FlipCut Supertrees: Towards Matrix Representation Accuracy in Polynomial Time

In computational phylogenetics, supertree methods provide a way to reconstruct larger clades of the Tree of Life. The supertree problem can be formalized in different ways, to cope with contradictory information in the input. In particular, there exist methods based on encoding the input trees in a matrix, and methods based on finding minimum cuts in some graph. Matrix representation methods compute supertrees of superior quality, but the underlying optimization problems are computationally hard. In contrast, graph-based methods have polynomial running time, but supertrees are inferior in quality. In this paper, we present a novel approach for the computation of supertrees called FlipCut supertree. Our method combines the computation of minimum cuts from graph-based methods with a matrix representation method, namely Minimum Flip Supertrees. Here, the input trees are encoded in a 0/1/?-matrix. We present a heuristic to search for a minimum set of 0/1-flips such that the resulting matrix admits a directed perfect phylogeny. We then extend our approach by using edge weights to weight the columns of the 0/1/?-matrix. In our evaluation, we show that our method is extremely swift in practice, and orders of magnitude faster than the runner up. Concerning supertree quality, our method is sometimes on par with the “gold standard” Matrix Representation with Parsimony.     

Performance evaluation of ambient services by combining robotic frameworks and a smart environment platform

Mobile robots and smart environments are two areas of research that can easily profit from each other. Smart environments, which are spaces unobtrusively equipped with sensors and actuators, providing ambient services to the people living within. Mobile robots inside those smart environments can use the existing infrastructure to increase their performance while decreasing the cost of local sensor systems. On the other side, evaluation of ambient services is often a laborious task. This work presents an approach that simplifies the evaluation by making use of two frameworks from robotics to perform tests in simulated smart environments. A method based on the language as action principle is used to extract realistic behavior of people living in real-world smart environments. Using this data, many different scenarios with varying configurations (different floor layouts, numbers and types of sensors, different number of people and pets) can easily be simulated and the performance of the ambient services evaluated.     

Pummelos as Concept Generators for Biomimetically Inspired Low Weight Structures with Excellent Damping Properties

Natural materials often exhibit excellent mechanical properties. An example of outstanding impact resistance is the pummelo fruit (Citrus maxima) which can drop from heights of 10 m and more without showing significant outer damage. Our data suggest that this impact resistance is due to the hierarchical organization of the fruit peel, called pericarp. The project presented in the current paper aims at transferring structural features from the pummelo pericarp to engineering materials, in our case metal foams, produced by the investment casting process. The transfer necessitates a detailed structural and mechanical analysis of the biological model on the one hand, and the identification and development of adequate materials and processes on the other hand. Based on this analysis, engineering composite foam structures are developed and processed which show enhanced damping and impact properties. The modified investment casting process and the model alloy Bi57Sn43 proved to be excellent candidates to make these bio‐inspired structures. Mechanical testing of both the natural and the engineering structures has to consider the necessity to evaluate the impact of the different hierarchical features. Therefore, specimens of largely varying sizes have to be tested and size effects cannot be ignored, especially as the engineering structures might be upscaled in comparison with the natural role model. All in all, the present results are very promising: the basis for a transfer of bio‐inspired structural hierarchical levels has been set.     

Subnanometer three-dimensional atom-probe investigation of segregation at MgO/Cu ceramic/metal heterophase interfaces.

Three-dimensional atom-probe (3DAP) microscopy has been applied to the study of segregation at ceramic/metal (C/M) interfaces. In this article, results on the MgO/Cu(X) (where X = Ag or Sb) systems are summarized. Nanometer-size MgO precipitates with atomically clean and atomically sharp interfaces were prepared in these systems by internal oxidation. Segregation of the ternary component (Ag or Sb) at the MgO/Cu heterophase interface was enhanced by extended low-temperature anneals. Magnesia precipitates in the 3DAP reconstructions were delineated as isoconcentration surfaces, and segregation of each ternary component at the C/M interfaces was analyzed with the proximity histogram method developed at Northwestern University. This method allows the direct extraction of the Gibbsian interfacial excess of solute at the C/M interfaces from the experimental data. A value of (3.2+/-2.0) x 10(17)m(-2) at 500 degrees C is obtained for the segregation of Ag at a MgO/Cu(Ag) interface, while a value of (2.9+/-0.9) x 10(18) m(-2) at 500 degrees C is obtained for the segregation of Sb at a MgO/Cu(Sb) interface. The larger Gibbsian excess for Sb segregation at this ceramic/metal heterophase interface is most likely due to the so-called pdeltaV effect.     

Development of a multifunctional coating system for laser-induced material transport

The aim of our research is to develop a novel surface coating for the use in laser microdissection and laser pressure catapulting (LMPC). LMPC is a contact- and contamination-free technique to separate histologic material and living cells for further proteomic and genomic analysis. Several physico-chemical functions must be included within the optimum coating system designed for this purpose, like optical absorption at the laser wavelength, combined with optical transparency in the visible region, a control of the laser ablation process, mechanical stability and biocompability for the adhesion of the histologic material.To achieve the optimum system the combination of several layers is required. The optical absorbance to capture the radiation energy from a frequency-tripled Nd:YAG laser (λ = 355 nm) is reached by a thin layer of zinc oxide (ZnO), deposited by hollow cathode gas flow sputtering. The laser ablation process is controlled by a polyelectrolyte multilayer, consisting of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS). The evaporation of chemisorbed water from the film is used to promote the catapulting process. For the mechanically stable, laser-dissectible layer organic coatings, like photoresists or lacquers, are suitable. Silica-containing polyacrylate nanocomposites were employed for this purpose.The investigation of the coating system included LMPC experiments with varying compositions of the layer system. The best results were obtained using a system consisting of ZnO, a polyelectrolyte multilayer deposited from 0.1 M Na₂SO₄ containing polymer solutions, and a 1.5-μm thick layer of the polyacrylate nanocomposite.To check the quality of the developed system, experiments with the commonly used poly(ethylene naphthalate) (PEN) foil were performed simultaneously. In addition to the determination of the parameters required for LMPC, quantitative real-time Polymerase Chain Reaction (rt-PCR) of the dissected material verified the benefit of the new system.     

Einfluß von thermophysikalischen Stoffdaten auf die Auslegung und den Betrieb von Destillationskolonnen

Influence of thermophysical data on the design and operation of distillation columns. It has become common practice in the petrochemical industry to utilize highly developed process simulators for the design of individual pieces of equipment or entire processes. Apart from actual model development, attention focusses on the calculation and use of efficient solution and converging algorithms in the development of such process simulators. Although frequent reference is made to the importance of the underlying material data in the literature and in practical applications there exist only scattered studies giving a suitable choice of the available substance data models and the sensitivity of the process variables to inaccuracy and uncertainty of the material data and the material data models. The present article illustrates the influence of material data (choice of model, sensitivity) for the example of the design and operation of distillation columns and several methods and recommendations are given for fast estimations. With the aid of appropriate examples, the influence of uncertainties in the underlying measured data and the phase equilibrium models on various process variables (plate number, reflux ratio, distillate and sump concentrations) is demonstrated.     

Hydrocarbon Footprints as a Record of Bumblebee Flower Visitation

Bumblebees leave traces of cuticular hydrocarbons on flowers they visit, with the amount deposited being positively related to the number of visits. We asked whether such footprint hydrocarbons are retained on flowers for sufficiently long periods of time so as to reflect bee visitation in pollination studies. In laboratory experiments, flower corollae (Primula veris, Digitalis grandiflora) visited by Bombus terrestris workers retained bee-derived nonacosenes (C₂₉H₅₈) in near-unchanged quantities for 24 hours, both at 15 and 25°C. Additionally, synthetic (Z)-9-tricosene applied to flower corollae of the deadnettle Lamium maculatum was retained for 48 hours in an unchanged quantity. In a field survey, the amount of footprint alkenes on flowers of comfrey (Symphytum officinale) plants was positively correlated with the number of bumblebee visits that those plants had received during the day. Together, these data suggest that flowers retain a long-term quantitative record of bumblebee visitation. The analysis of petal extracts by gas chromatography could provide a cheap and reliable way of quantifying bumblebee visits in landscape scale studies of pollination.     

Comprehensive modeling of optoelectronic nanostructures

This paper gives an overview of physics-based modeling of optoelectronic nanostructures, driven by diverse applications such as photovoltaics, solid-state lighting, communications and sensing. Despite this broad field of applications, some common challenges can be identified: accurate modeling of light-matter interaction, semi-coherent carrier transport in the presence of strong recombination, calculation of material properties and electromagnetic characteristics. In this contribution, the general purpose simulation framework tdkp/AQUA/LUMI is presented, with the focus on non-planar nanowire devices.     

Combinatorial corrosion study of the passivation of aluminium copper alloys

An Al_96.1–Cu_3.9 to Al_51.4–Cu_48.6 material library was obtained by thermal co-deposition and characterized by EDX and XRD. The crystallographic data reveals the presence of Al₂Cu and pure aluminium depending on the film composition and following the stoichiometry. Utilizing a scanning droplet cell setup, the zero current potential for anodization, the oxide formation factor and the dielectric constant of the oxide formed are presented with high resolution along the composition gradient.While the dielectric constant of the oxide formed remains nearly unaffected by the increasing copper content of the base material along the composition gradient, the zero current potential shows well defined steps between 6.9 and 8.5 at.% as well as between 20.9 and 26.7 at.% copper indicating an increased thickness of the native oxide present on the film. Additionally, starting around 25 at.% copper, oxygen evolution gradually superimposes the oxide growth and in turn significantly reduces the current efficiency for anodization. The formation of the intermetallic phase Al₂Cu was linked to both phenomena as it promotes the growth of native oxides and current leakage by oxygen evolution.