Stabilized column generation for highly degenerate multiple-depot vehicle scheduling problems

Column generation has proven to be efficient in solving the linear programming relaxation of large scale instances of the multiple-depot vehicle scheduling problem (MDVSP). However difficulties arise when the instances are highly degenerate. Recent research has been devoted to accelerate column generation while remaining within the linear programming framework. This paper presents an efficient approach to solve the linear relaxation of the MDVSP. It combines column generation, preprocessing variable fixing, and stabilization. The outcome shows the great potential of such an approach for degenerate instances.     

Optimal Constant-Window Backoff Scheme for IEEE 802.11 DCF in Single-Hop Wireless Networks Under Finite Load Conditions

Existing backoff scheme’s optimization of IEEE 802.11 DCF MAC protocol consider only saturated networks or asymptotic conditions. In real situations, traffic is bursty or streamed at low rates so that stations do not operate usually in saturated regime. In this work, we propose and analyze a backoff enhancement for IEEE 802.11 DCF that requires information only about the network size and that is quasi-optimal under all traffic loads. We first analyze the performance of DCF multiple access scheme under general load conditions in single-hop configuration and we provide an accurate delay statistics model that consider the self-loop probability in every backoff state. We prove then the short-term unfairness of the binary exponential backoff used in IEEE 802.11 by defining channel capture probability as fairness metric. Motivated by the results on fairness, we introduce the constant-window backoff scheme and we compare its performance to IEEE 802.11 DCF with Binary exponential backoff. The quasi-optimality of the proposed scheme is proved analytically and numerical results show that it increases, both the throughput and fairness, of IEEE 802.11 DCF while remaining insensitive to traffic intensity. The analysis is then extended to consider the finite queuing capacity at nodes buffers using results from the delay analysis. NS2 simulations validate the obtained results. Institut Eurecom’s research is partially supported by its industrial members: BMW Group Research & Technology—BMW Group Company, Bouygues Telecom, Cisco Systems, France Telecom , Hitachi Europe, SFR, Sharp, STMicroelectronics, Swisscom, Thales.     

The effect of particle size on the formation and structure of carbide-derived carbon on β-SiC nanoparticles by reaction with chlorine

Carbide-derived carbon (CDC) coatings were produced by reaction with pure chlorine gas on the surface of β-SiC nanoparticles. Various CDC thicknesses were obtained using moderate temperatures (565–635 °C) associated with a short time (30 min) of chlorination under atmospheric pressure. Such conditions enable controlled layer-by-layer silicon extraction from SiC material. Kinetics of CDC formation were assessed using three SiC laser pyrolysis-produced nanopowders of different average size. Under the same conditions, the smallest particle size material is more prone to chlorination and exhibits a thicker carbon coating. Effect of particle size distribution on reactivity with chlorine is also discussed. After achieving carbide to carbon partial conversion, tem observations show good covering and adherent carbon coatings on remaining SiC material, N₂ adsorption analysis show that CDC coating is microporous and has a specific surface area exceeding 1000 m² g⁻¹. Thermogravimetric analysis coupled with mass spectroscopy under He gas flow, is used to determine the thermal stability and the nature of volatile species trapped in the microporosity. Under an O₂ gas flow, the amount of CDC formed is measured by burning it off at temperatures of 400–750 °C, before the onset of oxidation of the remaining SiC.     

Continuous laser irradiation under ambient conditions: A simple way for the space-selective growth of gold nanoparticles inside a silica monolith

Thanks to the potential and various applications of metal-dielectric nanocomposites, their syntheses constitute an interesting subject in material research. In this work, we demonstrate the achievement of gold nanocrystals growth through a visible and continuous laser irradiation. The in situ and direct space-selective generation of metallic nanoparticles is localized under the surface within transparent silica monoliths. For that purpose, the porous silica monoliths are prepared using a sol-gel route and post-doped with gold precursors before the irradiation. The presence of Au nanoparticles inside the irradiated areas was evidenced using absorption spectroscopy, X-ray diffraction analysis and transmission electron microscopy. The comparison between the results obtained after a laser irradiation and by a simple heat-treatment reveals that the local precipitation of gold nanoparticles by continuous photo-irradiation occurs following a photo-thermal activated mechanism.     

A comparative study of the adsorption and desorption of o-xylene onto bentonite clay and alumina

In this paper, adsorptive performance of natural clay of bentonite type has been investigated as a potential VOC adsorbent on the basis its promising physical-chemical and morphological properties which were compared to commercial gamma-Al(2)O(3) solid. The vapour-solid adsorption isotherms of xylene were measured at different temperatures ranging from 300 to 373 K using dynamical method and the obtained data confronted to classical models such as Langmuir and Freundlich. On the other hand, the solids physico-chemical characteristics and adsorptive performances were correlated to some cost aspects because of their importance for design and engineering of adsorption plant. The results shows the interest of a local clay natural of bentonite type for treatment of VOCs emitted in working places regarding its performances and lower cost.     

Impact of network topology on the thermal and mechanical properties of lithium germanate glasses

In this work, we study the structure–topology–property relations of a series of melt-quenched lithium germanate glasses. These glasses exhibit the so-called germanate anomaly, that is, the germanium atoms feature a distribution of four-coordinated and higher coordinated germanium species, manifesting itself as anomalies in several material properties. Here, we couple variations in the number of atomic bond constraints with measured variations in thermal and mechanical properties, including thermal conductivity, Vickers hardness, and fracture toughness. For thermal conductivity, a strong correlation is found with sound velocity as well as with the volumetric constraint density. For hardness, a good correlation with volumetric constraint density is found, whereas, for fracture toughness, variations in network topology alone are insufficient to explain the composition–property relation. To account for this, we apply a recent model which incorporates knowledge of local structure, mechanical properties, and fracture patterns to predict the fracture toughness, showing a good qualitative agreement with the experimental data.     

Spatial optimization of an underhood cooling module – Towards an innovative control approach

The present paper reports a numerical investigation of spatial optimization of heat-exchanger by acting on its positioning in the vehicle’s cooling module. This analysis also elucidates how to act on the different parameters influencing heat-exchanger performance in order to optimize their functioning. A two-dimensional computation code permits optimizing the performance of the cooling module by positioning different heat exchangers, in both the driving and stop phases of the vehicle. The ultimate aim is to apply new control approaches to real vehicles so as to reduce pump and compressor energy consumption and thus fuel consumption. Compared to a reference “in-series” configuration of the cooling module HXs (in which the different HXs are superposed in the airflow direction), an “in-parallel” configuration (in which the different HX surfaces are in a row with respect to the air flow direction) increases the thermal power of the HXs by 4.4% and decreases the pressure losses by 0.9%.     

Optical flow 3D segmentation and interpretation: a variational method with active curve evolution and level sets

This study investigates a variational, active curve evolution method for dense three-dimensional (3D) segmentation and interpretation of optical flow in an image sequence of a scene containing moving rigid objects viewed by a possibly moving camera. This method jointly performs 3D motion segmentation, 3D interpretation (recovery of 3D structure and motion), and optical flow estimation. The objective functional contains two data terms for each segmentation region, one based on the motion-only equation which relates the essential parameters of 3D rigid body motion to optical flow, and the other on the Horn and Schunck optical flow constraint. It also contains two regularization terms for each region, one for optical flow, the other for the region boundary. The necessary conditions for a minimum of the functional result in concurrent 3D-motion segmentation, by active curve evolution via level sets, and linear estimation of each region essential parameters and optical flow. Subsequently, the screw of 3D motion and regularized relative depth are recovered analytically for each region from the estimated essential parameters and optical flow. Examples are provided which verify the method and its implementation     

COMPETENCE ONTOLOGY FOR DOMAIN KNOWLEDGE DISSEMINATION AND RETRIEVAL

In this paper, we present a competence ontology for domain knowledge dissemination and retrieval services, which has been used in the MDKT project (Management and Dissemination of Knowledge in Telecommunication). The main objective of this project is to set up a computerized knowledge management system related to a specific domain in order to develop the human resources expertise for the needs of the enterprise. In the case of this project, the knowledge is about wireless networking and is expressed in digital documents. Among all the ontologies that implement the knowledge needed by the system, the competence ontology plays a key role. The competence ontology defines at a meta-level the concept of competence and its relationships with other concepts such as document or user. Its instantiation is used to characterize a user model and a document model. This knowledge organization makes it possible to infer which document, or more generally which domain knowledge information, is suitable for a given person or to whom specific domain knowledge information should be disseminated.     

Auto‐calibration of a projector–camera stereo system for projection mapping

Standard camera and projector calibration techniques use a checkerboard that is manually shown at different poses to determine the calibration parameters. Furthermore, when image geometric correction must be performed on a three‐dimensional (3D) surface, such as projection mapping, the surface geometry must be determined. Camera calibration and 3D surface estimation can be costly, error prone, and time‐consuming when performed manually. To address this issue, we use an auto‐calibration technique that projects a series of Gray code structured light patterns. These patterns are captured by the camera to build a dense pixel correspondence between the projector and camera, which are used to calibrate the stereo system using an objective function, which embeds the calibration parameters together with the undistorted points. Minimization is carried out by a greedy algorithm that minimizes the cost at each iteration with respect to both calibration parameters and noisy image points. We test the auto‐calibration on different scenes and show that the results closely match a manual calibration of the system. We show that this technique can be used to build a 3D model of the scene, which in turn with the dense pixel correspondence can be used for geometric screen correction on any arbitrary surface.