• Geomechanics and Engineering
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• 제28권5호
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• pp.477-491
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• 2022

In the present study, the effects of thermal loading on the buckling and resonance frequency of graphene platelets (GPL) reinforced nano-composites are examined. Functionally graded (FG) material properties are considered in thickness direction for the thermal responses of the composite. The equivalent material properties are obtained using Halphin-Tsai nano-mechanical model for composite layers. Moreover, the effects of nano-scale sizes are taken into account, employing functionally modified couple stress (FMCS) parameter. In this regard, for the first time, it is demonstrated that at certain values of GPL weight fraction, thermal buckling occurs. In obtaining results of vibrational behavior, both analytical solution and deep neural network (DNN) methods are used. The DNN method needs low computational costs to predict the resonance behavior. A comprehensive parametric study is conducted to indicate the effects of several geometrical, material, and loading conditions on the vibrational and buckling behavior of cylindrical shell structures made of GPL-nanocomposites. It is shown that the effect of temperature change on the occurrence of buckling is vital while it has a negligible impact on the resonance frequency of the structure. Moreover, the size-dependency of the results is demonstrated, and it cannot be neglected in nano-scales.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.649-654
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• 2003

This paper is focused on the research of the ultra precision linear motor by using piezo stack actuators. The development of linear motor which can be controlled nano or micro scale is necessary for the precision manufacturing. Self-moving-cell principle is used for the design of linear motor Self-moving-cell linear motor is consisted of three cell structures, and each cell has two shells and one piezo-stack actuator. Each cell can do clamping and moving by two shell structures. The shell structure deformation by piezo stack actuator can move the linear motor by losing the clamping between the shall and guideway. This paper presents the design, manufacturing and test of the motor.

• Smart Structures and Systems
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• 제23권5호
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• pp.429-447
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• 2019

The present study analyzed free vibration of the three-layered micro annular/circular plate which its core and face sheets are made of saturated porous materials and FG-CNTRCs, respectively. The structure is subjected to magneto-electric fields and magneto-electro-mechanical pre loads. Mechanical properties of the porous core and also FG-CNTRC face sheets are varied through the thickness direction. Using dynamic Hamilton's principle, the motion equations based on MCS and FSD theories are derived and solved via GDQ as an efficient numerical method. Effect of different parameters such as pores distributions, porosity coefficient, pores compressibility, CNTs distribution, elastic foundation, multi-physical pre loads, small scale parameter and aspect ratio of the plate are investigated. The findings of this study can be useful for designing smart structures such as sensor and actuator.

• 반도체디스플레이기술학회지
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• 제21권4호
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• pp.1-5
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• 2022

We presented a micro hemi-sphere structure flexible film to improve the external quantum efficiency (EQE) in OLEDs. The micro hemi-sphere flexible film was fabricated with breath figure (BF) method and replica process. At 45 mg/mL of concentration, the size of the hemi-spheres was approximately 6.2 ㎛ were obtained which are the most circular shape. So, it was possible to yield the best performance with an improvement of 33 % in the EQE and the widest viewing angle ranging from 0° to 70°. As a result, the hemi-sphere film's size and distribution seem to play important roles in enhancing the EQE in OLEDs. Furthermore, the flexible hemi-sphere film based on polymeric materials could offer an effective, large-scale, mass-produced product and a simple process and approach to achieve high efficiency in flexible OLEDs.

• Structural Engineering and Mechanics
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• 제84권1호
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• pp.77-83
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• 2022

In the last ten years, many researchers have studied the vibrations of carbon nanotubes using different beam theories. The nano- and micro-scale systems have wavy shape and there is a demand for a powerful tool to mathematically model waviness of those systems. In accordance with the above mentioned lack for the modeling of the waviness of the curved tiny structure, a novel approach is employed by implementing the Timoshenko-beam model. Owing to the small size of the micro beam, these structures are very appropriate for designing small instruments. The vibrations of double walled carbon nanotubes (DWCNTs) are developed using the Timoshenko-beam model in conjunction with the wave propagation approach under support conditions to calculate the fundamental frequencies of DWCNTs. The frequency influence is observed with different parameters. Vibrations of the double walled carbon nanotubes are investigated in order to find their vibrational modes with frequencies. The aspect ratios and half axial wave mode with small length are investigated. It is calculated that these frequencies and ratios are dependent upon the length scale and aspect ratio.

• Structural Engineering and Mechanics
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• 제69권4호
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• pp.439-455
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• 2019

This research deals with thermo-electro-mechanical buckling analysis of the sandwich nano-beams with face-sheets made of functionally graded carbon nano-tubes reinforcement composite (FG-CNTRC) based on the nonlocal strain gradient elasticity theory (NSGET) considering various higher-order shear deformation beam theories (HSDBT). The sandwich nano-beam with FG-CNTRC face-sheets is subjected to thermal and electrical loads while is resting on Pasternak's foundation. It is assumed that the material properties of the face-sheets change continuously along the thickness direction according to different patterns for CNTs distribution. In order to include coupling of strain and electrical field in equation of motion, the nonlocal non-classical nano-beam model contains piezoelectric effect. The governing equations of motion are derived using Hamilton principle based on HSDBTs and NSGET. The differential quadrature method (DQM) is used to calculate the mechanical buckling loads of sandwich nano-beam as well as critical voltage and temperature rising. After verification with validated reference, comprehensive numerical results are presented to investigate the influence of important parameters such as various HSDBTs, length scale parameter (strain gradient parameter), the nonlocal parameter, the CNTs volume fraction, Pasternak's foundation coefficients, various boundary conditions, the CNTs efficiency parameter and geometric dimensions on the buckling behaviors of FG sandwich nano-beam. The numerical results indicate that, the amounts of the mechanical critical load calculated by PSDBT and TSDBT approximately have same values as well as ESDBT and ASDBT. Also, it is worthy noted that buckling load calculated by aforementioned theories is nearly smaller than buckling load estimated by FSDBT. Also, similar aforementioned structure is used to building the nano/micro oscillators.

• Advances in nano research
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• 제9권3호
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• pp.133-145
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• 2020

In this study, nonlinear vibrations and dynamic instabilities of a smart embedded micro shell conveying varied fluid flow and subjected to the combined electro-thermo-mechanical loadings are investigated. With the aim of designing new hydraulic sensors and actuators, the piezoelectric materials are employed for the body and the effects of applying electric field on the stability of the system as well as the induced voltage due to the dynamic behavior of the system are studied. The nonlocal piezoelasticity theory and the nonlinear cylindrical shell model in conjunction with the energy approach are utilized to mathematically modeling of the structure. The fluid flow is assumed to be isentropic, incompressible and fully develop, and for more generality of the problem both steady and time dependent flow regimes are considered. The mathematical modeling of fluid flow is also carried out based on a scalar potential function, time mean Navier-Stokes equations and the theory of slip boundary condition. Employing the modified Lagrange equations for open systems, the nonlinear coupled governing equations of motion are achieved and solved via the state space problem; forth order numerical integration and Bolotin's method. In the numerical results, a comprehensive discussion is made on the dynamical instabilities of the system (such as divergence, flutter and parametric resonance). We found that applying positive electric potential field will improve the stability of the system as an actuator or vibration amplitude controller in the micro electro mechanical systems.

• 대한기계학회논문집B
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• 제28권3호
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• pp.265-270
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• 2004

Experiment study on a down scaled two-phase catalytic reactor is presented. As a preliminary step for the development of catalytic reactor, nano-particulate catalyst was prepared. Perovskite La$\_$0.8/Sr$\_$0.2/CoO$_3$is chosen and synthesized as a catalyst considering superior catalytic performance in reduction and oxidation process where oxygen is involved among the reagent. Reactor that has a scale of 2${\times}$10${\times}$25mm was made by machining of A1 block as a layered structure considering further extension to micro-machining. Hydrogen peroxide of 70wt% was adopted as reactant and was provided to the reactor loaded with 1.5 g of catalyst. Reactant flow rate was varied by precision pump with a range of 0.15cc/min to 17.2cc/min. Temperature distribution within reactor was recorded by 3 thermocouples and total amount of liquid product was measured. Temperature distribution and factors that affect temperature were observed and relation between temperature distribution and production rate was also analyzed. Relative time scale plays a significant role in the performance of the reactor. To obtain steady state operation, appropriate ratio of flow rate, catalyst mass and reactor geometry is required and furthermore to get more efficient production rate temperature distribution should be evenly distributed. The database obtained by the experiment will be used as a design parameter for micro reactor.

• 한국미생물생명공학회:학술대회논문집
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• 한국미생물생명공학회 2004년도 Annual Meeting BioExibition International Symposium
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• pp.187-193
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• 2004

This paper covers the basic principles of the AFM and how these systems may be used to image biological materials and measure particle-surface interactions in process environments. e.g. visualize molecules and structure on surfaces in aqueous environments, measure forces of interaction of proteins and DNA, biosurface and cells. Examples of work include applications biological spore control agents control systems, process materials selection for example appropriate filters for biological processing, mechanical properties and bio-surface engineering.

• 한국광학회지
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• 제24권2호
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• pp.53-57
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• 2013

본 논문에서는 금속 슬릿 배열로 구성된 편광 선택 가능한 블레이즈드 회절 격자를 제안한다. 마이크로 스케일의 블레이즈드 회절 격자를 디자인 하고 이 구조에 추가적으로 나노스케일의 금속 슬릿 구조를 적용하여 편광 선택기능을 부여하였다. 이 소자에 대하여 사례 연구로 예를 디자인하여 FDTD(Finite Difference Time Domain method)방법을 이용한 전산모사를 통해 성능을 검증해 보았다. 임의의 디자인 사례에 대해 대략 77.61% 의 회절효율과 8.99의 편광선택비가 얻어졌으며 편광선택비를 높이기 위한 또 다른 디자인에서는 64.22%의 회절효율과 81.09의 편광선택비가 얻어졌다.