Geochemical modelling of arsenic and selenium leaching in alkaline water treatment sludge from the production of non-ferrous metals

Geochemical modelling of leaching of oxyanion forming elements such as arsenic (As) and selenium (Se) is frequently not successful. A consistent thermodynamic dataset of As and Se was therefore composed, not only including precipitation, but also adsorption and solid solution, and was applied to the pH-dependent leaching behaviour of As and Se in an alkaline residue with a pH 11.1 from the lime treatment of sulphuric acid wastewaters from the production of non-ferrous metals. The As and Se content ranged up to 6.7 wt% and 0.29 wt%, respectively and speciation analysis showed that 96.3% of As occured as arsenate whereas Se speciation comprised 79% selenate and 21.0% selenite. XRD and SEM/EDX analysis showed that arsenate occurred as rauenthalite (Ca(3)(AsO(4))(2).10H(2)O), associated with gypsum, the most important mineral. Arsenate and arsenite concentrations were only slightly below equilibrium with rauenthalite and calciumarsenite (CaHAsO(3)), respectively and consideration of adsorption and solid solution only marginally improved model predictions. Selenate (Se(VI)) and selenite (Se(IV)), on the other hand, were far from equilibrium with their corresponding calcium metalate. The application of solid solutions and adsorption of Se(VI) and Se(IV) oxyanions with gypsum, calcite and ettringite significantly improved model predictions but missing thermodynamic data and especially the lack of a comprehensive model for solid solution and surface exchange with calcite and ettringite still hampered efficient modelling.     

Robust design of tuned mass dampers installed on multi-degree-of-freedom structures subjected to seismic action

This study deals with robust optimum design of tuned mass dampers installed on multi-degree-of-freedom systems subjected to stochastic seismic actions, assuming the structural and seismic model parameters to be uncertain. A new global performance index for evaluating the efficiency of protection systems is proposed, as an alternative to commonly used local performance indices such as the maximum interstorey drift. The latter can be considered a good estimator of seismic damage, but it does not measure the whole structural integrity. The direct perturbation method based on first order approximation is adopted to evaluate the effects of uncertainties on the response. The robust design is formulated as a multi-objective optimization problem, in which both the mean and the standard deviation of the performance index are simultaneously minimized. A comparison of the effectiveness and robustness of tuned mass dampers designed using local or global performance indices is carried out, considering different levels of uncertainty.     

Numerical Calculation of the Interaction of Superfluid Vortices and a Rigid Sphere

We implement a method for the calculation of the effects of a solid sphere on the dynamics of superfluid vortices. We present in detail the derivation of the mathematical formulae used in a computational algorithm which avoids numerical singularities, as well as an adaptive algorithm for convergence tests and diagnostics of the method’s accuracy.     

High-resolution mapping of quantum efficiency of silicon photodiode via optical-feedback laser microthermography

We map the external quantum efficiency (QE) distribution of a silicon photodiode (PD) sample via a thermographic imaging technique based on optical-feedback laser confocal microscopy. An image pair consisting of the confocal reflectance image and the 2D photocurrent map is simultaneously acquired to delineate the following regions of interest on the sample: the substrate, the n-type region, the pn overlay, and the bonding pad. The 2D QE distribution is derived from the photocurrent map to quantify the optical performance of these sites. The thermal integrity of the sample is then evaluated by deriving the rate of change of QE with temperature T at each point on the silicon PD. These gradient maps function not only as stringent measures of local thermal QE activity but they also expose probable defect locations on the sample at high spatial resolution--a capability that is not feasible with existing bulk measurement techniques.     

Technologies for the removal of phenol from fluid streams: a short review of recent developments

The available technologies for the abatement of phenol from water and gaseous streams are briefly reviewed, and the recent advancements summarized. Separation technologies such as distillation, liquid–liquid extraction with different solvents, adsorption over activated carbons and polymeric and inorganic adsorbents, membrane pervaporation and membrane–solvent extraction, have been discussed. Destruction technologies such as non-catalytic, supercritical and catalytic wet air oxidation, ozonation, non-catalytic, catalytic and enzymatic peroxide wet oxidation, electrochemical and photocatalytic oxidation, supercritical wet gasification, destruction with electron discharges as well as biochemical treatments have been considered. As for the abatement of phenol from gases, condensation, absorption in liquids, adsorption on solids, membrane separation, thermal, catalytic, photocatalytic and biological oxidation have also been considered. The experimental conditions and the performances of the different techniques have been compared.     

Ecological compensation in spatial planning in Italy

Ecological compensation or biodiversity offsets are increasingly recognized as a key element for environmental sustainability; however, more attention has been paid so far to compensation applied at the project level rather than to spatial planning. Meanwhile, there is a growing acknowledgement that extensive environmental depletion is being caused by the cumulative effects of small developments allowed by spatial/land use plans. This paper aims to collect empirical evidence on the requirements for ecological compensation at a strategic level of decision-making – spatial planning – in Italy. Results indicate that spatial plans are increasingly introducing offset requirements for residual impacts of new urban developments; however, methodological and operational aspects are not sufficiently addressed and enforcement mechanisms appear weak. The lack of legal frameworks and of established methods appears to be the main element currently hindering biodiversity offset implementation at the planning level. It is suggested that, in the Italian context, a way to foster better implementation is the design of environmental stewardship schemes involving farmers, developers and planning authorities.     

The relative use of proximity, shape similarity, and orientation as visual perceptual grouping cues in tufted capuchin monkeys (Cebus apella) and humans (Homo sapiens).

Recent experimental results suggest that human and nonhuman primates differ in how they process visual information to assemble component parts into global shapes. To assess whether some of the observed differences in perceptual grouping could be accounted for by the prevalence of different grouping factors in different species, we carried out 2 experiments designed to evaluate the relative use of proximity, similarity of shape, and orientation as grouping cues in humans (Homo sapiens) and capuchin monkeys (Cebus apella). Both species showed similarly high levels of accuracy using proximity as a cue. Moreover, for both species, grouping by orientation similarity produced a lower level of performance than grouping by proximity. Differences emerged with respect to the use of shape similarity as a cue. In humans, grouping by shape similarity also proved less effective than grouping by proximity but the same was not observed in capuchins. These results suggest that there may be subtle differences between humans and capuchin monkeys in the weighting assigned to different grouping cues that may affect the way in which they combine local features into global shapes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Viscoplasticity based on additive decomposition of logarithmic strain and unified constitutive equations: Theoretical and computational considerations with reference to shell applications

In contrast to multiplicative models of finite strain plasticity and viscoplasticity, a framework of additive nature is developed in this paper. The theory is based on the additive decomposition of the logarithmic strain tensor. The stress conjugate to the logarithmic strain then plays the role of the thermodynamically driving force. The approach in this paper is motivated by the search for numerically accessible structures which can be extended to incorporate anisotropy as well. Specifically in this region, multiplicative formulations become extremely tedious. The evolution equations are of the unified type due to Bodner and Partom, and are modified so as to fit into the theoretical framework adopted. The numerical treatment of the problem is fully developed. Specifically, the algorithmic aspects of the approach are discussed and various applications to shell problems are considered. A shell theory with seven degrees of freedom, together with a four-node enhanced strain finite element formulation, is used. A central feature of the shell formulation is its eligibility to the application of a three-dimensional constitutive law.     

Remarks on excitability, stability and sign of equilibria in cooperative systems

The strict positivity of equilibria is known to be equivalent to asymptotic stability in excitable positive linear systems. In contrast with intuition, this property does not hold for nonlinear cooperative systems. However, weaker results are pointed out and proved to be effective in the analysis of several nonlinear cooperative systems.