• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.4
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• pp.365-375
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• 2006

The structural analysis for the secondary lining of tunnels is generally performed by a frame analysis model. This model requires a ground loosening load estimated by some empirical methods, but the load is likely to be subjective and too large. The ground load acting on the secondary lining is due to the loss of the supporting function of the first support members such as shotcrete and rockbolts. Therefore, the equilibrium condition of the ground and the first support members should be considered to estimate the ground load acting on the secondary lining. Ground-lining interaction model, shortly GLI model, is developed on the basis of the concept that the secondary lining supports the ground deformation triggered by the loss of the support capacity of the first support members. Accordingly, the GLI model can take into account the ground load reflecting effectively not only the complex ground conditions but the installed conditions of the first support members. The load acting on the secondary lining besides the ground load includes the groundwater pressure and earthquake load. For the structural reinforcement of the secondary lining based on the ultimate strength design method, the factored load and various load combination should be considered. Since the GLI model has difficulty in dealing with the factored load, introduced in this study is the superposition principle in which the section moment and force of the secondary lining estimated for individual loads are multiplied by the load factors. Finally, the design method of the secondary lining using the GLI model is applied to the case of a shallow subway tunnel.

• The Journal of Society for e-Business Studies
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• v.24 no.4
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• pp.49-78
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• 2019

In the context of knowledge sharing, network position has been a controversial subject. A central position in the network provides access to non-redundant knowledge, leading to more opportunities of knowledge sharing. On the other hand, as "bridging" relationships, its characteristics as a "weak tie" suggest innate lack of trust and reciprocity which is considered an impediment to share knowledge. This paper attempts to enlighten the underlying dynamic by examining the interaction between network centrality, motivation and ability in knowledge sharing. Furthermore, this paper examines the concept of knowledge sharing ability in depth by operationalizing the construct into three aspects: extensive and diverse knowledge, social media utilization ability and self-efficacy. The results show a partially supported three-way interaction, where the highest level of knowledge provision is reported when the employee has low network centrality, high autonomous motivation and high knowledge sharing ability, i.e. extensive and diverse prior knowledge. Though all models indicate strong associations between network centrality and knowledge sharing, this suggests an even greater power of motivation and ability that gives the strength to overcome unfavorable environments of peripheral position. Therefore, this paper offers an alternative explanation to the existing debate whether network centrality positively or negatively influences knowledge sharing.

• Bulletin of the Society of Naval Architects of Korea
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• v.54 no.4
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• pp.39-46
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• 2017

Jack-up drilling rigs are widely used in offshore oil and gas exploration industry. It is originally designed for use in the shallow waters less than 60m of water depth; there is growing demand for their use in deeper water depth over 150m and harsher environmental conditions. In this study, global in-place analysis of jack-up rig leg for North-sea oil well is performed through numerical analysis. Firstly, environmental conditions and seabed characteristics at the North-sea are collected and investigated measurements from survey report. Based on these data, design specifications are established and the overall basic design is performed. Dynamic characteristics of the jack-up rig for North-sea are considered in the global in-place analysis both leg and hull and the basic stability against overturning moment is also analyzed. The structural integrity of the jack-up rig leg/hull is verified through the code checks and the adequate safety margin is observed. The uncertainty in jack-up behaviour is greatly influenced by the uncertainties in the soil characteristics that determine the resistance of the foundation to the forces imposed by the jack-up structure. Among the risks above mentioned, the punch-through during pre-loading is the most frequently encountered foundation problem for jack-up rigs. The objective of this paper is to clarify the detailed structure and installation engineering matters for prove the structural safety of jack-up rigs during operation. With this intention the following items are addressed; - Characteristics of structural behavior considering soil effect against environmental loads - Modes of failure and related pre-loading procedure and parameters - Typical results of structural engineering and verification by actual measurement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1025-1037
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• 2015

Flexible base isolation bearings that separate superstructure from ground have been widely used in the construction field because they make a significant contribution to increasing the fundamental period of the structure, thereby decreasing response acceleration transmitted into the superstructure. However, the established bearing devices installed to uphold the whole building give rise to some problems involved with failure and collapse due to lack of the capacity as modern structures are getting more massive and higher. Therefore, this study suggests new isolation bearings assembled with additional restrainers enabled to reinforcing and recentering, and then evaluates their performance to withstand the seismic load. The superelastic shape memory alloy (SMA) bars are installed into the conventional lead-rubber bearing (LRB) devices in order to provide recentering forces. These new systems are modeled as component spring models for the purpose of conducting nonlinear dynamic analyses with near fault ground motion data. The LRB devices with steel bars are also designed and analyzed to compare their responses with those of new systems. After numerical analyses, ultimate strength, maximum displacement, permanent deformation, and recentering ratio are compared to each model with an aim to investigate which base isolation models are superior. It can be shown that LRB models with superelastic SMA bars are superior to other models compared to each other in terms of seismic resistance and recentering effect.

• Proceedings of the KSMRM Conference
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• 2003.10a
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• pp.103-105
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• 2003

After fifteen years of development, Magnetic Resonance (MR) technology for human imaging and spectroscopy is reaching a refined state with FDA approved 3T clinical products from Siemens, GE, and Philips. Broker has cleared CE approval with a 4T system. Varian supports a 4T system platform as well. Shielded magnets are standard at 3T from GE, Oxford, Magnex, and IGC. A shielded 4T whole body magnet is available from Oxford. Stronger switched gradients and dynamic shim coils, desired at any field, areespecially useful at higher static magnetic fields B0. In addition to the higher currents required for higher resolution slice or volume selection afforded by higher SNR, whole body gradient coils will be driven at increasing slew rates to meet the needs of new cardiac applications and other requirements. For example 3T and 4T systems are now being equipped with 2kV, 500A gradient coils and amplifiers capable of generating 4G/cm in 200msec, over a 67+/-cm bore diameter. High field EPI applications require oscillation rates at 1 kHz and higher. To achieve a benchmark 0.2 ppm shim over a 30cm sphere in a high field magnet, at least four stages of shimming need to be considered. 1) A good high field magnet will be built to a homogeneity spec. falling in the range of 100 to 150 ppm over this 30cm spherical "sweet spot" 2) Most modern high field magnets will also have superconducting shim coils capable of finding 1.5 ppm by their adjustment during system installation. 3) Passive ferro-magnetic shimming combined with 4) active, high order room temperature shim coils (as many as five orders are now being recommended) will accomplish 0.2 ppm over the 30cm sphere, and 0.1 ppm over a human brain in even the highest field magnets for human studies. Safety concerns for strong, fast gradients at any B0 field include acoustic noise and peripheral nerve stimulation. One or more of the mechanical decoupling methods may lead to quieter gradients. Patient positioning relative to asymmetric or short gradient coils may limit peripheral nerve stimulation at higher slew rates. Gradient designs combining a short coil for local speed and strength with a longer coil for coverage are being developed for 3T systems. Local gradients give another approach to maximizing performance over a limited region while keeping within the physiologically imposed dB0/dt performance limits.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.8
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• pp.929-934
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• 2012

This study was carried out to analyze the dynamic characteristics of laser tailor-welded blanks (TWBs) made of dissimilar materials. The analysis was performed using Hyper Works 10.0 with Solver LS-DYNA v.971. 2D-Shell was used as the modeling element, and the number of elements and nodes was 35,641 and 36,561, respectively. The impact speed was 10 km/h. To analyze the impact characteristics according to the height of the weld line for the upper and lower parts of the center pillar, the length of the lower part was set as 300 and 400 mm. When the lower part was made of SPFC980 steel with a length of 300 mm, the deformation was the smallest and the absorbed energy of the impact force was the largest. On based the lower part of center pillar, the position of TWB shows the shorter and the better value. In other words, the performance depended on the proportion of the upper part made of high-strength SABC1470 steel. A lower part made of SPFH590 steel showed large deformation. In contrast, a lower part made of SPFC980 steel showed significantly lesser deformation. Therefore, the impact performance of a lower part made of SPFC980 steel with a length of 300 mm showed the best analysis result.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.21-30
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• 2018

Building structures of apartment in korea conventionally adopt shear walls using coupling beams as seismic force-resisting systems. Energy dissipating devices employed the building structures are used instead of the coupling beams in order to increase the seismic performances by providing additional damping and stiffness. This study aims to introduce energy dissipating devices which are preferred in structural system and aims to investigate structural behaviors of shear wall structures employing such devices instead of coupling beams. In order for achieve research objectives, Finite Element Analysis and Nonlinear analysis was carry out. Finite Element Analysis results was correspond with experimental results and this is indicated that the device can provide sufficient additional damping and stiffness into shear wall structures. Throughout nonlinear static analyses, examples structures with the devices can enhance seismic performance of building structures due to their sufficient energy dissipating capacities. Especially, strength and ductility capacities were significantly improved when it is compared with the performance of building structures without the devices. Throughout nonlinear dynamic analyses, it was observed that structural damages can be mitigated due to reduced seismic demands for seismic force-resisting systems. It is especially noted due to the fact that story drifts, accelerations, shear demands are reduced by 15~18%, 20~28% and 15~20%, respectively.

• The Journal of Korean Physical Therapy
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• v.23 no.4
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• pp.29-36
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• 2011

Purpose: The purpose of this study was to evaluate the effect of 6-week sensorimotoor training on balance ability and lower limb muscle activation during gait in older adults. Methods: Twenty-four community-dwelling older adults between 65 and 90 years of age participated in this study. In the older adults of the experimental group (n=12), the sensorimotor training program was performed bare feet. General exercise was performed in the control group (n=12). Then, both groups exercised three times a week for forty minutes over a 6-week period. Balance ability was evaluated by One leg stand (OLS) test for determining the static balance and Timed Up & Go (TUG) test for determining the dynamic balance. In addition, muscle activation of the dominant lower limb tibialis anterior and gastrocnemius medialis muscles were measured by surface EMG to evaluate muscle activation during gait. Results: A significant improvement was seen in the one leg standing (OLS) time after exercise in both the sensorimotor training (SMT) group and general exercise (GE) group (p<0.05) and the change in the SMT group was greater than that in the GE group (p<0.05). A significant reduction was seen in the Timed Up & Go (TUG) test time after exercise in both the SMT group and GE group (p<0.05). Also, a significant increase was seen in muscle activation of tibialis anterior muscle after exercise in the SMT group (p<0.05), but no such significant increase was seen in the GE group (p>0.05). Conclusion: These results suggest that sensorimotor training improves the balance in older adults and has a more positive effect on muscular strength and gait. Sensorimotor training provided a variance of training environment and COG exercise of the body is thought to be a more effective exercise program that improves balance and gait ability in older adults.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.8
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• pp.699-705
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• 2015

Aircraft needs high lift-to-drag ratio and weight reduction of the structure for long endurance flight with a small power. Generally high aspect ratio wing is applied to HALE(High Altitude Long Endurance) aircraft. Also high modulus, and high strength CFRP(Carbon Fiber Reinforced Plastic) has been used in primary structures. and thin mylar(membrane material) film has been applied to skin of wing. As a result, wing is more flexible than the other structures. and the stiffness of thin mylar film has an affect on dynamic stability. In this study, the membrane characteristic of mylar film has been simulated using nonlinear gap elements. And equivalent modeling method using shell elements is presented using the nonlinear simulation result. The linear equivalent model has verified using the results of nonlinear membrane method. Proposed linear equivalent shell model has applied to mode analysis for estimate the effect of mylar mechanical properties on natural frequency.

• Applied Chemistry for Engineering
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• v.28 no.5
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• pp.506-512
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• 2017

The transfer reaction characteristics of tetracycline (TC) across a polarized water/1,2-dichloroethane (1,2-DCE) interface was studied via controlling both pH and ionic strength of the aqueous phase in conjunction with cyclic and differential pulse voltammetries. Formal transfer potential values of differently charged TC ionic species at the water/1,2-DCE interface were measured as a function of pH values of the aqueous solution, which led to establishing an ionic partition diagram for TC. As a result, we could identify which TC ionic species are more dominant in the aqueous or organic phase. Thermodynamic properties including the formal transfer potential, partition coefficient and Gibbs transfer energy of TC ionic species at the water/1,2-DCE interface were also estimated. In order to construct an electrochemical sensor for TC, a single microhole supported water/polyvinylchloride-2-nitrophenyloctylether (PVC-NPOE) gel interface was fabricated. A well-defined voltammetric response associated with the TC ion transfer process was achieved at pH 4.0 similar to that of using the water/1,2-DCE interface. Also the measured current increased proportionally with respect to the TC concentration. A $5{\mu}M$ of TC in pH 4.0 buffer solution with a dynamic range from $5{\mu}M$ to $30{\mu}M$ TC concentration could be analyzed when using differential pulse stripping voltammetry.