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Sangjun Oh,Soo-Hyeon Park,Chulhee Lee,Heekyung Choi,Wonwoo Park,Keeman Kim IEEE 2010 IEEE transactions on applied superconductivity Vol.20 No.3
<P>We have developed an apparatus to investigate the effect of transverse stress under axial strain on the critical current of superconducting strands. An internal tin Nb<SUB>3</SUB>Sn wire is soldered on a C-shape ring (called Pacman) made of 2% beryllium doped copper alloy and axial strain from -0.7 to 0.7% can be applied. The actual strain on a sample was estimated from a comparison with the critical current measurement results using a Walter spiral probe. Reversible transverse stress effects on the critical current were studied in this work and the transverse pressure was applied up to 40 MPa under ±0.5% axial strain. The critical current was initially increased about 3% as transverse load was applied and then decreased almost linearly under compressive axial strain. Similar behavior is observed under tensile axial strain but the critical current decreases rather sharply at higher load. A unified description based on 3 dimensional deviatoric strain was difficult for the sample studied in this work.</P>
Strain dependence of critical current in internal tin process Nb<sub>3</sub>Sn strands
Oh, Sangjun,Park, Soo Hyeon,Lee, Chulhee,Chang, Yongbok,Kim, Keeman,Park, Pyeong-Yeol IEEE 2005 IEEE transactions on applied superconductivity Vol.15 No.2
The development of a high performance superconducting magnet requires a thorough understanding of the strain effect in the critical current density (J<SUB>c</SUB>) of Nb<SUB>3</SUB>Sn strands. A modified version of the WASP device is used for the investigation of the strain effect. The spring is made of BeCu alloy and is capable of applying strain up to 0.7% reversibly at 4.2 K. Several types of high performance Nb<SUB>3</SUB>Sn strands (J<SUB>c</SUB>>1000 A/mm<SUP>2</SUP> at 12 T and 4.2 K) have been developed using internal tin process. A comparative study on the axial strain dependence of the critical current is performed.
Comparison of Dorsal and Medial Arthroscopic Approach to Canine Coxofemoral Joint: A Cadaveric Study
Sangjun Oh 대한수의학회 2023 Journal of Veterinary Science Vol.24 No.1
Background: Arthroscopic exploration of ventromedial part of canine coxofemoral joint is limited in conventional dorsal approach. Objectives: We evaluated the efficacy of a medial arthroscopic approach to the coxofemoral joint of dogs by analyzing the joint visible area and performing a safety analysis. Methods: Arthroscopic approaches to the coxofemoral joint were made in five cadavers using a traditional (dorsal) and novel (medial) approach. Three observers scored the visible area of images and videos of the acetabulum and femur. A safety analysis was performed via dissection of the medial hind limb. The distance between neurovascular structures and arthroscopic portals was measured. Results: The acetabulum was more visible in the dorsal than in the medial approach, with mean visualization scores of 16 ± 0.00 and 11.83 ± 1.26, respectively. The medioventral side of the femur was significantly more visible in the medial than in the dorsal approach, with mean visualization scores of 3.9 ± 0.99 and 6.93 ± 0.58, respectively. Safety analysis confirmed the medial portal site was safe, provided that the surgeon has comprehensive knowledge of the joint. The minimum distance from the arthroscopic medial portals to the nearest neurovascular structures was 2.5 mm. Conclusions: A medial arthroscopic approach to the canine coxofemoral joint has potential clinical application. Dorsal and medial approaches differ significantly and have distinct purposes. The medial approach is useful to access the ventromedial joint, making it an eligible diagnostic method for an arthroscopic evaluation of this area.
Sangjun Oh,Chulhee Lee,Heekyung Choi,Kyungmo Moon,Keeman Kim,Jiman Kim,Pyeong-Yeol Park IEEE 2008 IEEE transactions on applied superconductivity Vol.18 No.2
<P>We have developed a probe for the critical current measurements of low temperature superconducting strands at various field, temperature and strain. A 30 cm-long strand sample is soldered on a Walters spiral made of beryllium copper alloy and compressive or tensile axial strain can be applied up to 0.7%. Temperature control ability was tested using a MgB<SUB>2</SUB> wire up to 30 K. Three cernox sensors are attached on a spiral adjacent to the strand and the temperature of the spiral is controlled within plusmn50 mK of target temperature during the critical current measurement up to 80 A. Extensive critical current measurements have been carried out for an internal-tin processed Nb<SUB>3</SUB>Sn strand. It was found that the measured field, temperature and strain dependence of the critical current for the internal-tin Nb<SUB>3</SUB>Sn strand is in agreement with the recent scaling law based on strong coupling theory of superconductivity.</P>
Oh, Sangjun,Lee, Chulhee,Cho, K W,Kim, Keeman,Uglietti, D,Flü,kiger, R IOP Publishing Ltd 2007 Superconductor science & technology Vol.20 No.8
<P>We find a simple expression for the field dependences of the <I>n</I>-value for Nb<SUB>3</SUB>Sn strands which gives reasonable fits to empirical data. It is also found that a relationship between the <I>n</I>-value and the critical current, which is obtained from an assumed reduction of the flux line lattice shearing pinning force due to thermal activation, can describe the field dependence of the critical current. Using the relation between the <I>n</I>-value and the critical current, we propose a scaling law which we have called the Kramer model including thermal activation. It is shown that the proposed scaling law can explain the critical current data at 4.2 K, even at high field near the upper critical field. It is also compared with Ekin’s strain scaling law.</P>
Sangjun Oh,Oh, D.K.,Bae, C.J.,Kim, H.C.,Keeman Kim Institute of Electrical and Electronics Engineers 2007 IEEE transactions on applied superconductivity Vol.17 No.2
<P>We report detailed magnetization measurement results for two internal-tin Nb<SUB>3</SUB>Sn strands. The paramagnetic background of a Mitsubishi strand is about 4 times larger than that of a KAT strand below the transition temperature, which can be understood as combined effects of Pauli and Langevin paramagnetism. From magnetic relaxation measurement for the KAT strand, a possibility of surface barrier effect is discussed. After subtracting the paramagnetic background, reversible magnetization data are analysed using the Hao-Clem model and the Ginzburg-Landau parameters (kappa), the thermodynamic and the upper critical fields (B<SUB>c</SUB>,B<SUB>c2</SUB>) at various temperatures are obtained. The temperature dependences of kappa, B<SUB>c</SUB> and B<SUB>c2</SUB> are compared with the recent theoretical calculation results for Nb<SUB>3</SUB>Sn and also with widely used empirical formulas.</P>