• Bulletin of the Korean Mathematical Society
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• v.43 no.2
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• pp.443-459
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• 2006

The prey-predator system with a single cross-diffusion pressure is known to possess a local solution with the maximal existence time $T\;{\leq}\;{\infty}$. By obtaining the bounds of $W\array_2^1$-norms of the local solution independent of T we establish the global existence of the solution. And the long-time behaviors of the global solution are analyzed when the diffusion rates $d_1\;and\;d_2$ are sufficiently large.

• Korean Journal of Optics and Photonics
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• v.9 no.6
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• pp.428-432
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• 1998

We fabricated 1$\times$8 array of GaAs/AlGaAs quantum well infrared photodetectors for the long wavelength infrared detection which is based on the bound-continuum intersubband transition, and characterized its electrical and optical properties. The device was grown on SI-GaAs(100) by the molecular beam epitaxy and consisted of 25 period of 40 ${\AA} $ GaAs well and 500 ${\AA} $ $Al_{0.28} Ga_{0.72}$ As barrier. To reduce the possibility of interface states only the center 20 ${\AA} $ of the well was doped with Si ($N_D=2{\times}10^{18} cm^{-3}$). We etched the sample to make square mesas of 200$\times$200 $\mu\textrm{m}^2$ and made an ohmic contact on each pixel with Au/Ge. Current-voltage characteristics and photoresponse spectrum of each detector reveal that the array was highly uniform and stable. The spectral responsivity and the detectivity $D^＊$ were measured to be 180,260 V/W and $4.9{\times}10^9cm\sqrt{Hz}/W$ respectively at the peak wavelength of $\lambda$ =7.8 $\mu\textrm{m}$ and at T=10 K.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.12 s.354
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• pp.16-23
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• 2006

This paper presents the development of the fast Direction Finder using direct conversion method, which can intercept for short pulse signal of less' than 1 msec. in RF Down Converter, and CVDF(Correlative Vector Direction Finding) algorithm, which estimates DoA (Direction of Arrival). The configuration and characteristics of direction finder using 5-channel equi-spaced circular array antenna are presented and the direct conversion techniques for removing tuning time using I/Q demodulator are described. The CRLB of our model is derived, the principles of 2 kind of CVDF algorithm are explained and their characteristics are compared with CRLB w.r.t the number of samples and spacing ratio. The RF Down Converter prototype using direct conversion method is manufactured, the 2 kind of CVDF algorithm are applied and their performance are analyzed. Finally it is confirmed the LSE based CVDF algorithm is better than correlation-coefficient based except for ambiguity protection capabilities.