Numerical investigation of bus stop structures in Seoul for the reduction of fine dust entry

Journal of Mechanical Science and Technology - Fences and air curtains can effectively reduce fine dust entry into roadside bus structures, thus decreasing the exposure of passengers to particulate...     

Characteristics of dust-collection efficiency and ozone emission by high-voltage electrode shape of electrostatic precipitator for subway tunnel environment

Journal of Mechanical Science and Technology - The air pollution level of particulate matters in subway tunnel environments is severe. The present study conducted experimental measurements and...     

Parallel Signal Processing of a Wireless Pressure-Sensing Platform Combined with Machine-Learning-Based Cognition,Inspired by the Human Somatosensory System

Inspired by the human somatosensory system, pressure applied to multiple pressure sensors is received in parallel and combined into a representative signal pattern, which is subsequently processed using machine learning. The pressure signals are combined using a wireless system, where each sensor is assigned a specific resonant frequency on the reflection coefficient (S₁₁) spectrum, and the applied pressure changes the magnitude of the S₁₁ pole with minimal frequency shift. This allows the differentiation and identification of the pressure applied to each sensor. The pressure sensor consists of polypyrrole-coated microstructured poly(dimethylsiloxane) placed on top of electrodes, operating as a capacitive sensor. The high dielectric constant of polypyrrole enables relatively high pressure-sensing performance. The coils are vertically stacked to enable the reader to receive the signals from all of the sensors simultaneously at a single location, analogous to the junction between neighboring primary neurons to a secondary neuron. Here, the stacking order is important to minimize the interference between the coils. Furthermore, convolutional neural network (CNN)-based machine learning is utilized to predict the applied pressure of each sensor from unforeseen S₁₁ spectra. With increasing training, the prediction accuracy improves (with mean squared error of 0.12), analogous to humans' cognitive learning ability.     

Correlations and optimization of a heat exchanger with offset-strip fins

The thermo-flow characteristics of a heat exchanger with offset-strip fins are numerically investigated for various fin geometries and working fluids. Previous correlations underestimate f values in the laminar and turbulent regimes and overestimate j values in the laminar regime, as the blockage ratio increase. Therefore, new correlations, which apply to offset-strip fins with blockage ratios of greater than 20%, are presented. Even though the working fluid was changed, the f values did not vary. However, the j values differed according to the working fluid. New j correlations were suggested as functions of the Prandtl number. Design variables of the offset-strip fins in a fuel cooler were optimized by using the correlations and the design of experiment. As a result, the JF factor of the optimized offset-strip fin was enhanced by 24% compared with that of the reference offset-strip fin.     

Synthesis of metallic glass composites using phase separation phenomena

Phase separation phenomena in metallic glass systems have been explored by thermodynamic calculation and experimental method in the present study. Miscibility gap and spinodal curve for liquid phase in Gd–Ti–Al–Co/Cu systems have been calculated using the CALPHAD method. Based on the calculation result, various types of phase separation phenomena have been observed experimentally. Basically two types of structure are observed: interconnected-type structure by spinodal decomposition; and droplet-type structure by nucleation and growth mechanism. Multi-step phase separation occurs during cooling from the liquid, forming a hierarchical length scale composite structure. Depending on the glass-forming ability of the separated liquid phase, amorphous/amorphous or amorphous/crystalline composite structure can be obtained. The present study shows that there are several factors such as critical temperature, asymmetry and composition range of the spinodal curve which affect scale and morphology of the microstructure after phase separation.     

Changes in the microstructure and hydrogen storage properties of Ti-Cr-V alloys by ball milling and heat treatment

Changes in the microstructure and hydrogen storage properties of Ti-Cr-V alloys were investigated after a combination of ball milling and heat treatment. Two different sets of balls and vials made of tungsten carbide (WC) and stainless steel (STS) were used for milling the samples. Ball milling using WC balls and vials induced WC contamination, and it caused compositional changes in the matrix during heat treatment. When STS balls and vials were used, meanwhile, no peak of the second phase caused by contamination was found in the X-ray diffraction (XRD) data. In the case of the sample that completed only the milling process, the crystallite size calculated from the XRD data, 20-30 nm, agreed well with the grain size obtained from transmission electron microscopy (TEM). On the other hand, for the sample that was heat treated after milling, the strain decreased from 0.74% to 0.18%, the crystallite size increased to 70-80 nm, and the grain size grew up to the level of hundreds of nanometers. The changes in microstructure induced by the ball milling and heat treatment influenced the hydrogen storage properties, such as plateau pressure, hysteresis, and phase transformation with hydrogen absorption. Thus, the relationship between the microstructure and hydrogen storage properties can be explained.     

Synthesis and device application of hybrid host materials of carbazole and benzofuran for high efficiency solution processed blue phosphorescent organic light-emitting diodes

Highly efficient solution processed blue phosphorescent organic light-emitting diodes were developed using a carbazole–dibenzofuran hybrid host material. Asymmetric carbazole–dibenzofuran hybrid host material was synthesized by coupling reaction of phenylcarbazole and dibenzofuran, and it showed good film morphology and bipolar charge transport properties after solution coating. Blue phosphorescent organic light-emitting diodes fabricated by spin coating exhibited extremely high quantum efficiency of 23.9%, which was better than any other data reported for solution processed blue phosphorescent organic light-emitting diodes.     

Real time on-package freshness indicator for guavas packaging

A novel on-package color indicator has been fabricated based on bromophenol blue, and tests have been conducted to assess the freshness of guava (Psidium guajava L.). Bromophenol blue (BPB) was immobilized onto bacterial cellulose membrane via absorption method. The BPB/cellulose membrane as color indicator works based on pH decrease as the volatile organic compounds (e.g. acetic acid), produced gradually in the package headspace during developing of guava. Subsequently the color of the indicator will change from blue to green for over-ripe indication, which can be visible to the naked eye. The results showed that the color indicator could be used to determine the state of freshness of the guava at ambient condition (28–30 °C). The color change of the indicators reflects the pH of headspace of the guava packaging. Furthermore, it also in similar trends to the change of several parameters (soluble solids content, texture and sensory evaluation) that normally used to characterize the freshness of guava. Therefore, the indicator can be used for real time visual monitoring of freshness state of packaged guavas.     

Effect of pH on non-enzymatic browning reaction during γ-irradiation processing using sugar and sugar–glycine solutions

Effects of pH on the non-enzymatic browning reaction caused by γ-irradiation processing were investigated. The brown colour development of irradiated sugar–glycine solutions was greater in a buffer system than in deionized distilled water (DDW) with higher pH. Although browning of irradiated sugar solution without glycine was highly increased was in alkaline buffer, no browning was developed in DDW. The maximum browning of the solutions of sugar and sugar–glycine were observed at pH 10 and pH 8, respectively. The browning intensity was in the following order: sucrose ? fructose > glucose. Non-constant pH was observed in DDW (dropped pH between 1.58 and 2.03 units); however, the use of buffers was partially effective in keeping pH constant (pH dropped between 0.03 and 0.56 units). When the irradiated solutions of sugar with and without glycine were analyzed using reverse phase high performance liquid chromatography with diode-array detection (HPLC-DAD), three peaks were separated at 3.37 ± 0.04, 4.60 ± 0.02, and 2.53 ± 0.26 min, and the λ_max values of these peaks were the range 259–288 nm. The sum of the areas of these peaks at 260 nm increased with increasing pH. The results of this study indicated that conditions of the system, such as pH and media, can influence the non-enzymatic browning reaction during γ-irradiation.