Diffusion and Home Range Parameters from Rodent Population Measurements in Panama

Simple random walk considerations are used to interpret rodent population data collected in Hantavirus-related investigations in Panama regarding the short-tailed cane mouse, \emph{Zygodontomys brevicauda}. The diffusion constant of mice is evaluated to be of the order of (and larger than) 200 meters squared per day. The investigation also shows that the rodent mean square displacement saturates in time, indicating the existence of a spatial scale which could, in principle, be the home range of the rodents. This home range is concluded to be of the order of 70 meters. Theoretical analysis is provided for interpreting animal movement data in terms of an interplay of the home ranges, the diffusion constant, and the size of the grid used to monitor the movement. The study gives impetus to a substantial modification of existing theory of the spread of the Hantavirus epidemic which has been based on simple diffusive motion of the rodents, and additionally emphasizes the importance for developing more accurate techniques for the measurement of rodent movement.Comment: 18 pages, 5 figure

One-degree-of-freedom motion induced by modeled vortex shedding

The motion of an elastically supported cylinder forced by a nonlinear, quasi-static, aerodynamic model with the unusual feature of a motion-dependent forcing frequency was studied. Numerical solutions for the motion and the Lyapunov exponents are presented for three forcing amplitudes and two frequencies (1.0 and 1.1 times the Strouhal frequency). Initially, positive Lyapunov exponents occur and the motion can appear chaotic. After thousands of characteristic times, the motion changes to a motion (verified analytically) that is periodic and damped. This periodic, damped motion was not observed experimentally, thus raising questions concerning the modeling

A DNA damage-induced phosphorylation circuit enhances Mec1ATR Ddc2ATRIP recruitment to Replication Protein A

The cell cycle checkpoint kinase Mec1ATR and its integral partner Ddc2ATRIP are vital for the DNA damage and replication stress response. Mec1–Ddc2 “senses” single-stranded DNA (ssDNA) by being recruited to the ssDNA binding Replication Protein A (RPA) via Ddc2. In this study, we show that a DNA damage–induced phosphorylation circuit modulates checkpoint recruitment and function. We demonstrate that Ddc2–RPA interactions modulate the association between RPA and ssDNA and that Rfa1-phosphorylation aids in the further recruitment of Mec1–Ddc2. We also uncover an underappreciated role for Ddc2 phosphorylation that enhances its recruitment to RPA-ssDNA that is important for the DNA damage checkpoint in yeast. The crystal structure of a phosphorylated Ddc2 peptide in complex with its RPA interaction domain provides molecular details of how checkpoint recruitment is enhanced, which involves Zn2+. Using electron microscopy and structural modeling approaches, we propose that Mec1–Ddc2 complexes can form higher order assemblies with RPA when Ddc2 is phosphorylated. Together, our results provide insight into Mec1 recruitment and suggest that formation of supramolecular complexes of RPA and Mec1–Ddc2, modulated by phosphorylation, would allow for rapid clustering of damage foci to promote checkpoint signaling

Ranking and clustering of nodes in networks with smart teleportation

Random teleportation is a necessary evil for ranking and clustering directed networks based on random walks. Teleportation enables ergodic solutions, but the solutions must necessarily depend on the exact implementation and parametrization of the teleportation. For example, in the commonly used PageRank algorithm, the teleportation rate must trade off a heavily biased solution with a uniform solution. Here we show that teleportation to links rather than nodes enables a much smoother trade-off and effectively more robust results. We also show that, by not recording the teleportation steps of the random walker, we can further reduce the effect of teleportation with dramatic effects on clustering.Comment: 10 pages, 7 figure

Cultures of Nutrition: Classification, Food Policy, and Health

Nutrition policymakers frequently treat their knowledge of nutrition as acultural and universal. We analyze food guidelines in Mexico and Guatemala to draw attention to embedded, but often unrecognized, cultural values of standardization and individual responsibility. We suggest that nutrition policy would be improved by attending to the cultural values within nutrition science, and that nutrition guidelines should attend not only to other people’s cultures but to what we are calling “cultures of nutrition.” We conclude by offering an example of an adaptive approach to policy-making that may be useful for handling situations where many different cultures of nutrition collide

Ractopamine HCl improved cardiac hypertrophy but not poor growth, metabolic inefficiency, or greater white blood cells associated with heat stress in concentrate-fed lambs

Heat stress decreases livestock performance and well-being (Hahn, 1999; Nienaber and Hahn, 2007), causes metabolic dysfunction that decreases growth efficiency (O’Brien et al., 2010), and alters cardiovascular function (Crandall et al., 2008). Each year, heat stress costs the livestock industry up to $2.5 billion (St-Pierre et al., 2003). Ractopamine HCl acts as a nutrient repartitioning agent (Beermann, 2002); classified as a β adrenergic agonist (βAA), it shares pharmacological properties with adrenaline (Beermann, 2002). βAA increase muscle mass and decreases fat deposition through unknown mechanisms (Beermann, 2002). In feedlot cattle, they increase growth efficiency and improve carcass yield and merit (Scramlin et al., 2010; Buntyn et al., 2017), which increases profit and allows more meat to be produced from fewer animals. However, because βAA act via a stress system, it is unclear how the products affect animals under stress conditions. β1AA and β2AA can also cause tachycardia, heart palpitations, and arrhythmias (Sears, 2002). We hypothesize that β1AA combined with heat stress may overstimulate the adrenergic system, resulting is metabolic dysfunction and decreased performance. Sheep are a common model for cattle, and thus, the objective of this study was to determine the impact of ractopamine HCl on health and cardiovascular parameters, growth, and metabolic efficiency in feeder lambs