Showing papers by "Tokyo Institute of Technology published in 2022"

Recent Progress on Mixed-Anion Materials for Energy Applications

Abstract: Mixed-anion compounds, in which multiple anions such as O2−, N3−, and H− are contained in the same compound, have recently attracted attention. Because mixed-anion compounds have a unique crystal structure with multiple anions coordinated to cations, materials with fundamentally new and innovative functions are expected to be developed for various chemistry and physics applications, including catalysts, batteries, and superconductors. In this Account, recent progress in the development of new mixed-anion compounds by the MEXT mixed-anion project is described, with emphasis on results related to the development of materials used as photocatalysts/photoelectrodes, phosphors, secondary battery components, conductors, and thermoelectric materials. Mixed-anion compounds containing more than one anionic species in the same phase can exhibit emergent properties and/or functions that are unattainable with their single-anion counterparts. This Account describes recent progress in the development of new mixed-anion compounds for various applications related to energy, with emphasis on our interdisciplinary collaboration in a national project on mixed-anion materials.

Post-combustion CO2 capture and separation in flue gas based on hydrate technology：A review

Abstract: Hydrate-based CO2 separation technology is limited by complex formation conditions and low separation efficiency, makes it temporarily unable to realize commercial application. In this review, according to the superiority of additives in strengthening hydrate formation, the effects of different additives on the thermodynamics-kinetics of hydrate formation were systematically summarized, and the strengthening mechanism was further elaborated from the perspectives of hydrate structure change and gas selectivity. Among them, quaternary ammonium salt is more environmentally friendly, and the separation factor reached 37 with TBAF, more than 90 mol% CO2 captured by the two-stage hydrate + membrane separation method. In addition, based on the characteristics of nanoparticles in enhancing heat and mass transfer, the impact of nanoparticles on the formation of CO2 hydrate was summarized, which provided a new idea for the research of additives. More importantly, the effects of experimental conditions and process flow on separation efficiency were also summarized. Energy analysis showed that the use of thermodynamic additives significantly reduced the investment cost of the system by more than 50%. However, higher hydrate formation heat leads to higher energy consumption, and the presence of kinetic additives improves significantly, emphasizing the urgency of developing more stable and lower formation heat thermodynamic additives and exploring the effect of mixed additives on commercial applications. At present, stirring methods were mostly used to strengthen hydrate formation with higher energy consumption. Future research should also strive to carry out experimental measurements under static conditions, and constantly optimize the reaction vessel and process.

Post-combustion CO2 capture and separation in flue gas based on hydrate technology：A review

Abstract: Hydrate-based CO2 separation technology is limited by complex formation conditions and low separation efficiency, makes it temporarily unable to realize commercial application. In this review, according to the superiority of additives in strengthening hydrate formation, the effects of different additives on the thermodynamics-kinetics of hydrate formation were systematically summarized, and the strengthening mechanism was further elaborated from the perspectives of hydrate structure change and gas selectivity. Among them, quaternary ammonium salt is more environmentally friendly, and the separation factor reached 37 with TBAF, more than 90 mol% CO2 captured by the two-stage hydrate + membrane separation method. In addition, based on the characteristics of nanoparticles in enhancing heat and mass transfer, the impact of nanoparticles on the formation of CO2 hydrate was summarized, which provided a new idea for the research of additives. More importantly, the effects of experimental conditions and process flow on separation efficiency were also summarized. Energy analysis showed that the use of thermodynamic additives significantly reduced the investment cost of the system by more than 50%. However, higher hydrate formation heat leads to higher energy consumption, and the presence of kinetic additives improves significantly, emphasizing the urgency of developing more stable and lower formation heat thermodynamic additives and exploring the effect of mixed additives on commercial applications. At present, stirring methods were mostly used to strengthen hydrate formation with higher energy consumption. Future research should also strive to carry out experimental measurements under static conditions, and constantly optimize the reaction vessel and process.

First gadolinium loading to Super-Kamiokande

Abstract: In order to improve Super-Kamiokande’s neutron detection efficiency and to thereby increase its sensitivity to the diffuse supernova neutrino background flux, 13 tons of Gd2(SO4)3⋅8H2O (gadolinium sulfate octahydrate) was dissolved into the detector’s otherwise ultrapure water from July 14 to August 17, 2020, marking the start of the SK-Gd phase of operations. During the loading, water was continuously recirculated at a rate of 60 m3/h, extracting water from the top of the detector and mixing it with concentrated Gd2(SO4)3⋅8H2O solution to create a 0.02% solution of the Gd compound before injecting it into the bottom of the detector. A clear boundary between the Gd-loaded and pure water was maintained through the loading, enabling monitoring of the loading itself and the spatial uniformity of the Gd concentration over the 35 days it took to reach the top of the detector. During the subsequent commissioning the recirculation rate was increased to 120 m3/h, resulting in a constant and uniform distribution of Gd throughout the detector and water transparency equivalent to that of previous pure-water operation periods. Using an Am–Be neutron calibration source the mean neutron capture time was measured to be 115±1 μs, which corresponds to a Gd concentration of 111±2 ppm, as expected for this level of Gd loading. This paper describes changes made to the water circulation system for this detector upgrade, the Gd loading procedure, detector commissioning, and the first neutron calibration measurements in SK-Gd.

Millimetre-scale magnetocardiography of living rats with thoracotomy

Abstract: Abstract Magnetocardiography is a contactless imaging modality for electric current propagation in the cardiovascular system. Although conventional sensors provide sufficiently high sensitivity, their spatial resolution is limited to a centimetre-scale, which is inadequate for revealing the intra-cardiac electrodynamics such as rotational waves associated with ventricular arrhythmias. Here, we demonstrate invasive magnetocardiography of living rats at a millimetre-scale using a quantum sensor based on nitrogen-vacancy centres in diamond. The acquired magnetic images indicate that the cardiac signal source is well explained by vertically distributed current dipoles, pointing from the right atrium base via the Purkinje fibre bundle to the left ventricular apex. We also find that this observation is consistent with and complementary to an alternative picture of electric current density distribution calculated with a stream function method. Our technique will enable the study of the origin and progression of various cardiac arrhythmias, including flutter, fibrillation, and tachycardia.

Peptide-RNA Coacervates as a Cradle for the Evolution of Folded Domains

Abstract: Peptide-RNA coacervates can result in the concentration and compartmentalization of simple biopolymers. Given their primordial relevance, peptide-RNA coacervates may have also been a key site of early protein evolution. However, the extent to which such coacervates might promote or suppress the exploration of novel peptide conformations is fundamentally unknown. To this end, we used electron paramagnetic resonance spectroscopy (EPR) to characterize the structure and dynamics of an ancient and ubiquitous nucleic acid binding element, the helix-hairpin-helix (HhH) motif, alone and in the presence of RNA, with which it forms coacervates. Double electron–electron resonance (DEER) spectroscopy applied to singly labeled peptides containing one HhH motif revealed the presence of dimers, even in the absence of RNA. Moreover, dimer formation is promoted upon RNA binding and was detectable within peptide-RNA coacervates. DEER measurements of spin-diluted, doubly labeled peptides in solution indicated transient α-helical character. The distance distributions between spin labels in the dimer and the signatures of α-helical folding are consistent with the symmetric (HhH)2-Fold, which is generated upon duplication and fusion of a single HhH motif and traditionally associated with dsDNA binding. These results support the hypothesis that coacervates are a unique testing ground for peptide oligomerization and that phase-separating peptides could have been a resource for the construction of complex protein structures via common evolutionary processes, such as duplication and fusion.

Atg39 links and deforms the outer and inner nuclear membranes in selective autophagy of the nucleus

Abstract: In selective autophagy of the nucleus (hereafter nucleophagy), nucleus-derived double-membrane vesicles (NDVs) are formed, sequestered within autophagosomes, and delivered to lysosomes or vacuoles for degradation. In Saccharomyces cerevisiae, the nuclear envelope (NE) protein Atg39 acts as a nucleophagy receptor, which interacts with Atg8 to target NDVs to the forming autophagosomal membranes. In this study, we revealed that Atg39 is anchored to the outer nuclear membrane via its transmembrane domain and also associated with the inner nuclear membrane via membrane-binding amphipathic helices (APHs) in its perinuclear space region, thereby linking these membranes. We also revealed that autophagosome formation-coupled Atg39 crowding causes the NE to protrude toward the cytoplasm, and the tips of the protrusions are pinched off to generate NDVs. The APHs of Atg39 are crucial for Atg39 crowding in the NE and subsequent NE protrusion. These findings suggest that the nucleophagy receptor Atg39 plays pivotal roles in NE deformation during the generation of NDVs to be degraded by nucleophagy.

A Compact High-Power Noninverting Bidirectional Buck–Boost Chopper for Onboard Battery Energy Storage Systems

Abstract: This article proposes a noninverting bidirectional buck–boost chopper accompanied by an auxiliary converter for battery storage that is installed in a light rail vehicle. The proposed chopper is composed of two half-bridge cells called the main converter, an auxiliary converter consisting of many full-bridge converters connected in cascade, and a small-sized inductor. It is controlled such that the capacitors of the auxiliary converter store and release most of the chopper energy instead of relying solely on a bulky and heavy inductor. As a result, it is lighter and smaller than the four-switch noninverting buck–boost chopper. The operation, as well as the control of the proposed chopper, are experimentally tested using a down-scaled prototype. Furthermore, a comparison with the four-switch noninverting buck–boost chopper with respect to mass, volume, and efficiency is made to verify the efficacy of the proposed chopper.

Imaging translational control by Argonaute with single-molecule resolution in live cells

Abstract: A major challenge to our understanding of translational control has been deconvolving the individual impact specific regulatory factors have on the complex dynamics of mRNA translation. MicroRNAs (miRNAs), for example, guide Argonaute and associated proteins to target mRNAs, where they direct gene silencing in multiple ways that are not well understood. To better deconvolve these dynamics, we have developed technology to directly visualize and quantify the impact of human Argonaute2 (Ago2) on the translation and subcellular localization of individual reporter mRNAs in living cells. We show that our combined translation and Ago2 tethering sensor reflects endogenous miRNA-mediated gene silencing. Using the sensor, we find that Ago2 association leads to progressive silencing of translation at individual mRNA. Silencing was occasionally interrupted by brief bursts of translational activity and took 3-4 times longer than a single round of translation, consistent with a gradual increase in the inhibition of translation initiation. At later time points, Ago2-tethered mRNAs cluster and coalesce with P-bodies, where a translationally silent state is maintained. These results provide a framework for exploring miRNA-mediated gene regulation in live cells at the single-molecule level. Furthermore, our tethering-based, single-molecule reporter system will likely have wide-ranging application in studying RNA-protein interactions.

Live imaging of transcription sites using an elongating RNA polymerase II-specific probe.

Abstract: In eukaryotic nuclei, most genes are transcribed by RNA polymerase II (RNAP2), whose regulation is a key to understanding the genome and cell function. RNAP2 has a long heptapeptide repeat (Tyr1-Ser2-Pro3-Thr4-Ser5-Pro6-Ser7), and Ser2 is phosphorylated on an elongation form. To detect RNAP2 Ser2 phosphorylation (RNAP2 Ser2ph) in living cells, we developed a genetically encoded modification-specific intracellular antibody (mintbody) probe. The RNAP2 Ser2ph-mintbody exhibited numerous foci, possibly representing transcription "factories," and foci were diminished during mitosis and in a Ser2 kinase inhibitor. An in vitro binding assay using phosphopeptides confirmed the mintbody's specificity. RNAP2 Ser2ph-mintbody foci were colocalized with proteins associated with elongating RNAP2 compared with factors involved in the initiation. These results support the view that mintbody localization represents the sites of RNAP2 Ser2ph in living cells. RNAP2 Ser2ph-mintbody foci showed constrained diffusional motion like chromatin, but they were more mobile than DNA replication domains and p300-enriched foci, suggesting that the elongating RNAP2 complexes are separated from more confined chromatin domains.

Resilient Real-Valued Consensus in Spite of Mobile Malicious Agents on Directed Graphs

Abstract: This article addresses novel real-valued consensus problems in the presence of malicious adversaries that can move within the network and induce faulty behaviors in the attacked agents. By adopting several mobile adversary models from the computer science literature, we develop protocols which can mitigate the influence of such malicious agents. The algorithms follow the class of mean subsequence reduced (MSR) algorithms, under which agents ignore the suspicious values received from neighbors during their state updates. Different from the static adversary models, even after the adversaries move away, the infected agents may remain faulty in their values, whose effects must be taken into account. We develop conditions on the network structures for both the complete and non-complete directed graph cases, under which the proposed algorithms are guaranteed to attain resilient consensus. The tolerance bound for network conditions becomes more strict as the adversaries are allowed to have more power. Extensive simulations are carried out over random graphs to verify the effectiveness of our approach when the information of the adversarial agents in terms of their models and numbers is unknown to the agents.

Novel Fluorescence-Based Method for Rapid Quantification of Live Bacteria in River Water and Treated Wastewater

Abstract: Monitoring bacteria is essential for ensuring microbial safety of water sources, which include river water and treated wastewater. The plate count method is common for monitoring bacterial abundance, although it cannot detect all live bacteria such as viable but non-culturable bacteria, causing underestimation of microbial risks. Live/Dead BacLight kit, involving fluorochromes SYTO 9 and propidium iodide (PI), provides an alternative to assess bacterial viability using flow cytometry or microscopy. However, its application is limited due to the high cost of flow cytometry and the inapplicability of microscopy to most environmental waters. Thus, this study introduces the combination of BacLight Kit and fluorescence spectroscopy for quantifying live bacteria in river water and treated wastewater. Mixtures of live and dead Escherichia coli (E. coli) with various ratios and total cell concentrations were stained with SYTO 9 and PI and measured by fluorescence spectroscopy. The fluorescence emission peak area of SYTO 9 in the range of 500–510 nm at the excitation wavelength of 470 nm correlates linearly with the viable cell counts (R2 > 0.99, p < 0.0001) with only slight variations in the complex water matrix. The tested method can quantify the concentration of live E. coli from 3.67 × 104 to 2.70 × 107 cells/mL. This method is simple, sensitive and reliable for quantifying live bacteria in environmental water, which can be later integrated into real-time monitoring systems

Novel fluorescence-based method for rapid quantification of live bacteria in river water and treated wastewater

Abstract: Monitoring bacteria is essential for ensuring microbial safety of water sources, including river water and treated wastewater.

Rotating Kerr-Newman space-times in metric-affine gravity

Abstract: Abstract We present new rotating vacuum configurations endowed with both dynamical torsion and nonmetricity fields in the framework of Metric-Affine gauge theory of gravity. For this task, we consider scalar-flat Weyl-Cartan geometries and obtain an axisymmetric Kerr-Newman solution in the decoupling limit between the orbital and the spin angular momentum. The corresponding Kerr-Newman-de Sitter solution is also compatible with a cosmological constant and additional electromagnetic fields.

Predicting mangrove forest dynamics across a soil salinity gradient using an individual-based vegetation model linked with plant hydraulics

Abstract: Abstract. In mangrove forests, soil salinity is one of the most significant environmental factors determining forest distribution and productivity as it limits plant water uptake and carbon gain. However, salinity control on mangrove productivity through plant hydraulics has not been investigated by existing mangrove models. Here we present a new individual-based model linked with plant hydraulics to incorporate physiological characterization of mangrove growth under salt stress. Plant hydraulics was associated with mangroves' nutrient uptake and biomass allocation apart from water flux and carbon gain. The developed model was performed for two coexisting species – Rhizophora stylosa and Bruguiera gymnorrhiza – in a subtropical mangrove forest in Japan. The model predicted that the productivity of both species was affected by soil salinity through downregulation of stomatal conductance. Under low-soil-salinity conditions (< 28 ‰), B. gymnorrhiza trees grew faster and suppressed the growth of R. stylosa trees by shading that resulted in a B. gymnorrhiza-dominated forest. As soil salinity increased, the productivity of B. gymnorrhiza was significantly reduced compared to R. stylosa, which led to an increase in biomass of R. stylosa despite the enhanced salt stress (> 30 ‰). These predicted patterns in forest structures across the soil salinity gradient remarkably agreed with field data, highlighting the control of salinity on productivity and tree competition as factors that shape the mangrove forest structures. The model reproducibility of forest structures was also supported by the predicted self-thinning processes, which likewise agreed with field data. Aside from soil salinity, seasonal dynamics in atmospheric variables (solar radiation and temperature) were highlighted as factors that influence mangrove productivity in a subtropical region. This physiological principle-based improved model has the potential to be extended to other mangrove forests in various environmental settings, thus contributing to a better understanding of mangrove dynamics under future global climate change.