A high resolution synchrotron x-ray study of the weakly-incommensurate phase of high stage bromine-intercalated graphite

We report the results of a high resolution synchrotron x-ray scattering study of the weakly incommensurate stripe domain phase of high stage bromine-intercalated graphite. The translational order in this system is two-dimensional in nature.) We demonstrate power-law behaviour at five harmonics (G) of the mass density wave, and confirm the scaling of the structure factor withG ². Our results are consistent with recent theories of the two dimensional uniaxial commensurate-incommensurate transition, which are based on an entropically wandering domain wall picture of the incommensurate phase. We demonstrate that, in this system, the domain walls have a width much less than their separation so that significant molecular displacements from the commensurate sites occur within a unit cell. Close to the transition, we observe hysteresis.     

Comparison between two sufficient conditions for improvement of an optimal steady-state process by periodic operation

Two sufficient conditions for improvement of performance by cycling beyond that obtained at the best steady state are compared. It is shown that Condition I, which is derived from relaxed steady-state analysis, is always stronger than Condition II, which results from the maximum principle. That is, in every case in which Condition II guarantees improvement, Condition I does also. However, there are examples where Condition I assures improvement, while Condition II fails to indicate the possibility of greater performance by cyclic operation.     

Ein Beitrag zur Meßmethodik in der ElektronenstrahlMikroanalyse

Zusammenfassung Unter Berücksichtigung des Auflösungsvermögens des Elektronenstrahl-Mikroanalysators wurde eine allgemein anwendbare Meßmethode, das gezielte Linienscanning, entwickelt. Damit ist es möglich, Durchstrahlungseffekte zu erkennen und nur solche Analysenergebnisse auszuwerten, die signifikant für die zu analysierende Phase sind. Für den Fall des Vorliegens genügend großer Analysenbereiche ist die mit geringerem Zeitaufwand verbundene Schablonenmethode geeignet.Ein Vergleich der beiden Meßmethoden bei der Bestimmung der gegenseitigen Löslichkeit von MgO und CaO im Sinterdolomit ergab, daß das gezielte Linienscanning bessere Ergebnisse liefert als die Schablonenmethode.

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Contribution to the measurement methodology in electron beam microanalysis

Summary With consideration of the resolving capability of electron beam microanalysis, a measuring methodology has been developed that is generally applicable, namely directed line scanning. It thus becomes possible to recognize irradiation effects and to evaluate only such analytical findings that are of significance to the phase being analyzed. The pattern method that involves less consumption of time is suitable for those cases that involve with sufficiently greater analytical ranges.A comparison of the two measuring methods in the determination of the mutual solubility of MgO and CaO in sinter dolomite showed that directed line scanning gives better results than the pattern method.

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Für anregende Diskussionen dieser Probleme möchte ich dem Vorstand des Institutes, Herrn Prof. Dipl.-Ing. Dr.H. Malissa, meinen Dank aussprechen.     

A short efficient synthesis of 19-norandrost-4-ene-3,17-dione

A three-step conversion of 3aα-H-4α-(3′-propionic acid)-7aβ-methylhexahydro-1,5-indanedione into 19-norandrost-4-ene- 3,17-dione is described.     

Nuclear level mixing (NLM) experiments on polarized Na atoms chemisorbed on a W(110) surface

Nuclear level mixing (NLM) experiments were performed on polarized Na atoms chemisorbed on a clean and oxygen covered W(110) surface. Components of the electric field gradient tensor generated by the electronic environment of the nucleus were determined. Advantages and disadvantages of this method if compared to NMR measurements are listed briefly. The results are discussed in the framework of simple models.     

Dynamics of an Ising chain under local excitation: a scanning tunneling microscopy study of Si(100) dimer rows at 5 K

An extension of the classical Ising model to a situation including a source of spin-flip excitations localized on the scale of individual spins is considered. The scenario is realized by scanning tunneling microscopy of the Si(100) surface at low temperatures. Remarkable details, corresponding to the passage of phasons through the tunnel junction, are detected by the STM within the short span between two atoms comprising an individual Si dimer.     

A forest building process on simple graphs

Consider the following process on a simple graph without isolated vertices: order the edges randomly and keep an edge if and only if it contains a vertex which is not contained in some preceding edge. The resulting set of edges forms a spanning forest of the graph.The probability of obtaining $k$ components in this process for complete bipartite graphs is determined as well as a formula for the expected number of components in any graph. A generic recurrence and some additional basic properties are discussed.     

A comparative study on large scale kernelized support vector machines

Kernelized support vector machines (SVMs) belong to the most widely used classification methods. However, in contrast to linear SVMs, the computation time required to train such a machine becomes a bottleneck when facing large data sets. In order to mitigate this shortcoming of kernel SVMs, many approximate training algorithms were developed. While most of these methods claim to be much faster than the state-of-the-art solver LIBSVM, a thorough comparative study is missing. We aim to fill this gap. We choose several well-known approximate SVM solvers and compare their performance on a number of large benchmark data sets. Our focus is to analyze the trade-off between prediction error and runtime for different learning and accuracy parameter settings. This includes simple subsampling of the data, the poor-man’s approach to handling large scale problems. We employ model-based multi-objective optimization, which allows us to tune the parameters of learning machine and solver over the full range of accuracy/runtime trade-offs. We analyze (differences between) solvers by studying and comparing the Pareto fronts formed by the two objectives classification error and training time. Unsurprisingly, given more runtime most solvers are able to find more accurate solutions, i.e., achieve a higher prediction accuracy. It turns out that LIBSVM with subsampling of the data is a strong baseline. Some solvers systematically outperform others, which allows us to give concrete recommendations of when to use which solver.