An algorithmic approach for analysis of finite-source retrial systems with unreliable servers

This paper aims at presenting an approach for analyzing finite-source retrial systems with servers subject to breakdowns and repairs, using Generalized Stochastic Petri Nets (GSPNs). This high-level formalism allows a simple representation of such systems with different breakdown disciplines. From the GSPN model, a Continuous Time Markov Chain (CTMC) can be automatically derived. However, for multiserver retrial systems with unreliable servers, the models may have a huge state space. Using the GSPN model as a support, we propose an algorithm for directly computing the infinitesimal generator of the CTMC without generating the reachability graph. In addition, we develop the formulas of the main stationary performance and reliability indices, as a function of the number of servers, the size of the customer source and the stationary probabilities. Through numerical examples, we discuss the effect of the system parameters and the breakdown disciplines on performance.     

Improving the performance of a Seawater Greenhouse desalination system by assessment of simulation models for different condensers

The main aim of this paper was the development of a mathematical model for a new proposed passive condenser in order to enhance the performance of a humidification–dehumidification Seawater Greenhouse desalination system. Seawater Greenhouse desalination is used to create a cool environment and at the same time to produce fresh water for irrigation of crops grown inside the unit. The condenser in particular is currently one of the main bottlenecks in the commercialization of the technology. In addition to the current pump driven condenser, two new designs were considered: a passive cooling system with a condenser immersed in a water basin, and an external passive condenser connected to a basin of water placed on top of the cooling unit. The simulated condensate values for the proposed passive cooling condenser were compared with that of the actual measured values of the installed condenser. Preliminary results suggest that the passive condenser has a much greater water production capacity than the existing pump driven system. While the model for the proposed system still needs to be validated experimentally the initial study indicates that the passive containment cooling system is a promising improvement in the further development of greenhouse desalination.     

Fluoride removal from diluted solutions by Donnan dialysis using full factorial design

Excessive fluoride concentration in potable water can lead to fluorosis of teeth and bones. In the present study, Donnan dialysis (DD) is applied for the removal of fluoride ions from diluted sodium fluoride solutions. A four factor two level (2⁴) full factorial design was used to investigate the influence of different physico-chemical parameters on fluoride removal efficiency (Y _F ) and fluoride flux (J _F ) through anion exchange membrane. The statistical design determines factors which have the important effects on Donnan dialysis performance and studies all interactions among the considered parameters. The four significant factors were initial fluoride concentration, feed flow rate, temperature and agitation speed. The experimental results and statistical analysis show that the temperature and agitation speed have positive effects on fluoride removal efficiency and the initial fluoride concentration has a negative effect. In the case of fluoride flux, feed flow rate and initial concentration are the main effect and all factors have a positive effect. The interaction between studied parameters was not negligible on two responses. A maximum fluoride removal of 75.52% was obtained under optimum conditions and the highest value of fluoride flux obtained was 2.4 mg/cm²·h. Empirical regression models were also obtained and used to predict the flux and the fluoride removal profiles with satisfactory results.     

Salt effects on Origanum majorana fatty acid and essential oil composition

BACKGROUND: The effects of salt on the essential oil yield and fatty acid composition of aerial parts of two marjoram varieties were investigated. Plants with 6 leaves were treated with NaCl (75mM). RESULTS: Salt treatment led to a reduction in aerial part growth. Salinity increased the fatty acid content more significantly in Tunisian variety (TV) than in Canadian variety (CV). CV showed an increase in double‐bond index (DBI) and a decrease in malondialdehyde content under salt stress, while the opposite was observed in TV. The DBI was mainly affected by a strong reduction in oleic and linoleic acids in TV, whereas a strong stimulation of linoleic acid in CV was observed. Salt decreased and increased the essential oil yield in TV and CV respectively. The main constituents of the essential oil of TV were trans‐hydrate sabinene and terpinen‐4‐ol, which showed a significant decrease under salt stress. In contrast, the main constituents of the essential oil of CV were sabinene and trans‐hydrate sabinene, which showed a significant decrease and increase respectively under salt stress. CONCLUSION: Marjoram oil is a rich source of many compounds such as essential oils and fatty acids, but the distribution of these compounds differed significantly between the two varieties studied. Copyright © 2011 Society of Chemical Industry     

Effect of Silicon Additions on Structural and Microstructural Properties of Nanostructured FeCoNi Alloy Prepared by High-Energy Ball Milling

Silicon - Full use of experimental measurements obtained by the mean of the X-ray diffraction technique and the Rietveld refinement has been implemented to study the effects of the addition of Si...     

Elaboration of enriched margarine with lentisk oil and honey: Formulation,characterization, and monitoring of oxidative stability

This study focused on the use of lentisk oil and honey as natural sources to formulate margarine with ameliorated quality and oxidative stability. For this, five margarines were formulated with honey and different concentrations of lentisk oil. Analyses were performed on oil and honey used, and then physicochemical characterization and several oxidative stability tests were applied to assess margarine quality. The results showed a significant richness of lentisk oil and honey in total phenolics and total flavonoids and expressed good antioxidant activities. As well as the evaluation of oxidative stability of enriched margarines during 3 months of storage demonstrated that margarine added with 2% lentisk oil (M1) had the best resistance properties and longer Rancimat induction time (22.26 h), better than the control and margarines added with 5% (M2), 10% (M3), and 15% (M4) lentisk oil. Globally, margarines prepared with high concentrations of lentisk oil (M2–M4) were not different from the control, whereas only M1 was permitted to ameliorate the stability of margarine with a slight influence on physicochemical parameters. The elaboration of margarine supplemented with 2% lentisk oil improves the properties of the product, which could then be applied to margarine manufacturing.