$La(Mg_{1/2}Ti_{1/2})O_3$ 세라믹스의 구조 및 고주파 유전 특성 연구

여재현,백종후,남산,이확주,박현민,변재동,Yeo, Jae-Hyun,Baek, Jong-Hu,Nham, Sahn,Lee, Hwack-Joo,Park, Hyun-Min,Byun, Jae-Dong 한국재료학회 1999 한국재료학회지 Vol.9 No.9

$La(Mg_{1/2}Ti_{1/2})O_3$ 세라믹스의 구조 및 고주파 유전특성에 관한 연구를 하였다. $La(Mg_{1/2}Ti_{1/2})O_3$ 는 B site 양이온이 1:1 규칙화된 단사정 구조를 가지고 있었고 격자상수는 $a = 5.5467(3) {\AA}, b = 5.5616(3) {\AA}, c = 7.8426(5) {\AA} 그리고 \beta = 89.9589 (2)^{\circ}$ 로 밝혀졌고. $P2_1/n$의 공간군을 가지고 있었다. $La(Mg_{1/2}Ti_{1/2})O_3$ 내부에는 산소팔면체의 동상 및 역상 기울림이 존재하고 $a^_a^_c^_$ 기울림 구조를 가지고 있음을 알수 있었다. 또한 A site 양이온의 역 평행이동도 발견되었다. $1600^{\circ}C$ 이상에서 소결된 시료는 모두 95% 이상의 상대이론 밀도를 가지고 있었고 유전상수는 대략 28 정도였다. $1630^{\circ}C$ 에서 5시간 소결된 시료에서 최고높은 $Q\timesf_0$값, 63,000을 얻었다. LMT의 공진주파수 온도 계수는 $>-77 ppm/^{\circ}C ~ -79 ppm/^{\circ}C$였다. The crystal structure and the microwave dielectric properties of $La(Mg_{1/2}Ti_{1/2})O_3$ ceramics have been investigated. $La(Mg_{1/2}Ti_{1/2})O_3$ has the 1:1 ordered monoclinic structure with the lattice parameters of $a = 5.5467(3){\AA}, b = 5.5616(3){\AA}, c = 7.8426(5) {\AA} and \beta = 89.9589 (2)^{\circ}$ The spacegroup of LMT is $P2_1/n$. Monoclinic LMT has the in­phase and anti-phase tilting of octahedra with the $a^_a^_c^_$ tilting system. Anti-parallel shift of A-site cations was also found in LMT. The relative density of the specimens sintered above $1600^{\circ}C$ was ranged between 95 % and 96 % of the theoretical density and the dielectric constant of specimens was about 28. The highest $Q\timesf$ achieved in this investigation was 63,100 for the specimen sintered at $1630^{\circ}C$ for 5 hr. Temperature coefficient of resonance frequency ranged from $>-74 ppm/^{\circ}C ~ -79 ppm/^{\circ}C$.

시스템에어컨 에너지 효율 향상을 위한 주거 교체 사례연구

여재현(Jae Hyun Yeo),장헌덕(Heon Deock Jang),김동우(Dong Woo Kim),권민호(Min Ho Kwon),강윤태(Youn Tai Kang),가르산아쉬라프(Gharsan Ashraf) 대한설비공학회 2022 대한설비공학회 학술발표대회논문집 Vol.2022 No.11

Recently, due to its high efficiency advantage, the VRF system business has been rapidly growing since 2004. Considering that the replacement cycle of air conditioners is usually about 10 years, the time of replacement of the system air conditioners introduced in the early days has arrived, and interest in the cost and process of replacement is increasing due to the discontinuation and aging of the components of the existing systems. Therefore, we propose a site customizable replacement solution that can re-use the existing pipes while replacing the indoor and/or outdoor units in the residential market. In addition, we introduce residential replacement case studies that present system air conditioner energy efficiency improvements and various cost reductions.

수치풍동 기법을 이용한 정사각형 건물 주위의 풍압계수에 관한 연구

여재현(Jae Hyun Yeo),허남건(Nahmkeon Hur),원찬식(Chan-Shik Won),김사량(Sa Ryang Kim),최창근(Chang-Koon Choi) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-

In the present study, the pressure coefficient of a cubic building model is numerically simulated. Three turbulence models of standard k-ε, RNG k-ε and LES are adopted and the results are compared with the available experimental data. From the results, it has been found that RNG k-ε turbulence model and LES turbulence model were shown to predict fairly well the experimental pressure coefficient. In contrast, the results of the standard k-ε turbulence model showed large discrepancies in pressure coefficient on the side and top surfaces of the cubic building, which limits the applicability of the standard k-ε turbulence model on wind engineering.

An Efficient Algorithm for Broadcast Scheduling in TDMA Packet Radio Networks

여재현 ( Jae Hyun Yeo ),김세헌 ( Se Hun Kim ) 대한산업공학회 1999 대한산업공학회 춘계학술대회논문집 Vol.1999 No.-

광대역 이동통신 주파수 할당의 경제적 효과: 투입산출분석

장재혁 ( Ae Hyouk Jahng ),여재현 ( Jae Hyun Yeo ) 정보통신정책학회 2014 정보통신정책연구 Vol.21 No.3

그 동안 이동통신은 소비자 수요의 증가와 정보통신 기술의 발전이 맞물려 시장 환경을 빠르게 변화시켜 왔으며, 이동통신 산업 자체뿐만 아니라 관련 타 산업의 생산성 향상에 크게 기여해 왔다. 이처럼 이동통신은 경제성장 및 삶의 질 향상에 대한 기여도가 큼에 따라 국가경제의 핵심요소로 인식되어 정부 차원에서 다양한 산업활성화 정책들이 수행되었으나, 국내에서는 이동통신 서비스 제공의 기반이 되는 주파수 할당에 대한 효과를 정량화하려는 실질적인 연구는 그다지 활발한 편은 아니었다. 이에 본 연구에서는 2013년 8월 주파수 경매에 의해 할당된 1.8GHz 및 2.6GHz 대역 주파수가 광대역 이동통신 서비스 및 관련 산업의 혁신과 국가 경제에 미칠것으로 예상되는 효과를 정량적으로 산정하고자 하였다. 이를 위해 기술 및 산업의 속성에 따라 이동통신 산업을 크게 네트워크, 서비스, 단말기, 콘텐츠 등 4가지 산업부문별로 나누어 시장창출규모를 전망하고, 한국은행에서 발표된 산업연관표를 이용하여 파급효과를 모바일 광대역 산업 측면에서 분석하였다. 이러한 분석과 전망은 기술과 서비스의 발전에 따라 빠르게 변화하는 이동통신 시장에서 중장기 주파수 정책을 수립하는 데 유용한 정보를 제공할 것으로 기대한다. The mobile communication has dramatically changed the market environment in concert with the increasing consumer`s demand and the rapid development of information technology. It has also contributed to the productivity improvement of related other industries as well as the mobile communication industry itself. Like this, the mobile communication recognized the key element in national economy as high level in contribution to the economic growth and quality of life. However in recent years, Korea has carried out various policies to upgrade the mobile communication industry at government level. But, the study to quantify the effect of spectrum allocation, which is the base for providing mobile communication services, was not performed actively in Korea. Hence this study focuses on the quantification of the effect to the innovation services and the Korean economy from the latest broadband spectrum allocation so-called 1.8GHz and 2.6GHz band auction, that was closed on August 2013. To achieve this, we first classify the mobile industry into 4 kinds of sectors according to its technology and industry properties: network equipment, mobile services, mobile devices and mobile contents. We estimate market size for each sector. Along with this, the latest Input-output Tables, published in 2009 by the Bank of Korea, are used to analyse the impact to all industries from mobile broadband perspectives. These analyses and forecasts are expected to provide useful information to the medium and long-term spectrum policy in the rapid changing environment of the mobile market by the development of technology and service.

NUFLEX의 전후처리장치 개발

김사량(Sa Ryang Kim),여재현(Jae-Hyun Yeo),원찬식(Chan-Shik Won),허남건(Nahmkeon Hur) 한국전산유체공학회 2007 한국전산유체공학회 학술대회논문집 Vol.2007 No.-

A GUl based pre/post processor program, which is based on the MFC and OpenGL library in the Windows O/S, has been developed for NUFLEX. Using this program, users are able to generate and modify structured or unstructured grid geometries, set all the parameters for the solver, and observe the results of the simulation in graphic view by vector or scalar plots. The mesh geometry data can be imported from or exported to other programs by supporting functions for reading from and writing to CGNS data format files.

주파수의 경제적 가치를 고려한 할당대가 산정기준 분석

장희선(Hee-Seon Jang),여재현(Jae-Hyun Yeo),이광희(Kwang-Hee Lee),최기석(Ki-Seok Choi) 대한산업공학회 2008 대한산업공학회지 Vol.34 No.2

The determination of spectrum charges for the operators is a main issue to efficiently manage the limited radio spectrum resources. In this paper, we propose a model to compute the optimal charges for radio spectrum usage. The objective is to determine that will maximize the spectrum charges, and decision variables of ratios for actual or estimated revenues are considered. The spectrum charges are maximized under satisfying the least profit for operators based on Log-Linear demand function. The parameters of actual sales and minimum profit of operators are analyzed to make an efficient management for radio spectrum. The results show that the spectrum charges increase as the actual sales increase, but it decrease as the required minimum profit of operator increases. It is also observed that the government should increase the ratio for estimated sales if anticipating the poor market in the future, otherwise they should increase the ratio for actual sales to maximize the spectrum charges.

5년간 시행된 인공치아매식술에 관한 일차보고

김수민,조사현,조세인,계기성,여환호,김영균,정재현 大韓顎顔面成形再建外科學會 1996 Maxillofacial Plastic Reconstructive Surgery Vol.18 No.1

We experienced 152 endosseous implant surgery and prosthodontic restoration with edentulous jaw for 5 years from Mar. 1990. to Oct. 1995. 422 fixtures were implanted. the ratio of male to female was 1.38 : 1 and the range of age from 16 to 74 years. Most dominant group was 41 to 50 years group(36%). In our study, implant success rates showed 96% in mandible and 92% in maxilla. The major causes of implant failure of primery osseointegration(75%), overloading(15%), neurologic problem(5%), psychologic problem(5%).