Simple finite element‐based computation of distance functions in unstructured grids

A distance field is a representation of the closest distance from a point to a given surface. Distance fields are widely used in applications ranging from computer vision, physics and computer graphics and have been the subject of research of many authors in the last decade. Most of the methods for computing distance fields are devoted to Cartesian grids while little attention has been paid to unstructured grids. Finite element methods are well known for their ability to deal with partial differential equations in unstructured grids. Therefore, we propose an extension of the fast marching method for computing a distance field in a finite element context employing the element interpolation to hold the Eikonal property (∥?φ∥ = 1). A simple algorithm to develop the computations is also presented and its efficiency demonstrated through various unstructured grid examples. We observed that the presented algorithm has processing times proportional to the number of mesh nodes. Copyright © 2007 John Wiley & Sons, Ltd.     

The Lambert W function and the spectrum of some multidimensional time-delay systems

In this note we find an explicit expression for the eigenvalues of a retarded time-delay system with one delay, for the special case that the system matrices are simultaneously triangularizable, which includes the case where they commute. Using matrix function definitions we define a matrix version of the Lambert W function, from which we form the expression. We prove by counter-example that some expressions in other publications on Lambert W for time-delay systems do not always hold.     

Concentration jump experiments for the precise determination of rate constants of reverse reactions in the millisecond time range

Low dissociation or reverse rate constants of single-step or multistep complex formation equilibria are usually obtained with reduced precision from standard stopped-flow binding experiments by determination of the intercept of the concentration dependence of k(obs). Large and fast concentration jumps, based on two different step-motor-driven mixing setups, are performed with 60-300-fold dilutions that allow the precise, convenient, and independent determination of dissociation rate constants in the range of approximately 0.1-100 s(-1) in a single stopped-flow dissociation experiment. A theoretical basis is developed for the design and for the evaluation of such dilution experiments by considering the rebinding occurring during dissociation. The kinetics of three chemical systems are investigated, the binding of Mg2+ to 8-hydroxyquinoline as well as of Ca2+ and K+ to the cryptand [2.2.2], by carrying out standard stopped-flow binding as well as dissociation experiments employing various dilution factors. The advantage of the dilution method for investigating chemical and biological systems is emphasized.     

Structure–Function Insights into the Fungal Endo-Chitinase Chit33 Depict its Mechanism on Chitinous Material

Chitin is the most widespread amino renewable carbohydrate polymer in nature and the second most abundant polysaccharide. Therefore, chitin and chitinolytic enzymes are becoming more importance for biotechnological applications in food, health and agricultural fields, the design of effective enzymes being a paramount issue. We report the crystal structure of the plant-type endo-chitinase Chit33 from Trichoderma harzianum and its D165A/E167A-Chit33-(NAG)₄ complex, which showed an extended catalytic cleft with six binding subsites lined with many polar interactions. The major trait of Chit33 is the location of the non-conserved Asp117 and Arg274 acting as a clamp, fixing the distorted conformation of the sugar at subsite –1 and the bent shape of the substrate, which occupies the full catalytic groove. Relevant residues were selected for mutagenesis experiments, the variants being biochemically characterized through their hydrolytic activity against colloidal chitin and other polymeric substrates with different molecular weights and deacetylation percentages. The mutant S118Y stands out, showing a superior performance in all the substrates tested, as well as detectable transglycosylation capacity, with this variant providing a promising platform for generation of novel Chit33 variants with adjusted performance by further design of rational mutants’. The putative role of Tyr in binding was extrapolated from molecular dynamics simulation.     

An Efficient Web Page Change Detection System Based on an Optimized Hungarian Algorithm

This paper describes an efficient Web page change detection system based on three optimizations that were implemented on top of the Hungarian algorithm, which we employ to compare trees that correspond to HTML Web pages. The optimizations attempt to stop the comparator algorithm that employs this O(n³) algorithm before it completes all its iterations based on criteria having to do with properties of HTML and heuristics. Analysis and experimental results prove the effectiveness of these optimizations and their ability to render O(n²) performance, where n denotes the number of nodes in the tree. A complete system was implemented and used to carry out the performance experiments. This system includes functionalities and interfaces for processing user requests, fetching Web pages from the Internet, allowing users to select zones in Web pages to monitor, and highlighting changes on the Web pages being monitored     

Decentralized service discovery and selection in Internet of Things applications based on artificial potential fields

The Internet of Things (IoT) vision involves a future Internet integrated with real-world objects that can commonly offer their functionality trough services. In such pervasive environments of IoT networks, locating and invoking suitable services is quite challenging and traditional service discovery and selection approaches have been proven inadequate. In this paper, taking inspiration from natural metaphors, a decentralized service discovery and selection model is proposed. The model is based on artificial potential fields (APFs) which are formed upon each user service request and become active at points where services can be provided. Such points are termed as service provision nodes (SPNs). The strength of each APF depends on the percentage of requested services that can be provided by the respective SPN, as well as on SPN service load and availability with the aim to balance service load among SPNs. Service discovery and selection is then driven by artificial forces applied among user service requests and SPNs. Simulation results indicate that the proposed approach maintains satisfactory performance and scalability as the number of SPNs in an IoT network increase and efficient load balancing of the requested services among the SPNs in comparison with other approaches.     

Development of 70/30 Poly-<Emphasis Type="SmallCaps">l</Emphasis>-<Emphasis Type="SmallCaps">dl</Emphasis>-Lactic Acid Filaments for 3D Printers (Part 1): Filament Manufacturing and Characterization of Printed Samples for Use as Bioabsorbable Products

The aim of this work was to manufacture 70/30 poly-l-dl-lactic acid (PLDLLA) filaments for three-dimensional (3D) printers by using the extrusion technique and to study the properties of filaments and printed plates for surgical fracture stabilization. Different extrusion methodologies were tested and filaments were analyzed in terms of homogeneity, accuracy diameter, finishing surface morphology, and chemical degradation. X-ray diffraction and differential scanning calorimetry showed that the filaments have less crystallinity than does the raw material. Infrared and thermogravimetric analysis showed no evidence of chemical degradation. Surgical plates made with the filaments revealed small changes in the material properties after the printing process. PLDLLA filament extrusion and 3D printing are a promising way to satisfy the demand of implantable bioabsorbable products.     

Assessment of frictional resistance and surface roughness in orthodontic wires coated with two different nanoparticles

Several mechanical and biological factors may change the orthodontic wire frictional resistance (FR). Titanium dioxide (TiO₂) and silica dioxide (SiO₂) nanoparticle (NP) coatings may be used to improve the characteristics of materials, reducing FR between archwire and bracket. This in vitro study aimed to evaluate the FR of orthodontic wires with and without coating in both dry and wet environments and measure the surface roughness (SR). One hundred and eighty segments of rectangular Cr–Ni orthodontic wires (Morelli Co, Brazil) were divided into three groups according to the NP coating applied: TiO₂ group; SiO₂ group; and control group. The SR parameters were measured in an optical profilometer, the surface morphology was analyzed with scanning electron microscopy (SEM), and FR was performed in a universal testing machine in dry and wet environments (n = 30). The statistical analysis was performed using the Generalized Estimated Equations model with a Bonferroni post-test (α = 0.05). It was observed that SiO₂ NP coating decreased FR significantly when compared to the TiO₂ and control groups, in both environments (p < .001). The SiO₂ and TiO₂ groups presented statistically lower SR than the control group and were similar to each other (p < .001). The SiO₂ group presented the lower depth of Valley parameter than the TiO₂ group (p < .001). The SEM showed that the TiO₂ coating had the most heterogeneous surface morphology than the SiO₂ and control groups. The orthodontic wires with NP coating modified the FR and morphology. The SiO₂ coating reduced FR in both dry and wet environments and decreased SR.

• Titanium dioxide (TiO₂) and silica dioxide (SiO₂) nanoparticles coatings may be used to reduce frictional resistance (FR) between archwire and bracket as well as to improve surface morphology.
• The SiO₂ coating reduced FR in both dry and wet environments and decreased the SR of Cr–Ni orthodontic wire.
• The TiO₂ coating promoted the most heterogeneous surface morphology of Cr–Ni orthodontic wire.

     

Use of the smart technology for water quality control: feedback from large-scale experimentation

The main purpose of drinking water network is to ensure safe quality of water to users. However, accidental contamination and malicious attacks in water networks can degrade the water quality. Such critical events threat the human health and lead to harmful diseases. Water utilities are concerned by the control of water quality. Since conventional methods based on laboratory analyses require several days, online control technology presents good opportunity to rapid detection of any water contamination. Devices based on smart technology have been developed for real-time control of the water quality. However, the use of these devices is recent and yet requires investigations. This paper presents feedback of the use of the smart technology in a large-scale experimentation conducted at the campus of Lille University within the European project “SmartWater4Europe”. Two devices are used: S::CAN, which measures various parameters such as Conductivity and Turbidity and EventLab, which measures the variation of the refractive index. This paper presents the implementation of these devices, data storage and management as well as analysis of recorded data.