Search

Abstract High-quality superconductor/topological material heterostructures are highly desired for realisation of topological superconductivity and Majorana physics. Here, we demonstrate a method to directly draw nanoscale superconducting β-Sn patterns in the plane of a topological Dirac semimetal (TDS) α-Sn thin film by irradiating a focused ion beam and taking advantage of the heat-driven phase transition of α-Sn into superconducting β-Sn. The β-Sn nanowires embedded in a TDS α-Sn thin film exhibit a large superconducting diode effect (SDE), whose rectification ratio η reaches a maximum of 35% when the magnetic field is applied parallel to the current. The results suggest that the SDE may occur at the α-Sn/β-Sn interfaces where the TDS α-Sn becomes superconducting by a proximity effect. Our work thus provides a universal platform for investigating quantum physics and devices based on topological superconducting circuits of any shape.

Abstract The magnetic proximity effect (MPE) attracts much attention as a promising way for introducing ferromagnetism into a nonmagnetic electron-transport channel. Although the range of MPE is generally limited to the interface, it is extended to several tens of nm in high-quality semiconductor bilayers consisting of a nonmagnetic quantum well (QW) and an underlying ferromagnetic semiconductor (FMS) layer. To elucidate the mechanism of this long-range MPE, it is essential to observe the magnetically proximitized electronic structure of the nonmagnetic semiconductor. Here, by investigating the Shubnikov - de Haas oscillations in nonmagnetic n-type InAs QW / FMS (Ga,Fe)Sb bilayers, we successfully observe the spin-polarized Fermi surface of the InAs QW. The spontaneous spin-splitting energy in the conduction band of the InAs QW reaches 18 meV when applying a negative gate voltage. This large and gate-tunable spin-polarized Fermi surface of a magnetically proximitized InAs QW provides an ideal platform for novel spintronic and topological devices.

This paper presents a case study of the design, fabrication, and evaluation of an automotive rear-frame model made of variable axial composites (VAC), using a tailored fiber placement (TFP) technique. Conventionally, the design of a three-dimensional complex VAC structure places significant demands on mechanical engineering expertise (for anisotropic structural design) and on man-hours (for fiber-path CAD). The proposed methods facilitate the design of complex VAC structures with significantly reduced manpower requirements. A computational design method, anisotropic topology optimization, was used to create the base design. The fiber paths on the preform surfaces were generated using a Turing pattern algorithm (based on optimized fiber orientation distributions) subsequent to designing developable three-dimensional surfaces to fill the interior of the target structure. The preforms were fabricated using a computer numerical control (CNC) embroidery machine by stitching the raw fiber tow onto the base fabric in accordance with the generated fiber path data. After stacking the preforms in the mold, they were formed using vacuum-assisted resin-transfer molding (VaRTM). The static stiffness of the prototype was evaluated experimentally, and the results were compared with numerical simulations. This study demonstrates the potential for achieving further weight reduction in large-scale 3D structures by combining innovative computational design techniques with advanced fabrication methods.

A core design optimization process is developed as part of the design optimization support tool named ARKADIA (Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle) for an efficient and innovative core design process. The process comprises analyses integrated by neutronics, thermal-hydraulics in a fuel assembly, fuel integrity, and plant dynamics for safety assessment. The optimal design parameters are explored using the Bayesian optimization (BO) algorithm to reduce the number of iterative calculations and solve the optimization problem. This study defines a representative problem by identifying the objective functions, constraints, and design parameters for an actual core design based on previous core design experiences to efficiently develop the core design optimization process. Next, a constrained single-objective optimization problem, the simplified representative problem, is solved by the integrated analyses only with neutronics and plant dynamics using the BO algorithm to confirm the applicability of the optimization process for the representative problem. Consequently, the design parameters that optimized the objective function within constraints can be obtained. The optimal solution correlates well with the reference solution. Furthermore, the effectiveness of the optimization process is discussed by comparing an ordinary and a defined core design process.

Japan Atomic Energy Agency (JAEA) is developing an artificial intelligence (AI) aided integrated digital system: “Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle (ARKADIA)”, to provide the best possible solutions for challenges arising during the design process, safety assessment, and operation of a nuclear plant over its life cycle. Until 2023, the platform for a common function and subsystems, namely ARKADIA-Design for design study, ARKADIA-Safety for safety assessment, and ARKADIA-knowledge management system (KMS) for the knowledge base, are separately being developed. This paper describes the development concepts of the platform, the progress of the application study of design optimization in ARKADIA-Design, the progress of optimization model development and optimization functionality based on AI technology in ARKADIA-Safety, and the structure of the knowledge base and application of AI technology to ARKADIA-KMS. In subsystems, necessary modules and process integration to obtain an optimal solution in a designated problem of plant design have been advanced. For further development, a strategy for unifying the subsystems with the AI-aided platform into one system, ARKADIA, and the extension of capabilities of the numerical analyses and evaluation technologies required for plant design until 2028 are presented.

Abstract Spin injection using ferromagnetic semiconductors at room temperature is a building block for the realization of spin-functional semiconductor devices. Nevertheless, this has been very challenging due to the lack of reliable room-temperature ferromagnetism in well-known group IV and III-V based semiconductors. Here, we demonstrate room-temperature spin injection by using spin pumping in a BiSb/(Ga,Fe)Sb heterostructure, where (Ga,Fe)Sb is a ferromagnetic semiconductor (FMS) with high Curie temperature (T C) and BiSb is a topological insulator (TI). Despite the very small magnetization of (Ga,Fe)Sb at room temperature (45 emu/cc), we detected spin injection from (Ga,Fe)Sb by utilizing the large inverse spin Hall effect (ISHE) in BiSb. Our study provides the first demonstration of spin injection at room temperature from a FMS.

Magnetoresistance, where the electric resistance of a material changes under an applied magnetic field, is typically an even function of the applied magnetic field, due to the combination of time reversal and spatial inversion symmetries. Here, Takiguchi et al show an odd-parity magnetoresistance of remarkable size in edge channels of a semiconductor quantum well.

Abstract High-mobility two-dimensional carriers originating from surface Fermi arcs in magnetic Weyl semimetals are highly desired for accessing exotic quantum transport phenomena and for topological electronics applications. Here, we demonstrate high-mobility two-dimensional carriers that show quantum oscillations in magnetic Weyl semimetal SrRuO3 epitaxial films by systematic angle-dependent, high-magnetic field magnetotransport experiments. The exceptionally high-quality SrRuO3 films were grown by state-of-the-art oxide thin film growth technologies driven by machine-learning algorithm. The quantum oscillations for the 10-nm SrRuO3 film show a high quantum mobility of 3.5 × 103 cm2/Vs, a light cyclotron mass, and two-dimensional angular dependence, which possibly come from the surface Fermi arcs. The linear thickness dependence of the phase shift of the quantum oscillations provides evidence for the non-trivial nature of the quantum oscillations mediated by the surface Fermi arcs. In addition, at low temperatures and under magnetic fields of up to 52 T, the quantum limit of SrRuO3 manifests the chiral anomaly of the Weyl nodes. Emergence of the hitherto hidden two-dimensional Weyl states in a ferromagnetic oxide paves the way to explore quantum transport phenomena for topological oxide electronics.

Abstract To achieve a desirable magnitude of spin–orbit torque (SOT) for magnetization switching and realize multifunctional spin logic and memory devices utilizing SOT, controlling the SOT manipulation is vitally important. In conventional SOT bilayer systems, researchers have tried to control the magnetization switching behavior via interfacial oxidization, modulation of spin–orbit effective field, and effective spin Hall angle; however, the switching efficiency is limited by the interface quality. A current‐induced effective magnetic field in a single layer of a ferromagnet with strong spin–orbit interactions, the so‐called spin–orbit ferromagnet, can be utilized to induce SOT. In spin–orbit ferromagnet systems, electric field application has the potential for manipulating the spin–orbit interactions via carrier concentration modulation. In this work, it is demonstrated that SOT magnetization switching can be successfully controlled via an external electric field using a (Ga, Mn)As single layer. By applying a gate voltage, the switching current density can be solidly and reversibly manipulated with a large ratio of 14.5%, which is ascribed to the successful modulation of the interfacial electric field. The findings of this work help further the understanding of the magnetization switching mechanism and advance the development of gate‐controlled SOT devices.

The interface between perovskite-oxide SrTiO3 and other oxides realizes efficient spin-to-charge current conversion; however, the typically insulating oxides hinder the propagation of spin-currents. Here the authors achieve a record efficiency by replacing an oxide insulator with a strongly-correlated polar metal.

The Japan Atomic Energy Agency has been developing “Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle (ARKADIA)” to offer the best solutions for challenges in the design and operation of nuclear plants. A part of ARKADIA for design study, which included design optimization of components, is named as ARKADIA-Design. In the development of ARKADIA-Design, we have been developing a process to automatically optimize design parameters of structural components subjected to various kinds of loads, including thermal transients. In this paper, we propose a simplified procedure to estimate the failure probability of components subjected to thermal transients for design optimization. An objective function of this optimization is defined on the basis of failure probability of the components, because failure probability can be commonly used as an indicator of component integrity for various mechanisms, and it helps future introductions of a risk-informed performance-based approach to component design. To enable the necessary number of estimations for design optimization with practical calculation time, we aimed to reduce the number of analyses required for one estimation. For this purpose, we adopted the first-order second-moment (FOSM) method as the estimation method for failure probability in the process of optimization. An orthogonal table in the experiment design method is utilized to define the conditions of the analyses for evaluation of the mean and variance of thermal transient stress, which are used as inputs in the FOSM method. The superposition of ramp responses is also utilized to evaluate the time history of thermal transient stress instead of finite element analysis. The proposed procedure was applied in a demonstration study to optimize the thickness of a cylindrical vessel subjected to thermal transients derived from shutdown. We confirmed that the procedure can evaluate the failure probability depending on the cylinder thickness with practical calculation time.

In this manuscript, the authors grow very thin layers of FeAs in a matrix of InAs. The resulting superlattice displays ferromagnetism, with the Curie temperature varying depending on the layer thickness. These results further illustrate the wide array of intriguing ground states of materials with tetrahedral FeAs bonds

A direct reactor auxiliary cooling system (DRACS) under natural circulation (NC) conditions with a dipped-type direct heat exchanger (D-DHX) in the upper plenum of a reactor vessel (RV) has been investigated for enhancing the safety of sodium-cooled fast reactors. Studies of the past have revealed that core-plenum interactions, which consists of penetration of the coolant from D-DHXs into the subassemblies and the narrow gap between them (IWF: inter-wrapper flow), and the heat transfer through a wrapper tube among subassemblies (radial heat transfer), occurred and increased core cooling performance during the DRACS operation. Therefore, a multidimensional thermal-hydraulics analysis model in the RV using a computational fluid dynamics (CFD) code (RV-CFD model) was developed to evaluate the core cooling performance. For the design study, the RV-CFD model must simulate reasonable calculation costs while maintaining accuracy. In this study, the subchannel analysis method using the CFD code for fuel subassemblies (subchannel CFD model) was applied to the RV-CFD model. In the subchannel CFD model, the porous media approach was used to consider local geometry in the fuel subassembly, and the effective heat conductivity coefficients in a diffusion term of the energy equation were set to fit the actual radial thermal diffusion between subchannels. Two numerical simulations were compared to the experimental data obtained from the sodium experimental apparatus PLANDTL-1. In the first case, the focus was only the radial heat transfer without the D-DHX operation. In another case with the D-DHX operation, the IWF noticeably occurred, and the focus was on the core-plenum thermal interaction. The calculated sodium temperature in the core correlated well with the experimental results. The RV-CFD with subchannel CFD model was validated for core-plenum interactions during the DRACS with the D-DHX operation under NC conditions.

Despite various predictions, the evidence of Weyl fermions in oxide materials remains elusive. Here, the authors show evidence of Weyl fermions in quantum transport measurements in an epitaxial ferromagnetic oxide SrRuO3.

We have demonstrated a Si-based bottom-gate-type spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) with an electron inversion channel at room temperature and showed the enhancement of the room-temperature effective spin diffusion length by “spin drift”. Our spin MOSFET was fabricated on a (001)-oriented silicon-on-insulator (SOI) substrate with a p-type ultrathin (8 nm) Si layer, in which the channel length was 1.0 μm, the spin injector/detector electrodes were ferromagnetic multilayer (from top to bottom) Fe(4nm)/Mg(1nm)/MgO(1nm) tunnel junctions, and a 200-nm-thick buried oxide layer was used for the gate dielectric. Using various gate electric fields and source-drain electron currents, two types of spin-dependent transport signals were measured: spin-valve signals with an inplane magnetic field and Hanle signals with an out-of-plane magnetic field. Clear Hanle signals and spin-valve signals were obtained for various bias conditions. We analyzed the Hanle signals and the change of the spin-valve signals based on our original formulas that take into account the distribution of the lateral electric field along the electron transport, and revealed that the spin drift can enhance the effective spin diffusion length by the lateral electric field parallel to the electron transport in the inversion channel. The effective spin diffusion length becomes 3-13 times larger than the intrinsic spin diffusion length λS = 0.89 μm owing to the increase in the lateral electric field. It was confirmed that the spin drift is very useful to achieve larger spin-valve signals in spin MOSFETs with an electron inversion channel.

Healthcare workers (HCWs), especially frontline workers against coronavirus disease 2019 (COVID-19), are considered to be risky because of occupational exposure to infected patients. This study evaluated the correlation between seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies among HCWs and the implementation of personal protective equipment (PPE) & infection prevention and control (IPC). We recruited 1237 HCWs from nine public COVID-19-designated hospitals in Shiga Prefecture, central Japan, between 15-26 February 2021. All participants answered a self-administered questionnaire and provided blood samples to evaluate SARS-CoV-2 antibodies. A total of 22 cases (1·78%) were seropositive among the 1237 study participants. An unavoidable outbreak of SARS-CoV-2 had occurred at the terminal care unit of one hospital, before identifying and securely isolating this cluster of cases. Excluding with this cluster, 0·68% of HCWs were suspected to have had previous SARS-CoV-2 infections. Binomial logistic regression from individual questionnaires and seropositivity predicted a significant correlation with N95 mask implementation under aerosol conditions (p = 8.63e-06, aOR = 2.47) and work duration in a red zone (p = 2.61e-04, aOR = 1.99). The institutional questionnaire suggested that IPC education was correlated with reduced seropositivity at hospitals. Seroprevalence and questionnaire analyses among HCWs indicated that secure implementation of PPE and re-education of IPC are essential to prevent SARS-CoV-2 infection within healthcare facilities. Occupational infections from SARS-CoV-2 in healthcare settings could be prevented by adhering to adequate measures and appropriate use of PPE. With these measures securely implemented, HCWs should not be considered against as significantly risky or dirty by local communities.

We study the growth and properties of the quaternary-alloy ferromagnetic semiconductor (In0.94−x,Gax,Fe0.06)Sb (x = 5%–30%; the Fe concentration is fixed at 6%) grown by low-temperature molecular beam epitaxy. Reflection high-energy electron diffraction patterns, scanning transmission electron microscopy lattice images, and x-ray diffraction spectra indicate that the (In0.94−x,Gax,Fe0.06)Sb layers have a zinc blende crystal structure without any other second phase. The lattice constant of the (In0.94−x,Gax,Fe0.06)Sb films changes linearly with the Ga concentration x, indicating that Ga atoms substitute In atoms in the zinc-blende structure. We found that the carrier type of (In0.94−x,Gax,Fe0.06)Sb can be systematically controlled by varying x, being n-type when x ≤ 10% and p-type when x ≥ 20%. Characterization studies using magnetic circular dichroism spectroscopy indicate that the (In0.94−x,Gax,Fe0.06)Sb layers have intrinsic ferromagnetism with relatively high Curie temperatures (TC = 40–120 K). The ability to widely control the fundamental material properties (lattice constant, bandgap, carrier type, and magnetic property) of (In0.94−x,Gax,Fe0.06)Sb demonstrated in this work is essential for spintronic device applications.

In conventional magnetic tunnel junctions (MTJs), the tunnel magnetoresistance (TMR) monotonically decreases with increasing bias voltage, which limits the bias voltage range for the operation of MTJs. In our study, using double-barrier MTJs composed of Fe/MgO/Fe/γ-Al2O3 grown on a Nb-doped SrTiO3 substrate, we demonstrate unconventional bias dependences of the TMR, in which the TMR ratio increases with increasing bias voltage. We reveal that this behavior originates from the sharp giant resistance peak near zero bias likely induced by the Coulomb blockade effect via Fe impurities in γ-Al2O3, which are diffused from the Fe layer. The observed TMR ratio is 23% at a bias voltage of −4 V at 3.5 K, which is a very high value in this large bias voltage range. Our results offer a novel way to improve the bias voltage dependence of TMR.

To optimize the writing and reading performance of magnetic random-access memory (MRAM) devices, achieving current-induced spin–orbit torque (SOT) magnetization switching in perpendicularly magnetized full Heusler alloys is vitally important. For conventional SOT-metal bilayer systems, heavy metals (HMs) with a large spin Hall angle (θSH) are generally used for generating a spin current, which is injected into the adjacent ferromagnet (FM) layer and exerts a torque on the magnetization to switch it. However, the large resistivity of generally used HMs such as β-Ta and β-W can increase the Ohmic loss. In this article, we achieve full SOT switching in Heusler alloy Co2FeSi using low-resistivity Pd as a spin current generation source. The critical switching current density is found to be 3.7 × 107 A cm−2, which is in the same order of magnitude as that required for conventional HM/FM systems even though Pd has a smaller θSH than that of generally used HMs. Using harmonic Hall measurements, the damping-like and field-like effective fields per unit current density are estimated to be 56.9 (10−7 Oe A−1 cm2) and 39.8 (10−7 Oe A−1 cm2), respectively. This high efficiency can be attributed to the excellent lattice matching between Co2FeSi and Pd (only 2% mismatch), to a slight Pd diffusion, and possibly to the additional SOTs induced by the in-plane spin component generated in the Co2FeSi layer. Our finding will advance the development of SOT-MRAM devices with both better reading and writing performance.

Spinel-type CoFe2O4 is a ferrimagnetic insulator with the Néel temperature exceeding 790 K, and it shows strong cubic magnetocrystalline anisotropy (MCA) in bulk materials. However, when a CoFe2O4 film is grown on other materials, its magnetic properties are degraded so that so-called magnetically dead layers are expected to be formed in the interfacial region. We investigate how the magnetic anisotropy of CoFe2O4 is modified at the interface of CoFe2O4/Al2O3 bilayers grown on Si(111) using x-ray magnetic circular dichroism. We find that the thinner CoFe2O4 films have significantly smaller MCA values than bulk materials. The reduction in MCA is explained by the reduced number of Co2+ ions at the Oh site, as reported by a previous study [Wakabayashi et al., Phys. Rev. B 96, 104410 (2017)].

Abstract11 AbbreviationsBDI, Beck Depression Inventory; CFS, Chalder Fatigue Scale; EDSS, Expanded Disability Status Scale; HC, Health control subjects; MMSE, Mini-Mental State ExaminationMS, Multiple sclerosis; PASAT, Paced Auditory Serial Addition Test; QoL, Quality-of-lifeSD, Standard deviation; SDMT, Symbol Digit Modalities Test; VC, Visual cancellation;: Background: Depression and fatigue are debilitating symptoms in multiple sclerosis (MS), which affect cognitive function. This study investigated the association between depression and fatigue, and whether depression or fatigue influences cognition in MS patients. Methods: Twenty MS patients were included. The severity of fatigue was assessed using the Chalder Fatigue Scale (CFS), which classified CFS_Physical and CFS_Mental fatigue and MMSE. Depression was assessed using the Beck Depression Inventory (BDI). Attention deficit was evaluated using several tasks. The CFS scores, the BDI scores and performance during the attention tasks were compared between MS patients and healthy control subjects (HCs). Correlations between CFS sub-scores, BDI values, and participants’ attention performance were also investigated. Results: The total CFS, BDI, and MMSE scores were significantly worse in MS patients compared to HCs (p

Gas entrainment (GE) from cover gas, which is an inert gas to cover sodium coolant in the reactor vessel, is one of the key issues for Sodium-cooled fast reactors (SFRs) design to prevent unexpected effects to core reactivity. In this research series, evaluation method has been investigated for surface dimple depth growth of unstable drifting vortex dimples on the liquid surface in the reactor vessel. By using a computational fluid dynamics (CFD) code, analyses have been conducted to estimate the drifting vortex on water experiments in a circulating water tunnel. The unstable drifting flow vortexes on the water surface were generated as wake vortexes behind a plate obstacle. Downward flow velocity was induced by the bottom slit’s flow passing along the flow channel. In the previous study, the initial conditions of the gas entrainment were evaluated based on existing non-dimensional numbers method by using the STREAM-VIEWER code. However, the CFD predication accuracy of the detailed flow field itself was not clear especially for vortex frequency in the wake flow and detailed velocity profiles in the flow channel. In this study, to clarify the accuracy of CFD analysis, Strouhal numbers of vortex frequency and detailed flow velocity profiles were compared with experimental data which were measured by Particle Image Velocimetry (PIV) method. As the results, the Strouhal numbers of the vortex frequency behind the plate obstacle reasonably agreed with the experimental data.

Spin orbit torque enables an innovative method of manipulating the magnetization of ferromagnets by current injection. Here, Jiang et al. demonstrate efficient full spin–orbit torque switching with an activation current density of ∼3.4 × 105 A cm−2 in a single layer ferromagnetic semiconductor GaMnAs.

We investigate structural and transport properties of highly Ru-deficient SrRu0.7O3 thin films prepared by molecular beam epitaxy on (001) SrTiO3 substrates. To distinguish the influence of the two types of disorders in the films—Ru vacancies within lattices and disorders near the interface—SrRu0.7O3 thin films with various thicknesses (t = 1–60 nm) were prepared. It was found that the influence of the former dominates the electrical and magnetic properties when t ≥ 5–10 nm while that of the latter does when t ≤ 5–10 nm. Structural characterizations revealed that the crystallinity, in terms of the Sr and O sublattices, of SrRu0.7O3 thin films is as high as that of the ultrahigh-quality SrRuO3 ones. The Curie temperature (TC) analysis elucidated that SrRu0.7O3 (TC ≈ 140 K) is a material distinct from SrRuO3 (TC ≈ 150 K). Despite the large Ru deficiency (∼30%), the SrRu0.7O3 films showed metallic conduction when t ≥ 5 nm. In high-field magnetoresistance measurements, the fascinating phenomenon of Weyl fermion transport was not observed for the SrRu0.7O3 thin films irrespective of thickness, which is in contrast to the stoichiometric SrRuO3 films. The (magneto)transport properties suggest that a picture of carrier scattering due to the Ru vacancies is appropriate for SrRu0.7O3 and also that proper stoichiometry control is a prerequisite to utilizing the full potential of SrRuO3 as a magnetic Weyl semimetal and two-dimensional spin-polarized system. Nevertheless, the large tolerance in Ru composition (∼30%) to metallic conduction is advantageous for some practical applications where SrRu1−xO3 is used as an epitaxial conducting layer.

We report the structural and magnetic properties of the Fe-doped GaSb quantum dots (QDs) (nominal Fe concentration x = 4.7%–16.6%) grown on GaAs (001) substrates by molecular beam epitaxy. The QDs with nanometer-scale dimensions consist of two areas with different crystal structures, a zinc-blende GaAsSb wetting layer and a new phase of FeGaSb alloy that has a simple cubic lattice. The size and distribution of the QDs depend on the Fe concentration, as revealed by atomic force microscopy. Magnetic force microscopy measurements at zero applied magnetic field show the presence of ferromagnetism in the QDs at room temperature with an easy axis in the 1¯10 direction, which is consistent with magnetometry measurements. The Curie temperature in these QDs is very high (>400 K), which is promising for spintronic applications at room temperature.

We report large tunnel magnetoresistance (TMR) ratios of up to 219% at 300 K and 366% at 3.7 K obtained for a high-quality fully epitaxial double-barrier magnetic tunnel junction (MTJ) composed of Fe/MgO/Fe/γ-Al2O3/Nb-doped SrTiO3. The obtained TMR ratios are among the highest values reported in Fe/MgO/Fe structures. This result may be attributed to the small in-plane wave vectors of the tunneling electrons injected from the Nb-doped SrTiO3 electrode with a small carrier density, demonstrating good compatibility between the Fe-based MTJ and SrTiO3.

Fully natural circulation decay heat removal systems (DHRSs) are adopted for sodium fast reactors, which is a passive safety feature without any electrical pumps. It is needed to grasp the thermal-hydraulic phenomena in the reactor vessel and evaluate the coolability of the core under the natural circulation not only for the normal operating condition but also for severe accident conditions. In this paper, the numerical results of the preliminary analysis for the sodium experimental condition with the PLANDTL-2, in which the core and the upper plenum with a dipped-type direct heat exchanger (DHX) were modeled, are discussed to establish an appropriate numerical models for the reactor core including the gap region among the subassemblies and the DHX. The transient analysis simulating the reactor scram reveals that the 3-dimensional large scale flow structure is developed through the gaps in the whole of the core area during the reactor scram. The steady-state analysis coinciding Richardson number between the PLANDTL-2 and the reactor operation condition reveals that the hot spot and cold spot appear depending on the location of the DHX, which is caused by the complex thermal-hydraulic phenomena driven by the natural circulation. From these preliminary analyses, the characteristics of the thermal-hydraulics behavior in the PLANDTL-2 to be focused are extracted.

Abstract Background Polypoidal choroidal vasculopathy (PCV) consists of polyps that potentially cause massive subretinal hemorrhage and their branching vascular network (BVN) of feeder vessels. Although conventional indocyanine green angiography (IA) has shown anti-vascular endothelial growth factor (VEGF) agents and/or photodynamic therapy (PDT) to successfully induce polyp closure, the BVN appears resistant to these therapies and serves as the origin of recurrent active polyps. Recently introduced optical coherence tomography angiography (OCT-A) enables more frequent angiographic evaluation of polyps and the BVN than does conventional IA since it does not require intravenous fluorescent dye injection and is thus considered non-invasive. Case presentation Case 1. A 70-year-old male with PCV in his left eye suffered from vision deterioration (20/40) due to persistent subretinal fluid despite 42 intravitreal injections of ranibizumab (IVRs) over 5 years and 7 months. PDT was performed as an adjunct therapy 3 days after the 43rd IVR. IA at 3 months after PDT showed successful polyp closure but persisting BVN. However, more frequent evaluation with OCT-A starting at 1 week after PDT demonstrated complete regression of both the BVN and polyp. OCT-A at every subsequent outpatient visit depicted gradual re-perfusion of the BVN and the restoration of most of its original network at 3 months, which was compatible with IA findings. Neither OCTA nor IA revealed polyp recurrence at 3 months. Case 2. A 65-year-old female suffering from left vision deterioration due to PCV underwent 5 intravitreal injections of aflibercept. Since her subretinal fluid persisted, the treatment was switched to a combination of IVR and PDT. OCT-A revealed marked regression of the BVN and polyp at 2 weeks, but the BVN had regained its original shape at 2 months without any sign of polyp recurrence. Conclusions Differently from previous observations obtained by IA alone, more frequent non-invasive OCT-A examination revealed complete but transient regression of the BVN just after combination therapy with IVR and PDT.

Abstract A vertical spin metal-oxide-semiconductor field-effect transistor (spin MOSFET) is a promising low-power device for the post scaling era. Here, using a ferromagnetic-semiconductor GaMnAs-based vertical spin MOSFET with a GaAs channel layer, we demonstrate a large drain-source current I DS modulation by a gate-source voltage V GS with a modulation ratio up to 130%, which is the largest value that has ever been reported for vertical spin field-effect transistors thus far. We find that the electric field effect on indirect tunneling via defect states in the GaAs channel layer is responsible for the large I DS modulation. This device shows a tunneling magnetoresistance (TMR) ratio up to ~7%, which is larger than that of the planar-type spin MOSFETs, indicating that I DS can be controlled by the magnetization configuration. Furthermore, we find that the TMR ratio can be modulated by V GS. This result mainly originates from the electric field modulation of the magnetic anisotropy of the GaMnAs ferromagnetic electrodes as well as the potential modulation of the nonmagnetic semiconductor GaAs channel layer. Our findings provide important progress towards high-performance vertical spin MOSFETs.

Abstract High-speed magnetization control of ferromagnetic films using light pulses is attracting considerable attention and is increasingly important for the development of spintronic devices. Irradiation with a nearly monocyclic terahertz pulse, which can induce strong electromagnetic fields in ferromagnetic films within an extremely short time of less than ~1 ps, is promising for damping-free high-speed coherent control of the magnetization. Here, we successfully observe a terahertz response in a ferromagnetic-semiconductor thin film. In addition, we find that a similar terahertz response is observed even in a non-magnetic semiconductor and reveal that the electric-field component of the terahertz pulse plays a crucial role in the magnetization response through the spin-carrier interactions in a ferromagnetic-semiconductor thin film. Our findings will provide new guidelines for designing materials suitable for ultrafast magnetization reversal.

Abstract Understanding and controlling the interfacial magnetic properties of ferromagnetic thin films are crucial for spintronic device applications. However, using conventional magnetometry, it is difficult to detect them separately from the bulk properties. Here, by utilizing tunneling anisotropic magnetoresistance in a single-barrier heterostructure composed of La0.6Sr0.4MnO3 (LSMO)/LaAlO3 (LAO)/Nb-doped SrTiO3 (001), we reveal the presence of a peculiar strong two-fold magnetic anisotropy (MA) along the [110]c direction at the LSMO/LAO interface, which is not observed in bulk LSMO. This MA shows unknown behavior that the easy magnetization axis rotates by 90° at an energy of 0.2 eV below the Fermi level in LSMO. We attribute this phenomenon to the transition between the e g and t 2g bands at the LSMO interface. Our finding and approach to understanding the energy dependence of the MA demonstrate a new possibility of efficient control of the interfacial magnetic properties by controlling the band structures of oxide heterostructures.

Abstract Reducing the power consumption necessary for magnetization reversal is one of the most crucial issues facing spintronics devices. Electric field control of the magnetic anisotropy of ferromagnetic thin films is a promising method to solve this problem. However, the electric field is believed to be effective only within several nanometres of the surface in ferromagnetic metals because of its short Thomas-Fermi screening length, which prevents its practical application to devices. Herein, we successfully modulate the magnetic anisotropy of the entire region of the ferromagnetic layers in the elongated mesas of vertical spin field-effect transistors with widths as large as ~500 nm by applying an electric field to the side surface of the metallic GaMnAs-based mesas through an electric double layer. Our results will open up a new pathway for spintronics devices with ultra-low power consumption.

Reduction of power consumption for magnetization reversal in spintronic memory devices is of great importance. Here, Munetaet al. report the gate electric-field assisted control of the magnetic anisotropy of the density of states using quantum size effect in GaMnAs.

By using magnetic circular dichroism (MCD) spectroscopy with photon energy in both visible (1.5–5 eV) and infrared light regions (0.6–1.7 eV), we systematically investigate the band structure of p-type ferromagnetic semiconductor (Ga1−x,Fex)Sb with various Fe concentrations x = 2%–20% grown by low-temperature molecular beam epitaxy. We observed two peaks in the infrared MCD spectra that can be explained by the optical transitions related to the Fermi level (EF) located in an Fe-related impurity band (IB) in the bandgap. As x increases, the energy shifts of the two peaks suggest that the Fe-related IB extends into the bandgap and EF rises correspondingly. Furthermore, the mobility of hole carriers in these (Ga,Fe)Sb thin films estimated by Hall measurements is very low (0.2–2 cm2/Vs), which is consistent with our conclusion that the hole carriers and EF reside in the IB rather than in the valence band. Our results provide insights into the band structure of p-type ferromagnetic semiconductors (Ga,Fe)Sb with high Curie temperature, which is promising for the realization of spintronic devices operating at room temperature.

A large spin-splitting is essential for spintronic devices. Here, the authors observe a spontaneous spin-splitting energy of between 31.7 and 50 millielectronvolts in n-type indium iron arsenide at temperatures up to several tens of Kelvin, challenging the conventional theory of ferromagnetic semiconductors.

As semiconductors are doped with impurities, their useful electrical transport properties are degraded as their band structures are increasingly modified. Here, the authors demonstrate that the band ordering is restored in Mn-doped GaAs above a ferromagnetic transition at a critical concentration.

We demonstrate efficient intrinsic spin-to-charge current conversion in a two-dimensional electron gas using an all-epitaxial single-crystal heterostructure of LaSrMnO_{3}/LaAlO_{3}/SrTiO_{3}, which can suppress spin scattering and give us an ideal environment to investigate intrinsic spin-charge conversion. With decreasing temperature to 20 K, the spin-to-charge conversion efficiency is drastically enhanced to +6.7nm. Our band-structure calculation well reproduces this behavior and predicts further enhancement by controlling the density and relaxation time of the carriers.

Transmission magnetic circular dichroism (MCD) spectroscopy has been widely used to reveal the spin-dependent band structure of ferromagnetic semiconductors. In these previous studies, some band pictures have been proposed from the spectral shapes observed in transmission MCD; however, extrinsic signals originating from optical interference have not been appropriately considered. In this study, we calculate the MCD spectra taking into account the optical interference of the layered structure of samples and show that the spectral shape of MCD is strongly influenced by optical interference. To correctly understand the transmission MCD, we also calculate the intrinsic MCD spectra of GaMnAs that are not influenced by the optical interference. The spectral shape of the intrinsic MCD can be explained by the characteristic band structure of GaMnAs, that is, the spin-polarized valence band and the impurity band existing above the valence band top.

Some components of the neural circuits underlying innate odor-evoked responses have recently been elucidated. Odor information detected by the olfactory receptors is transmitted from the olfactory bulb to the cortical amygdala, where physiological and emotional states such as attraction or avoidance are controlled. Thus, activation of specific olfactory receptors can elicit changes in physiological and/or psychological state. Here, we examined on the odorant Hex-Hex Mix, which has been reported to induce anti-fatigue effects. Fatigue is a prevalent condition that is often related to overwork and psychological stress. Various anti-fatigue treatments have been developed, including supplements and odorants. However, the mechanisms underlying the anti-fatigue effects of these substances are currently unclear. In the present study, we analyzed the involvement of the olfactory system in the mechanisms underlying this effect. We identified the human olfactory receptors activated by Hex-Hex Mix, and evaluated whether activation of these olfactory receptors by a newly developed odorant elicited a similar anti-fatigue effect to Hex-Hex Mix. We assessed anti-fatigue effects with behavioral tests, and 17 healthy males performed the 2-back test as a fatigue-inducing task with or without exposure to the new odorant. Immediately before and after the task, participants performed a cognitive task to evaluate their level of mental fatigue. We found that the difference value of the correct response rate on the cognitive task in the evaluation session was significantly different between in the odorant condition and in the without-odorant condition during the fatigue-inducing session suggesting that the new odorant may improve performance in the fatigue-inducing condition. The results indicated that the new odorant activates the same olfactory receptors as Hex-Hex Mix, which has been reported to induce anti-fatigue effects. Our findings suggest that the olfactory receptors in the olfactory system may be involved in the attenuation of fatigue.

The ability to divide one's attention deteriorates in patients with childhood chronic fatigue syndrome (CCFS). We conducted a study using a dual verbal task to assess allocation of attentional resources to two simultaneous activities (picking out vowels and reading for story comprehension) and functional magnetic resonance imaging. Patients exhibited a much larger area of activation, recruiting additional frontal areas. The right middle frontal gyrus (MFG), which is included in the dorsolateral prefrontal cortex, of CCFS patients was specifically activated in both the single and dual tasks; this activation level was positively correlated with motivation scores for the tasks and accuracy of story comprehension. In addition, in patients, the dorsal anterior cingulate gyrus (dACC) and left MFG were activated only in the dual task, and activation levels of the dACC and left MFG were positively associated with the motivation and fatigue scores, respectively. Patients with CCFS exhibited a wider area of activated frontal regions related to attentional resources in order to increase their poorer task performance with massive mental effort. This is likely to be less efficient and costly in terms of energy requirements. It seems to be related to the pathophysiology of patients with CCFS and to cause a vicious cycle of further increases in fatigue.

Group-IV-based ferromagnetic semiconductor Ge1−xFex (GeFe) is one of the most promising materials for spin injection/detection in Si and Ge. In this paper, we demonstrate a systematic study of tunneling magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) composed of Fe/MgO/Ge1−xFex with various Fe concentrations (x = 0.065, 0.105, 0.140, and 0.175). With increasing x, the TMR ratio increases up to 1.5% when x≤ 0.105, and it decreases when x> 0.105. This is the first observation of the TMR ratio over 1% in MTJs containing a group-IV ferromagnetic semiconductor. With increasing x, while the Curie temperature of GeFe increases, the MgO surface becomes rougher, which is thought to be the cause of the upper limit of the TMR ratio. The quality of the MgO layer on GeFe is an important factor for further improvement of TMR in Fe/MgO/GeFe MTJs.

We investigated the electric-current-induced dynamics of bubble domains in a perpendicularly magnetized ferrimagnetic {Tb/Co}7 multilayer wire with a heavy-metal Pt cap layer. The {Tb/Co}7 wire with the transition-metal-dominant and rare-earth-dominant magnetizations was obtained by changing temperature. We found that the bubble domains moved to the electric current direction with growing in oblique angles when electric current pulses were applied. The oblique directions of the bubble-domain’s growth in the {Tb/Co}7 wire with the transition-metal-dominant and rare-earth-dominant magnetizations were opposite with each other. The micromagnetic simulations imply that these oblique growths are accounted by the spin injection from the Pt layer via the spin Hall effect.

In the design of the Advanced Sodium-cooled Fast Reactor in Japan, the mean velocity of the coolant is approximately 9 m/s in the primary hot leg (H/L) piping, which has a diameter of 1.27 m. The Reynolds number in the H/L piping reaches 4.2 × 107. Furthermore, a short elbow, which has Rc/D = 1.0 (Rc: curvature radius, D: pipe diameter), is used in the H/L piping to achieve a compact plant layout and reduces plant construction costs. In the H/L piping, flow-induced vibration (FIV) is a concern due to the excitation force caused by pressure fluctuation in the short elbow. In a previous study, the relation between flow separation and pressure fluctuations in the short elbow was investigated under the specific inlet condition of a flat velocity profile of time-averaged axial velocity and relatively low velocity fluctuation intensity. However, the inlet velocity condition of the H/L in a reactor may be a highly turbulent non-uniform profile owing to the complex geometry in the reactor vessel (R/V). In this report, the influence of inlet velocity condition on the unsteady velocity characteristics in the short elbow was studied. Although the flow around the inlet of the H/L in the R/V could not be simulated completely, the inlet velocity conditions were controlled by installing a perforated plate, which appropriately plugged the flow holes. Then, controlled flow patterns were established at a position 2D upstream of the elbow inlet. Observed flow structures by particle image velocimetry indicated that the inlet velocity profiles affected a circumferential secondary flow, which then affected an area of flow separation at the elbow. It was also found that the velocity fluctuation at low frequency components observed upstream of the elbow could remain in downstream of the elbow though its intensity was attenuated.

As part of the development of a flow-induced vibration evaluation methodology for the primary cooling piping in Japan sodium-cooled fast reactor, important factors were discussed in evaluating the flow-induced vibration for the hot-leg piping. To investigate a complex flow near the inlet of the hot-leg piping, a steady-state numerical analysis was carried out for the reactor upper plenum flow, which was simulated in a 1/10-scale reactor upper plenum experiment. Based on this analysis, experimental conditions on swirl inflow and deflected inflow that were identified as important factors were determined for flow-induced vibration experiments simulating only the hot-leg piping. In this study, the effect of the swirl inflow on flow pattern and pressure fluctuation onto the pipe wall was investigated in a 1/3-scale hot-leg pipe experiment. The experiment has indicated less significant for the pressure fluctuations, while the flow separation region was slightly influenced by the swirl inflow. Computational fluid dynamics simulation with a U-RANS approach results also appear in this paper. Through the simulations under the swirl inflow conditions of 0% and 5%, the validity of the U-RANS simulation was confirmed by comparison to the 1/3-scale hot-leg piping experiments.

Laser Doppler Velocimetry (LDV) measurements in a 90 degree elbow of which the curvature radius coincides with its inner diameter were examined for the cases of inflow from a long pipe, short pipe and swirl generator. Ensemble averaged flow distribution at the Reynolds number of 320000 based on the inner pipe diameter and bulk velocity shows that shortening the upstream pipe length to 4.9D from 10D induces the flow separation downstream of the elbow. Detailed observation suggests that shortening upstream pipe weakens the Prandtl's secondary flow of the first kind. Our swirl generator induced a swirling inflow with the non-dimensional angular momentum of 0.12 based on the inner pipe diameter and bulk velocity. The circumferential velocity distribution formed a shape like a Rankine combined vortex at the elbow inlet, and the accelerated axial velocity was observed at the vortex center. The axial velocity distribution however was found to be almost the same as that of the non-swirl inflow case in the latter half of the elbow. Frequency analyses showed that the Strouhal number by vortex shedding from the boundary layer occurring at the inner side of the elbow become 0.5, except for 0.6 in the case of the long pipe. The change of the Strouhal number is probably related with the boundary layer width and the local flow velocity.

Thermal striping caused by the mixing of fluids at different temperatures is one of the most important issues in the design of Sodium cooled Fast Reactors (SFRs), because it may cause high-cycle thermal fatigue in the structure and affect the structural integrity. A numerical simulation code named MUGTHES has been developed to investigate thermal striping phenomena and to estimate high-cycle thermal fatigue in SFRs. In this study, the numerical simulation of the WATLON which was a water experiment of the T-junction piping system conducted by the Japan Atomic Energy Agency (JAEA) was conducted to validate the MUGTHES as a typical problem of thermal striping and to investigate the temperature fluctuation generation mechanism relating to the unsteady motion of large eddy structures. In the numerical simulation, an approach using the large eddy simulation (LES) with the standard Smagorinsky model was employed to simulate large scale eddy motions in the T-pipe. To quantify the uncertainty of the numerical results, the Grid Convergence Index (GCI) estimation was examined using two modified methods from the Roache’s GCI method described in the ASME V&V-20 guideline and the Eça-Hoekstra’s least square version GCI. The modified least square version GCI was named SLS-GCI (Simplified Least Square version GCI estimation method). Three mesh arrangements were employed to estimate the GCI value for uncertainty quantification in the validation process. Through the GCI estimation, it was found that the SLS-GCI method could successfully quantify the uncertainty of the numerical results. The numerical results suggested that the fine mesh arrangement in this study could improve the temperature distribution in the wake and that the thermal mixing phenomena in the T-pipe were caused by the mutual interaction of the necklace-shaped vortex around the wake from the front of the branch jet, the horseshoe-shaped vortex, and Karman’s vortex motions in the wake.