• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 467
  • 158
  • 83
  • 61
  • 37
  • 35
  • 32
  • 12
  • 10
  • 8
  • 8
  • 8
  • 8
  • 8
  • 8
  • Tagged with
  • 1130
  • 154
  • 76
  • 75
  • 73
  • 73
  • 64
  • 64
  • 59
  • 56
  • 52
  • 48
  • 45
  • 42
  • 42
  • 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.
231

Synthetic and Structural Chemistry of Ligand-substituted Triosmium Clusters and a Rhenium(i) Complex

Lin, Chen-Hao 08 1900 (has links)
The reaction of 2-[(diphenylphosphino)methyl]-6-methylpyridine (PN) with Os3(CO)12-n(MeCN)n [where n = 0 (1), 1 (2), 2 (3)] has been investigated. Os3(CO)12 reacts with PN in the presence of Me3NO to afford the clusters Os3(CO)11(1-PN) (4) and 1,2-Os3(CO)10(1-PN)2 (5). X-ray diffraction analyses confirm the equatorial coordination of the phosphine(s) in 4 and 5, with the two phosphines in the latter cluster exhibiting a 1,2-trans orientation about the Os-Os vector that contains the two ligands. Treatment of the MeCN-substituted cluster Os3(CO)11(MeCN) and PN (1:1 ratio) in CH2Cl2 gives clusters 4 and 5, in addition to HOs3(η1-Cl)(CO)10(1-PN) (6) as a result of competitive activation of the reaction solvent. Cluster 6 contains 48e- and the diffraction structure reveals the presence of axial chloride and equatorial phosphine ligands which are located on adjacent osmium atoms. The bridging hydride ligand in 6 spans the Cl,P-substituted Os-Os vector. The reaction of Os3(CO)10(MeCN)2 with PN furnishes 5, 6, and 1,1-Os3(CO)10(2-PN) (7) in yields that are dependent on the reagent stoichiometry and reaction solvent. The solid-state structure of 7 confirms the chelation of the PN ligand to a single osmium atom via the pyridine and phosphine moieties at axial and equatorial sites, respectively. The bonding in 7 relative to other possible stereoisomers has been explored by DFT calculations, and the diffraction structure is computed as the thermodynamically most stable form of this cluster. Cluster 4 is photosensitive and CO loss gives 7, in addition to the formation of the dihydride H2Os3(CO)8[µ-CH(NC5H3)CH2PPh2] (8), whose origin derives from the double metalation of the C-6 methyl group of the PN ligand in 7. Photolysis of 7 yields 8 without detectable observation of the expected intermediate hydride HOs3(CO)9[µ-CH2(NC5H3)CH2PPh2]. The PN ligand in 7 undergoes P-C bond activation in toluene at 110 °C to afford the 50e cluster Os3(CO)9(µ-C6H4)(µ-PPh), which contains face-capping benzyne and phosphinidene moieties. The bonding between the benzyne moiety and the opened Os3 frame in 9 has been examined computationally, and these data are discussed relative to and π bonding contributions from the metalated aryl ring to the cluster polyhedron. Thermolysis of BrRe(CO)5 with 4-(2,2-dimethylhydrazino)dimethylhydrazone-3(Z)-penten-2-one in toluene at 70 °C furnishes the new β-diketimine-substituted complex fac-BrRe(CO)3[(Me2NNCMe)2CH2] (1) in 50-70 isolated yield. Product 1 is also obtained in comparable yield when the same reactants are irradiated at 366 nm at room temperature in fluid solution. Treatment of the parent ligand with the "lightly stabilized" rhenium compound fac-BrRe(CO)3(THF)2 affords 1 as the sole observable rhenium product. Complex 1 has been characterized in solution by IR and 1H NMR spectroscopy, and the molecular structure has been determined by single-crystal X-ray diffraction analysis.
232

IMPURITY CONTROL AND ANALYSIS OF ULTRA-PURE GALLIUM FOR INCREASING MOBILITY IN GALLIUM ARSENIDE GROWN BY MOLECULAR BEAM EPITAXY

Kyungjean Min (6635897) 14 May 2019 (has links)
<p></p><p>High mobility 2DEG (two-dimensional electron gas) confined in GaAs is a good platform to understand correlated electron systems and a promising candidate for qubit devices. For example, the non-Abelian feature of Fractional Quantum Hall state enabling topological quantum computation is only found in GaAs with high mobility. Theoretical calculations have shown that the mobility is inversely proportional to impurities in GaAs/AlGaAs heterstructures grown by Molecular Beam Epitaxy (MBE). In recent MBE experiments, the source Ga was found to be more important in the limitation of mobility than Al and As. A high mobility of 35 million cm<sup>2</sup>/Vs was recently observed when an 8N Ga (total nominal impurity concentration of ~10 ppb) source was used compared to 25 million cm<sup>2</sup>/Vs for a 7N Ga source. In addition, significant mobility increase was observed after in-situ distillation of the source Ga before growth. In order to clarify the mechanism of how the distillation contributed to the Ga purification, thus resulting in the mobility increase, the MBE in-situ distillation was analyzed by molecular distillation theory. Evaporation behavior of solvent Ga was analyzed including effects of evaporation from a crucible with receding liquid depth. Then impurity removal through molecular distillation was analyzed with molecular evaporation kinetics. The remaining 7N and 8N Ga after in-situ MBE distillation and growth were elementally analyzed by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) and compared with analyses of the starting 7N and 8N Ga from same lots. Due to the increased detection limit of ICP-MS in metal analysis, the concentrations of most impurity elements reached the detection limit of ~1-10 ppb. However, unusual high concentration of 690 ppb Ge was found in the 7N Ga, exceeding the nominal concentration of 7N (100 ppb). Significant decrease in Ge concentration was found in the comparison of initial ultra-pure Ga and remaining Ga for both grades of 7N and 8N. The significant Ge losses cannot be explained by atomic Ge evaporation due to the low vapor pressure of Ge. However, a hypothesis of Ge evaporation as GeO(g) by Ge active oxidation was proposed. In order to test the active oxidation of very dilute Ge in Ga in the MBE conditions with very low P(O<sub>2</sub>), the equilibrium P(GeO)-P(O<sub>2</sub>) vapor species diagram was calculated from thermodynamics. The analysis shows that even very dilute Ge in Ga of ~ 1 ppm concentration can be <a>actively oxidized in the extremely low P(O<sub>2</sub>) of MBE</a>. In order to prove active oxidation of Ge, molecular distillation of 7N Ga was performed in <a>a specially constructed high vacuum chamber. The 7N Ga with unusual high Ge concentration of 440 ppb (by GDMS analysis) was distilled for 16 h at 1360 K under the starting P(O<sub>2</sub>) of 3 x 10<sup>-6</sup> torr and the total pressure of 10<sup>-5</sup> torr. The chamber vacuum was monitored by Residual Gas Analyzer (RGA) and the residual Ga after 16 h distillation was analyzed by GDMS. In the GDMS analysis, significant Ge loss was found from 440 ppb to below the detection limit of 10 ppb, confirming Ge active oxidation hypothesis. The oxygen-assisted impurity removal in distillation also may be applicable to other impurities with high vapor pressure gaseous oxide, but low vapor pressure itself, such as Al, Si and Sn. </a></p><br><p></p>
233

Examination of the Relationships Between Environmental Exposures to Volatile Organic Compounds and Biochemical Liver Tests: Application of Canonical Correlation Analysis

Liu, Jing, Drane, Wanzer, Liu, Xuefeng, Wu, Tiejian 01 February 2009 (has links)
This study was to explore the relationships between personal exposure to 10 volatile organic compounds (VOCs) and biochemical liver tests with the application of canonical correlation analysis. Data from a subsample of the 1999-2000 National Health and Nutrition Examination Survey were used. Serum albumin, total bilirubin (TB), alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), alkaline phosphatase (ALP), and γ-glutamyl transferase (GGT) served as the outcome variables. Personal exposures to benzene, chloroform, ethylbenzene, tetrachloroethene, toluene, trichloroethene, o-xylene, m-,p-xylene, 1,4-dichlorobenzene, and methyl tert-butyl ether (MTBE) were assessed through the use of passive exposure monitors worn by study participants. The first two canonical correlations were 0.3218 and 0.2575, suggesting a positive correlation mainly between the six VOCs (benzene, ethylbenzene, toluene, o-xylene, m-,p-xylene, and MTBE) and the three biochemical liver tests (albumin, ALP, and GGT) and a positive correlation mainly between the two VOCs (1,4-dichlorobenzene and tetrachloroethene) and the two biochemical liver tests (LDH and TB). Subsequent multiple linear regressions show that exposure to benzene, toluene, or MTBE was associated with serum albumin, while exposure to tetrachloroethene was associated with LDH and total bilirubin. In conclusion, exposure to certain VOCs as a group or individually may influence certain biochemical liver test results in the general population.
234

Traduction des titres de brevets en français : Étude contrastive de substantifs composés en japonais, anglais et français / Translation of patent titles into French

Walle, Spencer Benjamin January 2020 (has links)
Cette étude porte sur la traduction de substantifs composés en japonais et en anglais vers le français. Ces deux langues-là permettent de produire des compositions enchaînées des types « NN », « NNN » etc. alors que cette forme de composition est beaucoup moins productive en français où l’on préfère souvent utiliser une préposition pour lier plusieurs substantifs. Dans la traduction de titres de brevets, souvent consistant entièrement en substantifs composés en japonais et en anglais, comment les traducteurs francophones s’attaquent-ils au problème de cette différence entre la langue source et la langue cible ? Les recherches antérieures ont produit des classifications diverses, parfois interlingues, pour l’analyse de substantifs composés. À partir d’un corpus composé de plus d’une centaine de titres de brevets comprenant plusieurs centaines de substantifs composés traduits par des traducteurs professionnels, ces classifications sont utilisées pour analyser les stratégies auxquelles recourent les traducteurs dans ce contexte très limité. Les résultats montrent entre autres une préférence marquée pour les compositions du type « N de N » en français et mettent au jour l’existence de certaines traductions très bien établies voire figées. / This study addresses the translation of compound nouns from Japanese and English into French. The former two languages allow for the production of concatenated compositions of the types "NN", "NNN" etc. whereas this form of composition is much less productive in French, which often prefers to use a preposition to link multiple nouns. In the translation of patent titles, often consisting entirely of compound nouns in Japanese and English, how do French-speaking translators tackle the problem of this difference between the source language and the target language? Previous research has produced various, sometimes interlingual, classifications for the analysis of compound nouns. From a corpus of more than a hundred patent titles comprising several hundred compound nouns translated by professional translators, these classifications are used to analyze the strategies used by translators in this very constrained context. The results show, among other things, a marked preference for compositions of the "N de N" type in French and reveal the existence of certain very well established or even fixed translations.
235

Impacts of Exposure to Polycyclic Aromatic Compounds (PACs) and Their Alkylated Congeners in North American River Otter (Lontra canadensis)

Thomas, Philippe 28 August 2020 (has links)
Polycyclic aromatic compounds (PACs) are a group of chemicals encompassing thousands of different aromatic, alkyl aromatic and heterocyclic hydrocarbons (i.e.- containing N, S, or O- atoms); 16 of which have been designated as priority pollutants due to their toxicity and prevalence. Several studies have highlighted increases in the concentrations of C1-C4 alkylated PACs and heterocyclic aromatic hydrocarbons such as dibenzothiophenes in the atmosphere, water, soil and sediments, plants, wildlife and fish in the Athabasca Oil Sands Region (AOSR). Although there has been considerable research attention related to the toxic, carcinogenic and mutagenic properties of PACs, there is an increasing awareness that these chemicals may also have profound endocrine disrupting properties in wildlife. North American river otter (Lontra canadensis) are good indicators of ecosystem health due to their ecology and sensitivity to environmental pollutants. In this thesis, we first demonstrated the utility of adopting paleotoxicological frameworks in defining environmental baseline levels of PACs and likely biological effects from exposure to these complex environmental mixtures. These methods allowed us to reconstruct historical PAC deposition patterns to impacted areas while simultaneously determining likely biological effects such as endocrine disruption. Next, we showed how PACs exhibited trophic dilution in a Boreal food chain dominated by river otters. Snails, prey and predator fish, as well as river otters were collected from four main study areas in the AOSR in northeastern Alberta, Canada. Bioaccumulation factors such as biota-sediment accumulation factors (BSAF) and trophic magnification factors (TMF) were used to evaluate the partitioning behavior of PACs in the environment and subsequent risks to biota. Our results revealed localized enrichment of certain PACs and subsequent metabolism in higher order vertebrates. Finally, we successfully combined ecotoxicological and physiological analyses paired with population genetic estimates to investigate endocrine disruption and population-level responses to exposure to PACs. River otters are known for their habitual use of latrine sites. Latrine sites represent a unique opportunity for biomonitoring programs to study river otters using indirect sampling methods. In this thesis, PACs were characterized and evaluated in sediment, lower and higher trophic biota with demonstrated impacts on endocrine processes and river otter population health. Effects-based assessments such as the ones presented in this thesis are more powerful for environmental monitoring programs than stressor-based assessment methods (such as describing presence/absence or levels of contaminants) as they provide greater biological context to monitoring data. In turn, these are helpful in selecting triggers for environmental effects monitoring or adaptive management programs.
236

Source Apportionment Analysis of Measured Volatile Organic Compounds in Corpus Christi, Texas

Abood, Ahmed T. 05 1900 (has links)
Corpus Christi among of the largest industrialized coastal urban areas in Texas. The strategic location of the city along the Gulf of Mexico allows for many important industries and an international business to be located. The cluster of industries and businesses in the region contribute to the air pollution from emissions that are harmful to the environment and to the people living in and visiting the area. Volatile organic compounds (VOC) constitute an important class of pollutants measured in the area. The automated gas chromatography (Auto GC) data was collected from Texas Commission of Environmental Quality (TCEQ) and source apportionment analysis was conducted on this data to identify key sources of VOC affecting this study region. EPA PMF 3.0 was employed in this sources apportionment study of measured VOC concentration during 2005 - 2012 in Corpus Christi, Texas. The study identified nine optimal factors (Source) that could explain the concentration of VOC at two urbane monitoring sites in the study region. Natural gas was found to be the largest contributor of VOC in the area, followed by gasoline and vehicular exhaust. Diesel was the third highest contributor with emissions from manufacturing and combustion processes. Refineries gases and evaporative fugitive emissions were other major contributors in the area; Flaring operations, solvents, and petrochemicals also impacted the measured VOC in the urban area. It was noted that he measured VOC concentrations were significantly influenced by the economic downturn in the region and this was highlighted in the annual trends of the apportioned VOC.
237

Fabrication of bulk crystal and thin film of Ⅱ-Ⅳ-Ⅴ2 type compound semiconductor ZnSnP2 for photovoltaic application / Ⅱ-Ⅳ-Ⅴ2型化合物半導体ZnSnP2のバルク結晶および薄膜作製と太陽電池材料への応用

Nakatsuka, Shigeru 23 March 2017 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20334号 / 工博第4271号 / 新制||工||1662(附属図書館) / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 安田 秀幸, 教授 酒井 明, 准教授 野瀬 嘉太郎 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
238

Design of novel semiconductor photocatalysts and cocatalysts toward efficient water splitting under visible light / 高効率可視光水分解を目指した新規半導体光触媒および助触媒の設計

Suzuki, Hajime 26 March 2018 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21119号 / 工博第4483号 / 新制||工||1697(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 阿部 竜, 教授 安部 武志, 教授 陰山 洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
239

Microwave-enhanced extraction of organic contaminants from soil

Punt, Monique M. January 1997 (has links)
No description available.
240

Anisotropic Optical Reflectance of Hg₂.₈₆AsF₆

Batalla, Erwin 09 1900 (has links)
Optical reflectance of the quasi two dimensional compound Hg₂.₈₆AsF₆ has been investigated in the optical range, 0.5 to 4 eV. The spectra clearly show a plasma edge at 3 eV. They are fitted to a Drude model and two Lorentz oscillators. From the plasma frequency and the model parameters values for the dc conductivity and the effective mass and an estimate of the crytsal anisotropy have been obtained. The results compare well with earlier electrical measurements on this compound. / Thesis / Master of Science (MSc)

Page generated in 0.0462 seconds