Proof-of-concept thermoelectric oxygen sensor exploiting oxygen mobility of GdBaCo2O5+{\delta}

In this paper, we demonstrate a proof-of-concept oxygen sensor based on the thermoelectric principle using polycrystalline $GdBaCo_2O_{5+\delta}$ where 0.45<${\delta}$<0.55 (GDCO). The lattice oxygen in layered double perovskite oxides is highly susceptible to the ambient oxygen partial pressure. The as-synthesized GDCO sample processed in ambient conditions shows pure orthorhombic ($P_{mmm}$ space group) phase and a ${\delta}$-value close to 0.5 as confirmed from X-ray diffraction reitveld refinement. The X-ray photoelectron spectroscopy shows significant $Co^{3+}$ oxidation state in non-octahedral sites in addition to $Co^{3+}$ and $Co^{4+}$ in octahedral sites. The insulator-to-metal transition (MIT) is observed at nearly 340 K as seen in electrical resistivity and seebeck coefficient measurements. The seebeck coefficient shows a large change of about 10-13 $\mu$V/K with time constant of ~20 sec, at room temperature (300 K) when the gas ambience changes from 100% oxygen to 100% nitrogen and vice versa, under a constant temperature gradient of 1 K. The response in seebeck is found to be particularly large below MIT. The diffusion of oxygen into the lattice leading to hole doping shows a large change in carrier concentration resulting in a large change in the seebeck coefficient in insulating state. On the other hand, due to insignificant increase in already large carrier concentration in metallic state the change in seebeck is minimal. Nevertheless, below MIT the response is fairly reproducible within stoichiometry ${\delta}$ = 0.5 $\pm$ 0.05. This principle shall be of significant utility to design the oxygen sensors which work at room temperature or even cryogenic temperatures

Lifestyle factors associated with obesity in a cohort of males in the central province of Sri Lanka: a cross-sectional descriptive study

Abstract Background Obesity has become a global epidemic. The prevalence of obesity has also increased in the South Asian region in the last decade. However, dietary and lifestyle factors associated with obesity in Sri Lankan adults are unclear. The objective of the current study was to investigate the association of dietary and lifestyle patterns with overweight and obesity in a cohort of males from the Central Province of Sri Lanka. Methods A total of 2469 males aged between 16 and 72 years ( x ¯ = 31 $$\overline{x}=31$$ ) were included in the study. The sample comprised individuals who presented for a routine medical examination at the National Transport Medical Institute, Kandy, Sri Lanka. The Body Mass Index (BMI) cutoff values for Asians were used to categorize the participants into four groups as underweight, normal weight, overweight or obese. The data on dietary and lifestyle patterns such as level of physical activity, smoking, alcohol consumption, sleeping hours and other socio demographic data were obtained using validated self-administered questionnaires. Multinomial logistic regression model was fitted to assess the associations of individual lifestyle patterns with overweight and obesity. Results The mean BMI of the study group was 22.7 kg m−2 and prevalence rates of overweight and obesity were 31.8 and 12.3%, respectively. Mean waist circumference of the participants was 78.6 cm with 17.1% of them being centrally obese. After adjusting for potential confounders, weight status was associated with older age (P < 0.0001), ethnicity (P = 0.0033) and higher income (P = 0.0006). While higher physical activity showed a trend for being associated with lower odds of being obese (odds ratio: 0.898 – confidence interval: 0.744–1.084), alcohol intake, consumption of fruits, level of education, sleeping hours, smoking, consumption of fish, meat, dairy, sweets or fried snacks were not significantly associated with the weight status. Conclusion The high prevalence rates of overweight and obesity in working-age males is a threatening sign for Sri Lanka. Since the prevalence rate is higher in certain ethnic groups and higher-income groups, targeted interventions for these groups may be necessary