Dependability analysis of semi-Markov systems

This paper presents a dependability analysis (Availability-Reliability-Maintainability, Mean times) for semi-Markov systems with finite state space, by a new method, based on algebraic calculus within a convolution algebra. This method permits us to obtain, by simple matrix calculus, closed form solutions of transition probabilities and dependability measures. It is a quite general method that does not need the semi-Markov kernel to be absolutely continuous. Thus we obtain, as an example, the classical availability formulae modelled by an alternating renewal process, by a simple algebraic calculus without probabilistic argument. A detailed application of the method is given.     

Microbiological quality of tomatoes and peppers produced under the good agricultural practices protocol AGRO 2-1 & 2-2 in Crete, Greece

The efficiency of the good agricultural practices (GAP) protocol AGRO 2-1 & 2-2, in advancing microbiological-quality of tomatoes and peppers, was studied in greenhouses at Ierapetra, Crete, Greece. The 240 tested vegetables-samples, produced under AGRO 2-1 & 2-2, showed satisfactory quality: Listeria monocytogenes absent per 25 g; Escherichia coli < 20 Colony Forming Units per gram (CFU/g); total coliforms 4.37–4.68 log CFU/g; aerobic plate counts 5.78–5.92 log CFU/g. Based on actual results and practices evaluation, we conclude that AGRO 2-1 & 2-2 can reduce microbial hazards for consumers and furthermore can establish practices in compliance to basic Euro-Retailer-Produce GAP (EUREPGAP) requirements.     

Evaluation of a multifunctional indicator for the electroanalytical determination of nitrite

The derivatisation of phloroglucinol by acidified nitrite has been investigated as a means through which the latter can be quantified within freshwater and saline samples. The resulting nitroso derivative is shown to provide a number of options through which an electroanalytical signal can be obtained. Three distinct species can be electrochemically addressed and their respective sensitivities and practical implementations have been evaluated. The technology has been successfully transferred from bulk electrode formats to a disposable screen-printed electrode platform that is more amenable to field analysis. The analytical viability of the resulting assay system has been critically assessed and validated through the determination of endogenous nitrite within lake water and through recovery experiments in seawater.     

Parlay‐based service provision in circuit‐ and packet‐switched telecommunications networks

The spectrum of potential value added services over Internet telephony is wide, but the current service provision solutions are inadequate or proprietary. The nature of Internet differs significantly from that of circuit switched network, however, VoIP architectures can capitalize service control architectures in the PSTN world. We describe such an architecture based on the intelligent network and the Parlay, employing distributed objects and mobile agents as enabling technologies. This architecture has been implemented in the PSTN and the Internet and it has provided a framework for service provisioning, augmenting the space of supported services. Copyright © 2004 John Wiley & Sons, Ltd.     

Strong buffering characteristics and swelling behavior of cationic copolymers

The swelling behavior of crosslinked cationic copolymers of 2-hydroxyethyl methacrylate with (3-methacryloylamino propyl) trimethylammonium chloride was investigated in various buffered solutions as a function of ionic strength and pH. The equilibrium degree of swelling increased as the pH decreased or as the cationic group-containing comonomer in the polymer increased. The water transport in such copolymers was controlled by a non-Fickian mechanism. These results can be used in the development of physiologically sensitive controlled drug delivery systems. © 1994 John Wiley & Sons, Inc.     

Self- and mutual-diffusion coefficients in the dodecane/polystyrene system

The self-diffusion coefficient of dodecane in cross-linked polystyrene was measured using pulsed gradient spin echo nuclear magnetic resonance (PGSE–NMR) spectroscopy. The concentration and temperature dependence of the diffusion coefficient was analyzed by the Fujita and Vrentas–Duda models. Parameters describing the Fujita model were determined from fitting of diffusion data to the PVT behavior of the system. Parameters describing the Vrentas–Duda model were determined from the analysis of the viscosity of dodecane, the viscoelastic relaxation properties, and the glass transition temperature of polystyrene as well as from the diffusion coefficient of the system, measured from independent experiments. Both the Fujita and Vrentas–Duda models described well the concentration and temperature dependence of the diffusion coefficient. Mutual diffusion coefficients were determined from these results. © 1994 John Wiley & Sons, Inc.     

Changes in the catechin and epicatechin content of grape seeds on storage under different water activity (aw) conditions

Storage effect on antioxidant content and capacity of grape seeds under different a_w conditions (a_w 0.33; 0.53; 0.75/50 days, 25 °C) was examined. Total phenol content (determined by the Folin–Ciocalteu method) decreased during storage though changes were trivial for samples stored at 33% or 53% RH. High level of humidity (75%) accelerated degradation and resulted in a ∼50% reduction of total phenol content. Minor loss of the DPPH radical scavenging activity (%RSA) of the extracts was observed. Catechin and epicatechin content monitored by RP-HPLC was reduced during storage, particularly at 75% RH. Epicatechin content proved to be less sensitive to water activity conditions than catechin content. Results of various in vitro assays (Folin–Ciocalteu, FRAP, DPPH, ABTS, CBA, ORAC and copper induced liposome oxidation) did not support difference in terms of resistance to oxidation. Based on the continuous release of gallic acid, our finding was related to hydrolytic reactions. Control of a_w of grape seeds can be of practical importance for the wine industry.     

Socially-Aware Multi-phase Opportunistic Routing for Distributed Mobile Social Networks

The work presented in this paper focuses on opportunistic routing in distributed Mobile Social Networks (MSNs). It proposes a novel routing protocol called Socially-Aware Multi-Phase Opportunistic (SAMPhO), where the routing procedure for each message is carried out in multiple phases. From the various socially aware metrics considered, ego-betweenness and tie strength are selected to be utilized according to the conditions of the social environment. Previous research on the area suggests that different metrics are useful in different conditions. However, only recently steps towards this direction are taken. To evaluate the proposed hypothesis, a simulated delay tolerant MSN was introduced in the OMNeT++ environment using a framework, developed as part of this work. It is called Socially-Aware Opportunistic Routing System (SAORS) and its modular design facilitates further research in opportunistic networks. The routing mechanism is divided in three independent stages, with SAORS focusing on providing the necessary functionality for the first one. The simulation results drawn clearly demonstrate the scalability and improved performance of SAMPhO, especially in highly social scenarios. It is shown to be both more efficient and effective than previous algorithms, in terms of bandwidth and memory utilization, and delivery rates respectively. However, it relies greatly on the accuracy of the social tie detection, since the copy generation is very limited.     

Channel Allocation to Multiservice Wireless Networks: A Collocation—Based Approach to Enhance Spectrum Utilization

A channel allocation (CA) scheme is proposed for wireless networks serving multiple services. The CA scheme is based on collocating the base stations of the wireless networks and restricting their coverage over common cells. The increased coverage granularity makes feasible a more efficient frequency reuse. A genetic algorithm approach is adopted to minimize the number of channels required by the multiservice networks, taking into account the intranetwork and intraservice constraints over a specific coverage area. To validate the proposed scheme and investigate its performance, the Philadelphia benchmark network is employed. Simulation results corresponding to a mix of digital TV and mobile services of various profiles demonstrate the capability of the proposed scheme to optimally allocate channels to multiservice wireless networks.     

On generalized logistic equations with a non-homogeneous differential operator

We consider a generalized logistic equation of superdiffusive type, driven by a non-homogeneous nonlinear differential operator, which incorporates the p-Laplacian, the (p, q)-differential operator and the generalized p-mean curvature differential operator. Using variational methods coupled with truncation and comparison techniques, we prove a bifurcation-type theorem describing the dependence of positive solutions on the parameter λ > 0.