Hydrosilylation crosslinking of silicone rubber catalyzed by bis (1,5-cyclooctadiene) di-μ,μ′-chlorodirhodium

Hydrosilylation vulcanization of addition silicone rubber catalyzed by bis (1,5-cyclooctadiene) di-μ,μ′-chlorodirhodium at 150° was studied. The course of vulcanization, rubber network density, and mechanical properties of the vulcanizate are discussed with respect to the structure and molecular weight of the reactive groups of telechelic and internal vinylmethylpolysiloxanes and crosslinking methyl (hydrogen) dimethyl siloxane copolymers. Molecular weights of the polysiloxane components as well as the ration of unsaturated and Si—H groups were optimized. The results are in agreement with the theory of rubber elasticity of polymer networks and show wide application possibilities of the catalyst used.     

Physico-chemical gradients and meromictic stratification in Cueva de la Mora and other acidic pit lakes of the Iberian Pyrite Belt

A marked vertical trend of increasing temperature and dissolved metal concentrations is observed in the monimolimnia of some meromictic pit lakes of the Iberian Pyrite Belt (IPB) in SW Spain. Temperature differences between the chemocline and the pit lake bottom can be as high as 15°C (e.g. Herrerías), and the respective concentration of some metals (e.g. Fe) and metalloids (e.g. As) can increase by several orders of magnitude (e.g. Cueva de la Mora). The redox conditions also change drastically from the upper and oxygenated mixolimnion (strongly oxidizing) to the lower and anoxic monimolimnion (moderately reducing). Processes such as the inflow of metal–sulphate laden ground water from flooded shafts and galleries, and other factors such as the pit geometry or the relative depth of the lakes, must be considered to account for the observed stratification pattern. The vertical profiles of physico-chemical parameters and water chemistry obtained in Cueva de la Mora and other meromictic pit lakes of the IPB are also compatible with a reactive bottom in which several geochemical and microbial reactions (including reductive dissolution of Fe³⁺ minerals, bacterial reduction of Fe³⁺ and SO₄ ²⁻ in pore waters within the sediments, and decomposition of organic matter) could be taking place.     

A methodology for predicting the severity of environmental impacts related to the construction process of residential buildings

This paper introduces a systematic approach for dealing with potential adverse environmental impacts at the pre-construction stage. The proposed methodology serves as an assessment tool for construction projects to measure the environmental performance of their construction activities. It also provides a consistent basis for comparisons and for future eco-labelling and environmental benchmarking among construction companies and construction sites. Within the methodological framework, nine categories of environmental aspects are proposed: atmospheric emissions; water emissions; waste generation; soil alteration; resource consumption; local issues; transport issues; effects on biodiversity; and incidents, accidents and potential emergency situations. The methodology includes 20 performance indicators developed with the help of a panel of experts. In order to avoid a typical shortcoming in environmental assessments methods, these environmental indicators, both direct and indirect, are always based on quantitative data available in the project documents. Significance limits for environmental aspects are also developed based on a statistical analysis of 55 new-start construction projects. Four case studies are provided to illustrate the practical use of the proposed methodology.     

Chemical modification of unsaturated polyesters influence of polyester's structure on thermal and viscoelastic properties of low styrene content copolymers

In this study, the chemical modification of unsaturated polyesters and the influence of polyester's structure on thermal and viscoelastic properties have been presented. The structure of unsaturated polyesters obtained in polycondensation of cyclohex‐4‐ene‐1,2‐dicarboxylic anhydride (THPA), maleic anhydride and only one suitable symmetrical glycol: ethylene glycol or 1,4‐butanediol (BDO) or 1,6‐hexanediol has been modified by peracetic acid. The selective oxidation of unsaturated polyesters conducted in mild time and temperature conditions was a successful and effective method to prepare new materials/unsaturated epoxy polyesters/containing epoxy groups in cycloaliphatic rings and carbon–carbon double bonds in polyester chain. The unsaturated epoxy polyesters were capable of both copolymerization with vinyl monomer and polyaddition reactions with suitable curing agent. Therefore, they were successfully used as a component of low styrene content copolymers. As was confirmed by DSC, DMA, and TGA analyses, polyester's structure had significant influence on thermal and viscoelastic properties of styrene copolymers. The properties of styrene copolymers prepared from unsaturated epoxy polyesters were considerably better compared with those obtained for styrene copolymers from unsaturated polyesters.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Prediction of Heavy Metals Mobility and Bioavailability in Contaminated Soil Using Sequential Extraction and Biosensors

Several chemical and biological methods have been developed in the last decade to evaluate heavy metals mobility and bioavailability in contaminated soils. In this study, two methods, Biomet sensors and chemical sequential extraction [potentially bioavailable assessment sequential extraction (PBASE) method], were used to predict heavy metals bioavailability in the surface and heavy metals mobility in the subsurface of smelter-contaminated soils, respectively. The heavy metals considered (arsenic, copper, iron, lead, and zinc) were those detected in a previous sampling campaign performed in the contaminated area. Biomet biosensor results indicated that 15–25% of Cu and Zn were bioavailable for plants and animals uptake in the soil surface, whereas higher values were obtained for As and Pb (>60%). In the soil subsurface, iron was identified as the less mobile element, followed by As and Pb, since they were mainly present in the nonsoluble fractions of PBASE method. In contrast, Cu and Zn showed similar distribution between the soluble and nonsoluble fractions. Therefore, PBASE and Biomet are useful and complementary methods which supply different information about heavy metals occurrence in contaminated soils: the first method indicates their potential mobility, whereas the second one shows their potential bioavailability for biota.     

A mixed integer linear formulation for the minimum label spanning tree problem

In this paper we deal with the minimum label spanning tree problem. This is a relevant problem with applications such as telecommunication networks or electric networks, where each edge is assigned with a label (such as a color) and it is intended to determine a spanning tree with the minimum number of different labels. We introduce some mixed integer formulations for this problem and prove that one of their relaxations always gives the optimal value. Finally we present and discuss the results of computational experiments.     

The differential equation counterpart of an individual-based model for yeast population growth

Computer simulations are increasingly used in biological fields. The amazing power, storage ability, and processing speeds available nowadays have enabled the implementation of computer individual-based models (IbMs) to simulate really complex biological populations. Computers can easily keep track of thousands of individuals (often called ’agents’), whose complex behaviours and large amounts of associated data were daunting only 20 years ago. As such, computer modelling has just entered a field where traditional PDE models used to reign alone. A study of the exchange and non-trivial relationship between these two fields, computer IbMs versus classic partial differential equations (PDEs), is appropriate. The aim of this paper is to compare both approaches through a relevant example, namely the evolution of a yeast population in a batch culture. Thus, this paper deals with the utilization of both classical mathematics and computer science in the solution of problems arising in microbiology. First, an IbM approach to study the evolution of a yeast batch culture is presented. Second, an equivalent PDE model is derived by using some techniques from the interacting particle systems field. Third, a comparison and discussion on the advantages and drawbacks of both modelling tools is given.     

Theoretical study of the influence of the morphology in polymer-based devices functioning

It is well known that the morphology of polymer-based optoelectronic devices can influence their efficiency, since the ways that polymer chains pack inside the active layer can influence not only the charge transport but also the optic properties of the device. By using a mesoscopic model we carried out computer experiments to study the influence of the polymer morphology on the processes of charge injection, transport, recombination and collection by the electrodes opposite to those where the injection of bipolar charge carriers take place. Our results show that for polymer layers where the conjugated segments have perpendicular and random orientation relative to the electrodes surface, the competition between charge collection and charge recombination is affected when the average conjugation length of the polymer strands increase. This effect is more pronounced with the increase of the potential barrier at polymer/electrode interfaces that limit charge injection and increase charge collection. For these molecular arrangements the intra-molecular charge transport plays a major role in device performance, being this effect negligible when the polymer molecules have their axis parallel to the electrodes. Although the polymer morphology modelled in this work is far from real, we believe that our model can give some insights on the role of the microstructure on the functioning of polymer-based devices.     

Optimal design of multiproduct batch plants considering duplication of units in series

A generalized disjunctive programming (GDP) model for the optimal design of multiproduct batch plants is presented. This general model manages the duplication of units in series to perform a given operation in the process, which is an alternative that has not been considered in previous general approaches. Unlike duplication in parallel, duplication in series is only applicable to some operations which present trade-offs between duplication and other cost-impacting elements in the batch process. In order to use a fixed time and size factor model some assumptions had to be made in the operations that allow the duplication in series. To show the effectiveness of this approach, a plant that produces multiple recombinant proteins is presented and solved.     

Color rendering properties of light continuously modulated by an electrochromic switchable device

Every chromogenic switchable window gives rise to considerable change of spectral power distribution of the light crossing trough. The filtered light continuously changes during charging/discharging of the device, seen as its coloration/discoloration. As this process occurs continuously, it causes continuous change of colors on an illuminated multicolored scene. The ability of an electrochromic (EC) switchable unit to modulate daylight and different artificial lights passing through it is studied here. The color rendering properties of such a variable light are evaluated. The range of the effect and its consequences on the color of a scene can be adequately described by the change in chroma and hue angle during the modulation of light. These effects were evaluated by different light sources shining through the same EC unit. © 2009 Wiley Periodicals, Inc. Col Res Appl, 34, 321–329, 2009