Neurons are sensitive to specific aspects of natural stimuli, which are according to different statistical criteria an optimal representation of the natural sensory input. Since these representations are purely sensory, it is still an open question whether they are suited to generate meaningful behavior. Here we introduce an optimization scheme that applies a statistical criterion to an agent s sensory input while taking its motor behavior into account. We first introduce a general cognitive model, and second develop an optimization scheme that increases the predictability of the sensory outcome of the agent s motor actions and apply this to a navigational paradigm.In the cognitive model, place cells divide the environment into discrete states, similar to hippocampal place cells. The agents learned the sensory outcome of its action by the state-to-state transition probabilities and the extent to which these motor actions are caused by sensory-driven reflexive behavior (obstacle avoidance). Navigational decision making integrates both learned components to derive the actions that are most likely to lead to a navigational goal. Next we introduced an optimization process that modified the state distributions to increase the predictability of the sensory outcome of the agent s actions.The cognitive model successfully performs the navigational task, and the differentiation between transitions and reflexive processing increases both behavioral accuracy, as well as behavioral adaptation to changes in the environment. Further, the optimized sensory states are similar to place fields found in behaving animals. The spatial distribution of states depends on the agent s motor capabilities as well as on the environment. We proofed the generality of predictability as a coding principle by comparing it to the existing ones. Our results suggest that the agent s motor apparatus can play a profound role in the formation of place fields and thus in higher sensory representations.

Presented investigation and quantification of natural remediation of highly contaminated surface water systems located in South Ural via humic substances is the first step for sustainable developing of nuclear industry. In the surface water systems, humic substances are shown to promote the immobilization of radionuclides and decreasing of the bioavailability for fish contamination in the investigated water bodies. As proved in this thesis, the influence of humic substances on radionuclide sorption is provided by their special properties of a reversible transform into micelles. The theoretical approach based on consideration of protons as fermion gas in water solution was assumed and applied to this phenomenon, being due to the duel nature of humic substances molecules. The influence of humic substances is quantified as a modified Henry s low of sorption. Investigation of changing of electrostatical status of micelles with increasing of humic substances concentration in water solution leads to modelling of remediation effect of humic substances in respect to influence on fish in contaminated waters. This effect was interpreted and quantified, based on properties of proteins of gill s cell membranes under certain conditions in water solution. Humic substances appreciably influence the chemical and biological interactions between radionuclides and the environment that has experienced increasing interest concerning the remedial uses of humic materials.

A question concerning not only modellers but also practitioners is: Under what circumstances can mutual cooperation be established and maintained by a group of people facing a common pool dilemma" A step before this question of institutional influences there is need for a different way of modelling human behaviour that does not draw on the rational actor paradigm, because this kind of modelling needs to be able to integrate various deviations from this theory shown in economic experiments. We have chosen a new approach based on observations in form of laboratory and field observations of actual human behaviour. We model human decision making as using an adaptive toolbox following the notion of Gigerenzer. Humans draw on a number of simple heuristics that are meaningful in a certain situation but may be useless in another. This is incorporated into our agent-based model by having agents perceive their environment, draw on a pool of heuristics to choose an appropriate one and use that heuristic.Behavioural differences can be incorporated in two ways. First, each agent has a number of attributes that differ in values, for example there are more and less cooperative agents. The second behavioural difference lies in the way, in which heuristics are chosen. With this modelling approach we contribute to a new way of modelling human behaviour, which is simple enough to be included into morecomplex models while at the same time realistic enough to cover actual decision making processes of humans. Modellers should be able to use this approach without a need to get deep into psychological, sociological or economic theory. Stakeholders in social dilemmas, who may be confronted with such a model should understand, why an agent decides in the way it does.

Die Basis für den therapeutischen Einsatz elektrischer Felder bei der Behandlung von Knochenbrüchen liegt in der Existenz von belastungsabhängigen elektrischen Potentialen im Knochen. Die zellulären Wirkungsmechanismen sind jedoch unverstanden. Um zu untersuchen, ob und wie elektrische Felder Wachstum und Differenzierung von Knochenzellen beeinflussen, wurden humane Osteosarcomazellen (HOS TE85) und aus Minischweinen isolierte primäre Osteoblasten mit elektrischen Feldern im Frequenzbereich von 0.1 Hz bis 100 kHz befeldet und verschiedene zelluläre Parameter zeitabhängig gemessen. Das elektrische Feld wurde mittels platinierten Platinelektroden appliziert, um ausreichend hohe Feldstärken bei gleichzeitig guter Kontrolle über die im Gewebe erzeugte Wellenform zu gewährleisten. Beim Einsatz von Elektroden müssen jedoch elektrochemische Reaktionen an der Elektrodenoberfläche berücksichtigt werden. Daher wurden verschiedene Elektroden für die in vivo- und in vitro-Stimulation mit elektrischen und numerischen Methoden untersucht und verglichen. Das führte einerseits zur Erarbeitung verschiedener Kriterien zur Auswahl geeigneter Elektrodenmaterialien und -geometrien. Andererseits konnten detaillierte Angaben zur effektiven Feldstärke und Feldverlauf in der Zellebene sowie zu elektrochemisch bedingten Nebenwirkungen gemacht werden. Es konnte gezeigt werden, dass elektrische Felder das Signalsystem und den Stoffwechsel von Knochenzellen im gesamten untersuchten Frequenzbereich beeinflussen. Die Richtung des Nettoeffekts war jedoch im oberen und im unteren Frequenzbereich unterschiedlich. Im Frequenzbereich über 1 kHz fanden wir immer eine Erhöhung des Wachstums und der Konzentration der "second messenger" und eine Herabsetzung der Konzentration der reaktiven Sauerstoffverbindungen (ROS). Bei Frequenzen unter 1 kHz wurde dagegen eine Erhöhung der Aktivität der alkalischen Phosphatase und des oxidativen Stress beobachtet. Signifikante Effekte traten jedoch nur bei Feldstärken oberhalb 100 V/m auf. Hinweise auf bevorzugte Frequenzen oder Wellenformen, die für "Fenstereffekte" sprechen würden, konnten nicht gefunden werden. Da alle zellulären Parameter an einem einheitlichen System gemessen wurden, ließen sich die Ergebnisse in ein Modell der feldinduzierten Signaltransduktion integrieren. Prinzipiell muss man von einem gemeinsamen Effekt mehrerer Signalwege ausgehen. Dabei kann die Erhöhung der intrazellulären Kalziumkonzentration als ein genereller Mechanismus der Feldwirkung angesehen werden. Dafür sind sowohl der Influx als auch die Freisetzung von Kalzium aus intrazellulären Speichern verantwortlich. Es konnte weiterhin gezeigt werden, dass auch cGMP und Prostaglandin E2, jedoch nicht cAMP an der Vermittlung der Feldwirkung beteiligt ist. Außerdem wurde die Translokation der mitogen-aktivierten Proteinkinase (MAPK) beeinflusst. Trotzdem sind die beobachteten Effekte relativ schwach im Vergleich zu publizierten klinischen Erfolgen. Es muss daher in vivo Verstärkungsmechanismen geben, die durch Untersuchungen an Zellkulturen nicht erfasst werden können. / The therapeutic use of electric fields in the treatment bone fracture healing is based on the existence of different load dependent electric potentials in bone. However, the cellular mechanisms of field action are still not understood. We investigated the effect of electric fields on proliferation and differentiation of human osteosarcoma cells (HOS TE85) and primary osteoblasts isolated from mini pigs. The cells were exposed to electric fields (0.1 Hz - 100 kHz) and various cellular parameters were measured. The field was applied using platinized platinum electrodes ensuring sufficiently strong electric fields and a well controlled wave form in the tissue. Nevertheless, in this case electrochemical reactions which occur at the electrode surface have to be taken into account. That’s why various electrodes for in vivo and in vitro stimulation are characterized by electrical and numerical methods leading not only to criteria for choosing electrode materials and geometries, but also providing detailed knowledge about the electric field induced in the tissue and electrochemically induced side effects. We found that cellular signaling as well as proliferation and differentiation of bone cells are influenced by electric fields in the whole investigated frequency range. Proliferation and the second messenger concentrations are increased at frequencies above 1 kHz, whereas below 1 kHz the alkaline phosphatase activity is increased. Significant effects were found only for electric fields above 100 V/m, but we could not find any hints on preferred frequencies or wave forms ruling out "window effects". Because all cellular parameters were measured within one experimental system, the results can be summarized in a signal transduction model for the action of electric fields. Generally, a common action of multiple signaling pathways has to be assumed. The increase of the intracellular calcium concentration can be considered as a general mechanism of field action. This increase is caused by calcium release from intracellular calcium stores as well as influx of extracellular calcium. Additionally, the concentration of cGMP and prostaglandin E2, but not that of cAMP is increased by the electric field. Furthermore, the translocation of the mitogen activated protein kinase (MAPK) is influenced. Nevertheless, the field effects found are weak compared to those published in clinical studies. We suppose that there are amplifying mechanisms in vivo which could not be seen during in vitro investigations.

Ultraschnelle Energietransferprozesse zwischen den Anregungszuständen organischer Pigmentmoleküle in photosynthetischen Lichtsammelkomplexen gehören zu den schnellsten bisher untersuchten biologischen Ereignissen. Diese Vorgänge wurden insbesondere auch für den Haupt-Antennenkomplex der höheren Pflanzen (LHCII) beobachtet, der mehr als die Hälfte des pflanzlichen Chlorophylls (Chl) bindet (5 Chl b und 7 Chl a pro Monomer). Offenbar ist dieser Pigment-Protein-Komplex entscheidend für Regulationsmechanismen verantwortlich, die eine schnelle Adaptation des Photosyntheseapparats an wechselnde Licht- bedingungen ermöglichen. Die Struktur von LHCII ist mit einer Auflösung von 3.4 Å bekannt und erlaubt (im Prinzip) die Berechnung des Anregungsenergietransfers auf Basis eines Förster-Mechanismus. In diesem Zusammenhang gibt es jedoch noch zahlreiche ungeklärte Fragen, die vor allem die Orientierung der Pigmente zueinander sowie deren mögliche starke (exzitonische) Wechselwirkung betreffen. Allerdings sind konventionelle spektroskopische Methoden nicht geeignet, diese Merkmale ausreichend aufzuklären. Aus diesem Grund wird in dieser Arbeit untersucht, inwieweit neuere laserspektroskopische Methoden wie die nichtlineare Polarisationsspektroskopie in der Frequenzdomäne (NLPF) zur Ermittlung unbekannter Parameter beitragen können. Anfänglich ergaben sich besonders Fragen der Anwendbarkeit der NLPF auf solche hoch- komplexen Untersuchungsobjekte sowie der Signifikanz eventuell erzielbarer Ergebnisse. Aufbauend auf einer parallel verfaßten Dissertation zu theoretischen Aspekten der NLPF- Methode [1] wurde daher ein vereinfachtes System modelliert, das die Heterogenität der individuellen Chl(e) im LHCII widerspiegelt. Die gewonnenen Resultate ließen vermuten, daß die reine Simulation von NLPF-Spektren nicht ausreicht, um eindeutige Aussagen über die Molekülparameter zu gewinnen. Um den benötigten zusätzlichen Erkenntnisgewinn zu erreichen, wurden daher Paralleluntersuchungen mit anderen laserspektroskopischen Methoden (nichtlineare Absorption mit fs-Pulsen, intensitätsabhängige NLPF, Einzelmolekülspektroskopie, Tieftemperatur-NLPF) sowie mit in vitro rekonstituierten Protein-Mutanten durchgeführt. Als Ergebnis konnte die Subbstruktur der Qy- Absorptionsbande der ersten angeregten Zustände der Chl(e) für LHCII ausreichend beschrieben werden. Darüber hinaus ergaben sich Aussagen zu exzitonischen Wechselwirkungen zwischen bestimmten Chl(en), die unter anderem Einfluß auf das Energie- transferverhalten haben. Diese zusätzlichen Untersuchungen erlaubten letztendlich eine Modellierung der bei Raum- temperatur an LHCII gemessenen NLPF-Spektren. Neben dem dabei implizit gewonnenen Verständnis der nichtlinearen optischen Eigenschaften im Bereich der Qy-Absorption ließen sich so Aussagen über bestimmte Modellparameter, besonders über die Orientierung von Übergangsdipolmomenten, ableiten. Abschließend wurde die Auswirkung der Erkenntnisse auf das Verständnis der Struktur-Funktionsbeziehungen für intra- und inter-komplexen Energietransfer erläutert. / Ultra-fast excitation energy transfer (EET) between excited states of organic pigment molecules in photosynthetic antenna complexes belongs to the fastest observed biological processes. Such EET phenomena has been studied to a large extent for the main light- harvesting complex of the higher plants (LHCII), which appears to play an exceptional role for the regulatory function (i.e. light adaptation) of the plant photosynthetic apparatus. The structure of this pigment-protein complex harboring more than 50 % of the total chlorophyll (Chl) content is known with 3.4 Å resolution and reveals the binding sites of 5 Chl b and 7 Chl a per monomeric unit. Based on this structure analysis, EET calculations are (in principle) available on the molecular level under the assumption of Förster-type transfer. However, several molecular features like mutual pigment orientations and electronic interactions between their transition dipoles are still rather uncertain. Since conventional spectroscopic techniques can hardly reveal the corresponding parameters, this work was aimed at the evaluation of newly introduced laser spectroscopic techniques with respect to these questions. In the beginning, suitability and significance of the method when applied to highly complicated structures like pigment-protein complexes were studied by modeling heterogeneous, LHCII-like absorption systems in NLPF experiments. Based on recent improvements in the NLPF theory by a parallel theoretical investigation [1], these simulations clarified the sensitivity of the NLPF method on numerous physical parameters. As a major consequence, unambiguous evaluations of NLPF measurements appear to require substantial additional information about the investigated system. Accordingly, several supplementary methods like nonlinear absorption (using fs-pulses), intensity-dependent NLPF, single- molecule spectroscopy, and NLPF at low temperatures were employed. These investigations revealed unique information about excitonic interaction between certain Chl(s), including implications for the overall EET scheme. The sub-structure model for the Qy-absorption region of LHCII was further essentially improved by the analysis of reconstituted proteins with selectively modified Chl binding residues in the amino-acid sequence. The sum of all complementary investigations allowed finally the evaluation of room temperature NLPF measurements of trimeric LHCII. Due to the unique selectivity of the spectra to individual transition-dipole directions, several orientation parameters have been obtained. Under this point of view, the NLPF method has indeed revealed a high potential as compared to conventional techniques like circular dichroism spectroscopy. Moreover, the understanding of nonlinear phenomena in the Qy-absorption region of LHCII as a consequence of molecular interaction provides further knowledge for the application of other nonlinear optical experiments. Concluding, implications of the obtained results for the structure-function relationship of intra- and inter-complex EET were elucidated.

No description available.

Modellierung, Analyse und Bewertung des chemischen Gewässerzustandes in Flussgebieten Der Schwerpunkt der chemischen Belastungen von Oberflächengewässern durch Abwasseremissionen verlagert sich in jüngerer Zeit, durch die Ertüchtigung der Abwasserreinigungsanlagen, von biologisch leicht abbaubaren organischen Substanzen hin zu Mikroverunreinigungen. Die Expositionsanalyse von Gewässersystemen gegen xenobiotische Substanzen mit dem Ziel einer Steuerung der Belastungen rückt immer mehr in den Vordergrund des Interesses (EG 2000, EG 2001). Am Beispiel des nordrhein-westfälischen Rheineinzugsgebiets wird in der vorliegenden Arbeit eine Analyse und Bewertung des chemischen Gewässerzustandes durch georeferenzierte Modellierung von Flussgebieten durchgeführt. Eingesetzt wird das Modellsystem GREAT-ER (Georeferenced Regional Exposure Assessment Tool for European Rivers). Der methodische Teil der Arbeit beschreibt die Kalibrierung des Modellsystems für das Einzugsgebiet des Rheins in Nordrhein-Westfalen. Weiter werden die für die Modellierung notwendigen Eingangsparameter verschiedener beispielhafter Substanzen aus verschiedenen Quellen hergeleitet. In den Anwendungsstudien werden Simulationsergebnisse für die Stoffe Bor, EDTA, HHCB, und Diclofenac sowie Diuron und Ammoniumstickstoff dargestellt und mit Messwerten der Gewässerkonzentrationen verglichen. Die Emissionsmengen für Bor und EDTA aus dem Gebrauch im Haushalt sind gut quantifizierbar. Beide Substanzen verhalten sich in den Gewässern konservativ und konnten deshalb für die Kalibrierung des Modellsystems genutzt werden. HHCB und Diclofenac sind Substanzen, die typischerweise über Haushaltsabwässer in die Gewässer gelangen, aus diesen jedoch gut eliminiert werden. Das Pestizid Diuron gelangt mit dem Oberflächenabfluss von versiegelten Flächen in das Abwasser und die Gewässer. Die Elimination aus den Gewässern ist gering. In der Arbeit wird eine Quantifizierung der Emissionsmengen auf Basis der versiegelten Flächen durchgeführt und damit eine räumliche Zuordnung der Eintragsmengen erreicht. Mit Ammoniumstickstoff wird schließlich die Gewässerexposition einer Substanz berechnet, die auch über diffuse Quellen in die Gewässer gelangt. Grundannahme ist hier, dass die Frachten aus Punktquellen die diffusen Einträge überlagern. In Abhängigkeit von der jeweiligen Substanz und Lage der Messstellen zeigen die Ergebnisse sowohl gute Übereinstimmung als auch stellenweise große Abweichungen zu den gemessenen Substanzkonzentrationen in den Gewässern. Für die auftretenden Abweichungen ergeben sich Erklärungsansätze, aber auch weiterer Untersuchungsbedarf wird deutlich. Die Ergebnisse der Arbeit belegen, dass das mit GREAT-ER entwickelte Werkzeug zur georeferenzierten Modellierung von Substanzkonzentrationen in Gewässern auf dem Gebiet der zeitlichen und räumlichen Analyse von realen Messwerten und im Rahmen eines Immissions- und Belastungsmanagements einsetzbar ist. Es können aus den Umgebungsparametern begründete Hypothesen zu lokalen Substanzkonzentrationen in Gewässern entwickelt werden, deren Informationsgehalt gegenüber Messung und generischer Modellierung höher ist.

Spatial Aspects of Chemical Exposure Assessment: A Tool for River Networks. Chemical exposure assessment has gained increasing attention in recent years. Its methodologies have enabled scientists and policy-makers to understand exposure paths and to identify environmental compartments of concern. Mathematical models are used for the prediction of a chemical's concentration in a certain compartment and in some cases also for predicting the duration or time of highest load. With the Geo-referenced Regional Exposure Assessment Tool for European Rivers (GREAT-ER) spatial aspects of regional exposure assessment are addressed for the "down-the-drain" path of consumer chemicals such as detergents. On the basis of a carefully developed simulation model (Boeije, 1999), this thesis describes the concept and realization of the developed software tool GREAT-ER. With data composition and processing on the one hand and application and analysis on the other hand, two crucial aspects in spatial exposure assessment are identified and discussed. Geo-referenced real-world data are not readily available in a usable form. An intermediate format is defined to separate the tasks of an initial preparation of raw data from the final aggregation leading to a directly usable data set. It is shown that the latter step can be fully automated and thus efficiently supports an iterative procedure of data quality improvement. The application of GREAT-ER to the substances LAS (readily degradable) and boron (inert) in four Yorkshire catchments demonstrates the ability to predict mean final effluent and in-stream concentrations with an average error of less than a factor of 2. Furthermore, regional summaries and risk characterization add useful information to judging a regional response to the (potential) release of a substance. In conclusion, the development and application of GREAT-ER has proven that geo-referenced exposure assessment is possible with regard to both quality and practicability. Future activities should focus on gaining further experiences in performing simulations, improving the tool itself and extending its abilities. Finally the integration of further models should be evaluated.

Sustainable use of species-rich moist forests is hampered by an insufficient understanding of their dynamics and long-term response to different wood harvesting strategies. This thesis contributes to a better understanding of natural forest dynamics, explores the productivity of native forests subjected to different management strategies, and quantifies the ecological impacts of these strategies. The thesis focuses on two study regions: tropical montane cloud forest (TMCF) in central Veracruz, Mexico, and Valdivian temperate rain forest (VTRF) in northern Chiloé Island, Chile. The process-based forest growth model FORMIND is applied to study natural forest succession, to assess long-term ecological implications of fuelwood extraction on TMCF, to explore the potential of secondary TMCF for provision of ecosystem services and fuelwood, and to compare potential harvesting strategies for VTRF regarding forest productivity and ecological consequences.Simulation results show that both forest types have a high potential for wood production. As wood extraction increases, the forest structure becomes simplified because large old trees disappear from the forest. The species composition shifts to tree species that are favoured by the respective harvesting strategy. The overall ecological impact increases linearly with the amount of extracted wood. Simulation results allow to define management strategies that balance conservation and production objectives, promote the regeneration of desired tree species, or minimise shifts in the species composition of the forest. Process-based forest models enhance our understanding of the dynamics of species-rich moist forests and are indispensable tools to assess long-term implications of anthropogenic disturbances on forest ecosystems. Thereby they contribute to the conservation and sustainable use of native forests outside protected areas.

Modelling and evaluating the aquatic fate of detergents - Abstract Within this thesis an environmental assessment and evaluation method for analysing aquatic ecotoxicological impacts of household laundry is developed. The methodology allows comparative assessments of different product alternatives, washing habits, and wastewater treatment techniques in order to identify their relevance with respect to waterborne discharges. Elements from both analytical tools Life Cycle Assessment (LCA) and Environmental Risk Assessment of chemicals (ERA) are combined in this methodology. The core consists of the Geography-referenced Regional Exposure Assessment Tool for European Rivers (GREAT-ER), which calculates concentrations of `down-the-drain' chemicals in surface waters due to point releases. In order to simulate the aquatic fate of detergents, a new GREAT-ER emission model is developed, called GREAT-ER product mode, which calculates calculates concentration increases of detergent ingredients in surface waters based on product formulations and assumptions concerning washing habits. Two evaluation methods, the Critical Length (CL) and the Product Risk Ratio (PRRx), are defined for evaluating the results. CL is the sum of mean concentration increases, divided by substance-specific no effect concentrations (NECs), over all river stretches and all ingredients weighted by the lengths of the stretches. PRRx is the (percentual) number of river stretches in a region, in which the x-percentiles of the predicted concentration increases of at least one ingredient exceed a substance-specific NEC. The emission model requires input data that can be derived from the functional unit of an LCA, which allows an assessment of other impact categories by using any existing LCA method. The methodology is applied to a case study which is based on scenarios given in the comprehensive product assessment `Washing and washing agents' (`Produktlinienanalyse', PLA). In order to apply the GREAT-ER product mode, the Rur river basin in Western North-Rhine Westphalia is chosen as study area. The catchment integration includes the development of a simple hydrological model that combines a nonlinear regression analysis with a local refinement procedure. The quality of the integration of the Rur catchment data is analysed by a comparison of monitoring data and predicted concentrations of detergent and cleaning agent ingredients using actual consumption data of the two years 1993 and 2000. The product mode results show that use habits have a larger influence on the results than product formulations. However, the largest influence is caused by varying wastewater treatment techniques. Boron and the surfactants are the most relevant detergent ingredients. Furthermore, using different detergents for white and coloured laundry lowers the predicted emissions significantly. Based on this methodology, sustainable development indicators (SDIs) for describing the aquatic aspects of household laundry are defined. CL is proposed as pressure indicator and PRRx as state indicator for describing aquatic aspects of the sustainability of household laundry in a region. Different regions can be compared by normalising the CL by the region's population and expressing the PRRx as a percentage of stretches in a region. Annually evaluating regional CLs and PRRxs allows the assessment whether a region is moving towards a more sustainable state. Concluding, the new method analyses and evaluates the environmental fate of detergents discharged after use via the wastewater pathway. It provides information not obtainable by other existing methods, which has been made possible due to the focussing on a specific application, for which the method is developed. Its application in the context of sustainable development offers a means to evaluate environmental implications of this important human activity.