• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.9
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• pp.1408-1414
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• 2004

The use of flip-chip technology has many advantages over other approaches for high-density electronic packaging. ACF (anisotropic conductive film) is one of the major flip-chip technologies, which has short chip-to-chip interconnection length, high productivity, and miniaturization of package. In this study, thermal fatigue lift of ACF bonding flip-chip package has been predicted. Elastic and thermal properties of ACF were measured by using DMA and TMA. Temperature dependent nonlinear hi-thermal analysis was conducted and the result was compared with Moire interferometer experiment. Calculated displacement field was well matched with experimental result. Thermal fatigue analysis was also conducted. The maximum shear strain occurs at the outmost located bump. Shear stress-strain curve was obtained to calculate fatigue life. Fatigue model for electronic adhesives was used to predict thermal fatigue life of ACF bonding flip-chip packaging. DOE (Design of Experiment) technique was used to find important design factors. The results show that PCB CTE (Coefficient of Thermal Expansion) and elastic modulus of ACF material are important material parameters. And as important design parameters, chip width, bump pitch and bump width were chose. 2$^{nd}$ DOE was conducted to obtain RSM equation far the choose 3 design parameter. The coefficient of determination ($R^2$) for the calculated RSM equation is 0.99934. Optimum design is conducted using the RSM equation. MMFD (Modified Method for feasible Direction) algorithm is used to optimum design. The optimum value for chip width, bump pitch and bump width were 7.87mm, 430$\mu$m, and 78$\mu$m, respectively. Approximately, 1400 cycles have been expected under optimum conditions. Reliability analysis was conducted to find out guideline for control range of design parameter. Sigma value was calculated with changing standard deviation of design variable. To acquire 6 sigma level thermal fatigue reliability, the Std. Deviation of design parameter should be controlled within 3% of average value.

• Journal of Applied Biological Chemistry
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• v.51 no.6
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• pp.262-271
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• 2008

Natural abundances of stable isotopes of nitrogen and carbon (${\delta}^{15}N$ and ${\delta}^{13}C$) are being widely used to study N and C cycle processes in plant and soil systems. Variations in ${\delta}^{15}N$ of the soil and the plant reflect the potentially variable isotope signature of the external N sources and the isotope fractionation during the N cycle process. $N_2$ fixation and N fertilizer supply the nitrogen, whose ${\delta}^{15}N$ is close to 0%o, whereas the compost as. an organic input generally provides the nitrogen enriched in $^{15}N$ compared to the atmospheric $N_2$. The isotope fractionation during the N cycle process decreases the ${\delta}^{15}N$ of the substrate and increases the ${\delta}^{15}N$ of the product. N transformations such as N mineralization, nitrification, denitrification, assimilation, and the $NH_3$ volatilization have a specific isotope fractionation factor (${\alpha}$) for each N process. Variation in the ${\delta}^{13}C$ of plants reflects the photosynthetic type of plant, which affects the isotope fractionation during photosynthesis. The ${\delta}^{13}C$ of C3 plant is significantly lower than, whereas the ${\delta}^{13}C$ of C4 plant is similar to that of the atmospheric $CO_2$. Variation in the isotope fractionation of carbon and nitrogen can be observed under different environmental conditions. The effect of environmental factors on the stomatal conductance and the carboxylation rate affects the carbon isotope fractionation during photosynthesis. Changes in the environmental factors such as temperature and salt concentration affect the nitrogen isotope fractionation during the N cycle processes; however, the mechanism of variation in the nitrogen isotope fractionation has not been studied as much as that in the carbon isotope fractionation. Isotope fractionation factors of carbon and nitrogen could be the integrated factors for interpreting the effects of the environmental factors on plants and soils.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.8
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• pp.36-43
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• 2003

In this study, a satellite payload module was optimized by considering local stabilities. As design constraints in the satellite structure, local instabilities such as wrinkling, dimpling, crippling for honeycomb structures and crippling failure mode for beams were considered in addition to frequency and stress constraints. The constraints for the local instabilities (uncommon in general structures) were taken for the optimization of a satellite structures under severe launching environments. The analysis was performed combining the finite element analysis and optimization program. From the optimization results, it was found that frequency, crippling and wrinkling were the most critical constraints to achieve the design goals. Also, the importance of each design variable was estimated. Finally, the optimum design of the payload module was achieved for various design constraints and design parameters.

• Journal of the Korean Institute of Gas
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• v.13 no.2
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• pp.30-35
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• 2009

The result of this research explains an interactive behavior of buried steel pipe located below hume pipe using concept of effective depth and effective length against their intersection angle and burial distance. The cover depth of upper rigid (hume) pipe is 1.0m and depth range of flexible (steel) pipe is 0.5m to 5m from beneath bottom of hume pipe. And one more variable is their intersection angle in this study, it was considered from $0^{\circ}$ to $90^{\circ}$. From the results of this study, the effective depth is proportionally increasing with its intersection angle and decreasing with distance increment between two pipes. Finally, the relationship between effective length and summation of occurred bending stress is defined.

• Health Policy and Management
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• v.30 no.3
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• pp.355-365
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• 2020

Background: This study is aimed to verify individual and regional-level factors affecting the depression of Koreans and to develop social programs for improving the depressive status. Methods: This study used individual-level variables from the Korean Community Health Survey (2018) and used the e-regional index of the Korean Statistical Information Service as the regional-level variable. A multi-level logistic regression was executed to identify individual and regional-level variables that were expected to affect the extent of depressive symptoms and to draw the receiver operating characteristic curve to compare the volume of impact between variables from both levels. Results: The results of the multi-level logistic regression analysis in regards to individual-level factors showed that older age, female gender, a lower income level, a lower education level, not having a spouse, the practice of walking, the consumption of breakfast higher levels of stress, and having high blood pressure or diabetes were associated with a greater increase in depressive symptoms. In terms of regional factors, areas with fewer cultural facilities and fewer car registration had higher levels of depressive symptoms. The comparison of area under the curve showed that individual factors had a greater influence than regional factors. Conclusion: This study showed that while both, individual and regional-level factors affect depression, the influence of the latter was relatively weaker as compared to the first. In this sense, it is necessary to develop programs focused on the individual, such as social prescribing at the local or community-level, rather than the city and nation-level approach that are currently prevalent.

• Steel and Composite Structures
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• v.26 no.4
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• pp.473-484
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• 2018

Free vibration of cross-ply laminated plates using a higher-order shear deformation theory is studied. The arbitrary number of layers is oriented in symmetric and anti-symmetric manners. The plate kinematics are based on higher-order shear deformation theory (HSDT) and the vibrational behaviour of multi-layered plates are analysed under simply supported boundary conditions. The differential equations are obtained in terms of displacement and rotational functions by substituting the stress-strain relations and strain-displacement relations in the governing equations and separable method is adopted for these functions to get a set of ordinary differential equations in term of single variable, which are coupled. These displacement and rotational functions are approximated using cubic and quantic splines which results in to the system of algebraic equations with unknown spline coefficients. Incurring the boundary conditions with the algebraic equations, a generalized eigen value problem is obtained. This eigen value problem is solved numerically to find the eigen frequency parameter and associated eigenvectors which are the spline coefficients.The material properties of Kevlar-49/epoxy, Graphite/Epoxy and E-glass epoxy are used to show the parametric effects of the plates aspect ratio, side-to-thickness ratio, stacking sequence, number of lamina and ply orientations on the frequency parameter of the plate. The current results are verified with those results obtained in the previous work and the new results are presented in tables and graphs.

• Korean Journal of Psychosomatic Medicine
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• v.6 no.2
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• pp.136-146
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• 1998

Objectives : This study was performed to evaluate the effects of PTSD on memory function, to investigate the difference of memory function between PTSD and non-PTSD patients, and to identify major variables correlated to PTSD scale and Memory Assessment Scale. Methods: The authors used PTSD-scale(Mississippi scale and Combat Exposure Scale) for measuring PTSD severity. And, Beck Depression Inventory was also used. Memory assessment scale was assessed by well trained psychologist. Thirty one Vietnam veterans who had been hospitalized were collected consecutively. These patients were evaluated by psychiatrists with interview and measurement for fifteen months since March, 1997. The collected data were analyzed by SPSS and the stastistic methods used for analysis Chi-square, t-test, and Pearson's correlation. Results : 1) There were significant differences in short-term memory and verbal memory between PTSD and non-PTSD in Vietnam veterans. 2) Mississippi scale and Combat Exposure Scale were negatively correlated to short-term memory and verbal memory(Pearson's correlation). 3) Religion status was a significant variable between PTSD and non-PTSD in Vietnam veterans. 4) There is no significant difference in visual memory and total memory scale between PTSD and Non-PTSD in Vietnam veterans Conclusions : Neuropsychological changes were found in the posttraumatic stress disorder. There were significant differences in short-term memory and verbal memory between PTSD and non-PTSD in Vietnam veterans. Mississippi scale and Combat Exposure Scale were negatively correlated to short-term memory and verbal memory. We suggest that neuropsychological test might be used for an objective assessment of patients with the combat related PTSD and be considered helpful in the assessment of patients with the diagnosis. And we also suggest rehabilitation strategies would be used to compensate for memory deficits in PTSD patients.

• Structural Engineering and Mechanics
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• v.72 no.5
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• pp.631-642
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• 2019

The objective of the present study is to examine the flexural behavior of two-span post-tensioned lightweight aggregate concrete (LWAC) beams using unbonded tendons and the reliability of the design provisions of ACI 318-14 for such beams. The parameters investigated were the effective prestress and loading type, including the symmetrical top one-point, two third-point, and analogous uniform loading systems. The unbonded prestressing three-wire strands were arranged with a harped profile of variable eccentricity. The total length of the beam, measured between both strand anchorages, was 11000 mm. The test results were compared with those compiled from simply supported LWAC one-way members, wherever possible. The ultimate load capacity of the present beam specimens was evaluated by the collapse mechanism of the plasticity theorem and the nominal section moment strength calculated following the provision of the ACI 318-14. The test results showed that the two-span post-tensioned LWAC beams had lower stress increase (Δf_ps) in the unbonded tendons than the simply supported LWAC beams with a similar reinforcement index. The effect of the loading type on Δf_ps and displacement ductility was less significant for two-span beams than for the comparable simply supported beams. The design equations for Δf_ps and Δf_ps proposed by ACI 318-14 and Harajli are conservative for the present two-span post-tensioned LWAC beams, although the safety decreases for the two-span beam, compared to the ratios between experiments and predictions obtained from simply supported beams.

• Journal of the Korean Society of Hazard Mitigation
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• v.2 no.1 s.4
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• pp.119-126
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• 2002

This paper presents the appropriateness for using high strength reinforcement according to the use of high strength concrete. Nine flexural tests were conducted on full-scale beam specimens according to the concrete strength, reinforcement strength and reinforcement ratio as main variable. The structural behavior was analyzed due to the flexural strength, stress-strain curve, deflections at yielding and fracture point, crack appearance and ductility factor. The member with high-strength reinforcements showed large deflection at yielding point and this was analyzed as a main cause to decrease the ductility factor. Structural behavior after yielding point, however, showed similarity to behavior of members with normal strength reinforcements of same stiffness. It was found that in the case of using reinforcements of $5500kgf/cm^2$ strength, the combination with concrete of $800kgf/cm^2$ strength demonstrated the great appropriateness which can increase the flexural capacity without any reduction of maximum reinforcement ratio.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.5
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• pp.29-34
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• 2017

In this paper, we report a method of improving the productivity of lead wire fabricated through the rolling process by increasing its linear velocity. The most important point to consider when raising the linear velocity is that the original specifications must still be adhered to. In other words, the dimensional tolerance must be satisfied when increasing the linear velocity of the wire without causing cracks. However, if the linear velocity of the wire is increased, the degree of reduction must also be increased, which causes more damage to the wire and increases the load on its surface. Therefore, we studied a three step rolling process which can satisfy the specifications of the wire produced through the two step rolling process and improve the productivity. In this study, only the roll gap of the three-stage rolling roller is assumed to be a variable, while the other conditions are the same as the field conditions. In addition, through the PIANO (Process Integration, Design and Optimization) tool, the (optimum?) surface roughness and maximum stress are maintained.