Class-E, Class-C, and Class-F power amplifiers based upon a finitenumber of harmonics

Class-E operation at UHF and microwave frequencies is achieved by using transmission-line networks to provide the drain harmonic impedances of an ideal class-E power amplifier (PA). This paper develops a technique for analysis of such amplifiers that are based upon a finite number of harmonics. The technique is generally applicable to classes E, C, and F as well as PAs with harmonic reactances not corresponding to those of established classes. The analysis shows that the maximum achievable efficiency depends not upon the class of operation, but upon the number of harmonics employed. For any set of harmonic reactances, the same maximum efficiency can be achieved by proper adjustment of the waveforms and the fundamental-frequency load reactance. The power-output capability depends upon the harmonic reactances and is maximum for class F     

The effect of a patient's risk-taking attitude on the cost effectiveness of testing strategies in the evaluation of pulmonary lesions

STUDY OBJECTIVES: To assess the health and cost effects of a patient's risk-taking attitudes about diagnostic tests. DESIGN: Cost-effectiveness analysis. SETTING: Diagnostic testing strategies used in the evaluation of a patient with a radiographically detected lung lesion were evaluated. Strategies included combinations of sputum, fine-needle aspiration, bronchoscopy, thoracoscopy, and expectant management. PATIENTS: Patient data were obtained from the Survival Epidemiology and End Results Program, MEDLINE search, National Center for Health Statistics, and the Universities of Iowa and Stanford, and Kaiser Permanente Hospital. INTERVENTIONS: Different patient risk-taking attitudes were simulated using decision analysis. MEASUREMENTS: Lifetime cost of medical care, life expectancy, and cost effectiveness. RESULTS: The cost effectiveness of competing strategies depended on patient attitudes about taking risks. For a patient averse to expectantly waiting without definitive knowledge of whether cancer was or was not present, testing strategies using invasive procedures, such as thoracoscopy, were more cost effective. In contrast, for a patient who was identical except that he or she was averse to tests with higher morbidity and mortality, strategies that involved expectantly waiting, instead of more invasive tests, were more cost effective. Small changes in some risk-taking attitudes resulted in large changes in cost effectiveness. CONCLUSIONS: Risk-taking attitudes influenced the cost effectiveness of testing strategies. Consideration of patient risk-taking attitudes in diagnostic testing appears warranted in setting clinical policies and making individual decisions.     

Nutzung von Kundendaten zur Minimierung des Forderungsausfallrisikos im Distanzhandel

Using Customer Data to Minimize the Risk of Default in Distance Selling In distance selling, customers and merchants get together in an anonymous way — at least for the first contact. Merchants have to form an opinion about the credibility of their customers to reduce the risk of defaults to a minimum. Various mechanisms to prevent such risks are known from the banking and insurance industry, e.g. consumer scoring, which is normally based on internal and external data about the credibility and buying patterns of customers. The focus of this article is on customer data with so called negative attributes as well as the ‘value’ of additional data (in particular Marketing data with so called positive attributes). There, especially the area of conflict between the economic necessity from the merchant’s perspective and resulting limitation of informational self-determination of the customer will be discussed.

Eingereicht am 2006-04-24, nach drei überarbeitungen angenommen am 2006-09-22 durch die Herausgeber des Schwerpunktthemas.     

Influence of Processing and Heat Treatment on Corrosion Resistance and Properties of High Alloyed Steel Coatings

Corrosion and abrasive wear are two important aspects to be considered in numerous engineering applications. Looking at steels, high-chromium high-carbon tool steels are proper and cost-efficient materials. They can either be put into service as bulk materials or used as comparatively thin coatings to protect lower alloyed construction or heat treatable steels from wear and corrosion. In this study, two different corrosion resistant tool steels were used for the production of coatings and bulk material. They were processed by thermal spraying and super solidus liquid phase sintering as both processes can generally be applied to produce coatings on low alloyed substrates. Thermally sprayed (high velocity oxygen fuel) coatings were investigated in the as-processed state, which is the most commonly used condition for technical applications, and after a quenching and tempering treatment. In comparison, sintered steels were analyzed in the quenched and tempered condition only. Significant influence of alloy chemistry, processing route, and heat treatment on tribological properties was found. Experimental investigations were supported by computational thermodynamics aiming at an improvement of tribological and corrosive resistance.     

Ionic Liquid Approach Toward Manufacture and Full Recycling of All‐Cellulose Composites

All‐cellulose composites (ACCs) are prepared from high‐strength rayon fibers and cellulose pulp. The procedure comprises the use of a pulp cellulose solution in the ionic liquid (IL) 1‐ethyl‐3‐methyl imidazolium acetate ([EMIM][OAc]) as a precursor for the matrix component. High‐strength rayon fibers/fabrics are embedded in this solution of cellulose in the IL followed by removal of the IL. Different concentrations of cellulose in the IL are investigated and the mechanical properties of the final ACCs are determined via tensile, bending, and impact testing. ACCs prepared in this study show mechanical properties comparable to thermoplastic glass fiber‐reinforced plastics. Apart from being bio‐based, they possess several advantages such as biodegradability and full recyclability. The recycling of ACCs is successfully demonstrated in several cycles by using the recycled cellulose for subsequent matrix preparation.     

Solid Particle Effects in Centi-scale Slurry Bubble Columns

Both solid particles and column diameter affect the gas holdup and flow regimes in slurry bubble columns, but investigations of the combined effects are not to be found. This study shows the simultaneous impacts on the overall gas holdup and flow regime transitions and determines the dominant effects in slurry bubble columns on the centi-scale containing solid particle concentrations up to 20 vol %. Additional tomography measurements are presented to visualize the gas phase flow and the spatial gas phase distribution in the column.     

Energy production from grassland – Assessing the sustainability of different process chains under German conditions

In many regions of Europe, grassland shapes the landscape and fulfils important functions in protecting nature, soil, and water. However, the traditional uses of grassland for forage production are vanishing with progress in breeding and structural adaptations in agriculture. On the other hand, the demand for biomass energy is rising due to political sustainability goals and financial measures to support renewable energy. Against this background, the Institute for Technology Assessment and Systems Analysis investigated the applicability, economic efficiency, and sustainability of different techniques for energy production from grassland as well as from grassland converted into maize fields or short-rotation poplars under German conditions. The results show that despite relatively high energy prices and the financial support for bioenergy, the effects of energy production from grassland on employment in agriculture and farmers' income are modest. What is beneficial are savings in non-renewable energy, reductions in greenhouse gas emissions, and local provision of energy carriers. If grassland biomass (grass silage or hay) is used for energy purposes, this brings the further advantages of preserving biodiversity and the cultural landscape and protecting of soil and groundwater. Negative impacts on sustainable development result from an increase in emissions, which leads to acidification, eutrophication, and risks to human health. The overall evaluation indicates that short-rotation poplars are comparatively advantageous from the economic and ecological point of view. Therefore, a development plan for grassland is required to identify areas where grassland could be used as an energy resource or where it would be favourable to install energy plantations with fast-growing perennial plants.     

Effect of tin on rats. 1. Inverse voltammetric determination of tin in the presence of lead in biological material after extraction]

By means of inverse polarography, the authors determined tin selectively after double extraction with diethylammonium diethyl dithiocarbamate (DADDTC) in perchloric solution. The recovery rates were: in potatoes, 91.7 +/- 5.8%; in beef kidney, 85.0 +/- 22.7%; in beef liver 79.9 +/- 13.8%; and in milk, 69.8 +/- 11.4%. Possible interferences from other elements with the tin determination are discussed.     

How to Render Frames and Influence People

Rendering systems generally treat the production of images as an objective process governed by the laws of physics. However, perception and understanding on the part of viewers are subjective processes influenced by a variety offactors. For example, in the presentation of architectural drawings, the apparent precision with which the drawings are made will affect whether the viewer considers the design as part of a preliminary design or as part of a final polished project, and to some extent the level of confidence the viewer has in the encoded information. In this paper we develop techniques for rendering images in a way that differs from the usual photorealistic or wire-frame output of renderers. In particular, our techniques allow a user to adjust the rendering of a scene to produce images using primitives with variable degrees of precision, from approximations that resemble vague “five-minute-sketches” to more mature but still hand-drawn images. We provide a theoretical framework for analysing the information flow from the computer to the user via such images. Finally, we describe the design and implementation of a prototypical renderer and show examples of its output.