Predicting group partitions in mobile ad hoc networks

Group mobility is prevalent in many mobile ad hoc network applications such as disaster recovery, military actions, etc., and group partitions are unavoidable in such kinds of dynamic networks. Group partition may occur when mobile nodes move in diverse mobility patterns and causes the network to be partitioned into disconnected components. It may result in severe link disconnections, which then interrupt intergroup communications. By examining the group mobility pattern, we can predict the possibility of network partitions, and thus minimize the amount of communication disruptions. In this paper, we introduce a system for predicting potential group partitions in mobile ad hoc networks. On the basis of historical group mobility information, a quadratic regression model is formulated to predict the direction and speed of a group's movement. A group's micromovement is ignored and is replaced by significant linear displacement to measure its mobility to improve the prediction accuracy. We also discuss the notion of safe distance between adjacent groups, based on which the time duration before the occurrence of group partitioning can be measured. Experimental results show that our proposed prediction method demonstrates its effectiveness and efficiency in group partition predictions such that remedial actions can be taken in advance to avoid network disconnection. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of Metal Concentrations in Red Tilapia (Oreochromis spp) from Three Sampling Sites in Jelebu, Malaysia Using Principal Component Analysis

Concentration of V, Mn, Fe, Co, Cu, Zn, As, Se, Cd, and Pb in muscle, liver, and gill tissues of red tilapia (Oreochromis spp) sampled from three different aquaculture sites which include earthen pond, ex-tin mining pool, and concrete tank in Jelebu, Negeri Sembilan, were determined using microwave-assisted digestion–inductively coupled plasma-mass spectrometry. Accumulation patterns relating organs and elements, as well as origins and elements, were evaluated using multivariate statistics. With the aid of principal component analysis, it is possible to visualize the distribution pattern of metals in different organs as well as clustering tendencies of tilapia samples according to the production sites. In general, levels of V, Co, Fe, Cu, Zn, Se, and Cd in liver were higher than those in muscles and gills, whereas Mn and Pb were higher in gills while As in muscles. Results from principal component analysis revealed that there are similar pattern of metal distribution among organs regardless of the production sites. It is also suggested that Cu, As, and Pb are the best describers in characterizing the studied organs, where liver tissues are associated with high Cu, gills with high Pb, and muscles with high As. On the other hand, V, Co, and Pb are observed to be key discriminants for sample origins.     

The role of iron in hexavalent chromium reduction by municipal landfill leachate

The function of iron (ferric (Fe(III)) and ferrous (Fe(II))) in the hexavalent chromium (Cr(VI)) reduction mechanism by bacteria in municipal landfill leachate (MLL) was assessed. Evidence of an "electron shuttle" mechanism was observed, whereby the Cr(VI) was reduced to trivalent chromium (Cr(III)) by Fe(II) with the resulting Fe(III) bacterially re-reduced to Fe(II). Typically, investigations on this electron shuttle mechanism have been performed in an artificial medium. As MLL comprises an elaborate mixture of bacteria, humic materials and organic and inorganic species, additional complexities were evident within the cycle in this study. Bioavailability of the Fe(III) for bacterial reduction, availability of bacterially produced Fe(II) for chemical Cr(VI) reduction and hydrolysis of Fe(II) and Fe(III) become prevalent during each phase of the shuttle cycle when MLL is present. Each of these factors contributes to the overall rate of bacterial Cr(VI) reduction in this media. This work highlights the need to consider local environmental conditions when assessing the bacterial reduction of Cr(VI).     

Germanium on sapphire substrates for system on a chip

Germanium on sapphire (GeOS) is proposed for system on a chip applications. Sapphire substrates are demonstrated to exhibit lower rf losses and superior crosstalk suppression compared with oxidised silicon handle wafers. Inductors on sapphire also show higher quality factor and better frequency response than those manufactured on an SOI platform. GeOS substrates have been manufactured by wafer bonding. Bond strengths of greater than 2900 mJ m⁻² have been obtained. Thin GeOS has been achieved by He/H₂ ion cut processes. A self-aligned W gate process on Ge has been established with processing temperature limited to 400 °C. P channel MOSTs exhibit low threshold voltage and a carrier mobility of about 400 cm² V⁻¹ s⁻¹.     

STABILITY AND RHEOLOGY OF HEAVY CRUDE OIL-IN-WATER EMULSION STABILIZED BY AN ANIONIC- NONIONIC SURFACTANT MIXTURE

ABSTRACT

The stability and rheology of an Egyptian Heavy crude oil-in-water emulsions stabilized by an anionic (TDS) and a nonionic (NPE) surfactants individually or in a mixture have been studied. The study reveals that, the viscosity of the crude oil decreases when it is emulsified with water in the form of an oil-in-water type of emulsion. The stability of the oil-in-water emulsion increases as the surfactant concentration and speed of mixing of the emulsion increases. Fresh water and synthetic formation water have been used to study the effect of aqueous phase salinity on the stability and viscosity of the emulsion. Surfactant dissolved in synthetic formation water has been utilized to find out the possibility of injecting the surfactant into a well bore to effect emulsification in the pump or tubing for enhancing the production of heavy crude oils as oil-in-water emulsion. The study revealed that, the viscosity of the emulsion containing fresh water is always less than that containing formation water, these findings have been correlated with the crude oil/water interracial tension (IFT) measurements The decreased IFT value results in a decrease in the average particle size of the dispersed crude oil leading     

适用于低渗透高矿化度油藏的新型聚合物弱凝胶驱油体系——以长庆油田陇东侏罗系油藏为例

针对长庆油田陇东侏罗系油藏渗透率低、地层水矿化度高等问题,研制出适合其特点的聚合物弱凝胶驱油体系,对其流变性、抗盐性、抗剪切性等进行了评价,并进行了岩心驱替实验.结果表明:在50℃条件下,质量浓度为1 500mg/L聚合物溶液的表观粘度由29.61 mPa·s增大到51.96 mPa·s;配制用水矿化度越高,体系粘度越低,但当矿化度达25 000 mg/L时,粘度在10 mPa·s以上;聚合物弱凝胶驱油体系溶液以0.1～0.8 cm/min的注入速度通过岩心,粘度保留率不低于75％;对于渗透率为450×10-3和63.7×10-3μm2的岩心,与注水相比,聚合物弱凝胶驱油体系的驱油效率分别提高了14.29％和16.67％.在HC油田的H2区6个井组实施了聚合物弱凝胶驱先导试验,吸水厚度由17.4m提高到19.5 m,动用程度由66.2％提高到67.4％,注水压力上升了5.1 MPa,注聚见效井20口,累积增油量为3447t.表明新型聚合物弱凝胶驱油体系是减缓低渗透油藏递减、改善吸水剖面、降低油井含水率的有效途径.     

Genetic manipulation of the pathway for diacetyl metabolism in Lactococcus lactis

Diacetyl is an important food flavor compound produced by certain strains of citrate-metabolizing lactic acid bacteria. Citrate is converted to pyruvate, from which diacetyl is produced via intermediate alpha-acetolactate. This paper reports the cloning and analysis of the gene (aldB) encoding alpha-acetolactate decarboxylase from Lactococcus lactis MG1363. Deletion of the MG1363 chromosomal aldB gene was achieved by double crossover homologous recombination. The mutant strain was found to produce diacetyl; alpha-acetolactate decarboxylase activity was eliminated. Overexpression of the cloned ilvBN genes (encoding an alpha-acetolactate synthase) in the aldB deletion strain produced even higher levels of alpha-acetolactate, acetoin, and diacetyl.     

Effects of embryo reduction from trichorionic triplets to twins

Sixty-six trichorionic triplet pregnancies reduced to twins were compared with 47 triplet pregnancies that were not reduced. The miscarriage rate was higher (7.6% compared with 2.6%) but the number delivering between 24 and 32 weeks was lower (8.2% compared with 24.0%). Since severe preterm delivery is associated with risks of neonatal death and severe handicap, embryo reduction of triplets to twins may not improve the chance of survival but may reduce the rate of handicap.