An electron-microscopic and X-ray study of complex exsolution textures in a cryptoperthitic alkali feldspar

1973 ◽  
Vol 8 (4) ◽  
pp. 461-466 ◽  
Author(s):  
C. Willaime ◽  
W. L. Brown ◽  
M. Gandais
Keyword(s):  
Alkali Feldspar ◽  
Electron Microscopic ◽  
X Ray

Direct visualization of phase-separated domains in lipid membranes

1978 ◽  
Vol 36 (2) ◽  
pp. 290-291
Author(s):  
S. W. Hui ◽  
T. P. Stewart
Keyword(s):  
Lipid Membranes ◽  
Structural Information ◽  
Freeze Fracture ◽  
Biological Molecules ◽  
Vacuum Drying ◽  
Direct Visualization ◽  
X Ray Diffraction ◽  
Electron Microscopic ◽  
X Ray ◽  
Hydrocarbon Chains

Direct electron microscopic study of biological molecules has been hampered by such factors as radiation damage, lack of contrast and vacuum drying. In certain cases, however, the difficulties may be overcome by using redundent structural information from repeating units and by various specimen preservation methods. With bilayers of phospholipids in which both the solid and fluid phases co-exist, the ordering of the hydrocarbon chains may be utilized to form diffraction contrast images. Domains of different molecular packings may be recgnizable by placing properly chosen filters in the diffraction plane. These domains would correspond to those observed by freeze fracture, if certain distinctive undulating patterns are associated with certain molecular packing, as suggested by X-ray diffraction studies. By using an environmental stage, we were able to directly observe these domains in bilayers of mixed phospholipids at various temperatures at which their phases change from misible to inmissible states.

Polarity Determination in Sphalerite and Wurtzite Structures

1990 ◽  
Vol 48 (2) ◽  
pp. 500-501
Author(s):  
Stuart McKernan ◽  
C. Barry Carter
Keyword(s):  
Opposite Polarity ◽  
Single Domain ◽  
Polar Material ◽  
Electron Microscopic ◽  
Dynamical Interaction ◽  
X Ray ◽  
Polarity Determination ◽  
The Absolute ◽  
Microscopic Techniques

The determination of the absolute polarity of a polar material is often crucial to the understanding of the defects which occur in such materials. Several methods exist by which this determination may be performed. In bulk, single-domain specimens, macroscopic techniques may be used, such as the different etching behavior, using the appropriate etchant, of surfaces with opposite polarity. X-ray measurements under conditions where Friedel’s law (which means that the intensity of reflections from planes of opposite polarity are indistinguishable) breaks down can also be used to determine the absolute polarity of bulk, single-domain specimens. On the microscopic scale, and particularly where antiphase boundaries (APBs), which separate regions of opposite polarity exist, electron microscopic techniques must be employed. Two techniques are commonly practised; the first [1], involves the dynamical interaction of hoLz lines which interfere constructively or destructively with the zero order reflection, depending on the crystal polarity. The crystal polarity can therefore be directly deduced from the relative intensity of these interactions.

X-Ray Microanalysis of Nickel and Cobalt Intensified Peroxidase- Antiperoxidase For Verification of Reaction Sites

1985 ◽  
Vol 43 ◽  
pp. 468-469
Author(s):  
A. Angel ◽  
K. Miller ◽  
V. Seybold ◽  
R. Kriebel
Keyword(s):  
Reaction Mechanisms ◽  
Visual Discrimination ◽  
Osmium Tetroxide ◽  
Ultrastructural Level ◽  
Microscopic Level ◽  
Electron Microscopic Level ◽  
Electron Microscopic ◽  
X Ray ◽  
Insoluble Polymer ◽  
Cytochemical Reaction

Localization of specific substances at the ultrastructural level is dependent on the introduction of chemicals which will complex and impart an electron density at specific reaction sites. Peroxidase-antiperoxidase(PAP) methods have been successfully applied at the electron microscopic level. The PAP complex is localized by addition of its substrate, hydrogen peroxide and an electron donor, usually diaminobenzidine(DAB). On oxidation, DAB forms an insoluble polymer which is able to chelate with osmium tetroxide becoming electron dense. Since verification of reactivity is visual, discrimination of reaction product from osmiophillic structures may be difficult. Recently, x-ray microanalysis has been applied to examine cytochemical reaction precipitates, their distribution in tissues, and to study cytochemical reaction mechanisms. For example, immunoreactive sites labelled with gold have been ascertained by means of x-ray microanalysis.

Factors in Photographic Emulsions for Low Dose Electron Crystallography

1980 ◽  
Vol 38 ◽  
pp. 230-231
Author(s):  
T.W. Jeng ◽  
W. Chiu
Keyword(s):  
Radiation Damage ◽  
Low Dose ◽  
Damage Effect ◽  
Photographic Emulsion ◽  
Electron Crystallography ◽  
Electron Microscopic ◽  
X Ray ◽  
Signal Contrast ◽  
Diffraction Patterns ◽  
Photographic Emulsions

With the advances in preparing biological materials in a thin and highly ordered form, and in maintaining them hydrated under vacuum, electron crystallography has become an important tool for biological structure investigation at high resolution (1,2). However, the electron radiation damage would limit the capability of recording reflections with low intensities in an electron diffraction pattern. It has been demonstrated that the use of a low temperature stage can reduce the radiation damage effect and that one can expose the specimen with a higher dose in order to increase the signal contrast (3). A further improvement can be made by selecting a proper photographic emulsion. The primary factors in evaluating the suitability of photographic emulsion for recording low dose diffraction patterns are speed, fog level, electron response at low electron exposure, linearity, and usable range of exposure. We have compared these factors with three photographic emulsions including Kodak electron microscopic plate (EMP), Industrex AA x-ray film (AA x-ray) and Kodak nuclear track film (NTB3).

scholarly journals Vascular Mineralization in the Monkey Brain

1994 ◽  
Vol 31 (5) ◽  
pp. 546-552 ◽  
Author(s):  
T. Yanai ◽  
T. Masegi ◽  
K. Ueda ◽  
J. Manabe ◽  
M. Teranishi ◽  
...  
Keyword(s):  
Periodic Acid ◽  
Electron Microscopic Examination ◽  
Electron Microscopic ◽  
Periodic Acid Schiff ◽  
X Ray ◽  
Vascular Walls ◽  
Dense Deposits ◽  
Calcium Phosphorus ◽  
Phosphorus Iron ◽  
The Media

Mineralization of various degrees was found in the brains of 79 (59%) of 134 cynomolgus monkeys ( Macaca fascicularis). There was no age dependency in the incidence or severity, nor were there any abnormalities in growth, weight gain, or neurologic signs, although a slight sex difference was observed. The lesions, which were basophilic and intensely positive for periodic acid-Schiff or von Kossa stain, occurred in the vascular walls of the globus pallidus in two types: globoid bodies with prominent concentric lamellar structures in and around the arteriolar and venular wall (type A) and fine granules in the media of small or medium-sized arteries (type B). Electron microscopic examination revealed dense deposits in the degenerated media of small or medium-sized arteries or the thickened walls of the arterioles. X-ray microanalysis demonstrated the presence of calcium, phosphorus, iron, zine, magnesium, and aluminum.

scholarly journals Quantified abundance of magnetofossils at the Paleocene–Eocene boundary from synchrotron-based transmission X-ray microscopy

2015 ◽  
Vol 112 (41) ◽  
pp. 12598-12603 ◽  
Author(s):  
Huapei Wang ◽  
Jun Wang ◽  
Yu-chen Karen Chen-Wiegart ◽  
Dennis V. Kent
Keyword(s):  
Magnetic Particles ◽  
Strong Field ◽  
Atlantic Coastal Plain ◽  
Magnetic Studies ◽  
Electron Microscopic ◽  
Natural Sediment ◽  
Full Field ◽  
X Ray ◽  
Transmission Electron ◽  
Carbon Isotope Excursion

The Paleocene–Eocene boundary (∼55.8 million years ago) is marked by an abrupt negative carbon isotope excursion (CIE) that coincides with an oxygen isotope decrease interpreted as the Paleocene–Eocene thermal maximum. Biogenic magnetite (Fe3O4) in the form of giant (micron-sized) spearhead-like and spindle-like magnetofossils, as well as nano-sized magnetotactic bacteria magnetosome chains, have been reported in clay-rich sediments in the New Jersey Atlantic Coastal Plain and were thought to account for the distinctive single-domain magnetic properties of these sediments. Uncalibrated strong field magnet extraction techniques have been typically used to provide material for scanning and transmission electron microscopic imaging of these magnetic particles, whose concentration in the natural sediment is thus difficult to quantify. In this study, we use a recently developed ultrahigh-resolution, synchrotron-based, full-field transmission X-ray microscope to study the iron-rich minerals within the clay sediment in their bulk state. We are able to estimate the total magnetization concentration of the giant biogenic magnetofossils to be only ∼10% of whole sediment. Along with previous rock magnetic studies on the CIE clay, we suggest that most of the magnetite in the clay occurs as isolated, near-equidimensional nanoparticles, a suggestion that points to a nonbiogenic origin, such as comet impact plume condensates in what may be very rapidly deposited CIE clays.

Twin memory and twin amnesia in anorthoclase

2000 ◽  
Vol 64 (2) ◽  
pp. 195-200 ◽  
Author(s):  
S. A. Hayward ◽  
E. K. H. Salje
Keyword(s):  
Phase Transitions ◽  
Transition Temperature ◽  
Alkali Feldspar ◽  
Spatial Distributions ◽  
X Ray Diffraction ◽  
Alkali Cations ◽  
X Ray ◽  
Natural Minerals ◽  
Synthetic Materials ◽  
Before And After

AbstractMany natural minerals and synthetic materials display twin microstructures resulting from displacive phase transitions. These microstructures may be removed temporarily from the sample by heating above the relevant transition temperature, though the twinning generally returns on subsequent cooling.In anorthoclase, the spatial distributions of twins before and after brief annealing above TC are often identical. This property appears to be a common feature in many materials which undergo ferroelastic phase transitions, and is known as ‘twin memory’. The atomic mechanisms responsible for this twin memory may be investigated by studying the annealing regimes required to remove the memory effect; how long must a sample be annealed, and at what temperature, to induce ‘twin amnesia’.High-resolution X-ray diffraction (XRD) has been used to investigate twin memory and twin amnesia in anorthoclase. In anorthoclase, the primary constraint on twin amnesia is thermodynamic, rather than kinetic. The critical temperature to induce amnesia correlates well with the top of the (Na, K) solvus in disordered alkali feldspar. For this reason, the proposed mechanism for twin memory involves the segregation of alkali cations in thin lamellae at the twin boundaries.

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