Table of Contents


    • Complexation of metal cations (mono-, di- and trivalent) to cucurbiturils: Insights from a DFT/SMD study

      pg(s) 3-6

      Recently, supramolecular complexes based on synthetic macrocyclic host molecules have received much attention due to their broad applications as drug delivery carriers, biological and chemical sensors, light-emitting materials, bioimaging agents, etc. Cucurbit[n]urils are cavitands known for their high affinity for various guest molecules, although some aspects of their coordination chemistry remain enigmatic. They are still not tested as metalloenzyme models and not much is known about their metal-binding properties. Furthermore, there is no systematic study on the key factors controlling the processes of metal coordination to these systems. In the
      computational study herein, DFT molecular modeling has been employed in order to investigate the interactions of biologically essential mono- (Na+), di- (Mg2+) and some trivalent (La3+, Lu3+) metal cations to cucurbit[n]urils and evaluate the major determinants shaping the process of recognition. The thermodynamic descriptors (Gibbs energies in the gas phase and in a water medium) of the corresponding complexation reactions have been estimated. The results obtained shed light on the mechanism of host–guest recognition and disclose which factors more specifically affect the metal binding process.

    • Terahertz emission induced by self-oscillations of current in semiconductor resonant tunneling structures

      pg(s) 7-9

      Based on the simultaneous measurements of radio-frequency intrinsic self-oscillations of current and terahertz (THz) light emission from a 30-period GaAs/AlGaAs weakly-coupled superlattice, it was concluded that self-oscillations of current arise due to the cyclic process of the electric-field domain boundary spatial expansion and shrinkage. The domain boundary expands over several SL periods due to the energy dissipation of tunneling electrons, resulting in the carrier trapping in several SL periods behind the leading edge of the domain boundary. In this region, the charge accumulation gives rise to the resonant detuning of subbands in adjacent quantum wells (QWs), creating the population inversion between the two subbands, which ensure the resonant tunneling along the SL axis. The electrons injected from the cathode restore the resonant coupling of subbands, the lower subband is emptied, and the intersubband radiative transitions allowed. The electroluminescence (EL) spectra of the SL demonstrate the main peak with the left and the right sidebands. The main peak is related to the intersubband electron transition energy, while the sidebands are associated with the resonant detuning energy of subbands in adjacent QWs (~ 4 meV). The two-photon pulsed THz emission (~ 4 meV) from a double-barrier GaAs/AlAs resonant tunneling diode biased into self-oscillation regime confirms the last assertion. There is the same cyclic mechanism of relaxation self-oscillations of current (accumulation and drain type), where the first THz pulse is triggered due to the carrier trapping by miniband states, resulting in the miniband energy shift up to higher energies. After the trap release time, the electrons lost their energy via the second THz pulse emission, and the miniband gets back to its steady state.


    • Traditional Tea Uses of Wild and Cultivated Plants in Albania and Kosovo, an Ethnobotanical Review

      pg(s) 10-19

      Folk uses of wild plants for tea making are particular strongly linked to specific biodiversity and cultural knowledge. As part of Mediterranean climate, Albania and Kosovo have a reach plant diversity. This literature review, based on ethnobotanical studies in both countries, gather wild and cultivated plant species used in the form of the herbal infusions, with an attempt to document diversity of plant species and information for making herbal tea. Results obtained showed that plants listed in this study represented by around 150 taxa, grouped in 53 families. The Lamiaceae with 25 species, Asteraceae with 20 and Rosaceae with 17 species were the most represented botanical families. In Albania are used 128 plant species, while on Kosovo 75 species. Of these, around 53 plant species used in both countries, 75 species have usage only in Albania and 22 only in Kosovo. A large portion of the wild plant reports to be used as tea making in both countries. The most used plants in both countries are Origanum vulgare L., Matricaria chamomilla L., Melissa officinalis L., Achillea millefolium L., Rosa canina L. etc.

    • The methodology of management of the tourist transport infrastructure developmentand its use in the tourism system

      pg(s) 20-23

      Today, as tourism is recognized as one of the priority sectors of the economy of Georgia and contributes to the socioeconomic development of the country, it is especially important to tudy the existing tourist transport infrastructure and introduce new innovative technologies in its management. As a result of the conducted research, we can conclude that the existing scientific-methodical and practical approaches in the field of tourism and transport cannot be considered effective enough to ensure the development of tourist transport infrastructure. An algorithm was developed for the development of tourist transport infrastructure. The mentioned method can be recommended in the field of tourism, for the development of tourist transport infrastructure.


    • Ten facts about American policy towards the Israeli-Palestinian conflict under President Joe Biden

      pg(s) 24-27

      The Israeli-Palestinian conflict (originally Israeli-Arab conflict) has been of interest to the current and former American presidents. The long-agreed U.S. policy regarding finding a solution to the conflict – the two-state solution, through a series of decisions, has been undermined by Donald Trump. Joe Biden, the current American president, has reversed, frozen, and continued some of Trump’s decisions to establish a new Israeli-Palestinian conflict environment aimed at restarting negotiations between the conflicted parties. A comparative analysis of Trump’s and Biden’s approach towards the conflict strengthened by the analysis of a formal White House document allows for the presentation of the current administration’s policy towards the conflict and the actors of the conflict. In this paper I have presented an analysis of ten vital aspects of Biden’s policy towards the Israeli-Palestinian conflict during his first term in office.

    • Institutional Risks in Bulgarian Political Life: 2020-2022

      pg(s) 28-30

      The text is focused on the crises in contemporary Bulgarian political life in the last two years and the institutional risks they hide. Special attention is paid to the distrust of the public in parliamentary democracy and the unwillingness of political parties to take responsibility in crisis situations. The role of President Rumen Radev and the importance of the presidential institution in the regime of caretaker governments are highlighted.

    • Integration of multi-vector training of university students on the basis of short-term educational programs built in the scientific process – minors

      pg(s) 31-32

      The experience of increasing the competitiveness of university graduates, including contributing to the solution of the state task of creating new jobs, is considered. The task is solved by introducing the minor into the educational process aimed at developing the entrepreneurship competencies of students. The minor is based on the disciplines of the initial courses of the curricula of technical specialties and fits well into the educational process.

    • Development of automation in Bulgaria in the 20th century

      pg(s) 33-35

      In the 8th decade of the 20th century, a state program was implemented to automate the entire production in the spirit of scientific and technical progress. More than 160 types of systems for the automation of technological processes have been developed, including individual high-performance machines, industrial robots and manipulators, managed with the most advanced microprocessor technology for its time, subsequently implemented in pilot complex automated workshops and production areas in various economic sites of the country. Prioritizing the production of means of automation of technological processes intensifies machine-building, intellectualizes labor and increases its productivity. Gradually, with our forces and means, experience and a base for further design and implementation of flexible automated production systems in all branches of industry are created. The achieved technical and organizational experience guarantees the membership of Bulgaria in the Permanent Commission on Mechanical Engineering at the SIV and its coordinating role in agreements for multilateral specialization and scientific and technical cooperation in the field of industrial manipulators and robots.