Author: Roberto Marquardt
Publisher: Elsevier
ISBN: 0128172355
Category : Science
Languages : en
Pages : 376
Book Description
Molecular Spectroscopy and Quantum Dynamics, an exciting new work edited by Professors Martin Quack and Roberto Marquardt, contains comprehensive information on the current state-of-the-art experimental and theoretical methods and techniques used to unravel ultra-fast phenomena in atoms, molecules and condensed matter, along with future perspectives on the field. - Contains new insights into the quantum dynamics and spectroscopy of electronic and nuclear motion - Presents the most recent developments in the detection and interpretation of ultra-fast phenomena - Includes a discussion of the importance of these phenomena for the understanding of chemical reaction dynamics and kinetics in relation to molecular spectra and structure
Molecular Spectroscopy and Quantum Dynamics
Author: Roberto Marquardt
Publisher: Elsevier
ISBN: 0128172355
Category : Science
Languages : en
Pages : 376
Book Description
Molecular Spectroscopy and Quantum Dynamics, an exciting new work edited by Professors Martin Quack and Roberto Marquardt, contains comprehensive information on the current state-of-the-art experimental and theoretical methods and techniques used to unravel ultra-fast phenomena in atoms, molecules and condensed matter, along with future perspectives on the field. - Contains new insights into the quantum dynamics and spectroscopy of electronic and nuclear motion - Presents the most recent developments in the detection and interpretation of ultra-fast phenomena - Includes a discussion of the importance of these phenomena for the understanding of chemical reaction dynamics and kinetics in relation to molecular spectra and structure
Publisher: Elsevier
ISBN: 0128172355
Category : Science
Languages : en
Pages : 376
Book Description
Molecular Spectroscopy and Quantum Dynamics, an exciting new work edited by Professors Martin Quack and Roberto Marquardt, contains comprehensive information on the current state-of-the-art experimental and theoretical methods and techniques used to unravel ultra-fast phenomena in atoms, molecules and condensed matter, along with future perspectives on the field. - Contains new insights into the quantum dynamics and spectroscopy of electronic and nuclear motion - Presents the most recent developments in the detection and interpretation of ultra-fast phenomena - Includes a discussion of the importance of these phenomena for the understanding of chemical reaction dynamics and kinetics in relation to molecular spectra and structure
Molecular Quantum Dynamics
Author: Fabien Gatti
Publisher: Springer Science & Business Media
ISBN: 3642452906
Category : Science
Languages : en
Pages : 281
Book Description
This book focuses on current applications of molecular quantum dynamics. Examples from all main subjects in the field, presented by the internationally renowned experts, illustrate the importance of the domain. Recent success in helping to understand experimental observations in fields like heterogeneous catalysis, photochemistry, reactive scattering, optical spectroscopy, or femto- and attosecond chemistry and spectroscopy underline that nuclear quantum mechanical effects affect many areas of chemical and physical research. In contrast to standard quantum chemistry calculations, where the nuclei are treated classically, molecular quantum dynamics can cover quantum mechanical effects in their motion. Many examples, ranging from fundamental to applied problems, are known today that are impacted by nuclear quantum mechanical effects, including phenomena like tunneling, zero point energy effects, or non-adiabatic transitions. Being important to correctly understand many observations in chemical, organic and biological systems, or for the understanding of molecular spectroscopy, the range of applications covered in this book comprises broad areas of science: from astrophysics and the physics and chemistry of the atmosphere, over elementary processes in chemistry, to biological processes (such as the first steps of photosynthesis or vision). Nevertheless, many researchers refrain from entering this domain. The book "Molecular Quantum Dynamics" offers them an accessible introduction. Although the calculation of large systems still presents a challenge - despite the considerable power of modern computers - new strategies have been developed to extend the studies to systems of increasing size. Such strategies are presented after a brief overview of the historical background. Strong emphasis is put on an educational presentation of the fundamental concepts, so that the reader can inform himself about the most important concepts, like eigenstates, wave packets, quantum mechanical resonances, entanglement, etc. The chosen examples highlight that high-level experiments and theory need to work closely together. This book thus is a must-read both for researchers working experimentally or theoretically in the concerned fields, and generally for anyone interested in the exciting world of molecular quantum dynamics.
Publisher: Springer Science & Business Media
ISBN: 3642452906
Category : Science
Languages : en
Pages : 281
Book Description
This book focuses on current applications of molecular quantum dynamics. Examples from all main subjects in the field, presented by the internationally renowned experts, illustrate the importance of the domain. Recent success in helping to understand experimental observations in fields like heterogeneous catalysis, photochemistry, reactive scattering, optical spectroscopy, or femto- and attosecond chemistry and spectroscopy underline that nuclear quantum mechanical effects affect many areas of chemical and physical research. In contrast to standard quantum chemistry calculations, where the nuclei are treated classically, molecular quantum dynamics can cover quantum mechanical effects in their motion. Many examples, ranging from fundamental to applied problems, are known today that are impacted by nuclear quantum mechanical effects, including phenomena like tunneling, zero point energy effects, or non-adiabatic transitions. Being important to correctly understand many observations in chemical, organic and biological systems, or for the understanding of molecular spectroscopy, the range of applications covered in this book comprises broad areas of science: from astrophysics and the physics and chemistry of the atmosphere, over elementary processes in chemistry, to biological processes (such as the first steps of photosynthesis or vision). Nevertheless, many researchers refrain from entering this domain. The book "Molecular Quantum Dynamics" offers them an accessible introduction. Although the calculation of large systems still presents a challenge - despite the considerable power of modern computers - new strategies have been developed to extend the studies to systems of increasing size. Such strategies are presented after a brief overview of the historical background. Strong emphasis is put on an educational presentation of the fundamental concepts, so that the reader can inform himself about the most important concepts, like eigenstates, wave packets, quantum mechanical resonances, entanglement, etc. The chosen examples highlight that high-level experiments and theory need to work closely together. This book thus is a must-read both for researchers working experimentally or theoretically in the concerned fields, and generally for anyone interested in the exciting world of molecular quantum dynamics.
Molecular Excitation Dynamics and Relaxation
Author: Leonas Valkunas
Publisher: John Wiley & Sons
ISBN: 3527653678
Category : Science
Languages : en
Pages : 414
Book Description
This work brings together quantum theory and spectroscopy to convey excitation processes to advanced students and specialists wishing to conduct research and understand the entire fi eld rather than just single aspects. Written by experienced authors and recognized authorities in the field, this text covers numerous applications and offers examples taken from different disciplines. As a result, spectroscopists, molecular physicists, physical chemists, and biophysicists will all fi nd this a must-have for their research. Also suitable as supplementary reading in graduate level courses.
Publisher: John Wiley & Sons
ISBN: 3527653678
Category : Science
Languages : en
Pages : 414
Book Description
This work brings together quantum theory and spectroscopy to convey excitation processes to advanced students and specialists wishing to conduct research and understand the entire fi eld rather than just single aspects. Written by experienced authors and recognized authorities in the field, this text covers numerous applications and offers examples taken from different disciplines. As a result, spectroscopists, molecular physicists, physical chemists, and biophysicists will all fi nd this a must-have for their research. Also suitable as supplementary reading in graduate level courses.
Quantum Mechanical Foundations of Molecular Spectroscopy
Author: Max Diem
Publisher: John Wiley & Sons
ISBN: 3527347925
Category : Science
Languages : en
Pages : 290
Book Description
A concise textbook bridging quantum theory and spectroscopy! Designed as a practical text, Quantum Mechanical Foundations of Molecular Spectroscopy covers the quantum mechanical fundamentals of molecular spectroscopy from the view of a professional spectroscopist, rather than a theoretician. Written by a noted expert on the topic, the book puts the emphasis on the relationship between spectroscopy and quantum mechanics, and provides the background information and derivations of the subjects needed to understand spectroscopy including: stationary energy states, transitions between these states, selection rules, and symmetry. The phenomenal growth of all forms of spectroscopy over the past eight decades has contributed enormously to our understanding of molecular structure and properties. Today spectroscopy covers a broad field including the modern magnetic resonance techniques, non-linear, laser and fiber-based spectroscopy, surface and surface-enhanced spectroscopy, pico- and femtosecond time resolved spectroscopy, and many more. This up-to-date resource discusses several forms of spectroscopy that are used in many fields of science, such as fluorescence, surface spectroscopies, linear and non-linear Raman spectroscopy and spin spectroscopy. This important text: Contains the physics and mathematics needed to understand spectroscopy Explores spectroscopic methods the are widely used in chemistry, biophysics, biology, and materials science Offers a text written by an experienced lecturer and practitioner of spectroscopic methods Includes detailed explanations and worked examples Written for chemistry, biochemistry, material sciences, and physics students, Quantum Mechanical Foundations of Molecular Spectroscopy provides an accessible text for understanding molecular spectroscopy.
Publisher: John Wiley & Sons
ISBN: 3527347925
Category : Science
Languages : en
Pages : 290
Book Description
A concise textbook bridging quantum theory and spectroscopy! Designed as a practical text, Quantum Mechanical Foundations of Molecular Spectroscopy covers the quantum mechanical fundamentals of molecular spectroscopy from the view of a professional spectroscopist, rather than a theoretician. Written by a noted expert on the topic, the book puts the emphasis on the relationship between spectroscopy and quantum mechanics, and provides the background information and derivations of the subjects needed to understand spectroscopy including: stationary energy states, transitions between these states, selection rules, and symmetry. The phenomenal growth of all forms of spectroscopy over the past eight decades has contributed enormously to our understanding of molecular structure and properties. Today spectroscopy covers a broad field including the modern magnetic resonance techniques, non-linear, laser and fiber-based spectroscopy, surface and surface-enhanced spectroscopy, pico- and femtosecond time resolved spectroscopy, and many more. This up-to-date resource discusses several forms of spectroscopy that are used in many fields of science, such as fluorescence, surface spectroscopies, linear and non-linear Raman spectroscopy and spin spectroscopy. This important text: Contains the physics and mathematics needed to understand spectroscopy Explores spectroscopic methods the are widely used in chemistry, biophysics, biology, and materials science Offers a text written by an experienced lecturer and practitioner of spectroscopic methods Includes detailed explanations and worked examples Written for chemistry, biochemistry, material sciences, and physics students, Quantum Mechanical Foundations of Molecular Spectroscopy provides an accessible text for understanding molecular spectroscopy.
The Semiclassical Way to Dynamics and Spectroscopy
Author: Eric J. Heller
Publisher: Princeton University Press
ISBN: 1400890292
Category : Science
Languages : en
Pages : 473
Book Description
A graduate-level text that examines the semiclassical approach to quantum mechanics Physical systems have been traditionally described in terms of either classical or quantum mechanics. But in recent years, semiclassical methods have developed rapidly, providing deep physical insight and computational tools for quantum dynamics and spectroscopy. In this book, Eric Heller introduces and develops this subject, demonstrating its power with many examples. In the first half of the book, Heller covers relevant aspects of classical mechanics, building from them the semiclassical way through the semiclassical limit of the Feynman path integral. The second half of the book applies this approach to various kinds of spectroscopy, such as molecular spectroscopy and electron imaging and quantum dynamical systems with an emphasis on tunneling. Adopting a distinctly time-dependent viewpoint, Heller argues for semiclassical theories from experimental and theoretical vantage points valuable to research in physics and chemistry. Featuring more than two hundred figures, the book provides a geometric, phase-space, and coordinate-space pathway to greater understanding. Filled with practical examples and applications, The Semiclassical Way to Dynamics and Spectroscopy is a comprehensive presentation of the tools necessary to successfully delve into this unique area of quantum mechanics. A comprehensive approach for using classical mechanics to do quantum mechanics More than two hundred figures to assist intuition Emphasis on semiclassical Green function and wave packet perspective, as well as tunneling and spectroscopy Chapters include quantum mechanics of classically chaotic systems, quantum scarring, and other modern dynamical topics
Publisher: Princeton University Press
ISBN: 1400890292
Category : Science
Languages : en
Pages : 473
Book Description
A graduate-level text that examines the semiclassical approach to quantum mechanics Physical systems have been traditionally described in terms of either classical or quantum mechanics. But in recent years, semiclassical methods have developed rapidly, providing deep physical insight and computational tools for quantum dynamics and spectroscopy. In this book, Eric Heller introduces and develops this subject, demonstrating its power with many examples. In the first half of the book, Heller covers relevant aspects of classical mechanics, building from them the semiclassical way through the semiclassical limit of the Feynman path integral. The second half of the book applies this approach to various kinds of spectroscopy, such as molecular spectroscopy and electron imaging and quantum dynamical systems with an emphasis on tunneling. Adopting a distinctly time-dependent viewpoint, Heller argues for semiclassical theories from experimental and theoretical vantage points valuable to research in physics and chemistry. Featuring more than two hundred figures, the book provides a geometric, phase-space, and coordinate-space pathway to greater understanding. Filled with practical examples and applications, The Semiclassical Way to Dynamics and Spectroscopy is a comprehensive presentation of the tools necessary to successfully delve into this unique area of quantum mechanics. A comprehensive approach for using classical mechanics to do quantum mechanics More than two hundred figures to assist intuition Emphasis on semiclassical Green function and wave packet perspective, as well as tunneling and spectroscopy Chapters include quantum mechanics of classically chaotic systems, quantum scarring, and other modern dynamical topics
Quantum Chemistry and Dynamics of Excited States
Author: Leticia González
Publisher: John Wiley & Sons
ISBN: 1119417759
Category : Science
Languages : en
Pages : 52
Book Description
An introduction to the rapidly evolving methodology of electronic excited states For academic researchers, postdocs, graduate and undergraduate students, Quantum Chemistry and Dynamics of Excited States: Methods and Applications reports the most updated and accurate theoretical techniques to treat electronic excited states. From methods to deal with stationary calculations through time-dependent simulations of molecular systems, this book serves as a guide for beginners in the field and knowledge seekers alike. Taking into account the most recent theory developments and representative applications, it also covers the often-overlooked gap between theoretical and computational chemistry. An excellent reference for both researchers and students, Excited States provides essential knowledge on quantum chemistry, an in-depth overview of the latest developments, and theoretical techniques around the properties and nonadiabatic dynamics of chemical systems. Readers will learn: ● Essential theoretical techniques to describe the properties and dynamics of chemical systems ● Electronic Structure methods for stationary calculations ● Methods for electronic excited states from both a quantum chemical and time-dependent point of view ● A breakdown of the most recent developments in the past 30 years For those searching for a better understanding of excited states as they relate to chemistry, biochemistry, industrial chemistry, and beyond, Quantum Chemistry and Dynamics of Excited States provides a solid education in the necessary foundations and important theories of excited states in photochemistry and ultrafast phenomena.
Publisher: John Wiley & Sons
ISBN: 1119417759
Category : Science
Languages : en
Pages : 52
Book Description
An introduction to the rapidly evolving methodology of electronic excited states For academic researchers, postdocs, graduate and undergraduate students, Quantum Chemistry and Dynamics of Excited States: Methods and Applications reports the most updated and accurate theoretical techniques to treat electronic excited states. From methods to deal with stationary calculations through time-dependent simulations of molecular systems, this book serves as a guide for beginners in the field and knowledge seekers alike. Taking into account the most recent theory developments and representative applications, it also covers the often-overlooked gap between theoretical and computational chemistry. An excellent reference for both researchers and students, Excited States provides essential knowledge on quantum chemistry, an in-depth overview of the latest developments, and theoretical techniques around the properties and nonadiabatic dynamics of chemical systems. Readers will learn: ● Essential theoretical techniques to describe the properties and dynamics of chemical systems ● Electronic Structure methods for stationary calculations ● Methods for electronic excited states from both a quantum chemical and time-dependent point of view ● A breakdown of the most recent developments in the past 30 years For those searching for a better understanding of excited states as they relate to chemistry, biochemistry, industrial chemistry, and beyond, Quantum Chemistry and Dynamics of Excited States provides a solid education in the necessary foundations and important theories of excited states in photochemistry and ultrafast phenomena.
Frontiers of Molecular Spectroscopy
Author: Jaan Laane
Publisher: Elsevier
ISBN: 0080932371
Category : Science
Languages : en
Pages : 741
Book Description
Much of what we know about atoms, molecules, and the nature of matter has been obtained using spectroscopy over the last one hundred years or so. In this book we have collected together twenty chapters by eminent scientists from around the world to describe their work at the cutting edge of molecular spectroscopy. These chapters describe new methodology and applications, instrumental developments, and theory which is taking spectroscopy into new frontiers. The range of topics is broad. Lasers are utilized in much of the research, but their applications range from sub-femtosecond spectroscopy to the study of viruses and also to the investigation of art and archeological artifacts. Three chapters discuss work on biological systems and three others represent laser physics. The recent advances in cavity ringdown spectroscopy (CRDS), surface enhanced Raman spectroscopy (SERS), two-dimensional correlation spectroscopy (2D-COS), and microwave techniques are all covered. Chapters on electronic excited states, molecular dynamics, symmetry applications, and neutron scattering are also included and demonstrate the wide utility of spectroscopic techniques. - Provides comprehensive coverage of present spectroscopic investigations - Features 20 chapters written by leading researchers in the field - Covers the important role of molecular spectroscopy in research concerned with chemistry, physics, and biology
Publisher: Elsevier
ISBN: 0080932371
Category : Science
Languages : en
Pages : 741
Book Description
Much of what we know about atoms, molecules, and the nature of matter has been obtained using spectroscopy over the last one hundred years or so. In this book we have collected together twenty chapters by eminent scientists from around the world to describe their work at the cutting edge of molecular spectroscopy. These chapters describe new methodology and applications, instrumental developments, and theory which is taking spectroscopy into new frontiers. The range of topics is broad. Lasers are utilized in much of the research, but their applications range from sub-femtosecond spectroscopy to the study of viruses and also to the investigation of art and archeological artifacts. Three chapters discuss work on biological systems and three others represent laser physics. The recent advances in cavity ringdown spectroscopy (CRDS), surface enhanced Raman spectroscopy (SERS), two-dimensional correlation spectroscopy (2D-COS), and microwave techniques are all covered. Chapters on electronic excited states, molecular dynamics, symmetry applications, and neutron scattering are also included and demonstrate the wide utility of spectroscopic techniques. - Provides comprehensive coverage of present spectroscopic investigations - Features 20 chapters written by leading researchers in the field - Covers the important role of molecular spectroscopy in research concerned with chemistry, physics, and biology
Dynamics of Molecular Excitons
Author: Seogjoo J. Jang
Publisher: Elsevier
ISBN: 0081023359
Category : Science
Languages : en
Pages : 242
Book Description
Dynamics of Molecular Excitons provides a comprehensive, but concise description of major theories on the dynamics of molecular excitons, intended to serve as a self-contained resource on the topic. Designed to help those new to this area gain proficiency in this field, experts will also find the book useful in developing a deeper understanding of the subject. The starting point of the book is the standard microscopic definition of molecular Hamiltonians presented in commonly accepted modern quantum mechanical notations. Major assumptions and approximations involved in constructing Frenkel-type exciton Hamiltonians, which are well established, but are often hidden under arcane notations and approximations of old publications, are presented in detail. This will help quantum chemists understand the major assumptions involved in the definition of commonly used exciton models. Rate theories of exciton dynamics, such as Förster and Dexter theories and their modern generalizations, are presented in a unified and detailed manner. In addition, important aspects that are often neglected, such as local field effect and the role of fluctuating environments, are discussed. Various quantum dynamics methods allowing coherent dynamics of excitons are presented in a systematic manner in the context of quantum master equations or path integral formalisms. The author also provides a detailed theoretical explanation for the major spectroscopic techniques probing exciton dynamics, including modern two-dimensional electronic spectroscopy, with a critical assessment of the implications of these spectroscopic measurements. Finally, the book includes a brief overview of major applications including an explanation of organic photovoltaic materials and natural light harvesting complexes.
Publisher: Elsevier
ISBN: 0081023359
Category : Science
Languages : en
Pages : 242
Book Description
Dynamics of Molecular Excitons provides a comprehensive, but concise description of major theories on the dynamics of molecular excitons, intended to serve as a self-contained resource on the topic. Designed to help those new to this area gain proficiency in this field, experts will also find the book useful in developing a deeper understanding of the subject. The starting point of the book is the standard microscopic definition of molecular Hamiltonians presented in commonly accepted modern quantum mechanical notations. Major assumptions and approximations involved in constructing Frenkel-type exciton Hamiltonians, which are well established, but are often hidden under arcane notations and approximations of old publications, are presented in detail. This will help quantum chemists understand the major assumptions involved in the definition of commonly used exciton models. Rate theories of exciton dynamics, such as Förster and Dexter theories and their modern generalizations, are presented in a unified and detailed manner. In addition, important aspects that are often neglected, such as local field effect and the role of fluctuating environments, are discussed. Various quantum dynamics methods allowing coherent dynamics of excitons are presented in a systematic manner in the context of quantum master equations or path integral formalisms. The author also provides a detailed theoretical explanation for the major spectroscopic techniques probing exciton dynamics, including modern two-dimensional electronic spectroscopy, with a critical assessment of the implications of these spectroscopic measurements. Finally, the book includes a brief overview of major applications including an explanation of organic photovoltaic materials and natural light harvesting complexes.
Attosecond Molecular Dynamics
Author: Marc J J Vrakking
Publisher: Royal Society of Chemistry
ISBN: 1788015134
Category : Science
Languages : en
Pages : 512
Book Description
Attosecond science is a new and rapidly developing research area in which molecular dynamics are studied at the timescale of a few attoseconds. Within the past decade, attosecond pump–probe spectroscopy has emerged as a powerful experimental technique that permits electron dynamics to be followed on their natural timescales. With the development of this technology, physical chemists have been able to observe and control molecular dynamics on attosecond timescales. From these observations it has been suggested that attosecond to few-femtosecond timescale charge migration may induce what has been called “post-Born-Oppenheimer dynamics”, where the nuclei respond to rapidly time-dependent force fields resulting from transient localization of the electrons. These real-time observations have spurred exciting new advances in the theoretical work to both explain and predict these novel dynamics. This book presents an overview of current theoretical work relevant to attosecond science written by theoreticians who are presently at the forefront of its development. It is a valuable reference work for anyone working in the field of attosecond science as well as those studying the subject.
Publisher: Royal Society of Chemistry
ISBN: 1788015134
Category : Science
Languages : en
Pages : 512
Book Description
Attosecond science is a new and rapidly developing research area in which molecular dynamics are studied at the timescale of a few attoseconds. Within the past decade, attosecond pump–probe spectroscopy has emerged as a powerful experimental technique that permits electron dynamics to be followed on their natural timescales. With the development of this technology, physical chemists have been able to observe and control molecular dynamics on attosecond timescales. From these observations it has been suggested that attosecond to few-femtosecond timescale charge migration may induce what has been called “post-Born-Oppenheimer dynamics”, where the nuclei respond to rapidly time-dependent force fields resulting from transient localization of the electrons. These real-time observations have spurred exciting new advances in the theoretical work to both explain and predict these novel dynamics. This book presents an overview of current theoretical work relevant to attosecond science written by theoreticians who are presently at the forefront of its development. It is a valuable reference work for anyone working in the field of attosecond science as well as those studying the subject.
Spectroscopy, Dynamics and Molecular Theory of Carbon Plasmas and Vapors
Author: Laszlo Nemes
Publisher: World Scientific
ISBN: 9812837647
Category : Science
Languages : en
Pages : 536
Book Description
This book is a stop-gap contribution to the science and technology of carbon plasmas and carbon vapors. It strives to cover two strongly related fields: the molecular quantum theory of carbon plasmas and carbon nanostructures; and the molecular and atomic spectroscopy of such plasmas and vapors. These two fields of research are strongly intertwined and thus reinforce one another.Even though the use of carbon nanostructures is increasing by the day and their practical uses are emerging, there is no modern review on carbon plasmas, especially from molecular theoretical and spectroscopic viewpoints. The importance of the present book is therefore great from both educational and practical aspects. This review might be the first step towards bringing such textbooks into existence for university education. Similarly, for applied and engineering works in carbon nanostructures, the book provides a theoretical salient point for technologists in the field.
Publisher: World Scientific
ISBN: 9812837647
Category : Science
Languages : en
Pages : 536
Book Description
This book is a stop-gap contribution to the science and technology of carbon plasmas and carbon vapors. It strives to cover two strongly related fields: the molecular quantum theory of carbon plasmas and carbon nanostructures; and the molecular and atomic spectroscopy of such plasmas and vapors. These two fields of research are strongly intertwined and thus reinforce one another.Even though the use of carbon nanostructures is increasing by the day and their practical uses are emerging, there is no modern review on carbon plasmas, especially from molecular theoretical and spectroscopic viewpoints. The importance of the present book is therefore great from both educational and practical aspects. This review might be the first step towards bringing such textbooks into existence for university education. Similarly, for applied and engineering works in carbon nanostructures, the book provides a theoretical salient point for technologists in the field.