• Journal of Power Electronics
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• v.15 no.1
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• pp.190-201
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• 2015

This paper uses the switching function approach to present a simple state model of the Vienna-type rectifier. The approach introduces the relationship between the DC-link neutral point voltage and the AC side phase currents. A novel direct power control (DPC) strategy, which is based on the sliding mode control (SMC) for Vienna I rectifiers, is developed using the proposed power model in the stationary ${\alpha}-{\beta}$ reference frames. The SMC-based DPC methodology directly regulates instantaneous active and reactive powers without transforming to a synchronous rotating coordinate reference frame or a tracking phase angle of grid voltage. Moreover, the required rectifier control voltages are directly calculated by utilizing the non-linear SMC scheme. Theoretically, active and reactive power flows are controlled without ripple or cross coupling. Furthermore, the fixed-switching frequency is obtained by employing the simplified space vector modulation (SVM). SVM solves the complicated designing problem of the AC harmonic filter. The simplified SVM is based on the simplification of the space vector diagram of a three-level converter into that of a two-level converter. The dwelling time calculation and switching sequence selection are easily implemented like those in the conventional two-level rectifier. Replacing the current control loops with power control loops simplifies the system design and enhances the transient performance. The simulation models in MATLAB/Simulink and the digital signal processor-controlled 1.5 kW Vienna-type rectifier are used to verify the fast responses and robustness of the proposed control scheme.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1538-1540
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• 2003

The composites were fabricated respectively 61vol.% ${\beta}$-SiC and 39vol.% $TiB_2$ spray-dried powders with the liquid forming additives of 12wt% $Al_2O_3+Y_2O_3$ by pressureless annealing at $1700^{\circ}C,\;1750^{\circ}C\;1800^{\circ}C$ for 4 hours. The result of phase analysis of composites by XRD revealed ${\alpha}$-SiC(6H), $TiB_2$, and YAG($Al_5Y_3O_{12}$) crystal phase. The relative density, the Young's modulus and fracture toughness showed respectively the highest value of 92.97%, 92.88Gpa and $4.4Mpa{\cdot}m^{1/2}$ for composites by pressureless annealing temperature $1700^{\circ}C$ at room temperature. The electrical resistivity showed the lowest value of $8.09{\times}10^{-3}{\Omega}{\cdot}cm$ for composite by pressureless annealing tempe rature $1700^{\circ}C$ at $25^{\circ}C$. The electrical resistivity of the SiC-$TiB_2$ composites was all positive temperature cofficient resistance (PTCR) in the temperature ranges from $25^{\circ}C$ to $700^{\circ}C$.

• Journal of Surface Science and Engineering
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• v.34 no.2
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• pp.89-96
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• 2001

N- or O-doped STS304 stainless films were synthesized by an unbalanced magnetron sputtering process with various argon and reactive gas ($N_2$, $O_2$) mixtures. These films were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), Auger electron spectroscopy (AES) and Knoop microhardness tester. The Results from X-ray diffraction (XRD) analysis showed that a STS304 stainless steel film synthesized without reactive gas using a bulk STS304 stainless steel target had a ferrite bcc structure ($\alpha$ phase), while the N-doped STS304 stainless film was consisted of a nitrogen supersaturated fcc structure, which hsa a strong ${\gamma}$(200) phase. In the O-doped films, oxide Phases ($Fe_2$$O_3$ and $Cr_2$$O_3$) were observed from the films synthesized under an excess $O_2$ flow rate of 9sccm. AES analysis showed that nitrogen content in N-doped films increased as the nitrogen flow rate increased. Approximately 43 at.%N in the N-doped film was measured using a nitrogen flow rate of 8sccm. In O-doped film, approximately 15 at.%O was detected using a $O_2$ flow rate of 12sccm. the Knoop microhardness value of N-doped film using a nitrogen flow rate of 8 sccm was measured to be approximately $H_{ k}$ 1200 and this high value could be attributed to the fine grain size and increased residual stress in the N-doped film.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.839-842
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• 2000

The mechanical and electrical properties of the hot-pressed and annealed $\beta$-SiC-ZrB$_2$ electroconductive ceramic composites were investigated as function of the liquid forming additives of $Al_2$O$_3$+Y$_2$O$_3$. Phase analysis of composites by XRD revelled $\alpha$ -SiC(6H), ZrB$_2$, and YAG(Al$_{5}$ Y$_3$O$_{12}$ ). Owing to crack deflection, crack bridging, phase transition and YAG of fracture toughness mechanism, the fracture toughness showed the highest value of 6.3MPa.m$^{1}$2/ for composites added with 24wt% $Al_2$O$_3$+Y$_2$O$_3$additives at room temperature. The resistance temperature coefficient respectively showed the value of 2.46$\times$10$^{-3}$ , 2.47$\times$10$^{-3}$ , 2.52$\times$ 10$^{-3}$ $^{\circ}C$ for composite added with 16, 20, 24wt% A1$_2$O$_3$+Y$_2$O$_3$additives. The electircal resistivity of the composites was all positive temperature coefficient resistance(PTCR) in the temperature range of $25^{\circ}C$ to 90$0^{\circ}C$.

• Korean Journal of Food Science and Technology
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• v.34 no.6
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• pp.1085-1090
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• 2002

Leuconostoc mesenteroides, the major bacterium in the initial phase of lactate-fermentation in kimchi, produces lactic acid, acetic acid, mannitol, and $CO_2$. It also secrets dextransucrase, which catalyzes the transfer reaction of glucose from sucrose to maltose, synthesizing mainly panose ($6^_2-{\alpha}-D-glucopyranosylmaltose)$, a probiotic oligosaccharide. To use the strain as a starer culture to produce high amount of panose during kimchi fermentation, we screened psychrotrophic strains showing fast growth rate at low temperature among the isolates of Leuconostoc sp. and selected two strains showing high dextransucrase activity. The strains were identified as Leuconostoc mesenteroides, which can be used as function added-starters for lactate-fermented foods.

• Korean Journal of Metals and Materials
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• v.50 no.11
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• pp.829-838
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• 2012

The microstructure, chemical composition, and lead isotope ratio of the Buddhist bell of Yongmoon Mountain Sangwonsa temple, which was selected as one of the three great bells of Korea by Japanese historians, were analyzed in order to estimate the origin of the material and the time of casting. The microstructure of the temple bell was composed of a copper matrix phase with ${\alpha}$, a face centered cubit lattice structure, a ${\delta}$ phase with $Cu_{41}$ $(Sn,Ag,Sb)_{11}$ as the chemical structural formula, dispersed lead and $Cu_2S$ particles, and locally agglomerated fine particles. Through analysis of the chemical composition of the bell, a criterion (Pb: 0-3.0 wt%, Sn: 10-15 wt%) for distinguishing the bells of the Shilla dynasty from the bells of the Koryo Chosun dynasty is proposed. Examining the lead isotope ratio of $^{207}Pb/^{206}Pb$ and $^{208}Pb/^{206}Pb$ of the Buddhist bell of Sangwonsa temple proved that the bell was fabricated using raw materials in South Korea, which led to the conclusion that the bell was cast in Korea and the top board of the bell has been damaged by an unknown individual. The criteria of distinguishing the bells from the Shilla dynasty from the bells of the Koryo Chosun dynasty presented for the first time in this research is expected to aid in identifying and estimating the previously unclear production years of other bells.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.4
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• pp.276-280
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• 2019

In this study, we investigated the crystal defects and grain boundary properties in a ZZCCC ($ZnO-Zn_2BiVO_6-Co_3O_4-Cr_2O_3-CaCO_3$) varistor, with the liquid-phase sintering aid $Zn_2BiVO_6$ developed by our laboratory. The ZZCCC varistor sintered at $1,200^{\circ}C$ exhibited excellent nonlinear current-voltage characteristics (${\alpha}=63$), with oxygen vacancy ($V_o^*$ ; 0.35 eV) as a main defect, and an apparent activation energy of 1.1 eV with an electrically single grain boundary. Therefore, among the various additives to improve the electrical properties of ZnO varistors, if $Zn_2BiVO_6$ is used as a liquid phase sintering aid, it will be ideal to use Co for the oxygen vacancy and Ca for the electrically single grain boundary. This will allow the good properties of ZnO varistors to be maintained up to high sintering temperatures.

• Korean Journal of Metals and Materials
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• v.49 no.4
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• pp.313-320
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• 2011

100 nm-thick hydrogenated amorphous silicon $({\alpha}-Si:H)$ films were deposited on a glass and glass/30 nm Ni substrates by inductively-coupled plasma chemical vapor deposition (ICP-CVD) at temperatures ranging from 100 to $550^{\circ}C$. The sheet resistance, microstructure, phase transformation and surface roughness of the films were characterized using a four-point probe, AFM (atomic force microscope), TEM (transmission electron microscope), AES (Auger electron spectroscopy), HR-XRD(high resolution X-ray diffraction), and micro-Raman spectroscopy. A nano-thick NiSi phase was formed at substrate temperatures >$400^{\circ}C$. AFM confirmed that the surface roughness did not change as the substrate temperature increased, but it increased abruptly to 6.6 nm above $400^{\circ}C$ on the glass/30 nm Ni substrates. HR-XRD and micro-Raman spectroscopy showed that all the Si samples were amorphous on the glass substrates, whereas crystalline silicon appeared at $550^{\circ}C$ on the glass/30 nm Ni substrates. These results show that crystalline NiSi and Si can be prepared simultaneously on Ni-inserted substrates.

• Korean Journal of Metals and Materials
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• v.46 no.12
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• pp.780-787
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• 2008

For the advanced high strength steels (AHSS), high-manganese TWIP (twinning induced plasticity) steels exhibit high tensile strength (800-1000 MPa) and high elongation (50-60%). However, the TWIP steels need to be understood of delayed fracture following the cup drawing test. Among the factors to cause delayed fracture, i.e, martensite transformation, hydrogen embrittlement and residual stress, the effects of martensite transformation (${\gamma}{\rightarrow}{\varepsilon}$ or ${\gamma}{\rightarrow}{\alpha}^{\prime}$) were investigated on the delayed fracture phenomenon. Microstructural phase analysis was conducted for cold rolled (20, 60, 80% reduction ratio) steels and tensile deformed (20, 40, 60% strain) steels. For the Al-added TWIP steels, no martensite phase was found in the cold rolled and tensile deformed specimen. But, the TWIP steels with no Al addition indicated the martensite transformation. The cup drawing specimens showed the martensite transformation irrespective of the Al-addition to the TWIP steel. However, the TWIP steel with no Al exhibited the larger amount of martensite than the case of the TWIP steel with Al addition. For the reason, it was possible to conclude that the Al addition suppressed the martensite transformation in TWIP steels, therefore preventing the delayed fracture effectively. However, it was interesting to note that the mechanism of delayed fracture should be incorporated with hydrogen embrittlement and/or residual stress as well as the martensite transformation.

• The Journal of the Convergence on Culture Technology
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• v.7 no.2
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• pp.157-163
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• 2021

This study attempted to find individual reasons for inducing cybercrime. The survey was conducted targeting investigators and security experts on 11 types of cybercrime. There are 16 internal factors that cause crime and classified according to Maslow's 5 steps. As a result of the survey on a total of 176 items, the credibility of the Cronbach's Alpha coefficient was 0.925. The result of the factor analysis is as follows. Factor analysis results are maslow phase 1 physiological desire is commercial, sykes. Phase 2 safety desires are not punishable and crowd. The three-stage social desire is impulsiveness, indifference, etc. The fourth stage of respect is anonymity and honor. The desire for self-reality in stage 5 has been reduced to indesity, a loss of moderation, morality, and media effects. In conclusion, the physiological desire, the desire for respect for the crime of infringing on the information and communication network, the desire for menstruation, the desire for self-realization for the crime of using information and communication networks, the desire for self-actualization for the crime of illegal content. It was in the order of desire.