The σ-model and its renormalization in a dimensionally regularised normal product formulation

The σ-model is re-examined in the light of the reformulation of the normal product method in dimensional regularisation. It is considered both as a prime example of, and testing ground for, these methods, and to display the dimensionally regularised renormalisation of the model. Explicit and spontaneous symmetry breakings are considered, and the PCAC relation and Goldstone theorem are examined and proved in the one loop approximation. The renormalisation group equation coefficients are also obtained to this order. Both arbitrary (renormalised) parametrisations, and the mass shell parametrisation with finite counterterms are considered. It is found that, in contrast with other treatments, these counter terms remain finite in the infra-red limit of a massless symmetric Lagrangian.     

Inversion von schwingungselastischen Streudaten

Ohne Zusammenfassung     

Multichannel mueller matrix ellipsometry for simultaneous real-time measurement of bulk isotropic and surface anisotropic complex dielectric functions of semiconductors

We have applied a dual rotating-compensator multichannel ellipsometer to acquire spectra ( approximately 2.0-4.6 eV) in all 16 elements of the Mueller matrix associated with a specularly reflecting surface, in a minimum time of 0.25 s. In this initial study, such results have been collected for the (110) silicon surface at an incidence angle of approximately 70 degrees and have been used to derive spectra in the bulk isotropic dielectric function epsilon (b)= epsilon (1b)-i epsilon (2b) and the surface-induced dielectric function anisotropy Delta epsilon =Delta epsilon (1)-iDelta epsilon (2). Thus, this instrument shows promise for simultaneous real-time measurement of epsilon (b) and Delta epsilon spectra in oblique reflection during the fabrication of semiconductor structures having bulk isotropic components.     

Isobutene polymerization using a chelating diborane co-initiator

Lewis acidic diborane 1 (J. Am. Chem. Soc. 1999, 121, 3244-3245) is highly effective for both proton- and cationogen-initiated isobutene polymerization in hydrocarbon media at low temperature. Reactions of diborane 1 with cumyl chloride and cumyl methyl ether were studied by variable-temperature 1H and 19F NMR spectroscopy. At low temperatures stable ion pairs 2a and 2b are formed; at higher temperatures these ion-pairs form phenyl-1,3,3-trimethylindan (3) with concomitant release of HCl to form 1 in the case of 2a or degradation of the anion (2b). Reaction between Ph3C-Cl and diborane 1 resulted in the generation of an ion-pair 4 consisting of the Ph3C cation very weakly associated with the chelated, mu-Cl counteranion as revealed by X-ray crystallography.     

First direct structural comparison of complexes of the same metal fragment to ketenes in both C,C- and C,O-bonding modes

Using a series of Ir(I) and Rh(I) ketene complexes, conclusions about the structure and bonding of complexes of the fundamentally important ketene ligand class are reached. In a unique comparison of X-ray structures of the same metal fragment to ketenes in both the eta(2)-(C,C) and the eta(2)-(C,O) binding mode, the Ir-Cl bond distances in complexes of trans-Cl(Ir)[P(i-Pr)(3)](2) to phenylketene [4, eta(2)-(C,C)] and diphenylketene [2a, eta(2)-(C,O)] are 2.371(3) and 2.285(2) A, respectively. This would be consistent with greater trans influence of a ketene ligand bound to a metal through its C=C bond than one connected by its C=O bond. Back-bonding of Ir(I) and Rh(I) to diphenylketene was assessed using trans-Cl(M)[P(i-Pr)(3)](2)[eta(2)-(C,O)-diphenylketene] (2a and 2d). Most bond lengths and angles are identical, but slightly greater back-bonding by Ir(I) is suggested by the somewhat greater deformation of the ketene C=C=O system [C-C-O angles are 136.6(4) and 138.9(4) in the Ir and Rh cases 2a and 2d, respectively]. Syntheses of new labeled ketenes Ph(2)C=(13)C=O and Ph(2)C=C=(18)O and their Ir(I) and Rh(I) complexes are reported, along with the generation of an Ir(I) complex of PhCH=(13)C=O. The effects of isotopic substitution on infrared absorption data for ketene complexes are presented for the first time. Preliminary normal coordinate mode analysis allowed definitive assignment of absorptions ascribed to the C-O stretching frequencies of coordinated ketenes, which are near the absorptions for aromatic ring systems commonly found as substituents on ketenes. For free diphenylketene and four of its complexes and a phenylketene complex characterized by X-ray diffraction, the magnitude of the (13)C-(13)C coupling between the two ketene carbons is correlated to carbon-carbon bond distance.     

The quantitative 19F-imaging of albumin at 1.5 T: a potential in-vivo tool

19F-MR-imaging has been used to quantitate albumin concentration in a phantom at 1.5 T. The experimentally derived relationship between albumin concentration and the T1 relaxation time of a fluorinated marker, tetrafluorosuccinic acid (TFSA) was used to calculate the albumin concentration from a quantitative 19F T1 map acquired using a gradient echo sequence. There was close correlation between calculated and actual BSA concentrations (r = 0.99, SE = 0.15). The potentially interfering effect of paramagnetic species on T1 relaxation times was also investigated. Relaxivity data show that albumin concentration measurements should be performed prior to any contrast agent administration.