The dimensions and numbers of small vesicles in cells, endothelial and mesothelial and the significance of these for endothelial permeability

Measurements were made of the diameters, numbers and other parameters of small, smooth-surfaced vesicles in the endothelium of blood capillaries and lymphatics, and in the mesothelial cells of the diaphragms of mice. Some measurements were also made on the aortic endothelium. With a few exceptions, there were no morphological differences between the various sites. It was found that between 25% and 35% of the non-nuclear cell volume was composed of vesicles, whose membranes accounted for about 55% of their volumes. Their internal volumes were ～ 70,000 nm³, totalling ～ 0·04 μm³/μm² of luminal surface area. For each 1 μm² there were ～ 135 vesicles attached to each surface membrane of the cell, and between ～ 200 and ～ 350 vesicles lying free in the cytoplasm. There was probably a slight amount of shrinkage during the preparation of the material, and the true linear dimensions were probably ～ 105% of those actually observed. Thus the values for the internal volumes were probably ～ 85,000 nm³ and ～005 μm³ respectively; the vesicular numbers were probably ～ 125 attached to each surface and between ～ 175 and ～ 300 free. The vesicles attached to the plasma membranes often had quite long stalks; these were estimated to be ～ 30 nm at the moment of rupture. Thus the vesicles must be released an appreciable distance away from the membrane. This modifies the conclusions of Shea & Karnovsky (1966), since it can now be shown that Brownian movement alone is capable of accounting for the release of the vesicles, their movements within the cells and their transportation of material. By combining these results with others estimating the endothelial permeability coefficients, it can be calculated that the average free lifetime of a vesicle is ～1½ sec, from union with one plasma membrane to the next. It can also be shown that the average time of such an attachment is ～ 2½ sec. There are many possible sources of error relating to these measurements; they must only be regarded as tentative. It appears likely, however, that they are of about the correct order of magnitude as they accord well with other data.     

A quantitative evaluation of the glomerular capillary endothelium in rat and human kidneys: Utilization of vascular perfusion,freeze-cracking of tissue,and scanning electron microscopy

Modern morphological investigation requires the use of a variety of technological approaches and the employment of rigorous morphometric analysis for an adequate evaluation of the structural and ultrastructural features of a tissue or organ. The introduction of the technique of freeze-cracking of tissue to expose new surfaces has made it possible to quantitate the normal surface characteristics of the glomerular capillaries of the mammalian kidney. This report describes the techniques used for the preparation and quantitative assessment of normal glomerular endothelial morphology. The techniques of in vivo and in vitro vascular perfusion of kidneys as a method of fixation and the freeze-cracking of tissue are outlined in detail. In addition, a morphometric analysis of the endothelial surface characteristics are described and values are reported for the control rat and human kidneys from transplant donors.     

On the wear debris of polyetheretherketone: fractal dimensions in relation to wear mechanisms

It has been recognized that wear debris contains extensive information about wear and friction of materials. Investigation of wear debris is important for tribological research. In order to find out an effective way that is able to diagnose and predict the wear state of polymers, the authors investigated the relationship between the wear debris morphology and the wear behaviour of the bulk material. Polyetheretherketone (PEEK) was employed as the model material. Its sliding wear and friction properties were measured by means of a pin-on-disc apparatus. At a constant sliding velocity of 1 m s⁻¹, the specific wear rate was independent of load under lower loading conditions (1–4 MPa) but increased with a rise in load under higher loading conditions (4–8 MPa). The coefficient of friction was insensitive to the variation of contact pressure. The possible mechanisms involved were analysed on the basis of the wear debris morphology as well as the wear performance. Fractal geometry, which describes non-Euclidean objects, was applied to the quantitative analysis of the boundary texture of the wear debris due to the fact that the qualitative assessment of the wear debris morphology was not effective enough to reflect the geometrical variation of the fragmental shapes. The experimental results demonstrated that the wear debris were fractals, and could be characterized with the fractal dimensions which were determined by the slit island method. In addition, it was found that the fractal dimension of the wear debris was closely related to the wear behaviour of PEEK, and can be regarded as a measure of wear rate.     

Cryotechnology for the structural analysis of lubricants in relation to their friction properties

A phenomenological model is developed to explain the friction and wear characteristics of high speed sliding contact between blade tips and shrouds in high performance turbomachinery. Equal emphasis is placed on thermal and mechanical mechanisms, and a synergistic relation between the two is derived which yields quantitative predictions of rubbing forces, friction coefficient, total heat input, heat split and relative wear rates between the blade and the shroud. The focal point of the model is a convecting plastic “shear mix” layer on each rubbing surface which is deduced to form regardless of the rub mechanisms initially assumed to prevail.     

Changes in the structure and composition of automobile big-end bearing materials and their relation to bearing failure

Changes in the composition and structure of automobile big end bearings during operation were examined by X-ray diffraction and electron probe X-ray microanalysis.     

Endocytosis: The different energy requirements for the uptake of particles by small and large vesicles into peritoneal macrophages

The uptake of various, different-sized particles by macrophages was studied using the electron microscope. In addition to observing normal cells, cells were examined which had been inhibited by exposing them to low temperature (4°C), and to a number of metabolic poisons. It was found that large particles (> 01 μm) enter the cells and are contained in large vesicles (0·1–5 μm). Small particles (< 50 nm) may also enter the cells by this process. They enter most frequently, however, by passing into small (～ 70 nm) vesicles. These may later coalesce and their contents adhere to give a second kind of large vesicle. The various inhibitors prevented the ingestion of the large particles (and of the small particles en masse) into large vesicles, but did not prevent their initial adsorption onto the plasma membranes. They did not prevent nearly normal numbers of small particles from entering the pre-existing small vesicles, nor their subsequent fusion into the second class of large vesicles.     

The buckling of annular plates in relation to the deep-drawing process

Based on a two-dimensional buckling model of an elastic-plastic annular plate and the well-known energy method, the critical conditions for the elastic buckling and the plastic buckling of the flange of a circular blank during the deep-drawing process are obtained to improve upon previously given results[1, 4]. The influence of a blankholder upon buckling and on the number of waves generated can also be quantitatively predicted.     

The STEM approach to the imaging of surfaces and small particles

The characteristics of scanning transmission electron microsopy, which make it a particularly powerful tool for the study of surfaces and small crystals, include the serial nature of the image signal which makes it amenable to recording and image processing procedures, the possibility of correlating the image data with microdiffraction patterns and microanalysis of chosen small regions and the possibilities for combining several different image signals obtained simultaneously. Images obtained from surfaces using reflected diffraction beams may be very sensitive to variations of surface structure but the resolution, depth of focus and contrast of the images are strongly dependent on the nature of the surface and the aperture sizes used in the microsope. Microdiffraction patterns may be obtained from small surface features. Electron energy loss analyses of the diffracted beams provides sensitive indications on surface electron excitations. Microdiffraction patterns obtained in transmission from regions of 1–5 nm diameter provide valuable information on the structure and defects of small crystals, such as those of platinum and gold which are of interest in relation to the study of catalysts.     

Measurements from electron micrographs of organelle size in relation to their shape: a refinement applied to the epidermal melanosome and basal lamella

The mean value of measurements of organelles made from electron-microscope sections cut in random planes is not an accurate expression of any important dimension of a nonspherical organelle; realistic measurements of organelles in electron micrographs must take into account the three-dimensional shape of the organelle. Stereological methods offer ways of calculating surface areas and volumes of organelles in electron-microscope sections but do not provide an easy means of deriving three-dimensional structures. If, however, the three-dimensional shape of an organelle is known, it is possible to select profiles which contain what is approximately a major or a minor axis. The frequency distribution of the values from profiles so chosen are skewed, and the median provides the best estimate of the dimension of the organelle. The median and the interquartile range (P₂₅–P₇₅) are presented for measurements made in this way of melanosomes and the basal lamella and lamina lucida of mammalian oral epithelium.     

On the use of dual numbers,vectors and matrices in instantaneous,spatial kinematics

This paper gives a self-contained account of the algebra of dual quantities, the differential-geometry of dual curves, and their application to theoretical space kinematics. The scope of the paper is mainly didactical, but its understanding by the reader requires a certain amount of mathematical maturity. Due to the way in which the matter is presented, the paper gives some formulae and facts about dual curves and dual motions which are not generally known.     

Nitric oxide: relation to integrity, injury, and healing of the gastric mucosa

Nitric oxide (NO) plays a multifaceted role in mucosal integrity. The numerous functions of NO and the double-edged role played by NO in most of them provide a great complexity to the NO action. The three enzymatic sources of NO, neuronal NO-synthase (nNOS), endothelial NOS (eNOS), and inducible NOS (iNOS), have been characterised in the gastrointestinal tract. The protective properties of the NO derived from constitutive NO-synthases (eNOS and nNOS) have already been well established. Less clear is the role assigned to iNOS. The simplistic initial view of low levels of NO synthesised by constitutive NOS being protective while exaggerated NO levels after iNOS induction leading irremediably to cytotoxicity is being questioned by new evidence. As initially reported for constitutive NOS, iNOS activity may be associated to reduced leukocyte-endothelium interaction and platelet aggregation as well as protection of mucosal microcirculation. Moreover, iNOS activity may be important to resolve inflammation by increasing apoptosis in inflammatory cells. It is entirely possible that a low level of expression of iNOS will reflect a positive host-defense response to challenge, but that exaggerated or uncontrolled expression of iNOS itself becomes detrimental. There is no doubt about the protective role of NO in physiological conditions. However, when the mucosa is threatened, the role of NO becomes multiple and the final effect will probably depend on the nature of the insult, the environment involved, and the interaction with other mediators.     

The biomechanical,chemical and physiological adaptations of the eggs of two Australian megapodes to their nesting strategies and their implications for extinct titanosaur dinosaurs

Megapodes are galliform birds endemic to Australasia and unusual among modern birds in that they bury their eggs for incubation in diverse substrates and using various strategies. Alectura lathami and Leipoa ocellata are Australian megapodes that build and nest in mounds of soil and organic matter. Such unusual nesting behaviours have resulted in particular evolutionary adaptations of their eggs and eggshells. We used a combination of scanning electron microscopy, including electron backscatter diffraction and energy‐dispersive X‐ray spectroscopy, to determine the fine structure of the eggshells and micro‐CT scanning to map the structure of pores. We discovered that the surface of the eggshell of A. lathami displays nodes similar to those of extinct titanosaur dinosaurs from Transylvania and Auca Mahuevo egg layer #4. We propose that this pronounced nodular ornamentation is an adaptation to an environment rich in organic acids from their nest mound, protecting the egg surface from chemical etching and leaving the eggshell thickness intact. By contrast, L. ocellata nests in mounds of sand with less organic matter in semiarid environments and has eggshells with weakly defined nodes, like those of extinct titanosaurs from AM L#3 that also lived in a semiarid environment. We suggest the internode spaces in both megapode and titanosaur species act as funnels, which concentrate the condensed water vapour between the nodes. This water funnelling in megapodes through the layer of calcium phosphate reduces the likelihood of bacterial infection by creating a barrier to microbial invasion. In addition, the accessory layer of both species possesses sulphur, which reinforces the calcium phosphate barrier to bacterial and fungal contamination. Like titanosaurs, pores through the eggshell are Y‐shaped in both species, but A. lathami displays unique mid‐shell connections tangential to the eggshell surface and that connect some adjacent pores, like the eggshells of titanosaur of AM L#4 and Transylvania. The function of these interconnections is not known, but likely helps the diffusion of gases in eggs buried in environments where occlusion of pores is possible.     

The topography of abraded surfaces in relation to contact area and mechanism of abrasion

The equation β = a ? bθ relating the slope β of the groove profile and the slope θ of the contact area-load curve for rubber replicas of abraded surfaces is examined theoretically and found to be based on simple geometrical factors. Contact area experiments using large scale rubber models of surfaces with parallel coplanar grooves confirm the theory. Friction experiments show that the value of a increases by a constant amount from the value for coplanar grooves when abraded surfaces with variable groove heights are studied. This increase in a is the same for widely different types of abrasive and abraded material. The value of b remains unchanged. Surface examination of the relative frequency distribution of abrasion groove amplitudes suggests that the constancy of the increase in a is based on a uniformity in the shape of the distribution for the different surfaces. Detailed examination of this distribution leads to the conclusion that abrasive wear occurs in layers which correspond to the layers of major plastic flow surrounding an abrasive grain and that there are two types of ploughing and two corresponding types of cutting which often coexist on an abraded surface. The results are of interest in relation to theories of wear.