A General-applications Direct Global Matrix Algorithm for Rapid Seismo-acoustic Wavefield Computations

A new matrix method for rapid wave propagation modeling in generalized stratified media, which has recently been applied to numerical simulations in diverse areas of underwater acoustics, solid earth seismology, and nondestructive ultrasonic scattering is explained and illustrated. A portion of recent efforts jointly undertaken at NATOSACLANT and NORDA Numerical Modeling groups in developing, implementing, and testing a new fast general-applications wave propagation algorithm, SAFARI, formulated at SACLANT is summarized. The present general-applications SAFARI program uses a Direct Global Matrix Approach to multilayer Green's function calculation. A rapid and unconditionally stable solution is readily obtained via simple Gaussian ellimination on the resulting sparsely banded block system, precisely analogous to that arising in the Finite Element Method. The resulting gains in accuracy and computational speed allow consideration of much larger multilayered air/ocean/Earth/engineering material media models, for many more source-receiver configurations than previously possible. The validity and versatility of the SAFARI-DGM method is demonstrated by reviewing three practical examples of engineering interest, drawn from ocean acoustics, engineering seismology and ultrasonic scattering

Applications of a Direct Fast Field/Reflectivity Method to Wave Propagation Modeling in Underwater Acoustic and Solid Earth Seismic Environments

A new method is discussed for exact rapid computation of the depth-dependent Green\u27s function occuring in full integral solutions to the acoustic and elastic Helmholtz wave equation, allowing calculations of underwater acoustic propagation loss and full wavefield synthetic seismograms, in range-independent plane stratified media

Fluid-structure interaction analysis of the aortic valve in young healthy, ageing and post treatment conditions

Optimal aortic valve function, limitation of blood damage, and frequency of thromboembolic events are all dependent upon the haemodynamics within the aortic root. Improved understanding of the young healthy physiological state via investigation of the fluid dynamics around and through the aortic valve is essential to identify detrimental changes leading to pathologies and develop novel therapeutic procedures. The aim of this study is to develop a numerical model that can support a better comprehension of the valve function and serve as a reference to identify the changes produced by specific pathologies and treatments. A Fluid-structure interaction (FSI) numerical model was developed and adapted to accurately replicate the conditions of a previous in vitro investigation into aortic valve dynamics, performed by means of particle image velocimetry (PIV). The model was validated on equivalent physical settings, in a pulse duplicator replicating the physiological healthy flow and pressure experienced in the left heart chambers. The resulting velocity fields and hydrodynamic valve performance indicators of the two analyses were qualitatively and quantitatively compared to validate the numerical model. The validated FSI model was then used to describe realistic young healthy, ageing and post treatment conditions, by eliminating the experimental and methodological limitations and approximations. In detail, in terms of treatments, both surgical and transcatheter valve replacement procedures were investigated. In terms of pathologies, typical alterations frequently due to ageing, namely thickening of the valve leaflets and progressive dilation of the aortic chamber, were studied. The analysis was performed by comparing the data obtained for the ageing and post treatment configurations with those of the young healthy root environment. The results were analysed in terms of leaflets kinematics, flow dynamics, pressure and valve performance parameters. The study suggests a new operating mechanism for the young healthy aortic valve leaflets considerably different from what reported in the literature to date and largely more efficient in terms of hydrodynamic performance

The Effect of Textbook Format on Mental Effort and Time on Task

Using Astin’s theory of student engagement as a framework, the purpose of this study was to determine whether a significant difference in engagement, as indicated by mental effort and time on task, existed for college students who used a digital game-based textbook versus students who used a traditional print based textbook. The results showed a statistically significant difference in engagement, Hotelling’s T2 (2, 52) = 25.11, p \u3c .001, D2=1.86.https://scholarworks.waldenu.edu/archivedposters/1135/thumbnail.jp

Numerical Techniques for Scattering from Submerged Objects

To represent the final results in terms of matrices, one expands all appropriate physical quantities in terms of partial wave basis states. This includes expansions for the incident and scattered fields and the surface quantities. The method then utilizes the Huygen-Poincare integral representation for both the exterior and interior solutions, leading to the required matrix equations. One thus deals with matrix equations, the complexity of which depends on the nature of the problem. It is shown that in general a transition matrix T can be obtained relating the incident field A with the scattered field f having the form T = PQ(-1), where f = TA. The structure of Q can be quite complicated and can itself be composed of other matrix inversions such as arise from layered objects. Recent improvements in this method appropriate for a variety of physical problems are focused on, and on their implementation. Results are outlined from scattering simulations for very elongated submerged objects and resonance scattering from elastic solids and shells. The final improvement concerns eigenfunction expansions of surface terms, arising from solution of the interior problem, obtained via a preconditioning technique. This effectively reduces the problem to that of obtaining eigenvalues of a Hermitian operator. This formalism is reviewed for scattering from targets that are rigid, sound-soft, acoustic, elastic solids, elastic shells, and elastic layered objects. Two sets of the more interesting results are presented. The first concerns scattering from elongated objects, and the second to thin elastic spheroids

The Wheels on the Bus Go Round and Round: Rethinking the St. Louis Busing Program

This autoethnography shares our personal experiences and counter-narratives in the St. Louis busing program. Through our mission we expound on experiences and real-life situations as seen through our lens as a student and a mother in the St. Louis busing program. Critical race theory (CRT) was used as an essential framework allowing us to focus on the following four tenets: counter-stories, permanence of racism, whiteness as property, interest convergence. (Anderson, et al., 2017). Critical race theory (CRT) is the framework in social sciences that examines society and culture as it relates to categorization of race, law and power (Lynn & Dixson, 2013). The purpose of our study was to take a closer look at the discriminatory practices and unfairness that took place in the St. Louis busing program. Our autoethnography has allowed for authenticity and truth as we tell our personal narratives as to why the St. Louis Busing program wasn’t all sunshine and roses

The Effect of Blended Learning on Language Proficiency of an EFL Class: An Empirical Study

The combination of online learning and face-to-face lessons have become a relevant learning model in English Language Teaching in the last years. The goal of this research study was to investigate the integration of such a blended learning approach in an EFL class in Bolivia. The study was conducted at a binational language institution, and it focused on the effect of blended learning on the students’ overall language proficiency and each language skill individually. Data was collected via a proficiency pre-test at the beginning of the experiment, two quizzes during the module, and a final exam, all of them to assess the students’ learning. This study also investigated the students and teacher\u27s attitudes towards the blended learning approach, for which individual interviews were conducted. The participants were 31 Bolivian students of parallel intermediate level classes of English. They were divided into a comparison group (n=18) and a treatment group (n=13). The results showed that, overall, the comparison group performed better than the treatment group. However, the treatment group performed equally or better than the comparison group in some language skills. Regarding the students’ and teacher\u27s attitudes towards the online lessons, they were positive regarding the interactivity and the feedback, but negative regarding the opportunities of communication in the online lessons