Synthesis and use of alpha-silyl-substituted alpha-hydroxyacetic acids

[reaction: see text] Rhodium-catalyzed oxygen transfer was used to generate benzyl 2-silyl-2-oxoacetates in good yields. The hydrogenation of these compounds led to chiral alpha-silyl-substituted alpha-hydroxyacetic acids. Resolution by means of HPLC using a chiral stationary phase afforded an enantiomerically pure representative of this class of compounds, which was successfully applied as a chiral ligand in an asymmetric aldol-type reaction.     

Die Verwendung des elektrischen Stromes als W?rmequelle

Ohne Zusammenfassung     

Self-organized criticality in the olami-feder-christensen model

A system is in a self-organized critical state if the distribution of some measured events obeys a power law. The finite-size scaling of this distribution with the lattice size is usually enough to assume that the system displays self-organized criticality. This approach, however, can be misleading. In this paper we analyze the behavior of the branching rate sigma of the events to establish whether a system is in a critical state. We apply this method to the Olami-Feder-Christensen model to obtain evidence that, in contrast to previous results, the model is critical in the conservative regime only.     

Nuclear shapes of the transitional nuclei 186, 188, 190, 192Os

Excitation functions at θ_lab = 130° have been measured for inelastic scattering of 13–24 MeV alpha particles from ^{186,188,190,192}Os. Data have been obtained for 0⁺, 2⁺, 4⁺, 2⁺' states in ^186,188,192Os and for 0⁺, 2⁺ states in ¹⁹⁰Os. Charge and mass quadrupole deformations, β₂^c and β₂^N, were deduced from coupled-channels analysis of the 2⁺ data. No simple model could provide good fits to the 4⁺ data over the entire energy range but the very deep interference minima observed establish the charge and mass hexadecapole moments, β₄^c and β₄^N, to be negative. The energies of the interference minima for the 4⁺ states could be reproduced by coupled-channels calculations only if large differences in β₄^c and β₄^N were allowed. Data for the (J, K)^π = (2, 2)⁺ states are inconsistent with an asymmetric rotational model.     

Quasi-TEM mode propagation in twin-wire THz waveguides

We numerically investigate the trade-offs between the dispersion properties,coupling efficiency,and geometrical constraints in dual-wire (twin-lead) terahertz (THz) waveguides.In particular,we show that their inherent linearly polarized quasi-transverse electromagnetic (TEM) modes exist for waveguide transverse dimensions comparable with the wavelength,enabling significant end-fire coupling (>10%) for numericalaperture limited Gaussian beams while supporting a relatively low-dispersion propagation of below 0.5 ps 2 /m,as desired for short-pulse time-domain spectroscopy applications.Starting from the dual-wire structure,we also demonstrate that low-dispersion tapers can be designed to improve coupling efficiency.     

Intermolecular rhodium(II)-catalyzed reactions with silicon-substituted carbonyl ylides

[reaction: see text] The Rh(II)-catalyzed reaction of benzyl 2-trialkylsilyl-2-diazoacetates with various acyclic and cyclic ketones affords novel dioxolanones via silicon-substituted carbonyl ylides in up to 98% yield.