Rheological Behavior of a Dispersion of Small Lipid Bilayer Vesicles

Rheological behavior of a dispersion of small nearly-unilamellar phospholipid bilayer vesicles has been investigated. We conducted steady-state shear experiments and linear viscoelastic experiments. In the dilute and semidilute regime the rheological behavior is similar to that of a hard-sphere dispersion as reported in the literature for viscoelastic measurements, but now also observed in steady shear experiments. The effect of the main acyl-chain phase transition, taking place at 23 °C, can be described with an increase of the effective volume fraction. As a result, with temperature variation one can obtain effective volume fractions larger than the maximum packing fraction for hard spheres. Near and above the maximum packing fraction a dynamic yield stress ty and a frequency independent storage modulus G' develop. In this concentration regime the rheological behavior is determined by the interplay between vesicle deformation and the intervesicle interaction, and so far, there is no indication which phenomenon is dominant. A comparison with recently reported measurements suggests that G' is proportional to a-3, where a is the vesicle radius. Furthermore, we show that ty = γcG' which is in agreement with theory. Here tγ is the dynamic yield stress and γc the critical strain which indicates the transition to nonlinear behavior in a viscoelastic experiment. There is a striking resemblance between our high concentration results and those reported in literature for vesicles in the so-called onion phase. To the best of our knowledge this is the first rheological study for concentrated nearly-unilamellar vesicle dispersions with volume fraction and temperature as variables

Irrational Resistance or Irrational Support? Performance Effects of Project Leader Status

In this study, we explore the effects of project leader status in new product development projects. We predict and find that that project leader status increases project performance up to a certain point after which it decreases performance. Further, status increases the variability of project performance, that is, it leads to more extreme performance in both directions

Great successes and great failures: The impact of project leader status on project performance and performance extremeness

Research supporting the Matthew Effect demonstrates that high-status actors experience performance benefits due to increased recognition of their work and greater opportunities and resources, but recent research also indicates that high-status actors face a greater risk of negative performance evaluations. In this paper, we seek to contribute to the status literature by reconciling these findings and ask: To what extent does status influence heterogeneity in performance evaluations? We explore how project leader status affects the performance of innovation projects in the video game industry. We hypothesize that there is an inverted U-shaped relationship between project leader status and project performance, and a positive relationship between project leader status and performance extremeness (i.e., performance variation). In order to test our hypotheses, we analyzed the performance of video game projects and computed the status of project leaders by applying a project affiliation social network analysis. We find that an intermediate level of status—neither too much nor too little—is positively associated with average project performance. We also reveal more extreme performance effects for high-status leaders: While some achieve superior project performance, others experience significant project failures. We therefore provide important theoretical and practical insights regarding how status affects the implementation of innovations. We also discuss the implications of these findings for the literature on middle-status conformity

Shear viscosity of an ordering latex suspension

The shear viscosity of a latex which is ordered at rest is studied as a function of the shear rate and volume fraction. At low shear rates and for moderate to high volume fractions, the flow curves show dynamic yield behavior which disappears below a volume fraction of 8%. At high shear rates, the onset to the high shear rate plateau of the viscosity can be observed. A new model for the shear viscosity for lattices at high volume fractions is described. This model is based upon theories for the shear viscosity of dilute lattices of Blachford et al. [J. Phys. Chem. 73, 1062 (1969)] and Russel [J. Fluid Mech. 85, 673 (1978)]. In terms of this model, the ordered latex is broken down under shear flow into ordered domains suspended in a disordered fluid. The larger the shear rate, the smaller the volume fraction of ordered domains. The experimental results can be described reasonably well with the model discussed here

The relationship between cholesterol crystals, foamy macrophages and haemosiderin in odontogenic cysts

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