6MV 선형가속기의 비대칭 조사야의 변화에 따른 선량분포

윤주호,이철수,염하용,Yoon, Joo-Ho,Lee, Chul-Soo,Yum, Ha-Yong 대한방사선치료학회 2000 大韓放射線治療技術學會誌 Vol.12 No.1

Recently linear accelerator in radiation therapy in asymmetric field has been easily used since the improvement and capability of asymmetrical field adjustment attached to the machine. It has been thought there have been some significant errors in dose calculation when asymmetrical radiation fields have been utilized in practice of radiation treatments if the fundamental data for dose calculation have been measured in symmetrical standard fields. This study investigated how much the measured data of dose distributions and their isodose curves are different between in asymmetrical and symmetrical standard fields, and how much there difference affect the error in dose calculation in conventional method measured in symmetrical standard field. The distributions of radiation dose were measured by photon diode detector in the water phantom (RFA-300P, Scanditronix, Sweden) as tissue equivalent material on utilization of 6 MV linear accelerator with source surface distance (SSD) 1000 mm. The photon diode detector has the velocity of 1 mm per second from water surface to 250 mm depth in the field size of $40mm{\times}40mm\;to\;250mm{\times}250mm\;symmetric\;field\;and\;40mm{\times}20mm\;to\;250mm{\times}125mm$ asymmetrical fields. The measurements of percent depth dose (PDD) and subsequent plotting of their isodose curves were performed from water surface to 250mm dmm from Y-center axis in $100mm{\times}50mm$ field in order to absence the variability of depth dose according to increasing field sizes and their affects to plotted isodose curves. The difference of PDD between symmetric and asymmetric field was maximum $4.1\%\;decrease\;in\;40mm{\times}20mm\;field,\;maximum\;6.6\%\;decrease\;in\;100mm{\times}50mm\;and\;maximum\;10.2\%\;decrease\;200mm{\times}100mm$, the larger decrease difference of PDD as the greater field size and as greater the depth, The difference of PDD between asymmetrical field and equivalent square field showed maximum $2.4\%\;decrease\;in\;60mm{\times}30mm\;field,\;maximum\;4.8\%\;decrease\;in\;150mm{\times}75mm\;and\;maximum\;6.1\%\;decrease\;in\;250mm{\times}125mm$, and the larger decreased differenced PDD as the greater field size and as greater the depth, these differences of PDD were out of $5\%$ of dose calculation as defined by international Commission on radiation unit and Measurements(ICRU). In the dose distribution of asymmetrical field (half beam) the plotted isodose curves were observed to have deviations by decreased PDD as greater as the blocking of the beam moved closer to the central axis, and as the asymmetrical field increased by moving the block 10 mm keeping away from the central axis, the PDD increased and plotted isodose curves were gradually more flattened, due to reduced amount of the primary beam and the fraction of low energy soft radiations by passing thougepth in asymmetrical field by moving independent jaw each 10 h beam flattening filter. As asymmetrical radiation field as half beam radiation technique is used, the radiation dosimetry calculated in utilizing the fundamental data which measured in standard symmetrical field should be converted on bases of nearly measured data in asymmetrical field, measured beam data flies of various asymmetrical field in various energy and be necessary in each institution.

Investigation of steric transition with field programming in frit inlet asymmetrical flow field-flow fractionation

Kim, Young Beom,Yang, Joon Seon,Moon, Myeong Hee Elsevier 2018 Journal of chromatography Vol.1576 No.-

<P><B>Abstract</B></P> <P>Steric transition in flow field-flow fractionation (FlFFF) was investigated under field programming by varying the channel thickness of a frit inlet asymmetrical FlFFF (FI-AF4). Steric transition is a typical inversion in sample elution mode from the increasing order of diameter (normal mode) to the opposite order (steric mode). Owing to the co-elution of two different-sized particles in the steric transition region where particles elute by the combination of the two elution modes, a loss of information in determining the accurate size of sample components in field-flow fractionation occurs. In this study, the effect of field programming on the steric transition in FI-AF4 was examined with the increase in channel thickness in order to increase the diffusional contribution of particle retention with the simultaneous reduction of steric contribution. This study demonstrated that the steric inversion diameter can be increased to >1 μm by programming the crossflow rate and by increasing the channel thickness to 350 and 490 μm. The present study also investigated the effects of outflow rate and initial field strength on the particle separation in field-programmed FI-AF4.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of field programming in Flow FFF on steric transition was studied. </LI> <LI> Steric transition was investigated with frit inlet asymmetrical Flow FFF channels. </LI> <LI> Steric inversion diameter (<I>d<SUB>i</SUB> </I>) in Flow FFF can be increased to >1 μm. </LI> <LI> Field programming with increased channel thickness was effective to increase <I>d<SUB>i</SUB> </I>. </LI> </UL> </P>

Analyse the Electric field of symmetrical and asymmetrical concentric electrodes

Arnon Singhasathein,Pasist Suwanapingkarl,Nattaphong Phanthuna,Taweesak Ted-I,Teepagon Teevarangsan,Tananan Yumonthian 한국인터넷방송통신학회 2015 Journal of Advanced Smart Convergence Vol.4 No.1

The different between two potential voltages can cause the electric field. The electric field is normally distributed along the radius of electrode, and hence it depends on the shape of electrodes. This paper analyses the distribution factor of electric field of symmetrical and asymmetrical concentric electrodes by using Finite Element technique. This allows an analysis the optimum safety clearance distance between two concentric electrodes. The symmetrical concentric electrode refers to Spherical-Spherical concentric electrodes and Cylindrical-Cylindrical concentric electrodes. It must be noted that the symmetrical electrodes are mostly applied for Gas Insulated Substation (GIS) equipments. The asymmetrical electrodes mention to Spherical (inner)-Cylindrical (outer) concentric electrodes and Cylindrical-Cube concentric electrodes, which present as the connection point of High Voltage (HV) cable. The simulations is also complies with the existing standards and regulations in order to ensure the accurate results.

A study of effects of electrode contacts on performance of organic-based light-emitting field-effect transistors

Kim, Dae-Kyu,Choi, Jong-Ho Elsevier 2018 Optical Materials Vol.76 No.-

<P><B>Abstract</B></P> <P>Herein is presented a comparative performance analysis of heterojunction organic-based light-emitting field-effect transistors (OLEFETs) with symmetric (Au only) and asymmetric (Au and LiF/Al) electrode contacts. The devices had a top source–drain contact with long-channel geometry and were produced by sequentially depositing <I>p</I>-type pentacene and <I>n</I>-type <I>N,N</I>′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (P13) using a neutral cluster beam deposition apparatus. The spectroscopic, structural and morphological properties of the organic thin films were examined using photoluminescence (PL) spectroscopy, X-ray diffraction (XRD) method, laser scanning confocal and atomic force microscopy (LSCM, AFM). Based upon the growth of high-quality, well-packed crystalline thin films, the devices demonstrated ambipolar field-effect characteristics, stress-free operational stability, and light emission under ambient conditions. Various device parameters were derived from the fits of the observed characteristics. The hole mobilities were nearly equal irrespective of the electrode contacts, whereas the electron mobilities of the transistors with LiF/Al drain electrodes were higher due to the low injection barrier. For the OLEFETs with symmetric electrodes, electroluminescence (EL) occurred only in the vicinity of the hole-injecting electrode, whereas for the OLEFETs with asymmetric electrodes, the emission occurred in the vicinity of both hole- and electron-injecting electrodes. By tuning the carrier injection and transport through high- and low-work function metals, the hole-electron recombination sites could be controlled. The operating conduction and light emission mechanism are discussed with the aid of EL images obtained using a charge-coupled device (CCD) camera.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The OLEFETs demonstrated ambipolar characteristics and light emission in air. </LI> <LI> The operating light emission mechanisms are discussed with the aid of EL images. </LI> <LI> The electron mobilities of the OFETs with LiF/Al drain electrodes were improved. </LI> </UL> </P>

Engineering Asymmetric Charge Injection/Extraction to Optimize Organic Transistor Performances

Rockson, Tonnah Kwesi,Baek, Seolhee,Jang, Hayeong,Choi, Giheon,Oh, Seungtaek,Kim, Jaehan,Cho, Hyewon,Kim, Se Hyun,Lee, Hwa Sung American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.10

<P>The introduction of an appropriate functionality on the electrode/active layer interface has been found to be an efficient methodology to enhance the electrical performances of organic field-effect transistors (OFETs). Herein, we efficiently optimized the charge injection/extraction characteristics of source/drain (S/D) electrodes by applying an asymmetric functionalization at each individual electrode/organic semiconductor (OSC) interface. To further clarify the functionalizing effects of the electrode/OSC interface, we systematically designed five different OFETs: one with pristine S/D electrodes (denoted as pristine S/D) and the remaining ones made by symmetrically or asymmetrically functionalizing the S/D electrodes with up to two different self-assembled monolayers (SAMs) based on thiolated molecules, the strongly electron-donating thiophenol (TP) and electron-withdrawing 2,3,4,5-pentafluorobenzenethiol (PFBT). Both the S and D electrodes were functionalized with TP (denoted as TP-S/D) in one of the two symmetric cases and with PFBT in the other (PFBT-S/D). In each of the two asymmetric cases, one of the S/D electrodes was functionalized with TP and the other with PFBT (to produce PFBT-S/TP-D and TP-S/PFBT-D OFETs). The vapor-deposited p-type dinaphtho[2,3-<I>b</I>:2′,3′-<I>f</I>]thieno[3,2-<I>b</I>]thiophene was used as the OSC active layer. The PFBT-S/TP-D case exhibited a field-effect mobility (μ<SUB>FET</SUB>) of 0.86 ± 0.23 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>, about three times better than that of the pristine S/D case (0.31 ± 0.12 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>). On the other hand, the μ<SUB>FET</SUB> of the TP-S/PFBT-D case (0.18 ± 0.10 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>) was significantly lower than that of the pristine case and even lower than those of the TP-S/D (0.23 ± 0.07 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>) and PFBT-S/D (0.58 ± 0.19 cm<SUP>2</SUP> V<SUP>-1</SUP> s<SUP>-1</SUP>) cases. These results were clearly correlated with the additional hole density, surface potential, and effective work function. In addition, the contact resistance (<I>R</I><SUB>C</SUB>) for the asymmetric PFBT-S/TP-D case was 10-fold less than that for the TP-S/PFBT-D case and more than five times lower than that for the pristine case. The results contribute a meaningful step forward in improving the electrical performances of various organic electronics such as OFETs, inverters, solar cells, and sensors.</P> [FIG OMISSION]</BR>

An oligomer semiconductor with an asymmetric cyclohexylhexyl end group for solution-processed organic field-effect transistors

Jeong, Yeong Hean,An, Tae Kyu,Lee, Min Cho,Lee, Min-Jung,Jung, Sun Young,Jeong, Yong Jin,Kim, Yun-Hi Elsevier 2020 Materials chemistry and physics Vol.241 No.-

<P><B>Abstract</B></P> <P>We report on the synthesis of an oligomer semiconductor, 2-(6-((6-cyclohexylhexyl)oxy)naphthalen-2-yl)anthracene (C-HNA), and research its potential application as a thin-film active layer for organic field-effect transistors (OFETs). The measured field-effect mobility of the spin-coated C-HNA films for OFETs was 2.3 × 10<SUP>−2</SUP> cm<SUP>2</SUP>/(V·s). The performance of the resulting OFETs was attributed to the packing tendency of the asymmetric oligomer, where the asymmetric cyclohexylated alkyl chains were vertically aligned to the substrates, which contributed to favorable charge transfer.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An asymmetric oligomer semiconductor is synthesized for organic electronics. </LI> <LI> The crystalline semiconductor film is successfully formed from the synthesized oligomer. </LI> <LI> The OFETs with the oligomer exhibited fairly good performances. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

P-Emitter의 길이, 구조가 Asymmetric SiC MOSFET 소자 성능에 미치는 영향

김동현,구상모 한국전기전자재료학회 2020 전기전자재료학회논문지 Vol.33 No.2

SiC MOSFET은 Si IGBT와 비교하여 힘든 스위칭 회로에서 보다 짧은 스위칭 시간 및 더 높은 속도와 더 낮은 손실을 가진다. 현재 시장에 나와있는 부품의 대부분은 SiC의 평면 DMOSFET을 기초로 한다. 평면 채널의 낮은 전도도를 줄이기 위해, 이 장치는 완전히 켜기 위해 높은 산화물 장에서 작동되어야 한다. 따라서 4MV/cm 이상의 영구적인 게이트 옥사이드 응장력의 결과로 발생할 수 있는 높은 전계 고장률에 특히 주의해야 한다. SiC 트렌치 MOSFET은 태양열, 구동장치, EV 충전소와 같은 장기적인 용도에 사용될 예정이다. 이것은 SiC 트렌치 MOSFET의 신뢰성은 확장된 시험으로 보장되고 검증되어야 하며 따라서 국소장의 신뢰성은 SiC 트렌치 MOSFET의 중요한 문제 중 하나이다. 본 논문에서는 차세대 전력반도체 소자인 4H-SiC MOSFET을 이용하여 구조적 변환을 통한 연구를 하였다. 우리는 TCAD 시뮬레이션을 이용하여 새로운 구조인 Asymmetric구조를 제안하였다. 이를 가지고 symmetric과의 전기적 특성을 비교 분석하였다. Asymmetric구조는 오른쪽에 P-emitter를 도입한 구조로, 2차원의 공핍 효과를 통해 전계 분포가 개선되며, 항복전압이 증가한다. 제안한 Asymmetric구조는 Symmetric구조보다 baliga figure of merit이 100% 더 높고 항복 전압이 약70% 향상되었다. In this letter, we propose and analyze a new asymmetric structure that can be used for next-generation power semiconductor devices. We compare and analyze the electrical characteristics of the proposed device with respect to those of symmetric devices. The proposed device has a p-emitter on the right side of the cell. The peak electric field is reduced by the shielding effect caused by the p-emitter structure. Consequently, the breakdown voltage is increased. The proposed asymmetric structure has an approximately 100% higher Baliga’s figure of merit (~94.22 MW/cm2) than the symmetric structure (~46.93 MW/cm2), and the breakdown voltage of the device increases by approximately 70%.

Asymmetrical flow field-flow fractionation coupled with multiple detections: A complementary approach in the characterization of egg yolk plasma

Dou, H.,Li, Y.,Choi, J.,Huo, S.,Ding, L.,Shen, S.,Lee, S. Elsevier 2016 Journal of Chromatography A Vol.1465 No.-

<P>The capability of asymmetrical flow field-flow fractionation (AF4) coupled with UV/VIS, multiangle light scattering (MALS) and quasi-elastic light scattering (QELS) (AF4-UV-MALS-QELS) for separation and characterization of egg yolk plasma was evaluated. The accuracy of hydrodynamic radius (Rh) obtained from QELS and AF4 theory (using both simplified and full expression of AF4 retention equations) was discussed. The conformation of low density lipoprotein (LDL) and its aggregates in egg yolk plasma was discussed based on the ratio of radius of gyration (R-g) to R-h together with the results from bio-transmission electron microscopy (Bio-TEM). The results indicate that the full retention equation is more relevant than simplified version for the Rh determination at high cross flow rate. The Rh from online QELS is reliable only at a specific range of sample concentration. The effect of programmed cross flow rate (linear and exponential decay) on the analysis of egg yolk plasma was also investigated. It was found that the use of an exponentially decaying cross flow rate not only reduces the AF4 analysis time of the egg yolk plasma, but also provides better resolution than the use of either a constant or linearly decaying cross flow rate. A combination of an exponentially decaying cross flow AF4-UV-MALS-QELS and the utilization of full retention equation was proved to be a useful method for the separation and characterization of egg yolk plasma. (C) 2016 Elsevier B.V. All rights reserved.</P>

Factors affecting measurement of channel thickness in asymmetrical flow field-flow fractionation

Dou, H.,Jung, E.C.,Lee, S. Elsevier 2015 Journal of chromatography Vol.1393 No.-

Asymmetrical flow field-flow fractionation (AF4) has been considered to be a useful tool for simultaneous separation and characterization of polydisperse macromolecules or colloidal nanoparticles. AF4 analysis requires the knowledge of the channel thickness (w), which is usually measured by injecting a standard with known diffusion coefficient (D) or hydrodynamic diameter (d<SUB>h</SUB>). An accurate w determination is a challenge due to its uncertainties arising from the membrane's compressibility, which may vary with experimental condition. In the present study, influence of factors including the size and type of the standard on the measurement of w was systematically investigated. The results revealed that steric effect and the particles-membrane interaction by van der Waals or electrostatic force may result in an error in w measurement.

Effect of asymmetrical flow field-flow fractionation channel geometry on separation efficiency

Ahn, J.Y.,Kim, K.H.,Lee, J.Y.,Williams, P.S.,Moon, M.H. Elsevier 2010 Journal of chromatography Vol.1217 No.24

The separation efficiencies of three different asymmetrical flow field-flow fractionation (AF4) channel designs were evaluated using polystyrene latex standards. Channel breadth was held constant for one channel (rectangular profile), and was reduced either linearly (trapezoidal profile) or exponentially (exponential profile) along the length for the other two. The effective void volumes of the three channel types were designed to be equivalent. Theoretically, under certain flow conditions, the mean channel flow velocity of the exponential channel could be arranged to remain constant along the channel length, thereby improving separation in AF4. Particle separation obtained with the exponential channel was compared with particle separation obtained with the trapezoidal and rectangular channels. We demonstrated that at a certain flow rate condition (outflow/inflow rate=0.2), the exponential channel design indeed provided better performance with respect to the separation of polystyrene nanoparticles in terms of reducing band broadening. While the trapezoidal channel exhibited a little poorer performance than the exponential, the strongly decreasing mean flow velocity in the rectangular channel resulted in serious band broadening, a delay in retention time, and even failure of larger particles to elute.