Effects of Sintering Condition on the Trapped Magnetic Field Properties for MgB2 Bulks Fabricated by in-situ Capsule Method

AbstractWe have studied the trapped field properties of MgB2 bulks which were fabricated by the in-situ capsule method under various sintering temperatures of 700-900̊C for 1-24h. The trapped field, BT (T), was 1.8-1.9 T for all the bulks approximately at 16K. The BT (T) values on the bulks sintered at 900̊C for 6h and at 800̊C for 24h were slightly lower than those of other bulks because of the decrease of critical current density, Jc, which originates from both the lower connectivity, K, and the promotion of the grain growth. The high temperature and/or the long periods sintering decrease the BT (T) value. From the obtained results, the sintering at 700-800̊C for 1-6h is the optimum condition to fabricate MgB2 bulks by the capsule method

Direct Observation and simulation of ladle pouring behaviour in die casting sleeve

The ladle pouring process is one part of die casting which has the advantages of high speed, good quality and mass production. The molten metal is quickly poured into the sleeve by tilting the ladle, and immediately injected into the die cavity with high speed and high pressure by advancing the plunger. Since the entrapment of air and the generation of solidified layer in the ladle pouring may cause the defects of cast products, it is necessary to simulate the ladle pouring behavior. In the present study, the pouring experiment into the sleeve using water and die casting aluminum alloy JIS-ADC12 are carried out to observe the flow behavior by tilting the ladle. The temperature of the dissolved metal is measured using a thermocouple to investigate heat transfer behavior. The flow behaviors in ladle pouring of water and molten aluminum alloy are simulated using ParticleworksTM of MPS software. The simulation results, when using water are almost the same actual wave behavior. It is difficult to simulate the wave behavior of molten aluminum alloy because there is a difference in wave behavior between water and molten aluminum alloy. On the other hands, it is clear that the molten aluminum alloy is not solidified during wave behavior in the early stage of pouring by the experiments. Therefore, we try to adjust the kinematic viscosity of molten metal and the thermal conductivity of sleeve die. As the result, the wave behavior and temperature of molten aluminum alloy after adjusting the parameters are almost agreed with the actual phenomena. Flow and heat transfer simulation using the MPS method is effective method that ladle pouring of molten aluminum alloy with free surface flow can be simulated accurately

Phase transition in Pr0.5Ca0.5CoO3 and related cobaltites

We present an extensive investigation (magnetic, electric and thermal measurements and X-ray absorption spectroscopy) of the Pr0.5Ca0.5CoO3 and (Pr1-yYy)0.7Ca0.3CoO3 (y=0.0625-0.15) perovskites, in which a peculiar metal-insulator (M-I) transition, accompanied with pronounced structural and magnetic anomalies, occurs at 76 K and 40-132 K, respectively. The inspection of the M-I transition using the XANES data of Pr L3-edge and Co K-edge proofs the presence of Pr4+ ions at low temperatures and indicates simultaneously the intermediate spin to low spin crossover of Co species on lowering the temperature. The study thus definitively confirms the synchronicity of the electron transfer between Pr3+ ions and Co^(3+/4+)O3 subsystem and the transition to the low-spin, less electrically conducting phase. The large extent of the transfer is evidenced by the good quantitative agreement of the determined amount of the Pr4+ species, obtained either from the temperature dependence of the XANES spectra or via integration of the magnetic entropy change over the Pr4+ related Schottky peak in the low-temperature specific heat. These results show that the average valence of Pr3+/Pr4+ ions increases (in concomitance with the decrease of the formal Co valence) below TMI for (Pr0.925Y0.075)0.7Ca0.3CoO3 up to 3.16+ (the doping level of the CoO3 subsystem decreases from 3.30+ to 3.20+), for (Pr0.85Y0.15)0.7Ca0.3CoO3 up to 3.28+ (the decrease of doping level from 3.30+ to 3.13+) and for Pr0.5Ca0.5CoO3 up to 3.46+ (the decrease of doping level from 3.50+ to 3.27+).Comment: 19 pages, 11 figure

Physical Properties, Star Formation, and Active Galactic Nucleus Activity in Balmer Break Galaxies at 0 < z < 1

We present a spectroscopic study with the derivation of the physical properties of 37 Balmer break galaxies, which have the necessary lines to locate them in star-forming-AGN diagnostic diagrams. These galaxies span a redshift range from 0.045 to 0.93 and are somewhat less massive than similar samples of previous works. The studied sample has multiwavelength photometric data coverage from the ultraviolet to MIR Spitzer bands. We investigate the connection between star formation and AGN activity via optical, mass-excitation (MEx) and MIR diagnostic diagrams. Through optical diagrams, 31 (84%) star-forming galaxies, 2 (5%) composite galaxies and 3 (8%) AGNs were classified, whereas from the MEx diagram only one galaxy was classified as AGN. A total of 19 galaxies have photometry available in all the IRAC/Spitzer bands. Of these, 3 AGN candidates were not classified as AGN in the optical diagrams, suggesting they are dusty/obscured AGNs, or that nuclear star formation has diluted their contributions. Furthermore, the relationship between SFR surface density (\Sigma_{SFR}) and stellar mass surface density per time unit (\Sigma_{M_{\ast}/\tau}) as a function of redshift was investigated using the [OII] \lambda3727, 3729, H\alpha \lambda6563 luminosities, which revealed that both quantities are larger for higher redshift galaxies. We also studied the SFR and SSFR versus stellar mass and color relations, with the more massive galaxies having higher SFR values but lower SSFR values than less massive galaxies. These results are consistent with previous ones showing that, at a given mass, high-redshift galaxies have on average larger SFR and SSFR values than low-redshift galaxies. Finally, bluer galaxies have larger SSFR values than redder galaxies and for a given color the SSFR is larger for higher redshift galaxies.Comment: preprint version, 36 pages, 17 figures, 3 tables, accepted for publication in the Astrophysical Journa

Pulsed-Field Magnetizing Characteristics of Rectangular-Shaped Gd-Ba-Cu-O Bulk Using Split- and Solenoid-Type Coils

We have investigated the trapped-held characteristics of a rectangular-shaped Gd-Ba-Cu-O bulk (33 × 33 × 15 mm$^3$) magnetized by pulsed-field magnetization (PFM) using split- and solenoid-type coils. A soft iron yoke was set below the bulk for the solenoid coil and two yokes are inserted in the bores of the split coil. The maximum trapped held B$_{Zmax}$ at the center of the bulk surface was 1.73 T at 40 K in the case of the solenoid coil, with a distorted profile. On the other hand B$_{Zmax}$ was enhanced to 3.05 T at 40 K for the split coil with two yokes for which a symmetric trapped-held profile was observed. The behavior of the magnetic flux motion indicated two conditions for the enhancement of the trapped held: that the magnetic flux intrudes easily into the bulk even for lower applied fields and then saturates with minimal flux creep. We have also investigated the electromagnetic and thermal properties of the bulk during PFM using a numerical simulation in which the magnetic flux tended to align along the z-axis due to the presence of the soft iron yoke. The use of the split coil with two yokes is effective in enhancing the trapped held for the rectangular-shaped bulks.This work was supported by Open Partnership Joint Projects of Japan Society for the Promotion of Science (JSPS) Bilateral Joint Research Projects, and JSPS KAKENHI grant number 23560002 and 15K04646. Dr. Mark Ainslie would like to acknowledge the support of a Royal Academy of Engineering Research Fellowship

Simulation of mechanical stresses in reinforced REBaCuO ring bulks during pulsed-field magnetization

Abstract: We have performed numerical simulations of the electromagnetic, thermal and mechanical properties of a REBaCuO ring-shaped bulk with various reinforcement structures during pulsed-field magnetization (PFM). Compressive and tensile electromagnetic stresses, σ θ mag , are developed in the ring-shaped bulk during the ascending and descending stages of PFM, respectively. These stresses increase at lower operating temperatures and for higher applied pulsed fields. In order to reduce these stresses, the ring-shaped bulk was fully encapsulated by outer and inner ring with upper and lower plates made by Al alloy. In particular, this reinforcement structure can achieve the lowest electromagnetic compressive stress, which corresponds to about 54% of that for a conventional ring reinforcement structure, and the electromagnetic tensile stress was also reduced. We also compared the simulation results of the electromagnetic stresses for the ring-shaped bulk to those for a disk-shaped bulk

Trapped field properties of GdBaCuO bulk superconductors of various diameters magnetized by pulsed fields using an identical split coil

In this paper, the trapped field properties of GdBaCuO disk bulk superconductors of various diameters during pulsed-field magnetization (PFM) using an identical split coil at 65 K have been investigated both experimentally and numerically. The maximum trapped field, BTmax, of the Φ43 mm bulk was larger than that of the Φ30 mm bulk. However, BTmax of the Φ65 mm bulk was smaller than that of the Φ43 mm bulk and the trapped field profile exhibited a distorted “C-shaped” profile. Using the numerical simulation, these results for the Φ65 mm bulk can be explained by an inhomogeneous temperature profile and the larger generated heat, Q, due to the lower cooling power of the refrigerator compared to the generated heat. The important issues to achieve higher and homogeneous trapped fields are discussed when using split-coil PFM for larger bulks