Relevant bibliographies by topics / Electric field gradient focusing

Contents

  1. Journal articles
  2. Dissertations / Theses
  3. Books
  4. Book chapters
  5. Conference papers
  6. Reports

Academic literature on the topic 'Electric field gradient focusing'

Author: Grafiati
Published: 4 June 2021
Last updated: 1 February 2022

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Journal articles on the topic "Electric field gradient focusing"

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Kelly, Ryan T., and Adam T. Woolley. "Electric field gradient focusing." Journal of Separation Science 28, no. 15 (October 2005): 1985–93. http://dx.doi.org/10.1002/jssc.200500228.

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Sun, Xuefei, Dan Li, Adam T. Woolley, Paul B. Farnsworth, H. Dennis Tolley, Karl F. Warnick, and Milton L. Lee. "Bilinear electric field gradient focusing." Journal of Chromatography A 1216, no. 37 (September 2009): 6532–38. http://dx.doi.org/10.1016/j.chroma.2009.07.050.

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Sun, Xuefei, Paul B. Farnsworth, H. Dennis Tolley, Karl F. Warnick, Adam T. Woolley, and Milton L. Lee. "Performance optimization in electric field gradient focusing." Journal of Chromatography A 1216, no. 1 (January 2009): 159–64. http://dx.doi.org/10.1016/j.chroma.2008.11.031.

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Koegler, Wendy S., and Cornelius F. Ivory. "Focusing proteins in an electric field gradient." Journal of Chromatography A 726, no. 1-2 (March 1996): 229–36. http://dx.doi.org/10.1016/0021-9673(95)01069-6.

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Anand, Robbyn K., Eoin Sheridan, Dzmitry Hlushkou, Ulrich Tallarek, and Richard M. Crooks. "Bipolar electrode focusing: tuning the electric field gradient." Lab Chip 11, no. 3 (2011): 518–27. http://dx.doi.org/10.1039/c0lc00351d.

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Petsev, Dimiter N., Gabriel P. Lopez, Cornelius F. Ivory, and Scott S. Sibbett. "Microchannel protein separation by electric field gradient focusing." Lab on a Chip 5, no. 6 (2005): 587. http://dx.doi.org/10.1039/b501538c.

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Humble, Paul H., John N. Harb, H. Dennis Tolley, Adam T. Woolley, Paul B. Farnsworth, and Milton L. Lee. "Influence of transport properties in electric field gradient focusing." Journal of Chromatography A 1160, no. 1-2 (August 2007): 311–19. http://dx.doi.org/10.1016/j.chroma.2007.04.013.

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Sun, Xuefei, Paul B. Farnsworth, Adam T. Woolley, H. Dennis Tolley, Karl F. Warnick, and Milton L. Lee. "Poly(ethylene glycol)-Functionalized Devices for Electric Field Gradient Focusing." Analytical Chemistry 80, no. 2 (January 2008): 451–60. http://dx.doi.org/10.1021/ac0713104.

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Hlushkou, Dzmitry, Robbyn K. Perdue, Rahul Dhopeshwarkar, Richard M. Crooks, and Ulrich Tallarek. "Electric field gradient focusing in microchannels with embedded bipolar electrode." Lab on a Chip 9, no. 13 (2009): 1903. http://dx.doi.org/10.1039/b822404h.

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Lin, Shu-Ling, Yuanyuan Li, Adam T. Woolley, Milton L. Lee, H. Dennis Tolley, and Karl F. Warnick. "Programed elution and peak profiles in electric field gradient focusing." ELECTROPHORESIS 29, no. 5 (March 2008): 1058–66. http://dx.doi.org/10.1002/elps.200700652.

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Dissertations / Theses on the topic "Electric field gradient focusing"

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Lin, Shu-Ling. "Electric Field Gradient Focusing-UV Detection for Protein Analysis." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1372.pdf.

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Kelly, Ryan Thomas. "Polymer Microchips for Capillary Electrophoresis and Electric Field Gradient Focusing of Biomolecules." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd1024.pdf.

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Sun, Xuefei. "Polymer Microfluidic Devices for Bioanalysis." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1836.

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Polymeric microchips have received increasing attention in chemical analysis because polymers have attractive properties, such as low cost, ease of fabrication, biocompatibility and high flexibility. However, commercial polymers usually exhibit analyte adsorption on their surfaces, which can interfere with microfluidic transport in, for example, chemical separations such as chromatography or electrophoresis. Usually, surface modification is required to eliminate this problem. To perform stable and durable surface modification, a new polymer, poly(methyl methacrylate-co-glycidyl methacrylate) (PGMAMMA) was prepared for microchip fabrication, which provides epoxy groups on the surface. Whole surface atom transfer radical polymerization (ATRP) and in-channel ATRP approaches were employed to create uniform and dense poly(ethylene glycol) (PEG)-functionalized polymer brush channel surfaces for capillary electrophoresis (CE) separation of biomolecules, such as peptides and proteins. In addition, a novel microchip material was developed for bioanalysis, which does not require surface modification, made from a PEG-functionalized copolymer. The fabrication is easy and fast, and the bonding is strong. Microchips fabricated from this material have been applied for CE separation of small molecules, peptides, proteins and enantiomers. Electric field gradient focusing (EFGF) is an attractive technique, which depends on an electric field gradient and a counter-flow to focus, concentrate and separate charged analytes, such as peptides and proteins. I used the PEG-functionalized copolymer to fabricate EFGF substrates. The separation channel was formed in an ionically conductive and protein resistant PEG-functionalized hydrogel, which was cast in a changing cross-sectional cavity in the plastic substrate. The hydrogel shape was designed to create linear or non-linear gradients. These EFGF devices were successfully used for protein focusing, and their performance was optimized. Use of buffers containing small electrolyte ions promoted rapid ion transport in the hydrogel for achieving the designed gradients. A PEG-functionalized monolith was incorporated in the EFGF separation channel to reduce dispersion and improve focusing performance. Improvement in peak capacity was proposed using a bilinear EFGF device. Protein concentration exceeding 10,000-fold was demonstrated using such devices.
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Liu, Yansheng. "Investigation of Novel Microseparation Techniques." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1816.pdf.

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Tenny, Joseph S. "Numerical Simulations in Electro-osmotic Flow." BYU ScholarsArchive, 2004. https://scholarsarchive.byu.edu/etd/186.

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The developing flow field in a parallel plate microchannel, induced by wall motion, has been modeled numerically. This type of flow simulates the physical driving mechanism that exists in electro-osmotically generated flow with large channel diameter-to-Debye length ratios (Z). The physics of the flow field were compared between the moving wall model (MWM) and electro-osmotic flow (EOF) at Reynolds numbers of 1 and 1800, and Z > 2500. Also, Z-values between 50 and 500 were studied to investigate the accuracy of the MWM. Results show that for Z-values greater than 100 the MWM shows good agreement with EOF. The dynamics of the developing flow field for the MWM were explored for channel length-to-hydraulic diameter ratios (aspect ratio) of 5, 10, 20 and 40 at ten Reynolds numbers, Re (based on the wall velocity), below Re < 2000. The results show that far from the inlet the maximum fluid velocity occurs at the walls, as is expected, and the minimum velocity occurs at the channel center. Near the channel inlet, however, the centerline velocity is not a minimum but reaches a local maximum due to a resulting pressure imbalance generated by the wall motion. As the aspect ratio increases, the centerline velocity tends to approach the wall velocity far downstream from the inlet. Increases in the Reynolds number have the opposite effect on the centerline velocity. The hydrodynamic developing region, defined by that section of the channel where the wall shear stress is changing, also depends on the channel aspect ratio and Re, and is greater than the developing region for classical pressure-driven flow of a parallel plate channel. Also, the flow field physics was analyzed for a process called electro-mobility focusing (EMF). EMF is a process that separates and detects species of like charge with the use of electro-phoresis and EOF utilizing a varying voltage gradient. The velocity distribution and the effective diffusion were solved for analytically, for both a linear and non-linear voltage gradient, using the MWM and the creeping flow approximations. The resulting equations aid in optimizing the detection system by forcing the lowest effective diffusion (uniform velocity profile) to the detection location.
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González, Tuñón Maria Pilar. "Electrophoretic field gradient focusing for the analysis of proteins." Thesis, University of Leeds, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439600.

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Wray, Thomas. "Developments in dynamic field gradient focusing : microfluidics and integration." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/7973/.

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Advances in modern science require the development of more robust and improved systems for electroseparations in chromatography. In response, the progress of a new analytical platform is discussed. DFGF (Dynamic Field Gradient Focusing) is a separation technique, first described in 1998, which exploits the differences in electrophoretic mobility and hydrodynamic area of analytes to result in separation. This is achieved by taking a channel and applying a hydrodynamic flow in one direction and a counteracting electric field gradient acting in the opposite direction, resulting in analytes reaching a focal point according to their electrophoretic mobility. Work through this project has seen innovations to improve existing DFGF devices, including the design and manufacture of a novel packing material, while developing the latest DFGF system. This incorporates a microfluidic separation channel, eliminating the need for packing material or monolith. The new microfluidic device also features whole-on-column UV detection. Improvements through the developments of this device are discussed, most notably the utilisation of a new rapid prototyping technique. Examples of applications undertaken with the new device are demonstrated including novel samples and integration with mass spectrometry and 2D-HPLC.
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Koch, Katrin. "Crystal structure, electron density and chemical bonding in inorganic compounds studied by the Electric Field Gradient." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-24233.

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The goal of solid state physics and chemistry is to gain deeper understanding of the basic principles of condensed matter. This ongoing process is achieved by the combination of experimental methods and theoretical models. One theoretical approach are the so-called first-principles calculations, which are based on the concept of density functional theory (DFT). In order to test the reliability of a band structure calculation, its results have to be compared with experiments. Since the electron density, the main constituent of DFT codes, cannot be directly determined experimentally with sufficient accuracy (e.g., by X-ray diffraction), other experimentally available properties are needed for the comparison with the calculation. A quantity that can be measured with high accuracy and that provides indirect information about the electron density is the electric field gradient (EFG). The EFG reflects local structural symmetry properties of the charge distribution surrounding a nucleus: the EFG is nonzero if the density deviates from cubic symmetry and therefore generates an inhomogeneous electric field at the nucleus. Since the EFG is highly sensitive to structural parameters and to disorder, it is a valuable tool to extract structural information. Furthermore, the evaluation of the EFG can provide valuable insight into the chemical bonding. Whereas the experimental determination of the quadrupole frequency and the closely related EFG has been possible for more than 70 years, reliable values for calculated EFGs could not be obtained before 1985, when an EFG module was implemented in the full-potential, linearised-augmented-plane-wave code WIEN. Since the full-potential local-orbital minimum-basis scheme FPLO is numerically very efficient and its local-orbital scheme allows an easy analysis of the different contributions to the EFG, one goal of this work was the implementation of an EFG module within the FPLO code. The newly implemented EFG module was applied to different systems: starting from simple metals, then approaching more complex systems and finally tackling strongly correlated oxides. Simultaneously, the EFGs for the studied compounds were determined experimentally by NMR spectroscopists. This close collaboration enables the comparison of the calculated EFGs with the experimental observations, which makes it possible to extract more physical and chemical information from the measured values regarding structural relaxation, distortion, the chemical bond or the relevance of electron correlation. In the last part of this work, the importance of corrections that go beyond the EFG are discussed. Such corrections arise for any multipole order of the hyperfine interactions, and are due to electron penetration into the nucleus. A correction similar to the isomer shift, coined here the &quot;quadrupole shift&quot; is examined in detail.
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Evans, James R. "The electric field gradient of octahedral iron in layer silicates: theory with applications to Mossbauer spectroscopy." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/22144.

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Evans, R. James. "The electric field gradient of octahedral iron(2+) in layer silicates: Theory with applications to Moessbauer spectroscopy." Thesis, University of Ottawa (Canada), 2001. http://hdl.handle.net/10393/8968.

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New electronic structure calculations of the electric field gradient (EFG) at octahedral Fe2+ sites in layer silicates are discussed. These calculations were done with the aim of providing a link between quadrupole splitting distributions from Mossbauer spectroscopy and the physical distributions of local environments within the material. Various distortions were applied to FeO610- and Fe(OH)6 4- clusters to simulate different local environments and the corresponding EFG's calculated. The electronic structure calculations were performed with the General Atomic and Molecular Electronic Structure System (GAMESS) and a self-consistent-charge-Xalpha method. An analytic model of the EFG using a classical electrostatic point charge model and crystal field theory is used to complement the electronic structure calculations. There is good qualitative agreement between the electronic structure calculations, the analytic model, and with experimental quadrupole splittings in micas. A geometric model of the octahedral sheet in a layer silicate is described, based on isometric flattening and counter-rotation as the main distortions, which can have one, two, or three unique sites. EFG distributions are then calculated using a variety of cases based on the geometric model and the calculated EFG vs. distortion curves. The most realistic distribution results from a case that assumes two unique site-types in a ratio of 2:1, with the height of each site and the inter-cation distance held constant throughout the sheet and the Fe--O bond length of one site-type allowed to vary with a Gaussian distribution.
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Books on the topic "Electric field gradient focusing"

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Koegler, Wendy S. Zone electric field gradient focusing: A novel technique for protein separation. 1994.

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D, Diebold, and United States. National Aeronautics and Space Administration., eds. Space charge enhanced plasma gradient effects of satellite electric field measurements. [Washington, DC: National Aeronautics and Space Administration, 1991.

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Wright, A. G. Timing with PMTs. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780199565092.003.0008.

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The timing capability of photomultipliers (PMTs) can be inferred from the basic laws of electron motion. The relationships between time dispersion and field strength, initial electron energy, angle of emission, and electrode spacing follow from these laws. For conventional PMTs, the major contribution to dispersion arises from the cathode-to-first-dynode region. The field gradient at the cathode primarily determines the timing. This is verified by examining the electron motion in non-uniform electric fields. The contribution from interdynode transitions is small for linear focussed PMTs. Monte Carlo simulations of output waveforms from scintillators agree with measurements. The performance of threshold, zero crossing, and constant fraction (CF) discriminators is examined, revealing the superiority of the CF types. Two organizations have made detailed timing measurements, some of which show sub-nanosecond jitter. Proximity focussed PMTs from Hamamatsu confirm time dispersion measured in picoseconds.
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Buchwald, Jed Z. Electrodynamics from Thomson and Maxwell to Hertz. Edited by Jed Z. Buchwald and Robert Fox. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199696253.013.20.

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This article examines developments in the field of electrodynamics from William Thomson and James Clerk Maxwell to Heinrich Hertz. It begins with a discussion of Michael Faraday’s work, focusing on his discovery of what was later termed ‘dielectric capacity’ and his role in the birth of field theory. It then considers Thomson’s unification of Faraday’s understanding of both electro- and magnetostatics with energy conservation, along with Maxwell’s extension of Thomson’s structure to cover electrodynamics, which for the first time brought to the fore issues concerning the electric current. It also describes Maxwellian electrodynamics and electromagnetic theory, Hermann Helmholtz’s development of a different form of electrodynamics, and Hertz’s work on electric waves.
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Marvin, Carolyn. When Old Technologies Were New. Oxford University Press, 1990. http://dx.doi.org/10.1093/oso/9780195063417.001.0001.

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In the history of electronic communication, the last quarter of the nineteenth century holds a special place, for it was during this period that the telephone, phonograph, electric light, wireless, and cinema were all invented. In When old Technologies Were New, Carolyn Marvin explores how two of these new inventions--the telephone and the electric light--were publicly envisioned at the end of the nineteenth century, as seen in specialized engineering journals and popular media. Marvin pays particular attention to the telephone, describing how it disrupted established social relations, unsettling customary ways of dividing the private person and family from the more public setting of the community. On the lighter side, she describes how people spoke louder when calling long distance, and how they worried about catching contagious diseases over the phone. A particularly powerful chapter deals with telephonic precursors of radio broadcasting--the "Telephone Herald" in New York and the "Telefon Hirmondo" of Hungary--and the conflict between the technological development of broadcasting and the attempt to impose a homogenous, ethnocentric variant of Anglo-Saxon culture on the public. While focusing on the way professionals in the electronics field tried to control the new media, Marvin also illuminates the broader social impact, presenting a wide-ranging, informative, and entertaining account of the early years of electronic media.
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Cao, Gang, and Lance DeLong. Physics of Spin-Orbit-Coupled Oxides. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780199602025.001.0001.

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Prior to 2010, most research on the physics and chemistry of transition metal oxides was dominated by compounds of the 3d-transition elements such as Cr, Mn, Fe, Co, Ni, and Cu. These materials exhibited novel, important phenomena that include giant magnetoresistance in manganites, as well as high-temperature superconductivity in doped La2CuO4 and related cuprates. The discovery in 1994 of an exotic superconducting state in Sr2RuO4 shifted some interest toward ruthenates. Moreover, the realization in 2008 that a novel variant of the classic Mott metal-insulator transition was at play in Sr2IrO4 provided the impetus for a burgeoning group of studies of the influence of strong spin-orbit interactions in “heavy” (4d- and 5d-) transition-element oxides. This book reviews recent experimental and theoretical evidence that the physical and structural properties of 4d- and 5d-oxides are decisively influenced by strong spin-orbit interactions that compete or collaborate with comparable Coulomb, magnetic exchange, and crystalline electric field interactions. The combined effect leads to unusual ground states and magnetic frustration that are unique to this class of materials. Novel couplings between the orbital/lattice and spin degrees of freedom, which lead to unusual types of magnetic order and other exotic phenomena, challenge current theoretical models. Of particular interest are recent investigations of iridates and ruthenates focusing on strong spin-orbit interactions that couple the lattice and spin degrees of freedom.
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Book chapters on the topic "Electric field gradient focusing"

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Hlushkou, D., U. Tallarek, and Richard M. Crooks. "Numerical Simulation of Electric Field Gradient Focusing and Separation of Analytes in Microchannels with Embedded Bipolar Electrode." In High Performance Computing in Science and Engineering, Garching/Munich 2009, 719–30. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-642-13872-0_60.

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Ambrosch-Draxl, C., P. Blaha, and K. Schwarz. "Electric Field Gradient Calculations of PrBa2Cu3O7." In Springer Series in Solid-State Sciences, 430–33. Berlin, Heidelberg: Springer Berlin Heidelberg, 1993. http://dx.doi.org/10.1007/978-3-642-84865-0_74.

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Lütgemeier, H., V. Florentiev, and A. Yakubovksi. "Electric Field Gradient of Ba in YBa2Cu3Oy." In Springer Series in Solid-State Sciences, 222–24. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84345-7_41.

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Galsin, Joginder Singh. "Electric Field Gradient in Dilute Cubic Alloys." In Impurity Scattering in Metallic Alloys, 351–76. Boston, MA: Springer US, 2002. http://dx.doi.org/10.1007/978-1-4615-1241-7_14.

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Cavalcante, F. H. M., A. W. Carbonari, R. F. L. Malavasi, G. A. Cabrera-Pasca, J. Mestnik-Filho, and R. N. Saxena. "Temperature dependence of electric field gradient in TbCoO3." In HFI/NQI 2007, 253–57. Berlin, Heidelberg: Springer Berlin Heidelberg, 2008. http://dx.doi.org/10.1007/978-3-540-85320-6_38.

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Matsumiya, R., M. Mihara, M. Ogura, K. Matsuta, M. Fukuda, T. Izumikawa, and T. Minamisono. "Electric field gradient at 12N implanted into ZnO." In HFI/NQI 2007, 309–13. Berlin, Heidelberg: Springer Berlin Heidelberg, 2008. http://dx.doi.org/10.1007/978-3-540-85320-6_47.

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Laakso, Harri, Robert F. Pfaff, and Thomas L. Aggson. "Plasma gradient effects on double probe electric field measurements." In Measurement Techniques in Space Plasmas: Fields, 73–78. Washington, D. C.: American Geophysical Union, 1998. http://dx.doi.org/10.1029/gm103p0073.

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Ambrosch-Draxl, C., P. Blaha, and K. Schwarz. "Charge Distribution and Electric Field Gradient Calculations for YBa2Cu3O7−x." In Springer Series in Solid-State Sciences, 338–42. Berlin, Heidelberg: Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-84345-7_64.

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Kalpakides, V. K., A. I. Arvanitakis, and E. P. Hadjigeorgiou. "The role of electric field gradient in modeling elastic ferroelectrics." In Recent Progress in the Mechanics of Defects, 77–90. Dordrecht: Springer Netherlands, 2010. http://dx.doi.org/10.1007/978-94-007-0314-8_9.

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Lima, Filipe Camargo Dalmatti Alves, Rafael Rodrigues do Nascimento, Marcos Brown Gonçalves, Stefaan Cottenier, Marília Junqueira Caldas, and Helena Maria Petrilli. "Electric field gradient and electronic properties of crown thioether compounds." In HFI / NQI 2010, 23–27. Dordrecht: Springer Netherlands, 2010. http://dx.doi.org/10.1007/978-94-007-1269-0_7.

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Conference papers on the topic "Electric field gradient focusing"

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Ge, Zhengwei, and Chun Yang. "Towards High Concentration Enhancement of Microfluidic Temperature Gradient Focusing of Sample Solutes." In ASME 2011 9th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2011. http://dx.doi.org/10.1115/icnmm2011-58273.

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This paper reports an improved technique to enhance microfluidic temperature gradient focusing (TGF) of sample solutes using Joule heating effects induced by a combined AC and DC electric field. By introducing the AC field component, additional Joule heating effects are obtained to generate temperature gradient for concentrating sample solutes, while the electroosmotic flow is suppressed under the high frequency AC electric field. Therefore, the required DC voltages for achieving certain sample concentration by Joule heating induced TGF technique are remarkably reduced. Moreover, the lower DC voltages lead to smaller electroosmotic flow (EOF), thereby reducing the backpressure effects due to the finite reservoir size. Concentration enhancements of sample solutes are improved by using a combined AC and DC electric field.
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Ge, Zhengwei, and Chun Yang. "Joule Heating Induced Temperature Gradient Focusing for Microfluidic Concentration of Samples." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-23134.

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Microfluidic concentration of sample species is achieved using the temperature gradient focusing (TGF) in a microchannel with a step change in the cross-section under a pure direct current (DC) field or a combined alternating current (AC) and DC electric field. Experiments were carried out to study the effects of applied voltage, buffer concentration and channel size on sample concentration in the TGF processes. These effects were analyzed and summarized using a dimensionless Joule number that is introduced in this study. In addition, Joule number effect in the Poly-dimethylsiloxane (PDMS)/PDMS microdevice was compared with the PDMS/Glass microdevice. A more than 450-fold concentration enhancement was obtained within 75 seconds in the PDMS/PDMS microdevice. Results also showed that the high frequency AC electric field which contributes to produce the temperature gradient and reduces the required DC voltage for the sample concentration. The lower DC voltage has generated slower electroosmotic flow (EOF), which reduces the backpressure effect associated with the finite reservoir size. Finally, a more than 2500-fold concentration enhancement was obtained within 14 minutes in the PDMS/PDMS microdevice, which was a great achievement in this TGF technique using inherent Joule heating effects.
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Tang, Gong Yue, and Chun Yang. "Joule Heating Induced Temperature Gradient Focusing in a Microfluidic Channel With a Sudden Change in Cross Section." In ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52197.

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Temperature gradient focusing is a recently developed technique for spatially focusing and separating ionic analytes in microchannels. The temperature gradient required for temperature gradient focusing can be generated either by an imposed temperature gradient or by Joule heating resulted from an applied electric field that also drives buffer flow. In this study, a numerical model describing the Joule heating induced temperature development and temperature gradient focusing is developed. The model consists of a set of governing equations including the Poisson-Boltzmann equation, the Laplace equation, the Navier-Stokes equations, the energy equations and the mass transport equation. As the thermophysical and electrical properties including the liquid dielectric constant, viscosity and electric conductivity are temperature-dependent, these governing equations are coupled, and therefore the coupled governing equations are solved numerically by using a CFD based numerical method. The numerical simulations agree well with the experimental results, suggesting that the valid mathematical model presented in this study.
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Shim, Jaesool, Prashanta Dutta, and Cornelius F. Ivory. "Focusing of Proteins in a Horseshoe Microchannel." In ASME 2008 International Mechanical Engineering Congress and Exposition. ASMEDC, 2008. http://dx.doi.org/10.1115/imece2008-67445.

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Ampholyte based isoelectric focusing (IEF) simulation was conducted to study dispersion of proteins in a horseshoe microchannel. Four model proteins (pls = 6.49, 7.1, 7.93 and 8.6) are focused in a 1 cm long horseshoe channel under an electric field of 300 V/cm. The pH gradient is formed in the presence of 25 biprotic carrier ampholytes (ΔpK = 3.0) within a pH range of 6 to 9. The proteins are focused at 380 sec in a nominal electric field of 300 V/cm. Our numerical results show that the band dispersions of a protein are large during the marching stage, but the dispersions are significantly reduced when the double peaks start to merge. This rearrangement of spreading band is very unique compared to linear electrokinetic phenomena (capillary electrophoresis, zone electrophoresis or electroosmosis) and is independent of channel position and channel shape. Hence, one can perform IEF in complex geometries without incorporating hyperturns.
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Ge, Zhengwei, and Chun Yang. "Microfluidics Concentration of Sample Solutes Using Joule Heating Effects Under Combined AC and DC Electric Field." In ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels collocated with 3rd Joint US-European Fluids Engineering Summer Meeting. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30451.

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Microfluidic concentration is achieved by utilizing Joule heating effect induced temperature gradient focusing (TGF) under a combined AC and DC electric field imposed in a straight microchannel with sudden expansion in cross-section. The introduction of AC electric field component services dual functions: one is to produce Joule heating effects for generating temperature gradient, and the other is to suppress electroosmotic flow with high frequencies. Therefore, the required DC voltage for achieving sample concentration with Joule heating induced TGF technique is remarkably reduced. The lower DC voltage can lead to smaller electroosmotic flow (EOF), thereby reducing the backpressure effect due to the finite reservoir size. It was demonstrated that using the proposed new TGF technique with Joule heating effect under a combined AC and DC field, more than 2500-fold concentration enhancement was obtained within 14 minutes in a PDMS/PDMS microdevice, which is an order of magnitude higher than the literature reported concentration enhancement achieved by microfluidic devices utilizing the Joule heating induced TGF technique.
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Dutta, Prashanta, Keisuke Horiuchi, Huanchun Cui, and Cornelius F. Ivory. "Multistage Isoelectric Focusing: A Novel On-Chip Bio-Separation Technique." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-79978.

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This experimental study reports a method to increase the resolving power of isoelectric focusing (IEF) on a polymeric microfluidic chip. Microfluidic chip is formed on poly-di-methyl siloxane (PDMS) using soft lithography and multilayer bonding technique. In this novel bioseparation technique, IEF is staged by first focusing protein species in a straight channel using broad-range ampholytes and then refocusing segments of that first channel into secondary channels that branch out from the first one. Experiments demonstrated that three fluorescent protein species within a segment of pH gradient in the first stage were refocused in the second stage with much higher resolution in a shallower pH gradient. A serially performed two-stage IEF was completed in less than 25 minutes under particularly small electric field strength up to 100 V/cm.
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Yoo, Kisoo, Prashanta Dutta, and Jin Liu. "Free Flow Isoelectric Focusing in a Microfluidic Device." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37629.

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In recent years, there are growing interests in the use of free flow isoelectric focusing (FFIEF). In FFIEF, a thin sheath of laminar flow is introduced perpendicular to the direction of the applied electric field for continuous separation of proteins and charged species. This technique is especially useful in microfluidic device since the electrophoretically separated bands do not have to be mobilized for detection or further analysis. In this study, a mathematical model is developed to simulate free flow isoelectric process in microfluidic devices considering electroneutrality and incompressibility of electrolytes. Our mathematical model is based on mass, momentum and charge conservation equations. A finite volume based numerical scheme is implemented to simulate two dimensional FFIEF in a microfluidic chip. Simulation results indicate that pH gradient forms as samples flow downstream and proteins can be separated effectively using this technique. A new design of microfluidic chip is proposed for separation for cardiac troponin I from serum albumin using FFIEF technique.
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Allam, Ahmed, Karim Sabra, and Alper Erturk. "Enhanced Sound Energy Harvesting by Leveraging Gradient-Index Phononic Crystals." In ASME 2020 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/smasis2020-2411.

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Abstract We explore the harvesting of acoustic waves by leveraging a 3D-printed gradient-index phononic crystal (GRIN-PC) lens design. The concept is demonstrated numerically and experimentally for audio frequency range acoustic waves in air. Unit cell design procedure to achieve the required refractive index profile and numerical simulations of the band structure are executed using a high-fidelity finite-element model, followed by 3D simulations of the acoustic wave field for validation of the lens performance. Performance enhancement by focusing acoustic waves is quantified along with the level of anisotropy in the resulting 3D lens design. Additionally, a fully coupled multiphysics framework is developed to cover acoustic-structure interaction, piezoelectric coupling, as well as electrical load impedance. Finite-element simulations include the GRIN-PC lens and the harvester components along with basic electrical load to quantify the electrical power. In the full numerical simulations, design parameters such as the unit cell design, aperture of the lens, directional effects and anisotropy are explored in detail. Specifically, efforts are summarized on the unit cell design to minimize the directional sensitivity, toward making the lens close to omnidirectional.
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Yazdi, Shahrzad H., Scott M. Davison, and Kendra V. Sharp. "Experimental Demonstration of Localized Flow Control in a Microchannel Using Induced-Charge Electroosmosis." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-11480.

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In this paper we investigate the use of induced charged electroosmosis (ICEO) as a means of providing localized flow control within bulk pressure-driven flow. Conductive posts are positioned in a microchannel in such a way that an AC electric field can be applied across them. This AC field induces an electric double layer (EDL), leading to ICEO flow around the conductive object. A pressure gradient is applied across the length of the channel to drive a background flow past the ICEO region. The combination of AC and pressure-driven flow fields is expected to create recirculation regions around the posts which could be useful for trapping particles or focusing the flow, e.g. for lab-on-a-chip applications. Numerical models of ICEO flow were developed and used to provide guidance for the design of microfluidic devices. These numerical models were also used to explore the number, position and shape of the conducting posts to create useful flow patterns. However, this paper focuses on the fabrication of and experiments within a prototypical microdevice. The device was fabricated from silicon dioxide and conducting gold pillars positioned in the glass channel. Experimental results obtained from this device have demonstrated localized ICEO-based flow control. Specifically, wake regions devoid of particles are created behind the posts.
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Tol, Serife, F. Levent Degertekin, and Alper Erturk. "Dramatic Enhancement of Elastic Wave Energy Harvesting Using a Gradient-Index Phononic Crystal Lens." In ASME 2016 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/smasis2016-9264.

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In this paper, we explore structure-borne elastic wave energy harvesting, both numerically and experimentally, by exploiting a Gradient-Index Phononic Crystal Lens (GRIN-PCL) structure. The proposed GRIN-PCL is formed by an array of blind holes with different diameters on an aluminum plate where the orientation and size of the blind holes are tailored to obtain a hyperbolic secant gradient distribution of refractive index guided by finite-element simulations of the lowest asymmetric mode Lamb wave band diagrams. Under plane wave excitation from a line source, experimentally measured wave field successfully validates the numerical simulation of wave focusing within the GRIN-PCL domain. A piezoelectric energy harvester disk located at the first focus of the GRIN-PCL yields an order of magnitude larger power output as compared to the baseline case of energy harvesting without the GRIN-PCL on the uniform plate counterpart for the same incident plane wave excitation. The power output is further improved by a factor of five using complex electrical load impedance matching through resistive-inductive loading as compared to purely resistive loading case.
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Reports on the topic "Electric field gradient focusing"

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Moretti, A. Electric Gradient Breakdown Results for the Orthogonal Box Cavity in a 3 T Magnetic Field. Office of Scientific and Technical Information (OSTI), June 2012. http://dx.doi.org/10.2172/1051692.

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2

Iselin, L. H. Using nitrogen-14 nuclear quadrupole resonance and electric field gradient information for the study of radiation effects. Office of Scientific and Technical Information (OSTI), December 1995. http://dx.doi.org/10.2172/527440.

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Evenson, W. E., A. G. McKale, H. T. Su, and J. A. Gardner. PAC (perturbed angular correlation) perturbation factor for spin 5/2 nuclei subject to a rapidly fluctuation EFC (electric field gradient). Office of Scientific and Technical Information (OSTI), January 1990. http://dx.doi.org/10.2172/6171195.

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