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Technology is transforming how we interact with the world around us. We rely more and more on mobile applications to plan our daily routines. Mobile applications are used for many areas of our life and how we travel is one of them. This article provides an overview of the development process and main architectural decisions of one such application which main purpose is to showcase the cultural and historical heritage of Bulgaria. [ABSTRACT FROM AUTHOR]

Liver transplantation is treatment of choice for patients with end stage liver disease (ESLD). However, due to high surgical risk and risk of complications from the immunosuppressive agents pose significant challenges in transplanting setting. The aim of our study was to evaluate survival after liver transplantation. In this paper survival analysis is used to determine the prognostic significance of age of the recipient at the time of transplantation, sex, Model for End-Stage Liver Disease (MELD) score, complications after transplantation and treatment of complications, and to model the time it takes for death. The data is obtained from 41 patients, who have been transplanted at the University Hospital "Lozenetz", Sofia, Bulgaria in the period 2006-2019. For estimating event (death) free survival rate the Kaplan–Meier method is used. Time to event is calculated as the time from study entry to first event or date of last contact. Multivariate analysis is conducted by using Cox proportional hazards regression. [ABSTRACT FROM AUTHOR]

This paper presents an interactive web based system with geolocation for the cultural and historic heritage in Bulgaria. The system uses a three-tier architecture with a presentation layer executed in a browser and the application is accessible over the Internet and allows the users to find cultural and historical content using three search strategies: by category, by keywords and by spatial search over an interactive map. We perform a case study on a real-world dataset from original research and provide some guidelines for future authors of such datasets. [ABSTRACT FROM AUTHOR]

In 2018 Bulgaria was the number 74 economy in the world in terms of GDP (constant 2011 international USD), the number 63 in total exports, the number 60 in total imports, and the number 47 most complex economy according to the Economic Complexity Index (ECI). Given the importance of imports for Bulgaria's economic development, and the ensuing implications, the central aim of this paper is to examine the dependence of imports on consumption, investment and exports in Bulgaria, using time series data for the period 2004-2018. This study examines the dependence of Bulgarian imports, using vector error correction model (VECM) and to examined the causal relationships among the four factors on the obtained model. The results indicated that, no matter in the short term or long term, consumption and export fluctuation is the reason why import change, while the investment fluctuation is not the reason for the growth of import. The consumption and export impact will produce great influence on import in the short term, but, in the long term, the influence will tend to be gentle. [ABSTRACT FROM AUTHOR]

Since the end of 2019, with the outbreak of the new virus COVID-19, the world changed entirely in many aspects, with the pandemia affecting the economies, healthcare systems and the global socium. As a result from this pandemic, scientists from many countries across the globe united in their efforts to study the virsus's behavior and are attempting to predict mathematically its infection model in order to limit its impact and developing new methods and models to achieve this goal. In this paper we explore a time-depended SEIR model, in which the dynamics of the infection in four groups from a selected target group (population), divided according to the infection, are modeled by a system of nonlinear ordinary differential equations. Several basic parameters are involved in the model: coefficients of infection rate, incubation rate, recovery rate. The coefficients are adaptable to each specific infection, for each individual country, and depend on the measures to limit the spread of the infection and the effectiveness of the methods of treatment of the infected people in the respective country. If such coefficients are known, solving the nonlinear system is possible to be able to make some hypotheses for the development of the epidemic. This is the reason for using Bulgarian COVID-19 data to first of all, solve the so-called "inverse problem" and to find the parameters of the current situation. Reverse logic is initially used to determine the parameters of the model as a function of time, followed by computer solution of the problem. Namely, this means predicting the future behavior of these parameters, and finding (and as a consequence applying mass-scale measures, e.g., distancing, disinfection, limitation of public events), a suitable scenario for the change in the proportion of the numbers of the four studied groups in the future. In fact, based on these results we model the COVID-19 transmission dynamics in Bulgaria and make a two-week forecast for the numbers of new cases per day, active cases and recovered individuals. Such model, as we show, has been successful for prediction analysis in the Bulgarian situation. We also provide multiple examples of numerical experiments with visualization of the results. [ABSTRACT FROM AUTHOR]

The paper presents and analyzes teachers' views and attitudes on their participation in continuous professional development (CPD) training courses and their usefulness for the improvement of digital knowledge and skills which are part of teacher digital competence – so much necessary for meeting the educational challenges of the 21st century. The findings discussed in this paper were obtained within a national research project carried out with the support of the Ministry of Education and Science at the end of 2019. The analysis of some of the research findings shows a relatively contradictory picture in terms of the relation between continuous professional development of teachers and the development of teachers' digital competences. On the one hand, a positive tendency is observed related to a very active participation in CPD training of Bulgarian teachers in the field of ICT implementation in the educational context for the past 5 years. On the other hand, the educators themselves give positive but not very high evaluations of the degree to which they have developed basic aspects of their digital competence as a result of the training courses. The way the Bulgarian students evaluate different aspects of their own digital competence developed as a result of the learning experience at school is also not markedly positive. The comparison between the teachers' self-evaluations of their discrete digital competences and the self-evaluations of students regarding their skills for using ICT acquired in the learning process is an adequate research approach through which an authentic idea could be construed about the efficiency of the CPD trainings of educational specialists in the field of digital and technological competence as well as about the existing challenges in this respect in Bulgaria. [ABSTRACT FROM AUTHOR]

This study examines the student teachers' satisfaction with e-learning science courses "Ecological education" and "Didactics of natural sciences in primary school" in a public university in Bulgaria. Richard R. Aman's satisfaction questionnaire was used to obtain data, regarding quality factors of satisfaction. These factors were integrated in the Quality concept for development of student teachers' satisfaction, based on building of their professional competencies. The results of analysis reveal that professional-competent student teachers feel satisfy with science courses, because they are successful. However, some of students would feel more satisfied, if they could get additional technological help and support. [ABSTRACT FROM AUTHOR]

The existence of infinitely many weak solutions for the fourth-order differential equation (φ p ( u ″ (t) )) ″ ​ ′ + w (φ p ( u ′ (t) )) ′ + a (t) φ p (u (t)) + b (t) φ q (u (t)) − c (t) φ r (u (t)) = 0 , for t ∈ [0, T] is studied. Here φ p (t) = | t | p − 2 t , 1 < p < q < r , w is a constant, and a, b, c are positive continuous functions on the interval [0, T]. The equation is considered with Dirichlet boundary conditions u (0) = u (T) = u ′ (0) = u ′ (T) = 0. An existence result is proved using the variational method and the symmetric mountain-pass theorem. Some earlier results of [L. Saavedra & S. Tersian, Nonlinear Analysis: Real World Applications 34, (2017), 507–519] and [S. Tersian, Proceedings of 48th Spring Conference of the Union of Mathematicians in Bulgaria, 2019, 27–34] are extended. [ABSTRACT FROM AUTHOR]