16,555 research outputs found
Principles of microfluidic actuation by modulation of surface stresses
Development and optimization of multifunctional devices for fluidic manipulation of films, drops, and bubbles require detailed understanding of interfacial phenomena and microhydrodynamic flows. Systems are distinguished by a large surface to volume ratio and flow at small Reynolds, capillary, and Bond numbers are strongly influenced by boundary effects and therefore amenable to control by a variety of surface treatments and surface forces. We review the principles underlying common techniques for actuation of droplets and films on homogeneous, chemically patterned, and topologically textured surfaces by modulation of normal or shear stresses
Verbally closed virtually free subgroups
A theorem of Myasnikov and Roman'kov says that any verbally closed subgroup
of a finitely generated free group is a retract. We prove that all free (and
many virtually free) verbally closed subgroups are retracts in any finitely
generated group.Comment: 5 pages. A Russian version of this paper is at
http://halgebra.math.msu.su/staff/klyachko/papers.htm . V.2: an example is
added. V.3: minor corrections in the proof of the Main Theorem. V.4:
terminology correctio
Generation of high-resolution surface temperature distributions
We have performed numerical calculations to study the generation of arbitrary temperature profiles with high spatial resolution on the surface of a solid. The characteristics of steady-state distributions and time-dependent heating and cooling cycles are examined, as well as their dependence on material properties and device geometry. Ideally, low-power consumption and fast response times are desirable. The simulations show that the achievable spatial resolution is on the order of the substrate thickness and that the response time t+ depends on the width of the individual heating elements. Moreover, the rise time t+ can be significantly shortened by deposition of a thermal insulation layer, which also reduces the power consumption and increases lateral resolution
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