• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.421-421
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• 2006

The light and energy-efficiency of classical liquid crystal displays is notoriously poor due to the use of absorption-based linear polarisers and colour filters. For instance, the light efficiency of PVAL polarisers is typically between 40 and 45 % and the colour filters have a typical efficiency below 35 % which results in a total light and energy-efficiency of the display below 10 %. In the past, a variety of polarizers were developed with an enhanced efficiency in generating linearly polarized light. Typically, these polarizers are based on the polarisationselective reflection, scattering or refraction of light i.e. one polarisation direction of light is directly transmitted to the LCD/viewer and the other polarization direction of light is depolarised and recycled which results in a typical efficiency for generating linearly polarized light of 70-85 %. Also, special colour filters have been proposed based on chiral-nematic reactive mesogens which increase the efficiency of generating colour. Despite the enormous progress in this field, a need persists for improved methods for generating polarized light and colour based on low cost optical components with a high efficiency. Here, the use of holographic phase gratings is reported for the generation of polarized light and colour. The phase grating are recorded in a photopolymer which is coated onto a backor frontlight for LCDs. Typically the recording is performed in the transmisson mode or in the waveguiding mode and slanted phase gratings are generated with their refractive index modulation at an angle between 20o and 45o with the normal of the substrate. It is shown that phase gratings with a high refractive index modulation and a high efficiency can be generated by a proper selection of the photopolymer and illumination conditions. These phase gratings coupleout linearly polarized light with a high contrast (> 100) and the light is directed directly to the LCD/viewer without the need for redirection foils. Dependent on the type of phase grating, the different colours are coupled-out at a slightly different angle which potentially increases the efficiency of classical colour filters. Moreover, the phase gratings are completely transparent in direct view which opens the possibility to use them in frontlights for LCDs. Holographic polarization gratings posses a periodic pattern in the polarization state of light (and not in the intensity of light). A periodic pattern in the polarization direction of linearly polarized light is obtained upon interference of two circularly polarized laser beams. In the second part of the lecture, it is shown that these periodic polarization patterns can be recorded in a linear photo-polymerizable polymer (LPP) and that such an alignment layer induces a period rotation in the director of (reactive and non-reactive) liquid crystals. By a proper design, optical components can be produced with only first order diffraction and with a very high efficiency (>0.98). It is shown that these diffraction gratings are potentially useful in projection displays with a high brightness and energy efficiency

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1998.04a
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• pp.83-89
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• 1998

In case of Radar Simulator ,the target ships should be generated and displayed on the monitor to provide the trainee with the feeling of real situation. The scenario methodology, which has been developed and used in Korea so far, however, has a fixed scenario, in which target ships are generated in the same manner at all time. As a result, the Radar simulator developed in Korea so far was in lack of training efficiency, as the trainee can get earily familiarized with the fixed scenaio. The paper, therefore, suggests the target ship generating methodology using random variables to improve the training efficiency of the existing simulator. In generating the target ships using this methodology, the speed, distance between the ships , and time interval of ships and time of ships were considered as a major factors which dterminie the ship's movements. The new methodology suggested was examined and found to generate target ships successfully giving a trainee the feeling of real situation.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.773-774
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• 2006

Nowadays, the global interests are concentrated on the preserving of the clean environment, and the diminishing of the dependence on the fossil energy, and among the possible alternative energies, the wind turbine generating system is considered to be the best suited to produce high efficiency energy, without affecting the natural environment. The permanent magnet generators were been used for the wind power generating, for long time, with continuous efforts to improve the generating efficiency. And the latest trend on it is to develop an AFPM(Axial Flux Permanent Magnet)type, which is composed in the structure of rotor and stator shaped in the disc forms, and the direction of the flux at the air gap runs in parallel to the shaft. This thesis is on the study concerning with the analysis of the characteristics of the 5 kW at 300rpm direct drive AFPM generator which is suitable for the small scale wind turbine generating system. In it, the Electro-magnetically Coreless AFPM was been analyzed, the prototype generators been made, concentrated on interpreting the characteristics of the power output, and verifying it through the theoretical study and practical tests.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.500-503
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• 1991

Fuel cells power generating system converts the chemical energy of a fuel directly into electrical energy. The merits of fuel cells power generating system are pollution free and high energy conversion efficiency. Fuel cells power generating system includes the DC/AC converter. DC source obtained from stack is converted to the constant AC voltage or current by the inverter. In this paper, the power control techniques for the fuel cells power generating system are described.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1991.10a
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• pp.59-63
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• 1991

Fuel cells power generating system converts the chemical energy of a fuel directly into electrical energy. The merits of fuel cells power generating system are pollution free and high energy conversion efficiency. Fuel cells power generating system includes the DC/AC converter. DC source obtained from stack is converted to the constant AC voltage or current by the inverter. In this paper, the power conditioner for the fuel cells power generating system are discribed. Some experiments are performed, for the power conversion system. The results show that the implimented experimental system may be applied to the practical fuel cells power generating system.

• Journal of Environmental Science International
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• v.23 no.1
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• pp.97-104
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• 2014

The sludge flotation/thickening apparatus equipped a micro-bubble generating pump was used to investigate micro-bubble generating properties on operational parameters. We evaluated micro-bubble generating properties as results to be operated the apparatus by operational parameters which are pump discharge pressure, air/water ratio(A/W ratio), air flow rate, and water flow rate. Micro-bubble generating efficiencies in pumps without recycling flow and with 50% of recycling flow was found to be very efficient on optimum A/W ratio from 1.06 to 3.62% and optimum A/W ratio from 1.05 to 4.06%, respectively. In condition of 3.6% of A/W ratio, we showed that the apparatus could be generated 36,000 ppm of micro-bubble concentration to be optimum treatment efficiency in sludge thickening process.

• Environmental and Resource Economics Review
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• v.17 no.1
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• pp.23-49
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• 2008

In this paper, we estimate whether changes in the economic environment a firm operates in affects technical efficiency. Since efficiency gains can manifest themselves in a variety of ways, we estimate for efficiency gains on annual generating plants input demand for expenses and fuel use. We find that generating plants reduced their workers and costs respectively by 6.8% in 1999 and 37.9% in 2001. However, they didn't show any systematic caloric consumption changes facing various economic environmental shocks. These results suggest that restructuring brought efficiency gains by replacing regulated monopoly with a more competitive firms in the context of the Korean electricity market.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.11
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• pp.1143-1148
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• 2004

In this study, photoresist stripping in semiconductor or LCD (liquid crystal display) fabrication processes using DIO, was investigated. In order to obtain the high PR stripping efficiency of DIO. we have developed new ozone-generating system with high ozone concentration and ozone-resolving system with high contact ratio. In this study, we obtained ozone gas concentrations of 11 % by new ozone-generating system, ozone-resolving efficiency of 99.5 % and maximum solubility of 130 ppm in deionized water. We applied the newly designed equipments to photoresist stripping processes and obtained similar results to SPM(sulfuric-peroxide mixture) process characteristics.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.353-362
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• 2009

In the process of turbine modernizations, the investigation of the influences of water passage roughness on radial flow machine performance is crucial and validates the efficiency step up between reduced scale model and prototype. This study presents the specific losses per component of a Francis turbine, which are estimated by CFD simulation. Simulations are performed for different water passage surface roughness heights, which represents the equivalent sand grain roughness height. As a result, the boundary layer logarithmic velocity profile still exists for rough walls, but moves closer to the wall. Consequently, the wall friction depends not only on roughness height but also on its shape and distribution. The specific losses are determined by CFD numerical simulations for each component of the prototype, taking into account its own specific sand grain roughness height. The model efficiency step up between reduced scale model and prototype value is finally computed by the assessment of specific losses on prototype and by evaluating specific losses for a reduced scale model with smooth walls. Furthermore, surveys of rough walls of each component were performed during the geometry recovery on the prototype and comparisons are made with experimental data from the EPFL Laboratory for Hydraulic Machines reduced scale model measurements. This study underlines that if rough walls are considered, the CFD approach estimates well the local friction loss coefficient. It is clear that by considering sand grain roughness heights in CFD simulations, its forms a significant part of the global performance estimation. The availability of the efficiency field measurements provides an unique opportunity to assess the CFD method in view of a systematic approach for turbine modernization step up evaluation. Moreover, this paper states that CFD is a very promising tool for future evaluation of turbine performance transposition from the scale model to the prototype.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.10
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• pp.458-463
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• 2003

In order to develope piezoelectric transformer for the ballast of fluorescent lamp, a new shape and electrode pattern of piezoelectric transformer has been investigated in this work. The composition of piezoelectric ceramics was 0.95Pb(Zr$_{0.51}$Ti$_{0.49}$)O$_3$+0.03Pb(Mn$_{1}$3/Nb$_{2}$3/)O$_3$+0.02Pb(Sb$_{1}$2/Nb$_{1}$2/)O$_3$. The sample prepared by this composition system showed the characteristics which has about 1200 of relative dielecric constant, 1100 of the mechanical quality factor, 0.53 of the electromechanical coupling coefficient, 320 pC/N of the piezoelectric constant d$_{33}$, 0.3 % of the dissipation factor. Diameter and thickness of disk-type piezoelectric transformer was 45 mm and 4 mm, respectively. The driving and generating electrode with their gap of 1mm were fabricated on the top surface. But the common electrode was fabricated on the whole bottom surface. The electrode surface ratio of driving and generating part on the top surface ranges from 1.4:1 to 3:1. We investigated the electrical characteristics with the variation of the electrode surface ratio of driving and generating part in the range of load resistance of 100 $\Omega$～70 k$\Omega$. The set-up voltage ratio of this piezoelectric transformer increases with increasing both the electrode surface of driving part and the load resistance. The set-up voltage ratio at no load resistance was more than 60 times. On the other hand, the efficiency decreases with increasing the electrode surface of driving part. In the case of the electrode surface of both 1.4:1 and 2:1, maximum efficiency showed above 97 % at load resistance of 2 k$\Omega$. However, in the case of the electrode surface of 3:1, maximum efficiency showed about 94 % at load resistance of 3 k$\Omega$.>.>.>.