125 research outputs found
The Role of Antonymy on Semantic Change
The role of antonymy in semantic change is investigated via the etymology of sets of English antonyms. The results show a developmental pattern wherein two words sharing an antonym tend to exhibit similar trajectories of semantic development. Metaphorical extension is proposed as the primary mechanism that produces this regularity with antonymy playing a secondary role. These results further support semantic change as regular, even in contexts not involving grammaticalization, and that furthermore, metaphor is not peripheral to language use. (See Lakoff & Johnson, 1980; Traugott & Dasher, 2002; Hopper & Traugott, 2003.) There are also implications for formal and cognitive representations that rely on antonymous relationships for modeling aspects of gradable predicates (such as Paradis, 2001; Kennedy & McNally, 2005)
Information Exchange in Global Production Networks: Increasing Transparency by Simulation, Statistical Experiments and Selection of Digitalization Activities
Today, companies of all industries are part of global production networks. They have a variety of performance relationships with suppliers and customers. Digitalization offers the potential to exchange more information between the partners of global production networks. This may improve operational performance. Especially within the three business processes order management, quality problem solving and engineering change management, a targeted increase in transparency promises a better handling of disruptions and an increase in robustness. This paper presents a simulation-based methodology for modeling production and business processes as well as information exchange in global production networks. Following the principles of Design of Experiment (DoE), screening test plans first carve out the impact of disruptions and information exchange on the performance of the production network. This is followed by the determination of the disruption-robust information exchange using Taguchi-experiments. Starting from the actual state of information exchange, digitalization activities to increase transparency are finally determined. The activities consist of the implementation of digitalization technologies and the stronger linkage of information systems. The paper ends with an application of the methodology to a global production network for plastic-metal components in the automotive supplier industry
Chemotactic response and adaptation dynamics in Escherichia coli
Adaptation of the chemotaxis sensory pathway of the bacterium Escherichia
coli is integral for detecting chemicals over a wide range of background
concentrations, ultimately allowing cells to swim towards sources of attractant
and away from repellents. Its biochemical mechanism based on methylation and
demethylation of chemoreceptors has long been known. Despite the importance of
adaptation for cell memory and behavior, the dynamics of adaptation are
difficult to reconcile with current models of precise adaptation. Here, we
follow time courses of signaling in response to concentration step changes of
attractant using in vivo fluorescence resonance energy transfer measurements.
Specifically, we use a condensed representation of adaptation time courses for
efficient evaluation of different adaptation models. To quantitatively explain
the data, we finally develop a dynamic model for signaling and adaptation based
on the attractant flow in the experiment, signaling by cooperative receptor
complexes, and multiple layers of feedback regulation for adaptation. We
experimentally confirm the predicted effects of changing the enzyme-expression
level and bypassing the negative feedback for demethylation. Our data analysis
suggests significant imprecision in adaptation for large additions.
Furthermore, our model predicts highly regulated, ultrafast adaptation in
response to removal of attractant, which may be useful for fast reorientation
of the cell and noise reduction in adaptation.Comment: accepted for publication in PLoS Computational Biology; manuscript
(19 pages, 5 figures) and supplementary information; added additional
clarification on alternative adaptation models in supplementary informatio
Differential Affinity and Catalytic Activity of CheZ in E. coli Chemotaxis
Pushβpull networks, in which two antagonistic enzymes control the
activity of a messenger protein, are ubiquitous in signal transduction pathways.
A classical example is the chemotaxis system of the bacterium
Escherichia coli, in which the kinase CheA and the
phosphatase CheZ regulate the phosphorylation level of the messenger protein
CheY. Recent experiments suggest that both the kinase and the phosphatase are
localized at the receptor cluster, and Vaknin and Berg recently demonstrated
that the spatial distribution of the phosphatase can markedly affect the
doseβresponse curves. We argue, using mathematical modeling, that the
canonical model of the chemotaxis network cannot explain the experimental
observations of Vaknin and Berg. We present a new model, in which a small
fraction of the phosphatase is localized at the receptor cluster, while the
remainder freely diffuses in the cytoplasm; moreover, the phosphatase at the
cluster has a higher binding affinity for the messenger protein and a higher
catalytic activity than the phosphatase in the cytoplasm. This model is
consistent with a large body of experimental data and can explain many of the
experimental observations of Vaknin and Berg. More generally, the combination of
differential affinity and catalytic activity provides a generic mechanism for
amplifying signals that could be exploited in other two-component signaling
systems. If this model is correct, then a number of recent modeling studies,
which aim to explain the chemotactic gain in terms of the activity of the
receptor cluster, should be reconsidered
Self-Organization of the Escherichia coli Chemotaxis Network Imaged with Super-Resolution Light Microscopy
Photoactivated localization microscopy analysis of chemotaxis receptors in bacteria suggests that the non-random organization of these proteins results from random self-assembly of clusters without direct cytoskeletal involvement or active transport
Proliferation of Ty3/gypsy-like retrotransposons in hybrid sunflower taxa inferred from phylogenetic data
<p>Abstract</p> <p>Background</p> <p>Long terminal repeat (LTR) retrotransposons are a class of mobile genetic element capable of autonomous transposition via an RNA intermediate. Their large size and proliferative ability make them important contributors to genome size evolution, especially in plants, where they can reach exceptionally high copy numbers and contribute substantially to variation in genome size even among closely related taxa. Using a phylogenetic approach, we characterize dynamics of proliferation events of <it>Ty3/gypsy</it>-like LTR retrotransposons that led to massive genomic expansion in three <it>Helianthus </it>(sunflower) species of ancient hybrid origin. The three hybrid species are independently derived from the same two parental species, offering a unique opportunity to explore patterns of retrotransposon proliferation in light of reticulate evolutionary events in this species group.</p> <p>Results</p> <p>We demonstrate that <it>Ty3/gypsy</it>-like retrotransposons exist as multiple well supported sublineages in both the parental and hybrid derivative species and that the same element sublineage served as the source lineage of proliferation in each hybrid species' genome. This inference is based on patterns of species-specific element numerical abundance within different phylogenetic sublineages as well as through signals of proliferation events present in the distributions of element divergence values. Employing methods to date paralogous sequences within a genome, proliferation events in the hybrid species' genomes are estimated to have occurred approximately 0.5 to 1 million years ago.</p> <p>Conclusion</p> <p>Proliferation of the same retrotransposon major sublineage in each hybrid species indicates that similar dynamics of element derepression and amplification likely occurred in each hybrid taxon during their formation. Temporal estimates of these proliferation events suggest an earlier origin for these hybrid species than previously supposed.</p
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