4,660 research outputs found
Towards the insulator-to-metal transition at the surface of ion-gated nanocrystalline diamond films
Hole doping can control the conductivity of diamond either through boron
substitution, or carrier accumulation in a field-effect transistor. In this
work, we combine the two methods to investigate the insulator-to-metal
transition at the surface of nanocrystalline diamond films. The finite boron
doping strongly increases the maximum hole density which can be induced
electrostatically with respect to intrinsic diamond. The ionic gate pushes the
conductivity of the film surface away from the variable-range hopping regime
and into the quantum critical regime. However, the combination of the strong
intrinsic surface disorder due to a non-negligible surface roughness, and the
introduction of extra scattering centers by the ionic gate, prevents the
surface accumulation layer to reach the metallic regime.Comment: 5 pages, 4 figure
When words matter: narratives and strategies in the Italian Jobs Act (2014–2016)
With the reforms of the so-called \u2018Jobs Act\u2019 (JA), Italy aimed to structurally reform its labour market and income-support system, through recalibration (i.e. a mix of both expansionary and retrenching measures) for old social policy risks, and some expansionary measures to face new social risks. The JA also became the symbol of opposite views about the Italian welfare state, being itself a reason for ideolo- gical conflict and coalition reshuffling in the Italian left. Ultimately, its increasing personalization around Renzi\u2019s divisive figure detracted from its functional and substantive matter. Hence, the JA reform provides an unparalleled vantage point to investigate the role of narrative stories in shaping policy contents and reforms. The paper aims to contribute to the literature on social policy reforms by com- bining a focus on narrative stories with the analytical perspective of the Multiple Stream Framework. Through qualitative analysis of offi- cial documents, of more than 500 newspaper articles and of selected in-depth interviews to key informants, this paper reconstructs the narratives about the JA reform, considering both the supporters and the challengers. Building on the Multiple Stream Framework, the paper focuses in particular on whether and how policy entrepreneurs took advantage of windows of opportunity by shaping the narrative stories. Results are twofold. First, the paper shows the variations of social policy reform narratives across actors. Second, it demonstrates the crucial role of policy entrepreneurs in shaping narrative stories as a strategy to couple the streams of problem, policy and politics
Characterizing the Implicit Bias of Regularized SGD in Rank Minimization
We study the bias of Stochastic Gradient Descent (SGD) to learn low-rank
weight matrices when training deep neural networks. Our results show that
training neural networks with mini-batch SGD and weight decay causes a bias
towards rank minimization over the weight matrices. Specifically, we show, both
theoretically and empirically, that this bias is more pronounced when using
smaller batch sizes, higher learning rates, or increased weight decay.
Additionally, we predict and observe empirically that weight decay is necessary
to achieve this bias. Unlike previous literature, our analysis does not rely on
assumptions about the data, convergence, or optimality of the weight matrices
and applies to a wide range of neural network architectures of any width or
depth. Finally, we empirically investigate the connection between this bias and
generalization, finding that it has a marginal effect on generalization
Ambipolar suppression of superconductivity by ionic gating in optimally-doped BaFe2(As,P)2 ultrathin films
Superconductivity (SC) in the Ba-122 family of iron-based compounds can be
controlled by aliovalent or isovalent substitutions, applied external pressure,
and strain, the combined effects of which are sometimes studied within the same
sample. Most often, the result is limited to a shift of the SC dome to
different doping values. In a few cases, the maximum SC transition at optimal
doping can also be enhanced. In this work, we study the combination of charge
doping together with isovalent P substitution and strain by performing ionic
gating experiments on BaFe(AsP) ultrathin films. We
show that the polarization of the ionic gate induces modulations to the
normal-state transport properties that can be mainly ascribed to surface charge
doping. We demonstrate that ionic gating can only shift the system away from
the optimal conditions, as the SC transition temperature is suppressed by both
electron and hole doping. We also observe a broadening of the resistive
transition, which suggests that the SC order parameter is modulated
nonhomogeneously across the film thickness, in contrast with earlier reports on
charge-doped standard BCS superconductors and cuprates.Comment: 10 pages, 5 figure
Evaluation of subsidence induced by long-lasting buildings load using InSAR technique and geotechnical data: The case study of a Freight Terminal (Tuscany, Italy)
This paper shows the results of the comparison between Multi-temporal Synthetic Aperture Radar (MTInSAR) products derived from different sensors (C-band ERS 1/2, Envisat, Sentinel-1 and X-band COSMO-SkyMed) and geotechnical data to investigate the driving factors of subsidence which affect a freight terminal located along the a coastal plain of Tuscany (central Italy). MTInSAR data have been acquired in a very long period, between 1992 and 2018 and were analyzed in terms of subsidence rates and deformation time series at building scale. The obtained results show that the oldest buildings are still affected by a deformation rate close to −5 mm/yr, whereas recent buildings register rates around −40 mm/yr. Time series of deformation suggest that the deformation rates decrease over time following time-dependent trend that approximates the typical consolidation curve for compressible soils. The geotechnical and stratigraphical analysis of the subsurface data (boreholes, cone penetration tests and dilatometer tests) highlights the presence of a 15 m thick layer formed of clay characterized by poor geotechnical characteristics. The comparison among InSAR data, subsurface geological framework and geotechnical reconstruction suggests a possible evaluation of the timing of the primary and secondary consolidation processes
Towards the insulator-to-metal transition at the surface of ion-gated nanocrystalline diamond films
Hole doping can control the conductivity of diamond either through boron
substitution, or carrier accumulation in a field-effect transistor. In this
work, we combine the two methods to investigate the insulator-to-metal
transition at the surface of nanocrystalline diamond films. The finite boron
doping strongly increases the maximum hole density which can be induced
electrostatically with respect to intrinsic diamond. The ionic gate pushes the
conductivity of the film surface away from the variable-range hopping regime
and into the quantum critical regime. However, the combination of the strong
intrinsic surface disorder due to a non-negligible surface roughness, and the
introduction of extra scattering centers by the ionic gate, prevents the
surface accumulation layer to reach the metallic regime.Comment: 5 pages, 4 figure
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