EPON bandwidth allocation algorithm based on automatic weight adaptation to provide client and service differentiation

In this article, a new dynamic bandwidth allocation algorithm for the upstream channel of Ethernet Passive Optical Networks, called DySLa, is proposed not only to provide service differentiation but also to offer subscriber differentiation. In contrast to previous methods in which the performance of each class of service is not insured, DySLa is continuously evaluating the mean packet delay and guarantees that the highest priority services fulfil the packet delay requirements in the access network for every type of client. Simulation results show that DySLa can maintain both the mean packet delay and packet loss ratio below the maximum upper bounds permitted for the most sensitive services of every class of customer. Moreover, DySLa outperforms other dynamic bandwidth allocation algorithms which provide service and client differentiation and it makes a fairer bandwidth distribution than those methods.

Reduction of hexavalent chromium by Sphaerotilus natans a filamentous micro-organism present in activated sludges

Wastewaters produced by various industries may contain undesirable amounts of hexavalent chromium (Cr(VI)), as chromate and dichromate, a hazardous metal affecting flora and animals of aquatic ecosystems as well as human health. One removal strategy comprises the microbial reduction of Cr(VI) to Cr(III), a less soluble chemical species that is less toxic than Cr(VI). In this work, the ability to reduce Cr(VI) of Sphaerotilus natans, a filamentous bacterium usually found in activated sludge systems, was evaluated. In aerobic conditions, S. natans was able to efficiently reduce Cr(VI) to Cr(III) from dichromate solutions ranging between 4.5 and 80 mg Cr(VI)l(-1) in the presence of a carbonaceous source. A simultaneous evaluation of the microbial respiratory activity inhibition was also carried out to analyze the toxic effect of Cr(VI). Cr(VI) reduction by S. natans was mathematically modeled; chromium(VI) reduction rate depended on both Cr(VI) concentration and active biomass concentration. Although it is known that S. natans removes heavy metal cations such as Cr(III) by biosorption, the ability of this micro-organism to reduce Cr(VI), which behaves as an oxyanion in aqueous solutions, is a novel finding. The distinctive capacity to reduce Cr(VI) to Cr(III) than remain soluble or precipitated becomes S. natans a potential micro-organism to decontaminate wastewaters.     

Biological and Abiotic Color Reduction of Paper Mill Effluents during Anaerobic Composting

Biological and abiotic sorptions as well as kinetic experiments were performed to elucidate the mechanism by which color was being removed from paper mill effluents using anaerobic composting. Experiments were performed using pulp mill upset tank wastewater (color = 5,500?PCU) and E stage filtrate (color = 10,300?PCU). Color removal experiments using active and gamma sterilized compost showed that the color removal capacity for both wastewaters was nine times higher when using active compost than for those reactors using gamma sterilized compost. Final decolorization for pulp mill upset tank and E stage filtrate was 91 and 83%, respectively, while only 33% decolorization was achieved with gamma sterilized compost. Kinetic tests also showed higher color degradation rates when using active compost compared to sterilized compost. Additional experiments demonstrated that biological color removal appears to be robust with respect to pH and is largely unaffected by pH over a range from pH 5 to 10, typical values for the effluents in paper mills. The effect of aging in sorption were tested and results showed that virgin compost could establish a microbial population in less than 50 days which resulted in a compost with sorption capacity similar to the aged compost.     

Chromium bioaccumulation: comparison of the capacity of two floating aquatic macrophytes

The capacity of Salvinia herzogii and Pistia stratiotes to remove Cr (III) from water and their behaviour at different Cr (III) concentrations were studied in outdoor experiments. Cr distribution in aerial parts and roots with time and the possible mechanisms of Cr uptake were analyzed. Both macrophytes efficiently removed Cr from water at concentrations of 1, 2, 4 and 6 mgCrL(-1). S. herzogii was the best adapted species. At a greater initial concentration, greater bioaccumulation rates were observed. Root Cr uptake was a rapid process that was completed within the first 24h. Cr uptake through direct contact between the leaves and the solution is the main cause of the increase of Cr in the aerial parts, Cr being poorly translocated from the roots to the aerial parts. Both mechanisms were fast processes. The Cr uptake mechanism involves two components: a fast component and a slow one. The former occurs mainly due to the roots and leaves adsorption and is similar for both species. The slow component is different for each species probably because in P. stratiotes a Cr precipitation occurs induced by the roots.     

Current measurement by Faraday effect on GEPOPU

The design of an optical current sensor to be used in a pulsed power generator is presented. The current sensor is based on the polarization rotation by the Faraday effect. GEPOPU is a pulsed power generator, 110 kA, 120 ns double transit time, 1.5 Ω coaxial geometry, and current rise time of 50 ns. Two different optical geometries surrounding the conductor were tried, using Amici roof prism and pentaprism to go around the current once, as a way to preserve the state of polarization along the optical path by means of complementary reflections within the sensing element. We believe this to be the first time that such large and rapidly varying currents have been measured with this configuration. The values obtained for both geometries agree with the values obtained with a Rogowski coil. The traces obtained are completely noise-free and no significant time lag has been observed between the current determined from the Faraday rotation and the current measured using a Rogowski coil.     

Fogging with antibrowning agents as an alternative to conventional immersion treatments to extend shelf life of mushrooms

Mushroom (Agaricus bisporus) is a highly perishable product and can be easily damaged when immersion in antibrowning solutions is performed; therefore, fogging application represents a less aggressive technique. The objective of this work was to evaluate the effect of different antibrowning agents (ascorbic acid, sodium metabisulphite and L-cysteine) applied by two methodologies (immersion and fogging) on the quality of mushrooms during storage at 5 °C. Weight losses, microstructural organisation, colour and texture changes were evaluated as quality indicators. Polyphenol oxidase activity, phenolic content and antioxidant activity were also evaluated. Fogging achieved browning inhibition without major changes in firmness, while immersion treatments inhibited browning but significant changes in firmness were found. Browning inhibition achieved by fogging showed similar results when compared to the conventional immersion treatments. Fogging has the advantage of being less aggressive than immersion while requiring a significantly smaller amount of antibrowning solution than traditional immersion.     

Postnatal testicular development in mouse species with different levels of sperm competition

Postcopulatory sexual selection leads to an increase in sperm numbers which is partly the result of an increase in relative testes mass and could also be the consequence of changes in testis architecture or function. Very little is known regarding developmental changes during the first spermatogenic wave that may lead to enhanced spermatogenic efficiency and increased sperm production. We examined testicular development after birth in four mouse species with different sperm competition levels to assess changes in testicular architecture and function. Differences in relative testes mass between species appeared soon after birth and were exacerbated thereafter. The volume of testes occupied by seminiferous tubules differed between species postnatally and were associated with sperm competition levels. Finally, changes over time in the proportions of tubules with different germ cell types were also associated with sperm competition levels, with the time taken for the transition between various cell stages being negatively associated with levels of sperm competition. We conclude that postnatal testis development differs between closely related species with different sperm competition levels influencing testis architecture and the rate of progression of spermatogenesis, leading to differences in testis function at reproductive maturity.     

5-Hydroxytryptophan as a precursor of a catalyst for the oxidation of NADH

Following oxidation of 5-hydroxytryptophan (5-HTPP) at a pyrolytic graphite electrode at pH 7.5, two quasi-reversible redox couples emerge at -0.170 and +0.032 V, respectively, due to oxidation products strongly adsorbed to the electrode surface. These redox processes have been electrochemically and kinetically characterized in terms of the dependence of the formal potential (E degrees ') with pH, variation of the current density with scan rate, operational stability, and electron-transfer rate constant (k(s)). The wave centered at +0.032 V could mediate the oxidation of NADH, exhibiting a strong and persistent electrocatalytic response. A quinone-imine structure has been proposed as the electrocatalytically active species. The kinetics of the reaction between the mediator and NADH has been characterized via rotating disk electrode voltammetry, and it has been found that the rate constant for the reaction is dependent on the solution concentration of NADH. 5-HTPP modified electrodes could be employed in the amperometric detection of NADH with a limit of detection in the nanomolar range. Moreover, 5-HTPP modified electrodes retain their electrocatalytic activity for at least one week. The potential application of these electrodes to amperometric biosensor is demonstrated.     

Ice VI freezing of meat: supercooling and ultrastructural studies

While "classical" freezing (to ice I) is disruptive to the microstructure of meat, freezing to ice VI has been found to preserve it. Ice VI freeze-substitution microscopy showed no traces of structural alteration on muscle fibres compared with the extensive damage caused by ice I freezing. The different signs of the freezing volume changes associated with these two ice phases is the most likely explanation for the above effects. Ice VI exists only at high pressure (632.4-2216 MPa) but can be formed and kept at room temperature. It was found that its nucleation requires a higher degree of supercooling than ice I freezing does, both for pure water and meat. Monitoring of the freezing process (by temperature and/or pressure measurements) is, thus, essential. The possible applications of ice VI freezing for food and other biological materials and the nucleation behaviour of this ice phase are discussed.