Beitrag zur asynchronen Linearmaschine mit parallelen Statorleitern und ortsabhängiger Sekundärleitfähigkeit

Übersicht Der Einfluß der Parallelschaltung der Statorleiter auf das Betriebsverhalten des asynchronen Linearmotors wird untersucht und insbesondere für den Fall verschwindender elektrischer Sekundärleitfähigkeit im Statoreintrittsbereich dargestellt. Zur Verdeutlichung werden die Ergebnisse mit denen des Linearmotors bei Reihenschaltung der Statorleiter und des umlaufenden Asynchronmotors verglichen.

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On the performance of the linear induction machine with stator conductors in parallel and with stator dependent conductivity of the secondary

Contents The influence of connecting the stator conductors in parallel on the performance of the linear induction machine is analysed. Particularly the case of secondary conductivity zero at the entrance zone is treated. The results are compared with the performance characteristics of the linear machine the stator conductors connected in series and of the rotating induction machine.

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Die Verfasser danken der Deutschen Forschungsgemeinschaft für die finanzielle Unterstützung des Forschungsvorhabens.     

Berechnung der Anlaufdaten von Asynchron-Käfigläufermotoren verschiedener Stabformen mit der Methode der finiten Differenzen

Übersicht Die spannungsabhängigen Anlaufströme und Drehmomente eines 2800 kW Asynchron-Käfigläufermotors werden mit der Methode der finiten Differenzen und einem neuen Block-SOR-Iterationsverfahren berechnet. Es wird ber die Ergebnisse für Rechteck-, Trapez- und andere Rotorstabformen berichtet. Die numerisch berechneten Daten werden mit den nach konventionellen Regeln ermittelten Zahlen verglichen. Der Sättigungseffekt ist unerwartet groß, als Folge des großen Nennstrombelages. Die ungesättigten werte stimmen sehr gut überein.

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On the calculation of the starting data of A.C. squirrel-cage motors with different bar shapes by the method of finite differences

Contents The voltage dependent starting currents and torques of a 2,800 kW 3-phase a.c. squirrel cage motor are calculated by the method of finite differences using a new block-SOR iteration technique. The paper describes the results for different rotor bars with rectangular, trapezoidal and other shapes. The calculated data are compared with conventionally determined figures. The saturation effect is rather large due to the high values of the rated current loading per air gap periphery. The unsaturated values agree very good.

     

Hydrogen Oxidation Catalyzed by Pt Supported on Carbon Nanofibers with Different Graphite Sheet Orientations

The kinetic study of hydrogen oxidation with or without the presence of CO has been used as a tool to study the relative oxygen and CO adsorption strength on Pt nanoparticles, which are important parameters for fuel cell catalysts. It was found that the activation energy, which is determined by the oxygen binding energy, is influenced by the CNF graphite sheet orientation, CNF oxygen groups and catalyst preparation method. A weaker bonding of oxygen was indicated for Pt nanoparticles supported on platelet compared to Pt on fishbone CNFs. Moreover, oxygen seemed to be more strongly bonded to Pt particles on CNFs prepared by deposition–precipitation compared to those prepared by incipient wetness impregnation and a metal-oxide colloid method. Enhanced CO-adsorption was indicated for Pt supported on carbon nanofibers with introduced oxygen groups.     

The geographical effects of the NAFTA on Canadian provinces

This paper investigates the effects of the North American Free Trade Agreement (NAFTA) on the Canadian provinces. A large body of research has emerged testing the effects of the Canada–US Free Trade Agreement and the NAFTA, but the majority of that research has analyzed the effect of free trade at the national scale despite the fact that different provinces have different industrial compositions and levels of integration with the US. It is found that there is a geographical component to the effect of the NAFTA, and this geographical component varies from province to province. I am grateful to Trevor J. Barnes for comments on an earlier draft of this paper.     

Micro-fibre and ultra-micro-fibre cloths, their physical characteristics, cleaning effect, abrasion on surfaces, friction, and wear resistance

The properties of 12 micro-fibre cloths and two ultra-micro-fibre cloths were studied and compared with conventional cleaning methods. The cloths made from micro-fibre and ultra-micro-fibre had very good cleaning effect. Scrubbing Plexiglas caused pitting and scratch marks on the Plexiglas surface with the largest damage being caused in dry condition. All the cloths tested were wear resistant. Most of the cloths showed high friction against the surfaces in damp condition. Micro- and ultra-micro-fibre cloths are good alternatives to conventional methods for cleaning interior surfaces. Furthermore, good cleaning results can be achieved without any use of polluting cleaning chemicals.     

Superchilled,chilled and frozen storage of Atlantic mackerel (Scomber scombrus) – effect on lipids and low molecular weight metabolites

Quality changes in Atlantic mackerel fillets during superchilled, chilled and frozen storage focusing on lipid quality, colour and changes in low molecular weight metabolites relevant for quality and safety were studied. Low formation of oxidation products was observed in chilled (up to 7 days), superchilled (up to 14 days) and frozen storage (up to one year). Only slight formation of TBARS was measured in the samples which correlated with the increasing fillet yellowness. The profile of low molecular weight compounds, analysed by high-resolution NMR, showed clear grouping of the different samples according to both treatment and storage time. The increase in K-value was highest in the chilled samples, reaching a K-value of 93 ± 3% on day 5, exceeding the proposed limit of human consumption (80%) while superchilling reached a K-value of ca 90 % after 14 days. Frozen samples showed acceptable quality in the whole storage period.     

Reversible photoswitching enables single-molecule fluorescence fluctuation spectroscopy at high molecular concentration

We demonstrate that photoswitchable markers enable fluorescence fluctuation spectroscopy at high molecular concentration. Reversible photoswitching allows precise control of the density of fluorescing entities, because the equilibrium between the fluorescent ON- and the dark OFF-state can be shifted through optical irradiation at a specific wavelength. Depending on the irradiation intensity, the concentration of the ON-state markers can be up to 1,000 times lower than the actual concentration of the labeled molecular entity. Photoswitching expands the range of single-molecule detection based experiments such as fluorescence fluctuation spectroscopy to large entity concentrations in the micromolar range.     

Efficiency bound of a solar-driven stirling heat engine system

A solar-driven Stirling engine is modelled as a combined system which consists of a solar collector and a Stirling engine. The performance of the system is investigated, based on the linearized heat loss model of the solar collector and the irreverisible cycle model of the Stirling engine affected by finite-rate heat transfer and regenerative losses. The maximum efficiency of the system and the optimal operating temperature of the solar collector are determined. Moreover, it is pointed out that the investigation method in the present paper is valid for other heat loss models of the solar collector as well, and the results obtained are also valid for a solar-driven Ericsson engine system using an ideal gas as its engine work substance. © 1998 John Wiley & Sons, Ltd.     

Synthesis and structural characteristics of polycyclic aromatic hydrocarbon-containing phenol formaldehyde resites

To probe the formation of polycyclic aromatic hydrocarbons (PAHs) during the carbonization, gasification, and liquefaction of coals and other solid fuels, nonsoftening phenol—formaldehyde (PF) co-resites are ideal since they facilitate the incorporation of individual PAHs into a highly crosslinked matrix. A series of PAH and diphenylalkane-containing phenolic co-resites have been prepared using phenol with, as the second component, 2-naphthol, 4-hydroxy diphenylmethane, 4,4′-dihydroxydiphenylethane, 1-(4-hydroxybenzyl)naphthalene, 9-(4-hydroxybenzyl)anthracene, and 9-(4-hydroxybenzyl)phenanthrene. A mole ratio of 3 : 1 (phenol : second phenolic constituent) was adopted to ensure that a reasonably high degree of crosslinking was achieved. The virtually complete elimination of ether and methylol functions from the resoles by curing at 200°C was monitored by solid-state ¹³C-NMR. The resites were also characterized by Fourier transform infrared spectroscopy. The volatile-matter contents of the PAH-containing resites were all higher than that of the normal resite. The carbonization of the 9-(4-hydroxybenzyl)anthracene-containing resite in a fluidized-bed reactor is used to illustrate the potential applications of the PAH-containing resites in fuel science. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 663–671, 1997