Continuous Levels‐of‐Detail and Visual Abstraction for Seamless Molecular Visualization

Molecular visualization is often challenged with rendering of large molecular structures in real time. We introduce a novel approach that enables us to show even large protein complexes. Our method is based on the level‐of‐detail concept, where we exploit three different abstractions combined in one visualization. Firstly, molecular surface abstraction exploits three different surfaces, solvent‐excluded surface (SES), Gaussian kernels and van der Waals spheres, combined as one surface by linear interpolation. Secondly, we introduce three shading abstraction levels and a method for creating seamless transitions between these representations. The SES representation with full shading and added contours stands in focus while on the other side a sphere representation of a cluster of atoms with constant shading and without contours provide the context. Thirdly, we propose a hierarchical abstraction based on a set of clusters formed on molecular atoms. All three abstraction models are driven by one importance function classifying the scene into the near‐, mid‐ and far‐field. Moreover, we introduce a methodology to render the entire molecule directly using the A‐buffer technique, which further improves the performance. The rendering performance is evaluated on series of molecules of varying atom counts.     

Approximate Symmetry Detection in Partial 3D Meshes

Symmetry is a common characteristic in natural and man‐made objects. Its ubiquitous nature can be exploited to facilitate the analysis and processing of computational representations of real objects. In particular, in computer graphics, the detection of symmetries in 3D geometry has enabled a number of applications in modeling and reconstruction. However, the problem of symmetry detection in incomplete geometry remains a challenging task. In this paper, we propose a vote‐based approach to detect symmetry in 3D shapes, with special interest in models with large missing parts. Our algorithm generates a set of candidate symmetries by matching local maxima of a surface function based on the heat diffusion in local domains, which guarantee robustness to missing data. In order to deal with local perturbations, we propose a multi‐scale surface function that is useful to select a set of distinctive points over which the approximate symmetries are defined. In addition, we introduce a vote‐based scheme that is aware of the partiality, and therefore reduces the number of false positive votes for the candidate symmetries. We show the effectiveness of our method in a varied set of 3D shapes and different levels of partiality. Furthermore, we show the applicability of our algorithm in the repair and completion of challenging reassembled objects in the context of cultural heritage.     

Study of the thermomechanical and electrical properties of conducting composites containing natural rubber and carbon black

This work describes the preparation and characterization of composite materials obtained by the combination of natural rubber (NR) and carbon black (CB) in different percentages, aiming to improve their mechanical properties, processability, and electrical conductivity, aiming future applications as transducer in pressure sensors. The composites NR/CB were characterized through optical microscopy (OM), DC conductivity, thermal analysis using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMA), thermogravimetry (TGA), and stress–strain test. The electrical conductivity varied between 10^?9 and 10 S m^?1, depending on the percentage of CB in the composite. Furthermore, a linear (and reversible) dependence of the conductivity on the applied pressure between 0 and 1.6 MPa was observed for the sample with containing 80 wt % of NR and 20% of CB. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

The cationic polymerization of α-methylstyrene in liquid sulfur dioxide initiated by the HI/I2 system

The polymerization of α-methylstyrene (αMeSty) initiated by HI/I₂ or HI in the presence of liquid sulfur dioxide has been investigated. The number-average molecular weight increased with the monomer concentration for reactions initiated by the HI/I₂ system. I₂ also participates in the initiation process, increasing the number-average polymer chain at higher monomer concentration. HI alone is also able to initiate the polymerization of αMeSty in the presence of SO₂. With this initiator, transfer reaction can be minimized in systems containing low amount of SO₂. Received: 19 December 1996/Revised: 27 January 1997/Accepted 29 January 1997     

Filters of implication reducts of basic algebras

Since basic algebras were introduced as a common generalization of MV-algebras and orthomodular lattices, their implication reducts form a common generalization of BCK-algebras and orthoimplication algebras introduced by J. C. Abbott. As shown in our previous paper, congruences in these implication reducts are in a one-to-one correspondence with their kernels. Hence, to characterize congruences it is enough to describe its kernels which is done in the paper.     

The effect of H2 treatment on the activity of activated carbon for the oxidation of organic contaminants in water and the H2O2 decomposition

In this work, hydrogen peroxide reactions, i.e. H₂O₂ decomposition and oxidation of organics in aqueous medium, were studied in the presence of activated carbon. It was observed that the carbon pre-treatment with H₂ at 300, 500, 700 and 800 °C resulted in an increase in activity for both reactions. The carbons were characterized by BET nitrogen adsorption, thermogravimetric analyses (TG), temperature programmed reduction (TPR), electron paramagnetic resonance (EPR), iodometric titration and determination of the acid/basic sites. TPR experiments showed that activated carbon reacts with H₂ at temperatures higher than 400 °C. The treatment produces a slight increase in the surface area. EPR analyses indicate the absence of unpaired electrons in the carbon. Iodometric titrations and TG analyses suggested that the treatment with H₂ generates reduction sites in the carbon structure, with concentration of approximately 0.33, 0.53, 0.59, 0.65 and 0.60 mmol/g for carbons treated at 25, 300, 500, 700 and 800 °C, respectively. It was also observed the appearance of basic sites which might be related to the reduction sites. It is proposed that these reducing sites in the carbon can activate H₂O₂ to generate HO^* radicals which can lead to two competitive reactions, i.e. the hydrogen peroxide decomposition or the oxidation of organics in water.     

Influence of anionic form on thermooxidation of TMAHP–cellulose

With the help of DTA, DTG elementary analysis of carbonized residues and ESR spectroscopy the influence of anionic form on thermooxidation of trimethylammoniumhydroxyprophyl (TMAHP)–cellulose was studied. At 300°C the percentage of carbon in carbonized residue thermolyzed in oxidative atmosphere is higher than for the sample degraded in inert atmosphere. The percentage of hydrogen decreases simultaneously. The concentration of free radicals in thermolyzed residue also increases due to the presence of oxygen. We propose that oxygen is abstracting the hydrogen atoms from polysaccharide and unpaired electrons on carbon atoms are produced. At 400°C the percentage of carbon in residues prepared at inert atmosphere is higher than for residue formed at oxidative atmosphere. Also the concentration of free radicals in thermolyzed residues obtained in inert atmosphere is greater than for those from oxidative ones. That is why suppose that at this temperature oxygen is bonded to polysaccharide residue and free radicals are terminated. From the semiquantitative DTA we can make the following sequence of samples according to their increasing thermooxidative effect: unmodified cellulose < A–HSO < A–Br^? < A–I^? < A–NO < A–H₂PO < A–CH₃COO^? < A–HCO < A–F^? < A–Cl^?1 < A–OH^p?.     

Relationship between crystalline structure and mechanical behavior in isotropic and oriented polyamide 6

Polyamide 6 (PA6) isotropic films and oriented cables were prepared by compression molding or by consecutive extrusion and cold‐drawing. These samples were isothermally annealed in the 120–200°C range and were then subjected to tensile tests at room temperature. Synchrotron wide‐angle X‐ray scattering (WAXS) and small‐angle X‐ray scattering (SAXS) patterns were obtained before and after mechanical failure. These data were related with the mechanical properties of the respective PA6 samples. The annealing of isotropic PA6 resulted in an increase in the Young's modulus (E) and yield stress (σ_y) values, which was attributed to the observed proportional reduction of the d‐spacings of the intersheet distances in both the α‐PA6 and γ‐PA6 polymorphs. Analysis of the WAXS and SAXS patterns of isotropic PA6 after break allowed the supposition of structural changes in the amorphous phase, with these being better pronounced with increasing annealing temperature; this made the samples less ductile. In oriented PA6 samples, annealing resulted in a drastic increase in the E and σ_y values accompanied by a phase transition from γ‐PA6 to α‐PA6 and a well‐pronounced reduction in the intersheet distances of both polymorphs. The stretching of the oriented samples led to an additional γ‐to‐α transition, whose extent was also related to structural changes in the amorphous phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2242–2252, 2007     

The Influence of the Acid Sites on the Methylamines Synthesis with Cu-HZSM-5 Zeolite

There is a high industrial demand for MMA and DMA, however, the production of TMA is favored with the commercial catalysts. This work tested the methanol amination reaction with HZSM-5 and Cu/HZSM-5 zeolites (%Cu = 1.2, 3.7 and 6.0). Regarding the MMA selectivity, light differences were observed among Cu/HZSM-5 catalysts and pure zeolite, although the catalysts containing 3.7% copper was slightly more selective to MMA than the other metallic catalysts studied. From these results it is suggested that the metal loading present in the catalysts leads to a modification in the nature of the acidic sites, in particular, the selectivity depends on ratio Brönsted/Lewis acid sites. This modifications would facilitate the amines desorption during the reaction.     

The potentiometric behaviour of copolymers of methacrylic acid in water-ethanol solutions

Summary The synthesis is reported of copolymers of styrene with methacrylic acid and of methyl methacrylate with methacrylic acid by radical copolymerization, of copolymers of methyl methacrylate with methacrylic acid by partial alkaline hydrolysis of poly(methyl methacrylate), and of block copolymers of styrene with methacrylic acid. Modified titration curves of all these copolymers were recorded in water and water-ethanol solutions. In a solution containing 50 mass.% ethanol, only small differences could be observed between the potentiometric behaviour of the individual copolymers and polymethacrylic acid. Also, there were no essential differences in any of the solvents used between the potentiometric behaviour of block copolymers of styrene with methacrylic acid, on the one hand, and polymethacrylic acid, on the other. On the contrary, maxima and minima were always observed on the modified titration curves of statistical copolymers with a higher content of the hydrophobic comonomer in solutions with a high water content. Thus, using the modified titration curves, it is possible to decide whether a given copolymer is of the block or statistical type.