• Advances in nano research
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• 제10권2호
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• pp.175-189
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• 2021

In this article, frequency characteristics, and sensitivity analysis of a size-dependent laminated composite cylindrical nanoshell under bi-directional thermal loading using Nonlocal Strain-stress Gradient Theory (NSGT) are presented. The governing equations of the laminated composite cylindrical nanoshell in thermal environment are developed using Hamilton's principle. The thermodynamic equations of the laminated cylindrical nanoshell are obtained using First-order Shear Deformation Theory (FSDT) and Fourier-expansion based Generalized Differential Quadrature element Method (FGDQM) is implemented to solve these equations and obtain natural frequency and critical temperature of the presented model. The novelty of the current study is to consider the effects of bi-directional temperature loading and sensitivity parameter on the critical temperature and frequency characteristics of the laminated composite nanostructure. Apart from semi-numerical solution, a finite element model was presented using the finite element package to simulate the response of the laminated cylindrical shell. The results created from finite element simulation illustrates a close agreement with the semi-numerical method results. Finally, the influences of temperature difference, ply angle, length scale and nonlocal parameters on the critical temperature, sensitivity, and frequency of the laminated composite nanostructure are investigated, in details.

• 열처리공학회지
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• 제37권1호
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• pp.1-8
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• 2024

Phase stability of tetragonal crystals in yttria-stabilized zirconia ceramics is dependent on the content of yttria and the heat-treatment condition, related with mechanical properties. In this study, we fabricated the 1.5 mol% yttria-stabilized zirconia (1.5Y-YSZ) ceramics by cold isostatic pressing (CIP) and post-sintering at temperature range of 1200 to 1350℃ for 2 hours and investigated the sintered properties and microstructural evolution. Sintered and microstructural parameters, i.e, apparent density, grain size and phase composition of 1.5Y-YSZ ceramics were mainly dependent on the sintering temperature. Maximum sintered density of 99.4 % and average grain size of 200-300 nm could be obtained from the heat-treatment condition above sintering temperature at 1300℃ for 2 hours, possessing the superior mechanical hardness with 1200 Hv. However, phase stability of tetragonal grains in 1.5 YSZ ceramics is very low, inducing the phase transformation to monoclinic crystals on specimen surface during cooling after heat-treatment.

• Structural Engineering and Mechanics
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• 제38권2호
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• pp.157-169
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• 2011

In this paper the time-dependent closed-form static solution of the suspended pre-stressed biconcave and biconvex cable trusses with unmovable, movable and elastic or viscoelastic yielding supports subjected to various types of vertical load is presented. Irvine's forms of the deflections and the cable equations are modified because the effects of the rheological behaviour needed to be incorporated in them. The concrete cable equations in the form of the explicit relations are derived and presented. From a solution of a vertical equilibrium equation for a loaded cable truss with rheological properties, the additional vertical deflection as a time-function is determined. The time-dependent closed-form model serves to determine the time-dependent response, i.e., horizontal components of cable forces and deflection of the cable truss due to applied loading at the investigated time considering effects of elastic deformations, creep strains, temperature changes and elastic supports. Results obtained by the present closed-form solution are compared with those obtained by FEM. The derived time-dependent closed-form computational model is used for a time-dependent simulation-based reliability assessment of cable trusses as is described in the second part of this paper.

• 조명전기설비학회논문지
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• 제28권6호
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• pp.68-74
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• 2014

The electrical parameters of soils are highly dependent on the various factors such as types of soil, chemical compositions, moisture content, temperature, frequency, and so on. The analysis of soil parameters is of fundamental importance in design of grounding systems. In this paper, we present the experimental results of frequency-dependent impedance, resistivity, permittivity of soils as functions of types of soil and moisture content. The impedance and resistivity of soils are decreased as the moisture content and the frequency increase. In particular, the variation of the soil resistivity with the frequency is pronounced in the conditions of high resistivity and low moisture content. On the contrary, the permittivity of soils are sharply decreased with increasing the frequency below 10kHz and the frequency-dependent permittivity of soils are highly changed in the conditions of high moisture and low resistivity.

• Food Science and Biotechnology
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• 제14권3호
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• pp.413-415
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• 2005

Time-dependent flow properties of commercial kochujang (hot pepper-soybean paste) were evaluated at various shear rates (5, 15, 25, and $35\;sec^{-1}$) and temperatures (5, 15, and $25^{\circ}C$). Flow properties of all samples showed thixotropic behaviors, which were qualitatively evaluated and quantitatively described by the Weltman, Hahn, and Figoni and Shoemaker models. Time-dependent flow properties of kochujang were found to vary over the range of the shear rate and temperature investigated. Time-dependent models of Weltman and Hahn were suitable ($R^2=0.923-0.987$) for commercial kochujang.

• 대한의용생체공학회:의공학회지
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• 제20권2호
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• pp.191-198
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• 1999

바이오피드백은 혈압 심박율, 말초체온, 호흡, 근전도 등과 같이 자율신경에 의해 지배받는 신체 기능들을 훈련을 통해 스스로 조절할 수 있게 하여 자율신경의 이상으로 인한 여러 가지 질병들을 치료할 수 있게 하는 방법이다. 븐 논문에서는 주정중독증 환자들을 대상으로 바이오피드백 훈련을 실시할 수 있도록 근전도, 호흡, 맥파, 말초체온, 피부전기전도도 등 다섯 가지 신호를 측정할 수 있는 바이오피드백 시스템을 개발하였다. 개발된 시스템을 이용해 주정중독증 환자들을 대상으로 바이오피드백 훈련을 실시하였다 이완 바이오피드백 훈련을 실행하였으며 생체신호변화에 대해 퍼지이론을 적용하여 긴장상태를 판단하였다. 8명의 주정중독증 환자들이 실험에 참가하였으며 측정된 데이터를 분석한 결과는 다음과 같다. 1) 환자 군은 일반인에 비해서 높은 긴장도 값을 보였다. 2) 환자들의 긴장도 값은 훈련 회수가 증가함에 따라 감소하는 추세를 보였다.

• Steel and Composite Structures
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• 제33권4호
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• pp.509-523
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• 2019

In the present work, the buckling analysis of micro sandwich plate with an isotropic/orthotropic cores and piezoelectric/polymeric nanocomposite face sheets is studied. In this research, two cases for core of micro sandwich plate is considered that involve five isotropic Devineycell materials (H30, H45, H60, H100 and H200) and an orthotropic material also two cases for facesheets of micro sandwich plate is illustrated that include piezoelectric layers reinforced by carbon and boron-nitride nanotubes and polymeric matrix reinforced by carbon nanotubes under temperature-dependent and hydro material properties on the elastic foundations. The first order shear deformation theory (FSDT) is adopted to model micro sandwich plate and to apply size dependent effects from modified strain gradient theory. The governing equations are derived using the minimum total potential energy principle and then solved by analytical method. Also, the effects of different parameters such as size dependent, side ratio, volume fraction, various material properties for cores and facesheets and temperature and humidity changes on the dimensionless critical buckling load are investigated. It is shown from the results that the dimensionless critical buckling load for boron nitride nanotube is lower than that of for carbon nanotube. It is illustrated that the dimensionless critical buckling load for Devineycell H200 is highest and lowest for H30. Also, the obtained results for micro sandwich plate with piezoelectric facesheets reinforced by carbon nanotubes (case b) is higher than other states (cases a and c).The results of this research can be used in aircraft, automotive, shipbuilding industries and biomedicine.

• 한국응용곤충학회지
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• 제61권4호
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• pp.577-590
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• 2022

콩줄기명나방은 콩과작물 특히 팥을 가해하는 해충으로 알려져 있다. 본 연구는 온도가 콩줄기명나방의 발육단계별 발육기간, 성충의 수명과 산란특성에 미치는 영향을 파악하고자 7, 10, 13, 16, 19, 22, 25, 28, 31, 34, 36℃ 항온조건에서 조사하였다. 알과 유충은 7, 10, 13℃를 제외한 항온조건에서 다음 생애단계로 성공적으로 발육하였다. 알, 유충, 번데기의 발육기간은 온도가 상승할수록 짧아지는 경향을 보였다. 콩줄기명나방 발육단계별 발육 최저, 최고 한계는 LRF와 SSI모델을 이용하여 계산하였고 발육영점온도와 유효적산온일도는 선형회귀분석을 이용하였다. 1령 유충 부화부터 성충출현까지의 발육영점온도와 유효적산온일도는 13.5℃와 384.5DD로 추정되었다. SSI모델을 이용한 부화부터 성충출현까지 발육 최저 및 최고온도는 19.4℃과 39.8℃였고 이들간의 차이 즉 발육적정온도범위는 20.4℃였다. 성충은 16℃와 34℃ 범위에서 부화하는 알을 생산하였고, 25℃에서 최대 약 416마리의 자손을 낳았다. 노화율, 나이별 생존율, 나이별 누적산란율, 온도의존 산란수에 관련된 성충모델들이 작성되었다. 본 연구에서 제시한 온도발육모형과 산란모형은 야외에서 콩줄기명나방의 개체군동태를 이해하고 콩과작물의 종합적인 해충군관리체계를 마련하는데 기초기반자료로 활용될 것으로 기대된다.

• 소성∙가공
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• 제20권3호
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• pp.229-235
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• 2011

The formability of magnesium alloy sheets at room temperature is generally low because of the inherently limited number of slip systems, but higher at temperatures over $150^{\circ}C$. Therefore, prior to the practical application of these materials, the forming limits should be evaluated as a function of the temperature and strain rate. This can be achieved experimentally by performing a series of tests or analytically by deriving the corresponding modeling approaches. However, before the formability analysis can be conducted, a model of flow stress, which includes the effects of strain, strain rate and temperature, should be carefully identified. In this paper, such procedure is carried out for Mg alloy AZ31 and the concept of flow stress surface is proposed. Experimental flow stresses at four temperature levels ($150^{\circ}C$, $200^{\circ}C$, $250^{\circ}C$, $300^{\circ}C$) each with the pre-assigned strain rate levels of $0.01s^{-1}$, $0.1s^{-1}$ and $1.0s^{-1}$ are collected in order to establish the relationships between these variables. The temperature-compensated strain rate parameter which combines, in a single variable, the effects of temperature and strain rate, is introduced to capture these relationships in a compact manner. This study shows that the proposed concept of flow stress surface is practically relevant for the evaluation of temperature and strain dependent formability.

• 센서학회지
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• 제31권3호
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• pp.163-167
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• 2022

In this study, we investigated a carbon nanotube (CNT) film sensor to detect hazardous and noxious substances distributed in seawater. The response change of the sensor was studied according to environmental temperature, and its temperature coefficient of resistance (TCR, α) was measured. The temperature of the CNT film (~50 ㎛) was in the range of 20-50 ℃, and αCNT was calculated to be -0.0011 %/ ℃. We experimentally confirmed that the CNT film had a smaller TCR value than that of the conventional sensor. Therefore, we investigated the response change of the CNT sensor according to temperature. The CNT sensor showed a relatively small error of approximately 2.3 % up to 30 ℃, which is within the temperature range of the seawater of the Korean Peninsula. However, when the temperature exceeded 40 ℃, the error in the CNT sensor increased by more than 5.2 %. We fabricated a metal oxide (ITO, indium-tin-oxide) film and compared its performance with that of the CNT sensor. The ITO sensor showed an error of >12.5 % at 30 ℃, indicating that in terms of the stability of the sensor to temperature, the CNT film sensor has superior performance.