Calibration Methods for Eddy Current Measurement Systems

Calibration of eddy current measurement systems is an important factor for attaining the accuracy and precision of measurement that quantitative nondestructive evaluation requires. The quantity of interest in most forms of eddy current inspection is △Z, the change in probe impedance induced by a flaw. Flaw signals produced by surface-breaking cracks are small; typical flaw signals for an air core probe amount to a few tenths of one percent of the probe’s impedance in air. Such small signals are easily obscured by the impedance changes caused by small variations in the height of the probe above the workpiece (lift-off). To discriminate against lift-off, conventional eddy current instruments determine the phase of △Z relative to lift-off and the magnitude of the component of △Z in quadrature with lift-off. But this information is not sufficient to perform flaw signal inversion; rather, the absolute magnitude and phase of △Z are necessary. Thus, quantitative inversion of eddy current signals to obtain flaw sizes requires methods for calibrating eddy current measurement system

Eddy-Current Probe Design

This paper describes theoretical and experimental work directed toward finding the optimum probe dimensions and operating frequency for eddy current detection of half-penny surface cracks in nonmagnetic conducting materials. The study applies to probes which excite an approximately uniform spatial field over the length of the crack at the surface of the material. In practical terms, this means that the probe is not smaller than the crack length in any of its critical dimensions

Surface Coverage Issues When Using Eddy Current Arrays

Over the past few years, the need for improved flaw detection sensitivity has motivated the development of imaging techniques for eddy current testing [1]. The imaging approach has a major advantage over more traditional eddy current detection methods as image processing routines may be applied to the eddy current images to enhance flaw detection capability. Smaller probes are also being developed to further improve the resolution and sensitivity of flaw detection. The use of smaller probes, however, requires shorter data acquisition sampling intervals. This forces a tradeoff between inspection resolution and inspection speed. The need for simultaneous improvement in both inspection resolution and speed has stimulated an interest in eddy current arrays. As a result, a powerful new eddy current array inspection technology is emerging

Inversion of Eddy Current Signals in a Nonuniform Probe Field

We present a simple analytical method for predicting the eddy current signal (ΔZ) produced by a surface flaw of known dimensions, when interrogated by a probe with spatially varying magnetic field. The model is easily parameterized, and we use it to construct inversion schemes which can extract overall flaw dimensions from multiposition, multifrequency measurements. Our method is a type of Born approximation, in which we assume that the probe’s magnetic field at the mouth of the flaw can be used as a boundary condition on the electromagnetic field solutions inside the flaw. To simplify the calculation we have chosen a “rectangular” 3-dimensional flaw geometry for our model. We describe experimental measurements made with a new broadband probe on a variety of flaws. This probe operates in a frequency range of 200 kHz to 20 MHz and was designed to make the multifrequency measurements necessary for inversion purposes. Since inversion requires knowledge of the probe’s magnetic field shape, we describe experimental methods which determine the interrogating field geometry for any eddy current probe

Improved Probe-Flaw Interaction Modeling, Inversion Processing, and Surface Roughness Clutter

In Reference 1 a first comparison was made of measured eddy current signals with calculations based on nonuniform probe-field interaction theory. These calculations followed the basic analysis developed in Reference 2. They used interrogating field distributions calculated by Dodd and Deeds theory for the air core coils of Reference 3. (Note that Fig. 6 in Reference 1 and Fig. 7 in Reference 3 should be interchanged). In Reference 1 theoretical and experimental plots of the flaw profile curve (a plot of △Z versus distance along the mouth of a surface breaking flaw) were found to be in good agreement, with regard to shape, for several selected EDM notch samples in aluminum. An iterative procedure was also developed for systematically varying the length, depth, and opening width to obtain a best fit to the experimental data.4 In the present paper a full inversion procedure is developed and illustrated for approximately rectangular-shaped EDM notches. The mathematical structure of the inversion problem is first examined and a solution is proposed. Physical reasoning, based on the form of the flaw profile curves, is then used to simplify the approach and to provide guidance in selection of the most suitable probe geometry. Other topics briefly addressed include, possible improvements in the theory for the region with a/§ close to unity and for more realistic flaw shapes (i.e., semi-elliptical, rather than rectangular), inaccuracies due to errors in the probe scan path, and background clutter due to surface roughness, machining marks, and micro-structure

Changes in calcium dynamics following the reversal of the sodium-calcium exchanger have a key role in AMPA receptor-mediated neurodegeneration via calpain activation in hippocampal neurons

Proteolytic cleavage of the Na(+)/Ca(2+) exchanger (NCX) by calpains impairs calcium homeostasis, leading to a delayed calcium overload and excitotoxic cell death. However, it is not known whether reversal of the exchanger contributes to activate calpains and trigger neuronal death. We investigated the role of the reversal of the NCX in Ca(2+) dynamics, calpain activation and cell viability, in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-stimulated hippocampal neurons. Selective overactivation of AMPA receptors caused the reversal of the NCX, which accounted for approximately 30% of the rise in intracellular free calcium concentration ([Ca(2+)](i)). The NCX reverse-mode inhibitor, 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea (KB-R7943), partially inhibited the initial increase in [Ca(2+)](i), and prevented a delayed increase in [Ca(2+)](i). In parallel, overactivation of AMPA receptors strongly activated calpains and led to the proteolysis of NCX3. KB-R7943 prevented calpain activation, cleavage of NCX3 and was neuroprotective. Silencing of NCX3 reduced Ca(2+) uptake, calpain activation and was neuroprotective. Our data show for the first time that NCX reversal is an early event following AMPA receptor stimulation and is linked to the activation of calpains. Since calpain activation subsequently inactivates NCX, causing a secondary Ca(2+) entry, NCX may be viewed as a new suicide substrate operating in a Ca(2+)-dependent loop that triggers cell death and as a target for neuroprotectio

Missing Momentum Reconstruction and Spin Measurements at Hadron Colliders

We study methods for reconstructing the momenta of invisible particles in cascade decay chains at hadron colliders. We focus on scenarios, such as SUSY and UED, in which new physics particles are pair produced. Their subsequent decays lead to two decay chains ending with neutral stable particles escaping detection. Assuming that the masses of the decaying particles are already measured, we obtain the momenta by imposing the mass-shell constraints. Using this information, we develop techniques of determining spins of particles in theories beyond the standard model. Unlike the methods relying on Lorentz invariant variables, this method can be used to determine the spin of the particle which initiates the decay chain. We present two complementary ways of applying our method by using more inclusive variables relying on kinematic information from one decay chain, as well as constructing correlation variables based on the kinematics of both decay chains in the same event.Comment: Version to appear in JHE

Protective Effects of Positive Lysosomal Modulation in Alzheimer's Disease Transgenic Mouse Models

Alzheimer's disease (AD) is an age-related neurodegenerative pathology in which defects in proteolytic clearance of amyloid β peptide (Aβ) likely contribute to the progressive nature of the disorder. Lysosomal proteases of the cathepsin family exhibit up-regulation in response to accumulating proteins including Aβ1–42. Here, the lysosomal modulator Z-Phe-Ala-diazomethylketone (PADK) was used to test whether proteolytic activity can be enhanced to reduce the accumulation events in AD mouse models expressing different levels of Aβ pathology. Systemic PADK injections in APPSwInd and APPswe/PS1ΔE9 mice caused 3- to 8-fold increases in cathepsin B protein levels and 3- to 10-fold increases in the enzyme's activity in lysosomal fractions, while neprilysin and insulin-degrading enzyme remained unchanged. Biochemical analyses indicated the modulation predominantly targeted the active mature forms of cathepsin B and markedly changed Rab proteins but not LAMP1, suggesting the involvement of enhanced trafficking. The modulated lysosomal system led to reductions in both Aβ immunostaining as well as Aβx-42 sandwich ELISA measures in APPSwInd mice of 10–11 months. More extensive Aβ deposition in 20-22-month APPswe/PS1ΔE9 mice was also reduced by PADK. Selective ELISAs found that a corresponding production of the less pathogenic Aβ1–38 occurs as Aβ1–42 levels decrease in the mouse models, indicating that PADK treatment leads to Aβ truncation. Associated with Aβ clearance was the elimination of behavioral and synaptic protein deficits evident in the two transgenic models. These findings indicate that pharmacologically-controlled lysosomal modulation reduces Aβ1–42 accumulation, possibly through intracellular truncation that also influences extracellular deposition, and in turn offsets the defects in synaptic composition and cognitive functions. The selective modulation promotes clearance at different levels of Aβ pathology and provides proof-of-principle for small molecule therapeutic development for AD and possibly other protein accumulation disorders

Methodological considerations in the analysis of fecal glucocorticoid metabolites in tufted capuchins (Cebus apella)

Analysis of fecal glucocorticoid (GC) metabolites has recently become the standard method to monitor adrenocortical activity in primates noninvasively. However, given variation in the production, metabolism, and excretion of GCs across species and even between sexes, there are no standard methods that are universally applicable. In particular, it is important to validate assays intended to measure GC production, test extraction and storage procedures, and consider the time course of GC metabolite excretion relative to the production and circulation of the native hormones. This study examines these four methodological aspects of fecal GC metabolite analysis in tufted capuchins (Cebus apella). Specifically, we conducted an adrenocorticotrophic hormone (ACTH) challenge on one male and one female capuchin to test the validity of four GC enzyme immunoassays (EIAs) and document the time course characterizing GC me- tabolite excretion in this species. In addition, we compare a common field-friendly technique for extracting fecal GC metabolites to an established laboratory extraction methodology and test for effects of storing “field extracts” for up to 1 yr. Results suggest that a corticosterone EIA is most sensitive to changes in GC production, provides reliable measures when extracted according to the field method, and measures GC metabolites which remain highly stable after even 12 mo of storage. Further, the time course of GC metabolite excretion is shorter than that described yet for any primate taxa. These results provide guidelines for studies of GCs in tufted capuchins, and underscore the importance of validating methods for fecal hormone analysis for each species of interest

Foot and ankle injuries during the Athens 2004 Olympic Games

<p>Abstract</p> <p>Background</p> <p>Major, rare and complex incidents can occur at any mass-gathering sporting event and team medical staff should be appropriately prepared for these. One such event, the Athens Olympic Games in 2004, presented a significant sporting and medical challenge. This study concerns an epidemiological analysis of foot and ankle injuries during the Games.</p> <p>Methods</p> <p>An observational, epidemiological survey was used to analyse injuries in all sport tournaments (men's and women's) over the period of the Games.</p> <p>Results</p> <p>A total of 624 injuries (525 soft tissue injuries and 99 bony injuries) were reported. The most frequent diagnoses were contusions, sprains, fractures, dislocations and lacerations. Significantly more injuries in male (58%) versus female athletes (42%) were recorded. The incidence, diagnosis and cause of injuries differed substantially between the team sports.</p> <p>Conclusion</p> <p>Our experience from the Athens Olympic Games will inform the development of public health surveillance systems for future Olympic Games, as well as other similar mass events.</p