models as Fictitious Play and Reinforcement Learning have found it hard to replicate this particular result. We develop a model that not only uses individual learning but also the “social learning” that operates through evolutionary selection. We find that the efficient and fair outcome emerges relatively quickly in our model. JEL classification: B52, D83 An erratum to this article can be found at