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Collective dynamics of cells in confined geometry regulate several biological processes including cell migration, proliferation, differentiation, and communication. In this work, combining simulation with experimental data, we studied the oscillatory motion of epithelial sheets in smaller areas of confinement, and we linked the monolayer maturation induced-jamming with the wave formation. We showed that epithelial cell populations with delayed jamming properties use the additional time available from this delay to coordinate their movement, generating wave motion in larger areas of confinement compared to control populations. Furthermore, the effects of combining geometric confinement with contact guiding micro-gratings on this wave formation were investigated. We demonstrated that collective migratory oscillations under large geometrical confinement depend on the jamming state of the cell monolayers. The early dynamical state of the experimental results obtained was simulated by self-propelled Voronoi computations, comparing cells with solid-like and fluid-like behavior. Together our model describes the wave formation under confinement and the nodal oscillatory dynamics of the early dynamic stage of the system. Insight Box: Collective behavior of cells in confined spaces impacts biological processes. Through experimental data combined with simulations, the oscillatory motion of epithelial sheets in small areas of confinement was described. A correlation between the level of cell jamming and the formation of waves was detected. Cell populations with delayed jamming presented wave motion in larger confinement areas. The effects of combining geometric confinement with substrate micro-gratings demonstrated that the collective migratory oscillations in large confinement areas rely on the jamming state of cells. The early dynamical state was simulated using self-propelled Voronoi computations that help to understand wave formation under confinement and the nodal oscillatory dynamics of early-stage systems. [ABSTRACT FROM AUTHOR]

A thorough model for the porous diffusion layer of a polymer electrolyte fuel cell (PEFC) is presented that accounts for multicomponent species diffusion, transport and formation of liquid water, heat transfer and electronic current transfer. The result reveals the great potential of downscaled polymer electrolyte membrane fuel cells in achieving enhanced power densities.

Open-cell aluminum foams were investigated using water to determine their hydraulic characteristics. Maximum fluid flow velocities achieved were 1.042 m/s. The permeability and form coefficient varied from 2.46 X [10.sup.-10] [m.sup.2] and 8701 [m.sup.-1] to 3529 X [10.sup.-10] [m.sup.2] and 120 [m.sup.-1], respectively. It was determined that the flowrate range influenced these calculated parameters, especially in the transitional regime where the permeability based Reynolds number varied between unity and 26.5. Beyond the transition regime where [Re.sub.K] [greater than or equal to] 30, the permeability and form coefficient monotonically approached values which were reported as being calculated at the maximum flow velocities attained. The results obtained in this study are relevant to engineering applications employing metal foams ranging from convection heat sinks to filters and flow straightening devices. [DOI: 10.1115/1.1429637]

Water condensation and freezing on asphalt roads can lead to slippery conditions, which are responsible for many winter accidents and have caused an overreliance on mostly environmentally damaging and pavement degrading deicing chemicals and salt, which requires active maintenance. Bitumen is a mechanically and chemically complex material mainly consisting of various hydrocarbon-based chemicals groups. Additionally, bitumen makes up approximately 5 wt.% of the asphalt concrete mixture because of its binder role and coating function of the aggregates, can control the bulk mechanical properties and surface properties of the asphalt mixture. Condensation as the first step and later freezing phenomena are investigated in this study and from ambient humidity toward understanding the fundamentals of icing on bituminous surfaces. Condensation experimental results show selective wettability of chemically and mechanically district bitumen surface domains. The effect of different bitumen modifiers of polyethylene terephthalate, polyamide (PA 66), polyacrylonitrile, and Sasobit wax at 1 wt.% were studied on condensation freezing and bitumen water affinity. [ABSTRACT FROM AUTHOR]

In the work presented in this paper a real time holographic interferometry technique is developed to measure instantaneously and nonintrusively the thickness distribution of a liquid sheet formed by the impingement of two liquid jets. The experimental results are compared with earlier largely unverified analytical predictions. It is shown that the assumption that the sheet thickness is inversely proportional to the radial distance from the impingement point is in principle good. The dependence of the theoretically obtained proportionality constant on the azimuthal angle, however, while exhibiting the same trend it also shows some quantitative differences. Reasons are given in the context of the work. In addition, a weak effect of the jet velocity on the proportionality constant is found to exist. In the theories no such effect was modeled. Finally, comparisons between theoretical and experimental isothickness contours show differences. Overall there appears to be a justification for improved theoretical studies including effects such as that of gravitation.

Research was conducted to study the role of key operating parameters that influence solder microdroplet deposition the electronics manufacturing industry. The study utilized a model that simulated the axisymmetric impact and solidification of a spherical,molten solder droplet on a flat horizontal multilayer composite substrate. Results showed that the presence of an oxide on the substrate surface increased the thermal contact resistance. They also indicated that a partial coverage of the surface of a pure-copper substrate by copper oxide would lead in thermal contact resistance.

Real time microholography is employed in measuring the transient concentration field in the vicinity of a growing dendrite. The growth of the dendrite is monitored by a charge-coupled device camera and a video recording system between the crystallization and solidification stages. Results show that concentration distribution directly next to a group of sharp dendritic tips is smoother than the structure of the interface itself.

A theoretical model based on the Lagrangian formulation is used to study the fluid dynamics and heat transfer phenomena which occur during the impingement of a picoliter size liquid solder droplet upon a multilayer, composite substrate. Results indicate that the temperature distribution in the solder droplet exhibits two-dimensional properties as its impact velocity increases.