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Improvement of electrical conductivity in glass bubble-carbon nanotube/ polyamide 6 hybrid scale composite through novel mechanical forming and segregated network morphology
No full textThe study suggests that GB-CNT/PA6 multiscale hybrid composite can be used to create a network structure with controllable electrical conductivity, making it a promising material for various practical applications. The paper introduces a new method for controlling electrical conductivity of composite materials by creating a segregated network morphology (SNM) using a glass bubble (GB)-carbon nanotube (CNT)/polyamide 6 (PA6) multiscale hybrid composite. Instead of relying solely on CNTs, the addition of GB allows for a more economical process by reducing the required CNT concentration to achieve the desired electrical conductivity. The paper also analyzes the effects of varying GB and CNT content on electrical conductivity based on percolation theory. The results demonstrate an 18.8 times increase in electrical conductivity with the SNM approach. The study proposes that this approach could be used to create composite materials with controllable electrical conductivity, making them suitable for various applications
Type-II Red Phosphorus: Wavy Packing of Twisted Pentagonal Tubes
No full textElemental phosphorus exhibits fascinating structural varieties and versatile properties. The unique nature of phosphorus bonds can lead to the formation of extremely complex structures, and detailed structural information on some phosphorus polymorphs is yet to be investigated. In this study, we investigated an unidentified crystalline phase of phosphorus, type-II red phosphorus (RP), by combining state-of-the-art structural characterization techniques. Electron diffraction tomography, atomic-resolution scanning transmission electron microscopy (STEM), powder X-ray diffraction, and Raman spectroscopy were concurrently used to elucidate the hidden structural motifs and their packing in type-II RP. Electron diffraction tomography, performed using individual crystalline nanowires, was used to identify a triclinic unit cell with volume of 5330 & ANGS;(3), which is the largest unit cell for elemental phosphorus crystals up to now and contains approximately 250 phosphorus atoms. Atomic-resolution STEM imaging, which was performed along different crystal-zone axes, confirmed that the twisted wavy tubular motif is the basic building block of type-II RP. Our study discovered and presented a new variation of building blocks in phosphorus, and it provides insights to clarify the complexities observed in phosphorus as well as other relevant systems
An Amiable Design of Cobalt Single Atoms as the Active Sites for Oxygen Evolution Reaction in Desalinated Seawater
No full textGreen fuel from water splitting is hardcore for future generations, and the limited source of fresh water (<1%) is a bottleneck. Seawater cannot be used directly as a feedstock in current electrolyzer techniques. Until now single atom catalysts were reported by many synthetic strategies using notorious chemicals and harsh conditions. A cobalt single-atom (CoSA) intruding cobalt oxide ultrasmall nanoparticle (Co3O4 USNP)-intercalated porous carbon (PC) (CoSA-Co3O4@PC) electrocatalyst was synthesized from the waste orange peel as a single feedstock (solvent/template). The extended X-ray absorption fine structure spectroscopy (EXAFS) and theoretical fitting reveal a clear picture of the coordination environment of the CoSA sites (CoSA-Co3O4 and CoSA-N4 in PC). To impede the direct seawater corrosion and chlorine evolution the seawater has been desalinated (Dseawater) with minimal cost and the obtained PC is used as an adsorbent in this process. CoSA-Co3O4@PC shows high oxygen evolution reaction (OER) activity in transitional metal impurity-free (TMIF) 1 M KOH and alkaline Dseawater. CoSA-Co3O4@PC exhibits mass activity that is 15 times higher than the commercial RuO2. Theoretical interpretations suggest that the optimized CoSA sites in Co3O4 USNPs reduce the energy barrier for alkaline water dissociation and simultaneously trigger an excellent OER followed by an adsorbate evolution mechanism (AEM)
Rethinking Internationalization of Higher Education: Technology, Intercultural Sensitivity, and EMI
No full textAmid intensive global competition in higher education (HE) for more than a decade, HE institutions of many non-English-speaking societies were recently faced with additional challenges during the excruciating time from pandemic. As the institutions have gradually overcome the time, the landscape of EFL education in line with the internationalization of HE is now differently viewed in terms of the place of technology in education as well as the issues of increased intercultural sensitivity and efficient English-medium instruction. This presentation focuses on these issues and seeks to rethink how these can be embedded into the internationalized HE in the post-pandemic era. First, based on a study on intercultural communication via an online social platform between Korean EFL learners and U.S. college students, the effect of technology on intercultural sensitivity of the learners from a Korean university devoted to internationalization and English-medium instruction. The technology, which hosts either synchronous videoconference classes or asynchronous message boards, is also examined to shed light on the relationship between motivational orientations and participation in online EFL classes. The quantitative analysis of the survey data and the subsequent qualitative analysis of the interviews reveal that these different technological interventions are closely related with the HE context of EMI. The findings further highlight the need for balanced, diversified uses of technology in EFL education over the next decade-key insights for developing a sustainable EMI policy in a truly global HE campus
Experimental estimation of radiation damage induced by 10B(n, ??)7Li reactions in Al-B4C neutron absorber discharged from spent nuclear fuel pool
No full textAl-B4C neutron absorbers in spent fuel pools have been assumed to have negligible radiation damage and helium generation from 10B(n, ??)7Li reactions. However, surveillance coupons have shown highly radiation-damaged microstructure. We conducted 200 keV He+ ion irradiation on Al 6061 at three different doses (0.1, 1, and 10 dpa) and compared the microstructures to the surveillance coupon. The neutron absorber's bubble size (25.9 ?? 7.4 nm) was most similar to the 10 dpa irradiated specimen (28.4 ?? 13.8 nm). Commercial neutron absorber (BORAL and MAXUS??) were also irradiated up to 10 dpa and showed preferential cavity formation along grain boundaries
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No full textDepartment of Urban and Environmental Engineering (Environmental Science and Engineering)clos
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Get PDFDepartment of PhysicsBulk photovoltaic effect characterized by the generation of a steady photocurrent without the aid of external p-n junction has attracted a lot of attention due to its novel physics and potential for high-performance solar cell device. Here, we show the electronic origin of the photovoltaic property of three different materials (organic molecular solids, organic-inorganic perovskite halide, and transition metal dichalcogenide nanotube) and present a pragmatic way to utilize the shift current for application of practical devices. The symmetry adjustment, doping, and geometrical change of those materials generate high photovoltaic effect. Our results provide a fundamental understanding of intriguing organic photovoltaic materials and pave a way for their practical application at room temperature.
This thesis provides an overview of the theory and technical treatment of the bulk photovoltaic effect, while also investigating an unexplored factor that was not analyzed in previous experiments. The introductory chapter (Chapter 1) presents the theoretical framework of the bulk photovoltaic effect and provides a concise review of recent advancements in both the theoretical understanding and experimental realization of this phenomenon. Chapter 2 focuses on the computational aspects related to the realization of the bulk photovoltaic effect using plane-wave and Wannier-function basis approaches. Specifically, the computational theories and technical details discussed include density functional theory, time-dependent density functional theory, and Wannier90. In Chapter 3, it is discovered that when infrared frequency light is applied to the low-temperature phase of TTF-CA, a substantial shift current is generated. Additionally, in the high-temperature phase, despite a net zero current, a non-vanishing shift current can still be produced due to the interchain effect. Chapter 4 indicates that the significant photocurrent observed in MAPbI3 and FAPbI3 primarily arises from the intrinsic electronic band properties near the Fermi level, which are rooted in the inorganic backbone of the materials. In contrast, the ferroelectric polarization of the hybrid halide perovskite is predominantly influenced by the ionic contribution of the molecular cation. The spatial charge shift that occurs upon excitation is attributed to the charge transfer from iodine to lead atoms within the backbone and is independent of the presence of cationic molecules. In Chapter 5, it is demonstrated that WS2 nanotubes exhibit a remarkable shift current in the infrared region, which surpasses previously reported values in the higher frequency range by a factor of four. This enhanced performance is attributed to the advantageous one-dimensional nanotube geometry, specifically the wall-to-wall charge shift, which is further maximized through a Janus-type heteroatomic configuration. To evaluate the nonlinear effect of a strong field and the nonadiabatic effect of atomic motion, direct real-time integration of the photoinduced current is carried out using time-dependent density functional theory.clos
Ex vivo relaxation rates and magnetic susceptibility changes of corpus callosum in aging rats
Get PDFDepartment of Biomedical EngineeringMyelin, the main component of white matter (WM), is a lipid-protein membrane structure that surrounds axon compactly in the nervous systems of vertebrates. Myelin exists in the form of a multi-lamellar sheath consisting of repeating units of the myelin bilayers and most of myelinated axons are distributed in WM. The main role of myelin is the electrical insulator for neurons, which increases the speed and efficiency of signal conduction. Since speed of action potential transmission is necessary to promote various neuronal functions, the measurements of myelin content are important for studies of normal development and neurodegenerative diseases.
In the evaluation of myelin, magnetic resonance imaging (MRI) is widely used as a noninvasive imaging technique that provides detailed anatomical images with various contrast mechanisms. Due to the limitation in MRI resolution and the size of myelinated axons (~ 1 ??m), myelin cannot be directly resolved by MRI. Also, the T2 value of non-aqueous protons of myelin (50 ??s < T2 < 1 ms) is too short to measure the signal in conventional MRI, making direct imaging difficult. Therefore, most MRI techniques currently used for myelin imaging are mainly based on indirect estimation of myelin.
Currently, various MRI techniques for indirectly examining the myelin content are being studied with their respective strengths and weaknesses. However, there is still no method that is considered gold standard in the field of myelin MRI. Studies comparing and analyzing the effects of volumetric parameters on myelin through various validation methods are still lacking. Therefore, the purpose of this study is to quantify volumetric changes in myelin, such as myelin volume fraction (MVF), in the corpus callosum (CC) of post-mortem aging rat brains through MRI-based measurements and histological/theoretical validations.
In the first section, the relationship with MVF was established through the MRI-derived values: longitudinal relaxation rate R1 and the magnetic susceptibility values obtained through quantitative susceptibility mapping (QSM). The absolute MVF values were determined by transmission electron microscopy (TEM) as a gold standard measure for comparison with the values obtained by the aforementioned MRI techniques. Also, QSM simulations were performed based on the TEM-derived structures to theoretically evaluate and understand the MR signal properties. Correlations of MVF versus MRI-derived values (R1 and magnetic susceptibility) showed a strong linear relationship. In addition, QSM simulation results established a linearly proportional relationship between simulated magnetic susceptibility and MVF. Statistically significant linear correlations between MRI-derived values and MVF demonstrated that variable myelin content in WM (i.e., CC) could be quantified across different stages of aging. These results further support that both MRI techniques (R1 and QSM) provide an efficient means to study the brain aging process with accurate volumetric quantification of myelin content in the WM.
In the second section, multiple spin echo sequence-based MRI-R2 values were measured to confirm that myelin volume information could be detected even when the short-T2 component (myelin water signal) was not detected due to the fixation effect. TEM-based quantification of MVF and corresponding Monte-Carlo simulation to estimate relaxation rates (R2,IE) due to diffusion in the presence of inhomogeneous magnetic field perturbation in intra- and extra-cellular (IE) spaces were respectively performed. A significant correlation between mean MRI-R2 and MVF values was observed, and the estimated R2,IE values of Monte-Carlo simulations in IE water signals were also positively correlated with MVF values. However, the magnitude of R2,IE values were much smaller than that those observed for MRI-R2 values, indicating that R2-related changes in MVF are likely dominated by the myelin water content. Such comparisons between independent parameters from MRI, TEM, and simulations support the suggestion that myelin water signals were indistinguishably mixed to exhibit mono-exponential R2, and still reflect the volumetric information of myelin.
In conclusion, it was confirmed that the proposed MRI-based measurements (R1, R2 and QSM) can be usefully used for the quantification of myelin volume in the post-mortem rat CC regions based on histological/theoretical validations (TEM and simulation).clos
Spatiotemporal Integration of Early Visual Processing: Visual Phenomena beyond the Critical Fusion Frequency
Get PDFDepartment of Biomedical Engineering (Human Factors Engineering)Our visual system integrates continuous signals to construct visual representation. This integration process involves combining visual inputs across both space and time. This spatiotemporal integration is inherently linked to motion. The movements of our eyes play a fundamental role in shaping our visual perception by spatially shifting the images projected on our retinas. The significance of considering the effects of eye movements on visual perception, resulting from these spatial modulations, has been consistently emphasized.
In the first part of the study, we focused on examining the influence of eye movements on the temporal sensitivity of the human visual system. Specifically, we assessed participants' ability to detect the flickering visual stimuli with and without the inclusion of eye movements. The findings revealed that the effects of eye movements varied depending on the spatial features of the stimuli. When eye movements were incorporated, participants were able to perceive flickering edges beyond their temporal limit, surpassing the critical fusion frequency (CFF). Furthermore, a significant positive correlation was observed between temporal sensitivity and the extent of eye movements executed during stimulus presentation.
To further elucidate the alterations in visual perception caused by the spatial characteristics of visual stimuli and the shifted retinal image resulting from eye movements, we developed a spatiotemporal integration model. This model aimed to emulate the spatiotemporal integration process occurring in our early visual system and was employed to encompass the observations made in this study.
In the second part of the study, we investigated the phenomena of visual persistence and the sense of reality associated with moving objects that move at a speed comparable to our eye movements (approximately 100 degrees per second). Introducing a Speedline, which connected two consecutively presented objects spatially, mitigated the smear effect on moving objects in terms of the range of visual persistence and perceived length. Additionally, the presence of the Speedline enhanced the resemblance between the moving objects in the display and the motion of objects in the real world, thereby amplifying the sense of reality in the object motion.
Overall, this study offers valuable insights into how eye movements impact visual perception, considering the spatial features of objects. The predictions made by the developed model suggest that the observed behavioral patterns, such as elevated temporal sensitivity to stimuli containing spatial edges, are outcomes of the spatiotemporal integration process occurring in our early visual system. By investigating the intricate relationship between eye movements, object motion, spatial characteristics of visual stimuli, and visual perception, we deepen our understanding of how visual system processes and integrates visual information.clos