ABSTRACT
Magnetic systems with competing anisotropies generally exhibit asymmetry between the maximum amplitudes of the right and left maxima in a magnetoimpedance curve. Small errors in positioning the samples at the experimental setup may also produce such asymmetry. In this work, we present a study on the sources of the asymmetry between magnetoimpedance peaks in systems that present the exchange bias phenomenon, by comparing a phenomenological model to experimental data. A set of samples with different repetitions of the NiFe/FeMn exchange-biased bilayer was used in this study. From the frequency evolution of the asymmetry, together with magnetization curves, we were able to identify the sources for the observed magnetoimpedance asymmetry found on our experimental data.
ABSTRACT
We investigate the magnetic nanoparticles hyperthermia in a non-adiabatic and radiating process through the calorimetric method. Specifically, we propose a theoretical approach to magnetic hyperthermia from a thermodynamic point of view. To test the robustness of the approach, we perform hyperthermia experiments and analyse the thermal behavior of magnetite and magnesium ferrite magnetic nanoparticles dispersed in water submitted to an alternating magnetic field. From our findings, besides estimating the specific loss power value from a non-adiabatic and radiating process, thus enhancing the accuracy in the determination of this quantity, we provide physical meaning to a parameter found in literature that still remained not fully understood, the effective thermal conductance, and bring to light how it can be obtained from experiment. In addition, we show our approach brings a correction to the estimated experimental results for specific loss power and effective thermal conductance, thus demonstrating the importance of the heat loss rate due to the thermal radiation in magnetic hyperthermia.
ABSTRACT
Cobalt-based oxides are among the most promising electrocatalysts for oxygen evolution reactions (OER). In this context, this work reports the synthesis of manganese-doped cobaltites using the Zeolitic-Imidazolate Frameworks 67 (ZIF-67) as template. The incorporation of manganese ions into ZIF-67 structure was evaluated in ethanol and methanol, in order to obtain the best synthetic route. Non-doped (ZIF-67C) and Mn-doped cobaltites (Mn/ZIF-67C(E) and Mn/ZIF-67C(M)) were obtained after thermal treatment at 350 °C. Structural and morphological properties were investigated and presence of Mn3+ and Mn4+ was confirmed by X-ray photoelectron spectroscopy (XPS) data and magnetization curves. The electrocatalytic activity in OER was investigated in alkaline medium for manganese cobaltites, and compared to the ZIF-67C. Overpotentials to generate a current of 10 mA cm-2 were 338 mV and 356 mV for Mn/ZIF-67C(E) and Mn/ZIF-67C(M), respectively. These results are superior to those found for similar materials in the literature. The material obtained in methanol (Mn/ZIF-67C(M)) presents lower overpotential, however, shows superior electrocatalytic performance for current density above 100 mA cm-2, therefore being an efficient electrode for commercial electrolysers.
ABSTRACT
OBJECTIVE: To evaluate the association between physical activity and the morphological, functional and physiological components of physical fitness in postmenopausal women. METHODS: A cross-sectional study of 162 postmenopausal women, 40-65 years of age, who verbally responded to the International Physical Activity Questionnaire applied to evaluate their level of physical activity. Physical fitness was evaluated by measuring body mass index, waist circumference, body fat percentage, maximum oxygen consumption, plasma levels of total and fractional cholesterol, triglycerides and fasting glucose, as well as blood pressure. RESULTS: Approximately 83.5% of the women were active, principal physical activities being household chores and transportation walking. Approximately 80% of the women were overweight or obese and presented a waist circumference indicative of high or very high risk for cardiovascular disease, and fat percentage above 33%. Over 50% were found to have low oxygen consumption. There were no significant differences between the groups of active and inactive women with respect to mean body mass index (p = 0.43), percentage of body fat (p = 0.60), hip-to-waist ratio (p = 0.93), waist circumference (p = 0.44), maximum VO2 (p = 0.32), total cholesterol (p = 0.43), fasting glucose (p = 0.73), and systolic (p = 0.79) or diastolic blood pressure (p = 0.48). Adjusted prevalence ratios also showed no significant differences between the groups. CONCLUSIONS: Habitual physical activity is not associated with variations in the components that are used to describe physical fitness. It is important to encourage physical activity and provide guidelines to ensure that it is carried out in the quantity, duration and intensity required for improving physical fitness level and obtaining health benefits.
