Droplet-based programmable processors promise to offer solutions to a wide range of applications in which chemical and biological analysis and/or small-scale synthesis are required, suggesting they will become the microfluidic equivalents of microprocessors by offering off-the-shelf solutions for almost any fluid based analysis or small scale synthesis problem. A general purpose droplet processor should be able to manipulate droplets of different compositions (including those that are electrically conductive or insulating and those of polar or non-polar nature), to control reagent titrations accurately, and to remain free of contamination and carry over on its reaction surfaces. In this article we discuss the application of dielectrophoresis to droplet based processors and demonstrate that it can provide the means for accurately titrating, moving and mixing polar or non-polar droplets whether they are electrically conductive or not. DEP does not require contact with control surfaces and several strategies for minimizing surface contact are presented. As an example of a DEP actuated general purpose droplet processor, we show an embodiment based on a scaleable CMOS architecture that uses DEP manipulation on a 32 x 32 electrode array having built-in control and switching circuitry. Lastly, we demonstrate the concept of a general-purpose programming environment that facilitates droplet software development for any type of droplet processor.
groupers and their associated reef fish assemblage near cape fear, north carolina, were observed using scuba and underwater stationary videography during a 7-mo period. fifty-seven sites were visited with stationary video and diver point counts of groupers were taken at each site. primary observations by both techniques were made on gag, Mycteroperca microlepis (goode and bean, 1879), and scamp, Mycteroperca phenax Jordan and swain, 1884, while other grouper species were noted for videos only. comparisons of gag and scamp density were made using baited and unbaited stationary camera deployments on high-and low-relief ledge habitats. inferred minimum population sizes by location ranged from 0 to 4 gag, 0 to 13 scamp, and 0 to 2 yellowmouth, Mycteroperca interstitialis (poey, 1860), using stationary video. estimated densities by video camera were highest for scamp at 480 ha −1. gag density was estimated at 145 ha-1 and yellowmouth grouper at 50 ha −1. in total, 68 fish species including groupers were recorded by video and richness by site ranged from 10 to 26 (n = 34; mean 18.9, sd 4.2). reef fish community structure as measured by mean bray-curtis dissimilarity between paired sites was 0.339 (0.219 sd) indicating a substantial overlap in species composition between most sites. given the economic importance of the snapper-grouper complex and the desire to develop non-extractive (or reduced impact) survey techniques, stationary video observations hold promise for monitoring changes in reef fish assemblages.
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