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.     

An expanded perspective on children's mental health.

Comments on three articles (see records 2005-11115-003, 2005-11115-004, and 2005-11115-005) on the status of children's mental health services in the United States, which appeared in the September 2005 issue of the American Psychologist. The current authors suggest that, although this series of articles provides important information, the articles fall short in meeting the mark of comprehensively describing the solutions necessary to effectively address the crisis facing children's mental health in this country. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ionic liquids with ammonium cations as lubricants or additives

A new class of more effective lubricants could lead to huge energy savings. Limited recent literature has suggested potential for using room-temperature ionic liquids as lubricants, however, only a few out of millions (or more) of species possible have been evaluated. In this study, a series of new protic alkylammonium ionic liquids were synthesized by neutralization and metathesis reactions, and have demonstrated promising lubricating properties as neat lubricants or lubricant additives, particularly for use with difficult-to-lubricate metals like aluminum. More than a 30% friction reduction was observed with ammonium-based ionic liquids compared to conventional hydrocarbon oils in reciprocating sliding tests of 52100 bearing steel on aluminum alloy 6061-T6511. The inherent polarity of ionic liquids is believed to provide strong adsorption to contact surfaces and can form a boundary lubricating film leading to friction and wear reductions. Other advantages of ionic liquids include (1) negligible volatility, (2) high thermal stability, (3) non-flammability, and (4) better intrinsic properties that may eliminate the need for more complex and expensive additive packages. With very flexible molecular structures, this new class of lubricants, particularly ammonium-based ionic liquids, can be tailored to fit a variety of applications.