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Dynamic Characteristics of a Hard Disk Drive Spindle System Due to Imperfect Shaft Roundness
Koak, K.Y.,Kim, H.W.,Jung, K.M.,Jang, G.H. IEEE 2009 IEEE transactions on magnetics Vol.45 No.11
<P>This paper proposes a modified Reynolds equation for the coupled journal and thrust fluid dynamic bearings (FDBs) to include variable film thickness due to imperfect roundness of a rotating shaft. A finite element method is used to solve the modified Reynolds equation to calculate the pressure. Reaction force, moment, and friction torque of FDBs are calculated by integrating the pressure and shear stress along the fluid film. The dynamic behavior of a hard disk drive (HDD) spindle system is investigated by solving the equations of motion with six degrees of freedom using the Runge-Kutta method. This research shows that the imperfect roundness of the shaft increases the nonlinearity of FDBs. Imperfect roundness of the shaft generates harmonics of the groove number plusmn 1 in the bearing reaction force and the displacement of the HDD spindle system even in the case of stationary grooved FDBs.</P>
Indocyanine green angiography of retinal astrocytomas associated with tuberous sclerosis
Nilufer Koak,Ali Osman Saatci,Suleyman Kaynak,Mehmet Hilmi Ergin,Guray Cray Ingil 대한안과학회 2003 Korean Journal of Ophthalmology Vol.17 No.2
As small astrocytic hamartomas can sometimes be missed during routine ophthalmoscopy in patients with tuberous sclerosis, fluorescein and/-or indocyanine green angiography maybe more helpful in identifying such small astrocytomas. In fluorescein angiography, astrocytomas show gradually increasing hyperfluorescence due to the vascular permeability of astrocytomas. In indocyanine green angiography, astrocytomas appear hypocyanescent, most prominently during the late phases. We report the indocyanine green angiographic findings of retinal astrocytomas in a patient with tuberous sclerosis.
규산질계(硅酸質系) 분체형(粉體型) 침투성(侵透性) 도포방수재(塗布防水材)의 부착성(附着性) 평가(評價)에 관(關)한 기초적(基礎的) 연구(硏究)
郭奎成 ( Koak Kyu Sung ),金上甲 ( Kim Sang Gab ),李東烈 ( Lee Dong Ryul ),吳祥根 ( Oh Sang Keun ) 한국구조물진단유지관리공학회 1997 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.1 No.1
This study deals with the effect on bond strength properties of waterproofing layer and mortar or concrete substrate applicated by Siliceous Slurry Coatings waterproofing materials. Properties of bond strength change condition of concrete substrate, temperature, moisture and curing and so on. The purpose of this study is that it makes the estimation value of bond strength of concrete wall and anticorrosive lager when coated siliceous slurry coatings as waterproofing materials for durability performance estimation depend on concrete watertightness.
Jai-Young Koak,Joo-Hee Lee,Ji-Man Park,Seong-Joo Heo,Seong-Kyun Kim,Ri-Cheng Zheng 대한치과보철학회 2014 The Journal of Advanced Prosthodontics Vol.6 No.5
PURPOSE The aim of present study was to identify characteristic and response of mouse bone marrow (BM) derived low-adherent bone marrow mesenchymal stem cells (BMMSCs) obtained by quantification of extracellular matrix (ECM). MATERIALS AND METHODS Non-adherent cells acquired by ECM coated dishes were termed low-adherent BMMSCs and these cells were analyzed by in vitro and in vivo methods, including colony forming unit fibroblast (CFU-f), bromodeoxyuridine (BrdU), multi-potential differentiation, flow cytometry and transplantation into nude mouse to measure the bone formation ability of these low-adherent BMMSCs. Titanium (Ti) discs with machined and anodized surfaces were prepared. Adherent and low-adherent BMMSCs were cultured on the Ti discs for testing their proliferation. RESULTS The amount of CFU-f cells was significantly higher when non-adherent cells were cultured on ECM coated dishes, which was made by 7 days culturing of adherent BMMSCs. Low-adherent BMMSCs had proliferation and differentiation potential as adherent BMMSCs in vitro. The mean amount bone formation of adherent and low-adherent BMMSCs was also investigated in vivo. There was higher cell proliferation appearance in adherent and low-adherent BMMSCs seeded on anodized Ti discs than machined Ti discs by time. CONCLUSION Low-adherent BMMSCs acquired by ECM from non-adherent cell populations maintained potential characteristic similar to those of the adherent BMMSCs and therefore could be used effectively as adherent BMMSCs in clinic.