Letteratura scientifica selezionata sul tema "HOx and RO2 radicals"
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Articoli di riviste sul tema "HOx and RO2 radicals":
1
Liao, J., L. G. Huey, D. J. Tanner, N. Brough, S. Brooks, J. E. Dibb, J. Stutz et al. "Observations of hydroxyl and peroxy radicals and the impact of BrO at Summit, Greenland in 2007 and 2008". Atmospheric Chemistry and Physics 11, n. 16 (23 agosto 2011): 8577–91. http://dx.doi.org/10.5194/acp-11-8577-2011.
Abstract (sommario):
Abstract. The Greenland Summit Halogen-HOx (GSHOX) Campaign was performed in spring 2007 and summer 2008 to investigate the impact of halogens on HOx (= OH + HO2) cycling above the Greenland Ice Sheet. Chemical species including hydroxyl and peroxy radicals (OH and HO2 + RO2), ozone (O3), nitrogen oxide (NO), nitric acid (HNO3), nitrous acid (HONO), reactive gaseous mercury (RGM), and bromine oxide (BrO) were measured during the campaign. The median midday values of HO2 + RO2 and OH concentrations observed by chemical ionization mass spectrometry (CIMS) were 2.7 × 108 molec cm−3 and 3.0 × 106 molec cm−3 in spring 2007, and 4.2 × 108 molec cm−3 and 4.1 × 106 molec cm−3 in summer 2008. A basic photochemical 0-D box model highly constrained by observations of H2O, O3, CO, CH4, NO, and J values predicted HO2 + RO2 (R = 0.90, slope = 0.87 in 2007; R = 0.79, slope = 0.96 in 2008) reasonably well and under predicted OH (R = 0.83, slope = 0.72 in 2007; R = 0.76, slope = 0.54 in 2008). Constraining the model to HONO observations did not significantly improve the ratio of OH to HO2 + RO2 and the correlation between predictions and observations. Including bromine chemistry in the model constrained by observations of BrO improved the correlation between observed and predicted HO2 + RO2 and OH, and brought the average hourly OH and HO2 + RO2 predictions closer to the observations. These model comparisons confirmed our understanding of the dominant HOx sources and sinks in this environment and indicated that BrO impacted the OH levels at Summit. Although, significant discrepancies between observed and predicted OH could not be explained by the measured BrO. Finally, observations of enhanced RGM were found to be coincident with under prediction of OH.
2
Whalley, L. K., M. A. Blitz, M. Desservettaz, P. W. Seakins e D. E. Heard. "Reporting the sensitivity of Laser Induced Fluorescence instruments used for HO<sub>2</sub> detection to an interference from RO<sub>2</sub> radicals and introducing a novel approach that enables HO<sub>2</sub> and certain RO<sub>2</sub> types to be selectively measured". Atmospheric Measurement Techniques Discussions 6, n. 4 (9 luglio 2013): 6249–92. http://dx.doi.org/10.5194/amtd-6-6249-2013.
Abstract (sommario):
Abstract. Laboratory studies have revealed that alkene-derived RO2 and longer-chain alkane-derived RO2 (>C3) radicals rapidly convert to HO2 and then to OH in the presence of NO in a Fluorescence Assay by Gas Expansion (FAGE) detection cell (Fuchs et al., 2011). Three different FAGE cells that have been used to make ambient measurements of OH and HO2 in the University of Leeds ground-based instrument have been assessed to determine the sensitivity of each cell, when operating in HO2 detection mode, to RO2 radicals. The sensitivity to this interference was found to be highly dependent on cell design and operating parameters. Under the operating conditions employed during fieldwork undertaken in the Borneo rainforest in 2008, an OH yield of 17% was experimentally determined for both ethene- and isoprene-derived RO2 radicals. The high pumping capacity of this system, resulting in a short residence time, coupled with poor mixing of NO into the ambient air-stream for the titration of HO2 to OH effectively minimised this potential interference. An OH yield of 46% was observed for ethene-derived RO2 radicals when a smaller detection cell was used, in which the mixing of NO into the ambient air was improved and the cell residence times were longer. For a newly developed ROx LIF cell, used for detection of HO2 and RO2 radicals, when running in HOx mode an OH yield of 95% was observed for ethene-derived RO2 radicals. In experiments in which conditions ensured the conversion of RO2 to OH was complete, the yields of OH from a range of different RO2 species agreed well with model predictions based on the Master Chemical Mechanism version 3.2. For ethene and isoprene derived RO2 species, the relative sensitivity of FAGE was found to be close to that for HO2 with an OH yield of 100% and 92% respectively. For the longer-chain alkane-derived RO2 radicals, model predicted OH yields were highly dependent upon temperature. A model predicted OH yield of 74% at 298 K and 36% at 255 K were calculated for cyclohexane derived RO2 radicals and an experimental yield of 38% was observed indicating that the temperature within the cell was below ambient owing to the supersonic expansion of the airstream in the low pressure cell. These findings suggest that observations of HO2 by some LIF instruments worldwide may be higher than the true value if the instruments were sensitive to these RO2 species. If this is the case, it becomes necessary to compare atmospheric chemistry model simulations to HO2* observations, where HO2&ast; = [HO2] + α [RO2] and α is the mean fractional contribution of the RO2 species that interfere RO2i). This methodology, however, relies on model simulations of speciated RO2 radicals, as instrumentation to make speciated RO2 measurements does not currently exist. Here we present an approach that enables the concentration of HO2 and RO2i to be selectively determined by varying the concentration of NO injected into a FAGE cell. Measurements of [HO2] and [RO2i] taken in London are presented.
3
Liao, J., L. G. Huey, D. J. Tanner, S. Brooks, J. E. Dibb, J. Stutz, J. L. Thomas, B. Lefer, C. Haman e K. Gorham. "Observations of hydroxyl and peroxy radicals and the impact of BrO at Summit, Greenland in 2007 and 2008". Atmospheric Chemistry and Physics Discussions 11, n. 4 (26 aprile 2011): 12725–62. http://dx.doi.org/10.5194/acpd-11-12725-2011.
Abstract (sommario):
Abstract. The Greenland Summit Halogen-HOx (GSHOX) Campaign was performed in spring~2007 and summer~2008 to investigate the impact of halogens on HOx (=OH + HO2) cycling above the Greenland Ice Sheet. Chemical species including hydroxyl and peroxy radicals (OH and HO2 + ROx), ozone (O3), nitrogen oxide (NO), nitric acid (HNO2), nitrous acid (HONO), reactive gaseous mercury (RGM), and bromine oxide (BrO) were measured during the campaign. The median midday values of HO2 + RO2 and OH concentrations observed by chemical ionization mass spectrometry (CIMS) were 2.7 × 108 molec cm−3 and 3.0 × 106 molec cm−3 in spring 2007, and 4.2 × 108 molec cm−3 and 4.1 × 106 molec cm−3 in summer~2008. A basic photochemical 0-D box model highly constrained by observations of H2O, O3, CO, CH4, NO, and J values predicted HO2 + RO2 (R = 0.90, slope = 0.87 in 2007; R = 0.79, slope = 0.96 in 2008) reasonably well and under predicted OH (R = 0.83, slope = 0.72 in 2007; R = 0.76, slope = 0.54 in 2008). Constraining the model to HONO observations did not significantly change the predictions. Including bromine chemistry in the model constrained by observations of BrO improved the correlation between observed and predicted HO2 + RO2 and OH, and brought the average hourly OH and HO2+RO2 predictions closer to the observations. These model comparisons confirmed our understanding of the dominant HOx sources and sinks in this environment and indicated that BrO impacted the OH levels at Summit. Although, significant discrepancies between observed and predicted OH could not be explained by the measured BrO. Finally, observations of enhanced RGM were found to be coincident with under prediction of OH.
4
Bottorff, Brandon, Michelle M. Lew, Youngjun Woo, Pamela Rickly, Matthew D. Rollings, Benjamin Deming, Daniel C. Anderson et al. "OH, HO2, and RO2 radical chemistry in a rural forest environment: measurements, model comparisons, and evidence of a missing radical sink". Atmospheric Chemistry and Physics 23, n. 18 (15 settembre 2023): 10287–311. http://dx.doi.org/10.5194/acp-23-10287-2023.
Abstract (sommario):
Abstract. The hydroxyl (OH), hydroperoxy (HO2), and organic peroxy (RO2) radicals play important roles in atmospheric chemistry. In the presence of nitrogen oxides (NOx), reactions between OH and volatile organic compounds (VOCs) can initiate a radical propagation cycle that leads to the production of ozone and secondary organic aerosols. Previous measurements of these radicals under low-NOx conditions in forested environments characterized by emissions of biogenic VOCs, including isoprene and monoterpenes, have shown discrepancies with modeled concentrations. During the summer of 2016, OH, HO2, and RO2 radical concentrations were measured as part of the Program for Research on Oxidants: Photochemistry, Emissions, and Transport – Atmospheric Measurements of Oxidants in Summer (PROPHET-AMOS) campaign in a midlatitude deciduous broadleaf forest. Measurements of OH and HO2 were made by laser-induced fluorescence–fluorescence assay by gas expansion (LIF-FAGE) techniques, and total peroxy radical (XO2) mixing ratios were measured by the Ethane CHemical AMPlifier (ECHAMP) instrument. Supporting measurements of photolysis frequencies, VOCs, NOx, O3, and meteorological data were used to constrain a zero-dimensional box model utilizing either the Regional Atmospheric Chemical Mechanism (RACM2) or the Master Chemical Mechanism (MCM). Model simulations tested the influence of HOx regeneration reactions within the isoprene oxidation scheme from the Leuven Isoprene Mechanism (LIM1). On average, the LIM1 models overestimated daytime maximum measurements by approximately 40 % for OH, 65 % for HO2, and more than a factor of 2 for XO2. Modeled XO2 mixing ratios were also significantly higher than measured at night. Addition of RO2 + RO2 accretion reactions for terpene-derived RO2 radicals to the model can partially explain the discrepancy between measurements and modeled peroxy radical concentrations at night but cannot explain the daytime discrepancies when OH reactivity is dominated by isoprene. The models also overestimated measured concentrations of isoprene-derived hydroxyhydroperoxides (ISOPOOH) by a factor of 10 during the daytime, consistent with the model overestimation of peroxy radical concentrations. Constraining the model to the measured concentration of peroxy radicals improves the agreement with the measured ISOPOOH concentrations, suggesting that the measured radical concentrations are more consistent with the measured ISOPOOH concentrations. These results suggest that the models may be missing an important daytime radical sink and could be overestimating the rate of ozone and secondary product formation in this forest.
5
Lew, Michelle M., Sebastien Dusanter e Philip S. Stevens. "Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence". Atmospheric Measurement Techniques 11, n. 1 (10 gennaio 2018): 95–109. http://dx.doi.org/10.5194/amt-11-95-2018.
Abstract (sommario):
Abstract. One technique used to measure concentrations of the hydroperoxy radical (HO2) in the atmosphere involves chemically converting it to OH by addition of NO and subsequent detection of OH. However, some organic peroxy radicals (RO2) can also be rapidly converted to HO2 (and subsequently OH) in the presence of NO, interfering with measurements of ambient HO2 radical concentrations. This interference must be characterized for each instrument to determine to what extent various RO2 radicals interfere with measurements of HO2 and to assess the impact of this interference on past measurements. The efficiency of RO2-to-HO2 conversion for the Indiana University laser-induced fluorescence–fluorescence assay by gas expansion (IU-FAGE) instrument was measured for a variety of RO2 radicals. Known quantities of OH and HO2 radicals were produced from the photolysis of water vapor at 184.9 nm, and RO2 radicals were produced by the reaction of several volatile organic compounds (VOCs) with OH. The conversion efficiency of RO2 radicals to HO2 was measured when NO was added to the sampling cell for conditions employed during several previous field campaigns. For these conditions, approximately 80 % of alkene-derived RO2 radicals and 20 % of alkane-derived RO2 radicals were converted to HO2. Based on these measurements, interferences from various RO2 radicals contributed to approximately 35 % of the measured HO2 signal during the Mexico City Metropolitan Area (MCMA) 2006 campaign (MCMA-2006), where the measured VOCs consisted of a mixture of saturated and unsaturated species. However, this interference can contribute more significantly to the measured HO2 signal in forested environments dominated by unsaturated biogenic emissions such as isoprene.
6
Hornbrook, R. S., J. H. Crawford, G. D. Edwards, O. Goyea, R. L. Mauldin III, J. S. Olson e C. A. Cantrell. "Measurements of tropospheric HO<sub>2</sub> and RO<sub>2</sub> by oxygen dilution modulation and chemical ionization mass spectrometry". Atmospheric Chemistry and Physics Discussions 10, n. 9 (28 settembre 2010): 22219–77. http://dx.doi.org/10.5194/acpd-10-22219-2010.
Abstract (sommario):
Abstract. An improved method for the measurement of hydroperoxy radicals (HO2) and organic peroxy radicals (RO2, where R is any organic group) has been developed that combines two previous chemical conversion/chemical ionization mass spectrometry (CIMS) peroxy radical measurement techniques. Applicable to both ground-based and aircraft platforms, the method provides good separation between HO2 and RO2 and frequent measurement capability with observations of both HO2 and HO2 + RO2 amounts each minute. This allows for analyses of measured [HO2]/[HO2 + RO2] ratios on timescales relevant to tropospheric photochemistry. By varying both [NO] and [O2] simultaneously in the chemical conversion region of the PeRCIMS (Peroxy Radical CIMS) inlet, the method exploits the changing conversion efficiency of RO2 to HO2 under different inlet [NO]/[O2] to selectively observe either primarily HO2 or the sum of HO2 and RO2. Two modes of operation have been established for ambient measurements: in the first half of the minute, RO2 radicals are measured at close to 100% efficiency along with HO2 radicals (low [NO]/[O2] = 2.53 × 10−5) and in the second half of the minute, HO2 is detected while the majority of ambient RO2 radicals are measured with approximately 15% efficiency (high [NO]/[O2] = 6.80 × 10−4). The method has been tested extensively in the laboratory under various conditions and for a variety of organic peroxy radicals relevant to the atmosphere and the results of these tests are presented. The modified PeRCIMS instrument has been deployed successfully using the current measurement technique on a number of aircraft campaigns, including on the NSF/NCAR C-130 during the MIRAGE-Mex and NASA INTEX-B field campaigns in the spring of 2006. A brief comparison of the peroxy radical measurements during these campaigns to a photochemical box model confirms that the PeRCIMS is able to successfully separate and measure HO2 and RO2 under the majority of tropospheric conditions.
7
Andrés-Hernández, M. D., D. Kartal, J. N. Growley, V. Sinha, E. Regelin, M. Martínez-Harder, V. Nenakhov et al. "Diel peroxy radicals in a semi industrial coastal area: nighttime formation of free radicals". Atmospheric Chemistry and Physics Discussions 12, n. 8 (7 agosto 2012): 19529–70. http://dx.doi.org/10.5194/acpd-12-19529-2012.
Abstract (sommario):
Abstract. Peroxy radicals were measured by a PeRCA (Peroxy Radical Chemical Amplifier) instrument in the boundary layer during the DOMINO (Diel Oxidant Mechanisms In relation to Nitrogen Oxides) campaign at a coastal, forested site influenced by urban-industrial emissions in Southern Spain in late autumn. Total peroxy radicals (RO2* = HO2 + ΣRO2) generally showed a daylight maximum between 10 and 50 pptv at 13:00 UTC, with an average of 18 pptv over the 15 days of measurements. Emissions from the industrial area of Huelva often impacted the measurement site at night during the campaign. The processing of significant levels of anthropogenic organics leads to an intense nocturnal radical chemistry accompanied by formation of organic peroxy radicals at comparable levels to those of summer photochemical conditions with peak events up to 60–80 pptv. The RO2 production initiated by reactions of NO3 with organic trace gases was estimated to be significant but not sufficient to account for the concentrations of RO2* observed in air masses carrying high pollutant loading. The nocturnal production of peroxy radicals seems therefore to be dominated by ozonolysis of volatile organic compounds. RO2* diurnal variations were consistent with other HO2 measurements available at the site. HO2/RO2* ratios generally varied between 0.3 and 0.4 in all wind directions. Occasional HO2/RO2* ≥ 1 seemed to be associated with periods of high RO2* variability and with RO2 interferences in the HO2 measurement in air masses with high RO2 load.
8
Ma, Xuefei, Zhaofeng Tan, Keding Lu, Xinping Yang, Xiaorui Chen, Haichao Wang, Shiyi Chen et al. "OH and HO<sub>2</sub> radical chemistry at a suburban site during the EXPLORE-YRD campaign in 2018". Atmospheric Chemistry and Physics 22, n. 10 (31 maggio 2022): 7005–28. http://dx.doi.org/10.5194/acp-22-7005-2022.
Abstract (sommario):
Abstract. The first OH and HO2 radical observation in Yangtze River Delta, one of the four major urban agglomerations in China, was carried out at a suburban site (Taizhou) in summer 2018 from May to June, aiming to elucidate the atmospheric oxidation capacity in this region. The maximum diurnal averaged OH and HO2 concentrations were 1.0×107 and 1.1×109 cm−3, respectively, which were the second highest HOx (sum of OH and HO2) radical concentrations observed in China. HONO photolysis was the dominant radical primary source, accounting for 42 % of the total radical initiation rate. Other contributions were from carbonyl photolysis (including HCHO, 24 %), O3 photolysis (17 %), alkene ozonolysis (14 %), and NO3 oxidation (3 %). A chemical box model based on the RACM2-LIM1 mechanism could generally reproduce the observed HOx radicals, but systematic discrepancy remained in the afternoon for the OH radical, when the NO mixing ratio was less than 0.3 ppb. An additional recycling mechanism equivalent to 100 ppt NO was capable to fill the gap. The sum of monoterpenes was on average up to 0.4 ppb during daytime, which was all allocated to α-pinene in the base model. A sensitivity test without monoterpene input showed the modeled OH and HO2 concentrations would increase by 7 % and 4 %, respectively, but modeled RO2 concentration would significantly decrease by 23 %, indicating that monoterpene was an important precursor of RO2 radicals in this study. Consequently, the daily integrated net ozone production would reduce by 6.3 ppb without monoterpene input, proving the significant role of monoterpene in the photochemical O3 production in this study. In addition, the generally good agreement between observed and modeled HOx concentrations suggested no significant HO2 heterogeneous uptake process during this campaign. Incorporation of HO2 heterogeneous uptake process would worsen the agreement between HOx radical observation and simulation, and the discrepancy would be beyond the combined measurement–model uncertainties using an effective uptake coefficient of 0.2. Finally, the ozone production efficiency (OPE) was only 1.7 in this study, a few folds lower than other studies in (sub)urban environments. The low OPE indicated a slow radical propagation rate and short chain length. As a consequence, ozone formation was suppressed by the low NO concentration in this study.
9
Xue, L. K., T. Wang, H. Guo, D. R. Blake, J. Tang, X. C. Zhang, S. M. Saunders e W. X. Wang. "Sources and photochemistry of volatile organic compounds in the remote atmosphere of western China: results from the Mt. Waliguan Observatory". Atmospheric Chemistry and Physics 13, n. 17 (2 settembre 2013): 8551–67. http://dx.doi.org/10.5194/acp-13-8551-2013.
Abstract (sommario):
Abstract. The chemistry of the natural atmosphere and the influence by long-range transport of air pollution are key issues in the atmospheric sciences. Here we present two intensive field measurements of volatile organic compounds (VOCs) in late spring and summer of 2003 at Mt. Waliguan (WLG, 36.28° N, 100.90° E, 3816 m a.s.l.), a baseline station in the northeast part of the Qinghai-Tibetan Plateau. Most VOC species exhibited higher concentrations in late spring than in summer. A typical diurnal variation was observed with higher nighttime levels, in contrast to results from other mountainous sites. Five different air masses were identified from backward trajectory analysis showing distinct VOC speciation. Air masses originating from the central Eurasian continent contained the lowest VOC levels compared to the others that were impacted by anthropogenic emissions from China and the Indian subcontinent. A photochemical box model based on the Master Chemical Mechanism (version 3.2) and constrained by a full suite of measurements was developed to probe the photochemistry of atmosphere at WLG. Our results show net ozone production from in situ photochemistry during both late spring and summer. Oxidation of nitric oxide (NO) by the hydroperoxyl radical (HO2) dominates the ozone production relative to the oxidation by the organic peroxy radicals (RO2), and the ozone is primarily destroyed by photolysis and reactions with the HOx (HOx = OH + HO2) radicals. Ozone photolysis is the predominant primary source of radicals (ROx = OH + HO2 + RO2), followed by the photolysis of secondary oxygenated VOCs and hydrogen peroxides. The radical losses are governed by the self and cross reactions among the radicals. Overall, the findings of the present study provide insights into the background chemistry and the impacts of pollution transport on the pristine atmosphere over the Eurasian continent.
10
Liu, Y. J., I. Herdlinger-Blatt, K. A. McKinney e S. T. Martin. "Production of methyl vinyl ketone and methacrolein via the hydroperoxyl pathway of isoprene oxidation". Atmospheric Chemistry and Physics Discussions 12, n. 12 (21 dicembre 2012): 33323–58. http://dx.doi.org/10.5194/acpd-12-33323-2012.
Abstract (sommario):
Abstract. The photo-oxidation chemistry of isoprene (C5H8) was studied in a continuous-flow chamber under conditions such that the reactions of isoprene-derived peroxyl radicals (RO2) were dominated by hydroperoxyl (HO2) pathway. A proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS) with switchable H3O+ and NO+ reagent ions was used for product analysis. The products methyl vinyl ketone (MVK; C4H6O) and methacrolein (MACR; C4H6O) were differentiated using NO+ reagent ions. The MVK and MACR yields were 4.3 ± 0.4% and 3.2 ± 0.3%, respectively, for HO2-dominant conditions at +25 °C and < 2% relative humidity. The respective yields were 41.1 ± 2.2% and 28.8 ± 1.2% for NO-dominant conditions. The yields for HO2-dominant conditions imply a concomitant yield (i.e., recycling factor) of hydrogen oxide radicals (HOx) of 15 ± 0.7% from the reaction of isoprene-derived RO2 with HO2. Other isoprene oxidation products, believed to be organic hydroperoxides, also contributed to the ion intensity at the same mass-to-charge (m/z) ratios as the MVK and MACR product ions, and these products were selectively removed from the gas phase using a variable temperature cold trap (−40 °C) in front of the PTR-TOF-MS. These hydroperoxide products were absent for NO-dominant conditions. When incorporated into regional and global chemical transport models, the yields of MVK and MACR and concomitant HOx yields reported in this study will improve the accuracy of simulations of the HO2 reaction pathway of isoprene, which has been shown to make a significant contribution to the total reactivity of isoprene-derived RO2 radicals on a global scale.
Tesi sul tema "HOx and RO2 radicals":
1
Kravtchenko, Florent. "Développement et validation d’un nouveau dispositif expérimental pour l’étude des réactions RO2 + HOx". Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1R067.
Abstract (sommario):
Dans l’atmosphère, la dégradation des polluants organiques tels que les Composés Organiques Volatils (COV) est initiée par le principal oxydant de l’atmosphère : le radical OH. Cette dégradation conduit à la formation d’autres radicaux, de type peroxyles : hydroperoxyles HO2 et alkylperoxyles RO2. Ces radicaux jouent un rôle prépondérant dans la chimie de la troposphère. La réactivité des radicaux RO2 et HOx (HO2 et OH) contrôle la capacité oxydante de l’atmosphère ainsi que la formation d’ozone troposphérique et de polluants secondaires. Dans les régions éloignées des activités humaines (dites également « environnements propres », par exemple les forêts tropicales ou la couche limite marine), où la concentration en oxydes d’azote (NOx) est faible, les réactions entre les radicaux RO2 et HOx dominent la chimie troposphérique. Cependant, cette chimie est encore mal connue et fait l’objet de controverses dans les travaux de la littérature. Les incertitudes et/ou le manque de données sur les constantes de vitesse et les rapports de branchement de ces réactions radicalaires peuvent conduire à d’importantes erreurs sur la modélisation de la concentration en ozone mais également en radicaux. C’est dans ce cadre qu’un nouveau dispositif expérimental innovant a été développé afin d’apporter de nouveaux résultats expérimentaux pour les réactions du type RO2+HOx. Celui-ci est composé d’un réacteur à écoulement rapide couplé à trois techniques complémentaires : la Fluorescence Induite par Laser (FIL) pour la mesure du radical OH, la spectroscopie à temps de déclin d’une cavité optique (cw-CRDS : continuous wave Cavity Ring-Down Spectroscopy) pour la mesure des radicaux HO2 et la Spectrométrie de Masse avec prélèvement par Faisceau Moléculaire (FM/SM) permettant la mesure d’espèces stables (produits de réaction) et radicalaires. Dans un premier temps, chacune des trois techniques expérimentales a été validée indépendamment, puis des mesures de constantes de vitesse de réactions connues, impliquant une espèce stable (éthane, propane, méthanol, CO) et le radical OH ont été réalisées afin de valider le dispositif expérimental dans son ensemble. Deux méthodes de génération des radicaux OH dans le réacteur ont été utilisées : à partir des réactions F+H2OOH+HF et H+NO2OH+NO. Un phénomène inexpliqué de recyclage de OH dans le réacteur a été observé pour tous les partenaires de réaction (excepté CO), lorsque les radicaux OH sont formés à partir de la réaction F+H2OOH +HF. Ceci a été confirmé lors de l’étude de réactions faisant intervenir les mêmes espèces deutérées. Dans ce manuscrit sont recensés les différents tests ayant été réalisés afin de comprendre ce phénomèneIn the atmosphere, the degradation of organic pollutants such as Volatile Organic Compounds (VOCs) is induced by the most important atmospheric oxidant: the hydroxyl radical OH. This degradation leads to the formation of peroxy radicals: hydroperoxy HO2 and alkylperoxy RO2. These radicals play a major role in tropospheric chemistry. The reactivity of RO2 and HOX (HO2 and OH) radicals controls the oxidative capacity of the atmosphere and the formation of tropospheric ozone and secondary pollutants. In remote environments (or “clean environment” such as tropical forests or marine boundary layer), where the concentration of nitrogen oxides (NOx) is low, the reactions between RO2 and HOx dominate the atmospheric chemistry. However, this chemistry is still poorly known and controversial in the literature. The uncertainties and/or lack of data on RO2+HOx reactions rates and branching ratios can lead to important errors on modelling of ozone and radical concentrations in the atmosphere. The aim of the present work is the development of a new and innovative experimental device to bring new experimental results for the reactions RO2 + HOx. The new setup consists of a fast flow tube coupled to three complementary techniques: Laser Induced Fluorescence (LIF) for OH radical measurements, continuous wave Cavity Ring-Down Spectroscopy (cw-CRDS) for HO2 radical measurements and Mass Spectrometry with Molecular Beam sampling (MB/MS) for measurement of stable reaction products and radical species. First, each of the three techniques has been validated independently, and then the validation of the complete system was done through the study of different known reactions between a stable species (ethane, propane, methanol, CO) and OH radicals. Two methods of OH radicals generation in the reactor were used: through the reaction F+H2OOH+HF and the reaction H+NO2OH+NO. An unexplained OH recycling phenomenon in the reactor has been observed for all reaction partners (except CO) when using F+H2O as precursors. This was confirmed during the study of reactions involving the same deuterated species. In this manuscript, the different tests that have been carried out in order to understand this phenomenon are described
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Shamas, Nesrine. "Understanding of atmospheric and indoor air chemistry through HOx radical measurements". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILR057.
Abstract (sommario):
Les radicaux HOx (OH+HO2) et RO2 sont impliqués dans les processus d'oxydation en phase gazeuse, générant des produits secondaires ayant un impact sur la qualité de l'air et la santé humaine. La compréhension de ces processus d'oxydation par la quantification de ces radicaux reste un défi en raison de leurs faibles concentrations (< ppt) et de leur réactivité élevée. Il n'existe que quelques instruments dans le monde permettant d'effectuer de telles mesures, dont l'instrument de l'Université de Lille (UL-FAGE: ). Il est basé sur la détection par LIF (Laser Induced Fluorescence) de OH à basse pression. Il permet la mesure directe de OH et la mesure indirecte de HO2 par conversion chimique en OH après l'ajout d'une faible concentration de NO à l'entrée de la cellule FAGE. Au cours de cette thèse, l'instrument a été amélioré pour la quantification des radicaux RO2. Deux mesures complémentaires permettent d'accéder à la concentration de RO2, soit en utilisant la cellule HO2 et en injectant une concentration élevée de NO à l'entrée de la cellule de détection, soit en couplant un réacteur de conversion ROx à une cellule FAGE. Cette technique est basée sur la conversion chimique en deux étapes des radicaux RO2 en HO2 dans le réacteur de conversion couplé à une cellule FAGE. Nous pouvons également mesurer un autre paramètre en utilisant une cellule FAGE couplée à une cellule de photolyse : la réactivité d'OH (somme des pertes OH).L'instrument UL-FAGE a été amélioré et utilisé au cours de cette thèse pour des mesures en laboratoire (configuration de réactivité) afin d'étudier les mécanismes d'oxydation importants pour la chimie intérieure et extérieure impliquant les radicaux HOx. Au cours de l'été 2022, l'UL-FAGE a participé à une campagne d'intercomparaison RO2 qui s'est déroulée dans la chambre SAPHIR (Jülich, Allemagne). Neuf groupes utilisant différents instruments ont participé à cette campagne. Les performances des instruments UL-FAGE pour la mesure de OH, HO2 et RO2 dans une large gamme de conditions chimiques atmosphériques (tels que la vapeur d'eau, le niveau en oxydes d'azote, la présence de divers composés organiques, chimie de jour et de nuit) ont été étudiées au cours de cette campagne. Enfin, l'UL-FAGE en configuration de quantification et de réactivité a été déployé pour une campagne de terrain (ACROSS) dans la forêt de Rambouillet, avec des mesures de réactivité à deux hauteurs différentes (au sol et au-dessus de la canopée) et des mesures de concentrations en radicaux au solHOx (OH+HO2) and RO2 radicals are involved in oxidation processes in the gas phase, generating secondary products impacting the air quality and human health. Understanding these oxidation processes through the quantification of these radicals is still challenging because of their low concentrations (
3
Assaf, Emmanuel. "Kinetic study of reactions with interest to atmospheric chemistry by simultaneous detection of OH and RO2 radicals coupled to laser photolysis". Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10095/document.
Abstract (sommario):
Les radicaux hydroxyle OH et hydroperoxyle HO2 jouent un rôle essentiel dans de nombreux processus d’oxydation dans l’atmosphère. La dégradation des composés organiques volatils dans les conditions troposphériques est généralement initiée par la réaction avec les radicaux OH, suivie par la réaction des produits d’oxydation avec l’oxygène. Dans le cadre de cette thèse, des études on été menées afin de mieux comprendre les mécanismes d’oxydation d’espèces d’intérêt atmosphérique. Pour cela, un système expérimental composé d’une photolyse laser couplée à des techniques spectroscopiques de détection résolues dans le temps: Laser Induced Fluorescence Induite par Laser (LIF, pour la détection des radicaux OH) et continuous-wave Cavity Ring-Down Spectroscopy (cw-CRDS, pour la détection des radicaux OH, HO2 et RO2) ont été utilisés. Après avoir mesuré le spectre ainsi que les sections efficaces d’absorption de quelques raies sélectionnées de OH, HO2 et RO2 dans la région du proche infrarouge, quatre système ont été étudiés avec les techniques mentionnées ci-dessus: CH3O2 + OH, C2H5O2 + OH, C3H7O2 + OH and C4H9O2 + OH. La constante de vitesse ainsi que le rendement de HO2 ont été déterminés pour ces quatre réactions. En outre, les constantes de vitesse de réactions secondaires telles que CH3O + HO2, CH3O + CH3O ou OH + HO2 ont été déterminéesThe hydroxyl radical OH and hydroperoxy radical HO2 radicals are key species in many oxidation processes in the atmosphere. The degradation of volatile organic compounds under tropospheric conditions is induced by reactions with hydroxyl radicals followed by the subsequent chemistry of the initial OH oxidation products with O2. This thesis was focused on the kinetic study of some of these atmospherically relevant reactions to better understand their oxidation mechanisms using an experimental system of laser photolysis coupled to Laser Induced Fluorescence (LIF, for OH radical) and continuous-wave Cavity Ring-Down Spectroscopy (cw-CRDS, for OH, HO2 and RO2 radicals) detection techniques. After determining the infrared spectrum of OH, HO2 and CH3O2 radicals in the near infrared region and the absorption cross-sections of few selected lines, four systems were studied with the above mentioned techniques: CH3O2 + OH, C2H5O2 + OH, C3H7O2 + OH and C4H9O2 + OH. The rate constant and the HO2 yield of the four reactions were determined. In addition, the rate constants of few secondary reactions such as CH3O + HO2, CH3O + CH3O or OH + HO2 have been determined
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Faloon, Kathleen Helen. "The development of a laboratory system to investigate the interactions of tropospheric aerosol and HOx radicals". Thesis, University of Birmingham, 2011. http://etheses.bham.ac.uk//id/eprint/2993/.
Abstract (sommario):
This thesis describes the development and application of a laboratory system to investigate the loss of peroxy radicals to aerosol. The laboratory system consisted of an aerosol flow tube coupled to a custom-built PEroxy Radical Chemical Amplifier (PERCA). Aerosol was generated using an atomiser and their distribution measured using a SMPS. New values of the HO2 uptake coefficient, γ , were obtained for wet and dry sodium chloride aerosol and dry ammonium sulphate aerosol. The mass accommodation coefficient, α, was also determined for NaCl. A box model was used to determine the implications of the new uptake coefficient of HO2 loss to NaCl aerosol for tropospheric chemistry in the marine boundary layer.
Libri sul tema "HOx and RO2 radicals":
1
Crosley, David R. Local measurement of tropospheric HOx: Summary of a workshop held at SRI International, Menlo Park, California, March 23-26, 1992. Hampton, Va: Langley Research Center, 1994.
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Samer, Rox. Lesbian Potentiality and Feminist Media in the 1970s. Duke University Press, 2022. http://dx.doi.org/10.1215/9781478022640.
Abstract (sommario):
In Lesbian Potentiality and Feminist Media in the 1970s, Rox Samer explores how 1970s feminists took up the figure of the lesbian in broad attempts to reimagine gender and sexuality. Samer turns to feminist film, video, and science fiction literature, offering a historiographical concept called “lesbian potentiality”—a way of thinking beyond what the lesbian was, in favor of how the lesbian signified what could have come to be. Samer shows how the labor of feminist media workers and fans put lesbian potentiality into movement. They see lesbian potentiality in feminist prison documentaries that theorize the prison industrial complex’s racialized and gendered violence and give image to Black feminist love politics and freedom dreaming. Lesbian potentiality also circulates through the alternative spaces created by feminist science fiction and fantasy fanzines like The Witch and the Chameleon and Janus. It was here that author James Tiptree, Jr./Alice B. Sheldon felt free to do gender differently and inspired many others to do so in turn. Throughout, Samer embraces the perpetual reimagination of “lesbian” and the lesbian’s former futures for the sake of continued, radical world-building.
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Alfaro Bernedo, Juan Oswaldo. Modelo Sistémico de Gestión Estratégica BSC-BI Virtual para la Sostenibilidad Universitaria. Fondo Editorial Professionals On Line, 2023. http://dx.doi.org/10.47422/fepol.21.
Abstract (sommario):
La necesidad de escribir este libro, surge como una inquietud personal para plasmar mis conocimientos y experiencia superior a los 40 años de ejercicio profesional en el ámbito de la gestión en instituciones públicas y privadas, así como en la docencia universitaria a nivel de pregrado y posgrado en varias universidades del país. El propósito es proponer un aporte a la gestión estratégica de las universidades públicas; el factor diferenciador y de valor respecto a otras publicaciones similares, radica en que, este modelo propuesto se orienta a una gestión estratégica soportada por modernas herramientas tecnológicas que, irónicamente, las condiciones excepcionales de aislamiento impuestas por la crisis sanitaria mundial derivadas del covid-19, aceleraron la transformación digital (que vino para quedarse) en todas las actividades humanas. En efecto, la pospandemia ha creado un escenario inédito e incierto para el desarrollo de las actividades institucionales; contexto en el cual, sin embargo, también han emergido oportunidades para articular, entre otros, de manera complementaria y sistémica modelos de gestión híbridos. De otro modo, sería un absurdo volver en el sentido literal y abstracta a la condición prexistente de la crisis sanitaria; pues el costo de la adaptación acelerada al nuevo escenario ha sido tan dramático pero útil a la vez que, el mandato imperativo de hoy es convivir inteligentemente con las herramientas tecnológicas que cumplen el rol de desintermediación de la presencialidad; es decir, estar ahí sin ir ahí, preservando o elevando los niveles de calidad de los procesos y productos en beneficio del ciudadano.
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Fader, Ayala. Hidden Heretics. Princeton University Press, 2020. http://dx.doi.org/10.23943/princeton/9780691169903.001.0001.
Abstract (sommario):
What would you do if you questioned your religious faith, but revealing that would cause you to lose your family and the only way of life you had ever known? This book tells the fascinating, often heart-wrenching stories of married ultra-Orthodox Jewish men and women in twenty-first-century New York who lead “double lives” in order to protect those they love. While they no longer believe that God gave the Torah to Jews at Mount Sinai, these hidden heretics continue to live in their families and religious communities, even as they surreptitiously break Jewish commandments and explore forbidden secular worlds in person and online. Drawing on five years of fieldwork with those living double lives and the rabbis, life coaches, and religious therapists who minister to, advise, and sometimes excommunicate them, the book investigates religious doubt and social change in the digital age. The Internet, which some ultra-Orthodox rabbis call more threatening than the Holocaust, offers new possibilities for the age-old problem of religious uncertainty. The book shows how digital media has become a lightning rod for contemporary struggles over authority and truth. It reveals the stresses and strains that hidden heretics experience, including the difficulties their choices pose for their wives, husbands, children, and, sometimes, lovers. In following those living double lives, who range from the religiously observant but open-minded on one end to atheists on the other, the book delves into universal quandaries of faith and skepticism, the ways digital media can change us, and family frictions that arise when a person radically transforms who they are and what they believe. In stories of conflicts between faith and self-fulfillment, the book explores the moral compromises and divided loyalties of individuals facing life-altering crossroads.
Capitoli di libri sul tema "HOx and RO2 radicals":
1
Amedro, Damien, Alexander E. Parker, Coralie Schoemaecker, Chaithanya Jain, Pranay Morajkar, Paul S. Monks, Koji Miyazaki, Yoshizumi Kajii e Christa Fittschen. "HOx and ROx Radicals in Atmospheric Chemistry". In Disposal of Dangerous Chemicals in Urban Areas and Mega Cities, 77–92. Dordrecht: Springer Netherlands, 2012. http://dx.doi.org/10.1007/978-94-007-5034-0_6.
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Calvert, Jack G., John J. Orlando, William R. Stockwell e Timothy J. Wallington. "Mechanisms of Reactions of HO2 and RO2 Radicals". In The Mechanisms of Reactions Influencing Atmospheric Ozone. Oxford University Press, 2015. http://dx.doi.org/10.1093/oso/9780190233020.003.0008.
Abstract (sommario):
The peroxy radicals are an important link in the reaction chain that develops ozone in the atmosphere through their reactions with NO. This chapter explores the kinetics and mechanisms of these RO2 reactions. In Chapters III and IV, the kinetics and mechanisms of the reactions of organic compounds with the major atmospheric oxidants [HO, NO3, and O3] were discussed. The organic radicals formed in these reactions add O2 to form organic peroxy radicals (RO2). The rate coefficient for these reaction is typically of the order of (10−12–10−11) cm3 molecule−1 s−1 under tropospheric conditions. One atmosphere (1 atm) of air contains 5 × 1018 molecule cm−3 of O2, and the lifetime of organic radicals with respect to addition of O2 to give peroxy radicals is 10–100 nanoseconds. Addition of O2 is essentially the sole atmospheric fate of the organic radicals formed during the oxidation of organic compounds. As examples, consider the HO-initiated oxidation of ethane and acetone (M is a third body, such as N2, which collisionally deactivates the nascent peroxy radical): . . . HO + CH3CH3 → CH3CH2 + H2O . . . . . . CH3CH2 + O2 + M → CH3CH2O2 + M . . . . . . HO + CH3C(O)CH3 → CH3C(O)CH2 + H2O . . . . . . CH3C(O)CH2 + O2 + M → CH3C(O)CH2O2 + M . . . Because of the rapidity and exclusivity of the O2 addition to alkyl radicals, the organic peroxy radicals (CH3CH2O2 and CH3C(O)CH2O2) can be thought of as the primary products of the initial oxidation step. HO2 radicals are formed in reactions of O2 with alkoxy radicals (e.g., CH3O) and by the association reaction of H atoms with O2: . . . CH3O + O2 → CH2O + HO2 . . . . . . H + O2 + M → HO2 + M . . . Peroxy radicals (HO2 and RO2) have a rich atmospheric chemistry and undergo reactions with NO, NO2, HO2, and other peroxy radicals (R′O2). Unimolecular isomerization is also an important fate for larger organic peroxy radicals where the peroxy radical can abstract a hydrogen atom from another part of the organic moiety (the peroxy radical bites its own tail). Reactions of peroxy radicals with NO3 radicals at night, and ClO and BrO radicals in maritime environments, can also be of importance on local scales.
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Sawyer, Donald T., e R. J. P. Williams. "Reactivity of Oxygen Radicals [HO•, RO•, HOO•, ROO-, and RC(O)O•]". In Oxygen Chemistry. Oxford University Press, 1992. http://dx.doi.org/10.1093/oso/9780195057980.003.0009.
Abstract (sommario):
Oxygen radicals are defined as those molecules that contain an oxygen atom with an unpaired, nonbonding electron (e.g., HO·). Although triplet dioxygen (·O2·) and superoxide ion (O2 - ·) come under this definition, their nonradical chemistry dominates their reactivity, which is discussed in Chapters 6 (·O2·) and 7 (O2-·). The hydroxyl radical (HO·) is the most reactive member of the family of oxygen radicals [HO·, RO·, ·O·, HOO·, ROO·, and RC(O)O·], and is the focus of most oxygen radical research. In the gas phase the dramatic example of oxygen radical reactivity with hydrocarbon substrates is combustion, which is initiated by HO· (or RO· or MO·) and propagated by ·O2· and ·O·.
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Calvert, Jack G., Richard G. Derwent, John J. Orlando, Geoffrey S. Tyndall e Timothy J. Wallington. "Mechanisms and End-Products of the Atmospheric Oxidation of Alkanes". In Mechanisms of Atmospheric Oxidation of the Alkanes, 174–288. Oxford University PressNew York, NY, 2008. http://dx.doi.org/10.1093/oso/9780195365818.003.0004.
Abstract (sommario):
Abstract In the previous two chapters, the kinetics of the reactions of the alkanes with the major atmospheric oxidants [OH, Cl, NO3, O(3P), and O3] have been discussed. These initiation reactions are followed by a series of rapid reactions involving the alkylperoxy (RO2) and alkoxy (RO) radicals, which lead, on a time-scale of minutes, to the first-generation end-products of the oxidation process. The chemistry of these radical species, and the end-products that result, are the topics of this chapter.
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"Oxidative Degradation". In Organic Chemistry of Drug Degradation, 48–109. The Royal Society of Chemistry, 2012. http://dx.doi.org/10.1039/bk9781849734219-00048.
Abstract (sommario):
This chapter contains three functional parts: an introduction (3.1), a description of several major types of autooxidative mechanisms (3.2–3.4), and a discussion of specific oxidation pathways of drugs with various functional groups and structures in relation to each type of the major autooxidative mechanisms (3.5). In Sections 3.2–3.4, the ubiquitously known Fenton reaction and the little known, but more relevant Udenfriend reaction, are discussed in terms of their roles in free radical-mediated autooxidation by activating molecular oxygen into several reactive oxygen species (ROS), that is, O2−˙/HO2˙, H2O2, and HO˙. The radical ROS then triggers radical chain reactions, in which process organic peroxyl radicals and hydroperoxides are the predominant intermediates. The latter can undergo homolytic cleavage, owing to their relatively low O–O bond dissociation energies, as well as metal ion-catalyzed heterolytic cleavage. The homolytic cleavage generates alkoxyl and hydroxyl radicals, while the heterolytic cleavage reproduces peroxyl radical. Non-radical reactions of peroxides were then discussed, in particular those responsible for the formation of N-oxide, S-oxide, and epoxide degradants. The general mechanism for a less known autooxidative degradation pathway, carbanion/enolate-mediated autooxidation (base-catalyzed autooxidation) is also discussed. This mechanism can be significant for those drug molecules containing somewhat “acidic” carbonated CHn moieties, particularly when the drugs are formulated in liquid form. In Section 3.5, more than 60 examples of drug autooxidation in real life scenarios, that is, oxidation occurring under ambient or various stability conditions, are presented and their underlying degradation mechanisms are discussed in details. These examples cover the functional groups, moieties, and structures that are commonly seen in drug molecules.
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Jaeglé, Lyatt, Daniel J. Jacob, William H. Brune e Paul O. Wennberg. "Chapter 14 Chemistry of HOx radicals in the upper troposphere". In Air Pollution Science for the 21st Century, 393–433. Elsevier, 2002. http://dx.doi.org/10.1016/s1474-8177(02)80017-1.
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Gonta, Maria Vasile, Larisa Mocanu e Veronica Porubin-Schimbator. "Advanced Oxidation Processes for Mineralization of Amoxicillin in Aqueous Solutions". In Handbook of Research on Water Sciences and Society, 315–40. IGI Global, 2022. http://dx.doi.org/10.4018/978-1-7998-7356-3.ch014.
Abstract (sommario):
This chapter presents the study of kinetics and mechanisms of transformation of EC (antibiotics) by advanced oxidation processes (AOPs): Fenton (H2O2/Fe(II)), UV photolysis (UV/H2O2/TiO2), and combined methods. The application of AOPs is based on the formation of reactive species such as hydroxyl radical, superoxide radical, hydroperoxyl radical (HO2•), and peroxyradical (ROO•) and takes place by electron transfer reaction, proton extraction by the production of organic radicals (R•) and electrophilic addition to the double bond or aromatic ring. The main objective of this research includes the optimization of the physico-chemical parameters that influence the oxidation process of amoxicillin (AMX). The effect of EC degradation/mineralization was determined according to the concentrations of hydrogen peroxide and catalyst (Fe(II), TiO2), UV intensity, environmental pH, and others. EC transformation rates and speed constants of HO• bimolecular reactions with different emerging contaminants using AOPs have been determined by homogeneous and heterogeneous catalysis.
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"Sugar, Shame, Love". In Radical Health, 52–81. Duke University Press, 2023. http://dx.doi.org/10.1215/9781478027393-003.
Abstract (sommario):
Because diabetes is so closely correlated to lifestyle, those experiencing it are often subjected to public shaming that is both insidious and overt, treated by family members, acquaintances, employee benefits administrators, journalists, and even health professionals as responsible for their condition. In response, Latinx cultural workers seek to imagine radical health in the face of a diabetes epidemic. This chapter begins with some thoughts about how diabetes might inform our evaluation of theories of embodiment and risk (focusing in particular on Lauren Berlant's slow death and Rob Nixon's slow violence). From this meditation, it moves into an analysis of texts (by Sonia Sotomayor, Tato Laviera, Virginia Grise and Irma Mayorga, and ire'ne lara silva) that simultaneously critique the social conditions that give rise to diabetes caseloads in Latinx communities and that reject the stigma associated with a diabetes diagnosis.
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J. Robinson, Andrew, Richard L. Darley e Alex Tonks. "Reactive Oxygen Species and Metabolic Re-Wiring in Acute Leukemias". In Acute Leukemias. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.94829.
Abstract (sommario):
Reactive oxygen species (ROS) is the collective term for several oxygen containing free radicals, such as hydrogen peroxide. ROS is important in innate immunity, protein folding in the endoplasmic reticulum and as a cell signalling molecule involved in cellular proliferation, survival, differentiation, and gene expression. ROS has been implicated in both hematopoietic stem cell quiescence and hematopoietic differentiation. Consequently, ROS is of considerable interest as a therapeutic target, with both pro-oxidant and anti-oxidant cellular modulation being explored. Recently, it has been established that increased ROS production in acute myeloid leukemia (AML) leads to increased glycolysis and metabolic reprogramming. It is often stated as a key tenet of the Warburg effect, that transformed cells, including AML, show increased aerobic glycolysis accompanied by increased cellular glucose uptake and lactate secretion. This review will summarize ROS state of the art in acute leukemia and how these reactive molecules re-wire metabolism in cancer cells. The review will focus on what are ROS? What are the sources of ROS in hematopoietic cells and their function and how this relates to the Warburg effect and regulation of metabolic pathways in acute leukemias.
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María Curieses Andrés, Celia, José Manuel Pérez de la Lastra, Celia Andrés Juan, Francisco J. Plou e Eduardo Pérez-Lebeña. "Reactivity and Applications of Singlet Oxygen Molecule". In Reactive Oxygen Species: Advances and Developments [Working Title]. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.112024.
Abstract (sommario):
Reactive oxygen species (ROS) are molecules produced in living organisms, in the environment, and in various chemical reactions. The main species include, among others, singlet oxygen (1O2), the superoxide anion radical (•O2−), the hydroxyl radical (HO•), and the hydroperoxyl radical (HOO•). In general, the reactivity of 1O2 is lower than that of HO• but even higher than that of •O2−. Singlet oxygen is the lowest energy excited state of molecular oxygen, but it is also a highly reactive species, which can initiate oxidation reactions of biomolecules such as amino acids, proteins, nucleic acids, and lipids, either by a direct reaction or by the induction of ROS. Singlet oxygen is a highly reactive electrophilic species that reacts with electron-rich molecules and is related to several types of pathologies. To inhibit the oxidation of biomolecules with this species, some substances act as antioxidants by performing a quenching effect. In this chapter, aspects such as its physicochemical properties, methods of generation and detection, as well as the reactivity of this molecule are detailed.
Atti di convegni sul tema "HOx and RO2 radicals":
1
Barari, Ghazal, Batikan Koroglu, Artëm E. Masunov e Subith Vasu. "Combustion of Aldehydes in the Negative Temperature Coefficient Region: Products and Pathways". In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-58025.
Abstract (sommario):
Aldehydes are major intermediates in oxidation and pyrolysis of hydrocarbons and particularly biofuels. While the high temperature oxidation chemistry of C3-C5 aldehydes have been studied in the literature, a comprehensive low temperature kinetics remains unaddressed. In this work, acetaldehyde, propanal, and 2-propenal (acrolein) oxidation was investigated at low-temperature combustion condition (500–700 K). The isomer specific products concentrations as well as the time-resolved profiles were studied using Sandia’s multiplexed photoionization mass spectroscopy (MPIMS) with synchrotron radiation from the Advanced Light Source (ALS). The laser pulsed photolysis generates chlorine atoms which react with aldehydes to form the parent radicals. In the presence of excess oxygen, these radicals react with O2 and form RO2 radicals. The temperature dependent products yields are determined for 500 K to 700 K and the competition between the channels contributing to the formation of each product is discussed. In acetaldehyde oxidation, the formation of the main products are associated with HO2 elimination channel from QOOH or direct H atom elimination from the parent radicals. In propanal oxidation, the most intensive signal peak was associated with acetaldehyde (m/z=44) which was formed through the reaction of α′-R with O2. α′-RO2 intermediate decomposes to acetaldehyde+OH+CO via Waddington mechanism and formation of five-member ring transition state. In 2-propenal oxidation, the unsaturated radical produced from α-R reacts with O2 to form the primary products.
2
Brumfield, Brian, Naoki Kurimoto, Xueliang Yang, Tomoya Wada, Pascal Diévart, Yiguang Ju e Gerard Wysocki. "In-situ diagnostics of HOx Radicals in Low- and Intermediate-Temperature Oxidation of Dimethyl Ether". In Optical Instrumentation for Energy and Environmental Applications. Washington, D.C.: OSA, 2014. http://dx.doi.org/10.1364/e2.2014.ew4a.2.
3
Takeuchi, Nobuo, Hiroshi Masusaki e Wu Shang-Qian. "Study On Stratospheric Trace Gas Measurement By 1.4 μm Laser Heterodyne Technique". In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/orsa.1991.owe5.
Abstract (sommario):
Trace gases are important in determining the dynamics, photochemistry, and radiation in the stratosphere. Water vapor1,2) is one of them. Its mixing ratio decreases with height up to the tropopause due to the saturation. The source of stratospheric water vapor is supposed mainly through the tropopause in the tropics region. The extraordinary dryness is a characteristic feature of the stratosphere. Its increase affects the global warming phenomena, and it also has a role as a source of stratospheric HOx radicals. In spite of importance, the behavior of water vapor is not sufficiently known. Global aspect will be clarified by UARS and EOS missions in addition to the currently operating SAGE sensor. Here we investigated the possibility of a compact, high sensitive laser heterodyne sensor (LHS) using a room-temperature operating laser diode (LD) in the near infrared (1.4 μm) region as the local oscillator. As well known, the diffraction limits the throughput of the available incident light power, which is unfavorable to shorter wavelength. However, the compactness and easy handling of a room-temperature operating LD prevails over the disadvantage, and may realize a compact low power-consumption balloon-borne/satellite-borne sensor.
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McCoy, Bernard, Peter MacInnes, Diogenes Angelidis, Robert Collins, Julio Sosa e Zain Rauf. "Optimizing Deepwater Rig Operations With Advanced Remotely Operated Vehicle Technology". In Offshore Technology Conference. OTC, 2021. http://dx.doi.org/10.4043/30970-ms.
Abstract (sommario):
Abstract In order for capital-intensive deepwater prospects to remain at investment grade potential, it is important the industry achieve meaningful improvement in capital efficiency. Achieving this goal will require a multi-faceted strategy in which advanced new technology and digital transformation will play a determining role. This paper will address the optimization of rig operations through deployment of an advanced Remotely Operated Vehicle (ROV) system that leverages precision robotics and automation technologies; reducing total cost of ownership (TCO) through increased rig productivity, operational certainty and overall utilization. Current ROV technology faces several key limitations which contribute to both schedule and cost variation. These inefficiencies are a combination of human skill variance, ROV system limitations and reliability. Advanced ROV systems have been deployed on two deepwater rigs to demonstrate that machine vision and precision robotics technologies will radically improve the predictability and efficiency of operations. Comprehensive metrics addressing safety, budget impact, cost avoidance & reduction, inventory reduction & non price TCO have been developed to capture the efficiencies and identify the net improvement to drilling and completion operations and yield outcome-based performance. An overview of the key deficiencies and limitations of legacy ROV operations will be conveyed, focusing on; i) High dependency on ROV pilot subsea task skills, ii) Worksite efficiency and ROV availability, iii) Restricted tooling capabilities per dive, iv) Rental tooling logistics and cost, v) Equipment reliability at depth, vi) Inefficient tooling changes, and vii) Dive duration and lost time efficiency launch/recovery time. An overview of how the advanced ROV system resolves these issues will be explained. In addition, an explanation of the productivity metrics will be conveyed, supported with data from the active offshore projects. Key conclusions from the data identify that enhanced robotics will achieve the objectives of i) Reducing schedule and cost risks which improve total cost of ownership, ii) Enhancing capability and improved wellsite efficiency, and iii) Increasing subsea data. The performance issues of legacy ROV operations and associated project cost impact is currently not widely recognized by the offshore drilling community. The realized limitations of such ROV operations and lack of useful performance metrics to identify non-productive time will be explained. The progression in robotic design that drives a new era of subsea robotic efficiency will be conveyed with results from offshore operations, combined with robust metrics that enable significant operational value and cost savings to be attained.
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Menkhoff, Thomas, e Gopalakrishnan Surianarayanan. "How Singapore’s Manufacturing Small and Medium Size Enterprises Embrace Industry 4.0". In 14th International Conference on Applied Human Factors and Ergonomics (AHFE 2023). AHFE International, 2023. http://dx.doi.org/10.54941/ahfe1003516.
Abstract (sommario):
Industry 4.0 adoption is expected to profoundly impact the entire spectrum of industries, especially in manufacturing. By using a confluence of automation, data, and digitalisation, Industry 4.0 aims to radically transform how organisations operate presently while increasing productivity, enhancing flexibility, reducing costs, and improving efficiency. More companies are strategically embracing Industry 4.0 approaches to leverage opportunities arising from newly connected computers and increasingly autonomous automation systems (e.g., robotics), equipped with intelligent machine learning algorithms that control the robotics without much human input. In these 'smart' factories, cyber-physical systems (i.e., independently operating systems that self-optimize and communicate with each other, and ultimately optimize production) monitor the physical manufacturing processes and play an increasingly important role in terms of decision-making. Industry 4.0 signifies three mutually interconnected factors, namely digitisation and integration of any technical-economic networks, digitisation of products and services, and new market models. At the core of this new smart manufacturing paradigm is the Internet of Things that drives the conversion of traditional factories into a 'smart' manufacturing environment called "Industry 4.0", resulting in an increasingly intelligent, connected, and autonomous factory with dynamic capabilities. Smart manufacturing technologies include big data processing, machine learning, advanced robotics, cloud computing, sensors technology, additive manufacturing, and augmented reality. By using predictive big data analytics, deep learning, or sentiment/image analysis, business leaders can identify patterns and trends in vast reams of big data. It allows them to make 'smarter' decisions (e.g., about the loss of customers or the necessary service inspection of equipment) and potentially to become more competitive in real-time. Based on case study research on small manufacturing firms in Singapore, we explore how local SMEs adopt Industry 4.0 solutions. We shed light on the drivers and barriers of Industry 4.0 adoption to better understand current business dynamics, potential human issues, focus areas, and initiatives to smoothen this implementation. The study is part of a wider Industry 4.0 study of key specialists and decision-makers across Government agencies, Institutes of Higher Learnings, suppliers of Industry 4.0 technology, business associations, etc. Technology push by the Government with robust funding and training support, skilled labour shortages including imported labour dependence, productivity issues and the pressure to innovate business models due to increased competition are propelling SMEs to adopt Industry 4.0. Some challenges include high investment costs, ROI concerns as well as capability and mindset issues. The paper contributes to the minimal Asian management literature about Industry 4.0 matters in Asian SMEs.
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Roberts, Bryony, Lindsay Harkema e Lori Brown. "Spatializing Reproductive Justice". In 112th ACSA Annual Meeting. ACSA Press, 2024. http://dx.doi.org/10.35483/acsa.am.112.42.
Abstract (sommario):
Coined in 1994 by a caucus of Black women activists, reproductive justice is the “human right to maintain personal bodily autonomy, have children, not have children, and parent the children we have in safe and sustainable communities”.1 After the overturn of Roe v. Wade, access to reproductive healthcare is radically restricted across the U.S., compounding systemic race, gender, and class-based inequities that have always made healthcare inaccessible for many. The landmark Dobbs v. Jackson Women’s Health Organization decision in 2022 rolled back nearly 50 years of reproductive rights protections and unleashed a plethora of laws that make it more difficult to access reproductive health care, riskier to assist those seeking care, and precarious to teach about issues of race, gender, and sexuality. As stated in the dissenting opinion by Justices Breyer, Sotomayor, and Kagan, “Whatever the exact scope of the coming laws, one result of today’s decision is certain: the curtailment of women’s rights, and of their status as free and equal citizens.”2 In the U.S. today, bodily autonomy and academic freedom are geographically situated. Within this context of curtailed freedoms, architects and educators must confront the spatial realities of these restrictions. New dialogues must emerge at architecture’s intersectional edges – between designers, activists, social justice advocates, legal experts, public health practitioners, and students – to explore how the built environment can better support human lives.