Showing papers by "University of Oldenburg published in 2009"

PanTHERIA: a species‐level database of life history, ecology, and geography of extant and recently extinct mammals

Abstract: Analyses of life-history, ecological, and geographic trait differences among species, their causes, correlates, and likely consequences are increasingly important for understanding and conserving biodiversity in the face of rapid global change. Assembling multispecies trait data from diverse literature sources into a single comprehensive data set requires detailed consideration of methods to reliably compile data for particular species, and to derive single estimates from multiple sources based on different techniques and definitions. Here we describe PanTHERIA, a species-level data set compiled for analysis of life history, ecology, and geography of all known extant and recently extinct mammals. PanTHERIA is derived from a database capable of holding multiple geo-referenced values for variables within a species containing 100 740 lines of biological data for extant and recently extinct mammalian species, collected over a period of three years by 20 individuals. PanTHERIA also includes spatial databases o...

Irradiance Forecasting for the Power Prediction of Grid-Connected Photovoltaic Systems

Abstract: The contribution of power production by photovoltaic (PV) systems to the electricity supply is constantly increasing. An efficient use of the fluctuating solar power production will highly benefit from forecast information on the expected power production. This forecast information is necessary for the management of the electricity grids and for solar energy trading. This paper presents an approach to predict regional PV power output based on forecasts up to three days ahead provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). Focus of the paper is the description and evaluation of the approach of irradiance forecasting, which is the basis for PV power prediction. One day-ahead irradiance forecasts for single stations in Germany show a rRMSE of 36%. For regional forecasts, forecast accuracy is increasing in dependency on the size of the region. For the complete area of Germany, the rRMSE amounts to 13%. Besides the forecast accuracy, also the specification of the forecast uncertainty is an important issue for an effective application. We present and evaluate an approach to derive weather specific prediction intervals for irradiance forecasts. The accuracy of PV power prediction is investigated in a case study.

How Many Bootstrap Replicates Are Necessary

Abstract: Phylogenetic Bootstrapping (BS) is a standard technique for inferring confidence values on phylogenetic trees that is based on reconstructing many trees from minor variations of the input data, trees called replicates. BS is used with all phylogenetic reconstruction approaches, but we focus here on the most popular, Maximum Likelihood (ML). Because ML inference is so computationally demanding, it has proved too expensive to date to assess the impact of the number of replicates used in BS on the quality of the support values. For the same reason, a rather small number (typically 100) of BS replicates are computed in real-world studies. Stamatakis et al. recently introduced a BS algorithm that is 1---2 orders of magnitude faster than previous techniques, while yielding qualitatively comparable support values, making an experimental study possible. In this paper, we propose stopping criteria , that is, thresholds computed at runtime to determine when enough replicates have been generated, and report on the first large-scale experimental study to assess the effect of the number of replicates on the quality of support values, including the performance of our proposed criteria. We run our tests on 17 diverse real-world DNA, single-gene as well as multi-gene, datasets, that include between 125 and 2,554 sequences. We find that our stopping criteria typically stop computations after 100---500 replicates (although the most conservative criterion may continue for several thousand replicates) while producing support values that correlate at better than 99.5% with the reference values on the best ML trees. Significantly, we also find that the stopping criteria can recommend very different numbers of replicates for different datasets of comparable sizes. Our results are thus two-fold: (i) they give the first experimental assessment of the effect of the number of BS replicates on the quality of support values returned through bootstrapping; and (ii) they validate our proposals for stopping criteria. Practitioners will no longer have to enter a guess nor worry about the quality of support values; moreover, with most counts of replicates in the 100---500 range, robust BS under ML inference becomes computationally practical for most datasets. The complete test suite is available at http://lcbb.epfl.ch/BS.tar.bz2 and BS with our stopping criteria is included in RAxML 7.1.0.

Geographical variation in predictors of mammalian extinction risk: big is bad, but only in the tropics

Abstract: Whereas previous studies have investigated correlates of extinction risk either at global or regional scales, our study explicitly models regional effects of anthropogenic threats and biological traits across the globe. Using phylogenetic comparative methods with a newly-updated supertree of 5020 extant mammals, we investigate the impact of species traits on extinction risk within each WWF ecoregion. Our analyses reveal strong geographical variation in the influence of traits on risk: notably, larger species are at higher risk only in tropical regions. We then relate these patterns to current and recent-historical human impacts across ecoregions using spatial modelling. The body-mass results apparently reflect historical declines of large species outside the tropics due to large-scale land conversion. Narrow-ranged and rare species tend to be at high risk in areas of high current human impacts. The interactions we describe between biological traits and anthropogenic threats increase understanding of the processes determining extinction risk.

Biodiversity in a complex world: consolidation and progress in functional biodiversity research.

Abstract: The global decline of biodiversity caused by human domination of ecosystems worldwide is supposed to alter important process rates and state variables in these ecosystems. However, there is considerable debate on the prevalence and importance of biodiversity effects on ecosystem function (BDEF). Here, we argue that much of the debate stems from two major shortcomings. First, most studies do not directly link the traits leading to increased or decreased function to the traits needed for species coexistence and dominance. We argue that implementing a trait-based approach and broadening the perception of diversity to include trait dissimilarity or trait divergence will result in more realistic predictions on the consequences of altered biodiversity. Second, the empirical and theoretical studies do not reflect the complexity of natural ecosystems, which makes it difficult to transfer the results to natural situations of species loss. We review how different aspects of complexity (trophic structure, multifunctionality, spatial or temporal heterogeneity, and spatial population dynamics) alter our perception of BDEF. We propose future research avenues concisely testing whether acknowledging this complexity will strengthen the observed biodiversity effects. Finally, we propose that a major future task is to disentangle biodiversity effects on ecosystem function from direct changes in function due to human alterations of abiotic constraints.

Creating Effective Collaborative Learning Groups in an Online Environment

Abstract: Collaborative learning in an online classroom can take the form of discussion among the whole class or within smaller groups. This paper addresses the latter, examining first whether assessment makes a difference to the level of learner participation and then considering other factors involved in creating effective collaborative learning groups. Data collected over a three year period (15 cohorts) from the Foundations course in the Master of Distance Education (MDE) program offered jointly by University of Maryland University College (UMUC) and the University of Oldenburg does not support the authors‟ original hypothesis that assessment makes a significant difference to learner participation levels in small group learning projects and leads them to question how much emphasis should be placed on grading work completed in study groups to the exclusion of other strategies. Drawing on observations of two MDE courses, including the Foundations course, their extensive online teaching experience, and a review of the literature, the authors identify factors other than grading that contribute positively to the effectiveness of small collaborative learning groups in the online environment. In particular, the paper focuses on specific instructional strategies that facilitate learner participation in small group projects, which result in an enhanced sense of community, increased skill acquisition, and better learning outcomes.

High-order harmonics from laser-irradiated plasma surfaces

Abstract: The investigation of high-order harmonic generation (HHG) of femtosecond laser pulses by means of laser-produced plasmas is surveyed. This kind of harmonic generation is an alternative to the HHG in gases and shows significantly higher conversion efficiency. Furthermore, with plasma targets there is no limitation on applicable laser intensity and thus the generated harmonics can be much more intense. In principle, harmonic light may also be generated at relativistic laser intensity, in which case their harmonic intensities may even exceed that of the focused laser pulse by many orders of magnitude. This phenomenon presents new opportunities for applications such as nonlinear optics in the extreme ultraviolet region, photoelectron spectroscopy, and opacity measurements of high-density matter with high temporal and spatial resolution. On the other hand, HHG is strongly influenced by the laser-plasma interaction itself. In particular, recent results show a strong correlation with high-energy electrons generated during the interaction process. The harmonics are a promising tool for obtaining information not only on plasma parameters such as the local electron density, but also on the presence of large electric and magnetic fields, plasma waves, and the (electron) transport inside the target. This paper reviews the theoretical and experimental progress on HHGmore » via laser-plasma interactions and discusses the prospects for applying HHG as a short-wavelength, coherent optical tool.« less

Mechanochemistry: the varied applications of mechanical bond-breaking

Abstract: Mechanochemistry means mechanical breakage of intramolecular bonds by external force and must be differentiated from molecular solid-state chemistry, where contacts between micronized molecular solids are created by the mechanical action for mutual approach of the reacting centers. After an outline of the mechanistic differences, the varied mechanochemistry is discussed. Grinding, milling, shearing, scratching, polishing, and rapid friction (for polymers also cutting, kneading, extruding) provide the mechanical impact for mechanochemistry, while sonication and shock waving for intramolecular bond breaking are generally described as thermal processes. The various types of mechanophysics (e.g., mechanoelectricity, conformational changes, thixotropy, rheopexy, stirring of Newtonian liquids or suspensions, etc.) are not treated here. Mechanochemistry covers solid-state reactions of infinitely covalent crystals, brittle metals, polymers, molecular solids with weak covalent bonds, strong intramolecular bond breakage in shearing Bridgman's anvil or by friction at lubrication of rapidly moving cold contacting surfaces, and single bond breaking or cutting. The diverse wealth of practical applications of mechanochemistry is outlined with typical examples for ceramics, mechanical alloying, hydrogen storage, organic syntheses, waste remediation, leachings, surface plasmas, radical formation, explosives, nanotube formation, nanoparticles grafting, polymer technology, radical initiation, scratch-less polishing, wear protection, lubrication, mechanochromism, nano-dissection, and many more.

Database of multichannel in-ear and behind-the-ear head-related and binaural room impulse responses

Abstract: An eight-channel database of head-related impulse responses (HRIRs) and binaural room impulse responses (BRIRs) is introduced. The impulse responses (IRs) were measured with three-channel behind-the-ear (BTEs) hearing aids and an in-ear microphone at both ears of a human head and torso simulator. The database aims at providing a tool for the evaluation of multichannel hearing aid algorithms in hearing aid research. In addition to the HRIRs derived from measurements in an anechoic chamber, sets of BRIRs for multiple, realistic head and sound-source positions in four natural environments reflecting daily-life communication situations with different reverberation times are provided. For comparison, analytically derived IRs for a rigid acoustic sphere were computed at the multichannel microphone positions of the BTEs and differences to real HRIRs were examined. The scenes' natural acoustic background was also recorded in each of the real-world environments for all eight channels. Overall, the present database allows for a realistic construction of simulated sound fields for hearing instrument research and, consequently, for a realistic evaluation of hearing instrument algorithms.

Leaf traits capture the effects of land use changes and climate on litter decomposability of grasslands across Europe

Abstract: Land use and climate changes induce shifts in plant functional diversity and community structure, thereby modifying ecosystem processes. This is particularly true for litter decomposition, an essential process in the biogeochemical cycles of carbon and nutrients. In this study, we asked whether changes in functional traits of living leaves in response to changes in land use and climate were related to rates of litter potential decomposition, hereafter denoted litter decomposability, across a range of 10 contrasting sites. To disentangle the different control factors on litter decomposition, we conducted a microcosm experiment to determine the decomposability under standard conditions of litters collected in herbaceous communities from Europe and Israel. We tested how environmental factors (disturbance and climate) affected functional traits of living leaves and how these traits then modified litter quality and subsequent litter decomposability. Litter decomposability appeared proximately linked to initial litter quality, with particularly clear negative correlations with lignin-dependent indices (litter lignin concentr tion, lignin:nitrogen ratio, and fiber component). Litter quality was directly related to community-weighted mean traits. Lignin-dependent indices of litter quality were positively correlated with community-weighted mean leaf dry matter content (LDMC), and negatively correlated with community-weighted mean leaf nitrogen concentration (LNC). Consequently, litter decomposability was correlated negatively with community-weighted mean LDMC, and positively with community-weighted mean LNC. Environmental factors (disturbance and climate) influenced community-weighted mean traits. Plant communities experiencing less frequent or less intense disturbance exhibited higher community-weighted mean LDMC, and therefore higher litter lignin content and slower litter decomposability. LDMC therefore appears as a powerful marker of both changes in land use and of the pace of nutrient cycling across 10 contrasting sites.

The Contribution of Environmental and Social Standards Towards Ensuring Legitimacy in Supply Chain Governance

Abstract: Increasingly, companies implement social and environmental standards as instruments towards corporate social responsibility (CSR) in supply chains. This is based on the assumption that such standards increase legitimacy among stakeholders. Yet, a wide variety of standards with different requirement levels exist and companies might tend to introduce the ones with low exigencies, using them as a legitimacy front. This strategy jeopardizes the reputation of social and environmental standards among stakeholders and their long-term trust in these instruments of CSR, meaning that all expenses for their implementation are of no avail for the companies. Therefore, this paper highlights which criteria are important for the selection, implementation and improvement in order to achieve a company's aim, but also to strengthen the legitimacy of social and environmental standards. This research is based on conceptual thought and some existing empirical research, comparing four different social and environmental standards, revealing weaknesses and strengths. It exposes the basic conditions for the success of such standards among stakeholders and identifies the need for more empirical data.

Group polarization in the team dictator game reconsidered

Abstract: While most papers on team decision-making find that teams behave more selfishly, less trustingly and less altruistically than individuals, Cason and Mui (1997) report that teams are more altruistic than individuals in a dictator game. Using a within-subjects design we re-examine group polarization by letting subjects make individual as well as team decisions in an experimental dictator game. In our experiment teams are more selfish than individuals, and the most selfish team member has the strongest influence on team decisions. Various explanations for the different findings in Cason and Mui (1997) and in our paper are discussed.

Dispersal failure contributes to plant losses in NW Europe.

Abstract: The ongoing decline of many plant species in Northwest Europe indicates that traditional conservation measures to improve the habitat quality, although useful, are not enough to halt diversity losses. Using recent databases, we show for the first time that differences between species in adaptations to various dispersal vectors, in combination with changes in the availability of these vectors, contribute significantly to explaining losses in plant diversity in Northwest Europe in the 20th century. Species with water- or fur-assisted dispersal are over-represented among declining species, while others (wind- or bird-assisted dispersal) are under-represented. Our analysis indicates that the 'colonization deficit' due to a degraded dispersal infrastructure is no less important in explaining plant diversity losses than the more commonly accepted effect of eutrophication and associated niche-based processes. Our findings call for measures that aim to restore the dispersal infrastructure across entire regions and that go beyond current conservation practices.

Innovation communities: the role of networks of promotors in Open Innovation

Abstract: Research on Open Innovation has increasingly emphasised the role of communities in creating, shaping and disseminating innovations. However, the comparability of many studies has been hampered by the lack of a precise definition of the community construct, and the research on Open Innovation has to date not been well connected to insights from research on the role of transformational leaders and the networking of champions and promotors across organisational boundaries. For this reason, this paper introduces a new construct of ‘innovation communities’ based on promotor theory, which it defines as ‘networks of promotors’. It proposes a comprehensive concept of the quality of interaction in innovation communities, and presents findings of three case studies, which explore the role of promotors and networks of promotors in Open Innovation. The case studies reveal that such transformational leaders as promotors, and especially their close and informal co-operation across functional and organisational boundaries, play a key role in Open Innovation.

Visual but not trigeminal mediation of magnetic compass information in a migratory bird.

Abstract: Magnetic compass information has a key role in bird orientation, but the physiological mechanisms enabling birds to sense the Earth's magnetic field remain one of the unresolved mysteries in biology. Two biophysical mechanisms have become established as the most promising magnetodetection candidates. The iron-mineral-based hypothesis suggests that magnetic information is detected by magnetoreceptors in the upper beak and transmitted through the ophthalmic branch of the trigeminal nerve to the brain. The light-dependent hypothesis suggests that magnetic field direction is sensed by radical pair-forming photopigments in the eyes and that this visual signal is processed in cluster N, a specialized, night-time active, light-processing forebrain region. Here we report that European robins with bilateral lesions of cluster N are unable to show oriented magnetic-compass-guided behaviour but are able to perform sun compass and star compass orientation behaviour. In contrast, bilateral section of the ophthalmic branch of the trigeminal nerve in European robins did not influence the birds' ability to use their magnetic compass for orientation. These data show that cluster N is required for magnetic compass orientation in this species and indicate that it may be specifically involved in processing of magnetic compass information. Furthermore, the data strongly suggest that a vision-mediated mechanism underlies the magnetic compass in this migratory songbird, and that the putative iron-mineral-based receptors in the upper beak connected to the brain by the trigeminal nerve are neither necessary nor sufficient for magnetic compass orientation in European robins.

Separating the influence of resource 'availability' from resource 'imbalance' on productivity-diversity relationships.

Abstract: One of the oldest and richest questions in biology is that of how species diversity is related to the availability of resources that limit the productivity of ecosystems. Researchers from a variety of disciplines have pursued this question from at least three different theoretical perspectives. Species energy theory has argued that the summed quantities of all resources influence species richness by controlling population sizes and the probability of stochastic extinction. Resource ratio theory has argued that the imbalance in the supply of two or more resources, relative to the stoichiometric needs of the competitors, can dictate the strength of competition and, in turn, the diversity of coexisting species. In contrast to these, the field of Biodiversity and Ecosystem Functioning has argued that species diversity acts as an independent variable that controls how efficiently limited resources are utilized and converted into new tissue. Here we propose that all three of these fields give necessary, but not sufficient, conditions to explain productivity-diversity relationships (PDR) in nature. However, when taken collectively, these three paradigms suggest that PDR can be explained by interactions among four distinct, non-interchangeable variables: (i) the overall quantity of limiting resources, (ii) the stoichiometric ratios of different limiting resources, (iii) the summed biomass produced by a group of potential competitors and (iv) the richness of co-occurring species in a local competitive community. We detail a new multivariate hypothesis that outlines one way in which these four variables are directly and indirectly related to one another. We show how the predictions of this model can be fit to patterns of covariation relating the richness and biomass of lake phytoplankton to three biologically essential resources (N, P and light) in a large number of Norwegian lakes.

Exploring dynamic localization with a Bose-Einstein condensate

Abstract: We report on the experimental observation of dynamic localization of a Bose-Einstein condensate in a shaken optical lattice, both for sinusoidal and square-wave forcing. The formulation of this effect in terms of a quasienergy band collapse, backed by the excellent agreement of the observed collapse points with the theoretical predictions, suggests the feasibility of systematic quasienergy band engineering.

Fats and oils as renewable feedstock for chemistry

Abstract: Agenda 21, the comprehensive plan of action for a sustainable development in the 21 century which was adopted by more than 180 governments in Rio de Janeiro in 1992, is encouraging the environmentally sound and sustainable use of renewable natural resources, interestingly in chapter 4 “Changing consumption patterns”[1]. It was estimated that about 120 billion tons carbon in biomass, equivalent to .80 billion tons of oil equivalents (toe), are generated globally year by year by photosynthesis [2]. About 5% are presently used by man. The global primary energy supply was in 2004 11.2 billion toe and was estimated to be in 2030 20.6 billion toe [3]. Obviously, there seems to be plenty of biomass available, continually generated by photosynthesis year after year. Moreover, mankind has been degrading, in historical times, some billion hectares of areas originally forested and covered with vegetation. Reforestation of these degraded areas is the greatest challenge on the way to a sustainable development. Neglect of reforestation implies that desertification will further progress, transforming more and more of the areas prone to desertification into new deserts [4]. Thus, there is enough land available for the production of biomass to be used as renewable feedstock. Chemists have much to contribute to meet this challenge [5, 6]. From a chemical point of view, about 75% of biomass is carbohydrates, 20% lignins and only about 5% fats and others. Obviously, the detailed knowledge of the chemistry of these biomolecules will be absolutely necessary on the way to a sustainable usage of biomass as renewable feedstock. At present, the feedstocks of the chemical industry are predominantly depleting fossil feedstocks – oil and natural gas – and only a small percentage are renewables, in Germany about 12%. Thus, the chemical industry will have to change its consumption pattern. The German Chemical Society stated in 2002, on the occasion of the World summit on sustainable development in Johannesburg: “Most products obtainable from renewable raw materials may at present not be able to compete with the products of the petrochemical industry, but this will change as oil becomes scarcer and oil prices rise” [7]. This is currently going on. Some examples of this breathtaking process will be discussed in this paper focused on polyols and middleand long-chain dicarboxylic acids. Moreover, the importance of cultivating new oil plants for chemical usage of the oil will be discussed shortly.

Role of the oligodendroglial cytoskeleton in differentiation and myelination.

Abstract: Oligodendrocytes, the myelin-forming cells of the central nervous system, are in culture characterized by an elaborate process network, terminating in flat membranous sheets that are rich in myelin-specific proteins and lipids, and spirally wrap axons forming a compact insulating layer in vivo. By analogy with other cell types, maintenance and stability of these processes, as well as the formation of the myelin sheath, likely rely on a pronounced cytoskeleton consisting of microtubules and microfilaments. While the specialized process of wrapping and compaction forming the myelin sheath is not well understood, considerably more is known about how cytoskeletal organization is mediated by extracellular and intracellular signals and other interaction partners during oligodendrocyte differentiation and myelination. Here, we review the current state of knowledge on the role of the oligodendrocyte cytoskeleton in differentiation with an emphasis on signal transduction mechanisms and will attempt to draw out implications for its significance in myelination.

Using happiness data for environmental valuation: issues and applications

Abstract: In addition to standard methods of environmental valuation, a novel approach has recently emerged which models individuals' self-rated happiness as a function of their incomes and the prevailing environmental conditions The estimated relationship is used to calculate the trade-off people would be willing to make between income and environmental conditions, ie the increase in income necessary to compensate individuals for any given decline in environmental quality While the basic idea is simple, the theoretical and empirical details may be complex, and they may vary from application to application This paper discusses the relevant conceptual and methodological issues and reviews applications to air and water pollution, noise nuisance, climate parameters, and natural hazards

Titanium-catalyzed hydroaminoalkylation of alkenes by C-H bond activation at sp3 centers in the alpha-position to a nitrogen atom.

Abstract: Hydroaminations of alkynes and alkenes have attracted much attention during the past few years. Both transformations allow the synthesis of nitrogen-containing molecules in a single step with 100 % atom efficiency. Besides other metal catalysts, titanium complexes have been used extensively for these reactions. Recently, we recognized during a study of the Ti-catalyzed intramolecular hydroamination of alkenes that the cyclization of 1-amino-5-hexenes to piperidines (Scheme 1) performed with the catalysts [Ti(NMe2)4] or