Etude expérimentale des mécanismes thermo-aérauliques lors d'un feu dans une charge de bois

International audienceNous proposons une étude expérimentale de la combustion d'une charge de copeaux de bois confinés dans une enceinte ventilée ou non ventilée. Nous avons étudié l'influence des paramètres relatifs au combustible (type de bois) et à l'aération (apport d'oxygène) sur l'évolution de la structure de la flamme et de sa température, de la perte de masse du bois et de la nature des émissions gazeux de sa combustion. Ce travail permet d'améliorer les connaissances disponibles sur les mécanismes thermo-aérauliques accompagnant la combustion du bois et offre un outil de validation aux modèles numériques disponibles

Influence of the source elevation on a pool fire in a forced ventilated enclosure

International audienceIn nuclear facilities, fires can spread until reaching the upper part of a closed and mechanically ventilated compartment. In this area of the room, the fire sources are under-oxygenated, but lie in an environment with significant radiative heat flux. Previous studies dealt with elevated fires, and results showed that source elevation affects two phenomena: the combustion process and the flows inside the room. The present study aims to understand the effects of elevation on the fire dynamic in a special ventilation configuration: fresh air inlet in the lower part of the compartment, and vitiated air exhaust in the upper part. A series of tests was carried out in a reduced-scale apparatus, with a 0.09 m diameter pan filled with dodecane liquid fuel and placed at various heights. Two aspects were analyzed: the mass loss rate (MLR) and the gas temperature inside the room. First of all, the experimental results confirm the coupled and antagonistic effects of decreasing oxygen concentration and increasing temperature on the mass loss rate that were already highlighted in the literature. In addition, these results also show the role played by the flame height on the change in the combustion regime. Finally, the vertical temperature stratification is much more pronounced when the fire is elevated until it reaches a maximum height. Beyond this limit, stratification starts to disappear

Inactivation of β-adrenergic receptors by N-ethylmalmeimide: Permissive role of β-adrenergic agents in relation to adenylate cyclase activation

The β1-adrenergic receptors of turkey erythrocyte membranes have been identified by the specific binding of the radiolabeled antagonist (-)-[3H]dihydroalprenolol. Binding of β-adrenergic agonists to these receptors sites sensitizes them to inactivation by the alkylating agent N-ethylmaleimide. A dose- and time-dependent decrease of 45 to 60% of the sites is commonly observed. Binding of (-)-3H-dihydroalprenolol and β-adrenergic agonists to the remaining sites occurs with the same characteristics as for the untreated receptor population. Kinetic experiments reveal that the rate of inactivation is proportional to the concentration of N-ethylmaleimide (between 5.5 and 450μM). In contrast, the rate of inactivation reaches a plateau value when increasing the concentration of the agonist. The rate of inactivation is half-maximal in presence of 1.3 μM (-)-epinephrine or 20μM (+)-epinephrine. This marked stereospecificity, along with the close identity of the above concentrations with the equilibrium dissociation constant (K(D)) of the epinephrine isomers for binding to the β-receptor (i.e. 2.0 μM for (-)-epinephrine and 21 μM for (+)-epinephrine) indicate that N-ethylmaleimide inactivates the agonist-bound form of the receptor. The second-order rate constant (k2) of the inactivation process, in the presence of 15 β-adrenergic ligands, was found to correlate with their capability to stimulate the adenylate cyclase activity, i.e. 'intrinsic activity'. Since all tested ligands were able to cause a complete and dose-dependent displacement of bound (-)-[3H]dihydroalprenolol, it is likely that both the intrinsic activity and k2 of each adrenergic ligand reflect an inherent property of the ligand-bound receptor. The proportionality between k2 and the intrinsic acid activity further suggests that β-adrenergic agonists 'induce' or 'favor' a conformational change of the receptor, resulting in adenylate cyclase activation and the uncovering of an alkylable group which becomes exposed to N-ethylmaleimide in the active conformation.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Isoproterenol and selective agonists stimulate similar atypical β-adrenoceptors in rat adipocytes

We have demonstrated previously that (-)isoproterenol triggers lipolysis in rat epididymal fat cells by stimulating both classical (β1, β2) and atypical β-adrenoceptors. The contribution of the classical β-adrenoceptors can be blocked by addition of 3 nM CGP12177{di-4-3[(1,1-dimethylethyl)amino]-(2-hydroxylpropoxy)1,3-dihy dro-2H-benzimidazol-2-one hydrochloride}. At higher concentrations, CGP12177 triggers lipolysis also, but by stimulating atypical β-adrenoceptors only. To find out whether (-)isoproterenol and CGP12177 stimulate similar atypical β-adrenoceptors, we compared their interaction with recognised β3-adrenoceptor antagonists: CGP20712 {1-[2-((3-carbamoyl-4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4-tr ifluoromethyl-2-imidazolyl)phenoxy]propan-2-ol} (βl-selective), ICI118551 [erythro-1-(7-methylindan-4-yloxy)-3-(isopropylamine)-butan-2-ol] (β2-selective) and the stereoisomers as well as the racemic mixture of propanolol (non-β1/β2-subtype selective) and of metoprolol (β1-selective). There was a highly significant relationship (r = 0.93) between the potencies of these antagonists for inhibiting the lipolytic response to (-)isoproterenol (in the absence of classical β-adrenoceptor stimulation) and CGP12177. In both cases, propranolol and metoprolol showed also the same degree of stereoselectivity. These findings suggest that (-)isoproterenol and CGP12177 stimulate the same type and/or form of atypical β-adrenoceptors in rat epididymal adipocytes.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Multiple beta adrenergic receptor subclasses mediate the l-isoproterenol- induced lipolytic response in rat adipocytes

l-Isoproterenol has been proposed to stimulate lipolysis in rat epididymal adipocytes via atypical beta adrenergic receptors, whereas radioligand binding studies only revealed the presence of beta1 adrenergic receptors on adipocyte membranes. We have made use of the unique properties of CGP12177 to evidence that both the beta1 and the atypical beta adrenergic receptor subtypes are mediating the lipolytic response of rat epididymal adipocytes to l-isoproterenol. CGP12177, an antagonist with high affinity for beta1 receptors, triggers lipolysis by specifically stimulating the atypical receptors. For this response, CGP12177 displays low potency (EC50 = 68 nM), but high intrinsic activity (94% relative to l-isoproterenol). At low concentrations (3 nM), CGP12177 inhibits the lipolytic response to 10 nM l- isoproterenol by 43%, indicating that at least this fraction of the response is beta1 receptor-mediated. The response to BRL37344, which is a selective agonist for the atypical receptors, is not inhibited by CGP12177. The pA2 values of the beta adrenergic antagonists propranolol, metoprolol and atenolol were calculated from the rightward shifts that they impose on dose- response curves of both I-isoproterenol and CGP12177. With I-isoproterenol, these values (6.54, 5.83 and 5.07, respectively) are lower than those expected for beta1 and beta2 receptors, indicating that atypical receptors are also involved in the lipolytic response to this agonist. With CGP12177, the pA2 values of propranolol, metoprolol and atenolol are even lower (5.80, 5.03 and 4.06, respectively), and are likely to be a more accurate reflection of their affinities for the atypical receptors.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Distinct In Vitro Binding Profile of the Somatostatin Receptor Subtype 2 Antagonist [177Lu]Lu-OPS201 Compared to the Agonist [177Lu]Lu-DOTA-TATE

Treatment of neuroendocrine tumours with the radiolabelled somatostatin receptor subtype 2 (SST2) peptide agonist [177Lu]Lu-DOTA-TATE is effective and well-established. Recent studies suggest improved therapeutic efficacy using the SST2 peptide antagonist [177Lu]Lu-OPS201. However, little is known about the cellular mechanisms that lead to the observed differences. In the present in vitro study, we compared kinetic binding, saturation binding, competition binding, cellular uptake and release of [177Lu]Lu-OPS201 versus [177Lu]Lu-DOTA-TATE using HEK cells stably transfected with the human SST2. While [177Lu]Lu-OPS201 and [177Lu]Lu-DOTA-TATE exhibited comparable affinity (KD, 0.15 ± 0.003 and 0.08 ± 0.02 nM, respectively), [177Lu]Lu-OPS201 recognized four times more binding sites than [177Lu]Lu-DOTA-TATE. Competition assays demonstrated that a high concentration of the agonist displaced only 30% of [177Lu]Lu-OPS201 bound to HEK-SST2 cell membranes; an indication that the antagonist binds to additional sites that are not recognized by the agonist. [177Lu]Lu-OPS201 showed faster association and slower dissociation than [177Lu]Lu-DOTA-TATE. Whereas most of [177Lu]Lu-OPS201 remained at the cell surface, [177Lu]Lu-DOTA-TATE was almost completely internalised inside the cell. The present data identified distinct differences between [177Lu]Lu-OPS201 and [177Lu]Lu-DOTA-TATE regarding the recognition of receptor binding sites (higher for [177Lu]Lu-OPS201) and their kinetics (faster association and slower dissociation of [177Lu]Lu-OPS201) that explain, to a great extent, the improved therapeutic efficacy of [177Lu]Lu-OPS201 compared to [177Lu]Lu-DOTA-TATE

Influence of the source elevation on a pool fire in a forced ventilated enclosure

International audienceIn nuclear facilities, fires can spread until reaching the upper part of a closed and mechanically ventilated compartment. In this area of the room, the fire sources are under-oxygenated, but lie in an environment with significant radiative heat flux. Previous studies dealt with elevated fires, and results showed that source elevation affects two phenomena: the combustion process and the flows inside the room. The present study aims to understand the effects of elevation on the fire dynamic in a special ventilation configuration: fresh air inlet in the lower part of the compartment, and vitiated air exhaust in the upper part. A series of tests was carried out in a reduced-scale apparatus, with a 0.09 m diameter pan filled with dodecane liquid fuel and placed at various heights. Two aspects were analyzed: the mass loss rate (MLR) and the gas temperature inside the room. First of all, the experimental results confirm the coupled and antagonistic effects of decreasing oxygen concentration and increasing temperature on the mass loss rate that were already highlighted in the literature. In addition, these results also show the role played by the flame height on the change in the combustion regime. Finally, the vertical temperature stratification is much more pronounced when the fire is elevated until it reaches a maximum height. Beyond this limit, stratification starts to disappear

Burning rate of elevated pool fire in a well-ventilated compartment: Effects of radiative heat fluxes

International audienceElevated pool fires are potentially exposed to the feedback of radiative heat fluxes from the ceiling that can modify the mass loss rate. In this regard, an experimental study was carried-out in a reduced-scale enclosure with a pool fire brought increasingly closer to the ceiling of the compartment. The objective is to study the effect on the mass loss rate of the increase in radiative heat fluxes without any air vitiation effect. The device is equipped with a mechanical ventilation system to allow the flame to develop in a well-oxygenated environment. The fire sources used are circular pans with diameters between 0.09 and 0.175 m, filled with dodecane. Results show that, as long as the flame does not impinge on the ceiling, the mass loss rate remains quasi-constant. On the other hand, when the flame impinges on the ceiling, the mass loss rate increases drastically and can be multiplied by a factor 2–3 compared to the reference value when the pool fire is located on the ground. Scaling parameters, showing the generic aspect of the results, are finally proposed considering a dimensionless elevation h*. It allows to gather all experimental data on the same curve for all the fire sources tested