Advanced eddy-current methods for quantitative NDE

The objectives of this dissertation were to devise and develop advanced eddy-current methods for quantitative NDE. The techniques used include time-domain methods (pulsed eddy current), frequency-domain methods (swept-frequency eddy current), and the photoinductive imaging method that combines eddy-current and laser-based thermal-wave techniques. We first developed theoretical models to predict the pulsed eddy current signal and showed this technique can be used to characterize metallic coatings on metal substrates. A feature-based rapid inversion method was developed to determine the conductivity and thickness of the coating simultaneously. In the second work, we studied the fundamentals of eddy current interactions with magnetic metals using swept-frequency eddy current method. We have found that the eddy current response of well-annealed, demagnetized commercially-pure nickel is dominated by a thin region at the sample\u27s surface that has a very significantly reduced permeability--i.e., a surface dead-layer. This dead layer may be due to the presence of surface damage. We calculated the impedance of the coil based on the hypothesized single layer structure and found excellent quantitative agreement between the model and experiment. These results may have important consequences for many aspects of the interaction of low frequency electromagnetic fields with magnetically soft metals. In the third work, we developed theoretical calculations and practical measurement methods using both swept-frequency eddy current and pulsed eddy current methods for determining the thickness, conductivity, and permeability of metallic coatings on metal substrates for the case when either coating, metal, or both are ferromagnetic. This work paves the way for development of new, quantitative methods to characterize surface layers on ferrous materials, such as depth of case hardening. In the fourth work, we applied the photoinductive imaging technique to characterize corner cracks on the surface around a bolt hole. The photoinductive signals reflect the geometrical shape of the triangular and rectangular electrical-discharge-machined (EDM) notches as well as real fatigue cracks. The results show promise for using this technique to characterize the shape, depth, and length of corner cracks. The capability of the photoinductive imaging technique is demonstrated in this work

Supersymmetric Mean-Field Theory of t-J Model

The supersymmetric formulation of t-J model is studied in this paper at the mean-field level where $\delta$-T phase diagram is computed. We find that slave-fermion-like spiral phase is stable at low doping concentration, and the slave-boson-like d-wave fermionic spin pairing state becomes energetically favourable when $\delta\geq$ 0.23. An improvement in free energy using Gutzwiller's method lowers the transition doping concentration to 0.06. We also point out the existence of new branches of excitations in the supersymmetric theory.Comment: 11 pages and 2 figure

Selection responses for the number of fertile eggs of the Brown Tsaiya duck (Anas platyrhynchos) after a single artificial insemination with pooled Muscovy (Cairina moschata) semen

A seven-generation selection experiment comprising a selected (S) and a control (C) line was conducted with the objective of increasing the number of fertile eggs (F) of the Brown Tsaiya duck after a single artificial insemination (AI) with pooled Muscovy semen. Both lines consisted of about 20 males and 60 females since parents in each generation and each female duck was tested 3 times, at 26, 29 and 32 weeks of age. The fertile eggs were measured by candling at day 7 of incubation. The selection criterion in the S line was the BLUP animal model value for F. On average, 24.7% of the females and 15% of the males were selected. The direct responses to the selection for F, and correlated responses for the number of eggs set (Ie), the number of total dead embryos (M), the maximum duration of fertility (Dm) and the number of hatched mule ducklings (H) were measured by studying the differences across the generations of selection between the phenotypic value averages in the S and C lines. The predicted genetic responses were calculated by studying the differences between the S and C lines in averaged values of five traits of the BLUP animal model. The selection responses and the predicted responses showed similar trends. There was no genetic change for Ie. After seven generations of selection, the average selection responses per generation were 0.40, 0.33, 0.42, 0.41 genetic standard deviation units for F, M, Dm, and H respectively. Embryo viability was not impaired by this selection. For days 2–8 after AI, the fertility rates (F/Ie) were 89.2% and 63.8%, the hatchability rates (H/F) were 72.5% and 70.6%, and (H/Ie) were 64.7% and 45.1% in the S and C lines respectively. It was concluded that upward selection on the number of fertile eggs after a single AI with pooled Muscovy semen may be effective in ducks to increase the duration of the fertile period and the fertility and hatchability rates with AI once a week instead of twice a week

Cascaded deep monocular 3D human pose estimation with evolutionary training data

End-to-end deep representation learning has achieved remarkable accuracy for monocular 3D human pose estimation, yet these models may fail for unseen poses with limited and fixed training data. This paper proposes a novel data augmentation method that: (1) is scalable for synthesizing massive amount of training data (over 8 million valid 3D human poses with corresponding 2D projections) for training 2D-to-3D networks, (2) can effectively reduce dataset bias. Our method evolves a limited dataset to synthesize unseen 3D human skeletons based on a hierarchical human representation and heuristics inspired by prior knowledge. Extensive experiments show that our approach not only achieves state-of-the-art accuracy on the largest public benchmark, but also generalizes significantly better to unseen and rare poses. Code, pre-trained models and tools are available at this HTTPS URL.Comment: Accepted to CVPR 2020 as Oral Presentatio

Quantitative Assessment of Corrosion in Aircraft Structures Using Scanning Pulsed Eddy Current

Eddy current nondestructive testing techniques are used extensively in industry for detection of hidden cracks and corrosion in multi-layer conductive structures such as those found in aircraft. Most conventional eddy current techniques employ a probe coil excited with a continuous sine wave. The changes in the probe’s impedance are detected (usually with an electronic bridge circuit) and displayed in real time on an impedance plane CRT display. Interpretation of the impedance-plane trajectories that result from scanning the probe over a defect is difficult; it involves a considerable amount of operator skill and knowledge and the equipment is sometimes difficult to set up and operate. We have developed an eddy current inspection system using the pulsed eddy current technique, which greatly reduces the possibility of operator errors and subjectivity in the quantitative interpretation of test results