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Literatura académica sobre el tema "OPAHs"

Autor: Grafiati

Publicado: 1 de junio de 2024

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Artículos de revistas sobre el tema "OPAHs"

Jo, Jungmin, Ji-Yi Lee, Kyoung-Soon Jang, Atsushi Matsuki, Amgalan Natsagdorj y Yun-Gyong Ahn. "Development of Quantitative Chemical Ionization Using Gas Chromatography/Mass Spectrometry and Gas Chromatography/Tandem Mass Spectrometry for Ambient Nitro- and Oxy-PAHs and Its Applications". Molecules 28, n.º 2 (12 de enero de 2023): 775. http://dx.doi.org/10.3390/molecules28020775.

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The concentration of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere has been continually monitored since their toxicity became known, whereas nitro-PAHs (NPAHs) and oxy-PAHs (OPAHs), which are derivatives of PAHs by primary emissions or secondary formations in the atmosphere, have gained attention more recently. In this study, a method for the quantification of 18 NPAH and OPAH congeners in the atmosphere based on combined applications of gas chromatography coupled with chemical ionization mass spectrometry is presented. A high sensitivity and selectivity for the quantification of individual NPAH and OPAH congeners without sample preparations from the extract of aerosol samples were achieved using negative chemical ionization (NCI/MS) or positive chemical ionization tandem mass spectrometry (PCI-MS/MS). This analytical method was validated and applied to the aerosol samples collected from three regions in Northeast Asia—namely, Noto, Seoul, and Ulaanbaatar—from 15 December 2020 to 17 January 2021. The ranges of the method detection limits (MDLs) of the NPAHs and OPAHs for the analytical method were from 0.272 to 3.494 pg/m3 and 0.977 to 13.345 pg/m3, respectively. Among the three regions, Ulaanbaatar had the highest total mean concentration of NPAHs and OPAHs at 313.803 ± 176.349 ng/m3. The contribution of individual NPAHs and OPAHs in the total concentration differed according to the regional emission characteristics. As a result of the aerosol samples when the developed method was applied, the concentrations of NPAHs and OPAHs were quantified in the ranges of 0.016~3.659 ng/m3 and 0.002~201.704 ng/m3, respectively. It was concluded that the method could be utilized for the quantification of NPAHs and OPAHs over a wide concentration range.

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Teng, Chong, Shimin Wu, Yaqing Sun y Guangyi Gong. "Determination of Parent and Oxygenated Polycyclic Aromatic Hydrocarbons (PAHs) in Waste Cooking Oil and Oil Deodorizer Distillate by GC–QQQ–MS". Journal of AOAC International 102, n.º 6 (1 de noviembre de 2019): 1884–91. http://dx.doi.org/10.5740/jaoacint.19-0085.

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Background: Polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs) are classes of contaminants that are present in the environment and food. They pose a great threat to human health because of their carcinogenicity and mutagenicity. Very few studies have focused on their concentration in waste cooking oil (WCO) and oil deodorizer distillate (ODD). Objective: This study aimed (1) to design a reliable method to determine 16 PAHs and 4 OPAHs in both WCO and ODD and (2) to determine and analyze PAH and OPAH concentrations in actual samples to provide references for further research. Method: The PAH determination approach included double liquid–liquid extraction, double solid-phase extraction, and GC–triple quadrupole tandem MS determination. Oxidation indices were determined by titrimetry. Results: The method reached good linearity (R2 > 0.99) and an acceptable recovery rate (55.01–126.16% for WCO and 57.48–128.97% for ODD). Ten WCO and five ODD samples were determined, and the total concentration of 16 PAHs varied from 16.34 to 239.01 and 101.08 to 198.04 μg/kg in WCO and ODD, respectively. Among the 16 PAHs, three-ring PAHs typically contributed the most. It was also found that the acid value has a strong correlation with the concentration of OPAHs, probably because of the contribution of free fatty acids to OPAH formation. Conclusions: The proposed method was effective in the analysis of PAHs and OPAHs in WCO and ODD.

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Teng, Chong, Shimin Wu, Yaqing Sun y Guangyi Gong. "Determination of Parent and Oxygenated Polycyclic Aromatic Hydrocarbons (PAHs) in Waste Cooking Oil and Oil Deodorizer Distillate by GC–QQQ–MS". Journal of AOAC INTERNATIONAL 102, n.º 6 (1 de noviembre de 2019): 1884–91. http://dx.doi.org/10.1093/jaoac/102.6.1884.

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Abstract Background: Polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs) are classes of contaminants that are present in the environment and food. They pose a great threat to human health because of their carcinogenicity and mutagenicity. Very few studies have focused on their concentration in waste cooking oil (WCO) and oil deodorizer distillate (ODD). Objective: This study aimed (1) to design a reliable method to determine 16 PAHs and 4 OPAHs in both WCO and ODD and (2) to determine and analyze PAH and OPAH concentrations in actual samples to provide references for further research. Method: The PAH determination approach included double liquid–liquid extraction, double solid-phase extraction, and GC–triple quadrupole tandem MS determination. Oxidation indices were determined by titrimetry. Results: The method reached good linearity (R2 > 0.99) and an acceptable recovery rate (55.01–126.16% for WCO and 57.48–128.97% for ODD). Ten WCO and five ODD samples were determined, and the total concentration of 16 PAHs varied from 16.34 to 239.01 and 101.08 to 198.04 μg/kg in WCO and ODD, respectively. Among the 16 PAHs, three-ring PAHs typically contributed the most. It was also found that the acid value has a strong correlation with the concentration of OPAHs, probably because of the contribution of free fatty acids to OPAH formation. Conclusions: The proposed method was effective in the analysis of PAHs and OPAHs in WCO and ODD.

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Sonego, Elisa, Bina Bhattarai y Lene Duedahl-Olesen. "Detection of Nitrated, Oxygenated and Hydrogenated Polycyclic Aromatic Compounds in Smoked Fish and Meat Products". Foods 11, n.º 16 (13 de agosto de 2022): 2446. http://dx.doi.org/10.3390/foods11162446.

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Polycyclic aromatic hydrocarbons (PAHs) are present in smoked food products. More toxic nitrated (NPAH) and oxygenated (OPAH) PAHs derivatives are found concomitantly to PAHs and are therefore believed to be found in smoked food products. However, only a few PAH analyses on food include these derivatives. We adjusted and successfully validated a GC-QTOFMS method including 13 NPAHs and 2 OPAHs as well as the 4 regulated PAHs for analysis of 14 smoked (13 fish and one bacon) and one pan fried fish samples.OPAHs were detected in the highest concentrations in 13 of 15 samples. Non-target screening revealed the presence of an additional four OPAHs and two methylated PAHs. Future food analysis should, based on these results, focus on PAH and oxygenated derivatives.

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Ringuet, J., E. Leoz-Garziandia, H. Budzinski, E. Villenave y A. Albinet. "Particle size distribution of nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) on traffic and suburban sites of a European megacity: Paris (France)". Atmospheric Chemistry and Physics Discussions 12, n.º 6 (6 de junio de 2012): 14169–96. http://dx.doi.org/10.5194/acpd-12-14169-2012.

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Abstract. The size distribution of particulate nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) was determined during two field campaigns at a traffic site in summer 2010 and at a suburban site during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) experiment in summer 2009. Both, OPAHs and NPAHs were strongly associated (>85%) to fines particles (Dp < 2.5 μm) increasing the interest of their study on a sanitary point of view. Results showed really different NPAH and OPAH particle size distributions between both sites. At traffic site, clearly bimodal (notably for NPAHs) particle size distributions (Dp = 0.14 and 1.4 μm) were observed, while the particle size distributions were more scattered at the suburban site, especially for OPAHs. Bimodal particle size distribution observed at traffic site for the NPAH could be assigned to the vehicle emissions and the particle resuspension. Broadest distribution observed at the suburban site could be attributed to the mass transfer of compounds by volatilization/sorption processes during the transport of particles in the atmosphere. Results also showed that the combination of the study of particle size distributions applied to marker compounds (primary: 1-nitropyrene; secondary: 2-nitrofluoranthene) and to NPAH or OPAH chemical profiles bring some indications on their primary and/or secondary origin. Indeed, 1,4-anthraquinone seemed only primary emitted by vehicles while 7-nitrobenz[a]anthracene, benz[a]antracen7,12-dione and benzo[b]fluorenone seemed secondarily formed in the atmosphere.

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Ringuet, J., E. Leoz-Garziandia, H. Budzinski, E. Villenave y A. Albinet. "Particle size distribution of nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) on traffic and suburban sites of a European megacity: Paris (France)". Atmospheric Chemistry and Physics 12, n.º 18 (28 de septiembre de 2012): 8877–87. http://dx.doi.org/10.5194/acp-12-8877-2012.

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Abstract. The size distribution of particulate nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) was determined during two field campaigns at a traffic site in summer 2010 and at a suburban site during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) experiment in summer 2009. Both, OPAHs and NPAHs were strongly associated (>85%) to fine particles (Dp< 2.5 μm) increasing the interest of their study on a sanitary point of view. Results showed really different NPAH and OPAH particle size distributions between both sites. At traffic site, clearly bimodal (notably for NPAHs) particle size distributions (Dp = 0.14 and 1.4 μm) were observed, while the particle size distributions were more scattered at the suburban site, especially for OPAHs. Bimodal particle size distribution observed at traffic site for the NPAH could be assigned to the vehicle emissions and the particle resuspension. Broadest distribution observed at the suburban site could be attributed to the mass transfer of compounds by volatilization/sorption processes during the transport of particles in the atmosphere. Results also showed that the combination of the study of particle size distributions applied to marker compounds (primary: 1-nitropyrene; secondary: 2-nitrofluoranthene) and to NPAH or OPAH chemical profiles bring some indications on their primary and/or secondary origin. Indeed, 1,4-anthraquinone seemed only primary emitted by vehicles while 7-nitrobenz[a]anthracene, benz[a]antracen7,12-dione and benzo[b]fluorenone seemed secondarily formed in the atmosphere.

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Kukuev, E. I. "Juvenile Individuals of Opahs (Lampridae) from the Atlantic and Pacific Oceans. Notes on the Systematics and Distribution of Opahs, Including the Description of a New Subgenus, Paralampris subgen. nov." Journal of Ichthyology 61, n.º 2 (marzo de 2021): 182–89. http://dx.doi.org/10.1134/s0032945221020089.

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Abstract Juvenile specimens of opahs (Lampridae) from the Southwest Atlantic, southeastern Pacific Ocean, and Gulf of Guinea are described. A taxonomic review of the composition of the family Lampridae is carried out, taking into account the recent revision of opah species of the genus Lampris and our own data. A new subgenus, Paralampris subgen. nov., has been identified.

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Elzein, Atallah, Rachel E. Dunmore, Martyn W. Ward, Jacqueline F. Hamilton y Alastair C. Lewis. "Variability of polycyclic aromatic hydrocarbons and their oxidative derivatives in wintertime Beijing, China". Atmospheric Chemistry and Physics 19, n.º 13 (10 de julio de 2019): 8741–58. http://dx.doi.org/10.5194/acp-19-8741-2019.

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Abstract. Ambient particulate matter (PM) can contain a mix of different toxic species derived from a wide variety of sources. This study quantifies the diurnal variation and nocturnal abundance of 16 polycyclic aromatic hydrocarbons (PAHs), 10 oxygenated PAHs (OPAHs) and 9 nitrated PAHs (NPAHs) in ambient PM in central Beijing during winter. Target compounds were identified and quantified using gas chromatography–time-of-flight mass spectrometry (GC-Q-ToF-MS). The total concentration of PAHs varied between 18 and 297 ng m−3 over 3 h daytime filter samples and from 23 to 165 ng m−3 in 15 h night-time samples. The total concentrations of PAHs over 24 h varied between 37 and 180 ng m−3 (mean: 97±43 ng m−3). The total daytime concentrations during high particulate loading conditions for PAHs, OPAHs and NPAHs were 224, 54 and 2.3 ng m−3, respectively. The most abundant PAHs were fluoranthene (33 ng m−3), chrysene (27 ng m−3), pyrene (27 ng m−3), benzo[a]pyrene (27 ng m−3), benzo[b]fluoranthene (25 ng m−3), benzo[a]anthracene (20 ng m−3) and phenanthrene (18 ng m−3). The most abundant OPAHs were 9,10-anthraquinone (18 ng m−3), 1,8-naphthalic anhydride (14 ng m−3) and 9-fluorenone (12 ng m−3), and the three most abundant NPAHs were 9-nitroanthracene (0.84 ng m−3), 3-nitrofluoranthene (0.78 ng m−3) and 3-nitrodibenzofuran (0.45 ng m−3). ∑PAHs and ∑OPAHs showed a strong positive correlation with the gas-phase abundance of NO, CO, SO2 and HONO, indicating that PAHs and OPAHs can be associated with both local and regional emissions. Diagnostic ratios suggested emissions from traffic road and coal combustion were the predominant sources of PAHs in Beijing and also revealed the main source of NPAHs to be secondary photochemical formation rather than primary emissions. PM2.5 and NPAHs showed a strong correlation with gas-phase HONO. 9-Nitroanthracene appeared to undergo a photodegradation during the daytime and showed a strong positive correlation with ambient HONO (R=0.90, P < 0.001). The lifetime excess lung cancer risk for those species that have available toxicological data (16 PAHs, 1 OPAH and 6 NPAHs) was calculated to be in the range 10−5 to 10−3 (risk per million people ranges from 26 to 2053 cases per year).

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Shahpoury, Pourya, Zoran Kitanovski y Gerhard Lammel. "Snow scavenging and phase partitioning of nitrated and oxygenated aromatic hydrocarbons in polluted and remote environments in central Europe and the European Arctic". Atmospheric Chemistry and Physics 18, n.º 18 (24 de septiembre de 2018): 13495–510. http://dx.doi.org/10.5194/acp-18-13495-2018.

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Abstract. Nitrated and oxygenated polycyclic aromatic hydrocarbons (N/OPAHs) are emitted in combustion processes and formed in polluted air. Their environmental cycling through wet deposition has hardly been studied. Fresh snow samples at urban and rural sites in central Europe, as well as surface snow from a remote site in Svalbard, were analysed for 17 NPAHs, 8 OPAHs, and 11 nitrated mono-aromatic hydrocarbons (NMAHs), of which most N/OPAHs as well as nitrocatechols, nitrosalicylic acids, and 4-nitroguaiacol are studied for the first time in precipitation. In order to better understand the scavenging mechanisms, the particulate mass fractions (θ) at 273 K were predicted using a multi-phase gas-particle partitioning model based on polyparameter linear free energy relationships. ∑NPAH concentrations were 1.2–17.6 and 8.8–19.1 ng L−1 at urban and rural sites, whereas ∑OPAHs were 79.8–955.2 and 343.3–1757.4 ng L−1 at these sites, respectively. 9,10-anthraquinone was predominant in snow aqueous and particulate phases. NPAHs were only found in the particulate phase with 9-nitroanthracene being predominant followed by 2-nitrofluoranthene. Among NMAHs, 4-nitrophenol showed the highest abundance in both phases. The levels found for nitrophenols were in the same range or lower than those reported in the 1980s and 1990s. The lowest levels of ∑N/OPAHs and ∑NMAHs were found at the remote site (3.5 and 390.5 ng L−1, respectively). N/OPAHs preferentially partitioned in snow particulate phase in accordance with predicted θ, whereas NMAHs were predominant in the aqueous phase, regardless of θ. It is concluded that the phase distribution of non-polar N/OPAHs in snow is determined by their gas-particle partitioning prior to snow scavenging, whereas that for polar particulate phase substances, i.e. NMAHs, is determined by an interplay between gas-particle partitioning in the aerosol and dissolution during in- or below-cloud scavenging.

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Niu, Yue, Ling Zhou, Huiqi Wang, Jiayu Dai, Ying Bao, Baohong Hou y Qiuxiang Yin. "Enhancing the Water Solubility of 9-Fluorenone Using Cyclodextrin Inclusions: A Green Approach for the Environmental Remediation of OPAHs". Crystals 13, n.º 5 (6 de mayo de 2023): 775. http://dx.doi.org/10.3390/cryst13050775.

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Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are toxic and carcinogenic compounds widely present in the natural environment, posing a serious threat to the environment and human health. However, the removal of OPAHs is mainly hindered by their low water solubility. Cyclodextrins (CDs) are frequently used to form inclusion complexes (ICs) with hydrophobic molecules to improve their solubility. In this study, we investigated the solubility enhancement ability of different CDs on 9-fluorenone, a common OPAH, through phase solubility experiments. We successfully prepared three solid ICs of 9-fluorenone with β-, hydroxypropyl-β-(HP-β-) and sulfobutylether-β-CD (SBE-β-CD) using the cooling crystallization method for the first time and characterized them via powder X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, etc. Molecular dynamics simulations were employed to investigate the binding modes and stable configurations of the ICs in the liquid phase and to explore the factors affecting their solubility enhancement ability. The results showed that all the CDs had a solubility enhancement effect on 9-fluorenone, with SBE-β-CD displaying the strongest effect, increasing the solubility of 9-fluorenone by 146 times. HP-β-CD, β-CD, α-CD, and γ-CD followed in decreasing order. Moreover, 9-fluorenone formed a ratio of 1:1 ICs to CDs. In addition, the interaction energy between SBE-β-CD and 9-fluorenone was the lowest among the CDs, which further validated the results of the phase solubility experiments from a theoretical perspective. Overall, this study provides a green method for the removal of 9-fluorenone pollutants in the environment and is expected to be applied to the removal and environmental remediation of other OPAHs.

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Tesis sobre el tema "OPAHs"

Mohammad, Ahmed Trifa. "Determination of OPAHs and PAHs in Particulate Matter from Ambient Air and Engine Emissions : Multidimensional Chromatography". Doctoral thesis, Stockholms universitet, Institutionen för miljövetenskap och analytisk kemi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-122046.

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Particulate matter (PM) is an air pollutant that seriously impacts human health. Epidemiological studies have shown associations between human exposure to urban air PM and lung cancer, respiratory and cardiovascular diseases. Polycyclic aromatic hydrocarbons (PAHs) and oxygenated polycyclic aromatic hydrocarbons (OPAHs) are two groups of compounds associated with PM in ambient air. These compounds are generated from the incomplete combustion of organic material of both natural and anthropogenic origin. PAHs are thought to play an important role in the adverse health outcomes from exposure to PM in air. OPAHs contain one or more carbonyl groups and could be more toxic to humans compared to their corresponding parent PAH. Measurement of these compounds at trace levels in complex matrices requires analytical methods with high selectivity and precision and low quantification limits. This thesis describes the development and application of analytical methods for the determination of PAHs and OPAHs in ambient air and engine exhaust PM. Extraction was performed using pressurized liquid extraction, and two different setups for liquid chromatography–gas chromatography (LC-GC) were employed for automated sample clean-up, separation and detection. The developed methods were validated using standard reference materials issued by the National Institute of Standards and Technology. The first methodology developed used off-line solid-phase extraction and on-line LC-GC/mass spectrometry (LC-GC/MS). This method provided low limits of quantification and high selectivity and was successfully applied to the determination of OPAHs and PAHs in PM from the urban atmosphere of Sulaymaniyah city in the Kurdistan region of Iraq. The concentration of benzo[a]pyrene in Sulaymaniyah city was three times higher than the legislated EU target value (1 ng/m3). Furthermore the analytical method was applied on exhaust PM of vehicles fuelled with various gasoline/ethanol blends. The emissions factors for PAHs and OPAHs were highest when using70% ethanol/gasoline blends at -7 °C. The second method developed provided fully automated clean-up, separation and detection of PAHs in PM extracts using a multidimensional 2D-LC/2D-GC system. Polar, mono/di-aromatic and alkane compounds were successively removed by the two-dimensional LC part of the system. Heart-cutting segments from the first GC column (first dimension) to the second GC column (second dimension) increased the resolution of poorly separated or co-eluted PAHs. The results were in good agreement with the certified values from NIST (±25%).

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.

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Sood, Kanika. "Combustion des nouveaux biocarburants : étude de la formation des Hydrocarbures Aromatiques Polycycliques Oxygénés (HAPOs) et les petites particules de suie (<10 nm)". Electronic Thesis or Diss., Université de Lille (2022-....), 2023. https://pepite-depot.univ-lille.fr/ToutIDP/EDSMRE/2023/2023ULILR088.pdf.

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Les biocarburants et autres produits chimiques dérivés de la biomasse sont désormais considérés comme un élément essentiel du portefeuille énergétique durable, où ils promettent de contribuer à la sécurité énergétique de notre société. Malgré l'intérêt indéniable que présentent ces biocarburants, leurs processus de combustion sont susceptibles de favoriser la formation d'HAPOs (Hydrocarbures Aromatiques Polycycliques Oxygénés) qui peuvent à terme contribuer à la formation de suie, et peuvent également en modifier profondément les propriétés. Le travail réalisé dans cette thèse a porté sur l'identification et la quantification des aromatiques oxygénés formés lors de la combustion d'un biocarburant à base de lignine dans des conditions de flamme. Des flammes laminaires prémélangées d'anisole (composé modèle de substitution pour la biomasse) et de mélanges de carburants hydrocarbonés (iso-octane et méthane) ont été étudiées à l'aide de la chromatographie en phase gazeuse avancée. Dans ce contexte, nous avons mis en œuvre une technique d'enrichissement de l'échantillon (piège de préconcentration de l'échantillon) avec un ensemble d'analyses chromatographiques in situ et ex situ (1D GC-MS, 1D GC-SPT-FID et 2D GC-MS) qui nous ont permis d'identifier un large panel de différents aromatiques oxygénés (~100). Ces résultats ont ensuite été utilisés pour analyser les voies de décomposition du combustible qui conduisent à la formation d'HAPOs. Avec l'identification, cette thèse fournit une base de données expérimentale quantitative détaillée en termes d'évolution de la fraction molaire par rapport à la hauteur de la flamme pour plusieurs aromatiques oxygénés et non oxygénés associés. D'autres biocarburants comme le 2,5-DMF et l'éthanol ont également été étudiés et les résultats expérimentaux ont montré que les différentes structures moléculaires des biocarburants conduisent à des différences significatives dans la formation d'espèces intermédiaires et de polluants. Ce travail met également en lumière des informations cruciales concernant la quantité et la taille des particules de suie formées dans ces flammes en utilisant LII et SMPS. Les résultats préliminaires des mesures de suie indiquent que la taille des particules de suie dans ces flammes est très petite (<10 nm)
Biofuels and other biomass-derived chemicals are now considered as a vital part of sustainable energy portfolio, where they promise to contribute to our society’s energy security. Despite the undeniable interest presented by these biofuels, their combustion processes are likely to enhance the formation of OPAHs (Oxygenated Polycyclic Aromatic Hydrocarbons) which may eventually contribute to the formation of soot, and may as well profoundly modify its properties. The work carried out in this thesis focused on the identification and quantification of the oxygenated aromatics formed during the combustion of a lignin-based biofuel in flame conditions. Laminar premixed flames of anisole (surrogate model compound for biomass) and hydrocarbon fuel blends (iso-octane and methane) have been investigated using Advanced Gas Chromatography. In this context, we implemented a sample enrichment technique (sample pre-concentration trap) with a set of in situ and ex situ chromatographic analysis (1D GC-MS, 1D GC-SPT-FID and 2D GC-MS) which enabled us to identify a large panel of different oxygenated (~100) aromatics. These results were then used to analyze the fuel decomposition pathways that lead to the formation of OPAHs. Together with identification, this thesis provides a detailed quantitative experimental database in terms of the evolution of the mole fraction with respect to the flame height for several oxygenated and associated non-oxygenated aromatics. Other biofuels like 2,5-DMF and ethanol were also studied and experimental results showed that the different molecular structures of biofuels lead to significant differences in the formation of intermediate species and pollutants. This work also highlights crucial information concerning the amount and the size of soot particles formed in such flames using LII and SMPS. Preliminary results from soot measurements indicate that the soot particle size in these flames is very small (<10 nm)

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Zhao, Qibin. "Oscillatory shearing in polymer opals". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709151.

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Campos, A. Patricio. "Opas norteamericanas en Chile". Tesis, Universidad de Chile, 2003. http://repositorio.uchile.cl/handle/2250/108210.

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Este seminario de título nació con el objetivo de investigar el “por qué las compañías norteamericanas, cuando lanzan una oferta pública de adquisición sobre alguna compañía chilena, la hacen por el 100% de ésta, o casi el 100%, sin embargo, los españoles o chilenos, cuando lanzan una oferta pública de adquisición, solo desean obtener el 51 % de la propiedad, es decir, tener el control de la compañía” Esta interrogante es difícil de responder, debido a que no se encuentra argumento teórico a esta cuestión, además, ¿por qué solo los norteamericanos lo hacen? ¿qué tienen de espaciales sus compañías o su legislación? Se llegó a la conclusión, de que la regulación norteamericana protege al accionista minoritario de las compañías que están siendo objeto de la oferta, pero no solo a las compañías objetivo en EEUU, sino en cualquier país. Si la compañía norteamericana no respeta su propia normativa porque esta comprado una compañía chilena en suelo chileno, los minoritarios chilenos pueden demandarlos en sus propios tribunales. La legislación española solo rige en dicho país, pero si sus compañías salen al extranjero, estas se rigen por las leyes locales. Como el mercado de valores chileno es altamente atomizado, si los 2 accionistas mayoritarios de una compañía deciden no participar de la oferta, la probabilidad de fracaso de ésta bordea el 100%, y si tan solo el mayoritario no quiere participar, la probabilidad de fracaso sigue siendo muy alta. Los españoles y chilenos, antes de lanzar una oferta pública de adquisición, tranzan paquetes accionarios con los controladores y luego lanzan una oferta por el porcentaje faltante para el 51%, como los norteamericanos no pueden comprar paquetes accionarios, éstos deben ofrecer comprar a todos los accionistas que estén dispuestos a vender, por ello es que lanzan ofertas por prácticamente la totalidad de la propiedad, en los casos analizados en este seminario, llagan a poseer más del 98% de la propiedad.

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Fuentes, Vega Marcela Alejandra. "OPAS. Teoría y evidencia". Tesis, Universidad de Chile, 2007. http://repositorio.uchile.cl/handle/2250/108442.

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El Problema de Agencia se define como una divergencia de intereses entre el Agente (insiders) y el Principal (outsiders) (*), es decir, el agente como maximizador, buscará el beneficio propio antes que el de la compañía. El Gobierno Corporativo es un concepto que tiene relación con la forma en que las empresas son dirigidas y controladas, en el que se incluye el conflicto mencionado. La necesidad de contar con un mercado de capitales que proteja adecuadamente a los accionistas minoritarios y permita aumentar la liquidez y transparencia del mercado junto con disminuir el costo de financiamiento de las empresas, han llevado al gobierno de Chile a la elaboración de la nueva Ley de OPAS, promulgada en Diciembre del año 2000. Dicha ley permite crear mejores Gobiernos Corporativos, estableciendo una mejor calidad de información entregada por las empresas, conformar comités de auditoría al interior de las sociedades anónimas abiertas, regular las relaciones entre partes relacionadas, mejorar los derechos de los tenedores de ADRs, entre otros. En Chile, se tiene que la mayoría de las sociedades anónimas son controladas por un solo accionista, familia o grupo económico. El problema, por lo tanto, se da entre los intereses del accionista controlador y los inversionistas (accionistas minoritarios, acreedores). Los conflictos respecto a la asignación de valor corporativo se pueden resumir como sigue: Extracción de valor de la Compañía y Premio por control.

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Phillips, Katherine Reece. "Sol-Gel Chemistry of Inverse Opals". Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493452.

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Controlling nano to microscale structuration enables one to alter a material’s optical, wetting, mechanical, and chemical properties. Structuration on this scale can be formed from spherical building blocks; in particular, monodisperse, spherical colloids assemble into crystals that can be used to template an ordered, porous structure known as an inverse opal. The structure’s porosity and periodicity provide control over both light (photonic effects) and fluid flow (wetting effects). Controlling the composition allows chemical functionality to be added to the ordered, porous structure. Inverse opals are widely used in many applications that take advantage of these properties, including optical, wetting, sensing, catalytic, and electrode applications; however, high quality structures are necessary to maintain consistent properties. Many of their properties stem from the structure itself, so controlling inverse opals’ structure (including the local composition) provides the ability to control their properties, with the potential to improve some applications and potentially enable additional ones. This thesis explores how molecular precursors can be used to control colloidal assembly and therefore alter the optical and wetting properties of high quality inverse opals. Using a bio-inspired approach, highly ordered, crack-free, silica inverse opals can be grown by co-assembling the colloidal template with a sol-gel matrix precursor using evaporation-induced self-assembly. Using sol-gel chemistry, the size, shape, and charge of the precursor can be controlled, which can be used to tune the colloidal assembly process. Here, we use the sol-gel chemistry of the precursors to control both the morphology and composition of these photonic structures. In particular, temperature-induced condensation of the silica sol-gel matrix alters the shape of an inverse opal’s pores (Chapter 2), and silica and titania precursors can be mixed to make hybrid oxide structures (Chapter 3). Additionally, rationally designed precursors enable the fabrication of crack-free inverse opals in materials beyond silica, which we show for titania as a proof-of-concept (Chapter 4). By controlling the structure and composition with sol-gel chemistry, we can tailor both the optical and wetting properties, as discussed in the second part of each chapter; these properties have important effects for the various applications. In this way, sol-gel chemistry can be used to assemble inverse opals with complex functionality.
Chemistry and Chemical Biology

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Aryal, Durga Prasad. "Theory and modelling of functional photonic opals". Thesis, University of Surrey, 2007. http://epubs.surrey.ac.uk/843026/.

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In this dissertation, we explore the optical properties of various opal-based photonic crystal structures. Particular attention is paid to the tunability of the optical properties, especially the photonic band gaps (PBG), with the motivation to apply these opal-based photonic crystals (PCs) to the design of functional surfaces and switchable windows. After reviewing the basic optical properties of inverse opals, two different types of opal-based photonic crystals, namely the Double-Shell Photonic Crystal (DSPC) and the Double-Inverse-Opal Photonic Crystal (DIOPC) are successively introduced and throroughly studied. In the DSPC structure, each sphere in the periodic photonic crystal structure is made of a hollow core, along with an accompanying shell of a different dielectric material; the resulting spherical structure is embedded in a high-index dielectric background. By contrast, the DIOPC is designed with an inverse opal backbone, in which the air pores are partially filled with a dielectric core sphere. In our work, two types of photonic bandgap tuning are examined, namely geometrical/positional, and tailoring of the materials' properties. A comparison of the proposed structures regarding their potential for experimental realization is also performed. Considering that the air shells in the DIOPC structure allow for relative movement of the dielectric cores inside them, we propose and study a completely novel approach to obtain a switchable complete band gap achieved, by shifting the spheres inside the air shells. After demonstrating that the complete photonic band gap is open for certain core sphere positions and is closed for others, we propose ways to optimise this new switching process. This optimisation leads to a maximum switching of the complete photonic band gap of 3.5%.Taking into account that in real-world situations, all photonic crystals possess a certain amount of structural imperfections, the last step of the study concerns the effects of disorder on the optical properties of opal-based photonic crystals. After discussing different types of disorder, in both the backbone and the core spheres, we conclude that to retain a complete PEG in the DIOPC structure, and thus the switching process, a maximum backbone disorder of 1 % should be reached experimentally, whereas the disorder on the core sphere does not affect the PEG as much. These investigations have been performed using both a plane-wave expansion method and a finite-difference time-domain method.

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Payet, Puccio José Antonio. "OPAs hostiles y medidas de protección". IUS ET VERITAS, 2016. http://repositorio.pucp.edu.pe/index/handle/123456789/123268.

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McCarthy, Laura Anne. "South Australian sedimentary opals : evidence for syngenetic deposition /". Title page, contents and abstract only, 2001. http://web4.library.adelaide.edu.au/theses/09SB/09sbm1234.pdf.

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Sütterlin, Martin. "New inverse hydogel opals as protein responsive sensors". Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2014/7017/.

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In this work, the development of temperature- and protein-responsive sensor materials based on biocompatible, inverse hydrogel opals (IHOs) is presented. With these materials, large biomolecules can be specifically recognised and the binding event visualised. The preparation of the IHOs was performed with a template process, for which monodisperse silica particles were vertically deposited onto glass slides as the first step. The obtained colloidal crystals with a thickness of 5 μm displayed opalescent reflections because of the uniform alignment of the colloids. As a second step, the template was embedded in a matrix consisting of biocompatible, thermoresponsive hydrogels. The comonomers were selected from the family of oligo(ethylene glycol)methacrylates. The monomer solution was injected into a polymerisation mould, which contained the colloidal crystals as a template. The space in-between the template particles was filled with the monomer solution and the hydrogel was cured via UV-polymerisation. The particles were chemically etched, which resulted in a porous inner structure. The uniform alignment of the pores and therefore the opalescent reflection were maintained, so these system were denoted as inverse hydrogel opals. A pore diameter of several hundred nanometres as well as interconnections between the pores should facilitate a diffusion of bigger (bio)molecules, which was always a challenge in the presented systems until now. The copolymer composition was chosen to result in a hydrogel collapse over 35 °C. All hydrogels showed pronounced swelling in water below the critical temperature. The incorporation of a reactive monomer with hydroxyl groups ensured a potential coupling group for the introduction of recognition units for analytes, e.g. proteins. As a test system, biotin as a recognition unit for avidin was coupled to the IHO via polymer-analogous Steglich esterification. The amount of accessible biotin was quantified with a colorimetric binding assay. When avidin was added to the biotinylated IHO, the wavelength of the opalescent reflection was significantly shifted and therefore the binding event was visualised. This effect is based on the change in swelling behaviour of the hydrogel after binding of the hydrophilic avidin, which is amplified by the thermoresponsive nature of the hydrogel. A swelling or shrinking of the pores induces a change in distance of the crystal planes, which are responsible for the colour of the reflection. With these findings, the possibility of creating sensor materials or additional biomolecules in the size range of avidin is given.
In dieser Arbeit wird die Entwicklung von temperatur- und proteinresponsiven Sensormaterialien auf Basis von biokompatiblen, inversen Hydrogelopalen (IHO) vorgestellt, mit welchen die spezifische Erkennung größerer Biomoleküle visuell ausgelesen werden kann. Die Darstellung der IHOs erfolgte mittels Templatverfahren, bei dem im ersten Schritt monodisperse Silicapartikel vertikal auf Objektträger abgeschieden wurden. Die so erhaltenen Kolloidkristalle mit einer Dicke von 5 μm zeigten opaleszente Reflexionen aufgrund der gleichförmigen Anordnung der Partikel. Im zweiten Schritt wurde das Templat in eine Matrix aus biokompatiblen, thermoresponsiven Hydrogelen eingebettet. Die Comonomere wurden aus der Familie der Oligo(ethylenglykol)methacrylate ausgewählt. Zur Synthese des Hydrogels wurde die Monomerlösung in eine Polymerisationsform injiziert, welche die Kolloidkristalle als Templat beinhaltete. Die Zwischenräume der Templatpartikel wurden mit der Monomerlösung gefüllt und das Hydrogelnetzwerk per UV-Polymerisation erhalten. Die Templatpartikel wurden anschließend nasschemisch heraus gelöst, so dass eine poröse innere Struktur erhalten wurde. Die regelmäßige Anordnung der Poren und damit die opaleszenten Reflexionen wurden dabei beibehalten, so dass diese Systeme als inverse Hydorgelopale bezeichnet werden. Ein Porendurchmesser von mehreren hundert Nanometer, sowie durchgängige Verbindungskanäle zwischen den einzelnen Poren sollten eine Diffusion von großen (Bio)molekülen erleichtern, was bei bisherigen Systemen ein Problem darstellte. Die Copolymerzusammensetzung wurde dabei so gewählt, dass ein Kollaps des Hydrogels über 35 °C stattfand. Alle Hydrogele zeigten ausgeprägte Quellung in Wasser unterhalb der kritischen Temperatur. Der Einbau von reaktiven Comonomeren mit Hydroxylgruppen gewährleistete dabei die Funktionalisierbarkeit des Hydrogels mit Erkennungsgruppen für entsprechende Analytmoleküle, wie z.B. Proteine. Als Testsystem wurde Biotin als Erkennungseinheit für Avidin in das Hydrogel mittels polymeranaloger Steglich Veresterung eingebaut. Die Menge an zugänglichem Biotin wurde dabei per colorimetrischem Bindungsassay quantifiziert. Dabei zeigte sich, dass sich die Wellenlänge der Reflexion nach Zugabe von Avidin zum biotinylierten inversen Hydrogelopal signifikant verschob und damit das Bindungsereignis visuell auslesbar ist. Dieser Effekt beruht auf dem veränderten Quellungsverhalten des Hydrogels nach Bindung des hydrophilen Proteins Avidin in Wasser, welches durch den thermosresponsiven Charakter des Hydrogels verstärkt ist. Ein Aufweiten oder Schrumpfen der Poren ändert die Abstände der gleichmäßig angeordneten Poren, welche für die Farbe des inversen Opals verantwortlich sind. Auf Basis dieser Erkenntnisse lassen sich möglicherweise Sensormaterialen für die Erkennung weiterer Biomoleküle in der Größenordnung von Avidin erstellen.

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Libros sobre el tema "OPAHs"

Charlotte, Ward, ed. Opals. Bethesda, MD: Gem Book Publishers, 1997.

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Ward, Fred. Opals. Malibu, CA: Gem Book Publishers, 2011.

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Ethan, Eric. Opals. New York: Gareth Stevens Pub., 2012.

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Hancock-Beaulieu, Micheline. Opacs. London: Library and Information Technology Centre, 1993.

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ill, Finney Pat, ed. Opa's stories. Houston, Tex: Colophon House, 1996.

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Jonge, Freek de. Opa's wijsvinger. Amsterdam: De Harmonie, 1993.

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Opa's wijsvinger. Amsterdam: De Harmonie, 1993.

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1963-, Vliet Helen van, ed. Opa's toverkoffer. Tilburg: Zwijsen, 2006.

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1874-1944, Custance Olive, ed. Opals: With, Rainbows. Poole [England]: Woodstock Books, 1996.

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Opa's droom: Novelle. Schoorl: Conserve, 1987.

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Míguez, H., A. Blanco, F. García-Santamaría, M. Ibisate, C. López, F. Meseguer, F. López-Tejeira y J. Sánchez-Dehesa. "Inverse Opals Fabrication". En Photonic Crystals and Light Localization in the 21st Century, 219–27. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0738-2_16.

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Vogel, Burkhard. "Phono-Amp with OPAs". En Slopes and Levels, 63–72. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-99443-3_8.

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Galisteo-López, Juan F., Luz K. Gil, Marta Ibisate y Cefe López. "Organic Opals: Properties and Applications". En Organic and Hybrid Photonic Crystals, 31–55. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-16580-6_2.

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Xiao, Huang, Han Xiao y Claudia Eckert. "OPARS: Objective Photo Aesthetics Ranking System". En Lecture Notes in Computer Science, 861–64. Berlin, Heidelberg: Springer Berlin Heidelberg, 2013. http://dx.doi.org/10.1007/978-3-642-36973-5_103.

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Armellini, C., A. Chiappini, A. Chiasera, Maurizio Ferrari, Yoann Jestin, E. Moser, Richard Retoux et al. "Fabrication and Characterization of Silica Opals". En Advances in Science and Technology, 118–26. Stafa: Trans Tech Publications Ltd., 2008. http://dx.doi.org/10.4028/3-908158-12-5.118.

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Egen, Marc, Rudolf Zentel, Patrick Ferrand, Stefanie Eiden, Georg Maret y Frank Caruso. "Preparation of 3D Photonic Crystals from Opals". En Photonic Crystals, 109–31. Weinheim, FRG: Wiley-VCH Verlag GmbH & Co. KGaA, 2006. http://dx.doi.org/10.1002/3527602593.ch6.

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Keller, Peter C. "Gemstones Formed from Surface Water: The Opals of Australia". En Gemstones and Their Origins, 19–33. Boston, MA: Springer US, 1990. http://dx.doi.org/10.1007/978-1-4684-6674-4_2.

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Fu, Ming, Ji Zhou, Bo Li, Qun Fang Xiao, Yue Hui Wang y Long Tu Li. "Optical Properties of Nanocrystalline Ag Doped Silica Inverse Opals". En Key Engineering Materials, 555–57. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-410-3.555.

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Moiseyenko, V., A. V. Yevchik, M. Dergachov, O. Spichak y V. Gorelik. "The Effects of Disorder on the Optical Spectra of Synthetic Opals". En Springer Proceedings in Physics, 315–27. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-18543-9_22.

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Norris, D. J. y Yu A. Vlasov. "The Complete Photonic Band Gap in Inverted Opals: How Can We Prove it Experimentally?" En Photonic Crystals and Light Localization in the 21st Century, 229–37. Dordrecht: Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0738-2_17.

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Liang, Lei, Yanling Wang, Bin Liu, Yongfei Li, Longhao Tang, Baojun Bai y Ye Zhang. "Synthesis and Application of a Low Formation Damage Clay Stabilizer". En SPE Conference at Oman Petroleum & Energy Show. SPE, 2022. http://dx.doi.org/10.2118/200039-ms.

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Abstract To develop a low formation damage clay stabilizer, a kind of organic polyether amine clay stabilizer (OPACS) was synthesized. Compared with the commercial clay stabilizers, the application performance of the OPACS was investigated. OPACS was synthesized with 1, 2-propanediol, 2-(chloromethyl)oxirane and ammonia as main raw materials. The molecular structure of OPACS were characterized by FTIR and NMR, and its anti-swelling performance was tested by centrifugation. Other performance, including its temperature resistance, acid and alkali resistance, elution resistance and etc., were also researched. Different permeability cores were used to test the formation damage of OPACS, and its anti-swelling mechanism was studied by SEM. The FTIR and NMR spectra showed that the expected product structure was synthesized. When the clay stabilizer was adding with 2.0 wt.%, the anti-swelling rate of OPACS was over 90% which was better than the commercial clay stabilizers (about 80%) we bought. At the temperature range of 20 °C-120 °C and the pH range of 2-12, the anti-swelling rate of OPACS changed less than 2.5%. In the long-term efficacy test, the elution recovery rate of OPACS was higher than 92% within the concentration between 0.5 wt.%-3.0 wt.%. Natural cores with different permeability were selected for core flow experiments. The test results showed that the permeability recovery rate of cores were more than 95% treated with OPACS, which meant the formation damage value was less than 5%. From the SEM of clay treated with different clay stabilizers, we could find out the structure of clay treated with OPACS was more compact than those treated with other stabilizers we bought. These results have shown that OPACS can effectively inhibit the water absorption swelling of clay and recovery formation damage, which are helpful to the EOR and friendly to the environment.

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Tanida, Jun, Yasunori Nishimura y Yoshiki Ichioka. "A Design of an Optical Parallel Multiprocessor Based on Optical Array Logic Modular Architecture". En Optical Computing. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/optcomp.1991.pdp1.

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Optical array logic (OAL) is proposed as a basis of parallel optical digital computing.1 This technique is applied to an optical digital computing system called OPALS (optical parallel array logic system).2 Processing of the OPALS is based on SIMD (single instruction multiple data) and iterative structures, which is designed to utilize the characteristics of OAL effectively. However, there are problems related to the structure of the OPALS. Since the OPALS has a closed architecture, it is difficult to extend the system. Although many data can be processed simultaneously, minute operations for a part of data cause processing inefficiency. In addition, necessity of three dynamic components in the OPALS results in complication of hardware and degradation of processing throughput. Thus a new concept for system construction is an important subject in OAL scheme.

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D'Andrea, A., Laura Pilozzi, D. Schiumarini y N. Tomassini. "Photonic band gap of opals and inverse opals". En Photonics, Devices, and Systems II, editado por Miroslav Hrabovsky, Dagmar Senderakova y Pavel Tomanek. SPIE, 2003. http://dx.doi.org/10.1117/12.498376.

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Bueno, Luciano A., Roberto Bertholdo, Djalma A. Barros Filho, Younes Messaddeq y Sidney J. L. Ribeiro. "Rare earth doped synthetic opals and inverse opals". En International Symposium on Optical Science and Technology, editado por Edward J. A. Pope, Helmut K. Schmidt, Bruce S. Dunn y Shuichi Shibata. SPIE, 2002. http://dx.doi.org/10.1117/12.456543.

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Tanida, J. y Y. Ichioka. "OPALS: Optical Parallel Array Logic System". En Optical Computing. Washington, D.C.: Optica Publishing Group, 1985. http://dx.doi.org/10.1364/optcomp.1985.tua4.

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A novel optical digital computing system called Optical Parallel Array Logic System (OPALS) is presented, which can execute cellular logic1 in parallel. The system is constructed on the basis of the concept of optical array logic. The pure optical version of the OPALS can be realized by using a dynamic optical coding technique and optical correlation by a multi-focus imaging system. Although the OPALS is still a conceptual system, it would be expected to be a prototype of optical digital computing systems in future.

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Liu, Yuan Bin, Jun Qiu, Rong Jin y Lin Hua Liu. "Artificial Opals: Reflection Spectra and Distribution Laws of Energy Transfer". En ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/mnhmt2016-6510.

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In this work, we investigated the reflection properties of artificial opals composed of submicron silica spheres with diverse structural parameters and under the effect of light in different states. Furthermore, the primary rules how the reflection properties of artificial opals convert as these factors changing have been revealed clearly. These factors can take effects in changing the shape, value, and position of the peak of the hemispherical reflectance of artificial opals. Then we got the distribution and propagation process of the Poynting vectors corresponding to the positions of the diffraction peak and the low reflectance in the artificial opals at normal and oblique incidence of P-polarization. Comparing with the theoretical interpretation which is a little complicated and nonobjective, this paper will provide a visual result to explain the reason why the structure has high reflectance in some spectral ranges.

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Marimuthu, K., D. Ganesh Gopal, Shivam Aditya y Varun Mittal. "Cryptanalysis of oPass". En 2014 International Conference on Advanced Communication, Control and Computing Technologies (ICACCCT). IEEE, 2014. http://dx.doi.org/10.1109/icaccct.2014.7019457.

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Sussman, Jason, David Snoswell, Andreas Kontogeorgos, Jeremy J. Baumberg y Peter Spahn. "Thermochromic Polymer Opals". En Conference on Lasers and Electro-Optics. Washington, D.C.: OSA, 2010. http://dx.doi.org/10.1364/cleo.2010.jwa51.

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Yang, F. S., M. E. Marhic y L. G. Kazovsky. "CW Fiber Optical Parametric Amplifier with Net Gain and Wavelength Conversion Efficiency Greater than One". En Photon Correlation and Scattering. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/pcs.1996.sub.5.

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In order to be useful in a wide range of communication applications, fiber optical parametric amplifiers (OPA’s) and wavelength converters should operate on a cw basis. Furthermore, conversion efficiency Gi should be greater than or equal to one, in order to avoid the substantial signal-to-noise ratio degradation which occurs if Gi ≪ 1. Currently silica-based fibers have the best characteristics for making fiber OPA’s. However, owing to the relative weakness of the third-order nonlinear susceptibility in such fibers, amplification by fiber OPA’s requires a high pump power and/or a large fiber length. Pulsed amplification has been reported by a number of groups. CW fiber parametric amplification with a 17 dBm pump has been reported, but with a gain insufficient to overcome fiber loss [1].

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Towrie, M., P. Matousek, A. W. Parker, F. P. Taday y W. T. Toner. "Two 40 Khz Repetition Rate Independently Tunable, Synchronised Femtosecond Pulses Generated In The Visible Using Optical Parametric Amplifiers". En The European Conference on Lasers and Electro-Optics. Washington, D.C.: Optica Publishing Group, 1996. http://dx.doi.org/10.1364/cleo_europe.1996.ctuo6.

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Many time-resolved spectroscopy techniques require two broadly and independently tunable, synchronised light pulses. Recent advances in short pulse laser technology and non-linear crystal materials have lead to rapid development of optical parametric oscillators (OPOs) and travelling wave optical parametric amplifiers (OPAs) capable of meeting these requirements. Our aim was to develop a multi-kilohertz repetition rate OPA system for femtosecond/picosecond, pump and probe time-resolved absorption and resonance Raman spectroscopies. We believe this work reports, for the first time, on synchronously pumped travelling wave OPAs. The design similar to that described in [1] was adopted for the development of the OPAs.

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Informes sobre el tema "OPAHs"

NMR Publikations. Vähennä ruokahävikkiä - Ympäristöystävällisen ja kannattavan ruokatalouden opas. Nordisk Ministerråd, septiembre de 2012. http://dx.doi.org/10.6027/anp2012-743.

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Melo-Velandia, Luis Fernando, Camilo Andrés Orozco-Vanegas y Daniel Parra-Amado. Ofertas Públicas de Adquisición y su efecto sobre las rentabilidades en el mercado accionario: El caso de NUTRESA y SURA en Colombia. Banco de la República, abril de 2022. http://dx.doi.org/10.32468/be.1195.

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Se emplea un estudio de eventos donde se evalúa si hay impactos significativos en las rentabilidades anormales del mercado accionario colombiano a partir de las ofertas públicas de adquisición (OPAs) realizadas sobre las empresas Nutresa y Sura. Definiendo el evento como el 17 de enero de 2022, el cual está relacionado con la adjudicación de las primeras OPAs y el anuncio de una segunda ronda de estas operaciones, se encuentra evidencia estadística de que dicho evento tuvo un efecto significativo sobre los retornos de las acciones estudiadas. En particular, se puede afirmar que, bajo las diferentes especificaciones estimadas, los retornos fueron estadísticamente diferentes durante el evento respecto a aquellos que se hubieran observado en tiempos normales sin la presencia del evento.

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Frank, Matthias, David N. Fittinghoff, Dan E. Bower, Owen B. Drury, John M. Dzenitis, Robert A. Buckles, Carter Munson y Carl H. Wilde. Line-of-sight measurements for the NIF Neutron Imaging System and determination of line-of-sight offsets in OPAS 90-135 images. Office of Scientific and Technical Information (OSTI), mayo de 2011. http://dx.doi.org/10.2172/1113514.

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Potential Benefits of Manmade Opals Demonstrated for First Time (Fact Sheet). Office of Scientific and Technical Information (OSTI), junio de 2012. http://dx.doi.org/10.2172/1045719.

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