• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.805-812
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• 2018

High pressure die casting is one of the precision casting methods. It is highly productivity and suitable for manufacturing components with complex shapes and accurate dimensions. Recently, there has been increasing demand for efficient heat dissipation components, to control the heat generated by devices, which directly affects the efficiency and life of the product. Die cast aluminum alloys with high thermal conductivity are especially needed for this application. In this study, the influence of elements added to the die cast aluminum alloy on its thermal conductivity was evaluated. The results showed that Mn remarkably deteriorated the thermal conductivity of the aluminum alloy. When Cu content was increased, the tensile strength of cast aluminum alloy increased, showing 1 wt% of Cu ensured the minimum mechanical properties of the cast aluminum. As Si content increased, the flow length of the alloy proportionally increased. The flow length of aluminum alloy containing 2 wt% Si was about 85% of that of the ALDC12 alloy. A heat dissipation component was successfully fabricated using an optimized composition of Al-1 wt%Cu-0.6 wt%Fe-2 wt%Si die casting alloy without surface cracks, which were turned out as intergranular cracking originated from the solidification contraction of the alloy with Si composition lower than 2 wt%.

• Journal of Hydrogen and New Energy
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• v.33 no.6
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• pp.776-785
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• 2022

Hydrogen combustion in modern gas-turbine engine is the cutting edge technology as carbon-free energy conversion system. Flashback of hydrogen flame, however, is inevitable and critical specially for premixed hydrogen combustion. Therefore, this experimental investigation is conducted to understand flashback phenomenon in premixed hydrogen combustion. In order to investigate flashback characteristics in premixed hydrogen (H₂)/air flame, we focus on pressure conditions and nozzle shapes. In general, quenching distance reduces as pressure of combustion chamber increases, causing flashback from boundary layer near wall. The flashback regime for reference and modified candidate configurations can broadly appear with increasing combustion chamber pressure. The later one can improve flashback-resist by compensating flow velocity at wall. Also, improved wall flow velocity profile of suggested contraction nozzle prevents entire flashback but causes local flashback at nozzle exit.

• Geomechanics and Engineering
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• v.34 no.5
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• pp.481-489
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• 2023

Drained cyclic triaxial tests were conducted on a saturated sand to examine its deformation characteristics under either axial or lateral cyclic loading condition. To apply lateral cyclic loading, the cell pressure was cycled while maintaining a constant vertical stress. The strain accumulations and flow direction in the soil were presented and discussed considering various initial stress ratios (η₀), cyclic stress amplitudes and cyclic stress paths. The results indicate that axial strain accumulation shows an exponential increase with the maximum stress ratio (η^max). The initial deviatoric stress has comparable effects with lateral cyclic stress amplitude on the accumulated axial strain. In contrast, the accumulated volumetric strain is directly proportional to the lateral cyclic stress amplitude but not much affected by η₀ values. Due to the anisotropy of the soil, the accumulated axial and lateral bulging strains are greater in lateral cyclic loading when compared to axial cyclic loading even though η^max is the same. It is also found that η^max affects soil's lateral deformation and increasing the ratio could change the lateral deformation from contraction to bulging. The flow direction depends on η^max in the sand under lateral cyclic loading, regardless of η₀ values and the cyclic stress amplitudes, and a large η^max could lead to great deviatoric strain but a little volumetric strain accumulation.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.41.2-42
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• 2020

Understanding how the filamentary structure plays a role in the formation of the prestellar cores and stars is a key issue to challenge. We have observed two prestellar cores in surrounding filamentary environments in 13CO, C180 (3-2) and HCO+ (4-3) molecular lines with the Heterodyne Array Receiver Program (HARP) of the James Clerk Maxwell Telescope (JCMT), in order to search for the evidence related to the possible flow motions along the filament and/or the radial accretion (or infalling motions) of gas material toward the dense cores from their surrounding filamentary cloud. In L1544, the velocity gradient of 1.6 km s-1 pc-1 toward the core was measured in a small branch of filament lying on a radial direction of main filament while no velocity gradient along the main axis of filament in both 13CO and C18O lines. In L694-2, we found the velocity gradient of 0.6 km s-1 pc-1 along the filament in only 13CO lines. The projected accretion rate of ~6 M◉ Myr-1 was estimated in both cases. The infall (or radially contracting) velocity of gas material was measured ~0.16 km s-1 in both 13CO and HCO+ lines and in both L1544 and L694-2, which leads to estimate a mass infall rate of ~20 M◉ Myr-1. Our analysis suggests that our targets are at a stage where the gravitational contraction dominates the mass accretion through the surrounding filamentary cloud. This is consistent with the fact that our targets are highly evolved prestellar cores on a verge of star formation. More detailed results will be presented at the meeting.

• Restorative Dentistry and Endodontics
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• v.34 no.2
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• pp.145-153
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• 2009

The purpose of this study was to evaluate the effect of instrument compliance on the polymerization shrinkage stress measurements of dental composites. The contraction strain and stress of composites during light curing were measured by a custom made stress-strain analyzer, which consisted of a displacement sensor, a cantilever load cell and a negative feedback mechanism. The instrument can measure the polymerization stress by two modes: with compliance mode in which the instrument compliance is allowed, or without compliance mode in which the instrument compliance is not allowed. A flowable (Filtek Flow: FF) and two universal hybrid (Z100: Z1 and Z250: Z2) composites were studied. A silane treated metal rod with a diameter of 3.0 mm was fixed at free end of the load cell, and other metal rod was fixed on the base plate. Composite of 1.0 mm thickness was placed between the two rods and light cured. The axial shrinkage strain and stress of the composite were recorded for 10 minutes during polymerization. and the tensile modulus of the materials was also determined with the instrument. The statistical analysis was conducted by ANOVA. paired t-test and Tukey's test (${\alpha}<0.05$). There were significant differences between the two measurement modes and among materials. With compliance mode, the contraction stress of FF was the highest: 3.11 (0.13). followed by Z1: 2.91 (0.10) and Z2: 1.94 (0.09) MPa. When the instrument compliance is not allowed, the contraction stress of Z1 was the highest: 17.08 (0.89), followed by FF: 10.11 (0.29) and Z2: 9.46 (1.63) MPa. The tensile modulus for Z1, Z2 and FF was 2.31 (0.18), 2.05 (0.20), 1.41 (0.11) GPa, respectively. With compliance mode. the measured stress correlated with the axial shrinkage strain of composite: while without compliance the elastic modulus of materials played a significant role in the stress measurement.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1732-1736
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• 2006

여수로는 월류시 한계류 상태와 고유속의 사류상태가 복합적으로 일어나는 복잡한 흐름형태를 가지고 있어 여수로의 단면설계시 수리적인면뿐만 아니라 구조적인 측면에서도 안정해야 하며 경제성이 고려되어야 한다. 그래서 고유속의 흐름을 갖는 여수로에 축소부를 고려할 경우 충격파에 의한 수위상승과 하류의 흐름 교란 등 수리학적인 불안정이 발생하기 때문에 설계시 경제적인 장점이 있음에도 불구하고 단면축소부를 고려하여 여수로를 설계하는 것은 현실적으로 많은 어려움이 있다. 본 연구에서는 단면축소를 고려한 여수로 설계를 위하여 3차원 수치모형인 Flow-3D를 이용하여 충격파로 인하여 발생하는 교차파 저감을 모의하기 위하여 수치실험을 실시하였다. 교차파 저감을 위해 축소부내에서 교차파가 발생하도록 축소부의 각도는 유입흐름 특성을 고려하여 적정하게 설정하였다. 수치실험결과 축소부의 각도가 작을수록 첫번째 교차파의 수위는 크게 발생하지 않으나 단면축소후 교차파가 하류로 전파되어 불안정한 흐름이 연속적으로 발생하고, 과대하게 설정할 경우 첫번째 발생하는 교차파에 의해 중앙부의 수위가 크게 상승하는 결과를 보였다. 또한 본 연구에서는 축소부단면내 회절판(diffractor) 설치전 후의 수리학적 거동을 모의하여 회절판의 흐름개선 효과를 검증하였다.

• The Journal of Korean Physical Therapy
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• v.9 no.1
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• pp.185-193
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• 1997

The purpose of this study was to investigate the neurophysiological mechanisms, assessment of muscle spasm and treatments that could apply to clinical field. Spasm is a painful pattern of contraction of muscle caused by chronic or acute trauma, excessive tension, or organic disorders. Aside from pain, muscle spasm creates shortenning of muscles and limits motion. Untreated spasm and protective immobility due to pain lead to decreased local blood flow in the muscles and result in a vicious cycle of muscle spasm and paul. The assessment of muscle spasm involve muscle tone assessment, tissue compliance, and joint ROM. Each of these aessessments utilize as a part of the patient's condition Clinical managements involve drug management and physical therapy. Expecially, physical therapy is one of the most important techniques to reduce muscle spasm. Physical therapy includes applying heat and cold, electrical stimulation, massage, and traction. This investigation should entourage phisical therapists to experiment further with various techniques to reduce muscle spasm.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.33-38
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• 1999

Muscle based face image synthesis is one of the most realistic approach to realize life-like agent in computer. Facial muscle model is composed of facial tissue elements and muscles. In this model, forces are calculated effecting facial tissue element by contraction of each muscle strength, so the combination of each muscle parameter decide a specific facial expression. Now each muscle parameter is decided on trial and error procedure comparing the sample photograph and generated image using our Muscle-Editor to generate a specific race image. In this paper, we propose the strategy of automatic estimation of facial muscle parameters from 2D marker movement using neural network. This also 3D motion estimation from 2D point or flow information in captered image under restriction of physics based fare model.

• The Korean Journal of Physiology
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• v.21 no.1
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• pp.91-101
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• 1987

The present experiment was carried out, in the rabbit and cat, in order to explore functional interrelationship between the vestibular semicircular canals and extraocular muscles, which are involved in the vestibulooculomotor reflex as the receptor and effector organ respectively. Semicircular canals were subjected to electrical stimulation, lymphatic fluid flow or acute freezing, and responses of the extraocular muscles were recorded in terms of changes in electromyographic activity and isometric tension. Electrical stimulation of a unilateral canal elicited contraction of the superio-medial muscle group (superior oblique, superior rectus and medial rectus muscles) in the ipsilateral eye and the inferio-lateral muscle group (inferior oblique, inferior rectus and lateral rectus muscles) in the contralateral eye. Thus a simple and distinct axiom was found in the pattern of the reflex-response of the extraocular muscles. Inhibition of the unilateral canals elicited the extraocular muscle responses contrary to those observed by excitation of the canal. Based on the present experimental results, it was demonstrated that the functional interrelations between the semicircular canals and extraocular muscles are rather equivalent in the frontal eyed cats (with binocular vision) and lateral eyed rabbits (with monocular vision). Therefore the previous thesis that the vestibuloocular relations vary from species to species awaits experimental reevaluation.

• Water for future
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• v.26 no.3
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• pp.87-101
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• 1993

A finite element model RIV-FEM2 for the hydrodynamic study in a river is developed based on two-dimensional shallow water wave equation and dissipative Galerkin's method. RIV-FEM2 consists of pre-processing, analysis processing and post-processing. Pre- and analysis processing is programmed with Fortran-77 and post-processing with turbo-Pascal respectively. The model is tested with two dimensional problems, including flow through bends, bridges, and symmetric contraction. The two dimensional tests shows stable and efficient results for various situations. Applicability of the model is verified by applying to natural river. The model will provide a basic contribution to the hydrodynamic analysis in a river.