Disordered, strongly scattering porous materials as miniature multipass gas cells

We investigate the interaction of light and gas in strongly scattering nano- and macroporous media. Manufacturing and structural characterization of ZrO(2), Al(2)O(3) and TiO(2) ceramics with different pore sizes, measurements of optical properties using photon time-of-flight spectroscopy, and high-resolution laser spectroscopy of O(2) at 760 nm are reported. We show that extreme light scattering can be utilized to realize miniature spectroscopic gas cells. Path length enhancement factors up to 750 are reached (5.4 m path through gas for light transmitted through a 7 mm ZrO(2) with 49% porosity and 115 nm pores).     

Generation and properties of snarks

For many of the unsolved problems concerning cycles and matchings in graphs it is known that it is sufficient to prove them for snarks, the class of non-trivial 3-regular graphs which cannot be 3-edge coloured.     

Pore size assessment based on wall collision broadening of spectral lines of confined gas: experiments on strongly scattering nanoporous ceramics with fine-tuned pore sizes

Wall collision broadening of absorption lines of gases confined in porous media is a recently opened domain of high-resolution spectroscopy. Here, we present an experimental investigation of its application for pore size assessment. We report on the manufacturing of nanoporous zirconia ceramics with well-defined pore sizes fine-tuned from 50 to 150 nm. The resulting pore structure is characterized using mercury intrusion porosimetry, and the optical properties of these strongly scattering materials are measured using femtosecond photon time-of-flight spectroscopy (transport mean free paths found to be tuned from 2.3 to 1.2 μm as the pore size increase). Wall collision line broadening is studied by performing near-infrared (760 nm) high-resolution diode laser spectroscopy of confined oxygen molecules. A simple method for quantitative estimation of the pore size is outlined and shown to produce results in agreement with mercury intrusion porosimetry. At the same time, the need for improved understanding of wall collision broadening is emphasized.     

Analytic sets extending the graphs of holomorphic mappings

Let D, D′ ⊂ ℂⁿ be bounded domains with smooth real analytic boundaries and ƒ: D → D′ be a proper holomorphic map. Our main result implies that if the graph of ƒ extends as an analytic set to a neighborhood of a poìnt (a, a′) ∈ ∂D × 3D′ with a′ ∈ cl_ƒ(a), then ƒ extends holomorphically to a neighborhood of a.     

Surface investigations with PAC

The present status of surface electric field gradients measured with perturbed γγ-angular correlations (PAC) is reviewed. Experiments concentrate on well-characterized, free surfaces of metals and applications to detection of probe sites and diffusion phenomena are discussed.     

Über die 1. und 2. Ableitungen der Bergmanschen Kernfunktion und ihr Randverhalten

Ohne ZusammenfassungHerrn Prof. Dr. Friedrich Sommer zum 60. Geburtstag gewidmet     

MTO and OsO4: an efficient catalytic couple for mild H2O2-based asymmetric dihydroxylation of olefins

A novel and robust system for osmium-catalyzed asymmetric dihydroxylation of olefins by aqueous H2O2 with methyltrioxorhenium (MTO) as electron transfer mediator (ETM) has been developed. The MTO is catalyzing the H2O2 oxidation of the chiral ligand to its mono-N-oxide, which in turn reoxidizes OsVI to OsVIII. Thus the (DHQD)2PHAL plays a dual role serving as the chiral inductor as well as the tertiary amine generating the N-oxide required for the recycling of osmium. The present catalytic system gives vicinal diols in good isolated yields and high enantiomeric excess (up to 99 % ee).