• Transactions of the Korean Society of Mechanical Engineers
• /
• v.17 no.10
• /
• pp.2437-2445
• /
• 1993

In this work, a new method is presented for generating the manipulator path which significantly reduces residual vibration under the torque constraints. The desired path is optimally designed so that the required movement can be achieved with minimum residual vibration. From the previous research works, the dynamic model had been established including both the link and the joint flexibilities. The performance index is selected to minimize the maximum amplitude of residual vibration. The path to be designed is developed by a combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems. The concept of correlation coefficients is used to select the minimum number of design variables, i.e. Fourier coefficients, the only ones which have a considerable effect on the reduction of residual vibration. A two-link Manipulator is used to evaluate this method. Results show that residual vibration can be drastically reduced by selecting an appropriate manipulator path to both of unlimited and torque-limited cases.

• Journal of Communications and Networks
• /
• v.13 no.5
• /
• pp.449-455
• /
• 2011

Inspired by fast Jacket transforms, we propose simple factorization and construction algorithms for the M-dimensional discrete Fourier transform (DFT) matrices underlying generalized Chinese remainder theorem (CRT) index mappings. Based on successive coprime-order DFT matrices with respect to the CRT with recursive relations, the proposed algorithms are presented with simplicity and clarity on the basis of the yielded sparse matrices. The results indicate that our algorithms compare favorably with the direct-computation approach.

• Advances in nano research
• /
• v.16 no.2
• /
• pp.175-186
• /
• 2024

Dynamical behaviors of one-dimensional (1D) nano-sized structures are of great importance in nanotechnology applications. Therefore, the torsional dynamic response of functionally graded nanorods which could be used to model the nano electromechanical systems or micro electromechanical systems with torsional motion about the center of twist is examined based on the theory of strain gradient nonlocal elasticity in this work. The mathematical background is constructed based on both strain gradient theory and Eringen's nonlocal elasticity theory. The equation of motions and boundary conditions of radially functionally graded nanorods are derived using Hamilton's principle and then transformed into the eigenvalue analysis by using Fourier sine series. A general coefficient matrix is obtained to assemble the Stokes' transformation. The case of a restrained functionally graded nanorod embedded in two elastic springs against torsional rotation is then deeply investigated. The effect of changing the functionally graded index, the stiffness of elastic boundary conditions, the length scale parameter and nonlocal parameter are investigated in detail.

• Bulletin of the Korean Mathematical Society
• /
• v.46 no.2
• /
• pp.209-227
• /
• 2009

We examine a unified approach of calculating the closed form solutions of option price under stochastic volatility models using stochastic calculus and the Fourier inversion formula. In particular, we review and derive the option pricing formulas under Heston and correlated Stein-Stein models using a systematic and comprehensive approach which were derived individually earlier. We compare the empirical performances of the two stochastic volatility models and the Black-Scholes model in pricing KOSPI 200 index options.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.18 no.1
• /
• pp.97-103
• /
• 2018

In satellite communication, modulated beacon signal is spreaded by gold sequence and the modulated beacon is transmitted via linear phase modulation. Due to the difference in characteristics of the satellite and the receiver on the ground, frequency offset (FO) occurs. An existing modulated beacon receiver is a method of synchronizing the frequency of a modulated beacon signal using FFT(Fast Fourier Transform), which not only increases the delay and complexity in terms of system implementation but also has a separate circuit for compensating the phase difference due to FO and phase offset from FFT points. In order to overcome this problem, this paper proposes and analyzes a scheme for compensating and demodulating the coarse FO and phase offset at one time using the 2-phase shaped characteristics of the modulated beacon signal. Also, through the simulation, the modulation index suitable for the proposed method is analyzed and the appropriate cumulative number is also analyzed.

• The Journal of Korean Physical Therapy
• /
• v.32 no.3
• /
• pp.152-156
• /
• 2020

Purpose: The subjective visual vertical (SVV) test is used to evaluate the otolith function in the inner ear. This study compared the different balance ability according to the results of the SVV in healthy adults. Methods: This study recruited 30 normal healthy subjects who did not have neurological and musculoskeletal disorders. The subjects were divided into experimental and control groups based on the results of SVV: experimental group, >2°; control group, <2°. The static balance ability was evaluated using the Fourier Index, which could evaluate the balance capacity objectively and quantitatively. Results: The mean angle of the SVV in the experimental and control groups was 4.44° and 0.59°, respectively. In the result of the Fourier series, the F1 frequency band in the experimental group showed a significantly higher value under one condition compared to the control group (p<0.05). In the F2-4 and F5-6 frequency bands, the experimental group showed a significant increase in the Fourier series value under the four conditions compared to the control group (p<0.05). In the F7-8 frequency band, significantly higher values of the Fourier series were observed in the experimental group under the three different conditions (p<0.05). Conclusion: These results showed increased trunk sway while maintaining static balance in the experimental group who showed a larger SVV angle compared to the control group. The SVV can be applied to evaluate the vestibular system and balance ability in normal adults.

• The Korean Journal of Rheology
• /
• v.10 no.3
• /
• pp.173-183
• /
• 1998

본 연구에서는 Advanced Rheometric Expansion System(ARES)를 사용하여 대진폭 진동 전단 변형하에서 발생하는 폴리이소부틸렌(PIB) 농후 용액의 비선형 점탄성 거동을 저 장탄성율과 동적점도의 변형량 의존성 및 응력파형의 fast Fourier transform(FFT) 해석을 통해 고찰하였다. 스트레인 진촉을 단계적으로 증가시키면서 측정한 동적 점탄성으로 부터 저장탄성율 및 동적점도의 선형응답한계를 결정하고 이들에 미치는 각주파수의 영향을 조사 하였다. 그리고 응력파형의 Fourier 전개로부터 유도되는 비선형 점탄성함수를 사용하여 비 선형 거동을 설명하였다. 끝으로 비선형 점탄성 거동의 정도를 나타내는 비선형 거동 지수 를 정의하고 이들에 미치는 각주파수의 영향에 대해 검토하였다. 이상의 연구를 통해 얻어 진 결과를 요약하면 다음과 같다.(1) 선형 응답한계는 고분자 용액의 특성시간의 역수보다 높은 각주파수 범위에서는 일정한 값을 유지하지만 특성시간의 역수보다 낮은 각주파수 영 역에서는 각주파수가 감소할수록 증가한다. (2)선형응답한계 이상의 대변형하에서는 3차비선 형 점탄성 함수 이상의 고차항의 영향이 크게 작용하며 이로인해 비선형 거동이 발생된다. (3) 스트레인 진폭을 단계적으로 증가시키면서 측정한 저장탄성율 및 동적점도의 변형량 의 존성은 응력파형의 Fourier transform으로부터 유도된 1차 비선형 점탄성 함수의 변형량 의 존성을 나타낸다 (4) 저장탄성율 및 동적점도의 변형량 의존성으로부터 유도된 비선형 거동 지수는 탄성적 서질과 점성적 성질에 대한 비선형 특성을 평가하기 위한 유요한 방법으로 인정된다. (5) 비선형 점탄성 거동의 정도를 나탄는 비선형 거동지수는 특정한 각주파수에서 최대치를 가지며 또한 탄성적 거동이 점성적 거동에 비해 더욱 큰 각주파수 의존성을 나타낸다.

• Journal of Acupuncture Research
• /
• v.32 no.2
• /
• pp.169-185
• /
• 2015

Objectives : The purpose of this study is to find the effects of Sa-am liver tonifying and sedating acupuncture on radial pulse. Methods : Sixty healthy people were divided into a liver tonifying acupuncture(LTA) group, liver sedating acupuncture(LSA) group, and control group. The LTA group and LSA group received acupuncture for 20 minutes with a supine position. The Control group took a rest without receiving acupuncture. Radial pulse was measured by three dimensional pulse imaging system(DMP-3000) at four different time points (before, right after, 30 minutes after, and 60 minutes after acupuncture). We compared the three groups and figure out determined the parameters which significantly changed after acupuncture treatment. Results : 1. Pulse period, T1/T, T4/T, (T-T4)/T, T4/(T-T4), T5/T significantly changed after acupuncture. 2. H4, pulse area, systolic pulse area, diastolic pulse area, radial augmentation index(RAI), and pulse power volume / min significantly changed after acupuncture. 3. Frequency of Fourier components, ratio of frequencies of Fourier components, magnitude of Fourier components, and ratio of magnitudes of Fourier components significantly changed after acupuncture. Conclusions : LTA and LSA have an effect on the radial pulse parameters. Further studies on radial pulse change using Sa-Am acupuncture are needed.

• Advances in nano research
• /
• v.12 no.5
• /
• pp.467-482
• /
• 2022

In the current work, static and free torsional vibration of functionally graded (FG) nanorods are investigated using Fourier sine series. The boundary conditions are described by the two elastic torsional springs at the ends. The distribution of functionally graded material is considered using a power-law rule. The systems of equations of the mechanical response of nanorods subjected to deformable boundary conditions are achieved by using the modified couple stress theory (MCST) and taking the effects of torsional springs into account. The idea of the study is to construct an eigen value problem involving the torsional spring parameters with small scale parameter and functionally graded index. This article investigates the size dependent free torsional vibration based on the MCST of functionally graded nano/micro rods with deformable boundary conditions using a Fourier sine series solution for the first time. The eigen value problem is constructed using the Stokes' transform to deformable boundary conditions and also the convergence and accuracy of the present methodology are discussed in various numerical examples. The small size coefficient influence on the free torsional vibration characteristics is studied from the point of different parameters for both deformable and rigid boundary conditions. It shows that the torsional vibrational response of functionally graded nanorods are effected by geometry, small size effects, boundary conditions and material composition. Furthermore, for all deformable boundary conditions in the event of nano-sized FG nanorods, the incrementing of the small size parameters leads to increas the torsional frequencies.

• Journal of the Korean Institute of Gas
• /
• v.16 no.6
• /
• pp.115-122
• /
• 2012

Polyurethane foams were synthesized with different contents and kinds of catalysts to know change of properties under various NCO index. UTM(universal testing machine), DSC(differential scanning calorimetry), SEM(scanning electron microscope) and FT-IR(Fourier transform spectroscopy) were used for studying the PUF's physical properties change. Compressive strength of PUF increased with increasing contents of catalyst. Glass transition temperature(Tg) and compressive strength of PUF using PC-8 and 33LV catalyst, increased with increasing NCO index at the aging. According to the results of Infrared spectral analysis, reduction of NCO peak was found in gelling catalyst, because unreacted NCO reacted with polyurethane. Although Tg and compressive strength of PUF using TMR-2, unchanged with increasing NCO index at the aging, because trimerization of isocyanate.