633 research outputs found
Stability of a granular layer on an inclined "fakir plane"
We present here experimental results on the effect of a forest of cylinder
obstacles (nails) on the stability of a granular layer over a rough incline, in
a so-called "fakir plane" configuration. The nail forest is found to increase
the stability of the layer, the more for the densest array, and such an effect
is recovered by a simple model taking into account the additional friction
force exerted by the pillar forest onto the granular layer
Dense granular flow around a penetrating object: Experiments and hydrodynamic model
We present in this Letter experimental results on the bidimensional flow
field around a cylinder penetrating into dense granular matter together with
drag force measurements. A hydrodynamic model based on extended kinetic theory
for dense granular flow reproduces well the flow localization close to the
cylinder and the corresponding scalings of the drag force, which is found to
not depend on velocity, but linearly on the pressure and on the cylinder
diameter and weakly on the grain size. Such a regime is found to be valid at a
low enough "granular" Reynolds number.Comment: 5 pages, 4 figure
Experimental velocity fields and forces for a cylinder penetrating into a granular medium
We present here a detailed granular flow characterization together with force
measurements for the quasi-bidimensional situation of a horizontal cylinder
penetrating vertically at a constant velocity in dry granular matter between
two parallel glass walls. In the velocity range studied here, the drag force on
the cylinder does not depend on the velocity V_0 and is mainly proportional to
the cylinder diameter d. Whereas the force on the cylinder increases with its
penetration depth, the granular velocity profile around the cylinder is found
stationary with fluctuations around a mean value leading to the granular
temperature profile. Both mean velocity profile and temperature profile exhibit
strong localization near the cylinder. The mean flow perturbation induced by
the cylinder decreases exponentially away from the cylinder on a characteristic
length \lambda, that is mainly governed by the cylinder diameter for large
enough cylinder/grain size ratio d/d_g: \lambda ~ d/4 + 2d_g. The granular
temperature exhibits a constant plateau value T_0 in a thin layer close to the
cylinder of extension \delta_{T_0} ~ \lambda/2 and decays exponentially far
away with a characteristic length \lambda_T of a few grain diameters (\lambda_T
~ 3d_g). The granular temperature plateau T_0 that scales as (V_0^2 d_g/d) is
created by the flow itself from the balance between the "granular heat"
production by the shear rate V_0/\lambda over \delta_{T_0} close to the
cylinder and the granular dissipation far away
Pre- and postnatal development of adipose depots in meat animals with a specific focus on the pig
Pre- and postnatal development of adipose depots in meat animals with a specific focus on the pig. 65. International Congress of Meat Science and Technology (ICoMST
Relevant heating of the quiet solar corona by Alfvén waves: a result of adiabaticity breakdown
International audienceIon heating by Alfvén waves has been considered for long as the mechanism explaining why thesolar corona has a temperature several orders of magnitude higher than the photosphere. Unfortu-nately, as the measured wave frequencies are much smaller than the ion cyclotron frequency, particleswere expected to behave adiabatically, impeding a direct wave-particle energy transfer to take place,except through decorrelating stochastic mechanisms related to broadband wave spectra. This paperproposes a new paradigm for this mechanism by showing it is actually much simpler, more general,and very efficient. Indeed, for measured wave amplitudes in the quiet corona, ion orbits are shownto cross quasi-periodically one or several slowly pulsating separatrices in phase space. Now, a sepa-ratrix is an orbit with an infinite period, thus much longer than the pulsation one. Therefore, eachseparatrix crossing cancels adiabatic invariance, and yields a very strong energy transfer from thewave, and thus particle heating. This occurs whatever be the wave spectrum, even a monochromaticone. The proposed mechanism is so efficient that it might lead to a self-organized picture of coronalheating: all Alfvén waves exceeding a threshold are immediately quenched and transfer their energyto the waves
From granular collapses to shallow water waves: A predictive model for tsunami generation
In this article, we present a predictive model for the amplitude of impulse
waves generated by the collapse of a granular column into a water layer. The
model, which combines the spreading dynamics of the grains and the wave
hydrodynamics in shallow water, is successfully compared to a large dataset of
laboratory experiments, and captures the influence of the initial parameters
while giving an accurate prediction. Furthermore, the role played on the wave
generation by two key dimensionless numbers, i.e., the global Froude number and
the relative volume of the immersed deposit, is rationalized. These results
provide a simplified, yet comprehensive, physical description of the generation
of tsunami waves engendered by large-scale subaerial landslides, rockfalls, or
cliff collapses in a shallow water
Pre- and postnatal adipose tissue development in farm animals: from stem cells to adipocyte physiology
To view supplementary material for this article, please visit http://dx.doi.org/10.1017/S1751731116000872Both white and brown adipose tissues are recognized to be differently involved in energy metabolism and are also able to secrete a variety of factors called adipokines that are involved in a wide range of physiological and metabolic functions. Brown adipose tissue is predominant around birth, except in pigs. Irrespective of species, white adipose tissue has a large capacity to expand postnatally and is able to adapt to a variety of factors. The aim of this review is to update the cellular and molecular mechanisms associated with pre- and postnatal adipose tissue development with a special focus on pigs and ruminants. In contrast to othertissues, the embryonic origin of adipose cells remains the subject of debate. Adipose cells arise from the recruitment of specific multipotent stem cells/progenitors named adipose tissue-derived stromal cells. Recent studies have highlighted the existence of a variety of those cells being able to differentiate into white, brown or brown-like/beige adipocytes. After commitment to the adipocyte lineage, progenitors undergo large changes in the expression of many genes involved in cell cycle arrest, lipid accumulation and secretory functions. Early nutrition can affect these processes during fetal and perinatal periods and can also influence or pre-determinate later growth of adipose tissue. How these changes may be related to adipose tissue functionalmaturity around birth and can influence newborn survival is discussed. Altogether, a better knowledge of fetal and postnatal adipose tissue development is important for various aspects of animal production, including neonatal survival, postnatal growth efficiency and health
Divergent selection on 63-day body weight in the rabbit: response on growth, carcass and muscle traits
The effects of selection for growth rate on weights and qualitative carcass and muscle traits were assessed by comparing two lines selected for live body weight at 63 days of age and a cryopreserved control population raised contemporaneously with generation 5 selected rabbits. The animals were divergently selected for five generations for either a high (H line) or a low (L line) body weight, based on their BLUP breeding value. Heritability (h2) was 0.22 for 63-d body weight (N = 4754). Growth performance and quantitative carcass traits in the C group were intermediate between the H and L lines (N = 390). Perirenal fat proportion (h2 = 0.64) and dressing out percentage (h2 = 0.55) ranked in the order L < H = C (from high to low). The weight and cross-sectional area of the Semitendinosus muscle, and the mean diameter of the constitutive myofibres were reduced in the L line only (N = 140). In the Longissimus muscle (N = 180), the ultimate pH (h2 = 0.16) and the maximum shear force reached in the Warner-Braztler test (h2 = 0.57) were slightly modified by selection
- …