Attritor suitable for extremely dense material

2016 ◽  
Vol 71 (3) ◽  
pp. 221
Keyword(s):  
Dense Material

Comparative Morphology of Intercellular Bridges Between Developing Germ Cells of the Ovary

1970 ◽  
Vol 28 ◽  
pp. 328-329
Author(s):  
J. R. Ruby ◽  
R. F. Dyer ◽  
R. G. Skalko ◽  
R. F. Gasser ◽  
E. P. Volpe
Keyword(s):  
Germ Cells ◽  
Rana Pipiens ◽  
Comparative Morphology ◽  
Dense Material ◽  
Individual Species ◽  
Microscope Examination ◽  
Electron Dense Material ◽  
Intercellular Bridges ◽  
Cytoplasmic Side ◽  
Intercellular Connections

An electron microscope examination of fetal ovaries has revealed that developing germ cells are connected by intercellular bridges. In this investigation several species have been studied including human, mouse, chicken, and tadpole (Rana pipiens). These studies demonstrate that intercellular connections are similar in morphology regardless of the species.Basically, all bridges are characterized by a band of electron-dense material on the cytoplasmic side of the tri-laminar membrane surrounding the connection (Fig.l). This membrane is continuous with the plasma membrane of the conjoined cells. The dense material, however, never extends beyond the limits of the bridge. Variations in the configuration of intercellular connections were noted in all ovaries studied. However, the bridges in each individual species usually exhibits one structural characteristic seldom found in the others. For example, bridges in the human ovary very often have large blebs projecting from the lateral borders whereas the sides of the connections in the mouse gonad merely demonstrate a slight convexity.

The Organization of Actin Filaments in the Stereocilia of the Bird Cochlea

1980 ◽  
Vol 38 ◽  
pp. 554-555
Author(s):  
E.J. Battles ◽  
D. DeRosier ◽  
J.C. Saunders ◽  
L.G. Tilney
Keyword(s):  
Hair Cell ◽  
Diffraction Pattern ◽  
Sea Urchin ◽  
Actin Filaments ◽  
Optical Diffraction ◽  
Dense Material ◽  
Apical Surface ◽  
Structural Rigidity ◽  
High Degree ◽  
Degree Of Order

Extending from the apical surface of each hair cell of the chick cochlea are from 75 to 200 microvilli or stereocllia and one true cllium, the kinocilium. The stereocllia are arranged in rows of progressively increasing length (Fig. 1). Within each tapering sterocilium is a bundle of actin filaments with over 900 filaments near the tip yet only approximately 25 at the base where filaments are enmeshed in a dense material (Fig. 1); from here some of the filaments enter the apical surface of the cell (cuticular plate) as a rootlet. Examination of longitudinal sections of the stereocilia (Fig. 2) show that the filaments are aligned parallel to each other and show considerable order. Examination of an optical diffraction pattern of this bundle (Fig. 4) reveal that the actin filaments are packed such that the crossover points of adjacent actin filaments are inregister. A prominent reflection at 125Å−1 demonstrates that the filaments are cjossbridged by a macromolecular bridge situated at an average of 125Å−1 intervals (Fig. 4) in transverse sections the filaments appear hexagonally packed although there are regions where the filaments are less ordered (Fig. 3). In images processed in the computer to remove, noise and enhance detail periodic nature of the bridge can be clearly seen (see arrows Fig. 5). This image resembles that of an actin paracrystal formed from sea urchin extract composed of bundles of actin filaments crossbridged by a second protein. Thus the actin filaments in the bird stereocilia by being cross-bridged and packed with a high degree of order and produces a structure with considerable structural rigidity. Embryos were studied at various stages in development in an attempt to determine how the stereocilia form and how does the actin packing develops. These stages will be discussed.

scholarly journals AN ELECTRON MICROSCOPE STUDY OF THE DEVELOPMENT OF A MOUSE HEPATITIS VIRUS IN TISSUE CULTURE CELLS

1965 ◽  
Vol 24 (1) ◽  
pp. 57-78 ◽  
Author(s):  
J. F. David-Ferreira ◽  
R. A. Manaker
Keyword(s):  
Electron Microscope ◽  
Inclusion Bodies ◽  
Hepatitis Virus ◽  
Mouse Hepatitis Virus ◽  
Dense Material ◽  
Virus Particles ◽  
Culture Cells ◽  
Tissue Culture Cells ◽  
Tubular Body ◽  
Number Of Particles

Samples taken at different intervals of time from suspension cultures of the NCTC 1469 line of mouse liver—derived (ML) cells infected with a mouse hepatitis virus have been studied with the electron microscope. The experiments revealed that the viruses are incorporated into the cells by viropexis within 1 hour after being added to the culture. An increasing number of particles are found later inside dense cytoplasmic corpuscles similar to lysosomes. In the cytoplasm of the cells from the samples taken 7 hours after inoculation, two organized structures generally associated and never seen in the controls are observed: one consists of dense material arranged in a reticular disposition (reticular inclusion); the other is formed by small tubules organized in a complex pattern (tubular body). No evidence has been found concerning their origin. Their significance is discussed. With the progression of the infection a system of membrane-bounded tubules and cisternae is differentiated in the cytoplasm of the ML cells. In the lumen of these tubules or cisternae, which are occupied by a dense material, numerous virus particles are observed. The virus particles which originate in association with the limiting membranes of tubules and cisternae are released into their lumen by a "budding" process. The virus particles are 75 mµ in diameter and possess a nucleoid constituted of dense particles or rods limiting an electron transparent core. The virus limiting membrane is sometimes covered by an outer layer of a dense material. In the cells from the samples taken 14 to 20 hours after inoculation, larger zones of the cell cytoplasm are occupied by inclusion bodies formed by channels or cisternae with their lumens containing numerous virus particles. In the samples taken 20 hours or more after the inoculation numerous cells show evident signs of degeneration.

The ultrastructure of M1-a-mediated resistance to powdery mildew infection in barley

1975 ◽  
Vol 53 (22) ◽  
pp. 2589-2597 ◽  
Author(s):  
H. H. Edwards
Keyword(s):  
Powdery Mildew ◽  
Host Cell ◽  
Electron Density ◽  
Epidermal Cells ◽  
Dense Material ◽  
Ultrastructural Changes ◽  
Electron Dense Material ◽  
Host Cytoplasm ◽  
Powdery Mildew Infection ◽  
Cell Protoplast

M1-a-mediated resistance in barley to invasion by the CR3 race of Erysiphe graminis f. sp. hordei does not occur in every host cell with the same speed and severity. In some cells ultrastructural changes within the host cell as a result of resistance will occur within 24 h after inoculation, whereas in other cells these changes may take up to 72 h. In some cells the ultrastructural changes are so drastic that they give the appearance of a hypersensitive death of the host cell, whereas in other cells the changes are very slight. In any case, at the end of these changes the fungus ceases growth. The ultrastructural changes occur in penetrated host epidermal cells as well as non-infected adjacent epidermal and mesophyll cells.The following ultrastructural changes have been observed: (1) an electron-dense material which occurs either free in the vacuole or adhering to the tonoplast (the material is granular or in large clumps); (2) an increased electron density of the host cytoplasm and nucleus; (3) a breakdown of the tonoplast so that the cytoplasmic constituents become dispersed throughout the cell lumen; and (4) the deposition of papillar-like material in areas other than the penetration site. The first three changes take place within the host cell protoplasts and are directly attributable to the gene M1-a. These changes are typical of stress or incompatibility responses and thus M1-a appears to trigger a generalized incompatibility response in the presence of race CR3. The papillar-like material occurs outside the host cell protoplast in the same manner as the papilla and probably is not directly attributable to M1-a.

Differential classification of dense material in a three-product cyclone

2004 ◽  
Vol 17 (5) ◽  
pp. 573-579 ◽  
Author(s):  
A. Mainza ◽  
M.S. Powell ◽  
B. Knopjes
Keyword(s):  
Dense Material

Microtubule-organizing centres and assembly of the double-spiral microtubule pattern in certain heliozoan axonemes

1981 ◽  
Vol 50 (1) ◽  
pp. 259-280
Author(s):  
J.C. Jones ◽  
J.B. Tucker
Keyword(s):  
Nuclear Envelope ◽  
Surface Membrane ◽  
Cold Treatment ◽  
Dense Material ◽  
Microtubule Assembly ◽  
Central Nucleus ◽  
Spiral Pattern ◽  
Microtubule Organizing Centres ◽  
Double Spiral ◽  
Actinophrys Sol

The double-spiral microtubule pattern is established by a self-linkage procedure when axopodial axonemes reassemble after cold treatment in multinucleate Echinosphaerium nucleofilum and mononucleate Actinophrys sol. Nuclei are related spatially to axoneme morphogenesis in both organisms but in rather different ways. Microtubules grow out in all directions from discrete clumps of dense material situated close to nuclei in E. nucleofilum as axonemal assembly begins. Each clump acts as a microtubule-organizing centre (MTOC) in so far as it is associated spatially with the assembly of microtubules for a single axoneme. The dense material spreads along the sides of a developing axoneme for several micrometers, where it probably promotes further microtubule assembly as the double-spiral pattern is established. Pattern is generated as microtubules that are randomly oriented to begin with become more closely juxtaposed and aligned with each other. There are indications that juxtaposition is brought about by the contractile action of a filamentous meshwork that interconnects the microtubules. Final positioning and alignment appears to be accomplished by a ‘zippering’ together of adjacent portions of microtubules that proceeds in both directions along the lengths of developing axonemes as self-linkage is effected. Considerable numbers of more or less radially oriented microtubules remain and project from the surface membrane of the single central nucleus during cold treatment of A. sol. Additional tubules assemble and become associated similarly with the nuclear envelope immediately after cold treatment. Initially these microtubules are not arranged in a double-spiral pattern, which is subsequently generated by procedures similar to those outlined above for E. nucleofilum. It is suggested that the surface of the nuclear envelope may act as an MTOC.

Visualization of changes in ciliary tip configuration caused by sliding displacement of microtubules in macrocilia of the ctenophore Beroe

1985 ◽  
Vol 79 (1) ◽  
pp. 161-179 ◽  
Author(s):  
S.L. Tamm ◽  
S. Tamm
Keyword(s):  
Electron Microscopy ◽  
Dense Material ◽  
Bend Angle ◽  
Two Dimensional ◽  
Electron Dense Material ◽  
Central Pair ◽  
Rest Position ◽  
Recovery Stroke ◽  
Dimensional Models ◽  
As If

Macrocilia from the lips of the ctenophore Beroe consist of multiple rows of ciliary axonemes surrounded by a common membrane, with a giant capping structure at the tip. The cap is formed by extensions of the A and central-pair microtubules, which are bound together by electron-dense material into a pointed projection about 1.5 micron long. The tip undergoes visible changes in configuration during the beat cycle of macrocilia. In the rest position at the end of the effective stroke (+30 degrees total bend angle), there is no displacement between the tips of the axonemes, and the capping structure points straight into the stomach cavity. In the sigmoid arrest position at the end of the recovery stroke (−60 degrees total bend angle), the tip of the macrocilium is hook-shaped and points toward the stomach in the direction of the subsequent effective stroke. This change in tip configuration is caused by sliding displacement of microtubules that are bound together at their distal ends. Electron microscopy and two-dimensional models show that the singlet microtubule cap acts as if it were hinged to the ends of the axonemes and tilted to absorb the microtubule displacement that occurs during the recovery stroke. The straight and hooked shapes of the tip are thought to help the ctenophore ingest prey.

The apical structure in Perophora annectens (tunicate) spermatozoa: fine structure, differentiation and possible role in fertilization

1984 ◽  
Vol 66 (1) ◽  
pp. 175-187
Author(s):  
M. Fukumoto
Keyword(s):  
Fine Structure ◽  
Golgi Apparatus ◽  
Dense Material ◽  
Electron Dense Material ◽  
Extracellular Materials ◽  
Small Blister

The apical structure in Perophora annectens spermatozoa is approximately 4 micron in length and it is helically coiled. Its major component is a striated structure, which may be analogous to a perforatorium. The plasmalemma enclosing the anterior quarter of the apical structure is covered by extracellular materials, the anterior ornaments. During spermiogenesis, the apical structure is first recognized as a small blister of the plasmalemma at the apex of the young spermatid. It develops into a conical protrusion and then into a finger-like process (approximately 1 micron in length). This process is transformed into an elongated process (approximately 4 micron in length) with electron-dense material in its core. Finally, the elongated process is helically coiled to form an apical structure in which electron-dense material forms dense striations. Vesicles (50-70 nm in diameter), presumably derived from the Golgi apparatus, have been recognized in the blisters of younger spermatids, and can be followed through to the finger-like process. In the finger-like process these vesicles are transformed into smaller vesicles (20-30 nm in diameter), which probably fuse with the anterior plasmalemma of the finger-like process. This suggests that chorion lysin(s) is associated with the anterior membrane enclosing the apical structure in these spermatozoa.

Bonaparte’s Bursting Buttons: A Thin Story

2013 ◽  
Author(s):  
Lars Öhrström
Keyword(s):  
Science Teachers ◽  
Dense Material ◽  
Alexander The Great ◽  
Military Leader ◽  
Napoleon Bonaparte ◽  
Popular Book ◽  
The Town ◽  
Warm Clothing

On my way to Vilnius, capital of Lithuania, one late November I realized that I had not packed any winter clothes. It turns out that I was not the first to make this blunder. None of the half a million or so Germans, French, Swiss, Poles, Italians, and other nationalities who passed through the town or in its vicinity in June 1812 had packed any winter clothes, something many of them were to later regret. They were on their way, although they did not know it at the time, to Moscow. What they also did not know was that they were going to make what was arguably the world’s worst aller-retour journey ever: Vilna to Moscow and back (at that time the town was known under its Polish name and had recently been acquired by the Russians in the process of the annihilation of the Polish state). It was June, and they were in a good mood, as the Russian Tsar had recently fled Vilna followed by his quarrelling generals, and they were under the command of possibly the most competent military leader since Alexander the Great: Napoleon Bonaparte. The lack of warm clothing was not going to bother me, however. By the morning the snow had melted, and luckily I was not on my way to Moscow on foot. I was in Vilnius to search for some buttons, preferably made of tin. The story of Napoleon’s buttons and their allegedly fateful role in the disastrous 1812 campaign is widespread among scientists and science teachers. This is partly due to the popular book with the same name by the chemists Penny LeCouteur and Jay Burreson, and I wanted to find out whether there could be any truth in it, or whether it was just another of the legends and rumours that has formed around this war. Briefly, the story goes like this: metallic tin is a dense material (lots of atoms per cubic centimetre) and was supposedly the material used for many of the buttons of what was known as la Grande Armée. Unfortunately, metallic tin has a nasty Mr Hyde variation, known as grey tin.

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