Ultrahigh Resolution Pulsed Laser-Induced Photoacoustic Detection of Multi-Scale Damage in CFRP Composites

This paper presents a photoacoustic non-destructive evaluation (pNDE) system with an ultrahigh resolution for the detection of multi-scale damage in carbon fiber-reinforced plastic (CFRP) composites. The pNDE system consists of three main components: a picosecond pulsed laser-based ultrasonic actuator, an ultrasound receiver, and a data acquisition/computing subsystem. During the operation, high-frequency ultrasound is generated by pulsed laser and recorded by an ultrasound receiver. By implementing a two-dimensional back projection algorithm, pNDE images can be reconstructed from the recorded ultrasound signals to represent the embedded damage. Both potential macroscopic and microscopic damages, such as surface notches and delamination in CFRP, can be identified by examining the reconstructed pNDE images. Three ultrasonic presentation modes including A-scan, B-scan, and C-scan are employed to analyze the recorded signals for the representation of the detected micro-scale damage in two-dimensional and three-dimensional images with a high spatial resolution of up to 60 µm. Macro-scale delamination and transverse ply cracks are clearly visualized, identifying the edges of the damaged area. The results of the study demonstrate that the developed pNDE system provides a non-destructive and robust approach for multi-scale damage detection in composite materials.Open Access fees paid for in whole or in part by the University of Oklahoma Libraries.Ye

Isolated DC/DC Converters for DC Distribution Grids in Rural Electrification

Roughly 840 million people, predominately from rural communities in sub-Sahara Africa, still lack access to electricity. The direct current (DC) microgrid is an emerging grid infrastructure that meshes efficiently with DC based technology such as photovoltaics, batteries, consumer electronics, and electric vehicles. This characteristic of DC microgrids designates them as a preferred solution for new grid infrastructures in rural electrification applications. In order to establish a DC microgrid, power electronic interfaces (PEI) are required for regulating power flow and interconnecting different grid components of the microgrid. In this thesis, the PEI (operating at 200-900 W) connecting a 350 V DC-microgrid to a solar home system (compatible with USB-C) is investigated. A unidirectional half-bridge LLC converter and a bidirectional dual active half-bridge (DAHB) converter (both utilizing gallium-nitride (GaN) transistors and planar transformers (PT)) are designed and tested. A working prototype of the half-bridge LLC converter with a center-tapped secondary is presented and the waveforms at maximum load and no-load conditions are analyzed. A complete design and efficiency approximation for a DAHB converter with a center-tapped secondary and active snubber circuits is included. In addition, simulations (in PLECS) of the designed DAHB converter provide waveform results for both the forward and reverse power flow direction. The results of the work discuss how high frequency operated, half-bridge isolated DC/DC topologies with GaN transistors and planar transformers are an excellent composition of technology for these rural electrification applications. The GaN transistor is most effective in a low voltage (up to 650 V), high performance scheme, and offers inherent benefits which allow for high frequency operation and thus, smaller passive components. Moreover, the effect of current collapse (an adverse effect in GaN transistors) is discussed and analyzed from a design standpoint. The benefits of planar transformers in low-medium power (up to 900 W) rural electrification applications and an in-depth PT design process are presented. Additionally, rural electrification safe extra-low voltage (SELV) standards require that PT designs must have reinforced (or double) isolation between primary and secondary windings. Taking this into consideration, two proposed PT configurations using a U-core and planar E-core, respectively, are compared. The main conclusions of this work aim to bridge the gap for the design and implementation of efficient DC microgrid variable power output converters for use in rural electrification applications.Electrical Engineering | Electrical Power Engineerin

Cytokine biomarkers and chronic pain: Association of genes, transcription, and circulating proteins with temporomandibular disorders and widespread palpation tenderness

For reasons unknown, temporomandibular disorder (TMD) can manifest as localized pain or in conjunction with widespread pain. We evaluated relationships between cytokines and TMD without or with widespread palpation tenderness (TMD−WPT or TMD+WPT, respectively), at protein, transcription factory activity, and gene levels. Additionally, we evaluated the relationship between cytokines and intermediate phenotypes characteristic of TMD and WPT. In a case-control study of 344 females, blood samples were analyzed for levels of 22 cytokines and activity of 48 transcription factors. Intermediate phenotypes were measured by quantitative sensory testing and questionnaires asking about pain, health, and psychological status. Single nucleotide polymorphisms (SNPs) coding cytokines and transcription factors were genotyped. TMD−WPT cases had elevated protein levels of pro-inflammatory cytokine MCP-1 and anti-inflammatory cytokine IL-1ra, whereas TMD+WPT cases had elevated levels of pro-inflammatory cytokine IL-8. MCP-1, IL-1ra, and IL-8 were differentially associated with experimental pain, self-rated pain, self-rated health, and psychological phenotypes. TMD−WPT and TMD+WPT cases had inhibited transcription activity of the anti-inflammatory cytokine TGFβ1. Interactions were observed between TGFβ1 and IL-8 SNPs: an additional copy of the TGFβ1 rs2241719 minor T allele was associated with twice the odds of TMD+WPT among individuals homozygous for the IL-8 rs4073 major A allele and half the odds of TMD+WPT among individuals heterozygous for rs4073. These results demonstrate how pro- and anti-inflammatory cytokines contribute to the pathophysiology of TMD and WPT in genetically-susceptible people. Furthermore, they identify MCP-1, IL-1ra, IL-8, and TGFβ1 as potential diagnostic markers and therapeutic targets for pain in patients with TMD