Refine
Year of publication
Document Type
- Doctoral Thesis (820)
- Article (212)
- Book (112)
- Contribution to a Periodical (102)
- Working Paper (62)
- Part of Periodical (21)
- Conference Proceedings (17)
- Other (16)
- Review (10)
- Master's Thesis (9)
Language
- German (813)
- English (501)
- French (75)
- Multiple languages (15)
- Russian (1)
Keywords
- Deutschland (81)
- Luxemburg (51)
- Stress (40)
- Schule (34)
- Schüler (30)
- Modellierung (28)
- Politischer Unterricht (28)
- Fernerkundung (25)
- Geschichte (24)
- Demokratie (23)
Institute
- Psychologie (210)
- Geographie und Geowissenschaften (209)
- Politikwissenschaft (125)
- Universitätsbibliothek (82)
- Rechtswissenschaft (77)
- Wirtschaftswissenschaften (66)
- Mathematik (65)
- Fachbereich 4 (57)
- Medienwissenschaft (57)
- Fachbereich 6 (50)
Many real-life phenomena, such as computer systems, communication networks, manufacturing systems, supermarket checkout lines as well as structural military systems can be represented by means of queueing models. Looking at queueing models, a controller may considerably improve the system's performance by reducing queue lengths, or increasing the throughput, or diminishing the overhead, whereas in the absence of a controller the system behavior may get quite erratic, exhibiting periods of high load and long queues followed by periods, during which the servers remain idle. The theoretical foundations of controlled queueing systems are led in the theory of Markov, semi-Markov and semi-regenerative decision processes. In this thesis, the essential work consists in designing controlled queueing models and investigation of their optimal control properties for the application in the area of the modern telecommunication systems, which should satisfy the growing demands for quality of service (QoS). For two types of optimization criterion (the model without penalties and with set-up costs), a class of controlled queueing systems is defined. The general case of the queue that forms this class is characterized by a Markov Additive Arrival Process and heterogeneous Phase-Type service time distributions. We show that for these queueing systems the structural properties of optimal control policies, e.g. monotonicity properties and threshold structure, are preserved. Moreover, we show that these systems possess specific properties, e.g. the dependence of optimal policies on the arrival and service statistics. In order to practically use controlled stochastic models, it is necessary to obtain a quick and an effective method to find optimal policies. We present the iteration algorithm which can be successfully used to find an optimal solution in case of a large state space.
Hamanns Rittergrabmäler
(2002)
Hamanns knight tombs - Reception and transformation of a French type The thesis deals with an important group of tombs in the history of medieval art. The object of research is a particular group of figurative tombs for nobles from Marburg, Cappenberg, Bielefeld and Münstereifel. These tombs were brought to art historians attention by Richard Hamann in the year 1929. For the first time the research at hand considers the tombs as particularly instructive examples thus strengthening the basis for medieval studies. They also explain the function of memorial sculpture in medieval history. Interdisciplinary approaches of medieval studies are combined with critical valuation of historical research as well as fundamental research and the interpretation of sources. The up-to-date unpublished sources from the starting point for the specific research of the tombs. Biographic-genealogical aspects, actual church law, the historical-social context and the memorial purpose are the research areas from which the meaning of tombs was elaborated, as well as taking into consideration the medieval mentality about death and memory. The results of the research give a new valuation of these tombs, which form a key position regarding the spectrum of their statement for the development of art history and memorial history in the 14th century. The tombs reveal contact between artist and patron. They help to find out more about social circumstances intertwined with medieval art comissions. These memorials prove the existence of artistic grave specialists in the western German region of the 14th century, who were recommendet in turn by the closely related noble familiy. On a social-cultural level these memorials show the importance of royal French art as a distinctive model further more expressing the need for oneself to express social status by the means of art. These memorials are closely related to certain people. They are crucial to the research of medieval memorial sculpture. The memorial from Cappenberg is a paradigm for the shift from a cult ideology to a pure economic ideology thus showing proof of patroned memorials. Whereas the tombs in Marburg, Bielefeld and Münstereifel are keyworks showing the relevance of spontaneous and private memorial of the dead.
Changes in the cardiovascular system are an often described state in eating disorders. Women with anorexia and bulimia nervosa and control persons were studied before and after a treatment in a psychosomatic clinic. Using different methods cardiovascular reactivity was evaluated in rest and during mental stress and exercise. Improvements after treatment were defined by weight gain, an increase of the trijodthyroninlevel and no more purging in the last three weeks. The anorectics showed higher epinephrinlevels than the other women. The cardiovascular parameters demonstrated an increase of parasympathic activity and a decrease of sympathetic activity in eating disorders. However, the reactivities on stressors showed no differences in comparison to the control group. No changes were observed during the treatment apart from the heartrate, which showed a tendency to increase in the last week of therapy. Because the improvements during the therapy were generally small, within the present study it could not be clarified wether the observed alterations are reversible. An increase of the parasympathic activity in autonome regulation of the heart in eating disorders has been demonstrated and the reactivity on stressors appears to be normal.
Ausgehend davon, daß die nachweislich prominente Berichterstattung über bezahltes Dating sich nicht auf einen hohen Nachrichtenwert zurückführen läßt, sondern auf verkaufstechnische Faktoren und vor allem auf das "kulturelle Potential" des Themas Jugend, untersucht die folgende Arbeit, welche Normen und Werte in der Darstellung des Phänomens propagiert wurden, und ob sich in der Darstellung Muster erkennen lassen.
Considering actual climatic and land use changes the problem of available water resources or the estimation of potential flood risks gain eco-political and economical relevance. Adequate assessments, thus, require precise process-based hydrological knowledge. Spatially distributed hydrological modelling enables a both abstractive and realistic description of hydrological processes, and therefore contributes to the understanding of the hydrological system- responses. Referring to the example of the mesoscale Ruwer basin (a tributary to the Mosel river), a modified version of the distributive modelling system PRMS/MMS (Precipitation Runoff Modeling System/Modular Modeling System) is applied to calculate spatially and temporally explicit water budgets. To achieve modelling results as precise as possible, integration of detailed land use information (spatial distribution of the existing land use classes, crop- and site-specific growth patterns) is necessary. This information is derived here by analysis of multitemporal, geometrically and radiometrically pre-processed Landsat TM-data. This enables separation of different land use classes and differentiated quantification of the leaf area index (LAI). The LAI is estimated by a spectral unmixing approach using statistically optimized endmember sets, referring to the example of winter grain and grassland plots. As a result, numerical inputs (coefficients for calculating evapotranspiration, interception storages) and extracted non-numerical (classified) information can be provided for hydrological modelling. The version of PRMS applied in this study allows important land use terms to be parameterized in high temporal resolution. Using model input derived from the available satellite data, simulation results are obtained that prove to be realistic compared to gauge data and with respect to their spatial differentiation. Results differ significantly from those obtained by using parameters from literature or by experience without distinguishing specific and site-dependent growth patterns. It can be concluded that the quality of modelling results notably improves by integration and quantitative analysis of remote sensing data; thus, these methods are a significant contribution to physically-based hydrological modelling.
Hydrodynamic processes play a fundamental role in the distribution of salt within mangrove-fringed estuaries and mangrove forests. In this thesis, two hydrodynamic processes and their ecological implications were examined. (1) Passive Irrigation and Functional Morphology of Crustacean Burrows in Rhizophora-forests. The mangrove Rhizophora excludes more than 90% of the seawater salt at water intake at the roots. By means of conductivity methods and resin casting, it was found that crustacean burrows play a key role in the removal of excess salt from the root zone. Salt diffuses from the roots into the burrows, and is efficiently flushed from the burrows by rainwater infiltration and tidal irrigation. The burrows contribute significantly to favourable conditions for the growth of Rhizophora trees. (2) Trapping of Mangrove Propagules due to Density-driven Secondary Circulation in Tropical Estuaries. In North East Australian estuaries, mangrove propagules are drifted upstream by density-driven axial surface convergences. Propagules accumulate in hydrodynamic traps upstream from suitable habitat, where they are trapped at least for the entire tropical dry season. Axial convergences may provide an efficient barrier for propagule exchange across estuaries. In such estuaries, mangrove populations can be regarded as floristically isolated, not unlike island communities, even though the populations lie on a continuous coastline. This effect may contribute to the disjunct distribution observed in some mangrove species. The outcomes of this work contribute to the understanding of the importance of salt as a growth and habitat-restricting factor in the mangrove environment.
The spatio-temporal changes of rangelands in the European Mediterranean are analysed with remote sensing and GIS-based methods, referring to an example of two mountain ranges in central Crete, Greece. The focus is to monitor and assess land degradation and its potential correlation with ecological and socio-economic boundary conditions. Particular attention is paid to the unique European Mediterranean setting and the Greek integration within the European Union. After a geometric correction of the satellite data, a radiometric pre-processing chain is employed to calculate reflectance values via a DEM-based atmospheric correction. The computation of pixel-wise soil and vegetation fractions is based on a spectral unmixing approach. A subsequent time-series analysis reveals spatially explicit trends, mean vegetation cover and phenological variability. Results do not only exhibit significant differences between the two test sites, but also within the respective regions. In both mountain ranges there extended areas with degrading vegetation patterns are revealed. However, along the Southern Cretan coast those processes are bound to a much lower base level of vegetation cover. Beyond trends and mean vegetation abundance, the phenological variability is another important figure which is employed to characterise plant communities from space. Moreover, a satellite-based map of soil development proves the correspondence between soil and vegetation degradation processes. Vegetation cover and change are then analysed with regard to aspect, slope, elevation and geological substrate to allow for a comparison of degradation processes and natural boundary conditions. In a second step, the analyses are extended to find interrelationships with socio-economic determinants. Based on these results the degradation risk for the grazing habitats of central Crete is assessed in differentiated ways. We neither encounter the scenario of irreversible degraded rangelands, nor a cultural landscape in an equilibrium under intense human influence.
Die ubiquitäre Verbreitung von Computern hat dazu geführt, daß immer mehr Arbeitsabläufe durch Software unterstützt werden. Mit der ISO 13407 liegt eine Normierung vor, die den Entwickler von Software dazu anhält, die Anforderungen der Benutzer an sein Produkt zu berücksichtigen. In den letzten Jahrzehnten hat sich die objektorientierte Softwareentwicklung als gängige Entwicklungsmethode durchgesetzt, die durch eine Kapselung von Methoden und Daten zu Objekten und durch ein iteratives Vorgehen geprägt ist. Dieses Vorgehen und die Anforderungen der Norm rücken die Perspektive des Benutzers ins Zentrum des Interesses des Softwareentwicklers. Damit die Anforderungen der Nutzer berücksichtigt werden können, fehlt ein Werkzeug, mit dem die Sicht auf den Arbeitsvorgang effizient, vollständig und zutreffend erhoben werden kann. In der Dissertationsschrift werden zuerst die Bedürfnisse der Beteiligten am Softwareentwicklungsprozeß, nämlich die der objektorientierten Entwickler einerseits und der Benutzer andererseits, aus den gängigen theoretischen Konzepten abgeleitet. Dann wird das Instrument zur Vorgangsanalyse (IVA) vorgestellt und die Konstruktion anhand der Bedürfnissen der Beteiligten erläutert. Beim Instrument zur Vorgangsanalyse handelt es sich um eine Kombination aus strukturierten Interview und Strukturlegetechnik, die die Aufgabe des Befragten und den umgebenden Arbeitsvorgang mit Hilfe eines einfachen Paper-Pencil- Verfahrens visualisiert. Im Anschluß an die Vorstellung des Verfahrens werden anhand der Gütekriterien für qualitative Verfahren Prüfkriterien abgeleitet, um das Instrument zu validieren. Es werden vier unterschiedliche Untersuchungen mit verschiedenen Herangehensweisen an die Klärung der Prüfkriterien vorgestellt. Die Ergebnisse dieser Überprüfung belegen, daß das Instrument zur Vorgangsanalyse geeignet ist, im Prozeß der objektorientierten Softwareentwicklung die Zusammenarbeit zwischen den Entwicklern und den Benutzern zu unterstützen.
Soziale Dienste in Taiwan
(2001)
Soziale Dienste sind Ausdruck einer wichtigen Form von Helfen innerhalb einer Gesellschaft. Die Entfaltungsmöglichkeit und der Entwicklungsgrad der sozialen Dienste sind nicht unabhängig von spezifischen räumlichen und zeitlichen Hintergründen, und sie werden auch von den gesamtgesellschaftlichen Bedingungen (z. B. politisch-rechtlichen, wirtschaftlichen, soziokulturellen Faktoren) beeinflusst. Um die Besonderheiten der sozialen Dienste innerhalb der taiwanesischen Gesellschaft zu verdeutlichen, sollen die oben erwähnten Hintergründe und Bedingungen analysiert und dargestellt werden. In Taiwan erfolgte die Entwicklung wohlfahrtsstaatlicher Institutionen und Programmen im Vergleich zu Westeuropa zeitlich schnellen. Dabei ist ein Zusammenhang zu sehen mit der gezielt vorangetriebenen wirtschaftlichen Modernisierung. Dies gilt auch für die Demokratisierungsbewegung, die gleichzeitig auf Druck von unten wie auf Initiative von oben ausging. Sozialpolitische Maßnahmen konnten nur dann Erfolg haben, wenn Systemvertrauen gewonnen werden konnte. Dies erwies sich in Taiwan als notwendig, weil in der taiwanesischen Gesellschaft traditionell nur eine Vertrauensbasis innerhalb überschaubarer Personenkreise bestand. In dieser Arbeit zeigte es sich, dass entgegen einer häufig geäußerten Behauptung von der Überlegenheit "asiatischer Werte" bestimmte kulturelle Muster (z. B. Drei-Generationen-Zusammenleben) angesichts eines rasanten sozialen Wandels anpassungshemmend wirken werden können. Es handelt sich im vorliegenden Fall um die innerfamiliäre Solidarität bei der Versorgung älterer Angehöriger. Wenn dieses Leitbild weiterhin Orientierung geben soll, müssen in der sich verändernden Gesellschaft unterstützende Maßnahmen entwickelt werden. Ohne entsprechende Innovationen auf diesem Gebiet und in verwandten Bereichen gerät der "Confucian welfare state" in Gefahr.
Wastewater treatment is of great financial concern in many states of Germany. In the rural areas of the Saarland (German state at the border to Luxembourg and France) investments for wastewater treatments in the next years will mount up to 400 mio. €. Nevertheless, decision makers are still left with the question, if these investments result in an effective and sustainable water treatment. To answer this question, the ministry of environment, related authorities and the University of the Saarland (Geographical Institute) started a Project to investigate seven small headwater catchments with predominantly Triassic series of Muschelkalk. Aims of this study were the following: (i) the description of the spatial variability of water chemistry upstream and downstream of small villages (in these villages only mechanically treated waste water is discharged into the brooks), (ii) calculation of nutrient loads of differently managed catchments (predominantly woodland, meadows or fields) and (iii) the relative importance of non-point pollution sources to point pollution sources. Results indicated that spatial variability of nitrate concentration during base-flow conditions was quite similar in intensively used agricultural areas. Nitrogen fluxes were predominantly controlled hydrologically. The nitrogen load (kg N per ha) from non-point pollution sources amounts from 32.5 to 43 kg N / ha * a in intensively used agricultural areas. This load, forecast to one square-km, is equal to the N-load of 800 " 1000 population equivalents. Thus, non-point pollution sources are a major part of the overall nitrogen pollution in the rural areas. The results are important criterias for the sewage disposal plan of the Saarland (disposal plans are obligate according to German water law) and can serve as a first part of a river basin management according to the European Water Framework Directive. To lower non-point N-pollution changes in agricultural management practices are necessary.
