• Journal of Internet Computing and Services
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• v.16 no.2
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• pp.27-40
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• 2015

Inferring firewall policy is to discover firewall policy by analyzing response packets as results of active probing without any prior information. However, a brute-force approach for generating probing packets is unavailable because the probing packets may be regarded as attack traffic and blocked by attack detection threshold of a firewall. In this paper, we propose a firewall policy inference method using an efficient probing algorithm which considers the number of source IP addresses, maximum probing packets per second and interval size of adjacent sweep lines as inference parameters to avoid detection. We then verify whether the generated probing packets are classified as network attack patterns by a firewall, and present the result of evaluation of the correctness by comparing original firewall policy with inferred firewall policy.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.493-502
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• 2007

Measurements of RT, EDT, $D_{50}$, $C_{50}$ and STI carried out in three different unoccupied University classrooms. For acoustic measurements, various sound sources are used (white noise, pistol shot, MLS and sweep signal). In this study, It found that interaction exists between sound source and place. Also there was high correlation between STI and various acoustic parameter.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.7
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• pp.1393-1397
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• 2009

A high-speed wavelength swept laser, which is based on oscillation characteristics of a fiber Fabry-Perot tunable filter, is described. The laser is constructed by using a semiconductor optical amplifier, a fiber Fabry-Perot tunable filter, and 3.348 km fiber ring cavity. The wavelength sweeps are repeatatively generated with the repetition period of 61 kHz which is the first parallel oscillation frequency of the Fabry-Perot tunable filter for the low power consumption. Mode-locking is implemented by 3.348 km fiber ring cavity for matching the fundamental of cavity roundtrip time to the sweep period. The wavelength tuning range of the laser is 87 nm(FWHM) and the average output power is 1.284 mW.

• Proceedings of the IEEK Conference
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• 2000.11b
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• pp.221-224
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• 2000

We have successfully demonstrated metal-ferroel-ectric-insulator-semiconductor (MFIS) devices using Al/LiNbO$_{3}$/SiN/Si structure. The SiN thin films were made into metal -insulator- semiconductor (MIS) devices by thermal evaporation of aluminum source in a dot away on the surface. The interface property of MFIS from 1MHz & quasistatic C-V is good and the memory window width is about 1.5V at 0.2V/s signal voltage sweep rate. The gate leakage current density of MFIS capacitors using a aluminum electrode showed the least value of 1x10$^{-8}$ A/$\textrm{cm}^2$ order at the electric field of 300㎸/cm. And the XRD patterns shows the probability of applications of LN for MFIS devices for FeRAMs on amorphous SiN buffer layer.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.1711-1712
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• 2007

액체탱크의 레벨을 정밀측정하는 데 FMCW(Frequency Modulated Continuous Wave)를 이용하고자 한다. 우리는 1GHz 대역폭으로 Sweep하는 Frequency Source Module을 개발하여 테스트 중이다. 개발한 송수신 모듈은 주파수의 송수신을 위한 주요부품들로 구성되는데, VCO(Voltage Controlled Oscillator), 서큘레이터(Circulator), 필터(Filter), 전력분배기(Power Divider), PLL(Phase Locked Loop)제어부, 믹서, 증폭기 등이 그것이다. 이들 부품들이 위치한 RF Board와, 패치로 구성한 안테나를 이용하여 마이크로웨이브 신호를 송수신할 수 있으며, 송수신한 신호 간의 차주파수(beat frequency)성분을 측정하면 거리정보를 획득할 수 있다. 차주파수의 아날로그신호는 DSP를 이용하여 FFT를 수행하여 주파수 성분을 찾아 거리계산을 하도록 개발하였다. 거리 측정의 성능에 영향을 미치는 가장 큰 요소는 안정된 주파수를 만들어 낼 수 있느냐 하는 것이다. 본 논문에서는 제작한 VCO 모듈을 비롯한 개발 중인 각 모듈들을 소개하였다. 향후 VCO의 선형성 개선과, 난반사에 대한 Echo Cancel 알고리듬을 적용하여 제품의 상용화를 목표로 한다.

• Journal of Biomedical Engineering Research
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• v.32 no.4
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• pp.285-288
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• 2011

In this study, we developed an optical coherence tomography(OCT) using a sweep-source laser whose center wavelength is 1310 nm and a probe of hand-held type. The developed hand-held probe targets to diagnose the middle ear, so it is miniaturized for ease and convenience of control. For the first time, we performed in-vivo clinical experiments on tympanic membrane(TM) perforation patients not reported from previous studies about OCT. The high-resolution sectional images of tympanic membrane perforation can be obtained. There aren't many studies about diagnostic instrument of the middle ear and diagnosis with sectional image of the middle ear, so the developed OCT system and hand-held probe are applicable to tympanic membrane perforation and other pathologic diagnosis in the middle ear.

• Atmosphere
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• v.24 no.3
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• pp.317-329
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• 2014

Eddy covariance data have been analyzed to investigate the influence of surface heterogeneity on turbulent transfer over farmland and industrial sites near Nakdong river, Korea, where both large and small scale heterogeneities co-exist. For this purpose, basic turbulent statistics, quadrant analysis and multi-resolution decomposition have been analyzed during the daytime. Basic turbulent statistics were compared with typical turbulent statistics in the surface layer. Such comparisons were in close agreement for momentum and heat at both sites but not for water vapor at industrial site. The correlation coefficient between water vapor and vertical velocity ($r_{wq}$) is relatively low and skewness of water vapor ($sk_q$) is very low at industrial site, possibly due to limited water source. For heat at both sites and water vapor at farmland, the quadrant analysis show similar behavior to that over homogeneous site but for water vapor at industrial site, the presence of river and limited water source at industrial site seems to influence on water vapor transfer by coherent eddy motion by increasing sweep contribution and decreasing ejection contribution. Multi-resolution decomposition analysis shows that large scale heterogeneity leads to low $r_{Tq}$ at large averaging time regardless of season at both sites and there are seasonal changes of $r_{Tq}$ in mid-averaging times at industrial site, possibly due to seasonal change of trees and grasses near the site.

• Korean Journal of Optics and Photonics
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• v.18 no.5
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• pp.309-316
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• 2007

We demonstrate the wavelength swept source and signal processing for the frequency domain optical coherence tomography. The laser output performance is improved by using a semiconductor optical amplifier with a booster amplifier. The laser generates 14 mW of average power of which wavelength shift in the lasing spectral shape is compensated. Adopting a Fabry-Perot etalon and digital signal processing, the broadening of the beat frequency due to the variance of wavelength-sweep-velocity is calibrated. The optical coherence tomography system shows 154.4 kHz of axial scanning speed, 0.95mm of depth range, and $12{\pm}0.37{\mu}m$ of axial resolution.

• The Journal of the Acoustical Society of Korea
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• v.39 no.5
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• pp.379-389
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• 2020

In this study, the flow and noise performances of high-speed fan motor unit for cordless vacuum cleaner is improved by optimizing the impeller which drives the suction air through flow passage of the cordless vacuum cleaner. Firstly, the unsteady incompressible Reynolds averaged Navier-Stokes (RANS) equations are solved to investigate the flow through the fan motor unit using the computational fluid dynamics techniques. Based on flow field results, the Ffowcs-Williams and Hawkings (FW-H) integral equation is used to predict flow noise radiated from the impeller. Predicted results are compared to the measured ones, which confirms the validity of the numerical method used. It is found that the strong vortex is formed around the mid-chord region of the main blades where the blade curvature change rapidly. Given that vortex acts as a loss for flow and a noise source for noise, impeller blade is redesigned to suppress the identified vortex. The response surface method using two factors is employed to determine the optimum inlet and outlet sweep angles for maximum flow rate and minimum noise. Further analysis of finally selected design confirms the improved flow and noise performance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.4
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• pp.906-911
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• 2004

In this paper, a VCDRO(Voltage Control Dielectric Resonator Oscillator) applied to FMCW(Frequency Modulated Continuous Wave)Radar as stable source is implemented and constructed with a MESFET(Metal-semiconductor Field-Effect Transistor) for low noise, a dielectric resonate. of high frequency selectivity, and high Q varator diode to obtain a good phase noise performance and stable sweep characteristics. The designed circuits is simulated thrash harmonic balance simulation technique to provide the optimum performance. The measured result of a fabricated VCDRO shows that output is 2.22㏈m at 12.05GHz, harmonic suppression -30㏈c, phase noise -130㏈c at 100KHz offset, and sweep range of varator diode $\pm$18.7MHz, respectively. This oscillator will be available to FMCW Radar.