Experimental Investigations of Exciting Forces Caused by Flow in Labyrinth Seals

The interaction of the flow through the labyrinth seals with the shaft of the rotor can have an effect on the stability of turbomachines. Thus, the excited forces, so-called cross forces or nonconservative forces, arise, which act perpendicular to the rotor eccentricity. This effect is caused by an unsymmetrical pressure distribution within the labyrinth cavities. Experimental studies were carried out for different types of labyrinth geometries: two staggered labyrinths with teeth on the stator and grooved rotor as well as a full and a convergent stepped labyrinth. These labyrinths can be found on the tip shrouding of bladings in steam or gas turbines. The following parameters were varied in the test facility: geometry of the labyrinth seals (number of cavities, inlet region), shaft rotation, pressure difference on the seal, entry swirl and eccentricity of the rotor. The results are presented for stiffness coefficients of the labyrinth seals, leakage flow and circumferential flow in each cavity which was measured with special probes. Generally, the inlet swirl has the greatest influence on the coefficients of the seals. The experimental results were compared with theoretical results and were in good agreement

Ratios of involved nodes in early breast cancer

INTRODUCTION: The number of lymph nodes found to be involved in an axillary dissection is among the most powerful prognostic factors in breast cancer, but it is confounded by the number of lymph nodes that have been examined. We investigate an idea that has surfaced recently in the literature (since 1999), namely that the proportion of node-positive lymph nodes (or a function thereof) is a much better predictor of survival than the number of excised and node-positive lymph nodes, alone or together. METHODS: The data were abstracted from 83,686 cases registered in the Surveillance, Epidemiology, and End Results (SEER) program of women diagnosed with nonmetastatic T1–T2 primary breast carcinoma between 1988 and 1997, in whom axillary node dissection was performed. The end-point was death from breast cancer. Cox models based on different expressions of nodal involvement were compared using the Nagelkerke R(2 )index (R(2)(N)). Ratios were modeled as percentage and as log odds of involved nodes. Log odds were estimated in a way that avoids singularities (zero values) by using the empirical logistic transform. RESULTS: In node-negative cases both the number of nodes excised and the log odds were significant, with hazard ratios of 0.991 (95% confidence interval 0.986–0.997) and 1.150 (1.058–1.249), respectively, but without improving R(2)(N). In node-positive cases the hazard ratios were 1.003–1.088 for the number of involved nodes, 0.966–1.005 for the number of excised nodes, 1.015–1.017 for the percentage, and 1.344–1.381 for the log odds. R(2)(N )improved from 0.067 (no nodal covariate) to 0.102 (models based on counts only) and to 0.108 (models based on ratios). DISCUSSION: Ratios are simple optimal predictors, in that they provide at least the same prognostic value as the more traditional staging based on counting of involved nodes, without replacing them with a needlessly complicated alternative. They can be viewed as a per patient standardization in which the number of involved nodes is standardized to the number of nodes excised. In an extension to the study, ratios were validated in a comparison with categorized staging measures using blinded data from the San Jose–Monterey cancer registry. A ratio based prognostic index was also derived. It improved the Nottingham Prognostic Index without compromising on simplicity

Experimentelle und theoretische Untersuchung der Stroemungskraefte in Labyrinthdichtungen von Turbomaschinen

Mit den Ergebnissen wird einerseits der bestehende Mangel an experimentellem Datenmaterial auf dem Gebiet der kurzen Labyrinthdichtungen verkleinert und andererseits werden den Konstrukteuren bei der Vorausberechnung des Schwingungsverhaltens von Turborotoren Unterlagen ueber das dynamische Verhalten (Steifigkeitseigenschaften) und das Durchflussverhalten von Labyrinthdichtungen zur Verfuegung gestellt. Die Ergebnisse sollen darueberhinaus auch Hinweise zur Optimierung der Dichtungsgeometrien im Hinblick auf beide Effekte geben. Insbesondere werden fuer eine Kamm-Nut-Labyrinthdichtung erstmals die kammerabhaengigen Reibbeiwerte in Umfangsrichtung sowohl fuer den Stator- als auch fuer den Rotorteil der Dichtung bestimmt. (orig./DG)The results reduce the existing lack of experimental data in the field of short labyrinth seals, on the one hand, and on the other hand, documents on the dynamic behaviour (stiffness properties) and the flow behaviour of labyrinth seals are made available to designers for precalculation of the vibration behaviour of turbine rotors. The results shouls also give instructions on the optimisation of the seal geometry with regard to both these effects. In particular, the coefficients of friction in the circumferential direction, depending on the chamber, for a comb-groove labyrinth seal are determined for the first time both for the stator part and the rotor part of the seal. (orig./DG)SIGLEAvailable from TIB Hannover: DW 7048 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Spalterregungskraefte Stroemungskraefte in Dichtlabyrinthen bei radialer und axialer Verschiebung des Rotors gegenueber dem Stator. Abschlussbericht

For the stability analysis of turbomachinery rotors one must have a knowledge of all forces that might influence the vibrational behavior of rotors. These also include previously insufficiently known flow forces generated in the chambers of labyrinth seals. Within the framework of the present research project, the lateral and resetting forces of various short labyrinth designs used in practical applications at the periphery of turbomachinery rotors were experimentally determined as a function of pressure ratio, pre-rotation and rotor rotation. At the same time the through-flow behaviour was measured. As a result now documents for determining the flow forces and flow rate are available to the user of such labyrinths. This also enables the designer to optimize labyrinths with respect to rotor stability and gap losses. The aerodynamic forces were determined from the pressure distribution at the circumference measured in each labyrinth chamber. It is shown that the geometry in particular of the first chamber and pre-rotation greatly influence the generation and amount of flow forces. The lateral force in general reaches a maximum in the first chambers, decaying more or less in the subsequent chambers depending on the relative size of frictional surfaces of the stator and rotor and depending on the magnitude and direction of rotor speed. The resetting force exhibits an alternating behavior usually well-developed from chamber to chamber so that its accumulated value for the labyrinth becomes very small. The linear dependence of flow forces from rotor eccentricity has been confirmed by the measurements. (orig.)Fuer die Stabilitaetsanalyse von Turbomaschinenrotoren muss man alle Kraefte kennen, die das Schwingungsverhalten der Rotoren beeinflussen koennen. Dazu gehoeren auch die bislang nur unzureichend bekannten Stroemungskraefte, die in den Kammern von Labyrinthdichtungen entstehen. Im Rahmen dieses Forschungsvorhabens wurden die Quer- und Rueckstellkraefte verschiedener in der Praxis an der Peripherie von Turbomaschinen-Laufraedern eingesetzter kurzer Labyrinthbauformen abhaengig von Druckverhaeltnis, Vordrall und Rotordrehung experimentell bestimmt. Gleichzeitig wurde das Durchflussverhalten gemessen. Als Ergebnis stehen dem Anwender derartiger Labyrinthe nun Unterlagen fuer die Ermittlung der Stroemungskraefte und des Durchflusses zur Verfuegung. Dadurch wird dem Konstrukteur auch eine Optimierung der Labyrinthe im Hinblick auf Rotorstabilitaet und auf Spaltverluste ermoeglicht. Die aerodynamischen Kraefte wurden aus der in jeder Labyrinthkammer gemessenen Verteilung des Druckes am Umfang ermittelt. Es zeigt sich, dass die Geometrie insbesondere der ersten Kammer und der Vordrall die Entstehung und die Groesse der Stroemungskraefte stark beeinflussen. Die Querkraft erreicht in den ersten Kammern im allgemeinen ein Maximum, in den folgenden Kammern klingt sie je nach relativer Groesse der Reibflaechen von Stator und Rotor und je nach Groesse und Richtung der Rotorgeschwindigkeit mehr oder weniger schnell ab. Die Rueckstellkraft zeigt ein meist ausgepraegt von Kammer zu Kammer alternierendes Verhalten, so dass ihr Summenwert fuer das Labyrinth sehr klein wird. Die lineare Abhaengigkeit der Stroemungskraefte von der Exzentrizitaet des Rotors wird durch die Messungen bestaetigt. (orig.)SIGLEAvailable from TIB Hannover: RA 1581(452) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekArbeitsgemeinschaft Industrieller Forschungsvereinigungen e.V., Koeln (Germany)DEGerman

Progress in imaging methods: insights gained into Plasmodium biology.

Over the past decade, major advances in imaging techniques have enhanced our understanding of Plasmodium spp. parasites and their interplay with mammalian hosts and mosquito vectors. Cryoelectron tomography, cryo-X-ray tomography and super-resolution microscopy have shifted paradigms of sporozoite and gametocyte structure, the process of erythrocyte invasion by merozoites, and the architecture of Maurer's clefts. Intravital time-lapse imaging has been revolutionary for our understanding of pre-erythrocytic stages of rodent Plasmodium parasites. Furthermore, high-speed imaging has revealed the link between sporozoite structure and motility, and improvements in time-lapse microscopy have enabled imaging of the entire Plasmodium falciparum erythrocytic cycle and the complete Plasmodium berghei pre-erythrocytic stages for the first time. In this Review, we discuss the contribution of key imaging tools to these and other discoveries in the malaria field over the past 10 years