• Korean Chemical Engineering Research
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• v.51 no.4
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• pp.411-417
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• 2013

To use as an anode material of lithium secondary battery, graphite-silicon composite powders are prepared by ball-milling with silicon nanoparticles (average diameter 100 nm, 0~50 wt%) and graphite powder (average diameter $15{\mu}m$) and their electrochemical properties are examined. As the silicon content increases, the graphite becomes smaller by the ball-milling and amorphous phase appears whereas the silicon do not suffer the change of nanocrystalline phases and embeds within the amorphous phase of graphite. Cyclic voltammetry at low scan rate reveals that typical oxidation peaks of graphite and silicon appear at 0.2~0.35 and 0.55~0.6 V, respectively, with higher reversibility for repeated cycles. In contrast, the high-scan-rate redox behavior is very irreversible for repeated cycles. High irreversible capacity is exhibited in the initial charging-discharging cycles, but it diminishes as the cycle number increases. The saturated discharge capacity achieves about 485 mAh $g^{-1}$ at 50th cycle for the composite of Si 20 wt%. This is due to the formation of amorphous graphite morphology by the adequate composition (C:Si=8:2 w/w), which efficiently buffers the volume change during alloying/dealloying between silicon and lithium.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.2
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• pp.94-99
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• 2010

This paper presents a charge pump architecture for correcting the current mismatch due to the PVT variation. In general, the current mismatch of the charge pump should be minimized to improve the phase noise and spur performance of the PLL. In order to correct the current mismatch of the charge pump, the current difference is detected by the replica charge pump and fed back into the main charge pump. This scheme is very simple and guarantees the high accuracy compared with the prior works. Also, it shows a good dynamic performance because the mismatch is corrected continuously. It is implemented in 0.13um CMOS process and the die area is $100{\mu}m\;{\times}\;160{\mu}m$. The voltage swing is from 0.2V to 1V at supply voltage of 1.2V. The charging and discharging currents are $100{\mu}A$, respectively and the current mismatch due to the PVT variation is less than 1%.

• Particle and aerosol research
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• v.9 no.2
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• pp.39-50
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• 2013

Real-time aerosol measuring instruments have been widely used for the measurement of atmospheric aerosol, diesel particulate matter, or material synthesis. A scanning mobility particle sizer (SMPS) measures the number size distribution of particles using electrical mobility detection technique. An aerodynamic particle sizer (APS) is used to determine the number concentration and the mean aerodynamic diameter of test particles. An electrical low-pressure impactor (ELPI) is a multi-stage impaction device to separate airborne particles into aerodynamic size classes using particle charging and electrical detection techniques. In this study, the performance of these instruments were evaluated to assess their ability to obtain mass concentrations from particle number concentration measurements made as a function of particle size. The effect of determination of particle density on the measurement of mass concentration was investigated for the three instruments.

• Polymer(Korea)
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• v.38 no.6
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• pp.827-831
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• 2014

An organic radical polymer (ORP) was prepared by radical polymerization and following oxidation into nitroxyl radical. Two different oxidation methods were employed and their radical concentrations were measured using electroparamagnetic resonance spectroscopy (EPR) and UV-visible absorption (UV-vis) spectroscopy. From these measurements, $H_2O_2-Na_2WO_4$ oxidation method exhibited a complete oxidation, which resulted in 97.6% spin concentration. Also, it was revealed that convenient and cheap UV-vis measurement was useful for preliminary radical concentration comparison. After applied as a cathode material in lithium ion batteries, ORP electrode showed a high initial capacity ($110mAh\;g^{-1}$), a good initial efficiency (96%), a very high rate performance (70% charging during 1.2 min) and stable cycle performance.

• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.6
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• pp.560-568
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• 2005

The proposed Multi-level PDP sustain Driver is composed of the semiconductor devices with low voltage rating compared to those used in the prior circuit proposed by L. Wether, and it has two resonant periods during the charging (rising period) and discharging (falling period) the PDP in the sustaining voltage waveforms. In accordance with the change of timing phase$(T_{r1},\;T_{i1},\;T_{r2})$, the performance characteristics of a commercial PDP module has been carried out and compared the characteristic with the 42V6, made of LG Electronics co., Experimental results show that the performance characteristics of PDP module are greatly influenced by the variation of $T_{i1}\;and\;T_{r2}$. The variation of $T_{r1}$ do not influence much on the performances of PDP. With the conditions that $T_{r1}=60ns,\;T_{i1}=120ns,\;and\;T_{r2}=350ns$, we could get the performances listed as the luminance is increased $14.6\%$, the power consumptions is decreased $5.9\%$, the panel efficiency is increased $24.2\%$, module efficiency is increased $21.2\%$, compared to those shown in the commercial PDP module (42V6). Therefore, the proposed multi-level PDP sustain driver expected to be suitable to actual PDP module application.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.92-100
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• 2016

It is informed that the Voice over LTE(VoLTE) which serves voice and message on IP networks is better in terms of economies of scale than the legacy voice service on 2G/3G circuit-switched networks because of its technological and cost efficiency. In addition, services of voice and data are running on a single LTE network and as a result VoLTE has the more economies of scope. But, there is no study about how much technology-efficiency VoLTE has compared to circuit-based voice service and how much voice charge can be reduced as VoLTE grows up. This paper analyzes empirically cost-efficiency of VoLTE against circuit-based voice service and quantifies the reduction of voice charge as 2G/3G voice traffic shifts to VoLTE. The results describe the first is that the average cost of the total voice traffic rises shortly just after the investment of LTE network for providing VoLTE but it will soon have a capacity available to reduce the charge due to VoLTE's outstanding cost efficiency on the assumption that voice traffic is fixed, and the second is that the charge can be cut to 60% of the current rate in case of all the voice traffic moves to VoLTE. The latter proves partially the validation of data-focusing pricing plan. Our results are expected to become basic data for network operators' establishing pricing strategies and for policy makers' inducing price cutting.

• Journal of Korean Physical Therapy Science
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• v.9 no.4
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• pp.83-94
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• 2002

Within physical therapy education, there has been increased attention to curricula and course that emphasize problem solving, clinical reasoning, and synthesis of information across traditional discipline-specific boundaries. This article describes the development implementation, and outcomes of a problem-based learning course in Physical therapy. The course was designed to help students to integrate the various elements of a physical therapy curriculum and to enhance their abilities to respond to an ever-changing health care environment. An evaluation of the course by the first 50 students who completed it revealed both strengths and weaknesses. Students responded that the course enhanced their professional behavior, including interpersonal communication skills, team work, and follow-through with professional responsibilities. The learning package was developed by the authors and implemented to a college students during three weeks of the first semester of 2001. Most studies which conducted PBL module development were short period or temporary PBL package application and evaluation rather than a whole semester's. While, this study carried on partial integrated PBL curriculum development and application with recomposing content of the two subjects to one subject Physical therapy which includes four PBL packages. This package was developed from a simple concept to complex and partial integrated PBL curriculum application systematically variable learning methods such as discussion, practice, lecture, video. There are 2 classes, each class has 25 students, in the college. Each class has 5 small groups consisting 5 students. Two tutors proceeded discussion charging each class also, they used multiple methods and materials like tutorials, self-directed learning, lecture, and video. The package is 5 grades and 5 hours per week and the rate of discussion, lecture is 4, 1 respectively. One of the most change is the increase of interaction between students and tutors. Whenever students need information and suggestion, they can visit tutors who provide reading materials and guide for the direction of self learning. Therefore, this study describes the PBL package development process and application during one semester recomposing contents of two subjects to Physical therapy concepts. Besides, it will contribute to active application of existing each subject to tutors who intend to convert as PBL methods. The study has significant meaning to show potentiality of partially integrated PBL application, using systematic PBL package development from two subjects contents. However, when students' need of yearning is over the extent of Introduction of Physical therapy and Rehabilitation medicine, tutors should set learning extent. So, there is limitation to attain completely integrated PBL education within one subject, therefore, it is high lighted to proceed development of integrated curriculum to maximize learning effects of PBL. It is exected that partial integrated PBL package development and application will distribute to prosper excellent physiotherapist in practice.

• Journal of Energy Engineering
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• v.16 no.4
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• pp.202-214
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• 2007

The concept of HSA (Home Service Aggregator) is derived from performing the energy IT business efficiently as well as successfully launcing a new service based on BPL (Broadband over Power Line). The HSA business using a BPL can extend the field of energy industry and an give a chance to create a new demand by consumer-oriented services. This study focuses on the exact evaluation of HSA business using BPL, and reasonable trusty evaluation should be the first step to launch the HSA business. In this study, the categories of cost are comprised of equipment (mainly RSM and MGW) cost, instalation cost, and maintenance cost. AMR (Automatic Meter Reading), internet integration billing service, integration charging service, internet service, sorority service, and electricity safety are listed for benefit. In this study, the ROI of HSA business is 0.9594, which is less than 1. However, that value does not consider the electricity safety benefit which is classified as a social benefit. Therefore, the value can be above 1 if it includes social and private benefits.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.8
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• pp.1795-1801
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• 2009

In this study, a portable flashlight which can manually generate the electricity by using sunlight was developed so that it can be used in the extreme environmental condition such as no-electricity condition. Battery is charged by using solar battery during the day, but when sunlight is not avalible during the night or rainy day, a handle is rotated to generate the electricity in order to charge the battery manually. To improve the brightness of the light, light is concentrated by using the optical lens. Low electric consumption circuit is used for the longer operating time by suppress electrical consumption while lamp is discharged. A circuit is designed and used for steady electrical curris dand voltage to insure steady battery charging. Super-discharge circuit and protection circuit are used for the super discharge of battery when it is not used for a long time. Also the constant charge is possible by using houseware adapter. As a result, a portable flashlight is designed to charge with sunlight during day, and with houseware adapter during night. A portable flashlight is also designed to irradiate longer distances by improvement of the brightness of the light using the optical lens. Thus, it forms white natural ray of light making possible for night reading.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.369-377
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• 2013

This paper deals with the state of charge(SOC) and life cycle evaluation algorithm for lead-acid battery, which is essential factor of the electric vehicle(EV) and the stabilization of renewable energy in the smart grid. In order to perform the effective operation of the lead-acid battery, SOC and life cycle evaluation algorithm is required. Specific gravity with the change of electrolyte temperature inside battery case should be obtained to evaluate the SOC of lead-acid battery, however it is difficult to measure the electrolyte temperature of sealed type lead-acid battery. To overcome this problem, this paper proposes the equation of thermal transmission to compensate internal temperature of the lead-acid battery. Also, it is difficult to exactly evaluate the life cycle of battery, depending on the operation conditions of lead-acid battery such as charging and discharging state, self discharging rate and environmental issue. In order to solve the problem, this paper presents the concept for gravity accumulation of charge and discharge cycle, which is the value converted at $20^{\circ}C$. By using the proposed algorithm, this paper propose the test device based on the Labview software. The simulation results show that it is a practical tool for the maintenance of lead-acid battery in the field of industry.