Ultrafast core-hole-induced dynamics in water probed by x-ray emission spectroscopy

The isotope effect and excitation-energy dependence have been measured in the oxygen K-edge x-ray emission spectrum (XES). The use of XES to monitor core decay processes provides information about molecular dynamics (MD) on an ultrafast time scale through the O1s lifetime of a few femtoseconds. Different nuclear masses give rise to differences in the dynamics and the observed isotope effect in XES is direct evidence of the importance of such processes. MD simulations show that even the excitation-energy dependence in the XES is mainly related to differences in core-excited-state dynamics.     

Hyperbolic Spirals as Surface Structures in Thin Layers

When thin layers of 4-chloro-3-methylphenol and a copolymer of methyl(methacrylate) and maleic acid dissolved in acetone are dried by solvent evaporation, various surface structures appear. Besides linear surface deformations that can ramify like fractals, spirals of the hyperbolic type have been found. The surface structures are due to crystallization processes and flows caused by surface tension differences. The spirals are surface elevations with grooves on both sides as shown by surface profile measurements by means of a microscope interferometer. The addition of surfactants reduces the structure formation. A large surfactant concentration prevents the structure formation. Copyright 2001 Academic Press.     

Structure and stability of vortices in dilute Bose-Einstein condensates at ultralow temperatures

We compute the structure of a quantized vortex line in a harmonically trapped dilute atomic Bose-Einstein condensate using the Popov version of the Hartree-Fock-Bogoliubov mean-field theory. The vortex is shown to be (meta)stable in a nonrotating trap even in the zero-temperature limit, thus confirming that weak particle interactions induce for the condensed gas a fundamental property characterizing "classical" superfluids. We present the structure of the vortex at ultralow temperatures and discuss the crucial effect of the thermal gas component to its energetic stability.     

Ab initio studies of structural features not easily amenable to experiment : Part 13. Structural consequences of methyl hyperconjugation in some CH3C(=X)Y systems

The molecular structures of several conformations of acetaldehyde, acetic acid and isobutene were completely refined by standard single determinant ab initio procedures on the 4–21G level. Calculated and experimental parameters are in close agreement in all the cases in which the experimental values can be considered as reliably established. In some examples, however, some essential structural features that should be found in CH₃C(=X)Y systems have not yet been resolved by any experimental technique. The structural consequences for methyl hyperconjugation in the various systems are discussed. The study demonstrates that high quality ab initio geometries can provide information which is complementary to experimental results. The calculations are particularly useful in discussing discrepancies between microwave and electron diffraction structures and in interpreting microwave substitution structure uncertainties which are often difficult to determine accurately.     

Tikhonov Regularization of Large Linear Problems

Many numerical methods for the solution of linear ill-posed problems apply Tikhonov regularization. This paper presents a new numerical method, based on Lanczos bidiagonalization and Gauss quadrature, for Tikhonov regularization of large-scale problems. An estimate of the norm of the error in the data is assumed to be available. This allows the value of the regularization parameter to be determined by the discrepancy principle.