Structure and spatial consistency of network-based space layouts for building and product design

Network-based space layouts are schematic models of whole spaces, subspaces, and related physical elements. They address diverse space modeling needs in building and product design. A schema (data model) for network-based space layouts is defined that is influenced by existing space schemas. Layout elements and selected spatial relations form a geometric network. The network is embedded in 3-space and facilitates analysis with graph and network algorithms. Spatial constraints on layout elements and spatial relations extend the schema to support spatial consistency checking. Spatially consistent layouts are required for reliable network analysis and desirable for layout modification operations. An operation is introduced that evaluates spatial constraints to detect and semi- or fully-automatically resolve spatial inconsistencies in a layout. A layout modeling system prototype that includes proof-of-concept implementations of the layout schema extended by spatial constraints and the inconsistency resolution operation is described. Layouts of a floor of an office building and a rack server cabinet have been modeled with the system prototype.     

Homogenization and crystallization of histidine ammonia-lyase by exchange of a surface cysteine residue

Histidase (histidine ammonia-lyase, EC 4.3.1.3) from Pseudomonasputida was expressed in Escherichia coli and purified. In theabsence of thiols the tetrameric enzyme gave rise to undefinedaggregates and suitable crystals could not be obtained. Thesolvent accessibility along the chain was predicted from theamino acid sequence. Among the seven cysteines, only one waslabeled as `solvent-exposed'. The exchange of this cysteineto alanine abolished all undefined aggregations and yieldedreadily crystals diffracting to 1.8 Å resolution.     

A channel flow cell system specifically designed to test the efficiency of redox shuttles in dye sensitized solar cells

The construction and use of a thin layer flow cell test system employing a TiO₂ working electrode, a platinum quasi-reference electrode and the ruthenium dye (H₂-dcbpy)Ru(NCS)₂ (H₂-dcbpy=2,2′-bipyridine-4,4′-dicarboxylic acid) is described. The efficient design enables significant advantages to be gained over presently available procedures for the measurement of photocurrents of dye-sensitized solar cells. The widely used iodide/triiodide redox shuttle system has been investigated over a wide range of conditions. A linear dependence of photocurrent on cation radius was revealed. Under certain conditions, the photocurrent measured in the presence of the Li⁺ cation is five times larger than when the (C₄H₉)₄N⁺ cation is used. Additionally, the addition of low concentrations of cations with small diameters has a significant catalytic enhancement effect on the photocurrent. Other redox shuttles, based on ferrocene, thiocyanate, triiodide and bromide, were tested for their performance in the flow cell and compared to iodide. However, despite some apparent thermodynamic advantages, the photocurrents obtained with these redox shuttles were more than two orders of magnitude lower than those measured with iodide. This finding implies that the efficiency of redox shuttles is limited by kinetic restraints rather than their thermodynamic properties and confirms that the iodide/triiodide system is the dominant redox shuttle.     

Design and analysis of a state observer for the temperature front of a retification column

In order to achieve optimal energy-saving, load-dependent operation of rectification columns, development and implementation of model-based control concepts are necessary. This paper reports on the design and step-by-step testing of a state observer for the estimation of two state variables which cannot be measured directly, namely the vapour rate and the location of mass transfer zone (temperature front) in the stripping section of a production column. The procedure is described, and the relevant simulation and operation results are presented and discussed. Initial experience, gained when the concept was put into practical operation, is reported.