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Foraging in space and timeLiesenjohann, Thilo January 2010 (has links)
All animals are adapted to the environmental conditions of the habitat they chose to live in. It was the aim of this PhD-project, to show which behavioral strategies are expressed as mechanisms to cope with the constraints, which contribute to the natural selection pressure acting on individuals. For this purpose, small mammals were exposed to different levels and types of predation risk while actively foraging. Individuals were either exposed to different predator types (airborne or ground) or combinations of both, or to indirect predators (nest predators). Risk was assumed to be distributed homogeneously, so changing the habitat or temporal adaptations where not regarded as potential options. Results show that wild-caught voles have strategic answers to this homogeneously distributed risk, which is perceived by tactile, olfactory or acoustic cues. Thus, they do not have to know an absolut quality (e.g., in terms of food provisioning and risk levels of all possible habitats), but they can adapt their behavior to the actual circumstances. Deriving risk uniform levels from cues and adjusting activity levels to the perceived risk is an option to deal with predators of the same size or with unforeseeable attack rates. Experiments showed that as long as there are no safe places or times, it is best to reduce activity and behave as inconspicuous as possible as long as the costs of missed opportunities do not exceed the benefits of a higher survival probability. Test showed that these costs apparently grow faster for males than for females, especially in times of inactivity. This is supported by strong predatory pressure on the most active groups of rodents (young males, sexually active or dispersers) leading to extremely female-biased operative sex ratios in natural populations.
Other groups of animals, those with parental duties such as nest guarding, for example, have to deal with the actual risk in their habitat as well. Strategies to indirect predation pressure were tested by using bank vole mothers, confronted with a nest predator that posed no actual threat to themselves but to their young (Sorex araneus). They reduced travelling and concentrated their effort in the presence of shrews, independent of the different nutritional provisioning of food by varying resource levels due to the different seasons. Additionally, they exhibited nest-guarding strategies by not foraging in the vicinity of the nest site in order to reduce conspicuous scent marks. The repetition of the experiment in summer and autumn showed that changing environmental constraints can have a severe impact on results of outdoor studies. In our case, changing resource levels changed the type of interaction between the two species.
The experiments show that it is important to analyze decision making and optimality models on an individual level, and, when that is not possible (maybe because of the constraints of field work), groups of animals should be classified by using the least common denominator that can be identified (such as sex, age, origin or kinship). This will control for the effects of the sex or stage of life history or the individual´s reproductive and nutritional status on decision making and will narrow the wide behavioral variability associated with the complex term of optimality. / Das Verhalten von Tieren ist das Ergebnis eines kontinuierlichen Anpassungsprozesses im Laufe der Evolution einer Art und damit der Veränderung der Umgebung in der es lebt und der Interaktion mit anderen Arten. Dies wird besonders deutlich im Verhalten von potentiellen Beutetieren, ihre Strategien beinhalten meist ein möglichst unauffälliges Verhalten im Zusammenspiel mit reduzierter Bewegung und möglichst guter Tarnung. Dementgegen stehen essentielle Bedürfnisse, wie zum Beispiel die Nahrungssuche, die Verteidigung von Ressourcen (zum Beispiel Territorien, Futterstellen) und die Suche nach Paarungspartnern. Beutetiere leben also in einem Spannungsfeld indem sie Ihr Verhalten optimieren müssen. Hierbei stehen die Ernährung, erfolgreiche Verpaarung und andere Chancen auf der einen Seite, die Vermeidung von Begegnungen mit Prädatoren auf der anderen.
Vor allem Kleinsäuger sind häufig als Beutetiere mit einer Vielzahl von Prädatoren aus der Luft und auf dem Boden konfrontiert. Sie müssen für die verschiedenen Bedrohungen adaptive Verhaltensanpassungen bereit haben und in der Lage sein, auf die optischen, olfaktorischen oder akustischen Signale, die die Gefahr durch Prädatoren anzeigen, mit plastischen Verhaltensmustern zu reagieren.
Die vorliegende Dissertation beschäftigt sich mit bisher als Konstanten behandelten Faktoren und untersucht anhand von Verhaltensexperimenten mit wilden Wühlmäusen (Microtus arvalis) folgende Fragestellungen:
- Wie verhalten sich Tiere, die einer homogenen Risikoverteilung ausgesetzt sind, zum Beispiel weil ihr Prädator genauso gross ist wie sie, im gleichen Habitat lebt und es keinen sicheren Ort gibt?
- Mit welchen Anpassungen reagieren Tiere, wenn sie gleichzeitig verschiedenen Prädatoren ausgesetzt sind?
- Wie unterscheiden sich die Nahrungssuchstrategien von Männchen und Weibchen?
- Wie verhalten sich laktierende Weibchen, die einer permanenten, indirekten Gefahr, z.B. durch einen Nestprädator ausgesetzt sind?
Die Ergebnisse der verschiedenen Versuche in künstlichen Arenen und Aussengehegen zeigen, dass die Mäuse in der Lage sind, adaptive Verhaltensanpassung an homogenes Risiko und verschiedene Prädationstypen abzurufen. So sind sie in der Lage, Luft- von Bodenprädatoren zu unterscheiden und jeweils das Verhalten zu zeigen, dass die größtmögliche Sicherheit mit sich bringt. Die simultane Kombination von verschiedenen Prädatoren bewirkt hierbei additive Effekte. Gibt es keine Auswahl zwischen Habitaten, sondern nur unterschiedliche homogene Risikolevel, reagieren sie auf steigendes Risiko immer mit verminderter Aktivität und konzentrieren ihre Nahrungssuche auf weniger Futterstellen, beuten diese dafür jedoch länger aus. Die Wertigkeit von Futterstellen und alternativen Optionen verändert sich also mit dem Risikolevel. Ähnliches zeigt sich auch in den unterschiedlichen Futtersuchstrategien von Männchen und Weibchen. Die untersuchte Art ist polygyn und multivoltin, dementsprechend verbinden die Männchen mit ihrer Nahrungssuche Aktivitäten wie die Suche nach Paarungspartnern und unterscheiden sich die Aktivitätsmuster zwischen Männchen und Weibchen. Zusätzlich zeigen die Ergebnisse, das laktierende Weibchen in der Lage sind, das Risiko für sich und für Ihre Jungen abzuschätzen, wenn sie mit einem Nestprädator (Sorex araneus) konfrontiert werden. Für die Interaktion zwischen diesen beiden Arten ist jedoch die Saison (und damit die Ressourcenlage), in der sie sich begegnen, von entscheidender Bedeutung. Wühlmäuse reagieren mit entsprechenden Verhaltensanpassungen zum Schutz des Nestes um die Überlebenschancen ihrer letzten Würfe im Herbst zu erhöhen.
Die vorliegende Arbeit konnte grundsätzliche Probleme der antiprädatorischen Verhaltensanpassung von Beutetieren klären und wichtige Faktoren der Entscheidungsfindung unter Prädationsdruck analysieren. Sie zeigt, dass Tiere das Risiko in ihrer Umgebung nicht unbedingt über direkt Signale wahrnehmen, sondern ihre Verhaltensstrategien einem empfundenen Gesamtrisikolevel anpassen. Dies ermöglicht ihnen, adaptive Strategien zu verfolgen, auch wenn sie keine Auswahl an sicheren Habitaten haben. Sie zeigt auch die unterschiedliche Wahrnehmung von Risiken durch Männchen und Weibchen, die durch die unterschiedlichen mit der Aktivität zusätzlich wahrgenommenen Chancen verknüpft zu sein scheint. Zusätzlich wurde der Einfluss des reproduktiven Status (z.B. laktierend), sowie der Ressourcenlage (z. B. je nach Saison) nachgewiesen.
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Privacy-Preserving Ontology Publishing:: The Case of Quantified ABoxes w.r.t. a Static Cycle-Restricted EL TBox: Extended VersionBaader, Franz, Koopmann, Patrick, Kriegel, Francesco, Nuradiansyah, Adrian, Peñaloza, Rafael 20 June 2022 (has links)
We review our recent work on how to compute optimal repairs, optimal compliant anonymizations, and optimal safe anonymizations of ABoxes containing possibly anonymized individuals. The results can be used both to remove erroneous consequences from a knowledge base and to hide secret information before publication of the knowledge base, while keeping as much as possible of the original information. / Updated on August 27, 2021. This is an extended version of an article accepted at DL 2021.
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On the numerical analysis of eigenvalue problemsGedicke, Joscha Micha 05 November 2013 (has links)
Die vorliegende Arbeit zum Thema der numerischen Analysis von Eigenwertproblemen befasst sich mit fünf wesentlichen Aspekten der numerischen Analysis von Eigenwertproblemen. Der erste Teil präsentiert einen Algorithmus von asymptotisch quasi-optimaler Rechenlaufzeit, der die adaptive Finite Elemente Methode mit einem iterativen algebraischen Eigenwertlöser kombiniert. Der zweite Teil präsentiert explizite beidseitige Schranken für die Eigenwerte des Laplace Operators auf beliebig groben Gittern basierend auf einer Approximation der zugehörigen Eigenfunktion in dem nicht konformen Finite Elemente Raum von Crouzeix und Raviart und einem Postprocessing. Die Effizienz der garantierten Schranke des Eigenwertfehlers hängt von der globalen Gitterweite ab. Der dritte Teil betrachtet eine adaptive Finite Elemente Methode basierend auf Verfeinerungen von Knoten-Patchen. Dieser Algorithmus zeigt eine asymptotische Fehlerreduktion der adaptiven Sequenz von einfachen Eigenwerten und Eigenfunktionen des Laplace Operators. Die hier erstmals bewiesene Eigenschaft der Saturation des Eigenwertfehlers zeigt Zuverlässigkeit und Effizienz für eine Klasse von hierarchischen a posteriori Fehlerschätzern. Der vierte Teil betrachtet a posteriori Fehlerschätzer für Konvektion-Diffusion Eigenwertprobleme, wie sie von Heuveline und Rannacher (2001) im Kontext der dual-gewichteten residualen Methode (DWR) diskutiert wurden. Zwei neue dual-gewichtete a posteriori Fehlerschätzer werden vorgestellt. Der letzte Teil beschäftigt sich mit drei adaptiven Algorithmen für Eigenwertprobleme von nicht selbst-adjungierten Operatoren partieller Differentialgleichungen. Alle drei Algorithmen basieren auf einer Homotopie-Methode die vom einfacheren selbst-adjungierten Problem startet. Neben der Gitterverfeinerung wird der Prozess der Homotopie sowie die Anzahl der Iterationen des algebraischen Löser adaptiv gesteuert und die verschiedenen Anteile am gesamten Fehler ausbalanciert. / This thesis "on the numerical analysis of eigenvalue problems" consists of five major aspects of the numerical analysis of adaptive finite element methods for eigenvalue problems. The first part presents a combined adaptive finite element method with an iterative algebraic eigenvalue solver for a symmetric eigenvalue problem of asymptotic quasi-optimal computational complexity. The second part introduces fully computable two-sided bounds on the eigenvalues of the Laplace operator on arbitrarily coarse meshes based on some approximation of the corresponding eigenfunction in the nonconforming Crouzeix-Raviart finite element space plus some postprocessing. The efficiency of the guaranteed error bounds involves the global mesh-size and is proven for the large class of graded meshes. The third part presents an adaptive finite element method (AFEM) based on nodal-patch refinement that leads to an asymptotic error reduction property for the adaptive sequence of simple eigenvalues and eigenfunctions of the Laplace operator. The proven saturation property yields reliability and efficiency for a class of hierarchical a posteriori error estimators. The fourth part considers a posteriori error estimators for convection-diffusion eigenvalue problems as discussed by Heuveline and Rannacher (2001) in the context of the dual-weighted residual method (DWR). Two new dual-weighted a posteriori error estimators are presented. The last part presents three adaptive algorithms for eigenvalue problems associated with non-selfadjoint partial differential operators. The basis for the developed algorithms is a homotopy method which departs from a well-understood selfadjoint problem. Apart from the adaptive grid refinement, the progress of the homotopy as well as the solution of the iterative method are adapted to balance the contributions of the different error sources.
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Range-based parameter estimation in diffusion modelsHenkel, Hartmuth 04 October 2010 (has links)
Wir studieren das Verhalten des Maximums, des Minimums und des Endwerts zeithomogener eindimensionaler Diffusionen auf endlichen Zeitintervallen. Zuerst beweisen wir mit Hilfe des Malliavin-Kalküls ein Existenzresultat für die gemeinsamen Dichten. Außerdem leiten wir Entwicklungen der gemeinsamen Momente des Tripels (H,L,X) zur Zeit Delta bzgl. Delta her. Dabei steht X für die zugrundeliegende Diffusion, und H und L bezeichnen ihr fortlaufendes Maximum bzw. Minimum. Ein erster Ansatz, der vollständig auf den elementaren Abschätzungen der Doob’schen und der Cauchy-Schwarz’schen Ungleichung beruht, liefert eine Entwicklung bis zur Ordnung 2 bzgl. der Wurzel der Zeitvariablen Delta. Ein komplexerer Ansatz benutzt Partielle-Differentialgleichungstechniken, um eine Entwicklung der einseitigen Austrittswahrscheinlichkeit für gepinnte Diffusionen zu bestimmen. Da eine Entwicklung der Übergangsdichten von Diffusionen bekannt ist, erhält man eine vollständige Entwicklung der gemeinsamen Wahrscheinlichkeit von (H,X) bzgl. Delta. Die entwickelten Verteilungseigenschaften erlauben es uns, eine Theorie für Martingalschätzfunktionen, die aus wertebereich-basierten Daten konstruiert werden, in einem parameterisierten Diffusionsmodell, herzuleiten. Ein Small-Delta-Optimalitätsansatz, der die approximierten Momente benutzt, liefert eine Vereinfachung der vergleichsweise komplizierten Schätzprozedur und wir erhalten asymptotische Optimalitätsresultate für gegen 0 gehende Sampling-Frequenz. Beim Schätzen des Drift-Koeffizienten ist der wertebereich-basierte Ansatz der Methode, die auf equidistanten Beobachtungen der Diffusion beruht, nicht überlegen. Der Effizienzgewinn im Fall des Schätzens des Diffusionskoeffizienten ist hingegen enorm. Die Maxima und Minima in die Analyse miteinzubeziehen senkt die Varianz des Schätzers für den Parameter in diesem Szenario erheblich. / We study the behavior of the maximum, the minimum and the terminal value of time-homogeneous one-dimensional diffusions on finite time intervals. To begin with, we prove an existence result for the joint density by means of Malliavin calculus. Moreover, we derive expansions for the joint moments of the triplet (H,L,X) at time Delta w.r.t. Delta. Here, X stands for the underlying diffusion whereas H and L denote its running maximum and its running minimum, respectively. In a first approach that entirely relies on elementary estimates, such as Doob’s inequality and Cauchy-Schwarz’ inequality, we derive an expansion w.r.t. the square root of the time parameter Delta including powers of 2. A more sophisticated ansatz uses partial differential equation techniques to determine an expansion of the one-barrier hitting time probability for pinned diffusions. For an expansion of the transition density of diffusions is known, one obtains an overall expansion of the joint probability of (H,X) w.r.t. Delta. The developed distributional properties enable us to establish a theory for martingale estimating functions constructed from range-based data in a parameterized diffusion model. A small-Delta-optimality approach, that uses the approximated moments, yields a simplification of the relatively complicated estimating procedure and we obtain asymptotic optimality results when the sampling frequency Delta tends to 0. When it comes to estimating the drift coefficient the range-based method is not superior to the method relying on equidistant observations of the underlying diffusion alone. However, there is an enormous gain in efficiency at the estimation for the diffusion coefficient. Incorporating the maximum and the minimum into the analysis significantly lowers the asymptotic variance of the estimators for the parameter in this scenario.
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Game Theory and Microeconomic Theory for Beamforming Design in Multiple-Input Single-Output Interference ChannelsMochaourab, Rami 24 July 2012 (has links) (PDF)
In interference-limited wireless networks, interference management techniques are important in order to improve the performance of the systems. Given that spectrum and energy are scarce resources in these networks, techniques that exploit the resources efficiently are desired. We consider a set of base stations operating concurrently in the same spectral band. Each base station is equipped with multiple antennas and transmits data to a single-antenna mobile user. This setting corresponds to the multiple-input single-output (MISO) interference channel (IFC). The receivers are assumed to treat interference signals as noise. Moreover, each transmitter is assumed to know the channels between itself and all receivers perfectly. We study the conflict between the transmitter-receiver pairs (links) using models from game theory and microeconomic theory. These models provide solutions to resource allocation problems which in our case correspond to the joint beamforming design at the transmitters. Our interest lies in solutions that are Pareto optimal. Pareto optimality ensures that it is not further possible to improve the performance of any link without reducing the performance of another link.
Strategic games in game theory determine the noncooperative choice of strategies of the players. The outcome of a strategic game is a Nash equilibrium. While the Nash equilibrium in the MISO IFC is generally not efficient, we characterize the necessary null-shaping constraints on the strategy space of each transmitter such that the Nash equilibrium outcome is Pareto optimal. An arbitrator is involved in this setting which dictates the constraints at each transmitter. In contrast to strategic games, coalitional games provide cooperative solutions between the players. We study cooperation between the links via coalitional games without transferable utility. Cooperative beamforming schemes considered are either zero forcing transmission or Wiener filter precoding. We characterize the necessary and sufficient conditions under which the core of the coalitional game with zero forcing transmission is not empty. The core solution concept specifies the strategies with which all players have the incentive to cooperate jointly in a grand coalition. While the core only considers the formation of the grand coalition, coalition formation games study coalition dynamics. We utilize a coalition formation algorithm, called merge-and-split, to determine stable link grouping. Numerical results show that while in the low signal-to-noise ratio (SNR) regime noncooperation between the links is efficient, at high SNR all links benefit in forming a grand coalition. Coalition formation shows its significance in the mid SNR regime where subset link cooperation provides joint performance gains.
We use the models of exchange and competitive market from microeconomic theory to determine Pareto optimal equilibria in the two-user MISO IFC. In the exchange model, the links are represented as consumers that can trade goods within themselves. The goods in our setting correspond to the parameters of the beamforming vectors necessary to achieve all Pareto optimal points in the utility region. We utilize the conflict representation of the consumers in the Edgeworth box, a graphical tool that depicts the allocation of the goods for the two consumers, to provide closed-form solution to all Pareto optimal outcomes. The exchange equilibria are a subset of the points on the Pareto boundary at which both consumers achieve larger utility then at the Nash equilibrium. We propose a decentralized bargaining process between the consumers which starts at the Nash equilibrium and ends at an outcome arbitrarily close to an exchange equilibrium. The design of the bargaining process relies on a systematic study of the allocations in the Edgeworth box. In comparison to the exchange model, a competitive market additionally defines prices for the goods. The equilibrium in this economy is called Walrasian and corresponds to the prices that equate the demand to the supply of goods. We calculate the unique Walrasian equilibrium and propose a coordination process that is realized by the arbitrator which distributes the Walrasian prices to the consumers. The consumers then calculate in a decentralized manner their optimal demand corresponding to beamforming vectors that achieve the Walrasian equilibrium. This outcome is Pareto optimal and lies in the set of exchange equilibria.
In this thesis, based on the game theoretic and microeconomic models, efficient beamforming strategies are proposed that jointly improve the performance of the systems. The gained results are applicable in interference-limited wireless networks requiring either coordination from the arbitrator or direct cooperation between the transmitters.
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Game Theory and Microeconomic Theory for Beamforming Design in Multiple-Input Single-Output Interference ChannelsMochaourab, Rami 11 May 2012 (has links)
In interference-limited wireless networks, interference management techniques are important in order to improve the performance of the systems. Given that spectrum and energy are scarce resources in these networks, techniques that exploit the resources efficiently are desired. We consider a set of base stations operating concurrently in the same spectral band. Each base station is equipped with multiple antennas and transmits data to a single-antenna mobile user. This setting corresponds to the multiple-input single-output (MISO) interference channel (IFC). The receivers are assumed to treat interference signals as noise. Moreover, each transmitter is assumed to know the channels between itself and all receivers perfectly. We study the conflict between the transmitter-receiver pairs (links) using models from game theory and microeconomic theory. These models provide solutions to resource allocation problems which in our case correspond to the joint beamforming design at the transmitters. Our interest lies in solutions that are Pareto optimal. Pareto optimality ensures that it is not further possible to improve the performance of any link without reducing the performance of another link.
Strategic games in game theory determine the noncooperative choice of strategies of the players. The outcome of a strategic game is a Nash equilibrium. While the Nash equilibrium in the MISO IFC is generally not efficient, we characterize the necessary null-shaping constraints on the strategy space of each transmitter such that the Nash equilibrium outcome is Pareto optimal. An arbitrator is involved in this setting which dictates the constraints at each transmitter. In contrast to strategic games, coalitional games provide cooperative solutions between the players. We study cooperation between the links via coalitional games without transferable utility. Cooperative beamforming schemes considered are either zero forcing transmission or Wiener filter precoding. We characterize the necessary and sufficient conditions under which the core of the coalitional game with zero forcing transmission is not empty. The core solution concept specifies the strategies with which all players have the incentive to cooperate jointly in a grand coalition. While the core only considers the formation of the grand coalition, coalition formation games study coalition dynamics. We utilize a coalition formation algorithm, called merge-and-split, to determine stable link grouping. Numerical results show that while in the low signal-to-noise ratio (SNR) regime noncooperation between the links is efficient, at high SNR all links benefit in forming a grand coalition. Coalition formation shows its significance in the mid SNR regime where subset link cooperation provides joint performance gains.
We use the models of exchange and competitive market from microeconomic theory to determine Pareto optimal equilibria in the two-user MISO IFC. In the exchange model, the links are represented as consumers that can trade goods within themselves. The goods in our setting correspond to the parameters of the beamforming vectors necessary to achieve all Pareto optimal points in the utility region. We utilize the conflict representation of the consumers in the Edgeworth box, a graphical tool that depicts the allocation of the goods for the two consumers, to provide closed-form solution to all Pareto optimal outcomes. The exchange equilibria are a subset of the points on the Pareto boundary at which both consumers achieve larger utility then at the Nash equilibrium. We propose a decentralized bargaining process between the consumers which starts at the Nash equilibrium and ends at an outcome arbitrarily close to an exchange equilibrium. The design of the bargaining process relies on a systematic study of the allocations in the Edgeworth box. In comparison to the exchange model, a competitive market additionally defines prices for the goods. The equilibrium in this economy is called Walrasian and corresponds to the prices that equate the demand to the supply of goods. We calculate the unique Walrasian equilibrium and propose a coordination process that is realized by the arbitrator which distributes the Walrasian prices to the consumers. The consumers then calculate in a decentralized manner their optimal demand corresponding to beamforming vectors that achieve the Walrasian equilibrium. This outcome is Pareto optimal and lies in the set of exchange equilibria.
In this thesis, based on the game theoretic and microeconomic models, efficient beamforming strategies are proposed that jointly improve the performance of the systems. The gained results are applicable in interference-limited wireless networks requiring either coordination from the arbitrator or direct cooperation between the transmitters.
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