Nanosized patterns as reference structures for macroscopic transport properties and vortex phases in YBCO films

This paper studies the striking correlation between nanosized structural patterns in YBCO films and macroscopic transport current. A nanosized network of parallel Josephson junctions laced by insulating dislocations is almost mimicking the grain boundary structural network. It contributes to the macroscopic properties and accounts for the strong intergranular pinning across the film in the intermediate temperature range. The correlation between the two networks enables to find out an outstanding scaling law in the (Jc,B) plane and to determine meaningful parameters concerning the matching between the vortex lattice and the intergranular defect lattice. Two asymptotic behaviors of the pinning force below the flux flow regime are checked: the corresponding vortex phases are clearly individuated.Comment: 4 pages, 4 figure

Scaling laws for ion irradiation effects in iron-based superconductors

We report on ion irradiation experiments performed on compounds belonging to the BaFe 2As 2 family, each one involving the partial substitution of an atom of the parent compound (K for Ba, Co for Fe, and P for As), with an optimal composition to maximize the superconducting critical temperature Tc. Employed ion beams were 3.5-MeV protons, 250-MeV Au ions, and 1.2-GeV Pb ions, but additional data from literature are also considered, thus covering a wide range of ions and energies. Microwave characterization based on the use of a coplanar waveguide resonator allowed us to investigate the irradiation-induced Tc degradation, as well as the increase of normal state resistivity and London penetration depth. The damage was quantified in terms of displacements per atom (dpa). From this broad and comprehensive set of experimental data, clear scaling laws emerge, valid in the range of moderate irradiation-induced disorder (dpa up to 5 × 10 - 3 were investigated). In these conditions, linear trends with dpa were found for all the modification rates, while a power law dependence on the ion energy was found for heavy-ion irradiation. All these scaling laws are reported and discussed throughout the paper

Synthesis and characterization of magnetic and antibacterial nanoparticles as filler in acrylic cements for bone cancer and comorbidities therapy

In this work an innovative formulation of bone cement for the treatment of bone tumor and its associated complications has been designed by preparing a new class of Fe3O4–Ag nanostructures, using gallic acid as a reducing agent. The obtained nanoparticles have been introduced in polymethyl methacrylate (PMMA)-based composite cement evaluating the insertion of different amounts and the use of different mixing methods. The morphology, the composition and the antibacterial effect of Fe3O4–Ag nanostructures have been investigated together with the morphology, the composition, the mechanical properties of the nanoparticles-containing composite cements as well as their antibacterial effect. The obtained results revealed a good antimicrobial effect of Fe3O4–Ag nanostructures, a significant influence of their amount and of the used mixing method on the particles dispersion and agglomeration in the PMMA matrix and, as a result, on the mechanical properties. In particular, a better dispersion of nanoparticles was obtained by using the mechanical mixing, reducing the tendency to agglomerate. The increase of nanoparticles amount induced a slight decrease of the mechanical properties; however, the introduction of 10% w/w of Fe3O4–Ag allowed to improve the composites ability to reduce the bacteria adhesion

Screening magnetic fields by a superconducting disk: a simple model

We introduce a simple approach to evaluate the magnetic field distribution around superconducting samples, based on the London equations; the elementary variable is the vector potential. This procedure has no adjustable parameters, only the sample geometry and the London length, $\lambda$, determine the solution. The calculated field reproduces quantitatively the measured induction field above MgB$_2$ disks of different diameters, at 20K and for applied fields lower than 0.4T. The model can be applied if the flux line penetration inside the sample can be neglected when calculating the induction field distribution outside the superconductor. Finally we show on a cup-shape geometry how one can design a magnetic shield satisfying a specific constraint

Magneto-plasmonic heterodimers: Evaluation of different synthesis approaches

Nanomedicine has gained huge attention in recent years with new approaches in medical diagnosis and therapy. Particular consideration has been devoted to the nanoparticles (NPs) in theranostic field with specific interest for magnetic and gold NPs (MNPs and GNPs) due to their peculiar properties under exposition to electromagnetic fields. In this paper, we aim to develop magneto-plasmonic heterodimer by combining MNPs and GNPs through a facile and reproducible synthesis and to investigate the influence of different synthesis parameters on their response to magnetic and optical stimuli. In particular, various syntheses were performed by changing the functionalization step and using or not a reducing agent to obtain stable NP suspensions with tailored properties. The obtained heterodimers were characterized through physical, chemical, optical, and magnetic analysis, in order to evaluate their size, shape, plasmonic properties, and superparamagnetic behavior. The results revealed that the shape and dimensions of the nanocomposites can be tuned by MNPs surface functionalization, as well as by the use of a reducing agent, giving rise to nanoplatform suitable for biomedical application, exploiting the gold absorbing peak in the specific gold absorbing range of GNPs, while maintaining the superparamagnetic behavior typical of the MNPs. The obtained nanocomposites can be proposed as potential candidates for cancer theranostics

Surveillance of Aflatoxin and Microbiota Related to Brewer's Grain Destined for Swine Feed in Argentina

Córdoba province in the center of Argentina is an important area of swine production. The use of industry by-product (brewer's grain) as feedstuff for swine is a regular practice and increases animal performance on these animals production. The occurrence of aflatoxin contamination is global, causing severe problems especially in developing countries. No reports on aflatoxin B1 production, micoflora, and potential aflatoxin B1 producing microorganism from brewer's grain are available. The aims of this study were (1) to isolate the microbiota species from brewer's grain, (2) to determine aflatoxin B1 natural contamination levels, and (3) to determine the ability of Aspergillus section Flavi isolates to produce aflatoxins in vitro. Physical properties, total fungal counts, lactic acid bacteria, and fungal genera distribution were determined on this substrate. In 65% of the samples, fungal counts were higher than recommended by GMP, and lactic bacterium counts ranged from 1.9 × 105 to 4.4 × 109 CFU g−1. Aspergillus spp. prevailed over other fungal genera. Aspergillus flavus was the prevalent species followed by A. fumigatus. Aflatoxin B1 levels in the samples were higher than the recommended limits (20 ng g−1) for complementary feedstuffs. Several Aspergillus section Flavi strains were able to produce aflatoxin B1  in vitro. Inadequate storage conditions promote the proliferation of mycotoxin-producing fungal species. Regular monitoring of feeds is required in order to prevent chronic and acute toxic syndromes related to this kind of contamination

Cobalt-Based Metallic Glass Microfibers for Flexible Electromagnetic Shielding and Soft Magnetic Properties

Thin and flexible materials that can provide efficient electromagnetic interference (EMI) shielding are urgently needed, particularly those that can be rapidly processed and withstand harsh environments. Cobalt-based metallic glasses stand out as prime candidates due to their excellent soft magnetic properties, satisfactory shielding features, and mechanical properties. Herein, a recently developed technique is used to fabricate metallic glass microfibers from Co66Fe4Mo2Si16B12 alloy. The produced microfibers are characterized for their size and uniformity by scanning electron microscopy and their amorphous structure is confirmed by X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The cobalt-based metallic glass microfibers show an EMI shielding factor that reaches five in the static regime and obtains an up to 25-fold increase of the attenuation constant in the Ku frequency band. This performance originates from the combination of soft magnetic properties and excellent electrical conductivity. In addition, the flexible microfibers exhibit excellent hardness and elasticity making them suitable for EMI shielding of complex geometries. Their hardness and elastic modulus are measured by nanoindentation to be 11.31 +/- 0.60 GPa, and 110.54 +/- 11.24 GPa, respectively.A novel method is used to fabricate flexible Co66Fe4Mo2Si16B12 metallic-glass microfibers for electronics, boasting a hardness of 11.31 +/- 0.60 GPa and an elastic modulus of 110.54 +/- 11.24 GPa. Their EMI shielding exhibits clear anisotropy with a factor of 5 and up to 25-fold increased attenuation in the Ku band. These properties position them well for EMI shielding in intricate geometries.imag

Soft Magnetic Properties and Electromagnetic Shielding Performance of Fe40Ni40B20 Microfibers

Fi(40)Ni(40)B(20) metallic glass is a key material among the many amorphous systems investigated thus far, owing to its high strength and appealing soft magnetic properties that make it suitable for use as transformer cores. In this study, Fi(40)Ni(40)B(20) microfibers are fabricated down to 5 mu m diameter. Three different melt-spinning wheel velocities: approximate to 51 m s(-1), approximate to 59 m s(-1), and approximate to 63 m s(-1) (MG1, MG2, MG3) are used. Their fully amorphous structure is confirmed using X-ray diffraction, and differential scanning calorimetry (DSC) traces reveal a larger relaxation profile for the higher-quenched microfiber. Vibrating sample magnetometer measurements showed a higher saturation magnetization of 136 emug(-1) for annealed metallic glass microfibers with a wheel velocity of 59.66 ms(-1). Cylindrical magnetic field shields are obtained by aligning and wrapping the fibers around a cast. The observed anisotropic static field shielding behavior is in accordance with the microfibers' anisotropic nature. Composite samples are also produced by embedding the microfibers in an epoxy matrix to investigate their electromagnetic properties at GHz frequencies. Inclusion of the microfibers increase the composite's attenuation constant by 20 to 25 times, making it an ideal candidate for applications in the communications frequency range

Twofold role of columnar defects in iron based superconductors

We report on the introduction of columnar defects in Ba1−x K x Fe2As2 and BaFe2(As1−x P x )2 single crystals via 1.2 GeV Pb irradiation. Scanning transmission electron microscopy analysis proves the formation of continuous defects along the ion tracks, with a diameter of about 3 nm, and a planar density compatible with the irradiation fluence. The twofold role of such defects, i.e. as pair breakers as well as pinning centers, is investigated by a microwave technique, allowing us to determine critical temperature T c , surface impedance and penetration depth λ L , and by magneto-optical imaging and superconducting quantum interference device magnetometry to evaluate the critical current density J c . The decrease of T c is quite modest and, together with λ L modifications, testifies the increase of pair-breaking scattering following irradiation. The dependence of J c on irradiation dose and temperature is due to the pinning landscape induced by the columnar defects, and shows the existence of an optimal irradiation dose to enhance the critical current