Tangling clustering of inertial particles in stably stratified turbulence

We have predicted theoretically and detected in laboratory experiments a new type of particle clustering (tangling clustering of inertial particles) in a stably stratified turbulence with imposed mean vertical temperature gradient. In this stratified turbulence a spatial distribution of the mean particle number density is nonuniform due to the phenomenon of turbulent thermal diffusion, that results in formation of a gradient of the mean particle number density, \nabla N, and generation of fluctuations of the particle number density by tangling of the gradient, \nabla N, by velocity fluctuations. The mean temperature gradient, \nabla T, produces the temperature fluctuations by tangling of the gradient, \nabla T, by velocity fluctuations. These fluctuations increase the rate of formation of the particle clusters in small scales. In the laboratory stratified turbulence this tangling clustering is much more effective than a pure inertial clustering that has been observed in isothermal turbulence. In particular, in our experiments in oscillating grid isothermal turbulence in air without imposed mean temperature gradient, the inertial clustering is very weak for solid particles with the diameter 10 microns and Reynolds numbers Re =250. Our theoretical predictions are in a good agreement with the obtained experimental results.Comment: 16 pages, 4 figures, REVTEX4, revised versio

Coping with citizen demands: a field study of suckling processes in dairy herds

In dairy farms calves and cows are usually separated shortly after birth but this practice raises the question of animal welfare. This social concern may lead to bring back dairy calves to their mother. Even though suckling is quite seldom in dairy production, some farmers are using such a practice for many years. The present study aims to better know farmer’s motivations, practical implementation and farmer’s perception of the impact of suckling on performance and animal behaviour. In January 2018 a semi-quantitative survey was performed on 44 farms where calves suckle at least 24 hours their mother or a nurse cow. The farming systems differed on the size (20 to 140 cows), the type (19 conventional, 25 organic farms), the suckling (28 by the mothers, 16 by nurses), and the breed. Results indicate that main farmers’ motivations are calves’ health (52%), better working conditions (41%) and saving time (34%), with little consideration on animal welfare (7%). Numerous practices were found in terms of allowance of daily cow-calf contact and suckling duration with a difference between male and female calves. According to farmers, these practices were efficient to improved calves’ health (70%), save time (75%) and improved working conditions (52%). Weaning was considered as a stressful situation, especially after long suckling periods. Cow mooing usually stopped 2.5 d after weaning. At least 34 farmers are fully satisfied with this practice. The main challenge appears to be the management of the wildness of future heifers, by investing time to manipulate calves before weaning. The results of this survey could help to propose solutions to farmers who want to cope with the societal demand of keeping calves with dams in dairy herds

Interactions with M cells and macrophages as key steps in the pathogenesis of enterohemorrhagic Escherichia coli infections

Enterohemorrhagic Escherichia coli (EHEC) are food-borne pathogens that can cause serious infections ranging from diarrhea to hemorrhagic colitis (HC) and hemolytic-uremic syndrome (HUS). Translocation of Shiga-toxins (Stx) from the gut lumen to underlying tissues is a decisive step in the development of the infection, but the mechanisms involved remain unclear. Many bacterial pathogens target the follicle-associated epithelium, which overlies Peyer's patches (PPs), cross the intestinal barrier through M cells and are captured by mucosal macrophages. Here, translocation across M cells, as well as survival and proliferation of EHEC strains within THP-1 macrophages were investigated using EHEC O157:H7 reference strains, isogenic mutants, and 15 EHEC strains isolated from HC/HUS patients. We showed for the first time that E. coli O157:H7 strains are able to interact in vivo with murine PPs, to translocate ex vivo through murine ileal mucosa with PPs and across an in vitro human M cell model. EHEC strains are also able to survive and to produce Stx in macrophages, which induce cell apoptosis and Stx release. In conclusion, our results suggest that the uptake of EHEC by M cells and underlying macrophages in the PP may be a critical step in Stx translocation and release in vivo. A new model for EHEC infection in humans is proposed that could help in a fuller understanding of EHEC-associated diseases

Bioactivity and structural properties of chimeric analogs of the starfish SALMFamide neuropeptides S1 and S2

The starfish SALMFamide neuropeptides S1 (GFNSALMFamide) and S2 (SGPYSFNSGLTFamide) are the prototypical members of a family of neuropeptides that act as muscle relaxants in echinoderms. Comparison of the bioactivity of S1 and S2 as muscle relaxants has revealed that S2 is ten times more potent than S1. Here we investigated a structural basis for this difference in potency by comparing the bioactivity and solution conformations (using NMR and CD spectroscopy) of S1 and S2 with three chimeric analogs of these peptides. A peptide comprising S1 with the addition of S2's N-terminal tetrapeptide (Long S1 or LS1; SGPYGFNSALMFamide) was not significantly different to S1 in its bioactivity and did not exhibit concentration-dependent structuring seen with S2. An analog of S1with its penultimate residue substituted from S2 (S1(T); GFNSALTFamide) exhibited S1-like bioactivity and structure. However, an analog of S2 with its penultimate residue substituted from S1 (S2(M); SGPYSFNSGLMFamide) exhibited loss of S2-type bioactivity and structural properties. Collectively, our data indicate that the C-terminal regions of S1 and S2 are the key determinants of their differing bioactivity. However, the N-terminal region of S2 may influence its bioactivity by conferring structural stability in solution. Thus, analysis of chimeric SALMFamides has revealed how neuropeptide bioactivity is determined by a complex interplay of sequence and conformation

Déléguer l'allaitement des veaux laitiers aux vaches ? Résultats d'enquêtes auprès des éleveurs

La séparation précoce mère-veau est une pratique courante dans la plupart des élevages laitiers, mais est sujette à de nombreuses interrogations tant chez les éleveurs (coûts engendrés, travail) que dans la société (bien-être animal). Des pratiques alternatives mises en place par certains éleveurs permettent aux veaux d'être allaités par leur mère ou une autre vache, appelée « nourrice ». Quoiqu’anciennes, ces pratiques demeurent peu connues et leur intégration aux conditions d’élevages modernes questionne. Des enquêtes ont ainsi été réalisées en 2018 pour connaître la motivation des éleveurs, la diversité et les conséquences de ces pratiques sur les résultats techniques. Cent deux élevages, identifiés par des réseaux divers (conseil en élevage, chambres d’agriculture, coopératives…), ont été enquêtés dans le Grand Ouest (n = 50), le Grand Est (n = 41) et le Massif central (n = 11), par téléphone (n = 56) ou sur place (n = 46). La taille médiane des troupeaux est de 60 vaches laitières (8 à 210), principalement constitués de vaches de race Montbéliarde et Holstein. Les élevages sont pour moitié en agriculture biologique (56%), avec une grande diversité de systèmes de traite et de logement (salle de traite en épi, robot, stabulation entravée, libre à logettes…). Trois grandes conduites d'allaitement des veaux, de la naissance à la vente ou au sevrage, ont été identifiées : 1/ les veaux sont allaités exclusivement par leur mère ; 2/ les veaux sont élevés par leur mère puis reçoivent une alimentation lactée artificielle (poudre ou lait entier) ; 3/ les veaux sont élevés par leur mère puis sous une vache nourrice. Elles diffèrent souvent au sein d’un même élevage (n = 62) entre les veaux destinés à la vente (mâles ou femelles) et les velles de renouvellement. La diversité des systèmes d'allaitement se retrouve dans tous les types d'élevages, quelle que soit leur taille ou leur localisation géographique. L'amélioration de la santé des animaux (n = 52), la diminution du temps de travail (n = 47) et des coûts d’élevage (n = 32) sont les principales motivations des éleveurs à mettre en place ces pratiques. Pour 80% d’entre eux, ces pratiques alternatives ont entrainé une diminution de la fréquence des diarrhées des veaux et une amélioration de leur croissance. La séparation tardive vache-veau demeure le point négatif de ces pratiques, avec des périodes de meuglements de 2,4 jours en moyenne. Certains éleveurs, ayant utilisé puis abandonné ces pratiques, pointent aussi d’autres limites (problèmes sanitaires, bâtiments inadaptés). Cette enquête, qui a permis de mieux connaître les pratiques d'allaitement des veaux laitiers par leur mère et sous nourrice, va être complétée par des enquêtes similaires et des expérimentations en fermes, au niveau européen, afin d’avoir une vision plus large de ces pratiques et de leurs impacts

Structural analysis of the starfish SALMFamide neuropeptides S1 and S2: The N-terminal region of S2 facilitates self-association

The neuropeptides S1 (GFNSALMFamide) and S2 (SGPYSFNSGLTFamide), which share sequence similarity, were discovered in the starfish Asterias rubens and are prototypical members of the SALMFamide family of neuropeptides in echinoderms. SALMFamide neuropeptides act as muscle relaxants and both S1 and S2 cause relaxation of cardiac stomach and tube foot preparations in vitro but S2 is an order of magnitude more potent than S1. Here we investigated a structural basis for this difference in potency using spectroscopic techniques. Circular dichroism spectroscopy showed that S1 does not have a defined structure in aqueous solution and this was supported by 2D nuclear magnetic resonance experiments. In contrast, we found that S2 has a well-defined conformation in aqueous solution. However, the conformation of S2 was concentration dependent, with increasing concentration inducing a transition from an unstructured to a structured conformation. Interestingly, this property of S2 was not observed in an N-terminally truncated analogue of S2 (short S2 or SS2; SFNSGLTFamide). Collectively, the data obtained indicate that the N-terminal region of S2 facilitates peptide self-association at high concentrations, which may have relevance to the biosynthesis and/or bioactivity of S2 in vivo

Random Operator Approach for Word Enumeration in Braid Groups

We investigate analytically the problem of enumeration of nonequivalent primitive words in the braid group B_n for n >> 1 by analysing the random word statistics and the target space on the basis of the locally free group approximation. We develop a "symbolic dynamics" method for exact word enumeration in locally free groups and bring arguments in support of the conjecture that the number of very long primitive words in the braid group is not sensitive to the precise local commutation relations. We consider the connection of these problems with the conventional random operator theory, localization phenomena and statistics of systems with quenched disorder. Also we discuss the relation of the particular problems of random operator theory to the theory of modular functionsComment: 36 pages, LaTeX, 4 separated Postscript figures, submitted to Nucl. Phys. B [PM

Combinatorics of bicubic maps with hard particles

We present a purely combinatorial solution of the problem of enumerating planar bicubic maps with hard particles. This is done by use of a bijection with a particular class of blossom trees with particles, obtained by an appropriate cutting of the maps. Although these trees have no simple local characterization, we prove that their enumeration may be performed upon introducing a larger class of "admissible" trees with possibly doubly-occupied edges and summing them with appropriate signed weights. The proof relies on an extension of the cutting procedure allowing for the presence on the maps of special non-sectile edges. The admissible trees are characterized by simple local rules, allowing eventually for an exact enumeration of planar bicubic maps with hard particles. We also discuss generalizations for maps with particles subject to more general exclusion rules and show how to re-derive the enumeration of quartic maps with Ising spins in the present framework of admissible trees. We finally comment on a possible interpretation in terms of branching processes.Comment: 41 pages, 19 figures, tex, lanlmac, hyperbasics, epsf. Introduction and discussion/conclusion extended, minor corrections, references adde

Random Convex Hulls and Extreme Value Statistics

In this paper we study the statistical properties of convex hulls of $N$ random points in a plane chosen according to a given distribution. The points may be chosen independently or they may be correlated. After a non-exhaustive survey of the somewhat sporadic literature and diverse methods used in the random convex hull problem, we present a unifying approach, based on the notion of support function of a closed curve and the associated Cauchy's formulae, that allows us to compute exactly the mean perimeter and the mean area enclosed by the convex polygon both in case of independent as well as correlated points. Our method demonstrates a beautiful link between the random convex hull problem and the subject of extreme value statistics. As an example of correlated points, we study here in detail the case when the points represent the vertices of $n$ independent random walks. In the continuum time limit this reduces to $n$ independent planar Brownian trajectories for which we compute exactly, for all $n$, the mean perimeter and the mean area of their global convex hull. Our results have relevant applications in ecology in estimating the home range of a herd of animals. Some of these results were announced recently in a short communication [Phys. Rev. Lett. {\bf 103}, 140602 (2009)].Comment: 61 pages (pedagogical review); invited contribution to the special issue of J. Stat. Phys. celebrating the 50 years of Yeshiba/Rutgers meeting

The effect of cigarette smoke exposure on the development of inflammation in lungs, gut and joints of TNFΔARE mice

The inflammatory cytokine TNF-alpha is a central mediator in many immune-mediated diseases, such as Crohn's disease (CD), spondyloarthritis (SpA) and chronic obstructive pulmonary disease (COPD). Epidemiologic studies have shown that cigarette smoking (CS) is a prominent common risk factor in these TNF-dependent diseases. We exposed TNF Delta ARE mice; in which a systemic TNF-alpha overexpression leads to the development of inflammation; to 2 or 4 weeks of air or CS. We investigated the effect of deregulated TNF expression on CS-induced pulmonary inflammation and the effect of CS exposure on the initiation and progression of gut and joint inflammation. Upon 2 weeks of CS exposure, inflammation in lungs of TNF Delta ARE mice was significantly aggravated. However, upon 4 weeks of CS-exposure, this aggravation was no longer observed. TNF Delta ARE mice have no increases in CD4+ and CD8+ T cells and a diminished neutrophil response in the lungs after 4 weeks of CS exposure. In the gut and joints of TNF Delta ARE mice, 2 or 4 weeks of CS exposure did not modulate the development of inflammation. In conclusion, CS exposure does not modulate gut and joint inflammation in TNF Delta ARE mice. The lung responses towards CS in TNF Delta ARE mice however depend on the duration of CS exposure