Influence of confinement by smooth and rough walls on particle dynamics in dense hard-sphere suspensions

We used video microscopy and particle tracking to study the dynamics of confined hard-sphere suspensions. Our fluids consisted of 1.1-μm-diameter silica spheres suspended at volume fractions of 0.33–0.42 in water-dimethyl sulfoxide. Suspensions were confined in a quasiparallel geometry between two glass surfaces: a millimeter-sized rough sphere and a smooth flat wall. First, as the separation distance (H) is decreased from 18 to 1 particle diameter, a transition takes place from a subdiffusive behavior (as in bulk) at large H, to completely caged particle dynamics at small H. These changes are accompanied by a strong decrease in the amplitude of the mean-square displacement (MSD) in the horizontal plane parallel to the confining surfaces. In contrast, the global volume fraction essentially remains constant when H is decreased. Second, measuring the MSD as a function of distance from the confining walls, we found that the MSD is not spatially uniform but smaller close to the walls. This effect is the strongest near the smooth wall where layering takes place. Although confinement also induces local variations in volume fraction, the spatial variations in MSD can be attributed only partially to this effect. The changes in MSD are predominantly a direct effect of the confining surfaces. Hence, both the wall roughness and the separation distance (H) influence the dynamics in confined geometries

A radical approach to radical innovation

Innovation pays. Amazon, Apple, Facebook, Google – nearly every one of today’s most successful companies has a talent for developing radical new ideas. But how best to encourage radical initiative taking from employees, and does their previous success or failure at it play a role

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

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

Imaging Local Acoustic Pressure in Microchannels

A method for determining the spatially resolved acoustic field inside a water-filled microchannel is presented. The acoustic field, both amplitude and phase, is determined by measuring the change of the index of refraction of the water due to local pressure using stroboscopic illumination. Pressure distributions are measured for the fundamental pressure resonance in the water and two higher harmonic modes. By combining measurement at a range of excitation frequencies, a frequency map of modes is made, from which the spectral line width an

Linear viscoelastic behavior of aggregated colloidal dispersions

The viscoelastic behavior of a depletion-flocculated dispersion of colloidal spheres is investigated at different volume fractions of the spheres, using a controlled stress and a dynamic rheometer. Combining the results, we obtain the storage G′ and loss G′′ moduli over a frequency range of 0.02<ω<200rad/s. The measured G′ gradually increases with increasing frequency, while G′′ almost remains constant, indicating a broad spectrum of relaxation times. To describe and explain the observed behavior of the moduli as a function of frequency and volume fraction in terms of microscopic parameters, a microrheological model based on the fractal concept is proposed. Comparing experimental results with model calculations, we find a good agreement between the two, with physically plausible parameter values

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

Cryptosporidium infections in children in Durban Seasonal variation, age distribution and disease status

One hundred and eleven of 1229 children (9%) aged &lt; 10 years admitted to King Edward VIII Hospital, Durban, with gastro-enteritis over a period of 1 year were found to harbour Cryptosporidium. Of these, 96 (89,7%) were &lt; 2 years of age. Cryptosporidium was the only potential pathogen identified in 80 of these patients (6,50/0). The prevalence in paediatric patients without gastro-enteritis was 2,4% (3/124). During the study period Cryptosporidium infections were significantly more prevalent during the high rainfall season (P = 0,03)