Nanoscale Simulation of Three-contact Graphene Ballistic Junctions

In this work, three-terminal ballistic junctions, made of three-branch graphene nanoribbons (GNRs), are considered and simulated at the nanometric scale. The analysis is carried out by a scattering matrix approach, in a discrete formulation optimized for GNR devices. The ballisticity and the scattering properties of the junction contribute to the nonlinear behaviour, as, in fact, a sinusoidal voltage between two GNR branches results in a non-sinusoidal current at the third branch. The input-output characteristic is hardly predictable at the nanoscale, as it depends on several cooperating factors, namely the potential distribution and the geometry of the junction. Several numerical examples are shown to illustrate the above concepts

Dirac Equation-Based Formulation for the Quantum Conductivity in 2D-Nanomaterials

bstract: Starting from the four component-Dirac equation for free, ballistic electrons with finite mass, driven by a constant d.c. field, we derive a basic model of scalar quantum conductivity, capable of yielding simple analytic forms, also in the presence of magnetic and polarization effects. The classical Drude conductivity is recovered as a limit case. A quantum-mechanical evaluation is provided for parabolic and linear dispersion, as in graphene, recovering currently used expressions as particular cases. Numerical values are compared with the ones from the literature in the case of graphene under d.c. applied field

Heart Rate Fractality Disruption as a Footprint of Subthreshold Depressive Symptoms in a Healthy Population

Psychopathology (and depression in particular) is a cardiovascular risk factor independent from any co-occurring pathology. This link is traced back to the mind-heart-body connection, whose underlying mechanisms are still not completely known. To study psychopathology in relation to the heart, it is necessary to observe the autonomic nervous system, which mediates among the parts of that connection. Its gold standard of evaluation is the study of heart rate variability (HRV). To investigate whether any association exists between the HRV parameters and sub-threshold depressive symptoms in a sample of healthy subjects

A machine-learning based bio-psycho-social model for the prediction of non-obstructive and obstructive coronary artery disease

Background: Mechanisms of myocardial ischemia in obstructive and non-obstructive coronary artery disease (CAD), and the interplay between clinical, functional, biological and psycho-social features, are still far to be fully elucidated. Objectives: To develop a machine-learning (ML) model for the supervised prediction of obstructive versus non-obstructive CAD. Methods: From the EVA study, we analysed adults hospitalized for IHD undergoing conventional coronary angiography (CCA). Non-obstructive CAD was defined by a stenosis < 50% in one or more vessels. Baseline clinical and psycho-socio-cultural characteristics were used for computing a Rockwood and Mitnitski frailty index, and a gender score according to GENESIS-PRAXY methodology. Serum concentration of inflammatory cytokines was measured with a multiplex flow cytometry assay. Through an XGBoost classifier combined with an explainable artificial intelligence tool (SHAP), we identified the most influential features in discriminating obstructive versus non-obstructive CAD. Results: Among the overall EVA cohort (n = 509), 311 individuals (mean age 67 ± 11 years, 38% females; 67% obstructive CAD) with complete data were analysed. The ML-based model (83% accuracy and 87% precision) showed that while obstructive CAD was associated with higher frailty index, older age and a cytokine signature characterized by IL-1β, IL-12p70 and IL-33, non-obstructive CAD was associated with a higher gender score (i.e., social characteristics traditionally ascribed to women) and with a cytokine signature characterized by IL-18, IL-8, IL-23. Conclusions: Integrating clinical, biological, and psycho-social features, we have optimized a sex- and gender-unbiased model that discriminates obstructive and non-obstructive CAD. Further mechanistic studies will shed light on the biological plausibility of these associations. Clinical trial registration: NCT02737982

Multimode Transverse Resonance of Multilayer Crystal Slabs

Abstract: An effective tool for accurate analysis and design of a wide range of optical devices involving three-dimensional (3-D) photonic crystals is provided. The advantages of using transverse resonance in conjunction with full-wave numerical solvers in order to characterize this kind of structures are highlighted. This paper focuses on the study of a practical example of an asymmetric crystal slab and shows the features of the proposed method in terms of accuracy and flexibility. The concept of Floquet modes of a periodic crystal is applied, and a multimode transverse equivalent network is developed in the aim of obtaining the resonant 3-D modes of the slab containing the photonic crysta

Advanced Techniques for the Investigation of the Combined Electromagnetic-Quantum Transport Phenomena in Carbon Nanodevices

In this contribution, we report on the analysis of charge transport in graphene nanoribbons by means of timedomain and frequency-domain techniques. The former can be applied in order to describe the Maxwell/Schroedinger coupled system of equations, and the letter are used to solve the Poisson/Schroedinger system in a quasi static framework. A frequency-domain example about the self-consistent solution of laterally coupled graphene nanoribbons is reported. A time-domain example is also reported, showing the effect of the self-generated electromagnetic field, that may affect the dynamics of the charge wavepacket

A new 3-D Transmission Line Matrix Scheme for the Combined Schrödinger-Maxwell Problem in the Electronic/Electromagnetic Characterization of Nanodevices

This paper introduces a novel technique in which Maxwell equations, discretized by the transmission line matrix method in a 3-D domain, are coupled to the Schrodinger equation and simultaneously solved. The aim is to develop a method that accounts for deterministic electromagnetic field dynamics together with the quantum phenomena, which are typical of nanodevices

Boundary Immittance Operators for the Schrödinger-Maxwell Problem of Carrier Dynamics in nanodevices

We have recently introduced a novel algorithm in which Maxwell equations, discretized by the transmission line matrix method, are coupled to the Schrödinger equation and simultaneously solved. The goal of this study is to develop a method that accounts for deterministic electromagnetic field dynamics together with the quantum coherent transport in the nanoscale environment. We present exact boundary conditions for the Schrödinger equation that rigorously model absorbtion and injection of charge at the terminal planes. As a nontrivial application of the above concept, we show the dynamics of a charge wavepacket from source to drain electrodes in a carbon nanotube transistor environment. We then compare computed characteristics with experimental ones reported in the literatur

Ballistic simulation of Ratchet effect in antidot lattices patterned on graphene

International audienceIn this contribution, we investigate the mechanism governing the Ratchet effect in patterned monolayer graphene, at the ballistic nanoscale. Still smaller than currently achievable and manifacturable devices, the simulated structures serve to exemplify the dependence of charge scattering on the arrangement of lattice defects, i.e. clusters of atomic vacancies of triangular shape. The ballistic Ratchet effect is seen as cumulative multimode scattering of carriers in correspondence of the lattice discontinuities. An atomistic model, based on the Scattering Matrix method and making use of TB approximation, has been applied. The latter, in contrast with continuum models, like Dirac or Kubo-Drude derived formulas, is capable of describing abrupt discontinuities at sub-micrometric scales, where graphene is likely to preserve its outstanding properties. We believe that this work is a first step in the direction of engineering and design of devices based on the ballistic Ratchet effect, like RF and THz detectors. Keywords—Graphene, Ratchet effect, ballistic electronics, RF and THz detector, antidot lattice

Dirac-Based Quantum Admittance of 2D Nanomaterials at Radio Frequencies

Starting from a rigorous finite mass, Dirac equation-based model, we investigate the R.F. quantum admittance of a monolayer 2D material under the action of an electromagnetic (e.m.) wave with axially directed vector potential. With some reasonable approximations, the analysis yields a relatively simple RLC-equivalent circuit with frequency-independent elements depending on the bias, temperature, effective mass, Fermi velocity and effective e.m. index of the material, losses and other relevant parameters