Circular Discontinuities Research Articles

Visual Analysis of Scientific Data: Comparison of 3D-Topographic, Color and Gray Scale Displays in a Feature Detection Task

Several display techniques were compared for representing scientific data in the context of a feature detection task. The data sets were rendered on a Silicon Graphics workstation using four display formats: linearized gray scale; rainbow scale; reduced hue (blue-green-yellow-white) scale; and a 3D-topographic format viewed in stereo. The task involved searching for features that were embedded in scientific data sets consisting of two spatial and one scalar variable. Data sets were drawn from three scientific domains: Landsat, medical MRI, and global atmospheric data bases. Two types of features were embedded within the data sets: circular (blob-like) discontinuities, and linear (cliff-like) discontinuities. Results showed a general advantage for the gray scale, and a marked disadvantage for the 3D-topographic format in both accuracy and response latency. Performance in the two color scale formats was intermediate, with the reduced hue scale supporting faster, if not more accurate performance than the full rainbow scale. Performance differences were found across data base domains, as well. Directions for future research are discussed.

Ultrastructure of the dinoflagellate Polykrikos: II. The nucleus and its connections to the flagellar apparatus

Electron microscopy of the colonial dinoflagellate Polykrikos kofoidi revealed a nuclear cortex formed of two electron-dense cortical layers directly beneath the nuclear envelope. Nuclear pores were confined to vesicular outpocketings of the nuclear envelope over circular discontinuities in the cortical layers. A conspicuous fibrous ribbon extended from the nucleus to the flagellar apparatus of each zooid. The ribbons resembled in their structure and position the attractophores of termite flagellates. Each flagellar apparatus consisted of two flagella, two elongate axial kinetosomes, an oblique kinetosome, and two roots of markedly different periodicities.

Interference Effect in Dynamic Stress Concentration : Effect of Cylindrical Wave on Circular Discontinuities

The dynamic stress concentration around circular discontinuities in an infinitely extended elastic plate, during passage of a cylindrical dilatation wave of which strength varies harmonically in time, is discussed. When the wave source is apart infinitely from discontinuities, the resulting dynamic stress concentration factor coincides with the result for a plane wave incidence. The influence of the proximity of wave source to discontinuities and the interference effect are studied in detail numerically for the cases of circular holes which exist in a finite domain. According to the results, (1) the maximum stress concentration factor is higher for greater incident wave curvature and (2) the maximum dynamic stress concentration factor approaches to a value which is higher than that of single hole, as the radius ratio between the holes becomes greater, when the radii of the curvature and of the reference hole are kept constant.

Elastic Analysis of Cylindrical Configurations With Stress Singularities

The problem of stress analysis of a circular cylinder is considered under conditions which give rise to stress singularities. Such stresses can be produced by circular boundary discontinuities or when boundaries are subject to mixed displacement and force conditions. General solutions are obtained using transformation of the cylindrical coordinates and these solutions converge in the singular region. The results predict exactly the singular behavior and the analysis generates solutions which can be used over a finite region of the cylinder. A numerical example is given showing the application of this analysis to a circular cylinder completely clamped at one end and loaded axially at the other. In this example the stresses and displacements from the present solution are matched with the corresponding quantities obtained from a finite-element analysis. The matching is performed at a finite distance from the stress singularity. Good agreement is obtained between the two solutions.

An electron microscope study of the nuclear envelope of amphibian oocytes

Immature oocytes from Triturus viridescens of two stages, both prior to yolk formation, were studied by electron microscopy. In the transition from the first to the second of these stages, two nuclear transformations, namely, undulation of the nuclear envelope and nucleolar shredding, apparently take place simultaneously. The nuclear outpocketings are usually bulbous. Infrequently, invaginations of the nuclear envelope occur. The nuclear envelope is composed of two membranes, each about 75 Å thick, which are separated by a perinuclear space which is 150 Å in width. The envelope is interrupted by small circular discontinuities, 800–1000 Å in diameter, which result from the union of the two membranes at regular intervals. It has been established that there are tubes within the discontinuities which are probably not interrupted by the nuclear envelope. Each tube is about 1000 Å in diameter and has a total height of 1500 Å. The annuli seen in tangential sections are considered to represent cross-sections of the tubes. Within or making up the tube walls are about 8 microcylinders which are seen in cross-section as subannuli. Many of the annuli were seen to contain a central granule about 150 Å in diameter. The nucleoli, which increase in size during the transition from one stage to another, are made up of granules about 150 Å in diameter. A new approach to the geometric interpretation of structures has been presented. X-rays of lucite models embedded in paraffin have been studied in order to determine that the conclusions regarding the structural relationships seen in electron micrographs were not optical illusions.