Ischemic carotid endothelium. Transmission electron microscopic studies

The endothelium of monkey and rabbit common carotid arteries subjected to ischemia was examined by transmission electron microscopy (TEM). The right carotid artery of 24 rhesus monkeys was occluded by proximal and distal placement of removable surgical clips for periods ranging from five minutes to four hours. A single clip was used to occlude the right carotid artery of 15 rabbits for periods ranging from 5 to 30 minutes. With TEM, numerous blebs, intracytoplasmic vacuoles, membranous whorls, and pseudopodia were found in the endothelium of arterial segments subjected to ischemia by double or single clipping for as little as five minutes. Following occlusion of one hour or longer, disruption of interendothelial junctions was also noted. These TEM findings were compared with earlier TEM studies of the response of endothelium to other injurious stimuli and with previous scanning electron microscopic studies in which the same ischemic models were utilized.     

High resolution electron microscopic study of the ordering processes in Ni4Mo alloy

We have studied the ordering processes of a Ni-20.1at.%Mo alloy using the many-beam imaging technique with the aid of an image processing method. No microdomain is detected in high resolution electron micrographs of the alloy quenched from 1000°C, but lattice modulations which probably be attributed to concentration waves appear parallel to the {210} planes at the initial ordering stage. It is revealed that the observed contrasts of D1_a-type and D0₂₂-type microdomains are apparently formed with superpositions of different pairs of the {210} lattice modulations. When the alloy is annealed at 650°C for 192 h, Ni₂Mo domains appear in between the Ni₄Mo domains, and their composition is determined to be the stoichiometry (32at.%Mo) by the energy dispersive X-ray (EDX) analysis. The superstructure images of Ni₄Mo and Ni₂Mo are discussed in comparison with computer simulations by the multislice method.     

High resolution transmission electron microscopy studies of the Ag/MgO interface

Ag layers with a thickness of 100 nm were deposited on {100} MgO substrates by molecular beam epitaxy (MBE). The substrates were produced by cleaving MgO single crystals and subsequent annealing in ultra high vacuum. X-ray texture measurements indicate a preferential orientation of Ag {100} planes parallel to the {100} surface of the MgO substrate. The atomistic structure of the Ag/MgO interface was imaged by high resolution transmission electron microscopy (HRTEM). Lattice images of Ag and MgO in parallel orientation show structural defects and lattice strain at the Ag/MgO interface, which are introduced by the lattice mismatch of 3% between Ag and MgO. The atomic resolution images are compared with the computer-simulated lattice image of a model structure. Finally our atomistic model of the Ag/MgO interface, which includes a misfit dislocation network is discussed in connection with theoretically calculated interfacial energies.     

Effect of undercooling on the microstructure of Ni-35 at. pct Mo (eutectic) and Ni-38 at. pct Mo (hypereutectic) alloys

Ni-35 at. pct Mo (eutectic) and Ni-38 at. pct Mo (hypereutectic) alloy specimens have been solidified from various levels of undercooling in the differential thermal analysis (DTA) and the electromagnetic levitation (EML) units in a pyrex/vycor bed. The evolution of the microstructure in the solidified specimens has been examined in terms of the degree of undercooling, the nature of the first phase to nucleate from the melt, and the specimen cooling rate. The melt has been observed to undercool more in the presence of intermetallic NiMo (β) phase as compared to that in the presence of nickel-rich solid solution (γ). The “anomalous eutectic” type of microstructure has been shown to result from the initial formation of the dendritic skeleton of either of the two phases, its segmentation due to convection and ripening, and the subsequent nucleation of the other phase in the interdendritic liquid regions. The recalescence behavior has been examined as a function of undercooling and the nature of the phase nucleating first in the melt.     

Micropyretic synthesis studies of Ni-, Al-, Ti-, and Nb-containing alloys

A series of new micropyretically synthesized complex intermetallics and intermetallic composites containing Ni, Al, Ti, and Nb have been studied. At the extremities of this series were the two alloys with the B₂ structure, namely, the NiAl and Nb₄₅Al₁₅Ti₄₀ intermetallic compounds, the former being brittle and the latter ductile. The alloys in the series were made by adding Ti and Nb to NiAl and processing them by micropyretic methods. In addition to the matrix B₂ phase, the synthesized alloys were found to contain other phases. Some of the alloys in the series were noted to possess high fracture toughness and oxidation resistance. A detailed microstructural characterization of the synthesized alloys was carried out. The mechanism of synthesis in the alloys has been established by microstructural examination of the partially reacted specimens by arresting the combustion process during the synthesis process.     

Scanning electron microscopic and immunohistochemical studies of pelvic endometriosis

The pathogenesis of pelvic endometriosis has been studied by using scanning electron and light microscopy, observing the surface structure of bluish lesions obtained from 26 patients during laparotomy. Paraffin sections included another 17 tissue samples of endometriosis, based on immunohistochemical responses to epithelial membrane antigen, keratin and vimentin. Ultrastructurally, the surface epithelial cells could not be detected in 13 out of 17 pelvic peritoneal endometriosis samples. In one case in which the surface peritoneal cells were seen histologically to dip into the subperitoneal stroma, many surface peritoneal infoldings were observed, and ciliated cells were detected at the edge of these infoldings. Ovarian endometriosis was composed of three types of cells, none of which had any cilia. These findings were observed in continuity with adjacent normal mesothelial cells. No characteristic structure of the endometrial surface was observed for the bluish lesion, but the gland surface of endometriosis located in the subperitoneal stroma initially had ciliated cells. The immunoreactions in both the columnar mesothelial cells with surface peritoneal infoldings and the glands of endometriotic tissues were similar to those of normal endometrial glands, but different from those of normal mesothelial cells. Pelvic endometriosis might originate by a process of metaplasia from the pelvic peritoneum.     

Identification of orbital lymphatics: enzyme histochemical light microscopic and electron microscopic studies

The presence of orbital lymphatics in the primate model is demonstrated using light and electron microscopic enzyme histochemistry. In addition, strictly morphological definitions of lymphatics, such as discontinuous basal lamina, thin and irregular walls, anchoring filaments, and attenuated endothelial cell cytoplasm, were applied. This study confirmed the presence of conjunctival lymphatics reported by others. It also clearly demonstrated the presence of orbital arachnoid and lacrimal gland lymphatics that have not been previously described. A few areas of the extraocular muscles and connective tissue at the orbital apex also showed evidence of the presence of lymphatic vessels. Additional work is needed to define the nature and extent of orbital lymphatics as well as their connection to the extraorbital lymphatic system.     

Electron microscopic studies of martensitic transformations in iron alloys and steels

It has been demonstrated by electron microscopy of Fe₃Pt and Fe₃Al(-C) martensites that the Bain distortion is unambiguously realized upon the fee to bec or bet martensite transformation in iron alloys and steels. Secondly, internal inhomogeneities in ferrous martensites are summarized, and discussed with regard to the uniqueness of the (112) twinning plane, the deviation of the martensite twin interface plane from (112), the nature of (Oil) twins in bct martensite, distribution of (112) twins and the nature of the midrib, dependency of the habit plane on internal inhomogeneities, and internal structures in thin martensite platelets. Accordingly, it is emphasized that in order to discuss consistently the correlation between the internal inhomogeneities and other crystallographic properties, all crystallographic properties should be measured for a given martensite plate. Finally, a recent study of an Fe-16.5 wt pet Mn-0.25 wt pct C alloy subjected to cyclic heating and cooling (400°C ⇌-l96°C) is introduced to show the existence of long period stacking order structures [15R(3•2)₃ and 18R(5•1)₃] in some ferrous alloys. Z. NISHIYAMA, formerly at the Institute of Scientific and Industrial Research, Osaka University     

High resolution study of ordering reactions in gold-chromium alloys

The ordering reactions in Au₄Cr and Au₃Cr alloys have been investigated using high resolution dark field and lattice imaging techniques. In all cases the ordered structures can be described in terms of compositional modulations as occur during spinodal decomposition. In alloys quenched from above the critical temperature sro microdomains of size 10 to 15? have been resolved with structures represented by modulations in composition along <420>. After aging the Au₄Cr alloy belowT _c the Dla lro phase appears as ordered domains of size 50 to 100? showing composition modulations with wavelength of 5d<531>. These domains grow in size up to 500? becoming finally the D1a fully ordered structure. A new observation has been mdde in the Au₃Cr alloy,viz that the lro structure is nonstoichiometricL1₀ withλ _[001] = 4?. The transformation from sro in this alloy occurs with the formation of a transitional ordered phase, (similar toDO ₂₂, which can be described in terms of composition modulations along [001], with wavelength equal to thec parameter (8?) of theDO ₂₂ structure. Lattice imaging of the two variants of superlattice planes in ordered Au₄Cr enabled the atomic arrangement in the area of translational and rotational antiphase boundaries to be determined. J. Dutkiewicz is on one year leave from the Institute of Metallurgy, Polish Academy of Sciences, 30-059 Krackow, ul. Reymonta 25, Poland.     

High resolution study of ordering reactions in gold-chromium alloys

The ordering reactions in Au₄Cr and Au₃Cr alloys have been investigated using high resolution dark field and lattice imaging techniques. In all cases the ordered structures can be described in terms of compositional modulations as occur during spinodal decomposition. In alloys quenched from above the critical temperature sro microdomains of size 10 to 15Å have been resolved with structures represented by modulations in composition along <420>. After aging the Au₄Cr alloy belowT _c the Dla lro phase appears as ordered domains of size 50 to 100Å showing composition modulations with wavelength of 5d<531>. These domains grow in size up to 500Å becoming finally the D1a fully ordered structure. A new observation has been mdde in the Au₃Cr alloy,viz that the lro structure is nonstoichiometricL1₀ withλ _[001] = 4Å. The transformation from sro in this alloy occurs with the formation of a transitional ordered phase, (similar toDO ₂₂, which can be described in terms of composition modulations along [001], with wavelength equal to thec parameter (8Å) of theDO ₂₂ structure. Lattice imaging of the two variants of superlattice planes in ordered Au₄Cr enabled the atomic arrangement in the area of translational and rotational antiphase boundaries to be determined.     

Ultrasound biomicroscopy. High-frequency ultrasound imaging of the eye at microscopic resolution

UBM presents us with a new method of imaging the anterior segment of the eye at high resolution. Its strengths lie in its ability to produce cross-sections of the living eye at microscopic resolution without violating the integrity of the globe. UBM, although lacking the resolution of optical microscopy, gives us images in living eyes without affecting the internal relationships of the structures imaged. There are many other applications of this new imaging method. Examples of other uses include imaging adnexal pathology, assessing corneal changes with refractive surgery, the assessment of trauma, and determination of intraocular lens position.     

Osteogenesis at the dental implant interface: high-voltage electron microscopic and conventional transmission electron microscopic observations

The osteogenesis of mandibular bone to endosteal dental implants was examined using an in vivo dog model. One half of the implants examined were unloaded implants, with the remaining one half prosthodontically loaded for 6 months. Undecalcified mandibular implant samples were examined with both high-voltage electron microscopy (HVEM) stereology and routine transmission electron microscopy. The osseous interface to integrated implants was shown to vary in its morphology. Mineralized bone was observed directly apposing the implant, often separated from the implant by an electron-dense deposit of approximately 50 nm. Within this densely mineralized matrix, osteocytes were routinely observed. Adjacent areas were shown to contain slightly wider zones of either a less dense mineralized matrix or, alternatively, unmineralized tissue. Other zones consisted of wider unmineralized matrices containing collagen fibers and osteoblasts. These latter zones were consistent with the appearance of an appositional type of bone growth. Because bone is a dynamic, actively remodeling tissue, a varied morphology of the support tissues to dental implant is not unexpected. Areas of mature bone interfacing with successfully integrated implants were demonstrated, as well as areas adjacent to the mature bone that were undergoing remodeling or mineralization. This study has also shown that HVEM stereology is a valuable research tool to investigate the oral tissue interface with dental implants.     

Transmission electron microscopic observations of mechanical twinning in metastable beta titanium alloys

Microstructure and crystallography of a stress-induced plate in metastableβ titanium alloys, Ti-V, Ti-Mo, Ti-Nb, Ti-Fe, were investigated by a combination of two surface trace analysis and transmission electron microscopy. Stress-inducedω phase transformation or {332} 〈113〉 twinning appeared in circumstances whereβ phase was very unstable. It was found that there were two types of {332} 〈113〉 twinning, depending on whether one variant ofω phase was preferentially induced in a twin or not. Stress-inducedω phase not relating to {332} 〈113〉 twinning was not observed in matrix. This suggests that stress-inducedω phase transformation is accompanied with {332} 〈113〉 twinning. Preferential formation of oneω variant was influenced not only by alloy system and its composition, but also by cooling rate from solution treatment temperature. The relation between athermalω structure and stress-inducedω phase transformation or plastic deformation mode is also discussed.     

High resolution tem studies of gold and palladium nano-particles

In the present work we analyze nano-particles of gold and palladium using a combination of High Resolution Electron Microscopy (HREM) and image processing techniques. The experimental results are compared with calculations of images using dynamical diffraction theory. We focus mainly on the decahedral (D_h) and icosahedral (Ic) Particles. We found that the decahedral particles correspond well with the model for a perfect MPT. The icosahedral particle on the other hand appears to be much more distorted than the MPT model predicts. Images of polycrystalline and amorphous particles are also shown. No significant differences between Au and Pd were found.     

Scanning and transmission electron microscopic studies of lesional epidermis in herpes zoster

The epidermal skin lesions of herpes zoster were studied by scanning (SEM) and transmission electron microscopy (TEM). When erythematous lesions were observed by TEM, many of the infected keratinocytes showed evidence of cell degeneration, being characterized by swollen nuclei, disappearance of desmosomes, and widening of intercellular spaces. Macrophages and/or lymphocytes migrated through the intercellular spaces between degenerated keratinocytes. In the vesicular lesions, SEM and TEM showed some infiltrating neutrophils, directly adhering to the virus-infected keratinocytes, with swollen nuclei and irregularly clumped chromatin. In some specimens, balloon-degenerated keratinocytes were observed in the cavity. In the pustular stage, ruptured keratinocytes and numerous neutrophils were observed in the reticular-degenerated epidermal tissue. These results suggest that, in herpes zoster, the epidermal damage may be due, at least in part, to cell-mediated host immunity as well as to the cytopathic effect of varicella-zoster virus.     

放电等离子烧结制备W-9.8Ni-4.2Fe合金的高温压缩性能

采用放电等离子烧结法,通过高温压缩性能测试和扫描电镜(SEM)观察,研究粉末制备工艺和烧结温度对W-9.8Ni-4.2Fe合金在800℃下高温压缩性能的影响。结果表明,高能球磨粉末烧结合金的硬度和高温压缩性能均优于混合粉末烧结合金;在1 150℃下球磨粉末烧结合金的压缩强度最高,达到1 150 MPa,但当烧结温度在1 050~1 250℃范围内变化时,烧结合金的压缩应力应变曲线变化并不显著。     

Solution hardening in aluminium-magnesium alloys: A nuclear magnetic resonance and transmission electron microscopic study

Pulsed nuclear magnetic resonance techniques as well as transmission electron microscopy have been applied to study dislocation motion in aluminium magnesium alloys (0.2–1.6 at.% Mg). The spin lattice relaxation rate in the rotating frame of ²⁷A1 has been been measured at 77 K as a function of strain at constant plastic strain rate ϵ. For finite strain rates, the movement of dislocations induces an additional relaxation rate arising from time fluctuations in the nuclear quadrupole interactions. From the motion-induced part of the relaxation rate the mean free path of mobile dislocations can be calculated. The NMR experiments are combined with transmission electron microscopic investigations to reveal the static structure of defects in the samples. The NMR measurements clearly indicate that fluctuations in the quadrupolar field caused by moving dislocations in AlMg are different compared to those in ultra pure Al. From the NMR data it could be concluded that moving dislocations advance over a number of solute atoms (order of 7) as described by Mott-Nabarro's model. On the other hand, Mott-Nabarro's model does not predict the effective solute spacing as a function of the concentration of solute atoms in accordance with NMR experiments.     

Vibrio cholerae adherence and colonization in experimental cholera: electron microscopic studies

Colonization of the intestinal epithelium by Vibrio cholerae was examined in two model systems, in ligated ileal loops of adult rabbits and in the patent gut of infant rabbits, using both scanning and transmission electron microscopy. Time studies in the adult model showed a lag period of up to 1 h before the attachment of significant numbers of the vibrios. The bacteria appeared initially in small patches on the sides of the villi, predominantly along the transverse furrows. The number of adherent bacteria steadily increased, reaching a maximum between 4 and 7 h, when a dense mat of bacteria several layers thick covered much of the villi. After this time there was a rapid decline in the number of V. cholerae bound. By 12 to 16 h only a few bacteria could be seen on the surface of the villi, which had a rough, patchy appearance at these later times. Globular protrusions, with vibrios attached, may play a role in the clearance of bacteria. Colonization and clearance in the patent intestine of the infant rabbit occurred much as in the adult model. However, the bacteria adhered more uniformly and there was no lag in attachment. In both models the majority of bacteria were aligned horizontally with the epithelial surface, but some were attached in an end-on manner, with their flagella extending into the lumen. The bacteria adhered via their surface coats directly to the tips of the microvilli, except for a few vibrios that were partly embedded into the brush border. Some changes in the microvilli occurred as a consequence of the bacterial attachment.