Comparison of water isotope-ratio determinations using two cavity ring-down instruments and classical mass spectrometry in continuous ice-core analysis

We present a detailed comparison between subsequent versions of commercially available wavelength-scanned cavity ring-down water isotope analysers (L2120-i and L2130-i, Picarro Inc.). The analysers are used in parallel in a continuous mode by adaption of a low-volume flash evaporation module. Application of the analysers to ice-core analysis is assessed by comparison between continuous water isotope measurements of a glacial ice-core from Severnaya Zemlya with discrete isotope-ratio mass spectrometry measurements performed on parallel samples from the same ice-core. The great advances between instrument versions, particularly in the measurement of δ²H, allow the continuous technique to achieve the same high level of accuracy and precision obtained using traditional isotope spectrometry techniques in a fraction of the experiment time. However, when applied to continuous ice-core measurements, increased integration times result in a compromise of the achievable depth resolution of the ice-core records.     

Theory of late-transition-metal alkyl and heteroatom bonding: analysis of Pt, Ru, Ir, and Rh complexes

Density functional and correlated ab initio methods were used to calculate, compare, and analyze bonding interactions in late-transition-metal alkyl and heteroatom complexes (M-X). The complexes studied include: (DMPE)Pt(CH(3))(X) (DMPE = 1,2-bis(dimethylphosphino)ethane), Cp*Ru(PMe(3))(2)(X) (Cp* = pentamethylcyclopentadienyl), (DMPE)(2)Ru(H)(X), (Tp)(CO)Ru(Py)(X) (Tp = trispyrazolylborate), (PMe(3))(2)Rh(C(2)H(4))(X), and cis-(acac)(2)Ir(Py)(X) (acac = acetylacetonate). Seventeen X ligands were analyzed that include alkyl (CR(3)), amido (NR(2)), alkoxo (OR), and fluoride. Energy decomposition analysis of these M-X bonds revealed that orbital charge transfer stabilization provides a straightforward model for trends in bonding along the alkyl to heteroatom ligand series (X = CH(3), NH(2), OH, F). Pauli repulsion (exchange repulsion), which includes contributions from closed-shell d(π)-p(π) repulsion, generally decreases along the alkyl to heteroatom ligand series but depends on the exact M-X complexes. It was also revealed that stabilizing electrostatic interactions generally decrease along this ligand series. Correlation between M-X and H-X bond dissociation energies is good with R(2) values between 0.7 and 0.9. This correlation exists because for both M-X and H-X bonds the orbital stabilization energies are a function of the orbital electronegativity of the X group. The greater than 1 slope when correlating M-X and H-X bond dissociation energies was traced back to differences in Pauli repulsion and electrostatic stabilization.     

Abelian Chern-Simons theory, Stokes’ theorem, and generalized connections

Generalized connections and their calculus have been developed in the context of quantum gravity. Here we apply them to abelian Chern-Simons theory. We derive the expectation values of holonomies in U(1) Chern-Simons theory using Stokes’ theorem, flux operators and generalized connections. A framing of the holonomy loops arises in our construction, and we show how, by choosing natural framings, the resulting expectation values nevertheless define a functional over gauge invariant cylindrical functions.The abelian theory considered in the present article is the test case for our method. It can also be applied to the non-abelian theory. Results will be reported in a companion article.     

Infinite partition regular matrices

We consider infinite matrices with entries from (and only finitely many nonzero entries on any row). A matrixA is partition regular over provided that, whenever the set of positive integers is partitioned into finitely many classes there is a vector with entries in such that all entries ofA lie in the same cell of the partition. We show that, in marked contrast with the situation for finite matrices, there exists a finite partition of no cell of which contains solutions for all partition regular matrices and determine which of our pairs of matrices must always have solutions in the same cell of a partition.