Search results for "fluid"
showing 10 items of 5513 documents
Numerical study of blow-up and stability of line solitons for the Novikov-Veselov equation
2017
International audience; We study numerically the evolution of perturbed Korteweg-de Vries solitons and of well localized initial data by the Novikov-Veselov (NV) equation at different levels of the 'energy' parameter E. We show that as |E| -> infinity, NV behaves, as expected, similarly to its formal limit, the Kadomtsev-Petviashvili equation. However at intermediate regimes, i.e. when |E| is not very large, more varied scenarios are possible, in particular, blow-ups are observed. The mechanism of the blow-up is studied.
Primary and secondary distributions after a small-amplitude potential step at disk electrode coated with conducting film
2011
Abstract The set of equations and boundary conditions for the “primary potential/current distribution” after a small-amplitude potential step has been analyzed for a film-coated disk electrode in contact with an electrolyte. The solution of these equations provides the overall short-time resistance of this system, Rtot, which is determined by the short-time resistance of the electrolyte solution in contact with the bare disk electrode, Rs, and the short-time film resistance to the current passage in the normal direction, R f = L f / κ f π r o 2 (ro, disk radius; Lf, film thickness; κf, its specific conductivity). The deviation of Rtot from the sum of these resistances, Rs + Rf, originates f…
Critical micellisation density: a SAS structural study of the unimer–aggregate transition of block-copolymers in supercritical CO2
2000
In this paper we report a SANS investigation of micelle formation by fluorocarbon-hydrocarbon block copolymers in supercritical CO2 (scCO2) at 313K. A sharp unimer-micelle transition is obtained due to the tuning of the solvating ability of scCO2 by profiling pressure. At high pressure the copolymer is in a monomeric state with a random coil structure. By lowering the pressure aggregates are formed with the hydrocarbon segments forming the core and the fluorocarbon segments forming the corona of spherical aggregates. This aggregateunimer transition is driven by the gradual penetration of CO2 molecules toward the core of the aggregate and is critically related to the density of the solvent, …
Isolation of human milk whey proteins by solid phase extraction with a polymeric material modified with gold nanoparticles
2017
Abstract This work describes a method for the isolation of human milk whey proteins by solid-phase extraction (SPE) with a polymeric material modified with gold nanoparticles. Human serum albumin, α-lactalbumin, lactoferrin and lysozyme were selected as target proteins to establish the performance of SPE support. Several experimental variables (pH and ionic strength) that affect the SPE protocol were investigated to achieve the maximum extraction efficiency. Under optimal conditions, the SPE sorbent gave excellent recoveries, and offered a high permeability and reusability (> 20 times). The feasibility of this methodology was successfully demonstrated by isolating the target proteins in a m…
Sample preparation strategies for the determination of psychoactive substances in biological fluids
2020
This review focuses on the existing analytical procedures for the determination of new psychoactive substances (NPS) in biological fluids by chromatographic methods. Direct analysis of samples is scarcely employed and most proposed methodologies include a sample pre-treatment in order to remove matrix interferents and, in some cases, pre-concentrate extracts. Current extraction methods for NPS determination in plasma/serum, urine, and oral fluids have been widely discussed, such as liquid-liquid, solid-phase, and micro extraction approaches, highlighting the advantages and drawbacks of the proposed extraction methodologies. Regarding microextraction approaches, techniques like microextracti…
Polymer-Functionalised Nanograins of Mg-Doped Amorphous Calcium Carbonate via a Flow-Chemistry Approach
2019
Calcareous biominerals typically feature a hybrid nanogranular structure consisting of calcium carbonate nanograins coated with organic matrices. This nanogranular organisation has a beneficial effect on the functionality of these bioceramics. In this feasibility study, we successfully employed a flow-chemistry approach to precipitate Mg-doped amorphous calcium carbonate particles functionalized by negatively charged polyelectrolytes&mdash
Carbon Nanomaterial Doped Ionic Liquid Gels for the Removal of Pharmaceutically Active Compounds from Water.
2019
Due to large drug consumption, pharmaceutically active compounds (PhACs) can be found as water contaminants. The removal of PhACs is a significant issue, as they can easily overtake traditional purification methods. Because of their surface properties, carbon nanomaterials are among the most efficient materials able to adsorb PhACs. However, their limitation is their recovery after use and their possible leakage into the aquatic system. Consequently, new hybrid supramolecular ionic liquid gels (HILGs) have been designed for the adsorption of some antibiotic drugs (ciprofloxacin and nalidixic acid) from water. The chemical&ndash
Immobilised Humic Substances as Low-Cost Sorbents for Emerging Contaminants
2021
Environmental pollution with contaminants of emerging concern (CECs) is a worldwide problem that is receiving increasing attention. Although these substances have been released in the aquatic environment for a long time, wastewater treatment plants are still incapable of removing emerging contaminants completely. Consequently, trace metals, metalloids and pharmaceuticals, as well as surfactant leftovers, are often found in environmental samples. Environmentally friendly and cost-effective sorbents such as humic substances can be used for purification if their sorption properties are increased by immobilization. To our knowledge, immobilized humic substances have not been widely studied as s…
Bill2d - a software package for classical two-dimensional Hamiltonian systems
2015
Abstract We present Bill2d , a modern and efficient C++ package for classical simulations of two-dimensional Hamiltonian systems. Bill2d can be used for various billiard and diffusion problems with one or more charged particles with interactions, different external potentials, an external magnetic field, periodic and open boundaries, etc. The software package can also calculate many key quantities in complex systems such as Poincare sections, survival probabilities, and diffusion coefficients. While aiming at a large class of applicable systems, the code also strives for ease-of-use, efficiency, and modularity for the implementation of additional features. The package comes along with a use…
Changes in fluid geochemistry and physico-chemical conditions of geothermal systems caused by magmatic input: The recent abrupt outgassing off the is…
2005
Abstract Hydrothermal systems and related vents can exhibit dramatic changes in their physico-chemical conditions over time as a response to varying activity in the feeding magmatic systems. Massive steam condensation and gas scrubbing processes of thermal fluids during their ascent and cooling cause further compositional changes that mask information regarding the conditions evolving at depth in the hydrothermal system. Here we propose a new stability diagram based on the CO2-CH4-CO-H2 concentrations in vapor, which aims at calculating the temperatures and pressures in hydrothermal reservoirs. To filter gas scrubbing effects, we have also developed a model for selective dissolution of CO2-…