Nonlinear Analysis of the Human Accommodation Systems PDF Download
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Author: Ahmed Bahgat Fattouh Abdel-Fattah
Publisher:
ISBN:
Category : Eye
Languages : en
Pages : 326
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Book Description
Author: Ahmed Bahgat Fattouh Abdel-Fattah
Publisher:
ISBN:
Category : Eye
Languages : en
Pages : 326
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Book Description
Author: Tri Le
Publisher:
ISBN: 9780542226847
Category : Engineering, Civil
Languages : en
Pages :
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The crystalline human lens is modeled by using the finite element software, ABAQUS/CAE Version 6.5-1 as an axisymmetric shell to study the optical power and displacement of anterior and posterior poles induced due to zonule traction. Several different element types were tested to obtain the optimum mesh. These elements were three and six-noded triangular hybrid and four-noded quadrilateral hybrid for modeling of the cortex and nucleus. Constant strain triangular and regular quadrilateral elements were examined for modeling the capsule. One dimensional two degree of freedom spring elements were used to model the anterior, posterior, and equatorial zonules. Six different lens profiles were selected to mathematically model the lens geometry, which included Lizak; Krueger A; Krueger B; Strenk A; Strenk B; and Trial lens. A displacement-based incremental loading history was applied to the equatorial zonule to conduct geometric nonlinear analysis. The converged solution was obtained by coupling Hilbert L-2 norm and equating external work done to internal system strain energy. The converged and optimum solution was compared with analytical solution reported in literature and was selected to conduct a comprehensive parametric study. (Abstract shortened by UMI.).
Author: Charles Wankel
Publisher: IAP
ISBN: 1617357537
Category : Business & Economics
Languages : en
Pages : 409
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Book Description
This volume has a bold agenda, in which academics create immersive worlds where the avatar is the center of the universe. As the virtual world grows, avatars move away from quasi-human interactions within virtual domiciles, gardens, and businesses to being blood cells in the blood stream, or to be firing neurons in the human brain, or creatures competing on the ocean floor or the surface of Mars or just about anything that can be imagined using the magic of photographic and artistic images, programming, narrative and avatars. What are the frameworks and strategies for building these environments? What are the things the avatar adapts and learns from in its environment? This book will examine such frameworks, strategies, examples and feedback systems to explore what it takes to create a global education environment for learning. This starts with engaging your avatar and is completed in a transformation in how you interact with the internet. Whether using the visual internet to learn or to interact with a customer about a product or service, this immersive interface can be a world that knows you and forms around your unique needs and interests.
Author: George K. Hung
Publisher: Springer Science & Business Media
ISBN: 1475758650
Category : Science
Languages : en
Pages : 777
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Book Description
Some of the best vision scientists in the world in their respective fields have contributed to chapters in this book. They have expertise in a wide variety of fields, including bioengineering, basic and clinical visual science, medicine, neurophysiology, optometry, and psychology. Their combined efforts have resulted in a high quality book that covers modeling and quantitative analysis of optical, neurosensory, oculomotor, perceptual and clinical systems. It includes only those techniques and models that have such fundamentally strong physiological, control system, and perceptual bases that they will serve as foundations for models and analysis techniques in the future. The book is aimed first towards seniors and beginning graduate students in biomedical engineering, neurophysiology, optometry, and psychology, who will gain a broad understanding of quantitative analysis of the visual system. In addition, it has sufficient depth in each area to be useful as an updated reference and tutorial for graduate and post-doctoral students, as well as general vision scientists.
Author:
Publisher:
ISBN:
Category : Cybernetics
Languages : en
Pages : 712
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Author:
Publisher:
ISBN:
Category : Medicine
Languages : en
Pages : 1230
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Author: Benjamin Coldrick
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Hewitt D. Crane
Publisher:
ISBN:
Category : Eye
Languages : en
Pages : 100
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Book Description
"This study has attempted to model the human visual-accommodation system, starting directly with the retinal image. The models that are developed are reasonably consistent with existing data and offer a certain degree of understanding of certain features of the data. The modeling is in three stages. Starting at the retina we ask: (1) What portion of the retinal picture is involved in accommodation control, (2) How that portion of the picture is processed to derive a measure of defocus, and (3) How that signal in turn is used to control the ciliary muscles. We tentatively conclude that the relevant portion of the retina is a central region of the fovea, having a diameter of some 30 minutes of arc, or 6 mils -- the diameter of a coarse human hair. As for processing of the retinal image, it is shown how neural circuits based on lateral inhibition can yield a measure of defocus that is consistent with experimental data over several orders of magnitude of object size and illumination. It is also shown how interaction between three such overlapping receptor regions could account for certain chromatic effects in accommodation control. As for the control system, we tentatively propose an intermittent control model in which accommodation correction cycles may be initiated by relatively abrupt changes in the retinal pattern, caused for example by involuntary eye-movement saccads or certain target movements. The case is argued for a control cycle involving a sampling of the accommodation error followed by a ballistic corrective movement. In terms of this control model the elusive lens "vibrations" appear to be no more than normal accommodation correction cycles, what we have termed "accommodation saccads." Apart from its role in accommodation control it is also noted how these lens vibrations could possibly increase the depth of field for strong accommodation. The models predict significant interaction between accommodation control and eye-movements. A number of experiments are proposed which would help elucidate the nature of this interaction."--Abstract.
Author: Lawrence Stark
Publisher: Springer Science & Business Media
ISBN: 1468407066
Category : Technology & Engineering
Languages : en
Pages : 442
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Book Description
To anyone who worked long on the functional organization of living systems, it seems obvious that the central problems arise from a multi plicity of closed loops Simultaneously active in the control of every act. Severally, they may be stable but, combined, they may crack up or break into schizogenetic oscillation. Whatever they are, linear or not, is beside the point, for in either case the same difficulty of analysis arises. Nor does it help our argument that we deal only with formal neurons or those having greater similitude to real ones. This limited Pitts and me, in 1943, to three theorems of Part III of our "Logical Calculus of Idea Immanent in Nervous Activity. " We still seek a transparent terminology in which to discern their properties. In the face of such difficulties it takes great courage to attempt a servo system analysis of the control mechanisms me diating any reflex if one would do this as a good engineer. Walt Whitman says of the "Beginners," "How dear and dreadful they are to the earth - appearing at intervals - How all times mischoose their objects of adulation and reward - And how the same price must still be paid for the same great services!" Larry Stark is a beginner. His book must not be mistaken for phys iology - and there is nothing wrong with his physiology.
Author:
Publisher:
ISBN:
Category : Radio
Languages : en
Pages : 366
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