We report on field-induced variations of the microwave surface resistance at 9.6 GHz of Ba0.6K0.4BiO3 crystals. Energy losses have been investigated as a function of the static magnetic field in the range of temperatures 4.2 K ÷ Tc. By analyzing the experimental results in the framework of the Coffey and Clem model we determine the temperature dependence of the first-penetration field, upper critical field and depinning frequency. The results show that the pinning energy of this bismuthate superconductor is weaker than those of cuprates. .Nf Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.) -74.25.Op Mixed state, critical fields, and surface sheaths PACS

Non-edible parts of crustaceans could be a rich source of valuable bioactive compounds such as the carotenoid astaxanthin and peptides, which have well-recognized beneficial effects. These compounds are widely used in nutraceuticals and pharmaceuticals, and their market is rapidly growing, suggesting the need to find alternative sources. The aim of this work was to set up a pilot-scale protocol for the reutilization of by-products of processed shrimp, in order to address the utilization of this valuable biomass for nutraceutical and pharmaceuticals application, through the extraction of astaxanthin-enriched oil and antioxidant-rich protein hydrolysates. Astaxanthin (AST) was obtained using “green extraction methods,” such as using fish oil and different fatty acid ethyl esters as solvents and through supercritical fluid extraction (SFE), whereas bioactive peptides were obtained by protease hydrolysis. Both astaxanthin and bioactive peptides exhibited bioactive properties in vitro in cellular model systems, such as antioxidant and angiotensin I converting enzyme (ACE) inhibitory activities (IA). The results show higher astaxanthin yields in ethyl esters fatty acids (TFA) extraction and significant enrichment by short-path distillation (SPD) up to 114.80 ± 1.23 µg/mL. Peptide fractions of <3 kDa and 3–5 kDa exhibited greater antioxidant activity while the fraction 5–10 kDa exhibited a better ACE-IA. Lower-molecular-weight bioactive peptides and astaxanthin extracted using supercritical fluids showed protective effects against oxidative damage in 142BR and in 3T3 cell lines. These results suggest that “green” extraction methods allow us to obtain high-quality bioactive compounds from large volumes of shrimp waste for nutraceutical and pharmaceutical applications.

PACS. 74.25.Nf -Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.) . PACS. 74.70.Ad -Metals; alloys and binary compounds (including A15, Laves phases, etc.). Abstract. -The real Rs(T ) and imaginary Xs(T ) parts of the surface impedance Zs(T ) = Rs(T ) + iXs(T ) in polycrystalline MgB2 samples of different density with the critical temperature Tc ≈ 38 K are measured at the frequency of 9.4 GHz and in the temperature range 5 ≤ T < 200 K. The normal skin-effect condition Rs(T ) = Xs(T ) at T ≥ Tc holds only for the samples of the highest density with roughness sizes not more than 0.1 µm. For such samples extrapolation T → 0 of the linear at T < Tc/2 temperature dependences λL(T ) = Xs(T )/ωµ0 and Rs(T ) results in values of the London penetration depth λL(0) ≈ 600Å and residual surface resistance Rres ≈ 0.8 mΩ. In the entire temperature range the dependences Rs(T ) and Xs(T ) are well described by the modified two-fluid model. c EDP Sciences

Field-induced variations of the microwave surface resistance, R s (H), have been investigated in high-density ceramic MgB 2 . At low temperatures, several peculiarities of the R s (H) curves cannot be justified in the framework of models reported in the literature. We suggest that they are ascribable to the unconventional vortex structure in MgB 2 , related to the presence of two gaps. On the contrary, the results near T c can be accounted for by the Coffey and Clem model, with fluxons moving in the flux-flow regime, provided that the anisotropy of the upper critical field is taken into due account.

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