Estudo de tochas de plasma através da teoria da similaridade

Orientador: Aruy MarottaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Nesta tese foram obtidas equações generalizadas para a característica tensão-corrente de umatocha de plasma de arco não transferido e de uma tocha de plasma de arco transferido, utilizando o método da Teoria da Similaridade. Para a tocha de arco não transferido, os dados experimentais foram obtidos para ar como gás plasmagênico e na faixa de correntes de 10 a 295 A. Para a tocha de arco transferido, os dados foram obtidos para argônio e faixa de correntes de 300 a 1500 A. A tocha de arco não transferido apresentou característica estática tensão-corrente descendente, enquanto a de arco transferido, a característica obtida foi dinâmica, com comportamento fortemente anômalo, com a presença de histerese, além de possuir ambos os ramos, o descendente e o ascendente. Os testes da tocha de arco transferido foram feitos num forno com paredes refratárias em atmosfera de argônio. Foram obtidas equações generalizadas tendo um, dois e três parâmetros adimensionais independentes, sendo a escolha da melhor equação generalizada baseada no coeficiente de correlação da regressão multilinear. O parâmetro adimensional da voltagem foi considerado como o parâmetro dependente. Em geral, para os parâmetros adimensionais independentes foram utilizados aqueles relacionados com as diversas modalidades de transferência da energia Joule do arco para outras modalidades de energia. Estas foram a convectiva, a radiativa, a turbulenta e a condutiva. As equações generalizadas obtidas para a tocha de arco não transferido apresentaram boa concordância para toda a faixa de dados experimentais. Já as equações para a tocha de arco transferido, devido à grande anomalia observada, foram limitadas à apenas a parte ascendente dos dados experimentais. O estudo experimental, realizado nesta tese pode contribuir para uma melhor compreensão dos fenômenos que ocorrem em tochas de plasma, como também, fornecer uma guia para a engenharia de projeto das tochasAbstract: In this thesis, generalized equations for the voltage-current characteristics have been obtained for a non transferred arc plasma torch and for a transferred arc plasma torch, using the method of the Theory of the Similarity. For the non transferred arc plasma torch, the experimental data was obtained for air as the plasmagenic gas and for currents of 10 to 295 A. For the transferred arc torch, the experiments were carried out for argon and currents of 300 to 1500 A. The non transferred plasma torch showed a descending voltage-current static characteristic, while the transferred plasma torch, the characteristic was dynamic, with strong anomalous behavior, consisting of the presence of hysteresis, besides possessing both the branches, the descendant and the ascendant. The tests of the transferred torch were carried out in an oven with refractory walls in argon atmosphere. Generalized equations had been obtained having one, two and three independent nondimensional parameters, being the choice of the best generalized equation based in the coefficient of correlation of the multilinear regression. The dimensionless parameter of the voltage was considered as the dependent parameter. In general, for the independent nondimensional parameters have been used those related with the diverse modalities of transference of the Joule energy of the arc to other modalities of energy. These had been the convective one, the radiative, the turbulent and the conductive one. The generalized equations obtained for the non transferred torch showed good agreement for all the range of experimental data. However, the equations for the transferred arc torch, due to their great observed anomaly, had been limited only to the ascending part of the experimental data. The experimental study, carried out in this thesis, might contribute to a better understanding of the phenomena taking place in plasma torches, as well, to provide a guide for their engineeringMestradoFísicaMestre em Físic

Synthesis and characterization of carbon nanostructires containing nitrogen

Orientador: Fernando AlvarezTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Nesta tese são apresentados os efeitos nas propriedades estruturais, eletrônicas e de emissão eletrônica por efeito de campo elétrico induzidos pela incorporação de nitrogênio em nanoestruturas de carbono. As nanoestruturas de carbono contendo nitrogênio foram preparadas por pulverização catódica (sputtering) de um alvo de grafite assistido, ou não, por um feixe iônico. A técnica permite atuar sobre os parâmetros de deposição induzindo mudanças nas propriedades estruturais, eletrônicas e de emissão eletrônica por efeito de campo elétrico. O papel do hélio na formação de nanoes-truturas de carbono contendo nitrogênio foi também explorado, mostrando que o gás nobre promove maior incorporação de nitrogênio. Isto é provavelmente devido à relativa alta condutividade térmica que apresenta o hélio, propriedade que modifica a cinética do crescimento das nanoestruturas. O estudo realizado permitiu entender o mecanismo de formação das nanoestruturas, mostrando que primeiramente o carbono alcança as partículas de Ni por difusão até a saturação do metal, iniciando a formação das camadas grafíticas sobre a partícula de Ni, camadas que foram observadas por microscopia eletrônica de transmissão de alta resolução. O estudo mostra, também, que os parâmetros importantes que controlam a incorporação de nitrogênio no material são a pressão parcial de nitrogênio na câmara de deposição, assim como a energia do feixe de íons assistindo a deposição.Foram estudadas três séries de amostras preparadas em atmosferas controladas. Na primeira série foi utilizado um feixe de íons de nitrogênio como feixe de assistência, e na segunda, uma mistura composta por duas espécies iônicas, íons de nitrogênio e hidrogênio. Com o auxilio da espectroscopia de elétrons fotoemitidos por raios-X observou-se a incorporação de nitrogênio nos filmes. A microscopia de força atômica revelou a presença de estruturas do tipo domo, distribuídas de maneira uniforme na superfície das amostras, apresentando uma densidade média de ~3×10 9 domos/cm 2as da primeira série, e ~1.4×10 9 domos/cm 2as da segunda série. Tanto a distribuição como a forma seguem o padrão estabelecido pelos precursores utilizados na preparação das nanoestruturas, i.e., ilhas de níquel que agem ao mesmo tempo como catalisadores e como suporte para as nanoestruturas. Na terceira série, as nanoestruturas foram crescidas sobre um filme de nitreto de titânio, depositado sobre substratos de Si, pulverizando um alvo de grafite em atmosferas de nitrogênio e hélio-nitrogênio. A densidade dos domos encontrada para esta série foi de ~5.3×10 10 domos/cm 2 . Os espectros Raman das três séries apresentam as bandas G e D, o que indica a presença estruturas grafíticas com distorções representadas pela banda D. A incorporação de nitrogênio ocasiona o alargamento da banda G e aumento da razão das intensidades das bandas D e G, respectivamente, indicando uma redução da ordem estrutural com a incorporação de Nitrogênio. Finalmente, para as três séries de amostras, fez-se também um estudo das propriedades de emissão eletrônica por efeito de campo elétrico. A emissão é predominantemente por tunelamento quântico (as curvas de densidade de corrente vs campo elétrico seguem o modelo de Fowler-Nordheim) e dependem da concentração de nitrogênio assim como do processo usado na preparação das amostrasAbstract: The subject of this thesis is establishing a link among the synthesis, structures, and field emission properties for nanostructured carbon materials containing nitrogen. The materials were prepared by ion beam assisted deposition and ion beam sputtering. The carbon material was obtained sputtering an ultra pure graphite target by an argon ion beam. The method allows controlling the deposition parameters to induce changes in the structural, electronic, and field emission properties. Also, the role of helium on the carbon containing nitrogen nanostructures was investigated. The remarkable thermal conductance of He modifying the growing kinetics was also studied. An important goal of the work was to elucidate the mechanism of the nanostructures formation. It was found that, at first, the carbon atoms reach the Ni particles saturating the metal particle, and then, the formation of stacked graphene starts on the metal particles. The graphene layers were observed by high resolution transmission electron microscopy. The results show that mainly two parameters control the nitrogen incorporation, namely, the deposition chamber nitrogen partial pressure and the energy of the nitrogen ion beam assisting the growth. Three sample series prepared in controlled atmospheres were studied. The first series was prepared assisting the growth with a nitrogen ion beam and, the second series by a nitrogen-hydrogen ion beam. The third sample series were prepared by ion beam sputtering on silicon substrate by sequentially depositing titanium nitride thin film, nanometric nickel particles and carbon. The carbon containing nitrogen nanostructures were grown in nitrogen and helium-nitrogen atmospheres. X-ray photoelectron spectroscopy analysis indicates nitrogen incorporation and it depends predominantly on the ion beam energy or on the nitrogen partial pressure. Atomic force microscopy reveals dome-like structures uniformly distributed on the surface of the samples, with ~3×10 9 domes/cm 2 for the first series, ~1.4×10 9 domes/cm 2 for the second, and ~5.3×10 10 domes/cm 2 for the third. Both distribution and shape follow the Ni island pattern, i.e. the Ni islandsact both as a catalytic and uphold. The three samples series were also analyzed by Raman spectros-copy, showing a defined G bands around 1593 cm -1 indicating the presence of graphitic structures. Also, are observed D bands indicating structural disorder. The disorder increases with the augment of the nitrogen content, as is shown by the augment of the D and G intensities ratio. Finally, the field emission properties of the three series were studied and the electron emission depends on the growing conditions in general, and on the nitrogen content in particular. The results show that the emission is predominantly by quantum tunneling and the current density vs. electric field curves follow the Fowler-Nordheim modelDoutoradoFísicaDoutor em Ciência

Method to obtain nonuniformity information from field emission behavior

Copyright © 2010 American Vacuum Society / American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Journal of Vacuum Science and Technology Part B: Microelectronics and Nanometer Structures, 28(3), Article number 441 and may be found at http://scitation.aip.org/content/avs/journal/jvstb/28/3/10.1116/1.3327928.This article describes the characterization of field emission from a planar cathode to a spherical anode with the approach curve method (ACM). In such a diode configuration the electric field strength at the cathode surface is nonuniform. This nonuniformity gives an extra degree of freedom and it allows the interpretation of the current-voltage and voltage-distance (V×d) curves in terms of nonuniformity. The authors apply the ACM to Cu emitters to explain the nonlinearity of the V×d curve in ACM measurements. This analysis provides a good insight into field emission phenomena, supporting a method for nonuniformity characterization based on field emission behavior

Impact of common cardio-metabolic risk factors on fatal and non-fatal cardiovascular disease in Latin America and the Caribbean: an individual-level pooled analysis of 31 cohort studies

Background: Estimates of the burden of cardio-metabolic risk factors in Latin America and the Caribbean (LAC) rely on relative risks (RRs) from non-LAC countries. Whether these RRs apply to LAC remains un- known. Methods: We pooled LAC cohorts. We estimated RRs per unit of exposure to body mass index (BMI), systolic blood pressure (SBP), fasting plasma glucose (FPG), total cholesterol (TC) and non-HDL cholesterol on fatal (31 cohorts, n = 168,287) and non-fatal (13 cohorts, n = 27,554) cardiovascular diseases, adjusting for regression dilution bias. We used these RRs and national data on mean risk factor levels to estimate the number of cardiovascular deaths attributable to non-optimal levels of each risk factor. Results: Our RRs for SBP, FPG and TC were like those observed in cohorts conducted in high-income countries; however, for BMI, our RRs were consistently smaller in people below 75 years of age. Across risk factors, we observed smaller RRs among older ages. Non-optimal SBP was responsible for the largest number of attributable cardiovascular deaths ranging from 38 per 10 0,0 0 0 women and 54 men in Peru, to 261 (Dominica, women) and 282 (Guyana, men). For non-HDL cholesterol, the lowest attributable rate was for women in Peru (21) and men in Guatemala (25), and the largest in men (158) and women (142) from Guyana. Interpretation: RRs for BMI from studies conducted in high-income countries may overestimate disease burden metrics in LAC; conversely, RRs for SBP, FPG and TC from LAC cohorts are similar to those esti- mated from cohorts in high-income countries

Influence of mealtime habits on the risk of weight gain and obesity in Mexican adults

International audienceObjective: To prospectively examine the extent to which mealtime habits influences the risk of weight gain and obesity in Mexican adults.Design: We performed a prospective cohort study. The Mealtime Habits Quality (MHQ) scale was used for assessing participants' MHQ; the outcomes of interest were gain ≥5 % of body weight, developing overweight/obesity and abdominal obesity, after 7 years of follow-up. In order to estimate the independent effect of MHQ on anthropometric indicators, generalized linear models were computed to obtain adjusted relative risks (95 % CI).Setting: The state of Morelos, Mexico.Subjects: Mexican adults (n 837) aged 18-70 years participating in a cohort study.Results: Compared with participants classified in the higher MHQ category, individuals in the middle and lower MHQ groups had a 4·1 (2·5, 6·7) and 6·2 (3·9, 9·7) fold greater risk of gain ≥5 % of body weight, respectively; 6·6 (2·8, 15·5) and 8·6 (3·7, 19·8) fold greater risk of becoming overweight/obese, respectively; and 3·8 (2·0, 7·3) and 5·3 (2·8, 9·8) fold greater risk of developing abdominal obesity, respectively.Conclusions: This study provides evidence about the influence of a set of mealtime habits on obesity indicators, showing that greater adherence to unadvisable mealtime habits increases the risk of developing unhealthy anthropometric indicators. Since the meal is one of the most important sources of food intake, and consequently weight status, the MHQ scale can be a useful population tool to predict weight gain and obesity

Mealtime habits and risk of developing the metabolic syndrome or insulin resistance among Mexican adults

International audienceMeals are an important source of food intake, contributing to body weight and health status. Previous studies have examined the relationship between isolated mealtime behaviours and the metabolic syndrome (MetS). The aim of this study was to examine the influence over time of ten interrelated mealtime habits on the risk of developing the MetS and insulin resistance (IR) among Mexican adults. We conducted a prospective cohort study with a sample of 956 health workers. The Mealtime Habits Quality (MHQ) scale is based on four mealtime situations (availability of time to eat, distractions while eating, environmental and social context of eating, and familiar or cultural eating habits), which were used to assess the participants' MHQ at the baseline (2004-2006) and follow-up (2010-2012) evaluations. The MetS was assessed using criteria from the National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) and the International Diabetes Federation (IDF). IR was defined using the homoeostasis model assessment. Crude and adjusted relative risks were calculated to estimate the relationship between MHQ and the risk of developing the MetS or IR. Participants classified in the lower MHQ category had an 8•8 (95 % CI 3•1, 25) and 11•1 (95 % CI 3•4, 36•1) times greater risk of developing the MetS (using the NCEP-ATP III and IDF criteria, respectively), and an 11•2 times (95 % CI 3•9, 31•5) greater likelihood of developing IR, compared with those in the higher MHQ group. This prospective study reveals that individuals who engaged in more undesirable than recommended mealtime behaviours had a >10-fold risk of developing the MetS or IR

Health workers cohort study: methods and study design

Objective . To examine different health outcomes that are associated with specific lifestyle and genetic factors. Materials and methods . From March 2004 to April 2006, a sample of employees from three different health and academic institutions, as well as their family members, were enrolled in the study after providing informed consent. At baseline and follow-up (2010-2013), participants completed a self-administered questionnaire, a physical examination, and provided blood samples. Results . A total of 10 729 partici- pants aged 6 to 94 years were recruited at baseline. Of these, 70% were females, and 50% were from the Mexican Social Security Institute. Nearly 42% of the adults in the sample were overweight, while 20% were obese. Conclusion . Oustudy can offer new insights into disease mechanisms and prevention through the analysis of risk factor information in a large sample of Mexicans

Health workers cohort study: methods and study design.

Objective:To examine different health outcomes that are associated with specific lifestyle and genetic factors.Materials and methods:From March 2004 to April 2006, a sample of employees from three different health and academic institutions, as well as their family members, were enrolled in the study after providing informed consent. At baseline and follow-up (2010-2013), participants completed a self-administered questionnaire, a physical examination, and provided blood samples.Results:A total of 10 729 participants aged 6 to 94 years were recruited at baseline. Of these, 70% were females, and 50% were from the Mexican Social Security Institute. Nearly 42% of the adults in the sample were overweight, while 20% were obese.Conclusion:Our study can offer new insights into disease mechanisms and prevention through the analysis of risk factor information in a large sample of Mexicans