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Michael G. Pollack

Bio: Michael G. Pollack is an academic researcher from Research Triangle Park. The author has contributed to research in topics: Digital microfluidics & Electrowetting. The author has an hindex of 52, co-authored 73 publications receiving 8885 citations. Previous affiliations of Michael G. Pollack include Duke University & United States Department of Energy Office of Science.


Papers
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Proceedings ArticleDOI
22 Jul 1997
TL;DR: In this paper, the authors proposed a new methodology for chemical detection of explosive particles associated with anti-personnel mines, which can be used to complement vapor detection of explosives with an electronic nose by remotely stimulating a target area with a high intensity, focused air ultrasonic beam whose energy can megasomcmally clean the target area of particles above a designed-for size.
Abstract: We report on a new methodology for chemical detection of explosive particles associated with anti-personnel mines. Traceparticle detection can be used to complement vapor detection of explosives with an electronic nose. Our approach is toremotely stimulate a target area with a high intensity, focused air ultrasonic beam whose energy can megasomcally clean thetarget area of particles above a designed-for size. We have designed a MEMS electrostatic transducer to test the concept.Nanogram particle detection will occur by collecting particles on an array of temperature sensitive MEMS sensors andirradiating the particles with 3-5 im wavelength infrared light. Explosive particles will selectively absorb the infrared energyat approximately 1600 cnf', decompose, and give offheat which can be detected.Keywords: explosive particle detection, ultrasound, land mines, nanogram particles, decomposition, MEMS, cantileverbeams 1. INTRODUCTION Recently, the idea ofusing chemical detection for finding land mines has gained attention as a result of successes achieved inthe use of trained dogs. Dogs have proven to be the most effective land mine detectors, although the dogs have limitedattention spans measured in tens of minutes. An electronic nose can work 24 hours a day! Since the land mine detectionproblem is huge, it will require full time noses in the search process.Dogs search by placing their noses close to the ground, inhaling vapors as well as solid particles of material. There have beenrecent successes in mimicking the vapor detection aspects of the smell sense in the "nose-on-a-chip" at Cal Tech, which candifferentiate among various vapors. 1 A complementary approach to obtaining increased chemical sensitivity is beingexplored at Duke University. One issue in vapor detection ofexplosives is that sampling at ambient temperatures may limitdetectability. An alternative is to collect particles as samples. Since plastic explosives are fabricated by creating a mixture ofground RDX or TNT with a binder substance, the putty-like material which is formed tends to capture particles to its surfacewhen contact is made. Additionally, because particles are distributed further by handling, the surface of the device and itssurrounding area are often heavily contaminated with particles ofexplosives. During diurnal temperature cycles the explosiveparticles attached to a buried mine diffuse their y to the surface of the ground. By sampling fine particles on the ground'ssurface in addition to vapors, it is possible that analysis and detectability may be enhanced. 2Significant success has been reported using trace explosive particles for substance identification.2 Indeed, both RDX and TNThave been detected at higher levels than expected when the vapor sampling system was augmented with a trace particle

12 citations

Patent
10 Aug 2006
TL;DR: In this paper, an apparatus is provided for generating a seal between a conduit and a reservoir well, which can include a mount including a first and second end, and a tube with a first end engaging the first end of the mount, and operable to hold a conduit having an end such that the conduit extends through the first aperture.
Abstract: Methods and Apparatuses for Generating a Seal Between a Conduit and a Reservoir Well According to one embodiment, an apparatus is provided for generating a seal between a conduit and a reservoir well The apparatus can include a mount including a first and second end The mount can also include a first aperture extending between the first and second ends The apparatus can also include a tube including a first end engaging the first end of the mount, and operable to hold a conduit having an end such that the conduit extends through the first aperture of the mount and the end of the conduit communicates with a reservoir well Further, the apparatus can include a nut operable to engage the mount and tube and seal the conduit to the first aperture of the mount such that air cannot communicate from the reservoir well through the first aperture of the mount

11 citations

Patent
25 Apr 2013
TL;DR: In this article, a method of manipulating a droplet comprising providing a substrate comprising a surface, an elongated transport electrode disposed on the substrate surface, and one or more wires for providing power to the transport electrode was presented.
Abstract: A method of manipulating a droplet comprising providing a substrate comprising a surface; an elongated transport electrode disposed on the substrate surface, the elongated transport electrode having a first and a second end and configured to impart a gradient force to the droplet; and one or more wires for providing power to the transport electrode; and providing power to the one or more wires to effect the gradient force and thereby transport the droplet along the length of the elongated transport electrode from the first end to the second end.

10 citations

Patent
05 Feb 2013
TL;DR: In this paper, the authors provided methods for manipulating droplets by placing the droplet on a surface comprising an array of electrodes and a substantially co-planer array of reference elements.
Abstract: Methods are provided for manipulating droplets. The methods include providing the droplet on a surface comprising an array of electrodes and a substantially co-planer array of reference elements, wherein the droplet is disposed on a first one of the electrodes, and the droplet at least partially overlaps a second one of the electrodes and an intervening one of the reference elements disposed between the first and second electrodes. The methods further include activating the first and second electrodes to spread at least a portion of the droplet across the second electrode and deactivating the first electrode to move the droplet from the first electrode to the second electrode.

8 citations

Patent
23 Oct 2006
TL;DR: In this paper, the authors provide a substrate including an arrangement of first, second and third electrodes, wherein the second electrode is interposed between the first and the third electrodes to form a droplet on the third electrode.
Abstract: Methods for performing microfluidic sampling are provided. The method includes providing a substrate including an arrangement of first, second and third electrodes, wherein the second electrode is interposed between the first and third electrodes. The method additionally includes causing a fluid input to continuously flow to the first electrode and biasing the first, second and third electrodes to a first voltage to cause a portion of the fluid input to spread across the second and third electrodes. The method further includes biasing the second electrode to a second voltage different from the first voltage to form a droplet on the third electrode, the droplet being separate from the fluid input.

8 citations


Cited by
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Journal ArticleDOI
TL;DR: A review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena as mentioned in this paper.
Abstract: Microfabricated integrated circuits revolutionized computation by vastly reducing the space, labor, and time required for calculations. Microfluidic systems hold similar promise for the large-scale automation of chemistry and biology, suggesting the possibility of numerous experiments performed rapidly and in parallel, while consuming little reagent. While it is too early to tell whether such a vision will be realized, significant progress has been achieved, and various applications of significant scientific and practical interest have been developed. Here a review of the physics of small volumes (nanoliters) of fluids is presented, as parametrized by a series of dimensionless numbers expressing the relative importance of various physical phenomena. Specifically, this review explores the Reynolds number Re, addressing inertial effects; the Peclet number Pe, which concerns convective and diffusive transport; the capillary number Ca expressing the importance of interfacial tension; the Deborah, Weissenberg, and elasticity numbers De, Wi, and El, describing elastic effects due to deformable microstructural elements like polymers; the Grashof and Rayleigh numbers Gr and Ra, describing density-driven flows; and the Knudsen number, describing the importance of noncontinuum molecular effects. Furthermore, the long-range nature of viscous flows and the small device dimensions inherent in microfluidics mean that the influence of boundaries is typically significant. A variety of strategies have been developed to manipulate fluids by exploiting boundary effects; among these are electrokinetic effects, acoustic streaming, and fluid-structure interactions. The goal is to describe the physics behind the rich variety of fluid phenomena occurring on the nanoliter scale using simple scaling arguments, with the hopes of developing an intuitive sense for this occasionally counterintuitive world.

4,044 citations

Journal ArticleDOI
TL;DR: An overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows is provided, highlighting topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.
Abstract: Microfluidic devices for manipulating fluids are widespread and finding uses in many scientific and industrial contexts. Their design often requires unusual geometries and the interplay of multiple physical effects such as pressure gradients, electrokinetics, and capillarity. These circumstances lead to interesting variants of well-studied fluid dynamical problems and some new fluid responses. We provide an overview of flows in microdevices with focus on electrokinetics, mixing and dispersion, and multiphase flows. We highlight topics important for the description of the fluid dynamics: driving forces, geometry, and the chemical characteristics of surfaces.

3,307 citations

01 May 2005

2,648 citations

Journal ArticleDOI
TL;DR: IDSA considers adherence to these guidelines to be voluntary, with the ultimate determination regarding their application to be made by the physician in the light of each patient's individual circumstances.
Abstract: It is important to realize that guidelines cannot always account for individual variation among patients. They are not intended to supplant physician judgment with respect to particular patients or special clinical situations. IDSA considers adherence to these guidelines to be voluntary, with the ultimate determination regarding their application to be made by the physician in the light of each patient's individual circumstances.

2,367 citations

Journal ArticleDOI
TL;DR: In this paper, the authors compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high.
Abstract: Electrowetting has become one of the most widely used tools for manipulating tiny amounts of liquids on surfaces. Applications range from 'lab-on-a-chip' devices to adjustable lenses and new kinds of electronic displays. In the present article, we review the recent progress in this rapidly growing field including both fundamental and applied aspects. We compare the various approaches used to derive the basic electrowetting equation, which has been shown to be very reliable as long as the applied voltage is not too high. We discuss in detail the origin of the electrostatic forces that induce both contact angle reduction and the motion of entire droplets. We examine the limitations of the electrowetting equation and present a variety of recent extensions to the theory that account for distortions of the liquid surface due to local electric fields, for the finite penetration depth of electric fields into the liquid, as well as for finite conductivity effects in the presence of AC voltage. The most prominent failure of the electrowetting equation, namely the saturation of the contact angle at high voltage, is discussed in a separate section. Recent work in this direction indicates that a variety of distinct physical effects?rather than a unique one?are responsible for the saturation phenomenon, depending on experimental details. In the presence of suitable electrode patterns or topographic structures on the substrate surface, variations of the contact angle can give rise not only to continuous changes of the droplet shape, but also to discontinuous morphological transitions between distinct liquid morphologies. The dynamics of electrowetting are discussed briefly. Finally, we give an overview of recent work aimed at commercial applications, in particular in the fields of adjustable lenses, display technology, fibre optics, and biotechnology-related microfluidic devices.

1,962 citations