• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2751-2761
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• 1994

A numerical investigation on the three-dimensional laminar natural convection heat transfer in the periodically fully developed PCB channel has been performed. When heat generating blocks mounted on the adiabatic wall make a channel with their facing shrouding wall, the flow inside the channel becomes periodically fully developed. A single module in the periodically fully developed region is chosen for computational domain in order to save computer storage and computational time. The periodic boundary condition is applied in the anlaysis. The effects of the parameters such as the Rayleigh number, the number of the modules, and the height of channel are examined to obtain the optimum condition for the enhancement of the cooling effectiveness. The result shows that the cooling effect is improved with increasing Rayleigh number and channel height, and decreasing the number of the module. The result also indicates that increasing the height of the channel and number of the module is recommended for a limited space.

• Journal of the Korea Society of Computer and Information
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• v.23 no.7
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• pp.1-10
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• 2018

In this paper, we propose the principles and design details of Automatic cable assembly test system and show its utility. Testing the cable assembly is required periodically or non-periodically in the system that the cable assembly performance is quite important like military equipment. There are several weaknesses when humans test the cable assembly manually. It not only takes much time but also could happen human error. To improve these disadvantages, I developed Automatic cable assembly test system. The system can be implemented by building switching control system that connect and disconnect the cable assembly and measuring devices. Through the result of the cable assembly test with this test system, we show this system makes test time short and improves of test reliability as compared with manual test.

• Proceedings of the Korea Crystallographic Association Conference
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• 2002.11a
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• pp.18-18
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• 2002

Although it was suggested in 1962 that an efficient wavelength conversion could be achieved using ferroelectric crystals of periodic 180° domains, it was not until 1990's that quasi-phase-matching (QPM) became realized, as technology for periodic poling of LiNbO₃ crystals was readily available. Since ferroelectric domain inversion brings about change of the sign of second-order nonlinear susceptibility, periodically poled ferroelectric structures provide an ideal way of achieving QPM for second-harmonic generation and optical parametric oscillation. Periodically poled ferroelectric domains can also be utilized for optical devices, such as Brags electrooptic modulators. fabrication of stable periodic domain structures depends on a number of poling parameters of a ferroelectric crystal, such as coercive field, internal field and electrical conductivity. We present poling kinetics of KNbO₃ crystals, which involve domain nucleation and growth, backswitching, relaxation of internal field. Optimum poling conditions were established by designing a proper wave shape of external field. We demonstrate an efficient second-harmonic generation using QPM in a periodically poled KNbO₃ crystal.

• Journal of the Chungcheong Mathematical Society
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• v.28 no.3
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• pp.391-396
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• 2015

$C^1$-generically, if a transitive diffeomorphism f is periodically expansive, then it is hyperbolic.

• 제어로봇시스템학회:학술대회논문집
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• 1987.10a
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• pp.842-846
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• 1987

This paper proves that a filter for scramble spectrum is realized by a periodically time-varying digital filter. Further, we propose a design method of this filter by using a bi-frequency map. As an example, we implemented this filter with Digital Signal Processor.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.7
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• pp.727-733
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• 2003

In order to realize miniaturized and low-impedance MMIC passive component, a novel microstripline structure employing periodically perforated ground metal was proposed. The novel microstripline structure showed much lower impedance, and shorter guided-wavelength than conventional one. Using the novel microstripline with periodically perforated ground metal, a miniaturized 15 $\Omega$ ratrace was fabricated. The line width of the ratrace was 20 $\mu\textrm{m}$, and the size of it was 0.375 mm$^2$, which is 9.3 % of conventional one. The ratrace exhibited good RF performances from 20 to 30 GHz.

• Journal of Advanced Marine Engineering and Technology
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• v.34 no.6
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• pp.840-845
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• 2010

In this paper, short-wavelength transmission line employing periodically arrayed capacitive devices (PACD) structures were developed for application to a development of miniaturized on-chip passive components on GaAs monolithic microwave integrated circuit (MMIC). The transmission line employing PACD structure showed a wavelength much shorter than conventional microstrip line. Concretely, the wavelength of the transmission line employing PACD structure was 8 % of the conventional microstrip line on GaAs substrate at 5GHz. And It was 38% of the microstrip line employing PPGM at 5GHz. It was recognized that the basic characteristics of the transmission line employing PACD structure were investigated for application to the miniaturized passive on-chip components.

• Korean Journal of Optics and Photonics
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• v.22 no.1
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• pp.1-4
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• 2011

A new fabrication technique of long-period fiber gratings with periodically surface-etched structures is proposed. Transmission characteristics of the periodically surface-etched long-period fiber gratings are improved by changing strain because of variation of coupling strength between the core and the cladding modes. The sensitivities of the periodically surface-etched long-period fiber gratings to strain, torsion, and ambient refractive index were measured. The strain and the torsion sensitivities were measured to be $-0.033\;dB/\mu\varepsilon$ and -1.30 nm m/rad, respectively. The ambient index sensitivity was measured to be -31.33 nm/RIU from a range from 1.33 to 1.42.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.1
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• pp.70-75
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• 2017

In this paper, we studied the RF characteristics of a voltage-controlled artificial transmission line employing periodically arrayed diodes for application to highly miniaturized wireless communication systems on an MMIC (monolithic microwave integrated circuit). According to the results, the novel voltage-controlled artificial transmission line employing periodically arrayed diodes exhibited a short wave length, which was only 35.2% that of the conventional transmission line, owing to increasing capacitance. In addition, it's effective permittivity and effective propagation constant exhibited considerably higher values than those of the conventional transmission line. Furthermore, attenuation constant of the voltage-controlled artificial transmission line was far higher than that of the conventional transmission line. Using the closed-form equation, we theoretically analyzed the equivalent circuit of the voltage-controlled artificial transmission line.

• Journal of the Korean Statistical Society
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• v.18 no.2
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• pp.125-134
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• 1989

This paper presents optimum simple step-stress accelerated life test plans for the case where the test process is observed periodically at intervals of the same length. Two types of failure data, periodically observed complete data and periodically observed censored data, are considered. An exponential life distribution with a mean that is a log-linear function of stress, and a cumulative exposure model for the effect of changing stress are assumed. For each type of data, the optimum test plan which minimizes the asymptotic variance of the maximum likelihood estimator of the mean life at a design stress is obtained and its behaviors are studied.