Dielectric Environment Sensitivity of Carbon Centers in Hexagonal Boron Nitride

A key advantage of utilizing van-der-Waals (vdW) materials as defect-hosting platforms for quantum applications is the controllable proximity of the defect to the surface or the substrate allowing for improved light extraction, enhanced coupling with photonic elements, or more sensitive metrology. However, this aspect results in a significant challenge for defect identification and characterization, as the defect's properties depend on the the atomic environment. This study explores how the environment can influence the properties of carbon impurity centers in hexagonal boron nitride (hBN). It compares the optical and electronic properties of such defects between bulk-like and few-layer films, showing alteration of the zero-phonon line energies and their phonon sidebands, and enhancements of inhomogeneous broadenings. To disentangle the mechanisms responsible for these changes, including the atomic structure, electronic wavefunctions, and dielectric screening, it combines ab initio calculations with a quantum-embedding approach. By studying various carbon-based defects embedded in monolayer and bulk hBN, it demonstrates that the dominant effect of the change in the environment is the screening of density-density Coulomb interactions between the defect orbitals. The comparative analysis of experimental and theoretical findings paves the way for improved identification of defects in low-dimensional materials and the development of atomic scale sensors for dielectric environments.

Variation in survival for adults with nasopharyngeal cancer in Europe, 1978-1989. EUROCARE Working Group

During the period 1978-1989, 2,054 new patients with nasopharyngeal carcinoma (NPC) were registered in the EUROCARE study, which, during 1985-1989 involved 45 population-based cancer registries in 17 countries. The follow-up time was at least 5 years. 48% of all cases were squamous cell carcinomas and 39% undifferentiated carcinomas, which were more frequent in males. The overall relative 1- and 5-year survival rates (data included from 8 countries with complete data) were 75 and 34%, respectively, for males, and 72 and 32%, respectively, for females, but in a multivariate analysis, there was no significant difference in risk between males and females (0.93 (0.84-1.01), hazard ratio (HR) with 95% confidence interval (95% CI) for females). The overall relative 5-year survival (data included from nine countries with complete data) declined with age, from 53% for patients aged 15-44 years to 31% for patients aged 65-74 years. For patients with undifferentiated tumours, higher survival rates were observed in Scandinavia, Slovakia and Mediterranean countries, with lower rates for patients from the U.K. and Estonia. Survival for patients with squamous cell carcinoma was lowest in Scotland, England and Estonia. In a multivariate analysis, there was a significant difference in risk of death between those with squamous cell carcinomas and those with undifferentiated (HR 0.82, 95% CI 0.74-0.90). Between 1978 and 1989, the prognosis did not change.