• Journal of Biosystems Engineering
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• 제29권1호
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• pp.9-20
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• 2004

On the basis of design theory of soil inversion, two types of moldboard plow with secondary soil mover was designed and constructed to invert furrow slice at same position with furrow bottom. A series of soil bin experiment was carried to investigate the performance of prototypes. First prototype of new concept plow showed two kinds of problems during the preliminary experiment. For the plowing depth of 6cut the prototype did not invert the furrow slice, instead it just cut furrow bottom and the furrow slice returned to the original position. For the plowing depth of 8cm, there was soil clogging problem at the rear part of plow. From the above results it was concluded that the first prototype can not be used for the inversion of furrow slice at same position with furrow bottom. Second prototype could invert furrow slice at the same position with furrow bottom, but the performance was affected by soil moisture content soil hardness and plowing speed very much. For the higher soil moisture content, for the higher soil hardness and higher plowing speed, the prototype showed higher soil inversion performance. For the second prototype the inversion ratio was almost 100%, inversion angle was in the range of 90 to 100 degree and side displacement was less than 4 cm. But the furrow slice was not continuous, it was cut in the length of 30 to 40 cm. The reason why the furrow slice was cut in that length is blamed for the design of moldboard surface. The specific draft of prototype was in the range of 37.24 kN/㎡ to 42.14 kN/㎡ this value is a little higher than that of the conventional plow, or from 30.38 kN/㎡ to 33.32 kN/㎡. But the difference was not so big. The inversion performance of the second prototype for the field experiment was much better than that of soil bin experiment due to the better soil and operational conditions. Sticky and compacted soil conditions, and higher plowing speed was suitable for the plowing operation of the second prototype

• 한국주조공학회지
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• 제39권2호
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• pp.21-25
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• 2019

Microstructural and corresponding hardness changes of TiFe compounds with Zr (0~6 at%) or Ce (0~3 at%) were studied using samples prepared at different solidification rates. In arc-melted (TiFe)-Zr samples, the $Fe_{23}$ $Zr_6$ and $(Ti,\;Zr)_2Fe$ phases formed in the TiFe matrix, while in the (TiFe)-Ce sample, the $CeO_2$ phase formed along the grain boundary of the TiFe matrix. As the Zr content was increased, the volume fractions of the $Fe_{23}$ $Zr_6$ and $(Ti,\;Zr)_2Fe$ phases increased, forming a network structure. Accordingly, the hardness values of the samples also increased. With a small addition of Ce of approximately 0.1 at%, the as-cast microstructure could be effectively refined, reducing the average grain boundary diameter from ${\sim}100{\mu}m$ to ${\sim}14{\mu}m$. In the rapidly solidified sample prepared through a melt-spinning method, the constituent phases were identical to those of the arc-melted samples while the grains were refined. The microstructural changes of TiFe alloys can affect the hydrogen storage ability as well as the mobility of the hydrogen atoms in the alloys.

• 한국항행학회논문지
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• 제11권1호
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• pp.1-8
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• 2007

본 논문에서는 해양/항공안전, 차량항법, 정밀농업, 정밀측량 등 우리사회 전반에 걸쳐 이용자가 급속히 확산되고 있는 GPS(Global Positioning System) 인프라에 대한 이용 불능상태를 대비하여 국가항법체계의 혼란을 예방하고 전파항법에 대한 BACK-UP 기능을 부여할 수 있는 지상 송신국 기반의 로란-C 항법의 활용을 제안하였다. 로란-C의 활용가치를 높이기 위한 위치오차 개선방안으로 ASF (Additional Secondary Phase Factor) 산출과 적용실험을 실시하였다. 그 결과로 로란-C 위치오차 100~400m를 10~65m로 현저히 개선할 수 있다는 결론에 도달하게 되었다. 또한 육상지역의 ASF보정테이블 이용 시 산출 범위는 복합매질과 굴곡면을 가만할 때 위도, 경도 10분 이내가 적절할 것으로 판단되며 향후 한반도 전역을 대상으로 한 ASF 보정테이블 적용시 현저한 위치오차개선과 GPS BACK-UP 기능수행이 가능할 것으로 판단되어진다.

• 열처리공학회지
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• 제13권1호
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• pp.27-34
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• 2000

This present study were investigated effect of Ni contents on the microstructure and strength characteristic in 9Cr ferritic heat-resistant steel added 1.7%W in place of Mo in order to restrain laves phase formation. The result obtained from this study are as follow. Volume fraction, number of particles per unite area and particle size of carbide decreased with increase of Ni contents. Other side, carbides of $M_{23}C_6$ type was mainly precipitated in this steel, but laves phases could not precipitated in spite of increasing of aging time. With increase of tempering temperature, hardness was increased, and maximum value was showed around 873k by secondary hardening due to precipitation of $W_2C$ type carbide and then, was decreased. Tensile and yield strength due to decrease precipitation amount of carbide and number of particles per unite area was decreased, but elongation and impact value was increased. In case of aged specimen after tempering than tempered specimen, strength was higher and elongation was lower due to increasing of precipitated amount of carbide and number of particles per unite area.

• Journal of the Korean Wood Science and Technology
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• 제46권5호
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• pp.527-540
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• 2018

본 연구에서는 온열욕 겸용을 위해 제작한 숯가마와 전통식 숯가마에서 제조한 백탄의 특성에 대해서 비교, 검토하였다. 온열욕 겸용 숯가마는 밀폐된 숯가마에서 발생하는 미세먼지 및 유해가스와 같은 환경문제를 최소화하고 편안함과 안전성을 고려하여 제작하였다. 온열욕 겸용 숯가마에서 제조한 백탄은 전통식 숯가마의 백탄보다 회분과 휘발분이 다소 높았고 고정탄소가 다소 낮았다. 온열욕 겸용 숯가마에서 생산된 백탄의 밀도는 기존의 전통식 숯가마 백탄보다 약간 높았지만, 평형함수율과 pH는 거의 차이가 없었다. 발열량, 정련도, 경도와 해부학적 구조는 숯가마에 따른 차이가 없었다. 결론적으로 온열욕 겸용을 위해 개량된 숯가마에서 제조한 백탄은 국립산림과학원의 품질인증기준을 충족하였고, 온열욕 겸용 숯가마는 목탄제조에도 적합한 것으로 판단되었다.

• Journal of Welding and Joining
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• 제32권2호
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• pp.48-53
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• 2014

This study was carried out to investigate the effect of postweld heat treatment(PWHT, 930, 1080, $1230^{\circ}C$) on the microstructure, phase formation, pitting corrosion and mechanical properties such as hardness, tensile strength and impact values of super duplex stainless steel(UNS S32750) multipass welds. Based on the microstructural examination and X-ray diffraction analysis, it was found that the ${\sigma}$ phase was formed in the welds heat treated at $930^{\circ}C$ in which the ferrite content greatly decreased into 5~10% in the welds. The secondary austenite was formed in the reheated zone of welds and redissolved into ferrite with increasing heat treatment temperatures. The tensile strength and impact values of welds heat treated at $930^{\circ}C$ were the lowest and revealed the brittle fracture surface. The weight loss by pitting corrosion increased with test temperatures. It was confirmed that pitting corrosion occurred mainly in secondary austenite of reheated zones. The postweld heat treatment temperature is recommended to be in the range of $1050{\sim}1150^{\circ}C$.

• 대한금속재료학회지
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• 제50권9호
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• pp.645-651
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• 2012

This study investigated changes in phase fraction caused by the addition of Mo, as well as the subsequent behaviour of N and its effect on the mechanical properties of welded 24Cr-N duplex stainless steel weld metals. Filler metal was produced by fixing the contents of Cr, Ni, N, and Mn while adjusting the Mo content to 1.4, 2.5, 3.5 wt%. The delta ferrite fraction increased as the Mo content increased. In contrast, the ${\gamma}$ fraction decreased and changed from a round to an acicular shape. Secondary austenite (${\gamma}^{\prime}$) was observed in all specimens in a refined form, but it decreased as the Mo content increased to the extent that it was nearly impossible to find any secondary austenite at 3.5 wt% Mo. Both tensile and yield strengths increased with the addition of Mo. In contrast, the highest value of ductility was observed at 1.41 wt% Mo. At all temperatures, impact energy absorption showed the lowest value at 3.5 wt% Mo, at which the amount of ${\delta}$-ferrite was greatest. There was no significant temperature dependence of the impact energy absorption values for any of the specimens. As the fraction of ${\gamma}$ phase decreased, the amount of N stacked in the ${\gamma}$ phase increased. Consequently, the stacking fault energy decreased, while the hardness of ${\gamma}$ increased.

• Advances in environmental research
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• 제9권4호
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• pp.233-249
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• 2020

To date, there is no central wastewater (WW) treatment plant in Erbil city, Kurdistan region, Iraq. Therefore, raw WW disposes to the environment and sometimes it used directly for irrigation in some areas of Erbil city. Disposal of the untreated WW to the natural environment and using for irrigation it causes problems for the people and the environment. The aims of the current work were to study the characteristics, design of primary and different secondary treatment units and reusing of produced WW. Raw WW samples from Ashty city-Erbil city were collected and analyzed for twenty three quality parameters such as Total Suspended Solids (TSS), total dissolved solids, total volatile and non-volatile solids, total acidity, total alkalinity, total hardness, five-day Biochemical Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), biodegradability ratio (BOD5/COD), turbidity, etc. Results revealed that some parameters such as BOD5 and TSS were exceeded the standards for disposal of WW. Design and calculations for primary and secondary treatment (biological treatment) processes were presented. Primary treatment units such as screening, grit chamber, and flow equalization tank were designed and detailed calculation were illustrated. While, Conventional Activated Sludge (CAS), Sequencing Batch Reactor (SBR) and Moving Bed Biofilm Reactors (MBBR) were applied for the biological treatment of WW. Results revealed that MBBR was the best and economic technique for the biological treatment of WW. Treated WW is suitable for reusing and there is no restriction on use for irrigation of green areas inside Ashty city campus.

• 한국주조공학회지
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• 제37권6호
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• pp.199-206
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• 2017

In this study, the variations of microstructures and tensile properties of Ti-(44-54)at.%Al binary alloys were investigated. The heat-treated microstructure depended greatly on their solidification structure and annealing temperature. We measured the variations of volume fractions of primary and secondary lamellar structure as a function of the heat treatment temperature in a Ti-47at.%Al alloy. The variation of ductility as a function of Al content was in good agreement with the change of fracture mode in the tensile fracture surface. It can be inferred that the variations of yield stress and hardness of ${\gamma}$ phase in a single ${\gamma}$-phase field region are enhanced by anti-site defects created by deviations from the stoichiometric composition. In a Ti-47at.%Al alloy within the (${\alpha}_2+{\gamma}$) two-phase field, the yield stress tended to be the maximum at a near equal volume fraction of lamellar and ${\gamma}$ grains. The ductility depended sensitively on the overall grain size and Al content. The calculation of fracture strain using Chan's model indicated that the change of ductility as a function of annealing temperature was primarily determined by the variations in the overall grain size and lamellar volume fraction.

• 한국재료학회지
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• 제19권2호
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• pp.85-89
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• 2009

Nano-crystalline hydroxyapatite (HAp) films were formed at the Ti surface by a single-step microarc oxidation (MAO), and HAp-zirconia composite (HZC) films were obtained by subsequent chemical vapor deposition (CVD) of zirconia onto the HAp. Through the CVD process, zero- and one-dimensional zirconia nanostructures having tetragonal crystallinity (t-ZrO2) were uniformly distributed and well incorporated into the HAp crystal matrix to form nanoscale composites. In particular, (t-$ZrO_2$) was synthesized at a very low temperature. The HZC films did not show secondary phases such as tricalcium phosphate (TCP) and tetracalcium phosphate (TTCP) at relatively high temperatures. The most likely mechanism for the formation of the t-$ZrO_2$ and the pure HAp at the low processing temperature was proposed to be the diffusion of $Ca^{2+}$ ions. The HZC films showed increasing micro-Vickers hardness values with increases in the t-$ZrO_2$ content. The morphological features and phase compositions of the HZC films showed strong dependence on the time and temperature of the CVD process. Furthermore, they showed enhanced cell proliferation compared to the $TiO_2$ and HAp films most likely due to the surface structure change.