On the stability and convergence of the finite section method for integral equation formulations of rough surface scattering

We consider the Dirichlet and Robin boundary value problems for the Helmholtz equation in a non-locally perturbed half-plane, modelling time harmonic acoustic scattering of an incident field by, respectively, sound-soft and impedance infinite rough surfaces.Recently proposed novel boundary integral equation formulations of these problems are discussed. It is usual in practical computations to truncate the infinite rough surface, solving a boundary integral equation on a finite section of the boundary, of length 2A, say. In the case of surfaces of small amplitude and slope we prove the stability and convergence as A→∞ of this approximation procedure. For surfaces of arbitrarily large amplitude and/or surface slope we prove stability and convergence of a modified finite section procedure in which the truncated boundary is ‘flattened’ in finite neighbourhoods of its two endpoints. Copyright © 2001 John Wiley & Sons, Ltd.

Thermal and spectrophotometric studies of new crosslinking method for collagen matrix with glutaraldehyde acetals

Despite the many existing crosslinking procedures, glutaraldehyde (GA) is still the method of choice used in the manufacture of bioprosthesis. The major problems with GA are: (a) uncontrolled reactivity due to the chemical complexity or GA solutions; (b) toxicity due to the release of GA from polymeric crosslinks; and (c) tissue impermeabilization due to polymeric and heterogeneous crosslinks formation, partially responsible for the undesirable calcification of the bioprosthesis. A new method of crosslinking glutaraldehyde acetals has been developed with GA in acid ethanolic solution, and after the distribution inside de matrix, GA is released to crosslinking. Concentrations of hydrochloride acid in ethanolic solutions between 0.1 and 0.001 mol/L with GA concentration between 0.1 and 1.0% were measured in an ultraviolet spectrophotometer to verify the presence of free aldehyde groups and polymeric compounds of GA. After these measurements, the solutions were used to crosslink bovine pericardium. The spectrophotometric results showed that GA was better protected in acetal forms for acid ethanolic solution with HCl at 0.003 mol/L and GA 1.0%(v/v). The shrinkage temperature results of bovine pericardium crosslinked with acetal solutions showed values near 85 C after the exposure to triethylamine vapors.

Geometry and combinatorics of the cutting angle method

Lower approximation of Lipschitz functions plays an important role in deterministic global optimization. This article examines in detail the lower piecewise linear approximation which arises in the cutting angle method. All its local minima can be explicitly enumerated, and a special data structure was designed to process them very efficiently, improving previous results by several orders of magnitude. Further, some geometrical properties of the lower approximation have been studied, and regions on which this function is linear have been identified explicitly. Connection to a special distance function and Voronoi diagrams was established. An application of these results is a black-box multivariate random number generator, based on acceptance-rejection approach.

Electrochemical performance of polyaniline nanofibres and polyaniline/multi-walled carbon nanotube composite as an electrode material for aqueous redox supercapacitors

Polyaniline (PANI) nanofibres are synthesized by interfacial polymerization and their electrochemical performance is evaluated in an aqueous redox supercapacitor constituted as a two-electrode cell. The initial specific capacitance of the cell is 554 F g−1 at a constant current of 1.0 A g−1, but this value rapidly decreases on continuous cycling. In order to improve the cycleability of the supercapacitor, a composite of polyaniline with multi-walled carbon nanotubes (CNTs) is synthesized by in situ chemical polymerization. Its capacitive behaviour is evaluated in a similar cell configuration. A high initial specific capacitance of 606 F g−1 is obtained with good retention on cycling. In both supercapacitors, the effect of charging potential on cycling performances is investigated.

Climate change sensitivity of comfort and energy performance criteria for offices

The climate change scenarios of the Intergovernmental Panel on Climate Change (IPCC) predict a significant increase in temperatures over the next decades. Architecture and building occupants have to respond to this change, but little information is currently available in how far the predicted changes are likely to affect comfort and energy performance in buildings. This study therefore investigates the climate change sensitivity of the following parameters: adaptive thermal comfort according to Ashrae Standard 55 and EN 15251, energy consumption, heating and cooling loads, and length of heating and cooling periods. The study is based on parametric simulations of typical office room configurations in the context of Athens, Greece. They refer to different building design priorities and account for different occupant behaviour by using an ideal and worst case scenario. To evaluate the impact of the climate change, simulations are compared based on a common standard weather data set for Athens, and a generated climate change data set for the IPCC A2 scenario. The results show a significant impact of the climate change on all investigated parameters. They also indicate that in this context the optimisation of comfort and energy performance is likely to be related to finding the best possible balance between building (design) and occupant behaviour and other contextual influences, rather than a straightforward optimisation of separated single parameters.

Learning from ordered sets and applications in collaborative ranking

Ranking over sets arise when users choose between groups of items. For example, a group may be of those movies deemed 5 stars to them, or a customized tour package. It turns out, to model this data type properly, we need to investigate the general combinatorics problem of partitioning a set and ordering the subsets. Here we construct a probabilistic log-linear model over a set of ordered subsets. Inference in this combinatorial space is highly challenging: The space size approaches (N!/2)6.93145N+1 as N approaches infinity. We propose a split-and-merge Metropolis-Hastings procedure that can explore the state-space efficiently. For discovering hidden aspects in the data, we enrich the model with latent binary variables so that the posteriors can be efficiently evaluated. Finally, we evaluate the proposed model on large-scale collaborative filtering tasks and demonstrate that it is competitive against state-of-the-art methods.

Evaluation of tender solutions for aviation training using discrete event simulation and best performance criteria

This paper describes a novel discrete event simulation (DES) methodology for the evaluation of aviation training tenders where performance is measured against “best performance” criteria. The objective was to assess and compare multiple aviation training schedules and their resource allocation plans against predetermined training objectives. This research originated from the need to evaluate tender proposals for the Australian Defence Aviation Training School that is currently undergoing aviation training consolidation and helicopter rationalization. We show how DES is an ideal platform for evaluating resource plans and schedules, and discuss metric selection to objectively encapsulate performance and permit an unbiased comparison. DES allows feasibility studies for each tender proposal to assure they satisfy system and policy constraints. Consequently, to create an objective and fair environment to compare tendered solutions, what-if scenarios have been strategically examined to consider improved implementations of the proposed solutions.

Effects of gamma-irradiation on caprolactam level from multilayer PA-6 films for food packaging: Development and validation of a gas chromatographic method

A gas chromatographic method to determine caprolactam in multilayer PA-6 films used for meat foodstuffs and cheese was developed and validated. A wide linear range (0.8-400 mu g/ml), RSD <= 4.1% and recovery higher than 90.0% were obtained for the chromatographic system, while precision and accuracy of the method showed RSD <= 3.8%, recovery from 95.5-100.0% and LOQ of 32 mu g/g. Irradiated (3, 7 and 12 kGy) and non-irradiated commercial films were analyzed. Most of them increased caprolactam levels with the increase of irradiation doses. (C) 2008 Elsevier Ltd. All rights reserved.

Development and Validation of a UV-Spectrophotometric Method for Determination of Flucloxacillin Sodium in Capsules

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Real power losses reduction and loading margin improvement via continuation method

This letter presents an alternative approach for reducing the total real power losses by using a continuation method. Results for two simple test systems and for the IEEE 57-bus system show that this procedure results in larger voltage stability margin. Besides, the reduction of real power losses obtained with this procedure leads to significant money savings and, simultaneously, to voltage profile improvement. Comparison between the solution of an optimal power flow and the proposed method shows that the latter can provide near optimal results and so, it can be a reasonable alternative to power system voltage stability enhancement.