Carbon kinetic isotope effect in the oxidation of methane by hydroxyl

The carbon kinetic isotope effect in the reaction of CH₄ with OH has an experimentally measured value of 1.003. The measurement was performed using a static system in which the source of OH was the gas-phase photolysis of H₂O₂ with ultraviolet light produced by a high-pressure mercury arc lamp. Implications for the tropospheric cycle of CH₄ are considered briefly.     

Einfaches Gerät zur Messung sehr kleiner Druckdifferenzen

A quadratic plate moves with very small clearance in an annular duct with a width of 1 cm². This plate is connected to a turnable spindle in the axis of the duct and can move with it against a thin spiral spring. On both sides of this plate pressures are applied, the difference of which is to be measured. Its amount can be read with a pointer on a scale. In measuring a small loss of gas will occur through the narrow slit between plate and annular duct. If this loss is not admissable, it can be avoided by using two equal instruments, of which one works as zero-instrument in a kind of compensation method. The loss of the second instrument is supplied from an additional source of gas. The instrument permits measurements with an accuracy of fractions of thousandth of a mm water column.

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Einfaches Gerät zur Messung sehr kleiner Druckdifferenzen

Zusammenfassung Eine quadratische Platte bewegt sich mit seht geringem Spiel in einem ringförmigen Kanal von l cm² Querschnitt, sie ist mit einer drehbaren Welle verbunden, die in der Achse des Kanals liegt und kann sich mit dieser gegen eine dünne Spiralfeder bewegen. Auf die beiden Seiten dieser Platte wirkt die zu messende Druckdifferenz und ihre Größe kann mit Hilfe eines Zeigers abgelesen werden. Die Messung ist mit einer geringen Menge überströmenden Gases durch den Spalt zwischen Platte und Ringkanal verbunden. Ist diese Überströmung nicht zulässig, so kann man sie durch Verwenden von zwei Geräten gleicher Art vermeiden, von denen das eine als Nullinstrument nach einer Art von Kompensationsverfahren arbeitet und der Gasverlust des anderen von einer zusätzlichen Gasquelle geliefert wird. Das Gerät erlaubt Messungen mit einer Genauigkeit von Bruchteilen eines Tausendstel mm Wassersäule.

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Prof. Dr.-Ing. U. Grigull zum 60. Geburtstag.     

The Mössbauer research community: A report

The Mössbauer research community has gone through various stages of development in its 30⁺ year history. Signs of maturity of the Mössbauer effect is shown in the number of experimental applications, the number of Mössbauer transitions that are available and the large number of scientists that have been and are involved with Mössbauer research. In recent years, there has been a significant increase in the number of publications using Mössbauer Spectroscopy to investigate both amorphous and high temperature superconductor materials. This overall growth in the Mössbauer scientific literature has been 6–7% per year since 1984, while during the preceding period there was no increase in the number of publications per year. The Mössbauer Effect Data Center continues to make use of the various developing technologies in the area of computers and communications. The Center recently completed a ten-year project of bringing together all its databases into one computer system. Also, the Center has recently completed the development of a new approach to the dissemination of information by making available subsets of the Mössbauer database on PC computer disks. The future of the Data Center will focus significant attention on networking strategies with the Mössbauer research community.     

Rayleigh-brillouin spectroscopy of syndiotactic poly(n-butyl methacrylate) near the glass transition

We present Rayleigh-Brillouin light scattering data of highly syndiotactic poly(n-butyl methacrylate) [PBMA] whose glass transition temperature as measured by DSC is 55°C. The Brillouin peak shifts, Brillouin peak widths, and Landau-Placzek ratios from ?15 to 130°C are reported. The Brillouin peak widths decrease continuously through the glass transition region. This indicates a continual decrease in the strength of processes whose relaxation times are about 10^?10 s with decreasing temperature even as the system becomes glassy. The Landau-Placzek ratio above the glass transition is about 3, indicating the high optical purity of our sample. This low Landau-Placzek ratio arises from the sample's homogeneous stereochemistry. Some of the anomalous behavior observed around 40–50°C in previous PBMA studies is explained in terms of syndiotactic regions within a largely atactic sample.     

Straightforward ring expansion of pyroglutamates to perhydro-1,3-diazepine-2,4-diones

[reaction: see text] Perhydro-1,3-diazepine-2,4-diones are rare and can only be prepared, up to now, by special methods. A new one-step protocol was developed, comprising N-carbamoylation using an isocyanate followed by intramolecular ring expansion. This new methodology provides a straightforward access to this interesting seven-membered skeleton.