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Heat shock protein 27 (HSP27) accumulates in stressed cells and helps them to survive adverse conditions. We have already shown that HSP27 has a function in the ubiquitination process that is modulated by its oligomerization/phosphorylation status. Here, we show that HSP27 is also involved in protein sumoylation, a ubiquitination-related process. HSP27 increases the number of cell proteins modified by small ubiquitin-like modifier (SUMO)-2/3 but this effect shows some selectivity as it neither affects all proteins nor concerns SUMO-1. Moreover, no such alteration in SUMO-2/3 conjugation is achievable by another HSP, such as HSP70. Heat shock factor 1 (HSF1), a transcription factor responsible for HSP expression, is one of the targets of HSP27. In stressed cells, HSP27 enters the nucleus and, in the form of large oligomers, binds to HSF1 and induces its modification by SUMO-2/3 on lysine 298. HSP27-induced HSF1 modification by SUMO-2/3 takes place downstream of the transcription factor phosphorylation on S303 and S307 and does not affect its DNA-binding ability. In contrast, this modification blocks HSF1 transactivation capacity. These data show that HSP27 exerts a feedback inhibition of HSF1 transactivation and enlighten the strictly regulated interplay between HSPs and HSF1. As we also show that HSP27 binds to the SUMO-E2-conjugating enzyme, Ubc9, our study raises the possibility that HSP27 may act as a SUMO-E3 ligase specific for SUMO-2/3. [ABSTRACT FROM AUTHOR]

In this paper we analyze efficiency of a magnetorheological (MR) fluid valve consisting of a flow channel placed inside a solenoid. The scope of the optimization is to find a proper geometry and dimensions of the flow channel in order to achieve the highest possible inlet pressure ΔP(H) at a given field strength H. We analyze two types of flow channels: spiral channels with different helix angles and packed beds of spherical and cylindrical particles with different aspect ratios, both nonmagnetic and paramagnetic. For the prediction of the valve discharge characteristics in the presence of the magnetic field of an arbitrary orientation, we have used our recent physical models for MR fluid flows through capillaries and porous media. We show that among spiral channels the most efficient is the one having the minimal helix angle, i.e. the densest winding of the spiral. At H=20 kA/m this channel provides the inlet pressure 9 times the pressure in the absence of the field. Comparing the porous beds, we conclude that those made of superparamagnetic material are always more effective than nonmagnetic beds. The shape of the bed particles has also been found to affect the inlet pressure by affecting porosity and tortuosity of the beds. The most effective bed consists of packed cylinders made of magnetically soft steel and having the length-to-diameter ratio of either 0.5 or 5. At H=20 kA/m these beds give the pressure near 40 times the pressure at zero field and thus show a higher effectiveness compared to spiral channels. [ABSTRACT FROM AUTHOR]

Measurement of average interparticle gap in chains of colloidal particles is realized by means of light scattering in silica suspensions or dynamic mechanical analysis in MR elastomers. For a silica volume fraction of 10% we find that the mean distance between particles inside chains drop off sharply with the increase of field; this behavior is attributed to the presence of a long range ionic repulsive force. We show that this experiment allows to obtain information about interparticle forces between colloidal particles. On the other hand the transmitted light is very sensitive to the size of the particles in the chain and to the gap between particles. In an other domain, namely elastomers containing chains of magnetic particles, the magnetostriction is also found to be determined by the interparticle gap. [ABSTRACT FROM AUTHOR]

We investigate a composite system formed by micrometer-sized silica spheres and a nematic liquid crystal with positive dielectric anisotropy. The surface of the spheres has been treated to obtain homeotropic alignment either by grafting molecules of n-Octadecyltrimetoxysilane or by using lecithin.In a glass cell with planar anchoring conditions, we have experimentally observed the dipole and the Saturn-ring configurations. Due to the planar treatment of the glass substrates the particles align and can form chains. We studied the effect of an electric field applied parallel to the direction of the rubbing, in the plane of the cell. [ABSTRACT FROM AUTHOR]

The hydrodynamic transport properties of hard-sphere dispersions are calculated for volume fractions (φ) spanning the dilute limit up to the fluid-solid transition at φ = 0.49. Particle distributions are generated by a Monte Carlo technique and the hydrodynamic interactions are calculated by Stokesian dynamics simulation. The effects of changing the number of particles in the simulation cell are investigated, and the scaling laws for the finite-size effects are derived. The effects of using various levels of approximation in computing both the far- and near-field hydrodynamic interactions are also examined. The transport properties associated with freely mobile suspensions—sedimentation velocities, self-diffusion coefficients, and effective viscosities—are determined here, while the corresponding properties of porous media are determined in a companion paper [Phys. Fluids 31, 3473 (1988)]. Comparison of the simulation results is made with both experiment and theory. In particular, the short-time selfdiffusion coefficients and the suspension viscosities are in excellent agreement with experiment. [ABSTRACT FROM AUTHOR]

The hydrodynamic transport properties of hard-sphere dispersions are calculated for volume fractions (φ) spanning the dilute limit up to the fluid-solid transition at φ = 0.49. Particle distributions are generated by a Monte Carlo technique and the hydrodynamic interactions are calculated by Stokesian dynamics simulation. The effects of changing the number of particles in the simulation cell are investigated, and the scaling laws for the finite-size effects are determined. The effects of using various levels of approximation in computing both the farand near-field hydrodynamic interactions are also examined. The transport properties associated with porous media—permeabilities and hindered diffusion coefficients—are determined here. The corresponding properties of freely mobile suspensions are determined in a companion paper [Phys. Fluids 31, 3462 (1988)]. [ABSTRACT FROM AUTHOR]