The Interaction of γ-Glycidoxypropyltrimethoxysilane with Oxidised Aluminium Substrates: The Effect of Drying Temperature

The interaction of γ-glycidoxypropyltrimethoxysilane (GPS) with oxidised aluminium substrates has been investigated in terms of the effect of the drying, or curing, temperature. Samples treated with aqueous solutions of GPS at concentrations of 1,4 and 8% v/v were cured at 25, 50, 93 and 120°C. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used to construct adsorption isotherms and determine the thicknesses of the various GPS coatings. A temperature effect induces subtle changes in the structure of the resulting films. The uptake of GPS is increasing with increasing concentration of GPS. The structure of the films changes at a threshold temperature between 50 to 93°C. XPS and ToF-SIMS data both indicate that the interaction of the GPS film on aluminium is different for low and high temperatures drying regimes. Using the Beer-Lambert equation, it was found that increasing the curing temperature leads to the variation of the thickness of silane films. This is interpreted in terms of changes in the crosslink density of the films and in their state of hydration and/or degradation.     

Functional verification of instruction processing units through control flow modeling

The design verification of state-of-the-art high-performance microprocessors has become a significant challenge for test engineers. Deep pipelines, multiple execution units, out-of-order and speculative execution techniques, typically found in such microprocessors, contribute much to this complexity. Conventional methods, which treat the processor as a logic state machine or apply architectural level tests, fail to provide coverage of all possible corner cases in the design. This paper presents a functional verification method for modern microprocessors, which is based on innovative models of the microprocessor architecture, intended to cover the testing of all corner cases. In order to test the models presented in this work, an architecture independent coverage measurement system has been developed. The models were tested with both random code and real world applications in order to determine which of the two achieves higher coverage.     

Solar Carboreduction of Alumina Under Vacuum

A preliminary study on carboreduction of alumina under vacuum, which was necessary before the solar reactor design, has been performed using an induction heater equipped with a graphite susceptor as the sample holder surrounded by a ceramic tube serving as the metal vapor deposit site. The primary objective was to study the forward and backward reactions as a function of temperature and CO partial pressure. It was concluded that at reaction temperatures above 1600°C and at an average CO partial pressure below 0.2 mbar, the amount of residual by-products in the graphite crucible was negligible, whereas tests with an average CO partial pressure of 2.6 mbar required temperatures above 1800°C to convert the stoichiometric reactants pellets fully. It was concluded that pure aluminum can be found only at deposit sites with temperatures below 600–700°C in tests with temperature and pressure suitable to prevent the volatile suboxide formation in the forward reaction. Based on these results, the solar reactor was designed with a sharp temperature drop from the hot to the cold area. The results of solar tests with different levels of CO partial pressure and temperature conditions reveal that the alumina to aluminum conversion is about 90% for reaction temperatures above the minimum temperature required for full conversion as predicted by the thermodynamic calculations at the appropriate pressure. However, at lower temperatures, a significant amount of solid Al₄C₃, Al₄CO₄, and volatile Al₂O can be formed in the forward reaction, leading to an increase of the residual by-product in the reactant holder as well as lower purity of the aluminum product and an increase of the alumina content in the deposits at the cold reactor’s zone. The observed nanocrystalline and amorphous morphology of the deposits caused by fast cooling in the cold zone will also be discussed.     

A novel method of reducing melting temperatures in SnAg and SnCu solder alloys

With the increasing use of lead-free solder alloys in modern electronics, low melting materials are often required to protect the heat-sensitive parts during soldering operation. Alloy systems based on Sn/Cu/Ag offer more reliable solutions and address the current problems involved with soldering process. Nanoparticles melt relatively at low temperatures compared to their bulk counter parts and we introduce a robust method of synthesizing nanoscale solder pastes for wave soldering applications. Nanoparticles of Sn-3.5Ag and Sn-0.7Cu alloys were prepared with stir casting followed by mechanical attrition. The size dependent melting properties of the eutectic alloys were studied by differential scanning calorimetry technique and the results showed a reduction of 4.7 and 5.0 °C melting temperatures in the alloys when reduced from bulk to 92 nm and 96 nm sizes respectively. The nanosize effects were also theoretically calculated and compared with experimental data.     

Effect of Co on oxygen reduction reaction catalyzed by Pt catalyst, and its implications for fuel cell contamination

The oxygen reduction reaction (ORR) catalyzed by Pt was studied in the presence of Co²⁺ using cyclic voltammetry (CV), rotating disk electrode (RDE), and rotating ring-disk electrode (RRDE) techniques in an effort to understand fuel cell cathode contamination caused by Co²⁺. Findings indicated that Co²⁺ could weakly adsorb on the Pt surface, resulting in a slight change in ORR exchange current densities. However, this weak adsorption had no significant effect on the nature of the ORR rate determining steps. The results from both RDE and RRDE indicated that the overall electron transfer number of the ORR in the presence of Co²⁺ was reduced, with ∼9% more H₂O₂ being produced. We speculate that the weakly adsorbed Co²⁺ on Pt could react with the H₂O₂ intermediate and form a Co²⁺-H₂O₂ intermediate, inhibiting the further reduction of H₂O₂ and thus resulting in more H₂O₂ production. The fuel cell performance drop observed in the presence of Co²⁺ could be attributed to the reduction in overall electron transfer number and the increase in H₂O₂ production. Higher production could intensify the attack by H₂O₂ and its radicals on membrane electrode assembly components, including the ionomer, carbon support, Pt particles, and membrane, leading to fuel cell degradation.     

Effectiveness of smart charging of electric vehicles under power limitations

This article investigates charging strategies for plug‐in hybrid electric vehicles (PHEV) as part of the energy system. The objective was to increase the combined all‐electric mileage (total distance driven using only the traction batteries in each PHEV) when the total charging power at each workplace is subject to severe limitations imposed by the energy system. In order to allocate this power optimally, different input variables, such as state‐of‐charge, battery size, travel distance, and parking time, were considered. The required vehicle mobility was generated using a novel agent‐based model that describes the spatiotemporal movement of individual PHEVs. The results show that, in the case of Helsinki (Finland), smart control strategies could lead to an increase of over 5% in the all‐electric mileage compared to a no‐control strategy. With a high prediction error, or with a particularly small or large battery, the benefits of smart charging fade off. Smart PHEV charging strategies, when applied to the optimal allocation of limited charging power between the cars of a vehicle fleet, seem counterintuitively to provide only a modest increase in the all‐electric mileage. A simple charging strategy based on allocating power to PHEVs equally could thus perform sufficiently well. This finding may be important for the future planning of smart grids as limiting the charging power of larger PHEV fleets will sometimes be necessary as a result of grid restrictions. Copyright © 2013 John Wiley & Sons, Ltd.     

Maximizing the configuration robustness for parallel multi-purpose machines under setup cost constraints

This paper focuses on the configuration of a parallel multi-purpose machines workshop. An admissible configuration must be chosen in order to ensure that a load-balanced production plan meeting the demand exists. Moreover, the demand is strongly subject to uncertainties. That is the reason why the configuration must exhibit robustness properties: the load-balancing performance must be guaranteed with regard to a given range of uncertainties. A branch-and-bound approach has been developed and implemented to determine a cost-constrained configuration that maximizes a robustness level. Computational results are reported for both academic and industrial-scale instances. More than 80% of the academic instances are solved to optimality by the proposed method. Moreover, this method appears to be a good heuristic for industrial-scale instances.     

Estimation of the turbulent kinetic energy dissipation rate from 2D-PIV measurements in a vessel stirred by an axial Mixel TTP impeller

The turbulent dissipation rate is a key parameter in stirred tanks and its local values may have a strong influence on the performance of many processes. However, the local dissipation rate estimation is far from easy in a stirred tank, especially near the impeller discharge where maximum values are encountered. The aim of this work is to estimate the dissipation rate in a vessel used for animal-cell cultures and stirred with a down-pumping axial impeller (Mixel TTP) from velocity fields measured by 2D-PIV. Special attention is paid to the assumptions necessary to estimate the dissipation rate from 2D measurements and to the influence of measurement spatial resolution on the estimated values. The analysis of isotropy ratios measured on vertical, horizontal and tangential planes shows that the turbulence in the impeller discharge is far from isotropic. Isotropy assumptions classically used to estimate the dissipation rate from 2D measurements may thus lead to erroneous values. Based on the measured isotropy ratios, a new relationship is proposed to estimate the dissipation rate in the impeller discharge. This relationship is then used to estimate the dissipation rate on a vertical plane located in the impeller discharge zone. In order to analyze the influence of the measurement spatial resolution on the estimated values of the dissipation, a total of 12 spatial resolutions are tested. Results show that if the spatial resolution is divided by a factor 2, the dissipation rate increases by 220%. For the smallest spatial resolution value used, the maximum dissipation rate estimated is 50 times higher than the mean overall dissipation rate and the corresponding minimum value of the Kolmogorov scale is nearly 3 times smaller than the Kolmogorov scale computed from the mean overall dissipation rate.     

Photopolymer: synthesis and characterization of poly(4‐methacryloyloxyphenyl‐4′‐chlorostyryl ketone)

Methacrylate monomer containing a photodimerizable α,β‐unsaturated ketone moiety was prepared and polymerized in ethyl methyl ketone at 70 °C using benzoyl peroxide as an initiator. The polymer was characterized by UV, IR, ¹H NMR and ¹³C NMR spectra. The molecular weights (M _w and M _n) of the polymer were determined by gel permeation chromotography. The thermal stability of the polymer was measured by thermogravimetric analysis in air and nitrogen. The glass transition temperature of the polymer was determined by differential scanning calorimetry. The photo reactivity of the polymer was investigated as thin film and in solution. © 2000 Society of Chemical Industry