The association of screen time with intake of potentially cariogenic food and oral health of school children aged 8-14 years-a cross-sectional study.

This study aimed to test the hypothesis that excessive screen time can affect the oral health of school children. In this observational cross-sectional study conducted in four schools in Delhi, National Capital Region (NCR), India, 497 school children aged 8-14 years were included. Convenience sampling was used to select schools. Data were extracted from a questionnaire pertaining to screen time and dietary habits, which was distributed to the school children during their first planned school visit. Seven days later, on their second school visit, the children were clinically examined by a calibrated examiner (κ = 0.9) for dental caries, plaque and gingival health using the following indices: Decayed, Missing, Filled teeth (DMFT)/decayed, extracted, filled teeth (deft), Silness-Loe plaque index (PI) and Loe-Silness gingival index (GI), respectively. Overall, 88.7% of the participants exhibited screen time of ≥2 h with maximum frequency for smartphones (93%), followed by television (84.7%). Significantly higher DMFT/deft values (3.20 ± 0.68 vs. 2.45 ± 0.35, p = 0.001), PI (1.04 ± 0.21 vs. 0.33 ± 0.10, p < 0.001) and GI (1.45 ± 0.34 vs. 0.12 ± 0.04, p < 0.001) were observed in those with screen time ≥2 h as compared to those with screen time <2 h. Data underwent statistical analysis with a significance threshold of p < 0.05. Excessive screen time can influence the eating patterns of children and contribute to higher DMFT, GI and PI.

Scattering of massless Dirac fermions in circular p-n junctions with and without magnetic field.

In the absence of a magnetic field, a scattered wavefunction inside a circular p-n junction in graphene exhibits an interference pattern with its high intensity maximum located around the caustics. We investigate the wavefunctions in the presence of a uniform magnetic field outside the circular region to show how the loci of the high intensity region changes by forming a Landau-level structure outside the circular region and a central high intensity region inside the circular p-n junction due to the strong reflection of massless Dirac fermions by the outside magnetic field. We conclude by suggesting experimental ways to detect such changes in pattern due to the effect of the magnetic field.

Reversal of Klein reflection by magnetic barriers in bilayer graphene.

Massless Dirac fermions in monolayer graphene exhibit total transmission when normally incident on a scalar potential barrier, a consequence of the Klein paradox originally predicted by O Klein for relativistic electrons obeying the 3 + 1 dimensional Dirac equation. For bilayer graphene, charge carriers are massive Dirac fermions and, due to different chiralities, electron and hole states are not coupled to each other. Therefore, the wavefunction of an incident particle decays inside a barrier as for the non-relativistic Schrödinger equation. This leads to exponentially small transmission upon normal incidence. We show that, in the presence of magnetic barriers, such massive Dirac fermions can have transmission even at normal incidence. The general consequences of this behavior for multilayer graphene consisting of massless and massive modes are mentioned. We also briefly discuss the effect of a bias voltage on such magnetotransport.