- 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.
Search results
Showing 111 to 115 of 115 (0.02 seconds)| 111 |
A Radio Frequency Quadrupole Instrument for use with Accelerator Mass Spectrometry: Application to Low Kinetic Energy Reactive Isobar Suppression and Gas–phase Anion Reaction StudiesEliades, John Alexander 21 August 2012 (has links)
A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed.
Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16.
Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined.
Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified.
|
| 112 |
Structure and Dynamics of Core-Excited SpeciesTravnikova, Oksana January 2008 (has links)
<p>In this thesis we have performed core-electron spectroscopy studies of gas phase molecular systems starting with smaller diatomic, continuing with triatomic and extending our research to more complex polyatomic ones. We can subdivide the results presented here into two categories: the first one focusing on electronic fine structure and effect of the chemical bonds on molecular core-levels and the other one dealing with nuclear dynamics induced by creation of a core hole. In our research we have mostly used synchrotron radiation based techniques such as X-ray Photoelectron (XPS), X-ray Absorption (XAS), normal and Resonant Auger (AES and RAS, respectively) and Energy-Selected Auger Electron PhotoIon COincidence (ES-AEPICO) spectroscopies.</p><p>We have demonstrated that resonant Auger spectroscopy can be used to aid interpretation of the features observed in XAS for Rydberg structures in the case of Cl<sub>2</sub> and C1s<sup>−1</sup>π*<sup>1</sup> states of allene molecules. The combined use of high-resolution spectroscopy with <i>ab initio</i> calculations can help the interpretation of strongly overlapped spectral features and disentangle their complex profiles. This approach enabled us to determine the differences in the lifetimes for core-hole 2p sublevels of Cl<sub>2</sub> which are caused by the presence of the chemical bond. We have shown that contribution in terms of the Mulliken population of valence molecular orbitals is a determining factor for resonant enhancement of different final states and fragmentation patterns reached after resonant Auger decays in N<sub>2</sub>O.</p><p>We have also performed a systematic study of the dependence of the C1s resonant Auger kinetic energies on the presence of different substituents in CH<sub>3</sub>X compounds. For the first time we have studied possible isomerization reaction induced by core excitation of acetylacetone. We could observe a new spectral feature in the resonant Auger decay spectra which we interpreted as a signature of core-excitation-induced keto-enol tautomerism.</p>
|
| 113 |
Structure and Dynamics of Core-Excited SpeciesTravnikova, Oksana January 2008 (has links)
In this thesis we have performed core-electron spectroscopy studies of gas phase molecular systems starting with smaller diatomic, continuing with triatomic and extending our research to more complex polyatomic ones. We can subdivide the results presented here into two categories: the first one focusing on electronic fine structure and effect of the chemical bonds on molecular core-levels and the other one dealing with nuclear dynamics induced by creation of a core hole. In our research we have mostly used synchrotron radiation based techniques such as X-ray Photoelectron (XPS), X-ray Absorption (XAS), normal and Resonant Auger (AES and RAS, respectively) and Energy-Selected Auger Electron PhotoIon COincidence (ES-AEPICO) spectroscopies. We have demonstrated that resonant Auger spectroscopy can be used to aid interpretation of the features observed in XAS for Rydberg structures in the case of Cl2 and C1s−1π*1 states of allene molecules. The combined use of high-resolution spectroscopy with ab initio calculations can help the interpretation of strongly overlapped spectral features and disentangle their complex profiles. This approach enabled us to determine the differences in the lifetimes for core-hole 2p sublevels of Cl2 which are caused by the presence of the chemical bond. We have shown that contribution in terms of the Mulliken population of valence molecular orbitals is a determining factor for resonant enhancement of different final states and fragmentation patterns reached after resonant Auger decays in N2O. We have also performed a systematic study of the dependence of the C1s resonant Auger kinetic energies on the presence of different substituents in CH3X compounds. For the first time we have studied possible isomerization reaction induced by core excitation of acetylacetone. We could observe a new spectral feature in the resonant Auger decay spectra which we interpreted as a signature of core-excitation-induced keto-enol tautomerism.
|
| 114 |
The rhizosphere effects of <i>Fagus sylvatica</i> L. and <i>Fraxinus excelsior</i> L. saplings on greenhouse gas fluxes between soil and atmosphere / Rhizosphären-Effekte der Jungpflanzen von <i>Fagus sylvatica</i> L. und <i>Fraxinus excelsior</i> L. auf den Treibhausgasaustausch von Boden und AtmosphäreFender, Ann-Catrin 06 June 2012 (has links)
No description available.
|
| 115 |
Fatores de controle das emissões de óxido nitroso (N2O) em tanque de aeração de estação de tratamento de esgotoBrotto, Ariane Coelho 27 April 2017 (has links)
Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-04-27T16:58:25Z
No. of bitstreams: 1
Dissertação Brotto, A. C.pdf: 1827218 bytes, checksum: d583ce8460c1efc5934c93cec6ef4c3d (MD5) / Made available in DSpace on 2017-04-27T16:58:25Z (GMT). No. of bitstreams: 1
Dissertação Brotto, A. C.pdf: 1827218 bytes, checksum: d583ce8460c1efc5934c93cec6ef4c3d (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências- Geoquímica Ambiental. Niterói, RJ / O estudo das emissões de óxido nitroso (N2O) em processos de tratamento
de esgoto tem se tornado necessário e urgente nos últimos anos visto à sua
contribuição às mudanças climáticas globais, já que este gás é responsável por 6%
do efeito estufa e tem se tornado a principal substância destruidora do ozônio
estratosférico do século XXI. Poucos são os estudos que quantificaram as emissões
de N2O diretamente em estações de tratamento de esgoto (ETEs) e a literatura
apresenta uma grande variação nos fatores de emissão (FEs) obtidos por eles. As
Diretrizes de 2006 do IPCC para Inventários de Gases do Efeito Estufa sugerem o
FE de 3,2 (2-8) g N2O pessoa-1 ano-1 para estimativas das emissões de N2O em
ETEs, que corresponde a 0,035% do nitrogênio total (NT) emitido como N2O. As
emissões de N2O em processo de tratamento de lodos ativados foram determinadas
no período de janeiro a julho de 2010 em uma ETE municipal no Estado do Rio de
Janeiro que trata aproximadamente 14,7 mil m3 dia-1 com média remoção de DQO
para o período de estudo de 73% e carga de NT afluente de 46 mg N L-1. Os
principais parâmetros operacionais relacionados às emissões de N2O em ETE foram
estudados, a saber, concentração de oxigênio dissolvido (OD), concentração de
nitrito (NO2
-), pH e temperatura. As maiores emissões de N2O foram observadas
quando a concentração de OD se encontrava entre 1,3 e 3,4 mg L-1, o pH entre 5,9 e
6,5 e temperatura acima de 30oC. Enquanto as menores emissões ocorreram em
concentrações de OD abaixo de 1,0 mg L-1 e acima de 4,0 mg L-1, e em pH acima de
6,5. O fluxo de N2O estimado é de 4,1 x 105 g N2O ano-1 e os FEs de N2O per capita,
por vazão de esgoto tratado e pela carga NT afluente são 8,1 g N2O pessoa-1 ano-1,
8,0 x 10-5 g N2O L -1 e 0,12%. O FE per capita estimado exclusivamente para o
tanque de aeração é aproximadamente 2,5 vezes superior ao proposto pelo IPCC
(2006) para inventários de emissões de N2O para países que possuam sistemas
centralizados de tratamento de esgoto com avançado controle dos processos de
nitrificação e desnitrificação. / The study of nitrous oxide (N2O) emissions from wastewater treatment
processes has become necessary and urgent in the last years due to its contribution
to global climate change, since this gas is responsible for 6% of the global
greenhouse effect and will become the main ozone-depleting substances (ODS) of
the 21st century. Few studies have quantified the direct emissions of N2O from
wastewater treatment plants (WWTPs) and literature shows a wide variation in the
emission factors (EFs) obtained by them. 2006 IPCC Guidelines for National
Greenhouse Gas Inventories suggests an EF to estimate N2O emissions from WWTP
of 3.2 (2.8) g N2O person-1 yr-1, which corresponds to 0.035% of total nitrogen
emitted as N2O. Emissions of N2O from a full-scale activated sludge process was
determined from January to July of 2010 during measurement campaign at a
municipal WWTP in the State of Rio de Janeiro that treat roughly 14,700 m3 day-1
with an average influent removal COD for the period of study of 73% and total
nitrogen load (TN) of 46 mg N L-1. The most important operational parameters
leading N2O emissions in WWTP were also studied, namely, dissolved oxygen
concentration (DO), nitrite (NO2
-) concentration, pH and temperature. The largest
emissions of N2O were observed when DO concentration was between 1.3 and 3.4
mg L-1, pH between 5.9 and 6.5 and temperatures above 30oC. While lower
emissions occurred in DO concentrations below 1.0 mg L-1 and above 4.0 mg L-1,
and at pH above 6.5. Total estimated annual flux of N2O is 4.1 x 105 g N2O yr-1 and
the EF of N2O estimated per capita, wastewater flow and the influent TN load are 8.1
g N2O person-1 yr-1, 8.0 x 10-5 g N2O L(wastewater)-1 and 0.12%. The per capita EF
estimated exclusively for the aeration tank is almost 3 times higher than that
proposed by the IPCC (2006) for N2O emission inventories for countries that
predominantly have advanced centralized WWTPs with nitrification and denitrification
steps.
|
Page generated in 0.0295 seconds