Numerical assessment of hydrodynamic and mixing characteristics for mixed electroosmotic and pressure-driven flow through a wavy microchannel with patchwise surface heterogeneity

The micromixing of two fluids plays a vital role in lab-on-a-chip devices. For obtaining better mixing efficiency, we propose a micromixer using patchwise surface potential heterogeneity and wavy wall. We numerically investigate the hydrodynamic and mixing characteristics for flow through a microchannel with a straight top wall and wavy bottom wall. The primary flow is actuated by an external pressure-gradient and patches are placed at the top wall with positive zeta potential, such that the reversed electroosmotic actuation forms the recirculation zones close to the top wall. The streamlines, flow velocity, recirculation zone velocity, species concentration, flow rate, and mixing efficiency are investigated by varying the relative pressure-gradient strength, Debye parameter, zeta potential and wavy surface amplitude. Two different configurations are considered by placing the patches at the top wall, opposite to the peaks and valleys of the bottom wavy surface, respectively. It reveals that the recirculation zone velocity increases with the increase in both Debye parameter and surface amplitude, whereas it decreases with relative pressure-gradient strength near the patch surfaces. The flow rate decreases with the increase in zeta potential and we also identify the values of zeta potential for chocking of flow in the microchannel. It reveals that the mixing efficiency monotonically increases with surface amplitude, and the variation with zeta potential is non-monotonic. We also identify the range of zeta potential for which the value of mixing efficiency is higher than 90% for different configurations of the channel.

Phase Behavior of Gradient Copolymer Melts with Different Gradient Strengths Revealed by Mesoscale Simulations

Design and preparation of functional nanomaterials with specific properties requires precise control over their microscopic structure. A prototypical example is the self-assembly of diblock copolymers, which generate highly ordered structures controlled by three parameters: the chemical incompatibility between blocks, block size ratio and chain length. Recent advances in polymer synthesis have allowed for the preparation of gradient copolymers with controlled sequence chemistry, thus providing additional parameters to tailor their assembly. These are polydisperse monomer sequence, block size distribution and gradient strength. Here, we employ dissipative particle dynamics to describe the self-assembly of gradient copolymer melts with strong, intermediate, and weak gradient strength and compare their phase behavior to that of corresponding diblock copolymers. Gradient melts behave similarly when copolymers with a strong gradient are considered. Decreasing the gradient strength leads to the widening of the gyroid phase window, at the expense of cylindrical domains, and a remarkable extension of the lamellar phase. Finally, we show that weak gradient strength enhances chain packing in gyroid structures much more than in lamellar and cylindrical morphologies. Importantly, this work also provides a link between gradient copolymers morphology and parameters such as chemical incompatibility, chain length and monomer sequence as support for the rational design of these nanomaterials.

Latitudinal Psychology: An Ecological Perspective on Creativity, Aggression, Happiness, and Beyond

Are there systematic trends around the world in levels of creativity, aggressiveness, life satisfaction, individualism, trust, and suicidality? This article suggests a new field, latitudinal psychology, that delineates differences in such culturally shared features along northern and southern rather than eastern and western locations. In addition to geographical, ecological, and other explanations, we offer three metric foundations of latitudinal variations: replicability (latitudinal gradient repeatability across hemispheres), reversibility (north-south gradient reversal near the equator), and gradient strength (degree of replicability and reversibility). We show that aggressiveness decreases whereas creativity, life satisfaction, and individualism increase as one moves closer to either the North or South Pole. We also discuss the replicability, reversibility, and gradient strength of (a) temperatures and rainfall as remote predictors and (b) pathogen prevalence, national wealth, population density, and income inequality as more proximate predictors of latitudinal gradients in human functioning. Preliminary analyses suggest that cultural and psychological diversity often need to be partially understood in terms of latitudinal variations in integrated exposure to climate-induced demands and wealth-based resources. We conclude with broader implications, emphasizing the importance of north-south replications in samples that are not from Western, educated, industrialized, rich, and democratic (WEIRD) societies.