• Wind and Structures
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• v.19 no.6
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• pp.649-663
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• 2014

The present paper discusses the characteristics of unsteady aerodynamic forces on long-span curved roofs. A forced vibration test is carried out in a wind tunnel to investigate the effects of wind speed, vibration amplitude, reduced frequency of vibration and rise/span ratio of the roof on the unsteady aerodynamic forces. Because the range of parameters tested in the wind tunnel experiment is limited, a CFD simulation is also made for evaluating the characteristics of unsteady aerodynamic forces on the vibrating roof over a wider range of parameters. Special attention is paid to the effect of reduced frequency of vibration. Based on the results of the wind tunnel experiment and CFD simulation, the influence of the unsteady aerodynamic forces on the dynamic response of a full-scale long-span curved roof is investigated on the basis of the spectral analysis.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.4
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• pp.126-132
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• 2008

The vibration and disturbances from operating the compact disk layer have an effect on the play ability. As the excitation sources of the compact disk player, there are the vibration of the motors and gears, impact by mechanical parts and the external excitations. So, most of the compact disk player have a anti-vibrational system, which is included some rubber or oil dampers. In this study, the vibration characteristics of rubber damper which is used home compact disk player are investigated. The materials and shape of rubber damper are changed, and the transmissibility is measured. As a conclusion, the natural frequency is moved to higher frequency and the transmissibility is reduced by the increasing rubber stiffness. In comparison to butyl rubber damper, the transmissibility of silicon damper was increased by larger restitution elasticity. The hollow damper was effective to reduced the transmissibility.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.1092-1094
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• 1992

Allowing for the fact that the load requiring for high speed has been incrased lately, this paper deals with a method that can consecutively convert the frequency from low frequency to high frequency. And this paper also shows the reduced effect of harmonics and the effectiveness or the proposed system, which are thoughly tested and proved through the experiments in the output frequency range of from 5Hz to 1200Hz.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.2
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• pp.69-74
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• 2004

In general the surge pressure generated in hydraulic systems causes noise, vibration and odd effect to the system. To reduce the surge pressure, high frequency PWM control of 20KHz was attempted. To estimate the braking noise caused by surge, a vehicle equipped with on-board ABS hydraulic modulator has been experimented with respect to the various breaking condition. Thorough this experiments, it was found that breaking noise has been reduced using high frequency PWM control method compare with low frequency method. To evaluate high frequency control m practice, including verification of general functionality, EMI tests was experimented. Its was found that it is necessary to have the solution to electromagnetic interference(EMI) generated by switching elements.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.9
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• pp.1720-1727
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• 2009

This paper presents that generation and propagation mechanism of low frequency current ripples generated by a rectification effect of an inverter in fuel cell generation system is analyzed. The ripple reduction methode using hardware components such as capacitors and inductors is examined to reduce low frequency current ripples. A new fast and robust low frequency current ripple elimination algorithm is then proposed to incorporate a single loop current controller, which directly controls fuel cell current, without any extra hardware. The proposed algorithm can completely eliminate this current ripple as well as an overshoot or undershoot is significantly reduced. And the de link voltage and output current are well regulated by inverter controller. The validity of proposed algorithm is verified both computer simulation using PSIM 6.0 and experiment with a 1kW laboratory prototype.

• Journal of Acupuncture Research
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• v.20 no.1
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• pp.177-190
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• 2003

Objective : This study was intended to investigate the analgesic effects of electroacupuncture(EA) on mechanical allodynia according to the frequency and intensity of EA. Also to know if mechanical allodynia and the analgesic effects of EA is related to the sympathetci nervous system and/or the purinergic system. Methods : mechanical allodynia-induced rats were produced by resecting S1-S2 nerve. The zusanli(ST36) was used for acupoint and the rats were divided into 4 groups. Each group was given different stimuli[low frequency low intensity-EA(LFLI-EA), low frequency high intensity-EA(LFHI-EA), high frequency low intensity-EA(LFHI-EA), high frequency high intensity-EA(HFHI-EA)]. Futhermore, to make sympathectomy6-OHDA and phentolamine were administered intraperitonially and the concentration of norepinephrine(NE) were measured. As a ATP blocker, suramin was applied for this study. Results : Comparing to control group, each of the 4 groups(LFLI-EA, LFHI-EA, HFLI-EA, HFHI-EA) showed a significant reduction of response frequency of mechanical allodynia. LFHI-EA was more effective than that of LFLI-EA. The LFHI-EA group also had longer lasting effects from the stimulation than the other groups. Sympathectomy didn't show any reduction of response frequency of mechanical allodynia.(Each n=6, n=4). Nor did both sympathectomy and ATP block. The response frequency wasn't reduced by sympathectomy or by sympathectomy and ATP block, but was significantly reduced with LFHI-EA Conclusions : These results suggest that EA has a significant analgesic effect on mechanical allodynia which has no connection with NE and/or ATP.

• Journal of Welding and Joining
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• v.14 no.5
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• pp.145-150
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• 1996

The variation of spatter generation in gas metal arc welding with welding conditions and wire compositions was investigated and interpreted in terms of arc stability. The transition range from a short circuit mode to a spray mode in the mixed gas welding showed an unstable arc and generated the largest amount of spatters. Titanium reduced spatters only in the globular mode of $CO_2$welding and silicon and manganese showed the same effect The effect of silicon and manganese, however, was no longer seen when titanium was added simultaneously to the wire. It is believed that deoxidizers easily form oxides on the anode and make the arc stable even in DCRP welding. The wires with deoxidizers also showed low short circuit frequency, resulting in the increase of large size spatters.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.2
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• pp.135-142
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• 2008

Experimental studies on the aerodynamic coupling effect on natural frequencies, critical speed and flutter instability of rotating disks are investigated in this paper. The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and damping and stiffness components. The experiments performed using a vacuum chamber and ASMO/DVD disks rotating in vacuum, open and enclosure in several gaps with stationary wall give three main results. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency of disks rotating in open air is larger than that in enclosure. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.10
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• pp.45-50
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• 1971

For the purpose of finding out the effect of heat treatment on biological response and mutation rate, rice seeds were heat treated before and after gamma irradiation. 1. At a dose of 20 KR, pre-irradiation heat treatment showed reduced biological damage and increased mutation rate as compared with non-heat treatment. 2. Mutation frequency was increased in post-treatment of heat shock than in pre-irradiation heat treatment and non-heat treatment. 3. Pre-irradiation heat treatment at 6$0^{\circ}C$ for 30 minutes markedly reduced the biological damage and increased the mutation rate. 4. Mutation spectrum in heat treatment was different from non-treatment.

• Korean Journal of Agricultural Science
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• v.48 no.1
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• pp.83-93
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• 2021

The 52-hour workweek policy in Korea is a system that limits the maximum working hours per week to 52 hours including holiday work, which has been treated separately from overtime work during a week. Although this policy is designed to improve the quality of life and create jobs, it may also reduce the income of some workers. In general, it can be assumed that reduced working hours increase consumption at home. This study analyzed the effect of the 52-hour work policy on meat consumption patterns with the ordered logit model. Major factors considered in this study include working hours, income, and consumption frequency. It distinguished domestic and workplace consumption. The results show that the policy has had an impact on meat consumption patterns both at home and at work. If there is no change in income and only the working hours decrease, meat consumption in households increases. On the other hand, if both income and working hours decrease, household meat consumption decreases. Moreover, reduced working hours decrease the frequency of office happy hour and meat consumption in the workplace. However, the 52-hour workweek policy applies only to workers working more than 52 hours per week; thus, it is difficult to determine the overall effect of the policy on national meat consumption patterns.