Highly fluorous complexes of nickel, palladium and platinum: solubility and catalysis in high pressure CO2

A variety of Group 10 metal complexes [MXY(dfppp)], M = Ni, X, Y = Cl, Br, M = Pd, Pt, X, Y = Cl or CH(3), containing the recently reported highly fluorous diphosphine ligand, dfppp, 1,3-bis[di(fluoroponytail)phosphino]propane, {(p-F(13)C(6)C(6)H(4))(2)P}(2)(CH(2))(3) have been synthesised. They have been characterised by NMR, mass spectrometry and microanalysis, with two platinum complexes, [PtCl(2)(dfppp)] and [PtClMe(dfppp)], structurally characterised by single crystal X-ray diffraction studies. The highly fluorous nature of the ligands affords the complexes good supercritical CO(2) solubility as measured by supercritical fluid extraction (SFE), and has allowed for the copolymerisation of CO and ethylene using [PdClMe(dfppp)] as the catalyst precursor and CO(2) as the solvent. Additionally, PtCl(2) complexes of the new ligands dfppb, {(p-F(13)C(6)C(6)H(4))(2)P}(2)(CH(2))(4), and dfpop, {(p-F(13)C(6)C(6)H(4)O)(2)P}(2)(CH(2))(3), have also been prepared and characterised.     

Chalcogenide Exchange Reaction of [RGa(μ3-Te)]4 with Elemental Sulfur and Selenium: A Density Functional Theory Study

Thermodynamic and mechanistic features of the chalcogen exchange reaction between [RGa( ₃-Te)]₄ and elemental sulfur or selenium have been studied employing density functional theory (DFT) calculations using the BL3YP basis set and Stuttgart pseudopotentials. For [MeGa( ₃-E)]₄ (E=S, Se, Te) the correlation between the calculated parameters and diffraction data for their isolable analogs is greater than 98%. Each step of the conversion of [MeGa( ₃-Te)]₄ to [MeGa( ₃-E)]₄ via [Me₄Ga₄( ₃-Te)_4–x ( ₃-E) _x ] (E=S, Se) is predicted to occur as a series of isolated reactions. The entropy change for each chalcogen exchange is small in magnitude and corresponds to the degree of cage distortion within the cubane molecules. Calculations performed on [MeGa( ₃-Te)]₄...S₈ and [MeGa( ₃-Te)]₄-S suggest that an increase in electrophilicity of the gallium next to a surface bound tellurium may result in nucleophilic cage opening for which intermediate structures are calculated.     

r-Process nucleosynthesis without excess neutrons

Matter expanding sufficiently rapidly and at high enough entropy per nucleon can enter a heavy-element synthesis regime heretofore unexplored. In this extreme regime, more similar to nucleosynthesis in the early universe than to that typical in stellar explosive environments, there is a persistent disequilibrium between free nucleons and abundant alpha particles, which allows heavy r-process nucleus production even in matter with more protons than neutrons. This observation bears on the issue of the site of the r process, on the variability of abundance yields from r-process events, and on constraints on neutrino physics derived from nucleosynthesis.     

T-ray computed tomography

We demonstrate a tomographic imaging modality that uses pulsed terahertz (THz) radiation to probe the optical properties of three-dimensional (3D) structures in the far-infrared. This THz-wave computed tomography (T-ray CT) system provides sectional images of objects in a manner analogous to conventional CT techniques such as x-ray CT. The transmitted amplitude and phase of broadband pulses of THz radiation are measured at multiple projection angles. The filtered backprojection algorithm is then used to reconstruct the target object, including both its 3D structure and its frequency-dependent far-infrared optical properties.     

Artifacts,assumptions, and ambiguity: Pitfalls in comparing experimental results to numerical simulations when studying electrical stimulation of the heart

Insidious experimental artifacts and invalid theoretical assumptions complicate the comparison of numerical predictions and observed data. Such difficulties are particularly troublesome when studying electrical stimulation of the heart. During unipolar stimulation of cardiac tissue, the artifacts include nonlinearity of membrane dyes, optical signals blocked by the stimulating electrode, averaging of optical signals with depth, lateral averaging of optical signals, limitations of the current source, and the use of excitation-contraction uncouplers. The assumptions involve electroporation, membrane models, electrode size, the perfusing bath, incorrect model parameters, the applicability of a continuum model, and tissue damage. Comparisons of theory and experiment during far-field stimulation are limited by many of these same factors, plus artifacts from plunge and epicardial recording electrodes and assumptions about the fiber angle at an insulating boundary. These pitfalls must be overcome in order to understand quantitatively how the heart responds to an electrical stimulus. (c) 2002 American Institute of Physics.     

From squeezed atom lasers to teleportation of massive articles

The development of the Raman atom laser promises to make available new techniques for accessing and manipulating the quantum statistical properties of Bose-Einstein condensates. In this work we show how, combined with the already existing methods for the manipulation of quantum states of light which are central to quantum optics, the Raman input-output coupling mechanisms potentially enable the production of quadrature squeezed and sub-Poissonian atomic beams, and entanglement between atomic and optical fields. We also propose a method of measuring the quantum statistics of the atomic beam by transferring them to an optical field. Finally, by combning these techniques, we propose a method of teleporting the atom laser beam from one trapped condensate to another.     

On the topological charge concentrated at a point

For SU(2) gauge fields over the 4-dimensional sphere with a finite number of points x₁, x₂, ..., and x_N removed, there are gauge transformations which modify the topological charge concentrated at x_j by adding n_j, where n₁, n₂, …, and n_N. are integers such that Σ^N_{j = 1}n_j = 0. However, the reduction modulo Z of the topological charge at a point is well defined, being given in terms of the secondary characteristic classes of Chern and Simons, except when the topological charge is indeterminate.