Exciting space-time surface plasmon polaritons by irradiating a nanoslit structure.

Space-time (ST) wave packets are propagation-invariant pulsed optical beams that travel freely in dielectrics at a tunable group velocity without diffraction or dispersion. Because ST wave packets maintain these characteristics even when only one transverse dimension is considered, they can realize surface-bound waves (e.g., surface plasmon polaritons at a metal-dielectric interface, which we call ST-SPPs) that have the same unique characteristics as their freely propagating counterparts. However, because the spatiotemporal spectral structure of ST-SPPs is key to their propagation invariance on the metal surface, their excitation methodology must be considered carefully. Using finite-difference time-domain simulations, we show that an appropriately synthesized ST wave packet in free space can be coupled to an ST-SPP via a single nanoscale slit inscribed in the metal surface. Our calculations confirm that this excitation methodology yields surface-bound ST-SPPs that are localized in all dimensions (and can thus be considered as plasmonic "bullets"), which travel rigidly at the metal-dielectric interface without diffraction or dispersion at a tunable group velocity.

Carbon dioxide uptake in a eutrophic stratified reservoir: Freshwater carbon sequestration potential.

Carbon capture and storage due to photosynthesis activities has been proposed as a carbon sink to mitigate climate change. To enhance such mitigation, previous studies have shown that freshwater lakes should be included in the carbon sink, since they may capture as much carbon as coastal areas. In eutrophic freshwater lakes, there is uncertainty about whether the equilibrium equation can estimate the partial pressure of carbon dioxide (pCO2), owing to the presence of photosynthesis due to phytoplankton, and pH measurement error in freshwater fluid. Thus, this study investigated the applicability of the equilibrium equation and revealed the need to modify it. The modified equilibrium equation was successfully applied to reproduce pCO2 based on total alkalinity and pH through field observations. In addition, pCO2 at the water surface was lower than the atmospheric partial pressure of carbon dioxide due to photosynthesis by phytoplankton during strong stratification. The stratification effect on low pCO2 was verified by using the Net Ecosystem Production (NEP) model, and a submerged freshwater plants such as Potamogeton malaianus were found to have high potential for dissolved inorganic carbon (DIC) sequestration in a freshwater lake. These results should provide a starting point toward more sophisticated methods to investigate the effect of freshwater carbon on DIC uptake in freshwater stratified eutrophic lakes.

Inductive Determination of Rate-Reaction Equation Parameters for Dislocation Structure Formation Using Artificial Neural Network.

The reaction-diffusion equation approach, which solves differential equations of the development of density distributions of mobile and immobile dislocations under mutual interactions, is a method widely used to model the dislocation structure formation. A challenge in the approach is the difficulty in the determination of appropriate parameters in the governing equations because deductive (bottom-up) determination for such a phenomenological model is problematic. To circumvent this problem, we propose an inductive approach utilizing the machine-learning method to search a parameter set that produces simulation results consistent with experiments. Using a thin film model, we performed numerical simulations based on the reaction-diffusion equations for various sets of input parameters to obtain dislocation patterns. The resulting patterns are represented by the following two parameters; the number of dislocation walls (p2), and the average width of the walls (p3). Then, we constructed an artificial neural network (ANN) model to map between the input parameters and the output dislocation patterns. The constructed ANN model was found to be able to predict dislocation patterns; i.e., average errors in p2 and p3 for test data having 10% deviation from the training data were within 7% of the average magnitude of p2 and p3. The proposed scheme enables us to find appropriate constitutive laws that lead to reasonable simulation results, once realistic observations of the phenomenon in question are provided. This approach provides a new scheme to bridge models for different length scales in the hierarchical multiscale simulation framework.

Recalcitrant dissolved organic carbon release and production from aquatic plants leachate.

Leached dissolved organic matter (DOM) from withered aquatic plants plays a critical role as a nutrient source for coastal waters, and potentially contributes to marine carbon fixation. In this study, withered seaweed (Ecklonia cava) and seagrass (Zostera japonica) were incubated under laboratory conditions to estimate the amount and decomposition properties of the resulting leached dissolved organic carbon (DOC) and fluorescence dissolved organic matter (FDOM). Concentrations of leached DOC from E. cava were higher than those from Z. japonica because the cell walls of the former were relatively more easily degraded and hydrolyzed than those of the latter. As humic-like fluorescence increased from the beginning of the incubation period, it was inferred that recalcitrant DOC (RDOC) leached directly from withered aquatic plants. Additionally, recalcitrant component production was attributed to the microbial carbon pump using labile DOC. Leached RDOC from withered aquatic plants contributes to blue carbon and CO2 uptake by photosynthesis.

Highly Dispersed Ni Nanoclusters Spontaneously Formed on Hydrogen Boride Sheets.

Hydrogen boride (HB) sheets are two-dimensional materials comprising a negatively charged hexagonal boron network and positively charged hydrogen atoms with a stoichiometric ratio of 1:1. Herein, we report the spontaneous formation of highly dispersed Ni nanoclusters on HB sheets. The spontaneous reduction reaction of Ni ions by the HB sheets was monitored by in-situ measurements with an ultraviolet-visible spectrometer. Acetonitrile solutions of Ni complexes and acetonitrile dispersions of the HB sheets were mixed in several molar ratios (the HB:Ni molar ratio was varied from 100:0.5 to 100:20), and the changes in the absorbance were measured over time. In all cases, the results suggest that Ni metal clusters grow on the HB sheets, considering the increase in absorbance with time. The absorbance peak position shifts to the higher wavelength as the Ni ion concentration increases. Transmission electron microscopy images of the post-reaction products indicate the formation of Ni nanoclusters, with sizes of a few nanometers, on the HB sheets, regardless of the preparation conditions. These highly dispersed Ni nanoclusters supported on HB sheets will be used for catalytic and plasmonic applications and as hydrogen storage materials.

Diameter-Change-Induced Transition in Buckling Modes of Defective Zigzag Carbon Nanotubes.

In general, the insertion of Stone-Wales (SW) defects into single-walled carbon nanotubes (SWNTs) reduces the buckling resistance of SWNTs under axial compression. The magnitude of reduction is more noticeable in zigzag-type SWNTs than armchair- or chiral-type SWNTs; however, the relation between the magnitude of reduction and aspect ratio of the zigzag SWNTs remains unclear. This study conducted molecular dynamics (MD) simulation to unveil the buckling performance of zigzag SWNTs exhibiting SW defects with various tube diameter. The dependencies of energetically favorable buckling modes and the SW-defect induced reduction in the critical buckling point on the tube diameter were investigated in a systematic manner. In particular, an approximate expression for the critical buckling force as a function of the tube diameter was formulated based on the MD simulation data.

Silica removal at sewage treatment plants causes new silica deficiency.

The dissolved silicate (DSi) concentration in coastal waters has decreased due to anthropogenic activities. Many studies have indicated that dam construction is a main reason for this reduction. However, recently, dam construction alone has not been sufficient to explain the DSi reduction in some coastal waters. In this study, we focused on silica removal at sewage treatment plants (STPs). DSi and particulate silica (PSi) concentrations were measured in STP influent and effluent waters from September 2020 to September 2021. Dissolution experiments on PSi were also conducted to estimate the fraction of soluble PSi in the STP influent. DSi and PSi were removed by 29.5% and 96.9%, respectively, at the STP. In addition, the soluble PSi in the STP influent accounted for 20.3% of the PSi removed. Therefore, in addition to the DSi removal in STPs, removal of soluble PSi can also cause potential DSi depletion in downstream and coastal waters. In addition to the effect of dams, the silica supply delivered to coastal waters may be further reduced in the future due to the progress of sewage treatment development in coastal areas.

Resonance-order-dependent plasmon-induced transparency in orthogonally arranged nanocavities.

We investigate plasmon-induced transparency (PIT) in a resonator structure consisting of two orthogonally arranged metal-insulator-metal nanocavities. Finite-difference time- domain simulations reveal that when both cavities in this structure resonate at the same frequency, the PIT effect can be used to induce spectral modulation. This spectral modulation depends on the resonance order of the cavity coupled directly to the external field, as it occurs when first-order resonance is exhibited but not with second-order resonance. We confirmed that this behavior is caused by the discrepancies between odd-order and even-order resonances using classical mechanical models analogous to nanocavities. By tuning the resonance frequency and resonance order of the cavities, one can modulate the spectrum of the resonator structure in an order-selective manner. The resonant order-dependent PIT provides insight into the development of metamaterials that function only at specific resonant orders for incident waves of various bands.

Coarse-Grained Molecular Dynamics Simulation of Polycarbonate Deformation: Dependence of Mechanical Performance by the Effect of Spatial Distribution and Topological Constraints.

Polycarbonate is an engineering plastic used in a wide range of applications due to its excellent mechanical properties, which are closely related to its molecular structure. We performed coarse-grained molecular dynamics (CGMD) calculations to investigate the effects of topological constraints and spatial distribution on the mechanical performance of a certain range of molecular weights. The topological constraints and spatial distribution are quantified as the number of entanglements per molecule (Ne) and the radius of gyration (Rg), respectively. We successfully modeled molecular structures with a systematic variation of Ne and Rg by controlling two simulation parameters: the temperature profile and Kuhn segment length, respectively. We investigated the effect of Ne and Rg on stress-strain curves in uniaxial tension with fixed transverse strain. The result shows that the structure with a higher radius of gyration or number of entanglements has a higher maximum stress (σm), which is mainly due to a firmly formed entanglement network. Such a configuration minimizes the critical strain (εc). The constitutive relationships between the mechanical properties (σm and εc) and the initial molecular structure parameters (Ne and Rg) are suggested.

Machine-Learning-Based Atomistic Model Analysis on High-Temperature Compressive Creep Properties of Amorphous Silicon Carbide.

Ceramic matrix composites (CMCs) based on silicon carbide (SiC) are used for high-temperature applications such as the hot section in turbines. For such applications, the mechanical properties at a high temperature are essential for lifetime prediction and reliability design of SiC-based CMC components. We developed an interatomic potential function based on the artificial neural network (ANN) model for silicon-carbon systems aiming at investigation of high-temperature mechanical properties of SiC materials. We confirmed that the developed ANN potential function reproduces typical material properties of the single crystals of SiC, Si, and C consistent with first-principles calculations. We also validated applicability of the developed ANN potential to a simulation of an amorphous SiC through the analysis of the radial distribution function. The developed ANN potential was applied to a series of creep test for an amorphous SiC model, focusing on the amorphous phase, which is expected to be formed in the SiC-based composites. As a result, we observed two types of creep behavior due to different atomistic mechanisms depending on the strain rate. The evaluated activation energies are lower than the experimental values in literature. This result indicates that an amorphous region can play an important role in the creep process in SiC composites.

First isolation and analysis of caesium-bearing microparticles from marine samples in the Pacific coastal area near Fukushima Prefecture.

A part of the radiocaesium from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident was emitted as glassy, water-resistant caesium-bearing microparticles (CsMPs). Here, we isolated and investigated seven CsMPs from marine particulate matter and sediment. From the elemental composition, the 134Cs/137Cs activity ratio, and the 137Cs activity per unit volume results, we inferred that the five CsMPs collected from particulate matter were emitted from Unit 2 of the FDNPP, whereas the two CsMPs collected from marine sediment were possibly emitted from Unit 3, as suggested by (i) the presence of calcium and absence of zinc and (ii) the direction of the atmospheric plume during the radionuclide emission event from Unit 3. The presence of CsMPs can cause overestimation of the solid-water distribution coefficient of Cs in marine sediments and particulate matter and a high apparent radiocaesium concentration factor for marine biota. CsMPs emitted from Unit 2, which were collected from the estuary of a river that flowed through a highly contaminated area, may have been deposited on land and then transported by the river. By contrast, CsMPs emitted from Unit 3 were possibly transported eastward by the wind and deposited directly onto the ocean surface.

Plasmonic topological quasiparticle on the nanometre and femtosecond scales.

At the interface of classical and quantum physics, the Maxwell and Schrödinger equations describe how optical fields drive and control electronic phenomena to enable lightwave electronics at terahertz or petahertz frequencies and on ultrasmall scales1-5. The electric field of light striking a metal interacts with electrons and generates light-matter quasiparticles, such as excitons6 or plasmons7, on an attosecond timescale. Here we create and image a quasiparticle of topological plasmonic spin texture in a structured silver film. The spin angular momentum components of linearly polarized light interacting with an Archimedean coupling structure with a designed geometric phase generate plasmonic waves with different orbital angular momenta. These plasmonic fields undergo spin-orbit interaction and their superposition generates an array of plasmonic vortices. Three of these vortices can form spin textures that carry non-trivial topological charge8 resembling magnetic meron quasiparticles9. These spin textures are localized within a half-wavelength of light, and exist on the timescale of the plasmonic field. We use ultrafast nonlinear coherent photoelectron microscopy to generate attosecond videos of the spatial evolution of the vortex fields; electromagnetic simulations and analytic theory confirm the presence of plasmonic meron quasiparticles. The quasiparticles form a chiral field, which breaks the time-reversal symmetry on a nanometre spatial scale and a 20-femtosecond timescale (the 'nano-femto scale'). This transient creation of non-trivial spin angular momentum topology pertains to cosmological structure creation and topological phase transitions in quantum matter10-12, and may transduce quantum information on the nano-femto scale13,14.

Coastal urbanization alters carbon cycling in Tokyo Bay.

The carbon budget of Tokyo Bay, a highly urbanized coastal basin, was estimated using a box model that incorporated inorganic and organic carbon data over an annual cycle (2011-2012). The surface water represented net autotrophic system in which the annual net community production (NCP) was 19 × 1010 gC year-1. The annual loading of dissolved inorganic carbon and total organic carbon (TOC) from freshwater inputs was 11.2 × 1010 and 4.9 × 1010 gC year-1, respectively. The annual TOC sedimentation rate was 3.1 × 1010 gC year-1, similar to the annual air-sea CO2 uptake (5.0 × 1010 gC year-1). Although the NCP and TOC loading from freshwater inputs were respectively 3.0 and 2.7 times lower than those in the 1970s, the TOC sedimentation rate was similar. Therefore, a relatively high carbon efflux from Tokyo Bay likely occurred in the 1970s, including CO2 efflux to the atmosphere and/or export of labile organic carbon to the open ocean. The changes in carbon flow between the 1970s and 2011-2012 resulted from improved water quality due to increased sewage treatment facilities and improved sewage treatment efficiency in the catchment, which decreased the amount of labile organic carbon flowing into the bay.

Changes in radioactive cesium concentrations from 2011 to 2017 in Fukushima coastal sediments and relative contributions of radioactive cesium-bearing microparticles.

Sedimentary cesium-137 concentrations around the Fukushima Daiichi Nuclear Power Plant (FDNPP) were measured from 2011 to 2017 at eight stations. Although high values were observed until 2013, decreasing trends were observed at the surface sediments of seven stations. We isolated 25 radioactive Cs-bearing microparticles (CsMPs; 1.0-5385 Bq per particle). The contribution ratio of CsMPs to each sample ranged from 4.1% to 99.5% (median 58.8%), with the contribution ratio of the CsMPs in the southern part of the FDNPP was low compared to that from the northern part. In the southern part of the FDNPP, small CsMPs that could not be isolated in this study were present in large quantities immediately after the accident, and gradually diffused away and/or were dissolved over time. In contrast, the CsMPs in the northern part of the FDNPP have most likely accumulated over time, as suggested by the silty nature of the sediments there.

Super typhoon induced high silica export from Arakawa River, Japan.

Dissolved silicate (DSi) and particulate silica (PSi) concentrations were measured at Arakawa River and at sewage treatment plants (STP) during October 2018 to October 2019. These included flooding observations after super Typhoon Hagibis. At ordinary water levels, the STP effluents were found to be the largest source of DSi in the river. Although DSi concentrations during the flooding events (165 µmol L-1) decreased by about 25% compared to that of ordinary water level (221 µmol L-1), PSi was more than sixteen times higher value (301 µmol L-1) compared to that of ordinary water level (18 µmol L-1). Loading amounts of DSi and PSi (± 1 standard error) were 1.5 × 108 (± 0.1 × 108) and 0.15 × 108 (± 0.02 × 108) mol year-1, respectively, excluding the data of Typhoon Hagibis. Loading amounts during flooding events of DSi and PSi were 1.2 × 108 (± 0.1 × 108) and 2.4 × 108 (± 0.4 × 108) mol 15 days-1, respectively. Although the silica loading at ordinary water level was mainly derived from DSi, the silica loading during flooding events was extremely large due to both high level of DSi and PSi; moreover, it was higher than the annual loading amount.

Generation of a Quantitative Luciferase Reporter for Sox9 SUMOylation.

Sox9 is a master transcription factor for chondrogenesis, which is essential for chondrocyte proliferation, differentiation, and maintenance. Sox9 activity is regulated by multiple layers, including post-translational modifications, such as SUMOylation. A detection method for visualizing the SUMOylation in live cells is required to fully understand the role of Sox9 SUMOylation. In this study, we generated a quantitative reporter for Sox9 SUMOylation that is based on the NanoBiT system. The simultaneous expression of Sox9 and SUMO1 constructs that are conjugated with NanoBiT fragments in HEK293T cells induced luciferase activity in SUMOylation target residue of Sox9-dependent manner. Furthermore, the reporter signal could be detected from both cell lysates and live cells. The signal level of our reporter responded to the co-expression of SUMOylation or deSUMOylation enzymes by several fold, showing dynamic potency of the reporter. The reporter was active in multiple cell types, including ATDC5 cells, which have chondrogenic potential. Finally, using this reporter, we revealed a extracellular signal conditions that can increase the amount of SUMOylated Sox9. In summary, we generated a novel reporter that was capable of quantitatively visualizing the Sox9-SUMOylation level in live cells. This reporter will be useful for understanding the dynamism of Sox9 regulation during chondrogenesis.

Expression of Hey2 transcription factor in the early embryonic ventricles is controlled through a distal enhancer by Tbx20 and Gata transcription factors.

Development of multi-chambered heart is associated with spatio-temporal regulation of gene expression. A basic helix-loop-helix transcription factor Hey2 is specifically expressed in the embryonic mouse ventricles and is indispensable for ventricular myocyte differentiation, compartment identity and morphogenesis of the heart. However, how Hey2 transcription is precisely regulated in the heart remains unclear. In this study, we identified a distal Hey2 enhancer conserved in the mouse and human to possess specific transcriptional activity in ventricular free wall myocytes at the looping stage of cardiac development. Deletion of the enhancer significantly decreased endogenous Hey2 expression in the ventricular myocardium but not in other tissues of mouse embryos. Mutation/deletion of the conserved binding sites for T-box and Gata proteins, but not NK-2 proteins, abolished the enhancer activity, and Tbx20 null mice completely lost the enhancer activity in the embryonic ventricles. Luciferase reporter analysis suggested that the ventricular enhancer activity was controlled by Tbx20 through its DNA binding and cooperative function with cardiac Gata proteins. These results delineate a regulatory mechanism of ventricular Hey2 expression and help fully understand molecular cascades in myocardial cell differentiation and cardiac morphogenesis during embryonic development.

The Efficacy of Sonazoid-enhanced Ultrasonography in Decision-making for Liver Abscess Treatment.

Objective The usefulness of contrast-enhanced ultrasonography (CEUS) for making decisions in the treatment of liver abscess is unknown. Methods We evaluated the internal blood flow in the arterial-predominant phase by CEUS using Sonazoid® in 21 patients. The stain area rate was evaluated in maximum parting plane of abscess in CEUS. Patients were divided into two groups: the vascular phase enhancement (VE) group, in which ≥50% of the abscess cavity was enhanced (12 patients), and the vascular phase non-enhancement (VNE) group, in which <50% of the abscess cavity was enhanced (9 patients). The rate of patients who were cured by conservative treatment alone was examined in both groups. The defect rate of all liver abscesses in the post-vascular phase was also evaluated. Results In the VE group, improvement by conservative treatment alone was obtained in 11 out of 12 patients (91.7%), while in the VNE group, improvement by conservative treatment alone was obtained in only 1 out of 9 patients (11.1%), a significant difference (p<0.001). In the VE group, one patient did not improve with conservative treatment alone because the abscess ruptured near the liver surface. In the VE group, the abscess size was smaller than in the VNE group. By examining the defect rate in the post-vascular phase, it was found that 16 out of 21 patients (76.2%) showed 71% or more defects. Conclusion The enhancement rate in the arterial-predominant phase of CEUS was considered useful for determining the treatment approach for liver abscess.

Importance of endothelial Hey1 expression for thoracic great vessel development and its distal enhancer for Notch-dependent endothelial transcription.

Thoracic great vessels such as the aorta and subclavian arteries are formed through dynamic remodeling of embryonic pharyngeal arch arteries (PAAs). Previous work has shown that loss of a basic helix-loop-helix transcription factor Hey1 in mice causes abnormal fourth PAA development and lethal great vessel anomalies resembling congenital malformations in humans. However, how Hey1 mediates vascular formation remains unclear. In this study, we revealed that Hey1 in vascular endothelial cells, but not in smooth muscle cells, played essential roles for PAA development and great vessel morphogenesis in mouse embryos. Tek-Cre-mediated Hey1 deletion in endothelial cells affected endothelial tube formation and smooth muscle differentiation in embryonic fourth PAAs and resulted in interruption of the aortic arch and other great vessel malformations. Cell specificity and signal responsiveness of Hey1 expression were controlled through multiple cis-regulatory regions. We found two distal genomic regions that had enhancer activity in endothelial cells and in the pharyngeal epithelium and somites, respectively. The novel endothelial enhancer was conserved across species and was specific to large-caliber arteries. Its transcriptional activity was regulated by Notch signaling in vitro and in vivo, but not by ALK1 signaling and other transcription factors implicated in endothelial cell specificity. The distal endothelial enhancer was not essential for basal Hey1 expression in mouse embryos but may likely serve for Notch-dependent transcriptional control in endothelial cells together with the proximal regulatory region. These findings help in understanding the significance and regulation of endothelial Hey1 as a mediator of multiple signaling pathways in embryonic vascular formation.

Lake water phosphate reduction with advanced wastewater treatment in watershed, at Lake Hamana, Shizuoka Prefecture, Japan, from 1995 to 2016.

Lake Hamana is a semi-enclosed brackish lake amid agricultural and residential land. Monthly vertical profiles of nutrients, total phosphorus (TP), and total nitrogen (TN) at twelve sampling stations in the lake were obtained from 1995 to 2016. Freshwater samples were also obtained from five stations in the river flowing into the lake. Significant decreases were seen in phosphate, TP, and TN concentrations at most lake and all river stations. Decrease in phosphate concentration reflects reduced organic matter and nutrient load into the lake due to increased sewage coverage. Nitrate concentration significantly increased at four stations, whereas ammonium and TN concentrations significantly decreased. This could be due to inefficient nitrification/denitrification of wastewater. At all stations, the nitrogen to phosphate ratio in surface water was higher than 16 and increased significantly. Therefore, phosphate limitation could be strengthened by the decrease in phosphate and increase in nitrate concentrations in the lake.