• Journal of the Institute of Electronics Engineers of Korea SD
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• v.48 no.12
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• pp.8-14
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• 2011

The optimal geometry of the gate field plate in AlGaN/GaN-on-Si HEMT has been proposed using two-dimensional device simulation to achieve a high breakdown voltage for a given gate-to-drain distance. It was found that the breakdown voltage was drastically enhanced due to the reduced electric field at the gate corner when a gate field plate was employed. The electric field distribution at the gate corner and the field plate edge was investigated as functions of field plate length and insulator thickness. According to the simulation results, the electric field at the gate corner can be successfully reduced even with the field plate length of 1 ${\mu}m$. On the other hand, when the field plate length is too long, the distance between field plate and drain electrode is reduced below a critical level, which eventually lowers the breakdown voltage. The highest breakdown voltage was achieved with the field plate length of 1 ${\mu}m$. According to the simulation results varying the $SiN_x$ film thickness for the fixed field plate length of 1 ${\mu}m$, the optimum thickness range of the $SiN_x$ film was 200 - 300 nm where the electric field strength at the field plate edge counterbalances that of the gate corner.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.64-69
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• 2006

Cathode materials of Al-doped $Li(Ni_{1/3}Co_{1/3}Mn_{1/3-x}Al_x)O_2$ (x=0.0, 0.005, 0.01 0.05) for lithium ion batteries were synthesized with ultra-sonic spray pyrolysis method and single-step heat treatment. No secondary phases were found in all synthesized powders. The intensity ratio of $I_{003}\;to\;I_{104}$, however, slightly decreased and the particle size increased with the Al contents. The cells with bare, 0.5 and 1.0 at% Al-doped powders showed the initial discharge capacities of 182, 180 and $184mAhg^{-1}$ in a voltage range of $3.0\sim4.5V$ at 1C rate, and the capacity retentions of 81, 77 and 78% at the end of 30 cycles, respectively. But in the voltage range of $3.0\sim4.6V$, the Al-doping significantly enhanced the cycle stability. For example, the discharge capacity after 50 cycles was maintained to 70% in the 0.5 at% Al-doped sample compared to only 30% in no doped sample. The improvement of the cycle stability was thought to be due to $Mn^{3+}$ ion decrease as the Al doping from the XPS analysis results.

• Clean Technology
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• v.20 no.4
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• pp.433-438
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• 2014

There is an increasing interest in the development of rechargeable batteries suitable for use in both hybrid electric vehicles and energy storage systems that require higher charge & discharge rates, bigger battery sizes and increased safety of the batteries. Spinel-type lithium titanium oxide ($Li_4Ti_5O_{12}$) as a potential anode for lithium ion batteries has many advantages. It is a zero-strain materials and it experiences no structural change during the charge/discharge precess. Thus, it has long cycle life due to its structural integrity. It also offers a stable operation voltage of approximately 1.55 V versus $Li^+/Li$, above the reduction potential of most organic electrolyte. In this study, Ru added $Li_4Ti_5O_{12}$ composites were synthesized by solid state process. The characteristics of active material were investigated with TGA-DTA, XRD, SEM and charge/discharge test. The capacity was reduced when Ru was added, however, the polarization decreased. The capacity rate of $Li_4Ti_5O_{12}$ with Ru (3%, 4%) addition was reduced during the charge/discharge precess with 10 C-rate as a high current density.

• Journal of Life Science
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• v.21 no.1
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• pp.96-101
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• 2011

S-Adenosyl-L-methionine synthtase (SAM-s) catalyzes the biosynthesis of SAM from ATP and L-methionine. SAM plays important roles in the primary and secondary metabolism of cells. A metK encoding a SAM-s was searched from Streptomyces natalensis producing natamycin, a predominantly a strong antifungal agent, inhibiting the growth of both yeasts and molds and preventing the formation of aflatoxin in filamentous fungi. To obtain the metK of S. natalensis, PCR using primers designed from the two highly conserved regions for metK genes of Streptomyces strains was carried out, and an intact 1.2-kb metK gene of S. natalensis was cloned by genomic Southern hybridization with PCR product as a probe. To identify the function of the cloned metK gene, it was inserted into pSET152ET for its high expression in the Streptomyces strain, and then introduced into S. lividans TK24 as a host by transconjugation using E. coli ET12567(pUZ8002). The high expression of metK in S. lividans TK24 induced actinorhodin production on R5 solid medium, and its amount in R4 liquid medium was 10-fold higher than that by exconjugant including only pSET152ET.

• Journal of the Microelectronics and Packaging Society
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• v.24 no.2
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• pp.49-53
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• 2017

We study on the change of electrical properties of two-dimensional (2D) $SnSe_2$ materials with respect to Cl doping as $SnSe_{1.994}Cl_{0.006}$ under a high temperature condition. (300~450 K) By the simple solid-state reaction method, non-and Cl-doped 2D $SnSe_2$ materials are successfully synthesized with negligible impurities as confirmed by X-ray diffraction. From the temperature dependence of resistivity, it is observed that the conduction mechanism is changed from hopping to degenerate conduction with Cl doping. By Hall effect measurement, an increase on electron carrier concentration from ${\sim}7{\times}10^{16}$ to ${\sim}3{\times}10^{18}cm^{-3}$ with Cl doping verifies that Cl is an effective electron donor which results in the encouraged carrier concentration. Detailed analysis for temperature dependent Hall mobility reveals that the electrical transports in high temperature regime are governed by the grain boundary-controlled mechanism for non-doped $SnSe_2$, which is effectively suppressed by Cl-doping as entering metallic transport regime.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.7
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• pp.1546-1553
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• 2015

In cognitive radio technology, the overall capacity of communications systems can be improved without allocating additional bands by allowing secondary system to utilize the band when a primary system who has right to use the band does not utilize it. Therefore, spectrum sensing to determine the existence of primary system is utmost important in the cognitive radio technology. In this work, we consider a novel cooperative spectrum sensing in cognitive cellular systems. Especially, we consider the case in which heterogeneous primary systems coexist, i.e., heterogenous transmission power and sensing requirement of primary system, such that only portion of users in cognitive cellular systems are able to detect the primary system. In this case, we propose new cooperative spectrum sensing with multiple sensing stages to properly detect the existence of primary systems in this kind of situations. Moreover, we analyze the performance of conventional cooperative spectrum sensing schemes such as OR-rule, AND-rule and MAJORITY-rule under the existence of heterogeneous primary systems. Finally, we investigate the performance of the proposed scheme through computer based simulations and show that the existence of primary systems can be determined accurately by using our proposed scheme.

• The Korean Journal of Applied Statistics
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• v.26 no.2
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• pp.335-347
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• 2013

There are various types of real world signals. For example, an electrocardiogram(ECG) represents myocardium activities (contraction and relaxation) according to the beating of the heart. ECG can be expressed as the fluctuation of ampere ratings over time. A signal is a composite of various types of signals. An orchestra (which boasts a beautiful melody) consists of a variety of instruments with a unique frequency; subsequently, each sound is combined to form a perfect harmony. Various research on how to to decompose mixed stationary signals have been conducted. In the case of non-stationary signals, there is a limitation to use methodologies for stationary signals. Huang et al. (1998) proposed empirical mode decomposition(EMD) to deal with non-stationarity. EMD provides a data-driven approach to decompose a signal into intrinsic mode functions according to local oscillation through the identification of local extrema. However, due to the repeating process in the construction of envelopes, EMD algorithm is not efficient and not robust to a noise, and its computational complexity tends to increase as the size of a signal grows. In this research, we propose a new method to extract a local oscillation embedded in a signal by utilizing the second derivative.

• The Korean Journal of Petroleum Geology
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• v.2 no.2 s.3
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• pp.83-90
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• 1994

Thermal maturation and diagenesis of the Gyeongsang Supergroup in the Euiseong area are studied by means of organic geochemical techniques and illite crystallinity. Black mudrocks of the Singdong Group contain organic matter of $0.5{\~}2{\%}$ derived from higher plants, being compared to type Ⅲ. Thermal maturity of organic matter reached dry gas generation phase. Tmax by Rock Eval pyrolysis varies between $578^{\circ}C$ and $593^{\circ}C$ regardless of stratigraphic position and localities, and vitrinite reflectance is about 2.9 and $3{\~}4{\%}Ro$ in the Jinju and the Nagdong Formations, respectively. Vitrinite reflectance measurements indicate that the maturation is mainly due to burial and partly to be affected by post-depositional intrusions. Illite crystallinity values from the Nagdong, Hasandong, Jiniu Formations and part of the Iljig Formation are plotted around the boundary between diagenesis and anchizone, indicating dry gas generation stage. However, the values are not dependent on stratigraphic position. The values from the Iljig, Hupyeongdong, Geomgog, and Sagog Formations fall into the range of anchizone, probably resulted from the post-depositional intrusions which occur locally. Both organic geochemical and illite crystallinity data indicate thermal maturation stage of dry gas generation. Diagenesis of the Gyeongsang strata is mostly controlled by burial, and partly affected by post-depositional intrusions. Paleotemperature of the Sindong Group is estimated at around $200^{\circ}C$ on the basis of illite crystallinity.

• Journal of health informatics and statistics
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• v.43 no.4
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• pp.245-254
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• 2018

Objectives: This paper examines how serious the appearance concerns of adolescents is in South Korean society by delving into the formation and changes of adolescents' appearance concerns. Methods: We conducted a secondary analysis of the data of multi-year tracing surveys which the National Youth Policy Institute opened to the public. The repeated Measures ANOVA, the paired t-test, and a chi-squared test were applied against the data. Results: It was found that about one out of ten adolescents experienced concerns that began as early as the upper grades of elementary school, reached its peak in middle school, and decreased afterwards. On the other hand, some of them faced enduring appearance concerns and seemed to suffer from it. One interesting finding is that adolescents once relieved from the concerns were free from it permanently. We also found that there were considerable differences between male and female adolescents in terms of the level of concerns they experienced, their peak periods, and other characteristics. Conclusions: Appearance concerns changes dynamically according to development of adolescence. Appearance concerns was less prevalent among adolescents than predicted, and it seemed considerably fluid. Our study not only confirms but also challenges some important findings of previous studies.

• Journal of Convergence for Information Technology
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• v.11 no.9
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• pp.109-114
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• 2021

Cr(VI)-quinoline compound[(C₉H₇NH)₂Cr₂O₇] was synthesized by the reaction between of quinoline and chromium(VI) trioxide, and structure was FT-IR, elemental analysis. The oxidation ability of benzyl alcohol greatly depends upon the dielectric constant of the used organic solvent, where carbon tetrachloride was worst and N,N'-dimethylformamide was best solvent. Noticeably, in N,N'-dimethylformamide solvent, Cr(VI)-quinoline compound oxidized substituted benzyl alcohols. The Hammett reaction constant(ρ)=-0.69(303K). As a resuit, Cr(VI)-quinoline compound was found as efficicent oxidizing agent that converted benzyl alcohol, allyl alcohol, primary alcohol and secondary alcohols to the corresponding aldehydes or ketones. Cr(VI)-quinoline compound was selective oxidizing agent of benzyl alcohol, allyl alcohol and primary alcohol in the presence of secondary alcohol ones.