Effect of fiber distributions on the mechanical performance of CMC materials: Virtual manufacturing and testing approach

Ceramic matrix composites (CMCs) exhibit superior thermal stability in an elevated temperature environment and thus are considered as a promising candidate material for gas turbine applications in the field of power generation industry. CMCs also have a higher fracture resistance than conventional technical ceramics owing to the coated ceramic fibers embedded in the matrix. However, the complex heterogeneous microstructure results in complicated damage and failure behavior at the fiber length scale, which appears non-linear stress-strain response at the macro length scale. When a crack is initiated in the matrix phase, the crack grows very rapidly since the ceramic matrix is a brittle material. However, the rapid crack propagation is restrained when the crack tip reaches the ductile coating interface. This fracture process occurring inside the CMC material results in a highly complicated post-peak response and makes its fracture toughness comparable to that of metals. The post-peak response is greatly influenced by local topology of fibers situated inside the composite material and thus the fracture toughness of a CMC may vary locally due to the irregular distribution of fibers. In the present study, the effect of fiber distributions on the post-peak response and the corresponding mechanical performance of a CMC material is closely investigated by utilizing representative volume elements (RVEs) with various fiber distributions. Two-dimensional square RVE enclosing randomly distributed circular fibers with coating layers is considered to represent the microstructure of a long-fiber-reinforced CMC material. Random, yet realistic distribution of fibers is achieved through the virtual force dispersion (VFD) algorithm. The present VFD algorithm arranges fibers with coating layers after the fibers are randomly seeded into a square RVE. Fibers should be rearranged after the random seed, since overlapped regions between fibers are unavoidable during the initial distribution process. The VFD algorithm assumes that fibers are connected through virtual springs, which provide repulsive forces between them. The VFD algorithm finds an equilibrium state in which the springs are completely relaxed and there exists no repulsive force in the system. In this manner, various RVEs with different fiber distributions are easily created for the next step of analysis. Please click Additional Files below to see the full abstract

Wind oscillation analysis of a suspension bridge coupled with CFD

This study conducted a CFD-2D coupled analysis of a suspension bridge subjected to wind loads. Previous studies found that rotational oscillation was due to differences in the restoring force at hanger cables and could generate torsional oscillations. However, due to uncertain external force terms, the previous studies could not be applied to analyze actual structures. To enable application in a real design process, this study proposed a methodology for determining the external force terms. The external force terms were determined with CFD, and a moment force term was added to equations of motion derived from dynamic equilibrium conditions. All constants and properties were calculated from an assumed cross section of superstructure. This methodology can be used not only to avoid torsional resonance but also in preliminary analysis in the bridge design stage

Improving Sample Quality of Diffusion Models Using Self-Attention Guidance

Following generative adversarial networks (GANs), a de facto standard model for image generation, denoising diffusion models (DDMs) have been actively researched and attracted strong attention due to their capability to generate images with high quality and diversity. However, the way the internal self-attention mechanism works inside the UNet of DDMs is under-explored. To unveil them, in this paper, we first investigate the self-attention operations within the black-boxed diffusion models and build hypotheses. Next, we verify the hypotheses about the self-attention map by conducting frequency analysis and testing the relationships with the generated objects. In consequence, we find out that the attention map is closely related to the quality of generated images. On the other hand, diffusion guidance methods based on additional information such as labels are proposed to improve the quality of generated images. Inspired by these methods, we present label-free guidance based on the intermediate self-attention map that can guide existing pretrained diffusion models to generate images with higher fidelity. In addition to the enhanced sample quality when used alone, we show that the results are further improved by combining our method with classifier guidance on ImageNet 128x128.Comment: Project Page: https://ku-cvlab.github.io/Self-Attention-Guidanc

Effects of Nonuniform Fiber Geometries on the Microstructural Fracture Behavior of Ceramic Matrix Composites

Microstructural fracture behavior of a ceramic matrix composite (CMC) with nonuniformly distributed fibers is studied in the presentation. A comprehensive numerical analysis package to study the effect of nonuniform fiber dimensions and locations on the microstructural fracture behavior is developed. The package starts with an optimization algorithm for generating representative volume element (RVE) models that are statistically equivalent to experimental measurements. Experimentally measured statistical data are used as constraints while the optimization algorithm is running. Virtual springs are utilized between any adjacent fibers to nonuniformly distribute the coated fibers in the RVE model. The virtual spring with the optimization algorithm can efficiently generate multiple RVEs that are statistically identical to each other. Smeared crack approach (SCA) is implemented to consider the fracture behavior of the CMC material in a mesh-objective manner. The RVEs are subjected to tension as well as the shear loading conditions. SCA is capable of predicting different fracture patterns, uniquely defined by not only the fiber arrangement but also the specific loading type. In addition, global stress-strain curves show that the microstructural fracture behavior of the RVEs is highly dependent on the fiber distributions

Varieties of indoctrination: the politicization of education and the media around the world

For many decades, scholars assumed voluntary compliance and citizens’ commitment to a regime’s principles and values to be critical for regime stability. A growing literature argues that indoctrination is essential to achieve this congruence. However, the absence of a clear definition and comprehensive comparative measures of indoctrination have hindered systematic research on such issues. In this paper, we fill this gap by synthesizing literature across disciplines to clarify the concept of indoctrination, focusing particularly on the politicization of education and the media. We then outline how the abstract concept can be operationalized, and introduce and validate an original expert-coded dataset on indoctrination that covers 160 countries from 1945 to the present. The dataset should facilitate a new generation of empirical inquiry on the causes and consequences of indoctrination

AD-YOLO: You Look ONly Once in Training Multiple Sound Event Localization and Detection

Sound event localization and detection (SELD) combines the identification of sound events with the corresponding directions of arrival (DOA). Recently, event-oriented track output formats have been adopted to solve this problem; however, they still have limited generalization toward real-world problems in an unknown polyphony environment. To address the issue, we proposed an angular-distance-based multiple SELD (AD-YOLO), which is an adaptation of the "You Look Only Once" algorithm for SELD. The AD-YOLO format allows the model to learn sound occurrences location-sensitively by assigning class responsibility to DOA predictions. Hence, the format enables the model to handle the polyphony problem, regardless of the number of sound overlaps. We evaluated AD-YOLO on DCASE 2020-2022 challenge Task 3 datasets using four SELD objective metrics. The experimental results show that AD-YOLO achieved outstanding performance overall and also accomplished robustness in class-homogeneous polyphony environments.Comment: 5 pages, 3 figures, accepted for publication in IEEE ICASSP 202

Service-led Catch-Up in the Indian Economy: Alternative Hypotheses on Tertiarization and the Leapfrogging Thesis

The experience of India in economic catch-up is unique when compared to other countries. First, the catch-up process of India was not only service-led, but also accompanied by a decoupling between manufacturing and services. Second, productivity performance in the service sector was higher than in the manufacturing sector in terms of the level as well as growth rate. Finally, exports in IT services led the tertiarization of the Indian economy. From this perspective, the trajectory of the Indian catch-up can be characterized as path-creating. Existing hypotheses on tertiarization do not fully account for such aspects of the uniqueness of the Indian experience. The leapfrogging argument in Neo-Schumpeterian economics provides a more plausible explanation of the Indian experience. The ICT revolution and the shift from hardware systems to client-server systems have created new markets for the global services trade. This paradigm shift lowered the costs of entry, including fixed investments, for Indian IT service firms and helped close the experience and skill gaps quickly. The industry-specific characteristics of the IT services industry and the country-specific advantages of India further lowered the costs of entry. With steady strategic and organizational innovations, Indian IT service firms succeeded in securing competitive advantages in the global market

Non-linear dynamic analysis of reinforced concrete bridge columns under vehicle impact loadings

A 3D nonlinear impact analysis was performed for reinforced concrete bridge columns under truck impact loadings. Three different boundary conditions were considered to investigate the effect of superstructures on the integral column during impact. Fixed bottom conditions and restraints in the loading direction at the top of the column (Model I) showed the largest damaged area. The dominant failure mode of the column was shear. However, Model II, which is equivalent to Model I with the top released, showed less damage, and the dominant failure modes were flexure rather than shear. In Model III, in which the effect of featured the superstructure was considered, the shear and flexural damage to the column were reduced due to the movement of the superstructures

A Qualitative Study on the Difference in Organizational Fit of IT Supporting Organizations

For many years, factors that increase the competitive advantage of organizations have been studied in organizational research. For an Information Technology (IT) organization, the main issues are the fitness of the IT and organization strategies and methods for revitalizing IT knowledge management (Earl, 2001; Rathnam, Johnsen, & Wen, 2005; Zack, 2002). However, there are few studies that have evaluated the competitiveness of an organization with reference to the correspondence of these constituent factors with organizational objectives. In this research a multi-contingency view was applied to Korean agencies, and the regional agencies with good performance and those with poor performance were compared with regard to this measure of fitness. The results of this study confirmed that the regions that received a favorable evaluation from experts exhibited good fit overall, and the constituent parts of the organization were consistent with the firm’s objectives

Reliable diameter control of carbon nanotube nanowires using withdrawal velocity

Carbon nanotube (CNT) nanobundles are widely used in nanoscale imaging, fabrication, and electrochemical and biological sensing. The diameter of CNT nanobundles should be controlled precisely, because it is an important factor in determining electrode performance. Here, we fabricated CNT nanobundles on tungsten tips using dielectrophoresis (DEP) force and controlled their diameters by varying the withdrawal velocity of the tungsten tips. Withdrawal velocity pulling away from the liquid-air interface could be an important, reliable parameter to control the diameter of CNT nanobundles. The withdrawal velocity was controlled automatically and precisely with a one-dimensional motorized stage. The effect of the withdrawal velocity on the diameter of CNT nanobundles was analyzed theoretically and compared with the experimental results. Based on the attachment efficiency, the withdrawal velocity is inversely proportional to the diameter of the CNT nanobundles; this has been demonstrated experimentally. Control of the withdrawal velocity will play an important role in fabricating CNT nanobundles using DEP phenomena.110Ysciescopu