• East Asian mathematical journal
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• v.34 no.5
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• pp.577-585
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• 2018

For the purpose of characterizing subharmonic or ${\mathcal{M}}$-subharmonic Hardy classes in the unit ball of ${\mathbb{C}}^n$, we establish fundamental identities between integral means in terms of volume integrals and Green's functions.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.5
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• pp.197-203
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• 2003

In this paper, we have presented millimeter-wave high conversion gain quadruple subharmonic mixers adopting the cascode harmonic generator The subharmonic mixers were successfully integrated by using 0.1 ${\mu}{\textrm}{m}$ GaAs pseudomorphic HEMTs(PHEMTs) and coplanar waveguide(CPW) structures. Measured output of 1st, 2nd and 4th harmonics of the fabricated cascode 4th harmonic generator are -21.42 dBm, -32.65 dBm and -13.45 dBm, respectively, for an input power of 10 dBm at 14.5 GHz. We showed that the highest conversion gain of 3.4 dB has obtained thus far at a LO power of 13 dBm from the fabricated subharmonic mixers. The millimeter-wave subharmonic mixer also ensure a high degree of isolation showing -53.6 dB in the LO-to-IF and -46.2 dB in the LO-to-RF, respectively, at a frequency of 14.5 GHz. The high conversion gain achieved in this work is the first report among the millimeter-wave subharmonic mixers.

• East Asian mathematical journal
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• v.19 no.2
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• pp.165-171
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• 2003

We show that any F-harmonic map from a compact manifold M to N is necessarily constant if N possesses a strictly-convex function, and prove 'Liouville type theorems' for F-harmonic maps. Finally, when the target manifold is the real line, we get a result for F-subharmonic functions.

• Structural Engineering and Mechanics
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• v.42 no.5
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• pp.677-699
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• 2012

This article studies the secondary resonances of a clamped-clamped microresonator under combined electrostatic and piezoelectric actuations. The electrostatic actuation is induced by applying the AC-DC voltage between the microbeam and the electrode plate that lies at the opposite side of the microbeam. The piezoelectric actuation is induced by applying the DC voltage between upper and lower sides of piezoelectric layer. It is assumed that the neutral axis of bending is stretched when the microbeam is deflected. The drift effect of piezoelectric layer (the phenomenon where there is a slow increase of the free strain after the application of a DC field) is neglected. The equations of motion are solved by using the multiple scale perturbation method. The system possesses a subharmonic resonance of order one-half and a superharmonic resonance of order two. It is shown that using the DC piezoelectric actuation, the sensitivity of AC-DC electrostatically actuated microresonator under subharmonic and superharmonic resonances may be tuned. In addition, it is shown that the tuning domain of the microbeam under combined electrostatic and piezoelectric actuations at subharmonic and superharmonic conditions is larger than the tuning domain of microbeam under only the electrostatic actuation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.2
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• pp.152-158
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• 2004

A low phase noise frequency synthesizer at X-Band which employs the subharmonic injection locking was designed and tested. The designed frequency synthesizer consists of a 1.75 GHz master oscillator - which also operates as a harmonic generator - and a 10.5 GHz slave oscillator. A 1.75 GHz master oscillator based on PLL technique used two transistors - one constitutes the active part of VCO and the other operates as a buffer amplifier as well as harmonic generator. The first stage operates a fixed locked oscillator and using the BJT transistor whose cutoff frequency is 45 GHz, the second stage is designed, operating as a harmonic generator. The 6th harmonic which is produced from the harmonic generator is injected into the following slave oscillator which also behaves as an amplifier having about 45 dB gain. The realized frequency synthesizer has a 7.4 V/49 mA, -0.5 V/4 mA of the low DC power consumption, 4.53 dBm of output power, and a phase noise of -95.09 dBc/Hz and -108.90 dBc/Hz at the 10 kHz and 100 kHz offset frequency, respectively.

• Communications of the Korean Mathematical Society
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• v.28 no.3
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• pp.511-516
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• 2013

We establish an easy proof of an integral identity using the unitary invariance, which is applied to compare harmonicity and M-harmonicity.

• Bulletin of the Korean Mathematical Society
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• v.45 no.2
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• pp.321-338
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• 2008

Let $\bar{M}$ be a smoothly bounded pseudoconvex complex manifold with a family of almost complex structures $\{L^{\tau}\}_{{\tau}{\in}I}$, $0{\in}I$, which extend smoothly up to bM, the boundary of M, and assume that there is ${\lambda}{\in}C^{\infty}$(bM) which is strictly subharmonic with respect to the structure $L^0|_{bM}$ in any direction where the Levi-form vanishes on bM. We obtain explicit estimates for the $\bar{\partial}$-Neumann problem in Sobolev spaces both in space and parameter variables. Also we get a similar result when $\bar{M}$ is strongly pseudoconvex.

• Bulletin of the Korean Mathematical Society
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• v.47 no.3
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• pp.623-632
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• 2010

A holomorphic function F defined on the unit disc belongs to $A^{p,{\alpha}}$ (0 < p < $\infty$, 1 < ${\alpha}$ < $\infty$) if $\int\limits_U|F(z)|^p \frac{1}{1-|z|}(1+log)\frac{1}{1-|z|})^{-\alpha}$ dxdy < $\infty$. For boundedness of the composition operator defined by $C_{fg}=g{\circ}f$ mapping Blochs into $A^{p,{\alpha}$ the following (1) is a sufficient condition while (2) is a necessary condition. (1) $\int\limits_o^1\frac{1}{1-r}(1+log\frac{1}{1-r})^{-\alpha}M_p(r,\lambda{\circ}f)^p\;dr$ < $\infty$ (2) $\int\limits_o^1\frac{1}{1-r}(1+log\frac{1}{1-r})^{-\alpha+p}(1-r)^pM_p(r,f^#)^p\;dr$ < $\infty$.

• ETRI Journal
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• v.33 no.6
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• pp.965-968
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• 2011

A 1.485-Gbit/s video signal transmission system at carrier frequencies of 240 GHz and 300 GHz was implemented and demonstrated. The radio frequency front-ends are composed of Schottky barrier diode subharmonic mixers (SHMs), frequency triplers, and diagonal horn antennas for the transmitter and receiver. Amplitude shift keying with an intermediate frequency of 5.94 GHz was utilized as the modulation scheme. A 1.485-Gbit/s video signal with a high-definition serial digital interface format was successfully transmitted over a wireless link distance of 4.2 m and displayed on an HDTV with a transmitted average output power of 20 ${\mu}W$ at a 300-GHz system.

• ETRI Journal
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• v.35 no.3
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• pp.386-396
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• 2013

A 10-Gbit/s wireless communication system operating at a carrier frequency of 300 GHz is presented. The modulation scheme is amplitude shift keying in incoherent mode with a high intermediate frequency (IF) of 30 GHz and a bandwidth of 20 GHz for transmitting a 10-Gbit/s baseband (BB) data signal. A single sideband transmission is implemented using a waveguide-tapered 270-GHz high-pass filter with a lower sideband rejection of around 60 dB. This paper presents an all-electronic design of a terahertz communication system, including the major modules of the BB and IF band as well as the RF modules. The wireless link shows that, aided by a clock and data recovery circuit, it can receive $2^7$-1 pseudorandom binary sequence data without error at up to 10 Gbit/s for over 1.2 m using collimating lenses, where the transmitted power is 10 ${\mu}W$.