Coarse-Grained Simulations of Membranes under Tension

We investigate the properties of membranes under tension by Monte-Carlo simulations of a generic coarse-grained model for lipid bilayers. We give a comprising overview of the behavior of several membrane characteristics, such as the area per lipid, the monolayer overlap, the nematic order, and pressure profiles. Both the low-temperature regime, where the membranes are in a gel phase, and the high-temperature regime, where they are in the fluid phase, are considered. In the gel state, the membrane is hardly influenced by tension. In the fluid state, high tensions lead to structural changes in the membrane, which result in different compressibility regimes. The ripple state, which is found at tension zero in the transition regime between the fluid and the gel phase, disappears under tension and gives way to an interdigitated phase. We also study the membrane fluctuations in the fluid phase. In the low tension regime the data can be fitted nicely to a suitably extended elastic theory. At higher tensions the elastic fit consistently underestimates the strength of long-wavelength fluctuations. Finally, we investigate the influence of tension on the effective interaction between simple transmembrane inclusions and show that tension can be used to tune the hydrophobic mismatch interaction between membrane proteins.Comment: 14 pages, 14 figures, accepted for publication in The Journal of Chemical Physic

Growth and Inequality in Public Good Games

In a novel experimental design we study public good games with dynamic interdependencies. Each agent's income at the end of a period serves as her endowment in the following period. In this setting growth and inequality arise endogenously allowing us to address new questions regarding their interplay and effect on cooperation levels. In stark contrast to standard public good experiments, we find that contributions are increasing over time even in the absence of punishment possibilities. Inequality and group income are positively correlated for poor groups, but negatively correlated for rich groups. There is very strong path dependence: inequality in early periods is strongly negatively correlated with group income in later periods. These results give new insights into why people cooperate and should make us rethink previous results from the literature on repeated public good games regarding the decay of cooperation in the absence of punishment

Spontaneous formation of complex micelles from homogeneous solution

We present an extensive computer simulation study of structure formation in amphiphilic block copolymer solutions after a quench from a homogeneous state. By using a mesoscopic field-based simulation method, we are able to access time scales in the range of a second. A phase diagram of final structures is mapped out as a function of the concentration and solvent-philicity of the copolymers. A rich spectrum of structures is observed, ranging from spherical and rodlike micelles and vesicles to toroidal and net-cage micelles. The dynamical pathways leading to these structures are analyzed in detail, and possible ways to control the structures are discussed briefly.Comment: PRL (in press

Intertidal mussel reefs change the composition and size distribution of diatoms in the biofilm

Migrating diatoms are microscopic ecosystem engineering organisms that have functional consequences on the seascape scale by significantly contributing to the microphytobenthos biofilm. The microphytobenthos biofilm is a thin photosynthesising layer that covers the sediment on intertidal flats. It fuels the food web, increases sediment stability, and enhances the deposition of particles, providing ecosystem services to coastal communities. Here we tested the effect of another ecosystem engineering habitat, intertidal blue mussel reefs, on the composition and properties of migrating diatom communities. Small-scale reefs constructed in the intertidal mimicked and reinforced the natural pattern in diatom community composition and function that we documented in the field. The field experiment adding small reefs to the intertidal ran from 30 April to 10 June 2015 and the field samples were collected around a natural blue mussel bed on the same tidal flat on 7 October 2015 (N 53.489 degrees, E 6.230 degrees). Both the constructed small-scale reefs and the natural reef changed the community composition of diatoms in the biofilm by promoting higher numbers of smaller-sized cells and species. Small diatoms have higher growth and gross photosynthesis rates, indicating that this explains the higher production and chlorophyll-a concentration of the biofilm measured on natural intertidal shellfish reefs. Our results showed that shellfish reefs have a large impact on biofilm functioning. However, biofilms are also fuel for the shellfish, indicating that the two very different ecosystem engineers may facilitate coexistence on tidal flats through a positive feedback loop

Mesoscopic simulations of the counterion-induced electroosmotic flow - a comparative study

We present mesoscopic simulations of the counterion-induced electroosmotic flow in different electrostatic coupling regimes. Two simulation methods are compared, Dissipative Particle Dynamics (DPD) and coupled Lattice-Boltzmann/Molecular Dynamics (LB/MD). A general mapping scheme to match DPD to LB/MD is developed. For the weak-coupling regime, analytic expressions for the flow profiles in the presence of partial-slip as well as no-slip boundary conditions are derived from the Poisson-Boltzmann and Stokes equations, which are in good agreement with the numerical results. The influence of electrofriction and partial slip on the flow profiles is discussed.Comment: 10 pages, 8 figures, 3 tables, additional references and minor changes in the tex

A Novel Gene Family Controls Species-Specific Morphological Traits in Hydra

Understanding the molecular events that underlie the evolution of morphological diversity is a major challenge in biology. Here, to identify genes whose expression correlates with species-specific morphologies, we compared transcriptomes of two closely related Hydra species. We find that species-specific differences in tentacle formation correlate with expression of a taxonomically restricted gene encoding a small secreted protein. We show that gain of function induces changes in morphology that mirror the phenotypic differences observed between species. These results suggest that “novel” genes may be involved in the generation of species-specific morphological traits

Production of an Anise-and Woodruff-like Aroma by Monokaryotic Strains of Pleurotus sapidus Grown on Citrus Side Streams

The production of natural flavors by means of microorganisms is of great interest for the food and flavor industry, and by-products of the agro-industry are particularly suitable as substrates. In the present study, Citrus side streams were fermented using monokaryotic strains of the fungus Pleurotus sapidus. Some of the cultures exhibited a pleasant smell, reminiscent of woodruff and anise, as well as herbaceous notes. To evaluate the composition of the overall aroma, liquid/liquid extracts of submerged cultures of a selected monokaryon were prepared, and the volatiles were isolated via solvent-assisted flavor evaporation. Aroma extract dilution analyses revealed p-anisaldehyde (sweetish, anisic-and woodruff-like) with a flavor dilution factor of 218 as a character impact compound. The coconut-like, herbaceous, and sweetish smelling acyloin identified as (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone also contributed to the overall aroma and was described as an aroma-active substance with an odor threshold in air of 0.2 ng L−1 to 2.4 ng L−1 for the first time. Supplementation of the culture medium with isotopically substituted L-tyrosine elucidated this phenolic amino acid as precursor of p-anisaldehyde as well as of (2S)-hydroxy-1-(4-methoxyphenyl)-1-propanone. Chiral analysis via HPLC revealed an enantiomeric excess of 97% for the isolated product produced by P. sapidus

Stress Response of Stone Martens and Red Foxes in Two Different Live Traps

Trapping of terrestrial animals is an important tool for harvest, pest control and research worldwide. To catch animals alive, animal welfare has to be ensured, which is reflected in different agreements on trading and trapping of animals between sovereign nations (Council Regulation [EEC] No 3254/91). The red fox (Vulpes vulpes) and stone marten (Martes foina) represent important predatory animals. Their influence on protected species as well as their increasing appearance in urban areas demand responsible handling. In our study, we evaluated 2 trap systems used for trapping red foxes and stone martens in accordance with criteria stipulated in the Agreement on International Humane Trapping Standards (AIHTS) and International Organisation for Standardisation 10990 Part 5 – Methods for Testing Restraining Traps (ISO 10990). In total, we captured 20 red foxes in a concrete pipe vault trap and 13 stone martens in a Strack’s wooden box trap in Schleswig-Holstein, Germany, and observed their behavior inside each trap. After anesthesia, a clinical examination of each animal was conducted, and blood and hair samples were taken. After euthanasia, radiological examinations of the full body were taken, and necropsies and histopathological investigations were performed. No trap-associated lesions were found. Hormone analysis showed no remarkable signs of stress for the animals, according to state-of-the-art methods. Apart from serum cortisol, the quotient of dehydroepiandrosterone in serum and hair seems to be the most predictive value on stress response of the 2 different species. Video observation of the trapped animals emerged as a valuable tool to estimate animal welfare by behavior. This study complements AIHTS and ISO 10990 criteria with results on behavior and hormone analysis, being an additional benefit when evaluating animal welfare of each trapping system

artbin: Extended sample size for randomized trials with binary outcomes

We describe the command artbin, which offers various new facilities for the calculation of sample size for binary outcome variables that are not otherwise available in Stata. While artbin has been available since 2004, it has not been previously described in the Stata Journal. artbin has been recently updated to include new options for different statistical tests, methods and study designs, improved syntax, and better handling of noninferiority trials. In this article, we describe the updated version of artbin and detail the various formulas used within artbin in different settings