• KIEAE Journal
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• v.17 no.3
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• pp.91-97
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• 2017

Purpose: Various studies on a light shelf are in progress, but it has the problem of glare occurrence. The present study suggested a diffusion film as the method for resolving the glare problem, and aimed to establish light shelf-related basic data by conducting the performance evaluation of a light shelf depending on the installation position of the diffusion film. Method: To carry out the light shelf performance evaluation depending on the diffusion film installation position, three cases were established: no diffusion film installation (Case 1), diffusion film installation on the reflector (Case 2), and diffusion film installation on the upper glass surface of the window for light shelf installation (Case 3); and the energy reduction performance, luminance, and luminance contrast were analyzed based on a testbed. Result: The conclusions of this study are as follows. 1) When the diffusion film was applied, the amount of light introduced through the light shelf decreased, and the average indoor illumination decreased accordingly. 2) For Case 3, the lighting energy reduction performance was identical to the lighting energy reduction efficiency of the existing light shelf; and for Case 2, it was found to be inappropriate as the lighting energy consumption increased compared to that of the existing light shelf. 3) The analysis of the glare for the cases established in this study showed that the luminance contrast was low for Case 3, and thus the glare problem could be minimized. 4) The specific angle of the light shelf could induce the glare problem by increasing the luminance depending on the external condition. 5) Based on the aforementioned contents, the installation position of the diffusion film for improving the lighting performance and glare problem of the light shelf was found to be the upper glass surface of the window for light shelf installation.

• Journal of Powder Materials
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• v.20 no.1
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• pp.13-18
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• 2013

In the present study, we systematically investigated the effect of Mn addition on nitrogenation behavior and magnetic properties of Sm-Fe powders produced by reduction-diffusion process. Alloy powders with only $Sm_2(Fe,Mn)_{17}$ single phase were successfully produced by the reduction-diffusion process. The coercivity of $Sm_2(Fe,Mn)_{17}$ powder rapidly increased during nitrogenation and reached the maximum of 637 Oe after 16 hours. After further nitrogenation, it decreased. In contrast, the coercivity of $Sm_2Fe_{17}$ powder gradually increased during nitrogenation for 24 hours. The coercivity of $Sm_2(Fe,Mn)_{17}$ powder was higher than that of $Sm_2Fe_{17}$ powder at the same condition of nitrogenation. It was considered that the Mn addition facilitates the nitrogenation of $Sm_2Fe_{17}$ powder and enhances the coercivity.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.842-846
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• 2010

In the present study, the reduction-diffusion method was employed to produce Sm-Fe alloy powder. It was confirmed that the amount of unreacted ${\alpha}-Fe$ in $Sm_2Fe_{17}$ matrix gradually decreased as the percentage of $Sm_2O_3$ increased. $Sm_2Fe_{17}$ single-phase powder was produced by the reduction-diffusion method with 40% excess $Sm_2O_3$. The Ca and Oxygen contents of the powder were approximately 300 ppm and 1600 ppm, respectively, after washing and acid treatment. By a subsequent nitrogenation, $Sm_2Fe_{17}N_x$ magnetic powders were produced. The coercivity of the powder increased with decreasing of the particle size by ball milling, and the highest coercivity of 2850 Oe was obtained after milling for 10 hours.

• Journal of the Korean Society of Combustion
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• v.4 no.2
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• pp.97-108
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• 1999

This numerical study was to investigate the effect of $CO_2$ addition on the structures and NOx formation characteristics in $CH_4$ counterflow diffusion flame. The importance of radiation effect was identified and $CO_2$ addition effect was investigated in terms of thermal and chemical reaction effect. Also the causes of NOx reduction were clarified by separation method of each formation mechanisms. The results were as follows : The radiation effect was intensified by $CO_2$ addition. Thermal effect mainly contributed to the changes in flame structure and the amount of NO formation but the chemical reaction effect also cannot be neglected. The reduction of thermal NO was dominant with respect to reduction rate, but that of prompt NO was dominant with respect to total amount.

• Proceedings of the IEEK Conference
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• 2003.11a
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• pp.461-464
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• 2003

This paper proposes the multi-level vector error diffusion for smear artifact reduction in the boundary regions. Smear artifact mainly results from a large accumulation of quantization error. Accordingly, to reduce these artifacts, the proposed method excludes the large quantization error in the error diffusion process by comparing the magnitude of the error vector with predetermined first threshold. In addition, if the vector norm of the difference between the error adjusted input vector and the primary co]or that has minimum vector norm for the error adjusted input vector is larger than second threshold, the error is excluded. As a result, the proposed method reduce smear artifact in the boundary region and produces visually pleasing halftone pattern.

• Nuclear Engineering and Technology
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• v.55 no.4
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• pp.1428-1438
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• 2023

A novel Fission Diffusion Synthetic Acceleration (FDSA) method is developed and implemented as a part of a hybrid neutronics method for source convergence acceleration and variance reduction in Monte Carlo (MC) criticality calculations. The acceleration of the MC calculation stems from constructing a synthetic operator and solving a low-order problem using information obtained from previous MC calculations. By applying the P₁ approximation, two correction terms, one for the scalar flux and the other for the current, can be solved in the low-order problem and applied to the transport solution. A variety of one-dimensional (1-D) and two-dimensional (2-D) numerical tests are constructed to demonstrate the performance of FDSA in comparison with the standalone MC method and the coupled MC and Coarse Mesh Finite Difference (MC-CMFD) method on both intended purposes. The comparison results show that the acceleration by a factor of 3-10 can be expected for source convergence and the reduction in MC variance is comparable to CMFD in both slab and full core geometries, although the effectiveness of such hybrid methods is limited to systems with small dominance ratios.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.3
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• pp.262-271
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• 2002

In PWM inverters used in traction motor drive systems, the switching frequency is restricted by their large power capacity and thus the electromagnetic acoustic noise is generated. To reduce such an audible noise, the new MRSF-PWM(Modified Random Switching Frequency PWM) method is proposed. In the Proposed MRSF-PWM method, both triangular wave and sawtooth wave are used together as carrier waves for harmonic diffusion and reference wave is generated by injecting 3rd harmonic into the stone wave to expand the linear control region of output voltages. To verify the validity of the proposed MRSF-PWM method, computer simulations are carried out. And the results show that the MRSF-PWM method is more excellent than other RPWM methods in the aspects of both linearity and harmonic diffusion md more effective than SPWM(Sinusoidal PWM) method for the reduction of an audible noise.

• Journal of Powder Materials
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• v.20 no.3
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• pp.197-202
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• 2013

A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffusion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solutions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to $10{\mu}m$ by controlling concentrations of the solutions and the average size of $2{\mu}m$ of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalting procedure, followed by reduction processes in Hydrogen ($H_2$) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and $Nd_2Fe_{14}B$ particles were formed. With Ca amount added to particles after $H_2$ reduction, intrinsic coercivity was changed from 1 to 10 kOe. In order to remove and leach CaO and residual Ca, de-ionized water and dilute acid were used. Acidic solutions were more effective to eliminate impurities, but Fe and Nd were dissolved out from the particles. Finally, $Nd_2Fe_{14}B$ magnetic particles were synthesized after washing in de-ionized water with a mean size of $2{\mu}m$ and their maximum energy product showed 9.23 MGOe.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.212-213
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• 2003

• Journal of Powder Materials
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• v.10 no.6
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• pp.436-442
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• 2003

The magnetic Nd-Fe-B powders were prepared by a thermochemical method, consisting of the processes of spray-drying, debinding, milling, H$_2$-reduction, Ca-reduction, and washing. The optimum process conditions were studied by microstructural and thermal analysis. The resultant Nd-Fe-B powder was spherical with the size of 1 ${\mu}{\textrm}{m}$. Effects of the process parameters of each step on the microstructure of the powders were investigated, and their magnetic properties were evaluated.