A Design of MAC Model Based on the Separation of Duties and Data Coloring: DSDC-MAC

Among the access control methods for database security, there is Mandatory Access Control (MAC) model in which the security level is set to both the subject and the object to enhance the security control. Legacy MAC models have focused only on one thing, either confidentiality or integrity. Thus, it can cause collisions between security policies in supporting confidentiality and integrity simultaneously. In addition, they do not provide a granular security class policy of subjects and objects in terms of subjects\u27 roles or tasks. In this paper, we present the security policy of Bell_LaPadula Model (BLP) model and Biba model as one complemented policy. In addition, Duties Separation and Data Coloring (DSDC)-MAC model applying new data coloring security method is proposed to enable granular access control from the viewpoint of Segregation of Duty (SoD). The case study demonstrated that the proposed modeling work maintains the practicality through the design of Human Resources management System. The proposed model in this study is suitable for organizations like military forces or intelligence agencies where confidential information should be carefully handled. Furthermore, this model is expected to protect systems against malicious insiders and improve the confidentiality and integrity of data

위성관측과 수치실험에서 본 한반도 집중호우 특성

학위논문 (박사)-- 서울대학교 대학원 : 지구환경과학부, 2015. 8. 손병주.In order to objectively classify heavy rain types over East Asia during the summer, K-means clustering was applied to the Tropical Rainfall Measuring System (TRMM) Precipitation Radar (PR) reflectivity profiles. Two main types of heavy rainfall were emerged: a well-developed deep convective system that is situated predominantly over mainland China (Type 1, cold type) and a medium-depth rain system that is mostly found in the oceanic region over the western periphery of the North Pacific high (Type 2, warm type). It is noted that Type 1 propagates eastward from mainland China toward the area including Korea and Japan whereas Type 2 expands northward with the progress of summer. Such different temporal evolution appears to bring in the coexistence of two rain types of heavy rainfall over the Korean peninsula. This study further examines the spatio-temporal evolution of cloud systems and thermodynamic/dynamic features associated with heavy rainfall types over the Korean peninsula using geostationary satellites and reanalysis data, respectively. It was revealed that the cold type is characterized by an eastward-moving oval-shaped cloud system, while the warm type is represented by a northeastward-moving broader system. The cold-type heavy rainfall was usually associated with a local cloud system induced by convective instability. In contrast, the large-scale synoptic forcings (i.e., low-level moisture convergence and high-level divergence) under moist-adiabatically near-neutral conditions are thought to facilitate the possibility of warm-type heavy rainfall over the Korean peninsula. Collision and coalescence processes in the lower cloud layer appear to be responsible cloud microphysics for forming heavy rainfall there. In order to examine whether the numerical experiments could provide evidences supporting the hypothesis of causing the warm-type as well as cold-type heavy rainfall, numerical experiments were taken with ideally prescribed thermodynamic conditions. Under the prescribed moist-adiabatically near-neutral conditions, the warm-type simulation results in a lower storm height, earlier onset of precipitation, and heavier precipitation through collision-coalescence process below the melting layer. The lack of upper-level snow and close interaction between super-cooled raindrops and ice particles at the initial stage were also noted in the warm-type experiment. In contrast, the growth of snow and graupel particles and melting process of ice particles appear to be responsible for the cold-type heavy rainfall. In real-case simulations, Double Moment 6-class (WDM6) scheme simulated the most realistic vertical structure of summertime heavy rainfall over the Korean peninsula among eight Weather and Research Forecasting (WRF) microphysics schemes by virtue of the smallest amount of snow and modified warm-rain physics. However, excessive graupel in the WDM6 scheme was thought to be a problem. In addition, a warm-type heavy rain event was reasonably simulated using the WRF model, implying the importance of large-scale environmental setup in the prediction of warm-type heavy rainfall. Therefore, improvement of microphysical parameterization based on observations and a better large-scale environment are thought to be important factors for enhancing the predictability of warm-type heavy rainfall over the Korean peninsula in the humid East Asian summer environment.Abstract i Table of Contents iii Lists of Figures iv 1. Introduction １ 2. Satellite observation ８ 2.1. Data and method ８ 2.2. East Asia １３ 2.2.1. Heavy rainfall type classification １３ 2.2.2. Seasonal evolution ２３ 2.2.3. Diurnal cycle ２７ 2.2.4. Environmental conditions ３０ 2.3. Korea ３４ 2.3.1. Cold-type heavy rainfall event ３５ 2.3.2. Warm-type heavy rainfall event ４１ 2.3.3. Cloud pattern composite ４７ 2.3.4. Synoptic environment composite ５０ 2.4. Conclusions ６５ 2.5. Additional statistics ６８ 2.5.1. Seasonal evolution (+September) ６８ 2.5.2. Influence of typhoon ７１ 2.5.3. Tropical distribution ７４ 3. Numerical experiments ７７ 3.1. Idealized simulation ７７ 3.1.1. Model setup ７８ 3.1.2. Storm evolution ７９ 3.1.3. Effect of wind shear ９７ 3.2. Real case simulation １０４ 3.2.1. Methodology １０６ 3.2.2. Comparison result １１１ 3.2.3. Discussion １２３ 3.3. Case study １２７ 3.4. Conclusions １３６ References １３９ 국문초록 １５１ 감사의 글 １５３Docto

Interfacial Dirac Cones from Alternating Topological Invariant Superlattice Structures of Bi2Se3

When the three-dimensional topological insulators Bi2Se3 and Bi2Te3 have an interface with vacuum, i.e., a surface, they show remarkable features such as topologically protected and spin-momentum locked surface states. However, for practical applications, one often requires multiple interfaces or channels rather than a single surface. Here, for the first time, we show that an interfacial and ideal Dirac cone is realized by alternating band and topological insulators. The multichannel Dirac fermions from the superlattice structures open a new way for applications such as thermoelectric and spintronics devices. Indeed, utilizing the interfacial Dirac fermions, we also demonstrate the possible power factor improvement for thermoelectric applications.open282

New Candidates for Topological Insulators : Pb-based chalcogenide series

Here, we theoretically predict that the series of Pb-based layered chalcogenides, Pb$_n$Bi$_2$Se$_{n+3}$ and Pb$_n$Sb$_2$Te$_{n+3}$, are possible new candidates for topological insulators. As $n$ increases, the phase transition from a topological insulator to a band insulator is found to occur between $n=2$ and 3 for both series. Significantly, among the new topological insulators, we found a bulk band gap of 0.40eV in PbBi$_2$Se$_4$ which is one of the largest gap topological insulators, and that Pb$_2$Sb$_2$Te$_5$ is located in the immediate vicinity of the topological phase boundary, making its topological phase easily tunable by changing external parameters such as lattice constants. Due to the three-dimensional Dirac cone at the phase boundary, massless Dirac fermions also may be easily accessible in Pb$_2$Sb$_2$Te$_5$

Multiple Dirac fermions from a topological insulator and graphene superlattice

Graphene and three-dimensional topological insulators are well-known Dirac materials whose bulk and surface states are governed by Dirac equations. They not only show good transport properties but also carry various quanta related to the geometrical phase such as charge, spin, and valley Hall conductances. Therefore, it is a great challenge to combine the two Dirac materials together, realizing multiple Dirac fermions. By using first-principles density-functional-theory calculations, we demonstrate such a system built from topological insulator-band insulator-graphene superlattice structures. Hexagonal boron nitride is proposed as an ideal band-insulating material in gluing graphene and topological insulators, providing a good substrate for graphene and a sharp interface with a topological insulator. The power factors for p-type doping are largely enhanced due to the charge-conducting channels through multiple Dirac cones. The systems characterized by the coexistence of the topologically protected interfacial and graphene Dirac cones can pave the way for developing integrated devices for electronics, spintronics and valleytronics applications.open5

Dirac cone engineering in Bi2Se3 thin films

In spite of the clear surface-state Dirac cone features in bismuth-based three-dimensional strong topological insulator materials, the Dirac point known as the Kramers point and the topological transport regime are located near the bulk valence band maximum. As a result of a nonisolated Dirac point, the topological transport regime cannot be acquired and there possibly exist scattering channels between surface and bulk states as well. We show that an ideal and isolated Dirac cone is realized in a slab geometry made of Bi2Se3 with appropriate substitutions of surface Se atoms. As an extension of Dirac cone engineering, we also investigate Bi2Se3 ultrathin films with asymmetric or magnetic substitutions of the surface atoms, which can be linked to spintronics applications.open191

The Effects of Air Pollution on Mortality in South Korea

AbstractIt is well known that air pollution has the negative effect on human health. This study is dealt with the relationship between air pollutant level and standardized mortality between 2005 and 2013 in Korea. The standardized mortality are collected by the 251 administrative districts using KOSIS (Korean Statistical Information Service) and the air pollutant data collected from air pollutant monitoring sites. The statistical interpolation technique is adapted to solve the problem of spatial misalignment between air pollutant and administrative districts. In addition, SaTScan is used to detecting the high relatively risk area based on spatial and temporal characteristics. It can help determining other external factors to mortality