• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.5
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• pp.619-624
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• 2013

A bendable electronic module is developed. In this module, thin silicon electronic chips are embedded in a polymer-based encapsulating adhesive between flexible copper-clad polyimide layers. During the qualification test of a harshly thermal-hygroscopic complex loading condition, delaminations occur inside the module layers. A finite element model is developed for the module. To investigate the effect of hygroscopic stress on delamination, the results of the thermal and thermal-hygroscopic loads are compared. The analysis results reveal that the hygroscopic effect more strongly affects delamination than does the thermal effect. The potential failure mechanisms of the module are investigated based on the stress analysis.

• Steel and Composite Structures
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• v.33 no.6
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• pp.793-803
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• 2019

Concrete-filled steel tubular (CFST) beam-columns are widely used owing to their good performance. They have high strength, ductility, large energy absorption capacity and low costs. Externally stiffened CFST beam-columns are not used widely due to insufficient design equations that consider all parameters affecting their behavior. Therefore, effect of various parameters (global, local slenderness ratio and adding hoop stiffeners) on the behavior of CFST columns is studied. An experimental study that includes twenty seven specimens is conducted to determine the effect of those parameters. Load capacities, vertical deflections, vertical strains and horizontal strains are all recorded for every specimen. Ratio between outer diameter (D) of pipes and thickness (t) is chosen to avoid local buckling according to different limits set by codes for the maximum D/t ratio. The study includes two loading methods on composite sections: steel only and steel with concrete. The case of loading on steel only, occurs in the connection zone, while the other load case occurs in steel beam connecting externally with the steel column wall. Two failure mechanisms of CFST columns are observed: yielding and global buckling. At early loading stages, steel wall in composite specimens dilated more than concrete so no full bond was achieved which weakened strength and stiffness of specimens. Adding stiffeners to the specimens increases the ultimate load by up to 25% due to redistribution of stresses between stiffener and steel column wall. Finally, design equations previously prepared are verified and found to be only applicable for medium and long columns.

• Nuclear Engineering and Technology
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• v.32 no.4
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• pp.395-409
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• 2000

Parametric studies were performed to assess the sensitivity in determining the maximum in-vessel heat removal capability from the core material relocated into the lower plenum of the reactor pressure vessel (RPV）during a core melt accident. A fraction of the sensible heat can be removed during the molten jet delivery from the core to the lower plenum, while the remaining sensible heat and the decay heat can be transported by rather complex mechanisms of the counter-current flow limitation (CCFL) and the critical heat flux (CHF）through the irregular, hemispherical gap that may be formed between the freezing oxidic debris and the overheated metallic RPV wall. It is shown that under the pressurized condition of 10MPa with the sensible heat loss being 50% for the reactors considered in this study, i.e. TMI-2, KORI-2 like, YGN-3&4 like and KNGR like reactors, the heat removal through the gap cooling mechanism was capable of ensuring the RPV integrity as much as 30% to 40% of the total core mass was relocated to the lower plenum. The sensitivity analysis indicated that the cooling rate of debris coupled with the sensible heat loss was a significant factor The newly proposed heat removal capability map (HRCM) clearly displays the critical factors in estimating the maximum heat removal from the debris in the lower plenum. This map can be used as a first-principle engineering tool to assess the RPV thermal integrity during a core melt accident. The predictive model also provided ith a reasonable explanation for the non-failure of the test vessel in the LAVA experiments performed at the Korea Atomic Energy Research Institute (KAERI), which apparently indicated a cooling effect of water ingression through the debris-to-vessel gap and the intra-debris pores and crevices.

• Journal of Technology Innovation
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• v.5 no.1
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• pp.206-222
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• 1997

The conventional analysis with which justifies government intervention of the private sector's innovation activities is the market failure approach. According to such analysis, fund allocation through autonomous market mechanisms is not optimal in technology financing because of the disparity between the desirable level of investment for society as a whole and that for private firms. To optimize the fund allocation, public policies such as subsidy, preferencial loan and venture capital investment programs are designed for technology development projects performed by private firms. They, however, have not been effective in increasing private investment for such projects. In most cases, it was found that little considerations given to the relationship between uncertainty embodied in technology development projects and each types of financing. With respect to optimizing fund allocation, technology development projects should be financed by different means according to their probability of success and the expected value of technology. Employing various theoretical models on financing decision-making we verify here that technology development projects to be supported by commercial banks or venture capital institutions is limited contingent upon levels of uncertainty adn expected value. Under the assumption that financial institutions are risk averse, loan or investment can be available only if the probability of success of the project is higher than the probability premium and the current market rate of interest. Therefore, the projects that have lower probability of success and/or small expected return are excluded from commercial loan or investment programs. However, the remaining projects, whose probability of success is low but with high expected return, may be applied under government subsidy programs. To achieve optimality of fund allocation and to activate technology financing, we conclude that there should be a systematic division of role among financial institutions including government commercial banks, and venture capital institutions.

• KCI Concrete Journal
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• v.12 no.2
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• pp.85-93
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• 2000

Potentially significant mechanical improvements in tension can be achieved by the incorporation of randomly distributed, short discrete fibers in concrete. The improvements due to the incorporation fibers significantly influence the composite stress - strain ($\sigma$-$\varepsilon$) characteristics. In general incorporating fibers in a plain concrete has relatively small effect on its precracking behavior. It, however, alters its post-cracking behavior quite significantly, resulting in greatly improved ductility, crack controls, and energy absorption capacity (or toughness). Therefore, a thorough understanding the complete tensile stress - strain ($\sigma$-$\varepsilon$) response of fiber reinforced concrete is necessary for proper analysis while using structural components made with fiber reinforced concrete. Direct tensile stress applied to a specimen is in principle the simplest configuration for determining the tensile response of concrete. However, problems associated with testing brittle materials in tension include (i) the problem related to gripping of the specimen and (ii) the problem of ensuring centric loading. Routinely, indirect tension tests for plain concrete, flexural and split-cylinder tests, have been used as simpler alternatives to direct uniaxial tension test. They are assumed to suitable for fiber reinforced concrete since typically such composites comprise 98% by volume of plain concrete. Clearly since the post-cracking characteristics are significantly influenced by the reinforcing parameters and interface characteristics, it would be fundamentally incorrect to use indirect tensile tests for determining the tensile properties of fiber reinforced concrete. The present investigation represents a systematic look at the failure and toughening mechanisms and macroscopic stress - strain ($\sigma$-$\varepsilon$) characteristics of fiber reinforced concrete in the uniaxial tension test. Results from an experimental parametric study involving used fiber quantity, type, and mechanical properties in the uniaxial tension test are presented and discussed.

• Journal of the Microelectronics and Packaging Society
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• v.21 no.3
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• pp.7-17
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• 2014

Power electronics modules are semiconductor components that are widely used in airplanes, trains, automobiles, and energy generation and conversion facilities. In particular, insulated gate bipolar transistors(IGBT) have been widely utilized in high power and fast switching applications for power management including power supplies, uninterruptible power systems, and AC/DC converters. In these days, IGBT are the predominant power semiconductors for high current applications in electrical and hybrid vehicles application. In these application environments, the physical conditions are often severe with strong electric currents, high voltage, high temperature, high humidity, and vibrations. Therefore, IGBT module packages involves a number of challenges for the design engineer in terms of reliability. Thermal and thermal-mechanical management are critical for power electronics modules. The failure mechanisms that limit the number of power cycles are caused by the coefficient of thermal expansion mismatch between the materials used in the IGBT modules. All interfaces in the module could be locations for potential failures. Therefore, a proper thermal design where the temperature does not exceed an allowable limit of the devices has been a key factor in developing IGBT modules. In this paper, we discussed the effects of various package materials on heat dissipation and thermal management, as well as recent technology of the new package materials.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.13
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• pp.5137-5142
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• 2014

Adriamycin (ADR) is an important chemotherapeutic agent frequently used in treatment of breast cancer. However, resistance to ADR results in treatment failure in many patients. Recent studies have indicated that microRNAs (miRNAs) may play an important role in such drug-resistance. In the present study, microRNA-452 (miR-452) was found to be significantly down-regulated in adriamycin-resistant MCF-7 cells (MCF-7/ADR) compared with the parental MCF-7 cells by miRNA microarray and real-time quantitative PCR (RT-qPCR). MiR-452 mimics and inhibitors partially changed the adriamycin-resistance of breast cancer cells, as also confirmed by apoptosis assay. In exploring the potential mechanisms of miR-452 in the adriamycin-resistance of breast cancer cells, bioinformatics analysis, RT-qPCR and Western blotting showed that dysregulation of miR-452 played an important role in the acquired adriamycin-resistance of breast cancer, maybe at least in part via targeting insulin-like growth factor-1 receptor (IGF-1R).

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.250-255
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• 2000

Damage induced by low velocity impact loading in aircraft composite laminates is the form of failure which is occurred frequently in aircraft. Low velocity impact can be caused either by maintenance accidents with tool drops or by in-flight impacts with debris. As the consequences of impact loading in composite laminates, matrix cracking, delamination and eventually fiber breakage for higher impact energies can be occurred. Even when no visible impact damage is observed, damage can exist inside of composite laminates and the carrying load of the composite laminates is considerably reduced. The reduction of strength and stiffness by impact loading occurs in compressive loading due to laminate buckling in the delaminated areas. The objective of this study is to determine inside damage of composite laminates by impact loading and to determine residual compressive strength and the damage growth mechanisms of impacted composite laminates. For this purpose a series of impact and compression after impact tests are carried out on composite laminates made of carbon fiber reinforced epoxy resin matrix with lay up pattern of $[({\pm}45)(0/90)_2]s$ and $[({\pm}45)(0)_3(90)(0)_3({\pm}45)]$. UT-C scan is used to determine impact damage characteristics and CAI(Compression After Impact) tests are carried out to evaluate quantitatively reduction of compressive strength by impact loading.

• Biomolecules & Therapeutics
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• v.14 no.1
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• pp.1-10
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• 2006

Drug dependence deals a heavy socioeconomic burden to the society. For adolescents, the damage from drug dependence is greater than adults considering their higher susceptibility to drug effect and increasing chance for violence leading to criminal punishment process. Habitual drug use depends on genetic and environmental factors and the complex interactions between the two. Mammalian model systems have been useful in understanding the neurochemical and cellular impacts of abused drugs on specific regions of the brain, and in identifying the molecular targets of drugs. More elucidation is required whether biological effects of drugs actually cause the habitual dependence at the cellular level. Although there is much insight available on the nature of drug abuse problems, none of the systems designed to help drug dependent individuals is efficient in screening functional ingredients of the drug, and thus resulting in the failure of helping drug dependent individuals recover from drug dependence. Alternative model systems draw the attention of researchers, such as the invertebrate model systems of nematodes (Caenorhabditis elegans) and fruit flies (Drosophila melanogaster). These models should provide new insight into the mechanisms leading to the behavior of drug users (even functional studies analyzing molecular mechanism), and screening useful components to help remove drug dependence among drug users. The relatively simple anatomy and gene expression of the invertebrate model systems should enable researchers to coordinate current knowledge on drug abuse. Furthermore, the invertebrate model systems should facilitate advance in experiments on the susceptibility of specific genetic backgrounds and the interaction between genetic factors to drug dependence.

• Molecular & Cellular Toxicology
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• v.2 no.3
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• pp.193-201
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• 2006

Cephalexin, one of most widely prescribed cephalosporin, has been reported to cause acute renal failure as a side effect in human and experimental animals. Although numerous animal studies have been reported for the cephalosporin nephrotoxicity, the molecular and cellular nephrotoxic mechanisms of cephalexin are still unknown. This investigation evaluated the time-dependent gene expression profile of kidney in mouse during cephalexin induced nephrotoxicity. C57BL/6 female mice were administered either saline or 1,000 mg/kg cephalexin intraperitoneally. Mice were sacrificed at 3, 6, and 24 hr after administration. Blood biochemical and histopathological results indicated cephalexin induced nephrotoxicity. Microarray experiment carried out using Affymetrix $GeneChip^{(R)}$. There were 198 informative genes that were significantly expressed >5-fold versus control at 3, 6, and 24 hr (p<0.01), of which 156 and 42 were up-and down-regulated, respectively. Major classes of up-regulated genes at 3, 6 hr included those involved in MAPK/Jak-STAT signaling pathway and immune response such as cytokine-cytokine receptor interaction and complement and coagulation cascades. At 24 hr, up-regulated genes were mainly involved in regeneration/repair and immune response; down-regulated genes were generally associated with transporters and intermediary metabolism. Among the up-regulated genes at 24 hr, several potential biomarkers on nephrotoxicity such as Kim-1, Fga, Timp1, and Slc34a2 were clustered in a same category. In addition, Tnfrsf12a and Lcn2 which were consistently up-regulated (>5 fold) were also included as potential biomarkers. These results may provide clues for elucidating the mechanism of cephalexin induced nephrotoxicity and evaluating potential biomarkers to assess nephrotoxicity.