• Korean Journal of Materials Research
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• v.11 no.3
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• pp.221-226
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• 2001

The basal slip (0001)1/3<1120 > dislocation velocity in sapphire ($\alpha$-$Al_2$$O_3$) single crystals was measured by four-point bending test. The bending experiment was carried out in the temperature range from 120$0^{\circ}C$ to $1400^{\circ}C$ at various engineering stresses 90MPa, 120MPa, and 150MPa. The velocity of such dislocations was estimated from the bending displacement rate of the four-point bend sample. The dependence of temperature and stress in dislocation velocity was investigated. The activation energy for dislocation velocity was determined to be about 2.2$\pm$0.4eV. In addition, the stress exponent (m) describing the stress dependence of dislocation velocities was in the range of 2.0$\pm$0.2.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.43 no.3 s.345
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• pp.1-8
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• 2006

In this paper, reliability (HCI, NBTI) and device performance of nano-scale CMOSFETs with different channel stress were investigated. It was shown that NMOS and PMOS performances were improved by tensile and compressive stress, respectively, as well known. It is shown that improved device performance is attributed to the increased mobility of electrons or holes in the channel region. However, reliability characteristics showed different dependence on the channel stress. Both of NMOS and PMOS showed improved hot carrier lifetime for compressive channel stress. NBTI of PMOS also showed improvement for compressive stress. It is shown that $N_{it}$ generation at the interface of $Si/SiO_2$ has a great effect on the reliability. It is also shown that generation of positive fixed charge has an effect in the NBTI. Therefore, reliability as well as device performance should be considered in developing strained-silicon MOSFET.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.4
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• pp.335-340
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• 2002

In this paper, the stress induced leakage currents of thin silicon oxides is investigated in the ULSI implementation with nano structure transistors. The stress and transient currents associated with the on and off time of applied voltage were used to measure the distribution of high voltage stress induced traps in thin silicon oxide films. The stress and transient currents were due to the charging and discharging of traps generated by high stress voltage in the silicon oxides. The transient current was caused by the tunnel charging and discharging of the stress generated traps nearby two interfaces. The stress induced leakage current will affect data retention in electrically erasable programmable read only memories. The oxide current for the thickness dependence of stress current, transient current, and stress induced leakage currents has been measured in oxides with thicknesses between 113.4${\AA}$ and 814${\AA}$, which have the gate area $10^3cm^2$. The stress induced leakage currents will affect data retention and the stress current, transient current is used to estimate to fundamental limitations on oxide thicknesses.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.69-72
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• 2002

The high temperature deformation behavior of SiCp/2124Al composite and 2124Al alloy was investigated by hot compression test in a temperature ranged $400~475^{\circ}C$ over a strain rate ranged $10^{-3}~1s^{-1}$. The billets of 2124Al alloy and SiCp/2124Al composite were fabricated by vacuum hot pressing process. The stress-strain curve during high temperature deformation exhibited a peak stress, and then the flow stress decreased gradually into a steady state stress with increasing the strain. It was found that the flow-softening behavior was attributed to the dynamic recovery, local dynamic recrystallization and dynamic precipitation during the deformation. The precipitation phases were identified as S' and S by TEM diffraction pattern. Base on the TEM inspection, the relationship between the Z-H parameter and subgrain size was found based on the experiment data. The dependence of flow stress on temperature and strain rate could be formulated well by a hyperbolic-sinusoidal relationship using the Zener-Hollomon parameter.

• Journal of Ocean Engineering and Technology
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• v.1 no.1
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• pp.104-110
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• 1987

Fatigue tests by axial loading (R = 0.05) were carried out to investigate fatigue crack growth characteristics of small surface cracks in 2 1/4 Cr-1 Mo steel at room temperature by using flat specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present test are determined as a function of the stress intensity factor range about a semi-elliptical crack, so that the application of linear fracture mechanics to the surface fatigue crack growth and to the fatigue crack growth into depth, and all the data obtained from tests were discussed in comparison with the data of Type 304 stainless steel and two type of mild steel under the same test conditions. The obtained results are as follows: 1)When the cycle ratios are same, surface fatigue crack length and its depth are almost same and fall within a narrow scatter band in spite of different stress levels. 2)Relations of the surface fatigue crack growth rate (da/dN) and fatigue crack growth rate into depth (db/dN) to its stress intensity factor range ($\Delta K_{Ia}, \Delta K_{Ib}$) can be plotted as a straight line at log-log diagram without dependence of stress level and coincide with the data of part-through crack in various steels.

• Korean Journal of Materials Research
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• v.23 no.3
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• pp.199-205
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• 2013

The mechanical properties and microstructures of aluminum-matrix composites fabricated by the dispersion of fine alumina particles less than $20{\mu}m$ in size into 6061 aluminum alloys are investigated in this study. In the as-quenched state, the yield stress of the composite is 40~85 MPa higher than that of the 6061 alloy. This difference is attributed to the high density of dislocations within the matrix introduced due to the difference in the thermal expansion coefficients between the matrix and the reinforcement. The difference in the yield stress between the composite and the 6061 alloy decreases with the aging time and the age-hardening curves of both materials show a similar trend. At room temperature, the strain-hardening rate of the composite is higher than that of the 6061 alloy, most likely because the distribution of reinforcements enhances the dislocation density during deformation. Both the yield stress and the strain-hardening rate of the T6-treated composite decrease as the testing temperature increases, and the rate of decrease is faster in the composite than in the 6061 alloy. Under creep conditions, the stress exponents of the T6-treated composite vary from 8.3 at 473 K to 4.8 at 623 K. These exponents are larger than those of the 6061 matrix alloy.

• Journal of Korean Public Health Nursing
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• v.13 no.1
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• pp.97-113
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• 1999

To investigate the actual condition of the adult-smoking in Chinan County. I used self-reporting questionnaires among 923 residents living in nine districts selected at random among the sites of eleven eup-myons from December 28. 1998 to January 6. 1999. collected data and analyized using SPSS. The smoking rate of adults in Chinan County was $36.9\%$. There was a significant difference in smoking rate according to the age. gender, education and job among general characteristics. The smoking rate in group of above 40s was about $40\%$ and that of the male took $55.5\%$ which was higher than that of female and the smoking rate of the people having high-school education was the highest$(46.2\%)$. With regard to the career. the smoking rate of the farmers ranked first$(46.1\%)$. Therefore anti-smoking business for smokers should be focused on above 40 years old, males. people having high school education and farmers. As the result of the survey of smoking habits of 340 people who smoke currently, the average smoking begining age was 21.8 and $81.5\%$ among them was between 16-25 years old. $4.4\%$ was under 15. during around the elementary school. Most motives to smoke were as followed; curiosity or taste$(33.6\%)$, relief of stress $(31.2\%)$, peer presure$(26.5\%)$ And considering the amount of the cigarette which is smoked per day, the case which is less than a pack of cigarettes was highest as $75.5\%$ and the people who smoke over one pack of cigarettes took $24.5\%$. As for the kind of tobacco which is smoked, how to smoke and the desire for the smoking, most case was toxin was moderate$(47.8\%)$ or mild$(46.9\%)$. shallowly$(49.0\%)$ or deeply$(46.3\%)$ and under stress$(33.4\%)$. after meals$(27.8\%)$, during drink$(15.7\%)$ and so on. The highest point marked among the factors of smoking motives was 'the reduce of negative emotion' $(3.27\pm1.00)$. followed by 'uncomfortable habits' $(2.87\pm1.02)$, 'addiction' $(2.84\pm1.06)$. 'habit' $(2.74\pm1.12)$. 'pleasure' $(2.70\pm1.04)$. 'stimulus' $(2.59\pm.90)$, 'sensation-exercise satisfaction' $(2.42\pm.97)$. Smokers smoke to reduce the negative emotions when angry in most common case. depressed. anxious. uncomfortable. lone. ashamed or embarrased. and intend to solve the certain problem. etc. Other motives are uncomfortable habit. addiction. habit. pleasure and the pursuit of stimulus. The level of nicotine dependence of adults m Chinan County was 10.57 which amount to 'high' wholly. As the resulf of the level of nicotine dependence score. the people who are low in the level of nicotine was $33.5\%$. the people who are high was $48.2\%$. very high was $18.4\%$. The approach for anti-smoking for smokers should be conducted differently according to the level of the nicotine. For the people who are in low level of nicotin dependence the prohibition of the smoking should be guided through the approach to foster strong will. for those who are in 'high' by acquiring proper method for the prohibition of smoking. and for those who are 'very high' the anti-smoking should be induced by providing proper program because of the possibility of the suffer from abstinence syndrome. The difference of the level of nicotine with the general characteristics of the objects had not statistically significant difference. The difference of the level of nicotine dependence accompanied by smoking habit had statistically significant difference according to the amount of smoke, the kind of tobacos. smoke inhale habit. In other words, the group of heavy smokers had higher level of the nicotine dependence than that of the light smokers relatively and the group which smoke strong taboaco has higher level of nicotine than that of which smoke mild or moderate. And the group of smokers who smoke deeply has higher level of nicotine than that who smoke shallowly or nonswallow. Aa a result of the analysis of the correlation between smoking motive factors and the level of nicotine, there was the indication that people who smoke for the decrease of the negative emotion. habit, pleasure. stimulus. sensation-exercise satisfaction had high level of the nicotine dependence. As the result of the anti-smoking will of smokers. $65.0\%$ of them had prohibition of smoking will. $29.3\%$ had no will to quit smoke. The most important reason for anti-smoking was health. $67.9\%$ had experience to try to quit smoke and the biggest reason to fail to quit smoking was the lack of the will power to keep anti-smoking. $52.8\%$ of them were advised to stop smoking from their spouses or children. only $2.8\%$ were by medical. The people who have the opinion to need anti-smoking education were $69.6\%$. Therefore when the business for the hygine of the mouth for adult is set. it should be centered on the people who have intention of prohibition of the smoking and help to quit smoking by way of other affirmative counter-program not smoking under stress.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.14 no.2
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• pp.112-120
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• 2015

In this study, the growth rate of surface cracks (da/dN) during the retardation period was analyzed in terms of effective stress intensity factor range(${\Delta}K_{eff}^*$) obtained by using the proposed effective plastic zone concept. Effective stress intensity factors obtained by using the effective plastic zone concept were smaller than those obtained by using Willenborg analysis. On the growth rate of surface cracks analyzed by ${\Delta}K$, the dependence of overload stress levels appears. On the growth rate by ${\Delta}K_{eff}$ obtained by Willenborg analysis, there is a linear relationship with two different slops between da/dN and ${\Delta}K_{eff}$. However, on the growth rate by ${\Delta}K_{eff}^*$ obtained by the proposed effective plastic zone concept, there is a linear relationship between da/dN and ${\Delta}K_{eff}^*$ that coincides with the results of constant amplitude loading.

• Journal of Ocean Engineering and Technology
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• v.8 no.1
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• pp.33-40
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• 1994

Welding of structure produces welding residual stresses which influence buckling strength, brittle fracture strength and cold crack on the weld parts. Therefore, it is very important to accurately analyze the residual stress before welding in order to guarantee the safety of weldment. If the weld length is long enough compared to the thickness and the breadth of plate, thermal and mechanical behaviors in the middle portion of the plate are assumed to be uniform along the thickness direction(z-axis). Thus, the following conditions(so-called plane deformation) can be assumed for the plate except near its end;1) distributions of stress and strain are independent on the z-axis;2) plane normal to z-axis before deformation remains plane during and after deformation. In this paper, plane-deformation thermal elasto-plastic problem is formulated by being based on the finite element method. Moreover special regards and paid to the fact that material properties in elastic and plastic region are temperature-dependence. And the method to solve the plane-deformation thermal elasto-plastic problem is shown by using the incremental technique. From the results of analysis, the characterisics of distribution of welding residual stress and plastic strain with the production mechanism are clarified.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.491-497
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• 2010

In this paper, we employed the classical molecular dynamics simulations using Tersoff's potential to calculate the elastic constants of the silicon carbide (SiC) crystal at high temperature. The elastic constants of the SiC crystal were calculated based on the stress-strain characteristics, which were drawn by the simulation using LAMMPS software. At the same time, the elastic constants of the SiC ceramics were measured at different temperatures by impulse excitation testing (IET) method. Based on the simulated stress-strain results, the SiC crystal showed the elastic deformation characteristics at the low temperature region, while a slight plastic deformation behavior was observed at high strain over $1,000^{\circ}C$ temperature. The elastic constants of the SiC crystal were changed from about 475 GPa to 425 GPa by increasing the temperature from RT to $1,250^{\circ}C$. When compared to the experimental values of the SiC ceramics, the simulation results, which are unable to obtain by experiments, are found to be very useful to predict the stress-strain behaviors and the elastic constant of the ceramics at high temperature.