• 대한기계학회논문집B
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• 제25권5호
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• pp.688-696
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• 2001

Vaporizing characteristics of two GDI injectors with different spray angles were investigated using exciplex fluorescence method. Injector I has narrower spray angle, while injector II has wider one. The exciplex system of fluorobenzene and DEMA in a non-fluorescing base fuel of hexane was employed. In quantifying concentration of fuel vapor, quenching of concentration and temperature was corrected. Droplet size and velocity were also measured by PDPA under non-vaporizing condition. From obtaining the images of liquid and vapor phases, vaporizing GDI sprays could be divided as two regions: cone and mixing regions. For injector I, vortex region was not developed. High concentration of fuel vapor due to vaporization of many fine droplets was distributed near the spray axis. For injector II, droplets with the diameter of about 10 $\mu$m were distributed in the vortex region. The vortex region had high concentration of fuel vapor due to vaporization of these droplets. Particularly, higher and lower concentrations of fuel vapor were balanced at 2ms after the start of injection for injector II.

• Journal of Plant Biology
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• 제36권3호
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• pp.195-201
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• 1993

The room temperature fluorescence induction of chloroplasts was utilized as a probe to locate the site of inhibition by mercury, copper and zinc on PS II by mercury. Inhibitory effect of Hg2+ on electron transport activity was notable as compared with Cu2+ and Zn2+. At concentrations of HgCl2 over 50 $\mu$M, activities of PS II and whole-chain electron transport decreased more than 70%, while that of PS I decreased about 10~30%. This suggests that PS II is more susceptible to Hg2+ than PS I is. In the presence of diphenylcarbazide (DPC), 50 $\mu$M HgCl2 inhibited the reduction of dichlorophenolindophenol (DCPIP) about 50%. Addition of heavy metals induced marked decrease in maximal variable fluorescence/initial fluorescence [(Fv)m/Fo], but no changes in Fo. With various concentrations of heavy metals, changes of chlorophyll a fluorescence emitted by PS II showed gradual decrease in photochemical quenching (qQ), which indicates an increase in reduced state of electron acceptor, QA. Especially, the addition of HgCl2 caused a notable decrease of qQ. In the presence of 50 $\mu$M CuCl2, energy-depended quenching (qE) was completely reduced, whereas in the presence of 50 $\mu$M CuCl2 and ZnCl2 it was still remained. The above results are discussed on the effects of mercury in relation to water-splitting system and plastoquinone (PQ) shuttle system.

• 한국전기전자재료학회논문지
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• 제19권5호
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• pp.432-436
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• 2006

The $ZnGa_2O_4$ and Mn, Cr-doped $ZnGa_2O_4$ Phosphors were synthesized through conventional solid state reactions. The XRD patterns show that the $ZnGa_2O_4$ has a (3 1 1) main peak and a spinel phase. The emission wavelength of $ZnGa_2O_4$ showed main peak of 420 nm and maximum intensity at the sintering temperature of $1100^{\circ}C$. In the crystalline $ZnGa_2O_4$, the Mn shows green emission (510 nm, $^4T_1-^6A_1$) with a quenching concentration of 0.6 mol%, and the Cr shows red emission (705 nm, $^4T_2-^4A_2$) with a quenching concentration of 2 mol%. These results indicate that $ZnGa_2O_4$ Phosphors hold promise for potential applications in field emission display devices with high brightness operating in full color regions.

• 한국재료학회지
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• 제13권10호
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• pp.673-676
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• 2003

We have investigated $Al_{x}$ $Ga_{l-x}$ N/GaN epilayers (x = 0.08, 0.15) grown by metal organic vapor phase epitaxy on sapphire with photoluminescence(PL), and persistent photoconductivity(PPC) experiments. An anomalous S-shaped shift behavior of temperature dependencies of PL peak energy is observed for the x = 0.15 sample. In PPC measurement, showed that the dark current recovery time of $Al_{x}$$Ga_{l-x}$ N/GaN epilayers mainly depends on the Al content. These behaviors are usually attributed to the presence of carrier localization states. All these phenomena are explained based on the alloy compositional fluctuations in the $Al_{x}$ /$Ga_{l-x}$ N/ epilayers. The photocurrent quenching observed in PPC measurements for $Al_{x}$ $Ga_{l-x}$ N/ epilayers less than 0.2 $\mu\textrm{m}$ thickness indicates that the presence of metastable state in the bandgap of GaN layer, and that the excess holes in the valence band recombine with free electrons.

• 한국재료학회지
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• 제4권5호
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• pp.524-534
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• 1994

소량의 misch metal과 Zr을 함유한 CuZnAI형상기억 합금의 변태온도에 미치는 열사이클 및 기계적 성질 변화에 대하여 고찰하였다. 합금원소 첨가에 따라 결정립에 매우 미세화 되었으며 용체화 처리후 100~$350^{\circ}C$구간에서 경도값 변화를 조사하기 위하여 post quench aging과 step quench aging처리한 결과 $200^{\circ}C$와 $250^{\circ}C$에서 최고의 경도값을 나타냈다. $M_f$온도이하에서 인당시험한 결과 파단강도와 연실율은 결저립이 미세할수록 증가하는 경향을 보였다. 또한 파단강도는 as quenching처리한 경우보다 post quench aging처리한 경우에 보다더 증가하였다. $\beta$-상에서의 시효는 $M_s$온도를 강하시켰으며 마르텐사이트상에서의 시효는 $A_s$ 온도를 증가시켰다. post quench aging 에 따른 $A_s$의 변화는 $\beta$에서의 회복율에 기여하였으며 변태온도 ($A_s-M_s$)히스테리시스는 열사이클에 의하여 증가하는 경향을 보였다.

• Fibers and Polymers
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• 제2권4호
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• pp.203-211
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• 2001

Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait\`s state equation. Flow analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise temperature field, a coordinate transformation technique was used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene.

• 열처리공학회지
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• 제23권6호
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• pp.315-322
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• 2010

Effect of hardenability, grain size and microstructural change according to the change of austenitizing temperature was analyzed in Jominy hardenability test of AISI 51B20 steel. Grain growth was small, 7 ${\mu}m$ and 12 ${\mu}m$ austenite grain sizes at austenitizing temperature of $900^{\circ}C$ and $1000^{\circ}C$, respectively, while rapid grain growth was observed up to 30 ${\mu}m$ austenite grain size at austenitizing temperature of $1100^{\circ}C$. As austenitizing temperature increased from $900^{\circ}C$ to $1100^{\circ}C$, hardenability in the region within 15 mm from end-quenched surface decreased due to the grains growth of bainite and martensite mixture, on the other hand the hardenability in the region exceeding 15 mm from end-quenched surface increased. Increased hardenability was attributed to different microstructures; pearlite, fine pearlite and bainite, and bainite and martensite structures at austenitizing temperature of $900^{\circ}C$, $1000^{\circ}C$ and $1100^{\circ}C$, respectively.

• 대한기계학회논문집A
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• 제35권4호
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• pp.383-391
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• 2011

최근 차체 경량화를 위한 여러 가지 방법 가운데 고온에서 가공하여 성형성을 확보하고, 이후 열처리를 통하여 고강도를 가질 수 있는 프레스 열간 성형 및 핫스탬핑 기술이 각광을 받고 있으며, 이에 따라 핫스탬핑용 재료인 보론 첨가 강판의 수요도 늘어나고 있는 추세이다. 본 연구에서는 핫스탬핑용보론 첨가 강판의 우수한 경화능을 보이는 임계 최적 열처리 조건을 파악하고자, Al+Si 코팅이 된 보론강판을 각기 다른 온도로 열처리하여 수냉 조건에 따른 기계적 특성 및 조직을 관찰하였다. 또한, 이 결과를 토대로 선별된 기계적 특성이 우수한 보론강 시험편과 일반 냉연 강판인 SPRC 340과 SPRC 590 2종류의 상대재를 활용하여 특정 점용접 조건에서 용접을 실시하고, 보론강 및 상대재의 기계적 특성 변화에 따른 용접 후의 기계적 특성 및 조직, 그리고 코팅층 유무에 따른 특성 변화를 연구하였다.

• 한국재료학회지
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• 제27권3호
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• pp.144-148
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• 2017

The effects of an excess of Bi on the piezoelectric and dielectric properties of $0.60Bi_{1+x}FeO_3-0.40BaTiO_3$ (x = 0, 0.01, 0.03, 0.05, 0.07) were investigated. The ceramics were processed through a conventional solid state reaction method and then quenched after sintering at different temperatures in the range of $980{\sim}1070^{\circ}C$. A single perovskite structure without any secondary phase was confirmed for all compositions and temperatures. It was found that excess Bi reduced the sintering temperatures, acted as a sintering aid and enhanced the properties in combination with quenching. Curie temperature ($T_C$) was found to slightly increase due to the presence of excess Bi; electrical properties were also improved by quenching. At x = 0.03 and $1030^{\circ}C$, remnant polarization ($2P_r$) was as high as $45.4{\mu}C/cm^2$ and strain at 40 kV/cm was up to 0.176 %.

• 한국주조공학회지
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• 제22권6호
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• pp.281-287
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• 2002

In order to investigate the variation of microstructure and property of the Electro-slag Remelted M2 steel, microstructure observation, hardness, and bending test were performed by using optical microscope. SEM/EDS, rockwell hardness tester, charpy impact tester and bending tester, respectively. It was revealed that the number of inclusions and content of gas elements(S, O, N) in M2 steel fabricated by ESR process decreased markedly compared to those of AIM. It seems to be due to refining effect of ESR process. The volume fraction of carbides in quenched and tempered specimens after austenitizing at 1150$^{\circ}C$ and 1240$^{\circ}C$ was measured. The volume fraction of grain boundary carbides were found to be similar for both specimens. However, The volume fraction of carbides in grain decreased with an increase of austenitizing temperature. When specimen was austenitized at 1150$^{\circ}C$, grain boundary carbides showed needle like morphology. But, the carbides were broken with an increase of austenitizing temperature. The specimen austenitized at 1240$^{\circ}C$ showed higher hardness and lower bending strength compared to that of 1150$^{\circ}C$. As expected, toughness increased with sub-zero quenching treatment.