The Dynamics of Location: Influence of Predation by Chaoborus Larvae on Rotifer Diel Vertical Migration Patterns

The locations of freshwater organisms in lakes are determined by the convergence of many competing factors. While predation pressure is one of these, also important are areas of food concentration and the physical and chemical constraints of a system. Diel vertical migration is a behavior exhibited by freshwater organisms in many taxa that is the result of balancing these factors. Diel vertical migration consists of movement by these organisms throughout the water column in accordance with a 24 hour cycle. This oscillation is generally driven by the competing factors of predation pressure and food acquisition, and is modified by physical and chemical requirements. In the Low Lake system during the summer of 2012, two groups of organisms were engaged in diel vertical migration: rotifers and Chaoborus. While some instars of Chaoborus were exhibiting a typical diel vertical migration pattern, the migration pattern of the rotifers was the opposite. While the migration pattern of the Chaoborus was likely driven by fish predation, that of the rotifers was driven by Chaoborus predation pressure resulting from their diel vertical migration. The migration patterns in both of these groups of organisms were also driven by differential locations of food resources. The migration patterns of rotifers and Chaoborus in Low Lake are an excellent example of how the changing locations of organisms in a lake are the result of balancing many factors that influence the fitness of these organisms

Mechanical limits of viral capsids

We study the elastic properties and mechanical stability of viral capsids under external force-loading with computer simulations. Our approach allows the implementation of specific geometries corresponding to specific phages such as $\phi$29 and CCMV. We demonstrate how in a combined numerical and experimental approach the elastic parameters can be determined with high precision. The experimentally observed bimodality of elastic spring constants is shown to be of geometrical origin, namely the presence of pentavalent units in the viral shell. A criterion for capsid breakage is defined, which explains well the experimentally observed rupture. From our numerics we find for the dependence of the rupture force on the F\"oppl-von K\'arm\'an (FvK) number a crossover from $\gamma^{2/3}$ to $\gamma^{1/2}$. For filled capsids high internal pressures lead to a stronger destabilization of viruses with a buckled ground state than unbuckled ones. Finally, we show how our numerically calculated energy maps can be used to extract information about the strength of protein-protein interactions from rupture experiments.Comment: 6 pages, 9 figure

Micro-Machinations: A DSL for Game Economies

In the multi-billion dollar game industry, time to market limits the time developers have for improving games. Game designers and software engineers usually live on opposite sides of the fence, and both lose time when adjustments best understood by designers are implemented by engineers. Designers lack a common vocabulary for expressing gameplay, which hampers specification, communication and agreement. We aim to speed up the game development process by improving designer productivity and design quality. The language Machinations has introduced a graphical notation for expressing the rules of game economies that is close to a designer’s vocabulary. We present the language Micro- Machinations (MM) that details and formalizes the meaning of a significant subset of Machination’s language features and adds sever

Induced fibrillation is equally effective as crystalloid cardioplegia in the protection of fetal myocardial function

AbstractBackgroundFetal cardiac intervention represents a potential advance in the treatment of congenital cardiac lesions that increase in complexity during development. Prenatal repair of a primary defect might prevent pathologic blood-flow patterns that can result in hypoplasia of a cardiac chamber or great vessel. However, strategies to optimize fetal myocardial protection have not been studied. A biventricular working fetal heart preparation was used to evaluate the cardioprotective properties of induced fibrillation and crystalloid cardioplegia.MethodsHearts from 16 fetal lambs at 115 to 125 days’ gestation were harvested and perfused with Krebs-Henseleit solution. The descending aorta was ligated distal to the ductal insertion and the branch pulmonary arteries were ligated to simulate the parallel circulation of the fetus. Hearts were arrested with normothermic fibrillation (n = 8) or hypothermic crystalloid cardioplegia (n = 8) before reperfusion with Krebs-Henseleit solution. Baseline and postarrest myocardial function measurements were obtained from analysis of pressure-dimension relationships.ResultsFibrillatory and cardioplegic arrest were equally effective at preserving postarrest systolic function (left ventricle, 70% ± 5% vs 68% ± 15%, P = .52; right ventricle, 68% ± 4.5% vs 65% ± 4.5%, P = .26) and preventing increased diastolic stiffness (left ventricle, 32% ± 5.3% vs 38% ± 11%, P = .24; right ventricle, 25% ± 3.3% vs 27% ± 2.1%, P = .46). Myocardial water content was unchanged in hearts arrested with fibrillation and cardioplegia (84% ± 1.5% vs 83.7% ± 0.9%, P = .71).ConclusionsNormothermic fibrillation and hypothermic crystalloid cardioplegia provide equal protection of the fetal myocardium. In the setting of diminished fetal myocardial reserve and because of the limited ability to manipulate the surrounding temperature in the fetus, normothermic fibrillation may be preferable for in utero repairs of selected congenital heart defects

Continuous melting of compact polymers

The competition between chain entropy and bending rigidity in compact polymers can be addressed within a lattice model introduced by P.J. Flory in 1956. It exhibits a transition between an entropy dominated disordered phase and an energetically favored crystalline phase. The nature of this order-disorder transition has been debated ever since the introduction of the model. Here we present exact results for the Flory model in two dimensions relevant for polymers on surfaces, such as DNA adsorbed on a lipid bilayer. We predict a continuous melting transition, and compute exact values of critical exponents at the transition point.Comment: 5 pages, 1 figur

On the hadronic contribution to sterile neutrino production

Sterile neutrinos with masses in the keV range are considered to be a viable candidate for warm dark matter. The rate of their production through active-sterile neutrino transitions peaks, however, at temperatures of the order of the QCD scale, which makes it difficult to estimate their relic abundance quantitatively, even if the mass of the sterile neutrino and its mixing angle were known. We derive here a relation, valid to all orders in the strong coupling constant, which expresses the production rate in terms of the spectral function associated with active neutrinos. The latter can in turn be expressed as a certain convolution of the spectral functions related to various mesonic current-current correlation functions, which are being actively studied in other physics contexts. In the naive weak coupling limit, the appropriate Boltzmann equations can be derived from our general formulae.Comment: 28 pages. v2: small clarifications added, published versio