431 research outputs found
A new apparatus for deep patterning of beam sensitive targets by means of high-energy ion beam
The paper reports on a high precision equipment designed to modify over
3-dimensions (3D) by means of high-energy gold ions the local properties of
thin and thick films. A target-moving system aimed at creating patterns across
the volume is driven by an x-y writing protocol that allows one to modify beam
sensitive samples over micrometer-size regions of whatever shape. The apparatus
has a mechanical resolution of 15 nm. The issue of the local fluence
measurement has been particularly addressed. The setup has been checked by
means of different geometries patterned on beam sensitive sheets as well as on
superconducting materials. In the last case the 3D modification consists of
amorphous nanostructures. The nanostructures create zones with different
dissipative properties with respect to the virgin regions. The main analysis
method consists of magneto-optical imaging that provides local information on
the electrodynamics of the modified zones. Features typical of non-linear
current flow hint at which pattern geometry is more functional to applications
in the framework of nanostructures across superconducting films.Comment: 7 page
Control of bulk superconductivity in a BCS superconductor by surface charge doping via electrochemical gating
The electrochemical gating technique is a powerful tool to tune the surface conduction properties
of various materials by means of pure charge doping, but its efficiency is thought to be hampered in
materials with a good electronic screening. We show that, if applied to a metallic superconductor
(NbN thin films), this approach allows observing reversible enhancements or suppressions of the bulk
superconducting transition temperature, which vary with the thickness of the films. These results
are interpreted in terms of proximity effect, and indicate that the effective screening length depends
on the induced charge density, becoming much larger than that predicted by standard screening
theory at very high electric fields
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 Fe3O4âAg 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 Fe3O4âAg 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 Fe3O4âAg 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 Fe3O4âAg 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, , determine the
solution. The calculated field reproduces quantitatively the measured induction
field above MgB 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
Damage of calcarenite stone in archaeological site: relationship between wheathering, pollution and biological agents
For thousand of years, when magnificence and beauty were the goals of architecture, stones were the most widely used durable materials. The deterioration of building stones causes irreparable damages to our cultural heritage, not only as loss of architecture and ancient art, but especially as loss of symbols of human cultural identity and continuity. Sun, frost, wind, rain, pollution etc. contribute to a gradual process of weathering. Biological activity also plays a role and its association with physico-chemical phenomena should be considered essential for understanding long term deterioration. In this contest appear necessary to understand the weight of each single environmental parameter in order to assess and to plan not only a suitable restoration project and a preventive maintenance but also to test natural products (specific biocides) to be used to limit the degradation caused by bio deterioration agents
We studied the influence and synergistic effects of climatic parameters (temperature, light irradiation, wind intensity, humidity), pollution (SO2, CO, NO2, Ozone and heavy metals), and biological attacks on a building placed between an archaeological site of Lavello, a little town located in the Basilicata Region, and the industrial area surrounding this town.
Moreover, X-ray diffraction, X-ray induced photoelectron spectroscopy (XPS), X-ray fluorescence spectrometry (XRF), ground penetrating radar and geo-electrical measurements (GPR and MGE), Fourier Transform Infrared spectroscopy (FT-IR) and biological investigations were carried out on powdered calcarenite and on stones samples.
Preliminary results show that climatic parameters and pollution undermine the structure and the compactness of stones (i.e. micro-fractures, increase of saltsâ concentration) favouring the biological colonization (bacteria, mushrooms and lichens) especially in southâeast direction of prevailing winds
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
Twofold role of columnar defects in iron based superconductors
We report on the introduction of columnar defects in Ba1âx K x Fe2As2 and BaFe2(As1âx 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
Nanostructuring of high-TC superconductors into micro-sized zones
A special apparatus was designed in order to âwriteâ, with nanometric resolution, microsizeâconfined nanostructures in oxide samples. The nanostructures are produced by high energy heavy ion irradiation that allows nanostructuring the sample over its full thickness. The properties of the nanostructured areas can be further modulated by choosing the proper energy and fluence of the incoming ion beam. We present this setâup and different kinds of nanostructured patterns created on high temperature superconducting films. We used the magnetoâoptical analysis to directly show the effect of the confined nanostructures on the micron scale. The confined nanostructured area, embedded in the virgin matrix, is demonstrated to be a fruitful element for designing a new class of devices
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