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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.

Charge transport in strongly correlated electron systems is not fully understood. Here, the authors show that resilient quasiparticles at finite frequency persist into the bad-metal regime near a Mott insulator, where dynamical localization results in a ‘displaced Drude peak’ and strongly enhanced dc resistivity.

Elucidation of the mechanism by which the shape of bones is formed is essential for understanding vertebrate development. Bones support the body of vertebrates by withstanding external loads, such as those imposed by gravity and muscle tension. Many studies have reported that bone formation varies in response to external loads. An increased external load induces bone synthesis, whereas a decreased external load induces bone resorption. This relationship led to the hypothesis that bone shape adapts to external load. In fact, by simulating this relationship through topology optimization, the internal trabecular structure of bones can be successfully reproduced, thereby facilitating the study of bone diseases. In contrast, there have been few attempts to simulate the external structure of bones, which determines vertebrate morphology. However, the external shape of bones may be reproduced through topology optimization because cells of the same type form both the internal and external structures of bones. Here, we constructed a three-dimensional topology optimization model to attempt the reproduction of the external shape of teleost vertebrae. In teleosts, the internal structure of the vertebral bodies is invariable, exhibiting an hourglass shape, whereas the lateral structure supporting the internal structure differs among species. Based on the anatomical observations, we applied different external loads to the hourglass-shaped part. The simulations produced a variety of three-dimensional structures, some of which exhibited several structural features similar to those of actual teleost vertebrae. In addition, by adjusting the geometric parameters, such as the width of the hourglass shape, we reproduced the variation in the teleost vertebrae shapes. These results suggest that a simulation using topology optimization can successfully reproduce the external shapes of teleost vertebrae. By applying our topology optimization model to various bones of vertebrates, we can understand how the external shape of bones adapts to external loads.

The dimer Mott insulator λ-(BEDT-STF)2GaCl4 undergoes no magnetic order down to the lowest temperatures, suggesting the formation of a novel quantum disordered state. Our frequency and temperature-dependent investigations of the dielectric response reveal a relaxor-like behavior below T≈100 K for all three axes, similar to other spin liquid candidates. Optical measurement of the charge-sensitive vibrational mode ν27(b1u) identifies a charge disproportionation Δρ≈0.04e on the dimer that exists up to room temperature and originates from inequivalent molecules in the weakly coupled dimers. The linewidth of the charge sensitive mode is broader than that of typical organic conductors, supporting the existence of a disordered electronic state.

The quantum spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3 has been established as the prime example of a genuine Mott insulator that can be tuned across the first-order insulator–metal transition either by chemical substitution or by physical pressure. Here, we explore the superconducting state that occurs at low temperatures, when both methods are combined, i.e., when κ-[(BEDT-TTF)1−x(BEDT-STF)x]2Cu2(CN)3 is pressurized. We discovered superconductivity for partial BEDT-STF substitution with x = 0.10–0.12 even at ambient pressure, i.e., a superconducting state is realized in the range between a metal and a Mott insulator without magnetic order. Furthermore, we observed the formation of a superconducting dome by pressurizing the substituted crystals; we assigned this novel behavior to disorder emanating from chemical tuning.

Thermodynamic picture induced by π-d interaction in a molecular magnetic superconductor κ-(BETS)2FeX4 (X = Cl, Br), where BETS is bis(ethylenedithio)tetraselenafulvalene, studied by single crystal calorimetry is reviewed. Although the S = 5/2 spins of Fe3+ in the anion layers form a three-dimensional long-range ordering with nearly full entropy of Rln6, a broad hump structure appears in the temperature dependence of the magnetic heat capacity only when the magnetic field is applied parallel to the a axis, which is considered as the magnetic easy axis. The scaling of the temperature dependence of the magnetic heat capacity of the two salts is possible using the parameter of |Jdd|/kB and therefore the origin of the hump structure is related to the direct magnetic interaction, Jdd, that is dominant in the system. Quite unusual crossover from a three-dimensional ordering to a one-dimensional magnet occurs when magnetic fields are applied parallel to the a axis. A notable anisotropic field-direction dependence against the in-plane magnetic field was also observed in the transition temperature of the bulk superconductivity by the angle-resolved heat capacity measurements. We discuss the origin of this in-plane anisotropy in terms of the 3d electron spin configuration change induced by magnetic fields.

Quasi-One and quasi-two dimensional organic conductors consisting of TTF derivatives such as BEDT-TTF (bis-(ethylene-dithio)-tetra-thia-fulvalene) and TMTCF (C = S; TMTTF: tetra-methyl-tetra-thia-fulvalene, C = Se; TMTSF: tetra-methyl-tetra-selena-fulvalene) have been well investigated in condensed matter physics because of interest in the emerging electric and magnetic properties, such as the spin density wave, charge order, superconductivity, anti-ferromagnetism, and so on. To probe the electronic state, nuclear magnetic resonance (NMR) is one of the most powerful tools as the microscopic magnetometer. A number of 13C-NMR studies have been performed of the double-site central 13C=13C bond substituted molecules. However, problems with the coupled spin system of 13C=13C complicated the interpretation for observations on NMR. Therefore, single-site 13C-enriched molecules are desired. We summarize the problem of Pake doublet and the preparation of the single-site 13C-susbstituted BEDT-TTF and TMTCF molecules. We also demonstrate the superiority of 13C-NMR of the single-site 13C-susbstituted molecule utilizing the hyperfine coupling tensor.

Organic conductors consisting of donor and anion molecules provide various important study fields such as superconductivity and electron correlation. π electrons are responsible for the emergence of these phenomena. On the other hand, the coexistent systems of π electrons and localized 3d spins have been realized by introducing magnetic anions. Such coexistent systems are called π-d systems. In π-d systems, various fascinating magnetic and conducting phenomena are observed due to the coupling of π electrons and localized 3d electrons (π-d interaction). One of the most striking phenomena is magnetic field-induced superconductivity, which is first observed in λ-(BETS)2FeCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene. On the other hand, λ-(BETS)2FeCl4 shows a metal-insulator transition accompanying an antiferromagnetic ordering at TN of 8.3K and the unconventional antiferromagnetic state that 3d spins behave as if they stay paramagnetic even below TN. These phenomena are also considered to be caused by the π-d interaction, but their mechanisms have not been demonstrated. Recently, a new λ-type π-d system of λ-(BEDT-STF)2FeCl4, where BEDT-STF is bis(ethylenedithio)dithiadiselenafulvalene, has been developed. In this review, the influence of bandwidth control by donor substitution and the dilution effect of magnetic ions on the magnetic properties of the π-d system will be discussed. We will demonstrate that site-selective magnetization measurements by 13CNMR and 57Fe Mössbauer measurements and heat capacity measurements provide important information to understand the mechanism of unconventional magnetic properties in π-d systems. We would also like to introduce the advantages of the 13CNMR measurements using one-sided-13C-enriched donor molecules, which are the key technique in our experiments. [ABSTRACT FROM AUTHOR]

We consider inverse problems for the first- and half-order time-fractional equation. We establish the stability estimates of Lipschitz type in inverse source and inverse coefficient problems by means of the Carleman estimates. [ABSTRACT FROM AUTHOR]

Angle-resolved heat capacity (ARHC) measurements with multi-directional magnetic fields for an organic superconductor λ-(BETS)2GaCl4 are performed to investigate the out-of-plane (polar angle) and in-plane (azimuthal angle) anisotropic features in the superconducting electronic heat capacity Cele. The polar angle (θ) dependences of Cele have a simple twofold periodicity caused by the anisotropy of the critical field Hc2. In contrast, the azimuthal angle (ϕ) dependences show asymmetric anisotropies including twofold and fourfold-like terms originating from the anisotropy of the superconducting gap function. From the results, we discuss the gap function from the perspective of the mixed symmetry caused by the antiferromagnetic spin fluctuation on the low-symmetry λ-type lattice. [ABSTRACT FROM AUTHOR]

Low-temperature heat capacity of the organic superconductor λ-(BETS)2GaCl4 in a temperature range between 0.6 and 10K was measured for a single crystal sample by relaxation calorimetry technique. The contribution of electronic heat capacity in the superconducting state shows T2 dependence at lower temperature that indicates the existence of quasi-particle excitations from the line-nodal gap structure of d-wave pairing. The recovery of the electronic heat capacity coefficient, γ by magnetic field shows H1/2 dependence that is consistent with the picture of line-nodal superconductor. In spite of the different packing from typical organic superconductors κ-(BEDT-TTF)2X, the λ-type BETS salt also shows a feature of d-wave symmetry pairing. [ABSTRACT FROM AUTHOR]

We present experimental evidence for the charge fluctuation in the spin-liquid candidate κ-(BEDT-TTF)2Cu2(CN)3. The temperature and pressure dependence of the Raman spectrum in the region of 1300-1600 cm-1 were measured. The charge-sensitive ν2 mode at 1500 cm-1 exhibited a linewidth broadening below 60K when the sample was slowly cooled. This broadening is induced by a structural change (increase in interdimer transfer integrals). The hydrostatic pressure significantly suppressed the broadening in the metallic phase. This result indicates that the linewidth broadening originates from the valence (charge) fluctuation within the BEDT-TTF dimer, because the screening effect suppresses the interdimer Coulomb interaction that causes the charge disproportionation. The line shape was analyzed using the fast fluctuating model and slow or static inhomogeneous model. [ABSTRACT FROM AUTHOR]

We performed tunneling spectroscopy (STS) measurement in an organic superconductor, partially deuterated κ-(BEDT-TTF-d[3,3])2Cu[N(CN)2]Br. We carried out angle-resolved STS on cut lateral surfaces by the focused ion beam (FIB) method as well as as-grown single-crystal surfaces. It was found that the d[3,3]-Br salt is a strong-coupling d-wave superconductor and that the nodal direction is at an angle of π/4 from the a*-axis, corresponding to the dx2-y2 symmetry in the bulk superconducting phase. It is understood that the electron correlation in the d[3,3]-Br salt is not strong enough on the basis of the spin fluctuation mechanism. On the other hand, we also observed two types of superconducting gap. This suggests the coexistence of the dx2-y2 and dxy symmetries. This indicates a change in the symmetry from dx2-y2 in the bulk superconducting phase to dxy around the insulating region with increasing electron correlation. [ABSTRACT FROM AUTHOR]

Electrical resistivity measurements under pressure were conducted on the organic conductor λ-(BEDT-STF)2GaCl4, which is situated between λ-(ET)2GaCl4 and λ-(BETS)2GaCl4. Magnetic susceptibility was also measured at ambient pressure. A drop in resistivity, which is associated with the superconducting transition, was observed at Tc5K above 1.22 GPa. The superconducting phase was confirmed by pair-breaking under a magnetic field. This is the first observation of superconductivity in λ-(BEDT-STF)2GaCl4. The temperature dependence of spin susceptibility suggests a two-dimensional antiferromagnetic spin system without any magnetic ordering. The phase adjacent to the superconducting phase in λ-type systems is not the antiferromagnetic phase, unlike the case for κ-(ET)2X. [ABSTRACT FROM AUTHOR]

Locomotive soft robots (SoRos) have gained prominence due to their adaptability. Traditional locomotive SoRo design is based on limb structures inspired by biological organisms and requires human intervention. Evolutionary robotics, designed using evolutionary algorithms (EAs), have shown potential for automatic design. However, EA-based methods face the challenge of high computational cost when considering multiphysics in locomotion, including materials, actuations, and interactions with environments. Here, we present a design approach for pneumatic SoRos that integrates gradient-based topology optimization with multiphysics material point method (MPM) simulations. This approach starts with a simple initial shape (a cube with a central cavity). The topology optimization with MPM then automatically and iteratively designs the SoRo shape. We design two SoRos, one for walking and one for climbing. These SoRos are 3D printed and exhibit the same locomotion features as in the simulations. This study presents an efficient strategy for designing SoRos, demonstrating that a purely mathematical process can produce limb-like structures seen in biological organisms. [ABSTRACT FROM AUTHOR]

The organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl has been studied for the examination of the conducting mechanism of the semiconducting behavior at high temperatures by 13C-NMR spectroscopy. We found that the temperature dependence of the linewidths and the spin-spin relaxation rate T2-1 showed a peak structure characterized by the hyperfine coupling constant in this region, suggesting a connection between ethylene motion and conducting electrons similar to that observed in κ-(BEDT-TTF)2Cu(NCS)2. Although all κ-(BEDT-TTF)2Cu[N(CN)2]Cl salt was thought to be an insulator at high temperature, our findings suggest that all κ-type salts at high temperatures could be in the same phase where the scattering caused by ethylene motion is added to bad metal. [ABSTRACT FROM AUTHOR]

We have performed ¹H NMR and 13C NMR measurements to investigate the coupling between molecular dynamics and the electronic state of β'-(BEDT-TTF)2ICl2. From the 1HNMR measurements, we observed a frequency-dependent anomaly in the nuclear spin-lattice relaxation rate ¹T-11 that originates from the slowing down of the ethylene motion. In the 13C NMR measurements, we found an anomaly in the linewidth of the NMR spectra at around 150 K, which is attributed to a nuclear spin-spin relaxation rate (13T2) anomaly. The magnitudes of the anomalies in the linewidth and in 13T-12 are related to the hyperfine coupling constant. These results suggest that the ethylene motion modulates the molecular orbital of the BEDT-TTF molecules and gives rise to a difference in the orbital energy between the "staggered" and "eclipsed" conformations. We propose that significant coupling exists between the ethylene motion and the electronic state of the molecular dimer and that the ethylene dynamics can trigger the emergence of charge degrees of freedom inside the dimers and cause the dielectric anomaly in β'-(BEDT-TTF)2ICl2. [ABSTRACT FROM AUTHOR]