Abstract. The cancer stem cell hypothesis suggests that mutated melanocyte stem cells are present in skin as precursors of melanoma cells. Nestin and CD133 have been described as markers of melanocytic stem cells. The aim of this study was to establish if melanocytic stem cells could have a prognostic significance in melanoma progression. An immunohistochemical study for nestin and CD133 was performed in 130 primary tumors and 32 nodal metastasis biopsy specimens to evaluate possible differences, and to compare the results with survival data and clinicopathological variables. Nestin was expressed in cytoplasm of nonpigmented tumor cells and in endothelial cells, especially at the invading tumor front. Nestin staining in stage I and II (according to the American Joint Committee on Cancer Staging system) melanoma patients significantly predicted poor survival (log-rank test, P=0.037), with lower survival rates in cases with nestin positivity in both tumoral and endothelial cells. CD133 staining was not associated with survival. There were no significant differences in nestin or CD133 expression between primary tumors and metastases. These results suggest that nestin expression in both tumoral and endothelial cells may be considered an important early prognostic marker in melanoma.
Early Tokamaks with circular cross-section plasmas were intrinsically vertically stable and no problems were reported on the control of the vertical position. However, the new concept of vertically elongated plasma cross-section with benefits to the energy confinement time led to vertical instabilities. Such instabilities can only be overcome by means of a complex closed feedback loop control system with a vertical position measurement, signal processing, control algorithm, power supplies and active actuating coils. The Tokamak Configuration Variable (TCV), with a powerful vertical position control system, with fast power supplies capable of response times under 0.1 ms, permits the stabilization of highly elongated plasmas. With the introduction of the new Advanced Plasma Control System (APCS) in the TCV a new vertical position observer was built to further explore the capabilities of the new system and solve the limitations that were detected by the introduction in the feedback loop of signal digitalization. The need for a new measure of the plasma vertical position is discussed as well as the method for building the observer and the validation of the measured position which is compared with the previous methods and measures.A summary of the ongoing work is made. We also discuss its aim and the goals that are expected to be achieved by exploring the new digital non-linear control algorithm capabilities of APCS.
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