• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.567-573
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• 2010

In this study, we evaluated the structural integrity and weight of a rocket motor with a torispherical dome by size optimization. Size optimization was achieved by first-order and sub-problem methods, using the Ansys Parametric Design Language (APDL). For rapid design verification, a modified 2D axisymmetric finite-element model was used, and the bolt pre-tension load was expressed as function of the ratio of the cross-sectional area. The thickness of the dome and the cylindrical part of the rocket motor were selected as the design parameters. Our results showed that the weight and structural integrity of the rocket motor at the initial design stage could be determined more rapidly and accurately with the modified 2D axisymmetric finite-element model than with the 3D finite-element model; further, the weight of the rocket motor could be saved to maximum of 17.6% within safety limit.

• The Journal of the Acoustical Society of Korea
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• v.19 no.6
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• pp.62-70
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• 2000

In usual language models(LMs), the probability has been estimated by selecting highly frequent words from a large text side database. However, in case of adopting LMs in a specific task, it is unnecessary to using the general method; constructing it from a large size tent, considering the various kinds of cost. In this paper, we propose a construction method of LMs using a small size text database in order to be used in specific tasks. The proposed method is efficient in increasing the low frequent words by applying same sentences iteratively, for it will robust the occurrence probability of words as well. We carried out continuous speech recognition(CSR) experiments on 200 sentences uttered by 3 speakers using LMs by iterative teaming(IL) in a air flight reservation task. The results indicated that the performance of CSR, using an IL applied LMs, shows an 20.4% increased recognition accuracy compared to those without it. This system, using the IL method, also shows an average of 13.4% higher recognition accuracy than the previous one, which uses context-free grammar(CFG), implying the effectiveness of it.

• Polymer(Korea)
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• v.33 no.5
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• pp.477-484
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• 2009

Suspension polymerization with hydrophobic silica as a stabilizer and AIBN as an initiator was conducted to synthesize PBMA particles and PBMA composite particles containing carbon black. Surface modification of silica particles by controlling pH revealed that 90% of them functioned as stabilizer and 10% were incorporated into PBMA particles. While stabilizer concentration had no impact on reaction kinetics and particle diameter, an increase in stabilizer concentration displayed an increase in molecular weights when it exceeded 1.67 wt%. An increase in initiator concentration and reaction temperature decreased molecular weights in close agreement with the theoretical equation. An increase in carbon black concentration from 1 to 7 wt%, relative to the monomer, showed a progressive decrease in reaction conversion. As carbon black was increased from 3 to 5 wt%, glass transition showed a $4^{\circ}C$ increase. The presence of carbon black was confirmed by TEM while its concentration was measured by TGA.

• Journal of Navigation and Port Research
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• v.32 no.3
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• pp.223-228
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• 2008

As most of small fishing boats made of FRP have been constructed by experience in Korea, some structural safety problems have been occurred occasionally. To improve the structural strength and reduce the costs for construction and operation, optimum design for small fishing boat was carried out in this study. The weight of fishing boat and the main dimensions of structural members are chosen as objective function and design variables, respectively. By the combination of global and local search methods, a hybrid optimization algorithm was developed to escape the local minima and reduce CPU time in analysis procedure, and finite element analysis was performed to determine the constraint parameters at each iteration step in optimization loop. Optimization results were compared with the real existing fishing boat, and the effects of optimum design were examined from points of view; structural strength, material cost, etc.

• The Journal of Korean Institute for Practical Engineering Education
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• v.4 no.2
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• pp.84-90
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• 2012

It is described that the total analysis of CD-R, a digital recording media, including the planning and performing chemical analysis of cross sectional structure of recording layer, dye composition and chemical structure as an example of design for chemical analysis. Since chemical analysis of unknown sample is often involved the complicated process requiring many experiences and knowledge, students feel difficulties in planning the procedure of chemical analysis and selecting analytical methods. Thus, an example of chemical analysis is provided here to help student understanding the hole procedure of CD-R analysis. In this study, SEM is used to determine the cross sectional structure of PC substrate and recoding layer of CD-R. The dyes in recording layer is dissolved with solvent and separated with using TLC, analyzed with using UV-Vis absorption spectrometer. Then, the chemical structure of each component is determined with using GC-MS, NMR and mass spectrometer.

• Journal of the Korean Chemical Society
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• v.43 no.4
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• pp.418-422
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• 1999

A method is described for the selective determination of Cr(III) and Cr(VI) in aqueous solutios by flame atomic absorption spectrometry. Selective extraction of $Cr_2O_7^{2-}$ was performed by Aliquat 336/NIBK from the mixtures of $Cr^{3+}$ and $Cr_2O_7^{2-}$, and the extraction of $Cr^{3+}$ was followed after complex formation with citrate by using the same extractant. The concentraction of each analyte in the extract was determined by $N_2O-C_2H_2$ flame atomic absorption spectrometry. The recoveries of $Cr^{3+}$ and $Cr_2O_7^{2-}$ from 50mL of aqueous solution ranging 0.1~1.0 ${\mu}g/mL$ as Cr respectively by single extractions with 5 mL of 1%(V/V) Aliquat 336/MIBK were resulted as 98.8∼101.7%.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.6
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• pp.777-784
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• 2006

This paper proposes a c-fuzzy model tree using partial least square method to predict the Chlorophyll-a concentration in each zone. First, cluster centers are calculated by fuzzy clustering method using all input and output attributes. And then, each internal node is produced according to fuzzy membership values between centers and input attributes. Linear models are constructed by partial least square method considering input-output pairs remained in each internal node. The expansion of internal node is determined by comparing errors calculated in parent node with ones in child node, respectively. On the other hands, prediction is performed with a linear model haying the highest fuzzy membership value between input attributes and cluster centers in leaf nodes. To show the effectiveness of the proposed method, we have applied our method to water quality data set measured at several stations. Under various experiments, our proposed method shows better performance than conventional least square based model tree method.

• Korean Journal of Ecology and Environment
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• v.52 no.3
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• pp.231-244
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• 2019

Zooplankton is essential biological assemblage in understanding the structure and function of aquatic ecosystems, since it plays as a linkage between primary producers and higher trophic level organisms such as fish. Although zooplankton has planktonic characteristics, the sampling and treatment methods for its community analyses are more complicated and variable compared with phytoplankton due to its high diversity in body size and species-specific depth selection behaviors. In the present paper, we reviewed representative classical methods for field sampling and treatments of freshwater zooplankton in relation with quantification of its community structure, and suggested appropriate methods depending on various research objectives.

• Korean Journal of Forensic Psychology
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• v.13 no.2
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• pp.121-145
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• 2022

The current study applied the random forest algorithm to Korean crime victim survey data collected biennially between 2010 and 2018 to explore the relationship between crime/victim characteristics and the victim's criminal damages. A total of 3,080 cases including gender, age (life cycle stage), type of crime, perpetrator acquisition, repeated victimization, psychological damage (depression, isolation, extreme fear, somatic symptoms, interpersonal problems, moving out to avoid people, suicidal impulses, suicide attempts), and emotional changes after victimization (changes in self-protection confidence, self-esteem, confidence in others, confidence in legal institutions, and respect for Korean legal system/law) were analyzed. Considering the features of data that are difficult to apply traditional statistical techniques, this study implemented random forest algorithms to predict crime and victim characteristics using the victim's criminal damages (psychological damage and emotional change) and selected good predictors using VSURF function in VSURF package for R. As a result of the analysis, it was confirmed that the relationship between the type of crime and depression, extreme fear, somatic symptoms, and interpersonal problems, between perpetrator acquisition and somatic symptoms and interpersonal problems, and between repeated victimization and changes in respect for Korean legal system/law. Gender and life cycle stage (youth/adult/elderly) were found to be related to extreme fear and changes in self-protection confidence, respectively. However, more empirical evidence should be aggregated to explain the results as meaningful. The results of this study suggest that it is necessary to enhance the experts' knowledge and educate them on cases about the relationship between crime/victim characteristics and criminal damage. Strengthening their interview strategy and knowledge about law/rules were also needed to increase the effectiveness of the Korean victim assessment system.

• The Journal of Engineering Geology
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• v.19 no.1
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• pp.71-79
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• 2009

Step-drawdown tests were conducted at four pumping Wells, two in porous media and two in fractured rocks, respectively. In general, P = 2.0 suggested by Jacob (1947) is applied to porous media and fractured rocks in terms of drawdowns of step-drawdown test. In an attempt to review problems of linear model (Jacob's graphic method) in interpreting the step-draw down test, the outcomes of well parameters (aquifer loss coefficient (B), well loss coefficient (C) and well loss exponent (P)) calculated from linear and nonlinear model (Labadie and Helweg's least-squares method) were compared and analyzed. The values of C and P calculated from linear and nonlinear models differed according to permeability of aquifer and the conditions of pumping well. The value C obtained from nonlinear models in porous media and fractured rocks is about $10^0{\sim}10^{-2}$ and $10^{-3}{\sim}10^{-6}$ times lower than in their linear models, respectively. The value P of porous media obtained from nonlinear model ranged from 2.123 to 2.775, while it ranged from 3.459 to 5.635 for fractured rocks. In case of nonlinear model, well loss highly depends on the value P. At this time, well efficiencies calculated from linear and nonlinear models were $1.56{\sim}14.89%$ for porous media and $8.73{\sim}24.71%$ for fractured rocks, showing a significant error according to chosen models. In nonlinear model, it was found that the regression analysis using the least squares method was very useful to interpret step-drawdown test in all aquifer.