• 한국인터넷방송통신학회논문지
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• 제9권1호
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• pp.103-107
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• 2009

본 논문은 WLAN(Wireless Local Area Network)용 이중대역 칩 안테나를 설계 제작하였고, 외장형 AP(Access Point) 안테나와 달리 작은 LAN카드에 내장된다. 안테나의 사이즈에 제한이 있으므로 가능한 유전율이 높은 유전체를 이용하였으며, 수급의 문제, 가격의 문제, 특성의 문제 등을 종합적으로 고려했을 때, 세라믹의 상대 유전율은 9.8, 두께는 3.5mm와 5mm를 사용하였다. 설계 제작된 세라믹 안테나는 IEEE 802.11.a,g 그리고 b까지 트리플 모드로 사용할 수 있을 뿐 아니라 광대역에서 사용할 수 있다. 사용가능한 주파수 밴드는 2.4~2.5GHz & 4.9~5.85GHz의 광대역 특성을 가지며, 전 주파수 대역에서 비교적 일정한 성능을 갖는다.

• Bulletin of the Korean Chemical Society
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• 제32권4호
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• pp.1138-1142
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• 2011

Kinetic studies for the reactions of Y-aryl phenyl chlorothiophosphates with X-pyridines have been carried out in acetonitrile at $35.0^{\circ}C$. The Hammett and Bronsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = 3-Ph, while the Hammett plots for substituent Y variations in the substrates are biphasic concave downwards (and partially upwards) with a break point at Y = H. The signs and magnitudes of the cross-interaction constant (${\rho}_{XY}$) are strongly dependent upon the nature of substituents, X and Y. The proposed mechanism is a stepwise process with a rate-limiting step change from bond breaking with the weaker electrophiles to bond formation with the stronger eletrophiles. The nonlinear free energy correlations of biphasic concave upward plots for substituent X variations in the nucleophiles are rationalized by a change in the attacking direction of the nucleophile from a backside with less basic pyridines to a frontside attack with more basic pyridines.

• 전기학회논문지
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• 제67권7호
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• pp.981-986
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• 2018

AC(alternating current) CB(circuit breaker) at the fault occurred in the existing AC distribution system is limiting the fault current through zero cross-point. However, DC(direct current) CB does not have zero cross-point. Therefore, arc occurred by on-off operation of DC CB is very huge. Nowadays, many research team are studying the way to decrease breaking time, which is one of the essential conditions in DC CB. We suggested novel arc-induction type DC CB in this paper. The proposed arc-induction type DC CB is composed of the mechanical Arc ring and DC CB. We confirmed the operation of arc-induction type DC CB through the HFSS(High Frequency Structure Simulator) 3D simulation program and performed the experiment for operation characteristics. Results showed that arcing time of the arc-induction type DC CB by using induction ring was faster than existing mechanical DC CB. On the transient system, we confirmed stable operation characteristics of the arc-induction type DC CB through the simulation and experimental results. We expect that the proposed arc-induction type DC CB technology is will go to stay ahead of the existing DC CB technology.

• Journal of Power Electronics
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• 제16권4호
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• pp.1306-1315
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• 2016

Modern power systems driven by high-power converters have become inevitable in view of the ever increasing demand for electric power. The total power loss can be reduced by limiting the switching losses in such power converters; increased power efficiency can thus be achieved. A reduced switching frequency that is less than a few hundreds of hertz is applied to power converters that produce output waveforms with high distortion. Selective harmonic elimination pulse width modulation (SHEPWM) is an optimized low switching frequency pulse width modulation method that is based on offline estimation. This method can pre-program the harmonic profile of the output waveform over a range of modulation indices to eliminate low-order harmonics. In this paper, a SHEPWM scheme for three-phase three-leg neutral point clamped inverter is proposed. Aside from eliminating the selected harmonics, the DC capacitor voltages at the DC bus are also balanced because of the symmetrical pulse pattern over a quarter cycle of the period. The technique utilized in the estimation of switching angles involves the firefly algorithm (FA). Compared with other techniques, FA is more robust and entails less computation time. Simulation in the MATLAB/SIMULINK environment and experimental verification in the very large scale integration platform with Spartan 6A DSP are performed to prove the validity of the proposed technique.

• 한국산업융합학회 논문집
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• 제23권2_2호
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• pp.289-299
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• 2020

The composition of convergence cross-section of the material is a technique that provides reasonable design and construction of structures. It is frequently used in medium-sized bridges and architectural structures. However, the structural behavioral spare capacity enhancement of the structure by the application of the convergence cross-section is still limited by the expandability due to the limiting state of each material. In order to overcome these limitations, this study reasonably analyzed the construction stages before and after the convergence cross-section constructed and developed a technique for forming multi-point boundary conditions using struts, which are compression members. Based on the existing cases, a reasonable construction step for forming the material composite section of the entire structural system of the structure was derived, and a numerical analysis model for a specific part was constructed to analyze the behavior of the strut application. As a result of this study, the effect of reducing the sectional force of 7.40% in beam-column joint and 6.31% in the center of girder was derived, and the deflection, which is a measure of the serviceability of the structure, improved by 54.41% from the installation and dismantling of strut members at each construction stage.

• 한국경영과학회지
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• 제42권1호
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• pp.19-28
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• 2017

Moments of stationary intervals and those of the counting process can be used for moment fittings of the point processes. As for the Markovian arrival processes, the moments of stationary intervals are given as a polynomial function of parameters whereas the moments of the counting process involve exponential terms. Therefore, moment fittings are more complicated with the counting process than with stationary intervals. However, in queueing network analysis, cross-correlation between point processes can be modeled more conveniently with counting processes than with stationary intervals. A Laplace-Stieltjies transform of the stationary intervals of MAP (3)s is recently proposed in minimal number of parameters. We extend the results and present the Laplace transform of the counting process of MAP (3)s. We also show how moments of the counting process such as index of dispersions for counts, IDC, and limiting IDC can be used for moment fittings. Examples of exact MAP (3) moment fittings are also presented on the basis of moments of stationary intervals and those of the counting process.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 추계학술대회 논문집 학회본부
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• pp.210-213
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• 1988

A new and accurate expression to derive a window area is presented with a sequence for daylighting design using Daylight Factor Method process not in its classical point--by-point method but in lumen method as in artificial lighting design process to consider daylight in the early stage of a building design process. Accepting CIE Overcast Sky as the worst state with the lowest sky luminance, a user of a room can have more available daylight in his or her room. In the design process uniformity is checked to ensure reasonably even daylighting by comparing the depth of the room with the computed limiting depth. After these steps the shape and position of window is altered, of which the Sky Component of Daylight Factor under an Overcast Sky, SCo, is investigated and computed in Composite Simpson Multiple Integral so that a building designer or an analyst can choose the best shape and location that satisfies his/her taste and purpose of the room.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2015년도 제46회 하계학술대회
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• pp.331-332
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• 2015

Since $20^{th}$ century, along with the rapid industrial advancement, the concentrated urban development in specific large cities have made people migrate to those cities, thus causing problems in the power system stability. In case of Korea, more than 40% of the power system demand comes from the consumers in Seoul Metropolitan area and the rate is expected to increase. With the continuous increase of power demand, in order to meet the demand for system reliability improvement, the power system was multi-looped for reliability enhancement, the problem of fault current happened. In this situation, there are several methods for fault current reduction likes current limiting reactor, replacing circuit breaker, splitting busses, etc. But these methods reached its limit, power system needs more fundamental solutions such as grid segmentation. In this paper, we assume grid segmentation already has been progressed using VSC BTB HVDC. Then, this paper discusses operating point of HVDC in metropolitan area considering loss minimization and handy flow control. The simulation is proceeded on 2027 KEPCO system.

• 한국시스템다이내믹스연구
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• 제12권1호
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• pp.131-153
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• 2011

The purpose of this study is to explore the applicability of the causal maps for estimating creativity. This study assumes that fluency, flexibility, originality and elaboration are elements of creativity; and there are common characteristics between systems and creative thinking. For this study, 30 students from the 5th grade create causal maps which are consisted of the contents of 'the water cycle in the earth'. The causal maps are analyzed and evaluated by focusing on the characteristics of creativity. In way of the marking causal maps based on creativity, each word is scored as 1 point on the basis of 30 points for fluency. Each word which is linked more than one word is scored 3 points for flexibility, but the maximum points are limited as 35 points. In originality, if it is approved each word is worthy as well as originality, it is scored as 10 points on the basis of 40 points. Lastly, each number of cycle loops is scored as 15 points for elaboration, and the maximum scores are limited as 45 points. As is stated above, the limiting of the maximum scores are designed based on corresponded to 10% students of participators. In the result of this study, the students' scores of evaluating creativity applied causal maps show similar patterns from relative point of view to the other results which were evaluated the creativity by credible organ. Consequently, it is recognized that the causal maps have the possibility of being able to estimate quantitatively the creativity.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1522-1539
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• 2002

In the present study, an explicit algebraic stress model is shown to be the exact tensor representation of algebraic stress model by directly solving a set of algebraic equations without resort to tensor representation theory. This repeals the constraints on the Reynolds stress, which are based on the principle of material frame indifference and positive semi-definiteness. An a priori test of the explicit algebraic stress model is carried out by using the DNS database for a fully developed channel flow at Rer = 135. It is confirmed that two-point correlation function between the velocity fluctuation and the Laplacians of the pressure-gradient i s anisotropic and asymmetric in the wall-normal direction. Thus, a novel composite algebraic Reynolds stress model is proposed and applied to the channel flow calculation, which incorporates non-local effect in the algebraic framework to predict near-wall behavior correctly.