701 research outputs found

    The impact of a massive migration flow on the regional population structure: The case of Italy

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    Low economic growth rates are a common problem in many developed countries in Europe. This paper aims to highlight the possible role of demographic factors. Problems of low growth may be exacerbated by an increase in dependency ratios. However, large-scale migrations have been shown to positively affect the age composition of a population. Focusing on Italy, we estimate the impact of migration on the working age population ratio, population size and gross domestic product. We also show that migration may affect the economic gap between the North and South, posing a new potential problem to policymakers.

    A current-voltage model for double Schottky barrier devices

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    Schottky barriers are often formed at the semiconductor/metal contacts and affect the electrical behaviour of semiconductor devices. In particular, Schottky barriers have been playing a major role in the investigation of the electrical properties of mono and two-dimensional nanostructured materials, although their impact on the current-voltage characteristics has been frequently neglected or misunderstood. In this work, we propose a single equation to describe the current-voltage characteristics of two-terminal semiconductor devices with Schottky contacts. We apply the equation to numerically simulate the electrical behaviour for both ideal and non-ideal Schottky barriers. The proposed model can be used to directly estimate the Schottky barrier height and the ideality factor. We apply it to perfectly reproduce the experimental current-voltage characteristics of ultrathin molybdenum disulphide or tungsten diselenide nanosheets and tungsten disulphide nanotubes. The model constitutes a useful tool for the analysis and the extraction of relevant transport parameters in any two-terminal device with Schottky contacts

    Charge transfer and trapping as origin of a double dip in the transfer characteristics of graphene based field-effect transistors

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    We discuss the origin of an additional dip other than the charge neutrality point observed in transfer characteristics of graphene-based field-effect transistors. The double-dip is proved to arise from charge transfer between graphene and metal electrodes, while charge storage at the graphene/SiO2 interface enhances it. Considering different Fermi energy from the neutrality point along the channel and partial charge pinning at the contacts, we propose a model which explains all features in gate voltage loops.Comment: 14 pages, 5 figure

    The impact of massive migration flow on regional population structure

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    Low economic growth rates are a common problem in many developed countries in Europe. This paper aims to highlight the possible role of demographic factors. Problems of low growth may be exacerbated by an increase in dependency ratios. However, large-scale migrations have been shown to positively affect the age composition of a population. Focusing on Italy, we estimate the impact of migration on the working age population ratio, population size and gross domestic product. We also show that migration may affect the economic gap between the North and South, posing a new potential problem to policymakers

    Screen-Printed Graphite Electrode Modified with Graphene-Co3O4 Nanocomposite: Voltammetric Assay of Morphine in the Presence of Diclofenac in Pharmaceutical and Biological Samples

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    This work focuses on the development of a novel electrochemical sensor for the determination of morphine in the presence of diclofenac. The facile synthesis of graphene-Co3O4 nanocomposite was performed. The prepared material (graphene-Co3O4 nanocomposite) was analyzed by diverse microscopic and spectroscopic approaches for its crystallinity, composition, and morphology. Concerning the electrochemical determinations, after drop-casting the as-fabricated graphene-Co3O4 nanocomposite on the surface of a screen-printed graphite electrode (SPGE), their electrochemical performance was scrutinized towards the morphine detection. It was also found that an SPGE modified by a graphene-Co3O4 nanocomposite exhibited better electrocatalytic activity for morphine oxidation than unmodified electrode. Under optimal conditions, the differential pulse voltammetry (DPV) was employed to explore the present sensor (graphene-Co3O4/SPGE), the findings of which revealed a linear dynamic range as broad as 0.02–575.0 ”M and a limit of detection (LOD) as narrow as 0.007 ÎŒM. The sensitivity was estimated to be 0.4 ”M/(”A cm2). Furthermore, the graphene-Co3O4/SPGE sensor demonstrated good analytical efficiency for sensing morphine in the presence of diclofenac in well-spaced anodic peaks. According to the DPV results, this sensor displayed two distinct peaks for the oxidation of morphine and diclofenac with 350 mV potential difference. In addition, the graphene-Co3O4/SPGE was explored for voltammetric determination of diclofenac and morphine in pharmaceutical and biological specimens of morphine ampoule, diclofenac tablet, and urine, where recovery rates close to 100% were recorded for all of the samples

    Field emission from two-dimensional GeAs

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    GeAs is a layered material of the IV-V groups that is attracting growing attention for possible applications in electronic and optoelectronic devices. In this study, exfoliated multilayer GeAs nanoflakes are structurally characterized and used as the channel of back-gate field-effect transistors. It is shown that their gate-modulated p-type conduction is decreased by exposure to light or electron beam. Moreover, the observation of a field emission current demonstrates the suitability of GeAs nanoflakes as cold cathodes for electron emission and opens up new perspective applications of two-dimensional GeAs in vacuum electronics. Field emission occurs with a turn-on field of ~80 V/{\mu}m and attains a current density higher than 10 A/cm^2, following the general Fowler-Nordheim model with high reproducibility.Comment: 10 pages, 3 figure

    Local characterization of ferromagnetic properties in ferromagnet/superconductor bilayer by Point Contact Andreev Reflection Spectroscopy

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    We realized point contact spectroscopy experiment on ferromagnet/superconductor bilayers. Differential conductance curves show several features that we explained within Bogoliubov-de Gennes formalism considering the presence of two interfaces in the normal-metal-tip/ferromagnet/superconductor device. We demonstrate that such configuration is suitable as local probe of the spin polarization and thickness of ferromagnetic layer, directly on bilayer areas. This is due to the high sensitivity of the Andreev surface states to the physical properties of the ferromagnetic interlayer

    MnCo2O4/NiCo2O4/rGO as a Catalyst Based on Binary Transition Metal Oxide for the Methanol Oxidation Reaction

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    The demands for alternative energy have led researchers to find effective electrocatalysts in fuel cells and increase the efficiency of existing materials. This study presents new nanocatalysts based on two binary transition metal oxides (BTMOs) and their hybrid with reduced graphene oxide for methanol oxidation. Characterization of the introduced three-component composite, including cobalt manganese oxide (MnCo2O4), nickel cobalt oxide (NiCo2O4), and reduced graphene oxide (rGO) in the form of MnCo2O4/NiCo2O4/rGO (MNR), was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray (EDX) analyses. The alcohol oxidation capability of MnCo2O4/NiCo2O4 (MN) and MNR was evaluated in the methanol oxidation reaction (MOR) process. The crucial role of rGO in improving the electrocatalytic properties of catalysts stems from its large active surface area and high electrical conductivity. The alcohol oxidation tests of MN and MNR showed an adequate ability to oxidize methanol. The better performance of MNR was due to the synergistic effect of MnCo2O4/NiCo2O4 and rGO. MN and MNR nanocatalysts, with a maximum current density of 14.58 and 24.76 mA/cm2 and overvoltage of 0.6 and 0.58 V, as well as cyclic stability of 98.3% and 99.7% (at optimal methanol concentration/scan rate of 20 mV/S), respectively, can be promising and inexpensive options in the field of efficient nanocatalysts for use in methanol fuel cell anodes
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