• Journal of the Korean association of regional geographers
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• v.1 no.1
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• pp.93-101
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• 1995

Nam Khane watershed, in the Northern Laos, consists of limestone plateau surrounded with steep slope(above 1000m), wide piedmont hill land(300-700m) and narrow alluvial plain. Opium on the plateau and up-land rice on the hill-side are cultivated for each, but its shifting agricultural activity, which degrades the forest and soil, has caused the serious environmental problems. MOS-1 satellite image and 40 points of soil samples are analyzed to identify the distribution of the shifting cultivation and to evaluate the environmental problems for Nam Khane watershed. The land use classification map is presented on the photo 2, and the value of each land use area by elevation level and soil property are showed on the table 2 and 3, respectively. Excessive agricultural activity of shifting cultivation in the Nam Khane watershed not only decreased the forest area, but also changed the primary forest of tree into secondary woodland of shrub. On the phase of soil property, it accelerated the soil and gully erosion, and acidification. To solve these environmental problems, the most important step is to settle the agriculture from shifting cultivation to permanent cropping.

• Korean Journal of Optics and Photonics
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• v.10 no.4
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• pp.328-334
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• 1999

Methylene blue-sensitized photopolymerizable material based on acrylamide is investigated with two-wave energy coupling experiments. Differently from other studies, self-diffraction oscillations are observed and the grating phase is determined without applying external electric fields, moving nonlinear materials, and phase shifting one of two writing beams. The phase grating showed a phase shift of $\pm$50$^{\circ}$ with respect to the intensity grating. Modified Kogelnik's coupled wave equation considering the mixed gratings of phase and absorption gratings and nonzero spatial phase shifts of the gratings with respect to the intensity interference patterns formed during the two-wave energy coupling is discussed in detail to understand these phenomenon.

• Journal of Electrical Engineering and Technology
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• v.3 no.3
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• pp.391-400
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• 2008

Multi-pulse topology of converters using elementary six-pulse GTO - VSC (gate turn off based voltage source converter) operated under fundamental frequency switching (FFS) control is widely adopted in high power rating static synchronous compensators (STATCOM). Practically, a 48-pulse ($6{\times}8$ pulse) configuration is used with the phase angle control algorithm employing proportional and integral (PI) control methodology. These kinds of controllers, for example the ${\pm}80MVAR$ compensator at Inuyama switching station, KEPCO, Japan, employs two stages of magnetics viz. intermediate transformers (as many as VSCs) and a main coupling transformer to minimize harmonics distortion in the line and to achieve a desired operational efficiency. The magnetic circuit needs altogether nine transformers of which eight are phase shifting transformers (PST) used in the intermediate stage, each rating equal to or more than one eighth of the compensator rating, and the other one is the main coupling transformer having a power rating equal to that of the compensator. In this paper, a two-level 48-pulse ${\pm}100MVAR$ STATCOM is proposed where eight, six-pulse GTO-VSC are employed and magnetics is simplified to single-stage using four transformers of which three are PSTs and the other is a normal transformer. Thus, it reduces the magnetics to half of the value needed in the commercially available compensator. By adopting the simple PI-controllers, the model is simulated in a MATLAB environment by SimPowerSystems toolbox for voltage regulation in the transmission system. The simulation results show that the THD levels in line voltage and current are well below the limiting values specified in the IEEE Std 519-1992 for harmonic control in electrical power systems. The controller performance is observed reasonably well during capacitive and inductive modes of operation.

• Korean Journal of Optics and Photonics
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• v.8 no.3
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• pp.189-193
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• 1997

Aspheric pick-up lenses are increasingly used in consumer products such as computer and multimedia, as their mass production has become possible owing to the injection molding process. However still much work needs to be done for more effective manufacture of aspheric lenses, one area of which is the in-line inspection of produced lenses. In this paper, we present a lateral-shearing interferometer that has specially been designed to have a high immunity to external vibration and atmospheric disturbance. The interferometer comprises four prisms. They are directly attached to each other using an immersion oil so that relative sliding motions between the prisms are allowed. Their relative displacement can readily generate necessary lateral-shearing and phase-shifting to determine the wavefront of the beam collimated by the lens under inspection. A special phase-measuring algorithm of arbitrary-bucket is adopted to compensate the phase-shifting error caused by the thickness reduction in the immersion oil. Zernike polynomial fitting has done for determinating quantitative aberration of aspheric pick-up lenses. The interferometer built in this work is robust to external mechanical vibration and atmospheric disturbance so that experimental results show that it has a repeatability of less than λ/100.

• Animal cells and systems
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• v.9 no.3
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• pp.153-160
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• 2005

Most living organisms exhibit the circadian rhythm in their physiology and behavior. Recent identification of several clock genes in mammals has led to the molecular understanding of how these components generate and maintain the circadian rhythm. Many reports have implicated the photic induction of either mPer1 or mPer2 in the hypothalamic region called the suprachiasmatic nucleus (SCN) to phase shift the brain clock. It is now established that peripheral tissues other than the brain also express these clock genes and that the clock machinery in these tissues work in a similar way to the SCN clock. To determine the role of the two canonical clock genes, mPer1 and mPer2, in the peripheral clock shift, stable HEK293EcR cell lines that can be induced and stably express these proteins were prepared. By regulating the expression of these proteins, it could be shown that induction of the clock genes, either mPer1 or mPer2 alone is not sufficient to cause clock phase shifting in these cells. Our real-time PCR analysis on these cells indicates that the induction of mPER proteins dampens the expression of the clock-specific transcription factor mBmal1. Altogether, our present data suggest that mPer1 and mPer2 may not function in clock shift or take part in differential roles on the peripheral circadian clock.

• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.387-390
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• 2005

Parameter estimation for the probability model of wavelet coefficients is essential to the wavelet-domain interpolation. However, phase uncertainty, one well-known drawback of the orthogonal wavelet transforms, make it difficult to estimate parameters. In this paper, we exploit a phase shifting matrix in order to improve the accuracy of estimation. Nonlinear modeling to capture the interscale characteristics is also described. The experimental results show that the proposed method outperforms the previous wavelet-domain interpolation method as well as the conventional bicubic method.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2007.11a
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• pp.319-322
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• 2007

In the development of paralleling techniques, Multi-Phase Interleaved(MPI) converter constitutes one of the most promising alternatives reported in the last years. This technique consists of a phase shifting of the control signals of several cells in parallel operating at the same switching frequency. As a result, the aggregated input and output current waveform exhibit lower ripple amplitude and smaller harmonics content than in synchronous or stochastic operation modes. Based on the inherent advantages of the MPI converter, in this paper, a control scheme, which can reduce current and voltage rifle, is proposed for PEMFC generation systems. The MPI boost converter is composed of several identical boost converters connected in parallel.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.267-276
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• 1997

We set up a four-wave holographic interferometer using a symmetric dual-beam illumination which is to measure in-plane and out-of-plane displacement simultaneously. In order to acquire the displacement phase map we applied the phase-shifting method and removed the noise of the phase map with least-squares fitting. In this approach the access to information relative to both the difference and sum of phases existing in the two arms of four-wave holographic interferometer was allowed. As a result, in-plane and out-of-plane displacement was measured to the accuracy of λ/40 and λ/100, respectively at λ=632.8nm

• Proceedings of the KIEE Conference
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• 1999.11a
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• pp.24-27
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• 1999

This paper proposed a method to reduce torque ripple of double-layer axial flux permanent magnet motor. Torque is generated by interacting between current of stator winding and airgap flux. In the case of slotless axial flux permanent magnet motor, only commutation torque component is significant. Hence, cogging and reluctance torque will not be considered. For this propose, we were supplied differential phase current in each winding and shifted rotor magnet. According to shifted rotor magnet and flux and phase of current were shifted, phase of developed torque in each side is difference. As a result, we could reduce the total torque ripple in motor and obtain minimum torque ripple in the case of 7.5 degree shifting angle between two rotors.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.22 no.7
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• pp.669-674
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• 2011

In this paper, a method for reduction of spurious signal in Digital RF Memory(DRFM) is proposed. Spurious response is a major performance issue of DRFM. This method is based on mixing a random phase LO signal into input IF signal and sampling it. The random phase LO signal is generated by high speed phase shifting characteristic of Direct Digital Synthesizer(DDS). Through this technique, we achieved an enhancement of 5~10 dB of spurious response.