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  1. Recent Advances and Future Trends in Extending the Service Life of Injection Moulding Tools: A Comprehensive Review

    Article • Journal of Mechanical Engineering and Manufacturing, February 2026, Australia Academic Press Pty Ltd

    Professor Angelos P. Markopoulos

  2. Experimental Research on the Ecological Recovery of Metals from Used Ni-MH Batteries

    Article • Materials, December 2025, MDPI AG

    Professor Angelos P. Markopoulos

  3. Surface Treatment and Analysis of 3D-Printed Plastic Molds for Prototype and Small-Series Injection Molding

    Article • Polymers, November 2025, MDPI AG

    Professor Angelos P. Markopoulos

  4. Enhanced polymer melt flow control in material extrusion: modified cross-WLF modeling and experimental validation of nozzle design for pressure reduction

    Article • Materials & Design, November 2025, Elsevier

    Professor Angelos P. Markopoulos

  5. Experimental Research on the Ecological Recovery of Metals from Used Ni-MH Batteries

    Article • October 2025, MDPI AG

    Professor Angelos P. Markopoulos

  6. Design and Manufacturing: An Industry 4.0 Perspective

    Article • Machines, October 2025, MDPI AG

    Prof. Dr Panagiotis Kyratsis, Professor Angelos P. Markopoulos

  7. Tribological Aspects of Slide Friction Diamond Burnishing Process

    Article • Materials, September 2025, MDPI AG

    Professor Angelos P. Markopoulos

  8. An advanced methodology for the development of highly accurate two temperature models (TTMs) to describe the material irradiation by an ultrashort laser

    Article • Optics & Laser Technology, October 2024, Elsevier

    Professor Angelos P. Markopoulos

  9. Investigation of Printing Speed Impact on the Printing Accuracy of Fused Filament Fabrication (FFF) ABS Artefacts

    Article • MANUFACTURING TECHNOLOGY, July 2024, Jan Evangelista Purkyne University in Usti nad Labem

    Professor Angelos P. Markopoulos

  10. AN EXPERIMENTAL INVESTIGATION OF THE MECHANICAL PROPERTIES OF FUSED FILAMENT FABRICATED NYLON-CARBON FIBER COMPOSITES

    Article • Cutting & Tools in Technological System, June 2024, National Technical University Kharkiv Polytechnic Institute

    Professor Angelos P. Markopoulos

  11. Advanced Machining Technology for Modern Engineering Materials

    Article • Materials, April 2024, MDPI AG

    Dr Muthuramalingam Thangaraj, Professor Angelos P. Markopoulos

  12. Investigation of the Influence of Machining Parameters and Surface Roughness on the Wettability of the Al6082 Surfaces Produced with WEDM

    Article • Materials, April 2024, MDPI AG

    Professor Angelos P. Markopoulos

  13. Advances and Trends in Non-Conventional, Abrasive and Precision Machining 2021

    Article • Machines, February 2024, MDPI AG

    Professor Angelos P. Markopoulos

  14. An Experimental and Numerical Study of the Laser Ablation of Bronze

    Article • Machines, January 2024, MDPI AG

    Professor Angelos P. Markopoulos

  15. The influence of Volumetric Energy Density on the mechanical behavior of PA12 parts produced by Powder Bed Fusion: An experimental and numerical study

    Article • Simulation Modelling Practice and Theory, January 2024, Elsevier

    Professor Angelos P. Markopoulos

  16. Fully ceramic versus steel gears: Potential, feasibility and challenges

    Article • Proceedings of the Institution of Mechanical Engineers Part C Journal of Mechanical Engineering Science, October 2023, SAGE Publications

    Professor Angelos P. Markopoulos

  17. Thickness, Adhesion and Microscopic Analysis of the Surface Structure of Single-Layer and Multi-Layer Metakaolin-Based Geopolymer Coatings

    Article • Coatings, October 2023, MDPI AG

    Professor Angelos P. Markopoulos

  18. Experimental Study οn the Infill Density Effect on Reduced Compressive Mechanical Properties οf Additively Manufactured ASA

    Article • Key Engineering Materials, September 2023, Trans Tech Publications

    Professor Angelos P. Markopoulos

  19. A Critical Assessment Regarding Two-Temperature Models: An Investigation of the Different Forms of Two-Temperature Models, the Various Ultrashort Pulsed Laser Models and Computational Methods

    Article • Archives of Computational Methods in Engineering, August 2023, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  20. Analysis on the Effect of Energy Density on Mechanical Properties of Selective Laser Sintering Processed Polyamide-12

    Article • August 2023, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  21. On the use of the Perlin noise function to calculate the laser absorption coefficient by rough surfaces

    Article • Simulation Modelling Practice and Theory, April 2023, Elsevier

    Professor Angelos P. Markopoulos

  22. Theoretical and experimental analysis of plasma radius expansion model in EDM: a comprehensive study

    Article • The International Journal of Advanced Manufacturing Technology, March 2023, Springer Science + Business Media

    Professor Angelos P. Markopoulos, Dr Muthuramalingam Thangaraj

  23. Evaluation of the Machinability of Ti-6Al-4V Titanium Alloy by AWJM Using a Multipass Strategy

    Article • Applied Sciences, March 2023, MDPI AG

    Professor Angelos P. Markopoulos

  24. Selected case studies regarding research-based education in the area of machine and civil assemblies

    Article • Technologia i Automatyzacja Montażu, January 2023, Rzeszow University of Technology

    Marek Magdziak, Professor Angelos P. Markopoulos

  25. Optimization of Wire EDM Process Parameters on Cutting Inconel 718 Alloy with Zinc-Diffused Coating Brass Wire Electrode Using Taguchi-DEAR Technique

    Article • Coatings, October 2022, MDPI AG

    Dr Muthuramalingam Thangaraj, Professor Angelos P. Markopoulos

  26. Effect of Printing Speed and Layer Height on Geometrical Accuracy of FDM-Printed Resolution Holes of PETG Artifacts

    Article • September 2022, MDPI AG

    Professor Angelos P. Markopoulos

  27. The Influence of Silicon Carbide Abrasive on Machining of Ti-6Al-4V by AWJ

    Article • September 2022, MDPI AG

    Professor Angelos P. Markopoulos

  28. Theoretical Assessment of the Role of Bond Material during Grinding of Superhard Materials with Diamond Wheels

    Article • Machines, July 2022, MDPI AG

    Professor Angelos P. Markopoulos

  29. An Optimalization Study on the Surface Texture and Machining Parameters of 60CrMoV18-5 Steel by EDM

    Article • Materials, May 2022, MDPI AG

    Professor Angelos P. Markopoulos

  30. Determination of the Efficiency of Hot Nano-Grinding of Mono-Crystalline Fcc Metals Using Molecular Dynamics Method

    Article • Micromachines, March 2022, MDPI AG

    Professor Angelos P. Markopoulos

  31. ON THE SURFACE ROUGHNESS OF 3D PRINTED PARTS WITH FDM BY A LOW-BUDGET COMMERCIAL PRINTER

    Article • Cutting & Tools in Technological System, March 2022, National Technical University Kharkiv Polytechnic Institute

    Professor Angelos P. Markopoulos

  32. Surface and Subsurface Quality of Titanium Grade 23 Machined by Electro Discharge Machining

    Article • Materials, December 2021, MDPI AG

    Professor Angelos P. Markopoulos

  33. Investigation of Surface Modification of 60CrMoV18-5 Steel by EDM with Cu-ZrO2 Powder Metallurgy Green Compact Electrode

    Article • Machines, November 2021, MDPI AG

    Professor Angelos P. Markopoulos

  34. Experimental Study on the Sustainability Assessment of AWJ Machining of Ti-6Al-4V Using Glass Beads Abrasive Particles

    Article • Sustainability, August 2021, MDPI AG

    Professor Angelos P. Markopoulos

  35. Evaluation of the Ability to Accurately Produce Angular Details by 3D Printing of Plastic Parts

    Article • Machines, July 2021, MDPI AG

    Professor Angelos P. Markopoulos

  36. Simulation of the Circulating Motion of the Working Medium and Metal Removal during Multi-Energy Processing under the Action of Vibration and Centrifugal Forces

    Article • Machines, June 2021, MDPI AG

    Professor Angelos P. Markopoulos

  37. EXPERIMENTAL INVESTIGATION OF SURFACE TOPOGRAPHY OF AL7075-T6 ALLOY MACHINED BY EDM

    Article • Cutting & Tools in Technological System, June 2021, National Technical University Kharkiv Polytechnic Institute

    Professor Angelos P. Markopoulos

  38. Modeling the energy action of vibration and centrifugal forces on the working medium and parts in a vibration machine oscillating reservoir with an impeller

    Article • MANUFACTURING TECHNOLOGY, June 2021, Jan Evangelista Purkyne University in Usti nad Labem

    Professor Angelos P. Markopoulos

  39. On the Modeling and Simulation of SLM and SLS for Metal and Polymer Powders: A Review

    Article • Archives of Computational Methods in Engineering, May 2021, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  40. Investigation on the Surface Quality Obtained during Trochoidal Milling of 6082 Aluminum Alloy

    Article • Machines, March 2021, MDPI AG

    Professor Angelos P. Markopoulos

  41. Advances and Trends in Non-Conventional, Abrasive and Precision Machining

    Article • Machines, February 2021, MDPI AG

    Professor Angelos P. Markopoulos

  42. Downscaled Finite Element Modeling of Metal Targets for Surface Roughness Level under Pulsed Laser Irradiation

    Article • Applied Sciences, January 2021, MDPI AG

    Professor Angelos P. Markopoulos

  43. A Comprehensive Study on Processing Ti–6Al–4V ELI with High Power EDM

    Article • Materials, January 2021, MDPI AG

    Professor Angelos P. Markopoulos

  44. CAD-Based 3D-FE Modelling of AISI-D3 Turning with Ceramic Tooling

    Article • Machines, January 2021, MDPI AG

    Prof. Dr Panagiotis Kyratsis, Dr Nikolaos Tapoglou, Professor Angelos P. Markopoulos

  45. On the Effect of Multiple Passes on Kerf Characteristics and Efficiency of Abrasive Waterjet Cutting

    Article • Metals, January 2021, MDPI AG

    Professor Angelos P. Markopoulos

  46. Sustainability Assessment, Investigations, and Modelling of Slot Milling Characteristics in Eco-Benign Machining of Hardened Steel

    Article • Metals, December 2020, MDPI AG

    Professor Angelos P. Markopoulos

  47. A comprehensive study on thermal modeling of SLM process under conduction mode using FEM

    Article • The International Journal of Advanced Manufacturing Technology, November 2020, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  48. Surface texture and integrity of electrical discharged machined titanium alloy

    Article • The International Journal of Advanced Manufacturing Technology, October 2020, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  49. Finite element simulation of friction and adhesion attributed contact of bio-inspired gecko-mimetic PDMS micro-flaps with SiO2 spherical surface

    Article • Bioinspiration & Biomimetics, September 2020, Institute of Physics Publishing

    Professor Angelos P. Markopoulos

  50. Molecular Dynamics Study of the Effect of Abrasive Grains Orientation and Spacing during Nanogrinding

    Article • Micromachines, July 2020, MDPI AG

    Professor Angelos P. Markopoulos

  51. Combination of an Improved 3D Geometry and Coupled Eulerian-Lagrangian Formulation for Turning Simulation

    Article • Materials Science Forum, May 2020, Trans Tech Publications

    Professor Angelos P. Markopoulos

  52. Advances in CAD/CAM/CAE Technologies

    Article • Machines, March 2020, MDPI AG

    Prof. Dr Panagiotis Kyratsis, Professor Angelos P. Markopoulos

  53. A New Approach in Surface Modification and Surface Hardening of Aluminum Alloys Using Friction Stir Process: Cu-Reinforced AA5083

    Article • Materials, March 2020, MDPI AG

    Professor Angelos P. Markopoulos

  54. Experimental Study on the Influence of Machining Conditions on the Quality of Electrical Discharge Machined Surfaces of aluminum alloy Al5052

    Article • Machines, March 2020, MDPI AG

    Professor Angelos P. Markopoulos

  55. Optimal Model Parameters of Inverse Kinematics Solution of a 3R Robotic Manipulator Using ANN Models

    Article • January 2020, IGI Global

    Professor Angelos P. Markopoulos

  56. Optimization of the Manufacturing Strategy, Machining Conditions, and Finishing of a Radial Impeller

    Article • Machines, December 2019, MDPI AG

    Professor Angelos P. Markopoulos

  57. The Use of the Kinetic Theory of Gases to Simulate the Physical Situations on the Surface of Autonomously Moving Parts During Multi-Energy Vibration Processing

    Article • Materials, September 2019, MDPI AG

    Professor Angelos P. Markopoulos

  58. Improving the effectiveness of combined grinding processes for processing superhard materials

    Article • Journal of Manufacturing Processes, July 2019, Elsevier

    Professor Angelos P. Markopoulos

  59. Electrical discharge machining modeling by coupling thermal analysis with deformed geometry feature

    Article • The International Journal of Advanced Manufacturing Technology, May 2019, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  60. Modeling of Ti6Al4V Alloy Orthogonal Cutting with Smooth Particle Hydrodynamics: A Parametric Analysis on Formulation and Particle Density

    Article • Metals, March 2019, MDPI AG

    Professor Angelos P. Markopoulos

  61. Meshless Methods for the Simulation of Machining and Micro-machining: A Review

    Article • Archives of Computational Methods in Engineering, March 2019, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  62. Application of Molecular Dynamics Simulations in Nano Manufacturing

    Article • Current Nanoscience, February 2019, Bentham Science Publishers

    Professor Angelos P. Markopoulos

  63. A Comparative Study between Regression and Neural Networks for Modeling Al6082-T6 Alloy Drilling

    Article • Machines, February 2019, MDPI AG

    Professor Angelos P. Markopoulos, Prof. Dr Panagiotis Kyratsis

  64. Influence of Ball-Burnishing Process on Surface Topography Parameters and Tribological Properties of Hardened Steel

    Article • Machines, January 2019, MDPI AG

    Professor Angelos P. Markopoulos

  65. Application of Aluminium Flakes in Fabrication of Open-Cell Aluminium Foams by Space Holder Method

    Article • Materials, August 2018, MDPI AG

    Professor Angelos P. Markopoulos

  66. Prediction of Thrust Force and Cutting Torque in Drilling Based on the Response Surface Methodology

    Article • Machines, June 2018, MDPI AG

    Professor Angelos P. Markopoulos, Prof. Dr Panagiotis Kyratsis

  67. Precision CNC Machining of Femoral Component of Knee Implant: A Case Study

    Article • Machines, March 2018, MDPI AG

    Professor Angelos P. Markopoulos

  68. Correlation Between Process Parameters and Cutting Forces in the Face Milling of Steel

    Article • January 2018, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  69. Molecular dynamics simulation of multi-pass nano-grinding process

    Article • MATEC Web of Conferences, January 2018, EDP Sciences

    Professor Angelos P. Markopoulos

  70. Design and Machining of the Femoral Component of Total Knee Implant

    Article • Solid State Phenomena, August 2017, Trans Tech Publications

    Professor Angelos P. Markopoulos, Dimitrios Manolakos

  71. Molecular Dynamics Simulation of Nano-Grinding with Multiple Abrasive Grains

    Article • Solid State Phenomena, August 2017, Trans Tech Publications

    Professor Angelos P. Markopoulos

  72. Computational Methods for the Assessment of Nanofluids in Abrasive Processes

    Article • Solid State Phenomena, August 2017, Trans Tech Publications

    Professor Angelos P. Markopoulos

  73. Effect of Cutting Feed and Chip Size Ratio on Cutting Force

    Article • Solid State Phenomena, August 2017, Trans Tech Publications

    Professor Angelos P. Markopoulos, István Deszpoth

  74. Optimal Model Parameters of Inverse Kinematics Solution of a 3R Robotic Manipulator Using ANN Models

    Article • International Journal of Manufacturing Materials and Mechanical Engineering, July 2017, IGI Global

    Professor Angelos P. Markopoulos

  75. A mathematically assisted methodology for the experimental calculation of the internal gear ratios to extend the lifecycle of a hobbing machine

    Article • International Journal of Mechanical Engineering Education, June 2017, SAGE Publications

    Professor Angelos P. Markopoulos

  76. Applicability of ANN models and Taguchi method for the determination of tool life in turning

    Article • MATEC Web of Conferences, January 2017, EDP Sciences

    Professor Angelos P. Markopoulos

  77. Modeling of hard machining

    Article • January 2017, Elsevier

    Professor Angelos P. Markopoulos

  78. Molecular Dynamics Model of Nano-metric Peripheral Grinding

    Article • Procedia CIRP, January 2017, Elsevier

    Professor Angelos P. Markopoulos

  79. Numerical Simulation of Grinding with Realistic Representation of Grinding Wheel and Workpiece Movements: A Finite Volumes Study

    Article • Procedia CIRP, January 2017, Elsevier

    Professor Angelos P. Markopoulos

  80. Thermotechnical modelling of hard turning: A computational fluid dynamics approach

    Article • Simulation Modelling Practice and Theory, January 2017, Elsevier

    Professor Angelos P. Markopoulos

  81. Modeling of micro- and nano-scale cutting

    Article • January 2017, Elsevier

    Professor Angelos P. Markopoulos

  82. Modeling Nano-Metric Manufacturing Processes with Molecular Dynamics Method: A Review

    Article • Current Nanoscience, December 2016, Bentham Science Publishers

    Professor Angelos P. Markopoulos

  83. Analysis of lead twist in modern high-performance grinding methods

    Article • IOP Conference Series Materials Science and Engineering, November 2016, Institute of Physics Publishing

    Professor Angelos P. Markopoulos

  84. Diamond grinding wheels production study with the use of the finite element method

    Article • Journal of Advanced Research, November 2016, Elsevier

    Professor Angelos P. Markopoulos

  85. MD simulation of laser micromachining

    Article • Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture, August 2016, SAGE Publications

    Professor Angelos P. Markopoulos

  86. Experimental and Numerical Investigation of the Influence of Cutting Speed and Feed Rate on Forces in Turning of Steel

    Article • Materials Science Forum, August 2016, Trans Tech Publications

    Professor Angelos P. Markopoulos

  87. Surface roughness prediction for the milling of Ti–6Al–4V ELI alloy with the use of statistical and soft computing techniques

    Article • Measurement, August 2016, Elsevier

    Professor Angelos P. Markopoulos

  88. On the use of back propagation and radial basis function neural networks in surface roughness prediction

    Article • Journal of Industrial Engineering International, March 2016, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  89. Molecular Dynamics Study of Abrasive Grain Morphology and Orientation in Nanometric Grinding

    Article • Key Engineering Materials, February 2016, Trans Tech Publications

    Professor Angelos P. Markopoulos, Dimitrios Manolakos

  90. Numerical Investigation of the Influence of Tool Rake Angle on Residual Stresses in Precision Hard Turning

    Article • Key Engineering Materials, February 2016, Trans Tech Publications

    Professor Angelos P. Markopoulos

  91. Assessment of Tool Life and Wear Intensity of CBN Tools in Hard Cutting

    Article • Key Engineering Materials, February 2016, Trans Tech Publications

    Professor Angelos P. Markopoulos

  92. Cutting Speed in Nano-Cutting as MD Modelling Parameter

    Article • International Journal of Manufacturing Materials and Mechanical Engineering, January 2016, IGI Global

    Professor Angelos P. Markopoulos

  93. Use of gamification in e-learning

    Article • January 2016, ACM (Association for Computing Machinery)

    Professor Angelos P. Markopoulos

  94. Loan Evaluation Applying Artificial Neural Networks

    Article • January 2016, ACM (Association for Computing Machinery)

    Professor Angelos P. Markopoulos

  95. Manufacturing processes of shape memory alloys

    Article • January 2016, Elsevier

    Professor Angelos P. Markopoulos

  96. Molecular dynamics simulation of material removal with the use of laser beam

    Article • January 2016, Elsevier

    Professor Angelos P. Markopoulos

  97. Some Features of the Surface Micro- and Macroprofile Formation at Flat Face Grinding with Spindle Axis Inclination

    Article • Applied Mechanics and Materials, November 2015, Trans Tech Publications

    Professor Angelos P. Markopoulos, Ivan Pyzhov

  98. Molecular dynamics modeling of a single diamond abrasive grain in grinding

    Article • Frontiers of Mechanical Engineering, May 2015, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  99. Gamification in engineering

    Article • International Journal of Mechanical Engineering Education, April 2015, SAGE Publications

    Professor Angelos P. Markopoulos

  100. The influence of cutting conditions and cutting tool geometry on the atomistic modeling of precision cutting

    Article • Engineering Solid Mechanics, January 2015, Growing Science

    Professor Angelos P. Markopoulos

  101. Investigation of the Effect of Cutting Conditions and Tool Edge Radius on Micromachining with the Use of the Finite Elements Method

    Article • International Journal of Materials Forming and Machining Processes, January 2015, IGI Global

    Professor Angelos P. Markopoulos

  102. Modeling of Micromachining

    Article • January 2014, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  103. Molecular Dynamics Modelling of Nanometric Cutting

    Article • Key Engineering Materials, October 2013, Trans Tech Publications

    Professor Angelos P. Markopoulos

  104. Finite Element Method in Machining Processes

    Article • January 2013, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  105. Application of FEM in Metal Cutting

    Article • August 2012, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  106. Cutting Mechanics and Analytical Modeling

    Article • August 2012, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  107. Finite Element Modeling

    Article • August 2012, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  108. Machining Processes

    Article • August 2012, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  109. Other Machining Processes and Modeling Techniques

    Article • August 2012, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  110. 3D Finite Element Modeling of High Speed Machining

    Article • International Journal of Manufacturing Materials and Mechanical Engineering, October 2011, IGI Global

    Professor Angelos P. Markopoulos

  111. Optical Properties of Manufactured III-Vs and II-VIs Short Wavelength Laser Structures

    Article • Current Nanoscience, August 2010, Bentham Science Publishers

    Professor Angelos P. Markopoulos

  112. Artificial neural network models for the prediction of surface roughness in electrical discharge machining

    Article • Journal of Intelligent Manufacturing, January 2008, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  113. On the finite element modelling of high speed hard turning

    Article • The International Journal of Advanced Manufacturing Technology, August 2007, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  114. Environmentally Friendly Precision Machining

    Article • Materials and Manufacturing Processes, January 2006, Taylor & Francis

    Professor Angelos P. Markopoulos

  115. Finishing of Hardened Boreholes: Grinding or Hard Cutting?

    Article • Materials and Manufacturing Processes, January 2004, Taylor & Francis

    Professor Angelos P. Markopoulos

  116. Nanotechnology and nanostructured materials: trends in carbon nanotubes

    Article • Precision Engineering, January 2004, Elsevier

    Professor Angelos P. Markopoulos

  117. Effect of the workpiece material on the heat affected zones during grinding: a numerical simulation

    Article • The International Journal of Advanced Manufacturing Technology, December 2003, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  118. Thermal Modelling of Surface Grinding Using Implicit Finite Element Techniques

    Article • The International Journal of Advanced Manufacturing Technology, September 2003, Springer Science + Business Media

    Professor Angelos P. Markopoulos

  119. Prediction of the collapse modes of PVC cylindrical shells under compressive axial loads using Artificial Neural Networks

    Article • Springer Science + Business Media

    Professor Angelos P. Markopoulos

  120. Simulation of Grinding by Means of the Finite Element Method and Artificial Neural Networks

    Article • IGI Global

    Professor Angelos P. Markopoulos