Influence of rearrangement of actin cytoskeleton on the overall material properties of ATDC5 cells during chondrogenesis

Studies show that when chondrocytes are cultured in 2D, they lose their phenotype. This change is reversed when the cells are embedded in a 3D culture system such as in agarose gel. Previous experiments in our lab showed that when prechodrocytic cells were embedded in agarose, chondrogenesis was triggered in these cells. This work attempts to understand the mechanical implications of this behavior. It also provides an estimate of the sensitivity of the apparatus that would be required to carry out compression loading experiments of gel-cell constructs that can distinguish between pre-chondrocytes and chondrocytes.;ATDC5 cells were cultured in 3D for 12 days and fluorescent images of the actin cytoskeletal structure of the cells were obtained. A major reorientation of the cytoskeletal structure (from stress-fiber to punctate appearance) was observed. This data was then used to construct a Finite Element model of cell. The cell was considered as a composite matrix and the actin as the embedded fibers. Radial deformations of the cell (difference in the corresponding undeformed and deformed radii of the cell at a particular angle w.r.t. loading axis) were calculated for 5 sets of experimental data. (Abstract shortened by UMI.)

Dietary fatty acid composition alters 11β-hydroxysteroid dehydrogenase type 1 gene expression in rat retroperitoneal white adipose tissue

The enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) amplifies intracellular glucocorticoid action by converting inactive glucocorticoids to their active forms in vivo. Adipose-specific overexpression of 11β-HSD1 induces metabolic syndrome in mice, whereas 11β-HSD1 null mice are resistant to it. Dietary trans and saturated fatty acids (TFAs and SFAs) are involved in the development of metabolic syndrome, whereas polyunsaturated fatty acids (PUFA) offer protection against this. Here, we report the effects of chronic feeding of different diets containing vanaspati (TFA rich), palm oil (SFA rich) and sunflower oil (PUFA rich) at 10%level on 11β-HSD1 gene expression in rat retroperitoneal adipose tissue. 11β-HSD1 gene expression was significantly higher in TFA rich diet-fed rats compared to SFA rich diet-fed rats, which in turn was significantly higher than PUFA rich diet-fed rats. Similar trend was observed in the expression of CCAAT-enhancer binding protein-α (C/EBP-α), the main transcription factor required for the expression of 11β-HSD1. We propose that TFAs and SFAs increase local amplification of glucocorticoid action in adipose tissue by upregulating 11β-HSD1 by altering C/EBP-α-gene expression. The increased levels of glucocorticoids in adipose tissue may lead to development of obesity and insulin resistance, thereby increasing the risk of developing metabolic syndrome

Orientation cues for high-flying nocturnal insect migrants: do turbulence-induced temperature and velocity fluctuations indicate the mean wind flow?

Migratory insects flying at high altitude at night often show a degree of common alignment, sometimes with quite small angular dispersions around the mean. The observed orientation directions are often close to the downwind direction and this would seemingly be adaptive in that large insects could add their self-propelled speed to the wind speed, thus maximising their displacement in a given time. There are increasing indications that high-altitude orientation may be maintained by some intrinsic property of the wind rather than by visual perception of relative ground movement. Therefore, we first examined whether migrating insects could deduce the mean wind direction from the turbulent fluctuations in temperature. Within the atmospheric boundary-layer, temperature records show characteristic ramp-cliff structures, and insects flying downwind would move through these ramps whilst those flying crosswind would not. However, analysis of vertical-looking radar data on the common orientations of nocturnally migrating insects in the UK produced no evidence that the migrants actually use temperature ramps as orientation cues. This suggests that insects rely on turbulent velocity and acceleration cues, and refocuses attention on how these can be detected, especially as small-scale turbulence is usually held to be directionally invariant (isotropic). In the second part of the paper we present a theoretical analysis and simulations showing that velocity fluctuations and accelerations felt by an insect are predicted to be anisotropic even when the small-scale turbulence (measured at a fixed point or along the trajectory of a fluid-particle) is isotropic. Our results thus provide further evidence that insects do indeed use turbulent velocity and acceleration cues as indicators of the mean wind direction

Fully developed turbulence and the multifractal conjecture

We review the Parisi-Frisch MultiFractal formalism for Navier--Stokes turbulence with particular emphasis on the issue of statistical fluctuations of the dissipative scale. We do it for both Eulerian and Lagrangian Turbulence. We also show new results concerning the application of the formalism to the case of Shell Models for turbulence. The latter case will allow us to discuss the issue of Reynolds number dependence and the role played by vorticity and vortex filaments in real turbulent flows.Comment: Special Issue dedicated to E. Brezin and G. Paris

Prediction of bulk and interfacial thermodynamic properties of polar mixtures by statistical associating fluid theory

textA Statistical Associating Fluid Theory (SAFT) for multi-component mixtures has been implemented in conjunction with a phase-stability and flash algorithm. The model has been extensively tested for various non-associating and associating mixtures and comparisons are made with the Peng-Robinson equation of state. Both Peng-Robinson and SAFT are equally suitable for simple nonassociating mixtures but SAFT clearly is more accurate when polar mixtures are modeled. The phase behavior of methanol-water-hydrocarbon mixtures is studied with the SAFT equation and the Peng-Robinson equation and comparisons are made with experimental liquid dropout data. The SAFT equation of state is shown to give better predictions for methanol-hydrocarbon and methanol-waterhydrocarbon mixtures over a range of pressures and compositions. The effect of methanol concentration and temperature on dew-point to bubble-point transition of a gas-condensate mixture is studied with the SAFT equation of state. The SAFT equation of state is coupled with the Gradient Theory to calculate the interfacial tension of pure components as well as multi-component mixtures. Pure component interaction parameters (cii) for the calculation of interfacial tension with the SAFT equation have been introduced. A mixing interaction coefficient for interfaces (mij) has been defined to satisfactorily predict the interfacial tension of certain mixtures such as water-methanol and waterethanol systems. The effect of temperature and pressure is studied for a methanewater mixture and it is shown that no further adjustable parameters need to be introduced to accurately predict the interfacial tension over a range of temperatures and pressures. Finally, the SAFT equation of state has also been integrated in to the reservoir simulator (UTCOMP) so as to be able to do flow simulations of complex polar mixtures. The flow simulations with SAFT have also been compared with experimental core flood studies and it is shown that both the PR and the SAFT equation give reasonable agreement with experimental data. However, it is shown that the SAFT based model predictions are slightly better during the methanol injection stage of the experiment. However, significantly larger computational time discourages the use of SAFT for such flow simulations.Chemical Engineerin

Lagrangian Measurements of Inertial Particle Accelerations in Grid Generated Wind Tunnel Turbulence

We describe Lagrangian measurements of water droplets in grid generated wind tunnel turbulence at a Taylor Reynolds number of Rλ= 250 and an average Stokes number (St) of approximately 0.1. The inertial particles are tracked by a high speed camera moving along the side of the tunnel at the mean flow speed. The standardized acceleration probability density functions of the particles have spread exponential tails that are narrower than those of a fluid particles (St ≈ 0) and there is a decrease in the acceleration variance with increasing Stokes number. A simple vortex model shows that the inertial particles selectively sample the fluid field and are less likely to experience regions of the fluid undergoing the largest accelerations. Recent direct numerical simulations compare favorably with these first measurements of Lagrangian statistics of inertial particles in highly turbulent flows