Core-level photoemission spectroscopy of nitrogen bonding in GaNxAs1–x alloys

The nitrogen bonding configurations in GaNxAs1–x alloys grown by molecular beam epitaxy with 0.07=0.03, the nitrogen is found to exist in a single bonding configuration – the Ga–N bond; no interstitial nitrogen complexes are present. The amount of nitrogen in the alloys is estimated from the XPS using the N 1s photoelectron and Ga LMM Auger lines and is found to be in agreement with the composition determined by x-ray diffraction

Standard Flaws for Eddy Current Probe Characterization

Calibration procedures for eddy current inspections often involve the use of artifact standards containing manufactured flaws. The manufactured flaw is assumed to be a good approximation of the type of flaw being sought during the inspection. These manufactured flaws are most often produced by electrical discharge machining (EDM), milling, or the controlled growth of fatigue cracks. With simple amplitude display inspection equipment this type of artifact is usually sufficient, but as more sophisticated inspection equipment is developed some drawbacks to the commonly accepted practice are becoming evident. Instruments that are sensitive to eddy current signal phase as well as amplitude can show considerable differences in phase between a relatively wide EDM notch or milled slot and a real fatigue crack [1]. The use of controlled growth fatigue cracks can also cause problems when forces at the crack’s tip drive the crack faces together, making electrical contact [2], In addition, estimates of crack depth will always be estimates until the crack is broken apart. We describe here a technique for consistently producing well characterized discontinuities in aluminum which are not subject to these problems

Modeling Inspectability for an Automated Eddy Current Measurement System

We have developed an automated eddy current measurement system in our laboratory for quantitative nondestructive evaluation applications. The heart of the measurement system is a precision impedance analyzer capable of measuring impedance or any impedance related quantity over a wide range in frequency (102–108 Hz). Data acquisition, processing, analysis, and display is accomplished with a personal computer. Computer-controlled x-y positioning stages permit measurements to be obtained for either one- or two-dimensional scans of the specimen. In this article we describe the measurement system and give examples of its use to measure flaw signals with a uniform-field eddy current probe [1]

Eddy-Current and Magnetic Measurements on Case-Hardened Steel

The problem of inspecting case-hardened steel has been of interest to industry for some time. A reliable nondestructive method is sought that will not only enable the depth-of-treatment to be established but will also provide some measure of a component’s bulk material properties and surface condition. While some methods can provide an adequate solution to the problem of measuring case depth, we will show the limitations and pitfalls awaiting the unwary. For example, small variations in heat-treatment conditions can lead to large differences in microstructure, and hence magnetic properties, of a steel. This can be especially true for the near surface layers of a component being treated. These variations in magnetic properties have a strong effect on eddy current and magnetic measurements and can lead to inaccurate results when measuring case depth. In addition, batch variations in material properties can also affect the measurements

Excitation spectrum of a two-component Bose-Einstein condensate in a ring potential

A mixture of two distinguishable Bose-Einstein condensates confined in a ring potential has numerous interesting properties under rotational and solitary-wave excitation. The lowest-energy states for a fixed angular momentum coincide with a family of solitary-wave solutions. In the limit of weak interactions, exact diagonalization of the many-body Hamiltonian is possible and permits evaluation of the complete excitation spectrum of the system.Comment: 4 pages, 1 figur

A Self-Calibrating Eddy-Current Instrument

The calibration of eddy-current measurement systems is a long-standing problem in nondestructive evaluation. Calibration serves a number of purposes: for equipment setup and validation, for equalizing responses from different probes and instruments, for setting detection thresholds, and for quantitative flaw sizing. The most commonly used calibration method is to scan the probe to be calibrated over simulated defects such as electrical-discharge machined (EDM) slots, saw cuts, or laboratory-produced fatigue cracks. This method has the virtue of calibrating probe and instrument at the same time on the same material as that to be inspected. But it has a number of disadvantages as well. First, a large number of artifact standards must be generated, certified, and maintained in the typical inspection organization; this can result in considerable expense. Second, the signals from EDM slots and saw cuts are not equivalent to the signals from actual defects, as discussed in another paper in these proceedings [1]. Third, quantitative flaw sizing can only be accomplished over a limited range with such calibration methodology, and the accuracy of sizing flaws with this method is brought into question by the aforementioned inequality of slots and cracks. Even if laboratory-produced cracks were to be used routinely for calibration (a prohibitively expensive option), quantitative sizing could be compromised by the occurrence of crack closure effects [2]

Calibration and Characterization of Eddy Current Probes by Photoinductive Field Mapping

The calibration of eddy-current measurement systems is a long-standing problem in nondestructive evaluation. Eddy-current probe calibration is needed for several reasons: to compensate for different probe sensitivities, to set detection thresholds, to validate instrument setup and operation, and to perform quantitative flaw sizing.1,2 The most frequently used calibration method is to scan the probe being calibrated over simulated defects such as electrical-discharge-machined (EDM) slots, saw cuts, or laboratory-produced fatigue cracks. This method has the virtue of calibrating probe and instrument at the same time and it can be performed on the same material as that to be inspected. But it has a number of disadvantages as well. First, a large number of artifact standards must be generated, certified, and maintained, resulting in considerable expense. Second, the signals from EDM slots and saw cuts are not equivalent to the signals from actual defects.3 Third, it is questionable whether quantitative flaw sizing can be performed using such a calibration method. Even if laboratory-produced cracks were to be used for routine calibration (a prohibitively expensive option), the accuracy of calibration or quantitative sizing could be compromised by the occurrence of crack closure effects.

Eddy-Current Measurements of Corrosion-Related Thinning in Aluminuium Lap Splices

The aging commercial aviation fleet requires new methods for detecting and characterizing corrosion. In particular, the need exists for a rapid and reliable method of nondestructively detecting and characterizing corrosion in layered aircraft skins. Aircraft skin consists of thin aluminum sheet. There are many joints at which these sheets are overlapped and attached to the airframe by fasteners that extend through the sheets and into the substructure. The overlapping aluminum sheets are generally separated by a thin gap, which may be filled with a sealant. Because of the overlapping nature of such joints, the second sheet and the substructure are not directly accessible from the surface

Edge Crack Detection: A Theoretical and Experimental Study

Detection of cracks close to an edge by conventional eddy current techniques is difficult, owing to the significant background signal from the edge. It is necessary to develop methods for minimizing the effect of the background signal, thereby increasing the probability of detection. The edge signal is known to be influenced by a number of factors and it is essential to characterize these in order to minimize its influence. This study aims at developing a good understanding of these factors so as to facilitate the development of such techniques. A boundary element method (BEM) approach was used to model the signal due to the edge and to compare with experimental measurements. Experiments were conducted on electro-discharge machined (EDM) slots in the vicinity of an edge using both absolute and differential probes. The influence of orientation of a differential probe on the signal from the crack and the edge was also studied. We report on the development of improved methods to reduce the influence of signal due to the edge by appropriate use of differential probes and with the aid of signal processing. An inexpensive physical technique which results in a improved detectability was also developed

Salen Mn Complexes Mitigate Radiation Injury in Normal Tissues

Salen Mn complexes, including EUK-134, EUK-189 and a newer cyclized analog EUK-207, are synthetic SOD/catalase mimetics that have beneficial effects in many models of oxidative stress. As oxidative stress is implicated in some forms of delayed radiation injury, we are investigating whether these compounds can mitigate injury to normal tissues caused by ionizing radiation. This review describes some of this research, focusing on several tissues of therapeutic interest, namely kidney, lung, skin, and oral mucosa. These studies have demonstrated suppression of delayed radiation injury in animals treated with EUK-189 and/or EUK-207. While an antioxidant mechanism of action is postulated, it is likely that the mechanisms of radiation mitigation by these compounds in vivo are complex and may differ in the various target tissues. Indicators of oxidative stress are increased in lung and skin radiation injury models, and suppressed by salen Mn complexes. The role of oxidative stress in the renal injury model is unclear, though EUK-207 does mitigate. In certain experimental models, salen Mn complexes have shown “mito-protective” properties, that is, attenuating mitochondrial injury. Consistent with this, EUK-134 suppresses effects of ionizing radiation on mitochondrial function in rat astrocyte cultures. In summary, salen Mn complexes could be useful to mitigate delayed radiation injury to normal tissues following radiation therapy, accidental exposure, or radiological terrorism. Optimization of their mode of delivery and other key pharmaceutical properties, and increasing understanding of their mechanism(s) of action as radiation mitigators, are key issues for future study