bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of transformers for power electronic converters
Authors: Milanov K G 
Published: July 2020

Abstract
A transformer is an integral part of power electronic equipment and it is usually the input stage of a high power converter. A good model of the transformer is needed to evaluate the performance parameters of power converters. This work represent 2 new methods for short-circuit test of single-phase transformers. The paper offers measurement methods that do not require powerful adjustable AC sources. Short circuit parameters can be determined by measuring the parameters of the transient when switching on: i) capacitor under zero initial conditions to an idle transformer or ii) by a transient process when connected to a non-powered short-circuit transformer of a capacitor under non-zero initial conditions. In order to accurately determine the period and the transition process in the event of a short circuit, it is suggested to include a parallel connected battery. PSpice is being used as a simulation tool for analysis and design of power electric circuits.
The value of the work done by an isotropic vector force field along an isotropic curve
Authors: Razpopov Dimitar , Dzhelepov Georgi 
Published: July 2020

Abstract
In the present paper we consider a 3-dimensional differentiable manifold M equipped with a Riemannian metric g and an endomorphism Q, whose third power is the identity and Q acts as an isometry on g. Both structures g and Q determine an associated metric f on (M,g,Q). The metric f is necessary indefinite and it defines isotropic vectors in the tangent space TpM at an arbitrary point p on M.
The physical forces are represented by vector fields. We investigate physical forces whose vectors are in TpM on (M,g,Q). Moreover, these vectors are isotropic and they act along isotropic curves. We study the physical work done by such forces.
Study on threshold capabilities of a copper bromide vapor laser
Authors: Fidanov D V 
Published: July 2020

Abstract
This paper presents theoretical and simulation results for the operating parameters of a copper bromide (CBr) laser. The CuBr active medium finds applications as both as a laser source and a vapor amplifier. A methodology is developed to serve as the basis for the solution of a two-dimensional quasi-stationary heat conductivity equation on the cross-section of the gas tube for modeling the temperature of the neutral gas and the electron temperature of the discharge. This methodology makes it possible to determine the maximum electrical power supplied and the maximum electron temperature in terms of thermal ionization and electric ionization resistance of the gas discharge. Analytical results are applied in computer simulations and for the assessment of parameters of an actual CuBr laser.
Modelling and estimate of the LTWM noise parameters
Authors: Prlinčević Bojan , Milivojević Zoran 
Published: July 2020

Abstract
In the first part of this paper, a statistical analysis of the noise in the image, as a result of the insertion of the watermark by Liu and Tan algorithm, was performed. After that, using the base of test image the noise model was created. Based on the model, an algorithm for estimating the statistical parameters of noise, LTWM algorithm, (μ and σ
2) in the image with a watermark, was created. In the second part of this paper there is a description of the experiment in which a comparative analysis of the accuracy of estimating statistical parameters by the proposed LTWM algorithm and Algorithms from [3], [6] - [8], was performed. Algorithms have been applied on watermarked images from the NRCS base. The results of MAE and MSE between true and estimated variance are shown in tables and diagrams. In addition, the execution time of the tested algorithms was measured. A detailed comparative analysis has shown that the proposed LTWM algorithm was more precise, and has a shorter execution time, compared to the analysed algorithms.
Intelligent virtual agent, learning how to reach a goal by making the least number of compromises
Authors: Budakova Dilyana , Petrova-Dimitrova Veselka , Dakovski Lyudmil 
Published: July 2020

Abstract
The learning process in the Q-learning algorithm is characterized by maximizing a single, numerical reward signal. However, there are tasks for which the requirements toward the way to reach a goal are complex. This paper proposes a modification to the Q-learning algorithm. In order to make the Q-learning agent find the optimal path to the goal by meeting particular complex criteria, the use of measures model (a model of environment criteria), represented as a new memory matrix, is introduced. If the goal cannot be reached by following the pre-set criteria, the learning agent can compromise a given criterion. The agent makes the least possible number of tradeoffs in order to reach the goal. If the criteria are arranged by their level of importance, then the agent can choose more in number and more acceptable compromises. The aim of the modification is to empower the learning agent to control the way of reaching a goal. The modified algorithm has been applied to training smart shopping-cart learning agents. The tests show improvement in their behaviour.
Testing of games through software agents managed by artificial neural networks
Authors: Trankov Miroslav , Hadzhikolev Emil , Hadzhikoleva Stanka 
Published: July 2020

Abstract
With the development of artificial neural networks, their use in different fields is increasing to optimize different activities. The availability of rich programming languages, various existing machine learning software libraries, along with the virtualization technologies has made intelligent technologies accessible not only to large corporations but also to individual programmers.
Game development is a complex process involving many specialists, experts in various fields. Single-game testing is an iterative process that covers different game development opportunities, different player abilities, as well as player interaction when working in a team. The question is, is it possible to use intelligent software agents in the game testing process in order to optimize the human, time and financial resources needed?
This article introduces our attempt to create an intelligent autonomous agent that plays the Brawl Stars game, managed by an artificial neural network. Initially, the agent is trained by collecting frames from a game that is being played by an experienced player. The frames are then processed and analyzed, and a neural network is trained, which directs the agent to conduct an autonomous game. The developed agent was used in two experiments that confirmed the great potential for the use of artificial neural networks in game testing.
Design of an automated railway crossing system with Verilog language in CPLD
Authors: Zhilevski M , Hristov V 
Published: July 2020

Abstract
In this paper the basic requirements for the automatic railways crossing devices are formulated. A block diagram, which consists of elements that make the automatic railways crossing systems are presented and their working principles are discussed. Based on the hardware description language - Verilog, a digital railway crossing control system is designed and is implemented with complex programmable logic device, taking into account the requirements. As an opportunity for practical application the controller CoolRunner II could be used. Simulation results with set input parameters are shown to represent the functionality of the designed system. The results obtained can be used for design, implementation, simulation and development of such types of systems in railway crossing automatics.
Logistics 4.0 and supply chain 4.0 in the automotive industry
Authors: Markov Krasimir , Vitliemov Pavel 
Published: July 2020

Abstract
The Industry 4.0 technologies give real benefits to the plants where they are implemented such as performance improvement, costs and delays reductions. The automotive plants are among the factories that could implement most of these technologies. Industry 4.0 can affect all of the processes which happen in the automotive industry manufacturing plants – engineering, production, logistics, management, etc. Analysis of all of the processes in one article is too complex task and due to this the paper is focused only on logistics and supply chain. The aim of this article is to investigate the potential possibilities for implementation of Logistics 4.0 and Supply Chain 4.0 in the automotive industry plants, in particular in Bulgaria. Specially designed survey was used as investigation method. It consists of two groups with proposals and assumptions. The survey was conducted by 12 automotive industry logistics experts who are on 6 different logistics positions. The results show that the production visibility (assembly lines connected to internet) and blockchain technologies have the biggest values to the logistics and supply chain. But the cybersecurity and faulty data are the main challenges in front of them.
Bead formation research in TIG welding of AISI 304 steel
Authors: Tongov Manahil , Dimitrova Rayna , Konstantinov Konstantin 
Published: July 2020

Abstract
On the basis of the experimental results in depositing strips of molten metal onto AISI 304 steel using the D-optimal plan of the experiment and processing of the got results, regression equations were obtained describing the dependence of the bead width and the penetration depth depending on the welding speed and the value of the welding current. In parallel, a regression equation is obtained connecting the arc voltage and the welding current.
Comparative analysis of sorption characteristics of Bulgarian grape seeds and flours and flakes produced by them
Authors: Durakova A G , Bogoeva A L , Krasteva A P , Temelkova M L 
Published: July 2020

AbstractThe present paper contains a comparative characteristics of results obtained from statics of the sorption characteristics of grape seeds and biologically active products obtained from them - full-fatted flour, defatted flour and full-fatted flakes. The statics of the sorption processes is conducted for three temperatures - 10°C, 25°C and 40°C and eight water activities in the range from 0.112 to 0.868. For all of the examined products the temperature rise leads to a decrease of their sorption capacity. For the description of the equilibrium curves of the examined products the three parametric modified models of Oswin, Halsey, Henderson, Chung-Pfost are used. By the method of the smallest squares, using a programme for nonlinear regression “Statistics”, the coefficients of the used models are calculated, as on the basis of universally used criteria of suitability, a relevant model is recommended for each of the four Bulgarian products. The calculation of the values of the monolayer moisture content (MMC) in water activities below 0.5 is done through linearization of the Brunauer-Emmett-Teller (BET) model. The obtained results for MMC vary within the range from 2.34% to 4.96% dry substance (d.b.) for the processes of adsorption and desorption.
Application machining robots in processing operations
Authors: Guergov S , Nikolova N G , Stefanov G 
Published: July 2020

Abstract
An approach for the realization of various technological operations (drilling, milling, boring, grinding, etc.) on the basis of a specially designed execution technological system and an industrial robot has been developed. In the end effector of it, instead of a complex and large-sized tool turret, the workpiece is established. The method of producing geometrical surfaces of the workpiece is through the following formative motions: the feed motions are performed by the robot and the primary cutting motions by the tools, which are clamping in the turrets of the technological modules.
Modeling and study of a novel electrothermal oscillator based on shape memory alloys
Authors: Mitrev R P , Atamas E I , Goncharov O I , Todorov T S , Iatcheva I I 
Published: July 2020

Abstract
The paper deals with mathematical modelling and experimental investigation of a novel electrothermal oscillator based on Shape Memory Alloys (SMA). The operation of the oscillator is based on a heated by DC electric current SMA wire, mounted with a pre-tension between the free ends of two symmetrically arranged cantilever beams. Crystallographic changes in the SMA wire, consisting in the transition between austenitic and martensitic phases due to the periodic heating and cooling, lead to its intermittent shortening and stretching and thus mechanical and electrical vibrations are generated. The mathematical model of the system is derived using Lagrange-Maxwell formalism, Joule–Lenz law and Newton’s law of cooling. Simulation results show two types of periodic motion – the first one with low frequency is due to the temperature variation in the wire and the second one is with much more higher frequency and is due to the mass and elastic properties of the system. Experimental validation of the mathematical model shows its suitability for description of the considered system dynamic behaviour.
Effect of P modifiers, SiC nanomodifiers and combinations them on the structure of a hypereutectic aluminum-silicon AlSi18 alloy
Authors: Panov Iv , Dochev B , Manolov V , Velikov A , Dyakova V , Kuzmanov P 
Published: July 2020

Abstract
Introduction. Studies have been carried out with the following types of an aluminum-silicon AlSi18 alloy: unmodified, modified by a standard P modifier, modified by a SiC nanomodifier, and modified by a combination of both types if modifiers. The paper discusses the influence of the different types of modifiers and the combination of them on the shape and size of the primary Si crystals and their distribution in the structure of the alloy, as well as on the shape and size of the Si crystals in the eutectic composition.
Influence of a P modifier, a nanosized SiC modifier, and a combination of them on the mechanical properties of a hypereutectic aluminium-silicon alloy AlSi18
Authors: Panov Iv , Dochev B , Manolov V , Velikov A , Dyakova V , Kuzmanov P 
Published: July 2020

Abstract
Introduction. The hypereutectic aluminium-silicon alloy AlSi18 has been modified by: a standard P modifier, introduced into the melt by means of the ligature CuP 0,4wt.%; a nanomodifier SiC 0,1wt.%; and a combination of these two. The influence of the different types of modifiers and their combination on the mechanical propertis of the alloy has been discussed. The mechanical properties of an unmodified AlSi18 alloy have been used as basic data to compare the obtained results with.
The influence of magnesium alloy AE42 test specimens deformation magnitude on their microstructure
Authors: Marcheva Y , Loukaycheva M , Tsonev V , Dimova B 
Published: July 2020

Abstract
It is known that the properties of metals and their alloys depend on their microstructure. An important aspect of microstructure study is the ability to predict the properties and the behavior of the material in the process of its exploitation taking into account determined structural changes and their relationship with the material properties. The goal of this work is to study the effect of the magnitude of the plastic deformation on the microstructure of magnesium alloy AE42 test specimens. This paper describes the actions to get test specimens with various magnitude of residual deformation. The microstructure of those test specimens is studied. The gathered results are discussed.
Diffusion of innovation in the Bulgarian dairy industry
Authors: Nikolova-Alexieva Valentina , Krasteva Irina 
Published: July 2020

Abstract
This report presents a study of the factors that influence the diffusion of innovation in Bulgarian dairy businesses. Maintaining high innovation activity and positive innovation potential is the result of the effective functioning of the innovation system. The different types, functions and factors, prerequisites and mechanisms for implementing the process of innovation diffusion are explored. It is proved that the efficiency of investment is determined by external factors, primarily by the level of economic concentration of the market of innovative products. As a results the external factors have a relatively greater impact on the economic efficiency of investing in innovation and and hence a significant direct impact on the diffusion of innovation in the dairy industry. The «highest» level of correlation is determined with the factor of economic concentration of the industry and the market of innovation project.
Why do Bulgarian wine producers innovate?
Authors: Pastarmadzhieva D , Angelova M 
Published: July 2020

Abstract
The positive effects of the innovations on the performance of the companies is inevitable. However, these effects can be numerous and it is important the entrepreneurs to be aware what they can expect. Thus, the aim of the current study is to identify the results, expected by the Bulgarian wine producers from the application of innovations and if their choice is associated to some factors. The object of the study is Bulgarian SMEs wine producers. The focus is their opinion as regards the expected results from the application of innovations. The results are obtained through survey, conducted from December 2019 to January 2020. The results show that the most expected results by the Bulgarian wine producers are the increase of competitiveness and efficiency of their enterprises.
Process mining in support of technological readiness level assessment
Authors: Markovska Veneta , Kabaivanov Stanimir 
Published: July 2020

Abstract
We develop a framework for assessing technological readiness level using available data on business processes. By constructing a network of actors and linking process steps together it is possible to estimate the complexity of organizational structure, examine the bottlenecks and analyse whether advantages of available technology are fully utilized. Using publicly available data on business event logs we also test an automated process mining procedure and suggest a measurement to link our results to the TRL.
Opportunities for process reengineering in Bulgarian bread production (a case study)
Authors: Damyanova-Bakardzhieva Magdalena 
Published: July 2020

Abstract
The aim of this paper is to outline the importance of business process reengineering and to prove that it could have great effects on the manufacturing industry. Sustainability becomes an important factor in production and the issue of energy efficiency is examined in the paper. The research is conducted in a bread producing factory. After reengineering, the company achieves better performance, cost minimization, increase in production and a significant energy efficiency improvement.
Enhancing the critical temperature of strained Niobium films
Authors: Choi Joonyoung , Kim Young-Kyoung , Kim Chang-Duk , Kim Sooran , Jo Younjung 
Published: July 2020

Abstract
The study of the high critical temperature (T
c) of hydrogen compounds under high pressure has resulted in a considerable focus on Bardeen–Cooper–Schrieffer superconductors. Nb has the highest T
c among the elemental metals at ambient pressure, so reviewing Nb films again is worthwhile. In this study, we investigated the factors that determine the T
c of Nb films by strain introduction and carrier doping. We deposited Nb films of various thicknesses onto Si substrates and evaluated the T
c variation with thickness. In-plane compressive strain in the (110) plane due to residual stress reduced the T
c. First-principles calculations showed that adjusting the density of states at the Fermi level is key for both strain-induced suppression and doping-induced enhancement of the Nb T
c. The application of hydrostatic pressure compensated for the intrinsic strain of the film and increased its T
c, which could also be enhanced by increasing the hole concentration with an electric double-layer transistor. A liquid electrolyte should be used as a pressure medium for applying hydrostatic pressure to increase the T
c of correlated materials, where this increase results from changes in material structure and carrier concentration.
Influence of pore size on the plastic deformation of c-axis-compressed magnesium single crystals
Authors: Xue Chun , Wang Huan-zhu , Chu Zhi-bing , Li Yu-Gui , Gui Hai-lian 
Published: July 2020

Abstract
The molecular dynamics method is used to establish a single crystal model of magnesium with different void sizes. Uniaxial compression along the c-axis is carried out at 300 K. Combined with the stress–strain curve, potential energy curve and dislocation density curve of the four models, the compression mechanical energy and structural evolution process of a single crystal of magnesium with different hole sizes are analysed. Results show that when the radius of the single spherical void is large, the elastic modulus is small, the yield stress is low, the potential energy value is large, and the absolute value is small, such conditions facilitate deformation. When the hole radius is small, complete closure under c-axis compression requires minimal time and deformation.
Earlier life leisure-time physical activity in relation to age-related frailty syndrome
Authors: Kolehmainen Laura , Havulinna Satu , Ngandu Tiia , Strandberg Timo , Levälahti Esko , Lehtisalo Jenni , Antikainen Riitta , Hietikko Elina , Peltonen Markku , Pölönen Auli , Soininen Hilkka , Tuomilehto Jaakko , Laatikainen Tiina , Rauramaa Rainer , Kivipelto Miia , Kulmala Jenni 
Published: July 2020

Abstract

Background
frailty syndrome is common amongst older people. Low physical activity is part of frailty, but long-term prospective studies investigating leisure-time physical activity (LTPA) during the life course as a predictor of frailty are still warranted. The aim of this study is to investigate whether earlier life LTPA predicts frailty in older age.

Methods
the Finnish Geriatric Intervention Study to Prevent Cognitive Impairment and Disability (FINGER) included older adults (aged 60–77 years) from the general population who were at increased risk of cognitive decline. Frailty was assessed for 1,137 participants at a baseline visit using a modified version of Fried’s phenotype, including five criteria: weight loss, exhaustion, weakness, slowness and low physical activity. Self-reported data on earlier life LTPA were available from previous population-based studies (average follow-up time 13.6 years). A binomial logistic regression analysis was used to investigate the association between earlier life LTPA and pre-frailty/frailty in older age.

Results
the prevalence of frailty and pre-frailty was 0.8% and 27.3%, respectively. In the analyses, pre-frail and frail groups were combined. People who had been physically very active (OR 0.37, 95% CI 0.23–0.60) or moderately active (OR 0.45, 95% CI 0.32–0.65) earlier in life had lower odds of becoming pre-frail/frail than individuals who had been sedentary.

Conclusions
frailty was rare in this relatively healthy study population, but almost a third of the participants were pre-frail. Earlier life LTPA was associated with lower levels of pre-frailty/frailty. The results highlight the importance of physical activity when aiming to promote healthy old age.