Dielectric spectroscopy on Bi3Zn2Sb3O14 ceramic: an approach based on the complex impedance

The dielectric properties and loss of Bi1.5ZnSb1.5O7 a poor-semiconducting ceramic were investigated by impedance spectroscopy, in the frequency range from 5 Hz to 13 MHz. Electric measurements were performed from 100 to 700 degreesC. Pyrochlore type phase was synthesized by the polymeric precursor method. Dense ceramic with 97% of the theoretical density was prepared by sintering via constant heating rate. The dielectric permittivity dependence as a function of frequency and temperature showed a strong dispersion at frequency lower than 10 kHz. The losses (tan delta) exhibit slight dependence with the frequency at low temperatures presenting a strong increase at temperatures higher than 400 degreesC. A decrease of the loss magnitude occurs with increasing frequency. Relaxation times were extracted using the dielectric functions Z(omega) and M(omega). The plots of the relaxation times tau(Z'), and tau(M) as a function of temperature follow the Arrhenius law, where a single slope is observed with activation energy values equal to 1.38 and 1.37 eV, respectively. (C) 2003 Elsevier Ltd. All rights reserved.

The Lactate Minimum Test protocol provides valid measures of cycle ergometer VO2 peak

Aim. The aim of the present study was to investigate the validity of the Lactate Minimum Test (LMT) for the determination of peak VO2 on a cycle ergometer and to determine the submaximal oxygen uptake (VO2) and pulmonary ventilation (VE) responses in an incremental exercise test when it is preceded by high intensity exercise (i.e., during a LMT).Methods. Ten trained male athletes (triathletes and cyclists) performed 2 exercise tests in random order on an electromagnetic cycle ergometer: 1) Control Test (CT): an incremental test with an initial work rate of 100 W, and with 25 W increments at 3-min intervals, until voluntary exhaustion; 2) LMT: an incremental test identical to the CT, except that it was preceded by 2 supramaximal bouts of 30-sec (similar to120% VO(2)peak) with a 30-sec rest to induce lactic acidosis. This test started 8 min after the induction of acidosis.Results. There was no significant difference in peak VO2 (65.6+/-7.4 ml.kg(-1).min(-1); 63.8+/-7.5 ml.kg(-1).min(-1) to CT and LMT, respectively). However, the maximal power output (POmax) reached was significantly higher in CT (300.6+/-15.7 W) than in the LMT (283.2+/-16.0 W).VO2 and VE were significantly increased at initial power outputs in LMT.Conclusion. Although the LMT alters the submaximal physiological responses during the incremental phase (greater initial metabolic cost), this protocol is valid to evaluate peak VO2, although the POmax reached is also reduced.

Aerobic fitness level typical of elite athletes is not associated with even faster VO2 kinetics during cycling exercise

The aim of this study was to address the question if the VO2 kinetics is further improved as the aerobic training status increases from trained to elite level athletes. Maximal oxygen uptake (VO(2)max), work-rate associated to VO(2)max (IVO(2)max) and VO2 kinetics of moderate (Mod) and maximal exercise (Max) were determined in fifty-five subjects. Then, they were assigned into three groups: low (LF), intermediate (IF) and high (HF) aerobic fitness level. In average, the VO(2)max of LF, IF and HF groups were, respectively, 36.0 +/- 3.1, 51.1 +/- 4.5 and 68.1 +/- 3.9 ml . kg . min(-1) (p <= 0.05 among each other). VO2 kinetics mean response time of both exercise intensities were significantly faster (p <= 0.05) in HF (Mod, 27.5 +/- 5.5 s; Max, 32.6 +/- 8.3 s) and IF (Mod, 25.0 +/- 3.1 s; Max, 42.6 +/- 10.4 s) when compared to LF (Mod, 35.7 +/- 7.9 s; Max: 57.8 +/- 17.8 s). We can conclude that VO2 kinetics is improved as the fitness level is increased from low to intermediate but not further improved as the aerobic fitness level increases from intermediate to high.

Microstructural development of ZnO varistor during reactive liquid phase sintering

The microstructural evolution, grain growth and densification for the varistor systems ZnO-Bi2O3 (ZB), ZnO-Bi2O3-Sb2O3 (ZBS), ZnO-Bi2O3-Sb2O3-MnO-Cr 2O3-CoO (ZBSCCM) were studied using constant heating rate sintering, scanning electron microscopy (SEM) and in situ phase formation measurement by high temperature X-ray diffraction (HT-XRD). The results showed that the densifying process is controlled by the formation and decomposition of the Zn2Bi3Sb3O14 pyrochlore (PY) phase for the ZBS and ZBSCCM systems. The addition of transition metals (ZBSCCM system) alters the formation and decomposition reaction temperatures of the pyrochlore phase and the morphology of the Zn7Sb2O12 spinel phase. Thus, the spinel grains act as inclusions and decrease the ZnO grain growth rate. Spinel grain growth kinetics in the ZBSCCM system showed an n value of 2.6, and SEM and HT-XRD results indicate two grain growth mechanisms based on coalescence and Ostwald ripening. © 1996 Chapman & Hall.

Effect of an acute β-adrenergic blockade on exercise intensity corresponding to the lactate minimum

β-Adrenoreceptor blockade is reported to impair endurance, power output and work capacity in healthy subjects and patients with hypertension. The purpose of this study was to investigate the effect in eighth athletic males of an acute β-adrenergic blockade with propranolol on their individual power output corresponding to a defined lactate minimum (LM). Eight fit males (cyclist or triathlete) performed a protocol to determine the power output corresponding to their individual LM (defined from an incremental exercise test after a rapidly induced exercise lactic acidosis). This protocol was performed twice in a double-blind randomized order by each athlete first ingesting propranolol (80mg) and in a second trial a placebo, 120 minutes respectively prior to the test sequence. The blood lactate concentration obtained 7 minutes after anaerobic exercise (a Wingate test) was significantly lower after acute β-adrenergic blockade (8.6 ± 1.6mM) than under the placebo condition (11.7 ± 1.6mM). The work rate at the LM was lowered from 215.0 ± 18.6 to 184.0 ± 18.6 watts and heart rate at the LM was reduced from 165 ± 1.5 to 132 ± 2.2 beats/minute as a result of the blockade. There was a non-significant correlation (r = 0.29) between the power output at the LM with and without acute β-adrenergic blockade. In conclusion, since the intensity corresponding to the LM is related to aerobic performance, the results of the present study, are able to explain in part, the reduction in aerobic power output produced during β-adrenergic blockade.

Effect of barium titanate seed particles on the sintering and lattice parameters in PbMg1/3Nb2/3O3 ceramics

PbMg1/3Nb2/3O3 (PMN) powder was prepared by citrate organic solution, and barium titanate (BT) seed particles were added to encourage the perovskite phase formation. Sintering was followed using the constant heating rate mode of a dilatometer, and it was observed that the seed concentration affected the PMN shrinkage rate and crystal structure. The study of the lattice parameters of the samples after the sintering process indicates that the diffusion of the titanium and of the barium inside perovskite and pyrochlore PMN phases occurs. Moreover, this substitution provoked a decrease of the lattice parameters as showed by the Rietveld refinement.

La suplementación pre-ejercicio con carbohidrato de alta concentración perjudica el rendimiento en el ejercicio de alta intensidad en bicicleta

Objectives. To evaluate the effects of pre-exercise high concentration carbohydrate supplementation on performance, cardiovascular, metabolic and hormonal responses during high intensity cycling exercise. Method. Seven male cyclists (28.7 ± 5.4 years; 65.2 ± 4.7 kg body weight), who performed two continuous exercise trials under placebo (PLA) or carbohydrate (CHO) ingestion at a work rate of 80% VO 2max until exhaustion, participated in the study. The cyclists received 5 ml.kg-1 of a maltodextrin solution diluted at a concentration of 10% (CHO) or placebo (PLA) at 60, 45 and 30 min pre-exercise. Results. A 5.4% reduction in the time to exhaustion was observed in the CHO trial compared to the PLA trial. In both trials, glucose and lactate levels were higher in the post-trial condition compared to pre-exercise values (p < 0.05). Free fatty acid levels were lower in the CHO group than in the PLA group both before and after the trial (p < 0.05). Insulinemia was higher during the pre-trial in the CHO group (42.7 ± 3.6 μU.ml-1) compared to the PLA condition (11.8 ± 3.3 μU.ml-1) (p < 0.05), and even decreased to 23.8 ± 5.1 μU.ml-1 during exercise after CHO intake (p < 0.05). No significant differences in plasma cortisol were observed between the two trials (p > 0.05). Conclusions. Pre-exercise high concentration CHO supplementation resulted in impaired performance in high intensity cycling exercise and decreased free fatty acid levels. © 2010 Revista Andaluza de Medicina del Deporte.

Poverty dynamics in Costa Rica with panel data from cross-sections

Includes bibliography

Proposta de metodologia para o gerenciamento de fonte radioativa e estimativa de dose efeiva em pacientes submetidos à terapia com iodeto de sódio I-131

Pós-graduação em Pesquisa e Desenvolvimento (Biotecnologia Médica) - FMB

Instituição ou instituído?: análise de uma prática escolar de inclusão

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cinética de sinterização do combustível nuclear 'UO IND. 2.'7%'Gd IND.2''O IND. 3': cálculo da curva mestre de sinterização

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Tendência e determinantes do aleitamento materno exclusivo em crianças menores de 6 meses no município de Bauru-SP

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influência do teor de cinza volante na reologia de argamassa de assentamento: fabricado com reciclagem de resíduos

As argamassas podem ser consideradas como um conjunto de partículas sólidas em suspensão (agregado miúdo), aglomerantes e água (pasta de cimento). Sendo assim, seu comportamento reológico durante a cura pode ser influenciado por fatores como a granulometria, composição e teor de água incorporado. Este trabalho estudou as características reológicas de seis composições de argamassas, em função do teor de cinza volante, como material de atividade pozolânica, em substituição parcial do cimento. A argamassa estudada utilizou como base agregado o resíduo da construção civil (RCC), devidamente caracterizado por difratometria e fluorescência de raios-X. Formularam-se composições de argamassas para os ensaios reológicos com adição de resíduo de construção civil (RCC) nas proporções de 95, 90, 85, 80, 75 e 70%; cinzas volantes (CV) 0, 5, 10, 15, 20 e 25% e 5% de Cimento Portland Comum (CP II- E 32), sendo que em cada amostra foi incorporado 35% de água. Utilizou-se o viscosímetro modelo VT 550, com sensor tipo cilindros coaxiais SV₁ – Haake a temperatura de 28ºC. Para avaliar o tempo de cura do material programou-se uma taxa de cisalhamento constante 53,4 s^-1 em 1h e 45min, sendo avaliado o torque em intervalos de 15min. Para a elaboração das curvas de fluxo e curvas de histerese, utilizou-se a taxa de cisalhamento entre 0 e 600 s^-1 no intervalo de tempo de 120s. Os resultados mostraram que a incorporação de cinza volante foi o principal fator para aumento do torque no tempo de cura das argamassas e mudança do comportamento de reópetico para tixotrópico, nos traços analisados. Os dados experimentais das formulações propostas ajustaram-se ao modelo reológico de Herschel-Bulkley.

O Futuro (1862-1863), Jornal das Famílias (1863-1878) e A Estação (1879-1904); três periódicos em que colaborou Machado de Assis

Machado de Assis (1839-1908) teve sua carreira marcada pela constante atividade de colaboração em periódicos, dentre os quais nos interessam particularmente O Futuro (18621863), o Jornal das Famílias (1863-1878) e A Estação (1879-1904). Por sua atuação constante e eficaz nesses veículos, o escritor foi considerado seu principal colaborador. As três revistas, por sua vez, marcaram sua presença no processo de formação de Machado: O Futuro presenciou o início da trajetória do escritor, e o Jornal das Famílias e A Estação, por seu longo período de circulação, ofereceram-lhe maior espaço para a prática e o aperfeiçoamento no gênero narrativo, principalmente na produção contos, essencial para a consagração de Machado de Assis no panorama da literatura brasileira. Assim sendo, é importante conhecer as principais características dessas revistas, uma vez que o perfil das publicações também devia ser levado em conta pelos escritores na produção de seus textos.

SnO2 dense ceramic microwave sintered with low resistivity

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)