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Efficient Optimization Method for Polynomial Selection
Suhri Kim(김수리),Heetaek Kwon(권희택),Yongseong Lee(이용성),Nam Su Chang(장남수),Kisoon Yoon(윤기순),Chang Han Kim(김창한),Young-Ho Park(박영호),Seokhie Hong(홍석희) 한국정보보호학회 2016 정보보호학회논문지 Vol.26 No.3
현재까지 알려진 가장 효율적인 인수분해 방법은 General Number Field Sieve (GNFS)를 이용하는 방법이다. CADO-NFS는 GNFS를 기반으로 구현된 공개된 소프트웨어로 RSA-704의 인수분해에 사용된 도구이다. CADO-NFS에서 다항식 선택은 크게 다항식을 생성하는 과정과 이를 최적화하는 과정으로 나누어져 있다. 그러나 CADO-NFS에서 다항식의 최적화 과정은 전체 다항식 선택 소요 시간 중 약 90%를 차지할 정도로 큰 부하를 주고 있다. 본 논문에서는 사전 연산 테이블을 이용하여 다항식 최적화 과정의 부하를 줄이는 방안을 제안한다. 제안하는 방법은 기존 CADO-NFS의 다항식과 같은 다항식을 선택하지만, 다항식 선택에 걸리는 시간은 약 40% 감소한다. Currently, General Number Field Sieve(GNFS) is known as the most efficient way for factoring large numbers. CADO-NFS is an open software based on GNFS, that was used to factor RSA-704. Polynomial selection in CADO-NFS can be divided into two stages – polynomial selection, and optimization of selected polynomial. However, optimization of selected polynomial in CADO-NFS is an immense procedure which takes 90% of time in total polynomial selection. In this paper, we introduce modification of optimization stage in CADO-NFS. We implemented precomputation table and modified optimization algorithm to reduce redundant calculation for faster optimization. As a result, we select same polynomial as CADO-NFS, with approximately 40% decrease in time.
KIM, Jungja,CEONG, Heetaek,WON, Yonggwan The Institute of Electronics, Information and Comm 2009 IEICE transactions on information and systems Vol.92 No.1
<P>In market-basket analysis, weighted association rule (WAR) discovery can mine the rules that include more beneficial information by reflecting item importance for special products. In the point-of-sale database, each transaction is composed of items with similar properties, and item weights are pre-defined and fixed by a factor such as the profit. However, when items are divided into more than one group and the item importance must be measured independently for each group, traditional weighted association rule discovery cannot be used. To solve this problem, we propose a new weighted association rule mining methodology. The items should be first divided into subgroups according to their properties, and the item importance, i.e. item weight, is defined or calculated only with the items included in the subgroup. Then, transaction weight is measured by appropriately summing the item weights from each subgroup, and the weighted support is computed as the fraction of the transaction weights that contains the candidate items relative to the weight of all transactions. As an example, our proposed methodology is applied to assess the vulnerability to threats of computer systems that provide networked services. Our algorithm provides both quantitative risk-level values and qualitative risk rules for the security assessment of networked computer systems using WAR discovery. Also, it can be widely used for new applications with many data sets in which the data items are distinctly separated.</P>
Park, Heetaek,Kim, Minkyung,Kang, ShinYoung,Kang, Byoungwoo The Royal Society of Chemistry 2019 Journal of materials chemistry. A, Materials for e Vol.7 No.21
<P>Tavorite LiVPO4F has great potential as a cathode material due to its high energy density, superior thermal stability and fast kinetics. It has been controversial whether the redox reaction pathway of LiVPO4F is symmetric or not, but the origin of such symmetric/asymmetric redox reaction pathways has not been clearly understood. By combining <I>ab initio</I> calculations with experiments, we found that oxygen defects on fluorine sites, OF<SUP>−</SUP>, can be a key factor that affects the symmetry of the redox pathway of LiVPO4F1−δOδ (<I>δ</I> < 1). The computational results indicate that (1) the thermodynamically metastable ‘triclinic’ polymorph of VPO4F1−δOδ, which maintains the structural symmetry of LiVPO4F, can be kinetically stabilized considering its marginally higher energy than the stable ‘monoclinic’ phase; and (2) the OF<SUP>−</SUP> defects slightly destabilize the intermediate phase (<I>x</I> = 0.667) (Li0.667VPO4F <I>versus</I> Li0.667VPO4F0.917O0.083), inferring that the presence of OF<SUP>−</SUP> defects can induce the asymmetric redox pathway of LiVPO4F1−δOδ. We also experimentally found that the concentration of OF<SUP>−</SUP> defects is critically affected by the synthesis process of LiVPO4F, and VPO4F with lower OF<SUP>−</SUP> concentration can support the possible presence of the metastable (triclinic) phase, leading to the redox pathway being prone to being symmetric. Therefore, controlling oxygen defects by a synthesis processes can affect electrochemical performance <I>via</I> different redox reaction pathways of LiVPO4F. This understanding provides further possibilities for improving the electrochemical performance.</P>
Park, Heetaek,Jung, Keeyoung,Nezafati, Marjan,Kim, Chang-Soo,Kang, Byoungwoo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.41
<P>The Na superionic conductor (aka Nasicon, Na1+xZr2SixP3-xO12, where 0 <= x <= 3) is one of the promising solid electrolyte materials used in advanced molten Na-based secondary batteries that typically operate at high temperature (over similar to 270 degrees C). Nasicon provides a 3D diffusion network allowing the transport of the active Na-ion species (i.e., ionic conductor) while blocking the conduction of electrons (i.e., electronic insulator) between the anode and cathode compartments of cells. In this work, the standard Nasicon (Na3Zr2Si2PO12, bare sample) and 10 at% Na-excess Nasicon (Na3.3Zr2Si2PO12, Na-excess sample) solid electrolytes were synthesized using a solid-state sintering technique to elucidate the Na diffusion mechanism (i.e., grain diffusion or grain boundary diffusion) and the impacts of adding excess Na at relatively low and high temperatures. The structural, thermal, and ionic transport characterizations were conducted using various experimental tools including X-ray diffraction ()MD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). In addition, an ab initio atomistic modeling study was carried out to computationally examine the detailed microstructures of Nasicon materials, as well as to support the experimental observations. Through this combination work comprising experimental and computational investigations, we show that the predominant mechanisms of Na-ion transport in the Nasicon structure are the grain boundary and the grain diffusion at low and high temperatures,, respectively. Also, it was found that adding 10 at% excess Na could give rise to a substantial increase in the total conductivity (e.g., 1.2 X 10(-4) S/cm at 300 degrees C) of Nasicon electrolytes resulting from the enlargement of the bottleneck areas in the Na diffusion channels of polycrystalline grains.</P>
강희택(Kang, Heetaek),김승운(Kim, Seungwoon) 대한경영학회 2016 대한경영학회 학술발표대회 발표논문집 Vol.2016 No.1
본 연구는 정보기술 수준에서 지각된 심미성, 지각된 가치, 사용자 만족간의 관계를 살펴보는 동시에 기업 수준에서 기업연상과 기업이미지간의 관계를 살펴보고, 이러한 요인이 재구매 행동과는 어떠한 관계가 있는지를 살펴보고자 하였다. 이를 위해 스마트폰 사용자들을 대상으로 설문조사를 실시하고 수집된 자료들을 통계적으로 분석하였다. 분석결과, 첫째, 지각된 심미성이 지각된 가치와 사용자 만족에 유의미한 영향을 미치는 것으로 나타났으며, 지각된 가치 또한 사용자 만족에 유의미한 영향을 미친다는 점을 확인하였다. 둘째, 기업연상인 기업의 사회적 책임 연상과 기업능력 연상이 모두 기업 이미지에 유의미한 영향을 미치는 것으로 나타났다. 이 중 기업의 사회적 책임 연상은 지각된 가치에도 유의미한 영향을 미쳤다. 셋째, 사용자 만족은 기업 이미지에 유의미한 영향을 미치며, 사용자 만족과 기업 이미지가 재구매의도에 유의미한 영향을 미치는 것으로 나타났다. This study is to examine the relationship between perceived aesthetics, perceived value and user satisfaction in an information technology level as well as that of corporate association and corporate image in a firm level, analysing the effects of these factors on repurchase behavior of smartphone users. In order to find out these relationships of the variables, this study conducted a survey from smartphone users and analysed the collected data statistically. As a result, this study finds that perceived aesthetics has a significant impact on perceived value and user satisfaction, and perceived value significantly influences user satisfaction. Secondly, both corporate social responsibility association and coporate ability association have significant influences on corporate image. Among these variables, corporate social responsibility association is also of importance on perceived value. Thirdly, user satisfaction has a significant impact on corporate image and user satisfaction and corporate image have been found to be significant factors influencing repurchase intention.
김현일(HyunIl Kim),박준영(JunYoung Park),백제현(JeHyun Baek),정희택(HeeTaek Jung) 한국전산유체공학회 2000 한국전산유체공학회지 Vol.5 No.2
It has been indicated that the rotor/stator interaction has distinct causes of unsteadiness, such as the viscous vortex shedding, wake/stator interaction and potential rotor/stator interaction. In this paper, the mechanism of unsteady potential interaction in one stage axial compressor is numerically investigated for blade row ratio 1:1 and 2:3 at design point and for blade TOW ratio 2:3 at off-design point in two-dimensional view point. The numerical technique used is the upwind scheme of Van-Leer's Flux Vector Splitting(FVS) and Cubic spline interpolation is applied on zonal interface. In this study the flow unsteadiness due to potential interaction are found to be larger in blade row ratio 2:3 than in 1:1. The total pressure rise in blade row ratio 2:3 is closer to the real value in design point than that in 1:1. The change of unsteady pressure amplitude according to the variation of stator exit pressure is very small.