• Journal of the Korean Society for Heat Treatment
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• v.34 no.6
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• pp.309-314
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• 2021

Due to the superior corrosion resistance and mechanical properties of TiAl alloy at high temperature, it has been utilized as a turbine wheel of a turbocharger. The dissimilar metallic bonding is usually applied to combine the TiAl turbine wheel with the SCM440 structural steel which is used as a driving shaft. In this study, the TiAl and SCM440 joint were fabricated by using a friction welding technique. During bonding process, to suppress the martensitic transformation and the formation of cracks, which might reduce a strength of the joints, Cu was used as an insert metal to relieve stress. As a result, the intermetallic compounds (IMCs) layer was observed at TiAl/Cu interface while no IMC formation was formed at SCM440/Cu interface. Since understanding of the IMCs effects on the mechanical performance of welded joint is also essential for ensuring the reliability and integrity of the turbocharger system, we estimated the nanohardness of welded joint region through nanoindentation. The relation between the microstructural feature and its mechanical property is discussed in detail.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.7
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• pp.21-27
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• 2022

This study was conducted to evaluate the structural stability of a CNC automatic lathe structure and avoid resonance. The analysis conditions were analyzed by applying the weight of the upper assembly. From the structural analysis, the stress and deformation were low, and the safety factor was high. From the dynamic characteristic analysis, it was determined that resonance does not occur because the natural frequency is outside the driving range. The error between the dynamic characteristic analysis and vibration test results is very low; thus, the reliability of the analysis results can be secured.

• Molecules and Cells
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• v.46 no.3
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• pp.153-164
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• 2023

Cancer stem cells (CSCs) are a small population of tumor cells characterized by self-renewal and differentiation capacity. CSCs are currently postulated as the driving force that induces intra-tumor heterogeneity leading to tumor initiation, metastasis, and eventually tumor relapse. Notably, CSCs are inherently resistant to environmental stress, chemotherapy, and radiotherapy due to high levels of antioxidant systems and drug efflux transporters. In this context, a therapeutic strategy targeting the CSC-specific pathway holds a promising cure for cancer. NRF2 (nuclear factor erythroid 2-like 2; NFE2L2) is a master transcription factor that regulates an array of genes involved in the detoxification of reactive oxygen species/electrophiles. Accumulating evidence suggests that persistent NRF2 activation, observed in multiple types of cancer, supports tumor growth, aggressive malignancy, and therapy resistance. Herein, we describe the core properties of CSCs, focusing on treatment resistance, and review the evidence that demonstrates the roles of NRF2 signaling in conferring unique properties of CSCs and the associated signaling pathways.

• Geomechanics and Engineering
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• v.37 no.6
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• pp.555-563
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• 2024

The reasonable setting of coal pillar width plays a key role in guaranteeing the steadiness of surrounding rock of fully mechanized caving gateroad driving along the next goaf. Based on the engineering background of the Bayangaole mine, the discrete element method was used to simulate the fracture evolution of coal pillars with different pillar widths. The results show that the damage rate of the coal pillar increases with the decrease in the width of the coal pillar. Once the coal pillar width is smaller than 6 m, cracks run through the coal pillar, and the coal pillar is completely damaged. In the middle of the coal pillar, which has a width of 6 m and above, there is a relatively complete area with low damage. The results show that the pillar width of 6 m is the most appropriate. Field tests prove that the reserved width of a 6 m small coal pillar can effectively control the surrounding rock deformation, ensuring the overall steadiness of the gateroad in the thick coal seam. It is hoped that this study will offer some reference for the determination of the reasonable size of the coal pillar.

• Korean Journal of Soil Science and Fertilizer
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• v.46 no.6
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• pp.659-664
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• 2013

The aim of this study is to determine the drought stress index through photochemical analysis in red pepper (Capsiumannuum L.). The photochemical interpretation was performed in the basis of the relation between Kautsky effect and Photosystem II (PSII) following the measurement of chlorophyll, pheophytin contents, and $CO_2$ assimilation in drought stressed 5-week-old red pepper plants. The $CO_2$ assimilation rate was severely lowered with almost 77% reduction of chlorophyll and pheophytin contents at four days after non-irrigation. It was clearly observed that the chlorophyll fluorescence intensity rose from a minimum level (the O level), in less than one second, to a maximum level (the P-level) via two intermediate steps labeled J and I (OJIP process). Drought factor index (DFI) was also calculated using measured OJIP parameters. The DFI was -0.22, meaning not only the initial inhibition of PSII but also sequential inhibition of PSI. In real, most of all photochemical parameters such as quantum yield of the electron transport flux from Quinone A ($Q_A$) to Quinone B ($Q_B$), quantum yield of the electron transport flux until the PSI electron acceptors, quantum yield of the electron transport flux until the PSI electron acceptors, average absorbed photon flux per PSII reaction center, and electron transport flux until PSI acceptors per cross section were profoundly reduced except number of QA reducing reaction centers (RCs) per PSII antenna chlorophyll (RC/ABS). It was illuminated that at least 6 parameters related with quantum yield/efficiency and specific energy fluxes (per active PSII RC) could be applied to be used as the drought stress index. Furthermore, in the combination of parameters, driving forces (DF) for photochemical activity could be deduced from the performance index (PI) for energy conservation from photons absorbed by PSII antenna until the reduction of PSI acceptors. In conclusion, photochemical responses and their related parameters can be used as physiological DFI.

• The Journal of Information Systems
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• v.22 no.2
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• pp.51-83
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• 2013

Personal creativity is critically important for organizations seeking to survive and thrive in today's highly turbulent business environments. Organizations must effectively identify and mobilize the creative resources of their members. When organizational members perceive a work environment that restricts or fails to encourage individual creative expression, a gap may exist between the level of individual creative potential and the actual amount of individual creativity practiced within the organization. In this situation, this paper will examine the impact of role conflict, role ambiguity, creative self-efficacy, and personal initiative on personal creativity. Creative self-efficacy is the subjective belief in one's personal ability to be creative, that is, a personal assessment of one's own creative potential. A strong internal belief in one's ability to successfully engage in creative behaviors is generally considered an important part of the creative process. Personal Initiative refers to behaviors, mainly directed toward work and organizational issues, that are characterized by the following aspects: self-starting, proactive, and persistent in overcoming barriers. Creativity-related creative self-efficacy and personal initiative are critical components to understand motivation that coordinates the relationship between perception and behavior of individual employees. Based on role theory, researchers have focused on role conflict and role ambiguity as the two key ingredients of role stress. Role ambiguity is defined as an evaluation about the lack of salient information needed to perform a role effectively. Role conflict results from two or more sets of incompatible demands involving work-related issues. Employees are usually pursued work-roles more than one in work-focused organization. Too many work-roles and perceived uncertainties at employee's work can be obstacles to personal creativity. In an analysis of results, while role conflict is not negatively related significantly to creative self-efficacy, role ambiguity is negatively related significantly to creative self-efficacy. While role conflict is significantly related to personal creativity, role ambiguity is negatively related significantly to personal creativity. Creative self-efficacy mediates the relationship among role conflict, role ambiguity, and employee creativity. Personal initiative mediates the relationship between creative self-efficacy and employee creativity. This paper shows that creative self-efficacy and personal initiative are the driving force behind personal creativity. Organizations can get some implications of creative-related role conflict and role ambiguity that employees have experienced. As a result, organizations must not only encourage creativity of employees by greater involvement but also encourage their input towards their-focused own works and tasks. And employees should be developed to pace with the organizational needs and development. Management must enable employees to think of new ideas and practices that promotes personal creativity.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.433-452
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• 2018

The shield tunneling method can minimize surface settlements by preventing the deformation of tunnel face and tunnel intrados due to tunnel excavation. For this purpose, it is very important to control the operating conditions of shield TBM. The face pressure and backfill pressure for tail void grouting should be the most important and immediate measure not only to restrain surface settlement, but also to influence the effective stress and pore water pressure around the circumstance of tunnel during excavation. The reaction of the ground to the application of face pressure and backfill pressure relies on the stiffness and permeability of ground. Especially, the reaction of saturated clayey ground formations, which shows the time-dependent deformation, is different from the permeable ground. Hence, in this paper it was investigated how the TBM operating conditions, ground stiffness, and permeability impact on the surface settlement of saturated clayey ground. For this purpose, a series of parametric studies were carried out by means of the stress-pore water pressure coupled FE analysis. The results show that the settlement of soft clayey ground is divided into the immediate settlement and consolidation settlement. Especially, the consolidation settlement depends on the ground stiffness and permeability. In addition, the existence of critical face pressure and backfill pressure was identified. The face pressure and backfill pressure above the critical value may cause an unexpected increase in the ground settlement.

• Journal of Ocean Engineering and Technology
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• v.28 no.2
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• pp.152-159
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• 2014

KRISO(Korea Research Institute of Ships & Ocean Engineering) designed and manufactured a pilot mining robot called "MineRo" in 2012. MineRo is composed of four track modules. In general, much time and money are needed for deep-sea tests. Therefore, a numerical analysis to predict the dynamic behaviors has to be performed before a deep-sea test. In the numerical analysis, the information about the mining robot and soil properties are the most important factors to analyze the driving performance and dynamic response of MineRo. A terra-mechanics model of extremely cohesive soft soil is implemented in the form of the relationships between the normal pressure and sinkage, and between the shear stress and shear displacement. It is possible to acquire information about MineRo from the CAD model in the design phase. The Wong model is applied to the terra-mechanics model. This model is necessary to acquire many soil coefficients for a numerical analysis. However, in soil testing, the amount of soil property data obtained is limited. Moreover, it is difficult to analyze all of the cases for the many soil coefficients. In this paper, the dynamic behaviors of MineRo are analyzed according to the driving velocity, steering ratio, and variable extremely cohesive soft soil properties using a table of orthogonal arrays. The dynamic responses of MineRo are the turning radius, sinkage, and slip ratio. The relationships between the dynamic responses and variable soil properties are derived for MineRo.

• Tunnel and Underground Space
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• v.30 no.5
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• pp.484-495
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• 2020

To numerically simulate the advance of EPB TBM, various type of numerical analysis methods have been adopted including discrete element method (DEM), finite element method (FEM), and finite difference method (FDM). In this paper, an EPB TBM driving model was proposed by using coupled DEM-FDM. In the numerical model, DEM was applied in the TBM excavation area, and contact properties of particles were calibrated by a series of triaxial tests. Since the ground around the excavation area was coupled with FDM, the horizontal stress considering the coefficient of earth pressure at rest could be applied. Also, the number of required particles was reduced and the efficiency of the analysis was increased. The proposed model can control the advance rate and rotational speed of the cutter head and screw conveyor, and derive the torque, thrust force, chamber pressure, and discharging during TBM tunnelling.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.4
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• pp.827-836
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• 2018

In this study, we developed a PC - based motorcycle simulator based on the development technology of a virtual patrol motorcycle training system. This simulator has been developed to be applied to a variety of fields such as driving training for beginners, driver factor research, and system development such as ABS, which can be seen in advanced models. The weight of the motorcycle operated by the patrol guards is more than 400Kg. There is a lot of risk due to the nature of work without prior practice. Therefore, we implemented a study on the untilization of physical stress and temporal pressure in emergency situations. In order to get a feeling that the motorcycle simulator is operating in real-life, it is important that the mutual reliable signal transmission and operation feel between the driver and the simulator. In order to achieve this, we developed a system that can apply the sub-systems of the actual vehicle to the motorcycle simulator in order to generate the same operation feeling as the actual vehicle. Based on these results, we have developed a method of generating a feedback queue.