Machine learning plasma-surface interface for coupling sputtering and gas-phase transport simulations

Thin film processing by means of sputter deposition inherently depends on the interaction of energetic particles with a target surface and the subsequent particle transport. The length and time scales of the underlying physical phenomena span orders of magnitudes. A theoretical description which bridges all time and length scales is not practically possible. Advantage can be taken particularly from the well-separated time scales of the fundamental surface and plasma processes. Initially, surface properties may be calculated from a surface model and stored for a number of representative cases. Subsequently, the surface data may be provided to gas-phase transport simulations via appropriate model interfaces (e.g., analytic expressions or look-up tables) and utilized to define insertion boundary conditions. During run-time evaluation, however, the maintained surface data may prove to be not sufficient. In this case, missing data may be obtained by interpolation (common), extrapolation (inaccurate), or be supplied on-demand by the surface model (computationally inefficient). In this work, a potential alternative is established based on machine learning techniques using artificial neural networks. As a proof of concept, a multilayer perceptron network is trained and verified with sputtered particle distributions obtained from transport of ions in matter based simulations for Ar projectiles bombarding a Ti-Al composite. It is demonstrated that the trained network is able to predict the sputtered particle distributions for unknown, arbitrarily shaped incident ion energy distributions. It is consequently argued that the trained network may be readily used as a machine learning based model interface (e.g., by quasi-continuously sampling the desired sputtered particle distributions from the network), which is sufficiently accurate also in scenarios which have not been previously trained

RNAhybrid: microRNA target prediction easy, fast and flexible

In the elucidation of the microRNA regulatory network, knowledge of potential targets is of highest importance. Among existing target prediction methods, RNAhybrid [M. Rehmsmeier, P. Steffen, M. Höchsmann and R. Giegerich (2004) RNA, 10, 1507–1517] is unique in offering a flexible online prediction. Recently, some useful features have been added, among these the possibility to disallow G:U base pairs in the seed region, and a seed-match speed-up, which accelerates the program by a factor of 8. In addition, the program can now be used as a webservice for remote calls from user-implemented programs. We demonstrate RNAhybrid's flexibility with the prediction of a non-canonical target site for Caenorhabditis elegans miR-241 in the 3′-untranslated region of lin-39. RNAhybrid is available at

Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors

We develop an understanding of the anomalous metal state of the parent compounds of recently discovered iron based superconductors starting from a strong coupling viewpoint, including orbital degrees of freedom. On the basis of an intermediate-spin (S=1) state for the Fe^{2+} ions, we derive a Kugel-Khomskii spin-orbital Hamiltonian for the active t_{2g} orbitals. It turns out to be a highly complex model with frustrated spin and orbital interactions. We compute its classical phase diagrams and provide an understanding for the stability of the various phases by investigating its spin-only and orbital-only limits. The experimentally observed spin-stripe state is found to be stable over a wide regime of physical parameters and can be accompanied by three different types of orbital orders. Of these the orbital-ferro and orbital-stripe orders are particularly interesting since they break the in-plane lattice symmetry -- a robust feature of the undoped compounds. We compute the magnetic excitation spectra for the effective spin Hamiltonian, observing a strong reduction of the ordered moment, and point out that the proposed orbital ordering pattern can be measured in resonant X-ray diffraction.Comment: 16 pages, 12 figure

Adsorption studies of DNA origami on silicon dioxide

Self-assembled DNA nanostructures promise low-cost ways to create nanoscale shapes. DNA nanostructures can also be used to position particles with nanometer precision. Yet, reliable and low-cost ways of integrating the structures with MEMS technology still have to be developed and innovations are of great interest to the field. We have examined in detail the adherence of DNA origami tiles on silicon oxide surfaces of wafers in dependence on pH-value and magnesium ion concentration. The results of this work will help to pursue new strategies of positioning DNA nanostruc-tures on SiO2. Precise control over the strength of structure-surface adhesion is a prerequisite of relia-ble processes

RNA Movies 2: sequential animation of RNA secondary structures

RNA Movies is a simple, yet powerful visualization tool in likeness to a media player application, which enables to browse sequential paths through RNA secondary structure landscapes. It can be used to visualize structural rearrangement processes of RNA, such as folding pathways and conformational switches, or to browse lists of alternative structure candidates. Besides extending the feature set, retaining and improving usability and availability in the web is the main aim of this new version. RNA Movies now supports the DCSE and RNAStructML input formats besides its own RNM format. Pseudoknots and ‘entangled helices’ can be superimposed on the RNA secondary structure layout. Publication quality output is provided through the Scalable Vector Graphics output format understood by most current drawing programs. The software has been completely re-implemented in Java to enable pure client-side operation as applet and web-start application available at the Bielefeld Bioinformatics Server http://bibiserv.techfak.uni-bielefeld.de/rnamovie

A tip-based source of femtosecond electron pulses at 30keV

We present a nano-scale photoelectron source, optimized towards ultrashort pulse durations and well-suited for time-resolved diffraction experiments. A tungsten tip, mounted in a suppressor-extractor electrode configuration, allows the generation of 30 keV electron pulses with an estimated pulse duration of 37 fs at the gun exit. We infer the pulse duration from particle tracking simulations, which are in excellent agreement with experimental measurements of the electron-optical properties of the source. We furthermore demonstrate femtosecond laser-triggered operation. Besides the short electron pulse duration, a tip-based source is expected to feature a large transverse coherence as well as a nanometric emittance.Comment: 4 pages, 3 figure

Einfluss des Gütemerkmals Lichtrichtung und Schattigkeit auf Störwirkung und visuellen Diskomfort

Ausgangspunkt für diese Arbeit bildet die zunehmende Verbreitung der LED-Technologie in Arbeitsstätten. Dabei zeichnet sich in der Leuchtenentwicklung ein Trend ab, hin zum Einsatz von LED-Arrays. Durch die Kombination verschiedener lichttechnischer Merkmale wie der kleinen Lichtquellengröße, der dichten Anordnung örtlich separierter Lichtpunkte sowie der starken Gerichtetheit des Lichts stellt das LED-Array eine Neuheit für das visuelle System dar. Die Ergebnisse dieser Arbeit zeigen, dass eine Kombination der o. g. Merkmale zu einer veränderten visuellen Wahrnehmung führen und Quelle visueller Ermüdung sein kann. Anhand dreier Laborversuche wurde ein Regelkreismodell zur Beanspruchungsregulation abgeleitet, welches Auswirkungen visueller Beanspruchung auf die Leistung erklärt und Kompensationsstrategien wie Leistungs- und Beanspruchungskompensation, Folgeerscheinungen von Ermüdung sowie Leistungsreduktion in sekundären Aufgaben beschreibt.The research work investigates the influence of shadow characteristics on various work tasks such as reading, visual-motor work and shape recognition. The experiments were designed to identify possible links between shadow characteristics and visual discomfort. Therefore, in addition to objective performance parameters, subjective measures of effort as well as visual complaints were recorded for the aforementioned work tasks. In the analysis of the three experiments, significant effects of light direction and shadow characteristics could be derived from objective measures of performance. Depending on the type of task, it was shown that this lighting quality criterion can act as contributing factor for disturbance and visual discomfort. The results of all three experiments are interpreted within the context of an overarching psychological framework, through which the regulation of work performance can be explained. The "Compensatory Control Model" describes the regulation of work performance at high workload and stress conditions taking into account the subjectively experienced effort. In the model, unfavorable lighting conditions served as a stressor, which created higher requirements for the task execution. Using the model, compensation effects (performance and effort compensation) can be explained, which could be observed in the subjects. The model links lighting quality criteria with safety and health at work. Particularly against the background of the increasing spread of LED technology with its characteristic features, such as the small source size and the strong directionality of the light, the need for a stronger investigation of this lighting quality criterion is pointed out. In the sections of the theoretical part, the problem is brought to the attention that light direction and shadow characteristics are hardly taken into account in standardization and regulation as factors for perception, visual fatigue or visual discomfort. Practical recommendations are given in the last part of the research report. On one hand the practical recommendations concern the need for adaptation of light direction and shadow characteristics to the type of work task. On the other hand, recommendations for lighting and luminaire design are given.In dieser Forschungsarbeit wurde der Einfluss des Gütemerkmals Lichtrichtung und Schattigkeit bei verschiedenen Arbeitstätigkeiten wie Lesetätigkeit, visuell-motorischer Arbeit und Formerkennung untersucht. Die Versuche waren darauf ausgerichtet, mögliche Zusammenhänge des Gütemerkmals mit dem visuellen Diskomfort aufzuzeigen. Bei allen Arbeitstätigkeiten wurden daher neben objektiven Leistungsparametern subjektive Beanspruchungsdaten sowie visuelle Beschwerden erfasst. Bei der Analyse der Teilversuche konnten signifikante Wirkungen von Lichtrichtung und Schattigkeit auf objektive Leistungsparameter der visuellen Wahrnehmung abgeleitet werden. In Abhängigkeit der Arbeitsaufgabe zeigten sich unterschiedliche Stufen der Beeinträchtigung, welche das Gütemerkmal mit Störwirkung und visuellem Diskomfort in Verbindung bringen. Die Ergebnisse der drei Teilversuche wurden in ein übergreifendes, psychologisches Modell eingeordnet, welches die Auswirkungen auf die Gesundheit von Beschäftigen erklärt und die Relevanz des Gütemerkmals für den Arbeitsschutz darstellt. Das Regelkreismodell beschreibt die Regulierung von Arbeitsleistung bei hoher Arbeitslast und Stressbedingungen unter Berücksichtigung der subjektiv erlebten Anstrengung. Im Modell fungierten die Beleuchtungsbedingungen als Stressor, welche höhere Anforderungen bei der Aufgabenausführung hervorriefen. Mithilfe des Modells können Kompensationseffekte (Leistungs- und Beanspruchungskompensation) erklärt werden, welche bei den Probanden beobachtet werden konnten. Besonders vor dem Hintergrund der zunehmenden Verbreitung der LED-Technologie mit ihren charakteristischen Merkmalen, wie der kleinen Quellengröße und der starken Gerichtetheit des Lichts wird die Notwendigkeit nach einer stärkeren Untersuchung dieses Gütemerkmals aufgezeigt. In den einzelnen Abschnitten des Theorieteils wird sukzessive zu einer Problemstellung hingeführt. Diese betrifft den Umstand, dass Lichtrichtung und Schattigkeit in Normung und Regelsetzung als Faktoren für Wahrnehmung, visuelle Ermüdung bzw. visuellen Diskomfort kaum Berücksichtigung finden. Nicht zuletzt werden Praxisempfehlungen ausgesprochen und weiterführender Forschungsbedarf aufgezeigt. Die Praxisempfehlungen betreffen einerseits die Anpassung von Lichtrichtung und Schattigkeit an den Kontext der Arbeitsaufgabe und andererseits Empfehlungen für die Lichtplanung und Leuchtengestaltung

Operating single quantum emitters with a compact Stirling cryocooler

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Review of Scientific Instruments 86, 013113 (2015) and may be found at https://doi.org/10.1063/1.4906548.The development of an easy-to-operate light source emitting single photons has become a major driving force in the emerging field of quantum information technology. Here, we report on the application of a compact and user-friendly Stirling cryocooler in the field of nanophotonics. The Stirling cryocooler is used to operate a single quantum emitter constituted of a semiconductor quantum dot (QD) at a base temperature below 30 K. Proper vibration decoupling of the cryocooler and its surrounding enables free-space micro-photoluminescence spectroscopy to identify and analyze different charge-carrier states within a single quantum dot. As an exemplary application in quantum optics, we perform a Hanbury-Brown and Twiss experiment demonstrating a strong suppression of multi-photon emission events with g(2)(0) < 0.04 from this Stirling-cooled single quantum emitter under continuous wave excitation. Comparative experiments performed on the same quantum dot in a liquid helium (LHe)-flow cryostat show almost identical values of g(2)(0) for both configurations at a given temperature. The results of this proof of principle experiment demonstrate that low-vibration Stirling cryocoolers that have so far been considered exotic to the field of nanophotonics are an attractive alternative to expensive closed-cycle cryostats or LHe-flow cryostats, which could pave the way for the development of high-quality table-top non-classical light sources.BMBF, 03V0630, Entwicklung einer Halbleiterbasierten Einzelphotonenquelle für die Quanteninformationstechnologie (QSOURCE)DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Robust and distributed top-n frequent-pattern mining with SAP BW accelerator

Mining for association rules and frequent patterns is a central activity in data mining. However, most existing algorithms are only moderately suitable for real-world scenarios. Most strategies use parameters like minimum support, for which it can be very difficult to define a suitable value for unknown datasets. Since most untrained users are unable or unwilling to set such technical parameters, we address the problem of replacing the minimum-support parameter with top-n strategies. In our paper, we start by extending a top-n implementation of the ECLAT algorithm to improve its performance by using heuristic search strategy optimizations. Also, real-world datasets are often distributed and modern database architectures are switching from expensive SMPs to cheaper shared-nothing blade servers. Thus, most mining queries require distribution handling. Since partitioning can be forced by user-defined semantics, it is often forbidden to transform the data. Therefore, we developed an adaptive top-n frequent-pattern mining algorithm that simplifies the mining process on real distributions by relaxing some requirements on the results. We first combine the PARTITION and the TPUT algorithms to handle distributed top-n frequent-pattern mining. Then, we extend this new algorithm for distributions with real-world data characteristics. For frequent-pattern mining algorithms, equal distributions are important conditions, and tiny partitions can cause performance bottlenecks. Hence, we implemented an approach called MAST that defines a minimum absolute-support threshold. MAST prunes patterns with low chances of reaching the global top-n result set and high computing costs. In total, our approach simplifies the process of frequent-pattern mining for real customer scenarios and data sets. This may make frequent-pattern mining accessible for very new user groups. Finally, we present results of our algorithms when run on the SAP NetWeaver BW Acceleratorwith standard and real business datasets