Technische Universität Darmstadt

About: Technische Universität Darmstadt is a education organization based out in Darmstadt, Germany. It is known for research contribution in the topics: Computer science & Context (language use). The organization has 17316 authors who have published 40619 publications receiving 937916 citations. The organization is also known as: Darmstadt University of Technology & University of Darmstadt.

Surface states, surface potentials, and segregation at surfaces of tin-doped In2O3

Abstract: Surfaces of In2O3 and tin-doped In2O3 (ITO) were investigated using photoelectron spectroscopy. Parts of the measurements were carried out directly after thin film preparation by magnetron sputtering without breaking vacuum. In addition samples were measured during exposure to oxidizing and reducing gases at pressures of up to 100 Pa using synchrotron radiation from the BESSY II storage ring. Reproducible changes of binding energies with temperature and atmosphere are observed, which are attributed to changes of the surface Fermi level position. We present evidence that the Fermi edge emission observed at ITO surfaces is due to metallic surface states rather than to filled conduction band states. The observed variation of the Fermi level position at the ITO surface with experimental conditions is accompanied by a large apparent variation of the core level to valence band maximum binding energy difference as a result of core-hole screening by the free carriers in the surface states. In addition segregation of Sn to the surface is driven by the surface potential gradient. At elevated temperatures the surface Sn concentration reproducibly changes with exposure to different environments and shows a correlation with the Fermi level position.

Passive micromixers for applications in the microreactor and μTAS fields

Abstract: An overview is given of current developments in micromixing technology, where the emphasis is on liquid mixing in passive micromixers. The mixers presented are differentiated by the hydrodynamic principle employed, and four important principles are discussed in some detail: hydrodynamic focusing, flow separation, chaotic advection, and split-and-recombine flows. It is shown that these principles offer excellent mixing performance in various dynamical regimes. Hydrodynamic focusing is a concept working very much independently of the Reynolds number of the flow. Flow separation offers rich dynamical behavior over a Reynolds number scale of several hundred, with superior performance compared to purely diffusive mixing already found at low Reynolds numbers. For chaotic advection, different implementations tailor-made for low and comparatively high Reynolds numbers exist, both leading to an exponential increase of the interface between two fluids. Split-and-recombine flows can only be realized in a close-to-ideal form in the low Reynolds number regime. Corresponding mixers can be equipped with comparatively wide channels, enabling a favorable ratio of throughput to pressure drop. The overview given in this article should enable a potential user of micromixing technology to select the most favorable concept for the application envisaged, especially in the field of chemical process technology

The soil fauna community in pure and mixed stands of beech and spruce of different age: trophic structure and structuring forces

Abstract: Scheu, S., Albers, D., Alphei, J., Buryn, R., Klages, U., Migge, S., Platner, C. andSalamon, J.-A. 2003. The soil fauna community in pure and mixed stands of beechand spruce of different age: trophic structure and structuring forces. – Oikos 101:225–238.This study investigates the response of the soil fauna community to replacement ofbeech by spruce or by mixed stands of beech and spruce. Stands of different age wereinvestigated in a factorial design with the factors tree species (beech and spruce) andstand age (30 and 120 years). The input of leaf/needle litter did not differ significantlybetween the study sites. By contrast, the amount of organic matter in upper soillayers (L/F, H/Ah) of spruce forests strongly exceeded that of beech forests particu-larly in mature stands. The increase in organic matter in spruce stands was notassociated by an increase in the amount of microbial biomass. Biomass of eight(bacterivorous, fungivorous and omnivorous nematodes, enchytraeids, earthworms,isopodes, mycetophilid and cecidomyiid Diptera) of the twelve microbi-detritivoroussoil animal groups studied was significantly increased in beech forests; only that ofone group (elaterid beetles) was increased in spruce forests and three groups did notrespond significantly (collembolans, oribatid mites, sciarid Diptera). This indicatesthat in the forests studied neither habitat space (amount of organic matter in L/FandH/Ah layers) nor the amount of microbial biomass controlled microbi-detritivores.Rather, the quality of litter materials and the concentration of microbial biomasstherein appeared to be most important. Herbivores and predators also were favouredby beech: the biomass of one (rhizophagous nematodes) of the three herbivorousgroups studied were significantly increased in beech stands and none in spruce stands;the biomass of four (predatory nematodes, centipedes, carabid and cantharid beetles)of the seven carnivorous groups studied were increased in beech stands, none inspruce stands. Generally, the biomass ratio between prey and predators was at aminimum in mature beech and mixed stands indicating more intense top-downcontrol in these forests. Overall, the study documents that replacement of beech byspruce strongly alters the soil food web. Mixed stands were more similar to sprucestands in respect to the biomass of soil animal groups but predator–prey interactionsappeared to be more similar in mature beech and mixed stands. Differences betweentree species usually were more pronounced in 120 compared to 30 years old standsindicating that the development of stand characteristics is slow.

Beyond the stars: exploiting free-text user reviews to improve the accuracy of movie recommendations

Abstract: In this paper we show that the extraction of opinions from free-text reviews can improve the accuracy of movie recommendations. We present three approaches to extract movie aspects as opinion targets and use them as features for the collaborative filtering. Each of these approaches requires different amounts of manual interaction. We collected a data set of reviews with corresponding ordinal (star) ratings of several thousand movies to evaluate the different features for the collaborative filtering. We employ a state-of-the-art collaborative filtering engine for the recommendations during our evaluation and compare the performance with and without using the features representing user preferences mined from the free-text reviews provided by the users. The opinion mining based features perform significantly better than the baseline, which is based on star ratings and genre information only.

Scaling up keystone effects from simple to complex ecological networks

Abstract: Predicting the consequences of species loss requires extending our traditional understanding of simpler dynamic systems of few interacting species to the more complex ecological networks found in natural ecosystems. Especially important is the scaling up of our limited understanding of how and under what conditions loss of ‘keystone’ species causes large declines of many other species. Here we explore how these keystone effects vary among simulations progressively scaled up from simple to more complex systems. Simpler simulations of four to seven interacting species suggest that species up to four links away can strongly alter keystone effects and make the consequences of keystone loss potentially indeterminate in more realistically complex communities. Instead of indeterminacy, we find that more complex networks of up to 32 species generally buffer distant influences such that variation in keystone effects is well predicted by surprisingly local ‘top-down’, ‘bottom-up’, and ‘horizontal‘ constraints acting within two links of the keystone subsystem. These results demonstrate that: (1) strong suppression of the competitive dominant by the keystone may only weakly affect subordinate competitors; (2) the community context of the target species determines whether strong keystone effects are realized; (3) simple, measurable, and local attributes of complex communities may explain much of the empirically observed variation in keystone effects; and (4) increasing network complexity per se does not inherently make the prediction of strong keystone effects more complicated.