Showing papers by "University of Mons published in 2018"

On the impact of security vulnerabilities in the npm package dependency network

Abstract: Security vulnerabilities are among the most pressing problems in open source software package libraries. It may take a long time to discover and fix vulnerabilities in packages. In addition, vulnerabilities may propagate to dependent packages, making them vulnerable too. This paper presents an empirical study of nearly 400 security reports over a 6-year period in the npm dependency network containing over 610k JavaScript packages. Taking into account the severity of vulnerabilities, we analyse how and when these vulnerabilities are discovered and fixed, and to which extent they affect other packages in the packaging ecosystem in presence of dependency constraints. We report our findings and provide guidelines for package maintainers and tool developers to improve the process of dealing with security issues.

Search for electroweak production of charginos and neutralinos in multilepton final states in proton-proton collisions at √s=13 TeV

Abstract: Results are presented from a search for the direct electroweak production of charginos and neutralinos in signatures with either two or more leptons (electrons or muons) of the same electric charge, or with three or more leptons, which can include up to two hadronically decaying tau leptons. The results are based on a sample of proton-proton collision data collected at $ \sqrt{s}=13 $ TeV, recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb$^{−1}$. The observed event yields are consistent with the expectations based on the standard model. The results are interpreted in simplified models of supersymmetry describing various scenarios for the production and decay of charginos and neutralinos. Depending on the model parameters chosen, mass values between 180 GeV and 1150 GeV are excluded at 95% CL. These results significantly extend the parameter space probed for these particles in searches at the LHC. In addition, results are presented in a form suitable for alternative theoretical interpretations.

Deep Learning for Plant Diseases: Detection and Saliency Map Visualisation

Abstract: Recently, many researchers have been inspired by the success of deep learning in computer vision to improve the performance of detection systems for plant diseases. Unfortunately, most of these studies did not leverage recent deep architectures and were based essentially on AlexNet, GoogleNet or similar architectures. Moreover, the research did not take advantage of deep learning visualisation methods which qualifies these deep classifiers as black boxes as they are not transparent. In this chapter, we have tested multiple state-of-the-art Convolutional Neural Network (CNN) architectures using three learning strategies on a public dataset for plant diseases classification. These new architectures outperform the state-of-the-art results of plant diseases classification with an accuracy reaching 99.76%. Furthermore, we have proposed the use of saliency maps as a visualisation method to understand and interpret the CNN classification mechanism. This visualisation method increases the transparency of deep learning models and gives more insight into the symptoms of plant diseases.

Observation of electroweak production of same-sign W boson pairs in the two jet and two same-sign lepton final state in proton-proton collisions at s√= 13 TeV

Abstract: The first observation of electroweak production of same-sign W boson pairs in proton-proton collisions is reported The data sample corresponds to an integrated luminosity of 359 fb^(−1) collected at a center-of-mass energy of 13 TeV with the CMS detector at the LHC Events are selected by requiring exactly two leptons (electrons or muons) of the same charge, moderate missing transverse momentum, and two jets with a large rapidity separation and a large dijet mass The observed significance of the signal is 55 standard deviations, where a significance of 57 standard deviations is expected based on the standard model The ratio of measured event yields to that expected from the standard model at leading order is 090 ± 022 A cross section measurement in a fiducial region is reported Bounds are given on the structure of quartic vector boson interactions in the framework of dimension-8 effective field theory operators and on the production of doubly charged Higgs bosons

Measurement of Atmospheric Neutrino Oscillations at 6-56 GeV with IceCube DeepCore.

Abstract: We present a measurement of the atmospheric neutrino oscillation parameters using three years of data from the IceCube Neutrino Observatory. The DeepCore infill array in the center of IceCube enabl ...

Search for resonant and nonresonant Higgs boson pair production in the b(b)over-barl nu l nu final state in proton-proton collisions at root s=13 TeV

Abstract: Searches for resonant and nonresonant pair-produced Higgs bosons (HH) decaying respectively into l nu l nu, through either W or Z bosons, and b (b) over bar are presented The analyses are based on a sample of proton-proton collisions at root s = 13 TeV, collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 359 fb(-1) Data and predictions from the standard model are in agreement within uncertainties For the standard model HH hypothesis, the data exclude at 95% confidence level a product of the production cross section and branching fraction larger than 72 fb, corresponding to 79 times the standard model prediction Constraints are placed on different scenarios considering anomalous couplings, which could affect the rate and kinematics of HH production Upper limits at 95% confidence level are set on the production cross section of narrow-width spin-0 and spin-2 particles decaying to Higgs boson pairs, the latter produced with minimal gravity-like coupling

Computational Design of Thermally Activated Delayed Fluorescence Materials: The Challenges Ahead

Abstract: Thermally activated delayed fluorescence (TADF) offers promise for all-organic light-emitting diodes with quantum efficiencies competing with those of transition-metal-based phosphorescent devices. While computational efforts have so far largely focused on gas-phase calculations of singlet and triplet excitation energies, the design of TADF materials requires multiple methodological developments targeting among others a quantitative description of electronic excitation energetics, fully accounting for environmental electrostatics and molecular conformational effects, the accurate assessment of the quantum mechanical interactions that trigger the elementary electronic processes involved in TADF, and a robust picture for the dynamics of these fundamental processes. In this Perspective, we describe some recent progress along those lines and highlight the main challenges ahead for modeling, which we hope will be useful to the whole TADF community.

Graphene-enhanced metal oxide gas sensors at room temperature: a review.

Abstract: Owing to the excellent sensitivity to gases, metal-oxide semiconductors (MOS) are widely used as materials for gas sensing. Usually, MOS gas sensors have some common shortages, such as relatively poor selectivity and high operating temperature. Graphene has drawn much attention as a gas sensing material in recent years because it can even work at room temperature, which reduces power consumption. However, the low sensitivity and long recovery time of the graphene-based sensors limit its further development. The combination of metal-oxide semiconductors and graphene may significantly improve the sensing performance, especially the selectivity and response/recovery rate at room temperature. In this review, we have summarized the latest progress of graphene/metal-oxide gas sensors for the detection of NO2, NH3, CO and some volatile organic compounds (VOCs) at room temperature. Meanwhile, the sensing performance and sensing mechanism of the sensors are discussed. The improved experimental schemes are raised and the critical research directions of graphene/metal-oxide sensors in the future are proposed.

Inclusive Search for a Highly Boosted Higgs Boson Decaying to a Bottom Quark-Antiquark Pair

Abstract: An inclusive search for the standard model Higgs boson (H) produced with large transverse momentum (p_T) and decaying to a bottom quark-antiquark pair (bb) is performed using a data set of pp collisions at √s = 13 TeV collected with the CMS experiment at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb^(−1). A highly Lorentz-boosted Higgs boson decaying to bb is reconstructed as a single, large radius jet, and it is identified using jet substructure and dedicated b tagging techniques. The method is validated with Z → bb decays. The Z → bb process is observed for the first time in the single-jet topology with a local significance of 5.1 standard deviations (5.8 expected). For a Higgs boson mass of 125 GeV, an excess of events above the expected background is observed (expected) with a local significance of 1.5 (0.7) standard deviations. The measured cross section times branching fraction for production via gluon fusion of H → bb with reconstructed p_T > 450 GeV and in the pseudorapidity range −2.5 < η < 2.5 is 74 ± 48 (stat)^(+17)_(−10)(syst) fb, which is consistent within uncertainties with the standard model prediction.

Biobased Epoxy Resin with Low Electrical Permissivity and Flame Retardancy: From Environmental Friendly High-Throughput Synthesis to Properties

Abstract: Recent years have witnessed significant advances in biobased epoxy resins to replace their petroleum-based counterparts, especially diglycidyl ether of bisphenol A type epoxy resin (DGEBA). However, for meeting a great variety of the requirements, long-standing challenges include environmentally friendly preparation of epoxy resin with few toxic byproducts and improving their properties. Herein, we report a facile method to synthesize new silicone-bridged difunctional epoxy monomers in high yield. They are derived from naturally occurring eugenol by introducing the methylsiloxane and phenylsiloxane linkers of different chain lengths into their molecular backbones. These synthesized liquid epoxy monomers have definitive molecular structure with high purity. These silicone-bridged difunctional epoxy monomers exhibit much lower viscosity (<2.5 Pa s) than commercial DGEBA epoxy (10.7 Pa s) suitable for composites and prepregs. After curing, they exhibit a dielectric permittivity as low as 2.8 and good intrins...

The dial-a-ride problem with electric vehicles and battery swapping stations

Abstract: The Dial-a-Ride Problem (DARP) consists of designing vehicle routes and schedules for customers with special needs and/or disabilities. The DARP with Electric Vehicles and battery swapping stations (DARP-EV) concerns scheduling a fleet of EVs to serve a set of pre-specified transport requests during a certain planning horizon. In addition, EVs can be recharged by swapping their batteries with charged ones from any battery-swap stations. We propose three enhanced Evolutionary Variable Neighborhood Search (EVO-VNS) algorithms to solve the DARP-EV. Extensive computational experiments highlight the relevance of the problem and confirm the efficiency of the proposed EVO-VNS algorithms in producing high quality solutions.

An artificial molecular machine that builds an asymmetric catalyst.

Abstract: Biomolecular machines perform types of complex molecular-level tasks that artificial molecular machines can aspire to. The ribosome, for example, translates information from the polymer track it traverses (messenger RNA) to the new polymer it constructs (a polypeptide) 1 . The sequence and number of codons read determines the sequence and number of building blocks incorporated into the biomachine-synthesized polymer. However, neither control of sequence2,3 nor the transfer of length information from one polymer to another (which to date has only been accomplished in man-made systems through template synthesis) 4 is easily achieved in the synthesis of artificial macromolecules. Rotaxane-based molecular machines5–7 have been developed that successively add amino acids8–10 (including β-amino acids 10 ) to a growing peptide chain by the action of a macrocycle moving along a mono-dispersed oligomeric track derivatized with amino-acid phenol esters. The threaded macrocycle picks up groups that block its path and links them through successive native chemical ligation reactions 11 to form a peptide sequence corresponding to the order of the building blocks on the track. Here, we show that as an alternative to translating sequence information, a rotaxane molecular machine can transfer the narrow polydispersity of a leucine-ester-derivatized polystyrene chain synthesized by atom transfer radical polymerization 12 to a molecular-machine-made homo-leucine oligomer. The resulting narrow-molecular-weight oligomer folds to an α-helical secondary structure 13 that acts as an asymmetric catalyst for the Julia–Colonna epoxidation14,15 of chalcones. The ring of a rotaxane molecule traverses a polymer track picking up leucine amino acids and synthesizing a homo-leucine oligomer, which in turn folds into an alpha helix and catalyses a chemical reaction.

Multifunctional graphene/POSS epoxy resin tailored for aircraft lightning strike protection

Abstract: This paper presents a first successful attempt to obtain a conductivity mapping at nanoscale level of a new multifunctional fire retardant graphene/polyhedral oligomeric silsesquioxane (POSS) epoxy resin using Tunneling Atomic Force Microscopy (TUNA) that is a very sensitive mode by which ultra-low currents ranging from 80 fA to 120 pA can be measured. The multifunctional material, specifically designed to meet structural aeronautical requirements, such as suitable thermal stability, fire resistance, mechanical performance and electrical conductivity, has proven to be a promising candidate in the field of aeronautic and aerospace composites. The results also highlight the great potentiality of TUNA technique to analyze conductive networks at nanodomain level. Through simultaneous topographic and current images acquisition, this technique enables a direct correlation of local topography with electrical properties of the nanofiller based samples. The intrinsic electrical conductivity of the manufactured polymeric systems allows TUNA measurements without using electrical conductive paint, which is usually employed for polymeric systems to ensure effective electrical contacts to the ground.

Impact of Pore Tortuosity on Electrode Kinetics in Lithium Battery Electrodes: Study in Directionally Freeze-Cast LiNi0.8Co0.15Al0.05O2 (NCA)

Abstract: Author(s): Delattre, B; Amin, R; Sander, J; De Coninck, J; Tomsia, AP; Chiang, YM | Abstract: The prevailing electrode fabrication method for lithium-ion battery electrodes includes calendering at high pressures to densify the electrode and promote adhesion to the metal current collector. However, this process increases the tortuosity of the pore network in the primary transport direction and imposes severe tradeoffs between electrode thickness and rate capability. With the aim of understanding the impact of pore tortuosity on electrode kinetics, and enabling cell designs with thicker electrodes and improved cost and energy density, we use here freeze-casting, a shaping technique able to produce low-tortuosity structures using ice crystals as a pore-forming agent, to fabricate LiNi0.8Co0.15Al0.05O2 (NCA) cathodes with controlled, aligned porosity. Electrode tortuosity is characterized using two complementary methods, X-ray tomography combined with thermal diffusion simulations, and electrochemical transport measurements. The results allow comparison across a wide range of microstructures, and highlight the large impact of a relatively small numerical change in tortuosity on electrode kinetics. Under galvanostatic discharge, optimized microstructures show a three- to fourfold increase in area-specific capacity compared to typical Li-ion composite electrodes. Hybrid pulse power characterization (HPPC) demonstrates improved power capability, while dynamic stress tests (DST) shows that an area-specific area capacity corresponding to 91% of the NCA galvanostatic C/10 capacity could be reached.

How Methylammonium Cations and Chlorine Dopants Heal Defects in Lead Iodide Perovskites

Abstract: DOI: 10.1002/aenm.201702754 cells has been raised from 3.8% in the first report[2] to over 20% today.[3] Such an unprecedented improvement has been triggered by the unique features of hybrid perovskites that make them attractive for solar-cell applications, including large optical absorption coefficients and high charge carrier mobility.[1] Despite these remarkable advances, the mechanism for photoinduced electron– hole (e–h) pair dissociation and transport in lead perovskites is still controversial. Exciton binding energies of 5–16 meV have been reported in MAPbI3, so only a fraction of weakly bound excitons likely coexist with free charge carriers at room temperature under solar illumination conditions.[5] It has been argued that e–h separation could be further assisted by fluctuations in the energy landscape associated with the positional dynamics of MA cations in pristine materials.[6–8] In polycrystalline films prepared from precursor solutions, defects are not as benign as initially thought,[9] as suggested by the recent demonstration of the grain-to-grain variation in photoluminescence (PL) intensity.[10] These reports are seemingly in conflict with the measured, significantly long, charge-carrier diffusion lengths in MAPbI3 films,[11] as these inhomogeneities should act as traps and sources of nonradiative recombination channels. Very interestingly, the e–h diffusion lengths in iodide-based perovskites can be further enhanced by incorporating a small amount of chlorine anions.[12,13] While it has been claimed that chlorine dopants yield polycrystalline film morphologies with improved charge transport properties,[14,15] possibly by smoothing out structural and energetic discontinuities at grain boundaries[16] or seeding crystallization of higher quality grains,[17,18] recent state-of-the-art studies point to the presence of residual Cl dopants remaining in thin films of MAPbI3. The enhanced PL intensity inside the grains with higher Cl concentration[10] may be explained by reduced trap-assisted nonradiative recombination, thereby increasing the lifetime and diffusion length of photoexcited electrons and holes.[14,15,21,22] However, a model relating charge-carrier decay dynamics to atomistic details of the excited-state electronic structure of Cldoped perovskites is severely lacking.[23] Here, we address these questions by means of a many-body description of the electronic excitations of pristine and defective perovskites that fully accounts for groundand excited-state Lead tri-iodide methylammonium (MAPbI3) perovskite polycrystalline materials show complex optoelectronic behavior, largely because their 3D semiconducting inorganic framework is strongly perturbed by the organic cations and ubiquitous structural or chemical inhomogeneities. Here, a newly developed time-dependent density functional theory-based theoretical formalism is taken advantage of. It treats electron–hole and electron–nuclei interactions on the same footing to assess the many-body excited states of MAPbI3 perovskites in their pristine state and in the presence of point chemical defects. It is shown that lead and iodine vacancies yield deep trap states that can be healed by dynamic effects, namely rotation of the methylammonium cations in response to point charges, or through slight changes in chemical composition, namely by introducing a tiny amount of chlorine dopants in the defective MAPbI3. The theoretical results are supported by photoluminescence experiments on MAPbI3−mClm and pave the way toward the design of defectfree perovskite materials with optoelectronic performance approaching the theoretical limits. Solar Cells

Rotator side chains trigger cooperative transition for shape and function memory effect in organic semiconductors.

Abstract: Martensitic transition is a solid-state phase transition involving cooperative movement of atoms, mostly studied in metallurgy. The main characteristics are low transition barrier, ultrafast kinetics, and structural reversibility. They are rarely observed in molecular crystals, and hence the origin and mechanism are largely unexplored. Here we report the discovery of martensitic transition in single crystals of two different organic semiconductors. In situ microscopy, single-crystal X-ray diffraction, Raman and nuclear magnetic resonance spectroscopy, and molecular simulations combined indicate that the rotating bulky side chains trigger cooperative transition. Cooperativity enables shape memory effect in single crystals and function memory effect in thin film transistors. We establish a molecular design rule to trigger martensitic transition in organic semiconductors, showing promise for designing next-generation smart multifunctional materials.

On the Evolution of Technical Lag in the npm Package Dependency Network

Abstract: Software packages developed and distributed through package managers extensively depend on other packages. These dependencies are regularly updated, for example to add new features, resolve bugs or fix security issues. In order to take full advantage of the benefits of this type of reuse, developers should keep their dependencies up to date by relying on the latest releases. In practice, however, this is not always possible, and packages lag behind with respect to the latest version of their dependencies. This phenomenon is described as technical lag in the literature. In this paper, we perform an empirical study of technical lag in the npm dependency network by investigating its evolution for over 1.4M releases of 120K packages and 8M dependencies between these releases. We explore how technical lag increases over time, taking into account the release type and the use of package dependency constraints. We also discuss how technical lag can be reduced by relying on the semantic versioning policy.

An Empirical Analysis of Technical Lag in npm Package Dependencies

Abstract: Software library packages are constantly evolving and increasing in number. Not updating to the latest available release of dependent libraries may negatively affect software development by not benefiting from new functionality, vulnerability and bug fixes available in more recent versions. On the other hand, automatically updating to the latest release may introduce incompatibility issues. We introduce a technical lag metric for dependencies in package networks, in order to assess how outdated a software package is compared to the latest available releases of its dependencies. We empirically analyse the package update practices and technical lag for the npm distribution of JavaScript packages. Our results show a strong presence of technical lag caused by the specific use of dependency constraints, indicating a reluctance to update dependencies to avoid backward incompatible changes.

Measurement of the Splitting Function in pp and Pb-Pb Collisions at sNN =5.02 TeV

Abstract: Data from heavy ion collisions suggest that the evolution of a parton shower is modified by interactions with the color charges in the dense partonic medium created in these collisions, but it is not known where in the shower evolution the modifications occur. The momentum ratio of the two leading partons, resolved as subjets, provides information about the parton shower evolution. This substructure observable, known as the splitting function, reflects the process of a parton splitting into two other partons and has been measured for jets with transverse momentum between 140 and 500 GeV, in pp and PbPb collisions at a center-of-mass energy of 5.02 TeV per nucleon pair. In central PbPb collisions, the splitting function indicates a more unbalanced momentum ratio, compared to peripheral PbPb and pp collisions.. The measurements are compared to various predictions from event generators and analytical calculations.

Robust singlet fission in pentacene thin films with tuned charge transfer interactions

Abstract: Singlet fission, the spin-allowed photophysical process converting an excited singlet state into two triplet states, has attracted significant attention for device applications. Research so far has focused mainly on the understanding of singlet fission in pure materials, yet blends offer the promise of a controlled tuning of intermolecular interactions, impacting singlet fission efficiencies. Here we report a study of singlet fission in mixtures of pentacene with weakly interacting spacer molecules. Comparison of experimentally determined stationary optical properties and theoretical calculations indicates a reduction of charge-transfer interactions between pentacene molecules with increasing spacer molecule fraction. Theory predicts that the reduced interactions slow down singlet fission in these blends, but surprisingly we find that singlet fission occurs on a timescale comparable to that in pure crystalline pentacene. We explain the observed robustness of singlet fission in such mixed films by a mechanism of exciton diffusion to hot spots with closer intermolecular spacings.

Tuning the Optoelectronic Properties of Two-Dimensional Hybrid Perovskite Semiconductors with Alkyl Chain Spacers.

Abstract: Layered two-dimensional organo-metal halide perovskites are currently in the limelight, largely because their versatile chemical composition offers the promise of tunable photophysical properties. We report here on (time-dependent) density functional theory [(TD)DFT] calculations of alkyl-ammonium lead iodide perovskites, where significant changes in the electronic structure and optical properties are predicted when using long versus short alkyl chain spacers. The mismatch between the structural organization in the inorganic and organic layers is epitomized for dodecyl chains that adopt a supramolecular packing similar to that of polyethylene, at the cost of distorting the inorganic frame and, in turn, opening the electronic band gap. These results rationalize recent experimental data and demonstrate that the optoelectronic properties of layered halide perovskite semiconductors can be modified through the use of electronically inert organic saturated chains.