Die Molekül- und Kristallstruktur von Di-μ-sulfato-μ-hydroxo- bis[triamminkobalt(III)]sulfat-8-Hydrat

The crystal structure of Di-μ-sulfato-μ-hydroxo-bis[triamminecobalt(III)] sulfate 8-hydrate has been determined from three-dimensional x-ray data collected by counter techniques. The structure was refined using 2515 independent reflections and the refinement converged to a conventional R factor (on F) of 3.8%. The compound crystallizes in the monoclinic space group C—P2/a, a = 14.122(9), b = 9.858(2), c = 18.81(2) Å, β = 139.3(4), Z = 2, d_obsd = 2.086 g/cm³ and d_calc = 2.14 g/cm³. Within the cation two bidentate SO₄-ligands form bridges between two cobalt atoms. There are two types of S? O bonds (1.50 Å endocyclic, 1.45 Å exocyclic).     

Synthesis of pyrroles from 1-dialkylamino-3-phosphoryl(or phosphanyl)allenes through 1,5-cyclization of conjugated azomethine ylide intermediates

1-Dialkylamino-1,3-diaryl-3-diphenylphosphanylallenes 3a-e are thermally converted into a-annulated 3,5-diarylpyrroles 6a-f and [a]-annulated benzo[c]azepines 7a,b,d. These transformations are likely to include conjugated azomethine ylide intermediates that can undergo either a 1,5- or a 1,7-electrocyclization. The periselectivity is markedly shifted toward 1,5-cyclization when the diphenylphosphanyl substituent is replaced by the diphenylphosphoryl group. Thus, 1-dialkylamino-3-(diphenylphosphoryl)allenes 4a-f yield pyrroles 6 exclusively and with improved yields, unless the 3-aryl substituent in the allene is too electron-rich (e.g., benzodioxol-5-yl, 4f --> 7f). The preparation and thermal transformation of aminoallenes 4 over three or four steps can be conducted as a one-pot procedure, thus providing a convenient synthesis of [a]-annulated 3,5-diarylpyrroles from enaminoketones.     

Different thermal reactivity of a 1,2-thiaphospholo[a]phosphirane in free and metal carbonyl complexed form

The W(CO)5 and Fe(CO)4 complexes of the bicyclic phosphirane 3,5,6,6-tetraphenyl-1-phospha-2-thiabicyclo[3.1.0]hex-3-ene undergo a thermal 2-phenylphosphirane --> dihydrophosphaisoindole ring expansion, while the free phosphirane suffers both a [2 + 1] cycloreversion and a fragmentation yielding a butadienyl sulfide.     

On transient behavior of non-premixed counter-flow diffusion flames within the REDIM based model reduction concept

In the present work non-stationary behavior of the counter-flow diffusion flame is examined in the context of the recently developed approach of model reduction called REaction–DIffusion Manifolds (REDIM) method. It is a natural extension of the ILDM approach which takes into account both the chemical reaction and the diffusion processes. It has been developed to treat both premixed and non-premixed regimes of combustion. In this work we investigate the ability of the concept to describe transient processes of extinction and re-ignition. A very simple flame configuration and transport model are considered in this current study for the sake of transparency because the main focus is on the transient and non-stationary behavior of flames. H₂/O₂/N₂ combustion system is considered in a non-premixed counter-flow diffusion 1D flame configuration. This study shows how the REDIM concept performs in the transient regimes; it interprets the effect of local extinction and reigniting phenomena using detailed and reduced models. It shows how the unstable/transient behavior of a detailed system can be successfully accounted with the help of the REDIM based reduced model.     

Analytical approach for CRLH-based antennas design

This paper presents an analytical model for CRLH (Composite Right-Left Handed) antennas preliminary design. The objective of this work is to develop a tool to estimate quickly the scattering and radiating characteristics of these CRLH-based structures. The analytical model provides thus a set of parameters which roughly fulfill desired requirements. Afterwards, the antenna designer can refine the CRLH-based antenna performances with full 3D electromagnetic simulation software.     

The extension of the ILDM concept to reaction–diffusion manifolds

In the present work, the method of simplifying chemical kinetics based on Intrinsic Low-Dimensional Manifolds (ILDMs) is modified to deal with the coupling of reaction and diffusion processes. Several problems of the ILDM method are overcome by a relaxation to an invariant system manifold (Reaction–Diffusion Manifold – REDIM). This relaxation process is governed by a multidimensional parabolic partial differential equation system, where, as an initial solution, an extended ILDM is used. Furthermore, a method for the solution and tabulation of the manifold is proposed in terms of generalized coordinates, with a subsequent procedure for the integration of the reduced system on the found manifold. This modification of the ILDM significantly improves the performance of the concept and allows us to extend its area of applicability. Illustrative comparative calculations of detailed and reduced models of flat laminar flames verify the approach.     

Pixel-by-pixel analysis of DCE MRI curve patterns and an illustration of its application to the imaging of the musculoskeletal system

Dynamic contrast enhanced (DCE) MRI is a widespread method that has found broad application in the imaging of the musculoskeletal (MSK) system. A common way of analyzing DCE MRI images is to look at the shape of the time-intensity curve (TIC) in pixels selected after drawing an ROI in a highly enhanced area. Although often applied to a number of MSK affections, shape analysis has so far not led to a unanimous correlation between these TIC patterns and pathology. We hypothesize that this might be a result of the subjective ROI approach. To overcome the shortcomings of the ROI approach (sampling error and interuser variability, among others), we created a method for a fast and simple classification of DCE MRI where time-curve enhancement shapes are classified pixel by pixel according to their shape. The result of the analysis is rendered in multislice, 2D color-coded images. With this approach, we show not only that differences on a short distance range of the TIC patterns are significant and cannot be appreciated with a conventional ROI analysis but also that the information that shape maps and conventional standard DCE MRI parameter maps convey are substantially different.     

Detailed investigation of ignition by hot gas jets

Experimental and numerical investigations of the ignition of hydrogen/air mixtures by jets of hot exhaust gases are reported. An experimental realisation of such an ignition process, where a jet of hot exhaust gas impinges through a narrow nozzle into a quiescent hydrogen/air mixture, possibly initiating ignition and combustion, is studied. High-speed laser-induced fluorescence (LIF) image sequences of the hydroxyl radical (OH) and laser Schlieren methods are used to gain information about the spatial and temporal evolution of the ignition process. Recording temporally resolved pressure traces yields information about ambient conditions for the process. Numerical experiments are performed that allow linking these observables to certain characteristic states of the gas mixture. The outcome of numerical modelling and experiments indicates the important influence of the hot jet temperature and speed of mixing between the hot and cold gases on the ignition process. The results show the quenching of the flame inside the nozzle and the subsequent ignition of the mixture by the hot exhaust jet. These detailed examinations of the ignition process improve the knowledge concerning flame transmission out of electrical equipment of the type of protection flameproof enclosure.     

Some Aspects of Time-Reversal in Chemical Kinetics

Chemical kinetics govern the dynamics of chemical systems leading towards chemical equilibrium. There are several general properties of the dynamics of chemical reactions such as the existence of disparate time scales and the fact that most time scales are dissipative. This causes a transient relaxation to lower dimensional attracting manifolds in composition space. In this work, we discuss this behavior and investigate how a time reversal effects this behavior. For this, both macroscopic chemical systems as well as microscopic chemical systems (elementary reactions) are considered.