Model-aided radiometric determination of photolysis frequencies in a sunlit atmosphere simulation chamber

In this work diurnal and seasonal variations of mean photolysis frequencies for the atmosphere simulation chamber SAPHIR at Forschungszentrum J&#252;lich are calculated. SAPHIR has a complex construction with UV permeable teflon walls allowing natural sunlight to enter the reactor volume. The calculations are based on external measurements of solar spectral actinic flux and a model considering the time-dependent impact of shadows from construction elements as well as the influence of the teflon walls. Overcast and clear-sky conditions are treated in a consistent way and different assumptions concerning diffuse sky radiance distributions are tested. Radiometric measurements inside the chamber are used for an inspection of model predictions. Under overcast conditions we obtain fractions of 0.74 and 0.67 of external values for photolysis frequencies <i>j</i>(NO₂) (NO₂+<i>h</i>&nu;&rarr;NO+O(³P)) and <i>j</i>(O¹D) (O₃+<i>h</i>&nu;&rarr;O₂+O(¹D)), respectively. On a clear sky summer day these values are time-dependent within ranges 0.65-0.86 and 0.60-0.73, for <i>j</i>(NO₂) and <i>j</i>(O¹D), respectively. A succeeding paper (Bohn et al., 2004) is dealing with an on-road test of the model approach by comparison with photolysis frequencies from chemical actinometry experiments within SAPHIR

Konstruktionen von Oberflächen mit aktiven Konturmodellen

Three-dimensional anatomical data are very important for medical diagnostics. It is often possible to characterize important properties of human organs represented in these data by a description of their surface, Examples of such properties are the location of the organs in the human body, location relative to other organs, size, shape and volume, and also the curvature of the surface. For a proper determination of these values an exact representation of the surface must be found. In this thesis, the concepts of active surfaces are used to calculate such a representation. By the application of user-given forces, a deformable template is fitted to a surface in an iterative process. This surface is implicitly given by the voxel-data, The process of deformation is guided by inner and outer energy terms. The inner energy is a measure of the stretching and the curvature of the template and is needed to minimize the distortion of the template in the deformation process. The outer energy is calculated from the measured voxel-data and ensures the fitting of the template to the data. Different possibilities of defining the energies and the derived forces are discussed. A discrete method as well as a method based on the principles of continuum mechanics are presented. The latter is discretized by the finte-element method. Furthermore a concept for the parallelization of the algorithm on a heterogeneous computersystem, coupled by a network, is presented. The algorithm has been tested and applied to the calculation of the mapping from the surface of the human brain onto the surface of a sphere. This transformation is non-linear and uniquely maps every point of the brain-surface to a point of a sphere. By means of this transformation it is possible to visualize several properties of the human brain-surface on a clearly arranged general ma