• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2053-2058
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• 2008

It was investigated thermal performances on two array types of a serial circulation and a two-way parallel circulation for six water-cooled cold plates covered with non-metallic material (polycarbonate, PC) to reduce weight of the cooling devices for humanoid robot cooling. Six cold plates attached on $10{\times}10\;mm^2$ copper base : $0.5{\times}0.5\;mm^2$ pin-finned surfaces of 1.5 mm high with 0.5 mm array spacing, was mounted on six copper heating blocks with isothermal conditions of $50{\sim}90^{\circ}C$, respectively. In order to compare thermal characteristics according to two circulation types, the surface temperatures of heating blocks and the cooling water temperatures at inlets and outlets of cold plates were measured. From the results, it was found that a two-way parallel circulation was better performance than a serial circulation in terms of total thermal resistance, total heat transfer rate, and surface temperature rises from $1^{st}$ heating block to last one for six multiple cold plates.

• 한국통신학회논문지
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• 제18권11호
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• pp.1607-1617
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• 1993

Manchester-Coded ASK 광 파장 분할 다중화(WDM) 시스템의 성능이 산탄잡음과 광섬유 비선형성에 의해 야기되는 four wave mixing(FWM)을 고려하여 평가된다. 그 결과는 non-return-to zero(NRZ)를 사용한 ASK 변조방식과 비교된다. 더구나, 최대 입력 파우어(FWM에 의해 제한)와 최소 입력 파우어(수신감도에 의해 제한)의 비로서 정의되는 동적범위(dynamic range)가 평가된다. 1.55 rm 16채널 WDM 시스템에 대해 ASK Manchester-Coded시스템의 동적범위는 NRZ보다 2.OdB 개선된다. 이 결과는 10 GHz 채널 간격과 1 Gbps/channel 비트율을 갖는 시스템에서 분산-이 동(dispersion-shifed) 광섬유와 기존의 광섬유의 경우 같다.

• 한국연소학회지
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• 제10권4호
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• pp.33-40
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• 2005

The propagation rates of advancing and retreating non-premixed edge flames in a slot-jet counterflow were measured as a function of strain rate for varying jet spacing, mixture strength, stoichiometric mixture fractions $(Z_{st})$ and Lewis numbers (Le). Methane and propane fuels were tested and nitrogen and carbon dioxide were used as inerts. As results, we could identify igniting fronts, retreating fronts, two total extinction limits, and short-length edge flames. A burner separation affected to a low extinction limit only. Regimes for advancing and retreating edges together with total extinction were mapped in terms of normalized flame thickness and heat loss factor for $CH_4/O_2/N_2$ mixtures. Edge flames for $Z_{st}$ > 0.5 behaved like a stronger mixture while for $Z_{st}$ < 0.5 showed deteriorated feature, because of relative locations of a non-premixed flame and intermediate species such as CO and $H_2$. Furthermore, due to the relative importance of heat loss, propagating speeds of edge flames were significantly enhanced in $CH_4/O_2/CO_2$ mixtures (Le < 1) demonstrating increasing stability limits. However $C_3H_8/O_2/N_2$ mixtures (Le > 1) showed opposite result.

• 한국인구학
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• 제25권1호
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• pp.5-32
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• 2002

이 연구는 한국의 인공임신중절의 실태 및 결정요인을 분석하고 인다. 한국보건사회연구원에서 조사한 2000년 전국 출산력 조사 원자료를 이용하여 한국의 유배우 여성들의 인공임신중절율 및 인공임신중절경험율을 여러 독립변수에 따라 분석하고 있다. 한국의 유배우 여성들이 인공임신중절을 행하는 가장 큰 이유는 원하지 않는 임신을 한데서 시작된다 그러나 원하지 않는 임신이라고 모두 인공임신중절로 귀결되는 것은 아니다. 결국 인공임신중절은 한국 사회에서 단산이나 터울을 조절하기 위한 방법으로 이용되고 있다. 그러나 인공임신중절을 택하는 이유는 매우 다양해서 첫 인공임신중절을 택한 가장 큰 이유는 혼전임신으로 밝혀지고 있고. 그 다음으로 중요한 이유는 경제적인 이유 때문에 인공임신중절을 택하는 것으로 나타나고 있다.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 춘계학술대회
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• pp.391-394
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• 2006

Growth characteristics of methane-propane clathrate hydrate, growing under different undercooling conditions, was investigated. After the water within pressurized vessel was fully saturated with guest gas molecules by agitation, medium was rapidly undercooled and maintained at the constant temperature. The growth of hydrate was always Initiated with film formations at the upper bounding surface of liquid pool. The visual observation using microscope revealed detailed features of subsequent crystal nucleation, migration, growth and interference occurring within liquid pool. A number of small crystals ascended and settled at the hydrate film. When undercooling was small $({\Delta}T=3.2K)$, some of the settled crystals slowly grew into faceted columns. As the undercooling increased, the downward growth of crystals underneath the hydrate film became dendritic and occurred with greater rate and with finer arm spacing. The shapes of the floating crystals were diverse and included octahedron and triangular or hexagonal platelet When the undercooling was small, the octahedral crystals were found dominant. As the undercooling increased, the shape of the floating crystals also became dendritic. The detailed characteristics of floating crystals were reported in this study.

• Steel and Composite Structures
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• 제24권6호
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• pp.727-740
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• 2017

The present paper studies the stability analysis of the continuously graded CNT-Reinforced Composite (CNTRC) panel stiffened by rings and stringers. The Stiffened Panel (SP) subjected to axial and lateral loads is reinforced by agglomerated CNTs smoothly graded through the thickness. A two-parameter Eshelby-Mori-Tanaka (EMT) model is adopted to derive the effective material moduli of the CNTRC. The stability equations of the CNRTC SP are obtained by means of the adjacent equilibrium criterion. Notwithstanding most available literature in which the stiffener effects were smeared out over the respective stiffener spacing, in the present work, the stiffeners are modeled as Euler-Bernoulli beams. The Generalized Differential Quadrature Method (GDQM) is employed to discretize the stability equations. A numerical study is performed to investigate the influences of different types of parameters involved on the critical buckling of the SP reinforced by agglomerated CNTs. The results achieved reveal that continuously distributing of CNTs adjacent to the inner and outer panel's surface results in improving the stiffness of the SP and, as a consequence, inclining the critical buckling load. Furthermore, it has been concluded that the decline rate of buckling load intensity factor owing to the increase of the panel angle is significantly more sensible for the smaller values of panel angle.

• 한국컴퓨터정보학회논문지
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• 제7권3호
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• pp.143-148
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• 2002

ATM망에서는 예측할 수 없는 트래픽의 변화로 셀 지연과 셀 손실이 발생할 수 있으며 고속의 셀 전송 특성으로 인해 폭주가 발생할 수 있다. 따라서 트래픽 제어는 ATM 망에서 필수적이며, 폭주현상을 줄이기 위한 여러 가지 방법들 가운데 하나가 셀 쉐이핑이다. 본 논문에서는 리키버켓과 TJW로 구성된 셀 쉐이핑 기법을 연구한다. 셀 쉐이퍼는 시간 윈도우를 가진 TJW와 토큰 풀을 가진 리키버켓, 간격제어 버퍼로 구성된다. BONeS시뮬레이터에서 ON/OFF트래픽 소스 모델을 이용하여 제안한 셀 쉐이핑 기법의 성능을 평가한 결과, 패킷화된 음성 트래픽과 고속 트래픽 소스 모두 셀 간격이 평균 비트율에 수렴하여 제어되는 것을 관찰할 수 있었다.

• 한국농촌건축학회논문집
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• 제21권1호
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• pp.37-44
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• 2019

Recently, various tourist products using hanok have increased rapidly. In the meantime, there is a steady demand for Hanok architecture. However, there are many negative perceptions about wood deformation and biodeterioration. Wood deformation and biodeterioration are related to moisture content. And the cracks occur in the process of removing water from the wood. Therefore, this study investigates the moisture content and cracks of dried hanok made of wood according to the drying method of wood. Drying methods include natural seasoning and artificial seasoning. There was a difference in moisture removal depending on drying period and method of natural seasoning. Drying time should be about 3 years for natural seasoning, so the moisture content of the wood is stable. In addition, the moisture absorption rate was low even in a humid environment where the voids were removed. However, natural seasoning is time consuming. Artificial seasoning, on the other hand, can quickly remove moisture from the wood and reduce porosity, but it is costly. Cracks that occur during the drying of wood may become problematic in appearance and stability due to wider spacing over time. As a result, the difference in the moisture content of the timber depending on the drying method and drying period of the wood was maintained even after the formation. These gaps appeared to be differences in moisture absorption in a wet environment.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권8호
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• pp.2606-2626
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• 2022

In this paper, a unmanned aerial vehicle (UAV) access deployment algorithm is proposed, which is based on an improved virtual force model to solve the poor coverage quality of UAVs caused by limited number of UAVs and random mobility of users in the deployment process of UAV base station. First, the UAV-adapted Harris Hawks optimization (U-AHHO) algorithm is proposed to maximize the coverage of users in a given hotspot. Then, a virtual force improvement model based on user perception (UP-VFIM) is constructed to sense the mobile trend of mobile users. Finally, a UAV motion algorithm based on multi-virtual force sharing (U-MVFS) is proposed to improve the ability of UAVs to perceive the moving trend of user equipments (UEs). The UAV independently controls its movement and provides follow-up services for mobile UEs in the hotspot by computing the virtual force it receives over a specific period. Simulation results show that compared with the greedy-grid algorithm with different spacing, the average service rate of UEs of the U-AHHO algorithm is increased by 2.6% to 35.3% on average. Compared with the baseline scheme, using UP-VFIM and U-MVFS algorithms at the same time increases the average of 34.5% to 67.9% and 9.82% to 43.62% under different UE numbers and moving speeds, respectively.

• ETRI Journal
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• 제45권1호
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• pp.45-59
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• 2023

In this paper, to optimize the average delay and power allocation (PA) for system users, we propose a resource scheduling scheme for wireless networks based on Cyclic Prefix Orthogonal Frequency Division Multiplexing (CP-OFDM) according to the first fifth-generation standards. For delay minimization, we solve a throughput maximization problem that considers CPOFDM systems with carrier aggregation (CA). Regarding PA, we consider an approach that involves maximizing goodput using an effective signal-to-noise ratio. An algorithm for jointly solving delay minimization through computation of required user rates and optimizing the power allocated to users is proposed to compose the resource allocation approach. In wireless network simulations, we consider a scenario with the following capabilities: CA, 256-Quadrature Amplitude Modulation, millimeter waves above 6 GHz, and a radio frame structure with 120 KHz spacing between the subcarriers. The performance of the proposed resource allocation algorithm is evaluated and compared with those of other algorithms from the literature using computational simulations in terms of various Quality of Service parameters, such as the throughput, delay, fairness index, and loss rate.