摘要:

AbstractA technique was developed to prepare archaeological fiber cross sections for electron microscopic examination and x‐ray analysis. Use of this new method allows chemical and morphological information to be obtained from the interior of a single fiber or yarn. Fibers are fractured while frozen and then freeze dried. Following mounting and carbon coating, fibers are examined by scanning and backscatter electron microscopy and then analyzed by using energydispersive spectrometry. Elemental distribution is mapped by using image‐processing software. In this report, the described technique is employed in the examination of ancient fibers from three different long‐term storage environments (moist buried, dry buried, museum stored). Data obtained by examining the interior of fibers such as these provide insight into the conditions of a fiber's growth, the treatments applied during the fiber's processing and use, and the conditions in which the fiber was s

ISSN:0741-0581    

DOI:10.1002/jemt.1060140102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractWe describe a new technique, time‐resolved cryotransmission electron microscopy (TRC‐TEM), that can be used to study changes in microstructure occurring during dynamic processes such as phase transitions and chemical reactions. The sample is prepared on an electron microscope grid maintained at a fixed temperature in a controlled atmosphere. The dynamic process is induced on the grid by a change in pH, salt, or reactant concentration by rapid mixing with appropriate solutions. Alternatively, induction is by rapid change of specimen temperature, or by controlled evaporation of a volatile component. We call such procedures on‐the‐grid processing. The dynamic process is permitted to run for a defined time and then the thin‐film specimen is thermally fixed by plunging into liquid ethane at its freezing point, producing a cryotransmission electron microscopy specimen. By repeating this procedure with varying delays between induction and sample fixation, we can observe transient microstructures. We demonstrate the use of TRC‐TEM to study the intermediate structures that form during the transitions between Lα, III, and HIIliquid crystalline phases in phospholipid systems. We also identify several other possible applications of t

ISSN:0741-0581    

DOI:10.1002/jemt.1060140103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractSeveral basic physical concepts of applying eq. Ik= IσNxt to surface microanalysis by reflection electron energy‐loss spectroscopy (REELS) are clarified. Here Ikand I are the integrated intensities of the core ionization edge and the low loss part, σ is the scattering cross section of element x with atomic concentration Nx, and t is the specimen thickness. The reflected inelastic electrons are found to be distributed almost symmetrically around the Bragg sports and can be reasonably described by a Lorentzian function. EELS microanalysis can be performed by using the diffracted sports. The ω correction, arising from the angular contributions of the neighbouring spots into the spectrometer collecting aperture, is required to be consid

ISSN:0741-0581    

DOI:10.1002/jemt.1060140104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractPeldri II, a fluorocarbon compound solid at room temperature, was used as a sublimation dehydrant in place of critical‐point drying (CPD) in freeze‐fractured cytochemistry. Its applicability to the fracture‐label replica method was demonstrated using freeze‐fractured rat pancreas labeled withHelix pomatialectin‐gold complex and phospholipase A2‐gold complex for the detection of glycoconjugates and phospholipids, respectively. No difference in morphology and labeling pattern was detected in CPD‐treated and Peldri II‐treated tissue samples. The use of Peldri II was further extended to freeze‐fractured rat duodenum labeled with wheat germ agglutininovomucoid‐gold complex. Again comparable results were obtained when duodenal samples were prepared according either to the conventional CPD method or to the Peldri II sublimation method. Freeze‐fractured replicas of hamster ovaries labeled withRicinus communisI‐gold complex revealed that Peldri II could also be used as a sublimation dehydrant for preparing tissue samples for examination in the scanning electron microscope by the backscattere

ISSN:0741-0581    

DOI:10.1002/jemt.1060140105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractCounts of cells and nuclei from sections provide information central to studying structural changes in cells, tissues, and organs. This study considers some of the practical problems associated with counting cells with the newer random and serial sectioning methods of stereology and tests the hypothesis that similar cell counts can be obtained with both random and serial sectioning methods.Using irregularly shaped nuclei from alveolar cells of the goat lung, we compared cell counts derived from random (electron microscopic) and serial sectioning (light microscopic) methods. The results showed that both sectioning methods gave similar cell counts (107/cm3of parenchyma) for type 1 epithelial cells (5.0 vs. 5.0;P=1.0), type 2 epithelial cells (8.6 vs. 9.8;P=0.42) and interstitial cells (34.6 vs. 33.4;P=0.64), provided that corrections were introduced for sectionrelated biases and that the nuclei of the random sectioning method were corrected for shape. We found counting biases of 5%–7% for nuclear shape and 16% for section compression. These observations support the hypothesis that similar cell counts can be obtained with random and serial sectioning, even when nuclei have irregular shape

ISSN:0741-0581    

DOI:10.1002/jemt.1060140106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractThis paper describes and compares the morphology of a relatively complex tissue, the exocrine pancreas, prepared by state‐of‐the‐art anhydrous cryoprocedures. Cryopreparative procedures are being used increasingly for a wide range of applications, for example, electron‐probe x‐ray microanalysis and immunocytochemical localization of antigenic molecules, because they preserve the composition of the specimen better than procedures involving aqueous media. Some doubts have remained concerning the morphology of cryosections and the precise identification of subcellular structures.We show that thin and sufficiently large cryosections of fresh biological tissues can be produced using commercially available hardware. The freeze‐dried cryosections display high intrinsic contrast, are stable under the beam, and allow identification of intracellular fin

ISSN:0741-0581    

DOI:10.1002/jemt.1060140107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractOxygen‐contaminated, melt‐spun, binary Ti‐Si alloys have been examined by using transmission electron microscopy. The microstructure of alloys in the range of 4 to 10% Si (by weight) are cellular and consist primarily of α‐Ti and the silicide Ti5Si3.Contained only within the Ti5Si3regions are small, approximately spherical particles which are ⩽ 10 nm in diameter. Due to their small size, the crystal structure of these particles could not be determined by using conventional diffraction techniques such as Selected Area or Convergent Beam Diffraction. By conducting a number of tilting experiments and observing the moire fringe patterns produced when various matrixTi5Si3planes were used to image the sample, the crystal structure of the particles and the orientation relationship which exists between them and the matrix were deduced. The unknown particles, termed the Z phase, were found to be hexagonal with slightly different lattice parameters from the matrix Ti5Si3.Their relationship with the matrix was such that they appeared to be totally coherent. This may indicate that Z is an oxide based on the intermetal

ISSN:0741-0581    

DOI:10.1002/jemt.1060140108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractWe examined the ultrastructure of the cell envelope in Type I,Methylomonas albus(BG8), and Type II,Methylosinus trichosporium(OB3b), methane‐oxidizing bacteria by using different fixatives, ruthenium red (RR) combinations and resins. We compared LR White and Spurrembedments with the following fixations: glutaraldehyde/OsO4, two glutaraldehyde‐paraformal dehyde, and two different en bloc ruthenium red procedures, one utilizing 0sO4and the other with glutaraldehyde/OsO4in sequential fixation. These fixations were also studied by scanning electron microscopy (SEM). Unfixed cells prepared by freeze etch were used for comparison. Transmission electron microscopy of BG8 embedded in LR White resin (with or without ruthenium red) preserved a layer of cup‐like structures that were not seen in Spurr resin‐embedded cells unless ruthenium red was used. For OB3b, the second RR method preserved beads and filaments where only “spikelike” structures were seen in all other fixations in both resins. By SEM, all fixations preserved a capsular slime layer of BG8 that was removed from some cells by both RR methods. In all SEM fixations, a bead layer was preserved in OB3b that was enhanced by RR. Filaments seen by freeze‐etch and thin‐section techniques were not seen in SEM. Presence or absence of particular envelope structures in these methanotrophs is dependent on the combination of fixatives and/or resins employed and is species‐specific. The chemical preparation methods used resulted in enhanced understanding of the structure and composition of

ISSN:0741-0581    

DOI:10.1002/jemt.1060140109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractFollowing the removal of polyethylene glycol (PEG) from thin sections, and viewing through the endothelial fenestrae and/or the interpedicel spaces, the rat renal glomerular basement membrane in situ was revealed to consist of meshworks and to be electron‐transparent when examined at right angles to the plane of the membrane. By subsequent platinum replication of the embedment‐free sections, the lamina densa of the basement membrane appeared as a veil composed of rather closely packed particles. The architecture of the slit diaphragm and the surface morphology of the endothelial cell membrane were also clearly revealed. The present results indicate that the PEG method, with or without replication, can provide valuable information on basement membrane morphol

ISSN:0741-0581    

DOI:10.1002/jemt.1060140110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY

摘要:

AbstractUntil recently high resolution TEM was the only imaging mode capable of probing the atomic lattice structure of crystals composing tooth enamel. Studies designed to determine the polyhedral shape of normal enamel crystals and initiation of carious lesions in enamel crystals were hampered and limited by interpretation of two‐dimensional TEM images from thin section and freeze fracture replica specimens lacking depth of field. The newly developed SE‐I signal mode for SEM (SE‐I/SE‐II ratio) can produce images of enamel crystals approaching beam diameter dimensions (0.7–2.0 nm), rivaling the resolution of the TEM technique and generating topographic contrasts for three dimensional imaging at very high magnification (≈︁1,000,000 X). Ultrathin chromium (Cr) films generate enriched high resolution SE‐I contrasts of enamel crystal surfaces and when imaged using an immersion lens field emission SEM operated at high voltage (20–30 KeV) produce unsurpassed topographic contrasts. Since the grain size of Cr is below the resolution of any SEM and is ultrathin (≈︁1 nm), then SE‐I images can provide a more accurate representation of enamel crystal structure than TEM methodologies.Our SE‐I SEM observations of normal human enamel crystals reveal fractured spicules which contain angled flat surfaces delineated by a prominent 2 nm wide SE‐I edge brightness contrast. Although microscopic observations often show crystals which are hexagonal in cross‐section, in both SEM and TEM many other growth habits, including rectangular or irregular crystals (30–40 nm in width) which contain “notches,” are also observed. More detailed morphological studies are therefore required to determine the most likely habit planes and their relevance to the function of the enamel crystals. The granular appearing fine structural contrast imposed ontolattice planes of sectioned enamel in TEM micrographs is also resolved with topographic contrasts in SE‐I micrographs. These granules probably represent one

ISSN:0741-0581    

DOI:10.1002/jemt.1060140111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1990

数据来源: WILEY