• 한국통신학회논문지
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• 제25권3B호
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• pp.472-486
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• 2000

This paper analysis the performance of joint receiving structure consisting of the decorrelating multiuser detection and beamfromenr-RAKE receive for DS-CDMA communication systems. In asynchronous transmission as the number of simultaneous users increase. the capacity of CDMA system becomes severly reduced due to the nonideal orthogonality between user-assigned PN sequences and improper power control. Accordingly, the CDMA receiving system becomes vulnerable to the multiple access interferences and the near-far problem under multipath fading channel environment. To withstand these undesired performance degradations, this paper proposes the new type of multiuser detection which has a form of the hybrid structure of concatenating beamformer-RAKE receiver and decorrelating multiuser detection. the beam former-RAKE receiver performs temporal and spatial diversity combining with alleviating fading effect and suppressing undesired interferences, and the multiuser detection plays a role of making the receiver robust to the near-far problem. Regarding the individual merit on the usage of either multiuser detection or beamformer-RAKE receiver, the hybrid one is expected to produce the enhanced performance in multipath fading CDMA channel. However major drawback of using decorrelating multiuser detection for practical deployment is arised from its computational complexity , which is exponentially increased as more number of users and transmitted symbols involve. To diminish the computational complexity, this paper exploits an efficient block Toeplitz inversion technique using matrix Levinson polynomial will be introduced. And this paper provided the mathematical analysis to show the efficiency of the proposed joint structure under the multipath propagation environment. And results of a series of exhaustive computer simulations are presented in order to demonstrate the overall performance of the proposed hybrid structure in multipath fading CDMA channel.

• 유통과학연구
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• 제19권1호
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• pp.61-73
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• 2021

Purpose: The transition from a traditional to a modern food distribution system induces several adjustments on the supply side since supermarkets must collect food on a larger scale and with higher quality standards. This situation becomes a real challenge for small scale farmers to access supply in a modern distribution channel. This gives rise to an original solution: supplying supermarkets through farmer associations or cooperatives. Based on this context of Vietnam linking to the case of distribution science, the paper proposes an industrial organization model of the food processing system in developing countries. The model presents the competitive relationship between two competing distribution systems: a traditional and a modern one. The former is composed of several retailers that sell their products on the traditional market while the latter is based on cooperatives that collect food and negotiate with supermarkets. The current study is to discuss the conditions under which the evolution of the food distribution system occurs by using the proposed model. Research design, data, and methodology: Based on the proposed model, the study explored the quantity flow from small producers to consumers through a Nash equilibrium and address the question of farmer repartition by a free-entry equilibrium. Results: The result shows that there is a unique positive equilibrium in the food market with participation of cooperative associations; Since farmers serve cooperative associations, they not only receive quantity incentive prices but also share profits within their organization. Conclusions: This study shows a unique distribution equilibrium where the profits of farmers working for middlemen and cooperatives are maximized. Further insights were discussed.

• 한국지형학회지
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• 제19권2호
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• pp.1-15
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• 2012

본 연구에서는 우리나라에 분포하는 3가지 유형의 5개 자연 구하도를 대상으로 형성시기와 형성과정을 분석하였다. 울진군 성산동 구하도는 약 2만5천~2만6천 년 전에 왕피천의 감입곡류 목 절단이 발생하면서 이전의 곡류부가 구하도로 변화되었고, 울진군 불영사 구하도는 약 9만 년 전에 감입곡류가 매우 심한 왕피천에 의한 곡류 목절단으로 형성되었다. 이를 통해 추론하면, 감입곡류 목 절단 구하도는 활발한 측방침식에 의해 목 절단이 발생하기 좋은 간빙기 또는 아간빙기의 후반에 주로 형성되는 것으로 판단된다. 태백시 구문소 구하도는 황지천과 철암천 사이 능선부 지하의 석회암에서 발생한 절리의 용식작용으로 인해, 약 4만 년 전에 두 하천이 동굴로 연결되어 합쳐지는 하천쟁탈 과정으로 형성된 것이며, 영양군 선바위 구하도는 약 1만4천 년 전에 동천과 반변천 사이의 하천쟁탈로, 고도가 높은 동천의 하류 쪽 유로가 구하도로 변화된 것이다. 그리고 충주시 장천리에서는 지난 빙기 최성기를 거치면서 약 1만년 전에 형성된 하중도로 인해 남한강의 유수가 동서로 분류되었고, 서쪽의 유로가 최근에 들어 구하도로 변화되었다.

• 한국통신학회논문지
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• 제30권7A호
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• pp.542-549
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• 2005

In this paper, the optimal pump light power of optical phase conjugator (OPC) and the compensation characteristics of distorted WDM channel signals are numerically investigated, when the OPC with highly-nonlinear dispersion shifted fiber (HNL-DSF) not be placed at the mid-way of total transmission length. The total dispersion of former half section and latter half section is assumed to be same each other in this approach. It is confirmed that, in WDM transmission systems with OPC deviated from the mid-way, the pump light power for best compensation must be flexible selected depending on the OPC position. This optimal pump light power is gradually increased as the OPC is gradually closer to the receiver. Consequently, it is possible to establish the compensation system independent on the OPC position by setting optimal pump light power connected with the OPC position.

• 한국재료학회지
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• 제9권2호
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• pp.139-143
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• 1999

Solidification simulation of gray cast iron sheave product was conducted with the consideration of graphite precipitation during solidification, and of casting processes such as post-inoculation method, treatment and rate, the result of which was aimed to be adopted in the field. In risering design(I), shrinkage cavities were predicted to occur in the part below the risers and center part of the product. While the former defect was considered to be due to the solidification behaviour of riser neck, the latter was due to the feeding channel. In design(II), the length of the riser neck was reduced and one top open riser was attached in the center of the product to prevent the formation of shrinkage cavities, whereby defect-free product was produced.

• Ecology and Resilient Infrastructure
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• 제6권3호
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• pp.154-162
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• 2019

대부분의 우리나라의 하천은 제방 축조에 의하여 수로와 홍수터 사이의 횡적연결성이 훼손되어 있다. 본 연구의 목적은 GIS를 이용하여 하천 횡적연결성을 간편하게 원격으로 평가하는 기법을 개발하고 중부지방의 대표적인 하천인 청미천에 적용하여 평가법의 효용성을 평가하는데 있다. 원격평가법의 평가항목은 제내지 서식지 환경 항목으로서 (1) 습지 유지 여부와 (2) 토지이용 특성을 연결성 항목으로서 (3) 제방 차단 여부, (4) 하천과의 연결성 및 (5) 육상 자연서식지와의 연결성으로 구성하였다. 개발된 평가법을 청미천에 시범 적용한 결과에 따르면 청미천의 제내지 옛홍수터는 제방 축조와 토지이용 변화로 횡적연결성이 크게 저하되어 있었다. 또한 GIS 원격 평가법에 의하여 청미천 옛홍수터의 횡적 연결성이 다양한 수준인 것으로 평가되었다. 연구에서 개발된 횡적연결성 원격 평가법은 앞으로 하천의 횡적연결성을 복원하는 다양한 시도에서 현재 연결성의 제한 요인을 파악하는데 유용한 도구로서 이용될 것으로 생각된다.

• 한국전자파학회논문지
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• 제8권2호
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• pp.151-160
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• 1997

본 논문에서는 억압 파일롯트를 이용하여 복소 지연 프로파일을 추정, 코히어런트 Rake 다이버시티 합성을 실현하는 동시에 얻어진 지연 프로파일의 극대점을 찾아 칩동기를 행하는 DS /CDMA 방식의 성능평가를 이동위성 채널에서 해보았다. 이를 위해 shadowed Rician 페이딩 시뮬레이터를 구성하여 그 포락선 변동특성을 조사 하였고 이론적인 오율해석을 병행하였다. 그 결과로서 Heavy shadowing인 경우 그 포락선 변동은 지상이동 통신채널의 Rayleigh 페이딩의 완만한 주기적 변동에 비해 랜덤한 특성을 가져 심각한 데이터 오류를 가져 오리라 예상할 수 있다. 또한 이론적 오율해석으로부터 DS /CDMA방식은 협대역 QPSK 방식에 비해 Average shadowing하에서 약 10 dB이상 개선되었다. 그리고 억압 파일롯트 채널을 이용한 DS /CDMA 방식은 이동위성 채널에서 파일롯트 채널대 송선전력비, $\beta$=-8dB, 복소지연 프로파일수 $N_{profile}$=32 일때 오율성능변에서 최적점을 나타내며, 이값을 이용했을 때 Light shadowing하의 오율특성은 이상적인 QPSK 오율특성과 같은 결과를 얻을 수 있었다.

• 한국정보과학회논문지:정보통신
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• 제30권4호
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• pp.461-473
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• 2003

멀티미디어 어플리케이션은 문자 위주의 어플리케이션과는 달리 데이타의 연속성 때문에 QoS(Quality of Service)에 매우 민감하다. 셀룰러 이동망에서 고속으로 이동중인 사용자의 멀티미디어 어플리케이션에 대해 QoS를 지속적으로 제공하기 위해서는 효율적인 호 수락 기법이 필요하다. 본 논문은 우선순위를 이용한 호 수락 제어를 통해 MH(Mobile Host)에게 지속적인 QoS를 제공하는 2SCA(2-Step Call Admission) 기법을 제시한다. 본 논문에서는 셀의 크기가 작고, 서로 중첩되어 있는 셀 구조를 가정하였으며, MH의 호를 신규호, 핸드오프호 및 QoS 상향조정호로 분류하여 각각 다른 처리 기법을 적용하였다. 2SCA 기법은 기본 호 수락제어와 응용 호 수락제어로 구성되어 있다. 전자는 셀의 가용 대역폭에 따라 호 수락을 결정하며, 후자는 기본 호 수락제어에서 블록킹된 호를 대상으로 각 호의 종류에 따라 DTT(Delay Tolerance Time), PQueue(Priority Queue), UpQueue(Upgrade Queue) 알고리즘을 적용하여 호 수락을 결정한다. 본 논문에서 제시된 2SCA 기법의 성능을 평가하기 위해, 신규호 블록킹률, 핸드오프호 드롭핑률, 대역폭 이용률을 측정하였다. 시뮬레이션 결과, 본 논문의 호 수락 기법이 CSP(Complete Sharing Policy), GCP(Guard Channel Policy) 그리고 AGCP(Adaptive Guard Channel Policy) 등과 같은 기존의 메커니즘보다 우수함을 알 수 있었다.

• Nuclear Medicine and Molecular Imaging
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• 제41권3호
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• pp.252-254
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• 2007

Image fusion is fast catching attention as Wagner pointed out in his 2006 version of the recent progress and development presented at the annual meeting of Society of Nuclear Medicine. Prototypical fusion of bone scan and radiograph was already attempted at in 1961 when Fleming et al. published an article on strontium-85 bone scan. They simply superimposed dot scan on radiograph enabling simultaneous assessment of altered bone metabolism and local bone anatomy. Indeed the parallel reading of images of bone scan and radiography, CT, MRI or ultrasonography has been practiced in nuclear medicine long since. It is fortunate that recent development of computer science and technology along with the availability of refined CT and SPECT machines has permitted us to open a new avenue to digitally produce precise fusion image so that they can readily be read, exchanged and disseminated using internet. Ten years ago fusion was performed using Bresstrahlung SPECT/CT and it is now achievable by PET/CT and SPECT/CT software and SPECT/CT hardware. The merit of image fusion is its feasibility of reliable assessment of morphological and metabolic change. It is now applicable not only to stationary organs such as brain and skeleton but also to moving organs such as the heart, lung and stomach. Recently, we could create useful fusion image of cardiac SPECT and 64-channel CT angiograph. The former provided myocardial metabolic profile and the latter vascular narrowing in two patients with coronary artery stenosis and myocardial ischemia. Arterial stenosis was severe in Case 1 and mild in Case 2.

• 오토저널
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• 제4권3호
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• pp.24-39
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• 1982

It has already been known that quenching effect is influenced greatly by stirring and changing coolant's temperature on quenching. But according to the past investigations its effect has not been taken into consideration quantitatively in the cooling process. The purpose of this study is that the influence of flow rate and temperature on the quenching effect of cooling water as quenching medium is quantitatively examined by using the open channel. The stream of water in this study is turbulent flow. The temperature of the specimen made of pure copper is measured by CA thermocouple in the vicinity of the surface and recorded by an automatic recorder during the quenching process in city water. The results obtained are as follows; 1. The quenching effect of cooling water generally increases with Reynolds Number(characteristic length; specimen diameter)as shown in the experimental formula; but at the realm of Reynolds Number from 1.2 * 10$^{4}$ to 9.2 * 10$^{4}$, the increasing rate of quenching effect shows little increase. 2. The increasing rate of quenching effect was increased under the flow rate of 221 cm/sec. On the other hand, it was decreased below this flow rate. 3. The quenching effect was influenced by the water temperature and the flow rate. But it was rather dependent upon the former than the latter. 4. Although the quenching effect appeared loosely in the water temperature of 50.deg. C, it was shown that the quenching effect increased in the low flow rate of 31 cm/sec. comparing with the still water. 5. It is desirable to design the quenching system to be over 1.2 * 10$^{4}$ in Reynolds Number or over, 3000$cm^{-1}$ / in V/v in order to increase the quenching effect of the system using open channel.annel.