9,651 research outputs found

    Essays on International Migration using Big Data Analytics

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    How can social big data help to understand issues related to international migration? Official data such as census, survey and administrative data have been traditionally the main data source to study migration. However, these data have some limitations. They are inconsistent across different nations because countries employ different definitions of international migration and characterisations of migrants. Moreover, collecting traditional data is costly and time consuming, thus tracking instantaneous ows of migrants becomes diffcult. This becomes even harder when tracking emigrants because of the lack of motivation from citizens to declare their departure. In recent years, however, we are provided with other alternative data sources for migration. The availability of social big data such as Facebook, and Twitter data allows us to study social behaviours both at large scale and at a granular level, and to peek into real-world phenomena. Although known to suffer from other types of issues, such as selection bias, these data could bring complementary value to standard statistics. In this work, we employ social big data to study international migration. We try to answer the question through an analysis of various phases of migration, using both traditional data and novel data sources. The first phase includes the journey, and we study migration stocks on Twitter, providing benefits and drawbacks of using such data to study international migration. Here, a generic methodology is developed to identify migrants within the Twitter population. This describes a migrant as a person who has the current residence different from the nationality. The residence is defined as the location where a user spends most of his/her time in a certain year. The nationality is inferred from linguistic and social connections to a migrant's country of origin. This methodology is validated first with an internal gold standard dataset and second with Italian register data and Eurostat, and shows strong performance scores and correlation coefficients. The second phase concerns the integration of migrants in the destination country and attachments to their home country. We explore Twitter data to build a novel methodology to quantify and understand migrants' different integration types. Here, We describe four different integration types which are assimilation, integration, marginalisation and separation using two dimensions: the preservation of links to the home country and culture, i.e. home attachment index, and creation of new links and adoption of cultural traits from the new residence country, i.e. destination attachment index. The two dimensions are validated by performing a null model analysis. It shows significant differences between the actual indices and the null model indices, confirming that the two indices are not produced at random. Lastly, We examine the effect of the presence of migrants on political choices of the natives, using a German case study. Specifically, We are interested in understanding whether exposure to reception centres for asylum-seekers in Berlin affected the votes obtained by the radical right AfD in the 2019 European elections, at the electoral district level. We analyse this relationship at a very small scale based on geo-localization techniques and high-resolution spatial data. We study this in a wide range of contextual conditions, including variables such as districts' socio-economic deprivation, the share of established non-European residents, and the geographical location of the districts. Overall the findings show that exposure to reception centres in Berlin is negatively correlated with the AfD vote share. However, the results show remarkable differences between East and West Berlin and between districts characterised by different levels of socio-economic deprivation. Exposure and AfD vote shares are more strongly correlated in Western districts and in better-of districts. This work is thus aimed at providing a practical contribution to international migration studies by offering novel methods and analyses for identifying, quantifying and understanding dynamics of migration to better shape the policies of international migration

    Enhancing quantum entanglement for continuous variables by a coherent superposition of photon subtraction and addition

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    We investigate how the entanglement properties of a two-mode state can be improved by performing a coherent superposition operation of photon subtraction and addition, proposed by Lee and Nha [Phys. Rev. A 82, 053812 (2010)], on each mode. We show that the degree of entanglement, the EPR-type correlation, and the performance of quantum teleportation can be all enhanced for the output state when the coherent operation is applied to a two-mode squeezed state. The effects of the coherent operation are more prominent than those of the mere photon subtraction and the addition particularly in the small squeezing regime, whereas the optimal operation becomes the photon subtraction in the large-squeezing regime.Comment: 6 pages, 6 figures, published versio

    Effects of Nd-doping on the structural, electrical, and multiferroic properties of Bi7Fe3Ti3O21 thin films

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    Aurivillius-phase six-layered Bi7Fe3Ti3O21 (BFTO21) and Nd-doped Bi6.4Nd0.6Fe3Ti3O21 (BNdFTO21) thin films were prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method in order to investigate their structural, electrical, and multiferroic properties. Doping the Bi sites of the BFTO21 with Nd-ions led to remarkable improvements in the electrical and the multiferroic properties. The electrical study of the BNdFTO21 thin film showed a low leakage current density of 4.38 × 10-6 A/cm at an applied electric field of 100 kV/cm, which was about one order of magnitude lower than that of the BFTO21 thin film. The ferroelectric P - E hysteresis loop of the BNdFTO21 thin film exhibited a large remnant polarization (2Pr) of 24 μC/cm2 and a low coercive electric field (2Ec) of 154 kV/cm at an applied electric field of 239 kV/cm. Furthermore, the magnetization and the coercive magnetic field that were observed for the BNdFTO21 thin film at room temperature were drastically enhanced compared to those observed for the BFTO21 thin film

    Effects of excessive Bi on the structure and the properties of Aurivillius Bi5.25La0.75Fe2Ti3O18 thin films

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    The effects of excessive Bi on the structural, electrical and multiferroic properties of the La-doped Bi6Fe2Ti3O18 (Bi5.25La0.75Fe2Ti3O18) thin films prepared on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method are reported. The structures of the thin films were studied by using X-ray diffraction, Raman scattering spectroscopy and scanning electron microscopy. From the experimental comparisons, a low electrical leakage current of 1.84 × 10-5 A/cm2 at 100 kV/cm and enhanced ferroelectric properties, such as a large remnant polarization (2Pr) of 10.5 μC/cm2 and a low coercive field (2Ec) of 400 kV/cm at 485 kV/cm, were observed for the 5% Biexcess La-doped Bi6Fe2Ti3O18 thin film. The formation of a stable bismuth layer-structured phase, a lower c-axis orientation, an optimum crystallinity and a dense microstructure with a smooth surface morphology correlate with the improved electrical and multiferroic properties of the 5% Bi-excessive Bi6Fe2Ti3O18 thin film

    Quantum linear amplifier enhanced by photon subtraction and addition

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    A deterministic quantum amplifier inevitably adds noise to an amplified signal due to the uncertainty principle in quantum physics. We here investigate how a quantum-noise-limited amplifier can be improved by additionally employing the photon subtraction, the photon addition, and a coherent superposition of the two, thereby making a probabilistic, heralded, quantum amplifier. We show that these operations can enhance the performance in amplifying a coherent state in terms of intensity gain, fidelity, and phase uncertainty. In particular, the photon subtraction turns out to be optimal for the fidelity and the phase concentration among these elementary operations, while the photon addition also provides a significant reduction in the phase uncertainty with the largest gain effect.Comment: published version, 7 pages, 9 figure

    The Correlation between Climate Change and Corporate Performance

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    38-43The purpose of the study is to verify the correlation of the climate change risk focusing on the influence of carbon emission on the corporate performance and discriminative response of corporate contingent upon the publishment of Sustainability Report. The results of this study show that there is a negative (-) relationship between Carbon emission intensity and corporate performance. And the negative influence of carbon emission intensity on corporate performance was found to be smaller for companies that published sustainability reports than for those that did not. This study provided empirical evidences on why corporate’s active reactive activities according to the climate change is essential for sustainable development
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