• Structural Engineering and Mechanics
• /
• v.8 no.6
• /
• pp.579-589
• /
• 1999

A new way to reduce the eigenvalue computation effort in structural dynamics is presented in this paper. The degrees of freedom of a structure may be classified into groups that are termed as sub-degrees of freedom. The eigenvalue analysis is performed with each of sub-degrees of freedom so that the computing time is much shortened. Since the dynamic coupling between sub-degrees of freedom is selected to be small and it may be considered as a perturbation, the perturbation algorithm is used to obtain an accuratae result. The accuracy of perturbation depends on the coupling between sub-degrees of freedom. The weaker the coupling is, the more accurate the result is. The procedure can be used to simplify a problem of three dimensions to that of two dimensions or from two dimensions to one dimension. The application to a truss and a space frame is shown in the paper.

• Journal of Information Processing Systems
• /
• v.11 no.3
• /
• pp.354-369
• /
• 2015

Recently, there has been an increasing demand of high data rates services, where several multiuser multiple-input multiple-output (MU-MIMO) techniques were introduced to meet these demands. Among these techniques, vector perturbation combined with linear precoding techniques, such as zero-forcing and minimum mean-square error, have been proven to be efficient in reducing the transmit power and hence, perform close to the optimum algorithm. In this paper, we review several fixed-complexity vector perturbation techniques and investigate their performance under both perfect and imperfect channel knowledge at the transmitter. Also, we investigate the combination of block diagonalization with vector perturbation outline its merits.

• Journal of Sensor Science and Technology
• /
• v.26 no.4
• /
• pp.251-258
• /
• 2017

According to recent studies by scientists about how to search for food, homes and the mates, it is found that the gradient information plays a key role. From cells to insects and large animals, they mostly either have special sensing organism or use a strategy to measure the gradient. Use of a perturbation as an additional input is introduced for sensor signal processing in order to get the gradient information. Different from typical approach, which calculates the gradient from differentiation, the proposed processing is done by a form of integration, thus it is very robust to noise. Discrete time domain analyses are given for one, two and three input functions for the estimation of the gradients. The amplitude and the frequency of the perturbation are two important parameters for this approach. A quantitative index to measure the effects of the amplitude is developed based on the linear regression analysis. The frequency of the perturbation is to be selected high enough to finish one period of the perturbation before the property is changed significantly with respect to time. Another quantitative index is proposed for guiding the selection of the frequency.

• Physical Therapy Korea
• /
• v.20 no.4
• /
• pp.47-54
• /
• 2013

The purpose of this study was to investigate the effects of active and passive postural perturbation on ankle dorsiflexor responses in stroke patients. The subjects consisted of 13 stroke patients. Using wireless electromyography, the patients' ankle dorsiflexor muscle responses were measured under the following conditions: active dorsiflexion (AD), active perturbation (AP), and passive perturbation (PP). Tibialis anterior muscle activity increased most significantly during PP of the affected side ($118.64{\pm}56.28$). The most significant increase for the non-affected side was in AD ($72.64{\pm}24.56$). Tibialis anterior muscle activity was compared under each condition. The affected side showed significant differences between PP and AD and between PP and AP (p<.05). The non-affected side showed not significant differences between each condition. The ratios of tibialis anterior muscle activity under AP to that under AD were 1.00 on the affected side and .75 on the non-affected side and the difference was not significant (p>.05). The ratios of tibialis anterior muscle activity under PP to that under AD were 3.30 on the affected side and 1.14 on the non-affected side and the difference was significant (p<.05). Passive perturbation improved tibialis anterior muscle activity on the affected side, and training based on this approach may have the potential to improve the ankle dorsiflexion of people with stroke.

• Korean Journal of Applied Biomechanics
• /
• v.26 no.4
• /
• pp.427-432
• /
• 2016

Objective: The goal of this study was to systematically investigate the postural stability of dancers by providing unexpected perturbations. Method: Six female dancers and college students participated in this study. Unpredictable wait-pull balance perturbations in the anterior direction were provided to the participants during standing. Three different perturbation intensities (low, moderate, and high intensity) were used by increasing perturbation forces. Spatial and temporal stability of postural control were measured by using margin of stability (MoS) and time to contact (TtC), respectively. Results: Both MoS and TtC at moderate intensity were significantly greater in the dancer group than in the control group, but no significant differences were found at low and high intensities between the groups. Conclusion: The present study showed spatial and temporal stability of dynamic postural control in dancers. We found that the dancers were more spatially and temporally stable than the ordinary participants in response to unexpected external perturbation when the perturbation intensity was moderate at two extreme intensity levels (low and high).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.7
• /
• pp.739-747
• /
• 2007

Dual-mode bandpass filter was designed by using periodic stepped impedance ring resonator with step perturbation. The periodic stepped impedance ring resonator has the effects of size reduction and $2^{nd}$ harmonic suppression by changing characteristic impedance ratio. The perturbation for dual-mode generation was also easily controlled by characteristic impedance ratio, and the variation of dual-mode resonant frequencies and attenuation pole frequencies were analyzed by the effect of step perturbation. Chip capacitors were used for input/output coupling, and the variation of center frequency by the coupling capacitance and step perturbation was also considered. From the results, two types of 2 GHz dual-mode bandpass filter were fabricated in size of $14{\times}14mm^2$, those have different attenuation poles and bandwidths. The measured results of proposed bandpass filters showed a good agreement with the calculated estimations, and those have insertion loss of 2.52, 0.52 dB and 3 dB bandwidth of 4.03, 15.02 %, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.46 no.6
• /
• pp.86-93
• /
• 2009

We investigate lattice-reduction-aided precoding techniques for multi-user multiple-input multiple-output (MIMO) channels. When assuming full knowledge of the channel state information only at the transmitter, a vector perturbation (VP) is a promising precoding scheme that approaches sum capacity and has simple receiver. However, its encoding is nondeterministic polynomial time (NP)-hard problem. Vector perturbation using lattice reduction algorithms can remarkably reduce its encoding complexity. In this paper, we propose a vector perturbation scheme using Seysen's lattice reduction (VP-SLR) with simultaneously reducing primal basis and dual one. Simulation results show that the proposed VP-SLR has better bit error rate (BER) and larger capacity than vector perturbation with Lenstra-Lenstra-Lovasz lattice reduction (VP-LLL) in addition to less encoding complexity.

• Computational Structural Engineering
• /
• v.5 no.3
• /
• pp.119-126
• /
• 1992

Most civil engineering structures such as bridges, power plants, and offshore platforms are apt to suffer structural damages over their service lives caused by adverse loadings, such as earthquakes, wind and wave forces. Accumulation of structural damages over a long period of time might cause catastrophic structural failure. Therefore, a methodology for monitoring the structural integrity is essential for assuring the safety of the existing structures. A method for the damage assessment of structures by the second order inverse modal perturbation technique is presented in this paper. Perturbation equation consists of a matrix equation involving matrices of structural changes(stiffness and mass matrix changes) and matrices of modal property changes(natural frequency and mode shape changes). The damages of a structure are represented as changes in the stiffness matrix. In this study, a second order perturbation equation is formulated for the damage assessment of structures, and solved by an iterative procedure. The effectiveness of the proposed method has been investigated through a series of example analysis. The estimated results for the structural damage indicated that the present method yields resonable estimates for the structural changes.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.9
• /
• pp.907-913
• /
• 2012

High-order perturbation solutions have been obtained for the simple physical model describing the liquid pool spreading with a continuous spill, and these are shown to improve over first-order perturbation solutions. The non-dimensional governing equations for the model are derived to obtain more general solutions. Non-dimensional parameters are sought as the governing parameters for the non-dimensional equations, and the non-dimensional evaporation rate is used as the perturbation parameter. The results show that the high-order solutions exhibit an improvement over the first-order solutions with respect to the pool volume as well as the spreading radius. In addition, as the order of the perturbation solutions increases, the difference between the numerical solutions and the perturbation solutions is significantly reduced. Finally, it is revealed that the third-order solutions are reasonable because they almost agree with the numerical solutions.

• Journal of The Korean Society of Integrative Medicine
• /
• v.4 no.3
• /
• pp.39-47
• /
• 2016

PURPOSE : This study attempts to find the effects of water perturbation exercise performed on stroke patients in their physiological cost index and gait ability tests. METHOD : The subjects were 30 stroke patients, water perturbation exercise group was performed 3 day per week, for 40 minutes a day, for a period of eight weeks. The physiological cost index and gait of all subjects were assessed by using the polar, 6 Minute Walk Test (6MWT), and 10 meter Walk Test(10mWT) at pre training and post training. Paired t-test was used to analyze change before and after intervention in group. Pearson's correlation was used to analyze correlation of all variables. RESULT : Water perturbation exercise group showed increased physiological cost index. Water perturbation exercise increased gait ability, showing a significant difference. Showing the correlation between the relatively high amount between physiological cost index and 6 minutes walking test. CONCLUSION : From the result of the study, we found that water perturbation exercise was effective in improving physiological cost index and gait ability. The patient is considered to be used by itself to involve the treatment and the risk of falling from the lowered state into the treatment method for the intensive treatment of stroke patients to be useful in improving the cardiovascular system and ability to walk. Through underwater training for stroke patients in the future on the basis of this study it is considered to require additional clinical studies on the impact on daily living and quality of life of stroke patients.