Cogeneration and Polygeneration Systems

Cogeneration and Polygeneration Systems
Author: Majid Amidpour,Mohammad Hasan Khoshgoftar Manesh
Publsiher: Academic Press
Total Pages: 416
Release: 2020-11-23
ISBN 10: 0128172495
ISBN 13: 9780128172490
Language: EN, FR, DE, ES & NL

Cogeneration and Polygeneration Systems Book Review:

Cogeneration and Polygeneration Systems explores the suite of state-of-the-art modeling, design, analysis and optimization procedures for creating and retooling optimally efficient combined heat and power (CHP) and polygeneration energy systems. The book adopts exergetic and thermoeconomic analysis and related modeling and simulation tools to inform performance and systems design in modern cogeneration plants. Chapters provide a methodical approach to the design, operation and troubleshooting of cogeneration systems when they are integrated with industrial processes. Cogeneration targets, environmental impacts, total site integration, and availability and reliability issues are addressed in-depth. Explores exergetic and exergoeconomic analysis for optimization purposes of CHP systems Addresses availability and reliability issues within cogeneration systems Reviews modern polygeneration systems based on renewable energy resources and fuel cells

Polygeneration Systems

Polygeneration Systems
Author: Francesco Calise,Laura Vanoli,Massimo Dentice D’Accadia,Maria Vicidomini
Publsiher: Academic Press
Total Pages: 452
Release: 2021-09-22
ISBN 10: 0128206268
ISBN 13: 9780128206263
Language: EN, FR, DE, ES & NL

Polygeneration Systems Book Review:

The support for polygeneration lies in the possibility of integrating different technologies into a single energy system, to maximize the utilization of both fossil and renewable fuels. A system that delivers multiple forms of energy to users, maximizing the overall efficiency makes polygeneration an emerging and viable option for energy consuming industries. Polygeneration Systems: Design, Processes and Technologies provides simple and advanced calculation techniques to evaluate energy, environmental and economic performance of polygeneration systems under analysis. With specific design guidelines for each type of polygeneration system and experimental performance data, referred both to single components and overall systems, this title covers all aspects of polygeneration from design to operation, optimization and practical implementation. Giving different aspects of both fossil and non-fossil fuel based polygeneration and the wider area of polygeneration processes, this book helps readers learn general principles to specific system design and development through analysis of case studies, examples, simulation characteristics and thermodynamic and economic data. Detailed economic data for technology to assist developing feasibility studies regarding the possible application of polygeneration technologies Offers a comprehensive list of all current numerical and experimental results of polygeneration available Includes simulation models, cost figures, demonstration projects and test standards for designers and researchers to validate their own models and/or to test the reliability of their results

Optimal Design and Operation of Energy Polygeneration Systems

Optimal Design and Operation of Energy Polygeneration Systems
Author: Yang Chen (Ph. D.),Massachusetts Institute of Technology. Department of Chemical Engineering
Publsiher: Unknown
Total Pages: 319
Release: 2013
ISBN 10: 1928374650XXX
ISBN 13: OCLC:844349540
Language: EN, FR, DE, ES & NL

Optimal Design and Operation of Energy Polygeneration Systems Book Review:

Polygeneration is a concept where multiple energy products are generated in a single plant by tightly integrating multiple processes into one system. Compared to conventional single-product systems, polygeneration systems have many economic advantages, such as potentially high profitability and high viability when exposed to market fluctuations. The optimal design of an energy polygeneration system that converts coal and biomass to electricity, liquid fuels (naphtha and diesel) and chemical products (methanol) with carbon dioxide (CO2) capture under different economic scenarios is investigated. In this system, syngas is produced by gasification of coal and/or biomass; purified by a cleaning process to remove particles, mercury, sulfur and CO2; and then split to different downstream sections such as the gas turbine, FT process and the methanol process. In this thesis, the optimal design with the highest net present value (NPV) is determined by optimizing equipment capacities, stream flow rates and stream split fractions. The case study results for static polygeneration systems reveal that the optimal design of polygeneration systems is strongly influenced by economic conditions such as feedstock prices, product prices, and potential emissions penalties for CO2. Over the range of economic scenarios considered, it can be optimal to produce a mixture of electricity, liquid fuels, and methanol; only one each; or mixtures in-between. The optimal biomass/coal feed ratio significantly increases when the carbon tax increases or the biomass price decreases. An economic analysis of the optimal static polygeneration designs yielded a slightly higher NPV than comparable single-product plants. The flexible operation is then considered for the energy polygeneration system. In real applications, product prices can fluctuate significantly seasonally or even daily. The profitability of the polygeneration system can potentially be increased if some operational flexibility is introduced, such as adjusting the product mix in response to changing market prices. The major challenge of this flexible design is the determination of the optimal trade-off between flexibility and capital cost because higher flexibility typically implies both higher product revenues and larger equipment sizes. A two-stage optimization formulation for is used for the optimal design and operation of flexible energy polygeneration systems, which simultaneously optimizes design decision variables (e.g., equipment sizes) and operational decision variables (e.g., production rate schedules) in several different market scenarios to achieve the best expected economic performance. Case study results for flexible polygeneration systems show that for most of market scenarios, flexible polygeneration systems achieved higher expected NPVs than static polygeneration systems. Furthermore, even higher expected NPVs could be obtained with increases in flexibility. The flexible polygeneration optimization problem is a potentially large-scale nonconvex mixed-integer nonlinear program (MINLP) and cannot be solved to global optimality by state-of-the-art global optimization solvers, such as BARON, within a reasonable time. The nonconvex generalized Benders decomposition (NGBD) method can exploit the special structure of this mathematical programming problem and enable faster solution. In this method, the nonconvex MINLP is relaxed into a convex lower bounding problem which can be further reformulated into a relaxed master problem according to the principles of projection, dualization and relaxation. The relaxed master problem yields an nondecreasing sequence of lower bounds for the original problem. And an nonincreasing sequence of upper bounds is obtained by solving primal problems, which are generated by fixing the integer variables in the original problem. A global optimal objective is obtained when the lower and upper bounds coincide. The decomposition algorithm guarantees to find an E-optimal solution in a finite number of iterations. In this thesis, several enhanced decomposition methods with improved relaxed master problems are developed, including enhanced NGBD with primal dual information (NGBD-D), piecewise convex relaxation (NGBD-PCR) and lift-and-project cuts (NGBD-LAP). In NGBD-D, additional dual information is introduced into the relaxed master problem by solving the relaxed dual of primal problem. The soobtained primal dual cuts can significantly improve the convergence rate of the algorithm. In NGBD-PCR, the piecewise McCormick relaxation technique is integrated into the NGBD algorithm to reduce the gap between the original problem and its convex relaxation. The domains of variables in bilinear functions can be uniformly partitioned before solution or dynamically partitioned in the algorithm by using the intermediate solution information. In NGBD-LAP, lift-and-project cuts are employed for solving the piecewise lower bounding problem. In all three enhanced decomposition algorithms, there is a trade-off between tighter relaxations and more solution times for subproblems. The computational advantages of the enhanced decomposition methods are demonstrated via case studies on the flexible polygeneration problems. The computational results show that, while NGBD can solve problems that are intractable for a state-ofthe- art global optimization solver (BARON), the enhanced NGBD algorithms help to reduce the solution time by up to an order of magnitude compared to NGBD. And enhanced NGBD algorithms solved the large-scale nonconvex MINLPs to [epsilon]-optimality in practical times (e.g., a problem with 70 binary variables and 44136 continuous variables was solved within 19 hours).

Cogeneration and Polygeneration Systems

Cogeneration and Polygeneration Systems
Author: Majid Amidpour,Mohammad Hasan Khoshgoftar Manesh
Publsiher: Academic Press
Total Pages: 406
Release: 2020-11-03
ISBN 10: 0128172509
ISBN 13: 9780128172506
Language: EN, FR, DE, ES & NL

Cogeneration and Polygeneration Systems Book Review:

Cogeneration and Polygeneration Systems explores the suite of state-of-the-art modeling, design, analysis and optimization procedures for creating and retooling optimally efficient combined heat and power (CHP) and polygeneration energy systems. The book adopts exergetic and thermoeconomic analysis and related modeling and simulation tools to inform performance and systems design in modern cogeneration plants. Chapters provide a methodical approach to the design, operation and troubleshooting of cogeneration systems when they are integrated with industrial processes. Cogeneration targets, environmental impacts, total site integration, and availability and reliability issues are addressed in-depth. Explores exergetic and exergoeconomic analysis for optimization purposes of CHP systems Addresses availability and reliability issues within cogeneration systems Reviews modern polygeneration systems based on renewable energy resources and fuel cells

Polygeneration with Polystorage

Polygeneration with Polystorage
Author: Kaveh Rajab Khalilpour
Publsiher: Academic Press
Total Pages: 583
Release: 2018-11-27
ISBN 10: 0128133074
ISBN 13: 9780128133071
Language: EN, FR, DE, ES & NL

Polygeneration with Polystorage Book Review:

Polygeneration with Polystorage: For Energy and Chemicals addresses the problem of both traditional and dispersed generation with a broad, multidisciplinary perspective. As the first book to thoroughly focus on the topic of polygeneration, users will find the problem presented from different scientific and technical domains down to both macro and micro levels. Detailed analyses and state-of-the-art developments in specific fields are included, focusing on storage in conventional energy supply chains and demand-side renewable polygeneration systems, management advice and the necessary market mechanisms needed to support them. This reference is useful for academics and professionals in conventional and unconventional energy systems. Includes an outlined framework towards polygeneration and polystorage down to both micro and macro levels Contains fluid and continuous chapters that provide detailed analysis and a review of the state-of-the-art developments in specific fields Addresses the wider global view of research advancement and potential in the role of polygeneration and polystorage in the move toward sustainability

Technoeconomic Assessment of Polygeneration Systems

Technoeconomic Assessment of Polygeneration Systems
Author: Cristina Gil de Moya
Publsiher: Unknown
Total Pages: 135
Release: 2008
ISBN 10: 1928374650XXX
ISBN 13: OCLC:1120620090
Language: EN, FR, DE, ES & NL

Technoeconomic Assessment of Polygeneration Systems Book Review:

This work focuses on the production of F-T diesel from wood biomass, considering three different systems: production of wood pellets, bioslurry via fast pyrolysis, and use of untreated biomass. This study aims to find the most energy efficient way in which the wood biomass can be transformed into synthetic diesel, and the importance of every step taking part in the entire system. The assessment of these routes considers the whole chain: extraction of biomass, transport of raw material to a local plant, pre-treatment if necessary, transport to the central gasification plant, gasification process and Fischer-Tropsch synthesis. The three BTL routes are compared by means of Primary Energy Factors (PEF). In order to obtain reliable results, the transport distance from the local plant to the central gasification plant and the moisture content of biomass have been modified. Primary energy factors, only taking into account the non-renewable part, have also been calculated. The results show that gasification process and Fischer-Tropsch synthesis are the decisive steps. At the moment, the use of untreated biomass seems to be the best option in spite of the high transport energy. However, when the moisture content is high (about 60%) and only the non-renewable part is considered then, the second route, which is based on bioslurry production, is the most energy efficient.

Island based Polygeneration Systems

Island based Polygeneration Systems
Author: Anonim
Publsiher: Unknown
Total Pages: 135
Release: 2021
ISBN 10: 9789178737529
ISBN 13: 9178737524
Language: EN, FR, DE, ES & NL

Island based Polygeneration Systems Book Review:

Advances in Energy Systems Engineering

Advances in Energy Systems Engineering
Author: Georgios M. Kopanos,Pei Liu,Michael C. Georgiadis
Publsiher: Springer
Total Pages: 839
Release: 2016-10-17
ISBN 10: 3319428039
ISBN 13: 9783319428031
Language: EN, FR, DE, ES & NL

Advances in Energy Systems Engineering Book Review:

This book provides a scientific framework for integrated solutions to complex energy problems. It adopts a holistic, systems-based approach to demonstrate the potential of an energy systems engineering approach to systematically quantify different options at various levels of complexity (technology, plant, energy supply chain, mega-system). Utilizing modeling, simulation and optimization-based frameworks, along with a number of real-life applications, it focuses on advanced energy systems including energy supply chains, integrated biorefineries, energy planning and scheduling approaches and urban energy systems. Featuring contributions from leading researchers in the field, this work is useful for academics, researchers, industry practitioners in energy systems engineering, and all those who are involved in model-based energy systems.

A Polygeneration Process Concept for Hybrid Solar and Biomass Power Plant

A Polygeneration Process Concept for Hybrid Solar and Biomass Power Plant
Author: Umakanta Sahoo
Publsiher: John Wiley & Sons
Total Pages: 294
Release: 2018-08-09
ISBN 10: 1119536308
ISBN 13: 9781119536307
Language: EN, FR, DE, ES & NL

A Polygeneration Process Concept for Hybrid Solar and Biomass Power Plant Book Review:

The global warming phenomenon as a significant sustainability issue is gaining worldwide support for development of renewable energy technologies. The term “polygeneration” is referred to as “an energy supply system, which delivers more than one form of energy to the final user.” For example, electricity, cooling and desalination can be delivered from a polygeneration process. The polygeneration process in a hybrid solar thermal power plant can deliver electricity with less impact on the environment compared to a conventional fossil fuel-based power generating system. It is also THE next generation energy production technique with the potential to overcome the undesirable intermittence of renewable energy systems. In this study, the polygeneration process simultaneous production of power, vapor absorption refrigeration (VAR) cooling and multi-effect humidification and dehumidification (MEHD) desalination system from different heat sources in hybrid solar-biomass (HSB) system with higher energy efficiencies (energy and exergy), primary energy savings (PES) and payback period are investigated, focusing on several aspects associated with hybrid solar-biomass power generation installations, such as wide availability of biomass resources and solar direct normal irradiance (DNI), and other technologies. Thermodynamic evaluation (energy and exergy) of HSB power has also been investigated, along with the VAR cooling system, the modelling, simulation, optimization and cost analysis of the polygeneration hybrid solar biomass system, all accompanied by multiple case studies and examples for practical applications. This volume provides the researcher, student and engineer with the intellectual tool needed for understanding new ideas in this rapidly emerging field. The book is also intended to serve as a general source and reference book for the professional (consultant, designer, contractor etc.) who is working in the field of solar thermal, biomass, power plant, polygeneration, cooling and process heat. It is a must-have for anyone working in this field.

Energy Systems Engineering

Energy Systems Engineering
Author: Anonim
Publsiher: John Wiley & Sons
Total Pages: 348
Release: 2008-10-13
ISBN 10: 9783527316946
ISBN 13: 3527316949
Language: EN, FR, DE, ES & NL

Energy Systems Engineering Book Review:

Inspired by the leading authority in the field, the Centre for Process Systems Engineering at Imperial College London, this book includes theoretical developments, algorithms, methodologies and tools in process systems engineering and applications from the chemical, energy, molecular, biomedical and other areas. It spans a whole range of length scales seen in manufacturing industries, from molecular and nanoscale phenomena to enterprise-wide optimization and control. As such, this will appeal to a broad readership, since the topic applies not only to all technical processes but also due to the interdisciplinary expertise required to solve the challenge. The ultimate reference work for years to come.

Model Predictive Control Strategies for Polygeneration Systems and Microgrids

Model Predictive Control Strategies for Polygeneration Systems and Microgrids
Author: Ramanunni Parakkal Menon
Publsiher: Unknown
Total Pages: 135
Release: 2017
ISBN 10: 1928374650XXX
ISBN 13: OCLC:1004967638
Language: EN, FR, DE, ES & NL

Model Predictive Control Strategies for Polygeneration Systems and Microgrids Book Review:

Mots-clés de l'auteur: Polygeneration ; Demand Response ; Model Predictive Control ; Distributed Generation ; Microgrid.

Modelling Environment for the Design and Optimisation of Energy Polygeneration Systems

Modelling Environment for the Design and Optimisation of Energy Polygeneration Systems
Author: Jordi Ortiga Guillén,Universitat Rovira i Virgili. Departament d'Enginyeria Mecànica,Universitat Rovira i Virgili. Escola Tècnica Superior d'Enginyeria de Tarragona
Publsiher: Unknown
Total Pages: 290
Release: 2010
ISBN 10: 9788469354148
ISBN 13: 8469354140
Language: EN, FR, DE, ES & NL

Modelling Environment for the Design and Optimisation of Energy Polygeneration Systems Book Review:

Development and Analysis of Micro Polygeneration Systems and Adsorption Chillers

Development and Analysis of Micro Polygeneration Systems and Adsorption Chillers
Author: Kyle Gluesenkamp
Publsiher: Unknown
Total Pages: 135
Release: 2012
ISBN 10: 1928374650XXX
ISBN 13: OCLC:854752455
Language: EN, FR, DE, ES & NL

Development and Analysis of Micro Polygeneration Systems and Adsorption Chillers Book Review:

A Polygeneration Process Concept for Hybrid Solar and Biomass Power Plant

A Polygeneration Process Concept for Hybrid Solar and Biomass Power Plant
Author: Umakanta Sahoo
Publsiher: John Wiley & Sons
Total Pages: 294
Release: 2018-08-03
ISBN 10: 1119536332
ISBN 13: 9781119536338
Language: EN, FR, DE, ES & NL

A Polygeneration Process Concept for Hybrid Solar and Biomass Power Plant Book Review:

The global warming phenomenon as a significant sustainability issue is gaining worldwide support for development of renewable energy technologies. The term “polygeneration” is referred to as “an energy supply system, which delivers more than one form of energy to the final user.” For example, electricity, cooling and desalination can be delivered from a polygeneration process. The polygeneration process in a hybrid solar thermal power plant can deliver electricity with less impact on the environment compared to a conventional fossil fuel-based power generating system. It is also THE next generation energy production technique with the potential to overcome the undesirable intermittence of renewable energy systems. In this study, the polygeneration process simultaneous production of power, vapor absorption refrigeration (VAR) cooling and multi-effect humidification and dehumidification (MEHD) desalination system from different heat sources in hybrid solar-biomass (HSB) system with higher energy efficiencies (energy and exergy), primary energy savings (PES) and payback period are investigated, focusing on several aspects associated with hybrid solar-biomass power generation installations, such as wide availability of biomass resources and solar direct normal irradiance (DNI), and other technologies. Thermodynamic evaluation (energy and exergy) of HSB power has also been investigated, along with the VAR cooling system, the modelling, simulation, optimization and cost analysis of the polygeneration hybrid solar biomass system, all accompanied by multiple case studies and examples for practical applications. This volume provides the researcher, student and engineer with the intellectual tool needed for understanding new ideas in this rapidly emerging field. The book is also intended to serve as a general source and reference book for the professional (consultant, designer, contractor etc.) who is working in the field of solar thermal, biomass, power plant, polygeneration, cooling and process heat. It is a must-have for anyone working in this field.

Efficiency of Biomass Energy

Efficiency of Biomass Energy
Author: Krzysztof J. Ptasinski
Publsiher: John Wiley & Sons
Total Pages: 784
Release: 2016-08-30
ISBN 10: 1119118158
ISBN 13: 9781119118152
Language: EN, FR, DE, ES & NL

Efficiency of Biomass Energy Book Review:

Details energy and exergy efficiencies of all major aspects of bioenergy systems Covers all major bioenergy processes starting from photosynthesis and cultivation of biomass feedstocks and ending with final bioenergy products, like power, biofuels, and chemicals Each chapter includes historical developments, chemistry, major technologies, applications as well as energy, environmental and economic aspects in order to serve as an introduction to biomass and bioenergy A separate chapter introduces a beginner in easy accessible way to exergy analysis and the similarities and differences between energy and exergy efficiencies are underlined Includes case studies and illustrative examples of 1st, 2nd, and 3rd generation biofuels production, power and heat generation (thermal plants, fuel cells, boilers), and biorefineries Traditional fossil fuels-based technologies are also described in order to compare with the corresponding bioenergy systems

ECOS 2012 The 25th International Conference on Efficiency Cost Optimization and Simulation of Energy Conversion Systems and Processes Perugia June 26th June 29th 2012

ECOS 2012 The 25th International Conference on Efficiency  Cost  Optimization and Simulation of Energy Conversion Systems and Processes  Perugia  June 26th June 29th  2012
Author: Enrico Sciubba,Giampaolo Manfrida,Umberto Desideri
Publsiher: Firenze University Press
Total Pages: 219
Release: 2012
ISBN 10: 9788866553229
ISBN 13: 8866553220
Language: EN, FR, DE, ES & NL

ECOS 2012 The 25th International Conference on Efficiency Cost Optimization and Simulation of Energy Conversion Systems and Processes Perugia June 26th June 29th 2012 Book Review:

Handbook of CO2 in Power Systems

Handbook of CO2 in Power Systems
Author: Qipeng P. Zheng,Steffen Rebennack,Panos M. Pardalos,Mario V. F. Pereira,Niko A. Iliadis
Publsiher: Springer Science & Business Media
Total Pages: 400
Release: 2012-06-05
ISBN 10: 3642274315
ISBN 13: 9783642274312
Language: EN, FR, DE, ES & NL

Handbook of CO2 in Power Systems Book Review:

The Handbook of CO2in Power Systems' objective is to include the state-of-the-art developments that occurred in power systems taking CO2emission into account. The book includes power systems operation modeling with CO2emissions considerations, CO2market mechanism modeling, CO2regulation policy modeling, carbon price forecasting, and carbon capture modeling. For each of the subjects, at least one article authored by a world specialist on the specific domain is included.

Optimal synthesis of multi product energy systems under neutrosophic environment

Optimal synthesis of multi product energy systems under neutrosophic environment
Author: John Frederick D. Tapia
Publsiher: Infinite Study
Total Pages: 15
Release: 2022
ISBN 10: 1928374650XXX
ISBN 13: 9182736450XXX
Language: EN, FR, DE, ES & NL

Optimal synthesis of multi product energy systems under neutrosophic environment Book Review:

This study develops a novel neutrosophic optimization model to address these uncertainties. It involves treating product demands, waste targets, and economic benefits as interval-valued neutrosophic numbers. Three characteristic functions under the neutrosophic environment are considered: membership, non-membership, and indeterminacy. Two case studies are used to illustrate the model: one involves a polygeneration plant, and another involves an integrated biorefinery. Sensitivity analyses were performed for each case, adjusting the levels of risk tolerance in the neutrosophic environment.

18th European Symposium on Computer Aided Process Engineering

18th European Symposium on Computer Aided Process Engineering
Author: Bertrand Braunschweig,Xavier Joulia
Publsiher: Elsevier
Total Pages: 1205
Release: 2008
ISBN 10: 0444532277
ISBN 13: 9780444532275
Language: EN, FR, DE, ES & NL

18th European Symposium on Computer Aided Process Engineering Book Review:

The 18th European Symposium on Computer Aided Process Engineering contains papers presented at the 18th European Symposium of Computer Aided Process Engineering (ESCAPE 18) held in Lyon, France, from 1-4 June 2008. The ESCAPE series brings the latest innovations and achievements by leading professionals from the industrial and academic communities. The series serves as a forum for engineers, scientists, researchers, managers and students from academia and industry to: - present new computer aided methods, algorithms, techniques related to process and product engineering, - discuss innovative concepts, new challenges, needs and trends in the area of CAPE. This research area bridges fundamental sciences (physics, chemistry, thermodynamics, applied mathematics and computer sciences) with the various aspects of process and product engineering. The special theme for ESCAPE-18 is CAPE for the Users! CAPE systems are to be put in the hands of end users who need functionality and assistance beyond the scientific and technological capacities which are at the core of the systems. The four main topics are: - off-line systems for synthesis and design, - on-line systems for control and operation, - computational and numerical solutions strategies, - integrated and multi-scale modelling and simulation, Two general topics address the impact of CAPE tools and methods on Society and Education. * CD-ROM that accompanies the book contains all research papers and contributions * International in scope with guest speeches and keynote talks from leaders in science and industry * Presents papers covering the latest research, key top areas and developments in Computer Aided Process Engineering

Sustainable Energy Technology and Policies

Sustainable Energy Technology and Policies
Author: Sudipta De,Santanu Bandyopadhyay,Mohsen Assadi,Deb A Mukherjee
Publsiher: Springer
Total Pages: 450
Release: 2017-12-21
ISBN 10: 9811071888
ISBN 13: 9789811071881
Language: EN, FR, DE, ES & NL

Sustainable Energy Technology and Policies Book Review:

This book presents a state-of-the-art compilation focusing on both technological and policy aspects of sustainable energy production and consumption, which deals with issues like the need for and planning of smart cities, alternative transport fuel options, sustainable power production, pollution control technologies etc. The book comprises contributions from experts from all over the world, and addresses energy sustainability from different viewpoints. Specifically, the book focuses on energy sustainability in the Indian scenario with a background of the global perspective. Contributions from academia, policy makers and industry are included to address the challenge from different perspectives. The contents of this book will prove useful to researchers, professionals, and policy makers working in the area of green and sustainable energy.