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Lee, Tae Kwon,Kong, Dae Sol,Jin, Da Woon,Yun, Shinhee,Yang, Chan-Ho,Jung, Jong Hoon ELSEVIER 2019 Current Applied Physics Vol.19 No.6
<P><B>Abstract</B></P> <P>We investigated the ferroelectricity in proton-irradiated flexible Pb(Zr<SUB>0.52</SUB>Ti<SUB>0.48</SUB>)O<SUB>3</SUB> (PZT) thick films and their non-volatile memory characteristics. The Ni-Cr metal foil substrate allowed high-quality polycrystalline PZT films with flexible functionality to be fabricated using conventional sol-gel and high-temperature annealing methods. The 10-MeV proton-irradiated PZT film exhibited an almost square polarization−electric field hysteresis curve with saturated (<I>P</I> <SUB>s</SUB>) and remnant (<I>P</I> <SUB> <I>r</I> </SUB>) polarizations of 18.9 and 17.0 μC/cm<SUP>2</SUP>, respectively; which are slightly lower than as-grown PZT with <I>P</I> <SUB>s</SUB> = 28.7 μC/cm<SUP>2</SUP> and <I>P</I> <SUB> <I>r</I> </SUB> = 24.3 μC/cm<SUP>2</SUP>. The <I>P</I> <SUB> <I>r</I> </SUB> did not decrease even after 1000 cycles of continuous bending and unbending at a bending radius of 2.14 mm and decreased slightly to ∼80% of its initial value after 10<SUP>5</SUP> s. Although the <I>P</I> <SUB> <I>r</I> </SUB> decreased to ∼55% after 10<SUP>10</SUP> cycles, the electric polarization remained switchable under positive and negative electric fields. These characteristics suggest that the flexible PZT films could be utilized in non-volatile memory device applications in environments with high doses of proton irradiation, such as those in aeronautics and nuclear power plants.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Sol-gel growth of flexible PZT thick films on a Ni-Cr metal foil substrate. </LI> <LI> Large saturated and remnant electric polarization in proton-irradiated films. </LI> <LI> Mechanical stability, long retention time, and high fatigue resistance even after the high energy proton-irradiation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
사무직 근로자의 수면의 질 및 직무스트레스와 우울과의 관련성
강미나,강수영,권수정,김현주,배재원,이보연,이예진,임의롬,정다영,조한솔 이화여자대학교 간호과학대학 2013 이화간호학회지 Vol.- No.47
Purpose: The purpose of this study was to understand the degree of depression, sleep quality, job stress and their association among office workers. Method: A self-administered questionnaire was distributed to 147 workers employed in 5 big enterprises, and 5 small and medium enterprises from October 21 to November 21, 2012. The questionnaires included socio-demographic and health-related characteristics, job-related characteristics, sleep quality, job stress (KOSS) and depression (CES-D). Result: Among all subjects, 23.1% was in the depression group (21 points and over in the CES-D score). Depressive level was positively correlated with job stress and quality of sleep. The adjusted odd ratio for the effects of sleep quality and job stress on depression significantly increased in the depression group compared to that of the normal group. Multiple regression analysis revealed that the following factors of influence had combined explanatory powers on depression: BMI, life satisfaction, quality of sleep, and job stress. Conclusion: The study revealed that complicated influences were exerted on the level of depression by variable factors, as well as socio-demographic characteristics, health-related characteristics, quality of sleep, and job stress. Specifically, the level of depression was influenced by the quality of sleep and job stress.
Kwon, Da-Sol,Choi, Hyeong Yeol,Lee, Byoung-Min,Jeong, Young Gyu,Yang, Donsik,Kim, Sang-Tae,Choi, Jae-Hak Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.471 No.-
<P><B>Abstract</B></P> <P>High performance electric heaters based on carbon micropatterns (CMs), which were fabricated from a novolac resin by proton beam lithography (PBL) and carbonization, have been explored in this study. For the purpose, well-defined negative-type novolac micropatterns with crosslinked network structures were fabricated by PBL at the optimized fluence of 5 × 10<SUP>15</SUP> ions cm<SUP>−2</SUP> and then carbonized to form CMs. The fabricated 60–nm–thick CMs were characterized to have a high electrical conductivity of 2.12 × 10<SUP>2</SUP> S cm<SUP>−1</SUP> and a high optical transmittance of 78%. In an application as electric heaters, the 60–nm–thick CMs showed a high maximum temperature of 141.7 °C at 60 V with an excellent heating rate of 16.06 °C s<SUP>−1</SUP>. Therefore, the prepared transparent electric heaters can be used in window defrosting/defogging, display, gas sensing, and medical equipment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Carbon micropatterns (CMs) were prepared by PBL and carbonization. </LI> <LI> The CMs showed high electrical conductivity and high optical transmittance. </LI> <LI> The CMs exhibited an excellent electric heating performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>This study describes the fabrication of novolac-derived carbon micropatterns by proton beam lithography and carbonization for high-performance electric film heaters.</P> <P>[DISPLAY OMISSION]</P>
Phase-Inverted Multifrequency HIFU Transducer for Lesion Expansion: A Simulation Study
Kwon, Da Sol,Sung, Jin Ho,Park, Chan Yuk,Jeong, Jong Seob IEEE 2018 and Frequency Control Vol.65 No.7
<P>It has been well known that the treatment time of high-intensity focused ultrasound (HIFU) surgery can be reduced by expanding the focal area per sonication. Previously, a dual-concentric transducer using phase-inverted signals was proposed to axially extend the focal area, but it has suffered from the deep notch point between two focal lobes. In this paper, we propose the improved HIFU transducer with dual-concentric aperture driven by phase-inverted multifrequency signals based on an inversion layer technique. The proposed transducer can generate the expanded focal zone with a significantly reduced level of the notch point between two focal lobes in the axial direction. The performance of the proposed transducer was investigated using finite element analysis simulation. The electrical impedance, one-way impulse response, and acoustic field of the transducer were simulated. Subsequently, the lesion volume was investigated by heat transfer simulation. In the proposed method, the level of the notch point was increased above −6 dB due to various phase interactions between the fundamental and harmonic frequency combinations and the inverted and noninverted frequency combinations. The −6-dB depth of field related to the necrotic lesion size was increased by 141% compared with the conventional single element transducer. Thus, the proposed transducer can be a potential way to enlarge coagulated lesion size resulting in a reduced overall treatment time of HIFU surgery.</P>
Da Sol Kim,Young Hoon Jo,Il Kwon Huh,Sung Moon Byun 한국문화재보존과학회 2022 보존과학회지 Vol.38 No.1
The Bigyeokjincheolloe (bomb shell), a scientific cultural heritage, has outstanding historical value for sustaining a gunpowder weapon of Joseon. In this study, the bomb shell was modeled through three-dimensional (3D) scanning centered on the external shape and γ-ray radiography-based on the internal shape. In particular, to improve the contrast in the radiographic image, optimization and image processing were performed. After these processes, the thickness of the inner wall (2.5 cm on average) and the positions of the three mold chaplets were clearly revealed. For exhibition purposes, the 3D model of the bomb shell was output to a 3D printer and the output was rendered realistic by coloring. In addition, the internal functional elements, such as Mokgok, fuse, mud, gunpowder, and caltrops, were reproduced through handwork. The results will contribute to the study of digital heritages in two ways. First, the internal and external shapes of the bomb shell were modeled by fusing two different technologies, namely, 3D scanning and γ-ray radiography. Second, the internal shape of the bomb shell was constructed from the original form data and the reproduction was utilized for museum exhibitions. The developed modeling approach will greatly expand the scope of museum exhibitions, from those centered on historical content to those centered on scientific content.