• Journal of Power Electronics
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• v.16 no.4
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• pp.1565-1577
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• 2016

For grid-connected LCL-filtered inverters, dual-loop current control with an inner-loop active damping (AD) based on capacitor current feedback is generally used for the sake of current quality. However, existing studies on capacitor current feedback AD with a control delay do not reveal the mathematical relation among the dual-loop stability, capacitor current feedback factor, delay time and LCL parameters. The robustness was not investigated through mathematical derivations. Thus, this paper aims to provide a systematic study of dual-loop current control in a digitally-controlled inverter. At first, the stable region of the inner-loop AD is derived. Then, the dual-loop stability and robustness are analyzed by mathematical derivations when the inner-loop AD is stable and unstable. Robust design principles for the inner-loop AD feedback factor and the outer-loop current controller are derived. Most importantly, ensuring the stability of the inner-loop AD is critical for achieving high robustness against a large grid impedance. Then, several improved approaches are proposed and synthesized. The limitations and benefits of all of the approaches are identified to help engineers apply capacitor current feedback AD in practice.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.5
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• pp.445-450
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• 2016

In this paper we study the effect of chaos in nonuniform instability with optical fiber based IoT networks. The transient response of optically controlled fiber has also described. Nonlinear optical fiber effects especially fiber scattering in networks has emerged as the essential means active optical devices. The paradigm instability in fiber Internet serves as a test for fundamental study of chaos and its suppression and exploitation in practical application in optical communication. This paper attempts to present a survey and some of our research findings on the nature of chaotic effect on Internet based optical communication. The transient response in optical fiber has been evaluated theoretically by calculating the variation of the scattering function. The lines has used under open ended termination containing optically induced region. The scattered optical waves in a fiber used in optic communications are temporally unstable above certain threshold intensity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.373-378
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• 2007

On the homodyne interferometers, high pass filter(HPF) is usually used to remove the electrical noise in the interferent signal. Heterodyne interferometer has modulating frequency is shifted in the frequency region where the electrical noise effect is minimized by HPF effect. However, on the homodyne interferometer, the interferent DC-component of homodyne interferometer is unfortunately eliminated by using a HPF because its shifted frequency does not exist. Moreover, this effect is more serious the vibration amplitude is smaller. So, when unstable interferent signals via HPF are demodulated, a velocity is distorted. In this work, the mathematical explanation for the distortion of the homodyne interferent signal using the HPF is given. New synthetic heterodyne LDV based on the homodyne interferometer by exciting the reference mirror is proposed for the cancellation of the distortion. The optimum excitation condition of the mirror to compensate the distortion is discussed. The numerical simulation using the commercial MATLAB code is provided to show the effect of the proposed synthetic heterodyne LDV. The experimental results are also given and the effect of the proposed LDV is discussed.

• Journal of Environmental Impact Assessment
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• v.8 no.4
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• pp.13-23
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• 1999

This study was carried out to investigate the degree of impact from road construction and forest fragmentation after urbanization. And this study was also conducted to compare the urban forest fragmentations of four cities, Taegu, Pohang, Kyungju, and Kumi, in Kyungpook, Korea, with referring the Landsat TM remotely sensed data. Taegu metropolitan city has the largest forest volume of our surveying sites, comparing with three other cities-Kyungju Pohang Kumi city in kyungpook, Korea. The forest has been fragmented during urbanization, the number of forest patch has been increased, therefore, the patch size has been smaller. The forest in Pohang and Kyungju city represented the intermediate aspect between Taegu Metropolitan city and Kumi city, it means forest of the region has been stable condition. Road construction brings to increasing edge habitat area. However, as the core area was decreased, the habitats have been unstable. This result can be a basis on the management of the forest which is the origin of biodiversity. Hereafter, if the research, based on the multi-temporal remote sensing data, is proceeded continuously, the forest fragmentation will be able to be reduced. We will be able to settle urban forest management more practically.

• Korean Journal of Clinical Laboratory Science
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• v.42 no.2
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• pp.97-102
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• 2010

The two new female cases of Angelman syndrome (AS) were described, which diagnosed on the basis of clinical features (dysmorphic facial features, severe mental retardation with absent speech, peculiar jerky movements, ataxic gait and paroxysms of inappropriate laughter) and neurophysiological findings. Failure to detect the deletion of the long arm of chromosome 15 or the absence of epileptic seizure were not considered sufficient to exclude a diagnosis of AS. Feeding problems, developmental delay and early signs of ataxia, especially tremor on handling objects and unstable posture when seated, proved effective as the clinical markers for early diagnosis of AS. Most of the authors agreed about the existence of three main EEG patterns in AS which may appear in isolation or in various combinations in the same patient. The most frequently observed pattern in children has prolonged runs of high amplitude rhythmic 2-3 Hz activity predominantly over the frontal region with superimposed interictal epileptiform discharges. High amplitude rhythmic 4-6 Hz activity, prominent in the occipital regions, with spikes, which can be facilitated by eye closure, is often seen in children under the age of 12 years. The EEG findings are characteristic of AS when seen in the appropriate clinical context and can be helpful to identify AS patients at an early age when genetic counselling may be particularly important.

• Journal of the Korean Society of Combustion
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• v.2 no.1
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• pp.1-8
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• 1997

Premixed combustion within porous ceramic media is numerically studied to understand burning characteristics and to find best configurations for burner implementations. Among many parameters, critical to burner performance, flame location and extinction coefficient are selected as major parameters for this study. The flame structure and burner performance with respect to these two parameters are observed. In the study, it is found that the location of flame is the most important in porous burner operation since it affects the rate of heat transfer and flame structure. Stability of the flame within the porous ceramic burner is discussed with respect to the flame location. It is found that to obtain high radiative output, the flame should be located downstream section of the burner. But the flame is to be unstable at most of downstream section except near the exit plane. To overcome this problem, new porous ceramic burner, using different ceramic properties in one burner instead of single property ceramic, is made and tested. With a combination of ceramics of high extinction coefficient at upstream and another material of low extinction coefficient at downstream of the burner, the flame can be stabilized at wider region of the burner with higher radiative output compared to the original burner configuration.

• Structural Engineering and Mechanics
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• v.68 no.1
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• pp.103-119
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• 2018

In the present research, an attempt is made to obtain a semi analytical solution for both nonlinear natural frequency and forced vibration of embedded functionally graded double layered nanoplates with all edges simply supported based on nonlocal strain gradient elasticity theory. The interaction of van der Waals forces between adjacent layers is included. For modeling surrounding elastic medium, the nonlinear Winkler-Pasternak foundation model is employed. The governing partial differential equations have been derived based on the Mindlin plate theory utilizing the von Karman strain-displacement relations. Subsequently, using the Galerkin method, the governing equations sets are reduced to nonlinear ordinary differential equations. The semi analytical solution of the nonlinear natural frequencies using the homotopy analysis method and the exact solution of the nonlinear forced vibration through the Harmonic Balance method are then established. The results show that the length scale parameters give nonlinearity of the hardening type in frequency response curve and the increase in material length scale parameter causes to increase in maximum response amplitude, whereas the increase in nonlocal parameter causes to decrease in maximum response amplitude. Increasing the material length scale parameter increases the width of unstable region in the frequency response curve.

• The Korean Journal of Quaternary Research
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• v.22 no.2
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• pp.1-5
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• 2008

Some reverse fault lines pass through the alluvial fans and west hill slope of Bulguksa mountains including Mt. Toham in the directions of N-S and NW-SE. The study area is known as relatively unstable, because of active faults. Assuming the record of earthquake in the Samguksagi, the architects in the construction of the Bulguksa temple should have recognized the possibility of breakdown from the earthquakes and the need for an unique structure against at that time. Against earthquakes, Greavee technique, a stonework construction technique following woothe one and use of Chushouok (Dongtleouok or Chumchaouok) were applied for the construction of Bulguksa temple. By designing the foundation stone with hole, a structure is prevented from motiff Ction that pillarsakdcede from a foundation stone in spite of horizontal load of earthquake while woot construction isaktrong frame at earthquake. The Bulguksa-temple isausually evaluated to be a beautiful architecture from the appeaultces like the weight balltced structure with unique decoration. ampressive architectures are beautiful in balance and harmony coming from the important and specific rolls in its own way by each part of whole structure. This beauty comes from the science.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.71-82
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• 1999

Irregular motions of nonlinear dynamic system are the result of an intrinsic characteristics that the system have, and sometimes occur unpredictable large motion. For a ship in a regular seaway, the capsizing occur because of this unexpectable motion. So, from the safety's point of view, nonlinear ship motions should be treated carefully. In this study, stable and unstable regions are investigated firstly under the variation of a control external force. Secondly, we consider the attractors to know how ship motions of the stable region that does not undergo capsizing change. Thirdly, bifurcation diagram is considered to study the range in detail where nonlinear chaotic motions are occurred.

• Bulletin of the Korean Chemical Society
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• v.29 no.10
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• pp.1937-1940
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• 2008

The P1 duplex of Tetrahymena group I ribozyme is the important system for studying the conformational changes in folding of ribozyme. The formation of the P1 duplex between IGS and substrate RNA and the catalytic activity of ribozyme require a variety of metal ions such as $Mg^{2+}$ and $Mn^{2+}$. In order to investigate the effect of the $Mg^{2+}$ concentration on the conformation of the P1 duplex, the NMR study was performed as a function of $Mg^{2+}$ concentration. This study revealed that the less stable AU-rich region formed duplex at $50{^{\circ}C}$ under high $Mg^{2+}$ concentration condition but melts out under low $Mg^{2+}$ concentration condition. It was also found that in the active conformation under 10 mM $MgCl_2$ condition, the unstable central G${\cdot}$U wobble pair maintains the significant base pairing up to $50{^{\circ}C}$. This study provides the information of the unique feature of the P1 duplex structure and the roll of $Mg^{2+}$ ion on the formation of the active conformation.