• Title/Summary/Keyword: Critical Distance

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Design And Implementation Of Web-based Counselling System For Learning By Problem Based Learning(PBL) Of Constructivism (구성주의적 문제중심학습(PBL)에 따른 웹기반 학습상담 시스템의 설계 및 구현)

  • Kwon, Hyung-Kyu
    • Journal of The Korean Association of Information Education
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    • v.6 no.2
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    • pp.212-224
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    • 2002
  • The purpose of this study is to design and implement the web-based counselling system in aspects of learning type and method by PBL in Constructivism. Learning problem is classified into learning difficulty, learning disability, emotional disability, memory/cognition, ADHD(attention deficit hyperactivity disorder), classwork, and school circumstance. Counselling for individual, offline visit, parents, electronic mail, and group with professionals who were involved in the design and implementation of learning counselling were used to supplement the clinic process for learning. The result of this study aims to administer the distance counselling system for learning without prominent computer knowledge. Each learner can solve diverse private learning problems which can be widely applied for situated learning. Also these online strategies by PBL indicate that providing learning types and methods are critical for overall understanding in online counselling system for learning.

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Limitation of effective length method and codified second-order analysis and design

  • Chan, S.L.;Liu, Y.P.;Zhou, Z.H.
    • Steel and Composite Structures
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    • v.5 no.2_3
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    • pp.181-192
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    • 2005
  • The effective length method for flexural (column) buckling has been used for many decades but its use is somewhat limited in various contemporary design codes to moderately slender structures with elastic critical load factor (${\lambda}_{cr}$) less than 3 to 5. In pace with the use of higher grade steel in recent years, the influence of buckling in axial buckling resistance of a column becomes more important and the over-simplified assumption of effective length factor can lead to an unsafe, an uneconomical or a both unsafe and uneconomical solution when some members are over-designed while key elements are under-designed. Effective length should not normally be taken as the distance between nodes multiplied by an arbitrary factor like 0.85, 1.0, 2.0 etc. Further, the classification of non-sway and sway-sensitive frames makes the conventional design procedure tedious to use and, more importantly, limited to simple regular frames. This paper describes the practical use of second-order analysis with section capacity check allowing for $P-{\delta}$ and $P-{\Delta}$ effects together with member and system imperfections. Most commercial software considers only the $P-{\Delta}$ effect, but not member and frame imperfections nor $P-{\delta}$ effect, and engineers must be very careful in their uses. A verification problem is also given for validation of software for this type of powerful second-order analysis and design. It is a trend for popular and advanced national design codes in using the second-order analysis as a norm for analysis and design of steel structures while linear analysis may only be used in very simple structures.

A study on early faults detection of pressurizer pressure control system using MTS (MTS를 이용한 가압기 압력 제어 계통의 조기 고장 감지에 대한 연구)

  • Cha, Jae-Min;Kim, Joon-Young;Shin, Junguk;Yeom, Choongseob;Kang, Seong-Ki
    • The Korean Journal of Applied Statistics
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    • v.29 no.7
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    • pp.1385-1398
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    • 2016
  • A pressurizer is a major equipment system in a nuclear power plant (NPP) and controls the reactor cooling system pressure within the allowable range. Faults in the pressurizer can be critical to the NPP; therefore, early fault detection in the pressurizer is significant for NPP safety. This study applies Mahalanobis Taguchi system (MTS), which is one of the promising pattern classification methods, based on the Mahalanobis distance concept and Taguchi quality engineering theory to the early fault detection problem of the pressurizer pressure control system. We conducted experiments using data from full scope NPP simulator based on a pressurizer pressure transmitter faults scenario to validate the faults detection performance of MTS. As a result, MTS can rapidly detect the faults compared to conventional faults detection based on single sensor monitoring.

Collision-Free Trajectory Planning for Dual Robot Arms Using Iterative Learning Concept (反復 學習槪念을 利용한 두 臺의 로봇의 衝突回避 軌跡計劃)

  • 정낙영;서일홍;최동훈
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.1
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    • pp.69-77
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    • 1991
  • A collision-free trajectory planning algorithm using an iterative learning concept is proposed for dual robot arms in a 3-D common workspace to accurately follow their specified paths with constant velocities. Specifically, a collision-free trajectory minimizing the trajectory error is obtained first by employing the linear programming technique. Then the total operating time is iteratively adjusted based on the maximum trajectory error of the previous iteration so that the collision-free trajectory has no deviation from the specified path and also that the operating time is near-minimal. To show the validity of the proposed algorithm, a numerical example is presented based on two planar robots.

An Economic Feasibility Analysis of a Hydrogen Fuel-Cell Vehicle Considering GHG (GHG를 고려한 수소연료전지 자동차의 경제성 분석)

  • Yang, Moon-Hee;Gim, Bong-Jin;Kim, Jong-Wook
    • New & Renewable Energy
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    • v.1 no.3 s.3
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    • pp.42-50
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    • 2005
  • This paper deals with the economic feasibility model and analysis of a hydrogen fuel-cell vehicle [FCV] against two similar types of non-business vehicles fueled with gasoline [GV] and diesel [DV] considering greenhouse gas [GHG]. Considering the price of vehicles and annual operating cost, we build a classical economic feasibility model. Since the economic feasibility could be affected by many input factors such as the prices of vehicles, the price of fuels, annual driving distance and so on, we estimate the average future values of input factors, which is defined as "the average case". Based on the average case, we assess the representative economic feasibility of a FCV with/without GHG, and by changing various annual driving distances, we assess its economy in terms of net-present value, internal rate of return, and payback period. In addition, we make some sensitivity analysis of its economic feasibility by changing the values of the critical input factors one at time. Based on the average case, it turns out that the consumer of a FCV could save 25,000 won/year for a GV, but the consumer could pay 120,000 won/year more for a DV. This indicates that gasoline vehicles could be replaced gradually by FCVs in Korean market which might be formed by those consumers driving annually more than approximately 14,800 km. As the results of our sensitivity analysis, it turns out that a FCV is no more economical if the difference of the prices between FCV and GV is more than 10,130,000 won or the price of hydrogen fuel could be more than 5,136 won/kg.

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Industry in a Networked World: Globalization and Localization of Industry" (네트워크세계의 산업: 산업의 세계화와 국지화)

  • 박삼옥
    • Journal of the Korean Geographical Society
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    • v.37 no.2
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    • pp.111-130
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    • 2002
  • Major purposes of this stud? are to analyze Korean firms'innovation networks and sources of knowledge for innovation and to understand their spatial dimensions. In the innovation networks, parent firms are most important for subcontracting firms, while suppliers, customers and competitors are relatively important for independent firms. However, in the future innovation networks, it is expected that government-sponsored research institutions and university wilt become more important on the one hand, networks with foreign firms will become more important on the other hand. Regarding the process of innovation, distance does not matter for the acquisition of codified knowledge. Spatial proximity is, however, critical for the acquisition of tacit knowledge because discussions and researches in a research division within a firm, personal networks of CEO and workers who are responsible for innovation activity, and inter-firm relations with suppliers and customer in a region are regarded important as sources of tacit knowledge. Overall, the innovation networks are different between the Capital Region and non-Capital Region as well as between the industrial complex and non-industrial complex, suggesting that different regional innovation strategies and policies should be established and implemented by considering such regional specificities. Finally, based on the results of this study several policy implications are suggested.

Raising Human Capital in Three U.S. Metropolitan Areas: Geographies of Educators Workforce Supply from Higher Education Institutions to Information Technology Companies (대학 인적자원 공급의 지리적 특성: 미국 3개 도시 지역의 정보통신업체를 사례로)

  • Kim, Hyung-Joo
    • Journal of the Korean Geographical Society
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    • v.40 no.5 s.110
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    • pp.533-552
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    • 2005
  • Human capital and higher education have been increasingly emphasized with the rise of a knowledge-based economy. Cities are recognized as places to attract human capital and spur economic development. Educated workforce supply is one of the critical parts to sustain IT industries, which have been leading recent economic development. This paper examines factors affecting geographies of educated workforce supply from colleges and universities to companies in U.S. metropolitan areas through questionnaire survey and interviews with IT companies and IT-related programs at colleges and universities. The results show that: (1) physical proximity between IT companies and colleges/universities enhances the degree of educated workforce supply from colleges/universities to IT companies; (2) IT companies which seek more specialized and rarer expertise recruit the workforce from colleges or universities over longer distance; (3) colleges and universities which offer a higher degree have geographically more extensive supply of educated workforce to IT companies than those which offer a lower degree; and (4) large IT companies have more geographically extensive supply of educated workforce to colleges/universities than small IT companies.

Design of a Reducer Gear for Small Electric Vehicles (소형 전기자동차용 감속기 설계)

  • Lee, Jae-gu;Kim, Sung-Hoon;Han, Sung-Gil;Shin, Yoo-In;Song, Chul Ki
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.19 no.9
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    • pp.116-121
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    • 2020
  • In recent times, fuel economy enhancement and environmental regulation compliance have become the main topics of interest in the automobile industry. Electric vehicles are desirable alternatives to the existing cars that employ internal combustion engines. Specifically, electric vehicles are equipped with inverters, motors, and a gearbox instead of engines and transmission mechanisms. The gearbox is a key component, used to transmit power from the electric motor to the wheel. Therefore, the design of the gearbox is critical. However, most engineers design gears based only on their experience because no standards pertaining to the design factor exist, other than those for the gear ratios. To overcome this problem, the structural stabilities must be examined considering the design factors of the gears. In this study, we considered the module and number of teeth as the main factors. The constraints corresponded to the final gear ratio and fixed distance between each axle of the shafts. Moreover, a structural analysis was conducted, and the variation trend of the maximum equivalent stress against changes in the gear module and number of teeth was examined. By performing such an analysis, the structural stability in the design of a gear system could be effectively investigated.

Removal of Nano-scaled Fluorescence Particles on Wafer by the Femtosecond Laser Shockwave (펨토초레이저 충격파에 의한 형광 나노입자 제거)

  • Park, Jung-Kyu;Cho, Sung-Hak;Kim, Jae-Gu;Chang, Won-Seok;Whang, Kyung-Hyun;Yoo, Byung-Heon;Kim, Kwang-Ryul
    • Journal of the Korean Society for Precision Engineering
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    • v.26 no.5
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    • pp.150-156
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    • 2009
  • The removal of tiny particles adhered to surfaces is one of the crucial prerequisite for a further increase in IC fabrication, large area displays and for the process in nanotechnology. Various cleaning techniques (wet chemical cleaning, scrubbing, pressurized jets and ultrasonic processes) currently used to clean critical surfaces are limited to removal of micrometer-sized particles. Therefore the removal of sub-micron sized particles from silicon wafers is of great interest. For this purpose various cleaning methods are currently under investigation. In this paper, we report on experiments on the cleaning effect of 100nm sized fluorescence particles on silicon wafer using the plasma shockwave occurred by femtosecond laser. The plasma shockwave is main effect of femtosecond laser cleaning to remove particles. The removal efficiency was dependent on the gap distance between laser focus and surface but in some case surface was damaged by excessive laser intensity. These experiments demonstrate the feasibility of femtosecond laser cleaning using 100nm size fluorescence particles on wafer.

Preparation of Ba2Mg(PO4)2:Eu Phosphors and Their Photoluminescence Properties Under UV Excitation (Ba2Mg(PO4)2:Eu 형광체의 합성과 자외선 여기하의 발광특성)

  • Tae, Se-Won;Jung, Ha-Kyun;Choi, Sung-Ho;Hur, Nam-Hwi
    • Korean Journal of Materials Research
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    • v.18 no.11
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    • pp.623-627
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    • 2008
  • For possible applications as luminescent materials for white-light emission using UV-LEDs, $Ba_2Mg(PO_4)_2:Eu^{2+}$ phosphors were prepared by a solid state reaction. The photoluminescence properties of the phosphor were investigated under ultraviolet ray (UV) excitation. The prepared phosphor powders were characterized to from a single phase of a monoclinic crystalline structure by a powder X-ray diffraction analysis. In the photoluminescence spectra, the $Ba_2Mg(PO_4)_2:Eu^{2+}$ phosphor showed an intense emission band centered at the 584 nm wavelength due to the f-d transition of the $Eu^{2+}$ activator. The optimum concentration of $Eu^{2+}$ activator in the $Ba_2Mg(PO_4)_2$ host, indicating the maximum emission intensity under the excitation of a 395 nm wavelength, was 5 at%. In addition, it was confirmed that the $Eu^{2+}$ ions are substituted at both $Ba^{2+}$ sites in the $Ba_2Mg(PO_4)_2$ crystal. On the other hand, the critical distance of energy transfer between $Eu^{2+}$ ions in the $Ba_2Mg(PO_4)_2$ host was evaluated to be approximately 19.3 A. With increasing temperature, the emission intensity of the $Ba_2Mg(PO_4)_2$:Eu phosphor was considerably decreased and the central wavelength of the emission peak was shifted toward a short wavelength.