Even when ideal solids are insulating, their states with crystallographic defects may have superfluid properties. It became clear recently that edge dislocations in 4He featuring a combination of microscopic quantum roughness and superfluidity of their cores may represent a new paradigmatic class of quasi-one-dimensional superfluids. The new state of matter, termed transverse quantum fluid (TQF), is found in a variety of physical setups. The key ingredient defining the class of TQF systems is infinite compressibility, which is responsible for all other unusual properties such as the quadratic spectrum of normal modes (or even the absence of sharp quasiparticles), irrelevance of the Landau criterion, off-diagonal long-range order at T = 0, and the exponential dependence of the phase slip probability on the inverse flow velocity. From a conceptual point of view, the TQF state is a striking demonstration of the conditional character of many dogmas associated with superfluidity, including the necessity of elementary excitations, in general, and the ones obeying Landau criterion in particular.

ABSTRACT The article problematizes tourism destination development in the European borderlands of Denmark–Germany, Sweden–Denmark and Sweden–Finland, where border crossing has been relatively free for decades, except for the time of Covid-19 pandemic border restrictions in 2020–2021. The research contributes to border studies and tourism studies by developing a framework for analyzing tourism destinations through the prism of the multilayered border, with a focus on destination images, attractions, and hosts. The reseach complements previous studies on tourism development and cross-border partnership in the European Union territory by investigating multiple tourism destinations in the border regions and by contemplating to what extent borders form a resource for destination promotion in the aftermath of the pandemic. The examination of regional tourism development through the prism of borders informs us about the compatibility of the idea of a “borderless” Europe with border region “realities.”