• Journal of the Korean Wood Science and Technology
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• v.22 no.2
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• pp.46-53
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• 1994

This study was conducted to investigate a feasibility of manufacturing wood fiber thermoplastic composites and to evaluate their mechanical properties. Wood fiber as a potential reinforcing filler was compounded with two thermoplastics (polypropylene and high density polyethylene) in high intensity thermokinetic plastic mixer aided with a wetting agent. It was found that wood fiber thermoplastic composites could be manufactured by injection molding process. The tensile and flexural strength of injection molded specimens were improved greatly with increasing wood fiber concentration. Tensile and flexural modulus increased proportionately with wood fiber concentration. Wood fiber provided reinforcement with thermoplastics in terms of strength and modulus. However, the percent elongation at break and energy to break were reduced with increasing wood fiber loadings. Impact strength also showed similar trend.

• Journal of radiological science and technology
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• v.43 no.6
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• pp.481-487
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• 2020

Radiation measurement technology has steadily improved and its usage is expanding in various industries such as nuclear medicine, security search, satellite, nondestructive testing, environmental industries and the domain of nuclear power plants (NPPs). Especially, the simultaneous measurements of gamma rays and neutrons can be even more critical for nuclear safety management of spent nuclear fuel and monitoring of the nuclear material. A semiconductor detector comprising cadmium, zinc, and tellurium (CZT) enables to detect gamma-rays due to the significant atomic weight of the elements via immediate neutron and gamma-ray detection. Semiconductor sensors might be used for nuclear safety management by monitoring nuclear materials and spent nuclear fuel with high spatial resolution as well as providing real-time measurements. We aim to introduce a portable nuclide-analysis device that enables the simultaneous measurements of neutrons and gamma rays using a CZT sensor. The detector has a high density and wide energy band gap, and thus exhibits highly sensitive physical characteristics and characteristics are required for performing neutron and gamma-ray detection. Portable nuclide-analysis device is used on NPP-decommissioning sites or the purpose of nuclear nonproliferation, it will rapidly detect the nuclear material and provide radioactive-material information. Eventually, portable nuclide-analysis device can reduce measurement time and economic costs by providing a basis for rational decision making.

• Journal of Environmental Science International
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• v.21 no.7
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• pp.845-853
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• 2012

Diethyl phthalate (DEP) is widely spread in the natural environment as an endocrine disruption chemicals (EDs). Therefore, in this study, ultrasound (US) and ultraviolet (UVC), including various applied power density (10-40 W/L), UV wavelengths (365 nm, 254 nm and 185 nm) and frequencies (283 kHz, 935 kHz) were applied to a DEP contaminated solution. The pseudo-first order degradation rate constants were in the order of $10^{-1}$ to $10^{-4}\;min^{-1}$ depending on the processes. Photolytic and sonophotolytic DEP degradation rate also were high at shortest UV wavelength (VUV) due to the higher energy of photons, higher molar absorption coefficient of DEP and increased hydroxyl radical generation from homolysis of water. Sonolytic DEP degradation rate increased with increase of applied input power and the dominant reaction mechanism of DEP in sonolysis was estimated as hydroxyl radical reaction by the addition of t-BuOH, which is a common hydroxyl radical scavenger. Moreover, synergistic effect of were also observed for sonophotolytic degradation with various UV irradiation.

• Structural Engineering and Mechanics
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• v.39 no.6
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• pp.767-793
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• 2011

An efficient edge-based smoothed finite element method (ES-FEM) has been recently developed for solving solid mechanics problems. The ES-FEM uses triangular elements that can be generated easily for complicated domains. In this paper, the complexity study of the ES-FEM based on triangular elements is conducted in detail, which confirms the ES-FEM produces higher computational efficiency compared to the FEM. Therefore, the ES-FEM offers an excellent platform for adaptive analysis, and this paper presents an efficient adaptive procedure based on the ES-FEM. A smoothing domain based energy (SDE) error estimate is first devised making use of the features of the ES-FEM. The present error estimate differs from the conventional approaches and evaluates error based on smoothing domains used in the ES-FEM. A local refinement technique based on the Delaunay algorithm is then implemented to achieve high efficiency in the mesh refinement. In this refinement technique, each node is assigned a scaling factor to control the local nodal density, and refinement of the neighborhood of a node is accomplished simply by adjusting its scaling factor. Intensive numerical studies, including an actual engineering problem of an automobile part, show that the proposed adaptive procedure is effective and efficient in producing solutions of desired accuracy.

• Advances in aircraft and spacecraft science
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• v.4 no.1
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• pp.21-35
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• 2017

Hydrogen peroxide is being considered as a monopropellant in micropropulsion systems for the next generation of miniaturized satellites ('nanosats') due to its high energy density, modest specific impulse and green characteristics. Efforts at the University of Vermont have focused on the development of a MEMS-based microthruster that uses a novel slug flow monopropellant injection scheme to generate thrust and impulse-bits commensurate with the intended micropropulsion application. The present study is a computational effort to investigate the initial decomposition of the monopropellant as it enters the catalytic chamber, and to compare the impact of the monopropellant injection scheme on decomposition performance. Two-dimensional numerical studies of the monopropellant in microchannel geometries have been developed and used to characterize the performance of the monopropellant before vaporization occurs. The results of these studies show that monopropellant in the lamellar flow regime, which lacks a non-diffusive mixing mechanism, does not decompose at a rate that is suitable for the microthruster dimensions. In contrast, monopropellant in the slug flow regime decomposes 57% faster than lamellar flow for a given length, indicating that the monopropellant injection scheme has potential benefits for the performance of the microthruster.

• Journal of Powder Materials
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• v.23 no.1
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• pp.15-20
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• 2016

Niobium is one of the most important and rarest metals, and is used in the electronic and energy industries. However, it's extremely high melting point and oxygen affinity limits the manufacture of Nb coating materials. Here, a Nb coating material is manufactured using a kinetic spray process followed by hot isotactic pressing to improve its properties. OM (optical microscope), XRD (X-ray diffraction), SEM (scanning electron microscopy), and Vickers hardness and EPMA (electron probe micro analyzer) tests are employed to investigate the macroscopic properties of the manufactured Nb materials. The powder used to manufacture the material has angular-shaped particles with an average particle size of $23.8{\mu}m$. The porosity and hardness of the manufactured Nb material are 0.18% and 221 Hv, respectively. Additional HIP is applied to the manufactured Nb material for 4 h under an Ar atmosphere after which the porosity decreases to 0.08% and the hardness increases to 253 Hv. Phase analysis after the HIP shows the presence of only pure Nb. The study also discusses the possibility of using the manufactured Nb material as a sputtering target.

• Nuclear Engineering and Technology
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• v.48 no.3
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• pp.650-659
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• 2016

As a type of accident-tolerant fuel, fully ceramic microencapsulated (FCM) fuel was proposed after the Fukushima accident in Japan. The FCM fuel consists of tristructural isotropic particles randomly dispersed in a silicon carbide (SiC) matrix. For a fuel element with such high heterogeneity, we have proposed a two-temperature homogenized model using the particle transport Monte Carlo method for the heat conduction problem. This model distinguishes between fuel-kernel and SiC matrix temperatures. Moreover, the obtained temperature profiles are more realistic than those of other models. In Part I of the paper, homogenized parameters for the FCM fuel in which tristructural isotropic particles are randomly dispersed in the fine lattice stochastic structure are obtained by (1) matching steady-state analytic solutions of the model with the results of particle transport Monte Carlo method for heat conduction problems, and (2) preserving total enthalpies in fuel kernels and SiC matrix. The homogenized parameters have two desirable properties: (1) they are insensitive to boundary conditions such as coolant bulk temperatures and thickness of cladding, and (2) they are independent of operating power density. By performing the Monte Carlo calculations with the temperature-dependent thermal properties of the constituent materials of the FCM fuel, temperature-dependent homogenized parameters are obtained.

• Applied Science and Convergence Technology
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• v.26 no.5
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• pp.133-138
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• 2017

We investigated the interface defect engineering and reaction mechanism of reduced transition layer and nitride layer in the active plasma process on 4H-SiC by the plasma reaction with the rapid processing time at the room temperature. Through the combination of experiment and theoretical studies, we clearly observed that advanced active plasma process on 4H-SiC of oxidation and nitridation have improved electrical properties by the stable bond structure and decrease of the interfacial defects. In the plasma oxidation system, we showed that plasma oxide on SiC has enhanced electrical characteristics than the thermally oxidation and suppressed generation of the interface trap density. The decrease of the defect states in transition layer and stress induced leakage current (SILC) clearly showed that plasma process enhances quality of $SiO_2$ by the reduction of transition layer due to the controlled interstitial C atoms. And in another processes, the Plasma Nitridation (PN) system, we investigated the modification in bond structure in the nitride SiC surface by the rapid PN process. We observed that converted N reacted through spontaneous incorporation the SiC sub-surface, resulting in N atoms converted to C-site by the low bond energy. In particular, electrical properties exhibited that the generated trap states was suppressed with the nitrided layer. The results of active plasma oxidation and nitridation system suggest plasma processes on SiC of rapid and low temperature process, compare with the traditional gas annealing process with high temperature and long process time.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.3
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• pp.149-154
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• 2009

Dense $5Cu_{0.6}Fe_{0.4}-Al_2O_3$ composite was consolidated from mechanically synthesized powders by pulsed current activated sintering method within 1 min. $5Cu_{0.6}Fe_{0.4}-Al_2O_3$ powder was synthesized from 3CuO and 2FeAI using the high energy ball milling. Dense $5Cu_{0.6}Fe_{0.4}-Al_2O_3$ with relative density of up to 95% was produced under simultaneous application of a 80 MPa pressure and the pulsed current. Mechanical properties and grain size of the composite were investigated.

• Nuclear Engineering and Technology
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• v.48 no.4
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• pp.893-905
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• 2016

Numerous advanced reactor concepts have been proposed to replace light water reactors ever since their establishment as the dominant technology for nuclear energy production. While most designs seek to improve cost competitiveness and safety, the implausibility of doing so with affordable materials or existing nuclear fuel infrastructure reduces the possibility of near-term deployment, especially in developing countries. The organic nuclear concept, first explored in the 1950s, offers an attractive alternative to advanced reactor designs being considered. The advent of high temperature fluids, along with advances in hydrocracking and reforming technologies driven by the oil and gas industries, make the organic concept even more viable today. We present a simple, cost-effective, and safe small modular nuclear reactor for offshore underwater deployment. The core is moderated by graphite, zirconium hydride, and organic fluid while cooled by the organic fluid. The organic coolant enables operation near atmospheric pressure and use of plain carbon steel for the reactor tank and primary coolant piping system. The core is designed to mitigate the coolant degradation seen in early organic reactors. Overall, the design provides a power density of 40 kW/L, while reducing the reactor hull size by 40% compared with a pressurized water reactor while significantly reducing capital plant costs.