A comparison of SQUID imaging techniques for small defects in nonmagnetic tubes

Although superconducting quantum interference devices (SQUIDs) provide an exquisitively sensitive means for measuring magnetic fields, their usage in the past has been limited chiefly to biomagnetic research. However, over the past few years interest in applying SQUID techniques to the field of nondestructive evaluation (NDE) has blossomed [1]. Many experiments have exploited the sensitivity of SQUIDs for diverse NDE applications, especially those requiring large separation distances between the sensor and the item to be inspected. Our work instead has focused on the potential to detect very small defects with SQUIDs, specifically in thin-walled tubes. In this paper, we discuss three different methods for creating magnetic fields in tubes. The methods comprise (a) directly injecting a current through the tube, (b) using a separate induction coil to create induced currents in the tube, and (c) utilizing a ferromagnetic tracer technique. To illustrate the capabilities of each method, we present two-dimensional maps of the spatial distribution of the magnetic field as measured by a SQUID magnetometer — that is, SQUID images. The images will also be used to compare the sensing methods with respect to such practical considerations as relative sensitivity and signal-to-noise ratio

Boundary Integral Equations for Modeling Arbitrary Flaw Geometries in Electric Current Injection NDE

The Electric Current Injection (ECI) method of nondestructive evaluation is applied to materials that are electrically conductive but not magnetically permeable, such as aluminum, magnesium, and titanium. It consists of detecting current-flow anomalies due to voids, nonmetallic inclusions and open cracks in the conducting material, through distortions introduced in the magnetic field generated by the sample [1]

A SQUID NDE Measurement Model Using BEM

As the commercial and military aircraft fleets age, additional resources are required to ensure their airworthiness. As the aircraft become older, the more likely they are to develop structural damage that may lead to unscheduled repairs or, in the worst case, accidents. Fatigue and corrosion are the two main causes of structural damage in aging aircraft and this research examines the use of a Superconducting QUantum Interference Device (SQUID) as a tool for Nondestructive Evaluation (NDE) to detect and characterize these aging aircraft problems. The primary advantage of using SQUIDs in NDE over other techniques is the ability to detect second layer cracks and corrosion commonly found in aircraft structures

A mathematical model for electrical stimulation of a monolayer of cardiac cells

BACKGROUND: The goal of our study is to examine the effect of stimulating a two-dimensional sheet of myocardial cells. We assume that the stimulating electrode is located in a bath perfusing the tissue. METHODS: An equation governing the transmembrane potential, based on the continuity equation and Ohm's law, is solved numerically using a finite difference technique. RESULTS: The sheet is depolarized under the stimulating electrode and is hyperpolarized on each side of the electrode along the fiber axis. CONCLUSIONS: The results are similar to those obtained previously by Sepulveda et al. (Biophys J, 55: 987–999, 1989) for stimulation of a two-dimensional sheet of tissue with no perfusing bath present

Electrotonic Signals along Intracellular Membranes May Interconnect Dendritic Spines and Nucleus

Synapses on dendritic spines of pyramidal neurons show a remarkable ability to induce phosphorylation of transcription factors at the nuclear level with a short latency, incompatible with a diffusion process from the dendritic spines to the nucleus. To account for these findings, we formulated a novel extension of the classical cable theory by considering the fact that the endoplasmic reticulum (ER) is an effective charge separator, forming an intrinsic compartment that extends from the spine to the nuclear membrane. We use realistic parameters to show that an electrotonic signal may be transmitted along the ER from the dendritic spines to the nucleus. We found that this type of signal transduction can additionally account for the remarkable ability of the cell nucleus to differentiate between depolarizing synaptic signals that originate from the dendritic spines and back-propagating action potentials. This study considers a novel computational role for dendritic spines, and sheds new light on how spines and ER may jointly create an additional level of processing within the single neuron

Genetic Basis of Myocarditis: Myth or Reality?

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Prostate carcinogenesis and Id-1 gene

Nondestructive evaluation methods are largely used for inspection of storage tanks and pipelines in the oil industry. The main goal is to detect and locate points of corrosion which can endanger the structural integrity or the watertightness, possibly causing leakage of oil to the environment, of catastrophic consequences. The occurrence of localized corrosion pits is of special concern, as they weaken the material strength and can initiate cracks at the pit cavity. In low-carbon steel samples, corrosion pits are typically shallow, roughly with the shape of a half-sphere [1]