Solving k-center Clustering (with Outliers) in MapReduce and Streaming, almost as Accurately as Sequentially.

Center-based clustering is a fundamental primitive for data analysis and becomes very challenging for large datasets. In this paper, we focus on the popular k-center variant which, given a set S of points from some metric space and a parameter k0, the algorithms yield solutions whose approximation ratios are a mere additive term \u3f5 away from those achievable by the best known polynomial-time sequential algorithms, a result that substantially improves upon the state of the art. Our algorithms are rather simple and adapt to the intrinsic complexity of the dataset, captured by the doubling dimension D of the metric space. Specifically, our analysis shows that the algorithms become very space-efficient for the important case of small (constant) D. These theoretical results are complemented with a set of experiments on real-world and synthetic datasets of up to over a billion points, which show that our algorithms yield better quality solutions over the state of the art while featuring excellent scalability, and that they also lend themselves to sequential implementations much faster than existing ones

Real-time control of reactive magnetron-sputter deposited optical filters by in situ spectroscopic ellipsometry

In situ spectroscopic ellipsometry was applied for real-time control of the reactive magnetron sputter process of optical coatings on glass. Single transparent films of SiO2, Si3N4 and SiOxNy with varying compositions as well as multilayer optical filters on transparent thick floatglass were fabricated. The process control system is based on an optical monitor for the deposition rate and the film composition in combination with a plasma control setup. The latter was developed for the short-term stabilization of the mid-frequency magnetron sputter process. The quality of the filters deposited using the control system is demonstrated by comparing the calculated reflectivity and transmission with the experimental ex situ data. The investigations show that for silicon oxynitride films, the combination of plasma control with ellipsometric control can be used for controlling the stoichiometry of the growing film

Optimization of the reflectivity of magnetron sputter deposited silver films

Silver films were deposited using direct current (dc) and midfrequency (MF) magnetron sputter deposition processes on floatglass in order to achieve maximum reflectivity over the entire visual and infrared spectral range. The films were investigated by means of ex situ and in situ spectroscopic ellipsometry, spectral photometry, electrical conductivity measurements, and atomic force microscopy. The following deposition parameters were varied: midfrequency and dc technique, power density, sputtering pressure, substrate temperature, sputtering gas (Ar, Kr, Ne), oxygen residual gas, and film thickness. With the aid of in situ spectroscopic ellipsometry, it can be shown that for certain process parameters an optimum layer thickness exists for achieving a maximum reflectivity in the visual spectral range. With increasing thickness, optical losses which are due to the formation of larger grains come into play. This optimum layer thickness is smaller for the films deposited by MF sputtering, indicating a smoother surface and smaller grain sizes compared to that of the dc mode. As a maximum value, a reflectivity of R=99.3% is achieved, which is close to the theoretical value, which was determined from the Drude fit parameters with respect to the resistivity. The resistivity of this film was found to be rho =2.4 mu Omega cm. The measured reflectivity of the sputter deposited films is comparable to e-beam evaporated silver films