Showing papers by "École Polytechnique de Montréal published in 2012"
TL;DR: It is found that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption, suggesting that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics.
Abstract: Under strong laser illumination, few-layer graphene exhibits both a transmittance increase due to saturable absorption and a nonlinear phase shift. Here, we unambiguously distinguish these two nonlinear optical effects and identify both real and imaginary parts of the complex nonlinear refractive index of graphene. We show that graphene possesses a giant nonlinear refractive index n2≃10−7 cm2 W−1, almost 9 orders of magnitude larger than bulk dielectrics. We find that the nonlinear refractive index decreases with increasing excitation flux but slower than the absorption. This suggests that graphene may be a very promising nonlinear medium, paving the way for graphene-based nonlinear photonics.
578 citations
TL;DR: The metaheuristic combines the exploration breadth of population-based evolutionary search, the aggressive-improvement capabilities of neighborhood-based metaheuristics, and advanced population-diversity management schemes and proves extremely competitive for the capacitated VRP.
Abstract: We propose an algorithmic framework that successfully addresses three vehicle routing problems: the multidepot VRP, the periodic VRP, and the multidepot periodic VRP with capacitated vehicles and constrained route duration. The metaheuristic combines the exploration breadth of population-based evolutionary search, the aggressive-improvement capabilities of neighborhood-based metaheuristics, and advanced population-diversity management schemes. Extensive computational experiments show that the method performs impressively in terms of computational efficiency and solution quality, identifying either the best known solutions, including the optimal ones, or new best solutions for all currently available benchmark instances for the three problem classes. The proposed method also proves extremely competitive for the capacitated VRP.
545 citations
TL;DR: In this article, the authors conduct a review of various commonly used measures of accessibility, with a particular view to clarifying their normative (i.e. prescriptive), as well as positive (e.g. descriptive) aspects.
497 citations
TL;DR: This paper discusses related advancements in modeling other key constructs such as learner motivation, emotional and attentional state, meta-cognition and self-regulated learning, group learning, and the recent movement towards open and shared learner models.
Abstract: In recent years, learner models have emerged from the research laboratory and research classrooms into the wider world. Learner models are now embedded in real world applications which can claim to have thousands, or even hundreds of thousands, of users. Probabilistic models for skill assessment are playing a key role in these advanced learning environments. In this paper, we review the learner models that have played the largest roles in the success of these learning environments, and also the latest advances in the modeling and assessment of learner skills. We conclude by discussing related advancements in modeling other key constructs such as learner motivation, emotional and attentional state, meta-cognition and self-regulated learning, group learning, and the recent movement towards open and shared learner models.
384 citations
TL;DR: It is shown that, in almost all releases of the four systems, classes participating in antipatterns are more change-and fault-prone than others and size alone cannot explain the higher odds of classes with antip atterns to underwent a (fault-fixing) change than other classes.
Abstract: Antipatterns are poor design choices that are conjectured to make object-oriented systems harder to maintain. We investigate the impact of antipatterns on classes in object-oriented systems by studying the relation between the presence of antipatterns and the change- and fault-proneness of the classes. We detect 13 antipatterns in 54 releases of ArgoUML, Eclipse, Mylyn, and Rhino, and analyse (1) to what extent classes participating in antipatterns have higher odds to change or to be subject to fault-fixing than other classes, (2) to what extent these odds (if higher) are due to the sizes of the classes or to the presence of antipatterns, and (3) what kinds of changes affect classes participating in antipatterns. We show that, in almost all releases of the four systems, classes participating in antipatterns are more change-and fault-prone than others. We also show that size alone cannot explain the higher odds of classes with antipatterns to underwent a (fault-fixing) change than other classes. Finally, we show that structural changes affect more classes with antipatterns than others. We provide qualitative explanations of the increase of change- and fault-proneness in classes participating in antipatterns using release notes and bug reports. The obtained results justify a posteriori previous work on the specification and detection of antipatterns and could help to better focus quality assurance and testing activities.
317 citations
TL;DR: In this article, the authors examined and assessed predictive methods for the saturated hydraulic conductivity of soils and found that most predictive methods were calibrated using laboratory permeability tests performed on either disturbed or intact specimens for which the test conditions were either measured or supposed to be known.
Abstract: This paper examines and assesses predictive methods for the saturated hydraulic conductivity of soils. The soil definition is that of engineering. It is not that of soil science and agriculture, which corresponds to “top soil” in engineering. Most predictive methods were calibrated using laboratory permeability tests performed on either disturbed or intact specimens for which the test conditions were either measured or supposed to be known. The quality of predictive equations depends highly on the test quality. Without examining all the quality issues, the paper explains the 14 most important mistakes for tests in rigid-wall or flexible-wall permeameters. Then, it briefly presents 45 predictive methods, and in detail, those with some potential, such as the Kozeny-Carman equation. Afterwards, the data of hundreds of excellent quality tests, with none of the 14 mistakes, are used to assess the predictive methods with a potential. The relative performance of those methods is evaluated and presented in graphs. Three methods are found to work fairly well for non-plastic soils, two for plastic soils without fissures, and one for compacted plastic soils used for liners and covers. The paper discusses the effects of temperature and intrinsic anisotropy within the specimen, but not larger scale anisotropy within aquifers and aquitards.
270 citations
TL;DR: In this article, the authors investigated the energy consumption and pellet properties of torrefied sawdust from a fluidized bed reactor, including moisture adsorption, pellet density and Meyer hardness.
229 citations
TL;DR: A review of the current knowledge concerning the use of the hybrid membrane process, applied either under a biological or an adsorption mode, in view to produce drinking water is presented in this paper.
227 citations
TL;DR: The prepared coaxial nanofibers (hollow and solid) have several potential applications due to the presence of chitosan on their outer surfaces, and have been produced using a coaxial electrospinning setup.
223 citations
01 Dec 2012
TL;DR: In this paper, the problem of releasing filtered signals that respect the privacy of the user data streams is addressed in a system theoretic context, and methods are developed to approximate a given filter by a differentially private version, so that the distortion introduced by the privacy mechanism is minimized.
Abstract: Emerging systems such as smart grids or intelligent transportation systems often require end-user applications to continuously send information to external data aggregators performing monitoring or control tasks. This can result in an undesirable loss of privacy for the users in exchange of the benefits provided by the application. Motivated by this trend, this paper introduces privacy concerns in a system theoretic context, and addresses the problem of releasing filtered signals that respect the privacy of the user data streams. Our approach relies on a formal notion of privacy from the database literature, called differential privacy, which provides strong privacy guarantees against adversaries with arbitrary side information. Methods are developed to approximate a given filter by a differentially private version, so that the distortion introduced by the privacy mechanism is minimized. Two specific scenarios are considered. First, the notion of differential privacy is extended to dynamic systems with many participants contributing independent input signals. Kalman filtering is also discussed in this context, when a released output signal must preserve differential privacy for the measured signals or state trajectories of the individual participants. Second, differentially private mechanisms are described to approximate stable filters when participants contribute to a single event stream, extending previous work on differential privacy under continual observation.
220 citations
TL;DR: A comparison between eight different methods for determining risk factors for work-related musculoskeletal disorders reveals that the various methods differ in their analyses of the same workstation.
TL;DR: The use of surface plasmon resonance (SPR) for the biodetection of pathogenic bacteria, using bacteriophages as the recognition elements, and it is found that the system permits label-free, real-time, specific, rapid and cost-effective detection of pathogens.
TL;DR: In this paper, the authors investigated the use of the downscaling method known as "morphing" to generate weather data files and assessed the impact of using these weather files on the energy performance of an actual NZEB.
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TL;DR: Methods are developed to approximate a given filter by a differentially private version, so that the distortion introduced by the privacy mechanism is minimized, and extended to dynamic systems with many participants contributing independent input signals.
Abstract: Emerging systems such as smart grids or intelligent transportation systems often require end-user applications to continuously send information to external data aggregators performing monitoring or control tasks. This can result in an undesirable loss of privacy for the users in exchange of the benefits provided by the application. Motivated by this trend, this paper introduces privacy concerns in a system theoretic context, and addresses the problem of releasing filtered signals that respect the privacy of the user data streams. Our approach relies on a formal notion of privacy from the database literature, called differential privacy, which provides strong privacy guarantees against adversaries with arbitrary side information. Methods are developed to approximate a given filter by a differentially private version, so that the distortion introduced by the privacy mechanism is minimized. Two specific scenarios are considered. First, the notion of differential privacy is extended to dynamic systems with many participants contributing independent input signals. Kalman filtering is also discussed in this context, when a released output signal must preserve differential privacy for the measured signals or state trajectories of the individual participants. Second, differentially private mechanisms are described to approximate stable filters when participants contribute to a single event stream, extending previous work on differential privacy under continual observation.
TL;DR: Cyanobacterial cells and toxins from environmental bloom samples were more resistant to chlorination than results obtained using laboratory cultured cells and dissolved standard toxins.
TL;DR: In this article, a comparative life cycle assessment of two water treatment plants: one enhanced conventional plant and one nanofiltration plant was performed using SimaPro software for inventory and impact assessment phases.
TL;DR: This work presents experimental and theoretical work that demonstrates that the nanobubble formation results from the generation of a nanoscale plasma around the particle due to the enhanced near-field rather than from the heating of the particle.
Abstract: The generation of nanobubbles around plasmonic nanostructures is an efficient approach for imaging and therapy, especially in the field of cancer research. We show a novel method using infrared femtosecond laser that generates ≈800 nm bubbles around off-resonance gold nanospheres using 200 mJ/cm2 45 fs pulses. We present experimental and theoretical work that demonstrate that the nanobubble formation results from the generation of a nanoscale plasma around the particle due to the enhanced near-field rather than from the heating of the particle. Energy absorbed in the nanoplasma is indeed more than 11 times the energy absorbed in the particle. When compared to the usual approach that uses nanosecond laser to induce the extreme heating of in-resonance nanoparticles to initiate bubble formation, our off-resonance femtosecond technique is shown to bring many advantages, including avoiding the particles fragmentation, working in the optical window of biological material and using the deposited energy more effi...
TL;DR: A new integrated framework that addresses the problems of thermal-visible video registration, sensor fusion, and people tracking for far-range videos is proposed, which demonstrates the advantage of the proposed framework in obtaining better results for both image registration and tracking than separate imageRegistration and tracking methods.
TL;DR: The proposed methodology for addressing the problem is based on an adaptive large neighborhood search heuristic, previously developed for the static version of the problem, and a comparison is provided with a myopic approach which does not consider scenarios of future requests.
Abstract: This paper considers a vehicle routing problem where each vehicle performs delivery operations over multiple routes during its workday and where new customer requests occur dynamically. The proposed methodology for addressing the problem is based on an adaptive large neighborhood search heuristic, previously developed for the static version of the problem. In the dynamic case, multiple possible scenarios for the occurrence of future requests are considered to decide about the opportunity to include a new request into the current solution. It is worth noting that the real-time decision is about the acceptance of the new request, not about its service which can only take place in some future routes (a delivery route being closed as soon as a vehicle departs from the depot). In the computational results, a comparison is provided with a myopic approach which does not consider scenarios of future requests.
TL;DR: Self-healing materials can be made from a variety of polymers and metallic materials as discussed by the authors, which can increase materials lifetime, reduce replacement costs, and improve product safety for real engineering applications.
Abstract: The development of self-healing materials is now being considered for real engineering applications. Over the past few decades, there has been a huge interest in materials that can self-heal, as this property can increase materials lifetime, reduce replacement costs, and improve product safety. Self-healing systems can be made from a variety of polymers and metallic materials. This paper reviews the main technologies currently being developed, particularly on the thermosetting composite polymeric systems. An overview of various self-healing concepts over the past decade is then presented. Finally, a perspective on future self-healing approaches using this biomimetic technique is offered. The intention is to stimulate debate and reinforce the importance of a multidisciplinary approach in this exciting field.
TL;DR: Cartilage repair strategies that elicit fibrocartilage, a mixture of collagen type I and type II, are predicted to show little tidemark/calcified cartilage regeneration and to develop a less stable repair tissue-bone interface.
Abstract: In the knee joint, the purpose of the cartilage-bone interface is to maintain structural integrity of the osteochondral unit during walking, kneeling, pivoting, and jumping--during which tensile, compressive, and shear forces are transmitted from the viscoelastic articular cartilage layer to the much stiffer mineralized end of the long bone. Mature articular cartilage is integrated with subchondral bone through a approximately 20 to approximately 250 microm thick layer of calcified cartilage. Inside the calcified cartilage layer, perpendicular chondrocyte-derived collagen type II fibers become structurally cemented to collagen type I osteoid deposited by osteoblasts. The mature mineralization front is delineated by a thin approximately 5 microm undulating tidemark structure that forms at the base of articular cartilage. Growth plate cartilage is anchored to epiphyseal bone, sometimes via a thin layer of calcified cartilage and tidemark, while the hypertrophic edge does not form a tidemark and undergoes continual vascular invasion and endochondral ossification (EO) until skeletal maturity upon which the growth plates are fully resorbed and replaced by bone. In this review, the formation of the cartilage-bone interface during skeletal development and cartilage repair, and its structure and composition are presented. Animal models and human anatomical studies show that the tidemark is a dynamic structure that forms within a purely collagen type II-positive and collagen type I-negative hyaline cartilage matrix. Cartilage repair strategies that elicit fibrocartilage, a mixture of collagen type I and type II, are predicted to show little tidemark/calcified cartilage regeneration and to develop a less stable repair tissue-bone interface. The tidemark can be regenerated through a bone marrow-driven growth process of EO near the articular surface.
TL;DR: The decomposition of hemicelluloses was found to be responsible for the significant changes of chemical, physical and mechanical properties of the torrefied sawdust, including energy content, particle size distribution and moisture absorption capacity.
TL;DR: Highy crystalline NiO nanoparticles are uniformly grown on the walls of carbon nanotubes (CNTs) by atomic layer deposition (ALD) at moderate temperature and exhibit excellent performance in the electro-oxidation of methanol.
Abstract: Highy crystalline NiO nanoparticles are uniformly grown on the walls of carbon nanotubes (CNTs) by atomic layer deposition (ALD) at moderate temperature.Their size and stoichiometry are controlled by the ALD process parameters. The obtained NiO/CNT hybrids exhibit excellent performance in the electro-oxidation of methanol.
TL;DR: Caffeine appeared to be a promising indicator of recent urban fecal contaminations, as shown by the significant correlation with FC (R(2)=0.45), while carbamazepine is a good indicator of cumulative persistence compounds.
TL;DR: Kinetic analysis of the oxidation of toxins in natural water revealed significant differences in their susceptibility to chlorine, saxitoxins being the easiest to oxidize, followed by cylindrospermopsin and microcystin-LR.
TL;DR: The method is applied to cases in Santiago, Chile, and Gatineau, Quebec, Canada, to identify activity purpose and time frame to characterize user behavior and to discover differences in behavioral activity patterns due to sociological, cultural, and geopolitical differences.
Abstract: During the past decade, a significant amount of research has been dedicated to the use of smart card data for various purposes. A method is presented for the detection and estimation of the location, time, duration, and purpose of activities undertaken by public transit users with the use of smart card databases and other available information about land use and user behavior. The method is applied to cases in Santiago, Chile, and Gatineau, Quebec, Canada, to identify activity purpose and time frame to characterize user behavior. The results obtained for each city are compared to discover differences in behavioral activity patterns due to sociological, cultural, and geopolitical differences.
TL;DR: An overview of current clinical applications for multimodality navigation and several commercially available methods of image-fusion and device navigation are reviewed along with an explanation of common tracking hardware and software.
Abstract: Personalized therapies play an increasingly critical role in cancer care: Image guidance with multimodality image fusion facilitates the targeting of specific tissue for tissue characterization and plays a role in drug discovery and optimization of tailored therapies. Positron-emission tomography (PET), magnetic resonance imaging (MRI), and contrast-enhanced computed tomography (CT) may offer additional information not otherwise available to the operator during minimally invasive image-guided procedures, such as biopsy and ablation. With use of multimodality image fusion for image-guided interventions, navigation with advanced modalities does not require the physical presence of the PET, MRI, or CT imaging system. Several commercially available methods of image-fusion and device navigation are reviewed along with an explanation of common tracking hardware and software. An overview of current clinical applications for multimodality navigation is provided.
11 Nov 2012
TL;DR: A year-long study involving more than 450 developers of a large enterprise, spanning more than 60 teams, to better understand risky changes, i.e., changes for which developers believe that additional attention is needed in the form of careful code or design reviewing and/or more testing is conducted.
Abstract: Modelling and understanding bugs has been the focus of much of the Software Engineering research today. However, organizations are interested in more than just bugs. In particular, they are more concerned about managing risk, i.e., the likelihood that a code or design change will cause a negative impact on their products and processes, regardless of whether or not it introduces a bug. In this paper, we conduct a year-long study involving more than 450 developers of a large enterprise, spanning more than 60 teams, to better understand risky changes, i.e., changes for which developers believe that additional attention is needed in the form of careful code or design reviewing and/or more testing. Our findings show that different developers and different teams have their own criteria for determining risky changes. Using factors extracted from the changes and the history of the files modified by the changes, we are able to accurately identify risky changes with a recall of more than 67%, and a precision improvement of 87% (using developer specific models) and 37% (using team specific models), over a random model. We find that the number of lines and chunks of code added by the change, the bugginess of the files being changed, the number of bug reports linked to a change and the developer experience are the best indicators of change risk. In addition, we find that when a change has many related changes, the reliability of developers in marking risky changes is negatively affected. Our findings and models are being used today in practice to manage the risk of software projects.
02 Jun 2012
TL;DR: Qualitatively studies a random sample of 400 performance and non-performance bug reports of Mozilla Firefox and Google Chrome across four dimensions and finds that developers and users face problems in reproducing performance bugs and have to spend more time discussing performance bugs than other kinds of bugs.
Abstract: Software performance is one of the important qualities that makes software stand out in a competitive market. However, in earlier work we found that performance bugs take more time to fix, need to be fixed by more experienced developers and require changes to more code than non-performance bugs. In order to be able to improve the resolution of performance bugs, a better understanding is needed of the current practice and shortcomings of reporting, reproducing, tracking and fixing performance bugs. This paper qualitatively studies a random sample of 400 performance and non-performance bug reports of Mozilla Firefox and Google Chrome across four dimensions (Impact, Context, Fix and Fix validation). We found that developers and users face problems in reproducing performance bugs and have to spend more time discussing performance bugs than other kinds of bugs. Sometimes performance regressions are tolerated as a trade-off to improve something else.
TL;DR: A femtosecond laser based transfection method using off-resonance plasmonic gold nanoparticles is described, which leads to a very high perforation rate, transfections efficiency three times higher than for conventional lipofection, and very low toxicity.