[가솔린엔진부문] 직동식 밸브트레인 시스템의 캠/태핏 접촉부의 혼합 윤활 해석

신홍주(Heungjoo Shin),조명래(Myungrae Cho),한동철(Dongchul Han) 한국자동차공학회 2000 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

This paper reports on the mixed lubrication characteristics between the cam and tapper contact surface on the direct acting type valvetrain systems. At first, the dynamic characteristics are solved by using the lumped mass method to determine the load conditions at the contact point. And then, the minimum oil film thickness is calculated with consideration of elastohydrodynamic line contact theory and friction force is obtained by using the mixed lubrication model which separates hydrodynamic and boundary friction. Finally, the average surface temperatures are calculated by using the flash temperatures theory. As results of analysis, there are some peak in the friction force due to the asperity contact friction, and flash temperature at the position of minimum oil film thickness. It is thought that there is some relation between the surface temperature and cam surface wear, therefore the analysis on the worn cam profile has been performed.

고민감도 센서 응용을 위한 금속 빗살무늬 나노전극쌍 개발

신흥주(Heungjoo Shin),심대식(Dae-Shick Shim),허정일(Jeong-Il Heo),김진로(Jin-Ro Kim),박형열(Hyung-Ryul Park),류윤하(Yun-Ha Ryu),Marc Madou 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11

This paper presents a simple nanofabrication technique for interdigitated array (IDA) nanoelectrodes enabling highly sensitive detection of dopamine by collecting electrochemical current amplified through redox cycling between the fingers of the IDA nanoelectrodes of high aspect ratio. The aspect ratio affecting the signal amplification dominantly can be controlled in deliberate manner through carbon-MEMS and electroplating processes. The carbon-MEMS process which consists of a conventional photolithography followed by pyrolysis converts micrometer size photoresist patterns into nanometer size glassy carbon structures but maximizing electrode aspect ratio is limited because of the non-isotropic volume shrinkage rate during the pyrolysis process. Directional gold electroplating processes onto pre-patterned the carbon nanoelectrodes without a mould overcame the limitation resulting in higher signal amplification compared to the bare carbon nanoelectrodes. The metal coated high aspect ratio IDA nanoelectrodes demonstrated the feasibility as a highly sensitive sensor of low cost for neurotransmitters, especially dopamine.

Current application of micro/nano-interfaces to stimulate and analyze cellular responses.

Cho, Yoon-Kyoung,Shin, Heungjoo,Lee, Sung Kuk,Kim, Taesung Pergamon Press [etc.] 2010 Annals of biomedical engineering Vol.38 No.6

<P>Microfabrication technologies have a high potential for novel approaches to access living cells at a cellular or even at a molecular level. In the course of reviewing and discussing the current application of microinterface systems including nanointerfaces to stimulate and analyze cellular responses with subcellular resolution, this article focuses on interfaces based on microfluidics, nanoparticles, and scanning electrochemical microscopy (SECM). Micro/nanointerface systems provide a novel, attractive means for cell study because they are capable of regulating and monitoring cellular signals simultaneously and repeatedly, leading us to an enhanced understanding and interpretation of cellular responses. Therefore, it is hoped that the integrated micro/nanointerfaces presented in this review will contribute to future developments of cell biology and facilitate advanced biomedical applications.</P>

Computational Analysis for Morphological Evolution in Pyrolysis for Micro/Nanofabrication

Yang, Myeongseok,Lee, Wooju,Shin, Heungjoo,Kim, Dongchoul Hindawi Limited 2015 Journal of nanomaterials Vol.2015 No.-

<P>Pyrolysis is recently proposed as an efficient fabrication technique of micro/nanoscale carbon structures. In order to understand the morphological evolution in pyrolysis and design the final shape of carbon structure, this study proposes a comprehensive model that incorporates the essential mechanisms of pyrolysis based on the phase field framework. Computational analysis with the developed model provides information about the effect of interface energy and kinetic rate on the morphological evolution in pyrolysis.</P>

Effects of hole patterns on surface temperature distributions in pool boiling

Seo, Han,Lim, Yeongjin,Shin, Heungjoo,Bang, In Cheol Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.120 No.-

<P><B>Abstract</B></P> <P>This paper presents the results of a study on critical heat flux (CHF) and boiling heat transfer (BHT) enhancements of a heating surface modified through the addition of holes of various dimensions. A layer of indium tin oxide was used as the heater material and holes of various patterns were incorporated onto the heating surfaces. The hole sizes and positions were controlled for precision using conventional microelectromechanical fabrication processes. Four types of heating surfaces were considered: (1) plain (i.e., no holes), (2) 9-hole, (3) 49-hole, and (4) 225-hole surfaces. For the 9 hole, 49 hole, and 225 hole patterned surfaces, and as compared to the plain heating surface, the CHF was enhanced by 16.7, 27.3, and 33.1%, respectively and heat transfer coefficients enhanced by 9.8, 26, and 26%, respectively. For the hole-patterned heating surfaces, distinct temperature distributions were observed consistently in the high heat flux regions – that is to say, the patterned areas exhibited lower temperature fields than the non-patterned areas. This indicates that heat was transferred more efficiently at the hole-patterned regions than at the neighboring non-patterned regions. The CHF and BHT performances were enhanced at the patterned surfaces because the high-temperature regions were well dispersed resulting in an increased effective heat transfer area. The CHF enhancement can be explained by the concept of the additional water supply on the heating surfaces.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of hole patterns and their role in CHF and BHT enhancement are reported. </LI> <LI> Distinct temperature distributions are observed in the high heat flux regions. </LI> <LI> Heat is transferred effectively at patterned regions than at neighboring regions. </LI> <LI> CHF enhancement is explained by additional water supply concept on heating surfaces. </LI> </UL> </P>

Mixed-scale poly(methyl methacrylate) channel network-based single-particle manipulation <i>via</i> diffusiophoresis

Hong, Jisoo,Kim, Beomsang,Shin, Heungjoo The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.30

<P>Despite the unique advantages of nanochannels imparted by their small size, their utility is limited by the lack of affordable and versatile fabrication methods. Moreover, nanochannel-incorporated fluidic devices require micro-sized conduit integration for efficient access of liquid samples. In this study, a simple and cost-effective fabrication method for mixed-scale channel networks <I>via</I> hot-embossing of poly(methyl methacrylate) (PMMA) using a carbon stamp is demonstrated. Due to its high rigidity, PMMA ensures collapse-free channel fabrication. The carbon stamp is fabricated using only batch microfabrication and has a convex architecture that allows the fabrication of a complex channel network <I>via</I> a single imprinting process. In addition, the microchannels are connected to nanochannels <I>via</I> three-dimensional (3D) microfunnels that serve as single-particle-entrapment chambers, ensuring smooth transport of samples into the nanochannels. Owing to the 3D geometry of the microfunnels and the small size of the nanochannels, a solute gradient can be generated locally at the microfunnel. This local solute gradient enables the entrapment of microparticles at the microfunnels <I>via</I> diffusiophoresis, which can manipulate the particle motion in a controllable manner, without any external equipment or additional electrode integration into the channels. To the best of our knowledge, this is the first report of diffusiophoresis-based single-particle entrapment.</P>

An electrochemical immunosensor based on a 3D carbon system consisting of a suspended mesh and substrate-bound interdigitated array nanoelectrodes for sensitive cardiac biomarker detection

Sharma, Deepti,Lee, Jongmin,Shin, Heungjoo Elsevier Applied Science 2018 Biosensors & bioelectronics Vol. No.

<P><B>Abstract</B></P> <P>We developed an electrochemical redox cycling-based immunosensor using a 3D carbon system consisting of a suspended mesh and substrate-bound interdigitated array (IDA) nanoelectrodes. The carbon structures were fabricated using a simple, cost-effective, and reproducible microfabrication technology known as carbon microelectromechanical systems (C-MEMS). We demonstrated that the 3D sub-micrometer-sized mesh architecture and selective modification of the suspended mesh facilitated the efficient production of large quantities of electrochemical redox species. The electrochemically active surfaces and small size of IDA nanoelectrodes with a 1:1 aspect ratio exhibited high signal amplification resulting from efficient redox cycling of electrochemical species (PAP/PQI) by a factor of ~25. The proposed selective surface modification scheme facilitated efficient redox cycling and exhibited a linear detection range of 0.001–100 ng/mL for cardiac myoglobin (cMyo). The specific detection of cMyo was also achieved in the presence of other interfering species. Moreover, the proposed 3D carbon system-based immunosensor successfully detected as low as ~0.4 pg/mL cMyo in phosphate-buffered saline and human serum.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An electrochemical redox cycling-based immunosensor using a 3D carbon system was developed. </LI> <LI> The 3D carbon systems consisted of a suspended mesh and substrate-bound interdigitated array (IDA) nanoelectrodes. </LI> <LI> A small gap between the sandwich immunoassay on the mesh and IDA nanoelectrodes ensured effective supply of redox species. </LI> <LI> Small size of the substrate-bound IDA nanoelectrodes resulted in efficient redox cycling. </LI> <LI> A detection limit of 0.43 pg/mL and linear range of 0.001–100 ng/mL for cardiac myoglobin detection were achieved. </LI> </UL> </P>

Self-heating hydrogen gas sensor based on an array of single suspended carbon nanowires functionalized with palladium nanoparticles

Seo, Junyoung,Lim, Yeongjin,Shin, Heungjoo Elsevier 2017 Sensors and actuators. B Chemical Vol.247 No.-

<P><B>Abstract</B></P> <P>This study reports the development of a novel hydrogen gas sensor based on an array of single suspended carbon nanowires (diameter ∼200nm, length ∼100μm) decorated with Pd nanoparticles (PdNPs) of various sizes for room temperature H<SUB>2</SUB> gas sensing. These sensors provide high sensitivity, a wide sensing range (10ppm – 5%), and complete gas response recovery in 5s with ultralow power consumption (30μW). Such performance is achieved using a novel suspended PdNP/carbon nanowire architecture, which offers enhanced mass transfer, high surface area to volume ratios, and good thermal insulation. This platform can be fabricated using simple batch microfabrication processes including carbon-MEMS and electrodeposition. The sensitivity and range of the sensor can be modulated by controlling Pd nanoparticle sizes (3–5nm PdNPs: 3.2% ppm<SUP>−1/2</SUP>, 10–1000ppm; 10–15nm PdNPs: 0.32% ppm<SUP>−1/2</SUP>, 700ppm – 5%). A wide sensing range is achieved by integrating nanowires with various sizes of PdNPs onto a chip. The electrical resistance of a suspended PdNP/carbon nanowire quickly and completely recovers its original state in a very short time via ultralow-power, Joule heat-based self-heating. This enables reproducible and long-term durable gas sensing.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hydrogen gas sensor based on an array of single suspended carbon nanowires decorated with Pd nanoparticles (PdNPs) of various sizes for room temperature H<SUB>2</SUB> gas sensing. </LI> <LI> Simple batch fabrication of composite suspended nanowire based gas sensor using carbon-MEMS and electrodeposition. </LI> <LI> Modulation of the sensitivity and range of the sensor by controlling Pd nanoparticle sizes. </LI> <LI> Wide sensing range by integrating nanowires with various sizes of PdNPs onto a chip. </LI> <LI> Quick and complete recovery of sensor signal in a very short time via ultralow-power, Joule heat-based self-heating. </LI> </UL> </P>

Monolithic carbon structures including suspended single nanowires and nanomeshes as a sensor platform

Lim, Yeongjin,Heo, Jeong-Il,Madou, Marc,Shin, Heungjoo Springer 2013 Nanoscale research letters Vol.8 No.1

<P>With the development of nanomaterial-based nanodevices, it became inevitable to develop cost-effective and simple nanofabrication technologies enabling the formation of nanomaterial assembly in a controllable manner. Herein, we present suspended monolithic carbon single nanowires and nanomeshes bridging two bulk carbon posts, fabricated in a designed manner using two successive UV exposure steps and a single pyrolysis step. The pyrolysis step is accompanied with a significant volume reduction, resulting in the shrinkage of micro-sized photoresist structures into nanoscale carbon structures. Even with the significant elongation of the suspended carbon nanowire induced by the volume reduction of the bulk carbon posts, the resultant tensional stress along the nanowire is not significant but grows along the wire thickness; this tensional stress gradient and the bent supports of the bridge-like carbon nanowire enhance structural robustness and alleviate the stiction problem that suspended nanostructures frequently experience. The feasibility of the suspended carbon nanostructures as a sensor platform was demonstrated by testing its electrochemical behavior, conductivity-temperature relationship, and hydrogen gas sensing capability.</P>

Highly sensitive hydrogen gas sensor based on a suspended palladium/carbon nanowire fabricated via batch microfabrication processes

Lim, Yeongjin,Lee, Yunjeong,Heo, Jeong-Il,Shin, Heungjoo Elsevier 2015 Sensors and actuators. B Chemical Vol.210 No.-

<P><B>Abstract</B></P> <P>We present a highly sensitive H<SUB>2</SUB> sensor based on a single Pd-functionalized carbon nanowire suspended ∼10μm above a substrate while monolithically bridging two carbon posts. The carbon nanowire and posts were fabricated using a batch carbon-microelectromechanical system (MEMS) process consisting of photolithography and pyrolysis. The pyrolysis process resulted in a significant volume reduction in which the nanowire diameter was reduced to ∼120nm from the original 1μm×1.5μm photoresist wire. Because of SiO<SUB>2</SUB> eaves formed by isotropic etching of the Si substrate, as well as the suspended geometry of the carbon nanowire, a single palladium evaporation process enabled selective palladium coating on the carbon nanowire without any nano-patterning processes. The electrical conductivity of the carbon nanowire was modulated by varying the pyrolysis temperature so that the electrical resistance along the suspended Pd/C nanowire was affected predominantly by hydrogen chemisorption onto the thin Pd layer enclosing the carbon core. The suspended functionalized wire showed better sensing capability compared to a Pd nanowire fabricated on the substrate with similar dimensions, because of enhanced mass transport. The suspended nanowire-based H<SUB>2</SUB> sensor quantified from 10 to 500ppm H<SUB>2</SUB> with percentile resistance changes of 5.9–129%.</P>