A variant of SARS-CoV-2 emerged in early summer 2020, presumably in Spain, and has since spread to multiple European countries. The variant was first observed in Spain in June and has been at frequencies above 40% since July. Outside of Spain, the frequency of this variant has increased from very low values prior to 15th July to 40-70% in Switzerland, Ireland, and the United Kingdom in September. It is also prevalent in Norway, Latvia, the Netherlands, and France. Little can be said about other European countries because few recent sequences are available. Sequences in this cluster (20A.EU1) differ from ancestral sequences at 6 or more positions, including the mutation A222V in the spike protein and A220V in the nucleoprotein. We show that this variant was exported from Spain to other European countries multiple times and that much of the diversity of this cluster in Spain is observed across Europe. It is currently unclear whether this variant is spreading because of a transmission advantage of the virus or whether high incidence in Spain followed by dissemination through tourists is sufficient to explain the rapid rise in multiple countries.

The dynamics following the photoexcitation of Na and Li atoms located on the surface of helium nanodroplets has been investigated in a joint experimental and theoretical study. Photoelectron spectroscopy has revealed that excitation of the alkali atoms via the (n + 1)s ←ns transition leads to the desorption of these atoms. The mean kinetic energy of the desorbed atoms, as determined by ion imaging, shows a linear dependence on excitation frequency. These experimental findings are analyzed within a three-dimensional, time-dependent density functional approach for the helium droplet combined with a Bohmian dynamics description of the desorbing atom. This hybrid method reproduces well the key experimental observables. The dependence of the observables on the impurity mass is discussed by comparing the results obtained for the (6)Li and (7)Li isotopes. The calculations show that the desorption of the excited alkali atom is accompanied by the creation of highly non-linear density waves in the helium droplet that propagate at supersonic velocities.

We present systematic results, based on density functional calculations, for the structure and energetics of 3He and 4He nanodroplets doped with alkaline earth atoms. We predict that alkaline earth atoms from Mg to Ba go to the center of 3He drops, whereas Ca, Sr, and Ba reside in a deep dimple at the surface of 4He drops, and Mg is at their center. For Ca and Sr, the structure of the dimples is shown to be very sensitive to the He-alkaline earth pair potentials used in the calculations. The 5s5p <-- 5s2 transition of strontium atoms attached to helium nanodroplets of either isotope has been probed in absorption experiments. The spectra show that strontium is solvated inside 3He nanodroplets, supporting the calculations. In the light of our findings, we emphasize the relevance of the heavier alkaline earth atoms for analyzing mixed 3He-4He nanodroplets, and in particular, we suggest their use to experimentally probe the 3He-4He interface.

The absorption spectra of the first electronic exited state of alkali metal atoms on helium nanodroplets formed of both 4He and 3He isotopes were studied experimentally as well as theoretically. In the experimental part new data on the 2p<--2s transition of lithium on 3He nanodroplets are presented. The absorption spectrum changes drastically when compared to 4He droplets, in contrast to sodium where only marginal differences were observed in former studies. To explain these large differences and to answer some still open questions concerning the interaction of alkali metal atoms with helium nanodroplets, a model calculation was performed. New helium density profiles as well as a refined model allowed us to achieve good agreement with the experimental findings. For the first time the red-shifted intensities in the lithium and sodium spectra are explained in terms of enhanced binding configurations in the excited state displaced spatially from the ground state configurations.