Bestimmung der Oberwellenstreuung und der Zahnkopfstreuung bei Drehfeldmaschinen mit Hilfe der Feldtheorie

Übersicht Es wird ein feldtheoretischer Ansatz zur Bestimmung der Selbst- und Gegeninduktivität einer einseitig genuteten Drehfeldmaschine verwendet. Die Streuinduktivität wird in Anlehnung an die konventionelle Theorie in einzelne Anteile aufgespalten. — Es zeigt sich, daß die Komponenten Oberwellenstreuung und Zahnkopfstreuung auch von der Wicklungsverteilung im ungenuteten Teil abhängen, ihre Summe aber nicht. Deshalb werden der Koeffizient der Oberwellenstreuung und der spezifische Leitwert der Zahnkopfstreuung unter Voraussetzung gleicher Wicklungsverteilung wie im genuteten Teil definiert und für ungesehnte Ganzlochwicklungen in Kurvenform dargestellt. Die Ergebnisse zeigen den Einfluß der bei der Vorausberechnung von Drehfeldmaschinen bisher nicht berücksichtigten Parameter.

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Determination of the harmonic leakage and tooth tip leakage inductances of three phase a. c. machines using the field theory

Contents Self- and mutual inductances of an a. c. machine with open slots on only one side of the air gap are determined by means of a field-theoretical approach. The leakage inductance is subdivided into its parts according to conventional definition. It is shown that only the sum of harmonic and tooth tip leakage is independant of the winding distribution on the other side of the air gap which is not slotted. Therefore the harmonic leakage coefficient and the specific tooth tip leakage permeance are shown in curves for integral slot windings of normal pitch under the assumption that the secondary winding is of the same distribution as the primary. The results show the influence of parameters which were not taken into account in machine design calculations hitherto.

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Verwendete Formelzeichen

Gößen A Vektorpotential - B Induktion - b Breite - e Einheitsvektor - f _w Wicklungsfaktor - G Stromdichte - H magnetische Feldstärke - I Strom - h Höhe - k _c Carter-Faktor - L Induktivität - l _i ideelle Länge - p Polpaarzahl - q Lochzahl (Nuten pro Pol und Strang) - s Leiterhöhe - w Windungszahl - Luftspalt - spezifischer Leitwert - ₀ Permeabilität der Luft - verketteter Fluß - Streukoeffizient - Teilung - i, j, k, m, n, v Zählgrößen, Ordnungszahlen Indizes d Oberwellen- (doppeltverkettet) - g Gegen- - h Haupt- - i Index für Nutpotential - k Index für Luftspaltpotential - l Luftspalt- - n Nut- - p Pol- - r ungenuteter (Sekundär-) Teil - s Selbst- - z Zahnkopf- - 1 Grundwelle     

46-year-old patient with hemorrhagic diathesis and renal artery aneurysms. Type IV Ehlers-Danlos syndrome

To establish the medium-term results of our transplant population, we retrospectively reviewed the charts of 51 consecutive patients who underwent orthotopic heart transplantation between July 1988 and April 1995. These patients comprised two groups: group A consists of 26 patients (age 6 days to 16.4 years, median 1.4 years) with no previous heart surgery, and group B consists of 25 patients (ages 0.1 to 14.3 years, median 8.3 years), all of whom had heart surgery before undergoing transplantation. There was no difference between these groups in early or late survival rates, and neither age at transplantation nor sex was an indicator of survival. There have been 14 deaths, six early (before hospital discharge) and eight late. Early deaths have predominantly been attributed to long-term ventilation and hemodynamic instability before transplantation, and late deaths to graft coronary artery disease (n = 4), acute coronary vasculitis (n = 3), and acute cellular rejection (n = 1). Although infection has resulted in significant morbidity (57 hospital admissions), there have been no late deaths resulting from infection. Sepsis accounts for four early deaths in chronically ill patients. Orthotopic heart transplantation in the pediatric patient with and without previous heart surgery is a viable option for those with end-stage heart disease and those in whom other surgical options carry a prohibitively high mortality rate.     

Application of the electrochemical microcapillary technique to study intergranular stress corrosion cracking of austenitic stainless steel on the micrometre scale

The electrochemical microcapillary technique was applied for the first time to study the electrochemical dissolution signals from single growing cracks due to stress corrosion cracking of thermally sensitised AISI 304 stainless steel in potassium tetrathionate solution. Potentiostatic current measurements on initiating cracks along grain boundaries were performed. Typical current signals of potentiostatic and potentiodynamic measurements consisted of a series of current peaks showing fast rise and exponential decay, sometimes interrupted by passive phases. The results indicate that stress corrosion crack growth is a discontinuous process of passive and active phases, which might be explained by the film rupture model.     

Observations on Finger-like Crack Growth at a Urethane Acrylate/Glass Interface

Interfacial crack growth behavior along a urethane acrylate/glass interface is characterized by the development of finger-like perturbations along the advancing crack front. The finger-like perturbations grow from a slightly irregular crack front until they reach a steady-state where the velocity of the finger tips equals the velocity of the finger valleys. Once the fingers reached steady-state, the crack velocity was dependent on the applied strain energy release rate via a power law relationship where the exponent was independent of test humidity; however, the multiplicative constant A decreased by an order of magnitude from 80 to 15% RH. The spacing of the fingers was found to be independent of the crack′s velocity and the relative humidity of the environment.     

ESBL-producing E. coli in Austrian sewage sludge

The aim of this study was to investigate the degree of contamination of sewage sludge with ESBL-producing Escherichia coli strains and the effectiveness of different sewage sludge treatment methods.Monthly sewage sludge samples were collected between January and September 2009 in 5 different sewage treatment plants and tested for the presence of ESBL E. coli. In addition, the number of colony forming units (CFU) of E. coli and coliform bacteria before and after the different sludge treatment methods (aerobic/anaerobic digestion, lime stabilization, and thermal treatment) was investigated.Of the 72 sewage sludge samples investigated, ESBL-positive E. coli were found in 44 (61.1%) sewage sludge samples. The classification of β-lactamase groups was carried out in 15 strains resulting in the detection of 2 different groups (CTX-M and TEM) of bla genes. All 15 of them had a CTX-M gene and 4 of these strains furthermore carried a TEM gene.With regard to the CFU of E. coli and coliform bacteria, thermal treatment and lime stabilization following dehydration sufficiently reduced pathogen concentrations. The plants using merely stabilization and dehydration showed an increase of E. coli and coliform bacteria and thus also an increase in ESBL-producing E. coli.