Improved column-switching liquid chromatographic method for the determination of the enantiomers of mefloquine

A liquid chromatographic method for the determination of the enantiomers of mefloquine has been improved. The chromatography involved two columns: an achiral cyanopropyl stationary phase for the quantification of (+/-)-mefloquine and a chiral naphthyl-urea stationary phase for the determination of the enantiomeric ratio. Compared with the previous method, which needed two detectors, this one used one detector-integrator to which the two columns are connected alternately by an automated column-switching system. The method is suitable for the quantification (0.05 microgram/ml) of mefloquine and the determination of enantiomeric ratios from 500-microliters plasma samples with ultraviolet detection.     

Cisapride reduces neonatal postoperative ileus: randomised placebo controlled trial

AIM: To assess the efficacy of cisapride in reducing ileus persisting to the tenth postoperative day after neonatal abdominal surgery. METHODS: A prospective, randomised, double blind trial comparing rectal cisapride (1.4-2.3 mg/kg/day) with placebo over seven days was undertaken in 33 neonates. RESULTS: Seven of 12 (58%) patients receiving placebo and eight of 11 (73%) receiving cisapride achieved a first sustained feed during treatment. Of those receiving cisapride, the first sustained feed occurred at 2.3 days (SEM 0.6) compared with 4.7 days (SEM 0.8) with placebo. By the seventh day the mean daily net enteral balance was 69 (SEM 18) ml/kg in the cisapride subgroup and 17 (SEM 8) ml/kg for those receiving placebo. Stool was passed on 6.3 (SEM 0.4) treatment days in the cisapride subgroup compared with 4.1 (SEM 1.0) treatment days in the placebo subgroup. CONCLUSION: Cisapride is effective in neonates with a prolonged ileus after abdominal surgery.     

An Eigen-Analysis of Compact Antenna Arrays and Its Application to Port Decoupling

Placing the radiators of antenna arrays closer than aggravates the problem of power mismatch. Based on efficiency considerations, a general analysis of this effect is presented, putting forward a simple tool to quantify, compare, and optimize the performance of antenna arrays. This analysis is not restricted with respect to the number of radiators or the degree of compactness. In order to improve power matching, a systematic approach for the design of lossless decoupling and matching networks based on 180 directional couplers is suggested for up to eight radiators. Implications of network losses, which have not yet received appropriate attention by researchers in the past, will be analyzed and discussed by means of a manufactured three-element prototype array.     

Koordination in Service Value Networks

The fundamental paradigm shift from traditional value chains to agile service value networks implies new economic and organizational challenges. As coordination mechanisms, auctions have proven to perform quite well in situations where intangible and heterogeneous goods are traded. Nevertheless, traditional approaches in the area of multidimensional combinatorial auctions are not quite suitable to enable the trade of composite services. A flawless service execution and therefore the requester’s valuation highly depends on the accurate sequence of the functional parts of the composition, meaning that in contrary to service bundles, composite services only generate value through a valid order of their components. The authors present an abstract model as a formalization of service value networks. The model comprehends a graph-based mechanism implementation to allocate multidimensional service offers within the network, to impose penalties for non-performance and to determine prices for complex services. The mechanism and the bidding language support various types of QoS attributes and their (semantic) aggregation. It is analytically shown that this variant is incentive compatible with respect to all dimensions of the service offer (quality and price). Based on these results, the authors numerically analyze strategic behavior of participating service providers regarding possible collusion strategies.     

Quantitative measurement of repetitive impact damage on ground silicon nitride surfaces

Structural ceramics are finding application in automotive and truck engines. Poppet valves and valve seats, for example, require resistance to surface damage from repetitive impacts. Grinding and finishing processes can leave microcracks or residual stresses in the surfaces of ceramics which can accelerate surface-initiated degradation processes. A ball-on-inclined plane, repetitive impact testing system has been developed to study the effects of finishing method on surface durability. Tests were performed by repeatedly striking ground alumina and silicon nitride flat specimens with a silicon nitride sphere and measuring the impact damage as a function of the number of strikes. One type of alumina and three types of silicon nitride ceramics were tested. A quantitative impact damage parameter (IDP), based on mechanical stylus profiling data, was developed for use in measuring small amounts of wear. When damage did not extend beyond the depth of valleys in the machined surfaces, the IDP exhibited an excellent linear correlation with the number of impacts of silicon nitride on both silicon nitride and alumina materials. When more extensive damage occurred, a method involving digitizing the area of the contact damage from photomicrographs provided a reasonable correlation with number of impacts. These two methods are compared. Scanning electron microscopy revealed features which can affect the accuracy of impact damage measurement. Implications of the technique are discussed.     

Chromium(III) compounds as catalysts for Hydrocarbon Oxidation and hydroperoxide decomposition

Chromium stearate and chromium acetylacetonate are very active catalysts both for the oxidation of hydrocarbons by molecular oxygen and for the decomposition of organic hydroperoxides. During these reactions they also catalyze the oxidation of secondary alcohols to the corresponding ketones by organic hydroperoxides. From organic hydroperoxides and chromium(III)compounds chromium (VI) compounds are formed which are probably the effective agents oxidizing secondary alcohols to ketones.     

Graphene oxide covalently functionalized with zinc phthalocyanine for broadband optical limiting

A soluble graphene oxide (GO) covalently functionalized with zinc phthalocyanine (PcZn), GO–PcZn, was synthesized by an amidation reaction. The formation of an amido bond between PcZn and GO has been confirmed by X-ray photoelectron and Fourier transform infrared spectroscopy. At the same level of linear extinction coefficient, GO–PcZn exhibited much larger nonlinear optical extinction coefficients and broadband optical limiting performance than GO at both 532 and 1064 nm, indicating a remarkable accumulation effect as a result of the covalent link between GO and PcZn.