Investigation of chemical looping combustion of natural gas at 1 MWth scale

Chemical looping combustion (CLC) is an advanced oxyfuel process that enables CO₂ capture with low efficiency penalty. CLC of gaseous fuels has successfully been demonstrated in several pilots up to 150 kW_th. Numerous oxygen carriers have been tested regarding fuel conversion performance and lifetime. This work is a scale-up study of gaseous fuel CLC to MW_th scale. A Ca-Mn-based oxygen carrier has been developed and manufactured in ton-scale prior to the present test. Investigations were conducted in a 1 MW_th CLC unit that was adapted to utilize natural gas as fuel. Stable CLC conditions were reached during tests with Ca-Mn-based material, and the transition to operation with ilmenite was studied. The fuel conversion was in the range of 80%. During operation, 99% of the unburned methane was converted in the post oxidation chamber. The solids circulation rate and the lifetime of solids were determined by means of solids samples from the process, which were investigated in terms of attrition and degree of oxidation. The solids circulation rate was 17 tons h^?1  MW^?1 which is higher than in former tests but lower compared to other units. The most important limiting factors of the fuel conversion are the low solids inventory of the fuel reactor and the oxygen carrier to fuel ratio that corresponds to the solids circulation.     

Spontaneous Crystallization of Perovskite Nanocrystals in Nonpolar Organic Solvents: A Versatile Approach for their Shape‐Controlled Synthesis

The growing demand for perovskite nanocrystals (NCs) for various applications has stimulated the development of facile synthetic methods. Perovskite NCs have often been synthesized by either ligand‐assisted reprecipitation (LARP) at room temperature or by hot‐injection at high temperatures and inert atmosphere. However, the use of polar solvents in LARP affects their stability. Herein, we report on the spontaneous crystallization of perovskite NCs in nonpolar organic media at ambient conditions by simple mixing of precursor–ligand complexes without application of any external stimuli. The shape of the NCs can be controlled from nanocubes to nanoplatelets by varying the ratio of monovalent (e.g. formamidinium⁺ (FA⁺) and Cs⁺) to divalent (Pb²⁺) cation–ligand complexes. The precursor–ligand complexes are stable for months, and thus perovskite NCs can be readily prepared prior to use. Moreover, we show that this versatile synthetic process is scalable and generally applicable for perovskite NCs of different compositions.     

Microstructured switchable mirror for polar molecules

By miniaturizing electrode geometries high electric fields can be produced using modest voltages. A planar array of 20 microm wide gold electrodes, spaced 20 microm apart, is made on a sapphire substrate. A voltage difference of up to 350 V is applied to adjacent electrodes, generating an electric field that decreases exponentially with distance from the substrate. This microstructured array can be used as a mirror for polar molecules and can be rapidly switched on and off. This is demonstrated by retro-reflecting a beam of state-selected ammonia molecules with a forward velocity of about 30 m/s.     

Aging is associated with increased collagen type IV accumulation in the basal lamina of human cerebral microvessels

Background  

Microvascular alterations contribute to the development of stroke and vascular dementia. The goal of this study was to evaluate age and hypertension related changes of the basal lamina in cerebral microvessels of individuals, who died from non-cerebral causes.     

Zur Theorie der stochastischen Beschleunigung. I

This work contains theoretical investigations on the stochastic acceleration in circular accelerators. The first part deals with the classical problem ofBurshtein, Kolomenskii andVeksler. This problem was formulated in a publication very clearly in 1955, but has not yet found an exact solution. The subject is the calculation of the probability that a charged particle is accelerated from the injection energy to the top energy of the apparatus (“probability of acceleration”), supposing that the particle has an equal chance at every circulation to increase or decrease its energy by a fixed amounteU ₀. The following investigation shows that this problem can be solved if properly formulated as a matrix equation, and that the solution is of a relatively simple closed form. This is the case, too, if the primary problem is extended by permitting particle losses during the acceleration process (“absorption”). The results are discussed, especially regarding the influence of absorption. Under certain conditions [(eU ₀ ²/SΣ (E _max?E _min)²] the probability of acceleration becomes independent of absorption and of the gap voltageU ₀.     

Optical rheology of biological cells

A step stress deforming suspended cells causes a passive relaxation, due to a transiently cross-linked isotropic actin cortex underlying the cellular membrane. The fluid-to-solid transition occurs at a relaxation time coinciding with unbinding times of actin cross-linking proteins. Elastic contributions from slowly relaxing entangled filaments are negligible. The symmetric geometry of suspended cells ensures minimal statistical variability in their viscoelastic properties in contrast with adherent cells and thus is defining for different cell types. Mechanical stimuli on time scales of minutes trigger active structural responses.     

Strategies for reliable automatic onset time picking of acoustic emissions and of ultrasound signals in concrete

Determining the onset of transient signals like seismograms, acoustic emissions or ultrasound signals is very time consuming if the onset is picked manually. Therefore, different approaches exist, especially in seismology. The concepts of the most popular approaches are summarized. An own approach adapted to ultrasound signals and acoustic emissions, based on the Akaike Information Criterion (AIC), is presented. The AIC-picker is compared to an automatic onset detection algorithm based on the Hinkley criterion and also adapted to acoustic emissions. Manual picks performed by an analyst are used as reference values. Both automatic onset detection algorithms are applied to ultrasound signals which are used to monitor the setting and hardening of concrete. They are also applied to acoustic emissions recorded during a pull-out test. The AIC-picker produces sufficient reliable results for ultrasound signals where the deviation from the manual picks varies between 2% and 4%. Concerning acoustic emissions, only 10% of the events result in a mislocation vector greater than 5mm. It can be shown that our AIC-picker is a reliable tool for automatic onset detection for ultrasound signals and acoustic emissions of varying signal to noise ratio.