Multiscale velocity correlation in turbulence: experiments, numerical simulations, synthetic signals

Multiscale correlation functions in high Reynolds number experimental turbulence, numerical simulations and synthetic signals are investigated. Fusion Rules predictions as they arise from multiplicative, almost uncorrelated, random processes for the energy cascade are tested. Leading and sub-leading contribution, in the inertial range, can be explained as arising from a multiplicative random process for the energy transfer mechanisms. Two different predictions for correlations involving dissipative observable are also briefly discussed

One-particle irreducible functional approach - a new route to diagrammatic extensions of DMFT

We present an approach which is based on the one-particle irreducible (1PI) generating functional formalism and includes electronic correlations on all length-scales beyond the local correlations of dynamical mean field theory (DMFT). This formalism allows us to unify aspects of the dynamical vertex approximation (D\GammaA) and the dual fermion (DF) scheme, yielding a consistent formulation of non-local correlations at the one- and two-particle level beyond DMFT within the functional integral formalism. In particular, the considered approach includes one-particle reducible contributions from the three- and more-particle vertices in the dual fermion approach, as well as some diagrams not included in the ladder version of D\GammaA. To demonstrate the applicability and physical content of the 1PI approach, we compare the diagrammatics of 1PI, DF and D\GammaA, as well as the numerical results of these approaches for the half-filled Hubbard model in two dimensions.Comment: 36 pages, 12 figures, updated versio

Influence of age at weaning and nutritive value of weaning diet on growth performance and caecal traits in rabbits

[EN] To investigate the relationship between dietary nutrient concentration and weaning age on growth performance and caecal characteristics of rabbits, a trial was carried out on 64 litters (eight rabbits/litter) comparing two weaning ages (25 vs. 34 d) and two diets (HC: high concentrated and LC: low concentrated diet) offered to the kits from 18 to 34 d of age. At 34 d of age 54 animals per group were caged individually and all were fed the LC diet until 45 d of age. All animals were then fed a standard fattening diet (37% neutral detergent fiber, 3.4% ether extract and 18.0% crude protein on dry matter basis) until slaughter at 80 d. The digestibility trial was performed from 56 to 60 d of age on another group of 16 rabbits (8 per diet). During the experimental period (18-80 d of age), feed intake and animal weights were recorded. Caecal volatile fatty acids were measured at 45 and 80 d of age, while microbiological analysis was performed at 25 and 34 d on healthy suckling rabbits. Digestibility of dry matter, protein, neutral detergent fiber, fat and energy was higher in rabbits fed the HC diet (by 7.7, 7.4, 13.1, 26.7, 10.6%, respectively; P<0.001) than in those fed the LC diet. Growth rate and feed conversion ratio (FCR) from 18 to 34 d improved by 7.7 and 9.5% in rabbits fed HC in comparison to the LC diet, respectively (P¿0.061). Diet offered around weaning did not influence growth rate or FCR from 34 to 80 d of age. Rabbits weaned earlier increased feed intake (by 67.8%) from 25 to 34 d, but reduced growth rate (by 26.8%) compared to animals weaned at 34 d (P<0.001). Early weaning reduced live weight during the entire fattening period (P¿0.018), as well as the FCR (by 4%; P<0.001). Caecal pH was lower at 45 d of age in rabbits weaned at 25 d than in those weaned at 34 d (5.53 vs. 5.83; P=0.019). Treatments did not affect total caecal VFA concentration, but HC diet decreased caecal acetic concentration and increased butyric acid level compared to the LC diet at 45 d (P¿0.001). HC diet tended to reduce caecal counts of Enterobacteriacae (P=0.093), while it did not affect facultative anaerobic bacteria, E. Coli and Costridium spp. The LC diet increased at 25 d the number of Clostridium perfringens in comparison with the HC group at the same age and in comparison with animals fed both two diets at 34 d (P<0.001). The values of E. Coli and Enterobacteriaceae increased (P¿0.008) from 25 to 34 d of age, whereas that of Clostridium spp. decreased. Weaning at 25 d increased mortality from 18 to 34 d compared with rabbits weaned at 34 d (7.02 vs. 2.46%, P=0.017). However, during the fattening period (34-80 d) rabbits weaned earlier showed lower mortality (7.41 vs. 17.6%; P=0.024).This work has been realized within the CUNISVEZZ research project financed by the Agricultural Department of the Regione Lombardia as part of the 2004 research and development plan, d.g.r. 30/04/2004 n. VII/17326. The authors wish to thank Nicoletta Cesari for her technical assistance.Cesari, V.; Grilli, G.; Ferrazzi, V.; Toschi, I. (2009). Influence of age at weaning and nutritive value of weaning diet on growth performance and caecal traits in rabbits. World Rabbit Science. 17(4):195-205. https://doi.org/10.4995/wrs.2009.64419520517

Effects of forcing in three dimensional turbulent flows

We present the results of a numerical investigation of three-dimensional homogeneous and isotropic turbulence, stirred by a random forcing with a power law spectrum, $E_f(k)\sim k^{3-y}$. Numerical simulations are performed at different resolutions up to $512^3$. We show that at varying the spectrum slope $y$, small-scale turbulent fluctuations change from a {\it forcing independent} to a {\it forcing dominated} statistics. We argue that the critical value separating the two behaviours, in three dimensions, is $y_c=4$. When the statistics is forcing dominated, for $y<y_c$, we find dimensional scaling, i.e. intermittency is vanishingly small. On the other hand, for $y>y_c$, we find the same anomalous scaling measured in flows forced only at large scales. We connect these results with the issue of {\it universality} in turbulent flows.Comment: 4 pages, 4 figure

Experimental assessment of a new form of scaling law for near-wall turbulence

Scaling laws and intermittency in the wall region of a turbulent flow are addressed by analyzing moderate Reynolds number data obtained by single component hot wire anemometry in the boundary layer of a flat plate. The paper aims in particular at the experimental validation of a new form of refined similarity recently proposed for the shear dominated range of turbulence, where the classical Kolmogorov-Oboukhov inertial range theory is inappropriate. An approach inspired to the extended self-similarity allows for the extraction of the different power laws for the longitudinal structure functions at several wall normal distances. A double scaling regime is found in the logarithmic region, confirming previous experimental results. Approaching the wall, the scaling range corresponding to the classical cascade-dominated range tends to disappear and, in the buffer layer, a single power law is found to describe the available range of scales. The double scaling is shown to be associated with two different forms of refined similarity. The classical form holds below the shear scale L s . The other, originally introduced on the basis of DNS data for a turbulent channel, is experimentally confirmed to set up above L s . Given the experimental diffulties in the evaluation of the instantaneous dissipation rate, some care is devoted to check that its one-dimensional surrogate does not bias the results. The increased intermittency as the wall is approached is experimentally found entirely consistent with the failure of the refined Kolmogorov-Oboukhov similarity and the establishment of its new form near the wall.Comment: 27 pages, 9 figure

Spin state of negative charge-transfer material SrCoO3

We employ the combination of the density functional and the dynamical mean-field theory (LDA+DMFT) to investigate the electronic structure and magnetic properties of SrCoO3, monocrystal of which were prepared recently. Our calculations lead to a ferromagnetic metal in agreement with experiment. We find that, contrary to some suggestions, the local moment in SrCoO3 does not arise from intermediate spin state, but is a result of coherent superposition of many different atomic states. We discuss how attribution of magnetic response to different atomic states in solids with local moments can be quantified.Comment: 5 pages, 5 figure

Anisotropic Ginzburg-Landau and Lawrence-Doniach Models for Layered Ultracold Fermi Gases

We study the anisotropic Ginzburg-Landau and Lawrence-Doniach models describing a layered superfluid ultracold Fermi gas in optical lattices. We derive the coefficients of the anisotropic Ginzburg-Landau and the mass tensor as a function of anisotropy, filling and interaction, showing that near the unitary limit the effective anisotropy of the masses is significantly reduced. The anisotropy parameter is shown to vary in realistic setups in a wide range of values. We also derive the Lawrence-Doniach model - often used to describe the 2D-3D dimensional crossover in layered superconductors - for a layered ultracold Fermi gas, obtaining a relation between the interlayer Josephson couplings and the Ginzburg-Landau masses. Comparing to the Ginzburg-Landau description, we find that the region of validity of the Lawrence-Doniach model is near the unitary limit.Comment: 15 pages, 4 figure

One-step growth and shaping by a dual plasma reactor of diamond nanocones arrays for the assembling of stable cold cathodes

Arrays of conical-shaped nanodiamond structures are formed on silicon substrate by a single-step CVD process from CH4/H-2 mixtures. The formation of these nanocones has been found to depend on interplay between growing and etching during the CVD process carried out in a dual-mode MW/RF plasma reactor. Morphology and structure of the conical-like systems can be controlled by varying the process parameters, and have been investigated by scanning electron microscopy (SEM), reflection high energy electron diffraction (RHEED) and micro-Raman spectroscopy. The Field Emission (FE) properties of different diamond nanocones arrays have been investigated and compared with those of analogous systems in order to assess the feasibility of the present nano-materials as electron emitters for cold cathodes. The FE behavior is discussed taking into account the structure of the different diamond nanocones

The central autonomic network at rest: Uncovering functional MRI correlates of time-varying autonomic outflow.

Peripheral measures of autonomic nervous system (ANS) activity at rest have been extensively employed as putative biomarkers of autonomic cardiac control. However, a comprehensive characterization of the brain-based central autonomic network (CAN) sustaining cardiovascular oscillations at rest is missing, limiting the interpretability of these ANS measures as biomarkers of cardiac control. We evaluated combined cardiac and fMRI data from 34 healthy subjects from the Human Connectome Project to detect brain areas functionally linked to cardiovagal modulation at rest. Specifically, we combined voxel-wise fMRI analysis with instantaneous heartbeat and spectral estimates obtained from inhomogeneous linear point-process models. We found exclusively negative associations between cardiac parasympathetic activity at rest and a widespread network including bilateral anterior insulae, right dorsal middle and left posterior insula, right parietal operculum, bilateral medial dorsal and ventrolateral posterior thalamic nuclei, anterior and posterior mid-cingulate cortex, medial frontal gyrus/pre-supplementary motor area. Conversely, we found only positive associations between instantaneous heart rate and brain activity in areas including frontopolar cortex, dorsomedial prefrontal cortex, anterior, middle and posterior cingulate cortices, superior frontal gyrus, and precuneus. Taken together, our data suggests a much wider involvement of diverse brain areas in the CAN at rest than previously thought, which could reflect a differential (both spatially and directionally) CAN activation according to the underlying task. Our insight into CAN activity at rest also allows the investigation of its impairment in clinical populations in which task-based fMRI is difficult to obtain (e.g., comatose patients or infants).This work was supported by the US National Institutes for Health (NIH), Office of the Director (OT2-OD023867 to VN); National Center for Complementary and Integrative Health (NCCIH), NIH (P01-AT009965, R61-AT009306, R33-AT009306, R01-AT007550 to VN); the National Institute for Arthritis and Musculoskeletal and Skin Diseases (NIAMS), NIH (R01-AR064367 to VN); the Medical Research Council (MRC), UK (MR/P01271X/1 to LP); the American Heart Association (16GRNT26420084 to RB)

Dynamics and statistics of heavy particles in turbulent flows

We present the results of Direct Numerical Simulations (DNS) of turbulent flows seeded with millions of passive inertial particles. The maximum Taylor's Reynolds number is around 200. We consider particles much heavier than the carrier flow in the limit when the Stokes drag force dominates their dynamical evolution. We discuss both the transient and the stationary regimes. In the transient regime, we study the growt of inhomogeneities in the particle spatial distribution driven by the preferential concentration out of intense vortex filaments. In the stationary regime, we study the acceleration fluctuations as a function of the Stokes number in the range [0.16:3.3]. We also compare our results with those of pure fluid tracers (St=0) and we find a critical behavior of inertia for small Stokes values. Starting from the pure monodisperse statistics we also characterize polydisperse suspensions with a given mean Stokes.Comment: 13 pages, 10 figures, 2 table