• 소음진동
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• 제7권3호
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• pp.439-447
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• 1997

In this study, the dynamic instabilities of a nonlinear elastic system subjected to follower forces are investigated. The two-degree-of-freedom double pendulum model with nonlinear geometry, cubic spring, and linear viscous damping is used for the study. The constant, the initial impact forces acting at the end of the model are considered. The chaotic nature of the system is identified using the standard methods, such as time histories, power density spectrum, and Poincare maps. The responses are chaotic and unpredictable due to the sensitivity to initial conditions. The sensitivities to parameters, such as geometric initial imperfections, magnitude of follower force, direction control constant, and viscous damping, etc., are analysed. Dynamic buckling loads are computed for various parameters, where the loads are changed drastically for the small change of parameters.

• 대한수학회논문집
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• 제20권4호
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• pp.695-702
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• 2005

We study the transformed measures with respect to the real parameters of a self-similar measure on a self-similar Can­tor set to give a simple proof for some result of its multifractal spectrum. A transformed measure with respect to a real parameter of a self-similar measure on a self-similar Cantor set is also a self­similar measure on the self-similar Cantor set and it gives a better information for multifractals than the original self-similar measure. A transformed measure with respect to an optimal parameter deter­mines Hausdorff and packing dimensions of a set of the points which has same local dimension for a self-similar measure. We compute the values of the transformed measures with respect to the real parameters for a set of the points which has same local dimension for a self-similar measure. Finally we investigate the magnitude of the local dimensions of a self-similar measure and give some correlation between the local dimensions.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권11호
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• pp.512-515
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• 2003

This paper is to investigate how partial discharge pulse signal can flow in 6.6㎸ motor stator windings. Pulse propagation is experimentally analyzed in stator windings using a variety of frequency-domain techniques. The experiments were performed on two stator windings in the laboratory. Spectrum analyzer(9KHz to 3㎓) with tracking generator(100kHz to 3㎓) was used. Sweep time of the tracking generator was looms. The frequency spectrum of the response signal was detected by active FET probe(1㎓). The active FET probe has a flat amplitude response up to 1㎓ without high frequency attenuation. The stator winding acts as a low-pass filter below 600KHz, the high-frequency components being highly declined. The resonance peaks show about 1.1MHz and 2MHz in low frequency of No. 1 and No. 2 stator windings, respectively. This low-frequency range indicates that attenuation is low. The peaks of partial discharge magnitude show about 900MHz, 1.6MHz in No. 1 stator winding and about 800KHz, 1.4MHz in No. 2 stator winding.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.770-773
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• 2006

In order to remove the whine noise which has high frequency spectrum related to the uniform tinning space in concrete pavements, randomization study of the tinning space has been done. One of the random tinning space proposed by the authors in the previous study has been applied to the certain region of tile Daegu-Pohang high way construction. In this study, the vehicle interior noise and vibration have been measured in the proposed random tinning road and compared with the data measured in the uniform tinning road. The results show that the magnitude of the peak spectrum is decreased by 18dB(A), and the overall noize level decreased by 4dB(A).

• ETRI Journal
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• 제18권3호
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• pp.181-193
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• 1996

A blue light emitting device has been successfully fabricated using a polymer with regulated conjugation length containing trimethylsilyl substituted phenylenevinylene units. Electroluminescence from the device has an emission maximum at 470 nm. The device shows typical diode characteristics with operating voltage of 20 V and the light becomes visible at a current density of less than $0.5;mA/cm^2$. The electroluminescence spectrum is virtually identical with the photoluminescence spectrum, indicating that the radiation mechanisms are the same for both. A light emitting device using the blend of a large band gap polymer and a small band gap polymer was also fabricated. Light emission from the small band gap polymer shows much improved quantum efficiency, but there is no light emission from the large band gap polymer. Quantum efficiency of the blend increases up to about two orders of magnitude greater than that of the small band gap polymer with increasing proportion of the large band gap polymer. The improvement in quantum efficiency is interpreted in terms of exciton transfer and the hole blocking behaviour of the large band gap polymer. Finally, we have fabricated a patterned flexible light emitting device using the high quantum efficiency polymer blend system.

• 천문학회지
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• 제32권1호
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• pp.55-63
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• 1999

NGC 6537 is an extremely high excitation bipolar planetary nebula. It exhibits a huge range of excitation from lines of [N I] to [Si VI]or [Fe VII], i.e. from neutral atoms to atoms requiring an ionization potential of $\~$167eV. Its kinematical structures are of special interest. We are here primarily concerned with its high resolution spectrum as revealed by the Hamilton Echelle Spectrograph at Lick Observatory (resolution $\~0.2{\AA}$) and supplemented by UV and near-UV data. Photoionization model reproduces the observed global spectrum of NGC 6537, the absolute H$\beta$ flux, and the observed visual or blue magnitude fairly well. The nebulosity of NGC 6537 is likely to be the result of photo-ionization by a very hot star of $T_{eff} \~ 180,000 K$, although the global nebular morphology and kinematics suggest an effect by strong stellar winds and resulting shock heating. NGC 6537 can be classified as a Peimbert Type I planetary nebula. It is extremely young and it may have originated from a star of about 5 $M_{\bigodot}$.

• Journal of information and communication convergence engineering
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• 제13권2호
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• pp.69-73
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• 2015

We focus on a sounding signal design for single-input single-output orthogonal frequency division multiplexing (SISO-OFDM) systems. We show that the frequency spectrum of an optimum sounding signal has a constant magnitude across the frequency band for the cases with or without Doppler effects. Simulation results show that the designed optimum sounding signal outperforms random sounding signals and that the performance of a maximal-length shift register sequence is indistinguishable from that of the optimum sounding signal.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1994년도 춘계학술대회 논문집
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• pp.75-78
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• 1994

Organic ultra thin films about 500${\AA}$ in thickness are fabricated by LB(Langmuir-Blodgett) technique and their gas detect properties are investigated. The LB films deposited are made of the specimen named as N-docosyl pyridinium(TCNQ) and the deposition is verified by capacitance conductivity measurement. From the study of gas detect properties with I-V characteristics and UV spectrum we have found that their conductivities were increased about 3 times of magnitude and peaks of UV spectrum were decreased.

• 한국군사과학기술학회지
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• 제22권5호
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• pp.581-589
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• 2019

Guided missiles assembled with the bolted joint are subjected to various shock loading conditions while flying in the air and operating on the ground or platform. Especially, It is important to analyze the effect of the shock load on the structure because it affects the structure for a short duration time while its acceleration magnitude is quite large. In this study, mechanical shock tests on the structure with the bolted joint have been carried out to measure the acceleration changes of the structure against external shock loads by electrical exciter. Variation of dynamic characteristics of a structure with fastening methods and fastening forces has been investigated through Shock Response Spectrum analysis.

• Journal of Biosystems Engineering
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• 제30권1호
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• pp.38-44
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• 2005

In this study, the acoustic response technique was applied to evaluate the maturity of melon nondestructively. The acoustic response signals through melon were obtained by microphone and signal conditioner with the lapse of days after fruit set. The acoustic parameters such as resonant frequencies and the spectrum energy ratio were analyzed. To investigate the relation between acoustic parameters and firmness of melon, the compression test was performed. Three resonant frequencies representing f1, f2 and f3 were 150 to 250 Hz, 300 to 400 Hz, and 450 to 550 Hz, respectively. The resonant frequencies were shifted to the lower frequencies and the magnitude of spectrum decreased as the maturity of melon increased. Some significant correlations were found between melon firmness and the spectrum energy ratio in some frequency ranges. It is possible to estimate the maturity of melon by acoustic response technique.