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

Measuring Gas Composition and Pressure Within Sealed Containers Using Acoustic Resonance Spectroscopy

Interim and long-term storage of carefully prepared plutonium material within hermetically sealed containers may generate dangerous gas pressures and compositions. The authors have been investigating the application of acoustic resonance spectroscopy to non-intrusively monitor changes in these parameters within sealed containers. In this approach a drum-like gas cavity is formed within the storage container which is excited using a piezoelectric transducer mounted on the outside of the container. The frequency response spectrum contains a series of peaks whose positions and widths are determined by the composition of the gas and the geometry of the cylindrical resonator; the intensities are related to the gas pressure. Comparing observed gas frequencies with theory gives excellent agreement. Small changes in gas composition, better than 1:1000, are readily measurable

Statistical properties of acoustic emission signals from metal cutting processes

Acoustic Emission (AE) data from single point turning machining are analysed in this paper in order to gain a greater insight of the signal statistical properties for Tool Condition Monitoring (TCM) applications. A statistical analysis of the time series data amplitude and root mean square (RMS) value at various tool wear levels are performed, �nding that ageing features can be revealed in all cases from the observed experimental histograms. In particular, AE data amplitudes are shown to be distributed with a power-law behaviour above a cross-over value. An analytic model for the RMS values probability density function (pdf) is obtained resorting to the Jaynes' maximum entropy principle (MEp); novel technique of constraining the modelling function under few fractional moments, instead of a greater amount of ordinary moments, leads to well-tailored functions for experimental histograms.Comment: 16 pages, 7 figure

The proangiogenic capacity of polymorphonuclear neutrophils delineated by microarray technique and by measurement of neovascularization in wounded skin of CD18-deficient mice

Growing evidence supports the concept that polymorphonuclear neutrophils (PMN) are critically involved in inflammation-mediated angiogenesis which is important for wound healing and repair. We employed an oligonucleotide microarray technique to gain further insight into the molecular mechanisms underlying the proangiogenic potential of human PMN. In addition to 18 known angiogenesis-relevant genes, we detected the expression of 10 novel genes, namely midkine, erb-B2, ets-1, transforming growth factor receptor-beta(2) and -beta(3), thrombospondin, tissue inhibitor of metalloproteinase 2, ephrin A2, ephrin B2 and restin in human PMN freshly isolated from the circulation. Gene expression was confi rmed by the RT-PCR technique. In vivo evidence for the role of PMN in neovascularization was provided by studying neovascularization in a skin model of wound healing using CD18-deficient mice which lack PMN infi ltration to sites of lesion. In CD18-deficient animals, neo- vascularization was found to be signifi cantly compromised when compared with wild- type control animals which showed profound neovascularization within the granulation tissue during the wound healing process. Thus, PMN infiltration seems to facilitate inflammation mediated angiogenesis which may be a consequence of the broad spectrum of proangiogenic factors expressed by these cells. Copyright (c) 2006 S. Karger AG, Basel

The International Urban Energy Balance Models Comparison Project: First Results from Phase 1

A large number of urban surface energy balance models now exist with different assumptions about the important features of the surface and exchange processes that need to be incorporated. To date, no com- parison of these models has been conducted; in contrast, models for natural surfaces have been compared extensively as part of the Project for Intercomparison of Land-surface Parameterization Schemes. Here, the methods and first results from an extensive international comparison of 33 models are presented. The aim of the comparison overall is to understand the complexity required to model energy and water exchanges in urban areas. The degree of complexity included in the models is outlined and impacts on model performance are discussed. During the comparison there have been significant developments in the models with resulting improvements in performance (root-mean-square error falling by up to two-thirds). Evaluation is based on a dataset containing net all-wave radiation, sensible heat, and latent heat flux observations for an industrial area in Vancouver, British Columbia, Canada. The aim of the comparison is twofold: to identify those modeling ap- proaches that minimize the errors in the simulated fluxes of the urban energy balance and to determine the degree of model complexity required for accurate simulations. There is evidence that some classes of models perform better for individual fluxes but no model performs best or worst for all fluxes. In general, the simpler models perform as well as the more complex models based on all statistical measures. Generally the schemes have best overall capability to model net all-wave radiation and least capability to model latent heat flux

Spatial and temporal patterns of surface-atmosphere energy exchange in a dense urban environment using scintillometry

Spatially-integrated measurements of the surface energy balance (SEB) are needed in urban areas to evaluate urban climate models and satellite observations. Scintillometers allow observations of sensible heat flux (QH) over much larger areas than techniques such as eddy covariance (EC), however methods are needed to partition between remaining unmeasured SEB terms. This is the first study to use observed spatial and temporal patterns of QH from a scintillometer network to constrain estimates of remaining SEB terms in a dense, heterogeneous urban environment. Results show that QH dominates the surface energy balance in central London throughout the year, with expected diurnal courses and seasonal trends in QH magnitude related to solar radiation input. Measurements also reveal a clear anthropogenic component of QH with winter (summer) weekday QH values 11.7% (5.1%) higher than weekends. Spatially, QH magnitude is correlated with vegetation and building land cover fraction in the measurement source areas. Spatial analysis provides additional evidence of anthropogenic influence with highest weekday/weekend ratios (1.55) from the City of London. Spatial differences are used to estimate horizontal advection and a novel method to estimate monthly latent heat flux is developed based on observed land cover and wet-dry surface variations in normalized QH. Annual anthropogenic heat emissions are estimated to be 46.3 W m−2 using an energy balance residual approach. The methods presented here have potential to significantly enhance understanding of urban areas, particularly in areas with tall buildings where there is little observational data

Severe paraneoplastic hypoglycemia in a patient with a gastrointestinal stromal tumor with an exon 9 mutation: a case report

BACKGROUND: Non-islet cell tumor induced hypoglycemia (NICTH) is a very rare phenomenon, but even more so in gastrointestinal stromal tumors. It tends to present in large or metastatic tumors, and can appear at any time in the progression of the disease. We present herein a case of NICTH in a GIST tumor and report an exon 9 mutation associated to it. CASE PRESENTATION: A thirty nine year-old man with a recurrent, metastatic gastrointestinal stromal tumor presented to the hospital with nausea, dizziness, loss of consciousness, and profound hypoglycemia (20 mg/dL). There was no evidence of factitious hypoglycemia. He was stabilized with a continuous glucose infusion and following selective vascular embolization, the patient underwent debulking of a multicentric 40 cm × 25 cm × 10 cm gastrointestinal stromal tumor. After resection, the patient became euglycemic and returned to his normal activities. Tumor analysis confirmed excessive production of insulin-like growth factor II m-RNA and the precursor protein, "big" insulin-like growth factor II. Mutational analysis also identified a rare, 6 bp tandem repeat insert (gcctat) at position 1530 in exon 9 of KIT. CONCLUSION: Optimal management of gastrointestinal stromal tumor-induced hypoglycemia requires a multidisciplinary approach, and surgical debulking is the treatment of choice to obtain immediate symptom relief. Imatinib or combinations of glucocorticoids and growth hormone are alternative palliative strategies for symptomatic hypoglycemia. In addition, mutations in exon 9 of the tyrosine kinase receptor KIT occur in 11–20% of GIST and are often associated with poor patient outcomes. The association of this KIT mutation with non-islet cell tumor induced hypoglycemia has yet to be established

Sources of acoustic emission during fatigue of Ti-6Al-4V: effect of microstructure

The fundamentals of acoustic emission (AE) analysis of fatigue cracking were applied to Ti-6Al-4V. The effect of microstructure on the characteristics of the AE events generated and the failure mechanisms which produced AE in Ti-6Al-4V were established. Lamellar microstructures generated one to two orders of magnitude more emission than equiaxed microstructures. The combination of larger grain size, more continuous α/β interfaces, more tortuous crack-front geometry, cleavage and intergranular fracture in lamellar microstructures accounts for the greater amount of emission. For lamellar microstructures, most AE events were generated in the upper 20% of the stress range, whereas in equiaxed microstructures, most events were generated at lower stresses. Most AE events were generated during crack opening and also at low stresses. AE events having high level intensities were also generated at stresses other than the peak stress. This is because in titanium alloys, which have both high strength and toughness, AE events are generated from both plastic zone extension and crack extension.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44721/1/10853_2004_Article_BF00542927.pd