Yavor Sofronov
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View article: Deposition and Properties of Nanostructured Multilayer Cr/(Cr/a-C)ml Coating on Stainless Steels
Deposition and Properties of Nanostructured Multilayer Cr/(Cr/a-C)ml Coating on Stainless Steels Open
This work presents the results of deposition by magnetron sputtering nanostructured multilayer Cr/(Cr/a-C)ml coatings on AISI 316L and AISI 321 steel substrates. Chemical compositions were confirmed through EDX analysis with scanning elect…
View article: Investigation of the Structural, Mechanical and Operational Properties of an Alloy AlSi18Cu3CrMn
Investigation of the Structural, Mechanical and Operational Properties of an Alloy AlSi18Cu3CrMn Open
A non-standardized hypereutectic aluminum–silicon alloy, AlSi18Cu3CrMn, was developed. To refine the structure of the studied composition, a phosphorus modifier was used in an amount of 0.04 wt %, and a complex modifying treatment was appl…
View article: Deposition of Multilayer Nanostructured Coating Cr/(Cr/a-C)ml on Alloy Steels
Deposition of Multilayer Nanostructured Coating Cr/(Cr/a-C)ml on Alloy Steels Open
A chromium/amorphous carbon (Cr/(Cr/a-C)ml) nanostructured multilayer coating with a chromium sublayer was deposited on 42CrMo4 (1.7225,BDS EN ISO 683-2:2018), 100Cr6 (1.3505, BDS EN ISO 683-17:2024), and HS18-0-1 (1.3355, BDS EN ISO 4957:…
View article: Study of Electrical Contact in a System for High Power Transmission Through Well Piping
Study of Electrical Contact in a System for High Power Transmission Through Well Piping Open
The study examines in detail the possibility of using well casing as a means for power transmission downhole to high-power equipment, such as pumps. The ultimate goal is to transmit single-phase AC to the well bottom and then convert it in…
View article: Integrating Virtual Engineering for Energy-Efficient Manufacturing in Harsh Industrial Conditions
Integrating Virtual Engineering for Energy-Efficient Manufacturing in Harsh Industrial Conditions Open
The increasing demand for sustainable and cost-effective solutions in industrial maintenance calls for innovative approaches in reproducing obsolete spare parts, particularly in aggressive operational environments. This study presents a me…
View article: Design Optimization for Enhanced Durability of Artificial Ski Slope Tiles
Design Optimization for Enhanced Durability of Artificial Ski Slope Tiles Open
This study presents an in-depth analysis of the design and functionality of artificial ski slopes, focusing on the innovative use of hexagonal tiles to create a realis-tic skiing experience. The research emphasizes the importance of optimi…
View article: Process Parameter Optimization through Virtual Simulations for Enhanced Durability of Artificial Ski Slope Tiles
Process Parameter Optimization through Virtual Simulations for Enhanced Durability of Artificial Ski Slope Tiles Open
This paper addresses the challenges encountered during the injection molding process to ensure high-quality production of parts. The main problem to deal with in the study is achieving uniform filling, effective cooling, and minimizing def…
View article: Optimization of Accuracy and Repeatability in Laser Micro-Processing Using Experimental Design
Optimization of Accuracy and Repeatability in Laser Micro-Processing Using Experimental Design Open
This study focuses on optimizing the laser micromachining process to achieve precise geometric features. The main objective is to develop a systematic approach for analyzing the process parameters that influence the repeatability of laser …
View article: Sustainable 3D Printing with Recycled PETG: Mechanical Characterization and Process Optimization in FDM Technology
Sustainable 3D Printing with Recycled PETG: Mechanical Characterization and Process Optimization in FDM Technology Open
As additive manufacturing becomes increasingly relevant for sustainable production, the mechanical reliability of parts made from recycled materials remains a subject of concern. In single-piece or low-volume manufacturing, the ability to …
View article: Sagitta frame – A universal system for ventricular puncture. Clinical correlation – Initial experience
Sagitta frame – A universal system for ventricular puncture. Clinical correlation – Initial experience Open
Introduction: Ventricular puncture is one of the most common neurosurgical procedures. Most frequently it is conducted in emergency situations and in practice the freehand technique is applied. This allows fast and easy drainage of the ven…
View article: Failure Modes and Effect Analysis of Turbine Units of Pumped Hydro-Energy Storage Systems
Failure Modes and Effect Analysis of Turbine Units of Pumped Hydro-Energy Storage Systems Open
In the present paper, the subject of investigation is the reliability assessment of the single-stage reversible Hydropower Unit No. 3 (HU3) in the Bulgarian Pumped Hydro-Electric Storage (PHES) plant “Chaira”, which processes the waters of…
View article: Failure Modes and Effect Analysis of Turbine Units of Pumped Hydro Energy Storage Systems
Failure Modes and Effect Analysis of Turbine Units of Pumped Hydro Energy Storage Systems Open
In the present paper subject of the investigations is the reliability assessment of the single-stage reversible Hydropower Unit No. 3 (HU3) in the Bulgarian Pumped Hy-dro-Electric Storage (PHES) plant “Chaira”, which processes …
View article: Towards a Sustainable Design and Circular Economy for Hybrid EV Batteries
Towards a Sustainable Design and Circular Economy for Hybrid EV Batteries Open
The HELIOS European project, funded by the H2020 Programme, aims to develop lighter, modular hybrid Li-ion battery packs for EVs that combine same-size modules with high-power and high-energy cells to meet customer demands for fast chargin…
View article: Investigation and Identification of the Causes of the Unprecedented Accident at the “Chaira” Pumped Hydroelectric Energy Storage
Investigation and Identification of the Causes of the Unprecedented Accident at the “Chaira” Pumped Hydroelectric Energy Storage Open
The present study deals with an accident analysis of the “Chaira” Bulgaria high-pressure Pumped Hydroelectric Energy Storage (PHES), especially the failures of the Francis large-scale Hydraulic Unit No. 4 (HU4). The causes of overloading a…
View article: Investigation and Identification of the Causes for the Unprecedented Accident at the "Chaira" Pumped Hydroelectric Energy Storage Plant
Investigation and Identification of the Causes for the Unprecedented Accident at the "Chaira" Pumped Hydroelectric Energy Storage Plant Open
The present study deals with an accident analysis of the “Chaira”- Bulgaria high pressure Pumped Hydroelectric Energy Storage (PHES), especially the failures of the Francis large scale Hydraulic Unit No. 4 (HU4). The causes of overloading …
View article: An Assessment of the Embedding of Francis Turbines for Pumped Hydraulic Energy Storage
An Assessment of the Embedding of Francis Turbines for Pumped Hydraulic Energy Storage Open
In this paper, analyses of Francis turbine failures for powerful Pumped Hydraulic Energy Storage (PHES) are conducted. The structure is part of PHES Chaira, Bulgaria (HA4—Hydro-Aggregate 4). The aim of the study is to assess the structure-…
View article: A MULTI-STEP APPROACH FOR ANALYZING THE NUMBER OF POLYMER INJECTION MOLDING GATE SPOTS AND THEIR POSITION IN T-RTM TECHNOLOGY
A MULTI-STEP APPROACH FOR ANALYZING THE NUMBER OF POLYMER INJECTION MOLDING GATE SPOTS AND THEIR POSITION IN T-RTM TECHNOLOGY Open
The purpose of this study is to present a multi-step approach for building a virtual analysis supporting the determination of the number and position of the injection molding gate spots in Resin Transfer Molding (RTM) and the relatively ne…
View article: Assessment of the Embedment of Francis Turbine for Pumped Hydraulic Energy Storage
Assessment of the Embedment of Francis Turbine for Pumped Hydraulic Energy Storage Open
In the paper analyzes of Francis turbine failures for a powerful Pumped Hydraulic Energy Storage (PHES) are conducted. The structure is part of the PHES Chaira, Bulgaria (HA4 - Hydro-Aggregate 4). The aim is assessment of the structure-to-…
View article: Heat transfer through protective face masks and respirators
Heat transfer through protective face masks and respirators Open
The paper presents results from the investigation of heat transfer through six types of face masks and respirators used for protection against particulate matter (PM) and virus transmission. The masks/respirators were studied in terms of t…
View article: MEASURING THE CARBON DIOXIDE CONCENTRATION UNDER PROTECTIVE FACE MASKS WITH A SENSOR SYSTEM
MEASURING THE CARBON DIOXIDE CONCENTRATION UNDER PROTECTIVE FACE MASKS WITH A SENSOR SYSTEM Open
Wearing face masks is a way to limit the spread of viral particles.However, their usage leads to the creation of a microenvironment between the mask and the face as the heat and mass transfer processes through the masks are impeded.As a re…
View article: Investigation of different FDM/FFF 3D printing methods for improving the surface quality of 3D printed parts
Investigation of different FDM/FFF 3D printing methods for improving the surface quality of 3D printed parts Open
This paper study presents an investigation of three different FDM/FFF 3D printing methods. For the purposes of the study a 3D model of a part with cylindrical surfaces is built. The created model is 3D printed using three different methods…
View article: New product development and production in extremely short terms – Safety goggles
New product development and production in extremely short terms – Safety goggles Open
Normally the new product development (NPD) is a long process and consumes a lot of time. The NPD is a multiple stage process, each of which require the usage of different methods, software, machine equipment and qualified experts responsib…
View article: RAPID MATERIALIZATION OF A SMALL SERIES OF BONE STRUCTURE REPLICATIONS FROM A DIGITALIZED MODEL, CREATED BY COMPUTER TOMOGRAPHY
RAPID MATERIALIZATION OF A SMALL SERIES OF BONE STRUCTURE REPLICATIONS FROM A DIGITALIZED MODEL, CREATED BY COMPUTER TOMOGRAPHY Open
The recreation of bone structures from the human body has very complex geometry and a lack of symmetry. A small series of vertebrae replications, digitized by computed tomography, could serve in exercises for medical students to help them …
View article: DESIGN OF SPECIALIZED SURGICAL SCREW INSERTED IN PLATE TYPE CERVICAL IMPLANT
DESIGN OF SPECIALIZED SURGICAL SCREW INSERTED IN PLATE TYPE CERVICAL IMPLANT Open
In the field of Implantology the screws are an important part because they transfer the loads that occur in the bones. Surgical screws are similar to those in Mechanical Engineering, but the materials should have specific characteristics l…
View article: Design and Development of an E-Textile Mat for Assuring the Comfort of Bedridden Persons
Design and Development of an E-Textile Mat for Assuring the Comfort of Bedridden Persons Open
An e-textile mat with capacitive textile sensors was designed and manufactured to monitor body position and prevent decubitus ulcers in the case of bedridden people. The sensors were incorporated through a process of machine embroidery wit…
View article: Accuracy evaluation of fixed prosthetic constructions made by milling and printing technologies and the influence of temperature changes
Accuracy evaluation of fixed prosthetic constructions made by milling and printing technologies and the influence of temperature changes Open
The aim of this study is to evaluate the internal and external fit accuracy of fixed metal-ceramic prosthetic constructions made by milling and printing technologies and the influence of temperature changes on this accuracy. An acrylic res…
View article: Investigation of the deviation during the information transfer from the prosthetic field to the laboratory scanners
Investigation of the deviation during the information transfer from the prosthetic field to the laboratory scanners Open
The aim of this work is to investigate the deviations during the first stage of the information transfer from the prosthetic field to the dental laboratory scanners for CAD/CAM technology. The first upper left molar on an artificial acryli…