Structure in the Velocity Space of Globular Clusters

We present an analysis of the velocity space of a sample of globular clusters (GC) with absolute proper motions. The vertical component of the velocity is found to be correlated with luminosity and galactocentric radius. We divided the sample into two luminosity groups above and below the peak of the luminosity function (LF), MV=-7.5, for Galactic GCs. The two groups display different kinematic behaviour according to the first and second statitical moments of the velocity distribution as well as distinct velocity ellipsoids. The velocity ellipsoid of the high luminosity clusters is aligned with the symmetry axes of the Galaxy, whereas the minor axis of the Low Luminosity group is strongly inclined relative to the Galactic rotation axis.Comment: 4 pages, 2 Poscript figures, uses new aa.cls. Astronomy and Astrophysics (Letters) accepte

Gravitational waves from coalescing binaries and Doppler experiments

Doppler tracking of interplanetary spacecraft provides the only method presently available for broad-band searches of low frequency gravitational waves. The instruments have a peak sensitivity around the reciprocal of the round-trip light-time T of the radio link connecting the Earth to the space-probe and therefore are particularly suitable to search for coalescing binaries containing massive black holes in galactic nuclei. A number of Doppler experiments -- the most recent involving the probes ULYSSES, GALILEO and MARS OBSERVER -- have been carried out so far; moreover, in 2002-2004 the CASSINI spacecraft will perform three 40 days data acquisition runs with expected sensitivity about twenty times better than that achieved so far. Central aims of this paper are: (i) to explore, as a function of the relevant instrumental and astrophysical parameters, the Doppler output produced by in-spiral signals -- sinusoids of increasing frequency and amplitude (the so-called chirp); (ii) to identify the most important parameter regions where to concentrate intense and dedicated data analysis; (iii) to analyze the all-sky and all-frequency sensitivity of the CASSINI's experiments, with particular emphasis on possible astrophysical targets, such as our Galactic Centre and the Virgo Cluster.Comment: 52 pages, LaTeX, 19 Postscript Figures, submitted to Phys. Rev.

Stellar population synthesis at the resolution of 2003

We present a new model for computing the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities. These predictions are based on a newly available library of observed stellar spectra. We also compute the spectral evolution across a larger wavelength range, from 91 A to 160 micron, at lower resolution. The model incorporates recent progress in stellar evolution theory and an observationally motivated prescription for thermally-pulsing stars on the asymptotic giant branch. The latter is supported by observations of surface brightness fluctuations in nearby stellar populations. We show that this model reproduces well the observed optical and near-infrared colour-magnitude diagrams of Galactic star clusters of various ages and metallicities. Stochastic fluctuations in the numbers of stars in different evolutionary phases can account for the full range of observed integrated colours of star clusters in the Magellanic Clouds. The model reproduces in detail typical galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We exemplify how this type of spectral fit can constrain physical parameters such as the star formation history, metallicity and dust content of galaxies. Our model is the first to enable accurate studies of absorption-line strengths in galaxies containing stars over the full range of ages. Using the highest-quality spectra of the SDSS EDR, we show that this model can reproduce simultaneously the observed strengths of those Lick indices that do not depend strongly on element abundance ratios [abridged].Comment: 35 pages, 22 figures, to appear in MNRAS; version with full resolution figures available at http://www.iap.fr/~charlot/bc2003/pape

Rationale and design of the multicenter catheter ablation of ventricular tachycardia before transcatheter pulmonary valve replacement in repaired tetralogy of Fallot study

Patients with repaired tetralogy of Fallot are at elevated risk for ventricular arrhythmia and sudden cardiac death. Over the past decade, the pathogenesis and natural history of ventricular tachycardia has become increasingly understood, and catheter ablation has emerged as an effective treatment modality. Concurrently, there has been great progress in the development of a versatile array of transcatheter valves that can be placed in the native right ventricular outflow tract for the treatment of long-standing pulmonary regurgitation. Although such valve platforms may eliminate the need for repeat cardiac operations, they may also impede catheter access to the myocardial substrates responsible for sustained macro-reentrant ventricular tachycardia. This manuscript provides the rationale and design of a recently devised multicenter study that will examine the clinical outcomes of a uniform, preemptive strategy to eliminate ventricular tachycardia substrates before transcatheter pulmonary valve implantation in patients with tetralogy of Fallot.Cardiolog

Abtragen und Bohren mit Festkoerperlasern Teilvorhaben: Herstellung von Fein- und Mikrobohrungen mit dem Festkoerperlaser. Abschlussbericht

Drilling holes in steel and ceramic with diameters in the #mu#-range is a difficult manufacturing process. With decreasing hole diameter, the costs quickly increase. The objectives of the reported project were to do basic research in drilling optimal holes with an Nd:YAG Q-switch-Laser emitting a TEM_0_0-Mode, in comparison to holes drilled by a standard laser system. The determination of the operation quality of the TEM_0_0-Mode-Laser was used as a basis for further experiments. Parameter studies with the aim of minimal hole diameter and conicality were done. Two processes for finishing the laser drilled hole were tested, and led to high-quality holes. The combination of these two manufacturing processes will shorten the processing time, and offer an economically efficient alternative to conventional processes. (orig./RHM)Das Bohren von Loechern in Stahl und Keramik mit Durchmessern im #mu#m-Bereich ist eine fertigungstechnisch anspruchsvolle Aufgabe. Mit sinkendem Bohrungsdurchmesser steigen die Fertigungskosten sehr stark an. Die Zielsetzung des dokumentierten Teilvorhabens war die Erarbeitung der prozesstechnischen Grundlagen zur Herstellung qualitativ hochwertiger Bohrungen mit einem im Grundmode arbeitenden Nd:YAG-Q-switch-Laser und Vergleichsweise mit einem marktueblichen Lasersystem. Die Bestimmung der Betriebseigenschaften des Grundmodelasers bildeten die Grundlage fuer den experimentellen Teil der Untersuchungen. In Parameterstudien wurden die erzielbaren minimalen Bohrlochdurchmesser im Hinblick auf eine geringe Konizitaet und gute Bohrlochqualitaet ermittelt. Zwei Verfahren der Nachbearbeitung lasergebohrter Loecher wurden eingesetzt und fuehrten zu qualitativ hochwertigen Bohrungen. Die Kombination dieser Verfahren reduziert die Gesamtbearbeitungszeit erheblich und bietet daher gerade fuer die Fertigung hoher Stueckzahlen eine wirtschaftliche Alternative. (orig./RHM)Available from TIB Hannover: F94B0396+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Praezisionsbearbeitung mit Festkoerperlaser: Fuegen. Teilprojekt: Werkstoffspezifische und verfahrensoptimierende Untersuchungen zum Fuegen von Werkstoffen geringer Schweisseignung mittels Nd:YAG-Laserstrahlung Abschlussbericht

Fundamental material-technical and process-optimizing investigations were done on laser welding of AlMg and AlLi alloys, ceramic particle reinforced Al alloys (PR-MMC), and Ni and Co based alloys, using Nd:YAG lasers with differing output powers and modes. The investigations on high temperature resistant heat-treatable Ni based alloys showed good results for Inconel 718 and Inconel X 750. The tendency of Rene 41 to form cracks can be reduced using suitable parameters. The MMC's are difficult to weld, and tend to spatter, even at low power densities. By using fluxing agents and wire filler (e.g. 'Ti-based reaction welding'), or by preheating, welding results can be considerably improved. Pore-free brazing could be achieved with an automatic power or wire soldering agent filler, using a bifocal processing head and a shielding gas chamber. For monitoring of the joining process, selected temperature, absorption and wavelength measuring methods (pyrometer, photo-diodes, thermo-camera) were used. Also, process monitoring using radiation detection through the optical fibre was employed. An on-line imaging system made it possible to obtain clear video images through the bright plasma plume using intense laser diode radiation. (orig.)SIGLEAvailable from TIB Hannover: F97B95+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Praezisionsbearbeitung mit Festkoerperlasern (Oberflaechenbehandlung). Veraenderungen der Randzoneneigenschaften von und mit Kupferbasiswerkstoffen durch Einsatz des Festkoerperlasers Abschlussbericht

Remelting, alloying and cladding of copper materials as well as steel cladding with aluminium multicomponent bronze by laser surface treatment have been investigated. The efficiency of Nd:YAG solid state lasers for finishing precision surface treatment of copper alloyed with chromium, tin, boron or aluminium as a function of alloy composition and process parameters has been demonstrated. Only in the cladding with aluminium bronze the CO_2 gas laser exhibited a lower power consumption. Wear resistance of tin bronzes in improved by surface remelting and alloying. Maximum wear resistance was found at boron alloyed copper surface zones. (WEN)SIGLEAvailable from TIB Hannover: F96B571+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Praezisionsbearbeitung mit CO_2-Hochleistungslasern (Abtragen). Teilvorhaben: Abtragen keramischer Werkstoffe Abschlussbericht

Available from TIB Hannover: F96B1352+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Werkstoff und verfahrenstechnische Untersuchungen zum dreidimensionalen Schweissen im Feinblechbereich Abschlussbericht

Investigations concerning 3-D laser welding were first carried out on flat steel sheets, galvanized/nongalvanized, in different spatial positions, followed by investigations on contoured test pieces and sample components. These investigations included problems concerning gap bridging ability and gap measurement. A further work packet is concerned with developments in peripheral areas. A concept for modularly-constructed, process-adapted processing gas supply, as well as a distance measurement and control system for deep welding using lasers have been developed. For path vector related applications of sensors, radial gas supply etc., a program-directed handling axis has been developed. Moreover, further developmental work has been done on quality control for lap joint welding using ultrasonic testing. Automatic testing of the degree of welding for steel sheets under 0.6 mm thickness, and for weld widths of 1 mm is possible. For quality assurence, a relational data bank for use on PC's was developed, which makes quick access to relevant data such as laser, handling system, material, etc. possible. (orig.)Zum 3D-Laserschweissen wurde zunaechst das Fuegen ebener Stahlbleche, verzinkt/unverzinkt, in beliebiger Raumlage, dann das von Konturproben und Musterbauteilen untersucht, einschliesslich der Problematik der Spaltueberbrueckbarkeit und Spaltmessung. Ein weiteres Arbeitspaket waren Entwicklungen im Bereich der Peripherie. So wurde neben einem Konzept zur modular aufgebauten, prozessangepassten Prozessgaszufuhr auch ein Abstandsmess-und -regelsystem fuer das Laserschweissen mit Tiefschweisseffekt entwickelt. Zur bahnvektorbezogenen Anwendung von Sensorik, radialer Gaszufuhr etc. wurde eine zusaetzliche programmeingebundene Handhabungsachse entwickelt. Weiterhin wurde fuer Schweissungen im Ueberlappstoss hinsichtlich der Qualtitaetskontrolle das Ultraschallpruefverfahren dahingehend weiterentwickelt, dass eine automatische Kontrolle auf Verschweissungsgrad fuer Blechdicken unter 0.6 mm und Schweissnahtbreiten von 1 mm moeglich ist. Zur Qualtitaetssicherung wurde eine relationale Datenbank auf PC-Basis errichtet, die schnellen Zugriff auf relevante Daten, wie Laser, Handhabungssystem, Werkstoff etc. ermoeglicht. (orig.)Available from TIB Hannover: F93B62+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman