• 대한전기학회논문지:전력기술부문A
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• 제51권10호
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• pp.510-517
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• 2002

The use of underground transmission cables has continuously increased in densely inhabited urban and suburban area. Due to a increasing demand of underground cables, two or more circuits are installed in parallel for several kilometers. It, however, has not been realized that the sheath circulating current is generated in the system where a large number of cables are laid in the same route. In this paper, sheath circulating current is analyzed by the EMTP and compared with the measured values. Unbalance arrangement of cables or cross-bonding length causes a significant effect on the magnitude of the sheath current. Sheath circulating current could be greatly reduced by the symmetrical configuration of cables and installation of the impedance reduction system. Especially, with the impedance system of 1Ω installed, the sheath circulating current is reduced by 85.7%.

• Bulletin of the Korean Chemical Society
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• 제28권9호
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• pp.1463-1466
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• 2007

Single phases of multi-component oxides films, ZrTiO4 and Ta2Zr6O17, could be synthesized by using the combinatorial approach through surface sol-gel route, coating the appropriate mole ratio of 100 mM zirconium butoxide, tantalum butoxide and titanium butoxide precursors on Pt/Ti/SiO2/Si (100) substrate, following pyrolysis at 450 oC, and annealing them at 770 oC. Both the films and bulks of ZrTiO4 and Ta2Zr6O17 showed very stable dielectric properties in temperature range, ?140 to 60 oC, and frequency range, 100 Hz to 1 MHz, promising their applications in wide range of temperatures and frequencies. The dielectric constants of the films were lower and a little more dependent on frequency than those of the bulks. The reduction of dielectric property in the film was mainly due to the interfacial effects that worked as series and parallel-connected capacitances toward the substantial film capacitance.

• Bulletin of the Korean Chemical Society
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• 제9권5호
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• pp.298-303
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• 1988

Kinetic studies on cupric ion ($Cu^{2+}$) oxidation of 1-benzyl- and 1-aryl-1,4-dihydronicotinamides (XNAH) in aqueous solution were performed. In the presence of dioxygen ($O_2$), the reaction followed first order kinetics with respect to both XNAH and $Cu^{2+}$. The oxidation reaction was found to be independent and parallel to the acid-catalyzed hydration reaction of XNAH. The catalytic role of $Cu^{2+}$ for the oxidation of XNAH in the presence of $O_2$ was attributed to $Cu^{2+}/Cu^+$ redox cycle by the reactions with XNAH and $O_2$. The second order rate constants of the Cu2+ oxidation reaction kCu, and acid-catalyzed hydration reaction $k_H$ were strongly dependent on the nature of the substituents in 1-aryl moiety. The slopes of log $k_{Cu}$ vs log $K_H$ and log $k_{Cu}$ vs ${\sigma}_p$ of the substituents plots were 1.64 and -2.2, respectively. This revealed the greater sensitivity of the oxidation reaction rate to the electron density on the ring nitrogen than the hydration reaction rate. A concerted two-electron transfer route involving XNAH-$Cu^{2+}$ complex was proposed for mechanism of the oxidation reaction.

• 한국항공운항학회지
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• 제30권3호
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• pp.19-27
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• 2022

Urban Air Mobility is expected to resolve some problems in urban transportation such as traffic congestion and air pollution. Various studies for a large-scale commercialization of UAM are being actively conducted. To that end, the UAM Traffic Management system aims at securing a safety and an efficiency of UAM operations. In this study, a risk assessment model is proposed to evaluate the risk of collision between a vehicle and surrounding obstacles. The proposed model is conceived from the past studies for determining a proper separation distance between parallel runways for their independent operations. The model calculates the risk that the surveillance system fails to meet a target level of safety for a given buffer zone size between a designed route and surrounding obstacles. The model is applied to one of the routes proposed in K-UAM roadmap to evaluate its performances.

• 대한공간정보학회지
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• 제13권3호
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• pp.69-77
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• 2005

도로건설에 대한 환경영향평가제도는 대부분의 사업이 타당성조사와 병행하여 실시하지 않고 계획이 확정된 후 사업실시단계에서 주로 오염의 저감방안을 검토하고 있어 입지의 타당성 등 근본적인 친환경적인 개발의 유도에 한계가 있다. 본 연구에서는 9개의 사전환경성 검토요소에 대한 지리정보체계의 공간분석기능을 도입하였으며, 개별 요소들의 평가결과를 통한 종합적인 검토를 수행할 수 있도록 사전 환경성검토 GIS 의사결정시스템을 구축하였다. 본 연구에서 개발한 사전환경성 검토 GIS 의사결정시스템과 기 구축된 GIS 데이터 활용을 통해 환경성 검토에 객관성 충족 및 시간비용 절감이 기대되어 사업초기에 도로 노선선정 시 사전환경성 검토에 활용 가능할 것이다. 또한, 본 연구에서 개발된 시스템을 통하여 수치적이고 시각적인 자료를 활용한 평가로 주민의 합의를 보다 용이하게 이끌어 낼 수 있고, 사업초기에 비용과 시간을 절감하면서 도로건설에 따른 환경성을 검토할 수 있을 것으로 기대된다.

• 한국화재소방학회논문지
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• 제32권6호
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• pp.46-54
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• 2018

국내에서 피난용 엘리베이터가 구비되어 준공된 고층건축물은 서울시 송파구에 위치한 롯데월드타워로 총 19대의 피난용 엘리베이터가 설치되어 있다. 이 건물의 피난계획에 따르면 19대의 피난용 엘리베이터는 비상시 5개의 피난안전층으로부터 피난층(1층)까지 수동 키에 의한 조작으로 셔틀 운행하면서 피난자를 탑승시켜 피난시키도록 규정되어 있다. 따라서 화재 등의 재난발생시 피난용 엘리베이터를 이용한 피난시나리오가 기존의 보행만으로 피난하는 피난시리나리오보다 피난소요시간을 어느 정도 단축할 수 있는가를 분석할 필요가 있다. 롯데월드타워를 대상으로 피난용 엘리베이터에 의한 최적 수송분담률을 40%로 설정한 전관동시 엘리베이터병행 피난시나리오의 피난소요시간이 1 h 2 min으로 산출된 반면, 엘리베이터를 전혀 이용하지 않고 보행만으로 피난하는 전관동시 보행피난시나리오의 피난소요시간은 1 h 29 min으로 산출되었다. 결과적으로 엘리베이터를 병행하여 보행피난하는 경우가 엘리베이터에 의존하지 않은 상태에서 보행으로만 피난하는 경우보다 27 min 정도의 피난소요시간 단축효과가 있는 것으로 도출되었다. 이러한 단축효과를 지속적으로 유지하기 위해서는 엘리베이터를 이용한 피난경로를 이루는 각 부분이 피난이 이루어지는 동안 연기, 화염, 복사열 등의 화재 또는 재난에 기인하는 위험으로부터 피난자를 방호할 수 있는 성능을 갖추고, 엘리베이터 이용 피난자의 상주위치에서 최종피난장소까지의 피난경로가 단절 없이 이어지고 인식이 용이하도록 관리되어야 한다.

• 한국통신학회논문지
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• 제38C권4호
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• pp.371-377
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• 2013

5톤 이상의 어선에는 VHF(Very High Frequency) 대역의 DSC(Digital Selective Calling)가 어선법과 선박안전법에 의무화되어 있다. 어선의 무선설비 관련 규정에는 안전운항을 확보하고 해양사고 발생시 신속하게 대응하기 위하여 선박의 소유자는 국토해양부장관의 고시에 따라 어선위치 자동발신 장치를 갖추도록 규정하고 있다. 따라서 어업정보통신국은 2012년 동해를 시작으로 남해와 서해에 연차적으로 VHF 해안국을 설치하고, 웹기반으로 리모트 콘트롤 및 모니터링에 의하여 DSC를 원격으로 운용하는 연안 VMS(Vessel Monitoring System) 구축사업이 추진중에 있다. 모든 어선의 VHF DSC는 GPS와 연동되며 DSC의 호출에 의하여 자동으로 위치정보를 중계소에 전송하게 된다. 본 논문에서는 동해권의 VHF DSC 해안국을 대상으로 통신해역 설정과 운용 그리고 등록선박의 항해에 따른 권역별 로밍서비스를 실현하는 항적추적과 RSSI (Received Signal Strength Indication) 기법을 병행하는 알고리즘을 연구하였다.

• 한국경영과학회지
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• 제3권1호
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• pp.31-46
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• 1978

Consider a time interval during which the demand for trips is fixed (e.g. the rush hour period). The traveller has a choice between various public modes, whose travel times and fares are fixed, and the automobile mode, for which travel time and cost depend on the volume of traffic flow on those roads, which are subject to congestion. We consider the equilibrium in terms of a representative travellerm, who choses for any trip the mode and route with the least combined money and time cost. When several (parallel) model or routes are chosen, then the combined cost of money and time must be equal among these. Our problem is first, to find the optimal flows of cars and of public mode carriers on the various links of their networks and second the optimal fares for trips by the variousmodes. The object is to minimize the total operating costs of the carriers and car plus the total time costs to travellers. The optimal fares are related to, but not identical with the dual variables of the underlying Nonlinear Program. They are equal to these dual variables only in the case, when congestion tolls on trips or on the use of specific roads are collected from automobile users. When such tolls are not collected, they must be passed on as subsidies to travellers using competing modes. The optimal fares of public modes are then reduced by the amounts of these subsidies. Note that subsidies are not a flat payment to public carriers, but are calculated on the basis of tickets sold. Fares and subsidies depend in general on tile period considered. They will be higher during periods of higher demand. When the assumption of fixed trip demand is relaxed, this tare system is no longer best, but only second best since too much traffic will, in general, be generated. The Free Rider Theorem states the following : Suppose road tolls can be charged, so that a best pricing system for public modes is posssible. Then there may exist free rides on some routes and modes, but never on a complete round trip.

• 한국전기전자재료학회논문지
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• 제33권2호
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• pp.147-150
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• 2020

Relatively pure YBCO was first synthesized by heating a mixture of metal carbonates at temperatures between 1,000 and 1,300 K, resulting in the reaction: 4BaCO₃+Y₂(CO₃)₃+6CuCO₃+(1/2_-x)O₂ → 2YBa₂Cu₃O_7-x+1/3CO₂. Modern syntheses of YBCO use the corresponding oxides and nitrates. The superconducting properties of YBa₂Cu₃O_7-x are sensitive to the value of x, i.e., its oxygen content. Only those materials with 0≤x≤0.65 are superconducting below Tc, and when x ~ 0.07, the material superconducts at the highest temperature, i.e., 95 K, or in the highest magnetic fields, i.e., 120 T and 250 T when B is perpendicular and parallel to the CuO₂ planes, respectively. In addition to being sensitive to the stoichiometry of oxygen, the properties of YBCO are influenced by the crystallization methods applied. YBCO is a crystalline material, and the best superconductive properties are obtained when crystal grain boundaries are aligned by careful control of annealing and quenching temperature rates. However, these alternative methods still require careful sintering to produce a quality product. New possibilities have arisen since the discovery of trifluoroacetic acid, a source of fluorine that prevents the formation of undesired barium carbonate (BaCO₃). This route lowers the temperature necessary to obtain the correct phase at around 700℃. This, together with the lack of dependence on vacuum, makes this method a very promising way to achieve a scalable YBCO bulk.

• 한국초지조사료학회지
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• 제17권1호
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• pp.1-10
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• 1997

Unreduced (2n) gametes are meiotic products (pollen or egg) having a sporophytic (somatic) chromosome number, resulting from abnormalities during either microsporogenesis or megasporogenesis. They occur naturally at a low frequency in many plant species. Unreduced (2n) gametes in plants can be identified for four possible ways as follow i) pollen size and/or shape differences between haploid (n) and diploid (2n) pollen, ii) ploidy analysis (chromosome number) of progeny or meiotic analysis (presence of dyads andlor triads at the microspore stage), iii) progeny performance and fertility and iv) dosage of isozyme and DNA markers. Unreduced (2n) gametes can be an effective breeding tool in synthesizing new cultivars, providing a unique method to maximizing heterozygosity, i.e., transferring a large proportion of the non-additive genetic effects (intra- and inter- locus interactions) h m parent to offspring and can also be used to overcome infertility of interploidy crosses. Sexual polyploidization through 2n gametes has been a major route to the formation of naturally occurring polyploids. The three mechanisms of 2n pollen formation in potato have been discovered as follow: i) parallel spindles (ps) or tripolar spindles (ts), ii) premature cytokinesis (pc-I, pc-2) and iii) synaptic mutants (sy-2, sy-3, sy-4). Genetic analysis indicated that the mechanisms of 2n gamete formation were controlled by single recessive gene in potato, alfalfa, red clover, etc., and by two recessive genes in wheat. The use of 2n gametes which can efficiently transfer germplasm fiom wild relatives to cultivated species, especially fiom diploid to tetraploid could make a contribution to the improvement of germplasm base in breeding programs.