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It is well known that natural ventilation is caused by the outdoor wind velocity and the indoor-outdoor temperature difference. Generally, natural ventilation is rarely caused by one effect alone, but by the coupled form of two effects. However, only the indoor-outdoor temperature difference (ΔT) was considered to evaluate the characteristic of thermal buoyancy-induced natural ventilation in this experimental study. The indoor-outdoor temperature differences were set to 5, 10, 20 and 30 °C. The measured ventilation rates by changing ΔT were compared to the calculation results based on the hydrostatic theory. From the experimental results, it was found that the ventilation rate is exponentially proportional to ΔT and the area ratio (AR) of the inlet opening to the outlet opening is an important factor to affect natural ventilation. However, the influence on a ventilation rate by AR nearly disappeared when AR exceeds over 5.0. In addition to it, it was identified that AR and a flow resistance coefficient of Cd for ventilation can be correlated as an exponential function and its form is exp(−3.6AR).

We propose a new graphical method for selecting a pair of optical and housing materials to simultaneously athermalize and achromatize an LWIR optical system. To have a much better opportunity to select the IR glasses and housing materials, an athermal glass map is expanded by introducing the DOE with negative chromatic power. Additionally, from the depth of focus in an LWIR optical system, the tolerable housing boundary is provided to realize an athermal and achromatic system even for not readily available housing material. Thus, we can effectively determine a pair of optical and housing materials by reducing the thermal shift to be less than the depth of focus. By applying this method to design a night vision camera lens, the chromatic and thermal defocuses are reduced to less than the depth of focus, over the specified waveband and temperature ranges.

With the vigorous spread of renewable energy, much attention has been paid to natural ventilation. The natural ventilator is usually classified into a passive type and an active type. In this study, the Venturi-type ventilator, which is one of the passive type and basically operated by the Bernoulli’s principle, was experimentally investigated to evaluate the ventilation characteristics according to the outdoor wind velocities and the opening area of a wall. It was confirmed from the experimental results that the ventilation rate of the Venturi-type ventilator was linearly increased and that the ventilation rate was affected by an intake opening area. The wider the intake opening size gets, the more the ventilation rate increases. Furthermore, the new coefficient of β, which reflects the pressure loss from the intake opening to the mixing zone of the Venturi-type ventilator was introduced and experimentally evaluated. The value of β, which was evaluated as about 0.08, provides the simple calculation means to estimate the ventilation rate through the Venturi-type ventilator only if the geometric dimensions are known.

The ventilation effect of a ventilation system, which is classified as the forced ventilation and natural ventilation, is predominantly dependent on the combination of air supply and discharge. Perhaps the simplest ventilation is merely supplying the air as it is. However, to improve the indoor working environment during the summer, an air supply that is cooled to some extent has been widely adopted. Recently, a cooling method utilizing the vaporization of water was introduced. In this study, the performance of an evaporation-type air supply unit that was produced by Japan K-company and was installed in a shoe-manufacturing plant in Busan was investigated. The purpose of the experiment was to measure how much the supplied air could be cooled. From this experimental study, we confirmed that the evaporation-type air supply system is efficient, capable of improving the working environment during the summer while minimizing the energy cost. †Corresponding Author, choi_s_h@naver.comⒸ 2016 The Korean Society of Mechanical Engineers

This paper presents a design method for improving the low relative illumination and large distortion due to widening the field of a system. A tele-centric optical system in image space was suggested to increase the relative illumination. Through the analyses of the third-order aberrations affected by introducing aspherical surfaces, we have proposed a method to determine analytically what surface should be aspheric to correct each aberration effectively. By utilizing this method to design a wide field lens, a tele-centric wide field lens with f-number of F/2.0 was obtained. Even though the field angle is 120 degrees, it has a very low distortion less than -2% and high relative illumination more than 73.7%. In conclusion, this analytic method for selecting aspherical surfaces is expected to serve as a useful way to find design solutions.

This paper presents a new graphical method for selecting a pair of optical glass and housing materials to simultaneously achromatize and athermalize a multilens system composed of many elements. To take into account the lens spacing and housing, we quantify the lens power, chromatic power, and thermal power by weighting the ratio of the paraxial ray height at each lens to them. In addition, we introduce the equivalent single lens and the expanded athermal glass map including a housing material. Even though a lens system is composed of many elements, we can simply identify a pair of glass and housing materials that satisfies the athermal and achromatic conditions. Applying this method to design a black box camera lens equipped with a 1/4-inch image sensor having a pixel width of $2{\mu}m$ , the chromatic and thermal defocusings are reduced to less than the depth of focus, over the specified ranges in temperature and frequency.

The purpose of this study is to investigate the effect of the impinging plate on combustion process in Diesel engine. Especially, the variation of exhaust emission and engine performance by the change of fuel injection timing and fuel injection pressure between the trial engine with impinging plate and the prototype engine were examined. The nitrogen oxide concentration of the trial engine decreased more than 50% compared to the prototype engine, however, smoke concentration of the trial engine indicated higher degree than the prototype engine. The smoke concentration, fuel consumption rate and exhaust gas temperature decreased as the fuel injection timing become faster, whereas the nitrogen oxide concentration decreased as the fuel injection timing is retarded. The nitrogen oxide concentration, fuel consumption rate and exhaust gas temperature decreased as the fuel injection pressure become lower. But smoke concentration decreased as the fuel injection pressure become higher.

This paper presents a new graphical method for selecting a pair of optical glasses to simultaneously achromatize and athermalize an imaging lens made of materials in contact. An athermal glass map that plots thermal glass constant versus inverse Abbe number is derived through analysis of optical glasses and plastic materials in visible light. By introducing the equivalent Abbe number and equivalent thermal glass constant, although it is a multi-lens system, we have a simple way to visually identify possible optical materials. Applying this method to design a phone camera lens equipped with quarter inch image sensor having 8-mega pixels, the thermal defocuses over $-20^{\circ}C$ to $+60^{\circ}C$ are reduced to be much less than the depth of focus of the system.

The wear behavior of epoxy matrix composites filled with nano sized silica particles is discussed in this paper. Especially, the variation of the coefficient of friction and the specific wear rate under the various applied load and sliding velocity were investigated for these materials. Wear tests of pin-on-disc mode were carried out and followed by scanning electron microscope observations. The presence of silica filler in epoxy composites was demonstrated significant influence on the friction and wear behavior of epoxy nanocomposites. With the incorporation of silica filler into the epoxy matrix, reduction of the coefficient of friction and specific wear rate were identified. Wear mechanism was discussed by analyzing the worn surface by scanning electron microscope as well.

On this work, the importance of industrial ventilation was investigated and examined the theoretical point and problems about general ventilation of factory exposed on high temperature during summer. As a case study, the ventilation planning of the printed circuit board (PCB) etching process for an electronic company was carried out and each of those characteristics were compared by installing actual ventilation systems and measuring the changing state of the working environment in accordance with ventilation method during summer. The purpose of the study is to present an efficient ventilation method for a factory with a closed structure under high temperature environment. In summary, for a factory with a sealed structure such as the target PCB manufacturing factory in this study, the forced supply and exhaust method was the most appropriate ventilation method for maintaining a low.

【The purpose of this paper is to investigate polarization characteristics of WC-based alloy coatings in alkaline solution. The coatings were fabricated with WC-CrC-Ni, WC-Co-Cr and WC-Co composite powders by HVOF process. Corrosion tests of coatings and substrate were carried out using potentiostat/galvanostat at solution with pH 8 and pH 13. Corrosion potential(Ecorr) and corrosion current density(Icorr) could be studied from polarization curve, and corrosion behavior was analyzed by SEM and EDS. WC-Co-Cr coating and WC-CrC-Ni coating showed more favorable anti-corrosion characteristics than WC-Co coating and substrate at solution with pH 8 and pH 13.】

This article aims at investigating the effect of applied load and sliding speed on wear behavior of thermally spraryed STS316 coating. STS316 coatings were fabricated by flame spray process according to optimal parameters on steel substrates. Dry sliding wear tests were performed on STS316 coating using four different applied load as 10, 15, 20 and 25 N and four different sliding speed as 15, 30, 45 and 60 rpm. Wear behavior on worn surface was investigated using scanning electron microscope(SEM) and energy disperive X-ray spectroscopy(EDS). The dominant wear mechanism of STS316 coating under low applied load and sliding speed was oxidation on worn surface. However, under high applied load and sliding speed the principal wear mechanism was abrasion on oxidation film and damage of oxidation film.

The purpose of this paper is to investigate polarization characteristics of heat-treated Ni-based self-flux alloy coating in alkaline solution. Ni-based self-flux alloy powder was sprayed to a steel substrate using flame spray process, and heat treatments were performed in a vacuum furnace at , , and . After heat treatments, corrosion tests were carried out using potentiostat/galvanostat at solution with pH 8 and pH 13. Corrosion potential(Ecorr) and corrosion current density(Icorr) could be analyzed from polarization curve. Anticorrosive effect of heat-treated coating at solution with pH 8 was relatively greater than at solution with pH 13. Heat-treated coating at showed the greatest anti-corrosion characteristics in alkaline solution.

This article describes effect of post heat treatment on wear characteristics of thermally sprayed Co-based self-flux alloy coating. Co-based self-flux alloy coatings were deposited on steel substrates using a flame spray process. Post heat treatments were carried out at 800, 900, 1000 and 1100℃ for 30min in a vacuum chamber. For analysis of effect of post heat treatment on mechanical properties, wear test and hardness test were performed for post heat-treated coating specimen. Microstructures of heat treated coating layer and wear track were examined using SEM and EDS. Wear loss and hardness became lower with increasing post heat treatment temperature. Key Words ： Co-based Self-flux Coating, Post Heat Treatment, Microstructure, Wear Microhardness **†김영식(교신저자) : 부경대학교 기계자동차공학과E-mail : Yeongsik@pknu.ac.kr, Tel : 051-629-6155 *이재홍 : 부경대학교 대학원**†Yeong-Sik Kim(corresponding author) : Department of Mechanical & Automotive Engineering, Pukyong National UniversityE-mail : Yeongsik@pknu.ac.kr, Tel : 051-629-6155*Jae-Hong Lee : Graduate School, Pukyong National University

This paper describes process optimization for thermal-sprayed Co-based self-flux alloy coating by Taguchi method. Co-based self-flux alloy coatings were fabricated according to orthogonal array using flame spray process. Hardness test and wear test were performed, the results were analyzed by analysis of variance(ANOVA) considering a multi response signal to noise ratio(MRSN). From the results of ANOVA, the optimal combination of the flame spray parameters on Co-based self-flux alloy coating could be predicted. The calculated hardness and wear rate of the coatings by ANOVA were found to be close to that of confirmation experimental result.

In the present study, process optimization for thermal-sprayed Ni-based alloy coating has been performed using Taguchi method and analysis of variance(ANOVA). Ni-based alloy coatings were fabricated by flame spray process on steel substrate, and the hardness test and wear test were performed. Experiments were designed as per Taguchi`s L9 orthogonal array and tests were conducted with different Oxygen gas flow, Acetylene gas flow, Powder feed rate and Spray distance. Multi response signal to noise ratio (MRSN) was calculated for the response variables and the optimum combination level of factors was obtained simultaneously using Taguchi`s parametric design.

Thermal spray coatings developed by deposition of splats, it formed by impacting molten droplets on substrates during thermal spray process. In this study, the Ni-based coatings were fabricated by thermal spray process with two different process parameters, oxygen gas flow and acetylene gas flow, with three different levels of each parameters. The morphology of splats and microstructure were observed by optical microscope. Hardness test were performed on the Ni-based coatings. It was confirmed that process parameters of thermal spray process have effect in morphology of splats. These effects also have important implications on the deposit microstructure and properties of Ni-based coatings.

Al/SiC composites were fabricated by thermal spray process, and the dry sliding wear tests were performed using the various sliding speed of 10, 30, 60 and 90 RPM through 1000 cycles. The applied load was 10 N and radius of wear track was 15 mm. Wear tracks on the Al/SiC composites were investigated using scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDS). In the case of sliding speed of 10 RPM, adhesive wear behavior caused by plastic deformation of composits surface was observed. In the cases of sliding speed of 30, 60, 90 RPM, abrasive wear behavior on the adhered layer formed by debris were observed. Through this study, it was found that the wear behavior of Al/SiC composites was mainly influenced by the sliding speed.

In this work, the parameter optimization for thermal-sprayed Al/SiC composites have been designed by orthogonal array and analysis of variance(ANOVA). Al/SiC composites were fabricated by flame spray process on steel substrate. The hardness of composites were measured using micro-vickers hardness tester, and these results were analyzed by ANOVA. The ANOVA results showed that the oxygen gas flow, powder feed rate and spray distance affect on the hardness of the Al/SiC composites. From the ANOVA results, the optimal combination of the flame spray parameters could be extracted. It was considered that experimental design using orthogonal array and ANOVA was efficient to determine optimal parameter of thermal-sprayed Al/SiC composites.

SiC particulate reinforced Al matrix composites with different SiC volume fractions were fabricated by thermal spray process. And the dry sliding wear test were performed on these composites using the applied load of 10 N, rotational speed of 30 rpm, radius of rotation 15 mm. Wear tracks on the Al/SiC composites were investigated using scanning electron microscope(SEM) and energy dispersive spectroscopy (EDS). It was observed that wear behavior of Al/SiC composites and formation of MML was changed dramatically according to reinforcement volume fraction.

Thermal spray technology provides wear-resistant coating on the surface of mechanical components. In this study, wear characteristics of SiCp reinforced Al matrix composite coatings were evaluated. SiCp reinforced Al matrix composite coatings were fabricated using the mixed powders which have different fraction of the SiC reinforcement, 0, 20, 40 and 60 vol% on Al 6061 substrate by thermal spray process. Dry sliding wear tests were performed on these coatings using varied sliding speeds and applied loads. Wear behavior of these Al-based composite coatings were investigated using scanning electron microscope(SEM), energy dispersive X-ray spectroscopy(EDX) and X-ray diffraction(XRD). The composites coatings reinforced with 40 vol% of SiC particles showed the most excellent wear resistance. Although the wear rate increased according to the increase in the applied load, it decreased according to the increase in the sliding speed. The major wear behavior of the SiCp reinforced Al matrix composite coatings is transferred from the adhesive wear to the abrasive wear according to the increase in the sliding speed and the applied load. These results were significantly influenced by the formation of mechanical mixed layer(MML).

The various process parameters of thermal spray process affects on quality of Ni-based coatings. Thus, there is need to analyze the effect of process parameters on quality of Ni-based coatings. In this paper, the effects of process parameters on hardness and wear rate of Ni-based coatings were investigated using 4 design of experiments. First, the Ni-based coatings were fabricated according to orthogonal array. The hardness tests and the wear tests were performed on the Ni-based coatings. The analysis of variance for the hardness and wear rate were carried out. As a results, the acetylene gas flow and the powder feed rate were identified as main factors effected on the hardness and the oxygen gas flow and the acetylene gas flow were identified as main factors effected on the wear rate. The full factorial experiments design with different levels was applied for investigation of effect of these main factors.

The present study tested the cytoprotective effect of methyleugenol in an in vivo ischemia model (i.e. middle cerebral artery occlusion (MCAO) for 1.5 h and subsequent reperfusion for 24 h) and further investigated its mechanism of action in in vitro cerebral ischemic models. When applied shortly after reperfusion, methyleugenol largely reduced cerebral ischemic injury. Methyleugenol decreased the caspase-3 activation and death of cultured cerebral cortical neurons caused by oxygen-glucose deprivation (OGD) for 1 h and subsequent re-oxygenation for 24 h. Methyleugenol markedly reduced superoxide generation in the ischemic brain and decreased the intracellular oxidative stress caused by OGD/re-oxygenation. It was found that methyleugenol elevated the activities of superoxide dismutase and catalase. Further, methyleugenol inhibited the production of nitric oxide and decreased the protein expression of inducible nitric oxide synthase. Methyleugenol down-regulated the production of pro-inflammatory cytokines in the ischemic brain as well as in immunostimulated mixed glial cells. The results indicate that methyleugenol could be useful for the treatment of ischemia/inflammation-related diseases.

This study aims at investigating the wear behavior of thermally sprayed Ni -based self-flux alloy coatings against different counterparts. Ni -based self-flux alloy powders were flame-sprayed onto a carbon steel substrate and then heat-treated at temperature of 1000 °C. Dry sliding wear tests were performed using the sliding speeds of 0.2 and 0.8 m/s and the applied loads of 5 and 20 N. AISI 52100, Al 2 O 3, Si 3 N 4 and ZrO 2 balls were used as counterpart materials. Wear behavior of Ni -based self-flux alloy coatings against different counterparts were studied using a scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDX). It was revealed that wear behavior of Ni -based self-flux alloy coatings were much influenced by counterpart materials.

In this study, an electro-optically Q-switched 2.70 μm emission Er:Cr:YSGG laser with a LiNbO3 Pockels cell is investigated and compared with a FTIR Q-switched scheme. It can obtain nanosecond pulse at a low voltage of 1.4 kV using a CaF2 polarizer and a LiNbO3 crystal with Brewster's angle cut ends. Wavelength generation of 2.70 μm was possible with a Fresnel loss at a rear mirror with a dielectric dichroic coating. The maximum output energy of 21.5 mJ (at 1 Hz repetition rate) was achieved in TEM21 mode using the output coupler with a reflectivity of 55% at 2.70 μm. The generated maximum pulse energy and pulse width were 13.3 mJ and 159 ns in TEM00 mode, respectively. The pulse width was shorter than 1.3 μs of the FTIR Q-switched scheme.

This paper deals with the design and test of a high temperature superconducting (HTS) power supply with YBCO coated conductor (CC) pancake load, also presents its operational characteristics through experiments. HTS power supply consists of two heaters, an electromagnet, a solenoid, and a pancake load of about 0.73 mH. The solenoid and pancake load were fabricated by using YBCO CC. The timing sequential control of two heaters and an electromagnet is an important factor to generate pumping-current in the pancake load. The heat transfer analysis of heater triggering parts of the YBCO CC solenoid according to the heater input was carried out. Based upon the analysis, the 3 A electromagnet current and the 0.55 A dc heater current were optimally derived, and 4 s, 8 s and 16 s for the pumping period were selected in this experiment. A region of the superconducting tape with a buried heating coil can be switched by means of its temperature change. In order to measure the pumping-current with respect to the magnet flux changes, a hall sensor was installed at the center of the YBCO CC pancake load. In the experiment, the maximum pumping current reached about 20 A.

This paper deals with the short-circuit characteristics, including current limiting and current distribution characteristics of non-inductive superconducting coil wound with stainless steel-stabilized coated conductor (CC). From the tests of current limiting characteristics, we concluded that: (1) stainless steel-stabilized CC is efficient in the reduction of the wires required and volume of bobbin. However, its current limitation was not as efficient due to its high resistivity; (2) proper thickness and intermediate resistivity between copper and stainless steel can be an optimal specification of stabilizer for resistive SFCLs. From current distribution measurement tests, we concluded that contact resistance, impedance and cooling condition plays a dominant role in the current distribution characteristics before the fault, during the fault and during the recovery, respectively.

SiC particulates reinforced Al matrix composites were fabricated by thermal spray process, and the dry sliding wear behavior against four different counterparts was investigated under a varying of the sliding speed and the applied load conditions. Al/SiC composites were fabricated by flame spraying, and the dry sliding wear tests were performed using the sliding speed of 0.4 m/s and 0.8 m/s at the applied load of 3 N. Sliding distance was kept at 1000 m for all the tests. Al2O3, ZrO2, Si3N4 and AISI 52100 balls were used as the counterparts. Wear tracks on the Al/SiC composites were investigated using scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). It was revealed that wear behavior of Al/SiC composites was much influenced by counterpart materials.

In this study, microstructure and wear behavior of thermally sprayed Fe-based alloy coatings were investigated. Fe-based alloy coatings were formed on a carbon steel substrate and then heat-treated at temperature of 700 oC for 20 minutes. Dry sliding wear tests were performed using the sliding speeds of 0.4 and 0.8 m/s, the applied loads of 3 and 6 N. Microstructure and wear behavior of as-sprayed and heat-treated Fe-based amorphous coatings were studied using a scanning electron microscope(SEM), transmission electron microscopy(TEM) and X-ray diffraction(XRD).

This study aims at investigating the effect of the sliding speed and the applied load on the dry sliding wear behavior of thermally sprayed Ni-based self-flux alloy coating. Ni-based self-flux alloy powders were flame-sprayed onto a carbon steel substrate and then these coatings were heat-treated at temperature of 1000 oC. Dry sliding wear tests were performed using the sliding speeds of 0.2, 0.4, 0.6 and 0.8 m/s and the applied loads of 5, 10, 15 and 20 N. AISI 52100 ball (diameter 8 mm) was used as counterpart material. Wear behavior of Ni-based self-flux alloy coatings was studied using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX). It was revealed that microstructure and wear behavior of the Ni-based self-flux alloy coatings were much influenced by the sliding speed and the applied load.

We conducted an inoculation test using nine open-pollinated families of pine trees to evaluate their susceptibility and mortality in different densities of pine wood nematode. Three-year-old nine open-pollinated pine families were inoculated with Bursaphelenchus xylophilus at levels of 3,000, 5,000, and 7,000 nematodes/seedling in greenhouse. There were no distinct patterns in latent period among three densities of B. xylophilus in all families. Most families showed the first disease symptoms of needle discoloration within 12-15 days after inoculation. However, open-pollinated progenies of Pinus densiflora showed the longest latent period because none of one-year-old needles were wilted until 14 days after inoculation with 5,000 and 7,000 nematodes. One-year-old needles were wilted earlier than current needles in all tested families with all densities of B. xylophilus. Current needles were not wilted until 14 days after inoculation in all seedlings. The mortality of all seedlings rapidly increased from 35 days to 49 days after inoculation, and all died within 80 days except two seedlings. A 3,000 nematodes/100 with sterilized distilled water are enough to screen 3-year-old pine seedlings for resistance to B. xylophilus.

Al-base composites have been widely applied in the automotive and aerospace industries. Such composites are mainly fabricated by cast, powder metallurgy and infiltration processes. In this study, Al/ Al 2 O 3 composite coatings were fabricated by a thermal spray process and their wear behaviors were investigated. Four kinds of Al/Al 2 O 3 composite coatings were fabricated using a flame spray apparatus with different mixture ratios of Al and Al 2 O 3 powders. A ball-on-disk type wear test was carried out for these composite coatings using a sliding speed of 0.2 m/sec and applied loads of 1 and 2 N, respectively. Microstructures and wear behaviors of the composite coatings were analyzed by SEM and XRD. It was revealed that the wear behaviors of Al/Al 2 O 3 composite coatings fabricated by a thermal spray process depend on the applied load and the mixture ratios of the Al and Al 2 O 3 powders.