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Channel Dimensions (channel + dimension)
Selected AbstractsBehaviour of a Moving Droplet under Electrowetting Actuation: Numerical SimulationTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2006K. Mohseni Abstract Numerical simulation of droplet transport in microchannels under electrostatic actuation is investigated. Volume-of-Fluid (VOF) technique is employed, in which electrowetting effects are implemented through Lippmann's relation in the form of modified contact angles at the boundary. A velocity of about 35 mm/s is achieved with the actuation of 40 V. The droplet flow under electrowetting actuation is characterized for the majority of the process parameters such as actuation voltage, channel dimension, electrode size, and resultant velocity. On étudie la simulation numérique du transport de gouttelettes dans des microcanaux lors d'une actuation électrostatique. On emploie la technique des volumes de fluide (VOF), dans laquelle les effets de l'électromouillage sont introduits dans la relation de Lippmann sous la forme d'angles de contact modifiés à la frontière. Une vitesse d'environ 35 mm/s est atteinte avec une actuation de 40 V. L'écoulement des gouttelettes dans l'actuation électromouillante est caractérisé pour la majorité des paramètres de procédé, tels que le voltage d'actuation, la dimension des canaux, la taille des électrodes et la vitesse résultante. [source] Wolves, trophic cascades, and rivers in the Olympic National Park, USAECOHYDROLOGY, Issue 2 2008Robert L. Beschta Abstract Gray wolves (Canis lupus) were extirpated in the early 1900s from the Olympic Peninsula of northwestern Washington. Thus, we studied potential cascading effects of wolf removal by undertaking a retrospective study of Roosevelt elk (Cervus elaphus) populations, riparian forests, and river channel morphology. For three riparian sites within the western portion of Olympic National Park, the age structure of black cottonwood and bigleaf maple indicated a pattern of significantly decreased recruitment (growth of seedlings/sprouts into tall saplings and trees) associated with intensive elk browsing in the decades following the loss of wolves. At a riparian site outside the park, which represented a refugium from elk browsing, cottonwood recruitment has been ongoing during the 20th century, indicating that climate and flow regimes, in the absence of intensive herbivory, have not limited the establishment and growth of this deciduous woody species. Using 1994 orthophotos, we also measured channel dimensions and planform morphology of 8-km-long river reaches at each vegetation sampling site and an additional reach outside the park. Channels inside the park versus those outside the park had greater percent braiding (37 vs 2%) and larger ratios of active channel width/wetted width (3·0 vs 1·5 m/m). Results for western Olympic National Park were consistent with a truncated trophic cascade hypothesis whereby ungulate browsing following the extirpation of wolves caused significant long-term impacts to riparian plant communities which, in turn, allowed increased riverbank erosion and channel widening to occur. Copyright © 2008 John Wiley & Sons, Ltd. [source] Numerical studies of electrokinetic control of DNA concentration in a closed-end microchannelELECTROPHORESIS, Issue 5 2010Yasaman Daghighi Abstract A major challenge in lab-on-a-chip devices is how to concentrate sample molecules from a dilute solution, which is critical to the effectiveness and the detection limit of on-chip bio-chemical reactions. A numerical study of sample concentration control by electrokinetic microfluidic means in a closed-end microchannel is presented in this paper. The present method provides a simple and efficient way of concentration control by using electrokinetic trapping of a charged species of interest, controlling liquid flow and separating different sample molecules in the microchannel. The electrokinetic-concentration process and the controlled transport of the sample molecules are numerically studied. In this system, in addition to the electroosmotic flow and the electrophoresis, the closed-end of the chamber causes velocity variation at both ends of the channel and induces a pressure gradient and the associated fluid movement in the channel. The combined effects determine the final concentration field of the sample molecules. The influences of a number of parameters such as the channel dimensions, electrode size and the applied electric field are investigated. [source] Design, process, and performance of all-epitaxial normally-off SiC JFETsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2009Rajesh K. Malhan Abstract This paper reviews the normally-off (N - off) and normally-on (N - on) SiC junction field effect transistor (JFET) concepts and presents an innovative all-epitaxial double-gate trench JFET (DGTJFET) structure. The DGTJFET design combines the advantages of lateral and buried gate JFET concepts. The lateral JFET advantage is the epitaxial definition of the channel width and the buried gate JFET advantage is the small cell size. In the DGTJFET process the epitaxial embedded growth in trenches facilitates the small cell pitch and the vertical direction of the channel. A detailed numerical simulation analysis compares the potential of the DGTJFET design with reported lateral channel and buried gate JFET structures. Migration enhanced embedded epitaxy (ME3) and planarization processes were developed to realize narrow cell pitch DGTJFETs for high-density power integration. The highly doped vertical channel of the DGTJFET defined by the ME3 growth process makes it possible to accurately control the sub-micron channel dimensions in order to realize a low specific on-state resistance (RON) and a high saturation current capability. The anisotropic nature of SiC is taken into account for the channel design considerations. The successful application of the new process technologies for the development of the all-epitaxial DGTJFETs is discussed. Fabricated 5.5 ,m cell pitch 4H-SiC DGTJFETs demonstrate the saturation current density capability of more than 1000 A/cm2. N - off and N - on DGTJFETs with 2.25 mm squared chip size and 9.5 ,m cell pitch output 15 A and 20 A at gate voltage of 2.5 V and drain voltage of 5.0 V. The specific RON of the N - off and N - on DGTJFETs is at room temperature 8.1 m , cm2 and 6.3 m, cm2, respectively, indicating that N - off devices can be realized at the expense of a slight increase in specific RON of approximately 25%. DGTJFETs with a 13 ,m drift layer doped to 5.0 × 1015 cm,3 are demonstrated with a breakdown voltage in the range of 1200 V to 1550 V at the wafer level with a leakage current below 10 ,A. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Multienzyme catalysis in microfluidic biochipsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2003Moo-Yeal Lee Abstract The attachment of enzymes to glass microfluidic channels has been achieved using a highly reactive poly(maleic anhydride- alt -,-olefin) (PMA)-based coating that is supplied to the microchannel in a toluene solution. The PMA reacts with 3-aminopropyltriethoxysilane groups linked to the glass surface to form a matrix that enables additional maleic anhydride groups to react with free amino groups on enzymes to give a mixed covalent,noncovalent immobilization support. Using a simple T-channel microfluidic design, with reaction channel dimensions of 200 ,m wide (at the center), 15 ,m deep, and 30 mm long giving a reaction volume of 90 nL, soybean peroxidase (SBP) was attached at an amount up to 0.6 ,g/channel. SBP-catalyzed oxidation of p -cresol was performed in aqueous buffer (with 20% [v/v], dimethylformamide) containing H2O2, with microfluidic transport enabled by electroosmotic flow (EOF). Michaelis,Menten kinetics were obtained with Km and Vmax values of 0.98 mM and 0.21 ,mol H2O2 converted/mg SBP per minute, respectively. These values are nearly identical to nonimmobilized SBP kinetics in aqueous,DMF solutions in 20-,L volumes in 384-well plates and 5-mL reaction volumes in 20-mL scintillation vials. These results indicate that SBP displays intrinsically native activity even in the immobilized form at the microscale, and further attests to the mild immobilization conditions afforded by PMA. Bienzymic and trienzymic reactions were also performed in the microfluidic biochip. Specifically, a combined Candida antarctica lipase B,SBP bienzymic system was used to convert tolyl acetate into poly(p -cresol), and an invertase,glucose oxidase SBP trienzymic system was used to take sucrose and generate H2O2 for SBP-catalyzed synthesis of poly(p -cresol). © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 83: 20,28, 2003. [source] Mixing in Sub-micron DuctsCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 3 2004E.B. Nauman Abstract This paper considers a class of fluidic devices, anticipated to become important in the near future, where characteristic channel dimensions are in the range 0.1 to 1.0 microns. Typical current applications of microfluidics have device sizes of 10 to 100 micron, this is sufficiently small to force laminar flow but not so small that molecular diffusion is a dominant factor. In the smaller devices contemplated here, diffusion is important and existing mixing strategies and correlations are no longer applicable. Novel results and interesting complexities are discussed for reactive, single and two phase flows in sub-micron channels. [source] | |||||||||||||