주형 응고시 공기틈형성에 의한 열전달과 응고층변형 거동의 연결 해석

유병길,이상현,이동녕 대한금속재료학회 1991 대한금속재료학회 학술대회 개요집 Vol.1991 No.0

전기회로에 대한 문제해결시 초등학생들이 적용하는 규칙

유병길,진은희 부산교육대학교 과학교육연구소 2003 科學敎育硏究 Vol.28 No.-

The results are as follows: (1) Elementary school students apply different rules to problem-solving on electric circuits which is consisted of batteries and bulb; (2) They apply the following rules; In a 4-th grader, the more bulbs and batteries are, the lighter bulbs are, in a 5-th grader, the more batteries are, the lighter bulbs are, and in a 6-th grader, the more bulbs are, the darker bulbs are and if bulbs are parallel, then bulbs become dark.

독립적인 이중 공진 모드 합성을 이용한 광대역 SDR 무전기 안테나 설계

유병길,동문호,조지행,한성우,Yu, Byunggil,Dong, Moo-Ho,Cho, Ji-Haeng,Han, Sung-Woo 한국군사과학기술학회 2014 한국군사과학기술학회지 Vol.17 No.1

In this paper, we have proposed a wide band antenna for manpack SDR(Software Defined Radio). The proposed antenna consists of feeding post, flexible gooseneck and two radiating elements composed of a upper and lower radiators. The upper radiator has a longer electrical length than the lower radiator in order to operate in the lower frequency. Also, the resonant frequency and impedance characteristics of the antenna can be adjusted independently for two radiators. Therefore, the proposed antenna can be achieved wide impedance bandwidth by the combination of two independent resonance modes. To analyze the characteristics of the antenna in the design process is employed the equivalent circuit theory and EM(Electro-Magnetic) simulation. The measurement results show that the proposed antenna have the sufficient wide bandwidth, above -3.4dBi of the gain and fairly good radiation pattern over the wide bandwidth.

테일러드블랭크 용접을 위한 전단 공정 연구

유병길,이경돈 대한용접접합학회 1999 대한용접·접합학회지 Vol.17 No.2

Weld bead quality in tailored blank(TB) is critically affected by edge preparation of sheets. The edge quality of prepared sheets for TB can be classified into straightness and the cross section quality of sheared plane such as a ratio of shear face, shear plane angle, etc. In order to have a good edg quality for butt-welding sheets, precision shearing will be recommended. In this paper, the feasibility of a conventional mechanical shearing as the edge preparation for tailored blanks is studyied. It reveals that fine shearing may not be the unique solution as it is generally accepted. To obtain the good shearing condition with a conventional mechanical shearing, experiments were carried out using Tahuchi method. The major parameters affecting a sheared contour are the clearance between upper blade and lower blade, and shear angle. The optimal shearing condition yields a very good straightness along the entire length of the cut, which gives a butt joint gap less than 10% of the base material thickness. The good cross section of sheared plane is also achieved in the optimal shearing condition such as a ratio of the shear face above 65%, a cross section's shear plane angle above 85%, little burr, which is providing finally good weld beads.

파이온 전기생성 반응에 대한 게이지 불변

유병길 한국물리학회 2005 새물리 Vol.51 No.6

Using the Born approximation, we developed a prescription for the gauge invariance of pion electroproduction with electromagnetic and hadronic form factors included. If generality in formulating the gauge invariance is to be ensured, the form factors must satisfy the Ward-Takahashi identity for current conservation and the generalized Ward-Takahashi identity for the $\gamma\pi NN$ interaction vertex. As a consequence, the Born approximation for electroproduction is obtained with gauge invariance, which is consistent with Ohta's prescription for hadronic form factors in photoproduction. Born 근사 (Born approximation)를 사용하여 전기 생성 (electroproduction) 반응을 기술할 때 진폭에 들어오는 전자기 형태인자 (electromagnetic form factor)와 강작용 (hadronic) 형태인자에 대해서 게이지 불변을 유지시키는 방법을 전개하였다. 게이지 불변을 유도하는 과정이 보편성을 가지기 위하여 이들 형태인자들은 전류 보존에 대한 Ward-Takahashi 항등식과 $\gamma\pi NN$ 작용점 (vertex)에 대해 일반화한 Ward-Takahashi 항등식 (generalized Ward-Takahashi identity)을 만족하도록 하였으며 그 결과 광생성 반응에서 강작용 형태인자에 대한 Ohta의 게이지 불변 방식과 부합되는 전기생성 반응의 Born 근사를 유도하였다.

Galvannealed steel의 점 용접성에 미치는 전극 팁의 영향

유병길,강춘식 대한용접접합학회 1987 대한용접·접합학회지 Vol.5 No.3

Effects of electrode tips shapes of spot welding on the galvannealed steel have been studied, and the results obtained from this studies are as follows. 1) Expulsion had no effect on the shear strength of the specimen but been observed on the tensile strength of the specimen. 2) Effect of holding time after welding was neglegible when the spot welding supplies enough heat input. 3) Depending on the sopt welding tip shape it has different weldbility. It has better weldability in the order of pointed shape, truncated shape and dome shape. But the effect of coolind was just the opposite of the above order.

SAPHIR와 LEPS의 하이퍼론 광생성 실험분석에서 본 공조입자의 기여

유병길 한국물리학회 2005 새물리 Vol.51 No.4

The SAPHIR cross sections and the LEPS beam polarization asymmetries for K+ and K+0photoproduction are analyzed in the isobar model. The role of the new N resonance D13(1895)claimed by KAON MAID is investigated in the SAPHIR data, and the consistency of both data sets with D13 is examined by using a simultaneous least-squares t. In explaining the LEPS data,the resonance structure optimized to the SAPHIR data shows a rapid increase in the t-channel contributions and in the ˜2. From the duality of the s and t-channels, the N resonance F15(1680) introduced to the K+ process and F15(2000) to the K+0 process are found to play the roles signifficantly optimizing the least square t. This indicates that the resonance structures considered in current models need to include the nucleon resonances of higher spin states for a consistent description of both data sets. $K^+\Lambda$와 $K^+\Sigma^{0}$ 광생성 반응에 대한 SAPHIR의 단면적측정과 LEPS의 편광 비대칭(beam polarization asymmetry) 측정결과를 isobar 모형을 사용하여 분석하였다. SAPHIR 실험을 분석할 때 KAON-MAID에서 주장하는 공명입자 $D_{13}(1895)$의 기여도를 조사해보고 이와 함께 두 실험 결과가 일관되게 기술될 수 있는지 살펴 보았다.이 모형으로 입사 광에너지 $E_{\gamma}=1.5$%부터 2.4 GeV 영역에서 $K^+\Lambda$에 대한 SAPHIR 실험결과에 최적화된 공조입자들로 LEPS 실험을 설명하려면 일반적으로 t-channel 교환입자의 기여만 아니라 최소 오차 $\chi^2$ 값도 급격히 증가한다. t-channel과 s-channel과의 duality 관점에서 $K^+ \Lambda$ 반응에 도입한 $F_{15}(1680)$와 $K^+\Sigma^0$에 도입한 $F_{15}(2000)$ 공명입자는 각 반응에서 불안정한 t-channel 기여도와 최소 오차 $\chi^2$ 값을 최적화시키는데 중요한 역활을 하며 두 실험을 일관되게 설명하기 위해서는 모형계산에서 스핀이 큰 핵자 공명입자가 더 고려되어야 한다는 것을 알 수 있었다.

초등학교 학생들의 빛에 대한 개념

유병길,곽수연 부산교육대학교 과학교육연구소 2003 科學敎育硏究 Vol.28 No.-

This study examined elementary school students' ideas about light. The results are as follows; Most students think light's travel distance is different between in the daytime and the night. It is because that children's ideas are strongly influenced by their egocentric or human-centered view of the world and that children don't have the scientific model which can integrate a various kinds of same conditions. And the students think light's travel distance is different as the type of illuminant. They think that the strong illuminant like the sun travel so far but the dim light from a candle doesn't go too far. So, we must teach that the light keeps traveling until it reaches something regardless of the type and strength of illuminant. I suggest that these misconceptions must be changed into the scientific concept through enough discussion after the activities.

전류 비유 모델에 의한 초등학생의 전류 개념 변화 분석

유병길,강인석,김병철,남만희,박선희,소하연,윤희정,이영아,이하룡,전병문,정승호 부산교육대학교 과학교육연구소 2000 科學敎育硏究 Vol.25 No.-

There exists a major impediment to learning electricity which may illuminate why direct presentation of scientists' ideas is too aggressive a strategy. This impediment lies in thinking that electricity is used up and in envisaging the light bulb as a consumer. This view is based on a powerful idea which summarises much of our experience; it declares that 'things get used up', 'you cannot get something for nothing', and 'intuitive thinking'. To replace this view with scientific view, we made the analogy model. It is suggested that the analogy model is more effective in teaching electricity circuits than conventional teaching method.

Martensitic Transformation in Cu-Zn-Al Shape Memory Alloy Single Crystal Studied

유병길 釜山工業大學校 基礎科學硏究所 1994 연구논문집 Vol.2 No.-