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Articles 70261 - 70290 of 77581

Full-Text Articles in Engineering

Analysis Of Periodic Orbits About The Martian Moons By Continuation Techniques, Frank Luria Dec 1990

Analysis Of Periodic Orbits About The Martian Moons By Continuation Techniques, Frank Luria

Theses and Dissertations

From a few known periodic orbits of Phobos and Deimos, continuation techniques were used to find entire families of stable orbits. These techniques involved varying a parameter, the Hamiltonian, of the system and analyzing how the orbital behavior changed with the parameter. Floquet multipliers, for stability analysis, were also computed. AUTO86, a continuation/bifurcation software package, was used in this study. Artificial energy dissipation had to be added to the conservative Hamiltonian system to enable use of AUTO.

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A Numerical Investigation Of The Series Reversion/Inversion And Series Reversion Of Lambert's Time Function, Michael P. Ward Dec 1990

A Numerical Investigation Of The Series Reversion/Inversion And Series Reversion Of Lambert's Time Function, Michael P. Ward

Theses and Dissertations

An expression for the semi-major axis as a function of time may be determined by performing a series reversion and inversion of Lambert's Time Function. Since the resulting series contains a singularity, it is desirable to perform only a reversion on the original series to obtain an expression for the inverse of the semi-major axis. Using a Lagrange expansion to obtain the coefficients for this series is very computer intensive. Therefore, alternative methods are presented. Also, each series was expanded into a continued fraction which provided greater accuracy than the series using the same number of coefficients. The accuracy was …

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Material Properties Of Silicon Carbide Fibers With Continuously Applied Sol-Gel Alumina Coatings, Christian C. Daehnick Dec 1990

Material Properties Of Silicon Carbide Fibers With Continuously Applied Sol-Gel Alumina Coatings, Christian C. Daehnick

Theses and Dissertations

An investigation was conducted to determine the effect of non-alpha- alumina coatings applied under varying conditions on some of the properties of silicon carbide fibers. Limited characterization of the coating by optical, scanning electron, and transmitted electron microscopy as well as energy- dispersive x-ray analysis was performed. Tensile tests were used to determine changes in elastic modulus, ultimate strength, and strain to failure of the coated fibers relative to uncoated fibers. The coatings were found to lower the mean value of the measured properties as their thickness increased, but the measurements were not accurate enough to determine if this corresponded …

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A Low-Cost Part-Task Flight Training System: An Application Of A Head Mounted Display, David A. Dahn Dec 1990

A Low-Cost Part-Task Flight Training System: An Application Of A Head Mounted Display, David A. Dahn

Theses and Dissertations

To investigate the feasibility of using head-mounted display(HMD) and Computer Image Generators(CIG) in a low cost part-task trainer, we created a prototype system. Our approach was to build a virtual world interface using a HMD to an existing flight simulator application. This allowed a CIG with only one graphics channel to drive the display. To investigate which class of computing platform was suitable for use as the CIG, a cooperative thesis effort was launched to host the simulator on a mini-computer and micro-computer platform. The appropriate CIG could then be determined through demonstration and comparison between the systems. A software …

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Recursive Optimization Of Digital Circuits, John Knutson Dec 1990

Recursive Optimization Of Digital Circuits, John Knutson

Theses and Dissertations

The goal of this thesis is twofold: first, to identify the advantages and disadvantages of existing optimization systems and second, to develop an optimization system that uses Boolean principles to generate a recursive realization of combinational logic. Current multi-level optimization systems fall into two categories: local optimization which removes redundancy by pattern matching on a local scale and global optimization which works with the equations that specify a circuit rather than with the circuit implementation itself. While global systems are very flexible and can produce near-optimal solutions, they are inherently complex. This research effort demonstrates that an effective global optimization …

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Model-Based Reasoning In Electronic Repair, Kenneth B. Cohen Dec 1990

Model-Based Reasoning In Electronic Repair, Kenneth B. Cohen

Theses and Dissertations

Diagnosis is the process of identifying the cause for an observed behavior of a system. Model-based reasoning uses knowledge of the behavior of the component and the interconnection of the components to diagnose a system. This thesis investigates the application of model-based reasoning to the problem of isolating faulty components of an analog electronic circuit. More specifically, this thesis describes an architecture for a model-based diagnostic system for electronic modules, implements an assumption-based truth maintenance system (one of the component parts of a model-based diagnostic system), and creates the interface between the truth maintenance system and the diagnostic system.

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A Study Of The Effects Of Noise Jamming On Radar Receivers, Paul E. Bishop Dec 1990

A Study Of The Effects Of Noise Jamming On Radar Receivers, Paul E. Bishop

Theses and Dissertations

A comprehensive study of the effects of noise jamming on various pulsed radar receiver types is proposed. First, a literature review on the sources of electrical noise and various jamming waveforms is presented. The power spectra for three noise jamming waveforms are rigorously derived. These cases are shot noise in a parallel-plate diode, a series of pulses with random amplitudes and intervals, and for a series of pulses with random amplitudes, spacing and phases. Next, the probability density functions for the output of linear and quadratic detectors are developed. For each detector type, the probability density functions for the cases …

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Interference Cancellation In Rf Signals Using Adaptive Array Techniques, Mark E. Brown Dec 1990

Interference Cancellation In Rf Signals Using Adaptive Array Techniques, Mark E. Brown

Theses and Dissertations

This study investigated the effectiveness of the Least Means Squared (LMS) algorithm against various types of common jammers. The LMS algorithm was implemented using the Block Oriented Systems Simulator (BOSS). The LMS algorithm was inserted at the output of a two element antenna array. The array was configured so as to have one-half wavelength spacing. A quadrature hybrid signal structure was used. The array was then tested against a barrage and sweep jammer. The barrage jammer testing consisted of varying each of the three available jammer parameters; power, frequency and angle of arrival individually. The sweep jammer testing consisted of …

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Silicon Hybrid Wafer Scale Integration (Wsi) Used To Fabricate A Hilbert Transform Integrated Circuit Module, Daniel J. Gaughan Dec 1990

Silicon Hybrid Wafer Scale Integration (Wsi) Used To Fabricate A Hilbert Transform Integrated Circuit Module, Daniel J. Gaughan

Theses and Dissertations

This research was performed in order to develop a superior processing schedule for fabricating Wafer-Scale Integration (WSI) circuit modules. This technology allows the design of circuitry that spans the entire surface of a silicon substrate wafer. The circuit element employed in this research was the Hilbert transform, a digital phase-shifting circuit. The transform was incorporated into a three Integrated Circuit (IC) die package that consisted of a mechanically supportive silicon wafer, three IC die, and a planarizing silicon wafer. The die were epoxied into this wafer using a Teflon block as a flat, and the combination was epoxied onto the …

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Network Reduction Using Error Prediction, Michael V. Gilsdorf Dec 1990

Network Reduction Using Error Prediction, Michael V. Gilsdorf

Theses and Dissertations

This thesis investigates gradient descent learning algorithms for multi-layer feed forward neural networks. A technique is developed which uses error prediction to reduce the number of weights/nodes in a network. The research begins by studying the first and second order back-prop training algorithms along with their convergence properties. A network is reduced by making an estimate of the amount of error which would occur when a weight(s) is removed. This error estimate is then used to determine if a particular weight is essential to the operation of the network. If not, it is removed and the network retrained. The process …

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Speech Coding And Compression Using Wavelets And Lateral Inhibitory Networks, Richard Ricart Dec 1990

Speech Coding And Compression Using Wavelets And Lateral Inhibitory Networks, Richard Ricart

Theses and Dissertations

The purpose of this thesis is to introduce the concept of lateral inhibition as a generalized technique for compressing time/frequency representations of electromagnetic and acoustical signals, particularly speech. This requires at least a rudimentary treatment of the theory of frames-which generalizes most commonly known time/frequency distributions--the biology of hearing, and digital signal processing. As such, this material, along with the interrelationships of the disparate subjects, is presented in a tutorial style. This may leave the mathematician longing for more rigor, the neurophysiological psychologist longing for more substantive support of the hypotheses presented, and the engineer longing for a reprieve from …

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Characterization Of An Air-To-Air Optical Heterodyne Communication System, Rebecca N. Seeger Dec 1990

Characterization Of An Air-To-Air Optical Heterodyne Communication System, Rebecca N. Seeger

Theses and Dissertations

The primary goal of this research was to determine the feasibility of air-to-air optical communications systems using coherent detection in a turbulent environment. Secondary goals were to determine (1) the signal-to-noise ratio (SNR) degradation due to turbulence and (2) the effect of varying the wavelength (1.5, 830, 904 nm), altitude (5000-12500 m), path length (40-160 km) and aperture side length (1-15 cm) on the turbulence affected SNR. The research was conducted under the following assumptions: (1) ideal transmitter and receiver, (2) equally sized, uniformly weighted, square transmitter and receiver apertures, (3) ideal tracking by the receiver, and (4) zero losses …

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Radar Image Processing For The Afit Anechoic Chamber, Brian K. Sanders Dec 1990

Radar Image Processing For The Afit Anechoic Chamber, Brian K. Sanders

Theses and Dissertations

The purpose of this study was to begin development of an Inverse Synthetic Aperture Radar imaging capability for the AFIT anechoic chamber. This began with an evaluation of the capabilities and limitations of the existing radar system and the chamber itself for this application. Then, after deciding on the image processing approach, software had to be written to collect the data necessary for image processing. This constituted the majority of this study, and resulted in a versatile, user-friendly program that automates the process of collecting data for high-resolution radar images. The program checks that the data to be collected will …

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Establishment Of A Fabrication And Measurement Capability For Aperture-Fed Stacked Patch Microstrip Antennas At The Air Force Institute Of Technology, Christopher I. Terry Dec 1990

Establishment Of A Fabrication And Measurement Capability For Aperture-Fed Stacked Patch Microstrip Antennas At The Air Force Institute Of Technology, Christopher I. Terry

Theses and Dissertations

Much time and effort has been applied to accurately model aperture- fed stacked patch microstrip antennas at the Air Force Institute of Technology (AFIT). The results of this study provide AFIT with the capability to fabricate and measure these antennas for comparison of measured radiation characteristics to the predicted characteristics. Basic microstrip patch antenna theory is reviewed, as well as the motivation leading to the development of aperture-fed stacked patch microstrip antennas. The fabrication process used to produce the two antennas manufactured for this study is described in detail. The construction of a small anechoic chamber for pattern measurements is …

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Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas Dec 1990

Angle Of Arrival Detection Through Artificial Neural Network Analysis Of Optical Fiber Intensity Patterns, Scott Thomas

Theses and Dissertations

The optical sensors of United States Air Force reconnaissance vehicles, such as satellites, are subject to temporary or permanent blinding from hostile (or threat) laser radiation. By detecting and determining the angle of arrival (AOA) of the hostile radiation, the reconnaissance vehicle may be able to protect its optical sensors by taking evasive maneuvers or by shutting down the optical sensor (such as closing a shutter) until the threat has passed. In addition, the vehicle can relay information to its ground terminal allowing the intelligence community to determine the source of the hostile laser radiation. This thesis demonstrated that an …

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Characterization Of Radar Signals Using Neural Networks, Daniel R. Zahirniak Dec 1990

Characterization Of Radar Signals Using Neural Networks, Daniel R. Zahirniak

Theses and Dissertations

Recent work concerning artificial neural networks has focused on decreasing network training times. Kernel Classifier networks, using radial basis functions (RBFs) as the kernel function, can be trained quickly with little performance degradation. Short training times are critical for systems which must adapt to changing environments. The function of Kernel Classifier networks is based on the principle that multivariate functions can be approximated via linear combinations of RBFs. RBFs can also perform probability density estimations, making classifications approximating a Baye's optimal descriminant. Methods used to set the RBF centers included matching the training data, Kohonen Training, K-Means Clustering and placement …

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Low Temperature Photoluminescence Study Of Holmium And Thulium Implanted Into Iii-V Semiconductors And Silicon, Eric Silkowski Dec 1990

Low Temperature Photoluminescence Study Of Holmium And Thulium Implanted Into Iii-V Semiconductors And Silicon, Eric Silkowski

Theses and Dissertations

Low temperature photoluminescence studies were performed on holmium implanted into InP, GaAs, and Si; and thulium implanted into AlGaAs, GaAs, and Si. Samples were annealed by the conventional furnace and rapid thermal techniques. None of the characteristic 4f emissions of holmium were found in the spectral region of .73 to 1.55 eV. AlGaAs:Tm showed strong thulium emissions in the .93 to 1.03 eV region. These emissions were studied and compared to those in GaAs:Tm. Low and high temperature annealed samples showed evidence of trivalent Tm centers. Temperature dependence studies showed that thulium 4f emissions were present above 200 K but …

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A Procedure For Performance Assessment Of Drugs Hypothesized To Be Effective In Controlling Motion Sickness, Zainab N. Ahmed Dec 1990

A Procedure For Performance Assessment Of Drugs Hypothesized To Be Effective In Controlling Motion Sickness, Zainab N. Ahmed

Theses and Dissertations

The Air Force Institute of Technology (AFIT) is conducting research into the effectiveness of certain drugs for controlling motion sickness. If the drugs are found to be useful, they must still be proven to have no harmful effects on the operator's performance abilities. There are many methods for assessing performance effects of drugs but very little standardization exists. The Unified Tri-Services Cognitive Performance Assessment Battery (UTC-PAB) is a performance assessment method designed to be used by all military branches. This will encourage standardization of drug testing, exchange of data, and comparability of methods. Five tests were chosen from the UTC-PAB …

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Debris Production In Hypervelocity Impact Asat Engagements, Stephen K. Remillard Dec 1990

Debris Production In Hypervelocity Impact Asat Engagements, Stephen K. Remillard

Theses and Dissertations

This study reviews laboratory experiments on hypervelocity impacts and applies the results from those experiments to predict the mass of debris produced, the number of particles, and the size distribution of the debris particles produced in an ASAT engagement using kinetic energy weapons. The three possible types of hypervelocity collisions are discussed and parameters are provided that will help predict what type of collisions will occur between a given projectile and a target satellite. Once the collision type is determined, various equations are supplied which can be used to calculate debris mass, etc. Next, a notional attack between a miniature …

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Proposed Design Of A Tactical Reconnaissance Satellite System, John D. T. Severance Dec 1990

Proposed Design Of A Tactical Reconnaissance Satellite System, John D. T. Severance

Theses and Dissertations

Tactical reconnaissance is a much needed wartime asset, yet with the deactivation of all active-duty RF-4C squadrons world-wide there appears to be a gap in this country's war-fighting capability. This study proposes a system which utilizes a constellation of small tactical satellites and mobile ground receiving stations that can fulfill the tactical reconnaissance mission. A literature review gives background information on resolution variables, the RF-4C, space reconnaissance, and sensing technologies. After defining system requirements and constraints, a basic system concept is determined. Three alternative systems, separated mostly by threat scenario, technology, and cost, are evaluated using Athey's Systematic Systems Approach. …

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Measuring The Effectiveness Of Space: Satellite Weather Systems, Steven T. Wilson Dec 1990

Measuring The Effectiveness Of Space: Satellite Weather Systems, Steven T. Wilson

Theses and Dissertations

Using concepts from multivariate utility theory, basic orbital mechanics, and information regarding operational and planned meteorological satellites, this thesis develops a meaningful MOE to support high-level decision making regarding the allocation, acquisition, and operational deployment of space meteorological satellite (METSAT) assets. Satellite meteorological systems were chosen because of the ready availability of pertinent unclassified data. However, the methodology presented may be applied to any type of space system.

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Feasibility Of Incorporation Of By-Pass Dust In Clay Bricks, Amr Aly Gamal El-Din Dec 1990

Feasibility Of Incorporation Of By-Pass Dust In Clay Bricks, Amr Aly Gamal El-Din

Archived Theses and Dissertations

No abstract provided.

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Development Of A Piezoelectric Polymer Film Pressure Transducer For Low Frequency And Dynamic Pressure Measurement, Ted H. Halley Dec 1990

Development Of A Piezoelectric Polymer Film Pressure Transducer For Low Frequency And Dynamic Pressure Measurement, Ted H. Halley

Theses and Dissertations

The purpose of this research was to investigate the characteristics of a small and inexpensive pressure transducer made from piezoelectric film. The pressure transducer was designed to be small and surface mountable so that the pressure distribution could be measured on an aerodynamic body. A charge reset technique was used to overcome the traditional limitations, low frequency measurements and charge decay, of a piezoelectric device.

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Analysis Of Hypersonic Blunt-Body Flows Using A Total Variation Diminishing Scheme And The Maccormack Scheme, Montgomery C. Hughson Dec 1990

Analysis Of Hypersonic Blunt-Body Flows Using A Total Variation Diminishing Scheme And The Maccormack Scheme, Montgomery C. Hughson

Theses and Dissertations

An explicit second-order accurate, total variation diminishing (TVD) scheme and the MacCormack scheme are applied to the Euler equations in axisymmetric form to study hypersonic blunt body flows. The modified flux approach of Harten, with modification by Yee, for two-dimensional flows is extended to treat axisymmetric flows. Calculated flow properties for the steady state, blunt body problem such as shock standoff distance, bow shock shape, surface pressure distribution and entropy jump conditions are compared to theory, results from the MacCormack scheme, and experimental data for Mach numbers of 3.0, 4.03, 5.06, 6.03 and 8.1. Additionally, the TVD and MacCormack schemes …

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H2 And H∞ Optimization With A Restricted Region Of Stability, Michael J. Mares Dec 1990

H2 And H∞ Optimization With A Restricted Region Of Stability, Michael J. Mares

Theses and Dissertations

Many modern control design methods, such as H2 and H∞ optimization, guarantee that the closed-loop system will be stable. To make further use of this guarantee, the portion of the s-plane considered to be stable is restricted to a region left of a vertical line some distance alpha from the imaginary axis. This alpha shift was accomplished in the state space equations, so standard computational tools still work. now the system is not only guaranteed to be stable, but also has some guaranteed speed for the time response. The equations for guaranteeing some arbitrary damping ratio were also …

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An Experimental Study Of A Sting-Mounted Single-Slot Circulation Control Wing, Michael E. Pelletier Dec 1990

An Experimental Study Of A Sting-Mounted Single-Slot Circulation Control Wing, Michael E. Pelletier

Theses and Dissertations

This wind tunnel study investigated the feasibility of using a sting and force balance to measure the aerodynamic forces and moments on a circulation control wing. A 20% this, 8.5% camber, single blowing slot, rectangular wing was designed, built, and tested in the AFIT 5-ft wind tunnel. Lift and drag coefficients were referenced to the stability axis. The Reynolds number for all tests was 950,000; angle of attack was varied from -6 to +6 degrees. Trends in the data were similar to two dimensional data, with the exception of high drag coefficients with increased blowing. Results show it is feasible …

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Impact Damage In Curved Graphite/Epoxy Panels With Clamped Edges, Ronald B. Perry Dec 1990

Impact Damage In Curved Graphite/Epoxy Panels With Clamped Edges, Ronald B. Perry

Theses and Dissertations

Graphite/epoxy curved cylindrical panels were impacted in the center by an impact machine capable of measuring load during the test. Load, deflection and strain as functions of time were measured for six symmetric layup configurations for impact energies of 0.5 to 4.5 ft-lb. Damage was produced in all panels for certain impact energies. The extent and location of damage was determined from C-scans and optical microscopy of panel cross-sections. The cross-sections indicated that both delamination and transverse cracking contribute to internal damage. An in-house nonlinear finite element code was used to predict the panel deflections and stresses. The analysis produced …

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A Linear Quadratic Regulator Weight Selection Algorithm For Robust Pole Assignment, Jeffrey D. Robinson Dec 1990

A Linear Quadratic Regulator Weight Selection Algorithm For Robust Pole Assignment, Jeffrey D. Robinson

Theses and Dissertations

An advantage of linear quadratic regulator (LQR) design is that it gives a robust system by guaranteeing stability margins. This property is used to develop an algorithm for placing robust poles. The algorithm chooses the positive semidefinite weighting matrix Q and positive definite weighting matrix R by attempting to place closed loop poles at a set of desired poles. If the desired poles lie outside the allowable LQR region, the algorithm finds the achievable poles inside the region that are closest to the desired poles. The solution requires using a gradient search technique to minimize a weighted eigenvalue difference cost …

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Modelling And Analysis Of Kernel Function And Development Of Equivalent Theodorsen Function For Three-Dimensional Aeroelastic Analysis, John K. Ryder Dec 1990

Modelling And Analysis Of Kernel Function And Development Of Equivalent Theodorsen Function For Three-Dimensional Aeroelastic Analysis, John K. Ryder

Theses and Dissertations

A fractional calculus model is developed for the kernal function under incompressible subsonic flow conditions for rectangular planform airfoils with small aspect ratio. A model valid for restricted regions of the kernel function for compressible subsonic flow conditions is also developed. Additionally, a method for numerically solving the pressure-downwash integral equation for rectangular planform wings of aspect ratio two through ten in incompressible flow is developed. An equivalent Theodorsen function for three- dimensional unsteady flow is developed, enabling the use of simpler two- dimensional aeroelastic equations of motion to fully capture the more complicated three-dimensional effects.

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Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe Dec 1990

Investigation Of Damage Mechanisms In A Cross-Ply Metal Matrix Composite Under Thermo-Mechanical Loading, Joel J. Schubbe

Theses and Dissertations

Metal matrix composites (MMCs) are rapidly becoming strong candidates for high temperature and high stiffness structural applications such as the Advanced Tactical Fighter (ATF). This study systematically investigated the failure modes and associated damage in a cross-ply, [0/90]2s SCS6/Ti-15-3 metal matrix composite under in-phase and out-of-phase thermomechanic fatigue. Initiation and progression of fatigue damage were recorded and correlated to changes in Young's Modulus of the composite material. Experimental results show an internal stabilization of reaction zone size but degradation and separation from constituent materials under extended cyclic thermal loading. Critical to damage were transverse cracks initiating in the 90° …

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