295 research outputs found

    Bacterial chemotaxis: sensory adaptation, noise filtering, and information transmission

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    Chemotaxis is a fundamental cellular process by which cells sense and navigate in their environment. The molecular signalling pathway in the bacterium Escherichia coli is experimentally well-characterised and, hence, ideal for quantitative analysis and modelling. Chemoreceptors sense gradients of a multitude of substances and regulate an intracellular signalling pathway, which modulates the swimming behaviour. We studied the chemotaxis pathway in E. coli (i) to quantitatively understand molecular interactions in the signalling network, (ii) to gain a systems view of the workings of the pathway, including the effects of noise generated by biomolecular reactions during signalling, and (iii) to understand general design principles relevant for many sensory systems. Specifically, we investigated the adaptation dynamics due to covalent chemoreceptor modification, which includes numerous layers of feedback regulation. In collaboration with an experimental group, we undertook quantitative experiments using wild-type cells and mutants for proteins involved in adaptation using in vivo fluorescence resonance transfer (FRET). We developed a dynamical model for chemotactic signalling based on cooperative chemoreceptors and adaptation of the sensory response. This model quantitatively explains an interesting asymmetry of the response to favourable and unfavourable stimuli observed in the experiments. In a whole-pathway description, we further studied the response to controlled concentration stimuli, as well as how fluctuations from the environment and due to intracellular signalling affect the detection of input signals. Finally, the chemotaxis pathway is characterised by high sensitivity, a wide dynamic range and the need for information transmission, properties shared with many other sensory systems. Based on FRET data, we investigated the emergence, limits and biological significance of Weber’s law which predicts that the system detects stimuli relative to the background stimulus. Furthermore, we studied the information transmission from input concentrations into intracellular signals. We connect Weber’s law, as well as information transmission, to swimming bacteria and predict typically encountered chemical inputs

    A Review of Algorithms for Retinal Vessel Segmentation

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    oai:ojs.pkp.sfu.ca:article/41This paper presents a review of algorithms for extracting blood vessels network from retinal images. Since retina is a complex and delicate ocular structure, a huge effort in computer vision is devoted to study blood vessels network for helping the diagnosis of pathologies like diabetic retinopathy, hypertension retinopathy, retinopathy of prematurity or glaucoma.  To carry out this process many works for normal and abnormal images have been proposed recently. These methods include combinations of algorithms like Gaussian and Gabor filters, histogram equalization, clustering, binarization, motion contrast, matched filters, combined corner/edge detectors, multi-scale line operators, neural networks, ants, genetic algorithms, morphological operators. To apply these algorithms pre-processing tasks are needed. Most of these algorithms have been tested on publicly retinal databases. We have include a table summarizing algorithms and results of their assessment

    The Genesis of Social Interactionism and Differentiation of Macro- and Microsociological Paradigms

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    This paper presents an historical outlook on the macro-micro distinction in modern sociology. It links the genesis of social interactionism and microsociology to the rise of Romantic philosophy and attempts to elaborate methodological principles dividing macro- and microscopic perspectives in sociology. Six ideal-typical distinctions are considered: natural vs. social universality, emergent properties vs. emergent processes, morphological structuralism vs. genetical interactionism, choice among socially structured alternatives vs. structuring appearance into reality, structural vs. emergent directionality, operational vs. hermeneutical analysis. The complementarity of the languages of macro- and microsociological theories is advocated as a foundation for the further elaboration of conceptual links between the two levels of analysis

    Aerospace Medicine and Biology: A continuing bibliography (supplement 249)

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    This bibliography lists 311 reports, articles and other documents introduced into the NASA scientific and technical information system in August 1983

    Aerospace medicine and biology: A continuing bibliography with indexes, supplement 188, January 1979

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    This bibliography lists 230 reports, articles, and other documents introduced into the NASA scientific and technical information system in December 1978

    Ritualization of Texts and Textualization of Ritual in the Codification of Taoist Liturgy

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    Early in the fifth century in China, the Taoist master began to edit a set of scriptures that had been revealed years earlier. These were the Ling-pao or Spiritual tures, considered to be the second major scriptural development of medieval Taoism. 1 In reconstructing corpus of Ling-pao scriptures from among a multitude and forgeries, Lu worked to present these texts as revelation of the Tao in history, thereby inhibiting further and securing some closure on an early canon. At however, Lu began to codify the ritual material contained scriptures to fashion the liturgical directives that for much of the subsequent Taoist tradition

    Evolutionary, ecological, and anthropogenic drivers of phenotypic diversity in ants

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    The drivers of phenotypic diversity have puzzled humanity for centuries. Functional trait approaches have helped advance the mechanistic understanding of the diversity of life forms. Previous work has shown that evolutionary history and environmental adaptation contribute to the observed diversity of phenotypes. However, most of our understanding comes from plants and studies that often neglect the influence of intraspecific variability. My thesis aims to investigate the drivers of phenotypic diversity across organizational levels using ants as study organisms. In Chapter 2, I examined the influence of evolutionary and environmental heterogeneity on the phenotypic diversity of ant lineages. I found a negative relationship between the diversity of climates occupied by ant genera and their phenotypic integration. This indicates that phenotypic integration may limit ant phenotypic diversification into new climatic zones. For Chapter 3, I examined geographic variation in community-wide patterns of phenotypic diversity, at different organizational levels (i.e., worker, colony, and species), along a 9° latitude gradient in Quebec, Canada. The results suggest that stressful environmental conditions typical of northern ecosystems exert a strong selection pressure on ant morphology causing shifts in optimal trait values of antennae length and eye size. Specifically, I found that shorter antennae and larger eyes possibly represent adaptations to cold, dry, and open habitats. In Chapter 4, I evaluated the impact of coffee plantation management practices on community-wide patterns of ant phenotypic diversity and composition. I found that intensified monocultures harbored phenotypically distinct ant communities. Moreover, community-wide phenotypic composition was more homogeneous in intensified plantations than in nearby forest patches or shade-grown plantations. This indicates that shade-grown strategies in coffee plantations buffer the impoverishment of ant phenotypic diversity following forest conversion, which could help preserve ecosystem services provided by ants. Overall, my thesis suggests that ant phenotypic diversity patterns are limited by phenotypic integration, vary among organizational levels (worker, colony, and species), and are influenced by anthropogenic disturbance across facets (taxonomic, phylogenetic, and functional). These findings have important implications for understanding how phenotypically complex organisms respond to climate change and provide guidance for conservation strategies targeting vulnerable lineages

    Bat Time Stories

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    since environments underlie a constant change, animals need to keep track of these changes by gathering information and by using this information to make decisions. During the course of evolution, cognitive abilities, information processing skills, have evolved in many species to cope with the requirements of diverse habitats. In this study I investigated the cognitive abilities involved in the foraging on renewable resources. Examples for such resources include nectar, fruits, or foliage. Renewable resources possess two qualities that can be used by an animal to optimise its foraging behaviour; first, once an animal discovers a location where such a resource can be found, it is profitable to return to this location later since most renewable resources are not mobile. Second, there is often a temporal pattern underlying the renewal process so that such a resource renews itself with a more or less constant production rate. Thus, it would be a clear advantage if an animal were able to remember the location and to estimate the production rate of a resource. To remember the location of a resource can save time and energy for searching, and the ability to assess the production rate would allow an animal to time its return so that the difference between the energy that is needed to travel to the resource and the energy gained at the resource is positive. I explored these possibilities in a flower-visiting bat, Glossophaga soricina, which forages mainly on floral nectar. This species will thus allow for the study of cognitive specialisations in the domains of spatial memory and interval timing. This study aimed at the following questions: 1.What spatial information will these bats use to relocate already visited flowers and how is this information encoded? 2.Can bats use temporal and qualitative information that can be obtained when visiting a flower to time their revisits? 3.What implications arise from these results for the dynamics on a population level? When relocating flowers, bats have several spatial stimuli available. However, some of these stimuli are spatially dissociated from the flower like conspicuous branches or leaves. When the spatial contiguity between a stimulus and a response location is not given, it is difficult or even impossible to form associations for some species. However, in the case of flower-visiting bats, it could be of advantage to use these stimuli in the relocation process. In chapter 2, I explored this possibility by providing the bats with additional cues in a task where they had to exploit an array of 64 flowers with 16 randomly distributed rewarding feeders. The additional cues were spatially separated from the rewarding feeders. Even though bats employed information from these spatially dissociated cues in the relocation process by forming single stimulus response location associations. However, the information obtained from additional cues seems, at least in this experiment, of subordinate importance since bats were even without cues able to achieve a good performance with respect to their spatial accuracy. Bats encounter in their environments different species of flowers that provide them with nectar. The quality with respect to nectar content of these flowers can differ considerably between as well as within species. In chapter 3, I investigated, whether flower-visiting bats can discriminate between different sugar water volumes. This was done in a two alternative forced choice task in which two sugar water volumes were presented to the bats, which differed. Bats discriminated well between the different sugar water volumes. An analysis on basis of a psychometric function that we obtained from the empirical data showed that the discrimination threshold seems to be even lower than the threshold for honeybees. The production rates of floral nectar underlie temporal patterns, and the ability to estimate the time interval since the last visit to a flower might help flower-visiting bats to time their revisits according to such patterns. In chapter 4, I examined, whether bats possess the ability to estimate small time intervals. For this purpose, I tested bats in a modified version of a fixed interval schedule, the peak procedure. Here, bats were rewarded after a fixed time after the onset of a signal. We analysed only empty trials, trials where no reward was given, that were interspersed with ordinary trials. Bats showed increasing response rates after the signal onset with maximum response rates at the fixed interval time. After the fixed interval time had elapsed, the response decreased again. This reaction has been already found in several other species. It shows that flower-visiting bats are able to estimate small time intervals, which might help them optimise their foraging bouts. In the previous two chapters, I looked at the perception of nectar volumes and time intervals separately. However, only when bats were able to integrate these two information, it could result in an optimisation of their foraging behaviour. Therefore, I confronted bats with six feeders with differing nectar secretion rates (chapter 5). Results showed that bats adopted their visitation pattern according to the underlying rates. Moreover, a computational model could provide evidence that bats possess reference memories for the two types of information. Thus, bats are able to estimate nectar production rates and direct their foraging decisions by this information. In all paradigms described above, bats foraged alone. However, under natural conditions this is seldom the case. In chapter 6, I explored the possible ecological implications from chapter 2 through 5 and speculated on the impact of the found cognitive abilities on foraging dynamics on a population level. I tested several bats in the rainforest in Costa Rica in a semi natural paradigm for their reaction to variable resources while foraging in a group with other individuals. And even though the amount of empirical data is not convincing yet, I cannot rule out the possibility that the cognitive abilities we found might also constitute the basis for the estimation of competitional pressure at certain resource locations, which could lead to an optimised exploitation of the standing crop. In this study I could provide evidence for the existence of several high level cognitive abilities in a flower-visiting bat. Through these cognitive abilities, bats can plan into the future and direct their foraging decision by the information they processed. It is probable that these cognitive abilities represent unique adaptations to the demands of the ecological niche of a flower-visiting bat

    Maurice Merleau-Ponty: Between Phenomenology and Structuralism

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    Made available in Digital Common by permission of James Schmidt, author and rights owner
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