• Journal of the Korean Ceramic Society
• /
• v.44 no.7
• /
• pp.343-348
• /
• 2007

Alumina/silver nanocomposites were fabricated using a soaking method through a sol-gel route to construct an intra-type nanostructure. The pulse electric-current sintering (PECS) technique was used to sinter the nanocomposites. Several specimens were annealed after sintering. The microstructure, mechanical properties, critical frontal process zone (FPZ) size, and thermo-mechanical properties of the nanocomposites were estimated. The relative densities of the specimens sintered at 1350 and $1450^{\circ}C$ were 95% and 99%, respectively. The maximum value of the three-point bending strength was found to be 780 MPa for the $2{\times}2{\times}10 mm$ specimen sintered at $1350^{\circ}C$. The fracture toughness of the specimen sintered at $1350^{\circ}C$ was measured to be $3.60 MPa{\cdot}m^{1/2}$ using the single-edge V-notched beam (SEVNB) technique. The fracture mode of the nanocomposites was transgranular, in contrast to the intergranular mode of monolithic alumina. The fracture morphology suggested that dislocations were generated around the silver nanoparticles dispersed within the alumina matrix. The specimens sintered at $1350^{\circ}C$ were annealed at $800^{\circ}C$ for 5 min, following which the maximum fracture strength became 810 MPa and the fracture toughness improved to $4.21 MPam^{1/2}$. The critical FPZ size was the largest for the specimen annealed at $800^{\circ}C$ for 5 min. Thermal conductivity of the alumina/silver nanocomposites sintered at $1350^{\circ}C$ was 38 W/mK at room temperature, which was higher than the value obtained with the law of mixture.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.6
• /
• pp.1302-1307
• /
• 2006

This study describes the preparation of high-performance photocatalyst and its environmental applications. We prepared visible-light response nano-particle photocatalyst exhibiting the similar photocatalytic activity with $TiO_2$, dispersed $TiO_2$ on $SiO_2$ with an active rutile type titanium oxide prepared at low temperature. The binder and stable photocatalytic $TiO_2$ sol for photocatalytic system were also prepared. Such products were evaluated by UV/Vis spectrometer, X-ray diffraction analysis, SEM, measurement of photocatalytic activities and surface area, mechanical properties of $TiO_2$-coated surfaces. The results obtained can be applied in efficient photocatalytic systems using POF and metal plate for the purification of air.

• Parasites, Hosts and Diseases
• /
• v.61 no.1
• /
• pp.2-14
• /
• 2023

Trichomonas vaginalis is a flagellated protozoan that causes trichomoniasis, a common nonviral sexually transmitted infection. T. vaginalis infection is asymptomatic in most infected men but can lead to chronic infection. The inflammatory response to chronic T. vaginalis infection may contribute to prostatic diseases, such as prostatitis and benign prostatic hyperplasia (BPH); however, studies on the relationship between T. vaginalis infection and prostate diseases are scarce. In this review, we discuss evidence from our studies on the involvement of T. vaginalis in the pathogenesis of prostate diseases, such as prostatitis and BPH. Studies of prostatitis have demonstrated that the attachment of T. vaginalis trophozoite to prostate epithelial cells (PECs) induces inflammatory cytokine production and inflammatory cell migration, leading to prostatitis. T. vaginalis also causes pathological changes, such as inflammatory cell infiltration, acinar changes, interstitial fibrosis, and mast cell infiltration, in prostate tissues of infected rats. Thus, T. vaginalis is considered an infectious agent that triggers prostatitis. Meanwhile, studies of prostatic hyperplasia revealed that mast cells activated by T. vaginalis-infected prostate cells secreted inflammatory mediators, such as β-hexosaminidase and tryptase, which promoted proliferation of prostate stromal cell (PSC). Moreover, interleukin-6 produced by proliferating PSCs induced the multiplication of BPH-1 epithelial cells as a result of stromal-epithelial interaction, suggesting that the proliferation of T. vaginalis-infected prostate cells can be induced through crosstalk with mast cells. These collective findings suggest that T. vaginalis contributes to the progression of prostatitis and prostatic hyperplasia by creating an inflammatory microenvironment involving PECs and PSCs.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 2000.06a
• /
• pp.59-64
• /
• 2000

Silicon nitride ceramics with various α/β phase ratio were fabricated by controlling sintering conditions of PECS process. Mechanical properties varied systematically with α/β ratio. Young's modulus and hardness increased with α-Si₃N₄ volume fraction, and fracture strength and toughness increased with β-Si₃N₄ content.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.15 no.2
• /
• pp.132-136
• /
• 2003

For the study of performance evaluation on different shape heat exchangers that have the same energy consumption in a refrigerator, we make performance evaluation coefficient (PEC) which can distinguish performance of different shape heat exchangers. The results were reported in order to compare with for the dry frosting and wet frosting test as various definition of PECs. Results showed that PEC of dry frosting test is higher than that of wet frosting test because attached water droplet increases pressure drop of air-side then this decreases performance of heat exchanger.

• The Korean Journal of Ceramics
• /
• v.5 no.4
• /
• pp.395-399
• /
• 1999

MgO/metal nanocomposite powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with magnesia powder. After calcined in air, these powders were reduced by hydrogen. Densified nanocomposites were successively obtained by Pulse Electric Current Sintering (PECS) process. The dispersed metal partical size depended on temperature and time in calcination and reduction processes. The phase analyses in the synthesized powders as a functioni of temperature were tracked using a dynamic high temperature X-ray diffractioni (HTXRD) system. Phase and crystallite size analyses were done using X-ray diffractioni and TEM. The MgO/metal nanocomposites were successfully fabricated, and ferromagnetic responses with enhanced coercive force were also investigated for these composites.

• Journal of Powder Materials
• /
• v.8 no.3
• /
• pp.210-213
• /
• 2001

$Si_3N_4$/TiN nano/nano-type composites were successfully fabricated by the combination of a mechano-chemical grinding (MCG) method and a short time sintering process, and their wear resistance was evaluated. Powder mixtures of $\alpha-Si_3N_4$and Ti were prepared using mechano-chemical grinding process and the resulting nanocomposite powder mixtures were consolidated using pulsed electric current sintering (PECS). TEM observation showed that the nano/nano-type composites consisted of homogeneous and very fine matrix grains with the size less than 100 nm. The obtained $Si_3N_4$-based nano/nano-type showed high wear resistance and electric discharge machinability.

• Proceedings of the Korean Information Science Society Conference
• /
• 2002.10d
• /
• pp.673-675
• /
• 2002

본 논문에서는 전자메일을 사용자 적합도(선호도)를 기준으로 분류함에 있어 좀더 사용자 선호도를 반영할 수 있는 시스템 구조를 제안한다. 사용자 선호도는 2단계에 걸쳐서 반영되는데, 1단계에서는 사용자 관련메일로 판단된 메일정보추출어구(MIWs)들로부터 사용자 동적 시소러스(DS)의 갱신을 통해 이뤄지며, 2단계에서는 DS로부터 추출된 키워드들을 갖고 유전자 알고리즘을 작동시킬 때, 사용자선호도 feedback을 받음으로서 이뤄진다. 테스트는 kaist뉴스그룹으로부터 임의로 추출된 5개 분야 10개씩의 메일을 sample로 사용하였으며, DS로부터 추출된 키워드가 유전자알고리즘 모듈을 통해 사용자 feedback을 받았을 때, 세대가 거듭함에 따라 사용자가 요구하는 threshold 값에 근사하게 관련키워드들이 수집되었다. 그 결과 사용자 전자메일분류시스템(PECS)의 성능도 폴더정보키워드(FIWs)의 변화에 따라 향상될 수 있음을 확인하였다.

• Proceedings of the Korean Information Science Society Conference
• /
• 2002.04b
• /
• pp.472-474
• /
• 2002

본 논문에서는 전자메일을 사용자 적합도(선호도)를 기준으로 분류하기 위한 구조를 제안한다. 분류는 1차 분류와 2차 분류로 나눠지는데, 1차 분류에서는 사용자 적합도를 판단하기 위해 사용자 관련 정보로부터 동적 시소러스를 구축하고, 구축된 시소러스와의 비교를 통해 사용자에게 유용한 메일인지 아닌지를 결정하고, 2차 분류에서는 사용자가 지정한 폴더키워드를 중심으로 사용자 시소러스로부터 유전자 알고리즘을 이용해 추출한 키워드들과의 적합도 비교를 통해서 특정 폴더로의 분류가 이뤄지게 된다 테스트에는 메일 정보값(Mail Information Word)을 추출하기 위해 HAM(Hangup Analysys Module)을 포함하는 메일정보추줄 에이전트를 사용하였고, mail의 subject와 본문(body)로부터 추출된 16개의 word정보와 시소러스 적합도 정보, 분류 적합도 정보를 하나의 데이터구조로 사용하였다. 이러한 통할된 시스템 구조와 data structure를 이용해 mail을 사용자의 선호도에 따라. 1차와 2차에 걸친 분류시 분류가 사용자 선호도에 근접하게 이루어 질 수 있음을 확인하였다.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.621-622
• /
• 2006

In this paper, we show some experimental results of binder-free WC sintered by Pulsed Electric Current Sintering (PECS) also known as Field Assisted Sintering Technology (FAST). These binder-free WC have extremely hardness and stiffness. However, these mechanical properties are dependent on the sintering condition, e.g., maximum temperature, applied pressure, etc. We show some relationship between mechanical properties and sintering condition to improve to sinter the binder-free WC.