105 research outputs found
Age-related shifts in hemispheric dominance for syntactic processing
No full textGenetic factors related to handedness, such as history of familial sinistrality, have been linked to neuroanatomical and neurophysiological differences in a variety of brain areas, including those associated with language. However, the functional implications of these differences remain unclear. Recent event-related potential (ERP) data from young adults have revealed that simple syntactic anomalies elicit a different pattern of lateralization depending upon the familial sinistrality of the participant. Whereas participants with left handed family members elicited a bilateral P600, a component that is typically seen in adult native speakers to syntactic processing difficulties, participants with no history of familial sinistrality showed a strongly lateralized response pattern, with P600 responses only following left hemisphere-biased presentations. Given that the aging literature has documented a tendency to change from asymmetry of function to a more bilateral pattern with advancing age, we tested the stability of this asymmetric response to syntactic violations by recording ERPs as 24 older adults (age 60+) with no history of familial sinistrality made grammaticality judgments on simple two-word phrases. Results showed that the asymmetric pattern observed in young adults indeed changes with age, such that P600 responses come to be elicited bilaterally even in individuals without familial sinistrality. These findings suggest that, as with many other cognitive functions, syntactic processing becomes more bilateral with age, possibly because of reduced interhemispheric inhibition.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2017-12-01The student, Michelle Leckey, accepted the attached license on 2015-11-09 at 11:38.The student, Michelle Leckey, submitted this Thesis for approval on 2015-11-09 at 11:46.This Thesis was approved for publication on 2015-11-11 at 09:30.DSpace SAF Submission Ingestion Package generated from Vireo submission #8770 on 2016-03-08 at 11:05:14Made available in DSpace on 2016-03-08T17:21:55Z (GMT). No. of bitstreams: 2
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Previous issue date: 2015-11-11Embargo set by: Seth Robbins for item 91495
Lift date: 2018-03-08T17:22:13Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 91495 on 2018-03-09T10:15:22Z
Multi-site delamination detection and quantification in composites through guided wave based global-local sensing
No full textAdvanced composite materials are contributing to a revolution in aerospace applications. Rapid inspection techniques for detecting and quantifying damage in large composites are critical for ensuring operability and safety of composite structures. Moreover, in the development and manufacturing of next-generation composite materials, rapid inspection techniques are imperative for evaluating and certifying the materials.
This paper presents a guided wave based global-local sensing method for rapid detection and quantification of delamination damage in large composite panels. The global-local approach uses a hybrid system consisting of a piezoelectric transducer (PZT) for generating guided waves and a non-contact scanning laser Doppler vibrometer (SLDV) for acquiring guided wave data. The global-local inspection is performed in two steps. First, a phased array configured of a small number of SLDV scan points (for example 10×10 points in a rectangular grid array) performs inspection over the entire plate to detect and locate damage (Figure 1a). Local areas are identified as potential damage regions for the second step. Then high density wavefield measurements are taken over the target damage areas and wavefield analysis is performed to quantitatively evaluate the damage (Figure 1b). For the proof of concept, the global-local approach is demonstrated on a carbon fiber reinforced polymer (CFRP) composite plate with two sites of impact-induced delamination damage. In the first step, the locations of two delamination sites are detected by the phased array method. In the second step, the delamination size and shape are evaluated through the wavefield analysis. The detected delamination location, size and shape agree well with those of ultrasonic C-scan.</p
Simulation of Guided Wave Interaction with In-Plane Fiber Waviness
No full textReducing the timeline for certification of composite materials and enabling the expanded use of advanced composite materials for aerospace applications are two primary goals of NASA's Advanced Composites Project (ACP). A key a technical challenge area for accomplishing these goals is the development of rapid composite inspection methods with improved defect characterization capabilities. Ongoing work at NASA Langley is focused on expanding ultrasonic simulation capabilities for composite materials. Simulation tools can be used to guide the development of optimal inspection methods. Custom code based on elastodynamic finite integration technique is currently being developed and implemented to study ultrasonic wave interaction with manufacturing defects, such as in-plane fiber waviness (marcelling). This paper describes details of validation comparisons performed to enable simulation of guided wave propagation in composites containing fiber waviness. Simulation results for guided wave interaction with in-plane fiber waviness are also discussed. The results show that the wavefield is affected by the presence of waviness on both the surface containing fiber waviness, as well as the opposite surface to the location of waviness
Syntax and semantics: Similarities in late positive components
No full textThe ERP component known as the (syntactic) P600 has long been associated with syntactic processing as it has consistently been seen to have a larger amplitude to critical words in sentences that contain syntactic violations or complex structure. With the later discovery of a morphologically similar component that was sensitive to violations that were more semantic in nature (semantic P600), P600 theories moved to encompass these findings into theoretical frameworks that explained how the same component could be seen in these two different instances. This is despite the fact that there has been no empirical investigation into whether or not these two positivities are in fact reflecting the same kind of underlying processing. This thesis aims to do this investigative work, using central and lateralised ERP paradigms and investigating individual differences such as familial sinistrality and aging to assess whether or not these two components are consistently elicited under the same conditions.
Experiment 1 looked at sentences containing violations known to elicit the syntactic P600 or the semantic P600. The results showed that participants differed in their responses to the syntactic P600 sentences dependent on familial sinistrality profile (whether or not the individual had left handed relatives) but did not differ in response to the semantic P600 sentences. Experiment 2 followed up on these initial differences using a lateralised version of Experiment 1, biasing processing to each hemisphere individually in order to assess lateralisation patterns. The results showed that participants of differing familial sinistrality profiles differed in terms of their hemispheric contributions to processing these sentences. While those with no history of familial sinistrality had a lateralised response to the syntactic P600 sentences, the group which did have a history of familial sinistrality showed a bilateral pattern, as did both groups in response to the semantic P600 sentences. This difference in eliciting conditions again indicates that the two types of P600 responses may not be the same. Experiment 3 examined the processing of the sentences in an older adult sample. Distributional changes in the form of a frontal shift have previously been seen for the syntactic P600 in older adults, and this same pattern was found again here. However, the same shift was not seen for the semantic P600 sentences, adding further evidence to the proposal that the semantic and syntactic variants of the P600 are not reflecting the same type of processing.
Taken together, the experiments in the thesis cast doubt on the multitude of theories that assume both syntactic and semantic variants of the P600 to be the same and argue that domain is an imperfect basis on which to categorise morphologically similar components.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-08-01The student, Michelle Leckey, accepted the attached license on 2019-06-12 at 07:05.The student, Michelle Leckey, submitted this Dissertation for approval on 2019-06-12 at 07:10.This Dissertation was approved for publication on 2019-06-12 at 13:40.DSpace SAF Submission Ingestion Package generated from Vireo submission #14030 on 2019-11-26 at 13:03:25Made available in DSpace on 2019-11-26T20:49:10Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-06-12Embargo set by: Seth Robbins for item 112899
Lift date: 2021-11-26T20:49:41Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 112899 on 2021-11-27T10:15:30Z
Aerogel to simulate delamination and porosity defects in carbon-fiber reinforced polymer composites
No full textNumerically stable finite difference simulation for ultrasonic NDE in anisotropic composites
No full textInvestigation of Ultrasonic Wave Scattering Effects using Computational Methods
No full textAdvances in computational power and expanded access to computing clusters has made mathematical modeling of complex wave effects possible. We have used multi-core and cluster computing to implement analytical and numerical models of ultrasonic wave scattering in fluid and solid media (acoustic and elastic waves). We begin by implementing complicated analytical equations that describe the force upon spheres immersed in inviscid and viscous fluids due to an incident plane wave. Two real-world applications of acoustic force upon spheres are investigated using the mathematical formulations: emboli removal from cardiopulmonary bypass circuits using traveling waves and the micromanipulation of algal cells with standing waves to aid in biomass processing for algae biofuels. We then move on to consider wave scattering situations where analytical models do not exist: scattering of acoustic waves from multiple scatterers in fluids and Lamb wave scattering in solids. We use a numerical method called finite integration technique (FIT) to simulate wave behavior in three dimensions. The 3D simulations provide insight into experimental results for situations where 2D simulations would not be sufficient. The diverse set of scattering situations explored in this work show the broad applicability of the underlying principles and the computational tools that we have developed. Overall, our work shows that the movement towards better availability of large computational resources is opening up new ways to investigate complicated physics phenomena.Applied ScienceDoctor of Philosophy (Ph.D.
Energy Analysis Method for Hidden Damage Detection
No full textA method of detecting internal defects in composites or other multilayer materials includes generating a wavefield on a surface of the material. Wavefield data is collected from the wavefield on the surface, and the measured wavefield data is processed to provide measured energy data. The method may include generating simulated or predicted energy data for the multilayer material that is compared to the simulated energy data to determine if the multilayer material has internal defects or damage below the surface. The method can be utilized to detect and/or quantify damage or other defects that are "hidden" by damage that is closer to the surface of the material
Notice of Removal: The effect of in-plane and out-of-plane fiber waviness on guided waves
No full textDetection of Manufacturing Defects via Wavefield Image Processing Techniques: An Experimental Study
No full textDefects that occur during the manufacturing of a composite can have drastic effects on the intended strength or durability of composite structures. These defects include gaps and overlaps in the prepreg tow-tape that can occur during Automated Fiber Placement (AFP) system operations, as well as unintended fiber waviness caused by differential thermal loading during curing cycles. Wavefield imaging offers a non-contact method of detecting various anomalies in composites, and emerging technologies can enable rapid wavefield acquisition. In this work, composite samples were created with intentional and analogous manufacturing defects such as the ones mentioned, and full guided wavefield data was captured using a Laser Doppler Vibrometer (LDV) while guided waves were excited in the sample. Studies of the data were performed using wavenumber analysis methods, such as Multi-Frequency Local Wavenumber Technique which has been used to detect delamination in composites. Other wavenumber analysis methodologies were developed guided by finite-difference simulation results. The results of these wavenumber analysis methods will be presented, as well as a brief discussion of the defect simulations.</p
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