We present a tight-binding study of donor impurities in Si, demonstrating the adequacy of this approach for this problem by comparison with effective mass theory and experimental results. We consider the response of the system to an applied electric field: donors near a barrier material and in the presence of an uniform electric field may undergo two different ionization regimes according to the distance of the impurity to the Si/barrier interface. We show that for impurities ∼ 5 nm below the barrier, adiabatic ionization is possible within switching times of the order of one picosecond, while for impurities ∼ 10 nm or more below the barrier, no adiabatic ionization may be carried out by an external uniform electric field. Our results are discussed in connection with proposed Si:P quantum computer architectures.

SARS-CoV-2 is the causative agent of the current COVID-19 pandemic. Disease clinical manifestations range from asymptomatic to severe multiple organ damage. SARS-CoV-2 uses ACE2 as a cellular receptor, which is abundantly expressed in the small intestine, allowing viral replication in the gastrointestinal tract. Viral RNA has been detected in the stool of COVID-19 patients and viable viruses had been isolated in some of these samples. Thus, a putative role of SARS-CoV-2 fecal-oral transmission has been argued. SARS-CoV-2 is shed in human excreta and further disposed in the sewerage or in the environment, in poor basic sanitation settings. Wastewater-based epidemiology (WBE) is a valuable population level approach for monitoring viral pathogens and has been successfully used in different contexts. This review summarizes the current global experience on SARS-CoV-2 WBE in distinct continents and viral detection in polluted surface water. The advantages and concerns of this strategy for SARS-CoV-2 surveillance are discussed. Outcomes suggest that WBE is a valuable early warning alert and a helpful complementary surveillance tool to subside public health response, to tailor containment and mitigation measures and to determine target populations for testing. In poor sanitation settings, contaminated rivers could be alternatively used as a source for environmental surveillance.

By means of periodic density functional calculations, we have studied the effect of dual doping on the stability and electronic structure of graphene. To this end, we substituted two carbon atoms with one 2p element (B, N, or O) and one 3p element (Al, Si, P or S). We determined that, in all cases, dual doping is much easier to attain than the introduction of only one dopant into the graphene framework. We demonstrate that this conclusion does not depend on the chemical species used to compute the formation energies. Moreover, we show what condition the dopants must satisfy to prefer dual doping over monodoping. Regarding the electronic properties, we found that, in most cases, the gaps computed at the HSE level for the dual-doped graphenes are smaller than those estimated for monodoped graphenes, despite the lower concentration of dopant present in the latter. In effect, for some dual-doped graphenes, the structures of the Dirac cones were found to be preserved, and gaps as small as 0.02 eV were computed.

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