Nd:YAG 레이저의 동작특성에 관한 연구 : 3단 병렬 순차 충·방전 방식 적용 3-mesh parallel sequence charge and discharge method

김희제,홍정환,김병균,박구렬,이동훈,김휘영 釜山大學校生産技術硏究所 1999 生産技術硏究所論文集 Vol.56 No.-

펄스형 Nd:YAG 레이저는 가공물질과 쉽게 반응하고, 램프에 의해서 연속발진은 물론 정상발진, Q-스이치 및 모드동기 발진까지 다양한 발진 형태가 가능하며 재료가공 및 계측용으로 널리 사용되어지고 있다. 재료가공에 있어서는 가공목적에 따라 에너지 밀도를 제어하는 것이 매우 중요하다. 에너지 밀도의 제어는 레이저 출력의 펄스반복률을 제어하는 방법이 주로 사용된다. 본 연구에서는 펄스형 Nd:YAG 레이저의 펄스반복률을 제어할 수 있는 3단 병렬 순차 충·방전 방식의 레이저 전원회로를 설계 및 제작하여 반복율에 따른 플래쉬램프의 전류파형 및 레이저 출력의 안정도와 신뢰성을 확인할 수 있었고, 펄스반복율은 30∼150[pps]까지, 30[pps]씩 증가시켰을 경우, 레이저 출력 효율은 약 5% 씩 감소한 반면, 축력은 약 4W 씩 증가하였다. A pulsed Nd:YAG laser interacts with processing materials easily, having different kinds of oscillators, such as CW by lamp, Q-switching, mode locking and so on. A pulsed Nd:YAG laser has been used in a wide variety of fields : measuring, materrial processing, and so on. In a material processing, it's very important to control an energy density according to the processing purpose. It is mainly used to control the energy density to vary pulse repetition rate. In this study, we designed and fabricated the 3-mesh parallel sequency charge and discharge circuit of which the pulse repetition was to be controlled. As increasing a repetition rate, we could find the stability and the reliability of laser output as well as flashlamp current waveform. When increasing a repetition rate from 30 to 150[pps] by 30[pps], we also found that the efficiency of lase output decreased by about 5%, while the output increased by about 4W.

An Exprimental Study of Postoperative Intraabdominal Adhesions

이봉우,최봉락,양동휘,김인호,손수상,강중신 啓明大學校 醫科大學 1986 계명의대학술지 Vol.5 No.2

수술후 나타나는 장유착은 적지 않은 빈도를 나타내며 보편화된 개복 수술후 증가된 유착성 장폐색증은 외과영역에서 중요한 문제의 하나로 많은 연구보고가 되고 있으며 유착의 형성은 기계적, 세균학적 및 화학적 외상 즉 복강내 외상이나 손상후의 치유과정의 한단계로 유착이 나타난다고 한다. 장유착의 원인과 이차적인 병태생리학적인 변화에 대한 충분한 이해를 갖고 조기에 적절한 치료를 하면 이병율과 사망율을 감소시킬 수 있는 질환이다. 저자들은 한국산 성숙된 가토를 이용하여 실시한 실험적 연구로써 도끼 60마리를 각 20마리씩 3군으로 나누어 관찰하였다. 즉 모든 토끼는 ether로 open drip마취를 하고 정중선 복별절개로 개복한 후 5.0+ 5.0cm정도의 전벽복막을 점상 출혈이 나타날 때 까지 찰과상을 형성시켜 그 결과를 관찰하였다. 제1군의 20마리는 단지 scratching method만 시행한 control group으로 하고 제2군의 20마리에서는 scratchiing method 후 복강내 polyethylene feeding tube를 넣고 매일 50ㅊㅊ의 생리식염수를 중비하였으며 제3군 20마리에서는 복강투석액인 peritosol solution으로 생리식염수 대신에 매일 50cc씩 복강내에 주입하여 관찰 비교하였다. 모든 토끼들은 개복술 10일후 재 개복하여 복막의 유착과 소장간의 유착정도를 관찰비교하여 다음과 같은 결과를 얻었기에 문헌고찰과 함께 보고하는 바이다. Control group에서는 20예중 유착정도가 15예에서 나타나 75%를 나타내었고 생리식염수 투여군에서는 20예중 13예에서 나타나 65%의 유착을 나타내었으며 peritosol군에서는 20예중 9예로서 45%로 감소된 유착양상을 나타내었다. 본 실험에서는 peritosol투여군이 control group이나 생리식염수 투여군보다 실험적 유착상태가 적은 것에 유의를 하였으며 아직 인체에 peritosol세척 시도는 못해 보았지만, 본실험과 같은 효과가 있다면 술후 장유착 예방에 의의가 있을 것으로 사료되어 보고 드리는 바이다.

원형 Cavity를 이용한 펄스형 Nb:YAG 레이저의 출력특성 및 병렬메쉬 회로의 최적화

홍정환,송금영,양동민,김휘영,김희제 부산대학교 생산기술연구소 2001 生産技術硏究所論文集 Vol.60 No.-

본 연구에서는 기존의 타원형 cavity가 아닌 원형 cavity를 설계 및 제작하여 그 동작특성에 관하여 연구하였다. 그 결과 타원형 cavity 보다 다소 적은 레이저 출력 효율 2.1%를 얻었다. 원형 cavity는 타원형 cavity 보다 컴팩트하며 제작하기가 용이하고, 제작 단가가 저렴하다는 장점이 있다. 입력에너지, 입력전압 및 펄스 폭을 동일하게 했을 경우 주회로 병렬 메쉬회로수를 최적화하고자 한다. PFN 회로를 1단에서 8단까지 PSPICE로 모의시험한 전류파형과 실제 실험한 전류파형이 거의 일치하였다. 그 결과 500㎲이상의 펄스 폭에서 6단 메쉬가 최적의 병렬 메쉬라는 결론을 얻었다. In this study, we have deigned and manufactured not only a present elliptic cavity but also a circular cavity, and experimented the operational characteristics. As a result, we obtained the maximum efficiency of 2.1% that was not less than that of an elliptic cavity. A circular cavity is much more compact and is easier to be manufactured than an elliptic cavity. And it can be made at a low cost. When the input energy, input voltage, and pulse width were in the same condition, we tried to decide the optimization of the mesh number of a parallel-mesh circuit which was connected with main power supply. The PSPICE simulation waveform of PFP(Pulse Forming network) circuit ranging from 1-mesh to 8-mesh nearly corresponded with the real current waveform obtained through a practical experiment. From these experimental results, we obtained the result that 6-mesh was the optimal parallel-mesh circuit in case that the pulse width was more than 500㎲.

Photocorrosion-Assisted Transformation of Metal Selenide Nanocrystals into Crystalline Selenium Nanowires

Kim, Whi Dong,Baum, Fá,bio,Kim, Dahin,Lee, Kangha,Moon, Jun Hyuk,Lee, Doh C. The American Chemical Society 2014 CRYSTAL GROWTH AND DESIGN Vol.14 No.3

<P>We report the transformation of several metal selenide nanocrystals (NCs), including PbSe, CdSe, ZnSe, and PbSe/CdSe core/shell NCs, in dimethyl sulfoxide (DMSO) in acidic solutions at room temperature. In this study, the DMSO solution of metal selenide NCs was mixed with nitric acid, which was used to adjust the pH of the solution. Upon mixing, the metal selenide NCs readily transformed into crystalline selenium (trigonal structure) nano- or microwires under ambient light, whereas little or no transformation occurred in the dark. Photocorrosion, where the photogenerated carriers within the NCs participate in the cleavage of the metal and selenium atoms, turns out to be responsible for the transformation. DMSO removes organic ligands on the NC surface and creates surface trap sites for photoinduced charge carriers. Then, nitric acid helps shift the reduction potentials, thereby promoting a “cathodic reduction”. In this sense, the photocorrosion rate can be controlled by several parameters, such as the absorption cross section of the selenide NCs and the pH. The diameter and shape of the resulting selenium wires help gauge the transformation rate and thus unveil the transformation mechanism.</P><P>Semiconductor selenide nanocrystals transform into crystalline selenium nanowires after mixing with dimethyl sulfoxide in acidic solution. The transformation appears to occur via photocorrosion, whose kinetics depends upon the energy gap of the original selenide nanocrystals.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cgdefu/2014/cgdefu.2014.14.issue-3/cg4017849/production/images/medium/cg-2013-017849_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cg4017849'>ACS Electronic Supporting Info</A></P>

Three-dimensional heterostructure of metallic nanoparticles and carbon nanotubes as potential nanofiller

Kim, Whi Dong,Huh, Jun Young,Ahn, Ji Young,Lee, Jae Beom,Lee, Dongyun,Hong, Suck Won,Kim, Soo Hyung Springer 2012 NANOSCALE RESEARCH LETTERS Vol.7 No.1

<P>The effect of the dimensionality of metallic nanoparticle-and carbon nanotube-based fillers on the mechanical properties of an acrylonitrile butadiene styrene (ABS) polymer matrix was examined. ABS composite films, reinforced with low dimensional metallic nanoparticles (MNPs, 0-D) and carbon nanotubes (CNTs, 1-D) as nanofillers, were fabricated by a combination of wet phase inversion and hot pressing. The tensile strength and elongation of the ABS composite were increased by 39% and 6%, respectively, by adding a mixture of MNPs and CNTs with a total concentration of 2 wt%. However, the tensile strength and elongation of the ABS composite were found to be significantly increased by 62% and 55%, respectively, upon addition of 3-D heterostructures with a total concentration of 2 wt%. The 3-D heterostructures were composed of multiple CNTs grown radially on the surface of MNP cores, resembling a sea urchin. The mechanical properties of the ABS/3-D heterostructured nanofiller composite films were much improved compared to those of an ABS/mixture of 0-D and 1-D nanofillers composite films at various filler concentrations. This suggests that the 3-D heterostructure of the MNPs and CNTs plays a key role as a strong reinforcing agent in supporting the polymer matrix and simultaneously serves as a discrete force-transfer medium to transfer the loaded tension throughout the polymer matrix.</P>

Pushing the Efficiency Envelope for Semiconductor Nanocrystal-Based Electroluminescence Devices Using Anisotropic Nanocrystals

Kim, Whi Dong,Kim, Dahin,Yoon, Da-Eun,Lee, Hyeonjun,Lim, Jaehoon,Bae, Wan Ki,Lee, Doh C. American Chemical Society 2019 Chemistry of materials Vol.31 No.9

<P>Colloidal semiconductor nanocrystals hold great promise in display technologies, as the tunable energy levels and narrow emission bandwidth allow for wide gamut in color space. Impetus for energy-efficient, high-color-quality display has driven the surge of interest in electrically driven quantum dot-based light-emitting diodes (QD-LEDs). While extensive efforts have led to synthesis of QDs with near-unity photoluminescence quantum yield and fabrication of QD-LEDs with external quantum efficiency reaching to the theoretical limit (∼20%), low out-coupling factor poses a challenge in the way of improving the device performance when spherical QDs are used. Geometrically anisotropic nanocrystals (NCs) such as nanorods or nanoplatelets represent a unique possible solution to enhancing light extraction efficiency. In this Perspective, we highlight important design principles of individual anisotropic NCs and their assembly in the context of LED applications.</P> [FIG OMISSION]</BR>

Biological and Antibacterial Activities of the Natural Herb <i>Houttuynia cordata</i> Water Extract against the Intracellular Bacterial Pathogen <i>Salmonella</i> within the RAW 264.7 Macrophage

Kim, Gon Sup,Kim, Dong Hyeok,Lim, Jeong Ju,Lee, Jin Ju,Han, Dae Yong,Lee, Whi Min,Jung, Won Chul,Min, Won Gi,Won, Chung Gil,Rhee, Man Hee,Lee, Hu Jang,Kim, Suk Pharmaceutical Society of Japan 2008 BIOLOGICAL & PHARMACEUTICAL BULLETIN Vol.31 No.11

<P>Salmonellosis is a major bacterial zoonosis that causes a variety of disease syndromes, from self-limiting enteritis to fatal infection in animals and food-borne infection and typhoid fever in humans. Recently, the emergence of multidrug-resistant strains of <I>Salmonella</I> sp. has caused more serious problems in public health. The present study investigated the antibacterial effects of <I>Houttuynia cordata</I> water extract (HCWE) against murine salmonellosis. In RAW 264.7 cells, there was no detectable cytotoxic effect of HCWE at any concentration between 25 and 100 μg/ml after 8-h incubation. The antibacterial activity of HCWE was then examined in a <I>Salmonella enterica</I> serovar (<I>Salmonella typhimurium</I>), and was found to increase in a dose-dependent manner at concentrations from 25 to 100 μg/ml during 8-h incubation. HCWE also affected RAW 264.7 cells including morphologic change and bacterial uptake, but there was no significant difference in bacterial replication in RAW 264.7 cells. With HCWE alone, nitric oxide (NO) production by RAW 264.7 cells did not increase, but when RAW 264.7 cells were infected by <I>S. typhimurium</I>, with or without HCWE, NO production with HCWE was 2-fold higher than that without HCWE. Treatment with HCWE did not affect inducible NO synthase (iNOS) mRNA expression by RAW 264.7 cells, but when RAW 264.7 cells with HCWE were infected by <I>S. typhimurium</I>, iNOS mRNA expression was increased during 8-h incubation. Furthermore, HCWE showed virulence reduction effects in <I>S. typhimurium</I>-infected BALB/c mice. After a lethal dose of <I>S. typhimurium</I>, the mortality rate in the HCWE untreated group was 100% at 7 d, but the HCWE 25, 50, and 100 μg/ml groups survived until 11, 17, and 23 d, respectively. These data suggest that HCWE is stable and beneficial in the treatment of bacterial infection including intracellularly replicating pathogens and may solve antimicrobial misuse and overuse.</P>

Controlled Vortex Formation and Facilitated Energy Transfer within Aggregates of Colloidal CdS Nanorods

Kim, Whi Dong,Chae, Weon-Sik,Bae, Wan Ki,Lee, Doh C. American Chemical Society 2015 Chemistry of materials Vol.27 No.8

<P>Vortex formation is observed in transmission electron microscopy (TEM) images of colloidal CdS nanorod (NR) aggregates. Upon adding polar (poor) solvents into the NR dispersion, the NRs passivated with alkylphosphonic acids start flocculating. When NR clusters are deposited on a TEM grid, the tips of the NRs are immobilized on the substrate, and capillary forces give rise to a net inward tilting as the solvent evaporates, eventually leading to the formation of vortices. Solvent polarity turns out to play a critical role in controlling the structure of vortices. Fluorescence lifetime imaging microscopy (FLIM) of the ensembles reveals that the vortex structures have profound influence on the energy transfer rate within the NR assembly.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2015/cmatex.2015.27.issue-8/cm5042925/production/images/medium/cm-2014-042925_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm5042925'>ACS Electronic Supporting Info</A></P>

Stacking of Colloidal CdSe Nanoplatelets into Twisted Ribbon Superstructures: Origin of Twisting and Its Implication in Optical Properties

Kim, Whi Dong,Yoon, Da-Eun,Kim, Dahin,Koh, Sungjun,Bae, Wan Ki,Chae, Weon-Sik,Lee, Doh C. American Chemical Society 2019 The Journal of Physical Chemistry Part C Vol. No.

<P>Relatively large faces of colloidal CdSe nanoplatelets (NPLs) drive the anisotropic nanomaterials into one-dimensional superstructures through stacking of NPLs when solvent evaporates. We observe that the assembly could result in the formation of <I>twisted ribbon</I> superstructures with varying pitch length depending on lateral dimensions of CdSe NPLs. Transmission electron microscopy images and simulated projection reveal that stacked NPLs are distorted. The estimation of the contact area between distorted NPLs suggests that this distortion leads to lower energy of overall nanoribbon superstructures. The average pitch length of superstructures on the lateral dimension of NPLs depends on the dimension of NPLs as it alters the distortion angle of NPLs and thus the rotation angle between NPLs. We investigate the energy transfer between NPLs in the context of the lateral dimension of NPLs and the geometric structure of their superstructures via transient photoluminescence decay measurements. Our analysis on the energy-transfer rate indicates that extinction coefficients, which are determined by lateral dimension of NPLs, are more responsible for the energy-transfer change than the rotation angle between CdSe NPLs within twisted ribbon superstructures. The dependence of the energy-transfer rate on the lateral dimension of NPLs highlights the importance of geometry of individual NPLs in the context of optical properties of NPLs in ensemble.</P> [FIG OMISSION]</BR>

Metal tips on pyramid-shaped PbSe/CdSe/CdS heterostructure nanocrystal photocatalysts: study of Ostwald ripening and core/shell formation

Kim, Whi Dong,Lee, Sooho,Pak, Chaewon,Woo, Ju Young,Lee, Kangha,Baum, Fá,bio,Won, Jonghan,Lee, Doh C. The Royal Society of Chemistry 2014 Chemical communications Vol.50 No.14

<P>We report ripening of metal particles anchored on pyramid-shaped heterostructure nanocrystals. The ‘intra-particle’ ripening results in a large metal tip at one corner with the other three tips vanishing. Investigation reveals that the ripening and core/shell formation affects photocatalytic activities <I>via</I> the Fermi level change.</P> <P>Graphic Abstract</P><P>The Ostwald ripening of metal nanoparticles on pyramid-shaped nanocrystals is elucidated. The controlled overgrowth of the metal shell on existing metal cocatalysts enables the study of the effects of the Fermi level upon photocatalysis using heterostructure nanocrystals. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc48919a'> </P>