Добірка наукової літератури з теми "NOx precursors"
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Статті в журналах з теми "NOx precursors"
1
Xu, Liting, Qilei Yang, Lihua Hu, Dong Wang, Yue Peng, Zheru Shao, Chunmei Lu, and Junhua Li. "Insights over Titanium Modified FeMgOx Catalysts for Selective Catalytic Reduction of NOx with NH3: Influence of Precursors and Crystalline Structures." Catalysts 9, no. 6 (June 24, 2019): 560. http://dx.doi.org/10.3390/catal9060560.
Повний текст джерелаАнотація:
Titanium modified FeMgOx catalysts with different precursors were prepared by coprecipitation method with microwave thermal treatment. The iron precursor is a key factor affecting the surface active component. The catalyst using FeSO4 and Mg(NO3)2 as precursors exhibited enhanced catalytic activity from 225 to 400 °C, with a maximum NOx conversion of 100%. Iron oxides existed as γ-Fe2O3 in this catalyst. They exhibited highly enriched surface active oxygen and surface acidity, which were favorable for low-temperature selective catalytic reduction (SCR) reaction. Besides, it showed advantage in surface area, spherical particle distribution and pores connectivity. Amorphous iron-magnesium-titanium mixed oxides were the main phase of the catalysts using Fe(NO3)3 as a precursor. This catalyst exhibited a narrow T90 of 200/250–350 °C. Side reactions occurred after 300 °C producing NOx, which reduced the NOx conversion. The strong acid sites inhibited the side reactions, and thus improved the catalytic performance above 300 °C. The weak acid sites appeared below 200 °C, and had a great impact on the low-temperature catalytic performance. Nevertheless, amorphous iron-magnesium-titanium mixed oxides blocked the absorption and activation between NH3 and the surface strong acid sites, which was strengthened on the γ-Fe2O3 surface.
2
Morin, S., R. Sander та J. Savarino. "Simulation of the diurnal variations of the oxygen isotope anomaly (Δ<sup>17</sup>O) of reactive atmospheric species". Atmospheric Chemistry and Physics Discussions 10, № 12 (14 грудня 2010): 30405–51. http://dx.doi.org/10.5194/acpd-10-30405-2010.
Повний текст джерелаАнотація:
Abstract. The isotope anomaly (Δ17O) of secondary atmospheric species such as nitrate (NO3−) or hydrogen peroxyde (H2O2) has potential to provide useful constrains on their formation pathways. Indeed, the Δ17O of their precursors (NOx, HOx etc.) differs and depends on their interactions with ozone, which is the main source of non-zero Δ17O in the atmosphere. Interpreting variations of Δ17O in secondary species requires an in-depth understanding of the Δ17O of their precursors taking into account non-linear chemical regimes operating under various environmental settings. We present results from numerical simulations carried out using the atmospheric chemistry box model (CAABA/MECCA) to explicitly compute the diurnal variations of the isotope anomaly of short-lived species such as NOx and HOx. Δ17O was propagated from ozone to other species (NO, NO2, OH, HO2, RO2, NO3, N2O5, HONO, HNO3, HNO4, H2O2) according to the classical mass-balance equation, through the implementation of various sets of hypotheses pertaining to the transfer of Δ17O during chemical reactions. The model confirms that diurnal variations in Δ17O of NOx are well predicted by the photochemical steady-state relationship during the day, but that at night a different approach must be employed (i.e. "fossilization" of the Δ17O of NOx as soon as the photolytical lifetime of NOx drops below ca. 5 min). We quantify the diurnally-integrated isotopic signature (DIIS) of sources of atmospheric nitrate and H2O2 under the various environmental conditions analyzed, which is of particular relevance to larger-scale implementations of Δ17O where high computational costs cannot be afforded.
3
SINHA, PRIYANKA, Siddharth Singh, and POOJA SAROJ. "Relationship of Surface Ozone (O3) with its precursors and meteorological parameters over New Delhi, India." MAUSAM 73, no. 4 (September 30, 2022): 829–42. http://dx.doi.org/10.54302/mausam.v73i4.5510.
Повний текст джерелаАнотація:
In the present study, continuous measurements of Surface Ozone (O3), Oxides of Nitrogen (NOx (NO+ NO2)), and carbon monoxide (CO), monitored at five different locations in Delhi National Capital Region have been studied for the period 2013 – 2019. The five monitoring locations used are namely IMD Lodi Road, IGI Airport Palam, CV Raman Dheerpur, CRRI Mathura Road, and NCMRWF Noida. The average hourly concentration of O3, NO, NO2, CO, NOx (NO + NO2), and OX(NO2 +O3) are found in the range of 32.44 ppb to 36.57 ppb, 19.46 to 28.09 ppb, 20.83 to 26.89 ppb,1.67 to 1.89 ppm,43.04 to 54.99 ppb, and 54.06 to 60.99 ppb respectively during the study period. Diurnal variation of NOx and CO Concentrations show higher values during the morning (0600-0900h) and late evening (1900-2400h) hours while the highest concentrations of ozone have been observed during afternoon hours. The relationship between NO, NO2, and surface O3 as a function of NOx has also been examined during daylight hours (0500hrs IST to 1900 hrs IST) and chemical coupling of the three species i.e. NO, NO2 and O3 have been studied. The ground-level concentration of Ozone has been found to decrease with increasing NOx concentration during the daytime. The variations in concentrations of oxidants (NO2 + O3) with the concentration of [NOx] have been studied to examine the contributing pollution sources of oxidants at all the study sites. The average rate of change of O3 concentrations (dO3/dt) has been examined at all five locations. The monthly and diurnal variation of oxidants [OX] at all the study locations has shown a strong positive correlation with temperature whereas a negative correlation with humidity.
4
Wang, Yujue, Min Hu, Yuchen Wang, Jing Zheng, Dongjie Shang, Yudong Yang, Ying Liu, et al. "The formation of nitro-aromatic compounds under high NO<sub><i>x</i></sub> and anthropogenic VOC conditions in urban Beijing, China." Atmospheric Chemistry and Physics 19, no. 11 (June 7, 2019): 7649–65. http://dx.doi.org/10.5194/acp-19-7649-2019.
Повний текст джерелаАнотація:
Abstract. Nitro-aromatic compounds (NACs), as important contributors to the light absorption by brown carbon, have been widely observed in various ambient atmospheres; however, their formation in the urban atmosphere was little studied. In this work, we report an intensive field study of NACs in summer 2016 at an urban Beijing site, characterized by both high-NOx and anthropogenic VOC dominated conditions. We investigated the factors that influence NAC formation (e.g., NO2, VOC precursors, RH and photolysis) through quantification of eight NACs, along with major components in fine particulate matter, selected volatile organic compounds, and gases. The average total concentration of the quantified NACs was 6.63 ng m−3, higher than those reported in other summertime studies (0.14–6.44 ng m−3). 4-Nitrophenol (4NP, 32.4 %) and 4-nitrocatechol (4NC, 28.5 %) were the top two most abundant NACs, followed by methyl-nitrocatechol (MNC), methyl-nitrophenol (MNP), and dimethyl-nitrophenol (DMNP). The oxidation of toluene and benzene in the presence of NOx was found to be a more dominant source of NACs than primary biomass burning emissions. The NO2 concentration level was found to be an important factor influencing the secondary formation of NACs. A transition from low- to high-NOx regimes coincided with a shift from organic- to inorganic-dominated oxidation products. The transition thresholds were NO2 ∼ 20 ppb for daytime and NO2∼25 ppb for nighttime conditions. Under low-NOx conditions, NACs increased with NO2, while the NO3- concentrations and (NO3-)/NACs ratios were lower, implying organic-dominated products. Under high-NOx conditions, NAC concentrations did not further increase with NO2, while the NO3- concentrations and (NO3-)/NACs ratios showed increasing trends, signaling a shift from organic- to inorganic-dominated products. Nighttime enhancements were observed for 3M4NC and 4M5NC, while daytime enhancements were noted for 4NP, 2M4NP, and DMNP, indicating different formation pathways for these two groups of NACs. Our analysis suggested that the aqueous-phase oxidation was likely the major formation pathway of 4M5NC and 3M5NC, while photo-oxidation of toluene and benzene in the presence of NO2 could be more important for the formation of nitrophenol and its derivatives. Using the (3M4NC+4M5NC) ∕ 4NP ratios as an indicator of the relative contribution of aqueous-phase and gas-phase oxidation pathways to NAC formation, we observed that the relative contribution of aqueous-phase pathways increased at elevated ambient RH and remained constant at RH > 30 %. We also found that the concentrations of VOC precursors (e.g., toluene and benzene) and aerosol surface area acted as important factors in promoting NAC formation, and photolysis as an important loss pathway for nitrophenols.
5
Holland, Rayne, Katya Seifert, Eric Saboya, M. Anwar H. Khan, Richard G. Derwent, and Dudley E. Shallcross. "Elucidating the Effects of COVID-19 Lockdowns in the UK on the O3-NOx-VOC Relationship." Atmosphere 15, no. 5 (May 16, 2024): 607. http://dx.doi.org/10.3390/atmos15050607.
Повний текст джерелаАнотація:
The unprecedented reductions in anthropogenic emissions over the COVID-19 lockdowns were utilised to investigate the response of ozone (O3) concentrations to changes in its precursors across various UK sites. Ozone, volatile organic compounds (VOCs) and NOx (NO+NO2) data were obtained for a 3-year period encompassing the pandemic period (January 2019–December 2021), as well as a pre-pandemic year (2017), to better understand the contribution of precursor emissions to O3 fluctuations. Compared with pre-lockdown levels, NO and NO2 declined by up to 63% and 42%, respectively, over the lockdown periods, with the most significant changes in pollutant concentrations recorded across the urban traffic sites. O3 levels correspondingly increased by up to 30%, consistent with decreases in the [NO]/[NO2] ratio for O3 concentration response. Analysis of the response of O3 concentrations to the NOx reductions suggested that urban traffic, suburban background and suburban industrial sites operate under VOC-limited regimes, while urban background, urban industrial and rural background sites are NOx-limited. This was in agreement with the [VOC]/[NOx] ratios determined for the London Marylebone Road (LMR; urban traffic) site and the Chilbolton Observatory (CO; rural background) site, which produced values below and above 8, respectively. Conversely, [VOC]/[NOx] ratios for the London Eltham (LE; suburban background) site indicated NOx-sensitivity, which may suggest the [VOC]/[NOx] ratio for O3 concentration response may have had a slight NOx-sensitive bias. Furthermore, O3 concentration response with [NO]/[NO2] and [VOC]/[NOx] were also investigated to determine their relevance and accuracy in identifying O3-NOx-VOC relationships across UK sites. While the results obtained via utilisation of these metrics would suggest a shift in photochemical regime, it is likely that variation in O3 during this period was primarily driven by shifts in oxidant (OX; NO2 + O3) equilibrium as a result of decreasing NO2, with increased O3 transported from Europe likely having some influence.
6
Morin, S., R. Sander та J. Savarino. "Simulation of the diurnal variations of the oxygen isotope anomaly (Δ<sup>17</sup>O) of reactive atmospheric species". Atmospheric Chemistry and Physics 11, № 8 (19 квітня 2011): 3653–71. http://dx.doi.org/10.5194/acp-11-3653-2011.
Повний текст джерелаАнотація:
Abstract. The isotope anomaly (Δ17O) of secondary atmospheric species such as nitrate (NO3−) or hydrogen peroxide (H2O2) has potential to provide useful constrains on their formation pathways. Indeed, the Δ17O of their precursors (NOx, HOx etc.) differs and depends on their interactions with ozone, which is the main source of non-zero Δ17O in the atmosphere. Interpreting variations of Δ17O in secondary species requires an in-depth understanding of the Δ17O of their precursors taking into account non-linear chemical regimes operating under various environmental settings. This article reviews and illustrates a series of basic concepts relevant to the propagation of the Δ17O of ozone to other reactive or secondary atmospheric species within a photochemical box model. We present results from numerical simulations carried out using the atmospheric chemistry box model CAABA/MECCA to explicitly compute the diurnal variations of the isotope anomaly of short-lived species such as NOx and HOx. Using a simplified but realistic tropospheric gas-phase chemistry mechanism, Δ17O was propagated from ozone to other species (NO, NO2, OH, HO2, RO2, NO3, N2O5, HONO, HNO3, HNO4, H2O2) according to the mass-balance equations, through the implementation of various sets of hypotheses pertaining to the transfer of Δ17O during chemical reactions. The model results confirm that diurnal variations in Δ17O of NOx predicted by the photochemical steady-state relationship during the day match those from the explicit treatment, but not at night. Indeed, the Δ17O of NOx is "frozen" at night as soon as the photolytical lifetime of NOx drops below ca. 10 min. We introduce and quantify the diurnally-integrated isotopic signature (DIIS) of sources of atmospheric nitrate and H2O2, which is of particular relevance to larger-scale simulations of Δ17O where high computational costs cannot be afforded.
7
Cheng, Shan, Kehui Yao, Hong Tian, Ting Yang, and Lianghui Chen. "Synergistic Catalytic Effects on Nitrogen Transformation during Biomass Pyrolysis: A Focus on Proline as a Model Compound." Molecules 29, no. 13 (June 30, 2024): 3118. http://dx.doi.org/10.3390/molecules29133118.
Повний текст джерелаАнотація:
To investigate the control mechanisms of NOx precursors and the synergistic effects of composite catalysts during proline pyrolysis, a systematic series of experiments was conducted utilizing composite catalysts with varying Fe-Ca ratios. Product distribution analysis was employed to elucidate the catalysts’ mechanisms in reducing NOx precursor emissions. The synergistic interactions between Fe and Ca were quantitatively assessed through comparative theoretical and experimental release calculations. The results indicate that an increase in the Fe content in the catalyst led to a rise in amine concentrations from 0.9% to 2.95%, implying that Fe facilitates the generation of amine-N through ring-opening and substitution reactions. When the Fe to Ca ratio was balanced at 1:1, nitrogen predominantly participated in the formation of purines via cyclization and substitution reactions. Additionally, all composite catalysts exhibited a suppressive effect on the release of NOx precursors, attributed to their significant enhancement of solid product retention. Fe-Ca composite catalyst synergistically inhibits the release of gaseous nitrogen. Notably, the strongest synergistic effect was observed with a 1:3 Fe to Ca ratio, which reduced the release of NH3 by 38.7% and HCN by 53.6% during proline pyrolysis. This study offers valuable insights into the control of NOx precursors and the optimization of nitrogen-rich biomass pyrolysis processes.
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Marais, E. A., D. J. Jacob, J. L. Jimenez, P. Campuzano-Jost, D. A. Day, W. Hu, J. Krechmer, et al. "Aqueous-phase mechanism for secondary organic aerosol formation from isoprene: application to the Southeast United States and co-benefit of SO<sub>2</sub> emission controls." Atmospheric Chemistry and Physics Discussions 15, no. 21 (November 13, 2015): 32005–47. http://dx.doi.org/10.5194/acpd-15-32005-2015.
Повний текст джерелаАнотація:
Abstract. Isoprene emitted by vegetation is an important precursor of secondary organic aerosol (SOA), but the mechanism and yields are uncertain. Aerosol is prevailingly aqueous under the humid conditions typical of isoprene-emitting regions. Here we develop an aqueous-phase mechanism for isoprene SOA formation coupled to a detailed gas-phase isoprene oxidation scheme. The mechanism is based on aerosol reactive uptake probabilities (γ) for water-soluble isoprene oxidation products, including sensitivity to aerosol acidity and nucleophile concentrations. We apply this mechanism to simulation of aircraft (SEAC4RS) and ground-based (SOAS) observations over the Southeast US in summer 2013 using the GEOS-Chem chemical transport model. Emissions of nitrogen oxides (NOx ≡ NO + NO2) over the Southeast US are such that the peroxy radicals produced from isoprene oxidation (ISOPO2) react significantly with both NO (high-NOx pathway) and HO2 (low-NOx pathway), leading to different suites of isoprene SOA precursors. We find a mean SOA mass yield of 3.3 % from isoprene oxidation, consistent with the observed relationship of OA and formaldehyde (a product of isoprene oxidation). The yield is mainly contributed by two immediate gas-phase precursors, isoprene epoxydiols (IEPOX, 58 % of isoprene SOA) from the low-NOx pathway and glyoxal (28 %) from both low- and high-NOx pathways. This speciation is consistent with observations of IEPOX SOA from SOAS and SEAC4RS. Observations show a strong relationship between IEPOX SOA and sulfate aerosol that we explain as due to the indirect effect of sulfate on aerosol acidity and volume, rather than a direct mechanistic role for sulfate. Isoprene SOA concentrations increase as NOx emissions decrease (favoring the low-NOx pathway for isoprene oxidation), but decrease as SO2 emissions decrease (due to the effect of sulfate on aerosol acidity and volume). The US EPA projects 2013–2025 decreases in anthropogenic emissions of 34 % for NOx (leading to 7 % increase in isoprene SOA) and 48 % for SO2 (35 % decrease in isoprene SOA). The combined projected decreases in NOx and SO2 emissions reduce isoprene SOA yields from 3.3 to 2.3 %. Reducing SO2 emissions decreases sulfate and isoprene SOA by a similar magnitude, representing a factor of 2 co-benefit for PM2.5 from SO2 emission controls.
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Schroeder, Jason R., Chenxia Cai, Jin Xu, David Ridley, Jin Lu, Nancy Bui, Fang Yan, and Jeremy Avise. "Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period." Atmospheric Chemistry and Physics 22, no. 19 (October 10, 2022): 12985–3000. http://dx.doi.org/10.5194/acp-22-12985-2022.
Повний текст джерелаАнотація:
Abstract. The South Coast Air Basin (SoCAB), which includes the city of Los Angeles and is home to more than 15 million people, frequently experiences ozone (O3) levels that exceed ambient air quality standards. While strict regulation of O3 precursors has dramatically improved air quality over the past 50 years, the region has seen limited improvement in O3 over the past decade despite continued reductions in precursor emissions. One contributing factor to the recent lack of improvement is a gradual transition of the underlying photochemical environment from a VOC-limited regime (where VOC denotes volatile organic compound) towards an NOx-limited one. The changes in human activity prompted by COVID-19-related precautions in spring and summer of 2020 exacerbated these existing changes in the O3 precursor environment. Analyses of sector-wide changes in activity indicate that emissions of NOx decreased by 15 %–20 % during spring (April–May) and by 5 %–10 % during summer (June–July) relative to expected emissions for 2020, largely due to changes in mobile-source activity. Historical trend analysis from two indicators of O3 sensitivity (the satellite HCHO/NO2 ratio and the O3 weekend/weekday ratio) revealed that spring of 2020 was the first year on record to be on average NOx-limited, while the “transitional” character of recent summers became NOx-limited due to COVID-19-related NOx reductions in 2020. Model simulations performed with baseline and COVID-19-adjusted emissions capture this change to an NOx-limited environment and suggest that COVID-19-related emission reductions were responsible for a 0–2 ppb decrease in O3 over the study period. Reaching NOx-limited territory is an important regulatory milestone, and this study suggests that deep reductions in NOx emissions (in excess of those observed in this study) would be an effective pathway toward long-term O3 reductions.
10
Marais, E. A., D. J. Jacob, J. L. Jimenez, P. Campuzano-Jost, D. A. Day, W. Hu, J. Krechmer, et al. "Aqueous-phase mechanism for secondary organic aerosol formation from isoprene: application to the southeast United States and co-benefit of SO<sub>2</sub> emission controls." Atmospheric Chemistry and Physics 16, no. 3 (February 11, 2016): 1603–18. http://dx.doi.org/10.5194/acp-16-1603-2016.
Повний текст джерелаАнотація:
Abstract. Isoprene emitted by vegetation is an important precursor of secondary organic aerosol (SOA), but the mechanism and yields are uncertain. Aerosol is prevailingly aqueous under the humid conditions typical of isoprene-emitting regions. Here we develop an aqueous-phase mechanism for isoprene SOA formation coupled to a detailed gas-phase isoprene oxidation scheme. The mechanism is based on aerosol reactive uptake coefficients (γ) for water-soluble isoprene oxidation products, including sensitivity to aerosol acidity and nucleophile concentrations. We apply this mechanism to simulation of aircraft (SEAC4RS) and ground-based (SOAS) observations over the southeast US in summer 2013 using the GEOS-Chem chemical transport model. Emissions of nitrogen oxides (NOx ≡ NO + NO2) over the southeast US are such that the peroxy radicals produced from isoprene oxidation (ISOPO2) react significantly with both NO (high-NOx pathway) and HO2 (low-NOx pathway), leading to different suites of isoprene SOA precursors. We find a mean SOA mass yield of 3.3 % from isoprene oxidation, consistent with the observed relationship of total fine organic aerosol (OA) and formaldehyde (a product of isoprene oxidation). Isoprene SOA production is mainly contributed by two immediate gas-phase precursors, isoprene epoxydiols (IEPOX, 58 % of isoprene SOA) from the low-NOx pathway and glyoxal (28 %) from both low- and high-NOx pathways. This speciation is consistent with observations of IEPOX SOA from SOAS and SEAC4RS. Observations show a strong relationship between IEPOX SOA and sulfate aerosol that we explain as due to the effect of sulfate on aerosol acidity and volume. Isoprene SOA concentrations increase as NOx emissions decrease (favoring the low-NOx pathway for isoprene oxidation), but decrease more strongly as SO2 emissions decrease (due to the effect of sulfate on aerosol acidity and volume). The US Environmental Protection Agency (EPA) projects 2013–2025 decreases in anthropogenic emissions of 34 % for NOx (leading to a 7 % increase in isoprene SOA) and 48 % for SO2 (35 % decrease in isoprene SOA). Reducing SO2 emissions decreases sulfate and isoprene SOA by a similar magnitude, representing a factor of 2 co-benefit for PM2.5 from SO2 emission controls.
Дисертації з теми "NOx precursors"
1
Choi, Yunsoo. "Spring to summer transitions of ozone and its precursors over North America and photochemistry over Antarctica." Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-06262007-144619/.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2008.Cunnold, Derek, Committee Member ; Nenes, Athanasios, Committee Member ; Black, Robert, Committee Member ; Russell, Armistead (Ted), Committee Member ; Wang, Yuhang, Committee Chair.
2
Bertus, Thomas. "Devenir de l'azote lors de la combustion de biomasse dans le lit d'une chaudière à grille." Electronic Thesis or Diss., Ecole nationale des Mines d'Albi-Carmaux, 2024. http://www.theses.fr/2024EMAC0013.
Повний текст джерелаАнотація:
La combustion de biomasse dans des chaudières industrielles à grille produit plusieurs espèces polluantes dont les oxydes d'azote, aussi appelés NOx. Ces molécules sont nocives pour l'environnement (causes de pluies acides, gaz à effet de serre). Ces polluants sont majoritairement formés par l'oxydation de l'azote initialement contenu dans la biomasse. La limitation de leurs émissions est donc un enjeu important dans le domaine de la combustion de biomasse. Pour y parvenir, le recours à la modélisation est courant. La chimie de l'azote en phase gaz est bien connue ; la modélisation du devenir de l'azote dans la phase gaz au-dessus du lit ne pose donc pas de problème. En revanche, les phénomènes régissant la combustion hétérogène du lit de biomasse restent mal connus. Cela se traduit par une mauvaise prédiction de la forme de l'azote en sortie de lit. L'objectif de cette thèse est alors de proposer un modèle de lit permettant de fournir des données d'entrée fiables à un modèle numérique de chaudière ne simulant que la phase gaz. Pour ce faire, un modèle a été développé sur MATLAB à partir du code BASIC développé par l'Université de Aalborg. Ce modèle de lit est un modèle de type 1D Euler-Euler pouvant modéliser le lit d'une chaudière biomasse via l'approche de la colonne mobile. La chimie de l'azote a été ajoutée à ce modèle et un modèle à deux températures a également été implémenté. Pour confronter le modèle, des expériences en lit fixe traversé ont été réalisées. Pour cela, un dispositif expérimental existant a été adapté afin de pouvoir quantifier l'azote dans les différents produits de la combustion. Trois séries d'expériences ont été réalisées sur ce dispositif expérimental. La première consistait à comparer le devenir de l'azote de trois agrocombustibles lors de leur pyrolyse et de leur combustion. La deuxième série consistait en une étude paramétrique sur l'influence de la taille des particules et de la température de combustion sur les émissions de NOx lors de la combustion de panneaux de particules. La troisième série est une étude de l'influence du traitement chimique de panneaux de particules sur les émissions de NOx lors d'une pyrolyse ou d'une combustion. Les résultats des expériences en lit fixe traversé ont permis de caler certains paramètres cinétiques du modèle 1D. Le modèle développé constitue une première étape dans la modélisation des émissions d'espèces azotées lors de la combustion d'un lit de biomasseBiomass combustion in industrial-scale biomass grate-fired boilers produces several types of pollutants, including nitrogen oxides. These species, also known as NOx, are harmful to the environment because they cause acid rain and are greenhouse gases. These pollutants are mostly formed by the oxidation of the nitrogen that was initially present in the biomass. NOx emissions are a primary concern for biomass boiler manufacturers. Modeling is a great help in reducing NOx emissions. The gas phase chemistry of nitrogen is well known so gas phase reactions involving NOx species above the bed are not a problem. However, the chemistry governing the heterogeneous combustion of the fuel bed remains poorly understood. In particular, the nature of the nitrogen gases exiting the bed is not accurately predicted. The objective of this work is to provide a bed model capable of predicting the gas phase composition at the exit of the bed, with a particular focus on nitrogen species. To this end, a bed model was developed using MATLAB. This model is based on the BASIC model developed by the University of Aalborg. This is a 1D Euler-Euler bed that employs the walking column approach to simulate a biomass grate-fired boiler bed. Two significant modifications were made to the model: the incorporation of thermal non-equilibrium and the inclusion of nitrogen chemistry. To validate the model, experiments were conducted in a cross-fired fixed bed reactor. An existing experimental device was adapted to enable the quantification of nitrogen in all products. Three series of experiments were conducted. The first series compared the fate of nitrogen of three agrofuels during the pyrolysis and combustion. The second series investigated the influence of particle size and temperature on the fate of nitrogen during particleboard combustion and pyrolysis. The third series focused on the influence of chemical treatment on NOx emissions for three chemically treated particleboards. The results obtained with the experimental setup allowed us to fix some kinetic data for the model. This model represents a first step towards the prediction of nitrogen gas production in a biomass bed
3
Wei, Manqing. "Synthesis of Precursors to Non-isocyanate Polyurethanes." Thesis, North Dakota State University, 2018. https://hdl.handle.net/10365/29167.
Повний текст джерелаАнотація:
Biobased diamines are excellent precursors for the synthesis of non-isocyanate polyurethanes (NIPUs). We have prepared several biobased diamines using three different reactions for their synthesis. In the first method, we have carried out chain elongation of cellulose-derived 2,5-diformylfuran by the Henry reaction followed by reduction of the nitroalkene. Yields of the key step: Hantzsch Ester reduction, were 70-80%. Method two involves the Friedel-Crafts alkylation of furfurylamine with different ketones under acidic conditions. Yields of large-scale alkylation reaction were 60-77%. In method three, we combined the Henry reaction and Friedel-Crafts alkylation techniques to access diamines from hemicellulose-derived furfural. These diamines can be reacted with carbonates to access hydroxyalkylcarbamates in good yields, around 80%. We have also developed a novel method for accessing biscarbamates directly from dialdehydes in good yields, 70-94%. The hydroxyalkylcarbamates and biscarbamates are valuable precursors to obtain polyurethanes via the phosgene-free route.
4
Jiang, Yuan. "Precursor phases in non-classical crystallization." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2011/5246/.
Повний текст джерелаАнотація:
The main objective of this thesis is to understand molecular crystallization as a multistep process with or without polymeric additives, including transient liquid-liquid phase separation, nanocrystal nucleation within the dense phase, and subsequent nanocrystal self-assembly or self-organization in sequence.
The thesis starts with a quaternary model system, containing DL-Glutamic acid (Glu), polyethyleneimine (PEI), water, and EtOH, for the understanding of multistep precipitation of Glu with PEI as an additive. The experiments were performed by mixing Glu-PEI aqueous solution with a non-solvent EtOH. First, the phase diagram of the quaternary system is determined, obtaining precipitate, coacervates, or homogeneous mixtures by varying Glu/PEI w/w and water/EtOH v/v. Coacervation is observed to occur over a wide range of Glu/PEI with various volumes. The composition of coacervates is conveniently characterized by nuclear magnetic resonance spectroscopy. The observed coacervates are thermodynamically stable phases rich in solute, which is different from metastable polymer-induced liquid precursors. The combination of atomic force microscopy, small angle scattering, and ξ-potential measurements confirms the coexistence of monomers and Glu/PEI complexes and the aggregation of complexes in Glu-PEI-water systems. This suggests that there might be a direct structural transformation between the Glu-PEI complexes in aqueous solution and the metastable liquid precursors in a water-EtOH mixture.
The multistep mechanism of Glu precipitation with PEI as an additive is investigated thereafter. The combination of stopped flow and small angle scattering demonstrates that the initially formed liquid precursors pass through an alteration of growth and coalescence. Combined with results from optical microscopy and scanning electron microscopy, the nucleation of nanoplatelets happens within each liquid precursor droplet, and nanoplatelets reorient themselves and self-organize into a radial orientation in the crystalline microspheres.
The recipe was then extended to the precipitation of organics in other oppositely charged amino acid-polyelectrolyte systems.
After the success in preparing hierarchical microspheres in solution, the similar recipe can be extended to the preparation of patterned thin films on substrate. By dipping a quaternary DL-Lys·HCl (Lys)–polyacrylic acid (PAA)–water–EtOH dispersion on a hydrophilic slide, the fast evaporation process of the volatile solvent EtOH is responsible for the homogeneous nucleation of NPs. Then, the following complete evaporation causes the mesocrystallization of a continuous spherulitic thin film along the receding line of the liquid, which again transforms into a mesocrystalline thin film. Furthermore, annealing is used to optimize the property of mesocrystalline thin films. As evaporation is a non-equilibrium process, it can be used to tune the kinetics of crystallization. Therefore, hierarchical or periodical thin films are obtainable by starting the evaporation from microspheres recrystallization, obtaining mesocrystalline thin films with 4 hierarchy levels. The results reveal that evaporation provides an easy but effective way for the formation of patterned structures via the positioning of NPs after their fast nucleation, resulting in different kinds of patterns by controlling the concentration of NPs, solvent evaporation rate, and other physical forces.
Non-classical crystallization is not limited to crystallizations with polymeric additives. We also observed the nucleation and growth of a new molecular layer on the growing DL-Glu·H2O crystals from a supersaturated mother liquor by using an in-situ atomic force microscopy (AFM), where the nucleation and growth of a molecular layer proceed via amorphous nanoparticle (NP) attachment and relaxation process before the observation of the growth of a newly formed molecular layer. NP attachment to the crystal surface is too fast to observe by using in-situ AFM. The height shrinkage of NPs, combined to the structural transformation from 3D amorphous NPs to 2D crystalline layer, is observed during the relaxation process. The nucleation and growth of a newly formed molecular layer from NP relaxation is contradictory to the classical nucleation theory, which hypothesizes that nuclei show the same crystallographic properties as a bulk crystal. The formation of a molecular layer by NP attachment and relaxation rather than attachment of single molecules provides a different picture from the currently held classical nucleation and growth theory regarding the growth of single crystals from solution.Das Hauptziel dieser Arbeit ist das Verständnis der molekularen Kristallisation, sowohl mit als auch ohne polymere Additive, als einen mehrstufigen Prozess. Dieser beinhaltet eine transiente flüssig-flüssig Phasentrennung, die Nukleation von Nanokristallen in der dichten flüssigen Precursor-Phase so wie eine anschließende nanokristalline Selbstorganisation. Die Arbeit beginnt mit Untersuchungen an einem quaternären Modelsystem bestehend aus DL-Glutamat (Glu), Polyethylenimin (PEI), Wasser und Ethanol. Das Phasendiagramm dieses quaternären Systems wird durch Variation der Glu/PEI w/w und Wasser/EtOH v/v Verhältnisse bestimmt, wobei Präzpitat aus polymerinduzierten flüssigen Precursor, Koazervate oder homogene Mischungen erhalten werden Das thermodynamisch stabile Koazervat kann als Referenz für das Verständnis von flüssigen Precursorn angesehen werden, welche in der Natur metastabil und transient sind. Der mehrstufige Mechanismus der Glu-Präzipitation mit PEI als Additiv wird dann mittels Neutronen Kleinwinkelstreuung untersucht. Dies zeigt, dass die ursprünglich gebildeten flüssigen Precursor noch vor der Nukleation von Nanokristallen einen Wechsel von Wachstum und Koaleszenz durchlaufen. Die Ergebnisse aus optischer- und Eletronenmikroskopie zeigen, dass sowohl die flüssigen Precursor Superstrukturen ausbilden als auch, dass die Nukleation von Nanoplättchen in jedem einzelnen Precursor Tropfen von statten geht. Dies geschieht noch bevor sich die Nanoplättchen selbst in einer radialen Orientierung ausrichten. Diese Studie liefert die Kinetik der Präzipitation von organischen Stoffen in Gegenwart von polymeren Additiven. Eine ähnliche Vorgehensweise wie für die Herstellung von Mikrokügelchen kann für die Darstellung von gemusterten Filmen angewandt werden. Die homogene Nukleation von Nanopartikeln (NPs) findet während der Verdampfung einer quarternären DL-Lys·HCl-Polyacrylsäure-Wasser-Ethanol Dispersion auf einer hydrophilen Oberfläche statt. Die darauffolgende vollständige Verdampfung löst die Mesokristallisation eines kontinuierlichen sphärolithischen dünnen Films aus, welcher sich wiederum in einen mesokristallinen dünnen Film umwandelt. Mesokristalline Filme mit 4 Hierarchiestufen bzw. auch periodische Filme werden durch die Verdampfung der Mikrokügelchen-Dispersion erhalten. Die Ergebnisse zeigen, dass die Verdampfung eine einfache aber effektive Methode zur Herstellung von verschieden gemusterten hierarchischen Filmen darstellt. Nicht-klassische Kristallisation wird auch in der Abwesenheit von polymeren Additiven beobachtet. Wir verfolgen mittels Rasterkraftmikroskop (AFM) die Nukleation und das Wachstum einer neuen molekularen Schicht auf wachsenden DL-Glu·H2O Kristallen aus übersättigter Mutterlauge. Die Bildung einer neuen molekularen Schicht verläuft durch die Anlagerung von amorphen Nanopartikeln. Das Schrumpfen der NPs zusammen mit der strukturellen Änderung von dreidimensionalen NPs zu 2D Schichten wird während dieses Relaxationsprozesses beobachtet. Schließlich kommt es zu der Ausbildung einer neuen molekularen Schicht. Die Bildung einer molekularen Schicht durch die Anlagerung von Nanopartikeln aus der Lösung und die darauffolgende Relaxation liefert ein abweichendes Bild zu der bisher gängigen klassischen Theorie des Kristallwachstums.
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Redshaw, Carl. "Oxo and organoimido precursors for non-aqueous polytungstate synthesis." Thesis, University of Newcastle Upon Tyne, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328135.
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Specchia, Michael. "Precursori non statistici di previsione dei terremoti." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
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I terremoti sono considerati una delle peggiori calamità naturali a causa del loro enorme impatto sulle vite e proprietà. La loro bassa prevedibilità è dovuta alla complessità del fenomeno e dall’impossibilità di accesso all’osservazione diretta della sorgente e dal parametro dello stress che non può essere misurato direttamente. Inoltre, la causalità, l’origine in faglie sconosciute e l’insorgere non sempre costante di eventuali precursori rendono il lavoro ancora più difficile. Di conseguenza, l’elevata incertezza associata alle loro previsioni, nonostante la grande quantità di dati sperimentali, il grandissimo impegno di scienziati e ricercatori e la formulazione di diverse teorie, ancora oggi non si riesce a comprendere a pieno il fenomeno. La prevedibilità si basa sullo studio e sul monitoraggio di precursori sismici, ovvero cambiamenti insoliti nell’intero regime ambientale fisico e chimico su scala regionale antecedenti a un terremoto. Gli studi si concentrano su anomalie di tipo sismico, geodetico, elettromagnetico, idrologico e chimico.
Recenti progressi sono dovuti in gran parte allo sviluppo e al miglioramento di strumenti di rilevazione e monitoraggio che hanno portato ad una maggiore quantità e precisione delle misurazioni.
Al momento la mitigazione dei danni è possibile grazie alla realizzazione di carte di probabilità e l’adozione di misure preventive e di emergenza.
La ricerca sulla previsione dei terremoti non sta procedendo in maniera significativa, e tutto il lavoro fatto risulta essere ancora a uno stadio primitivo e in feroce controversie scientifiche. Tuttavia il campo di ricerca è promettente, anche se difficile, inoltre i benefici di una soluzione anche parziale al problema della previsione sono così enormi da non poterne fare a meno.
Si è infatti arrivati alla conclusione che alcuni precursori possono dare un importante contributo, se opportunamente correlati tra loro, nella comprensione del fenomeno sismico e del suo accadimento.
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Wolf, Stefan Leo Philipp [Verfasser]. "Liquid Precursors in Non-Classical Crystallization / Stefan Leo Philipp Wolf." Konstanz : KOPS Universität Konstanz, 2017. http://d-nb.info/1188564587/34.
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Junior, Mario Godinho. "Síntese e caracterização do BIMEVOX pelo método dos precursores poliméricos." Universidade de São Paulo, 2002. http://www.teses.usp.br/teses/disponiveis/88/88131/tde-20082015-165222/.
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As cerâmicas do tipo BIMEVOX, onde ME= metal dopante com estequiometria Bi4Me2xV2(1-x)Ox(11-3x), são conhecidas como eletrólitos sólidos e a utilização destes materiais está voltada principalmente para dispositivos como: sensores de oxigênio, células de combustíveis, conversão de energia, baterias e dispositivos associados à condução iônica. Dada a dificuldade de obter-se materiais policristalinos de alta densidade, buscou-se o método dos precursores poliméricos para obter-se um pó com maior área superficial específica e, consequentemente aumentar a densificação, para melhorar assim a condutividade iônica do oxigênio. As cerâmicas BIMEVOX dopadas com 20% de Titânio em relação ao Vanádio (BITIVOX.20) foram as que apresentaram a maior condutividade, sendo de 5,39 x10-4 (Ω.cm)-1 à temperatura de 200 °C com uma a densidade relativa de 98% Esses resultados são uns dos melhores até o momento reportado na literaturaThe BIMEVOX type ceramics present the general formula Bi4Me2xV2(1-x)Ox(11-3x), in which Me stands for the doping metal. They are known as soiid electrolytes and the utilization of these materiais is mairly directed towards devices such as: oxygen sensors, fuel cells, energy conversion, batteries and devices associated to the ionic conduction. Due to the difficulty of obtaining high density polycrystalline materiais, it was used the polymeric precursor method to produced a powder with higher specific surface area and therefore increase the densification, in order to improve the ionic conductivity of oxygen. BIMEVOX ceramics with titanium presenting a doping levei of 20 mol%, in relation to vanadium, (BITIVOX.20) where the ones that presented the highest conductivity, reaching the value of 5,39 x10-4 (Ω.cm)-1 at the temperature of 200 °C with a relative density of 98%. These figures represent one of the best results reported up to now in the literature
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Boniol, Paul. "Detection of anomalies and identification of their precursors in large data series collections." Electronic Thesis or Diss., Université Paris Cité, 2021. http://www.theses.fr/2021UNIP5206.
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Les larges collections de séries temporelles deviennent une réalité dans un grand nombre de domaines scientifiques et sociaux, comme la finance, les sciences de l’environnement, l’astrophysique, les neurosciences, l’ingénierie ou les métiers du numérique. Il y a donc un intérêt et un besoin de plus en plus importants de développer des techniques efficaces pour analyser et traiter ce type de données. De manière informelle, une série temporelle est une séquence ordonnée de points ou de valeurs. Une fois les séries collectées et disponibles, les utilisateurs ont souvent besoin de les étudier pour en extraire de la valeur et de la connaissance. Ces analyses peuvent être simples, comme sélectionner des fenêtres temporelles, mais aussi complexes, comme rechercher des similarités entre des séries ou détecter des anomalies, souvent synonymes d’évolutions soudaines et inhabituelles possiblement non souhaitées, voire de dysfonctionnements du système étudié. Ce dernier type d’analyse représente un enjeu crucial pour des applications dans un large éventail de domaines partageant tous le même objectif : détecter les anomalies le plus rapidement possible pour éviter la survenue de tout événement critique, comme par exemple de prévenir les dégradations et donc d’allonger la durée de vie des systèmes. Par conséquent, dans ce travail de thèse, nous traitons les trois objectifs suivants : (i) l’exploration non-supervisée de séries temporelles pour la détection rétrospective d’anomalies à partir d’une collection de séries temporelles. (ii) la détection non-supervisée d’anomalies en temps réel dans les séries temporelles. (iii) l’explication de la classification d’anomalies connues dans les séries temporelles, afin d’identifier de possibles précurseurs. Dans ce manuscrit, nous introduisons d’abord le contexte industriel qui a motivé la thèse, des définitions fondamentales, une taxonomie des séries temporelles et un état de l’art des méthodes de détection d’anomalies. Nous présentons ensuite nos contributions scientifiques en suivant les trois axes mentionnés précédemment. Ainsi, nous décrivons premièrement deux solutions originales, NormA (basée sur une méthode de clustering de sous-séquences de la série temporelle à analyser) et Series2Graph (qui s’appuie sur une transformation de la séries temporelle en un réseau orienté), pour la tâche de détection non supervisée de sous-séquences anormales dans les séries temporelles statiques (i.e., n’évoluant pas dans le temps). Nous présentons dans un deuxième temps la méthode SAND (inspiré du fonctionnement de NormA) développée pour répondre à la tâche de détection non-supervisée de sous-séquences anormales dans les séries temporelles évoluant de manière continue dans le temps. Dans une troisième phase, nous abordons le problème lié à l’identification supervisée des précurseurs. Nous subdivisons cette tâche en deux problèmes génériques : la classification supervisée de séries temporelles d’une part, l’explication des résultats de cette classification par l’identification de sous-séquences discriminantes d’autre part. Enfin, nous illustrons l’applicabilité et l’intérêt de nos développements au travers d’une application portant sur l’identification de précurseurs de vibrations indésirables survenant sur des pompes d’alimentation en eau dans les centrales nucléaires françaises d’EDFExtensive collections of data series are becoming a reality in a large number of scientific and social domains. There is, therefore, a growing interest and need to elaborate efficient techniques to analyze and process these data, such as in finance, environmental sciences, astrophysics, neurosciences, engineering. Informally, a data series is an ordered sequence of points or values. Once these series are collected and available, users often need to query them. These queries can be simple, such as the selection of time interval, but also complex, such as the similarities search or the detection of anomalies, often synonymous with malfunctioning of the system under study, or sudden and unusual evolution likely undesired. This last type of analysis represents a crucial problem for applications in a wide range of domains, all sharing the same objective: to detect anomalies as soon as possible to avoid critical events. Therefore, in this thesis, we address the following three objectives: (i) retrospective unsupervised subsequence anomaly detection in data series. (ii) unsupervised detection of anomalies in data streams. (iii) classification explanation of known anomalies in data series in order to identify possible precursors. This manuscript first presents the industrial context that motivated this thesis, fundamental definitions, a taxonomy of data series, and state-of-the-art anomaly detection methods. We then present our contributions along the three axes mentioned above. First, we describe two original solutions, NormA (that aims to build a weighted set of subsequences that represent the different behaviors of the data series) and Series2Graph (that transform the data series in a directed graph), for the task of unsupervised detection of anomalous subsequences in static data series. Secondly, we present the SAND (inspired from NormA) method for unsupervised detection of anomalous subsequences in data streams. Thirdly, we address the problem of the supervised identification of precursors. We subdivide this task into two generic problems: the supervised classification of time series and the explanation of this classification’s results by identifying discriminative subsequences. Finally, we illustrate the applicability and interest of our developments through an application concerning the identification of undesirable vibration precursors occurring in water supply pumps in the French nuclear power plants of EDF
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Tse, Erin. "The role of amyloid precursor protein in neuronal and non-neuronal cell lines." Thesis, Aston University, 2015. http://publications.aston.ac.uk/27532/.
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Models of Alzheimer’s disease (AD) have provided useful insights into the pathogenesis and mechanistic pathways that lead to its development. One emerging idea about AD is that it may be described as a hypometabolic disorder due to the reduction of glucose uptake in AD brains. Inappropriate processing of Amyloid Precursor Protein (APP) is considered central to the initiation and progression of the disease. Although the exact role of APP misprocessing is unclear, it may play a role in neuronal metabolism before the onset of neurodegeneration. To investigate the potential role of APP in neuronal metabolism, the SHSY5Y neuroblastoma cell line was used to generate cell lines that stably overexpress wild type APP695 or express Swedish mutated-APP observed in familial AD (FAD), both under the control of the neuronal promoter, Synapsin I. The effects of APP on glucose uptake, cellular stress and energy homeostasis were studied extensively. It was found that APP-overexpressing cells exhibited decreased glucose uptake with changes in basal oxygen consumption in comparison to control cell lines. Similar studies were also performed in fibroblasts taken from FAD patients compared with control fibroblasts. Previous studies found FAD-derived fibroblasts displayed altered metabolic profiles, calcium homeostasis and oxidative stress when compared to controls. As such, in this study fibroblasts were studied in terms of their ability to metabolise glucose and their mitochondrial function. Results show that FAD-derived fibroblasts demonstrate no differences in mitochondrial function, or response to oxidative stress compared to control fibroblasts. However, control fibroblasts treated with Aβ1-42 demonstrated changes in glucose uptake. This study highlights the importance of APP expression within non-neuronal cell lines, suggesting that whilst AD is considered a brain-associated disorder, peripheral effects in non-neuronal cell types should also be considered when studying the effects of Aβ on metabolism.
Книги з теми "NOx precursors"
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Moore, Kenneth. Alternative fire extinguishing agents: Non-violatile precursors to olefinic bromofluorocarbons. Lowell, Mass: Toxics Use Reduction Institute, University of Massachusetts Lowell, 1993.
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2
A, Reckhow David, AWWA Research Foundation, and United States. Environmental Protection Agency., eds. Long-term variability of BDOM and NOM as precursors in watershed sources. Denver, Colo: Awwa Research Foundation, 2007.
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Crawford, Alec. Alternative fire extinguishing agents: Non-volatile precursors to olefinic bromofluorocarbons : final report. Lowell, Mass: Toxics Use Reduction Institute. University of Massachusetts Lowell, 1994.
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Curinga, Luisa, and Marco Rapetti, eds. Skrjabin e il Suono-Luce. Florence: Firenze University Press, 2019. http://dx.doi.org/10.36253/978-88-6453-807-5.
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Skrjabin, figura eccentrica nel panorama musicale di inizio secolo, ha spesso suscitato tanto i più accesi entusiasmi quanto le critiche più feroci. Importanti ricerche effettuate negli ultimi decenni in Italia e all’estero hanno tuttavia condotto a una visione più equilibrata dell’uomo e della sua opera. I contributi ospitati nel presente volume provengono in buona parte dal convegno Svetozvuk, il ‘Suono-Luce’ (Conservatorio Cherubini di Firenze, 2015), e intendono apportare un tassello significativo agli studi skrjabiniani affrontando tematiche diverse e complementari. Lo sfaccettato caleidoscopio che ne risulta mette in luce il ruolo chiave di Skrjabin nel Novecento, non solo in quanto precursore della multimedialità, ma soprattutto come creatore di un linguaggio originalissimo destinato a influenzare generazioni di musicisti di differente formazione.
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Fernández-Armesto, Felipe. Amerigo: The man who gave his name to America. New York: Random House Trade Paperbacks, 2008.
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Fernández-Armesto, Felipe. Amerigo: The man who gave his name to America. New York: Random House, 2007.
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Fernández-Armesto, Felipe. Amerigo: The man who gave his name to America. New York: Random House Trade Paperbacks, 2008.
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Rees, Paula L., Klaus Nusslein, Gladys Makdissy, Greg Devine, and David A. Reckhow. Long-Term Variability of BDOM and NOM as Precursors in Watershed Sources. American Water Works Association, 2007.
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Long-Term Variability of BDOM and NOM As Precursors in Watershed Sources. IWA Publishing, 2008.
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Deegan, Patrick. Porphyria. Edited by Patrick Davey and David Sprigings. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780199568741.003.0179.
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This chapter discusses six diseases caused by inborn errors of metabolism affecting the biosynthesis of haem. Haem is a tetracyclic metal-binding compound involved in oxygen transport (in haemoglobin and myoglobin) and redox reactions (e.g. in the cytochrome P450 system). Each of these conditions is caused by a single gene defect in one of the enzymes involved in the biosynthesis of haem. Inheritance is usually autosomal dominant with incomplete penetrance. The enzyme defect results in disease, not as a result of deficiency of the reaction product, but as a result of accumulation of precursors. Early, soluble precursors, 5-aminolaevulinic acid, and porphobilinogen (not porphyrins as such) are neurotoxic and, when present in great excess, as occurs when flux through the haem synthetic pathway is increased in response to particular medications or hormones, lead to acute neurovisceral crises. Later cyclical precursors (porphyrins) in the pathway are also water soluble and excreted in urine, but are susceptible to activation by electromagnetic radiation in the visible spectrum and are converted to free-radical metabolites that cause pain, inflammation, and tissue damage in the skin. The final haem precursors (also porphyrins) are hydrophobic and excreted in the bile and faeces and are also activated by light to toxic metabolites.
Частини книг з теми "NOx precursors"
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Verma, Nidhi, Anita Lakhani, and K. Maharaj Kumari. "Surface O3 and Its Precursors (NOx, CO, BTEX) at a Semi-arid Site in Indo-Gangetic Plain: Characterization and Variability." In Urban Air Quality Monitoring, Modelling and Human Exposure Assessment, 119–35. Singapore: Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-15-5511-4_9.
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Wang, Chi-Yuen, and Michael Manga. "Hydrologic Precursors." In Lecture Notes in Earth System Sciences, 343–68. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-64308-9_13.
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AbstractPredicting earthquakes is a long-desired goal. The main challenge is to identify precursory signals that reliably predict the impending earthquake. Since hydrological and hydrogeochemical properties and processes can be very sensitive to minute strains, the hope is that measurements from hydrological systems might record precursory rock deformation that would otherwise be undetectable. Of the many hundreds of studies, we review a subset to illustrate how signals can be challenging to interpret and highlight questions raised by observations—examples come from China, Japan, Taiwan, India, the USA, Russia, France, Italy and Iceland. All are retrospective studies. Some signals seem to have no other explanation than being precursory, however, rarely is enough data available to undertake a thorough analysis. Some hydrological precursors might be recording deformation events that are slower than traditional earthquakes (and hence usually harder to detect). Long times series of data are critical for both identifying putative precursors and assessing their origin and reliability.
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Zha, Xian-Hu, Jie Zhou, Per Eklund, Xiaojing Bai, Shiyu Du, and Qing Huang. "Non-MAX Phase Precursors for MXenes." In 2D Metal Carbides and Nitrides (MXenes), 53–68. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-19026-2_4.
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Nishimura, Toshiyuki, S. Ishihara, Yoshiki Yoshioka, and Hidehiko Tanaka. "Synthesis of Non-Oxide Ceramic Fine-Powders from Organic Precursors." In SiAlONs and Non-oxides, 269–72. Stafa: Trans Tech Publications Ltd., 2008. http://dx.doi.org/10.4028/3-908454-00-x.269.
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Goossens, W. R. A., and J. B. H. F. van Rensbergen. "Krypton-85, a Minor Greenhouse Gas Precursor." In Non-CO2 Greenhouse Gases: Why and How to Control?, 231–35. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-0982-6_26.
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Mikami, Yoshiki. "Non-Human-Papillomavirus (HPV)-Related Adenocarcinomas and Their Precursors." In Pathology of the Cervix, 185–99. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-51257-0_9.
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Roy, Amrita, Titash Mondal, Kinsuk Naskar, and Anil K. Bhowmick. "Synthesis and Characterization of Graphene from Non-Conventional Precursors." In Graphene-Rubber Nanocomposites, 53–79. Boca Raton: CRC Press, 2022. http://dx.doi.org/10.1201/9781003200444-3.
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Sugahara, Yoshiyuki, Hiroaki Nakashima, Seiichi Koyama, and Yusuke Mori. "Preparation of Precursors for Aluminum Nitride-Based Ceramic Composites from Cage-Type and Cyclic Building Blocks." In SiAlONs and Non-oxides, 249–50. Stafa: Trans Tech Publications Ltd., 2008. http://dx.doi.org/10.4028/3-908454-00-x.249.
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Gershon, Michael D., Gladys Teitelman, and Taube P. Rothman. "Development of Enteric Neurons from Non-Recognizable Precursor Cells." In Ciba Foundation Symposium 83 - Development of the Autonomic Nervous System, 51–69. Chichester, UK: John Wiley & Sons, Ltd., 2008. http://dx.doi.org/10.1002/9780470720653.ch3.
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Murphy, Gillian M. "From Precursor to Cancer: Field Cancerization and the Opportunities for Therapy." In Non-Surgical Treatment of Keratinocyte Skin Cancer, 1–7. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-540-79341-0_1.
Повний текст джерелаТези доповідей конференцій з теми "NOx precursors"
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Reis Gonçalves, Sara Nuza Oliveira dos, Maysa Lorena Figueiredo Martins, Paulo Roberto Ribeiro Soares Junior, Domingos Sávio de Resende, and Augusto Cesar da Silva Bezerra. "Desempenho fotocatalítico de material álcali-ativado à base de lama vermelha e escória de alto forno." In XX ENCONTRO NACIONAL DE TECNOLOGIA DO AMBIENTE CONSTRUÍDO, 1–13. UFAL, 2024. http://dx.doi.org/10.46421/entac.v20i1.6192.
Повний текст джерелаАнотація:
Uma das preocupações da indústria da mineração é a grande quantidade de resíduos gerados. Além de causar impactos ao meio ambiente, esses resíduos ocupam extensas áreas para disposição final. Na mesma linha, o tratamento de águas residuárias se torna casa vez mais desafiador, em vista da diversidade de contaminantes. O presente trabalho investigou o desempenho de materiais álcali-ativados (MAAs) aplicados à descontaminação de água, com precursores à base de lama vermelha e escória de alto forno. O MAA foi desenvolvido visando otimização das relações precursor-ativador. A caracterização das matérias primas indicou granulometria composta por partículas finas, alta concentração de elementos formadores de rede e presença de goethita fotoativa. Os resultados reportaram resistência à compressão até 27 MPa, o que indicou matriz álcali-ativada coesa. A remoção de compostos orgânicos atingiu 96,5% e foi confirmada pela descoloração da solução de corante. Além disso, o processo de fotocatálise pode ser o principal mecanismo para descontaminação. Esses achados podem auxiliar no desenvolvimento de novos materiais sustentáveis de baixo custo para aplicações ambientais.
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Hall, Asha, Mulugeta Haile, Robert Haynes, Michael Coatney, and Jin Yoo. "Structural Health Sensing of Damage Precursors using Magnetostrictive Particles Embedded in Composite Structures." In Vertical Flight Society 70th Annual Forum & Technology Display, 1–7. The Vertical Flight Society, 2014. http://dx.doi.org/10.4050/f-0070-2014-9639.
Повний текст джерелаАнотація:
Over the last two decades, tremendous progress has been made in structural health monitoring (SHM) using various sensing techniques such as acoustic emission, eddy current, strain gages, to diagnose damage in aerospace, mechanical and civil infrastructures. Despite this progress, there are still many challenges to address in SHM. Among these challenges is detection of precursors to matrix cracking, fiber/matrix debonding, and delamination. Magnetostrictive smart materials such as Terfenol-D (Tb0.3Dy0.7Fe1.92) (Etrema Products Inc., IA, USA) have proven useful as non-contact strain sensors using Hall Effect or pick-up coil to measure change in magnetization due to strain. In this study, our team will conduct a specific number of fatigue cycles at 1, 100, 1,000, 10,000, 100,000, and 1,000,000 cycles. After each fatigue loading a destructive examination of the specimen surface will be conducted by Scanning Electron Microscope (SEM). By this systematic evaluation, the phenomenon of crazing, the propagation of micro-cracks and delaminations, and the factors that lead to catastrophic failure will be investigated, thereby enabling correlation of the current damage state to the magnetization.
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Paraschiv, Spiru. "ANALYSIS OF URBAN TRAFFIC POLLUTION UNDER SUMMER AND WINTER CONDITIONS." In 10th SWS International Scientific Conferences on SOCIAL SCIENCES - ISCSS 2023. SGEM WORLD SCIENCE, 2023. http://dx.doi.org/10.35603/sws.iscss.2023/s14.61.
Повний текст джерелаАнотація:
Urban pollution caused by traffic has become a global issue in recent years. Urban pollution is significantly influenced by weather conditions, and the study examines the impact of meteorological parameters such as temperature, solar radiation, precipitation, atmospheric pressure, and wind speed on the pollution levels of O3, NO, NO2, NOx, and SO2 in summer compared to winter. During summer, the average concentration of O3 is higher than in winter, while the average concentrations of NO2, NO, NOx, which are precursors to ozone formation, are lower than in winter. However, the concentration of SO2 is much higher in summer than in winter. This study indicates that pollution is more pronounced in summer with O3 and SO2. This ozone pollution is primarily due to nitrogen oxides reacting with other chemicals under the influence of solar radiation. The correlation coefficients between O3, NO2, NO, NOx concentrations and meteorological parameters have varied significantly in both seasons. High concentrations of O3 have a strong negative correlation with NO2, NO, and NOx, and a strong positive correlation with solar radiation.
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Mastrovito, Marco, Antonio Ferrante, Sergio M. Camporeale, Federico Bonzani, and Rosanna Ninni. "Opto-Acoustical Flame Monitoring of CCGT: Searching for Humming Precursors." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27876.
Повний текст джерелаАнотація:
Modern gas turbines are prone to trigger and sustain pressure oscillations induced by heat release in their combustor; these oscillations, called humming, can cause severe damage on the machine structure, or, on a less detrimental level, can limit gas turbine performance from load point of view or NOx emissions, increasing their concentration in flue gas. Thermoacoustic oscillation problem, although deeply investigated during the last 15 years, is far from being solved, so that both theoretical and experimental approaches are being used in order to improve basic knowledge of this phenomenon. With this aim an optoelectronic detector based system has been developed to be installed on a 270MW gas turbine to detect radiative energy release fluctuations due to thermoacoustic oscillations. This optoelectronic device has been used in combination with standard piezoelectric sensors with the target to get a better insight of the humming phenomenon. A data analysis method based on well established data processing techniques has been applied to data gathered from the field. The ensemble of data processing techniques seems to offer a method to evaluate the actual risk of thermoacoustic instabilities. This is the very first application of the proposed tool, and a long way has to be run before it is assessed as a prognostic device. Nevertheless in the h.o. of the authors, this first application encourages the continuation of developing the tool extending the base of monitored plants.
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Han, X., and S. K. Aggarwal. "A Numerical Investigation on Counterflow Flames of Biodiesel/Diesel Surrogate Blends." In ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/gt2013-95718.
Повний текст джерелаАнотація:
There is significant interest in increasing the use of biodiesel fuels especially by blending them with petroleum diesel. Biodiesels typically consist of long-chain saturated and unsaturated hydrocarbons along with an alkyl (methyl, ethyl or butyl) ester functional group. Previous studies have demonstrated that the combustion and emission characteristics of biodiesel fuels are mostly determined by the hydrocarbon chain length and the number and location of unsaturated bonds in their molecular structure. The present study aims to characterize the combustion and emission behavior of biodiesel/diesel surrogate blends by simulating PPFs burning blends of n-heptane, methyl decanoate and methyl-9-decenoate. A recently developed reduced mechanism for these blends is employed, and the effects of the blend composition on NOx and PAH emissions from these flames are examined. Results indicate that NOx emissions are only slightly reduced by the addition of C10 methyl esters. However, the formation of PAH precursors is noticeably affected by the surrogate blend. Results also indicate the need for further improving the reduced mechanism, especially with regards to some key reactions and species, which are important for accurately predicting the intermediate hydrocarbon species including PAH precursors.
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Rohkamp, Marius, Alexander Rabl, Benedikt Gündling, Mohammad Reza Saraji-Bozorgzad, Christopher Mull, Jan Bendl, Carsten Neukirchen, et al. "Detailed Gaseous and Particulate Emissions of an Allison 250-C20B Turboshaft Engine." In ASME Turbo Expo 2023: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-101273.
Повний текст джерелаАнотація:
Abstract Aviation is known to be one of the most significant contributors to air pollutants. This includes gaseous emissions, like carbon-dioxide (CO2) and nitrogen oxides (NOx), and also particulate matter (PM), especially in the form of soot. This study conducted emission measurements on an Allison 250-C20B turboshaft engine operating on Jet A-1 fuel with a focus on gaseous compounds (e.g. ozone precursors) and PM, regarding their number and mass concentration. The different engine loading points were chosen based on the percentage thrust ratios of the International Civil Aviation Organization (ICAO) Landing and Take-Off-Cycle (LTO-Cycle). A standard FTIR/O2/FID system to measure general combustion compounds e.g. CO2, carbon-monoxide (CO), unburned hydrocarbons (UHC), and NOx, was used for the gaseous measurements. For the investigation of the volatile organic compounds (VOC), which are known to act as ozone precursors, a gas-chromatograph (GC) was applied. Different measurement methods were used to characterize the PM emissions. For the particle size distribution (PSD), we used two types of electrical mobility analyzers (SMPS and DMS500) and an aerodynamic aerosol classifier (AAC). All measurement systems yielded comparable PSD results, indicating reliable results. The particle measurement methods all show increasing aerosol diameter modes (electrical and aerodynamic) with increased engine loading. The aerosol diameter modes were shifting from 29 nm to 65 nm. Furthermore, the size and shape of different individual particles were evaluated with a scanning electron microscope (SEM). In addition, a correlation between the injection system and the particle formation was established. Gaseous turboshaft engine emissions show high CO and UHC values in Ground Idle (GI) level. NOx levels were the highest at Take-Off (TO) conditions. Acetylene and ethylene were the most significant contributors to ozone formation.
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Riebl, Sebastian, Marina Braun-Unkhoff, and Uwe Riedel. "A Study on the Emissions of Alternative Aviation Fuels." In ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/gt2016-57361.
Повний текст джерелаАнотація:
Currently, the aviation sector is seeking for alternatives to kerosene from crude oil, as part of the efforts combating climate change by reducing greenhouse gas (GHG) emissions, in particular carbon dioxide (CO2), and ensuring security of supply at affordable prices. Several synthetic jet fuels have been developed including sustainable bio-kerosene, a low-carbon fuel. Over the last years, the technical feasibility as well as the compatibility of alternative jet fuels with today’s planes has been proven However, when burning a jet fuel, the exhaust gases are a mixture of many species, going beyond CO2 and water (H2O) emissions, with nitrogen oxides (NOx), carbon monoxide (CO), unburned hydrocarbons (UHC) including aromatic species and further precursors of particles and soot among them. These emissions have an impact on the local air quality as well as on the climate (particles, soot, contrails). Therefore, a detailed knowledge and understanding of the emission patterns when burning synthetic aviation fuels is inevitable. In the present paper, these issues are addressed by studying numerically the combustion of four synthetic jet fuels (Fischer-Tropsch fuels). For reference, two types of crude-oil based kerosenes (Jet A-1 and Jet A) are considered, too. Plug flow calculations were performed by using a detailed chemical-kinetic model validated previously. The composition of the multi-component jet fuels were imaged by using the surrogate approach. Calculations were done for relevant temperatures, pressures, residence times, and fuel equivalence ratios φ. Results are discussed for NOx, CO as well as benzene and acetylene as major soot precursors. According to the predictions, the NOx and CO emissions are within about ± 10% for all fuels considered, within the parameter range studied: T = 1800 K, T = 2200 K; 0.25 ≤ φ ≤ 1.8; p = 40 bar; t = 3 ms. The aromatics free GtL (Gas to Liquid) fuel displayed higher NOx values compared to Jet A-1/A. In addition, synthetic fuels show slightly lower (better) CO emission data than Jet A-1/A. The antagonist role of CO and NOx is apparent. Major differences were predicted for benzene emissions, depending strongly on the aromatics content in the specific fuel, with lower levels predicted for the synthetic aviation fuels. Acetylene levels show a similar, but less pronounced, effect.
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Prakash, Shashvat, Yedidia Neumeier, and Ben T. Zinn. "Blowout Margin Estimation Based on Two Precursor Types." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27874.
Повний текст джерелаАнотація:
Lean, premixed combustion has been aggressively pursued in recent years because it offers a practical approach for reducing emissions of nitrogen oxides (NOx) from gas turbines. However, lean premixed flames pose a greater risk of blowout. Studies on swirl and dump stabilized flames have shown that as a flame approaches blowout, distinctive precursors occur, such as pockets of localized extinctions and brief flame shape transitions to a thin ‘tornado’ configuration. For this study, both precursor types are detected using separate, dedicated optical sensors. Observations indicate that the tornado mode is part of the blowout process in a 127 mm long combustor and that a localized extinction precursor immediately precedes the tornado mode transition. Despite the causality, the statistics of tornado bursts and localized extinctions suggest a ‘memoryless’ Poisson process, where the occurrence of one event type does not influence the time until the next event of the same type. Localized extinctions have been used previously for blowout margin estimation, and are well suited for the purpose because the occurrence frequency increases with diminishing margin. However, the signals commonly used to detect localized extinction events are noisy due to the nature of the flame; thus, detection is prone to false alarms. Detecting tornado bursts, by comparison, is less ambiguous but such events occur too rarely for blowout mitigation applications. The shortcomings of both precursor detection methods can be addressed by combining observations of both precursor types in a meaningful manner. The presence of tornado bursts indicates that the flame is near blowout; this fact can be used to calibrate margin estimation routines based upon localized extinction. However, this approach would require two sensors since any one optical sensor cannot directly differentiate both precursor types. A single sensor approach can be developed whereby the causal relationship between the two precursor types is exploited. Local extinctions with longer duration times can potentially perturb the flame into an alternate flow configuration. The presence of these tornado ‘triggers’ manifest as an increase in the low frequency content of the chemiluminescence signal. A low pass filter with the appropriate cutoff frequency can differentiate between the tornado-triggering and benign, inconsequential localized extinctions. Therefore, the same signal that detects localized extinctions can be filtered to capably predict tornado mode shifts. This scheme will enable robust margin detection and minimize sensitivity to noise.
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Durocher, Antoine, Jiayi Wang, Gilles Bourque, and Jeffrey M. Bergthorson. "Impact of Boundary Condition and Kinetic Parameter Uncertainties on NOx Predictions in Methane-Air Stagnation Flame Experiments." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59404.
Повний текст джерелаАнотація:
Abstract A comprehensive understanding of uncertainty sources in experimental measurements is required to develop robust thermochemical models for use in industrial applications. Due to the complexity of the combustion process in gas turbine engines, simpler flames are generally used to study fundamental combustion properties and measure concentrations of important species to validate and improve modelling. Stable, laminar flames have increasingly been used to study nitrogen oxide (NOx) formation in lean-to-rich compositions in low-to-high pressures to assess model predictions and improve accuracy to help develop future low-emissions systems. They allow for non-intrusive diagnostics to measure sub-ppm concentrations of pollutant molecules, as well as important precursors, and provide well-defined boundary conditions to directly compare experiments with simulations. The uncertainties of experimentally-measured boundary conditions and the inherent kinetic uncertainties in the nitrogen chemistry are propagated through one-dimensional stagnation flame simulations to quantify the relative importance of the two sources and estimate their impact on predictions. Measurements in lean, stoichiometric, and rich methane-air flames are used to investigate the production pathways active in those conditions. Various spectral expansions are used to develop surrogate models with different levels of accuracy to perform the uncertainty analysis for 15 important reactions in the nitrogen chemistry and the 6 boundary conditions (ϕ, Tin, uin, du/dzin, Tsurf, P) simultaneously. After estimating the individual parametric contributions, the uncertainty of the boundary conditions are shown to have a relatively small impact on the prediction of NOx compared to kinetic uncertainties in these laboratory experiments. These results show that properly calibrated laminar flame experiments can, not only provide validation targets for modelling, but also accurate indirect measurements that can later be used to infer individual kinetic rates to improve thermochemical models.
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Endres, Derek, and Sandip Mazumder. "Computational Study of Pulsed Metal-Organic Chemical Vapor Deposition of Aluminum Nitride." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-65525.
Повний текст джерелаАнотація:
Particles of aluminum nitride (AlN) have been observed to form during epitaxial growth of AlN films by metal organic chemical vapor deposition (MOCVD). Particle formation is undesirable because particles do not contribute to the film growth, and are detrimental to the hydraulic system of the reactor. It is believed that particle formation is triggered by adducts that are formed when the group-III precursor, namely tri-methyl-aluminum (TMAl), and the group-V precursor, namely ammonia (NH3), come in direct contact in the gas-phase. Thus, one way to eliminate particle formation is to prevent the group-III and the group-V precursors from coming in direct contact at all in the gas-phase. In this article, pulsing of TMAl and NH3 is numerically investigated as a means to reduce AlN particle formation. The investigations are conducted using computational fluid dynamics (CFD) analysis with the inclusion of detailed chemical reaction mechanisms both in the gas-phase and at the surface. The CFD code is first validated for steady-state (non-pulsed) MOCVD of AlN against published data. Subsequently, it is exercised for pulsed MOCVD with various pulse widths, precursor gas flow rates, wafer temperature, and reactor pressure. It is found that in order to significantly reduce particle formation, the group-III and group-V precursors need to be separated by a carrier gas pulse, and the carrier gas pulse should be at least 5–6 times as long as the precursor gas pulses. The studies also reveal that with the same time-averaged precursor gas flow rates as steady injection (non-pulsed) conditions, pulsed MOCVD can result in higher film growth rates because the precursors are incorporated into the film, rather than being wasted as particles. The improvement in growth rate was noted for both horizontal and vertical reactors, and was found to be most pronounced for intermediate wafer temperature and intermediate reactor pressure.
Звіти організацій з теми "NOx precursors"
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Soloviev, Vladimir, Andrii Bielinskyi, and Viktoria Solovieva. Entropy Analysis of Crisis Phenomena for DJIA Index. [б. в.], June 2019. http://dx.doi.org/10.31812/123456789/3179.
Повний текст джерелаАнотація:
The Dow Jones Industrial Average (DJIA) index for the 125-year-old (since 1896) history has experienced many crises of different nature and, reflecting the dynamics of the world stock market, is an ideal model object for the study of quantitative indicators and precursors of crisis phenomena. In this paper, the classification and periodization of crisis events for the DJIA index have been carried out; crashes and critical events have been highlighted. Based on the modern paradigm of the theory of complexity, a spectrum of entropy indicators and precursors of crisis phenomena have been proposed. The entropy of a complex system is not only a measure of uncertainty (like Shannon's entropy) but also a measure of complexity (like the permutation and Tsallis entropy). The complexity of the system in a crisis changes significantly. This fact can be used as an indicator, and in the case of a proactive change as a precursor of a crisis. Complex systems also have the property of scale invariance, which can be taken into account by calculating the Multiscale entropy. The calculations were carried out within the framework of the sliding window algorithm with the subsequent comparison of the entropy measures of complexity with the dynamics of the DJIA index itself. It is shown that Shannon's entropy is an indicator, and the permutation and Tsallis entropy are the precursors of crisis phenomena to the same extent for both crashes and critical events.
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Rouseff, Russell L., and Michael Naim. Characterization of Unidentified Potent Flavor Changes during Processing and Storage of Orange and Grapefruit Juices. United States Department of Agriculture, September 2002. http://dx.doi.org/10.32747/2002.7585191.bard.
Повний текст джерелаАнотація:
Citrus juice flavor quality traditionally diminishes after thermal processing and continuously during storage. Our prior studies found that four of the five most potent off-aromas formed during orange juice storage had not been identified. The primary emphasis of this project was to characterize and identify those potent flavor degrading aroma volatiles so that methods to control them could be developed and final flavor quality improved. Our original objectives included: 1 Isolate and characterize the most important unidentified aroma impact compounds formed or lost during pasteurization and storage. 2. Determination of thiamine and carotenoid thermal decomposition and Strecker degradation pathways in model solutions as possible precursors for the unidentified off-flavors. 3. Evaluate the effectiveness of an "electronic nose" to differentiate the headspace aromas of from untreated and heat pasteurized orange and grapefruit juices. 4. Use model systems of citrus juices to investigate the three possible precursor pathways (from 2) for flavor impact compounds formed or lost during pasteurization or storage. RESULTS - The components responsible for citrus storage off flavors and their putative precursors have now been identified. Certain carotenoids (b-carotene) can thermally degrade to produce b-ionone and b-damascenone which are floral and tobacco smelling respectively. Our GC-O and sensory experiments indicated that b-damascenone is a potential storage off-flavor in orange juice. Thiamine (Vitamin B1) degradation produces 2-methyl-3-furan thiol, MFT, and its dimer bis(2- methyl-3-furyl) disulfide which both produce meaty, savory aromas. GC-O and sensory studies indicated that MFT is another storage off-flavor. Methional (potato aroma) is another off flavor produced primarily from the reaction of the native amino acid, methionine, and oxidized ascorbic acid (vitamin C). This is a newly discovered pathway for the production of methional and is more dominant in juices than the classic Maillard reaction. These newly identified off flavors diminish the flavor quality of citrus juices as they distort the flavor balance and introduce non-typical aromas to the juice flavor profile. In addition, we have demonstrated that some of the poor flavor quality citrus juice found in the market place is not only from the production of these and other off flavors but also due to the absence of desirable flavor components including several potent aldehydes and a few esters. The absence of these compounds appears to be due to incomplete flavor volatile restoration after the making of juice concentrates. We are the first to demonstrate that not all flavor volatiles are removed along with water in the production of juice concentrate. In the case of grapefruit juice we have documented which flavor volatiles are completely removed, which are partially removed and which actually increase because of the thermal process. Since more that half of all citrus juices is made into concentrate, this information will allow producers to more accurately restore the original flavor components and produce a juice with a more natural flavor. IMPLICATIONS - We have shown that the aroma of citrus juices is controlled by only 1-2% of the total volatiles. The vast majority of other volatiles have little to no direct aroma activity. The critical volatiles have now been identified. The ability to produce high quality citrus juices requires that manufacturers know which chemical components control aroma and flavor. In addition to identifying the critical flavor components (both positive and negative), we have also identified several precursors. The behavior of these key aroma compounds and their precursors during common manufacturing and storage conditions has been documented so manufacturers in Israel and the US can alter production practices to minimize the negative ones and maximize the positive ones.
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Moderski, R. Soft X-ray Precursors of the Non-Thermal Flares in Blazars - Theoretical Predictions. Office of Scientific and Technical Information (OSTI), April 2004. http://dx.doi.org/10.2172/826919.
Повний текст джерела
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Hok, Saphon. Synthesis of SHAL and SHAL Precursor Standard, CRADA No. TC02174.0. Office of Scientific and Technical Information (OSTI), May 2014. http://dx.doi.org/10.2172/1330797.
Повний текст джерела
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Hok, S., and R. Balhorn. Synthesis of SHAL and SHAL Precursor Standard, CRADA No. TC02174.0. Office of Scientific and Technical Information (OSTI), March 2021. http://dx.doi.org/10.2172/1773580.
Повний текст джерела
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Singh, Anjali. Amino Acids: Building Blocks of Proteins. ConductScience, June 2022. http://dx.doi.org/10.55157/cs20220612.
Повний текст джерелаАнотація:
Amino acids are essential organic compounds serving as protein building blocks. Recognized for their biological roles, they underpin proteins' structure and interactions. Classified by polarity and nutritional necessity, essential amino acids, not synthesized by the body, include histidine, leucine, lysine, and more, while non-essential ones are produced internally. These molecules exhibit diverse functions, from neurotransmitter precursor synthesis to immune support. Industries leverage amino acids in animal feed, artificial sweeteners, flavor enhancers, and drug manufacturing, highlighting their vital role in various applications beyond biological systems.
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Santander Muñoz, Margareth, Jader Rodríguez Cortina, Fabrice Vaillant, and Sebastian Escobar Parra. Correlación entre los fenómenos que gobiernan la transformación poscosecha del cacao (Theobroma cacao L.) y la formación del sabor y aroma en el chocolate. Corporación Colombiana de Investigación Agropecuaria - AGROSAVIA, 2016. http://dx.doi.org/10.21930/agrosavia.poster.2016.11.
Повний текст джерелаАнотація:
La transformación de las semillas de cacao no ha sido investigada de manera controlada en función de su optimización. Su estudio permitiría conocer las condiciones más favorables para que se generen los precursores claves que iniciden en la formación del flavor en el chocolate. El objetivo de este fue correlacionar el posible efecto de fenómenos asociados a la transformación de las semillas de cacao, sobre atributos de calidad en el chocolate
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Bielinskyi, Andrii O., Serhii V. Hushko, Andriy V. Matviychuk, Oleksandr A. Serdyuk, Сергій Олексійович Семеріков, Володимир Миколайович Соловйов, Андрій Іванович Білінський, Андрій Вікторович Матвійчук, and О. А. Сердюк. Irreversibility of financial time series: a case of crisis. Криворізький державний педагогічний університет, December 2021. http://dx.doi.org/10.31812/123456789/6975.
Повний текст джерелаАнотація:
The focus of this study to measure the varying irreversibility of stock markets. A fundamental idea of this study is that financial systems are complex and nonlinear systems that are presented to be non-Gaussian fractal and chaotic. Their complexity and different aspects of nonlinear properties, such as time irreversibility, vary over time and for a long-range of scales. Therefore, our work presents approaches to measure the complexity and irreversibility of the time series. To the presented methods we include Guzik’s index, Porta’s index, Costa’s index, based on complex networks measures, Multiscale time irreversibility index and based on permutation patterns measures. Our study presents that the corresponding measures can be used as indicators or indicator-precursors of crisis states in stock markets.
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Gould, Melissa, Bill Bruce, Chris Alexander, and Michael Rosenfeld. PR-186-224500-R01 Assessment of Non-Welded Pipeline Repair Methods to Reduce Pipeline Blowdowns. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), May 2024. http://dx.doi.org/10.55274/r0000066.
Повний текст джерелаАнотація:
Non-welded repairs, such as fiber-reinforced composite systems and clamps with elastomer seals, may degrade over the life of the pipeline. As pipelines get older, it is important to evaluate the available repair options, and those currently installed, for continued service. This project explored the degradation associated with these non-welded repairs and provides practical guidance on how to assess, limit, or extend their service life. This will facilitate a reduction in Greenhouse Gas (GHG) emissions from a potential leak of a non-welded/temporary repair, allowing operators to either plan for their replacement with a permanent in-service repair or justify their continued use without arbitrary replacement. This research was a recommended next step following PRCI Project MATR-3-15, Methods to Reduce Pipeline Blowdowns to Effectuate Repairs and Inspections. It is a precursor to MATR-3-15B, which is expected to conclude in 2025.
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Zoido, Pablo, Facundo Albornoz, Andrea Prieto, Gonzalo Almeyda, Jenny Carolina Hernández Cardozo, Victoria Oubiña, and Milton Calderón. Multiplicar aprendizajes: tutorías a distancia para potenciar la escuela. Banco Interamericano de Desarrollo, December 2023. http://dx.doi.org/10.18235/0005309.
Повний текст джерелаАнотація:
Las tutorías remotas son una de las estrategias que más impacto han mostrado para recuperar y acelerar aprendizajes, pero hay menos evidencia respecto de los efectos de las tutorías en los tutores. Este documento presenta una investigación que buscó identificar estos efectos desde las percepciones y representaciones de los tutores, a través de una metodología mixta. El documento aporta un instrumento para medir la percepción de efectividad tutora y la relación tutora de manera simple, rápida y confiable. Se encuentra que los tutores perciben que las tutorías impactaron positivamente en su percepción de efectividad como docentes y generaron una buena relación tutora, aunque no se encontraron diferencias significativas por género, edad ni grado de estudios. Los tutores asocian una efectividad tutora a la atención personalizada, el fortalecimiento de habilidades blandas y precursores del aprendizaje, retroalimentación y reconocimiento a su labor, y desafíos pedagógicos.