• Journal of the Korean Physical Society
• /
• 제73권12호
• /
• pp.1827-1833
• /
• 2018

X-ray grating interferometry has been an active area of research in recent years. In particular, various studies have been carried out for the practical use of the x-ray grating interferometer in medical and industrial fields. For the commercialization of the system, it needs to be optimized for its application. In this study, we have developed a prototype of the compact high energy x-ray grating interferometer of which the high effective energy and compactness is of our primary feature of design. We have designed the Talbot-Lau x-ray interferometer in a symmetrical geometry with an effective energy of 54.3 keV. The system has a source-to-analyzer grating distance of 788.4 mm, which is compact enough for a commercial product. In a normal operation, it took less than ten seconds to acquire a set of phase stepping images. The acquired images had a maximum visibility of about 15%, which is relatively high compared with the visibilities of the other high-energy grating interferometric systems reported so far.

• 대한금속재료학회지
• /
• 제49권1호
• /
• pp.85-91
• /
• 2011

Alnico magnets can be used as magnetic bearings for the precise electric power measuring instruments such as watt-hour meters because they have high remanence ($B_r$), relatively high maximum energy product ($(BH)_{max}$), and excellent temperature stability. In this study, Alnico composite magnets were fabricated by appropriately mixing alnico alloy powders with epoxy resin and binder. The Alnico powders mixed with epoxy resin and a hardening agent with a mixing ratio of 96:4 were pressed and then cured to be a toroid-type ring magnet with an outer diameter (${\Phi}_{out}$) of 15 mm, an inner diameter (${\Phi}_{in}$) of 6.5 mm and a thickness (t) of 2.5 mm, respectively. The magnetic properties of the Alnico ring magnets were varied with the mixing ratio of Alnico powders that possess different average particle sizes. The Alnico ring magnet prepared by mixing 5 wt% of $50{\mu}m$ (small size) powder, 15~20 wt% of $150{\mu}m$ (medium size) powder, and 75~80 wt% of $300{\mu}m$ (large size) powder showed the best magnetic properties (remanent induction, coercive force, maximum energy product, and surface flux density). In addition, measurements of temperature and moisture characteristics for the Alnico ring magnets showed that the surface flux densities of the N and S poles decreased little and the repulsive distance between the magnets decreased as small as 0.05 mm after 10 days.

• 한국자기학회지
• /
• 제6권1호
• /
• pp.48-53
• /
• 1996

자이로스코프에서 기울어진 회전자를 바로 세우는 역할을 하는 것이 토커이다. 본 연 구에서는 최대입력각속도 조건을 만족하면서 주어진 자석성능으로 최대의 특성을 낼 수 있는 설계에 대하여 알아보고자 한다. 자이로스코프의 기계적 치수가 결정되면 토커의 치수는 제한된다. 즉 코일이 위치하는 공간이 제한되므로 코일의 굵기가 결정되면 권선수도 정해지게 된다. 이 치수들을 이용하여 토커의 환산계수를 계산한 후, 코 일에 흐를 수 있는 최대 전류를 계산하면, 최대 입력각속도가 계산되어진다. 토커의 특성해석은 3차원 유한요소법을 이용하였으며, 유한요소 해석 결과로부터 토커의 환산 계수를 계산하였다. 실제 제작한 자이로의 성능실험을 통하여 제안된 토커 설계 알고리즘의 유용함을 입증한다.

• Journal of Information Processing Systems
• /
• 제16권6호
• /
• pp.1343-1358
• /
• 2020

In the stagewise arithmetic orthogonal matching pursuit algorithm, the weak threshold used in sparsity estimation is determined via maximum iterations. Different maximum iterations correspond to different thresholds and affect the performance of the algorithm. To solve this problem, we propose an improved variable weak threshold based on the stagewise arithmetic orthogonal matching pursuit algorithm. Our proposed algorithm uses the residual error value to control the weak threshold. When the residual value decreases, the threshold value continuously increases, so that the atoms contained in the atomic set are closer to the real sparsity value, making it possible to improve the reconstruction accuracy. In addition, we improved the generalized Jaccard coefficient in order to replace the inner product method that is used in the stagewise arithmetic orthogonal matching pursuit algorithm. Our proposed algorithm uses the covariance to replace the joint expectation for two variables based on the generalized Jaccard coefficient. The improved generalized Jaccard coefficient can be used to generate a more accurate calculation of the correlation between the measurement matrixes. In addition, the residual is more accurate, which can reduce the possibility of selecting the wrong atoms. We demonstrate using simulations that the proposed algorithm produces a better reconstruction result in the reconstruction of a one-dimensional signal and two-dimensional image signal.

• 환경위생공학
• /
• 제16권1호
• /
• pp.61-65
• /
• 2001

To review mass transfer trays from a process of view, the dependence of efficiency in loading ranges and maximum loadings with an acceptable efficiency of traditional tray have to be known. It is reported about the performance of the metallic Dualflex, relatively new high performance packing. Absorption, desorption and rectification tests as well as pressure drop and maximum capacity are concerned, indicate the superiority of the Dualflex over the general packing of comparable, main process. The process engineering characteristics show that Dualflex can be applied for all mass transfer precesses and it is to be recommended especially for those high capacity separations which requite allow low pressure drop because of the thermal sensibility of the product or because of the need of energy saving.

• Earthquakes and Structures
• /
• 제1권1호
• /
• pp.93-108
• /
• 2010

This paper investigates the seismic performance of existing reinforced concrete frames with wide beams mainly designed for gravity loads, as typically found in the seismic-prone Mediterranean area before the introduction of modern codes. The seismic capacity is evaluated in terms of the overall amount of input energy that the frame can dissipate/absorb up to collapse. This approach provides a quantitative evaluation that can be useful for selecting and designing an appropriate retrofit strategy. Six prototype frames representative of past construction practices in the southern part of Spain are designed, and the corresponding non-linear numerical models are developed and calibrated with purposely conducted tests on wide beam-column subassemblages. The models are subjected to sixteen earthquake records until collapse by applying the incremental dynamic analysis method. It is found that the ultimate energy dissipation capacity at the story level is markedly low (about 1.36 times the product of the lateral yield strength and yield displacement of the story), giving values for the maximum amount of energy that the frame can dissipate which are from one fourth to half of that required in moderate-seismicity regions.

• Bulletin of the Korean Chemical Society
• /
• 제20권10호
• /
• pp.1136-1144
• /
• 1999

The collision-induced reaction of gas-phase atomic hydrogen with hydrogen atoms chemisorbed on a silicon (001)-(2×1) surface is studied by use of the classical trajectory approach. The model is based on reaction zone atoms interacting with a finite number of primary system silicon atoms, which then are coupled to the heat bath, i.e., the bulk solid phase. The potential energy of the Hads‥Hgas interaction is the primary driver of the reaction, and in all reactive collisions, there is an efficient flow of energy from this interaction to the Hads-Si bond. All reactive events occur on a subpicosecond scale, following the Eley-Rideal mechanism. These events occur in a localized region around the adatom site on the surface. The reaction probability shows the maximum near 700K as the gas temperature increases, but it is nearly independent of the surface temperature up to 700 K. Over the surface temperature range of 0-700 K and gas temperature range of 300 to 2500 K, the reaction probability lies at about 0.1. The reaction energy available for the product states is small, and most of this energy is carried away by the desorbing H2 in its translational and vibrational motions. The Langevin equation is used to consider energy exchange between the reaction zone and the bulk solid phase.

• 방사성폐기물학회지
• /
• 제19권2호
• /
• pp.271-278
• /
• 2021

In this study, a chlorination technique for recycling Li₂ZrO₃, a reaction product of ZrO₂-assisted rinsing process, was investigated to minimize the generation of secondary radioactive pyroprocessing waste. It was found that the reaction temperature was a key parameter that determined the reaction rate and maximum conversion ratio. In the temperature range of 400-600℃, an increase in the reaction temperature resulted in a profound increase in the reaction rate. Hence, according to the experimental results, a reaction temperature of at least 450℃ was proposed to ensure a Li₂ZrO₃ conversion ratio that exceeded 80% within 8 h of the reaction time. The activation energy was found to be 102 ± 2 kJ·mol^-1·K^-1 between 450 and 500℃. The formation of LiCl and ZrO₂ as reaction products was confirmed by X-ray diffraction analysis. The experimental results obtained at various total flow rates revealed that the overall reaction rate depends on the Cl₂ mass transfer rate in the experimental condition. The results of this study prove that the chlorination technique provides a solution to minimize the amount of radioactive waste generated during the ZrO₂-assisted rinsing process.

• 한국환경과학회지
• /
• 제17권3호
• /
• pp.351-357
• /
• 2008

In order to develope an efficient way for the synthesis of highly pure 1,4-sorbitan solution from sorbitol, some experimental studies were performed. The reaction showed first order reaction with activation energy of 118.3 KJ/mol. Color of the product solutions changed to brown with reaction temperature and reaction time. The equilibrium contents of 1,4-sorbitan increased with decrease in reaction pressure, but the content of major impurity, sorbide, showed maximum about 550 torr vacuum with $H_3PO_4$ catalyst. The reasonable catalyst configuration was 0.26 wt% PTSA and 1 wt% $H_3PO_2$ and optimum reaction temperature and pressure range was $110\sim120^{\circ}C$ and $700\sim720$ torr vacuum, respectively. At optimum reaction conditions, we could obtain white product solutions of highly pure 1,4-sorbitan with sorbide less than 10 wt%. This white product solution is advantageous for preparation of high quality span, anti-fogging agent.

• 한국환경보건학회지
• /
• 제30권5호
• /
• pp.395-401
• /
• 2004

In this study, lots of methods have been studing to utilize energy and decrease contaminated effluents. There has been great progress on IGCC (Integrated gasification combined cycle) to reduce thermal energy losses. The following results have been conducted from desulfurization experiments using waste shell to remove $H_{2}S$. Unreacted core model ior desulfuriration rate prediction of sorbent was indicated. These were linear relationship between time and conversion. So co-current diffusion resistance was conducted reaction rate controlling step. The sulfidation rate is likely to be controlled primarily by countercurrent diffusion through the product layer of calcium sulfide(CaS) formed. Maximum desulfurization capacity was observed at 0.631 mm for lime, oyster and hard-shelled mussel. The kinetics of the sorption of $H_{2}S$ by CaO is sensitive to the reaction temperature and particle size at $800^{\circ}C$, and the reaction rate of oyster was faster than the calcined limestone at $700^{\circ}C$.