The Experts below are selected from a list of 324 Experts worldwide ranked by ideXlab platform
Céline Poncet-legrand - One of the best experts on this subject based on the ideXlab platform.
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Characterization of oxidized tannins: comparison of depolymerization methods, Asymmetric Flow field-Flow fractionation and small-angle X-ray scattering
Analytical and Bioanalytical Chemistry, 2011Co-Authors: Aude Vernhet, Stéphane Dubascoux, Helene Fulcrand, Eric Dubreucq, B. Cabane, Céline Poncet-legrandAbstract:Condensed tannins are a major class of plant polyphenols. They play an important part in the colour and taste of foods and beverages. Due to their chemical reactivity, tannins are not stable once extracted from plants. A number of chemical reactions can take place, leading to structural changes of the native structures to give so-called derived tannins and pigments. This paper compares results obtained on native and oxidized tannins with different techniques: depolymerization followed by high-performance liquid chromatography analysis, small-angle X-ray scattering (SAXS) and Asymmetric Flow field-Flow fractionation (AF4). Upon oxidation, new macromolecules were formed. Thioglycolysis experiments showed no evidence of molecular weight increase, but thioglycolysis yields drastically decreased. When oxidation was performed at high concentration (e.g., 10 g L−1), the weight average degree of polymerization determined from SAXS increased, whereas it remained stable when oxidation was done at low concentration (0.1 g L−1), indicating that the reaction was intramolecular, yet the conformations were different. Differences in terms of solubility were observed; ethanol being a better solvent than water. We also separated soluble and non-water-soluble species of a much oxidized fraction. Thioglycolysis showed no big differences between the two fractions, whereas SAXS and AF4 showed that insoluble macromolecules have a weight average molecular weight ten times higher than the soluble ones. FigureComparison of UV and MALLS fractograms obtained with water-soluble and -insoluble fractions of oxidized tannins in EtOH. Water-insoluble fractions exhibit a broader size distribution and has a weight average molecular weight about ten times larger than the -soluble one
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Characterization of oxidized tannins: comparison of depolymerization methods, Asymmetric Flow field-Flow fractionation and small angle X-ray scattering
Analytical and Bioanalytical Chemistry, 2011Co-Authors: Aude Vernhet, Stéphane Dubascoux, Helene Fulcrand, Eric Dubreucq, B. Cabane, Céline Poncet-legrandAbstract:Condensed tannins are a major class of plant polyphenols. They play an important part in the colour and taste of foods and beverages. Due to their chemical reactivity, tannins are not stable once extracted from plants. A number of chemical reactions can take place, leading to structural changes of the native structures to give so-called derived tannins and pigments. This paper compares results obtained on native and oxidized tannins with different techniques: depolymerization followed by high-performance liquid chromatography analysis, small-angle X-ray scattering (SAXS) and Asymmetric Flow field-Flow fractionation (AF4). Upon oxidation, new macromolecules were formed. Thioglycolysis experiments showed no evidence of molecular weight increase, but thioglycolysis yields drastically decreased. When oxidation was performed at high concentration (e.g., 10 gL−1), the weight average degree of polymerization determined from SAXS increased, whereas it remained stable when oxidation was done at low concentration (0.1 gL−1), indicating that the reaction was intramolecular, yet the conformations were different. Differences in terms of solubility were observed; ethanol being a better solvent than water. We also separated soluble and non-water-soluble species of a much oxidized fraction. Thioglycolysis showed no big differences between the two fractions, whereas SAXS and AF4 showed that insoluble macromolecules have a weight average molecular weight ten times higher than the soluble ones.
Aude Vernhet - One of the best experts on this subject based on the ideXlab platform.
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Characterization of oxidized tannins: comparison of depolymerization methods, Asymmetric Flow field-Flow fractionation and small-angle X-ray scattering
Analytical and Bioanalytical Chemistry, 2011Co-Authors: Aude Vernhet, Stéphane Dubascoux, Helene Fulcrand, Eric Dubreucq, B. Cabane, Céline Poncet-legrandAbstract:Condensed tannins are a major class of plant polyphenols. They play an important part in the colour and taste of foods and beverages. Due to their chemical reactivity, tannins are not stable once extracted from plants. A number of chemical reactions can take place, leading to structural changes of the native structures to give so-called derived tannins and pigments. This paper compares results obtained on native and oxidized tannins with different techniques: depolymerization followed by high-performance liquid chromatography analysis, small-angle X-ray scattering (SAXS) and Asymmetric Flow field-Flow fractionation (AF4). Upon oxidation, new macromolecules were formed. Thioglycolysis experiments showed no evidence of molecular weight increase, but thioglycolysis yields drastically decreased. When oxidation was performed at high concentration (e.g., 10 g L−1), the weight average degree of polymerization determined from SAXS increased, whereas it remained stable when oxidation was done at low concentration (0.1 g L−1), indicating that the reaction was intramolecular, yet the conformations were different. Differences in terms of solubility were observed; ethanol being a better solvent than water. We also separated soluble and non-water-soluble species of a much oxidized fraction. Thioglycolysis showed no big differences between the two fractions, whereas SAXS and AF4 showed that insoluble macromolecules have a weight average molecular weight ten times higher than the soluble ones. FigureComparison of UV and MALLS fractograms obtained with water-soluble and -insoluble fractions of oxidized tannins in EtOH. Water-insoluble fractions exhibit a broader size distribution and has a weight average molecular weight about ten times larger than the -soluble one
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Characterization of oxidized tannins: comparison of depolymerization methods, Asymmetric Flow field-Flow fractionation and small angle X-ray scattering
Analytical and Bioanalytical Chemistry, 2011Co-Authors: Aude Vernhet, Stéphane Dubascoux, Helene Fulcrand, Eric Dubreucq, B. Cabane, Céline Poncet-legrandAbstract:Condensed tannins are a major class of plant polyphenols. They play an important part in the colour and taste of foods and beverages. Due to their chemical reactivity, tannins are not stable once extracted from plants. A number of chemical reactions can take place, leading to structural changes of the native structures to give so-called derived tannins and pigments. This paper compares results obtained on native and oxidized tannins with different techniques: depolymerization followed by high-performance liquid chromatography analysis, small-angle X-ray scattering (SAXS) and Asymmetric Flow field-Flow fractionation (AF4). Upon oxidation, new macromolecules were formed. Thioglycolysis experiments showed no evidence of molecular weight increase, but thioglycolysis yields drastically decreased. When oxidation was performed at high concentration (e.g., 10 gL−1), the weight average degree of polymerization determined from SAXS increased, whereas it remained stable when oxidation was done at low concentration (0.1 gL−1), indicating that the reaction was intramolecular, yet the conformations were different. Differences in terms of solubility were observed; ethanol being a better solvent than water. We also separated soluble and non-water-soluble species of a much oxidized fraction. Thioglycolysis showed no big differences between the two fractions, whereas SAXS and AF4 showed that insoluble macromolecules have a weight average molecular weight ten times higher than the soluble ones.
Vincent A Hackley - One of the best experts on this subject based on the ideXlab platform.
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rational strategy for characterization of nanoscale particles by Asymmetric Flow field Flow fractionation a tutorial
Analytica Chimica Acta, 2014Co-Authors: Julien Gigault, John M Pettibone, Charlene Schmitt, Vincent A HackleyAbstract:This tutorial proposes a comprehensive and rational measurement strategy that provides specific guidance for the application of Asymmetric-Flow field Flow fractionation (A4F) to the size-dependent separation and characterization of nanoscale particles (NPs) dispersed in aqueous media. A range of fractionation conditions are considered, and challenging applications, including industrially relevant materials (e.g., metal NPs, Asymmetric NPs), are utilized in order to validate and illustrate this approach. We demonstrate that optimization is material dependent and that polystyrene NPs, widely used as a reference standard for retention calibration in A4F, in fact represent a class of materials with unique selectivity, recovery and optimal conditions for fractionation; thus use of these standards to calibrate retention for other materials must be validated a posteriori. We discuss the use and relevance of different detection modalities that can potentially yield multi-dimensional and complementary information on NP systems. We illustrate the fractionation of atomically precise nanoclusters, which are the lower limit of the nanoscale regime. Conversely, we address the upper size limit for normal mode elution in A4F. The protocol for A4F fractionation, including the methods described in the present work is proposed as a standardized strategy to realize interlaboratory comparability and to facilitate the selection and validation of material-specific measurement parameters and conditions. It is intended for both novice and advanced users of this measurement technology.
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gold nanorod separation and characterization by Asymmetric Flow field Flow fractionation with uv vis detection
Analytical and Bioanalytical Chemistry, 2013Co-Authors: Julien Gigault, Robert I. Maccuspie, Vincent A HackleyAbstract:The application of Asymmetric-Flow field Flow fractionation (A4F) for low aspect ratio gold nanorod (GNR) fractionation and characterization was comprehensively investigated. We report on two novel aspects of this application. The first addresses the analytical challenge involved in the fractionation of positively charged nanoparticles by A4F, due to the interaction that exists between the negatively charged native membrane and the analyte. We show that the mobile phase composition is a critical parameter for controlling fractionation and mitigating the membrane-analyte interaction. A mixture of ammonium nitrate and cetyl trimethyl ammonium bromide at different molar ratios enables separation of GNRs with high recovery. The second aspect is the demonstration of shape-based separation of GNRs in A4F normal mode elution (i.e., Brownian mode). We show that the elution of GNRs is due both to aspect ratio and a steric-entropic contribution for GNRs with the same diameter. This latter effect can be explained by their orientation vector inside the A4F channel. Our experimental results demonstrate the relevance of the theory described by Beckett and Giddings for non-spherical fractionation (Beckett and Giddings, J Colloid and Interface Sci 186(1):53–59, 1997). However, it is shown that this theory has its limit in the case of complex GNR mixtures, and that shape (i.e., aspect ratio) is the principal material parameter controlling elution of GNRs in A4F; the apparent translational diffusion coefficient of GNRs increases with aspect ratio. Finally, the performance of the methodology developed in this work is evaluated by the fractionation and characterization of individual components from a mixture of GNR aspect ratios.
Zhongqiu Liu - One of the best experts on this subject based on the ideXlab platform.
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Effect of vertical length on Asymmetric Flow and inclusion transport in vertical-bending continuous caster
Powder Technology, 2018Co-Authors: Zhongqiu LiuAbstract:Abstract A large eddy simulation (LES) model has been developed to simulate the transient fluid Flow, heat transfer and solidification processes in various vertical-bending continuous casting casters with 0 to 5 m of vertical length. The LES with dynamic sub-grid model is used to calculate the transient turbulent Flow inside the liquid pool. The enthalpy-porosity approach is used to simulate the heat transfer and solidification of steel in the caster. A criterion is developed using the user-defined functions to model the motion and entrapment of inclusion in the caster based on the Lagrangian approach. The 1/4 and 1/2 inclusion band defects located in a steel plate are found by the UT method, and the distribution of inclusions is intermittent and Asymmetric. The transient and Asymmetric Flow pattern has been obtained in a one-third-scale vertical-bending type water model of mold. The Asymmetric Flow inside the liquid pool is identified a periodical behavior. The oscillating motion of Asymmetric Flow inside the mold is induced by the turbulence, rather than the curve shape of the caster. The maximum impact depths of the lower recirculation Flow for various casters are almost around 2.8 m below the top surface of the mold. The time for inclusion removal from top surface can be divided into three periods: 3.5–6.5 s, 6.5–30 s, and 30 s after injection. The vertical length has a less effect on the removal ratio of inclusions from the top surface, but determines the entrapment positions of inclusions.
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Transient Asymmetric Flow and Bubble Transport Inside a Slab Continuous-Casting Mold
Metallurgical and Materials Transactions B, 2013Co-Authors: Zhongqiu Liu, Maofa JiangAbstract:A one third scale water model experiment was conducted to observe the Asymmetric Flow and vortexing Flow inside a slab continuous-casting mold. Dye-injection experiment was used to show the evolution of the transient Flow pattern in the liquid pool without and with gas injection. The spread of the dye was not symmetric about the central plane. The Flow pattern inside the mold was not stationary. The black sesames were injected into water to visualize the vortexing Flow pattern on the top surface. The changes of shape and location of single vortex and two vortices with time had been observed during experiments. Plant ultrasonic testing (UT) of slabs was used to analyze the slab defects distribution, which indicated that the defects are intermittent and Asymmetric. A mathematical model has been developed to analyze the time-dependent Flow using the realistic geometries, which includes the submerged entry nozzle (SEN), actual mold, and part of the secondary cooling zone. The transient turbulent Flow of molten steel inside the mold has been simulated using the large eddy simulation computational approach. Simulation results agree acceptably well with the water model experimentally observed and plant UT results. The oscillating motions of jet and the turbulence naturally promote the Asymmetric Flow even without the effects of slide gate nozzle or the existence of clogs inside the SEN. The periodic behavior of transient fluid Flow in the mold is identified and characterized. The vortexing Flow is resulted from Asymmetric Flow in the liquid pool. The vortices are located at the low-velocity side adjacent to the SEN, and the positions and sizes are different. Finally, the model is applied to investigate the influence of bubble size and casting speed on the time-dependent bubble distribution and removal fraction from the top surface inside the mold.
Maria Vittoria Salvetti - One of the best experts on this subject based on the ideXlab platform.
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stability analysis and control of the Flow in a symmetric channel with a sudden expansion
Physics of Fluids, 2012Co-Authors: Andrea Fani, Simone Camarri, Maria Vittoria SalvettiAbstract:The laminar Flow in two-dimensional diffusers may produce either symmetric or nonsymmetric steady solutions, depending on the value of the Reynolds number as compared with some critical value. The stability properties of the Flow are studied in the context of linear theory. In this context, a sensitivity analysis of the Flow instability is carried out with respect to perturbations that may be produced by a realistic passive control, thus providing qualitative hints and quantitative information for the control design. Following the so-obtained information, a passive control is built by introducing a small cylinder in the Flow with the aim of stabilizing the unstable symmetric Flow configuration in the diffuser. The effectiveness of this control is finally assessed by direct numerical simulation. It is shown that the introduction of the cylinder, placed following the indications of the linear sensitivity analysis in the stable Asymmetric Flow configuration, allows a steady completely symmetric or less Asymmetric Flow to be recovered. The Flow transient between the uncontrolled Asymmetric solution and the symmetric controlled one is analyzed in terms of streamlines and vorticity evolution; the effects of the cylinder introduction on Flow dissipation are also assessed.
