Showing papers by "Tokyo Institute of Technology published in 2023"

Swelling‐induced Mechanochromism in Multinetwork Polymers

Abstract: We report a novel and versatile approach to achieving swelling-induced mechanochemistry using a multinetwork (MN) strategy that enables polymer networks to repeatedly swell with monomers and solvents. The isotropic expansion of the first network (FN) provides sufficient force to drive the mechanochemical scission of a radical-based mechanophore, difluorenylsuccinonitrile (DFSN). Although prompt recombination generally occurs in such highly mobile environments, the resulting pink radicals are kinetically stabilized in the gels, probably due to limited diffusion in the extended polymer chains. Moreover, the DFSN embedded in the isotropically strained chain exhibits increased thermal reactivity, which can be reasonably explained by an entropic contribution of the FN to the dissociation. The utility of the MN polymers is demonstrated not only in terms of swelling-force-induced network modification, but also in the context of tunable reactivity of the dissociative unit through proper design of the hierarchical network architecture.

Prevalence of Repeating Earthquakes in the Continental Crust and Subducting Slabs: Triggering of Earthquakes by Aseismic Slip

Abstract: Repeating earthquakes, or repeaters, which repeatedly rupture the same location and release the strain energy, are interpreted as repeated ruptures of an isolated asperity patch surrounded by a stable sliding regime. While repeaters are frequently observed along plate-boundary faults, the occurrence of repeater sequences are reported in various tectonic settings. Here we systematically investigate whether repeaters occur in the continental crust and subducting slabs beneath the Japanese Islands and show a prevalence of repeaters in both locations. The crustal and intraslab repeaters show the power-law decay of seismicity rates that is identical to that along plate-boundary faults and occur on well-defined fault planes coincidentally with non-repeating earthquakes. These observations suggest that repeaters share a common generation process independent of the tectonics regime and are not distinct from non-repeaters in their source locations and occurrence times. We thus infer that repeaters and non-repeaters are both generated by ruptures of locked asperities in response to stress loading by aseismic slip in the surrounding stable regime. Repeater sequences can be observed when aseismic slip is large enough to rupture an isolated asperity more than twice, while no repeaters are generated when the amount of aseismic slip is not sufficient to cause multiple ruptures at an isolated asperity. Since an earthquake cannot be triggered unless the amount of the aseismic stress loading exceeds the strength of asperities at the fault, hidden aseismic slip probably occurs repeatedly and frequently during an interseismic period.

Plastic loss of motile cilia in the gills of <i>Polypterus</i> in response to high <scp> CO ₂ </scp> or terrestrial environments

Abstract: The evolutionary transition of vertebrates from water to land during the Devonian period was accompanied by major changes in animal respiratory systems in terms of physiology and morphology. Indeed, the fossil record of the early tetrapods has revealed the existence of internal gills, which are vestigial fish-like traits used underwater. However, the fossil record provides only limited data on the process of the evolutionary transition of gills from fish to early tetrapods. This study investigated the gills of Polypterus senegalus, a basal ray-finned/amphibious fish which shows many ancestral features of stem Osteichthyes. Based on scanning electron microscopy observations and transcriptome analysis, the existence of motile cilia in the gills was revealed which may create a flow on the gill surface leading to efficient ventilation or remove particles from the surface. Interestingly, these cilia were observed to disappear after rearing in terrestrial or high CO2 environments, which mimics the environmental changes in the Devonian period. The cilia re-appeared after being returned to the original aquatic environment. The ability of plastic changes of gills in Polypterus revealed in this study may allow them to survive in fluctuating environments, such as shallow swamps. The ancestor of Osteichthyes is expected to have possessed such plasticity in the gills, which may be one of the driving forces behind the transition of vertebrates from water to land.

Sarcopenia: Molecular mechanism and current nutritional approach

Abstract: Sarcopenia is characterized by a gradual slowing of movement due to loss of muscle mass and quality, loss of power and strength, increased risk of injury from falls, and often frailty. In this article, we focus on recent advances in nutritional approaches to control sarcopenia. Because nutritional studies in humans are rather limited, this article includes many results from nutritional studies in mammals. The combination of supplements containing amino acids and resistance training is the gold standard for preventing sarcopenia. Protein (amino acid) supplements alone do not have a significant effect on muscle strength or muscle mass in sarcopenia. Tea catechins, soy isoflavones, and ursolic acid are interesting candidates to combat sarcopenia, but both more systematic basic research on this treatment and, of course, clinical studies in humans are needed. Mild caloric restriction (CR, 15–25%) may also be effective against age-related muscle atrophy in humans.

In vitro cellular biocompatibility and in vivo degradation behavior of calcium phosphate-coated ZK60 magnesium alloy

Abstract: Calcium phosphate (Ca-P) surface coating is a simple but effective way to enhance both corrosion resistance and biocompatibility of ZK60 magnesium alloy. However, cell compatibility on different Ca-P layers coated on ZK60 alloy has seldom been investigated. In this study, the effects of type, morphology and corrosion protection of several Ca-P coatings formed at pH 6.5, 7.8 and 10.2 on cell behavior were examined by using an osteoblastic cell line MC3T3-E1. Furthermore,in vivobehavior in rabbits of the alloy coated with the optimum Ca-P layer was also studied. It was found that the surface factors governed the cell morphology and density. The coating morphology plays a dominant role in these surface factors. The sample coated at pH 7.8 showed the best cellular biocompatibility, suggesting that the hydroxyapatite (HAp) layer formed at pH 7.8 was the optimum coating. In rabbits, this optimum coating enhanced remarkably the corrosion resistance of the alloy. During implantation, the outermost crystals of the HAp coating were shortened and thinned due to the dissolution of HAp caused by the body fluid of the rabbits. It is indicated that ZK60 alloy coated at pH 7.8 can be applied as a biodegradable implant.

High pressure studies of transition metal oxides

Abstract: Transition metal oxides exhibit a wide variety of functions—such as metallic conductivity, superconductivity, magnetism, magnetoresistance, ferroelectricity, piezoelectricity and even catalytic activity—depending on the composition and structure. High pressure stabilizes dense structures with large coordination numbers such as perovskites, and also stabilizes cations with unusually high valences, such as Fe 4+ and Ni 3+ . Because of these clear trends, high-pressure syntheses of functional transition metal oxides are intensively performed. Transition metal oxides prepared by high-pressure synthesis and investigations of structural and property changes under pressure will be reviewed.

Spatiotemporal variability of current and future sub‐daily rainfall in Japan using state‐of‐the‐art high‐quality datasets

Abstract: Using potentially best available rainfall data sets for the entire country of Japan (spatial scales of 1- and 20-km), we analyze the 1–24 hr and city-scale (1–400 km2) extreme rainfalls for both current (2006–2020) and future periods (2081–2109) at 1.5 K global warming scenario, complementing previous work that focuses on either coarse spatial and temporal scales or other warming scenarios (e.g., RCP and 2 K warming scenarios). A peak-over-threshold (POT)-based approach is applied to compute areal reduction factor (ARF) for subsequently establishing intensity-duration-area-frequency (IDAF) curves. Our results reveal that ARF values generally decrease with increasing area size and increase with longer duration and are affected by multiple underlying physical phenomena. Moreover, we find a greater increase in the rainfall intensities for shorter durations and higher return periods, ranging from 9.4% (1-hr) to 6.2% (24-hr), averaged for all return periods and 8.3% (25-year) to 7.3% (2-year), averaged for all rainfall durations. Spatially, extreme rainfall intensities are projected to increase by 8.9% in northern Japan (albeit with a less intense rainfall intensity in the current period), which is greater than the rest of the country (6.8%), underscoring the need to focus more on infrastructure designs in northern Japan. The projected IDAF curves further display an increase in the frequency of extreme events at city-scale, for example, 25-year extreme rainfall events in 2006–2020 would likely be 5-10-year events in 2081–2109. Our results with the state-of-the-art data and implementable approach can be utilized for policymaking to reduce the warming-induced risks in Japan and beyond.

The Effect of the Axle End Structure and Number of Through‐Space Bonds on the Properties of Rotaxane Crosslinked Polymers

Abstract: A rotaxane crosslinker (RC) is known to toughen the resulting rotaxane crosslinked polymer (RCP) via a stress dispersion effect that is attributed to the movable nature of the crosslinking structure. To evaluate this toughening mechanism in detail, a series of structure-definite RCs equipped with different axle end structures or different numbers of wheel components were synthesized, and subjected to free radical polymerization with a vinyl monomer to obtain RCPs. Analyses of the obtained RCPs revealed that the size of the axle end structure should be well-balanced to produce a strong toughening effect, and a [3]rotaxane crosslinker works more effectively than [2]rotaxane to toughen RCPs. The mobility of the crosslinking points, in terms of rotational and flipping movements, was more crucial to toughening the RCP than that of translational movement along the axle. The first observation of the above crucial findings proved the utility of the systematic molecular design used in this study.

Identification of Surgical Forceps Using YOLACT++

Abstract: Forceps tracking in laparoscopic surgery contributes to improved surgical outcomes. We identified forceps by deep learning. Since it is important to identify forceps in real-time, we selected YOLACT++ for fast and accurate segmentation and verified whether the detection speed can be maintained in the video. We annotated a total of 2537 images combining multiple datasets including various surgical environments, and divided them into training, validation, and test data at a ratio of approximately 8:1:1. In training, the hyperparameters were adjusted while performing holdout validation to determine the optimal combination of hyperparameters that maximized the identification speed. The training was conducted with a batch size of 32, a number of iterations of 100106, and a number of epochs of 1588, and the results showed that the forceps identification speed was 25.79 fps and accuracy was 84.31%. The results of the test using the trained model with this hyperparameter showed that the forceps identification speed was 28.01 fps and accuracy was 71.42% for images, and the forceps identification speed was 17.70 fps for the video (frame rate 60 fps, resolution 584 × 328).

Search of Complex Transcendental Roots of a Combination of a Nonlinear Equation and a Polynomial

Abstract: Target nonlinear equation is limited within ordinary differential equations with one-point boundary value or two-point boundary value problems, and the order of a polynomial is assumed to be finite and it is assumed that at least one complex solution exists (which may be real). The purpose is to find numerically at least one root (not necessarily all of them). Examples are similar equations to Chandrasekhar’s white dwarf equation, nonlinear differential equation exactly expressible through Weierstrass function, and some internal gas explosion equations.

Direct observation of transient species and chemical reactions in a pore observed by synchrotron radiation

Abstract: Here, we have described the direct observation of transient chemical species and chemical reactions using synchrotron radiation. Direct observation of transient and unstable chemical species by X-ray diffraction can greatly enhance our understanding of chemical reactions. On top of that, the use of pores in coordination networks has various applications and is a promising method to elucidate the structure of molecular species that do not inherently crystallize. In particular, kinetic assembly of coordination networks can generate interactive sites in the pores, which is very useful for trapping unstable species. Thus, the methodology using porous coordination networks, i.e., crystalline molecular flasks, allows us to observe a variety of crystalline phase reactions. At the same time, the development of synchrotron radiation and X-ray detectors has made it possible to challenge the microscopic crystals found in MOF crystals. This means that structural analysis is now possible with a smaller amount of target guest sample. In addition, spectroscopic methods and theoretical calculations have been developed to elucidate the electronic structure of these chemical species.

Hurwitz class numbers with level and modular correspondences

Abstract: In this paper, we prove Hurwitz-Eichler type formulas for Hurwitz class numbers with each level $ M $ when the modular curve $ X_0(M) $ has genus zero. A key idea is to calculate intersection numbers of modular correspondences with the level in two different ways. A generalization of Atkin-Lehner involutions for $ \Gamma_0(M) $ and its subgroup $ \Gamma_0^{(M')}(M) $ is introduced to calculate intersection multiplicities of modular correspondences at cusps.

Photoelectrochemical Water Oxidation Using Cobalt Phosphate‐Modified Nitrogen‐Doped Titania Nanotube Arrays

Abstract: Water Splitting In article number 2200229, Kazuhiko Maeda, Hyunwoong Park, and co-workers accomplished stable photoelectrochemical water oxidation driven by sunlight to yield oxygen gas with cobalt phosphate-modified, nitrogen-doped titania nanotube arrays, which can absorb visible light with wavelengths as long as 580 nm.

Minimal mass blow-up solutions for nonlinear Schrödinger equations with a potential

Abstract: We consider a mass critical nonlinear Schrödinger equation with a real-valued potential. In this work, we construct a minimal mass solution that blows up at finite time, under weaker assumptions on spatial dimensions and potentials than Banica, Carles, and Duyckaerts (2011). Moreover, we show that the blow-up solution converges to a blow-up profile. Furthermore, we improve some parts of the arguments in Raphaël and Szeftel (2011) and Le Coz, Martel, and Raphaël (2016).

Experimental phase diagram study of the TiAl-rich part of the Ti–Al–Ni ternary system

Abstract: Phase equilibria of the TiAl-rich part of the Ti–Al–Ni ternary system have been studied experimentally by scanning electron microscopy and electron probe micro-analysis of heat-treated alloys. Partial isothermal sections involving the liquid, β-Ti, α-Ti, α2-Ti3Al, γ-TiAl and τ3-Al3NiTi2 phases were constructed between 1623 and 1273 K. Eight three-phase regions of the L + β + α, L + α + γ, L + β + γ, β + α + γ, L + β + τ3, β + γ + τ3, β + α2 + τ3 and α2 + γ + τ3 were derived. Extrapolations of these tie-triangles indicate the occurrence of three transition-type reactions; L + α = β + γ at around 1593 K, L + γ = β + τ3 at around 1553 K, and β + γ = α + τ3 at around 1393 K. The Ni solid solubility in the α and α2 phase is extremely low, less than 1 at.% in all studied temperature ranges.

Priority-based state machine synthesis that relaxes behavior design of multi-arm manipulators in dynamic environments

Abstract: This paper presents a framework governing multiple state machines (SMs) to generate behaviors for kinematically-coupled multi-arm robots. A SM is one of the most used tools to switch controllers in robotics, however, it represents only one motion at a certain time. Such a limit of representation not only restricts the potential of the kinematical redundancy but also significantly increases the number of situations we have to consider in behavior design. To relax the problem, this paper provides a distributed design scheme and an online synthesis method for SMs. The base of the framework is a task-priority-based control method for redundant robots. We expand it by introducing an abstract data structure specialized in robotic behaviors. The abstract reformulation naturally connects with SMs so that the framework realizes parallelism of sequential logic. A priority queue constructed in each control loop integrates SMs designed for each effector, and the framework automatically generates whole-body behaviors online. In dynamic simulations, the framework governs four SMs and achieves reaching tasks with a dual-arm manipulator at 1 kHz. It is shown that the loose coupling of the SMs yields reactive and flexible decisions in a dynamic environment.

A study on the design methods of “the garden city” planning by Yoshikazu Uchida: Focusing on the process of making his planning

Abstract: Yoshikazu Uchida—the famous Japanese architect and the director of Dojunkai—made a residential plan named the “garden city plan” just before the Great Kanto Earthquake. In this study, the authors report the design methods of his plan with focusing on the process done by Uchida from 1919 to 1922. By making a comparison between the three drawings, the following four design methods of his plan are found out. First, his plan has a graded configuration of the street system. Second, shops are placed around circular plazas and along a main road. Thirdly, there is a diversity in the arrangement of public buildings. Fourthly, specific open space is surrounded by buildings. These design methods share characteristics with those of Dojunkai's residential districts. Therefore, one of the reasons why Dojunkai realized the design methods of modern residential planning in its estates after the Great Kanto Earthquake is because Uchida had practiced the above-mentioned design methods on his drawings through the “garden city plan.”

Hydride Anion Substitution Boosts Thermoelectric Performance of Polycrystalline SrTiO ₃ via Simultaneous Realization of Reduced Thermal Conductivity and High Electronic Conductivity

Abstract: The development of environmentally benign thermoelectric materials with high energy conversion efficiency (ZT) continues to be a long-standing challenge. So far, high ZT has been achieved using heavy elements to reduce lattice thermal conductivity (κlat). However, it is not preferred to use such elements because of their environmental load and high material cost. Here a new approach utilizing hydride anion (H−) substitution to oxide ion is proposed for ZT enhancement in thermoelectric oxide SrTiO3 bulk polycrystals. Light element H− substitution largely reduces κlat from 8.2 W/(mK) of SrTiO3 to 3.5 W/(mK) for SrTiO3−xHx with x = 0.216. The mass difference effect on phonon scattering is small in the SrTiO3−xHx, while local structure distortion arising from the distributed Ti−(O,H) bond lengths strongly enhances phonon scattering. The polycrystalline SrTiO3−xHx shows high electronic conductivity comparable to La-doped SrTiO3 single crystal because the H− substitution does not form a grain boundary potential barrier and thus suppresses electron scattering. As a consequence, SrTiO3−xHx bulk exhibits maximum ZT = 0.11 at room temperature and the ZT value increases continuously up to 0.22 at T = 657 K. The H− substitution idea offers a new approach for ZT enhancement in thermoelectric materials without utilizing heavy elements.

Molecular clusters

Abstract: Clusters are ultrasmall particles with about 1 nm size composed of a dozen atoms and show peculiar catalytic, optical, and magnetic activities. In contrast to bulks and nanoparticles, adding or eliminating only a single atom drastically changes a cluster's properties due to its amorphous structure and quantum size effects. Interestingly, some clusters called superatoms have atom-mimic electronic configurations and characteristics; thus, the periodic table of clusters has been proposed. Recent developments allow us to obtain clusters in the gas, liquid, and solid phases and use them as materials. Clusters will be new building blocks in future science.

Site‐Selective Synthesis and Concurrent Immobilization of Imine‐Based Covalent Organic Frameworks on Electrodes Using an Electrogenerated Acid

Abstract: Imine-based covalent organic frameworks (COFs) are crystalline porous materials with prospective uses in various devices. However, general bulk synthetic methods usually produce COFs as powders that are insoluble in most of the common organic solvents, arising challenges for the subsequent molding and fixing of these materials on substrates. Here, we report a novel synthetic methodology that utilizes an electrogenerated acid (EGA), which is produced at an electrode surface by electrochemical oxidation of a suitable precursor, acting as an effective Brønsted acid catalyst for imine bond formation from the corresponding amine and aldehyde monomers. Simultaneously, it provides the corresponding COF film deposited on the electrode surface. The COF structures obtained with this method exhibited high crystallinities and porosities, and the film thickness could be controlled. Furthermore, such process was applied for the synthesis of various imine-based COFs, including a three-dimensional (3D) COF structure.

Detecting directional forces in the evolution of grammar: A case study of the English perfect with intransitives across EEBO, COHA, and Google Books

Abstract: Abstract Languages have diverse characteristics that have emerged through evolution. In modern English grammar, the perfect is formed with have +PP (past participle), but in earlier English, the be +PP form also existed. It is widely recognised that the auxiliary verb BE was replaced by HAVE throughout evolution, except for some special cases. However, whether this evolution was caused by natural selection or random drift is still unclear. Here we examined directional forces in the evolution of the English perfect with intransitive by combining three large-scale data sources: Early English Books Online (EEBO), Corpus of Historical American English (COHA), and Google Books. We found that most intransitive verbs exhibited an apparent transition from be +PP to have +PP, most of which were classified as ‘selection’ by a deep neural network-based model. These results suggest that the English perfect could have evolved through natural selection rather than random drift, and provide insights into the cultural evolution of grammar.