• The Journal of Korean Society for Neurotherapy
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• v.22 no.3
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• pp.19-23
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• 2018

Purpose The purpose of this study was to investigate the change of balance ability by performing closed chain exercise on stable support surface and unstable support surface in twenties. Methods This study randomly selected 15 students in the closed chain exercise group on the stable support side and 15 on the closed chain exercise group on the unstable support side. Balance ability was measured before and after the start of exercise and static balance was measured by OLT(One Leg Standing Test) and FRT (Functional Reach Test). Result The changes of the function reach test of the closed chain movement according to the ground type were significant in the unstable and stable support surfaces and the change of function reach test after the intervention in the two groups was significantly improved compared with the closed chain movement respectively. The one leg standing test changes of the closed chain movement according to the ground type showed significant results on the unstable and stable support surfaces, but there was no significant difference in the one leg standing test changes after intervention between the two groups. Conclusion The effect of closed chain training on ground type is unstable. The change of function reach test and one leg standing test of the closed chain exercise group on the stable support surface resulted in significant changes after exercise, but there was a significant difference in the balance ability of function reach test change after intervention between the groups.

• Communications of the Korean Mathematical Society
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• v.11 no.3
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• pp.825-829
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• 1996

We prove that if G is the fundamental group of a closed surface or a Seifert fibered space and K is a finitely generated subgroup of G, and if for any element g in G there exists an integer $n_g$ such that $g^{n_g}$ belongs to K, then K is of finite index in G.

• Bulletin of the Korean Mathematical Society
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• v.56 no.2
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• pp.515-520
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• 2019

We give new evidence that "complicated" Heegaard surfaces behave like incompressible surfaces. More precisely, suppose that a closed connected orientable 3-manifold M contains a closed connected incompressible surface F which separates M into two (connected) components $M_1$ and $M_2$. Let S be a Heegaard surface of M. Our result is that if the Hempel distance of S is at least four, then S is isotoped so that $S{\cap}M_i$ is incompressible for each i = 1, 2.

• Korean Journal of Computational Design and Engineering
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• v.3 no.2
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• pp.135-139
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• 1998

The hodograph, which are usually defined as the derivative of parametric curve or surface, is useful far various geometric operations. It is known that the hodographs of Bezier curves and surfaces can be represented in the closed form. However, the counterparts of rational Bezier curves and surface have not been discussed yet. In this paper, the equations are derived, which are the closed form of rational Bezier curves and surfaces. The hodograph of rational Bezier curves of degree n can be represented in another rational Bezier curve of degree 2n. The hodograph of a rational Hazier surface of degree m×n with respect to a parameter can be also represented in rational Bezier surface of degree 2m×2n. The control points and corresponding weight of the hodographs are directly computed using the control points and weights of the given rational curves or surfaces.

• Journal of the Institute of Convergence Signal Processing
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• v.4 no.3
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• pp.21-26
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• 2003

A new method to realize 3-dimensional object pattern recognition system using Fourier-based feature extractor has been proposed. The procedure to obtain the invariant feature vector is as follows ; A closed surface is generated by tracing the surface of object using the 3-dimensional polar coordinate. The centroidal distances between object's geometrical center and each closed surface points are calculated. The distance vector is translation invariant. The distance vector is normalized, so the result is scale invariant. The Fourier spectrum of each normalized distance vector is calculated, and the spectrum is rotation invariant. The Fourier-based feature generating from above procedure completely eliminates the effect of variations in translation, scale, and rotation of 3-dimensional object with closed-surface. The experimental results show that the proposed method has a high accuracy.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2003.10a
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• pp.116-116
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• 2003

• Advances in biomechanics and applications
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• v.1 no.2
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• pp.85-93
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• 2014

In this paper, two procedures of enumerating the axial rotation are proposed using the unit sphere of the spherical rotation coordinate system specifying 3D rotation. If the trajectory of the movement is known, the integration of the axial component of the angular velocity plus the geometric effect equal to the enclosed area subtended by the geodesic path on the surface of the unit sphere. If the postures of the initial and final positions are known, the axial rotation is determined by the angular difference from the parallel transport along the geodesic path. The path dependency of the axial rotation of the three dimensional rigid body motion is due to the geometric effect corresponding to the closed loop discontinuity. Firstly, the closed loop discontinuity is examined for the infinitesimal region. The general closed loop discontinuity can be evaluated by the summation of those discontinuities of the infinitesimal regions forming the whole loop. This general loop discontinuity is equal to the surface area enclosed by the closed loop on the surface of the unit sphere. Using this quantification of the closed loop discontinuity of the axial rotation, the geometric effect is determined in enumerating the axial rotation. As an example, the axial rotation of the arm by the Codman's movement is evaluated, which other methods of enumerating the axial rotations failed.

• Korean Journal of Mathematics
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• v.25 no.4
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• pp.555-561
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• 2017

We show that a closed curve invariant under inversions with respect to two intersecting circles intersecting at angle of an irrational multiple of $2{\pi}$ is a circle. This generalizes the well known fact that a closed curve symmetric about two lines intersecting at angle of an irrational multiple of $2{\pi}$ is a circle. We use the result to give a different proof of that a compact embedded cmc surface in ${\mathbb{R}}^3$ is a sphere. Finally we show that a closed embedded cmc surface which is invariant under the spherical reflections about two spheres, which intersect at an angle that is an irrational multiple of $2{\pi}$, is a sphere.

• PNF and Movement
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• v.16 no.3
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• pp.433-439
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• 2018

Purpose: Visual information is one of the most important factors for postural balance. The purpose of this study was to investigate the effect of visual deprivation on the lower extremities and trunk muscle activity on an unstable surface during quiet standing. Methods: Fifteen healthy males from a university population participated in this study. Surface electromyography of the rectus abdominis, the erector spinalis, the vastus femoris oblique, the semitendinosis, the tibialis anterior, and the medial gastrocnemius was measured using EMG equipment (Telemyo 2400, Noraxon, USA). The participants were asked to maintain postural balance on an unstable surface (Balance pad, Airex, USA) for 30 seconds with eyes open and with eyes closed during quiet standing. The Wilcoxon test was used to compare the muscle activity of the lower extremities and the trunk between open and closed eyes on an unstable surface. Results: The muscle activity of the trunk and the lower extremities was increased more with eyes closed than with eyes open on the unstable surface during quiet standing. Conclusion: The findings from this study suggest that visual information could alter lower extremity and trunk muscle activity. Therefore, visual deprivation can be used as a method to improve postural balance.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.3
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• pp.211-219
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• 2014

Closed cracks are difficult to detect using conventional ultrasonic testing because most incident ultrasound passes completely through these cracks. Nonlinear ultrasound inspection using sub-harmonic frequencies a promising method for detecting closed cracks. To implement this method, a sub-harmonic phased array (PA) is proposed to visualize the length of closed cracks in solids. A sub-harmonic PA generally consists of a single transmitter and an array receiver, which detects sub-harmonic waves generated from closed cracks. The PA images are obtained using the total focusing method (TFM), which (with a transmitter and receiving array) employs a full matrix in the observation region to achieve fine image resolution. In particular, the receiving signals are measured using a laser Doppler vibrometer (LDV) to collect PA images for both fundamental and sub-harmonic frequencies. Oblique incidence, which is used to boost sub-harmonic generation, inevitably produces various surface waves that contaminate the signals measured in the receiving transducer. Surface wave interference often degrades PA images severely, and it becomes difficult to read the closed crack's position from the images. Various methods to prevent or eliminate this interference are possible. In particular, enhancing images with signal processing could be a highly cost-effective method. Because periodic patterns distributed in a PA image are the most frequent interference induced by surface waves, spatial frequency filtering is applicable for removing these waves. Experiments clearly demonstrate that the spatial frequency filter improves PA images.