Naomi E. Chayen, John R. Helliwell, and Edward H. Snell
- Published in print:
- 2010
- Published Online:
- May 2010
- ISBN:
- 9780199213252
- eISBN:
- 9780191707575
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199213252.003.0015
- Subject:
- Physics, Crystallography: Physics
Unusual diffraction geometries may seem a curiosity but may stimulate novel avenues of application. Not least they illustrate a diversity of diffraction‐measuring possibilities. Laue diffraction ...
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Unusual diffraction geometries may seem a curiosity but may stimulate novel avenues of application. Not least they illustrate a diversity of diffraction‐measuring possibilities. Laue diffraction including 3‐dimensional detector arrangements is described. The particular congestion of neutron Laue diffraction patterns with big crystals is highlighted. The large‐angle oscillation technique is discussed including the principle with the Ewald sphere construction and practical examples of ‘LOT’ diffraction patterns. Ultra‐fine‐phi‐slicing with perfect or near‐perfect crystals is described. Particular success has been obtained with Laue diffraction where applications to time‐resolved structural intermediates using synchrotron radiation as well as hydrogen and hydration in macromolecular structure are described.Less
Unusual diffraction geometries may seem a curiosity but may stimulate novel avenues of application. Not least they illustrate a diversity of diffraction‐measuring possibilities. Laue diffraction including 3‐dimensional detector arrangements is described. The particular congestion of neutron Laue diffraction patterns with big crystals is highlighted. The large‐angle oscillation technique is discussed including the principle with the Ewald sphere construction and practical examples of ‘LOT’ diffraction patterns. Ultra‐fine‐phi‐slicing with perfect or near‐perfect crystals is described. Particular success has been obtained with Laue diffraction where applications to time‐resolved structural intermediates using synchrotron radiation as well as hydrogen and hydration in macromolecular structure are described.
Naomi E. Chayen, John R. Helliwell, and Edward H. Snell
- Published in print:
- 2010
- Published Online:
- May 2010
- ISBN:
- 9780199213252
- eISBN:
- 9780191707575
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199213252.003.0018
- Subject:
- Physics, Crystallography: Physics
Crystallography is a powerful technique but also one that has limitations. There are a number of complementary techniques that significantly add to the information available crystallographically.
Crystallography is a powerful technique but also one that has limitations. There are a number of complementary techniques that significantly add to the information available crystallographically.
Clarke E. Cochran
David E. Guinn (ed.)
- Published in print:
- 2006
- Published Online:
- September 2006
- ISBN:
- 9780195178739
- eISBN:
- 9780199784943
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/0195178734.003.0020
- Subject:
- Religion, Philosophy of Religion
There is a tendency to see the current challenges to Catholic health care ministry as unprecedented, and the particular shape they take certainly is. But there has always been pressure. The reason is ...
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There is a tendency to see the current challenges to Catholic health care ministry as unprecedented, and the particular shape they take certainly is. But there has always been pressure. The reason is simple: whatever the dominant political, economic, or medical system of a given time and place, Catholic identity must always be at an ethical angle. Catholics faithful to Jesus' words and deeds are “resident aliens” in every society.Less
There is a tendency to see the current challenges to Catholic health care ministry as unprecedented, and the particular shape they take certainly is. But there has always been pressure. The reason is simple: whatever the dominant political, economic, or medical system of a given time and place, Catholic identity must always be at an ethical angle. Catholics faithful to Jesus' words and deeds are “resident aliens” in every society.
Andreas Kirsch and Natalia Grinberg
- Published in print:
- 2007
- Published Online:
- September 2008
- ISBN:
- 9780199213535
- eISBN:
- 9780191707629
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199213535.003.0002
- Subject:
- Mathematics, Applied Mathematics
This chapter studies some examples of inverse scattering problems in which the data operator fails to be normal. The impedance boundary condition, the reconstruction from limited-angle data, and the ...
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This chapter studies some examples of inverse scattering problems in which the data operator fails to be normal. The impedance boundary condition, the reconstruction from limited-angle data, and the reconstruction of near field data, are used as examples. The chapter begins with the direct scattering problem and recalls results on uniqueness and existence of solutions, then the properties of the far field patterns is presented. For the impedance boundary condition, or the limited data case, or the near field data case the corresponding data-operator fails to be normal. Nevertheless, the characterization by the inf-condition holds. The chapter also proves the characterization of the domain D by the convergence of a Picard series for a combination of the self adjoint parts ¦F+F*¦2 and (F-F*)2i of the data operator F. The characterization is based on a general abstract result from functional analysis.Less
This chapter studies some examples of inverse scattering problems in which the data operator fails to be normal. The impedance boundary condition, the reconstruction from limited-angle data, and the reconstruction of near field data, are used as examples. The chapter begins with the direct scattering problem and recalls results on uniqueness and existence of solutions, then the properties of the far field patterns is presented. For the impedance boundary condition, or the limited data case, or the near field data case the corresponding data-operator fails to be normal. Nevertheless, the characterization by the inf-condition holds. The chapter also proves the characterization of the domain D by the convergence of a Picard series for a combination of the self adjoint parts ¦F+F*¦2 and (F-F*)2i of the data operator F. The characterization is based on a general abstract result from functional analysis.
Michael Brady, Xiao-Bo Pan, Veit Schenk, Melissa Terras, Paul Robertson, and Nicholas Molton
- Published in print:
- 2005
- Published Online:
- January 2012
- ISBN:
- 9780197262962
- eISBN:
- 9780191734533
- Item type:
- chapter
- Publisher:
- British Academy
- DOI:
- 10.5871/bacad/9780197262962.003.0003
- Subject:
- Archaeology, Archaeological Methodology and Techniques
It is agreed that stilus tablets are very important documentary sources, however they are the most difficult to decipher. The difficulties in deciphering them is due to the rough surface of the ...
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It is agreed that stilus tablets are very important documentary sources, however they are the most difficult to decipher. The difficulties in deciphering them is due to the rough surface of the tablets, the low brightness contrast of the incisions, the dense wood-grain lines, and the badly stained and pitted nature of the tablets. All of these posit a challenge for conventional two-dimensional (2D) image analysis. This chapter aims to provide a system that would aid the historian in interpreting stilus tablets by improving the legibility of the tablets. It provides novel ways of determining the texts incised on the tablets. One of these is the use of three-dimensional (3D) image analysis techniques. Such a technique is capable of detecting incisions, compared to the 2D image analysis, and is portable and inexpensive. Another method that can be used is the use of shadow stereo. This method employs low raking angle light close to the plane of the tablet at different elevations. The chapter also discusses the image formation process and the process of choosing elevations for each azimuth direction. The chapter also includes a discussion on realizing the shadow stereo algorithm.Less
It is agreed that stilus tablets are very important documentary sources, however they are the most difficult to decipher. The difficulties in deciphering them is due to the rough surface of the tablets, the low brightness contrast of the incisions, the dense wood-grain lines, and the badly stained and pitted nature of the tablets. All of these posit a challenge for conventional two-dimensional (2D) image analysis. This chapter aims to provide a system that would aid the historian in interpreting stilus tablets by improving the legibility of the tablets. It provides novel ways of determining the texts incised on the tablets. One of these is the use of three-dimensional (3D) image analysis techniques. Such a technique is capable of detecting incisions, compared to the 2D image analysis, and is portable and inexpensive. Another method that can be used is the use of shadow stereo. This method employs low raking angle light close to the plane of the tablet at different elevations. The chapter also discusses the image formation process and the process of choosing elevations for each azimuth direction. The chapter also includes a discussion on realizing the shadow stereo algorithm.
Christopher Scull
- Published in print:
- 2019
- Published Online:
- May 2020
- ISBN:
- 9780197266588
- eISBN:
- 9780191896040
- Item type:
- chapter
- Publisher:
- British Academy
- DOI:
- 10.5871/bacad/9780197266588.003.0018
- Subject:
- Archaeology, Historical Archaeology
Conventional models of state formation and the ways in which early polities might be expressed in the archaeological record for England in the 7th century have emphasised the importance of ...
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Conventional models of state formation and the ways in which early polities might be expressed in the archaeological record for England in the 7th century have emphasised the importance of long-distance exchange in promoting socio-economic complexity. Such models, however, are open to challenge or refinement from interpretations that would emphasise other social dynamics, and beg serious questions about the relationships between agrarian production, elite acquisition and consumption and structures of power and jurisdiction. This chapter presents a critical evaluation of some current assumptions and approaches, and examines the interpretative questions in the light of recent evidence from south-east Suffolk, often seen as the heartland of the early kingdom of the East Angles.Less
Conventional models of state formation and the ways in which early polities might be expressed in the archaeological record for England in the 7th century have emphasised the importance of long-distance exchange in promoting socio-economic complexity. Such models, however, are open to challenge or refinement from interpretations that would emphasise other social dynamics, and beg serious questions about the relationships between agrarian production, elite acquisition and consumption and structures of power and jurisdiction. This chapter presents a critical evaluation of some current assumptions and approaches, and examines the interpretative questions in the light of recent evidence from south-east Suffolk, often seen as the heartland of the early kingdom of the East Angles.
Albert R. Rice
- Published in print:
- 2009
- Published Online:
- May 2009
- ISBN:
- 9780195343281
- eISBN:
- 9780199867813
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780195343281.003.0003
- Subject:
- Music, History, Western
For the basset horn, the second chapter develops a precise definition; lists defining features; identifies and defines terminology; establishes origins and history; paints an historical picture; ...
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For the basset horn, the second chapter develops a precise definition; lists defining features; identifies and defines terminology; establishes origins and history; paints an historical picture; discusses instructional materials; lists makers chronologically; and describes extant instruments.Less
For the basset horn, the second chapter develops a precise definition; lists defining features; identifies and defines terminology; establishes origins and history; paints an historical picture; discusses instructional materials; lists makers chronologically; and describes extant instruments.
GÜNTHER DISSERTORI, IAN G. KNOWLES, and MICHAEL SCHMELLING
- Published in print:
- 2009
- Published Online:
- January 2010
- ISBN:
- 9780199566419
- eISBN:
- 9780191708060
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199566419.003.0010
- Subject:
- Physics, Particle Physics / Astrophysics / Cosmology
This chapter examines the QCD lagrangian, focusing on the gauge group governing the dynamics of strong interactions. Experiments are described which verify that QCD is based on the gauge group SU(3). ...
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This chapter examines the QCD lagrangian, focusing on the gauge group governing the dynamics of strong interactions. Experiments are described which verify that QCD is based on the gauge group SU(3). After explaining how the so-called colour factors allow pinpointing of the gauge symmetry, experimental observables sensitive to the colour factors are introduced and experimental distributions are compared to theoretical predictions. The results show that the dynamics of QCD are consistent with the expected SU(3) symmetry, the correct ratio of the strengths of the quark-gluon to the gluon-gluon coupling, and the number of colour states of the gluon. The results are also interpreted as a limit on the mass of the gluino, the supersymmetric partner of the gluon.Less
This chapter examines the QCD lagrangian, focusing on the gauge group governing the dynamics of strong interactions. Experiments are described which verify that QCD is based on the gauge group SU(3). After explaining how the so-called colour factors allow pinpointing of the gauge symmetry, experimental observables sensitive to the colour factors are introduced and experimental distributions are compared to theoretical predictions. The results show that the dynamics of QCD are consistent with the expected SU(3) symmetry, the correct ratio of the strengths of the quark-gluon to the gluon-gluon coupling, and the number of colour states of the gluon. The results are also interpreted as a limit on the mass of the gluino, the supersymmetric partner of the gluon.
Claire Nightingale and Jonathan Sandy
- Published in print:
- 2014
- Published Online:
- November 2020
- ISBN:
- 9780198714828
- eISBN:
- 9780191916793
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780198714828.003.0020
- Subject:
- Clinical Medicine and Allied Health, Dentistry
Simon Parsons and William Clegg
- Published in print:
- 2009
- Published Online:
- September 2009
- ISBN:
- 9780199219469
- eISBN:
- 9780191722516
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199219469.003.0015
- Subject:
- Physics, Crystallography: Physics
This chapter takes the next step beyond the refinement of a crystal structure, to look at the meaning and significance of the results. Various geometrical features can be calculated from atomic ...
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This chapter takes the next step beyond the refinement of a crystal structure, to look at the meaning and significance of the results. Various geometrical features can be calculated from atomic coordinates: bond lengths and angles, other interatomic distances, torsion angles, etc., all with associated standard uncertainties, the values of which are important for assessing the significance of differences. Least-squares planes can be fitted to groups of atoms, and dihedral angles calculated between pairs of planes. Various parameters are used to describe ring conformations. Hydrogen bonding is one of the intermolecular interactions for which geometrical criteria have been established. Atomic displacement parameters can be analysed in terms of correlated motion of rigid groups. Mathematical formulae are presented for many of these calculations.Less
This chapter takes the next step beyond the refinement of a crystal structure, to look at the meaning and significance of the results. Various geometrical features can be calculated from atomic coordinates: bond lengths and angles, other interatomic distances, torsion angles, etc., all with associated standard uncertainties, the values of which are important for assessing the significance of differences. Least-squares planes can be fitted to groups of atoms, and dihedral angles calculated between pairs of planes. Various parameters are used to describe ring conformations. Hydrogen bonding is one of the intermolecular interactions for which geometrical criteria have been established. Atomic displacement parameters can be analysed in terms of correlated motion of rigid groups. Mathematical formulae are presented for many of these calculations.
J. C. Garrison and R. Y. Chiao
- Published in print:
- 2008
- Published Online:
- September 2008
- ISBN:
- 9780198508861
- eISBN:
- 9780191708640
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198508861.003.0008
- Subject:
- Physics, Atomic, Laser, and Optical Physics
The classical concept of a paraxial wave is extended to quantum optics as a condition on the state vector, and the family of vectors obeying this condition defines a paraxial Hilbert space. Field ...
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The classical concept of a paraxial wave is extended to quantum optics as a condition on the state vector, and the family of vectors obeying this condition defines a paraxial Hilbert space. Field operators acting on this space are approximated by the product of a slowly-varying envelope operator and a classical carrier wave. This permits the discussion of Gaussian pulses and paraxial wave packets. This treatment is extended to obtain an expansion of state vectors and field operators in powers of the opening angle of the cone of paraxial rays. The leading term in the expansion yields the component of the angular momentum along the propagation axis as a sum of well defined orbital- and spin-parts. With the same technique, it is shown that approximate localization of photons is possible for localization volumes much larger that the mean wavelength in the paraxial state.Less
The classical concept of a paraxial wave is extended to quantum optics as a condition on the state vector, and the family of vectors obeying this condition defines a paraxial Hilbert space. Field operators acting on this space are approximated by the product of a slowly-varying envelope operator and a classical carrier wave. This permits the discussion of Gaussian pulses and paraxial wave packets. This treatment is extended to obtain an expansion of state vectors and field operators in powers of the opening angle of the cone of paraxial rays. The leading term in the expansion yields the component of the angular momentum along the propagation axis as a sum of well defined orbital- and spin-parts. With the same technique, it is shown that approximate localization of photons is possible for localization volumes much larger that the mean wavelength in the paraxial state.
Eaton E. Lattman, Thomas D. Grant, and Edward H. Snell
- Published in print:
- 2018
- Published Online:
- September 2018
- ISBN:
- 9780199670871
- eISBN:
- 9780191749575
- Item type:
- book
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/oso/9780199670871.001.0001
- Subject:
- Physics, Soft Matter / Biological Physics
The technique of small angle solution scattering has been revolutionized in the last two decades. Exponential increases in computing power, parallel algorithm development, and the development of ...
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The technique of small angle solution scattering has been revolutionized in the last two decades. Exponential increases in computing power, parallel algorithm development, and the development of synchrotron, free-electron X-ray sources, and neutron sources, have combined to allow new classes of studies for biological specimens. These include time-resolved experiments in which functional motions of proteins are monitored on a picosecond timescale, and the first steps towards determining actual electron density fluctuations within particles. In addition, more traditional experiments involving the determination of size and shape, and contrast matching that isolate substructures such as nucleic acid, have become much more straightforward to carry out, and simultaneously require much less material. These new capabilities have sparked an upsurge of interest in solution scattering on the part of investigators in related disciplines. Thus, this book seeks to guide structural biologists to understand the basics of small angle solution scattering in both the X-ray and neutron case, to appreciate its strengths, and to be cognizant of its limitations. It is also directed at those who have a general interest in its potential. The book focuses on three areas: theory, practical aspects and applications, and the potential of developing areas. It is an introduction and guide to the field but not a comprehensive treatment of all the potential applications.Less
The technique of small angle solution scattering has been revolutionized in the last two decades. Exponential increases in computing power, parallel algorithm development, and the development of synchrotron, free-electron X-ray sources, and neutron sources, have combined to allow new classes of studies for biological specimens. These include time-resolved experiments in which functional motions of proteins are monitored on a picosecond timescale, and the first steps towards determining actual electron density fluctuations within particles. In addition, more traditional experiments involving the determination of size and shape, and contrast matching that isolate substructures such as nucleic acid, have become much more straightforward to carry out, and simultaneously require much less material. These new capabilities have sparked an upsurge of interest in solution scattering on the part of investigators in related disciplines. Thus, this book seeks to guide structural biologists to understand the basics of small angle solution scattering in both the X-ray and neutron case, to appreciate its strengths, and to be cognizant of its limitations. It is also directed at those who have a general interest in its potential. The book focuses on three areas: theory, practical aspects and applications, and the potential of developing areas. It is an introduction and guide to the field but not a comprehensive treatment of all the potential applications.
C. Mathew Mate
- Published in print:
- 2007
- Published Online:
- January 2008
- ISBN:
- 9780198526780
- eISBN:
- 9780191712098
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780198526780.003.0005
- Subject:
- Physics, Condensed Matter Physics / Materials
The energies associated with surfaces — surface energy, interfacial energy, surface tension, and work of adhesion — drive many surface phenomena including tribological ones such as adhesion and ...
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The energies associated with surfaces — surface energy, interfacial energy, surface tension, and work of adhesion — drive many surface phenomena including tribological ones such as adhesion and friction. This chapter discusses the physical origins of surface energies for liquids and solids, and how the concepts of capillary pressure, capillary condensation, wetting, and work of adhesion are derived from surface energy. Further, this chapter covers the different methods for measuring surface energies, including a thorough discussion of the most common method to measure the surface energy of solids: contact angle measurements of liquid droplets on surfaces. The chapter also introduces how surface energies and surface tensions lead to adhesion and adhesion hysteresis between contacting surfaces, which is followed up in the subsequent chapters on surface forces.Less
The energies associated with surfaces — surface energy, interfacial energy, surface tension, and work of adhesion — drive many surface phenomena including tribological ones such as adhesion and friction. This chapter discusses the physical origins of surface energies for liquids and solids, and how the concepts of capillary pressure, capillary condensation, wetting, and work of adhesion are derived from surface energy. Further, this chapter covers the different methods for measuring surface energies, including a thorough discussion of the most common method to measure the surface energy of solids: contact angle measurements of liquid droplets on surfaces. The chapter also introduces how surface energies and surface tensions lead to adhesion and adhesion hysteresis between contacting surfaces, which is followed up in the subsequent chapters on surface forces.
Alexandre Simionovici, Pierre Bleuet, Bruno Golosio, and Christian Schroer
- Published in print:
- 2008
- Published Online:
- May 2008
- ISBN:
- 9780199213245
- eISBN:
- 9780191707582
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199213245.003.0008
- Subject:
- Physics, Condensed Matter Physics / Materials
In cases where the effect of interest changes the direction of the incoming radiation, the image pixels are no longer decoupled and the sample has to be scanned sequentially using a small focused ...
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In cases where the effect of interest changes the direction of the incoming radiation, the image pixels are no longer decoupled and the sample has to be scanned sequentially using a small focused beam to avoid the information from different regions of the sample being convoluted irreversibly. This chapter describes such scanning methods. Three examples are presented: tomography using fluorescent X-ray radiation, tomography exploiting the absorption fine structure near the absorption edges, and tomography utilizing small-angle scattering from mesoscopic structures within the sample.Less
In cases where the effect of interest changes the direction of the incoming radiation, the image pixels are no longer decoupled and the sample has to be scanned sequentially using a small focused beam to avoid the information from different regions of the sample being convoluted irreversibly. This chapter describes such scanning methods. Three examples are presented: tomography using fluorescent X-ray radiation, tomography exploiting the absorption fine structure near the absorption edges, and tomography utilizing small-angle scattering from mesoscopic structures within the sample.
Arne Haaland
- Published in print:
- 2008
- Published Online:
- May 2008
- ISBN:
- 9780199235353
- eISBN:
- 9780191715594
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199235353.003.0017
- Subject:
- Physics, Condensed Matter Physics / Materials
The chapter opens with a description of the structures of derivatives of divalent O, S, Se or Te (i.e., dihydrogen, dimethyl, and dichloro derivatives). It is pointed out that when two particularly ...
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The chapter opens with a description of the structures of derivatives of divalent O, S, Se or Te (i.e., dihydrogen, dimethyl, and dichloro derivatives). It is pointed out that when two particularly bulky atoms or groups are bonded to the same oxygen atom, the valence angle (at the oxygen atom) is frequently found to be larger than predicted by the VSEPR model. The O-O bond distance in dioxygen difluoride (FOOF) is 24 pm shorter than in hydrogen peroxide, while the O-F bond distance is 18 pm longer than in OF2. These observations are rationalized in terms of delocalization of lone pair electrons at the O atom into antibonding O-F orbitals. The structures of derivatives of tetra- or hexa-valent S, Se, or Te (e.g., Te(CH3)4, Te(CH3)6, SF6, SeF6, or TeF6) are described and rationalized in terms of delocalized molecular orbitals.Less
The chapter opens with a description of the structures of derivatives of divalent O, S, Se or Te (i.e., dihydrogen, dimethyl, and dichloro derivatives). It is pointed out that when two particularly bulky atoms or groups are bonded to the same oxygen atom, the valence angle (at the oxygen atom) is frequently found to be larger than predicted by the VSEPR model. The O-O bond distance in dioxygen difluoride (FOOF) is 24 pm shorter than in hydrogen peroxide, while the O-F bond distance is 18 pm longer than in OF2. These observations are rationalized in terms of delocalization of lone pair electrons at the O atom into antibonding O-F orbitals. The structures of derivatives of tetra- or hexa-valent S, Se, or Te (e.g., Te(CH3)4, Te(CH3)6, SF6, SeF6, or TeF6) are described and rationalized in terms of delocalized molecular orbitals.
Wolfgang Treimer
- Published in print:
- 2008
- Published Online:
- May 2008
- ISBN:
- 9780199213245
- eISBN:
- 9780191707582
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199213245.003.0015
- Subject:
- Physics, Condensed Matter Physics / Materials
Refraction and small-angle scattering can provide unique imaging signals in situations where absorption- or other attenuation-based effects are insufficient. Attenuation contrast is low in cases ...
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Refraction and small-angle scattering can provide unique imaging signals in situations where absorption- or other attenuation-based effects are insufficient. Attenuation contrast is low in cases where either the absolute values of the attenuation coefficients of the individual components of the object are low, or the differences between the various components are small. In such cases, other contrast mechanisms have to be employed for imaging such as the phase contrast described in the previous chapter. This chapter discusses two additional contrast mechanisms: refraction tomography and small-angle scattering tomography. Experimental results for both techniques are presented.Less
Refraction and small-angle scattering can provide unique imaging signals in situations where absorption- or other attenuation-based effects are insufficient. Attenuation contrast is low in cases where either the absolute values of the attenuation coefficients of the individual components of the object are low, or the differences between the various components are small. In such cases, other contrast mechanisms have to be employed for imaging such as the phase contrast described in the previous chapter. This chapter discusses two additional contrast mechanisms: refraction tomography and small-angle scattering tomography. Experimental results for both techniques are presented.
Alan Gilchrist
- Published in print:
- 2012
- Published Online:
- September 2012
- ISBN:
- 9780199597277
- eISBN:
- 9780191741883
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780199597277.003.0006
- Subject:
- Psychology, Cognitive Psychology, Vision
Every perceptual experience has an objective and a subjective side. We see object size, independent of distance, but we also see that distant objects project smaller images. Early modern conceptions ...
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Every perceptual experience has an objective and a subjective side. We see object size, independent of distance, but we also see that distant objects project smaller images. Early modern conceptions focused on local stimulation and thus on the subjective aspect. Helmholtz and Hering emphasized the objective aspect. Helmholtz split visual experience into two stages, with sensation representing the subjective side and perception, through cognitive processes, the objective side. Gestalt theory denied this dualism, rejecting both sensory and cognitive stages. Despite contrary evidence, the sensation/perception dualism persists, in brightness models and past experience theories. That we can detect visual angle and luminance does not mean that these are raw sensations out of which perception of size and lightness is built. Size and color constancy are truly visual, not cognitive. Instructions to subjects in vision experiments must avoid the proximal mode on the one hand and cognitive judgments on the other.Less
Every perceptual experience has an objective and a subjective side. We see object size, independent of distance, but we also see that distant objects project smaller images. Early modern conceptions focused on local stimulation and thus on the subjective aspect. Helmholtz and Hering emphasized the objective aspect. Helmholtz split visual experience into two stages, with sensation representing the subjective side and perception, through cognitive processes, the objective side. Gestalt theory denied this dualism, rejecting both sensory and cognitive stages. Despite contrary evidence, the sensation/perception dualism persists, in brightness models and past experience theories. That we can detect visual angle and luminance does not mean that these are raw sensations out of which perception of size and lightness is built. Size and color constancy are truly visual, not cognitive. Instructions to subjects in vision experiments must avoid the proximal mode on the one hand and cognitive judgments on the other.
Robert G. Cook and Carl Erick Hagmann
- Published in print:
- 2012
- Published Online:
- May 2012
- ISBN:
- 9780195334654
- eISBN:
- 9780199933167
- Item type:
- chapter
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780195334654.003.0004
- Subject:
- Psychology, Cognitive Neuroscience, Cognitive Psychology
This chapter examines early visual processing in birds revealed by the analysis of multi-element textured arrays. Pigeons, and presumably most other species of birds, share many common properties ...
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This chapter examines early visual processing in birds revealed by the analysis of multi-element textured arrays. Pigeons, and presumably most other species of birds, share many common properties with humans regarding the early registration and grouping of visual information. Overall, perceptual grouping involves spatially parallel processes that cover an extensive area of their frontal visual field. Initially, this information is separated into different streams that map the features of visual dimensions like color, orientation, brightness, and likely other features associated with different shapes, such as terminations, angles, parallelism, or curvature. The critical outputs from these different streams are the identity and location of linear edges and boundaries and their relation to larger homogeneous regions of highly similar elements. These outputs are critically involved in the construction of object shape and surface relations, as well as in the determination of figure-ground status. These different streams converge to produce a multidimensional map where this information is combined.Less
This chapter examines early visual processing in birds revealed by the analysis of multi-element textured arrays. Pigeons, and presumably most other species of birds, share many common properties with humans regarding the early registration and grouping of visual information. Overall, perceptual grouping involves spatially parallel processes that cover an extensive area of their frontal visual field. Initially, this information is separated into different streams that map the features of visual dimensions like color, orientation, brightness, and likely other features associated with different shapes, such as terminations, angles, parallelism, or curvature. The critical outputs from these different streams are the identity and location of linear edges and boundaries and their relation to larger homogeneous regions of highly similar elements. These outputs are critically involved in the construction of object shape and surface relations, as well as in the determination of figure-ground status. These different streams converge to produce a multidimensional map where this information is combined.
Joachim Frank
- Published in print:
- 2006
- Published Online:
- April 2010
- ISBN:
- 9780195182187
- eISBN:
- 9780199893416
- Item type:
- book
- Publisher:
- Oxford University Press
- DOI:
- 10.1093/acprof:oso/9780195182187.001.0001
- Subject:
- Biology, Biochemistry / Molecular Biology
In this book, the mathematical principles and working methods of single-particle reconstruction are described; a method designed to retrieve three-dimensional structural information from electron ...
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In this book, the mathematical principles and working methods of single-particle reconstruction are described; a method designed to retrieve three-dimensional structural information from electron micrographs showing thousands of “copies” of biological molecules trapped in a thin layer of ice. This technique is uniquely suited to obtain three-dimensional images of molecular machines in different functional states, as it dispenses with the need for crystals. The book starts with an introduction of image formation in the electron microscope, which includes the definition of the contrast transfer function. Next, averaging techniques and tools for image alignment, multivariate data analysis, and classification are described. An introduction into the mathematical principles underlying reconstruction of an object from its projections is followed by detailed accounts on how projection angles are determined, and how reconstruction is done in practice. The book concludes with a chapter on interpretation of density maps reconstructed, including methods for segmentation as well as fitting and docking of atomic coordinates.Less
In this book, the mathematical principles and working methods of single-particle reconstruction are described; a method designed to retrieve three-dimensional structural information from electron micrographs showing thousands of “copies” of biological molecules trapped in a thin layer of ice. This technique is uniquely suited to obtain three-dimensional images of molecular machines in different functional states, as it dispenses with the need for crystals. The book starts with an introduction of image formation in the electron microscope, which includes the definition of the contrast transfer function. Next, averaging techniques and tools for image alignment, multivariate data analysis, and classification are described. An introduction into the mathematical principles underlying reconstruction of an object from its projections is followed by detailed accounts on how projection angles are determined, and how reconstruction is done in practice. The book concludes with a chapter on interpretation of density maps reconstructed, including methods for segmentation as well as fitting and docking of atomic coordinates.
Dan Margalit and Matt Clay (eds)
- Published in print:
- 2017
- Published Online:
- May 2018
- ISBN:
- 9780691158662
- eISBN:
- 9781400885398
- Item type:
- book
- Publisher:
- Princeton University Press
- DOI:
- 10.23943/princeton/9780691158662.001.0001
- Subject:
- Mathematics, Geometry / Topology
Geometric group theory is the study of the interplay between groups and the spaces they act on, and has its roots in the works of Henri Poincaré, Felix Klein, J.H.C. Whitehead, and Max Dehn. This ...
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Geometric group theory is the study of the interplay between groups and the spaces they act on, and has its roots in the works of Henri Poincaré, Felix Klein, J.H.C. Whitehead, and Max Dehn. This book brings together leading experts who provide one-on-one instruction on key topics in this exciting and relatively new field of mathematics. It's like having office hours with your most trusted math professors. An essential primer for undergraduates making the leap to graduate work, the book begins with free groups—actions of free groups on trees, algorithmic questions about free groups, the ping-pong lemma, and automorphisms of free groups. It goes on to cover several large-scale geometric invariants of groups, including quasi-isometry groups, Dehn functions, Gromov hyperbolicity, and asymptotic dimension. It also delves into important examples of groups, such as Coxeter groups, Thompson's groups, right-angled Artin groups, lamplighter groups, mapping class groups, and braid groups. The tone is conversational throughout, and the instruction is driven by examples. It features numerous exercises and in-depth projects designed to engage readers and provide jumping-off points for research projects.Less
Geometric group theory is the study of the interplay between groups and the spaces they act on, and has its roots in the works of Henri Poincaré, Felix Klein, J.H.C. Whitehead, and Max Dehn. This book brings together leading experts who provide one-on-one instruction on key topics in this exciting and relatively new field of mathematics. It's like having office hours with your most trusted math professors. An essential primer for undergraduates making the leap to graduate work, the book begins with free groups—actions of free groups on trees, algorithmic questions about free groups, the ping-pong lemma, and automorphisms of free groups. It goes on to cover several large-scale geometric invariants of groups, including quasi-isometry groups, Dehn functions, Gromov hyperbolicity, and asymptotic dimension. It also delves into important examples of groups, such as Coxeter groups, Thompson's groups, right-angled Artin groups, lamplighter groups, mapping class groups, and braid groups. The tone is conversational throughout, and the instruction is driven by examples. It features numerous exercises and in-depth projects designed to engage readers and provide jumping-off points for research projects.
