OPUS 4 | Search

The Social System of the Round-Eared Sengi(Macroscelides proboscideus) (2009)

Melanie Schubert

In the present study, I investigated the social system of the round-eared sengi (Macroscelides proboscideus), a small crepuscular mammal that lives in deserts and semi-deserts in Southern Africa. For studying the evolution of monogamy in this species, I determined the social organisation and male mate guarding in wild animals in the Goegap Nature Reserve, South Africa. Data were collected over three successive breeding seasons and one non-breeding season by radio-tracking and trapping over a period of 2.5 years. Additionally, extra-pair attempts of paired round-eared sengi males were studied under laboratory conditions using direct behavioural observations and morphological and physiological characteristics of males. In the field, the population was characterised by balanced adult sex ratios and by a lack in sexual dimorphism in body mass. Round-eared sengis lived in perennial territorial male-female-pairs. However, males maintained much larger areas than females that were sensitive to population density and the presence of neighbouring males. At higher density males used smaller areas than at lower population density, but the number of neighbouring males was fairly constant throughout the whole study. Male space use appeared to be primarily limited by the presence of neighbouring males. In contrast, females maintained smaller-sized territories despite changes in population density. Some paired males attempted to take over widowed females, but shifted back to their original home range following the intrusion of an un-paired male, possibly because of a low variation (about 10 %) in body mass. Female reproduced 2-3 litters during a long breeding season with an asynchronous birth interval between neighbouring females, favouring pre-copulatory and oestrus mate guarding. Males over-mark their females’ scent while following, possibly for concealing the females’ reproductive state and advertisement of the paired status, thereby decreasing the risk of intrusions by competitors. Mate guarding incurred costs, because, overall, males lost about 5 % of their body mass. On the individual level, male body mass loss was negatively related to the intensity of mate guarding during the pre-copulatory period. Furthermore, guarding was inversely correlated with male body mass in the pre-copulatory period and with the number of neighbouring males during oestrus, indicating that males vary their guarding effort in relation to their physical capabilities and the competitive environment. In addition, both sexes demonstrated promiscuous tendencies in the experimental study. Female sexual behaviour with male neighbours was positively related to the time neighbouring males spent in the females’ area and to male marking behaviour. Intruding males were attacked by resident males. Aggression experienced by intruding males was associated with body mass loss (about 4%) in these animals; the same was found for marking behaviour in the neighbouring area. Furthermore, glucocorticoid levels, determined from analyses of faeces and urine samples, positively correlated with male body mass loss and also with male marking behaviour of intruding males, indicating costs of this behaviour. In conclusion, pair-living is the predominant social organisation in round-eared sengis. Males suffered from a limited opportunity to monopolise more than a single female that may have resulted from females living solitarily in small exclusive territories, balanced adult sex ratios and a low variation in body mass between males. However, both sexes have promiscuous tendencies. Female reproduced asynchronously and advertised their reproductive status, so that males pursued two behavioural tactics: Males engage in mate guarding for ensuring paternity and also in extra-pair attempts with neighbouring females, possibly for increasing their reproductive success. Since both male tactics were energetic costly they may serve as honest signals of quality providing only higher quality males with the opportunity to enhance their reproductive success, which in turn may be advantageous for females in terms of genetic benefits.

Characterization of phase transitions by the analysis of crystal structures (2009)

Joachim Angelkort

In this thesis results of the investigations of the mechanisms of solid-solid phase transitions are reported on basis of the exemplary characterization of the phase transition of the metalorganic compound Eu(SC36H49)2 and of the inorganic transition-metal compounds TiI3 and CrOCl. The phase transitions were surveyed temperature dependently by the performance of single-crystal X-ray diffraction experiments and measurements of the magnetic susceptibility. The X-ray diffraction experiments were carried out as data collections of integrated intensities of reflections and as measurements of profiles on selected reflections in so-called omega-2theta maps. The data sets of the integrated intensities were used to determine the crystal structures at different temperatures. By the comparison of the high- and the low-temperature crystal structures the mechanisms of the phase transitions of the compounds Eu(SC36H49)2 and TiI3 were determined. Furthermore the transition temperatures of all three compounds were determined by temperature-dependent measurements of intensities of superstructure reflections. From the omega-2theta maps the monoclinic lattice distortion of the low-temperature phase of CrOCl was determined.

Plant Species and Functional Diversity along Altitudinal Gradients, Southwest Ethiopian Highlands (2009)

Desalegn Wana Dalacho

Understanding how biodiversity is organized across space and time has long been a central focus of ecologists and biogeographers. Altitudinal patterns of richness gradients are one of such striking patterns in the landscape. Despite its historical and ecological importance as a heuristic natural experimental site for development of ecological theories, the emergent patterns and mechanisms that structure them are poorly understood. This is partly because of the complex relationships of species to the environment and the choice of the response variable itself, i.e. using taxonomic richness as a metrics of diversity. This thesis, therefore, applies plant functional types (hereafter PFTs) approach to study the response of vegetation to environmental factors in the southwest Ethiopian highlands. It focuses on the classification of the vegetation into a few main plant functional response categories and relate them to environmental variables. For pattern identification and mechanistic explanations, a deconstructive approach of the taxonomic richness into its constituent components was used. Furthermore, the potential effects of land use/land cover change and global warming on the biodiversity of the study area was investigated. The results reveal that the application of plant functional types is a promising tool to understand vegetation-environment relationships. Local topographic attributes (altitude and slope) and soil properties found to structure the variance in the relative abundance of PFTs along environmental gradients. Moreover, specific response to drought favours the abundance of species with thorns/spines and tussocks in the lowlands as opposed to chilling which favours rosettes and rhizomes PFTs in the highlands. Concerning patterns of richness along altitudinal gradients, various structures of richness appear for total vascular plant species and growth forms. Woody plants, graminoids and climbers showed a uni-modal structure while ferns and herbs revealed an increasing pattern of richness along the altitudinal gradient. By contrast, total vascular plants species richness did not show any strong response to altitudinal gradients. Climate related water-energy dynamics, species area relationships due to the physical shape of the mountain, local topographic and soil conditions were found to be predominant factors structuring the observed richness in the study area. The threats to biodiversity loss due to land use/land cover change and global warming is eminent in the study area. Land conversion for agricultural purposes was a pervasive process that had a deleterious effect on the biodiversity of the study area. Population growth, socio-economic challenges (poverty) and government policy regimes drive land cover change processes. In addition, recent climate change poses a serious challenge to the biodiversity of the study area. The results of model predictions indicated that biodiversity of the study area will suffer severe consequences of lowland biotic attrition (i.e. the net loss of species richness in the tropical lowlands caused by altitudinal range shifts in the absence of new species arriving), range gap shifts and contraction, and extinction due to expected warming at the end of this century. The model also predicted that endangered and endemic species with restricted elevational ranges will disproportionately suffer from range contraction and extinction due to warming. In conclusion, the plant functional types approach was found to be an essential tool to reduce complexity of the vegetation of the study system and to elucidate vegetation-environment relationships. Moreover, the identification of emergent patterns and attributing them to mechanistic explanations are pre-requisites for conservation planning to save biodiversity of the study area. The study also evidenced that land use/land cover change and global warming will present strong threats to the loss of biodiversity in the study area. Salvaging biodiversity in the future requires the consideration of the effect of land use and climate change on vegetation responses. Consequently, nature conservation strategies and future reserve designs should take into account options of human assisted migration across fragmented landscapes and creating dispersal routes for species to track to new thermal niches.

Reputation in Multi Agent Systems and the Incentives to Provide Feedback (2009)

Miriam Heitz Stefan König

The emergence of the Internet leads to a vast increase in the number of interactions between parties that are completely alien to each other. In general, such transactions are likely to be subject to fraud and cheating. If such systems use computerized rational agents to negotiate and execute transactions, mechanisms that lead to favorable outcomes for all parties instead of giving rise to defective behavior are necessary to make the system work: trust and reputation mechanisms. This paper examines different incentive mechanisms helping these trust and reputation mechanisms in eliciting users to report own experiences honestly.

Eine empirische Studie zum Einsatz von schülerzentrierten Unterrichtsmethoden im Natur- und Technik-Unterricht zum Thema "Wasser - Grundlage des Lebens" (2009)

Sabine Gerstner

Das Themengebiet „Wasser“ stellt einen wichtigen Schwerpunkt im Natur- und Technik-Unterricht der 5. Klasse an Gymnasien dar. Laut Lehrplan des bayrischen Kultusministeriums ist dabei auch „Naturwissenschaftliches Arbeiten“ in den Unterricht einzubeziehen. Der Einsatz schülerzentrierter Unterrichtsformen wie „Lernen an Stationen“ und „Concept Mapping“ bietet sich hierfür an. In der vorliegenden Arbeit wurde daher der Einfluss beider Unterrichtsmethoden auf kognitive und motivationale Variablen empirisch untersucht. Obwohl ein Lernen an Stationen innerhalb der Lehrerschaft hin und wieder als ein „Spaßunterricht“ mit einem nur geringen Einfluss auf kognitives Lernen angesehen wird, wurde dieses in der ersten Teilstudie einem lehrerzentrierten Unterricht gegenübergestellt. Auf beide Unterrichtsformen, welche exakt gleiche Themen behandelten, folgte eine Concept Mapping Phase zur Wissenssicherung. Somit konnte deren Einfluss auf den kurz- und langfristigen Wissenserwerb und die Motivation der Schüler getestet werden. Es zeigte sich, dass die Schüler in beiden Unterrichtsformen einen vergleichbaren langfristigen Lernerfolg erreichten, obwohl den getesteten Schülern die Methode des Lernen an Stationen bis dato gänzlich unbekannt war. Auch die Methode des Concept Mapping wurde in den Testklassen zum ersten Mal eingesetzt und wirkte sich dennoch, verglichen mit einer Kontrollgruppe ohne Konsolidierungsphase, positiv auf den kurzfristigen Wissenserwerb aus. Das gemessene Interesse, die wahrgenommene Wahlfreiheit und Kompetenz der Schüler war bei beiden Unterrichtsformen sehr hoch und unterschied sich nicht. In der zweiten Teilstudie wurden die erstellten Concept Maps bezüglich ihrer Qualität untersucht. Es zeigte sich, dass nach dem lehrerzentrierten Unterricht komplexere Concept Maps produziert wurden als dies nach dem Stationenlernen der Fall war. Dabei wurde zudem ein Geschlechtereffekt gemessen. Mädchen erstellten demnach die komplexeren Maps. Die Interaktion der Variablen „Geschlecht“ und „Anzahl von Wissensnetzen innerhalb einer Concept Map“ zeigte einen signifikanten Effekt auf das langfristig erworbene Wissen. Die dritte Teilstudie lieferte Einblick in das Langeweileempfinden von Schülern während des regulären Natur- und Technik-Unterrichts. Der Einsatz eines Langeweilefragebogens nach Lohrmann (2008) wurde in dieser Studie zum ersten Mal im Natur- und Technik-Unterricht angewandt. Eine Clusteranalyse erbrachte vier Schülertypen: „Optimal geforderte“ und „mäßig geforderte“ Schüler auf der einen Seite sowie Schüler, die regelrecht während des Unterrichts „abschalten“ oder „gelangweilt“ sind. Besonders hohes Interesse an neuen Unterrichtsformen (Lernen an Stationen) zeigten vor allem die Schüler, die bereits mit dem regulären Natur- und Technik-Unterricht sehr zufrieden waren. Alle drei Studien zusammengenommen lieferten neue Indizien für die Effektivität von schülerzentrierten Unterrichtsformen im Natur- und Technik-Unterricht an Gymnasien. Es konnte gezeigt werden, dass die hier angeführten schülerorientierten Unterrichtsformen ohne Probleme und längere Einführungsphasen eingesetzt werden können. Bereits deren erster Einsatz liefert vergleichbare Resultate sowohl im kurzfristig als auch langfristig erworbenen Wissen. Schon allein diese Ergebnisse sollten daher Lehrer in ihrem Vorhaben bekräftigen, konsequent auch auf neue Lernformen zu setzen.

The evolution of Saharan dust input on Lanzarote (Canary Islands) – influenced by human activity in the Northwest Sahara during the early Holocene? (2009)

Hans von Suchodoletz Hedi Oberhänsli Dominik Faust Markus Fuchs Cécile Blanchet Tobias Goldhammer Ludwig Zöller

An overall Holocene increase of Saharan dust input to the Canary Islands and to the North Canary Basin is accompanied by a strong coarsening of Saharan dust in loess-like sediments deposited on Lanzarote from ~7–8 ka. No similar coarsening events are indicated in investigations of the sedimentological record for the last 180 ka, a period showing several dramatic climate changes. Therefore a mobilisation of Holocene dust by anthropogenic activity in the northwest Sahara east of the Canary Islands is assumed. Although scarce archaeological data from the coastal area of that region does not point to strong anthropogenic activity during the early Holocene, a high density of unexplored archaeological remains is reported from the coastal hinterlands in the Western Sahara. Thus, the hypothesis of early anthropogenic activity cannot be excluded.

Proceedings of the 11th European Agent Systems Summer School Student Session (2009)

Tina Balke Serena Villata Daniel Villatoro

This volume contains the papers presented at the Student Session of the 11th European Agent Systems Summer School (EASSS) held on 2nd of September 2009 at Educatorio della Providenza, Turin, Italy. The Student Session, organised by students, is designed to encourage student interaction and feedback from the tutors. By providing the students with a conference-like setup, both in the presentation and in the review process, students have the opportunity to prepare their own submission, go through the selection process and present their work to each other and their interests to their fellow students as well as internationally leading experts in the agent field, both from the theoretical and the practical sector.

First principles phase diagram calculations in group IV carbides and Mg2SiO4 liquid from Molecular Dynamics (2009)

Omar Adjaoud

Atomistic simulations on stability and physical properties of Earth materials are playing an increasingly important role in high pressure mineralogy. Such computations can provide guidance for experimental studies and insight into underlying causes of observations, or explore conditions and properties that are inaccessible to experiments at the current time. A variety of approaches have been applied in such research, with density functional theory based methods having become a reliable tool in computational mineral sciences. Despite this progress there are interesting problems which density functional theory based methods are not able to tackle on a routine basis. These include computations of phase diagrams and transport properties in liquids. The sub-solidus phase diagrams of the binary systems TiC-ZrC, TiC-HfC, ZrC-HfC at ambient pressure are computed based on electronic structure and energy calculations within density functional theory. Formation energies for a large number of supercells with compositions of (M1,M2)C, M1, M2 = Ti, Zr, or Hf, are computed by a plane-wave pseudopotential method. The energies serve as a basis for fitting cluster expansion Hamiltonians that are used to explore the sub-solidus phase diagram, i.e. stability of ordered intermediate compounds and the degree of miscibility in the systems by Monte Carlo simulations. Hamiltonians can be fit to the formation energies of the cells directly or after taking into account vibrational free energy. As it is prohibitive to compute vibrational free energy for all configurations they are approximated by the transferable force constant scheme: nearest neighbor force constants are computed for the end-member crystals with imposed but varying lattice parameters. The resulting bond stiffness versus bond length relationships are applied to the superstructures, using the relaxed bond lengths and their chemical identities as predictor. Significant miscibility gaps were predicted for the binaries TiC-ZrC and HfC-TiC, with consolute temperature in excess of 2000 K, in good agreement with experiments. The system HfC-ZrC shows complete miscibility at room temperature. Approximately symmetric phase diagram for HfC-TiC and asymmetric phase diagrams for HfC-ZrC and TiC-ZrC were predicted. With the success of the method in the simple carbide systems similar computations can now be performed for geologically relevant mineral families. Mg2SiO4 liquid at high pressure is of central importance in our understanding of melts that occur in the deep Earth and in particular in the early history of our planet, when it was in a magma ocean stage. Due to high melting temperatures little is known experimentally about its high pressure thermodynamic and transport properties that govern magma ocean structure and dynamics. Molecular dynamics simulations now fill this gap. Currently, density functional theory based computations are restricted to a few hundred atoms and a few picoseconds. While such simulations allow for determination of thermodynamic properties, longer run durations and larger cells are necessary to obtain transport properties such as diffusivity and viscosity with sufficient precision. By contrast, semi-empirical pair potentials provide an efficient route to perform large-scale molecular dynamics simulations. They suffer, however, from the fact that the transferability of the potentials to different conditions is not guaranteed. The development of aspherical flexible potentials that are fit to density functional theory results bridge the gap between ab-initio methods and classical potentials. Comprehensive large-scale molecular dynamics simulations using the aspherical ionic model were performed on Mg2SiO4 melt to obtain thermodynamic properties as well as diffusivity and viscosity. The pressure-temperature range covered was 0-32 GPa and 2600-3200 K. The thermodynamic parameters agree well with density functional theory based results: the Grüneisen parameter $gamma$ was found to increase significantly with pressure. Diffusivity is predicted to decrease and viscosity to increase with pressure. Both transport properties were readily fit with closed Arrhenius expression. Independent estimates on diffusivity and viscosity allows an examination of their relation through the Eyring equation, often employed to compute viscosity from diffusivity data. The proportionality factor between them, the translation distance for a diffusion event $lambda$, is determined as $lambda$=18 AA at 0 GPa, and decreases with pressure. This is in good agreement with previous molecular dynamics simulations using classical potentials, but significantly larger than other estimates of $lambda$ based on experimental data that yield 2.8 AA $ < lambda < $ 5 AA. Combining the thermodynamic and viscosity fits a magma ocean adiabat and the associated viscosity profile were computed.

Private Altersvorsorge in Deutschland - Empirische Analyse der Einflussfaktoren für private Altersvorsorge am Beispiel der Riester-Rente. (2009)

Christian Pfarr

Mit Einführung der Riester-Rente im Jahr 2001 wurde in Deutschland der Weg in eine private, staatlich geförderte Altersvorsorge geebnet. Die Determinanten, die den Ab-schluss einer Riester-Rente beeinflussen, sind allerding nur rudimentär erforscht. In der vorliegenden Arbeit wurde mit Daten des Sozioökonomischen Panels zunächst die Zu-friedenheit mit den sozialen Sicherungssystemen und die Bereitschaft für private Altersvorsorge mittels Ordered Probit Modellen für das Jahr 2002 analysiert. Es zeigt sich, dass besonders diejenigen, die bereits für das Alter vorsorgen, auch einer staatlich ge-förderten Riester-Rente eher zu geneigt sind als solche, die sich mit diesem Themenfeld bisher nicht beschäftigt haben. In einem zweiten Schritt wurde für die Jahre 2004, 2006 und 2007 in einer Panelanalyse die Wahrscheinlichkeit für den Besitz einer Riester-Rente empirische überprüft. Die Ergebnisse zeigen, dass besonders Frauen, Ostdeutsche und Personen, bei denen Kinder unter 16 Jahren im Haushalt leben, besonders von der Riester-Rente angesprochen werden. Es wird aber auch für die Analyse der Riester-Rente deutlich, dass Mitnahmeeffekte eine bedeutende Rolle spielen.

Sintering kinetics and properties of highly pure lead zirconate titanate ceramics (2009)

Xianliang Huang

Lead zirconate titanate (PZT) has been widely applied in actuators and sensors due to its excellent piezoelectric and ferroelectric properties. However, impurities, one of the major problems involved in the mass production of PZT ceramics, have not attracted enough attention. In this thesis, investigations on the effects of impurities from the raw materials on the sintering and properties of lead zirconate titanate with a composition of PbZr0.53Tit.47O3 were conducted. The impact of starting materials, lead nonstoichiometry, and dopants was examined. The sintering behavior was monitored in a thermo-optical dilatometer and a kinetic-field approach was employed to obtain the activation energy for sintering of PZT ceramics with different compositions. The bulk ceramics were characterized in terms of microstructure, dielectric, piezoelectric and ferroelectric properties. At first, a comparison in sintering between the PZT samples prepared from industrially used (IM) and highly pure raw materials (HM) was made. Reduced sintering temperatures and higher densification rate were observed on the IM sample owing to the secondary phase on the grain boundary. Different electric properties of these two samples were also evidenced. To evaluate their contributions to the observed difference of IM and HM samples, various impurities, which were identified in the IM raw materials, were added in the highly pure samples. It was shown that the sintering was changed through the formation of charged vacancies (impurity Na, Fe, Al, Y) or melt phase (Si) with low melting point. The most important impurity species was identified as Na, Y and Si and their effect on the ceramics properties was investigated as a function of dopant concentration. They showed grain growth inhibition effect on PZT ceramics. The strongest effect was achieved by doping with Na. The grain size was reduced from 13µm of undoped PZT to 2µm at a doping level of 1mol%. The dielectric constant was increased with Na doping, which was attributed to the decreasing grain size. In addition, because of the oxygen vacancies caused by the Na doping, “hard” piezoelectric behavior and ferroelectric properties were observed. Rare earth impurity, such as Y, with a valence and ion radius between A site and B site elements in PZT lattice, results in a combination of “soft” and “hard” characteristics. Melt phase formed from Si showed deteriorated effect on the properties of PZT ceramics. Deviations from the stoichiometric composition could result when the impurities were not considered in the weight fractions of the raw materials. The lead content in the system was affected by the crystalline phase of starting components as well. PbO concentration was changed during calcination depending on the formation kinetics of intermediate lead titanate. Sintering temperatures were dramatically reduced and densification rates were strongly enhanced by the introduction of lead oxide excess. The reason was believed to be associated with the liquid phase formed by PbO during sintering because of its low melting point. Rapid densification was observed at low level of PbO excess. However, a sluggish rearrangement process with low densification rate occurred in the PZT with 3.0% PbO excess at a temperature below the melting point of PbO. A small force (as small as 0.1MPa) on the sample could result in rapid densification and an additional densification maximum was evidenced. The tetragonal lattice distortion in the lead deficient samples was verified by Rietveld refinement, from which internal stress was introduced and attributed to the high dielectric constant. Moreover, the increasing amount of lead deficiency could result in the segregation of ZrO2. It shifts the Zr/Ti ratio to the Ti-rich side, which may be attributed to a higher dielectric constant as well. The lead excess is favorable in improving both the microstructure and electrical properties of PZT ceramics. However, deteriorated properties were found in the samples in which the lead oxide excess is beyond a certain level (1.5 mol% PbO). The kinetic field diagram was constructed using the shrinkage data from the optical dilatometry. Different dependence of activation energy on the fractional density was observed. It is attributed to the variation in the activation energies in densification and grain growth. By fitting the iso-strain lines, activation energy between 350-360 kJ/mol was obtained for densification of pure HM PZT sample and samples doped with 0.5% Na or Si. Smaller values were acquired for grain growth. Although liquid phase was present in Si-doped samples and the ones with PbO excess, a better match can be achieved using a solid state sintering model. The enhanced inhomogeneity and the rapid densification were suggested to explain the difficulty in fitting the sintering curves of 1.5wt%PbO added sample.

Refine

Author

Year of publication

Document Type

Language

Keywords

Institute

93 search hits