Distribution and mobility of mercury in soils from an old mining area in Mieres, Asturias (Spain)

Mercury content in soils near abandoned mine wastes in the mercury mining area of Mieres (Asturias, Spain) is highly elevated as a result of the long period of mining and abundant Hg production. In this work, an evaluation of Hg concentration, distribution, and mobility in three soil samples from the immediate vicinity of a chimney used for vapour evacuation during pyrometallurgical treatment of the ore was carried out. For that purpose, total Hg contents were determined for the original samples and their grain-size subsamples. The study of mercury mobility in the original samples and in the different particle-size subsamples was made by the application of a sequential extraction method. Results showed that Hg concentration in soils decreases directly with the distance from the chimney and the dispersion of Hg is not influenced by the topographic height of the site tested. The sample collected in the base of the chimney exhibited appreciable amounts of mobile Hg. In general, a higher Hg concentration was found for the finest particle-size subsamples. Hg mobility was found to be higher for quite developed soils. The sample collected downstream from the chimney showed a significant Hg mobile content as a result of a more intensive weathering. An increase of Hg mobility at decreasing particle size was found in all three analysed samples.     

Fatty acid biosynthesis during embryogenesis in the amphibianBufo arenarum Hensel

The fatty acid composition and biosynthesis of fatty acids were studied during early embryogenesis of the toadBufo arenarum Hensel. The ova and stages up to the 6 1/2 day embryo have similar fatty acid compositions, with ca. 70% unsaturated acids. The eggs and embryo were permeable to acetate and impermeable to palmitic, linoleic, and eicosa-8,11,14-trienoic acid. Labeled acetate was incorporated by the eggs into the saturated acids-lauric, myristic, palmitic, stearic, arachidic, and behenic-and into the unsaturated acids-myristoleic, palmitoleic, oleic, and eicosaenoic acids. During segmentation and gastrulation, de novo biosynthesis of fatty acids increased, desaturation to myristoleic, palmitoleic, and oleic acids was enhanced; and fatty acids were esterified to triglycerides, phosphatidyl choline, and phosphatidyl ethanolamine. The feeding embryo (11 days) changed the pattern of incorporation to less incorporation into triglycerides.     

Gold Stabilized with Iridium on Ceria–Niobia Catalyst: Activity and Stability for CO Oxidation

Topics in Catalysis - Monometallic gold and iridium, and bimetallic gold–iridium on ceria–niobia (Nb2O5–CeO2) catalysts were synthesized by deposition–precipitation with...     

Convergence of a lowest-order finite element method for the transmission eigenvalue problem

The transmission eigenvalue problem arises in scattering theory. The main difficulty in its analysis is the fact that, depending on the chosen formulation, it leads either to a quadratic eigenvalue problem or to a non-classical mixed problem. In this paper we prove the convergence of a mixed finite element approximation. This approach, which is close to the Ciarlet–Raviart discretization of biharmonic problems, is based on Lagrange finite elements and is one of the less expensive methods in terms of the amount of degrees of freedom. The convergence analysis is based on classical abstract spectral approximation result and the theory of mixed finite element methods for solving the stream function–vorticity formulation of the Stokes problem. Numerical experiments are reported in order to assess the efficiency of the method.     

System reliability-based design optimization and risk-based optimization: a benchmark example considering progressive collapse

System Reliability-Based Design Optimization (RBDO) considers a single system failure probability constraint. The formulation allows different failure modes to compete with each other. Very few methods and benchmark examples involving optimal design considering system behaviour with progressive failure can be found in the literature. In this article, the conventional System RBDO formulation is compared with a risk-based formulation. A benchmark example involving progressive failure of hyper-static truss is addressed. It is demonstrated that typical System RBDO formulations always lead to isostatic structures, since the formulation does not offer any incentive for the permanence of hyper-static members. In the risk-based formulation, failure costs are differentiated with respect to primary member failure, in hyper-static structures (existence of warning before eventual collapse), and failure of isostatic members (no warning). In this formulation, optimal designs also include hyper-static structures. Results presented herein are relevant in the modern context of robust design considering progressive collapse.     

Maximum volumetric production of β‐galactosidase by Kluyveromyces fragilis in fed‐batch culture with automatic control

The production of β‐galactosidase by Kluyveromyces fragilis was studied in different culture systems, with dissolved oxygen concentration control and using defined media. An operating strategy of fed‐batch culture with automatic control of substrate addition regulated by dissolved oxygen concentration, consisting of the replacement of variable volumes of broth by fresh medium (once the fed‐batch culture has finished), was designed. The volumetric enzyme productivity (Q_p, 13 600 UI dm^?3 h^?1) obtained was 38% higher than that reached in continuous culture of K fragilis with dissolved oxygen concentration control and far higher than that obtained by batch culture of K fragilis under the same aeration conditions. © 2002 Society of Chemical Industry     

Nutritive value of methyl linoleate and its thermal decomposition products

Methyl linoleate was heated for 10 hrs. at 300°C, in the absence of air and fractionated by alembic distillation and urea adduct-formation. Intestinal absorptions of the urea adduct-forming monomeric nonadduct-forming monomeric, and dimeric fractions were determined. It was found that dimers were half as well absorbed as the monomers. When fed to rats, dimers were better accepted and exhibited some toxicity symptoms different from the non-adduct-forming monomers. The dimers caused diarrhea, irritability, and loss of hair during the early period of administration. The nonadduct-forming monomers were lethal and produced an increase in liver weight. Both fractions depressed growth. With the technical assistance of Oscar giacomantone and Perla Mordujovich.     

Improved toughness in HIPS obtained from different styrene/butadiene‐graded block copolymers through modification of the polydispersity index of the PS block

The polymerization of styrene in the presence of graded block copolymers with a polystyrene/polybutadiene composition of 40/60, 30/70, and 20/80 and with a polydispersity index (M_w /M_n ) in the polystyrene block varying from 1.1 to 1.6 was studied. As the polydispersity index of the polystyrene block increases, an improvement of up to 50% in the Izod impact toughness of the produced high‐impact polystyrene was achieved. The rubber particle morphology type, the size, and the volume fraction of the rubber phase particles could be modified through changes in the composition of the graded block copolymer. The changes that occurred in the rubber phase were mainly generated by the variation in the interfacial tension between the phases, and this variation was principally attributed to an increase in the polydispersity index of the polystyrene block in the precursor copolymer. POLYM. ENG. SCI., 46:1333–1341, 2006. © 2006 Society of Plastics Engineers