The method of in situ high pressure neutron diffraction was employed to measure reliable diffraction patterns to help illuminate the density-driven structural transformations in GeO2, SiO2, B2O3 and GeSe2 glass. The majority of this neutron diffraction work employed the diffractometer D4c at the ILL with a Paris-Edinburgh press which enabled the pressure range from ambient to 8 GPa to be accessed. In the cases of GeO2 and GeSe2 glass, the neutron diffraction with isotopic substitution (NDIS) protocol was developed to provide benchmark experimental results to test the results obtained from various molecular dynamics simulations using different theoretical schemes. For GeO2 glass, from a combination of neutron diffraction and molecular dynamics results, it was found that the increase in density of the glass initially occurs through a reorganisation of corner-shared GeO4 tetrahedra on an intermediate length scale as the pressure is increased from ambient to 5 GPa. At higher pressures, there is a progression from a tetrahedral to an octahedral glass, via the formation of 5-fold coordinated Ge atoms which have a predominantly square pyramidal geometry. In the work on SiO2 and B2O3 glass the pressure range for the in situ high pressure neutron diffraction results was extended to 14.5 GPa and 17.5 GPa, respectively, by using the PEARL diffractometer at ISIS. For both materials the neutron diffraction results provide complementary information to pressure x-ray diffraction studies helping to elucidate the mechanism of network collapse. In the case of SiO2 glass, densification over the measured pressure range occurs predominantly by a reorganisation of corner shared SiO4 tetrahedra on an intermediate length scale. In the case of B2O3 glass, the B-O coordination number changes from 3 to ∼ 3.9 at the pressure is increased from ∼ 8 to 17.5 GPa. For GeSe2 glass, from a combination of neutron diffraction and molecular dynamics results, it was found that the density increase from ambient pressure up ∼ 8 GPa occurs by a reorganisation of both corner and edge-sharing GeSe4 tetrahedra on an intermediate length scale. Above this pressure, 5- and 6-fold coordinated Ge atoms start to form at a similar density and homopolar bonds play an intimate role in the formation of these higher coordinated polyhedra.

Made available in DSpace on 2014-06-11T19:27:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-06-23Bitstream added on 2014-06-13T20:56:38Z : No. of bitstreams: 1 martins_mb_me_botfmvz.pdf: 732603 bytes, checksum: aaa29421580edf9cbe7e5d86e1091b6f (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Universidade Estadual Paulista (UNESP) / Este trabalho objetivou avaliar o turnover e a meia-vida do carbono nas fezes e sangue de ovelhas alimentadas com plantas C3 e C4, pela técnica dos isótopos estáveis. Oito ovelhas da raça Santa Inês, após um período de adaptação de 45 dias recebendo 50% de feno de alfafa e 50% de silagem de milho, foram distribuídas ao acaso em dois tratamentos: o primeiro consistiu de animais que receberam feno de alfafa (C3-FA) e o segundo, dos animais que receberam apenas silagem de milho (C4-SM). Para mensurar o turnover de carbono (substituição isotópica) nas fezes e sangue em determinado intervalo de tempo, foi utilizada a função exponencial do tempo. Apenas os valores isotópicos das fezes atingiram o patamar de equilíbrio, indicando valores de meia-vida de 1,2 e 1,0 dias para os tratamentos C3-FA e C4-SM, respectivamente. Já no sangue, o tempo de coleta dos dados (104 dias) foi insuficiente para encontrar o patamar de equilíbrio isotópico, indicando uma troca de carbono lenta. De acordo com os resultados deste estudo, pode-se concluir que o sangue apresenta turnover lento indicando o sinal isotópico de dietas antigas; e as fezes, turnover rápido, indicadas para refletir dietas recentes, próximas da fase de avaliação / The aim of this work was to evaluate the carbon turnover and half-life on feces and blood sheep, fed on C3 and C4 plants, using the stable isotopes technique. Eight Santa Ines sheep, after 45 days as adjustment period receiving 50% of alfalfa hay and 50% of corn silage, were randomly assigned to two treatments: the first one the animals fed on alfalfa hay (C3-FA) and the second one the animals fed on only corn silage (C4-SM). The time exponential function was used to measure the carbon turnover (isotope substitution) on feces and blood in a certain period of time. Only the isotope feces values reached the plateau value, indicating half-life of 1.2 and 1.0 days for C3-FA and C4-SM treatment, respectively. The data collection time (104 days) for blood was not enough to find a plateau isotope, indicating a slow carbon exchange. So we can infer that the blood has a slow turnover, indicating isotopic signal of ancient diets; and the feces showed a fast turnover, being used to reflect recent diet, next to the evaluation period

The rotational microwave spectra of the three isotopes (^13CH_3^12C^15N, ^12CH_3^13C^15N, and ^13CH_3^13C^15N) of the methyl cyanide molecule in the v_8=3, v_8=2, v_7=1 and v_4=1 vibrational energy levels for the rotational components 1£J£5 (for a range of frequency 17-95 GHz.) were experimentally and theoretically examined. Rotational components in each vibration were measured to determine the mutual interactions in each vibration between any of the vibrational levels investigated. The method of isotopic substitution was employed for internal tuning of each vibrational level by single and double substitution of ^13C in the two sites of the molecule. It was found that relative frequencies within each vibration with respect to another vibration were shifted in a systematic way. The results given in this work were interpreted on the basis of these energy shifts. Large departure between experimentally measured and theoretically predicted frequency for the quantum sets (J, K=±l, ϑ=±1), Kϑ-l in the v_8=3 vibrational states for the ^13c and ^15N tagged isotopes of CH_3CN showed anomalous behavior which was explained as being due to Fermi resonance. Accidently strong resonances (ASR) were introduced to account for some departures which were not explained by Fermi resonance.

Orientador: Carlos Ducatti / Banca: Marcelo Zacarias Moreira / Banca: Cyntia Ludovico Martins / Resumo: Este trabalho objetivou avaliar o turnover e a meia-vida do carbono nas fezes e sangue de ovelhas alimentadas com plantas C3 e C4, pela técnica dos isótopos estáveis. Oito ovelhas da raça Santa Inês, após um período de adaptação de 45 dias recebendo 50% de feno de alfafa e 50% de silagem de milho, foram distribuídas ao acaso em dois tratamentos: o primeiro consistiu de animais que receberam feno de alfafa (C3-FA) e o segundo, dos animais que receberam apenas silagem de milho (C4-SM). Para mensurar o turnover de carbono (substituição isotópica) nas fezes e sangue em determinado intervalo de tempo, foi utilizada a função exponencial do tempo. Apenas os valores isotópicos das fezes atingiram o patamar de equilíbrio, indicando valores de meia-vida de 1,2 e 1,0 dias para os tratamentos C3-FA e C4-SM, respectivamente. Já no sangue, o tempo de coleta dos dados (104 dias) foi insuficiente para encontrar o patamar de equilíbrio isotópico, indicando uma troca de carbono lenta. De acordo com os resultados deste estudo, pode-se concluir que o sangue apresenta turnover lento indicando o sinal isotópico de dietas antigas; e as fezes, turnover rápido, indicadas para refletir dietas recentes, próximas da fase de avaliação / Abstract: The aim of this work was to evaluate the carbon turnover and half-life on feces and blood sheep, fed on C3 and C4 plants, using the stable isotopes technique. Eight Santa Ines sheep, after 45 days as adjustment period receiving 50% of alfalfa hay and 50% of corn silage, were randomly assigned to two treatments: the first one the animals fed on alfalfa hay (C3-FA) and the second one the animals fed on only corn silage (C4-SM). The time exponential function was used to measure the carbon turnover (isotope substitution) on feces and blood in a certain period of time. Only the isotope feces values reached the plateau value, indicating half-life of 1.2 and 1.0 days for C3-FA and C4-SM treatment, respectively. The data collection time (104 days) for blood was not enough to find a plateau isotope, indicating a slow carbon exchange. So we can infer that the blood has a slow turnover, indicating isotopic signal of ancient diets; and the feces showed a fast turnover, being used to reflect recent diet, next to the evaluation period / Mestre

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