• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.10 s.352
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• pp.118-125
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• 2006

A new error amplifier is presented for fast transient response of DC-DC converters. The amplifier has low quiescent current to achieve high power conversion efficiency, but it can supply sufficient current during large signal operation. Two comparators detect large-signal variations, and turn on extra current supplier if necessary. The amount of extra current is well controlled, so that the system stability can be guaranteed in various operating conditions. The simulation results show that the new error amplifier achieves significant improvement in transient response than the conventional one.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.4
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• pp.731-736
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• 2017

In this paper, we propose a simplified tag collection algorithm to improve the performances of ISO/IEC 18000-7, which is a standard for an active RFID system. The proposed algorithm modifies the collection command that enables to start a tag collection round. The modified collection command includes the results of the listen period response for the previous collection round. Tags that receive the collection command check the collision status for their responses. If there is no collision, tags transmit their additional data and go into the sleep mode without the point-to-point read command and sleep command. A collection round for the standard consists of a collection command and response, a read command and response, and sleep command. On the other hand, in the proposed algorithm, a collection round consists of a collection command and response. The simulation results showed that the proposed algorithm can improve the identification delay about 16% compared with the standard when the number of tags are 300.

• The Transactions of the Korean Institute of Power Electronics
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• v.14 no.2
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• pp.120-127
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• 2009

This paper proposes a new Pulse Frequency Modulation(PFM)-Series Boost Capacitor(SBC) full bridge DC/DC Converter which features a high efficiency and high power density. The proposed converter controls the output voltage by varying the voltage across the series boost capacitor according to switching frequency and has no freewheeling period due to 50% fixed duty operation. As a result, its conduction loss is lower than that of the conventional phase shift full bridge converter. Moreover, ZVS of all power switches can be ensured along wide load ranges and output current ripple is very small. Therefore, it has very desirable merits such as a small output inductor, high efficiency, and improved heat generation. This paper performs a rationale and PSIM simulation of the proposed converter. Finally, experimental results from a 1.2kW(12V, 100A) prototype are presented to confirm the operation, validity and features of the proposed converter.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.5 no.1
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• pp.65-74
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• 1985

This study is an experimental analysis for local scour of the riverbed at pier. The basic equation with dimensionless elements(Pier Reynolds Number, Dimensionless Turbulence Intensity) is derived through dimensional analysis. After testing the goodness of fit of data, the coefficients are determined by multiple regression analysis. In the region where the value of the attack angle is near 20 degrees, there exists a transition region where the slope of equation with Pier Reynolds Number changes from positive to negative and that of equation with Dimensionless Turbulence Intensity changes from negative to positive adversely. As a result of testing the equation suggested on this study by using the data of the Institute of National Construction, it is found that the scour depth and width at pier can be predicted approximately.

• Korean Journal of Environment and Ecology
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• v.5 no.1
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• pp.32-41
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• 1991

A survey of subalpine zone (altitude is 1,360-1,410m) in Mt. Chiri, was conducted using 25 sample plots of 500$m^2$ size. The classification by TWINSPAN and DCA ordination were applied to the study area in order to classify them into several groups based on woody plants and environmental variables. By TWINSPAN techniques, the plant community were divided into five groups by importance value of Abies nephrolepis. The dividing groups are Fraxinus rhynchophylla - Magnolia sieboldii community, Quercus mongolica - Rhododendron schlippenbachii community, Q. mongolica - F. rhynchophylla - Acer pseudo-sieboldianum community, Q. mongolica- A. nephrolepis- Rh. schlippenbachii community, and A. nephrolepis- Pinus densiflora - Rh. schlippenbachii community. The successional trends of tree species by both techniques seem to be from Q. mongolica to A. nephrolepis in the canopy layer. It was no difference between the stand scores of DCA and environmental variables.

• The Journal of the Acoustical Society of Korea
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• v.13 no.1E
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• pp.11-19
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• 1994

Hidden Markov Models (HMM's) with explicit state duration density (HMM/SD) can represent the time-varying characteristics of speech signals more accurately. However, such an advantage is reduced in relatively smooth state duration densities or ling bounded duration. To solve this problem, we propose HMM's with global path constraint (HMM/GPC) where the transition between states occur only within prescribed time slots. HMM/GPC explicitly limits state durations and accurately describes the temproal structure of speech simply and efficiently. HMM's formed by combining HMM/GPC with HMM/SD are also presented (HMM/SD+GPC) and performances are compared. HMM/GPC can be implemented with slight modifications to the conventional Viterbi algorithm. HMM/GPC and HMM/SD_GPC not only show superior performance than the conventional HMM and HMM/SD but also require much less computation. In the speaket independent isolated word recognition experiments, the minimum recognition eror rate of HMM/GPC(1.6%) is 1.1% lower than the conventional HMM's and the required computation decreased about 57%.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.142-155
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• 2000

In this paper, we propose an efficient policing mechanism for Markov model-based traffic descriptors of VBR MPEG video traffic. A VBR video sequence is described by a set of traffic descriptors using a scene-basedMarkov model to the network for the effective resource allocation and accurate QoS prediction. The networkmonitors the input traffic from the source using a proposed new policing method. for policing the steady statetransition probability of scene states, we define two representative monitoring parameters (mean holding andrecurrence time) for each state. For frame level cell rate policing of each scene state, accumulated average cellrates for the frame types are compared with the model parameters. We propose an exponential bounding functionto accommodate dynanic behaviors during the transient period. Our simulation results show that the proposedpolicing mechanism for Markovian traffic descriptors monitors the sophisticated traffic such as MPEG videoeffectively and well protects network resources from the nalicious or misbehaved traffic.

• Journal of Korean Society on Water Environment
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• v.34 no.5
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• pp.503-513
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• 2018

Freshwater cyanobacterial genus Dolichospermum is one of the most commonly spotted types of phytoplankton, whereas a limited number of studies on morphology of Dolichospermum spp. have been performed in South Korea. The purpose of this study is to investigate the succession pattern of cyanobacteria after weir construction, as well as morphological characteristics of Dolichospermum spp. from natural samples collected in the weir regions of Nakdong River. A total of 31 cyanobacterial taxa observed in this study were classified as belonging to 15 genera, 5 families, and 3 orders. Among them, morphological characteristics in the four species were classified into genus Dolichospermum, for most of the planktic former members of the genus Anabaena, were observed through light microscopy. Water bloom frequently occurred in the middle region of Nakdong River, the maximum number of cyanobacterial species appeared in the lower region of Nakdong River. The appearance of order Chrooccocales was only observed during summer when population density of Microcystis aeruginosa reached an annual peak. In contrast, filamentous cyanobacteria was observed throughout the whole year, even if when water temperature was lower than $5^{\circ}C$. It implied that the low-temperature-adapted filamentous cyanobacteria can grow in a range of water temperatures. Coil diameter of D. crassum from natural samples was $75{\sim}140{\mu}m$ ($ave.=91.3{\mu}m$; n = 94), slightly larger than those reported by previous studies. Dolichospemum smithii ($Kom{\grave{a}}rek$) Wacklin et al. 2009, was described for the first time in Nakdong River.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.49 no.7
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• pp.10-16
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• 2012

In this paper, we tried to realize a next generation MILES detection system which is robust to optical noise using a narrow band interference optical filter. Applying a narrow band interference optical filter which has the wavelength range of 895~915nm to the LASER wavelength of 900nm, we could obtain detection characteristics robust to strong optical noise which can be occurred in street battles. However, the MILES detection system has the blind range of detection in the incident angle range of $30^{\circ}{\sim}90^{\circ}$. To solve this problem we proposed a method of incident angle scatter using refractors. Applying a concave meniscus lens refractor which has diopter of 5.4 to the MILES detection system, we could eliminate the blind angle of detection.

• Journal of the Korean Geographical Society
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• v.39 no.6 s.105
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• pp.863-872
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• 2004

The coastal alluvial plain, sand dune, tidal nat might be the most prominent coastal landscape in western coast of Korea. The purpose of this paper is to examine the irrigation and drainage systems of the alluvial plain in the tidal coast. This study is concerned on the geomorphological and cultural landscapes of the alluvial plain in the western coast of the South Jeolla Province. The alluvial deposits have developed mainly by the actions of tidal currents, rather than transporting sediments by stream. The transformation of plain has been affected by human agency since 1920's. Dwellers have constructed the reservoir, banks, dammed pools, lock gates, and tide-dykes for the reclamation, irrigation, and drainage on the alluvial plain, coastal sanddune, and tidal flats.