Density distribution and size sorting in fish schools: an individual-based model

In fish schools the density varies per location and often individuals are sorted according to familiarity and/or body size. High density is considered advantageous for protection against predators and this sorting is believed to be advantageous not only to avoid predators but also for finding food. In this paper, we list a number of mechanisms and we study, with the help of an individual-based model of schooling agents, which spatial patterns may result from them. In our model, schooling is regulated by the following rules: avoiding those that are close by, aligning to those at intermediate distances, and moving towards others further off. Regarding kinship/familiarity, we study patterns that come about when agents actively choose to be close to related agents (i.e., ‘active sorting'). Regarding body size, we study what happens when agents merely differ in size but behave according to the usual schooling rules (‘size difference model'), when agents choose to be close to those of similar size, and when small agents avoid larger ones (‘risk avoidance'). Several spatial configurations result: during ‘active sorting' familiar agents group together anywhere in the shoal, but agents of different size group concentrically, whereby the small agents occupy the center and the large ones the periphery (‘size difference model' and ‘active sorting'). If small agents avoid the risk of being close to large ones, however, small agents end up at the periphery and large ones occupy the center (‘risk avoidance'). Spatial configurations are also influenced by the composition of the group, namely the percentage of agents of each type. Furthermore, schools are usually oblong and their density is always greatest near the front. We explain the way in which these patterns emerge and indicate how results of our model may guide the study of spatial patterns in real animal

Simulations of the social organization of large schools of fish whose perception is obstructed

Individual-based models have shown that simple interactions among moving individuals (repulsion, attraction and alignment) result in travelling schools that resemble those of real fish. In most models individuals interact with all neighbours within sensory range which usually includes almost all the individuals of the school. Thus, it implies (almost) global perception. However, in reality in large groups, individuals will only interact with their neighbours close by, because they cannot perceive those farther away, since they are masked by closer ones. Here, we have developed a new model to investigate how such obstruction of perception influences aspects of social organization in schools of up to 10,000 individuals. We will show that in small schools of up to approximately 30 individuals group shape and density resembles that obtained with global perception, because in small schools hardly anyone is masked by others: school shape is oblong and the density is highest in the frontal half of the school. With increasing group size, from approximately 200 individuals onwards, internal density becomes variable over time, regions of high and low density develop at any location within a school, and group shape becomes more complex, in the sense that inward bounds and appendages occur more frequently. The complexity of shape and internal structure arises because, due to their limited perception, individuals interact relatively more locally in larger schools. In case of global perception, however, shape remains elliptical for all group sizes and in groups above 1000 individuals, the schools become unrealistically dense. In sum, our results show that obstructed perception in itself suffices to generate a realistic organization of large schools and that no extra rules for 'coping' with many individuals are needed. (C) 2012 Elsevier B.V. All rights reserved

Partizipative Stadtteilentwicklung Winterthur-Töss : Evaluationsbericht zur Startphase

Der vorliegende Evaluationsbericht behandelt die Startphase des "Projekts Töss" im Winterthurer Stadtteil Töss (2005-2007). Das Hauptziel des Projekts Töss ist die Verbesserung der Lebensqualität in Töss, einem Stadtteil im demografischen und infrastrukturellen Umbruch. In Zusammenarbeit mit einem Team aus Fachleuten verschiedener Hochschulen wurde ein partizipativer Stadtteil-Entwicklungs-Prozess entwickelt und durchgeführt. Es resultierten 28 Projekte und -ideen, die vom Stadtrat grösstenteils umgesetzt werden. Zudem institutionalisierte sich die Bewegung in einem Dachverband der organisierten Bevölkerung von Töss sowie in einer interdepartementalen Projektleitung der Verwaltung

Inter-layer and inter-subject variability of diurnal gene expression in human skin

The skin is the largest human organ with a circadian clock that regulates its function. Although circadian rhythms in specific functions are known, rhythms in the proximal clock output, gene expression, in human skin have not been thoroughly explored. This work reports 24 h gene expression rhythms in two skin layers, epidermis and dermis, in a cohort of young, healthy adults, who maintained natural, regular sleep-wake schedules. 10% of the expressed genes showed such diurnal rhythms at the population level, of which only a third differed between the two layers. Amplitude and phases of diurnal gene expression varied more across subjects than layers, with amplitude being more variable than phases. Expression amplitudes in the epidermis were larger and more subject-variable, while they were smaller and more consistent in the dermis. Core clock gene expression was similar across layers at the population-level, but were heterogeneous in their variability across subjects. We also identified small sets of biomarkers for internal clock phase in each layer, which consisted of layer-specific non-core clock genes. This work provides a valuable resource to advance our understanding of human skin and presents a novel methodology to quantify sources of variability in human circadian rhythms.Peer Reviewe

Global parameter search reveals design principles of the mammalian circadian clock

Background: Virtually all living organisms have evolved a circadian (~24 hour) clock that controls physiological and behavioural processes with exquisite precision throughout the day/night cycle. The suprachiasmatic nucleus (SCN), which generates these ~24 h rhythms in mammals, consists of several thousand neurons. Each neuron contains a gene-regulatory network generating molecular oscillations, and the individual neuron oscillations are synchronised by intercellular coupling, presumably via neurotransmitters. Although this basic mechanism is currently accepted and has been recapitulated in mathematical models, several fundamental questions about the design principles of the SCN remain little understood. For example, a remarkable property of the SCN is that the phase of the SCN rhythm resets rapidly after a 'jet lag' type experiment, i.e. when the light/ dark (LD) cycle is abruptly advanced or delayed by several hours. Results: Here, we describe an extensive parameter optimization of a previously constructed simplified model of the SCN in order to further understand its design principles. By examining the top 50 solutions from the parameter optimization, we show that the neurotransmitters' role in generating the molecular circadian rhythms is extremely important. In addition, we show that when a neurotransmitter drives the rhythm of a system of coupled damped oscillators, it exhibits very robust synchronization and is much more easily entrained to light/dark cycles. We were also able to recreate in our simulations the fast rhythm resetting seen after a 'jet lag' type experiment. Conclusion: Our work shows that a careful exploration of parameter space for even an extremely simplified model of the mammalian clock can reveal unexpected behaviours and non-trivial predictions. Our results suggest that the neurotransmitter feedback loop plays a crucial role in the robustness and phase resetting properties of the mammalian clock, even at the single neuron level

Implications of embodiment and situatedness on the social organization of fish schools

In this thesis we investigate how the social organization of fish schools is influenced by the morphology and the sensory capabilities of the individuals as well as by those of their predators. We do this by means of individual-based models. Here, behavior at the group-level (schooling) is a consequence of local interactions, i.e. the responses of individuals to their neighbors and the interactions between predator and prey.We demonstrate how modeling the embodiment and the perceptual capabilities (situatedness) both of the individuals and of the predator influences their interaction and therefore the patterns at the group-level. Representing the individuals’ body affects the inter-individual spacing, such that large individuals occupy more space compared to small ones. Modeling the individuals’ situatedness, by reflecting the masking of distant neighbors by closer ones, restricts interaction to the local environment of the individual. This influences many schooling characteristics, such as nearest neighbor distance or group speed, and in mixed schools of large and small individuals it leads to the segregation of the two sizes. In large groups school shape becomes complex and variable and the distribution of individuals heterogeneous, with regions of high and low density occurring anywhere in the school. Modeling morphological and sensory constraints of a predator affects its success in capturing prey and, therefore, influences whether schooling behavior is beneficial for the individuals or not. We demonstrate that when the predator is confusable, i.e. when its sensory capabilities to detect the movements of individuals in a group are limited, schooling is almost always beneficial. In summary, incorporating aspects of embodiment and situatedness leads to more realistic models, first, because the real world is reflected more accurately, and, second, because they lead to a more realistic social organization of the simulated schools

Density distribution and size sorting in fish schools: an individual-based model

In fish schools the density varies per location and often individuals are sorted according to familiarity and/or body size. High density is considered advantageous for protection against predators and this sorting is believed to be advantageous not only to avoid predators but also for finding food. In this paper, we list a number of mechanisms and we study, with the help of an individual-based model of schooling agents, which spatial patterns may result from them. In our model, schooling is regulated by the following rules: avoiding those that are close by, aligning to those at intermediate distances, and moving towards others further off. Regarding kinship/familiarity, we study patterns that come about when agents actively choose to be close to related agents (i.e., 'active sorting'). Regarding body size, we study what happens when agents merely differ in size but behave according to the usual schooling rules ('size difference model'), when agents choose to be close to those of similar size, and when small agents avoid larger ones ('risk avoidance'). Several spatial configurations result: during 'active sorting' familiar agents group together anywhere in the shoal, but agents of different size group concentrically, whereby the small agents occupy the center and the large ones the periphery ('size difference model' and 'active sorting'). If small agents avoid the risk of being close to large ones, however, small agents end up at the periphery and large ones occupy the center ('risk avoidance'). Spatial configurations are also influenced by the composition of the group, namely the percentage of agents of each type. Furthermore, schools are usually oblong and their density is always greatest near the front. We explain the way in which these patterns emerge and indicate how results of our model may guide the study of spatial patterns in real animals. Copyright 2005.assortment; density distribution; fish; self-organization; school form; spatial structure

On prey grouping and predator confusion in artificial fish schools

In two simulation models the benefit of schooling underpredatory pressure is investigated. It appears that if a predator cannot become confused by prey, grouping is seldom beneficial. If prey, however, can confuse a predator, schooling appears to protect prey under a whole range of parameters. Using an evolutionary approach we found that, in the case of a confusable predator, cohesive groups with a consistent forward movement evolve most frequently, but that milling stationary groups also prove to be effective. We suggest that the predator protection in moving and stationary groups rely on different mechanisms, among other things, on a kind of altruistic behaviour

High-Performance Adder Circuit Generators in Parameterized Structural VHDL

In ASIC design, arithmetic components are usually selected from tooland technology-dependent libraries providing very limited flexibility and choice of circuit structures. With the possibility of parameterized structural circuit descriptions at the gate-level in VHDL, versatile circuit generators can be implemented which are highly independent of tool platforms and design technologies. This enables the realization of a universal and comprehensive library of efficient arithmetic components in form of a collection of synthesizable VHDL code entities. In a first step, high-performance adder generators were implemented using this method. Additionally, valuable experience was gained with respect to the implementation of circuit generators using parameterized structural VHDL. This work was funded by MICROSWISS (Microelectronics Program of the Swiss Government). In ASIC design, arithmetic components are usually selected from tool- and technologydependent libraries providing very limited flexibility and choice of circuit structures. With the possibility of parameterized structural circuit descriptions at the gate-level in VHDL, versatile circuit generators can be implemented which are highly independent of tool platforms and design technologies. This enables the realization of a universal and comprehensive library of efficient arithmetic components in form of a collection of synthesizable VHDL code entities. In a first step, high-performance adder generators were implemented using this method. Additionally, valuable experience was gained with respect to the implementation of circuit generators using parameterized structural VHDL.