University of Dayton

Laser-based manufacturing processes typically require fluid flow for fume exhaustion, inert chemical interaction, cooling, etc. Traditionally, measuring flow field characteristic requires high expertise and expensive high-speed equipment and therefore is not typically investigated as a parameter space. Event-based cameras have been recently developed for use as sensors for Particle Image Velocimetry (PIV) and show great results in wind tunnels and manufacturing environments as a simpler option for particle tracking. The ability to have a relatively cheap and simple method setup allows for laser process parameter and system verification. In this work, the objective is to integrate a cost-effective, high-frequency flow-sensing method into laser machining research to better understand the role of airflow in process control. A 532nm CW laser with cylindrical optics was used to create a laser sheet to illuminate ejected debris from laser ablation processes. Multiple materials, fluences, hatch patterns, and bulk laser power ablation experiments were performed on our 300W Amplitude Tangor workstation while measuring particle and fume extraction of the flow field. These in-situ measurements gave insight into the volatility of the laser ablation process and the best practices for predictable laser manufacturing. As ultrashort pulsed industrial laser processing emerges on large areas and complex surfaces, developing methods to retain expected laser-material interactions becomes very important.

ABSTRACT In 1999, the internationally applicable role of the internal audit function was redefined to be a trusted advisor to the organization rather than a stereotypical “corporate watchdog.” However, even today there is no clear understanding of what characteristics are associated with an internal audit function’s adopting a trusted advisor role, nor of what benefits the trusted advisor role yields for the organization. Using survey data from 250 chief audit executives, we find that a mix of professional and interpersonal internal audit characteristics is associated with adopting a trusted advisor role. Additionally, we find associations between trusted advisor internal audit functions and perceived benefits to the organization such as audit effectiveness, efficiency, and usability of audit outputs. Our findings contribute to the academic knowledge on the evolution of internal audit functions and identify incentives for adopting trusted advisor roles. Data Availability: Raw data were generated at a national Institute of Internal Auditors chapter. Derived data supporting the findings of this study are available from the first author on request. JEL Classifications: M40; M42; G34; G32; M4; G3.

Quantitative phase imaging enables label-free visualization of transparent and weakly absorbing cells with the transport of intensity equation, derived from the paraxial wave equation widely used for its simple and non-interferometric approach. However, it struggles with noise and high-frequency details, which are strongly influenced by the choice of defocus distance. In this study, we enhance the feature of retrieved phase through the recursive transport of intensity and phase equations using frequency-domain filtering. The filter identifies the frequency range where the phase transfer functions of transport of intensity and the contrast transfer function converge, enabling accurate and feature-enhanced phase reconstruction while mitigating diffraction and noise artifacts. The study establishes the upper limit of allowable frequency information in the phase image, with particular relevance to weak-phase samples. The proposed concept has been verified through numerical simulations, considering the initial (ground-truth) phase as a weak-phase sample. For experimental validation, the method is first tested using a resolution chart and subsequently applied to onion peels.

Instabilities and Turing patterns in stochastic spatiotemporal systems in which a fraction of an evolving population, after undergoing a series of dynamic transitions, returns to its original state, remain largely unexplored. Adopting an epidemic model incorporating reinfections as an exemplar of such a system, we present stability and pattern-formation analyses of the stochastic reaction-diffusion equations that represent the model. Saturation effects in epidemic spread lead to nonlinear considerations, while random environmental effects motivate a stochastic term. Turing bifurcation and the emergence of equilibrium patterns are analysed with respect to three fundamental parameters - reinfection, saturation, and noise intensity. Using higher-order stability analysis and stochastic averaging, we find the Turing instability and also uncover self–organized, distinct equilibrium patterns of infection spread. Additionally, results elucidating the effects of stochastic excitation and its intensity, as well as the competing influence of saturation and reinfection on stability and pattern formation, are presented. The results are also expected to be broadly significant beyond epidemic modelling, for studies of noise-induced instabilities and morphogenesis in spatiotemporal nonlinear dynamical systems.