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[en] LaRu4As12 with the critical temperature = 10.4 K displays several features which point at a non-singlet superconducting order parameter, although the bcc crystal structure of the filled skutterudites does not favour the emergence of multiple energy gaps. LaRu4As12 displays an unexpected enhancement of the lower critical field deep in superconducting state which can be attributed to the existence of two superconducting gaps. At = 0.4 K, the local magnetization measurements were performed utilizing miniaturized Hall sensors.
[en] Non-uniform superconducting states raise great interest in the scientific community. One of the most famous is the FFLO state, predicted in the 1960's. It is characterized by a higher critical field than the uniform superconducting state. The FFLO state appears at low critical temperature, which makes it difficult to observe experimentally. In this presentation, we will show that adding spin-orbit interaction allows the modulated phase to appear at high critical temperature.The system studied consists of a superconducting nanowire with Zeeman field and Rashba spin-orbit interaction.
[en] The thermodynamic parameters of the superconducting state in PtH at the pressure 76 GPa have been examined. The calculations have been carried out in the framework of the Eliashberg formalism. It has been found that the critical temperature changes in the range from 30.6 K to 16.8 K, depending on the assumed value of the Coulomb pseudopotential μ* element of (0.1, 0.3). The other thermodynamic quantities differ significantly from the predictions of the classical BCS theory. In particular: (i) The parameter 2Δ(0)/kBTC reaches the values from 4.25 to 3.98, where Δ(0) denotes the low temperature order parameter. (ii) The ratio of the specific heat jump (ΔC) to the specific heat in the normal state (CN) takes the values from 2.07 to 1.97. (iii) Finally, TCCN (TC)/HC2 (0) element of (0.145 to 0.156), where HC (0) is the low-temperature thermodynamic critical field. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
[en] A model for uniaxial media which computed an irreversible component that lies along the easy axis and a reversible component that is sensitive to off-axis fields has been developed. By assuming that the distribution of critical fields is Gaussian, then the major loop will be an error function. For small rotating fields, the magnetization will oscillate between two extreme values on the same side of the origin. For larger fields, the irreversible magnetization can change sign and the magnetization will rotate about the origin. We start with a demagnetized specimen, then apply a field that starts along the easy axis and then rotates about the origin. For the first 90°, the magnetization will follow a circular path. Beyond that point the irreversible magnetization will start to change, and the magnetization will start to spiral in towards the origin. Therefore, we will get asymmetrical loops which can be compared with experiment.
[en] This paper demonstrates the effects of hot isostatic pressure (HIP) on the structure and transport critical parameters of in situ MgB2 wires without a barrier. Our results show that only HIP and nano-boron allow the formation of more high-field pinning centers, which lead to the increase in critical current density (Jc) at high applied magnetic fields. Nano-boron and annealing at a low pressure increase the Jc in the low magnetic field. This indicates that nano-particles create more high-field pinning centers. In addition, the results show that nano-boron improves the connection between the grains. Scanning electron microscope results show that HIP increases the reaction rate between Mg and B, density, and homogeneity of the MgB2 material. Additionally, HIP allows to create a structure with small grains and voids and eliminates the significance of the number of voids. High isostatic pressure allows to obtain high Jc of 10 A/mm2 (at 4.2 K) in 10 T and increases irreversible magnetic field (Birr) and upper critical field (Bc2). Measurements show that these wires have high critical temperature of 37 K.
[en] In this paper, the key issues in the development of reactor critical heat flux (CHF) correlation such as cold wall effect, non-uniform heating factor and statistical treatment of data have been studied, and based on the published CHF trial data we completed the localization of CHF correlation fitting and determination of the corresponding limit value. With a detailed statistical analysis of the calculation results, we established a rigorous method to determine the DNBR limits of CHF correlation. (authors)
[en] Iron-based superconductors are very promising candidates for high-field applications owning to their ultrahigh upper critical field (Hc2) and very small anisotropy. For practical application, wires and tapes with high mechanical strength are essential. In this work, using Monel alloy as an outer reinforcing sheath, 7-filament Sr1−x Kx Fe2As2/Ag/Monel composite tapes with various thicknesses were developed based on the powder-in-tube method. Through microhardness characterization, it is found that the transport critical current density ( J c) of the tapes has a heavy dependence on the mass density of the Sr-122 phase, which varies widely according to the cold-work parameters and heat treatment temperatures for the tapes. In large-scale applications, conductors are usually designed to work under compressive state for safety, and so the compressive strain dependence of transport Jc was investigated for our tapes, which shows almost no Jc degradation under a large compressive strain of 0.6%. The transport Jc for the rolled tapes can be further significantly enhanced to 3.6 × 104 A cm−2 (4.2 K, 10 T) by a hot-press process. These results suggest the great potential of Monel/Ag composite sheath for developing high-strength and high Jc performance iron-based superconducting wires and tapes for high-field applications. (paper)
[en] In this study, the effects of the compaction method for (Mg+2B) powders on the apparent density and superconducting properties of MgB2 bulk superconductor were investigated. The raw powders used in this study were nano-sized boron (B) and spherical magnesium (Mg). A batch of a powder mixture of (Mg+2B) was put in a steel mold and uniaxially pressed at 1 ton or 3 tons into pellets. Another batch of the powder mixture was uniaxially pressed at 1 ton and then pressed isostatically at 1800 kg/cm2 in the water chamber. All pellets were heat-treated at 650℃ for 1 h in flowing argon gas for the formation of MgB2. The apparent density of powder compacts pressed at 3 ton was higher than that at 1 ton. The cold isostatic pressing (CIP) in a water chamber allowed further increase of the apparent density of powder compacts, which influenced the pellet density of the final products (MgB2). The compaction methods (uniaxial pressing and CIP) did not affect the formation of MgB2 and superconducting critical temperature (Tc) of MgB2, but affected the critical current density (Jc) of MgB2 significantly. The sample with the high apparent density showed high Jc at 5 K and 20 K at applied magnetic fields (0-5 T)
[en] In this paper, divergence and flutter instabilities of supported piezoelectric nanotubes containing flowing fluid are investigated. To take the size effects into account, the nonlocal elasticity theory is implemented in conjunction with the Euler-Bernoulli beam theory incorporating surface stress effects. The Knudsen number is applied to investigate the slip boundary conditions between the flow and wall of nanotube. The nonlocal governing equations of nanotube are obtained using Newtonian method, including the influence of piezoelectric voltage, surface effects, Knudsen number and nonlocal parameter. Applying Galerkin approach to transform resulting equations into a set of eigenvalue equations under the simple-simple (S-S) and clamped-clamped (C-C) boundary conditions. The effects of the piezoelectric voltage, surface effects, Knudsen number, nonlocal parameter and boundary conditions on the divergence and flutter boundaries of nanotubes are discussed. It is observed that the fluid-conveying nanotubes with both ends supported lose their stability by divergence first and then by flutter with increase in fluid velocity. Results indicate the importance of using piezoelectric voltage, nonlocal parameter and Knudsen number in decrease of critical flow velocities of system. Moreover, the surface effects have a significant role on the eigenfrequencies and critical fluid velocity.