Biology Commons^™

Secondary Electron Emission Induced By Electron Bombardment Of Polycrystalline Metallic Targets, R. Bindi, H. Lanteri, P. Rostaing

Scanning Microscopy

The aim of the present paper is the analysis of the backward secondary electron emission phenomenon, under electron bombardment, on the basis of experimental and theoretical results. Among the theoretical models, we will mention the phenomenological models, those which use a Monte-Carlo type simulation method, and those based on the numerically solved Boltzmann transport equation.

To correlate experimental and theoretical results on all the data characterizing this phenomenon, it is necessary to use an appropriate description for the excitation process of the internal secondary electrons; it also needs a complete description of the transport process for the excited electrons, which …

External Shape Of Enamel Crystals, H. Warshawsky

Scanning Microscopy

Biological hydroxyapatite crystals are either small, as in bone and dentin, or large as in enamel. Enamel crystallites are unique since each is initiated and grows in length, thickness and width until the entire layer of enamel is secreted. In maturation, these extremely long crystallites grow only in thickness and width. Crystal growth in vitro follows physico-chemical principles, but lacks biological intelligence; in vivo this intelligence is contributed by protein templates. The location of the organic template in enamel is congruent with the crystallite, constituting the crystal ghost. Since crystals cannot accommodate proteins, the explanation is logically inconsistent. In sections, …

X-Ray Microanalysis Of Cells In Suspension And The Application Of This Technique To The Study Of The Thymus Gland, A. Warley

Scanning Microscopy

Although X-ray microanalysis has become a well established technique in the study of tissues there are still relatively few papers reporting results from cells in culture. Our early investigations on freshly isolated murine thymocytes reported higher than expected concentrations of Na and Cl in these cells but subsequent studies have shown that these high concentrations are artefactual. Rat thymocytes that have been isolated and incubated for a short time to allow them to recover from the isolation procedure have lower concentrations of Na and Cl. Sections prepared from pellets of cells which have been concentrated by centrifugation in a microhaematocrit …

Scanning Electron Microscopy Of Vascular Smooth Muscle Cells From Rat Muscular Arteries, William J. Krizmanich, Robert M. K. W. Lee

Scanning Microscopy

The use of scanning electron microscopy (SEM) for the examination of medial smooth muscle cells (SMC) is limited by the presence of connective tissue mass in the adventitia obscuring the detailed structure of the SMC. This study deals with the description of a method which selectively removes the connective tissue, allowing three dimensional observation of SMC using SEM. A number of methods were tried. One method involving post fixation with 2% Os0₄ used in conjunction with HCl proved most successful in removing the extracellular matrix of large mesenteric arteries from spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto normotensive rats …

Multiplane Sectioning And Scanning Electron Microscopy As A Method For Studying The Three-Dimensional Structure Of Mature Dental Enamel, S. Risnes

Scanning Microscopy

A method is described where teeth are sectioned/ground along at least two planes, etched, and viewed at various angles in the SEM in order to study the three-dimensional structure of enamel. This multiplane sectioning-scanning electron microscopy (MPS-SEM) method has been applied to the study of rat and human enamel. The method demonstrates in a direct way the complex three-dimensional structure of rat incisor enamel; the path of prisms and the distribution of interprismatic substance. The different appearance of alternate prism rows as seen in the longitudinal plane is seen to be due to prisms in alternate rows being inclined to …

Analysis Of Clean Transition Metal Surfaces By Core Level Spectroscopy, M. C. Desjonquères, D. Sébilleau, G. Tréglia, D. Spanjaard, C. Guillot, D. Chauveau, J. Lecante

Scanning Microscopy

The shifts in the binding energy of core electrons detected by high resolution X-ray photoelectron spectroscopy are a very sensitive probe of the chemical bonding of the excited atom. Since the surface atoms have their geometrical environment perturbed, their core levels are shifted from their bulk positions. A very large number of experiments have been performed on the 4f core level positions of tantalum and tungsten for various orientations of the surface plane. Systematic trends have been put forward and explained by theoretical models. Furthermore, the analysis of the angular variation of the core level line intensities gives structural information …

Studies On The Occurrence And Elemental Composition Of Bacteria In Freshwater Plankton, K. N. Booth, D. C. Sigee, E. Bellinger

Scanning Microscopy

The occurrence and cation content of bacteria in a eutrophic freshwater lake (Rostherne Mere, Cheshire, UK) were investigated over a one year sampling period in relation to cation changes in the lake surface water and phytoplankton.

Scanning electron microscope examination of trawl-net and filtered samples demonstrated bacterial association with Anabaena, Aphanizomenon and diatoms. Direct counts of associated and unassociated bacteria showed that increases in bacterial population relate to population decline of major algal constituents.

Spectrophotometric determination of selected cation levels in the lake water demonstrated wide fluctuations throughout the sampling period, with elevated levels of transition metals before and at …

The Fine Structure Of The Human Placental Villus As Revealed By Scanning Electron Microscopy, G. J. Burton

Scanning Microscopy

Scanning electron microscopy of the placenta has a history of only twenty years. During that time, however, there have been dramatic advances in instrument technology coupled with the refinement of preparative techniques designed to reduce fixation artifacts to a minimum. As a result many of the early claims must be amended or suitably qualified, and this is one aim of the present review.

Much new data on the internal structure of the placental villus is also presented. By means of the partial digestion technique it is now possible to describe the three dimensional configuration of the various components of the …

Electron Probe Micro-Analysis And Laser Microprobe Mass Analysis Of Material Leached From A Limestone Cathedral, L. A. Leysen, J. K. De Waele, E. J. Roekens, R. E. Van Grieken

Scanning Microscopy

Electron probe X-ray micro-analysis (EPXMA) and Laser microprobe mass analysis (LAMMA), were applied to characterize the leachate of sandy limestones of a Belgian cathedral.

Individual suspended particles, found in water that was sprayed over the cathedral walls ("1 each ate water"), were sized and analyzed by automated EPXMA-analysis, and classified with hierarchical cluster methods. LAMMA was used to gather more information about particles, present in the solution, as well as in suspension.

It was found that the leachate from black walls, had a high sulphate concentration and a large variety of particles in suspension, with different morphology and composition, with …