The basic aim of chemistry experiments of transactinide elements (TAN) is to establish their place in the periodic table of the elements, i.e. to determine if their chemical behavior is similar to the one of supposed homologs. In this contribution I will try to give an overview of all chemical experiments on element 108, hassium (Hs) that have been reported to date. Based on the systematics of the periodic table, Hs is expected to be a member of group 8 and therefore homologous to osmium (Os) and ruthenium (Ru). As a member of the transactinide series, its experimental investigation is complicated by low production cross-sections and short half-lives. It has therefore been successfully investigated only recently. Already in the seventies of the last century, several authors mentioned the tetroxides of the two heavier group 8 elements, Ru and Os, to be very outstanding compounds with respect to their unusually high volatility. A possible HsO{sub 4} was considered suitable for isolating Hs from unwanted by-products of the nuclear production reaction. While RuO{sub 4}4 is rather unstable, OsO{sub 4} is well-known to be a stable compound and is widely used in organic chemistry. Recent theoretical calculations on the electronic structure and properties …

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Now in its 10th year, the twice-yearly TOP500 list of supercomputers serves as a ''Who's Who'' in the field of High Performance Computing (HPC). The TOP500 list was started in 1993 as a project to compile and publish twice a year a list of the most powerful supercomputers in the world. But it is more than just a ranking system and serves as major source of information to analyze trends in HPC. The list of manufacturers active in this market segment has changed continuously and quite dramatically during the 10 year history of this project. And while the architectures of the systems in the list have also seen a constant change, it turns out that the overall increase in the performance levels recorded is rather smooth and predictable. HPC performance levels grow exponentially. The most important single factor for this growth is - of course the increase of processor performance described by Moore's Law. However, the TOP500 list clearly illustrates that HPC performance has actually outpaced Moore's Law, due to the increasing processor numbers in HPC systems. On the other hand changes in computer architecture make it more and more of a challenge to achieve high performance efficiencies in the …

Iterative image estimation methods have been widely used in emission tomography. Accurate estimate of the uncertainty of the reconstructed images is essential for quantitative applications. While theoretical approach has been developed to analyze the noise propagation from iteration to iteration, the current results are limited to only a few iterative algorithms that have an explicit multiplicative update equation. This paper presents a theoretical noise analysis that is applicable to a wide range of preconditioned gradient type algorithms. One advantage is that proposed method does not require an explicit expression of the preconditioner and hence it is applicable to some algorithms that involve line searches. By deriving fixed point expression from the iteration based results, we show that the iteration based noise analysis is consistent with the xed point based analysis. Examples in emission tomography and transmission tomography are shown.