Portfolio approaches for constraint optimization problems

Within the Constraint Satisfaction Problems (CSP) context, a methodology that has proven to be particularly performant consists of using a portfolio of different constraint solvers. Nevertheless, comparatively few studies and investigations have been done in the world of Constraint Optimization Problems (COP). In this work, we provide a generalization to COP as well as an empirical evaluation of different state of the art existing CSP portfolio approaches properly adapted to deal with COP. The results obtained by measuring several evaluation metrics confirm the effectiveness of portfolios even in the optimization field, and could give rise to some interesting future research.     

Interactive teaching of task-oriented robot grasps

This paper focuses on the problem of grasp stability and grasp quality analysis. An elegant way to evaluate the stability of a grasp is to model its wrench space. However, classical grasp quality measures suffer from several disadvantages, the main drawback being that they are not task related. Indeed, constructive approaches for approximating the wrench space including also task information have been rarely considered. This work presents an effective method for task-oriented grasp quality evaluation based on a novel grasp quality measure. We address the general case of multifingered grasps with point contacts with friction.The proposed approach is based on the concept of programming by demonstration and interactive teaching, wherein an expert user provides in a teaching phase a set of exemplar grasps appropriate for the task. Following this phase, a representation of task-related grasps is built. During task planning and execution, a grasp could be either submitted interactively for evaluation by a non-expert user or synthesized by an automatic planning system. Grasp quality is then assessed based on the proposed measure, which takes into account grasp stability along with its suitability for the task. To enable real-time evaluation of grasps, a fast algorithm for computing an approximation of the quality measure is also proposed. Finally, a local grasp optimization technique is described which can amend uncertainties arising in supplied grasps by non-expert users or assist in planning more valuable grasps in the neighborhood of candidate ones.The paper reports experiments performed in virtual reality with both an anthropomorphic virtual hand and a three-fingered robot hand. These experiments suggest the effectiveness and task relevance of the proposed grasp quality measure.     

Complexity analysis of blast-induced vibrations in underground mining:A case study

Blasting in geological bodies is an industrial process acting in an environment characterized by high uncertainties (natural joints,faults,voids,abrupt structural changes),which are transposed into the...     

Recent progress in GeSi electro-absorption modulators

Electro-absorption from GeSi heterostructures is receiving growing attention as a high performance optical modulator for short distance optical interconnects. Ge incorporation with Si allows strong modulation mechanism using the Franz–Keldysh effect and the quantum-confined Stark effect from bulk and quantum well structures at telecommunication wavelengths. In this review, we discuss the current state of knowledge and the on-going challenges concerning the development of high performance GeSi electro-absorption modulators. We also provide feasible future prospects concerning this research topic.     

High Temperature Oxidation and Microstructural Evolution of Modified MCrAlY Coatings

Thermal sprayed MCrAlY coatings are widely used as a bond coat in thermal barrier systems to protect the substrate from corrosion and high temperature oxidation and to improve the compatibility between the ceramic top coat and metallic substrate. In this paper, the high temperature oxidation resistance of MCrAlY coatings with modified compositions was evaluated; in particular, the effect of the addition of reactive and refractory elements (Ta, Re, Si, and Hf) was investigated. MCrAlY coatings were obtained by high velocity oxygen fuel spray and vacuum plasma spray techniques; samples were exposed to air at 1423 K (1150 °C) and the oxidation kinetics were evaluated by measuring the thickness of the thermally grown oxide (TGO) scale at several exposure times. Experimental data confirmed that the oxidation resistance of MCrAlY coatings is strictly related to the amount of the reactive and refractory elements in the starting powders and that a thorough understanding of the microstructural modifications taking place during oxidation is essential for controlling TGO growth and thermal barriers’ durability.     

External Shape Differences between Sympatric Populations of Commercial Clams <Emphasis Type="Italic">Tapes decussatus</Emphasis> and <Emphasis Type="Italic">T. philippinarum</Emphasis>

The actual Italian production of clams is chiefly sustained by the native Tapes decussatus and the fortuitously imported Tapes philippinarum. Both species are commercialized as “Vongola verace”, but the commercial value of T. philippinarum is lower. The discrimination of species by sight is usually difficult and it cannot be done by observation based on shell morphology but only when animals open their valves hence displaying the two siphons. In this study, we propose a new, noninvasive method to discriminate individuals of both species based on the analysis of the external shape of their shells. Accordingly, in sympatric populations at two sites of the Po river outlet, we have chosen individuals (63 for T. decussatus and 57 for T. philippinarum) of comparable commercial size for which a certain genetic discrimination was previously done. Pictures of the left side valve were taken for all specimens. Their profiles were analyzed with the elliptic Fourier analysis. The mean outline for each species was graphically extracted. The coefficients of the harmonic equations were analyzed by multivariate classification (partial least squares discriminant analysis [PLSDA]). Results showed a high percentage of correct classification of individuals of both species (96.6%). Contour analysis reflected the overall shell shape and thus identified morphological aspects that were difficult to recognize and quantify in sight. The high percentage of correct classifications obtained by combining the analysis of elliptic Fourier harmonics with PLSDA demonstrated the feasibility of this method to discriminate species with a high level of resemblance.     

Layer-oriented simulation tool

The Layer-Oriented Simulation Tool (LOST) is a numerical simulation code developed for analysis of the performance of multiconjugate adaptive optics modules following a layer-oriented approach. The LOST code computes the atmospheric layers in terms of phase screens and then propagates the phase delays introduced in the natural guide stars' wave fronts by using geometrical optics approximations. These wave fronts are combined in an optical or numerical way, including the effects of wave-front sensors on measurements in terms of phase noise. The LOST code is described, and two applications to layer-oriented modules are briefly presented. We have focus on the Multiconjugate adaptive optics demonstrator to be mounted upon the Very Large Telescope and on the Near-IR-Visible Adaptive Interferometer for Astronomy (NIRVANA) interferometric system to be installed on the combined focus of the Large Binocular Telescope.     

A decision support system for optimal deployment of sonobuoy networks based on sea current forecasts and multi-objective evolutionary optimization

A decision support system for the optimal deployment of drifting acoustic sensor networks for cooperative track detection in underwater surveillance applications is proposed and tested on a simulated scenario. The system integrates sea water current forecasts, sensor range models and simple drifting buoy kinematic models to predict sensor positions and temporal network performance. A multi-objective genetic optimization algorithm is used for searching a set of Pareto optimal deployment solutions (i.e. the initial position of drifting sonobuoys of the network) by simultaneously optimizing two quality of service metrics: the temporal mean of the network area coverage and the tracking coverage. The solutions found after optimization, which represent different efficient tradeoffs between the two metrics, can be conveniently evaluated by the mission planner in order to choose the solution with the desired compromise between the two conflicting objectives. Sensitivity analysis through the Unscented Transform is also performed in order to test the robustness of the solutions with respect to network parameters and environmental uncertainty. Results on a simulated scenario making use of real probabilistic sea water current forecasts are provided showing the effectiveness of the proposed approach. Future work is envisioned to make the tool fully operational and ready to use in real scenarios.     

Combining AVHRR and ATSR satellite sensor data for operational boreal forest fire detection

The potential to combine data from two different satellite systems was studied to increase fire detection sensitivity and image acquisition frequency in real-time fire detection and fire control. A fully automatic fire detection algorithm was applied to all scenes that were acquired using both satellite systems. Local fire authorities were notified about each detected fire in their territory using real-time fire reports that were sent by telefax. The average time from the start of National Oceanic and Atmospheric Administration (NOAA), Advanced Very High Resolution Radiometer (AVHRR) image acquisition until the sending of a telefax fire report was 25 min. During the straw-burning season in April 2000, the Along Track Scanning Radiometer (ATSR) instrument detected twice as many fires as the AVHRR per unit image area. The main reason for this may be the average resolution cell of the ATSR, which is half the size of that of the AVHRR in terms of area. The response from fire authorities was used to estimate the number of correct alerts and false alarms. A false alarm rate of 12% and 7% was obtained in the fire seasons of 1999 and 2000, respectively.