The Octonions

The octonions are the largest of the four normed division algebras. While somewhat neglected due to their nonassociativity, they stand at the crossroads of many interesting fields of mathematics. Here we describe them and their relation to Clifford algebras and spinors, Bott periodicity, projective and Lorentzian geometry, Jordan algebras, and the exceptional Lie groups. We also touch upon their applications in quantum logic, special relativity and supersymmetry.Comment: 56 pages LaTeX, 11 Postscript Figures, some small correction

Proto-type installation of a double-station system for the optical-video-detection and orbital characterisation of a meteor/fireball in South Korea

We give a detailed description of the installation and operation of a double-station meteor detection system which formed part of a research & education project between Korea Astronomy Space Science Institute and Daejeon Science Highschool. A total of six light-sensitive CCD cameras were installed with three cameras at SOAO and three cameras at BOAO observatory. A double-station observation of a meteor event enables the determination of the three-dimensional orbit in space. This project was initiated in response to the Jinju fireball event in March 2014. The cameras were installed in October/November 2014. The two stations are identical in hardware as well as software. Each station employes sensitive Watec-902H2 cameras in combination with relatively fast f/1.2 lenses. Various fields of views were used for measuring differences in detection rates of meteor events. We employed the SonotaCo UFO software suite for meteor detection and their subsequent analysis. The system setup as well as installation/operation experience is described and first results are presented. We also give a brief overview of historic as well as recent meteor (fall) detections in South Korea. For more information please consult http://meteor.kasi.re.kr .Comment: Technical/instrumentation description of a professional meteor detection system, 23 pages, 20 figures (color/monochrome), 5 tables, submitted to the Journal of Korean Astronomical Society (JKAS, http://jkas.kas.org/, http://jkas.kas.org/history.html

Properties of Magnesia Composites According to Replacement Ratio of Perlite

Recently, passive and zero-energy construction has increased in Korea due to the government`s continuous application of budget-conscious policies for establishments. Accordingly, construction materials are being advanced, and the required performance standards for insulation materials are increasing. However, problems such as fire vulnerability and degradation of physical properties for organic and inorganic insulation materials are shown, so it is necessary to solve this problem. The objective of this research is to examine the properties of the composites by analyzing the flexural breaking load, impact resistance, density, VOCs concentration reduction rate, and fine dust concentration reduction rate of the composites manufactured based on the perlite substitution rate of the magnesia composites. The flexural breaking load test of the composites was assessed according to ‘KS F 3504’, a gypsum board standard and the impact resistance was assessed according to ‘KS F 4715’. The performance evaluation of adsorption performance of air pollutants of the VOCs and fine dust in the context of the small chamber technique suggested by Hanbat University. The results of this study are as follows: The flexural breaking load according to the perlite replacement rate tended to decrease as the perlite replacement rate increased. It is determined that the flexural breaking load is reduced by generating a large amount of pores inside due to the perlite porous structure characteristics. In the case of impact resistance, the impact resistance tended to increase as the perlite displacement rate increased. It is determined that the volume of the binder in the board is reduced, and pores inside the board are generated due to perlite, which is a porous material, thereby reducing the overall bonding force of the board. In the case of VOCs and fine dust concentrations, the VOCs and fine dust concentration reduction rates tended to increase as the perlite replacement rate increased. In the case of the perlite displace rate of 30%, the VOCs concentration decreased by 82.6%, and the fine dust concentration decreased by 87.9%. It has been established that the porous properties of perlite used to create a huge number of pores in the hardened body cause the concentration to be lowered physically through adsorption. This study\u27s findings are thought to be fundamental information for securing the engineering properties and air pollution absorption of magnesia composites blended with perlite

Probabilistic safety assessment-based importance analysis of cyber-attacks on nuclear power plants

With the application of digital technology to safety-critical infrastructures, cyber-attacks have emerged as one of the new dangerous threats. In safety-critical infrastructures such as a nuclear power plant (NPP), a cyber-attack could have serious consequences by initiating dangerous events or rendering important safety systems unavailable. Since a cyber-attack is conducted intentionally, numerous possible cases should be considered for developing a cyber security system, such as the attack paths, methods, and potential target systems. Therefore, prior to developing a risk-informed cyber security strategy, the importance of cyber-attacks and significant critical digital assets (CDAs) should be analyzed. In this work, an importance analysis method for cyber-attacks on an NPP was proposed using the probabilistic safety assessment (PSA) method. To develop an importance analysis framework for cyber-attacks, possible cyber-attacks were identified with failure modes, and a PSA model for cyber-attacks was developed. For case studies, the quantitative evaluations of cyber-attack scenarios were performed using the proposed method. By using quantitative importance of cyber-attacks and identifying significant CDAs that must be defended against cyber-attacks, it is possible to develop an efficient and reliable defense strategy against cyber-attacks on NPPs