131 research outputs found
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
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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
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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
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