University of Konstanz

About: University of Konstanz is a education organization based out in Konstanz, Baden-Württemberg, Germany. It is known for research contribution in the topics: Population & Membrane. The organization has 12115 authors who have published 27401 publications receiving 951162 citations. The organization is also known as: University of Constance & Universität Konstanz.

Signal processing times in bacterial chemotaxis.

Abstract: The bacterium Escherichia coli responds to changes in the concentrations of various chemicals in its environment1. A cell swims along a smooth trajectory (runs), moves erratically for a brief time (tumbles) and then runs again, choosing a new direction at random2. If a run happens to carry the cell up a gradient of an attractant (such as aspartate, serine and certain sugars), the occupancy of the appropriate chemoreceptor increases with time3,4 and a signal is sent to the flagellar motors that increases their counterclockwise bias5. On the average, this extends favourable runs and the cell moves up the gradient. The receptors for aspartate and serine6–8 are proteins found in the cytoplasmic membrane, known as methyl-accepting chemotaxis proteins9,10, and are the products of the tar and tsr genes11. A cell can adapt to sustained changes of receptor occupancy by carboxymethylating these proteins12; it is not known, however, how these proteins signal the flagellar motors or how the signal controls the direction of flagellar rotation. Products of several che genes involved in signalling and adaptation have been identified13,14, but with the exception of a methyltransferase15 (the cheR product) and a demethylase16 (the cheB product), their functions are largely unknown. In an attempt to learn more about the events that trigger a chemotactic response, we have now exposed cells to rapid changes in the concentration of attractants and repellents and measured the time required for flagellar reversal. In wild-type cells and in cells containing a cheR–cheB deletion, the response latency is ∼0.2 s. In cheZ mutants, it is much longer.

Relationship Between Backward Stochastic Differential Equations and Stochastic Controls: A Linear-Quadratic Approach

Abstract: It is well known that backward stochastic differential equations (BSDEs) stem from the study on the Pontryagin type maximum principle for optimal stochastic controls. A solution of a BSDE hits a given terminal value (which is a random variable) by virtue of an it additional martingale term and an indefinite initial state. This paper attempts to explore the relationship between BSDEs and stochastic controls by interpreting BSDEs as some stochastic optimal control problems. More specifically, associated with a BSDE, a new stochastic control problem is introduced with the same dynamics but a definite given initial state. The martingale term in the original BSDE is regarded as the control, and the objective is to minimize the second moment of the difference between the terminal state and the terminal value given in the BSDE. This problem is solved in a closed form by the stochastic linear-quadratic (LQ) theory developed recently. The general result is then applied to the Black--Scholes model, where an optimal mean-variance hedging portfolio is obtained explicitly in terms of the option price. Finally, a modified model is investigated, where the difference between the state and the expectation of the given terminal value at any time is taken into account.

Recursive Wang tiles for real-time blue noise

Abstract: Well distributed point sets play an important role in a variety of computer graphics contexts, such as anti-aliasing, global illumination, halftoning, non-photorealistic rendering, point-based modeling and rendering, and geometry processing. In this paper, we introduce a novel technique for rapidly generating large point sets possessing a blue noise Fourier spectrum and high visual quality. Our technique generates non-periodic point sets, distributed over arbitrarily large areas. The local density of a point set may be prescribed by an arbitrary target density function, without any preset bound on the maximum density. Our technique is deterministic and tile-based; thus, any local portion of a potentially infinite point set may be consistently regenerated as needed. The memory footprint of the technique is constant, and the cost to generate any local portion of the point set is proportional to the integral over the target density in that area. These properties make our technique highly suitable for a variety of real-time interactive applications, some of which are demonstrated in the paper.Our technique utilizes a set of carefully constructed progressive and recursive blue noise Wang tiles. The use of Wang tiles enables the generation of infinite non-periodic tilings. The progressive point sets inside each tile are able to produce spatially varying point densities. Recursion allows our technique to adaptively subdivide tiles only where high density is required, and makes it possible to zoom into point sets by an arbitrary amount, while maintaining a constant apparent density.

The North Atlantic Oscillation and plankton dynamics in two European lakes –‐ two variations on a general theme

Abstract: Summary Long-term data on water temperature, phytoplankton biovolume, Bosmina and Daphnia abundance and the timing of the clear-water phase were compared and analysed with respect to the influence of the North Atlantic Oscillation (NAO) in two strongly contrasting lakes in central Europe. In small, shallow, hypertrophic Muggelsee, spring water temperatures and Daphnia abundance both increased more rapidly than in large, deep, meso/oligotrophic Lake Constance. Because of this, the clear-water phase commenced approximately three weeks earlier in Muggelsee than in Lake Constance. In Muggelsee, the phytoplankton biovolume during late winter/early spring was related to the NAO index. In Lake Constance, where phytoplankton growth was inhibited by intense downward mixing during all years studied, this was not the case. However, in both lakes, interannual variability in water temperature, in Daphnia spring population dynamics and in the timing of the clear-water phase, were all related to the interannual variability of the NAO index. The Daphnia spring population dynamics and the timing of the clear-water phase appear to be synchronized by the NAO despite large differences between the lakes in morphometry, trophic status and flushing and mixis regimes, and despite the great distance between the lakes (∼700 km). This suggests that a great variety of lakes in central Europe may possibly have exhibited similar interannual variability during the last 20 years.

Phycodnaviridae--large DNA algal viruses.

Abstract: Members and prospective members of the family Phycodnaviridae are large icosahedral, dsDNA (180 to 560 kb) viruses that infect eukaryotic algae. The genomes of two phycodnaviruses have been sequenced: the 331 kb genome of Paramecium bursaria chlorella virus (PBCV-1) and more recently, the 336 kb genome of the Ectocarpus siliculosus virus (EsV-1). EsV-1 has ∼ 231 protein-encoding genes whereas, the slightly smaller PBCV-1 genome has 11 tRNA genes and ∼ 375 protein-encoding genes. Surprisingly, the two viruses only have 33 genes in common, of which 17 have no counterparts in the databases. The low number of homologous genes between the two viruses can probably be attributed to their different life styles. PBCV-1 is a lytic virus that infects a unicellular, endosymbiotic freshwater green alga whereas, EsV-1 is a lysogenic virus that infects a free-living filamentous marine brown alga. Furthermore, accumulating evidence indicates that the phycodnaviruses and their genes are ancient, thus allowing significant differences to have evolved. This review briefly describes some of the biological properties of the phycodnaviruses, focusing on PBCV-1 and EsV-1, and then compares their genomes.