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The application of temperature compensation strategies is important when using a guided wave structural health monitoring system. It has been shown by different authors that the influence of changing environmental and operational conditions, especially temperature, limits performance. This paper quantitatively describes two different methods to compensate(More)
A spatially sparse array of conventional piezoelectric transducers is attached to a part surface to monitor its structural health. Artificial flaws are incrementally added to simulate damage progression. The structure is flooded with ultrasonic energy by transmitting on a single transducer, and waveforms are recorded from other transducers in the array.(More)
A number of tomographic and phased-array methods have been proposed for generating two dimensional images of plate-like structures using sparse arrays of spatially distributed ultrasonic transducers. The phased array differential approach is considered here whereby pulse echo and through transmission signals are recorded before and after localized damaged(More)
Guided wave structural health monitoring is a challenging problem, in part because of the complexity of signals received in a real structure containing geometrical features and boundaries. Signals scattered from damage can be one or two orders of magnitude smaller in amplitude than the direct arrival. Detection of these small, scattered signals is often(More)
Permanently attached piezoelectric sensors arranged in a spatially distributed array are under consideration for structural health monitoring systems incorporating active ultrasonic methods. Most damage detection and localization methods that have been proposed are based upon comparing monitored signals to baselines recorded from the structure prior to(More)
Studies were initiated to identify nicotinic acetylcholine receptor (nAChR) subunits and subtypes expressed in the developing immune system and cell types on which nAChR are expressed. Reported here are reverse transcription-polymerase chain reactions (RT-PCR) studies of nAChR alpha2-alpha7 and beta2-beta4 subunit gene expression using fetal or neonatal(More)
This study examined predictors of posttraumatic stress disorder (PTSD) symptoms in adults who, as children, had a parent diagnosed with cancer. Possible predictors of adulthood PTSD examined were peritraumatic dissociation, satisfaction with social support, coping through denial, behavioral disengagement and self-distraction, and whether or not the parent(More)
Permanently mounted ultrasonic transducers have the potential to interrogate large areas of a structure, and thus be effective global sensors for structural health monitoring. Recorded signals, although very sensitive to damage, are long, complex, and difficult to interpret compared to pulse echo and through transmission signals customary for nondestructive(More)
Attached ultrasonic sensors can detect changes caused by crack initiation and growth if the wave path is directed through the area of critical crack formation. Dynamics of cracks opening and closing under load cause nonlinear modulation of received ultrasonic signals, enabling small cracks to be detected by stationary sensors. A methodology is presented(More)