Impact of silver addition on the superconducting performances of Bi2Sr2Ca0.925Na0.075Cu2Oy:Ag composite fibers

The results used in this manuscript has been partially taken from master thesis of B. Atilla named “Determination of Magnetoresistance Properties of Bi2Sr2Ca0,925Na0,075Cu2Oy Superconductors Added with Different Proportions of Silver (Ag)”, directed by Prof. Dr. B. Özçelik.This work studies the impact of metallic Ag addition on the microstructural, electrical, superconducting, and magnetic properties of Bi2Sr2Ca0.925Na0.075Cu2Oy. Samples with 0, 1, 3, 5 wt% were prepared from precursors produced by sol-gel method, followed by texturing through the laser floating zone (LFZ) technique. The normal state and residual resistivity values decrease with Ag addition up to 3 wt% (from 7.61 to 2.54, and from 1.85 to 0.25 mΩ.cm, respectively), reflecting the reduction of porosity and the improvement of grains alignment and connectivity. Irreversibility line (IL) shifts towards high temperature with the introduction of Ag, confirming the higher grains connectivity in Ag-containing samples. Moreover, the increase of Hirr (from 28.9 to 43.1 T), Hc2 (from 64.6 to 85.9 T), and Jc (from 4x104 to 1.2x105 A/cm2) values with Ag addition also point out to the improvement of grains connectivity and flux pinning energies induced by Ag addition.M. A. Madre and A. Sotelo wish to thank the Gobierno de Aragón (Research Group T 54–20R) for funding.Peer reviewe

Role of Y substitution for Ca-site on magneto-resistivity properties of Bi-2212 superconductor rods prepared by LFZ

This comprehensive study delves into the effect of partial Y3+ substitution for Ca2+ in Bi2Sr2CaCu2O8+y superconducting rods prepared by the laser floating zone method (LFZ). The critical transition temperatures (Tconset, Tc, Tcoffset), activation energy (U), irreversibility field (Hirr), upper critical magnetic field (Hc2), coherence length (ξ), and penetration depth (λ) are determined by means of magneto-resistivity measurements performed between 0 and 5 T. According to the resistivity-temperature graph for zero fields, Tcoffset values tend to decrease regularly from 90.8 K to 87.1 K, and the residual resistivity values increase steadily from 0.14 to 9.7 mΩ .cm with the Y-content. The change of these two parameters is a sign that Y-introduction into the Bi-2212 matrix undermines the inter-grain coupling and increases the level of permanent-defects in the crystalline structure. However, the relatively high Tcoffset values and extremely low residual resistivity, especially in the pure and low Y-substituted samples, reflect the success of the LFZ process in growing homogeneous and well-oriented Bi-2212 grains. The resistivity transition broadening is observed when the applied field increases and Tcoffset values decrease dramatically, i.e. from 90.8 K to 72.1 K for the pure sample and from 87.1 K to 48.2 K for the 0.20Y-substituted ones. The calculated U values using the TAFF model decrease with the increase of the Y-content and the magnetic field. In addition, the magnetic field and temperature dependence of U is expressed by using U(H,T)~ΔT H−η equation. Deduced parameters of Hirr and Hc2 from magneto-resistivity curves and theoretical findings of ξ and λ also favor the degradation of U values with the augmentation of Y-content in the Bi-2212 rods.A. Sotelo and M.A. Madre acknowledge the Spanish MINECO-FEDER project (MAT2017-82183-C3-1-R) and the Aragón Government (Research Group T54-20R) for financial support.Peer reviewe

Significant enhancement of superconducting performances of Bi-2212 fibers through combined sodium substitution and LFZ process

This paper reports the microstructure, magnetoresistivity, electrical and superconducting properties of Bi-2212 fibers with Na+ ions incorporated into a superconducting matrix prepared by a polymer solution method and additionally textured through the laser floating zone process. XRD patterns showed that Bi-2212 phase is the major one with mostly (00ℓ) diffractions due to the grain alignment, independently of Na content. SEM micrographs showed that samples are composed of well-stacked and oriented grains. The irreversibility field (Hirr), upper critical magnetic field (Hc2), coherence length (ξ), and activation energies (U) have been calculated using magnetoresistivity measurements and explained based on the thermally activated flux flow (TAFF) model. Considering the resistivity-temperature graph for zero field, Tc values tend to increase from 84.8 K (for the pure sample) to 93.2 K (for 0.075Na sample), slightly decreasing for higher content. Besides, transition temperature width (ΔTc = Tconset − Tcoffset) decreases with the increment in the Na content and reaches its minimum value (ΔTc = 3.7 K) in 0.075Na sample. However, broadening of superconducting transition has been observed with applied field and Tc values decreased to 76.1 K for the pure sample and 86.8 K for 0.075Na sample. Likewise, the activation energies of the samples also decreases significantly with the increase of the magnetic field and the activation energies of the Na-containing samples are found to be higher than the pure sample at each magnetic field value. Hc2(0) values are calculated as 33.8, 43.8, 50.1, 33.1, and 21.4 T for 0.0, 0.075, 0.10, and 0.20 T Na samples, respectively. As a consequence, referring to all experimental results and theoretical findings, the superconducting characteristics improve regularly with Na-doping until x = 0.075 due to increment in the interaction of superconducting clusters, decrement in weak-links and stabilization of charge carriers in CuO2 conducting planes.A. Sotelo and M. A. Madre acknowledge Spanish MINECO-FEDER (Project MAT2017-82183-C3-1-R) and Gobierno de Aragón-FEDER (Research Group T 54-20R) for funding. Authors would like to acknowledge the use of Servicio General de Apoyo a la Investigación-SAI, Universidad de Zaragoza.Peer reviewe

Quercetin protects rat skeletal muscle from ischemia reperfusion injury

In this study, we investigated the potential beneficial effects of quercetin on skeletal muscle ischemia reperfusion injury. Twenty-four Sprague–Dawley type rats were randomly divided into four groups. In the sham group, only gastrocnemius muscle were removed and given no quercetin. In ischemia group, all the femoral artery, vein and collaterals were occluded in the left hindlimb by applying tourniquate under general anaesthesia for three hours but reperfusion was not done. In the Quercetin + Ischemia reperfusion group, quercetin (200 mg kg−1 dose orally) was given during one-week reoperation and later ischemia reperfusion model was done. Finally, gastrocnemius muscle samples were removed to measure biochemical parameters. The biomarkers, MDA levels, SOD, CAT and GPx activities, were evaluated related to skeletal muscle ischemia reperfusion injury. MDA levels reduced and SOD, CAT and GPx activities increased significantly in Quercetin + Ischemia reperfusion group. Results clearly showed that Quercetin have a protective role against oxidative damage induced by ischemia reperfusion in rats. © 2016 Informa UK Limited, trading as Taylor & Francis Group

Safety of once-or twice-daily dosing of non-vitamin K antagonist oral anticoagulants (NOACs) in patients with nonvalvular atrial fibrillation: A NOAC-TR study

Once-daily dosing of non-vitamin K antagonist oral anticoagulants (NOACs) may increase patient adherence to treatment but may also be associated with a higher risk of bleeding. In this study, we investigated the adherence to once-or twice-daily dosing of NOACs and the risk of bleeding in nonvalvular atrial fibrillation (NVAF) patients. This multicenter cross-sectional study, conducted between 1 September 2015 and 28 February 2016, included 2214 patients receiving NOACs for at least 3 months, due to NVAF. Patients receiving once-daily or twice-daily NOAC doses were 1:1 propensity score matched for baseline demographic characteristics and the presence of other diseases. The medication adherence was assessed by the 8-item Morisky Medication Adherence Scale. Risk factors were investigated in relation to minor and major bleeding. The mean age of patients was 71 ± 10 years, and 53% of the patients were women. The medication adherence was lower in patients receiving twice-daily NOAC doses compared to once-daily-dose group (47% versus 53%, p = 0.001), and there was no difference between the groups in terms of minor (15% versus 16%, p = 0.292) and major bleeding (3% versus 3%, p = 0.796). Independent risk factors for bleeding were non-adherence to medication (OR: 1.62, 95% CI: 1.23–2.14, p = 0.001), presence of 3 or more other diseases (OR: 10.3, 95% CI: 5.3–20.3, p < 0.001), and HAS-BLED (Hypertension, Abnormal renal and liver function, Stroke, Bleeding, Labile INR, Elderly, Drugs or alcohol) score (OR: 4.84, 95% CI: 4.04–5.8, p < 0.001). In summary, the once-daily dose of NOACs was associated with increased patient adherence to medication, while it was not associated with bleeding complications. © 2018 ABMSFBIH