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Academic literature on the topic 'Concentration gradients'

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Published: 4 June 2021
Last updated: 1 February 2022

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Journal articles on the topic "Concentration gradients"

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Chittur K, Subramaniam, Aishwarya Chandran, Ashwini Khandelwal, and Sivakumar A. "Energy Conversion using electrolytic concentration gradients." MRS Proceedings 1774 (2015): 51–62. http://dx.doi.org/10.1557/opl.2015.758.

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ABSTRACTSalinity gradient is an enormous source of clean energy. A process for potential generation from an ionic concentration gradient produced in single and multicell assembly is presented. The ionic gradient is created using a fuel cell type cell with a micro-porous ion exchange membrane, both anionic (AEM) and cationic (CEM). Various salinity gradients, Salt : Fresh, from 100 : 0 to 16000 : 0 was established using NaCl solution, in the electrode chambers. A potential of 20 mV/cm to 25 mV/cm can be realized at ambient temperatures and pressures for a bipolar AEM/CEM cell. The performance was optimized for various static and dynamic flow rates of the saline and fresh water. The cell performance can further be optimized for Membrane Electrode System (MES) morphology. A multicell unit was assembled and the results presented for various conditions like concentration gradients, flow rates and pressure. The thermodynamic and electrical efficiency needs to be evaluated for various gradients and flow rates. The relation with number of valance electrons/ ion and the potential generated changes for various dynamic condition of salinity. The higher the salinity gradient the larger is the potential generated. This is limited by the membrane characteristics. There exists a monotonic relation between the number of valence electron/ion/unit time and the potential generated up to about 16000 concentration. The membrane characteristics have been studied for optimal ion crossover for various gradients and flow. The graph between ln (gradient) versus Voltage provides insights into this process. This presents a very cost effective and clean process of energy conversion.
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Lagator, Mato, Hildegard Uecker, and Paul Neve. "Adaptation at different points along antibiotic concentration gradients." Biology Letters 17, no. 5 (May 2021): 20200913. http://dx.doi.org/10.1098/rsbl.2020.0913.

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Antibiotic concentrations vary dramatically in the body and the environment. Hence, understanding the dynamics of resistance evolution along antibiotic concentration gradients is critical for predicting and slowing the emergence and spread of resistance. While it has been shown that increasing the concentration of an antibiotic slows resistance evolution, how adaptation to one antibiotic concentration correlates with fitness at other points along the gradient has not received much attention. Here, we selected populations of Escherichia coli at several points along a concentration gradient for three different antibiotics, asking how rapidly resistance evolved and whether populations became specialized to the antibiotic concentration they were selected on. Populations selected at higher concentrations evolved resistance more slowly but exhibited equal or higher fitness across the whole gradient. Populations selected at lower concentrations evolved resistance rapidly, but overall fitness in the presence of antibiotics was lower. However, these populations readily adapted to higher concentrations upon subsequent selection. Our results indicate that resistance management strategies must account not only for the rates of resistance evolution but also for the fitness of evolved strains.
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Carlow, G. R., and M. Zinke-Allmang. "Clustering across concentration gradients." Canadian Journal of Physics 72, no. 11-12 (November 1, 1994): 812–17. http://dx.doi.org/10.1139/p94-107.

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Clustering experiments on surfaces are of fundamental interest to verify theoretical concepts for phase-separation processes such as statistical self-similarity and scaling behaviour. Unfortunately, often the differences between theoretical models are too small to be studied with standard sample preparation techniques, as experimental uncertainties result in variations in the results of the same order of magnitude as the effects that we want to study. In this paper we study a modified approach where two different initial morphologies are prepared on the same surface so that the dynamic processes occur in parallel under identical conditions. From observations of clustering near the concentration step we find that the material transfer during late stage ripening is limited to within a distance that is less than the diffusion length. This result is in agreement with a theoretical model that predicts that the interface is confined to a width of the order of the cluster–cluster distance. The two sides beyond this length evolve independently.
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Alicia, Toh G. G., Chun Yang, Zhiping Wang, and Nam-Trung Nguyen. "Combinational concentration gradient confinement through stagnation flow." Lab on a Chip 16, no. 2 (2016): 368–76. http://dx.doi.org/10.1039/c5lc01137j.

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Williams, Ian, Sangyoon Lee, Azzurra Apriceno, Richard P. Sear, and Giuseppe Battaglia. "Diffusioosmotic and convective flows induced by a nonelectrolyte concentration gradient." Proceedings of the National Academy of Sciences 117, no. 41 (September 28, 2020): 25263–71. http://dx.doi.org/10.1073/pnas.2009072117.

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Glucose is an important energy source in our bodies, and its consumption results in gradients over length scales ranging from the subcellular to entire organs. Concentration gradients can drive material transport through both diffusioosmosis and convection. Convection arises because concentration gradients are mass density gradients. Diffusioosmosis is fluid flow induced by the interaction between a solute and a solid surface. A concentration gradient parallel to a surface creates an osmotic pressure gradient near the surface, resulting in flow. Diffusioosmosis is well understood for electrolyte solutes, but is more poorly characterized for nonelectrolytes such as glucose. We measure fluid flow in glucose gradients formed in a millimeter-long thin channel and find that increasing the gradient causes a crossover from diffusioosmosis-dominated to convection-dominated flow. We cannot explain this with established theories of these phenomena which predict that both scale linearly. In our system, the convection speed is linear in the gradient, but the diffusioosmotic speed has a much weaker concentration dependence and is large even for dilute solutions. We develop existing models and show that a strong surface–solute interaction, a heterogeneous surface, and accounting for a concentration-dependent solution viscosity can explain our data. This demonstrates how sensitive nonelectrolyte diffusioosmosis is to surface and solution properties and to surface–solute interactions. A comprehensive understanding of this sensitivity is required to understand transport in biological systems on length scales from micrometers to millimeters where surfaces are invariably complex and heterogeneous.
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Goodhill, Geoffrey J., Ming Gu, and Jeffrey S. Urbach. "Predicting Axonal Response to Molecular Gradients with a Computational Model of Filopodial Dynamics." Neural Computation 16, no. 11 (November 1, 2004): 2221–43. http://dx.doi.org/10.1162/0899766041941934.

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Axons are often guided to their targets in the developing nervous system by attractive or repulsive molecular concentration gradients. We propose a computational model for gradient sensing and directed movement of the growth cone mediated by filopodia. We show that relatively simple mechanisms are sufficient to generate realistic trajectories for both the short-term response of axons to steep gradients and the long-term response of axons to shallow gradients. The model makes testable predictions for axonal response to attractive and repulsive gradients of different concentrations and steepness, the size of the intracellular amplification of the gradient signal, and the differences in intracellular signaling required for repulsive versus attractive turning.
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Jones, D. P. "Intracellular diffusion gradients of O2 and ATP." American Journal of Physiology-Cell Physiology 250, no. 5 (May 1, 1986): C663—C675. http://dx.doi.org/10.1152/ajpcell.1986.250.5.c663.

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Endogenous enzymes with different subcellular localizations provide in situ probes to study O2 and ATP concentration at various sites within cells. Results from this approach indicate that substantial intracellular concentration gradients occur under some O2- and ATP-limited conditions. These studies, along with electron microscopic analyses and mathematical modeling, indicate that clustering and distribution of mitochondria are major factors in determining the magnitude and location of the concentration gradients. The mitochondria appear to be clustered in sites of high ATP demand to maximize ATP supply under conditions of limited production. The size of such clusters is limited by the magnitude of the O2 gradient needed to provide adequate O2 concentrations for mitochondrial function within the clusters. Thus microheterogeneity of metabolite concentrations can occur in cells without membranal compartmentation and may be important in determining the rates of various high-flux processes.
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Weber, Christoph A., Chiu Fan Lee, and Frank Jülicher. "Droplet ripening in concentration gradients." New Journal of Physics 19, no. 5 (May 17, 2017): 053021. http://dx.doi.org/10.1088/1367-2630/aa6b84.

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Day, Charles. "Concentration gradients promote antibiotic resistance." Physics Today 65, no. 8 (August 2012): 20. http://dx.doi.org/10.1063/pt.3.1670.

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Reenstra, W. W., and J. G. Forte. "Characterization of K+ and Cl- conductances in apical membrane vesicles from stimulated rabbit oxyntic cells." American Journal of Physiology-Gastrointestinal and Liver Physiology 259, no. 5 (November 1, 1990): G850—G858. http://dx.doi.org/10.1152/ajpgi.1990.259.5.g850.

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K+ and Cl- conductance pathways in apical membrane vesicles (SA vesicles) of stimulated oxyntic cells have been characterized. SA vesicles were prepared from rabbit fundic mucosa after stimulation of acid secretion with histamine. Conductive K+ and Cl- fluxes were assayed by several methods: by their effects on pH gradient formation by endogenous H(+)-K(+)-ATPase, by the protonophore-induced dissipation of preformed pH gradients, and by the effects of channel blockers. pH gradient formation by H(+)-K(+)-ATPase required K+ and was greatly reduced when the permeant anion chloride was replaced by gluconate or sulfate. In the presence of 75 mM K+, 1 mM Cl- was sufficient for generation of near maximal pH gradients, as was 5 mM K+ in the presence of 75 mM Cl-. At all K+ and Cl- concentrations tested, the ATP-generated formation of pH gradients was inhibited and the dissipation of these pH gradients stimulated by the protonophore tetrachlorosalicylanilide (TCS). Similar effects of TCS were also seen when Cl- was replaced by impermeant anions. Both processes were blocked by the K+ channel inhibitor Ba2+. The Ki for Ba2+ inhibition of pH gradient formation was 1.5 microM at 5 mM K+ and was proportional to the 3rd power of the K+ concentration. At 75 mM K+ the Cl- channel blocker diphenylamine-2-carboxylate inhibited ATP-dependent pH gradient formation when the Cl- concentration was 1 mM; however, when the Cl- concentration was greater than 5 mM no inhibition was observed. The membrane potential-sensitive dye DISC (5) was used to measure membrane potential generated by K+ gradients.(ABSTRACT TRUNCATED AT 250 WORDS)
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Dissertations / Theses on the topic "Concentration gradients"

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Zaleski, Christopher John. "Electrochemical concentration gradients in deep eutectic solvents." Thesis, University of Leicester, 2015. http://hdl.handle.net/2381/32232.

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Concentration gradients present in the solution during the redox chemistry of selected metals and conducting polymer (poly(3,4ethylenedioxythiophene) (PEDOT)) films redox cycled in Deep Eutectic Solvents (DES) were observed for the first time through the application of the Probe Beam Deflection (PBD) technique combined with the Electrochemical Quartz Crystal Microbalance (EQCM). Suitability of choline chloride (ChCl) based DES for applications as electrolytes in PEDOT based charge storage devices has also been investigated using EQCM. The combination of carefully optimized experimental parameters (temporally extended chronoamperometry and slow scan rate voltammetry) with modified design of the instrument (reduced probe’s distance of approach) allowed for in-situ observations of electrochemically induced concentration gradients in DES based systems. During the studies of electroactive polymer films, complete determination of mobile species transfers in PEDOT/Ethaline and PEDOT/Propaline systems has been achieved. The application of PBD-EQCM technique in studies of metal electrodeposition from DES allowed for monitoring metal speciation in dynamic and quantitative fashion. EQCM study of ChCl based DES indicated Ethaline as the most promising potential electrolyte for PEDOT based charge storage devices. Additionally, an unusual mass exchange process has been detected in PEDOT/Propaline and PEDOT/Acetaline processes. This work has shown a novel, affordable and non-invasive route for observation of electrode/electrolyte interface processes in DES. The experimental protocol developed can potentially be implemented in further studies of DES as well as Ionic Liquids.
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Gardiner, Allen Brooke. "Measurement of concentration gradients in photoresist films and study of the influence of these gradients on photoresist performance /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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McQuinn, Chris. "Design of a mechanical device for fabricating protein concentration gradients to study cell adhesion." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18728.

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The binding interaction between specialized proteins within the extracellular matrix (ECM) and specific membrane receptors in cells are pivotal for regulating cell adhesion and migration. Current methods used to generate patterned ECM substrates for the study of migration involve technically complicated devices that are expensive and demand specialized training. Some are also not applicable to the microscopic scale relevant for cells or provide inadequate substrates for growing sensitive cells such as neurons. This Masters thesis introduces an effective method to pattern proteins with micron scale precision at a reasonable financial cost and requires minimal training. The method is based on a device called the squeegee that uses a PDMS (polydimethyl siloxane) barrier to precisely control exposure of protein from solution onto specific areas of a glass surface to regulate adsorption time. The patterns may be produced with a range of proteins on a multitude of glass surfaces. The squeegee method recreated an ECM in the form of graded protein patterns, including continuous gradients and stepped gradients. Mammalian epithelial cells (CHO-K1) were cultured on a surface comprised of a fibronectin stepped gradient and shown to increase in cell spreading with increasing fibronectin surface density. Other proteins were successfully pattered including netrin-1, an important guidance cue in the developing mammalian spinal cord.
L'interaction entre les protéines spécialisées qui sont dans la matrice extracellulaire (MEC) et les récepteurs à la limite de la membrane d'un organisme cellulaire est essentielle à la migration des cellules. Les méthodes actuelles pour étudier la migration impliquent l'utilisation d'appareils techniquement complexes, dispendieux et requérant une formation spécifique. De plus, ces méthodes ne sont pas applicables à l'échelle microscopique des organismes cellulaires ou sont inadéquates pour cultiver des cellules spécialisées. Ce mémoire de maîtrise introduit une méthode ayant un faible rapport coût-efficacité pour modeler les protéines avec une précision micrométrique et qui requiert peu de connaissances techniques. Il est possible de produire ces modèles avec une gamme de protéines et sur une multitude de surfaces de verre. La base de cette méthode est un appareil qui est nommé « la racle » qui utilise une barrière de polydimethyl siloxane (PDMS) pour contrôler précisément l'adsorption de protéine d'une solution sur une surface de verre. La méthode qui utilise la racle a permis de recréer des MEC sous forme de gradients de protéines, comprenant aussi bien des pentes continues que des marches d'escalier. Des cellules épithéliales de mammifères (CHO-K1) ont été cultivées sur une surface ayant un gradient de fibronectine en marche d'escalier, les cellules ont montré une augmentation dans leur étalement proportionnelle à la densité de surface de fibronectine.
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Safronov, Grigory. "Formation and disintegration of small-scale concentration gradients of trace metals on aggregate scale." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=974021512.

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Welsche, Mathias Markus [Verfasser], and Roland [Akademischer Betreuer] Zengerle. "Determination of enzyme kinetics in micro concentration gradients = Bestimmung von Enzym-Kinetiken in Mikro-Konzentrationsgradienten." Freiburg : Universität, 2013. http://d-nb.info/1123475792/34.

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Bui, Hanh. "A COMPARISON OF TWO COMMERCIAL STRIPS WITH PREDEFINED ANTIBIOTIC CONCENTRATION GRADIENTS FOR SUSCEPTIBILITY TESTING OF PERIODONTAL BACTERIAL PATHOGENS." Master's thesis, Temple University Libraries, 2013. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/216515.

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Oral Biology
M.S.
Objectives: Systemic antibiotics are generally recognized as providing a beneficial impact in treatment of both aggressive and chronic periodontitis. Since strains of periodontal pathogens among periodontitis patients may vary in their antibiotic drug resistance, the American Academy of Periodontology recommends antimicrobial susceptibility testing of suspected periodontal pathogens prior to administration of systemic periodontal antibiotic therapy, to reduce the risk of a treatment failure due to pathogen antibiotic resistance. E-test and MIC Test Strip assays are two in vitro antimicrobial susceptibility testing systems employing plastic- and paper-based, respectively, carriers loaded with predefined antibiotic gradients covering 15 two-fold dilutions. To date, no performance evaluations have been carried out comparing the Etest and MIC Test Strip assays in their ability to assess the in vitro antimicrobial susceptibility of periodontal bacterial pathogens. As a result, the purpose of this study was to compare the in vitro performance of E-test and MIC Test Strip assays in assessing minimal inhibitory concentration (MIC) values of four antibiotics frequently utilized in systemic periodontal antibiotic therapy against 11 fresh clinical subgingival isolates of the putative periodontal pathogen, Prevotella intermedia/ nigrescens, and to compare the distribution of P. intermedia/ nigrescens strains identified with interpretative criteria as "susceptible" and "resistant" to each of the four antibiotics using MIC values determined by the two antimicrobial susceptibility testing methods. Methods: Standardized cell suspensions, equivalent to a 2.0 McFarland turbidity standard, were prepared with 11 fresh clinical isolates of P. intermedia/nigrescens, each recovered from the subgingival microbiota of United States chronic periodontitis subjects, and plated onto to the surfaces of culture plates containing enriched Brucella blood agar. After drying, pairs of antibiotic-impregnated, quantitative, gradient diffusion strips from two manufacturers (E-test, bioMérieux, Durham, NC, USA, and MIC Test Strip, Liofilchem s.r.l., Roseto degli Abruzzi, Italy) for amoxicillin, clindamycin, metronidazole, and doxycycline were each placed apart from each other onto the inoculated enriched Brucella blood agar surfaces, so that an antibiotic test strip from each manufacturer was employed per plate against each P. intermedia/ nigrescens clinical isolate for antibiotic susceptibility testing. After 48-72 hours anaerobic jar incubation, individual MIC values for each antibiotic test strip against P. intermedia/nigrescens were read in μg/ml at the point where the edge of the bacterial inhibition ellipse intersected with the antibiotic test strip. MIC50, MIC90, and MIC range were calculated and compared for each of the test antibiotics, with essential agreement (EA) values determined per test antibiotic for the level of outcome agreement between two antimicrobial susceptibility testing methods. In addition, the identification of antibiotic "susceptible" and "resistant" strains among the P. intermedia/nigrescens clinical isolates was determined for each test antibiotic using MIC interpretative criteria from the MIC interpretative standards developed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) for gram-negative anaerobic bacteria for amoxicillin, clindamycin, and metronidazole findings, and from the French Society of Microbiology breakpoint values for anaerobic disk diffusion testing for doxycycline data. Results: For amoxicillin, higher MIC50 and MIC90 values against the P. intermedia/ nigrescens strains were found with the MIC Test Strip assay than with E-test strips, resulting in a relatively low EA value of 45.5% between the two susceptibility testing methods. A higher percentage of amoxicillin "resistant" P. intermedia/nigrescens strains (72.7%) were identified by MIC Test Strips as compared to E-test strips (54.5%), although both methods found the same proportion of amoxicillin "susceptible" strains (27.3%). For clindamycin, both susceptibility testing methods provided identical MIC values (EA value = 100%), and exactly the same distributions of "susceptible" and "resistant" strains of P. intermedia/nigrescens. For metronidazole, only very poor agreement (EA value = 9.1%) was found between the two susceptibility testing methods, with MIC Test Strips exhibiting markedly higher MIC50 and MIC90 values against P. intermedia/nigrescens as compared to E-test strips. However, the distribution of "susceptible" and "resistant" P. intermedia/ nigrescens were identical between the two susceptibility testing methods. For doxycycline, relatively good agreement (EA value = 72.7%) was found in MIC concentrations between the two susceptibility testing methods, although generally lower MIC values were associated with MIC Test Strips. In addition, identical distributions of "susceptible" and "resistant" P. intermedia/nigrescens were provided by both susceptibility testing methods. Conclusions: Relative to MIC values measured against periodontal strains of P. intermedia/nigrescens, MIC Test Strips gave higher MIC values with amoxicillin and metronidazole, equal MIC values with clindamycin, and lower MIC values with doxycycline, as compared to MIC values measured with the E-test assay. Relative to the identification of antibiotic "susceptible" periodontal P. intermedia/ nigrescens strains, both susceptibility testing methods provided identical findings, suggesting that both methods appear to be interchangeable for clinical decision making in regard to identification of antibiotic-sensitive strains of periodontal P. intermedia/nigrescens. However, for epidemiologic surveillance of drug susceptibility trends, where exact MIC values are important to track over time, the relatively higher proportion of non-exact MIC differences between the two susceptibility testing methods argues against using them interchangeably. Instead, one or the other method should be used consistently for such studies. Further comparative studies of the E-test and MIC Test Strip assays are indicated using other periodontopathic bacterial species besides P. intermedia/ nigrescens, and to assess the reproducibility of MIC values provided by both in vitro susceptibility testing methods over time.
Temple University--Theses
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Huraux, Karine. "Morphologies et gradients de concentration induits par le séchage dans des solutions polymères et des gels." Paris 6, 2008. http://www.theses.fr/2008PA066457.

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Cette thèse présente l’étude de morphologies de surface induites, à la surface de films polymères et de gels, par le séchage. La première partie porte sur la séparation de phases induite par évaporation du solvant dans des films réalisés à partir d’un mélange de deux polymères immiscibles, l’un vitreux, l’autre cristallin à température ambiante, en solvant commun. La morphologie obtenue dépend des conditions de séchage et des propriétés physicochimiques du système. Nous avons mis en évidence, en fonction de la composition du mélange, une inversion de morphologie. L’étude d’une composition donnée permet de distinguer, en fonction de la vitesse de séchage, différents régimes. La seconde partie traite de la formation, à la surface de gels chimiques de polyalcool vinylique, d’instabilités de plissement dépendant des conditions de séchage et de synthèse. Cette morphologie est attribuée à la formation d’une peau vitreuse qui subit, lors de la contraction du gel, une force de compression relaxée par la formation de plis. Nos travaux confirment expérimentalement l’existence de cette peau vitreuse (microscopie à force atomique) et estiment son épaisseur par simulation.
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Kozawa, Kathleen Hiromi. "Investigation of pollution concentrations and pollution concentration gradients in communities adjacent to the ports of Los Angeles and Long Beach using a mobile monitoring platform." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1723112471&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.

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Meierdierks, Jana [Verfasser], and Peter [Akademischer Betreuer] Grathwohl. "Soil-Atmosphere Exchange of PAHs : The Determination of Concentration Gradients with Passive Samplers / Jana Meierdierks ; Betreuer: Peter Grathwohl." Tübingen : Universitätsbibliothek Tübingen, 2019. http://d-nb.info/1205002448/34.

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Anthony, James Lee. "The influence of turbulence, temperature, and nutrient concentration gradients on sediment-water exchanges of nitrogen and phosphorus in lakes." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3284439.

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Books on the topic "Concentration gradients"

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L, Tracy Linda, Wilson William K, and United States. Forest Service. Northern Research Station, eds. Chloride concentration gradients in tank-stored hydraulic fracturing fluids following flowback. Newtown Square, PA: U.S. Dept. of Agriculture, Forest Service, Northern Research Station, 2011.

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Stewart, Renée. Ontogenetic changes in dietary and tissue metal concentration in wild yellow perch (Perca flavescens) from a metal contamination gradient. Sudbury, Ont: Laurentian University, 2003.

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United States. National Aeronautics and Space Administration., ed. Fugacity and concentration gradients in a gravity field. [Washington, DC]: National Aeronautics and Space Administration, 1986.

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Immobilized pH Gradients: Theory and Methodology. Elsevier Science Publishing Company, 1990.

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T, Chai A., Sun D. J, and United States. National Aeronautics and Space Administration., eds. Convective flows in enclosures with vertical temperature or concentration gradients. [Washington, DC]: National Aeronautics and Space Administration, 1989.

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An-Ti, Chai, Sun D. J, and United States. National Aeronautics and Space Administration., eds. Convective flows in enclosures with vertical temperature or concentration gradients. [Washington, DC]: National Aeronautics and Space Administration, 1989.

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Narayanan, Ramachandran, and George C. Marshall Space Flight Center., eds. A photometric technique for determining fluid concentration using consumer-grade hardware. [Marshall Space Flight Center, Ala.]: National Aeronautics and Space Administration, Marshall Space Flight Center, 1999.

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Williams, M. G., and P. J. Stopford. The Influence of Concentration Gradients Across the Outlets of a Gas Centrifuge. AEA Technology Plc, 1986.

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Moore, Kathryn Jean. Combined concentration gradients of neurotrophic factors act in synergy to guide neurite outgrowth. 2004.

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Fourier transform infrared and Raman spectroscopic characterization of homogeneous solution concentration gradients near a container wall at different temperatures. Huntsville, AL: Dept. of Chemistry, the University of Alabama in Huntsville, 1991.

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Book chapters on the topic "Concentration gradients"

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Deamer, David. "Concentration Gradients." In Encyclopedia of Astrobiology, 1. Berlin, Heidelberg: Springer Berlin Heidelberg, 2014. http://dx.doi.org/10.1007/978-3-642-27833-4_226-4.

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Deamer, David. "Concentration Gradients." In Encyclopedia of Astrobiology, 533. Berlin, Heidelberg: Springer Berlin Heidelberg, 2015. http://dx.doi.org/10.1007/978-3-662-44185-5_226.

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Deamer, David. "Concentration Gradients." In Encyclopedia of Astrobiology, 354–55. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-11274-4_226.

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Yoo, Han-Ill. "Diffusion in Concentration Gradients." In Lectures on Kinetic Processes in Materials, 145–72. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-25950-1_4.

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Meyer, Tobias, Nancy L. Allbritton, and Elena Oancea. "Regulation of Nuclear Calcium Concentration." In Ciba Foundation Symposium 188 - Calcium Waves, Gradients and Oscillations, 252–78. Chichester, UK: John Wiley & Sons, Ltd., 2007. http://dx.doi.org/10.1002/9780470514696.ch14.

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Lavoie, Pascal, and Mark P. Taylor. "Alumina Concentration Gradients in Aluminium Reduction Cells." In Advances in Molten Slags, Fluxes, and Salts, 791–98. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2016. http://dx.doi.org/10.1002/9781119333197.ch84.

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Talman, S. J., and E. H. Perkins. "Concentration Gradients Associated With Acid Gas Injection." In Acid Gas Injection and Related Technologies, 347–59. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2011. http://dx.doi.org/10.1002/9781118094273.ch21.

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Lavoie, Pascal, and Mark P. Taylor. "Alumina Concentration Gradients in Aluminium Reduction Cells." In Advances in Molten Slags, Fluxes, and Salts: Proceedings of the 10th International Conference on Molten Slags, Fluxes and Salts 2016, 791–98. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-48769-4_84.

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Serra, Roberto, and Marco Villani. "A CA Model of Spontaneous Formation of Concentration Gradients." In Lecture Notes in Computer Science, 385–92. Berlin, Heidelberg: Springer Berlin Heidelberg, 2008. http://dx.doi.org/10.1007/978-3-540-79992-4_50.

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Tessier, Jayson, Katie Cantin, and David Thor Magnusson. "Investigation of Alumina Concentration Gradients Within Hall-Héroult Electrolytic Bath." In The Minerals, Metals & Materials Series, 515–22. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-72284-9_68.

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Conference papers on the topic "Concentration gradients"

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Sukumar, Pavithra, and Mohammad A. Qasaimeh. "Microfluidic mixing elements for concentration gradients." In 2018 Advances in Science and Engineering Technology International Conferences (ASET). IEEE, 2018. http://dx.doi.org/10.1109/icaset.2018.8376904.

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Calhoon, William, and Neeraj Sinha. "Detonation Wave Propagation in Concentration Gradients." In 43rd AIAA Aerospace Sciences Meeting and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2005. http://dx.doi.org/10.2514/6.2005-1167.

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Lee, Jacky S. H., Yandong Hu, and Dongqing Li. "Electrokinetic Concentration Gradient Generation Using a Converging-Diverging Microchannel." In ASME 3rd International Conference on Microchannels and Minichannels. ASMEDC, 2005. http://dx.doi.org/10.1115/icmm2005-75116.

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Creation of concentration gradients is important in the study of biological and chemical processes that are sensitive to concentration variations. This paper presents a simple method to generate a linear concentration gradient in electroosmotic flow in microchannels with converging and diverging geometries. The method is based on the enhanced diffusive mixing inside the microchannel. By varying the converging-diverging geometries, the degree of diffusive mixing can be controlled. Different concentration gradients can be obtained by varying the applied potential and the geometry. Concentration profiles with minimal axial variations can be achieved with a deviation of 7% and 3% over a channel length of 3mm and 1mm, respectively, for a 400μm wide microchannel. Although the underlying physics and mechanisms for creating concentration profiles in a converging-diverging microchannel are the same as a T-shaped micromixer, the converging-diverging microchannel can produce desired concentration profiles in a much shorter distance (shorter by a factor of 2∼3.5 compared to a T-shape mixer). A serially connected concentration gradient generator is also realized with the ability to generate two concentration gradient ranges in the same microchannel. Numerical simulations and experiments were carried out to investigate the factors contributed to the generation of the concentration gradients.
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Qasaimeh, Mohammad A., Melina Astolfi, Michal Pyzik, Silvia Vidal, and David Juncker. "Neutrophil dynamics during migration in microfluidic concentration gradients." In 2014 40th Annual Northeast Bioengineering Conference (NEBEC). IEEE, 2014. http://dx.doi.org/10.1109/nebec.2014.6972913.

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Kudriakov, S., M. Kuznetsov, E. Studer, and J. Grune. "Hydrogen-Air Deflagration in the Presence of Longitudinal Concentration Gradients." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-66619.

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Hydrogen gathering at the top of the containment or reactor building may occur due to an interaction of molten corium and water followed by a severe accident of a nuclear reactor (like TMI, Chernobyl, Fukushima accidents). It accumulates usually in a containment of nuclear reactor as a stratified semi-confined layer of hydrogen-air mixture. Depending on the local concentration and/or presence and activation of mitigation devices, hydrogen may burn following different combustion regimes. Thus, there is a need to estimate the severity of a combustion process under given geometrical configuration, scale, ignition position, and uniformity and composition of combustible mixture. A series of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the LACOMECO European project is devoted to flame propagation in an obstructed large scale cylinder vessel with vertical hydrogen concentration gradients. A 33 m3 volume divided in two sub-compartments, lower (21.6 m3) and upper (11.2 m3), separated by round duplex door of 1 m diameter with a metal structure with 6 layers of wooden plates reproduce real geometry of obstructions with a blockage ratio of 0.33–0.43. A sampling probes method is used to control real distribution of hydrogen. Practically linear positive and negative vertical concentration gradients in the range from 4 % to 13 % are created prior to ignition. Pressure sensors (PCB type), ion probes and thermocouples are used in the experiments to monitor dynamics of hydrogen combustion. The process of flame propagation is investigated depending on hydrogen concentration gradient and ignition positions. Critical conditions for flame acceleration-deceleration and quenching of the flame due to hydrogen concentration gradient are the main scopes of the work. The experimental data obtained during the project will be used for safety analysis, risk assessment and as benchmark experiments for CFD numerical codes validation.
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Selimović, Šeila, Woo Young Sim, Sang Bok Kim, Yun Ho Jang, Won Gu Lee, Masoud Khabiry, Hojae Bae, Sachin Jambovane, Jong Wook Hong, and Ali Khademhosseini. "Exponential Concentration Gradients in Microfluidic Devices for Cell Studies." In ASME 2011 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2011. http://dx.doi.org/10.1115/sbc2011-53529.

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Microscale technologies are a powerful tool in many biological and chemical applications, as they utilize only small reagent volumes. Microfluidics is especially well compatible with biological materials and applications, for example protein crystallization, high throughput assay analysis, and various cell studies. In that context, non-linear gradients of particles and molecules as well as efficient mixing of the components inside the lab-on-a-chip are crucial for many experimental studies: testing of and analyzing biological responses to different analyte concentration levels, studying the native cell microenvironment or cellular responses during different growth and proliferation stages. Thus, a microfluidic approach that allows for generation of different concentration gradients and specifically exponential gradients emerges as a helpful technology, and is also compatible with cells.
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WANG, L., A. CHAI, and D. SUN. "Convective flows in enclosures with vertical temperature or concentration gradients." In 27th Aerospace Sciences Meeting. Reston, Virigina: American Institute of Aeronautics and Astronautics, 1989. http://dx.doi.org/10.2514/6.1989-69.

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Lin, Yu-Sheng, and Chunfei Hu. "Effectively anticancer drug concentration gradients by using 3D microfluidic chip." In 2017 International Conference on Optical MEMS and Nanophotonics (OMN). IEEE, 2017. http://dx.doi.org/10.1109/omn.2017.8051475.

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Kudriakov, S., E. Studer, M. Kuznetsov, and J. Grune. "Experimental and Numerical Investigation of H2-Air Deflagration in the Presence of Concentration Gradients." In 2013 21st International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/icone21-16910.

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A set of experiments performed at Karlsruhe Institute of Technology (KIT) in the framework of the LACOMECO European project is devoted to flame propagation in an obstructed large scale facility A3 (of 8 m height and 33 m3 volume) with initially vertical hydrogen concentration gradients. Almost linear positive and negative (relative to gravity) concentration gradients are created prior to ignition in the range from 4% to 13%, and the process of flame acceleration is investigated depending on hydrogen concentration gradient and ignition positions. In this paper we describe the A3 facility and analyse the experimental data obtained during the project. The results of numerical simulation performed using Europlexus code are presented together with the critical discussions and conclusions.
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Knauer, Oliver S., Andreas Braeuer, Matthias C. Lang, and Alfred Leipertz. "Measurement of Concentration and Temperature Gradients at Binary Mixture Boiling Bubbles." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22054.

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Due to the high heat flux available, nucleate boiling is one of the most utilized processes for the transfer of large amounts of heat in chemical or power engineering applications. Nevertheless, the basic physical phenomena of this kind of heat transfer are physically not well understood, especially for multi-component mixtures in which the heat transfer coefficient is a function of the mixture composition. To apprehend the binary mixture boiling phenomena, the knowledge of the composition and temperature field surrounding a boiling bubble near the heater surface is of great impact. These quantities are measured at individual boiling bubbles by means of laser-optical methods without disturbing the system and with high spatial resolution. An optical accessible and temperature adjustable boiling chamber for the generation of single bubbles of acetone-isopropanol mixtures was constructed. As the vapor-liquid equilibriums (VLE) of these mixtures show a large gap between the saturated liquid and vapor line, significant composition alterations occur during the phase transition. Concentration and temperature gradients have been measured along a line by linear Raman spectroscopy. Due to the species specific Raman shift and the linear superposition of the inelastic scattered light intensities, qualitative and quantitative composition information can be achieved. In alcohols, e.g. isopropanol, the molecules can develop hydrogen bonds, which have an impact on the shape of the O-H bind signal in the Raman spectrum. As the ratio of molecules with and without hydrogen bonds changes with temperature, the temperature of the liquid phase can be derived from the spectra as well. The results show an enhancement of isopropanol, the less volatile component, near the phase boundary due to preferential evaporation of acetone. Furthermore, a not expected depletion of isopropanol approximately 0.75 mm away from the bubble was measured. The detected temperature increases near the boiling bubble, indicating a heat transfer from the gas phase to the surrounding liquid. The temperature distribution also has a minimum at the same position as the isopropanol distribution. A species conservation calculation with simplified assumptions was carried out and validated the measured composition distribution in the liquid surrounding a boiling bubble.
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Reports on the topic "Concentration gradients"

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Edwards, Pamela J., Linda L. Tracy, and William K. Wilson. Chloride concentration gradients in tank-stored hydraulic fracturing fluids following flowback. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station, 2011. http://dx.doi.org/10.2737/nrs-rp-14.

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Ward, Nicholas, Julia Indivero, Cailene Gunn, Wenzhi Wang, Vanessa Bailey, and Nate McDowell. Longitudinal gradients in tree stem greenhouse gas concentrations across six Pacific Northwest coastal forests. Office of Scientific and Technical Information (OSTI), August 2020. http://dx.doi.org/10.2172/1648314.

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Katherine Barbeau. Characterizing the production and retention of dissolved iron as Fe(II) across a natural gradient in chlorophyll concentrations in the Southern Drake Passage - Final Technical Report. Office of Scientific and Technical Information (OSTI), April 2007. http://dx.doi.org/10.2172/901921.

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