Vinylogous Urethane Vitrimers

Vitrimers are a new class of polymeric materials with very attractive properties, since they can be reworked to any shape while being at the same time permanently cross‐linked. As an alternative to the use of transesterification chemistry, we explore catalyst‐free transamination of vinylogous urethanes as an exchange reaction for vitrimers. First, a kinetic study on model compounds reveals the occurrence of transamination of vinylogous urethanes in a good temperature window without side reactions. Next, poly(vinylogous urethane) networks with a storage modulus of ≈2.4 GPa and a glass transition temperature above 80 °C are prepared by bulk polymerization of cyclohexane dimethanol bisacetoacetate, m‐xylylene diamine, and tris(2‐aminoethyl)amine. The vitrimer nature of these networks is examined by solubility, stress‐relaxation, and creep experiments. Relaxation times as short as 85 s at 170 °C are observed without making use of any catalyst. In addition, the networks are recyclable up to four times by consecutive grinding/compression molding cycles without significant mechanical or chemical degradation.     

Functional analysis of hydrogen photoproduction in respiratory-deficient mutants of Chlamydomonas reinhardtii

In this paper, mitochondrial mutants of Chlamydomonas reinhardtii defective for respiratory complex I (NADH:ubiquinone oxidoreductase), complex III (ubiquinol cytochrome c oxidoreductase) and both complexes I and III were analyzed for H₂ photoproduction. Several parameters were followed during the S-deficiency stage and the anaerobic stage leading to H₂ photoproduction. At the early aerobic S-deficiency stage, starch and neutral lipids accumulated in all strains but their amount was significantly decreased in mutants compared to wild type. During the H₂ photoproduction process, whereas starch content strongly decreased in all strains, neutral lipid amount remained nearly unchanged, suggesting that starch degraded by glycolysis is the preferential substrate for energy production during anaerobiosis. The mutants displayed a decrease in H₂ photoproduction correlating to the number of active mitochondrial proton-pumping sites lost in the strains. Our results thus highlight the critical role of oxidative phosphorylation during the first (aerobic) stage of S-starvation when carbon resources are accumulated.     

Investigation of Binding‐Site Homology between Mushroom and Bacterial Tyrosinases by Using Aurones as Effectors

Tyrosinase is a copper‐containing enzyme found in plants and bacteria, as well as in humans, where it is involved in the biosynthesis of melanin‐type pigments. Tyrosinase inhibitors have attracted remarkable research interest as whitening agents in cosmetology, antibrowning agents in food chemistry, and as therapeutics. In this context, commercially available tyrosinase from mushroom (TyM) is frequently used for the identification of inhibitors. This and bacterial tyrosinase (TyB) have been the subjects of intense biochemical and structural studies, including X‐ray diffraction analysis, and this has led to the identification of structural homology and divergence among enzymes from different sources. To better understand the behavior of potential inhibitors of TyM and TyB, we selected the aurone family—previously identified as potential inhibitors of melanin biosynthesis in human melanocytes. In this study, a series of 24 aurones with different hydroxylation patterns at the A‐ and B‐rings were evaluated on TyM and TyB. The results show that, depending on the hydroxylation pattern of A‐ and B‐rings, aurones can behave as inhibitors, substrates, and activators of both enzymes. Computational analysis was performed to identify residues surrounding the aurones in the active sites of both enzymes and to rationalize the interactions. Our results highlight similarities and divergence in the behavior of TyM and TyB toward the same set of molecules.     

Dust emission by powder handling: Influence of the hopper outlet on the dust plume

Dust generation in solids handling involving free fall of bulk materials and impacts on a stockpile can cause many problems in industry and be a great danger for operators health. This paper describes an experimental set up to characterize the dust plume formed in free fall of powders from a hopper and investigates the influence of various outlet geometries on the dust plume. For this purpose an image analysis technique was developed to quantify the characteristics of the dust plume.     

Two-material optimization of plate armour for blast mitigation using hybrid cellular automata

With the increased use of improvised explosive devices in regions at war, the threat to military and civilian life has risen. Cabin penetration and gross acceleration are the primary threats in an explosive event. Cabin penetration crushes occupants, damaging the lower body. Acceleration causes death at high magnitudes. This investigation develops a process of designing armour that simultaneously mitigates cabin penetration and acceleration. The hybrid cellular automaton (HCA) method of topology optimization has proven efficient and robust in problems involving large, plastic deformations such as crash impact. Here HCA is extended to the design of armour under blast loading. The ability to distribute two metallic phases, as opposed to one material and void, is also added. The blast wave energy transforms on impact into internal energy (IE) inside the solid medium. Maximum attenuation occurs with maximized IE. The resulting structures show HCA's potential for designing blast mitigating armour structures.     

Enhanced multiobjective particle swarm optimization in combination with adaptive weighted gradient-based searching

This article proposes a new multiobjective optimization method for structural problems based on multiobjective particle swarm optimization (MOPSO). A gradient-based optimization method is combined with MOPSO to alleviate constraint-handling difficulties. In this method, a group of particles is divided into two groups—a dominated solution group and a non-dominated solution group. The gradient-based method, utilizing a weighting coefficient method, is applied to the latter to conduct local searching that yields superior non-dominated solutions. In order to enhance the efficiency of exploration in a multiple objective function space, the weighting coefficients are adaptively assigned considering the distribution of non-dominated solutions. A linear optimization problem is solved to determine the optimal weighting coefficients for each non-dominated solution at each iteration. Finally, numerical and structural optimization problems are solved by the proposed method to verify the optimization efficiency.     

Stochastic Motion and the Level Set Method in Computer Vision: Stochastic Active Contours

Based on recent work on Stochastic Partial Differential Equations (SPDEs), this paper presents a simple and well-founded method to implement the stochastic evolution of a curve. First, we explain why great care should be taken when considering such an evolution in a Level Set framework. To guarantee the well-posedness of the evolution and to make it independent of the implicit representation of the initial curve, a Stratonovich differential has to be introduced. To implement this differential, a standard Ito plus drift approximation is proposed to turn an implicit scheme into an explicit one. Subsequently, we consider shape optimization techniques, which are a common framework to address various applications in Computer Vision, like segmentation, tracking, stereo vision etc. The objective of our approach is to improve these methods through the introduction of stochastic motion principles. The extension we propose can deal with local minima and with complex cases where the gradient of the objective function with respect to the shape is impossible to derive exactly. Finally, as an application, we focus on image segmentation methods, leading to what we call Stochastic Active Contours.     

A global security architecture for intrusion detection on computer networks

Detecting all kinds of intrusions efficiently requires a global view of the monitored network. Built to increase the security of computer networks, traditional IDS's are unfortunately unable to give a global view of the security of a network. To overcome this situation, we are developing a distributed SOC (Security Operation Center) which is able to detect attacks occurring simultaneously on several sites in a network and to give a global view of the security of that network. In this article, we present the global architecture of our system, called DSOC as well as several methods used to test its accuracy and performance.     

A direct-conversion CMOS transceiver for the 802.11a/b/g WLAN standard utilizing a Cartesian feedback transmitter

A fully integrated dual-band transceiver is implemented in 0.18-/spl mu/m CMOS and is compliant with the IEEE 802.11a/b/g standards. The direct-conversion transceiver occupies 12 mm/sup 2/ in a QFN-40 package. A fractional-N synthesizer operates at twice the channel frequency, covering continuously bands from 4.9 to 5.9 GHz, as well as the 2.4-GHz band. The 5- and 2.4-GHz receivers achieve a sensitivity level below -73 dBm in the 54-Mb/s mode and below -93 dBm in the 6-Mb/s mode, while consuming 230 mW. A fast RSSI-channel power-detection system allows to power-down signal processing in the listen mode. The 5- and 2.4-GHz transmitters implement a wideband Cartesian feedback loop for enhanced EVM performances and improved spectrum masks compliance. The transmitters deliver -2-dBm average power with an EVM of 3% in the 54-Mb/s mode while consuming 300 mW.