1,721,096 research outputs found
A PUMA-G receptor élettani és kórélettani szerepe az agyi vérkeringésben. = Role of the PUMA-G receptor in the cerebral circulation.
No full textEredményeink szerint a PUMA-G receptor nem játszik szignifikáns szerepet az agykérgi véráramlás szabályozásában sem élettani sem pedig kórélettani körülmények között. Igazoltuk az epidermális Langerhans-sejtek szerepét a nikotinsav-okozta flush- reakció a közvetíttésében, mely adatok egyúttal arra utalnak, hogy a Langerhans-sejteknek élettani/kórélettani szerepe lehet a bőr véráramlásának szabályozásában. Eredményeink szerint a nikotinsav a PUMA-G receptor által közvetített mechanizmussal csökkenti a sebocyták zsírtartalmát egérben, ami felveti a PUMA-G receptor agonisták alkalmazásának lehetőségét az acne és seborrhea kezelésére. Leírtuk, hogy hypoxia és hypercapnia során az endocannabinoid felszabadulás agykérgi véráramlás-csökkenést okoz, aminek hátterében az excitatorikus glutamáterg neurotranszmisszió preszinaptikus gátlását feltételezzük. Igazoltuk, hogy az endogén CO képződés egyrészt tónusosan gátolja a hypothalamikus nitrogén monoxid szintetáz (NOS) aktivitást, másrészt pedig stimulálja a PGE2?felszabadulást és e két úton keresztül indirekt módon képes befolyásolni a hypothalamus véráramlását. Más agyi régiókban, pl. a parietális agykéregben az endogén CO NOS-t gátló hatása dominál és így véráramlás-csökkenést okoz. Megállapítottuk, hogy a neutrális szfingomielináz reaktív oxigén szabadgyökök által közvetített, de NOX2-től független módon csökkenti az a. carotis kontrakciós válaszait. | Our results indicate that the PUMA-G receptor has no significant role in the regulation of the cerebrocortical blood flow under physiological or pathophysiological conditions. We proved that epidermal Langerhans-cells mediate the nicotinic acid induced flush reaction indicating that these cells may play important roles in the regulation of the dermal blood flow. Nicotinic acid inhibits lipogenesis in sebocytes which effect is mediated by the PUMA-G receptor. Therefore, PUMA-G agonists may be beneficial in the treatment of seborrhea and acne. We described that endogenous CO suppresses hypothalamic NOS activity but stimulates PGE2-release at the same time. Both of these effects indirectly influence the hypothalamic circulation. In the parietal cortex CO reduces blood flow via inhibition of NO synthesis. In preliminary experiments we found that neutral sphingomyelinase suppresses the contractile responses of the carotid artery via NOX2-independent generation of reactive oxygen species
Nanostructred catalysts for photo-oxidation of endocrine disrupting chemicals
No full textRemoval of four Endocrine disrupting chemicals (EDCs) Estrone (E1), 17-β-estradiol (E2), Estriol (E3) and 17-α-ethynylestradiol (EE2) were investigated using UV oxidation and combined with Nafion/iron catalyst. Immobilization of iron on the perfluorosulfonic polymer, Nafion® has been investigated as a carrier for the oxidation of pollutants by hydroxyl radicals (heterogenous photo-Fenton mechanism). However, the low surface area of Nafion, less than 0.2 m2/g, usually results in low pollutant degradation rates. Sol-gel technology was used to produce a high surface area poly(dimethylsiloxane) (PDMS) modified Nafion/silica composite suitable for catalysis of the photo-Fenton reaction without significant leaching of iron. The incorporation of Nafion into silica greatly increases the accessibility of Nafion/iron loaded active site. PDMS reinforces the structure of silica and maintains the transparency of the composite, which is essential for efficient Photo-Fenton reactions. These composites were utilized for the decomposition of estrogens which are Estrone (E1), 17-β-estradiol (E2), Estriol (E3) and 17-α-ethynylestradiol (EE2). In consequence, it is clear that the composite effectively catalyses the photo-Fenton reaction to remove estrone. The presence of iron through the use of the catalyst leads to rapid degradation of the estrone compared to just H2O2 and UV light alone. It was found that the addition of only 8.5 mg/L H2O2 produced more than conversion of estrogens within 60 min
Dimensionless Analysis Of Slurry Photocatalytic Reactors Using Two-Flux And Six-Flux Radiation Absorption-Scattering Models
No full textPhotocatalytic oxidation (PCO) over titanium dioxide (TiO2) is a "green" sustainable process for the treatment and purification of water and wastewater. However,the application of PCO for wastewater treatment on an industrial scale is currently hindered by a lack of simple mathematical models that can be readily applied to reactor design. Current models are either too simplistic or too rigorous to be useful in photocatalytic reactor design, scale-up, and optimization. In this paper a simple mathematical model is presented for slurry, annular, photocatalytic reactors that still retains the essential elements of a rigorous approach while providing simple solutions. The model extends the applicability of the thin-film model of photocatalytic reactors previously presented to include the case of geometrically thick photoreactors (i.e., those reactors in which the thickness of the annular zone is significant as compared to the outer radius of the reactor). The model uses a novel six-flux absorption-scattering model to represent the radiation field in the reaction space, which assumes that scattered photons follow the route of the six directions of the Cartesian coordinates. The model was successfully validated with experimental results from the photocatalytic oxidation of the pesticide isoproturon in an experimental reactor. The mathematical model presented may be used as a tool for the design, scale-up, and optimization of annular photocatalytic reactors for water treatment and purification
Physiological response of electroactive bacteria via secretion of extracellular polymeric substances in microbial electrochemical processes: A review
Full text linkMicrobial electrochemical processes involving microbial catalyzed electrochemical reactions are directly/indirectly related to the electroactive bacteria (EAB) physiological secretion of extracellular polymeric substances (EPS) with favorable biofilm dispersion. EPS harbor cytochrome-like substances, and thus accelerate extracellular electron transfer (EET) processes resulting in the simultaneous removal of environmental contaminants or in the conversion of dissolved CO2 to key-block chemicals. This review holistically documents case-studies in the last five years focusing on EAB and their physiological release of EPS in response to external stimuli. The important role played by EPS in the performance of microbial electrochemical systems and the relationship of the EPS compositional diversity with the process parameters is reviewed. Targeting the physiological response of electroactive bacteria towards the release of EPS with precise compositional diversity provides tremendous opportunities for optimizing microbial electrochemical processes. This review provides kernels, quantitative approaches and promising advanced techniques guiding further research directions in this exciting field
Six-flux absorption-scattering models for photocatalysis under wide-spectrum irradiation sources in annular and flat reactors using catalysts with different optical properties
No full textThe photocatalytic oxidation of 2-hydroxybenzoic acid (2-HBA) in an annular tubular reactor (R1) and a flat rectangular open channel reactor (R2), which were irradiated with light sources emitting in the UVB, UVA and visible range of the solar radiation spectrum, and using two photocatalysts, titanium dioxide (TiO2 P25) and Ag-modified TiO2 P25 (Ag@TiO2) was modeled. The local volumetric rate of photon absorption (LVRPA) in the reactors was evaluated by the six-flux absorption scattering model (SFM). The Langmuir-Hinshelwood kinetic model of the degradation of a model contaminant on irradiated aqueous suspensions of TiO2 P25 and Ag@TiO2 was combined with the SFM radiation model and light emission models to determine local reaction rates, and further integrated with the reactors hydrodynamics and material balances to model the degradation of 2-HBA in the photoreactors. The linear source spherical emission (LSSE) and extensive source superficial diffuse emission (ESSDE) models were compared in terms of incident and transmitted photon fluxes through the reactor. It was shown that both LSSE and ESSDE models could be successfully applied for the modeling of annular and flat reactors, considering the emission from tubular fluorescent light sources. Since current research calls for materials with wide absorption in the solar radiation spectrum, spanning from the UV to the visible, therefore, the SFM model was adapted to consider such wide distribution. The optical properties of the photocatalysts were averaged over narrow wavelength ranges of the solar spectrum, wherein the contributions by the UVA, UVB and visible light irradiation to the LVRPA and contaminant degradation rate were separated. The effects of catalyst concentration, liquid velocity profile and the photon flux from different light sources on the 2-HBA degradation rate were explored. The “intrinsic” reaction kinetic constants of 2-HBA photocatalytic oxidation independent of reactor type, catalyst concentration, irradiance levels and hydrodynamic conditions were determined by fitting the experimental data to the model results. It was shown that the model parameters were independent of the type of catalyst used, although the catalyst exhibited significantly different optical properties
Photocatalytic mineralization and degradation kinetics of sulphamethoxazole and reactive red 194 over silver-zirconium co-doped titanium dioxide: Reaction mechanisms and phytotoxicity assessment
Full text linkThe photodegradation and phytotoxicity of the pharmaceutical antibiotic, sulphamethoxazole (SMX) and the azo-dye reactive-red-194 (RR194) under visible-light irradiation of TiO2 nanoparticles modified by silver and zirconium was investigated. The results indicated that sulphamethoxazole and its toxic degradation by product, 3-amino-5-methylisoxazole and RR-194 could be degraded efficiently by the co-doped Zr/Ag-TiO2 catalyst. PL studies and ROS generation results suggested that the effective charge separation was carried out while irradiation of the modified TiO2 nanoparticles. Phytotoxicity tests demonstrated lower percentage of germination in P. vulgaris (40%), V. radiata (30%) and P. lunatus (30%) of the seeds treated with 50 ppm of SMX, compared to the seeds treated with the degradation products (100%). The results with 50 ppm of RR-194 also showed lower percentage of germination in P. vulgaris (40%), V. radiata (50%) and P. lunatus (30%) compared to the degradation products (100%). Furthermore, significant increase in root and shoot development was observed in the seeds treated with the degraded products when compared with SMX and RR-194. Overall, this study contributes to further understanding the photodegradation mechanisms, degradation products and environmental fate of SMX and RR-194 in water which helps in the evaluation and mitigation of the environmental risk of SMX and RR-194 for water reuse and crop irrigation
Photocatalytic oxidation of multicomponent solutions of herbicides: Reaction kinetics analysis with explicit photon absorption effects
No full textThe intrinsic reaction kinetics of the photocatalytic oxidation (PCO) of the herbicides isoproturon, simazine and propazine over irradiated TiO2 (Degussa P25) suspensions was studied in single-component and in multicomponent systems. Experiments were carried out at different photon fluxes and different herbicide concentrations in the range below 1 mg L-1. The results were analyzed in terms of a Langmuir-Hinshelwood (L-H) kinetic model previously established for multicomponent solutions of herbicides, but including the explicit effect of photon absorption. This was accomplished by modeling the radiation field in the reactor with the Six-Flux Absorption-Scattering Model (SFM) (i.e., scattered photons follow the route of the six directions of the Cartesian coordinates) using optical parameters averaged across the spectrum of the incident radiation. The intrinsic reaction kinetic constants of isoproturon, simazine and propazine independent of the radiation field in the reactor were determined. The oxidation rate of the herbicides was found to follow half-order dependence with respect to the local volumetric rate of photon absorption (LVRPA), in the range of photon fluxes investigated. The established model was found to be appropriate to predict the time-dependent degradation profiles of the herbicides in single- and multicomponent systems not only at all radiation intensities investigated in this study but also when one or two herbicides were present in excess of the others in the mixture. Using this simple approach, intrinsic kinetic data can be obtained. © 2006 Elsevier B.V. All rights reserved
Modelling of an annular photocatalytic reactor for water purification: oxidation of pesticides
No full textPhotocatalytic oxidation (PCO) over titanium dioxide (TiO2) is a “green” sustainable process for the treatment and purification of water and wastewater. However, the application of PCO for wastewater treatment on an industrial scale is currently hindered by a lack of simple mathematical models that can be readily applied to reactor design. Current models are either too simplistic or too rigorous to be useful in photocatalytic reactor design, scale-up, and optimization. In this paper a simple mathematical model is presented for slurry, annular, photocatalytic reactors that still retains the essential elements of a rigorous approach while providing simple solutions. The model extends the applicability of the thin-film model of photocatalytic reactors previously presented to include the case of geometrically thick photoreactors (i.e., those reactors in which the thickness of the annular zone is significant as compared to the outer radius of the reactor). The model uses a novel six-flux absorption-scattering model to represent the radiation field in the reaction space, which assumes that scattered photons follow the route of the six directions of the Cartesian coordinates. The model was successfully validated with experimental results from the photocatalytic oxidation of the pesticide isoproturon in an experimental reactor. The mathematical model presented may be used as a tool for the design, scale-up, and optimization of annular photocatalytic reactors for water treatment and purification
Modeling the photocatalytic oxidation of carboxylic acids on aqueous TiO2 suspensions and on immobilized TiO2-chitosan thin films in different reactor geometries irradiated by UVA or UVC light sources
No full textPhotocatalytic reactor models incorporating radiation transport parameters and intrinsic kinetic parameters of photocatalytic decomposition of single-compound and mixtures of oxalic (OA) and formic acid (FA), in both slurry suspensions and immobilized photocatalytic thin films, were validated in two well-mixed annular photoreactors geometries irradiated with either UVA or UVC radiation. The six-flux absorption scattering model (SFM) predicted the radiation field in a titanium dioxide (TiO2 P25) catalyst suspension, the local volumetric rate of photon absorption (LVRPA) at each point of the reactor and, after volumetric integration, the lumped VRPA. The model combining the lumped VRPA, the kinetics models describing the adsorption and photocatalytic decomposition of OA and FA and the material balance of the reacting species was fitted to the experimental results of photocatalytic decomposition of OA and FO in a slurry TiO2 suspension, to determine the OA and FA intrinsic reaction kinetics parameters. Such intrinsic parameters were then used with the average surface rate of photon absorption (SRPA) to model and predict the photocatalytic oxidation of OA and FA on non-porous TiO2–chitosan films immobilized on glass plates immersed in the photoreactor. The models for both slurry suspensions and immobilized photocatalysts predicted the degradation and mineralization of OA and FA and of a mixture of them under diverse experimental conditions. This study demonstrates a systematic methodology for determining intrinsic reaction kinetics rate parameters of water contaminants that can also be used to represent the photocatalytic oxidation of such contaminants in irradiated slurries and in immobilized photocatalytic thin films and in any photoreactor geometry
CFD modeling of pharmaceuticals and CECs removal by UV/H2O2 process in helical microcapillary photoreactors and evaluation of OH radical rate constants
No full textProcess intensification by tailored secondary flow in helical microcapillary film (MCF) photoreactors was unveiled by computational fluid dynamics, and it was revealed for the removal of six common contaminants of emerging concern CECs (the antiviral Acyclovir, the antiretrovirals Stavudine and Zidovudine, and the biocidal antifungal agents Methylisothiazolinone, Benzisothiazolinone and Isoxazole) in water by UV hydrogen peroxide. The MCF photoreactors consisted of fluoropolymer films containing 10 microchannels with diameter varying from 100 to 1000 μm coiled around a UVC lamp. In contrast to a MCF with straight channels, mixing intensification by secondary flow (Dean vortices) caused by the helical shape of the microcapillary strongly enhanced the radial fluid mixing, further supplementing the transport of the reacting species by Taylor-Aris dispersion. The intensity of the Dean vortices formed was correlated to the Dean (De) and Schmidt (Sc) numbers through a new correlation for the radial Peclet, which established that these become significant when De1.94Sc>67. Thus, the second-order reaction rate constant of the six CECs with OH• radicals (kOH) determined in a helical MCF photoreactor increased (4.4% up to 37.9%) in comparison to those determined assuming a MCF photoreactor with plug flow. In addition, the helical shape of the MCF significantly diminished mass transfer limitations and decreased the CECs Electrical Energy per Order Reduction (EEO), paving the way for scaling-up of helical microcapillary photoreactor technology. This study shows how micromixing can be successfully exploited to design more efficient microcapillary photoreactors
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