Controlled production of atomic oxygen and nitrogen in a pulsed radio-frequency atmospheric-pressure plasma

International audienceRadio-frequency driven atmospheric pressure plasmas are efficient sources for the production of reactive species at ambient pressure and close to room temperature. Pulsing the radio-frequency power input provides additional control over species production and gas temperature. Here, we demonstrate the controlled production of highly reactive atomic oxygen and nitrogen in a pulsed radio-frequency ( ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn001.gif] 13.56 MHz) atmospheric-pressure plasma, operated with a small ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn002.gif] 0.1 % air-like admixture ( ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn003.gif] \rm N_2 / ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn004.gif] \rm O_2 at ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn005.gif] 4:1 ) through variations in the duty cycle. Absolute densities of atomic oxygen and nitrogen are determined through vacuum-ultraviolet absorption spectroscopy using the DESIRS beamline at the SOLEIL synchrotron coupled with a high resolution Fourier-transform spectrometer. The neutral-gas temperature is measured using nitrogen molecular optical emission spectroscopy. For a fixed applied-voltage amplitude (234?V), varying the pulse duty cycle from 10% to 100% at a fixed 10?kHz pulse frequency enables us to regulate the densities of atomic oxygen and nitrogen over the ranges of ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn006.gif] (0.18±0.03) ? ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn007.gif] (3.7±0.1)× 10^20 ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn008.gif] \rm m^-3 and ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn009.gif] (0.2±0.06) ? ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn010.gif] (4.4±0.8) × 10^19 ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn011.gif] \rm m^-3 , respectively. The corresponding 11?K increase in the neutral-gas temperature with increased duty cycle, up to a maximum of ##IMG## [http://ej.iop.org/images/0022-3727/50/45/455204/daa8da2ieqn012.gif] (314±4) K, is relatively small. This additional degree of control, achieved through regulation of the pulse duty cycle and time-averaged power, could be of particular interest for prospective biomedical applications

The epidemiological burden of obesity in childhood: a worldwide epidemic requiring urgent action

Background: In recent decades, the prevalence of obesity in children has increased dramatically. This worldwide epidemic has important consequences, including psychiatric, psychological and psychosocial disorders in childhood, and increased risk of developing noncommunicable diseases later in life. Treatment of obesity is difficult, and children with excess weight are likely to become adults with obesity. These trends have led World Health Organization (WHO) member states to endorse a target of no increase in obesity in childhood by 2025. Main body: Estimates of overweight in children aged under 5 years are available jointly from UNICEF, WHO and the World Bank. Country-level estimates of obesity in children aged from 2 to 4 years have been published by the Institute for Health Metrics and Evaluation (IHME). For children aged from 5 to 19, obesity estimates are available from the NCD Risk Factor Collaboration. The global prevalence of overweight in children aged under 5 years has increased modestly, but with heterogeneous trends in low- and middle-income regions, while the prevalence of obesity in children aged from 2 to 4 has increased moderately. For children aged 5 to 19, obesity was relatively rare in 1975, but was much more common in 2016. Conclusions: It is recognised that the key drivers of this epidemic form an obesogenic environment, which includes changing food systems and reduced physical activity. Although cost-effective interventions such as WHO “best buys” have been identified, political will and implementation have so far been limited. There is therefore a need to implement effective programmes and policies in multiple sectors to address overnutrition, undernutrition, mobility and physical activity. To be successful, the obesity epidemic must be a political priority, with these issues addressed both locally and globally. This must involve coordinated work by governments, civil society, private corporations and other key stakeholders

Pulsed Laser Ablation of the Solid Targets in a Liquid Environment

In this paper, the viability of laser ablation of gold target immersed in medical distillated water used to produce nanoparticles having morphological, structural and compositional properties for medical applications is explored. The morphological properties were investigated by means of scanning electron microscopy (SEM). Energy-dispersive X-ray spectroscopy (EDX) analysis was used to reveal the composition of resulting particles. The absorbance in the wavelengths range of 300-800 nm can be assigned to the small gold nanoparticles