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Sliding wear behavior of magnetorheological fluid for brass with and without magnetic field

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Transactions of Nonferrous Metals Society of China 2013年第2期23卷 400-405页

作者： Wan-Li SONG Chul-Hee LEE seung-bok choi Department of Mechanical Engineering Inha University

A pin-on-disc wear apparatus was used to carry out the tribological experiment of brass to investigate the effect of a magnetorheological （MR） fluid on the interfacial surface with and without magnetic field. A series of tests were performed at the loads of 20-100 N and rotating speeds of 127-425 r/min for 2 h. The friction coefficient and wear rate were monitored by the wear apparatus, while the microstructures of the worn surfaces were observed by scanning electron microscope （SEM）. In addition, the chemical composition of worn surfaces was analyzed by energy dispersive X-ray spectroscopy （EDS）. Test results show different friction and wear performance of the MR fluid with and without magnetic field. At the same time, the effects of various normal loads and rotating speeds on the tribological behavior were investigated. Through the investigation of the morphologies of the wom surfaces under the magnetic field, it is found that the MR particles are clearly evident on the wom surface and the plastic flow of ridges causes the lateral extrusion. This directly indicates that abrasive wear is the predominant wear mechanism observed with MR fluid.

关键词： magnetorheological fluid sliding wear brass magnetic field friction coefficient

Characteristics of Micro Electrochemical Polishing to Improve the Surface Quality of the Stainless Steel Tube

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Journal of Iron and Steel Research International 2012年第S2期19卷 1137-1140页

作者： seung-Gun choi Sung-Hyun Kim Eun-Sang Lee seung-bok choi Myeong-woo Cho School of Mechanical Engineering Inha University Department of Mechanical Engineering Inha University

Electrochemical polishing is the anodic dissolution process without contact with tools,is a surface treatment method to make a surface planarization using an electrochemical reaction with low applied *** surface quality is mainly affected by the many process *** improve the surface quality,the control of parameters is very *** aim of this study is to investigate the characteristic of electrochemical polishing effect for inner diameter of Stainless Steel *** order to analyze the characteristics of surface quality were measured in terms of temperature, applied current and machining *** investigation can enhance the surface quality of inner diameter Stainless Steel ***,we have verified improved results by using selected optimal conditions.

关键词： Electrochemical polishing surface quality applied current

Wave-tide-surge coupled model simulation for Typhoon Maemi

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Acta Oceanologica Sinica 2007年第1期26卷 35-47页

作者： choi Byung Ho KIM Dong Chule KIM Young bok KIM Hyun seung Department of Civil and Environmental Engineering Sungkyunkwan UniversitySuwon 440-746Korea Korean Ocean Science and Engineering Corporation Seoul 152-050Korea

Reasonably accurate predictions of wave heights, current and elevations during storm events are vital information for marine operations and design of offshore and coastal structures in the surrounding seas of Korea Peninsula. Ocean circulation and wind-wave models have traditionally been run separately, but recent researches have identified potentially important interactions between current and wave motions. The coupled tide-surge and the WAM wave models at the atmospheric boundary layer and bottom boundary layer around the Korea Peninsula are applied for the Typhoon Maemi （0314） event. Communication between the models is aehievod using MPI. Results are compared with coastal tide gauges and moored wave buoys and comparisons are also made between wave computations from the coupled model and the independent third generation wave models. Results suggest that applying the fide-surge-coupled model can be an effective means of obtaining wave and storm surge predictions simultaneously.

关键词： wave-tide-surge coupled simulation Typhoon Maemi wave models

Therapeutic potential of exercise-hormone irisin in Alzheimer's disease

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Neural Regeneration Research 2025年第6期20卷 1555-1564页

作者： Eunhee Kim Rudolph ETanzi Se Hoon choi Genetics and Aging Research Unit MassGeneral Institute for Neurodegenerative DiseaseDepartment of NeurologyMassachusetts General HospitalHarvard Medical SchoolCharlestownMAUSA McCance Center for Brain Health Massachusetts General HospitalBostonMAUSA

Irisin is a myokine that is generated by cleavage of the membrane protein fibronectin type Ⅲ domain-containing protein 5(FNDC5) in response to physical exercise. Studies reveal that irisin/FNDC5 has neuroprotective functions against Alzheimer's disease, the most common form of dementia in the elderly, by improving cognitive function and reducing amyloid-β and tau pathologies as well as neuroinflammation in cell culture or animal models of Alzheimer's disease. Although current and ongoing studies on irisin/FNDC5 show promising results, further mechanistic studies are required to clarify its potential as a meaningful therapeutic target for alleviating Alzheimer's disease. We recently found that irisin treatment reduces amyloid-β pathology by increasing the activity/levels of amyloid-β-degrading enzyme neprilysin secreted from astrocytes. Herein, we present an overview of irisin/FNDC5's protective roles and mechanisms against Alzheimer's disease.

关键词： Alzheimer's disease exercise fibronectin typeⅢdomain-containing protein 5(FNDC5) irisin

Absorption-Dominant mmWave EMI Shielding Films with Ultralow Reflection using Ferromagnetic Resonance Frequency Tunable M-Type Ferrites

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Nano-Micro Letters 2023年第6期15卷 1-23页

作者： Horim Lee seung Han Ryu Suk Jin Kwon Jae Ryung choi Sang‑bok Lee Byeongjin Park Composites Research Division Korea Institute of Materials Science797 ChangwondaeroSeongsan‑GuChangwonGyeongsangnam‑Do 51508Republic of Korea

Although there is a high demand for absorption-dominant electromagnetic interference(EMI) shielding materials for 5G millimeter-wave(mmWave) frequencies, most current shielding materials are based on reflection-dominant conductive materials. While there are few absorption-dominant shielding materials proposed with magnetic materials, their working frequencies are usually limited to under 30 GHz. In this study, a novel multi-band absorption-dominant EMI shielding film with M-type strontium ferrites and a conductive grid is proposed. This film shows ultralow EMI reflection of less than 5% in multiple mmWave frequency bands with sub-millimeter thicknesses, while shielding more than 99.9% of EMI. The ultralow reflection frequency bands are controllable by tuning the ferromagnetic resonance frequency of M-type strontium ferrites and composite layer geometries. Two examples of shielding films with ultralow reflection frequencies, one for 39 and 52 GHz 5G telecommunication bands and the other for 60 and 77 GHz autonomous radar bands, are presented. The remarkably low reflectance and thinness of the proposed films provide an important advancement toward the commercialization of EMI shielding materials for 5G mmWave applications.

关键词： 5G communication MmWave EMI shielding M-type ferrites

Apolipoprotein A-I binding protein-mediated neuroprotection in glaucomatous neuroinflammation and neurodegeneration

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Neural Regeneration Research 2025年第5期20卷 1414-1415页

作者： Sinwoo Hwang seunghwan choi Soo-Ho choi Keun-Young Kim Yury I.Miller Won-Kyu Ju Hamilton Glaucoma Center and Shiley Eye Institute The Viterbi Family Department of OphthalmologyUniversity of California San DiegoLa JollaCAUSA Department of Medicine University of California San DiegoLa JollaCAUSA National Center for Microscopy and Imaging Research Department of NeurosciencesUniversity of California San DiegoLa JollaCAUSA

Glaucoma is a multifactorial eye disorder that can cause vision loss and irreversible blindness,affecting individ uals aged 40 to 80 yea rs *** to the aging population,it is expected that the number of people affected by glaucoma will surpass 111 million by 2040 as the disease becomes more *** primarily contributes to optic nerve axon loss and the progressive degeneration of retinal ganglion cells (RGCs),subsequently leading to vision impairment.

关键词： irreversible pass primarily

Acute and chronic excitotoxicity in ischemic stroke and late-onset Alzheimer's disease

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Neural Regeneration Research 2025年第7期20卷 1981-1988页

作者： Shan Ping Yu Emily choi Michael QJiang Ling Wei Department of Anesthesiology Emory University School of MedicineAtlantaGAUSA Center for Visual and Neurocognitive Rehabilitation Atlanta Veterans Affairs Medical CenterDecaturGAUSA

Stroke and Alzheimer's disease are common neurological disorders and often occur in the same *** comorbidity of the two neurological disorders represents a grave health threat to older *** review presents a brief background of the development of novel concepts and their clinical *** activity of glutamatergic N-methyl-D-aspartate receptors and N-methyl-D-aspartate receptor-mediated Ca^(2+)influx is critical for neuronal *** ischemic insult induces prompt and excessive glutamate release and drastic increases of intracellular Ca^(2+)mainly via N-methyl-D-aspartate receptors,particularly of those at the extrasynaptic *** Ca^(2+)-evoked neuronal cell death in the ischemic core is dominated by necrosis within a few hours and days known as acute ***,mild but sustained Ca^(2+)increases under neurodegenerative conditions such as in the distant penumbra of the ischemic brain and early stages of Alzheimer's disease are not immediately toxic,but gradually set off deteriorating Ca^(2+)-dependent signals and neuronal cell loss mostly because of activation of programmed cell death *** on the Ca^(2+)hypothesis of Alzheimer's disease and recent advances,this Ca^(2+)-activated“silent”degenerative excitotoxicity evolves from years to decades and is recognized as a unique slow and chronic *** N-methyl-D-aspartate receptor subunit GluN3A,primarily at the extrasynaptic site,serves as a gatekeeper for the N-methyl-D-aspartate receptor activity and is neuroprotective against both acute and chronic *** stroke and Alzheimer's disease,therefore,share an N-methyl-D-aspartate receptor-and Ca^(2+)-mediated mechanism,although with much different time *** is thus proposed that early interventions to control Ca^(2+)homeostasis at the preclinical stage are pivotal for individuals who are susceptible to sporadic late-onset Alzheimer's disease and Alzheimer's disease-related

关键词： Ca^(2+)hypothesis cognitive deficits hyperactivity late-onset Alzheimer's disease neurodegeneration N-methyl-D-aspartate receptors N-methyl-D-aspartate receptor subunits pathogenesis preventive treatment

Ex situ aging effect on sulfonated poly(ether ether ketone) membrane:Hydration-dehydration cycling and hydrothermal treatment

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Journal of Energy Chemistry 2022年第7期31卷 583-592,I0014页

作者： seung-Young choi Kyeong Sik Jin Polymer&Materials Chemistry Department of ChemistryLund UniversitySE-22100Sweden Center for Hydrogen·Fuel Cell Research Korea Institute of Science and Technology(KIST)Seoul 02792Republic of Korea Pohang Accelerator Laboratory Pohang University of Science and Technology(POSTECH)PohangKyungbuk 37673Republic of Korea

Prolonged hydrothermal treatment for sulfonated poly(ether ether ketone) membranes induces mechanical degradation and developing hydrophilic-hydrophobic phase separation, simultaneously. The enhanced phase separation provides incremental proton conductivity to the membranes, whereas mechanical degradation drastically reduces device stability. On this basis, we describe here the effects of two different ex situ aging processes on sulfonated poly(ether ether ketone) membranes: hydrationdehydration cycling and prolonged hydrothermal treatment. Both aged membranes exhibited enhanced phase separation under the hydrated conditions, as characterized by small angle X-ray ***, when the aged membranes were dried again, the nanostructure of the membranes aged via the hydration-dehydration cycling was recoverable, whereas that of the membranes aged via prolonged hydrothermal treatment was irreversible. Furthermore, the two differently aged membranes showed clear differences in thermal, mechanical, and electrochemical properties. Finally, we implemented both aged membranes in fuel cell application. The sample aged via hydration-dehydration cycling maintained its improved cell performance, whereas the sample aged via hydrothermal treatment showed drastically reduced cell performance after durability test for 50 h.

关键词： Sulfonated poly(ether ether ketone) Humidity cycle test Ex situ aging Proton exchange membrane Fuel cell

Optimal Design of Bobbinless Rotary Magnetorheological Material Based Brake

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Journal of Iron and Steel Research International 2012年第S1期19卷 495-500页

作者： NGUYEN Quoc-hung choi seung-bok SONG Byung-keun Department of Mechanical Engineering Inha UniversityIncheon 402-751Korea Department of Mechanical System Engineering University of IncheonIncheon 406-840Korea

The paper presents a novel configuration in order to improve the compactness and manufacturing cost of magneto-rheological material(or fluid)based brakes(MRB in short).In conventional configurations of MRBs,the coil is normally wound on a nonmagnetic bobbin which is placed on the *** causes difficulties in manufacturing of the brake and the bottle-neck problem of magnetic *** the proposed configuration,the coil is wound directly on the inner cylinder of the *** this case,the inner cylinder of the housing should be designed in a special shape that maximizes the magnetic flux across the MR fluid(MRF)*** proposing of the new configuration of the MRBs,the modeling of the MRBs is performed based on Bingham rheological model of the *** optimal design of the proposed MRBs and conventional MRBs is then performed based on finite element analysis results of magnetic circuit of the MRBs.A comparative work between the optimal parameters of the proposed MRBs and conventional MRBs is conducted and the advanced performance characteristics of the proposed MRBs are investigated.

关键词： magneto-rheological fluid magneto-rheological brake optimal design finite element method