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Author: J.R. Fryer
Publisher: Springer Science & Business Media
ISBN: 940113278X
Category : Science
Languages : en
Pages : 388
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Book Description
Maximum Entropy (ME) techniques have found widespread applicability in the reconstruction of incomplete or noisy data. These techniques have been applied in many areas of data analysis including imaging, spectroscopy, and scattering [Gull and Skilling, 1984]. The techniques have proven particularly useful in astronomy [Narayan and Nityanada, 1984]. In many of these applications the goal of the reconstruction is the detection of point objects against a noisy background. In this work we investigate the applicability of ME techniques to data sets which have strong components which are periodic in space or time. The specific interest in our laboratory is High Resolution Electron Micrographs of beam sensitive materials. However, ME techniques are of general interest for all types of data. These data mayor may not have a spatial or temporal character. Figure 1 shows an HREM image of the rigid-rod polymer poly(paraphenylene benzobisoxazole) (PBZO). The 0.55 nm spacings in the image correspond to the lateral close-packing between the extended polymer molecules. Near the center of this crystallite there is evidence for an edge dislocation. In HREM images both the frequency and position of the infonnation is important for a proper interpretation. Therefore, it is necessary to consider how image processing affects the fidelity of this information in both real and Fourier space.
Author: J.R. Fryer
Publisher: Springer Science & Business Media
ISBN: 940113278X
Category : Science
Languages : en
Pages : 388
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Book Description
Maximum Entropy (ME) techniques have found widespread applicability in the reconstruction of incomplete or noisy data. These techniques have been applied in many areas of data analysis including imaging, spectroscopy, and scattering [Gull and Skilling, 1984]. The techniques have proven particularly useful in astronomy [Narayan and Nityanada, 1984]. In many of these applications the goal of the reconstruction is the detection of point objects against a noisy background. In this work we investigate the applicability of ME techniques to data sets which have strong components which are periodic in space or time. The specific interest in our laboratory is High Resolution Electron Micrographs of beam sensitive materials. However, ME techniques are of general interest for all types of data. These data mayor may not have a spatial or temporal character. Figure 1 shows an HREM image of the rigid-rod polymer poly(paraphenylene benzobisoxazole) (PBZO). The 0.55 nm spacings in the image correspond to the lateral close-packing between the extended polymer molecules. Near the center of this crystallite there is evidence for an edge dislocation. In HREM images both the frequency and position of the infonnation is important for a proper interpretation. Therefore, it is necessary to consider how image processing affects the fidelity of this information in both real and Fourier space.
Author: D. Dorset
Publisher: Springer Science & Business Media
ISBN: 9401589712
Category : Science
Languages : en
Pages : 447
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Book Description
The re-emergent field of quantitative electron crystallography is described by some of its most eminent practitioners. They describe the theoretical framework for electron scattering, specimen preparation, experimental techniques for optimum data collection, the methodology of structure analysis and refinement, and a range of applications to inorganic materials (including minerals), linear polymers, small organic molecules (including those used in nonlinear optical devices), incommensurately modulated structures (including superconductors), alloys, and integral membrane proteins. The connection between electron crystallography and X-ray crystallography is clearly defined, especially in the utilisation of the latest methods for direct determination of crystallographic phases, as well as the unique role of image analysis of high-resolution electron micrographs for phase determination. Even the aspect of multiple beam dynamic diffraction (once dreaded because it was thought to preclude ab initio analysis) is considered as a beneficial aid for symmetry determination as well as the elucidation of crystallographic phases, and as a criterion for monitoring the progress of structure refinement. Whereas other texts have hitherto preferentially dealt with the analysis of electron diffraction and image data from thin organic materials, this work discusses - with considerable optimism - the prospects of looking at `harder' materials, composed of heavier atoms. Audience: Could be used with profit as a graduate-level course on electron crystallography. Researchers in the area will find a statement of current progress in the field.
Author: Thomas E. Weirich
Publisher: Springer Science & Business Media
ISBN: 1402039204
Category : Science
Languages : en
Pages : 533
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Book Description
During the last decade we have been witness to several exciting achievements in electron crystallography. This includes structural and charge density studies on organic molecules complicated inorganic and metallic materials in the amorphous, nano-, meso- and quasi-crystalline state and also development of new software, tailor-made for the special needs of electron crystallography. Moreover, these developments have been accompanied by a now available new generation of computer controlled electron microscopes equipped with high-coherent field-emission sources, cryo-specimen holders, ultra-fast CCD cameras, imaging plates, energy filters and even correctors for electron optical distortions. Thus, a fast and semi-automatic data acquisition from small sample areas, similar to what we today know from imaging plates diffraction systems in X-ray crystallography, can be envisioned for the very near future. This progress clearly shows that the contribution of electron crystallography is quite unique, as it enables to reveal the intimate structure of samples with high accuracy but on much smaller samples than have ever been investigated by X-ray diffraction. As a tribute to these tremendous recent achievements, this NATO Advanced Study Institute was devoted to the novel approaches of electron crystallography for structure determination of nanosized materials.
Author: D. Dorset
Publisher: Springer
ISBN: 9780792348764
Category : Science
Languages : en
Pages : 464
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Book Description
The re-emergent field of quantitative electron crystallography is described by some of its most eminent practitioners. They describe the theoretical framework for electron scattering, specimen preparation, experimental techniques for optimum data collection, the methodology of structure analysis and refinement, and a range of applications to inorganic materials (including minerals), linear polymers, small organic molecules (including those used in nonlinear optical devices), incommensurately modulated structures (including superconductors), alloys, and integral membrane proteins. The connection between electron crystallography and X-ray crystallography is clearly defined, especially in the utilisation of the latest methods for direct determination of crystallographic phases, as well as the unique role of image analysis of high-resolution electron micrographs for phase determination. Even the aspect of multiple beam dynamic diffraction (once dreaded because it was thought to preclude ab initio analysis) is considered as a beneficial aid for symmetry determination as well as the elucidation of crystallographic phases, and as a criterion for monitoring the progress of structure refinement. Whereas other texts have hitherto preferentially dealt with the analysis of electron diffraction and image data from thin organic materials, this work discusses - with considerable optimism - the prospects of looking at `harder' materials, composed of heavier atoms. Audience: Could be used with profit as a graduate-level course on electron crystallography. Researchers in the area will find a statement of current progress in the field.
Author: Edgar A. Silinsh
Publisher: Springer Science & Business Media
ISBN: 3642814646
Category : Science
Languages : en
Pages : 404
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Book Description
This book is based on the results of many years of experimental work by the author and his colleagues, dealing with the electronic properties of organic crystals. E. Silinsh has played a leading role in pOinting out the importance of the polarization energy by an excess carrier, in determining not only the character of the carrier mobility in organic crystals, but in determining the band gap and the nature of the all-important trapping site in these crystals. The one-electron model of electronic conductivity that has been so successful in dealing with inorganic semiconductors is singular ly unsuccessful in rationalizing the unusual physical properties of organic crystals. A many-body theory is required, and the experimental manifestation of this is the central role played by the crystal polarization enerqies in transferring the results obtained with the isolated molecule, to the solid. The careful studies of E. Silinsh in this field have shown tn detail how this polarization energy develops around the excess carrier (and also the hole-electron pair) sitting on a molecular site in the crystal. As with all insulators, trapping sites playa dominant role in reducing the magnitude of ~he current that can theoretically pass through the organic crystal. It is usually the case that these trapping sites are energetically distributed within the forbidden band of the crystal. For many years, an exponential distribution has shown itself to be useful and reasonably correct: However,' E.
Author: Norbert Karl
Publisher: Springer Science & Business Media
ISBN: 3642762530
Category : Science
Languages : en
Pages : 169
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Book Description
Lattice defects of organic molecular crystals affect their optical or electrical properties by changing the local energy structure. Lattice defects also playa very important role in the chemical and physical properties, for example, as an active site of a catalyst or an initiating point of a solid state reaction. However, very little has been reported on the defect structure of real organic crystals. In the past ten years it became clear that the origin and the structure of the defects depend on the geometrical and chemical nature of the building units of the crystal, the molecules. Molecular size, form and anisotropy, charge distribution, etc. cause the characteristic structure of the defect. Accordingly, a defect structure found in one compound may not be found in others. The defect structure of an organic crystal cannot be defined solely by the displacement of the molecular center from the normal lattice site. A rotational displacement of a molecule is frequently accompanied by a parallel shift of the molecular center. In addition to the usual geometrical crystallographic defects, chemical defects are important too which originate, for example, from differences in the substitution sites of molecules carrying side groups. In order to reveal such defect structures, direct imaging of molecules by high resolution electron microscopy is the only direct method.
Author: D.L. Dorset
Publisher: Springer Science & Business Media
ISBN: 1475766211
Category : Science
Languages : en
Pages : 455
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Book Description
This authoritative text on electron diffraction and crystal structure analysis is the first to describe direct phasing techniques in electron crystallography. Written for electron diffractionists and electron microscopists, this fully illustrated volume presents methods for specimen preparation, data collection and structure analysis. Chapters feature numerous detailed examples of actual structure analyses and contain over 350 illustrations.
Author: Jack D. Dunitz
Publisher: Wiley-VCH
ISBN:
Category : Science
Languages : en
Pages : 520
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Book Description
This book is the second corrected reprint of â2X-Ray Analysisâ2, published in 1979 and consists of two parts. Part one is about Crystal Structure Analysis, part two deals with Molecular Structure. All the information in this volume is of considerable value especially to those engaged in, or about to embark upon, X-ray crystal structure analysis.
Author: Peter W. Hawkes
Publisher: Springer Nature
ISBN: 3030000699
Category : Technology & Engineering
Languages : en
Pages : 1561
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Book Description
This book features reviews by leading experts on the methods and applications of modern forms of microscopy. The recent awards of Nobel Prizes awarded for super-resolution optical microscopy and cryo-electron microscopy have demonstrated the rich scientific opportunities for research in novel microscopies. Earlier Nobel Prizes for electron microscopy (the instrument itself and applications to biology), scanning probe microscopy and holography are a reminder of the central role of microscopy in modern science, from the study of nanostructures in materials science, physics and chemistry to structural biology. Separate chapters are devoted to confocal, fluorescent and related novel optical microscopies, coherent diffractive imaging, scanning probe microscopy, transmission electron microscopy in all its modes from aberration corrected and analytical to in-situ and time-resolved, low energy electron microscopy, photoelectron microscopy, cryo-electron microscopy in biology, and also ion microscopy. In addition to serving as an essential reference for researchers and teachers in the fields such as materials science, condensed matter physics, solid-state chemistry, structural biology and the molecular sciences generally, the Springer Handbook of Microscopy is a unified, coherent and pedagogically attractive text for advanced students who need an authoritative yet accessible guide to the science and practice of microscopy.
Author: Angelo Gavezzotti
Publisher: Elsevier
ISBN: 0128237481
Category : Science
Languages : en
Pages : 304
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Book Description
The Crystalline States of Organic Compounds is a broad survey of the techniques by which molecular crystals are investigated, modeled, and applied, starting with the fundamentals of intra- and intermolecular bonding supplemented by a concise tutorial on present-day diffraction methods, then proceeding to an examination of crystallographic databases with their statistics and of such fundamental and fast-growing topics as intermolecular potentials, polymorphism, co-crystallization, and crystal structure prediction by computer. A substantial part of the book is devoted to the techniques of choice in modern simulation, Monte Carlo and molecular dynamics, with their most recent developments and application to formed crystals and to the concomitant phases involved in nucleation and growth. Drawing on the decades-long experience of its author in teaching and research in the field of organic solid state, The Crystalline States of Organic Compounds is an indispensable source of key insights and future directions for students and researchers at any level, in academia and in industry. Condenses theoretical information and practical methods in a single resource Provides a guide on the use of crystallographic databases, structure statistics, and molecular simulations Includes a large number of worked examples and tutorials, with extensive graphics and multimedia
