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Surface oxidation in a van der Waals ferromagnet Fe3-xGeTe2
김동섭,기정연,이지은,Liu Yu,김영학,김남동,황춘규,김원동,Petrovic Cedomir,이동렬,Jang Chaun,류혜진,최준우 한국물리학회 2021 Current Applied Physics Vol.30 No.-
We investigate the surface oxidation in a van der Waals ferromagnet Fe3-xGeTe2, a material widely utilized for spintronic applications. While known for its relative air-insensitivity, exposure to air during the handling process (e.g. device or heterostructure fabrication) can lead to reduction or disappearance of its magnetic signal. Comparison of x-ray absorption and x-ray magnetic circular dichroism spectra between pristine and air-exposed Fe3-xGeTe2 confirm a naturally oxidized surface layer on the material. The surface oxide layer has predominantly Fe3+ content. X-ray absorption spectroscopy done on micron-sized exfoliated Fe3-xGeTe2 flakes reveal that the change in the surface chemical properties can be quite significant for thin flakes. The surface modulation of Fe3- xGeTe2 can lead to inaccuracies in characterizing its interfacial magnetic and spin transport properties, and complicate device and heterostructure fabrication processes.
김진영,기정연,임선우,Shang Guo Piao,정병하,윤혜은,황현석,최범순,김진,양철우 대한의학회 2012 Journal of Korean medical science Vol.27 No.2
Sirolimus (SRL) is a promising drug for replacing calcineurin inhibitors. We performed this study to determine the optimal time of conversion from cyclosporine (CsA) to SRL in an experimental model of chronic CsA nephropathy. Three separate studies were performed. In the first study, SRL was given to rats with or without CsA for 4 weeks. In the second study, rats were treated initially with CsA for 1 week, and then switched to SRL (early conversion). In the third study, CsA was given for 4 weeks and then replaced by SRL for 4 weeks treatment of CsA (late conversion). The influence of SRL on CsA-induced renal injury was evaluated by assessing renal function, histopathology (interstitial inflammation and fibrosis), and apoptotic cell death. Combined CsA and SRL treatment significantly impaired renal function, increased apoptosis, and interstitial fibrosis and inflammation compared with CsA or SRL treatment alone. Early conversion to SRL did not change renal function, histopathology, or apoptosis compared with early CsA withdrawal. By contrast,late conversion to SRL significantly aggravated these parameters compared with late CsA withdrawal. In conclusion, early conversion from CsA to SRL is effective in preventing CsAinduced renal injury in a setting of CsA-induced renal injury.
김수현,오은지,기정연,송현국,최종영,문인성,김동구,양철우,한동희,윤혜은 대한의학회 2009 Journal of Korean medical science Vol.24 No.-
The CD4+CD25+ T regulatory cells (Tregs) play an important role in immune tolerance in experimental transplantation but the clinical significance of circulating Tregs in the peripheral blood is undetermined. In 50 kidney transplant (KT) recipients, 29 healthy controls and 32 liver transplant (LT) recipients, the frequency of Tregs was measured with flow cytometry before and after transplantation. In the KT recipients, IL-10 secretion was measured with an enzyme-linked immunospot (ELISPOT) assay. The median frequency of circulating Tregs before KT was similar to that in healthy controls but significantly lower than that in LT patients before transplantation. The frequency of Tregs was significantly decreased in patients with subclinical acute rejection compared with those without subclinical acute rejection. Calcineurin inhibitors (CNIs) and anti-CD25 antibody decreased the frequency of Tregs but mTOR inhibitor did not. The frequency of donor-specific IL-10 secreting cells did not correlate with the number of Tregs. The frequency of circulating Tregs in KT recipients is strongly affected by CNIs and anti-CD25 antibody, and a low frequency of Tregs is associated with subclinical acute rejection during the early posttransplant period.
김국태,김동옥,기정연,서일완,최영성,최준우,이동렬 한국물리학회 2021 Current Applied Physics Vol.30 No.-
The induced Pt magnetization in a Pt/Co/Pt thin film structure is studied. The normally nonmagnetic Pt acquires a magnetic moment due to the magnetic proximity effect at the Co–Pt interfaces. Element specific Pt structural and magnetic properties are characterized by synchrotron-based resonant x-ray reflectivity and x-ray resonant magnetic reflectivity measurements. An advanced analysis method based on Bayesian inference is used for model fitting of the x-ray data. Using this method, we retrieve the best fit values of material parameters (e.g., thickness, interfacial roughness) from the data. Analysis of x-ray reflectivity data of this specific system shows that the Pt magnetization and Co–Pt interfacial roughness is significantly different between the top and bottom Pt layers, with both values being larger in the top Pt. The successful application of this Bayesian method to study the magnetic and structural properties of a thin film system demonstrates its effectiveness for x-ray reflectivity data analysis.
민혜숙,차진주,김기태,김정은,기정연,김현욱,이지은,한지영,정낙신,차대룡,강영선 대한의학회 2016 Journal of Korean medical science Vol.31 No.9
The concentration of adenosine in the normal kidney increases markedly during renal hypoxia, ischemia, and inflammation. A recent study reported that an A3 adenosine receptor (A3AR) antagonist attenuated the progression of renal fibrosis. The adriamycin (ADX)-induced nephropathy model induces podocyte injury, which results in severe proteinuria and progressive glomerulosclerosis. In this study, we investigated the preventive effect of a highly selective A3AR antagonist (LJ1888) in ADX-induced nephropathy. Three groups of six-week-old Balb/c mice were treated with ADX (11 mg/kg) for four weeks and LJ1888 (10 mg/kg) for two weeks as following: 1) control; 2) ADX; and 3) ADX + LJ1888. ADX treatment decreased body weight without a change in water and food intake, but this was ameliorated by LJ1888 treatment. Interestingly, LJ1888 lowered plasma creatinine level, proteinuria, and albuminuria, which had increased during ADX treatment. Furthermore, LJ1888 inhibited urinary nephrin excretion as a podocyte injury marker, and urine 8-isoprostane and kidney lipid peroxide concentration, which are markers of oxidative stress, increased after injection of ADX. ADX also induced the activation of proinflammatory and profibrotic molecules such as TGF-β1, MCP-1, PAI-1, type IV collagen, NF-κB, NOX4, TLR4, TNFα, IL-1β, and IFN-γ, but they were remarkably suppressed after LJ1888 treatment. In conclusion, our results suggest that LJ1888 has a renoprotective effect in ADX-induced nephropathy, which might be associated with podocyte injury through oxidative stress. Therefore, LJ1888, a selective A3AR antagonist, could be considered as a potential therapeutic agent in renal glomerular diseases which include podocyte injury and proteinuria.