The Role of FGF Signaling in Retinal Development

The development of the retina is a precise balance between intrinsic competence and extrinsic factors. This interplay is known to regulate the generation of cell types in the developing retina and similar mechanisms have been found in other regions of the CNS. In the developing retina, FGFs are a large family of secreted polypeptide growth factors. Fgf15 is the major Fgf expressed during retinal development in mice. Fgf15 is an example of an FGF that has been shown to control proliferation, cell fate specification, differentiation and migration during development. In this thesis I used analysis of specific genes throughout retinal development, as well as characterization of Fgf receptor mutant mice and Fgf15 knockout explant retina. The preliminary data presented evidence that Fgf15 is a good candidate for an extrinsic factor that may regulate retinal progenitor cell proliferation in the developing retina. When combined with the expression data, these findings suggest that in the absence of Fgf signaling, retinal progenitor cells fail to complete their normal developmental program

Particle Population Balances in a Refuse Derived Fuel Fired Circulating Fluidized Bed Combustor

With a population balance model the effects of changes in the operation of a circulating fluidized bed combustor on the bed inventory are simulated. Feeding, discharge and recirculation of solids as well as separation effects in the combustion chamber and in the cyclone are considered. The model predictions are compared with measurements at the refuse-derived fuel incineration plant Neumuenster. The simulation shows that by sieving of the ash withdrawn from the bottom of the combustion chamber and recycling the fine fractions to the bed the non-elutriable fraction of the ash in the bottom zone of the circulating fluidized bed (CF B) can be kept at a low level

Dynamic flowsheet simulation of gas and solids flows in a system of coupled fluidized bed reactors for chemical looping combustion

A novel flowsheet simulation environment is applied to the Chemical Looping Combustion of solid fuels in order to capture dynamic behavior of fluid dynamics inside the system. The process itself is carried out in the majority of cases in a pair of strongly coupled fluidized bed reactors. The plant operated at the TUHH, which is simulated there, comprises a circulating fluidized bed air reactor and a two-stage bubbling bed fuel reactor demonstrated in the Figure. The modelled riser of the circulating fluidized bed system consists of a dense bottom phase and a dilute upper part. The fuel reactors are implemented bubbling bed reactors with a freeboard of elutriated particles and a dense bubbling bed with two phases. The cyclone is modelled according to Muschelknautz. The two loop seals are considered as divided bubbling beds. Please click Additional Files below to see the full abstract

Catalyst Attrition in the CFB Riser

Catalyst attrition in the CFB riser was experimentally investigated in a pilot scale CFB system consisting of a 400 mm diameter riser with a height of 15 m, a return leg and a two-stage cyclone separation. The catalyst loss of the CFB system was measured. In order to discern between attrition occurring in the cyclones and in the riser the system was simulated by a population balance approach which takes the separation efficiency of the cyclone system into account. On the basis of the experimental investigation an empirical correlation for catalyst attrition in the CFB riser has been developed which accounts for the influence of the gas velocity and the catalyst mass in the riser

CHALLENGES WITH THE COUPLING OF FLUIDIZED BEDS FOR CHEMICAL LOOPING COMBUSTION

In the present work the system of interconnected fluidized bed reactors of a Chemical Looping Combustion (CLC) process is simulated in pilot plant scale and 100 MWth scale. Attrition models, derived from small scale laboratory experiments, are employed to predict the behavior of a large scale CLC process in terms of attrition and oxygen carrier (OC) losses. Realistic circulation mass flows of OC are calculated and the sources of the losses are further investigated. Different arrangements of cyclones are evaluated for their potential to improve the solids recovery. For example the introduction of a second-stage cyclone separation for the air reactor reduces the OC losses significantly