An experimental performance analysis of a cold region stationary photovoltaic system

Choi, Wongyu,Warren, Ryan D.,Pate, Michael B. Techno-Press 2016 Advances in energy research Vol.4 No.1

A grid-connected photovoltaic (PV) system comprised of multicrystalline silicon (mc-Si) modules was installed in a cold climate region in the U.S. This roof-mounted stationary PV system is a real-world application of PV for building energy generation in International Energy Conservation Code (IECC) Climate Zone 5 (and possibly similar climate zones such as 6, 7 and 8), and it served the purposes of research, demonstration, and education. The importance of this work is highlighted by the fact that there has been less emphasis on solar PV system in this region of the U.S. because of climate and latitude challenges. The system is equipped with an extensive data acquisition system capable of collecting performance and meteorological data while visually displaying real-time and historical data through an interactive online interface. Experimental data was collected and analyzed for the system over a one-year period with the focus of the study being on measurements of power production, energy generation, and efficiency. The annual average daily solar insolation incident upon the array was found to be $4.37kWh/m^2$. During the first year of operation, the PV system provided 5,801 kWh (1,264 kWh/kWp) of usable AC electrical energy, and it was found to operate at an annual average conversion efficiency and PR of 10.6 percent and 0.79, respectively. The annual average DC to AC conversion efficiency of the inverter was found to be 94 percent.

A Study of the Relationship between Structure and Properties of Cadmium Phosphate Glasses

Wongyu Choi,Taehee Kim,Donggun Gwoo,Kyungbum Kee,Jong-Hwan Kim,Kyung-Suk Han,류봉기 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.1

It analysed the structure and chemical durability which it follows in CdO content in Cadmium phosphate glasses. We prepared glasses with the composition, xCdO-(100-x)P2O5 (x = 10 mol. % to 50 mol. %), and analyzed their density (ρ), molar volume (VM), glass transition/softening temperature (Tg/Td), thermal expansion coefficient (α), fourier transform infrared spectroscopy, and dissolution rate. All of these of the values were found to vary with the CdO content of the glasses. It is observed that the dissolution rate increase with with CdO contents. This suggests that Cadmium ion breaks the p-o-p bonds.

몰리브덴이 첨가된 이산화바나듐으로 표면처리한 탄소계 전도성판의 전기저항특성

최원규(Wongyu Choi),정혜미(Hye-Mi Jung),이종현(Jonghyun Lee),임세준(Sejoon Im),엄석기(Sukkee Um) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

Vanadium pentoxide (V₂O?) powder was prepared and mixed with Molybdenum Oxides (MoO3) to form Mo-doped and -undoped VO₂ films by a sol-gel method on graphite conductive substrates. X-Ray diffraction (XRD) and scanning electron microscopy (SEM) was used to investigate the chemical compositions and microstructures of the Mo-doped and -undoped VO₂ films. The variation of electrical resistance was measured as a function of temperature and stoichiometric composition between vanadium and molybdenum. In this study, it was found that Mo-doped and -undoped VO₂ shows the typical negative temperature coefficient (NTC) behavior. As the amount of the molybdenum increases, the electrical resistance of Modoped VO₂ film gets reduced under the transition temperature and a linear decrease in the transition temperature is observed. From these experimental results, we can conclude that the electrical resistance behavior with temperature change of VO₂ films can be utilized as a self-heating source with the electrical current flowing through the graphite substrate.

DRAM-Latency Optimization Inspired by Relationship between Row-Access Time and Refresh Timing

Wongyu Shin,Jungwhan Choi,Jaemin Jang,Jinwoong Suh,Youngsuk Moon,Yongkee Kwon,Lee-Sup Kim IEEE 2016 IEEE Transactions on Computers Vol. No.

<P>It is widely known that relatively long DRAM latency forms a bottleneck in computing systems. However, DRAM vendors are strongly reluctant to decrease DRAM latency due to the additional manufacturing cost. Therefore, we set our goal to reduce DRAM latency without any modification in the existing DRAM structure. To accomplish our goal, we focus on an intrinsic phenomenon in DRAM: electric charge variation in DRAM cell capacitors. Then, we draw two key insights: i) DRAM row-access latency of a row is a function of the elapsed time from when the row was last refreshed, and ii) DRAM row-access latency of a row is also a function of the remaining time until the row is next refreshed. Based on these two insights, we propose two mechanisms to reduce DRAM latency: NUAT-1 and NUAT-2. NUAT-1 exploits the first key insight and NUAT-2 exploits the second key insight. For evaluation, circuit-and system-level simulations are performed, which show the performance improvement for various environments.</P>

Q-DRAM: Quick-Access DRAM with Decoupled Restoring from Row-Activation

Wongyu Shin,Jungwhan Choi,Jaemin Jang,Jinwoong Suh,Yongkee Kwon,Youngsuk Moon,Hongsik Kim,Lee-Sup Kim IEEE 2016 IEEE Transactions on Computers Vol. No.

<P>The relatively high latency of DRAM is mostly caused by the long row-activation time which in fact consists of sensing and restoring time. Memory controllers cannot distinguish between them since they are performed consecutively by a single row-activation command. If these two steps are separated, the restoring can be delayed until DRAM access is uncongested. Hence, we propose Quick-Access DRAM (Q-DRAM) which discriminates between sensing and restoring. Our approach is to allow destructive access (i.e., only sensing is performed without restoring by a row-activation command) using per-bank multiple row-buffers. We call the destructive access and per-bank multiple row-buffers quick-access and quick-buffers (q-buffers) respectively. In addition, we propose Quick-access Trigger (Q-TRIGGER) and RESTORER to utilize Q-DRAM. Q-TRIGGER makes a decision whether quick-access is required or not, and RESTORER decides when to restore the data at the destructed cell. Specifically, RESTORER detects the proper timing to hide restoring time by predicting data bus occupation and by exploiting bank-level locality. Evaluations show that Q-DRAM significantly improved performance for both single-and multi-core systems.</P>

Rank-Level Parallelism in DRAM

Shin, Wongyu,Jang, Jaemin,Choi, Jungwhan,Suh, Jinwoong,Kwon, Yongkee,Moon, Youngsuk,Kim, Lee-Sup IEEE 2017 IEEE Transactions on Computers Vol. No.

<P>DRAM systems are hierarchically organized: Channel-Rank-Bank. A channel is connected to multiple ranks, and each rank has multiple banks. This hierarchical structure facilitates creating parallelisms in DRAM. The current DRAM architecture supports bank-level parallelism; as many rows as banks can be moved simultaneously at bank-level. However, rank-level parallelism is not supported. For this reason, only one column can be accessed at a time, although each rank has its own data bus that can carry a column. Namely, current DRAM operations do not exploit the structural opportunity created by multiple ranks. We, therefore, propose a novel DRAM architecture supporting rank-level parallelism. Thereby, as many columns as ranks can be moved concurrently at rank-level. In this paper, we illustrate the rank-level parallelism and its benefit in DRAM operations.</P>

Photo-Reduction of Graphene Oxide by Using Photographic Flash-Light

Chae, Wongyu,Kim, Minha,Kim, Donguk,Park, Jin-Hong,Choi, Wonseok,Lee, Jaehyeong American Scientific Publishers 2018 Science of advanced materials Vol.10 No.1

<P>In this work, we investigate the reduction of graphene oxide using a photographic flash-light. GO thin films were spray-coated to thicknesses of similar to 150, 200 and 300 nm on slide glass, and these films were reduced by photographic flash-light irradiation with 3000 Ws charged power at room temperature under ambient conditions. We studied the thickness effect of the GO thin films, which is an important parameters for the photo-thermal method. The 300-nm-thick GO thin film was fully reduced under flash-light irradiation, and thus its structure and chemical composition changed. The irradiated GO thin films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and scanning electron microscopy.</P>

Bank-Group Level Parallelism

Shin, Wongyu,Jang, Jaemin,Choi, Jungwhan,Suh, Jinwoong,Kim, Lee-Sup IEEE 2017 IEEE Transactions on Computers Vol. No.

<P>DDR4 SDRAM introduced a new hierarchy in DRAM organization: bank-group (BG). The main purpose of BG is to increase I/O bandwidth without growing DRAM-internal bus-width. We, however, found that other benefits can be derived from the new hierarchy. To achieve the benefits, we propose a new DRAM architecture using the BG-hierarchy, leading to a creation of BG-Level Parallelism (BGLP). By exploiting BGLP, the overall parallelism grows in DRAM operations. We also argue that BGLP is a feasible solution in the cost-sensitive DRAM industry because the additional cost is negligible and only cost-insensitive area needs to be modified.</P>

Portfolio Optimization: An Introductory Survey Focused on Formulations

Bong-Geun Choi,JaeYong Lee,Wongyu Lee,Jang Ho Kim 대한산업공학회 2022 대한산업공학회 춘계학술대회논문집 Vol.2022 No.6

독일 바이에른 주의 정보 교육과정 분석

최희정 ( Heejeong Choi ),이원규 ( Wongyu Lee ),김자미 ( Jamee Kim ) 한국컴퓨터교육학회 2019 컴퓨터교육학회 논문지 Vol.22 No.1

제 4차 산업혁명 시대의 도래로 세계 각국은 변화하는 사회에 대처하기 위해 정보교육을 강화하고 있다. 본 연구는 독일의 정보 교육과정 분석을 통해 독일의 정보교육 동향을 파악하여, 한국의 정보교육과의 차이를 비교하였다. 독일의 정보교육 분석은 독일 교육의 중심이라 할 수 있는 바이에른 주의 정보교육 내용과 변화를 중심으로 하였다. 분석 결과, 첫째, 초등교육에서는 ‘정보’를 통합교과적 측면에서 접근하고 있으며, 활용 중심의 교육이었다. 둘째, 중등교육에서 충분한 이수시간 확보를 통해 이론과 실습을 경험할 수 있는 교육을 진행하고 있었다. 셋째, 정보교과를 입시에 반영하여, 고등교육과의 연계를 충분히 반영하였다. 분석을 토대로, 체계적인 정보교육을 위해서는 초등교육부터 많은 시수를 확보할 필요가 있으며, 중등교육과 고등교육의 연계를 고려해야 함을 확인하였다. With the advent of the age of the 4th Industrial Revolution, countries around the world are reinforcing informatics education to cope with changing society. The purpose of this study is to analyze the trends in German informatics education through the analysis of the German informatics curriculum, and provide implications for the informatics education of Korea. The analysis of German informatics education focused on the contents and changes of the informatics education of Bayern, which can be said to be the center of German education. As a result of this analysis, first, elementary education approaches ‘informatics’ from the viewpoint of integrated curriculums. Second, secondary education provides education that makes it possible to experience theory and practice by securing sufficient credit hours. Third, they reflected informatics subjects in entrance examinations, and sufficiently ensured links to higher education. This analysis confirmed that systematic informatics education requires many credit hours from elementary education, and links with secondary and higher education must be taken into consideration.