Some very transparent cells in the optical tract of vertebrates, such as the lens fiber cells, possess certain types of specialized intermediate filaments (IFs) that have essential significance for their transparency. The exact mechanism describing why the IFs are so important for transparency is unknown. Recently, transparency was described also in the retinal Müller cells (MCs). We report that the main processes of the MCs contain bundles of long specialized IFs, each about 10 nm in diameter; most likely, these filaments are the channels providing light transmission to the photoreceptor cells in mammalian and avian retinas. We interpret the transmission of light in such channels using the notions of quantum confinement, describing energy transport in structures with electroconductive walls and diameter much smaller than the wavelength of the respective photons. Model calculations produce photon transmission efficiency in such channels exceeding 0.8, in optimized geometry. We infer that protein molecules make up the channels, proposing a qualitative mechanism of light transmission by such structures. The developed model may be used to describe light transmission by the IFs in any transparent cells.

The specialized intermediate filaments (IFs) have critical importance for the clearness and uncommon transparency of the vertebrates' lens fiber cells, although the physical mechanisms involved are poorly understood. Recently, an unusual low-scattering light transport was also described in the retinal Müller cells. Exploring the function of the IFs in the Müller cells, we have studied the morphology and distribution pattern of the IFs and other cytoskeletal filaments inside the Müller cell main processes in the foveolar part of the avian (Pied Flycatcher) retina. We found that some IFs surrounded by globular nanoparticles (that we suggest are crystallines) are present in almost every part of the Müller cells that span the retina, including the microvilli. Unlike the IFs implicated in the mechanical architecture of the cell, these IFs are not connected to any specific cellular membranes. Instead, they are organized into bundles, passing inside the cell from the endfeet to the photoreceptor, following the geometry of the processes and repeatedly circumventing numerous obstacles. We believe that all of the presently reported data effectively confirms that the model of nanooptical channels built of the intermediate filaments [Makarov et al., 2015, Khmelinskii et al., 2015] may provide a viable explanation of the Müller cell transparency.

Presently we continue our studies of the quantum mechanism of light energy transmission in the form of excitons by axisymmetric nanostructures with electrically conductive walls. Using our theoretical model, we analyzed the light energy transmission by biopolymers forming optical channels within retinal Müller cells. There are specialized intermediate filaments (IF) 10 – 18 nm in diameter, built of electrically conductive polypeptides. Presently, we analyzed the spectral selectivity of these nanostructures. We found that their transmission spectrum depends on their diameter and wall thickness. We also considered the classical approach, comparing the results with those predicted by the quantum mechanism. We performed experimental measurements on model quantum waveguides, made of rectangular nanometer-thick chromium (Cr) tracks. The optical spectrum of such waveguides varied with their thickness. We compared the experimental absorption/transmission spectra with those predicted by our model, with good agreement between the two. We report that the observed spectra may be explained by the same mechanisms as operating in metal nanolayers. Both the models and the experiment show that Cr nanotracks have high light transmission efficiency in a narrow spectral range, with the spectral maximum dependent on the layer thickness. Therefore, a set of intermediate filaments with different geometries may provide light transmission over the entire visible spectrum with a very high (∼90%) efficiency. Thus, we believe that high contrast and visual resolution in daylight are provided by the quantum mechanism of energy transfer in the form of excitons, whereas the ultimate retinal sensitivity of the night vision is provided by the classical mechanism of photons transmitted by the Müller cell light-guides.

Our paper tackles the novel issues of the economic impacts and innovations in tourism marketing in the 21st century. The paper examines the economic impact of tourism and its influence on the economy and the tourism industry in general from the angle of innovations in the tourism marketing and the new challenges for the tourism industry brought about by the COVID-19 pandemic that disrupted international tourism and caused major economic losses to the industry. We analyse the changes that the coronavirus pandemic made to the tourism industry and focus on the novel trends in tourism marketing that embeds the new informational technologies such as virtual reality (VR), augmented reality (AR), online Zoom tours, and other novelties that emerged after the lockdowns and social distancing imposed in the first half of 2020 in order to prevent the spread of the coronavirus infection. Our results show that tourism marketing in the 21st century should be based on sustainable management and provide the right answers to questions about the impacts of tourism on the economy without sacrificing positive economic growth. We also show that information technologies might offer viable alternatives to massive international over-tourism and package tours ensuring both the safety of travel and deeper immersion into the travel experience before, during, and after the trip. Our outcomes might be useful for tourism scholars, policymakers, as well as stakeholders specializing in international tourism marketing.

Birds which possess high visual acuity, such as eagles and falcons, are known to have retinas with a deep conically curved central foveal pit. There have been different attempts to explain the importance of this particular shape of the fovea in visual resolution. Recently, the function of Müller cells as “light fibers” was discovered, showing how the endfeet of Müller cells trap the light and then transfer it to a single cone photoreceptor. Here we describe how the endfeet of Müller cells line the walls of the foveal pit in the Pied Flycatcher, and how the Müller cell body extends its processes towards individual cones, forming machinery that could allow for light transfer from the pit wall to the photoreceptor layer alongside the pit. We describe how this construction may send an image from the fovea to the cones, and also, how the angular positioning of Müller cells, being optical extensions of the cones, has the advantage of being much denser than on a flat or slightly curved fovea. We, therefore, suggest that this type of optic fiber alignment can be used as a novel type of “amplifying array” that simply increases the amount of megapixels at the photoreceptor cell layer.

This paper focuses on the consumer preferences for the so-called “smart homes” (also known as “smart houses”) which represent a novel addition and a product of the on-going digitalization and the deployment of the Internet of Things (IoT). The major scientific contribution of our study is the empirical model build on the data from the online questionnaire conducted with randomly selected respondents (N = 523) from four European Union (EU) countries and Russia. Even though our results are subject to limitations (no Southern of Northern European countries are included in the scope of this research, which might have yielded different results due to the differences in wealth of citizens and climate in comparison to the Central and Eastern European countries or Germany), they demonstrate that the users included in our sample generally feel inclined to the smart homes technologies and perceive them as a plausible means for improving the safety and security of their lives. On the other hand, some respondents from our sample expressed their concerns over the cybersecurity and technology dependence issues associated with smart homes. It is also apparent that younger respondents (aged 16–35) featured in our research are more worried about their personal data being monitored and analyzed (with a pending threat of leakages). All these results are original and constitute an important scientific value-added to the field of research in smart home technologies and their acceptance by the general public. We demonstrate that the further enhancement of smart homes, and the increase of their popularity and affordability among the customers both in the Central and Eastern European countries and beyond, might depend on the development of the smart grids which these smart homes are an integral part of. The reliability of the smart systems constitutes the key element for achieving the satisfaction of the smart homes residents, and hence needs to be achieved and secured in an effective way. This would ensure the right mix and balance of energy security and efficiency for all customers involved in this process.

Our paper deals with the specifi c aspects of immigration and the eff ects that the integration of immigrant groups may have in the national income. Th rough an appropriate analysis, this research attempts to provide a description of the immigration phenomenon in the EU, the consequences of it in the labor markets and the relation with the distinct integration policies implemented by the EU countries. Since the European Union enables free mobility among its Member States, certain EU countries have become attractive destinations because of the working conditions and/or employment opportunities. As a result, some EU nations have experienced the infl ow of large amount of immigrants and disturbances on their labor markets. With regard to the above, the concept of immigration surplus stipulating that immigration phenomenon might trigger off a process of redistribution of wealth that could in turn enhance the volume of production and increase the national income can be applied for analyzing these processes. In addition, we fi nd that deeper integration of immigrants into host countries can lead to higher levels of economic success. Th erefore, we conclude that the high level of integration may lead to an increase in the immigration surplus of the host countries.

We consider the distribution of the intermediate filaments (IFs) in the retinal cells of the Pied flycatcher (Ficedula hypoleuca, Passeriformes, Aves) in the foveolar zone, which has the most specialized morphology, where the passerines have neither the rods nor the second-order neurons that service these rods, with only the single and double cones acting as photoreceptors. We report that single IFs span Müller cells (MC) lengthwise, while long cylindrical bundles of IFs (IFBs)