A systematic correlation between two-dimensional flow topology and the abstract statistics of turbulence

Velocity differences in the direct enstrophy cascade of two-dimensional turbulence are correlated with the underlying flow topology. The statistics of the transverse and longitudinal velocity differences are found to be governed by different structures. The wings of the transverse distribution are dominated by strong vortex centers, whereas, the tails of the longitudinal differences are dominated by saddles. Viewed in the framework of earlier theoretical work this result suggests that the transfer of enstrophy to smaller scales is accomplished in regions of the flow dominated by saddles.Comment: 4 pages, 4 figure

Diet Quality and Food Limitation Affect the Dynamics of Body Composition and Digestive Organs in a Migratory Songbird (Zonotrichia Albicollis)

Migrating songbirds interrupt their feeding to fly between stopover sites that may vary appreciably in diet quality. We studied the effects of fasting and food restriction on body composition and digestive organs in a migratory songbird and how these effects interacted with diet quality to influence the rate of recovery of nutrient reserves. Food limitation caused whitethroated sparrows to reduce both lean and fat reserves, with about 20% of the decline in lean mass represented by a decline in stomach, small intestine, and liver. During refeeding on diets similar in nutrient composition to either grain or fruit, foodlimited grain-fed birds ate 40% more than did control birds, and they regained body mass, with on average 60% of the increase in body mass composed of lean mass including digestive organs. In contrast, food-limited fruit-fed birds did not eat more than did control birds and did not regain body mass, suggesting that a digestive constraint limited their food intake. The interacting effects of food limitation and diet quality on the dynamics of body composition and digestive organs in sparrows suggest that the adequacy of the diet at stopover sites can directly influence the rate of recovery of body reserves in migrating songbirds and hence the pace of their migration

On the sampling requirements for measuring moments of eddy variability

The expected errors in first and second moments (means, variances, and covariances) calculated from data records of finite length are analyzed, using formulae based on the spectra. The physical processes from which the data are taken are assumed to be stationary and quasinormal. Asymptotic approximations to these errors (in inverse powers of the record length) are also discussed and compared with the exact expressions...

Independence day: Post-fledging movements and behavior of adult Eastern Towhees (\u3cem\u3ePipilo erythrophthalmus\u3c/em\u3e) in landscapes managed for American Woodcock (\u3cem\u3eScolopax minor\u3c/em\u3e)

Umbrella species management offers a potential solution to the financial and logistical challenges of managing for the many declining species in early-successional forests, a habitat that is also critical for many mature and young forest songbird species during the post-fledging and post-breeding period. We investigated the movements of adult Eastern Towhees (Pipilo erythrophthalmus) during the post-fledging period in 4 km2 landscapes managed for American Woodcock (Scolopax minor), a popular umbrella species candidate for young forest management. Home range size (mean = 2.8 ha, SE 0.33) did not differ during the post-fledging period between adult towhees inhabiting landscapes designated as high-likelihood (HL) or low-likelihood (LL) of woodcock use. Adults moved distances of ∼37–47 m per day during the first 3 weeks of the post-fledging period and this did not differ between the 2 landscapes. In contrast, once their young became independent, adults moved longer distances in HL compared to LL landscapes (49.5 m [SE 2.9] and 36.7 m [SE 3.6], respectively) and these distances increased with home range size and patch size. Landscape features within 100 m of the towhee home range best explained variation in towhee movement distance. Young forest habitat was also the predominant forest type used by adult towhees caring for fledglings throughout the post-fledging period. These results suggest that early successional forest management for woodcock can provide effective breeding habitat for towhees, but likely at a smaller spatial scale than typically managed for woodcock

Seasonal Changes in Composition of Lipid Stores in Migratory Birds: Causes and Consequences

It is well established that birds use fat stores to primarily fuel migration; however, few studies have focused on the causes and consequences of observed seasonal changes in fatty acid composition of fat stores in birds. We propose and test two hypotheses that address the causes of these seasonal changes in composition of fat stores: (1) diet composition determines fatty acid composition of fat stores, and (2) birds selectively metabolize and store certain fatty acids during migration in lieu of changing their diet. When we offered Red-eyed Vireos (Vireo olivaceous) choices between diets that differed only in fatty acid composition, vireos preferred diets with more triolein over diets with more tristearin and tripalmitin, and these preferences were similar between seasons. We also collected fat samples six times throughout the year from captive Red-eyed Vireos fed one of two diets differing in fatty acid composition, and found that fatty acid composition of stored fat differed by diet and changed over time, although these changes were not season-specific or consistent with the selective-metabolism hypothesis.Thus, fatty acid composition of stored fat was primarily a product of diet composition; selective metabolism possibly played a minor, but important, role. Given recent evidence that fatty acid composition of birds affects their energy expenditure during intense exercise, the implication is that birds at stopover sites can influence the fatty acid composition of their body fat by selective feeding, and this can significantly affect the energetic cost of migration

The Fat of the Matter: How Dietary Fatty Acids Can Affect Exercise Performance

Fatty-acid composition of fat stores affects exercise performance in a variety of vertebrates although few such studies focus on flying vertebrates such as migratory birds, which are exceptional exercisers. We first discuss the natural variation in quality of fat available in natural foods eaten by migratory birds and their behavioral preferences for specific fatty acids in these foods. We then outline three proposed hypotheses for how dietary fatty acids can affect exercise performance, and some of the evidence to date that pertains to these hypotheses with special emphasis on the exercise performance of migratory birds. In theory, selectively feeding on certain long-chain unsaturated fatty acids may be advantageous because (1) such fatty acids may be metabolized more quickly and may stimulate key facets of aerobic metabolism (fuel hypothesis); (2) such fatty acids may affect composition and key functions of lipid-rich cell membranes (membrane hypothesis); and (3) such fatty acids may directly act as signaling molecules (signal hypothesis). Testing these hypotheses requires cleverly designed experiments that can distinguish between them by demonstrating that certain fatty acids stimulate oxidative capacity, including gene expression and activity of key oxidative enzymes, and that this stimulation changes during exercise

Consistency of post-Newtonian waveforms with numerical relativity

General relativity predicts the gravitational wave signatures of coalescing binary black holes. Explicit waveform predictions for such systems, required for optimal analysis of observational data, have so far been achieved using the post-Newtonian (PN) approximation. The quality of this treatment is unclear, however, for the important late-inspiral portion. We derive late-inspiral waveforms via a complementary approach, direct numerical simulation of Einstein's equations. We compare waveform phasing from simulations of the last $\sim 14$ cycles of gravitational radiation from equal-mass, nonspinning black holes with the corresponding 2.5PN, 3PN, and 3.5PN orbital phasing. We find phasing agreement consistent with internal error estimates based on either approach, suggesting that PN waveforms for this system are effective until the last orbit prior to final merger.Comment: Replaced with published version -- one figure removed, text and other figures updated for clarity of discussio

On the properties of steady states in turbulent axisymmetric flows

We experimentally study the properties of mean and most probable velocity fields in a turbulent von K\'arm\'an flow. These fields are found to be described by two families of functions, as predicted by a recent statistical mechanics study of 3D axisymmetric flows. We show that these functions depend on the viscosity and on the forcing. Furthermore, when the Reynolds number is increased, we exhibit a tendency for Beltramization of the flow, i.e. a velocity-vorticity alignment. This result provides a first experimental evidence of nonlinearity depletion in non-homogeneous non-isotropic turbulent flow.Comment: latex prl-stationary-051215arxiv.tex, 9 files, 6 figures, 4 pages (http://www-drecam.cea.fr/spec/articles/S06/008/

Satellite data relay and platform locating in oceanography. Report of the In Situ Ocean Science Working Group

The present and future use of satellites to locate offshore platforms and relay data from in situ sensors to shore was examined. A system of the ARGOS type will satisfy the increasing demand for oceanographic information through data relay and platform location. The improved ship navigation provided by the Global Positioning System (GPS) will allow direct observation of currents from underway ships. Ocean systems are described and demand estimates on satellite systems are determined. The capabilities of the ARGOS system is assessed, including anticipated demand in the next decade

Toward faithful templates for non-spinning binary black holes using the effective-one-body approach

We present an accurate approximation of the full gravitational radiation waveforms generated in the merger of non-eccentric systems of two non-spinning black holes. Utilizing information from recent numerical relativity simulations and the natural flexibility of the effective-one-body (EOB) model, we extend the latter so that it can successfully match the numerical relativity waveforms during the last stages of inspiral, merger and ringdown. By ``successfully'' here, we mean with phase differences < 8% of a gravitational-wave cycle accumulated by the end of the ringdown phase, maximizing only over time of arrival and initial phase. We obtain this result by simply adding a 4-post-Newtonian order correction in the EOB radial potential and determining the (constant) coefficient by imposing high-matching performances with numerical waveforms of mass ratios m1/m2 = 1, 3/2, 2 and 4, m1 and m2 being the individual black-hole masses. The final black-hole mass and spin predicted by the numerical simulations are used to determine the ringdown frequency and decay time of three quasi-normal-mode damped sinusoids that are attached to the EOB inspiral-(plunge) waveform at the EOB light-ring. The EOB waveforms might be tested and further improved in the future by comparison with extremely long and accurate inspiral numerical-relativity waveforms. They may already be employed for coherent searches and parameter estimation of gravitational waves emitted by non-spinning coalescing binary black holes with ground-based laser-interferometer detectors.Comment: 15 pages, 9 figure