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 | Authors: Oh, S.; Kim, K.; ; Abstract: There are a lot of experimental reports on the scaling of flux pinning in the form of $F=F_{m}b^{1/2}(1-b)^{2}$ , with $b=B/B_{c2}$. The temperature dependence of $F_{m}$ is approximately proportional to $B_{c2}^{5/2}$, whereas the strain dependence of $F_{m}$ is reported to be proportional to the upper critical field Bc2. In this work, we re-analyze our previous data with the Kramer model including the pin-breaking dynamic pinning force $(F_{p})$ for a low field region. It is shown that the extrapolated upper critical field $B_{c2}^{ast}$, strongly depend on the ratio between the mean of the parameter $K_{p}$ for $F_{p}$ $(≪!K_{p}!>)$ and the parameter $K_{s}$ for the flux line lattice shearing pinning force $F_{s}$. It is found that the strain dependence of $F_{m}$ at 4.2 K is approximately proportional to $(B_{c2}^{ast})^{1.5}$. We further compare the data with the prediction of our recent scaling theory based on Eliashberg theory of strongly coupled superconductors. It is shown that the strain dependence of $F_{m}$ at 4.2 K is proportional to $B_{c2}^{5/2} kappa ^{ - 2}$, consistent with the temperature dependence of $F_{m}$. Moreover, this model agrees reasonably well even with the data in a high compressive strain region (≪$-$0.8%). |
| Authors: Adachi, Y.; Kawai, J.; Uehara, G.; Miyamoto, M.; Tomizawa, S.; Kawabata, S.; ; Abstract: A 75-ch SQUID biomagnetometer system for the measurement of the cervical spinal cord evoked magnetic field (SCEF) was developed for the purpose of the noninvasive functional diagnosis of the spinal cord. The sensor array has 25 SQUID vector sensors arranged along the cylindrical surface to fit to the shape of the subject's neck. The magnetic fields, not only in the direction radial to the subject's body surface but also in the tangential direction, are observed in the area of 80 mm$,times,$ 90 mm at one time. The dewar has a unique shape with a cylindrical main body and a protrusion from its side surface. The sensor array is installed in the protruded part. This design is optimized to detect magnetic signals at the back of the neck of the subject sitting in a reclining position. We applied the developed SQUID system to the cervical SCEF measurement of normal subjects who were given electric pulse stimulation to their median nerves at the wrists. The evoked magnetic signals were successfully detected at the cervixes of all subjects. A characteristic pattern of transition of the SCEF distribution was observed as a reproducible result and the signal components propagating along the spinal cord were found in the time varying SCEF distribution. We expect that the investigation of the propagating signal components would help to establish a noninvasive functional diagnosis of the spinal cord. |
| Authors: Konin, A. M.; Kiprijanovic, O. L.; ; Abstract: Theoretical model of the fast fault current limiter based on an air core transformer, the secondary winding of which is loaded with high-$T_{c}$ superconductor (HTSC) sample, has been analyzed. The fault current limiter was designed to protect a strong magnetic field pulse generation system. Transformer parameters and HTSC sample resistance in the normal state have been chosen to provide the fault current limitation efficiency. The current limiting dynamics was investigated by solving nonlinear system of equations. A detailed explanation of the results is presented. It is shown that application of the fault current limiter allows us to increase the initial reservoir capacitor voltage of the protected system up to 2.6 times. |
| Authors: Nadarajah, S.; Kotz, S.; ; |
| Authors: Powell, I. A.; Perold, W. J.; ; Abstract: The design and simulation of a complementary output switching logic (COSL) compatible, voltage state, switching logic comparator (SLC), and a flash analog-to-digital converter (ADC) for high-speed applications, with multigigahertz input bandwidth, is presented. A detailed design for the SLC is provided and verified with simulations. The comparator is then optimized utilizing Monte Carlo yield predictions. The optimized comparator is incorporated into the construction of a 4-bit quantizer of an ADC. The Gray-code output is converted into binary using COSL gates. The functionality, linearity, maximum input bandwidth, and dynamic range of the 4-bit ADC is verified by simulation, using a number of special input waveforms. The performance of the comparator and the 4-bit ADC are also evaluated with thermal noise incorporated into simulations. Beat frequency simulations and Fourier spectra are also used in the evaluation of the ADC performance. A fully functional 4-bit ADC, with a maximum input bandwidth of 10 GHz for a clock speed of 20 GHz, was achieved through simulations. Beat frequency simulations revealed that the comparators have an input bandwidth greater than 19 GHz with sufficient dynamic range for an ADC of greater than 6 bits of resolution. Due to the fact that the aperture time for the ADC is dependent on the rise time of the sampling pulse and not the width of the pulse, a much smaller aperture time is obtained which directly translates to higher input bandwidth. |
| Authors: Takahashi, K.-I.; Awaji, S.; Nishijima, G.; Watanabe, K.; ; |
| Authors: Webber, R. J.; Burroughs, C. J.; Radparvar, M.; ; Abstract: We report on the performance of a 1-V dc programmable Josephson voltage standard (PJVS) operating on a commercially available Gifford–McMahon cryocooler at 4 K. The NIST-fabricated niobium superconductor-normal metal-superconductor junction chip has been shown to operate successfully as integrated with this cryopackage, generating 1.229 V at the maximum operating frequency of 19.364 GHz with Shapiro steps at constant voltage that are flat to within less than 100 nV. Because of the large operating margin (greater than 1 mA), these steps were highly stable and immune from noise. Differences in behavior of the PJVS in liquid helium and on the cryocooler are discussed. This demonstration paves the way towards automated warming and cooling of the Josephson device and a fully automated voltage standard system. |
| Authors: Zhang, G. M.; Knoll, D. J.; Nguyen, D. N.; Sastry, P. V. P. S. S.; Wang, X.; Schwartz, J.; ; Abstract: Alternating current (ac) loss and quench behavior measurements were performed on a YBa$_{2}$ Cu$_{3}$ O$_{x}$ coated conductor at 45 K. The minimum quench energies (MQEs) and the quench propagation velocities were measured as a function of transport current and frequency. AC losses were measured at the corresponding temperature and frequencies to quantify the internal thermal load during ac quench measurements. It was found that the direct current (dc) and ac quench behavior are similar, but that the MQE for dc experiments is higher than the corresponding ac cases. This difference is not seen in the normal zone propagation velocity data, indicating that the difference in MQE is minimal if the ac losses are included in the energy calculation. The ac experiments show that the MQE and propagation velocity varies weakly with frequency. |
| Authors: Zheng, X.; Yang, Y.; ; Abstract: The lateral force on a rectangular permanent magnet (PM) above a cylindrical high-temperature superconductor (HTS) is numerically calculated during lateral traverses at different cooling heights (CHs). The simulations are based upon the critical state model of Bean. Our simulation results show that the lateral force on the PM is influenced by the initial cooling conditions of the HTS. This conclusion agrees with a previous experimental finding. The calculations show that there is a transition CH. The levitating body is laterally stable when the initial CH is less than the transition CH, whereas, when the initial CH is above the transition CH, the levitating body is possibly laterally unstable. The effects of the dimensions of the system, the physical parameters, and the levitating height during lateral traverses on the transition CH are presented. |
| Authors: Zhu, X.; Lei, H.; Shi, D.; Zhang, L.; Wang, L.; Sun, Y.; Song, W.; Dou, S.; Yang, J.; Gu, H.; ; Abstract: Chemical solution deposition (CSD) is used to prepare LaMnO$_{3}$ (LMO) buffer layers on different substrates. The results show that biaxially oriented LMO films can be successfully prepared on single-crystal SrTiO $_{3}$ (STO) and STO buffered single-crystal LaAlO$_{3}$ substrates when humid 4%H$_{2}$–N$_{2}$ annealing atmosphere is used. The orientation of LMO–Ni is (110)-oriented even when the annealing atmosphere is humid 4%H$_{2}$ –N$_{2}$ . When CSD-derived STO–Ni is used as a template, biaxially oriented LMO buffer layers with c-axis orientation can be successfully prepared. The results provide an effective route to prepare LMO-based buffer layers using CSD. |
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