Locality and stability of the cascades of two-dimensional turbulence

We investigate and clarify the notion of locality as it pertains to the cascades of two-dimensional turbulence. The mathematical framework underlying our analysis is the infinite system of balance equations that govern the generalized unfused structure functions, first introduced by L'vov and Procaccia. As a point of departure we use a revised version of the system of hypotheses that was proposed by Frisch for three-dimensional turbulence. We show that both the enstrophy cascade and the inverse energy cascade are local in the sense of non-perturbative statistical locality. We also investigate the stability conditions for both cascades. We have shown that statistical stability with respect to forcing applies unconditionally for the inverse energy cascade. For the enstrophy cascade, statistical stability requires large-scale dissipation and a vanishing downscale energy dissipation. A careful discussion of the subtle notion of locality is given at the end of the paper.Comment: v2: 23 pages; 4 figures; minor revisions; resubmitted to Phys. Rev.

Sound production mechanism in the semiterrestrial crab Neohelice granulata (Brachyura, Varunidae)

Very few studies of sound production in the Brachyura have simultaneously identified the type of individuals (e.g. sex) producing acoustic signals, the structures involved in making sound and the social context. The emission and type of sound signals in Neohelice granulata were previously characterized, but the sex and the body structures involved in the sound production mechanism were not determined. In the present study, experiments conducted in the laboratory demonstrated that acoustic signals were produced by males through an up-down movement of the cheliped by rubbing the merus against the pterygostomial area of the carapace. The micromorphology of the merus showed that it has a ridge of tubercles which may act as a plectrum, while the pterygostomial area bears tubercles and might function as the pars stridens. Acoustic signals were displayed more frequently in the presence of receptive females. Agonistic encounters among males also occurred more often in the presence of receptive females. We propose that Neohelice granulata males use their chelipeds to produce sound signals in a mating context, probably to attract the receptive female and/or to repel other males when a receptive female is present. Thus, the display might have a reproductive function influencing mate choice.Fil: Sal Moyano, María Paz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Ceraulo, Maria. Consiglio Nazionale delle Ricerche; ItaliaFil: Mazzola, Salvatore. Consiglio Nazionale delle Ricerche; ItaliaFil: Buscaino, Giuseppa. Consiglio Nazionale delle Ricerche; ItaliaFil: Gavio, Maria Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Roles of forest bioproductivity, transpiration and fire in a nine-year record of cave dripwater chemistry from southwest Australia

Forest biomass has the potential to significantly impact the chemistry and volume of diffuse recharge to cave dripwater via the processes of nutrient uptake, transpiration and forest fire. Yet to-date, this role has been under-appreciated in the interpretation of speleothem trace element records from forested catchments. In this study, the impact of vegetation is examined and quantified in a long-term monitoring program from Golgotha Cave, SW Australia. The contribution of salts from rain and dry-deposition of aerosols and dissolved elements from soil mineral and bedrock dissolution to dripwater chemistry are also examined. This study is an essential pre-requisite for the future interpretation of trace element data from SW Australian stalagmite records, whose record of past environmental change will include alterations in these biogeochemical fluxes. Solute concentrations in dripwater vary spatially, supporting the existence of distinct flow paths governed by varying amounts of transpiration as well as nutrient uptake by deeply-rooted biomass. Applying principal components analysis, we identify a common pattern of variation in dripwater Cl, Mg, K, Ca, Sr and Si, interpreted as reflecting increasing transpiration, due to forest growth. Mass-balance calculations show that increasing elemental sequestration into biomass has the largest impact on SO4, providing an explanation for the overall falling dripwater SO4 concentrations through time, in contrast to the transpiration-driven rising trend dominating other ions. The long-term rise in transpiration and nutrient uptake driven by increased forest bioproductivity and its impact on our dripwater chemistry is attributed to i. the post-fire recovery of the forest understorey after fire impacted the site in 2006 CE; ii. and/or increased water and nutrient demand as trees in the overlying forest mature. The impact of climate-driven changes on the water balance is also examined. Finally, the implications for interpreting SW Australian speleothem trace element records are discussed

An Evolutionary Reduction Principle for Mutation Rates at Multiple Loci

A model of mutation rate evolution for multiple loci under arbitrary selection is analyzed. Results are obtained using techniques from Karlin (1982) that overcome the weak selection constraints needed for tractability in prior studies of multilocus event models. A multivariate form of the reduction principle is found: reduction results at individual loci combine topologically to produce a surface of mutation rate alterations that are neutral for a new modifier allele. New mutation rates survive if and only if they fall below this surface - a generalization of the hyperplane found by Zhivotovsky et al. (1994) for a multilocus recombination modifier. Increases in mutation rates at some loci may evolve if compensated for by decreases at other loci. The strength of selection on the modifier scales in proportion to the number of germline cell divisions, and increases with the number of loci affected. Loci that do not make a difference to marginal fitnesses at equilibrium are not subject to the reduction principle, and under fine tuning of mutation rates would be expected to have higher mutation rates than loci in mutation-selection balance. Other results include the nonexistence of 'viability analogous, Hardy-Weinberg' modifier polymorphisms under multiplicative mutation, and the sufficiency of average transmission rates to encapsulate the effect of modifier polymorphisms on the transmission of loci under selection. A conjecture is offered regarding situations, like recombination in the presence of mutation, that exhibit departures from the reduction principle. Constraints for tractability are: tight linkage of all loci, initial fixation at the modifier locus, and mutation distributions comprising transition probabilities of reversible Markov chains.Comment: v3: Final corrections. v2: Revised title, reworked and expanded introductory and discussion sections, added corollaries, new results on modifier polymorphisms, minor corrections. 49 pages, 64 reference

Active and passive fields face to face

The statistical properties of active and passive scalar fields transported by the same turbulent flow are investigated. Four examples of active scalar have been considered: temperature in thermal convection, magnetic potential in two-dimensional magnetohydrodynamics, vorticity in two-dimensional Ekman turbulence and potential temperature in surface flows. In the cases of temperature and vorticity, it is found that the active scalar behavior is akin to that of its co-evolving passive counterpart. The two other cases indicate that this similarity is in fact not generic and differences between passive and active fields can be striking: in two-dimensional magnetohydrodynamics the magnetic potential performs an inverse cascade while the passive scalar cascades toward the small-scales; in surface flows, albeit both perform a direct cascade, the potential temperature and the passive scalar have different scaling laws already at the level of low-order statistical objects. These dramatic differences are rooted in the correlations between the active scalar input and the particle trajectories. The role of such correlations in the issue of universality in active scalar transport and the behavior of dissipative anomalies is addressed.Comment: 36 pages, 20 eps figures, for the published version see http://www.iop.org/EJ/abstract/1367-2630/6/1/07

Low-Dose Imaging in a New Preclinical Total-Body PET/CT Scanner.

Ionizing radiation constitutes a health risk to imaging scientists and study animals. Both PET and CT produce ionizing radiation. CT doses in pre-clinical in vivo imaging typically range from 50 to 1,000 mGy and biological effects in mice at this dose range have been previously described. [ <sup>18</sup> F]FDG body doses in mice have been estimated to be in the range of 100 mGy for [ <sup>18</sup> F]FDG. Yearly, the average whole body doses due to handling of activity by PET technologists are reported to be 3-8 mSv. A preclinical PET/CT system is presented with design features which make it suitable for small animal low-dose imaging. The CT subsystem uses a X-source power that is optimized for small animal imaging. The system design incorporates a spatial beam shaper coupled with a highly sensitive flat-panel detector and very fast acquisition (<10 s) which allows for whole body scans with doses as low as 3 mGy. The mouse total-body PET subsystem uses a detector architecture based on continuous crystals, coupled to SiPM arrays and a readout based in rows and columns. The PET field of view is 150 mm axial and 80 mm transaxial. The high solid-angle coverage of the sample and the use of continuous crystals achieve a sensitivity of 9% (NEMA) that can be leveraged for use of low tracer doses and/or performing rapid scans. The low-dose imaging capabilities of the total-body PET subsystem were tested with NEMA phantoms, in tumor models, a mouse bone metabolism scan and a rat heart dynamic scan. The CT imaging capabilities were tested in mice and in a low contrast phantom. The PET low-dose phantom and animal experiments provide evidence that image quality suitable for preclinical PET studies is achieved. Furthermore, CT image contrast using low dose scan settings was suitable as a reference for PET scans. Total-body mouse PET/CT studies could be completed with total doses of <10 mGy

Finite time singularities in a class of hydrodynamic models

Models of inviscid incompressible fluid are considered, with the kinetic energy (i.e., the Lagrangian functional) taking the form ${\cal L}\sim\int k^\alpha|{\bf v_k}|^2d^3{\bf k}$ in 3D Fourier representation, where $\alpha$ is a constant, $0<\alpha< 1$. Unlike the case $\alpha=0$ (the usual Eulerian hydrodynamics), a finite value of $\alpha$ results in a finite energy for a singular, frozen-in vortex filament. This property allows us to study the dynamics of such filaments without the necessity of a regularization procedure for short length scales. The linear analysis of small symmetrical deviations from a stationary solution is performed for a pair of anti-parallel vortex filaments and an analog of the Crow instability is found at small wave-numbers. A local approximate Hamiltonian is obtained for the nonlinear long-scale dynamics of this system. Self-similar solutions of the corresponding equations are found analytically. They describe the formation of a finite time singularity, with all length scales decreasing like $(t^*-t)^{1/(2-\alpha)}$, where $t^*$ is the singularity time.Comment: LaTeX, 17 pages, 3 eps figures. This version is close to the journal pape

Mapping opportunities and challenges for rewilding in Europe

Farmland abandonment takes place across the world due to socio-economic and ecological drivers. In Europe agricultural and environmental policies aim to prevent abandonment and halt ecological succession. Ecological rewilding has been recently proposed as an alternative strategy. We developed a framework to assess opportunities for rewilding across different dimensions of wilderness in Europe. We mapped artificial light, human accessibility based on transport infrastructure, proportion of harvested primary productivity (i.e., ecosystem productivity appropriated by humans through agriculture or forestry), and deviation from potential natural vegetation in areas projected to be abandoned by 2040. At the continental level, the levels of artificial light were low and the deviation from potential natural vegetation was high in areas of abandonment. The relative importance of wilderness metrics differed regionally and was strongly connected to local environmental and socio-economic contexts. Large areas of projected abandonment were often located in or around Natura 2000 sites. Based on these results, we argue that management should be tailored to restore the aspects of wilderness that are lacking in each region. There are many remaining challenges regarding biodiversity in Europe, but megafauna species are already recovering. To further potentiate large-scale rewilding, Natura 2000 management would need to incorporate rewilding approaches. Our framework can be applied to assessing rewilding opportunities and challenges in other world regions, and our results could guide redirection of subsidies to manage social-ecological systems

Mouse Odf2 localizes to centrosomes and basal bodies in adult tissues and to the photoreceptor primary cilium

Odf2 (outer dense fiber 2) is the major protein of the cytoskeleton of the sperm tail. In somatic cells, it is a component of the centrosome in which it is located in the appendages of the mother centriole. Additionally, as shown previously by forced expression in cultured cells, Odf2 localizes to centrioles, basal bodies, and primary cilia, which are all structurally and functionally interconnected. The importance of Odf2 has become obvious by the absence of primary cilia in Odf2-deficient cells and by the embryonic lethality of the Odf2 gene trap insertional mouse. However, nothing is known about the endogenous localization of Odf2 in the tissues of adult mice. We show here that Odf2 protein localizes to centrosomes, to photoreceptor primary cilia, and to basal bodies of ciliated cells of the respiratory epithelium and of the kidney. Our results thus suggest that Odf2 contributes to assorted ciliopathies