• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.2
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• pp.16-23
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• 2013

An experimental study has been conducted to investigate the effects of equivalence ratio on the propagation characteristics of $CH_4$-air premixed flame intervened by an ultrasonic standing wave. A Schlieren photography was used for the flame structure visualization, and the flame propagation behavior was investigated in detail throughout the post-processing analysis. It is found that the structural variation of methane/air premixed flame caused by the intervention of ultrasonic standing wave give rise to the enhancement of combustion reaction and flame propagation velocity. Effectiveness of the standing wave on the flame velocity decreases as the equivalence ratio increases. Larger flame velocity with the standing wave becomes undistinguishable in a specific range of equivalence ratios.

• Computers and Concrete
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• v.21 no.6
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• pp.607-622
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• 2018

A non-linear finite element model (FEM) was constructed using a three-dimensional software (ATENA-3D) to investigate the effect of strengthening on the behavior of prestressed hollow-core (PHC) slabs with or without openings. The slabs were strengthened using near surface mounted (NSM)-carbon fiber reinforced polymer (CFRP) strips. The constructed model was validated against experimental results that were previously reported by the authors. The validated FEM was then used to conduct an extensive parametric study to examine the influence of prestressing reinforcement ratio, compressive strength of concrete and strengthening reinforcement ratio on the behavior of such slabs. The FEM results showed good agreement with the experimental results where it captured the cracking, yielding, and ultimate loads as well as the mid-span deflection with a reasonable accuracy. Also, an overall enhancement in the structural performance of these slabs was achieved with an increase in prestressing reinforcement ratio, compressive strength of concrete, external reinforcement ratio. The presence of openings with different dimensions along the flexural or shear spans reduced significantly the capacity of the PHC slabs. However, strengthening these slabs with 2 and 4 (64 and $128mm^2$ that represent reinforcement ratios of 0.046 and 0.092%) CFRP strips was successful in restoring the original strength of the slab and enhancing post-cracking stiffness and load carrying capacity.

• Journal of the Korean institute of surface engineering
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• v.54 no.5
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• pp.260-266
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• 2021

Synthesizing low-dimensional structures of oxide semiconductors is a promising approach to fabricate highly efficient gas sensors by means of possible enhancement in surface-to-volume ratios of their sensing materials. In this work, vertically aligned zinc oxide (ZnO) nanorods are successfully synthesized on a transparent glass substrate via seed-mediated hydrothermal synthesis method with the use of a ZnO nanoparticle seed layer, which is formed by thermally oxidizing a sputtered Zn metal film. Structural and optical characterization by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy reveals the successful preparation of the ZnO nanorods array of the single hexagonal wurtzite crystalline phase. From gas sensing measurements for the nitrogen dioxide (NO₂) gas, the vertically aligned ZnO nanorod array is observed to have a highly responsive sensitivity to NO₂ gas at relatively low concentrations and operating temperatures, especially showing a high maximum sensitivity to NO₂ at 250 ℃ and a low NO₂ detection limit of 5 ppm in dry air. These results along with a facile fabrication process demonstrate that the ZnO nanorods synthesized on a transparent glass substrate are very promising for low-cost and high-performance NO₂ gas sensors.

• Imaging Science in Dentistry
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• v.50 no.4
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• pp.331-337
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• 2020

Purpose: As cone-beam computed tomography (CBCT) has become the most widely used 3-dimensional (3D) imaging modality in the dental field, storage space and costs for large-capacity data have become an important issue. Therefore, if 3D data can be stored at a clinically acceptable compression rate, the burden in terms of storage space and cost can be reduced and data can be managed more efficiently. In this study, a deep learning network for super-resolution was tested to restore compressed virtual CBCT images. Materials and Methods: Virtual CBCT image data were created with a publicly available online dataset (CQ500) of multidetector computed tomography images using CBCT reconstruction software (TIGRE). A very deep super-resolution (VDSR) network was trained to restore high-resolution virtual CBCT images from the low-resolution virtual CBCT images. Results: The images reconstructed by VDSR showed better image quality than bicubic interpolation in restored images at various scale ratios. The highest scale ratio with clinically acceptable reconstruction accuracy using VDSR was 2.1. Conclusion: VDSR showed promising restoration accuracy in this study. In the future, it will be necessary to experiment with new deep learning algorithms and large-scale data for clinical application of this technology.

• Journal of Veterinary Clinics
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• v.37 no.6
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• pp.317-323
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• 2020

The aims of this study were to describe the appearance and size of the normal canine prostate using magnetic resonance (MR) imaging and to calculate the apparent diffusion coefficient (ADC) values. MR images were obtained from seven intact male beagle dogs using a 1.5 T MR unit. The sequences included pre- and post-contrast T1- and T2-weighted imaging with and without fat saturation. The signal intensity of the prostate was compared with the adjacent musculature, fat, and urine in the urinary bladder. We recorded the mean prostatic length, width, and height and the length of the sixth lumbar vertebral body (L6). In addition, the prostatic length (rL), width (rW), and height (rH) ratios to L6 were calculated. Diffusion-weighted images of the prostate were obtained and ADC values were calculated. The prostate was bilobed and oval-shaped, homogenous on T1-weighted images, and heterogeneous with radiating lines on T2-weighted images. Post-contrast T1-weighted sequences showed contrast enhancement of the central and radiating striations. The prostatic capsule was clearly identified on post-contrast T1-weighted images with fat saturation. The ADC values were 1.72-2.04 × 10-3mm2/sec (mean, 1.88 × 10-3mm2/sec). Knowledge of the normal appearance of the prostate on MR images is essential to assess prostatic diseases in dogs.

• Structural Engineering and Mechanics
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• v.76 no.6
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• pp.737-749
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• 2020

A hybrid bridge deck is proposed, which includes steel bars, concrete and glass-fiber-reinforced-polymer (GFRP) plates with channel sections. The steel bar in the negative moment region can increase the flexural stiffness, improve the ductility, and reduce the GFRP ratio. Three continuous decks with different steel bar ratios and a simply supported deck were fabricated and tested to study the mechanical performance. The failure mode, deflection, strain distribution, cracks and support reaction were tested and discussed. The steel bar improves the mechanical performance of continuous decks, and a theoretical method is proposed to predict the deformation and the shear capacity. The experimental results show that all specimens failed with shear failure in the positive moment region. The increase of steel bar ratio in the negative moment region can achieve an enhancement in the flexural stiffness and reduce the deflection without increasing GFRP. Moreover, the continuous deck can achieve a yield load, and the negative moment can be carried by GFRP plates after the steel bar yields. Finally, a nonlinear analytical method for the deflection calculation was proposed and verified, with considering the moment redistribution, non-cracked sections and nonlinearity of material. In addition, a simplified calculation method was proposed to predict the shear capacity of GFRP-concrete decks.

• Korean Journal of Metals and Materials
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• v.49 no.9
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• pp.720-725
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• 2011

W-Ni-Fe heavy alloys have been used in various fields, such as kinetic energy penetrators and radiation shielding materials, due to their high density and good mechanical properties. In this study, the sintering of W-Ni-Fe alloys with various Ni/Fe ratios was demonstrated to improve the mechanical properties and penetration capabilities of heavy alloys by formation of interfacial phase. The microstructural changes and the mechanical properties of the W-Ni-Fe alloys after liquid-phase sintering were investigated. The Vickers hardness and tensile strength of the 95W1.3Ni3.7Fe sample, which had coated W grains by $Fe_7W_6$ phase (${\mu}$-phase), were 450 Hv and 1560 MPa, respectively. As a result, enhancement of the mechanical properties was considered to have uniformly generated ${\mu}$-phase around W grains.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.1
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• pp.93-97
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• 2023

A triboelectric nanogenerator (TENG) is a device that converts mechanical energy into electrical energy, and has been considered as a substitute for continuous power supply due to its high performance, simple structure and eco-friendliness. Recently, it is important to develop a TENG using a non-toxic material in order to use it as a power source for wearable, attachable, and body-embeddable electronics. Here, we developed a human friendly TENG using polyvinyl chloride (PVC) gel containing acetyl tributyl citrate (ATBC), a non-toxic plasticizer. PVC gels were fabricated using various ratios of PVC and ATBC, and optimized by investigating dielectric properties, surface potential, output performance, and durability. The PVC gel based TENG generates output signals of 73 V and 4.3 μA, i.e., a 5-fold enhancement in the output power compared to pristine PVC-based TENG. In addition, the PVC gel can be stretched over 500% of strain. This study is expected to be helpful in the future development of non-toxic wearable TENG.

• Journal of the Korean institute of surface engineering
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• v.56 no.4
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• pp.219-226
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• 2023

Utilizing low-dimensional structures of oxide semiconductors is a promising approach to fabricate relevant gas sensors by means of potential enhancement in surface-to-volume ratios of their sensing materials. In this work, vertically aligned cupric oxide (CuO) nanorods are successfully synthesized on a transparent glass substrate via seed-mediated hydrothermal synthesis method with the use of a CuO nanoparticle seed layer, which is formed by thermally oxidizing a sputtered Cu metal film. Structural and optical characterization by x-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy reveals the successful preparation of the CuO nanorods array of the single monoclinic tenorite crystalline phase. From gas sensing measurements for the nitrogen monoxide (NO) gas, the vertically aligned CuO nanorod array is observed to have a highly responsive sensitivity to NO gas at relatively low concentrations and operating temperatures, especially showing a high maximum sensitivity to NO at 200 ℃ and a low NO detection limit of 2 ppm in dry air. These results along with a facile fabrication process demonstrate that the CuO nanorods synthesized on a transparent glass substrate are very promising for low-cost and high-performance NO gas sensors.

• Nuclear Engineering and Technology
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• v.56 no.2
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• pp.477-484
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• 2024

Experimental investigations on gamma - rays attenuation parameters and dielectric spectroscopic properties were done on a polymeric mixture with chemical composition (100-x) polyethylene + x basalt, where x = 0, 1, 3, 5, 10, and 20 wt%. Using the melting blending technique,six nanocomposite polymeric samples were prepared. The linear attenuation coefficient µ of each prepared set of samples was measured using a gamma-ray spectrometer including High Purity Germanium detector (HPGe) at energies 662.5, 1173.24, and 1332.51 keV. Based on the measured values of (µ) and sample density, the other effective shielding parameters were calculated. The values of µ showed an increase with increasing the dopant ratios from 0.0 up to 20.0 wt%. In addition, the µ values decreased with the photon's energy. The µ values were found 0.0847 up to 0.1175 cm^-1, 0.0571 up to 0.0855 cm^-1, and 0.0543 up to 0.075 cm^-1 at 662.5, 1173.24, and 1332.51 keV. for B0 up to B20, respectively. The ATR spectroscopy was done on the prepared samples, and a good evidence of adding the filler to the pure polyethylene (HDPE) was obtained. Besides, an enhancement in dielectric constant by insertion of basalt NPs also recorded and can be attributed to the large dielectric constant of basalt compared to pure HDPE.