Flexible casting of modular self-aligning microfluidic assembly blocks

The recent shift among developers of microfluidic technologies toward modularized "plug and play" construction reflects the steadily increasing realization that, for many would-be users of microfluidic tools, traditional clean-room microfabrication is prohibitively complex and/or expensive. In this work, we present an advanced modular microfluidic construction scheme in which pre-fabricated microfluidic assembly blocks (MABs) can be quickly fashioned, without expertise or specialized facilities, into sophisticated microfluidic devices for a wide range of applications. Specifically, we describe three major advances to the MAB concept: (1) rapid production and extraction of MABs using flexible casting trays, (2) use of pre-coated substrates for simultaneous assembly and bonding, and (3) modification of block design to include automatic alignment and sealing structures. Finally, several exemplary applications of these MABs are demonstrated in chemical gradient synthesis, droplet generation, and total internal reflection fluorescence microscopy.     

Evolution of spatiotemporal patterns during the electrodissolution of metals: Experiments and simulations

Spatiotemporal patterns including accelerating fronts, rotating waves, and homogeneous oscillations evolve during the electrodissolution of metals like cobalt and iron that exhibit passivity under potentiostatic control. The nature of the patterns is determined by long-range (nonlocal) coupling through the electric field which in turn is influenced by the geometry of the electrochemical cell, the applied potential, and the conductivity of the electrolyte. A two-variable model in a three-dimensional geometry is presented which is able to simulate the essential features of the experimental system.(c) 2002 American Institute of Physics.     

High frequency behavior of a rolling ball and simplification of the separation equation

The Chaplygin separation equation for a rolling axisymmetric ball has an algebraic expression for the effective potential V (z = cosθ, D, λ) that is difficult to analyze. We simplify this expression for the potential and find a 2-parameter family for when the potential becomes a rational function of z = cosθ. Then this separation equation becomes similar to the separation equation for the heavy symmetric top. For nutational solutions of a rolling sphere, we study a high frequency ω ₃-dependence of the width of the nutational band, the depth of motion above V(z _min,D, λ) and the ω ₃-dependence of nutational frequency $\tfrac{{2\pi }} {T} $ .     

Arrow-Mangasarian Sufficient Conditions for Controlled Semimartingales

Abstract

This article shows a version of Arrow's generalization of Manga-sarian's sufficient conditions valid for controlled stochastic differential equations driven by semimartingales. The infinite horizon case is covered. An example is given.     

On bifurcation for semilinear elliptic Dirichlet problems and the Morse–Smale index theorem

We study bifurcation from a branch of trivial solutions of semilinear elliptic Dirichlet boundary value problems on star-shaped domains, where the bifurcation parameter is introduced by shrinking the domain. In the proof of our main theorem we obtain in addition a special case of an index theorem due to S. Smale.     

Observing individual fish behavior in fish aggregations: tracking in dense fish aggregations using a split-beam echosounder

Acoustic instruments are important tools for observing the behavior of aquatic organisms. This paper presents a simple but efficient method for improving the tracking of closely spaced targets using a split-beam echosounder. The traditional method has been a stepwise approach from the detection of echoes, rejection of apparently multiple targets and then tracking the remainder. This is inefficient because the split-beam angles are not included in the initial detection; rather they are only used in the rejection criteria before the subsequent tracking. A simple track-before-detection method is presented, where the phase angles, echo intensities, ranges, and times are used simultaneously, resulting in better detection and tracking of the individual fish. Two test data sets were analyzed to determine the effectiveness of this method at discriminating individual tracks from within dense fish aggregations. The first data set was collected by lowering a split-beam transducer into a herring layer. The second data set, also collected with a split-beam transducer, was from a caged aggregation of feeding herring larvae. Results indicate the potential of target tracking, using a split-beam echosounder, as a tool for understanding interindividual behavior.