ERROR ESTIMATION, GRID SELECTION AND CONVERGENCE VERIFICATION IN LARGE EDDY SIMULATION

Large eddy simulation (LES) is a modeling approach to simulation of turbulence, in which the large and energy containing eddies are directly resolved, while the smaller scales are modeled. The ``coarse-graining'' length scale (the length scale below which the turbulent eddies are modeled) is an important modeling parameter that is directly tied to the computational grid. As a result, the LES grid controls both the numerical and modeling errors and in most cases (given that the LES model is consistent) becomes the most important factor in determining the accuracy of the solution. The main goal of this dissertation is to enable a systematic approach to grid selection and convergence-verification in LES. Systematic grid selection consists of five essential ingredients: (i) an ``error-indicator'' that identifies the regions of error generation, (ii) some knowledge of the directional structure of error generation (i.e., an anisotropic measure of error generation at each location), (iii) a model that describes the connection between the error generation and the filter/grid resolution (i.e., how it changes with a change in the resolution), (iv) criteria that describe the most ``optimal'' distribution of the error-indicator in space and in direction, and (v) a robust method for convergence-verification. Items (i), (ii), (iv) and (v) are all addressed in this dissertation, while item (iii) has not been a subject of extensive research here (because of its somewhat lower importance compared to the other four). Three error-indicators are introduced that are different in terms of their underlying assumptions, complexity, potential accuracy, and extensibility to more complex flows and more sophisticated formulations of the problem of ``optimal'' grid selection. Two of these error-indicators are inherently anisotropic, while the third one is only a scalar but can be combined with either of the other two to enable anisotropic error-estimation. The ``optimal'' distributions of these error-indicators are discussed in detail, that, combined with a model to connect the error-indicator and the grid/filter resolution, describe our ``optimal'' grid selection criteria. Additionally, a more robust approach for convergence-verification in LES is proposed, and is combined with error-estimation and ``optimal'' grid selection/adaptation to form a systematic algorithm for large eddy simulation. The proposed error-estimation, grid selection, and convergence-verification methods are tested on the turbulent channel flow and the flow over a backward-facing step, with good results in all cases, and grids that are quite close to what is know as ``best practice'' for LES of these flows

Subcutaneous panniculitis-like T-cell lymphoma

Review on Subcutaneous panniculitis-like T-cell lymphoma, with data on clinics and the genes possibly involved

Erythroderma: A clinical study of 97 cases

BACKGROUND: Erythroderma is a rare skin disorder that may be caused by a variety of underlying dermatoses, infections, systemic diseases and drugs. METHODS: We reviewed the clinical, laboratory and biopsy material of 97 patients diagnosed with erythroderma who were treated in our department over a 6-year period (1996 through 2002). RESULTS: The male-female ratio was 1.85:1. The mean age at diagnosis was 46.2 years. The most common causative factors were dermatoses (59.7%), followed by drug reactions (21.6%), malignancies (11.3%) and idiopathic causes (7.2%). Carbamazepine was the most common drug (57.1%). The best clinicopathologic correlation was found in cutaneous T-cell lymphoma and pityriasis rubra pilaris related erythroderma. Apart from scaling and erythema that were present in all patients, pruritus was the most common finding (97.5%), followed by fever (33.6%), lymphadenopathy (21.3%), edema (14.4%) and hyperkeratosis (7.2%). CONCLUSION: This study outlines that underlying etiologic factors of erythroderma may show geographic variations. Our series had a high percentage of erythroderma secondary to preexisting dermatoses and a low percentage of idiopathic cases. There was no HIV-infected patient among our series based on multiple serum antibody tests. The clinical features of erythroderma were identical, irrespective of the etiology. The onset of the disease was usually insidious except in drug-induced erythroderma, where it was acute. The group associated with the best prognosis was that related to drugs

Assessment of grid anisotropy effects on LES models with different length scales

The effect of the eddy viscosity length scale on the accuracy of large eddy simulation (LES) is investigated for several commonly used subgrid models. Multiple types of length scales are considered, both purely geometric length scales (including the cube-root of the cell volume and the maximum cell dimension) and length scales that depend on both the grid and the flow. The assessment is focused on how the LES prediction changes for increasingly anisotropic grids, in forced isotropic turbulence and channel flow at high Reynolds number. While some length scales perform better than others, the main conclusion is that no single length scale produces LES results that are completely independent of the grid anisotropy. Since every model and length scale tested produces accurate results on at least one grid and inaccurate results on at least one other grid, the study shows clearly the need to assess LES models on multiple grids with multiple different anisotropy ratios

ABO blood groups, rhesus factor and pemphigus

Background: Pemphigus is an autoimmune blistering disease of the skin and mucous membranes with significant mortality and morbidity. Genetic factors are known to be involved in pemphigus. Several studies have reproducibly shown significant associations of ABO blood groups with various autoimmune human diseases. Aim: To study the relationship between ABO and Rhesus (D) blood groups and pemphigus in Iranian patients. Materials and Methods: Data on age, sex, ABO and Rhesus blood type and clinicopathological diagnosis of the patients with pemphigus were collected. A total of 573 patients with pemphigus were assessed for their association with ABO or Rhesus (D) blood groups and compared with the normal population in the area. Results: The distribution of ABO and Rhesus blood groups in patients with pemphigus was similar to the normal local population in Iran. No relationship was found between ABO or Rhesus blood groups and the phenotype of pemphigus. Conclusion: It appears that there is no association between ABO or Rhesus (D) blood groups and the frequency of pemphigus variants in comparison with normal population in Iran