Frequency-Dependent Selection at Rough Expanding Fronts

Microbial colonies are experimental model systems for studying the colonization of new territory by biological species through range expansion. We study a generalization of the two-species Eden model, which incorporates local frequency-dependent selection, in order to analyze how social interactions between two species influence surface roughness of growing microbial colonies. The model includes several classical scenarios from game theory. We then concentrate on an expanding public goods game, where either cooperators or defectors take over the front depending on the system parameters. We analyze in detail the critical behavior of the nonequilibrium phase transition between global cooperation and defection and thereby identify a new universality class of phase transitions dealing with absorbing states. At the transition, the number of boundaries separating sectors decays with a novel power law in time and their superdiffusive motion crosses over from Eden scaling to a nearly ballistic regime. In parallel, the width of the front initially obeys Eden roughening and, at later times, passes over to selective roughening.Comment: 11 pages, 10 figure

Spotting, collecting and documenting negative polarity items

As the nature of negative polarity items (NPIs) and their licensing contexts is still under much debate, a broad empirical basis is an important cornerstone to support further insights in this area of research. The work discussed in this paper is intended as a contribution to realizing this objective. The authors briefly introduce the phenomenon of NPIs and outline major theories about their licensing and also various licensing contexts before discussing our major topics: Firstly, a corpus-based retrieval method for NPI candidates is described that ranks the candidates according to their distributional dependence on the licensing contexts. Our method extracts single-word candidates and is extended to also capture multi-word candidates. The basic idea for automatically collecting NPI candidates from a large corpus is that an NPI behaves like a kind of collocate to its licensing contexts. Manual inspection and interpretation of the candidate lists identify the actual NPIs. Secondly, an online repository for NPIs and other items that show distributional idiosyncrasies is presented, which offers an empirical database for further (theoretical) research on these items in a sustainable way

Collective dynamics in a monolayer of squirmers confined to a boundary by gravity

We present a hydrodynamic study of a monolayer of squirmer model microswimmers confined to a boundary by strong gravity using the simulation method of multi-particle collision dynamics. The squirmers interact with each other via their self-generated hydrodynamic flow fields and thereby form a variety of fascinating dynamic states when density and squirmer type are varied. Weak pushers, neutral squirmers, and pullers have an upright orientation. With their flow fields they push neighbors away and thereby form a hydrodynamic Wigner fluid at lower densities. Furthermore, states of fluctuating chains and trimers, of kissing, and at large densities a global cluster exist. Finally, pushers at all densities can tilt against the wall normal and their in-plane velocities align to show swarming. It turns into chaotic swarming for strong pushers at high densities. We characterize all these states quantitatively.DFG, 87159868, GRK 1558: Kollektive Dynamik im Nichtgleichgewicht: in kondensierter Materie und biologischen SystemenDFG, 237143019, SPP 1726: Mikroschwimmer - Von Einzelpartikelbewegung zu kollektivem VerhaltenTU Berlin, Open-Access-Mittel - 201

Ideate. Collaborate. Repeat. A Research Agenda for Idea Generation, Collaboration and Evaluation in Open Innovation

Open innovation has been and remains to be a rapidly changing field of research in Information Systems and various other disciplines. With the rise of professional open innovation platforms and the emergence of crowdsourcing as well as employee-driven innovation, studies on the front-end of open innovation – namely idea generation, collaboration and evaluation – are facing new challenges. In this structured literature review, we analyze a large body of prior research in order to derive a framework, which is able to classify and reflect the lively debate on open innovation. In addition, we identify important implications for practitioners with advise on the design of open innovation systems. Moreover, our study identifies several promising areas for future research

Role Assignment Adaptation: An Intentional Forgetting Approach

In organizations the distribution of tasks is a rising challenge in complex and dynamic environments. By structuring responsibilities and expectations for task processing in roles, organizations provide a transparent approach for collaboration. However, if tasks are being generated unexpectedly, actors who enact multiple roles might be overloaded in dynamic environments. By focusing on relevant information in terms of an intentional forgetting mechanism, actors could overcome these overload situations. Therefore, we provide an agent-based simulation to model and analyze effects of intentional forgetting by adapting role assignments in dynamic environments. The agent architecture utilizes separated revision functions to control an agent’s perception and belief acquisition to focus on relevant information. The model is tested using a case-study in a simulated emergency response scenario. The simulation results show that adapting role assignments at runtime improves team performance significantly

When Life Gives You Lemons: How rating scales affect user activity and frustration in collaborative evaluation processes

Initiators of open innovation processes involving customers or employees often face vast amounts of idea proposals. These proposals vary greatly in terms of quality, which is why organizers often engage the users themselves in the evaluation process. Building on the concept of information overload, we evaluate the effects of three distinct rating scales on users’ activity and frustration measures. On the basis of an open innovation campaign for employees of a public-private institution in Germany, we systematically compare the novel “bag of lemons” method with conventional Likert scales and up-down-voting schemes. Our results demonstrate that the “bag of lemons”-approach yields higher levels of user activity, but is also perceived as significantly more frustrating. We find this effect to be fully mediated by perceived information overload, which points to potential avenues for the design of stimulating yet tolerably complex Information Systems for open innovation and rating techniques

The electricity market deregulation and its influence on R&D in green electricity generation : John Sutton's model on technology and market structure and its application to the electricity market

Only abstract. Paper copies of master’s theses are listed in the Helka database (http://www.helsinki.fi/helka). Electronic copies of master’s theses are either available as open access or only on thesis terminals in the Helsinki University Library.Vain tiivistelmä. Sidottujen gradujen saatavuuden voit tarkistaa Helka-tietokannasta (http://www.helsinki.fi/helka). Digitaaliset gradut voivat olla luettavissa avoimesti verkossa tai rajoitetusti kirjaston opinnäytekioskeilla.Endast sammandrag. Inbundna avhandlingar kan sökas i Helka-databasen (http://www.helsinki.fi/helka). Elektroniska kopior av avhandlingar finns antingen öppet på nätet eller endast tillgängliga i bibliotekets avhandlingsterminaler.The first part of this thesis is an elaboration on the Market Structure and Technology approach. As an introduction to the discussion on the approach an overview on what has been done by different economists (starting from Schumpeter) over time is provided. As theoretic foundation Sutton's gametheoretic model on "Technology and Market Structure" is considered. This thesis tries to show its compatibility to the electricity market and whether it can expiain changes in the market structure and consequentiy technologicai advances in green electricity generation. An introduction to the model considering a linear demand model wili start the analysis of Sutton's model. Thereafter, the basic setting of Sutton's game-theoretic approach wili broaden the analysis. The second part of this thesis wili enhance the model specification, the deregulation in the electricity market in Finland and Germany and the potential market structure development in the electricity industry. Criticai remarks on the modei's suitability wili foliow. Furthermore will be pointed out which problems occur by unravelling the levei of the observable variables from Sutton's model using existing data on Germany and Finland's electricity markets. Because of statisticai deficiencies for available data on the proxy variables resuits of a smali survey on the electricity generating industry in Finland, which could be used for further research in the area, wili be presented. Finally, conciuding remarks wili evaluate the model's suitability and the potentiai threats to the levei of concentration in the electricity market as weli as the influence on R&D in green technologie

Statistical properties of microbial phenotypes and colony growth

Cells are the fundamental units of which all life forms are composed. To understand the elementary organization of life, it is therefore meaningful to start the investigation on the single cell level.Modern microscopy permits the examination of both subcellular processes and collective microbial behavior. In this microscopic regime, fluctuations are of eminent importance. As this noise is an inherent property of such systems, life evolved robust systems, which work effectively in spite of severe fluctuations. Moreover, life also makes use of these fluctuations for its benefit. For modeling purposes in this field of research, concepts from statistical mechanics and from the analysis of stochastic processes can be applied to account for the fluctuations. This work is roughly divided into two parts, which also address the background, concepts and literature of the corresponding topics. The first part is concerned with the modeling of intracellular processes, for which noise is important. In this context two publications, which arose from collaborations with experimental biophysicists, are discussed: In gene therapy external genetic material is injected into cells to remedy deficient behavior. To characterize this process, fluorophore encoding plasmids were administered to eukaryotic cells by means of two chemical transfection methods. The distribution of expression levels is explained by several strongly stochastic steps during transfection and subsequent quasi-deterministic gene expression. The second collaboration addresses the switching kinetics between different phenotypes in bacteria. In the case at hand, the emergence of "competence" in B. subtilis is studied. This ability (to take up genetic material from the extracellular medium) is strongly regulated by a network of interacting genes. While the different phenotypes are associated with stable fixed points of non-linear differential equations, switching between phenotypes relies on fluctuations in the small number of mRNA molecules. The second part of this work elaborates on collective, stochastic growth of many cells in an expanding colony. The corresponding manuscript analyzes a theoretical model with methods from statistical mechanics. Microbial colony growth is sometimes seen as a model system for range expansion or colonization processes. Inspired by experiments, a stochastic surface growth process, in the form of a generalized Eden model, is set up and analyzed. The model explicitly takes into account selection between two strains, irreversible mutations, and the roughness of the propagating colony front. The asymmetric character of mutations implies the existence of an absorbing state, where only the mutant strain is at the front of the expanding population. Hence, the model combines two interesting branches of non-equilibrium statistical mechanics: phase transitions to absorbing states and dynamic surface roughening. As usual for these processes, one can define critical exponents, which describe the divergence of observables near the phase transition, and admit organization of models into universality classes. It turns out that the coupling between roughening dynamics and population dynamics induces qualitative different behavior. As a consequence, the model cannot be assigned to any universality class currently known

Gravity-induced dynamics of a squirmer microswimmer in wall proximity

We perform hydrodynamic simulations using the method of multi-particle collision dynamics and a theoretical analysis to study a single squirmer microswimmer at high Péclet number, which moves in a low Reynolds number fluid and under gravity. The relevant parameters are the ratio α of swimming to bulk sedimentation velocity and the squirmer type β. The combination of self-propulsion, gravitational force, hydrodynamic interactions with the wall, and thermal noise leads to a surprisingly diverse behavior. At α > 1 we observe cruising states, while for α < 1 the squirmer resides close to the bottom wall with the motional state determined by stable fixed points in height and orientation. They strongly depend on the squirmer type β. While neutral squirmers permanently float above the wall with upright orientation, pullers float for α larger than a threshold value ath and are pinned to the wall below αth. In contrast, pushers slide along the wall at lower heights, from which thermal orientational fluctuations drive them into a recurrent floating state with upright orientation, where they remain on the timescale of orientational persistence.DFG, 325093850, Open Access Publizieren 2017 - 2018 / Technische Universität Berli

Evolution of a Fossil Subduction Zone: Insights from the Tauern Window, Eastern Alps

Subduction zones play a crucial role in the evolution of Earth's lithosphere. In many orogens, deeply subducted coherent high-pressure (HP) nappes were exhumed from deep to shallow parts of subduction channels. This process significantly affects the deformation pattern and internal structure of the orogen. Exhumation seems to occur preferentially during the transition from subduction to collision, when dense oceanic lithosphere has been consumed entirely and more buoyant continental lithosphere from a passive continental margin enters the subduction zone. Here, we present a detailed study on the structural, kinematic, and metamorphic evolution of a well-preserved paleo-subduction channel within the Tauern Window (Alps). First, we reevaluated the metamorphic history and regional tectono-stratigraphy of the tectonic units in the central Tauern Window. These units originate from the Alpine Tethys oceanic domain and the adjacent European passive continental margin. They experienced HP conditions during Alpine subduction, which was followed by exhumation to their current position in the Alpine nappe stack. By integrating new structural data and the well-preserved stratigraphy of the ocean-continent transition, we reconstructed the structure and kinematics of the nappes in great detail. Notably, we document a recumbent, tens-of-kilometers-scale sheath fold formed during pervasive top-to-the-foreland shear. This sheath fold comprises an isoclinally folded thrust that transported ophiolite relicts from the former Alpine Tethys onto a distal part of the European continental margin during early stages of subduction. It formed under HP conditions, immediately after the Europe-derived rocks in its core reached their maximum burial depth. The non-cylindrical shape of the sheath fold suggests its nucleation at a promontory of the former margin, inherited from Mesozoic rifting and subsequently amplified to a sheath geometry during top-to-the-foreland shear in the subduction zone. To gain insight into the temperature (T) structure of the sheath fold, we employed Raman spectroscopy on carbonaceous material (RSCM) thermometry on a large number of samples with high spatial resolution. The systematic spatial temperature trends reveal distinct domains related to the original subduction metamorphism and later T-dominated (Barrovian) metamorphic overprint. Integrating the peak-temperature pattern with the fold geometry unveils a two-stage process of nappe formation and sheath folding during exhumation. Our results highlight the existence of considerable along-strike heterogeneity within the deep portion of a fossil subduction zone, likely influenced by inherited rift structures and exhumation processes. Understanding such heterogeneities is crucial for interpreting seismic sections and numerical simulations of subduction zones, emphasizing the need to consider three-dimensional complexities beyond the idealized cylindrical models often used. By unraveling the structural and metamorphic evolution of exhumed HP nappes in the Tauern Window, this study contributes to a better understanding of the dynamic processes operating within subduction zones and their implications for mountain building