Ab-initio study of gap opening and screening effects in gated bilayer graphene

The electronic properties of doped bilayer graphene in presence of bottom and top gates have been studied and characterized by means of Density Functional Theory calculations. Varying independently the bottom and top gates it is possible to control separately the total doping charge on the sample, and the average external electric field acting on the bilayer. We show that, at fixed doping level, the band gap at the K point in the Brillouin zone depends linearly on the average electric field, whereas the corresponding proportionality coefficient has a non-monotonic dependence on doping. We find that the DFT-calculated band gap at K, for small doping levels, is roughly half of the band gap obtained with standard Tight Binding approach. We show that this discrepancy arises from an underestimate, in the TB model, of the screening of the system to the external electric field. In particular, on the basis of our DFT results we observe that, when the bilayer graphene is in presence of an external electric field, both an interlayer and an intralayer screening occur. Only the interlayer screening is included in TB calculations, while both screenings are fundamental for the description of the band gap opening. We finally provide a general scheme to obtain the full band structure of the gated bilayer graphene, for an arbitrary value of the external electric field and of the doping.Comment: 15 pages 20 figures, accepted for publication in Physical Review

Two-dimensional analysis of the double-resonant 2D Raman mode in bilayer graphene

By computing the double-resonant Raman scattering cross-section completely from first principles and including electron-electron interaction at the $GW$ level, we unravel the dominant contributions for the double-resonant 2D-mode in bilayer graphene. We show that, in contrast to previous works, the so-called inner processes are dominant and that the 2D-mode lineshape is described by three dominant resonances around the $K$ point. We show that the splitting of the TO phonon branch in $\Gamma-K$ direction, as large as 12 cm$^{-1}$ in $GW$ approximation, is of great importance for a thorough description of the 2D-mode lineshape. Finally, we present a method to extract the TO phonon splitting and the splitting of the electronic bands from experimental data.Comment: 5 pages Main + 6 pages Supplementary Material. Accepted for publication in Physical Review Letter

Acute Delta Hepatitis in Italy spanning three decades (1991–2019): Evidence for the effectiveness of the hepatitis B vaccination campaign

Updated incidence data of acute Delta virus hepatitis (HDV) are lacking worldwide. Our aim was to evaluate incidence of and risk factors for acute HDV in Italy after the introduction of the compulsory vaccination against hepatitis B virus (HBV) in 1991. Data were obtained from the National Surveillance System of acute viral hepatitis (SEIEVA). Independent predictors of HDV were assessed by logistic-regression analysis. The incidence of acute HDV per 1-million population declined from 3.2 cases in 1987 to 0.04 in 2019, parallel to that of acute HBV per 100,000 from 10.0 to 0.39 cases during the same period. The median age of cases increased from 27 years in the decade 1991-1999 to 44 years in the decade 2010-2019 (p < .001). Over the same period, the male/female ratio decreased from 3.8 to 2.1, the proportion of coinfections increased from 55% to 75% (p = .003) and that of HBsAg positive acute hepatitis tested for by IgM anti-HDV linearly decreased from 50.1% to 34.1% (p < .001). People born abroad accounted for 24.6% of cases in 2004-2010 and 32.1% in 2011-2019. In the period 2010-2019, risky sexual behaviour (O.R. 4.2; 95%CI: 1.4-12.8) was the sole independent predictor of acute HDV; conversely intravenous drug use was no longer associated (O.R. 1.25; 95%CI: 0.15-10.22) with this. In conclusion, HBV vaccination was an effective measure to control acute HDV. Intravenous drug use is no longer an efficient mode of HDV spread. Testing for IgM-anti HDV is a grey area requiring alert. Acute HDV in foreigners should be monitored in the years to come

Caratteristiche meccaniche degli elastici extraorali - Analisi dinamica (I Parte)

Aim: This was to compare craniofacial and body growth during prepubebertal period using direct medical anthropemetry for body and craniofacial measurement. Methods: the sample consits of 100 patiets (48 male, 52 female), aged between 7 and 12 years. Thirty craniofacial and bodymeasurements of height, width, leght and circumference were made on each subject. Statistical analysis: Comparisons were made of averanges, percentanges and standard deviation, for three growth patterns during prepubertal period: cranial, facial and body growth pattern. Linear correlation coefficient (r)were calculated to evaluete the intensity of the interdependence between variables using BMDT Dynamic software. Results: Skull and face measurements increase less then body dimensions, but those for the face increased more than for the skull, which was valid both for male and female. Differences between males and females were determineted for standing height, mandibular height (T-Go) and lower facial height (Sto-Gn). Conclusions: No body parameters was found to be a good indicator of facial growth during this period. the jaw was found to be the facial area that showed the higher developmen

Probing the electrostatic environment of bilayer graphene using Raman spectra

The Raman shift, broadening, and relative Raman intensities of bilayer graphene are computed as functions of the electron concentration. We include dynamic effects for the phonon frequencies and we consider the gap induced in the band structure of bilayer graphene by an external electric field. We show that from the analysis of the Raman spectra of gated bilayer graphene it is possible to quantitatively identify the amount of charges coming from the atmosphere and from the substrate. These findings suggest that Raman spectroscopy of bilayer graphene can be used to characterize the electrostatic environment of few-layers graphene

Pr\ue9valence des cristaux de pyrophosphate de calcium et d\u2019urate monosodique dans le liquide synovial de patients avec un diagnostic d\u2019arthropathie \ue9tabli

Objectif. \u2013 L\u2019objectif principal de cette \ue9tude \ue9tait de d\ue9terminer la fr\ue9quence de la pr\ue9sence de cristaux d\u2019urate monosodique (UMS) et de pyrophosphate de calcium (PPC) dans le liquide synovial (LS) obtenu chez des patients avec ant\ue9c\ue9dent de maladie articulaire diagnostiqu\ue9e. M\ue9thodes. \u2013 Nous avons \ue9tudi\ue9 les r\ue9sultats d\u2019analyse de LS provenant de 5020 \ue9chantillons, parmi lesquels 2370 \ue9chantillons avec un diagnostic \ue9tabli. Les donn\ue9es sur les caract\ue9ristiques du LS, l\u2019\ue2ge, le sexe, le diagnostic et la dur\ue9e de la maladie ont \ue9t\ue9 obtenues \ue0 partir des archives \ue9lectroniques des patients. R\ue9sultats. \u2013 La pr\ue9valence des cristaux de PPC dans le LS \ue9tait de 22,28 % dans l\u2019arthrose, 8,28 % dans la polyarthrite rhumato\uefde (PR), 3,82 % dans le rhumatisme psoriasique (RP), 2,79 % dans les autres spondyloarthropathies (SpA), 10 % dans l\u2019arthrite septique (AS), 0,66 % dans la goutte et 9,18 % dans les autres pathologies rhumatismales. La pr\ue9valence des cristaux d\u2019UMS dans le LS \ue9tait de 0,30 % dans la PR, 3,34 % dans le RP, 0,70 % dans les autres SpA, 0,80 % dans le rhumatisme \ue0 cristaux de PPCD, 0 % dans l\u2019arthrose, l\u2019arthrite r\ue9actionnelle, l\u2019AS, l\u2019arthrite juv\ue9nile idiopathique (AJI) et les pathologies diverses. Dans le groupe de patients arthrosiques, nous avons constat\ue9 que l\u2019\ue2ge et les indices inflammatoires dans le LS \ue9taient plus \ue9lev\ue9s en cas de pr\ue9sence de cristaux de PPC (p < 0,0001). Dans la PR, nous avons retrouv\ue9 un \ue2ge plus avanc\ue9 dans le groupe avec pr\ue9sence de cristaux de PPC (p = 0,001) avec moins de signes inflammatoires (p = 0,022). Conclusion. \u2013 Les cristaux peuvent \ueatre d\ue9tect\ue9s plus fr\ue9quemment que pr\ue9vu dans les LS d\u2019articulations avec diagnostic a priori bien \ue9tabli. Cela souligne l\u2019importance de l\u2019analyse du LS dans le diagnostic des comorbidit\ue9s possibles li\ue9es \ue0 la pr\ue9sence de cristaux