Distributed constraint optimization with MULBS: A case study on collaborative meeting scheduling

This paper introduces MULBS, a new DCOP (distributed constraint optimization problem) algorithm and also presents a DCOP formulation for scheduling of distributed meetings in collaborative environments. Scheduling in CSCWD can be seen as a DCOP where variables represent time slots and values are resources of a production system (machines, raw-materials, hardware components, etc.) or management system (meetings, project tasks, human resources, money, etc). Therefore, a DCOP algorithm must find a set of variable assignments that maximize an objective function taking constraints into account. However, it is well known that such problems are NP-complete and that more research must be done to obtain feasible and reliable computational approaches. Thus, DCOP emerges as a very promising technique: the search space is decomposed into smaller spaces and agents solve local problems, collaborating in order to achieve a global solution. We show with empirical experiments that MULBS outperforms some of the state-of-the-art algorithms for DCOP, guaranteeing high quality solutions using less computational resources for the distributed meeting scheduling task.     

Modeling of the condyle elements within a biomechanical knee model

The development of a computational multibody knee model able to capture some of the fundamental properties of the human knee articulation is presented. This desideratum is reached by including the kinetics of the real knee articulation. The research question is whether an accurate modeling of the condyle contact in the knee will lead to reproduction of the complex combination of flexion/extension, abduction/adduction, and tibial rotation observed in the real knee. The model is composed by two anatomic segments, the tibia and the femur, whose characteristics are functions of the geometric and anatomic properties of the real bones. The biomechanical model characterization is developed under the framework of multibody systems methodologies using Cartesian coordinates. The type of approach used in the proposed knee model is the joint surface contact conditions between ellipsoids, representing the two femoral condyles, and points, representing the tibial plateau and the menisci. These elements are closely fitted to the actual knee geometry. This task is undertaken by considering a parameter optimization process to replicate experimental data published in the literature, namely that by Lafortune and his coworkers in 1992. Then kinematic data in the form of flexion/extension patterns are imposed on the model corresponding to the stance phase of the human gait. From the results obtained, by performing several computational simulations, it can be observed that the knee model approximates the average secondary motion patterns observed in the literature. Because the literature reports considerable inter-individual differences in the secondary motion patterns, the knee model presented here is also used to check whether it is possible to reproduce the observed differences with reasonable variations of bone shape parameters. This task is accomplished by a parameter study, in which the main variables that define the geometry of condyles are taken into account. It was observed that the data reveal a difference in secondary kinematics of the knee in flexion versus extension. The likely explanation for this fact is the elastic component of the secondary motions created by the combination of joint forces and soft tissue deformations. The proposed knee model is, therefore, used to investigate whether this observed behavior can be explained by reasonable elastic deformations of the points representing the menisci in the model.     

A qualitative human-centric evaluation of flexibility in middleware implementations

Today middleware is much more powerful, more reliable and faster than it used to be. Nevertheless, for the application developer, the complexity of using middleware platforms has increased accordingly. The volume and variety of application contexts that current middleware technologies have to support require that developers be able to anticipate the widest possible range of execution environments, desired and undesired effects of different programming strategies, handling procedures for runtime errors, and so on. This paper shows how a generic framework designed to evaluate the usability of notations (the Cognitive Dimensions of Notations Framework, or CDN) has been instantiated and used to analyze the cognitive challenges involved in adapting middleware platforms. This human-centric perspective allowed us to achieve novel results compared to existing middleware evaluation research, typically centered around system performance metrics. The focus of our study is on the process of adapting middleware implementations, rather than in the end product of this activity. Our main contributions are twofold. First, we describe a qualitative CDN-based method to analyze the cognitive effort made by programmers while adapting middleware implementations. And second, we show how two platforms designed for flexibility have been compared, suggesting that certain programming language design features might be particularly helpful for developers.     

How landscape ruggedness influences the performance of real-coded algorithms: a comparative study

Ruggedness has a strong influence on the performance of algorithms, but it has been barely studied in real-coded optimization, mainly because of the difficulty of isolating it from a number of involved topological properties. In this paper, we propose a framework consisting of increasing ruggedness function sets built by a mechanism which generates multiple funnels. This mechanism introduces different levels of sinusoidal distortion which can be controlled to isolate the singular influence of some related features. Some commonly used measures of ruggedness have been applied to analyze these sets of functions, and a numerical study to compare the performance of some representative algorithms has been carried out. The results confirm that ruggedness has an influence on the performance of the algorithm, proving that it depends on the multi-funnel structure and peak features, such as height and relative size of the global peak, and not on the number of peaks.     

The GPU on the simulation of cellular computing models

Membrane Computing is a discipline aiming to abstract formal computing models, called membrane systems or P systems, from the structure and functioning of the living cells as well as from the cooperation of cells in tissues, organs, and other higher order structures. This framework provides polynomial time solutions to NP-complete problems by trading space for time, and whose efficient simulation poses challenges in three different aspects: an intrinsic massively parallelism of P systems, an exponential computational workspace, and a non-intensive floating point nature. In this paper, we analyze the simulation of a family of recognizer P systems with active membranes that solves the Satisfiability problem in linear time on different instances of Graphics Processing Units (GPUs). For an efficient handling of the exponential workspace created by the P systems computation, we enable different data policies to increase memory bandwidth and exploit data locality through tiling and dynamic queues. Parallelism inherent to the target P system is also managed to demonstrate that GPUs offer a valid alternative for high-performance computing at a considerably lower cost. Furthermore, scalability is demonstrated on the way to the largest problem size we were able to run, and considering the new hardware generation from Nvidia, Fermi, for a total speed-up exceeding four orders of magnitude when running our simulations on the Tesla S2050 server.     

What can you verify and enforce at runtime?

The underlying property, its definition, and representation play a major role when monitoring a system. Having a suitable and convenient framework to express properties is thus a concern for runtime analysis. It is desirable to delineate in this framework the sets of properties for which runtime analysis approaches can be applied to. This paper presents a unified view of runtime verification and enforcement of properties in the Safety-Progress classification. First, we extend the Safety-Progress classification of properties in a runtime context. Second, we characterize the set of properties which can be verified (monitorable properties) and enforced (enforceable properties) at runtime. We propose in particular an alternative definition of ??property monitoring?? to the one classically used in this context. Finally, for the delineated sets of properties, we define specialized verification and enforcement monitors.     

SIMCAN: A flexible, scalable and expandable simulation platform for modelling and simulating distributed architectures and applications

In this paper we propose a new simulation platform called SIMCAN, for analyzing parallel and distributed systems. This platform is aimed to test parallel and distributed architectures and applications. The main characteristics of SIMCAN are flexibility, accuracy, performance, and scalability. Thence, the proposed platform has a modular design that eases the integration of different basic systems on a single architecture. Its design follows a hierarchical schema that includes simple modules, basic systems (computing, memory managing, I/O, and networking), physical components (nodes, switches, …), and aggregations of components. New modules may also be incorporated as well to include new strategies and components. Also, a graphical configuration tool has been developed to help untrained users with the task of modelling new architectures. Finally, a validation process and some evaluation tests have been performed to evaluate the SIMCAN platform.     

Passive internet-based crane teleoperation with haptic aids

Crane operation is a challenging task, due to the combined problem of obstacle avoidance and load swing suppression in underactuated conditions. This paper presents a human-machine interface that increases the operator’s perception of a gantry crane’s workspace. With this aim, a virtual environment resembling the workspace is connected with a haptic device. This allows the user to receive not only visual but also tactile feedback, thus increasing maneuvering safety. Additionally, this capability is integrated in a teleoperation setup, adopting a passivity-based control approach that guarantees overall stability. This includes also the design of controllers by means of the IDA-PBC method. Experimental results carried out with a laboratory crane show its feasibility for internet-based teleoperation and demonstrate the improvements on the system performance.     

TEM characterization of some crude or air heat-treated SiC Nicalon fibres

Commercial Nicalon fibres were prepared by thin transverse sectioning and studied by transmission electron microscopy. A progressive tilting of the incident beam allows us to explore the selected-area diffraction (SAD) pattern along two orthogonal directions, increasing the tilting angle (dark-field (DF) imaging). The lattice fringes technique was also used. The samples were Nicalon 001, 101 and 201 fibres, the latter also being studied after heat treatment in air at 1300° C for 48 h. The SAD pattern of the 001 fibre only shows the SiC, 1 1 intense halo whereas the other samples show all the SiC (1 1 1, 2 2 0 and 31 1) strongly scattered beams, indicating a microcrystalline state. Correspondingly, DF imaging does not indicate any localized measurable scattering domain for 001. Only bright dots can be seen, less than 1 nm in size. The other fibres show SiC microcrystals respectively 2 nm (1 01 ), 3 nm (201 ) and up to 7 nm (heat-treated 201) in extent. Free aromatic carbon, shaped in small units less than 1 nm in size fills up the interstices between SiC. These units tend to lie flat on SiC. In heat-treated fibres, they form incomplete layers around the edges. In addition, the heat-treated 2 01 fibre show a 1m thick layer of cristobalite at the fibre surface. These crystals are polytypes.     

Effects of ZrO2 precursors on the synthesis of V-ZrSiO4 solid solutions by the sol-gel method

The preparation of V-ZrSiO₄ solid solutions starting from different ZrO₂ precursors by using sol-gel methods is reported. The starting materials were hydrolysed and the dried gels were fired at a temperature between 500 and 900 °C with soaking times of 12h. The organic character of zirconia precursors was stronger, i.e. the starting material had more carbon atoms, a higher temperature was necessary to make the first crystalline phase appear (ZrO₂(tetragonal)) and the temperature range for the whole phase transformation was narrower. In all dried gel samples the presence of infrared bands which might be associated with either Si-O-Zr or Si-O-V was not observed. On the other hand, some bands could be attributed to a silica network and ZrO₈ groups. The main steps in V-ZrSiO₄ solid solutions were confirmed. ZrO₂(tetragonal) is crystallized on heating from an amorphous sample. The ZrO₂(tetragonal) ZrO₂(monoclinic) phase transformation then occurs and immediately afterwards the zircon formation begins. Finer textures in samples were obtained from polymeric gels rather than for colloidal gel samples, as seen from the scanning electron micrographs.