Author: Shahriyar Kaboli
Publisher: John Wiley & Sons
ISBN: 1119772184
Category : Technology & Engineering
Languages : en
Pages : 388
Book Description
Resilient Power Electronic Systems Discover an advanced reference offering a powerful novel approach to the design and use of reliable and fault-tolerant power electronic systems In Resilient Power Electronic Systems, a team of accomplished researchers deliver an insightful treatment of the challenges faced by practitioners and researchers working with power electronic converters and attempting to analyze internal and external failure mechanisms. The authors expertly present advanced techniques for reducing noise effects on fault detection and prognosis. Comprised of thirteen chapters, the authors discuss the concepts of resilience and effective operative life in the context of power electronics. The differences between reliable and efficient systems are discussed, as well as the nature of these differences in complex systems. Finally, the book explores various methods to improve the resilience of power converters. Resilient Power Electronic Systems is packed with features, including illustrations, practice problems, and PowerPoint presentations. The book also includes: A thorough introduction to the application of power electronics in various industries, as well as the concept of resilience in a power converter Comprehensive explorations of resilience against fault tolerance, including fault-tolerant power converters and resilient power converters Practical discussions of the state-of-the-art in resilient power converters, including examinations of mission-critical applications In-depth examinations of internal and external fault in power converters with mission-critical applications Resilient Power Electronic Systems is an indispensable resource for researchers, professionals, and postgraduate students studying power electronics. It’s also an ideal reference for research and development engineers working with the design and development of power electronic converters.
Resilient Power Electronic Systems
Author: Shahriyar Kaboli
Publisher: John Wiley & Sons
ISBN: 1119772184
Category : Technology & Engineering
Languages : en
Pages : 388
Book Description
Resilient Power Electronic Systems Discover an advanced reference offering a powerful novel approach to the design and use of reliable and fault-tolerant power electronic systems In Resilient Power Electronic Systems, a team of accomplished researchers deliver an insightful treatment of the challenges faced by practitioners and researchers working with power electronic converters and attempting to analyze internal and external failure mechanisms. The authors expertly present advanced techniques for reducing noise effects on fault detection and prognosis. Comprised of thirteen chapters, the authors discuss the concepts of resilience and effective operative life in the context of power electronics. The differences between reliable and efficient systems are discussed, as well as the nature of these differences in complex systems. Finally, the book explores various methods to improve the resilience of power converters. Resilient Power Electronic Systems is packed with features, including illustrations, practice problems, and PowerPoint presentations. The book also includes: A thorough introduction to the application of power electronics in various industries, as well as the concept of resilience in a power converter Comprehensive explorations of resilience against fault tolerance, including fault-tolerant power converters and resilient power converters Practical discussions of the state-of-the-art in resilient power converters, including examinations of mission-critical applications In-depth examinations of internal and external fault in power converters with mission-critical applications Resilient Power Electronic Systems is an indispensable resource for researchers, professionals, and postgraduate students studying power electronics. It’s also an ideal reference for research and development engineers working with the design and development of power electronic converters.
Publisher: John Wiley & Sons
ISBN: 1119772184
Category : Technology & Engineering
Languages : en
Pages : 388
Book Description
Resilient Power Electronic Systems Discover an advanced reference offering a powerful novel approach to the design and use of reliable and fault-tolerant power electronic systems In Resilient Power Electronic Systems, a team of accomplished researchers deliver an insightful treatment of the challenges faced by practitioners and researchers working with power electronic converters and attempting to analyze internal and external failure mechanisms. The authors expertly present advanced techniques for reducing noise effects on fault detection and prognosis. Comprised of thirteen chapters, the authors discuss the concepts of resilience and effective operative life in the context of power electronics. The differences between reliable and efficient systems are discussed, as well as the nature of these differences in complex systems. Finally, the book explores various methods to improve the resilience of power converters. Resilient Power Electronic Systems is packed with features, including illustrations, practice problems, and PowerPoint presentations. The book also includes: A thorough introduction to the application of power electronics in various industries, as well as the concept of resilience in a power converter Comprehensive explorations of resilience against fault tolerance, including fault-tolerant power converters and resilient power converters Practical discussions of the state-of-the-art in resilient power converters, including examinations of mission-critical applications In-depth examinations of internal and external fault in power converters with mission-critical applications Resilient Power Electronic Systems is an indispensable resource for researchers, professionals, and postgraduate students studying power electronics. It’s also an ideal reference for research and development engineers working with the design and development of power electronic converters.
Resilient Power Electronic Systems
Author: Shahriyar Kaboli
Publisher: John Wiley & Sons
ISBN: 1119772206
Category : Technology & Engineering
Languages : en
Pages : 388
Book Description
Resilient Power Electronic Systems Discover an advanced reference offering a powerful novel approach to the design and use of reliable and fault-tolerant power electronic systems In Resilient Power Electronic Systems, a team of accomplished researchers deliver an insightful treatment of the challenges faced by practitioners and researchers working with power electronic converters and attempting to analyze internal and external failure mechanisms. The authors expertly present advanced techniques for reducing noise effects on fault detection and prognosis. Comprised of thirteen chapters, the authors discuss the concepts of resilience and effective operative life in the context of power electronics. The differences between reliable and efficient systems are discussed, as well as the nature of these differences in complex systems. Finally, the book explores various methods to improve the resilience of power converters. Resilient Power Electronic Systems is packed with features, including illustrations, practice problems, and PowerPoint presentations. The book also includes: A thorough introduction to the application of power electronics in various industries, as well as the concept of resilience in a power converter Comprehensive explorations of resilience against fault tolerance, including fault-tolerant power converters and resilient power converters Practical discussions of the state-of-the-art in resilient power converters, including examinations of mission-critical applications In-depth examinations of internal and external fault in power converters with mission-critical applications Resilient Power Electronic Systems is an indispensable resource for researchers, professionals, and postgraduate students studying power electronics. It’s also an ideal reference for research and development engineers working with the design and development of power electronic converters.
Publisher: John Wiley & Sons
ISBN: 1119772206
Category : Technology & Engineering
Languages : en
Pages : 388
Book Description
Resilient Power Electronic Systems Discover an advanced reference offering a powerful novel approach to the design and use of reliable and fault-tolerant power electronic systems In Resilient Power Electronic Systems, a team of accomplished researchers deliver an insightful treatment of the challenges faced by practitioners and researchers working with power electronic converters and attempting to analyze internal and external failure mechanisms. The authors expertly present advanced techniques for reducing noise effects on fault detection and prognosis. Comprised of thirteen chapters, the authors discuss the concepts of resilience and effective operative life in the context of power electronics. The differences between reliable and efficient systems are discussed, as well as the nature of these differences in complex systems. Finally, the book explores various methods to improve the resilience of power converters. Resilient Power Electronic Systems is packed with features, including illustrations, practice problems, and PowerPoint presentations. The book also includes: A thorough introduction to the application of power electronics in various industries, as well as the concept of resilience in a power converter Comprehensive explorations of resilience against fault tolerance, including fault-tolerant power converters and resilient power converters Practical discussions of the state-of-the-art in resilient power converters, including examinations of mission-critical applications In-depth examinations of internal and external fault in power converters with mission-critical applications Resilient Power Electronic Systems is an indispensable resource for researchers, professionals, and postgraduate students studying power electronics. It’s also an ideal reference for research and development engineers working with the design and development of power electronic converters.
Power Systems Resilience
Author: Naser Mahdavi Tabatabaei
Publisher: Springer
ISBN: 3319944428
Category : Technology & Engineering
Languages : en
Pages : 366
Book Description
This book presents intuitive explanations of the principles and applications of power system resiliency, as well as a number of straightforward and practical methods for the impact analysis of risk events on power system operations. It also describes the challenges of modelling, distribution networks, optimal scheduling, multi-stage planning, deliberate attacks, cyber-physical systems and SCADA-based smart grids, and how to overcome these challenges. Further, it highlights the resiliency issues using various methods, including strengthening the system against high impact events with low frequency and the fast recovery of the system properties. A large number of specialists have collaborated to provide innovative solutions and research in power systems resiliency. They discuss the fundamentals and contemporary materials of power systems resiliency, theoretical and practical issues, as well as current issues and methods for controlling the risk attacks and other threats to AC power systems. The book includes theoretical research, significant results, case studies, and practical implementation processes to offer insights into electric power and engineering and energy systems. Showing how systems should respond in case of malicious attacks, and helping readers to decide on the best approaches, this book is essential reading for electrical engineers, researchers and specialists. The book is also useful as a reference for undergraduate and graduate students studying the resiliency and reliability of power systems.
Publisher: Springer
ISBN: 3319944428
Category : Technology & Engineering
Languages : en
Pages : 366
Book Description
This book presents intuitive explanations of the principles and applications of power system resiliency, as well as a number of straightforward and practical methods for the impact analysis of risk events on power system operations. It also describes the challenges of modelling, distribution networks, optimal scheduling, multi-stage planning, deliberate attacks, cyber-physical systems and SCADA-based smart grids, and how to overcome these challenges. Further, it highlights the resiliency issues using various methods, including strengthening the system against high impact events with low frequency and the fast recovery of the system properties. A large number of specialists have collaborated to provide innovative solutions and research in power systems resiliency. They discuss the fundamentals and contemporary materials of power systems resiliency, theoretical and practical issues, as well as current issues and methods for controlling the risk attacks and other threats to AC power systems. The book includes theoretical research, significant results, case studies, and practical implementation processes to offer insights into electric power and engineering and energy systems. Showing how systems should respond in case of malicious attacks, and helping readers to decide on the best approaches, this book is essential reading for electrical engineers, researchers and specialists. The book is also useful as a reference for undergraduate and graduate students studying the resiliency and reliability of power systems.
Power Electronics in Renewable Energy Systems and Smart Grid
Author: Bimal K. Bose
Publisher: John Wiley & Sons
ISBN: 1119515629
Category : Technology & Engineering
Languages : en
Pages : 756
Book Description
The comprehensive and authoritative guide to power electronics in renewable energy systems Power electronics plays a significant role in modern industrial automation and high- efficiency energy systems. With contributions from an international group of noted experts, Power Electronics in Renewable Energy Systems and Smart Grid: Technology and Applications offers a comprehensive review of the technology and applications of power electronics in renewable energy systems and smart grids. The authors cover information on a variety of energy systems including wind, solar, ocean, and geothermal energy systems as well as fuel cell systems and bulk energy storage systems. They also examine smart grid elements, modeling, simulation, control, and AI applications. The book's twelve chapters offer an application-oriented and tutorial viewpoint and also contain technology status review. In addition, the book contains illustrative examples of applications and discussions of future perspectives. This important resource: Includes descriptions of power semiconductor devices, two level and multilevel converters, HVDC systems, FACTS, and more Offers discussions on various energy systems such as wind, solar, ocean, and geothermal energy systems, and also fuel cell systems and bulk energy storage systems Explores smart grid elements, modeling, simulation, control, and AI applications Contains state-of-the-art technologies and future perspectives Provides the expertise of international authorities in the field Written for graduate students, professors in power electronics, and industry engineers, Power Electronics in Renewable Energy Systems and Smart Grid: Technology and Applications offers an up-to-date guide to technology and applications of a wide-range of power electronics in energy systems and smart grids.
Publisher: John Wiley & Sons
ISBN: 1119515629
Category : Technology & Engineering
Languages : en
Pages : 756
Book Description
The comprehensive and authoritative guide to power electronics in renewable energy systems Power electronics plays a significant role in modern industrial automation and high- efficiency energy systems. With contributions from an international group of noted experts, Power Electronics in Renewable Energy Systems and Smart Grid: Technology and Applications offers a comprehensive review of the technology and applications of power electronics in renewable energy systems and smart grids. The authors cover information on a variety of energy systems including wind, solar, ocean, and geothermal energy systems as well as fuel cell systems and bulk energy storage systems. They also examine smart grid elements, modeling, simulation, control, and AI applications. The book's twelve chapters offer an application-oriented and tutorial viewpoint and also contain technology status review. In addition, the book contains illustrative examples of applications and discussions of future perspectives. This important resource: Includes descriptions of power semiconductor devices, two level and multilevel converters, HVDC systems, FACTS, and more Offers discussions on various energy systems such as wind, solar, ocean, and geothermal energy systems, and also fuel cell systems and bulk energy storage systems Explores smart grid elements, modeling, simulation, control, and AI applications Contains state-of-the-art technologies and future perspectives Provides the expertise of international authorities in the field Written for graduate students, professors in power electronics, and industry engineers, Power Electronics in Renewable Energy Systems and Smart Grid: Technology and Applications offers an up-to-date guide to technology and applications of a wide-range of power electronics in energy systems and smart grids.
Enhancing the Resilience of the Nation's Electricity System
Author: National Academies of Sciences, Engineering, and Medicine
Publisher: National Academies Press
ISBN: 0309463076
Category : Science
Languages : en
Pages : 171
Book Description
Americans' safety, productivity, comfort, and convenience depend on the reliable supply of electric power. The electric power system is a complex "cyber-physical" system composed of a network of millions of components spread out across the continent. These components are owned, operated, and regulated by thousands of different entities. Power system operators work hard to assure safe and reliable service, but large outages occasionally happen. Given the nature of the system, there is simply no way that outages can be completely avoided, no matter how much time and money is devoted to such an effort. The system's reliability and resilience can be improved but never made perfect. Thus, system owners, operators, and regulators must prioritize their investments based on potential benefits. Enhancing the Resilience of the Nation's Electricity System focuses on identifying, developing, and implementing strategies to increase the power system's resilience in the face of events that can cause large-area, long-duration outages: blackouts that extend over multiple service areas and last several days or longer. Resilience is not just about lessening the likelihood that these outages will occur. It is also about limiting the scope and impact of outages when they do occur, restoring power rapidly afterwards, and learning from these experiences to better deal with events in the future.
Publisher: National Academies Press
ISBN: 0309463076
Category : Science
Languages : en
Pages : 171
Book Description
Americans' safety, productivity, comfort, and convenience depend on the reliable supply of electric power. The electric power system is a complex "cyber-physical" system composed of a network of millions of components spread out across the continent. These components are owned, operated, and regulated by thousands of different entities. Power system operators work hard to assure safe and reliable service, but large outages occasionally happen. Given the nature of the system, there is simply no way that outages can be completely avoided, no matter how much time and money is devoted to such an effort. The system's reliability and resilience can be improved but never made perfect. Thus, system owners, operators, and regulators must prioritize their investments based on potential benefits. Enhancing the Resilience of the Nation's Electricity System focuses on identifying, developing, and implementing strategies to increase the power system's resilience in the face of events that can cause large-area, long-duration outages: blackouts that extend over multiple service areas and last several days or longer. Resilience is not just about lessening the likelihood that these outages will occur. It is also about limiting the scope and impact of outages when they do occur, restoring power rapidly afterwards, and learning from these experiences to better deal with events in the future.
Power Electronics Diploma Interview Q&A: Career Guide
Author: Sumitra Kumari
Publisher: Sumitra Kumari
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 218
Book Description
Prepare for success in the Power Electronics industry with our comprehensive guide! Dive into a collection of interview-tested questions and detailed answers designed to equip you with the knowledge and confidence needed to ace your Power Electronics diploma Jobs interviews. Whether you're a recent graduate or a seasoned professional, this power electronics interview questions book provides valuable insights, practical scenarios, and career guidance to help you excel. Ensuring you stand out and secure your dream job in the dynamic world of Power Electronics. Your pathway to a successful career starts here! Whether you're aiming for a position as a Power Electronics Engineer, Technician, or pursuing advanced roles in Research and Development, this power electronics book is an indispensable resource to help you shine in interviews and land your dream job. Equip yourself with the knowledge and confidence needed to ace Power Electronics interviews and embark on a successful and fulfilling career in this dynamic field!
Publisher: Sumitra Kumari
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 218
Book Description
Prepare for success in the Power Electronics industry with our comprehensive guide! Dive into a collection of interview-tested questions and detailed answers designed to equip you with the knowledge and confidence needed to ace your Power Electronics diploma Jobs interviews. Whether you're a recent graduate or a seasoned professional, this power electronics interview questions book provides valuable insights, practical scenarios, and career guidance to help you excel. Ensuring you stand out and secure your dream job in the dynamic world of Power Electronics. Your pathway to a successful career starts here! Whether you're aiming for a position as a Power Electronics Engineer, Technician, or pursuing advanced roles in Research and Development, this power electronics book is an indispensable resource to help you shine in interviews and land your dream job. Equip yourself with the knowledge and confidence needed to ace Power Electronics interviews and embark on a successful and fulfilling career in this dynamic field!
Reliability of Power Electronic Converter Systems
Author: Henry Shu-hung Chung
Publisher: IET
ISBN: 1849199019
Category : Technology & Engineering
Languages : en
Pages : 502
Book Description
The main aims of power electronic converter systems (PECS) are to control, convert, and condition electrical power flow from one form to another through the use of solid state electronics. This book outlines current research into the scientific modeling, experimentation, and remedial measures for advancing the reliability, availability, system robustness, and maintainability of PECS at different levels of complexity.
Publisher: IET
ISBN: 1849199019
Category : Technology & Engineering
Languages : en
Pages : 502
Book Description
The main aims of power electronic converter systems (PECS) are to control, convert, and condition electrical power flow from one form to another through the use of solid state electronics. This book outlines current research into the scientific modeling, experimentation, and remedial measures for advancing the reliability, availability, system robustness, and maintainability of PECS at different levels of complexity.
Power Electronics in Smart Electrical Energy Networks
Author: Ryszard Michal Strzelecki
Publisher: Springer Science & Business Media
ISBN: 1848003188
Category : Technology & Engineering
Languages : en
Pages : 422
Book Description
“Power Electronics in Smart Electrical Energy Networks” introduces a new viewpoint on power electronics, re-thinking the basic philosophy governing electricity distribution systems. The proposed concept fully exploits the potential advantages of renewable energy sources and distributed generation (DG), which should not only be connected but also fully integrated into the distribution system in order to increase the efficiency, flexibility, safety, reliability and quality of the electricity and the networks. The transformation of current electricity grids into smart (resilient and interactive) networks necessitates the development, propagation and demonstration of key enabling cost-competitive technologies. A must-read for professionals in power engineering and utility industries, and researchers and postgraduates in distributed electrical power systems, the book presents the features, solutions and applications of the power electronics arrangements useful for future smart electrical energy networks.
Publisher: Springer Science & Business Media
ISBN: 1848003188
Category : Technology & Engineering
Languages : en
Pages : 422
Book Description
“Power Electronics in Smart Electrical Energy Networks” introduces a new viewpoint on power electronics, re-thinking the basic philosophy governing electricity distribution systems. The proposed concept fully exploits the potential advantages of renewable energy sources and distributed generation (DG), which should not only be connected but also fully integrated into the distribution system in order to increase the efficiency, flexibility, safety, reliability and quality of the electricity and the networks. The transformation of current electricity grids into smart (resilient and interactive) networks necessitates the development, propagation and demonstration of key enabling cost-competitive technologies. A must-read for professionals in power engineering and utility industries, and researchers and postgraduates in distributed electrical power systems, the book presents the features, solutions and applications of the power electronics arrangements useful for future smart electrical energy networks.
Pathways to a Smarter Power System
Author: Ozan Erdinc
Publisher: Academic Press
ISBN: 0081025939
Category : Technology & Engineering
Languages : en
Pages : 444
Book Description
Pathways to a Smarter Power System studies different concepts within smart grids that are used in both industry and system regulators (e.g. distribution and transmission system operators) and research. This book covers these concepts from multiple perspectives and in multiple contexts, presenting detailed technical information on renewable energy systems, distributed generation and energy storage units, methods to activate the demand side of power systems, market structure needs, and advanced planning concepts and new operational requirements, specifically for power system protection, technological evolvements, and requirements regarding technology in ICT, power electronics and control areas. This book provides energy researchers and engineers with an indispensable guide on how to apply wider perspectives to the different technological and conceptual requirements of a smarter power system. - Includes concepts regarding conceptual and technological needs and investment planning suggestions for smart grid enabling strategies - Contains new electric power system operational concepts required by industry, along with R&D studies addressing new solutions to potential operational problems - Covers pathways to smarter power systems from successful existing examples to expected short, medium and long-term possibilities
Publisher: Academic Press
ISBN: 0081025939
Category : Technology & Engineering
Languages : en
Pages : 444
Book Description
Pathways to a Smarter Power System studies different concepts within smart grids that are used in both industry and system regulators (e.g. distribution and transmission system operators) and research. This book covers these concepts from multiple perspectives and in multiple contexts, presenting detailed technical information on renewable energy systems, distributed generation and energy storage units, methods to activate the demand side of power systems, market structure needs, and advanced planning concepts and new operational requirements, specifically for power system protection, technological evolvements, and requirements regarding technology in ICT, power electronics and control areas. This book provides energy researchers and engineers with an indispensable guide on how to apply wider perspectives to the different technological and conceptual requirements of a smarter power system. - Includes concepts regarding conceptual and technological needs and investment planning suggestions for smart grid enabling strategies - Contains new electric power system operational concepts required by industry, along with R&D studies addressing new solutions to potential operational problems - Covers pathways to smarter power systems from successful existing examples to expected short, medium and long-term possibilities
Power Electronics-Enabled Autonomous Power Systems
Author: Qing-Chang Zhong
Publisher: John Wiley & Sons
ISBN: 1118803523
Category : Technology & Engineering
Languages : en
Pages : 491
Book Description
Power systems worldwide are going through a paradigm shift from centralized generation to distributed generation. This book presents the SYNDEM (i.e., synchronized and democratized) grid architecture and its technical routes to harmonize the integration of renewable energy sources, electric vehicles, storage systems, and flexible loads, with the synchronization mechanism of synchronous machines, to enable autonomous operation of power systems, and to promote energy freedom. This is a game changer for the grid. It is the sort of breakthrough — like the touch screen in smart phones — that helps to push an industry from one era to the next, as reported by Keith Schneider, a New York Times correspondent since 1982. This book contains an introductory chapter and additional 24 chapters in five parts: Theoretical Framework, First-Generation VSM (virtual synchronous machines), Second-Generation VSM, Third-Generation VSM, and Case Studies. Most of the chapters include experimental results. As the first book of its kind for power electronics-enabled autonomous power systems, it • introduces a holistic architecture applicable to both large and small power systems, including aircraft power systems, ship power systems, microgrids, and supergrids • provides latest research to address the unprecedented challenges faced by power systems and to enhance grid stability, reliability, security, resiliency, and sustainability • demonstrates how future power systems achieve harmonious interaction, prevent local faults from cascading into wide-area blackouts, and operate autonomously with minimized cyber-attacks • highlights the significance of the SYNDEM concept for power systems and beyond Power Electronics-Enabled Autonomous Power Systems is an excellent book for researchers, engineers, and students involved in energy and power systems, electrical and control engineering, and power electronics. The SYNDEM theoretical framework chapter is also suitable for policy makers, legislators, entrepreneurs, commissioners of utility commissions, energy and environmental agency staff, utility personnel, investors, consultants, and attorneys.
Publisher: John Wiley & Sons
ISBN: 1118803523
Category : Technology & Engineering
Languages : en
Pages : 491
Book Description
Power systems worldwide are going through a paradigm shift from centralized generation to distributed generation. This book presents the SYNDEM (i.e., synchronized and democratized) grid architecture and its technical routes to harmonize the integration of renewable energy sources, electric vehicles, storage systems, and flexible loads, with the synchronization mechanism of synchronous machines, to enable autonomous operation of power systems, and to promote energy freedom. This is a game changer for the grid. It is the sort of breakthrough — like the touch screen in smart phones — that helps to push an industry from one era to the next, as reported by Keith Schneider, a New York Times correspondent since 1982. This book contains an introductory chapter and additional 24 chapters in five parts: Theoretical Framework, First-Generation VSM (virtual synchronous machines), Second-Generation VSM, Third-Generation VSM, and Case Studies. Most of the chapters include experimental results. As the first book of its kind for power electronics-enabled autonomous power systems, it • introduces a holistic architecture applicable to both large and small power systems, including aircraft power systems, ship power systems, microgrids, and supergrids • provides latest research to address the unprecedented challenges faced by power systems and to enhance grid stability, reliability, security, resiliency, and sustainability • demonstrates how future power systems achieve harmonious interaction, prevent local faults from cascading into wide-area blackouts, and operate autonomously with minimized cyber-attacks • highlights the significance of the SYNDEM concept for power systems and beyond Power Electronics-Enabled Autonomous Power Systems is an excellent book for researchers, engineers, and students involved in energy and power systems, electrical and control engineering, and power electronics. The SYNDEM theoretical framework chapter is also suitable for policy makers, legislators, entrepreneurs, commissioners of utility commissions, energy and environmental agency staff, utility personnel, investors, consultants, and attorneys.