Effect of temperature on particle shape, size, and polycrystallinity of Nd-Fe-B powders obtained by hydrogen decrepitation

This work presents a detailed study of hydrogen decrepitation (HD) to obtain monocrystalline Nd-Fe-B powder. The effect of decrepitation temperature has been investigated to optimize both particle size and shape. Differential scanning calorimetry was applied to analyze the hydrogenation kinetics of Nd2Fe14B and Nd-rich phases in the range of 25 to 300 C. Thermogravimetry and X-ray diffraction allowed determining the hydrogen absorption of the whole alloy and the matrix phase, respectively. While scanning electron microscopy (SEM) was used to visualize particle shape and size, dynamic image analysis was applied to evaluate quantitatively these properties. The high monocrystallinity of the powder was confirmed by electron backscattering diffraction. The partial pressure of hydrogen required to initiate the hydrogenation reactions decreases when the temperature increases. The hydrogen absorbed by the whole alloy and, in particular, by the Nd2Fe14B phase decreases with temperature. Below 150 C, the hydrogen absorbed by the Nd2Fe14B phase produces a significant transgranular cracking that is undesirable for particle shape. At 300 C, the fast and limited absorption of hydrogen by the Nd-rich phase causes insufficient intergranular fracture and, hence, polycrystallinity. Between 150 and 300 C, the controlled fragmentation resulted in monocrystalline particles with a more equiaxial shape, which is a suitable precursor to develop anisotropic ultrafine powders by the hydrogenation, disproportionation, desorption, recombination (HDDR) process

Higgs Sector of the Minimal Left-Right Symmetric Model

We perform an exhaustive analysis of the most general Higgs sector of the minimal left-right symmetric model (MLRM). We find that the CP properties of the vacuum state are connected to the Higgs spectrum: if CP is broken spontaneously, the MLRM does not approach the Standard Model in the limit of a decoupling left-right symmetry breaking scale. Depending on the size of the CP phases scenarios with extra non-decoupling flavor-violating doublet Higgses or very light SU(2) triplet Higgses emerge, both of which are ruled out by phenomenology. For zero CP phases the non-standard Higgses decouple only if a very unnatural fine-tuning condition is fulfilled. We also discuss generalizations to a non-minimal Higgs sector.Comment: brief discussion of non-minimal Higgs sectors added, journal versio

Neutrino Masses and Lepton Flavour Violation in Thick Brane Scenarios

We address the issue of lepton flavour violation and neutrino masses in the ``fat-brane'' paradigm, where flavour changing processes are suppressed by localising different fermion field wave-functions at different positions (in the extra dimensions) in a thick brane. We study the consequences of suppressing lepton number violating charged lepton decays within this scenario for lepton masses and mixing angles. In particular, we find that charged lepton mass matrices are constrained to be quasi-diagonal. We further consider whether the same paradigm can be used to naturally explain small Dirac neutrino masses by considering the existence of three right-handed neutrinos in the brane, and discuss the requirements to obtain phenomenologically viable neutrino masses and mixing angles. Finally, we examine models where neutrinos obtain a small Majorana mass by breaking lepton number in a far away brane and show that, if the fat-brane paradigm is the solution to the absence of lepton number violating charged lepton decays, such models predict, in the absence of flavour symmetries, that charged lepton flavour violation will be observed in the next round of rare muon/tau decay experiments.Comment: 33 pages, 9 eps figure

Lactacidemia e concentrações séricas de aspartato aminotransferase e creatinoquinase em equinos da raça Quarto de Milha usados em provas de laço em dupla

O presente estudo teve por objetivo avaliar a influência do exercício físico de alta intensidade e curta duração (provas de laço em dupla) sobre a lactacidemia e as concentrações séricas de aspartato aminotransferase (AST) e creatinoquinase (CK) em equinos durante competição realizada no estado do Espírito Santo. Para tal foram obtidas amostras de soro e plasma de 20 equinos, da raça Quarto de Milha ou mestiços, em três momentos assim definidos: no repouso, uma semana antes da prova atlética, já com o animal em treinamento (T0); antes da prova atlética (T1) e imediatamente após o término da mesma (T2). As referidas amostras foram encaminhadas ao Laboratório Clínico do Centro Universitário Vila Velha (UVV) para as análises. Na avaliação da lactacidemia, os resultados registrados nos momentos T0, T1 e T2 foram, respectivamente, de 0,49±0,24mmol/L, 0,93±0,16mmol/L e 9,86±2,09mmol/L. Na avaliação da atividade sérica de AST, os resultados registrados nos momentos T0, T1e T2 foram, respectivamente, de 189,1±43,6 UI/L, 210,2±46,7 UI/L e 173,1±33,5 UI/L. Por fim, a avaliação da atividade sérica da CK nos momentos T0,T1 e T2 foram,respectivamente, de 110,9±35,2 UI/L, 51,8±15,4 UI/L e 88,2±33,5 UI/L. A análise dos resultados demonstrou que o exercício físico imposto levou ao aumento significativo de lactato plasmático e CK sérica e não alterou o AST sérico e que a interpretação destes resultados permitiu concluir que os equinos usados estavam aptos ao nível de exercício físico imposto