• 분석과학
• /
• 제28권1호
• /
• pp.33-39
• /
• 2015

CdS 양자점 입자는 특정 파장의 빛을 방출하는 반도체 나노 결정으로 이러한 광학적 특성 때문에 질병 진단 시약, 광학기술, 미디어 산업 및 태양전지와 같은 다양한 분야에서 응용되는 물질이다. 방출하는 빛의 색은 입자의 크기에 의존하기 때문에 CdS 양자점 입자의 크기 및 크기분포를 정확하게 분석하는 것이 필요하다. 본 연구에서는 CdS 양자점 입자를 감마-선 조사법(${\gamma}$-ray irradiation method)을 이용하여 합성하고, 크기 및 크기 분포도를 결정하기 위하여 침강 장-흐름 분획법 (SdFFF)를 이용하였다. 침강 장-흐름 분획법을 이용한 CdS 양자점 입자의 정확한 분석을 위하여 분석조건의 최적화(유속, 외부장 세기, field-programming)에 대하여 조사되었다. 투과 전자 현미경(transmission electron microscopy, TEM)으로 확인된 단일 입자의 크기는 ~4 nm 였으며, 단일 입자의 응집으로 생성된 2차 입자 크기의 평균은 159 nm로 확인되었다. 첨가된 입자 안정제의 농도가 증가할수록 CdS 양자점 입자의 크기가 감소하는 경향성을 확인하였다. 침강 장-흐름 분획법, 투과 전자 현미경, 그리고 동적 광 산란법(dynamic light scattering, DLS)으로 결정된 CdS 양자점 크기는 각각 126, 159, 그리고 152 nm 였다. 본 연구의 결과로 침강 장-흐름 분획법은 비교적 넓은 크기분포를 갖는 다양한 종류의 무기입자의 크기 및 크기 분포도를 결정하는데 유용한 방법임을 확인하였다.

• 한국입자에어로졸학회지
• /
• 제15권3호
• /
• pp.91-104
• /
• 2019

In this study, hourly measurements of $PM_{2.5}$ and its major chemical constituents such as organic and elemental carbon (OC and EC), and ionic species were made between January 15 and February 10, 2018 at the air pollution intensive monitering station in Gwangju. In addition, 24-hr integrated $PM_{2.5}$ samples were collected at the same site and analyzed for OC, EC, water-soluble OC (WSOC), humic-like substance (HULIS), and ionic species. Over the whole study period, the organic aerosols (=$1.6{\times}OC$) and $NO_3{^-}$ concentrations contributed 26.6% and 21.0% to $PM_{2.5}$, respectively. OC and EC concentrations were mainly attributed to traffic emissions with some contribution from biomass burning emissions. Moreover, strong correlations of OC with WSOC, HULIS, and $NO_3{^-}$ suggest that some of the organic aerosols were likely formed through atmospheric oxidation processes of hydrocarbon compounds from traffic emissions. For the period between January 18 and 22 when $PM_{2.5}$ pollution episode occurred, concentrations of three secondary ionic species ($=SO{_4}^{2-}+NO_3{^-}+NH_4{^+}$) and organic matter contributed on average 50.8 and 20.1% of $PM_{2.5}$, respectively, with the highest contribution from $NO_3{^-}$. Synoptic charts, air mass backward trajectories, and local meteorological conditions supported that high $PM_{2.5}$ pollution was resulted from long-range transport of haze particles lingering over northeastern China, accumulation of local emissions, and local production of secondary aerosols. During the $PM_{2.5}$ pollution episode, enhanced $SO{_4}^{2-}$ was more due to the long-range transport of aerosol particles from China rather than local secondary production from $SO_2$. Increasing rate in $NO_3{^-}$ was substantially greater than $NO_2$ and $SO{_4}^{2-}$ increasing rates, suggesting that the increased concentration of $NO_3{^-}$ during the pollution episode was attributed to enhanced formation of local $NO_3{^-}$ through heterogenous reactions of $NO_2$, rather than impact by long-range transportation from China.

• 한국대기환경학회지
• /
• 제17권2호
• /
• pp.133-145
• /
• 2001

The receptor modeling is one of the statistical methods to achieve reasonable air pollution strategies. The pur-pose of this study was to survey the concentration variability oi inorganic elements and ionic species in the PM-10 particles, to qualitatively characterize emission sources by an advanced algorithm called positive matrix factoriza-tion(PMF) as a receptor model that can strictly provide results in every loading matrix. A total of 254 samples was collected by a PM-10 high volume air sampler from Mar. 1997 to Feb. 1998 in Kyung Hee University at Suwon Campus. Fourteen chemical species(Zn, Cu, Fe, Pb, Al, Mn, $Na^{+}$, NH$_4$+, $K^{+}$, $Mg^{2+}$, $Ca^{2+}$, $SO_4^{2-}$, $NO_{3}^{-}$, and $Cl^{-}$) were determined by AAS and IC methods. The study results showed that the average monthly concentration of PM-10 particles were 86.3$\mu\textrm{g}$/$\textrm{m}^3$ in March (maximum) and 28.5$\mu\textrm{g}$/$\textrm{m}^3$ in August(minimum), respectively. The concentrations of Na+, NH$_4$+, $K^{+}$ and $Cl^{-}$ in winter, $Mg^{2+}$, $Ca^{2+}$ and $NO_{3}^{-}$, in spring, and $SO_4^{2-}$ in summer showed the largest peak concentration for the respective season. Through and app-lication of a PMF program of Pm-10 concentration data of Suwon, 9 sources were qualitatively identified , such as incineration source, oil burning source, soil related source, open burning source automobile source, coal burning sources, secondary sulfate related source, and secondary nitrate related source.

• 한국수소및신에너지학회논문집
• /
• 제20권6호
• /
• pp.505-511
• /
• 2009

The hydriding and electrochemical characteristics of Zr-based $AB_2$ alloy produced by gas atomization have been extensively examined. For the particle morphology of the as-cast and gas-atomized powders, it can be seen that the mechanically crushed powders are irregular, while the atomized powder particles are spherical. The increase of jet pressure of gas atomization process results in the decrease of hydrogen storage capacity and the slope of plateau pressure significantly increases. TEM and EDS studies showed the increase of jet pressure in the atomization process accelerated the phase separation within grain of the gas-atomized alloy, which brought about a poor hydrogenation property. However, the gas-atomized $AB_2$ alloy powders produced by jet pressure of 50 bar kept up the reversible $H_2$ storage capacity and discharge capacity similar to the mechanically crushed particles. In addition, the electrode of gas-atomized Zr-based $AB_2$ alloy of 50 bar showed improved cyclic stability over that of the cast and crushed particulate, which is attributed to the restriction of crack propagation by grain boundary and dislocation with ch/discharging cycling.

• Plant Resources
• /
• 제3권3호
• /
• pp.163-172
• /
• 2000

We compared microstructural features of the ordered cell and disordered leaves in Citrus junos Sieb. by electron microscopy. In the cell of the ordered leaves, many chloroplasts and large vacuoles were particularly observed. Also a lot of vessel, companion cell and big nucleus were presented in vascular bundle regions. The mitochondria and the other organelles were interspersed among the chloroplasts in a thin, peripheral layer of cytoplasm. The chloroplast possessed typical grana and intergranal lamellae, numerous starch grains and a few small osmophilic globules. Besides, microbodies were closely associated with the mitochondria and the chloroplast. The process of the formation of the secondary cell wall from primary cell wall was observed the vessel elements, the tonoplast wall and the secondary cell wall. It was observed that the oil sac with the unique perfume distributed the adjacent cell wall. In the cell of disordered leaves, the all of the organelles were thrust toward the cell wall due to the fusion of vacuoles in the cells. It was observed that a lot of the very small particles spreaded in the cytoplasm. The loss of unique perfume of the leaves was resulted in the destruction of the oil sac. Also, there was not observed grana, lamellae, starch and osmophillic globules in the chloroplast. The small distributed organelles was not observed but the elongation of the cell wall was proceed no longer. Therefore, the plasma membrane diverged from the cell wall. All of organelles in the cell had poor function and deformation. A massive vacuole was fulfilled in single cell and the vacuole contains a lot of large and small particles. The organelles were presented on the side of the cell wall according to the enlargement of vacuole and they were observed to be breakdown.

• 한국의학물리학회지:의학물리
• /
• 제33권4호
• /
• pp.108-113
• /
• 2022

Purpose: Proton therapy has been used for optimal cancer treatment by adapting its Bragg-peak characteristics. Recently, a tissue-sparing effect was introduced in ultrahigh-dose-rate (FLASH) radiation; the high-energy transmission proton beam is considered in proton FLASH therapy. In measuring high-energy/ultrahigh-dose-rate proton beam, Faraday Cup is considered as a dose-rate-independent measurement device, which has been widely studied. In this paper, the feasibility of the simply designed Faraday Cup (Poor Man's Faraday Cup, PMFC) for transmission proton FLASH therapy is investigated. Methods: In general, Faraday cups were used in the measurement of charged particles. The simply designed Faraday Cup and Advanced Markus ion chamber were used for high-energy proton beam measurement in this study. Results: The PMFC shows an acceptable performance, including accuracy in general dosimetric tests. The PMFC has a linear response to the dose and dose rate. The proton fluence was decreased with the increase of depth until the depth was near the proton beam range. Regarding secondary particles backscatter from PMFC, the effect was negligible. Conclusions: In this study, we performed an experiment to investigate the feasibility of PMFC for measuring high-energy proton beams. The PMFC can be used as a beam stopper and secondary monitoring system for transmission proton beam FLASH therapy.

• 한국환경과학회지
• /
• 제19권11호
• /
• pp.1423-1436
• /
• 2010

The effects of meteorological and reclaiming conditions on the reduction of suspended particles are investigated using a computational fluid dynamics (CFD) model with the k-$\varepsilon$ turbulence closure scheme based on the renormalization group (RNG) theory. Twelve numerical experiments with different meteorological and reclaiming conditions are performed. For identifying the meteorological characteristics of the target area and providing the inflow conditions of the CFD model, the observed data from the automatic weather station (AWS) near the target area is analyzed. Complicated flow patterns such as flow distortion, horse-shoe vortex, recirculation zone, and channeling flow appeared due to the topography and buildings in the domain. Specially, the flow characteristics around the reclamation area are affected by the reclaiming height, reclaiming size and windbreak height. Reclaiming height affected the wind speed above the reclaiming area. Windbreak induces more complicated flow patterns around the reclaiming area as well as within the reclaiming area. In front of the windbreak, flow is distorted as it impinges on the windbreak. As a result, upward flow is generated there. Behind the windbreak, a secondary circulation, so called, a recirculation zone is generated and flow is reattached at the end of the recirculation zone (reattachment point). At the lower part of the recirculation zone, there is a reverse flow toward the windbreak. Flow passing to the reattachment point starts to be recovered. Total amounts of suspended particles are calculated using the frictional and threshold frictional velocities, erosion potential function, and the number of surface disturbance. In the case of a 10 m-reclaiming and northerly wind, the amount of suspended particles is largest. In the presence of 5 m windbreak, the friction velocity above the reclaiming area is largely reduced. As a result, the total amount of the suspended particles largely decreases, compared to the case with the same reclaiming and meteorological conditions except for the windbreak The calculated suspended particle amounts are used as the emission rate of the dispersion model simulations and the dispersion characteristics of the suspended particles are analyzed.

• 한국지반공학회논문집
• /
• 제29권11호
• /
• pp.61-72
• /
• 2013

Sabkha층 탄산질 모래의 입자파쇄발생시 이차압축특성을 파악하기 위하여 압밀시험을 수행하여 입자파쇄응력을 파악하였다. 입자파쇄 항복응력에서 순간적으로 발생한 입자파쇄 압축침하를 해석하기 위하여 이차압축률 대신 이차 파쇄압축률 $C_{{\alpha}{\epsilon}}{^*}$를 도입하였다. 입자파쇄 발생시의 간극비 $e_p{^*}$와 침하량 $H_p{^*}$가 이차압축거동의 기준점으로 사용되었다. 일차압축지수와 이차파쇄압축률을 비교한 결과 현장 Sabkha층의 경우 $C_{{\alpha}{\epsilon}}{^*}/C_c$ 값이 0.0105~0.0187로 나타났으며 일반적인 석영질 사질토에 비해 입자파쇄 발생으로 인한 이차압축거동이 매우 크게 나타났다. 동일한 재하응력에서는 Sabkha층의 심도가 깊을수록 입자파쇄침하량과 이차파쇄압축률이 증가함을 확인할 수 있었다.

• Asian Journal of Atmospheric Environment
• /
• 제5권2호
• /
• pp.86-96
• /
• 2011

The positive matrix factorization (PMF2) and multilinear engine (ME2) models have been shown to be powerful environmental analysis techniques and have been successfully applied to the assessment of ambient particulate matter (PM) source contributions. Because these models are difficult to apply practically, the US EPA developed a more user-friendly version of the PMF. The initial version of the EPA PMF model does not provide any rotational capabilities; for this reason, the model was upgraded to include rotational functions in the EPA PMF ver. 2.0. In this study, PMF and EPA PMF modeling identified ten particulate matter sources including secondary sulfate I, vehicle gasoline, secondary sulfate II, secondary nitrate, secondary sulfate III, incinerators, aged sea salt, airborne soil particles, oil combustion, and diesel emissions. All of the source profiles determined by the two models showed excellent agreement. The calculated average concentrations of $PM_{2.5}$ were consistent between the PMF2 and EPA PMF ($17.94{\pm}0.30{\mu}g/m^3$ and $17.94{\pm}0.30\;{\mu}g/m^3$, respectively). Also, each set of estimated source contributions of the PMF2 and EPA PMF showed good agreement. The results from the new EPA PMF version applying rotational functions were consistent with those of PMF2. Therefore, the updated version of EPA PMF with rotational capabilities will provide more reasonable solutions compared with those of PMF2 and can be more widely applied to air quality management.

• 한국지반공학회논문집
• /
• 제40권1호
• /
• pp.39-46
• /
• 2024

전 지구적 기후변화에 따른 용수확보 방안으로 인공함양 기법이 활용되고 있다. 함양률을 감소시키는 클로깅 문제는 인공함양 기법의 활용에 큰 장애가 되고 있다. 이 연구는 하천수 주입 과정에서 발생할 가능성이 있는 클로깅 평가를 위한 기초자료를 확보하기 위해 인공함양 예정 지역 충적층의 토양 조직과 광물 특성을 분석하였다. 충적층 쇄설성 입자의 주요 구성 광물은 석영, 정장석, 사장석, 흑운모 등이며, 공극을 충진하는 주요 2차 광물은 일라이트, 카오린나이트, Fe-산화광물이다. 2차 광물로서 탄산염 혹은 황산염 광물의 산출이 없는 것은 인공함양 실험 전인 연구 지역 충적층에서는 지하수와 지표수 간의 반응에 의한 화학적 클로깅은 발생하지 않았음을 시사한다. 인공함양 실험과 관련된 화학적 클로깅에 대한 평가를 위해 대수층 내 공극에서 2차 광물의 생성과 성장과 같은 충적층의 토양특성에 대한 모니터링이 필요하다.