Electron crystallography

1996 ◽  
Vol 52 (5) ◽  
pp. 753-769 ◽  
Author(s):  
D. L. Dorset
Keyword(s):  
Inorganic Materials ◽  
Electron Crystallography ◽  
Data Set ◽  
Bonding Parameters ◽  
Resolution Electron ◽  
Experimental Parameters ◽  
History Of ◽  
Controversial Topic ◽  
Kinematical Data ◽  
High Resolution Electron Micrographs

The idea of solving unknown crystal structures from experimental electron-diffraction intensities and high-resolution electron micrographs has remained a controversial topic in the 60 year history of electron crystallography. In this review it will be shown that the application of modern direct phasing techniques, familiar to X-ray crystallographers, has decisively proven that such ab initio determinations are, in fact, possible. This statement does not, by any means, refute the existence of the several significant scattering perturbations identified by diffraction physicists. Rather, it does affirm that experimental parameters can be controlled to ensure that a `quasi-kinematical' data set can be collected from many types of specimens. Numerous applications have been made to various types of specimens, ranging from small organics to proteins, and also some inorganic materials. While electron crystallography may not be the optimal means for determining accurate bonding parameters, it is often the method of choice when only microcrystalline specimens are available.

3-D diffraction intensities of the crotoxin complex crystal

1986 ◽  
Vol 44 ◽  
pp. 162-163
Author(s):  
B.V.V. Prasad ◽  
L.L. Degn ◽  
T.-W. Jeng ◽  
W. Chiu
Keyword(s):  
High Resolution ◽  
Intensity Data ◽  
Electron Crystallography ◽  
Data Set ◽  
Crotalus Durissus Terrificus ◽  
Cold Stage ◽  
Resolution Electron ◽  
Diffraction Patterns ◽  
Crotalus Durissus ◽  
Complex Crystal

The crotoxin complex, a neurotoxin from the venom of the Brazilian rattlesnake, Crotalus durissus terrificus, forms thin crystals suitable for high resolution electron crystallography. These crystals grow to variable completions of the unit cell, making it difficult to merge the intensity data from different crystals. This difficulty is overcome by collecting as many electron diffraction patterns (EDP) as possible from a single crystal tilted from +60° to -60°. Several series of approximately twenty EDP's were collected using a Philips 400 equipped with a cold stage at MRC, Cambridge in Dr. R. Henderson's laboratory. We report here our progress in synthesizing a 3-D intensity data set from these series.

Structure Determination of Atomically Controlled Crystal Architectures Grown within Single Wall Carbon Nanotubes

2005 ◽  
Vol 11 (5) ◽  
pp. 401-409 ◽  
Author(s):  
Angus I. Kirkland ◽  
Rüdiger R. Meyer ◽  
J. Sloan ◽  
J.L. Hutchison
Keyword(s):  
Carbon Nanotubes ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Inorganic Materials ◽  
Single Wall Carbon Nanotubes ◽  
Objective Lens ◽  
Data Set ◽  
Resolution Electron ◽  
Wide Range ◽  
Resolution Imaging

Indirect high resolution electron microscopy using one of several possible data-set geometries offers advantages over conventional high-resolution imaging in enabling the recovery of the complex wavefunction at the specimen exit plane and simultaneously eliminating the aberrations present in the objective lens. This article discusses results obtained using this method from structures formed by inorganic materials confined within the bores of carbon nanotubes. Such materials are shown to be atomically regulated due to their confinement, leading to integral layer architectures that we have termed “Feynman crystals.” These one-dimensional (1D) crystals also show a wide range of structural deviations from the bulk, including unexpected lattice distortions, and in some cases entirely new forms have been observed.

The High Resolution Appearance of Biological Substrates

1969 ◽  
Vol 27 ◽  
pp. 416-417
Author(s):  
Glen B. Haydon
Keyword(s):  
High Resolution ◽  
Phase Image ◽  
Biological Structure ◽  
Electron Microscopic ◽  
Thin Sections ◽  
Resolution Electron ◽  
Discrete Structures ◽  
Large Phase ◽  
Biological Substrates ◽  
High Resolution Electron Micrographs

High resolution electron microscopic study of negatively stained macromolecules and thin sections of tissue embedded in a variety of media are difficult to interpret because of the superimposed phase image granularity. Although all of the information concerning the biological structure of interest may be present in a defocused electron micrograph, the high contrast of large phase image granules produced by the substrate makes it impossible to distinguish the phase ‘points’ from discrete structures of the same dimensions. Theory predicts the findings; however, it does not allow an appreciation of the actual appearance of the image under various conditions. Therefore, though perhaps trivial, training of the cheapest computer produced by mass labor has been undertaken in order to learn to appreciate the factors which affect the appearance of the background in high resolution electron micrographs.

Limits for high-resolution electron microscopy of inorganic materials?

1987 ◽  
Vol 45 ◽  
pp. 4-5
Author(s):  
David J. Smith
Keyword(s):  
Electron Microscopy ◽  
Spherical Aberration ◽  
High Resolution Electron Microscopy ◽  
Inorganic Materials ◽  
Atomic Scale ◽  
Resolution Limit ◽  
Contrast Transfer Function ◽  
Existing Problems ◽  
Resolution Electron ◽  
Electron Microscopes

The era of atomic-resolution electron microscopy has finally arrived. In virtually all inorganic materials, including oxides, metals, semiconductors and ceramics, it is possible to image individual atomic columns in low-index zone-axis projections. A whole host of important materials’ problems involving defects and departures from nonstoichiometry on the atomic scale are waiting to be tackled by the new generation of intermediate voltage (300-400keV) electron microscopes. In this review, some existing problems and limitations associated with imaging inorganic materials are briefly discussed. The more immediate problems encountered with organic and biological materials are considered elsewhere.Microscope resolution. It is less than a decade since the state-of-the-art, commercially available TEM was a 200kV instrument with a spherical aberration coefficient of 1.2mm, and an interpretable resolution limit (ie. first zero crossover of the contrast transfer function) of 2.5A.

Dynamic low-dose electron diffraction and imaging of phase transitions in polymers

1993 ◽  
Vol 51 ◽  
pp. 890-891
Author(s):  
David C. Martin ◽  
Jun Liao
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Electron Diffraction ◽  
Low Dose ◽  
Dark Field ◽  
Continuous Change ◽  
Selected Area Electron Diffraction ◽  
Resolution Electron ◽  
Chain Axis ◽  
High Resolution Electron Micrographs

By careful control of the electron beam it is possible to simultaneously induce and observe the phase transformation from monomer to polymer in certain solid-state polymcrizable diacetylenes. The continuous change in the crystal structure from DCHD diacetylene monomer (a=1.76 nm, b=1.36 nm, c=0.455 nm, γ=94 degrees, P2l/c) to polymer (a=1.74 nm, b=1.29 nm, c=0.49 nm, γ=108 degrees, P2l/c) occurs at a characteristic dose (10−4C/cm2) which is five orders of magnitude smaller than the critical end point dose (20 C/cm2). Previously we discussed the progress of this phase transition primarily as observed down the [001] zone (the chain axis direction). Here we report on the associated changes of the dark field (DF) images and selected area electron diffraction (SAED) patterns of the crystals as observed from the side (i.e., in the [hk0] zones).High resolution electron micrographs (HREM), DF images, and SAED patterns were obtained on a JEOL 4000 EX HREM operating at 400 kV.

Shot-noise simulations of HREM images of polymer crystals

1989 ◽  
Vol 47 ◽  
pp. 342-343
Author(s):  
Philippe Pradère ◽  
Edwin L. Thomas
Keyword(s):  
Low Dose ◽  
Molecular Level ◽  
High Resolution Electron Microscopy ◽  
Crystal Defects ◽  
Inorganic Materials ◽  
Photographic Emulsion ◽  
Polymer Crystals ◽  
Resolution Electron ◽  
Recent Developments ◽  
Lattice Images

High Resolution Electron Microscopy (HREM) is a very powerful technique for the study of crystal defects at the molecular level. Unfortunately polymer crystals are beam sensitive and are destroyed almost instantly under the typical HREM imaging conditions used for inorganic materials. Recent developments of low dose imaging at low magnification have nevertheless permitted the attainment of lattice images of very radiation sensitive polymers such as poly-4-methylpentene-1 and enabled molecular level studies of crystal defects in somewhat more resistant ones such as polyparaxylylene (PPX) [2].With low dose conditions the images obtained are very noisy. Noise arises from the support film, photographic emulsion granularity and in particular, the statistical distribution of electrons at the typical doses of only few electrons per unit resolution area. Figure 1 shows the shapes of electron distribution, according to the Poisson formula :

The Contribution of Phonon-Scattered Electrons to High-Resolution Electron Micrographs of Crystals

1990 ◽  
Vol 48 (1) ◽  
pp. 62-63
Author(s):  
H. Kohl
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
High Resolution Electron Microscopy ◽  
Static Potential ◽  
Qualitative Comparison ◽  
The Past ◽  
Resolution Electron ◽  
High Resolution Images ◽  
High Resolution Electron Micrographs ◽  
Extract Information

High-Resolution Electron Microscopy is able to determine structures of crystals and interfaces with a spatial resolution of somewhat less than 2 Å. As the image is strongly dependent on instrumental parameters, notably the defocus and the spherical aberration, the interpretation of micrographs necessitates a comparison with calculated images. Whereas one has often been content with a qualitative comparison of theory with experiment in the past, one is currently striving for quantitative procedures to extract information from the images [1,2]. For the calculations one starts by assuming a static potential, thus neglecting inelastic scattering processes.We shall confine the discussion to periodic specimens. All electrons, which have only been elastically scattered, are confined to very few directions, the Bragg spots. In-elastically scattered electrons, however, can be found in any direction. Therefore the influence of inelastic processes on the elastically (= Bragg) scattered electrons can be described as an attenuation [3]. For the calculation of high-resolution images this procedure would be correct only if we had an imaging energy filter capable of removing all phonon-scattered electrons. This is not realizable in practice. We are therefore forced to include the contribution of the phonon-scattered electrons.

Economics of respiratory disease in dairy replacement heifers

2020 ◽  
Vol 21 (2) ◽  
pp. 143-148
Author(s):  
Michael W. Overton
Keyword(s):  
Respiratory Disease ◽  
Milk Production ◽  
Incident Case ◽  
Data Set ◽  
Dairy Heifers ◽  
The Usa ◽  
History Of ◽  
On Farm ◽  
The Impact ◽  
Selective Culling

AbstractBovine respiratory disease (BRD) is a frequent disease concern in dairy cattle and is most commonly diagnosed in young dairy heifers. The impact of BRD is highly variable, depending on the accuracy and completeness of detection, effectiveness of treatment, and on-farm culling practices. Consequences include decreased rate of weight gain, a higher culling risk either as heifers or as cows, delayed age at first service, delayed age at first calving, and in some cases, lower future milk production. In this data set of 104,100 dairy replacement heifers from across the USA, 36.6% had one or more cases diagnosed within the first 120 days of age with the highest risk of new cases occurring prior to weaning. Comparison of the raising cost for heifers with BRD and those without a recorded history of BRD resulted in an estimated cost per incident case occurring in the first 120 days of age of $252 or $282, depending upon whether anticipated future milk production differences were considered or not. Current market conditions contributed to a cost estimate that is significantly higher than previously published estimates, driven in part by the losses associated with selective culling of a subset of heifers that experienced BRD.

Characteristics and Care of U.S. Nursing Home Residents with a History of Chronic Mental Illness

2000 ◽  
Vol 19 (S2) ◽  
pp. 1-17 ◽  
Author(s):  
Charles D. Phillips ◽  
Kathleen M. Spry
Keyword(s):  
Nursing Home ◽  
Nursing Home Residents ◽  
Minimum Data Set ◽  
Chronic Mental Illness ◽  
Data Set ◽  
Minimum Data ◽  
Troubles Mentaux ◽  
History Of ◽  
Resident Assessment ◽  
Medicaments Psychotropes

RÉSUMÉTrès peu de recherches ont été effectuées sur les pensionnaires des maisons de soins ayant manifestés des troubles mentaux chroniques sans démence avant leur entrée en institution. Les données du Minimum Data Set for Nursing Home Resident Assessment and Care Screening (MDS) de 1993 ont été utilisées pouranalyser les différences dans les caractéristiques et les soins se rapportant à ce type de pensionnaires par rapport aux autres pensionnaires. Cette enquête portait sur 70 000 pensionnaires du Kansas, du Maine, du Mississippi et du Dakota du Sud. Les caractéristiques des pensionnaires qui éprouvaient ce type de troubles mentaux chroniques étaient plus fréquemment les suivantes: sexe masculin, 65 ans et plus, bénéficiaires de Medicaid, moins médicalement inaptes et niveau plus élevé de problèmes de comportements. Ces pensionnaires reçoivent aussi davantage de médicaments psychotropes et suivant une thérapie, la prévalence de la thérapie étant cependant moins éleveé. Les informations recueillies pourraient laisser croire que les soins accordés à ces pensionnaires ne sont pas des plus appropriés.

scholarly journals The complete mitochondrial genome of the intertidal spider (Desis jiaxiangi) provides novel insights into the adaptive evolution of the mitogenome and the evolution of spiders

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
Fan Li ◽  
Yunyun Lv ◽  
Zhengyong Wen ◽  
Chao Bian ◽  
Xinhui Zhang ◽  
...  
Keyword(s):  
Positive Selection ◽  
Adaptive Evolution ◽  
Physiological Activity ◽  
Complete Mitochondrial Genome ◽  
Dynamic Environment ◽  
Data Set ◽  
History Of ◽  
Complete Mitogenome ◽  
Selection Signal ◽  
Positive Selection Signal

Abstract Background Although almost all extant spider species live in terrestrial environments, a few species live fully submerged in freshwater or seawater. The intertidal spiders (genus Desis) built silk nests within coral crevices can survive submerged in high tides. The diving bell spider, Argyroneta aquatica, resides in a similar dynamic environment but exclusively in freshwater. Given the pivotal role played by mitochondria in supplying most energy for physiological activity via oxidative phosphorylation and the environment, herein we sequenced the complete mitogenome of Desis jiaxiangi to investigate the adaptive evolution of the aquatic spider mitogenomes and the evolution of spiders. Results We assembled a complete mitogenome of the intertidal spider Desis jiaxiangi and performed comparative mitochondrial analyses of data set comprising of Desis jiaxiangi and other 45 previously published spider mitogenome sequences, including that of Argyroneta aquatica. We found a unique transposition of trnL2 and trnN genes in Desis jiaxiangi. Our robust phylogenetic topology clearly deciphered the evolutionary relationships between Desis jiaxiangi and Argyroneta aquatica as well as other spiders. We dated the divergence of Desis jiaxiangi and Argyroneta aquatica to the late Cretaceous at ~ 98 Ma. Our selection analyses detected a positive selection signal in the nd4 gene of the aquatic branch comprising both Desis jiaxiangi and Argyroneta aquatica. Surprisingly, Pirata subpiraticus, Hypochilus thorelli, and Argyroneta aquatica each had a higher Ka/Ks value in the 13 PCGs dataset among 46 taxa with complete mitogenomes, and these three species also showed positive selection signal in the nd6 gene. Conclusions Our finding of the unique transposition of trnL2 and trnN genes indicates that these genes may have experienced rearrangements in the history of intertidal spider evolution. The positive selection signals in the nd4 and nd6 genes might enable a better understanding of the spider metabolic adaptations in relation to different environments. Our construction of a novel mitogenome for the intertidal spider thus sheds light on the evolutionary history of spiders and their mitogenomes.

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