• Journal of the Korean Society of Visualization
• /
• v.15 no.3
• /
• pp.14-19
• /
• 2017

Increase of blood viscosity significantly changes the flow resistance and wall shear stress which are related with cardiovascular diseases. For measurement of blood viscosity, microfluidic method has proposed by monitoring pressure between sample and reference flows in the downstream of a microchannel with two inlets. However, it is difficult to apply this method to unknown flow conditions. To measure blood viscosity under unknown flow conditions, a microfluidic method based on micro particle image velocimetry(PIV) is proposed in this study. Flow rate in the microchannel was estimated by assuming velocity profiles represent mean value along channel depth. To demonstrate the measurement accuracy of flow rate, the flow rates measured at the upstream and downstream of a T-shaped microchannel were compared with injection flow rate. The present results indicate that blood viscosity could be reasonably estimated according to shear rate by measuring the interfacial width and flow rate of blood flow. This method would be useful for understanding the effects of hemorheological features on the cardiovascular diseases.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.32 no.4
• /
• pp.418-430
• /
• 2012

The present paper reviews the micro and nano nondestructive evaluation(NDE) technique that is possible to investigate the surface and measure the acoustic properties. The technical theory, features and applications of the ultrasonic atomic force microscopy(UAFM) and scanning acoustic microscopy(SAM) are illustrated. Especially, these technologies are possible to evaluate the mechanical properties in micro/nano structure and surface through the measurement of acoustic properties in addition to the observation of surface and subsurface. Consequently, it is thought that technique developments and applications of these micro/nano NDE in advanced industrial parts together with present nondestructive industry are widely possible hereafter.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.10
• /
• pp.1303-1313
• /
• 1997

A micro-macroscopic analysis on the conduction-controlled directional casting of Al-Cu alloys is performed, in which emphases are placed on the microstructural features. In order to facilitate the solution procedure, an iterative micro-macroscopic coupling algorithm is developed. The predicted results show that the effect of finite back diffusion on the transient solidification process in comparison with the lever rule depends essentially on the initial concentration of an alloy. In the final casting, the eutectic fraction is distributed in an increasing-decreasing-increasing pattern, each mode of which is named the chill, interior and end zones. This nonuniformity per se suffices to justify the necessity of this work because it originates from the combined effects of finite back diffusion and cooling path-dependent nature of the eutectic formation. As the cooling rate is enhanced, not only the influence depths of boundaries narrow, but also the eutectic fractions in the chill and interior zones increase. In addition, it is revealed for the first time that the micro segregation band is formed in response to a sudden change in cooling rate during the directional casting. An increasing change creates an overshooting band in the eutectic fraction distribution, and vice versa.

• Nuclear Engineering and Technology
• /
• v.56 no.10
• /
• pp.4103-4114
• /
• 2024

This research aimed to develop lead-free polymer composites based on poly-methyl methacrylate (PMMA) and embedded with tungsten carbide (WC) micro and nanoparticles for use in radiation protection applications. PMMA was filled with 20 %, 40 %, and 60 % by weight of WC micro- and nanoparticles. The shielding features of the proposed polymer mixtures were evaluated at different radioactive sources of different energies using the HPGe detector. The results revealed that the investigated composites containing micro and nano-structured WC particles showed superior radiation shielding at 81 keV due to the K-edge of the W element occurring at 69.5 keV. The findings also demonstrated that composites loaded with WC nanoparticles were more effective in shielding gamma radiation than those loaded with WC microparticles, even at the same filler wt.%. Furthermore, the sample containing 60 % by weight of nano-WC, coded as P-60nWC, had superior shielding performance than other polymer-based composites reported in the literature. Thus, the proposed nano-WC/PMMA composites can be effectively employed in radiation facilities as alternative environmentally and lead-free radiation shielding materials to protect people and the environment from the harmful risks of gamma radiation.

• Steel and Composite Structures
• /
• v.38 no.3
• /
• pp.337-353
• /
• 2021

Micro-electro-mechanical systems (MEMS) are widely employed in sensors, biomedical devices, optic sectors, and micro-accelerometers. New reinforcement materials such as carbon nanotubes as well as graphene platelets provide stiffer structures with controllable mechanical specifications by changing the graphene platelet features. This paper deals with buckling analyses of functionally graded graphene platelets micro plates with two piezoelectric layers subjected to external applied voltage. Governing equations are based on Kirchhoff plate theory assumptions beside the modified couple stress theory to incorporate the micro scale influences. A uniform temperature change and external electric field are regarded along the micro plate thickness. Moreover, an external in-plane mechanical load is uniformly distributed along the micro plate edges. The Hamilton's principle is employed to extract the governing equations. The material properties of each composite layer reinforced with graphene platelets of the considered micro plate are evaluated by the Halpin-Tsai micromechanical model. The governing equations are solved by the Navier's approach for the case of simply-supported boundary condition. The effects of the external applied voltage, the material length scale parameter, the thickness of the piezoelectric layers, the side, the length and the weight fraction of the graphene platelets as well as the graphene platelets distribution pattern on the critical buckling temperature change and on the critical buckling in-plane load are investigated. The outcomes illustrate the reduction of the thermal buckling strength independent of the graphene platelets distribution pattern while meanwhile the mechanical buckling strength is promoted. Furthermore, a negative voltage, -50 Volt, strengthens the micro plate stability against the thermal buckling occurrence about 9% while a positive voltage, 50 Volt, decreases the critical buckling load about 9% independent of the graphene platelet distribution pattern.

• Journal of the Korean Society of Combustion
• /
• v.19 no.4
• /
• pp.21-27
• /
• 2014

MGT (micro gas turbines) have been gaining particular attentions with a variety of commercial and military applications due to their advantages such as compact size, simple operability, easy maintenance, and low emissions. This study deals with development processes of an annular combustor applied to MGT. Preliminary design methodologies are used to size the main components of the combustor. Key design features such as liner temperatures and pressure losses are evaluated. Results show that the estimated liner temperatures are within acceptable range. Dominant factors for pressure losses are estimated to be air admission holes and burner swirlers.

• Journal of the Korean Society of Systems Engineering
• /
• v.15 no.2
• /
• pp.39-46
• /
• 2019

The purpose of this paper is to present the results of the study, applying Systems Engineering(SE) method, on the feasibility of developing a Melt-down Proof Modular Micro Reactor(MDP-MMR) for its future deployment in Korea. The reactor is being developed by NCSU (North Carolina State University) due to its advantage of melt-down proof nature of the reactor core. For this paper, the characteristics of the MDP-MMR has been studied in terms of fuel characteristics, inherent safety features and passive safety system. The NCSU's development process has been reviewed applying the SE method, and further research is recommended for the feasibility study on deploying such a modular micro reactor in Korea.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.11
• /
• pp.47-54
• /
• 2003

Research during the past several years has established the effectiveness of acoustic emission (AE)-based sensing methodologies for machine condition analysis and process. AE has been proposed and evaluated for a variety of sensing tasks as well as for use as a technique for quantitative studies of manufacturing process. STD11 has been known as difficult-to-cut materials. The micro-grooving machine was developed for this study and the experiments were performed using CBN blade for machining STD11. Evaluating the machining conditions, frequency spectrum analysis of acoustic emission (AE) signals according to each conditions were applied. Fuzzy clustering method for associating the preprocessor outputs with the appropriate decisions was followed by frequency spectrum analysis. FFT is used to decompose AE signal into different frequency bands in time domain, the root mean square (RMS) values extracted from the decomposed signal of each frequency band were used as features.

• Proceedings of the Korean Information Science Society Conference
• /
• 2005.07b
• /
• pp.286-288
• /
• 2005

MicroRNA (miRNA)는 작은 크기의 RNA분자로서 동식물의 유전자 발현 과점을 직접적으로 조절하는 인자로 알려져 있다. MiRNA는 보통 목표 유전자의 3'-UTR 영역에 상보성을 갖고 결합함으로써 작용하며 특히 miRNA의 5'부분의 8 nt 정도가 seed로서 중요하다고 알려져 있다. 반면 최근의 연구에 따르면 seed 부분의 서열의 조성 및 양상이 변화함에 따라 특이도가 결정됨을 알 수 있지만 기존의 컴퓨터를 이용한 miRNA 목표 유전자 예측 방법들은 이러한 정보를 활용하지 못한다. 본 논문에서는 열역학적인 수치와 서열의 조성뿐 아니라 miRNA:mRNA pair의 위치에 기반한 정보들을 학습에 자질로서 포함하여 목표 유전자를 예측한다. 그 결과는 위치 기반 자질이 학습 성능 향상에 중요하게 기여함을 보여준다.

• 제어로봇시스템학회:학술대회논문집
• /
• 2001.10a
• /
• pp.38.3-38
• /
• 2001

In the planetary surface exploration , micro-rovers or nano-rovers are very attractive choices for a surface exploration system providing mobility functions and other features required in the surface probe missions at small mass and relatively small cost. This paper surveys and summarizes the requirements for Mars exploration rovers in micro or nano scale and outlines the control concepts for navigation including the obstacle/hazard avoidance and the path planning. In this context, autonomous reaction capabilities are the key elements to control design in conjunction with the remote control schemes to deal with the significant signal propagation delays. Other navigation and control aspects such as the instrument fine positioning and the flip-over of the rovers are also briefly introduced. The current technical limitations of the micro- and nano-rovers are summarized.