Influence of thiourea on the nucleation of copper on polycrystalline platinum

The influence of thiourea on the nucleation of copper from a 0.30 M CuSO4-1 M H2SO4 solution on polycrystalline platinum electrodes covered by a copper adlayer was investigated. In the case of diffusion controlled nucleation and growth the conditioning potential, that is, the potential of the electrode prior to the application of a large negative potential step, has a strong influence on the nucleation transients. This can result in either a promotion or an inhibition of the nucleation (which is characterized by a change in the nucleation rate constant and/or the site density) depending on the applied potential and the concentration of thiourea. In the region of mixed kinetics and for a fixed value of the conditioning potential (0.175 V vs Cu2+|Cu, that is, in the region of strongest inhibition), a new and rather unexpected effect was observed. Thus, after an induction period, which is proportional to the concentration of thiourea, the current increases sharply to a much higher value, but after reaching a maximum drops again to its original value. At present there is no ready explanation for this phenomenon, which has been called 'nucleation outbursts', but it deserves more investigation because the linearity between the induction time and the concentration of thiourea might have practical applications.     

Crystalline structures of intercalate molecular complexes of syndiotactic polystyrene with two fluorescent guests: 1,3,5-Trimethyl-benzene and 1,4-dimethyl-naphthalene

The crystal structures of two molecular complex phases of syndiotactic polystyrene (s-PS) with 1,3,5-trimethyl-benzene (TMB) and 1,4-dimethyl-naphthalene (DMN) have been described. These structures present a monoclinic unit cell in which the s(2/1)2 polymer helices and guest molecules are packed according the space group P2₁/a and unit cell constants: a=17.3 Å, b=15.4 Å, c=7.8 Å and γ=95.7° for s-PS/TMB and a=17.4 Å, b=17.2 Å, c=7.8 Å and γ=116.4° for s-PS/DMN. Both structures can be described as intercalates, since they present ac layers of polymer helices alternated to layers of contiguous guest molecules and a guest/monomeric-unit molar ratio of 1/2, as recently observed only for s-PS/norbornadiene molecular complex. On the basis of a comparison between crystalline structures and X-ray diffraction data of several s-PS molecular complexes, a simple criterion to anticipate their clathrate or intercalate nature has been suggested.     

MONTE CARLO SIMULATION OF AGGREGATION PROCESSES STRUCTURAL PROPERTIES OF DEPOSITIONAL AGGREGATES

The usefulness of Monte Carlo simulation of aggregation phenomena is discussed and applied in analysis of the structure of particle deposits. The structural properties of depositional aggregates in single and multiparticle regimes are obtained and expressed in terms of fractal geometrical concepts. These properties are related to the Peclet number and to the concentration in the non-aggregate (vapour) phase. The topological properties of the aggregates are obtained from random walk simulation, thus confirming the anomalous properties of these structures, even in the case of multiparticle simulations, i.e. for high values of the concentration in the vapour phase.     

Energy Production in Water Distribution Networks: A PAT Design Strategy

Pump operating as turbine (PAT) is an effective source of reducing the equipment cost in small hydropower plants. However, the manufacturers provide poor information on the PAT performance thus representing a limit for its wider diffusion. Additional implementation difficulties arise under variable operating conditions, characteristic of water distribution networks (WDNs). WDNs allow to obtain widespread and globally significant amount of produced energy by exploiting the head drop due to the network pressure control strategy for leak reductions. Thus a design procedure is proposed that couples a parallel hydraulic circuit with an overall plant efficiency criteria for the market pump selection within a WDN. The proposed design method allows to identify the performance curves of the PAT that maximizes the produced energy for an assigned flow and pressure-head distribution pattern. Finally, computational fluid dynamics (CFD) is shown as a suitable alternative for performance curve assessment covering the limited number of experimental data.     

Modelling progressive hardening of shotcrete in convergence-confinement approach to tunnel design

The progressive hardening of shotcrete used for tunnel supports is of great importance because it influences the support response to ground movements and therefore the stresses induced in the shotcrete lining. This paper presents anew model, which can take into consideration the hardening of concrete and provides the convergence-confinement curve of the supported tunnel. The model is used to back-analyse the measurements taken in the Kielder Experimental tunnel and presented in technical literature. An axisymmetrial numerical model (FLAC code) has been also set up for comparison with the proposed model results. Both the in-situ measurements and the numerical results using FLAC are in good agreement with those computed using the proposed convergence-confinement method.     

A super-peer model for resource discovery services in large-scale Grids

As deployed Grids increase from tens to thousands of nodes, peer-to-peer (P2P) techniques and protocols can be used to implement scalable services and applications. The super-peer model is a novel approach that helps the convergence of P2P models and Grid environments and can be used to deploy a P2P information service in Grids. A super-peer serves a single physical organization in a Grid, and manages metadata associated to the resources provided by the nodes of that organization. Super-peers connect to each other to form a peer network at a higher level. This paper examines how the super-peer model can handle membership management and resource discovery services in a multi-organizational Grid. A simulation analysis evaluates the performance of a resource discovery protocol; simulation results can be used to tune protocol parameters in order to increase search efficiency.     

Back-analysis techniques for the improvement of the understanding of rock in underground constructions

In many cases, it is necessary to realize design and begin the construction of underground works with only an approximate understanding of the geomechanical parameters of the rock mass that are necessary for a correct definition of the construction technique and of the support structures. The purpose of back-analysing the measured displacements of the tunnel perimeter and the loads on the support structures during the construction of the work is to calibrate the initial estimations of the geomechanical parameters of the ground.Today the use of the back-analysis procedure is not so common and, when it is used, it does not follow a scientific scheme. Full advantage is not taken of the monitoring data, with the consequence of a waste of money.Computers are nowadays able to quickly perform many numerical analyses and therefore the time is ripe to set up a correct back-analysis procedure to use together with a calculation model of the problem, when monitoring data are available. The principles on which the treatment of information derived from the monitoring of underground works during their construction is based are shown in this paper.The paper proposes new efficient mathematical back-analysis techniques for the problem under consideration and some interesting examples.Finally, a real case is presented to which back-analysis was applied.     

Designing of radial bolting in tunnels

The effect of geometrical and mechanical parameters of bolting on the stress-strain state of rock mass around a tunnel is estimated using a specifically developed numerical method.Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 72–83, July–August, 2004.     

Comparison of the expansion ability of fermented maize flour and cassava starch during baking

The modifications occurring during the fermentation (at 20 or 35 °C) and drying (under the sun or in an oven at 40 °C) of maize flour (ogi) and cassava starch along with their expansion ability during baking were characterised and compared. A high temperature accelerated the fermentation but favoured lactic acid synthesis for maize ogi and butyric acid for cassava starch. The increase in acidity was higher for maize, but dried maize ogi did not evidence any expansion ability whatever the experimental conditions. Cassava starch that had been fermented at 20 °C then sun‐dried presented the highest expansion ability. It was associated with low paste viscosities and high swelling and solubilisation values. When the fermentation was carried out at 35 °C, an annealing of cassava starch occurred that delayed starch gelatinisation and which could be involved in its lower baking expansion ability. © 2000 Society of Chemical Industry     

Oxidative stability of red wine stored in packages with different oxygen permeability

A young red wine was aged in containers with different oxygen permeability, i.e. glass, polyethyleneterephtalate (PET) and polyethyleneterephtalate including an oxygen scavenger (PETA), to determine variations in antioxidant components and antioxidant activity, determined as radical scavenging activity. The phenolic composition and the antioxidant activity of the wine were evaluated during approximately 24 weeks of storage at 20 or 30 °C. Significant changes were observed in total anthocyanin concentration in all samples, while other indexes such as total phenolics and total flavonoids remained stable during storage in all conditions. The antioxidant activity diminished in all samples, with differences between the various containers, both at 20 and 30 °C. HPLC analysis showed that important changes occurred in some flavonoid components (catechin, epicatechin, procyanidin TB2) and in most anthocyanidins in all storage conditions, with greater degradation at 30 °C and in PET bottles. Samples stored in PETA bottles showed the highest stability. The research demonstrated that ageing-related changes during storage are influenced by the oxygen permeability of the containers and can be slowed by the use of PET materials with enhanced oxygen barrier capacity.