• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.6
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• pp.577-580
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• 2016

One of the effective jamming methods to disturb monopulse radars is a wavefront distortion. Most well-known wavefront distortion is the cross eye technique which uses two transmitters. The cross eye can make angle error regardless of monopulse radar structure but high accuracies of phase and amplitude between two transmitters should be needed to make large angle error. Thus, the accuracies of phase and amplitude are essentially required performance parameters for implementation of wavefront distortion systems and the required values of accuracy is dependant on amount of angle error. In this paper, we derive expressions for minimum required values of phase difference and amplitude ratio according to amount of angle error and analyze the results.

• Korean Journal of Optics and Photonics
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• v.8 no.1
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• pp.1-6
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• 1997

The amplitude impulse S(x) of an interferometric optical imaging system for λ=193 nm(ArF laser) and NA=0.5 is derived for the pupil with superposed three Gauss pupils $A_1$($\omega$), $A_{2-}$($\omega$) and $A_{2+}$($\omega$). It is shown that FWHM of S(x) can be far less than the Rayleigh's criterion of resolution $\frac{1}{2}{\epsilon}_R$, where ${\epsilon}_R$ is equal to λ=193 nm in the present case of NA=0.5. The three Gauss pupils are provided in an optical system which consists of a Twyman-Green interferometer and an imaging system. The system is proposed and relevent optical components are discussed. Siloxane polymer is suggested for fabrications of amplitude modulation plates. In the present work, we assumed the system is free from aberration and linear. The case that the system has residual aberrations is important, and further work is necessary.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.1
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• pp.25-34
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• 2010

Fretting damage reduces fatigue life of the material due to low amplitude cyclic sliding and changes in the contact surfaces of strongly connected machine and structures such as bolt, key, fixed rivet and connected shaft, which have relative slip of repeatedly very low frequency amplitude. In this study, the fretting fatigue behavior of 7050-T7451 aluminum alloys used mainly in aircraft and automobile industry were evaluated. The plain fatigue test and fretting fatigue test under cyclic bending load carried out commercial bending fatigue tester and specially devised equipments to cause fretting damage. From these experimental work, the following results obtained: (1) The plain fatigue limit for stress ratio R=-l was about 151MPa. (2) In case of fretting fatigue, fatigue limit for stress ratio R=-l about 72MPa, the fatigue limit for R=0 about 81MPa, and the fatigue limit for R=0.3 about 93MPa. (3) The fatigue limit reduction rates by the fretting damage were about 52%(R=-1), 46%(R=0) and 38%(R=0.3) respectively. (4) The fatigue limit reduction rate decreased with stress ratio increase. In fretting bending test, as stress ratio increased, occurrence of initial oblique crack by fretting decreased or phased out, so that fracture surfaces were formed by plain fatigue crack occurrence, and such tendency was notable as stress amplitude increased. (5) Tire tracks and rubbed scars were observed in the fracture surface and contacted surface.

• Journal of the Korean Society of Safety
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• v.6 no.4
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• pp.81-87
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• 1991

We propose the crack growth rate equation which will model fatigue crack growth rate behavior such that constant stress amplitude fatigue crack growth behavior can be predicted. Constant stress amplitude fatigue tests are conducted for four materials under three stress ratios of R＝0.2, R＝0.4 and R＝0.6. Materials which have different mechanical properties i.e. stainless steel, low carbon steel, medium carbon steel and aluminum alloy are used. Through constant stress amplitude fatigue test by using unloading elastic compliance method, it is confirmed that crack closure is a close relationship with fatigue crack propagation. We describe simply fatigue crack propagation behavior as a function of the effective stress intensity factor range ($\Delta$ $K_{eff}$＝U .$\Delta$K) for all three regions (threshold region, stable region). The fatigue crack growth rate equation is given by da / dN＝A($\Delta$ $K_{eff}$­$\Delta$ $K_{o}$ )$^{m}$ / ($\Delta$ $K_{eff}$­$\Delta$K) Where, A and m are material constants, and $\Delta$ $K_{o}$ is stress intensity factor range at low $\Delta$K region. $K_{cf}$ is critical fatigue stress intensity factor.actor.

• Journal of Magnetics
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• v.19 no.4
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• pp.353-356
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• 2014

The aim of the present study was to examine whether mental practice (MP) in conjunction with repetitive transcranial magnetic stimulation (rTMS) can improve the upper limb function of sub-acute stroke patients. This study was conducted with 32 subjects who were diagnosed with hemiparesis by stroke. The experimental group consisted of 16 members upon each of whom was performed MP in conjunction with rTMS, whreas the control group consisted of 16 members upon each of whom was performed MP and sham rTMS. Both groups received traditional physical therapy for 30 minutes a day, 5 days a week, for 6 weeks; additionally, they received mental practice for 15 minutes a day. The experimental group was instructed to perform rTMS, and the control group was instructed to apply sham rTMS for 15 minutes. A motor cortex excitability analysis was performed by motor evoked potentials (MEPs), and upper limb function was evaluated by Fugl-Meyer Assessment (FMA) and the Box and Block test (BBT). Results showed that the amplitude, latency, FMA, and BBT of the experimental group and the latency, FMA, and BBT of the control group were significantly improved after the experiment (p<0.05). Significant differences were found between the groups in amplitude and latency after the experiment (p<0.05). The results showed that MP in conjunction with rTMS is more effective in improving upper limb function than MP alone.

• Journal of Magnetics
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• v.20 no.4
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• pp.427-431
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• 2015

The aim of this study was to investigate whether repetitive transcranial magnetic stimulation (rTMS) can improve motor recovery in the lower extremities of the patients with subacute stage spinal cord injury (SCI). This study was conducted with 19 subjects diagnosed with paraplegia because of SCI. The experimental group included 10 subjects who underwent active rTMS, and the control group included 9 subjects who underwent sham rTMS. The SCI patients in the experimental group underwent conventional rehabilitation therapy, and active rTMS was applied daily to the hotspot of the lesional hemisphere. The SCI patients in the control group underwent sham rTMS and conventional rehabilitation therapy. The participants in both the groups received therapy five days per week for six weeks. Latency, amplitude, and velocity were assessed before and after the six-week therapy period. A significant difference in post-treatment gains for the latency and velocity was observed between the experimental and control groups (p < 0.05). However, no significant differences in the amplitude were observed between the two groups (p > 0.05). The results of this study indicate that rTMS may be beneficial in improving motor recovery in the lower extremities of subacute stage SCI patients.

• Journal of the Korean earth science society
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• v.28 no.4
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• pp.491-496
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• 2007

We performed R band time-series CCD photometric observations of the 55 Pandora for 2 nights using the 0.6 m telescope equipped with 2K CCD camera at SOAO (Sobaeksan Optical Astronomical Observatory). From the observation we determined its rotation period $P=0.^d2007=4.^h8168$, and maximum amplitude $0.281\;{\pm}\;0.001$. We also derived the pole position ${\lambda}_p(^o)=342$, ${\beta}_p(^o)=64$, and the shape parameter a/b = 1.27, b/c = 1.31 by applying Amplitude-Magnitude method.

• Biomedical Science Letters
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• v.18 no.4
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• pp.391-398
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• 2012

The conventional blink reflex has limited clinical application since it displays a wide range of change in the responses. Thus, we studied the blink reflex using the averaging process which is engaged in evoked potential studies in order to measure various responses such as latency, amplitude, and duration, which have been difficult to measure due to their wide ranges of changes. Among the Bell's palsy patient group, 13 patients who had the symptoms of incomplete palsy were examined to assess the results of the blink reflex through the averaging process. The subjects were 54 people in a normal group (108 eyes) and 18 patients (36 eyes) with Bell's palsy. For the study method, the conventional blink reflex and the blink reflex using the averaging process were measured for the people in the normal group, while in the Bell's palsy group, only the blink reflex using the averaging process was analyzed. In the case of the normal group, the blink reflex using the averaging process could measure all of the latency, amplitude, and duration. It was also observed that the latency, amplitude, and duration of R1, ipsilateral R2, and contralateral R2 significantly differed on the affected side of the Bell's palsy patients, compared to the unaffected side. The blink reflex using the averaging process should be more effective than the conventional method since the former can evaluate the latency, amplitude, and duration for Bell's palsy, while the latter can only assess latency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.9
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• pp.955-964
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• 2010

In this paper, a compensation method of the amplitude and phase errors from the T/R(Transmit/Receive) modules in an active SAR(Synthetic Aperture Radar) system is introduced. The errors are defined and classified, and characterized by analyzing the measurement data acquired from the pilot test. To compensate these errors, a control methodology of T/R modules output is proposed. Before the compensation is applied, 16 T/R modules integrated on the active SAR antenna show the amplitude in 28.2~29.0 dBm and the phase in $101.7^{\circ}{\sim}165.2^{\circ}$. After the compensation, the amplitude and phase are distributed in 27.4~28.0 dBm and $116.1^{\circ}{\sim}120.0^{\circ}$ respectively. The antenna beam patterns generated by the array theory with the distributions are compared, and the proposed method is verified as good to apply for the active SAR system.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.6
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• pp.258-263
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• 2017

The effect of cooling rate on the damping capacity of pure Mg was studied. Two Mg samples with different cooling rates were prepared by heat treatment at 873 K for 24 h, followed by water quenching and by furnace cooling to room temperature, respectively. The average grain sizes of the Mg samples were almost identical regardless of the cooling rate, but more twins were observed in the sample with faster cooling rate. The calculated vacancy fraction was higher in the fast cooling sample than the slow cooling one. It is noted that the fast cooling sample exhibited lower damping capacity both in the strain-amplitude independent and strain-amplitude dependent regions. Higher values of vacancy concentration and number density of twins in the fast cooling sample are considered to be responsible for the deteriorated damping capacity in the strain-amplitude independent and strain-amplitude dependent regions, respectively.