• The Journal of Korean Physical Therapy
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• v.20 no.2
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• pp.1-10
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• 2008

Purpose: This study examines the effects of elastic band of resistance exercise for balance control of the elderly. Methods: Thirty of eighty participants in experiment subjects who demonstrated balance-impairment through the use of primary screening tests including the one leg standing test (OLST), functional reach test (FRT) and timed up and go (TUG) were selected as subjects. Fifteen subjects that underwent muscle-strengthening exercise using an elastic band were selected as the exercise group and fifteen subjects were selected as a control group. Subjects undertook a home-based exercise program three times per week for 9 weeks. Muscle strength, functional assessment and a balance test were quantitatively measured before and after the exercise regimen. Results: After muscle strengthening exercises, changes in maximal voluntary isometric contraction (MVIC) showed a significant increase in all of the lower extremity muscles of the exercise group subjects. There were statistically significant differences between the exercise and control groups for changes in the OLST, FRT and TUG, which are functional assessments of balance ability, and changes of the unit path length and circumference area, measurement items of quantitative analysis. In addition, from examining correlations between MVIC, balance ability, it was found that an increase of muscle strength in the hip joint group of muscles among the lower extremity muscles had greater improvement in correlation with balance ability in this elderly population. Conclusion: Resistance exercise using elastic bands had significant effects on muscle strengthening in elderly subjects, with a resultant increase of lower extremity muscle strength with significant improvement of balance ability.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1246-1251
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• 2003

The fracture behaviors of Zr-based bulk amorphous metals(BAMs) having compositions of $Zr_{55}Al_{10}Ni_{5}Cu_{30}$, were investigated under impact loading and quasi-static conditions. For experiments, a newly devised instrumented impact testing apparatus and the subsize Charpy specimens were used. The influences of loading rate and the notch shape on the fracture behavior of the Zr-based BAM were examined. The Zr-based BAMs showed an elastic deformation behavior without any plastic deformation on it before fracture. Most fracture energies were absorbed in the process of the crack initiation. The maximum load and fracture absorbed energy under quasi-static condition were larger than those under impact condition. However, there existed relatively insignificant notch shape effect. Fracture surfaces under impact loading were smoother than those under quasi-static loading. The absorbed fracture energy appeared differently depending on the extent of the vein-like pattern region due to the shear bands developed at the notch tip. It can be found that the fracture energy of the Zr-Al-Ni-Cu alloy is closely related with the development of shear bands during fracture.

• Advances in aircraft and spacecraft science
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• v.6 no.1
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• pp.31-49
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• 2019

Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, helicopter blades, engine rotors, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness and inertia forces on a structure. The conventional method for designing a rotor blade to be free from flutter instability throughout the helicopter's flight regime is to design the blade so that the aerodynamic center (AC), elastic axis (EA) and center of gravity (CG) are coincident and located at the quarter-chord. While this assures freedom from flutter, it adds constraints on rotor blade design which are not usually followed in fixed wing design. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called "stop-bands". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. In this work, we analyze the flutter characteristics of a helicopter blades with a periodic change in their sandwich material using a finite element structural model. Results shows great improvements in the flutter forward speed of the rotating blade obtained by using periodic design and increasing the number of periodic cells.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1630-1635
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• 2003

The deformation and fracture behaviors of a bulk amorphous metal, Zr-based one (Zr$\_$41.2/Ti$\_$13.8/Cu$\_$12.5/Ni$\_$10/Be$\_$22.5/: Vitreloy), were investigated over a strain rate range (7x10$\^$-4/～4 s$\^$-1/). The uniaxial compression test and the indentation test using 3mm-diameter WC balls were carried out under quasi-static loading conditions. As a result, at the uniaxial compressive state, the fracture stress of the material was very high (～1,700MPa) and the elastic strain limit was about 2%. The fracture strength showed a strain rate independent behavior up to 4 s$\^$-1/. Using indentation tests, the plastic deformation behavior of the Zr-based BAM up to a large strain value of 15% could be achieved, even though it was the deformation under locally constrained condition. The Meyer hardness of the Zr-based BAM measured by static indentation tests was about 5 GPa and it revealed negligible strain hardening behavior. At indented sites, the plastic indentation occurred forming a crater and well-developed multiple shear bands were generated around it along the direction of 45 degree when the indentation load exceeded 7kN. With increasing indentation load, shear bands became dense. The fracture surface of the specimen after uniaxial compressive tests showed vein-like pattern, typical morphology of many BAMs.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.252-263
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• 1995

It is visualized that dislocations move straightly in polycrystalline structure and the trans-grain dislocation moving occur from yield point to ultimate tensile stress. Some fracturemodes in uniaxial tensile test are ilustrated in order to explain that after the ultimate point the grains deforms by twins and the rotations of grains make cracks at the grain-boundaries by the incompatibility . The luders banks. which propagates along the axis of the specimen, are twin bands whcih are formed by rearrangement of the atoms within the structure of three-dimensional crystallizing $\pi$-bondings. The fatigue limit can be found through the atom's rolling back motion during elastic deformation inthe uniaxial tensile test by the change of the gradient.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.2 no.3
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• pp.227-230
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• 2002

A new iris segmentation and recognition method is described. Combining a statistical classification and elastic boundary fitting, the iris is first segmented robustly and accurately. Once the iris is segmented, one-dimensional signals are computed in the iris and decomposed into multiple frequency bands. Each decomposed signal is approximated by a piecewise linear curve connecting a small set of node points. The node points represent features of each signal. The similarity measture between two iris images is the normalized cross-correlation coefficients between simplified signals.

• Korea-Australia Rheology Journal
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• v.19 no.2
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• pp.81-88
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• 2007

Blends of collagen dispersion (COL) with poly(vinyl alcohol) (PVA) in different weight ratios were investigated by oscillatory rheometry, Fourier transform-infrared spectroscopy and scanning electron microscopy. It was found that even with 80% of PVA, the COL/PVA blends behaved more like collagen dispersion than pure PVA solution in the dynamic thermal and frequency processing, for instance, a dominant elastic appearance (G'>G"), a similar shear thinning behavior and the thermal denaturation below $40^{\circ}C$. However, influence on the blend behaviour by PVA was noticeable, for instance, an increase of dynamic denaturation temperature, the decreasing intensity of amide I, II and III bands as well as the diminishing irregular pores on the surface of blends. The interaction between collagen and PVA could be observed, especially at the regions with low content or high content of PVA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.10C
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• pp.844-850
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• 2008

This paper stated the proposed algorithm to certify the characteristics of artificial explosion sounds traveled through underground bedrock medium. Artificial explosion that travel through underground bedrock had an attenuation within high frequency bands in increase of a distance with multiple transmission paths phenomenon and inhomogeneity of geological status. In this paper, explosion experiment was made in underground tunnel to verify efficiency of proposed algorithm. The could certify the characteristics of artificial explosion sounds as extracted and numerically quantified the characterized parameter with collected sound sample that traveled through underground bedrock channel.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.671-674
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• 2004

In this study a program 'SAPONC-FRANCE' which is able to evaluate and analysis the elastic behavior property of the domestic FRANCE type containment under pressurization and depressurization in periodic structural integrity test (SIT) was developed. The readings of EAU system that is composed of the pendulum, invar-wire, leveling-pot, bench-mark, thermocouples and acoustic strain gauges were used as input data for operating the program. This program provides the prediction lines and bands of the pressure-strain(or displacement) relationship of concrete due to the changing of inner volume under pressurization and depressurization in SIT of the domestic FRANCE type containment.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.155-159
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• 2000

Microstructural processes during high cycle fatigue are investigated according to plastic-strain hardening, crack formation, crack propagation and fracture. It is shown that the fatigue test resembles the uniaxial tensile test. The logarithm of the number of cycles to failure is proportional to the elongation in the tensile test. Under high cycle fatigue test, the strain is normally elastic. If the strain is absolutly elastic, fatigue could not result. But this is over simplication. Nearly all metals undergo a minor amount of plastic strain even at low stress. Damage accumulation leadling to crack formation can continue in the persistent slip bands at very low average plastic strain amplitude. In the ten­s sile test the overall specimen follows the failure procedure whilst in the high cycle fatigue test the local persistent slip band follows the failure procedure. However accumulations of strain per unit volume in the deforming region before failure in both cases are equal locally.