• International Journal of Aeronautical and Space Sciences
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• v.10 no.2
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• pp.148-160
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• 2009

By the development of recent technology, a new variant of rotorcrafts having four rotors start drawing attention from aerial-robotics engineers more than before. Its potential spans from just being control device test bed to performing difficult task such as carrying surveillance device to unreachable places. In this regards, modeling a quad-rotor is significant in analyzing its dynamic behavior and in synthesizing control system for such a vehicle. This paper summarizes the modeling of a mini quad-rotor aerial vehicle. A first principle approach is considered for deriving the model based on Euler-Newton equations of motion. The result of the modeling is a simulation platform that is expected to acceptably predict the dynamic behavior of the quad-rotor in various flight conditions. Linear models associated with different flight condition can be extracted for the purpose of control synthesis.

• Structural Engineering and Mechanics
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• v.7 no.2
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• pp.159-180
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• 1999

The present paper shows a new non-tensorial approach to derive basic equations for various structural analyses. It can be used directly in numerical computation procedures. The aim of the paper is, however, to show that the approach serves as an excellent tool for analytical purposes also, working as a link between analytical and numerical techniques. The paper gives a method to derive, at first, expressions for strains in general beam and shell analyses, and secondly, the governing equilibrium equations. The approach is based on the utilization of local fixed Cartesian coordinate systems. Applying these, all the definitions required are the simple basic ones, well-known from the analyses in common global coordinates. In addition, the familiar principle of virtual work has been adopted. The method will be, apparently, most powerful in teaching the theories of curved beam and shell structures for students not familiar with tensor analysis. The final results obtained have no novelty value in themselves, but the procedure developed opens through its systematic and graphic progress a new standpoint to theoretical considerations.

• Nuclear Engineering and Technology
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• v.44 no.8
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• pp.889-896
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• 2012

Recent progress in the computational fluid dynamics methods of two- and multiphase phase flows has already started opening up new exciting possibilities for using complete multidimensional models to simulate boiling systems. Combining this new theoretical and computational approach with novel experimental methods should dramatically improve both our understanding of the physics of boiling and the predictive capabilities of models at various scale levels. However, for the multidimensional modeling framework to become an effective predictive tool, it must be complemented with accurate mechanistic closure laws of local boiling mechanisms. Boiling heat transfer has been studied quite extensively before. However, it turns out that the prevailing approach to the analysis of experimental data for both pool boiling and forced-convection boiling has been associated with formulating correlations which normally included several adjustable coefficients rather than based on first principle models of the underlying physical phenomena. One reason for this has been the tendency (driven by practical applications and industrial needs) to formulate single expressions which encompass a broad range of conditions and fluids. This, in turn, makes it difficult to identify various specific factors which can be independently modeled for different situations. The objective of this paper is to present a mechanistic modeling concept for both pool boiling and forced-convection boiling. The proposed approach is based on theoretical first-principle concepts, and uses a minimal number of coefficients which require calibration against experimental data. The proposed models have been validated against experimental data for water and parametrically tested. Model predictions are shown for a broad range of conditions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.12
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• pp.767-775
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• 2014

New material design has obtained tremendous attention in material science community as the performance of new materials, especially in nano length scale, could be greatly improved to applied in modern industry. In certain conditions limiting experimental synthesis of these new materials, new approach by computer simulation has been proposed to be applied, being able to save time and cost. Recent development of computer systems with high speed, large memory, and parallel algorithms enables to analyze individual atoms using first principle calculation to predict quantum phenomena. Beyond the quantum level calculations, mesoscopic scale and continuum limit can be addressed either individually or together as a multi-scale approach. In this article, we introduced current endeavors on material design using analytical theory and computer simulations in multi-length scales and on multi-physical properties. Some of the physical phenomena was shown to be interconnected via a cross-link rule called 'cross-property relation'. It is suggested that the computer simulation approach by multi-physics analysis can be efficiently applied to design new materials for multi-functional characteristics.

• Wind and Structures
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• v.8 no.2
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• pp.89-106
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• 2005

For estimating the vortex excited vibrations of overhead transmission lines, the Energy Balance Principle (EBP) is well established for spans damped near the ends. Although it involves radical simplifications, the method is known to give useful estimates of the maximum vibration levels. For very long spans, there often is the need for a large number of in-span fittings, such as in-span Stockbridge dampers, aircraft warning spheres etc. This adds complexity to the problem and makes the energy balance principle in its original form unsuitable. In this paper, a modified version of EBP is described taking into account in-span damping and in particular also aircraft warning spheres. In the first step the complex transcendental eigenvalue problem is solved for the conductor with in-span fittings. With the thus determined complex eigenvalues and eigenfunctions a modified energy balance principle is then used for scaling the amplitudes of vibrations at each resonance frequency. Bending strains are then estimated at the critical points of the conductor. The approach has been used by the authors for studying the influence of in-span Stockbridge dampers and aircraft warning spheres; and for optimizing their positions in the span. The modeling of the aircraft warning sphere is also described in some detail.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.22
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• pp.173-197
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• 2004

Letter of Credit between buyer and seller in International Trade Transaction is the means of payment which makes International Trade operate smoothly by guaranteeing an exporter against non-payment and an importer against non-delivery. Therefore, the parties to a sale apply UCP500 established by the International Chamber of Commerce, in accordance with principle of the freedom of contract among the parties concerned, to look to their own legal stability. However, we may recognize some cases to have been applied principle of faith and trust, one of the dominant principles of the civil law, by the Korean Supreme Court and other cases to have not been applied that principle by the Korean Supreme Court. The Court shall apply UCP500 strictly as long as the parties concerned adopt UCP500 in view of the legal stability. In other words, in case that the Court applies principle of faith and trust to the case related to L/C, this rule - principle of faith and trust - should apply to the subject matter which have not stipulated in UCP500 under certain restriction. We suggest keeping in mind points to korean companies as follows; First, the parties to a sale shall understand L/C basis transaction and principles related to L/C deeply. Second, the exporter shall prepare documents in compliance with L/C and fulfil his or her obligation according to UCP500 and L/C related to the contract. Third, as buyer or importer, when he or she receive the shipping documents with discrepancies from the notifying bank, he or she makes him or herself clear to all the parties concerned. Fourth, as bank, she shall examine all the documents according to UCP500 and L/C related to the contract, and if any document with discrepancies, the bank, by all means, shall approach applicant first, and then decide whether to pay the credit amount to beneficiary or not to.

• Language and Information
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• v.2 no.1
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• pp.177-213
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• 1998

conflicting criterial used in identifying words have called the lexical integrity principle into question. That is, cases where the morphological word does not coincide with the syntactic word have notivated the syntactic view of word derivation, as pointed out by Bresnan and Mchombo(1995). Further, the implicit desire to make the clausal structure of Korean parallel to those posited for English(Chomsky 1991) and French(Pollock 1989) has also led most of the current literature on Korean morphology to claim that Korean verbal inflections head their own functional projections such as AgrP, TP, and MP im syntax. In this paper, I will first argue against such a syntactic view. After reviewing some basic properties of Korean verbal inflections, I will show that the evidence from mismatch phenomena supports the lexical integrity principle over the head-movement theories of word derivation. Then, I will propose a theory of lexical grammar which maintains the lexical integrity principle while retaining the effects of functional projections and syntactic movement.

• Research in Community and Public Health Nursing
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• v.8 no.1
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• pp.133-143
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• 1997

This study measures the subjectivity of nursing students' experience in community fields through community nursing practice. The purpose of this study is as follows: 1) to find out typologies based on opinions and attitudes toward community nursing practice. 2) to describe the characteristic of each type. 3) to provide alternative strategies for solving community nursing practice problems. A Q-Methodological method was used for that purpose. As a research method, Q-statements were collected through indepth interviews and review of the current literature. For this study 34 Q-statements were selected. 24 nursing students were subjects for the research. The 24 nursing students sorted 34 Q-statements using the principle of Forced Normal Distribution. The principle of Forced Normal Distribution, which has nine scales to measure individual opinions, was called, a Q- Factor Analysis by using a PC Quanl Program to supply the material. According to the results of this study, there were three categories of opinion concerning community nursing practice. The first type is the realistic problem-oriented approach: the second type is the self-responsibility or pursuit of life meaning approach: the third type is the group approach for problem solving. As a result, we need to develop and revise a more realistic way of community nursing practice for nursing students. Finally, the result of this study will provide to the educational program alternative strategies for community nursing practice for nursing students.

• Steel and Composite Structures
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• v.52 no.5
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• pp.525-541
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• 2024

This study uses the state-space approach to study the bending behavior of Levy-type functionally graded (FG) plates sandwiched between two piezoelectric layers. The coupled governing equations are obtained using Hamilton's principle and Maxwell's equation based on the efficient four-variable refined plate theory. The partial differential equations (PDEs) are converted using Levy's solution technique to ordinary differential equations (ODEs). In the context of the state-space method, the higher-order ODEs are simplified to a system of first-order equations and then solved. The results are compared with those reported in available references and those obtained from Abaqus FE simulations, and good agreements between results confirm the accuracy and efficiency of the approach. Also, the effect of different parameters such as power-law index, aspect ratio, type of boundary conditions, thickness-to-side ratio, and piezoelectric thickness are studied.

• Structural Engineering and Mechanics
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• v.7 no.2
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• pp.225-240
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• 1999

This paper presents a mechanistic approach to uniaxial viscoelastic constitutive modeling of asphalt concrete that accounts for damage evolution under cyclic loading conditions. An elasticviscoelastic correspondence principle in terms of pseudo variables is applied to separately evaluate viscoelasticity and time-dependent damage growth in asphalt concrete. The time-dependent damage growth in asphalt concrete is modeled by using a damage parameter based on a generalization of microcrack growth law. Internal state variables that describe the hysteretic behavior of asphalt concrete are determined. A constitutive equation in terms of stress and pseudo strain is first established for controlled-strain mode and then transformed to a controlled-stress constitutive equation by simply replacing physical stress and pseudo strain with pseudo stress and physical strain. Tensile uniaxial fatigue tests are performed under the controlled-strain mode to determine model parameters. The constitutive equations in terms of pseudo strain and pseudo stress satisfactorily predict the constitutive behavior of asphalt concrete all the way up to failure under controlled-strain and -stress modes, respectively.