• 제목/요약/키워드: built-in potential

검색결과 393건 처리시간 0.03초

Strong Carrier Localization and Diminished Quantum-confined Stark Effect in Ultra-thin High-Indium-content InGaN Quantum Wells with Violet Light Emission

  • Ko, Suk-Min;Kwack, Ho-Sang;Park, Chunghyun;Yoo, Yang-Seok;Yoon, Euijoon;Cho, Yong-Hoon
    • 한국진공학회:학술대회논문집
    • /
    • 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
    • /
    • pp.293-293
    • /
    • 2014
  • Over last decade InGaN alloy structures have become the one of the most promising materials among the numerous compound semiconductors for high efficiency light sources because of their direct band-gap and a wide spectral region (ultraviolet to infrared). The primary cause for the high quantum efficiency of the InGaN alloy in spite of high threading dislocation density caused by lattice misfit between GaN and sapphire substrate and severe built-in electric field of a few MV/cm due to the spontaneous and piezoelectric polarizations is generally known as the strong exciton localization trapped by lattice-parameter-scale In-N clusters in the random InGaN alloy. Nonetheless, violet-emitting (390 nm) conventional low-In-content InGaN/GaN multi-quantum wells (MQWs) show the degradation in internal quantum efficiency compared to blue-emitting (450 nm) MQWs owing higher In-content due to the less localization of carrier and the smaller band offset. We expected that an improvement of internal quantum efficiency in the violet region can be achieved by replacing the conventional low-In-content InGaN/GaN MQWs with ultra-thin, high-In-content (UTHI) InGaN/GaN MQWs because of better localization of carriers and smaller quantum-confined Stark effect (QCSE). We successfully obtain the UTHI InGaN/GaN MQWs grown via employing the GI technique by using the metal-organic chemical vapor deposition. In this work, 1 the optical and structural properties of the violet-light-emitting UTHI InGaN/GaN MQWs grown by employing the GI technique in comparison with conventional low-In-content InGaN/GaN MQWs were investigated. Stronger localization of carriers and smaller QCSE were observed in UTHI MQWs as a result of enlarged potential fluctuation and thinner QW thickness compared to those in conventional low-In-content MQWs. We hope that these strong carrier localization and reduced QCSE can turn the UTHI InGaN/GaN MQWs into an attractive candidate for high efficient violet emitter. Detailed structural and optical characteristics of UTHI InGaN/GaN MQWs compared to the conventional InGaN/GaN MQWs will be given.

  • PDF

태안해안국립공원의 번식기 조류상과 관리 (Avifauna and Management of Breeding Season in Taeanhaean National Park)

  • 백인환;진선덕;유재평;백운기
    • 한국환경생태학회지
    • /
    • 제24권2호
    • /
    • pp.139-146
    • /
    • 2010
  • 태안해안국립공원의 번식기에 서식하는 조류 현황을 파악하기 위하여 공원내 해안선 지역과 10개의 도서 지역을 선정하여 2009년 7월 5일부터 9일까지 3개 팀으로 나누어 동시 조사하였다. 전체 관찰종은 58종 7,323개체였고, 해안선 지역은 48종 6,187개체, 도서 지역은 33종 1,136개체였다. 공원내 최우점종은 괭이갈매기로서 약 60%에 이르며, 공원과 인접한 도서에서 집단 번식한 개체로 추정된다. 한편, 연안 지역에서만 관찰된 조류는 흰뺨검둥오리, 물닭, 중백로 등 25종 318개체이고, 도서 지역에서만 관찰된 조류는 가마우지, 칼새, 섬개개비 등 10종 308개체였다. 도서지역에서는 가의도를 비롯한 유인도서에서 종과 개체수가 높게 나타났는데, 도서 면적과 수자원 유무, 다양한 서식지와 관련 있는 것으로 판단된다. 과거 자료와 금번 조사 결과, 주요 우점종은 유사한 경향을 보이고 있으며, 2007년 기름유출 사고 지역임에도 2004년보다 수조류가 증가한 점에서 회복되어가는 것으로 판단된다. 현재 태안해안국립공원과 인접한 연안은 매립과 조력발전소가 조성 및 예정되고 있고, 도서지역은 펜션증가 등이 예상되면서 중요한 서식지 훼손과 교란이 예상된다. 이러한 위협요인에 대비하고, 공원의 적절한 관리를 위해서는 조류정보가 부족한 도서 지역에 대한 조류모니터링을 강화하거나 탐조가의 조류결과를 효율적으로 관리할 수 있는 조류정보시스템이 우선적으로 필요하다고 판단된다.

반사율 변경이 가능한 롤링타입형 광선반 개발 (Development of Rolling Type Light-Shelf with Adjustable Reflectivity)

  • 김경수;심형준;이행우;서장후;김용성
    • KIEAE Journal
    • /
    • 제16권5호
    • /
    • pp.57-64
    • /
    • 2016
  • Purpose: Recently, lighting energy consumption in buildings has been gradually increasing and more studies are being carried out in order to solve this problem. Especially, the efficiency of the light-shelf system, which is a natural lighting system, has been recognized as a potential solution in addressing this problem and so various studies regarding the light-shelf system are being conducted. However, if high luminance material is used for the light-shelf system, glaring may occur in certain circumstances even though such material increases efficiency, and there are also difficulties related to maintenance and management in the case of an external light-shelf system. Therefore, the purpose of this study is to suggest modifications in relation to the reflectivity of the light-shelf system and introduce a rolling type light-shelf system with built-in cleaning equipment. In addition, a performance evaluation technique was established to verify its effectiveness. Method: In this study, we reviewed previous studies related to the light-shelf system and its performance. Then a testbed was established to assess the performance of the rolling-type light-shelf system suggested in this study. Also, the performance of the rolling-type light-shelf system suggested in this study was compared and analyzed with that of existent light-shelf systems in order to better verify the performance, and the uniformity ratio of illumination and lighting energy consumption were calculated for this purpose. Result: The results of the performance evaluation are as follows. 1) The performance evaluation result of the light-shelf system on the day of the summer solstice shows that $30^{\circ}$ is appropriate for the angle of light-shelf system, and the depth of the incoming natural light also increases as the angle of the light shelf increases. 2) It is possible to improve the uniformity ratio of illumination by increasing the reflectivity of the light shelf, and the reason for this is the increase in the amount of incoming light entering indoors due to the increased reflectivity of the light shelf. 3) The rolling type light-shelf system suggested in this study enables energy saving in comparison with existent light-shelf systems, and when the external illuminance decreases to 60,000 lx and 40,000 lx during the summer solstice due to factors such as the weather, the suggested light-shelf system can save energy by 12.1% and 5.1% respectively. Thus the light-shelf system proposed in this study is deemed to be effective in reducing energy costs.

Ecological Functions and Losses of Traditional Korean Village Groves

  • Lee, D.-W.;Park, C.-R.
    • 한국제4기학회지
    • /
    • 제18권2호통권23호
    • /
    • pp.65-66
    • /
    • 2004
  • There have been groves, in many cases, along with hedgerows and remnant forests around a traditional Korean village. A village grove is very closely connected to the life of residents. Sometimes it was a holy place where important village festivals were held, and became a resting place for farmers, especially in sunny summer. As a matter of fact, it is noted that traditional Korean village groves had been fostered for many purpose as religion, Confucianism, scenery, sanitation, traffic guard, public security, agriculture, hunting, and military and public uses were included in Chosun Govemor General(1938). Village groves were usually located at the outlet of watershed inside which a village was built. In addition, village groves used to be established along part of mountain ranges, streams and streets. A unique type of village grove, called bibosoop was fostered especially where the outlet of watershed was largely opened. In other cases, it was placed where a part of mountain range was relatively low, or where village residents were likely to see ugly objects such as a huge cliff, stony upland with an unvegetated area and the like(Kim and Jang 1994). In a sense, a sheltebelt is a sort of bibosoop as it is a landscape element to complement places that are exposed to strong winds. However, it is comparable to other typical bibosoop that is situated at a topographically very specific zone of watershed. In this paper, we will address potential functions of Korean village groves from a perspective of modern landscape ecology and show current status of some remnants, based on preliminary surveys. A village grove functions as barrier or filter of objects such as water, nutrients, and other elements and habitat of wildlife (park et al. 2003, Lee 2004). The village grove slows down the flow of water and air, maintains soil moisture an hinders soil erosion, enabling cultivation of crops and bringing up creatures nearby. It contributes to enhancing biodiversity. Birds rest on shrubby and woody trees of the element. Presumably, other organisms may also inhabit the village groves and take advantage of it when those move from a forest patch to others. Emerging insects acclimate themselves in the shade of the green space before they fly to sunny air. Besides the village grove acts as a component of agroforestry system as leaf litter is shed from a grove to an asjacent agricultural area, and transformed into green manure(Lee 2004). By the way, many of the landscape elements were destroyed or declined in Koea during the past several decades. The losses have been parallel or linked to environmental degradation. Unfortunately, we have a little reliable data as for how many groves have disappeared in Korea until now. There has been no complete census on the village groves in Korea, and the viewpoints of survey were to a degree different depending on surveyors. So, it is difficult to analyze the temporal and spatial change of village groves. Currently, national inventory data of Korean village groves are available in three reports. We reviewed the locations of village groves and arranged those according to the present administrative units, DONG. With the limited data, we found that at least 484 of village groves were recorded in South Korea. Among all provinces, village groves were most in Gyeongsanbuk-Do Province and least in Chungcheongbuk-Do Province(Table 1). This is a preliminary report prepared while some quantitative data regarding functions and lossers of the village groves are being collected. More detailed data will be introduced in the near future.

  • PDF

장기유출의 수문적 모형개발을 위한 주요 수계별 단위도 유도 (Determination of Unit Hydrograph for the Hydrological Modelling of Long-term Run-off in the Major River Systems in Korea)

  • 엄병현;박근수
    • 한국농공학회지
    • /
    • 제26권4호
    • /
    • pp.52-65
    • /
    • 1984
  • In general precise estimation of hourly of daily distribution of the long-term run-off should be very important in a design of source of irrigation. However, there have not been a satisfying method for forecasting of stationar'y long-term run-off in Korea. Solving this problem, this study introduces unit-hydrograph method frequently used in short-term run-off analysis into the long-term run-off analysis, of which model basin was selected to be Sumgin-river catchment area. In the estimation of effective rainfall, conventional method neglects the Soil moisture condition of catchment area, but in this study, the initial discharge (qb) occurred just before rising phase of the hydrograph was selected as the index of a basin soil moisture condition and then introduced as 3rd variable in the analysis of the reationship between cumulative rainfall and cumulative loss of rainfall, which built a new type of separation method of effective rainfall. In next step, in order to normalize significant potential error included in hydrological data, especially in vast catchment area, Snyder's correlation method was applied. A key to solution in this study is multiple correlation method or multiple regressional analysis, which is primarily based on the method of least squres and which is solved by the form of systems of linear equations. And for verification of the change of characteristics of unit hydrograph according to the variation of a various kind of hydrological charateristics (for example, precipitation, tree cover, soil condition, etc),seasonal unit hydrograph models of dry season(autumn, winter), semi-dry season (spring), rainy season (summer) were made respectively. The results obtained in this study were summarized as follows; 1.During the test period of 1966-1971, effective rainfall was estimated for the total 114 run-off hydrograph. From this estimation results, relative error of estimation to the ovservation value was 6%, -which is mush smaller than 12% of the error of conventional method. 2.During the test period, daily distribution of long-term run-off discharge was estimated by the unit hydrograph model. From this estimation results, relative error of estimation by the application of standard unit hydrograph model was 12%. When estimating by each seasonal unit bydrograph model, the relative error was 14% during dry season 10% during semi-dry season and 7% during rainy season, which is much smaller than 37% of conventional method. Summing up the analysis results obtained above, it is convinced that qb-index method of this study for the estimation of effective rainfall be preciser than any other method developed before. Because even recently no method has been developed for the estimation of daily distribution of long-term run-off dicharge, therefore estimation value by unit hydrograph model was only compared with that due to kaziyama method which estimates monthly run-off discharge. However this method due to this study turns out to have high accuracy. If specially mentioned from the results of this study, there is no need to use each seasonal unit hydrograph model separately except the case of semi-dry season. The author hopes to analyze the latter case in future sudies.

  • PDF

소규모 지역 공공도서관의 공간 구성과 이용 특성 연구 - 미국 앤아버 공공도서관 브랜치의 사례조사를 중심으로 - (A Study on Space Design and Space Uses of Community Based Small Public Libraries - Focused on the Cases of Ann Arbor District Library in the United States -)

  • 문은미
    • 한국실내디자인학회논문집
    • /
    • 제19권5호
    • /
    • pp.217-225
    • /
    • 2010
  • Today's public libraries in communities are on the processes of changes to integrate information and communication technology into traditional library system in order to support current users' demands for the new digital era. The purpose of this study is to examine the changing characters on space design and space uses of community based public libraries by conducting case studies of three branch libraries which were built after 2004 in Ann Arbor, Michigan in the United States. As the conclusion of this research, the findings of the case studies are utilized as basic data for planning and design guidelines for public libraries as community resources. The study summarizes the characteristics of space design and space uses in public libraries as follow; first, the floor plans of small-scale public libraries are open visually as well as spatially. The space organization of the libraries is arranged by potential noise levels, as placing noisy spaces near the entrance halls and quiet spaces at the back. Main book shelves are located in the middle of the library buildings, while seats are arranged along the window sides. By placing various kinds of furniture in open reading areas, library users can select different types of seats and tables for their comforts. Second. the survey of observation also finds that a large number of users often use library computers and personal computers to connect the internet at the libraries. These personal computer users who are new user group in community based libraries preferred to sit in casual study areas and individual tables with one or two seats only. Third, the libraries, in addition, develop and provide various programs and events for people in communities. Especially, the programs for children, the elderly and new comers from the abroad are well prepared, thus provide opportunities for them to visit the libraries in regular bases. The survey finds that family entertainment and leisure activities are the important parts of the program as well as renting music CD and movie DVD are also important reasons for people to come. Thus, the libraries prepare high quality children's space and CD shelves near the entrance hall.

Control and Analysis of an Integrated Bidirectional DC/AC and DC/DC Converters for Plug-In Hybrid Electric Vehicle Applications

  • Hegazy, Omar;Van Mierlo, Joeri;Lataire, Philippe
    • Journal of Power Electronics
    • /
    • 제11권4호
    • /
    • pp.408-417
    • /
    • 2011
  • The plug-in hybrid electric vehicles (PHEVs) are specialized hybrid electric vehicles that have the potential to obtain enough energy for average daily commuting from batteries. The PHEV battery would be recharged from the power grid at home or at work and would thus allow for a reduction in the overall fuel consumption. This paper proposes an integrated power electronics interface for PHEVs, which consists of a novel Eight-Switch Inverter (ESI) and an interleaved DC/DC converter, in order to reduce the cost, the mass and the size of the power electronics unit (PEU) with high performance at any operating mode. In the proposed configuration, a novel Eight-Switch Inverter (ESI) is able to function as a bidirectional single-phase AC/DC battery charger/ vehicle to grid (V2G) and to transfer electrical energy between the DC-link (connected to the battery) and the electric traction system as DC/AC inverter. In addition, a bidirectional-interleaved DC/DC converter with dual-loop controller is proposed for interfacing the ESI to a low-voltage battery pack in order to minimize the ripple of the battery current and to improve the efficiency of the DC system with lower inductor size. To validate the performance of the proposed configuration, the indirect field-oriented control (IFOC) based on particle swarm optimization (PSO) is proposed to optimize the efficiency of the AC drive system in PHEVs. The maximum efficiency of the motor is obtained by the evaluation of optimal rotor flux at any operating point, where the PSO is applied to evaluate the optimal flux. Moreover, an improved AC/DC controller based Proportional-Resonant Control (PRC) is proposed in order to reduce the THD of the input current in charger/V2G modes. The proposed configuration is analyzed and its performance is validated using simulated results obtained in MATLAB/ SIMULINK. Furthermore, it is experimentally validated with results obtained from the prototypes that have been developed and built in the laboratory based on TMS320F2808 DSP.

치(置)와 화(和)의 개념으로 분석한 남계서원의 경관짜임 (Landscape Composition Based on Placement and Harmony in the Namgea Suhwon)

  • 노재현;신상섭
    • 한국조경학회지
    • /
    • 제37권4호
    • /
    • pp.72-85
    • /
    • 2009
  • 본 연구는 인간 활동을 담는 형식과 의미의 총체라 할 수 있는 서원, 그 중에서도 경상남도 함양의 남계서원을 대상으로 공간 및 시각구성상에 내재된 형식미와 의미 파악을 통해 서원 조영에 담겨진 경관짜임 원리를 풀이하고 현대 유사 전통적 공간의 경관설계 시 적용하기 위한 착안점을 구하기 위해 시도되었다. 남계서원은 생성과 풍요를 거쳐 초월과 회귀로 이어지는 비산비야(非山非野)의 풍수적 명처[연화부수형]에 생거사유(生居死幽) 형국에서부터 치(置)와 화(和)를 이루고 있다. 그리고 사당-내삼문-강당-동서재-외삼문으로 이어지는 위계는 일상제-삼신-오제로 연결되는 삼신오제사상의 투영이자 주자가례에 의한 예제적 틀을 준용한 비례부동(非禮不動)의 의미 넣기 기법이다. 또한 남계서원의 환경설계에는 산수의 물질적 대립 항 그리고 전후(前後), 종횡(縱橫), 동정(動靜)이라는 방향과 운동의 이진부호적 복합체계를 개입시켜, 경직된 축선을 고집하지 않으면서도 자연지형에 밀착된 건물과 마당의 공간 및 시각구성상의 비대칭 균형원칙을 추구하여 '치와 화'의 교집합 공간을 구축하였다. 한편, 건물 이름 짓기는 학문수양과 관련하여 성리학적 가르침과 풍수사신사(風水四神砂) 구조와 연계시켜 이루어짐으로서 기능과 의미를 일체화시킨 치와 화의 경관 놓기와 경관 맞추기가 드러나고 있다. 또한, 건물과 마당의 폐쇄감으로 볼 때 강학(講學) 및 유상(遊賞)공간 그리고 제향공간은 그 공간성격에 따라 개방감과 위요감, 긴장감과 안도감, 상승감과 위계감이 적절히 부여되는 등 청각적으로 의사 전달이 가능한 인간적 척도 개념이 반영되고 있다. 남계서원의 초기 건립과 이후의 변모과정에서 드러난 자연과 유연하게 이어지는 기능, 완결을 지향하는 비완결의 열림 그리고 긴장과 이완이 반복되는 동세적 아름다움을 구현하기 위한 치(置-놓기)와 자연과 일체감을 갖는 질서와 연속, 기념성과 일상성의 공유 등을 구현하기 위한 화(和-맞추기)의 경관짜임 의도는 오늘날 토지이용계획은 물론 캠퍼스 환경설계 분야에 시사하는 바가 크다.

The application of Fourier transform near infrared (FT-NIR) spectroscopy in the wine industry of South Africa

  • Van Zyl, Anina;Manley, Marena;Wolf, Erhard E.H.
    • 한국근적외분광분석학회:학술대회논문집
    • /
    • 한국근적외분광분석학회 2001년도 NIR-2001
    • /
    • pp.1257-1257
    • /
    • 2001
  • Fourier transform near infrared (FT-NIR) spectroscopy was used as a rapid method to measure the $^{o}Brix$ content and to discriminate between different must samples in terms of their fee amino nitrogen (FAN) values. FT-NIR spectroscopy was also used as a rapid method to discriminate between Chardonnay wine samples in terms of the status of the male-lactic fermentation (MLF). This was done by monitoring the conversion of malic to lactic acid and thereby determining whether MLF has started, is underway or has been completed followed by classification of the samples. Furthermore, FT-NIR spectroscopy was applied as a rapid method to discriminate between table wine samples in terms of the ethyl carbamate (EC) content. EC in wine can pose a health threat and need to be monitored by determining the EC content in relation to the regulatory limits set by the authorities. For each of the above mentioned parameters, $QUANT+^{TM}$ methods were built and calibrations derived and it was found that a very strong correlation existed in the sample set for the FT-NIR spectroscopic predictions of $^{o}Brix$ (r = 0.99, SECV = 0.306), but the correlations for the FAN (r = 0.61, SECV = 272.1), malic acid (r = 0.58, SECV = 1.06), lactic acid (r = 0.51, SECV = 1.14) and EC predictions (r = 0.47, SECV = 3.67) were not as good. Soft Independent Modeling by Class Analogy (SIMCA) diagnostics and validation was applied as a sophisticated discrimination method. The must samples could be classified in terms of their FAN values when SIMCA was applied, obtaining results with recognition rates exceeding 80%. When SIMCA diagnostics and validation were applied to determine the progress of conversion of malic to lactic acid and the EC content, again results with recognition rates exceeding 80% were obtained. The evaluation of the applicability of FT-NIR spectroscopy measurement of FAN, $^{o}Brix$ values, malic acid, lactic acid and EC content in must and wine shows considerable promise. FT-NIR spectroscopy has the potential to reduce the analytical times considerably in a range of measurements commonly used during the wine making process. Where conventional FT-NIR calibrations are not effective, SIMCA methods can be used as a discriminative method for rapid classification of samples. SIMCA can replace expensive, time-consuming, quantitative analytical methods, if not completely, at least to some extent, because in many processes it is only needed to know whether a specific cut off point has been reach or not or whether a sample belongs to a certain class or not.

  • PDF

영국 화이트 가든(White Garden)의 초화류 설계기법 - 20C 초반 작정된 시싱허스트, 배링턴 코트를 중심으로 - (A Study on the Design Method of Flowering Plants Used in the English White Gardens - Focusing on Sissinghurst, Barrington Court Built in the Early 20th Century -)

  • 박은영
    • 한국전통조경학회지
    • /
    • 제28권4호
    • /
    • pp.144-153
    • /
    • 2010
  • 정원을 만드는데 있어서 정원설계가들은 특정한 색을 이용하여 원칙을 정하고 소재를 수집하여 각자의 미의식으로 결합해가는 기법을 사용한다. 본 연구에서는 흰색을 배색의 주조톤으로 하여 유명한 정원인 제킬(Gertrude Jekyll)의 배링턴 코트(Barrington court)와 비타(Vita Sackvill-West)의 시싱허스트(Sissinghurst)의 화이트 가든에 사용된 초화류의 종류와 특성을 통해 설계기법을 연구한다. 사용된 개별식물을 계절, 색, 형태, 초장, 향기로 구분하여 분석하고, 화이트 가든 조성 시 초화류의 미적 결합방식을 제킬과 비타의 작품을 통해 살펴보았다. 제킬은 봄의 신선함을 위한 정원으로 초롱꽃류(Campanula spp.), 백합류(Lilium spp.)를 위주로 식재하였다. 비타(Vita Sackvill-West)는 주로 여름밤의 달빛을 겨냥한 정원으로 델피니움류(Delphinium spp.), 장미류(Rosa spp.)가 대표적인 수종이다. 꽃의 색은 흰색계열로 조성하였으나, 순수한 흰색에서부터 아이보리색과 실버색을 포함하였으며, 꽃의 형태는 흰색의 단일색에서 오는 단조로움을 피하기 위해 강한 형태를 사용하였다. 또한 잎의 색은 흰꽃이 잘 돋보일 수 있도록 연록색, 연회색, 밝은 녹황색 잎을 조합하였다. 전반적으로 차가운 색상 계열을 사용하여 신비감과 시원함, 청정함, 밤에 빛이 반사되었을 때 흰꽃과 더불어 매혹적이고 애상적인 이미지를 추구하였다. 화이트 가든의 조경사적 의의는 색의 잠재력을 발견하고 범위를 제한하지 않는 재식설계기법의 아이디어와 기술로 주제색상을 통한 정원설계의 시발점이 되었으며, 미적 원리에 의한 결합으로 정원예술의 발전에 기여하였다.