Efficient Eddy Current Models for Evaluation of Thin Conductive Coatings on Ferromagnetic Substrates

Eddy current testing is widely used to determine physical characteristics of materials and to detect flaws by measurements of the electrical impedance of an eddy current probe. In this paper two analytical models allowing to determine properties of non-magnetic conductive coatings on ferromagnetic conductive substrates, are reported. Operating at a single frequency, two following quantities can be determined: permeability-to-conductivity ratio of the substrate and thickness-conductivity product of the coating [1, 2]. The method was validated using both long solenoids and air core surface coils, and was applied to the evaluation of zinc coatings on steel wires and sheets. The theoretical solutions given for high arguments are compact, and allow fast inversion, respectively around 400 and 10 ms for a pancake surface coil and for a long encircling solenoid. Two series of samples: Ø2.2 mm low carbon steel electro galvanized wires and 0.75–20 mm thick hot dip galvanized sheets, were inspected. Steel sheet samples with artificial coatings, as aluminum foils glued from both sides, were also examined. Experimental data of the coil electrical impedance were compared to those predicted. Agreement between theory and experiment is excellent. The technique developed has an extremely low sensitivity to the substrate conductivity and permeability variations [2]. A DC magnetic field, significantly diminishing the permeability of the substrate, almost does not influence results of the coating thickness determination. The agreement between measured thickness and that obtained by other methods is excellent. The accuracy of the thickness determination typically about 1 μ is obtained

Genetic architecture of the APM1 gene and its influence on adiponectin plasma levels and parameters of the metabolic syndrome in 1,727 healthy Caucasians

Copyright: Copyright 2008 Elsevier B.V., All rights reserved.The associations of the adiponectin (APM1) gene with parameters of the metabolic syndrome are inconsistent. We performed a systematic investigation based on fine-mapped single nucleotide polymorphisms (SNPs) highlighting the genetic architecture and their role in modulating adiponectin plasma concentrations in a particularly healthy population of 1,727 Caucasians avoiding secondary effects from disease processes. Genotyping 53 SNPs (average spacing of 0.7 kb) in the APM1 gene region in 81 Caucasians revealed a two-block linkage disequilibrium (LD) structure and enabled comprehensive tag SNP selection. We found particularly strong associations with adiponectin concentrations for 11 of the 15 tag SNPs in the 1,727 subjects (five P values <0.0001). Haplotype analysis provided a thorough differentiation of adiponectin concentrations with 9 of 17 haplotypes showing significant associations (three P values <0.0001). No significant association was found for any SNP with the parameters of the metabolic syndrome. We observed a two-block LD structure of APM1 pointing toward at least two independent association signals, one including the promoter SNPs and a second spanning the relevant exons. Our data on a large number of healthy subjects suggest a clear modulation of adiponectin concentrations by variants of APM1, which are not merely a concomitant effect in the course of type 2 diabetes or coronary artery disease.publishersversionPeer reviewe

Human Mesenchymal Stem Cells Self-Renew and Differentiate According to a Deterministic Hierarchy

BACKGROUND:Mesenchymal progenitor cells (MPCs) have been isolated from a variety of connective tissues, and are commonly called "mesenchymal stem cells" (MSCs). A stem cell is defined as having robust clonal self-renewal and multilineage differentiation potential. Accordingly, the term "MSC" has been criticised, as there is little data demonstrating self-renewal of definitive single-cell-derived (SCD) clonal populations from a mesenchymal cell source. METHODOLOGY/PRINCIPAL FINDINGS:Here we show that a tractable MPC population, human umbilical cord perivascular cells (HUCPVCs), was capable of multilineage differentiation in vitro and, more importantly, contributed to rapid connective tissue healing in vivo by producing bone, cartilage and fibrous stroma. Furthermore, HUCPVCs exhibit a high clonogenic frequency, allowing us to isolate definitive SCD parent and daughter clones from mixed gender suspensions as determined by Y-chromosome fluorescent in situ hybridization. CONCLUSIONS/SIGNIFICANCE:Analysis of the multilineage differentiation capacity of SCD parent clones and daughter clones enabled us to formulate a new hierarchical schema for MSC self-renewal and differentiation in which a self-renewing multipotent MSC gives rise to more restricted self-renewing progenitors that gradually lose differentiation potential until a state of complete restriction to the fibroblast is reached

Foetal haemoglobin, blood transfusion, and retinopathy of prematurity in very preterm infants:A pilot prospective cohort study

Purpose To identify if there is an association between foetal haemoglobin (HbF) concentration and retinopathy of prematurity (ROP) in very preterm infants. Patients and methods Prospective cohort study. Infants born <32 weeks’ gestational age or <1501 g in two tertiary neonatal units between January 2012 and May 2013 (n=42) were enrolled. HbF and adult haemoglobin (HbA) concentrations were measured using high-pressure liquid chromatography from blood samples sent as part of routine neonatal care once routinely requested laboratory tests had been performed. Clinical data were obtained from case notes. We calculated odds ratios (ORs) (95% confidence intervals (CIs)) to quantify the relationship between initial and mean %HbF with ROP severity (none, stages 1–3). Results A total of 42 infants were recruited: mean gestation 28.0 weeks (SD 1.91); mean birth weight 1042 g (SD 264). Six infants died before ROP screening; 14/36 developed ROP (39%); and 22/36 (61%) did not. Infants who developed ROP had similar initial %HbF (83.3 vs 92.3%, P=0.06), but significantly lower mean %HbF (61.75 vs 91.9%, P=0.0001) during their inpatient stay than those who did not develop ROP. In ordinal logistic regression models adjusted for birth weight, gestation and transfusion volume, mean post-natal %HbF was negatively associated with ROP severity: adjusted OR 0.94 (0.90–0.99), while initial %HbF at birth was not: adjusted OR 1.05 (0.97–1.16). Conclusion Replacing HbF by HbA during transfusion may promote ROP development by rapidly increasing oxygen availability to the retina. Conversely, maintaining a higher %HbF may be a protective factor against ROP

The Alpha Linolenic Acid Content of Flaxseed is Associated with an Induction of Adipose Leptin Expression

Dietary flaxseed has cardioprotective effects that may be achieved through its rich content of the omega-3 fatty acid, alpha linolenic acid (ALA). Because ALA can be stored in adipose tissue, it is possible that some of its beneficial actions may be due to effects it has on the adipose tissue. We investigated the effects of dietary flaxseed both with and without an atherogenic cholesterol-enriched diet to determine the effects of dietary flaxseed on the expression of the adipose cytokines leptin and adiponectin. Rabbits were fed one of four diets: a regular (RG) diet, or a regular diet with added 0.5% cholesterol (CH), or 10% ground flaxseed (FX), or both (CF) for 8 weeks. Levels of leptin and adiponectin expression were assessed by RT-PCR in visceral adipose tissue. Consumption of flaxseed significantly increased plasma and adipose levels of ALA. Leptin protein and mRNA expression were lower in CH animals and were elevated in CF animals. Changes in leptin expression were strongly and positively correlated with adipose ALA levels and inversely correlated with levels of en face atherosclerosis. Adiponectin expression was not significantly affected by any of the dietary interventions. Our data demonstrate that the type of fat in the diet as well as its caloric content can specifically influence leptin expression. The findings support the hypothesis that the beneficial cardiovascular effects associated with flaxseed consumption may be related to a change in leptin expression

Blue-Emitting Butterfly-Shaped 1,3,5,9-Tetraarylpyrenes: Synthesis, Crystal Structures, and Photophysical Properties

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Organic Letters (copyright © American Chemical Society) after peer review and technical editing by the publisher. To access the final edited and published work see: http://dx.doi.org/10.1021/ol400265

Two-dimensional finite element model for a long rectangular eddy current surface coil

An eddy current model for predicting the electrical impedance variation of a long rectangular surface coil due to a surface breaking defect in layered conductors is reported. The method is based on transforming a three-dimensional eddy current problem into the spatial frequency domain and solving the transformed diffusion problem for a limited number of the spatial spectrum components. The transformed problem has been assumed to be quasitwo dimensional (2D) for a long rectangular surface coil and formulated in terms of a two-component transformed vector magnetic potential A and scalar electric potential . The 2D problems have been solved with the finite element method using triangle elements. The system of algebraic equations was obtained using the Galerkin weak formulation and solved with the Gaussian elimination method. A high accuracy solution with ten spatial frequency components takes around 4 min on a Pentium 200 MHz PC. The accuracy of the solution has been tested experimentally at 200 kHz on coated stainless steel samples using a rectangular surface coil with the length-to-width ratio around 6. Agreement between theory and experiment is excellent. Discrepancies between the theory and experiment are within 15% and typically less. The method is useful for eddy current nondestructive evaluation and modeling, and can be also applied for the case of buried defects and for general multilayer coatings' problem. (C) 2000 American Institute of Physics. [S0034-6748(00)01002-9]

Inversion of Eddy Current Data for Conductive Films and Coatings Thickness and Conductivity Measurement

Eddy current testing is currently used to determine the physical characteristics of a conductive specimen and to detect defects by measurements of electrical impedance of an eddy current probe. In this study we developed two systems of coils allowing to determine properties of conductive coatings and foils. A probe contained two plane rectangular coils connected in series and separated by a fixed distance. A coated plate or a foil was placed between the coils and the coil impedance was measured using a digital impedancemeter. The discussed probe had a large length-to-width ratio and was modeled using the simple two-conductor line model, which express solutions in terms of the integrals containing no Bessel but, only common trigonometric functions, which considerably reduces the inversion time. The method allows reproducible measurements on coated conductive sheets. Aluminum 15–45 μm layers have been measured on steel and stainless steel substrates.</p

Thickness and conductivity determination of thin nonmagnetic coatings on ferromagnetic conductive substrates using surface coils

An eddy current technique for determining parameters of a thin nonmagnetic conductive coating on a ferromagnetic conductive sheet metal is reported. Under several conditions the electrical impedance of a coil is shown to be a function of two independent quantities: the substrate permeability-to-conductivity ratio and the coating thickness-conductivity product. Thus, thickness or conductivity of the coating can be determined independently of the variations of magnetic and electrical properties of the substrate. Simple analytic formulae for the electrical impedance of circular and rectangular surface coils are obtained and applied to predict the behavior of split wound surface coils. The performance of the method was tested in the frequency range 20-100 kHz on 1.5 mm thick low carbon steel sheers coated with 15-45 mu m thick aluminum layers and on two series of 0.75-2.0 mm thick hot dip galvanized low carbon steel sheets of 9-20 mu m coating thickness. The experiment was carried out using printed surface coils of rectangular and circular shape. Agreement between theory and experiment is excellent. The mathematical inversion carried out using the obtained formulae and the Newton-Raphson method takes about 450 ms on a Pentium 133 MHz PC. Discrepancies between the eddy current thicknesses and those obtained by other techniques were typically below 1 mu m. An uncertainty in the thickness or conductivity determination better than 2% is obtained. The method has an extremely low sensitivity to variations in the substrate permeability. A large change in the substrate permeability, implying large changes in the coil electrical impedance, does not significantly influence the determined coating thickness. When the permeability change is about a factor of 10, additional errors in the thickness determination typically do not exceed 0.5 mu m. (C) 1998 American Institute of Physics