Enhancing Room Temperature Phosphorescence from Organic Molecules by Internal Heavy Atom Effect and External Agents

Room temperature phosphorescence has gained a great deal of attention due to its significant importance in practical application such as phosphorescence organic light emitting diode (PhOLED). Bright room temperature phosphorescence has also been utilized in the field of bio-imaging and oxygen indicators which were not practically achievable by using phosphorescent materials. Heavy-metal complexes such as iridium complex are commonly used for room temperature phosphorescence but their potential toxicity and instability particularly in case of blue phosphors still remain to be solved. Room temperature phosphorescence from metal-free organic phosphors has attracted much attention in recent years since metal-free phosphors were presented as bright as organometallic compounds, quantum dots, and fluorescent molecules at room temperature. In previous study, our group focused on the development of host-guest systems to suppress vibration of phosphors such as doped crystal, amorphous rigid polymer and immobilization between polymer and phosphors via hydrogen bonding or covalent bonding. However, the quantum yield is still much lower than that of conventional fluorescent dyes. For example, the best quantum yield of room temperature phosphorescence is around 30% in polymer matrix. The low quantum yield prevents it from utilizing real phosphorescent applications. In this dissertation, we focused on how to improve further phosphorescence quantum yield by improving phosphorescence radiative decay as well as suppressing non-radiative decay. First, general molecular design principles to achieve bright room temperature phosphorescence from metal-free organic phosphors are thoroughly discussed. By synthesizing a series of molecules and analyzing their photophysical properties, we discovered how molecular structures affect the non-radiative decay pathway by intramolecular vibration, and both phosphorescent radiative decay and non-radiative decay by intermolecular vibration. Molecular design strategies to tune the phosphorescent color without significantly decreasing the phosphorescence quantum yield were also discussed. We also developed a new scheme to improve the phosphorescent radiative decay and consequently enhance the emission intensity by incorporating an external component such as plasmonic nanometals and adapting metal organic frameworks (MOFs). Through a systematic investigation on localized surface plasmon resonance (LSPR) based phosphorescence enhancement, we built insightful understanding on the LSRP based phosphorescence enhancement mechanism and revealed optimized conditions to achieve brightest phosphorescence. Finally, MOF was investigated with organic phosphor molecules as an organic ligand. MOF-polystyrene (PS) composite having a organic phosphor ligand produced bright room temperature phosphorescence by suppressing molecular vibrational dissipation and enhancing the phosphorescent radiative decay. A summary of future perspective of metal-free organic phosphors to overcome their limitations and to realize futuristic potential applications is provided in the last chapter of the dissertation.PHDMacromolecular Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143915/1/jaehunj_1.pd

Teacher Collaboration between Physical and Special Educators to Promote Physical Activity for Students with Disabilities

School-aged children with disabilities have difficulty in meeting current physical activity guidelines (Stanish et al., 2019). As such, there is a need for providing effective physical activity promotion programs for school-aged children with disabilities. School settings can be the right place to promote physical activity for children with disabilities because many professionals are involved in helping children with disabilities. Teacher collaboration between physical and special educators has been suggested in the promotion of a physically active lifestyle for children with disabilities (Klein & Hollingshead, 2015). However, collaboration between physical educators and other subject matter teachers is lacking (Rizzo, 2013). To promote teacher collaboration, it is important to understand a teachers’ intentions and self-efficacy toward teacher collaboration and factors influencing teacher collaboration. Therefore, the present study was aimed to understand teacher collaboration between physical and special educators

Seeing Through the Conversation: Audio-Visual Speech Separation based on Diffusion Model

The objective of this work is to extract target speaker's voice from a mixture of voices using visual cues. Existing works on audio-visual speech separation have demonstrated their performance with promising intelligibility, but maintaining naturalness remains a challenge. To address this issue, we propose AVDiffuSS, an audio-visual speech separation model based on a diffusion mechanism known for its capability in generating natural samples. For an effective fusion of the two modalities for diffusion, we also propose a cross-attention-based feature fusion mechanism. This mechanism is specifically tailored for the speech domain to integrate the phonetic information from audio-visual correspondence in speech generation. In this way, the fusion process maintains the high temporal resolution of the features, without excessive computational requirements. We demonstrate that the proposed framework achieves state-of-the-art results on two benchmarks, including VoxCeleb2 and LRS3, producing speech with notably better naturalness.Comment: Project page with demo: https://mm.kaist.ac.kr/projects/avdiffuss

STEER: Unified Style Transfer with Expert Reinforcement

While text style transfer has many applications across natural language processing, the core premise of transferring from a single source style is unrealistic in a real-world setting. In this work, we focus on arbitrary style transfer: rewriting a text from an arbitrary, unknown style to a target style. We propose STEER: Unified Style Transfer with Expert Reinforcement, a unified frame-work developed to overcome the challenge of limited parallel data for style transfer. STEER involves automatically generating a corpus of style-transfer pairs using a product of experts during decoding. The generated offline data is then used to pre-train an initial policy before switching to online, off-policy reinforcement learning for further improvements via fine-grained reward signals. STEER is unified and can transfer to multiple target styles from an arbitrary, unknown source style, making it particularly flexible and efficient. Experimental results on a challenging dataset with text from a diverse set of styles demonstrate state-of-the-art results compared to competitive baselines. Remarkably, STEER outperforms the 175B parameter instruction-tuned GPT-3 on overall style transfer quality, despite being 226 times smaller in size. We also show STEER is robust, maintaining its style transfer capabilities on out-of-domain data, and surpassing nearly all baselines across various styles. The success of our method highlights the potential of RL algorithms when augmented with controllable decoding to overcome the challenge of limited data supervision.Comment: for associated code, see https://github.com/shallinan1/STEERStyleTransfe

Meta-Analysis of Physical Activity Levels in Youth With and Without Disabilities

The purpose of this study was to explore the current levels of physical activity among youth with disabilities using meta-analysis. The search identified 11 publications including 729 participants (age 4-20 yr). The overall effect size for 11 studies was Hedges g = 0.60 (SE = 0.18, 95% confidence interval [CI] [0.24, 0.96], p .85). Results also suggested that the differences in physical activity between youth with and without disabilities were affected by age (13 yr, g = 0.37, SE = 0.10, 95% CI [0.18, 0.57], p .6)

Quantitative agreement of Dzyaloshinskii-Moriya interactions for domain-wall motion and spin-wave propagation

The magnetic exchange interaction is the one of the key factors governing the basic characteristics of magnetic systems. Unlike the symmetric nature of the Heisenberg exchange interaction, the interfacial Dzyaloshinskii-Moriya interaction (DMI) generates an antisymmetric exchange interaction which offers challenging opportunities in spintronics with intriguing antisymmetric phenomena. The role of the DMI, however, is still being debated, largely because distinct strengths of DMI have been measured for different magnetic objects, particularly chiral magnetic domain walls (DWs) and non-reciprocal spin waves (SWs). In this paper, we show that, after careful data analysis, both the DWs and SWs experience the same strength of DMI. This was confirmed by spin-torque efficiency measurement for the DWs, and Brillouin light scattering measurement for the SWs. This observation, therefore, indicates the unique role of the DMI on the magnetic DW and SW dynamics and also guarantees the compatibility of several DMI-measurement schemes recently proposed.Comment: 24 pages, 5 figure

Universal field-tunable terahertz emission by ultrafast photoinduced demagnetization in Fe, Ni, and Co ferromagnetic films

We report a universal terahertz (THz) emission behavior from simple Ni, Fe, and Co metallic ferromagnetic films, triggered by the femtosecond laser pulse and subsequent photoinduced demagnetization on an ultrafast time scale. THz emission behavior in ferromagnetic films is found to be consistent with initial magnetization states controlled by external fields, where the hysteresis of the maximal THz emission signal is observed to be well-matched with the magnetic hysteresis curve. It is experimentally demonstrated that the ultrafast THz emission by the photoinduced demagnetization is controllable in a simple way by external fields as well as pump fluences. © 2020, The Author(s).1