• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2011년도 하계학술대회
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• pp.137-140
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• 2011

A precoding strategy is one of the representative interference management techniques in cognitive radio (CR) network which is a typical interference-limited environment. The interference minimization approach to precoding is an appropriate scheme to mitigate the interference efficiently while it may cause the capacity loss of the desired channel. The precoding scheme for the maximal capacity of the desired channel improves the capacity of the desired channel while it increases the interference power and finally causes the capacity loss of the interfered users. Therefore, we propose a precoding scheme which satisfies these two conflicting goals and manages the interference signal in such an interference-limited environment. The proposed scheme consists of two steps. First, the precoder nulls out the largest singular value of the interference channel to mitigate the dominant interference signal based on the interference minimization approach. Second, the transmitter calculates the sum capacities per mode and selects a mode to maximize the sum capacity. In the second step, each mode consists of the right singular vectors corresponding to the singular values except the largest singular value eliminated in the first step. Simulation results show that the proposed precoding scheme not only efficiently mitigate the interference signal, but also has the best performance in terms of the sum capacity in a MIMO-based CR network.

• 한국태양에너지학회 논문집
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• 제30권5호
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• pp.93-99
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• 2010

Nucleate pool boiling experiments with constant heat flux condition were performed using pure R113 for various channel heights under saturated pool condition. A circular heater of 1mm diameter, with artificial cavity in the center, fabricated using MEMS technique and the high-speed controller were used to maintain the constant heat flux. Images of bubble growth were taken at 5,000 frames per second using a high-speed CCD camera. The bubble geometry was obtained from the captured bubble images. The effects of channel height on the bubble growth behaviors were analyzed as dimensional scales for the initial and thermal growth regions. The parameters for the bubble growth behaviors were bubble radius, bubble growth rate, and bubble shapes. These phenomena require further analysis for various surface angles, but this study will provide good experimental data with constant heat flux boundary condition for such works.

• 한국통신학회논문지
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• 제34권9B호
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• pp.892-899
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• 2009

주파수 분할 재사용 기법은 셀룰러 시스템의 성능을 향상시키기 위한 기술이다. 주파수 분할 재사용 기반시스템에 대한 기존 연구에서는 호의 발생과 채널 선택 과정을 설명하고 있지 않다. 따라서 본 논문에서는 단말의 채널 선택 과정을 설명하고 주파수 분할 재사용 기반 시스템의 성능을 분석한다. 성능은 채널 사용률과 호 차단 확률로 나타낸다. 본 논문의 결과는 차후 주파수 분할 재사용 기반 시스템의 성능 분석에 추가되어 실제적인 시스템의 성능 분석을 가능하게 할 것이다.

• Journal of Communications and Networks
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• 제15권4호
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• pp.352-361
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• 2013

Combining multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) with a massive number of transmit antennas (massive MIMO-OFDM) is an attractive way of increasing the spectrum efficiency or reducing the transmission energy per bit. The effectiveness of Massive MIMO-OFDM is strongly affected by the channel state information (CSI) estimation method used. The overheads of training frame transmission and CSI feedback decrease multiple access channel (MAC) efficiency and increase the CSI estimation cost at a user station (STA). This paper proposes a CSI estimation scheme that reduces the training frame length by using a novel pilot design and a novel unitary matrix feedback method. The proposed pilot design and unitary matrix feedback enable the access point (AP) to estimate the CSI of the signal space of all transmit antennas using a small number of training frames. Simulations in an IEEE 802.11n channel verify the attractive transmission performance of the proposed methods.

• Steel and Composite Structures
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• 제42권3호
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• pp.315-323
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• 2022

Shear connectors are key elements that ensure integrity in a composite system. The primary purpose of a shear connector is to bring a high degree of interaction between composite elements. A wide variety of connectors are available for hot-rolled composite construction, connected to the beam through welding. However, with cold-formed members being very thin, welding of shear connectors is not desirable in cold-formed composite constructions. Shear connectors for cold-formed elements are limited in studies as well as in the market. Hence in this study, three different types of shear connectors, namely, single-channel, double channel, and self-tapping screw, were considered, and their performance assessed by the Push-out test as per Eurocode 4. The connection between channel shear connectors and the beam was made using self-tapping screws to avoid welding. The performance of the connectors was analyzed based on their ultimate capacity, characteristic capacity, ductility, and slippage during loading. Strength to weight ratio was also carried out to understand the proposed connectors' suitability for conventional ones. The results showed relatively higher initial stiffness and ductility for double channel connectors than other connectors. Also, self-tapping screws had a higher strength to weight ratio with low ductility.

• 한국임상약학회지
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• 제19권2호
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• pp.167-179
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• 2009

Hypertension is one of the most common chronic diseases and it causes cardiovascular and cerebrovascular disease. While antihypertensive drug use increased, it took 15% of national health insurance drug expenditure. This study aimed to examine the pattern of antihypertensive drug prescription using National Health Insurance claims database and compare it with recommendations of Korea Hypertension Treatment Guidelines. Among the antihypertensive drugs, calcium channel blocker(64.4%) was most commonly prescribed class, and diuretics(44.6%), angiotensin II receptor blocker(33.3%), angiotensin converting enzyme inhibitor(11.7%) was followed. Approximately 81% of antihypertensives prescription were without cardiovascular or cerebrovascular disease, and among the comorbid conditions, diabetes(10.7%) was most common. calcium channel blocker(62.3%) was mostly prescribed class for hypertension with angina pectoris, angiotensin receptor blocker(45.3%) with myocardial infarction, diuretics(70.2%) and calcium channel blocker(49.5%) with congestive heart failure. For Hypertension with cerebrovascular disease, calcium channel blocker(68.0%) and angiotensin receptor blocker(43.3%) were prescribed mainly. When it comes to diabetes, calcium channel blocker(57.2%) was still mostly prescribed and angiotensin receptor blocker(45.9%) followed. But in hospitals and tertiary hospitals, angiotensin receptor blocker(65.7, 66.1%) was mostly prescribed for the patients with diabetes. For Hypertension with chronic renal disease, angiotensin receptor blocker(59.5%), calcium channel blocker(56.5%), diuretics(54.6%) were mainly used. Average number of classes per prescribing was $1.89{\pm}0.89$ class, average days per prescribing was $33{\pm}19$ day. Among the hypertension without comorbidity, 40.5% of prescription was monotherapy and 58.8% of polytherapy included diuretics. Among the outpatient prescriptions, calcium channel blocker was the most commonly used class, and the prescription pattern in clinic did not closely followed recommendations of Hypertension Treatment Guidelines.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2006년도 학술발표회 논문집
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• pp.1002-1006
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• 2006

Temperature monitoring techniques per depth have been recognized as important information in the reservoir environmental issues. However, old measurement method by single temperature sensor and cable type has demerits not only for its limited measuring location but for its inconvenience of users. In this study, multi-channel temperature monitoring system was introduced and executed experiment for actual application feasibility evaluation. Both type of new techniques such as multi-channel addressable built-in temperature sensor and fiber optic multi sensor were tested in Daechung and Imha reservoir. As a result, it was proved that these kinds of temperature monitoring skills had very good performance and availability for a output of spatial, simultaneous thermal distribution focused on the user's convenience. And these measuring method and thermal data will be useful for providing basic information in a water resources investigation like reservoir stratification and environmental problems.

• 태양에너지
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• 제9권1호
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• pp.62-69
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• 1989

This analysis is to investigate the influence of inflow angle when cooling air flows into PC (Printed Circuit) board channels. Flow between PC board channels with heat generating blocks is assumed laminar, incompressible, two-dimensional. Geometric parameters (block spacing (S), block height (H), block width (W) and channel height (L)) are held fixed. Inflow angle variations are $-10^{\circ},\;0^{\circ},\;10^{\circ}$, where uniform heat flux per unit axial length Q (W/m) from heated block surfaces is generated. The governing equations for velocity and temperature are solved by SIMPLE (Semi-Implicit Method Pressure for Linked Equation) algorithm. Nusselt number on each block surfaces is analyzed after a numerical calculation result. The result shows that the assumption on parallel inflow (inflow angle to channel, $0^{\circ}$) to PC board channels can be used without large error even when inflow' angle is varied.

• JSTS:Journal of Semiconductor Technology and Science
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• 제6권1호
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• pp.43-51
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• 2006

80-nm self-aligned n-and p-channel I-MOS devices were demonstrated by using a novel fabrication method featuring double sidewall spacer, elevated drain structure and RTA process. The fabricated devices showed a normal transistor operation with extremely small subthreshold swing less than 12.2 mV/dec at room temperature. The n- and p-channel I-MOS devices had an ON/OFF current of 394.1/0.3 ${\mu}A$ and 355.4/8.9 ${\mu}A$ per ${\mu}m$, respectively. We also investigated some critical issues in device design such as the junction depth of the source extension region and the substrate doping concentration.

• 한국통신학회논문지
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• 제21권8호
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• pp.2033-2042
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• 1996

In this papre, we describe a recently implemented echo canceller for digital cellular communication of Code Division Multiple Access(CDMA) that features time sharing of digital signal processor(DSP) over four channels in one DSP to reduce per channel costs. In the Public Land Mobile Network(PLMN), it is important to cancel the echo reflected from the Public Switched Telephone Network(PSTN) side. In case of digital mobile system, the round-trip delay of the echo is in excess of about 180 milliseconds due to frame-by-frame voice coding. It is necessary to cancel the echo in PLMN. We have developed a multi-channel echo canceller tht operates with Time Switch Module in a Mobile Switching Center(MSC). The general echo canceller needs PCM trunk interface circuits and the tone detection and disabling circuits, but the multi-channel echo canceller linked with Time Switch Module does not need them. Therefore we could develop the effective and economical echo canceller.