Browsing by Author "Hristova S."

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    CHALLENGES TO THE ORGANIZATION OF WORKPLACES IN THE INDUSTRIAL ENTERPRISE
    (2024-01-01) Hristova S.
    In recent years modern business has faced several challenges. From 2020 until now, Bulgaria and the world have faced a number of challenges, starting with the Covid crisis, economic and political crises. They inevitably affect the work of each business and in a particular burden of production. The purpose of the report is to examine the process of organization of workplaces in enterprises, to highlight the challenges in it and to indicate ways to deal with them.
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    Chercher de l'eau: The switching mechanism of the rotary switch ethyl-2-(2-(quinolin-8-yl)hydrazono)-2-(pyridin-2-yl)acetate
    (2020-05-01) Deneva V.; Vassilev N.; Hristova S.; Yordanov D.; Hayashi Y.; Kawauchi S.; Fennel F.; Völzer T.; Lochbrunner S.; Antonov L.
    The E/Z switching mechanism of the rotary switch ethyl-2-(2-(quinolin-8-yl)hydrazono)-2-(pyridin-2-yl)acetate was studied by NMR, UV–Vis, and ultrafast spectroscopy and modeled by advanced quantum-chemical calculations. Three possible mechanisms were considered theoretically: out-of-plane rotation, in-plane inversion and proton transfer. Neither of them correctly describes the experimental data by using implicit solvation. Taking into account the existence of water in the used solvents, which influence the measured rate constants, an explicit solvation was attempted in the quantum-chemical calculations. According to a simplified model, the water molecules form a wire, being able to transfer the proton from Z to E form of the switch. This leads to substantially lower transition states and corresponds to the experimentally observed rate constants. This information shines new light on the mechanism of isomerization in the rotary switches and on the understanding of the mechanism of hydrazone tautomerism as a whole.
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    Monotone-iterative method for solving antiperiodic nonlinear boundary value problems for generalized delay difference equations with maxima
    (2013-09-23) Golev A.; Hristova S.; Nenov S.
    A nonlinear generalized difference equation with both delays and the maximum value of the unknown function over a discrete past time interval are studied. A nonlinear boundary value problem of antiperiodic type for the given difference equation is set up. One of the main characteristics of the considered difference equation is the presence of the unknown function in both sides of the equation. It leads to impossibility for using the step method for explicit solving of the nonlinear difference equation. In this paper, an approximate method, namely, the monotone iterative technique, is applied to solve the problem. An important feature of the given algorithm is that each successive approximation of the unknown solution is equal to the unique solution of an appropriately constructed initial value problem for a linear difference equation with ``maxima,`` and an algorithm for its explicit solving is given. Also, each approximation is a lower/upper solution of the given nonlinear boundary value problem. The suggested scheme for approximate solving is computer realized, and it is applied to a particular example, which is a generalization of a model in population dynamics. © 2013 Angel Golev et al.
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    Stability on a cone in terms of two measures for differential equations with “maxima”
    (2010-01-01) Dishliev A.; Hristova S.
    Stability in terms of two measures for nonlinear differential equations with “maxima” is studied. A special type of stability in terms of two measures is defined. The new type of stability generalizes some of the known in the literature. Sufficient conditions for the defined stability are obtained. Cone-valued continuous Lyapunov functions are applied. Method of Razumikhin as well as comparison method for scalar ordinary differential equations have been employed. The usefulness of the introduced definition and the obtained sufficient conditions is illustrated through an example. © 2010, Duke University Press. All rights reserved.
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    Stability on a cone in terms of two measures for differential equations with “maxima”
    (2010-01-01) Dishliev A.; Hristova S.
    Stability in terms of two measures for nonlinear differential equations with “maxima” is studied. A special type of stability in terms of two measures is defined. The new type of stability generalizes some of the known in the literature. Sufficient conditions for the defined stability are obtained. Cone-valued continuous Lyapunov functions are applied. Method of Razumikhin as well as comparison method for scalar ordinary differential equations have been employed. The usefulness of the introduced definition and the obtained sufficient conditions is illustrated through an example. © 2010, Duke University Press. All rights reserved.
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    THE COMPANY CULTURE IMPACT ON STAFF TURNOVER IN THE MANUFACTURING INDUSTRY IN BULGARIA
    (2021-01-01) Hristova S.
    This article is devoted to the process of staff turnover in general and in the manufacturing industry (including metallurgy and chemical industry in particular). Statistics for the last years for this process in Bulgaria are presented and the current trends are taken into account. Different authors' views on the most important aspects of the staff turnover process are considered. Approaches are expressed, how with the help of the company culture, the process can be managed.