Iron-sheathed MgB2 wires doped with 0, 1.3 and 2.52 wt% carbon protected nickel superparamagnetic nanoparticles (the average diameter of the particles is 20 nm) and sintered at 650 °C were prepared. X-ray diffraction patterns and magnetization measurements showed that neither substitution of C for B nor substitution of Ni for Mg occurred during the synthesis process. Scanning electron microscopy imaging of the doped sample revealed a homogeneous distribution of nickel particles within the MgB2 matrix. Transport (magnetoresistivity R(T,B) and critical current density Jc(B) in the temperature range 1.5–40 K) and magnetic measurements (magnetic hysteresis loops at temperatures below and above the superconducting transition temperature) were performed on Fe-sheathed wires and the superconducting cores of these wires. A small enhancement of the irreversibility field Birr(t = Tirr(B)/Tirr(0)) of the doped wires was observed in the low field range. Significant enhancement of Jc(B), especially at low temperature (5 K), was observed: at 5 K and 10 T, for both doped wires, Jc is 2.5 times larger than that for the undoped wire.

A systematic study of the influence of doping MgB 2 with single domain magnetic nanoparticles of NiCoB alloy, uncoated and coated with SiO 2 , has been performed. Electrical resistivity, transport critical current density, J c (B, T), and magnetization of well characterized undoped and doped with 1.38 and 2.67 wt% of NiCoB particles (both uncoated and coated) MgB 2 wires have been investigated in the temperature interval 2-300 K and in magnetic field B ≤ 16 T. The superconducting transition temperature, T c , decreases approximately linearly with the amount of dopand and the intergranular connectivity (the active cross-sectional area fraction, A F ) is also reduced upon doping. Reduction of critical fields (irreversibility field, B irr , and upper critical field, B c2 ) of doped wires was observed in the whole temperature interval, but an enhancement of J c of doped wires with respect to the undoped one was observed at low temperature (5 K). Common scaling of J c (B, T) curves, B irr (T) and volume pinning force, F p , for doped and undoped wires indicates that the main mechanism of flux pinning is the same in both types of samples.

We use Gaudin's Fermi-Bose mapping operator to calculate exact solutions for the Lieb-Liniger model in a linear (constant-force) potential (the constructed exact stationary solutions are referred to as the Lieb-Liniger-Airy wave functions). The ground-state properties of the gas in the wedgelike trapping potential are calculated in the strongly interacting regime by using Girardeau's Fermi-Bose mapping and the pseudopotential approach in the 1/c approximation (c denotes the strength of the interaction). We point out that quantum dynamics of Lieb-Liniger wave packets in the linear potential can be calculated by employing an N -dimensional Fourier transform as in the case of free expansion.

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