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A Study of Predicting Method of Residual Stress Using Artificial Neural Network in $CO_2$Arc welding
Cho, Y.,Rhee, S.,Kim, J.H. The Korean Welding and Joining Society 2001 International journal of Korean welding society Vol.1 No.2
A prediction method for determining the welding residual stress by artificial neural network is proposed. A three-dimensional transient thermo-mechanical analysis has been performed for the $CO_2$ arc welding using the finite element method. The first part of numerical analysis performs a three-dimensional transient heat transfer analysis, and the second part then uses the results of the first part and performs a three-dimensional transient thermo-elastic-plastic analysis to compute transient and residual stresses in the weld. Data from the finite element method are used to train a back propagation neural network to predict the residual stress. Architecturally, the fully interconnected network consists of an input layer for the voltage and current, a hidden layer to accommodate the failure mechanism mapping, and an output layer for the residual stress. The trained network is then applied to the prediction of residual stress in the four specimens. It is concluded that the accuracy of the neural network predicting method is fully comparable with the accuracy achieved by the traditional predicting method.
Cho, Y.,Lee, W.,Kim, H. Royal Society of Chemistry 2014 Journal of materials chemistry. A, Materials for e Vol.2 No.30
A novel synthetic process referred to as a protective coating method was developed for the fabrication of a carbon-supported Pt2Ni1 nanoparticle measuring approximately 5 nm in size with a Pt-rich shell via thermal treatment. A 3 to 5 nm thick potypyrrole layer encapsulating the surface of the Pt/C catalyst simultaneously acted as a sponge to absorb the Ni precursor and a physical barrier to inhibit the inevitable increase in particle size during the thermal treatment. The PPy layer does not behave as a poison to the catalyst because it is completely decomposed without carbonization on the Pt surface during the heat treatment in a H-2-Ar mixture. As a result, the resultant Pt2Ni1/C catalyst with a Pt-rich shell exhibited improved stability under acidic conditions and catalytic activity in an oxygen reduction reaction.
Cho, Y.,Challa, S.,Moquin, D.,Genga, R.,Ray, T.D.,Guildford, M.,Chan, F.K.M. Cell Press ; MIT Press 2009 Cell Vol.137 No.6
Programmed necrosis is a form of caspase-independent cell death whose molecular regulation is poorly understood. The kinase RIP1 is crucial for programmed necrosis, but also mediates activation of the prosurvival transcription factor NF-κB. We postulated that additional molecules are required to specifically activate programmed necrosis. Using a RNA interference screen, we identified the kinase RIP3 as a crucial activator for programmed necrosis induced by TNF and during virus infection. RIP3 regulates necrosis-specific RIP1 phosphorylation. The phosphorylation of RIP1 and RIP3 stabilizes their association within the pronecrotic complex, activates the pronecrotic kinase activity, and triggers downstream reactive oxygen species production. The pronecrotic RIP1-RIP3 complex is induced during vaccinia virus infection. Consequently, RIP3<SUP>-/-</SUP> mice exhibited severely impaired virus-induced tissue necrosis, inflammation, and control of viral replication. Our findings suggest that RIP3 controls programmed necrosis by initiating the pronecrotic kinase cascade, and that this is necessary for the inflammatory response against virus infections.
Enhanced energy harvesting based on surface morphology engineering of P(VDF-TrFE) film
Cho, Y.,Park, J.B.,Kim, B.S.,Lee, J.,Hong, W.K.,Park, I.K.,Jang, J.E.,Sohn, J.I.,Cha, S.,Kim, J.M. Elsevier 2015 Nano energy Vol.16 No.-
Polyvinylidene fluoride (PVDF) has great potential for its use as an energy harvesting material as it exhibits not only outstanding piezoelectric and electrostatic characteristics resulting from ferroelectric effects, but also remarkably robust stability against repeated mechanical stress compared to inorganic materials. We report enhanced performances of poly(vinylidenefluoride-co-trifluoroethylene) (P(VDF-TrFE)) based energy generators with wider range of selections of flexible substrates through a surface morphology engineering using solvent annealing method as the key technology for simple and cost-effective fabrication at room temperature. It is clearly revealed that a solvent annealed P(VDF-TrFE) film is crystallised at room temperature and that the surface morphology is changed from a rough surface into a smooth and flat surface with increasing annealing time. This surface morphology engineering results in 8 times enhanced output voltage and current of the energy generators because of well-aligned electrical dipoles. We also demonstrate a highly transparent and flexible energy generator by employing graphene electrodes with the solvent annealed P(VDF-TrFE) film, which can be effectively harvesting various mechanical energy sources.
Miniaturised dual-band implantable antenna for wireless biotelemetry
Cho, Y.,Yoo, H. IET 2016 Electronics letters Vol.52 No.12
<P>A miniaturised implantable antenna with dual-band operation the Medical Implant Communications Service (MICS) (402-405 MHz) and Industrial, Scientific, and Medical (ISM) (2400.0-2483.5 MHz) bands is presented. The size of the proposed antenna is 31.5 mm(3) (8.75 mm x 7.2 mm x 0.5 mm) which is the smallest size compared to previous implantable antennas. A serpentine-shaped radiating patch and open-end slot placed on the ground plane are used for miniaturisation. The performance of the antenna was evaluated from measurements and is based on good agreement with simulations.</P>
Challenges of organic rice farming in Jeonnam Province, Korea
Cho, Y.,Nicholas, P.,Lee, J. Korean Association of Organic Agriculture 2011 韓國有機農業學會誌 Vol.19 No.S
The production practices, productivity and economic performance of organic and non-chemical rice farming were compared in Jeonnam Province, Korea. Korean organic rice farming showed a lack of use of resistant varieties and rotational cropping systems as well as less use of farm wastes and a high dependency upon external inputs. When compared with no-chemical rice production practices very little differences were found. However, organic rice farming showed 15% to 18% higher profits than no-chemical farming even though the productivity was arguably similar between the two farming types. This may encourage more farmers to convert to organic production rather than non-chemical farming as the farming practices are very similar, thereby resulting in increased supply of organic products and decreased prices for organic rice near future. There is a need to more greatly differentiate organic farming practices and products from those of no-chemical farming.
H<sub>2</sub> effects on diesel combustion and emissions with an LPL-EGR system
Cho, Y.,Song, S.,Chun, K.M. Pergamon Press ; Elsevier Science Ltd 2013 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.38 No.23
In this study, we examined H<SUB>2</SUB> effects on the combustion and emissions of a diesel engine with low-pressure loop (LPL) exhaust gas recirculation (EGR). We converted a 2.2-L four-cylinder direct-injection diesel engine satisfying Euro5 for H<SUB>2</SUB> supply. An LPL-EGR system replaced the high-pressure loop (HPL) EGR system. For all tests, the brake mean effective pressure (BMEP) was kept at 4 bar and the EGR ratio was varied from 9 to 42%. The H<SUB>2</SUB> energy percentage was varied from 0 to 7.4% independently to evaluate the H<SUB>2</SUB> effects and EGR effects separately. The heat release rate was calculated from the measured cylinder pressure. We found that substitution of H<SUB>2</SUB> for diesel fuel made the premixed burn fraction larger, and reduced the nitrous oxide (NOx) and particulate matter (PM) emissions simultaneously. For example, the NOx emissions were reduced by 36% for an EGR of 42% and an H<SUB>2</SUB> percentage of 7.4%. PM emissions were reduced by 18% for an EGR of 35% and an H<SUB>2</SUB> percentage of 7.4% compared with diesel fuel only cases.
Cho, Y.,Kim, S.,Pyo, S.,Park, Y.S.,Kim, S.J.,Yun, H.,Do, J. Pergamon Press 2010 Polyhedron Vol.29 No.9
The solvothermal synthesis and crystal structures of two new lead(II) compounds, bis(ethylenediamine)lead(II) chloride, Pb(en)<SUB>2</SUB>l<SUB>2</SUB> and mono(ethylenediamine)lead(II) chloride, Pb(en)Cl<SUB>2</SUB>, are reported. A detailed comparison of the two structures is given. In 1, the Pb(II) center is coordinated by two chlorine atoms and four nitrogen atoms from three en ligands, which act as either chelating or bridging ligands, allowing links to other Pb(II) centers. This creates an infinite linear chain of Pb(en)<SUB>2</SUB>l<SUB>2</SUB> In 2, the Pb(II) center is chelated by one en ligand and is coordinated by six chlorine atoms, including two unusually weak Pb-Cl bonds (>3.5A) connected through μ<SUB>2</SUB> and μ<SUB>4</SUB>Cl to build a neutral layer of Pb(en)Cl<SUB>2</SUB>units. Complex 1 contains a hemidirected Pb(II), while complex 2 has a (pseudo-)hemidirected Pb(II). TGA and high-temperature controlled powder-XRD studies show that compound 1 decomposes to compound 2 near 150<SUP>o</SUP>, and finally to PbCl<SUB>2</SUB>above 320<SUP>o</SUP>