• Journal of electromagnetic engineering and science
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• 제6권1호
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• pp.53-61
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• 2006

In this paper, we present parametric studies for the optimum design of a hexagonal plate monopole antenna. The dependence of the antenna performance on various geometric parameters is investigated using a commercial electromagnetic software, from which an optimum design of a hexagonal plate monopole antenna is derived. Guidelines for determining initial parameter values are given. The diameter of the circular ground plane is minimized tlo 1/5 wavelength at the lowest operating frequency. The antenna impedance matching is controlled by adjusting the gap between the plate and the ground plane, the plate base width, and the base bevel angle. The antenna proposed in. this paper shows a reflection coefficient less than -10 dB and a $2.0{\sim}6.2$ dBi gain over $3{\sim}20$ GHz frequencies.

• 대한치과교정학회지
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• 제19권1호
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• pp.137-151
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• 1989

To help arrive at a more accurate diagnosis of anteroposterior apial base relationship on each individual case, it is important to compare the interpretation in the same population on a longitudinal basis. The author studied on the changes of the anteroposterior apical base relationship using serial lateral cephalometric roentgenograms of 15 boys and 27 girls aged from 6 to 13 years of Korean children. Following results were obtained 1. Norms of Korean boys and girls were established. 2. With ages, there was a gradual decrease of ANB, AXB angle, and there was a gradual increase of facial angle, A-B plane angle, APDI. 3. Wits appraisal does not change significantly with ages. 4. No significant differences were observed in the changes between male and female subjects for all absolute values between the ages of 6 years and 12 years, but significant differences were observed in ANB, AXB, A-B plane angle of the age of 13 years. No significant differences were observed in the changes between male and female subjects for all incremental values between the ages of 6 years and 13 years.

• Structural Engineering and Mechanics
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• 제44권5호
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• pp.663-680
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• 2012

Previous major earthquakes revealed that most damage of the buried segmented pipelines occurs at the joints of the pipelines. It has been proven that the differential motions between the pipe segments are one of the primary reasons that results in the damage (Zerva et al. 1986, O'Roueke and Liu 1999). This paper studies the combined influences of ground motion spatial variations and local soil conditions on the seismic responses of buried segmented pipelines. The heterogeneous soil deposits surrounding the pipelines are assumed resting on an elastic half-space (base rock). The spatially varying base rock motions are modelled by the filtered Tajimi-Kanai power spectral density function and an empirical coherency loss function. Local site amplification effect is derived based on the one-dimensional wave propagation theory by assuming the base rock motions consist of out-of-plane SH wave or combined in-plane P and SV waves propagating into the site with an assumed incident angle. The differential axial and lateral displacements between the pipeline segments are stochastically formulated in the frequency domain. The influences of ground motion spatial variations, local soil conditions, wave incident angle and stiffness of the joint are investigated in detail. Numerical results show that ground motion spatial variations and local soil conditions can significantly influence the differential displacements between the pipeline segments.

• Journal of Advanced Marine Engineering and Technology
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• 제10권1호
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• pp.65-73
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• 1986

Surface fatigue crack propagation tests by plane bending fatigue were conducted on the welding specimens of an aluminium alloy, A5083-0, having an edge through thickness notch to study the fatigue crack growth characteristics. Moreover, the experiments were performed in order to clarify the fatigue crack initiation and growth. The properties of fatigue crack growth were quantitatively inspected in welded metal, heat-affected zone and base metal of the welding specimens. The main results obtained are summarized as follows: 1. It is found that the hardness distributions of A5083-0 aluminium alloy weldments are quite different with those of steel material weldments, so that the hardness distribution becomes lower in the following order: base metal, heat-affected zone and weld metal. 2. It is observed that the grain size of this specimen weldment appears to be almost equal to the base metal, when TIC welding method is adopted. 3. In a surface fatigue crack initiation and growth, the fatigue crack does not begin by opening-closing mechanism until hardening is saturated at the crack tip. 4. The fatigue crack growth characteristics of A5083-0 alluminium alloy weldments can be concluded.$${\frac{da}{dn}}=C({\Delta}K)^n=3.8{\times}10^{-9}{({\frac}{1}{2}{\Delta}S_t{\sqrt{{\pi}a}})}^{2.4}$$

• 한국농공학회지
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• 제18권1호
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• pp.4071-4078
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• 1976

The authors analyzed the seepage by means of the following mathmatical solutions of the Laplace Equations on the given boundary conditions. The boundaries of the flow region are of two types i) impervious boundaries (${\Phi}$=constant), and ii) reservoir boundaries (${\Phi}$=constant). The corresponding w plane, bounding the flow region, is the rectangle in Fig. 8-a. As the z plane and w plane are both polygons, by means of the Schwarz-Christoffel transformation the flow region in each of these planes can be mapped con for mally onto the same half of an auxiliary t plane, there by yielding, say, the functions z=f1(t) and w=f2(t). Then, either by eliminating the variable t or by using t as a parameter, the function w=f(z) can be established.

• 한국초등수학교육학회지
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• 제15권3호
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• pp.509-531
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• 2011

이 연구는 현재와 같은 평면도형의 넓이 지도가 효과적인 방법인가를 알아보려는 것이다. 지금까지 학교에서 평면도형의 넓이를 지도할 때는 학생들이 실측하는 활동이 없다. 도형의 필요한 곳에 수치 정보가 주어져 있고 필요한 보조선이 그어져 있다. 이런 상황에서 학생들이 넓이를 구하는 과제에서 실제로 하는 것은 주어진 수치를 공식에 대입하여 계산하는 것 뿐이다. 이 연구는 그렇게 학습한 학생들은 올바른 넓이 측정 능력을 획득하지 못했다는 점을 밝히고, 어떤 방향으로 도형 넓이 지도가 개선되어야 할 것인지를 제안하고 있다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.135-137
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• 1995

A new design method is proposed for a fuzzy PD controller. By analyzing phase plane characteristics we can build and optimize the rule base of fuzzy logic controller. Also, a new gain tuning method is used to improve performance in the transient and steady state. The improved performance of the new methodology is shown by an application to the design of control system with a highly nonlinear actuator.

• Korean Journal of Mathematics
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• 제32권2호
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• pp.259-284
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• 2024

In present study, we introduce ruled surfaces whose base curve is the Salkowski curve in Euclidean 3-space and whose generating lines consist of the Frenet vectors of this curve (tangent, principal normal and binormal vectors). Then, we produce regular surfaces from a vector with real coefficients, which is a linear combination of these vectors, and we examine some special cases for these surfaces. Moreover, we present some geometric properties and graphics of all these surfaces.

• 한국항공우주학회지
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• 제40권9호
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• pp.737-744
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• 2012

유한체적법을 이용하여 설정된 가상의 노즐 조건에 따라 비행체 배기플룸의 SE와 PE에 의한 열복사 저부가열 해석 연구를 수행하였다. 저부면에서의 복사열유속을 얻기 위해 배기플룸은 흡수, 방사 및 산란하는 매질을 고려하였다. 저부면은 차가운 흑체이고 비회색가스와 입자의 복사 물성치는 회색가스가중합법(WSGGM)을 사용하였다. 후방 몬테카를로 방법을 사용한 기존의 연구와 비교하여 검증한 후, 입자의 농도, 온도, 그리고 등방성 또는 이방성 산란에 따른 복사저부가열을 해석하였다. 그 결과, 복사열유속은 노즐 출구와의 거리가 멀어지거나 비행 고도가 증가할수록 감소하고 입자의 온도가 높아질수록 복사열유속은 증가한다. 또한 전방산란은 PE를 증가시키고 후방산란은 SE를 증가시켰다.

• 대한수학회논문집
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• 제9권4호
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• pp.905-915
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• 1994

Let $M_g$ be the moduli space of isomorphism classes of genus g smooth curves. It is a quasi-projective variety of dimension 3g - 3, when $g > 2$. It is known that a complete subvariety of $M_g$ has dimension $< g-1 [D]$. In general it is not known whether this bound is rigid. For example, it is not known whether $M_4$ has a complete surface in it. But one knows that there is a complete curve through any given finite points [H]. Recently, an explicit example of a complete curve in moduli space is given in [G-H]. In [G-H] they constructed a complete curve of $M_3$ as an intersection of five hypersurfaces of the Satake compactification of $M_3$. One way to get a complete curve of $M_3$ is to find a complete one dimensional family $p : X \to B$ of plane quartics which gives a nontrivial morphism from the base space B to the moduli space $M_3$. This is because every non-hyperelliptic smooth curve of genus three can be realized as a nonsingular plane quartic and vice versa. This paper has come out from the effort to find such a complete family of plane quartics. Since nonsingular quartics form an affine space some fibers of p must be singular ones. In this paper, due to the semistable reduction theorem [M], we search singular plane quartics which can occur as singular fibers of the family above. We first list all distinct plane quartics in terms of singularities.