The treatment of Ag,Pd, Au and Pt electrodes with OH<Superscript>•</Superscript> radicals reveals information on the nature of the electrocatalytic centers

The treatment of Ag, Pd, Au and Pt electrodes with OH^• radicals can be used to get information on the nature of the electrocatalytic sites. Atomic force microscopy (AFM) measurements, various electrochemical techniques, and chemical solution analysis show a more or less effective surface dissolution of these metals upon OH^• treatment. The effect of the surface alterations on the electrocatalytic activity with respect to the quinone/hydroquinone system revealed distinct differences between Ag and Au (previous studies) on one side, and Pt and Pd on the other side. Whereas, in case of Pt and Pd, the electrocatalytic properties are obviously related to the regular surface atoms, in case of Ag and Au the active centers are highly reactive surface atoms which can be removed by OH^• radicals.     

Solid state electrochemical reactions in systems with miscibility gaps

Cyclic voltammograms of electroactive solid compounds with partial immiscibility between the oxidized and reduced phases can exhibit a splitting of the peaks. If the free energy of transformation between the oxidized and reduced phases is small, the formal potentials of the redox pair will be almost the same in both solid phases. This results in an inert potential range in which no appreciable electrochemical activity is possible. The kinetic implications of this situation have been analysed in relation to the width of the miscibility gap. The diffusion of ions in the particle, which is hindered by the immiscibility, can proceed when a transition zone between the two phases exists in which the crystal structure is changed. If there is no such transition zone the voltammogram will display several spikes, which are caused by the collapse of concentration barriers at the sharp interfaces between the two phases in the mixed crystals. Received: 14 October 1999 / Accepted: 4 November 1999     

Photobiomodulation Therapy for Attenuating the Dystrophic Phenotype of Mdx Mice

This study analyzed photobiomodulation therapy (PBMT) effects on regenerative, antioxidative, anti-inflammatory and angiogenic markers in the dystrophic skeletal muscle of mdx mice, the experimental model of Duchenne muscular dystrophy (DMD), during the acute phase of dystrophy disease. The following groups were set up: Ctrl (control group of normal wild-type mice; C57BL/10); mdx (untreated mdx mice); mdxPred (mdx mice treated with prednisolone) and mdxLA (mdx mice treated with PBMT). The PBMT was carried out using an Aluminum Gallium Arsenide (AIGaAs; IBRAMED® laserpulse) diode, 830 nm wavelength, applied on the dystrophic quadriceps muscle. The mdxLA group showed a degenerative and regenerative area reduction simultaneously with a MyoD level increase, ROS production and inflammatory marker reduction and up-regulation in the VEGF factor. In addition, PBMT presented similar effects to prednisolone treatment in most of the parameters analyzed. In conclusion, our results indicate that PBMT in the parameters selected attenuated the dystrophic phenotype of mdx mice, improving skeletal muscle regeneration; reducing the oxidative stress and inflammatory process; and up-regulating the angiogenic marker.     

Analytische Mannigfaltigkeiten in Riemannschen Bereichen

Ohne Zusammenfassung     

Contrast optimization of two-photon processes after a microstructured hollow-core fiber demonstrated for dye molecules

We demonstrate selective excitation of dyes with overlapping absorption spectra in solution with pulses transmitted through a hollow-core fiber. Thereto we show how dispersive effects occurring in the fiber can be compensated and what the limiting pulse energies are. Furthermore, an overview over various phase parameterizations is given and we examine which are best used when optimizing a two-photon fluorescence contrast of two dyes in a sample. This could be relevant for future endoscopic applications as well as state of the art two-photon microscopy.     

Low-rank canonical-tensor decomposition of potential energy surfaces: application to grid-based diagrammatic vibrational Green's function theory

ABSTRACT

A new method is proposed for a fast evaluation of high-dimensional integrals of potential energy surfaces (PES) that arise in many areas of quantum dynamics. It decomposes a PES into a canonical low-rank tensor format, reducing its integral into a relatively short sum of products of low-dimensional integrals. The decomposition is achieved by the alternating least squares (ALS) algorithm, requiring only a small number of single-point energy evaluations. Therefore, it eradicates a force-constant evaluation as the hotspot of many quantum dynamics simulations and also possibly lifts the curse of dimensionality. This general method is applied to the anharmonic vibrational zero-point and transition energy calculations of molecules using the second-order diagrammatic vibrational many-body Green's function (XVH2) theory with a harmonic-approximation reference. In this application, high dimensional PES and Green's functions are both subjected to a low-rank decomposition. Evaluating the molecular integrals over a low-rank PES and Green's functions as sums of low-dimensional integrals using the Gauss–Hermite quadrature, this canonical-tensor-decomposition-based XVH2 (CT-XVH2) achieves an accuracy of 0.1 cm^?1 or higher and nearly an order of magnitude speedup as compared with the original algorithm using force constants for water and formaldehyde.     

Nilpotent bases for distributions and control systems

Let V(M) be the Lie algebra (infinite dimensional) of real analytic vector fields on the n-dimensional manifold M. Necessary conditions that a real analytic k-dimensional distibution on M have a local basis which generates a nilpotent subalgebra of V(M) are derived. Two methods for sufficient conditions are given, the first depending on the existence of a solution to a system of partial differential equations, the second using Darboux's theorem to give a computable test for an (n ? 1)-dimensional distribution. A nonlinear control system in which the control variables appear linearly can be transformed into an orbit equivalent system whose describing vector fields generate a nilpotent algebra if the distribution generated by the original describing vector fields admits a nilpotent basis. When this is the case, local analysis of the control system is greatly simplified.     

A new approach to variable selection in least squares problems

The title Lasso has been suggested by Tibshirani (1996) as acolourful name for a technique of variable selection which requiresthe minimization of a sum of squares subject to an l₁ bound on the solution. This forces zero components in the minimizingsolution for small values of . Thus this bound can functionas a selection parameter. This paper makes two contributionsto computational problems associated with implementing the Lasso:(1) a compact descent method for solving the constrained problemfor a particular value of is formulated, and (2) a homotopymethod, in which the constraint bound becomes the homotopyparameter, is developed to completely describe the possibleselection regimes. Both algorithms have a finite terminationproperty. It is suggested that modified Gram-Schmidt orthogonalizationapplied to an augmented design matrix provides an effectivebasis for implementing the algorithms.