Dimensional analysis of a planetary mixer for homogenizing of free flowing powders: Mixing time and power consumption

International audiencePowder mixing is crucial to the processing stages in many industries. However, there is still a paucity of information about the effects of process parameters on mixing efficiency. This paper investigates the homogenization of free flowing granular materials with a planetary mixer, TRIAXE (R), examining the effect of the ratio of impeller rotational speeds (N-R/N-G) on the mixing process. First, a dimensional analysis carried out with mixing time and power consumption as target variables, established that both a Froude number and N-R/N-G controlled the process for the given free flowing powder mixture and planetary mixer. A further theoretical approach also suggested that these two dimensionless ratios which control hydrodynamics can be reduced to a modified Froude number providing that the maximum linear velocity achieved (mu(ch)) by the planetary mixer is introduced, replacing the dual impeller rotational speeds (N-R and N-G). Mixing time and power experiments validated the above hypothesis. Homogeneity tests performed in a granular media showed that the length of path achieved by the impeller governs the obtained mixing level. Finally, this work reflected that (i) dimensional analysis was also well suited to model powder homogenization with a planetary mixer. (ii) A concise set of dimensionless numbers governing mixing phenomena can be deduced through the introduction of the maximum linear velocity as obtained in previous studies on gas/liquid and miscible liquids mixing processes

Derivation of dimensionless relationships for the agitation of powders of different flow behaviours in a planetary mixer

International audienceThis study investigates the bulk agitation of free flowing or nearly cohesive granular materials in a pilot-scale planetary mixer equipped with a torque measurement system. Our major aim is to investigate the effect of the flow properties of several powders, as well as that of the set of experimental conditions (engine speeds N-R and N-G), on the power consumption of such a mixer. Thanks to a previous dimensional analysis of the system, this influence is studied through the variations of the power P with a characteristic speed rich, defined from engine speeds and geometrical considerations. Two relationships involving dimensionless numbers are derived to describe the agitation process: N-pG = f (F-rG, Nu(R)/Nu(G) )and N-pM = f(Fr-M). For free flowing powders, a linear relationship is observed when plotting P against u(ch), and he resulting process relationship linking dimensionless numbers is Np-M = 15Fr(M)(-1). In the more cohesive case, power values vary around an average value (P = 54W) and the resulting process relationship is Np-M = 1.8072Fr(M)(-1.467). It is argued that the exponent in the representation of N-pM against Fr-M may be a useful parameter for powder classification, and should be linked to powder rheometrical considerations

Performance of Pyridylthiourea-Polyethylenimine Polyplex for siRNA-Mediated Liver Cancer Therapy in Cell Monolayer, Spheroid, and Tumor Xenograft Models

Medical application of siRNAs relies on methods for delivering nucleic acids into the cytosol. Synthetic carriers, which assemble with nucleic acids into delivery systems, show promises for cancer therapy but efficiency remains to be improved. In here, the effectiveness of pyridylthiourea‐polyethylenimine (πPEI), a siRNA carrier that favors both polyplex disassembly and endosome rupture upon sensing the acidic endosomal environment, in 3 experimental models of hepatocellular cancer is tested. The πPEI‐assisted delivery of a siRNA targeting the polo‐like kinase 1 into Huh‐7 monolayer produces a 90% cell death via a demonstrated RNA interference mechanism. Incubation of polyplex with Huh‐7 spheroids leads to siRNA delivery into the superficial first cell layer and a 60% reduction in spheroid growth compared to untreated controls. Administration of polyplexes into mice bearing subcutaneous implanted Huh‐7Luc tumors results in a reduced tumor progression, similar to the one observed in the spheroid model. Altogether, these results support the in vivo use of synthetic and dedicated polymers for increasing siRNA‐mediated gene knockdown, and their clinical promise in cancer therapeutics

The Wnt Receptor Ryk Reduces Neuronal and Cell Survival Capacity by Repressing FOXO Activity During the Early Phases of Mutant Huntingtin Pathogenicity

The Wnt receptor Ryk is an evolutionary-conserved protein important during neuronal differentiation through several mechanisms, including γ-secretase cleavage and nuclear translocation of its intracellular domain (Ryk-ICD). Although the Wnt pathway may be neuroprotective, the role of Ryk in neurodegenerative disease remains unknown. We found that Ryk is up-regulated in neurons expressing mutant huntingtin (HTT) in several models of Huntington's disease (HD). Further investigation in Caenorhabditis elegans and mouse striatal cell models of HD provided a model in which the early-stage increase of Ryk promotes neuronal dysfunction by repressing the neuroprotective activity of the longevity-promoting factor FOXO through a noncanonical mechanism that implicates the Ryk-ICD fragment and its binding to the FOXO co-factor β-catenin. The Ryk-ICD fragment suppressed neuroprotection by lin-18/Ryk loss-of-function in expanded-polyQ nematodes, repressed FOXO transcriptional activity, and abolished β-catenin protection of mutant htt striatal cells against cell death vulnerability. Additionally, Ryk-ICD was increased in the nucleus of mutant htt cells, and reducing γ-secretase PS1 levels compensated for the cytotoxicity of full-length Ryk in these cells. These findings reveal that the Ryk-ICD pathway may impair FOXO protective activity in mutant polyglutamine neurons, suggesting that neurons are unable to efficiently maintain function and resist disease from the earliest phases of the pathogenic process in HD. © 2014 Tourette et al

Plant reproductive strategies in floodplains: The effect of agricultural practices and inundation

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Positioning of Nuclei in Arabidopsis Root Hairs: An Actin-Regulated Process of Tip Growth

In growing Arabidopsis root hairs, the nucleus locates at a fixed distance from the apex, migrates to a random position during growth arrest, and moves from branch to branch in a mutant with branched hairs. Consistently, an artificial increase of the distance between the nucleus and the apex, achieved by entrapment of the nucleus in a laser beam, stops cell growth. Drug studies show that microtubules are not involved in the positioning of the nucleus but that subapical fine F-actin between the nucleus and the hair apex is required to maintain the nuclear position with respect to the growing apex. Injection of an antibody against plant villin, an actin filament-bundling protein, leads to actin filament unbundling and movement of the nucleus closer to the apex. Thus, the bundled actin at the tip side of the nucleus prevents the nucleus from approaching the apex. In addition, we show that the basipetal movement of the nucleus at root hair growth arrest requires protein synthesis and a functional actin cytoskeleton in the root hair tube