Mechanics of extended masses in general relativity

The "external" or "bulk" motion of extended bodies is studied in general relativity. Compact material objects of essentially arbitrary shape, spin, internal composition, and velocity are allowed as long as there is no direct (non-gravitational) contact with other sources of stress-energy. Physically reasonable linear and angular momenta are proposed for such bodies and exact equations describing their evolution are derived. Changes in the momenta depend on a certain "effective metric" that is closely related to a non-perturbative generalization of the Detweiler-Whiting R-field originally introduced in the self-force literature. If the effective metric inside a self-gravitating body can be adequately approximated by an appropriate power series, the instantaneous gravitational force and torque exerted on it is shown to be identical to the force and torque exerted on an appropriate test body moving in the effective metric. This result holds to all multipole orders. The only instantaneous effect of a body's self-field is to finitely renormalize the "bare" multipole moments of its stress-energy tensor. The MiSaTaQuWa expression for the gravitational self-force is recovered as a simple application. A gravitational self-torque is obtained as well. Lastly, it is shown that the effective metric in which objects appear to move is approximately a solution to the vacuum Einstein equation if the physical metric is an approximate solution to Einstein's equation linearized about a vacuum background.Comment: 39 pages, 2 figures; fixed equation satisfied by the Green function used to construct the effective metri

Electromagnetic self-forces and generalized Killing fields

Building upon previous results in scalar field theory, a formalism is developed that uses generalized Killing fields to understand the behavior of extended charges interacting with their own electromagnetic fields. New notions of effective linear and angular momenta are identified, and their evolution equations are derived exactly in arbitrary (but fixed) curved spacetimes. A slightly modified form of the Detweiler-Whiting axiom that a charge's motion should only be influenced by the so-called "regular" component of its self-field is shown to follow very easily. It is exact in some interesting cases, and approximate in most others. Explicit equations describing the center-of-mass motion, spin angular momentum, and changes in mass of a small charge are also derived in a particular limit. The chosen approximations -- although standard -- incorporate dipole and spin forces that do not appear in the traditional Abraham-Lorentz-Dirac or Dewitt-Brehme equations. They have, however, been previously identified in the test body limit.Comment: 20 pages, minor typos correcte

Effects of exenatide and liraglutide on heart rate, blood pressure and body weight : systematic review and meta-analysis

Objectives: To synthesise current evidence for the effects of exenatide and liraglutide on heart rate, blood pressure and body weight. Design: Meta-analysis of available data from randomised controlled trials comparing Glucagon-like peptide-1 (GLP-1) analogues with placebo, active antidiabetic drug therapy or lifestyle intervention. Participants: Patients with type 2 diabetes. Outcome measures: Weighted mean differences between trial arms for changes in heart rate, blood pressure and body weight, after a minimum of 12-week follow-up. Results: 32 trials were included. Overall, GLP-1 agonists increased the heart rate by 1.86 beats/min (bpm) (95% CI 0.85 to 2.87) versus placebo and 1.90 bpm (1.30 to 2.50) versus active control. This effect was more evident for liraglutide and exenatide long-acting release than for exenatide twice daily. GLP-1 agonists decreased systolic blood pressure by −1.79 mm Hg (−2.94 to −0.64) and −2.39 mm Hg (−3.35 to −1.42) compared to placebo and active control, respectively. Reduction in diastolic blood pressure failed to reach statistical significance (−0.54 mm Hg (−1.15 to 0.07) vs placebo and −0.50 mm Hg (−1.24 to 0.24) vs active control). Body weight decreased by −3.31 kg (−4.05 to −2.57) compared to active control, but by only −1.22 kg (−1.51 to −0.93) compared to placebo. Conclusions: GLP-1 analogues are associated with a small increase in heart rate and modest reductions in body weight and blood pressure. Mechanisms underlying the rise in heart rate require further investigation

The distribution of species range size: a stochastic process

The major role played by environmental factors in determining the geographical range sizes of species raises the possibility of describing their long-term dynamics in relatively simple terms, a goal which has hitherto proved elusive. Here we develop a stochastic differential equation to describe the dynamics of the range size of an individual species based on the relationship between abundance and range size, derive a limiting stationary probability model to quantify the stochastic nature of the range size for that species at steady state, and then generalize this model to the species-range size distribution for an assemblage. The model fits well to several empirical datasets of the geographical range sizes of species in taxonomic assemblages, and provides the simplest explanation of species-range size distributions to date

Effect of Transport Vibration on Quality of Minimally Processed and Packaged Fresh-Cut Cantaloupe

This study was undertaken to determine the quality of packaged fresh cut cantaloupe subjected to transport vibration after treating with various anti-browning agents. Cantaloupe (Cucumis melo) pieces were dipped in two anti-browning solutions: Treatment- A (2% ascorbic acid + 1% calcium chloride + 0.5% citric acid) and Treatment-B (3% NatureSeal™) for 2 minutes and packaged in bio-based clamshell containers and vibrated for 60 minutes (ASTM 4169, Truck assurance level II). Vibration of cut-cantaloupe packaged in sample containers had a positive effect on the flavor and overall liking. The overall liking scores were higher than 6(slightly like) on a hedonic scale of 1–9 for all samples except for vibrated-Treatment-A. The texture of vibrated cut-cantaloupe deteriorated with time, which was partially supported by firmness values obtained using a Kramer shear press. Treatment-B cut-cantaloupe subjected to vibration performed better than Treatment-A for appearance, flavor, texture and overall acceptability. No off-odor, sliminess or mold growth was observed in any of the samples during 10-day storage at 5°C ± 0.3°C. The sensory panel examined the final quality of fresh-cut fruit for several quality parameters at day 1, 4, 7 and 10 after being vibrated and stored in bio-based packaging made from Poly (lactide) (PLA) polymer. These findings are significant for quality preservation of cut-cantaloupe during transportation and distribution channels

Linearity and Scaling of a Statistical Model for the Species Abundance Distribution

We derive a linear recursion relation for the species abundance distribution in a statistical model of ecology and demonstrate the existence of a scaling solution

How geckos stick in nature: ecology and biomechanics of gecko feet

Phenotype and performance play a fundamental role in evolution and ecology. Studies of form and function often use correlations between morphology, performance, and habitat use to examine patterns of ecomorphology and morphological adaptation. Geckos, of the taxonomic group Gekkota, are an understudied yet diverse clade of lizards in which studies of form and function would greatly improve our understanding of their evolution. Geckos have the rather unique trait of adhesive toe pads, enabling them to use arboreal and rocky environments in a way few other creatures can. Gecko toe pad morphology and adhesive abilities are highly variable across species, suggesting ecological adaptations may have driven their evolution, yet few studies has considered gecko adhesive morphology and performance in an ecological context. In this study, we quantified morphology, adhesive performance, and habitat use of 13 gecko species from Queensland, Australia including tropical, arid, arboreal, and rock-dwelling species. We found toe detachment angle to be correlated with residual limb length. We also found residual limb length to be correlated with the use of arboreal and rock microhabitats as well as negatively correlated with perch diameter. This study is one of the first examples investigating gecko adhesive performance and specific microhabitat parameters. We suggest additional comparative studies investigating gecko limb kinematics and setal mechanics to corroborate our observational results