Darrell k nordstrom (31 risultati)

- Rilegato
Da: HPB-Red, Dallas, TX, U.S.A.HPB-Red
Contatta il venditoreVenditore con 5 stelleCondizione: Usato - Buono
EUR 64,68
EUR 3,23 spedizioneSpedito in U.S.A.Quantità: 1 disponibili
hardcover. Condizione: Good. Connecting readers with great books since 1972! Used textbooks may not include companion materials such as access codes, etc. May have some wear or writing/highlighting. We ship orders daily and Customer Service is our top priority.

- Rilegato
Da: Books Puddle, New York, NY, U.S.A.Books Puddle
Contatta il venditoreVenditore con 4 stelleCondizione: Nuovo
EUR 78,18
EUR 3,43 spedizioneSpedito in U.S.A.Quantità: 1 disponibili
Condizione: New. pp. 244.

- Rilegato
Da: Majestic Books, Hounslow, Regno UnitoMajestic Books
Contatta il venditoreVenditore con 4 stelleCondizione: Nuovo
EUR 77,17
EUR 7,58 spedizioneSpedito da Regno Unito a U.S.A.Quantità: 1 disponibili
Condizione: New. pp. 244 76 Illus.
Lingua: Inglese
Editore: Springer Nature (Sie), 2020
Da: Books in my Basket, New Delhi, IndiaBooks in my Basket
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 41,73
EUR 18,00 spedizioneSpedito da India a U.S.A.Quantità: 4 disponibili
Aggiungi al carrelloN.A. Condizione: New. ISBN:9783662601679.

- Brossura
Da: Ria Christie Collections, Uxbridge, Regno UnitoRia Christie Collections
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 73,32
EUR 13,97 spedizioneSpedito da Regno Unito a U.S.A.Quantità: Più di 20 disponibili
Condizione: New. In.

Groundwater Geochemistry: A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
Broder J. J. Merkel, Darrell K. Nordstrom, Britta Planer-Friedrich
- Brossura
Da: Chiron Media, Wallingford, Regno UnitoChiron Media
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 69,74
EUR 18,06 spedizioneSpedito da Regno Unito a U.S.A.Quantità: 10 disponibili
Paperback. Condizione: New.

Groundwater Geochemistry : A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
Merkel, Broder J.; Planer-Friedrich, Britta; Nordstrom, Darrell Kirk (EDT)
- Brossura
Da: GreatBookPrices, Columbia, MD, U.S.A.GreatBookPrices
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 87,55
EUR 2,27 spedizioneSpedito in U.S.A.Quantità: Più di 20 disponibili
Condizione: New.

Groundwater Geochemistry : A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
Merkel, Broder J.; Planer-Friedrich, Britta; Nordstrom, Darrell Kirk (EDT)
- Brossura
Da: GreatBookPricesUK, Woodford Green, Regno UnitoGreatBookPricesUK
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 72,72
EUR 17,49 spedizioneSpedito da Regno Unito a U.S.A.Quantità: Più di 20 disponibili
Condizione: New.

- Brossura
Da: Mispah books, Redhill, SURRE, Regno UnitoMispah books
Contatta il venditoreVenditore con 4 stelleCondizione: Nuovo
EUR 66,06
EUR 29,15 spedizioneSpedito da Regno Unito a U.S.A.Quantità: 1 disponibili
paperback. Condizione: New. NEW. SHIPS FROM MULTIPLE LOCATIONS. book.

Lingua: Inglese
Editore: Springer-Verlag Berlin and Heidelberg GmbH & Co. KG, Berlin, 2008
- Brossura
Da: Grand Eagle Retail, Bensenville, IL, U.S.A.Grand Eagle Retail
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 102,69
Spedizione gratuitaSpedito in U.S.A.Quantità: 1 disponibili
Paperback. Condizione: new. Paperback. To understand hydrochemistry and to analyze natural as well as man-made impacts on aquatic systems, hydrogeochemical models have been used since the 1960s and more frequently in recent times. Numerical groundwater flow, transport, and geochemical models are important tools besides classical… deterministic and analytical approaches. Solving complex linear or non-linear systems of equations, commonly with hundreds of unknown parameters, is a routine task for a PC. Modeling hydrogeochemical processes requires a detailed and accurate water analysis, as well as thermodynamic and kinetic data as input. Thermodynamic data, such as complex formation constants and solubility-products, are often provided as databases within the respective programs. However, the description of surface-controlled reactions (sorption, cation exchange, surface complexation) and kinetically controlled reactions requires additional input data. Unlike groundwater flow and transport models, thermodynamic models, in principal, do not need any calibration. However, considering surface-controlled or kinetically controlled reaction models might be subject to calibration. Typical problems for the application of geochemical models are: speciation determination of saturation indices adjustment of equilibria/disequilibria for minerals or gases mixing of different waters modeling the effects of temperature stoichiometric reactions (e.g. titration) reactions with solids, fluids, and gaseous phases (in open and closed systems) sorption (cation exchange, surface complexation) inverse modeling kinetically controlled reactions reactive transport Hydrogeochemical models depend on the quality of the chemical analysis, the boundary conditions presumed by the program, theoretical concepts (e.g. This second edition remains a comprehensive book on the subject. It offers beginners and advanced modelers alike a minimum theoretical background and a strong focus on the practical solution of geochemical modeling with PHREEQC. Shipping may be from multiple locations in the US or from the UK, depending on stock availability.

- Brossura
Da: Books Puddle, New York, NY, U.S.A.Books Puddle
Contatta il venditoreVenditore con 4 stelleCondizione: Nuovo
EUR 103,98
EUR 3,43 spedizioneSpedito in U.S.A.Quantità: 4 disponibili
Condizione: New. pp. 230.

- Rilegato
Da: Antiquariat Bookfarm, Löbnitz, GermaniaAntiquariat Bookfarm
Contatta il venditoreVenditore con 5 stelleCondizione: Usato - Molto buono
EUR 66,28
EUR 40,00 spedizioneSpedito da Germania a U.S.A.Quantità: 1 disponibili
Hardcover. Condizione: Gut. 2. ed. 230 S. Ehem. Bibliotheksexemplar mit Signatur und Stempel. GUTER Zustand, ein paar Gebrauchsspuren. Ex-library with stamp and library-signature. GOOD condition, some traces of use. 9783540746676 Sprache: Englisch Gewicht in Gramm: 550.

- Rilegato
Da: Antiquariat Bookfarm, Löbnitz, GermaniaAntiquariat Bookfarm
Contatta il venditoreVenditore con 5 stelleCondizione: Usato - Molto buono
EUR 66,28
EUR 40,00 spedizioneSpedito da Germania a U.S.A.Quantità: 1 disponibili
Hardcover. Condizione: Gut. 2. ed. 230 S. Ehem. Bibliotheksexemplar mit Signatur und Stempel. GUTER Zustand, ein paar Gebrauchsspuren. Ex-library with stamp and library-signature. GOOD condition, some traces of use. 9783540746676 Sprache: Englisch Gewicht in Gramm: 550.

- Rilegato
Da: Ria Christie Collections, Uxbridge, Regno UnitoRia Christie Collections
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 104,07
EUR 13,97 spedizioneSpedito da Regno Unito a U.S.A.Quantità: Più di 20 disponibili
Condizione: New. In.

Groundwater Geochemistry: A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
Merkel, Broder J./ Nordstrom, Darrell K. (Editor)/ Planer-Friedrich, Britta
- Brossura
Da: Revaluation Books, Exeter, Regno UnitoRevaluation Books
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 111,11
EUR 11,66 spedizioneSpedito da Regno Unito a U.S.A.Quantità: 2 disponibili
Paperback. Condizione: Brand New. 2nd edition. 230 pages. 9.00x6.00x0.75 inches. In Stock.

Groundwater Geochemistry | A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
- Brossura
Da: preigu, Osnabrück, Germaniapreigu
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 68,35
EUR 70,00 spedizioneSpedito da Germania a U.S.A.Quantità: 5 disponibili
Taschenbuch. Condizione: Neu. Groundwater Geochemistry | A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems | Broder J. Merkel (u. a.) | Taschenbuch | xi | Englisch | 2017 | Springer | EAN 9783662517505 | Verantwortliche Person für die EU: Springer Verlag GmbH, Tiergartenstr. 17, 69121 Heidelberg, juergen[…dot]hartmann[at]springer[dot]com | Anbieter: preigu.

Groundwater Geochemistry : A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
- Brossura
Da: AHA-BUCH GmbH, Einbeck, GermaniaAHA-BUCH GmbH
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 78,17
EUR 61,88 spedizioneSpedito da Germania a U.S.A.Quantità: 1 disponibili
Taschenbuch. Condizione: Neu. Druck auf Anfrage Neuware - Printed after ordering - To understand hydrochemistry and to analyze natural as well as man-made impacts on aquatic systems, hydrogeochemical models have been used since the 1960's and more frequently in recent times. Numerical groundwater flow, transport, and geochemical… models are important tools besides classical deterministic and analytical approaches. Solving complex linear or non-linear systems of equations, commonly with hundreds of unknown parameters, is a routine task for a PC. Modeling hydrogeochemical processes requires a detailed and accurate water analysis, as well as thermodynamic and kinetic data as input. Thermodynamic data, such as complex formation constants and solubility-products, are often provided as databases within the respective programs. However, the description of surface-controlled reactions (sorption, cation exchange, surface complexation) and kinetically controlled reactions requires additional input data. Unlike groundwater flow and transport models, thermodynamic models, in principal, do not need any calibration. However, considering surface-controlled or kinetically controlled reaction models might be subject to calibration. Typical problems for the application of geochemical models are: - speciation - determination of saturation indices - adjustment of equilibria/disequilibria for minerals or gases - mixing of different waters - modeling the effects of temperature - stoichiometric reactions (e.g. titration) - reactions with solids, fluids, and gaseous phases (in open and closed systems) - sorption (cation exchange, surface complexation) - inverse modeling - kinetically controlled reactions - reactive transport Hydrogeochemical models depend on the quality of the chemical analysis, the boundary conditions presumed by the program, theoretical concepts (e.g.

- Rilegato
Da: Mispah books, Redhill, SURRE, Regno UnitoMispah books
Contatta il venditoreVenditore con 4 stelleCondizione: Usato - Come nuovo
EUR 116,51
EUR 29,15 spedizioneSpedito da Regno Unito a U.S.A.Quantità: 1 disponibili
Hardcover. Condizione: Like New. LIKE NEW. SHIPS FROM MULTIPLE LOCATIONS. book.

Groundwater Geochemistry : A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
Merkel, Broder J.; Planer-Friedrich, Britta; Nordstrom, Darrell Kirk (EDT)
- Brossura
Da: GreatBookPricesUK, Woodford Green, Regno UnitoGreatBookPricesUK
Contatta il venditoreVenditore con 5 stelleCondizione: Usato - Come nuovo
EUR 150,13
EUR 17,49 spedizioneSpedito da Regno Unito a U.S.A.Quantità: Più di 20 disponibili
Condizione: As New. Unread book in perfect condition.

- Brossura
Da: Mispah books, Redhill, SURRE, Regno UnitoMispah books
Contatta il venditoreVenditore con 4 stelleCondizione: Usato - Come nuovo
EUR 140,53
EUR 29,15 spedizioneSpedito da Regno Unito a U.S.A.Quantità: 1 disponibili
Paperback. Condizione: Like New. LIKE NEW. SHIPS FROM MULTIPLE LOCATIONS. book.

Groundwater Geochemistry : A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
Merkel, Broder J.; Planer-Friedrich, Britta; Nordstrom, Darrell Kirk (EDT)
- Brossura
Da: GreatBookPrices, Columbia, MD, U.S.A.GreatBookPrices
Contatta il venditoreVenditore con 5 stelleCondizione: Usato - Come nuovo
EUR 172,32
EUR 2,27 spedizioneSpedito in U.S.A.Quantità: Più di 20 disponibili
Condizione: As New. Unread book in perfect condition.

Groundwater Geochemistry : A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems
- Rilegato
Da: AHA-BUCH GmbH, Einbeck, GermaniaAHA-BUCH GmbH
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 114,36
EUR 62,68 spedizioneSpedito da Germania a U.S.A.Quantità: 1 disponibili
Buch. Condizione: Neu. Druck auf Anfrage Neuware - Printed after ordering - To understand hydrochemistry and to analyze natural as well as man-made impacts on aquatic systems, hydrogeochemical models have been used since the 1960's and more frequently in recent times. Numerical groundwater flow, transport, and geochemical models… are important tools besides classical deterministic and analytical approaches. Solving complex linear or non-linear systems of equations, commonly with hundreds of unknown parameters, is a routine task for a PC. Modeling hydrogeochemical processes requires a detailed and accurate water analysis, as well as thermodynamic and kinetic data as input. Thermodynamic data, such as complex formation constants and solubility-products, are often provided as databases within the respective programs. However, the description of surface-controlled reactions (sorption, cation exchange, surface complexation) and kinetically controlled reactions requires additional input data. Unlike groundwater flow and transport models, thermodynamic models, in principal, do not need any calibration. However, considering surface-controlled or kinetically controlled reaction models might be subject to calibration. Typical problems for the application of geochemical models are: - speciation - determination of saturation indices - adjustment of equilibria/disequilibria for minerals or gases - mixing of different waters - modeling the effects of temperature - stoichiometric reactions (e.g. titration) - reactions with solids, fluids, and gaseous phases (in open and closed systems) - sorption (cation exchange, surface complexation) - inverse modeling - kinetically controlled reactions - reactive transport Hydrogeochemical models depend on the quality of the chemical analysis, the boundary conditions presumed by the program, theoretical concepts (e.g.

Lingua: Inglese
Editore: Springer-Verlag Berlin and Heidelberg GmbH & Co. KG, Berlin, 2008
- Brossura
Da: AussieBookSeller, Truganina, VIC, AustraliaAussieBookSeller
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 156,35
EUR 31,85 spedizioneSpedito da Australia a U.S.A.Quantità: 1 disponibili
Paperback. Condizione: new. Paperback. To understand hydrochemistry and to analyze natural as well as man-made impacts on aquatic systems, hydrogeochemical models have been used since the 1960s and more frequently in recent times. Numerical groundwater flow, transport, and geochemical models are important tools besides classical… deterministic and analytical approaches. Solving complex linear or non-linear systems of equations, commonly with hundreds of unknown parameters, is a routine task for a PC. Modeling hydrogeochemical processes requires a detailed and accurate water analysis, as well as thermodynamic and kinetic data as input. Thermodynamic data, such as complex formation constants and solubility-products, are often provided as databases within the respective programs. However, the description of surface-controlled reactions (sorption, cation exchange, surface complexation) and kinetically controlled reactions requires additional input data. Unlike groundwater flow and transport models, thermodynamic models, in principal, do not need any calibration. However, considering surface-controlled or kinetically controlled reaction models might be subject to calibration. Typical problems for the application of geochemical models are: speciation determination of saturation indices adjustment of equilibria/disequilibria for minerals or gases mixing of different waters modeling the effects of temperature stoichiometric reactions (e.g. titration) reactions with solids, fluids, and gaseous phases (in open and closed systems) sorption (cation exchange, surface complexation) inverse modeling kinetically controlled reactions reactive transport Hydrogeochemical models depend on the quality of the chemical analysis, the boundary conditions presumed by the program, theoretical concepts (e.g. This second edition remains a comprehensive book on the subject. It offers beginners and advanced modelers alike a minimum theoretical background and a strong focus on the practical solution of geochemical modeling with PHREEQC. Shipping may be from our Sydney, NSW warehouse or from our UK or US warehouse, depending on stock availability.

- Brossura
- Print on Demand
Da: BuchWeltWeit Ludwig Meier e.K., Bergisch Gladbach, GermaniaBuchWeltWeit Ludwig Meier e.K.
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 69,54
EUR 23,00 spedizioneSpedito da Germania a U.S.A.Quantità: 2 disponibili
Taschenbuch. Condizione: Neu. This item is printed on demand - it takes 3-4 days longer - Neuware -To understand hydrochemistry and to analyze natural as well as man-made impacts on aquatic systems, hydrogeochemical models have been used since the 1960's and more frequently in recent times. Numerical groundwater flow, transport,… and geochemical models are important tools besides classical deterministic and analytical approaches. Solving complex linear or non-linear systems of equations, commonly with hundreds of unknown parameters, is a routine task for a PC. Modeling hydrogeochemical processes requires a detailed and accurate water analysis, as well as thermodynamic and kinetic data as input. Thermodynamic data, such as complex formation constants and solubility-products, are often provided as databases within the respective programs. However, the description of surface-controlled reactions (sorption, cation exchange, surface complexation) and kinetically controlled reactions requires additional input data. Unlike groundwater flow and transport models, thermodynamic models, in principal, do not need any calibration. However, considering surface-controlled or kinetically controlled reaction models might be subject to calibration. Typical problems for the application of geochemical models are: - speciation - determination of saturation indices - adjustment of equilibria/disequilibria for minerals or gases - mixing of different waters - modeling the effects of temperature - stoichiometric reactions (e.g. titration) - reactions with solids, fluids, and gaseous phases (in open and closed systems) - sorption (cation exchange, surface complexation) - inverse modeling - kinetically controlled reactions - reactive transport Hydrogeochemical models depend on the quality of the chemical analysis, the boundary conditions presumed by the program, theoretical concepts (e.g. 244 pp. Englisch.

- Brossura
- Print on Demand
Da: Majestic Books, Hounslow, Regno UnitoMajestic Books
Contatta il venditoreVenditore con 4 stelleCondizione: Nuovo
EUR 105,33
EUR 7,58 spedizioneSpedito da Regno Unito a U.S.A.Quantità: 4 disponibili
Condizione: New. Print on Demand pp. 230.

- Brossura
- Print on Demand
Da: moluna, Greven, Germaniamoluna
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 64,33
EUR 48,99 spedizioneSpedito da Germania a U.S.A.Quantità: Più di 20 disponibili
Kartoniert / Broschiert. Condizione: New. Dieser Artikel ist ein Print on Demand Artikel und wird nach Ihrer Bestellung fuer Sie gedruckt. Fills a gap in modern text books, focusing on the solution of practical hydrogeochemical questions with the help of PhreeqCTo understand hydrochemistry and to analyze natural as well as man-m…ade impacts on aquatic systems, hydrogeochemical models have b.

- Brossura
- Print on Demand
Da: Biblios, frankfurt am main, HESSE, GermaniaBiblios
Contatta il venditoreVenditore con 4 stelleCondizione: Nuovo
EUR 108,37
EUR 9,95 spedizioneSpedito da Germania a U.S.A.Quantità: 4 disponibili
Condizione: New. PRINT ON DEMAND pp. 230.

- Rilegato
- Print on Demand
Da: BuchWeltWeit Ludwig Meier e.K., Bergisch Gladbach, GermaniaBuchWeltWeit Ludwig Meier e.K.
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 106,99
EUR 23,00 spedizioneSpedito da Germania a U.S.A.Quantità: 2 disponibili
Buch. Condizione: Neu. This item is printed on demand - it takes 3-4 days longer - Neuware -To understand hydrochemistry and to analyze natural as well as man-made impacts on aquatic systems, hydrogeochemical models have been used since the 1960's and more frequently in recent times. Numerical groundwater flow, transport, and ge…ochemical models are important tools besides classical deterministic and analytical approaches. Solving complex linear or non-linear systems of equations, commonly with hundreds of unknown parameters, is a routine task for a PC. Modeling hydrogeochemical processes requires a detailed and accurate water analysis, as well as thermodynamic and kinetic data as input. Thermodynamic data, such as complex formation constants and solubility-products, are often provided as databases within the respective programs. However, the description of surface-controlled reactions (sorption, cation exchange, surface complexation) and kinetically controlled reactions requires additional input data. Unlike groundwater flow and transport models, thermodynamic models, in principal, do not need any calibration. However, considering surface-controlled or kinetically controlled reaction models might be subject to calibration. Typical problems for the application of geochemical models are: - speciation - determination of saturation indices - adjustment of equilibria/disequilibria for minerals or gases - mixing of different waters - modeling the effects of temperature - stoichiometric reactions (e.g. titration) - reactions with solids, fluids, and gaseous phases (in open and closed systems) - sorption (cation exchange, surface complexation) - inverse modeling - kinetically controlled reactions - reactive transport Hydrogeochemical models depend on the quality of the chemical analysis, the boundary conditions presumed by the program, theoretical concepts (e.g. 244 pp. Englisch.

- Brossura
- Print on Demand
Da: buchversandmimpf2000, Emtmannsberg, BAYE, Germaniabuchversandmimpf2000
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 74,89
EUR 60,00 spedizioneSpedito da Germania a U.S.A.Quantità: 1 disponibili
Taschenbuch. Condizione: Neu. This item is printed on demand - Print on Demand Titel. Neuware -To understand hydrochemistry and to analyze natural as well as man-made impacts on aquatic systems, hydrogeochemical models have been used since the 1960¿s and more frequently in recent times. Numerical groundwater flow, transport, and… geochemical models are important tools besides classical deterministic and analytical approaches. Solving complex linear or non-linear systems of equations, commonly with hundreds of unknown parameters, is a routine task for a PC. Modeling hydrogeochemical processes requires a detailed and accurate water analysis, as well as thermodynamic and kinetic data as input. Thermodynamic data, such as complex formation constants and solubility-products, are often provided as databases within the respective programs. However, the description of surface-controlled reactions (sorption, cation exchange, surface complexation) and kinetically controlled reactions requires additional input data. Unlike groundwater flow and transport models, thermodynamic models, in principal, do not need any calibration. However, considering surface-controlled or kinetically controlled reaction models might be subject to calibration. Typical problems for the application of geochemical models are: ¿ speciation ¿ determination of saturation indices ¿ adjustment of equilibria/disequilibria for minerals or gases ¿ mixing of different waters ¿ modeling the effects of temperature ¿ stoichiometric reactions (e.g. titration) ¿ reactions with solids, fluids, and gaseous phases (in open and closed systems) ¿ sorption (cation exchange, surface complexation) ¿ inverse modeling ¿ kinetically controlled reactions ¿ reactive transport Hydrogeochemical models depend on the quality of the chemical analysis, the boundary conditions presumed by the program, theoretical concepts (e.g.Springer-Verlag KG, Sachsenplatz 4-6, 1201 Wien 244 pp. Englisch.

- Brossura
- Print on Demand
Da: moluna, Greven, Germaniamoluna
Contatta il venditoreVenditore con 5 stelleCondizione: Nuovo
EUR 93,00
EUR 48,99 spedizioneSpedito da Germania a U.S.A.Quantità: Più di 20 disponibili
Bundle. Condizione: New. Dieser Artikel ist ein Print on Demand Artikel und wird nach Ihrer Bestellung fuer Sie gedruckt. Fills a gap in modern text books, focusing on the solution of practical hydrogeochemical questions with the help of PhreeqCTo understand hydrochemistry and to analyze natural as well as man-made impacts on aq…uatic systems, hydrogeochemical models have b.