• Advances in nano research
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• 제16권5호
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• pp.509-519
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• 2024

In this study, the static analysis of carbon nanotube-reinforced composites (CNTRC) beams resting on a Winkler-Pasternak elastic foundation is presented. The developed theories account for higher-order variation of transverse shear strain through the depth of the beam and satisfy the stress-free boundary conditions on the top and bottom surfaces of the beam. To study the effect of carbon nanotubes distribution in functionally graded (FG-CNT), we introduce in the equation of CNT volume fraction a new exponent equation. The SWCNTs are assumed to be aligned and distributed in the polymeric matrix with different patterns of reinforcement. The rule of mixture is used to describe the material properties of the CNTRC beams. The governing equations were derived by employing Hamilton's principle. The models presented in this work are numerically provided to verify the accuracy of the present theory. The analytical solutions are presented, and the obtained results are compared with the existing solutions to verify the validity of the developed theories. Many parameters are investigated, such as the Pasternak shear modulus parameter, the Winkler modulus parameter, the volume fraction, and the order of the exponent in the volume fraction equation. New results obtained from bending and stresses are presented and discussed in detail. From the obtained results, it became clear the influence of the exponential CNTs distribution and Winkler-Pasternak model improved the mechanical properties of the CNTRC beams.

• 한국세라믹학회지
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• 제40권11호
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• pp.1067-1072
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• 2003

Zn-Pr-Co-Cr-Dy 산화물계로 구성된 바리스터 세라믹스의 전기적 안정성을 몇 가지 DC 가속열화 스트레스 조건하에서 0.0∼2.0 mol% Dy$_2$O$_3$ 첨가량의 변화에 따라 조사하였다. 바리스터 세라믹스의 밀도는 Dy$_2$O$_3$ 첨가량이 0.5 mol%까지 증가하였으며, 보다 많이 첨가하면 감소하는 것으로 나타났다. 밀도는 전도경로와 밀접한 관계로 인해서 안정성에 큰 영향을 미치는 것으로 나타났다. Dy$_2$O$_3$ 첨가는 바리스터 세라믹스의 비직선 지수를 45 이상, 누설전류를 대략 1.0 $\mu$A 이하로 비직선성을 크게 개선시켰다. DC 스트레스 조건 0.95 V$_{1mA}$/15$0^{\circ}C$/24 h에서 안정성을 조사한 결과, 0.5 mol% 첨가시 상대적으로 가장 높은 안정성을 나타내었다. 전압-전류특성에 있어서 바리스터 전압, 비직선 지수, 누설전류의 변화율은 각각 -0.9%, -14.4%, +483.3%이었으며, 유전특성에 있어서 비유전율 및 손실계수의 변화는 각각 +7.1%, +315.4%이었다. 그 외의 바리스터 세라믹스는 낮은 밀도 때문에 열폭주 현상을 나타내는 매우 불안정한 특성을 나타내었다.다.

• 지식경영연구
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• 제22권4호
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• pp.119-133
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• 2021

각 산업에서 대량의 데이터가 생산되면서, 빠른 경영 의사결정을 위해 시계열 패턴 예측 연구가 수많이 진행되고 있다. 하지만 데이터에 내재된 불확실성으로 인해 비선형 시계열 데이터의 특정 패턴을 예측하는 데 한계가 존재하고, 기업경영의 전략적 의사결정 어려움이 존재한다. 또한, 최근 수십 년간 불규칙한 랜덤워크 모형의 시계열 데이터 예측을 위해 산업의 목적에 맞는 금융시장 데이터를 대상으로 다양한 연구가 진행되고 있지만, 특정 규칙을 예측하고 지속가능의 기업목적 달성 어려움이 있다. 본 연구에서는 룰렛 데이터와 금융시장 데이터를 Chaos 분석기법을 이용하여 예측 결과를 비교분석하고 유의미한 결과를 도출하였다. 그리고, 본 연구는 카오스 분석이 시계열 자료를 분석하는데 있어 새로운 방법을 모색하는데 유용함을 확인하였다. 룰렛 게임의 특성을 한국 주가지수 선물의 시계열과 비교 분석하여 추세가 확인되는 경우 예측력을 높일 수 있다는 점을 도출하였으며, 불확실성이 높고 랜덤워크가 존재하는 비선형 시계열 데이터가 특정한 패턴을 가지고 있는지 판단하는데 의의가 있다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 영호남학술대회 논문집
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• pp.179-184
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• 2000

The I-V characteristics of $ZnO-Pr_6O_{11}-CoO-Dy_2O_3$ based varistors were investigated in the $Pr_6O_{11}/CoO$ composition ratio range of 0.5/0.5 to 1.0/1.0 and sintering temperature range of 1300 to $1350^{\circ}C$ as the basic study to develop the advanced $Pr_6O_{11}$-based ZnO varistors. All varistors except for $Pr_6O_{11}$/CoO = 0.5/1.0 exhibited the best I-V characteristics at $1350^{\circ}C$. However, the varistors with $Pr_6O_{11}$/CoO= 0.5/1.0 exhibited the best I-V characteristics at $1350^{\circ}C$. The varistors with $Pr_6O_{11}$/CoO= 0.5/1.0 of all varistors exhibited the best I-V characteristics, which the nonlinear exponent is 36.9 and the leakage current is 7.6 ${\mu}A$ Therefore, it was estimated that ZnO-$Pr_6O_{11}-CoO-Dy_2O_3$ ceramics with $Pr_6O_{11}$/CoO= 0.5/1.0 will be usefully used as varistor materials in the future.

• Journal of Acupuncture Research
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• 제18권2호
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• pp.67-78
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• 2001

The aim of this study was to examine the effects of low frequency electroacupuncture(EA) at the $B_{62}$ (Shinmaek) $K_6$(Chohae) on vascular dementia in humans using nonlinear dynamics. Electroencephalogram(EEG) is a multi-scaled signal consisting of several components of time series with different dominant frequency ranges and different origins. Nonlinear measures of the EEG like the correlation dimension ($D_2$) and the first positive Lyapunov exponent ($L_1$) reflect the complexity of the EEG. In this study, $D_2$ was used as a measure of complexity. Sixteen channel EEG study was carried out in six subjects (5 females and 1 males; $age=83.83{\pm}7.19years$). We found that the baseline $D_2$ values of the EEG at F4 and F8 channels (P<0.01) were lowered than during the acupuncture treatment, indicating decreased complexity of the EEG. However, the comparison with that before and after the treatment shows no significant differences in all channels.

• Steel and Composite Structures
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• 제49권3호
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• pp.307-323
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• 2023

In this research, the study of the thermoelastic flexural analysis of silicon carbide/Aluminum graded (FG) sandwich 2D uniform structure (plate) under harmonic sinusoidal temperature load over time is presented. The plate is modeled using a simple two dimensional integral shear deformation plate theory. The current formulation contains an integral terms whose aim is to reduce a number of variables compared to others similar solutions and therefore minimize the computation time. The transverse shear stresses vary according to parabolic distribution and vanish at the free surfaces of the structure without any use of correction factors. The external load is applied on the upper face and varying in the thickness of the plates. The structure is supposed to be composed of "three layers" and resting on nonlinear visco-Pasternak's-foundations. The governing equations of the system are deduced and solved via Hamilton's principle and general solution. The computed results are compared with those existing in the literature to validate the current formulation. The impacts of the parameters (material index, temperature exponent, geometry ratio, time, top/bottom temperature ratio, elastic foundation type, and damping coefficient) on the dynamic flexural response are studied.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1689-1691
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• 1999

The conduction characteristics of $Pr_6O_{11}$-based ZnO varistor were investigated. ZnO-$Pr_6O_{11}$-CoO-$Sm_2O_3$-based ZnO varistor were sintered at $1300^{\circ}C$ and $1350^{\circ}C$ in the addition range $0.0\sim2.0mol%$ $Sm_2O_3$, respectively. ZnO varistors which are added with 1.0mol% at each temperature exhibited best excellent conduction characteristics, namely the nonlinear exponent was 42.05 at $1300^{\circ}C$, 36.79 at $1350^{\circ}C$ and leakage current was $9.16{\mu}A$ at $1300^{\circ}C$, $11.7{\mu}A$ at $1350^{\circ}C$. Consequently, it is estimated that ZnO-$Pr_6O_{11}$-CoO-$Sm_2O_3$-based ZnO varistors, which $Sm_2O_3$ is added 1.0mol% is to be used as a basic composition of $Pr_6O_{11}$-based ZnO varistors.

• 농촌계획
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• 제14권2호
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• pp.55-64
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• 2008

This study aims to analyze the sensitivity of WSM(weighted scenario method)-AHP method according to variation of nonlinear exponent for accessibility criteria, which are used to make urbanization potential maps with the optimal weighting value for multiple criteria in grid-based GIS technique. Besides this study tried to develop WSM-AHP2 which is simplified by using rank of the potential value for each scenario. The two methods were applied to the test area, Suwon city located south area of Seoul, with time series land-use maps of 1986 and 1996. The evaluation system of urbanization potential have 7 criteria including 6 accessibility criteria. The results of WSM-AHP2, the optimal weighting values and their corresponding potential maps, have almost similar with those of WSM-AHP. In the application of CA(cellular automata) model for expansion of urbanized area using the three potential maps by WSM-AHP, WSM-AHP2, and specialists's AHP evaluation, it also showed that the accuracy of simulation for actual urban area is the highest in the potential map of WSM-AHP, followed by WSM-AHP2 and specialists's AHP evaluation. From the results of this study, WSM-AHP and simplified WSM-AHP2 will be used to generate the optimal potential maps for land-use planning in urban fringe area.

• Safety and Health at Work
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• 제4권1호
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• pp.46-51
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• 2013

Objectives: Load carrying tasks are recognized as one of the primary occupational factors leading to slip and fall injuries. Nevertheless, the mechanisms associated with load carrying and walking stability remain illusive. The objective of the current study was to apply local dynamic stability measure in walking while carrying a load, and to investigate the possible adaptive gait stability changes. Methods: Current study involved 25 young adults in a biomechanics research laboratory. One tri-axial accelerometer was used to measure three-dimensional low back acceleration during continuous treadmill walking. Local dynamic stability was quantified by the maximum Lyapunov exponent (maxLE) from a nonlinear dynamics approach. Results: Long term maxLE was found to be significant higher under load condition than no-load condition in all three reference axes, indicating the declined local dynamic stability associated with load carrying. Conclusion: Current study confirmed the sensitivity of local dynamic stability measure in load carrying situation. It was concluded that load carrying tasks were associated with declined local dynamic stability, which may result in increased risk of fall accident. This finding has implications in preventing fall accidents associated with occupational load carrying.

• Advances in nano research
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• 제9권3호
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• pp.211-220
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• 2020

This paper investigates the effect of linear and non-linear distribution of carbon nanotube volume fraction in the FG-CNTRC beams on the critical buckling by using higher-order shear deformation theories. Here, the material properties of the CNTRC beams are assumed to be graded in the thickness direction according to a new exponential power law distribution in terms of the carbon nanotube volume fractions. The single-walled carbon nanotube is aligned and distributed in the polymeric matrix with different patterns of reinforcement; the material properties of the CNTRC beams are described by using the rule of mixture. The governing equations are derived through using Hamilton's principle. The Navier solution method is used under the specified boundary conditions for simply supported CNTRC beams. The mathematical models provided in this work are numerically validated by comparison with some available results. New results of critical buckling with the non-linear distribution of CNT volume fraction in different patterns are presented and discussed in detail, and compared with the linear distribution. Several aspects of beam types, CNT volume fraction, exponent degree (n), aspect ratio, etc., are taken into this investigation. It is revealed that the influences of non-linearity distribution in the beam play an important role to improve the mechanical properties, especially in buckling behavior. The results show that the X-Beam configuration is the strongest among all different types of CNTRC beams in supporting the buckling loads.