On the Emergence of Cooperation in the Repeated Prisoner's Dilemma

This article explores which parameters of the repeated Prisoner's Dilemma lead to cooperation. Using simulations, I demonstrate that the potential function of the stochastic evolutionary dynamics of the Grim Trigger strategy is useful to predict cooperation between Q-learners. The frontier separating the parameter spaces that induce either cooperation or defection can be determined based on the kinetic energy exerted by the respective basins of attraction. When the incentive compatibility constraint of the Grim Trigger strategy is slack, a sudden increase in the observed cooperation rates occurs when the ratio of the kinetic energies approaches a critical value, which itself is a function of the discount factor, multiplied by a correction factor to account for the effect of the algorithms' exploration probability. Using metadata from laboratory experiments, I provide evidence that the insights obtained from the simulations are also useful to explain the emergence of cooperation between humans. The observed cooperation rates show a positive gradient at the frontier characterized by an exploration probability of approximately five percent. In the context of human-to-human interaction, the exploration probability can be viewed as the belief about the opponent's probability to deviate from the equilibrium action

HIV prevention cascades to improve programmes and interventions

Most countries will miss the UNAIDS target of reducing new HIV infections by 75% by 2020 compared to 2010. HIV prevention cascades have been proposed to assist in the advocacy for and planning, monitoring, and improved delivery of HIV prevention programmes and interventions by identifying gaps in effective use of prevention methods, similar to treatment cascades. The overarching aim of this thesis was to develop and pilot-test a generic HIV prevention cascade framework that can be used for different populations, prevention methods, and purposes. This proposed prevention cascade consists of three steps of motivation to use a prevention method, access to it, and effective use in a priority population. Characterising reasons underlying gaps across motivation, access, and effective use creates a comprehensive framework. To develop this framework, I conducted consultations and data analyses. In a study of data from eastern and southern Africa, I demonstrated increases in both non-regular partnerships and condom use, exemplifying complexities of population-level HIV risks and challenges in defining priority populations for prevention cascades. As it has previously been proposed as the first step in prevention cascades, I analysed HIV risk perception using longitudinal data from Manicaland, Zimbabwe. Results suggest that 1) risk perception can be accurate as there were associations between perceptions and actual HIV acquisition but there were considerable gaps in risk perception and 2) increasing risk perception was associated with condom use but fractions of condom use attributable to risk perception were small, highlighting that HIV prevention behaviour is influenced by a range of factors. The importance of structural factors for HIV prevention was underlined by analyses of cash transfers and HIV prevention in Manicaland. Finally, I operationalised the proposed HIV prevention cascade framework using newly collected data from Manicaland, demonstrating the utility of the concept for identifying gaps in prevention.Open Acces

Derivation of subset product lines in FeatureIDE

The development and configuration of software product lines can be challenging tasks. During development, engineers often need to focus on a particular subset of features that is relevant for them. In such cases, it would be beneficial to hide other features and their implementation. During product configuration, requirements of potentially multiple stakeholders need to be considered. Therefore, configuration often happens in stages, in which different people contribute configuration decisions for different features. Moreover, in some cases, stakeholders want to share a set of products rather than a specific one. In all these cases, the necessary operation is the same: some features from the product line are assigned a value (e.g., via a partial configuration) while other features remain configurable. In this work, we propose a subset operation that takes a product line and a partial configuration to derive a subset product line comprising only the desired subset of features and implementation artifacts. Furthermore, we present, evaluate, and publish our implementation of the proposed subset operation within the FeatureIDE framework

A fingerprint based metric for measuring similarities of crystalline structures

Measuring similarities/dissimilarities between atomic structures is important for the exploration of potential energy landscapes. However, the cell vectors together with the coordinates of the atoms, which are generally used to describe periodic systems, are quantities not suitable as fingerprints to distinguish structures. Based on a characterization of the local environment of all atoms in a cell we introduce crystal fingerprints that can be calculated easily and allow to define configurational distances between crystalline structures that satisfy the mathematical properties of a metric. This distance between two configurations is a measure of their similarity/dissimilarity and it allows in particular to distinguish structures. The new method is an useful tool within various energy landscape exploration schemes, such as minima hopping, random search, swarm intelligence algorithms and high-throughput screenings

The emerging role of dipeptidyl peptidase 3 in pathophysiology

Dipeptidyl peptidase 3 (DPP3), a zinc-dependent aminopeptidase, is a highly conserved enzyme among higher animals. The enzyme cleaves dipeptides from the N-terminus of tetra- to decapeptides, thereby taking part in activation as well as degradation of signalling peptides critical in physiological and pathological processes such as blood pressure regulation, nociception, inflammation and cancer. Besides its catalytic activity, DPP3 moonlights as a regulator of the cellular oxidative stress response pathway, e.g., the Keap1-Nrf2 mediated antioxidative response. The enzyme is also recognized as a key modulator of the renin-angiotensin system. Recently, DPP3 has been attracting growing attention within the scientific community, which has significantly augmented our knowledge of its physiological relevance. Herein, we review recent advances in our understanding of the structure and catalytic activity of DPP3, with a focus on attributing its molecular architecture and catalytic mechanism to its wide-ranging biological functions. We further highlight recent intriguing reports that implicate a broader role for DPP3 as a valuable biomarker in cardiovascular and renal pathologies and furthermore discuss its potential as a promising drug target

It Takes Two to Tang: Coupling of Angiogenesis and Osteogenesis for Bone Regeneration

Bone regeneration is a complex process requiring highly orchestrated interactions between different cells and signals to form new mineralized tissue. Blood vessels serve as a structural template, around which bone development takes place, and also bring together the key elements for bone homeostasis into the osteogenic microenvironment, including minerals, growth factors and osteogenic progenitor cells. Vascular endothelial growth factor (VEGF) is the master regulator of vascular growth and it is required for effective coupling of angiogenesis and osteogenesis during both skeletal development and postnatal bone repair. Here, we will review the current state of knowledge on the molecular cross-talk between angiogenesis and osteogenesis. In particular, we will focus on the role of VEGF in coupling these two processes and how VEGF dose can control the outcome, addressing in particular: (1) the direct influence of VEGF on osteogenic differentiation of mesenchymal progenitors; (2) the angiocrine functions of endothelium to regulate osteoprogenitors; (3) the role of immune cells, e.g., myeloid cells and osteoclast precursors, recruited by VEGF to the osteogenic microenvironment. Finally, we will discuss emerging strategies, based on the current biological understanding, to ensure rapid vascularization and efficient bone formation in regenerative medicine