• 소성∙가공
• /
• 제16권7호
• /
• pp.516-520
• /
• 2007

As the springback of sheet metal during unloading nay cause deviation from a desired shape, accurate prediction of springback is essential for the design of sheet stamping operations. On the removal of the applied load the specimen loses its elastic strain by contracting around the contour of the block, the radius $\rho$ can be determined by the residual differential strain. Therefore in this study the springback estimated by the residual differential strain is experimentally validated through the comparison with those obtained by U-bending test. The springback characteristics of two analytical models are also estimated at various processing conditions such as thickness, curvature of radius and drawing strain. The model based on residual differential strain has an applied transition strain where the springback undergoes a dramatic decrease. Both models show that springback decreases with increased strip thickness and with decreased radius of curvature. For no applied tension, the model based on residual differential strain predicts more springback as compared to the moment based model.

• 한국전자통신학회논문지
• /
• 제10권6호
• /
• pp.671-676
• /
• 2015

협력네트워크는 중계기를 이용하여 데이터를 전송함으로서 음영지역을 해소하고 가상의 다중입출력 구성을 통해 통신성능을 향상시킬 수 있다. 본 논문에서는 송신기와 중계기 사이에서는 동기변조 방식을 이용하고 중계기와 수신기 사이에서는 차등변조 방식을 이용하는 부분차등변조 방식을 적용한 협력네트워크의 성능을 중계기의 위치에 따라 분석한다. 성능분석은 송신기와 수신기사이의 직접파가 존재하는 시스템과 존재하지 않는 시스템 두 가지를 고려하는데, 직접파는 차등변조 방식을 적용한다. 또한 전체시스템이 차등변조 방식을 이용했을 경우에 중계기 위치에 따른 성능을 부분차등변조 방식과 비교한다. 시스템의 성능은 송신기와 수신기 사이의 심벌오류율을 이용한다.

• KIEAE Journal
• /
• 제16권6호
• /
• pp.13-19
• /
• 2016

Purpose: In this study, we examined outdoor air fraction using historical data of actual Air Handling Unit (AHU) in the existing building during intermediate season and analyzed optimal outdoor air fraction by control types for economizer. Method: Control types for economizer which was used in analysis are No Economizer(NE), Differential Dry-bulb Temperature(DT), Diffrential Enthalpy(DE), Differential Dry-bulb Temperature+Differential Enthalpy(DTDE), and Differential Enthalpy+Differential Dry-bulb Temperature (DEDT). In addition, the system heating and cooling load were analyzed by calculating the outdoor air fraction through existing AHU operating method and control types for economizer. Result: Optimized outdoor air fraction through control types was the lowest in March and distribution over 50% was shown in May. In case of DE control type, outdoor air fraction was the highest of other control types and the value was average 63% in May. System heating load was shown the lowest value in NE, however, system cooling load was shown 1.7 times higher than DT control type and 5 times higher than DE control type. For system heating load, DT and DTDE is similar during intermediate season. However, system cooling load was shown 3 times higher than DE and DEDT. Accordingly, it was found as the method to save cooling energy most efficiently with DE control considering enthalpy of outdoor air and return air in intermediate season.

• 한국정보통신학회:학술대회논문집
• /
• 한국해양정보통신학회 2003년도 추계종합학술대회
• /
• pp.932-934
• /
• 2003

본 논문에서는 시간 간격을 두고 촬영한 홍채 영상의 차영상을 이용하여 홍채 변화를 분석하여 홍채 변화에 따라 환자의 건강 진단에 활용할 수 있는 방법에 대해 연구하였다. 시간 간격을 두고 촬영한 홍채 영상의 차영상은 시간에 따른 변화를 명확히 보여줌으로써 질병의 조기진단 및 질병의 전개과정 등을 알아보는데 유용하게 쓰일 수 있다. 홍채 진단 시스템의 경우 홍채 외부 영역은 진단에 도움이 되지 않기에 홍채 영역만을 추출하기 위해 케니 에지 검출기를 이용하여 홍채 영역을 추출하고 이전에 촬영한 영상과 현재 촬영한 영상의 차영상을 이용하여 변화를 비교 분석하였다.

• 한국강구조학회 논문집
• /
• 제15권3호
• /
• pp.313-320
• /
• 2003

본 연구는 등분포 축하중과 자유단의 집중하중으로 구성된 조합하중을 받는 등단면 기둥을 대상으로 휨과 전단변형을 고려한 비선형 미분 방정식을 유도하고, 미분 변환을 적용한 수치해석을 실시하여 좌굴 하중을 구하고 좌굴 후 거동 해석을 수행하였다. 자유단의 여러가지 기울기에 따른 좌굴하중을 구하였으며, 미분 변환으로 얻어진 본 연구의 결과는 기존의 연구 결과와 양호한 대응을 나타냈다. 본 연구를 통하여 미분 변환법이 좌굴 후 거동 해석과 같은 비선형 미분방정식의 해법에 적용될 수 있음을 확인하였고, 향후 좀 더 복잡하고 다양한 문제에도 응용될 수 있을 것으로 기대된다.

• Structural Engineering and Mechanics
• /
• 제33권6호
• /
• pp.675-696
• /
• 2009

In this paper, a unified solution method is presented for the classical beam theory. In Strength of Materials approach, the geometry, material properties and load system are known and related with the unknowns of forces, moments, slopes and deformations by applying a classical differential analysis in addition to equilibrium, constitutive, and kinematic laws. All these relations are expressed in a unified formulation for the classical beam theory. In the special case of simple beams, a system of four linear ordinary differential equations of first order represents the general mechanical behaviour of a straight beam. These equations are solved using the numerical differential quadrature method (DQM). The application of DQM has the advantages of mathematical consistency and conceptual simplicity. The numerical procedure is simple and gives clear understanding. This systematic way of obtaining influence line, bending moment, shear force diagrams and deformed shape for the beams with geometric and load discontinuities has been discussed in this paper. Buckling loads and natural frequencies of any beam prismatic or non-prismatic with any type of support conditions can be evaluated with ease.

• 한국통신학회논문지
• /
• 제22권4호
• /
• pp.685-695
• /
• 1997

In this paper, a new CMOS continuous-time fully-differential current-mode integrator is proposed as a basic building block of the low-voltage high frequency current-mode active filter. The proposed integrator is composed of the CMOS complementary circuit which can extend transconductance of an integrator. Therefore, the unity gain frequency which is determined by a small-signal transconductance and a MOSFET gate capacitance can be expanded by the complementary transconductance of the proposed integrator. And also the magnitude of pole and zero are increased. The unity gain frequency of the proposed integrator is increased about two times larger than that of the conventional continuous-time fully-differential integrator with NMOS-gm. These results are verified by the small signal analysis and the SPICE simulation. As an application circuit of the proposed fully-differential current-mode integrator, the three-pole Chebyshev lowpass filter is designed using 0.8.$\mu$m CMOS processing parameters. SPICE simulation predicts a 3-dB bandwidth of 148MHz and power dissipation of 4.3mW/pole for the three-pole filter with 3-V power supply.

• 한국수학교육학회지시리즈E:수학교육논문집
• /
• 제19권4호
• /
• pp.733-767
• /
• 2005

During the past decades, there has been a fundamental change in the objectives and nature of mathematics education, as well as a shift in research paradigms. The changes in mathematics education emphasize learning mathematics from realistic situations, students' invention or construction solution procedures, and interaction with other students of the teacher. This shifted perspective has many similarities with the theoretical . perspective of Realistic Mathematics Education (RME) developed by Freudental. The RME theory focused the guide reinvention through mathematizing and takes into account students' informal solution strategies and interpretation through experientially real context problems. The heart of this reinvention process involves mathematizing activities in problem situations that are experientially real to students. It is important to note that reinvention in a collective, as well as individual activity, in which whole-class discussions centering on conjecture, explanation, and justification play a crucial role. The overall purpose of this study is to examine the developmental research efforts to adpat the instructional design perspective of RME to the teaching and learning of differential equation is collegiate mathematics education. Informed by the instructional design theory of RME and capitalizes on the potential technology to incorporate qualitative and numerical approaches, this study offers as approach for conceptualizing the learning and teaching of differential equation that is different from the traditional approach. Data were collected through participatory observation in a differential equations course at a university through a fall semester in 2003. All class sessions were video recorded and transcribed for later detailed analysis. Interviews were conducted systematically to probe the students' conceptual understanding and problem solving of differential equations. All the interviews were video recorded. In addition, students' works such as exams, journals and worksheets were collected for supplement the analysis of data from class observation and interview. Informed by the instructional design theory of RME, theoretical perspectives on emerging analyses of student thinking, this paper outlines an approach for conceptualizing inquiry-oriented differential equations that is different from traditional approaches and current reform efforts. One way of the wars in which thus approach complements current reform-oriented approaches 10 differential equations centers on a particular principled approach to mathematization. The findings of this research will provide insights into the role of the mathematics teacher, instructional materials, and technology, which will provide mathematics educators and instructional designers with new ways of thinking about their educational practice and new ways to foster students' mathematical justifications and ultimately improvement of educational practice in mathematics classes.

• 한국통신학회논문지
• /
• 제25권3A호
• /
• pp.399-405
• /
• 2000

본 논문에서는 블록암호시스템의 대표적인 방법인 IDEA(International Date Encryption Algorithm)알고리즘을 다룬다. IDEA 알고리즘에서의 키생성 알고리즘을 분석함으로서, 라운드별 사용되는 키 비트열과 사용되지 않는 키 비트열을 분류한다. 이를 이용하여 MA(Multiplication/Addition) 구조를 생략한 형태의 IDEA 알고리즘에 대한 MSB (Most Significant Bit) 차분에 의한 차분 분석법(differential analysis)과 입력계열과 각 라운드별 사용 키계 열의 LSB(Least Significant Bit) 비트만을 사용하는 선형 분석법(linear analysis)을 제안한다.

• 천문학논총
• /
• 제32권1호
• /
• pp.37-39
• /
• 2017

We present the first results of a new data analysis pipeline for processing extragalactic AKARI/IRC images. The main improvements of the pipeline over the standard analysis are the removal of Earth shine and image distortion correction. We present the differential number counts of the AKARI/IRC S11 filter in the IRAC validation field. The differential number counts are consistent with S11 AKARI NEP deep and $12{\mu}m$ WISE NEP number counts, and with a phenomenological backward evolution galaxy model, at brighter fluxes densities. There is a detection of fainter galaxies in the IRAC validation field.