• Korean Journal of Applied Biomechanics
• /
• v.26 no.2
• /
• pp.143-151
• /
• 2016

Objective: The purpose of this study was to investigate the effect of fatigue induction on ground reaction force (GRF) components, postural stability, and vertical jump performance in Taekwondo athletes. Method: Ten Taekwondo athletes (5 men, 5 women; mean age, $22.30{\pm}2.62years$; mean height, $174.21{\pm}9.20cm$; mean body weight, $67.28{\pm}12.56kg$) participated in this study. Fatigue was induced by a short period of strenuous exercise performed on a motorized treadmill. The analyzed variables included vertical jump performance, static stability (mediolateral [ML], center of pressure [COP], anteroposterior [AP] COP, ${\Delta}COPx$, ${\Delta}COPy$, and COP area), postural stability index values (ML stability index [MLSI], AP stability index [APSI], vertical stability index [VSI], dynamic postural stability index [DPSI]), and GRF components (ML force, AP force, peak vertical force [PVF], and loading rate). To analyze the variables measured in this study, PASW version 22.0 was used to calculate the mean and standard deviation, while a paired t-test was used to evaluate the pre- versus post-fatigue results. Pearson's correlation coefficients among variables were also analyzed. The statistical significance level was set at ${\alpha}$ = .05. Results: Vertical jump performance decreased significantly after the induction of fatigue, while AP COP, ${\Delta}COPx$, COP area, APSI, VSI, and DPSI increased significantly. PVF and loading rate increased significantly after the induction of fatigue, while the postural stability variables (AP COP, ${\Delta}COPy$, COP area, APSI, VSI, DPSI) were similarly correlated with GRF components (PVF, loading rate) after fatigue was achieved (r = .600, $R^2$ = 37%). Conclusion: These results suggest that the induction of fatigue can decrease postural stability and exercise performance of Taekwondo athletes during training and competition sessions.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.29 no.4
• /
• pp.360-367
• /
• 2009

The acoustic emission(AE) behavior of reinforced concrete slab under flexural loading was investigated to assess the integrity. This study was aimed at identifying the characteristics of AE response associated with damage development. By applying cyclic loading in various load steps, it was able to differentiate each AE source such as distributed micro crack initiation, friction, flexural crack and localized diagonal tension crack. The secondary peak and the change of AE hit rate gave valuable criteria fur assessment. From the analysis of the felicity ratio, furthermore, it was shown that this values can be used for evaluating the degree of concrete damage. Based on the experimental results, this approach for practical AE application may provide a promising method for estimating the level of damage and distress in concrete structures.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.36 no.4
• /
• pp.307-314
• /
• 2008

Loading noise generated by steady aerodynamic force exerted on the rotating body surface is theoretically analyzed and its radiation characteristics is examined as a fundamental research of helicopter rotor noise. For simplicity, the force exerted on each blade is not distributed but concentrated at one point and the noise is evaluated by using Lowson' exact formula with a discussion of the physical meaning of each term in the formula. For a single point force rotating with various angular frequencies, we investigated the radiation characteristics and theoretically explained the physical behavior at near and far-field. By investigating the amplitude of acoustic pressure with various distances, we observed the different decreasing ratio at near- and far-field with the discussion of the effect of acceleration of angular frequency. Finally, the phenomenon that the noise level is reduced everywhere as the number of blade increases is explained with the suggestion of a noise reduction idea, the limitations of this study, and the future research topics.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.11
• /
• pp.1896-1911
• /
• 1997

Effects of fiber-matrix interphases on the micro-and macro-mechanical behaviors of unidirectionally fiber-reinforced composites subjected to transverse shear loading at remote distance have been studied. The interphases between fibers and matrix have been modeled by the spring-layer which accounts for continuity of tractions, but allows radial and circumferential displacement jumps across the interphase that are linearly related to the normal and tangential tractions. Numerical calculations for basic cells of the composites have been carried out using the boundary element method. For an undamaged composite the micro-level stresses at the matrix side of the interphase and effective shear stiffness have been computed as functions of fiber volume ratio $V_f$ and interphase stiffness k. Results are presented for various interphase stiffnesses from the perfect bonding to the case of total debonding. For a square array composite the results show that for a high interphase stiffness k>10, an increase of $V_f$ increases the effective transverse shear modulus G over bar of the composite. For a relatively low interphase stiffness k<1, it is shwon that an increase of $V_f$ slightly decreases the effective transverse shear modulus. For the perfect bonding case, G over bar for a hexagonal array composite is slightly larger than that for a square array composite. Also for a damaged composite partially debonded at the interphase, local stress fields and effective shear modulus are calculated and a decrease in G over bar has been observed.

• The Korean Journal of Pain
• /
• v.11 no.1
• /
• pp.86-90
• /
• 1998

Background: There are no controlled studies assessing the effect of metoclopramide and droperidol administered epidurally for the prevention of nausea and vomiting associated with epidural morphine. This study was undertaken to compare the effectiveness of continuous epidural metoclopramide and droperidol in reducing nausea and vomiting associated with epidural morphine. Methods: Ninty patients undergoing elective gynecologic surgery were randomly assigned to one of three study groups; Group A(n=30) patients received continuous infusion of epidural morphine(6.0 mg/day) following a bolus loading dose of 3.0 mg; Group B(n=30), epidural mixture of morphine and droperidol(5.0 mg/day) following a bolus loading dose(morphine 3.0 mg, droperidol 1.5 mg); Group C, (n=30), epidural mixture of morphine and metoclopramide(20 mg/day) following a bolus loading dose(morphine 3.0 mg, metoclopramide 10 mg). For the 24 postoperative hours, the incidence of nausea and vomiting, degree of pain, level of sedation and other adverse effects were evaluated. Results: Incidence of nausea and vomiting, and number of patients who required antiemetic therapy were significantly less in Group B and C than in Group A(P<0.05). Patients in Group A and C were less sedated than those in Group B. Conclusions: We conclude metoclopramide is more effective than droperidol for postoperative nausea and vomiting due to its lower of sedative effect.

• Journal of KIISE
• /
• v.42 no.12
• /
• pp.1623-1628
• /
• 2015

As the performance of mobile devices has increased, high-end multicore CPUs have become the norm in smartphones. However, such high performance devices are exposed to the problem of battery depletion due to the energy consumption caused by software performance, and despite increases in battery capacity. The required resources are dynamic and varied, and further user interaction is highly random; thus, Linux-based power management such as DVFS is needed to fulfill requirements. In order to reduce power consumption, we propose a method to restrict the CPU frequency of data download while maintaining user reactivity. This can supplement the weakness of existing Linux-based power management techniques like DVFS in relation to webpage loading. Through the implementation of our method at the application level, we confirm that energy consumption from webpage loading is reduced.

• Journal of the Korea Concrete Institute
• /
• v.28 no.2
• /
• pp.187-196
• /
• 2016

The current seismic design code prescribes that coupling beam should be reinforced using diagonally bundled bars. However, the use of a diagonally bundled bars has a negative effect on constructability and economic efficiency. In the present study, the seismic performance of 4 coupling beams with the different details of reinforcement was evaluated through a cyclic reversal loading test. The specimens were constructed to measure the results of the experimental variable regarding the details of shear reinforcement. Next, the seismic performance of the coupled shear wall system evaluated by methods proposed in the FEMA P695. The cyclic reversal loading test results of this study showed that the performance of coupling beams with relaxed reinforcement detail was almost similar to that of a coupling beam with the ACI detail and meet the level which requested from standard. The result of the seismic evaluation showed that all coupling beams are satisfied with the design code and seismic performance.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.10
• /
• pp.1281-1289
• /
• 2011

This paper deals with several statistical distribution functions for the analysis of fatigue life data of composite laminates for small wind-turbine blades. A series of tensile tests was performed on triaxial glass/epoxy laminates for loading directions of $0^{\circ}$, $45^{\circ}$, and $90^{\circ}$. Then, fatigue tests were carried out to determine the fatigue life at the aforementioned loading directions and the fatigue stresses at four levels. Two-parameter Weibull, three-parameter Weibull, normal, and log-normal distributions were used to fit the fatigue life data of the triaxial composite laminates. The three-parameter Weibull distribution most accurately described the fatigue life data measured experimentally for all the cases considered. Furthermore, the variation of fatigue life was simultaneously affected by the loading direction and fatigue stress level.

• Journal of the Society of Naval Architects of Korea
• /
• v.47 no.1
• /
• pp.67-75
• /
• 2010

Submarine and deep sea diving structures are generally designed based on their ultimate strength. Fatigue strength at welded joint must be also taken into account because working stress is increased due to the increasing of diving depth and using high yield steel. The pressure hulls of submarine are subjected to fluctuating compressive loading. But in addition to the calculated stresses, high residual tensile stresses at welded part have to be considered. The state of stress level of pressure hull is tensile at surface and compressive at deep diving depth. This paper presents the results of an experimental investigation on the crack initiation and growth at the weld toe of T welded joints of HY-100 steel plate under constant amplitude loading. It is also investigated the phenomenon of the fatigue failure and test methods. Fatigue tests have been using real scaled local structural models of full penetration T-welded joint, which is a part of the cylindrical shell structures reinforced by ring stiffeners. Several load ratios under constant amplitude loading are considered in the tests. Crack initiation and growth characteristics are examined based on the beach marks of the cracked section of the test specimens. A design stress-life curve including the design formula is suggested according to tested data.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.29 no.7A
• /
• pp.786-793
• /
• 2004

Autonomous data rate control scheme of current IxEV-DO uplink networks can not supper the various QoS requirements of heterogeneous traffics nor hold rise-over-thermal OtoT) constraints. In this paper, an uplink resource management scheme called the modified weighted g-fair (MWGF) scheduler with RoT filling is proposed and evaluated for heterogeneous traffics in cdma2000 type uplink networks. The proposed scheme belongs to a family of centralized resource management schemes and offers QoS guarantee by using priority metrics as well as lower system loading by holding RoT constraints using RoT filling method. With some case-study simulations, the proposed algorithms shows lower average delays of real time users compared to that of autonomous rate control by 29 - 40 ％. It also shows the 1.0 - 1.3 dB lower received RoT level than autonomous rate control schemes, leading to lower network loading.