Download or read book Investigating the Formation Mechanism of Polycyclic Aromatic Hydrocarbons and Adapting Particle Swarm Optimization Techniques to Search Large Data Sets written by Daniel P. Caputo and published by . This book was released on 2010 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: The unidentified infrared bands (UIBs) have been attributed to emission from polycyclic aromatic hydrocarbons (PAHs). The UIBs at 3.3 and 11.3 [mu]m, among others, are seen in many astrophysical environments, with the notable exception of carbon-rich AGB stars (C stars). PAHs are expected to form around C stars, yet only a few show the UIBs and all of these have hot companions. This makes C stars with hot companions an ideal environment to study the conditions associated with PAH formation and processing. We present new observations, taken using the Gemini North telescope, of several C stars with hot companions in order to understand the distribution of PAHs responsible for the emerging UIB emission. As the size of data and model sets continue to increase, more efficient ways are needed to sift through the available information. We also present a computational method which will efficiently search large parameter spaces to either map the space or find individual data/models of interest. This is done through a heavily modified Particle Swarm Optimization algorithm.

Download or read book Theoretical Modelling and Mechanistic Study of the Formation and Atmospheric Transformations of Polycyclic Aromatic Compounds and Carbonaceous Particles written by Antonius Indarto and published by Universal-Publishers. This book was released on 2010-06-11 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Polycyclic Aromatic Hydrocarbons (PAHs) and soot share the same origin (incomplete combustion or pyrolysis) and nature, namely structural and electronic features. The purpose of the research work discussed in this thesis is to offer a theoretical contribution to elucidate some aspects of PAH and soot particle formation. The interest in carrying out such a work lies on one hand in the ubiquitous presence of both species in the environment, on the other hand on the concern for their impact on both human health, specifically involving the respiratory system, and climate, in particular as regards global warming. Thus, a better knowledge on the formation mechanisms of PAHs and soot could then help the efforts to reduce their concentration in our atmosphere. Since the formation mechanisms still presents unclear aspects, the suggestions and indications which can be offered by a theoretical study come out to be complementary to the large amount of experimental data collected so far. In setting up models aimed to mimic what happens in real pyrolysis or combustion situations, we have exploited the fact that PAHs and soot share as a common trait the presence of condensed unsaturated cycles (whose aromatic character can be variable). Thus, though types of soot of different origin will exhibit, on a larger scale, a variety of structural traits, we have chosen an assortment of PAH-like models to study different processes, together with other smaller unsaturated closed and open shell species that are known to play a role in the synthesis course. A preliminary phase of the study was aimed to assess which computational level could be both dependable and affordable to investigate the growth of a PAH-like radical when it is adsorbed onto soot platelets (particle phase). Then the Bittner-Howard variant of the widely accepted Hydrogen Abstraction Acetylene Addition (HACA) growth mechanism has been explored by Density Functional Theory (DFT) at the level mentioned above, both in the gas and particle phases, and over a wide range of temperatures. A parallel mechanism, differing from HACA, based on polyynes and characterized by the proliferation of radical centers, has also been studied for a variety of models at a multiconfigurational theory level. To the end, we have explored several reaction pathways starting from the addition of the propargyl radical to butadiyne.

Download or read book Predictive Modeling of Polycyclic Aromatic Hydrocarbon Formation During Pyrolysis written by Mengjie Liu (Ph. D.) and published by . This book was released on 2020 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt: Polycyclic aromatic hydrocarbons (PAHs), large molecules comprised of multiple aromatic rings like anthracene or pyrene, are a notable intermediate and byproduct in combustion or pyrolysis of hydrocarbon fuels. On their own, they have been shown to pose a significant health risk, with certain PAHs being linked to increased cancer risk in humans. In addition, PAHs are known to play an important role as building blocks towards larger particles, known as soot or black carbon, which contribute a significant fraction of atmospheric PM2.5 pollution (particulate matter with diameters under 2.5 [mu]m). These particulates pose additional health risks and can also contribute to global climate change via radiative forcing. This motivates interest in understanding the chemical pathways leading to the formation of these PAHs, which could inform better models to predict PAH emissions and optimize methods to reduce their formation. This thesis presents methods to improve the capabilities of automatic mechanism generation software in modeling the complex chemistry involved in PAH formation. In particular, it focuses on the Reaction Mechanism Generator (RMG) software, an open-source package developed primarily in Python. RMG automatically identifies species and reactions which are relevant at conditions of interest to aid construction of detailed mechanisms, but it has not been previously applied for PAH chemistry. To do so, new algorithms were developed to improve treatment of aromaticity and chemical resonance to better reflect the true behavior of molecules within the limitations of programmatic representations. The effect of polycyclic ring strain on parameter estimation was also investigated, highlighting challenges in capturing 3D conformational effects using the existing estimation frameworks and methods to address them. These improvements to fundamental algorithms play an important role in how thermochemical and kinetic parameters are estimated. The combined utility of these developments is demonstrated by the generation of a detailed mechanism for modeling PAH formation up to pyrene in acetylene pyrolysis, which represents an important milestone in RMG capabilities. Analysis of the model provides insight into the relative contributions of various PAH formation pathways, revealing that hydrogen abstraction, acetylene addition pathways are the key contributors to PAH formation in this system.

Download or read book Polycyclic Aromatic Hydrocarbons and Astrophysics written by A. Léger and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 405 pages. Available in PDF, EPUB and Kindle. Book excerpt: The near Infra-Red emission of the Interstellar Medium is a very puzzling subject. In the brightest regions, where spectroscopic observa tions are possible from the ground, several bands (3.3 - 3.4 - 6.2 - 7.7 - 8.6 - 11.3 ~m) have been observed since 1973. The absence of satisfying explanation was so obvious that they were called "Unidenti fied IR Emission Bands". The puzzle still increased when were known the first results of the general IR sky survey made by the satellite IRAS. On a large scale, the near IR emission of the Interstellar medium was expected to be very small but it was observed to be about one third of the total IR emission for our own galaxy ..• The situation has moved in 1984 when it was suggested that a class of stable organic molecules, the Polycyclic Aromatic Hydrocarbons (PAH's) could be at the origin of this near IR emission. Initially based on the required refractory character of particules that should be heated to high temperature without subliming, this hypothesis leads to a sugges tive spectroscopic similarity with the observed astronomical bands. This hypothesis is attractive and it has many implications, for ins tance, the PAHs would be the most abundant organic molecules in the universe. However, many points have to be clarified and the different consequences of this suggestion should be explored.

Download or read book Polycyclic Aromatic Hydrocarbons written by Kazuichi Hayakawa and published by Springer. This book was released on 2018-02-05 with total page 267 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book reviews Polycyclic Aromatic Hydrocarbons (PAHs) and Nitropolycyclic Aromatic Hydrocarbons (NPAHs) contamination in the context of environmental pollution in Asia. It is comprised of the following sections: 1. Fundamental Chemistry and General Characteristics; 2. Analytical Methods; 3. Emission Source and Atmospheric Behavior; 4. Atmospheric Polycyclic Aromatic Hydrocarbons and PM2.5; 5. Polycyclic Aromatic Hydrocarbons in Marine Environments; 6. Metabolic Activation/Toxicities; and 7. Environmental Standards and Guidelines. This volume concentrates on the Far East due to the massive consumption of coal and petroleum in China, which has led to considerable levels of air pollution. High concentration of atmospheric PM2.5 in Beijing have been reported since January 2013 and exposure to such high concentrations may cause respiratory, cardiac and lung diseases. Gathering contributions from international experts, this volume provides a valuable reference guide for global researchers and students interested in learning from the East Asian experience.

Download or read book Handbook of Polycyclic Aromatic Hydrocarbons written by Alf Bjørseth and published by . This book was released on 1983 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Polycyclic Aromatic Hydrocarbons written by Ronald G. Harvey and published by VCH Publishers. This book was released on 1997 with total page 667 pages. Available in PDF, EPUB and Kindle. Book excerpt: A resurgence of interest in the chemistry of polycyclic aromatic hydrocarbons (PAHs) has been stimulated by the discovery of the fullerenes and the identification of the active metabolites of the carcinogenic polycyclic hydrocarbons. PAHs are widespread environmental pollutants. Improved understanding of their mechanisms of carcinogenesis has important implications for human cancer. PAHs also are finding increasing application in the synthesis of dyes, drugs, and numerous other types of compounds. This volume is a timely, comprehensive survey of the chemistry of PAHs. It brings together in a single volume all essential information on the physical and spectral properties, methods of synthesis, chemical reactions, and molecular structures of a broad range of polyarenes, both alternant and nonalternant. A total of 358 ring systems are covered, 233 of which are nonalternant PAH compounds. This is the most complete account of the chemistry of PAHs currently available.

Download or read book Polynuclear Aromatic Hydrocarbons written by Marcus Cooke and published by . This book was released on 1982 with total page 992 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Polycyclic Aromatic Hydrocarbons and Dust in Regions of Massive Star Formation written by Els Peeters and published by . This book was released on 2002 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Carcinogenic Effects of Polycyclic Aromatic Hydrocarbons written by Andreas Luch and published by . This book was released on 2005 with total page 489 pages. Available in PDF, EPUB and Kindle. Book excerpt: 1. Polycyclic aromatic hydrocarbon-induced carcinogenesis - an introduction / Andreas Luch -- 2. Metabolic activation and detoxification of polycyclic aromatic hydrocarbons / Andreas Luch and William M. Baird -- 3. Biomonitoring of polycyclic aromatic hydrocarbons - human exposure / Albrecht Seidel -- 4. Macromolecular adducts as biomarkers of human exposure to polycyclic aromatic hydrocarbons / David H. Phillips -- 5. DNA damage and mutagenesis induced by polycyclic aromatic hydrocarbons / Ahmad Besaratinia and Gerd P. Pfeifer -- 6. Mechanisms of repair of polycyclic aromatic hydrocarbon-induced DNA damage / Hanspeter Naegeli and Nicholas E. Geacintov -- 7. Aberrant gene expression and cell signalling/epigenetic effects induced by polycyclic aromatic hydrocarbons / Pablo Steinberg -- 8. Indicator assays for polycyclic aromatic hydrocarbon-induced genotoxicity / Hansruedi Glatt -- 9. Tumorigenicity of polycyclic aromatic hydrocarbons / Shantu Amin and Karam El-Bayoumy -- 10. Genetic susceptibility to polycyclic aromatic hydrocarbon-induced carcinogenesis / Ari Hirvonen -- 11. Polycyclic aromatic hydrocarbon-induced carcinogenesis - an integrated view / Andreas Luch

Download or read book Polycyclic aromatic hydrocarbons under high temperature conditions written by Martín Sarobe Ugarriza and published by . This book was released on 1998 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental Investigation of Polycyclic Aromatic Hydrocarbons as Catalysts for Molecular Hydrogen Formation in the Interstellar Medium written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Kinetic and Product Studies of the Heterogeneous Reactions of Surface bound Polycyclic Aromatic Hydrocarbons Wiht Selected Atmospheric Oxidants written by Nana-Owusua Alecia Kwamena and published by . This book was released on 2008 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Growth of Unsaturated Cyclic and Polycyclic Aromatic Hydrocarbons Reactions Under the Conditions of the Interstellar Medium written by and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hydrocarbons, in particular polycyclic aromatic hydrocarbons (PAHs), have been long discussed to be carriers of interstellar infrared (IR) emission and ultraviolet (UV) absorption features. Yet, their origin in dense phases of the interstellar medium (ISM), such as molecular clouds, remains unclear. In this work, growth mechanisms based on ion-molecule reactions between cationic PAHs/hydrocarbons and methyne (CH) were investigated. The reaction type and the precursor were derived and selected from known chemical and physical properties of the ISM. These chemical reactions were characterised by calculating branching ratios (based on cross sections) and capture rate coefficients, minimum reaction paths, reaction enthalpies, thermal equilibrium constants, and microcanonic isomerisation and radiative deactivation rate coefficients. In order to cope with the variety of reaction parameters, a hierarchic workflow scheme was set up. First, the reaction potential energy surface was sampled by molecular dynamics simulations. Then, minimum energy paths of the most probable reaction channels were investigated. Finally, molecular and kinetic properties of stationary points were calculated. The quantum chemical level of theory was increased at each step from DFTB (tight-binding density-functional), to DFT, and finally to post-Hartree-Fock methods. Results on CH based hydrocarbon growth showed the transition from non-cyclic hydrocarbons to cyclic and aromatic structures and from cyclic to polycyclic aromatic hydrocarbons. Additionally, the reactive collisions between hydrocarbons and CH were found to produce sufficient energy for isomerisation and fragmentation processes even at ultra low temperatures. In all, the results indicate that methyne might be a proper precursor for the formation of large interstellar PAHs.

Download or read book Formation of Polycyclic Aromatic Hydrocarbons PAH in Laminar Premixed Flat Atmospheric Flames written by Marco J. Castaldi and published by . This book was released on 1997 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Mechanisms of Metabolism and Toxicity of Polycyclic Aromatic Hydrocarbons in Rat Testis written by Antonis Georgellis and published by . This book was released on 1989 with total page 53 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Chemistry Research and Applications written by Guilherme C. Bandeira and published by Nova Science Publishers. This book was released on 2012 with total page 425 pages. Available in PDF, EPUB and Kindle. Book excerpt: