@article{3781, abstract = {We bound the difference in length of two curves in terms of their total curvatures and the Fréchet distance. The bound is independent of the dimension of the ambient Euclidean space, it improves upon a bound by Cohen-Steiner and Edelsbrunner, and it generalizes a result by Fáry and Chakerian.}, author = {Fasy, Brittany Terese}, issn = {2064-8316}, journal = {Acta Scientiarum Mathematicarum}, number = {1-2}, pages = {359 -- 367}, publisher = {Springer Nature}, title = {{The difference in length of curves in R^n}}, doi = {10.1007/BF03651375}, volume = {77}, year = {2011}, } @inproceedings{3383, author = {Heisenberg, Carl-Philipp J}, booktitle = {The FEBS Journal}, location = {Torino, Italy}, number = {S1}, pages = {24 -- 24}, publisher = {Wiley}, title = {{Invited Lectures ‐ Symposia Area}}, doi = {10.1111/j.1742-4658.2011.08136.x}, volume = {278}, year = {2011}, } @article{3368, abstract = {Tissue surface tension (TST) is an important mechanical property influencing cell sorting and tissue envelopment. The study by Manning et al. (1) reported on a mathematical model describing TST on the basis of the balance between adhesive and tensile properties of the constituent cells. The model predicts that, in high-adhesion cell aggregates, surface cells will be stretched to maintain the same area of cell–cell contact as interior bulk cells, resulting in an elongated and flattened cell shape. The authors (1) observed flat and elongated cells at the surface of high-adhesion zebrafish germ-layer explants, which they argue are undifferentiated stretched germ-layer progenitor cells, and they use this observation as a validation of their model.}, author = {Krens, Gabriel and Möllmert, Stephanie and Heisenberg, Carl-Philipp J}, journal = {PNAS}, number = {3}, pages = {E9 -- E10}, publisher = {National Academy of Sciences}, title = {{Enveloping cell layer differentiation at the surface of zebrafish germ layer tissue explants}}, doi = {10.1073/pnas.1010767108}, volume = {108}, year = {2011}, } @article{3373, abstract = {The use of optical traps to measure or apply forces on the molecular level requires a precise knowledge of the trapping force field. Close to the trap center, this field is typically approximated as linear in the displacement of the trapped microsphere. However, applications demanding high forces at low laser intensities can probe the light-microsphere interaction beyond the linear regime. Here, we measured the full nonlinear force and displacement response of an optical trap in two dimensions using a dual-beam optical trap setup with back-focal-plane photodetection. We observed a substantial stiffening of the trap beyond the linear regime that depends on microsphere size, in agreement with Mie theory calculations. Surprisingly, we found that the linear detection range for forces exceeds the one for displacement by far. Our approach allows for a complete calibration of an optical trap.}, author = {Jahnel, Marcus and Behrndt, Martin and Jannasch, Anita and Schaeffer, Erik and Grill, Stephan}, journal = {Optics Letters}, number = {7}, pages = {1260 -- 1262}, publisher = {Optica Publishing Group}, title = {{Measuring the complete force field of an optical trap}}, doi = {10.1364/OL.36.001260}, volume = {36}, year = {2011}, } @article{3393, abstract = {Unlike unconditionally advantageous “Fisherian” variants that tend to spread throughout a species range once introduced anywhere, “bistable” variants, such as chromosome translocations, have two alternative stable frequencies, absence and (near) fixation. Analogous to populations with Allee effects, bistable variants tend to increase locally only once they become sufficiently common, and their spread depends on their rate of increase averaged over all frequencies. Several proposed manipulations of insect populations, such as using Wolbachia or “engineered underdominance” to suppress vector-borne diseases, produce bistable rather than Fisherian dynamics. We synthesize and extend theoretical analyses concerning three features of their spatial behavior: rate of spread, conditions to initiate spread from a localized introduction, and wave stopping caused by variation in population densities or dispersal rates. Unlike Fisherian variants, bistable variants tend to spread spatially only for particular parameter combinations and initial conditions. Wave initiation requires introduction over an extended region, while subsequent spatial spread is slower than for Fisherian waves and can easily be halted by local spatial inhomogeneities. We present several new results, including robust sufficient conditions to initiate (and stop) spread, using a one-parameter cubic approximation applicable to several models. The results have both basic and applied implications.}, author = {Barton, Nicholas H and Turelli, Michael}, issn = {1537-5323}, journal = {American Naturalist}, number = {3}, pages = {E48 -- E75}, publisher = {University of Chicago Press}, title = {{Spatial waves of advance with bistable dynamics: Cytoplasmic and genetic analogues of Allee effects}}, doi = {10.1086/661246}, volume = {178}, year = {2011}, } @article{22556, abstract = {Numerous studies across multiple disciplines search for insights on the effects of climate change at local spatial scales and at fine time resolutions. This study presents an overall methodology of using a weather generator for downscaling an ensemble of climate model outputs. The downscaled predictions can explicitly include climate model uncertainty, which offers valuable information for making probabilistic inferences about climate impacts. The hourly weather generator that serves as the downscaling tool is briefly presented. The generator is designed to reproduce a set of meteorological variables that can serve as input to hydrological, ecological, geomorphological, and agricultural models. The generator is capable of reproducing a wide set of climate statistics over a range of temporal scales, from extremes, to low-frequency interannual variability; its performance for many climate variables and their statistics over different aggregation periods is highly satisfactory. The use of the weather generator in simulations of future climate scenarios, as inferred from climate models, is described in detail. Using a previously developed methodology based on a Bayesian approach, the stochastic downscaling procedure derives the frequency distribution functions of factors of change for several climate statistics from a multi-model ensemble of outputs of General Circulation Models. The factors of change are subsequently applied to the statistics derived from observations to re-evaluate the parameters of the weather generator. Using embedded causal and statistical relationships, the generator simulates future realizations of climate for a specific point location at the hourly scale. Uncertainties present in the climate model realizations and the multi-model ensemble predictions are discussed. An application of the weather generator in reproducing present (1961–2000) and forecasting future (2081–2100) climate conditions is illustrated for the location of Tucson (AZ). The stochastic downscaling is carried out using simulations of eight General Circulation Models adopted in the IPCC 4AR, A1B emission scenario.}, author = {Fatichi, Simone and Ivanov, Valeriy Y. and Caporali, Enrica}, issn = {0309-1708}, journal = {Advances in Water Resources}, keywords = {Weather generator, Stochastic downscaling, Climate change, Hydro-meteorology, Rainfall model}, number = {4}, pages = {448--467}, publisher = {Elsevier}, title = {{Simulation of future climate scenarios with a weather generator}}, doi = {10.1016/j.advwatres.2010.12.013}, volume = {34}, year = {2011}, } @article{3375, abstract = {By exploiting an analogy between population genetics and statistical mechanics, we study the evolution of a polygenic trait under stabilizing selection, mutation and genetic drift. This requires us to track only four macroscopic variables, instead of the distribution of all the allele frequencies that influence the trait. These macroscopic variables are the expectations of: the trait mean and its square, the genetic variance, and of a measure of heterozygosity, and are derived from a generating function that is in turn derived by maximizing an entropy measure. These four macroscopics are enough to accurately describe the dynamics of the trait mean and of its genetic variance (and in principle of any other quantity). Unlike previous approaches that were based on an infinite series of moments or cumulants, which had to be truncated arbitrarily, our calculations provide a well-defined approximation procedure. We apply the framework to abrupt and gradual changes in the optimum, as well as to changes in the strength of stabilizing selection. Our approximations are surprisingly accurate, even for systems with as few as five loci. We find that when the effects of drift are included, the expected genetic variance is hardly altered by directional selection, even though it fluctuates in any particular instance. We also find hysteresis, showing that even after averaging over the microscopic variables, the macroscopic trajectories retain a memory of the underlying genetic states.}, author = {de Vladar, Harold and Barton, Nicholas H}, journal = {Journal of the Royal Society Interface}, number = {58}, pages = {720 -- 739}, publisher = {Royal Society}, title = {{The statistical mechanics of a polygenic character under stabilizing selection mutation and drift}}, doi = {10.1098/rsif.2010.0438}, volume = {8}, year = {2011}, }