• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 365
  • 96
  • 57
  • 32
  • 15
  • 12
  • 9
  • 6
  • 5
  • 4
  • 4
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 713
  • 625
  • 533
  • 115
  • 82
  • 77
  • 72
  • 70
  • 65
  • 62
  • 59
  • 59
  • 58
  • 54
  • 54
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
241

Effects of Cyclodextrin on Extraction and Fungal Remediation of Polycyclic Aromatic Hydrocarbon-contaminated Mahoning River Sediment

Pabba, Sowmya 02 September 2008 (has links)
No description available.
242

Time-Dependent Density-Functional Description of the <sup>1</sup>L<sub>a</sub> State in Polycyclic Aromatic Hydrocarbons

Richard, Ryan M. 20 July 2011 (has links)
No description available.
243

Photoluminescence by Interstellar Dust

Vijh, Uma Parvathy 05 October 2005 (has links)
No description available.
244

Studies on π-extended helicenes / π拡張ヘリセンに関する諸研究

Nakakuki, Yusuke 23 March 2022 (has links)
京都大学 / 新制・課程博士 / 博士(工学) / 甲第23927号 / 工博第5014号 / 新制||工||1783(附属図書館) / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 松田 建児, 教授 杉野目 道紀, 教授 生越 友樹 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
245

Source apportionment of polycyclic aromatic hydrocarbons in diverse environmental media using receptor and physico-chemical models

Sofowote, Uwayemi 10 1900 (has links)
This thesis focused on the interpretation of environmental data obtained from chemical analyses of complex and divergent environmental media. Environmental monitoring of pollutants yields large datasets which may be difficult to process using simplistic univariate approaches. Polycyclic aromatic hydrocarbons (PAH) are environmental organic contaminants that have important health implications and are ubiquitous in the environment. These compounds are regularly monitored in all environmental compartments but delineating their impacting sources from analytical data is usually challenging and thus not routinely attempted. The work contained in this thesis discusses how source information can be obtained by the application of (a) qualitative relationships, (b) physico-chemical models dealing with phase change and partitioning, as well as (c) receptor models using factor analysis to P AH data collected in samples from the atmosphere and in suspended sediments. There are unique concepts and new applications embodied in this thesis. They include: (a) The development and definition of a new diagnostic relationship that discriminates between industrial and urban sources of P AH, (b) the integration of qualitative diagnostic correlations with measured concentration data to improve the diagnostic potential of these simple non-multivariate relationships, (c) the integration of local meteorological data with receptor modeling using factor analysis to explicitly identify impacting PAH source regions, and finally (d) the first known instance of the use of a hybridized receptor modeling methodology to explicitly identify, quantify and spatially map the potential source regions of P AH on a hemispheric scale. An additional effect of the work contained herein is that it shows how much information which could be useful to environmentalists and policy-makers in designing effective abatement and control strategies if available is usually left un-extracted from environmental monitoring activities. / Thesis / Doctor of Philosophy (PhD)
246

Cross-Conjugation Effects on Fused β, β'–π–Extended Porphyrins

Washburn, Spenser L. 12 1900 (has links)
Cross-conjugation in molecules has been seen in nature for many years but was not pursued due to the difficulty of their synthesis and their lack of stability. Recently, it has become more interesting due to the rise of molecular electronics. Linear conjugation serves well as the wires to conduct electrons, but molecular electronics are made up of more than just wires. Molecules are needed that possess an on/off switch that can allow or deter conduction. Cross-conjugated systems show promise in their ability to be turned on or off from external stimuli. Pentacene quinone is a well-known cross-conjugated molecule that already shows promise in the field of molecular semiconductors. By synthetically fusing the pentacene quinone to the β, β' positions of a porphyrin, it has been shown that both the solubility and stability have been greatly improved. This has allowed us to pursue functionalization of the quinone moiety. Several new cross-conjugated pentacene quinone fused porphyrin systems were synthesized and studied. It was found that cross-conjugated platinum porphyrins show enhanced fluorescence, and phosphorescence that shifts toward the Near IR. Additionally, strong electron withdrawing groups show potential in charge transfer, and a lower HOMO to LUMO gap, while mildly withdrawing groups have a higher HOMO to LUMO gap. Furthermore, a new method to introduce halogenated methine bridges at the pentacene quinone core was developed, thus opening the doors to new polycyclic aromatic hydrocarbons to be synthesized and studied.
247

The synthesis of some substituted 7-(1-Naphthyl)- Benz(a)Anthracenes

Lewis, Claude Irenius 29 November 2012 (has links)
Many benz(a)anthracene derivatives are able to produce cancer in the experimental animal. There is a correlation between the calculated total electronic charge of the K-region and this carcinogenic activity. There is also ample proof that benz(a)anthracene derivatives are honed to the skin through quinoid type bonds in the K"region. However, the prediction of physiological activity of benz(a)anthracenes is still unreliable because of the limitations of the theoretical model described by existing theories. The purpose of this work was to synthesize some substituted benz(a)anthracenes with a shielded K-region and with a different L-region electron density than in 7-phenyl-bena(a)anthracene in the hope of increasing our knowledge regarding molecular structure-physiological relationship. / Ph. D.
248

The preparation of polynuclear compounds containing the thiophene ring system

Quo, Sih-gwan January 1959 (has links)
The process of C. K. Bradsher for preparing mesosubstituted anthracene and 1,2-benzanthracene derivatives has been widely extended. The purpose of this research was to extend this process to the thiophene series, in addition to continuing some work on the 9-(dimethyl)- phenylanthracene series and some newly developed l,2-dimethyl-10-phenyl)-anthracene series. 2'-Thienyl-2-benzylbenzophenone was prepared and cyclized to 9-(2-thienyl)-anthracene by the conventional methods in good yields. 3'-Thienyl-2-benzylbenzophenone was prepared in a different way, indirect and tedious. Thiophene was iodinated to tetraiodothiophene and tetraiodothiophene was reduced with aluminum-amalgam to 3-iodothiophene. 3-Thienylmagnesiumiodide was prepared by the entrainment technique and condensed with 2-cyanodiphenylmethane to 3'-thienyl-2-benzylbenzophenone. This ketone was cyclized to 9-(3'-thienyl)-anthracene by the standard acid mixture. 2-(1-Naphthylmethyl)-phenyl-2-thienylketimine formed from the condensation between 2-(1'-naphthylmethyl)- benzonitrile and 2-thienylmagnesiumbromide resisted hydrolysis to the corresponding ketone but cyclized quantitatively to 10-(2-thienyl)-l,2-benzanthracene. Following the classical Bradsher process, the reaction between 2-thienylmagnesiumbromide and o-chlorobenzaldehyde was unsuccessful because the hydrol formed was so reactive that it polymerized rapidly and ended up with tars. A cross-condensation reaction between 2-ethynylmagnesium bromide and o-chlorobenzylchloride was utilized to give the expected 2-(2'-chlorobenzyl)- thiophene in one step. This new procedure has been widely extended to the other series. It is preferred to. the conventional Bradsher process and the Friedel-Crafts method in terms of time, chemicals, and unequivocal products formed. 2-(2'-Chlorobenzyl)-thiophene so formed by the new procedure was converted by von Braun reaction to the corresponding nitrile and the nitrile was allowed to react with phenylmagnesiumbromide to give 2-(2-thienylmethyl)-benzophenone. The above ketone was cyclized almost quantitatively to 4-phenyl-thiophanthrene. The thiophene-containing ketones prepared in this research are very viscous oils. In order to have crystalline derivatives for identification purposes these ketones were oxidized to the corresponding diketones. 2-Thienyl-2-benzylbenzophenone and 2-(2'-thienylmethyl)- benzophenone gave the identical diketone, 2-benzoyl-2'- thienyl-benzophenone. 3 1 -Thienyl-2-benzylbenzophenone was oxidized to anthraquinone by using 25% sulfuric .acid, acetic acid and sodium dichromate. The formation of anthraquinone indicates that the monoketone cyclized first and then split off the thiophene ring. Apparently, the 3-thienyl group is more susceptible to oxidation than the 2’-thienyl group. A study of the oxidation of anthracene derivatives for structure proof was made using 9-phenylanthracene as a model compound. It was oxidized to 10-phenyl-10-hydroxyanthrone which resisted further oxidation to anthraquinone. It is obvious that the tertiary alcohol system stabilized the phenyl ring. In continuing the work on the 9-(dimethyl)-phenylanthracene series, the yields of three ketimine salts and one ketone were improved. Satisfactory analytical data was obtained for 2’,6’-dimethyl-2-benzylbenzophenone. In an attempt to overcome the steric effects offered by 2,6-ortho groups, 2-(2',3'-dimethylbenzyl)-benzonitrile was prepared. The starting material for this series, l-bromo-2,3-dimethylbenzene has been prepared in 47% yield by diazotization in comparison with the previous yield of 30%. / Doctor of Philosophy
249

Simplified real-time PAH measurement techniques

Pierce, Timothy L. January 1982 (has links)
The increased use of residential wood and coal stoves in recent years h.as caused a growing concern for polycyclic aromatic hydrocarbon (PAH) emissions from these stoves. Design of stoves that reduce PAH emissions has been hampered because existing PAH measurement techniques are slow, complex, and expensive. This study investigates two simple, inexpensive, real-time PAH measurement techniques which might be suitable for testing stoves. The first uses a device, called the "moving tape sampler" (MTS), that collects particulate samples on filter paper tape and uses sensitized flourescence to measure total PAH on the tape. The MTS results are compared to the results of a conventional PAH measurement technique, but no definite relationship between the two is found. Uncertainties about the conventional technique make it unclear whether one or both of the techniques give incorrect emission rates. The second method is the use of CO and NO<sub>x</sub> as proxy compounds to infer PAH emissions. A plot of CO emission factors against PAH emission factors suggest CO as a proxy for PAH emissions while a similar plot for NO<sub>x</sub> gives some evidence of NO<sub>x</sub> being an "inverse" proxy for PAH emissions. The lack of a trusted PAH measurement technique has hampered the evaluation of both the MTS and proxy techniques. / Master of Science
250

The synthesis and reactions of 2-(1-Naphthylmethyl)-2'- Carboxybenzophenone

Greenwood, Edward James 09 November 2012 (has links)
The structures of the six new compounds and the TNF molecular complex were substantiated by satisfactory elemental analyser. The infrared and ultraviolet absorption spectra of the six new compounds were recorded. / Master of Science

Page generated in 0.281 seconds