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AISI 4140 시편의 미세단조 공정 충격력 및 표면 변형량 측정
정창호(Chang-ho Jung),홍민성(Min-Sung Hong),전용호(Youngho Jeon) 한국생산제조학회 2018 한국생산제조학회지 Vol.27 No.5
The micro-forging process improves the surface quality of the workpiece by micro tip impacting. In this study, the impact force is generated using a terfenol-D oscillator (ETREMA Product. lnc.), and it is measured when the actual impact is in action. The experimental results show that the amplitude of the force in the no-load state is approximately 325.6 N, and the impact force is 116.6 N and 118.6 N when the static load is changed. As the output of the oscillator was changed by energy loss and structural damping, the impact force was found to be as 29.1 N and 36.4 N, respectively. The impact test was performed on the AISI 4140 specimen under these conditions, and the deformation of the surface was measured and compared. Hence, the impact force measurement results obtained in this study can be used as an important parameter for the optimization of micro-forging process.
Energy Use and Division of Capital Stock in Endogenous R&D Model
Youngho Chang 한국경제연구학회 2010 Korea and the World Economy Vol.11 No.3
This study constructs an endogenous R&D model in which energy and capital are employed to produce the intermediate goods, and the division of capital is assumed. Following the conventional endogenous R&D model, it incorporates energy use into the production of intermediate goods; meanwhile, capital is divided into two classes ? one is invested in final goods sector directly, the other is allocated for the production of intermediate goods. With this modification, the study finds that the rising energy prices would spur the substitution of capital for intermediate goods in the final goods sector; such a substitution could alleviate the energy price shock. Contrasting with the existing literature, the present model finds that the growth rate of energy prices needs not to impede the rate of output growth. Rather the increasing energy price could spur innovations for energy technology, and then stimulate economic growth. It also finds that a tax aiming to energy conservation (e.g., a carbon tax) needs not to impede the economic growth; on the contrary, the tax could favor the economic growth if it is time-increasing and moderate. For the sake of energy conservation, the study suggests a policy that imposes a tax on energy use and subsidizes capital use.
Speculation and Commodity Prices
Youngho Chang,Zhen Chuan Chua,Qiu Xia Eu,Shaun Wong Wei Xiang 이화여자대학교 이화사회과학원 2013 사회과학연구논총 Vol.29 No.1
This paper attempts to identify the role of financial speculation in commodity price movements, while exploring other possible influences such as the role of spare capacity and the role of rapidly developing countries, through intensive commodity import surges. Both fundamentals and speculation appear to jointly determine crude oil prices. Speculative activity does play a supporting role in price determination but it is not the only driver. Fundamentals such as net imports, the result of consumption and production dynamics, are important in price determination. Attempts at investigating the role of spare capacity, however, found that capacity bottle neck is not an important cause of recent price movements. A production level is still primarily the most important driver on prices of wheat and is heavily reliant on weather. Speculation does not have a significant effect of prices, but position limits may disrupt hedging activity that helps stabilize wheat prices. Even though speculation have some influence on crude oil prices, setting an across the board position limit may harm the price stability in wheat markets. Market wide position limits should consider the impacts on the futures market as a whole rather than piecemeal.
정보보호 : 하둡 상에서 ARIA 알고리즘을 이용한 HDFS 데이터 암호화 기법의 설계 및 구현
송영호 ( Youngho Song ),신영성 ( Youngsung Shin ),장재우 ( Jae Woo Chang ) 한국정보처리학회 2016 정보처리학회논문지. 컴퓨터 및 통신시스템 Vol.5 No.2
최근 소셜 네트워크 서비스(SNS)의 발전으로 빅데이터가 출현하였고, 이를 분석하기 위한 분산 병렬 플랫폼으로 하둡이 개발되었다. 하둡을 사용하는 기업은 개인적인 정보가 포함된 데이터를 분석하여 마케팅 등에 활용하고 있다. 이에 따라, 하둡에 저장된 센서티브(sensitive) 데이터의 유출을 방지하기 위한 데이터 암호화 연구가 수행되었다. 하지만 기존 데이터 암호화에 대한 연구는 국외 표준인AES 암호화 알고리즘만을 지원하는 한계점이 존재한다. 한편 정부에서는 데이터 암호화 알고리즘으로 ARIA 알고리즘을 국내 표준으로 지정하였다. 본 논문에서는 하둡 상에서 ARIA 알고리즘을 이용한 HDFS 데이터 암호화 기법을 제안하였다. 첫째, 제안하는 암호화 기법은 하둡의 분산 컴퓨팅 환경에서 ARIA 암호화 및 복호화를 수행하는 HDFS 블록 분할 컴포넌트를 제공한다. 둘째, 제안하는 암호화 기법은 데이터의 마지막 블록이 128비트 단위의 데이터가 아닐 경우, 더미(dummy) 데이터를 추가하여 암호화 및 복호화를 수행하는 가변길이 데이터 처리 컴포넌트를 제공한다. 마지막으로 성능 평가를 통해, 제안하는 ARIA 기반 암호화 기법이 텍스트 문자열 처리 응용 및 과학 데이터 분석 응용에서 효과적으로 사용될 수 있음을 보였다. Due to the growth of social network systems (SNS), big data are realized and Hadoop was developed as a distributed platform for analyzing big data. Enterprises analyze data containing users’ sensitive information by using Hadoop and utilize them for marketing. Therefore, researches on data encryption have been done to protect the leakage of sensitive data stored in Hadoop. However, the existing researches support only the AES encryption algorithm, the international standard of data encryption. Meanwhile, Korean government choose ARIA algorithm as a standard data encryption one. In this paper, we propose a HDFS data encryption scheme using ARIA algorithms on Hadoop. First, the proposed scheme provide a HDFS block splitting component which performs ARIA encryption and decryption under the distributed computing environment of Hadoop. Second, the proposed scheme also provide a variable-length data processing component which performs encryption and decryption by adding dummy data, in case when the last block of data does not contains 128 bit data. Finally, we show from performance analysis that our proposed scheme can be effectively used for both text string processing applications and science data analysis applications.
Computational Screening of Indirect-Gap Semiconductors for Potential Photovoltaic Absorbers
Kang, Youngho,Youn, Yong,Han, Seungwu,Park, Jiwon,Oh, Chang-Seok American Chemical Society 2019 Chemistry of materials Vol.31 No.11
<P>Photovoltaic (PV) absorbers are key components of PV cells used to harvest solar energy, which is an attractive renewable energy resource. In this study, a high-throughput computational screening is conducted to discover potential PV absorbers. While direct-gap semiconductors are usually favored as PV absorbers, herein, we focus on indirect-gap semiconductors that could exhibit a long lifetime of photocarriers because of the low probability of band-to-band recombination, enabling high-performance PV cells. From the Materials Project database, we screen semiconductors considering the direct band gap, the difference between the direct and indirect band gaps, and the effective mass of carriers as selection metrics. Taking low costs and earth abundance of constituent elements into account, we suggest GeAs<SUB>2</SUB>, SiAs<SUB>2</SUB>, and NaSbS<SUB>2</SUB> as particularly promising indirect-gap semiconductors. Their absorption and defect properties are analyzed in detail, providing a route to engineering materials with high efficiency.</P> [FIG OMISSION]</BR>
그물구조 WDM 망 설계 알고리즘과 망 설계 시스템 연구
이영호,장용원,박노익,이순석,김영부,조기성 한국경영과학회 2005 韓國經營科學會誌 Vol.30 No.1
In this paper, we deal with a mesh network design problem arising form the deployment of WDM for the optical internet. The mesh network consists of mesh topology for satisfying traffic demand while minimizing the cost of WDM, OXC, and fiber cables. The problem seeks to find an optimal routing of traffic demands in the network such that the total cost is minimized. We formulated the problem as a mixed-integer programming model and devise a tabu search heuristic procedure. Also we develop an optical internet design system that implements the proposed tabu search heuristic procedure. We demonstrate the computational efficacy of the proposed algorithm, compared with CPLEX 8.0.
GOPES: Group Order-Preserving Encryption Scheme Supporting Query Processing over Encrypted Data
( Hyunjo Lee ),( Youngho Song ),( Jae-woo Chang ) 한국정보처리학회 2018 Journal of information processing systems Vol.14 No.5
As cloud computing has become a widespread technology, malicious attackers can obtain the private information of users that has leaked from the service provider in the outsourced databases. To resolve the problem, it is necessary to encrypt the database prior to outsourcing it to the service provider. However, the most existing data encryption schemes cannot process a query without decrypting the encrypted databases. Moreover, because the amount of the data is large, it takes too much time to decrypt all the data. For this, Programmable Order-Preserving Secure Index Scheme (POPIS) was proposed to hide the original data while performing query processing without decryption. However, POPIS is weak to both order matching attacks and data count attacks. To overcome the limitations, we propose a group order-preserving data encryption scheme (GOPES) that can support efficient query processing over the encrypted data. Since GOPES can preserve the order of each data group by generating the signatures of the encrypted data, it can provide a high degree of data privacy protection. Finally, it is shown that GOPES is better than the existing POPIS, with respect to both order matching attacks and data count attacks.