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Changing business models is a topical issue in a pandemic. Recent research has shown that the search for environmentally friendly and sustainable solutions in various sectors has become relevant. The article aims to promote cooperation and adaptation of good practices between countries. Comparing the country’s history and economic situation and economic development and traditions can be seen as a precondition for success. The article examines the introduction of sharing economy and the creation of environment-friendly trends establishing a circular economy by minimizing the population’s expenses, online business growth, and accessibility of Internet technologies. The article explores the difference between the linear economic model and the circular model by adopting sharing and the efficient joint use of materials to enhance and assess sustainable development. Based on a combination of theoretical and practical research, the article explores the dynamic system and development model of sharing a circular economy. The new concept of circular economy does not promote the overproduction of new goods but the rational use of already produced ones, which significantly reduces the amount of waste generated at all stages of the product life cycle. Population groups by different income groups for sharing services are analysed. An analysis of the price characteristics of popular sharing products was used from data from Internet portals. One concludes that due to the increase in Internet users, especially mobile apps, and social networks, C2C sharing has become quite popular over the past years. Other areas also show positive development indicators but have less demand, affecting supply. Based on an in-depth study of the economic situation in Ukraine, the authors have critically chosen an industry to set as an example with the actual business situation. Therefore, three packages were created: pessimistic, standard and optimistic ones with different characteristics of implementing circular economic projects. The chosen method allows rational management decisions for attracting financing and sustainable solutions. The company’s business scenarios analysed in the article will allow to choose a system based on circular economy principles successfully.

The present investigation concerns the potentiality of Rhodopseudomonas sp. cells to produce clean energy such as molecular hydrogen (H2). The abovementioned goal could be reached by improving the capability of purple non-sulfur bacteria to produce H2 via a photofermentative process through the enzyme nitrogenase. Rhodopseudomonas sp. cells were immobilized in calcium alginate gel beads and cultured in a cylindrical photobioreactor at a working volume of 0.22 L. The semi-continuous process, which lasted for 11 days, was interspersed with the washing of the beads with the aim of increasing the H2 production rate. The maximum H2 production rate reached 5.25 ± 0.93 mL/h with a total output of 505 mL. The productivity was 40.9 μL (of H2)/mg (of cells)/h or 10.2 mL (of H2)/L (of culture)/h with a light conversion efficiency of 1.20%.

The present paper describes the experimental campaign executed at the ENEA Brasimone Research Centre aiming at supporting the development of a PbLi/water heat exchanger suitable for the lithium–lead loops of the dual coolant lithium lead and the water cooled lithium lead breeding blankets of the EU DEMO fusion reactor. The experiments were performed in a test section named HERO, installed inside the main vessel of the lead–bismuth eutectic-cooled pool-type facility CIRCE. The test section hosts a steam generator bayonet tube mock-up in relevant scale, which was selected as a promising configuration for DEMO purposes. For the thermal-hydraulic characterization of the component, five tests were executed at different water pressures (6, 8, 12 MPa, two tests at 10 MPa), and liquid metal flow rates (40, 33, 27, 20, 10 kg/s). The experimental outcomes proved the technological feasibility of this novel steam generator and its suitability for the DEMO PbLi loops. The activity was completed with a post-test analysis using two versions of the system code RELAP5. Because the experiments were executed with lead–bismuth eutectic, a scaling analysis is proposed to find the equivalence with PbLi. RELAP5 code was applied to recalculate the experimental data using PbLi as working fluid.

The braking system of a racing car is one of the main design challenges. The flow around and inside the wheel of an F1 car with all braking system components is analyzed in order to evaluate the heat transfer after a braking event. Very few studies have been published on this topic, mainly due to the high confidentiality level in the racing car sector. In the present work, using an actual geometry of an early 2000s F1 car, the braking system is simulated using a CFD approach. The boundary conditions for the wheel and brake system are taken from the simulation of a vehicle model with a front wing. Different heat transfer phenomena are progressively added to the model in order to understand their effects, including thermal convection only, radiation and conjugate heat transfer. Two different vehicle velocities are simulated to quantify and compare the heat removal after a braking event. The different heat transfer mechanisms have dramatic effects on the prediction of the brake cooling results, and these are quantified in order to understand the limitations of the simplified approaches. Finally, the influence of the ambient pressure at two different altitudes on the heat transfer from a braking event is studied.

Today, as a result of the advancement of technology and increasing environmental problems, the need for clean energy has considerably increased. In this regard, hydrogen, which is a clean and sustainable energy carrier with high energy density, is among the well-regarded and effective means to deliver and store energy, and can also be used for environmental remediation purposes. Renewable hydrogen energy carriers can successfully substitute fossil fuels and decrease carbon dioxide (CO2) emissions and reduce the rate of global warming. Hydrogen generation from sustainable solar energy and water sources is an environmentally friendly resolution for growing global energy demands. Among various solar hydrogen production routes, semiconductor-based photocatalysis seems a promising scheme that is mainly performed using two kinds of homogeneous and heterogeneous methods, of which the latter is more advantageous. During semiconductor-based heterogeneous photocatalysis, a solid material is stimulated by exposure to light and generates an electron–hole pair that subsequently takes part in redox reactions leading to hydrogen production. This review paper tries to thoroughly introduce and discuss various semiconductor-based photocatalysis processes for environmental remediation with a specific focus on heterojunction semiconductors with the hope that it will pave the way for new designs with higher performance to protect the environment.

In the era of limited resources and progressive environmental degradation, the circular economy is a practical application of sustainable development. It is an alternative, but also competitive way to achieve economic growth in accordance with the principles of sustainable development. This issue was considered in this paper in the context of the Ukrainian economy. The Ukrainian economy’s transformation into a circular one needs to find ways to choose practical tools for such a transition, considering the destructive impact of economic activities on the environment, population, and economy. The goal was to develop a method of choosing tools for the circular transformations of economic activities for each cluster and to reduce man-made damage to the environment. Cluster analysis, fuzzy C-means method, and grouping of economic activities were used. Two analyzed sectors turned out to be the most interesting: mining and quarrying, and electricity, gas, steam, and air conditioning supply, which were finally assigned to the cluster with a high level of destructive impact, defined as ‘environmentally unfriendly’. The proposed method allows the choice of circular transformation tools for economic activities depending on the destructive impact of these economic activities within each cluster.

This paper aims to study the limitations and performances of the main energy storage devices commonly used in energy harvesting applications, namely super-capacitors (SC) and lithium polymer (LiPo) batteries. The self-discharge phenomenon is the main limitation to the employment of SCs to store energy for a long time, thus reducing efficiency and autonomy of the energy harvesting system. Therefore, the analysis of self-discharge trends was carried out for three different models of commercial SCs, describing the phenomenon in terms of self-discharge rate and internal resistance. In addition, physical interpretations concerning the self-discharge mechanism based on the experimental data are provided, thus explaining the two super-imposed phenomena featured by distinct time constants. Afterwards, the dependence of self-discharge phenomenon from the charging time duration (namely, SCs charged at 5 V and then kept under charge for one or five hours) was analyzed; by comparing the voltage drop during the self-discharge process, a self-discharge reduction for longer charging durations was obtained and the physical interpretation provided (at best −6.8% after 24 h and −13.4% after 120 h). Finally, self-discharge trends of two commercial 380 mAh LiPo batteries (model LW 752035) were acquired and analyzed; the obtained results show an open circuit voltage reduction of only 0.59% in the first 24 h and just 1.43% after 124 h.

Small scale urban green-blue infrastructure (indicated as GBI hereafter) comprises huge underexploited areas for urban development and planning. This review article aims to highlight the relevance and knowledge gaps regarding GBI from the perspective of the food–energy–water (FEW) nexus, these being key resources for the survival of human communities. In particular, this review was focused on publications on urban ecosystem services (positive effects) and dis-services (negative effects) associated with different GBI typologies. The review proved that GBI can contribute environmentally, socially, and economically to FEW security and urban sustainability. Yet, such positive effects must be considered against ecosystem dis-services tradeoffs, including urban food production, commonly connected with heavy water and energy consumption, specifically under dry climate conditions, and sometimes related to an excessive use of manure, pesticides, or fertilizers. These conditions could pose either a risk to water quality and local insect survival or serve enhanced mosquito breeding because of irrigation. Up to now, the review evidenced that few nexus modeling techniques have been discussed in terms of their benefits, drawbacks, and applications. Guidance is provided on the choice of an adequate modeling approach. Water, energy, and food are intrinsically associated physically. However, depending on their management, their tradeoffs are often increased. There is a need to minimize these tradeoffs and to build up synergies between food, energy, and water using a holistic approach. This is why the FEW nexus approach offers good insights to address the relation between three important individual resource components of sustainability.