• Advances in aircraft and spacecraft science
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• v.9 no.5
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• pp.449-462
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• 2022

Space-telescopes placed in the Sun-Earth second Lagrange point (L2) observe the sky following a scan strategy that is usually based on a spin-precession motion. Knowing which regions of the sky will be more observed by the instrument is important for the science operations and the instrument calibration. Computing sky observation parameters numerically (discretizing time and the sky) can consume large amounts of time and computational resources, especially when high resolution isrequired.This problem becomesmore critical if quantities are evaluated at detector level instead of considering the instrument entire Field of View (FoV). In previous studies, the authors have derived analytic solutions for quantities that characterize the observation of each point in the sky in terms of observation time according to the scan strategy parameters and the instrument FoV. Analytic solutions allow to obtain results faster than using numerical methods as well as capture detailed characteristics which can be overseen due to discretization limitations. The original approach is based on the analytic expression of the instrument trace over the sky. Such equations are implicit and thusrequiresthe use of numeric solversto compute the quantities.In this work, a new and simpler approach for computing one ofsuch quantities(mean observation time) is presented.The quantity is first computed for pure spin motion and then the effect of the spin axis precession is incorporated under the assumption that the precession motion is slow compared to the spin motion.In this sense, this new approach further simplifies the analytic approach, sparing the use of numeric solvers, which reduces the complexity of the implementation and the computing time.

• Structural Engineering and Mechanics
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• v.56 no.4
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• pp.549-567
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• 2015

A first-order moment method (FORM) reliability analysis is commonly used for structural stability analysis. It requires the values and partial derivatives of the performance to function with respect to the random variables for the design. These calculations can be cumbersome when the performance functions are implicit. A Gaussian process (GP)-based response surface is adopted in this study to approximate the limit state function. By using a trained GP model, a large number of values and partial derivatives of the performance functions can be obtained for conventional reliability analysis with a FORM, thereby reducing the number of stability analysis calculations. This dynamic renewed knowledge source can provide great assistance in improving the predictive capacity of GP during the iterative process, particularly from the view of machine learning. An iterative algorithm is therefore proposed to improve the precision of GP approximation around the design point by constantly adding new design points to the initial training set. Examples are provided to illustrate the GP-based response surface for both structural and non-structural reliability analyses. The results show that the proposed approach is applicable to structural reliability analyses that involve implicit performance functions and structural response evaluations that entail time-consuming finite element analyses.

• Journal of the Korea Society for Simulation
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• v.15 no.3
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• pp.115-124
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• 2006

XML is rapidly becoming technologies for information exchange and representation. It causes many research issues such as semantic modeling methods, security, conversion far interoperability with other models, and so on. Especially, the most important issue for its practical application is how to achieve the interoperability between XML model and relational model. Until now, many suggestions have been proposed to achieve it. However several problems still remain. Most of all, the exiting methods do not consider implicit referential integrity relations, and it causes incorrect data delivery. One method to do this has been proposed with the restriction where one semantic is defined as only one same name in a given database. In real database world, this restriction cannot provide the application and extensibility. This paper proposes a noble conversion (RDB-to-XML) algorithm based on the similarity checking technique. The key point of our method is how to find implicit referential integrity relations between different field names presenting one same semantic. To resolve it, we define an enhanced implicity referentiai integrity relations extraction algorithm based on a widely used ontology, WordNet. The proposed conversion algorithm is more practical than the previous-similar approach.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.79-87
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• 2013

An isogeometric topological shape optimization method is developed using the level sets and Heaviside enrichments. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set functions, which facilitates to handle complicated topological shape changes. The Heaviside enrichment improves the isogeometric analysis by adding some enrichment functions to model the internal boundaries. The proposed topological shape optimization method has several benefits: exact geometric models can be obtained using the isogeometric approach and the limitation of tensor-product patches can be overcome using the Heaviside enrichments to represent the internal voids. Even in a single patch, discontinuous displacement fields as well as smooth stress field can be obtained. Since the level sets offer the implicit moving boundary inside the domain, it is easy to represent the topological shape variations in the isogeometric analysis using Heaviside enrichments.

• Steel and Composite Structures
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• v.5 no.2_3
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• pp.87-101
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• 2005

This paper describes of an overview to the strength rules in the Australian AS4100 Steel Structures Code that was first issued in Limit States Format in 1990. It focuses on pertinent and characteristic issues, such as the means of analysis for second order effects in frames, and highlights how the tiered approach may lead to efficient design using advanced analysis techniques. It also considers design against buckling in some detail, and shows how advanced solutions may be readily incorporated into the design rules. Implicit in the formulations are the necessity for ductility of the steel, and the scope of the code is limited to steels that display this necessary ductility characteristic.

• Knowledge Management Research
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• v.7 no.1
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• pp.65-80
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• 2006

Recently, Korean economy is boosted by the active introduction of many venture businesses full of entrepreneurship. It has been widely accepted implicitly that success of the venture business originates from unique style of knowledge management. This assumption looks natural when we consider the fact that success of the venture business heavily depends on differentiated intelligent asset or knowledge. However, such implicit belief has never been tested empirically. To fill the research void like this, this paper proposes an empirical derivation of key success factors from the venture businesses listed in KOSDAQ. To add rigor to our results, we performed regression analysis by using the derived key success factors as independent variables, and introducing organization efficiency, job satisfaction, and accomplishment motivation as dependent variables. Regression results showed that our approach is justified from the statistical perspective.

• Ocean Systems Engineering
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• v.5 no.4
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• pp.301-318
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• 2015

The present investigations introduce the shell-finite element discretization for the dynamics of slender marine pipelines. A long catenary pipeline, corresponding to a particular Steel Catenary Riser (SCR), is investigated under long-standing cyclic loading. The long structure is divided into smaller tubular parts which are discretized with 8-node planar shell elements. The transient analysis of each part is carried out by the implicit time integration scheme, within a Finite Elements (FE) solver. The time varying external loads and boundary conditions on each part are the results of a prior solution of an integrated line-dynamics model. The celebrated FE approximation can produce a more detailed stress distribution along the structural surface than the simplistic "line-dynamics" approach.

• Transactions of Materials Processing
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• v.3 no.1
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• pp.84-96
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• 1994

Simulation of 3 dimensional large irregularly shaped stamping process by a dynamic approach, based on an explicit time integration scheme, has been shown to be highly efficient and robust in comparison to traditional, implicit, quasi-static ones. The objective of the work is to evaluate the results from explicit code in application to deep drawing of rectangular cup and stamping of automotive front fender, in which deformation, force, thickness distribution are calculated. The method of predicting spring back and formability by and explicit code are suggested and applied to the processes.

• Journal of Korean Society of Transportation
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• v.8 no.2
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• pp.27-41
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• 1990

In this study the economic impacts of government support of shipping industry in the labor rich country are appraised in a general equilibrium model. Shipping industry subsidies (which are supposed to be supplied by lump-sum tax) will decrease disposable income by shifting productive resources from traded goods to the comparatively disadvantageous transport sector, and at the same time reduce the implicit tariff effect by lowering transport costs. The net effect of shipping industry subsidies is to increase social welfare because the latter positive effect of shipping industry subsidies is to increase social welfare because the latter positive effect dominates the former negative effect. Such an increase in social welfare can never be expected from competitive traded goods industry subsidies in the case of which social welfare will actually decrease because of inefficient resource allocation resulting from the subsidies. In addition it is worth noting that the subsidies on the most capital intensive shipping industry will rectify unevenness in income distribution by raising relative price of labor contrary to subsidies on capital intensive traded goods.

• Proceedings of the Korean Institute of Intelligent Systems Conference
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• 1998.06a
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• pp.113-117
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• 1998

We propose a way to show the inherent learning complexity for the multilayer perceptron. We display the solution space and the error surfaces on the input space of a single neuron with two inputs. The evolution of its weights will follow one of the two error surfaces. We observe that when we use the back-propagation(BP) learning algorithm (1), the wight cam not jump to the lower error surface due to the implicit continuity constraint on the changes of weight. The self-relaxation approach is to explicity find out the best combination of all neurons' two error surfaces. The time complexity of training a multilayer perceptron by self-relaxationis exponential to the number of neurons.