• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.12
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• pp.79-86
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• 2008

This paper presents the experimental results of impulse breakdown characteristics in $SF_6/N_2$ gas mixtures under a highly non-uniform electric field with a change in temperature. The test temperature ranges from -25[$^{\circ}C$] to 25[$^{\circ}C$]. The processes of impulse preliminary breakdown developments were analyzed by the measurements of current pulse and luminous signals. As a result, the temperature dependance of breakdown voltage for the negative polarity was much stronger than that for the positive polarity. When increasing the temperature, The leader stepping time for the negative polarity was shown to be longer than that for the positive polarity. The results presented in this paper can be used as a useful information in designing the gas insulation lines with prominent ability for lightning surge.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.681-682
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• 2012

• Smart Structures and Systems
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• v.14 no.6
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• pp.1269-1289
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• 2014

With the sub-stepping technique, the numerical analysis in real-time dynamic hybrid testing is split into the response analysis and signal generation tasks. Two target computers that operate in real-time may be assigned to implement these two tasks, respectively, for fully extending the simulation scale of the numerical substructure. In this case, the integration time-step of solving the dynamic response of the numerical substructure can be dozens of times bigger than the sampling time-step of the controller. The time delay between the real and desired feedback forces becomes more striking, which challenges the well-developed delay compensation methods in real-time dynamic hybrid testing. This paper focuses on displacement prediction and force correction for delay compensation in the real-time dynamic hybrid testing with a large integration time-step. A new displacement prediction scheme is proposed based on recently-developed explicit integration algorithms and compared with several commonly-used prediction procedures. The evaluation of its prediction accuracy is carried out theoretically, numerically and experimentally. Results indicate that the accuracy and effectiveness of the proposed prediction method are of significance.

• Earthquakes and Structures
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• v.13 no.3
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• pp.279-288
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• 2017

Having the ability to keep on yielding stable solutions in problems involving high potential of instability, composite time integration methods have become very popular among scientists. These methods try to split a time step into multiple sub-steps so that each sub-step can be solved using different time integration methods with different behaviors. This paper proposes a new composite time integration in which a time step is divided into two sub-steps; the first sub-step is solved using the well-known Newmark method and the second sub-step is solved using Simpson's Rule of integration. An unconditional stability region is determined for the constant parameters to be chosen from. Also accuracy analysis is perform on the proposed method and proved that minor period elongation as well as a reasonable amount of numerical dissipation is produced in the responses obtained by the proposed method. Finally, in order to provide a practical assessment of the method, several benchmark problems are solved using the proposed method.

• Korean Journal of Optics and Photonics
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• v.10 no.5
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• pp.430-438
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• 1999

We have utilized soft-aperturing by gain media to develop a high-power tunable Ti:Sapphire laser with sub-40-fs and broad tuning range. The tunable spectral range was only limited by the bandwidth of mirrors. We made use of knife-edge slits near an intra-cavity prism controlled by micro-stepping-motors to tune the center wavelength continuously. The tunability of the center wavelength was ranged from 770 nm to 870 nm, and the measured pulsewidth was sub-40 fs throughout the above spectral range. The shortest pulsewidth was about 17 fs at the center wavelength of 820 nm and the spectral bandwidth was 72 nm. At 5 W pumping power of the Ar-ion laser we obtained average output power of 440 mW~580 mW. For the cw and Kerr-lens mode-lodking conditions, we have evaluated the value of an amplitude modulation to be ${\gamma}=2.5{\times}10^{-8}/W$ from the calculated waists of a Gaussian beam on the Ti:sapphire crystal surface. Using this result we demonstrate that the generation of sub-40-fs Kerr-lens mode-locked pulse can be described by the Ginzberg-Landau model which is a weak pulse shaping model.

• Korean Journal of Acupuncture
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• v.22 no.2
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• pp.57-74
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• 2005

Objective : Frutus gardeniae, seed of Gardenia jasminoides Ellis is one of the crude drugs used for the treatment of inflammatory condition in oriental medicine. Methodes : The present study aimed to examine the analgesic effect and anti-inflammatory effect of Frutus gardeniae extract (FGE) on a rat model of ankle sprain pain, and the relations between FGE-induced effect and endogenous nitric oxide (NO) and inducible NO synthase (iNOS), cyclooxygenase-2 (COX-2), and c-Fos protein expression in the spinal cord. As a chronic pain model, ankle sprain pain model was used to test the effect of FCE injection applied to acupuncture point. After the induction of ankle sprain, rats subsequently showed a reduced stepping force of the affected limb for at least the next 4 days. The reduced stepping force of the limb was presumably due to a painful knee. FGE dissolved in normal saline was injected several acupoints. Results : After the treatment, behavioral tests measuring stepping force were periodically conducted during the next 8 hours. FGE produced significant improvement of stepping force of the hindlimb affected by the ankle sprain lasting at least 4 hours. FGE produced the improvement of stepping force of the affected hindlimb in a dose-dependent manner. In addition, FGE injection showed inhibitory effect on the paw edema induced by ankle sprain. Both NO production and iNOS, COX-2 protein expression increased by ankle sprain were suppressed by FGE. FGE on combination with electroacupuncture (EA) produced more powerful and longer lasting improvement of stepping force of the hindlimb affected by the ankle sprain than either FGE or EA did. The present study suggest that FGE produces a potent analgesic effect on the ankle sprain pain model of the rat and that FGE-induced analgesia modulate endogenous NO through the suppression of iNOS/COX-2 protein expression.

• Journal of computational fluids engineering
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• v.13 no.2
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• pp.27-41
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulation of three-dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence-free flow field at each physical time step. An implicit time integration method with local time stepping was implemented to accelerate the convergence in the pseudo-time sub-iteration procedure. The one-equation Spalart-Allmaras turbulence model has been adopted to solve high-Reynolds number flow fields. The flow solver was parallelized to minimize the CPU time and to overcome the computational overhead. This method has been applied to calculate steady and unsteady flow fields around submarine configurations and a 3-D infinite cylinder. Validations were made by comparing the predicted results with those of experiments or other numerical results. It was demonstrated that the present method is efficient and robust for the prediction of steady and unsteady incompressible flow fields.

• Journal of muscle and joint health
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• v.19 no.1
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• pp.16-26
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• 2012

Purpose: The purpose of this study was to investigate the effects of lumbar stabilization exercise on balance ability in patients with adolescent idiopathic scoliosis. Methods: This study was one group pretest-posttest design. Twenty young idiopathic scoliosis patients were recruited for this study. They had the lumbar stabilization exercise program for 40 minutes a day, three times per week for 3 weeks. The lumbar trunk muscle endurance test and clinical balance tests (functional forward reach, functional lateral reach, Fukuda 50-stepping, one leg standing with eyes open and eyes closed) were measured before and after the lumbar stabilization exercise. Results: There were significant differences between pre-and post-test in absolute value of the difference between right and left lateral reach, distance of Fukud 50-stepping and one leg standing on the each side with eyes closed(p<.05). The results showed that the lumbar trunk muscle endurance significantly increased(p<.05). Conclusion: In this study indicated that the lumbar stabilization exercise was effective on balance ability and lumbar trunk muscle endurance in patients with young idiopathic scoliosis.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1613-1626
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• 2002

This paper presents hybrid control of an active suspension system with a full-car model by using H$\sub$$\infty$/ and nonlinear adaptive control methods. The full-car model has seven degrees of freedom including heaving, pitching and rolling motions. In the active suspension system, the controller shows good performance: small gains from the road disturbances to the heaving, pitching and rolling accelerations of the car body. Also the controlled system must be robust to system parameter variations. As the control method, H$\sub$$\infty$/ controller is designed so as to guarantee the robustness of a closed-loop system in the presence of uncertainties and disturbances. The system parameter variations are taken into account by multiplicative uncertainty model and the system robustness is guaranteed by small gain theorem. The active system with H$\sub$$\infty$/ controller can reduce the accelerations of the car body in the heaving, pitching and rolling directions. The nonlinearity of a hydraulic actuator is handled by nonlinear adaptive control based on the back-stepping method. The effectiveness of the controllers is verified through simulation results in both frequency and time domains.

• International Journal of Aeronautical and Space Sciences
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• v.2 no.2
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• pp.28-38
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• 2001

A numerical method for the assessment and correction of tunnel wall interference effects on forced-oscillation testing is presented. The method is based on the wall pressure signature method using computed wall pressure distributions. The wall pressure field is computed using unsteady three-dimensional full Navier-Stokes solver for a 70-degree pitching delta wing in a wind tunnel. Approximately-factorized alternate direction implicit (AF-ADI) scheme is advanced in time by solving block tri-diagonal matrices. The algebraic Baldwin-Lomax turbulence, model is included to simulate the turbulent flow effect. Also, dual time sub-iteration with, local, time stepping is implemented to improve the convergence. The computed wall pressure field is then imposed as boundary conditions for Euler re-simulation to obtain the interference flow field. The static computation shows good agreement with experiments. The dynamic computation demonstrates reasonable physical phenomena with a good convergence history. The effects of the tunnel wall in upwash and blockage are analyzed using the computed interference flow field for several reduced frequencies and amplitudes. The corrected results by pressure signature method agree well with the results of free air conditions.