• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.11
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• pp.3121-3129
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• 2009

Conventional marine radar systems utilize pulse radar which is capable of high-power transmissions and is effective for remote detection purposes. A pulse radar is most commonly used on medium or large vessels due to its expensive installation and maintenance costs. I propose the use of a Frequency Modulated Continuous Wave (FMCW) radar system operated at low-power and high-resolution instead of the conventional pulse-radar based system. The transmitted and received signals of the FMCW radar system were theoretically analyzed and radar signal processing design and simulation experiments were performed to detect the range and speed. Intermediate Frequency (IF) signal mixed with virtual transmit and receive signals were generated to perform FMCW radar signal processing simulations where the IF signal underwent noise reduction through a lowpass filter. The maximum frequency was derived through the sample interval of the FFT size instead of using A/D converter. This maximum frequency was used to get the frequency range and frequency speed which were in turn used to calculate the range and speed. The virtual beat frequency generated using MATLAB is utilized to analyze the beat frequency used in the actual FMCW radar system signal processing. The differences in the range and speed of the beat frequency signals are processed and analyzed.

• Coupled systems mechanics
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• v.2 no.2
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• pp.159-174
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• 2013

The present work aims at investigating the nonlinear dynamics, bifurcations, and stability of an axially accelerating beam with an intermediate spring-support. The problem of a parametrically excited system is addressed for the gyroscopic system. A geometric nonlinearity due to mid-plane stretching is considered and Hamilton's principle is employed to derive the nonlinear equation of motion. The equation is then reduced into a set of nonlinear ordinary differential equations with coupled terms via Galerkin's method. For the system in the sub-critical speed regime, the pseudo-arclength continuation technique is employed to plot the frequency-response curves. The results are presented for the system with and without a three-to-one internal resonance between the first two transverse modes. Also, the global dynamics of the system is investigated using direct time integration of the discretized equations. The mean axial speed and the amplitude of speed variations are varied as the bifurcation parameters and the bifurcation diagrams of Poincare maps are constructed.

• Journal of Ocean Engineering and Technology
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• v.6 no.1
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• pp.69-77
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• 1992

The natural frequencies of a beam on elastic foundation are investigated in the present paper. The inhomogeneous elastic foundation can be modelled as a combination of distributed translational spring, rotational spring, intermediate supports and dampers. The natural frequencies and mode shapes of the system are obtained by using the Galerkin's method, and also compared with the results in the literature. Furthermore, the natural frequencies of the beam with elastically mounted masses, which can be used as vibration absorbers, are obtained by an efficient numerical scheme suggested in the present paper.

• Korean Journal of English Language and Linguistics
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• v.4 no.1
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• pp.83-102
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• 2004

The purpose of this paper is to find out some major characteristics of intermediate-advanced Korean learners' English by corpus- linguistically analyzing their essays in comparison with native speakers'. We construct a corpus of CBT TOEFL essays by Korean learners, NNS1 (94076 words in 402 texts), and its sub-corpus, NNS2 (14291 words in 45 texts), and then a corpus of model essays written or meticulously edited by native speakers, NS (14833 words in 35 texts). We compare NNS1 and NNS2 with NS, and with some other corpora, in terms of high-frequency words, and show that Korean learners' writings have more features of informal writing than those of formal writing, which is in accord with the reports in Granger (1998) that EFL writings by European advanced learners are characterized by informality.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.433-441
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• 2001

Natural convection of a fluid with intermediate Prand시 number of Pr=0.2 in a horizontal annulus is considered, and the bifurcation phenomena and chaotic flows are numerically investigated. The unsteady two-dimensional streamfunction-vorticity equation is solved with finite difference method. The steady downward flow with two counter-rotating eddies bifurcates to a simple periodic flow with a fundamental frequency. And afterwards, second Hopf bifurcation occurs, and a quasi-periodic flow with two incommensurable frequencies appears. However, a new time-periodic flow is established after experiencing quasi-periodic states. As Rayleigh number is increased further, the chaotic flow regime is reached after a sequence of successive Hopf bifurcation to quasi-periodic and chaotic flow regimes. A scenario similar to the Ruelle-Takens-Newhouse scenario of the onset of chaos is observed.

• Korean Journal of Applied Biomechanics
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• v.28 no.3
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• pp.187-191
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• 2018

Objective: The purpose of the present study is to investigate the effect of a muscle activity by applying the complex exercise method of sling in accordance with the provision of various vibration intensities for paraplegia-spinal cord injury. Method: The subjects of the study were 15 men in their 40s and 50s with lower limb disabilities and low potential risk, who were randomly divided into a sling exercise group (SG n=4), a sling with low frequency vibration group (SLVG n=4), a sling with mid-frequency vibration group (SMVG n=4), and a sling with high frequency group (SHVG n=4) in accordance with the provision of slings and vibration stimuli. The vibratory intensity provided was divided into low frequency (30 Hz), mid-frequency (50 Hz), and high frequency (70 Hz). The anterior deltoid (AD), the posterior deltoid (PD), the pectoralis major (PM), the upper trapezius (UT), the latissimus dorsi (LD), and the multifidus (MF) were measured to compare and analyze muscle activity. Results: The closed kinetic chain (CKC) exercise to the shoulder joint showed higher muscle activity in most muscles for the SMVG, and statistically significant differences in the anterior deltoid (AD), the pectoralis major (PM), and the multifidus (MF) in particular. Conclusion: The intermediate frequency (50 Hz) string vibration was the effective vibration stimuli for Closed kinetic chain (CKC) exercises.

• Journal of Advanced Navigation Technology
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• v.2 no.1
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• pp.22-33
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• 1998

In the coherent-on-receiver radar system using the magnetron source, frequency synthesizer is employed as a STALO(Stable Local Oscillator) to keep the intermediate frequency stable. In this paper, X-band(8.4GHz~9.7GHz) single loop frequency synthesizer is designed and implemented by an indirect frequency synthesis technique. Phase comparison is performed by a digital PLL(Phase-Locked Loop) chip and the loop filter is designed for the low phase noise. The effects of loop component characteristics on the output phase noise are analyzed for single loop structures, and the calculated results are compared with the measured data.

• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.6
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• pp.1058-1063
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• 2010

In this paper, we designed self-frequency synchronizing circuit using image rejection mixer(IRM) and single-sideband(SSB) up-converter which can effectively eliminate the image frequencies occurred in multi-channel super-heterodyne receivers and help us to match inter-channel phase. Also the self-frequency synchronizing circuit simplifies system because there need no extra devices for making intermediate frequency(IF) by creating the local signal within several nanoseconds by means of generating the same frequency of IF signal and modulating radio frequency(RF) signal. We adopt the limiting amplifier for the purpose of protecting the circuit from spurious signals which come from the front end side having wide instantaneous bandwidth characteristics and constantly injecting same level into the input local signal of IRM. The IRM we fabricated has image rejection ratio of 27dB, which is good over 7dB for foreign company's. Also, the SSB up-converter we fabricated has 1dB compression point of 18dBm, which is good over 16dB for foreign company's. And the size is compact about one-forth.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.6
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• pp.161-167
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• 2017

Recently, small radar has been reduced in size and power consumption to cope with various operating environments. It also requires the development of a small millimeter wave radar with high range resolution to disable the system of target with a single strike. In this paper, we design and implement a signal processor that can be used in small millimeter wave radar. The signal processor for the small millmeter wave radar is designed with a digital IF(Intermediate Frequency) receiver and DFT(Discrete Fourier Transform) module capable of real time FFT operation for miniaturization and low power consumption. Also it was to leverage the FPGA(Field Programmable Gate Array) and DAC(Digital Analog Converter) as a means for correcting the distortion of signals that can occur in the receive path of the small millimeter wave radar to create a RF signal that is used by the system. Finally, we verified the signal processor presented through performance test

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.1
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• pp.219-226
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• 2000

In this paper, we design and implement a IF(intermediate frequency) module for WLL(wireless local loop) CDMA(code division multiple access) basestation. The implemented IF transceiver is consists of transmitter, receiver and local oscillator. The considered signal bandwidth is 10 MHz and the local carrier frequency is 40 MHz. As test results, the If transmitter output power is -5dBm $\pm3dB$when the baseband input is -10dBm $\pm3dB$, and the IF receiver output power is -10dBm $\pm3dB$when the IF input is -5dBm $\pm3dB$. Also the AGC(automatic gain control) circuit has dynamic range of 9 dB from -7dBm to +2dBm with output power 2dBm. And the group delay characteristic is analyzed by comparing the phase delay from 1 MHz to 5 MHz and the phase distortion is very low. We can conclude that this IF system can be applied to high speed data rate communication system.