RESUMO
AgI-type pyrotechnics are widely used in the field of weather modification, as a kind of artificial ice nuclei. However, their precipitation yield remains an intensively studied area. In this paper, we present a study of AgI-type pyrotechnic nucleant-induced water condensation promoted by femtosecond laser filaments in a cloud chamber. It is found that when 50-ml sample was irradiated by the laser filaments, the particles condensed on the glass slide are more soluble and slightly larger (5-15 µm). The irradiation of the laser filament on the nucleant rarely induces the generation of particles of sizes larger than 1 µm; however, it increases the decay time of particles from 13 to 18 min by the creation of numerous small particles. The amount of snow on the cold bottom plate increases by 4.2-13.1% in 2 h, compared to that without the irradiation of the laser filament. These results are associated with the production of high-concentration HNO3 by the laser filament. The concentration of HNO3 in the melt water increases by more than ten times when the sample was irradiated by the laser filaments.
RESUMO
Water condensation and precipitation induced by 22-TW 800-nm laser pulses at 1 Hz in an open cloud chamber were investigated in a time-resolved manner. Two parts of precipitation in two independent periods of time were observed directly following each laser shot. One part started around the filament zone at t < 500 µs and ended at t â 1.5 ms after the arrival of the femtosecond laser pulse. The other following the laser-induced energetic air motion (turbulence), started at t â 20 ms and ended at t â 120 ms. Meanwhile, the phase transitions of large-size condensation droplets with diameters of 400-500 µm from liquid to solid (ice) in a cold area (T < -30 °C) were captured at t â 20 ms.
RESUMO
A large bulk band gap is critical for the application of two-dimensional topological insulators (TIs) in spintronic devices operating at room temperature. On the basis of first-principles calculations, we predict BiXH (X = OH, SH) monolayers as TIs with an extraordinarily large bulk gap of 820 meV for BiOH and 850 meV for BiSH, and propose a tight-binding model considering spin-orbit coupling to describe the electronic properties of BiXH. These large gaps are entirely due to the strong spin-orbit interaction related to the pxy orbitals of the Bi atoms of the honeycomb lattice. The orbital filtering mechanism can be used to understand the topological properties of BiXH. The XH groups simply remove one branch of orbitals (pz of Bi) and reduce the trivial 6-band lattice into a 4-band, which is topologically non-trivial. The topological characteristics of BiXH monolayers are confirmed by nonzero topological invariant Z2 and a single pair of gapless helical edge states in the bulk gap. Owing to these features, the BiXH monolayers of the large-gap TIs are an ideal platform to realize many exotic phenomena and fabricate new quantum devices working at room temperature.
RESUMO
Based on first-principles hybrid functional calculations, we demonstrate the formation of two-dimensional (2D) topological insulators (TIs) of Pb/Sb honeycombs on Ge(111) semiconductor surface. We show that 1/3 Cl-covered Ge(111) surface offers an ideal template for metal deposition. When Pb and Sb atoms are deposited on Cl-Ge(111) surface, they spontaneously form a hexagonal lattice (Pb/Sb@Cl-Ge(111)). The Pb/Sb@Cl-Ge(111) exhibits a 2D TI state with large bulk gap of 0.27 eV for Pb@Cl-Ge(111) and 0.81 eV for Sb@Cl-Ge(111). The mechanism of 2D TI state is the substrate orbital-filtering effect that effectively removes the p z bands of Pb(Sb) away from the Fermi level, leaving behind only the p x and p y orbitals at the Fermi level. Our findings pave another way for future design of 2D topological insulators on conventional semiconductor surface, which promotes the application of 2D TIs in spintronics and quantum computing devices at room-temperature.