• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.373-379
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• 2010

EMAT has been applied in various fields for flaw detection and material characterization because it has noncontact property in wave generation and a good mode selectivity. Unfortunately, however, EMAT shows low signal to noise ratio relative to commercial contact transducer because of low energy conversion efficiency. If the phase matching through the control of time delay between each coil consisting of the array EMAT is accomplished, it is expected that it will be a solution for the improvement of low signal to noise ratio. In this experiment, the phased array EMATs which consists of 3 or 4 meander coils and one big magnet were fabricated for surface and vertical shear wave generation. Effect of phased delay control on signal directivity and amplitude enhancement was verified. A slit with the depth of 0.5 mm and a side-drill hole of 0.5 mm diameter were clearly detected by fabricated phased array EMATs, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.207-207
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• 2012

Si quantum dot (QD) imbedded in a $SiO_2$ matrix is a promising material for the next generation optoelectronic devices, such as solar cells and light emission diodes (LEDs). However, low conductivity of the Si quantum dot layer is a great hindrance for the performance of the Si QD-based optoelectronic devices. The effective doping of the Si QDs by semiconducting elements is one of the most important factors for the improvement of conductivity. High dielectric constant of the matrix material $SiO_2$ is an additional source of the low conductivity. Active doping of B was observed in nanometer silicon layers confined in $SiO_2$ layers by secondary ion mass spectrometry (SIMS) depth profiling analysis and confirmed by Hall effect measurements. The uniformly distributed boron atoms in the B-doped silicon layers of $[SiO_2(8nm)/B-doped\;Si(10nm)]_5$ films turned out to be segregated into the $Si/SiO_2$ interfaces and the Si bulk, forming a distinct bimodal distribution by annealing at high temperature. B atoms in the Si layers were found to preferentially substitute inactive three-fold Si atoms in the grain boundaries and then substitute the four-fold Si atoms to achieve electrically active doping. As a result, active doping of B is initiated at high doping concentrations above $1.1{\times}10^{20}atoms/cm^3$ and high active doping of $3{\times}10^{20}atoms/cm^3$ could be achieved. The active doping in ultra-thin Si layers were implemented to silicon quantum dots (QDs) to realize a Si QD solar cell. A high energy conversion efficiency of 13.4% was realized from a p-type Si QD solar cell with B concentration of $4{\times}1^{20}atoms/cm^3$. We will present the diffusion behaviors of the various dopants in silicon nanostructures and the performance of the Si quantum dot solar cell with the optimized structures.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.2
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• pp.207-218
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• 2017

Improving fuel consumption, particularly that of commercial vehicles, has become a global concern. The reduction in logistics cost has been a key issue in efforts to improve fuel economy and efficiency of transportation equipment. Typical technologies for reducing reduce fuel usage include air resistance reduction technologies, tire rolling resistance technologies, and idle technologies among others. Air resistance technology is a highly effective method that can be easily applied in a short period. As with air resistance technology, several devices involving side skirt, boat tail and gap fairing have been developed based on an analytical 3-D modeling technique for reducing air resistance attributed to the vehicle configuration. The devices were on a 45 feet tractor-trailer and the emission test was done using PEMS equipment. Fuel economy was evaluated by introducing several devices to reduce outer air resistance. The test was conducted by changing the experimental method of SAE J1321 Joint TMC/SAE Fuel Consumption Test Procedure - Type II test. As a result, air resistance decreased by at least 15 % and fuel economy improved by at least 13 %. This study sought to reduce greenhouse gas and improve fuel economy by applying several devices to a test vehicle to lower air resistance.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.126-131
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• 2017

Numerical analysis using commercial CFD code was carried out to develop the drag force type vertical axis hydraulic turbine for the improvement of the production efficiency of small hydro energy at low flow velocity condition. Blade pressure changes and internal flows were analyzed according to the presence or absence of the hydraulic turbine blade holes at flow velocity of less than 1.0~3.0 m/s. According to the numerical results, the pressure and flow velocity is severly affected by the flow velocity in turbine blade with no holes, while the influence of flow velocity is comparatively decreased in turbine blade with holes. It is also found that the pressure and flow velocity on the blade surface with holes are evenly distributed with no singular location and it is believed that forming a hole in the blade may be helpful in terms of structural safety.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.1
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• pp.41-47
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• 2012

Recently, due to the rapid rise of the international oil price, the burden of fuel oil expense is relatively increasing in a ship. And the international restriction of the greenhouse gas which was generated from the burning of fuel oil is also rapidly strengthened. Therefore, to reduce the greenhouse gas and fuel oil consumption, many shipping company adopted the low speed navigation and it was focused on the improvement of fuel consumption efficiency and the usage of alternative energy in the marine engine development field. In this paper, the fuel oil consumption according to the ship's speed was measured in the actual seas and analyzed the shop test results in the shipyard and the ship navigation data from the abstract log. And then it was proposed that the ship's economic speed was 14~15kts and the optimum rpm was 140~150 in specific sea conditions.

• Journal of the Korean Wood Science and Technology
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• v.29 no.4
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• pp.103-110
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• 2001

Bio-kraft pulping of Populus alba${\times}$glandulosa pretreated with white-rot fungus, Phanerochaete chrysosporium KCCM 34740, was investigated The biopulping efficiency was evalued based on fungal pretreatment time and properties of bio-kraft pulp (pulp yield, freeness, WRY, kappa number and brightness) in comparison to the controls. Pretreatment of poplar wood chips with Phanerochaete chrysosporium KCCM 34740 for 10days resulted in a some increase in screened yield (by 2%). According to increase of fungal incubation time, decrease in freeness (CSF) and increase in WRY were observed And bio-kraft pulping also led to improvement of physical properties of handsheet. As a result of bio-beating effect, we expect the saving of chemicals in kraft cooking process and energy consumption in beating process.

• Membrane Journal
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• v.25 no.2
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• pp.85-98
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• 2015

A global trend of replacing metal or glass containers with polymer-based packaging materials has been prevalent in the food packaging industry due to their ease in processibility, excellent transparency, and good cost efficiency. Barrier polymers tend to show low permeabilities for atmospheric gases such as oxygen, carbon dioxide, and water vapor, which allow them to be utilized in the food and beverage packaging industry. With the current global trend, expansion of polymeric packaging materials to new markets such as oxygen sensitive juices, flavored water, and energy drinks requires improved $CO_2$ and $O_2$ barrier properties. The improvement of the existing polymer-based barrier platform will enable a rapid market impact. In this paper, the current barrier technologies such as (1) antiplasticization-induced barrier materials, (2) synergistic effect of antiplasticization and crystallization, (3) new barrier polymers, (4) nanocomposite materials, and (5) polymer blending are introduced with their characterization techniques for the development of advanced packaging materials.

• Journal of Powder Materials
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• v.25 no.1
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• pp.1-6
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• 2018

Uniform $TiO_2$ blocking layers (BLs) are fabricated using ultrasonic spray pyrolysis deposition (USPD) method. To improve the photovoltaic performance of dye-sensitized solar cells (DSSCs), the BL thickness is controlled by using USPD times of 0, 20, 60, and 100 min, creating $TiO_2$ BLs of 0, 40, 70, and 100 nm, respectively, in average thickness on fluorine-doped tin oxide (FTO) glass. Compared to the other samples, the DSSC containing the uniform $TiO_2$ BL of 70 nm in thickness shows a superior power conversion efficiency of $7.58{\pm}0.20%$ because of the suppression of electron recombination by the effect of the optimized thickness. The performance improvement is mainly attributed to the increased open-circuit voltage ($0.77{\pm}0.02V$) achieved by the increased Fermi energy levels of the working electrodes and the improved short-circuit current density ($15.67{\pm}0.43mA/cm^2$) by efficient electron transfer pathways. Therefore, optimized $TiO_2$ BLs fabricated by USPD may allow performance improvements in DSSCs.

• Journal of Drive and Control
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• v.10 no.4
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• pp.1-6
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• 2013

With aggravation of environmental contamination and energy resource exhaustion, Hybrid Electric Vehicles (HEV) that can be economically operated with low fuel consumption are receiving greater attention. For performance improvement of such HEV, the development of efficient transmission can be seen as one of core technologies such as performance of components and driving strategy. Dual clutch transmission (DCT) is actively studied as a transmission type for HEV due to its advantages of having excellent power transmission efficiency based on manual transmission characteristic, resolving the problem of power interruption, and realizing driving convenience of automatic transmission (AT). In this paper, one diesel HEV equipped with 6-Speed DCT, modelled using MATLAB/Simulink, and a performance simulator developed for this vehicle are introduced. Driving simulation with driving cycles such as FTP75 and NYCC was performed using the developed performance simulator, and the simulated results regarding state of charge and fuel economy, when AT and DCT are applied to this diesel hybrid vehicle respectively, are compared. This performance simulator can be utilized to develop a control algorithm for improving the fuel economy of HEV with DCT.

• Journal of Power System Engineering
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• v.22 no.6
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• pp.51-57
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• 2018

In Korea, the Air Quality Conservation Act and the Petroleum and Petroleum Substitute Fuel Business Act stipulate certain quality standards for fuels distributed in Korea, thereby striving to reduce vehicle performance and emissions. Domestic petroleum products import and produce all the crude oil from each oil refiner so that the quality of the petroleum product is different according to the characteristics of the crude oil. As a result, vehicles have been improved by using the physical properties calculated through the physical property measurement that has tried to improve the accuracy of the measurement of the energy consumption efficiency of the automobile by using standard fuel from abroad. In this study, the same test procedure and method as the test method of domestic gasoline vehicle emission are applied using four samples of gasoline and the latest gasoline vehicle which are actually distributed, and the performance evaluation is performed. The purpose of this study is to contribute to improvement of vehicle technology and fuel quality by collecting necessary basic data and obtaining data on the effect of differences in gasoline property on vehicle emissions. The results of the test showed that the emission of gases (NMOG, CO) from gasoline vehicles was the most influenced by the sulfur content, unlike the previous studies that the vehicles emission had the greatest influence on the distillation characteristics and the specific gravity of aromatic compounds. The catalytic reaction such as the poisoning action of the three-way catalyst which is the abatement device was interfered and the emission was increased. The distillation characteristics and specific gravity of aromatic compounds were found to affect the emission of vehicles. According to the physical properties of the fuel, the emission difference was 28.0% in the urban mode and 17.6 % in the highway mode.