Evaluation of thermally-dried Kluyveromyces marxianus as baker’s yeast

The aim of the present study was to evaluate the use of thermally-dried Kluyveromyces marxianus as baker’s yeast. Bread samples produced by thermally-dried K. marxianus were compared with samples produced by wet K. marxianus culture and by commercial baker’s yeast. The type of the culture had no effect on loaf weight, loaf volume, specific loaf volume, density or moisture loss, in contrast to pH, total titrable acidity (TTA), and moisture content. The use of thermally-dried K. marxianus resulted in lower pH values and higher TTA, while the bread samples showed higher resistance to spoilage as counts of moulds and yeasts were significantly lower during preservation. The SPME GC/MS analysis of volatiles and the preliminary sensory evaluation showed no significant differences in the profile of aroma-related compounds or overall quality of the tested samples.     

Evolution of aggregate size and fractal dimension during Brownian coagulation

Fractal aggregate coagulation is described within a general framework of multivariate population dynamics. The effect of aggregate morphology on the coagulation rate, is taken into account explicitly, introducing in addition to aggregate particle size, the aggregate fractal dimension, as a second independent variable. A simple constitutive law is derived for determining the fractal dimension of an aggregate, resulting from a coagulation event between aggregates with different fractal dimensions. An efficient Monte Carlo method was implemented to solve the resulting bivariate Brownian coagulation equation, in the limits of continuum and free molecular flow regimes. The results indicate that as the population mean fractal dimension goes from its initial value towards its asymptotic value, the distribution of fractal dimension remains narrow for both flow regimes. The evolution of the mean aggregate size in the continuum regime is found to be nearly independent of aggregate morphology. In the free molecular regime however, the effects of aggregate morphology, as embodied in its fractal dimension, become more important. In this case the evolution of the aggregate size distribution cannot be described by the traditional approach, that employs a constant fractal dimension.     

Essential oil composition of Pistacia lentiscus L. and Myrtus communis L.: Evaluation of antioxidant capacity of methanolic extracts

The seasonal variation of the essential oil composition, the antioxidant activity (DPPH, FRAP assays) and the total phenolic content (Folin-Ciocalteu assay) of two aromatic wild plants, Pistacia lentiscus L. (Anacardiaceae) and Myrtus communis L. (Myrtaceae), grown in Zakynthos, a Greek island, was investigated. The essential oil was obtained by hydrodistillation and subsequently analysed by GC–MS.     

Trading wind power through physically settled options and short‐term electricity markets

Wind power producers participating in today's electricity markets face significant variability in revenue streams, with potential high losses mostly due to wind's limited predictability and the intermittent nature of the generated electricity. In order to further expand wind power generation despite such challenges, it is important to maximize its market value and move decisively towards economically sustainable and financially viable asset management. In this paper, we introduce a decision‐making framework based on stochastic optimization that allows wind power producers to hedge their position in the market by trading physically settled options in futures markets in conjunction with their participation in the short‐term electricity markets. The proposed framework relies on a series of two‐stage stochastic optimization models that identify a combined trading strategy for wind power producers actively participating in both financial and day‐ahead electricity markets. The proposed models take into consideration penalties from potential deviations between day‐ahead market offers and real‐time operation and incorporates different preferences of risk aversion, enabling a trade‐off between the expected profit and its variability. Empirical analysis based on data from the Nordic region illustrates high efficiency of the stochastic model and reveals increased revenues for both risk neutral and risk averse wind producers opting for combined strategies.     

Selenium content in selected foods from the Greek market and estimation of the daily intake

The total selenium content of foods purchased from the North West part of Greece was determined using hydride generation atomic fluorescence spectroscopy. The results of this study were within the range from other countries. The overall mean average of selenium concentration of the foods examined, in decreasing order, was found in sesame seeds (783.1 ng g(-1)), fish (246 ng g(-1)), legumes (162.5 ng g(-1)), eggs (123 ng g(-1)), bread (91.9 ng g(-1)), meat (71.7 ng g(-1)), cheese (69.8 ng g(-1)), yoghurt (23.6 ng g(-1)), nuts (19.6 ng g(-1)), milk (15.4 ng g(-1)), vegetables (6.5 ng g(-1)) and fruits (3.4 ng g(-1)). Considering the average daily individual consumption of these foods by Greeks, the average daily dietary intake of selenium supplied by this source is 39.3 microg per capita.     

Gas and liquid phase fuels desulphurization for hydrogen production via reforming processes

The present work focuses on the development of efficient desulphurization processes for multi-fuel reformers for hydrogen production. Two processes were studied: liquid hydrocarbon desulphurization and H₂S removal from reformate gases. For each process, materials with various chemical compositions and microporous structures were synthesized and characterized with respect to their physicochemical properties and desulphurization ability. In the case of liquid phase desulphurization, the adsorption of sulphur compounds contained in diesel fuel under ambient conditions was studied employing as sorbents, zeolite-based materials, i.e. NaY, HY and metal ion-exchanged NaY and HY, as well as a high-surface area activated carbon (AC), for three different diesel fuels with sulphur content varying between 5 and 180 ppmw. Among all sorbents studied, AC showed the best desulphurization performance followed by cerium ion-exchanged HY. The gas phase desulphurization experiments involved the evaluation of zinc-based mixed oxides, synthesized by non-conventional (combustion synthesis) techniques on high steam content reformate gas mixtures.     

Complete semi‐analytical treatment of weakly singular integrals on planar triangles via the direct evaluation method

A complete semi‐analytical treatment of the four‐dimensional (4‐D) weakly singular integrals over coincident, edge adjacent and vertex adjacent triangles, arising in the Galerkin discretization of mixed potential integral equation formulations, is presented. The overall analysis is based on the direct evaluation method, utilizing a series of coordinate transformations, together with a re‐ordering of the integrations, in order to reduce the dimensionality of the original 4‐D weakly singular integrals into, respectively, 1‐D, 2‐D and 3‐D numerical integrations of smooth functions. The analytically obtained final formulas can be computed by using typical library routines for Gauss quadrature readily available in the literature. A comparison of the proposed method with singularity subtraction, singularity cancellation and fully numerical methods, often used to tackle the multi‐dimensional singular integrals evaluation problem, is provided through several numerical examples, which clearly highlights the superior accuracy and efficiency of the direct evaluation scheme. Copyright © 2010 John Wiley & Sons, Ltd.     

Efficient automatic discovery of ‘hot’ itemsets

In real life applications the dominant model of the single support, which assumed all itemsets to be of the same nature and importance proved defective. The non-homogeneity of the itemsets on one hand and the non-uniformity of their number of appearances on the other require that we use different approaches. Some techniques have been proposed thus far trying to address these inefficiencies, but then new more demanding questions arose such as which itemsets are more interesting than others, what distinguishes them and how should they be identified, and finally how they should be effectively handled. Furthermore one common drawback of all approaches is that they have a tremendous lag in discovering new relationships and work only with long existing relationships or patterns. We propose a method that finds what we define as ‘hot’ itemsets in our database, deals with all problems described above and yet proves very efficient.     

Metal ion determination by flame atomic absorption spectrometry through reagentless coacervate phase separation-extraction into lamellar vesicles

The phase separation of lamellar vesicles of anionic surfactants in aqueous solutions and its application as a novel liquid coacervate extraction procedure was examined. Solutions of lauric acid sodium salt separate into two phases in the presence of alkaline earth metals and a water miscible cosurfactant. It is proven that the surfactant phase is built of a perplexed network of multilamellar vesicles consisting of densely packed bilayers. Several factors affecting the formation of this new phase as well as its analytical utility in the preconcentration of metallic ions were assessed on the basis of better exploitation of this new nonspecific extraction technique. In essence, although the procedure to arrive at the optimum conditions seems laborious, the delivered method is straightforward, alleviating the requirement for prereaction with a complexing agent and highly reproducible under the optimum experimental conditions. As an analytical demonstration, the method was successfully applied to the determination of Cd(2+) and Zn(2+) in natural waters. Recoveries were higher than 95%, and detection limits as low as 3 microg L(-)(1) were accomplished by preconcentrating only 10 mL of sample volume in the presence of 0.45% (w/v) anionic surfactant.     

An efficient algorithm for checking the robust stability of a polytope of polynomials

An efficient algorithm for checking the robust stability of a polytope of polynomials is proposed. This problem is equivalent to a zero exclusion condition at each frequency. It is shown that such a condition has to be checked at only afinite number of frequencies. We formulate this problem as aparametric linear program which can be solved by the Simplex procedure, with additional computations between steps consisting of polynomial evaluations and calculation of positive polynomial roots. Our algorithm requires a finite number of steps (corresponding to frequency checks) and in the important case when the polytope of parameters is a hypercube, this number is at most of orderO(m ³ n ²), wheren is the degree of the polynomials in the family andm is the number of parameters. Supported by NASA under Contract No. NCC2-477 and by a Charles Powell Foundation Grant.