Results 1 - 10 of 701
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[en] In the chiral limit, the amplitude of the decay π0 → γγ is determined by the anomaly induced on the neutral iso-triplet axial current by the EM field. The amplitude is thus given in terms of the only available quantities in that limit, namely, the fine structure and the pion-decay constants.
[en] The fine structure found by Gu, Hill and Rosenwald between asymptotic theory eigenfrequencies and the observed eigenfrequencies reported by Hill and Gu is interpreted as the result of conditions not being met for the applicability of asymptotic theory at one or more radii in the solar interior. From an inversion of the observed fine structure, reasonably good agreement is obtained between observation and theory for either a localized perturbation in internal structure at r/R ∼ 0.06 or at r/R ∼ 0.23. The latter solution is, however, the better one. The amplitude of the perturbation in the mean molecular weight required to produce the fine structure is also inferred. 11 refs., 2 figs
[en] Doppler-free two-photon laser spectroscopy has been employed for excited transitions between the 1S and 2S states in muonium. An unambiguous signal could be observed. The frequency interval was determined to be Δν1S-2S = 2 455 529 002(33)(46) MHz, where the first error arises from statistics and the second one is due to systematic effects which mainly are related to the properties of the high power pulsed laser system. There is agreement with a prior less accurate independent experiment at KEK and with QED theory within two standard deviations. The Lamb shift contributions are tested at the 8 · 10-3 level. The muonium-hydrogen and muonium-deuterium isotope shifts of the 1S-2S transition have a high potential for a precise mass determination of the positive muon. The experiment yields at present m1S-2Sμ = 105.658 80(29)(43) MeV/c2
[en] The nature of the fine structure of high order, low degree five minute period solar oscillations following from various postulated forms of spherical rotation is predicted. The first and second order effects of rotation are included
[en] The EXAFS spectra of Cu and Pd foil from many different beamlines and synchrotrons are compared to address the dependence of the amplitude reduction factor (S02) on beamline specific parameters. Even though S02 is the same parameter as the EXAFS coordination number, the value for S02 is given little attention, and is often unreported. The S02 often differs for the same material due to beamline and sample attributes, such that no importance is given to S02-values within a general range of 0.7 to 1.1. EXAFS beamlines have evolved such that it should now be feasible to use standard S02 values for all EXAFS measurements of a specific elemental environment. This would allow for the determination of the imaginary energy (Ei) to account for broadening of the EXAFS signal rather than folding these errors into an effective S02-value. To test this concept, we model 11 Cu-foil and 6 Pd-foil EXAFS spectra from around the world to compare the difference in S02- and Ei-values.
[en] The effects of various chemical substitutions and induced lattice disorder in the Ce- and Pu-based 115 superconductors are reviewed, with particular emphasis on results from x-ray absorption fine structure (XAFS) measurements. The PuCoGa5 system offers the opportunity to follow changes in magnetic and electronic properties due to lattice disorder as a function of time in the same samples, in addition to the more traditional approach of perturbing the superconducting state through chemical substitutions. The reviewed work establishes a baseline for such future studies by determining the intrinsic lattice order in the 115 system, successfully understanding disorder as introduced through chemical substitutions in the Ce-based 115s, and beginning to explore the surprisingly large role of self-irradiation damage directly on the PuCoGa5 lattice. These studies lay the foundation for the harder future work toward measuring chemical substitutions in PuCoGa5, correlating effects with non-Fermi liquid behavior, and obtaining a better structural picture of the distortions induced by α-decay of the plutonium nucleus.
[en] The line fluxes of the far-infrared fine-structure ionic and atomic transitions in the narrow-line regions (NLRs) of active galaxies are predicted using a standard photoionization model. Using the observed H β flux of the Seyfert 2 galaxy NGC 1068, and assuming the standard conditions in active galaxies NLRs, it appears that [CII] 158μm, [OI] 63μm, [NIII] 57μm, [NII] 122μm and [OIII] 88μm and 52μm are all detectable at high resolution (R=104) with the Long Wavelength Spectrometer (LWS) on board of the next ESA satellite ISO
[en] Throughout this book many examples for the close relationship between the macroscopic properties and the local structure of liquid and amorphous metals and alloys are given. Complementing the conventional X-ray, electron and neutron scattering techniques the analysis of the 'Extended X-ray Absorption Fine Structure' (EXAFS) has been developed to a reliable method for structural analysis. Although the phenomenon is known since the thirties of the century, its application for the determination of local geometrical parameters has only been introduced about ten years ago. The development of the method has been greatly stimulated by extensive theoretical work, e.g. more refined calcualtions of complex scattering amplitudes and by the availability of synchrotron radiation as an intense X-ray continuum source. Two aspects are discussed in this paper: i) The basic principles of EXAFS and the usual data evaluation techniques demonstrated for crystalline Fe. ii) Applications on amorphous systems, the modifications of the data evaluation due to nonsymmetric pair distributions and the comparison with other methods for structure determination. (orig.)