The role of heat-conducting walls in the measurement of heat and mass transport in transient grating experiments

We present a two-dimensional model to account for the role of heat-conducting walls in the measurement of heat transport and Soret-effect-driven mass transport in transient holographic grating experiments. Heat diffusion into the walls leads to non-exponential decay of the temperature grating. Under certain experimental conditions it can be approximated by an exponential function and assigned an apparent thermal diffusivity D_{th, app} < D_{th, s}, where D_th,s is the true thermal diffusivity of the sample. The ratio D_{th, app}/D_{th, s} depends on only three dimensionless parameters, d /l_s, κ_s/κ_w, and D_{th, s}/D_{th, w}. d is the grating period, l_s the sample thickness, κ_s and κ_w the thermal conductivities of sample and wall, respectively, and D_th,w the thermal diffusivity of the wall. If at least two measurements are performed at different d /l_s, both D_th,s and κ_s can be determined. Instead of costly solving PDEs, D_th,s can be obtained by finding the zero of an analytic function. For thin samples and large grating periods, heat conduction into the walls plays a predominant role and the concentration grating in binary mixtures is no longer one-dimensional. Nevertheless, the normalized heterodyne diffraction efficiency of the concentration grating remains unaffected and the true thermal and collective diffusion coefficient and the correct Soret coefficient are still obtained from a simple one-dimensional model.     

Self-organization of gold atoms on a polar FeO(111) surface

The spatial distribution of single Au atoms on a thin FeO film has been investigated by low-temperature scanning tunneling microscopy and spectroscopy. The adatoms preferentially adsorb on distinct sites of the Moiré cell formed by the oxide layer and the Pt(111) support and arrange into a well-ordered hexagonal superlattice with 25 angstroms lattice constant. The self-organization is the consequence of an inhomogeneous surface potential within the FeO Moiré cell and substantial electrostatic repulsion between the adatoms.     

Multi-waveguide excitation in fs laser written waveguide arrays

We introduce a new technique to excite multiple waveguides in fs laser written waveguide arrays. Using a microstructured grating, we were able to couple almost all of the power of the laser beam into multiple waveguides in one- and two-dimensional lattices. Tilting the sample a defined phase shift between adjacent waveguides can be obtained, which allows anomalous diffraction and refraction to be studied. PACS 42.79.-e; 42.79.Gn; 42.82.Et; 42.25.Kb     

The Ultra-Quasi-Metrically Injective Hull of a T 0-Ultra-Quasi-Metric Space

Jointly with E. Kemajou, in previous work we constructed the so-called Isbell-hull of a T ₀-quasi-metric space. In this article we continue these investigations by presenting a similar construction in the category of T ₀-ultra-quasi-metric spaces and contracting maps. Comparable studies in the area of ultra-metric spaces have been conducted before by Bayod and Martínez-Maurica.     

Next‐to‐next‐to‐leading order post‐Newtonian spin(1)‐spin(2) Hamiltonian for self‐gravitating binaries

We present the next‐to‐next‐to‐leading order post‐Newtonian (PN) spin(1)‐spin(2) Hamiltonian for two self‐gravitating spinning compact objects. If both objects are rapidly rotating, then the corresponding interaction is comparable in strength to a 4PN effect. The Hamiltonian is checked via the global Poincaré algebra with the center‐of‐mass vector uniquely determined by an ansatz.     

Constant-factor approximations for Capacitated Arc Routing without triangle inequality

Given an undirected graph with edge costs and edge demands, the Capacitated Arc Routing problem (CARP) asks for minimum-cost routes for equal-capacity vehicles so as to satisfy all demands. Constant-factor polynomial-time approximation algorithms were proposed for CARP with triangle inequality, while CARP was claimed to be NP-hard to approximate within any constant factor in general. Correcting this claim, we show that any factor  α$\alpha$ approximation for CARP with triangle inequality yields a factor  α$\alpha$ approximation for the general CARP.     

Rhodium-Catalyzed Amination of Aromatic Olefins [1]

Summary.  The oxidative amination of styrene with secondary amines in the presence of cationic rhodium catalysts yields regiospecifically the corresponding anti-Markovnikov enamines. Styrene as the hydrogen acceptor gave concomitantly ethylbenzene. In the presence of 1,5-cyclooctadiene (cod) preferential reduction to cyclooctene takes place. The addition of cod reduces the rate of the reaction, but also the amount of ethylbenzene produced. Here, for the first time the ratio of enamine: ethylbenzene is > 1, which is favourable in case of more expensive styrene derivatives. A screening of various ligands for oxidative amination reveals that hemilabile 2-(ω-phosphino-n-alkyl)-pyridines are superior ligands for this reaction compared to simple alkyl and aryl phosphines. Received May 30, 2000. Accepted July 11, 2000     

Understanding the Buoy Effect of Surface-Enriched Pt Complexes in Ionic Liquids: A Combined ARXPS and Pendant Drop Study**

Recently, we demonstrated that Pt catalyst complexes dissolved in the ionic liquid (IL) [C₄C₁Im][PF₆] can be deliberately enriched at the IL surface by introducing perfluorinated substituents, which act like buoys dragging the metal complex towards the surface. Herein, we extend our previous angle-resolved X-ray photoelectron spectroscopy (ARXPS) studies at complex concentrations between 30 and 5 %_mol down to 1 %_mol and present complementary surface tension pendant drop (PD) measurements under ultraclean vacuum conditions. This combination allows for connecting the microscopic information on the IL/gas interface derived from ARXPS with the macroscopic property surface tension. The surface enrichment of the Pt complexes is found to be most pronounced at 1 %_mol. It also displays a strong temperature dependence, which was not observed for 5 %_mol and above, where the surface is already saturated with the complex. The surface enrichment deduced from ARXPS is also reflected by the pronounced decrease in surface tension with increasing concentration of the catalyst. We furthermore observe by ARXPS and PD a much stronger surface affinity of the buoy-complex as compared to the free ligands in solution. Our results are highly interesting for an optimum design of IL-based catalyst systems with large contact areas to the surrounding reactant/product phase, such as in supported IL phase (SILP) catalysis.     

Protein analysis of laser capture micro-dissected tissues revealed cell-type specific biological functions in developing barley grains

Both the nucellar projection (NP) and endosperm transfer cells (ETC) of the developing barley grain (harvested 8 days after flowering) were isolated by laser capture micro-dissection combined with pressure catapulting. Protein extracts were analyzed by nanoUPLC separation combined with ESI-Q-TOF mass spectrometry. The majority of the ～160 proteins identified were involved in translation, protein synthesis, or protein destination. The NP proteome was enriched for stress defense molecules, while proteins involved in assimilate transport and the mobilization of nutrients were common to both the NP and the ETC. The combined qualitative and quantitative protein profiling allowed for the identification of several proteins showing tissue specificity in their expression, which underlines the distinct biological functions of these two tissues within the developing barley grain.