• Applied Chemistry for Engineering
• /
• v.30 no.6
• /
• pp.757-761
• /
• 2019

The catalytic yields of POM to hydrogen over M(1)-Ni(5)/AlCeO₃ (M = La, Ce, Y) were investigated using a fixed bed flow reactor under atmosphere. The crystal phase behavior of reduced La(1)-Ni(5)/AlCeO₃ catalysts before and after the reaction were studied via XRD analysis. FESEM and EDS analyses were further performed to show the uniformed distribution of La, Ni, and Ce metal particles on the catalyst surface. XPS results showed O^2-, O₂^2- species and metal ions such as Ce³⁺, Ce⁴⁺, La³⁺ and Ni²⁺ etc. were on the catalyst surface. When 1 wt% of La was added to Ni(5)/AlCeO₃ catalyst, Ni2p_3/2 and Ce3d_5/2 increased 52.7 and 6.3%, respectively. The yield of hydrogen on the La(1)-Ni(5)/AlCeO₃ catalyst was 89.1%, which was much better than that of M(1)-Ni(5)/AlCeO₃ (M = Ce, Y). As Ce⁴⁺ ions of CeO₂ produced by the reaction of AlCeO₃ with oxygen were substitute to La³⁺, it made oxygen vacancies in the lattice and further improved the hydrogen yield by increasing the dispersion of Ni atoms with strong metal-support interaction (SMSI) effect.

• Polymer(Korea)
• /
• v.30 no.6
• /
• pp.464-470
• /
• 2006

Diblock copolymers consisting of methoxy Poly (ethylene glycol) (MPEG) and poly (${\epsilon}-ca$ prolactone) (PCL), poly(${\delta}-valerolactone$) (PVL), poly(L-lactide) (PLLA), or poly(L-lactide-co-glycolide) (PLGA) were prepared to compare the characterization of diblock copolymers as a drug carrier. MPEG-PCL, MPEG-PVL, MPEG-PLLA, and MPEG-PLGA diblock copolymers were synthesized by the ring-opening polymerization of ${\epsilon}$-caprolactone or ${\delta}$-valerolactone in the presence of $HCl{\cdot}Et_2O$ as a monomer activator at room temperature and by the ring-opening polymerization of L-lactide or a mixture of L-lactide and glycolide in the presence of stannous octoate at $130^{\circ}C$, respectively. The synthesized diblock copolymers were characterized with $^1H-NMR$, GPC, DSC, and XRD. The micellar characterization of MPEG-polyester diblock copolymers in an aqueous phase was carried out by using NMR, dynamic light scattering, AFM, and fluorescence techniques. Most micelles exhibited a spherical shape in AFM. Thus, ore confirmed that the micelles formed with MPEG-polyester diblock copolymers have possibility as a potential hydrophobic drug delivery vehicle because a hydrophobic drug could be preferentially distributed in the micelle core.

• Journal of Radiation Protection and Research
• /
• v.29 no.3
• /
• pp.187-196
• /
• 2004

The health effects resulting from severe accidents of typical 1,000MWe KSNP(Korea Standard Nuclear Plant) PWR and typical 600MWe CANDU(CANada Deuterium Uranium) plants were estimated and compared. The population distribution of the site extending to 80km for both site were considered. The releaese fraction for various source term categories(STC) and core inventories were used in the estimation of the health effects risks by using the MACCS2(MELCOR Accident Consequence Code System2) code. Individuals are assumed to evacuate beyond 16km from the site. The health effects considered in this comparative study are early and cancer fatality risk, and the results are presented as CCDF(Complementary Cumulative Distribution Function) curves considering the occurrence probability of each STC's. According to the results, the early and cancer fatality risks of PHWR plants we lower than those of PWR plants. This is attributed the fact that the amount of radioactive mateials that released to the atmosphere resulting from the postulated severe accidents of PHWR plants are smaller than that of PWR plants. And, the dominating initiating event of STC that shows maximum early and cancer fatality risk is SGTR(Steam Generator Tube Rupture) for both plants. Therefore, the appropriated actions must be taken to reduce the occurrence probability and the amounts of radioactive materials released to the environment in order to protect the public for both PWR and PHWR plants.

• Polymer(Korea)
• /
• v.33 no.2
• /
• pp.158-163
• /
• 2009

In this study, we synthesized a series of dendritic polystyrene-b-linear poly (t-butyl acrylate) copolymers with well-defined molecular architectures. The hydroxyl group located at the focal point of the second generation dendron bearing polystyrene ($M_n$ = 1000 g/mol) peripheries was converted into amine group via the following stepwise reactions: 1) tosylatoin, 2) azidation, and 3) reduction. On the other hand, the linear poly (t-butyl acrylate)s were prepared by an atom transfer radical polymerization (ATRP) of t-butyl acrylate where benzyl 2-bromopropanoate and Cu(I)Br/PMDETA were used as initiator and catalyst, respectively. To convert the end group of prepared poly (t-butyl acrylate) s into carboxylic acid, a debenzylation was performed using Pd/C catalyst under $H_2$ atmosphere. In the final step, dendritic-linear block copolymers were obtained through a simple amide coupling reaction mediated by 4-(dimethylamino) pyridine(DMAP) and N,N'-diisopropylcarbodiimide(DIPC). The resulting diblock copolymers were shown to have well-defined molecular weights and narrow molecular weight distributions as supported by $^1H$-NMR spectroscopy and gel permeation chromatography(GPC).

• Journal of the Korean Chemical Society
• /
• v.66 no.2
• /
• pp.136-149
• /
• 2022

Chemistry focuses on explaining macroscopic phenomena at the microscopic level with particles, such as atoms or molecules. Explanation using particles are bound to be considered as abstract by students, because it was dealing with invisible objects. For that reason, the science national curriculum presented to middle school students the explanation of the units related to the composition of matter. Therefore, understanding about the composition of matter in middle school students becomes an important basis for learning of chemistry, and it is necessary to investigate their understanding about composition of matter. In this study, students' understanding about 'composition of matter' region, which is first presented to middle school students, was confirmed at an overall level. In this line, this study analyzed the results of the items in the composition of matter region, and analyzed items were used in the National Assessment of Educational Achievement (NAEA) from 2015 to 2019. We analyzed the 9 items presented in the NAEA according to the response rate of options and response rate distribution curve, and explained the characteristics of understanding derived by each achievement level were examined. According to the analyzed results by dividing the conceptions about elements, atoms, and ions, students above the proficient achievement-level had scientific conceptions overall, but students below the basic achievement-level had inconsistent or naive conceptions. Based on the results for each item, this study discussed some implications to be considered or to be improved on teaching-learning for 'composition of matter'.

• Journal of the Korean Magnetics Society
• /
• v.4 no.1
• /
• pp.12-19
• /
• 1994

The crystallization behavior of the amorphous $Fe_{73.5}Cu_{1}Nb_{3}Si_{16.5}B_{6}$ alloy with isothermal annealing at $552^{\circ}C$ was studied by $M\"{o}ssbauer$ spectroscopy. The amorphous phase was revealed to coexist together with $Do_{3}-FeSi$ nanocrystalline and Cu-duster in annealed alloys by $M\"{o}ssbauer$ spectrum analysis. At the early stage of crystallization, Si content of FeSi is high due to the creation of Cu-cluster, and decreases with annealing until 60 minutes, which results in the increase in the mean hyperfine field of FeSi, and thereafter keeps constant. After 60 minutes, the decrease in the mean hyperfine field of the residual armrphous, in spite of a slight change in the volume fraction of the FeSi and the residual armrphous, is caused by the increase in the content of Nb and B in residual amorphous phase. Both directions of the hyperfine field, those of the FeSi and the residual amorphous, become randomly oriented in about 60 minutes. For FeSi and Cu-duster, the Avrami exponents are 0.51 and O.65, the activation energies are 2.35 eV and 2.44 eV, and the incubation times are 2.4 minutes and 0.8 minutes respectively. Earlier formation of Cu-duster than that of FeSi is coincidence with the fact that Cu atom promotes the nucleation of the FeSi.

• Korean Journal of Mineralogy and Petrology
• /
• v.33 no.1
• /
• pp.1-10
• /
• 2020

The atomic structures of silicate liquids at high pressure provide insights into the transport properties including thermal conductivities or elemental partitioning behavior between rocks and magmas in Earth's interior. Whereas the local electronic structure around silicon may vary with the arrangement of the nearby oxygens, the detailed nature of such relationship remains to be established. Here, we explored the atomic origin of the pressure-induced changes in the electronic structure around silicon by calculating the partial electronic density of states and L₃-edge X-ray absorption spectra of SiO₂ polymorphs. The result showed that the Si PDOS at the conduction band varies with the crystal structure and local atomic environments. Particularly, d-orbital showed the distinct features at 108 and 130 eV upon the changes in the coordination number of Si. Calculated Si XAS spectra showed features due to the s,d-orbitals at the conduction band and varied similarly with those observed in s,d-orbitals upon changes in the crystal structures. The calculated Si XAS spectrum for α-quartz was analogous to the experimental Si XRS spectrum for SiO₂ glass, implying the overall similarities in the local atomic environments around the Si. The edge energies at the center of gravity of XAS spectra were closely related to the Si-O distance, thus showing the systematic changes upon densification. Current results suggest that the Si L_2,3-edge XRS, sensitive probe of the Si-O distance, would be useful in unveiling the densification mechanism of silicate glasses and melts at high pressure.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2016.02a
• /
• pp.277.2-277.2
• /
• 2016

현재 화합물 반도체 나노구조는 광학적, 전기적 특성을 기반으로 하는 단전자 트랜지스터, 적외선 검출기, 레이저, 태양전지와 같은 분야에 응용하기 위한 많은 연구가 진행되고 있다. 특히 양자점은 3차원으로 구속되어 있는 상태 밀도를 갖고 있어 레이저 응용 시 낮은 문턱 전류 밀도, 높은 이득, 높은 열적 안정성을 기대되고 있지만 양자점의 운반자 수집과 열적 안정성의 한계가 여전히 존재한다. 이러한 문제를 해결하기 위해 다양한 방법이 연구되고 있으며, 그 중 단층 양자점에 비해 운반자 수집과 열적 안정성이 뛰어난 다층 양자점이 결합된 구조에 대한 연구가 활발히 이루어지고, 다층으로 성장된 양자점 구조는 양자점의 크기 분포 조절이 용이하고 양자점 층간의 전기적 결합력이 강한 특성이 있다. 본 연구에서는 분자 선속 에피 성장법(Molecular Beam Epitaxy; MBE)과 원자 층 교대 성장법(Atomic Layer Epitaxy; ALE)으로 CdTe/ZnTe 다층 양자점을 ZnTe 장벽층의 두께를 변화하면서 성장 후 광학적 특성을 연구하였다. 저온 광루미네센스 측정(Photoluminescence; PL)을 통하여 ZnTe 장벽층 두께가 증가할수록 양자점의 PL 피크가 높은 에너지로 이동함을 알 수 있었는데, 이는 ZnTe 장벽층의 두께가 증가할수록 양자점 층간의 결합력이 감소하면서 양자점의 크기가 작아졌기 때문이다. 그리고 ZnTe 장벽층의 두께가 증가할수록 PL 세기가 커지는 것을 알 수 있었는데, 이는 ZnTe 장벽층의 두께가 증가할수록 더 많은 운반자가 양자점으로 구속되기 때문이다. 또한 온도 의존 광루미네센스 측정 결과 ZnTe 장벽층의 두께가 증가할수록 열적 활성화 에너지가 커지는 것을 관찰하였고, 시분해 광루미네센스 측정을 통해 ZnTe 장벽층의 두께에 따른 운반자 동역학에 대해 연구하였다. 이와 같은 결과 CdTe/ZnTe 다층 양자점 구조에서 장벽층의 두께에 따른 광학적 특성에 대해 이해 할 수 있었다.

• Journal of Astronomy and Space Sciences
• /
• v.18 no.3
• /
• pp.209-218
• /
• 2001

Global exposure time distribution through all-sky survey, one of main science missions of KAISTSAT-1, has been simulated. Exposure time distribution has its minimum on the celestial equator and increases with moving to polar regions according to the present mission operation scenario. SAA (South Atlantic Anomaly) and the moon can make further decreases of exposure time around the celestial equator Effects of SAA on all-sky survey exposure time can be compensated with a simple observational scheduling, orbit exchange between orbits allocated to all-sky survey passing through the SAA region and ones allocated to upper atmosphere observations not affected by SAA. It, however, seems that present exposure time distribution is not adequate for the concrete study of the evolution of interstellar medium. A scheme for active time allocation is needed for redistribution of exposure times weighted around the celestial poles, and additional studies on the advanced mission operation and the observational scheduling are also needed.

• Nuclear Engineering and Technology
• /
• v.24 no.1
• /
• pp.86-97
• /
• 1992

The purpose of this paper is to evaluate the direct vessel injection design from a pressurized thermal shock(PTS) viewpoint for the Combustion Engineering System 80+ A break of the main steam line from zero power and a 0.05 ft$^2$small break loss-of-coolant accident (LOCA) from full power were selected as the potential PTS events. In order to investigate the stratification effects in the reactor downcomer region, the fluid mixing analysis was performed using the COMMIX-IB code for steam line break and using the REMIX code for 0.05 ft$^2$small break LOCA. The stress distributions within the reactor vessel walls experiencing the pressure and the temperature transients were calculated using the OCA-P code for both events. The results of the analysis showed that a small break LOCA without decay heat presented the greatest challenge to the vessel, however, there is no crack initiation through end-of-life of the vessel with consideration of decay heat.