46 research outputs found
Improved Flat Frequency Response of Conical Shellular Metamaterial-Enabled Flat Panel Loudspeaker
No full textA piezoelectric flat panel loudspeaker operates by utilizing a piezoelectric film actuator to vibrate a diaphragm, offering advantages in miniaturization, embedding, and spatial efficiency. However, achieving high sound pressure levels (SPL) at low frequencies and maintaining a flat frequency response remains challenging. This study presents a Conical Shellular Sandwich Diaphragm (CSSD), derived from conical shellular metamaterials, which combines lightweight properties with high stiffness. The CSSD enhances low-frequency SPL and improves frequency response flatness through structural optimization, eliminating the need for complex systems. Finite element analysis identifies optimal geometric parameters for the CSSD unit cell, resulting in an 11.5 dB increase in low-frequency SPL and a 53% reduction in peak-dip deviation across the 200 Hz-20 kHz range, compared to a conventional Flat Panel Diaphragm (FPD). These enhancements stem from a reduction in the CSSD's effective mass (meff) to one-hundredth of an equivalent-volume FPD and an increase in effective bulk modulus (keff) relative to structures with the same mass. Experimental tests of 3D-printed CSSD and FPD prototypes integrated with piezoelectric actuators match the simulation results. This study demonstrates the potential of mechanical metamaterials to address design limitations in flat panel loudspeakers, enabling improved sound quality and simpler configurations for commercial use.
Zero Poisson's ratio metamaterial and meander-inspired diaphragms for enhancing low-frequency performance in flat-panel loudspeaker
No full textFlat-panel loudspeakers, designed with a planar configuration, provide space-efficient audio solutions; however, they frequently exhibit limitations in low-frequency performance due to constrained diaphragm displacement. This study addresses the challenge of enhancing low-frequency sound pressure levels in flat-panel loudspeakers while preserving their slim profiles. We demonstrate that integrating metamaterial-inspired Zero Poisson's Ratio Diaphragms (ZPD) and Edge-Patterned Diaphragms (EPD) significantly improves low-frequency sound pressure levels in piezoelectric flat-panel loudspeakers. The selection of ZPD and EPD designs leverages the unique monoclastic behavior of zero Poisson's ratio structures and the high displacement characteristics of meanderspring patterns, respectively, which results in increased diaphragm flexibility and displacement. Our finite element analysis, supported by experimental results, shows that both ZPD and EPD designs enhance sound pressure levels below 200 Hz compared to a conventional bare diaphragm, achieving maximum enhancements of 11.6 dB and 20.0 dB, respectively. These findings advance the field by introducing diaphragm designs that exploit zero Poisson's ratio principles and structural patterns to improve acoustic performance without increasing overall thickness. The proposed metamaterials and structural designs demonstrate considerable potential for acoustic applications across multimedia systems, portable devices, and automotive audio, where superior low-frequency response in slim-profile loudspeakers is highly beneficial.
Navigating the Meanings of Social Justice, Teaching for Social Justice, and Multicultural Education
No full textThis article uses well-received contemporary scholarship—works by Iris Young, Nancy Fraser, Morva McDonald, Connie North, and Geneva Gay—to illuminate a high degree of coherence among the substantive meanings of social justice, teaching for social justice, and multicultural education. Based on these relationships, the article suggests that social justice is an inherent feature and goal of multicultural education, and the discourses between teaching for social justice and multicultural education should be mutually associated with one another to more effectively promote social justice. The article closes by outlining personal literacy that has the potential to enrich research and practice in multicultural education.</jats:p
A Critical Review of Literature on English as a Global Language Published in Korea
No full textThis study aimed to explore key issues and findings in the
literature on global Englishes published in Korea, employing a
critical perspective. A total of 84 journal articles published
between the year 1992 and April 2023 were gathered from the
database provided by Korea Education and Research
Information Service. The search terms used were lingua franca
English, world Englishes, English as an international
language, and global Englishes. Qualitative analysis was
conducted using the scoping review method to identify major
topics and issues within the literature. The analysis revealed a
recurring issue: While teachers and students acknowledged the
importance of teaching and learning global Englishes, they were
constrained to adhere to the North American English variety due
to the prevailing hegemony of the native speaker paradigm. This
constraint negatively affected both teachers and students in
developing competence in English. In terms of research
landscape, there was a discernable impact of change in English
education policies and curricula on some of the studies, but not
all. The study concludes with implications and suggestions
drawn from its findings
Crafting a Third Space: Teacher Beliefs and Practices in Curriculum Reform for Multicultural Education
No full textThesis (Ph.D.)--University of Washington, 2016-06This qualitative case study examined South Korean elementary teachers’ beliefs about the goals of multicultural education in relation to practices and contexts within social studies instruction. The first research question examined the distinguishing features of South Korean elementary teachers’ beliefs about the goals of multicultural education. The second research question explored how individual teachers’ underlying beliefs about the goals of multicultural education interacted with the practices of classroom-based multicultural curriculum reform. A five-fold framework of teaching for social justice and complexity theory perspectives provided the theoretical bases for the study. Grounded in sociological theory, North’s (2009) framework of teaching for social justice includes five types of social justice literacies that students are expected to learn in order to promote social justice and equity. These are functional, relational, critical, democratic, and visionary literacy. Based on this framework, I assumed that teachers’ beliefs about the goals of multicultural education can be understood by analyzing how their perceptions of these five literacies are related to or interact with one another. Contextualized in the field of psychology, complexity theory contends that one’s beliefs are a system that involves interactions between implicit beliefs and explicit beliefs, and interactions with other systems such as practices and contexts. Based on complexity theory, this study regarded individual teachers’ beliefs as a complex system that includes active interactions among various beliefs, and as an open system which consistently interacts with the practices and contexts. This study used a comparative case studies method. The research settings were Seoul and Gyeonggi Province, South Korea. Six elementary school teachers who engaged in classroom-based curriculum reform for multicultural education participated in this study. Data were collected from semi-structured interviews, stimulated recall interviews, classroom observations, and documents. Data analysis included a constant comparative method, and it contributed to building a substantive theory outlining teacher beliefs and practices in multicultural curriculum reform. Four major findings emerged from the data. They were • Generally, the teachers tended to identify five social justice literacies as fundamental goals of multicultural education, but at a deeper level, they were grouped into two categories according to whether or not they were committed to teaching critical literacy. • Teachers not committed to teaching critical literacy were not aware of dilemmas related to multicultural curriculum reform, and used particular contexts to justify the inappropriateness of teaching critical literacy. By comparison, teachers committed to teaching critical literacy usually faced two types of dilemmas in the classroom-based multicultural curriculum reform practices. These dilemmas were between contradictory beliefs (Type 1) and between belief and context (Type 2). •. Teachers who did not resolve the dilemmas either did not teach critical literacy at all or taught critical literacy as secondary. • A democratic school and community, and a teacher’s strategies for dealing with the contextual obstacles, helped her resolve the dilemmas, and more actively advocate for teaching critical consciousness. Based on these findings, a substantive theory outlining three stages of teachers’ beliefs and practices in classroom-based multicultural curriculum reform evolved. These stages included pre-encounter stage, encounter stage, and post-encounter stage. The findings implied that individual teachers need differentiated scaffolding to further develop their current levels of multicultural education engagement. Recommendations for future research and practices were also provided to fill the gaps between theories and actions
A three-dimensional photoacoustic and ultrasound automated breast volume scanner (PAUS-ABVS) for breast cancer patients
No full textBreast cancer screening with mammography is less effective in women with dense breast tissue, prompting the use of ultrasound (US) imaging. While two- (2D) and three-dimensional (3D) US improve cancer detection, their low specificity leads to frequent unnecessary biopsies. Operator dependence on 2D US has led to the development of 3D automated breast volume scanners (ABVS), but challenges remain in distinguishing benign from malignant lesions. We developed a 3D photoacoustic and ultrasound (PAUS)-ABVS system that integrates a large field-of-view, 768-element transducer to improve diagnostic accuracy. In a clinical study of 61 patients with 36 benign and 30 malignant lesions, multispectral photoacoustic imaging was used to measure blood volume and oxygen saturation within lesions. When combined with standard US BI-RADS (breast imaging reporting and data system) scores, the system achieved a sensitivity of 96.7% and specificity of 66.7%. This performance matched the best outcomes of 2D PAUS and outperformed conventional US. Our results suggest that the PAUS-ABVS can support more accurate breast cancer diagnosis while reducing unnecessary biopsies.
Parkin Promotes Mitophagic Cell Death in Adult Hippocampal Neural Stem Cells Following Insulin Withdrawal
No full textRegulated cell death (RCD) plays a fundamental role in human health and disease. Apoptosis is the best-studied mode of RCD, but the importance of other modes has recently been gaining attention. We have previously demonstrated that adult rat hippocampal neural stem (HCN) cells undergo autophagy-dependent cell death (ADCD) following insulin withdrawal. Here, we show that Parkin mediates mitophagy and ADCD in insulin-deprived HCN cells. Insulin withdrawal increased the amount of depolarized mitochondria and their colocalization with autophagosomes. Insulin withdrawal also upregulated both mRNA and protein levels of Parkin, gene knockout of which prevented mitophagy and ADCD. c-Jun is a transcriptional repressor of Parkin and is degraded by the proteasome following insulin withdrawal. In insulin-deprived HCN cells, Parkin is required for Ca2+ accumulation and depolarization of mitochondria at the early stages of mitophagy as well as for recognition and removal of depolarized mitochondria at later stages. In contrast to the pro-death role of Parkin during mitophagy, Parkin deletion rendered HCN cells susceptible to apoptosis, revealing distinct roles of Parkin depending on different modes of RCD. Taken together, these results indicate that Parkin is required for the induction of ADCD accompanying mitochondrial dysfunction in HCN cells following insulin withdrawal. Since impaired insulin signaling is implicated in hippocampal deficits in various neurodegenerative diseases and psychological disorders, these findings may help to understand the mechanisms underlying death of neural stem cells and develop novel therapeutic strategies aiming to improve neurogenesis and survival of neural stem cells
Crafting a third space: Integrative strategies for implementing critical citizenship education in a standards-based classroom
No full textWalking Back into Origins of My Stereotypes and Biases: Exploring Prospective Teachers’ Development of Cultural Critical Consciousness
No full textThe Ethics of Difference in Teaching Culturally Marginalized Students: Content Analysis of Exemplary Multicultural Education Cases
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