124 research outputs found
When Michigan Changed the World
http://deepblue.lib.umich.edu/bitstream/2027.42/168165/1/2020-Feb_When_UM_Changed_the_World.pd
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A biophysical analysis of the occlusal wear of dental materials
An artificial oral environment was used to clinically simulate the dental wear process and surface friction between opposing maxillary and mandibular elements. Measurement of surface friction between occlusal surfaces of natural premolar teeth demonstrated large variation. High viscosity lubricants and surfactant containing lubricants were capable of reducing the surface friction. The enamel appeared otherwise insensitive to natural and artificial salivary fluids. Orientation of opposing enamel prisms was critical for reduction of interocclusal friction. A critical choice of prosthetic dental materials evaluted for wear included amalgam, porcelain, and composite opposed by a natural third molar palatal cusp. The wear of amalgam was slight (volume loss 0.0307 .0036 mm^3 and depth .072 .0017 mm at 300K masticatory cycles) and wear of the opposing enamel was not measurable. SEM demonstrated smearing between the amalgam and the enamel cusp, thus supporting an adhesive wear mechanism. The wear of porcelain (volume .165 .037 mm^3, depth .127 .02 mm at 300K masticatory cycles) demonstrated a ploughing effect on the surface supporting an abrasive wear mechanism. The composite wear was intermediate(volume .046 .007 mm^3, depth .059 .01 mm). Posterior composites are thought to wear by an abrasive as well as fatigue mechanism. The artificial mouth demonstrated a high correlation (0.98) with clinical studies.Wear of enamel opposed by enamel demonstrated a degree of variability. The physiologic occlusal orientation between enamel pairs appeared important. A finite element model of a natural and crowned premolar tooth was developed consisting of 586 triangular elements and 343 nodes using ANSYS and IFECS finite element analysis software. Validation of the model was achieved via a physical model of a natural premolar tooth with strain gages. A new full coverage restoration design employing layering of composite restorative materials was proposed and tested. The model predicted a problem of fatigue crack propagation through the restoration which was confirmed in preliminary clinical trials. This provided further evidence for the fatigue mechanism of wear in composite restorations. On the basis of the wear studies conducted, recommendations for restorative treatment design were presented
Information resources management, 1984-1989: A bibliography with indexes
This bibliography contains 768 annotated references to reports and journal articles entered into the NASA scientific and technical information database 1984 to 1989
Report of the Third General Meeting of the International Network for Development Information Exchange (INDIX)
Meeting: International Network for Development Information Exchange, General Meeting, 3d, 13-15 Sept. 1995, Koebenhavn, D
Finite elements software and applications
The contents of this thesis are a detailed study of the software
for the finite element method. In the text, the finite element method
is introduced from both the engineering and mathematical points of view.
The computer implementation of the method is explained with samples of
mainframe, mini- and micro-computer implementations. A solution is
presented for the problem of limited stack size for both mini- and
micro-computers which possess stack architecture.
Several finite element programs are presented. Special purpose
programs to solve problems in structural analysis and groundwater flow
are discussed. However, an efficient easy-to-use finite element program
for general two-dimensional problems is presented. Several problems in
groundwater flow are considered that include steady, unsteady flows in
different types of aquifers. Different cases of sinks and sources in
the flow domain are also considered. The performance of finite element
methods is studied for the chosen problems by comparing the numerical
solutions of test problems with analytical solutions (if they exist) or
with solutions obtained by other numerical methods. The polynomial
refinement of the finite elements is studied for the presented problems
in order to offer some evidence as to which finite element simulation
is best to use under a variety of circumstances
From diversity to convergence : British computer networks and the Internet, 1970-1995
The Internet's success in the 21st century has encouraged analysts to investigate the origin of this network. Much of this literature adopts a teleological approach. Works often begin by discussing the invention of packet switching, describe the design and development of the ARPANET, and then examine how this network evolved into the Internet. Although the ARPANET was a seminal computer network, these accounts usually only briefly consider the many other diverse networks that existed. In addition, apart from momentary asides to alternative internetworking solutions, such as the Open Systems Interconnection (OSI) seven-layer reference model, this literature concentrates exclusively on the ARPANET, the Internet, and the World Wide Web. While focusing on these subjects is important and therefore justified, it can leave the reader with the impression that the world of networking started with the ARPANET and ended with the Internet. This thesis is an attempt to help correct this misconception.
This thesis analyses the evolution of British computer networks and the Internet between the years 1970 and 1995. After an introduction in Chapter 1, the thesis analyses several networks. In Chapters 2 and 3, the focus is on academic networks, especially JANET and SuperJANET. Attention moves to videotex networks in Chapter 4, specifically Prestel, and in Chapter 5, the dissertation examines electronic mail networks such as Telecom Gold and Cable & Wireless Easylink. Chapter 6 considers online services, including CompuServe, American Online, and the Microsoft Network, and the thesis ends with a conclusion in Chapter 7. All of the networks discussed used protocols that were incompatible with each other which limited the utility of the networks for their users. Although it was possible that OSI or another solution could have solved this problem, the Internet's protocols achieved this objective. This thesis shows how the networks converged around TCP/IP
NASA Tech Briefs, June 1990
Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences
From diversity to convergence : British computer networks and the Internet, 1970-1995
The Internet's success in the 21st century has encouraged analysts to investigate the origin of this network. Much of this literature adopts a teleological approach. Works often begin by discussing the invention of packet switching, describe the design and development of the ARPANET, and then examine how this network evolved into the Internet. Although the ARPANET was a seminal computer network, these accounts usually only briefly consider the many other diverse networks that existed. In addition, apart from momentary asides to alternative internetworking solutions, such as the Open Systems Interconnection (OSI) seven-layer reference model, this literature concentrates exclusively on the ARPANET, the Internet, and the World Wide Web. While focusing on these subjects is important and therefore justified, it can leave the reader with the impression that the world of networking started with the ARPANET and ended with the Internet. This thesis is an attempt to help correct this misconception. This thesis analyses the evolution of British computer networks and the Internet between the years 1970 and 1995. After an introduction in Chapter 1, the thesis analyses several networks. In Chapters 2 and 3, the focus is on academic networks, especially JANET and SuperJANET. Attention moves to videotex networks in Chapter 4, specifically Prestel, and in Chapter 5, the dissertation examines electronic mail networks such as Telecom Gold and Cable & Wireless Easylink. Chapter 6 considers online services, including CompuServe, American Online, and the Microsoft Network, and the thesis ends with a conclusion in Chapter 7. All of the networks discussed used protocols that were incompatible with each other which limited the utility of the networks for their users. Although it was possible that OSI or another solution could have solved this problem, the Internet's protocols achieved this objective. This thesis shows how the networks converged around TCP/IP.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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