• Journal of Ecology and Environment
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• 제48권2호
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• pp.173-181
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• 2024

Background: Pollination is an ecosystem service of utmost importance for agriculture. In this context, the study aimed to evaluate the pollination service of naturally occurring bees and after densification with colonies of stingless bees (Nannotrigona testceicornis and Tetragonisca angustula) in commercial strawberry plantation. The study was carried out in the four seasons of the year and under two experimental conditions: natural pollination (NP) and pollination under bee densification. The supply of flowers and bee density were estimated. For bee densification, four boxes of colonies of Iraí bees and four of Jataí bees were placed near the strawberry plantation. Five treatments were established for each condition, considering NP and pollination with bee densification on different days from flower anthesis, ranging from the 1st to the 5th day. Fruits were harvested, quantified, and submitted to evaluations to determine biometry, degree of deformity, and percentage of fertilized achenes. Results: There was a higher density in summer compared to other seasons in both conditions evaluated. The weight was greater (20.19 g) when fruits were pollinated on the first day after floral anthesis under pollination conditions with bee densification. It was observed that free pollination provided fruits with greater a greater of deformation of flowers on the fourth and fifth day after anthesis. However, when bee density became higher, the greatest degree of deformity was observed only in fifth-day fruits. The densification with stingless bees provided a 50% increase in the number of bees present on strawberry plants in summer and also a 15% increase in fruit weight and the occurrence of a lower degree of fruit deformity. Conclusions: Density with stingless bees provided a 50% increase in the number of bees present on strawberry plant in the summer, with an improvement in fruit quality and aggregate commercial value, providing a 15% increase in fruit weight and a lower degree of deformity under the conditions of densification of Iraí (N. testceicornis) and Jataí (T. angustula) bees. Under the evaluated conditions, the introduction of stingless bee boxes in the summer is recommended.

• 한국분말재료학회지
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• 제15권5호
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• pp.365-370
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• 2008

In this study, bottom-up powder processing and top-down severe plastic deformation processing approaches were combined in order to achieve both full density and grain refinement with least grain growth. The numerical modeling of the powder process requires the appropriate constitutive model for densification of the powder materials. The present research investigates the effect of representative powder yield function of the Shima-Oyane model and the critical relative density model. It was found that the critical relative density model is better than the Shima-Oyane model for powder densification behavior, especially for initial stage.

• 대한기계학회논문집A
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• 제22권2호
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• pp.330-342
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• 1998

The effect of rubber mold on densification behavior of pure iron powder was investigated under cold isostatic pressing. The thickness effect of rubber mold was also studied. The elastoplastic constitutive equation based on the yield function of Shima and Oyane was implemented into the finite element program(ABAQUS) to predict compaction responses of metal powder under cold isostatic pressing. The hyperelastic constitutive equation based on Moony-Rivlin and Ogden strain energy potentials was also employed to analyze deformation of rubber mold. The coefficients of the strain energy potentials were obtained from tension and volumetric compression data of rubber. Finite element results were compared with experimental data for densification of pure iron powder under cold isostatic pressing.

• 한국세라믹학회지
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• 제36권11호
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• pp.1261-1265
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• 1999

Effect of SiC particle size of the densification of Al2O3-SiC composite during pressureless sintering was investigated. Two types of SiC powders having average particle size of 0.15${\mu}{\textrm}{m}$ and 3${\mu}{\textrm}{m}$ were used. Densification rate of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was slower than that of the specimen containg 3${\mu}{\textrm}{m}$ SiC particles. Although the relative density of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was below 90% of theoretical density after sintering at 155$0^{\circ}C$ the complete closure of open pores occurred. Therefore full densification could be obtained by subsequent HIP. On the other hand in the specimen containing 3${\mu}{\textrm}{m}$ SiC particles the complete closed pore was observed at 95% of theoretical density. Such a fast pore closure in the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles is likely to occur as a result of dense reaction layer formation on the specimen surface which is attributed to the high reactivity of small size particles with sintering atmosphere.

• 한국분말재료학회지
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• 제4권2호
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• pp.113-121
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• 1997

The densification of the compacts of Co+32%Cr+20%W+l.5%C, Co+32%Cr+20%W+3.0%C and Co+32%Cr+20%W+4.5%C sintered under $H_2$ gas or vacuum was investigated. The effect of V and B addition on the densification was also investigated. The densification of these compacts were always incomplete regardless of sintering atmosphere, temperature and time. The amounts of oxygen and carbon in compacts sintered in $H_2$ for 3.6ks at 1523K were 0.105~0.160 mass% and 0.33~0.89 mass%, respectively. And those in vacuum were 0.028~0.032% and 0.957~4.08%, respectively. Relative density(Ds) of Co+29%Cr+17%W+3.0%C compact containing 6%V and Co+32%Cr+20%W+2.97%C compact containing 0.03%B were 99 and 100%, respectively, indicating complete densification by solid phase sintering. Victors hardness of sintered compacts containing 6%V or 0.03%B were 632 and 568, showing 50~60% increase in comparison to those without V or B. These results can be explained in terms of oxidation/reduction of oxides and equilibrium pressure of CO in isolated pore, instead of presence of liquid formation and grain boundary separation from pores due to large grain growth.

• 한국세라믹학회지
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• 제52권6호
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• pp.449-454
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• 2015

The fabrication process of zirconia gel-casting was studied to obtain dense zirconia on a large scale or with complicated shapes. As an experimental parameter, two different particle sizes ($0.1{\mu}m$ and $0.7{\mu}m$) of zirconia powder were applied to the gel-casting process. The viscosity behavior of slurries incorporating 40 vol% of zirconia powder was examined as a function of the dispersant content and the solid load to determine the optimum dispersion conditions. In addition, the gelation time with an initiator, the de-binding behavior, and the main factors affecting densification were examined. The densification of the gel-casted zirconia green body depended on the mixing ratio between the monomer and the dimer and on the zirconia particle size. A green body with a small particle size of $0.1{\mu}m$ showed less densification, with a relative density of 93%. This may be due to the excess number of bubbles created through interactions between the larger particle surface and polymer additives during the ball-milling process.

• 한국재료학회지
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• 제23권4호
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• pp.250-254
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• 2013

In order to increase the toughness of ZTA(zirconia toughened alumina) ceramics, the present study focused on rearrangement and densification of particles according to the particle size of the parent material. When rough alumina was used for production of ZTA, densification behavior was observed in the specimen sintered at a temperature over $1550^{\circ}C$. However, it was found that the densification behavior was occurred in the specimen sintered at $1450^{\circ}C$ when fine alumina powder was used. High relative density exceeding 98% was obtained when fine alumina powder was mixed with 15 wt% of 3Y-TZP and sintered at $1600^{\circ}C$. Also, a hardness of 1820.2 Hv was obtained when a specimen containing 10 wt% of 3Y-TZP was sintered at $1600^{\circ}C$. In the case of 3Y-TZP containing rough alumina powder that had been sintered the hardness value was around 1720.3 Hv. It was predicted that an improved toughening effect in ZTA could be achieved by using finer alumina powder as the parent material.

• 한국세라믹학회지
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• 제32권7호
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• pp.783-792
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• 1995

Sol-Gel derived ferroelectric PZT thin films were fabricated on ITO/Glass and Si/SiO2 substrates. In order to investigate the effect of catalysts on the densification and crystallization of PZT thin films, a nitric acid or ammonium hydroxide was added to the PZT stock solution at the state of partial hydrolysis reaction. The measured pH for a stable PZT sol was 5.2~9.3. In case of an acid-catalyzed PZT sol, a highly condensed particulate PZT sol was formed by accelerating the hydrolysis reaction. But weakly branched polymeric PZT sol was formed with a base-catalyzed condition. The difference in densification behavior was not found in the pH range of added catalyst, but the refractive index of PZT thin film was increased rapidly as the annealing temperature increased. The PZT thin film annealed at 54$0^{\circ}C$ for 10 min was fully densified and its refractive index was above 2.4. When the annealing temperature increased, the transition from the pyrochlore phase to perovskite appeared at 54$0^{\circ}C$. The base-catalyzed PZT thin film suppressed to form the pyrochlore phase and proceeded effectively to convert the perovskite phase. This was due to the formation of polymeric molecular structure by controlling the hydrolysis and condensation reaction through the additiion of the ammonium hydroxide.

• Nuclear Engineering and Technology
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• 제17권2호
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• pp.116-128
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• 1985

본 논문에는 이산화 우라늄 소결체의 노내고밀화현상을 온도와 미세구조의 함수로 정화하게 예측할 수 있는 기계론적 이론 모형이 개발.기술되어있다. 이 모형은 $UO_2$ 소결체의 결정 입계내에서 공극(vacancy)이 생성 이동되고, 결정입계에서 공극이 소멸되는 현상을 고려하고 있으며, 이 과정에서 일어나는 고밀화의 크기가 핵분열율, 조사시간, $UO_2$ 소결체밀도, 기공 크기의 분포, 결정입크기 및 온도의 함수로 기술되어 있다. 본 모형의 기공 수축에 대한 결과식은 Assmann과 Stehle가 유도한 4개의 온도 영역에 대한 결과식과는 상이한 것으로서, 소결체의 모든 온도 영역에 직접 적용된다. 본 모형에 의한 노내고밀화 크기의 예측치는 실험자료와 아주 잘 일치하며, KEFDA 전산코드에 사용된 경험적 실험 연산식에 비하여 고밀화의 경향과 절대치를 보다 정확히 예측한다.

• 한국세라믹학회지
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• 제46권5호
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• pp.467-471
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• 2009

Effects of boron and carbon on the densification and thermal decomposition of an AlN-SiC-$TiB_2$ system were investigated. $SiO_2$ was mostly removed by the addition of carbon, while $Al_2O_3$ formed $Al_4O_4C$ and promoted the densification of the systems above $1850^{\circ}C$. Rather porous specimens were obtained without the additives after hot pressing at $2100^{\circ}C$, while densification was mostly completed at $2000^{\circ}C$ by using the additives. The sintering temperature decreased further to $1950^{\circ}C$ by applying spark plasma sintering. The additives promoted the shrinkage of AlN by forming a liquid phase which was originated from the carbo- and boro-thermal reduction of $Al_2O_3$ and AlN.