ALBERT

Notes: Contents The boundary integral equation method is applied to permeance computation. Results obtained cover typical practical cases: permeance between parallel ferromagnetic prisms and permeance between parallel ferromagnetic prism and cylinder. The approach proposed and the results obtained can be used in the design of electromagnetic systems.

Notes: Contents An automatic finite element analysis procedure is developed with the employment of a self-adaptive refinement technique. The process of mesh generation, being usually a highly interactive process, is transformed into a batch—oriented process. A characteristic of the algorithm is that the generated tetrahedra have a very high aspect ratio (nearly equilateral), while the presence of sliver elements is completely avoided. The generation of high quality tetrahedra makes possible the approximation of curved surfaces directly in the refinement process. The inconsistence of forms in the numerical presentation of the magnetic inductionB is used as an error estimator, so that high error regions are recognized and refined. The proposed procedure presents reduced computational requirements, making it very well suited for the solution of 3-D problems. Application to the shielding by a magnetic permeable spherical shell shows the ability to tackle problems with complicated geometry and solve them with high accuracy.

Notes: Contents This paper describes an application of the three dimensional infinite element for modelling open boundary conditions in the finite element analysis of electromagnetic field problems. The infinite element has four nodes and is compatible with conventional cuboids. It is shown that the infinite element serves not only to obtain higher calculation precision in the interior—finite element region, but also gives very good results in the exterior region.

Notes: Contents In this paper different methods for calculating the air-gap field of induction motors are compared. A “modified one-dimensional field calculation” is proposed, combining the advantages of short computing times and high accuracy of the one- and two-dimensional field calculation, respectively. The different methods are checked against experiments: The total leakage coefficient and the radiated audible noise of induction motors are investigated. Both, the modified one-dimensional and the two-dimensional theory give results which are in good agreement to the measurements.

Notes: Contents The temperature field over the whole cross section of an asynchronous electric machine (windings, stator and rotor core, insulation, air gap) is calculated under both steady-state and transient conditions. Thermal sources (copper losses) depend on rotor slip, deep-bar effect and windings temperature. All these quantities are, in the transient condition, functions of time. The thermal part of this coupled electro-thermal process is solved by the finite element method (FEM), while the electromagnetic part is dealt with by the equivalent circuit of the asynchronous machine. The air-gap problem is specially treated. The presented method can be applied to other electric machines having negligible axial thermal heat flow.

Notes: Übersicht Die Rotorströme in aus U-Umrichtern gespeisten Asynchronmaschinen werden analysiert. Die Stromverläufe sind je nach Größe des Grundschwingungsschlupfes sehr unterschiedlich. Dabei auftretende Gesetzmäßigkeiten werden herausgestellt. Beim Leerlauf entstehen beträchtliche Unterschiede in der Strombelastung der einzelnen Stränge. Bei Belastung bilden die Rotorströme abhängig vom Schlupf entweder ein symmetrisches oder ein unsymmetrisches Stromsystem, wobei die Ströme auch nichtperiodisch sein können.

Notes: Contents The large and small signal dynamic analysis of LLCC-type parallel resonant converter operating in continous-conduction mode under fixed frequency, variable duty-ratio (pulse-width modulation) control is presented in this paper. The nonlinear and small-signal equations of the converter including the supply and output rectifiers are derived. The influence of the converter operation on the supply input power factor and how the input rectifier affects the small-signal dynamics of the converter are discussed.

Notes: Übersicht Eine Methode zur Berechnung der Driftbeweglichkeitsprofile in Feldeffekttransistoren wird vorgestellt. Das Verfahren nutzt lediglich frequenzabhängige Admittanzen eines Schottky-Kontaktes und die Niederfeldsteilheit des Bauelementes, die beide dirckt auf dem Wafer an einem Spitzenmeßplatz gewonnen werden. Die frequenzabhängigen Admittanzmessungen führen zu Gate-Source-Kapazitäten des Transistors, die nicht durch parasitäre Effekte verfälscht werden. Die Meßtechnik eignet sich für automatisierte Routineuntersuchungen an Feldeffekttransistoren auf sämtlichen Halbleitermaterialien. Als Beispiele werden Beweglichkeitsprofile in LDD- und BPLDD-GaAs-MESFET mit langen, kurzen, weiten und engen Kanälen diskutiert. Zusätzlich wird der Einfluß der Akzeptorkonzentration in der Pufferschicht auf die Transporteigenschaften des Kanals untersucht. Die diskutierten Strukturen sind Bauelemente, wie sie in kommerziell erhältlichen digitalen GaAs-LSI-Schaltungen eingesetzt werden.

Notes: Contents This paper deals with the problem of modelling the nonlinear behaviour of transformers for simulating transients. Many approaches have been published to this end. Implemented into transient programs computing time increases, a disadvantage when simulating large systems. The object of this paper is to present a simple method with fairly accurate results. It is based on the approach to substitute the hysteresis characteristic of transformers by a piecewise linear saturation curve including remanence. This method allows to implement the modelling of three-phase transformers into a transient program.

Notes: Contents Special geometries of electrodes were designed to determine the dominant mechanism of surface charge accumulation. It was found that the charge transport in the gas is dominant, and consequently, the normal field at spacer surfaces as well as the ionization behaviour at electrode surfaces play important roles in charge accumulation in SF6.

Notes: Übersicht Es wird ein numerisches 3D-Berechnungsverfahren vorgestellt, mit dem die elektromagnetischen (EM-) Felder bei induktiver Hochfrequenz-(HF-) oder Banderwärmung, also im Fall dünner stromführender Schichten, simuliert werden. Darüber hinaus lassen sich Leistungs- und Kraftverteilungen sowie integrale Größen, wie z. B. Impedanz, Spannung und Wirkleistung, ermitteln. Für das Berechnungsprogramm werden die prozeßrelevanten Teile der betrachteten Anlagen entsprechend ihrer elektromagnetischen Eigenschaften bestimmten Gruppen zugeordnet. Für jede Gruppe gelten spezifische Randbedingungen an der Oberfläche bezüglich der EM-Felder. Das Berechnungsprogramm basiert auf der Boundary-Element-Methode (BEM) und berücksichtigt die anlagenspezifischen Symmetrien, so daß Rechner genutzt werden können, die in Forschung und Entwicklung heute allgemein zugänglich sind (PC, Workstation). Am Beispiel zweier Anwendungsfälle wird die Leistungsfähigkeit des entwickelten Programmpaketes aufgezeigt.

Notes: Übersicht Ausgehend von den Grund- und Oberströmen des Stators und Rotors sowie den Flußverkettungen werden die parasitären synchronen Drehmomente als Funktion der Zeit analytisch ohne Vernachlässigungen in und außerhalb synchroner Schleichdrehzahlen berechnet. Aus der Bilanz der Wirkleistungen wird der zeitliche Mittelwert der synchronen Momente ermittelt. Für eine einfache Näherung unter Vernachlässigung der ohmschen Widerstände wird der zu erwartende Fehler angegeben. Der Einfluß von Nutenschrägung oder von magnetischen Nutenverschlußkeilen auf die synchronen Momente wird an Beispielen gezeigt. Beim Einphasen-Kondensatormotor treten mehr synchrone Schleichdrehzahlen mit größeren synchronen Momenten auf als beim vergleichbaren Drehstrommotor. Beim Einphasenmotor mit Spannungsanschnittsteuerung mittels Wechselstromsteller kommen weitere synchrone Drehmomente bei höheren Schleichdrehzahlen hinzu. Messungen bestätigen die Rechenwerte.

Notes: Contents Asymmetry of the supply voltage of a load and variation of its RMS value deteriorate supply quality, similarly as asymmetry of the load current, its reactive component, and variation of the current RMS value deteriorate loading quality. A method for adaptively improving the supply and loading quality with respect to the load unbalance and the voltage asymmetry is suggested and analyzed in this paper. The discussed method can be implemented for the development of an adaptive compensator for both the load balancing and supply voltage symmetrization. It was shown, moreover, that only three samples per periodT of two voltages and two currents are needed for generating the control signals for the adaptive operation of such a compensator.

Notes: Übersicht Zur Berechnung des gewichteten Oberschwingungsgehaltes (THF) der Spannungskurvenform von Vollpolsynchrogeneratoren wird ein Berechnungsalgorithmus aufgezeigt. Er beinhaltet die Leitwertschwankungen, die aus der Ständer-und aus der Polradnutzung resultieren. Die einzelnen Einflußfaktoren werden anhand von Rechesbneispielen diskurtiert. Der Vergleich mit den Meßwerten einer gefertigten Versuchsmaschine bestätigt die Richtigkeit des Berechnungsverfahrens.

Notes: Übersicht In dem vorliegenden Beitrag wird ein umrichtergespeister Asynchronmaschinenantrieb mit kapazitivem Filter vorgestellt, dessen Stromzwischenkreisumrichter in einem eingeschränkten Drehzahlbereich um die Bemessungsdrehzahl vollständig fremdgeführt arbeitet. Der Entwurf einer rotorflußorientierten Regelung der Statorstromkomponenten berücksichtigt dabei insbesondere das Betriebsverhalten des maschinengeführten Stromrichters. Dies führt letztendlich zum Einsatz eines linearen, zeitdiskreten Zustandsreglers mit zeitvarianten Reglerparametern. Meßergebnisse im maschinengeführten Arbeitsbereich eines realisierten Laborantriebs veranschaulichen die sich ergebenden günstigen Betriebsbedingungen für die Drehstromasynchronmaschine.

Notes: Übersicht Die zusätzlichen Stromwärmeverluste im Läufer ändern sich bei einem Drehzahlstellantrieb je nach Betriebsweise des Umrichters beträchtlich. Im Blockbetrieb ist der Gesamtverlust kaum vom Lastzustand (Schlupf) abhängig. Im Synchronismus sind die Verluste jedoch ungleichmäßig auf die einzelnen Läuferstränge oder Stäbe verteilt. Die Maxima und Minima der Stabverluste stehen im Synchronismus etwa im Verhältnis 10:1 zueinander. Die Verluste in dem am stärksten beaufschlagten Läuferstab liegen nicht wesentlich niedriger als im Bemessungsbetrieb. Die gesamten zusätzlichen Stromwärmeverluste wachsen bei konstanter Speisefrequenz quadratisch mit der Spannung. Im Feldschwächbereich nehmen sie in Abhängigkeit von der Speisefrequenz ungefähr nach der Funktion 1/ω1,52 ab.

Notes: Contents The paper describes a new algorithm for measuring frequency at a power system bus. The algorithm is based on the Newton-Raphson iterative method using the digitized voltage samples at a relay location. The mathematical development of the algorithm is presented and the effects of key parameters that affect the performance of the algorithm are discussed. The algorithm is encompassing the Newton-Raphson method, which is very common for load flow studies. The algorithm shows a high measurement accuracy over a wide range of frequency changes. To demonstrate the efficiency of the proposed algorithm, results of a numerical experiment are presented.

Notes: Übersicht Der stationäre Zustand eines elektrischen Energieversorgungsnetzes läßt sich durch die Mitkomponente der Torspannungen vollständig beschreiben. Sie wird bisher mit Hilfe einer aufwendigen Netzzustandsestimation berechnet. Hier werden stattdessen Methoden und Einrichtungen zur direkten synchronen Messung der Spannungsmitkomponente in den Netztoren behandelt. Die zur Netzzustandsbeschreibung wesentlichen Phasenwinkel lassen sich auf 0.1° genau messen. Dies fordert eine Zeitsynchronisation zwischen den Netzknoten mit weniger als 5μs Abweichung. Der dynamische kinetische Netzzustand wird somit detailliert beobachtbar.

Notes: Übersicht In dieser Arbeit beschäftigen wir uns mit der numerischen Berechnung des Rückstreuquerschnittes des semiinfiniten Kreiskegels. Wir behandeln sowohl den Fall der Beugung skalarer Wellen am schallweichen und schallharten Kreiskegel als auch den der Beugung elektromagnetischer Wellen am ideal leitenden Kreiskegel. Unter Zuhilfenahme des Eulerschen Summatiosverfahrens werden die über die Lösung der jeweiligen Randwertprobleme gewonnenen Multipolentwicklungen der Rückstreuquerschnitte für alle Kegelöffnungswinkel numerisch ausgewertet und mit bekannten analytischen Näherungsausdrücken für spitze und stumpfe Kegel verglichen. Wir werden u. a. zeigen, daß die physikalisch optische Näherungsmethode im Falle des Kreiskegels den richtigen Radarrückstreuquerschnitt liefert.

Notes: Übersicht Wegen zunehmender Umweltbelastungen gibt es wieder verstärkte Entwicklungsanstrengungen zugunsten elektrisch angetriebener Fahrzeuge. Der wesentliche Nachteil autonomer elektrisch angetriebener Fahrzeuge besteht nach wie vor in deren Abhängigkeit von einer kontinuierlichen elektrischen Energiequelle, die in den meisten Fällen durch eine elektrochemische Speicherbatterie bereitgestellt wird. Aufgrund physikalischer Beschränkungen bleibt deren Leistungsdichte und Kapazität jedoch weit hinter der von flüssigen Kraftstoffen zurück. Eine mögliche Alternative besteht in der Verwendung einer Bordstromversorgung, mit einem Generator der durch eine thermische Kraftmaschine angetrieben wird. In diesem Fall dient die Batterie nur als Kurzzeitspeicher, was deren Kosten, Gewicht und Preis wesentlich reduziert. Der Mittelwert der elektrischen Leistung kann direkt vom Generator zum elektrischen Fahrantrieb geführt werden. Um Gewicht und Volumen der Bordstromversorgung zu reduzieren, wird im folgenden die Verwendung eines schnellaufenden Generators, der direkt an eine Gasturbine gekoppelt werden könnte, vorgeschlagen. Der Aufsatz befaßt sich ausschließlich mit dem elektromechanischen Teil der Bordstromversorgung. Experimentelle Ergebnisse mit einem Generatorsystem im Leistungsbereich von 10 kW bei 36 000 min−1 werden vorgestellt.

Notes: Contents A new general equivalence transformation for cascades of lossless nonuniform transmission lines (NTL's) and lumped reactance two-ports (LRT's) is presented. Based on this transformation a new synthesis method for NTL's and NTL-LRT cascades is established, by means of which microwave filters and matching sections can be constructed on the basis of a rational function of the complex frequency. Thus, given specifications can practically be met arbitrarily well. In contrast to others the new method is at the same time exact and easy to handle. A synthesis example is given at the end.

Notes: Contents Static problems involving anisotropic media have long been in the interest of geoelectromagneticists. Solving problems of that kind have been, however, quite cumbersome and lengthly, involving coordinate scaling procedures with lots of indexed variables. The image method stands as an attractive alternative since no coordinates are involved and the image concept gives a quasi-physical quantity which can be handled just like ordinary physical sources. The present paper gives a simple method for deriving the image sources based on a transmissionline analogy. The problems treated are PEC (perfectly electrically conducting) and PMC (perfectly magnetically conducting) boundaries together with anisotropic impedance boundaries and interfaces of two anisotropic media with similar anisotropies.

Notes: Übersicht Zur Berechnung rotationssymmetrischer Probleme der Magnetostatik wird die Integralgleichungsmethode verwendet, die nur eine Diskretisierung des magnetisierbaren Materials erfordert. Um kurze Rechenzeiten zu gewährleisten, werden die Magnetisierung in jedem Element als konstant angenommen und die Fernfeldwirkung von Spulen sowie der magnetisierten Elemente geeignet angenähert. Die erreichbaren Genauigkeiten werden diskutiert und die erforderlichen Rechenzeiten aufgezeigt.

Notes: Übersicht Das jeweilige maximale Drehmoment einer wechselrichtergespeisten Kurzschlußläufer-Asynchronmaschine ist durch die Begrenzung von Wechselrichter-Ausgangsstrom und Ausgangsspannung bestimmt. Im Feldschwächbereich wird der Leistungsteil bestmöglich ausgenutzt, wenn der Wechselrichter stets mit der beim gewählten Pulssteuerverfahren maximal möglichen Aussteuerung betrieben wird. Das maximal erreichbare Drehmoment wird analytisch berechnet und ein einfaches Verfahren zur schnellen Regelung von Drehmoment und Gesamtflußbetrag hergeleitet. Im Feldschwächbereich sind die ohne Spannungsstellreserve erreichten Drehmoment-Anregelzeiten kleiner als die besten bisher veröffentlichten Werte.

Notes: Übersicht Die Wirksamkeit von Filtern wird meist nach ihrer Übertragungsfunktion beurteilt, also nach dem Frequenzgang im stationären Zustand. Berechnungen in Echtzeit müssen jedoch rasch ablaufen, der Einschwingvorgang der Filter sollte dem Endwert in wenigen Schritten möglichst nahe kommen. Für jeden Anwendungsfall ist ein passender Kompromiß zwischen Übertragungs- und Einschwingverhalten des Filters zu schließen. Hierzu werden Voll- und Teilperiodenfilter auch für Anregung mit aperiodischem Anteil optimiert, sowie serielle Doppelfilter und Filter mit schrittweise vergrößertem Fenster untersucht. Ein Anwendungsbeispiel ist die Impedanzberechnung beim Kurzschlußschutz der Hochspannungsnetze.

Notes: Übersicht Mittels Finite-Differenzen-Zeitschrittverfahrens werden Drehmoment und Drehzahl als Funktion der Zeit und der Rotor-Startposition für mehrere Motoren berechnet und mit Messungen verglichen. Wenn das Gesamtdrehmoment infolge eines synchronen Satteldrehmomentes negativ wird, kann ein Motor trotzdem anlaufen, je nach Einschaltzeitpunkt und Rotor-Startposition. Beim schnellen Hochlauf reduziert sich die Häufigkeit des Hängenbleibens. Das Massenträgheitsmoment spielt keine spürbare Rolle, Keilriemen oder elastische Kupplungen erhöhen die Gefahr des Hängenbleibens wesentlich. Die Eisensättigung kann sowohl eine Verkleinerung als auch Vergrößerung der synchronen Drehmomente bewirken. Bei voller Spannung nehmen diese meistens erheblich ab, beim γ/Δ-Anlauf sind sie jedoch oft noch voll vorhanden. Die Eisensättigung erzeugt zusätzlich starke Pendelmomente (mit 300 Hz im Stillstand) und bei Nutenzahlen |Z 1−Z 2|=4p neue Schleichdrehzahlen. Die stationär und ohne Eisensättigung gemessenen oder berechneten synchronen Momente stellen nur ein erstes Kriterium für die Brauchbarkeit eines Motors dar.

Notes: Übersicht Die Verbesserung des Dämpfungsverhaltens von Energieversorgungssystemen kann durch die gemeinsame Steuerung der Wirk- und der Blindleistung erreicht werden. Hierzu wird als Stellglied ein Wirkleistungsspeicher benötigt, der über Stromrichterschaltungen an das Netz gekoppelt ist. Zur Ansteuerung wird eine optimale Steuerstrategie entwickelt, welche die Zustandsvariablen des Systems nutzt. Da letztere meßtechnisch nicht alle erfaßbar sind, müssen lokale elektrische Signale gefunden werden, mit denen eine möglichst gute Pendeldämpfung durchführbar ist. Diese sind in ihrer Wirkung zu vergleichen.

Notes: Contents The vector spherical multipole analysis is applied to determine the shielding effectiveness and the scattering cross sections of a homogeneous spherical shell with arbitrary thickness and material parameters. This canonical EMC-problem is formulated as a classical three-domain-problem and then solved rigorously with respect to the continuity-conditions of the tangential field components. Numerical results are presented especially for a shell material with low conductivity. In case of a well conducting thin shell an asymptotic evaluation of the multipole solution leads exactly to the results obtained byKaden, but in addition the amplitude of the shielding effectiveness at the resonance frequencies can be predicted.

Notes: Übersicht In diesem Beitrag werden die Feldverteilungen in axial unendlich ausgedehnten Rechteckleitern vorgestellt, wie sie sich bei linienförmiger Einspeisung eingeprägten Gleich- und Wechselstroms ergeben. Die Rückleiter sind wie die Stromeinspeisung und -ableitung in axialer Richtung ebenfalls als unendlich ausgedehnt vorausgesetzt. Die physikalischen Lösungen dieser zweidimensionalen Randwertprobleme, im folgenden als punktförmig erregte Flächenleiter bezeichnet, erhält man über die allgemeinen Lösungen der Laplace- bzw. Helmholtz-Gleichung durch Vorgabe der problemspezifischen Randwerte. Dabei erzwingt die komplexe Struktur der Lösungen eine numerische Auswertung, die geforderte Anschaulichkeit liefert deren graphische Darstellung.

Notes: Contents This paper presents a technique for realizing PAM capability in the case of a resonant dc link three phase inverter equipped with GTO thyristors. A new quasi resonant dc link circuit together with a sinusoidal PAM for an inverter fed drive are proposed in order to reduce the power losses in the machine and in the inverter. An improved dynamic behavior is also discussed in the paper. The harmonic analysis of the output voltage is presented for different operation modes.

Notes: Contents Following the approach of Neumann and Lindell [1] we derive an image line source that produces in a homogeneous medium the same electric field as a point charge inside a layered dielectric sphere. The image charge density function for the sphere with two interfaces is solved analytically, and approximations are derived in the case of a thin layer and a low-contrast layer. An image expression for the thin-layered sphere with three interfaces is developed. We suggest that point charge approximations of the image charge may be used to speed up computations of the electric potential on the scalp due to sources in the brain.

Notes: Übersicht Ein neues Raumzeigersteuerschema für dreistufige am Dreiphasennetz arbeitende Pulsumrichter wird vorgestellt. Es basiert auf einem Steuerverfahren für dreiphasige, zweistufige Motorwechselrichter. Die Erweiterung auf dreistufige Pulsumrichter und die dazugehörige Steuertabelle werden gezeigt. Dieses Verfahren erreicht eine symmetrische Spannungsaufteilung auf der Gleichspannungsseite auch bei unsymmetrischer Belastung des Zwischenkreises. Messungen an einem Versuchaaufbau werden gezeigt.

Notes: Übersicht Es werden Stäbe mit nicht völliger Transposition und Stäbe mit massiven und hohlen Leitern (welche verschiedene spezifische Leitfähigkeiten haben können) sowie Spulen mit mehreren Einzelleitern in der Windung untersucht. Es wird auch die Verteilung der Verluste in einzelnen Stäben dargestellt.

Notes: Übersicht In der Automatisierungstechnik ist es üblich, das Verhalten dynamischer Systeme durch Strukturbilder darzustellen. Diese Beschreibungsart hat sich jedoch bei Stromrichterschaltungen bislang nicht durchsetzen können. Am Beispiel selbstgeführter U-Pulswechselrichter wird gezeigt, daß sich auch Schaltungen der Leistungselektronik durch aussagefähige Strukturbilder beschreiben lassen. Hierzu ist eine Arithmetisierung der logischen Systemgleichungen notwendig. Man erhält dann zur Nachbildung der Schaltvorgänge nichtlineare Netzwerke, die aus Multiplizierern und Addierern (MA-Netze) bestehen. Dadurch wird das dynamische Systemverhalten übersichtlich beschreibbar.

Notes: Contents An adaptive control procedure using state feedback is applied to a generator in a multimachine power system for the purpose of placing in a desired manner the eigenvalues of the linearized model of the controlled synchronous generator. The simulation results of the study show that the adaptive regulator performs satisfactorily in a multimachine environment, when operating in conjunction with the conventional regulators of the other system generators.

Notes: Contents The wave equation for fast moving charges approaching a screen is solved. The solution provides insight into the dynamics of charge imaging and is also of practical interest in the analysis of fast moving electrons in modern electro-optic devices-e.g. in color television picture tubes

Notes: Übersicht Zur Ermittlung der inneren elektromagnetischen Kräfte wird das Luftspaltfeld analysiert. Bei periodischer und phasensymmetrischer Speisung lassen sich die Radial- und Tangentialkraftwellen analytisch aus den Drehfeldern berechnen, während man zur Berücksichtigung der durch die asynchrone Taktung bedingten Abweichungen der Ströme auf eine numerische Berechnung anhand der Wechselfelder angewiesen ist. Das Berechnungsverfahren wird mit experimentellen Untersuchungen der Geräusche an einem 1,5-MW-Motor überprüft. Durch eine Abstimmung der Strang-, Nuten- und Polpaarzahlen können die Pendelmomente eliminiert und bei Beachtung des schwingungstechnischen Verhaltens auch die Geräusche minimiert werden.

Notes: Contents The frequency inverter current spectrum generates a complex magnetic field in the airgap producing attracting forces having a wide spectrum and leads to audible noise. A mathematical model is presented, predicting vibrations of a permanent magnet machine, based on the modal analysis technique including mechanical damping. Modal forces produced by the magnetic field, are related to the supply currents using a finite element calculation. Experimental results are presented.

Notes: Übersicht Bei der Netzsimulation konkurrieren Zustandsnachbildung und Differenzenleitwertverfahren. Analog zu den Differenzenleitwertverfahren DLV, SDLV1, SDLV2 und SDLV3 werden im Zustandsraum die Verfahren ZDGL, ZDGL1, ZDGL2 und ZDGL3 abgeleitet. Am Beispiel einer Synchronmaschine wird gezeigt, daß die mathematisch am weitesten entwickelten Verfahren SDLV3 und ZDGL3 den anderen Verfahren deutlich überlegen sind. ZDGL3 erfordert aber eine wesentlich höhere Rechenzeit und kann bei extrem hoher Schrittweite instabil werden.

Notes: Contents An increase in the power handling capability of forced commutated inverters stipulates a higher operating voltage. A direct approach is to connect GTOs in series. Since the most common snubber circuits for GTO inverters are not suitable for arrangements in series, this paper presents a new snubber topology especially suited for such circuits and offering design advantages at high power levels. Following a description of available snubber techniques and their problems, the new snubber circuit is presented and analyzed theoretically as well as by using computer simulation.

Notes: Übersicht Aufgrund des zunehmenden Einsatzes von glasfaserverstärkten Kunststoffen (GFK) in der Freiluftisoliertechnik ist das Verhalten der Werkstoffe unter Feuchtigkeitseinfluß von großem Interesse. In diesem Aufsatz wird der Transportmechanismus von Wasser in GFK beschrieben und mathematisch behandelt. Der Einfluß der aufgenommenen Feuchtigkeit auf die dielektrischen Kenngrößen der Werkstoffe wird untersucht und ein Verfahren zur Berechnung der Dielektrizitätszahl anhand der gemessenen Wasseraufnahmekurven entwickelt. Der Einfluß der Werkstoffzusammensetzung wird ebenfalls diskutiert.

Notes: Contents In this paper a frequency domain analysis of buried dielectric cylindrical targets is given. An integral equation, which is solved by Galerkin's method along with plane wave basis functions, is used to obtain the scattered field. Numerical results in the frequency as well as the time domain-via FFT-for various underground bodies in various depths are given. The results show the applicability of the method in the target identification process.

Notes: Übersicht Trotz moderner Schätzverfahren ist die Parameterschätzung nichtlinearer und zeitvarianter Prozesse bei gestörten Meßsignalen schwierig. Dies ist auch der Fall bei der Frequenzmessung im elektrischen Energieversorgungsnetz. Um unter diesen Bedingungen gute Resultate zu erhalten, wird ein rekursives Parameterschätzverfahren aus dem ursprünglichen nichtrekursiven Newton-Raphson-Verfahren abgeleitet. Darüberhinaus wird in diesem neuen Verfahren eine Anpassung des Gedächtnisfaktors vorgeschlagen, die sowohl die Konvergenzeigenschaften als auch die Genauigkeit verbessert. Durch Simulationsrechnungen werden Erfahrungen bei der Anwendung des neuen rekursiven Parameterschätzverfahrens für die Frequenzmessung im Netzschutz gewonnen. Bei zahlreichen Eingangssignalen konnte das verbesserte Verfahren mit Erfolg eingesetzt werden, während das ursprüngliche versagte.

Notes: Übersicht Die Reflexions- und Transmissionseigenschaften einer ebenen, verlustbehafteten, dünnen Schicht, die sich zwischen zwei homogenen, verlustfreinen Halbräumen befindet, wird analytisch im Zeitbereich untersucht. Die unter beliebigem Einfallswinkel auf die Schicht auftreffende homogene, ebene TEM-Welle darf deshalb eine beliebig vorgebbare Wellenform besitzen. Es wird gezeigt, daß für dünne Schichten Reflexions- und Durchgangsfaktoren angegeben werden können. Aus den Reflexionsfaktoren werden Oberflächenimpedanzen zum Einsatz in FDTD-Algorithmen entwickelt. Anschließend werden die Resultate auf den Fall, daß beide Halbräume unterschiedliche Materialeigenschaften besitzen, erweitert und in numerischen Simulationen angewendet.

Notes: Contents The vector spherical multipole technique is applied to calculate the electromagnetic field within a spherical domain bounded by a perfectly conducting shell and interiorly covered by an arbitrary number of absorbing layers. The structure serves as a cononical model for an anechoic chamber. By analogy to the definition of the shielding effectiveness for a closed spherical shield a normalized chamber effectiveness is introduced, which characterizes the empty chamber performance. To make available an appropriate test source for the numerical evaluation in Part II, the multipole amplitudes of an arbitrarily polarized and located electromagnetic elementary source (Hertz dipole and Fitzgerald dipole; Huygens source) are deduced.

Notes: Contents This paper presents a new method, called Indirect Two-Speed Method (ITSM), for obtaining electrical and shaft torques in an induction motor drive by means of measuring the speeds of both lumped-inertia elements assigned to a second order model. The measuring is realized by using high-resolution digital tachometers (represented by incremental encoders), two frequency measurement systems based on the Double-Buffered Method, digitalfiltering of the raw speed data and numerical differentiation of the filtered speed data.

Notes: Content For electric machines with their permanent magnet assemblies stabilized in air, a certain amount of irreversible loss of magnetization will occur in permanent magnets when magnet material with knee points in the demagnetization curve is used. To estimate quantitatively the irreversible demagnetization loss in permanent magnet machines, the maximum loss of magnetization, the remanent flux loss and the demagnetization area are defined as their three figures of merits. A series of design curves for predicting the irreversible demagnetization loss for arc-shaped permanent magnets stabilized in air is presented in the paper. The effects of material characteristics, magnet geometry and its magnetic orientation on these merits are also discussed. Design curves are obtained from field computation results by using the multi-hysteresis-loop PM model recently proposed by the first author. These design curves are useful for permanent magnet machine designers.

Notes: Contents This paper presents a method to construct a general purpose time domain simulator for power electronic drives of electrical machines. The electrical machine is modelled by the two-dimensional finite element method. An efficient formulation for handling strongly nonlinear power electronic components is presented. the power electronic circuit and the connections of windings of the machine may have an arbitrary topology which is given by a net-list file (SPICE-type input file). The method is based on the handling of the field and the circuit models as a single system of equations. The applicability of the mehod is investigated with three example cases. Two of the example simulations are verified by measurements.

Notes: Übersicht Es wird ein Berechnungsverfahren zur Bestimmung der Meßempfindlichkeit von Exzentrizitätsüberwachungseinrichtungen mittels Meßspulen vorgestellt. Dieses berücksichtigt die Bedämpfung der Exzentrizitätsfelder durch einen Dämpferkäfig und durch parallel geschaltete Wicklungszweige. Der Berechnungsalgorithmus wird am Beispiel einer 30 MVA Vollpol-Synchronmaschine überprüft. Hinsichtlich der Überwachung der statischen Exzentrizität zeigt sich eine gute Übereinstimmung zwischen Messung und Rechnung.

Notes: Übersicht Die Arbeit beschreibt das Aufmagnetisieren einer Asynchronmaschine, deren Drehzahl und Magnetisierungszustand unbekannt ist. Grundgedanke dabei ist, durch kurzzeitiges Schalten des Umrichters in den Zustand “Kurzschluß” und Auswertung des Stromverlaufs auf den momentanen Magnetisierungszustand und die aktuelle Drehzahl zu schließen. Durch Aufbringen einer flußparallelen Stromkomponente wird dann der Fluß aufgebaut. Durch abwechselnde Kurzschlußauswertung und Flußaufbau gelingt es, die Maschine sicher aufzumagnetisieren, sofern die Drehzahl ein gewisses Minimum übersteigt. Für sehr kleine Drehzahlen wird eine alternative Methode zum Flußaufbau vorgestellt, die ebenfalls auf der Auswertung des Stromverlaufs zufolge eines definierten Spannungstestsignals beruht.

Notes: Content This paper is dealing with the power density versus electric field characteristic of microwave-excited discharges on the example of typical CO2 laser gas discharges. The fundamentals of the method are a simple electric equivalent circuit for the excitation structure and the assumption of a fixed reduced electric field intensity within the plasma. This operating field is enforced by the plasma under stationary conditions and can be calculated using an electron balance under consideration of the non-Maxwellian electron energy distribution function. The calculations turn out that c.w. excitation with microwaves is involved with considerable plasma power densities. In the case of the CO2 laser this requires special discharge channel designs for effective gas cooling. Besides a discussion of the plasma characteristic, measurements taken from a microwave applicator are presented and compared to the calculations.

Notes: Contents In this paper analytic relations are developed for the calculation of the shell losses in three phase arrangements with nonmagnetic enclosure, for the steady state and the short circuit conditions. The phase conductors are taken as filamentary. The losses result as Fourier series ofn terms. Parametric investigations showed that a restriction on two terms gives results of great accuracy for the steady state losses. The analytic relations for the short circuit losses calculation are cumbersome. These losses can be calculated from the steady state losses, that are given from simpler relations, by an appropriate coefficient given here from the relevant curves.

Notes: Abstract Encapsulated micro mechanical sensors were fabricated using glass-silicon anodic bonding and an electrical feedthrough structure. Two parallel plates which can be used not only for capacitive sensors but also electrostatic actuators are adopted for integrated sensors as capacitive pressure sensors, accelerometers and resonating sensors. Micromachining technologies were developed for these packaged micro sensors. These include silicon etching technologies as laser assisted etching, deep RIE and in-process thickness monitoring during wet etching. Anodic bonding technologies which enable to incorporate a circuit inside the package and to keep a sealed cavity at a high vacuum are also developed.

Notes: Abstract The high precision accelerometer consists of 5 silicon wafers and packages by silicon fusion bonding. The sensor has a capacitance measuring principle and works in an open loop or closed loop operation mode. The etching process for the realization of thin beams and seismic mass, the silicon fusion bonding and the metallization process are described.

Notes: Abstract The Π theorem of Dimensional Analysis, usually applied to the inference of physical laws, is for the first time applied to the derivation of interpolation curves of numerical data, leading to a simplified dependence on a reduced number of arguments Π, dimensionless combination of variables. In particular, Monte Carlo modelling of electron beam lithography is considered and the backscattering coefficient η addressed, in case of a general substrate layer, in the elastic regime and in the energy range 5 to 100 keV. The many variables involved (electron energy, substrate physical constants and thickness) are demonstrated to ultimately enter in determining η through asingle dimensionless parameter Π0. Thus, a scaling law is determined, an important guide in microsystem designing, indicating, if any part of the configuration is modified, how the other parameters should change (or “scale”) without affecting the result. Finally, a simple law η=83 Π0 is shown to account for all variations of the parameters over all substrates of the periodic table.

Notes: Abstract Reliability and functionality of microsystems, i.e. of small scale integrated electronic, mechanical and optical components, largely depend on their mechanical and thermal constitution. Thermo-mechanical aspects of component and system reliability become more and more important with growing miniaturization as the local physical parameters and field quantities show an increase in sensitivity due to inhomogeneities in local stresses, strains and temperature fields. Since there is usually a lack of information about the local material parameters, a pure field simulation cannot, as a rule, solve the problem. The state of the art of microsystem design more and more requires direct “coupling” between simulation tools (including e.g. FE modelling) and advanced physical experiments. The authors have combined various laser technique, scanning microscopy, and X-ray diffraction with numerical field simulation. The investigations have been directed towards current problems of mechanical and thermal reliability in electronic packaging, crack and fracture behaviour within the interconnected regions and life time estimation. Special problems of mechanical behaviour in solder joints are discussed taking into account local plasticity as well as creep effects.

Notes: Abstract Modular fabrication of polysilicon surface-micromachined structures after completion of a conventional CMOS electronic process is described. Key process steps include tungsten metallization with contact diffusion barriers, LPCVD oxide and nitride passivation of the CMOS, rapid thermal processing for stress-relief annealing of the structural polysilicon film, implementation of a sacrificial spin-on-glass planarization, and the final microstructure release in hydrofluoric acid. Modularity of the process enables independent modification of either the CMOS or the microstructure process sequences. This technology is used in the fabrication of various types of sensors and actuators.

Notes: Abstract Thermal bubble powered micro mechanical actuators have been successfully demonstrated in working liquids. Micro mechanical plates which function as the mechanical actuators are 70×60×2 μm3 in size. They have been fabricated by surface-micromachining technology and suspended 2 μm above the substrate by the supports of cantilever beams. Micro thermal bubbles which are generated by heavily phosphorus doped polysilicon line resistive heaters have been used to lift the mechanical plates in a controllable manner. The typical current required to generate a single, spherical thermal bubble as the actuation source on top of the micro line resistors (60×2×0.3 μm3 in size) is 8.4 mA (80 m Watt) in FC 43 liquid (an inert, dielectrical fluid available from the 3M company). The thermal bubbles have been demonstrated to actuate the mechanical plate perpendicularly to the substrate with a maximum elevation distance of 140 μm and a maximum actuation force of 2 μN. This new actuation mechanism is expected to find applications for micro fluidic devices.

Notes: Looks at the development of a new ultrasonic meter for the gas supplyindustry and explaining the transit time measurement principle on which itworks and the performance characteristics of the new meter. Concludes thatthe ultrasound gas meter could also have medical applications includinganaesthetics and hospital ward monitoring. There have been limited productionruns of the new gas meter and extensive trials are taking place in severalcountries.

Notes: An overview of radio telemetry, concentrating on low power,short-range systems which can be operated without equipment licences.Describes transmission mechanisms, aerials and the two main types of analoguemodulation: amplitude modulation [AM] and frequency modulation [FM].Outlines the developments in radio data links and modulation schemes, thebenefits of networks and the various methods of encoding data. Concludes thatone of the biggest problems in radio telemetry is the different regulationsacross Europe making it virtually impossible to design a transmitter that isacceptable in more than one country. However, in Europe the situation isslowly changing, with new common standards for defining, evaluating andtesting equipment coming into effect.

Notes: Describes how radio telemetry can interface with process control systemssuch as supervisory control and data acquisition [SCADA] and distributedcontrol systems [DCS] greatly increasing their power and efficiency. Outlinesthe basis of radio telemetry, the behaviour of electromagnetic waves,frequency and wavelengths. Uses the water industry as an example of the useof a large scale and sophisticated SCADA system to provide date collectionand control links over a large area. Concludes that the versatility of radiotelemetry coupled with its cost-effectiveness means that thistechnology can help to expand and improve communications in an increasingnumber of industries.

Notes: Examines the "Supertag" automatic identification system which is aninnovative electronic replacement for barcodes and which can also function asan anti shoplifting device. Each Supertag is a single integrated circuit chipplus a printed flat aerial. Using radio links, Supertag readers are capableof multiple identification and counting at electronic speed. Outlines thetechnical developments which brought about "electronic counting" and comparesthem with conventional RFID systems. Describes the potential used forSupertag including its ability to "read" the entire contents of a supermarkettrolley in a second, making it very attractive for use in the retailindustry.

Notes: Describes the basic optical concepts of infrared gas detection inrelation to industrial applications and considers the electro opticcomponents at the heart of the analyzers, the infrared detectors themselves.Discusses the choice of detectors for a given application and looks at thepros and cons of thermal detectors and quantum detectors. Notes the possibleneed to cool quantum detectors to improve their signal to noise andresponsivity characteristics. Concludes with the possibility for customconfigurations and lists the various application of infrared gas detectionincluding uses in the transport industry, petrochemical industry andhospitals.

Notes: Analyses the effects of temperature on the behaviour of ultrasonicsensors applied to object recognition. Describes the measurement systememployed, the environmental considerations of ultrasonic sensors and looks atthe most commonly used parameters to analyse the echo form in the recognitionprocess. Evaluates the performance of the parametric model of the ultrasonicecho signal with a comparative study of different ultrasonictransducers.

Notes: Describes a biometric security system, the EyeDentify retinal scanner,which works by mapping the vascular pattern on the retinal portion of theeyeball, using a specially designed camera. Outlines the three modes of theretinal scanner: enrolment, verification and recognition and theuniqueness and stability of retinal identification. Concludes that owing tothe unmatched accuracy and ability to run in a time "recognition" mode, retinal scanners are utilized in the world's most secure areas.

Notes: The journal features concise, up-to-date reports on significant new findings in applied physics. Emphasizing rapid dissemination for key data and new physical insights, Physics of Plasmas offers prompt publication of new experimental and theoretical papers bearing on applications of physics phenomena to all branches of science, engineering, and modern technology. The journal emphasizes coverage of significant new topics, such as in recent years, high-Tc superconductors, diamond films, porous silicon, and fullerenes. It prints papers which report results of research in nuclear physics and related fields such as nuclear astrophysics.

Notes: A simple and sensitive method for detecting small forces applied to an optically trapped microsphere utilizes the transmitted beam of the trapping laser to monitor microsphere deflections within the potential well of the trap. The rms dynamic displacement detection sensitivity measured in the frequency range from 1 Hz to 10 kHz is ∼1 nm in the radial direction and ∼10 nm along the z (optic) axis. Radiation trapping force constants were calibrated against viscous drag on microspheres in the range between the Rayleigh (r〈0.2λ) and Mie (r(very-much-greater-than)λ) size regimes. For a 1-μm-diam polystyrene sphere trapped with a 60 mW beam the rms spontaneous thermal motion limits the force sensitivity to better than 10−12 N and lateral spatial resolution to ∼10 nm in a frequency range from 1 Hz to the viscous rolloff frequency ∼1 kHz. The measured maximum trapping efficiencies are compared with the theoretical predictions of the ray-optics approximation.

Notes: An optical spectrometer for the study of low level optical absorption and reflection of spread monolayers at the air-water interface is described. This spectrometer is suitable for measurements at wavelengths from ∼350 to 800 nm and has a precision of ∼2×10−5 in terms of effective optical density. It employs a dual beam design utilizing fiber optic bundles to guide light and a multichannel photodiode array detection system. Instrumental control and data gathering are designed within Labwindows software. Representative spectral absorption data from chlorophyll a degradation kinetics are presented by way of illustration. Comparison of chlorophyll a reflection and absorption is also given.

Notes: A high-precision, computer-controlled monochromator of modest cost is described. The folded sine bar is used for the grating drive that provides high linearity even for large scanning angles. With a 200 steps/turn stepper motor and 600 grooves/mm grating, the minimum step size in first order is 0.05 nm, which can be further reduced. Over the 300–750 nm range, a bandpass better than 0.1 nm and a reproducibility of ±0.05 nm can be achieved. The stray light rejection of 8.9×10−7 at 5.5 nm from the laser line is remarkable for this single grating instrument. Its performance promises to be an important tool for most forms of laser spectroscopy.

Notes: A new, low cost, vibrating reed mechanical spectrometer has been developed. The setup consists of a pulse train generation system for capacitive excitation of the specimen in one of its flexural vibration modes and of a capacitive current measuring and amplification circuit for detection of the specimen oscillation. The used detection method is convenient for low damping levels (internal friction, Q−1≤0.02) and low vibration amplitudes (≤0.1 μm) only. The resonance frequency and the mechanical energy dissipation are derived by numerical analysis of the measured freely decaying vibrations. In terms of experimental performance several such analysis methods (Hilbert transformation method, zero-transition method, nonlinear fitting) are evaluated. The system's performance is illustrated with some informative examples.

Notes: This article describes the construction and operation of a source of 2–5 keV argon atoms for use in the strong (1–7 T) B-field environment of a photoelectron spectromicroscope. The velocity spread of the atom beam has been determined from the time of flight. Atom-induced secondary-electron yield measurements on selected areas of various metallic elemental samples are described and the results show that yields differ by up to a factor of 4×103 between elements and trend towards lower yields with increasing atomic number. A number of ultraviolet photoelectron spectra of the fast-atom sputter-cleaned sample surfaces are also presented. These spectra are angle-integrated over the full 2π of electron-emission angles.

Notes: A scanning tunneling microscope (STM) has been developed, dedicated for use on artificially fabricated nanostructures at low temperatures. With this STM mesoscopic phenomena can be studied, combining the unique possibilities of scanning tunneling microscopy and artificially fabricated nanostructures for investigating the physics in this regime. The STM is vibration insensitive, has reliable coarse approach mechanisms in three dimensions, and operates at low temperatures. In order to be able to position the tip above the structure of interest, also a searching strategy has been developed. In this article we describe design and operation of the STM and demonstrate searching.

Notes: Geometrical distortions of scanning tunneling or atomic force microscope pictures can be caused by delayed response of the piezo-ceramics and errors of the nonlinear feedback system. The images are adversely affected mostly at the boundaries where the tip motion is reversed and also at surface steps. Assuming logarithmic corrections for the time dependence of the piezo response and for the feedback nonlinearity, it is shown how these errors can be eliminated. The procedure is applied to three test samples: well-ordered clean single-crystal gold and copper surfaces, for which the correction parameters are determined as a function of temperature, scan velocity, and the place where the tips move into the scanned area. Gathering this information from various test samples, a data base can be built up that can be used to correct other samples recorded under the same conditions.

Notes: To image the orientational order in a broad class of biological and manufactured materials, a new microscope has been developed that integrates laser scanning microscopy with polarization modulation polarimetry. Polarimetry allows quantitative characterization of the molecular orientation and the degree of order through characterization of optical anisotropy. Combined with laser scanning microscopy, it is used here to image the anisotropy with high spatial resolution, sensitivity, and speed. The design of the microscope is presented; and the vast improvement in sensitivity achieved using PM-LSM over conventional polarization microscopy is illustrated by imaging the linear dichroism of ultrathin Langmuir–Blodgett polymer films. PM-LSM allows imaging of the magnitude and orientation of linear dichroism in films as thin as three molecular layers (∼66 A(ring)) at high resolution by rastering a diffraction limited spot of laser light across the sample. The rate of image acquisition is over 2000 pixels/s, two to three orders of magnitude faster than the previous methods of imaging optical anisotropy.

Notes: A microscanning electron microscope (SEM) column has been constructed as an attachment of an ultrahigh-vacuum chamber with a 70 mm diam flange to observe microstructures on a solid surface. The micro-SEM column is 26 mm diam and 140 mm long and operated in an energy range from 100 eV to 3 keV. It consists of a thermal-field-emission (TFE) gun and two magnetic lenses. The excitation of the objective lens for 3 kV electrons is 250 A T at a working distance of 10 mm. The saturated temperature of the objective lens at the excitation of 250 A T is approximately 50 °C and the vacuum of the chamber is 2×10−10 Torr. The electron probe is adjustable against a specimen position from the outside of the vacuum by movement of the SEM column with screws. The spot size of the electron probe is 100 A(ring) at 3 kV and 3000 A(ring) at 300 eV in conditions of a working distance of 10 mm and a probe current of 3×10−11 A.

Notes: An atomic force/scanning tunneling (AFM/STM) microscope intended for operation inside a scanning electron microscope (SEM) is described. This AFM/STM/SEM system enables us to image a sample conventionally by SEM as well as to investigate the local surface topography by AFM or STM. This device incorporates a new method for monitoring AFM cantilever deflection that utilizes the focused electron beam of the SEM.

Notes: We present a new method for measuring time-resolved photoluminescence on a time scale of microseconds and milliseconds using correlational analysis, and we demonstrate it to work on porous silicon and GaP:Fe. We modulate the pumping laser with a pseudorandom binary sequence which yields correlational properties similar to white noise. The photoluminescence decay is computed via cross correlation of the detector signal with the pumping sequence. The presented method is highly sensitive, simple in application, and inexpensive.

Notes: A new characterization method of materials processed by ion beams or laser beams using a two-color interferometer with two frequency-doubling optical crystals is described, based on the dispersion property of the materials. Resolution of measurement is improved to an optical phase of 1° (subnanometers) by use of a heterodyne technique with acousto-optic modulators.

Notes: A commercially available flat flame burner with a sintered porous bronze disk was used to stabilize premixed H2/air flames at atmospheric pressure. Temperatures for various stoichiometries, flow rates, and heights above the burner disk have been measured by coherent anti-Stokes Raman scattering with an accuracy of ≈2.5%. The corresponding exhaust gas compositions have been derived from equilibrium calculations. This burner together with the data presented in this article can be used for the verification or calibration of a variety of measuring techniques in combustion research.

Notes: An improved model of the plasma column erosion is proposed for the understanding of the resistivity dependence of the plasma delay in a silicon surface barrier detector (SSBD). The resistivity of a SSBD has influence in the electric field strength in a depletion layer with the presence of a dielectric plasma column. The plasma delay for two SSBD's with different resistivities was measured with 61 MeV 16O ions, and the results are clearly reproduced by this model.

Notes: We describe here several types of mass spectrometry in which the mass selectivity is combined with a highly selective laser ionization method to achieve both high sensitivity and very high selectivity. These methods combine the most sensitive and highly selective laser ionization methods with mass selectivity in order to improve on both the sensitivity and the Z and A selectivity previously achievable in detecting atomic species. Applications of these methods include the dating of geophysical specimens, the on line analysis of rare short-lived isotopes produced in high-energy collisions, the detection of low levels of heavy metals or radioactive isotopes in biological samples, the detection of impurities in ultrapure materials, and a host of other applications. Because some versions of this method offer sensitivity to a hundred atoms of a particular isotope of an element in a macroscopic sample, there are new possibilities for fundamental studies of rare events. Several types of facilities for elemental and isotopic analysis will be described.

Notes: The performance of a simple wavemeter for measuring changes in wavelength of a pulsed dye laser is described. Details of optics and electronic circuitary used, along with the algorithm for wavelength measurement, are given. Using this instrument wavelength changes of a dye laser could be measured, as well as introduced through a user interface, with an accuracy of 1 ppm.

Notes: Optical interference fringe measurements of the thickness of weakly absorbing media can be rapid, accurate, and nondestructive. When the refractive index n of the sample is known, it will give us the layer thickness d. If, however, n is unknown, at least two independent spectrophotometric measurements are needed to obtain both n and d. A statistically based scheme is proposed to analyze the interference pattern in order to determine the refractive index and the thickness of the sample. The absolute interference order is also determined with the proposed technique. The major approximation inherent in the method is that the layer must be weakly absorbing and nondispersive over the wavelength region of interest. The method is applied to determine the optical constants of a uniaxial medium with the optical axis parallel to the faces.

Notes: A small UHV chamber that fits in the sample compartment of a commercial Fourier transform infrared spectrometer (IBM-98, Brucker) has been designed and constructed to acquire reflection/absorption spectra of species adsorbed and/or condensed on metal films vapor deposited in situ on the surface of a quartz-crystal microbalance (QCM). The QCM is mounted on a variable-temperature Au-plated Cu block, which houses a second (reference) QCM, attached in turn to a liquid-He cold finger. The unique capabilities of this apparatus make it possible to correlate quantitatively various spectral characteristics, including peak widths and intensities, with the absolute mass of adsorbed and/or condensed material per unit area m, or coverage, over a wide range of m and temperatures. Results obtained using tetrahydrofuran (THF) condensed on freshly vapor deposited gold films have shown that the sensitivity of the instrument is sufficient to detect mTHF on the order of a single monolayer. Plots of the intensity of the most prominent THF peak at 1064 cm−1 as a function of mTHF were found to deviate significantly from linearity in the range 0.1〈mTHF〈2.8 μg/cm2. In addition, the relative intensities of the most prominent THF peaks for even the largest mTHF examined differed markedly from those of bulk-like THF, an effect that can be attributed to a preferential orientation of THF microcrystals with respect to the underlying substrate. In the case of coverages on the order of one monolayer, such spectral behavior may arise from specific adsorbate/substrate interactions, which can cause a lowering in the molecular symmetry and/or distortions in the structure of the adsorbate. Evidence in support of a Au-induced THF activation was obtained from independent temperature programmed desorption (TPD) measurements involving perdeuterated THF (TDF) performed in a separate UHV system. In particular, for exposures of about 1.5 L, the TPD spectra for the largest m/e features, i.e., 80, 48, and 30, revealed the presence of a peak centered at a higher temperature (∼180 K) than that found for much larger exposures (120 K).

Notes: A scanning-tunneling microscope (STM) of the scanning-sample type with transducers for the measurement of the position in all three axes has been developed. Motions in the X-, Y-, and Z-axis are straight and rectangular to a high degree and the capacitance transducers are calibrated in situ by plane mirror laser-interferometry. With these qualities as part of the design, the Abbe error may be minimized. X-Y-capacitance transducers and X-Y-piezo actuators are part of analog servo loops, thus providing positioning in the X-Y-plane to a desired coordinate. The STM is mainly built from commercially available parts.

Notes: A UHV-compatible, high-temperature scanning tunneling microscope (STM) with a sample stage incorporating a Si wafer as a resistive heater is described. The design allows for rapid interchange of scanning tubes so that the maximum scan size can be varied. The thermal stability of the microscope is excellent, allowing real-time studies of faceting and grain growth of metal surfaces at temperatures up to 400 °C with a long term drift of ∼0.05 A(ring)/s.

Notes: A special theoretical concept involving the harmonic magnetic-field measurement and analysis method using a fixed angle Hall probe was developed at the Synchrotron Radiation Research Center (SRRC) for measuring as well as analyzing the triple bending achromat magnets of the storage ring. The method can be used to simulate the harmonic magnetic-field calculation of the two-dimensional (2D) "magnet'' program. This method has a quite simple mechanism. The Hall plate was fixed at a 0° angle with respect to the horizontal plane of magnet to measure only the vertical field. Additionally, the 2D nonlinear least-square fitting was used to fit the mapping data so as to find the normal and skew multipole field strength. If necessary, the angle of Hall probe could be rotated 90° precisely for measuring the horizontal field. Consequently, the skew dipole field could be obtained. A real-time Hall-probe automatic magnetic-field measurement system was also developed for fulfilling the concept of the harmonic field measurement. Some special mapping trajectories for different kinds of magnets were discussed to match this special theoretical concept with the analysis methodology. This was done so as to obtain the reliable and accurate harmonic field strength. The accuracy and precision of the harmonic field strength measurement and analysis of this method being better than ±0.01% was confirmed by experimental results.

Notes: An experimental technique for the accurate measurement of the conductivity in liquid mixtures at a constant temperture is described. The equipment is fully computerized, the conductimeter and the burette being controlled through the IEEE-488 and the RS-232C interfaces, respectively. The automatic procedure provides the measurement of the experimental parameters for each concentration as a statistical average of 2400 data. It permits an increase in the accuracy of the results, optimizing the time and avoiding human mistakes along the set of measurements.

Notes: A flow reactor system for catalytic reaction studies is described. The system is equipped with a movable gas sampling device and on-line mass spectrometry (MS), allowing time- and space-resolved measurements of gas composition and temperature. Results from H2 oxidation on Pt are used to illustrate the system performance. Spatial variations of H2, O2, and H2O concentrations can be measured, e.g., during mass transport limited conditions. Temporal variations in H2, O2, and H2O during chemical oscillations are well resolved close to the catalyst, but successively smeared away at increasing distance. The special design of the gas sampling probe allows quantible MS measurement even of H2O and other "difficult'' gases, and of gas temperature variations.

Notes: An NO-selective electrode was developed as an easily applicable tool for a real-time nitric oxide (NO) measurement. The working electrode (0.2 mm diam) was made from Pt/Ir alloy coated with a three-layered membrane. The counterelectrode was made from a carbon fiber. When a stable NO donor, S-nitroso-N-acetyl-dl-penicillamine, was applied, the electrode current increased in a dose-dependent fashion. The current and calculated NO concentration showed a linear relationship in the range from 0.2 nM (S/N=1) to 1 μM of NO. The response of the electrode was 1.14±0.09 s. The effects of temperature, pH, and chemicals other than NO on the electrode current were also evaluated. Electrodes which were placed in the luminal side of rat aortic rings exhibited 30 pA of current due to NO generation induced by the addition of 10−6 M of acetylcholine. The current was eliminated in the presence of 50 μM NG-monomethyl-L-arginine, an inhibitor of NO synthase. Thus, this NO-selective electrode is applicable to real-time NO assay in biological systems.

Notes: Fluidized bed combustion systems have been widely applied in the combustion of solid fossil fuels, particularly by the power generation industry. Recently, attention has shifted from the conventional bubbling fluidized bed (BFB) to circulating fluidized bed (CFB) combustion systems. Inherent advantages of CFB combustion such as uniform temperatures, excellent mixing, high combustion efficiencies, and greater fuel flexibility have generated interest in the feasibility of CFB combustion systems applied to the thermal remediation of contaminated soils and sludges. Because it is often difficult to monitor and analyze the combustion phenomena that occurs within a full scale fluidized bed system, the need exists for smaller scale research facilities which permit detailed measurements of temperature, pressure, and chemical specie profiles. This article describes the design, construction, and operation of a pilot-scale fluidized bed facility developed to investigate the thermal remediation characteristics of contaminated soils and sludges. The refractory-lined reactor measures 8 m in height and has an external diameter of 0.6 m. The facility can be operated as a BFB or CFB using a variety of solid fuels including low calorific or high moisture content materials supplemented by natural gas introduced into the fluidized bed through auxiliary fuel injectors. Maximum firing rate of the fluidized bed is approximately 300 kW. Under normal operating conditions, internal wall temperatures are maintained between 1150 and 1350 K over superficial velocities ranging from 0.5 to 4 m/s.Contaminated material can be continuously fed into the fluidized bed or introduced as a single charge at three different locations. The facility is fully instrumented to allow time-resolved measurements of gaseous pollutant species, gas phase temperatures, and internal pressures. The facility has produced reproducible fluidization results which agree well with the work of other researchers. Minimum fluidization velocities (Umf) ranging from 0.4 to 2.3 m/s were experimentally determined for various sizes and types of material. Static wall pressure varied between 2.6 and 12.9 kPa along the length of the reactor over the range of superficial velocities. Superficial velocity was found to significantly influence the behavior of the axial pressure profiles, particularly in the slugging and turbulent regimes of operation. In addition to fluidization tests, initial combustion tests were performed while burning natural gas and operating with an inert silica sand bed. Results indicate that combustion of natural gas occurred to only a limited extent within the bed. The lowest CO2 and the highest CO concentrations (1.9% and 0.9%, respectively) were found 0.5 m above the expanded bed surface. Maximum measured gas temperatures (1400 K) were also observed in this region. These results indicate that ignition occurred immediately above the bed surface and combustion proceeded in the freeboard section. Although significant quantities of NOx (45.0 ppm) and CO2 (7.2%) were formed further downstream in the freeboard of the reactor, the combustion process was found to be essentially complete before the entrance to the cyclone.

Notes: We propose an application for the NTC (negative temperature coefficient) thermistor miniature bead as a sensor to measure the volume flowing through a microporous membrane over a 0–15 cm3/min range. Only one thermistor is used and small temperature changes that can occur during the experiment can be ignored. No compensation or linearity circuitry is used [C. Yang, M. Kümmel, and H. Soeberg, Sensors and Actuators 15, 51 (1988)]. Assembly is easy and it can be adapted to automatic control, for example, to control the flow of a peristaltic pump by connection to an A/D D/A board and computer. When the experimental data was fitted to a potential type curve (y=axb), a sensitivity between 5% and 8% and a correlation coefficient of 0.99 were obtained. The response of the sensor when the flow changes is immediate, although the time taken for the measurement to stabilize is dependent on the size of the variation (between 4 and 7 s). The fitting curve is used to determine the volume flow that is caused by a pressure gradient applied to the membrane placed between two bulks with the same fluid.

Notes: The design and construction of a digital X–Y scan generator used in conjunction with a scanning tunneling microscope and a data acquisition card for the purpose of digitizing images are presented here. The unit generates triangular waveform voltages for the piezoelectric elements and equally spaced pulses in the X and Y directions. The "n×n'' triggering pulses are used to initiate digital to analog conversions in a data acquisition card thus obtaining a symmetrical digitized image. The generator is well suited as a scan generator for any lab-built tunneling microscope.

Notes: Successful operation of a multijoule output TE CO2 laser using a new magnetic-spiker sustainer excitation circuit is reported. The use of the new excitation circuit has resulted in a significant reduction (∼90%) in the amount of sustainer pulse energy that has to pass through the magnetic switch. In addition, the new circuit technique allows operation of the discharge at reduced voltage (∼50%) and extends the range of excitation current pulse durations (up to ∼7 μs) over which arc-free discharges can be formed. The laser has produced a typical output of 5 J at an overall efficiency of ∼13% from a helium-free gas mixture at a pressure of 400 mbar.