Life cycle assessment of MSF,MED and RO desalination technologies

In this work, a comparison of the commonly deployed commercial desalination technologies worldwide—multistage flash (MSF), multieffect evaporation and reverse osmosis (RO)—is assessed by applying life cycle analysis (LCA). LCA, a powerful, and internationally accepted tool used to examine environmental cradle-to-grave consequences of making and using products and services, identifies and quantifies energy and material usage and waste discharges. The International Standard Organization (ISO) 14000 impact factors, which are internationally accepted standard indicators for environmental impact assessment, have been evaluated, and different evaluation methods (Centre for Environmental Studies (CML) 2 baseline 2000, Eco-Points 97 and Eco-Indicator 99) have been applied to different scenarios. The assessment includes the entire life cycle of each desalination process, encompassing extraction and processing raw materials, manufacturing, transportation and distribution, plant operation and final reject disposal.     

A qualitative assessment of the referral system at district level in Zimbabwe: implications on efficiency and effective delivery of health services

This exploratory study describes the nature and magnitude of the problem of health referrals, health-seeking behavior, perceptions, and knowledge at the district level in Zimbabwe. Data were obtained from focus groups with 159 persons in Tsholotsho and 132 persons in Murewa; from discussions with health personnel from the 6 health centers in Murewa and the 2 rural hospitals in Tsholotsho; and from records among a systematic sample of 400 new outpatients during October 1993 and March 1994 in Murewa district. Findings indicate that 71.8% in outpatient departments at Murewa Hospital had no access to a health center. 24.3% by-passed the health center for treatment at the hospital. 3.8% were referred by health centers. The absolute number of referrals did not change during 1991-93. However, the number directly accessing services from outside the district rose. Focus group participants reported their intention to use the nearest clinic for an illness. In Tsholotsho, people initially used the village community worker/headman. If illness was perceived as serious, patients would go to a hospital. For minor illness, people used traditional herbal remedies. If illness did not change after remedies, the clinic was consulted. Some illnesses were perceived as outside the realm of medicine. Most distinguished between a health center and a hospital, but were unaware of the important, superior functions of the health center. Most did not understand the logic behind the referral system, but appreciated referrals and not the cost of hospital treatment or transportation. The community was unaware of Ward Health Teams. Many did not understand the new fee policy introduced in 1994.     

Microencapsulation of sulfur by calcium alginate

The sulfur blooms on surface of rubber compounds cause loss of the needed tack for formation of multiply articles like tires. Although insoluble sulfur can be used to mitigate this problem, it is expensive to manufacture with a complex and hazardous process. This work examines an alternative approach that involves microencapsulation of soluble sulfur in alginate-based matrix. The formulations and procedures are developed and evaluated. Alginate crosslinking time, controlled temperature change (e.g., from 10 to 36°C), and the drying method were found to be critical to achieving high encapsulation efficiencies. The higher temperature (36°C) helped with the mass transfer limited removal of CS₂ used for dissolving sulfur, and treatment of crosslinked beads with oil prior to air-drying improved sulfur encapsulation. Formulated beads had higher than 65% sulfur content (>80%, oil-free basis) with almost 90% of the beads being <150 μm. The process parameters can be adjusted to make even smaller beads.     

A scalable multi‐level preconditioner for matrix‐free µ‐finite element analysis of human bone structures

The recent advances in microarchitectural bone imaging disclose the possibility to assess both the apparent density and the trabecular microstructure of intact bones in a single measurement. Coupling these imaging possibilities with microstructural finite element (µFE) analysis offers a powerful tool to improve bone stiffness and strength assessment for individual fracture risk prediction. Many elements are needed to accurately represent the intricate microarchitectural structure of bone; hence, the resulting µFE models possess a very large number of degrees of freedom. In order to be solved quickly and reliably on state‐of‐the‐art parallel computers, the µFE analyses require advanced solution techniques. In this paper, we investigate the solution of the resulting systems of linear equations by the conjugate gradient algorithm, preconditioned by aggregation‐based multigrid methods. We introduce a variant of the preconditioner that does not need assembling the system matrix but uses element‐by‐element techniques to build the multilevel hierarchy. The preconditioner exploits the voxel approach that is common in bone structure analysis, and it has modest memory requirements, at the same time robust and scalable. Using the proposed methods, we have solved in 12min a model of trabecular bone composed of 247 734 272 elements, yielding a matrix with 1 178 736 360 rows, using 1024 CRAY XT3 processors. The ability to solve, for the first time, large biomedical problems with over 1 billion degrees of freedom on a routine basis will help us improve our understanding of the influence of densitometric, morphological, and loading factors in the etiology of osteoporotic fractures such as commonly experienced at the hip, spine, and wrist. Copyright © 2007 John Wiley & Sons, Ltd.     

Control of action potential duration alternans in canine cardiac ventricular tissue

Cardiac electrical alternans, characterized by a beat-to-beat alternation in action potential waveform, is a naturally occurring phenomenon, which can occur at sufficiently fast pacing rates. Its presence has been putatively linked to the onset of cardiac reentry, which is a precursor to ventricular fibrillation. Previous studies have shown that closed-loop alternans control techniques that apply a succession of externally administered cycle perturbations at a single site provide limited spatially-extended alternans elimination in sufficiently large cardiac substrates. However, detailed experimental investigations into the spatial dynamics of alternans control have been restricted to Purkinje fiber studies. A complete understanding of alternans control in the more clinically relevant ventricular tissue is needed. In this paper, we study the spatial dynamics of alternans and alternans control in arterially perfused canine right ventricular preparations using an optical mapping system capable of high-resolution fluorescence imaging. Specifically, we quantify the spatial efficacy of alternans control along 2.5 cm of tissue, focusing on differences in spatial control between different subregions of tissue. We demonstrate effective control of spatially-extended alternans up to 2.0 cm, with control efficacy attenuating as a function of distance. Our results provide a basis for future investigations into electrode-based control interventions of alternans in cardiac tissue.     

Plant biotechnology and food crop development in Sub-Saharan Africa

Biotechnology represents the newest challenge in the ongoing scientific progress in this millennium. Indeed what were seen as promising technologies a few years ago have already produced results; new crop varieties, animal species and agricultural processes. In crop improvement, for example, biotechnology has produced a wide range of applications including micro-propagation of crop varieties for commercial purposes, somatic embryogenesis, inter-specific crosses, gene transfers, and disease control and haploid production. Although modest in comparison with the prospects originally envisaged, mankind cannot but acknowledge these achievements, the regulatory control and commercial exploitation of biotechnology on standards of living of the human society.     

Evaluation of two Compton camera models for scintimammography

We study the performance of a Si/LaBr₃:Ce Compton camera model for scintimammography, and compare it with a Si/NaI(Tl) model of similar geometry. The GEANT4 simulation toolkit was used to study the behaviour of the cameras at 511 keV. Certain simulation steps, such as the modelling of radionuclide decay times, scintillation photon transport and interactions with photomultipliers, as well as detector dead time corrections were included to make the modelling of the cameras more realistic than previous studies. The Si/LaBr₃:Ce Compton camera shows superior efficiency of 2.0×10⁻³ and resolution of 5.3 mm over the Si/NaI(Tl) Compton camera model which has the efficiency of 1.6×10⁻³ and resolution of 6.9 mm at a source-to-scatterer distance of interest, 2.5 cm. A similar result sequence is obtained for two breast tumours of 5 mm diameter embedded in the medial region of an average-size breast phantom of thickness 5 cm. Notably, the signal-to-noise ratios (SNR) obtained for the Si/LaBr₃:Ce camera are 9.7 and 3.4 for tumour/background radiation uptakes of 10:1 and 6:1, whereas 6.8 and 2.4 were obtained for the Si/NaI(Tl) camera model for the same tumour/background radiation uptakes respectively. It is therefore envisioned that with lower cost, LaBr₃:Ce could replace NaI(Tl) as the Compton camera absorber.     

A model for transport of hydrogen sulfide in oil- and water-saturated porous media

In several oilfields, reservoir souring by generation of hydrogen sulfide (H₂S) occurs in secondary recovery during which seawater is injected into originally sweet reservoirs. At the production site, high concentrations of H₂S can cause severe damage to both equipment and human personnel. Proper modeling of H₂S concentration in produced fluids can be useful for decision-making during field development design. We present a model for the transport of H₂S in an oil- and water-saturated, water-wet porous medium. The different retardation mechanisms for the H₂S are described. For the adsorption of H₂S to rock, we include two distinct phases of adsorption. In addition, we introduce a functional relationship between adsorption capacity and permeability. As H₂S mixes with oil, fractions become immobile as part of the residual oil.     

Effect of complement (C3) depletion on the generation of memory in rabbits primed with antigens of Trypanosoma evansi

Using the antibody response during secondary exposure of rabbits primed with antigens of Trypanosoma evansi as an indirect measure of immunological memory, it was shown that C3 decomplementaemia resulted in a reduced antibody response, with IgM being predominant in the sera samples followed by IgG and then IgA [corrected]. While significant differences were observed in the levels of IgG produced by the C3-depleted and C3-intact rabbits no differences were recorded in the levels of IgM and IgA produced by the two groups after C3 decomplementaemia. These results demonstrate that C3 depletion did not abolish memory of the T. evansi antigen in these rabbits but only modified the magnitude and pattern of their response. The host response to reinfection may be affected by such changes as those observed in this study.