Beiträge zur Mikrobestimmung von Kohlenstoff-14 und Tritium

Die Verwendung Con¹⁴C und Tritium zur Lösung kinetischer und analylischer Probleme erfordert zuverlässige Analysenmethoden. Es wird iiber die Herstellimg von Meβgasen durch Naβcerbrennung mil Chromsäure-Jodsäure-Gemischen, Trockenverbrennung in Gegenwart Con Katalysatoren wie Kupferoxid, Kobaltoxid und Zersetzungsprodukte des Silberpermanganats und durch Umsetziingentm geschlossenen Rohr berichtet. Die Aktivitätsniessungen erfolgten auf cerschiedene IVeise. Hier werden besonders die Ergebnisse diskutiert, die durch Ionisationskammermessungen erzielt wurden. Schlieβlich werden einfache Apparaturen zur routinemäβigen Durchfiihrung von Mikroanalysen beschrieben.     

Absolutbestimmung der spezifischen Aktivität 35S-haltiger Substanzen

Als wesentlichste Vorausselzungen für eine präzise Absolutbestimmung der spezifischen Aktivität ³³S-haltiger Substanzen werden die Sorption von SO₂ an den Zählrohren und der Füllapparatur, die Beeinflussung des Gasentladungsmechanismus im beschränkten Proportionalbereich durch negativ geladene SO₂-Ionen und die kinetischen Isotopieeffekte bei nicht hundertprozentiger Überführung der Ausgangssubstanzen zu Meβgas untersucht. Speziell beschrieben werden die Umsetzung von Natriumsulfat bzw. Schwefelsäure in wäβriger Lösung und Thioharstoff zu Bariumsulfat und dessen Verbrennung zu Schwefeldioxid. Der Gesamtfehlre, mit dem die Angabe der spezifischen Aktivität für die genannten Ausgangssubstanzen behaftel ist, wird angegeben.     

Characterisation of baroque tin amalgam mirrors of the historical Green Vault in Dresden

The historical Green Vault, one of Europe’s most sumptuous treasure chambers, has reopened in September 2006 in the Dresden Royal Palace. For the baroque presentation of the artworks the special properties of tin amalgam mirrors are of great importance. A comprehensive analytic characterisation was necessary for restoration and reconstruction. The different original casting glasses were analysed in respect of chemical composition, roughness, waviness and optical properties like chromaticity coordinates and transmittance. The microstructure of the tin amalgam layers were investigated on metallographic cross-sections and by X-ray diffraction. The investigations reveal that the tin amalgam layers are composed of γ-HgSn_6-10 phase with a grain size between 5 and 50 μm surrounded by a thin mercury phase with about 2 wt. % tin. However the most important property of the baroque tin amalgam mirrors is a relative low reflectivity of about 59% which is drastically lower than for silver mirrors with a reflectivity of about 96%. According to the characterisation results a suitable glass for reconstruction was selected. The mirror layers were produced by historical tin amalgam technology for the rooms not destroyed by bombarding of Dresden in February 1945. For the completely destroyed Jewel Room pure tin layers were deposited by magnetron sputtering. The results show that this new technology enables an adequate substitute for the original tin amalgam layers. PACS  61.66.-f; 74.25.Gz; 61.10.Nz; 68.37.Hk     

Hard disks on the hyperbolic plane

We examine a simple hard disk fluid with no long range interactions on the two-dimensional space of constant negative Gaussian curvature, the hyperbolic plane. This geometry provides a natural mechanism by which global crystalline order is frustrated, allowing us to construct a tractable model of disordered monodisperse hard disks. We extend free-area theory and the virial expansion to this regime, deriving the equation of state for the system, and compare its predictions with simulation near an isostatic packing in the curved space.     

UTILIZATION OF TOOLS FOR SUCCESSFUL. TROUBLESHOOTING OF STRUCTURAL PROBLEMS

A structural failure problem was solved using an integrated and iterative program of testing and analysis. The steps taken in solving the problem were: analytical calculations; operational testing; qualifications of analytical results; problem identification; design of corrective action; and confirmatory testing.     

Vortex lattice transitions in YNi2B2C

We have performed extensive small-angle neutron scattering (SANS) diffraction studies of the vortex lattice in single crystal YNi₂B₂C for B‖c. High-resolution SANS, combined with a field-oscillation vortex lattice preparation technique, allows us to separate Bragg scattered intensities from two orthogonal domains and accurately determine the unit cell angle, β. The data suggest that upon increasing field there is a finite transition width where both low- and high-field distorted hexagonal vortex lattice phases, mutually rotated by 45°, coexist. The smooth variation of diffracted intensity from each phase through the transition corresponds to a redistribution of populations between the two types of domains.     

Flow phenomena in floppy tubes

Collapsible tubes, which occur all over the body, have unique properties from the point of view of both physics and physiology. A brief review is attempted of first the basic observable properties, followed by simple theory to explain the steady-flow aspects and an overview of the somewhat more complex theories for unsteady flow, in particular the flow-induced oscillations. The experimental evidence from laboratory studies is reviewed with particular emphasis on the dynamical system aspects. A final section looks at the current position and prospects.