A dual element based geometric element transformation method for all-hexahedral mesh smoothing

Due to their increased complexity hexahedral elements are more challenging with respect to mesh generation and mesh improvement techniques than tetrahedral elements. In particular, there is a lack of geometry-based all-hexahedral smoothing methods for mesh quality improvement being easy to implement, practicable, and efficient. The recently introduced geometric element transformation method represents a new promising element oriented smoothing concept to resolve this deficiency. By giving a dual octahedron based regularizing transformation this new approach is adapted in order to smooth all-hexahedral meshes. First numerical tests indicate that the resulting smoothing method yields high quality results at least comparable to those of a state of the art global optimization-based approach while being significantly faster.     

Algorithms for Marketing-Mix Optimization

Algorithms for determining quality/cost/price tradeoffs in saturated markets are considered. A product is modeled by d real-valued qualities whose sum determines the unit cost of producing the product. This leads to the following optimization problem: given a set of n customers, each of whom has certain minimum quality requirements and a maximum price they are willing to pay, design a new product and select a price for that product in order to maximize the resulting profit.     

Topological Implications of Selfish Neighbor Selection in Unstructured Peer-to-Peer Networks

Current peer-to-peer (P2P) systems often suffer from a large fraction of freeriders not contributing any resources to the network. Various mechanisms have been designed to overcome this problem. However, the selfish behavior of peers has aspects which go beyond resource sharing. This paper studies the effects on the topology of a P2P network if peers selfishly select the peers to connect to. In our model, a peer exploits locality properties in order to minimize the latency (or response times) of its lookup operations. At the same time, the peer aims at not having to maintain links to too many other peers in the system. By giving tight bounds on the price of anarchy, we show that the resulting topologies can be much worse than if peers collaborated. Moreover, the network may never stabilize, even in the absence of churn. Finally, we establish the complexity of Nash equilibria in our game theoretic model of P2P networks. Specifically, we prove that it is NP-hard to decide whether our game has a Nash equilibrium and can stabilize.     

SYNTACTIC SIMPLIFICATION AND SEMANTIC ENRICHMENT—TRIMMING DEPENDENCY GRAPHS FOR EVENT EXTRACTION

In our approach to event extraction, dependency graphs constitute the fundamental data structure for knowledge capture. Two types of trimming operations pave the way to more effective relation extraction. First, we simplify the syntactic representation structures resulting from parsing by pruning informationally irrelevant lexical material from dependency graphs. Second, we enrich informationally relevant lexical material in the simplified dependency graphs with additional semantic meta data at several layers of conceptual granularity. These two aggregation operations on linguistic representation structures are intended to avoid overfitting of machine learning‐based classifiers which we use for event extraction (besides manually curated dictionaries). Given this methodological framework, the corresponding JReX system developed by the Julie Lab Team from Friedrich‐Schiller‐Universität Jena (Germany) scored on 2nd rank among 24 competing teams for Task 1 in the “BioNLP’09 Shared Task on Event Extraction,” with 45.8% recall, 47.5% precision and 46.7% F1‐score on all 3,182 events. In more recent experiments, based on slight modifications of JReX and using the same data sets, we were able to achieve 45.9% recall, 57.7% precision, and 51.1% F1‐score.     

A.I.K.E.F.: Adaptive hybrid model for space plasma simulations

The interaction between magnetized space plasmas and obstacles like comets, asteroids or planets is determined by a variety of physical processes that occur simultaneously on significantly different length and time scales. Frequently the dynamics of individual ions play a key role for the shape of the interaction region: strong velocity shear between light and heavy plasma constituents, non-Maxwellian particle distributions due to pick up and asymmetries in the magnetic field topology are crucial in determining this type of interaction. Covering these processes is beyond the scope of any Magnetohydrodynamic (MHD) model. In order to account for these effects we have developed a new adaptive hybrid code A.I.K.E.F. (Adaptive Ion-Kinetic Electron-Fluid). The code operates on Cartesian meshes that can adapt to the physical structures in both, space and time. To the authors' knowledge, there is no other adaptive hybrid simulation code in space plasma physics to the present day. Adaptivity is implemented by means of Hybrid-Block-AMR, that is individual octs are refined rather than entire blocks, where an oct is one eighth of a block. In order to account for a reasonable number of particles in each cell, particles are refined via splitting and merging. Both procedures conserve mass, momentum and kinetic energy. The code is implemented in C++ and efficiently parallelized for distributed systems by means of the Message Passing Interface (MPI). In order to demonstrate the validity of our newly developed code we have applied it to a series of fundamental test scenarios. On the one hand we demonstrate that the dispersion relation as well as the propagation characteristics of MHD and whistler mode waves are quantitatively reproduced by our simulation code. Wave propagation remains unaffected when traveling through regions that include different refinement levels. On the other hand we verify that the results obtained on high resolution uniform meshes are identical to the results from adaptive simulations that use coarse base meshes but include various levels of refinement. A remarkable speedup could be observed: the adaptive simulations required 71 times less CPU-hours than the uniform mesh simulations. Finally, we present a first series of global, three-dimensional simulations for the interaction of Mercury with the solar wind and a real time study of Titan's plasma interaction during a magnetosheath excursion.     

Surface state defining factors as key to the strength of ceramic micro parts

The mechanical properties of ceramic parts are strongly influenced by the quality of the surface. In the present work it is demonstrated that for the surface quality, material specific properties (sintering activity, grain morphology) as well as process-related factors (debinding and sintering) are vitally important. For the exemplarily investigated materials zirconium dioxide (ZrO₂) and silicon nitride (Si₃N₄) the surface morphology of micro specimens turned out to be the limiting factor for high bending strength. Due to its fine and homogenous microstructure ZrO₂ allows the formation of very smooth surfaces with correspondingly high characteristic strength up to 3,000 MPa. Si₃N₄ is characterized by a highly anisotropic microstructure, pronounced grain growth, and thereby high surface roughness. Although both materials reveal virtually the same strength level in macro dimensions, in micro dimensions Si₃N₄ seems to be the inferior choice with a maximum strength of 1,200 MPa.     

Aluminum–germanium wafer bonding of (AlGaIn)N thin-film light-emitting diodes

Eutectic aluminum–germanium wafer bonding was used to fabricate (AlGaIn)N thin-film light-emitting diodes (LEDs). Wafer bonding was carried out on 2″ wafer level at a bond temperature of 470 °C using patterned Al bond pads on the GaN-on-sapphire LED epiwafer and plain Ge substrates. The microstructure of the joint formation was characterized via cross-section analysis using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Scanning acoustic microscopy was used to investigate the bond interface. The shear strength was determined to be 1–2 kN/cm². The formation of a liquid Al–Ge phase is evident from cross-section analysis and optical microscopy. During solidification, Al and Ge are separated into distinct phases again, which is revealed by EDX. The obtained bond is not free of micro-voids, yet it is mechanically stable and suited for the fabrication of thin-film LEDs by removing the sapphire substrate via laser lift-off, which is also demonstrated.     

An apparatus for immersing trapped ions into an ultracold gas of neutral atoms

We describe a hybrid vacuum system in which a single ion or a well-defined small number of trapped ions (in our case Ba(+) or Rb(+)) can be immersed into a cloud of ultracold neutral atoms (in our case Rb). This apparatus allows for the study of collisions and interactions between atoms and ions in the ultracold regime. Our setup is a combination of a Bose-Einstein condensation apparatus and a linear Paul trap. The main design feature of the apparatus is to first separate the production locations for the ion and the ultracold atoms and then to bring the two species together. This scheme has advantages in terms of stability and available access to the region where the atom-ion collision experiments are carried out. The ion and the atoms are brought together using a moving one-dimensional optical lattice transport which vertically lifts the atomic sample over a distance of 30 cm from its production chamber into the center of the Paul trap in another chamber. We present techniques to detect and control the relative position between the ion and the atom cloud.     

An assay for local quality in cryo-electron micrographs of single particles

High quality of the cryo-electron micrographs is of crucial importance for the success of single particle three-dimensional reconstruction methods. In analyzing some micrographs from cryo-electron microscopy specimens, we found an extraordinary variability, within the same micrograph, in the appearance of particles. We developed a method for analyzing the variability of local image quality, using correspondence analysis of local power spectra. With this technique, we discovered a strong systematic variation of the envelope modulating an otherwise unchanged contrast transfer function. The underlying causes may be uncontrollable effects, such as variations in the thickness of ice, instability of the holey carbon, and charging. The method of assaying, resulting in "local quality maps", may be useful as a general tool for screening micrographs used as input for reconstructions.     

Investigation of biocide efficacy by photoacoustic biofilm monitoring

The undesired growth of biofilms on solid surfaces is often termed biofouling. Biofilms consist mainly of water and microbial cells which are embedded in a biopolymer matrix. Biofouling lowers the water quality and increases the frictional resistance in tubes. Further, biofilms increase the pressure differences in membrane processes and can clog filtration membranes, valves, and nozzles. For investigation and improvement of biocide efficacy and anti-fouling strategies, on-line and in situ monitoring of the biofilm is necessary. In this study, photoacoustic spectroscopy (PAS) was employed for biofilm monitoring. PAS allows the depth-resolved investigation of growth and detachment processes of biofilms. Strategies based on the oxidant hydrogen peroxide were compared to popular isothiazolinone biocides. Hydrogen peroxide allowed a very fast and efficient removal of attached biofilms, whereas no effect on the biofilm matrix was observed in most cases when isothiazolinone biocides were used.