Interaction between superconductor and ferromagnetic domains in iron sheath: peak effect in MgB2/Fe wires

Interaction between the superconductor and ferromagnet in MgB2/Fe wires results in either a plateau or a peak effect in the field dependence of transport critical current, Ic(H). This is in addition to magnetic shielding of external field. Current theoretical models cannot account for the observed peak effect in Ic(H). This paper shows that the theoretical explanation of the peak effect should be sought in terms of interaction between superconductor and magnetic domain structure, obtained after re-magnetization of the iron sheath by the self-field of the current. There is a minimum value of critical current, below which the re-magnetization of the iron sheath and peak effect in Ic(H) are not observed

Effect of carbon nanotube doping on critical current density of MgB2 superconductor

The effect of doping MgB2 with carbon nanotubes on transition temperature, lattice parameters, critical current density and flux pinning was studied for MgB2-xCx with x = 0, 0.05, 0.1, 0.2 and 0.3. The carbon substitution for B was found to enhance Jc in magnetic fields but depress Tc. The depression of Tc, which is caused by the carbon substitution for B, increases with increasing doping level, sintering temperature and duration. By controlling the extent of the substitution and addition of carbon nanotubes we can achieve the optimal improvement on critical current density and flux pinning in magnetic fields while maintaining the minimum reduction in Tc. Under these conditions, Jc was enhanced by two orders of magnitude at 8T and 5K and 7T and 10K. Jc was more than 10,000A/cm2 at 20K and 4T and 5K and 8.5T, respectively

Mechanochemical-treated Cr-promoted vanadyl pyrophosphate catalyst for n-butane oxidation to maleic anhydride

Cr-promoted vanadium phosphate (VPO) catalyst was synthesized by mechanotreating VOHPO4·0.5H2O in cyclohexane for 2 hr using a high energy planetary ball miller followed by calcination in a flow of n-butane/air mixture at 673 K. The physico-chemical properties of the sample were investigated by several characterization techniques such as BET, XRD, redox titration, SEM, and TPR. The data were compared to the unmilled material. BET surface area measurement of the milled catalyst showed that it possesses higher surface area (13.2 m2 g−1) compared to the unmilled catalyst (6.4 m2 g−1). Milling also caused a slight increment in the average oxidation state of vanadium as well as the percentage of V5+ oxidation state. XRD pattern of the milled material revealed that the major diffraction peaks were broadened thus indicating a reduction of particle size. SEM micrographs showed the lost in the blossom morphology and the formation of layer packages, with more circular particles in the milled catalyst. The amount of active lattice oxygen species being removed from V4+-O− pairs increased significantly for mechanochemical treated Cr-doped VPO catalyst leads to the enhancement of the catalytic activity for n-butane oxidation to maleic anhydride

Mechanism of Enhancement in Electromagnetic Properties of MgB2 by Nano SiC Doping

A comparative study of pure, SiC, and C doped MgB2 wires has revealed that the SiC doping allowed C substitution and MgB2 formation to take place simultaneously at low temperatures. C substitution enhances Hc2, while the defects, small grain size, and nanoinclusions induced by C incorporation and low-temperature processing are responsible for the improvement in Jc. The irreversibility field (Hirr) for the SiC doped sample reached the benchmarking value of 10 T at 20 K, exceeding that of NbTi at 4.2 K. This dual reaction model also enables us to predict desirable dopants for enhancing the performance properties of MgB2

Correlated enhancement of Hc2 and Jc in carbon nanotube-doped MgB2

The use of MgB2 in superconducting applications still awaits for the development of a MgB2-based material where both current-carrying performance and critical magnetic field are optimized simultaneously. We achieved this by doping MgB2 with double-wall carbon nanotubes (DWCNT) as a source of carbon in polycrystalline samples. The optimum nominal DWCNT content for increasing the critical current density, Jc is in the range 2.5-10%at depending on field and temperature. Record values of the upper critical field, Hc2(4K) = 41.9 T (with extrapolated Hc2(0) ~ 44.4 T) are reached in a bulk sample with 10%at DWCNT content. The measured Hc2 vs T in all samples are successfully described using a theoretical model for a two-gap superconductor in the dirty limit first proposed by Gurevich et al.Comment: 12 pages, 3 figure

Surface induced selective delamination of amphiphilic ABA block copolymer thin films

This is the result of an ongoing collaboration with Dr. N. Sommerdijk’s Biomaterials group at the University of Eindhoven (the Netherlands) and illustrates the close collaboration that exists in pursuing the design and application of novel polymeric materials between the two groups. This details work on a physical phenomenon (selective delamination) and key materials (amphiphilic block copolymers) that have subsequently been applied in the design of novel biomaterials. These results have appeared in a larger body of work including Advanced Materials, Angewandtie Chemie International Edition and the Journal of Materials Chemistry

Optimal Power Allocation by Imperfect Hardware Analysis in Untrusted Relaying Networks

CCBY By taking a variety of realistic hardware imperfections into consideration, we propose an optimal power allocation (OPA) strategy to maximize the instantaneous secrecy rate of a cooperative wireless network comprised of a source, a destination and an untrusted amplify-and-forward (AF) relay. We assume that either the source or the destination is equipped with a large-scale multiple antennas (LSMA) system, while the rest are equipped with a single-antenna. To prevent the untrusted relay from intercepting the source message, the destination sends an intended jamming noise to the relay, which is referred to as destination-based cooperative jamming (DBCJ). Given this system model, novel closed-form expressions are presented in the high signal-to-noise ratio (SNR) regime for the ergodic secrecy rate (ESR) and the secrecy outage probability (SOP). We further improve the secrecy performance of the system by optimizing the associated hardware design. The results reveal that by beneficially distributing the tolerable hardware imperfections across the transmission and reception radio-frequency (RF) front ends of each node, the system & #x2019;s secrecy rate may be improved. The engineering insight is that equally sharing the total imperfections at the relay between the transmitter and the receiver provides the best secrecy performance. Numerical results illustrate that the proposed OPA together with the most appropriate hardware design significantly increases the secrecy rate