Aleksandar Georgiev - Academia.edu (original) (raw)

Papers by Aleksandar Georgiev

Open Access Macedonian Journal of Medical Sciences, Jul 10, 2022

BACKGROUND: An accurate diagnosis is essential for the effective treatment of prostate cancer (PC... more BACKGROUND: An accurate diagnosis is essential for the effective treatment of prostate cancer (PCa) and for the patients' well-being. AIM: Thе main purpose of this study was to assess the utility of multiparametric magnetic resonance imaging (mp-MRI) for initial detection of PCa among the Bulgarian population of men with prostate diseases. MATERIALS AND METHODS: Fifty-three patients, aged 44 to 82 years, were evaluated for clinically significant PCa. Assessment methods included prostate-specific antigen (PSA) serum levels, transrectal ultrasonography (TRUS), GE Discovery 3T MRI, and 12-core TRUS biopsy. RESULTS: mp-MRI showed 83.20% concordance with TRUS biopsy: sensitivity of 91.43% (76.90-98.20), specificity of 75.00% (34.90-96.80), positive predictive values 94.10% (82.80-98.20) and negative predictive values 66.70% (38.70-86.40). Of the patients classified in prostate imaging-reporting and data system (PI-RADS) levels 4 and 5, 94.12% had positive TRUS biopsy, as well as 44.40% of PI-RADS had level 3. Irrespective of the patients' age and PSA, PI-RADS was found to be a significant predictor of a positive TRUS biopsy (p = 0.009). PSA serum levels showed a low concordance with TRUS biopsy (area under the curve = 0.539; 95% confidence interval [CI]: 0.363-0.712) and a low, although significant, correlation with PI-RADS (rs = 0.416; 95% CI: 0.164-0.617). CONCLUSION: According to our findings, mp-MRI and TRUS biopsy have a high level of concordance for the initial detection of PCa. The incorporation of mp-MRI into the diagnostic pathway for PCa can significantly reduce the number of incorrect diagnoses based on PSA serum levels and/or suspicious physical and digital examinations.

21st Century Media and Communications

The article examines the media coverage of two books intended for children and teenagers that con... more The article examines the media coverage of two books intended for children and teenagers that concern taboo themes, such as sexual education and same-sex partnership. A similarity in the coverage is demonstrated where limited conservative stances become overrepresented through a large number of publications in a short period of time. The results are presented with regard to media effects and the formation of attitudes in a wide range of recipients of mediatized messages.

The combined muscle-skeletal traumas (MST) are very frequent over the last few years. The emergen... more The combined muscle-skeletal traumas (MST) are very frequent over the last few years. The emergency care try to save the life of the patient and to receive resuscitation treatment. The role of Trauma surgeon is to choose the right moment for surgery. Aim: To present the management of patient with combined height injury, fracture stabilization, partial foot amputation, local flaps, skin grafting and HIFU – thermotherapy as scar treatment. Materials and methods: 40 years old mail patient, injured after a fall from 8 meters in an elevator shaft. After resuscitation treatment to control the shock the Imaging results are: burst fracture of L3 with spinal canal stenosis, fracture of the sacral bone Denis I, fracture of the right humerus in the proximal third, Monteggia fracture of the left arm, fracture of the proximal third of the right tibia as well as comminuted fractures of both calves and of both heel bones. Results: After a few operations his final result was well healed bone fractu...

Energies, Nov 5, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Clinical Case Reports

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

2019 16th Conference on Electrical Machines, Drives and Power Systems (ELMA)

The paper presents the results from the studies of the operating parameters of a medium-voltage c... more The paper presents the results from the studies of the operating parameters of a medium-voltage cable line. The studies have been conducted by means of a computer model, developed in MatLab/Simulink. Results have been obtained, concerning the influence of the load over the line on the generated by the line reactive capacitive power and on the losses of power and voltage. The necessity to connect a compensating reactor to the line has been established and the parameters of the reactor have been determined. The influence of the compensating reactor on the operational parameters of the line has been studied.

Bacground: Peripheral arterial disease is the most common disease of arterial vessels in this ana... more Bacground: Peripheral arterial disease is the most common disease of arterial vessels in this anatomical region. Symptoms may range from intermittent claudication to pain even at rest. The claudication is expressed by the occurrence of pain in the affected limb in physical effort and resolves at rest. Pain, usually appears distally from the narrow or clogged area of the vessel. When atherosclerotic changes affect the superficial femoral artery and/or popliteal artery, pain commonly occurs in the calf region of the affected limb. Aim: Analysis of frequency and type of vessel changes in femoro - popliteal anatomical region and correlations of the disease with ankle brachial index. Patients and methods: The study includes 400 patients (250 men and 150 women aged between 60 and 75. All patients under investigation exhibit one or more symptoms of PAD and their complaints date for at least 2 years. All CT studies included in the study are performed on 256 slice CT with automatic injection...

Radiology Case Reports, 2022

The novel coronavirus pandemic outbreak caused extreme public fear, health concerns, and psycholo... more The novel coronavirus pandemic outbreak caused extreme public fear, health concerns, and psychological distress, especially in oncology patients. The presented rare case is of a 40-year-old female with thymoma type B, with rapid progression, due to fear from the COVID-19 pandemic. Biopsy and histological verification of the tumor show a B-type thymoma with a high proliferative index. The fear of infection is causing avoidant behavior and leads to suboptimal therapy in some oncology patients that will have severe consequences. We can conclude that adequate, personalized, and most importantly, active psychological care is necessary and should be implemented for cancer patients. To be prepared for a future lockdown, it may be helpful to urge patients to seek alternative forms of social contact, such as online and mobile communications, to combat depression lockdown effects.

Radiology Case Reports, 2021

Gastric lipomas are very rare benign tumors. Only around 217 cases have been reported. Most gastr... more Gastric lipomas are very rare benign tumors. Only around 217 cases have been reported. Most gastric lipomas are found incidentally; however, larger neoplasms can be symptomatic. The presented 64 years old male with incidental finding of pyloric lipoma adds another example to the few documented in the literature. The patient had symptoms of breath shortness and lack of energy two months after COVID 19 pneumonia. A low dose CT scan with iodine contrast enhancement of the chest and upper abdomen led to the diagnose. The diagnosis of gastric lipoma can be achieved through diagnostic imaging or the combination of endoscopic techniques. Treatment can be carried out by endoscopy, robotic or classical surgery.

Radiology Case Reports, 2021

An ectopic kidney is defined as an atypically placed kidney, due to improper migration from the f... more An ectopic kidney is defined as an atypically placed kidney, due to improper migration from the fetal pelvis, during embryogenesis. The presented CT scan of 72-year-old male with pain and visible hematuria reveals that the right kidney is located in the pelvis. The ectopic kidney has malrotation with a calcified artery and 2 veins. One draining in the right common iliac vein and the other connected to the left common iliac vein-near the bifurcation of vena cava inferior. Usually, pelvic ectopy is asymptomatic. However, it may lead to elevated blood pressure, increased risk of stone formation, infections, and traumatism, due to the atypical anatomical position. Variations in the anatomy of the kidney and its vascular supply are of clinical importance. It is possible to encounter a radiological, surgical, or cancer case, such as the presented.

2021 International Conference Automatics and Informatics (ICAI), 2021

Honeypot system is available for use by popular operating systems, and there is no limit to hardw... more Honeypot system is available for use by popular operating systems, and there is no limit to hardware. The system provides a security solution useful for most companies that want to protect their information and feel protected from cyberattacks. This article shows a conceptual model for securing a network. The architecture of a machine-learning model and honeypot system for protecting the network are presented.

The world power generation is in a process of transition from fossil fuels to renewable and susta... more The world power generation is in a process of transition from fossil fuels to renewable and sustainable power sources. The part of the electricity from alternative energy technologies is growing rapidly. New engineering approaches and devices are continuously created by the researchers in the field of power engineering, aimed at obtaining energy with less harm for the environment and the life on the planet. The present work is an initial evaluation of the possibilities for marine energy conversion in the Balkan region. The focus is on energy from the sea including energy from waves, currents, salinity, temperature difference etc. The main purpose of the work is on the basis of assessment of the power potential determined by the geographical characteristics of the seas in the region and the scientific, technological and economical level to make some conclusions about the prospects in this area.

Increased scientific and technological efforts have been made recently to reduce the carbon dioxi... more Increased scientific and technological efforts have been made recently to reduce the carbon dioxide emissions in the environment as a main cause of the global warming. The general trend is using Renewable Energy Sources. The aim of the present work is a brief review of the advantages of the hybrid thermal systems (HTS) using Renewable Energy Sources. The article presents methods and instruments for mathematical modeling and simulations of the main components of the HTS and its operation as a whole.

The measuring system of an installation with ground source heat pump and solar collectors for air... more The measuring system of an installation with ground source heat pump and solar collectors for air conditioning of residential buil dings is presented in this article. The sensors for parameter measuring of the system and the devic es for data collecting and treatment are described. An analysis is performed which parameter s are to be measured at different installation working modes - heating, cooling and cof the ground by means of various sources of energy.

Renewable Energy, 2021

Abstract During the last decade, there was an increased interest in wind turbine icing. Most of t... more Abstract During the last decade, there was an increased interest in wind turbine icing. Most of the icing studies are related to horizontal axis wind turbine icing (HAWT). Vertical axis wind turbine (VAWT) icing is seldomly reported in the literature. Compared to the HAWT blade VAWT blade operates under various angles of attack. Therefore, ice accretion shapes on static VAWT blade must be considered under different angles of attack. In the present study, a novel approach to predict ice accretion shapes on VAWT is described. Ice accretion shapes are obtained at a range of angles of attack between -25° and 25° using FENSAP-ICE which is the state-of-art icing simulation tool. Moving reference frame (MRF) was used to consider rotating effect on droplet field. The present method helped to draw the following conclusions. Firstly, the whole leading edge is covered by ice. Secondly, in rime ice conditions smooth ice shape is obtained, which does not significantly affect aerodynamic performance. Whereas in glaze ice conditions bumpy ice shapes causing massive flow separation and lift force degradation. Finally, iced VAWT loses up to 60% of power performance due to rime ice conditions. In glaze ice conditions VAWT is unable to produce power.

Energy, 2021

Abstract The article discusses the theoretical and practical foundations of the study of the poss... more Abstract The article discusses the theoretical and practical foundations of the study of the possibility of obtaining volatile combustible substances released during special heat treatment of coal, with the aim of replacing ignition fuel oil at thermal power plants. The results of an experimental study of the coals of the Saryadyr field of three Kazakhstan deposits with the aim of obtaining volatile combustible substances, as well as the possibility of using these combustible substances as starting fuel, are presented. The results of calculating the heat of combustion of the gas obtained from the presented coal samples at different heating temperatures showed that with an increase in the heating temperature, the heat of combustion of combustible gases obtained from coal samples also increases. For all the coal samples under consideration, the maximum value of the heat of combustion is traced at a heating temperature of 600°C. The greatest value is observed for the coal of the Shubarkul deposit - 22.1 MJ/m3, and the minimum value for the brown coal of the Saryadyr deposit is 13.5 MJ/m3. According to the results of experimental studies, we can conclude that of the three presented coals for producing combustible gas, the most suitable are the coals of the Shubarkul and Maikuben deposits. For use in the boiler unit as a starting fuel, it is sufficient to heat coal to temperatures of 350-450°C.

Energies, 2020

Shallow geothermal energy systems (SGES) may take different forms and have recently taken conside... more Shallow geothermal energy systems (SGES) may take different forms and have recently taken considerable attention due to energy geo-structures (EGS) resulting from the integration of heat exchange elements in geotechnical structures. Still, there is a lack of systematic design guidelines of SGES. Hence, in order to contribute towards that direction, the current study aims at reviewing the available SGES modeling options along with their various aspects and practices. This is done by first presenting the main analytical and numerical models and methods related to the thermal behavior of SGES. Then, the most important supplementary factors affecting such modeling are discussed. These include: (i) the boundary conditions, in the form of temperature variation or heat flow, that majorly affect the predicted thermal behavior of SGES; (ii) the spatial dimensions that may be crucial when relaxing the infinite length assumption for short heat exchangers such as energy piles (EP); (iii) the de...

IOP Conference Series: Materials Science and Engineering, 2020

The aim of this paper is to investigate the processes of earth faults occurrence in a wind farm n... more The aim of this paper is to investigate the processes of earth faults occurrence in a wind farm network, integrated into the electric power system. The wind power farm is realized with squirrel-cage induction generators (SCIG). Each generator has a 0.69/21kV step-up transformer. The connection of the wind power farm to the electric power system is implemented through a step-up substation with a single 21/115kV transformer. The star center of the transformer 21kV winding is grounded by means of a 40 ohm resistor. A synthesized in MatLab/Simulink computer model investigates the processes of earth faults occurrence in the medium-voltage (MV) network of the wind farm. Results have been obtained, concerning the influence of the earth fault location on the transient voltages and currents at both rated torque of the generators and no-operating generators. When there is an earth fault in one of the lines, the voltages and currents of the MV network are asymmetrical and higher harmonics of t...

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, 2020

Purpose The aim of this paper is a steady-state analysis of the basic electrical characteristics ... more Purpose The aim of this paper is a steady-state analysis of the basic electrical characteristics of a wind farm with squirrel-cage induction generators (SCIG), integrated into a high power system. The SCIG are connected to the system by means of a step-up substation 21/115 kV, realized by cable lines. Design/methodology/approach The analyses have been done with the help of a computer model, developed in MATLAB/Simulink. Findings Results have been obtained, concerning the influence of the SCIG on the active and reactive power, on the power factor and the voltage deviation in the cases of only one generator operating, all generators operating and disabled generators. Practical implications The analysis has been carried out for an operating wind farm in the power system. The obtained results are applicable for optimizing and managing the modes of operation of the wind farm. Originality/value A mathematical model for studying the electrical parameters of an SCIG integrated into a high p...

Open Access Macedonian Journal of Medical Sciences, Jul 10, 2022

BACKGROUND: An accurate diagnosis is essential for the effective treatment of prostate cancer (PC... more BACKGROUND: An accurate diagnosis is essential for the effective treatment of prostate cancer (PCa) and for the patients' well-being. AIM: Thе main purpose of this study was to assess the utility of multiparametric magnetic resonance imaging (mp-MRI) for initial detection of PCa among the Bulgarian population of men with prostate diseases. MATERIALS AND METHODS: Fifty-three patients, aged 44 to 82 years, were evaluated for clinically significant PCa. Assessment methods included prostate-specific antigen (PSA) serum levels, transrectal ultrasonography (TRUS), GE Discovery 3T MRI, and 12-core TRUS biopsy. RESULTS: mp-MRI showed 83.20% concordance with TRUS biopsy: sensitivity of 91.43% (76.90-98.20), specificity of 75.00% (34.90-96.80), positive predictive values 94.10% (82.80-98.20) and negative predictive values 66.70% (38.70-86.40). Of the patients classified in prostate imaging-reporting and data system (PI-RADS) levels 4 and 5, 94.12% had positive TRUS biopsy, as well as 44.40% of PI-RADS had level 3. Irrespective of the patients' age and PSA, PI-RADS was found to be a significant predictor of a positive TRUS biopsy (p = 0.009). PSA serum levels showed a low concordance with TRUS biopsy (area under the curve = 0.539; 95% confidence interval [CI]: 0.363-0.712) and a low, although significant, correlation with PI-RADS (rs = 0.416; 95% CI: 0.164-0.617). CONCLUSION: According to our findings, mp-MRI and TRUS biopsy have a high level of concordance for the initial detection of PCa. The incorporation of mp-MRI into the diagnostic pathway for PCa can significantly reduce the number of incorrect diagnoses based on PSA serum levels and/or suspicious physical and digital examinations.

21st Century Media and Communications

The article examines the media coverage of two books intended for children and teenagers that con... more The article examines the media coverage of two books intended for children and teenagers that concern taboo themes, such as sexual education and same-sex partnership. A similarity in the coverage is demonstrated where limited conservative stances become overrepresented through a large number of publications in a short period of time. The results are presented with regard to media effects and the formation of attitudes in a wide range of recipients of mediatized messages.

The combined muscle-skeletal traumas (MST) are very frequent over the last few years. The emergen... more The combined muscle-skeletal traumas (MST) are very frequent over the last few years. The emergency care try to save the life of the patient and to receive resuscitation treatment. The role of Trauma surgeon is to choose the right moment for surgery. Aim: To present the management of patient with combined height injury, fracture stabilization, partial foot amputation, local flaps, skin grafting and HIFU – thermotherapy as scar treatment. Materials and methods: 40 years old mail patient, injured after a fall from 8 meters in an elevator shaft. After resuscitation treatment to control the shock the Imaging results are: burst fracture of L3 with spinal canal stenosis, fracture of the sacral bone Denis I, fracture of the right humerus in the proximal third, Monteggia fracture of the left arm, fracture of the proximal third of the right tibia as well as comminuted fractures of both calves and of both heel bones. Results: After a few operations his final result was well healed bone fractu...

Energies, Nov 5, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Clinical Case Reports

This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

2019 16th Conference on Electrical Machines, Drives and Power Systems (ELMA)

The paper presents the results from the studies of the operating parameters of a medium-voltage c... more The paper presents the results from the studies of the operating parameters of a medium-voltage cable line. The studies have been conducted by means of a computer model, developed in MatLab/Simulink. Results have been obtained, concerning the influence of the load over the line on the generated by the line reactive capacitive power and on the losses of power and voltage. The necessity to connect a compensating reactor to the line has been established and the parameters of the reactor have been determined. The influence of the compensating reactor on the operational parameters of the line has been studied.

Bacground: Peripheral arterial disease is the most common disease of arterial vessels in this ana... more Bacground: Peripheral arterial disease is the most common disease of arterial vessels in this anatomical region. Symptoms may range from intermittent claudication to pain even at rest. The claudication is expressed by the occurrence of pain in the affected limb in physical effort and resolves at rest. Pain, usually appears distally from the narrow or clogged area of the vessel. When atherosclerotic changes affect the superficial femoral artery and/or popliteal artery, pain commonly occurs in the calf region of the affected limb. Aim: Analysis of frequency and type of vessel changes in femoro - popliteal anatomical region and correlations of the disease with ankle brachial index. Patients and methods: The study includes 400 patients (250 men and 150 women aged between 60 and 75. All patients under investigation exhibit one or more symptoms of PAD and their complaints date for at least 2 years. All CT studies included in the study are performed on 256 slice CT with automatic injection...

Radiology Case Reports, 2022

The novel coronavirus pandemic outbreak caused extreme public fear, health concerns, and psycholo... more The novel coronavirus pandemic outbreak caused extreme public fear, health concerns, and psychological distress, especially in oncology patients. The presented rare case is of a 40-year-old female with thymoma type B, with rapid progression, due to fear from the COVID-19 pandemic. Biopsy and histological verification of the tumor show a B-type thymoma with a high proliferative index. The fear of infection is causing avoidant behavior and leads to suboptimal therapy in some oncology patients that will have severe consequences. We can conclude that adequate, personalized, and most importantly, active psychological care is necessary and should be implemented for cancer patients. To be prepared for a future lockdown, it may be helpful to urge patients to seek alternative forms of social contact, such as online and mobile communications, to combat depression lockdown effects.

Radiology Case Reports, 2021

Gastric lipomas are very rare benign tumors. Only around 217 cases have been reported. Most gastr... more Gastric lipomas are very rare benign tumors. Only around 217 cases have been reported. Most gastric lipomas are found incidentally; however, larger neoplasms can be symptomatic. The presented 64 years old male with incidental finding of pyloric lipoma adds another example to the few documented in the literature. The patient had symptoms of breath shortness and lack of energy two months after COVID 19 pneumonia. A low dose CT scan with iodine contrast enhancement of the chest and upper abdomen led to the diagnose. The diagnosis of gastric lipoma can be achieved through diagnostic imaging or the combination of endoscopic techniques. Treatment can be carried out by endoscopy, robotic or classical surgery.

Radiology Case Reports, 2021

An ectopic kidney is defined as an atypically placed kidney, due to improper migration from the f... more An ectopic kidney is defined as an atypically placed kidney, due to improper migration from the fetal pelvis, during embryogenesis. The presented CT scan of 72-year-old male with pain and visible hematuria reveals that the right kidney is located in the pelvis. The ectopic kidney has malrotation with a calcified artery and 2 veins. One draining in the right common iliac vein and the other connected to the left common iliac vein-near the bifurcation of vena cava inferior. Usually, pelvic ectopy is asymptomatic. However, it may lead to elevated blood pressure, increased risk of stone formation, infections, and traumatism, due to the atypical anatomical position. Variations in the anatomy of the kidney and its vascular supply are of clinical importance. It is possible to encounter a radiological, surgical, or cancer case, such as the presented.

2021 International Conference Automatics and Informatics (ICAI), 2021

Honeypot system is available for use by popular operating systems, and there is no limit to hardw... more Honeypot system is available for use by popular operating systems, and there is no limit to hardware. The system provides a security solution useful for most companies that want to protect their information and feel protected from cyberattacks. This article shows a conceptual model for securing a network. The architecture of a machine-learning model and honeypot system for protecting the network are presented.

The world power generation is in a process of transition from fossil fuels to renewable and susta... more The world power generation is in a process of transition from fossil fuels to renewable and sustainable power sources. The part of the electricity from alternative energy technologies is growing rapidly. New engineering approaches and devices are continuously created by the researchers in the field of power engineering, aimed at obtaining energy with less harm for the environment and the life on the planet. The present work is an initial evaluation of the possibilities for marine energy conversion in the Balkan region. The focus is on energy from the sea including energy from waves, currents, salinity, temperature difference etc. The main purpose of the work is on the basis of assessment of the power potential determined by the geographical characteristics of the seas in the region and the scientific, technological and economical level to make some conclusions about the prospects in this area.

Increased scientific and technological efforts have been made recently to reduce the carbon dioxi... more Increased scientific and technological efforts have been made recently to reduce the carbon dioxide emissions in the environment as a main cause of the global warming. The general trend is using Renewable Energy Sources. The aim of the present work is a brief review of the advantages of the hybrid thermal systems (HTS) using Renewable Energy Sources. The article presents methods and instruments for mathematical modeling and simulations of the main components of the HTS and its operation as a whole.

The measuring system of an installation with ground source heat pump and solar collectors for air... more The measuring system of an installation with ground source heat pump and solar collectors for air conditioning of residential buil dings is presented in this article. The sensors for parameter measuring of the system and the devic es for data collecting and treatment are described. An analysis is performed which parameter s are to be measured at different installation working modes - heating, cooling and cof the ground by means of various sources of energy.

Renewable Energy, 2021

Abstract During the last decade, there was an increased interest in wind turbine icing. Most of t... more Abstract During the last decade, there was an increased interest in wind turbine icing. Most of the icing studies are related to horizontal axis wind turbine icing (HAWT). Vertical axis wind turbine (VAWT) icing is seldomly reported in the literature. Compared to the HAWT blade VAWT blade operates under various angles of attack. Therefore, ice accretion shapes on static VAWT blade must be considered under different angles of attack. In the present study, a novel approach to predict ice accretion shapes on VAWT is described. Ice accretion shapes are obtained at a range of angles of attack between -25° and 25° using FENSAP-ICE which is the state-of-art icing simulation tool. Moving reference frame (MRF) was used to consider rotating effect on droplet field. The present method helped to draw the following conclusions. Firstly, the whole leading edge is covered by ice. Secondly, in rime ice conditions smooth ice shape is obtained, which does not significantly affect aerodynamic performance. Whereas in glaze ice conditions bumpy ice shapes causing massive flow separation and lift force degradation. Finally, iced VAWT loses up to 60% of power performance due to rime ice conditions. In glaze ice conditions VAWT is unable to produce power.

Energy, 2021

Abstract The article discusses the theoretical and practical foundations of the study of the poss... more Abstract The article discusses the theoretical and practical foundations of the study of the possibility of obtaining volatile combustible substances released during special heat treatment of coal, with the aim of replacing ignition fuel oil at thermal power plants. The results of an experimental study of the coals of the Saryadyr field of three Kazakhstan deposits with the aim of obtaining volatile combustible substances, as well as the possibility of using these combustible substances as starting fuel, are presented. The results of calculating the heat of combustion of the gas obtained from the presented coal samples at different heating temperatures showed that with an increase in the heating temperature, the heat of combustion of combustible gases obtained from coal samples also increases. For all the coal samples under consideration, the maximum value of the heat of combustion is traced at a heating temperature of 600°C. The greatest value is observed for the coal of the Shubarkul deposit - 22.1 MJ/m3, and the minimum value for the brown coal of the Saryadyr deposit is 13.5 MJ/m3. According to the results of experimental studies, we can conclude that of the three presented coals for producing combustible gas, the most suitable are the coals of the Shubarkul and Maikuben deposits. For use in the boiler unit as a starting fuel, it is sufficient to heat coal to temperatures of 350-450°C.

Energies, 2020

Shallow geothermal energy systems (SGES) may take different forms and have recently taken conside... more Shallow geothermal energy systems (SGES) may take different forms and have recently taken considerable attention due to energy geo-structures (EGS) resulting from the integration of heat exchange elements in geotechnical structures. Still, there is a lack of systematic design guidelines of SGES. Hence, in order to contribute towards that direction, the current study aims at reviewing the available SGES modeling options along with their various aspects and practices. This is done by first presenting the main analytical and numerical models and methods related to the thermal behavior of SGES. Then, the most important supplementary factors affecting such modeling are discussed. These include: (i) the boundary conditions, in the form of temperature variation or heat flow, that majorly affect the predicted thermal behavior of SGES; (ii) the spatial dimensions that may be crucial when relaxing the infinite length assumption for short heat exchangers such as energy piles (EP); (iii) the de...

IOP Conference Series: Materials Science and Engineering, 2020

The aim of this paper is to investigate the processes of earth faults occurrence in a wind farm n... more The aim of this paper is to investigate the processes of earth faults occurrence in a wind farm network, integrated into the electric power system. The wind power farm is realized with squirrel-cage induction generators (SCIG). Each generator has a 0.69/21kV step-up transformer. The connection of the wind power farm to the electric power system is implemented through a step-up substation with a single 21/115kV transformer. The star center of the transformer 21kV winding is grounded by means of a 40 ohm resistor. A synthesized in MatLab/Simulink computer model investigates the processes of earth faults occurrence in the medium-voltage (MV) network of the wind farm. Results have been obtained, concerning the influence of the earth fault location on the transient voltages and currents at both rated torque of the generators and no-operating generators. When there is an earth fault in one of the lines, the voltages and currents of the MV network are asymmetrical and higher harmonics of t...

COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, 2020

Purpose The aim of this paper is a steady-state analysis of the basic electrical characteristics ... more Purpose The aim of this paper is a steady-state analysis of the basic electrical characteristics of a wind farm with squirrel-cage induction generators (SCIG), integrated into a high power system. The SCIG are connected to the system by means of a step-up substation 21/115 kV, realized by cable lines. Design/methodology/approach The analyses have been done with the help of a computer model, developed in MATLAB/Simulink. Findings Results have been obtained, concerning the influence of the SCIG on the active and reactive power, on the power factor and the voltage deviation in the cases of only one generator operating, all generators operating and disabled generators. Practical implications The analysis has been carried out for an operating wind farm in the power system. The obtained results are applicable for optimizing and managing the modes of operation of the wind farm. Originality/value A mathematical model for studying the electrical parameters of an SCIG integrated into a high p...