• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05a
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• pp.96-99
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• 2004

The combination of mechano-chemical activation and Self-propagating High-temperature Synthesis (SHS) has widened the possibilities for both methods. For YBCO systems the investigation showed that a short-term mechano-chemical activation of initial powders before SHS leads to single-phase and ultra-fine products. A new technique for preparation ultra-fine high-temperature superconductors of YBCO composition with a grain size d ＜1 ${\mu}{\textrm}{m}$ is developed. The specific feature of the technique is formation of the YBa$_2$Cu$_3$O$_{7-{\delta}}$ crystalline lattice directly from an X-ray amorphous state arising as a result of mechanical activation of the original oxide mixture. The technique allows the stage of formation of any intermediate reaction products to be ruled out. X-ray and magnetic studies of ultra-fine high temperature superconductors (HTS) are carried out. Dimension effects associated with the microstructure peculiarities are revealed. A considerable enhancement of inter-grain critical currents is found to take place in the ultra-fine samples.fine samples.

• Molecules and Cells
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• v.25 no.4
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• pp.479-486
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• 2008

Mitogen-activated protein kinases (MAPKs) play an indispensable role in activation of the myogenic program, which is responsive to mechanical stimulation. Although there is accumulating evidence of mechanical force-mediated cellular responses, the role of MAPK in regulating the myogenic process in myoblasts exposed to cyclic stretch is unclear. Cyclic stretch induced the proliferation of C2C12 myoblasts and inhibited their differentiation into myotubes. In particular, it induced persistent phosphorylation of p38 kinase, and decreased the level of phosphorylation of extracellular-signal regulated kinase (ERK). Partial inhibition of p38 phosphorylation increased cellular levels of MyoD and p-ERK in stretched C2C12 cells, along with increased myotube formation. Treatment with $10{\mu}M$ PD98059 prevented myogenin expression in response to a low dose of SB203580 ($3{\mu}M$) in the stretched cells, suggesting that adequate ERK activation is also needed to allow the cells to differentiate into myotubes. These results suggest that cyclic stretch inhibits the myogenic differentiation of C2C12 cells by activating p38-mediated signaling and inhibiting ERK phosphorylation. We conclude that p38 kinase, not ERK, is the upstream signal transducer regulating cellular responses to mechanical stretch in skeletal muscle cells.

• Journal of Powder Materials
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• v.26 no.2
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• pp.107-111
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• 2019

The activation energy to create a phase transformation or for the reaction to move to the next stage in the milling process can be calculated from the slop of the DSC plot, obtained at the various heating rates for mechanically activated Al-Ni alloy systems by using Kissinger's equation. The mechanically activated material has been called "the driven material" as it creates new phases or intermetallic compounds of AlNi in Al-Ni alloy systems. The reaction time for phase transformation by milling can be calculated using the activation energy obtained from the above mentioned method and from the real required energy. The real required energy (activation energy) could be calculated by subtracting the loss energy from the total input energy (calculated input energy from electric motor). The loss energy and real required energy divided by the reaction time are considered the "metabolic energy" and "the effective input energy", respectively. The milling time for phase transformation at other Al-Co alloy systems from the calculated data of Al-Ni systems can be predicted accordingly.

• The Journal of Korea Robotics Society
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• v.19 no.2
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• pp.203-212
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• 2024

Simultaneous motion is essential in the activities of daily living (ADL). For motion intention recognition, surface electromyogram (sEMG) and corresponding motion label is necessary. However, this process is time-consuming and it may increase the burden of the user. Therefore, we propose a simultaneous motion recognition framework using data augmentation based on muscle activation model. The model consists of multiple point sources to be optimized while the number of point sources and their initial parameters are automatically determined. From the experimental results, it is shown that the framework has generated the data which are similar to the real one. This aspect is quantified with the following two metrics: structural similarity index measure (SSIM) and mean squared error (MSE). Furthermore, with k-nearest neighbor (k-NN) or support vector machine (SVM), the classification accuracy is also enhanced with the proposed framework. From these results, it can be concluded that the generalization property of the training data is enhanced and the classification accuracy is increased accordingly. We expect that this framework reduces the burden of the user from the excessive and time-consuming data acquisition.

• Journal of the Korean Society for Precision Engineering
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• v.2 no.1
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• pp.53-61
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• 1985

This study is concerned with creep mechanism of SUS 316 under high stresses. Creep tests were conducted at temperatures between $480^{\circ} and $820^{\circ}C and stresses between 7.6 and 24.6$kg/mm^2$. To investigate the mechanism of the steady-state creep under high stresses, work hardening coefficient and activation energy are obtained. The activation energy was calculated by means of the temperature differential test together with the method of correlating the creep rates against the inverse of the absolute temperature for different stresses and strains. From the experimental results and their analyzed facts, it is concluded that the steady-state creep behavior of SUS 316 under high stresses is controlled by dislocation glide mechanism.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.16-22
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• 2006

Stainless steel has widely been used in various industrial fields because it has high corrosion resistance. But, we have little design data about the creep life prediction of SUS316L stainless steel. Therefore, in this study, a series of creep tests and study on them under 16 constant stress and temperature combined conditions have been performed to get the creep design data and life prediction of SUS316L stainless steels and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated about 10. And last, the creep rupture fractographs show the intergranular ductile fracture with many dimples.

• Proceeding of EDISON Challenge
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• 2017.03a
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• pp.650-652
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• 2017

the aim of this study was to observe the combined effect of the CRT and LVAD on electromechanical cardiac behavior under LBBB and RBBB conditions computationally. We performed simulation by using advanced electromechanics model of failing ventricle combined with lumped model represents circulatory system, CRT and LVAD. We analyzed seven failing ventricle model including normal sinus rhythm, LBBB, LBBB coupled with CRT, LBBB coupled with CRT and LVAD, RBBB, RBBB coupled with CRT, and RBBB coupled with CRT and LVAD. We compared the effect from CRT and the effect from combined CRT and LVAD to both under LBBB and RBBB conditions. The results showed that the combined CRT and LVAD contributed a better hemodynamic compared to single CRT. This combined system synchronized the electrical activation greatly under LBBB and slightly under RBBB. It also shortened mechanical activation time which resulted short electromechanical delay. More importantly, the combined system produced better mechanical responses under both LBBB and RBBB conditions.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.969-970
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• 2006

In present work, manufacturing technologies of titanium hydride powder were studied for recycling of titanium tuning chip and for this, attrition ball milling was carried out under $H_2$ pressure of 0.5 MPa. Ti chips were completely transformed into $TiH_2$ within several hundred seconds. Dehydrogenation process $TiH_2$ powders is consist of two reactions: one is reaction of $TiH_2$ to $TiH_x$ and the other decomposition of $TiH_x$ to Ti and $H_2$. The former reaction shows relatively low activation energy and it is suggested that the reaction is caused by introduction of defects due to milling.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.4
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• pp.703-707
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• 1989

The ignition of solid particle under strong convective heating has been investigated by applying an asymptotic analysis to a semi-infinite body for varying values of gas recovery temperature and convective heat transfer coefficient. It was found that if the scale of the reaction zone is much smaller than the characteristic length of the body size, then infinite body theory can be used to estimate the ignition delay time. Furthermore, the convective heat transfer coefficient was found to have more influence on predicting the ignition delay times of particle exposed to an incident shock wave rather than the gas recovery temperature.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1209-1216
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• 2006

An AZ31 magnesium alloy was tested at constant temperatures ranging from 423 to 473 K (0.46 to 0.51 Tm) under constant stresses. All of the creep curves exhibited two types depending on stress levels. At low stress (${\sigma}/ G < 4 {\times}10^{-3}$), the creep curve was typical of class A (Alloy type) behavior. However, at high stresses (${\sigma}/ G > 4 {\times}10^{-3}$), the creep curve was typical of class M (Metal type) behavior. At low stress level, the stress exponent for the steady-state creep rate was of 3.5 and the true activation energy for creep was 101 kJ/mole which is close to that for solute diffusion. It indicates that the dominant deformation mechanism was glide-controlled dislocation creep. At low stress level where n=3.5, the present results are in good agreement with the prediction of Fridel model.