Search results for "Axia"
showing 10 items of 638 documents
Evolution Within a Bizarre Phylum: Homologies of the First Echinoderms
1998
SYNOPSIS. The Extraxial/Axial Theory (EAT) of echinoderm skeletal homologies describes two major body wall types: axial and extraxial. The latter is subdivided into perforate and imperforate regions. Each of the regions has a distinctly different source in early larval development. Axial skeleton originates in the rudiment, and develops in association with the pentaradially arranged hydrocoel according to specific ontogenetic principles. Perforate and imperforate extraxial regions are associated with the left and right somatocoels respectively, are not governed by ontogenetic principles of plate addition, and are products of the non-rudiment part of the larval body. The morphology of even t…
Arrays in rays: terminal addition in echinoderms and its correlation with gene expression
2005
Summary The echinoderms are deuterostomes that superimpose radial symmetry upon bilateral larval morphology. Consequently, they are not the first animals that come to mind when the concepts of segmentation and terminal addition are being discussed. However, it has long been recognized that echinoderms have serial elements along their radii formed in accordance with the ocular plate rule (OPR). The OPR is a special case of terminal growth, forming elements of the ambulacra that define the rays in echinoderms. New elements are added at the terminus of the ray, which may or may not be marked by a calcified element called the terminal plate (the “ocular” of sea urchins). The OPR operates in eve…
On the instability of an axially moving elastic plate
2010
Problems of stability of an axially moving elastic band travelling at constant velocity between two supports and experiencing small transverse vibrations are considered in a 2D formulation. The model of a thin elastic plate subjected to bending and tension is used to describe the bending moment and the distribution of membrane forces. The stability of the plate is investigated with the help of an analytical approach. In the frame of a general dynamic analysis, it is shown that the onset of instability takes place in the form of divergence (buckling). Then the static forms of instability are investigated, and critical regimes are studied as functions of geometric and mechanical problem param…
Ocular biometry with swept-source optical coherence tomography
2020
This study aimed to summarize the outcomes reported when swept-source optical coherence tomography (SS-OCT) is used for ocular biometry. A literature search was performed to identify publications reporting clinical outcomes of patients measured with commercial SS-OCT. Twenty-nine studies were included in this review. A comprehensive analysis of the available data was performed, focusing on parameters used for intraocular lens (IOL) power calculation in cataract surgery, including keratometry, central corneal thickness, white-to-white distance, anterior chamber depth, lens thickness, axial length, IOL power, and pupil diameter. Different metrics for repeatability, reproducibility, and agreem…
Evaluation of 6 biometers based on different optical technologies
2021
This study shows that optical biometers based on different technologies provide repeatable measurements for different ocular parameters and, when compared, statistically significant differences between them were found when measuring most parameters.
Laser-induced anisotropy in terbium-gallium garnet
1998
Ga5O12 crystal when illuminated at the terbium ion resonance, becomes optically uniaxial. The optical axis is found to be along the beam-propagation axis. The origin of this symmetry breakdown is a thermal effect. Our observation of a conoscopic pattern is accounted for by a quadratic stress and refractive index distribution model. By spatial integration of the conoscopic pattern, the laser-induced stress birefringence variation as a function of the incident beam power is determined.
Quantitative ultrasound predicts bone mineral density and failure load in human lumbar vertebrae
2006
Quantitative ultrasound is in widespread clinical use for assessment of bone quality at peripheral skeletal sites, but has not yet been applied to those sites in the axial skeleton, such as the spine and hip, where osteoporotic fractures are common.Ultrasound measurements were made in 11 cadaveric vertebrae and relationships with bone mineral density and failure load were investigated. An ultrasonic imaging system was used to measure speed of sound, broadband ultrasonic attenuation, and attenuation at a single frequency, through the vertebral body in the sagittal plane. Ultrasonic measurements were averaged over a region of interest centrally within the vertebral body, and were calculated w…
Sudden sensorineural hearing loss as prodromal symptom of anterior inferior cerebellar artery infarction.
2011
Sudden sensorineural hearing loss is a clinical condition characterized by a sudden onset of unilateral or bilateral hearing loss. In recent years sudden deafness has been frequently described in association with anterior inferior cerebellar artery (AICA) infarction generally presenting along with other brainstem and cerebellar signs such as ataxia, dysmetria and peripheral facial palsy. The authors report a rare clinical case of a 53-year-old man who suddenly developed hearing loss and tinnitus without any brainstem or cerebellar signs. Computed tomography of his brain was normal, and the audiological results localized the lesion causing deafness to the inner ear. Surprisingly, magnetic re…
Relativistic beaming and gamma-ray brightness of blazars
2009
We investigate the dependence of gamma-ray brightness of blazars on intrinsic properties of their parsec-scale radio jets and the implication for relativistic beaming. By combining apparent jet speeds derived from high-resolution VLBA images from the MOJAVE program with millimetre-wavelength flux density monitoring data from Metsahovi Radio Observatory, we estimate the jet Doppler factors, Lorentz factors, and viewing angles for a sample of 62 blazars. We study the trends in these quantities between the sources which were detected in gamma-rays by the Fermi Large Area Telescope (LAT) during its first three months of science operations and those which were not detected. The LAT-detected blaz…
Some Optimization Problems
2013
In this chapter, the problems of safety analysis and optimization of a moving elastic plate travelling between two rollers at a constant axial velocity are considered. We will use a model of a thin elastic plate subjected to bending and in-plane tension (distributed membrane forces). We will study transverse buckling (divergence) of the plate and its brittle and fatigue fracture caused by fatigue crack growth under cyclic in-plane tension (loading). Our aim is to find the safe ranges of velocities of an axially moving plate analytically under the constraints of longevity and stability. In the end of this chapter, the expressions for critical buckling velocity and the number of cycles before…