Experimentelle und analytische Untersuchungen zum Zündverhalten stark verdünnter C2H2/O2-Gemische

Zusammenfassung Das Zündverhalten homogener Gasgemische bestehend aus Argon mit C₂H₂+O₂-Anteilen von 2% wird bei ?quivalenzverh?ltnissen von ϕ=0,2; 0,5; 1,0 und 2,0 hinter Sto?wellen experimentell untersucht. Kriterium für das Ende der Induktionsperiode ist das starke Ansteigen der OH-Konzentration, die durch Absorptions- oder Emissionsverfahren gemessen wird. Die Gaszust?nde sind in einem Temperaturbereich 1000 K≦T≦1560 K bei Drücken zwischen 0,6 und 1,3 bar variiert worden. Die Me?werte lassen sich durch eine Korrelationsgleichung darstellen mit τ in μs und Konzentrationen in mol cm⁻³. Mit Hilfe eines reaktionskinetischen Modells bestehend aus 29 Elementarreaktionen werden Computersimulationen des Zündverhaltens der verschiedenen Gemische durchgeführt. Die übereinstimmung zwischen berechneten und gemessenen OH-Induktionszeiten erscheint zufriedenstellend, wenn man bedenkt, da? keine kinetische Anpassung vorgenommen worden ist.     

Value and limits of μ-CT for nondemineralized bone tissue processing

An experimental approach was performed on 20 giant rabbits to establish the possibilities and limitations of μ-CT for routine processing of nondemineralized bone tissue. Hydroxyapatite (HA) or β-tricalciumphosphate (β-TCP) bead implants or a melange of both, microchambered and solid, were implanted into a standardized and precise defect in the patellar groove. The bone-healing phase was chosen for the histology considering 1 or 2 days, and 2, 3, and 6 weeks. Normal X-ray and μ-CT were applied on all specimens; five specimens in the 6-week stage were additionally processed according to the full range of conventional nondemineralized bone processing methods. μ-CT increased the possibilities of nondemineralized histology with respect to bone morphometry and a complete sequence of sections, thus providing a complete analysis of the bone response. μ-CT was limited in differentiating bone quality, cell analyses, and mineralization stages. The investigation based on normal X-rays is limited to defining integration and excluding the fibrous and bony encapsulation of loose implants. μ-CT allows a 3D evaluation of newly formed bone which is clearly marked against the ceramic implant. It does not allow, however, for the differentiation between woven and lamellar bone, the presentation of the canalicular lacunar system, or on the cell level, revealing canaliculi or details of the mineralization process which can be documented by high-resolution microradiography. Titer dynamics of bone formation remains the domain of polychromatic sequential labeling. The complete sequence of μ-CT slices enhances the possibilities for routine histology, tremendously allowing to the focus on detail histology to topographically well-defined cuts, thus providing more precise conclusions which take into consideration the whole implant.     

Inhibitory deficits in older adults: List-method directed forgetting revisited.

In list-method directed forgetting, participants are cued to intentionally forget a previously studied list while remembering a subsequently presented 2nd list. Results from prior research are inconclusive on whether older adults show deficits in this type of task. In 3 experiments, the authors reexamined the issue and compared younger and older adults' responsiveness to the forget cue. Across the experiments, the forget cue was varied within and between participants, the 2 lists were unrelated and related to each other, and recall of the lists was required simultaneously and successively. In none of the 3 experiments did any age-related difference in directed forgetting performance emerge. List-method directed forgetting is assumed to reflect retrieval inhibition. The present results thus challenge the proposal of a general inhibitory deficit in older adults' memory performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Process optimization for efficient biomediated PHA production from animal-based waste streams

Conventional polymers are made of crude oil components through chemical polymerization. The aim of the project ANIMPOL is to produce biopolymers by converting lipids into polyhydroxyalkanoates (PHA) in a novel process scheme to reduce dependence on crude oil and decrease greenhouse gas emissions. PHA constitutes a group of biobased and biodegradable polyesters that may substitute fossil-based polymers in a wide range of applications. Waste streams from slaughtering cattle are used as substrate material. Lipids from rendering are used in this process scheme for biodiesel production. Slaughtering waste streams may also be hydrolyzed to achieve higher lipid yield. Biodiesel then is separated into a high- and low-quality fraction. High-quality biodiesel meets requirements for sale as fuel and low quality is used for PHA production as carbon source. Selected offal material is used for acid hydrolysis and serves as a source of organic nitrogen as well as carbon source for PHA-free biomass with high production rate in fermentation process. Nitrogen is a limiting factor to control PHA production during the fermentation process. It is available for bacterial growth from hydrolyzed waste streams as well as added separately as NH₄OH solution. Selected microbial strains are used to produce PHA from this substrate. The focus of the paper is about an overview of the whole process with the main focus on hydrolysis, to look for the possibility of using offal hydrolysis as an organic nitrogen substitute. The process design is optimized by minimizing waste streams and energy losses through cleaner production. Ecological evaluation of the process design will be done through footprint calculation according to Sustainable Process Index methodology.     

Amplitude and phase recovery of rotationally symmetric beams

Two methods are presented for the amplitude and phase recovery of optical beams with rotational symmetry. These are the tomographic method based on the ambiguity function and the one-step wavefront recovery based on the measurement of a phase-space distribution closely related to the Wigner distribution function. The results obtained from these two methods are compared, and the appropriateness of using either one of them for specific situations is discussed.     

Solving constrained combinatorial optimization problems via importance sampling in the grand canonical ensemble

Combinatorial optimization problems are usually NP-hard. These problems are generally tackled by heuristic or branch-and-bound methods. The aim of this paper is to tackle constrained combinatorial optimization problems by importance Monte Carlo sampling. For this, we show that every constrained combinatorial optimization problem can be represented by a thermodynamical system in a suitable grand canonical ensemble given by the quantities of temperature, volume, and chemical potential. In order to find optimum solutions of the optimization problem, the grand canonical Monte Carlo method can be applied to the corresponding thermodynamical system. This method will amount to importance sampling, i.e. good feasible solutions of the optimization problem will be preferably sampled, provided that the intensive quantities of temperature and chemical potential are appropriately chosen. Our approach extends the standard importance sampling approach in the canonical ensemble to tackle unconstrained combinatorial optimization problems. The knapsack problem is considered as a prototype example.