Electromigration-Induced Flow of Islands and Voids on the Cu(001) Surface

Electromigration-induced flow of islands and voids on the Cu(001) surface is studied at the atomic scale. The basic drift mechanisms are identified using a complete set of energy barriers for adatom hopping on the Cu(001) surface, combined with kinetic Monte Carlo simulations. The energy barriers are calculated by the embedded atom method, and parameterized using a simple model. The dependence of the flow on the temperature, the size of the clusters, and the strength of the applied field is obtained. For both islands and voids it is found that edge diffusion is the dominant mass-transport mechanism. The rate limiting steps are identified. For both islands and voids they involve detachment of atoms from corners into the adjacent edge. The energy barriers for these moves are found to be in good agreement with the activation energy for island/void drift obtained from Arrhenius analysis of the simulation results. The relevance of the results to other FCC(001) metal surfaces and their experimental implications are discussed.Comment: 9 pages, 13 ps figure

A formally verified compiler back-end

This article describes the development and formal verification (proof of semantic preservation) of a compiler back-end from Cminor (a simple imperative intermediate language) to PowerPC assembly code, using the Coq proof assistant both for programming the compiler and for proving its correctness. Such a verified compiler is useful in the context of formal methods applied to the certification of critical software: the verification of the compiler guarantees that the safety properties proved on the source code hold for the executable compiled code as well

Visualization, simulation and validation for cyber-virtual systems

We present our framework for visualization, simulation and validation of cyber-physical systems in industrial automation during development, operation and maintenance. System models may represent an existing physical part - for example an existing robot installation - and a software simulated part - for example a possible future extension of the physical industrial automation setup. We call such systems cyber-virtual systems. Here, we present our VxLab infrastructure for visualization using combined large screens and its applications in industrial automation. The methodology for simulation and validation motivated in this paper is based on this infrastructure. We are targeting scenarios, where industrial sites which may be in remote locations are modeled, simulated and visualized. Modeling, simulation and the visualization can be done from different locations anywhere in the world. Here, we are also concentrating on software modeling challenges related to cyber-virtual systems and simulation, testing, validation and verification techniques applied to them. Software models of industrial sites require behavioral models of both human and machine oriented aspects such as workflows and the components of the industrial sites such as models for tools, robots, workpieces and other machinery as well as communication and sensor facilities. Furthermore, facilitating collaboration between sites and stakeholders, experts and operators is an important application of our work

Indexing music by mood: design and integration of an automatic content-based annotator

In the context of content analysis for indexing and retrieval, a method for creating automatic music mood annotation is presented. The method is based on results from psychological studies and framed into a supervised learning approach using musical features automatically extracted from the raw audio signal. We present here some of the most relevant audio features to solve this problem. A ground truth, used for training, is created using both social network information systems (wisdom of crowds) and individual experts (wisdom of the few). At the experimental level, we evaluate our approach on a database of 1,000 songs. Tests of different classification methods, configurations and optimizations have been conducted, showing that Support Vector Machines perform best for the task at hand. Moreover, we evaluate the algorithm robustness against different audio compression schemes. This fact, often neglected, is fundamental to build a system that is usable in real conditions. In addition, the integration of a fast and scalable version of this technique with the European Project PHAROS is discussed. This real world application demonstrates the usability of this tool to annotate large-scale databases. We also report on a user evaluation in the context of the PHAROS search engine, asking people about the utility, interest and innovation of this technology in real world use cases.This research has been partially funded by the EU Project PHAROS IST-2006-045035

On the Runtime Enforcement of Timed Properties

International audienceRuntime enforcement refers to the theories, techniques, and tools for enforcing correct behavior of systems at runtime. We are interested in such behaviors described by specifications that feature timing constraints formalized in what is generally referred to as timed properties. This tutorial presents a gentle introduction to runtime enforcement (of timed properties). First, we present a taxonomy of the main principles and concepts involved in runtime enforcement. Then, we give a brief overview of a line of research on theoretical runtime enforcement where timed properties are described by timed automata and feature uncontrollable events. Then, we mention some tools capable of runtime enforcement, and we present the TiPEX tool dedicated to timed properties. Finally, we present some open challenges and avenues for future work. Runtime Enforcement (RE) is a discipline of computer science concerned with enforcing the expected behavior of a system at runtime. Runtime enforcement extends the traditional runtime verification [12-14, 42, 43] problem by dealing with the situations where the system deviates from its expected behavior. While runtime verification monitors are execution observers, runtime enforcers are execution modifiers. Foundations for runtime enforcement were pioneered by Schneider in [98] and by Rinard in [95] for the specific case of real-time systems. There are several tutorials and overviews on runtime enforcement for untimed systems [39, 47, 59], but none on the enforcement of timed properties (for real-time systems). In this tutorial, we focus on runtime enforcing behavior described by a timed property. Timed properties account for physical time. They allow expressing constraints on the time that should elapse between (sequences of) events, which is useful for real-time systems when specifying timing constraints between statements, their scheduling policies, the completion of tasks, etc [5, 7, 88, 101, 102]. This tutorial comprises four stages: 1. the presentation of a taxonomy of concepts and principles in RE (Sec. 1); 2. the presentation of a framework for the RE of timed properties where specifications are described by timed automata (preliminary concepts are recalled in Sec. 2, the framework is overviewed in Sec. 3, and presented in more details in Sec. 4); 3. the demonstration of the TiPEX [82] tool implementing the framework (Sec. 5); 4. the description of some avenues for future work (Sec. 6)