Seung-Yeon Cho

Changes in neck muscle electromyography and forward head posture of children when carrying schoolbags

This study tested the effects of three alternative types of backpack on head posture and neck muscle electromyography (EMG) in children. Four loading conditions were tested: no pack; a backpack; a double pack; a modified double pack (designed with a backpack and a front pack weighing 10% and 5% of body weight, respectively). Dependent variables were neck muscle activity, forward head angle and forward head distance (the perpendicular distance from C7 to a vertical line through the tragus of the ear). Fifteen children were asked to walk at a speed of 0.8 m/s on a treadmill. The EMG activity of upper trapezius, sternocleidomastoid and midcervical paraspinals muscles and the forward head angle and forward head distance were all significantly higher when carrying a backpack than for the other conditions. When carrying a double pack, there was a backward head posture characterised by an increased negative forward head angle, decreased forward head distance, increased sternocleidomastoid EMG signal and decreased midcervical paraspinals EMG signal, compared to carrying no pack. When carrying a modified double pack, the forward head angle and forward head distance decreased when compared to carrying a backpack. These findings indicate that the modified double pack minimises postural deviation.

Formaldehyde Removal Efficiency Using Nano-size Carbon Colloids

The purpose of this study was to assess the removal efficiency of formaldehyde using nano-size carbon colloid (NCC), which was produced by a comparatively easy and cheap method. In this study, nano-size carbon colloid based on water was produced by an electro-chemical method. The particles which have mostly a spherical shape with a diameter of, what is called, “nano-size” were produced. Non-woven fabric filter, which is currently on the market as a medium filter, was used for the removal efficiency test. Known concentration (0.5 ppm) of formaldehyde standard gas was used as a pollutant. The overall results indicate that: (1) nano-size carbon colloid which has a stable dispersibility, and of which diameter is approximately 10 nm or less was produced; (2) filters treated with nano-size carbon colloids showed a higher removal efficiency, 44.47 µg of HCHO removed/g of carbon and 19.28 µg of HCHO removed/g of carbon when compared to the control experiment using a normal carbon filter. The normal carbon filter system could only achieve 1.45 µg of HCHO removed/g of carbon.

Polarity effect of the thimble-type ionization chamber at a low dose rate

It is known that the current collected from an ionization chamber exposed to a constant radiation intensity changes in magnitude when the polarity of the collecting potential is reversed. It is called the polarity effect of the ionization chamber. There are many possible causes that induce the polarity effect and one of them can be a field distortion due to a potential difference between the guard electrode and the collector. We studied how much the polarity effect depends on the design of the electrodes in the thimble-type ionization chamber. Two thimble-type ionization chambers, which had different electrode structures, were designed and fabricated at KAERI. We calculated the field distortions due to the potential difference between the guard electrode and the collector for the two ionization chambers. MAXWELL and Garfield were employed to calculate the electron drift lines inside the chamber. The polarity effects of the two ionization chambers were measured, and they were consistent with the field calculation. We could conclude that the polarity effect is mostly induced from the field distortion due to the potential difference between the guard electrode and the collector in our experiment and it depends significantly on the design of the electrodes.