Average Power Factor and Power Efficiency for Traction Duty Cycles

The line-side characteristics of ac traction drives are usually specified in terms of the power factor. By standards, this factor is defined for steady state conditions only. An average power factor throughout a load cycle according to the normal operation of a railway drive is presented. Different approaches to an average power factor have been reported in the literature. The approach presented here is based on a physical background. In contrast to previous definitions of an average power factor the new factor has the value of one if and only if constant active power is taken from the supply throughout the load cycle. As the power consumption as a function of time is rather a characteristic of the load cycle than of the power converter it is further suggested that the new average power factor be split into two factors, one specifying the load cycle, the other describing the converter.     

Predictive simulation of nanoparticle precipitation based on the population balance equation

Nanoparticle precipitation is an interesting process to generate particles with tailored properties. In this study we investigate the impact of various process steps such as solid formation, mixing and agglomeration on the resulting particle size distribution (PSD) as representative property using barium sulfate as exemplary material. Besides the experimental investigation, process simulations were carried out by solving the full 1D population balance equation coupled to a model describing the micromixing kinetics based on a finite-element Galerkin h-p-method. This combination of population balance and micromixing model was applied successfully to predict the influence of mixing on mean sizes (good quantitative agreement between experimental data and simulation results are obtained) and gain insights into nanoparticle precipitation: The interfacial energy was identified to be a critical parameter in predicting the particle size, poor mixing results in larger particles and the impact of agglomeration was found to increase with supersaturation due to larger particle numbers. Shear-induced agglomeration was found to be controllable through the residence time in turbulent regions and the intensity of turbulence, necessary for intense mixing but undesired due to agglomeration. By this approach, however, the distribution width is underestimated which is attributed to the large spectrum of mixing histories of fluid elements on their way through the mixer. Therefore, an improved computational fluid dynamics-based approach using direct numerical simulation with a Lagrangian particle tracking strategy is applied in combination with the coupled population balance-micromixing approach. We found that the full DNS-approach, coupled to the population balance and micromixing model is capable of predicting not only the mean sizes but the full PSD in nanoparticle precipitation.     

Shear bond strength tests of zirconia veneering ceramics after chipping repair

All ceramic systems are replacing the classical metal–ceramic crowns in dental practice. Zirconium dioxide (zirconia) core associated with veneering ceramic provides both good mechanical and aesthetic properties of prosthetic restorations. However, such zirconia crowns may be affected by defects of adaptation, too tight contacts in the proximal area and fissures of the ceramic veneer. The latter produces chipping; this requires a reattachment, therefore a second burning of the zirconia–ceramic interface. Such an additional procedure may affect the mechanical resistance of the ceramic veneer and the bond between the zirconia core and the ceramic veneer. The aim of this study was to evaluate the alterations of this shear bond strength (SB) between the zirconia core and the ceramic veneer, as produced by the first set of complete burning procedures and by the second correction burning of the dental restorations. Thirty-three zirconia discs were veneered with ceramic material and the SB was evaluated for each sample. Each ceramic cylinder detached from the zirconia was bonded on the core through a new layer of dentin and another burning procedure; the SB was tested again. The results of the two SB tests were compared; the statistical analysis concluded that there is an approximately 10% decrease of the resistance after the second burning. Also, the spread of the values for each test showed the high impact of the human factor on such dental restorations. In all the tests, the weakest area proved to be the interface between the zirconia core and the layered ceramics.     

Power Converters for Feeding Asynchronous Traction Motors of Single-Phase AC Vehicles

Asynchronous induction motors are very well suited to powerful traction drives. For electric locomotives and motor coaches with single-phase supply, a power conversion on the vehicle is necessary. Three different types of static power converters for this application are described. Indirect ac converters with direct voltage link have been developed successfully in the past. For indirect ac converters with direct current link some problems are discussed. At last a self-commutated direct ac converter with suppressed dc link is presented.     

Delay and reward choice in ADHD: An experimental test of the role of delay aversion.

Children with attention deficit/hyperactivity disorder (ADHD) choose smaller sooner (SS) over larger later (LL) rewards more than controls. Here we assess the contributions of impulsive drive for immediate rewards (IDIR) and delay aversion (DAv) to this pattern. We also explore the characteristics of, and the degree of familiality in, ADHD SS responders. We had 360 ADHD probands; 349 siblings and 112 controls (aged between 6 to 17 years) chose between SS (1 point after 2 s) and LL reward (2 points after 30 s) outcomes on the Maudsley Index of Delay Aversion (Kuntsi, Oosterlaan, & Stevenson, 2001): Under one condition SS choice led to less overall trial delay under another it did not. ADHD participants chose SS more than controls under both conditions. This effect was larger when SS choice reduced trial delay. ADHD SS responders were younger, had lower IQ, more conduct disorder and had siblings who were more likely to be SS responders themselves. The results support a dual component model in which both IDIR and DAv contribute to SS choice in ADHD. SS choice may be a marker of an ADHD motivational subtype. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prediction of aggregation kinetics based on surface properties of nanoparticles

Aggregation of nanoscaled particles is a challenge to be met when controlling or tailoring particle size distributions (PSDs) in many areas including precipitation, dip-coating and milling. Control of aggregation can be achieved for sparingly soluble salts through stabilization by electrostatic repulsive particle-particle interaction. The presented work shows a combined experimental/numerical approach to quantitatively determine the stability using barium sulfate as the model substance. The experimental data is obtained by measuring the temporal evolution of the PSD. A detailed aggregation model is presented based on the population balance equation including the influence of particle-particle interactions via the so-called stability ratio W. Values for this ratio are determined by a parameter estimation strategy from the experimental data and then successfully correlated via the surface charge density to the adsorption of potential-determining ions (H⁺- and Ba²⁺-ions in the investigated system). The model is validated and its ability to capture the influence of ionic strength and particle size is tested successfully. Many insights are gained and favorable feed concentrations for the production of nanoparticles through precipitation identified. Thus the presented multi-scale approach relating the aggregation behavior to surface properties is not only well-suited for finding optimal stability but also to determine surface properties of nanoparticles.     

The generalizability of the Youth Self-Report syndrome structure in 23 societies.

As a basis for theories of psychopathology, clinical psychology and related disciplines need sound taxonomies that are generalizable across diverse populations. To test the generalizability of a statistically derived 8-syndrome taxonomic model for youth psychopathology, confirmatory factor analyses (CFAs) were performed on the Youth Self-Report (T. M. Achenbach & L. A. Rescorla, 2001) completed by 30,243 youths 11-18 years old from 23 societies. The 8-syndrome taxonomic model met criteria for good fit to the data from each society. This was consistent with findings for the parent-completed Child Behavior Checklist (Achenbach & Rescorla, 2001) and the teacher-completed Teacher's Report Form (Achenbach & Rescorla, 2001) from many societies. Separate CFAs by gender and age group supported the 8-syndrome model for boys and girls and for younger and older youths within individual societies. The findings provide initial support for the taxonomic generalizability of the 8-syndrome model across very diverse societies, both genders, and 2 age groups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)