• 한국인터넷방송통신학회논문지
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• 제16권6호
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• pp.319-327
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• 2016

본 논문에서는 나무나 염소 뿔처럼 대부분의 동식물이 대칭임을 살펴본다. 또한 DNA를 가지고 있는 인간의 신체 역시 대칭이다. 피보나치수열, 식물의 나선, 동물의 대수 나선에서 볼 수 있는 것은 대칭이다. 해바라기 꽃은 원형이다. 원(元)은 원점을 중심으로 회전을 해도 모양이 꼭 같으므로 회전대칭이다. 공간상의 회전변환을 넘어서, 시간 공간의 대칭적 변환으로 일반화하면 아인슈타인의 특수상대성 이론이 시공간 변환관계이다. 동식물의 나선은 좌우 나선들이 대칭을 이루며 그 속에는 element-wise inverse가 존재한다. Hadamard 행렬 중 가운데 하중 값을 2로 준 것은 자연대수의 밑 2와 같고, 나선 행렬은 Symmetric하며 역행렬은 element-wise inverse이다.

• 대한수학회보
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• 제60권6호
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• pp.1463-1475
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• 2023

In this paper, we introduce a class of rings generalizing unit regular rings and being a subclass of semipotent rings, which is called idempotent unit regular. We call a ring R an idempotent unit regular ring if for all r ∈ R - J(R), there exist a non-zero idempotent e and a unit element u in R such that er = eu, where this condition is left and right symmetric. Thus, we have also that there exist a non-zero idempotent e and a unit u such that ere = eue for all r ∈ R - J(R). Various basic characterizations and properties of this class of rings are proved and it is given the relationships between this class of rings and some well-known classes of rings such as semiperfect, clean, exchange and semipotent. Moreover, we obtain some results about when the endomorphism ring of a module in a class of left R-modules X is idempotent unit regular.

• 대한수학회보
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• 제59권3호
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• pp.529-545
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• 2022

This article concerns a ring property that arises from combining one-sided duo factor rings and centers. A ring R is called right CIFD if R/I is right duo by some proper ideal I of R such that I is contained in the center of R. We first see that this property is seated between right duo and right π-duo, and not left-right symmetric. We prove, for a right CIFD ring R, that W(R) coincides with the set of all nilpotent elements of R; that R/P is a right duo domain for every minimal prime ideal P of R; that R/W(R) is strongly right bounded; and that every prime ideal of R is maximal if and only if R/W(R) is strongly regular, where W(R) is the Wedderburn radical of R. It is also proved that a ring R is commutative if and only if D₃(R) is right CIFD, where D₃(R) is the ring of 3 by 3 upper triangular matrices over R whose diagonals are equal. Furthermore, we show that the right CIFD property does not pass to polynomial rings, and that the polynomial ring over a ring R is right CIFD if and only if R/I is commutative by a proper ideal I of R contained in the center of R.

• 한국지반공학회논문집
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• 제20권9호
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• pp.177-189
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• 2004

되메움되는 공간의 형상은 현장의 여건에 따라 수직 및 대칭 경사 또는 비대칭 경사를 포함하는 다양한 형태를 취할 수 있다. Kellogg(1993)는 대칭적으로 경사진 되메움 공간에서의 응력은 수직한 조건에서의 응력과는 다른 경계 조건이므로 이를 고려한 되메움 토압 이론식과 수평응력비를 제안하였다. Kellogg(1993)는 경사진 벽면에서 발생되는 응력을 되메움 흙의 단순한 내부마찰각으로 가정하였다. 이에 문(1997)은 경사진 벽면에서의 응력의 상태는 벽면마찰과 주응력의 회전방향에 따라 달라질 것을 예상하여 되메움 공간이 비대칭으로 형성되는 경우, 기존의 Kellogg(1993) 이론식에 대한 수정 Kellogg 이론식을 제안한 바 있다. 본 연구에서는 비대칭한 되메움 공간의 수평응력을 문(1997)의 수정 Kellogg 이론식에 기존 Kellogg(1993)의 수평응력비를 적용한 경우와 비대칭인 좌, 우측의 되메움 경사를 고려한 평균 수평응력비를 적용한 경우에 대하여 실내모형 토조실험과 수치해석으로 비구 검토하였다. 결과에 의하면 수정된 Kellogg 이론식에 Kellogg(1993)의 대칭한 조건에서의 수평응력비를 비대칭한 조건에 적용시킬 경우 경사진 벽면에서의 수평응력은 실험, 수치해석 결과에 매우 유사한 양상을 보이고 있으나 보다 수직한 벽면에서의 수평응력은 그 크기가 실험, 수치해석의 결과와는 상이한 결과를 보였다. 한편 비대칭 경사면 좌, 우측의 평균수평응력비를 수정 Kellogg 이론식에 적용하였을 경우에는 보다 수직한 면에서의 수평응력은 실험 및 수치해석 결과와 매우 유사한 결과를 나타냈다. 이러한 결과는 되메움 공간이 비대칭 조건을 형성하는 경우에는 좌, 우측 벽면 경사에 대한 평균 수평응력비의 적용이 고려되어져야 할 것으로 판단된다.

• 대한치과보철학회지
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• 제29권1호
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• pp.23-37
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• 1991

The understanding the natureof occlusal tooth contacts of natural dentition is important for correct diagnosis and treatment of diseases developed in stomatognatic system. Several investigator have studied the distribution of tooth contacts in maximum intercuspation and have reported contact locations with respect to the tooth position. Many methods have been clinically applied for the occlusal analysis in the intercuspal position. However, there are few quantative methods. This study analyzed the new software version of the T-Scan system to record and analyze occlusal contact balance in the anterior-posterior and right-left directions. Six time moment statistics and five moment statistics were calculated in the midsagittal and the incisal axes of the occlusal plane. In the present study, informed consent was obtained from 100 subjects with natural dentitions. The results were as follows ; 1. The mean of the dental arch length & width were 48.78, 65.32mm in whole population, 49.09mm, 65.50mm in males, 48.78mm, 64.63mm in females, respectively. 2. The mean of TLR & PLR were 0.193mm(left), 0.311mm(left), respectively. Therefore, the distribution of tooth contacts was bilaterally symmetric. 3. The mean of TFB & PFB were 29.168mm, 29.055mm, and that of LFB & RFB were 29.627mm, 29.587mm, respectively, and the qualitative center of occlusal contacts was the firtst molar. 4. The mean of LL & RL were 31.666mm, 31.377mm, respectively, and the quantitative center of occlusal force was the first molar. 5. The mean of LF & RF were 60.237N, 59.276N, respectively and Left-right moment was 72.491Nmm. Therfore, the distribution of occlusal force was bilaterally balanced.

• 설비공학논문집
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• 제4권4호
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• pp.243-252
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• 1992

A mixed convection heat transfer from two vertical parallel plates has been studied numerically by the finite difference method. Effects of the Grashof number, the relative length, $L_2/L_1$. the dimensionless temperature ratio, ${\Phi}_2/{\Phi}_1$ and the dimensionless plate spacing, $b/L_1$ are examined for the heat transfer. Independent of the Grashof numbers and $L_2/L_1$, the dimensionless vertical velocity distributions skewed on the left plate as ${\Phi}_2/{\Phi}_1$ decreased. The dimensionless vertical velocity distribution for $Gr/Re^2=1$ and ${\Phi}_2/{\Phi}_1=1.0$ is skewed to the right plate $L_2/L_1=0.5$, symmetric at $L_2/L_1=1.0$ and skewed to the left plate at $L_2/L_1=1.5$. But for $Gr/Re_2=10.0$ and ${\Phi}_2/{\Phi}_1=1.0$ reversed velocity patterns are obtained. Regardless of the Grashof numbers and $L_2/L_1$, the mean Nusselt nembers on the inside surface of the left plate decreases and those of the right inside surface increases as ${\Phi}_2/{\Phi}_1$ increases. Temperature, velocity and mean Nusselt number distributions are apparently not affected by $L_2/L_1$.

• 한국화재소방학회논문지
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• 제22권4호
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• pp.11-19
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• 2008

소형선박 기관실의 자연발화 방지를 위한 적합한 환기조건을 제시하기 위하여 급, 배기구 수와 위치를 변화시키면서 나타나는 유동장과 온도장을 CFD시뮬레이션을 수행하여 분석하였다. 급, 배기구 수와 위치에 따라 유동형태가 상이하게 나타났으며, 배기구를 천장에 배치시킬 경우는 세로대칭선에 대해 좌우 측천장의 중앙에 위치하는 것이 열 제거에 더 효과적임을 알 수 있었다. 급, 배기구 수를 증가시킬 때는 배기구수를 증가시키는 것이 더 적합한 환기조건이며, 소형선박 기관실의 자연발화방지에 가장 적합한 환기조건은 급기구는 가로대칭선에 대해 전후 측 천장의 중앙에, 배기구는 양측 벽 중앙에 배치시키는 경우로 예측되었다.

• 한국수학교육학회지시리즈A:수학교육
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• 제46권3호
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• pp.273-292
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• 2007

The purpose of this study was to find out how second, fourth and sixth graders understood the main contents related to spatial sense in the Seventh National Mathematics Curriculum. For this purpose, this study examined students' understanding of the main contents of congruence transformation (slide, flip, turn), mirror symmetry, cubes, congruence and symmetry. An investigation was conducted and the subjects included 483 students. The main results are as follows. First, with regards to congruence transformation, whereas students had high percentages of correct answers on questions concerning slide, they had lower percentages on questions concerning turn. Percentages of correct answers on flip questions had significant differences among the three grades. In addition, most students experienced difficulties in describing the changes of shapes. Second, students understood the fact that the right and the left of an image in a mirror are exchanged, but they had poor overall understanding of mirror symmetry. The more complicated the cubes, the lower percentages of correct answers. Third, students had a good understanding of congruences, but they had difficulties in finding out congruent figures. Lastly, they had a poor understanding of symmetry and, in particular, didn't distinguish a symmetric figure of a line from a symmetric figure of a point.

• Journal of Mechanical Science and Technology
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• 제15권5호
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• pp.656-664
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• 2001

A theoretical analysis is performed to describe the qualitative behavior of transient buoyant flows in a vertical channel. Consideration is given to the case of a fluid with a pre-existing stratification. The fluid motion is generated by giving impulsive anti-symmetric step-changes in temperature at the vertical left ad right sidewalls. The qualitative character of the flow is shown to be classified in the Rayleigh number (Ra)-Prandtl number ($sigma$) diagram. The transitory approach to the steady state can be monotonic or oscillatory, depending on ($sigma$-1)$^2$$pi$$^4$ 4$sigma$$R_a$. The prominent characteristics of time-dependent flow are discussed for large $R_a$. The profiles of temperature and velocity in the transient phase are depicted, which disclose distinctive time scales of motion. The transient process is shown to be sensitive to the Prandtl number. The detailed evolutions of flow and temperature fields are illustrated for large $R_a$.

• Journal of Chest Surgery
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• 제15권1호
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• pp.21-26
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• 1982

Fourteen cases of funnel deformity, 11 were male and the others female, treated over a eleven-year period, are presented. The overall results with the methods described by the authors, Wada, Shannon, Adkins and Ravitch appear to be excellent. The symmetric depression was more common In children under the age of 12 years and asymmetric one Increased after the age of 12. Six cases of abnormal cardiac auscultatory findings revealed no consistent hemodynamic abnormalities. An 21-year-old female was associated with left lung agenesis and dextroversion of the heart, and a 6-year-old boy with congenital bronchogenic cyst who underwent right upper lobectomy. EKG changes associated with the anomaly were observed in all. Pulmonary function test showed the range from normal to moderate restriction which did not Improve in only one patient after operation, but the patient did not complain any restriction In activity. Some transient complications were developed which resulted in improvement.