Defect classification using a new feature for pulsed eddy current sensors

The objective of this study is to identify defects such as surface cracks, subsurface defects and metal losses using feature based pulsed eddy current sensors. A new feature, termed as the rising point, related to the propagation time of electromagnetic waves in metallic targets is proposed for defect classification. Experimental studies of the validation, robustness of the new feature of rising time are reported. In addition to other features, defects can be detected and quantified robustly and lift-off can also be derived from the rising time. Conclusion and further work are derived on the basis of the findings.     

脉冲涡流和电磁声换能器双探头无损检测

在许多情况下，只应用一种NDT技术存在不足，这就迫使NDT操作人员使用一种以上的技术以保证检测出危害被检物使用寿命或功能的缺陷。但分别实施多种技术的检测，就会延长检验时间。介绍了一种新的NDT设施，采用两种不同的非接触无损检测技术进行互补，即电磁声换能器（EMAT）和脉冲涡流（PEC）探头。检测结果表明，脉冲涡流和电磁声换能器因是非接触，所以可应用于材料生产过程中的自动在线检验，也可用于在役检验。     

Multiple sensors on pulsed eddy-current detection for 3-D subsurface crack assessment

This paper proposes the use of multiple sensors in pulsed eddy-current detection for three-dimensional (3-D) subsurface flaw imaging. A normalization technique has been proposed to eliminate the characteristic variation among the Hall devices used in the probe and lift off effects. A principal component analysis-based feature extraction that provides orthogonal information for multiple sensor fusion has been introduced and investigated. Using the features of multiple projection coefficients, 3-D surface flaws can be measured and reconstructed. The experimental tests have illustrated that the proposed method has delivered more defect information than the conventional peak value and time for pulsed eddy-current sensors.     

Making numbers count: The early development of numerical inferences.

Two experiments examined preschool children's ability to draw inferences about numerosity from correspondences between sets. In Experiment 1, 3- and 4-year-old children made numerical inferences about a hidden set from their own counts of a corresponding visible set and also from numerical information about that set stated by the experimenter. Experiment 2 contrasted a count condition with a move condition, in which children's attention was not explicitly drawn to the numerosity of the visible set. Again, children were able to make numerical inferences as early as 3 years of age. However, differences between the 2 conditions implicate production deficiencies in young children's use of counting as a problem-solving strategy when they are not explicitly told to count. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective information use in the development of search behavior.

Age differences in children's use of various sources of information about object location were examined in a study of search behavior in 3-, 4-, and 7-yr-olds. The 2 principal sources of information were general associative knowledge about the typical locations of objects (location specificity) and explicit verbal statements about object location. Age differences in the results reflected increasing utilization of the 2 sources of information when each was considered separately. More importantly, the design allowed consideration of Ss' ability to combine the information to limit search. In this respect, the findings reveal sophisticated information integration on the part of even the youngest Ss tested. At all ages, Ss were able to combine both sources of information when both were relevant and to ignore irrelevant location-specificity information when the verbal information was logically superordinate. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Infants' understanding of visible displacements.

Two studies examined 54 9-mo-old and 54 12-mo-old infants' understanding of visible displacements and whether infants understand that the object has been deleted from its initial hiding place as part of its displacement to a new location. Displacement problems were compared with 2-object problems on which separate objects were hidden at the 1st and 2nd hiding place so that the initial object was not deleted from the 1st displacement location. Nondisplacement problems, on which the object remained at the 1st hiding place while the experimenter moved her visibly empty hand to the 2nd place, were also included in the 1-object condition. Although Exp I showed equivocal results, Exp II provided clear evidence that even 9-mo-olds have at least a limited sensitivity to the deletion component of displacements. In that experiment, the 9-mo-olds searched significantly more at the 2nd than at the 1st hiding place on displacement problems, and the distribution of their searches across the 2 visited locations on those problems was significantly different than on 2-object problems. Although their performance was less consistent than that of 12-mo-olds, there was no evidence that they suffered from any systematic misunderstanding that separated them from the older Ss. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dual EMAT and PEC non-contact probe: applications to defect testing

For many non-destructive testing (NDT) applications, more information and greater reliability can be gained by using different techniques for defect detection, especially when the methods are particularly sensitive to different types of defects. However, this will often lead to a much longer and more expensive test and is not always practical due to time and cost constraints. We have previously discussed initial experiments using a new dual-probe combining electromagnetic acoustic transducers (EMATs) generating and detecting ultrasonic surface waves, and a pulsed eddy current (PEC) sensor [1]. This enables more reliable detection and sizing of surface and near-surface defects, with a reduced testing time compared to using two NDT techniques separately. In this paper, we present experiments using the dual-probe on samples which are more representative of real defects, for example testing for surface defects in rails. Several aluminium calibration samples containing closely spaced and angled slots have been measured, in addition to rail samples containing manufactured and real defects. The benefits of using the dual-probe are discussed.     

Feature extraction and selection for defect classification of pulsed eddy current NDT

Pulsed eddy current (PEC) is a new emerging nondestructive testing (NDT) technique using a broadband pulse excitation with rich frequency information and has wide application potentials. This technique mainly uses feature points and response signal shapes for defect detection and characterization, including peak point, frequency analysis, and statistical methods such as principal component analysis (PCA). This paper introduces the application of Hilbert transform to extract a new descending feature point and use the point as a cutoff point of sampling data for detection and feature estimation. The response signal is then divided by the conventional rising, peak, and the new descending points. Some shape features of the rising part and descending part are extracted. The characters of shape features are also discussed and compared. Various feature selection and integrations are proposed for defect classification. Experimental studies, including blind tests, show the validation of the new features and combination of selected features in defect classification. The robustness of the features and further work are also discussed.     

From objects to quantities: Developments in preschool children's judgments about aggregate amount.

The impact of object boundaries on children's developing quantitative reasoning was examined in a study of children's judgments about aggregate amount. Children at ages 3, 4. and 5 years were asked to help a Cookie Monster get as much to eat as possible by choosing between alternative collections that differed in the number and size of the cookies they contained and also in aggregate amount. Results indicated that children were heavily influenced by the size of individual cookies at 3 years of age but were generally unsuccessful in aggregating size information across multiple cookies until 5 years. The contrast between children's sensitivity to object sizes from an early age and the relatively late achievement of accurate judgments of aggregate amount underscores the significance for quantitative development of the distinction between discrete objects and mathematical quantities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)