Identification of Acoustic Emission Source Mechanisms

Identification of mechanisms generating acoustic emission during deformation of materials is often difficult because several mechanisms may be potentially or actually operating simultaneously. Identification of sources which are actually contributing significantly to the acoustic emission can often be accomplished by testing material with different process histories, by microstructural examination before and after deformation, and by using different stress states. Mechanisms which operate simultaneously in one stress state may· operate predominantly in different strain ranges in another stress state. Further confirmation of the mechanisms involved can be obtained by measurement of physical parameters, other than acoustic emission, during deformation which are sensitive to the proposed generation mechanisms for the acoustic emission. Several examples of the use of these techniques will be shown. The sources of acoustic emission in 7075 aluminum were identified by testing in the T6 and T651 tempers, by testing in both tension and compression, and by measurement of internal friction as a function of strain. Dislocation motion was shown to be the major source of acoustic emission in beryllium by testing beryllium of different purity, heat treatment, and origin (powder metallurgy or cast and worked) in both tension and compression combined with microstructural observations. Confirmation that the source was dislocation motion and identification of the type of dislocation activity involved was made by internal friction measurements during deformation. Acoustic emission from hydrogen assisted crack growth in an austenitic stainless steel was separated from other sources of emission by holding at constant load. Cracking was also monitored by observing changes in the apparent elastic modulus of a sample as hydrogen-assisted cracks propagated in it

Tungsten resonance integrals and Doppler coefficients First quarterly progress report, Jul. - Sep. 1965

Resonance integrals and Doppler coefficients of samples of natural tungsten, tungsten isotopes, and uranium oxide tungsten fue

Recognition of 3-D Objects from Multiple 2-D Views by a Self-Organizing Neural Architecture

The recognition of 3-D objects from sequences of their 2-D views is modeled by a neural architecture, called VIEWNET that uses View Information Encoded With NETworks. VIEWNET illustrates how several types of noise and varialbility in image data can be progressively removed while incornplcte image features are restored and invariant features are discovered using an appropriately designed cascade of processing stages. VIEWNET first processes 2-D views of 3-D objects using the CORT-X 2 filter, which discounts the illuminant, regularizes and completes figural boundaries, and removes noise from the images. Boundary regularization and cornpletion are achieved by the same mechanisms that suppress image noise. A log-polar transform is taken with respect to the centroid of the resulting figure and then re-centered to achieve 2-D scale and rotation invariance. The invariant images are coarse coded to further reduce noise, reduce foreshortening effects, and increase generalization. These compressed codes are input into a supervised learning system based on the fuzzy ARTMAP algorithm. Recognition categories of 2-D views are learned before evidence from sequences of 2-D view categories is accumulated to improve object recognition. Recognition is studied with noisy and clean images using slow and fast learning. VIEWNET is demonstrated on an MIT Lincoln Laboratory database of 2-D views of jet aircraft with and without additive noise. A recognition rate of 90% is achieved with one 2-D view category and of 98.5% correct with three 2-D view categories.National Science Foundation (IRI 90-24877); Office of Naval Research (N00014-91-J-1309, N00014-91-J-4100, N00014-92-J-0499); Air Force Office of Scientific Research (F9620-92-J-0499, 90-0083

Observations on the Pearl Oyster Fishery of Kuwait

The pearl oyster fishery of Kuwait was monitored daily from January 1989 to May 1990. Landings of pearl oysters in 1989 totaled 287 tons with a market value of U.S. $1.0 million. Commercial pearls (\u3e3 mm) were estimated to be present in one of every 4200 oysters. Most of the pearl oysters landed were new recruits with hinge lengths between 40-56 mm. There was a curvilinear relationship between total weight and size of oysters (length) and the sex ratio approached 1:1. Spawning occurs throughout the year, with a spat settlement peak in early fall. Over the size range examined there was no relationship between the size of oysters and the size of pearls and subsequent resource management strategies are discussed

Catastrophic Phase Transitions and Early Warnings in a Spatial Ecological Model

Gradual changes in exploitation, nutrient loading, etc. produce shifts between alternative stable states (ASS) in ecosystems which, quite often, are not smooth but abrupt or catastrophic. Early warnings of such catastrophic regime shifts are fundamental for designing management protocols for ecosystems. Here we study the spatial version of a popular ecological model, involving a logistically growing single species subject to exploitation, which is known to exhibit ASS. Spatial heterogeneity is introduced by a carrying capacity parameter varying from cell to cell in a regular lattice. Transport of biomass among cells is included in the form of diffusion. We investigate whether different quantities from statistical mechanics -like the variance, the two-point correlation function and the patchiness- may serve as early warnings of catastrophic phase transitions between the ASS. In particular, we find that the patch-size distribution follows a power law when the system is close to the catastrophic transition. We also provide links between spatial and temporal indicators and analyze how the interplay between diffusion and spatial heterogeneity may affect the earliness of each of the observables. We find that possible remedial procedures, which can be followed after these early signals, are more effective as the diffusion becomes lower. Finally, we comment on similarities and differences between these catastrophic shifts and paradigmatic thermodynamic phase transitions like the liquid-vapour change of state for a fluid like water

LATEST : A Model of Saccadic Decisions in Space and Time

Peer reviewedPostprin

AVIRIS ground data-processing system

The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) has been under development at JPL for the past four years. During this time, a dedicated ground data-processing system has been designed and implemented to store and process the large amounts of data expected. This paper reviews the objectives of this ground data-processing system and describes the hardware. An outline of the data flow through the system is given, and the software and incorporated algorithms developed specifically for the systematic processing of AVIRIS data are described

Tungsten resonance integrals and Doppler coefficients Third quarterly report, Jan. - Mar. 1966

Reactivities, Doppler coefficients, and resonance integrals for tungsten isotope