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Small-scale analysis of brittle-to-ductile transition behavior in pure tungsten

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Journal of Materials Science & Technology 2022年第10期105卷 242-258页

作者： Yeonju Oh Won-Seok ko Nojun Kwak Jae-il Jang Takahito Ohmura heung Nam Han Department of Materials Science and Engineering&Research Institute of Advanced Materials Seoul National UniversitySeoul 08826South Korea School of Materials Science and Engineering University of UlsanUlsan 44610South Korea Division of Materials Science and Engineering Hanyang UniversitySeoul04763South Korea National Institute for Materials Science 1-2-1 SengenTsukubaIbaraki 305-0047Japan

Tungsten as a material exhibits broad and increasingly important applications;however,the characterization of its ductile-to-brittle transition(BDT)is currently limited to large-scale scenarios and destructive *** this study,we overcome this challenge by implementing small-scale techniques to provide a comprehensive understanding of the BDT behavior of pure *** order to predict the failure mode at various temperature ranges,the practical fracture analysis diagram has been proposed to describe the resistance to shear flow and cracking behavior with *** temperature nano-indentation tests have provided the inherent mechanical responses corresponding to the maximum shear stress at various temperatures,which is required for dislocation activities in an atomic scaled activation *** one hand,atomistic simulations have provided the temperature dependence of brittle fracture stress,where the atomic bonds break due to intergranular or intragranular *** considered four tungsten specimens having various microstructures prepared using different processing conditions of cold-rolling and post-annealing,and their BDT ranges were inferred using the obtained fracture analysis diagram with the statistical data *** fracture analysis diagram of each specimen obtained were compared with the direct observation of fracture responses in macroscopic mechanical tests,which conclusively indicated that the small-scale inherent mechanical properties are greatly relevant to the macroscopic BDT behavior in pure *** on the BDT estimations by small-scale characterization,we provided further insights into the factors affecting the BDT behavior of tungsten,focusing on the contributions of different types of dislocations.

关键词： Brittle-to-ductile transition Nano-indentation Molecular dynamics Dislocation Tungsten

Multi-Bandgap Monolithic Metal Nanowire Percolation Network Sensor Integration by Reversible Selective Laser-Induced Redox

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Nano-Micro Letters 2022年第3期14卷 216-228页

作者： Junhyuk Bang Yeongju Jung Hyungjun Kim Dongkwan Kim Maenghyo cho Seung Hwan ko Applied Nano and Thermal Science Lab Department of Mechanical EngineeringSeoul National University1 Gwanak‑roGwanak‑guSeoul 151‑742Republic of Korea Department of Mechanical Engineering Seoul National University1 Gwanak‑roGwanak‑guSeoul 08826Republic of Korea Institute of Advanced Machines and Design Institute of Engineering ResearchSeoul National UniversitySeoul 08826Republic of Korea

Active electronics are usually composed of semiconductor and metal electrodes which are connected by multiple vacuum deposition steps and photolithography ***,the presence of interface of dissimilar material between semiconductor and metal electrode makes various problems in electrical contacts and mechanical *** ideal electronics should not have defective interfaces of dissimilar *** this study,we developed a novel method to fabricate active electronic components in a monolithic seamless fashion where both metal and semiconductor can be prepared from the same monolith material without creating a semiconductor-metal interface by reversible selective laser-induced redox(rSLIR)***,rSLIR can control the oxidation state of transition metal(Cu)to yield semiconductors with two different bandgap states(Cu_(2)O and CuO with bandgaps of 2.1 and 1.2 eV,respectively),which may allow multifunctional sensors with multiple bandgaps from the same *** novel method enables the seamless integration of single-phase Cu,Cu_(2)O,and CuO,simultaneously while allowing reversible,selec-tive conversion between oxidation states by simply shining laser ***,we fabricated a flexible monolithic metal-semiconduc-tor-metal multispectral photodetector that can detect multiple *** unique monolithic characteristics of rSLIR process can provide next-generation electronics fabrication method overcoming the limitation of conventional photolithography methods.

关键词： Monolithic integration Seamless interface Multi-bandgap nanowire Laser-induced redox Multispectral photodetector

Effect of solid-solution strengthening on deformation mechanisms and strain hardening in medium-entropy V_(1-x)Cr_(x)CoNi alloys

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Journal of Materials Science & Technology 2022年第13期108卷 270-280页

作者： Hyun Chung Dae Woong Kim Woo Jin cho heung Nam Han Yuji Ikeda Shoji Ishibashi Fritz Körmann Seok Su Sohn Department of Materials Science and Engineering Korea UniversitySeoul 02841South Korea Center for High Entropy Alloys Pohang University of Science and TechnologyPohang 37673South Korea Department of Materials Science and Engineering and Research Institute of Advanced Materials Seoul National UniversitySeoul 08826South Korea Institute for Materials Science University of StuttgartPfaffenwaldring 55Stuttgart 70569Germany Computational Materials Design Max-Planck-Institut für Eisenforschung GmbHMax-Planck-Strabe 1Düsseldorf 40237Germany Research Center for Computational Design of Advanced Functional Materials(CD-Fmat) National Institute of Advanced Industrial Science and Technology(AIST)TsukubaIbaraki 305-8568Japan Department of Materials Science and Engineering Delft University of TechnologyMekelweg2Delft 2628 CDthe Netherlands

High-and medium-entropy alloys(HEAs and MEAs)possess high solid-solution *** investigations have been conducted on its impact on yield strength,however,there are limited reports regarding the relation between solid-solution strengthening and strain-hardening *** addition,no attempt has been made to account for the dislocation-mediated plasticity;most works focused on twinning-or transformation-induced plasticity(TWIP or TRIP).In this work we reveal the role of solidsolution strengthening on the strain-hardening rate via systematically investigating evolutions of deformation structures by controlling the Cr/V ratio in prototypical V_(1-x)Cr_(x)CoNi *** the TWIP of CrCoNi with the dislocation slip of V_(0.4)Cr_(0.6)CoNi,the hardening rate of CrCoNi was superior to slip-band refinements of V_(0.4)Cr_(0.6)CoNi due to the dynamic Hall-Petch ***,as V content increased further to V_(0.7)Cr_(0.3)CoNi and VCoNi,their rate of slip-band refinement in V_(0.7)Cr_(0.3)CoNi and VCoNi with high solid-solution strength surpassed that of *** it is generally accepted in conventional alloys that deformation twinning results in a higher strain-hardening rate than dislocation-mediated plasticity,we observed that the latter can be predominant in the former under an activated huge solid-solution strengthening *** high solid-solution strength lowered the cross-slip activation and consequently retarded the dislocation rearrangement rate,i.e.,the dynamic *** delay in the hardening rate decrease,therefore,increased the strain-hardening rate,results in an overall higher strain-hardening rate of V-rich alloys.

关键词： Medium-entropy alloy Tensile property Solid-solution strength Strain-hardening rate Stacking fault energy

Micro/nano-wrinkled elastomeric electrodes enabling high energy storage performance and various form factors

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Carbon Energy 2023年第12期5卷 137-152页

作者： Changeun Yoo Seokmin Lee Yongkwon Song Woojae Chang Moon Kyu Park Younji ko Jinhan cho Department of Chemical and Biological Engineering Korea UniversitySeoulSeongbuk-guRepublic of Korea KU-KIST Graduate School of Converging Science and Technology Korea UniversitySeoulSeongbuk-guRepublic of Korea Soft Hybrid Materials Research Center Advanced Materials Research DivisionKorea Institute of Science and Technology(KIST)Seongbuk-guSeoulRepublic of Korea

Stretchable elastomer-based electrodes are considered promising energy storage electrodes for next-generation wearable/flexible electronics requiring various shape ***,these elastomeric electrodes suffer from the limited electrical conductivity of current collectors,low charge storage capacities,poor interfacial interactions between elastomers and conductive/active materials,and lack of shape *** this study,we report hierarchically micro/nano-wrinkle-structured elastomeric electrodes with notably high energy storage performance and good mechanical/electrochemical stabilities,simultaneously allowing various form *** this study,a swelling/deswelling-involved metal nanoparticle(NP)assembly is first performed on thiol-functionalized polydimethylsiloxane(PDMS)elastomers,generating a micro-wrinkled structure and a conductive seed layer for subsequent *** the assembly of metal NPs,the conformal electrodeposition of Ni and NiCo layered double hydroxides layers with a homogeneous nanostructure on the micro-wrinkled PDMS induces the formation of a micro/nano-wrinkled surface morphology with a large active surface area and high electrical *** on this unique approach,the formed elastomeric electrodes show higher areal capacity and superior rate capability than conventional elastomeric electrodes while maintaining their electrical/electrochemical properties under external mechanical *** notable mechanical/electrochemical performance can be further enhanced by using spiral-structured PDMS(stretchability of~500%)and porous-structured PDMS(areal capacity of~280μAh cm^(-2)).

关键词： elastomeric electrodes electrodeposition micro/nano-wrinkled structures

Investigation on the magnetomechanical behavior of trilayered GM actuator

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Journal of Rare Earths 2008年第2期26卷 264-267页

作者： heung-Shik Lee chongdu cho Department of Mechanical Engineering Inha University Yonghyun-dong Nam-ku Incheon 402-751 South Korea

In this article, it was suggested a TbFe/Co/Dy trilayered GM （Giant Magnetostrictive） film type actuator and investigated the magnetomechanical characteristics of the actuator for micro application. The trilayered films were fabricated at different thickness ratios to get an optimized structure. TbFe had positive GM properties, and cobalt, dysprosium layers made the magnetostriction property of composite film increase in low magnetic field. To fabricate the Si based microactuator with trilayered film, micromachining processes including RIE （Reactive Ion Etching） and selective DC magnetron sputtering techniques were combined. The deposited film thicknesses were measured by X-ray diffraction （XRD）. As a result, the magnetization of the film on the fabricated actuator was observed to characterize the magnetic properties of the TbFe/Co/Dy film using VSM （Vibrating Sample Magnetometer）. The magnetostriction of the actuator was determined by measuring the differences of curvature of the film coated silicon substrates using the optical cantilever method, and the deflections were also estimated under the external magnetic field lower than 0.5T for micro-system applications.

关键词： GM actuator magnetostriction trilayered film magnetron sputtering magnetization rare earths

Posterior reversible encephalopathy syndrome following uneventful clipping of an unruptured intracranial aneurysm:A case report

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World Journal of Clinical Cases 2023年第19期11卷 4723-4728页

作者： Joseph Hwang Won-Ho cho Seung-Heon Cha Jun-Kyueng ko Department of Neurosurgery Biomedical Research InstitutePusan National University HospitalSchool of MedicinePusan National UniversityBusan 49241South Korea

BACKGROUND Posterior reversible encephalopathy syndrome(PRES)is characterized mainly by occipital and parietal lobe involvement,which can be reversible within a few ***,we report a rare case of PRES that developed after craniotomy for an unruptured intracranial aneurysm(UIA).CASE SUMMARY A 59-year-old man underwent clipping surgery for the treatment of UIA arising from the left middle cerebral *** surgery was performed uneventfully,and he regained consciousness quickly immediately after the *** the 4th hour after surgery,he developed a disorder of consciousness and *** resonance imaging revealed cortical and subcortical T2/FLAIR hyperintensities in the parietal,occipital,and frontal lobes ipsilaterally,without restricted diffusion,consistent with unilateral *** conservative treatment,his symptoms and radiological findings almost completely disappeared within *** our case,the important causative factor of PRES was suspected to be a sudden increase in cerebral perfusion pressure associated with temporary M1 *** Our unique case highlights that,to our knowledge,this is the second report of PRES developing after craniotomy for the treatment of *** must keep PRES in mind as one of the causes of perioperative neurological abnormality following clipping of an UIA.

关键词： Clipping Magnetic resonance imaging Posterior reversible encephalopathy syndrome Unruptured intracranial aneurysm Case report

Optimization of image capturing method of wear particles for condition diagnosis of machine parts

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中国有色金属学会会刊：英文版 2009年第B9期19卷 215-219页

作者： Yon-Sang cho heung-Sik PARK Department of Materials Engineering Dong-A University

Wear particles are inevitably occurred from moving parts, such as a piston-cylinder made from steel or hybrid materials. And a durability of these parts must be evaluated. The wear particle analysis has been known as a very effective method to foreknow and decide a moving situation and a damage of machine parts by using the digital computer image processing. But it is not laid down to calculate shape parameters of wear particle and wear volume. In order to apply image processing method in a durability evaluation of machine parts, it needs to verify the reliability of the calculated data by the image processing and to lay down the number of images and the amount of wear particles in one image. In this work, the lubricated friction experiment was carried out in order to establish the optimum image capture with the 1045 specimen under experiment condition. The wear particle data were calculated differently according to the number of image and the amount of wear particle in one image. The results show that capturing conditions need to be more than 140 wear particles in one image and over 40 images for the reliable data. Thus, the capturing method of wear particles images was optimized for condition diagnosis of machine moving parts.

关键词：计算机图像处理磨损颗粒机械零件优化条件诊断方法拍摄图像处理方法运动部件

Muscular atrophy and weakness in the lower extremities in Behçet’s disease: A case report and review of literature

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World Journal of Clinical Cases 2021年第20期9卷 5647-5654页

作者： koh-Woon Kim Jae-heung cho Department of korean Medicine Rehabilitation College of Korean MedicineKyung Hee UniversitySeoul 02447South Korea

BACKGROUND In Behçet’s disease(BD),very few cases of muscular involvement have been reported *** natural history and therapeutic protocol for muscular involvement in BD are obscure due to the low incidence of peripheral neuropathy or myopathy in *** purpose of our study was to report a rare case of BD with chronic,focal forms of neuromyopathy and review the relevant *** SUMMARY We herein report the case of a 54-year-old man who presented with progressive muscular atrophy and weakness of both thighs 2 years after the presentation of the cardinal symptoms of *** past medical history,electrophysiological study,neurological examination,blood tests,magnetic resonance imaging study,and histological exam were performed for the differential *** literature on muscular involvement in BD was *** examination revealed that muscular involvement was predominantly localized in the proximal parts of the lower *** enhancement of several thigh muscles was observed on magnetic resonance imaging,which corresponded with the clinical *** study of one of the enhanced muscles showed denervation atrophy of the muscle with superimposed myopathic changes,while electrophysiological studies only suggested *** To our knowledge,this is the first case of neurogenic muscular atrophy with a specific set of clinical,radiological,electrophysiological,and histological findings reported in BD.

关键词： Behçet’s disease Muscular atrophy Muscular weakness Neuropathy Myopathy Case report

High-Performance Perovskite Quantum Dot Solar Cells Enabled by Incorporation with Dimensionally Engineered Organic Semiconductor

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Nano-Micro Letters 2022年第12期14卷 272-285页

作者： Seyeong Lim Dae Hwan Lee Hyuntae choi Yelim choi Dong Geon Lee Sung Beom cho Seonkyung ko Jongmin choi Younghoon Kim Taiho Park Department of Chemical Engineering Pohang University of Science and Technology(POSTECH)Pohang 37673Republic of Korea Department of Materials Science and Engineering Hanyang UniversitySeoul 04763Republic of Korea Center of Materials Digitalization Korea Institute of Ceramic Engineering and Technology(KICET)Jinju 52851Republic of Korea Department of Materials Science and Engineering Ajou UniversitySuwon 16499Republic of Korea Department of Energy Science and Engineering Daegu Gyeongbuk Institute of Science and Technology(DGIST)Daegu 42988Republic of Korea Department of Chemistry Kookmin UniversitySeoul 02707Republic of Korea

Perovskite quantum dots(PQDs)have been considered promising and effective photovoltaic absorber due to their superior optoelectronic properties and inherent material merits combining perovskites and ***,they exhibit low moisture stability at room humidity(20-30%)owing to many surface defect sites generated by inefficient ligand exchange *** surface traps must be re-passivated to improve both charge transport ability and moisture *** address this issue,PQD-organic semiconductor hybrid solar cells with suitable electrical properties and functional groups might dramatically improve the charge extraction and defect *** organic semiconductors are typically low-dimensional(1D and 2D)and prone to excessive self-aggregation,which limits chemical interaction with *** this work,we designed a new 3D star-shaped semiconducting material(Star-TrCN)to enhance the compatibility with *** robust bonding with Star-TrCN and PQDs is demonstrated by theoretical modeling and experimental *** Star-TrCN-PQD hybrid films show improved cubic-phase stability of CsPbI_(3)-PQDs via reduced surface trap states and suppressed moisture *** a result,the resultant devices not only achieve remarkable device stability over 1000 h at 20-30%relative humidity,but also boost power conversion efficiency up to 16.0%via forming a cascade energy band structure.

关键词： CsPbI3 quantum dots Star-shaped organic semiconductors Hybrid perovskite quantum dots Solar cell stability High-efficiency photovoltaics