Showing papers by "Laval University published in 1971"

The elasto‐plastic indentation of a half‐space by a rigid sphere

Abstract: Using the finite element method, a detailed study of the deformations and stresses produced in an elastic-perfectly plastic half-space indented by a rigid sphere was done. The analysis covers the transition region from the maximum elastic contact load to a state where this load has been increased one hundredfold. Experimental results available in the literature are in good agreement with the analysis. In solving repeatedly the large number of linear equations involved in the solution of the problem, it was found profitable, in order to save computer time, to modify the direct elimination method. This technique is described in some details in the paper.

A Light- And Electron-Microscope Study of the Nucleolus During Growth of the Oocyte in the Prepubertal Mouse

Abstract: The ordered changes which occur in the structural organization of the nucleolus during growth of the mouse oocyte have been studied by both light and electron microscopy. All observations have been made on those oocytes whose growth is initiated on the day of birth and completed by postnatal day 14 in prepubertal animals of the ICR albino mouse strain. During that period the oocyte nucleolus undergoes an approximate 90-fold increase in volume. During the unilaminar follicle stage (from birth to postnatal day 4), the growing nucleolus exhibits an overall reticulated-type of structure consisting of: (1) a moderately electron-dense fibrillogranular component occupying most parts of the nucleolar framework; (2) an electron-transparent nucleoplasm-like component filling the numerous interstices of the nucleolar framework; (3) an electron-dense fibrillar component located in the peripheral portion of a number of small islands widely and uniformly scattered within the nucleolar framework, and (4) a slightly less-dense fibrillar component situated in the central portion of these same islands and referred to as fibrillar centres. Increase in nucleolar volume during that stage is brought about mainly through an increase in the overall dimensions of the fibrillogranular framework, accompanied by a parallel increase in the number and, to a certain extent, the size of its electron-transparent interstices. During the bilaminar follicle stage (postnatal day 5 through 8), the following structural and organizational changes take place more or less concomitantly within the still enlarging nucleolar mass: (1) the fibrillogranular framework becomes predominantly fibrillar in texture as a result of what appears to be an unravelling or unfolding of its constituent granules of ribosomal dimensions; (2) the nucleolar interstices decrease rapidly both in number and size because of the accumulation within their interior of a material the texture and density of which match that present in the nucleolar framework itself; and (3) a number of rounded electron-transparent spaces, the nucleolar vacuoles, make their appearance in the regions formerly occupied by some of the fibrillar islands and adjacent interstices. Increase in nucleolar volume during that stage is largely due to the appearance and subsequent enlargement of the nucleolar vacuoles in question. During the plurilaminar follicle stage (postnatal day 9 through 14), the following sequential events take place within the nucleolar mass: (1) a moderately electron-dense fibrillogranular material accumulates within the nucleolar vacuoles; (2) this fibrillogranular material, which eventually fills all vacuolar spaces, undergoes degranulation and a concomitant increase in density, eventually matching that of the rest of the nucleolar mass; (3) all remnants of the lightly stained nucleolar interstices disappear from view; and (4) the fully grown rounded nucleolus finally appears as a dense, compact mass, exclusively fibrillar in texture, and exhibiting no internal structural organization. An attempt is made to interpret these changes in the light of current knowledge concerning thearchitectural and functional organization of the mammalian nucleolus in general. The observations are consistent with the view that the nucleolus, during growth of the primary oocyte, is the site of massive synthesis and storage of nucleolar material.

Changes in Lipid Composition during Greening of Etiolated Pea Seedlings.

Abstract: After 7 days of germination in the dark, the three sections of pea seedlings studied (cotyledons, stems, and young leaves) are rich in linoleic acid; after illumination of the seedlings a very significant increase in linolenic acid is observed in the young leaves section, whereas only small variations are noted in the fatty acid composition of the other sections. The increase in linolenic acid results from the increase in galactolipid content of the young leaves; these already linolenic acid-rich galactolipids are present but only in small amounts in the etiolated seedlings (10% of total lipid).Variations in composition of the other lipid classes (phospholipids and neutral fats) were also studied. The possibility of fatty acid transport from the cotyledons toward the young leaves during the synthesis of the photosynthetic apparatus is discussed.

A study of the peculiarities of austenite during the formation of bainite

Abstract: The formation of bainite in steel is generally accompanied by an enrichment in carbon of the adjacent austenite which can become remarkably stable as evidenced by its very slow transformation rate and its very lowMs point. This paper presents the results of a study of this residual austenite in an SAE-9262 steel. Both the carbon content and the amount of retained austenite have been determined as a function of transformation temperature. It has been shown that the carbon content of the enriched austenite passes through a maximum of 1.7 pct at a reaction temperature of 400°C. However, this remarkably high carbon content falls short of the one predicted by the Kinsman-Aaronson extrapolation of theA3 curve thus indicating that the bainitic transformation cannot be considered simply as an extension of the proeutectoid transformation. In view of the inadequacy of the standard thermodynamics theory of theBs temperature, a kinetic point of view is proposed for the definition of this temperature.

Differential staining patterns of heterochromatin in man.

Abstract: QUINACRINE staining1 can be used to distinguish between different heterochromatic segments in various organisms and Giemsa staining has been used to locate constitutive heterochromatin in human chromosomes2. In using both these techniques on human chromosome preparations we have found certain specific staining properties of hetero-chromatic segments which suggest the existence of at least two different constitutive heterochromatins.

An ultrastructural study of the neurosecretory cells of the medial vascular preiasmatic gland, the preoptic recess and the anterior part of the suprachiasmatic area. I. Cytoplasmic inclusions resembling nucleoi.

Abstract: A distinctive cytoplasmic inclusion, termed nucleolus-resembling body, was identified in the neurons, but not in the glial cells, of the medial vascular prechiasmatic gland, the preoptic recess and the anterior part of the suprachiasmatic area in the rat. This ultrastructure which lacks a limiting membrane is made of an entanglement of tightly packed filaments, 60–70 A in diameter. Each filament consists of smaller units, 15–20 A thick. Usually, only one such ultrastructure is present in a cell, but at time two were identified. It is present in most neurosecretory cells. It is surrounded by polyribosomes in the perikaryon of the nerve cells. Furthermore, it is linked to peripherally located ribosomes by means of filaments, 70 A in diameter. A possible function in protein synthesis of structural components, such as neurofilaments, is hypothesized. Two distinctive fibrillar areas were identified in the nucleolus according to the tightness with which fibrils were packed together. Their significance is discussed. Nucleolar extrusions were never observed in our studies. Paranucleolar and coiled bodies were identified in the nuclear sap. The mechanism of formation and the significance of these bodies are discussed.

Theoretical and clinical considerations in anaesthesia for secreting carcinoid tumors

Abstract: The recent discovery that both serotonin and bradykinin were involved in the clinical manifestations of the carcinoid syndrome, has important implications in the management of anaesthesia. In this report we reviewed the fundamental aspects underlying the biochemistry, the physiology, and the pharmacology of the secreting carcinoid tumor. Bradykinin and associated peptides were traced from their origin in the lysomal granules to their inactivation in the blood, the liver and the lungs. The pharmacological opportunity to block this proteolytic system with anti-peptidases (Trasylol, Iniprol, EACA), was stressed. Serotonin metabolism was also described. The pharmacodynamic pattern, involved in serotonin synthesis, uptake, storage, release, and degradation, was followed from the serotoninergic granule to the urinary excretion of 5 HIAA. The choice of drugs available to interfere with the steps of this sequence was emphasized. We also reported our clinical experience with the management of anaesthesia in 16 cases of carcinoid tumors, 7 of which were functional and secreting. The carcinoid attacks which occurred during anaesthesia were classified in two categories, namely the bradykininergic and the serotoninergic dysfunctions. Accordingly, preventive and corrective measures described were related to a more specific approach to these incidents with either bradykininolytic or serotoninolytic agents. This integration of new pharmacological knowledge with a clearer understanding of the clinical profile of the carcinoid attacks can result in a better management of the emergencies likely to arise during anaesthesia.

Analysis of the Effect of Linear Smear on Photographic Images

Abstract: The effect on the photographic image of the linear smear due to nonuniform relative motion between the image and the film during exposure can be expressed in terms of a complex transfer function. An expression for the equivalent spread function, valid for a restricted class of motions, is given. The case of smear due to uniformly accelerated relative motion is worked out in detail. One surprising result is that, for the same extent of smear, the modulus of the transfer function due to uniformly accelerated relative motion is, at all frequencies, equal to or greater than the modulus of the transfer function due to uniform relative motion

An ultrastructural study of sites of granule extrusion in the anterior pituitary of the rat.

Abstract: Secretory granule extrusion in cells of the rat anterior pituitary was studied by electron microscopy. After appropriate stimulation, corticotrophs, somatotrophs and thyrotrophs showed both “in vivo” and “in vitro” (tissue culture) the extrusion of granules by reverse pinocytosis (exocytosis). In contrast, this phenomenon is not observed in gonadotrophs. Granule extrusion takes place only at those parts of the cell which are in contact with the basement membrane. This directed release seems to favor a quicker diffusion of hormones to the circulatory system.

Lignofibrils on the external cell wall surface of cultured plant cells.

Abstract: Small strands and bundles of strands extend from the outside surface of suspension-cultured cells of Daucus, Ipomoea , and Phaseolus into the medium. This fibrous cell coat is present in all samples from various growth stages but appears to increase in quantity in the order Ipomoea < Phaseolus < Daucus . The bundles are often many microns in length and display great variation in frequency, size, and form. Identification of the composition of the strands and bundles as lignin is consistent with the following observations: alkaline nitrobenzene oxidation of the strands to compounds which resemble monomers of wood lignin; resistance of the strands to pronase, trypsin, pectinase, and lipase; strong irreversible adsorption of heavy metals; deposition of silver granules by treatment with silver nitrate-hexamine reagent; extraction of the bundles with aqueous dioxane (Bjorkman procedure); presence in quantity of a structured form of Klason lignin; and existence of material giving a positive test with the Wiesner reagent. Large individual strands (lignofibrils) from Phaseolus show the form of a flat ribbon with very thin branches at irregular intervals. This form does not vary with preparatory techniques, although its electron opacity does. Intercellular spaces display considerable structure and sometimes contain sheets of fibrillar material merging with both the middle lamella between the cells and the surface bundles facing the medium. These sheets are probably another form of association of the lignofibrils. It is suggested that natural fibrous lignin may be a much commoner component of plant tissue than suspected hitherto.

Humidity in anaesthesiology. IV. Determination of the alveolar humidity and temperature in the dog.

Abstract: During general anaesthesia in dogs ventilated with a dry gas and using a nonrebreathing system, measurements of relative humidity and temperature directly from the alveolar cavity disclosed the constant pattern of saturation at body temperature. Maximal hyperventilation did not modify this biological constant.

Altering the time cycle of heat treatment by preannealing prior to grain growth

Abstract: Preannealing is found to alter the time cycle of grain growth in lead and lead-tin alloys by modifying the kinetics of grain boundary migration. Aging at a low temperature prior to annealing at a high temperature shows the influence of residual strains in the early stage of grain growth. A model is proposed to explain the deviation of the growth kinetics from the theoretical t1/2 law when the samples are annealed immediately after primary recrystallization in terms of a superposition of a strain-induced and a surface tension-induced grain boundary migration. Preannealing by using multiple anneals at the same temperature enables simulation of many different alloys by changing the amount of impurities segregated at grain boundaries. In zone refined material, a good agreement between the Cahn theory and the experimental results is observed; in lead-tin alloys, grain growth kinetics are understood in terms of a superposition of the influences of the solute and of other lattice defects.

Equilibrium anionic polymerization of α‐methylstyrene in p‐dioxane

Abstract: The equilibrium anionic polymerization of α-methylstyrene in p-dioxane, with potassium as initiator, has been investigated at 5, 15, 25, and 40°C by using high-vacuum techniques. The comparison of these results with those obtained previously for the equilibrium polymerization of α-methylstyrene in tetrahydrofuran revealed that, although the values of ΔG1c, the free-energy change upon the polymerization of 1 mole of liquid monomer to 1 bases-mole of liquid amorphous polymer of infinite chain length, are the same for both systems, there is a distinct effect of the solvent. This effect is reflected in the value of monomer equilibrium concentration and its variation with polymer concentration and is explained in terms of a solvent–monomer and solvent–polymer interaction parameter.

Identification of the ACTH secreting cells in the rat pituitary

Abstract: Dans le but d'identifier la cellule hypophysaire responsable de la secretion d'ACTH chez le rat, des etudes morphologiques, en microscopie optique et electronique, furent entreprises chez des animaux surrenalectomises, c'est-a-dire dans des conditions ou la secretion d'ACTH est specifiquement augmentee. Le prelevement des hypophyses fut effectue a des intervalles allant de 1 a 21 jours apres surrenalectomie. Des hypophyses d'animaux surrenalectomises et traites par la dexamethasone, un inhibiteur de la secretion d'ACTH, furent egalement etudiees. Il decoule de ces experiences qu'un type cellulaire est stimule en meme temps que la secretion d'ACTH augmente. Cette cellule, hypertrophiee apres surrenalectomie, possede une forme irreguliere et est tres souvent en contact avec les cellules somatotropes; son ergastoplasme peu developpe contraste avec un appareil de Golgi tres important. Les granules secretoires corticotropes ont un diametre d'environ 200 mμ, sont peu abondants et disposes le long de la membrane cellulaire. Ces granules n'ont cependant pas ete caracterises en microscopie optique. L'administration de dexamethasone provoque une regression specifique de la cellule corticotrope ainsi qu'une accumulation des granules secretoires dans le cytoplasme. Chez l'animal intact, il devient possible d'identifier la cellule corticotrope qui possede les caracteristiques generales de la cellule stimulee, mais dont le cytoplasme et l'appareil de Golgi sont peu importants.

Multiphoton Ionization of Molecules

Abstract: This work reports the first attempt at multiphoton ionization of molecules of iodine, heavy water, and carbon tetrachloride. Despite the occurrence of many different ions, only ${\mathrm{I}}^{+}$, ${\mathrm{D}}^{+}$, and C$\mathrm{Cl}_{3}^{}{}_{}{}^{+}$, respectively, were observed quantitatively using the technique of multiphoton ionization of atoms. "Saturation" was observed.

The Nuclear-Ribosomal System during Neuronal Differentiation and Development

Abstract: Electron microscopic investigations on the maturing cytoplasmic organelles and on the growth of neuronal processes were formerly reported in several developing neurons (1, 2, 3, 4, 5, 6, 7). In contrast, the differentiation of the nuclear components in the maturing neuron was little investigated. To the best of the authors’ knowledge, no systematic ultrastructural study on the nuclear maturation is as yet available.

Further ultrastructural data on the cytoplasmic nucleolus resembling bodies or nematosomes. Their relationship with the subsynaptic web and a cytoplasmic filamentous network.

Abstract: An electron microscope study of the rat supraoptic nucleus, substantia nigra, neostriatum and periventricular preoptic area demonstrates that nematosomes are present within the perikaryon of neurons located in these structures. The latter structure may be found in close association with the subsynaptic web of axosomatic synapses. Numerous micro-filaments fan out from the nematosome and link the latter organelle to the ribosomes, the cytoplasmic membranes and the plasma membrane thus establishing an interwoven filamentous cytoplasmic network. A possible close relationship between the nematosomes and the neurofilaments and neurotubules is discussed.