1-Boraadamantane: reactivity towards mono-1-alkynyltin, -germanium and -silicon compounds — synthesis of 4-methylene-3-borahomoadamantanes

The reaction of 1-boraadamantane 1 with 1-alkynyltin (3), -germanium (4), and -silicon compounds (5) leads to enlargement of the tricyclic system by formation of 4-methylene-3-borahomoadamantanes (6–9). These are 1,1-organoboration reactions which proceed by cleavage of the M---C bond (M=Sn, Ge, Si). There is evidence for 1,1-deorganoboration which apparently take place much more readily than for non-cyclic analogues, most likely as the result of the strained tricyclic system. When 2-ethyl-1-boraadamantane (2) is used, again 3-borahomoadamantanes are formed, the isomers 15–18. The product distribution is sensitive to steric effects. However, it appears that the B---C(H)Et bond in 2 is slightly more reactive than the B---CH₂ bonds. All products were characterised by ¹H-, ¹¹B-, ¹³C-, ²⁹Si- and ¹¹⁹Sn-NMR.     

Hydrogen and oxygen isotopes of water from inclusions in minerals: design of a new crushing system and on‐line continuous‐flow isotope ratio mass spectrometric analysis

An analytical line for stable isotope analyses of water recovered from fluid inclusions in minerals was built and successfully tested. The line is based on the principle of continuous‐flow analysis of water via high‐temperature reduction on glassy carbon. It includes a custom‐designed set of high‐efficiency crushers and a cryo‐focusing cell. This paper provides details of the line design and discusses strategies for line conditioning and mitigation of memory effects. The line allows measurements of hydrogen and oxygen isotopes during a single acquisition. The precision of the analyses depends on the amount of water released from the inclusions. The best results are obtained for samples containing at least 0.1–0.2 µL (0.06–0.11 µmol) H₂O. For such samples precision is better than 1.5‰ for δD and 0.5‰ for δ¹⁸O (1σ). Smaller amounts of water can be measured but at lower precision. Analyses of modern calcite formed under stable conditions in a deep cave allowed assessment of the accuracy of the analyses. The δD values measured in fluid inclusions of this working standard match the δD value of the parent water, and the oxygen isotope values agree within ca. 0.5‰. This indicates that fluid inclusions trapped in calcite at near‐ambient temperatures (e.g. speleothems and low‐temperatures phreatic calcite) faithfully preserve the original isotopic composition of the parent waters. Copyright © 2009 John Wiley & Sons, Ltd.     

Heat kernel expansion in the covariant perturbation theory

Working within the framework of the covariant perturbation theory, we obtain the coincidence limit of the heat kernel of an elliptic second order differential operator that is applicable to a large class of quantum field theories. The basis of tensor invariants of the curvatures of a gravity and gauge field background, to the second order, is derived, and the form factors acting on them are obtained in two integral representations. The results are verified by the functional trace operation, by the short proper time (Schwinger–DeWitt) expansions, as well as by the computation of the Green function for the two-dimensional scalar field model.     

Uncertainty of measurement. Twenty years afterwards

The application of the concept “uncertainty” causes considerable difficulties. In this paper an analysis of the intrinsic contradictions of the concept itself and its relationship with the statements of metrology is given with the aim of establishing possible reasons for these difficulties. As a result of this analysis several examples are presented to demonstrate the conflicts of the concept and its several statements in the general fundamental notions of metrology. Received: 16 February 2001 / Revised: 2 April 2001 / Accepted: 9 April 2001