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See detailA kinetic model of the formation of the hot oxygen geocorona. 1: Quiet geomagnetic conditions
Shematovich, V. I.; Bisikalo, D. V.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1994), 99

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by ... [more ▼]

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by chemical processes usually considered as a source of hot oxygen (photodissociation of O2 and dissociative recombination of O2(+) and NO(+) ions). The evolution of the system is described stochastically as a series of random Markovian processes. The energy distribution function of the thermal and non-thermal O(3P) atoms and of the nonthermal O(1D) atoms is calculated from the thermospheric collision-dominated region to the exosphere where the gas flow is virtually collisionless. The model is applied to equatorial latitudes for conditions of low solar and geomagnetic activity. Numerical simulations show that the distribution function of thermal oxygen is increasingly perturbed by collisions with the hot oxygen population at high altitudes and departs significantly from a Maxwellian distribution at all altitudues. The number density and temperature of the nonthermal oxygen atoms are derived from their microscopic distribution function and found tobe in qualitative agreement with previous theoretical and experimental estimates. [less ▲]

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See detailA kinetic model of the formation of the hot oxygen geocorona. 2: Influence of O(+) ion precipitation
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg

in Journal of Geophysical Research (1995), 100

A model for the oxygen geocorona near the exobase solving the nonlinear Boltzmann equation with a Monte Carlo method is used to calculate the distribution of the hot oxygen atoms during geomagnetically ... [more ▼]

A model for the oxygen geocorona near the exobase solving the nonlinear Boltzmann equation with a Monte Carlo method is used to calculate the distribution of the hot oxygen atoms during geomagnetically disturbed nighttime conditions. The precipitation of energetic O(+) ions and the subsequent enhancement of the hot O corona at high latitudes is simulated for the September 17, 1971, storm conditions. It is found that in such circumstances, the O(+) precipitation is a significant source of superthermal O atoms leading to important perturbations of the velocity distribution of the bulk oxygen population. The effective gas temperature near the exobase is similar to that in the undisturbed atmosphere, but the hot O density rises considerably over the quiet condition values. [less ▲]

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See detailKinetic of the hydrolysis of pectin galacturonic acid chains and quantification by ionic chromatography
Garna, H.; Mabon, N.; Nott, Katherine ULg et al

in Food Chemistry (2006), 96(3), 477-484

These experiments were designed to develop a rapid, repeatable and accurate analysis method for the quantification of galacturonic acid of pectins. Different pectin hydrolysis procedures (chemical and ... [more ▼]

These experiments were designed to develop a rapid, repeatable and accurate analysis method for the quantification of galacturonic acid of pectins. Different pectin hydrolysis procedures (chemical and enzymatic) were carried out with H2SO4, TFA and HCl at different acid concentrations (0.2, 1 and 2 M) and temperatures (80 and 100 degrees C). Enzymatic and combined chemical and enzymatic hydrolysis of pectin were also studied. A acid hydrolysis under drastic conditions (100 degrees C) is insufficient for complete hydrolysis and results in low recovery of galacturonic acid residues. Mild chemical hydrolysis (0.2, 1 and 2 M H2SO4 72 h at 80 degrees C) is also insufficient for complete depolymerization. Its main advantage is cleavage of the galacturonic acid chains into oligomeric forms without any degradation within 72 h of hydrolysis. However, enzymatic hydrolysis with VL9 for 2 h at 50 degrees C and combined chemical and enzymatic hydrolysis (0.2 M TFA at 80 degrees C for 72 h and VL9) give high recovery of this acid. Analysis of the liberated sugar residue by HPAEC allows us to determine the galacturonic acid composition of this polysaccharide accurately with high selectivity and sensitivity in one assay without the need for derivatization. (c) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailKinetic properties of the alpha(2) homo-oligomeric glycine receptor impairs a proper synaptic functioning
Mangin, J. A.; Baloul, M.; de Carvalho, L. P. et al

in Journal of Physiology-London (2003), 553(2), 369-386

Ionotropic glycine receptors (GlyRs) are present in the central nervous system well before the establishment of synaptic contacts. Immature nerve cells are known, at least in the spinal cord, to express ... [more ▼]

Ionotropic glycine receptors (GlyRs) are present in the central nervous system well before the establishment of synaptic contacts. Immature nerve cells are known, at least in the spinal cord, to express alpha(2) homomeric GlyRs, the properties of which are relatively unknown compared to those of the adult synaptic form of the GlyR (mainly alpha(1)/beta heteromeres). Here, the kinetics properties of GlyRs at the single-channel level have been recorded in real-time by means of the patch-clamp technique in the outside-out configuration coupled with an ultra-fast flow application system (< 100 µs). Recordings were performed on chinese hamster ovary (CHO) cells stably transfected with the a, GlyR subunit. We show that the onset, the relaxation and the desensitisation of α(2) homomeric GlyR-mediated currents are slower by one or two orders of magnitude compared to synaptic mature GlyRs and to other ligand-gated ionotropic channels involved in fast synaptic transmission. First latency analysis performed on single GlyR channels revealed that their slow activation time course was due to delayed openings. When synaptic release of glycine was mimicked (1 mM glycine; 1 ms pulse duration), the opening probability of α(2) homomeric GlyRs was low (P-o ≈ 0.1) when compared to mature synaptic GlyRs (P-o = 0.9). This low P-o is likely to be a direct consequence of the relatively slow activation kinetics of α(2) homomeric GlyRs when compared to the activation kinetics of mature α(1)/β GlyRs. Such slow kinetics suggest that embryonic α(2) homomeric GlyRs cannot be activated by fast neurotransmitter release at mature synapses but rather could be suited for a non-synaptic paracrine-like release of agonist, which is known to occur in the embryo. [less ▲]

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See detailKinetic properties of the Bacillus licheniformis Penicillin-binding proteins
Lepage, Sophie; Galleni, Moreno ULg; Lakaye, Bernard ULg et al

in Biochemical Journal (1995), 309

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See detailThe kinetic properties of the carboxy terminal domain of the Bacillus licheniformis 749/I BlaR penicillin-receptor shed a new light on the derepression of beta-lactamase synthesis
Duval, Valérie; Swinnen, Marc; Lepage, Sophie et al

in Molecular Microbiology (2003), 48(6), 1553-1564

To study the properties of the BlaR penicillin-receptor involved in the induction of the Bacillus licheniformis beta-lactamase, the water-soluble carboxy terminal domain of the protein (BlaR-CTD) was ... [more ▼]

To study the properties of the BlaR penicillin-receptor involved in the induction of the Bacillus licheniformis beta-lactamase, the water-soluble carboxy terminal domain of the protein (BlaR-CTD) was overproduced in the periplasm of Escherichia coli JM105 and purified to protein homogeneity. Its interactions with various beta-lactam antibiotics were studied. The second-order acylation rate constants k(2)/K' ranged from 0.0017 to more than 1 muM(-1) s(-1) and the deacylation rate constants were lower than 4x10(-5) s(-1) . These values imply a rapid to very rapid formation of a stable acylated adduct. BlaR-CTD is thus one of the most sensitive penicillin-binding proteins presently described. In the light of these results, the kinetics of beta-lactamase induction in Bacillus licheniformis were re-examined. When starting with a rather high cell density, a good beta-lactamase substrate such as benzylpenicillin is too sensitive to beta-lactamase-mediated hydrolysis to allow full induction. By contrast, a poor beta-lactamase substrate (7-aminocephalosporanic acid) can fully derepress beta-lactamase expression under conditions where interference of the antibiotic with cell growth is observed. These results suggest that acylation of the penicillin receptor is a necessary, but not sufficient, condition for full induction. [less ▲]

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See detailKinetic study of 1,2-dichloroethane hydrodechlorination with a Pd-Ag/SiO2 sol-gel catalyst
Heinrichs, Benoît ULg; Delhez, P.; Schoebrechts, Jean-Paul et al

in 1st European Congress on Chemical Engineering, ECCE1 (Vol. 4, pp. 2919-2922) (1997, May 04)

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See detailKinetic study of 4-nitrophenol photocatalytic degradation over a Zn2+ doped TiO2 catalyst prepared through an environmentally friendly aqueous sol–gel process
Malengreaux, Charline ULg; Pirard, Sophie ULg; Bartlett, John et al

in Chemical Engineering Journal (2014), 245

A kinetic study of the photocatalytic degradation of 4-nitrophenol (4-NP) under UV–visible light (330 nm < k < 800 nm) has been performed via a rigorous chemical engineering approach over a Zn2+ doped ... [more ▼]

A kinetic study of the photocatalytic degradation of 4-nitrophenol (4-NP) under UV–visible light (330 nm < k < 800 nm) has been performed via a rigorous chemical engineering approach over a Zn2+ doped TiO2 catalyst prepared through an environmentally friendly aqueous sol–gel process. The experiments have been performed at three temperatures to enable the global activation energy to be estimated. The influence of the illumination intensity has also been considered. The possibility of internal and external diffusion limitations has been studied and the results obtained demonstrated that there is no diffusional limitation during the photocatalytic degradation of the 4-NP using the selected catalyst. Therefore, the apparent specific reaction rate measured corresponds to the actual reaction rate of the chemical reaction. Parameter adjustments show that the kinetic model that provides the best fit to the experimental data corresponds to a first order reaction. A sequence of elementary steps has been considered and a pseudo-steady state approach based upon the stationary state hypothesis for reaction intermediates has been applied to obtain a kinetic rate expression in agreement with the experimental data. The mean values of the reaction rate constant found at 283 K, 288 K and 293 K are respectively equal to k1 = 0.094 ± 0.003 m3 h- 1 kgcatalyst- 1; k2 = 0.119 ± 0.004 m3 h- 1 kgcatalyst- 1 and k3 = 0.150 ± 0.023 m3 h- 1 kg catalyst-1 and the global activation energy of the degradation reaction was evaluated as 40 kJ mol-1. A phenomenological kinetic mechanism is proposed to describe the reaction at a molecular scale. Finally, statistical validations and residuals analysis have been performed to confirm that the first order model is suitable to represent the 4-NP photocatalytic degradation over time. Such studies are essential to design a reactor for water pollutant degradation on an industrial scale. [less ▲]

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See detailKinetic Study of Interaction between Brl 42715, Beta-Lactamases, and D-Alanyl-D-Alanine Peptidases
Matagne, André ULg; Ledent, Philippe; Monnaie, Didier et al

in Antimicrobial Agents and Chemotherapy (1995), 39(1), 227-31

A detailed kinetic study of the interactions between BRL 42715, a beta-lactamase-inhibiting penem, and various beta-lactamases (EC 3.5.2.6) and D-alanyl-D-alanine peptidases (DD-peptidases, EC 3.4.16.4 ... [more ▼]

A detailed kinetic study of the interactions between BRL 42715, a beta-lactamase-inhibiting penem, and various beta-lactamases (EC 3.5.2.6) and D-alanyl-D-alanine peptidases (DD-peptidases, EC 3.4.16.4) is presented. The compound was a very efficient inactivator of all active-site serine beta-lactamases but was hydrolyzed by the class B, Zn(2+)-containing enzymes, with very different kcat values. Inactivation of the Streptomyces sp. strain R61 extracellular DD-peptidase was not observed, and the Actinomadura sp. strain R39 DD-peptidase exhibited a low level of sensitivity to the compound. [less ▲]

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See detailKinetic study of Lactococcus lactis strains (SLT6 and SLT10) growth on papain-hydrolysed whey
Ziadi, Manel; Rezouga, Feriel; Bouallagui, Hassib et al

in World Journal of Microbiology & Biotechnology (2010), 26(12), 2223-2230

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See detailA kinetic study of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition using a Fe-Co/Al2O3 catalyst
Pirard, Sophie ULg; Douven, Sigrid ULg; Bossuot, Christophe et al

in Carbon (2007), 45(6), 1167-1175

A kinetic study was performed to describe the initial specific rate of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition (CCVD) on a bimetallic cobalt-iron catalyst at high ... [more ▼]

A kinetic study was performed to describe the initial specific rate of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition (CCVD) on a bimetallic cobalt-iron catalyst at high temperature using ethylene decomposition to solid carbon and gaseous hydrogen. The study uses a mass spectrometer that allows reaction rate to be inferred from the exhaust gas composition measurements. The aim is to obtain a better understanding of the elementary steps involved in the production of carbon nanotubes so as to derive phenomenological kinetic models in agreement with experimental data. The best models assume the elimination of the first hydrogen atom from adsorbed ethylene as rate determining step and involve a hydrogen adsorption weak enough to be neglected. It was proved that hydrogen partial pressure has no influence on initial reaction rate of carbon nanotube synthesis with the catalyst used for this study. Activation energy and ethylene adsorption enthalpy were found to be equal to around 130 and - 130 kJ mol(-1), respectively. (C) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailKinetic study of p-nitrophenol photodegradation with modified TiO2 xerogels
Tasseroul, Ludivine ULg; Pirard, Sophie ULg; Lambert, Stéphanie ULg et al

in Chemical Engineering Journal (2012), 191

TiO2 xerogels were sensitized in one step by the in situ introduction of nickel (II) tetra(4-carboxyphenyl)porphyrin (TCPPNi) into the TiO2 matrix during sol–gel synthesis. Crystalline photoactive phase ... [more ▼]

TiO2 xerogels were sensitized in one step by the in situ introduction of nickel (II) tetra(4-carboxyphenyl)porphyrin (TCPPNi) into the TiO2 matrix during sol–gel synthesis. Crystalline photoactive phase TiO2-anatase was obtained without high thermal treatments and was determined by X-ray diffraction. The presence of TCPPNi in TiO2 xerogels was established by DR-UV/Vis and FT-IR spectroscopy. The introduction of porphyrin led to a diminution of the specific surface area of TiO2 xerogels, and this diminution was analyzed by nitrogen adsorption–desorption. The particle size was estimated by SEM. The xerogel surface charge state, which influences the interactions between pollutant and TiO2, was determined by measurement of the point of zero charge. The photoactivity of xerogels was evaluated for p-nitrophenol degradation in aqueous medium at 20 ◦C. Results showed that porphyrin doped TiO2 degraded more than 40% of the p-nitrophenol whereas non doped TiO2 xerogel degraded only 10% of the compound. Moreover, porphyrin was found to improve the photoactivity of TiO2 xerogels in a similar way to UV-A pretreatment. A kinetic study of p-nitrophenol degradation was then performed. Results showed that one type of active site corresponding to the hole of electron–hole pairs was created at the TiO2 surface by light and that the rate determining step was the reaction between the adsorbed p-nitrophenol molecule and the adsorbed OH• radical. The apparent activation energy was found to be equal to 12 kJ mol−1. [less ▲]

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See detailKinetic study of the acid hydrolysis of various oligofructose samples
Blecker, Christophe ULg; Fougnies, C.; Van Herck, J. C. et al

in Journal of Agricultural and Food Chemistry (2002), 50(6), 1602-1607

The kinetic of acid hydrolysis of five commercially available oligofructose samples used as food ingredients has been investigated as a function of the dry matter concentration, reaction pH, and ... [more ▼]

The kinetic of acid hydrolysis of five commercially available oligofructose samples used as food ingredients has been investigated as a function of the dry matter concentration, reaction pH, and temperature. The initial fructose release rate is found to be roughly proportional to the inverse of the average polymerization degree in number. A pseudo first order kinetic is found with respect to the fructosyl chain end concentration and to the proton concentration. Arrhenius plot is found to reasonably fit the data in a relatively wide temperature range (7-130 degreesC). The results allow the estimation of the fructose release rate in many foodstuff processing conditions. [less ▲]

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