• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1704-1708
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• 2008

Many studies have emphasized the importance of resistive exercise to maintain a healthy human body, particular in prevention of weakening of physical strength. Recently, some studies advocated that an application of vibration as a supplementary means in a regular training was effective in encouraging physical strength. Aim of the current study was, therefore, to identify if an application of vibration in a resistive exercise was effective in encouraging physical strength as that in a regular training. A 3-dimensional virtual lower extremity model for a healthy male and virtual leg-press model were generated and synchronized. Dynamic leg-press exercises on a slide machine with/without extra load and on a footboard with vibration as well as on a slide machine with extra load were analyzed. The results of the current indicated that the application of the vibration on the dynamic leg-press exercise might be not greatly effective in encouraging physical strength, compared with the dynamic leg press exercise with extra load. It was, however, thought that the application of the vibration might be helpful to elderly individuals because the reduced maximum muscle strength appeared by the effect of the vibration may avoid a muscular spasm, which can be driven from a high muscle strength sometimes produced during the leg-press exercise with extra load.

• Smart Structures and Systems
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• 제14권4호
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• pp.559-567
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• 2014

The model of unit dynamic reliability of repairable k/n (G) system with unit strength degradation under repeated random shocks has been developed according to the stress-strength interference theory. The unit failure number is obtained based on the unit failure probability which can be computed from the unit dynamic reliability. Then, the transfer probability function of the repairable k/n (G) system is given by its Markov property. Once the transfer probability function has been obtained, the probability density matrix and the steady-state probabilities of the system can be retrieved. Finally, the dynamic reliability of the repairable k/n (G) system is obtained by solving the differential equations. It is illustrated that the proposed method is practicable, feasible and gives reasonable prediction which conforms to the engineering practice.

• Structural Engineering and Mechanics
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• 제22권1호
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• pp.107-130
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• 2006

The paper deals with the numerical solution of the dynamic problem of masonry structures. Masonry is modelled as a non-linear elastic material with zero tensile strength and infinite compressive strength. Due to the non-linearity of the adopted constitutive equation, the equations of the motion must be integrated directly. In particular, we apply the Newmark or the Hilber-Hughes-Taylor methods implemented in code NOSA to perform the time integration of the system of ordinary differential equations obtained from discretising the structure into finite elements. Moreover, with the aim of evaluating the effectiveness of these two methods, some dynamic problems, whose explicit solutions are known, have been solved numerically. Comparisons between the exact solutions and the corresponding approximate solutions obtained via the Newmark and Hilber-Hughes-Taylor methods show that in the cases under consideration both numerical methods yield satisfactory results.

• The Journal of Korean Physical Therapy
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• 제27권5호
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• pp.345-350
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• 2015

Purpose: This study was conducted to determine the effects of ankle joint position during closed kinetic chain (CKC) exercise on knee extensor strength and balance in patients with chronic stroke. Methods: Sixteen patients with chronic stroke participated in the study. Participants were randomly assigned to two groups: $15^{\circ}$ ankle joint plantar flexion group (n=8) and ankle joint neutral group (n=8) during CKC exercise. All participants underwent conventional physical therapy for 30 minutes. In addition, the experimental group ($15^{\circ}$ ankle joint plantar flexion group) and control group (ankle joint neutral group) participated in a 20-minute CKC exercise program. In both groups exercise was performed three times a week for four weeks. Outcomes including knee extensor strength and balance ability (Five times sit-to-stand test, Timed up and go test, and Balancia) were measured before and after exercise. Results: Significant differences in knee extensor strength and balance ability were observed between pre- and post-exercise in all groups (p<0.05). The improvement of knee extensor strength and dynamic balance was significantly higher in the experimental group than in the control group (p<0.05). Conclusion: These findings demonstrated that $15^{\circ}$ ankle joint plantar flexion during closed kinetic chain exercise is effective in improvement of knee extensor strength and dynamic balance in patients with chronic stroke.

• 한국산학기술학회논문지
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• 제21권2호
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• pp.212-220
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• 2020

본 연구는 미세 현미경 레이저 요추 디스크 절제술을 시행한 환자를 대상으로 기존의 전통적 재활플그램인 요부 안정화 운동에 SEBT 프로그램을 적용한 재활운동이 등척성 요부근력과 동적균형능력 그리고 관절가동범위에 어떠한 영향을 미치는 지를 규명하고자 실시되었다. 연구대상자는 미세 현미경 레이저 요추 디스크 절제술을 받은 후 6주간 보존적 치료를 받은 환자 14명을 대상으로, 요부안정화운동(Lumbar Stabilizing Exercise Group, LSG, n=7)과 SEBT+요부안정화운동그룹(SEBT Exercise +Lumbar Stabilizing Exercise Group, SLSG, n=7)을 8주간 실시하였다. 본 연구의 결과에서, 요부의 등척성 근력 비율(72°와 0°)은 LSG(p=.007)와 SLSG(p=.024) 모두 유의하게 감소하였으며 동적균형능력을 검사하기 위한 Y-balance test의 세 방향 도달 거리에 대한 결과는 SLSG와 LSG의 모든 방향에서 유의한 증가를 보였고 동적균형 능력은 좌측(LSG, p=.010; SLSG, p=.002)과 우측(LSG, p=.002; SLSG, p=.002) 모두 유의하게 증가하였다. 또한 관절가동범위는 LSG(p=.006)와 SLSG(p=.017) 두 집단 모두에서 유의하게 증가하였다. 이상의 결과에서 8주간의 재활운동 후, 전통적인 요부안정화 운동과 요부안정화운동에 SEBT프로그램을 추가한 재활운동 모두 등척성 요부근력과 동적균형능력 그리고 관절가동범위에 긍정적인 효과가 나타났으며 이후에 SEBT 프로그램만의 효과를 검증하는 후속연구가 필요할 것으로 사료된다.

• 소성∙가공
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• 제4권2호
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• pp.159-168
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• 1995

The torsion tests in the range of $550~800^{\circ}C$, $5.0{\times}10^{-3}~5.0{\times}10^0/sec$ were performed to study the effects of strain rate$(\.{\varepsilon})$ and temperature(T) on the hot strength of Cu-Zn alloy. High temperature flow stresses of this alloy increased with increasing $\.{\varepsilon}$ and/or decreasing T, and than the more grain refinement could be obtained. The flow curves exhibited a peak followed by a steady steady state regime as a result of dynamic recrystallization. The hot strength dependence of $\.{\varepsilon}$ and T was described by a hyperbolic sine law, $\.{\varepsilon}=A(sinh0.017{\sigma})^4.81$exp(-216KJ/mol). Hot strength could be reduced at the arbitary condition, $\.{\varepsilon}$ and T, by constitutive parameter Z(Zenner-Hollomon parameter), $Z=A(sinh{\alpha}{\sigma})^n=\.{\varepsilon}$exp(Q/RT).

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.464-467
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• 2002

This paper presents investigation of damping characteristics of squeeze mode type MR (magneto-Rheological) mount experimentally. Since damping property of the MR fluid is changed by variation of the applied magnetic field strength, squeeze mode type MR mount proposed in the study has variable damping characteristics according to the applied magnetic field strength. Impact and excitation tests were performed to investigate the dynamic properties of squeeze mode type MR mount. Responses of the mount were compared in proportion to the applied magnetic field strength. The experimental results show that the mount can effectively reduce vibration amplitude in a wide frequency range by changing the applied magnetic field strength.

• 한국농공학회지
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• 제39권4호
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• pp.75-81
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• 1997

This study was performed to evaluate the engineering properties of surlightweight polymer concrete using synthetic lightweight aggregate. The following conclusions were drawn; 1. The unit weight was in the range of 0.849~0.969t/$m^3$, the unit weights of those concrete were decreased by 58 ~ 63% than that of the normal cement concrete. 2. The highest strength was achieved by $P_1$, and compressive strength was increased by 93% and bending strength by 364% than that of the normal cement concrete, respectively. 3. The ultrasonic pulse velocity was in the range of 2, 346~2, 702m/s, which was low compared to that of the normal cement concrete. 4. The dynamic modulus of elasticity was in the range of $1.561{\times} 10{^5}~1.916{\times} 10{^5}kgf/cm^2$, which was approximately 52~98% of that of the normal cement concrete. 5. The compressive and bending strength were increased with the increase of unit weight. But, the dynamic modulus of elasticity and ultrasonic pulse velocity were decreased with the increase of unit weight.

• 한국농공학회지
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• 제45권6호
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• pp.128-135
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• 2003

This study is performed to examine the physical and mechanical properties of concrete using recycled aggregate and industrial by-products. The test results show that the unit weight, compressive and flexural strength, ultrasonic pulse velocity and dynamic modulus of elasticity are decreased with increasing the content of recycled aggregate. But, the absorption ratio is increased with increasing the content of recycled aggregate. The unit weight is 2,237∼2,307 kg/$\textrm{m}^3$, the absorption ratio is 2.96∼4.12%, the compressive strength is 415∼532 kgf/$\textrm{cm}^2$, the flexural strength is 75∼96 kgf/$\textrm{cm}^2$, the ultrasonic pulse velocity is 4,350∼4,949 m/s and the dynamic modulus of elasticity is $390\times10^3\;∼\;465\times10^3$ kg f/$\textrm{cm}^2$, respectively These recycled aggregate concrete can be used for high strength concrete.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1126-1133
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• 2005

The effects of mean particle size and uniformity coefficient of dredged soils to the liquefaction resistance strength and dynamic characteristics are experimentally studied in this paper. Representative 4 mean particle sizes and 3 uniformity coefficients were selected and 12 representative particle size distribution curves which have different mean particle sizes and uniformity coefficients, were artificially manufactured using the real dredged river soil. Cyclic triaxial tests and torsional shear tests were carried out to analyze the effect of mean particle size and uniformity coefficient to the liquefaction resistance strength and dynamic characteristics of soils.