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Sample records for reversed electroosmotic flow

  1. Charge Inversion and Flow Reversal in a Nanochannel Electro-osmotic Flow

    NASA Astrophysics Data System (ADS)

    Qiao, R.; Aluru, N. R.

    2004-05-01

    Ion distribution and velocity profiles for electro-osmotic flow in a 3.49nm wide slit channel with a surface charge density of -0.285 C/m2 are studied using molecular dynamics simulations. Simulation results indicate that the concentration of the co-ion exceeds that of the counterion in the region 0.53nm away from the channel wall, and the electro-osmotic flow is in the opposite direction to that predicted by the classical continuum theory. The charge inversion is mainly caused by the molecular nature of water and ions. The flow reversal is caused by the immobilization of counterions adsorbed on the channel wall and due to the charge inversion phenomena.

  2. Separation of chemical warfare agent degradation products by the reversal of electroosmotic flow in capillary electrophoresis.

    PubMed

    Nassar, A E; Lucas, S V; Jones, W R; Hoffland, L D

    1998-03-15

    We report the development of analyses for nerve agent degradation products or related species by the reversal of electroosmotic flow in capillary electrophoresis (CE). The developed methods were used in this laboratory for analysis of samples in the second and third official proficiency tests (International Round-Robins) for the Provisional Technical Secretariat/Preparatory Commission for the Organization for the Prohibition of Chemical Weapons, and those results are reported here. Analytes studied include methylphosphonic acid (a dibasic acid), the monoisopropyl ester of ethylphosphonic acid, and the monoalkyl esters of methylphosphonic acid (R = ethyl, isopropyl, isobutyl, pinacolyl (3,3-dimethyl-2-butyl), cyclohexyl, and 2-ethylhexyl). The cationic surfactants used here for the reversal of electroosmotic flow are didodecyldimethylammonium hydroxide and cetyltrimethylammonium hydroxide. CE methods using conductivity or indirect UV detection provide a good separation efficiency and very high sensitivity for the analysis of such compounds. The detection limits for these species were about 75 micrograms/L when using conductivity detection and about 100 micrograms/L when using indirect UV detection. Because pH plays an important role in the CE separation of the alkylphosphonic acids and their monoesters, the influence of pH on these separation systems was investigated. Electrolytes were stable for at least 3 months. Excellent separation efficiency and freedom from interference due to common anions were obtained in the developed methods which typically achieved complete separations in less than 3 min. The method was applied to aqueous leachates of soil, wipes of surfaces, and vegetation sampled from a field site known to have been exposed to nerve agents and subsequently cleaned up. The data from these environmental samples indicated that the method can be expected to be useful for environmental monitoring.

  3. Microfluidic point-of-care blood panel based on a novel technique: Reversible electroosmotic flow.

    PubMed

    Mohammadi, Mahdi; Madadi, Hojjat; Casals-Terré, Jasmina

    2015-09-01

    A wide range of diseases and conditions are monitored or diagnosed from blood plasma, but the ability to analyze a whole blood sample with the requirements for a point-of-care device, such as robustness, user-friendliness, and simple handling, remains unmet. Microfluidics technology offers the possibility not only to work fresh thumb-pricked whole blood but also to maximize the amount of the obtained plasma from the initial sample and therefore the possibility to implement multiple tests in a single cartridge. The microfluidic design presented in this paper is a combination of cross-flow filtration with a reversible electroosmotic flow that prevents clogging at the filter entrance and maximizes the amount of separated plasma. The main advantage of this design is its efficiency, since from a small amount of sample (a single droplet [Formula: see text]10 μl) almost 10% of this (approx 1 μl) is extracted and collected with high purity (more than 99%) in a reasonable time (5-8 min). To validate the quality and quantity of the separated plasma and to show its potential as a clinical tool, the microfluidic chip has been combined with lateral flow immunochromatography technology to perform a qualitative detection of the thyroid-stimulating hormone and a blood panel for measuring cardiac Troponin and Creatine Kinase MB. The results from the microfluidic system are comparable to previous commercial lateral flow assays that required more sample for implementing fewer tests.

  4. Microfluidic point-of-care blood panel based on a novel technique: Reversible electroosmotic flow

    PubMed Central

    Mohammadi, Mahdi; Madadi, Hojjat; Casals-Terré, Jasmina

    2015-01-01

    A wide range of diseases and conditions are monitored or diagnosed from blood plasma, but the ability to analyze a whole blood sample with the requirements for a point-of-care device, such as robustness, user-friendliness, and simple handling, remains unmet. Microfluidics technology offers the possibility not only to work fresh thumb-pricked whole blood but also to maximize the amount of the obtained plasma from the initial sample and therefore the possibility to implement multiple tests in a single cartridge. The microfluidic design presented in this paper is a combination of cross-flow filtration with a reversible electroosmotic flow that prevents clogging at the filter entrance and maximizes the amount of separated plasma. The main advantage of this design is its efficiency, since from a small amount of sample (a single droplet ∼10 μl) almost 10% of this (approx 1 μl) is extracted and collected with high purity (more than 99%) in a reasonable time (5–8 min). To validate the quality and quantity of the separated plasma and to show its potential as a clinical tool, the microfluidic chip has been combined with lateral flow immunochromatography technology to perform a qualitative detection of the thyroid-stimulating hormone and a blood panel for measuring cardiac Troponin and Creatine Kinase MB. The results from the microfluidic system are comparable to previous commercial lateral flow assays that required more sample for implementing fewer tests. PMID:26396660

  5. Electroosmotic shear flow in microchannels.

    PubMed

    Mampallil, Dileep; van den Ende, Dirk

    2013-01-15

    We generate and study electroosmotic shear flow in microchannels. By chemically or electrically modifying the surface potential of the channel walls a shear flow component with controllable velocity gradient can be added to the electroosmotic flow caused by double layer effects at the channel walls. Chemical modification is obtained by treating the channel wall with a cationic polymer. In case of electric modification, we used gate electrodes embedded in the channel wall. By applying a voltage to the gate electrode, the zeta potential can be varied and a controllable, uniform shear stress can be applied to the liquid in the channel. The strength of the shear stress depends on both the gate voltage and the applied field which drives the electroosmotic shear flow. Although the stress range is still limited, such a microchannel device can be used in principle as an in situ micro-rheometer for lab on a chip purposes.

  6. Joule heating effects on electroosmotic entry flow.

    PubMed

    Prabhakaran, Rama Aravind; Zhou, Yilong; Patel, Saurin; Kale, Akshay; Song, Yongxin; Hu, Guoqing; Xuan, Xiangchun

    2017-03-01

    Electroosmotic flow is the transport method of choice in microfluidic devices over traditional pressure-driven flow. To date, however, studies on electroosmotic flow have been almost entirely limited to inside microchannels. This work presents the first experimental study of Joule heating effects on electroosmotic fluid entry from the inlet reservoir (i.e., the well that supplies fluids and samples) to the microchannel in a polymer-based microfluidic chip. Electrothermal fluid circulations are observed at the reservoir-microchannel junction, which grow in size and strength with the increasing alternating current to direct current voltage ratio. Moreover, a 2D depth-averaged numerical model is developed to understand the effects of Joule heating on fluid temperature and flow fields in electrokinetic microfluidic chips. This model overcomes the problems encountered in previous unrealistic 2D and costly 3D models, and is able to predict the observed electroosmotic entry flow patterns with a good agreement.

  7. Ionic Origin of Electro-osmotic Flow Hysteresis

    NASA Astrophysics Data System (ADS)

    Lim, Chun Yee; Lim, An Eng; Lam, Yee Cheong

    2016-02-01

    Electro-osmotic flow, the driving of fluid at nano- or micro- scales with electric field, has found numerous applications, ranging from pumping to chemical and biomedical analyses in micro-devices. Electro-osmotic flow exhibits a puzzling hysteretic behavior when two fluids with different concentrations displace one another. The flow rate is faster when a higher concentration solution displaces a lower concentration one as compared to the flow in the reverse direction. Although electro-osmotic flow is a surface phenomenon, rather counter intuitively we demonstrate that electro-osmotic flow hysteresis originates from the accumulation or depletion of pH-governing minority ions in the bulk of the fluid, due to the imbalance of electric-field-induced ion flux. The pH and flow velocity are changed, depending on the flow direction. The understanding of electro-osmotic flow hysteresis is critical for accurate fluid flow control in microfluidic devices, and maintaining of constant pH in chemical and biological systems under an electric field.

  8. Ionic Origin of Electro-osmotic Flow Hysteresis

    PubMed Central

    Lim, Chun Yee; Lim, An Eng; Lam, Yee Cheong

    2016-01-01

    Electro-osmotic flow, the driving of fluid at nano- or micro- scales with electric field, has found numerous applications, ranging from pumping to chemical and biomedical analyses in micro-devices. Electro-osmotic flow exhibits a puzzling hysteretic behavior when two fluids with different concentrations displace one another. The flow rate is faster when a higher concentration solution displaces a lower concentration one as compared to the flow in the reverse direction. Although electro-osmotic flow is a surface phenomenon, rather counter intuitively we demonstrate that electro-osmotic flow hysteresis originates from the accumulation or depletion of pH-governing minority ions in the bulk of the fluid, due to the imbalance of electric-field-induced ion flux. The pH and flow velocity are changed, depending on the flow direction. The understanding of electro-osmotic flow hysteresis is critical for accurate fluid flow control in microfluidic devices, and maintaining of constant pH in chemical and biological systems under an electric field. PMID:26923197

  9. Electroosmotic Flow in Nanofluidic Channels

    PubMed Central

    2015-01-01

    We report the measurement of electroosmotic mobilities in nanofluidic channels with rectangular cross sections and compare our results with theory. Nanofluidic channels were milled directly into borosilicate glass between two closely spaced microchannels with a focused ion beam instrument, and the nanochannels had half-depths (h) of 27, 54, and 108 nm and the same half-width of 265 nm. We measured electroosmotic mobilities in NaCl solutions from 0.1 to 500 mM that have Debye lengths (κ–1) from 30 to 0.4 nm, respectively. The experimental electroosmotic mobilities compare quantitatively to mobilities calculated from a nonlinear solution of the Poisson–Boltzmann equation for channels with a parallel-plate geometry. For the calculations, ζ-potentials measured in a microchannel with a half-depth of 2.5 μm are used and range from −6 to −73 mV for 500 to 0.1 mM NaCl, respectively. For κh > 50, the Smoluchowski equation accurately predicts electroosmotic mobilities in the nanochannels. However, for κh < 10, the electrical double layer extends into the nanochannels, and due to confinement within the channels, the average electroosmotic mobilities decrease. At κh ≈ 4, the electroosmotic mobilities in the 27, 54, and 108 nm channels exhibit maxima, and at 0.1 mM NaCl, the electroosmotic mobility in the 27 nm channel (κh = 1) is 5-fold lower than the electroosmotic mobility in the 2.5 μm channel (κh = 100). PMID:25365680

  10. Electroosmotic Entry Flow with Joule Heating Effects

    NASA Astrophysics Data System (ADS)

    Prabhakaran, Rama; Kale, Akshay; Xuan, Xiangchun

    Electrokinetic flow, which transports liquids by electroosmosis and samples by electrophoresis, is the transport method of choice in microfluidic chips over traditional pressure-driven flows. Studies on electrokinetic flows have so far been almost entirely limited to inside microchannels. Very little work has been done on the electroosmotic fluid entry from a reservoir to a microchannel, which is the origin of all fluid and sample motions in microchips. We demonstrate in this talk that strong vortices of opposite circulating directions can be generated in electroosmotic entry flows. We also develop a two-dimensional depth-averaged numerical model of the entire microchip to predict and understand the fluid temperature and flow fields at the reservoir-microchannel junction.

  11. Electroosmotic flow hysteresis for dissimilar ionic solutions

    PubMed Central

    Lim, An Eng; Lam, Yee Cheong

    2015-01-01

    Electroosmotic flow (EOF) with two or more fluids is commonly encountered in various microfluidics applications. However, no investigation has hitherto been conducted to investigate the hysteretic or flow direction-dependent behavior during the displacement flow of solutions with dissimilar ionic species. In this investigation, electroosmotic displacement flow involving dissimilar ionic solutions was studied experimentally through a current monitoring method and numerically through finite element simulations. The flow hysteresis can be characterized by the turning and displacement times; turning time refers to the abrupt gradient change of current-time curve while displacement time is the time for one solution to completely displace the other solution. Both experimental and simulation results illustrate that the turning and displacement times for a particular solution pair can be directional-dependent, indicating that the flow conditions in the microchannel are not the same in the two different flow directions. The mechanics of EOF hysteresis was elucidated through the theoretical model which includes the ionic mobility of each species, a major governing parameter. Two distinct mechanics have been identified as the causes for the EOF hysteresis involving dissimilar ionic solutions: the widening/sharpening effect of interfacial region between the two solutions and the difference in ion concentration distributions (and thus average zeta potentials) in different flow directions. The outcome of this investigation contributes to the fundamental understanding of flow behavior in microfluidic systems involving solution pair with dissimilar ionic species. PMID:25945139

  12. Electro-osmotic flow in polygonal ducts.

    PubMed

    Wang, Chang-Yi; Chang, Chien-Cheng

    2011-06-01

    The paper presents semi-analytical solutions to electro-osmotic (EO) flow through polygonal ducts under the Debye-Hückel approximation. Analytical series solutions assisted with numerical collocations are found to yield very fast convergence. The solutions have practical applications as the pores of EO membranes are mostly hexagonal, stacked densely in a beehive-like matrix. In addition, we develop simple asymptotic approximations that would be applicable to all EO tube flows of small as well as large dimensionless electrokinetic width. This facilitates investigation of analytical structures of general EO flows in all shapes of tubes, including the present geometries. In particular, for thick electrical double layers, the flow rate of EO is related to the corresponding viscous Poiseuille flow rate, while for thin electrical double layers, the flow rate is shown to be characterized by the cross-sectional area and the perimeter length of the tubes.

  13. Electro-osmotic flow in bicomponent fluids

    NASA Astrophysics Data System (ADS)

    Bazarenko, Andrei; Sega, Marcello

    The electroosmotic flow (EOF) is a widely used technique that uses the action of external electric fields on solvated ions to move fluids around in microfluidics devices. For homogeneous fluids, the characteristics of the flow can be well approximated by simple analytical models, but in multicomponent systems such as oil-in-water droplets one has to rely to numerical simulations. The purpose of this study is to investigate physical properties of the EOF in a bicomponent fluid by solving the coupled equations of motions of explicit ions in interaction with a continuous model of the flow. To do so we couple the hydrodynamics equations as solved by a Shan-Chen Lattice-Boltzmann method to the molecular dynamics of the ions. The presence of explicit ions allows us to go beyond the simple Poisson-Boltzmann approximations, and investigate a variety of EOF regimes. ETN-COLLDENSE (H2020-MCSA-ITN-2014, Grant No. 642774).

  14. Electroosmotic flow in single PDMS nanochannels

    NASA Astrophysics Data System (ADS)

    Peng, Ran; Li, Dongqing

    2016-06-01

    The electroosmotic flow (EOF) velocity in single PDMS nanochannels with dimensions as small as 20 nm is investigated systematically by the current slope method in this paper. A novel method for the fabrication of single nanochannels on PDMS surfaces is developed. The effects of channel size, ionic concentration of the electrolyte solution and electric field on the EOF velocity in single nanochannels are investigated. The results show that the EOF velocity in smaller nanochannels with overlapped electric double layers (EDL) is proportional to the applied electric field but is smaller than the EOF velocity in microchannels under the same applied electric field. The EOF velocity in relatively large nanochannels without the overlap of EDLs is independent of the channel size and is the same as that in microchannels under the same applied electric field. Furthermore, in smaller nanochannels with overlapped EDLs, the EOF velocity depends on the ionic concentration and also on the channel size. The experimental results reported in this paper are valuable for the future studies of electrokinetic nanofluidics.The electroosmotic flow (EOF) velocity in single PDMS nanochannels with dimensions as small as 20 nm is investigated systematically by the current slope method in this paper. A novel method for the fabrication of single nanochannels on PDMS surfaces is developed. The effects of channel size, ionic concentration of the electrolyte solution and electric field on the EOF velocity in single nanochannels are investigated. The results show that the EOF velocity in smaller nanochannels with overlapped electric double layers (EDL) is proportional to the applied electric field but is smaller than the EOF velocity in microchannels under the same applied electric field. The EOF velocity in relatively large nanochannels without the overlap of EDLs is independent of the channel size and is the same as that in microchannels under the same applied electric field. Furthermore, in

  15. Electroosmotic flow rectification in pyramidal-pore mica membranes.

    PubMed

    Jin, Pu; Mukaibo, Hitomi; Horne, Lloyd P; Bishop, Gregory W; Martin, Charles R

    2010-02-24

    We demonstrate here a new electrokinetic phenomenon, Electroosmotic flow (EOF) rectification, in synthetic membranes containing asymmetric pores. Mica membranes with pyramidally shaped pores prepared by the track-etch method were used. EOF was driven through these membranes by using an electrode in solutions on either side to pass a constant ionic current through the pores. The velocity of EOF depends on the polarity of the current. A high EOF velocity is obtained when the polarity is such that EOF is driven from the larger base opening to the smaller tip opening of the pore. A smaller EOF velocity is obtained when the polarity is reversed such that EOF goes from tip to base. We show that this rectified EOF phenomenon is the result of ion current-rectification observed in such asymmetric-pore membranes.

  16. Electroosmotic Flow Rectification in Pyramidal-Pore Mica Membranes

    SciTech Connect

    Jin, P.; Mukaibo, H.; Horne, L.; Bishop, G.; Martin, C. R.

    2010-02-01

    We demonstrate here a new electrokinetic phenomenon, Electroosmotic flow (EOF) rectification, in synthetic membranes containing asymmetric pores. Mica membranes with pyramidally shaped pores prepared by the track-etch method were used. EOF was driven through these membranes by using an electrode in solutions on either side to pass a constant ionic current through the pores. The velocity of EOF depends on the polarity of the current. A high EOF velocity is obtained when the polarity is such that EOF is driven from the larger base opening to the smaller tip opening of the pore. A smaller EOF velocity is obtained when the polarity is reversed such that EOF goes from tip to base. We show that this rectified EOF phenomenon is the result of ion current-rectification observed in such asymmetric-pore membranes.

  17. Electroosmotic flow in microchannels with nanostructures.

    PubMed

    Yasui, Takao; Kaji, Noritada; Mohamadi, Mohamad Reza; Okamoto, Yukihiro; Tokeshi, Manabu; Horiike, Yasuhiro; Baba, Yoshinobu

    2011-10-25

    Here we report that nanopillar array structures have an intrinsic ability to suppress electroosmotic flow (EOF). Currently using glass chips for electrophoresis requires laborious surface coating to control EOF, which works as a counterflow to the electrophoresis mobility of negatively charged samples such as DNA and sodium dodecyl sulfate (SDS) denatured proteins. Due to the intrinsic ability of the nanopillar array to suppress the EOF, we carried out electrophoresis of SDS-protein complexes in nanopillar chips without adding any reagent to suppress protein adsorption and the EOF. We also show that the EOF profile inside a nanopillar region was deformed to an inverse parabolic flow. We used a combination of EOF measurements and fluorescence observations to compare EOF in microchannel, nanochannel, and nanopillar array chips. Our results of EOF measurements in micro- and nanochannel chips were in complete agreement with the conventional equation of the EOF mobility (μ(EOF-channel) = αC(i)(-0.5), where C(i) is the bulk concentration of the i-ions and α differs in micro- and nanochannels), whereas EOF in the nanopillar chips did not follow this equation. Therefore we developed a new modified form of the conventional EOF equation, μ(EOF-nanopillar) ≈ β[C(i) - (C(i)(2)/N(i))], where N(i) is the number of sites available to i-ions and β differs for each nanopillar chip because of different spacings or patterns, etc. The modified equation of the EOF mobility that we proposed here was in good agreement with our experimental results. In this equation, we showed that the charge density of the nanopillar region, that is, the total number of nanopillars inside the microchannel, affected the suppression of EOF, and the arrangement of nanopillars into a tilted or square array had no effect on it.

  18. Highly efficient electroosmotic flow through functionalized carbon nanotube membranes

    NASA Astrophysics Data System (ADS)

    Wu, Ji; Gerstandt, Karen; Majumder, Mainak; Zhan, Xin; Hinds, Bruce J.

    2011-08-01

    Carbon nanotube membranes with inner diameter ranging from 1.5-7 nm were examined for enhanced electroosmotic flow. After functionalization via electrochemical diazonium grafting and carbodiimide coupling reaction, it was found that neutral caffeine molecules can be efficiently pumped via electroosmosis. An electroosmotic velocity as high as 0.16 cm s-1 V-1 has been observed. Power efficiencies were 25-110 fold improved compared to related nanoporous materials, which has important applications in chemical separations and compact medical devices. Nearly ideal electroosmotic flow was seen in the case where the mobile cation diameter nearly matched the inner diameter of the single-walled carbon nanotube resulting in a condition of using one ion is to pump one neutral molecule at equivalent concentrations.

  19. Electro-osmotic flow through a two-dimensional screen-pump filter.

    PubMed

    Liu, Ying-Hong; Kuo, Chih-Yu; Chang, Chien C; Wang, Chang-Yi

    2011-09-01

    The electro-osmotic flow driven by a screen pump, composed of a line array of evenly spaced identical rectangular solid blocks, is investigated under the Debye-Hückel approximation. The geometry of the screen pump is determined by the spacing and aspect ratio of the solid blocks. A constant surface zeta potential is assumed on the block surface. The method of eigenfunction series expansion is applied to solve analytically for the applied electric field, electric charge potential in the fluid, and flow field. Because of the low Reynolds number, Stokes equations are applied for the flow. The analytic result is first confirmed by comparing with the exact solution of the electro-osmotic flow in an infinite channel. Then different geometries of the screen pump and the effect of the electrokinetic width are computed for their influence on the flow rate. Recirculating eddies and reversing flow are found even though the applied electric driving field is unidirectional.

  20. Helmholtz-Smoluchowski velocity for viscoelastic electroosmotic flows.

    PubMed

    Park, H M; Lee, W M

    2008-01-15

    Many biofluids such as blood and DNA solutions are viscoelastic and exhibit extraordinary flow behaviors, not existing in Newtonian fluids. Adopting appropriate constitutive equations these exotic flow behaviors can be modeled and predicted reasonably using various numerical methods. However, the governing equations for viscoelastic flows are not easily solvable, especially for electroosmotic flows where the streamwise velocity varies rapidly from zero at the wall to a nearly uniform velocity at the outside of the very thin electric double layer. In the present investigation, we have devised a simple method to find the volumetric flow rate of viscoelastic electroosmotic flows through microchannels. It is based on the concept of the Helmholtz-Smoluchowski velocity which is widely adopted in the electroosmotic flows of Newtonian fluids. It is shown that the Helmholtz-Smoluchowski velocity for viscoelastic fluids can be found by solving a simple cubic algebraic equation. The volumetric flow rate obtained using this Helmholtz-Smoluchowski velocity is found to be almost the same as that obtained by solving the governing partial differential equations for various viscoelastic fluids.

  1. Numerical analysis of mixing enhancement for micro-electroosmotic flow

    NASA Astrophysics Data System (ADS)

    Tang, G. H.; He, Y. L.; Tao, W. Q.

    2010-05-01

    Micro-electroosmotic flow is usually slow with negligible inertial effects and diffusion-based mixing can be problematic. To gain an improved understanding of electroosmotic mixing in microchannels, a numerical study has been carried out for channels patterned with wall blocks, and channels patterned with heterogeneous surfaces. The lattice Boltzmann method has been employed to obtain the external electric field, electric potential distribution in the electrolyte, the flow field, and the species concentration distribution within the same framework. The simulation results show that wall blocks and heterogeneous surfaces can significantly disturb the streamlines by fluid folding and stretching leading to apparently substantial improvements in mixing. However, the results show that the introduction of such features can substantially reduce the mass flow rate and thus effectively prolongs the available mixing time when the flow passes through the channel. This is a non-negligible factor on the effectiveness of the observed improvements in mixing efficiency. Compared with the heterogeneous surface distribution, the wall block cases can achieve more effective enhancement in the same mixing time. In addition, the field synergy theory is extended to analyze the mixing enhancement in electroosmotic flow. The distribution of the local synergy angle in the channel aids to evaluate the effectiveness of enhancement method.

  2. Electro-osmotic flow over a charged superhydrophobic surface

    NASA Astrophysics Data System (ADS)

    Zhao, Hui

    2010-06-01

    Bubbles can be trapped inside textured structures such as grooves, forming a superhydrophobic surface. A superhydrophobic surface has a large effective hydrodynamic slip length compared to a smooth hydrophobic surface and holds the promise of enhancing electrokinetic flows that find many interesting applications in microfluidics. However, recent theoretical studies suggested that electro-osmotic flows over a weakly charged superhydrophobic surface [the zeta potential of the surface is smaller than the thermal potential (25 mV)] can only be enhanced when liquid-gas interfaces are charged [T. M. Squires, Phys. Fluids 20, 092105 (2008); Bahga , J. Fluid Mech. 644, 245 (2010)]. So far there is little work reported when the zeta potential of the surface is comparable or even larger than the thermal potential. In this paper we numerically investigate electro-osmotic flows over a periodically striped slip-stick surface by solving the standard Poisson-Nernst-Planck equations. Our results indicate that at large zeta potentials, even if liquid-gas interfaces are charged, the nonuniform surface conduction due to the mismatch between surface conductions over no-shear and no-slip regions leads to electric field lines penetrating the double layer and thus the nonuniform surface conduction weakens the tangential component of the electric field which primarily drives electro-osmotic flows. Our results imply that, in the presence of strong nonuniform surface conduction, enhanced electro-osmotic flows over a superhydrophobic surface are possible only in certain conditions. In particular, the enhancement due to the slip can potentially be lost at large zeta potentials. Similar loss of the enhancement of a charged particle’s electrophoretic mobility due to the slip was reported by Khair and Squires [Phys. Fluids 21, 042001 (2009)].

  3. Electro-osmotic flow of semidilute polyelectrolyte solutions

    NASA Astrophysics Data System (ADS)

    Uematsu, Yuki; Araki, Takeaki

    2013-09-01

    We investigate electro-osmosis in aqueous solutions of polyelectrolytes using mean-field equations. A solution of positively charged polyelectrolytes is confined between two negatively charged planar surfaces, and an electric field is applied parallel to the surfaces. When electrostatic attraction between the polymer and the surface is strong, the polymers adhere to the surface, forming a highly viscous adsorption layer that greatly suppresses the electro-osmosis. Conversely, electro-osmosis is enhanced by depleting the polymers from the surfaces. We also found that the electro-osmotic flow is invertible when the electrostatic potential decays to its bulk value with the opposite sign. These behaviors are well explained by a simple mathematical form of the electro-osmotic coefficient.

  4. Electro-osmotic flows in rectangular cavities

    NASA Astrophysics Data System (ADS)

    Meleshko, Viatcheslav; Trofimchuk, Alexandre; Gourjii, Alexandre; Bezym'yana, Elina

    2010-11-01

    The talk presents the results of investigation of the microfluidics mixing processes in a rectangular cavity flows induced by elctro-osmotic excitation. Enhanced mixing plays an important role in biological and chemical pharmaceutics analysis in microfluidics systems. Analytical solution is presented for the velocity field in the cavity under various electric potential distributions. The location of the periodic points in the flow are accurately established and the structure of stable and unstable manifolds is discussed. The optimal form of excitation is suggested in order to obtain most effective mixing regime in the cavity. The regular and chaotic regions are identified under various condition of excitation. Finally, we compare numerical and analytical solutions with the results of laboratory experiments for real microfluidic flows.

  5. Electro-osmotic flow of a model electrolyte.

    PubMed

    Zhu, Wei; Singer, Sherwin J; Zheng, Zhi; Conlisk, A T

    2005-04-01

    Electro-osmotic flow is studied by nonequilibrium molecular dynamics simulations in a model system chosen to elucidate various factors affecting the velocity profile and facilitate comparison with existing continuum theories. The model system consists of spherical ions and solvent, with stationary, uniformly charged walls that make a channel with a height of 20 particle diameters. We find that hydrodynamic theory adequately describes simple pressure-driven (Poiseuille) flow in this model. However, Poisson-Boltzmann theory fails to describe the ion distribution in important situations, and therefore continuum fluid dynamics based on the Poisson-Boltzmann ion distribution disagrees with simulation results in those situations. The failure of Poisson-Boltzmann theory is traced to the exclusion of ions near the channel walls resulting from reduced solvation of the ions in that region. When a corrected ion distribution is used as input for hydrodynamic theory, agreement with numerical simulations is restored. An analytic theory is presented that demonstrates that repulsion of the ions from the channel walls increases the flow rate, and attraction to the walls has the opposite effect. A recent numerical study of electro-osmotic flow is reanalyzed in the light of our findings, and the results conform well to our conclusions for the model system.

  6. Measurement of electroosmotic flow in capillary and microchip electrophoresis.

    PubMed

    Wang, Wei; Zhou, Fang; Zhao, Liang; Zhang, Jian-Rong; Zhu, Jun-Jie

    2007-11-02

    Microfluidics is the science and technology of systems that process or manipulate small amounts of fluids, using channels with dimensions of tens of micrometers. Electroosmotic flow (EOF) is an important characteristic of fluids in microchannels. In this paper, EOF generation, effects on separation and definition of EOF are introduced. And EOF measurement methods on capillary electrophoresis (CE) and microchip CE are systematically reviewed based on detection principle, hallmarks of EOF measurement methods are presented, the devices and signals are also schematically described. This paper offers researchers a guidance to obtain an estimate of EOF mobility in capillary and microchip electrophoresis.

  7. Analyses of gibberellins in coconut (Cocos nucifera L.) water by partial filling-micellar electrokinetic chromatography-mass spectrometry with reversal of electroosmotic flow.

    PubMed

    Ge, Liya; Yong, Jean Wan Hong; Tan, Swee Ngin; Hua, Lin; Ong, Eng Shi

    2008-05-01

    In this paper, we present the results of simultaneous screening of eight gibberellins (GAs) in coconut (Cocos nucifera L.) water by MEKC directly coupled to ESI-MS detection. During the development of MEKC-MS, partial filling (PF) was used to prevent the micelles from reaching the mass spectrometer as this is detrimental to the MS signal, and a cationic surfactant, cetyltrimethylammonium hydroxide, was added to the electrolyte to reverse the EOF. On the basis of the resolution of the neighboring peaks, different parameters (i.e., the pH and concentration of buffer, surfactant concentrations, length of the injected micellar plug, organic modifier, and applied separation voltage) were optimized to achieve a satisfactory PF-MEKC separation of eight GA standards. Under optimum conditions, a baseline separation of GA standards, including GA1, GA3, GA5, GA6, GA7, GA9, GA12, and GA13, was accomplished within 25 min. Satisfactory results were obtained in terms of precision (RSD of migration time below 0.9%), sensitivity (LODs in the range of 0.8-1.9 microM) and linearity (R2 between 0.981 and 0.997). MS/MS with multiple reaction monitoring (MRM) detection was carried out to obtain sufficient selectivity. PF-MEKC-MS/MS allowed the direct identification and confirmation of the GAs presented in coconut water (CW) sample after SPE, while, the quantitative analysis of GAs was performed by PF-MEKC-MS approach. GA1 and GA3 were successfully detected and quantified in CW. It is anticipated that the current PF-MEKC-MS method can be applicable to analyze GAs in a wide range of biological samples.

  8. Electro-osmotic flow of Eyring fluids in a circular microtube with Navier's slip boundary condition

    NASA Astrophysics Data System (ADS)

    Tan, Zhen; Liu, Jie

    2017-08-01

    Electro-osmotic flows of non-Newtonian fluids play an important role in microdevices and microfluidic systems. A theoretical and numerical analyses are conducted to explore the characteristics of electro-osmotic flow of non-Newtonian Eyring fluids in a circular microtube under the Navier's slip boundary condition. The exact solution of velocity distribution as well as corresponding approximate solution is obtained. The effects of slip length, electrokinetic parameter and non-Newtonian characteristics on the electro-osmotic flows are discussed and plotted graphically.

  9. Multi-scale simulation method for electroosmotic flows

    NASA Astrophysics Data System (ADS)

    Guo, Lin; Chen, Shiyi; Robbins, Mark O.

    2016-10-01

    Electroosmotic transport in micro-and nano- channels has important applications in biological and engineering systems but is difficult to model because nanoscale structure near surfaces impacts flow throughout the channel. We develop an efficient multi-scale simulation method that treats near-wall and bulk subdomains with different physical descriptions and couples them through a finite overlap region. Molecular dynamics is used in the near-wall subdomain where the ion density is inconsistent with continuum models and the discrete structure of solvent molecules is important. In the bulk region the solvent is treated as a continuum fluid described by the incompressible Navier-Stokes equations with thermal fluctuations. A discrete description of ions is retained because of the low density of ions and the long range of electrostatic interactions. A stochastic Euler-Lagrangian method is used to simulate the dynamics of these ions in the implicit continuum solvent. The overlap region allows free exchange of solvent and ions between the two subdomains. The hybrid approach is validated against full molecular dynamics simulations for different geometries and types of flows.

  10. A handy liquid metal based electroosmotic flow pump.

    PubMed

    Gao, Meng; Gui, Lin

    2014-06-07

    A room temperature liquid metal based electroosmotic flow (EOF) pump has been proposed in this work. This low-cost EOF pump is convenient for both fabrication and integration. It utilizes polydimethylsiloxane (PDMS) microchannels filled with the liquid-metal as non-contact pump electrodes. The electrode channels are fabricated symmetrically to both sides of the pumping channel, having no contact with the pumping channel. To test the pumping performance of the EOF pump, the mean flow velocities of the fluid (DI water) in the EOF pumps were experimentally measured by tracing the fluorescent microparticles in the flow. To provide guidance for designing a low voltage EOF pump, parametric studies on dimensions of the electrode and pumping channels were performed in this work. According to the experimental results, the pumping speed can reach 5.93 μm s(-1) at a driving voltage of only 1.6 V, when the gap between the electrode and the pumping channel is 20 μm. Injecting a room temperature liquid metal into microchannels can provide a simple, rapid, low-cost but accurately self-aligned way to fabricate microelectrodes for EOF pumps, which is a promising method to achieve the miniaturization and integration of the EOF pump in microfluidic systems. The non-contact liquid electrodes have no influence on the fluid in the pumping channel when pumping, reducing Joule heat generation and preventing gas bubble formation at the surface of electrodes. The pump has great potential to drive a wide range of fluids, such as drug reagents, cell suspensions and biological macromolecule solutions.

  11. Investigation on entrance length for electroosmotic flow in circular and noncircular cross section nanochannel

    NASA Astrophysics Data System (ADS)

    Yaakub, Tuan Norjihan Tuan; Yunas, Jumril; Majlis, Burhanuddin Yeop

    2017-09-01

    Characteristics of bulk electroosmotic flow in nanochannel are different to microchannel because the electric double layer (EDL) becomes comparable to the channel height. This work presents a numerical investigation on the entrance length of pure electroosmotic flow inside 3D rectangular, cylinder and triangular nanochannel with same channel length. The electric field is fixed at 250 kV/cm for all models. A finite element analysis has been performed to solve the governing equation for laminar flow under the influenced of an electric field. The entry length estimation for fully developed electroosmotic laminar flow in a circular and noncircular cross sections are compared by evaluating the electroosmotic velocity magnitude and flow profiles at the centre line cut plane inside the nanochannel. The entrance length in nanochannel is found shorter in a smaller depth flow in rectangular, cylinder and triangular channels. While the triangular nanochannel has the shortest entry length for fully developed laminar flow compare to other cross section shape models. The effect of a step change in ζ-potential on the channel wall surface to the electroosmotic flow entrance length is also presented.

  12. Analytical and numerical study of the electro-osmotic annular flow of viscoelastic fluids.

    PubMed

    Ferrás, L L; Afonso, A M; Alves, M A; Nóbrega, J M; Pinho, F T

    2014-04-15

    In this work we present semi-analytical solutions for the electro-osmotic annular flow of viscoelastic fluids modeled by the Linear and Exponential PTT models. The viscoelastic fluid flows in the axial direction between two concentric cylinders under the combined influences of electrokinetic and pressure forcings. The analysis invokes the Debye-Hückel approximation and includes the limit case of pure electro-osmotic flow. The solution is valid for both no slip and slip velocity at the walls and the chosen slip boundary condition is the linear Navier slip velocity model. The combined effects of fluid rheology, electro-osmotic and pressure gradient forcings on the fluid velocity distribution are also discussed.

  13. Development of polymeric coatings for control of electro-osmotic flow in ASTP MA-011 electrophoresis technology experiment

    NASA Technical Reports Server (NTRS)

    Patterson, W. J.

    1976-01-01

    The development of a methyl cellulose based coating system for control of electro-osmotic flow at the walls of electrophoresis cells is described. Flight electrophoresis columns were coated with this system, resulting in a flight set of six columns. In flight photography of MA-011 electrophoretic separations verified control of electro-osmotic flow.

  14. Analytical and numerical study of electroosmotic slip flows of fractional second grade fluids

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoping; Qi, Haitao; Yu, Bo; Xiong, Zhen; Xu, Huanying

    2017-09-01

    This work investigates the unsteady electroosmotic slip flow of viscoelastic fluid through a parallel plate micro-channel under combined influence of electroosmotic and pressure gradient forcings with asymmetric zeta potentials at the walls. The generalized second grade fluid with fractional derivative was used for the constitutive equation. The Navier slip model with different slip coefficients at both walls was also considered. By employing the Debye-Hückel linearization and the Laplace and sin-cos-Fourier transforms, the analytical solutions for the velocity distribution are derived. And the finite difference method for this problem was also given. Finally, the influence of pertinent parameters on the generation of flow is presented graphically.

  15. Analysis of electroosmotic flow of power-law fluids in a slit microchannel.

    PubMed

    Zhao, Cunlu; Zholkovskij, Emilijk; Masliyah, Jacob H; Yang, Chun

    2008-10-15

    Electroosmotic flow of power-law fluids in a slit channel is analyzed. The governing equations including the linearized Poisson-Boltzmann equation, the Cauchy momentum equation, and the continuity equation are solved to seek analytical expressions for the shear stress, dynamic viscosity, and velocity distribution. Specifically, exact solutions of the velocity distributions are explicitly found for several special values of the flow behavior index. Furthermore, with the implementation of an approximate scheme for the hyperbolic cosine function, approximate solutions of the velocity distributions are obtained. In addition, a generalized Smoluchowski velocity is introduced by taking into account contributions due to the finite thickness of the electric double layer and the flow behavior index of power-law fluids. Calculations are performed to examine the effects of kappaH, flow behavior index, double layer thickness, and applied electric field on the shear stress, dynamic viscosity, velocity distribution, and average velocity/flow rate of the electroosmotic flow of power-law fluids.

  16. Effect of heat transfer on rotating electroosmotic flow through a micro-vessel: haemodynamical applications

    NASA Astrophysics Data System (ADS)

    Sinha, A.; Mondal, A.; Shit, G. C.; Kundu, P. K.

    2016-08-01

    This paper theoretically analyzes the heat transfer characteristics associated with electroosmotic flow of blood through a micro-vessel having permeable walls. The analysis is based on the Debye-Hückel approximation for charge distributions and the Navier-Stokes equations are assumed to represent the flow field in a rotating system. The velocity slip condition at the vessel walls is taken into account. The essential features of the rotating electroosmotic flow of blood and associated heat transfer characteristics through a micro-vessel are clearly highlighted by the variation in the non-dimensional flow velocity, volumetric flow rate and non-dimensional temperature profiles. Moreover, the effect of Joule heating parameter and Prandtl number on the thermal transport characteristics are discussed thoroughly. The study reveals that the flow of blood is appreciably influenced by the elctroosmotic parameter as well as rotating Reynolds number.

  17. Novel elution strategy for monitoring DNA counter-migration in the presence of electroosmotic flow.

    PubMed

    Zabzdyr, Jennifer L; Lillard, Sheri J

    2004-06-25

    The migration behavior of native (i.e., unlabelled) DNA in the presence of electroosmotic flow (EOF) was investigated in bare fused-silica capillaries. Employing a novel elution strategy, the influence of EOF on the net mobility of DNA was assessed by collecting the DNA that migrated anodically (i.e., against EOF) and out of the capillary inlet. Various conditions of pH and buffer-zone continuity were employed to characterize this phenomenon. Tris acid (TA, pH 5.14) and Tris base (TB, pH 9.36) were used as buffers in continuous systems, in which the capillary and the inlet reservoir contain the same buffer, and discontinuous systems, in which the capillary contains either TA or TB, and the inlet reservoir contains water. DNA that was ejected into the inlet vial was subsequently analyzed by capillary electrophoresis-laser-induced fluorescence. Both phiX174/HaeIII DNA and the beta-actin product of single-cell reverse transcriptase-polymerase chain reaction were used as DNA samples in this study. The mechanism of elution was found to depend on bulk flow, in the case of continuous solutions. However, with the discontinuous system, a localized decrease in EOF generated in the capillary tip appeared to impact elution. These findings serve to introduce an alternative approach for characterizing the mobility of highly charged species.

  18. Electro-osmotic flow of couple stress fluids in a micro-channel propagated by peristalsis

    NASA Astrophysics Data System (ADS)

    Tripathi, Dharmendra; Yadav, Ashu; Anwar Bég, O.

    2017-04-01

    A mathematical model is developed for electro-osmotic peristaltic pumping of a non-Newtonian liquid in a deformable micro-channel. Stokes' couple stress fluid model is employed to represent realistic working liquids. The Poisson-Boltzmann equation for electric potential distribution is implemented owing to the presence of an electrical double layer (EDL) in the micro-channel. Using long wavelength, lubrication theory and Debye-Huckel approximations, the linearized transformed dimensionless boundary value problem is solved analytically. The influence of electro-osmotic parameter (inversely proportional to Debye length), maximum electro-osmotic velocity (a function of external applied electrical field) and couple stress parameter on axial velocity, volumetric flow rate, pressure gradient, local wall shear stress and stream function distributions is evaluated in detail with the aid of graphs. The Newtonian fluid case is retrieved as a special case with vanishing couple stress effects. With increasing the couple stress parameter there is a significant increase in the axial pressure gradient whereas the core axial velocity is reduced. An increase in the electro-osmotic parameter both induces flow acceleration in the core region (around the channel centreline) and it also enhances the axial pressure gradient substantially. The study is relevant in the simulation of novel smart bio-inspired space pumps, chromatography and medical micro-scale devices.

  19. Electroosmotic flow and Joule heating in preparative continuous annular electrochromatography.

    PubMed

    Laskowski, René; Bart, Hans-Jörg

    2015-09-01

    An openFOAM "computational fluid dynamic" simulation model was developed for the description of local interaction of hydrodynamics and Joule heating in annular electrochromatography. A local decline of electrical conductivity of the background eluent is caused by an electrokinetic migration of ions resulting in higher Joule heat generation. The model equations consider the Navier-Stokes equation for incompressible fluids, the energy equation for stationary temperature fields, and the mass transfer equation for the electrokinetic flow. The simulations were embedded in commercial ANSYS Fluent software and in open-source environment openFOAM. The annular gap (1 mm width) contained an inorganic C8 reverse-phase monolith as stationary phase prepared by an in situ sol-gel process. The process temperature generated by Joule heating was determined by thermal camera system. The local hydrodynamics in the prototype was detected by a gravimetric contact-free measurement method and experimental and simulated values matched quite well.

  20. Analytical solution of two-fluid electro-osmotic flows of viscoelastic fluids.

    PubMed

    Afonso, A M; Alves, M A; Pinho, F T

    2013-04-01

    This paper presents an analytical model that describes a two-fluid electro-osmotic flow of stratified fluids with Newtonian or viscoelastic rheological behavior. This is the principle of operation of an electro-osmotic two-fluid pump as proposed by Brask et al. [Tech. Proc. Nanotech., 1, 190-193, 2003], in which an electrically non-conducting fluid is transported by the interfacial dragging viscous force of a conducting fluid that is driven by electro-osmosis. The electric potential in the conducting fluid and the analytical steady flow solution of the two-fluid electro-osmotic stratified flow in a planar microchannel are presented by assuming a planar interface between the two immiscible fluids with Newtonian or viscoelastic rheological behavior. The effects of fluid rheology, shear viscosity ratio, holdup and interfacial zeta potential are analyzed to show the viability of this technique, where an enhancement of the flow rate is observed as the shear-thinning effects are increased.

  1. Electroosmotic flow in a water column surrounded by an immiscible liquid.

    PubMed

    Movahed, Saeid; Khani, Sina; Wen, John Z; Li, Dongqing

    2012-04-15

    In this paper, we conducted numerical simulation of the electroosmotic flow in a column of an aqueous solution surrounded by an immiscible liquid. While governing equations in this case are the same as that in the electroosmotic flow through a microchannel with solid walls, the main difference is the types of interfacial boundary conditions. The effects of electric double layer (EDL) and surface charge (SC) are considered to apply the most realistic model for the velocity boundary condition at the interface of the two fluids. Effects on the flow field of ς-potential and viscosity ratio of the two fluids were investigated. Similar to the electroosmotic flow in microchannels, an approximately flat velocity profile exists in the aqueous solution. In the immiscible fluid phase, the velocity decreases to zero from the interface toward the immiscible fluid phase. The velocity in both phases increases with ς-potential at the interface of the two fluids. The higher values of ς-potential also increase the slip velocity at the interface of the two fluids. For the same applied electric field and the same ς-potential at the interface of the two fluids, the more viscous immiscible fluid, the slower the system moves. The viscosity of the immiscible fluid phase also affects the flatness of the velocity profile in the aqueous solution. Copyright © 2012 Elsevier Inc. All rights reserved.

  2. Joule heating effects on electroosmotic flow in insulator-based dielectrophoresis.

    PubMed

    Sridharan, Sriram; Zhu, Junjie; Hu, Guoqing; Xuan, Xiangchun

    2011-09-01

    Insulator-based dielectrophoresis (iDEP) is an emerging technology that has been successfully used to manipulate a variety of particles in microfluidic devices. However, due to the locally amplified electric field around the in-channel insulator, Joule heating often becomes an unavoidable issue that may disturb the electroosmotic flow and affect the particle motion. This work presents the first experimental study of Joule heating effects on electroosmotic flow in a typical iDEP device, e.g., a constriction microchannel, under DC-biased AC voltages. A numerical model is also developed to simulate the observed flow pattern by solving the coupled electric, energy, and fluid equations in a simplified two-dimensional geometry. It is observed that depending on the magnitude of the DC voltage, a pair of counter-rotating fluid circulations can occur at either the downstream end alone or each end of the channel constriction. Moreover, the pair at the downstream end appears larger in size than that at the upstream end due to DC electroosmotic flow. These fluid circulations, which are reasonably simulated by the numerical model, form as a result of the action of the electric field on Joule heating-induced fluid inhomogeneities in the constriction region.

  3. Induced-charge electroosmotic flow around dielectric particles in uniform electric field.

    PubMed

    Zhang, Fang; Li, Dongqing

    2013-11-15

    The current research of induced-charge electroosmotic flow (ICEOF) is mostly confined to systems with ideally or fully polarizable surfaces (e.g., metal). However, most materials in nature have various degrees of polarizability, which directly affects the induced charges and subsequently the induced-charge electroosmotic flow. This paper studied the effect of the polarizability of the materials on the ICEOF. An analytical expression of the induced potential on the surface of a dielectric particle in a uniform electrical field was derived. Three-dimensional transient numerical simulations of the ICEOF and the motion of dielectric particles were performed to study the effect of the polarizability. Simulation results show that the transportation of the dielectric particle in a microchannel is not affected by the polarizability of the particle; however, the interaction of two dielectric particles is sensitive to the polarizability of the particles.

  4. Effect of analyte adsorption on the electroosmotic flow in microfluidic channels.

    PubMed

    Ghosal, Sandip

    2002-02-15

    The predictability and constancy over time of the electroosmotic flow in microchannels is an important consideration in microfluidic devices. A common cause for alteration of the flow is the adsorption of analytes to channel walls, for example, during capillary electrophoresis of proteins. It is shown that certain experimental data, published by Towns and Regnier (Towns, J. K; Regnier, F. E. Anal. Chem. 1992, 64, 2473-2478.), on the anomalous elution times for proteins in capillary electrophoresis can be explained using a simple model for analyte adsorption that uses a result first reported by Anderson and Idol (Anderson, J. L.; Idol, W. K Chem. Eng. Commun. 1985, 38, 93-106.) on the electroosmotic flux in capillaries with axial variations in zeta-potential. It is suggested that it might be possible to use such a model to dynamically correct for altered elution times in capillary electrophoretic devices.

  5. Influence of moderate Joule heating on electroosmotic flow velocity, retention, and efficiency in capillary electrochromatography.

    PubMed

    Chen, Guofang; Tallarek, Ulrich; Seidel-Morgenstern, Andreas; Zhang, Yukui

    2004-07-30

    The influence of Joule heating on electroosmotic flow velocity, the retention factor of neutral analytes, and separation efficiency in capillary electrochromatography was investigated theoretically and experimentally. A plot of electrical current against the applied electrical field strength was used to evaluate the Joule heating effect. When the mobile phase concentration of Tris buffer exceeded 5.0 mM in the studied capillary electrochromatography systems using particulate and monolithic columns (with an accompanying power level of heat dissipation higher than 0.35 W/m), the Joule heating effect became clearly noticeable. Theoretical models for describing the variation of electroosmotic flow velocity with increasing applied field strength and the change of retention factors for neutral analytes with electrical field strength at higher Tris buffer concentrations were analyzed to explain consequences of Joule heating in capillary electrochromatography. Qualitative agreement between experimental data and implications of the theoretical model analysis was observed. The decrease of separation efficiency in capillary electrochromatography with macroporous octadecylsilica particles at high buffer concentration can be also attributed to Joule heating mainly via the increased axial diffusion of the analyte molecules and dispersion of solute bands by a nonuniform electroosmotic flow profile over the column cross-section. However, within a moderate temperature range, the contribution of the macroscopic velocity profile in the column arising from radial temperature gradients is insignificant.

  6. Electroosmotic flow through a cylindrical nanopore in a charged membrane of finite thickness

    NASA Astrophysics Data System (ADS)

    Mao, Mao; Ghosal, Sandip; Sherwood, John D.

    2014-11-01

    We present numerical solutions to the coupled Nernst-Planck-Poisson-Stokes equation for electroosmotic flow through a cylindrical nanopore. The pore traverses a dielectric membrane with uniform surface charge. A multi-physics solver that incorporates electrostatics, ionic transport and electroosmotic flow is developed using the OpenFOAM CFD library. In the limit of small surface charge and weak applied electric field, the numerical results of fluid flux agree with theory when the thickness of the pore h is either very small or very large compared to the pore radius a. For intermediate h / a , our simulation agrees with the composite model of electroosmotic conductance [Sherwood et al. Langmuir (in press)]. When the finite permittivity of the dieletric membrane is taken into account, pairs of toroidal counter rotating eddies appear at the corner of the nanopore that expand to fill the entire pore as the pore radius is decreased. We discuss how the topology of the eddies/stagnation points varies as the aspect ratio of the pore increases. Supported by the NIH under Grant 4R01HG004842.

  7. Effects of analyte velocity modulation on the electroosmotic flow in capillary electrophoresis.

    PubMed

    Demana, T; Guhathakurta, U; Morris, M D

    1992-02-15

    Modulation of the electroosmotic flow in capillary zone electrophoresis by modulation of the driving voltage gives rise to a flow profile that changes between laminar and flat profiles. The changing flow profile induces a radial movement of sample species to and from the capillary surface. The induced sample concentration gradient can be monitored by carefully probing the capillary surface. The resulting signal is a derivative of the normal-shaped peak. Derivative-shaped peaks can be observed with cations, but not with anions. Anions are unable to approach the double-layer region and therefore are unaffected by the modulation process.

  8. Nonuniform electro-osmotic flow on charged strips and its use in particle trapping.

    PubMed

    Liu, Shui-Jin; Hwang, Shyh-Hong; Wei, Hsien-Hung

    2008-12-02

    In this article, we investigate theoretically electro-osmotic flow set up by charged strips on an otherwise uncharged surface. Starting with a single-strip problem we demonstrate that for simple polynomial surface charge distributions several basic solutions can be derived in closed forms constituted by the analogous idea-flow solutions, which provide a more lucid way of revealing the flow features. These solutions reveal two types of flow topology: simple draining-in/pumping-out streaming and a pair of microvortices for symmetric and antisymmetric surface charge distributions, respectively. For an arbitrary surface charge distribution, more complicated flow structures can be found by the superposition of these basic solutions. We further extend the analysis to two uniformly charged strips and show how the flow characteristics vary with the strips' dimensions and surface zeta potentials. The far-field velocity behavior is also asymptotically identified and indicates that the hydrodynamic nature of the flow is typically long-range. An application to particle trapping with electro-osmotic vortices is also investigated theoretically for the first time. We show that in collaboration with short-range attraction effects the trapping can be facilitated by symmetric vortices with a converging stagnation point, but not by asymmetric vortices.

  9. Electroosmotic flow measurements in a freely suspended liquid film: Experiments and numerical simulations.

    PubMed

    Hussein Sheik, Abdulkadir; Bandulasena, H C Hemaka; Starov, Victor; Trybala, Anna

    2017-03-17

    Fluid flow profiles in free liquid films stabilised by anionic and cationic surfactants under an external electric field were investigated. Depthwise velocity fields were measured at the mid region of the free liquid film by confocal μ-PIV and corresponding numerical simulations were performed using Finite Element Method (FEM) to model the system. Depthwise change in velocity profiles was observed with electroosmotic flow dominating in the vicinity of the gas-liquid and solid-liquid interfaces while backpressure drives fluid in the opposite direction at the core of the film. It was also found that the direction of the flow at various sections of the films depends on the type of surfactant used, but flow features remained the same. Numerical simulations predicted the flow profiles with reasonable accuracy; however, asymmetry of the actual film geometry caused deviations at the top half of the computational domain. Overall, electroosmotic flow profiles within a free liquid film is similar to that of the closed-end solid microchannel. However, the flow direction and features of the velocity profiles can be changed by selecting various types of surfactants. The free liquid films thickness was selected to match dimensions of foam Plateau border. Hence these findings will be useful in developing a separation system based on foam electrokinetics. This article is protected by copyright. All rights reserved.

  10. Electroosmotic pumps for microflow analysis

    PubMed Central

    Wang, Xiayan; Wang, Shili; Gendhar, Brina; Cheng, Chang; Byun, Chang Kyu; Li, Guanbin; Zhao, Meiping; Liu, Shaorong

    2009-01-01

    With rapid development in microflow analysis, electroosmotic pumps are receiving increasing attention. Compared to other micropumps, electroosmotic pumps have several unique features. For example, they are bi-directional, can generate constant and pulse-free flows with flow rates well suited to microanalytical systems, and can be readily integrated with lab-on-chip devices. The magnitude and the direction of flow of an electroosmotic pump can be changed instantly. In addition, electroosmotic pumps have no moving parts. In this article, we discuss common features, introduce fabrication technologies and highlight applications of electroosmotic pumps. PMID:20047021

  11. Comparison of the Nernst-Planck model and the Poisson-Boltzmann model for electroosmotic flows in microchannels.

    PubMed

    Park, H M; Lee, J S; Kim, T W

    2007-11-15

    In the analysis of electroosmotic flows, the internal electric potential is usually modeled by the Poisson-Boltzmann equation. The Poisson-Boltzmann equation is derived from the assumption of thermodynamic equilibrium where the ionic distributions are not affected by fluid flows. Although this is a reasonable assumption for steady electroosmotic flows through straight microchannels, there are some important cases where convective transport of ions has nontrivial effects. In these cases, it is necessary to adopt the Nernst-Planck equation instead of the Poisson-Boltzmann equation to model the internal electric field. In the present work, the predictions of the Nernst-Planck equation are compared with those of the Poisson-Boltzmann equation for electroosmotic flows in various microchannels where the convective transport of ions is not negligible.

  12. Effects of non-Newtonian power law rheology on mass transport of a neutral solute for electro-osmotic flow in a porous microtube

    PubMed Central

    Mondal, Sourav; De, Sirshendu

    2013-01-01

    Mass transport of a neutral solute for a power law fluid in a porous microtube under electro-osmotic flow regime is characterized in this study. Combined electro-osmotic and pressure driven flow is conducted herein. An analytical solution of concentration profile within mass transfer boundary layer is derived from the first principle. The solute transport through the porous wall is also coupled with the electro-osmotic flow to predict the solute concentration in the permeate stream. The effects of non-Newtonian rheology and the operating conditions on the permeation rate and permeate solute concentration are analyzed in detail. Both cases of assisting (electro-osmotic and poiseulle flow are in same direction) and opposing flow (the individual flows are in opposite direction) cases are taken care of. Enhancement of Sherwood due to electro-osmotic flow for a non-porous conduit is also quantified. Effects if non-Newtonian rheology on Sherwood number enhancement are observed. PMID:24404046

  13. Experimental Verification of Overlimiting Current by Surface Conduction and Electro-Osmotic Flow in Microchannels

    NASA Astrophysics Data System (ADS)

    Nam, Sungmin; Cho, Inhee; Heo, Joonseong; Lim, Geunbae; Bazant, Martin Z.; Moon, Dustin Jaesuk; Sung, Gun Yong; Kim, Sung Jae

    2015-03-01

    Direct evidence is provided for the transition from surface conduction (SC) to electro-osmotic flow (EOF) above a critical channel depth (d ) of a nanofluidic device. The dependence of the overlimiting conductance (OLC) on d is consistent with theoretical predictions, scaling as d-1 for SC and d4 /5 for EOF with a minimum around d =8 μ m . The propagation of transient deionization shocks is also visualized, revealing complex patterns of EOF vortices and unstable convection with increasing d . This unified picture of surface-driven OLC can guide further advances in electrokinetic theory, as well as engineering applications of ion concentration polarization in microfluidics and porous media.

  14. Solute-solvent interactions in micellar electrokinetic chromatography: IV. Characterization of electroosmotic flow and micellar markers.

    PubMed

    Fuguet, Elisabet; Ràfols, Clara; Bosch, Elisabeth; Rosés, Martí

    2002-01-01

    A wide study of the compounds and procedures mostly used to determine the electroosmotic flow (EOF) and micelle elution times has been done in seven different micellar electrokinetic chromatography (MEKC) systems. These systems are formed from mixtures of an aqueous buffer with the surfactants sodium dodecyl sulfate, lithium dodecyl sulfate, lithium perfluorooctane sulfonate, sodium cholate, sodium deoxycholate, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide. The solvation parameter model has been used to evaluate the usefulness of the compounds studied as EOF or micellar markers in each of the seven MEKC systems. It is demonstrated that methanol, acetonitrile and formamide are the best EOF markers, and that dodecanophenone is the best micellar marker.

  15. Fluid mechanics of electroosmotic flow and its effect on band broadening in capillary electrophoresis.

    PubMed

    Ghosal, Sandip

    2004-01-01

    Electroosmotic flow (EOF) usually accompanies electrophoretic migration of charged species in capillary electrophoresis unless special precautions are taken to suppress it. The presence of the EOF provides certain advantages in separations. It is an alternative to mechanical pumps, which are inefficient and difficult to build at small scales, for transporting reagents and analytes on microfluidic chips. The downside is that any imperfection that distorts the EOF profile reduces the separation efficiency. In this paper, the basic facts about EOF are reviewed from the perspective of fluid mechanics and its effect on separations in free solution capillary zone electrophoresis is discussed in the light of recent advances.

  16. Self-regulating dynamic control of electroosmotic flow in capillary electrophoresis

    SciTech Connect

    Huan-Tsung Chang; Yeung, E.S. )

    1993-03-01

    Capillary electrophoresis (CE), primarily because of the impressive separation power and the compatibility with large biomolecules, has established itself as an important separation tool over the past several years. One of the major barriers limiting the broad, routine application of the technique is the validation of the reliability of migration times and the quantitative accuracy when dealing with real samples. In particular, sample matrices can alter the nature of the surface of the inner wall of the capillary, leading to irreproducible results. Even when the temperature is constant and when adsorption of the analytes onto the capillary wall can be neglected, which is the case of pure zone electrophoresis (CZE), the [zeta] potential of the wall can still be altered by the injected ions. In this report, the authors demonstrate the utility of a concept for maintaining a constant electroosmotic flow rate for sample ions in CZE, independent of the changing sample matrix composition. Such an interactive control of electroosmotic flow has the advantage that the instantaneous flow rate need not be monitored. Once the stationary front is established, no further external intervention is needed. 23 refs., 2 tabs.

  17. Visualizing the transient electroosmotic flow and measuring the zeta potential of microchannels with a micro-PIV technique.

    PubMed

    Yan, Deguang; Nguyen, Nam-Trung; Yang, Chun; Huang, Xiaoyang

    2006-01-14

    We have demonstrated a transient micro particle image velocimetry (micro-PIV) technique to measure the temporal development of electroosmotic flow in microchannels. Synchronization of different trigger signals for the laser, the CCD camera, and the high-voltage switch makes this measurement possible with a conventional micro-PIV setup. Using the transient micro-PIV technique, we have further proposed a method on the basis of inertial decoupling between the particle electrophoretic motion and the fluid electroosmotic flow to determine the electrophoretic component in the particle velocity and the zeta potential of the channel wall. It is shown that using the measured zeta potentials, the theoretical predictions agree well with the transient response of the electroosmotic velocities measured in this work.

  18. A Portable Liquid Chromatograph with a Battery-operated Compact Electroosmotic Pump and a Microfluidic Chip Device with a Reversed Phase Packed Column.

    PubMed

    Ishida, Akihiko; Fujii, Mitsutaka; Fujimoto, Takehiro; Sasaki, Shunsuke; Yanagisawa, Ichiro; Tani, Hirofumi; Tokeshi, Manabu

    2015-01-01

    A compact and lightweight liquid chromatography system is presented with overall dimensions of 26 cm width × 18 cm length × 21 cm height and weight of 2 kg. This system comprises a battery-operated compact electroosmotic pump, a manual injector, a microfluidic chip device containing a packed column and an electrochemical detector, and a USB bus-powered potentiostat. The pumping system was designed for microfluidic-based reversed-phase liquid chromatography in which an electroosmotically generated water stream pushes the mobile phase via a diaphragm for the output. The flow rate ranged from 0 to 10 μL/min and had a high degree of precision. The pumping system operated continuously for over 24 h with dry batteries. The column formed in the microfluidic device was packed with 3-μm ODS particles with a length of 30 mm and a diameter of 0.8 mm. The results presented herein demonstrate the performance of the pumping system and the column using alkylphenols, catecholamine, catechin, and amino acids.

  19. Numerical prediction of ac electro-osmotic flows around polarized electrodes

    NASA Astrophysics Data System (ADS)

    Suh, Y. K.; Kang, S.

    2009-04-01

    In this paper we present an interactive numerical method that can predict ac electro-osmotic flows around completely polarized electrodes. In this method the slip velocity on the electrode surface is calculated by numerically solving the Laplace equation for the potential in the bulk coupled with the dynamical equation for the surface charge density on the electrodes; here the dynamical equation has been derived from the asymptotic solutions of the Poisson-Nernst-Planck equation for the potential drop across the electrical thin layer near the electrode. A unique feature of this study is that the effect of nonspecific ion adsorption is considered. The numerical code was applied to the two-dimensional ac electro-osmotic flow above a pair of coplanar electrodes, and the solutions compared well with the experimental data reported in the literature. We investigated the effect of various parameters on the slip velocity distribution, such as the ac frequency, the electrode length, the effective Stern-layer thickness, and the adsorption coefficients.

  20. Numerical prediction of ac electro-osmotic flows around polarized electrodes.

    PubMed

    Suh, Y K; Kang, S

    2009-04-01

    In this paper we present an interactive numerical method that can predict ac electro-osmotic flows around completely polarized electrodes. In this method the slip velocity on the electrode surface is calculated by numerically solving the Laplace equation for the potential in the bulk coupled with the dynamical equation for the surface charge density on the electrodes; here the dynamical equation has been derived from the asymptotic solutions of the Poisson-Nernst-Planck equation for the potential drop across the electrical thin layer near the electrode. A unique feature of this study is that the effect of nonspecific ion adsorption is considered. The numerical code was applied to the two-dimensional ac electro-osmotic flow above a pair of coplanar electrodes, and the solutions compared well with the experimental data reported in the literature. We investigated the effect of various parameters on the slip velocity distribution, such as the ac frequency, the electrode length, the effective Stern-layer thickness, and the adsorption coefficients.

  1. Multiscale modeling of electroosmotic flow: Effects of discrete ion, enhanced viscosity, and surface friction

    NASA Astrophysics Data System (ADS)

    Bhadauria, Ravi; Aluru, N. R.

    2017-05-01

    We propose an isothermal, one-dimensional, electroosmotic flow model for slit-shaped nanochannels. Nanoscale confinement effects are embedded into the transport model by incorporating the spatially varying solvent and ion concentration profiles that correspond to the electrochemical potential of mean force. The local viscosity is dependent on the solvent local density and is modeled using the local average density method. Excess contributions to the local viscosity are included using the Onsager-Fuoss expression that is dependent on the local ionic strength. A Dirichlet-type boundary condition is provided in the form of the slip velocity that is dependent on the macroscopic interfacial friction. This solvent-surface specific interfacial friction is estimated using a dynamical generalized Langevin equation based framework. The electroosmotic flow of Na+ and Cl- as single counterions and NaCl salt solvated in Extended Simple Point Charge (SPC/E) water confined between graphene and silicon slit-shaped nanochannels are considered as examples. The proposed model yields a good quantitative agreement with the solvent velocity profiles obtained from the non-equilibrium molecular dynamics simulations.

  2. Electro-osmotic flow in a wavy microchannel: Coherence between the electric potential and the wall shape function

    NASA Astrophysics Data System (ADS)

    Shu, Y. C.; Chang, C. C.; Chen, Y. S.; Wang, C. Y.

    2010-08-01

    The electro-osmotic flow through a wavy microchannel is studied under the Debye-Hückel approximation. An analytic solution by perturbation with appropriate averaging is carried out up to the second-order in terms of the small amplitude of corrugation. It is shown that the wavelength and phase difference of the corrugations can be utilized to control the flow relative to the case of flat walls. In particular, for thick electric double layers the electro-osmotic flow can be enhanced at long-wavelength corrugations because of the coherence between the electric potential and the wall shape function. Notably, these findings are not restricted to small amplitudes of corrugation. By applying the Ritz method to solve for the electro-osmotic flow, it is found that the enhancement becomes even greater (up to 30%) with increases in corrugation. Moreover, the nonlinear Poisson-Boltzmann equation is solved by finite difference to study the electro-osmotic flow in terms of the relative strength of the zeta potential. The issue of overlapped electric double layers when they are very thick is also discussed. The relative flow rate is shown to increase under the following conditions: (i) completely out-of-phase corrugations with long wavelength and large amplitude, (ii) small zeta potential, and (iii) slight overlapping of electric double layers.

  3. Electroosmotic flow of a viscoplastic material through a slit channel with walls of arbitrary zeta potential

    NASA Astrophysics Data System (ADS)

    Ng, Chiu-On; Qi, Cheng

    2013-10-01

    Electroosmotic (EO) flow is known to have a nearly uniform velocity profile, but such a plug-flow velocity can be considerably diminished if the fluid is a viscoplastic material having a yield stress. This paper aims to investigate the reduction of EO velocity (also known as Smoluchowski slip velocity) due to a yield stress as a function of the material rheological parameters and the zeta potential. Three rheological models are considered: Casson, Herschel-Bulkley, and Bingham fluids. In the absence of pressure forcing and without the Debye-Hückel approximation, the problems of EO flow of these materials in a slit channel with walls uniformly charged with an arbitrary zeta potential are analytically solved. Analytical expressions are deduced for the reduced Smoluchowski velocity under the limiting conditions of very small and very large zeta potentials. It is shown that qualitatively different asymptotic behaviors will be exhibited by materials of different models.

  4. Oscillatory electroosmotic flow in a parallel-plate microchannel under asymmetric zeta potentials

    NASA Astrophysics Data System (ADS)

    Peralta, M.; Arcos, J.; Méndez, F.; Bautista, O.

    2017-06-01

    In this work, we conduct a theoretical analysis of the start-up of an oscillatory electroosmotic flow (EOF) in a parallel-plate microchannel under asymmetric zeta potentials. It is found that the transient evolution of the flow field is controlled by the parameters {R}ω , {R}\\zeta , and \\bar{κ }, which represent the dimensionless frequency, the ratio of the zeta potentials of the microchannel walls, and the electrokinetic parameter, which is defined as the ratio of the microchannel height to the Debye length. The analysis is performed for both low and high zeta potentials; in the former case, an analytical solution is derived, whereas in the latter, a numerical solution is obtained. These solutions provide the fundamental characteristics of the oscillatory EOFs for which, with suitable adjustment of the zeta potential and the dimensionless frequency, the velocity profiles of the fluid flow exhibit symmetric or asymmetric shapes.

  5. Experimental and theoretical investigations of non-Newtonian electro-osmotic driven flow in rectangular microchannels.

    PubMed

    Huang, Yi; Chen, Juzheng; Wong, TeckNeng; Liow, Jong-Leng

    2016-07-20

    With the development of microfluidics, electro-osmotic (EO) driven flow has gained intense research interest as a result of its unique flow profile and the corresponding benefits in its application in the transportation of sensitive samples. Sensitive samples, such as DNA, are incapable of enduring strong flow shear induced by conventional hydrodynamic driven methods. EO driven flow is thus a niche area. However, even though there are a few research studies focusing on bio-fluidic samples related to EO driven flow, the majority of them are merely theoretical modeling without solid evidence from experiments due to the inherent complex rheological behavior of the bio-fluids. Challenges occur when the EO driven mechanism meets with complex rheology; vital questions such as can the zeta potential still be assumed to be constant when dealing with fluids with complex rheology? and "Does the shear thinning effect enhance electro-osmotic driven flow?" need to be answered. We conducted experiments using current monitoring and microscopy fluorescence methods, and developed a theoretical model by coupling a generalized Smoluchowski approach with the power-law constitutive model. We calculated the zeta potential and compared the experimental results with modeling to answer the questions. The results show a reduction of zeta potential in the presence of PEO aqueous solutions. A constant zeta potential is also indicated by varying the PEO concentration and the electric field strength.The shear thinning effect is also addressed via experimental data and theoretical calculations. The results show a promising enhancement of the EO driven velocity due to the shear thinning effect.

  6. Influence of varying electroosmotic flow on the effective diffusion in electric field gradient separations.

    PubMed

    Maynes, Daniel; Tenny, Joseph; Webbd, Brent W; Lee, Milton L

    2008-02-01

    Recently the use electric field gradient focusing (EFGF) to enhance focusing of proteins has been proposed and explored to provide significant improvement in separation resolution. The objective of EFGF is to focus proteins of specific electrophoretic mobilities at distinct stationary locations in a column or channel. This can be accomplished in a capillary by allowing the electric potential to vary in the streamwise direction. Because the electric field is varying, so also is the electrokinetic force exerted on the proteins and the electroosmotic velocity of the buffer solution. Due to the varying electric field, the Taylor diffusion characteristics will also vary along the column, causing a degradation of peak widths of some proteins, dependent on their equilibrium positions and local velocity distributions. The focus of this paper is an analysis that allows characterization of the local Taylor diffusion and resulting protein band peak width as a function of the local magnitude of the EOF relative to the average fluid velocity for both cylindrical and rectangular channels. In general the analysis shows that as the ratio of the local electroosmotic velocity to the average velocity deviates from unity, the effective diffusion increases significantly. The effectiveness of EFGF devices over a range of protein diffusivities, capillary diameters, flow velocities, and electric field gradient is discussed.

  7. Influence of atomistic physics on electro-osmotic flow: an analysis based on density functional theory.

    PubMed

    Nilson, Robert H; Griffiths, Stewart K

    2006-10-28

    Molecular density profiles and charge distributions determined by density functional theory (DFT) are used in conjunction with the continuum Navier-Stokes equations to compute electro-osmotic flows in nanoscale channels. The ion species of the electrolyte are represented as centrally charged hard spheres, and the solvent is treated as a dense fluid of neutral hard spheres having a uniform dielectric constant. The model explicitly accounts for Lennard-Jones interactions among fluid and wall molecules, hard sphere repulsions, and short range electrical interactions, as well as long range Coulombic interactions. Only the last of these interactions is included in classical Poisson-Boltzmann (PB) modeling of the electric field. Although the proposed DFT approach is quite general, the sample calculations presented here are limited to symmetric monovalent electrolytes. For a prescribed surface charge, this DFT model predicts larger counterion concentrations near charged channel walls, relative to classical PB modeling, and hence smaller concentrations in the channel center. This shifting of counterions toward the walls reduces the effective thickness of the Debye layer and reduces electro-osmotic velocities as compared to classical PB modeling. Zeta potentials and fluid speeds computed by the DFT model are as much as two or three times smaller than corresponding PB results. This disparity generally increases with increasing electrolyte concentration, increasing surface charge density and decreasing channel width. The DFT results are found to be comparable to those obtained by molecular dynamics simulation, but require considerably less computing time.

  8. A glass fiber sheet-based electroosmotic lateral flow immunoassay for point-of-care testing.

    PubMed

    Oyama, Yuriko; Osaki, Toshihisa; Kamiya, Koki; Kawano, Ryuji; Honjoh, Tsutomu; Shibata, Haruki; Ide, Toru; Takeuchi, Shoji

    2012-12-21

    We have developed a quantitative immunoassay chip targeting point-of-care testing. To implement a lateral flow immunoassay, a glass fiber sheet was chosen as the material for the microfluidic channel in which the negative charge on the fiber surfaces efficiently generates the electroosmotic flow (EOF). The EOF, in turn, allows controllable bound/free separation of antigen/antibody interactions on the chip and enables precise determination of the antigen concentration. In addition, the defined size of the porous matrix was suitable for the filtration of undesired large particles. We confirmed the linear relationship between the concentration of analyte and the resulting fluorescence intensity from the immunoassay of two model analytes, C-reactive protein (CRP) and insulin, demonstrating that analyte concentration was quantitatively determined within the developed chip in 20 min. The limits of detection were 8.5 ng mL(-1) and 17 ng mL(-1) for CRP and insulin, respectively.

  9. Modelling of electrokinetic phenomena involving confined polymers: Applications to DNA separation and electroosmotic flow control

    NASA Astrophysics Data System (ADS)

    Tessier, Frederic

    Microfluidic and nanofluidic technology is revolutionizing experimental practices in analytical chemistry, molecular biology and medicine. Indeed, the development of systems of small dimensions for the processing of fluids heralds the miniaturization of traditional, cumbersome laboratory equipment onto robust, portable and efficient microchip devices (similar to the electronic microchips found in computers). Moreover, the conjunction of scale between the smallest man-made device and the largest macromolecules evolved by Nature is fertile ground for the blooming of our knowledge about the key processes of life. In fact, the conjunction is threefold, because modern computational resources also allow us to contemplate a rather explicit modelling of physical systems between the nanoscale and the microscale. In the five articles comprising this thesis, we present the results of computer simulations that address specific questions concerning the operation of two different model systems relevant to the development of small-scale fluidic devices for the manipulation and analysis of biomolecules. First, we use a Bond-Fluctuation Monte Carlo approach to study the electrophoretic drift of macromolecules across an entropic trap array built for the length separation of long, double-stranded DNA molecules. We show that the motion of the molecules is consistent with a simple balance between electric and entropic forces, in terms of a single characteristic parameter. We also extract detailed information on polymer deformation during migration, predict the separation of topoisomers, and investigate innovative ratchet driving regimes. Secondly, we present theoretical derivations, numerical calculations and Molecular Dynamics simulation results for an electrolyte confined in a capillary of nanoscopic dimensions. In particular, we study the effectiveness of neutral grafted polymer chains in reducing the magnitude of electroosmotic flow (fluid flow induced by an external electric field

  10. Electro-osmotic flows through topographically complicated porous media: Role of electropermeability tensor

    NASA Astrophysics Data System (ADS)

    Bandopadhyay, Aditya; DasGupta, Debabrata; Mitra, Sushanta K.; Chakraborty, Suman

    2013-03-01

    In the present work, we consider a framework for characterizing electro-osmotic flows in topographically complicated porous media and derive an effective up-scaled transport parameter to quantify this. We term this parameter the electro-permeability, which characterizes the electro-osmotic flow through composite porous media in analogy with Darcy's law. The electro-permeability tensor, thus introduced, serves a simple means of relating the volume flow rate with the applied electric field without going into the intricacies of the microstructure of the porous domain. First, we consider cases where the solid fractions have a fractal dimension generated by the Mandelbrot set, purely for the sake of demonstration. Based on such considerations, we employ the method of homogenization to obtain the effective electro-permeability parameter from the numerical simulations executed over a representative volume element. Our derived electro-permeability tensor components exhibit functional relationships with the solid or liquid fraction as well as the topography of the porous medium. Having established these functional relationships, we evaluate the tensor components for a binary composite porous medium in which one constituent has markedly high ζ potential than the other constituent, for illustration with potential relevance in microfluidics. We establish the sensitivity of the electro-permeability tensor on the domain morphology, solid fraction, ratio of solid fractions of the two phases having the two different ζ potential values, and the ζ potential contrast and compare it with equivalent Darcy permeability for the same. We thus provide a simple mathematical framework that may be immensely helpful for devising a computationally efficient way of characterizing electro-osmosis through topographically complicated porous media.

  11. Exact solution of an electroosmotic flow for generalized Burgers fluid in cylindrical domain

    NASA Astrophysics Data System (ADS)

    Khan, Masood; Farooq, Asma; Khan, Waqar Azeem; Hussain, Mazhar

    The present paper reports a theoretical study of the dynamics of an electroosmotic flow (EOF) in cylindrical domain. The Cauchy momentum equation is first simplified by incorporating the electrostatic body force in the electric double layer and the generalized Burgers fluid constitutive model. The electric potential distribution is given by the linearized Poisson-Boltzmann equation. After solving the linearized Poisson-Boltzmann equation, the Cauchy momentum equation with electrostatic body force is solved analytically by using the temporal Fourier and finite Hankel transforms. The effects of important involved parameters are examined and presented graphically. The results obtained reveal that the magnitude of velocity increases with increase of the Debye-Huckel and electrokinetic parameters. Further, it is shown that the results presented for generalized Burgers fluid are quite general so that results for the Burgers, Oldroyd-B, Maxwell and Newtonian fluids can be obtained as limiting cases.

  12. Experimental verification of overlimiting current by surface conduction and electro-osmotic flow in microchannels.

    PubMed

    Nam, Sungmin; Cho, Inhee; Heo, Joonseong; Lim, Geunbae; Bazant, Martin Z; Moon, Dustin Jaesuk; Sung, Gun Yong; Kim, Sung Jae

    2015-03-20

    Direct evidence is provided for the transition from surface conduction (SC) to electro-osmotic flow (EOF) above a critical channel depth (d) of a nanofluidic device. The dependence of the overlimiting conductance (OLC) on d is consistent with theoretical predictions, scaling as d(-1) for SC and d(4/5) for EOF with a minimum around d=8  μm. The propagation of transient deionization shocks is also visualized, revealing complex patterns of EOF vortices and unstable convection with increasing d. This unified picture of surface-driven OLC can guide further advances in electrokinetic theory, as well as engineering applications of ion concentration polarization in microfluidics and porous media.

  13. Electro-osmotic flow through nanopores in thin and ultrathin membranes

    NASA Astrophysics Data System (ADS)

    Melnikov, Dmitriy V.; Hulings, Zachery K.; Gracheva, Maria E.

    2017-06-01

    We theoretically study how the electro-osmotic fluid velocity in a charged cylindrical nanopore in a thin solid state membrane depends on the pore's geometry, membrane charge, and electrolyte concentration. We find that when the pore's length is comparable to its diameter, the velocity profile develops a concave shape with a minimum along the pore axis unlike the situation in very long nanopores with a maximum velocity along the central pore axis. This effect is attributed to the induced pressure along the nanopore axis due to the fluid flow expansion and contraction near the exit or entrance to the pore and to the reduction of electric field inside the nanopore. The induced pressure is maximal when the pore's length is about equal to its diameter while decreasing for both longer and shorter nanopores. A model for the fluid velocity incorporating these effects is developed and shown to be in a good agreement with numerically computed results.

  14. Analytical solution of combined electroosmotic/pressure driven flows in two-dimensional straight channels: finite Debye layer effects.

    PubMed

    Dutta, P; Beskok, A

    2001-05-01

    Analytical results for the velocity distribution, mass flow rate, pressure gradient, wall shear stress, and vorticity in mixed electroosmotic/pressure driven flows are presented for two-dimensional straight channel geometry. We particularly analyze the electric double-layer (EDL) region near the walls and define three new concepts based on the electroosmotic potential distribution. These are the effective EDL thickness, the EDL displacement thickness, and the EDL vorticity thickness. We show that imposing Helmholtz-Smoluchowski velocity at the edge of the EDL as the velocity matching condition between the EDL and the bulk flow region is incomplete under spatial bulk flow variations across the finite EDL. However, the Helmholtz-Smoluchowski velocity can be used as the appropriate slip velocity on the wall. We discuss the limitations of this approach in satisfying the global conservation laws.

  15. Bi-directional flow induced by an AC electroosmotic micropump with DC voltage bias.

    PubMed

    Islam, Nazmul; Reyna, Jairo

    2012-04-01

    This paper discusses the principle of biased alternating current electroosmosis (ACEO) and its application to move the bulk fluid in a microchannel, as an alternative to mechanical pumping methods. Previous EO-driven flow research has looked at the effect of electrode asymmetry and transverse traveling wave forms on the performance of electroosmotic pumps. This paper presents an analysis that was conducted to assess the effect of combining an AC signal with a DC (direct current) bias when generating the electric field needed to impart electroosmosis (EO) within a microchannel. The results presented here are numerical and experimental. The numerical results were generated through simulations performed using COMSOL 3.5a. Currently available theoretical models for EO flows were embedded in the software and solved numerically to evaluate the effects of channel geometry, frequency of excitation, electrode array geometry, and AC signal with a DC bias on the flow imparted on an electrically conducting fluid. Simulations of the ACEO flow driven by a constant magnitude of AC voltage over symmetric electrodes did not indicate relevant net flows. However, superimposing a DC signal over the AC signal on the same symmetric electrode array leads to a noticeable net forward flow. Moreover, changing the polarity of electrical signal creates a bi-directional flow on symmetrical electrode array. Experimental flow measurements were performed on several electrode array configurations. The mismatch between the numerical and experimental results revealed the limitations of the currently available models for the biased EO. However, they confirm that using a symmetric electrode array excited by an AC signal with a DC bias leads to a significant improvement in flow rates in comparison to the flow rates obtained in an asymmetric electrode array configuration excited just with an AC signal. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Scaling Law for Cross-stream Diffusion in Microchannels under Combined Electroosmotic and Pressure Driven Flow.

    PubMed

    Song, Hongjun; Wang, Yi; Pant, Kapil

    2013-01-01

    This paper presents an analytical study of the cross-stream diffusion of an analyte in a rectangular microchannel under combined electroosmotic flow (EOF) and pressure driven flow to investigate the heterogeneous transport behavior and spatially-dependent diffusion scaling law. An analytical model capable of accurately describing 3D steady-state convection-diffusion in microchannels with arbitrary aspect ratios is developed based on the assumption of the thin Electric Double Layer (EDL). The model is verified against high-fidelity numerical simulation in terms of flow velocity and analyte concentration profiles with excellent agreement (<0.5% relative error). An extensive parametric analysis is then undertaken to interrogate the effect of the combined flow velocity field on the transport behavior in both the positive pressure gradient (PPG) and negative pressure gradient (NPG) cases. For the first time, the evolution from the spindle-shaped concentration profile in the PPG case, via the stripe-shaped profile (pure EOF), and finally to the butterfly-shaped profile in the PPG case is obtained using the analytical model along with a quantitative depiction of the spatially-dependent diffusion layer thickness and scaling law across a wide range of the parameter space.

  17. Scaling Law for Cross-stream Diffusion in Microchannels under Combined Electroosmotic and Pressure Driven Flow

    PubMed Central

    Song, Hongjun; Wang, Yi; Pant, Kapil

    2012-01-01

    This paper presents an analytical study of the cross-stream diffusion of an analyte in a rectangular microchannel under combined electroosmotic flow (EOF) and pressure driven flow to investigate the heterogeneous transport behavior and spatially-dependent diffusion scaling law. An analytical model capable of accurately describing 3D steady-state convection-diffusion in microchannels with arbitrary aspect ratios is developed based on the assumption of the thin Electric Double Layer (EDL). The model is verified against high-fidelity numerical simulation in terms of flow velocity and analyte concentration profiles with excellent agreement (<0.5% relative error). An extensive parametric analysis is then undertaken to interrogate the effect of the combined flow velocity field on the transport behavior in both the positive pressure gradient (PPG) and negative pressure gradient (NPG) cases. For the first time, the evolution from the spindle-shaped concentration profile in the PPG case, via the stripe-shaped profile (pure EOF), and finally to the butterfly-shaped profile in the PPG case is obtained using the analytical model along with a quantitative depiction of the spatially-dependent diffusion layer thickness and scaling law across a wide range of the parameter space. PMID:23554584

  18. Thermal characteristics of time-periodic electroosmotic flow in a circular microchannel

    NASA Astrophysics Data System (ADS)

    Moghadam, Ali Jabari

    2015-10-01

    A theoretical analysis is performed to explore the thermal characteristics of electroosmotic flow in a circular microchannel under an alternating electric field. An analytical approach is presented to solve energy equation, and then, the exact solution of temperature profiles is obtained by using the Green's function method. This study reveals that the temperature field repeats itself for each half-period. Frequency has a strong influence on the thermal behavior of the flow field. For small values of the dimensionless frequency (small channel size, large kinematic viscosity, or small frequency), the advection mechanism is dominant in the whole domain and the resultant heating (Joule heating and wall heat flux) can be transferred by the complete flow field in the axial direction; while, the middle portion of the flow field at high dimensionless frequencies does not have sufficient time to transfer heat by advection, and the bulk fluid temperature, especially in heating, may consequently become greater than the wall temperature. In a particular instance of cooling mode, a constant surface temperature case is temporarily occurred in which the axial temperature gradient will be zero. For relatively high frequencies, the unsteady bulk fluid temperature in some radial positions at some moments may be equal to the wall temperature; hence instantaneous cylindrical surfaces with zero radial heat flux may occur over a period of time. Depending on the value and sign of the thermal scale ratio, the quasi-steady-state Nusselt number (time-averaged at one period) approaches a specific value as the electrokinetic radius becomes infinity.

  19. Thermal transport characteristics of combined electroosmotic and pressure driven flow in soft nanofluidics.

    PubMed

    Matin, M H; Ohshima, H

    2016-08-15

    The present study deals with thermal transport characteristics of an electrolyte solution flowing through a slit nanochannel with polyelectrolyte walls, known as soft nanochannel. The sources of the fluid flow are the pressure gradient along the channel axis and the electrokinetic effects that trigger an electroosmotic flow under the impact of a uniformly applied electric field. The polyelectrolyte layer (PEL) is denoted as a fixed charge layer (FCL) and the electrolyte ions can be present both inside and outside the PEL. Therefore, the PEL-electrolyte interface acts as a semi-penetrable membrane. To the best of our knowledge, the thermal analysis of mixed electrokinetically and pressure driven flow in such soft nanochannels has never been addressed. The Poisson-Boltzmann equation is solved assuming the Debye-Huckel linearization for the low electric potential to provide us with analytical closed form solutions for the conservation equations. The conservation equations are solved to obtain the electric potential; velocity and temperature distributions in terms of governing dimensionless parameters. Also results for the Nusselt number are presented and discussed in detail.

  20. Surface instability of a thin electrolyte film undergoing coupled electroosmotic and electrophoretic flows in a microfluidic channel.

    PubMed

    Ray, Bahni; Reddy, Puchalapalli Dinesh Sankar; Bandyopadhyay, Dipankar; Joo, Sang W; Sharma, Ashutosh; Qian, Shizhi; Biswas, Gautam

    2011-11-01

    We consider the stability of a thin liquid film with a free charged surface resting on a solid charged substrate by performing a general Orr-Sommerfeld (O-S) analysis complemented by a long-wave (LW) analysis. An externally applied field generates an electroosmotic flow (EOF) near the solid substrate and an electrophoretic flow (EPF) at the free surface. The EPF retards the EOF when both the surfaces have the same sign of the potential and can even lead to the flow reversal in a part of the film. In conjunction with the hydrodynamic stress, the Maxwell stress is also considered in the problem formulation. The electrokinetic potential at the liquid-air and solid-liquid interfaces is modelled by the Poisson-Boltzmann equation with the Debye-Hückel approximation. The O-S analysis shows a finite-wavenumber shear mode of instability when the inertial forces are strong and an LW interfacial mode of instability in the regime where the viscous force dominates. Interestingly, both the modes are found to form beyond a critical flow rate. The shear (interfacial) mode is found to be dominant when the film is thick (thin), the electric field applied is strong (weak), and the zeta-potentials on the liquid-air and solid-liquid interfaces are high (small). The LW analysis predicts the presence of the interfacial mode, but fails to capture the shear mode. The change in the propagation direction of the interfacial mode with the zeta-potential is predicted by both O-S and LW analyses. The parametric range in which the LW analysis is valid is thus demonstrated.

  1. An analysis of steady/unsteady electroosmotic flows through charged cylindrical nano-channels

    NASA Astrophysics Data System (ADS)

    Nayak, A. K.

    2013-11-01

    The steady/unsteady electroosmotic flow in an infinitely extended cylindrical channel with diameters ranging from 10 to 100 nm has been investigated. A mixture of (NaCl + H2O) is considered for the numerical calculation of the mass, potential, velocity, and mixing efficiency. Results are obtained for the channel diameters are small, equal, or greater than the electric double layer (EDL) both for steady and unsteady cases. In the present discussion, a symmetrical distribution of mole fractions is considered at the wall interface. Hence, the velocity and potential are symmetrical in nature toward the centerline of the channel, and also identical in nature at maximum and minimum time levels (i.e., at π/2 and 3 π/2 for a periodic function) in the transient case. In case of steady flows, the velocity and potential satisfy the chemical equilibrium condition at the centerline. It is observed that the electric double layer reaches a local equilibrium in the presence of electroosmosis when the channel length is long compared to the characteristic hydraulic diameter and the flow is essentially one-dimensional, which depends only on channel diameter. Comparisons of NP (Nernst Plank) model with PB (Poisson-Boltzmann) model are achieved out for different published results at larger channel diameters.

  2. Electro-osmotically driven MHD flow and heat transfer in micro-channel

    NASA Astrophysics Data System (ADS)

    Shit, G. C.; Mondal, A.; Sinha, A.; Kundu, P. K.

    2016-05-01

    A theoretical analysis is presented for electro-osmotic flow (EOF) of blood in a hydrophobic micro-channel with externally applied magnetic field. The lumen of micro-channels is assumed to be porous medium in addition to the consideration of permeability of the channel walls. The effects of slip velocity and thermal-slip are taken into consideration. The governing equations in the electrical double layer (EDL) together with the Poisson-Boltzmann equation and the body force exerted by the applied potential are furthermore considered. The flow is governed by the non-Newtonian viscoelastic fluid model. These equations along with the thermal energy equation are approximated by assuming that the channel height is much greater than the thickness of electrical double layer consisting the stern and diffusive layers. The problem is solved analytically and the computed results have presented graphically for various values of the dimensionless parameters. The results presented here have significant impact on the therapeutic treatment in hyperthermia as well as in controlling blood flow and heat transfer in micro-channels.

  3. Non-isothermal electro-osmotic flow in a microchannel with charge-modulated surfaces

    NASA Astrophysics Data System (ADS)

    Bautista, Oscar; Sanchez, Salvador; Mendez, Federico

    2015-11-01

    In this work, we present an theoretical analysis of a nonisothermal electro-osmotic flow of a Newtonian fluid over charge-modulated surfaces in a microchannel. Here, the heating in the microchannel is due to the Joule effect caused by the imposition of an external electric field. The study is conducted through the use of perturbation techniques and is validated by means of numerical simulations. We consider that both, viscosity and electrical conductivity of the fluid are temperature-dependent; therefore, in order to determine the heat transfer process and the corresponding effects on the flow field, the governing equations of continuity, momentum, energy and electric potential have to be solved in a coupled manner. The principal obtained results evidence that the flow patterns are perturbed in a noticeable manner in comparison with the isothernal case. Our results may be used for increasing microfluidics mixing by conjugating thermal effects with the use of charge-modulated surfaces. This work has been supported by the research grants no. 220900 of Consejo Nacional de Ciencia y Tecnología (CONACYT) and 20150919 of SIP-IPN at Mexico. F. Méndez acknowledges also the economical support of PAPIIT-UNAM under contract number IN112215.

  4. Acid-induced transient isotachophoretic stacking of basic drugs in co-electroosmotic flow capillary zone electrophoresis.

    PubMed

    Quirino, Joselito P; Breadmore, Michael C

    2012-01-01

    Online sample concentration or stacking of basic drugs by transient isotachophoresis with the injection of an acid in co-electroosmotic flow capillary zone electrophoresis was studied experimentally and with computer simulation. The acid stacking strategy afforded an order of magnitude improvement in concentration sensitivity for model tricyclic antidepressant and β blocker drugs. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. Polymer capture by electro-osmotic flow of oppositely charged nanopores.

    PubMed

    Wong, C T A; Muthukumar, M

    2007-04-28

    The authors have addressed theoretically the hydrodynamic effect on the translocation of DNA through nanopores. They consider the cases of nanopore surface charge being opposite to the charge of the translocating polymer. The authors show that, because of the high electric field across the nanopore in DNA translocation experiments, electro-osmotic flow is able to create an absorbing region comparable to the size of the polymer around the nanopore. Within this capturing region, the velocity gradient of the fluid flow is high enough for the polymer to undergo coil-stretch transition. The stretched conformation reduces the entropic barrier of translocation. The diffusion limited translocation rate is found to be proportional to the applied voltage. In the authors' theory, many experimental variables (electric field, surface potential, pore radius, dielectric constant, temperature, and salt concentration) appear through a single universal parameter. They have made quantitative predictions on the size of the adsorption region near the pore for the polymer and on the rate of translocation.

  6. Deformations of a pre-stretched elastic membrane driven by non-uniform electroosmotic flow

    NASA Astrophysics Data System (ADS)

    Bercovici, Moran; Boyko, Evgeniy; Gat, Amir

    2016-11-01

    We study viscous-elastic dynamics of fluid confined between a rigid plate and a pre-stretched elastic membrane subjected to non-uniform electroosmotic flow, and focus on the case of a finite-size membrane clamped at its boundaries. Considering small deformations of a strongly pre-stretched membrane, and applying the lubrication approximation for the flow, we derive a linearized leading-order non-homogenous 4th order diffusion equation governing the deformation and pressure fields. We derive a time-dependent Green's function for a rectangular domain, and use it to obtain several basic solutions for the cases of constant and time varying electric fields. In addition, defining an asymptotic expansion where the small parameter is the ratio of the induced to prescribed tension, we obtain a set of four one-way coupled equations providing a first order correction for the deformation field. Funded by the European Research Council (ERC) under the Horizon 2020 Research and Innovation Programme, Grant agreement No. 678734 (MetamorphChip).

  7. Hydrodynamic dispersion of a neutral non-reacting solute in electroosmotic flow

    SciTech Connect

    S. K. Griffiths; R. H. Nilson

    1999-06-01

    Analytical methods are employed to determine the axial dispersion of a neutral non-reacting solute in an incompressible electroosmotic flow. In contrast to previous approaches, the dispersion is obtained here by solving the time-dependent diffusion-advection equation in transformed spatial and temporal coordinates to obtain the two-dimensional late-time concentration field. The coefficient of dispersion arises as a separation eigenvalue, and its value is obtained as a necessary condition for satisfying all of the required boundary conditions. Solutions based on the Debye-Huckel approximation are presented for both a circular tube and a channel of infinite width. These results recover the well-known solutions for dispersion in pressure-driven flows when the Debye length is very large. In this limit, the axial dispersion is proportional to the square of the Peclet number based on the characteristic transverse dimension of the tube or channel. In the tilt of very small Debye lengths, the authors find that the dispersion varies as the square of the Peclet number based on the Debye length. Simple approximations to the coefficient of dispersion as a function of the Debye length and Peclet number are also presented.

  8. Conditions for similitude between the fluid velocity and electric field in electroosmotic flow

    SciTech Connect

    E. B. Cummings; S. K. Griffiths; R. H. Nilson; P. H. Paul

    1999-04-01

    Electroosmotic flow is fluid motion driven by an electric field acting on the net fluid charge produced by charge separation at a fluid-solid interface. Under many conditions of practical interest, the resulting fluid velocity is proportional to the local electric field, and the constant of proportionality is everywhere the same. Here the authors show that the main conditions necessary for this similitude are a steady electric field, uniform fluid and electric properties, an electric Debye layer that is thin compared to any physical dimension, and fluid velocities on all inlet and outlet boundaries that satisfy the Helmholtz-Smoluchowski relation normally applicable to fluid-solid boundaries. Under these conditions, the velocity field can be determined directly from the Laplace equation governing the electric potential, without solving either the continuity or momentum equations. Three important consequences of these conditions are that the fluid motion is everywhere irrotational, that fluid velocities in two-dimensional channels bounded by parallel planes are independent of the channel depth, and that such flows exhibit no dependence on the Reynolds number.

  9. Capillary electrophoresis: Imaging of electroosmotic and pressure driven flow profiles in fused silica capillaries

    NASA Technical Reports Server (NTRS)

    Williams, George O., Jr.

    1996-01-01

    This study is a continuation of the summer of 1994 NASA/ASEE Summer Faculty Fellowship Program. This effort is a portion of the ongoing work by the Biophysics Branch of the Marshall Space Flight Center. The work has focused recently on the separation of macromolecules using capillary electrophoresis (CE). Two primary goals were established for the effort this summer. First, we wanted to use capillary electrophoresis to study the electrohydrodynamics of a sample stream. Secondly, there was a need to develop a methodology for using CE for separation of DNA molecules of various sizes. In order to achieve these goals we needed to establish a procedure for detection of a sample plug under the influence of an electric field Detection of the sample with the microscope and image analysis system would be helpful in studying the electrohydrodynamics of this stream under load. Videotaping this process under the influence of an electric field in real time would also be useful. Imaging and photography of the sample/background electrolyte interface would be vital to this study. Finally, detection and imaging of electroosmotic flow and pressure driven flow must be accomplished.

  10. Reversing Flow Test Facility

    NASA Astrophysics Data System (ADS)

    Roach, P. D.

    1986-04-01

    The Reversing Flow Test Facility (RFTF) is intended for the study of fluid flow and heat transfer under the reversing-flow conditions that occur in Stirling engines. The facility consists of four major parts: (1) Mechanical Drive - two cylinders with cam-driven pistons which generate the reversing gas flow, (2) Test Section - a U-shaped section containing instrumented test pieces, (3) Instruments -l high-speed transducers for measuring gas pressure and temperature, piston positions, and other system parameters, and (4) Data Acquisition System - a computer-based system able to acquire, store, display and analyze the data from the instruments. The RFTF can operate at pressures up to 8.0 MPa, hot-side temperatures to 800 deg. C, and flow-reversal frequencies to 50 Hz. Operation to data has used helium as the working gas at pressures of 3.0 and 6.0 MPa, at ambient temperature, and at frequencies from 1 to 50 Hz. The results show that both frictional and inertial parts of the pressure drop are significant in the heater, coolers and connecting tubes; the inertial part is negligible in the regenerators. In all cases, the frictional part of the pressure drop is nearly in phase with the mass flow.

  11. Miniature liquid flow sensor and feedback control of electroosmotic and pneumatic flows for a micro gas analysis system.

    PubMed

    Ohira, Shin-Ichi; Toda, Kei

    2006-01-01

    Accurate liquid flow control is important in most chemical analyses. In this work, the measurement of liquid flow in microliters per minute was performed, and feedback control of the flow rate was examined. The flow sensor was arranged on a channel made in a polydimethylsiloxane (PDMS) block. The center of the channel was cooled by a miniature Peltier device, and the change in temperature balance along the channel formed by the flow was measured by two temperature sensors. Using this flow sensor, feedback flow control was examined with two pumping methods. One was the electroosmotic flow method, made by applying a high voltage (HV) between the reagent and waste reservoirs; the other was the piezo valve method, in which a micro-valve-seat was fabricated in a PDMS cavity with a silicone diaphragm. The latter was adopted for a micro gas analysis system (microGAS) for measuring atmospheric H2S and SO2. The obtained baselines were stable, and better limits of detection were obtained.

  12. Electroosmotic flow and ionic conductance in a pH-regulated rectangular nanochannel

    NASA Astrophysics Data System (ADS)

    Sadeghi, Morteza; Saidi, Mohammad Hassan; Sadeghi, Arman

    2017-06-01

    Infinite series solutions are obtained for electrical potential, electroosmotic velocity, ionic conductance, and surface physicochemical properties of long pH-regulated rectangular nanochannels of low surface potential utilizing the double finite Fourier transform method. Closed form expressions are also obtained for channels of large height to width ratio for which the depthwise variations vanish. Neglecting the Stern layer impact, the effects of EDL (Electric Double Layer) overlap, multiple ionic species, and association/dissociation reactions on the surface are all taken into account. Moreover, finite-element-based numerical simulations are conducted to account for the end effects as well as to validate the analytical solutions. We show that, with the exception of the migratory ionic conductivity, all the physicochemical parameters are strong functions of the channel aspect ratio. Accordingly, a slit geometry is not a good representative of a rectangular channel when the width is comparable to the height. It is also observed that the distribution of the electrical potential is not uniform over the surface of a charge-regulated channel. In addition, unlike ordinary channels for which an increase in the background salt concentration is always accompanied by higher flow rates, quite the opposite may be true for a pH-regulated duct at higher salt concentrations.

  13. Effect of nanostructures orientation on electroosmotic flow in a microfluidic channel

    NASA Astrophysics Data System (ADS)

    Eng Lim, An; Lim, Chun Yee; Cheong Lam, Yee; Taboryski, Rafael; Rui Wang, Shu

    2017-06-01

    Electroosmotic flow (EOF) is an electric-field-induced fluid flow that has numerous micro-/nanofluidic applications, ranging from pumping to chemical and biomedical analyses. Nanoscale networks/structures are often integrated in microchannels for a broad range of applications, such as electrophoretic separation of biomolecules, high reaction efficiency catalytic microreactors, and enhancement of heat transfer and sensing. Their introduction has been known to reduce EOF. Hitherto, a proper study on the effect of nanostructures orientation on EOF in a microfluidic channel is yet to be carried out. In this investigation, we present a novel fabrication method for nanostructure designs that possess maximum orientation difference, i.e. parallel versus perpendicular indented nanolines, to examine the effect of nanostructures orientation on EOF. It consists of four phases: fabrication of silicon master, creation of mold insert via electroplating, injection molding with cyclic olefin copolymer, and thermal bonding and integration of practical inlet/outlet ports. The effect of nanostructures orientation on EOF was studied experimentally by current monitoring method. The experimental results show that nanolines which are perpendicular to the microchannel reduce the EOF velocity significantly (approximately 20%). This flow velocity reduction is due to the distortion of local electric field by the perpendicular nanolines at the nanostructured surface as demonstrated by finite element simulation. In contrast, nanolines which are parallel to the microchannel have no effect on EOF, as it can be deduced that the parallel nanolines do not distort the local electric field. The outcomes of this investigation contribute to the precise control of EOF in lab-on-chip devices, and fundamental understanding of EOF in devices which utilize nanostructured surfaces for chemical and biological analyses.

  14. Rotating electro-osmotic flow over a plate or between two plates.

    PubMed

    Chang, Chien-Cheng; Wang, Chang-Yi

    2011-11-01

    In this paper, we investigate rotating electro-osmotic (EO) flow over an infinite plate or in a channel formed by two parallel plates. The analysis is based on the Debye-Hückel approximation for charge distributions and the Navier-Stokes equation for a transport electrolyte in the rotating frame. It is shown that, for the single plate, the nondimensional speed of system rotation ω is the singly most important parameter, while for the channel, in addition to ω, the nondimensional electrokinetic width K also plays an important role. However, the parameter ω≡η(2) has different natural appearances in the respective cases of a single plate (SP) and two plates (TPs). More precisely, η(SP) measures the ratio λ(D)/L(K) of the Debye length to the Ekman depth, while η(TP) measures the ratio L/L(K) of the channel width to the Ekman depth. The effect of rotation is always to reduce the axial flow rate along the direction of the applied electric field, accompanied by a (secondary) transverse flow. In the SP case, the plot on the velocity plane for each ω shows an interesting closed EO Ekman spiral. The size of the spiral shrinks with increasing ω. The transverse flow is so significant that the volume transport associated with the EO Ekman spiral turns clockwise 45° to the applied field near ω=0 and gradually turns at a right angle to the applied field as ω is increased. In contrast, in the TP case, the transverse flow rate is smaller than the axial flow rate when ω is small. The transverse flow rates at all K are observed to reach their maxima at ω of order 1. The volume transport is nearly at a zero angle to the applied field near ω=0 and gradually turns to 45° to the applied field as ω is increased. In the limit of ω→∞, for both SP and TP cases, the entire system forms a rigid body rotation-there is neither axial nor transverse flow.

  15. Numerical study of active control of mixing in electro-osmotic flows by temperature difference using lattice Boltzmann methods.

    PubMed

    Alizadeh, A; Wang, J K; Pooyan, S; Mirbozorgi, S A; Wang, M

    2013-10-01

    In this paper, the effect of temperature difference between inlet flow and walls on the electro-osmotic flow through a two-dimensional microchannel is investigated. The main objective is to study the effect of temperature variations on the distribution of ions and consequently internal electric potential field, electric body force, and velocity fields in an electro-osmotic flow. We assume constant temperature and zeta potential on walls and use the mean temperature of each cross section to characterize the Boltzmann ion distribution across the channel. Based on these assumptions, the multiphysical transports are still able to be described by the classical Poisson-Boltzmann model. In this work, the Navier-Stokes equation for fluid flow, the Poisson-Boltzmann equation for ion distribution, and the energy equation for heat transfer are solved by a couple lattice Boltzmann method. The modeling results indicate that the temperature difference between walls and the inlet solution may lead to two symmetrical vortices at the entrance region of the microchannel which is appropriate for mixing enhancements. The advantage of this phenomenon for active control of mixing in electro-osmotic flow is the manageability of the vortex scale without extra efforts. For instance, the effective domain of this pattern could broaden by the following modulations: decreasing the external electric potential field, decreasing the electric double layer thickness, or increasing the temperature difference between inlet flow and walls. This work may provide a novel strategy for design or optimization of microsystems. Copyright © 2013 Elsevier Inc. All rights reserved.

  16. Surface Charge, Electroosmotic Flow and DNA Extension in Chemically Modified Thermoplastic Nanoslits and Nanochannels

    PubMed Central

    Uba, Franklin I.; Pullagurla, Swathi R.; Sirasunthorn, Nichanun; Wu, Jiahao; Park, Sunggook; Chantiwas, Rattikan; Cho, Yoonkyoung; Shin, Heungjoo; Soper, Steven A.

    2014-01-01

    Thermoplastics have become attractive alternatives to glass/quartz for microfluidics, but the realization of thermoplastic nanofluidic devices has been slow in spite of the rather simple fabrication techniques that can be used to produce these devices. This slow transition has in part been attributed to insufficient understanding of surface charge effects on the transport properties of single molecules through thermoplastic nanochannels. We report the surface modification of thermoplastic nanochannels and an assessment of the associated surface charge density, zeta potential and electroosmotic flow (EOF). Mixed-scale fluidic networks were fabricated in poly(methylmethacrylate), PMMA. Oxygen plasma was used to generate surface-confined carboxylic acids with devices assembled using low temperature fusion bonding. Amination of the carboxylated surfaces using ethylenediamine (EDA) was accomplished via EDC coupling. XPS and ATR-FTIR revealed the presence of carboxyl and amine groups on the appropriately prepared surfaces. A modified conductance equation for nanochannels was developed to determine their surface conductance and was found to be in good agreement with our experimental results. The measured surface charge density and zeta potential of these devices were lower than glass nanofluidic devices and dependent on the surface modification adopted, as well as the size of the channel. This property, coupled to an apparent increase in fluid viscosity due to nanoconfinement, contributed to the suppression of the EOF in PMMA nanofluidic devices by an order of magnitude compared to the micro-scale devices. Carboxylated PMMA nanochannels were efficient for the transport and elongation of λ-DNA while these same DNA molecules were unable to translocate through aminated nanochannels. PMID:25369728

  17. Suppression of ion conductance by electro-osmotic flow in nano-channels with weakly overlapping electrical double layers

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Guo, Lingzi; Zhu, Xin; Ran, Qiushi; Dutton, Robert

    2016-08-01

    This theoretical study investigates the nonlinear ionic current-voltage characteristics of nano-channels that have weakly overlapping electrical double layers. Numerical simulations as well as a 1-D mathematical model are developed to reveal that the electro-osmotic flow (EOF) interplays with the concentration-polarization process and depletes the ion concentration inside the channels, thus significantly suppressing the channel conductance. The conductance may be restored at high electrical biases in the presence of recirculating vortices within the channels. As a result of the EOF-driven ion depletion, a limiting-conductance behavior is identified, which is intrinsically different from the classical limiting-current behavior.

  18. Observation of electro-osmotic flow echoes in porous media by nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Bendel, P.; Bernardo, M.; Dunsmuir, J. H.; Thomann, H.

    2003-04-01

    A method for assessing the time reversibility of molecular displacements in fluids is presented. The method utilizes pulsed field gradient NMR experiments, in which the flow driving force is inverted during the magnetization lifetime in each measurement cycle. The method is suitable for opaque three-dimensional systems and short displacements, and provides inherent separation between thermal diffusion and displacements driven by externally controlled forces. This approach was applied to study the time reversibility of an electric-field-driven flow of water in natural sand samples, over time scales of up to 0.4 s and displacement scales of the order of one particle diameter. It is demonstrated that the intensity loss of the NMR signal, caused by flow-induced phase dispersion, is fully refocused upon inversion of the polarity of the applied electric field, resulting in flow echoes.

  19. Ion fluxes and electro-osmotic fluid flow in electrolytes around a metallic nanowire tip under large applied ac voltage.

    PubMed

    Poetschke, M; Bobeth, M; Cuniberti, G

    2013-09-10

    Motivated by the analysis of electrochemical growth of metallic nanowires from solution, we studied ion fluxes near nanoelectrodes in a binary symmetric electrolyte on the basis of the modified Poisson-Nernst-Planck equations in the strongly nonlinear region at large applied ac voltage. For an approximate calculation of the electric field near the nanowire tip, concentric spherical blocking electrodes were considered with radius of the inner electrode being of typically a few ten nanometers. The spatiotemporal evolution of the ion concentrations within this spherical model was calculated numerically by using the finite element method. The potential drop at the electric double layer, the electric field enhancement at the electrode surface, and the field screening in the bulk solution were determined for different bulk concentrations, ac voltages, and frequencies. The appearance of ac electro-osmotic fluid flow at the tip of a growing metallic nanowire is discussed, based on an estimation of the body force in the liquid near the nanowire tip, which was modeled by a cylinder with hemispherical cap. Electric field components tangential to the electrode surface exist near the contact between cylinder and hemisphere. Our analysis suggests that ac electro-osmotic flow causes an additional convective transport of metal complexes to the tip of the growing metal nanowire and thus affects the nanowire growth velocity.

  20. A perturbative thermal analysis for an electro-osmotic flow in a slit microchannel based on a Lubrication theory

    NASA Astrophysics Data System (ADS)

    Ramos, Ali; Mendez, Federico; Bautista, Oscar; Lizardi, José

    2016-11-01

    In this work, we develop a new thermal analysis for an electro-osmotic flow in a rectangular microchannel. The central idea is very simple: the Debye length that defines the length of the electrical double-layer depends on temperature T. Therefore, if exists any reason to include variable temperature effects, the above length should be utilized with caution because it appears in any electro-osmotic mathematical model. For instance, the presence of the Joule effect is a source that can generate important longitudinal temperature gradients along the microchannel and the isothermal hypothesis is no longer valid. In this manner, the Debye length is altered and as a consequence, new longitudinal temperature gradient terms appear into the resulting governing equations. These terms are enough to change the electric potential and the flow field. Taking into account the above comments, in the present study the momentum equations together with the energy, Poisson and Ohmic current conservation equations are solved by using a regular perturbation technique. For this purpose, we introduce a dimensionless parameter α that measures the temperature deviations of a reference temperature.

  1. Electroosmotic flows of non-Newtonian power-law fluids in a cylindrical microchannel.

    PubMed

    Zhao, Cunlu; Yang, Chun

    2013-03-01

    EOF of non-Newtonian power-law fluids in a cylindrical microchannel is analyzed theoretically. Specially, exact solutions of electroosmotic velocity corresponding to two special fluid behavior indices (n = 0.5 and 1.0) are found, while approximate solutions are derived for arbitrary values of fluid behavior index. It is found that because of the approximation for the first-order modified Bessel function of the first kind, the approximate solutions introduce largest errors for predicting electroosmotic velocity when the thickness of electric double layer is comparable to channel radius, but can accurately predict the electroosmotic velocity when the thickness of electric double layer is much smaller or larger than the channel radius. Importantly, the analysis reveals that the Helmholtz-Smoluchowski velocity of power-law fluids in cylindrical microchannels becomes dependent on geometric dimensions (radius of channel), standing in stark contrast to the Helmholtz-Smoluchowski velocity over planar surfaces or in parallel-plate microchannels. Such interesting and counterintuitive effects can be attributed to the nonlinear coupling among the electrostatics, channel geometry, and non-Newtonian hydrodynamics. Furthermore, a method for enhancement of EOFs of power-law fluids is proposed under a combined DC and AC electric field. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Numerical solution of a multi-ion one-potential model for electroosmotic flow in two-dimensional rectangular microchannels.

    PubMed

    Van Theemsche, Achim; Deconinck, Johan; Van den Bossche, Bart; Bortels, Leslie

    2002-10-01

    A new more general numerical model for the simulation of electrokinetic flow in rectangular microchannels is presented. The model is based on the dilute solution model and the Navier-Stokes equations and has been implemented in a finite-element-based C++ code. The model includes the ion distribution in the Helmholtz double layer and considers only one single electrical' potential field variable throughout the domain. On a charged surface(s) the surface charge density, which is proportional to the local electrical field, is imposed. The zeta potential results, then, from this boundary condition and depends on concentrations, temperature, ion valence, molecular diffusion coefficients, and geometric conditions. Validation cases show that the model predicts accurately known analytical results, also for geometries having dimensions comparable to the Debye length. As a final study, the electro-osmotic flow in a controlled cross channel is investigated.

  3. Study of electro-osmotic flows in microchannels packed with variable porosity media via lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Chai, Zhenhua; Guo, Zhaoli; Shi, Baochang

    2007-05-01

    In this article, electro-osmotic flow (EOF) in microchannels packed with a variable porosity medium is studied using the lattice Boltzmann method (LBM). The present lattice Boltzmann model is constructed based on the generalized porous medium equation for EOF and validated by comparing the numerical solution with the approximate analytical solution. A detailed parametric study has been presented for EOF in microchannels filled with a variable porosity medium. It is found that the variations of porosity, particle size, ζ potential, applied electric field strength, and tortuosity significantly affect the flow pattern. Numerical results also indicate that the variation of the porosity near the wall has an important influence on the velocity profile, and should not be neglected in practice.

  4. Mass flow-rate control through time periodic electro-osmotic flows in circular microchannels

    NASA Astrophysics Data System (ADS)

    Chakraborty, Suman; Ray, Subhashis

    2008-08-01

    The present study is directed towards devising a scientific strategy for obtaining controlled time-periodic mass flow-rate characteristics through the employment of pulsating electric fields in circular microchannels by exploiting certain intrinsic characteristics of periodic electro-osmosis phenomenon. Within the assumption of thin electrical double layers, the governing equations for potential distribution and fluid flow are derived, corresponding to a steady base state and a time-varying perturbed state, by assuming periodic forms of the imposed electrical fields and the resultant velocity fields. For sinusoidal pulsations of the electric field superimposed over its mean, a signature map depicting the amplitudes of the mass flow rate and the electrical field as well as their phase differences is obtained from the theoretical analysis as a function of a nondimensional frequency parameter for different ratios of the characteristic electric double layer thickness relative to the microchannel radius. Distinctive characteristics in the signature profiles are obtained for lower and higher frequencies, primarily attributed to the finite time scale for momentum propagation away from the walls. The signature characteristics, obtained from the solution of the prescribed sinusoidal electric field, are subsequently used to solve the "inverse" problem, where the mass flow rate is prescribed in the form of sinusoidal pulsations and the desired electric fields that would produce the required mass flow-rate variations are obtained. The analysis is subsequently extended for controlled triangular and trapezoidal pulsations in the mass flow rate and the required electric fields are successfully obtained. It is observed that the higher the double layer thickness is in comparison to the channel radius, the more prominent is the deviation of the shape of the required electric field pulsation from the desired transience in the mass flow-rate characteristics. Possible extensions of the

  5. Speciation of mercury by hydrostatically modified electroosmotic flow capillary electrophoresis coupled with volatile species generation atomic fluorescence spectrometry.

    PubMed

    Yan, Xiu-Ping; Yin, Xue-Bo; Jiang, Dong-Qing; He, Xi-Wen

    2003-04-01

    A novel method for speciation analysis of mercury was developed by on-line hyphenating capillary electrophoresis (CE) with atomic fluorescence spectrometry (AFS). The four mercury species of inorganic mercury Hg(II), methymercury MeHg(I), ethylmercury EtHg(I), and phenylmercury PhHg(I) were separated as mercury-cysteine complexes by CE in a 50-cm x 100-microm-i.d. fused-silica capillary at 15 kV and using a mixture of 100 mmol L(-1) of boric acid and 12% v/v methanol (pH 9.1) as electrolyte. A novel technique, hydrostatically modified electroosmotic flow (HSMEOF) in which the electroosmotic flow (EOF) was modified by applying hydrostatical pressure opposite to the direction of EOF was used to improve resolution. A volatile species generation technique was used to convert the mercury species into their respective volatile species. A newly developed CE-AFS interface was employed to provide an electrical connection for stable electrophoretic separations and to allow on-line volatile species formation. The generated volatile species were on-line detected with AFS. The precisions (RSD, n = 5) were in the range of 1.9-2.5% for migration time, 1.8-6.3% for peak area response, and 2.3-6.1% for peak height response for the four mercury species. The detection limits ranged from 6.8 to 16.5 microg L(-1) (as Hg). The recoveries of the four mercury species in the water samples were in the range of 86.6-111%. The developed technique was successfully applied to speciation analysis of mercury in a certified reference material (DORM-2, dogfish muscle).

  6. Transport and reaction of nanoliter samples in a microfluidic reactor using electro-osmotic flow

    NASA Astrophysics Data System (ADS)

    Arumbuliyur Comandur, Kaushik; Bhagat, Ali Asgar S.; Dasgupta, Subhashish; Papautsky, Ian; Banerjee, Rupak K.

    2010-03-01

    The primary focus of the paper is to establish both numerical and experimental methods to control the concentration of samples in a microreactor well. The concentration of the reacting samples is controlled by varying the initial sample size and electric field. Further, the paper numerically investigates the feasibility of mixing and reacting nanoliter samples with a wide variation in reaction rates in the microreactor driven by electro-osmotic pumping. Two discrete samples are measured and transported to the microreactor simultaneously by electro-osmotic pinching and switching. The transported samples are mixed in the microreactor and floated for 4.5 s for reaction to occur. It is seen that the normalized concentration of the product increases from 0.25 to 0.45 during that period. Also the effects of sample size and applied electric field on sample concentration during the switching process are studied. It is found that the normalized final sample concentration increases from 0.03 to 0.11 with an increase in sample size from 60 to 150 µm, at a constant electric field. Further, by increasing the electric field from 100 to 1000 V cm-1, at a constant sample size, there is a significant decrease in the final concentration of the sample from 0.14 to 0.04. Our studies also show that the normalized product concentration depends on the reaction rate and increases from 0.28 to 0.48 as the reaction rate increases from 10 L mol-1 s-1 to 105 L mol-1 s-1. However, the increase in the reaction rate beyond 105 L mol-1 s-1 does not influence the product concentration for the present design of the microreactor. Our microreactor with improved mixing can be used for assessing reactions of biological samples. The optimized sample size along with a controlled electric field for sample injection forms the basis for developing a prototype of a microreactor device for high throughput drug screening.

  7. Instantaneous velocity measurement of AC electroosmotic flows by laser induced fluorescence photobleaching anemometer with high temporal resolution

    NASA Astrophysics Data System (ADS)

    Zhao, Wei; Yang, Fang; Qiao, Rui; Wang, Guiren; Rui Qiao Collaboration

    2015-11-01

    Understanding the instantaneous response of flows to applied AC electric fields may help understand some unsolved issues in induced-charge electrokinetics and enhance performance of microfluidic devices. Since currently available velocimeters have difficulty in measuring velocity fluctuations with frequency higher than 1 kHz, most experimental studies so far focus only on the average velocity measurement in AC electrokinetic flows. Here, we present measurements of AC electroosmotic flow (AC-EOF) response time in microchannels by a novel velocimeter with submicrometer spatial resolution and microsecond temporal resolution, i.e. laser-induced fluorescence photobleaching anemometer (LIFPA). Several parameters affecting the AC-EOF response time to the applied electric signal were investigated, i.e. channel length, transverse position and solution conductivity. The experimental results show that the EOF response time under a pulsed electric field decreases with the reduction of the microchannel length, distance between the detection position to the wall and the conductivity of the solution. This work could provide a new powerful tool to measure AC electrokinetics and enhance our understanding of AC electrokinetic flows.

  8. Electro-osmotic infusion for joule heating soil remediation techniques

    DOEpatents

    Carrigan, Charles R.; Nitao, John J.

    1999-01-01

    Electro-osmotic infusion of ground water or chemically tailored electrolyte is used to enhance, maintain, or recondition electrical conductivity for the joule heating remediation technique. Induced flows can be used to infuse electrolyte with enhanced ionic conductivity into the vicinity of the electrodes, maintain the local saturation of near-electrode regions and resaturate a partially dried out zone with groundwater. Electro-osmotic infusion can also tailor the conductivity throughout the target layer by infusing chemically modified and/or heated electrolyte to improve conductivity contrast of the interior. Periodic polarity reversals will prevent large pH changes at the electrodes. Electro-osmotic infusion can be used to condition the electrical conductivity of the soil, particularly low permeability soil, before and during the heating operation. Electro-osmotic infusion is carried out by locating one or more electrodes adjacent the heating electrodes and applying a dc potential between two or more electrodes. Depending on the polarities of the electrodes, the induced flow will be toward the heating electrodes or away from the heating electrodes. In addition, electrodes carrying a dc potential may be located throughout the target area to tailor the conductivity of the target area.

  9. Mechanism of porous core electroosmotic pump flow injection system and its application to determination of chromium(VI) in waste-water.

    PubMed

    Gan, W E; Yang, L; He, Y Z; Zeng, R H; Cervera, M L; de la Guardia, M

    2000-04-03

    An electroosmotic pump flow injection system is introduced in this paper. According to electroosmotic theory, the pump's properties were described. A large flow range (mul min(-1)-ml min(-1)), moderate carrier pressure (>0.15 MPa), reduced performance voltage (<500 V) and stable flow rate (RSD<3.0% in 4 h) are the main properties of the pump. NH(4)OH (0.35 mM) was used as carrier for improving the pump's flow stability. The electroosmotic efficiency of the pump's medium, porous core, can be recovered and regenerated. A sandwich zone was used for sample and reagent introduction in order to adapt to the pump performance. Flow injection-spectrophotometry was employed for the determination of Cr(VI) in waste-water, based on the formation of the complex with 1,5-diphenylcarbazide and absorbance measurement at 540 nm. Within the calibration range of 0-7.0 mg l(-1) of Cr(VI), the RSD was 0.4% (n=5). The recovery of 0.70 mg l(-1) Cr(VI) added to the waste-water sample was 94.5+/-2.0% (n=5).

  10. Interfacial phenomena and dynamic contact angle modulation in microcapillary flows subjected to electroosmotic actuation.

    PubMed

    Chakraborty, Debapriya; Chakraborty, Suman

    2008-09-02

    The dynamic evolution of an incompressible liquid meniscus inside a microcapillary is investigated, under the combined influences of viscous, capillary, intermolecular, pondermotive, and electroosmotic effects. In the limit of small capillary numbers, an advancing meniscus shape is shown to merge smoothly with the precursor film, using matched asymptotic analysis. A scaling relationship is also established for the dynamic contact angle as a nondimensional function of the capillary number and the applied electrical voltage. The analysis is further generalized by invoking a kinetic slip model for overcoming the constraints of meniscus tip singularity. The kinetic slip model is subsequently utilized to analyze the interfacial dynamics from the perspective of the results obtained from the matched asymptotic analysis. A generalization is achieved in this regard, which may provide a sound basis for controlling the topographical features of a dynamically evolving meniscus in a microcapillary subjected to electrokinetic effects. These results are also in excellent agreement with the experimental findings over a wide range of capillary number values.

  11. Influence of electroosmotic flow on the ionic current rectification in a pH-regulated, conical nanopore

    NASA Astrophysics Data System (ADS)

    Lin, Dong-Huei; Lin, Chih-Yuan; Tseng, Shiojenn; Hsu, Jyh-Ping

    2015-08-01

    The ionic current rectification (ICR) is studied theoretically by considering a pH-regulated, conical nanopore. In particular, the effect of electroosmotic flow (EOF), which was often neglected in previous studies, is investigated by solving a set of coupled Poisson, Nernst-Planck, and Navier-Stokes equations. The behaviors of ICR under various conditions are examined by varying solution pH, bulk ionic concentration, and applied electric potential bias. We show that the EOF effect is significant when the bulk ionic concentration is medium high, the pH is far away from the iso-electric point, and the electric potential bias is high. The percentage deviation in the current rectification ratio arising from neglecting the EOF effect can be on the order of 100%. In addition, the behavior of the current rectification ratio at a high pH taking account of EOF is different both qualitatively and quantitatively from that without taking account of EOF.The ionic current rectification (ICR) is studied theoretically by considering a pH-regulated, conical nanopore. In particular, the effect of electroosmotic flow (EOF), which was often neglected in previous studies, is investigated by solving a set of coupled Poisson, Nernst-Planck, and Navier-Stokes equations. The behaviors of ICR under various conditions are examined by varying solution pH, bulk ionic concentration, and applied electric potential bias. We show that the EOF effect is significant when the bulk ionic concentration is medium high, the pH is far away from the iso-electric point, and the electric potential bias is high. The percentage deviation in the current rectification ratio arising from neglecting the EOF effect can be on the order of 100%. In addition, the behavior of the current rectification ratio at a high pH taking account of EOF is different both qualitatively and quantitatively from that without taking account of EOF. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03433g

  12. Mixing enhancement of low-Reynolds electro-osmotic flows in microchannels with temperature-patterned walls.

    PubMed

    Alizadeh, A; Zhang, L; Wang, M

    2014-10-01

    Mixing becomes challenging in microchannels because of the low Reynolds number. This study aims to present a mixing enhancement method for electro-osmotic flows in microchannels using vortices caused by temperature-patterned walls. Since the fluid is non-isothermal, the conventional form of Nernst-Planck equation is modified by adding a new migration term which is dependent on both temperature and internal electric potential gradient. This term results in the so-called thermo-electrochemical migration phenomenon. The coupled Navier-Stokes, Poisson, modified Nernst-Planck, energy and advection-diffusion equations are iteratively solved by multiple lattice Boltzmann methods to obtain the velocity, internal electric potential, ion distribution, temperature and species concentration fields, respectively. To enhance the mixing, three schemes of temperature-patterned walls have been considered with symmetrical or asymmetrical arrangements of blocks with surface charge and temperature. Modeling results show that the asymmetric arrangement scheme is the most efficient scheme and enhances the mixing of species by 39% when the Reynolds number is on the order of 10(-3). Current results may help improve the design of micro-mixers at low Reynolds number. Copyright © 2014 Elsevier Inc. All rights reserved.

  13. Electroosmotic flow in capillary channels filled with nonconstant viscosity electrolytes: exact solution of the Navier-Stokes equation.

    PubMed

    Otevrel, Marek; Klepárník, Karel

    2002-10-01

    The partial differential equation describing unsteady velocity profile of electroosmotic flow (EOF) in a cylindrical capillary filled with a nonconstant viscosity electrolyte was derived. Analytical solution, based on the general Navier-Stokes equation, was found for constant viscosity electrolytes using the separation of variables (Fourier method). For the case of a nonconstant viscosity electrolyte, the steady-state velocity profile was calculated assuming that the viscosity decreases exponentially in the direction from the wall to the capillary center. Since the respective equations with nonconstant viscosity term are not solvable in general, the method of continuous binding conditions was used to solve this problem. In this method, an arbitrary viscosity profile can be modeled. The theoretical conclusions show that the relaxation times at which an EOF approaches the steady state are too short to have an impact on a separation process in any real systems. A viscous layer at the wall affects EOF significantly, if it is thicker than the Debye length of the electric double layer. The presented description of the EOF dynamics is applicable to any microfluidic systems.

  14. Ion exclusion and electrokinetic effects resulting from electro-osmotic flow of salt solutions in charged silica nanopores.

    PubMed

    Haria, Neil R; Lorenz, Christian D

    2012-05-07

    Silica nanopores are the focus of significant scientific interest due to their potential in a wide variety of applications including desalination membranes. In this paper, the results of extensive all-atom molecular dynamics simulations of the electro-osmotic flow of 0.5 M monovalent (NaCl) and divalent (CaCl(2)) ionic solutions through cylindrical charged silica nanopores are presented. The silica nanopores are produced such that they capture the experimentally observed interfacial properties. The results provide an atomistic description of the ion transport through pores of diameters of 1.5 nm, 2.0 nm, 2.5 nm and 3.0 nm. In doing so, the effect of pore size on ion pairing, ion hydration, and water orientation for each ionic solution was investigated. Also, the transport of the ions through the nanopores is studied, and it is found that in the monovalent solutions the Cl(-) ions are excluded from the nanopores of all sizes. Whereas in the divalent solutions, there is no such preferential exclusion of either ion. This is due to the fact that the interfacial charge is fully compensated for by the Ca(2+) ions while it is not the case for the Na(+) ions.

  15. Stagnation point reverse flow combustor

    NASA Technical Reports Server (NTRS)

    Zinn, Ben T. (Inventor); Neumeier, Yedidia (Inventor); Seitzman, Jerry M. (Inventor); Jagoda, Jechiel (Inventor); Weksler, Yoav (Inventor)

    2008-01-01

    A method for combusting a combustible fuel includes providing a vessel having an opening near a proximate end and a closed distal end defining a combustion chamber. A combustible reactants mixture is presented into the combustion chamber. The combustible reactants mixture is ignited creating a flame and combustion products. The closed end of the combustion chamber is utilized for directing combustion products toward the opening of the combustion chamber creating a reverse flow of combustion products within the combustion chamber. The reverse flow of combustion products is intermixed with combustible reactants mixture to maintain the flame.

  16. Flow batteries for microfluidic networks: configuring an electroosmotic pump for nonterminal positions.

    PubMed

    He, Chiyang; Lu, Joann J; Jia, Zhijian; Wang, Wei; Wang, Xiayan; Dasgupta, Purnendu K; Liu, Shaorong

    2011-04-01

    A micropump provides flow and pressure for a lab-on-chip device, just as a battery supplies current and voltage for an electronic system. Numerous micropumps have been developed, but none is as versatile as a battery. One cannot easily insert a micropump into a nonterminal position of a fluidic line without affecting the rest of the fluidic system, and one cannot simply connect several micropumps in series to enhance the pressure output, etc. In this work we develop a flow battery (or pressure power supply) to address this issue. A flow battery consists of a +EOP (in which the liquid flows in the same direction as the field gradient) and a -EOP (in which the liquid flows opposite to the electric field gradient), and the outlet of the +EOP is directly connected to the inlet of the -EOP. An external high voltage is applied to this outlet-inlet joint via a short gel-filled capillary that allows ions but not bulk liquid flow, while the +EOP's inlet and the -EOP's outlet (the flow battery's inlet and outlet) are grounded. This flow battery can be deployed anywhere in a fluidic network without electrically affecting the rest of the system. Several flow batteries can be connected in series to enhance the pressure output to drive HPLC separations. In a fluidic system powered by flow batteries, a hydraulic equivalent of Ohm's law can be applied to analyze system pressures and flow rates.

  17. Electroosmotic access resistance of a nanopore

    NASA Astrophysics Data System (ADS)

    Ghosal, Sandip; Sherwood, John D.; Mao, Mao

    2014-11-01

    Electroosmotic flow through a nanopore that traverses a dielectric membrane with a fixed surface charge density is considered. In the limit where the surface charge is small and the applied electric field weak, the reciprocal theorem is used to derive an expression for the electroosmotic flux through the pore up to quadratures over the fluid volume. Thus, an ``electroosmotic conductance'' (the fluid flux per unit applied voltage) may be defined in analogy to the corresponding electrical conductance of a hole in an insulating membrane immersed in a uniform conductor. In the limit when the membrane is thick compared to the pore diameter, the usual result for the electroosmotic conductance through long cylindrical channels (which varies inversely as the membrane thickness) is recovered. The electroosmotic conductance is shown to approach a finite value for an infinitely thin membrane: this residual electroosmotic resistance (inverse of conductance) is analogous to the concept of ``access resistance of a pore'' in the corresponding electrical problem. The dependence of the electroosmotic conductance on pore radius, Debye length and membrane thickness is investigated. Reference: Supported by the NIH under Grant 4R01HG004842. SG acknowledges a visiting professorship at Cambridge University funded by the Leverhulme Trust, UK. JDS thanks DAMTP (Cambridge University) and Institut de Mecanique des Fluides de Toulouse for hospitality.

  18. Contact line dynamics of electroosmotic flows of incompressible binary fluid system with density and viscosity contrasts

    NASA Astrophysics Data System (ADS)

    Mondal, Pranab Kumar; DasGupta, Debabrata; Bandopadhyay, Aditya; Ghosh, Uddipta; Chakraborty, Suman

    2015-03-01

    We consider electrically driven dynamics of an incompressible binary fluid, with contrasting densities and viscosities of the two phases, flowing through narrow fluidic channel with walls with predefined surface wettabilities. Through phase field formalism, we describe the interfacial kinetics in the presence of electro-hydrodynamic coupling and address the contact line dynamics of the two-fluid system. We unveil the interplay of the substrate wettability and the contrast in the fluid properties culminating in the forms of two distinct regimes—interface breakup regime and a stable interface regime. Through a parametric study, we demarcate the effect of the density and viscosity contrasts along with the electrokinetic parameters such as the surface charge and ionic concentration on the underlying contact-line-dynamics over interfacial scales.

  19. The generation of concentration gradients using electroosmotic flow in micro reactors allowing stereoselective chemical synthesis.

    PubMed

    Skelton, V; Greenway, G M; Haswell, S J; Styring, P; Morgan, D O; Warrington, B H; Wong, S Y

    2001-01-01

    The stereoselective control of chemical reactions has been achieved by applying electrical fields in a micro reactor generating controlled concentration gradients of the reagent streams. The chemistry based upon well-established Wittig synthesis was carried out in a micro reactor device fabricated in borosilicate glass using photolithographic and wet etching techniques. The selectivity of the cis (Z) to trans (E) isomeric ratio in the product synthesised was controlled by varying the applied voltages to the reagent reservoirs within the micro reactor. This subsequently altered the relative reagent concentrations within the device resulting in Z/E ratios in the range 0.57-5.21. By comparison, a traditional batch method based on the same reaction length, concentration, solvent and stoichiometry (i.e., 1.0:1.5:1.0 reagent ratios) gave a Z/E in the range 2.8-3.0. However, when the stoichiometric ratios were varied up to ten times as much, the Z/E ratios varied in accordance to the micro reactor i.e., when the aldehyde is in excess, the Z isomer predominates whereas when the aldehyde is in low concentrations, the E isomer is the more favourable form. Thus indicating that localised concentration gradients generated by careful flow control due to the diffusion limited non-turbulent mixing regime within a micro reactor, leads to the observed stereo selectivity for the cis and trans isomers.

  20. Flow of Power-Law Liquids in a Hele-Shaw Cell Driven by Non-Uniform Electroosmotic Slip in the Case of Strong Depletion

    NASA Astrophysics Data System (ADS)

    Boyko, Evgeniy; Bercovici, Moran; Gat, Amir

    2016-11-01

    We analyze flow of a non-Newtonian fluid in a Hele-Shaw cell, subjected to spatially non-uniform electroosmotic flow. We specifically focus on power-law fluids with wall depletion properties and derive a p-Poisson equation governing the pressure field, as well as a set of linearized equations representing its asymptotic approximation for weakly non-Newtonian behavior. To investigate the effect of non-Newtonian properties on the resulting fluidic pressure and velocity, we consider several configurations in one and two dimensions, and calculate both exact and approximate solutions. We show that the asymptotic approximation is in good agreement with exact solutions even for fluids with significant non-Newtonian behavior. The asymptotic model thus enables prediction of the flow and pressure fields for non-Newtonian fluids, and may be particularly useful for the analysis and design of microfluidic systems involving electro-kinetic transport of such fluids.

  1. Reversed flow above a plate with suction

    NASA Technical Reports Server (NTRS)

    Lin, S. P.; Tobak, M.

    1986-01-01

    A minor extension is developed for Kovasznay's (1948) solution, and an exact solution is presented for Navier-Stokes equations that may represent the reversed flow about a flat plate with suction. This exact solution is the result of a search for a solution that may serve as an exact basic flow for a model stability analysis of nonparallel flows involving flow reversal.

  2. Influence of material transition and interfacial area changes on flow and concentration in electro-osmotic flows.

    PubMed

    Rani, Sudheer D; You, Byoung-Hee; Soper, Steve A; Murphy, Michael C; Nikitopoulos, Dimitris E

    2013-04-03

    This paper presents a numerical study to investigate the effect of geometrical and material transition on the flow and progression of a sample plug in electrokinetic flows. Three cases were investigated: (a) effect of sudden cross-sectional area change (geometrical transition or mismatch) at the interface, (b) effect of only material transition (i.e. varying ζ-potential), and (c) effect of combined material transition and cross-sectional area change at the interface. The geometric transition was quantified based on the ratio of reduced flow area A2 at the mismatch plane to the original cross-sectional area A1. Multiple simulations were performed for varying degrees of area reduction i.e. 0-75% reduction in the available flow area, and the effect of dispersion on the sample plug was quantified by standard metrics. Simulations showed that a 13% combined material and geometrical transition can be tolerated without significant loss of sample resolution. A 6.54% reduction in the flow rates was found between 0% and 75% combined material and geometrical transition. Copyright © 2013 Elsevier B.V. All rights reserved.

  3. Flow of power-law liquids in a Hele-Shaw cell driven by non-uniform electro-osmotic slip in the case of strong depletion

    NASA Astrophysics Data System (ADS)

    Boyko, Evgeniy; Bercovici, Moran; Gat, Amir D.

    2016-11-01

    We analyze flow of non-Newtonian fluids in a Hele-Shaw cell, subjected to spatially non-uniform electroosmotic slip. Motivated by their potential use for increasing the characteristic pressure fields, we specifically focus on power-law fluids with wall depletion properties. We derive a p-Poisson equation governing the pressure field, as well as a set of linearized equations representing its asymptotic approximation for weakly non-Newtonian behavior. To investigate the effect of non-Newtonian properties on the resulting fluidic pressure and velocity, we consider several configurations in one- and two-dimensions, and calculate both exact and approximate solutions. We show that the asymptotic approximation is in good agreement with exact solutions even for fluids with significant non-Newtonian behavior, allowing its use in the analysis and design of microfluidic systems involving electro-kinetic transport of such fluids.

  4. Determination of nerve agent degradation products by capillary electrophoresis using field-amplified sample stacking injection with the electroosmotic flow pump and contactless conductivity detection.

    PubMed

    Xu, Li; Hauser, Peter C; Lee, Hian Kee

    2009-07-31

    In the present study, field-amplified sample stacking injection using the electroosmotic flow pump (FAEP) was developed for the capillary electrophoretic separation of the four nerve agent degradation products methylphosphonic acid (MPA), ethyl methylphosphonic acid (EMPA), isopropyl methylphosphonic acid (IMPA) and cyclohexyl methylphosphonic acid (CMPA). Coupled to contactless conductivity detection, direct quantification of these non-UV active compounds could be achieved. Sensitivity enhancement of up to 500 to 750-fold could be obtained. The newly established approach was applied to the determination of the analytes in river water and aqueous extracts of soil. Detection limits of 0.5, 0.7, 1.4 and 2.7 ng/mL were obtained for MPA, EMPA, IMPA and CMPA, respectively, in river water and 0.09, 0.14, 0.44 and 0.22 microg/g, respectively, in soil.

  5. Effect of interfacial Maxwell stress on time periodic electro-osmotic flow in a thin liquid film with a flat interface.

    PubMed

    Mayur, Manik; Amiroudine, Sakir; Lasseux, Didier; Chakraborty, Suman

    2014-03-01

    Electro-osmotic flows (EOF) have seen remarkable applications in lab-on-a-chip based microdevices owing to their lack of moving components, durability, and nondispersive nature of the flow profiles under specifically designed conditions. However, such flows may typically suffer from classical Faradaic artifacts like electrolysis of the solvent, which affects the flow rate control. Such a problem has been seen to be overcome by employing time periodic EOFs. Electric field induced transport of a conductive liquid is another nontrivial problem that requires careful study of interfacial dynamics in response to such an oscillatory flow actuation. The present study highlights the role of electric field generated Maxwell stress and free surface potential along with the electric double layer thickness and forcing frequency, toward influencing the interfacial transport and fluid flow in free-surface electro-osmosis under a periodically varying external electric field, in a semi-analytical formalism. Our results reveal interesting regimes over which the pertinent interfacial phenomena as well as bulk transport characteristics may be favorably tuned by employing time varying electrical fields.

  6. Effect of surface charge density and electro-osmotic flow on ionic current in a bipolar nanopore fluidic diode

    NASA Astrophysics Data System (ADS)

    Pal Singh, Kunwar; Kumar, Manoj

    2011-10-01

    We have simulated bipolar nanopore fluidic diodes for different values of surface charge densities, electrolyte concentrations, and thickness of transition zone. Nanopore enrichment leads to increased nanopore conductivity with the surface charge density at low electrolyte concentrations. Potential drop across the nanopore and electric field inside the nanopore decreases. Forward current and ionic current rectification peaks for a specific value of surface charge density. Even though the electro-osmotic current component remains small as compared to other components, its non-inclusion in the modeling leads to serious errors in the solutions. Significant ion current rectification can be obtained even if transition zone between oppositely charged zones is not narrow. The effect of the surface charge is screened by counterions at higher electrolyte concentrations, which leads to reduced electrolyte polarization and a decrease in the ion current rectification.

  7. Streamwise Oscillation of Airfoils into Reverse Flow

    NASA Astrophysics Data System (ADS)

    Granlund, Kenneth; Jones, Anya; Ol, Michael

    2015-11-01

    An airfoil in freestream is oscillated in streamwise direction to cyclically enter reverse flow. Measured lift is compared to analytical blade element theories. Advance ratio, reduced frequency and angle of attack is varied within those typical for helicopters. Experimental results reveal that lift does not become negative in the flow reversal part, contradicting one theory and supported by another. Flow visualization reveal the leading edge vortex advecting against the freestream to a point in front of the leading edge.

  8. Orthogonal optical force separation simulation of particle and molecular species mixtures under direct current electroosmotic driven flow for applications in biological sample preparation.

    PubMed

    Staton, Sarah J R; Terray, Alex; Collins, Greg E; Hart, Sean J

    2013-04-01

    Presented here are the results from numerical simulations applying optical forces orthogonally to electroosmotically induced flow containing both molecular species and particles. Simulations were conducted using COMSOL v4.2a Multiphysics® software including the particle tracking module. The study addresses the application of optical forces to selectively remove particulates from a mixed sample stream that also includes molecular species in a pinched flow microfluidic device. This study explores the optimization of microfluidic cell geometry, magnitude of the applied direct current electric field, EOF rate, diffusion, and magnitude of the applied optical forces. The optimized equilibrium of these various contributing factors aids in the development of experimental conditions and geometry for future experimentation as well as directing experimental expectations, such as diffusional losses, separation resolution, and percent yield. The result of this work generated an optimized geometry with flow conditions leading to negligible diffusional losses of the molecular species while also being able to produce particle removal at near 100% levels. An analytical device, such as the one described herein with the capability to separate particulate and molecular species in a continuous, high-throughput fashion would be valuable by minimizing sample preparation and integrating gross sample collection seamlessly into traditional analytical detection methods.

  9. Electro-osmotic flow of power-law fluid and heat transfer in a micro-channel with effects of Joule heating and thermal radiation

    NASA Astrophysics Data System (ADS)

    Shit, G. C.; Mondal, A.; Sinha, A.; Kundu, P. K.

    2016-11-01

    A mathematical model has been developed for studying the electro-osmotic flow and heat transfer of bio-fluids in a micro-channel in the presence of Joule heating effects. The flow of bio-fluid is governed by the non-Newtonian power-law fluid model. The effects of thermal radiation and velocity slip condition have been examined in the case of hydrophobic channel. The Poisson-Boltzmann equation governing the electrical double layer field and a body force generated by the applied electric potential field are taken into consideration. The results presented here pertain to the case where the height of the channel is much greater than the thickness of electrical double layer comprising the Stern and diffuse layers. The expressions for flow characteristics such as velocity, temperature, shear stress and Nusselt number have been derived analytically under the purview of the present model. The results estimated on the basis of the data available in the existing scientific literatures are presented graphically. The effects of thermal radiation have an important bearing on the therapeutic procedure of hyperthermia, particularly in understanding the heat transfer in micro-channel in the presence of electric potential. The dimensionless Joule heating parameter has a reducing impact on Nusselt number for both pseudo-plastic and dilatant fluids, nevertheless its impact on Nusselt number is more pronounced for dilatant fluid. Furthermore, the effect of viscous dissipation has a significant role in controlling heat transfer and should not be neglected.

  10. Stable electroosmotically driven actuators

    NASA Astrophysics Data System (ADS)

    Sritharan, Deepa; Motsebo, Mylene; Tumbic, Julia; Smela, Elisabeth

    2013-04-01

    We have previously presented "nastic" actuators based on electroosmotic (EO) pumping of fluid in microchannels using high electric fields for potential application in soft robotics. In this work we address two challenges facing this technology: applying EO to meso-scale devices and the stability of the pumping fluid. The hydraulic pressure achieved by EO increases with as 1/d2, where d is the depth of the microchannel, but the flow rate (which determines the stroke and the speed) is proportional to nd, where n is the number of channels. Therefore to get high force and high stroke the device requires a large number of narrow channels, which is not readily achievable using standard microfabrication techniques. Furthermore, for soft robotics the structure must be soft. In this work we present a method of fabricating a three-dimensional porous elastomer to serve as the array of channels based on a sacrificial sugar scaffold. We demonstrate the concept by fabricating small pumps. The flexible devices were made from polydimethylsiloxane (PDMS) and comprise the 3D porous elastomer flanked on either side by reservoirs containing electrodes. The second issue addressed here involves the pumping fluid. Typically, water is used for EO, but water undergoes electrolysis even at low voltages. Since EO takes place at kV, these systems must be open to release the gases. We have recently reported that propylene carbonate (PC) is pumped at a comparable rate as water and is also stable for over 30 min at 8 kV. Here we show that PC is, however, degraded by moisture, so future EO systems must prevent water from reaching the PC.

  11. Time-reversed, flow-reversed ballistics simulations

    SciTech Connect

    Zernow, L.; Chapyak, E. J.; Scheffler, D. R.

    2001-01-01

    Two-dimensional simulations of planar sheet jet formation are studied to examine the hydrodynamic issues involved when simulations are carried out in the inverse direction, that is, with reversed time and flow. Both a realistic copper equation of state and a shockless equation of state were used. These studies are an initial step in evaluating this technique as a ballistics design tool.

  12. On the stability of reverse flow vortices

    NASA Astrophysics Data System (ADS)

    Troshkin, O. V.

    2016-12-01

    The nonlinear stability of vortex zones of reverse flows in a plane-parallel ideal incompressible flow is proved. The zones originate at large values of a dimensionless parameter taken in the inflow part of the boundary, the so-called vorticity level. Positive or negative values of this parameter lead to a left- or right-hand oriented vortex, respectively.

  13. Time Reversal Acoustic in a flowing medium

    NASA Astrophysics Data System (ADS)

    Luong, Trung Dung; Arora, Manish; Hies, Thomas; Ohl, Claus-Dieter; Claus-Dieter Ohl grou Team; DHI Water; Environment (S) Pte. Ltd. Collaboration

    2013-11-01

    We explore the effect of flow on time reversal acoustics (TRA). Traditionally, TRA has been studied in static conditions, while a motion of the medium is expected to degrade the spatio-temporal focussing of the sound pulse. Here, we study the effect of the flow with a TRA system at 1MHz. A controlled flow is added between the emitter and receiver. Additional, a metallic plate is utilized to increases the numerical aperture of the emitting transducer. The impulse response of the non-flowing system, is recorded and time reversed. Then, the response of the hydrophone is recorded in presence and absence of the flow. It is found that the time reversed signal focuses on at the hydrophone in both the cases. In the absence of flow, the focus signal is observed to be shifted in the time domain. Furthermore, there is a drop in the peak-to-peak value of the focus signal in the presence of flow. For a flow rate of 3 cm/s (Re ~ 1000), a distinct shift in the time domain and a reduction of the peak is obtained. The results will be discussed and compared with numerical simulation of TRA under flow conditions.

  14. Mantle flow reversals in cylindrical Earth models

    NASA Astrophysics Data System (ADS)

    Ghias, Sanaz R.; Jarvis, Gary T.

    2007-12-01

    We employ a two-dimensional model of mantle convection in a cylindrical shell to study the influence of curvature on the phenomenon of spontaneous flow reversal, which has been found previously only in plane layer models in Cartesian geometry. Our model includes rigidly moving plates, with weak zones at each end, and uniformly distributed internal heat sources. Surface plates in this model are passive in that their lateral velocities reflect the overall buoyancy in the underlying mantle and, at each time step, match the average surface velocity that would occur in the absence of plates. Our principal finding is that flow reversals, similar to those in plane layers, are also found in our cylindrical shell models, thereby attesting to the robustness of this feature. We conduct systematic investigations of the impact on the flow reversal behavior of varying degree of curvature, plate thickness, internal heating rate and aspect ratio of the convection cells. Flow reversals are driven by a build-up of internally heated material adjacent to a major mantle downwelling. When thermal instabilities develop in the upper boundary layer they develop into intermediate sinking plumes which disrupt the build-up of hot material near sinking plumes. Accordingly, parameter values which tend to stabilize the upper thermal boundary layer (low degree of curvature, high plate thickness, small aspect ratio and intermediate internal heating rate) favor regular flow reversals.

  15. Concentration Polarization and Nonequilibrium Electro-osmotic Instability at an Ion-Selective Surface Admitting Normal Flow

    NASA Astrophysics Data System (ADS)

    Khair, Aditya

    2011-11-01

    We revisit and build upon on the prototypical problem of ion transport across a flat ideal ion-selective surface. Specifically, we examine the influence of imposed fluid flows on concentration polarization (CP) and electrokinetic instability at over-limiting currents. We consider an ion-selective surface, or membrane, that admits a uniform flow across itself. The membrane contacts an electrolyte, whose concentration is uniform in a well-mixed region at a prescribed distance from the membrane. A voltage across the system drives an ionic current, leading to CP in the ``unstirred layer'' between the membrane and well-mixed bulk. The CP reflects a balance between advection of ions with the ``normal flow'' and diffusion. A Peclet number, Pe, parameterizes their relative importance; note, Pe is signed, as the flow can be toward or away from the membrane. An asymptotic analysis for thin Debye layers reveals a nonlinear CP profile, in contrast to the familiar linear profile at Pe=0. Next, we consider over-limiting currents, wherein a non-equilibrium space-charge layer emerges near the membrane surface. Finally, we examine the instability of the quiescent concentration polarization due to second-kind electro-osmosis in the space-charge layer. A stability analysis shows that the imposed normal flow can enhance or retard the instability, depending on its direction.

  16. Analysis of induced-charge electro-osmotic flow in a microchannel embedded with polarizable dielectric blocks

    NASA Astrophysics Data System (ADS)

    Zhao, Cunlu; Yang, Chun

    2009-10-01

    Within the frame work of classic electromagnetic theory, a general electrical boundary condition describing the induced-charge electrokinetic phenomena at the liquid-dielectric interface is proposed in the present study. Two well-known limiting cases, i.e., perfectly insulating and perfectly polarizable wall boundary conditions, can be recovered from the present electrical boundary condition. By utilizing the proposed boundary condition, the induced-charge electro-osmosis (ICEO) flow in an infinitely long microchannel patterned with two symmetric polarizable dielectric blocks is investigated analytically. Fourier transform method is invoked to solve a biharmonic equation, which governs the (ICEO) flow field described by the stream function. Dimensionless parameters are introduced, and their effects on flow characteristics are analyzed. It is found that an increase in polarizability of the dielectric block enhances the slip velocity on its surface and thus induces a pair of counter-rotating vortices. Also, increasing the natural zeta potential on the upstream and downstream of the insulating microchannel walls leads to extinction of the vortex near the upstream insulating microchannel and suppression of the vortex near the downstream insulating microchannel.

  17. Unsteady Airloads on Airfoils in Reverse Flow

    NASA Astrophysics Data System (ADS)

    Lind, Andrew; Jones, Anya

    2014-11-01

    This work gives insight into the influence of airfoil characteristics on unsteady airloads for rotor applications where local airfoil sections may operate at high and/or reverse flow angles of attack. Two-dimensional wind tunnel experiments have been performed on four airfoil sections to investigate the effects of thickness, camber, and trailing edge shape on unsteady airloads (lift, pressure drag, and pitching moment). These model rotor blades were tested through 360 deg of incidence for 104 <=Re <=106 . Unsteady pressure transducers were mounted on the airfoil surface to measure the high frequency, dynamic pressure variations. The temporal evolution of chordwise pressure distributions and resulting airloads is quantified for each airfoil in each of the three unsteady wake regimes present in reverse flow. Specifically, the influence of the formation, growth, and shedding of vortices on the surface pressure distribution is quantified and compared between airfoils with a sharp geometric trailing edge and those with a blunt geometric trailing edge. These findings are integral to mitigation of rotor blade vibrations for applications where airfoil sections are subjected to reverse flow, such as high-speed helicopters and tidal turbines.

  18. An AC electroosmotic micropump for circular chromatographic applications.

    PubMed

    Debesset, S; Hayden, C J; Dalton, C; Eijkel, J C T; Manz, A

    2004-08-01

    Flow rates of up to 50 microm s(-1) have been successfully achieved in a closed-loop channel using an AC electroosmotic pump. The AC electroosmotic pump is made of an interdigitated array of unequal width electrodes located at the bottom of a channel, with an AC voltage applied between the small and the large electrodes. The flow rate was found to increase linearly with the applied voltage and to decrease linearly with the applied frequency. The pump is expected to be suitable for circular chromatography for the following reasons: the driving forces are distributed over the channel length and the pumping direction is set by the direction of the interdigitated electrodes. Pumping in a closed-loop channel can be achieved by arranging the electrode pattern in a circle. In addition the inherent working principle of AC electroosmotic pumping enables the independent optimisation of the channel height or the flow velocity.

  19. Minimizing tissue damage in electroosmotic sampling

    PubMed Central

    Hamsher, Amy E.; Xu, Hongjuan; Guy, Yifat; Sandberg, Mats; Weber, Stephen G.

    2010-01-01

    Electroosmotic sampling is a potentially powerful method for pulling extracellular fluid into a fused-silica capillary in contact with the surface of tissue. An electric field is created in tissue by passing current through an electrolyte-filled capillary and then through the tissue. The resulting field acts on the counter ions to the surface charges in the extracellular space to create electroosmotic fluid flow within the extracellular space of a tissue. Part of the development of this approach is to define conditions under which electroosmotic sampling minimizes damage to the tissue, in this case organotypic hippocampal slice cultures (OHSCs). We have assessed tissue damage by measuring fluorescence resulting from exposing sampled tissue to propidium iodide solution 16 – 24 h after sampling. Sampling has been carried out with a variety of capillary diameters, capillary tip-tissue distance, and applied voltages. Tissue damage is negligible when the power (current × potential drop) created in the tissue is less than 120 µW. In practical terms, smaller capillary IDs, lower voltages, and greater tissue to capillary distances lead to lower power. PMID:20698578

  20. Electro-osmotically driven liquid delivery method and apparatus

    DOEpatents

    Rakestraw, David J.; Anex, Deon S.; Yan, Chao; Dadoo, Rajeev; Zare, Richard N.

    1999-01-01

    Method and apparatus for controlling precisely the composition and delivery of liquid at sub-.mu.L/min flow rate. One embodiment of such a delivery system is an electro-osmotically driven gradient flow delivery system that generates dynamic gradient flows with sub-.mu.L/min flow rates by merging a plurality of electro-osmotic flows. These flows are delivered by a plurality of delivery arms attached to a mixing connector, where they mix and then flow into a receiving means, preferably a column. Each inlet of the plurality of delivery arms is placed in a corresponding solution reservoir. A plurality of independent programmable high-voltage power supplies is used to apply a voltage program to each of the plurality of solution reservoirs to regulate the electro-osmotic flow in each delivery arm. The electro-osmotic flow rates in the delivery arms are changed with time according to each voltage program to deliver the required gradient profile to the column.

  1. Electro-osmotically driven liquid delivery method and apparatus

    DOEpatents

    Rakestraw, D.J.; Anex, D.S.; Yan, C.; Dadoo, R.; Zare, R.N.

    1999-08-24

    Method and apparatus are disclosed for controlling precisely the composition and delivery of liquid at sub-{micro}L/min flow rate. One embodiment of such a delivery system is an electro-osmotically driven gradient flow delivery system that generates dynamic gradient flows with sub-{micro}L/min flow rates by merging a plurality of electro-osmotic flows. These flows are delivered by a plurality of delivery arms attached to a mixing connector, where they mix and then flow into a receiving means, preferably a column. Each inlet of the plurality of delivery arms is placed in a corresponding solution reservoir. A plurality of independent programmable high-voltage power supplies is used to apply a voltage program to each of the plurality of solution reservoirs to regulate the electro-osmotic flow in each delivery arm. The electro-osmotic flow rates in the delivery arms are changed with time according to each voltage program to deliver the required gradient profile to the column. 4 figs.

  2. A facile and versatile approach for controlling electroosmotic flow in capillary electrophoresis via mussel inspired polydopamine/polyethyleneimine co-deposition.

    PubMed

    Fu, Qifeng; Li, Xiuju; Zhang, Qihui; Yang, Fengqing; Wei, Weili; Xia, Zhining

    2015-10-16

    Electroosmotic flow (EOF), which reveals the charge property of capillary inner surface, has an important impact on the separation performance and reproducibility of capillary electrophoresis (CE). In this study, a novel, facile and versatile method to achieve diverse and controllable EOF in CE was reported based on the co-deposition of mussel-inspired polydopamine (PDA) and branched polyethyleneimine (PEI) on the capillary inner surface as the hybrid functional coating. After these PDA/PEI co-deposited columns were reinforced by the post-incubation of FeCl3, various magnitude and direction of EOF in CE could be easily achieved by varying a number of preparation parameters, including the mass ratio of DA/PEI and the molecular weight of PEI (including PEI-600, PEI-1800, PEI-10000 and PEI-70000). The separation effectiveness and stability of the hybrid coated columns were verified by the analysis of aromatic acids and aniline derivatives. The results showed that the controllable and diverse EOF was important in enhancing the separation performance of the analytes. The baseline separation of all the five aromatic acids can be achieved in 7 min with high separation efficiency by using the PDA/PEI-600 co-deposited column with the mass ratio of 6:1. On the other hand, with the PDA/PEI-70000 co-deposited column with the mass ratio of 6:1, the aniline compounds were easily baseline separated within 10 min. By contrast, using the bare and PDA coated columns, the migration of the aromatic acids was very slow and the baseline separation of the aniline compounds cannot be obtained. Moreover, the co-deposited columns showed long lifetime and good stability. The relative standard deviations for intra-day, inter-day and capillary-to-capillary repeatability of the PDA/PEI-600 co-deposited column with the mass ratio of 6:1, which was reinforced by the post-incubation of FeCl3, were all lower than 5%. Copyright © 2015 Elsevier B.V. All rights reserved.

  3. Electroosmotic Pumps with Frits Synthesized from Potassium Silicate.

    PubMed

    Nilsson, Sara; Erlandsson, Per G; Robinson, Nathaniel D

    2015-01-01

    Electroosmotic pumps employing silica frits synthesized from potassium silicate as a stationary phase show strong electroosmotic flow velocity and resistance to pressure-driven flow. We characterize these pumps and measure an electroosmotic mobility of 2.5 × 10(-8) m(2)/V s and hydrodynamic resistance per unit length of 70 × 10(17) Pa s/m(4) with a standard deviation of less than 2% even when varying the amount of water used in the potassium silicate mixture. Furthermore, we demonstrate the simple integration of these pumps into a proof-of-concept PDMS lab-on-a-chip device fabricated from a 3D-printed template.

  4. Electroosmotic Pumps with Frits Synthesized from Potassium Silicate

    PubMed Central

    Robinson, Nathaniel D.

    2015-01-01

    Electroosmotic pumps employing silica frits synthesized from potassium silicate as a stationary phase show strong electroosmotic flow velocity and resistance to pressure-driven flow. We characterize these pumps and measure an electroosmotic mobility of 2.5×10-8 m2/V s and hydrodynamic resistance per unit length of 70 ×1017 Pa s/m4 with a standard deviation of less than 2% even when varying the amount of water used in the potassium silicate mixture. Furthermore, we demonstrate the simple integration of these pumps into a proof-of-concept PDMS lab-on-a-chip device fabricated from a 3D-printed template. PMID:26629907

  5. Electroosmotic decontamination of concrete

    SciTech Connect

    Bostick, W.D.; Bush, S.A.; Marsh, G.C.; Henson, H.M.; Box, W.D.; Morgan, I.L.

    1993-03-01

    A method is described for the electroosmotic decontamination of concrete surfaces, in which an electrical field is used to induce migration of ionic contaminants from porous concrete into an electrolyte solution that may be disposed of as a low-level liquid radioactive waste (LLRW); alternately, the contaminants from the solution can be sorbed onto anion exchange media in order to prevent contaminant buildup in the solution and to minimize the amount of LLRW generated. We have confirmed the removal of uranium (and infer the removal of {sup 99}Tc) from previously contaminated concrete surfaces. In a typical experimental configuration, a stainless steel mesh is placed in an electrolyte solution contained within a diked cell to serve as the negative electrode (cathode) and contaminant collection medium, respectively, and an existing metal penetration (e.g., piping, conduit, or rebar reinforcement within the concrete surface) serves as the positive electrode (anode) to complete the cell. Typically we have achieved 70 to >90% reductions in surface activity by applying <400 V and <1 A for 1--3 h (energy consumption of 0.4--12 kWh/ft{sup 2}).

  6. Two types of flow reversal events observed in magnetotail

    NASA Astrophysics Data System (ADS)

    Shinohara, I.; Nagai, T.; Fujimoto, M.; Kojima, H.; Zenitani, S.

    2015-12-01

    Geotail survey in magnetotail provides us with about 200 rapid flow reversal events where tailward flow (< -500 km/s) turns to earthward flow (> +300 km/s) within 10 minutes. We selected 46 definite flow reversal events from them in order to study the physics of X-lines, removing events where stationary plasma and/or tail lobe components are observed at the timing of flow reversals. We found that flow reversal events can be classified into two types according to electron heating/acceleration and low frequency wave activity. About 2/3 of the flow reversal events look "active." In these events, strong electron heating/acceleration and existence of ion-electron decoupling region are commonly observed. The intense wave active in the lower-hybrid frequency range is also observed even in high β region around the neutral sheet. These features are consistent with the collisionless reconnection model demonstrated by recent full kinetic numerical simulations. In contrast, other 1/3 of flow reversal events do not present any of them. No visible ion-electron decoupling is found in these "non-active" flow reversal events. This new finding indicates that the strong wave activity in the electric field would be related to the ion-electron decoupling process and that wave activity is a possible indicator for liveliness of reconnection (= evidence of fast electron flow). The fact that the non-active flow reversals tend to be distributed at the outer fringes of the active flow reversal regions implies that they are related to the three-dimensional structure of magnetic reconnection. In this presentation, we will discuss physical meaning of the difference between active and non-active flow reversal events. It is hard to discuss further collectively the nature of the non-active flow reversals only with single spacecraft measurements. This would be a good topic to be explored using multi-spacecraft data.

  7. Induced-charge electroosmotic trapping of particles.

    PubMed

    Ren, Yukun; Liu, Weiyu; Jia, Yankai; Tao, Ye; Shao, Jinyou; Ding, Yucheng; Jiang, Hongyuan

    2015-05-21

    Position-controllable trapping of particles on the surface of a bipolar metal strip by induced-charge electroosmotic (ICEO) flow is presented herein. We demonstrate a nonlinear ICEO slip profile on the electrode surface accounting for stable particle trapping behaviors above the double-layer relaxation frequency, while no trapping occurs in the DC limit as a result of a strong upward fluidic drag induced by a linear ICEO slip profile. By extending an AC-flow field effect transistor from the DC limit to the AC field, we reveal that fixed-potential ICEO exceeding RC charging frequency can adjust the particle trapping position flexibly by generating controllable symmetry breaking in a vortex flow pattern. Our results open up new opportunities to manipulate microscopic objects in modern microfluidic systems by using ICEO.

  8. Fabrication and characterization of a fritless microfabricated electroosmotic pump with reduced pH dependence.

    PubMed

    Razunguzwa, Trust T; Timperman, Aaron T

    2004-03-01

    A fritless electroosmotic pump with reduced pH dependence has been fabricated on a glass microchip and its performance characterized. The chip design consists of two 500-microm channels, one packed with anion exchange beads and the other packed with cation exchange beads, which produce convergent electroosmotic flow streams. The electroosmotically pumped solution flows away from the intersection of the two pumping channels through a field-free channel. This simple design allows for the production of a fritless electroosmotic pump and easy replacement of the ion exchange beads whose charged surfaces generate the flow. The pump was found to produce volumetric flow rates of up to 2 microL/min for an applied voltage of 3 kV at a pH of 6.8. Moreover, the electroosmotic pump can generate high flow rates over an extended pH range of at least 2-12, a significant advantage over previously fabricated electroosmotic pumps, which typically have a more limited range in which they can achieve high flow rates.

  9. High Pressure Reverse Flow APS Engine

    NASA Technical Reports Server (NTRS)

    Senneff, J. M.

    1972-01-01

    A design and test demonstration effort was undertaken to evaluate the concept of the reverse flow engine for the APS engine application. The 1500 lb (6672 N) thrust engine was designed to operate on gaseous hydrogen and gaseous oxygen propellants at a mixture ratio of 4 and to achieve the objective performance of 435 sec (4266 Nsec/kg) specific impulse. Superimposed durability requirements called for a million-cycle capability with 50 hours duration. The program was undertaken as a series of tasks including the initial preliminary design, design of critical test components and finally, the design and demonstration of an altitude engine which could be used interchangeably to examine operating parameters as well as to demonstrate the capability of the concept. The program results are reported with data to indicate that all of the program objectives were met or exceeded within the course of testing on the program. The analysis effort undertaken is also reported in detail and supplemented with test data in some cases where prior definitions could not be made. The results are contained of these analyses as well as the test results conducted throughout the course of the program. Finally, the test data and analytical results were combined to allow recommendations for a flight weight design. This preliminary design effort is also detailed.

  10. Reciprocating pump with partial flow reversal

    SciTech Connect

    Frazier, T.L.; Dozier, J.D.

    1986-01-21

    This patent describes a reciprocating type pump for lifting fluid from wells and for other similar applications where operating conditions make its actions subject to blockage by mobile fines. The pump consists of a number of interactive components. The first component described in the patent is a pump barrel with a standing check valve at the bottom. The next components detailed are a pump plunger with a traveling check valve at the bottom and a mechanism for reciprocating the plunger in the barrel over a predetermined stroke distance with upper and lower limits on the motion. A principal feature of the patent which is discussed at length is the existence of a port in the barrel which is located above the middle of the stroke distance. Similarly, a means associated with the plunger for closing the port during that portion of the stroke distance when the plunger is below the level of the port is elucidated upon. The final component modality which is represented in the patent is a mechanism for biasing the traveling check valve closed against back pressure of less than a predetermined value such that the fluid is pumped back to reverse flow and thus effects the unblocking of the mobile fines during a portion of the stroke distance of each cycle.

  11. Effect of linear polymer additives on the electroosmotic characteristics of agarose gels in ultrathin-layer electrophoresis.

    PubMed

    Lengyel, T; Guttman, A

    1999-08-20

    Electroosmotic properties of agarose gels with low, medium, high and super high electroendosmosis (EEO) were evaluated based on the apparent electric field mediated mobility of a neutral, fluorescent marker under constant field strength using ultrathin-layer separation configuration. Electroosmotic flow mobility values were measured in different gel concentrations and also in the absence and the presence of various linear polymer additives. Under ultrathin-layer separation conditions, a slight decrease in electroosmotic flow mobility was observed with increasing agarose gel concentration of 1 to 3% for all agarose gels investigated. When linear polymer additives, such as linear polyacrylamide, hydroxyethyl cellulose or polyethylene oxide were added to 1% low electroendosmosis agarose gel, significant reduction of the electroosmotic flow properties were observed with increasing additive concentration. Effect of the intrinsic electroosmotic properties of the various electroendosmosis agaroses on the apparent mobilities and separation performance of double-stranded DNA fragments during automated ultrathin-layer agarose gel electrophoresis was also investigated.

  12. Extensional instability in electro-osmotic microflows of polymer solutions

    NASA Astrophysics Data System (ADS)

    Bryce, R. M.; Freeman, M. R.

    2010-03-01

    Fluid transport in microfluidic systems typically is laminar due to the low Reynolds number characteristic of the flow. The inclusion of suspended polymers imparts elasticity to fluids, allowing instabilities to be excited when substantial polymer stretching occurs. For high molecular weight polymer chains we find that flow velocities achievable by standard electro-osmotic pumping are sufficient to excite extensional instabilities in dilute polymer solutions. We observe a dependence in measured fluctuations on polymer concentration which plateaus at a threshold corresponding to the onset of significant molecular crowding in macromolecular solutions; plateauing occurs well below the overlap concentration. Our results show that electro-osmotic flows of complex fluids are disturbed from the steady regime, suggesting potential for enhanced mixing and requiring care in modeling the flow of complex liquids such as biopolymer suspensions.

  13. Electroosmotic transport in polyelectrolyte-grafted nanochannels with pH-dependent charge density

    NASA Astrophysics Data System (ADS)

    Chen, Guang; Das, Siddhartha

    2015-05-01

    "Smart" polyelectrolyte-grafted or "soft" nanochannels with pH-responsiveness have shown great promise for applications like manipulation of ion transport, ion sensing and selection, current rectification, and many more. In this paper, we develop a theory to study the electroosmotic transport in a polyelectrolyte-grafted (or soft) nanochannel with pH-dependent charge density. In one of our recent studies, we have identified that explicit consideration of hydrogen ion concentration is mandatory for appropriately describing the electrostatics of such systems and the resulting monomer concentration must obey a non-unique, cubic distribution. Here, we use this electrostatic calculation to study the corresponding electroosmotic transport. We establish that the effect of pH in the electroosmotic transport in polyelectrolyte-grafted nanochannels introduces two separate issues: first is the consideration of the hydrogen and hydroxyl ion concentrations in describing the electroosmotic body force, and second is the consideration of the appropriate drag force that bears the signature of this cubic monomeric distribution. Our results indicate that the strength of the electroosmotic velocity for the pH-dependent case is always smaller than that for the pH-independent case, with the extent of this difference being a function of the system parameters. Such nature of the electroosmotic transport will be extremely significant in suppressing the electroosmotic flow strength with implications in large number applications such as capillary electrophoresis induced separation, electric field mediated DNA elongation, electrophoretic DNA nanopore sequencing, and many more.

  14. Reversed flow injection spectrophotometric determination of chlorate.

    PubMed

    Chuesaard, Thanyarat; Wonganan, Tharinee; Wongchanapiboon, Teerapol; Liawruangrath, Saisunee

    2009-09-15

    An interfacing has been developed to connect a spectrophotometer with a personal computer and used as a readout system for development of a simple, rapid and sensitive reversed flow injection (rFI) procedure for chlorate determination. The method is based on the oxidation of indigo carmine by chlorate ions in an acidic solution (dil. HCl) leading to the decrease in absorbance at 610 nm. The decrease in absorbance is directly related to the chlorate concentration present in the sample solutions. Optimum conditions for chlorate were examined. A linear calibration graph over the range of 0.1-0.5 mg L(-1) chlorate was established with the regression equation of Y=104.5X+1.0, r(2)=0.9961 (n=6). The detection limit (3 sigma) of 0.03 mg L(-1), the limit of quantitation (10 sigma) of 0.10 mg L(-1) and the RSD of 3.2% for 0.3 mg L(-1) chlorate (n=11) together with a sample throughput of 92 h(-1) were obtained. The recovery of the added chlorate in spiked water samples was 98.5+/-3.1%. Major interferences for chlorate determination were found to be BrO(3)(-), ClO(2)(-), ClO(-) and IO(3)(-) which were overcome by using SO(3)(2-) (as Na(2)SO(3)) as masking agent. The method has been successfully applied for the determination of chlorate in spiked water samples with the minimum reagent consumption of 14.0 mL h(-1). Good agreement between the proposed rFIA and the reference methods was found verified by Student's t-test at 95% confidence level.

  15. Concentration distribution for pollutant dispersion in a reversal laminar flow

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Chen, G. Q.

    2017-08-01

    Pollutant transport in reversal laminar flows gains its significance in various coastal regions. Since oscillation in the flow introduces much complexity into the transport process, little progress has been made to illustrate the evolution of concentration distribution. In this work, the first order expansion of the generalized dispersion model, as a simplified applicable method based on the previously proposed Aris-Gill expansion (Wang and Chen, 2016b,c), is applied to analytically study the pollutant dispersion in an open channel reversal laminar flow. This method is conveniently used to accurately predict the two-dimensional concentration evolution characteristic of peak concentration position and duration. The vertical concentration difference is determined to be tremendous and vary periodically, and the peak concentration appears at the freesurface or bottom depending on the reversal amplitude. The approach for vertical concentration to uniformity in the dispersion process lasts longer remarkably in reversal flows than that in steady flows.

  16. Electroosmotic pumps and their applications in microfluidic systems

    PubMed Central

    Wang, Xiayan; Cheng, Chang; Wang, Shili; Liu, Shaorong

    2009-01-01

    Electroosmotic pumping is receiving increasing attention in recent years owing to the rapid development in micro total analytical systems. Compared with other micropumps, electroosmotic pumps (EOPs) offer a number of advantages such as creation of constant pulse-free flows and elimination of moving parts. The flow rates and pumping pressures of EOPs matches well with micro analysis systems. The common materials and fabrication technologies make it readily integrateable with lab-on-a-chip devices. This paper reviews the recent progress on EOP fabrications and applications in order to promote the awareness of EOPs to researchers interested in using micro- and nano-fluidic devices. The pros and cons of EOPs are also discussed, which helps these researchers in designing and constructing their micro platforms. PMID:20126306

  17. Ultrafast high-pressure AC electro-osmotic pumps for portable biomedical microfluidics.

    PubMed

    Huang, Chien-Chih; Bazant, Martin Z; Thorsen, Todd

    2010-01-07

    This paper details the development of an integrated AC electro-osmotic (ACEO) microfluidic pump for dilute electrolytes consisting of a long serpentine microchannel lined with three dimensional (3D) stepped electrode arrays. Using low AC voltage (1 V rms, 1 kHz), power (5 mW) and current (4.5 mA) in water, the pump is capable of generating a 1.3 kPa head pressure, a 100-fold increase over prior ACEO pumps, and a 1.3 mm/s effective slip velocity over the electrodes without flow reversal. The integrated ACEO pump can utilize low ionic strength solutions such as distilled water as the working solution to pump physiological strength (100 mM) biological solutions in separate microfluidic devices, with potential applications in portable or implantable biomedical microfluidic devices. As a proof-of-concept experiment, the use of the ACEO pumps for DNA hybridization in a microfluidic microarray is demonstrated.

  18. Reverse-flow strategy in biofilters treating CS₂ emissions.

    PubMed

    Rojo, Naiara; Gallastegui, Gorka; Gurtubay, Luis; Barona, Astrid; Elías, Ana

    2013-04-01

    The bacteriostatic properties of carbon disulphide (CS₂) hamper its biodegradation in conventional biofilters. The response of four biofilters operating in downflow mode and reverse-flow mode was compared in a laboratory-scale plant treating CS₂ under sudden short-term changes in operating conditions. A process shutdown for 24 h, an inlet concentration increase and an interruption of the inlet air humidification for 48 h at an empty bed residence time (EBRT) of 240 s did not impact significantly on biodegradation performance, regardless of flow mode. Nevertheless, a reduction in the EBRT to 60 s resulted in a significant decrease in removal efficiency in all the biofilters. The CS₂ degradation profile showed that the reverse-flow mode strategy rendered a more homogenous distribution of biomass along the bed height. The benefits of the reverse-flow mode were demonstrated even when the unidirectional flow mode was re-established.

  19. Calculations of unsteady turbulent boundary layers with flow reversal

    NASA Technical Reports Server (NTRS)

    Nash, J. F.; Patel, V. C.

    1975-01-01

    The results are presented of a series of computational experiments aimed at studying the characteristics of time-dependent turbulent boundary layers with embedded reversed-flow regions. A calculation method developed earlier was extended to boundary layers with reversed flows for this purpose. The calculations were performed for an idealized family of external velocity distributions, and covered a range of degrees of unsteadiness. The results confirmed those of previous studies in demonstrating that the point of flow reversal is nonsingular in a time-dependent boundary layer. A singularity was observed to develop downstream of reversal, under certain conditions, accompanied by the breakdown of the boundary-layer approximations. A tentative hypothesis was advanced in an attempt to predict the appearance of the singularity, and is shown to be consistent with the calculated results.

  20. Reverse Flow Engine Core Having a Ducted Fan with Integrated Secondary Flow Blades

    NASA Technical Reports Server (NTRS)

    Kisska, Michael K. (Inventor); Princen, Norman H. (Inventor); Kuehn, Mark S. (Inventor); Cosentino, Gary B. (Inventor)

    2014-01-01

    Secondary air flow is provided for a ducted fan having a reverse flow turbine engine core driving a fan blisk. The fan blisk incorporates a set of thrust fan blades extending from an outer hub and a set of integral secondary flow blades extending intermediate an inner hub and the outer hub. A nacelle provides an outer flow duct for the thrust fan blades and a secondary flow duct carries flow from the integral secondary flow blades as cooling air for components of the reverse flow turbine engine.

  1. Electro-osmotically induced convection at a permselective membrane

    NASA Astrophysics Data System (ADS)

    Rubinstein, I.; Zaltzman, B.

    2000-08-01

    The paper is concerned with convection at an ion exchange electrodialysis membrane induced by nonequilibrium electro-osmosis in the course of concentration polarization under the passage of electric current through the membrane. Derivation of nonequilibrium electro-osmotic slip condition is recapitulated along with the linear stability analysis of quiescent electrodiffusion through a flat ion exchange membrane. Results of numerical calculation for nonlinear steady state convection, developing from the respective instability, are reported along with those for a slightly wavy membrane. Besides these results, we report those of time dependent calculations for periodic and chaotic oscillations, resulting from instability of the respective steady state flows, and also the results of recent experiments with modified membranes. These latter rule in favor of electro-osmotic versus bulk electroconvective origin of overlimiting conductance through ion exchange membranes.

  2. Flow instability and flow reversal in heated annular multichannels with initial downward flow

    SciTech Connect

    Guerrero, H.N.; Hart, C.M.

    1992-01-01

    Experimental and theoretical results are presented regarding the stability of initial downward flow of single phase water in parallel annular channels of the Savannah River Site (SRS) fuel assembly. The test was performed on an electrically heated prototypic mockup of a Mark-22 fuel assembly. The test conditions consisted of mass fluxes, from 98--294 kg/m[sup 2]-sec, and inlet water temperatures of 25[degrees]C and 40[degrees]C. With increased power to the heaters, flow instability was detected, characterized by flow fluctuations and flow redistribution among subchannels of the outer flow channel. With increased power, a condition was observed indicating local subchannel flow reversals where certain subchannel fluid temperatures were high at the inlet and low at the exit. With additional power increased, a critical heat flux condition was observed indicating local subchannel flow reversals where certain subchannel fluid temperatures were high at the inlet and low at the exit. With additional power increases, a critical heat flux condition was reached in the outer channel.

  3. Flow instability and flow reversal in heated annular multichannels with initial downward flow

    SciTech Connect

    Guerrero, H.N.; Hart, C.M.

    1992-12-31

    Experimental and theoretical results are presented regarding the stability of initial downward flow of single phase water in parallel annular channels of the Savannah River Site (SRS) fuel assembly. The test was performed on an electrically heated prototypic mockup of a Mark-22 fuel assembly. The test conditions consisted of mass fluxes, from 98--294 kg/m{sup 2}-sec, and inlet water temperatures of 25{degrees}C and 40{degrees}C. With increased power to the heaters, flow instability was detected, characterized by flow fluctuations and flow redistribution among subchannels of the outer flow channel. With increased power, a condition was observed indicating local subchannel flow reversals where certain subchannel fluid temperatures were high at the inlet and low at the exit. With additional power increased, a critical heat flux condition was observed indicating local subchannel flow reversals where certain subchannel fluid temperatures were high at the inlet and low at the exit. With additional power increases, a critical heat flux condition was reached in the outer channel.

  4. Reversal of theta rhythm flow through intact hippocampal circuits.

    PubMed

    Jackson, Jesse; Amilhon, Bénédicte; Goutagny, Romain; Bott, Jean-Bastien; Manseau, Frédéric; Kortleven, Christian; Bressler, Steven L; Williams, Sylvain

    2014-10-01

    Activity flow through the hippocampus is thought to arise exclusively from unidirectional excitatory synaptic signaling from CA3 to CA1 to the subiculum. Theta rhythms are important for hippocampal synchronization during episodic memory processing; thus, it is assumed that theta rhythms follow these excitatory feedforward circuits. To the contrary, we found that theta rhythms generated in the rat subiculum flowed backward to actively modulate spike timing and local network rhythms in CA1 and CA3. This reversed signaling involved GABAergic mechanisms. However, when hippocampal circuits were physically limited to a lamellar slab, CA3 outputs synchronized CA1 and the subiculum using excitatory mechanisms, as predicted by classic hippocampal models. Finally, analysis of in vivo recordings revealed that this reversed theta flow was most prominent during REM sleep. These data demonstrate that communication between CA3, CA1 and the subiculum is not exclusively unidirectional or excitatory and that reversed inhibitory theta signaling also contributes to intrahippocampal synchrony.

  5. A dynamic model of the electroosmotic droplet switch

    NASA Astrophysics Data System (ADS)

    Barz, Dominik P. J.; Steen, Paul H.

    2013-09-01

    A capillary switch is a bi-stable system of liquid/gas interfaces with a trigger to toggle back and forth between the two stable equilibrium states. We use an electro-osmotic pump as trigger. The pump, consisting of two electrodes and a porous substrate arranged between the droplets, moves volume between the droplets. This bistable system is called an electro-osmotic droplet switch. With the pump off, for low total volumes, the stable states are a pair of identical sub-hemispherical droplets or, for large enough total volumes, a large-small droplet configuration (two mirror-symmetric states). With the pump on, these stationary states are shifted and, if the pump strength is too great, there are no stationary states at all. In this article, we report the pump-on behavior as a modification of the pump-off behavior. To build the dynamic model of the system, we first develop a characterization of the electro-osmotic pump in the spirit of the Blake-Kozeny correlation for viscous flow through a packed bed. The control-volume model is based on center-of-mass motion. Model predictions compare favorably to observation.

  6. Dynamics of poloidal flows in enhanced reverse shear bifurcation

    SciTech Connect

    Srinivasan, R.; Avinash, K.

    2005-07-15

    A simple reduced enhanced reverse shear (RERS) model is constructed to study the dynamics of poloidal flows during the ERS transition. This model predicts that a reversal of poloidal flow shear occurs just prior to the transition, as seen in experiment [R. E. Bell et al., Phys. Rev. Lett. 81, 1429 (1998)]. This transition front propagates until the radial location where the safety factor (q) is minimum and becomes locked there due to insufficient input power to overcome the threshold requirement for the bifurcation. This study also reveals that there can be many routes to ERS transition depending upon various tunable parameters.

  7. Remagnetization of lava flows spanning the last geomagnetic reversal

    NASA Astrophysics Data System (ADS)

    Vella, Jérôme; Carlut, Julie; Valet, Jean-Pierre; Goff, Maxime Le; Soler, Vicente; Lopes, Fernando

    2017-08-01

    Large directional changes of remanent magnetization within lava flows that cooled during geomagnetic reversals have been reported in several studies. A geomagnetic scenario implies extremely rapid geomagnetic changes of several degrees per day, thus difficult to reconcile with the rate of the earth's core liquid motions. So far, no complete rock magnetic model provides a clear explanation. We revisited lava flows sandwiched between an underlying reverse and an overlying normal polarity flow marking the last reversal in three distinct volcanic sequences of the La Palma Island (Canary archipelago, Spain) that are characterized by a gradual evolution of the direction of their remanent magnetization from bottom to top. Cleaning efficiency of thermal demagnetization was not improved by very rapid heating and cooling rates as well as by continuous demagnetization using a Triaxe magnetometer. We did not observe partial self-reversals and minor changes in magnetic grain sizes are not related to the within-flow directional changes. Microscopic observations indicate poor exsolution, which suggests post-cooling thermochemical remagnetization processes. This scenario is strongly reinforced by laboratory experiments that show large resistance to thermal demagnetization when thermoremanence was acquired over a long time period. We speculate that in the present situation exsolution was reactivated during in field reheating and yielded formation of new magnetite, yet magnetic domain state rearrangements could also play a role. Initial reheating when the overlying flow took place, albeit moderate (less than 200-300 °C), was enough to produce overlying components with significantly higher unblocking temperatures.

  8. Hemodynamics and transient flow reversal in real deployed stents

    NASA Astrophysics Data System (ADS)

    Metcalfe, Ralph; Ionescu, Mircea

    2011-11-01

    Restenosis rates caused by neointimal hyperplasia are relatively high (~ 30 %) after stent implantation in stenosed arteries. The flow around stent struts under steady and unsteady conditions using computational hemodynamics (CHD) was studied to identify contributing factors to the formation of low and oscillating wall shear stress regions that have been shown to promote endothelial dysfunction and atherosclerotic plaque formation in arteries. Datasets of the Neuroform, BxVelocity, and Taxus stents deployed in straight polymer tubes were obtained from high resolution micro computed tomography. Finite volume CHD simulations of steady and unsteady flow with and without flow reversal were performed. Stagnation zones were noticed adjacent to the strut junctions as the flow enters and exits the stent cells. The stagnation zones were larger in the case of the stents with larger strut diameter (BxVelocity, Taxus), wider strut junctions and larger angles between the struts. Unsteady flow simulations showed enhanced flow reversal with thicker struts and large regions of recirculation flow developing inside the stent at Reynolds numbers higher than 200. It was shown that alterations in blood flow due to real stent deployment (strut prolapse, junction misalignment) cannot be captured with computer generated stent models, that stent specific geometry, and time dependent flow effects can locally alter the wall shear stress and stagnation zones.

  9. Simultaneous separation of five major ribonucleic acids by capillary electrophoresis with laser-induced fluorescence in the presence of electroosmotic flow: application to the rapid screening of 5S rRNA from ovarian cancer cells.

    PubMed

    Shih, Ya-Chu; Liao, Ching-Ru; Chung, I-Che; Chang, Yu-Sun; Chang, Po-Ling

    2014-10-17

    RNA integrity is important in RNA studies because poor RNA quality may impact downstream methodologies. This study proposes a rapid and cost-effective method for the determination of RNA integrity based on CE-LIF in the presence of electroosmotic flow. The proposed method uses poly(ethylene) oxide (Mavg=4,000,000 Da) as a sieving matrix for total RNA separation. Ethidium bromide (μg mL(-1)) was dissolved in a polymer solution as an interchelating dye for on-column fluorescent labeling. The 28S rRNA, 18S rRNA, 5.8S rRNA, 5S rRNA and tRNA from the total human RNA extracted from the cells were fully separated using the proposed method. The lowest detectable concentration of total RNA achieved was 100 pg μL(-1) with a 6 min sample injection followed by on-column concentration. In addition, the temperature-induced degradation of total RNA was observed by CE-LIF. The electropherograms revealed more fragmentation of 28S and 18S rRNAs by temperature-induced hydrolysis compared with the 5.8S rRNA, 5S rRNA and tRNA. Therefore, the results indicated that RNA degradation should be considered for long-term, high-temperature incubations in RNA-related experiments involving RNA hybridization. The proposed method is furthermore, applied to the determination of 5S rRNA overexpressed in ovarian cancer cells as compared to the cervical cancer cells. Overall, CE-LIF is highly promising for rapid screening of ovarian cancers without tedious pre-amplification steps. Copyright © 2014 Elsevier B.V. All rights reserved.

  10. Turbulence, flow and transport: hints from reversed field pinch

    NASA Astrophysics Data System (ADS)

    Vianello, N.; Antoni, V.; Spada, E.; Spolaore, M.; Serianni, G.; Cavazzana, R.; Bergsåker, H.; Cecconello, M.; Drake, J. R.

    2006-04-01

    The interplay between sheared E × B flows and turbulence has been experimentally investigated in the edge region of the Extrap-T2R reversed field pinch experiment. Electrostatic fluctuations are found to rule the momentum balance equation representing the main driving term for sheared flows which counterbalances anomalous viscous damping. The driving role of electrostatic fluctuations is proved by the spatial structure of the Reynolds stress and by the time behaviour of the mean energy production term which supports the existence of an energy exchange from the small scales of turbulence to the larger scales of the mean flow.

  11. In-situ measurement of electroosmotic drag coefficient in Nafion membrane for the PEMFC.

    PubMed

    Peng, Zhe; Morin, Arnaud; Huguet, Patrice; Schott, Pascal; Pauchet, Joël

    2011-11-10

    A new method based on hydrogen pump has been developed to measure the electroosmotic drag coefficient in representative PEMFC operating conditions. It allows eliminating the back-flow of water which leads to some errors in the calculation of this coefficient with previously reported electrochemical methods. Measurements have been performed on 50 μm thick Nafion membranes both extruded and recast. Contrary to what has been described in most of previous published works, the electroosmotic drag coefficient decreases as the membrane water content increases. The same trend is observed for temperatures between 25 and 80 °C. For the same membrane water content, the electroosmotic drag coefficient increases with temperature. In the same condition, there is no difference in drag coefficient for extruded Nafion N112 and recast Nafion NRE212. These results are discussed on the basis of the two commonly accepted proton transport mechanisms, namely, Grotthus and vehicular.

  12. Unsteady Aerodynamics of Static Airfoils in Reverse Flow

    NASA Astrophysics Data System (ADS)

    Lind, Andrew; Jones, Anya

    2013-11-01

    Wind tunnel experiments have been conducted on two-dimensional blunt and sharp trailing edge airfoils held at static angles of attack in reverse flow for three Reynolds numbers. The current work is aimed at advancing the understanding of fully developed reverse flow for high-speed helicopter applications, and evaluates the potential for blunt trailing edge airfoils to mitigate unsteady rotor blade airloads in this flow regime. Time-resolved particle image velocimetry measurements at post-stall angles of attack have revealed the evolution of a trailing edge vortex formed by the roll-up of vorticity generated in a separated shear layer. Proper orthogonal decomposition (POD) was applied to the flow field measurements to improve the identification and tracking of dominant flow structures. Unsteady force balance measurements have captured non-structural vibrations with frequency content which correlates well with that of the temporal coefficients for the first two POD spatial modes. These vibrations vary in frequency with angle of attack and are shown to be linked with trailing edge vortex shedding. The findings presented here give fundamental insight towards the development of efficient rotor blades for high-speed helicopters.

  13. Temperature and pressure measurements at cold exit of counter-flow vortex tube with flow visualization of reversed flow

    NASA Astrophysics Data System (ADS)

    Yusof, Mohd Hazwan bin; Katanoda, Hiroshi; Morita, Hiromitsu

    2015-02-01

    In order to clarify the structure of the cold flow discharged from the counter-flow vortex tube (VT), the temperature and pressure of the cold flow were measured, and the existence and behavior of the reversed flow at the cold exit was studied using a simple flow visualization technique consisting of a 0.75mm-diameter needle, and an oil paint droplet. It is observed through this experiment that the Pitot pressure at the cold exit center can either be lower or higher than atmospheric pressure, depending on the inlet pressure and the cold fraction, and that a reversed flow is observed when the Pitot pressure at the cold exit center is lower than atmospheric pressure. In addition, it is observed that when reducing the cold fraction from unity at any arbitrary inlet pressure, the region of reversed and colder flow in the central part of cold exit extends in the downstream direction.

  14. Electrolyte management for effective long-term electro-osmotic transport in low-permeability soils.

    PubMed

    Cherepy, Nerine J; Wildenschild, Dorthe

    2003-07-01

    Electro-osmosis, a coupled-flow phenomenon in which an applied electrical potential gradient drives water flow, may be used to induce water flow through fine-grained sediments. Test cell measurements of electro-osmotic transport in clayey cores extracted from the 27-31 m depth range of the Lawrence Livermore National Laboratory site indicate the importance of pH control within the anode and cathode reservoirs. In our first experiment, pH was not controlled. As a result, carbonate precipitation and metals precipitation occurred near the cathode end of the core, with acidification near the anode. The combination of these acid and base reactions led to the decline of electro-osmotic flow by a factor of 2 in less than one pore volume. In a second experiment, long-term water transport (>21 pore volumes) at stable electro-osmotic conductivity (k(eo) approximately 1 x 10(-9) m2/s-V) was effected with anode reservoir pH > 8, and cathode reservoir pH < 6. Hydraulic conductivity (k(h)) of the same core was 4 x 10(-10) m/s under a 0.07 MPa hydraulic gradient without electro-osmosis. Stable electro-osmotic flow was measured at a velocity of 4 x 10(-7) m/s under a 4 V/cm voltage gradient, and no hydraulic gradient-3 orders of magnitude greater than the hydraulic flow. We also observed chloroform production in the anode reservoir, resulting from electrochemical production of chlorine gas reacting with trace organics. The chloroform was transported electro-osmotically to the cathode, without measurable loss to adsorption, volatilization, or degradation.

  15. Concentration polarization and nonequilibrium electroosmotic slip in dense multiparticle systems.

    PubMed

    Nischang, Ivo; Reichl, Udo; Seidel-Morgenstern, Andreas; Tallarek, Ulrich

    2007-08-28

    Electrical field-induced concentration polarization (CP) and CP-based nonequilibrium electroosmotic slip are studied in fixed beds of strong cation-exchange particles using confocal laser scanning microscopy (CLSM) and the macroscopic electroosmotic flow (EOF) dynamics. A key property of the investigated fixed beds is the coexistence of quasi-electroneutral macroporous regions between the micrometer-sized particles and the ion-permselective (here, cation-selective) intraparticle mesopores with a mean size of 10 nm. The application of an external electrical field to the particles induces depleted and enriched CP zones along their anodic and cathodic interfaces, respectively, by the local interplay of diffusive and electrokinetic transport. The intensity and dimension of the CP zones depend on the applied electrical field strength and the fluid-phase ionic strength. With increasing field strength a limiting current density through a particle is approached, meaning that charge transport locally through a particle becomes controlled by the dynamics in the adjoining extraparticle convective-diffusion boundary layer (depleted CP zone). In this regime a nonequilibrium electrical double layer can be induced electrokinetically in the depleted CP zone and intraparticle pore space, resulting in nonlinear EOF in the interparticle macropore space. The local CP dynamics analyzed by CLSM is successfully correlated with the onset of nonlinearity in the macroscopic EOF dynamics. We further demonstrate that multiparticle effects arising in fixed beds (random close packings) of ion-permselective particles modulate significantly the local pattern of CP and intensity of the nonequilibrium electroosmotic slip with respect to the undisturbed single-particle picture.

  16. Applications of Electro-Osmotic Transport in the Processing of Textiles

    SciTech Connect

    Cooper, J.F.; Krueger, R.; Hopper, R.; Cherepy, N.

    1999-11-29

    We report development of a pilot process for the industrial rinsing of fabrics. This process combines hydraulic (pressure-driven) transport with electro-osmotic transport. It reduces the total amount of water required in certain rinsing operations by a factor of about five. Cotton exhibits an electro-osmotic transport coefficient of about 6 x 10{sup -9} m{sup 2}/s-V resulting from a partial ionization of hydroxyl groups on the cellulose polymer substrate. This process applies a field transverse to the fabric to effect the movement of water in the spaces between the 10 {micro}m cotton fibers which constitute the yam. The field strength is adjusted so that the induced electro-osmotic flux is comparable to a pressure-driven flux, which moves preferentially in the more open channels between the yams. For a fixed current density, solution conductivity and electro-osmotic transport vary inversely. The process is most practical for removal of liquids of relatively low conductivity (<500 {micro}S/cm). For removal of solutions of conductivity greater than 1200 {micro}S/cm, the rate of electro-osmotic flow may be too low to benefit the rinsing process if current densities are restricted to practical levels of about 30 mA/cm{sup 2}. Electra-osmotic transport may have important applications in wet processing of extremely fine textiles, such as micro fiber fabrics. In addition to rinsing, electro-osmotic transport may also be used to speed the penetration of chemicals and dyestuffs that are applied to the surface of wet textiles.

  17. Zig-zag arrangement of four electrodes for ac electro-osmotic micropumps

    NASA Astrophysics Data System (ADS)

    Hrdlička, J.; Červenka, P.; Přibyl, M.; Šnita, D.

    2011-07-01

    This paper deals with the mathematical modeling of traveling-wave ac electro-osmotic micropumps with a zig-zag arrangement of microelectrodes. A mathematical model based on the Poisson-Nernst-Planck-Navier-Stokes description is used in this study within the physically relevant ranges of the model parameters. We present an extensive set of parametrical studies concerning the dependence of the net velocity on a variety of parameters. We also demonstrate limits of the validity of the commonly used Capacitor-Resistor-Capacitor model. In order to achieve high net velocities, we found that there are the optimal values of the electrode length, the shift between the top and bottom electrode arrays, and the signal frequency. Performance of the zig-zag micropumps is evaluated by the means of back-pressure loads. The suggested zig-zag design brings two main benefits: (i) it allows an easier construction of four-phase traveling-wave micropumps without the need of spatially complicated electrode connections, and (ii) the zig-zag pumps can provide higher flow rates than those with single-sided coplanar arrangements. Another robust feature of the proposed zig-zag system is that a single flow reversal is observed at the ac frequency approximately six times higher than the reciprocal resistor-capacitor time even in low-amplitude regimes.

  18. The phase reversal phenomenon at flow separation and reattachment

    NASA Technical Reports Server (NTRS)

    Stack, J. Pete; Mangalam, S. M.; Kalburgi, V.

    1988-01-01

    Tests were conducted on two different airfoils, one of them in a low-turbulence tunnel, to detect laminar separation and turbulent reattachment locations. A 'nonintrusive' multielement sensor consisting of a large number of closely spaced individual nickel films was vacuum deposited on a thin substrate and bonded to the airfoil model surface. Each sensor element was a part of an independent constant temperature anemometer system. Time history as well as spectral analysis of signals from surface film gauges were used to determine the surface shear flow characteristics. A major breakthrough was achieved with the discovery of phase reversal in low-frequency dynamic shear stress signals across regions of flow separation and reattachment.

  19. Mirror reading can reverse the flow of time.

    PubMed

    Casasanto, Daniel; Bottini, Roberto

    2014-04-01

    How does culture shape our concepts? Across many cultures, people conceptualize time as if it flows along a horizontal timeline, but the direction of this implicit timeline is culture specific: Later times are on the right in some cultures but on the left in others. Here we investigated whether experience reading can determine the direction and orientation of the mental timeline, independent of other cultural and linguistic factors. Dutch speakers performed space-time congruity tasks with the instructions and stimuli written in either standard, mirror-reversed, or rotated orthography. When participants judged temporal phrases written in standard orthography, their reaction times were consistent with a rightward-directed mental timeline, but after brief exposure to mirror-reversed orthography, their mental timelines were reversed. When standard orthography was rotated 90° clockwise (downward) or counterclockwise (upward), participants' mental timelines were rotated, accordingly. Reading can play a causal role in shaping people's implicit time representations. Exposure to a new orthography can change the direction and orientation of the mental timeline within minutes, even when the new space-time mapping directly contradicts the reader's usual mapping. To account for this representational flexibility, we propose the hierarchical mental metaphors theory, according to which culturally conditioned mappings between space and time are specific instances of a more general mapping, which is conditioned by the relationship between space and time in the physical world. Conceptualizations of time are culture specific at one level of analysis but may be universal at another.

  20. ac electroosmotic pumping induced by noncontact external electrodes.

    PubMed

    Wang, Shau-Chun; Chen, Hsiao-Ping; Chang, Hsueh-Chia

    2007-09-21

    Electroosmotic (EO) pumps based on dc electroosmosis is plagued by bubble generation and other electrochemical reactions at the electrodes at voltages beyond 1 V for electrolytes. These disadvantages limit their throughput and offset their portability advantage over mechanical syringe or pneumatic pumps. ac electroosmotic pumps at high frequency (>100 kHz) circumvent the bubble problem by inducing polarization and slip velocity on embedded electrodes,1 but they require complex electrode designs to produce a net flow. We report a new high-throughput ac EO pump design based on induced-polarization on the entire channel surface instead of just on the electrodes. Like dc EO pumps, our pump electrodes are outside of the load section and form a cm-long pump unit consisting of three circular reservoirs (3 mm in diameter) connected by a 1x1 mm channel. The field-induced polarization can produce an effective Zeta potential exceeding 1 V and an ac slip velocity estimated as 1 mmsec or higher, both one order of magnitude higher than earlier dc and ac pumps, giving rise to a maximum throughput of 1 mulsec. Polarization over the entire channel surface, quadratic scaling with respect to the field and high voltage at high frequency without electrode bubble generation are the reasons why the current pump is superior to earlier dc and ac EO pumps.

  1. Compliant Metal Enhanced Convection Cooled Reverse-Flow Annular Combustor

    NASA Technical Reports Server (NTRS)

    Paskin, Marc D.; Acosta, Waldo A.

    1994-01-01

    A joint Army/NASA program was conducted to design, fabricate, and test an advanced, reverse-flow, small gas turbine combustor using a compliant metal enhanced (CME) convection wall cooling concept. The objectives of this effort were to develop a design method (basic design data base and analysis) for the CME cooling technique and tben demonstrate its application to an advanced cycle, small, reverse-flow combustor with 3000 F (1922 K) burner outlet temperature (BOT). The CME concept offers significant improvements in wall cooling effectiveness resulting in a large reduction in cooling air requirements. Therefore, more air is available for control of burner outlet temperature pattern in addition to the benefit of improved efficiency, reduced emissions, and smoke levels. Rig test results demonstrated the benefits and viability of the CME concept meeting or exceeding the aerothermal performance and liner wall temperature characteristics of similar lower temperature-rise combustors, achieving 0.15 pattern factor at 3000 F (1922 K) BOT, while utilizing approximately 80 percent less cooling air than conventional, film-cooled combustion systems.

  2. Thermal inertia and reversing buoyancy in flow in porous media

    NASA Astrophysics Data System (ADS)

    Menand, Thierry; Raw, Alan; Woods, Andrew W.

    2003-03-01

    The displacement of fluids through porous rocks is fundamental for the recharge of geothermal and hydrocarbon reservoirs [Grant et al., 1982; Lake, 1989], for contaminant dispersal through the groundwater [Bear, 1972] and in controlling mineral reactions in permeable rocks [Phillips, 1991]. In many cases, the buoyancy force associated with density differences between the formation fluid and the displacing fluid controls the rate and pattern of flow through the permeable rock [Phillips, 1991; Barenblatt, 1996; Turcotte and Schubert, 2002]. Here, using new laboratory experiments, we establish that a striking range of different flow patterns may develop depending on whether this density contrast is associated with differences in temperature and/or composition between the two fluids. Owing to the effects of thermal inertia in a porous rock, thermal fronts lag behind compositional fronts [Woods and Fitzgerald, 1993; Turcotte and Schubert, 2002], so that two zones of different density develop in the region flooded with injected fluid. This can lead to increasing, decreasing or even reversing buoyancy in the injected liquid; in the latter case it may then form a double-flood front, spreading along both the upper and lower boundary of the rock. Recognition of these different flow regimes is key for predicting sweep efficiency and dispersal patterns in natural and engineered flows, and offers new opportunities for the enhanced recovery of natural resources in porous rocks.

  3. Convective flow reversal in self-powered enzyme micropumps

    PubMed Central

    Ortiz-Rivera, Isamar; Shum, Henry; Agrawal, Arjun; Sen, Ayusman; Balazs, Anna C.

    2016-01-01

    Surface-bound enzymes can act as pumps that drive large-scale fluid flows in the presence of their substrates or promoters. Thus, enzymatic catalysis can be harnessed for “on demand” pumping in nano- and microfluidic devices powered by an intrinsic energy source. The mechanisms controlling the pumping have not, however, been completely elucidated. Herein, we combine theory and experiments to demonstrate a previously unreported spatiotemporal variation in pumping behavior in urease-based pumps and uncover the mechanisms behind these dynamics. We developed a theoretical model for the transduction of chemical energy into mechanical fluid flow in these systems, capturing buoyancy effects due to the solution containing nonuniform concentrations of substrate and product. We find that the qualitative features of the flow depend on the ratios of diffusivities δ=DP/DS and expansion coefficients β=βP/βS of the reaction substrate (S) and product (P). If δ>1 and δ>β (or if δ<1 and δ<β), an unexpected phenomenon arises: the flow direction reverses with time and distance from the pump. Our experimental results are in qualitative agreement with the model and show that both the speed and direction of fluid pumping (i) depend on the enzyme activity and coverage, (ii) vary with the distance from the pump, and (iii) evolve with time. These findings permit the rational design of enzymatic pumps that accurately control the direction and speed of fluid flow without external power sources, enabling effective, self-powered fluidic devices. PMID:26903618

  4. Electricity generation using continuously recirculated flow electrodes in reverse electrodialysis

    NASA Astrophysics Data System (ADS)

    Liu, Fei; Coronell, Orlando; Call, Douglas F.

    2017-07-01

    Capacitive flow electrode systems that generate electricity from salinity gradients are limited by low power densities, inefficient electrical current collection, and complex system operation. We show here the proof-of-concept that a single reverse electrodialysis cell using continuously recirculated activated carbon flow electrodes can generate uninterrupted electricity from an artificial sea/river water gradient. Power densities reached 61 ± 5.7 mW m-2 (normalized to total membrane surface area) and current densities 2.4 ± 0.13 A m-2 when a 10% by weight carbon loading was used with graphite plate current collectors. Using high-surface area graphite brush current collectors, maximum power densities increased more than 320% to 260 ± 8.7 mW m-2 and maximum current densities more than 400% to 14 ± 0.59 A m-2. The performance improvements were attributed to a more than 80% decrease in electrode resistances when brushes were used instead of plates. A control static capacitive electrode system obtained slightly higher average power densities (290 ± 8.7 mW m-2), but could not produce it continuously, highlighting the operational advantage of the recirculated flow electrode design.

  5. Reverse-flow apparatus for enhanced colorimetric detection of bacteriuria.

    PubMed Central

    Wallis, C; Melnick, J L

    1984-01-01

    The reverse-flow apparatus is a new device for enhancing the detection of bacteria in urine. Bacteria are trapped onto a customized filter, and the pigments, crystals, and other interfering substances in the urine pass through the filter and are discarded. The bacteria are backflushed and are recovered as a concentrate, and the concentrate is then processed through the previously described colorimetric bacteriuria detection device. A total of 1,000 urine samples were obtained from randomly selected patients and were cultured on agar. Upon enumeration of the colonies, 160 urine samples were shown to contain more than 10(5) CFU/ml. In the bacteriuria detection device, 150 urine samples could not be processed (pigmenters and cloggers), and of the 850 urine samples processed, 127 were culture positive for 10(5) CFU/ml or greater, and 150 urine samples contained between 10(4) and 10(5) CFU/ml. At 10(5) CFU/ml, there were 140 false-positives and 14 false-negatives. When duplicate urine samples were processed through and concentrated by our new reverse-flow apparatus, all samples, including the above pigmenters and cloggers, could be tested in the bacteriuria detection device. The 150 unprocessable samples described above yielded 33 additional bacteria-positive urines, 23 at the 10(5)-CFU/ml cutoff and 10 at the 10(4)-to-10(5)-CFU/ml cutoff. There were 105 false-positives at 10(5) CFU/ml and only 2 false-negatives at the same level of bacteria. At 10(4) to 10(5) CFU/ml there was only 1% false-positive and 4% false-negative. The reverse-flow apparatus allows greater specificity and sensitivity in the rapid bacteriuria test. Urine containing 10(4) CFU/ml or more can now be detected with a 96% sensitivity in a total processing time of less than 2 min. Images PMID:6392325

  6. Measuring microchannel electroosmotic mobility and zeta potential by the current monitoring method.

    PubMed

    Shao, Chenren; Devoe, Don L

    2013-01-01

    Electroosmotic flow (EOF) is an electrokinetic flow control technique widely used in microfluidic systems for applications including direct electrokinetic pumping, hydrodynamic pressure generation, and counterflow for microfluidic separations. During EOF, an electric field is applied along the length of a microchannel containing an electrolyte, with mobile ions near the charged microchannel walls experiencing a Coulomb force due to electrostatic interactions with the applied electric field that leads to bulk solution movement. The goal of this laboratory is to experimentally determine the fixed channel surface charge (zeta potential) and electroosmotic mobility associated with a given microchannel substrate material and buffer solution, using a simple current monitoring method to measure the average flow velocity within the microchannel. It is a straightforward experiment designed to help students understand EOF physics while gaining hands-on experience with basic world-to-chip interfacing. It is well suited to a 90-min laboratory session for up to 12 students with minimal infrastructure requirements.

  7. Reverse flow facial artery as recipient vessel for perforator flaps.

    PubMed

    Hölzle, Frank; Hohlweg-Majert, Bettina; Kesting, Marco R; Mücke, Thomas; Loeffelbein, Denys J; Wolff, Klaus-Dietrich; Wysluch, Andreas

    2009-01-01

    In perforator flaps, anastomosis between flap and recipient vessels in the neck area is often difficult due to small vessel diameter and short pedicle. The aim of this study was to investigate whether the retrograde flow of the distal, paramandibular part of the facial artery would provide sufficient pressure and size to perfuse perforator flaps. Before and after occlusion of the contralateral facial artery, retrograde and anterograde arterial pressure was measured on both sides of the facial artery in 50 patients. The values were compared with the mean systemic arterial pressure. Diameters of facial arteries in the paramandibular region and perforator flap vessels were evaluated by morphometry. Arterial pressure in the distal facial artery with retrograde flow was 76% of the systemic arterial pressure. The latter equaled approximately the anterograde arterial pressure in the proximal end of the facial artery. Mean arterial pressure of the facial arteries decreased after proximal occlusion of the contralateral facial artery, which was not significant (P = 0.09). Mean diameter of the distal facial arteries in the mandibular region was 1.6 mm (range 1.3-2.2 mm; standard deviation 0.3 mm; n = 50), that of the perforator flap arteries 1.3 mm (0.9-2.6 mm; 0.4 mm; n = 20). Facial arteries, based on reverse flow, successfully supported all 20 perforator flaps. Retrograde pulsatile flow in the distal facial artery sustains perforator flaps even if the contralateral facial artery is occluded. Proximity of the distal facial arteries to the defect compensates for short pedicles. Matching diameters of the arteries are ideal for end-to-end anastomosis. Copyright 2009 Wiley-Liss, Inc. Microsurgery 2009.

  8. Computation of unsteady turbulent boundary layers with flow reversal and evaluation of two separate turbulence models

    NASA Technical Reports Server (NTRS)

    Cebeci, T.; Carr, L. W.

    1981-01-01

    A procedure which solves the governing boundary layer equations within Keller's box method was developed for calculating unsteady laminar flows with flow reversal. This method is extended to turbulent boundary layers with flow reversal. Test cases are used to investigate the proposition that unsteady turbulent boundary layers also remain free of singularities. Turbulent flow calculations are performed. The governing equations for both models are solved. As in laminar flows, the unsteady turbulent boundary layers are free from singularities, but there is a clear indication of rapid thickening of the boundary layer with increasing flow reversal. Predictions of both turbulence models are the same for all practical purposes.

  9. Ion Exchange Resin Bead Decoupled High-Pressure Electroosmotic Pump

    PubMed Central

    Yang, Bingcheng; Zhang, Feifang; Liang, Xinmiao; Dasgupta, Purnendu K.; Liu, Shaorong

    2009-01-01

    We describe an electroosmotic pump (EOP) that utilizes a cation exchange resin bead as the electric field decoupler. The resin bead serves as a electrical grounding joint without fluid leakage, thus eliminating electrolytic gas interference from the flow channels. The arrangement is easy to practice from readily available components, displays a very low electrical resistance, and is capable of bearing high backpressure (at least 3200 psi). We use a silica xerogel column as the EOP element to pump water and demonstrate a complete capillary ion chromatograph (CIC), which uses a similar bead based microelectrodialytic generator (μ-EDG) to generate a KOH eluent from the pumped water. We observed good operational stability of the complete arrangement over long periods. PMID:19449862

  10. Electroosmotic dewatering of dredged sediments: bench-scale investigation.

    PubMed

    Reddy, Krishna R; Urbanek, Adam; Khodadoust, Amid P

    2006-01-01

    The Indiana Harbor (Indiana, USA) has not been dredged since 1972 due to lack of a suitable disposal site for dredged sediment. As a result of this, over a million cubic yards of highly contaminated sediment has accumulated in the harbor. Recently, the United States Army Corps of Engineers (USACE) has selected a site for the confined disposal facility (CDF) and is in the process of designing it. Although dredging can be accomplished rapidly, the disposal in the CDF has to be done slowly to allow adequate time for consolidation to occur. The sediment possesses very high moisture content and very low hydraulic conductivity, which cause consolidation to occur slowly. Consolidation of the sediment is essential in order to achieve adequate shear strength of sediments and also to provide enough air space to accommodate the large amount of sediment that requires disposal. Currently, it has been estimated that if a one 3-foot (0.9-m) thick layer of sediment was disposed of at the CDF annually, it would take approximately 10 years to dispose of all the sediment that is to be dredged from the Indiana Harbor. This study investigated the feasibility of using an electroosmotic dewatering technology to accelerate dewatering and consolidation of sediment, thereby allowing more rapid disposal of sediment into the CDF. Electroosmotic dewatering essentially involves applying a small electric potential across the sediment layer, thereby inducing rapid flow as a result of physico-chemical and electrochemical processes. A series of bench-scale electrokinetic experiments were conducted on actual dredged sediment samples from the Indiana Harbor to investigate dewatering rates caused by gravity alone, dewatering rates caused by gravity and electric potential, and the effects of the addition of polymer flocculants on dewatering of the sediments. The results showed that electroosmotic dewatering under an applied electric potential of 1.0VDC/cm could increase the rate of dewatering and

  11. An on-chip electroosmotic micropump with a light- addressable potentiometric sensor

    NASA Astrophysics Data System (ADS)

    Li, Xue-liang; Liu, Shi-bin; Fan, Ping-ping; Werner, Carl Frederik; Miyamoto, Koichiro; Yoshinobu, Tatsuo

    2017-03-01

    An on-chip electroosmotic (EO) micropump (EOP) was integrated in a microfluidic channel combined with a light-addressable potentiometric sensor (LAPS). The movement of EO flow towards right and left directions can be clearly observed in the microfluidic channel. The characteristics of photocurrent-time and photocurrent-bias voltage are obtained when buffer solution passes through the sensing region. The results demonstrate that the combination of an on-chip EOP with an LAPS is feasible.

  12. Gliding arc in tornado using a reverse vortex flow

    SciTech Connect

    Kalra, Chiranjeev S.; Cho, Young I.; Gutsol, Alexander; Fridman, Alexander; Rufael, Tecle S.

    2005-02-01

    The present article reports a new gliding arc (GA) system using a reverse vortex flow ('tornado') in a cylindrical reactor (gliding arc in tornado, or GAT), as used to preserve the main advantages of traditional GA systems and overcome their main drawbacks. The primary advantages of traditional GA systems retained in the present GAT are the possibility to generate transitional plasma and to avoid considerable electrode erosion. In contrast to a traditional GA, the new GAT system ensures much more uniform gas treatment and has a significantly larger gas residence time in the reactor. The present article also describes the design of the new reactor and its stable operation regime when the variation of GAT current is very small. These features are understood to be very important for most viable applications. Additionally the GAT provides near-perfect thermal insulation from the reactor wall, indicating that the present GAT does not require the reactor wall to be constructed of high-temperature materials. The new GAT system, with its unique properties such as a high level of nonequilibrium and a large residence time, looks very promising for many industrial applications including fuel conversion, carbon dioxide conversion to carbon monoxide and oxygen, surface treatment, waste treatment, flame stabilization, hydrogen sulfide treatment, etc.

  13. Effect of capillary geometry on predicting electroosmotic volumetric flowrates in porous or fibrous media.

    PubMed

    Pascal, Jennifer; Oyanader, Mario; Arce, Pedro

    2012-07-15

    Electrokinetic-based methods are used in a variety of applications including drug delivery and separation of biomolecules, among others. Many of these applications feature a fibrous or a porous medium that can be modeled by using capillary bundle models to predict the behavior of the electroosmotic flow within the particular system. The role of geometry in predicting volumetric flowrates in porous media is investigated by modeling the electroosmotic flow in idealized capillaries of rectangular, cylindrical, and annular geometries. This is achieved by the coupling of electrostatics and continuum hydrodynamics to obtain analytical expressions that govern the electrokinetically - driven volumetric flow within these idealized capillary geometries. A previous study developed a model to compare the cylindrical and annular capillary geometries by utilizing two methods that compare the areas of the two geometries. The methods used in this previous work will also be used in the present contribution to compare the volumetric flowrates in the cylindrical and annular capillaries with a rectangular capillary. Illustrative results will be presented to aid in the understanding of the influence of the various geometrical and electrostatic parameters that arise from the analysis of these volumetric flowrates. It was found that the electroosmotic volumetric flowrates are significantly affected by the capillary geometry. Copyright © 2012. Published by Elsevier Inc.

  14. Electroosmotic fluid motion and late-time solute transport at non-negligible zeta potentials

    SciTech Connect

    S. K. Griffiths; R. H. Nilson

    1999-12-01

    Analytical and numerical methods are employed to determine the electric potential, fluid velocity and late-time solute distribution for electroosmotic flow in a tube and channel when the zeta potential is not small. The electric potential and fluid velocity are in general obtained by numerical means. In addition, new analytical solutions are presented for the velocity in a tube and channel in the extremes of large and small Debye layer thickness. The electroosmotic fluid velocity is used to analyze late-time transport of a neutral non-reacting solute. Zeroth and first-order solutions describing axial variation of the solute concentration are determined analytically. The resulting expressions contain eigenvalues representing the dispersion and skewness of the axial concentration profiles. These eigenvalues and the functions describing transverse variation of the concentration field are determined numerically using a shooting technique. Results are presented for both tube and channel geometries over a wide range of the normalized Debye layer thickness and zeta potential. Simple analytical approximations to the eigenvalues are also provided for the limiting cases of large and small values of the Debye layer thickness. The methodology developed here for electroosmotic flow is also applied to the Taylor problem of late-time transport and dispersion in pressure-driven flows.

  15. A low-voltage nano-porous electroosmotic pump.

    PubMed

    Ai, Ye; Yalcin, Sinan E; Gu, Diefeng; Baysal, Oktay; Baumgart, Helmut; Qian, Shizhi; Beskok, Ali

    2010-10-15

    A low-voltage electroosmotic (EO) micropump based on an anodic aluminum oxide (AAO) nano-porous membrane with platinum electrodes coated on both sides has been designed, fabricated, tested, and analyzed. The maximum flow rate of 0.074 ml min(-1) V(-1) cm(-2) for a membrane with porosity of 0.65 was obtained. A theoretical model, considering the head loss along the entire EO micropump system and the finite electrical double layer (EDL) effect on the flow rate, is developed for the first time to analyze the performance of the EO micropump. The theoretical and experimental results are in good agreement. It is revealed that the major head loss could remarkably decrease the flow rate, which thus should be taken into account for the applications of the EO micropump in various Lab-on-a-chip (LOC) devices. However, the effect of the minor head loss on the flow rate is negligible. The resulting flow rate increases with increasing porosity of the porous membrane and kappaa, the ratio of the radius of the nanopore to the Debye length.

  16. Effect of Trailing Edge Shape on the Unsteady Aerodynamics of Reverse Flow Dynamic Stall

    NASA Astrophysics Data System (ADS)

    Lind, Andrew; Jones, Anya

    2015-11-01

    This work considers dynamic stall in reverse flow, where flow travels over an oscillating airfoil from the geometric trailing edge towards the leading edge. An airfoil with a sharp geometric trailing edge causes early formation of a primary dynamic stall vortex since the sharp edge acts as the aerodynamic leading edge in reverse flow. The present work experimentally examines the potential merits of using an airfoil with a blunt geometric trailing edge to delay flow separation and dynamic stall vortex formation while undergoing oscillations in reverse flow. Time-resolved and phase-averaged flow fields and pressure distributions are compared for airfoils with different trailing edge shapes. Specifically, the evolution of unsteady flow features such as primary, secondary, and trailing edge vortices is examined. The influence of these flow features on the unsteady pressure distributions and integrated unsteady airloads provide insight on the torsional loading of rotor blades as they oscillate in reverse flow. The airfoil with a blunt trailing edge delays reverse flow dynamic stall, but this leads to greater downward-acting lift and pitching moment. These results are fundamental to alleviating vibrations of high-speed helicopters, where much of the rotor operates in reverse flow.

  17. FLUX ENHANCEMENT IN CROSSFLOW MEMBRANE FILTRATION: FOULING AND IT'S MINIMIZATION BY FLOW REVERSAL

    SciTech Connect

    Shamsuddin Ilias

    2005-01-25

    Fouling problems are perhaps the single most important reason for relatively slow acceptance of ultrafiltration in many areas of chemical and biological processing. To overcome the losses in permeate flux associated with concentration polarization and fouling in cross flow membrane filtration, we investigated the concept of flow reversal as a method to enhance membrane flux in ultrafiltration. Conceptually, flow reversal prevents the formation of stable hydrodynamic and concentration boundary layers at or near the membrane surface. Further more, periodic reversal of the flow direction of the feed stream at the membrane surface results in prevention and mitigation of membrane fouling. Consequently, these advantages are expected to enhance membrane flux significantly. A crossflow membrane filtration unit was designed and built to test the concept of periodic flow reversal for flux enhancement. The essential elements of the system include a crossflow hollow fiber membrane module integrated with a two-way valve to direct the feed flow directions. The two-way valve is controlled by a controller-timer for periodic reversal of flow of feed stream. Another important feature of the system is that with changing feed flow direction, the permeate flow direction is also changed to maintain countercurrent feed and permeate flows for enhanced mass transfer driving force (concentration difference). In this report, we report our application of Flow Reversal technique in clarification of apple juice containing pectin. The presence of pectin in apple juice makes the clarification process difficult and is believed to cause membrane fouling. Of all compounds found in apple juice, pectin is most often identified as the major hindrance to filtration performance. Based on our ultrafiltration experiments with apple juice, we conclude that under flow reversal conditions, the permeate flux is significantly enhanced when compared with the conventional unidirectional flow. Thus, flow reversal

  18. Electroosmotically induced hydraulic pumping on microchips: differential ion transport

    PubMed

    Culbertson; Ramsey; Ramsey

    2000-05-15

    The theory behind and operation of an electroosmotically induced hydraulic pump for microfluidic devices is reported. This microchip functional element consists of a tee intersection with one inlet channel and two outlet channels. The inlet channel is maintained at high voltage while one outlet channel is kept at ground and the other channel has no electric potential applied. A pressure-induced flow of buffer is created in both outlet channels of the tee by reducing electroosmosis in the ground channel relative to that of the inlet channel. Spatially selective reduction of electroosmosis is accomplished by coating the walls of the ground channel with a viscous polymer. The pump is shown to differentially transport ions down the two outlet channels. This ion discrimination ability of the pump is examined as a function of an analyte's electrophoretic velocity. In addition, we demonstrate that an anion can be rejected from the ground channel and made to flow only into the field-free channel if the electrophoretic velocity of the anion is greater than the pressure-generated flow in the ground channel. The velocity threshold at which anion rejection occurs can be selectively tuned by changing the flow resistance in the field-free channel relative to the ground channel.

  19. Thrust-reverser flow investigation on a twin-engine transport

    NASA Technical Reports Server (NTRS)

    Gatlin, Gregory M.; Quinto, P. Frank

    1988-01-01

    An investigation was conducted in the NASA Langley 14 x 22 foot Subsonic Tunnel to study the effects of engine thrust reversing on an aft-mounted twin-engine transport and to develop effective testing techniques. Testing was done over a fixed and a moving-belt ground plane and over a pressure instrumented ground board. Free-stream dynamic pressure was set at values up to 12.2 psf, which corresponded to a maximum Reynolds number based on the mean aerodynamic chord of 765,000. The thrust reversers examined included cascade, target and four-door configurations. The investigation focused on the range of free-stream velocities and engine thrust-reverser flow rates that would be typical for landing ground-roll conditions. Flow visualization techniques were investigated, and the use of water or smoke injected into the reverser flow proved effective to determine the forward progression of the reversed flow and reingestion limits. When testing over a moving-belt ground plane, as opposed to a fixed ground plane, forward penetration of the reversed flow was reduced. The use of a pressure-instrumented ground board enabled reversed flow ground velocities to be obtained, and it provided a means by which to identify the reversed flow impingement point on the ground.

  20. Static internal performance of a nonaxisymmetric vaned thrust reverser with flow splay capability

    NASA Technical Reports Server (NTRS)

    Bangert, Linda S.; Leavitt, Laurence D.

    1989-01-01

    An investigation was conducted in the Static Test Facility of the Langley 16-Foot Transonic Tunnel on a dual-port, nonaxisymmetric, block-and-turn type thrust reverser model with vane cascades in the reverser ports which turned the flow in the splay direction and aided in turning the flow in the reverse direction. Splaying reverser flow is a method of delaying to lower landing ground roll speeds the reingestion of hot exhaust flow into the inlets. Exhaust flow splay can also help prevent the impingement of hot exhaust gases on the empennage surfaces when the reverser is integrated into an actual airframe. The vane cascades consisted of two sets of perpendicular vanes with a variable number of turning and splay vanes. A skewed vane box was also tested which had only one set of vanes angled to provide both turning and splay. Vane cascades were designed to provide different amounts of flow splay in the top and bottom ports. Inner doors, trim tabs, and an orifice plate all provided means of varying the port area for reverser flow modulation. The outer door position was varied as a means of influencing the flow reverse angle. Nozzle pressure ratio was varied from 1.75 to approximately 6.00.

  1. Experimental Investigation of a Yawed Airfoil in Reverse Flow Dynamic Stall

    NASA Astrophysics Data System (ADS)

    Smith, Luke; Lind, Andrew, , Dr.; Jones, Anya, , Dr.

    2016-11-01

    When a rotating blade enters high advance ratio flight, a significant portion of the blade is subject to reverse flow, where flow travels from the blade's geometric trailing edge to the geometric leading edge. The purpose of this work is to determine the influence of spanwise flow on a blade undergoing dynamic stall in reverse flow. Without spanwise flow, an oscillating sharp trailing edge airfoil in reverse flow experiences separation about its sharp aerodynamic leading edge, leading to the formation of a dynamic stall vortex at low angles of attack. With spanwise flow, an airfoil experiences a delay in lift stall, possibly due to the convection of a vortex along the freestream. This work characterizes the three-dimensional flow field of an oscillating airfoil at static yaw angles in reverse flow. Time-resolved velocity fields and chordwise pressure distributions are presented for several span locations, reduced frequencies, and Reynolds numbers. The unsteady velocity fields allow for the identification of dynamic stall vortex locations, and the unsteady pressure distributions allow for the analysis of spanwise variation in aerodynamic forces. By comparing the yawed and un-yawed cases, this work illustrates the relative importance of spanwise flow in reverse flow dynamic stall.

  2. Electro-Osmotic Remediation of Fine-Grained Sediments

    SciTech Connect

    Cherepy, N.J.; McNab, W.W.; Wildenschild, D.; Ruiz, R.; Elsholz, A.

    1999-11-22

    The coupled-flow phenomenon, electro-osmosis, whereby water flow results from an applied electrical potential gradient, is being used at Lawrence Livermore National Laboratory to induce water flow through deep (25-40 meters below surface) fine-grained sediments. The scoping work described here lays the groundwork for implementation of this technology to remediate solvent-contaminated clayey zones at the LLNL site. The electro-osmotic conductivity (k{sub e}) measured in-situ between two 37 m deep wells, 3 m apart of 2.3 x 10{sup -9} m{sup 2}/s-V is in good agreement with the value determined from bench-top studies on the core extracted from one of the wells of 0.94 {+-} 0.29 x 10{sup -9} m{sup 2}/s-V. Hydraulic conductivity (k{sub h}) of the same core is measured to be 2.03 {+-} 0.36 x 10{sup -10} m/s. Thus, a voltage gradient of 1 V/cm produces an effective hydraulic conductivity of {approx}1 x 10{sup -7} m/s; an increase in conductivity of nearly three orders of magnitude.

  3. Electroosmotic properties of microfluidic channels composed of poly(dimethylsiloxane).

    PubMed

    Ren, X; Bachman, M; Sims, C; Li, G P; Allbritton, N

    2001-10-25

    Microfluidic devices fabricated from polymers exhibit great potential in biological analyses. Poly(dimethylsiloxane) (PDMS) has shown promise as a substrate for rapid prototyping of devices. Despite this, disagreement exists in the literature as to the ability of PDMS to support electroosmotic (EO) flow and the stability of that flow over time. We demonstrate that in low ionic strength solutions near neutral in pH. oxidized PDMS had a four-fold greater EO mobility (mu(eo)) compared to native PDMS. The greater mu(eo) was maintained irrespective of whether glass or PDMS was used as a support forming one side of the channel. This enhanced mu(eo) was preserved as long as the channels were filled with an aqueous solution. Upon exposure of the channels to air, the mobility decreased by a factor of two with a half-life of 9 h. The EO properties of the air-exposed, oxidized PDMS were regenerated by exposure to strong base. High ionic strength, neutral in pH buffers compatible with living eukaryotic cells diminished the EO flow in the oxidized PDMS devices to a much greater extent than in the native PDMS devices. For analyses utilizing intact and living cells, oxidation of PDMS may not be an effective strategy to substantially increase the mu(eo).

  4. FLUX ENHANCEMENT IN CROSSFLOW MEMBRANE FILTRATION: FOULING AND IT'S MINIMIZATION BY FLOW REVERSAL

    SciTech Connect

    Shamsuddin Ilias

    2004-06-14

    Fouling problems are perhaps the single most important reason for relatively slow acceptance of ultrafiltration in many areas of chemical and biological processing. To overcome the losses in permeate flux associated with concentration polarization and fouling in cross flow membrane filtration, we investigated the concept of flow reversal as a method to enhance membrane flux in ultrafiltration. Conceptually, flow reversal prevents the formation of stable hydrodynamic and concentration boundary layers at or near the membrane surface. Further more, periodic reversal of the flow direction of the feed stream at the membrane surface results in prevention and mitigation of membrane fouling. Consequently, these advantages are expected to enhance membrane flux significantly. A crossflow membrane filtration unit was designed and built to test the concept of periodic flow reversal for flux enhancement. The essential elements of the system include a crossflow hollow fiber membrane module integrated with a two-way valve to direct the feed flow directions. The two-way valve is controlled by a controller-timer for periodic reversal of flow of feed stream. Another important feature of the system is that with changing feed flow direction, the permeate flow direction is also changed to maintain countercurrent feed and permeate flows for enhanced mass transfer driving force (concentration difference). In our previous report, we reported our work on UF of BSA. In this report, we report our continuing application of Flow Reversal technique in clarification of apple juice containing pectin. The presence of pectin in apple juice makes the clarification process difficult and is believed to cause membrane fouling. Of all compounds found in apple juice, pectin is most often identified as the major hindrance to filtration performance. Laboratory-scale tests on a hollow-fiber ultrafiltration membrane module using pectin in apple juice as feed show that under flow reversal conditions, the

  5. Flux Enhancement in Crossflow Membrane Filtration: Fouling and It's Minimization by Flow Reversal

    SciTech Connect

    Shamsuddin Ilias

    2005-08-04

    Fouling problems are perhaps the single most important reason for relatively slow acceptance of ultrafiltration in many areas of chemical and biological processing. To overcome the losses in permeate flux associated with concentration polarization and fouling in cross flow membrane filtration, we investigated the concept of flow reversal as a method to enhance membrane flux in ultrafiltration. Conceptually, flow reversal prevents the formation of stable hydrodynamic and concentration boundary layers at or near the membrane surface. Further more, periodic reversal of the flow direction of the feed stream at the membrane surface results in prevention and mitigation of membrane fouling. Consequently, these advantages are expected to enhance membrane flux significantly. A crossflow membrane filtration unit was designed and built to test the concept of periodic flow reversal for flux enhancement. The essential elements of the system include a crossflow hollow fiber membrane module integrated with a two-way valve to direct the feed flow directions. The two-way valve is controlled by a controller-timer for periodic reversal of flow of feed stream. Another important feature of the system is that with changing feed flow direction, the permeate flow direction is also changed to maintain countercurrent feed and permeate flows for enhanced mass transfer driving force (concentration difference). Three feed solutions (Bovine serum albumin (BSA), apple juice and citrus fruit pectin) were studied in crossflow membrane filtration. These solutes are well-known in membrane filtration for their fouling and concentration polarization potentials. Laboratory-scale tests on a hollow-fiber ultrafiltration membrane module using each of the feed solutes show that under flow reversal conditions, the permeate flux is significantly enhanced when compared with the conventional unidirectional flow. The flux enhancement is dramatic (by an order of magnitude) with increased feed concentration and

  6. Fingerprinting Reverse Proxies Using Timing Analysis of TCP Flows

    DTIC Science & Technology

    2013-09-01

    sites can increase their client throughput by utilizing reverse proxy servers that increase their potential for sales or advertising . From a more... advertising . The ability to reliably identify reverse proxies is valuable to better understand a network topology as well as identify possible vector...As the Internet spread globally, privacy and security became more desirable for online communication, banking, e -commerce, and data storage to name a

  7. Coronary competitive reverse flow: Imaging findings at CT angiography and correlation with invasive coronary angiography.

    PubMed

    Li, Minghua; Liu, Shuyong; Zhang, Jiayin; Lu, Zhigang; Wei, Meng; Chun, Eun-Ju; Lu, Bin

    2015-01-01

    To study the imaging features of coronary competitive reverse flow and incidence of a "reverse attenuation gradient" in coronary CT angiography (CTA) with correlation to invasive coronary angiography (ICA). Patients who had undergone coronary CTA and ICA within 2 weeks were retrospectively identified in our database and reviewed. All cases with ICA-confirmed competitive reverse flow or chronic total occlusions (CTOs) were included for further analysis. The "reverse attenuation gradient sign" was defined as a reverse intraluminal opacification gradient of vessels which showed higher opacification in more distal compared with proximal segments. ICA findings were recorded and served as the reference to identify the clinical implications of this sign. In total, 134 patients (mean age, 68.1 ± 11.3 years; range, 38-90 years; 104 men) were included in our study. ICA revealed 11 cases of coronary competitive reverse flow and 123 cases of CTO. A reverse attenuation gradient sign was present in 9 of 11 patients (82%) with coronary competitive reverse flow and 72 of 123 (59%) chronically occluded coronary arteries. Myocardial bridges, distal collateral filling, as well as direct visualization of collateral connection were all more frequent in cases with coronary competitive reverse flow group compared with cases with a CTO. The reverse attenuation gradient sign distal to an upstream coronary severe stenosis indicates the presence of competitive collateral flow. Coronary CTA is able to correctly detect coronary competitive collateral flow and differentiate it from CTOs. Copyright © 2015 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.

  8. Analysis of HRCT-derived xylem network reveals reverse flow in some vessels.

    PubMed

    Lee, Eric F; Matthews, Mark A; McElrone, Andrew J; Phillips, Ronald J; Shackel, Kenneth A; Brodersen, Craig R

    2013-09-21

    Long distance water and nutrient transport in plants is dependent on the proper functioning of xylem networks, a series of interconnected pipe-like cells that are vulnerable to hydraulic dysfunction as a result of drought-induced embolism and/or xylem-dwelling pathogens. Here, flow in xylem vessels was modeled to determine the role of vessel connectivity by using three dimensional xylem networks derived from High Resolution Computed Tomography (HRCT) images of grapevine (Vitis vinifera cv. 'Chardonnay') stems. Flow in 4-27% of the vessel segments (i.e. any section of vessel elements between connection points associated with intervessel pits) was found to be oriented in the direction opposite to the bulk flow under normal transpiration conditions. In order for the flow in a segment to be in the reverse direction, specific requirements were determined for the location of connections, distribution of vessel endings, diameters of the connected vessels, and the conductivity of the connections. Increasing connectivity and decreasing vessel length yielded increasing numbers of reverse flow segments until a maximum value was reached, after which more interconnected networks and smaller average vessel lengths yielded a decrease in the number of reverse flow segments. Xylem vessel relays also encouraged the formation of reverse flow segments. Based on the calculated flow rates in the xylem network, the downward spread of Xylella fastidiosa bacteria in grape stems was modeled, and reverse flow was shown to be an additional mechanism for the movement of bacteria to the trunk of grapevine.

  9. Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system

    NASA Astrophysics Data System (ADS)

    Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

    2015-12-01

    We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices.

  10. Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system

    PubMed Central

    Altmeyer, Sebastian; Do, Younghae; Lai, Ying-Cheng

    2015-01-01

    We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices. PMID:26687638

  11. Induced charge electro-osmotic concentration gradient generator

    PubMed Central

    Jain, Mranal; Yeung, Anthony; Nandakumar, K.

    2010-01-01

    Biomolecule gradients play an important role in the understanding of various biological processes. Typically, biological cells are exposed to linear and nonlinear concentration gradients and their response is studied for understanding cell growth, cell migration, and cell differentiation mechanisms. Recent studies have demonstrated the use of microfluidic devices for precise and stable concentration gradient generation. However, most of the reported devices are geometrically complex and lack dynamic controllability. In this work, a novel microfluidic gradient generator is presented which utilizes the induced charge electro-osmosis (ICEO) by introducing conducting obstacle in the microchannel. With the ICEO flow component, significant transverse convection can be generated within the microchannel, which can, in turn, be used to create nonlinear as well as asymmetric gradients. The characteristics of the developed concentration gradient are dependent on the interplay between fixed charge electro-osmotic and ICEO flows. It is shown that the proposed device can switch between linear and nonlinear gradients by just altering the applied electric field. Finally, the formation of user-defined concentration profiles (linear, convex, and concave) is demonstrated by varying the conducting obstacle size. PMID:20644679

  12. Fast three dimensional ac electro-osmotic pumps with nonphotolithographic electrode patterning

    PubMed Central

    Senousy, Y. M.; Harnett, C. K.

    2010-01-01

    Three dimensional (3D) stepped electrodes dramatically improve the flow rate and frequency range of ac electro-osmotic pumps, compared to planar electrodes. However, the fabrication of 3D stepped electrodes for ac electro-osmosis (ACEO) pumps usually involves several processing steps. This paper demonstrates results from ACEO pumps produced by a faster and less expensive method to fabricate the 3D electrodes—extending the previous work to disposable devices. The method is based on shadowed evaporation of metal on an insulating substrate that can be injection molded. Flow velocities through the 3D ACEO pump are similar to those seen in the previous work. PMID:20697462

  13. FLUX ENHANCEMENT IN CROSSFLOW MEMBRANE FILTRATION: FOULING AND IT'S MINIMIZATION BY FLOW REVERSAL

    SciTech Connect

    Shamsuddin Ilias

    2002-03-14

    Fouling problems are perhaps the single most important reason for relatively slow acceptance of ultrafiltration in many areas of chemical and biological processing. To overcome the losses in permeate flux associated with concentration polarization and fouling in cross flow membrane filtration, we investigated the concept of flow reversal as a method to enhance membrane flux in ultrafiltration. Conceptually, flow reversal prevents the formation of stable hydrodynamic and concentration boundary layers at or near the membrane surface. Further more, periodic reversal of the flow direction of the feed stream at the membrane surface results in prevention and mitigation of membrane fouling. Consequently, these advantages are expected to enhance membrane flux significantly. A crossflow membrane filtration unit was designed and built to test the concept of periodic flow reversal for flux enhancement. The essential elements of the system include a crossflow hollow fiber membrane module integrated with a two-way valve to direct the feed flow directions. The two-way valve is controlled by a controller-timer for periodic reversal of flow of feed stream. Another important feature of the system is that with changing feed flow direction, the permeate flow direction is also changed to maintain countercurrent feed and permeate flows for enhanced mass transfer driving force (concentration difference). Bovine serum albumin (BSA) is a well-studied model solute in membrane filtration known for its fouling and concentration polarization capabilities. Laboratory-scale tests on a hollow-fiber ultrafiltration membrane module using BSA solution as feed show that under flow reversal conditions, the permeate flux is significantly enhanced when compared with the conventional unidirectional flow. The flux enhancement is dramatic (by an order of magnitude) with increased feed concentration and operating transmembrane pressure.

  14. Effect of reverse flow on the pattern of wall shear stress near arterial branches.

    PubMed

    Kazakidi, A; Plata, A M; Sherwin, S J; Weinberg, P D

    2011-11-07

    Atherosclerotic lesions have a patchy distribution within arteries that suggests a controlling influence of haemodynamic stresses on their development. The distribution near aortic branches varies with age and species, perhaps reflecting differences in these stresses. Our previous work, which assumed steady flow, revealed a dependence of wall shear stress (WSS) patterns on Reynolds number and side-branch flow rate. Here, we examine effects of pulsatile flow. Flow and WSS patterns were computed by applying high-order unstructured spectral/hp element methods to the Newtonian incompressible Navier-Stokes equations in a geometrically simplified model of an aorto-intercostal junction. The effect of pulsatile but non-reversing side-branch flow was small; the aortic WSS pattern resembled that obtained under steady flow conditions, with high WSS upstream and downstream of the branch. When flow in the side branch or in the aortic near-wall region reversed during part of the cycle, significantly different instantaneous patterns were generated, with low WSS appearing upstream and downstream. Time-averaged WSS was similar to the steady flow case, reflecting the short duration of these events, but patterns of the oscillatory shear index for reversing aortic near-wall flow were profoundly altered. Effects of reverse flow may help explain the different distributions of lesions.

  15. Effect of reverse flow on the pattern of wall shear stress near arterial branches

    PubMed Central

    Kazakidi, A.; Plata, A. M.; Sherwin, S. J.; Weinberg, P. D.

    2011-01-01

    Atherosclerotic lesions have a patchy distribution within arteries that suggests a controlling influence of haemodynamic stresses on their development. The distribution near aortic branches varies with age and species, perhaps reflecting differences in these stresses. Our previous work, which assumed steady flow, revealed a dependence of wall shear stress (WSS) patterns on Reynolds number and side-branch flow rate. Here, we examine effects of pulsatile flow. Flow and WSS patterns were computed by applying high-order unstructured spectral/hp element methods to the Newtonian incompressible Navier–Stokes equations in a geometrically simplified model of an aorto-intercostal junction. The effect of pulsatile but non-reversing side-branch flow was small; the aortic WSS pattern resembled that obtained under steady flow conditions, with high WSS upstream and downstream of the branch. When flow in the side branch or in the aortic near-wall region reversed during part of the cycle, significantly different instantaneous patterns were generated, with low WSS appearing upstream and downstream. Time-averaged WSS was similar to the steady flow case, reflecting the short duration of these events, but patterns of the oscillatory shear index for reversing aortic near-wall flow were profoundly altered. Effects of reverse flow may help explain the different distributions of lesions. PMID:21508011

  16. Computational and experimental investigation of subsonic internal reversing flows

    NASA Technical Reports Server (NTRS)

    Rhodes, James A.; Esker, Barbara S.; Smith, C. F.

    1992-01-01

    The flow inside a model exhaust configuration was studied using both experimental and computational techniques. The hardware was tested at the NASA Lewis Research Center's Powered Lift Facility at tailpipe total pressure to ambient static pressure ratios ranging from 1.0 to 5.0. The flow simulations were obtained using the two 3-D Navier-Stokes CFD codes run on the Lewis Cray Y-MP computer. Both codes produced oscillatory solutions due to the inflow boundary condition reflecting acoustic waves. The CFD solutions correctly predicted the flow separation along the inside elbow of the takeoff and also along the walls of the ventral duct. Mass flow rates were overpredicted due to underprediction of the turbulent energy dissipation and subsequent total pressure loss.

  17. Blade Sections in Streamwise Oscillations into Reverse Flow

    DTIC Science & Technology

    2015-05-07

    fixed incidence of 6 degrees is taken as a nominally attached-flow case, and agrees reasonably well with Isaacs ’ theory. A fixed incidence of 20...degrees is taken as a nominally attached-flow case, and agrees reasonably well with Isaacs ’ theory. A fixed incidence of 20 degrees is taken as a...here the wing or rotor angle of attack may remain either constant or change, while the free-stream velocity oscillates. Greenberg (Ref. 18) and Isaacs

  18. Asymmetrical reverse vortex flow due to induced-charge electro-osmosis around carbon stacking structures

    NASA Astrophysics Data System (ADS)

    Sugioka, Hideyuki

    2011-05-01

    Broken symmetry of vortices due to induced-charge electro-osmosis (ICEO) around stacking structures is important for the generation of a large net flow in a microchannel. Following theoretical predictions in our previous study, we herein report experimental observations of asymmetrical reverse vortex flows around stacking structures of carbon posts with a large height (~110 μm) in water, prepared by the pyrolysis of a photoresist film in a reducing gas. Further, by the use of a coupled calculation method that considers boundary effects precisely, the experimental results, except for the problem of anomalous flow reversal, are successfully explained. That is, unlike previous predictions, the precise calculations here show that stacking structures accelerate a reverse flow rather than suppressing it for a microfluidic channel because of the deformation of electric fields near the stacking portions; these structures can also generate a large net flow theoretically in the direction opposite that of a previous prediction for a standard vortex flow. Furthermore, by solving the one-dimensional Poisson-Nernst-Plank (PNP) equations in the presence of ac electric fields, we find that the anomalous flow reversal occurs by the phase retardation between the induced diffuse charge and the tangential electric field. In addition, we successfully explain the nonlinearity of the flow velocity on the applied voltage by the PNP analysis. In the future, we expect to improve the pumping performance significantly by using stacking structures of conductive posts along with a low-cost process.

  19. Modelling the equilibrium bed topography of submarine meanders that exhibit reversed secondary flows

    NASA Astrophysics Data System (ADS)

    Darby, Stephen E.; Peakall, Jeff

    2012-08-01

    Submarine meandering channels formed by turbidity currents are common; however, their location on the ocean floor and their inactive status make it difficult to measure process dynamics and bed morphology. Conceptual models have, therefore, instead been developed by analogy with the well understood mechanics of fluvial bends. However, unlike fluvial currents, in turbidity currents the downstream velocity maximum typically occurs near the bed and recent experimental and theoretical studies suggest that, under certain hydraulic and morphological conditions, this forces the secondary flow to exhibit the reverse sense to that encountered in fluvial bends. Herein the possible morphological implications of a reversal of secondary flow are explored by modelling the force balance on sediment grains moving through either (i) field and laboratory submarine meander bends that are known to exhibit ‘reversed' secondary flows, or (ii) inactive submarine meander bends where the nature of the secondary flow in the formative turbidity currents can be inferred to be reversed. Exploratory simulations are undertaken for a single hypothetical submarine bend with morphological properties based on nine relic meanders observed on the floor of the Gulf of Alaska. Reconstructions of secondary flow properties within the Gulf of Alaska bends indicate that they likely exhibited reversed secondary flows. Results of the exploratory simulations indicate that, unlike typical fluvial meanders, the transverse bed profile gradient of the hypothetical bend is very low and the point bar is located downstream of the bend apex.

  20. END-DIASTOLIC FLOW REVERSAL LIMITS THE EFFICACY OF PEDIATRIC INTRAAORTIC BALLOON PUMP COUNTERPULSATION

    PubMed Central

    Bartoli, Carlo R.; Rogers, Benjamin D.; Ionan, Constantine E.; Koenig, Steven C.; Pantalos, George M.

    2013-01-01

    OBJECTIVE Counterpulsation with an intraaortic balloon pump (IABP) has not achieved the same successes or clinical use in pediatric patients as in adults. In a pediatric animal model, IABP efficacy was investigated to determine whether IABP timing with a high-fidelity blood pressure signal may improve counterpulsation therapy versus a low-fidelity signal. METHODS In Yorkshire piglets (n=19, 13.0±0.5 kg) with coronary ligation-induced acute ischemic left ventricular failure, pediatric IABPs (5 or 7cc) were placed in the descending thoracic aorta. Inflation and deflation were timed with traditional criteria from low-fidelity (fluid-filled) and high-fidelity (micromanometer) blood pressure signals during 1:1 support. Aortic, carotid, and coronary hemodynamics were measured with pressure and flow transducers. Myocardial oxygen consumption was calculated from coronary sinus and arterial blood samples. Left ventricular myocardial blood flow and end-organ blood flow were measured with microspheres. RESULTS Despite significant suprasystolic diastolic augmentation and afterload reduction at heart rates of 105±3bmp, left ventricular myocardial blood flow, myocardial oxygen consumption, the myocardial oxygen supply/demand relationship, cardiac output, and end-organ blood flow did not change. Statistically significant end-diastolic coronary, carotid, and aortic flow reversal occurred with IABP deflation. Inflation and deflation timed with a high-fidelity versus low-fidelity signal did not attenuate systemic flow reversal or improve the myocardial oxygen supply/demand relationship. CONCLUSIONS Systemic end-diastolic flow reversal limited counterpulsation efficacy in a pediatric model of acute left ventricular failure. Adjustment of IABP inflation and deflation timing with traditional criteria and a high-fidelity blood pressure waveform did not improve IABP efficacy or attenuate flow reversal. End-diastolic flow reversal may limit the efficacy of IABP counterpulsation therapy

  1. Avalanches, breathers, and flow reversal in a continuous Lorenz-96 model.

    PubMed

    Blender, R; Wouters, J; Lucarini, V

    2013-07-01

    For the discrete model suggested by Lorenz in 1996, a one-dimensional long-wave approximation with nonlinear excitation and diffusion is derived. The model is energy conserving but non-Hamiltonian. In a low-order truncation, weak external forcing of the zonal mean flow induces avalanchelike breather solutions which cause reversal of the mean flow by a wave-mean flow interaction. The mechanism is an outburst-recharge process similar to avalanches in a sandpile model.

  2. Compliant Metal Enhanced Convection Cooled Reverse-Flow Annular Combustor

    DTIC Science & Technology

    1994-06-01

    contained 12 piloted-air blast fuel nozzles each surrounded by an axial swirler. Design point operating conditions are given in Table I. Figure 2 ...shows the CME combustor predicted airflow distribution at the design point 2 Table I Combustor design conditions. CMC combustor Wa (liner flow...and exits through the slots between the tiles. A 2 -D heat transfer model was used to predict wall temperature as a function of tile side length for

  3. Turbulence Modeling for Thrust Reverser Flow Field Prediction Methods

    DTIC Science & Technology

    1992-12-01

    Barata 28 of a normal impinging jet at H/D = 5 and Vj/V_. = 30 indicate that the shear stress in the vortex is roughly an order of magnitude less than...Speed Afterbody Flows," 1. Propulsion and Power, Vol. 7, No. 4, 1991, pp. 607-616 28. Barata , J. M. M., Durao, D. F. G., and Heitor, M. V., "Turbulent

  4. [Reversal of portal blood flow in cirrhosis. Clinical, endoscopic and ultrasound endoscopic correlations in 72 patients].

    PubMed

    Letard, J C; Boustière, C; Romy, P; Jouffre, C; Patouillard, B; Etaix, J P; Barthélémy, C; Veyret, C; Audigier, J C

    1993-01-01

    From January to December 1991, the portal venous system was evaluated by Doppler ultrasonography in 72 patients with liver cirrhosis. The objectives of this study were to evaluate the prevalence of spontaneous reversal of blood flow in the portal vein and to assess the relationship between Doppler ultrasound investigation and clinical, biochemical, endoscopic (70 patients), and endosonographic (44 patients) features. Reversed flow was quite frequent (alternating: 17%, permanent: 22%) and its prevalence did not differ in relation to age, sex, serum gammaglobulin concentration and Child-Pugh class. In patients with reversed portal venous flow, the prevalence of hepatic encephalopathy was higher (39% vs 13.5%, P < 0.05), but the prevalence of esophageal or gastric varices was not related to that pattern. Endosonography detected gastric wall abnormalities in a higher proportion of patients with reversed portal flow than in patients without it (P < 0.05). This study suggests that reversal of flow in the portal vein could play a role in the development of the gastric wall abnormalities in liver cirrhosis, which are detected by endosonography but not by endoscopy.

  5. Wave propagation reversal for wavy vortices in wide-gap counter-rotating cylindrical Couette flow

    NASA Astrophysics Data System (ADS)

    Altmeyer, S.; Lueptow, Richard M.

    2017-05-01

    We present a numerical study of wavy supercritical cylindrical Couette flow between counter-rotating cylinders in which the wavy pattern propagates either prograde with the inner cylinder or retrograde opposite the rotation of the inner cylinder. The wave propagation reversals from prograde to retrograde and vice versa occur at distinct values of the inner cylinder Reynolds number when the associated frequency of the wavy instability vanishes. The reversal occurs for both twofold and threefold symmetric wavy vortices. Moreover, the wave propagation reversal only occurs for sufficiently strong counter-rotation. The flow pattern reversal appears to be intrinsic in the system as either periodic boundary conditions or fixed end wall boundary conditions for different system sizes always result in the wave propagation reversal. We present a detailed bifurcation sequence and parameter space diagram with respect to retrograde behavior of wavy flows. The retrograde propagation of the instability occurs when the inner Reynolds number is about two times the outer Reynolds number. The mechanism for the retrograde propagation is associated with the inviscidly unstable region near the inner cylinder and the direction of the global average azimuthal velocity. Flow dynamics, spatio-temporal behavior, global mean angular velocity, and torque of the flow with the wavy pattern are explored.

  6. Arterial microanastomoses on the reverse flow of the internal carotid artery reverse flow: an extreme solution in free-flap revascularisation. How we do it.

    PubMed

    Baj, A; Bolzoni, A; Torretta, S; Pignataro, L

    2014-10-01

    Microvascular free tissue transfer in head and neck reconstruction requires suitable recipient vessels, which are frequently compromised by prior surgery, radiotherapy, or size of the tumour. A surgical description of an arterial free flap pedicle anastomosis on the reverse internal carotid arterial flow in a vessel-depleted neck is presented. A 66-year-old male with a relapse of hypopharyngeal squamous cell carcinoma previously treated with both surgical and radiation therapy for carcinoma of the tongue and the larynx was successfully reconstructed using a free forearm flap with reverse internal carotid arterial flow. The involvement of the carotid glomus and prior surgery excluded the other vessels as recipients. The forearm free flap survived without any complications. This procedure can be considered an alternative rescue technique for salvage reconstruction in a vessel-depleted neck.

  7. Electro-osmotic mobility of non-Newtonian fluids.

    PubMed

    Zhao, Cunlu; Yang, Chun

    2011-03-23

    Electrokinetically driven microfluidic devices are usually used to analyze and process biofluids which can be classified as non-Newtonian fluids. Conventional electrokinetic theories resulting from Newtonian hydrodynamics then fail to describe the behaviors of these fluids. In this study, a theoretical analysis of electro-osmotic mobility of non-Newtonian fluids is reported. The general Cauchy momentum equation is simplified by incorporation of the Gouy-Chapman solution to the Poisson-Boltzmann equation and the Carreau fluid constitutive model. Then a nonlinear ordinary differential equation governing the electro-osmotic velocity of Carreau fluids is obtained and solved numerically. The effects of the Weissenberg number (Wi), the surface zeta potential (ψ¯s), the power-law exponent(n), and the transitional parameter (β) on electro-osmotic mobility are examined. It is shown that the results presented in this study for the electro-osmotic mobility of Carreau fluids are quite general so that the electro-osmotic mobility for the Newtonian fluids and the power-law fluids can be obtained as two limiting cases.

  8. Electro-osmotic mobility of non-Newtonian fluids

    PubMed Central

    Zhao, Cunlu; Yang, Chun

    2011-01-01

    Electrokinetically driven microfluidic devices are usually used to analyze and process biofluids which can be classified as non-Newtonian fluids. Conventional electrokinetic theories resulting from Newtonian hydrodynamics then fail to describe the behaviors of these fluids. In this study, a theoretical analysis of electro-osmotic mobility of non-Newtonian fluids is reported. The general Cauchy momentum equation is simplified by incorporation of the Gouy–Chapman solution to the Poisson–Boltzmann equation and the Carreau fluid constitutive model. Then a nonlinear ordinary differential equation governing the electro-osmotic velocity of Carreau fluids is obtained and solved numerically. The effects of the Weissenberg number (Wi), the surface zeta potential (ψ¯s), the power-law exponent(n), and the transitional parameter (β) on electro-osmotic mobility are examined. It is shown that the results presented in this study for the electro-osmotic mobility of Carreau fluids are quite general so that the electro-osmotic mobility for the Newtonian fluids and the power-law fluids can be obtained as two limiting cases. PMID:21503161

  9. Reversing flow development in a separating turbulent boundary layer

    NASA Astrophysics Data System (ADS)

    Santos, Leonardo; Lang, Amy; Wahidi, Redha; Bonacci, Andrew

    2016-11-01

    Fast swimming sharks have micro-structures on their skin consisting of bristling scales. These scales are hypothesized to bristle in response to backflow generated from the separated turbulent boundary layer (TBL) in regions of adverse pressure gradient (APG) on the shark body. Vortices are trapped in the cavities between the scales, which induce momentum exchange between the higher momentum fluid in the outer flow and that in the separated region. This momentum exchange causes reattachment of the separated TBL, causing the scales to return to the unbristled location, and the cycle continues. The rows of scales have widths that are comparable to the spanwise length scale of the intermittent backflow patches that appear in the region of incipient detachment of TBLs. In this experimental investigation, correlations between the shark scale's width and the spanwise size of the low backflow streaks are examined, as well as details of the incipient detachment region. The experiments are conducted in a water tunnel facility and the flow field is measured using PIV. Turbulent boundary layers are subjected to an APG via a rotating cylinder. Separated TBLs are investigated on a flat plate. The authors would like to greatfully acknowledge the Army Research Office for funding this project.

  10. Multi-scale symbolic time reverse analysis of gas-liquid two-phase flow structures

    NASA Astrophysics Data System (ADS)

    Wang, Hongmei; Zhai, Lusheng; Jin, Ningde; Wang, Youchen

    Gas-liquid two-phase flows are widely encountered in production processes of petroleum and chemical industry. Understanding the dynamic characteristics of multi-scale gas-liquid two-phase flow structures is of great significance for the optimization of production process and the measurement of flow parameters. In this paper, we propose a method of multi-scale symbolic time reverse (MSTR) analysis for gas-liquid two-phase flows. First, through extracting four time reverse asymmetry measures (TRAMs), i.e. Euclidean distance, difference entropy, percentage of constant words and percentage of reversible words, the time reverse asymmetry (TRA) behaviors of typical nonlinear systems are investigated from the perspective of multi-scale analysis, and the results show that the TRAMs are sensitive to the changing of dynamic characteristics underlying the complex nonlinear systems. Then, the MSTR analysis is used to study the conductance signals from gas-liquid two-phase flows. It is found that the multi-scale TRA analysis can effectively reveal the multi-scale structure characteristics and nonlinear evolution properties of the flow structures.

  11. An enzyme-based reversible CNOT logic gate realized in a flow system.

    PubMed

    Moseley, Fiona; Halámek, Jan; Kramer, Friederike; Poghossian, Arshak; Schöning, Michael J; Katz, Evgeny

    2014-04-21

    An enzyme system organized in a flow device was used to mimic a reversible Controlled NOT (CNOT) gate with two input and two output signals. Reversible conversion of NAD(+) and NADH cofactors was used to perform a XOR logic operation, while biocatalytic hydrolysis of p-nitrophenyl phosphate resulted in an Identity operation working in parallel. The first biomolecular realization of a CNOT gate is promising for integration into complex biomolecular networks and future biosensor/biomedical applications.

  12. Electroosmotically enhanced dewatering/deliquoring of fine-particle coal: Final report, January 1--December 31, 1988

    SciTech Connect

    Sami, Sedat; Davis, P.hilip K.; Smith, James G.

    1989-03-01

    This research is an investigation of the use of electroosmosis to dewater/deliquor ultrafine coal. Post-beneficiation dewatering/deliquoring methods for ultrafine coal are inadequate and generally require subsequent thermal drying. Thermal drying is not only expensive and time consuming, it also does not recover liquids for reuse in beneficiation processes. The degree of difficulty associated with dewatering increases as surface forces become more important than gravimetric forces. Electroosmotic flow has advantages for dewatering because it is much less sensitive to pore size than hydraulic gradient flow for the 1 to 75 ..mu..m ultrafine size range. The first year of this project focused upon preparation of ultrafine coal samples, development of test equipment and test cells, identification of variables affecting electroosmosis, and trial runs. Techniques and procedures not previously used by researchers of electroosmotic dewatering have revealed important information about the dynamics of the electroosmosis process. The identification of the first few millimeters of the cathode region of the cell as the sink for most of the energy input into the process provides the potential for improving efficiency by concentrating the second year effort on intervention in that region. Information gathered about differences in FTIR spectra as a function of location in the dewatering cell will be investigated. Changes in pH with temperature and by the application of electroosmotic current flow will receive attention, as well. 178 refs., 16 figs.

  13. On the reverse flow ceiling jet in pool fire-ventilation crossflow interactions in a simulated aircraft cabin interior

    NASA Technical Reports Server (NTRS)

    Kwack, E. Y.; Bankston, C. P.; Shakkottai, P.; Back, L. H.

    1989-01-01

    The behavior of the reverse flow ceiling jet against the ventilation flow from 0.58 to 0.87 m/s was investigated in a 1/3 scale model of a wide body aircraft interior. For all tests, strong reverse-flow ceiling jets of hot gases were detected well upstream of the fire. Both thicknesses of the reverse-flow ceiling jet and the smoke layer increased with the fire-crossflow parameter. The thickness of the smoke layer where the smoke flows along the main flow below the reverse-flow ceiling jet was almost twice that of the reverse-flow ceiling jet. Detailed spatial and time-varying temperatures of the gas in the test section were measured, and velocity profiles were also measured using a temperature compensated hot film.

  14. On the reverse flow ceiling jet in pool fire-ventilation crossflow interactions in a simulated aircraft cabin interior

    NASA Technical Reports Server (NTRS)

    Kwack, E. Y.; Bankston, C. P.; Shakkottai, P.; Back, L. H.

    1989-01-01

    The behavior of the reverse flow ceiling jet against the ventilation flow from 0.58 to 0.87 m/s was investigated in a 1/3 scale model of a wide body aircraft interior. For all tests, strong reverse-flow ceiling jets of hot gases were detected well upstream of the fire. Both thicknesses of the reverse-flow ceiling jet and the smoke layer increased with the fire-crossflow parameter. The thickness of the smoke layer where the smoke flows along the main flow below the reverse-flow ceiling jet was almost twice that of the reverse-flow ceiling jet. Detailed spatial and time-varying temperatures of the gas in the test section were measured, and velocity profiles were also measured using a temperature compensated hot film.

  15. Acute increase in reversal blood flow during counterpulsation is associated with vasoconstriction and changes in the aortic mechanics.

    PubMed

    Bia, Daniel; Zócalo, Yanina; Armentano, Ricardo; de Forteza, Eduardo; Cabrera-Fischer, Edmundo

    2007-01-01

    While the effects of increases in forward blood flow on the arterial diameter and elasticity are known, the effects of reversal flow on the arterial properties remain to be characterized. The intra-aortic balloon pumping (IABP), the device most frequently used in circulatory support, acts generating changes in aortic flow (i.e. increasing reversal flow). Recently, in vitro studies showed that flow reversion reduces the endothelial release of relaxing factors. Hence, vascular smooth muscle (VSM) dependent changes in the aortic properties would be expected during IABP. The aim was to analyze the changes in flow during IABP and to characterize the potential effects of reversal blood flow on the aortic biomechanics. Pressure, flow and diameter were measured in sheep, before and during IABP circulatory support. Potential effects of IABP-dependent high reversal flow conditions on viscous and elastic aortic modulus were analyzed, using isobaric analysis. Flow and pressure waveforms were analyzed in the time domain, and the contribution of oscillatory forward and backward waves to the IABP-dependent changes in flow patterns were evaluated. We found that IABP changed mainly diastolic blood flow, with an increase in the reversal flow, secondary to an increase in the oscillatory backward wave amplitude. The acute increase in reversal flow during IABP was associated with vasoconstriction and changes in the aortic mechanics, possibly due to VSM activation.

  16. Reversals.

    ERIC Educational Resources Information Center

    National Center on Educational Media and Materials for the Handicapped, Columbus, OH.

    Selected from the National Instructional Materials Information System (NIMIS)--a computer based on-line interactive retrieval system on special education materials--the bibliography covers nine materials for remediating reversals in handicapped students at the early childhood and elementary levels. Entries are presented in order of NIMIS accession…

  17. Direct and reverse pollen-mediated gene flow between GM rice and red rice weed

    PubMed Central

    Serrat, X.; Esteban, R.; Peñas, G.; Català, M. M.; Melé, E.; Messeguer, J.

    2013-01-01

    Potential risks of genetically modified (GM) crops must be identified before their commercialization, as happens with all new technologies. One of the major concerns is the proper risk assessment of adventitious presence of transgenic material in rice fields due to cross-pollination. Several studies have been conducted in order to quantify pollen-mediated gene flow from transgenic rice (Oryza sativa) to both conventional rice and red rice weed (O. sativa f. spontanea) under field conditions. Some of these studies reported GM pollen-donor rice transferring GM traits to red rice. However, gene flow also occurs in the opposite direction, in a phenomenon that we have called reverse gene flow, resulting in transgenic seeds that have incorporated the traits of wild red rice. We quantified reverse gene flow using material from two field trials. A molecular analysis based on amplified fragment length polymorphisms was carried out, being complemented with a phenotypic identification of red rice traits. In both field trials, the reverse gene flow detected was greater than the direct gene flow. The rate of direct gene flow varied according to the relative proportions of the donor (GM rice) and receptor (red rice) plants and was influenced by wind direction. The ecological impact of reverse gene flow is limited in comparison with that of direct gene flow because non-shattered and non-dormant seeds would be obtained in the first generation. Hybrid seed would remain in the spike and therefore most of it would be removed during harvesting. Nevertheless, this phenomenon must be considered in fields used for elite seed production and in developing countries where farmers often keep some seed for planting the following year. In these cases, there is a higher risk of GM red rice weed infestation increasing from year to year and therefore a proper monitoring plan needs to be established.

  18. Low-voltage electroosmotic pumping using polyethylene terephthalate track-etched membrane

    NASA Astrophysics Data System (ADS)

    Wang, Ceming; Wang, Lin; Xue, Jianming

    2012-09-01

    We present experimental investigations of electroosmotic (EO) pumping using polyethylene terephthalate (PET) track-etched membrane at a low applied voltage. An EO pump based on PET track-etched membrane has been designed and fabricated. Pumping performance of the device is experimentally studied in terms of flow rate as a function of applied voltage and KCl aqueous concentration. The PET track-etched membrane EO pump can generate flow rates on the order of 10 μl min-1 cm-2 at several applied volts. The measured flow rate tends to decrease with increasing KCl aqueous concentration. In addition, we study the EO flow in cylindrical nanopore with use of a continuum model, composed of Nernst Planck equations, Poisson equation and Navier Stokes equations.

  19. Adaptation of the Leishman-Beddoes Dynamic Stall Model for Reverse Flow

    NASA Astrophysics Data System (ADS)

    Lind, Andrew; Jones, Anya

    2016-11-01

    The Leishman-Beddoes dynamic stall model has long been used for the prediction of unsteady airloads acting on rotorcraft and wind turbines. However, little work has been completed that attempts to model the unsteady airloads experienced by a blade in the reverse flow region of a high advance ratio rotor. The present work describes modifications to the Leishman-Beddoes model and evaluates its suitability for the prediction of unsteady airloads for a sinusoidally oscillating NACA 0012 in reverse flow. Specifically, the ability of the model to capture early dynamic stall vortex formation (due to the sharp aerodynamic leading edge) and delayed reattachment is assessed. Results from the modified Leishman-Beddoes model are compared to measured unsteady pressure distributions for reduced frequencies up to 0.511 and a maximum pitch angle of 25 degrees. The model is also evaluated against numerical simulations of reverse flow dynamic stall where complete pressures distributions (and thus unsteady airloads) are available. This work is foundational for the development of more complex low-order models of the reverse flow region of a high advance ratio rotor where the time-varying local freestream and spanwise flow are also expected to play an important role.

  20. Electro-osmotic transport in wet processing of textiles

    DOEpatents

    Cooper, J.F.

    1998-09-22

    Electro-osmotic (or electrokinetic) transport is used to efficiently force a solution (or water) through the interior of the fibers or yarns of textile materials for wet processing of textiles. The textile material is passed between electrodes that apply an electric field across the fabric. Used alone or in parallel with conventional hydraulic washing (forced convection), electro-osmotic transport greatly reduces the amount of water used in wet processing. The amount of water required to achieve a fixed level of rinsing of tint can be reduced, for example, to 1--5 lbs water per pound of fabric from an industry benchmark of 20 lbs water/lb fabric. 5 figs.

  1. Electro-osmotic transport in wet processing of textiles

    DOEpatents

    Cooper, John F.

    1998-01-01

    Electro-osmotic (or electrokinetic) transport is used to efficiently force a solution (or water) through the interior of the fibers or yarns of textile materials for wet processing of textiles. The textile material is passed between electrodes that apply an electric field across the fabric. Used alone or in parallel with conventional hydraulic washing (forced convection), electro-osmotic transport greatly reduces the amount of water used in wet processing. The amount of water required to achieve a fixed level of rinsing of tint can be reduced, for example, to 1-5 lbs water per pound of fabric from an industry benchmark of 20 lbs water/lb fabric.

  2. Structural and temporal requirements for geomagnetic field reversal deduced from lava flows.

    PubMed

    Singer, Brad S; Hoffman, Kenneth A; Coe, Robert S; Brown, Laurie L; Jicha, Brian R; Pringle, Malcolm S; Chauvin, Annick

    2005-03-31

    Reversals of the Earth's magnetic field reflect changes in the geodynamo--flow within the outer core--that generates the field. Constraining core processes or mantle properties that induce or modulate reversals requires knowing the timing and morphology of field changes that precede and accompany these reversals. But the short duration of transitional field states and fragmentary nature of even the best palaeomagnetic records make it difficult to provide a timeline for the reversal process. 40Ar/39Ar dating of lavas on Tahiti, long thought to record the primary part of the most recent 'Matuyama-Brunhes' reversal, gives an age of 795 +/- 7 kyr, indistinguishable from that of lavas in Chile and La Palma that record a transition in the Earth's magnetic field, but older than the accepted age for the reversal. Only the 'transitional' lavas on Maui and one from La Palma (dated at 776 +/- 2 kyr), agree with the astronomical age for the reversal. Here we propose that the older lavas record the onset of a geodynamo process, which only on occasion would result in polarity change. This initial instability, associated with the first of two decreases in field intensity, began approximately 18 kyr before the actual polarity switch. These data support the claim that complete reversals require a significant period for magnetic flux to escape from the solid inner core and sufficiently weaken its stabilizing effect.

  3. Flow reversal of fully developed double diffusive mixed convection in a vertical channel

    NASA Astrophysics Data System (ADS)

    Makhatar, Nur Asiah Mohd; Saleh, Habibis; Hashim, Ishak

    2015-10-01

    The mixed convection flow within a vertical channel having internal heat generation at a rate proportional to a power of the temperature difference is considered. The analysis is concerning the studies of occurrence of flow reversal and the effects of three dimensionless parameters, identified as the internal heat parameter (G), a mixed convection parameter (λ) and the exponent (p) in the local heating term on the fully developed double diffusive mixed convection flow in a vertical channel. The governing equations are solved numerically via MAPLE. It was found that flow reversal occurs with larger values of internal heat parameter and mixed convection parameter, but smaller values of local-heating exponent. They also show that, unlike the internal heat parameter and the local-heating exponent, the mixed convection parameter do not give any significant effect on the temperature.

  4. Blood-clotting-inspired reversible polymer-colloid composite assembly in flow

    NASA Astrophysics Data System (ADS)

    Chen, Hsieh; Fallah, Mohammad A.; Huck, Volker; Angerer, Jennifer I.; Reininger, Armin J.; Schneider, Stefan W.; Schneider, Matthias F.; Alexander-Katz, Alfredo

    2013-01-01

    Blood clotting is a process by which a haemostatic plug is assembled at the site of injury. The formation of such a plug, which is essentially a (bio)polymer-colloid composite, is believed to be driven by shear flow in its initial phase, and contrary to our intuition, its assembly is enhanced under stronger flowing conditions. Here, inspired by blood clotting, we show that polymer-colloid composite assembly in shear flow is a universal process that can be tailored to obtain different types of aggregates including loose and dense aggregates, as well as hydrodynamically induced ‘log’-type aggregates. The process is highly controllable and reversible, depending mostly on the shear rate and the strength of the polymer-colloidbinding potential. Our results have important implications for the assembly of polymer-colloid composites, an important challenge of immense technological relevance. Furthermore, flow-driven reversible composite formation represents a new paradigm in non-equilibrium self-assembly.

  5. Blood-clotting-inspired reversible polymer-colloid composite assembly in flow.

    PubMed

    Chen, Hsieh; Fallah, Mohammad A; Huck, Volker; Angerer, Jennifer I; Reininger, Armin J; Schneider, Stefan W; Schneider, Matthias F; Alexander-Katz, Alfredo

    2013-01-01

    Blood clotting is a process by which a haemostatic plug is assembled at the site of injury. The formation of such a plug, which is essentially a (bio)polymer-colloid composite, is believed to be driven by shear flow in its initial phase, and contrary to our intuition, its assembly is enhanced under stronger flowing conditions. Here, inspired by blood clotting, we show that polymer-colloid composite assembly in shear flow is a universal process that can be tailored to obtain different types of aggregates including loose and dense aggregates, as well as hydrodynamically induced 'log'-type aggregates. The process is highly controllable and reversible, depending mostly on the shear rate and the strength of the polymer-colloidbinding potential. Our results have important implications for the assembly of polymer-colloid composites, an important challenge of immense technological relevance. Furthermore, flow-driven reversible composite formation represents a new paradigm in non-equilibrium self-assembly.

  6. Reversing Flows and Heat Spike: Caused by Solar g-Modes?

    NASA Technical Reports Server (NTRS)

    Mayr, Hans G.; Wolff, Charles L.

    2003-01-01

    The Quasi Biennial Oscillation in the Earth s upper atmosphere has an analog deep inside the Sun. As on Earth, the flow is east or west, it is at low latitude, and it reverses direction in a roughly periodic manner. The period in the solar case is 1.3 years. It was detected using solar oscillations similar to the way earthquakes are used to study the Earth's interior. But its cause was not known. We showed that global oscillations (g-modes) can supply enough angular momentum to drive zonal flows with the observed reversal period. This required a calculation of wave dissipation rates inside each flow and in the turbulent layer that separates any two flows of opposite sign. Heat that this process leaves behind causes a thermal spike inside the Sun at the same depth. This may explain an anomaly in observed sound speed that has had no sure explanation.

  7. Dynamic deformation and recovery response of red blood cells to a cyclically reversing shear flow: Effects of frequency of cyclically reversing shear flow and shear stress level.

    PubMed

    Watanabe, Nobuo; Kataoka, Hiroyuki; Yasuda, Toshitaka; Takatani, Setsuo

    2006-09-01

    Dynamic deformation and recovery responses of red blood cells (RBCs) to a cyclically reversing shear flow generated in a 30-microm clearance, with the peak shear stress of 53, 108, 161, and 274 Pa at the frequency of 1, 2, 3, and 5 Hz, respectively, were studied. The RBCs' time-varying velocity varied after the glass plate velocity without any time lag, whereas the L/W change, where L and W were the major and minor axes of RBCs' ellipsoidal shape, exhibited a rapid increase and gradual decay during the deformation and recovery phase. The time of minimum L/W occurrence lagged behind the zero-velocity time of the glass plate (zero stress), and the delay time normalized to the one-cycle duration remained constant at 8.0%. The elongation of RBCs at zero stress time became larger with the reversing frequency. A simple mechanical model consisting of an elastic linear element during a rapid elongation period and a parallel combination of elements such as a spring and dashpot during the nonlinear recovery phase was suggested. The dynamic response behavior of RBCs under a cyclically reversing shear flow was different from the conventional shape change where a steplike force was applied to and completely released from the RBCs.

  8. Maximizing fluid delivered by bubble-free electroosmotic pump with optimum pulse voltage waveform.

    PubMed

    Tawfik, Mena E; Diez, Francisco J

    2017-03-01

    In generating high electroosmotic (EO) flows for use in microfluidic pumps, a limiting factor is faradaic reactions that are more pronounced at high electric fields. These reactions lead to bubble generation at the electrodes and pump efficiency reduction. The onset of gas generation for high current density EO pumping depends on many parameters including applied voltage, working fluid, and pulse duration. The onset of gas generation can be delayed and optimized for maximum volume pumped in the minimum time possible. This has been achieved through the use of a novel numerical model that predicts the onset of gas generation during EO pumping using an optimized pulse voltage waveform. This method allows applying current densities higher than previously reported. Optimal pulse voltage waveforms are calculated based on the previous theories for different current densities and electrolyte molarity. The electroosmotic pump performance is investigated by experimentally measuring the fluid volume displaced and flow rate. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. A novel duplex finding of superficial epigastric vein flow reversal to diagnose iliocaval occlusion.

    PubMed

    Kolluri, Raghu; Fowler, Brian; Ansel, Gary; Silver, Mitchell

    2017-05-01

    Although duplex ultrasound (DUS) imaging is the current gold standard in the diagnosis of femoropopliteal deep venous thrombosis, it is not an optimal diagnostic modality to diagnose iliocaval occlusion. Screening for iliocaval occlusion thus remains a challenge for clinicians because of the lack of a reliable noninvasive technique. This challenge results in most patients undergoing computed tomography venography or magnetic resonance venography or invasive venography and intravascular ultrasound imaging. This study reports a novel, yet simple, reproducible and intuitive, surface DUS finding of physiologic flow reversal within the superficial epigastric vein (SEV) as a sign of proximal iliocaval occlusion (ICO). This was a retrospective study of 15 patients who were diagnosed with ICO based on the finding of SEV flow reversal on DUS imaging. Patient demographics, presenting CEAP C scores, ICO characteristics, correlation with advanced imaging, and short-term follow-up findings are reported. Physiologic reversal of the SEV resulted in confirmation of ICO in all patients who underwent advanced imaging, including computed tomography venography or traditional venogram along with intravascular ultrasound imaging. All patients who underwent follow-up DUS scans demonstrated normalization of the SEV flow after ICO recanalization. ICO can result in deep venous thrombosis, post-thrombotic syndrome, and chronic venous insufficiency. Physiologic flow reversal in SEV is diagnostic of ICO. To the best of our knowledge, this is the first report of this novel DUS finding. Copyright © 2017 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.

  10. Phase diagram for the onset of rolling waves and flow reversal in inclined falling films

    NASA Astrophysics Data System (ADS)

    Rohlfs, Wilko; Scheid, Benoit; Kneer, Reinhold

    2014-11-01

    The onset of rolling waves and the onset of flow reversal in inclined falling films is investigated in dependence of the Reynolds and the inclination number. For this, the weighted integral boundary layer model (WIBL) and direct numerical simulations (DNS) are used. Analytical criteria for the onset of rolling waves and flow reversal based on the wave celerity, the average film thickness and the maxi-mum/minimum film thickness have been approximated using self-similar parabolic velocity profiles. This approximation has been validated by second-order WIBL and DNS simulations. It is shown that the various transitions in the phase diagram for homoclinic solutions (waves of infinite wave length) are strongly dependent on the inclination, but independent on the streamwise viscous dissipation effect. Compared to the onset of flow reversal, the onset of rolling waves occurs for higher Reynolds numbers, resulting in a regime in which flow reversal and non-rolling waves coexist. Furthermore, simulation results for limit cycles (finite wave length) reveal a strong increase of the critical Reynolds number with the excitation frequency. Institute of Heat and Mass Transfer, Augustinerbach 6, 52056 Aachen, Germany.

  11. Correlations of the cycle-averaged Nusselt number in a periodically reversing pipe flow

    SciTech Connect

    Xiaoguo Tang; Cheng, P. )

    1993-03-01

    An experiment has been initiated to study oscillatory heat transfer in a periodically reversing pipe flow. A multivariate statistical analysis was employed to obtain a correlation equation for the cycle-averaged Nusselt number in terms of the three similarity parameters: the Reynolds number, the dynamic Reynolds number, and the dimensionless fluid displacement.

  12. Modeling the Material Flow and Heat Transfer in Reverse Dual-Rotation Friction Stir Welding

    NASA Astrophysics Data System (ADS)

    Shi, L.; Wu, C. S.; Liu, H. J.

    2014-08-01

    Reverse dual-rotation friction stir welding (RDR-FSW) is a novel modification of conventional friction stir welding (FSW) process. During the RDR-FSW process, the tool pin and the assisted shoulder are separated and rotate with opposite direction independently, so that there are two material flows with reverse direction. The material flow and heat transfer in RDR-FSW have significant effects on the microstructure and properties of the weld joint. A 3D model is developed to quantitatively analyze the effects of the separated tool pin and the assisted shoulder which rotate in reverse direction on the material flow and heat transfer during RDR-FSW process. Numerical simulation is conducted to predict the temperature profile, material flow field, streamlines, strain rate, and viscosity distributions near the tool. The calculated results show that as the rotation speed of the tool pin increases, the temperature near the tool gets higher, the zone with higher temperature expands, and approximately symmetric temperature distribution is obtained near the tool. Along the workpiece thickness direction, the calculated material flow velocity and its layer thickness near the tool get lowered because the effect of the shoulder is weakened as the distance away from the top surface increases. The model is validated by comparing the predicted values of peak temperature at some typical locations with the experimentally measured ones.

  13. Arteriovenous flow reversal, experimental investigations. I. Complete flow reversal of the small intestine and of the rear extremity of the dog.

    PubMed

    Gottlob, R; Kunlin, J; Lengua, F

    1985-01-01

    Segments of the small intestine and hind extremities of dogs were perfused under the condition of complete arterio-venous flow reversal (AVFR). In the intestinal segments, the peripheral resistance under AVFR conditions was 4.4 times higher than under orthograde perfusion. Petechiae and hemorhagic infarction were observed. The average flow resistance of the hind extremities was 2.4 times higher than the resistance in control extremities. The pO2 and the O2 saturation in the blood, outflowing from the AVFR extremity was lower than in the control extremity, however, the pO2 was higher. The oxygen consumption was somewhat lower than in the control extremity. It is concluded that by complete AVFR an extremity may be supplied sufficiently with oxygen at least temporarily.

  14. Potential reversal and the effects of flow pattern on galvanic corrosion of lead.

    PubMed

    Arnold, Roger B; Edwards, Marc

    2012-10-16

    Simplistic conventional models predict that a greater mass of lead will be released from lead pipes exposed to higher velocity and flow durations. However, if galvanic Pb-Cu connections are present, or if a highly protective Pb(IV) scale can be formed, reduced flow can markedly increase the mass of lead release to water and resultant consumer exposure. Three chemical mechanisms were identified that can reduce lead release at higher flow including (1) formation of Pb(IV), (2) potential reversal of Pb:Cu couples, after which galvanic corrosion sacrifices copper and lead is protected, and (3) reduced formation of corrosive microenvironments at lead surfaces in galvanic couples. Potential reversal occurred only in the presence of free chlorine with continuous flow, and it did not occur with chloramine, with intermittent flow, or if orthophosphate was present. For both disinfectants, electrochemical measurements supported a mass balance of lead release demonstrating that a greater total mass of lead release occurred with intermittent flow than with continuous flow.

  15. An experimental study of static and oscillating rotor blade sections in reverse flow

    NASA Astrophysics Data System (ADS)

    Lind, Andrew Hume

    The rotorcraft community has a growing interest in the development of high-speed helicopters to replace outdated fleets. One barrier to the design of such helicopters is the lack of understanding of the aerodynamic behavior of retreating rotor blades in the reverse flow region. This work considers two fundamental models of this complex unsteady flow regime: static and oscillating (i.e., pitching) airfoils in reverse flow. Wind tunnel tests have been performed at the University of Maryland (UMD) and the United States Naval Academy (USNA). Four rotor blade sections are considered: two featuring a sharp geometric trailing edge (NACA 0012 and NACA 0024) and two featuring a blunt geometric trailing edge (ellipse and cambered ellipse). Static airfoil experiments were performed at angles of attack through 180 deg and Reynolds numbers up to one million, representative of the conditions found in the reverse flow region of a full-scale high-speed helicopter. Time-resolved velocity field measurements were used to identify three unsteady flow regimes: slender body vortex shedding, turbulent wake, and deep stall vortex shedding. Unsteady airloads were measured in these three regimes using unsteady pressure transducers. The magnitude of the unsteady airloads is high in the turbulent wake regime when the separated shear layer is close to the airfoil surface and in deep stall due to periodic vortex-induced flow. Oscillating airfoil experiments were performed on a NACA 0012 and cambered ellipse to investigate reverse flow dynamic stall characteristics by modeling cyclic pitching kinematics. The parameter space spanned three Reynolds numbers (165,000; 330,000; and 500,000), five reduced frequencies between 0.100 and 0.511, three mean pitch angles (5,10, and 15 deg), and two pitch amplitudes (5 deg and 10 deg). The sharp aerodynamic leading edge of the NACA 0012 airfoil forces flow separation resulting in deep dynamic stall. The number of associated vortex structures depends strongly

  16. Predicting Flow Reversals in a Computational Fluid Dynamics Simulated Thermosyphon Using Data Assimilation

    PubMed Central

    Reagan, Andrew J.; Dubief, Yves; Dodds, Peter Sheridan; Danforth, Christopher M.

    2016-01-01

    A thermal convection loop is a annular chamber filled with water, heated on the bottom half and cooled on the top half. With sufficiently large forcing of heat, the direction of fluid flow in the loop oscillates chaotically, dynamics analogous to the Earth’s weather. As is the case for state-of-the-art weather models, we only observe the statistics over a small region of state space, making prediction difficult. To overcome this challenge, data assimilation (DA) methods, and specifically ensemble methods, use the computational model itself to estimate the uncertainty of the model to optimally combine these observations into an initial condition for predicting the future state. Here, we build and verify four distinct DA methods, and then, we perform a twin model experiment with the computational fluid dynamics simulation of the loop using the Ensemble Transform Kalman Filter (ETKF) to assimilate observations and predict flow reversals. We show that using adaptively shaped localized covariance outperforms static localized covariance with the ETKF, and allows for the use of less observations in predicting flow reversals. We also show that a Dynamic Mode Decomposition (DMD) of the temperature and velocity fields recovers the low dimensional system underlying reversals, finding specific modes which together are predictive of reversal direction. PMID:26849061

  17. Predicting Flow Reversals in a Computational Fluid Dynamics Simulated Thermosyphon Using Data Assimilation.

    PubMed

    Reagan, Andrew J; Dubief, Yves; Dodds, Peter Sheridan; Danforth, Christopher M

    2016-01-01

    A thermal convection loop is a annular chamber filled with water, heated on the bottom half and cooled on the top half. With sufficiently large forcing of heat, the direction of fluid flow in the loop oscillates chaotically, dynamics analogous to the Earth's weather. As is the case for state-of-the-art weather models, we only observe the statistics over a small region of state space, making prediction difficult. To overcome this challenge, data assimilation (DA) methods, and specifically ensemble methods, use the computational model itself to estimate the uncertainty of the model to optimally combine these observations into an initial condition for predicting the future state. Here, we build and verify four distinct DA methods, and then, we perform a twin model experiment with the computational fluid dynamics simulation of the loop using the Ensemble Transform Kalman Filter (ETKF) to assimilate observations and predict flow reversals. We show that using adaptively shaped localized covariance outperforms static localized covariance with the ETKF, and allows for the use of less observations in predicting flow reversals. We also show that a Dynamic Mode Decomposition (DMD) of the temperature and velocity fields recovers the low dimensional system underlying reversals, finding specific modes which together are predictive of reversal direction.

  18. A novel, neutral hydroxylated octadecyl acrylate monolith with fast electroosmotic flow velocity and its application to the separation of various solutes including peptides and proteins in the absence of electrostatic interactions.

    PubMed

    Karenga, Samuel; El Rassi, Ziad

    2010-10-01

    A neutral hydroxylated octadecyl monolith (ODM-OH) for reversed-phase capillary electrochromatography has been developed. The ODM-OH was prepared by the in situ polymerization of octadecyl acrylate and pentaerythritol triacrylate (PETA) in a ternary porogenic solvent. Pentaerythritol triacrylate possesses a hydroxyl functional group, which imparts the monolith with a hydrophilic group, thus the acronym ODM-OH. The ODM-OH column exhibited cathodal EOF over a wide range of pH and ACN concentration in the mobile phase despite the fact that it was devoid of any fixed charges. This ODM-OH monolith exhibited stronger EOF than its counterpart the ODM made from the in situ polymerization of octadecyl acrylate and trimethylolpropane trimethacrylate. Similar to ODM, it is believed that the EOF was due to the adsorption of ions from the mobile phase onto the surface of the monolith thus imparting the neutral monolithic column the zeta potential necessary to support the EOF. The higher EOF exhibited by ODM-OH was due to the presence of polar OH groups on its surface, which would favor stronger adsorption of ions from the mobile phase. The wide applications of the neutral ODM-OH column were demonstrated in the separation of a wide range of small and large solutes. As a typical result, the ODM-OH was able to separate proteins quite rapidly yielding 200,000 plates/m.

  19. Computational fluid dynamics evaluation of flow reversal treatment of giant basilar tip aneurysm.

    PubMed

    Alnæs, Martin Sandve; Mardal, Kent-Andre; Bakke, Søren; Sorteberg, Angelika

    2015-10-01

    Therapeutic parent artery flow reversal is a treatment option for giant, partially thrombosed basilar tip aneurysms. The effectiveness of this treatment has been variable and not yet studied by applying computational fluid dynamics. Computed tomography images and blood flow velocities acquired with transcranial Doppler ultrasonography were obtained prior to and after bilateral endovascular vertebral artery occlusion for a giant basilar tip aneurysm. Patient-specific geometries and velocity waveforms were used in computational fluid dynamics simulations in order to determine the velocity and wall shear stress changes induced by treatment. Therapeutic parent artery flow reversal lead to a dramatic increase in aneurysm inflow and wall shear stress (30 to 170 Pa) resulting in an increase in intra-aneurysmal circulation. The enlargement of the circulated area within the aneurysm led to a re-normalization of the wall shear stress and the aneurysm remained stable for more than 8 years thereafter. Therapeutic parent artery flow reversal can lead to unintended, potentially harmful changes in aneurysm inflow which can be quantified and possibly predicted by applying computational fluid dynamics. © The Author(s) 2015.

  20. Poleward Boundary of Auroral Bulge and Plasma Sheet Flow Reversal Region Location During Substorms

    NASA Astrophysics Data System (ADS)

    Despirak, I. V.; Yahnin, A. G.

    Data from the Geotail spacecraft situated in the night side plasma sheet during 1996- 1997 were used to select events of the tailward-to-Earthward fast plasma flow rever- sals. Then a subset was extracted including those events when UV auroral images were available from the Polar satellite. The Polar data supported by ground-based ob- servations showed that the auroral substorms were in progress during the flow reversal events. For every moment of the flow reversal observations we determined the au- roral bulge poleward boundary latitude at the meridian of the Geotail footprint and compared this latitude with the Geotail location in the magnetosphere. We found that within the range of 10-30 RE the auroral bulge latitude increases proportionally to the reversal region distance from the Earth. Moreover, tailward (Earthward) flows have a tendency to be observed when Geotail footprint is poleward (equatorward) of the poleward edge of bright auroras. This agrees with the idea that reconnection is the source of discrete auroras during substorms.

  1. Reynolds stress flow shear and turbulent energy transfer in reversed field pinch configuration

    NASA Astrophysics Data System (ADS)

    Vianello, Nicola; Spolaore, Monica; Serianni, Gianluigi; Regnoli, Giorgio; Spada, Emanuele; Antoni, Vanni; Bergsåker, Henric; Drake, James R.

    2003-10-01

    The role of Reynolds Stress tensor on flow generation in turbulent fluids and plasmas is still an open question and the comprehension of its behavior may assist the understanding of improved confinement scenario. It is generally believed that shear flow generation may occur by an interaction of the turbulent Reynolds stress with the shear flow. It is also generally believed that this mechanism may influence the generation of zonal flow shears. The evaluation of the complete Reynolds Stress tensor requires contemporary measurements of its electrostatic and magnetic part: this requirement is more restrictive for Reversed Field Pinch configuration where magnetic fluctuations are larger than in tokamak . A new diagnostic system which combines electrostatic and magnetic probes has been installed in the edge region of Extrap-T2R reversed field pinch. With this new probe the Reynolds stress tensor has been deduced and its radial profile has been reconstructed on a shot to shot basis exploring differen plasma conditions. These profiles have been compared with the naturally occurring velocity flow profile, in particular during Pulsed Poloidal Current Drive experiment, where a strong variation of ExB flow radial profile has been registered. The study of the temporal evolution of Reynolds stress reveals the appearance of strong localized bursts: these are considered in relation with global MHD relaxation phenomena, which naturally occur in the core of an RFP plasma sustaining its configuration.

  2. Numerical investigation of enhanced dilution zone mixing in a reverse flow gas turbine combustor

    NASA Astrophysics Data System (ADS)

    Crocker, D. S.; Smith, C. E.

    1995-04-01

    An advanced method for dilution zone mixing in a reverse flow gas turbine combustor was numerically investigated. For long mixing lengths associated with reverse flow combustors (X/H greater than 2.0), pattern factor was found to be mainly driven by nozzle-to-nozzle fuel flow and/or circumferential airflow variations; conventional radially injected dilution jets could not effectively mix out circumferential nonuniformities. To enhance circumferential mixing, dilution jets were angled to produce a high circumferential (swirl) velocity component. The jets on the outer liner were angled in one direction while the jets on the inner liner were angled in the opposite direction, thus enhancing turbulent shear at the expense of jet penetration. Three-dimensional CFD calculations were performed on a three-nozzle (90 deg) sector, with different fuel flow from each nozzle (90, 100, and 110% of design fuel flow). The computations showed that the optimum configuration of angled jets reduced the pattern factor by 60% compared to an existing conventional dilution hole configuration. The radial average temperature profile was adequately controlled by the inner-to-outer liner dilution flow split.

  3. Performance of 1.15-pressure-ratio fan stage at several rotor blade setting angles with reverse flow

    NASA Technical Reports Server (NTRS)

    Kovich, G.; Moore, R. D.

    1976-01-01

    A 51 cm diameter low pressure ratio fan stage was tested in reverse flow. Survey flow data were taken over the range of rotative speed from 50 percent to 100 percent design speed at several rotor blade setting angles through both flat and feather pitch. Normal flow design values of pressure ratio and weight flow were 1.15 and 29.9 kg/sec with a rotor tip speed of 243.8 m/sec. The maximum thrust in reverse flow was 52.5 percent of design thrust in normal flow.

  4. Low-voltage electroosmotic pumps fabricated from track-etched polymer membranes.

    PubMed

    Wang, Ceming; Wang, Lin; Zhu, Xiaorui; Wang, Yugang; Xue, Jianming

    2012-05-07

    Track-etched polymer membranes are used to realize low-voltage electroosmotic (EO) pumps. The nanopores in polycarbonate (PC) and polyethylene terephthalate (PET) membranes were fabricated by the track-etching technique, the pore diameter was controlled in the range of 100 to 250 nm by adjusting the etching time. The results show that these EO pumps can provide high flow rates at low applied voltages (2-5 V). The maximum normalized flow rate is as high as 0.12 ml min(-1) V(-1) cm(-2), which is comparable to the best values of previously demonstrated EO pumps. We attribute this high performance to the unique properties of the track-etched nanopores in the membranes.

  5. RELAP5 analyses of two hypothetical flow reversal events for the advanced neutron source reactor

    SciTech Connect

    Chen, N.C.J.; Wendel, M.W.; Yoder, G.L. Jr.

    1995-09-01

    This paper presents RELAP5 results of two hypothetical, low flow transients analyzed as part of the Advanced Neutron Source Reactor safety program. The reactor design features four independent coolant loops (three active and one in standby), each containing a main curculation pump (with battery powered pony motor), heat exchanger, an accumulator, and a check valve. The first transient assumes one of these pumps fails, and additionally, that the check valve in that loop remains stuck in the open position. This accident is considered extremely unlikely. Flow reverses in this loop, reducing the core flow because much of the coolant is diverted from the intact loops back through the failed loop. The second transient examines a 102-mm-diam instantaneous pipe break near the core inlet (the worst break location). A break is assumed to occur 90 s after a total loss-of-offsite power. Core flow reversal occurs because accumulator injection overpowers the diminishing pump flow. Safety margins are evaluated against four thermal limits: T{sub wall}=T{sub sat}, incipient boiling, onset of significant void, and critical heat flux. For the first transient, the results show that these limits are not exceeded (at a 95% non-exceedance probability level) if the pony motor battery lasts 30 minutes (the present design value). For the second transient, the results show that the closest approach of the fuel surface temperature to the local saturation temperature during core flow reversal is about 39{degrees}C. Therefore the fuel remains cool during this transient. Although this work is done specifically for the ANSR geometry and operating conditions, the general conclusions may be applicable to other highly subcooled reactor systems.

  6. Effect on fan flow characteristics of length and axial location of a cascade thrust reverser

    NASA Technical Reports Server (NTRS)

    Dietrich, D. A.

    1975-01-01

    A series of static tests were conducted on a model fan with a diameter of 14.0 cm to determine the fan operating characteristics, the inlet static pressure contours, the fan-exit total and static pressure contours, and the fan-exit pressure distortion parameters associated with the installation of a partial-circumferential-emission cascade thrust reverser. The tests variables included the cascade axial length, the axial location of the reverser, and the type of fan inlet. It was shown that significant total and static pressure distortions were produced in the fan aft duct, and that some configurations induced a static pressure distortion at the fan face. The amount of flow passed by the fan and the level of the flow distortions were dependent upon all the variables tested.

  7. Bifurcations of limit cycles in open and closed loop reverse flow reactors

    NASA Astrophysics Data System (ADS)

    Russo, Lucia; Crescitelli, Silvestro; Brasiello, Antonio

    2013-10-01

    The present work analyses the bifurcations of limit cycles in open and loop reverse flow reactors. The open loop system consists of a reactor where the flow direction is periodically forced whereas in the closed loop system, the flow inversion is dictated by a control law which activates when the temperature at the edge of catalytic bed falls below the set-point value. We performed the bifurcation analysis of the open loop system as the switch time is varied and we constructed the solution diagram through the application of continuation technique. Many Naimark-Sacker bifurcations leading to quasi-periodic regimes have been found on the limit cycles branches. Finally, we compared these limit cycles with those of the closed loop system where the flow inversion is dictated by a control system which acts if the temperature measured at the edge of reactor falls below a set-point value.

  8. Reversal of cortical information flow during visual imagery as compared to visual perception.

    PubMed

    Dentico, Daniela; Cheung, Bing Leung; Chang, Jui-Yang; Guokas, Jeffrey; Boly, Melanie; Tononi, Giulio; Van Veen, Barry

    2014-10-15

    The role of bottom-up and top-down connections during visual perception and the formation of mental images was examined by analyzing high-density EEG recordings of brain activity using two state-of-the-art methods for assessing the directionality of cortical signal flow: state-space Granger causality and dynamic causal modeling. We quantified the directionality of signal flow in an occipito-parieto-frontal cortical network during perception of movie clips versus mental replay of the movies and free visual imagery. Both Granger causality and dynamic causal modeling analyses revealed an increased top-down signal flow in parieto-occipital cortices during mental imagery as compared to visual perception. These results are the first direct demonstration of a reversal of the predominant direction of cortical signal flow during mental imagery as compared to perception.

  9. Reversal of cortical information flow during visual imagery as compared to visual perception

    PubMed Central

    Dentico, Daniela; Cheung, Bing Leung; Chang, Jui-Yang; Guokas, Jeffrey; Boly, Melanie; Tononi, Giulio; Van Veen, Barry

    2014-01-01

    The role of bottom-up and top-down connections during visual perception and the forming of mental images was examined by analyzing high-density EEG recordings of brain activity using two state-of-the-art methods for assessing the directionality of cortical signal flow: state-space Granger causality and dynamic causal modeling. We quantified the directionality of signal flow in an occipito-parieto-frontal cortical network during perception of movie clips versus mental replay of the movies and free visual imagery. Both Granger causality and dynamic causal modeling analyses revealed increased top-down signal flow in parieto-occipital cortices during mental imagery as compared to visual perception. These results are the first direct demonstration of a reversal of the predominant direction of cortical signal flow during mental imagery as compared to perception. PMID:24910071

  10. Reverse-flow combustor for small gas turbines with pressure-atomizing fuel injectors

    NASA Technical Reports Server (NTRS)

    Norgren, C. T.; Mularz, E. J.; Riddlebaugh, S. M.

    1978-01-01

    A reverse flow combustor suitable for a small gas turbine (2 to 3 kg/s mass flow) was used to evalute the effect of pressure atomizing fuel injectors on combustor performance. In these tests an experimental combustor was designed to operate with 18 simplex pressure atomizing fuel injectors at sea level takeoff conditions. To improve performance at low power conditions, fuel was redistributed so that only every other injector was operational. Combustor performance, emissions, and liner temperature were compared over a range of pressure and inlet air temperatures corresponding to simulated idle, cruise, and takeoff conditions typical of a 16 to 1 pressure ratio turbine engine.

  11. Tidal reversal and flow velocities using temperature and specific conductance in a small wetland creek

    NASA Astrophysics Data System (ADS)

    Eaton, Timothy T.

    2016-11-01

    Characterizing flow dynamics in very small tidal creeks is complicated and not well suited to methods developed for upland streams or coastal estuaries, due to low flows, bidirectionality and shallow waters. Simple instrumentation enables thermal and salinity signals to be used to observe flow directions and estimate velocities in these settings. Using multiple inexpensive sensors over 500 m along a tidally influenced wetland creek, I demonstrate how advection of temperature and specific conductance pulses reveal flood and ebb tides and the temporary reversal of flow by warmer, estuarine water from the receiving embayment. The sequential rise of temperature upstream was most evident under hot and dry conditions, after daily peak air temperatures of 25 °C or above, and was subdued or disrupted under cooler or rainy conditions in summertime. Changes in specific conductance at successive sites upstream were less susceptible to environmental influences and confirm tidal flood velocity of between 0.07 and 0.37 m/s. The tidally-induced flow reversal suggests that periodic high tide conditions can interfere with rapid dispersal of pollution discharges, such as from the combined sewer overflow (CSO) located upstream of the studied creek reach. This low-cost approach of temperature and specific conductance sensing in vegetated coastal wetlands where access, precise elevation control and creek discharge measurements are difficult, provides a simple way of tracking water masses when sufficient contrast exists between water sources.

  12. Analysis of pressure drop and heat transfer data from the reversing flow test facility

    SciTech Connect

    Roach, P D; Bell, K J

    1989-05-01

    The Reversing Flow Test Facility is part of the heat engine R and D capabilities at Argonne National Laboratory. The facility permits the study of heat transfer and pressure drop under conditions of rapidly reversing flow. This report summarizes the results that have been obtained to date from more than 100 data sets that cover a wide range of temperatures, pressures, and frequencies. Pressure drop data are presented as normalized pressure drop vs. the Reynolds number calculated from the amplitude of the oscillatory flow. Heat transfer data for the regenerators are presented as regenerator effectiveness vs. Reynolds number. Three significant conclusions are derived from our analysis of the data: (1) no frequency dependence is observed in either the pressure drop or the heat transfer data, (2) the measured pressure drops for the heater and coolers are distinctly higher than those calculated from steady-flow correlations, and (3) the heat transfer coefficient in the heater is about 80 percent of that predicted by steady-flow correlations. The correlations presented here provide the basis for improving existing models. 4 refs., 20 figs., 3 tabs.

  13. Method of electric field flow fractionation wherein the polarity of the electric field is periodically reversed

    DOEpatents

    Stevens, Fred J.

    1992-01-01

    A novel method of electric field flow fractionation for separating solute molecules from a carrier solution is disclosed. The method of the invention utilizes an electric field that is periodically reversed in polarity, in a time-dependent, wave-like manner. The parameters of the waveform, including amplitude, frequency and wave shape may be varied to optimize separation of solute species. The waveform may further include discontinuities to enhance separation.

  14. First Signs of Flow Reversal Within a Separated Turbulent Boundary Layer

    NASA Astrophysics Data System (ADS)

    Hammerton, Jared; Lang, Amy

    2015-11-01

    A shark's skin is covered in millions of microscopic scales that have been shown to be able to bristle in a reversing flow. The motive of this project is to further explore a potential bio-inspired passive separation control mechanism which can reduce drag. To better understand this mechanism, a more complete understanding of flow reversal within the turbulent boundary layer is required. In order to capture this phenomenon, water tunnel testing at The University of Alabama was conducted. Using a long flat plate and a rotating cylinder, a large turbulent boundary layer and adverse pressure gradient were generated. Under our testing conditions the boundary layer had a Reynolds number of 200,000 and a boundary layer height in the testing window of 5.6 cm. The adverse pressure gradient causes the viscous length scale to increase and thus increase the size of the individual components of the turbulent boundary layer. This will make the low speed streaks approximately 1 cm in width and thus large enough to measure. Results will be presented that test our hypothesis that the first signs of flow reversal will occur within the section of lowest momentum located furthest from the wall, or within the low speed streaks. This Project was funded by NSF REU Site Award 1358991.

  15. Flow dynamics and sediment transport over a reversing barchan, Changli, China

    NASA Astrophysics Data System (ADS)

    Yuxiang, Dong; Hesp, Patrick A.; Dequan, Huang; Namikas, S. L.

    2017-02-01

    The flow and sediment transport over a reversing 6.9 m-high barchan dune is examined on the Changli Gold Coast in Hebei Province, China. Wind velocity profiles are non-logarithmic, exhibit rapid accelerations up slope, and display near-surface jets at the dune crest and downwind lee slope. From the windward lower slope to dune crest, the wind speed at 5 cm height increased by 55%. The windward slope is a slipface and therefore has a significantly greater gradient than most 'normal' windward slopes, and the magnitude of speed-up is significantly greater (speed-up ratio of 5.25). The majority of sediment was transported in the 0-4 cm height above the bed range. Maximum total sediment flux occurred at the dune crest and was greater than the total flux from three other sites combined. The leeward mid-slope sedimentation rate is strongly influenced by the sediment plume streaming upwards and downwind from the actively reversing dune crest. Dunes in the process of reversing display quite different wind flow and sedimentation patterns than when the dune is in 'normal' flow conditions.

  16. Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field.

    PubMed

    Tasaka, Yuji; Igaki, Kazuto; Yanagisawa, Takatoshi; Vogt, Tobias; Zuerner, Till; Eckert, Sven

    2016-04-01

    Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q. We explored convection regimes in a parameter range, at 2×10^{3}flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra/Q=10, where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach.

  17. Regular flow reversals in Rayleigh-Bénard convection in a horizontal magnetic field

    NASA Astrophysics Data System (ADS)

    Tasaka, Yuji; Igaki, Kazuto; Yanagisawa, Takatoshi; Vogt, Tobias; Zuerner, Till; Eckert, Sven

    2016-04-01

    Magnetohydrodynamic Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with a square horizontal cross section and aspect ratio of five. Systematic flow measurements were performed by means of ultrasonic velocity profiling that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two-dimensional rolls arranged parallel to the magnetic field. The number of rolls has the tendency to decrease with increasing Rayleigh number Ra and to increase with increasing Chandrasekhar number Q . We explored convection regimes in a parameter range, at 2 ×103flow reversals in which five rolls periodically change the direction of their circulation with gradual skew of the roll axes can be considered as the most remarkable one. The regime appears around a range of Ra /Q =10 , where irregular flow reversals were observed in Yanagisawa et al. We performed the proper orthogonal decomposition (POD) analysis on the spatiotemporal velocity distribution and detected that the regular flow reversals can be interpreted as a periodic emergence of a four-roll state in a dominant five-roll state. The POD analysis also provides the definition of the effective number of rolls as a more objective approach.

  18. Reversible and Irreversible Flow-Induced Phase Transitions in Micellar Solutions

    NASA Astrophysics Data System (ADS)

    Vasudevan, Mukund; Buse, Eric; Krishna, Hare; Kalyanaraman, Ramki; Shen, Amy; Khomami, Bamin; Sureshkumar, Radhakrishna

    2008-07-01

    It is well known that rodlike/wormlike micelles can self-organize under flow to form viscoelastic gel phases. Flow-induced structure (FIS) formation is typically accompanied by an enhancement in the shear viscosity. While configurational dynamics of and collisions between micelles in flow and electrostatic inter-micelle interactions are recognized as the key factors that influence such phase transitions, there are no universally applicable criteria for the onset strain rate as function of salt/surfactant concentration. Further, FIS formation is generally considered reversible, i.e., the structure disintegrates quickly upon flow cessation. In this work, first, we examine the effect of salt concentration on the critical strain rate for CTAB/NaSal solutions of rodlike micelles and show that a "self-similar" phase transition regime, characterized by a constant critical strain, exists. Second, we show that under strong (elongational) flow conditions, the phase transition is irreversible, leading to the formation of permanent nanogels that are stable long after the flow is stopped. Atomic force microscopy shows that the gel phase obtained under strong flow conditions consists of highly aligned micelles.

  19. Laboratory Investigation of Electro-Osmotic Remediation of Fine-Grained Sediments

    SciTech Connect

    Cherepy, N.; Wildenschild, D.; Elsholz, A.

    2000-02-23

    Electro-osmosis, a coupled-flow phenomenon in which an applied electrical potential gradient drives water flow, may be used to induce water flow through fine-grained sediments. We plan to use this technology to remediate chlorinated solvent-contaminated clayey zones at the LLNL site. The electro-osmotic conductivity (k{sub e}) determined from bench-top studies for a core extracted from a sediment zone 36.4-36.6 m below surface was initially 7.37 x 10{sup -10} m{sup 2}/s-V, decreasing to 3.44 x 10{sup -10} m{sup 2}/s-V, after electro-osmotically transporting 0.70 pore volumes of water through it (195 ml). Hydraulic conductivity (k{sub h}) of the same core was initially measured to be 5.00 x 10{sup -10} m/s, decreasing to 4.08 x 10{sup -10} m/s at the end of processing. This decline in permeability is likely due to formation of a chemical precipitation zone within the core. Water splitting products and ions electromigrate and precipitate within the core; H{sup +} and metal cations migrate toward the cathode, and OH{sup -} from the cathode moves toward the anode. We are now exploring how to minimize this effect using pH control. The significance of this technology is that for this core, a 3 V/cm voltage gradient produced an initial effective hydraulic conductivity of 2.21 x 10{sup -7} m/s, >400x greater than the initial hydraulic conductivity.

  20. Reverse capillary flow of condensed water through aligned multiwalled carbon nanotubes.

    PubMed

    Yun, Jongju; Jeon, Wonjae; Alam Khan, Fakhre; Lee, Jinkee; Baik, Seunghyun

    2015-06-12

    Molecular transport through nanopores has recently received considerable attention as a result of advances in nanofabrication and nanomaterial synthesis technologies. Surprisingly, water transport investigations through carbon nanochannels resulted in two contradicting observations: extremely fast transport or rejection of water molecules. In this paper, we elucidate the mechanism of impeded water vapor transport through the interstitial space of aligned multiwalled carbon nanotubes (aligned-MWCNTs)--capillary condensation, agglomeration, reverse capillary flow, and removal by superhydrophobicity at the tip of the nanotubes. The origin of separation comes from the water's phase change from gas to liquid, followed by reverse capillary flow. First, the saturation water vapor pressure is decreased in a confined space, which is favorable for the phase change of incoming water vapor into liquid drops. Once continuous water meniscus is formed between the nanotubes by the adsoprtion and agglomeration of water molecules, a high reverse Laplace pressure is induced in the mushroom-shaped liquid meniscus at the entry region of the aligned-MWCNTs. The reverse Laplace pressure can be significantly enhanced by decreasing the pore size. Finally, the droplets pushed backward by the reverse Laplace pressure can be removed by superhydrophobicity at the tip of the aligned-MWCNTs. The analytical analysis was also supported by experiments carried out using 4 mm-long aligned-MWCNTs with different intertube distances. The water rejection rate and the separation factor increased as the intertube distance decreased, resulting in 90% and 10, respectively, at an intertube distance of 4 nm. This mechanism and nanotube membrane may be useful for energy-efficient water vapor separation and dehumidification.

  1. Reverse capillary flow of condensed water through aligned multiwalled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Yun, Jongju; Jeon, Wonjae; Alam Khan, Fakhre; Lee, Jinkee; Baik, Seunghyun

    2015-06-01

    Molecular transport through nanopores has recently received considerable attention as a result of advances in nanofabrication and nanomaterial synthesis technologies. Surprisingly, water transport investigations through carbon nanochannels resulted in two contradicting observations: extremely fast transport or rejection of water molecules. In this paper, we elucidate the mechanism of impeded water vapor transport through the interstitial space of aligned multiwalled carbon nanotubes (aligned-MWCNTs)—capillary condensation, agglomeration, reverse capillary flow, and removal by superhydrophobicity at the tip of the nanotubes. The origin of separation comes from the water’s phase change from gas to liquid, followed by reverse capillary flow. First, the saturation water vapor pressure is decreased in a confined space, which is favorable for the phase change of incoming water vapor into liquid drops. Once continuous water meniscus is formed between the nanotubes by the adsoprtion and agglomeration of water molecules, a high reverse Laplace pressure is induced in the mushroom-shaped liquid meniscus at the entry region of the aligned-MWCNTs. The reverse Laplace pressure can be significantly enhanced by decreasing the pore size. Finally, the droplets pushed backward by the reverse Laplace pressure can be removed by superhydrophobicity at the tip of the aligned-MWCNTs. The analytical analysis was also supported by experiments carried out using 4 mm-long aligned-MWCNTs with different intertube distances. The water rejection rate and the separation factor increased as the intertube distance decreased, resulting in 90% and 10, respectively, at an intertube distance of 4 nm. This mechanism and nanotube membrane may be useful for energy-efficient water vapor separation and dehumidification.

  2. Method and apparatus for cold gas reinjection in through-flow and reverse-flow wave rotors

    NASA Technical Reports Server (NTRS)

    Nalim, M. Razi (Inventor); Paxson, Daniel E. (Inventor)

    1999-01-01

    A method and apparatus for cold gas reinjection in through-flow and reverse-flow wave rotors having a plurality of channels formed around a periphery thereof. A first port injects a supply of cool air into the channels. A second port allows the supply of cool air to exit the channels and flow to a combustor. A third port injects a supply of hot gas from the combustor into the channels. A fourth port allows the supply of hot gas to exit the channels and flow to a turbine. A diverting port and a reinjection port are connected to the second and third ports, respectively. The diverting port diverts a portion of the cool air exiting through the second port as reinjection air. The diverting port is fluidly connected to the reinjection port which reinjects the reinjection air back into the channels. The reinjection air evacuates the channels of the hot gas resident therein and cools the channel walls, a pair of end walls of the rotor, ducts communicating with the rotor and subsequent downstream components. In a second embodiment, the second port receives all of the cool air exiting the channels and the diverting port diverts a portion of the cool air just prior to the cool air flowing to the combustor.

  3. Reversible logic gates based on enzyme-biocatalyzed reactions and realized in flow cells: a modular approach.

    PubMed

    Fratto, Brian E; Katz, Evgeny

    2015-05-18

    Reversible logic gates, such as the double Feynman gate, Toffoli gate and Peres gate, with 3-input/3-output channels are realized using reactions biocatalyzed with enzymes and performed in flow systems. The flow devices are constructed using a modular approach, where each flow cell is modified with one enzyme that biocatalyzes one chemical reaction. The multi-step processes mimicking the reversible logic gates are organized by combining the biocatalytic cells in different networks. This work emphasizes logical but not physical reversibility of the constructed systems. Their advantages and disadvantages are discussed and potential use in biosensing systems, rather than in computing devices, is suggested.

  4. Intravesical electro-osmotic administration of mitomycin C.

    PubMed

    Di Stasi, Savino M; Verri, Cristian; Celestino, Francesco; De Carlo, Francesco; Pagliarulo, Vincenzo

    2016-10-04

    Bladder cancer is very common and most cases are diagnosed as nonmuscle invasive disease, which is characterized by its propensity to recur and progress. Intravesical therapy is used to delay recurrence and progression, while cystectomy is reserved for patients who are refractory to transurethral resection and intravesical therapy. There is an increasing interest in methods to enhance the delivery of intravesical chemotherapeutic agents to improve efficacy. In vitro and in vivo studies demonstrated that electro-osmosis of mitomycin C (MMC) is more effective in delivering this drug into the urothelium, lamina propria, and superficial muscle layers of the bladder wall than is passive transport. Higher MMC tissue concentrations might have a clinical impact in the treatment of nonmuscle invasive bladder cancer (NMIBC). In randomized trials, intravesical electro-osmotic MMC was associated with superior response rate in high-risk NMIBC cancer, compared with passive diffusion MMC transport. New strategies such as intravesical Bacillus Calmette-Guerin (BCG) combined with electro-osmotic MMC as well as intravesical pre-operative electro-osmotic MMC provided promising results in terms of higher remission rates and longer remission times.Device-assisted intravesical chemotherapy may be a useful ancillary procedure in the treatment of NMIBC. Its evaluation must be planned with respect to the technical functioning of equipment and their use for a clear purpose to avoid the financial and human costs associated with incorrect therapies.

  5. Flow reversal in traveling-wave electrokinetics: an analysis of forces due to ionic concentration gradients.

    PubMed

    García-Sánchez, P; Ramos, A; González, A; Green, N G; Morgan, H

    2009-05-05

    Pumping of electrolytes using ac electric fields from arrays of microelectrodes is a subject of current research. The behavior of fluids at low signal amplitudes (<2-3 V(pp)) is in qualitative agreement with the prediction of the ac electroosmosis theory. At higher voltages, this theory cannot account for the experimental observations. In some cases, net pumping is generated in the direction opposite to that predicted by the theory (flow reversal). In this work, we use fluorescent dyes to study the effect of ionic concentration gradients generated by Faradaic currents. We also evaluate the influence of factors such as the channel height and microelectrode array shape in the pumping of electrolytes with traveling-wave potentials. Induced charge beyond the Debye length is postulated to be responsible for the forces generating the observed flows at higher voltages. Numerical calculations are performed in order to illustrate the mechanisms that might be responsible for generating the flow.

  6. Dilution jet configurations in a reverse flow combustor. M.S. Thesis Final Report

    NASA Technical Reports Server (NTRS)

    Zizelman, J.

    1985-01-01

    Results of measurements of both temperature and velocity fields within a reverse flow combustor are presented. Flow within the combustor is acted upon by perpendicularly injected cooling jets introduced at three different locations along the inner and outer walls of the combustor. Each experiment is typified by a group of parameters: density ratio, momentum ratio, spacing ratio, and confinement parameter. Measurements of both temperature and velocity are presented in terms of normalized profiles at azimuthal positions through the turn section of the combustion chamber. Jet trajectories defined by minimum temperature and maximum velocity give a qualitative indication of the location of the jet within the cross flow. Results of a model from a previous temperature study are presented in some of the plots of data from this work.

  7. Dilution Jet Behavior in the Turn Section of a Reverse Flow Combuster

    NASA Technical Reports Server (NTRS)

    Riddlebaugh, S. M.; Lipshitz, A.; Greber, I.

    1982-01-01

    Measurements of the temperature field produced by a single jet and a row of dilution jets issued into a reverse flow combustor are presented. The temperature measurements are presented in the form of consecutive normalized temperature profiles, and jet trajectories. Single jet trajectories were swept toward the inner wall of the turn, whether injection was from the inner or outer wall. This behavior is explained by the radially inward velocity component necessary to support irrotational flow through the turn. Comparison between experimental results and model calculations showed poor agreement due to the model's not including the radial velocity component. A widely spaced row of jets produced trajectories similar to single jets at similar test conditions, but as spacing ratio was reduced, penetration was reduced to the point where the dilution jet flow attached to the wall.

  8. Network modeling for reverse flows of end-of-life vehicles

    SciTech Connect

    Ene, Seval; Öztürk, Nursel

    2015-04-15

    Highlights: • We developed a network model for reverse flows of end-of-life vehicles. • The model considers all recovery operations for end-of-life vehicles. • A scenario-based model is used for uncertainty to improve real case applications. • The model is adequate to real case applications for end-of-life vehicles recovery. • Considerable insights are gained from the model by sensitivity analyses. - Abstract: Product recovery operations are of critical importance for the automotive industry in complying with environmental regulations concerning end-of-life products management. Manufacturers must take responsibility for their products over the entire life cycle. In this context, there is a need for network design methods for effectively managing recovery operations and waste. The purpose of this study is to develop a mathematical programming model for managing reverse flows in end-of-life vehicles’ recovery network. A reverse flow is the collection of used products from consumers and the transportation of these products for the purpose of recycling, reuse or disposal. The proposed model includes all operations in a product recovery and waste management network for used vehicles and reuse for vehicle parts such as collection, disassembly, refurbishing, processing (shredding), recycling, disposal and reuse of vehicle parts. The scope of the network model is to determine the numbers and locations of facilities in the network and the material flows between these facilities. The results show the performance of the model and its applicability for use in the planning of recovery operations in the automotive industry. The main objective of recovery and waste management is to maximize revenue and minimize pollution in end-of-life product operations. This study shows that with an accurate model, these activities may provide economic benefits and incentives in addition to protecting the environment.

  9. Aortic stiffness determines diastolic blood flow reversal in the descending thoracic aorta: potential implication for retrograde embolic stroke in hypertension.

    PubMed

    Hashimoto, Junichiro; Ito, Sadayoshi

    2013-09-01

    Aortic stiffening often precedes cardiovascular diseases, including stroke, but the underlying pathophysiological mechanisms remain obscure. We hypothesized that such abnormalities could be attributable to altered central blood flow dynamics. In 296 patients with uncomplicated hypertension, Doppler velocity pulse waveforms were recorded at the proximal descending aorta and carotid artery to calculate the reverse/forward flow ratio and diastolic/systolic flow index, respectively. Tonometric waveforms were recorded on the radial artery to estimate aortic pressure and characteristic impedance (Z0) and to determine carotid-femoral (aortic) and carotid-radial (peripheral) pulse wave velocities. In all subjects, the aortic flow waveform was bidirectional, comprising systolic forward and diastolic reverse flows. The aortic reverse/forward flow ratio (35 ± 10%) was positively associated with parameters of aortic stiffness (including pulse wave velocity, Z0, and aortic/peripheral pulse wave velocity ratio), independent of age, body mass index, aortic diameter, and aortic pressure. The carotid flow waveform was unidirectional and bimodal with systolic and diastolic maximal peaks. There was a positive relationship between the carotid diastolic/systolic flow index (28 ± 9%) and aortic reverse/forward flow ratio, which remained significant after adjustment for aortic stiffness and other related parameters. The Bland-Altman plots showed a close time correspondence between aortic reverse and carotid diastolic flow peaks. In conclusion, aortic stiffness determines the extent of flow reversal from the descending aorta to the aortic arch, which contributes to the diastolic antegrade flow into the carotid artery. This hemodynamic relationship constitutes a potential mechanism linking increased aortic stiffness, altered flow dynamics, and increased stroke risk in hypertension.

  10. Aortic Blood Flow Reversal Determines Renal Function: Potential Explanation for Renal Dysfunction Caused by Aortic Stiffening in Hypertension.

    PubMed

    Hashimoto, Junichiro; Ito, Sadayoshi

    2015-07-01

    Aortic stiffness determines the glomerular filtration rate (GFR) and predicts the progressive decline of the GFR. However, the underlying pathophysiological mechanism remains obscure. Recent evidence has shown a close link between aortic stiffness and the bidirectional (systolic forward and early diastolic reverse) flow characteristics. We hypothesized that the aortic stiffening-induced renal dysfunction is attributable to altered central flow dynamics. In 222 patients with hypertension, Doppler velocity waveforms were recorded at the proximal descending aorta to calculate the reverse/forward flow ratio. Tonometric waveforms were recorded to measure the carotid-femoral (aortic) and carotid-radial (peripheral) pulse wave velocities, to estimate the aortic pressure from the radial waveforms, and to compute the aortic characteristic impedance. In addition, renal hemodynamics was evaluated by duplex ultrasound. The estimated GFR was inversely correlated with the aortic pulse wave velocity, reverse/forward flow ratio, pulse pressure, and characteristic impedance, whereas it was not correlated with the peripheral pulse wave velocity or mean arterial pressure. The association between aortic pulse wave velocity and estimated GFR was independent of age, diabetes mellitus, hypercholesterolemia, and antihypertensive medication. However, further adjustment for the aortic reverse/forward flow ratio and pulse pressure substantially weakened this association, and instead, the reverse/forward flow ratio emerged as the strongest determinant of estimated GFR (P=0.001). A higher aortic reverse/forward flow ratio was also associated with lower intrarenal forward flow velocities. These results suggest that an increase in aortic flow reversal (ie, retrograde flow from the descending thoracic aorta toward the aortic arch), caused by aortic stiffening and impedance mismatch, reduces antegrade flow into the kidney and thereby deteriorates renal function.

  11. Evidence from lava flows for complex polarity transitions: The new composite Steens Mountain reversal record

    USGS Publications Warehouse

    Jarboe, N.A.; Coe, R.S.; Glen, J.M.

    2011-01-01

    Geomagnetic polarity transitions may be significantly more complex than are currently depicted in many sedimentary and lava-flow records. By splicing together paleomagnetic results from earlier studies at Steens Mountain with those from three newly studied sections of Oregon Plateau flood basalts at Catlow Peak and Poker Jim Ridge 70-90 km to the southeast and west, respectively, we provide support for this interpretation with the most detailed account of a magnetic field reversal yet observed in volcanic rocks. Forty-five new distinguishable transitional (T) directions together with 30 earlier ones reveal a much more complex and detailed record of the 16.7 Ma reversed (R)-to-normal (N) polarity transition that marks the end of Chron C5Cr. Compared to the earlier R-T-N-T-N reversal record, the new record can be described as R-T-N-T-N-T-R-T-N. The composite record confirms earlier features, adds new west and up directions and an entire large N-T-R-T segment to the path, and fills in directions on the path between earlier directional jumps. Persistent virtual geomagnetic pole (VGP) clusters and separate VGPs have a preference for previously described longitudinal bands from transition study compilations, which suggests the presence of features at the core-mantle boundary that influence the flow of core fluid and distribution of magnetic flux. Overall the record is consistent with the generalization that VGP paths vary greatly from reversal to reversal and depend on the location of the observer. Rates of secular variation confirm that the flows comprising these sections were erupted rapidly, with maximum rates estimated to be 85-120 m ka-1 at Catlow and 130-195 m ka-1 at Poker Jim South. Paleomagnetic poles from other studies are combined with 32 non-transitional poles found here to give a clockwise rotation of the Oregon Plateau of 11.4???? 5.6?? with respect to the younger Columbia River Basalt Group flows to the north and 14.5???? 4.6?? with respect to cratonic

  12. Flow behaviour analysis of reversible pump-turbine in "S" characteristic operating zone

    NASA Astrophysics Data System (ADS)

    Zhang, S. Q.; Shi, Q. H.; Zhang, K. W.

    2012-11-01

    The pumped storage plant undertakes the task for peak regulation, frequency modulation, phase modulation and accident standby in the electric grid system. Since the design consideration of a pumped storage plant is different from the conventional hydropower plant, the "S" shaped characteristic of pump-turbine will appear in four quadrants characteristic curves, and this characteristic will lead to a series of instabilities while the pump-turbine start at low water head. This paper presents the CFD simulation results of a pump-turbine model with the full flow passage which are compared with model test results. Based on the comparison, the hydraulic reason of the "S" shaped characteristic is discussed and a new concept of partial reverse pump is put forward, i.e. the reverse flow at inlet of runner is the real hydraulic cause of "S" shaped characteristic of a pump-turbine when the unit discharge descends to a certain degree. With the decrease of unit discharge, the effect of partial reverse pump becomes more and more obvious, which leads to an increase of head and finally results the "S" shaped characteristic of a pump-turbine.

  13. Spectroscopic Measurement of Ion Flow During Merging Start-up of Field-Reversed Configuration

    NASA Astrophysics Data System (ADS)

    Oka, Hirotaka; Inomoto, Michiaki; Tanabe, Hiroshi; Annoura, Masanobu; Ono, Yasushi; Nemoto, Koshichi

    2012-10-01

    The counter-helicity merging method [1] of field-reversed configuration (FRC) formation involves generation of bidirectional toroidal flow, known as a ``sling-shot.'' In two fluids regime, reconnection process is strongly affected by the Hall effect [2]. In this study, we have investigated the behavior of toroidal bidirectional flow generated by the counter-helicity merging in two-fluids regime. We use 2D Ion Doppler Spectroscopy to mesure toroidal ion flow during merging start-up of FRC from Ar gas. We defined two cases: one case with a radially pushed-in X line (case I) and the other case with a radially pushed-out X line(case O). The flow during the plasma merging shows radial asymmetry, as expected from the magnetic measurement, but finally relaxes to a unidirectional flow in plasma current direction in both cases. We observed larger toroidal flow in the plasma current direction in case I after FRC is formed, though the FRC in case O has larger magnetic flux. These results suggest that more ions are lost during merging start-up in case I. This selective ion loss might account for stability and confinement of FRCs probably maintained by high energy ions.[4pt] [1] Y. Ono, et al., Nucl. Fusion 39, pp. 2001-2008 (1999).[0pt] [2] M. Inomoto, et al., Phys. Rev. Lett., 97, 135002, (2006)

  14. Measurements of Reversing Flows with Non-zero Mean in Porous Media

    NASA Astrophysics Data System (ADS)

    Hsu, Chin-Tsau; Fu, Huili

    1996-11-01

    The accurate prediction of the pressure drop in a regenerator (packed with porous materials) is crucial to the design of a Stirling engine or a cryocooler. To date, the most popularly-used pressure-drop correlation is still largely based on the data of steady flows. Since the regenerators are operating under the periodically reversing flows, the pressure-drop correlation should comprise two elements: amplitude and phase correlations. There exist some measurements on the pressure drop across a packed column subjected to oscillating flows; but only the amplitude correlations were reported and the results showed considerable difference from those of steady flows. In this study, experiments were performed for oscillating flows through cylinders packed with woven-screens. Both the pressure and the velocity were measured. The mean flows were set to have zero and non-zero means. The pressure-drop and velocity signals were averaged over constant phase angle referencing to the displacement signal of a piston drive. Our results indicate that there are considerable phase angle difference between the pressure-drop and the velocity. This indicates that the transient inertia effect can not be neglected in the pressure-drop correlation.

  15. Nanometer-thick lateral polyelectrolyte micropatterns induce macrosopic electro-osmotic chaotic fluid instabilities

    NASA Astrophysics Data System (ADS)

    Wessling, M.; Morcillo, L. Garrigós; Abdu, S.

    2014-03-01

    Electro-convective vortices in ion concentration polarization under shear flow have been of practical relevance for desalination processes using electrodialysis. The phenomenon has been scientifically disregarded for decades, but is recently embraced by a growing fluid dynamics community due its complex superposition of multi-scale gradients in electrochemical potential and space charge interacting with emerging complex fluid momentum gradients. While the visualization, quantification and fundamental understanding of the often-chaotic fluid dynamics is evolving rapidly due to sophisticated simulations and experimentation, little is known whether these instabilities can be induced and affected by chemical topological heterogeneity in surface properties. In this letter, we report that polyelectrolyte layers applied as micropatterns on ion exchange membranes induce and facilitate the electro-osmotic fluid instabilities. The findings stimulate a variety of fundamental questions comparable to the complexity of today's turbulence research.

  16. Nanometer-thick lateral polyelectrolyte micropatterns induce macrosopic electro-osmotic chaotic fluid instabilities

    PubMed Central

    Wessling, M.; Morcillo, L. Garrigós; Abdu, S.

    2014-01-01

    Electro-convective vortices in ion concentration polarization under shear flow have been of practical relevance for desalination processes using electrodialysis. The phenomenon has been scientifically disregarded for decades, but is recently embraced by a growing fluid dynamics community due its complex superposition of multi-scale gradients in electrochemical potential and space charge interacting with emerging complex fluid momentum gradients. While the visualization, quantification and fundamental understanding of the often-chaotic fluid dynamics is evolving rapidly due to sophisticated simulations and experimentation, little is known whether these instabilities can be induced and affected by chemical topological heterogeneity in surface properties. In this letter, we report that polyelectrolyte layers applied as micropatterns on ion exchange membranes induce and facilitate the electro-osmotic fluid instabilities. The findings stimulate a variety of fundamental questions comparable to the complexity of today's turbulence research. PMID:24598972

  17. Development of stable low-electroosmotic mobility coatings. [for use in electrophoresis systems in space

    NASA Technical Reports Server (NTRS)

    Vanderhoff, J. W.; Micale, F. J.

    1979-01-01

    Long-time rinsings of the Z6040-methlycellulose coating used successfully on the ASTP MA=011 experiment indicate the permanency of this coating is inadequate for continuous flowing systems. Two approaches are described for developing coatings which are stable under continuous fluid movement and which exhibit finite and predictable electroosmotic mobility values while being effective on different types of surfaces, such as glass, plastics, and ceramic alumina, such as is currently used as the electrophoresis channel in the GE-SPAR-CPE apparatus. The surface charge modification of polystyrene latex, especially by protein absorption, to be used as model materials for ground-based electrophoresis experiments, and the preliminary work directed towards the seeded polymerization of large-particle-size monodisperse latexes in a microgravity environment are discussed.

  18. Reducing Electroosmotic Flow Enables DNA Separations in Ultrathin Channels.

    DTIC Science & Technology

    1998-08-01

    systems with on-column detection. B. Schematic diagram of EOF in traditional CE systems . ...23 Figure 2-2: Schematic diagram of EOF in CE systems ...of the CE/ultrathin channel system for characterization studies. B. Schematic diagram of the CE/ultrathin channel system for separation studies 49...Development of an Integrated DNA Separation System ; Hietpas, P. B., Ed.; The Pennsylvannia State University: University Park, PA, 1997, pp 1-168. 19

  19. Bilateral nasal ala reconstruction of the cocaine-injured nose with 2 free reverse-flow helical rim flaps.

    PubMed

    Castello, Jose R; Taglialatela Scafati, Salvatore; Sánchez, Olaya

    2014-09-01

    Cocaine abuse can lead to nasal deformity because of local ischemia and subsequent fibrosis. Reconstruction can be challenging. We present a case of bilateral microsurgical nasal ala reconstruction with 2 reverse-flow helical rim flap.

  20. Network modeling for reverse flows of end-of-life vehicles.

    PubMed

    Ene, Seval; Öztürk, Nursel

    2015-04-01

    Product recovery operations are of critical importance for the automotive industry in complying with environmental regulations concerning end-of-life products management. Manufacturers must take responsibility for their products over the entire life cycle. In this context, there is a need for network design methods for effectively managing recovery operations and waste. The purpose of this study is to develop a mathematical programming model for managing reverse flows in end-of-life vehicles' recovery network. A reverse flow is the collection of used products from consumers and the transportation of these products for the purpose of recycling, reuse or disposal. The proposed model includes all operations in a product recovery and waste management network for used vehicles and reuse for vehicle parts such as collection, disassembly, refurbishing, processing (shredding), recycling, disposal and reuse of vehicle parts. The scope of the network model is to determine the numbers and locations of facilities in the network and the material flows between these facilities. The results show the performance of the model and its applicability for use in the planning of recovery operations in the automotive industry. The main objective of recovery and waste management is to maximize revenue and minimize pollution in end-of-life product operations. This study shows that with an accurate model, these activities may provide economic benefits and incentives in addition to protecting the environment.

  1. Reverse flow injection spectrophotometric determination of iodate and iodide in table salt.

    PubMed

    Xie, Zhihai; Zhao, Jingchan

    2004-05-28

    A very simple and sensitive reverse flow injection method is described for the determination of iodate and iodide. The iodate reacts with excess iodide in acidic medium to form tri-iodide, which can be spectrophotometrically monitored at 351nm, and the absorbance is directly related to the concentration of iodate in the sample. The determination of iodide is based on oxidizing iodide to iodate. The calibration curve is linear in the range of 0.02-3.0mugml(-1) I with r(2)=0.9998, and the limit of detection is 0.008mugml(-1) I. The chemical and flow injection variables were studied and optimized to make the procedure suitable for quantitating iodate and iodide in table salts. It is shown that the reverse flow injection analysis could greatly improve the sensitivity and precision for determination of iodate with a relative standard deviation of 0.9%. A complete analysis, including sampling and washing, could be performed in 35s. The procedure was applied successfully to the determination of iodate and iodide in table salts, and the results were statistically compared with results determined by standard iodometry method.

  2. Improvement of sensitivity in flow analysis by exploiting a multi-reversed software-assisted system.

    PubMed

    Neira, José Y; González, Elizabeth; Nóbrega, Joaquim A

    2007-09-15

    A multi-reversed flow system software-assisted was developed for improvement of sensitivity in flow analysis. The performance of the flow system proposed was evaluated by using as a model the conventional Griess' colorimetric reaction for determination of nitrite in waters. The manifold incorporated three 3-way solenoid valves, a relay box solenoid actuated, a peristaltic pump, and a photometric detector. A tailored software was designed and written in Visual Basic 6.0 which allows full control of all flow system components and simultaneous acquisition and processing of the data. The sensitivity measured as the slope of the calibration curve was improved 2.5- and 1.4-fold regarding those obtained by continuous- and stopped-flow systems, respectively. Other valuable features such as analytical throughput of 55 determinations per hour, limit of detection of 5mugL(-1) (3sigma(blank)/slope), relative standard deviation<2% (n=8), and a linear dynamic range up to 1800mugL(-1) were also achieved.

  3. Sheared E×B flow and plasma turbulence viscosity in a Reversed Field Pinch

    NASA Astrophysics Data System (ADS)

    Vianello, N.; Antoni, V.; Spada, E.; Spolaore, M.; Serianni, G.; Regnoli, G.; Zuin, M.; Cavazzana, R.; Bergsåker, H.; Cecconello, M.; Drake, J. R.

    2004-11-01

    The relationship between electromagnetic turbulence and sheared plasma flow in Reversed Field Pinch configuration is addressed. The momentum balance equation for a compressible plasma is considered and the terms involved are measured in the outer region of Extrap-T2R RFP device. It results that electrostatic fluctuations determine the plasma flow through the electrostatic component of Reynolds Stress tensor. This term involves spatial and temporal scales comparable to those of MHD activity. The derived experimental perpendicular viscosity is consistent with anomalous diffusion, the latter being discussed in terms of electrostatic turbulence background and coherent structures emerging from fluctuations. The results indicate a dynamical interplay between turbulence, anomalous transport and mean E×B profiles. The momentum balance has been studied also in non-stationary condition during the application of Pulsed Poloidal Current Drive, which is known to reduce the amplitude of MHD modes.

  4. Effect of fuel injector type on performance and emissions of reverse-flow combustor

    NASA Technical Reports Server (NTRS)

    Norgren, C. T.; Riddlebaugh, S. M.

    1981-01-01

    The combustion process in a reverse-flow combustor suitable for a small gas turbine engine was investigated to evaluate the effect of fuel injector type on performance and emissions. Fuel injector configurations using pressure-atomizing, spill-flow, air blast, and air-assist techniques were compared and evaluated on the basis of performance obtained in a full-scale experimental combustor operated at inlet conditions corresponding to takeoff, cruise, low power, and idle and typical of a 16:1-pressure-ratio turbine engine. Major differences in combustor performance and emissions characteristics were experienced with each injector type even though the aerodynamic configuration was common to most combustor models. Performance characteristics obtained with the various fuel injector types could not have been predicted from bench-test injector spray characteristics. The effect of the number of operating fuel injectors on performance and emissions is also presented.

  5. Absent or reversed end diastolic flow velocity in the umbilical artery and necrotising enterocolitis.

    PubMed Central

    Malcolm, G; Ellwood, D; Devonald, K; Beilby, R; Henderson-Smart, D

    1991-01-01

    Absent or reversed end diastolic flow (AREDF) velocities in the umbilical artery were identified in 25 high risk pregnancies. In six pregnancies the fetus was abnormal and all but one of these ended in perinatal death. Of the 19 morphologically normal fetuses, three died in utero and there were four neonatal or infant deaths. The mortality rate was 48% for all pregnancies and 37% for those with morphologically normal fetuses. There was a highly significant increased risk for the development of necrotising enterocolitis in these morphologically normal fetuses with AREDF (53%) compared with controls (6%) who did have umbilical artery end diastolic flow velocities in fetal life. There were no significant differences between the matched pairs for parameters of neonatal outcome chosen to reflect neonatal morbidity. These findings demonstrate the close association between AREDF and necrotising enterocolitis that appears to be independent of other variables such as degree of growth retardation, prematurity, and perinatal asphyxia. PMID:1863128

  6. Effect of broad properties fuel on injector performance in a reverse flow combustor

    NASA Technical Reports Server (NTRS)

    Raddlebaugh, S. M.; Norgren, C. T.

    1983-01-01

    The effect of fuel type on the performance of various fuel injectors was investigated in a reverse flow combustor. Combustor performance and emissions are documented for simplex pressure atomizing, spill flow, and airblast fuel injectors using a broad properties fuel and compared with performance using Jet A fuel. Test conditions simulated a range of flight conditions including sea level take off, low and high altitude cruise, as well as a parametric evaluation of the effect of increased combustor loading. The baseline simplex injector produced higher emission levels with corresponding lower combustion efficiency with the broad properties fuel. There was little or not loss in performance by the two advanced concept injectors with the broad properties fuel. The airblast injector proved to be especially insensitive to fuel type.

  7. Effect of the Reversal of Air Flow upon the Discharge Coefficient of Durley Orifices

    NASA Technical Reports Server (NTRS)

    Ware, Marsden

    1921-01-01

    Experiments were conducted to obtain information on the relationship between the coefficients for flow in two directions through thin plate orifices at low velocities. The results indicate that the ratio of the orifice discharge coefficient from standard orifice C(sub s)(sup 1) to the discharge coefficient from the reverse flow C(sub s) is always less than unity with increasing ratio of box area to orifice area. Even for areas as low as twenty, the ratios of the coefficients are not much less than unity. It is probable, however, that when the ratio of box area is less than twenty, the ratio of discharge coefficients would be greatly reduced. Specific results are given for the case of an apparatus for the laboratory testing of superchargers.

  8. Electrodynamics of the plasma flow reversal in the late evening auroral oval

    NASA Astrophysics Data System (ADS)

    Behm, D. A.

    1982-12-01

    Electric and magnetic field measurements taken by two Nike-Tomahawk sounding rockets, launched from Andoya, Norway into the late evening auroral oval, are presented. Flight 18.1005, launched into quiet magnetic conditions, passed over a quiet auroral arc and over a region of plasma flow reversal. The flow reversal was interpreted as the Harang discontinuity. The second flight, 18.1004, was launched into a breakup aurora and through the westward electrojet. Horizontal current strengths were inferred from dc magnetic field measurements and calculated from the measured dc electric field and calculated conductivities for both flights. The calculated currents disagreed with the magnetic field measurements. The disagreement was larger for flight 18.1004, supporting the conclusion that neutral winds play a role in driving horizontal currents. A major emphasis was placed on the performance of the triaxial fluxgate magnetometer as compared to the proton precession magnetometer. It was shown that northward and vertical magnetic field components could be obtained with some difficulty, but that determination of the eastward component was not possible.

  9. Reverse flow first dorsal metacarpal artery flap for covering the defect of distal thumb.

    PubMed

    Checcucci, Giuseppe; Galeano, Mariarosaria; Zucchini, Maura; Zampetti, Pier Giuseppe; Ceruso, Massimo

    2014-05-01

    Reconstruction of distal thumb injuries still remains a challenge for hand surgeons. Surgical treatment includes the use of local, regional, and free flaps. The purpose of this report is to present the results of the use of a sensitive reverse flow first dorsal metacarpal artery (FDMA) flap. The skin flap was designed on the radial side of the proximal phalanx of the index finger based on the ulnar and radial branch of the FDMA and a sensory branch of the superficial radial nerve. This neurovascular flap was used in five patients to cover distal soft-tissue thumb defects. All flaps achieved primary healing except for one patient in whom superficial partial necrosis of the flap occurred, and the defect healed by second intention. All patients maintained the thumb original length and were able to return to their previous daily activities. The reverse flow FDMA flap is a reliable option to cover immediate and delayed defects of distal thumb, offering acceptable functional and cosmetic outcomes in respect to sensibility, durability, and skin-match.

  10. Axial flow reversal and its significance in air-sparged hydrocyclone (ASH) flotation

    SciTech Connect

    Miller, J.D.; Das, A.; Yin, D.

    1995-12-31

    In recent years the potential of air-sparged hydrocyclone (ASH) flotation for fine coal cleaning has been demonstrated both in pilot plant testing and in a plant-site demonstration program. Further improvements in the ASH technology will depend, to some extent, on improved understanding of the complex multiphase fluid flow. Froth transport plays a very important role in determining the efficiency of fine coal cleaning by ASH flotation. It should be noted that the surface of zero axial velocity is of particular significance in froth transport because the location of this surface actually accounts for the amount of froth being transported to the overflow. In this regard, the axial flow reversal has been examined based on specially designed tracer experiments. On the basis of these experimental results, modeling efforts were made to characterize the flow pattern in the ASH. The theoretical predictions based on turbulent fluid dynamic considerations were found to describe experimental observations regarding the surface of zero axial velocity. These results that define the surface of zero axial velocity together with froth phase features established from X-ray CT measurements provide an excellent description of the flow characteristics in ASH flotation and explain the effect of various process variables, such as dimensionless area (A*), dimensionless flowrate (Q*), inlet pressure, percent solids, etc., on flotation recovery. On this basis it is expected that further advances in the design and operation of the ASH system can be made, leading to more efficient use of the ASH technology for fine coal cleaning.

  11. Effect of flow rate and concentration difference on reverse electrodialysis system

    NASA Astrophysics Data System (ADS)

    Kwon, Kilsugn; Han, Jaesuk; Kim, Daejoong

    2013-11-01

    Various energy conversion technologies have been developed to reduce dependency on limited fossil fuels, including wind power, solar power, hydropower, ocean power, and geothermal power. Among them, reverse electrodialysis (RED), which is one type of salinity gradient power (SGP), has received much attention due to high reliability and simplicity without moving parts. Here, we experimentally evaluated the RED performance with several parameters like flow rate of concentrated and dilute solution, concentration difference, and temperature. RED was composed of endplates, electrodes, spacers, anion exchange membrane, and cation exchange membrane. Endplates are made by a polypropylene. It included the electrodes, flow field for the electrode rinse solution, and path to supply a concentrated and dilute solution. Titanium coated by iridium and ruthenium was used as the electrode. The electrode rinse solution based on hexacyanoferrate system is used to reduce the power loss generated by conversion process form ionic current to electric current. Maximum power monotonously increases as increasing flow rate and concentration difference. Net power has optimal point because pumping power consumption increases with flow rate. This work was supported by Basic Science Research Program (Grat No. NRF-2011-0009993) through the National Research Foundation of Korea.

  12. Generating electrospray from microchip devices using electroosmotic pumping

    SciTech Connect

    Ramsey, R.S.; Ramsey, J.M.

    1997-03-15

    A method of generating electrospray from solutions emerging from small channels etched on planer substrates in described. The fluids are delivered using electroosmotically induced pressures and are sprayed electrostatically from the terminus of a channel by applying an electrical potential of sufficient amplitude to generate the electrospray between the microchip and a conductor spaced from the channel terminus. No major modification of the microchip is required other than to expose a channel opening. The principles that regulate the fluid delivery are described and demonstrated. A spectrum for a test compound, tetrabutylammonium iodide, that was continuously electrophoresed was obtained by coupling the microchip to an ion trap mass spectrometer. 35 refs., 6 figs.

  13. Curvature-induced secondary microflow motion in steady electro-osmotic transport with hydrodynamic slippage effect

    NASA Astrophysics Data System (ADS)

    Lim, Jin-Myoung; Chun, Myung-Suk

    2011-10-01

    In order to exactly understand the curvature-induced secondary flow motion, the steady electro-osmotic flow (EOF) is investigated by applying the full Poisson-Boltzmann/Navier-Stokes equations in a whole domain of the rectangular microchannel. The momentum equation is solved with the continuity equation as the pressure-velocity coupling achieves convergence by employing the advanced algorithm, and generalized Navier's slip boundary conditions are applied at the hydrophobic curved surface. Two kinds of channels widely used for lab-on-chips are explored with the glass channel and the heterogeneous channel consisting of glass and hydrophobic polydimethylsiloxane, spanning thin to thick electric double layer (EDL) problem. According to a sufficiently low Dean number, an inward skewness in the streamwise velocity profile is observed at the turn. With increasing EDL thickness, the electrokinetic effect gets higher contribution in the velocity profile. Simulation results regarding the variations of streamwise velocity depending on the electrokinetic parameters and hydrodynamic fluid slippage are qualitatively consistent with the predictions documented in the literature. Secondary flows arise due to a mismatch of streamline velocity between fluid in the channel center and near-wall regions. Strengthened secondary flow results from increasing the EDL thickness and the contribution of fluid inertia (i.e., electric field and channel curvature), providing a scaling relation with the same slope. Comparing with and between the cases enables us to identify the optimum selection in applications of curved channel for enhanced EOF and stronger secondary motion relevant to the mixing effect.

  14. Analysis of the flow field generated near an aircraft engine operating in reverse thrust. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Ledwith, W. A., Jr.

    1972-01-01

    A computer solution is developed to the exhaust gas reingestion problem for aircraft operating in the reverse thrust mode on a crosswind-free runway. The computer program determines the location of the inlet flow pattern, whether the exhaust efflux lies within the inlet flow pattern or not, and if so, the approximate time before the reversed flow reaches the engine inlet. The program is written so that the user is free to select discrete runway speeds or to study the entire aircraft deceleration process for both the far field and cross-ingestion problems. While developed with STOL applications in mind, the solution is equally applicable to conventional designs. The inlet and reversed jet flow fields involved in the problem are assumed to be noninteracting. The nacelle model used in determining the inlet flow field is generated using an iterative solution to the Neuman problem from potential flow theory while the reversed jet flow field is adapted using an empirical correlation from the literature. Sample results obtained using the program are included.

  15. Microfluidic system with integrated electroosmotic pumps, concentration gradient generator and fish cell line (RTgill-W1)--towards water toxicity testing.

    PubMed

    Glawdel, Tomasz; Elbuken, Caglar; Lee, Lucy E J; Ren, Carolyn L

    2009-11-21

    This study presents a microfluidic system that incorporates electroosmotic pumps, a concentration gradient generator and a fish cell line (rainbow trout gill) to perform toxicity testing on fish cells seeded in the system. The system consists of three mechanical components: (1) a toxicity testing chip containing a microfluidic gradient generator which creates a linear concentration distribution of toxicant in a cell test chamber, (2) an electroosmotic (EO) pump chip that controls the flow rate and operation of the toxicity chip, and (3) indirect reservoirs that connect the two chips allowing for the toxicant solution to be pumped separately from the electroosmotic pump solution. The flow rate and stability of the EO pumps was measured and tested by monitoring the gradient generator using fluorescence microscopy. Furthermore, a lethality test was performed with this system setup using a rainbow trout gill cell line (RTgill-W1) as the test cells and sodium dodecyl sulfate as a model toxicant. A gradient of sodium dodecyl sulfate, from 0 to 50 microg mL(-1), was applied for 1 hr to the attached cells, and the results were quantified using a Live/Dead cell assay. This work is a preliminary study on the application of EO pumps in a living cell assay, with the potential to use the pumps in portable water quality testing devices with RTgill-W1 cells as the biosensors.

  16. Reverse flow events and small-scale effects in the cusp ionosphere

    NASA Astrophysics Data System (ADS)

    Spicher, A.; Ilyasov, A. A.; Miloch, W. J.; Chernyshov, A. A.; Clausen, L. B. N.; Moen, J. I.; Abe, T.; Saito, Y.

    2016-10-01

    We report in situ measurements of plasma irregularities associated with a reverse flow event (RFE) in the cusp F region ionosphere. The Investigation of Cusp Irregularities 3 (ICI-3) sounding rocket, while flying through a RFE, encountered several regions with density irregularities down to meter scales. We address in detail the region with the most intense small-scale fluctuations in both the density and in the AC electric field, which were observed on the equatorward edge of a flow shear, and coincided with a double-humped jet of fast flow. Due to its long-wavelength and low-frequency character, the Kelvin-Helmholtz instability (KHI) alone cannot be the source of the observed irregularities. Using ICI-3 data as inputs, we perform a numerical stability analysis of the inhomogeneous energy-density-driven instability (IEDDI) and demonstrate that it can excite electrostatic ion cyclotron waves in a wide range of wave numbers and frequencies for the electric field configuration observed in that region, which can give rise to the observed small-scale turbulence. The IEDDI can seed as a secondary process on steepened vortices created by a primary KHI. Such an interplay between macroprocesses and microprocesses could be an important mechanism for ion heating in relation to RFEs.

  17. CO2 Dissociation by Low Current Gliding Discharge in the Reverse Vortex Flow

    NASA Astrophysics Data System (ADS)

    Gutsol, Alexander

    2012-10-01

    If performed with high energy efficiency, plasma-chemical dissociation of carbon dioxide can be a way of converting and storing energy when there is an excess of electric energy, for example generated by solar elements of wind turbines. CO2 dissociation with efficiency of up to 90% was reported earlier for low pressure microwave discharge in supersonic flow. A new plasma-chemical system uses a low current gliding discharge in the reverse vortex flow of plasma gas. The system is a development of the Gliding Arc in Tornado reactor. The system was used to study dissociation of CO2 in wide ranges of the following experimental parameters: reactor pressure (15-150 kPa), discharge current (50-500 mA), gas flow rate (3-30 liters per minute), and electrode gap length (1-10 cm). Additionally, the effect of thermal energy recuperation on CO2 dissociation efficiency was tested. Plasma chemical efficiency of CO2 dissociation is very low (about 3%) in a short discharge at low pressures (about 15 kPa) when it is defined by electronic excitation. The highest efficiency (above 40%) was reached at pressures 50-70 kPa in a long discharge with thermal energy recuperation. It means that the process is controlled by thermal dissociation with subsequent effective quenching. Plasma chemical efficiency was determined from the data of chromatographic analysis and oscilloscope electric power integration, and also was checked calorimetrically by the thermal balance of the system.

  18. Water Flow inside Polamide Reverse Osmosis Membranes: A Non-Equilibrium Molecular Dynamics Study.

    PubMed

    Song, Yang; Xu, Fang; Wei, Mingjie; Wang, Yong

    2017-02-23

    Water flow inside polyamide (PA) reverse osmosis (RO) membranes is studied by steady state nonequilibrium molecular dynamics (NEMD) simulations in this work. The PA RO membrane is constructed with the all-atom model, and the density and average pore size obtained thereby are consistent with the latest experimental results. To obtain the time-independent water flux, a steady state NEMD method is used under various pressure drops. The water flux in our simulations, which is calculated under higher pressure drops, is in a linear relation with the pressure drops. Hence, the water flux in lower pressure drops can be reliably estimated, which could be compared with the experimental results. The molecular details of water flowing inside the membrane are considered. The radial distribution function and residence time of water around various groups of polyamide are introduced to analyze the water velocities around these groups, and we find that water molecules flow faster around benzene rings than around carboxyl or amino groups in the membrane, which implies that the main resistance of mass transport of water molecules comes from the carboxyl or amino groups inside the membranes. This finding is in good consistency with experimental results and suggests that less free carboxyl or amino groups should be generated inside RO membranes to enhance water permeance.

  19. Electro-convective versus electroosmotic instability in concentration polarization.

    PubMed

    Rubinstein, Isaak; Zaltzman, Boris

    2007-10-31

    Electro-convection is reviewed as a mechanism of mixing in the diffusion layer of a strong electrolyte adjacent to a charge-selective solid, such as an ion exchange (electrodialysis) membrane or an electrode. Two types of electro-convection in strong electrolytes may be distinguished: bulk electro-convection, due to the action of the electric field upon the residual space charge of a quasi-electro-neutral bulk solution, and convection induced by electroosmotic slip, due to electric forces acting in the thin electric double layer of either quasi-equilibrium or non-equilibrium type near the solid/liquid interface. According to recent studies, the latter appears to be the likely source of mixing in the diffusion layer, leading to 'over-limiting' conductance in electrodialysis. Electro-convection near a planar uniform charge selective solid/liquid interface sets on as a result of hydrodynamic instability of one-dimensional steady state electric conduction through such an interface. We compare the results of linear stability analysis obtained for instabilities of this kind appearing in the full electro-convective and limiting non-equilibrium electroosmotic formulations. The short- and long-wave aspects of these instabilities are discussed along with the wave number selection principles.

  20. Embolisation of the Gastroduodenal Artery is Not Necessary in the Presence of Reversed Flow Before Yttrium-90 Radioembolisation

    SciTech Connect

    Daghir, Ahmed A.; Gungor, Hatice; Haydar, Ali A.; Wasan, Harpreet S.; Tait, Nicholas P.

    2012-08-15

    Introduction: The gastroduodenal artery (GDA) is usually embolised to avoid nontarget dispersal before yttrium-90 (Y{sup 90}) radioembolisation to treat liver metastases. In a minority of patients, there is retrograde flow in the GDA. The purpose of this study was to determine if there is any increased risk from maintaining a patent GDA in patients with reversed flow. Materials and Methods: A retrospective review was performed of all patients undergoing Y{sup 90} radioembolisation at our institution. The incidence of toxicities arising from nontarget radioembolisation by way of the GDA (gastric/duodenal ulceration, gastric/duodenal bleeding, and pancreatitis) and death occurring within 2 months of treatment were compared between the reversed and the antegrade GDA groups. Results: Ninety-two patients underwent preliminary angiography. Reversed GDA flow was found on angiography in 14.1% of cases; the GDA was not embolised in these patients. The GDA was coiled in 55.7% of patients with antegrade GDA flow to prevent inadvertent dispersal of radioembolic material. There was no increased toxicity related to nontarget dispersal by way of the GDA, or increased early mortality, in patients with reversed GDA flow (P > 0.05). Conclusion: In patients with reversed GDA flow, maintenance of a patent GDA before administration of Y{sup 90} radioembolisation does not increase the risk of toxicity from nontarget dispersal. Therapeutic injection, with careful monitoring to identify early vascular stasis, may be safely performed beyond the origin of the patent GDA. A patent GDA with reversed flow provides forward drive for infused particles and may allow alternative access to the hepatic circulation.

  1. Statistical theory of reversals in two-dimensional confined turbulent flows

    NASA Astrophysics Data System (ADS)

    Shukla, Vishwanath; Fauve, Stephan; Brachet, Marc

    2016-12-01

    It is shown that the truncated Euler equation (TEE), i.e., a finite set of ordinary differential equations for the amplitude of the large-scale modes, can correctly describe the complex transitional dynamics that occur within the turbulent regime of a confined two-dimensional flow obeying Navier-Stokes equation (NSE) with bottom friction and a spatially periodic forcing. The random reversals of the NSE large-scale circulation on the turbulent background involve bifurcations of the probability distribution function of the large-scale circulation. We demonstrate that these NSE bifurcations are described by the related TEE microcanonical distribution which displays transitions from Gaussian to bimodal and broken ergodicity. A minimal 13-mode model reproduces these results.

  2. Statistical theory of reversals in two-dimensional confined turbulent flows.

    PubMed

    Shukla, Vishwanath; Fauve, Stephan; Brachet, Marc

    2016-12-01

    It is shown that the truncated Euler equation (TEE), i.e., a finite set of ordinary differential equations for the amplitude of the large-scale modes, can correctly describe the complex transitional dynamics that occur within the turbulent regime of a confined two-dimensional flow obeying Navier-Stokes equation (NSE) with bottom friction and a spatially periodic forcing. The random reversals of the NSE large-scale circulation on the turbulent background involve bifurcations of the probability distribution function of the large-scale circulation. We demonstrate that these NSE bifurcations are described by the related TEE microcanonical distribution which displays transitions from Gaussian to bimodal and broken ergodicity. A minimal 13-mode model reproduces these results.

  3. Steady shear rheometry of dissipative particle dynamics models of polymer fluids in reverse Poiseuille flow.

    PubMed

    Fedosov, Dmitry A; Karniadakis, George Em; Caswell, Bruce

    2010-04-14

    Polymer fluids are modeled with dissipative particle dynamics (DPD) as undiluted bead-spring chains and their solutions. The models are assessed by investigating their steady shear-rate properties. Non-Newtonian viscosity and normal stress coefficients, for shear rates from the lower to the upper Newtonian regimes, are calculated from both plane Couette and plane Poiseuille flows. The latter is realized as reverse Poiseuille flow (RPF) generated from two Poiseuille flows driven by uniform body forces in opposite directions along two-halves of a computational domain. Periodic boundary conditions ensure the RPF wall velocity to be zero without density fluctuations. In overlapping shear-rate regimes the RPF properties are confirmed to be in good agreement with those calculated from plane Couette flow with Lees-Edwards periodic boundary conditions (LECs), the standard virtual rheometer for steady shear-rate properties. The concentration and the temperature dependence of the properties of the model fluids are shown to satisfy the principles of concentration and temperature superposition commonly employed in the empirical correlation of real polymer-fluid properties. The thermodynamic validity of the equation of state is found to be a crucial factor for the achievement of time-temperature superposition. With these models, RPF is demonstrated to be an accurate and convenient virtual rheometer for the acquisition of steady shear-rate rheological properties. It complements, confirms, and extends the results obtained with the standard LEC configuration, and it can be used with the output from other particle-based methods, including molecular dynamics, Brownian dynamics, smooth particle hydrodynamics, and the lattice Boltzmann method.

  4. Nongassing long-lasting electro-osmotic pump with polyaniline-wrapped aminated graphene electrodes.

    PubMed

    Kumar, Rudra; Jahan, Kousar; Nagarale, Rajaram K; Sharma, Ashutosh

    2015-01-14

    An efficient nongassing electro-osmotic pump (EOP) with long-lasting electrodes and exceptionally stable operation is developed by using novel flow-through polyaniline (PANI)-wrapped aminated graphene (NH2-G) electrodes. The NH2-G/PANI electrode combines the excellent oxidation/reduction capacity of PANI with the exceptional conductivity and inertness of NH2-G. The flow rate varies linearly with voltage but is highly dependent on the electrode composition. The flow rates at a potential of 5 V for pristine NH2-G and PANI electrodes are 71 and 100 μL min(-1) cm(-2), respectively, which increase substantially by the use of NH2-G/PANI electrode. It increased from 125 to 182 μL min(-1) cm(-2) as the fraction of aniline increased from 66.63 to 90.90%. The maximum flux obtained is 40 μL min(-1) V(-1) cm(-2) with NH2-G/PANI-90.9 electrodes. The assembled EOP remained exceptionally stable until the electrode columbic capacity was fully utilized. The prototype shown here delivered 8.0 μL/min at a constant applied voltage of 2 V for over 7 h of continuous operation. The best EOP produces a maximum stall pressure of 3.5 kPa at 3 V. These characteristics make it suitable for a variety of microfluidic/device applications.

  5. Study of an electroosmotic pump for liquid delivery and its application in capillary column liquid chromatography.

    PubMed

    Chen, Lingxin; Ma, Jiping; Guan, Yafeng

    2004-03-05

    A packed-bed electroosmotic pump (EOP) was constructed and evaluated. The EOP consisted of three capillary columns packed in parallel, a gas-releasing device, Pt electrodes and a high-voltage power supply. The EOP could generate output pressure above 5.0 MPa and constant flow rate in the range of nl/min to a few microl/min for pure water, pure methanol, 2 mM potassium dihydrogenphosphate buffer, the buffer-methanol mixture and the pure water-methanol mixture at applied potentials less than 20 kV. The composition of solvent before/after pumping was quantitatively determined by using a gas chromatograph equipped with both flame ionization detector and thermal conductivity detector. It was found that there were no apparent changes in composition and relative concentrations after pumping process for a methanol-ethanol-acetonitrile mixture and a methanol-water mixture. Theoretical aspect of the EOP was discussed in detail. An capillary HPLC system consisting of the EOP, an injection valve, a 15 cm x 320 microm i.d., 5 microm Spherigel C18 stainless steel analytical column, and an on-column UV detector was connected to evaluate the performance of the EOP. A comparative study was also carried out with a mechanical capillary HPLC pump on the same system. The results demonstrated that the reproducibility of flow rate and the pulsation-free flow property of the EOP are superior to that of mechanical pump in capillary HPLC application.

  6. Electro-osmotic drag coefficient of water and methanol in polymer electrolytes at elevated temperatures

    SciTech Connect

    Weng, D.; Wainright, J.S.; Landau, U.; Savinell, R.F.

    1996-04-01

    The electro-osmotic drag coefficient of water in two polymer electrolytes was experimentally determined as a function of water activity and current density for temperatures up to 200 C. The results show that the electro-osmotic drag coefficient varies from 0.2 to 0.6 in Nafion{reg_sign}/H{sub 3}PO{sub 4} membrane electrolyte, but is essentially zero in phosphoric acid-doped PBI (polybenzimidazole) membrane electrolyte over the range of water activity considered. The near-zero electro-osmotic drag coefficient found in PBI indicates that this electrolyte should lessen the problems associated with water redistribution in proton exchange membrane fuel cells.

  7. A rapid and reversible skull optical clearing method for monitoring cortical blood flow

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Zhao, Yanjie; Shi, Rui; Zhu, Dan

    2016-03-01

    In vivo cortex optical imaging is of great important for revealing both structural and functional architecture of brain with high temporal-spatial resolution. To reduce the limitation of turbid skull, researchers had to establish various skull windows or directly expose cortex through craniotomy. Here we developed a skull optical clearing method to make skull transparent. Laser speckle contrast imaging technique was used to monitor the cortical blood flow after topical treatment with the optical clearing agents. The results indicated that the image contrast increased gradually, and then maintained at a high level after 15 min for adult mice, which made the image quality and resolution of micro-vessels nearly approximate to those of exposed cortex. Both the cortical blood flow velocity almost kept constant after skull became transparent. Besides, the treatment of physiological saline on the skull could make skull return to the initial state again and the skull could become transparent again when SOCS retreated it. Thus, we could conclude that the skull optical clearing method was rapid, valid, reversible and safe, which provided us available approach for performing the cortical structural and functional imaging at high temporal-spatial resolution.

  8. Flow and heat transfer of plane surfaces moving in parallel and reversely to the free stream

    NASA Astrophysics Data System (ADS)

    Lin, Hsiao-Tsung; Huang, Shih-Feng

    1994-01-01

    Two types of classical forced convection problems have been extensively studied for the past years. They are the Blasius problem of a steady flow over a stationary flat plate; and the Sakiadis problem of a plate moving continuously in a quiescent ambient fluid. In this paper, we study the general forced convection problem of surface moving continuously in a flowing stream by using a quite different transformation to obtain similarity solutions. The present solutions are very accurate for any relative speed of the surface and the free stream over a wide range of Prandtl number between 0.01 and 10 000. We study not only the case of a plane surface moving in parallel to the free stream but also the case of a surface moving reversely. The latter case has not been studied previously. For application convenience, very accurate correlation equations are proposed for predicting the wall friction and heat transfer for any velocity ratio of the surface and the free stream.

  9. The significance of visualising coronary blood flow in early onset severe growth restricted fetuses with reverse flow in the ductus venosus.

    PubMed

    Rizzo, Giuseppe; Capponi, Alessandra; Pietrolucci, Maria Elena; Boccia, Claudio; Arduini, Domenico

    2009-07-01

    To evaluate the incidence and significance of coronary blood flow visualisation in early onset severe intrauterine growth restriction (IUGR) fetuses and to assess its relationship with the presence of reverse flow in ductus venosus (DV). The examination of coronary artery was performed at a gestational age <26 weeks in 19 IUGR fetuses from mothers without medical complications and characterised by the presence of reverse flow in DV. Visualisation or non-visualisation of coronary circulation were compared with fetal and neonatal outcome. Coronary flow was seen in 7/19 (36.8%) of the IUGR fetuses and these fetuses showed a higher incidence of fetal death (71.4%vs. 16.6%, p = 0.044), delivery or fetal death at an earlier gestational age (23.71 vs. 26.57 weeks, p = 0.011) and a lower birthweight (310 vs. 586 g, p = 0.011). Kaplan-Meier survival analysis demonstrated that visualisation or non-visualisation of coronary flow in such fetuses provides an independent contribution in the prediction of the time interval between Doppler study and delivery or fetal death (chi square = 15.36, p < 0.001). Visualisation of coronary flow in IUGR fetuses with reverse flow in the DV identifies a subgroup of fetuses with a poorer fetal and neonatal outcome.

  10. Phenomenological theory of electro-osmotic effect and water management in polymer electrolyte proton-conducting membranes

    SciTech Connect

    Eikerling, M.; Kornyshev, A.A.; Kharkats, Yu.I.; Volfkovich, Yu.M.

    1998-08-01

    Partial dehydration of the proton-conducting membrane under working conditions is one of the major problems in low-temperature fuel cell technology. In this paper a model, which accounts for the electro-osmotically induced drag of water from anode to cathode and the counterflow in a hydraulic pressure gradient is proposed. A balance of these flows determines a gradient of water content across the membrane, which causes a decline of the current-voltage performance. Phenomenological transport equations coupled with the capillary pressure isotherm are used, involving the conductivity, permeability, and electro-osmotic drag coefficients dependent on the local water content. The effects of membrane parameters on current-voltage performance are investigated. A universal feature of the obtained current-voltage plots is the existence of a critical current at which the potential drop across the membrane increases dramatically due to the dehydration of membrane layers close to the anode. For a membrane with zero residual conductivity in its dry parts, the critical current is a limiting current. Well below the critical current the effect of dehydration is negligible and the current-voltage plot obeys Ohm`s law. The shape of the capillary pressure isotherm determines the nonohmic corrections. A comparison of the results of this study to those of the pertinent diffusion-type models reveals qualitatively different features, the convection model is found to be closer to experimental observations.

  11. High-Pressure Open-Channel On-Chip Electroosmotic Pump for Nanoflow High Performance Liquid Chromatography

    PubMed Central

    2015-01-01

    Here, we construct an open-channel on-chip electroosmotic pump capable of generating pressures up to ∼170 bar and flow rates up to ∼500 nL/min, adequate for high performance liquid chromatographic (HPLC) separations. A great feature of this pump is that a number of its basic pump units can be connected in series to enhance its pumping power; the output pressure is directly proportional to the number of pump units connected. This additive nature is excellent and useful, and no other pumps can work in this fashion. We demonstrate the feasibility of using this pump to perform nanoflow HPLC separations; tryptic digests of bovine serum albumin (BSA), transferrin factor (TF), and human immunoglobulins (IgG) are utilized as exemplary samples. We also compare the performance of our electroosmotic (EO)-driven HPLC with Agilent 1200 HPLC; comparable efficiencies, resolutions, and peak capacities are obtained. Since the pump is based on electroosmosis, it has no moving parts. The common material and process also allow this pump to be integrated with other microfabricated functional components. Development of this high-pressure on-chip pump will have a profound impact on the advancement of lab-on-a-chip devices. PMID:24495233

  12. High-pressure open-channel on-chip electroosmotic pump for nanoflow high performance liquid chromatography.

    PubMed

    Wang, Wei; Gu, Congying; Lynch, Kyle B; Lu, Joann J; Zhang, Zhengyu; Pu, Qiaosheng; Liu, Shaorong

    2014-02-18

    Here, we construct an open-channel on-chip electroosmotic pump capable of generating pressures up to ∼170 bar and flow rates up to ∼500 nL/min, adequate for high performance liquid chromatographic (HPLC) separations. A great feature of this pump is that a number of its basic pump units can be connected in series to enhance its pumping power; the output pressure is directly proportional to the number of pump units connected. This additive nature is excellent and useful, and no other pumps can work in this fashion. We demonstrate the feasibility of using this pump to perform nanoflow HPLC separations; tryptic digests of bovine serum albumin (BSA), transferrin factor (TF), and human immunoglobulins (IgG) are utilized as exemplary samples. We also compare the performance of our electroosmotic (EO)-driven HPLC with Agilent 1200 HPLC; comparable efficiencies, resolutions, and peak capacities are obtained. Since the pump is based on electroosmosis, it has no moving parts. The common material and process also allow this pump to be integrated with other microfabricated functional components. Development of this high-pressure on-chip pump will have a profound impact on the advancement of lab-on-a-chip devices.

  13. Electrostatic interactions and electro-osmotic properties of semipermeable surfaces

    NASA Astrophysics Data System (ADS)

    Maduar, Salim R.; Vinogradova, Olga I.

    2016-10-01

    We consider two charged semipermeable membranes which bound bulk electrolyte solutions and are separated by a thin film of salt-free liquid. Small ions permeate into the gap, which leads to a steric charge separation in the system. To quantify the problem, we define an effective surface charge density of an imaginary impermeable surface, which mimics an actual semipermeable membrane and greatly simplifies the analysis. The effective charge depends on separation, generally differs from the real one, and could even be of the opposite sign. From the exact and asymptotic solutions of the nonlinear Poisson-Boltzmann equation, we obtain the distribution of the potential and of ions in the system. We then derive explicit formulae for the disjoining pressure in the gap and electro-osmotic velocity and show that both are controlled by the effective surface charge.

  14. Electroosmotic sampling. Application to determination of ectopeptidase activity in organotypic hippocampal slice cultures.

    PubMed

    Xu, Hongjuan; Guy, Yifat; Hamsher, Amy; Shi, Guoyue; Sandberg, Mats; Weber, Stephen G

    2010-08-01

    We hypothesize that peptide-containing solutions pulled through tissue should reveal the presence and activity of peptidases in the tissue. Using the natural zeta-potential in the organotypic hippocampal slice culture (OHSC), physiological fluids can be pulled through the tissue with an electric field. The hydrolysis of the peptides present in the fluid drawn through the tissue can be determined using capillary HPLC with electrochemical detection of the biuret complexes of the peptides following a postcolumn reaction. We have characterized this new sampling method by measuring the flow rate, examining the use of internal standards, and examining cell death caused by sampling. The sampling flow rate ranges from 60 to 150 nL/min with a 150 microm (ID) sampling capillary with an electric field (at the tip of the capillary) from 30 to 60 V/cm. Cell death can be negligible with controlled sampling conditions. Using this sampling approach, we have electroosmotically pulled Leu-enkephalin through OHSCs to identify ectopeptidase activity in the CA3 region. These studies show that a bestatin-sensitive aminopeptidase may be critical for the hydrolysis of exogenous Leu-enkephalin, a neuropeptide present in the CA3 region of OHSCs.

  15. Optimizing electroosmotic pumping rates in a rectangular channel with vertical gratings

    NASA Astrophysics Data System (ADS)

    Lai, Anison K. R.; Chang, Chien-Cheng; Wang, Chang-Yi

    2017-08-01

    The Helmholtz-Smoluchowski (H-S) velocity is known to be an accurate and useful formula for estimating the electro-osmotic (EO) flow rates in a simple micro-channel with a thin electric-double layer. However, in case the channel cross section is not so simple, the usefulness of H-S velocity could be sharply limited. A case of fundamental interest representing this situation is a rectangular channel (comprising parallel plates) with built-in vertical gratings, in which the surfaces inside the channel may develop different normalized zeta potentials α (on the gratings) and β (on the side walls). In this study, analytical solutions are pursued under the Debye-Hückel approximation to obtain EO pumping rates in a rectangular channel with vertical gratings. In particular, we identify the conditions under which the H-S formula can be properly applied and investigate how the EO flow rates may deviate from those predicted by the H-S velocity with varying physical parameters. Moreover, a diagram of the optimal EO pumping rates on the α-β plane is introduced that accounts for the general features of the analysis, which is consistent with a mathematical model and may serve as a convenient guide for engineering design and applications.

  16. Electroosmotic pump performance is affected by concentration polarizations of both electrodes and pump

    PubMed Central

    Suss, Matthew E.; Mani, Ali; Zangle, Thomas A.; Santiago, Juan G.

    2010-01-01

    Current methods of optimizing electroosmotic (EO) pump performance include reducing pore diameter and reducing ionic strength of the pumped electrolyte. However, these approaches each increase the fraction of total ionic current carried by diffuse electric double layer (EDL) counterions. When this fraction becomes significant, concentration polarization (CP) effects become important, and traditional EO pump models are no longer valid. We here report on the first simultaneous concentration field measurements, pH visualizations, flow rate, and voltage measurements on such systems. Together, these measurements elucidate key parameters affecting EO pump performance in the CP dominated regime. Concentration field visualizations show propagating CP enrichment and depletion fronts sourced by our pump substrate and traveling at order mm/min velocities through millimeter-scale channels connected serially to our pump. The observed propagation in millimeter-scale channels is not explained by current propagating CP models. Additionally, visualizations show that CP fronts are sourced by and propagate from the electrodes of our system, and then interact with the EO pump-generated CP zones. With pH visualizations, we directly detect that electrolyte properties vary sharply across the anode enrichment front interface. Our observations lead us to hypothesize possible mechanisms for the propagation of both pump- and electrode-sourced CP zones. Lastly, our experiments show the dynamics associated with the interaction of electrode and membrane CP fronts, and we describe the effect of these phenomena on EO pump flow rates and applied voltages under galvanostatic conditions. PMID:21516230

  17. Electroosmotic Sampling. Application to Determination of Ectopeptidase Activity in Organotypic Hippocampal Slice Cultures

    PubMed Central

    Xu, Hongjuan; Guy, Yifat; Hamsher, Amy; Shi, Guoyue; Sandberg, Mats; Weber, Stephen G.

    2010-01-01

    We hypothesize that peptide-containing solutions pulled through tissue should reveal the presence and activity of peptidases in the tissue. Using the natural ζ-potential in the organotypic hippocampal slice culture (OHSC), physiological fluids can be pulled through the tissue with an electric field. The hydrolysis of the peptides present in the fluid drawn through the tissue can be determined using capillary HPLC with electrochemical detection of the biuret complexes of the peptides following a postcolumn reaction. We have characterized this new sampling method by measuring the flow rate, examining the use of internal standards, and examining cell death caused by sampling. The sampling flow rate ranges from 60 to 150 nL/min with a 150 μm (ID) sampling capillary with an electric field (at the tip of the capillary) from 30 to 60 V/cm. Cell death can be negligible with controlled sampling conditions. Using this sampling approach, we have electroosmotically pulled Leu-enkephalin through OHSCs to identify ectopeptidase activity in the CA3 region. These studies show that a bestatin-sensitive aminopeptidase may be critical for the hydrolysis of exogenous Leu-enkephalin, a neuropeptide present in the CA3 region of OHSCs. PMID:20669992

  18. Stent revascularization restores cortical blood flow and reverses tissue hypoxia in atherosclerotic renal artery stenosis but fails to reverse inflammatory pathways or glomerular filtration rate.

    PubMed

    Saad, Ahmed; Herrmann, Sandra M S; Crane, John; Glockner, James F; McKusick, Michael A; Misra, Sanjay; Eirin, Alfonso; Ebrahimi, Behzad; Lerman, Lilach O; Textor, Stephen C

    2013-08-01

    Atherosclerotic renal artery stenosis (ARAS) is known to reduce renal blood flow, glomerular filtration rate (GFR) and amplify kidney hypoxia, but the relationships between these factors and tubulointerstitial injury in the poststenotic kidney are poorly understood. The purpose of this study was to examine the effect of renal revascularization in ARAS on renal tissue hypoxia and renal injury. Inpatient studies were performed in patients with ARAS (n=17; >60% occlusion) before and 3 months after stent revascularization, or in patients with essential hypertension (n=32), during fixed Na(+) intake and angiotensin converting enzyme/angiotensin receptors blockers Rx. Single kidney cortical, medullary perfusion, and renal blood flow were measured using multidetector computed tomography, and GFR by iothalamate clearance. Tissue deoxyhemoglobin levels (R(2)*) were measured by blood oxygen level-dependent MRI at 3T, as was fractional kidney hypoxia (percentage of axial area with R(2)*>30/s). In addition, we measured renal vein levels of neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α. Pre-stent single kidney renal blood flow, perfusion, and GFR were reduced in the poststenotic kidney. Renal vein neutrophil gelatinase-associated lipocalin, tumor necrosis factor-α, monocyte chemoattractant protein-1, and fractional hypoxia were higher in untreated ARAS than in essential hypertension. After stent revascularization, fractional hypoxia fell (P<0.002) with increased cortical perfusion and blood flow, whereas GFR and neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α remained unchanged. These data demonstrate that despite reversal of renal hypoxia and partial restoration of renal blood flow after revascularization, inflammatory cytokines and injury biomarkers remained elevated and GFR failed to recover in ARAS. Restoration of vessel patency alone failed to

  19. A Systematic Review of Outcomes and Complications of Primary Fingertip Reconstruction Using Reverse-Flow Homodigital Island Flaps.

    PubMed

    Regmi, Subhash; Gu, Jia-xiang; Zhang, Nai-chen; Liu, Hong-jun

    2016-04-01

    Fingertip reconstruction using reverse-flow homodigital island flaps has been very popular over the years. However, the outcomes of reconstruction have not been clearly understood. In these circumstances, a systematic review of available literature is warranted. To assess the outcomes and complications of fingertip reconstruction using reverse-flow homodigital island flaps. To justify the usage of reverse-flow homodigital island flaps for fingertip reconstruction. A PubMed [MEDLINE] electronic database was searched (1985 to 15 April 2015). Retrospective case series that met the following criteria were included: (1) Study reported primary data; (2) Study included at least five cases of fingertip defects treated using reverse-flow homodigital island flaps; (3) Study reported outcomes and complications of fingertip reconstruction, either primary or delayed, using reverse-flow homodigital island flaps; (4) The study presented at least one of the following functional outcomes: Static two-point discrimination, return-to-work time, range of motion of distal interphalangeal joints; (5) The study presented at least one complication. Two review authors independently assessed search results, and two other review authors analyzed the data and resolved disagreements. The following endpoints were analyzed: survival rate of the flap, sensibility, and functional outcomes and complications. Eight studies were included in this review. The included studies were published between 1995 and 2014, and a total of 207 patients with 230 fingertip defects were reported. The overall survival rate of the flap was 98 % (including partial survival). The mean static two-point discrimination (2PD) was 7.2 mm. The average range of motion of the DIP joint was 63°. The average return-to-work time was 7 weeks after injury. On average, 2 % of the patient had complete flap necrosis, 5 % had partial flap necrosis, 4 % developed venous congestion, 4 % developed flexion contracture, and 12 % experienced

  20. Flow structure in continuous flow electrophoresis chambers

    NASA Technical Reports Server (NTRS)

    Deiber, J. A.; Saville, D. A.

    1982-01-01

    There are at least two ways that hydrodynamic processes can limit continiuous flow electrophoresis. One arises from the sensitivity of the flow to small temerature gradients, especially at low flow rates and power levels. This sensitivity can be suppressed, at least in principle, by providing a carefully tailored, stabilizing temperature gradient in the cooling system that surrounds the flow channel. At higher power levels another limitation arises due to a restructuring of the main flow. This restructuring is caused by buoyancy, which is in turn affected by the electro-osmotic crossflow. Approximate solutions to appropriate partial differential equations have been computed by finite difference methods. One set of results is described here to illustrate the strong coupling between the structure of the main (axial) flow and the electro-osmotic flow.

  1. Reversed flow of Atlantic deep water during the Last Glacial Maximum.

    PubMed

    Negre, César; Zahn, Rainer; Thomas, Alexander L; Masqué, Pere; Henderson, Gideon M; Martínez-Méndez, Gema; Hall, Ian R; Mas, José L

    2010-11-04

    The meridional overturning circulation (MOC) of the Atlantic Ocean is considered to be one of the most important components of the climate system. This is because its warm surface currents, such as the Gulf Stream, redistribute huge amounts of energy from tropical to high latitudes and influence regional weather and climate patterns, whereas its lower limb ventilates the deep ocean and affects the storage of carbon in the abyss, away from the atmosphere. Despite its significance for future climate, the operation of the MOC under contrasting climates of the past remains controversial. Nutrient-based proxies and recent model simulations indicate that during the Last Glacial Maximum the convective activity in the North Atlantic Ocean was much weaker than at present. In contrast, rate-sensitive radiogenic (231)Pa/(230)Th isotope ratios from the North Atlantic have been interpreted to indicate only minor changes in MOC strength. Here we show that the basin-scale abyssal circulation of the Atlantic Ocean was probably reversed during the Last Glacial Maximum and was dominated by northward water flow from the Southern Ocean. These conclusions are based on new high-resolution data from the South Atlantic Ocean that establish the basin-scale north to south gradient in (231)Pa/(230)Th, and thus the direction of the deep ocean circulation. Our findings are consistent with nutrient-based proxies and argue that further analysis of (231)Pa/(230)Th outside the North Atlantic basin will enhance our understanding of past ocean circulation, provided that spatial gradients are carefully considered. This broader perspective suggests that the modern pattern of the Atlantic MOC-with a prominent southerly flow of deep waters originating in the North Atlantic-arose only during the Holocene epoch.

  2. Determination of nitrate and nitrite in Hanford defense waste(HDW) by reverse polarity capillary zone electrophoresis (RPCE)method

    SciTech Connect

    Metcalf, S.G.

    1998-06-10

    This paper describes the first application of reverse polarity capillary zone electrophoresis (RPCE) for rapid and accurate determination of nitrate and nitrite in Hanford Defense Waste (HDW). The method development was carried out by using Synthetic Hanford Waste (SHW), followed by the analysis of 4 real HDW samples. Hexamethonium bromide (HMB) was used as electroosmotic flow modifier in borate buffer at pH 9.2 to decrease the electroosmotic flow (EOF) in order to enhance the speed of analysis and the resolution of nitrate and nitrite in high ionic strength HDW samples. The application of this capillary zone electrophoresis method, when compared with ion chromatography for two major components of HDW, nitrate and nitrite slightly reduced analysis time, eliminated most pre-analysis handling of the highly radioactive sample, and cut analysis wastes by more than 2 orders of magnitude. The analysis of real HDW samples that were validated by using sample spikes showed a concentration range of 1.03 to 1.42 M for both nitrate. The migration times of the real HDW and the spiked HDW samples were within a precision of less than 3% relative standard deviation. The selectivity ratio test used for peak confirmation of the spiked samples was within 96% of the real sample. Method reliability was tested by spiking the matrix with 72.4 mM nitrate and nitrite. Recoveries for these spiked samples were 93-103%.

  3. Reversible chemical delithiation/lithiation of LiFePO4: towards a redox flow lithium-ion battery.

    PubMed

    Huang, Qizhao; Li, Hong; Grätzel, Michael; Wang, Qing

    2013-02-14

    Reversible chemical delithiation/lithiation of LiFePO(4) was successfully demonstrated using ferrocene derivatives, based on which a novel energy storage system--the redox flow lithium-ion battery (RFLB), was devised by integrating the operation flexibility of a redox flow battery and high energy density of a lithium-ion battery. Distinct from the recent semi-solid lithium rechargeable flow battery, the energy storage materials of RFLB stored in separate energy tanks remain stationary upon operation, giving us a fresh perspective on building large-scale energy storage systems with higher energy density and improved safety.

  4. Reversible Information Flow across the Medial Temporal Lobe: The Hippocampus Links Cortical Modules during Memory Retrieval

    PubMed Central

    Cooper, Elisa; Henson, Richard N.

    2013-01-01

    A simple cue can be sufficient to elicit vivid recollection of a past episode. Theoretical models suggest that upon perceiving such a cue, disparate episodic elements held in neocortex are retrieved through hippocampal pattern completion. We tested this fundamental assumption by applying functional magnetic resonance imaging (fMRI) while objects or scenes were used to cue participants' recall of previously paired scenes or objects, respectively. We first demonstrate functional segregation within the medial temporal lobe (MTL), showing domain specificity in perirhinal and parahippocampal cortices (for object-processing vs scene-processing, respectively), but domain generality in the hippocampus (retrieval of both stimulus types). Critically, using fMRI latency analysis and dynamic causal modeling, we go on to demonstrate functional integration between these MTL regions during successful memory retrieval, with reversible signal flow from the cue region to the target region via the hippocampus. This supports the claim that the human hippocampus provides the vital associative link that integrates information held in different parts of cortex. PMID:23986252

  5. Large Eddy Simulation of the Vortex End in Reverse-Flow Centrifugal Separators

    NASA Astrophysics Data System (ADS)

    Pisarev, Gleb I.; Hoffmann, Alex C.; Peng, Weiming; Dijkstra, Henk A.

    2009-09-01

    Different CFD models of reverse-flow centrifugal separators, specifically swirl tubes, have been built in order to study and analyse in detail the phenomenon of the "end of the vortex." The present numerical work is based on—and compared with—previous experimental studies of this phenomenon. The numerical models were built in complete agreement with the geometrical configurations and operating conditions used in these earlier experimental studies [1, 2]. Two different types of swirl tubes were analyzed. One type was an in principle long tube with variable length in which the dependence on the vessel length of the behavior of the vortex core in a simple, well-defined geometry was studied. The other type was equipped with a wide "dust collection vessel" at the bottom, the depth of which was varied, to study the behaviour of the vortex core in a widely-used geometry. 3-D LES simulations were carried out using the commercial CFD package Star-CD. The bending of the vortex core to the wall of the vessel and its precessional motion, constituting the phenomenon of the end of the vortex, was seen in both types of geometries, and the obtained results are in very good agreement, both qualitatively and to an extent quantitatively, with previous experimental results [2].

  6. Use of horizontal subsurface flow constructed wetlands to treat reverse osmosis concentrate of rolling wastewater.

    PubMed

    Xu, Jingcheng; Zhao, Gang; Huang, Xiangfeng; Guo, Haobo; Liu, Wei

    2017-03-04

    According to the characteristics of the reverse osmosis concentrate (ROC) generated from iron and steel company, we used three sets of parallel horizontal subsurface flow (HSF) constructed wetlands (CWs) with different plants and substrate layouts to treat the high-salinity wastewater. The plant growth and removal efficiencies under saline condition were evaluated. The evaluation was based entirely on routinely collected water quality data and the physical and chemical characteristics of the plants (Phragmites australis, Typha latifolia, Iris wilsonii, and Scirpus planiculmis). The principal parameters of concern in the effluent were chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP). The results showed that the CWs were able to remove COD, TN, and TP from ROC. S. planiculmis was not suitable for the treatment of high-saline wastewater. The sequence of metals accumulated in CW plants was K>Ca>Na>Mg>Zn>Cu. More than 70% of metals were accumulated in the aboveground of P. australis. The CW filled with gravel and manganese ore and planted with P. australis and T. latifolia had the best performance of pollutant removal, with average removal of 49.96%, 39.45%, and 72.01% for COD, TN, and TP, respectively. The effluent water quality met the regulation in China. These results suggested that HSF CW planted with P. australis and T. latifolia can be applied for ROC pollutants removal.

  7. Experimental and numerical study of mixed convection with flow reversal in coaxial double-duct heat exchangers

    SciTech Connect

    Mare, Thierry; Voicu, Ionut; Miriel, Jacques; Galanis, Nicolas; Sow, Ousmane

    2008-04-15

    Velocity vectors in a vertical coaxial double-duct heat exchanger for parallel ascending flow of water under conditions of laminar mixed convection have been determined experimentally using the particle image velocimetry technique. The measured velocity distributions for large annular flow rates, resulting in an essentially isothermal environment for the stream in the inner tube, are in very good agreement with corresponding numerical predictions. For flow rates of the same order of magnitude in the inner tube and the annulus, and corresponding temperature differences of about 20 C, experimental observations show that flow reversal occurs simultaneously in both streams over large axial distances for both heating and cooling of the flow in the inner tube. (author)

  8. [Evaporating Droplet and Imaging Slip Flows

    NASA Technical Reports Server (NTRS)

    Larson, R. G.

    2002-01-01

    In this report, we summarize work on Evaporating Droplet and Imaging Slip Flows. The work was primarily performed by post-doc Hue Hu, and partially by grad students Lei Li and Danish Chopra. The work includes studies on droplet evaporation and its effects on temperature and velocity fields in an evaporating droplet, new 3-D microscopic particle image velocimetry and direct visualization on wall slip in a surfactant solution. With the exception of the slip measurements, these projects were those proposed in the grant application. Instead of slip flow, the original grant proposed imaging electro-osmotic flows. However, shortly after the grant was issued, the PI became aware of work on electro-osmotic flows by the group of Saville in Princeton that was similar to that proposed, and we therefore elected to carry out work on imaging slip flows rather than electro-osmotic flows.

  9. A computational study of the plasma-flow interplay in a reverse vortex microwave discharge for CO2 conversion

    NASA Astrophysics Data System (ADS)

    Vermeiren, Vincent; Bogaerts, Annemie; Plasmant University Of Antwerp Team

    2016-09-01

    The problem of global warming due to greenhouse gas emission is one of the most prominent and urgent problems of the 21st century. Recently, surface wave produced plasmas, created by a microwave discharge, have shown to be very efficient in the conversion of the main emitted greenhouse gas, namely CO2. This is the result of a high thermodynamic inequilibrium in which the CO2 is efficiently dissociated through vibrational excitation. Very promising results have been obtained in experiments using a reverse vortex gas flow. Although it is known that reverse vortex gas flows tend to create a pressure and temperature drop in the center, it is unclear which effect the flow and the plasma have on each other. In this study we model this interplay between the reverse vortex gas flow and the plasma, to get a deeper understanding of the underlying processes. As a first step, Argon gas is used due to its simpler chemistry, limiting the computational costs. In a next step, a reduced chemistry set of CO2 will be implemented.

  10. Optimization of multiple turbine arrays in a channel with tidally reversing flow by numerical modelling with adaptive mesh.

    PubMed

    Divett, T; Vennell, R; Stevens, C

    2013-02-28

    At tidal energy sites, large arrays of hundreds of turbines will be required to generate economically significant amounts of energy. Owing to wake effects within the array, the placement of turbines within will be vital to capturing the maximum energy from the resource. This study presents preliminary results using Gerris, an adaptive mesh flow solver, to investigate the flow through four different arrays of 15 turbines each. The goal is to optimize the position of turbines within an array in an idealized channel. The turbines are represented as areas of increased bottom friction in an adaptive mesh model so that the flow and power capture in tidally reversing flow through large arrays can be studied. The effect of oscillating tides is studied, with interesting dynamics generated as the tidal current reverses direction, forcing turbulent flow through the array. The energy removed from the flow by each of the four arrays is compared over a tidal cycle. A staggered array is found to extract 54 per cent more energy than a non-staggered array. Furthermore, an array positioned to one side of the channel is found to remove a similar amount of energy compared with an array in the centre of the channel.

  11. Implicit time-marching solution of the Navier-Stokes equations for thrust reversing and thrust vectoring nozzle flows

    NASA Technical Reports Server (NTRS)

    Imlay, S. T.

    1986-01-01

    An implicit finite volume method is investigated for the solution of the compressible Navier-Stokes equations for flows within thrust reversing and thrust vectoring nozzles. Thrust reversing nozzles typically have sharp corners, and the rapid expansion and large turning angles near these corners are shown to cause unacceptable time step restrictions when conventional approximate factorization methods are used. In this investigation these limitations are overcome by using second-order upwind differencing and line Gauss-Siedel relaxation. This method is implemented with a zonal mesh so that flows through complex nozzle geometries may be efficiently calculated. Results are presented for five nozzle configurations including two with time varying geometries. Three cases are compared with available experimental data and the results are generally acceptable.

  12. Effects of verapamil, nifedipine, and daflon on the viability of reverse-flow island flaps in rats.

    PubMed

    Kilinc, Hidir; Aslan, Suleyman Serkan; Bilen, Bilge Turk; Eren, Ahmet Tuna; Karadag, Nese; Karabulut, Aysun Bay

    2013-11-01

    Reverse-flow flaps are preferable in reconstructive surgery due to their several advantages. However, they may have venous insufficiency and poor blood flow. In this study, effects of various pharmacological agents on the viability of reverse-flow flaps were investigated. Forty Sprague-Dawley rats were used. Superficial epigastric artery- and superficial epigastric vein-based reverse-flow island flaps were preferred. The rats were divided into 4 groups. Group 1 was considered as the control group. Group 2 was given verapamil 0.3 mg/kg per day, group 3 nifedipine 0.5 mg/kg per day, and group 4 Daflon 80 mg/kg per day for 7 days. On day 7, viable flap areas were measured, angiography was performed, serum nitric oxide levels were evaluated, and histopathological examination was done.The mean flap viability rate was 67.59% (±13.12259) in group 1, 77.38% (±4.12506) in group 2, 74.57% (±3.44780) in group 3, and 85.39% (±4.36125) in group 4 (P = 0.001). The mean nitric oxide level was 31.66 μmol/dL (±2.42212) in group 1, 51.00 μmol/dL (±2.96648) in group 2, 34.00 μmol/dL (±2.96648) in group 3, and 47.66 μmol/dL (±2.80476) in group 4 (P = 0.001). On angiography, there were vessel dilations and convolutions in group 2; capillaries became noticeable, and anastomotic vessels extended toward the more distal part of the flaps in group 4. Histological examinations showed severe inflammation in group 3 and minimal inflammation and venous vasodilatation in group 2.Verapamil and Daflon in therapeutic doses significantly increased the viability of reverse-flow island flaps. However, nifedipine did not make a significant contribution to the flap viability. The results of this study will contribute to the literature about the hemodynamics of reverse-flow island flaps and guide further studies on the issue.

  13. Stent Revascularization Restores Cortical Blood Flow and Reverses Tissue Hypoxia in Atherosclerotic Renal Artery Stenosis, But Fails To Reverse Inflammatory Pathways or GFR

    PubMed Central

    Saad, Ahmed; Herrmann, Sandra M.S.; Crane, John; Glockner, James F; Mckusick, Michael A; Misra, Sanjay; Eirin, Alfonso; Ebrahimi, Behzad; Lerman, Lilach O.; Textor, Stephen C.

    2013-01-01

    Background Atherosclerotic renal artery stenosis (ARAS) is known to reduce renal blood flow (RBF), glomerular filtration rate (GFR) and amplify kidney hypoxia, but the relationships between these factors and tubulo-interstitial injury in the post-stenotic kidney are poorly understood. The purpose of this study was to examine the effect of renal revascularization in ARAS on renal tissue hypoxia and renal injury. Methods and Results Inpatient studies performed in ARAS patients (n = 17), more than 60% occlusion) before and 3 months after stent revascularization, or patients with essential hypertension (EH) (n = 32), during fixed Na+ intake and ACE/ARB Rx. Single-kidney (SK) cortical, medullary perfusion and RBF measured using multidetector CT, and GFR by iothalamate clearance. Tissue deoxyhemoglobin levels (R2*) measured by Blood Oxygen Level Dependent (BOLD) MRI at 3T, as was fractional kidney hypoxia (% of axial area with R2* > 30/s). In addition, we measured renal vein levels of Neutrophil gelatinase-associated lipocalin (NGAL), monocyte chemotactic protein-1 (MCP-1) and Tumor necrosis factor (TNF-α). Pre-stent SK-RBF, perfusion, and GFR were reduced in the post-stenotic kidney. Renal vein NGAL, TNF-α, MCP-1 and fractional hypoxia were higher in untreated ARAS than EH. After stent revascularization, fractional hypoxia fell (p < 0.002) with increased cortical perfusion and blood flow, while GFR and NGAL, MCP-1 and TNF-α remained unchanged. Conclusions These data demonstrate that despite reversal of renal hypoxia and partial restoration of RBF after revascularization, inflammatory cytokines and injury biomarkers remained elevated and GFR failed to recover in ARAS. Restoration of vessel patency alone failed to reverse tubulointerstitial damage and partly explains the limited clinical benefit of renal stenting. These results identify potential therapeutic targets for recovery of kidney function in renovascular disease. PMID:23899868

  14. CO2 saturated water as two-phase flow for fouling control in reverse electrodialysis.

    PubMed

    Moreno, J; de Hart, N; Saakes, M; Nijmeijer, K

    2017-08-09

    When natural feed waters are used in the operation of a reverse electrodialysis (RED) stack, severe fouling on the ion exchange membranes and spacers occurs. Fouling of the RED stack has a strong influence on the gross power density output; which can decrease up to 50%. Moreover, an increase in the pressure loss occurs between the feed water inlet and outlet, increasing the pumping energy and thus decreasing the net power density that can be obtained. In this work, we extensively investigated the use of CO2 saturated water as two-phase flow cleaning for fouling mitigation in RED using natural feed waters. Experiments were performed in the REDstack research facility located at the Afsluitdijk (the Netherlands) using natural feed waters for a period of 60 days. Two different gas combinations were experimentally investigated, water/air sparging and water/CO2 (saturated) injection. Air is an inert gas mixture and induces air sparging in the stack. In the case of CO2, nucleation, i.e. the spontaneous formation of bubbles, occurs at the spacer filaments due to depressurization of CO2 saturated water, inducing cleaning. Results showed that stacks equipped with CO2 saturated water can produce an average net power density of 0.18 W/m(2) under real fouling conditions with minimal pre-treatment and at a low outside temperature of only 8 °C, whereas the stacks equipped with air sparging could only produce an average net power density of 0.04 W/m(2). Electrochemical impedance spectroscopy measurements showed that the stacks equipped with air sparging increased in stack resistance due to the presence of stagnant bubbles remaining in the stack after every air injection. Furthermore, the introduction of CO2 gas in the feed water introduces a pH decrease in the system (carbonated solution) adding an additional cleaning effect in the system, thus avoiding the use of environmentally unwanted cleaning chemicals. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights

  15. Graphitic carbon coupled poly(anthraquinone) for proton shuttle flow-in-a-cell application.

    PubMed

    Mathi, Selvam; Kumar, Rudra; Nagarale, Rajaram K; Sharma, Ashutosh

    2017-03-13

    Coupled electron and proton transport are an integral part of non-gassing electro-osmotic pumps (EOP). The kinetics of the electrode limits the kinetics of the electron transfer and hence the flow. This is observed in the present study with newly synthesized graphitic carbon covalently coupled to poly(anthraquinone) (PAQ). When EOP with identical electrodes were assembled, proton shuttle maintained the reversible flow, which was linearly dependent on the ks values. A Laviron plot was used to calculate the electron-transfer rate constant ks and transfer coefficient α, and their linear dependency on content of graphitic carbon was observed. The best ks value obtained was 0.67 s(-1) for 15PAQ. The sandwich-type flow-in-a-cell showed the best result of ∼40 μL min(-1) cm(-1) V(-1) electro-osmotic flux for 15PAQ. It reveals that a balanced combination of graphitic carbon and PAQ is the prime requirement for high-performance electrode materials to be used in microfluidic devices and energy applications.

  16. Effects of flow-path variations on internal reversing flow in a tailpipe offtake configuration for ASTOVL aircraft

    NASA Technical Reports Server (NTRS)

    Mcardle, Jack G.; Esker, Barbara S.

    1993-01-01

    A one-third-scale model of a generic tailpipe offtake system for an advanced short takeoff, vertical landing (ASTOVL) aircraft was tested at the NASA Lewis Research Center Powered Lift Facility. The basic model consisted of a tailpipe with a center body to form an annulus simulating turbine outflow with no swirl; twin offtake ducts with elbows at the ends to turn the flow to a downward direction; flow control nozzles at the ends of the elbows; and a blind flange at the end of the tailpipe to simulate a closed cruise nozzle. The offtake duct-to-tailpipe diameter ratio was 0.74. Modifications of a generic nature were then made to this basic configuration to measure the effects of flow-path changes on the flow and pressure-loss characteristics. The modifications included adding rounded entrances at the forward edges of the offtake openings, blocking the tailpipe just aft the openings instead of at the cruise nozzle, changing the location of the openings along the tailpipe, removing the center body, and varying the Mach number (flow rate) over a wide range in the tailpipe ahead of the openings by changing the size of the flow control nozzles. The tests were made with unheated air at tailpipe-to-ambient pressure ratios from 1.4 to 5. Results are presented and compared with performance graphs, total-pressure contour plots, paint streak flow visualization photographs, and a flow-angle probe traverse at the offtake entrance.

  17. Effects of discrete-electrode arrangement on traveling-wave electroosmotic pumping

    NASA Astrophysics Data System (ADS)

    Liu, Weiyu; Shao, Jinyou; Ren, Yukun; Wu, Yupan; Wang, Chunhui; Ding, Haitao; Jiang, Hongyuan; Ding, Yucheng

    2016-09-01

    Traveling-wave electroosmotic (TWEO) pumping arises from the action of an imposed traveling-wave (TW) electric field on its own induced charge in the diffuse double layer, which is formed on top of an electrode array immersed in electrolyte solutions. Such a traveling field can be merely realized in practice by a discrete electrode array upon which the corresponding voltages of correct phase are imposed. By employing the theory of linear and weakly nonlinear double-layer charging dynamics, a physical model incorporating both the nonlinear surface capacitance of diffuse layer and Faradaic current injection is developed herein in order to quantify the changes in TWEO pumping performance from a single-mode TW to discrete electrode configuration. Benefiting from the linear analysis, we investigate the influence of using discrete electrode array to create the TW signal on the resulting fluid motion, and several approaches are suggested to improve the pumping performance. In the nonlinear regime, our full numerical analysis considering the intervening isolation spacing indicates that a practical four-phase discrete electrode configuration of equal electrode and gap width exhibits stronger nonlinearity than expected from the idealized pump applied with a single-mode TW in terms of voltage-dependence of the ideal pumping frequency and peak flow rate, though it has a much lower pumping performance. For model validation, pumping of electrolytes by TWEO is achieved over a confocal spiral four-phase electrode array covered by an insulating microchannel; measurement of flow velocity indicates the modified nonlinear theory considering moderate Faradaic conductance is indeed a more accurate physical description of TWEO. These results offer useful guidelines for designing high-performance TWEO microfluidic pumps with discrete electrode array.

  18. Analysis of HRCT-derived xylem network reveals reverse flow in some vessels

    USDA-ARS?s Scientific Manuscript database

    Flow in xylem vessels is modeled based on constructions of three dimensional xylem networks derived from High Resolution Computed Tomography (HRCT) images of grapevine (Vitis vinifera) stems. Flow in 6-14% of the vessels was found to be oriented in the opposite direction to the bulk flow under norma...

  19. Issues in measure-preserving three dimensional flow integrators: Self-adjointness, reversibility, and non-uniform time stepping

    SciTech Connect

    Finn, John M.

    2015-03-01

    Properties of integration schemes for solenoidal fields in three dimensions are studied, with a focus on integrating magnetic field lines in a plasma using adaptive time stepping. It is shown that implicit midpoint (IM) and a scheme we call three-dimensional leapfrog (LF) can do a good job (in the sense of preserving KAM tori) of integrating fields that are reversible, or (for LF) have a 'special divergence-free' property. We review the notion of a self-adjoint scheme, showing that such schemes are at least second order accurate and can always be formed by composing an arbitrary scheme with its adjoint. We also review the concept of reversibility, showing that a reversible but not exactly volume-preserving scheme can lead to a fractal invariant measure in a chaotic region, although this property may not often be observable. We also show numerical results indicating that the IM and LF schemes can fail to preserve KAM tori when the reversibility property (and the SDF property for LF) of the field is broken. We discuss extensions to measure preserving flows, the integration of magnetic field lines in a plasma and the integration of rays for several plasma waves. The main new result of this paper relates to non-uniform time stepping for volume-preserving flows. We investigate two potential schemes, both based on the general method of Ref. [11], in which the flow is integrated in split time steps, each Hamiltonian in two dimensions. The first scheme is an extension of the method of extended phase space, a well-proven method of symplectic integration with non-uniform time steps. This method is found not to work, and an explanation is given. The second method investigated is a method based on transformation to canonical variables for the two split-step Hamiltonian systems. This method, which is related to the method of non-canonical generating functions of Ref. [35], appears to work very well.

  20. Vortex pairing and reverse cascade in a simulated two-dimensional rocket motor-like flow field

    NASA Astrophysics Data System (ADS)

    Chakravarthy, Kalyana; Chakraborty, Debasis

    2017-07-01

    Two-dimensional large eddy simulation of a flow experiment intended for studying and understanding transition and parietal vortex shedding has brought to light some interesting features that have never been seen in previous similar simulations and have implications for future computational work on combustion instabilities in rocket motors. The frequency spectrum of pressure at head end shows a peak at the expected value associated with parietal vortex shedding but an additional peak at half this frequency emerges at downstream location. Using vorticity spectra at various distances away from the wall, it is shown that the frequency halving is due to vortex pairing as hypothesized by Dunlap et al. ["Internal flow field studies in a simulated cylindrical port rocket chamber," J. Propul. Power 6(6), 690-704 (1990)] for a similar experiment. As the flow transitions to turbulence towards the nozzle end, inertial range with Kolmogorov scaling becomes evident in the velocity spectrum. Given that the simulation is two-dimensional, such a scaling could be associated with a reverse energy cascade as per Kraichnan-Leith-Bachelor theory. By filtering the simulated flow field and identifying where the energy backscatters into the filtered scales, the regions with a reverse cascade are identified. The implications of this finding on combustion modeling are discussed.

  1. In-situ monitoring the realkalisation process by neutron diffraction: Electroosmotic flux and portlandite formation

    SciTech Connect

    Castellote, Marta . E-mail: martaca@ietcc.csic.es; Llorente, Irene; Andrade, Carmen; Turrillas, Xavier; Alonso, Cruz; Campo, Javier

    2006-05-15

    Even though the electroosmotic flux through hardened cementitious materials during laboratory realkalisation trials had been previously noticed, it has never been in-situ monitored, analysing at the same time the establishment of the electroosmotic flux and the microstructure changes in the surroundings of the rebar. In this paper, two series of cement pastes, cast with CEM I and CEM I substituted in a 35% by fly ash, previously carbonated at 100% CO{sub 2}, were submitted to realkalisation treatments followed on line by simultaneous acquisition of neutron diffraction data. As a result, it has been possible to confirm the electroosmosis as the driving force of carbonates towards the rebar and to determine the range of pH in the anolyte in which most of the relevant electroosmotic phenomena takes place. On the other hand, the behaviour of the main crystalline phases involved in the process has been monitored during the treatment, with the precipitation of portlandite as main result.

  2. The electroosmotic droplet switch: countering capillarity with electrokinetics.

    PubMed

    Vogel, Michael J; Ehrhard, Peter; Steen, Paul H

    2005-08-23

    Electroosmosis, originating in the double-layer of a small liquid-filled pore (size R) and driven by a voltage V, is shown to be effective in pumping against the capillary pressure of a larger liquid droplet (size B) provided the dimensionless parameter sigmaR(2)/epsilon|zeta|VB is small enough. Here sigma is surface tension of the droplet liquid/gas interface, epsilon is the liquid dielectric constant, and zeta is the zeta potential of the solid/liquid pair. As droplet size diminishes, the voltage required to pump electroosmotically scales as V approximately R(2)/B. Accordingly, the voltage needed to pump against smaller higher-pressure droplets can actually decrease provided the pump poresize scales down with droplet size appropriately. The technological implication of this favorable scaling is that electromechanical transducers made of moving droplets, so-called "droplet transducers," become feasible. To illustrate, we demonstrate a switch whose bistable energy landscape derives from the surface energy of a droplet-droplet system and whose triggering derives from the electroosmosis effect. The switch is an electromechanical transducer characterized by individual addressability, fast switching time with low voltage, and no moving solid parts. We report experimental results for millimeter-scale droplets to verify key predictions of a mathematical model of the switch. With millimeter-size water droplets and micrometer-size pores, 5 V can yield switching times of 1 s. Switching time scales as B(3)/VR(2). Two possible "grab-and-release" applications of arrays of switches are described. One mimics the controlled adhesion of an insect, the palm beetle; the other uses wettability to move a particle along a trajectory.

  3. Fouling and its reversibility in relation to flow properties and module design in aerated hollow fibre modules for membrane bioreactors.

    PubMed

    Pollet, S; Guigui, C; Cabassud, C

    2008-01-01

    Nowadays, most membrane bioreactors are using membranes submerged in the biomass and aeration in the concentrate compartment to limit or to control fouling. An important issue for the design of modules or membrane bundles in MBRs is to understand how the air/liquid flow is behaving and influencing fouling and its reversibility in relationship to the module properties. This paper focuses on an innovative and very specific process, in which HF membranes are put in a cartridge outside the activated sludge tank and a recycling loop is associated to the cartridge in order to decrease concentration of foulant species at the membrane surface and mass transfer resistance. Recycling operates with a very low liquid velocity in the module (a few cm.s(-1)) which constitutes a specificity of this process in terms of filtration operation. The aim of this study is to characterise two-phase flow and its effects on fouling and fouling reversibility at the scale of a semi-industrial bundle of outside/in hollow fibres, and as a function of bundle properties (packing density, fibre diameter), using specific methods to characterise the flow and fouling effects. Two modules were used showing a different packing density. Filtration was operated at constant permeate flux with clay suspension at 0.65 g.l(-1) in the same hydrodynamic conditions. Fouling kinetics and irreversibility were characterised by an adapted step method, and gas and liquid flows were characterised at global scale by residence time distribution analyses and gas hold-up. Fouling velocities are clearly influenced by gas velocity. The proportion of dead to total volume in the module is mainly affected by the liquid flow velocity and module design. The module with the higher fibre diameter and the lower packing density showed better performances in terms of fouling which was correlated with better flow properties.

  4. Local measurements of tearing mode flows and the magnetohydrodynamic dynamo in the Madison Symmetric Torus reversed-field pinch

    SciTech Connect

    Ennis, D. A.; Gangadhara, S.; Den Hartog, D. J.; Ebrahimi, F.; Fiksel, G.; Prager, S. C.; Craig, D.; Anderson, J. K.

    2010-08-15

    The first localized measurements of tearing mode flows in the core of a hot plasma are presented using nonperturbing measurements of the impurity ion flow. Emission from charge exchange recombination is collected by a novel high optical throughput duo spectrometer providing localized ({+-}1 cm) measurements of C{sup +6} impurity ion velocities resolved to <500 m/s with high bandwidth (100 kHz). Poloidal tearing mode flows in the Madison Symmetric Torus reversed-field pinch are observed to be localized to the mode resonant surface with a radial extent much broader than predicted by linear magnetohydrodynamic (MHD) theory but comparable to the magnetic island width. The relative poloidal flow amplitudes among the dominant core modes do not reflect the proportions of the magnetic amplitudes. The largest correlated flows are associated with modes having smaller magnetic amplitudes resonant near the midradius. The MHD dynamo due to these flows on the magnetic axis is measured to be adequate to balance the mean Ohm's law during reduced tearing activity and is significant but does not exclude other dynamo mechanisms from contributing during a surge in reconnection activity.

  5. Time-domain delay-and-sum beamforming for time-reversal detection of intermittent acoustic sources in flows.

    PubMed

    Rakotoarisoa, Ifanila; Fischer, Jeoffrey; Valeau, Vincent; Marx, David; Prax, Christian; Brizzi, Laurent-Emmanuel

    2014-11-01

    This study focuses on the identification of intermittent aeroacoustic sources in flows by using the time-domain beamforming technique. It is first shown that this technique can be seen as a time-reversal (TR) technique, working with approximate Green functions in the case of a shear flow. Some numerical experiments investigate the case of an array measurement of a generic acoustic pulse emitted in a wind-tunnel flow, with a realistic multi-arm spiral array. The results of the time-domain beamforming successfully match those given by a numerical TR technique over a wide range of flow speeds (reaching the transonic regime). It is shown how the results should be analyzed in a focusing plane parallel to the microphone array in order to estimate the location and emission time of the pulse source. An experimental application dealing with the aeroacoustic radiation of a bluff body in a wind-tunnel flow is also considered, and shows that some intermittent events can be clearly identified in the noise radiation. Time-domain beamforming is then an efficient tool for analyzing intermittent acoustic sources in flows, and is a computationally cheaper alternative to the numerical TR technique, which should be used for complex configurations where the Green function is not available.

  6. Clinical significance of reversal of flow in the vertebral artery identified on cerebrovascular duplex ultrasound.

    PubMed

    Policha, Aleksandra; Baldwin, Melissa; Lee, Victoria; Adelman, Mark A; Rockman, Caron; Berland, Todd; Cayne, Neal S; Maldonado, Thomas S

    2017-09-18

    Reversal of flow in the vertebral artery (RFVA) is an uncommon finding on cerebrovascular duplex ultrasound examination. The clinical significance of RFVA and the natural history of patients presenting with it are poorly understood. Our objective was to better characterize the symptoms and outcomes of patients presenting with RFVA. A retrospective review was performed of all cerebrovascular duplex ultrasound studies performed at our institution between January 2010 and January 2016 (N = 2927 patients). Individuals with RFVA in one or both vertebral arteries were included in the analysis. Seventy-four patients (74/2927 patients [2.5%]) with RFVA were identified. Half of the patients were male. Mean age at the time of the first ultrasound study demonstrating RFVA was 71 years (range, 27-92 years); 78% of patients had hypertension, 28% were diabetic, and 66% were current or former smokers. Indications for the ultrasound examination were as follows: 44% screening/asymptomatic, 7% anterior circulation symptoms, 20% posterior circulation symptoms, 28% follow-up studies after cerebrovascular intervention, and 5% upper extremity symptoms. At the time of the initial ultrasound examination, 21 patients (28%) had evidence of a prior carotid intervention (carotid endarterectomy or carotid stenting), 21 patients had evidence of moderate (50%-79%) carotid artery stenosis (CAS) in at least one carotid artery, and 12 patients (16%) had evidence of severe (>80%) CAS. Of the 15 patients presenting with posterior circulation symptoms, 11 (73%) had evidence of concomitant CAS. In contrast, 22 of the 59 patients (37%) without posterior circulation symptoms had duplex ultrasound findings of CAS (P = .01). The mean duration of follow-up was 28 ± 22 months. Follow-up data were available for 63 patients (85%), including the 15 patients who presented with posterior circulation symptoms. Of these 15 patients, 5 underwent subclavian artery revascularization, including balloon

  7. Particle Deformation and Concentration Polarization in Electroosmotic Transport of Hydrogels through Pores

    SciTech Connect

    Vlassiouk, Ivan V

    2013-01-01

    In this article, we report detection of deformable, hydrogel particles by the resistive-pulse technique using single pores in a polymer film. The hydrogels pass through the pores by electroosmosis and cause formation of a characteristic shape of resistive pulses indicating the particles underwent dehydration and deformation. These effects were explained via a non-homogeneous pressure distribution along the pore axis modeled by the coupled Poisson-Nernst-Planck and Navier Stokes equations. The local pressure drops are induced by the electroosmotic fluid flow. Our experiments also revealed the importance of concentration polarization in the detection of hydrogels. Due to the negative charges as well as branched, low density structure of the hydrogel particles, concentration of ions in the particles is significantly higher than in the bulk. As a result, when electric field is applied across the membrane, a depletion zone can be created in the vicinity of the particle observed as a transient drop of the current. Our experiments using pores with openings between 200 and 1600 nm indicated the concentration polarization dominated the hydrogels detection for pores wider than 450 nm. The results are of importance for all studies that involve transport of molecules, particles and cells through pores with charged walls. The developed inhomogeneous pressure distribution can potentially influence the shape of the transported species. The concentration polarization changes the interpretation of the resistive pulses; the observed current change does not necessarily reflect only the particle size but also the size of the depletion zone that is formed in the particle vicinity.

  8. Removal of volatile organic compounds from air streams by making use of a microwave plasma burner with reverse vortex flows

    NASA Astrophysics Data System (ADS)

    Kim, Ji H.; Ma, Suk H.; Cho, Chang H.; Hong, Yong C.; Ahn, Jae Y.

    2014-01-01

    We developed an atmospheric-pressure microwave plasma burner for removing volatile organic compounds (VOCs) from polluted air streams. This study focused on the destruction of the VOCs in the high flow rate polluted streams required for industrial use. Plasma flames were sustained by injecting liquefied natural gas (LNG), which is composed of CH4, into the microwave plasma torch. With its high temperature and high density of atomic oxygen, the microwave torch attained nearly complete combustion of LNG, thereby providing a large-volume, high-temperature plasma flame. The plasma flame was applied to reactors in which the polluted streams were in one of two vortex flows: a conventional vortex reactor (CVR) or a reverse vortex reactor (RVR). The RVR, using a plasma power of 2 kW and an LNG flow of 20 liters per minute achieved a destruction removal efficiency (DRE) of 98% for an air flow rate of 5 Nm3/min polluted with 550 pm of VOCs.. For the same experimental parameters, the CVR provided a DRE of 90.2%. We expect that this decontamination system will prove effective in purifying contaminated air at high flow rates.

  9. Impact of the BEA zeolite morphology on isobutane adsorption followed by Reversed-Flow Inverse Gas Chromatography.

    PubMed

    Batalha, N; Soualah, A; Pinard, L; Pouilloux, Y; Lemos, F; Belin, T

    2012-10-19

    The mass transfer phenomena of isobutane (i-C4) were investigated at 343K on three protonic BEA zeolites. Defined by their crystallites sizes and degrees of aggregation, these samples were characterized by Reversed-Flow Inverse Gas Chromatography (RF-GC). This simple technique, used in conjunction with numerical computation, allowed the determination of physicochemical quantities like local monolayer capacities, probability density functions and diffusion coefficients in a time-resolved way. This study enabled to conclude that the effective diffusion coefficient was affected by the size of the zeolite agglomerate whereas the surface diffusion depended on the zeolite crystallite size. Copyright © 2012 Elsevier B.V. All rights reserved.

  10. Hydrogen production from continuous flow, microbial reverse-electrodialysis electrolysis cells treating fermentation wastewater.

    PubMed

    Watson, Valerie J; Hatzell, Marta; Logan, Bruce E

    2015-11-01

    A microbial reverse-electrodialysis electrolysis cell (MREC) was used to produce hydrogen gas from fermentation wastewater without the need for additional electrical energy. Increasing the number of cell pairs in the reverse electrodialysis stack from 5 to 10 doubled the maximum current produced from 60 A/m(3) to 120 A/m(3) using acetate. However, more rapid COD removal required a decrease in the anolyte hydraulic retention time (HRT) from 24 to 12 h to stabilize anode potentials. Hydrogen production using a fermentation wastewater (10 cell pairs, HRT=8 h) reached 0.9±0.1 L H2/Lreactor/d (1.1±0.1 L H2/g-COD), with 58±5% COD removal and a coulombic efficiency of 74±5%. These results demonstrated that consistent rates of hydrogen gas production could be achieved using an MREC if effluent anolyte COD concentrations are sufficient to produce stable anode potentials.

  11. X-ray Diffraction Studies of Forward and Reverse Plastic Flow in Nanoscale Layers during Thermal Cycling

    SciTech Connect

    Gram, Michael D; Carpenter, John S; Payzant, E Andrew; Misra, Amit; Anderson, Peter M

    2013-01-01

    The biaxial stress-strain response of layers within Cu/Ni nanolaminates is determined from in-plane x-ray diffraction spectra during heating/cooling. Thinner (11 nm) Cu and Ni layers with coherent, cube-on-cube interfaces reach ~1.8 GPa (Cu) and ~2.9 GPa (Ni) without yielding. Thicker (21 nm) layers with semi-coherent interfaces exhibit unusual plastic phenomena, including extraordinary plastic work hardening rates, and forward vs. reverse plastic flow with small (~10%) changes in stress, and evidence that threshold plastic stress in Ni layers is altered by preceding plastic flow in Cu layers. Line energy, pinning strength, net interfacial dislocation density and hardness are provided.

  12. A modified DRIL procedure by flow reversal of an aborted distal cephalic vein for critical hand ischaemia.

    PubMed

    Danzer, D; Czerny, M; Widmer, M K

    2011-09-01

    Treatment of dialysis access-related hand ischaemia with preservation of the access remains an issue. We report the case of a patient presenting critical hand ischaemia 2 years after proximalisation of a distal radio-cephalic fistula with preservation of the original access. After valvulotomy, the distal cephalic vein was used as in situ bypass and directly anastomosed to the distal brachial artery, providing a direct flow to the hand. This procedure relieved the hand ischaemia without sacrificing the functioning fistula. Six months later, the fistula and bypass were still patent, showing that flow reversal of a previous fistula can be an efficient strategy to correct dialysis access-related hand ischaemia in selected cases.

  13. Recovery of rectified signals from hot-wire/film anemometers due to flow reversal in oscillating flows.

    PubMed

    Yang, Yingchen; Jones, Douglas L; Liu, Chang

    2010-01-01

    Hot-wire/film anemometers have been broadly used in experimental studies in fluid mechanics, acoustics, and ocean engineering. Yet, it is well known that hot-wire/film anemometers rectify the signal outputs due to the lack of sensitivity to flow direction. This main drawback, in turn, makes them less useful for diverse fluctuating flow measurements. To solve this issue, a rectification recovery method has been developed based on reconstruction of the Fourier series expansion in conjunction with signal-squaring approach. This signal recovery method was experimentally examined and proven to be successful for both conventional and microfabricated hot-wire/film anemometers. The method was further applied to dipole field measurements, with data from recovered signals perfectly matching the analytical model of the dipole field.

  14. Internal reversing flow in a tailpipe offtake configuration for SSTOVL aircraft

    NASA Technical Reports Server (NTRS)

    Mcardle, Jack G.; Esker, Barbara S.; Rhodes, James A.

    1992-01-01

    A generic one-third scale model of a tailpipe offtake system for a supersonic short takeoff vertical landing (SSTOVL) aircraft was tested at LeRC Powered Lift Facility. The model consisted of a tailpipe with twin elbows, offtake ducts, and flow control nozzles, plus a small ventral nozzle and a blind flange to simulate a blocked cruise nozzle. The offtake flow turned through a total angle of 177 degrees relative to the tailpipe inlet axis. The flow split was 45 percent to each offtake and 10 percent to the ventral nozzle. The main test objective was to collect data for comparison to the performance of the same configuration predicted by a computational fluid dynamics (CFD) analysis. Only the experimental results are given - the analytical results are published in a separate paper. Performance tests were made with unheated air at tailpipe-to-ambient pressure ratios up to 5. The total pressure loss through the offtakes was as high as 15.5 percent. All test results are shown as graphs, contour plots, and wall pressure distributions. The complex flow patterns in the tailpipe and elbows at the offtake openings are described with traversing flow angle probe and paint streak flow visualization data.

  15. Internal reversing flow in a tailpipe offtake configuration for SSTOVL aircraft

    NASA Technical Reports Server (NTRS)

    Mcardle, Jack G.; Esker, Barbara S.; Rhodes, James A.

    1992-01-01

    A generic one-third scale model of a tailpipe offtake system for a supersonic short takeoff vertical landing (SSTOVL) aircraft was tested at LeRC Powered Lift Facility. The model consisted of a tailpipe with twin elbows, offtake ducts, and flow control nozzles, plus a small ventral nozzle and a blind flange to simulate a blocked cruise nozzle. The offtake flow turned through a total angle of 177 degrees relative to the tailpipe inlet axis. The flow split was 45 percent to each offtake and 10 percent to the ventral nozzle. The main test objective was to collect data for comparison to the performance of the same configuration predicted by a computational fluid dynamics (CFD) analysis. Only the experimental results are given - the analytical results are published in a separate paper. Performance tests were made with unheated air at tailpipe-to-ambient pressure ratios up to 5. The total pressure loss through the offtakes was as high as 15.5 percent. All test results are shown as graphs, contour plots, and wall pressure distributions. The complex flow patterns in the tailpipe and elbows at the offtake openings are described with traversing flow angle probe and paint streak flow visualization data.

  16. The gelatinous extracellular matrix facilitates transport studies in kelp: visualization of pressure-induced flow reversal across sieve plates

    PubMed Central

    Knoblauch, Jan; Peters, Winfried S.; Knoblauch, Michael

    2016-01-01

    Background and Aims In vascular plants, important questions regarding phloem function remain unanswered due to problems with invasive experimental procedures in this highly sensitive tissue. Certain brown algae (kelps; Laminariales) also possess sieve tubes for photoassimilate transport, but these are embedded in large volumes of a gelatinous extracellular matrix which isolates them from neighbouring cells. Therefore, we hypothesized that kelp sieve tubes might tolerate invasive experimentation better than their analogues in higher plants, and sought to establish Nereocystis luetkeana as an experimental system. Methods The predominant localization of cellulose and the gelatinous extracellular matrix in N. luetkeana was verified using specific fluorescent markers and confocal laser scanning microscopy. Sieve tubes in intact specimens were loaded with fluorescent dyes, either passively (carboxyfluorescein diacetate; CFDA) or by microinjection (rhodamine B), and the movement of the dyes was monitored by fluorescence microscopy. Key Results Application of CFDA demonstrated source to sink bulk flow in N. luetkeana sieve tubes, and revealed the complexity of sieve tube structure, with branches, junctions and lateral connections. Microinjection into sieve elements proved comparatively easy. Pulsed rhodamine B injection enabled the determination of flow velocity in individual sieve elements, and the direct visualization of pressure-induced reversals of flow direction across sieve plates. Conclusions The reversal of flow direction across sieve plates by pressurizing the downstream sieve element conclusively demonstrates that a critical requirement of the Münch theory is satisfied in kelp; no such evidence exists for tracheophytes. Because of the high tolerance of its sieve elements to experimental manipulation, N. luetkeana is a promising alternative to vascular plants for studying the fluid mechanics of sieve tube networks. PMID:26929203

  17. Issues in measure-preserving three dimensional flow integrators: Self-adjointness, reversibility, and non-uniform time stepping

    NASA Astrophysics Data System (ADS)

    Finn, John M.

    2015-03-01

    Properties of integration schemes for solenoidal fields in three dimensions are studied, with a focus on integrating magnetic field lines in a plasma using adaptive time stepping. It is shown that implicit midpoint (IM) and a scheme we call three-dimensional leapfrog (LF) can do a good job (in the sense of preserving KAM tori) of integrating fields that are reversible, or (for LF) have a "special divergence-free" (SDF) property. We review the notion of a self-adjoint scheme, showing that such schemes are at least second order accurate and can always be formed by composing an arbitrary scheme with its adjoint. We also review the concept of reversibility, showing that a reversible but not exactly volume-preserving scheme can lead to a fractal invariant measure in a chaotic region, although this property may not often be observable. We also show numerical results indicating that the IM and LF schemes can fail to preserve KAM tori when the reversibility property (and the SDF property for LF) of the field is broken. We discuss extensions to measure preserving flows, the integration of magnetic field lines in a plasma and the integration of rays for several plasma waves. The main new result of this paper relates to non-uniform time stepping for volume-preserving flows. We investigate two potential schemes, both based on the general method of Feng and Shang [Numer. Math. 71, 451 (1995)], in which the flow is integrated in split time steps, each Hamiltonian in two dimensions. The first scheme is an extension of the method of extended phase space, a well-proven method of symplectic integration with non-uniform time steps. This method is found not to work, and an explanation is given. The second method investigated is a method based on transformation to canonical variables for the two split-step Hamiltonian systems. This method, which is related to the method of non-canonical generating functions of Richardson and Finn [Plasma Phys. Controlled Fusion 54, 014004 (2012

  18. Issues in measure-preserving three dimensional flow integrators: Self-adjointness, reversibility, and non-uniform time stepping

    DOE PAGES

    Finn, John M.

    2015-03-01

    Properties of integration schemes for solenoidal fields in three dimensions are studied, with a focus on integrating magnetic field lines in a plasma using adaptive time stepping. It is shown that implicit midpoint (IM) and a scheme we call three-dimensional leapfrog (LF) can do a good job (in the sense of preserving KAM tori) of integrating fields that are reversible, or (for LF) have a 'special divergence-free' property. We review the notion of a self-adjoint scheme, showing that such schemes are at least second order accurate and can always be formed by composing an arbitrary scheme with its adjoint. Wemore » also review the concept of reversibility, showing that a reversible but not exactly volume-preserving scheme can lead to a fractal invariant measure in a chaotic region, although this property may not often be observable. We also show numerical results indicating that the IM and LF schemes can fail to preserve KAM tori when the reversibility property (and the SDF property for LF) of the field is broken. We discuss extensions to measure preserving flows, the integration of magnetic field lines in a plasma and the integration of rays for several plasma waves. The main new result of this paper relates to non-uniform time stepping for volume-preserving flows. We investigate two potential schemes, both based on the general method of Ref. [11], in which the flow is integrated in split time steps, each Hamiltonian in two dimensions. The first scheme is an extension of the method of extended phase space, a well-proven method of symplectic integration with non-uniform time steps. This method is found not to work, and an explanation is given. The second method investigated is a method based on transformation to canonical variables for the two split-step Hamiltonian systems. This method, which is related to the method of non-canonical generating functions of Ref. [35], appears to work very well.« less

  19. Issues in measure-preserving three dimensional flow integrators: Self-adjointness, reversibility, and non-uniform time stepping

    SciTech Connect

    Finn, John M.

    2015-03-15

    Properties of integration schemes for solenoidal fields in three dimensions are studied, with a focus on integrating magnetic field lines in a plasma using adaptive time stepping. It is shown that implicit midpoint (IM) and a scheme we call three-dimensional leapfrog (LF) can do a good job (in the sense of preserving KAM tori) of integrating fields that are reversible, or (for LF) have a “special divergence-free” (SDF) property. We review the notion of a self-adjoint scheme, showing that such schemes are at least second order accurate and can always be formed by composing an arbitrary scheme with its adjoint. We also review the concept of reversibility, showing that a reversible but not exactly volume-preserving scheme can lead to a fractal invariant measure in a chaotic region, although this property may not often be observable. We also show numerical results indicating that the IM and LF schemes can fail to preserve KAM tori when the reversibility property (and the SDF property for LF) of the field is broken. We discuss extensions to measure preserving flows, the integration of magnetic field lines in a plasma and the integration of rays for several plasma waves. The main new result of this paper relates to non-uniform time stepping for volume-preserving flows. We investigate two potential schemes, both based on the general method of Feng and Shang [Numer. Math. 71, 451 (1995)], in which the flow is integrated in split time steps, each Hamiltonian in two dimensions. The first scheme is an extension of the method of extended phase space, a well-proven method of symplectic integration with non-uniform time steps. This method is found not to work, and an explanation is given. The second method investigated is a method based on transformation to canonical variables for the two split-step Hamiltonian systems. This method, which is related to the method of non-canonical generating functions of Richardson and Finn [Plasma Phys. Controlled Fusion 54, 014004 (2012

  20. The Number of Perforators Included in Reversed Flow Posterior Interosseous Artery Flap: Does It Affect the Incidence of Venous Congestion?

    PubMed Central

    Shaker, Ayman A.; Elbarbary, Amir S.; Sayed, Mohamed A.; Elghareeb, Mohamed A.

    2016-01-01

    Background: The purpose of this study is to decrease the incidence of venous congestion occurring in the reversed flow posterior interosseous artery flap used for coverage of hand defects. Methods: This may be achieved by studying the incidence of venous congestion in flaps including only 1 perforator and comparing the results with others including more than 1 perforator both in small and large sized flaps. Results: This study showed that inclusion of only 1 perforator in the flap decreased the incidence of venous congestion with complete flap loss in flaps to 5%. Also, it decreased the incidence of venous congestion with partial flap loss in flaps to 10%. Conclusions: The small sized reversed flow posterior interosseous artery flap should be less than 40 cm2 and should include only 1 perforator to decrease the incidence of venous congestion with partial and complete loss of the flap. The level of evidence for this study is the type II prospective comparative study. PMID:28293513

  1. Integrating Reverse-Electrodialysis Stacks with Flow Batteries for Improved Energy Recovery from Salinity Gradients and Energy Storage.

    PubMed

    Zhu, Xiuping; Kim, Taeyoung; Rahimi, Mohammad; Gorski, Christopher A; Logan, Bruce E

    2017-02-22

    Salinity gradient energy can be directly converted into electrical power by using reverse electrodialysis (RED) and other technologies, but reported power densities have been too low for practical applications. Herein, the RED stack performance was improved by using 2,6-dihydroxyanthraquinone and ferrocyanide as redox couples. These electrolytes were then used in a flow battery to produce an integrated RED stack and flow battery (RED-FB) system capable of capturing, storing, and discharging salinity gradient energy. Energy captured from the RED stack was discharged in the flow battery at a maximum power density of 3.0 kW m(-2) -anode, which was similar to the flow batteries charged by electrical power and could be used for practical applications. Salinity gradient energy captured from the RED stack was recovered from the electrolytes as electricity with 30 % efficiency, and the maximum energy density of the system was 2.4 kWh m(-3) -anolyte. The combined RED-FB system overcomes many limitations of previous approaches to capture, store, and use salinity gradient energy from natural or engineered sources.

  2. Is Gene Flow Promoting the Reversal of Pleistocene Divergence in the Mountain Chickadee (Poecile gambeli)?

    PubMed Central

    Manthey, Joseph D.; Klicka, John; Spellman, Garth M.

    2012-01-01

    The Pleistocene glacial cycles left a genetic legacy on taxa throughout the world; however, the persistence of genetic lineages that diverged during these cycles is dependent upon levels of gene flow and introgression. The consequences of secondary contact among taxa may reveal new insights into the history of the Pleistocene’s genetic legacy. Here, we use phylogeographic methods, using 20 nuclear loci from regional populations, to infer the consequences of secondary contact following divergence in the Mountain Chickadee (Poecile gambeli). Analysis of nuclear data identified two geographically-structured genetic groups, largely concordant with results from a previous mitochondrial DNA (mtDNA) study. Additionally, the estimated multilocus divergence times indicate a Pleistocene divergence, and are highly concordant with mtDNA. The previous mtDNA study showed a paucity of sympatry between clades, while nuclear patterns of gene flow show highly varied patterns between populations. The observed pattern of gene flow, from coalescent-based analyses, indicates southern populations in both clades exhibit little gene flow within or between clades, while northern populations are experiencing higher gene flow within and between clades. If this pattern were to persist, it is possible the historical legacy of Pleistocene divergence may be preserved in the southern populations only, and the northern populations would become a genetically diverse hybrid species. PMID:23152877

  3. The formation of reverse shocks in magnetized high energy density supersonic plasma flows

    SciTech Connect

    Lebedev, S. V. E-mail: l.suttle10@imperial.ac.uk; Suttle, L.; Swadling, G. F.; Bennett, M.; Bland, S. N.; Burdiak, G. C.; Chittenden, J. P.; Grouchy, P. de; Hall, G. N.; Hare, J. D.; Kalmoni, N.; Niasse, N.; Patankar, S.; Smith, R. A.; Suzuki-Vidal, F.; Burgess, D.; Clemens, A.; Ciardi, A.; Sheng, L.; Yuan, J.; and others

    2014-05-15

    A new experimental platform was developed, based on the use of supersonic plasma flow from the ablation stage of an inverse wire array z-pinch, for studies of shocks in magnetized high energy density physics plasmas in a well-defined and diagnosable 1-D interaction geometry. The mechanism of flow generation ensures that the plasma flow (Re{sub M} ∼ 50, M{sub S} ∼ 5, M{sub A} ∼ 8, V{sub flow} ≈ 100 km/s) has a frozen-in magnetic field at a level sufficient to affect shocks formed by its interaction with obstacles. It is found that in addition to the expected accumulation of stagnated plasma in a thin layer at the surface of a planar obstacle, the presence of the magnetic field leads to the formation of an additional detached density jump in the upstream plasma, at a distance of ∼c/ω{sub pi} from the obstacle. Analysis of the data obtained with Thomson scattering, interferometry, and local magnetic probes suggests that the sub-shock develops due to the pile-up of the magnetic flux advected by the plasma flow.

  4. Determination of electroosmotic and electrophoretic mobility of DNA and dyes in low ionic strength solutions.

    PubMed

    Lallman, Joshua; Flaugh, Rachel; Kounovsky-Shafer, Kristy L

    2017-08-23

    Nanocoding, a genome analysis platform, relies on very low ionic strength conditions to elongate DNA molecules up to 1.06 (fully stretched DNA = 1). Understanding how electroosmotic and electrophoretic forces vary, as ionic strength decreases, will enable better Nanocoding devices, or other genome analysis platforms, to be developed. Using gel electrophoresis to determine overall mobility (includes contributions from electrophoretic and electroosmotic forces) in different ionic strength conditions, linear DNA molecules (pUC19 (2.7 kb), pBR322 (4.4 kb), ΦX174 (5.4 kb), and PSNAPf-H2B (6.2 kb)) were analyzed in varying gel concentrations (1.50, 1.25, 1.00, 0.75, and 0.50%). Additionally, buffer concentration (Tris-EDTA, TE) was varied to determine free solution mobility at different ionic strength solutions. As ionic strength decreased from 13.8 to 7.3 mM, overall mobility increased. As TE buffer decreased (< 7.3 mM), overall mobility drastically decreased as ionic strength decreased. Rhodamine B dye was utilized to determine the electroosmotic mobility. As the ionic strength decreased, electroosmotic mobility increased. The experimental electrophoretic mobility was compared to theoretical considerations for electrophoretic mobility (Pitts and Debye-Hückel-Onsager). Electroosmotic forces decreased the overall mobility of DNA molecules and bromophenol blue migration in a gel matrix as ionic strength decreased. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. An Improved Theoretical Model for A-TIG Welding Based on Surface Phase Transition and Reversed Marangoni Flow

    NASA Astrophysics Data System (ADS)

    Sándor, T.; Mekler, C.; Dobránszky, J.; Kaptay, G.

    2013-01-01

    It is experimentally shown that a thin layer of silica flux leads to an increased depth of weld penetration during activated TIG (=A-TIG) welding of Armco iron. The oxygen-content is found higher in the solidified weld metal and it is linked to the increased depth of penetration through the reversed Marangoni convection. It is theoretically shown for the first time that the basic reason of the reversed Marangoni convection is the phenomenon called "surface phase transition" (SPT), leading to the formation of a nano-thin FeO layer on the surface of liquid iron. It is shown that the ratio of dissolved oxygen in liquid iron to the O-content of the silica flux is determined by the wettability of silica particles by liquid iron. It is theoretically shown that when the silica flux surface density is higher than 15 µg/mm2, reversed Marangoni flow will take place along more than 50 pct of the melted surface. Comparing the SPT line with the dissociation curves of a number of oxides, they can be positioned in the following order of their ability to serve as a flux for A-TIG welding of steel: anatase-TiO2 (best)-rutile-TiO2 (very good)-silica-SiO2 (good)-alumina-Al2O3 (does not work). Anatase (and partly rutile) are self-regulating fluxes, as they provide at any temperature just as much dissolved oxygen as needed for the reversed Marangoni convection, and not more. On the other hand, oxygen can be over-dosed if silica, and other, less stable oxides (such as iron oxides) are used.

  6. Reversible and irreversible flow-induced phase transition in micellar solutions

    NASA Astrophysics Data System (ADS)

    Sureshkumar, Radhakrishna; Vasudevan, Mukund; Buse, Eric; Krishna, Hare; Kalyanaraman, Ramki; Khomami, Bamin; Shen, Amy

    2008-03-01

    It is well known that wormlike micelles form shear-induced structures (SIS). SIS formation is typically accompanied by the appearance of a gel-like phase. While both configurational dynamics of the micelles in flow and electrostatics are recognized as the key factors that influence such phase transitions, there are no universally applicable criteria for the onset strain rate as function of salt concentration. In this work, first, we examine the effect of salt concentration on the critical strain rate for CTAB/NaSal solutions and show that a ``self-similar'' phase transition regime exists. Second, we show that under strong (elongational) flow conditions, the phase transitions are irreversible, leading to the formation of gels that are stable even after the flow is stopped. Results obtained from atomic force microscopy studies of the structure of such gels will be presented.

  7. Reversal and amplification of zonal flows by boundary enforced thermal wind

    NASA Astrophysics Data System (ADS)

    Dietrich, W.; Gastine, T.; Wicht, J.

    2017-01-01

    Zonal flows in rapidly-rotating celestial objects such as the Sun, gas or ice giants form in a variety of surface patterns and amplitudes. Whereas the differential rotation on the Sun, Jupiter and Saturn features a super-rotating equatorial region, the ice giants, Neptune and Uranus harbour an equatorial jet slower than the planetary rotation. Global numerical models covering the optically thick, deep-reaching and rapidly rotating convective envelopes of gas giants reproduce successfully the prograde jet at the equator. In such models, convective columns shaped by the dominant Coriolis force typically exhibit a consistent prograde tilt. Hence angular momentum is pumped away from the rotation axis via Reynolds stresses. Those models are found to be strongly geostrophic, hence a modulation of the zonal flow structure along the axis of rotation, e.g. introduced by persistent latitudinal temperature gradients, seems of minor importance. Within our study we stimulate these thermal gradients and the resulting ageostrophic flows by applying an axisymmetric and equatorially symmetric outer boundary heat flux anomaly (Y20) with variable amplitude and sign. Such a forcing pattern mimics the thermal effect of intense solar or stellar irradiation. Our results suggest that the ageostrophic flows are linearly amplified with the forcing amplitude q⋆ leading to a more pronounced dimple of the equatorial jet (alike Jupiter). The geostrophic flow contributions, however, are suppressed for weak q⋆, but inverted and re-amplified once q⋆ exceeds a critical value. The inverse geostrophic differential rotation is consistently maintained by now also inversely tilted columns and reminiscent of zonal flow profiles observed for the ice giants. Analysis of the main force balance and parameter studies further foster these results.

  8. Conversion of methane to hydrogen in a reversible flow superadiabatic inert porous medium reactor

    NASA Astrophysics Data System (ADS)

    Alabbadi, N. M.; Al-Musa, A. S.; Dmitrenko, Yu. M.; Martynenko, V. V.; Shabunya, S. I.; Al-Maiman, S. I.; Al-Enazi, K. B.; Al-Zhuhani, M. S.

    2011-11-01

    Using the analysis of the experimental data on partial oxidation of methane as an example, we have shown that the chemical processes in the inert medium of a reciprocating flow reactor can be modeled with good accuracy by the standard kinetic scheme for homogeneous processes due to the fact that the gas flow in the region of combustion is described by two temperatures — the gas and framework temperatures. Such a modification of the chemical model requires neither changing the recognized mechanism of homogeneous chemistry nor correcting the volume heat transfer coefficient.

  9. Experimental Observations About The Behavior of The Sheet Flow On Sand Bed Streams and The Reversal Gradation Effect.

    NASA Astrophysics Data System (ADS)

    Bateman, A.; Aguilar, C.; Roquer, R.; Andreatta, A.; Velasco, D.

    In our land, Catalonia, exists a lot of torrential ephemeral streams. Which are char- acterized by a great floods during typical convective storms. Sediment transport rates are very important in this gravel/sand torrent. Usually, near the cities, they show a 2- 3% slope bed profile. Engineering works or actuations have to deal with this kind of dynamic systems. The stabilization of this torrents is one of the aim of our research at the Polytechnic University of Catalonia (Hydraulic, Marine and environmental De- partment). Typical experiments in a hydraulic flume was normally used to observe the behavior of stabilization structures. The first step in the research is to know the general evolution of the bed profile. Agradation and degradation experiments in a laboratory flume of 20 m length was car- ried out to study the behavior of the steady and unsteady flow with sediment transport. The hydraulic regime of the experiments was set to be supercritical flat bed; sand flow rates about 300gr/s which gives near a 2% equilibrium slope. The most interesting results of those experiments was the reversal gradation of the sand sizes measured along the flume in the final steady state. This kind of effect was reported by Luca Solari and Gary Parker 2000. A 1-D numerical model to solve the Exner and Saint_Venant implicit system of equation were used to compare the evolu- tion of the different experiments. The sheet sand flow produces a great resistance to flow, the experiments shows the influence exhorted by the sand discharge in the flow resistance factor.

  10. Analysis of Transient and Steady State Neutral Flows in a Field Reversed Configuration Thruster

    DTIC Science & Technology

    2011-05-03

    stagnation temperature of 300 K. The carrier gas was molecular nitrogen in a ll cases except for one where neon was used. Transient evolution of gas flow...Navier-Stokes equations is CFD++ 8 developed by Metacomp Technologies, Inc. CFD++ is a flexible computational fluid dynamics software suite for the...intermolecular potential was assumed to be a variable hard sphere. Energy redistribution in molecular colli- sions between the internal and translational modes

  11. One- and two-dimensional Stirling machine simulation using experimentally generated reversing flow turbuulence models

    SciTech Connect

    Goldberg, L.F.

    1990-08-01

    The activities described in this report do not constitute a continuum but rather a series of linked smaller investigations in the general area of one- and two-dimensional Stirling machine simulation. The initial impetus for these investigations was the development and construction of the Mechanical Engineering Test Rig (METR) under a grant awarded by NASA to Dr. Terry Simon at the Department of Mechanical Engineering, University of Minnesota. The purpose of the METR is to provide experimental data on oscillating turbulent flows in Stirling machine working fluid flow path components (heater, cooler, regenerator, etc.) with particular emphasis on laminar/turbulent flow transitions. Hence, the initial goals for the grant awarded by NASA were, broadly, to provide computer simulation backup for the design of the METR and to analyze the results produced. This was envisaged in two phases: First, to apply an existing one-dimensional Stirling machine simulation code to the METR and second, to adapt a two-dimensional fluid mechanics code which had been developed for simulating high Rayleigh number buoyant cavity flows to the METR. The key aspect of this latter component was the development of an appropriate turbulence model suitable for generalized application to Stirling simulation. A final-step was then to apply the two-dimensional code to an existing Stirling machine for which adequate experimental data exist. The work described herein was carried out over a period of three years on a part-time basis. Forty percent of the first year`s funding was provided as a match to the NASA funds by the Underground Space Center, University of Minnesota, which also made its computing facilities available to the project at no charge.

  12. Electro-osmotic drag effect on the methanol permeation for sulfonated poly(ether ether ketone) and nafion 117 membranes.

    PubMed

    Chi, Nguyen Thi Que; Bae, Byungchan; Kim, Dukjoon

    2013-11-01

    Electro-osmotic drag effect on the methanol permeation was investigated for sulfonated poly(ether ether ketone) (sPEEK) membrane, and its result was compared with that of Nafion 117 membrane. The electro-osmotic drag coefficient was determined from the limiting current density measured at different temperature. The methanol permeability of sPEEK membrane increased with temperature but its temperature dependence was not as strong as that of Nafion 117 membrane. The methanol permeability or the total methanol flux of Nafion 117 membrane was at least twice higher than that of sPEEK70 membrane (sPEEK membrane with 70% sulfonation degree), as the methanol permeation was highly contributed by the electro-osmotic drag effect. This higher electro-osmotic drag of Nafion 117 membrane is attributed to the bigger ion cluster and waster channel in nanophase and thus more free water absorption than sPEEK membrane.

  13. An in situ measurement of extracellular cysteamine, homocysteine, and cysteine concentrations in organotypic hippocampal slice cultures by integration of electroosmotic sampling and microfluidic analysis.

    PubMed

    Wu, Juanfang; Xu, Kerui; Landers, James P; Weber, Stephen G

    2013-03-19

    We demonstrate an all-electric sampling/derivatization/separation/detection system for the quantitation of thiols in tissue cultures. Extracellular fluid collected from rat organotypic hippocampal slice cultures (OHSCs) by electroosmotic flow through an 11 cm (length) × 50 μm (i.d.) sampling capillary is introduced to a simple microfluidic chip for derivatization, continuous flow-gated injection, separation, and detection. With the help of a fluorogenic, thiol-specific reagent, ThioGlo-1, we have successfully separated and detected the extracellular levels of free reduced cysteamine, homocysteine, and cysteine from OHSCs within 25 s in a 23 mm separation channel with a confocal laser-induced fluorescence (LIF) detector. Attention to the conductivities of the fluids being transported is required for successful flow-gated injections. When the sample conductivity is much higher than the run buffer conductivities, the electroosmotic velocities are such that there is less fluid coming by electroosmosis into the cross from the sample/reagent channel than is leaving by electroosmosis into the separation and waste channels. The resulting decrease in the internal fluid pressure in the injection cross pulls flow from the gated channel. This process may completely shut down the gated injection. Using a glycylglycine buffer with physiological osmolarity but only 62% of physiological conductivity and augmenting the conductivity of the run buffers solved this problem. Quantitation is by standard additions. Concentrations of cysteamine, homocysteine, and cysteine in the extracellular space of OHSCs are 10.6 ± 1.0 nM (n = 70), 0.18 ± 0.01 μM (n = 53), and 11.1 ± 1.2 μM (n = 70), respectively. This is the first in situ quantitative estimation of endogenous cysteamine in brain tissue. Extracellular levels of homocysteine and cysteine are comparable with other reported values.

  14. An in situ Measurement of Extracellular Cysteamine, Homocysteine and Cysteine Concentrations in Organotypic Hippocampal Slice Cultures by Integration of Electroosmotic Sampling and Microfluidic Analysis

    PubMed Central

    Wu, Juanfang; Xu, Kerui; Landers, James P.; Weber, Stephen G.

    2013-01-01

    We demonstrate an all-electric sampling/derivatization/separation/detection system for the quantitation of thiols in tissue cultures. Extracellular fluid collected from rat organotypic hippocampal slice cultures (OHSCs) by electroosmotic flow through an11 cm (length) × 50 μm (ID) sampling capillary is introduced to a simple microfluidic chip for derivatization, continuous flow-gated injection, separation and detection.With the help of a fluorogenic, thiol-specific reagent, ThioGlo-1, we have successfully separated and detected the extracellular levels of free reduced cysteamine, homocysteineand cysteinefrom OHSCs within 25 s in a 23 mm separation channel with a confocal laser induced fluorescence (LIF) detector. Attention to the conductivities of the fluids being transported is required for successful flow-gated injections.When the sample conductivity is much higher than the run buffer conductivities, the electroosmotic velocities are such that there is less fluid coming by electroosmosis into the cross from the sample/reagent channel than is leaving by electroosmosis into the separation and waste channels. The resulting decrease in the internal fluid pressure in the injection cross pulls flow from the gated channel. This process may completely shut down the gated injection. Using a glycylglycine buffer with physiological osmolarity but only 62% of physiological conductivity and augmenting the conductivity of the run buffers solved this problem. Quantitation is by standard additions. Concentrations of cysteamine, homocysteine and cysteine in the extracellular space of OHSCs are10.6±1.0 nM (n=70), 0.18±0.01 μM (n=53) and 11.1±1.2 μM (n=70), respectively. This is the first in situquantitative estimation of endogenous cysteamine in brain. Extracellular levels of homocysteine and cysteine are comparable with other reported values. PMID:23330713

  15. Reverse roll-coating flow: a computational investigation towards high-speed defect free coating

    NASA Astrophysics Data System (ADS)

    Belblidia, F.; Tamaddon-Jahromi, H. R.; Echendu, S. O. S.; Webster, M. F.

    2013-11-01

    A finite element Taylor-Galerkin pressure-correction algorithm is employed to simulate a high-speed defect-free roll-coating flow, which substantiates a coating process with a free meniscus surface. Findings are applicable across a wide range of coating sectors in optimisation of coating performance, which targets adaptive and intelligent process control. Industrially, there is a major drive towards using new material products and raising coating line-speeds, to address increased efficiency and productivity. This study has sought to attack these issues by developing an effective predictive toolset for high-speed defect-free coatings. Here, time-stepping/finite element methods are deployed to model this free-surface problem that involves the transfer of a coating fluid from a roller to a substrate (of prescribed wet-film thickness). This procedure is used in conjunction with a set of constitutive equations capable of describing the relevant fluid-film rheology in appropriate detail. Quantities of pressure, lift and drag have been calculated streamwise across the flow domain, and streamline patterns reveal a large recirculating vortex around the meniscus region. Such pressure distributions across the domain display a positive peak which decreases as nip-gap size increases. Further analysis has been conducted, mimicking the presence of a wetting line, whilst varying boundary conditions at the nip. Observation has shown that such inclusion would serve as a relief mechanism to the positive peak pressures generated around the nip zone. Here, through an elasto-hydrodynamic formulation, the elastic deformation of a rubber roll cover (elastomer) has also been introduced, which offers fresh insight into the process with respect to nip-flow behaviour, and allows for the analysis of both positive and negative nip-gaps.

  16. Electromagnetic treatment to old Alzheimer's mice reverses β-amyloid deposition, modifies cerebral blood flow, and provides selected cognitive benefit.

    PubMed

    Arendash, Gary W; Mori, Takashi; Dorsey, Maggie; Gonzalez, Rich; Tajiri, Naoki; Borlongan, Cesar

    2012-01-01

    Few studies have investigated physiologic and cognitive effects of "long-term" electromagnetic field (EMF) exposure in humans or animals. Our recent studies have provided initial insight into the long-term impact of adulthood EMF exposure (GSM, pulsed/modulated, 918 MHz, 0.25-1.05 W/kg) by showing 6+ months of daily EMF treatment protects against or reverses cognitive impairment in Alzheimer's transgenic (Tg) mice, while even having cognitive benefit to normal mice. Mechanistically, EMF-induced cognitive benefits involve suppression of brain β-amyloid (Aβ) aggregation/deposition in Tg mice and brain mitochondrial enhancement in both Tg and normal mice. The present study extends this work by showing that daily EMF treatment given to very old (21-27 month) Tg mice over a 2-month period reverses their very advanced brain Aβ aggregation/deposition. These very old Tg mice and their normal littermates together showed an increase in general memory function in the Y-maze task, although not in more complex tasks. Measurement of both body and brain temperature at intervals during the 2-month EMF treatment, as well as in a separate group of Tg mice during a 12-day treatment period, revealed no appreciable increases in brain temperature (and no/slight increases in body temperature) during EMF "ON" periods. Thus, the neuropathologic/cognitive benefits of EMF treatment occur without brain hyperthermia. Finally, regional cerebral blood flow in cerebral cortex was determined to be reduced in both Tg and normal mice after 2 months of EMF treatment, most probably through cerebrovascular constriction induced by freed/disaggregated Aβ (Tg mice) and slight body hyperthermia during "ON" periods. These results demonstrate that long-term EMF treatment can provide general cognitive benefit to very old Alzheimer's Tg mice and normal mice, as well as reversal of advanced Aβ neuropathology in Tg mice without brain heating. Results further underscore the potential for EMF treatment

  17. Flow reversal at low voltage and low frequency in a microfabricated ac electrokinetic pump.

    PubMed

    Gregersen, Misha Marie; Olesen, Laurits Højgaard; Brask, Anders; Hansen, Mikkel Fougt; Bruus, Henrik

    2007-11-01

    Microfluidic chips have been fabricated in Pyrex glass to study electrokinetic pumping generated by a low-voltage ac bias applied to an in-channel asymmetric metallic electrode array. A measurement procedure has been established and followed carefully resulting in a high degree of reproducibility of the measurements over several days. A large coverage fraction of the electrode array in the microfluidic channels has led to an increased sensitivity allowing for pumping measurements at low bias voltages. Depending on the ionic concentration a hitherto unobserved reversal of the pumping direction has been measured in a regime, where both the applied voltage and the frequency are low, V(rms)<1.5 V and f<20 kHz , compared to previously investigated parameter ranges. The impedance spectrum has been thoroughly measured and analyzed in terms of an equivalent circuit diagram to rule out trivial circuit explanations of our findings. Our observations agree qualitatively, but not quantitatively, with theoretical electrokinetic models published in the literature.

  18. Reverse-flow anterolateral thigh perforator: an ad hoc flap for severe post-burn knee contracture.

    PubMed

    Ismail, H A; El-Bassiony, L E

    2016-03-31

    We evaluate function outcomes of the reverse-flow ALT perforator flap to reconstruct severe post-burn knee contracture. Between October 2012 and December 2014, 10 patients with severe post-burn knee contracture were subjected to reconstruction with 10 ipsilateral reversed-flow ALT perforator flaps. All the patients were male. Ages ranged from 15 to 47 years (mean = 32 years). Time from burn injury to patient presentation ranged from 2-8 months. All patients demonstrated post-burn flexion contracture of the knee joint, ranging from 35 to 75 degrees. Flap sizes ranged from 8×16 to 12×26 cm. The flaps and skin grafts were carried out without major complications. Only minor complications occurred, such as transient, mild congestion immediately after inset in two flaps. Two flaps developed superficial necrosis at the distal edge. One case sustained partial skin graft loss due to haematoma. One case complained of skin hyperpigmentation and hypertrophic scars around the graft. Secondary debulking procedures were required in two cases. The entire donor sites were closed by partial thickness skin graft with acceptable appearance, except one case that was closed primarily. Eight out of ten patients (80%) demonstrated gradual improvement in range of knee motion after a specialized rehabilitation program. Two patients (20%) did not get back full range of motion. RALT perforator flap is the cornerstone for the reconstruction of soft-tissue defects around the knee with acceptable aesthetic and functional results provided that the following items are fulfilled: inclusion of muscle cuff around the pedicle, the pivot point, prevention of pedicle compression after transfer and early surgical intervention on the post-burn knee contracture.

  19. Anatomical consideration of reverse-flow island flap transfers from the midpalm for finger reconstruction.

    PubMed

    Omokawa, S; Tanaka, Y; Ryu, J; Clovis, N

    2001-12-01

    Primary soft-tissue coverage for large palmar defects of the fingers is a difficult problem for cases in which homodigital or heterodigital flaps cannot be used. The aim of this study was to explore the vascular and neural anatomy of the midpalmar area to assess the possibility of reverse island flaps from this area. In 24 cadaver hands perfused with a silicone compound, the arterial pattern of the superficial palmar arch and common palmar digital artery was examined. The cutaneous perforating arteries and nerve branches supplying the midpalmar area were dissected, and the number, location, and arterial diameter of these branches were measured. In six other specimens, the common palmar digital artery was injected to determine the skin territory supplied by the artery. The superficial palmar arch contained the three common palmar digital arteries and its terminal branch coursed along the radial margin of the index metacarpus. This terminal branch had three to six cutaneous perforators (diameter range, 0.1 to 0.5 mm) and supplied the radial aspect of the midpalmar area located over the ulnar half of the adductor pollicis muscles. The midpalmar area was divided into two regions-the proximal and distal-according to the vascular distributions. The proximal region contained dense aponeurosis and thin subcutaneous tissue, and the cutaneous perforators were rather sparse (between three and nine) and had a small diameter (0.1 to 0.3 mm). The distal region, which had loose aponeurosis and abundant subcutaneous tissue, had a rich vascular supply from the common and proper digital artery. Perforating arteries of this region coursed frequently in an oblique fashion and the number of perforators (between eight and 15) and their arterial diameters (diameter range, 0.1 to 0.5 mm) were higher than those of the proximal region. The area of skin perfused by the common palmar digital artery was 5 x 3 cm at the distal midpalmar region. There were three to five cutaneous nerve branches

  20. Lubricant flow analysis for effective lubrication of tractor forward/reverse clutch.

    PubMed

    Noh, Daekyung; Kim, Soochul; Kim, Yongjoo; Jang, Joosup

    2017-04-01

    Owing to the high power requirements of tractors, their low-power transmission gears often experience durability problems such as burning of the clutch. The operation of tractors under high load conditions also causes clutch slip, with the consequent longer operation duration exacerbating the burning of the friction plate. Solving this problem requires effective lubricant distribution. This was achieved in the present study by the development of an analysis model for predicting the lubricant flow rate. The reliability of the model was verified by comparing its predictions for various operation conditions with experimental measurements. Using the model, it was determined that effective distribution of the lubricant could be achieved without significant modification of the system, by only adjusting the gaps between the clutch piston and the housing, and between the separation plates and the case.

  1. Numerical simulation of electro-osmotic consolidation coupling non-linear variation of soil parameters

    NASA Astrophysics Data System (ADS)

    Wu, Hui; Hu, Liming; Wen, Qingbo

    2017-06-01

    Electro-osmotic consolidation is an effective method for soft ground improvement. A main limitation of previous numerical models on this technique is the ignorance of the non-linear variation of soil parameters. In the present study, a multi-field numerical model is developed with the consideration of the non-linear variation of soil parameters during electro-osmotic consolidation process. The numerical simulations on an axisymmetric model indicated that the non-linear variation of soil parameters showed remarkable impact on the development of the excess pore water pressure and degree of consolidation. A field experiment with complex geometry, boundary conditions, electrode configuration and voltage application was further simulated with the developed numerical model. The comparison between field and numerical data indicated that the numerical model coupling of the non-linear variation of soil parameters gave more reasonable results. The developed numerical model is capable to analyze engineering cases with complex operating conditions.

  2. Flow mechanism of self-induced reversed limit-cycle wing rock for a chined forebody configuration

    NASA Astrophysics Data System (ADS)

    Shi, Wei; Deng, Xueying; Wang, Yankui; Li, Qian

    2015-11-01

    The wing rock phenomenon reduces the maneuverability and affects the flight safety of modern advanced fighters, such as the F-35, which have chined forebodies. Understanding the flow mechanism is critical to suppressing this phenomenon. In this study, experiments were conducted to reveal the motion and flow behavior over a chined forebody configuration. The tests were performed in a wind tunnel at an angle of attack of 50∘ with a Reynolds number of 1.87 × 105. Reversed limit-cycle oscillation was discovered in the free-to-roll tests. The unstable rolling moment around zero roll angle in the static case suggests that the model tends to be driven away from zero roll angle. Thus, the model cannot maintain its equilibrium at zero roll angle during free-to-roll motion. The unstable rolling moment is generated by the wing vortex structure above the upward wing, which is induced by the forebody asymmetric vortices. During wing rock, the wing vortex structure appears above the upward wing at a large roll angle after crossing zero roll angle owing to a time lag in the forebody vortex position, which is conducive to the motion. The forebody asymmetric vortices are thus the key to induce and maintain the motion.

  3. Electro-Osmotic Pulse Technology for Control of Water Seepage in Various Civil Works Structures

    DTIC Science & Technology

    2006-10-01

    Moisture at 2L/3 Figure 18. Moisture content vs time for saturated test cell not under influence of EOP. ERDC TR-06-9 23 Electrical Current...Intrusion Control in Concrete Structures. U.S. Army Corps of Engineers Electrical /Mechanical Technology Transfer Conference paper . Reuss, F. F. 1809...Electro-Osmotic Effect on Moisture Content in Saturated Cells................ 21 Electrical Current Through the Test Cells

  4. Electrode kinetic and electro-kinetic effects in electroosmotic dewatering of clay suspensions

    SciTech Connect

    Vijh, A.K.

    1997-05-01

    Lockhart`s remarks on the author`s previous interpretation of the electrochemical aspects of the electroosmotic dewatering (EOD) of clay suspensions are analyzed to provide some further clarification. Based on Lockhart`s excellent work, the authors put forward here novel electrochemical interpretations of some features of the following experimental observations: (1) Galvani dewatering; (2) the dewatering efficiency; and (3) high voltage needed for dewatering Al-kaolinite and aluminum electrode effect.

  5. Applying solubilization treatment to reverse clogging in laboratory-scale vertical flow constructed wetlands.

    PubMed

    Guofen, Hua; Wei, Zhu; Lianfang, Zhao; Yunhui, Zhang

    2010-01-01

    Substrate clogging is characterized as a frequently occurring operational problem for subsurface-flow constructed wetlands. The application of solubilization treatment to reduce clogging was tested in lab-scaled setups to provide a promising solution. The performance of solubilization treatment on reducing clogging and the related effects on plants and biofilms in the wetland system were investigated in this paper. The results showed that the infiltration rate and available porosity of wetland substrate increased as a function of increased dosage of NaOH, HCl, NaClO, and detergent, respectively. Among the four solvents, it appeared that NaClO had the most obvious effects on reducing clogging and the infiltration rate and effective porosity recovered to 69% of the original condition. The two possible reasons for solubilization were the flocculents' structure of the clogs was broken up or parts of the organic clogs were dissolved. The function of adding NaOH and NaClO was to dissolve the protein and polysaccharides of the organic clogs; the function of adding HCl was to release the anaerobic gas wrapped in the organic clogs. Furthermore, experiments results also showed that the solubilized solvents did not demonstrate a long-term negative effect on plants and biofilms.

  6. Analysis of dynamic stall using unsteady boundary-layer theory. [effect of pitch rate on the delay in forward movement of the rear flow reversal point

    NASA Technical Reports Server (NTRS)

    Scruggs, R. M.; Nash, J. F.; Singleton, R. E.

    1974-01-01

    The unsteady turbulent boundary layer and potential flow about a pitching airfoil are analyzed using numerical methods to determine the effect of pitch rate on the delay in forward movement of the rear flow reversal point. An explicit finite difference scheme is used to integrate the unsteady boundary layer equations, which are coupled at each instant of time to a fully unsteady and nonlinear potential flow analysis. A substantial delay in forward movement of the reversal point is demonstrated with increasing pitch rate, and it is shown that the delay results partly from the alleviation of the gradients in the potential flow, and partly from the effects of unsteadiness in the boundary layer itself. The predicted delay in flow-reversal onset, and its variation with pitch rate, are shown to be in reasonable agreement with experimental data relating to the delay in dynamic stall. From the comparisons it can be concluded (a) that the effects of time-dependence are sufficient to explain the failure of the boundary layer to separate during the dynamic overshoot, and (b) that there may be some link between forward movement of the reversal point and dynamic stall.

  7. Temperature evolution on Rh/Al{sub 2}O{sub 3} catalyst during partial oxidation of methane in a reverse flow reactor

    SciTech Connect

    Simeone, M.; Menna, L.; Salemme, L.; Allouis, C.

    2010-04-15

    Catalytic partial oxidation of methane was investigated in a reverse flow reactor with commercial Rh/Al{sub 2}O{sub 3} catalyst in pellets. The process is carried out in a catalytic fixed bed reactor and switching of feed flow direction is obtained through four electrovalves synchronized in pairs. Temperature profile along the catalyst bed was measured by fast IR thermography and product composition was measured with a continuous gas analyzer. Feed direction switching time, water to methane ratio and inert section length were investigated as process parameters. Data of catalyst bed temperature evolution during the flow cycle are presented, discussed and related to reactor performance as a function of reverse flow switching period. The effect of water addition to the reacting mixture on the dynamics of catalyst bed temperature evolution is also presented. (author)

  8. Electro-osmotic pumping and ionic conductance measurements in porous membranes

    NASA Astrophysics Data System (ADS)

    Vajandar, Saumitra K.

    Electro-osmotic (EO) pumps directly convert electrical energy into fluids' kinetic energy, which have many advantages such as a simple and compact structure, no mechanical moving parts, and easy integration. In general, it is easy for EO pumps to generate enough pressure but it has been a challenge for EO pumps to produce a high flowrate. EO pumps have found applications in various micro-/nano-electro-mechanical systems (MEMS/NEMS) and have the potential to impact a variety of engineering fields including microelectronics cooling and bio-analytical systems. This dissertation focuses on the design, fabrication and characterization of EO pumps based on two novel porous membrane materials: SiO2-coated anodic porous alumina and SiNx-coated porous silicon. High quality porous alumina membranes of controllable pore diameters in the range of 30-100 nm and pore lengths of 60-100 mum were fabricated by electrochemical anodization. The pores are straight, uniform and hexagonally close-packed with a high porosity of up to 50%. The inner surface of the pore was coated with a thin layer (˜5 nm) of SiO2 conformally to achieve a high zeta potential. The EO pumping flowrate of the fabricated anodic alumina membranes, coated and uncoated, was experimentally measured. Results indicate that the high zeta potential of the SiO2 coating increases the pumping flowrate even though the coating reduces the porosity of the membrane. The nanostructured SiO2-coated porous anodic alumina membranes can provide a normalized flowrate of 0.125 ml/min/V/cm2 under a low effective applied voltage of 3 V, which sets a record high normalized flowrate under low applied voltage. To realize field effect control of EO pumping, we designed and fabricated SiNx-coated porous silicon membranes with the silicon core as the electrode to apply a transverse gate potential. The gate potential will modulate the zeta potential of the pore wall and thereby provide control over the EO flowrate. The membranes were

  9. Investigation of wing upper surface flow-field disturbance due to NASA DC-8-72 in-flight inboard thrust-reverser deployment

    NASA Technical Reports Server (NTRS)

    Hamid, Hedayat U.; Margason, Richard J.; Hardy, Gordon

    1995-01-01

    An investigation of the wing upper surface flow-field disturbance due to in-flight inboard thrust reverser deployment on the NASA DC-8-72, which was conducted cooperatively by NASA Ames, the Federal Aviation Administration (FAA), McDonnell Douglas, and the Aerospace Industry Association (AIA), is outlined and discussed in detail. The purpose of this flight test was to obtain tufted flow visualization data which demonstrates the effect of thrust reverser deployment on the wing upper surface flow field to determine if the disturbed flow regions could be modeled by computational methods. A total of six symmetric thrust reversals of the two inboard engines were performed to monitor tuft and flow cone patterns as well as the character of their movement at the nominal Mach numbers of 0.55, 0.70, and 0.85. The tufts and flow cones were photographed and video-taped to determine the type of flow field that occurs with and without the thrust reversers deployed. In addition, the normal NASA DC-8 onboard Data Acquisition Distribution System (DADS) was used to synchronize the cameras. Results of this flight test will be presented in two parts. First, three distinct flow patterns associated with the above Mach numbers were sketched from the motion videos and discussed in detail. Second, other relevant aircraft parameters, such as aircraft's angular orientation, altitude, Mach number, and vertical descent, are discussed. The flight test participants' comments were recorded on the videos and the interested reader is referred to the video supplement section of this report for that information.

  10. An Investigation of Physics and Control of Flow Passing a NACA 0015 in Fully-Reversed Condition

    NASA Astrophysics Data System (ADS)

    Clifford, Christopher J.

    Flow control experiments were performed on a NACA 0015 airfoil in fully-reversed condition, which is anticipated to occur on the retreating blade side of advanced helicopters such as slowed-rotor compound rotorcraft. Control was achieved using nanosecond dielectric barrier discharge (NS-DBD) plasma actuators. The Reynolds number based on a chord length of 203 mm was fixed at 5.0 · 105, corresponding to a freestream velocity of ˜38 m/s. Two angles of attack were considered: α = 0° and 15°, each of which is relevant to a particular implementation of slowed-rotor technology. At α = 0°, the flow resembles that of a flow behind a cylinder. A von Karman vortex street formed in the wake where alternating vortex shedding occurred at a Strouhal number of 0.12. Excitation was performed using an NS-DBD on one side of the airfoil, with plasma formation just upstream of the separation line. However, there was no discernible influence upon the baseline behavior. At α = 15°, fully separated flow on the suction side extended well beyond the airfoil with naturally shed vortices at a Strouhal number of 0.19. Plasma actuation was evaluated at both the aerodynamic leading-edge (ALE) and aerodynamic trailing-edge (ATE) of the airfoil. The flow responded to the plasma actuation at the ALE by generating organized coherent structures in the shear layer over the separated region. Moderate excitation around the natural shedding Strouhal number had the most significant effects: synchronizing the shedding from the ALE and ATE, creating moderately sized structures that convected far downstream, greatly reducing the separation area, increasing lift, and decreasing drag. Excitation at much higher Strouhal numbers resulted in the flow returning to its natural shedding state, but with less coherent structures that diffused in the wake. This reduced the separation area and significantly reduced drag. Plasma actuation at the ATE caused a reduction in the magnitude of the fundamental and

  11. Kinetics of HIV-1 Latency Reversal Quantified on the Single-Cell Level Using a Novel Flow-Based Technique

    PubMed Central

    Martrus, G.; Niehrs, A.; Cornelis, R.; Rechtien, A.; García-Beltran, W.; Lütgehetmann, M.; Hoffmann, C.

    2016-01-01

    ABSTRACT HIV-1 establishes a pool of latently infected cells early following infection. New therapeutic approaches aiming at diminishing this persisting reservoir by reactivation of latently infected cells are currently being developed and tested. However, the reactivation kinetics of viral mRNA and viral protein production, and their respective consequences for phenotypical changes in infected cells that might enable immune recognition, remain poorly understood. We adapted a novel approach to assess the dynamics of HIV-1 mRNA and protein expression in latently and newly infected cells on the single-cell level by flow cytometry. This technique allowed the simultaneous detection of gagpol mRNA, intracellular p24 Gag protein, and cell surface markers. Following stimulation of latently HIV-1-infected J89 cells with human tumor necrosis factor alpha (hTNF-α)/romidepsin (RMD) or HIV-1 infection of primary CD4+ T cells, four cell populations were detected according to their expression levels of viral mRNA and protein. gagpol mRNA in J89 cells was quantifiable for the first time 3 h after stimulation with hTNF-α and 12 h after stimulation with RMD, while p24 Gag protein was detected for the first time after 18 h poststimulation. HIV-1-infected primary CD4+ T cells downregulated CD4, BST-2, and HLA class I expression at early stages of infection, proceeding Gag protein detection. In conclusion, here we describe a novel approach allowing quantification of the kinetics of HIV-1 mRNA and protein synthesis on the single-cell level and phenotypic characterization of HIV-1-infected cells at different stages of the viral life cycle. IMPORTANCE Early after infection, HIV-1 establishes a pool of latently infected cells, which hide from the immune system. Latency reversal and immune-mediated elimination of these latently infected cells are some of the goals of current HIV-1 cure approaches; however, little is known about the HIV-1 reactivation kinetics following stimulation with

  12. The Reverse-Flow Facial Artery Buccinator Flap for Skull Base Reconstruction: Key Anatomical and Technical Considerations.

    PubMed

    Farzal, Zainab; Lemos-Rodriguez, Ana M; Rawal, Rounak B; Overton, Lewis J; Sreenath, Satyan B; Patel, Mihir R; Zanation, Adam M

    2015-12-01

    Objective To highlight key anatomical and technical considerations for facial artery identification, and harvest and transposition of the facial artery buccinator (FAB) flap to facilitate its future use in anterior skull base reconstruction. Only a few studies have evaluated the reverse-flow FAB flap for skull base defects. Design Eight FAB flaps were raised in four cadaveric heads and divided into thirds; the facial artery's course at the superior and inferior borders of the flap was measured noting in which incisional third of the flap it laid. The flap's reach to the anterior cranial fossa, sella turcica, clival recess, and contralateral cribriform plate were studied. A clinical case and operative video are also presented. Results The facial artery had a near vertical course and stayed with the middle (⅝) or posterior third (⅜) of the flap in the inferior and superior incisions. Seven of eight flaps covered the sellar/planar regions. Only four of eight flaps covered the contralateral cribriform region. Lastly, none reached the middle third of the clivus. Conclusions The FAB flap requires an understanding of the facial artery's course, generally seen in the middle third of the flap, and is an appropriate alternative for sellar/planar and ipsilateral cribriform defects.

  13. Rapid detection of measles virus using reverse transcription loop-mediated isothermal amplification coupled with a disposable lateral flow device.

    PubMed

    Xu, Changping; Feng, Yan; Chen, Yin; Gao, Jian; Lu, Yiyu

    2016-06-01

    The measles virus (MeV) causes a highly contagious disease and efforts to reduce its spread are critical. A reverse transcription loop-mediated isothermal amplification assay coupled with a disposable lateral flow device (RT-LAMP-LFD) was developed for the rapid detection of MeV. The assay was performed in 40 min at an optimal temperature of 58 °C, with endpoint results visualized directly. A probe that was complementary to the RT-LAMP amplicon was designed to enhance assay specificity. Detection limit of the assay was 8.8 copies/μL synthetic RNA, which equals the sensitivity of real-time RT-PCR. Clinical specimens were used to validate the RT-LAMP-LFD in provincial Center for Disease Control and Prevention (CDC) (n = 245) and six municipal CDCs (n = 249). The results obtained using RT-LAMP-LFD and real-time RT-PCR were highly concordant. The RT-LAMP-LFD is rapid, stable, and does not require expensive equipment, which can be used for routine MeV monitoring in CDC laboratories.

  14. Sequential determination of multi-nutrient elements in natural water samples with a reverse flow injection system.

    PubMed

    Lin, Kunning; Ma, Jian; Yuan, Dongxing; Feng, Sichao; Su, Haitao; Huang, Yongming; Shangguan, Qipei

    2017-05-15

    An integrated system was developed for automatic and sequential determination of NO2(-), NO3(-), PO4(3-), Fe(2+), Fe(3+) and Mn(2+) in natural waters based on reverse flow injection analysis combined with spectrophotometric detection. The system operation was controlled by a single chip microcomputer and laboratory-programmed software written in LabVIEW. The experimental parameters for each nutrient element analysis were optimized based on a univariate experimental design, and interferences from common ions were evaluated. The upper limits of the linear range (along with detection limit, µmolL(-1)) of the proposed method was 20 (0.03), 200 (0.7), 12 (0.3), 5 (0.03), 5 (0.03), 9 (0.2) µmolL(-1), for NO2(-), NO3(-), PO4(3-), Fe(2+), Fe(3+) and Mn(2+), respectively. The relative standard deviations were below 5% (n=9-13) and the recoveries varied from 88.0±1.0% to 104.5±1.0% for spiked water samples. The sample throughput was about 20h(-1). This system has been successfully applied for the determination of multi-nutrient elements in different kinds of water samples and showed good agreement with reference methods (slope 1.0260±0.0043, R(2)=0.9991, n=50).

  15. Anthocyanin and flavonoid production from Perilla frutescens: pilot plant scale processing including cross-flow microfiltration and reverse osmosis.

    PubMed

    Meng, Linghua; Lozano, Yves; Bombarda, Isabelle; Gaydou, Emile; Li, Bin

    2006-06-14

    Extraction and concentration at a pilot plant scale of anthocyanins and flavonoids from Perilla frutescens var. frutescens harvested in the Guangzhou area of China were investigated. The study of extraction efficiency using mineral acids and organic acids showed that 0.01 mol/L nitric acid was the most suitable to extract flavonoids from this slightly red leaf cultivar. The red extract contained 12 mg/L (as cyanidin equivalent) anthocyanins and other flavones. The multistep process included cross-flow microfiltration (CFM) with a ceramic type membrane, reverse osmosis (RO), and rotating evaporation (RE). The filtration fluxes were high and constant for CFM (150 L/h/m2 at 0.6 b) and for RO (22 L/h/m2 at 40 b). The red extract was concentrated 9.4 times by RO and then 5.4 times by RE. It contained 422 mg/L anthocyanins, representing 77% of the total extracted anthocyanin. The proportion of flavonoids was found unchanged during processing. The concentrated extract showed a pH of 2.7, and its free acidity was found to be 46% of the acidity added for extraction, because of the buffering capacity of the extract. At the concentration level reached, a crystallized deposit occurred and was identified as tartrate.

  16. Reverse flow injection spectrophotometric determination of ciprofloxacin in pharmaceuticals using iron from soil as a green reagent.

    PubMed

    Palamy, Sysay; Ruengsitagoon, Wirat

    2017-09-13

    A novel reverse flow injection spectrophotometric method for the determination of ciprofloxacin was successfully combined with the on-line introduction of an iron solution extracted from soil as green reagent. The assay was optimized by a univariate method to select the optimum conditions for the highest absorbance and highest stability of the complex. Beer-Lambert's law (λmax=440nm) is obeyed in the range 0.5-50μgmL(-1) with a correlation coefficient (r(2)) of 0.9976 and 0.9996 using soil as green reagent from Khon Kaen, Thailand and Vientiane, Laos, respectively. The average percentage recoveries were in the range of 98.55-102.14% and the precision was in the range of 0.80-1.73%. The limit of detection and the limit of quantitation were 0.20 and 0.69μgmL(-1), respectively, with a sampling rate of over 46samplesh(-1). The method was successfully applied to the determination of ciprofloxacin in commercial pharmaceutical formulations. The results were in good agreement with those obtained by the reference HPLC method using a t-test at 95% of confidence level for comparison. This method is suitable for laboratories looking for alternative analytical methods using green reagents. Copyright © 2017 Elsevier B.V. All rights reserved.

  17. Inductively coupled plasma mass spectrometric detection for multielement flow injection analysis and elemental speciation by reversed-phase liquid chromatography

    SciTech Connect

    Thompson, J.J.; Houk, R.S.

    1986-10-01

    The feasibility of using an inductively coupled plasma mass spectrometer as a multielement detector for flow injection analysis (FIA) and ion-pair reversed-phase liquid chromatography was investigated. Sample introduction was by ultrasonic nebulization with aerosol desolvation. Absolute detection limits for FIA ranged from 0.01 to 0.1 ng for most elements using 10-..mu..L injection. Over 30 elements were surveyed for their response to both anionic and cationic ion pairing reagents. The separation and selective detection of various As and Se species were demonstrated, yielding detection limits near 0.1 ng (as element) for all six species present. Determination of 15 elements in a single injection with multiple ion monitoring produced similar detection limits. Isotope ratios were measured with sufficient precision (better than 2%) and accuracy (about 1%) on eluting peaks of Cd and Pb to demonstrate that liquid chromatography/inductively coupled plasma mass spectrometry should make speciation studies with stable tracer isotopes feasible.

  18. Evidence for a new geomagnetic reversal from lava flows in Idaho: discussion of short polarity reversals in the Brunhes and late Matuyama Polarity Chrons

    USGS Publications Warehouse

    Champion, D.E.; Lanphere, M.A.; Kuntz, M.A.

    1988-01-01

    K-Ar ages and paleomagnetic data for basalt samples from a new core hole (site E) at the Idaho National Engineering Laboratory (INEL) indicate that the age of the reversed polarity event recorded in Snake River Plain lavas is older than 465 ?? 50 ka (1000 years before present) reported previously by Champion et al. (1981). A review of data documenting short reversal records from volcanic and sedimentary rocks shows that there is evidence for eight polarity subchrons in the Brunhes and two besides the Jaramillo in the late Matuyama. These 10 short subchrons begin to indicate the many short events that Cox (1968) hypothesized must exist if polarity interval lengths have a Poisson distribution. The mean sustained polarity interval length since late Matuyama Chron time is 90 000 years. The similarity of this number with the 105-year period of the Earth's orbital eccentricity suggests anew that linkage between geomagnetic, paleoclimatic, and possible underlying Earth orbital parameters should be evaluated. -from Authors

  19. Label-free viscosity measurement of complex fluids using reversal flow switching manipulation in a microfluidic channel

    PubMed Central

    Jun Kang, Yang; Ryu, Jeongeun; Lee, Sang-Joon

    2013-01-01

    The accurate viscosity measurement of complex fluids is essential for characterizing fluidic behaviors in blood vessels and in microfluidic channels of lab-on-a-chip devices. A microfluidic platform that accurately identifies biophysical properties of blood can be used as a promising tool for the early detections of cardiovascular and microcirculation diseases. In this study, a flow-switching phenomenon depending on hydrodynamic balancing in a microfluidic channel was adopted to conduct viscosity measurement of complex fluids with label-free operation. A microfluidic device for demonstrating this proposed method was designed to have two inlets for supplying the test and reference fluids, two side channels in parallel, and a junction channel connected to the midpoint of the two side channels. According to this proposed method, viscosities of various fluids with different phases (aqueous, oil, and blood) in relation to that of reference fluid were accurately determined by measuring the switching flow-rate ratio between the test and reference fluids, when a reverse flow of the test or reference fluid occurs in the junction channel. An analytical viscosity formula was derived to measure the viscosity of a test fluid in relation to that of the corresponding reference fluid using a discrete circuit model for the microfluidic device. The experimental analysis for evaluating the effects of various parameters on the performance of the proposed method revealed that the fluidic resistance ratio (RJL/RL, fluidic resistance in the junction channel (RJL) to fluidic resistance in the side channel (RL)) strongly affects the measurement accuracy. The microfluidic device with smaller RJL/RL values is helpful to measure accurately the viscosity of the test fluid. The proposed method accurately measured the viscosities of various fluids, including single-phase (Glycerin and plasma) and oil-water phase (oil vs. deionized water) fluids, compared with conventional methods. The proposed

  20. Label-free viscosity measurement of complex fluids using reversal flow switching manipulation in a microfluidic channel.

    PubMed

    Jun Kang, Yang; Ryu, Jeongeun; Lee, Sang-Joon

    2013-01-01

    The accurate viscosity measurement of complex fluids is essential for characterizing fluidic behaviors in blood vessels and in microfluidic channels of lab-on-a-chip devices. A microfluidic platform that accurately identifies biophysical properties of blood can be used as a promising tool for the early detections of cardiovascular and microcirculation diseases. In this study, a flow-switching phenomenon depending on hydrodynamic balancing in a microfluidic channel was adopted to conduct viscosity measurement of complex fluids with label-free operation. A microfluidic device for demonstrating this proposed method was designed to have two inlets for supplying the test and reference fluids, two side channels in parallel, and a junction channel connected to the midpoint of the two side channels. According to this proposed method, viscosities of various fluids with different phases (aqueous, oil, and blood) in relation to that of reference fluid were accurately determined by measuring the switching flow-rate ratio between the test and reference fluids, when a reverse flow of the test or reference fluid occurs in the junction channel. An analytical viscosity formula was derived to measure the viscosity of a test fluid in relation to that of the corresponding reference fluid using a discrete circuit model for the microfluidic device. The experimental analysis for evaluating the effects of various parameters on the performance of the proposed method revealed that the fluidic resistance ratio ( R J L / R L , fluidic resistance in the junction channel ( R J L ) to fluidic resistance in the side channel ( R L )) strongly affects the measurement accuracy. The microfluidic device with smaller R J L / R L values is helpful to measure accurately the viscosity of the test fluid. The proposed method accurately measured the viscosities of various fluids, including single-phase (Glycerin and plasma) and oil-water phase (oil vs. deionized water) fluids, compared with conventional

  1. ac electro-osmotic micropump by asymmetric electrode polarization

    NASA Astrophysics Data System (ADS)

    Wu, Jie (Jayne)

    2008-01-01

    ac electro-osmosis (ACEO) has emerged recently as a promising strategy for fluid transport at microscale. With an array of planar interdigital electrodes immersed in an electrolyte, different charging mechanisms at electrode/electrolyte interface and electrokinetic surface flows can be induced by nonuniform electrical fields. To implement ACEO micropump, asymmetry in an electrode pair is essential to generate net flow, which has been typically achieved through asymmetric electrode geometries. This work proposes asymmetric electrode polarization processes to break the electrode symmetry. A dc bias is superimposed onto ac potentials, so that the two electrodes in a pair undergo capacitive charging or Faradaic charging separately. Applying such signals, pumping action has been demonstrated with only a few volts of applied voltage and a power consumption in the range of milliwatts. Pumping velocity by asymmetric electrode polarization exhibits an exponential dependency on voltage.

  2. Low-Power, Low-Voltage Electroosmotic Actuator for an Implantable Micropumping System Intended for Drug Delivery Applications

    NASA Astrophysics Data System (ADS)

    Getpreecharsawas, Jirachai

    An electroosmotic (EO) actuator offers a low-power, low-voltage alternative in a diaphragm-based periodic displacement micropump intended for an implantable drug delivery system. The actuator utilizes an electroosmosis mechanism to transport liquid across a membrane to deflect the pumping diaphragms in a reciprocating manner. In the study, the membrane made of porous nanocrystalline silicon (pnc-Si) tens of nanometers in thickness was used as the promising EO generator with low power consumption and small package size. This ultrathin membrane provides the opportunity for electrode integration such that the very high electric field can be generated across the membrane with the applied potential under 1 volt for low flow rate applications like drug delivery. Due to such a low applied voltage, the challenge, however, imposes on the capability of generating the pumping pressure high enough to deflect the pumping diaphragms and overcome the back pressure normally encountered in the biological tissue and organ. This research identified the cause of weak pumping pressure that the electric field inside the orifice-like nanopores of the ultrathin membrane is weaker than conventional theory would predict. It no longer scales uniformly with the thickness of membrane, but with the pore length-to-diameter aspect ratio for each nanopore. To enhance the pumping performance, the pnc-Si membrane was coated with an ultrathin Nafion film. As a result, the induced concentration difference across the Nafion film generates the osmotic pressure against the back pressure allowing the EO actuator to maintain the target pumping flow rate under 1 volt.

  3. Free-Flow Open-Chamber Electrophoresis

    NASA Technical Reports Server (NTRS)

    Sharnez, Rizwan; Sammons, David W.

    1994-01-01

    Free-flow open-chamber electrophoresis variant of free-flow electrophoresis performed in chamber with open ends and in which velocity of electro-osmotic flow adjusted equal to and opposite mean electrophoretic velocity of sample. Particles having electrophoretic mobilities greater than mean mobility of sample particles move toward cathode, those with mobilities less move toward anode. Technique applied to separation of components of mixtures of biologically important substances. Sensitivity enhanced by use of tapered chamber.

  4. Impact of higher alginate expression on deposition of Pseudomonas aeruginosa in radial stagnation point flow and reverse osmosis systems.

    PubMed

    Herzberg, Moshe; Rezene, Tesfalem Zere; Ziemba, Christopher; Gillor, Osnat; Mathee, Kalai

    2009-10-01

    Extracellular polymeric substances (EPS) have major impact on biofouling of reverse osmosis (RO) membranes. On one hand, EPS can reduce membrane permeability and on the other, EPS production by the primary colonizers may influence their deposition and attachment rate and subsequently affect the biofouling propensity of the membrane. The role of bacterial exopolysaccharides in bacterial deposition followed by the biofouling potential of an RO membrane was evaluated using an alginate overproducing (mucoid) Pseudomonas aeruginosa. The mucoid P. aeruginosa PAOmucA22 was compared with its isogenic nonmucoid prototypic parent PAO1 microscopically in a radial stagnation point flow (RSPF) system for their bacterial deposition characteristics. Then, biofouling potential of PAO1 and PAOmucA22 was determined in a crossflow rectangular plate-and-frame membrane cell, in which the strains were cultivated on a thin-film composite, polyamide, flat RO membrane coupon (LFC-1) under laminar flow conditions. In the RSPF system, the observed deposition rate of the mucoid strain was between 5- and 10-fold lower than of the wild type using either synthetic wastewater medium (with ionic strength of 14.7 mM and pH 7.4) or 15 mM KCl solution (pH of 6.2). The slower deposition rate of the mucoid strain is explained by 5- to 25-fold increased hydrophilicity of the mucoid strain as compared to the isogenic wild type, PAO1. Corroborating with these results, a significant delay in the onset of biofouling of the RO membrane was observed when the mucoid strain was used as the membrane colonizer, in which the observed time for the induced permeate flux decline was delayed (ca. 2-fold). In conclusion, the lower initial cell attachment of the mucoid strain decelerated biofouling of the RO membrane. Bacterial deposition and attachment is a critical step in biofilm formation and governed by intimate interactions between outer membrane proteins of the bacteria and the surface. Shielding these

  5. Rotation profile flattening and toroidal flow shear reversal due to the coupling of magnetic islands in tokamaks

    SciTech Connect

    Tobias, B.; Chen, M.; Classen, I. G. J.; Domier, C. W.; Fitzpatrick, R.; Grierson, B. A.; Luhmann, N. C.; Muscatello, C. M.; Okabayashi, M.; Olofsson, K. E. J.; Paz-Soldan, C.

    2016-04-15

    The electromagnetic coupling of helical modes, including those having different toroidal mode numbers, modifies the distribution of toroidal angular momentum in tokamak discharges. This can have deleterious effects on other transport channels as well as on magnetohydrodynamic (MHD) stability and disruptivity. At low levels of externally injected momentum, the coupling of core-localized modes initiates a chain of events, whereby flattening of the core rotation profile inside successive rational surfaces leads to the onset of a large m/n = 2/1 tearing mode and locked-mode disruption. Furthermore, with increased torque from neutral beam injection, neoclassical tearing modes in the core may phase-lock to each other without locking to external fields or structures that are stationary in the laboratory frame. The dynamic processes observed in these cases are in general agreement with theory, and detailed diagnosis allows for momentum transport analysis to be performed, revealing a significant torque density that peaks near the 2/1 rational surface. However, as the coupled rational surfaces are brought closer together by reducing q95, additional momentum transport in excess of that required to attain a phase-locked state is sometimes observed. Rather than maintaining zero differential rotation (as is predicted to be dynamically stable by single-fluid, resistive MHD theory), these discharges develop hollow toroidal plasma fluid rotation profiles with reversed plasma flow shear in the region between the m/n = 3/2 and 2/1 islands. Additional forces expressed in this state are not readily accounted for, and therefore, analysis of these data highlights the impact of mode coupling on torque balance and the challenges associated with predicting the rotation dynamics of a fusion reactor-a key issue for ITER. Published by AIP Publishing.

  6. Rotation profile flattening and toroidal flow shear reversal due to the coupling of magnetic islands in tokamaks

    DOE PAGES

    Tobias, B.; Chen, M.; Classen, I. G. J.; ...

    2016-04-15

    The electromagnetic coupling of helical modes, including those having different toroidal mode numbers, modifies the distribution of toroidal angular momentum in tokamak discharges. This can have deleterious effects on other transport channels as well as on magnetohydrodynamic (MHD) stability and disruptivity. At low levels of externally injected momentum, the coupling of core-localized modes initiates a chain of events, whereby flattening of the core rotation profile inside successive rational surfaces leads to the onset of a large m/n = 2/1 tearing mode and locked-mode disruption. Furthermore, with increased torque from neutral beam injection, neoclassical tearing modes in the core may phase-lockmore » to each other without locking to external fields or structures that are stationary in the laboratory frame. The dynamic processes observed in these cases are in general agreement with theory, and detailed diagnosis allows for momentum transport analysis to be performed, revealing a significant torque density that peaks near the 2/1 rational surface. However, as the coupled rational surfaces are brought closer together by reducing q95, additional momentum transport in excess of that required to attain a phase-locked state is sometimes observed. Rather than maintaining zero differential rotation (as is predicted to be dynamically stable by single-fluid, resistive MHD theory), these discharges develop hollow toroidal plasma fluid rotation profiles with reversed plasma flow shear in the region between the m/n = 3/2 and 2/1 islands. Additional forces expressed in this state are not readily accounted for, and therefore, analysis of these data highlights the impact of mode coupling on torque balance and the challenges associated with predicting the rotation dynamics of a fusion reactor-a key issue for ITER. Published by AIP Publishing.« less

  7. Rotation profile flattening and toroidal flow shear reversal due to the coupling of magnetic islands in tokamaks

    NASA Astrophysics Data System (ADS)

    Tobias, B.; Chen, M.; Classen, I. G. J.; Domier, C. W.; Fitzpatrick, R.; Grierson, B. A.; Luhmann, N. C.; Muscatello, C. M.; Okabayashi, M.; Olofsson, K. E. J.; Paz-Soldan, C.

    2016-05-01

    The electromagnetic coupling of helical modes, even those having different toroidal mode numbers, modifies the distribution of toroidal angular momentum in tokamak discharges. This can have deleterious effects on other transport channels as well as on magnetohydrodynamic (MHD) stability and disruptivity. At low levels of externally injected momentum, the coupling of core-localized modes initiates a chain of events, whereby flattening of the core rotation profile inside successive rational surfaces leads to the onset of a large m/n = 2/1 tearing mode and locked-mode disruption. With increased torque from neutral beam injection, neoclassical tearing modes in the core may phase-lock to each other without locking to external fields or structures that are stationary in the laboratory frame. The dynamic processes observed in these cases are in general agreement with theory, and detailed diagnosis allows for momentum transport analysis to be performed, revealing a significant torque density that peaks near the 2/1 rational surface. However, as the coupled rational surfaces are brought closer together by reducing q95, additional momentum transport in excess of that required to attain a phase-locked state is sometimes observed. Rather than maintaining zero differential rotation (as is predicted to be dynamically stable by single-fluid, resistive MHD theory), these discharges develop hollow toroidal plasma fluid rotation profiles with reversed plasma flow shear in the region between the m/n = 3/2 and 2/1 islands. The additional forces expressed in this state are not readily accounted for, and therefore, analysis of these data highlights the impact of mode coupling on torque balance and the challenges associated with predicting the rotation dynamics of a fusion reactor—a key issue for ITER.

  8. Rotation profile flattening and toroidal flow shear reversal due to the coupling of magnetic islands in tokamaks

    SciTech Connect

    Tobias, B.; Grierson, B. A.; Okabayashi, M.; Chen, M.; Domier, C. W.; Luhmann, N. C.; Muscatello, C. M.; Classen, I. G. J.; Fitzpatrick, R.; Olofsson, K. E. J.; Paz-Soldan, C.

    2016-05-15

    The electromagnetic coupling of helical modes, even those having different toroidal mode numbers, modifies the distribution of toroidal angular momentum in tokamak discharges. This can have deleterious effects on other transport channels as well as on magnetohydrodynamic (MHD) stability and disruptivity. At low levels of externally injected momentum, the coupling of core-localized modes initiates a chain of events, whereby flattening of the core rotation profile inside successive rational surfaces leads to the onset of a large m/n = 2/1 tearing mode and locked-mode disruption. With increased torque from neutral beam injection, neoclassical tearing modes in the core may phase-lock to each other without locking to external fields or structures that are stationary in the laboratory frame. The dynamic processes observed in these cases are in general agreement with theory, and detailed diagnosis allows for momentum transport analysis to be performed, revealing a significant torque density that peaks near the 2/1 rational surface. However, as the coupled rational surfaces are brought closer together by reducing q{sub 95}, additional momentum transport in excess of that required to attain a phase-locked state is sometimes observed. Rather than maintaining zero differential rotation (as is predicted to be dynamically stable by single-fluid, resistive MHD theory), these discharges develop hollow toroidal plasma fluid rotation profiles with reversed plasma flow shear in the region between the m/n = 3/2 and 2/1 islands. The additional forces expressed in this state are not readily accounted for, and therefore, analysis of these data highlights the impact of mode coupling on torque balance and the challenges associated with predicting the rotation dynamics of a fusion reactor—a key issue for ITER.

  9. High-precision 40Ar/^{39}Ar Ages for the Matuyama-Brunhes Reversal and the Big Lost Subchron from Lava Flows on La Palma, Canary Islands

    NASA Astrophysics Data System (ADS)

    Relle, M.; Singer, B.; Hoffman, K.; Battle, A.; Laj, C.; Carracedo, J.; Guillou, H.

    2001-05-01

    The timing of geomagnetic reversals, excursions or events is crucial to understanding the frequency of geomagnetic field instability. A detailed study of 36 lava flows comprising two stratigraphic sequences on the island of La Palma, Canary Islands revealed a complex record of 3 distinct geomagnetic events. The Matuyama-Brunhes (M-B) reversal is recorded in 5 transitionally magnetized lava flows from the north side of the Barranco de Los Tilos. The isochron ages for 3 of these lavas are defined by 11 incremental heating experiments and yielded a weighted mean age* of 796.3\\pm9.0 ka (2\\sigma). On the basis of paleomagnetic results and 2 imprecise K-Ar ages (Abdel-Monem et al., 1972), lavas in the south side of Los Tilos Barranco were previously thought to record the M-B reversal. The lowermost lavas have a weak remanence that may suggest transitioning field behavior. 40Ar/^{39}Ar isochrons from 4 of these flows were defined by 11 separate incremental-heating experiments, and gave a weighted mean age of 823.2\\pm8.6 ka. This anomalous, but not fully transitional, field behavior, 27\\pm17 ka prior to the M-B reversal, may evince a precursor to the M-B reversal as suggested in some marine sediment records. Further up section are two normal polarity flows that gave 40Ar/^{39}Ar isochrons of 751.9\\pm8.1 ka and 675.0\\pm15.7 ka, confirming the highly episodic nature of volcanism that preserves this geomagnetic record. Directly above these normal flows are nine transitionally magnetized lavas with VGPs over India and the section is capped by one normal polarity flow. The 40Ar/^{39}Ar isochrons of 5 lavas, including the uppermost normal flow, were defined by 14 separate experiments and gave a weighted mean age of 578.6\\pm7.8 ka. From these same transitional lavas, Quidelleur et al. (1999, EPSL) reported 3 unspiked K-Ar ages with a weighted mean of 602\\pm24 ka (2\\sigma) and proposed a new event called the "La Palma" excursion. The 40Ar/^{39}Ar age presented here is a

  10. Reverse polarity capillary zone electrophoresis analysis of nitrate and nitrite in natural water samples

    SciTech Connect

    Metcalf, S.G.

    1998-06-11

    This paper describes the application of reverse polarity capillary zone electrophoresis (RPCE) for rapid and accurate determination of nitrate and nitrite in natural water samples. Using hexamethonium bromide (HMB) as an electroosmotic flow modifier in a borate buffer at pH 9.2, the resolution of nitrate and nitrite was accomplished in less than 3 minutes. RPCE was compared with ion chromatographic (IC) and cadmium reduction flow injection analysis (Cd-FIA) methods which are the two most commonly used standard methods for the analysis of natural water samples for nitrate and nitrite. When compared with the ion chromatographic method for the determination of nitrate and nitrite, RPCE reduced analysis time, decreased detection limits by a factor of 10, cut laboratory wastes by more than two orders of magnitude, and eliminated interferences commonly associated with IC. When compared with the cadmium reduction method, RPCE had the advantage of simultaneous determination of nitrate and nitrite, could be used in the presence of various metallic ions that normally interfere in cadmium reduction, and decreased detection limits by a factor of 10.

  11. Influence of catalyticity of a porous medium on the concentration limit of filtration combustion of a water-organic mixture in a reversible flow reactor

    NASA Astrophysics Data System (ADS)

    Dobrego, K. V.; Koznacheev, I. A.

    2012-09-01

    The problem on oxidation purification of water in a reversible flow reactor with the use of a catalyst has been studied by numerical methods. We have made comparative studies of the concentration limits of mixture combustion attained in inert and catalytic porous media reactors at varied values of the liquid flow rate, the reactor length, the heat loss coefficient, and the size of the packed bed. It has been established that the use of a catalyst leads to an insignificant decrease in the concentration limit: 11.6% against 13.4% (adiabatic case) and 12.5% against 13.9% (standard insulation).

  12. Design of a pulsed-mode fluidic pump using a venturi-like reverse flow diverter. [With no packing glands, mechanical seals or moving parts

    SciTech Connect

    Smith, G.V.; Lewis, B.E.

    1987-02-01

    This report presents a design procedure for pulsed-mode, venturi-like reverse flow diverter (RFD) pumping systems. Design techniques are presented for systems in which the output line area is allowed to vary proportionally with the throat area of the RFD as well as situations in which the output line area is held constant. The results show that for cases in which the output line area is allowed to vary, an optimum RFD throat area exists for a given input pressure. For situations in which the output line area is held constant, the average output flow decreases in almost a linear fashion with increasing RFD throat area. 6 refs., 8 figs.

  13. Reactive oxygen species are generated by the respiratory complex II--evidence for lack of contribution of the reverse electron flow in complex I.

    PubMed

    Moreno-Sánchez, Rafael; Hernández-Esquivel, Luz; Rivero-Segura, Nadia A; Marín-Hernández, Alvaro; Neuzil, Jiri; Ralph, Stephen J; Rodríguez-Enríquez, Sara

    2013-02-01

    Succinate-driven oxidation via complex II (CII) may have a significant contribution towards the high rates of production of reactive oxygen species (ROS) by mitochondria. Here, we show that the CII Q site inhibitor thenoyltrifluoroacetone (TTFA) blocks succinate + rotenone-driven ROS production, whereas the complex III (CIII) Qo inhibitor stigmatellin has no effect, indicating that CII, not CIII, is the ROS-producing site. The complex I (CI) inhibitor rotenone partially reduces the ROS production driven by high succinate levels (5 mm), which is commonly interpreted as being due to inhibition of a reverse electron flow from CII to CI. However, experimental evidence presented here contradicts the model of reverse electron flow. First, ROS levels produced using succinate + rotenone were significantly higher than those produced using glutamate + malate + rotenone. Second, in tumor mitochondria, succinate-driven ROS production was significantly increased (not decreased) by rotenone. Third, in liver mitochondria, rotenone had no effects on succinate-driven ROS production. Fourth, using isolated heart or hepatoma (AS-30D) mitochondria, the CII Qp anti-cancer drug mitochondrially targeted vitamin E succinate (MitoVES) induced elevated ROS production in the presence of low levels of succinate(0.5 mm), but rotenone had no effect. Using sub-mitochondrial particles, the Cu-based anti-cancer drug Casiopeina II-gly enhanced succinate-driven ROS production. Thus, the present results are inconsistent with and question the interpretation of reverse electron flow from CII to CI and the rotenone effect on ROS production supported by succinate oxidation. Instead, a thermodynamically more favorable explanation is that, in the absence of CIII or complex IV (CIV) inhibitors (which, when added, facilitate reverse electron flow by inducing accumulation of ubiquinol, the CI product), the CII redox centers are the major source of succinate-driven ROS production.

  14. Electroosmotic transport of mannitol across human nail during constant current iontophoresis.

    PubMed

    Dutet, Julie; Delgado-Charro, M Begoña

    2010-06-01

    This work aimed to elucidate the role of electroosmosis during trans-nail iontophoresis. Passive and iontophoretic experiments were performed after short hydration (10-15 min) of human nail tips. The electroosmotic fluxes of mannitol were determined during anodal and cathodal iontophoresis and at different pH values. Passive controls were also carried out. Four sets of experiments were performed: (a) three anodal delivery experiments using different nails, at pH 4.0, 5.0 and 7.4, (b) one anodal delivery experiment that kept the same nails across two pH stages, (c) one experiment, comprising an anodal delivery stage (pH 4 and 7.4) followed by a cathodal delivery stage (pH 7.4 and 4), which kept the same nails across the different polarities and pH stages, and (d) a passive experiment keeping the same nails across different pH values (4 and 7.4). The fluxes of mannitol measured were very variable and little difference between passive and electroosmotic transport was observed. Cathodal and anodal fluxes were not always significantly different. Experiments which minimised internail variability suggested that the nails were negatively charged at physiological pH, and that this negative charge was lost at pH 4. These results suggest a modest and highly variable contribution of electroosmosis to the iontophoretic transungual flux.

  15. Fabrication and study of AC electro-osmotic micropumps

    NASA Astrophysics Data System (ADS)

    Guo, Xin

    In this thesis, microelectrode arrays of micropumps have been designed, fabricated and characterized for transporting microfluid by AC electro-osmosis (ACEO). In particular, the 3D stepped electrode design which shows superior performance to others in literature is adopted for making micropumps, and the performance of such devices has been studied and explored. A novel fabrication process has also been developed in the work, realizing 3D stepped electrodes on a flexible substrate, which is suitable for biomedical use, for example glaucoma implant. There are three major contributions to ACEO pumping in the work. First, a novel design of 3D "T-shaped" discrete electrode arrays was made using PolyMUMPsRTM process. The breakthrough of this work was discretizing the continuous 3D stepped electrodes which were commonly seen in the past research. The "T-shaped" electrodes did not only create ACEO flows on the top surfaces of electrodes but also along the side walls between separated electrodes. Secondly, four 3D stepped electrode arrays were designed, fabricated and tested. It was found from the experiment that PolyMUMPsRTM ACEO electrodes usually required a higher driving voltage than gold electrodes for operation. It was also noticed that a simulation based on the modified model taking into account the surface oxide of electrodes showed a better agreement with the experimental results. It thus demonstrated the possibility that the surface oxide of electrodes had impact on fluidic pumping. This methodology could also be applied to metal electrodes with a native oxide layer such as titanium and aluminum. Thirdly, a prototype of the ACEO pump with 3D stepped electrode arrays was first time realized on a flexible substrate using Kapton polyimide sheets and packaged with PDMS encapsulants. Comprehensive experimental testing was also conducted to evaluate the mechanical properties as well as the pumping performance. The experimental findings indicated that this fabrication

  16. [Prognostic factors of perinatal short-term outcome in severe placental insufficiency using Doppler sonography to assess end-diastolic absent and reverse blood flow in umbilical arteries].

    PubMed

    Frauenschuh, I; Wirbelauer, J; Karl, S; Girschick, G; Rehn, M; Zollner, U; Frambach, T; Dietl, J; Müller, T

    2015-02-01

    Significant placental insufficiency, indicated by Doppler ultrasound findings of absent or reverse end-diastolic flow velocities (AREDV), is associated with increased morbidity and mortality. Analysis of blood flow in the ductus venosus should assist in early intrauterine recognition of threatened foetuses. 58 high-risk pregnancies with umbilical AREDV were repeatedly examined (n=364). Doppler findings were correlated with neonatal signs of deterioration (ratio of normoblasts to leukocytes, pH, base excess, Apgar score), as well as short-term morbidity [need for intubation, duration of assisted respiration, evidence of respiratory distress syndrome (RDS), bronchopulmonary dysplasia (BPD), necrotising enterocolitis (NEC), intraventricular haemorrhage (IVH grade III+IV)] against the analysis of the blood flow findings (normal or increased pulsitility, absence or reverse end-diastolic flow) in the umbilical arteries (AU), the middle cerebral arteries (ACM) and ductus venosus (DV) relating these to birth weight and the duration of the pregnancy. The median period of observation was 12.8 days, 48% of the foetuses showed an abnormal ductus venosus flow and 26% an absent venous or reverse end-diastolic flow. The median date of delivery was 30 weeks, with a mean birth weight of 816 g. 93% were live births with 12% dying postnatally. Although the criteria for postnatal morbidity (BPD, NEC, IVH III+IV) and mortality did not correlate with changes in arterial and venous Doppler parameters in our group, there was a significant relationship between the normoblast count, known to be a marker of chronic hypoxia. The Apgar 10 minte score, umbilical arterial pH and base excess were correlated with changes in the DV flow curves. Healthy survival started, irrespective of arterial or venous blood flow criteria, from 27+0 weeks of pregnancy. If born between 27.0 and 30+6 weeks, the infants were more likely to be healthy the less the blood flow had been compromised. A birth weight

  17. Epithelial fluid transport: protruding macromolecules and space charges can bring about electro-osmotic coupling at the tight junctions.

    PubMed

    Rubashkin, A; Iserovich, P; Hernández, J A; Fischbarg, J

    2005-12-01

    The purpose of the present work is to investigate whether the idea of epithelial fluid transport based on electro-osmotic coupling at the level of the leaky tight junction (TJ) can be further supported by a plausible theoretical model. We develop a model for fluid transport across epithelial layers based on electro-osmotic coupling at leaky tight junctions (TJ) possessing protruding macromolecules and fixed electrical charges. The model embodies systems of electro-hydrodynamic equations for the intercellular pathway, namely the Brinkman and the Poisson-Boltzmann differential equations applied to the TJ. We obtain analytical solutions for a system of these two equations, and are able to derive expressions for the fluid velocity profile and the electrostatic potential. We illustrate the model by employing geometrical parameters and experimental data from the corneal endothelium, for which we have previously reported evidence for a central role for electro-osmosis in translayer fluid transport. Our results suggest that electro-osmotic coupling at the TJ can account for fluid transport by the corneal endothelium. We conclude that electro-osmotic coupling at the tight junctions could represent one of the basic mechanisms driving fluid transport across some leaky epithelia, a process that remains unexplained.

  18. The Electroosmotic Effects Arising from the Interaction of the Selectively Anion and Selectively Cation Permeable Parts of Mosaic Membranes

    PubMed Central

    Carr, Charles W.; Sollner, Karl

    1964-01-01

    It has been previously shown, theoretically and in model system experiments, that mosaic membranes composed of anion-selective (electropositive) and cation-selective (electronegative) parts interposed between electrolytic solutions of different concentrations give rise to local electrical circuits. In this work with model systems it is shown that these currents produce electroosmosis. In systems with permselective electronegative membranes and KCl solutions, the electroosmotic water transport was 16 moles/faraday. With the permselective electronegative membrane replaced by more porous electronegative membranes, the electroosmotic effects were about twice as high. With Li salts, the water transport was considerably larger. A system with a permselective electropositive membrane of 50 cm2 effective area and an electronegative membrane of 120 cm2 gave internally generated currents up to 20 ma. In extrapolating from the results with macromodels to effects with true mosaics, i.e. microsystems, it is stressed that current depends on the linear distance over which membranes interact. In true mosaic membranes, the current pathways will be of the same order as the dimensions of individual membrane microelements; the sum of all local microcurrents will be correspondingly larger than the current in the macromodel, and the electroosmotic effects will be proportionately greater. Electroosmotic effects with true charge-mosaic membranes may be of the same order or larger than the liquid transport by normal and anomalous osmosis which might occur across the individual parts of the charge-mosaic. PMID:14185581

  19. Experimental localization of an acoustic sound source in a wind-tunnel flow by using a numerical time-reversal technique.

    PubMed

    Padois, Thomas; Prax, Christian; Valeau, Vincent; Marx, David

    2012-10-01

    The possibility of using the time-reversal technique to localize acoustic sources in a wind-tunnel flow is investigated. While the technique is widespread, it has scarcely been used in aeroacoustics up to now. The proposed method consists of two steps: in a first experimental step, the acoustic pressure fluctuations are recorded over a linear array of microphones; in a second numerical step, the experimental data are time-reversed and used as input data for a numerical code solving the linearized Euler equations. The simulation achieves the back-propagation of the waves from the array to the source and takes into account the effect of the mean flow on sound propagation. The ability of the method to localize a sound source in a typical wind-tunnel flow is first demonstrated using simulated data. A generic experiment is then set up in an anechoic wind tunnel to validate the proposed method with a flow at Mach number 0.11. Monopolar sources are first considered that are either monochromatic or have a narrow or wide-band frequency content. The source position estimation is well-achieved with an error inferior to the wavelength. An application to a dipolar sound source shows that this type of source is also very satisfactorily characterized.

  20. Influence of pH*-value of methanolic electrolytes on electroosmotic flow in hydrophilic coated capillaries.

    PubMed

    Belder, D; Elke, K; Husmann, H

    2000-01-28

    The dependency of EOF on the H+-concentration and the related so called pH* value of methanolic electrolytes has been examined with poly(ethylene glycol) (PEG), poly(vinyl alcohol) (PVA) and uncoated capillaries. These results were compared with the pH dependency of EOF of these capillaries using aqueous buffers. In uncoated capillaries the dependency of EOF on the pH(*)-value is very similar for aqueous and methanolic electrolytes. The EOF increases with increasing H+-concentration and pH-hysteresis is observed. In PVA coated capillaries the EOF is strongly reduced over wide pH* or pH ranges for both methanolic electrolytes and aqueous buffers. The EOF in PEG coated capillaries is surprisingly directed to the anode with methanolic electrolytes whereas a reduced cathodic EOF is observed in aqueous electrolytes. The anodic EOF of PEG-coated capillaries in methanolic electrolytes is independent of the pH*-value. The usefulness of PEG- and PVA-coated capillaries for adjusting the EOF in non-aqueous electrolytes for the analysis of isomeric organic acids was demonstrated.

  1. Electrophoretic mobilities of neutral analytes and electroosmotic flow markers in aqueous solutions of Hofmeister salts.

    PubMed

    Křížek, Tomáš; Kubíčková, Anna; Hladílková, Jana; Coufal, Pavel; Heyda, Jan; Jungwirth, Pavel

    2014-03-01

    Small neutral organic compounds have traditionally the role of EOF markers in electrophoresis, as they are expected to have zero electrophoretic mobility in external electric fields. The BGE contains, however, ions that have unequal affinities to the neutral molecules, which in turn results in their mobilization. In this study we focused on two EOF markers-thiourea and DMSO, as well as on N-methyl acetamide (NMA) as a model of the peptide bond. By means of CE and all atom molecular dynamics simulations we explored mobilization of these neutral compounds in large set of Hofmeister salts. Employing a statistical mechanics approach, we were able to reproduce by simulations the experimental electrophoretic mobility coefficients. We also established the role of the chemical composition of marker and the BGE on the measured electrophoretic mobility coefficient. For NMA, we interpreted the results in terms of the relative affinities of cations versus anions to the peptide bond. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Comparison of the performance of forward fill/flush and reverse fill/flush flow modulation in comprehensive two-dimensional gas chromatography.

    PubMed

    Krupčík, Jan; Gorovenko, Roman; Špánik, Ivan; Sandra, Pat; Giardina, Matthew

    2016-09-30

    The performances of forward flow fill and flush (FFF) and of reverse flow fill and flush (RFF) in flow modulated comprehensive two-dimensional gas chromatography (GC×GC) using the same volume of the sampling channel have been studied and compared. Sample models include a reference mixture of hydrocarbons at low concentration, a petroleum reformate product and the essential oil of Rosa damascena Miller. The latter samples contain solutes in different concentrations but some up to 30% allowing to study overloading phenomena in detail. For solutes injected at low quantity, the performance of FFF and RFF is similar. For solutes present in a sample at high quantity, RFF guarantees less broadening and spreading resulting in better quantitation. Copyright © 2016 Elsevier B.V. All rights reserved.

  3. Amazon river flow regime and flood recessional agriculture: Flood stage reversals and risk of annual crop loss

    NASA Astrophysics Data System (ADS)

    Coomes, Oliver T.; Lapointe, Michel; Templeton, Michael; List, Geneva

    2016-08-01

    The annual flood cycle is an important driver of ecosystem structure and function in large tropical rivers such as the Amazon. Riparian peasant communities rely on river fishing and annual floodplain agriculture, closely adapted to the recession phase of the flood pulse. This article reports on a poorly documented but important challenge facing farmers practicing flood recessional agriculture along the Amazon river: frequent, unpredictable stage reversals (repiquetes) which threaten to ruin crops growing on channel bars. We assess the severity of stage reversals for rice production on exposed river mud bars (barreales) near Iquitos, Peru. Crop loss risk is estimated based on a quantitative analysis of 45 years of daily Amazon stage data and field data from floodplain communities nearby in the Muyuy archipelago, upstream of Iquitos. Rice varieties selected, elevations of silt rich bars where rice is sown, as well as planting and harvest dates are analyzed in the light of the timing, frequencies and amplitudes of observed stage reversals that have the potential to destroy growing rice. We find that unpredictable stage reversals can produce substantial crop losses and shorten significantly the length of average growing seasons on lower elevation river bars. The data reveal that local famers extend planting down to lower bar elevations where the mean probabilities of re-submergence before rice maturity (due to reversals) approach 50%, below which they implicitly consider that the risk of crop loss outweighs the potential reward of planting.

  4. Analysis of traveling-wave electro-osmotic pumping with double-sided electrode arrays

    NASA Astrophysics Data System (ADS)

    Yeh, Hung-Chun; Yang, Ruey-Jen; Luo, Win-Jet

    2011-05-01

    In this paper, a series of numerical simulations was performed to investigate the pumping performance of electro-osmotic micropumps containing electrode arrays patterned on the upper and lower sides of a microchannel. The simulations have been analyzed with a linear electro-osmotic model based upon the Debye-Hückel theory of the double layer. The potential drop across the diffuse layer is assumed to be less than 25 mV (kBT/e), and there is a linear response between the surface charge and the voltage drop across the double layer. The double layer is not resolved but is lumped into effective parameters that are imported from the Debye-Hückel and Stern layers. We examined the effects of the relative positioning of the electrodes in the opposing arrays (i.e., symmetrical or staggered), and the phase lag and the angular frequency of the alternating current (ac) signals applied to the electrodes within the two arrays. A critical height of the microchannel was observed, below which the interactions of the applied electrical potentials on the walls became significant. The optimum pumping effect was obtained when the electrode arrays were symmetrical to one another around the centerline of the channel and were activated by ac potentials with a 0° phase shift. The corresponding angular frequency of the maximum pumping velocity for different phase shifts of the applied ac signals was also determined. Overall, the simulation results presented in this paper provide a useful insight into the optimal design parameters and operating conditions for micropumps containing two arrays of microelectrodes on the microchannel walls.

  5. Analysis of traveling-wave electro-osmotic pumping with double-sided electrode arrays.

    PubMed

    Yeh, Hung-Chun; Yang, Ruey-Jen; Luo, Win-Jet

    2011-05-01

    In this paper, a series of numerical simulations was performed to investigate the pumping performance of electro-osmotic micropumps containing electrode arrays patterned on the upper and lower sides of a microchannel. The simulations have been analyzed with a linear electro-osmotic model based upon the Debye-Hückel theory of the double layer. The potential drop across the diffuse layer is assumed to be less than 25 mV (k(B)T/e), and there is a linear response between the surface charge and the voltage drop across the double layer. The double layer is not resolved but is lumped into effective parameters that are imported from the Debye-Hückel and Stern layers. We examined the effects of the relative positioning of the electrodes in the opposing arrays (i.e., symmetrical or staggered), and the phase lag and the angular frequency of the alternating current (ac) signals applied to the electrodes within the two arrays. A critical height of the microchannel was observed, below which the interactions of the applied electrical potentials on the walls became significant. The optimum pumping effect was obtained when the electrode arrays were symmetrical to one another around the centerline of the channel and were activated by ac potentials with a 0° phase shift. The corresponding angular frequency of the maximum pumping velocity for different phase shifts of the applied ac signals was also determined. Overall, the simulation results presented in this paper provide a useful insight into the optimal design parameters and operating conditions for micropumps containing two arrays of microelectrodes on the microchannel walls. © 2011 American Physical Society

  6. Scanning electrochemical microscopy of membrane transport in the reverse imaging mode.

    PubMed

    Uitto, O D; White, H S

    2001-02-01

    Scanning electrochemical microscopy (SECM), operated in reverse imaging mode (RIM), has been used to visualize the steady-state transport of molecules entering into porous membranes. RIM imaging is advantageous for investigating transport across biological membranes in situations where the SECM tip can access only the exterior membrane surface. Examples of RIM images of a synthetic membrane (mica with pores filled with the ion-selective polymer Nafion) and a biological membrane (hairless mouse skin) recorded during diffusive and iontophoretic transport, are reported. RIM imaging during diffusive transport allows visualization of the depletion of solute molecules in the solution adjacent to the pore openings. However, an accumulation of solute molecules above the pore opening is observed during iontophoresis, which is a consequence of the separation of the solute from the solvent (i.e., ultrafiltration). The separation results from differences in the rates of molecule transfer across the pore/solution interface when electroosmotic flow is operative. The results suggest that RIM imaging may be useful for measuring the kinetics of interfacial molecule transfer at biological membranes.

  7. Microfluidic flow counterbalanced capillary electrophoresis.

    PubMed

    Xia, Ling; Dutta, Debashis

    2013-04-07

    Flow counterbalanced capillary electrophoresis (FCCE) offers a powerful approach to realizing difficult charge based separations in compact microchip devices with application of relatively small electrical voltages. The need for dynamically controlling the pressure-gradient in the FCCE column however presents a significant challenge in implementing this technique on the microchip platform. In this article, we report the use of a simple on-chip pumping unit that allows precise introduction of a periodic pressure-driven backflow into a microfluidic separation channel enabling an FCCE analysis. The backflow in our device was produced by fabricating a shallow segment (0.5 μm deep) downstream of the analysis column (5 μm deep) and applying an electric field across it. A mismatch in the electroosmotic transport rate at the interface of this segment was shown to yield a pressure-gradient that could reverse the flow of the analyte bands without inverting the direction of the electric field. Although such a pressure-gradient also led to additional band broadening in the system, overall, the separation resolution of our device was observed to improve with an increasing number of back-and-forth sample passes through the analysis channel. For our current design, the corresponding improvement in the effective separation length was as much as 52% of the actual distance travelled by the chosen FITC-labeled amino acid samples. The reported device is well suited for further miniaturization of the FCCE method to the nanofluidic length scale which likely would improve its performance, and is easily integrable to other analytical procedures on the microchip platform for lab-on-a-chip applications.

  8. Corona anemometry for qualitative measurement of reversing surface flow with application to separation control by external excitation

    NASA Technical Reports Server (NTRS)

    Durbin, P. A.; Mckinzie, D. J.

    1987-01-01

    An corona anemometer which detects gas flow by the displacement of an ion beam is described, and experiments are performed using the anemometer to investigate the active control of diffusor separation by periodic forcing. The apparatus is applied to the separated flow over a rearward facing ramp. An oscillating vane is attached to the surface near the separation point. It is suggested that the enhancement in turbulent energy produced by the oscillating vane is due to drastic modification of the wake shear flow, and not to vane-produced turbulence.

  9. Simultaneous determination of nanomolar nitrite and nitrate in seawater using reverse flow injection analysis coupled with a long path length liquid waveguide capillary cell.

    PubMed

    Feng, Sichao; Zhang, Min; Huang, Yongming; Yuan, Dongxing; Zhu, Yong

    2013-12-15

    A reverse flow injection analysis (rFIA) method coupled with 1m liquid waveguide capillary cell and spectrophotometric detection for simultaneous determination of nanomolar nitrite and nitrate in seawater was developed. The design of two analytical channels sharing the same detection system in the proposed method allowed the analysis of both nitrite and nitrate with single sample injection. Different strategies of reagent injection were investigated to obtain a higher sensitivity and a better peak shape. A dual-wavelength detection mode was chosen to eliminate the light source shifting and sample matrix interference. Experimental parameters were optimized based on a univariate experimental design and the matrix effect from seawater was preliminarily investigated. The proposed method had high sensitivity with detection limit of 0.6 nmol L(-1) for both nitrite and nitrate. The linearity was 2-500 nmol L(-1) for both analytes, and the upper limit could be extended by choosing a lower sensitivity detection wavelength. The analytical results of 26 surface seawater samples obtained with the proposed method showed good agreement with those using a reference method operated using an automated segmented flow analyzer. The proposed method could greatly minimize the trouble introduced by bubbles in the segmented flow analyzer. It also had the advantages of high precision and high sample throughput (nitrite and nitrate detected in triplicate; 5 h(-1)). Compared to normal flow injection analysis, the rFIA method is superior due to its lower reagent consumption, less dispersion of sample, as well as higher sensitivity.

  10. Long-term successful outcome of severe hand ischemia using arterialization with reversal of venous flow: case report.

    PubMed

    Chloros, George D; Li, Zhongyu; Koman, L Andrew

    2008-09-01

    The management of unreconstructible vascular lesions in the hand is a challenge with limited options for treatment. After 22 years of hand ischemia, involving management with reverse interpositional vein grafting, periarterial sympathectomy, and partial finger amputations, a 62-year-old man underwent arterialization of the venous system of the hand for unreconstructible distal vascular lesions as a salvage procedure. At 7-year follow-up, the patient is pain-free with good functional and health-related quality of life outcomes and no further amputations. This procedure may be considered as a salvage alternative to prevent additional amputation in selected patients.

  11. Modeling the Effects of Changing Seasonal River Flow Rates on the Mixing of Reverse Osmosis Plant Effluent into the Pasquotank River in North Carolina

    NASA Astrophysics Data System (ADS)

    Fischer, K. M.; Hankinson, S. D.

    2004-12-01

    The goal of this research, begun Fall 2004, is to assess the seasonal impact of effluent from a reverse osmosis (RO) plant on the water of the Pasquotank River, a trunk river of Albemarle Sound in northeast North Carolina. Currently, the plant discharges about 103,000 gallons of high salinity (16 ppt) processed groundwater into Chantilly Bay in the Pasquotank River (0-3 ppt, depending on season) over an eight-hour operational day. The impact of the RO effluent on water chemistry and physical properties along the river bottom depends on the flow rate of the river. The Pasquotank is slower flowing (anecdotally, reverse flowing at times) during the generally dry summer season and faster flowing during the rainy winter season. This varying river flow rate may result in various effluent zones: a pool of effluent on the riverbed, a plume of effluent dissipating with downstream distance, or a minimal effluent signal near the outlet manifold. Modeling of seasonal data for the current rate of effluent discharge allows prediction of the effects of tripling the daily volume of RO plant discharge through round-the-clock plant operation, an outcome that seems likely in the near future due to residential growth in the county served by the plant. Data from fall and early winter 2004 will be presented. Water parameters (salinity/conductivity, temperature, pH, turbidity, Secchi depth, dissolved oxygen content, and dissolved major cation concentrations) are measured biweekly at nine surface stations (three water depths at each station) in the general vicinity of the effluent discharge outlet. Similar parameters are measured biweekly for Pasquotank River water at two stations upstream and two stations downstream of the outlet. River flow rates and discharge rates are measured weekly. The results of modeling using a two-end member mixing model and a normative analysis treatment will be presented. Additionally, modeling results for various possible changes (relocation of discharge

  12. Geometric Effects on Power Generation by Reverse Electrodialysiswith Self-induced Electrolyte Flow in Ion-Selective Nanochannels

    NASA Astrophysics Data System (ADS)

    Kim, Byoung Jae; Kim, Dong-Kwon; Lee, Seung-Hyun

    2012-11-01

    Recently, solid-state nanofluidic channels or nanopores have been demonstrated experimentally to serve as ion-selective membranes for small reverse electrodialysis systems. Ions of opposite charge to that of the surface (counter-ions) are attracted toward the surface while ions of like charge (co-ions) are repelled from the surface. As a result, the counter-ions are preferentially transported over the co-ions in the charged nanochannels. Under a concentration gradient, the ions diffuse spontaneously across the nanochannels, and a portion of the Gibbs free energy of mixing can be harvested continuously from the nanochannels by means of the net diffusion current. In the present study, power generation by reverse eletrodialysis in ion-selective nanochannels is numerically investigated by solving the Nernst-Planck equation for the ionic concentrations, the Poisson equation for the electric potential, and the Navier-Stokes equation for the electrolyte velocity simultaneously. We elucidated the effect of various parameters on power generation such as geometry of channel cross section, channel length, hydraulic diameter and the surface charge density etc. Corresponding Author.

  13. Stacking open-capillary electroosmotic pumps in series to boost the pumping pressure to drive high-performance liquid chromatographic separations

    DOE PAGES

    He, Chiyang; Zhu, Zaifang; Gu, Congying; ...

    2012-01-09

    Numerous micropumps have been developed, but few of them can produce adequate flow rate and pressure for high-performance liquid chromatography (HPLC) applications. We have recently developed an innovative hybrid electroosmotic pump (EOP) to solve this problem. The basic unit of a hybrid pump consists of a +EOP (the pumping element is positively charged) and a -EOP (the pumping element is negatively charged). The outlet of the +EOP is then joined with the inlet of the -EOP, forming a basic pump unit, while the anode of a positive high voltage (HV) power supply is placed at the joint. The inlet andmore » outlet of this pump unit are electrically grounded. With this configuration, we can stack many of such pump units in series to boost the pumping power. In this work, we describe in details how an open-capillary hybrid EOP is constructed and characterize this pump systematically. We also show that a hybrid EOP with ten serially stacked pump units can deliver a maximum pressure of 21.5 MPa (~3100 psi). Here, we further demonstrate the feasibility of using this hybrid EOP to drive eluents for HPLC separations of proteins and peptides.« less

  14. Stacking open-capillary electroosmotic pumps in series to boost the pumping pressure to drive high-performance liquid chromatographic separations

    SciTech Connect

    He, Chiyang; Zhu, Zaifang; Gu, Congying; Lu, Joann; Liu, Shaorong

    2012-01-09

    Numerous micropumps have been developed, but few of them can produce adequate flow rate and pressure for high-performance liquid chromatography (HPLC) applications. We have recently developed an innovative hybrid electroosmotic pump (EOP) to solve this problem. The basic unit of a hybrid pump consists of a +EOP (the pumping element is positively charged) and a -EOP (the pumping element is negatively charged). The outlet of the +EOP is then joined with the inlet of the -EOP, forming a basic pump unit, while the anode of a positive high voltage (HV) power supply is placed at the joint. The inlet and outlet of this pump unit are electrically grounded. With this configuration, we can stack many of such pump units in series to boost the pumping power. In this work, we describe in details how an open-capillary hybrid EOP is constructed and characterize this pump systematically. We also show that a hybrid EOP with ten serially stacked pump units can deliver a maximum pressure of 21.5 MPa (~3100 psi). Here, we further demonstrate the feasibility of using this hybrid EOP to drive eluents for HPLC separations of proteins and peptides.

  15. Stacking open-capillary electroosmotic pumps in series to boost the pumping pressure to drive high-performance liquid chromatographic separations.

    PubMed

    He, Chiyang; Zhu, Zaifang; Gu, Congying; Lu, Joann; Liu, Shaorong

    2012-03-02

    Numerous micropumps have been developed, but few of them can produce adequate flow rate and pressure for high-performance liquid chromatography (HPLC) applications. We have recently developed an innovative hybrid electroosmotic pump (EOP) to solve this problem. The basic unit of a hybrid pump consists of a +EOP (the pumping element is positively charged) and a -EOP (the pumping element is negatively charged). The outlet of the +EOP is then joined with the inlet of the -EOP, forming a basic pump unit, while the anode of a positive high voltage (HV) power supply is placed at the joint. The inlet and outlet of this pump unit are electrically grounded. With this configuration, we can stack many of such pump units in series to boost the pumping power. In this work, we describe in details how an open-capillary hybrid EOP is constructed and characterize this pump systematically. We also show that a hybrid EOP with ten serially stacked pump units can deliver a maximum pressure of 21.5 MPa (∼3100 psi). We further demonstrate the feasibility of using this hybrid EOP to drive eluents for HPLC separations of proteins and peptides.

  16. The effect of reverse remodeling on intraventricular flow in the LVAD-assisted heart studied in a mock circulatory loop

    NASA Astrophysics Data System (ADS)

    Moon, Juyeun

    Advanced heart failure patients may receive a Left Ventricular Assist Device (LVAD) to improve blood flow. An LVAD is a surgically implanted mechanical pump. After an LVAD is implanted, the heart often undergoes volume reduction and exhibits signs of restoration of normal cardiac geometry and function. Clinical studies show a reduction in left ventricle (LV) vortex circulation and kinetic energy (KE) after LVAD implantation, which we hypothesize is due to LV volume (LVV) reduction. The goal of this study is to measure the LV flow and vortex dynamics in LV models representing the volume reduction in the LVAD-assisted heart using Particle Image Velocimetry (PIV). Three silicone LV models were created with volume variation, and studied separately in the SDSU cardiac simulator to see the effects of ejection fraction (EF), LVV, and LVAD support on LV flow. Thoratec Heartmate II LVAD was used and the 2D velocity field in the LV mid-plane was measured for a full cardiac cycle. This field was further analyzed using MATLAB to calculate the pulsatility index along with the vortex circulation and KE of the large clockwise (CW) and smaller counter-clockwise (CCW) vortices that form in the LV. The effect of EF on LV flow without LVAD support was studied in the 100 and 150 ml LV models and produces a clear increase in vortex circulation, KE, and pulsatility with higher EF. The effect of LVV in the absence of LVAD support was compared for matched EF. The vortex circulation and KE of the CW vortex showed a decrease with decreased LVV. Addition of the LVAD to the LV resulted in an increase in flow as well as an increase in vortex circulation and KE. The pulsatility decreases with LVV reduction. The studies demonstrate that vortex circulation and KE are decreased with LVV and EF, and increased with the addition of an LVAD. Because LVAD patients are often experiencing all of these simultaneously, the net effect on the EF flow in not always clearly predictable. The results help to

  17. Experimental validation benchmark data for CFD of transient convection from forced to natural with flow reversal on a vertical flat plate

    DOE PAGES

    Lance, Blake W.; Smith, Barton L.

    2016-06-23

    Transient convection has been investigated experimentally for the purpose of providing Computational Fluid Dynamics (CFD) validation benchmark data. A specialized facility for validation benchmark experiments called the Rotatable Buoyancy Tunnel was used to acquire thermal and velocity measurements of flow over a smooth, vertical heated plate. The initial condition was forced convection downward with subsequent transition to mixed convection, ending with natural convection upward after a flow reversal. Data acquisition through the transient was repeated for ensemble-averaged results. With simple flow geometry, validation data were acquired at the benchmark level. All boundary conditions (BCs) were measured and their uncertainties quantified.more » Temperature profiles on all four walls and the inlet were measured, as well as as-built test section geometry. Inlet velocity profiles and turbulence levels were quantified using Particle Image Velocimetry. System Response Quantities (SRQs) were measured for comparison with CFD outputs and include velocity profiles, wall heat flux, and wall shear stress. Extra effort was invested in documenting and preserving the validation data. Details about the experimental facility, instrumentation, experimental procedure, materials, BCs, and SRQs are made available through this paper. As a result, the latter two are available for download and the other details are included in this work.« less

  18. Experimental validation benchmark data for CFD of transient convection from forced to natural with flow reversal on a vertical flat plate

    SciTech Connect

    Lance, Blake W.; Smith, Barton L.

    2016-06-23

    Transient convection has been investigated experimentally for the purpose of providing Computational Fluid Dynamics (CFD) validation benchmark data. A specialized facility for validation benchmark experiments called the Rotatable Buoyancy Tunnel was used to acquire thermal and velocity measurements of flow over a smooth, vertical heated plate. The initial condition was forced convection downward with subsequent transition to mixed convection, ending with natural convection upward after a flow reversal. Data acquisition through the transient was repeated for ensemble-averaged results. With simple flow geometry, validation data were acquired at the benchmark level. All boundary conditions (BCs) were measured and their uncertainties quantified. Temperature profiles on all four walls and the inlet were measured, as well as as-built test section geometry. Inlet velocity profiles and turbulence levels were quantified using Particle Image Velocimetry. System Response Quantities (SRQs) were measured for comparison with CFD outputs and include velocity profiles, wall heat flux, and wall shear stress. Extra effort was invested in documenting and preserving the validation data. Details about the experimental facility, instrumentation, experimental procedure, materials, BCs, and SRQs are made available through this paper. As a result, the latter two are available for download and the other details are included in this work.

  19. Experimental validation benchmark data for CFD of transient convection from forced to natural with flow reversal on a vertical flat plate

    SciTech Connect

    Lance, Blake W.; Smith, Barton L.

    2016-06-23

    Transient convection has been investigated experimentally for the purpose of providing Computational Fluid Dynamics (CFD) validation benchmark data. A specialized facility for validation benchmark experiments called the Rotatable Buoyancy Tunnel was used to acquire thermal and velocity measurements of flow over a smooth, vertical heated plate. The initial condition was forced convection downward with subsequent transition to mixed convection, ending with natural convection upward after a flow reversal. Data acquisition through the transient was repeated for ensemble-averaged results. With simple flow geometry, validation data were acquired at the benchmark level. All boundary conditions (BCs) were measured and their uncertainties quantified. Temperature profiles on all four walls and the inlet were measured, as well as as-built test section geometry. Inlet velocity profiles and turbulence levels were quantified using Particle Image Velocimetry. System Response Quantities (SRQs) were measured for comparison with CFD outputs and include velocity profiles, wall heat flux, and wall shear stress. Extra effort was invested in documenting and preserving the validation data. Details about the experimental facility, instrumentation, experimental procedure, materials, BCs, and SRQs are made available through this paper. As a result, the latter two are available for download and the other details are included in this work.

  20. Drumlins in reverse gear: observations against the relationship between drumlin stoss and lee asymmetry and flow direction

    NASA Astrophysics Data System (ADS)

    Spagnolo, M.; Clark, C. D.; Hughes, A. L.; Jordan, C.

    2008-12-01

    A well-known characteristic of drumlins is their longitudinal asymmetry in morphology with steep upstream slope angles (stoss) and more gentle downstream tails (lee). This characteristic is the main cue for deducing flow direction from drumlin fields. However, and although commonly accepted, few studies have actually quantified this drumlin property. How many drumlins in a field show this asymmetric form? Does it match with flow direction? Here we analyse drumlins from our mapping program of Great Britain, based on a high resolution DTM (5 m horizontal resolution, 0.7-1 m vertical accuracy) and yielding a GIS database of over 25,000 drumlins recorded as polygons, defined by their perimeter break-of-slope. Using GIS techniques we analysed long-profile asymmetry and compared this with the flow direction as derived from other information such as moraines, eskers, and spatial context within the ice sheet. Because drumlins may lie on a non- horizontal surface (i.e. hillslope), the first stage of analysis was to 'terrain correct' them. With all their bases adjusted to a horizontal plane, the highest point now also approximates the thickest part of the drumlin. We then computed a simple measure of asymmetry (Harry and Trenhaile, 1987) as the ratio of distances AB/(AB+BC), where A and C are the most upstream and downstream points respectively and B is the summit. In this paper we present the statistics of this analysis applied to the large sample of drumlins. The surprising result is that British drumlins are far from being "classically" asymmetrical. This is discussed in comparison to previous work and for its implication on drumlin formation theories.

  1. Stress-sensitive nutrient consumption via steady and non-reversing dynamic shear in continuous-flow rotational bioreactors.

    PubMed

    Belfiore, Laurence A; Bonani, Walter; Leoni, Matteo; Belfiore, Carol J

    2009-05-01

    Stress-sensitive biological response is simulated in a modified parallel-disk viscometer that implements steady and unidirectional dynamic shear under physiological conditions. Anchorage-dependent mammalian cells adhere to a protein coating on the surface of the rotating plate, receiving nutrients and oxygen from an aqueous medium that flows radially and tangentially, accompanied by transverse diffusion in the z-direction toward the active surface. This process is modeled as radial convection and axial diffusion with angular symmetry in cylindrical coordinates. The reaction/diffusion boundary condition on the surface of the rotating plate includes position-dependent stress-sensitive nutrient consumption via the zr- and zTheta-elements of the velocity gradient tensor at the cell/aqueous-medium interface. Linear transport laws in chemically reactive systems that obey Curie's theorem predict the existence of cross-phenomena between scalar reaction rates and the magnitude of the second-rank velocity gradient tensor, selecting only those elements of nabla v experienced by anchorage-dependent cells that are bound to protein-active sites. Stress sensitivity via the formalism of irreversible thermodynamics introduces a zeroth-order contribution to heterogeneous reaction rates that must be quenched when nutrients, oxygen, chemically anchored cells, or vacant active protein sites are not present on the surface of the rotating plate. Computer simulations of nutrient consumption profiles via simple nth-order kinetics (i.e., n=1,2) suggest that rotational bioreactor designs should consider stress-sensitivity when the shear-rate-based Damköhler number (i.e., ratio of the stress-dependent zeroth-order rate of nutrient consumption relative to the rate of nutrient diffusion toward active cells adhered to the rotating plate) is greater than approximately 25% of the stress-free Damköhler number. Rotational bioreactor simulations are presented for simple 1st-order, simple 2nd

  2. AC electro-osmotic mixing induced by non-contact external electrodes.

    PubMed

    Wang, Shau-Chun; Chen, Hsiao-Ping; Lee, Chia-Yu; Yu, Chun-Ching; Chang, Hsueh-Chia

    2006-10-15

    We demonstrate efficient mixing in a micro-fluidic reservoir smaller than 10 microL using ac electro-osmosis driven by field-induced polarization. Our mixing device, of that electrodes are outside of the mixing unit, consists of three circular reservoirs (3mm in diameter) connected by a 1 mm x 1 mm channel. Unlike dc electro-osmosis, whose polarization is from charged substrate functional groups, this new mechanism uses the external field to capacitively charge the surface and the surface capacitance becomes the key factor in the electrokinetic mobility. The charging and mixing are enhanced at tailor-designed channel corners by exploiting the high normal fields at geometric singularities. The induced surface dielectric polarization and the resulting electric counter-ion double layer produce an effective Zeta potential in excess of 1 V, over one order of magnitude larger than the channel Zeta potential. The resulting ac electro-osmotic slip velocity scales quadratically with respect to the applied field, in contrast to the linear scaling of dc electro-osmosis and at 1cm/s and larger, exceeds the classical dc values by two orders of magnitude. The polarization is non-uniform at the corners due to field leakage to the dielectric substrate and the inhomogeneous slip velocity produces intense mixing vortices that effectively homogenize solutes in 30s in a 3mm reservoir, in contrast to hour-long mixing by pure diffusion.

  3. Band spreading in two-dimensional microchannel turns for electrophoretic or electroosmotic species transport

    SciTech Connect

    S. K. Griffiths; R. H. Nilson

    2000-03-01

    Analytical and numerical methods are employed to investigate species transport by electrophoretic or electroosmotic motion in the curved geometry of a two-dimensional turn. Closed-form analytical solutions describing the turn-induced diffusive and dispersive spreading of a species band are presented for both the low and high Peclet number limits. The authors find that the spreading due to dispersion is proportional to the product of the turn included angle and the Peclet number at low Peclet numbers. It is proportional to the square of the included angle and independent of the Peclet number when the Peclet number is large. A composite solution applicable to all Peclet numbers is constructed from these limiting behaviors. Numerical solutions for species transport in a turn are also presented over a wide range of the included angle and the mean turn radius. Based on comparisons between the analytical and numerical results, the authors find that the analytical solutions provide very good estimates of both dispersive and diffusive spreading provided that the mean turn radius exceeds the channel width. These new solutions also agree well with data from a previous study. Optimum conditions minimizing total spreading in a turn are presented and discussed.

  4. Binary electroosmotic-pump nanoflow gradient generator for miniaturized high-performance liquid chromatography.

    PubMed

    Zhou, Lei; Lu, Joann Juan; Gu, Congying; Liu, Shaorong

    2014-12-16

    High-performance liquid chromatography (HPLC) plays an important role in biotechnology, and a majority of chromatographic separations use gradient elution. While gradient generators can be built in different formats, binary pumps or quaternary pumps are most frequently used for gradient generator constructions. We have recently developed a high-pressure electroosmotic pump (EOP); the pump can be manufactured at a cost of a few hundred dollars. However, it is challenging to use this pump to deliver a gradient eluent directly. In this study, we first improve the monolith preparation by applying a pressure to the monomer solution during polymerization. We assemble a binary EOP gradient generator and discuss the relationship between the gradient profile and voltage applied to the EOP. We demonstrate the feasibility of the binary EOP gradient generator for generating a smooth and reproducible nanoflow gradient. After integration of the gradient generator into a miniaturized HPLC system, we use the HPLC system for separating peptide mixtures from trypsin-digested proteins. The performance comparison between the above miniaturized HPLC system and an Agilent 1200 HPLC system exhibits comparable efficiencies, resolutions, and peak capacities.

  5. Conversion of Methane to Hydrogen in a Reversible Flow Reactor in the Process of Filtration Combustion of Fuel Mixtures Enriched with Oxygen

    NASA Astrophysics Data System (ADS)

    Dmitrenko, Yu. M.; Klyovan, R. A.

    2013-11-01

    This paper considers the process of partial oxidation of methane to syngas in a reversible flow reactor in the process of filtration combustion of fuel mixtures enriched with oxygen in an inert porous medium. Experimental studies have been made of the influence of the volume concentration of oxygen in the initial fuel mixture on the basic parameters of the conversion process — the maximum temperature in the combustion wave and the composition of reaction products. Investigations have been carried out for fuel mixtures having different calorific values under the same filtration conditions. It has been shown that the addition of oxygen to the initial methane-air mixture permits increasing considerably the efficiency of the conversion process.

  6. Control of ion gyroscale fluctuations via electrostatic biasing and sheared E×B flow in the C-2 field reversed configuration

    NASA Astrophysics Data System (ADS)

    Schmitz, L.; Ruskov, E.; Deng, B. H.; Binderbauer, M.; Tajima, T.; Gota, H.; Tuszewski, M.

    2016-03-01

    Control of radial particle and thermal transport is instrumental for achieving and sustaining well-confined high-β plasma in a Field-Reversed Configuration (FRC). Radial profiles of low frequency ion gyro-scale density fluctuations (0.5≤kρs≤40), consistent with drift- or drift-interchange modes, have been measured in the scrape-off layer (SOL) and core of the C-2 Field-Reversed Configuration (FRC), together with the toroidal E×B velocity. It is shown here that axial electrostatic SOL biasing controls and reduces gyro-scale density fluctuations, resulting in very low FRC core fluctuation levels. When the radial E×B flow shearing rate decreases below the turbulence decorrelation rate, fluctuation levels increase substantially, concomitantly with onset of the n=2 instability and rapid loss of diamagnetism. Low turbulence levels, improved energy/particle confinement and substantially increased FRC life times are achieved when E×B shear near the separatrix is maintained via axial SOL biasing using an annular washer gun.

  7. Inhibition and reversal of platelet aggregation by alphaIIbbeta3 antagonists depends on the anticoagulant and flow conditions: differential effects of Abciximab and Lamifiban.

    PubMed

    Frojmovic, Mony; Labarthe, Benoit; Legrand, Chantal

    2005-11-01

    Shear influences platelet aggregate formation and stability, as well as the inhibitory capacities of antithrombotic drugs. We compared the inhibitory and disaggregating properties of two distinct alphaIIbbeta3 antagonists, Abciximab and Lamifiban, on platelet aggregation induced by adenosine diphosphate (ADP) (5 micromol/l) in platelet-rich plasma (PRP), in an aggregometer (poorly defined low shear, <100/s) and in a microcouette at arterial shear rate (1,000/s). Platelet aggregation was detected by changes in light transmission in the aggregometer (TA), and by particle counting with a flow cytometer (PA). Lamifiban (1 mumol/l) completely inhibited TA or PA induced by ADP in citrated PRP in the aggregometer or microcouette. In contrast, Abciximab (2 micromol/l) only partially inhibited PA in the microcouette while blocking both TA and PA in the aggregometer. Moreover, Abciximab did not reverse platelet aggregates formed either in the microcouette or in the aggregometer, whereas Lamifiban caused complete reversal. On the contrary, Abciximab completely inhibited platelet aggregation induced by ADP in hirudin/d-Phe-Pro-Arg-chloromethylketone PRP in the microcouette. Our results demonstrate a marked dependence of inhibitory capacity of Abciximab on shear conditions, with citrate anticoagulant responsible for the residual aggregation, in contrast to Lamifiban, another alphaIIbbeta3 antagonist interacting with a distinct site on beta3.

  8. In situ microscopy reveals reversible cell wall swelling in kelp sieve tubes: one mechanism for turgor generation and flow control?

    PubMed

    Knoblauch, Jan; Tepler Drobnitch, Sarah; Peters, Winfried S; Knoblauch, Michael

    2016-08-01

    Kelps, brown algae (Phaeophyceae) of the order Laminariales, possess sieve tubes for the symplasmic long-distance transport of photoassimilates that are evolutionarily unrelated but structurally similar to the tubes in the phloem of vascular plants. We visualized sieve tube structure and wound responses in fully functional, intact Bull Kelp (Nereocystis luetkeana [K. Mertens] Postels & Ruprecht 1840). In injured tubes, apparent slime plugs formed but were unlikely to cause sieve tube occlusion as they assembled at the downstream side of sieve plates. Cell walls expanded massively in the radial direction, reducing the volume of the wounded sieve elements by up to 90%. Ultrastructural examination showed that a layer of the immediate cell wall characterized by circumferential cellulose fibrils was responsible for swelling and suggested that alginates, abundant gelatinous polymers of the cell wall matrix, were involved. Wall swelling was rapid, reversible and depended on intracellular pressure, as demonstrated by pressure-injection of silicon oil. Our results revive the concept of turgor generation and buffering by swelling cell walls, which had fallen into oblivion over the last century. Because sieve tube transport is pressure-driven and controlled physically by tube diameter, a regulatory role of wall swelling in photoassimilate distribution is implied in kelps.

  9. Separation of peptides on mixed mode of reversed-phase and ion-exchange capillary electrochromatography with a monolithic column.

    PubMed

    Wu, Ren'an; Zou, Hanfa; Fu, Hongjing; Jin, Wenhai; Ye, Mingliang

    2002-05-01

    The mixed mode of reversed phase (RP) and strong cation-exchange (SCX) capillary electrochromatography (CEC) based on a monolithic capillary column has been developed. The capillary monolithic column was prepared by in situ copolymerization of 2-(sulfooxy)ethyl methacrylate (SEMA) and ethylene dimethacrylate (EDMA) in the presence of porogens. The sulfate group provided by the monomer SEMA on the monolithic bed is used for the generation of the electroosmotic flow (EOF) from the anode to the cathode, but at the same time serves as a SCX stationary phase. A mixed-mode (RP/SCX) mechanism for separation of peptides was observed in the monolithic column, comprising hydrophobic and electrostatic interaction as well as electrophoretic migration at a low pH value of mobile phase. A column efficiency of more than 280,000 plates/m for the unretained compound has been obtained on the prepared monoliths. The relative standard deviations observed for t(0) and retention factors of peptides were about 0.32% and less than 0.71% for ten consecutive runs, respectively. Effects of mobile phase compositions on the EOF of the monolithic column and on the separation of peptides were investigated. The selectivity on separation of peptides in the monolithic capillary column could be easily manipulated by varying the mobile phase composition.

  10. Deformability of human red blood cells exposed to a uniform shear stress as measured by a cyclically reversing shear flow generator.

    PubMed

    Watanabe, Nobuo; Arakawa, Yasuyuki; Sou, Atsushi; Kataoka, Hiroyuki; Ohuchi, Katsuhiro; Fujimoto, Tetsuo; Takatani, Setsuo

    2007-05-01

    Red blood cells (RBCs) suspended in a dextran solution were at first loaded with a uniform shear stress of 21, 43 and 64 Pa for the duration of 0, 10, 20, 30, 45 and 60 min, respectively, followed with measurement of the dynamic deformation in terms of stretching and recovery, using a cyclically reversing sinusoidal shear flow with the peak stress of 128 Pa at 2 Hz. The L/W value, where L and W were the major and minor axis length of the RBC images, was derived to compare the effects of the uniform shear stress level and the exposure time. The exposure to the uniform shear stress of 21 Pa for the duration of as long as 60 min caused statistically insignificant L/W change in comparison to the control RBCs with L/W of 4.6 +/- 0.1. The exposure to 43 and 64 Pa for longer than 45 and 20 min, respectively, induced statistically significant change in the maximal L/W when compared to that of 21 Pa (p < 0.05). The composition of the maximal L/W values varied depending on the stress level and exposure time; with 21 Pa, the majority of cells exhibited the maximal L/W larger than 4.0 and few cells less than 2.0, whereas with the increase in the stress level to 43 and 64 Pa, cells having less than 2.0 exceeded 50%. Cyclic reversing shear flow is a useful means to measure dynamic deformation capability of RBCs which may be sub-hemolytically sheared without lysis.

  11. Radiometric and paleomagnetic evidence for the Emperor reversed polarity event at 0.46 ± 0.05 M.Y. in basalt lava flows from the eastern Snake River Plain, Idaho

    USGS Publications Warehouse

    Champion, Duane E.; Dalrymple, G. Brent; Kuntz, Mel A.

    1981-01-01

    K-Ar and paleomagnetic data from cores through a sequence of basalt flows in the eastern Snake River Plain provide evidence for a brief (0.005 to 0.01 m.y.) reversal of the geomagnetic field 0.46 ± 0.05 m.y. ago. This reversed polarity event has also been found in sea-floor magnetic anomalies and in sediment cores and is probably the Emperor event of Ryan [1972].

  12. Radiometric and paleomagnetic evidence for the Emperor reversed polarity event at 0.46 ± 0.05 M.Y. in basalt lava flows from the eastern Snake River Plain, Idaho

    NASA Astrophysics Data System (ADS)

    Champion, Duane E.; Dalrymple, G. Brent; Kuntz, Mel A.

    1981-10-01

    K-Ar and paleomagnetic data from cores through a sequence of basalt flows in the eastern Snake River Plain provide evidence for a brief (0.005 to 0.01 m.y.) reversal of the geomagnetic field 0.46 ± 0.05 m.y. ago. This reversed polarity event has also been found in sea-floor magnetic anomalies and in sediment cores and is probably the Emperor event of Ryan [1972].

  13. Effect of the polarity reversal frequency in the electrokinetic-biological remediation of oxyfluorfen polluted soil.

    PubMed

    Barba, Silvia; Villaseñor, José; Rodrigo, Manuel A; Cañizares, Pablo

    2017-03-03

    This work studies the feasibility of the periodic polarity reversal strategy (PRS) in a combined electrokinetic-biological process for the remediation of clayey soil polluted with a herbicide. Five two-weeks duration electrobioremediation batch experiments were performed in a bench scale set-up using spiked clay soil polluted with oxyfluorfen (20 mg kg(-1)) under potentiostatic conditions applying an electric field between the electrodes of 1.0 V cm(-1) (20.0 V) and using PRS with five frequencies (f) ranging from 0 to 6 d(-1). Additionally, two complementary reference tests were done: single bioremediation and single electrokinetic. The microbial consortium used was obtained from an oil refinery wastewater treatment plant and acclimated to oxyfluorfen degradation. Main soil conditions (temperature, pH, moisture and conductivity) were correctly controlled using PRS. On the contrary, the electroosmotic flow clearly decreased as f increased. The uniform soil microbial distribution at the end of the experiments indicated that the microbial activity remained in every parts of the soil after two weeks when applying PRS. Despite the adapted microbial culture was capable of degrade 100% of oxyfluorfen in water, the remediation efficiency in soil in a reference test, without the application of electric current, was negligible. However, under the low voltage gradients and polarity reversal, removal efficiencies between 5% and 15% were obtained, and it suggested that oxyfluorfen had difficulties to interact with the microbial culture or nutrients and that PRS promoted transport of species, which caused a positive influence on remediation. An optimal f value was observed between 2 and 3 d(-1).

  14. Performance of a continuous flow microbial reverse-electrodialysis electrolysis cell using a non-buffered substrate and catholyte effluent addition.

    PubMed

    Hidayat, Syarif; Song, Young-Hyun; Park, Joo-Yang

    2017-09-01

    A continuous flow microbial reverse-electrodialysis electrolysis cell (MREC) was operated under non-buffered substrate with various flow rates of catholyte effluent into anode chamber to investigate the effects on the hydrogen gas production. Adding the catholyte effluent to the anolyte influent resulted in increased salt concentration in the anolyte influent. The increasing anolyte influent salt concentration to 0.23M resulted in improved hydrogen gas production, Coulombic recovery, yield, and hydrogen production rate to 25±1.4mL, 83±5%, 1.49±0.15mol-H2/mole-COD, 0.91±0.03m(3)-H2/m(3)-Van/day, respectively. These improvements were attributed to the neutral pH rather than increase in anolyte conductivity as there was no significant improvement in the reactor performance when the NaCl was directly added to the reactor. These results show that addition of catholyte effluent into the anode chamber improved the MREC performance. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Potential of the reversed-inject differential flow modulator for comprehensive two-dimensional gas chromatography in the quantitative profiling and fingerprinting of essential oils of different complexity.

    PubMed

    Cordero, Chiara; Rubiolo, Patrizia; Cobelli, Luigi; Stani, Gianluca; Miliazza, Armando; Giardina, Matthew; Firor, Roger; Bicchi, Carlo

    2015-10-23

    In this study, the first capillary flow technology reverse-inject differential flow modulator was implemented with different column configurations (lengths, diameters and stationary phase coupling) and detector combinations (mass spectrometry--MS and flame ionization detection--FID) to evaluate its potential in the quantitative profiling and fingerprinting of medium-to-highly complex essential oils. In particular, a parallel dual-secondary column dual-detection configuration that has shown to improve the information potential also with thermally modulated GC × GC platforms (MS identification reliability and accurate FID quantitation), was tested. Several system performance parameters (separation measure SGC × GC, modulation ratio MR, separation space used and peak symmetry) were evaluated by analyzing a mixture of volatiles of interest in the flavor and fragrance field. The systems demonstrating the best chromatographic performance were selected for quantitative profiling of lavender and mint essential oils and fingerprinting of vetiver essential oil. Experimental results demonstrate that careful tuning of column dimensions and system configurations yields improved: (a) selectivity; (b) operable carrier gas linear velocities at close-to-optimal values; (c) (2)D separation power by extending the modulation period and (d) handling of overloaded peaks without dramatic losses in resolution and quantitative accuracy.

  16. Fit-to-Flow (F2F) interconnects: universal reversible adhesive-free microfluidic adaptors for lab-on-a-chip systems.

    PubMed

    Chen, Arnold; Pan, Tingrui

    2011-02-21

    World-to-chip (macro-to-micro) interface continues to be one of the most complicated, ineffective, and unreliable components in the development of emerging lab-on-a-chip systems involving integrated microfluidic operations. A number of irreversible (e.g., adhesive gluing) and reversible techniques (e.g., press fitting) have attempted to provide dedicated fluidic passage from standard tubing to miniature on-chip devices, none of which completely addresses the above concerns. In this paper, we present standardized adhesive-free microfluidic adaptors, referred to as Fit-to-Flow (F2F) Interconnects, to achieve reliable hermetic seal, high-density tube packing, self-aligned plug-in, reworkable connectivity, straightforward scalability and expandability, and applicability to broad lab-on-a-chip platforms; analogous to the modular plug-and-play USB architecture employed in modern electronics. Specifically, two distinct physical packaging mechanisms are applied, with one utilizing induced tensile stress in elastomeric socket to establish reversible seal and the other using negative pressure to provide on demand vacuum shield, both of which can be adapted to a variety of experimental configurations. The non-leaking performance (up to 336 kPa) along with high tube-packing density (of 1 tube/mm(2)) and accurate self-guided alignment (of 10 μm) have been characterized. In addition, a 3D microfluidic mixer and a 6-level chemical gradient generator paired with the corresponding F2F Interconnects have been devised to illustrate the applicability of the universal fluidic connections to classic lab-on-a-chip operations.

  17. Tuning the Stability of Organic Active Materials for Nonaqueous Redox Flow Batteries via Reversible, Electrochemically Mediated Li + Coordination

    SciTech Connect

    Carino, Emily V.; Staszak-Jirkovsky, Jakub; Assary, Rajeev S.; Curtiss, Larry A.; Markovic, Nenad M.; Brushett, Fikile R.

    2016-03-24

    We describe an electrochemically mediated interaction between Li+ and a promising active material for nonaqueous redox flow batteries (RFBs), 1,2,3,4-tetrahydro-6,7-dimethoxy-1,1,4,4-tetramethylnaphthalene (TDT), and the impact of this structural interaction on material stability during voltammetric cycling. TDT could be an advantageous organic positive electrolyte material for nonaqueous RFBs due to its high oxidation potential, 4.21 V vs Li/Li+, and solubility of at least 1.0 M in select electrolytes. Although results from voltammetry suggest TDT displays Nernstian reversibility in many nonaqueous electrolyte solutions, bulk electrolysis reveals significant degradation in all electrolytes studied, the extent of which depends on the electrolyte solution composition. Results of subtractively normalized in situ Fourier transform infrared spectroscopy (SNIFTIRS) confirm that TDT undergoes reversible structural changes during cyclic voltammetry in propylene carbonate and 1,2-dimethoxyethane solutions containing Li+ electrolytes, but irreversible degradation occurs when tetrabutylammonium (TBA+) replaces Li+ as the electrolyte cation in these solutions. By combining the results from SNIFTIRS experiments with calculations from density functional theory, solution-phase active species structure and potential-dependent interactions can be determined. We find that Li+ coordinates to the Lewis basic methoxy groups of neutral TDT and, upon electrochemical oxidation, this complex dissociates into the radical cation TDT•+ and Li+. The improved cycling stability in the presence of Li+ relative to TBA+ suggests that the structural interaction reported herein may be advantageous to the design of energy storage materials based on organic molecules.

  18. Fluid mechanics of continuous flow electrophoresis

    NASA Technical Reports Server (NTRS)

    Saville, D. A.; Ostrach, S.

    1978-01-01

    The following aspects of continuous flow electrophoresis were studied: (1) flow and temperature fields; (2) hydrodynamic stability; (3) separation efficiency, and (4) characteristics of wide gap chambers (the SPAR apparatus). Simplified mathematical models were developed so as to furnish a basis for understanding the phenomena and comparison of different chambers and operating conditions. Studies of the hydrodynamic stability disclosed that a wide gap chamber may be particularly sensitive to axial temperature variations which could be due to uneven heating or cooling. The mathematical model of the separation process includes effects due to the axial velocity, electro-osmotic cross flow and electrophoretic migration, all including the effects of temperature dependent properties.

  19. Field Effect Flow Control in a Polymer T-Intersection Microfluidic Network

    NASA Technical Reports Server (NTRS)

    Sniadecki, Nathan J.; Chang, Richard; Beamesderfer, Mike; Lee, Cheng S.; DeVoe, Don L.

    2003-01-01

    We present a study of induced pressure pumping in a polymer microchannel due to differential electroosmotic flow @OF) rates via field-effect flow control (FEFC). The experimental results demonstrate that the induced pressure pumping is dependent on the distance of the FEFC gate from the cathodic gate. A proposed flow model based on a linearly-decaying zeta potential profile is found to successfully predict experimental trends.

  20. Field Effect Flow Control in a Polymer T-Intersection Microfluidic Network

    NASA Technical Reports Server (NTRS)

    Sniadecki, Nathan J.; Chang, Richard; Beamesderfer, Mike; Lee, Cheng S.; DeVoe, Don L.

    2003-01-01

    We present a study of induced pressure pumping in a polymer microchannel due to differential electroosmotic flow @OF) rates via field-effect flow control (FEFC). The experimental results demonstrate that the induced pressure pumping is dependent on the distance of the FEFC gate from the cathodic gate. A proposed flow model based on a linearly-decaying zeta potential profile is found to successfully predict experimental trends.

  1. Comparison of cryogenic and differential flow (forward and reverse fill/flush) modulators and applications to the analysis of heavy petroleum cuts by high-temperature comprehensive gas chromatography.

    PubMed

    Duhamel, Chloé; Cardinael, Pascal; Peulon-Agasse, Valérie; Firor, Roger; Pascaud, Laurent; Semard-Jousset, Gaëlle; Giusti, Pierre; Livadaris, Vincent

    2015-03-27

    The development of new efficient conversion processes to transform heavy petroleum fractions into valuable products, such as diesel, requires improved chemical knowledge of the latter. High-temperature comprehensive gas chromatography (HT-GC × GC) has proven to be a powerful technique for characterizing such complex samples. This paper reports on an evaluation of the performances of four different differential flow modulators, including two original ones that have not been previously described in the literature, in terms of dispersion, peak intensity, peak capacity and overloading. These modulators, all of which are based on Agilent capillary flow technology (CFT), are forward fill/flush (FFF) differential flow modulators with an integrated collection channel or an adjustable channel (new) and reverse fill/flush (RFF) differential flow modulators with an integrated collection channel (new) or an adjustable channel. First, the optimization of the collection channel dimensions is described. Second, an RFF and an FFF differential flow modulator possessing the same collection channel were compared. The reverse differential flow modulation significantly reduced band broadening compared to forward differential flow modulation, and the peak intensity doubled for every modulated peak when an RFF differential flow modulator was used. Then, an RFF differential flow modulator and CO2 dual-jet modulator were compared. Whereas the percentages of separation space used were similar (61% with the HT-GC × GC method using a cryogenic modulator and 59% with the method using an RFF differential flow modulator), the peak capacities were at least three times more important with differential flow modulation due to the greater length of the column used in the second dimension. The results demonstrate that the RFF differential flow modulator is an excellent tool for studying heavy petroleum cuts. It demonstrates the best performances and it is the most versatile modulator. In its two

  2. Reverse Phase-ultra Flow Liquid Chromatography-diode Array Detector Quantification of Anticancerous and Antidiabetic Drug Mangiferin from 11 Species of Swertia from India

    PubMed Central

    Kshirsagar, Parthraj R.; Gaikwad, Nikhil B.; Panda, Subhasis; Hegde, Harsha V.; Pai, Sandeep R.

    2016-01-01

    Background: Genus Swertia is valued for its great medicinal potential, mainly Swertia chirayita (Roxb. ex Fleming) H. Karst. is used in traditional medicine for a wide range of diseases. Mangiferin one of xanthoids is referred with enormous pharmacological potentials. Objective: The aim of the study was to quantify and compare the anticancerous and antidiabetic drug mangiferin from 11 Swertia species from India. The study also evaluates hierarchical relationships between the species based on mangiferin content using multivariate analysis. Materials and Methods: The reverse phase-ultra flow liquid chromatography-diode array detector analyses was performed and chromatographic separation was achieved on a Lichrospher 100, C18e (5 μm) column (250–4.6 mm). Mobile phase consisting of 0.2% triethylamine (pH-4 with O-phosphoric acid) and acetonitrile (85:15) was used for separation with injection volume 20 μL and detection wave length at 257 nm. Results: Results indicated that concentration of mangiferin has been found to vary largely between Swertia species collected from different regions. Content of mangiferin was found to be highest in Swertia minor compared to other Swertia species studied herein from the Western Ghats and Himalayan region also. The same was also evident in the multivariate analysis, wherein S. chirayita, S. minor and Swertia paniculata made a separate clade. Conclusion: Conclusively, the work herein provides insights of mangiferin content from 11 Swertia species of India and also presents their hierarchical relationships. To best of the knowledge this is the first report of higher content of mangiferin from any Swertia species. SUMMARY The present study quantifies and compares mangiferin in 11 species of Swertia from India. The study also evaluates hierarchical relationships between the species based on mangiferin content using multivariate analysis. The mangiferin content was highest in S. minor compared to the studied Swertia species. To the

  3. Impact of leakage current and electrolysis on FET flow control and pH changes in nanofluidic channels†

    PubMed Central

    Oh, Youn-Jin; Bottenus, Danny; Ivory, Cornelius F.

    2010-01-01

    We have fabricated multiple-internal-reflection Si infrared waveguides integrated with an array of nanochannels sealed with an optically transparent top cover. The channel walls consist of a thin layer of SiO2 for electrical insulation, and gate electrodes surround the channel sidewalls and bottom to manipulate their surface charge and ζ-potential in a fluidic field effect transistor (FET) configuration. This nanofluidic device is used to probe the transport of charged molecules (Alexa 488) and to measure the pH shift in nanochannels in response to an electrical potential applied to the gate. During gate biasing for FET operation, laser-scanning confocal fluorescence microscopy (LS-CFM) is used to visualize the flow of fluorescent dye molecules (Alexa 488), and multiple internal reflection-Fourier transform infrared spectroscopy (MIR-FTIRS) is used to probe the characteristic vibrational modes of fluorescein pH indicator and measure the pH shift. The electroosmotic flow of Alexa 488 is accelerated in response to a negative gate bias, whereas its flow direction is reversed in response to a positive gate bias. We also measure that the pH of buffered electrolyte solutions shifts by as much as a pH unit upon applying the gate bias. With prolonged application of gate bias, however, we observe that the initial response in flow speed and direction as well as pH shift becomes reversed. We attribute these anomalous flow and pH shift characteristics to a leakage current that flows from the Si gate through the thermally grown SiO2 to the electrolyte solution. PMID:19458870

  4. Impact of leakage current and electrolysis on FET flow control and pH changes in nanofluidic channels.

    PubMed

    Oh, Youn-Jin; Bottenus, Danny; Ivory, Cornelius F; Han, Sang M

    2009-06-07

    We have fabricated multiple-internal-reflection Si infrared waveguides integrated with an array of nanochannels sealed with an optically transparent top cover. The channel walls consist of a thin layer of SiO2 for electrical insulation, and gate electrodes surround the channel sidewalls and bottom to manipulate their surface charge and zeta-potential in a fluidic field effect transistor (FET) configuration. This nanofluidic device is used to probe the transport of charged molecules (Alexa 488) and to measure the pH shift in nanochannels in response to an electrical potential applied to the gate. During gate biasing for FET operation, laser-scanning confocal fluorescence microscopy (LS-CFM) is used to visualize the flow of fluorescent dye molecules (Alexa 488), and multiple internal reflection-Fourier transform infrared spectroscopy (MIR-FTIRS) is used to probe the characteristic vibrational modes of fluorescein pH indicator and measure the pH shift. The electroosmotic flow of Alexa 488 is accelerated in response to a negative gate bias, whereas its flow direction is reversed in response to a positive gate bias. We also measure that the pH of buffered electrolyte solutions shifts by as much as a pH unit upon applying the gate bias. With prolonged application of gate bias, however, we observe that the initial response in flow speed and direction as well as pH shift becomes reversed. We attribute these anomalous flow and pH shift characteristics to a leakage current that flows from the Si gate through the thermally grown SiO2 to the electrolyte solution.

  5. Determination of alternative and conventional chelating agents as copper(II) complexes by capillary zone electrophoresis--the first use of didecyldimethylammonium bromide as a flow reversal reagent.

    PubMed

    Laamanen, Pirkko-Leena; Matilainen, Rose

    2007-02-12

    A capillary zone electrophoresis (CZE) method for analyzing 11 chelating agents [beta-alaninediacetic acid (beta-ADA), trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetic acid (HEDTA), N-(2-hydroxyethyl)iminodiacetic acid (HEIDA), iminodiacetic acid (IDA), methylglycinediacetic acid (MGDA), nitrilotriacetic acid (NTA), 1,3-diaminopropane-N,N,N',N'-tetraacetic acid (PDTA) and triethylenetetraaminehexaacetic acid (TTHA)] as negatively charged copper(II) complexes has been established. Both conventional and alternative chelating agents were included in this study, because they are used side by side in industrial applications. In this study, didecyldimethylammonium bromide (DMDDAB) was successfully used as a flow reversal reagent for