Search

The organic system, $\kappa$-[(BEDT-TTF)$_{1-x}$(BEDT-STF)$_x$]$_2$Cu$_2$(CN)$_3$, showing the Mott transition between a nonmagnetic Mott insulating (NMI) state and a Fermi liquid (FL), is systematically studied by calorimetric measurements. An increase of the electronic heat capacity at the transition from the NMI state to the FL state which keeps the triangular dimer lattice demonstrates that the charge sector lost in the Mott insulating state is recovered in the FL state. We observed that the remaining low-energy spin excitations in the Mott insulating state show unique temperature dependence, and that the NMI state has a larger lattice entropy originating from the frustrated lattice, which leads to the Pomeranchuk-like effect on the electron localization. Near the Mott boundary, an unexpected enhancement and magnetic-field dependence of heat capacity are observed. This anomalous heat capacity is different from the behavior in the typical first-order Mott transition and shows similarities with quantum critical behavior. To reconcile our results with previously reported scenarios about a spin gap and the first-order Mott transition, further studies are desired., Comment: 9 pages, 4 figures

The electronic properties of molecular conductors can be readily varied via physical or chemical pressure as it enlarges the bandwidth W. This enables them to cross the Mott insulator-to-metal phase transition by reducing electronic correlations U/W. Here we introduce an alternative path by spatially expanding the molecular orbitals when partially replacing sulfur by selenium in the constituting bis-(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) molecules of the title compound. We characterize how the insulating quantum-spin-liquid state is tuned via a Mott transition to the metallic Fermi-liquid state crossing a narrow region of superconductivity. The transport, dielectric, and optical measurements reveal that at this first-order phase transition, metallic regions coexist in the insulating matrix leading to pronounced percolative effects, which are most obvious in the strong enhancement of the dielectric constant at low temperatures.

Cellular structures manifest their outstanding mechanical properties in many biological systems. One key challenge for designing and optimizing these geometrically complicated structures lies in devising an effective geometric representation to characterize the system's spatially varying cellular evolution driven by objective sensitivities. A conventional discrete cellular structure, e.g., a Voronoi diagram, whose representation relies on discrete Voronoi cells and faces, lacks its differentiability to facilitate large-scale, gradient-based topology optimizations. We propose a topology optimization algorithm based on a differentiable and generalized Voronoi representation that can evolve the cellular structure as a continuous field. The central piece of our method is a hybrid particle-grid representation to encode the previously discrete Voronoi diagram into a continuous density field defined in a Euclidean space. Based on this differentiable representation, we further extend it to tackle anisotropic cells, free boundaries, and functionally-graded cellular structures. Our differentiable Voronoi diagram enables the integration of an effective cellular representation into the state-of-the-art topology optimization pipelines, which defines a novel design space for cellular structures to explore design options effectively that were impractical for previous approaches. We showcase the efficacy of our approach by optimizing cellular structures with up to thousands of anisotropic cells, including femur bone and Odonata wing., Comment: 23 pages, 20 figures

The two-dimensional organic superconductor $\ensuremath{\lambda}\ensuremath{-}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ exhibits pronounced charge fluctuations below $T\ensuremath{\approx}150$ K, in contrast to the sibling compound $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ that remains metallic down to milli-Kelvin. Infrared spectroscopy reveals only minor splitting in the vibrational features of the latter compound, common to other strongly dimerized $\ensuremath{\kappa}$-type salts. When the organic molecules are arranged in the $\ensuremath{\lambda}$-type pattern, however, a strong vibrational ${\ensuremath{\nu}}_{27}({b}_{1u})$ mode is present that forms a narrow doublet. Most important, when cooling $\ensuremath{\lambda}\ensuremath{-}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ below 150 K, two weak side modes appear due to charge disproportionation that amounts to $2\ensuremath{\delta}=0.14e$. In analogy to the ${\ensuremath{\beta}}^{\ensuremath{'}\ensuremath{'}}$-type organic conductors, we propose that charge fluctuations play an important role in emerging of unconventional superconductivity in $\ensuremath{\lambda}\ensuremath{-}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ at ${T}_{c}=4.7$ K. We discuss the possibility of a charge-density wave that coexists with the proposed spin-density-wave state.

Advanced manufacturing processes such as additive manufacturing offer now the capability to control material placement at unprecedented length scales and thereby dramatically open up the design space. This includes the considerations of new component topologies as well as the architecture of material within a topology offering new paths to creating lighter and more efficient structures. Topology optimization is an ideal tool for navigating this multiscale design problem and leveraging the capabilities of advanced manufacturing technologies. However, the resulting design problem is computationally challenging as very fine discretizations are needed to capture all micro-structural details. In this paper, a method based on reduction techniques is proposed to perform efficiently topology optimization at multiple scales. This method solves the design problem without length scale separation, i.e., without iterating between the two scales. Ergo, connectivity between space-varying micro-structures is naturally ensured. Several design problems for various types of micro-structural periodicity are performed to illustrate the method, including applications to infill patterns in additive manufacturing.

In this work, the thermodynamic properties of the organic superconductor $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ are investigated to study a high-field superconducting state known as the putative Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We observed a small thermodynamic anomaly in the field ${H}_{\mathrm{FFLO}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}10$ T, which corresponds to the Pauli limiting field ${H}_{\mathrm{P}}$. This anomaly probably originates from a transition from a uniform superconducting state to the FFLO state. ${H}_{\mathrm{FFLO}}$ does not show a strong-field angular dependence due to a quasi-isotropic paramagnetic effect in $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$. The thermodynamic anomaly at ${H}_{\mathrm{FFLO}}$ is smeared out. and the low-temperature upper critical field ${H}_{\mathrm{c}2}$ changes significantly if fields are not parallel to the conducting plane, even for a deviation of $\ensuremath{\sim}0.{5}^{\ensuremath{\circ}}$. This behavior indicates that the high-field state is very unstable, as it is influenced by the strongly anisotropic orbital effect. Our results are consistent with the theoretical predictions on the FFLO state and show that the high-field superconductivity is probably an FFLO state in $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ from a thermodynamic point of view.

We performed $^{13}\mathrm{C}$ NMR measurements on an organic superconductor $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{B}\mathrm{E}\mathrm{T}\mathrm{S})}_{2}\mathrm{Ga}{\mathrm{Cl}}_{4}$ [BETS: bis(ethylenedithio)tetraselenafulvalene] to investigate the pressure effect on the spin density wave (SDW) fluctuations at low temperatures, which were observed at ambient pressure. We found that the spin-lattice relaxation rate divided by temperature $(1/{T}_{1}T)$ is significantly enhanced at low temperatures at 3 kbar, implying enhancement of the SDW fluctuation. When further pressure is applied, increase in $1/{T}_{1}T$ at low temperatures is suppressed and $1/{T}_{1}T$ becomes temperature independent, indicating the Fermi liquid state. Moreover, we revealed that the Korringa factor under pressure becomes double compared to its value at ambient pressure, suggesting a significant change in electron correlation. We discuss the effect of the SDW fluctuation and the electron correlation on the unconventional superconductivity.

We performed angular and temperature-dependent electron-spin-resonance measurements in the quasi-two-dimensional organic conductor $\ensuremath{\kappa}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{I}$. The interlayer spin diffusion is much weaker compared to the Cl and Br analogs, which are antiferromagnetic insulator and paramagnetic metal, respectively; $\ensuremath{\kappa}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{I}$ behaves insulating when cooled below $T=200\phantom{\rule{4pt}{0ex}}\mathrm{K}$. A spin gap ($\mathrm{\ensuremath{\Delta}}\ensuremath{\approx}18\phantom{\rule{4pt}{0ex}}\mathrm{K}$) opens at low temperatures leading to a spin-singlet state. Due to intrinsic disorder a substantial number of spins ($\ensuremath{\sim}1%$) remains unpaired. We observe additional signals below $T=4\phantom{\rule{4pt}{0ex}}\mathrm{K}$ with a pronounced anisotropy indicating the presence of local magnetic moments coupled to some fraction of those unpaired spins.

For the unconventional organic superconductor $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ [BETS = bis(ethylenedithio) tetraselenafulvalene], the importance of both spin and charge degrees of freedom has been discussed based on the broadening of the NMR linewidth due to charge disproportionation and the occurrence of a spin-density-wave phase near the superconducting phase. NMR with the nuclear spin of $1/2$, previously used for studying organic conductors, is an effective method for revealing electronic states microscopically; however, it cannot distinguish between charge and spin anomalies. To resolve this problem, in this paper, we performed $^{69,71}\mathrm{Ga}$-NMR measurements, which enabled us to study both charge and spin dynamics using different gyromagnetic ratios and quadrupole moments between two isotopes. The spin-lattice relaxation rate is dominated by electric-field gradient fluctuations originating from molecular dynamics above 150 K and, below this temperature, it is dominated by spin fluctuations derived from the $\ensuremath{\pi}$ electrons of BETS layers. This change in the relaxation mechanism is considered to be due to the development of interactions between ${\mathrm{GaCl}}_{4}$ ions and BETS layers upon freezing of the molecular motion by cooling. Below 150 K, the contribution of spin fluctuations monotonically increases, and no increase in the charge fluctuation was observed, suggesting that the spin degree of freedom plays a major role in low-temperature physical properties. Our findings will aid theoretical studies on superconducting properties.

We performed $^{13}\mathrm{C}$-NMR measurements on an organic superconductor $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ to investigate the superconducting (SC) gap symmetry, where BETS stands for bis(ethylenedithio)tetraselenafulvalene. As the temperature approaches 0 K, the Knight shift in the SC state decreases; the nuclear spin-lattice relaxation rate $1/{T}_{1}$ shows cubic temperature dependence below the SC transition temperature ${T}_{c}$ without a coherence peak. These results can be understood in terms of $d$-wave superconductivity. Moreover, an increase in $1/{T}_{1}T$ at lower temperatures was observed just above ${T}_{c}$; this behavior can be interpreted as an effect of spin-density-wave (SDW) fluctuation. We suggest that the $d$-wave superconductivity of $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ originates from SDW fluctuation.

This paper examines the determinants of corporate savings in a cross-country panel setting. Specifically, it employs firm-level data covering more than 540,000 firm-year observations for 12 advanced and emerging market economies. Panel regression results suggest that reductions in statutory corporate income tax rates can explain one-third of the rise in corporate savings (defined as net financial assets) in 2003-17. This finding is supported by a propensity scores matching analysis of the effects of changes in corporate income tax rates.

We have performed $^{13}\mathrm{C}$ NMR measurements on $\ensuremath{\lambda}\ensuremath{-}{(\mathrm{BEDT}\ensuremath{-}\mathrm{STF})}_{2}{\mathrm{FeCl}}_{4}$ to reveal the mechanism of unconventional paramagneticlike behavior observed in $\ensuremath{\lambda}$-type molecular $\ensuremath{\pi}\ensuremath{-}d$ systems. $^{13}\mathrm{C}$ NMR spectra and nuclear spin-lattice relaxation rate $1/{T}_{1}$ revealed that the $\ensuremath{\pi}$ and $3d$ electron systems undergo an antiferromagnetic transition simultaneously at 16 K with the assistance of the $\ensuremath{\pi}\ensuremath{-}d$ interaction. We found that the sublattice magnetizations of the $\ensuremath{\pi}$ and $3d$ spins show different temperature dependence below ${T}_{\mathrm{N}}$, which is derived from the magnetic coupling between the two sublattice systems with different magnetic natures. We discuss the relationship between the two different magnetization processes and the unconventional magnetic behavior in $\ensuremath{\lambda}$-type molecular $\ensuremath{\pi}\ensuremath{-}d$ system.

This paper identifies the electronic state just close to the superconducting phase in a system of organic conductors lambda-(BETS)2GaBrxCl4-x as a spin-density-wave state, using nuclear magnetic resonance and resistivity measurements. This finding explains the unexplainable enhancement of spin fluctuation at low temperatures in lambda-(BETS)2GaCl4 and suggests that the superconductivity of lambda-type salts is mediated by spin-density-wave fluctuations.

We consider a half-order time-fractional diffusion equation in an arbitrary dimension and investigate inverse problems of determining the source term or the diffusion coefficient from spatial data at an arbitrarily fixed time under some additional assumptions. We establish the stability estimate of Lipschitz type in the inverse problems and the proofs are based on the Bukhgeim-Klibanov method by using Carleman estimates., Comment: 26 pages

A family of organic conductors, α-(BEDT-TTF)2MHg(SCN)4, is known to show the density wave (DW) state for M = Tl, K, and Rb salts, or the superconducting (SC) state for M = NH4 salt at low temperatu...

Influences of coarse aggregate on the mechanical properties of Strain Hardening Cementitious Composite (SHCC) were experimentally investigated at the material and structural level. In the experiments, maximum size and volume fraction of coarse aggregate were varied as parameters. Direct uni-axial tensile tests and bending tests were carried out in order to evaluate the mechanical performance such as tensile strength and elongation capacity of SHCC itself. And also, bending-shear loading tests of steel reinforced SHCC (R/SHCC) beams were conducted. As the results, decreasing of tensile performances of SHCC in material level were observed by an increasing of the volume fraction of coarse aggregate. However, shear capacity of R/SHCC beam did not decrease. Both the tensile performance and the aggregate interlocking has effect on the mechanical behavior of R/SHCC beam failed in diagonal shear. It was suggested that these two mechanisms are the trade-off relation and the aggregate interlocking had significant effect on the shear capacity in this study., This is an accepted version of the article presented at Strain-Hardening Cement-Based Composites, RILEM Bookseries 15, DOI 10.1007/978-94-024-1194-2_16., 4th International Conference on Strain-Hardening Cement-Based Composites (SHCC4) From 18 September 2017 to 20 September 2017 Dresden, Germany

We consider the first and half order time fractional equation with the zero initial condition. We investigate an inverse source problem of determining the time-independent source factor by the data at an arbitrarily fixed time and we establish the conditional stability estimate of H\"older type in our inverse problem. Our method is based on the Bukhgeim-Klibanov method by means of the Carleman estimate. We also derive the Carleman estimate for the first and half order time fractional diffusion equation., Comment: 19 pages

This paper deals with a design method for boundary shapes using filtering techniques based on a partial differential equation (PDE). In shape optimization, it is known that oscillatory boundaries appear when design variables are directly assigned to the design boundaries. In addition, during the optimization process, discretized elements in a computational domain are distorted due to extremely large shape changes along the design boundaries. The distorted elements may cause accuracy deterioration or numerical instability in a forward problem. In this paper, we propose a shape optimization method by using the PDE as a low pass filter which prevents the oscillatory boundaries of the optimized design. For restricting the shape distortion of the discretized elements, the shear deformation of the elements is constrained in the optimization problem. Mathematical programming is used to find the boundary shapes under the KKT conditions. The effectiveness of the proposed method is demonstrated through numerical examples in solid and fluid mechanics.

Optical studies of the density wave (DW) salt of $\ensuremath{\alpha}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{KHg}(\mathrm{SCN})}_{4}$ revealed a pseudogap due to a charge fluctuation below ${T}^{*}\ensuremath{\simeq}$ 200 K. Moreover, $^{13}\mathrm{C}$-NMR studies of the DW salt of $\ensuremath{\alpha}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{RbHg}(\mathrm{SCN})}_{4}$ and of the superconductivity (SC) salt of $\ensuremath{\alpha}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{NH}}_{4}\mathrm{Hg}{(\mathrm{SCN})}_{4}$ suggested that the NMR line width of the A site increased and the charge disproportionation in the A column developed below ${T}^{*}$. These phenomena may be due to the development of a horizontal stripe modulation of the local charge density. However, whether the horizontal stripe modulation develops or not and the relationships among ${T}^{*}$ anomalies, the pseudogap, and line broadening, were unclear. In this study, $^{13}\mathrm{C}$-NMR measurements were obtained of the metallic salt of $\ensuremath{\alpha}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{TlHg}(\mathrm{SeCN})}_{4}$, and its electronic structure was compared with those of the DW and SC salts. The NMR line width of the A site and ${\ensuremath{\chi}}_{\mathrm{B}}/{\ensuremath{\chi}}_{\mathrm{C}}$ in Rb(SCN) and $\mathrm{NH}{}_{4}$(SCN) increased and deviated from that in Tl(SeCN) below ${T}^{*}$, suggesting the development of the instability of horizontal stripe modulation in Rb(SCN) and $\mathrm{NH}{}_{4}$(SCN) and that ${T}^{*}$ anomalies could be due to the instability.

The physical properties of the organic conductor $\ensuremath{\kappa}\text{\ensuremath{-}}(\mathrm{BEDT}\text{\ensuremath{-}}{\mathrm{TTF})}_{2}{\mathrm{Cu}[\mathrm{N}(\mathrm{CN})}_{2}]\mathrm{I}$ $(\ensuremath{\kappa}\text{\ensuremath{-}}\mathrm{I})$ are inconsistent with the universal phase diagram of isostructural $\ensuremath{\kappa}$-Br and $\ensuremath{\kappa}$-Cl. To systematically understand $\ensuremath{\kappa}$-type salts, we measured and compared $^{13}\mathrm{C}$ NMR spectra of $\ensuremath{\kappa}$-I, $\ensuremath{\kappa}$-Br, and $\ensuremath{\kappa}$-Cl. The $\ensuremath{\kappa}$-I spectra manifested abrupt line broadening below 40 K due to the development of electronic inhomogeneity and an increase in the spin-lattice relaxation rate divided by temperature $1/{T}_{1}T$ down to the lowest temperature, suggesting an enhanced antiferromagnetic (AF) fluctuation. These results imply that AF fluctuation without long-range order in $\ensuremath{\kappa}$-I is induced by electronic inhomogeneity, which disturbs the development of coherency. Consequently, $\ensuremath{\kappa}$-I is an insulator with AF fluctuation at low temperature similar to x-ray-irradiated $\ensuremath{\kappa}$-Cl. We suggest that not only pressure but also disorder is a key parameter in the physical properties of $\ensuremath{\kappa}$-type salts.

An electron paramagnetic resonance study for an organic superconductor ${\ensuremath{\beta}}^{\ensuremath{'}\ensuremath{'}}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{4}[({\mathrm{H}}_{3}\mathrm{O})\mathrm{Ga}{({\mathrm{C}}_{2}{\mathrm{O}}_{4})}_{3}]\phantom{\rule{0.16em}{0ex}}\ifmmode\cdot\else\textperiodcentered\fi{}\phantom{\rule{0.16em}{0ex}}{\mathrm{C}}_{6}{\mathrm{H}}_{5}{\mathrm{NO}}_{2}$ reveals that superconductivity coexists uniformly with the charge ordered state in one material. In the charge ordered state, the interplane spin exchange is gapped, while the in-plane conductivity is not significantly modified. This anisotropic behavior is explained by an exotic charge ordered state, in which molecular-site-selective carrier localization coexists with conducting carriers on other molecules. The relationship between superconductivity and this conductive charge ordered state is investigated.

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.

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., Author summary In this paper, we developed a computational method to investigate the relationship between three-dimensional bone shape and external loads imposed on bones. Many studies report 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 the shape of bones adapts to external load. However, it remains unclear whether this hypothesis can explain the shape of bones. Here, we constructed a three-dimensional mathematical model that imitates the cellular activities of bone formation to attempt the reproduction of the shape of teleost vertebrae. In teleosts, the shape of the vertebrae differs among the species. We set the multiple types of external load conditions in the simulations and compared the simulation results with different teleost vertebrae. The produced structures that can resist the deformation of the surrounding tissues exhibited multiple structural features similar to the vertebrae of several teleost species. This result shows that the formation of bone shape can be explained by the adaptation to external load.

λ-type molecular π–d systems are coupled systems consisting of π electron systems with strong magnetic interactions and 3d electron systems with weak magnetic interactions. They exhibit an unconven...

In this paper, we propose grayscale-free topology optimization for a reactor design problem where the electromagnetic performance needs to be optimized. A reactor is an electric device to boost electric voltage, and is used as a part of a DC-DC converter in electric and hybrid vehicles. When designing reactors, we need to consider many performance indicators such as inductance and fringing loss. In general, high-performance reactor design that satisfies all requirements is not obvious, and topology optimization is promising for such non-trivial design problems. In this paper, we therefore establish a framework for the electromagnetic design of an in-vehicle reactor on the basis of boundary tracking type level-set topology optimization, which realizes grayscale-free topology optimization. Because of its grayscale-free characteristic, the established framework can completely resolve the numerical problems caused by the so-called grayscale elements. We present several numerical examples to demonstrate the usefulness of the established framework, and we discuss the possibilities for the expansion of the established framework to more difficult and valuable design problems.

Orthotropic elastic moduli of composite structures can be identified by nonlinear least squares fit between measured and computed natural frequencies. However, due to measurement errors contained in the measured natural frequencies and mode shapes, the process of elastic moduli identification is error-prone. This paper proposes an efficient method to estimate the errors in the elastic moduli caused by the measurement errors in the natural frequencies. The method utilizes an efficient semi-analytic expression of the sensitivities of the eigenvalues with respect to the orthotropic elastic moduli. First, the first-order approximation of the analytic sensitivity of orthotropic elastic moduli with respect to the measurement errors is introduced. The approximation is then used to estimate the variability of the identified elastic moduli due to the measurement errors. It is shown that the aspect ratio of the test specimen greatly affects the standard deviation of the identified elastic moduli. Second, using the first-order approximation, the effects of aspect ratio of the test specimen as well as the values of the elastic moduli are further investigated. Based on the results of numerical experiments, guidelines for the dimension of the test specimen for the elastic moduli identification are proposed.

In this paper, a combined numerical–experimental methodology for the identification of elastic moduli of orthotropic media is presented. Special attention is given to the laminated electrical steel sheets, which are modeled as orthotropic media with nine independent engineering elastic moduli. The elastic moduli are determined specifically for use with finite element vibration analyses. We propose a three-step methodology based on a conventional nonlinear least squares fit between measured and computed natural frequencies. The methodology consists of: (1) successive augmentations of the objective function by increasing the number of modes, (2) initial condition updates, and (3) appropriate selection of the natural frequencies based on their sensitivities on the elastic moduli. Using the results of numerical experiments, it is shown that the proposed method achieves more accurate converged solution than a conventional approach. Finally, the proposed method is applied to measured natural frequencies and mode shapes of the laminated electrical steel sheets. It is shown that the method can successfully identify the orthotropic elastic moduli that can reproduce the measured natural frequencies and frequency response functions by using finite element analyses with a reasonable accuracy.

We performed heat capacity measurements on the molecular π–d system λ-(BEDT-STF)2FeCl4 to discuss the unconventional paramagnetic-like behavior. We observed a Schottky-type anomaly below TN of 16 K...

To verify the effect of geometrical frustration, we artificially distort the triangular lattice of the quasi-two-dimensional organic conductor $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{CN})}_{3}$ [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene] by analogous-molecular substitution and apply $^{13}\mathrm{C}$ NMR of bulk and substituted sites, electric conductivity, and static magnetic susceptibility measurements. The results indicate that the magnetic characteristics of the substituted sample are quantitatively similar to those of the pure sample. Moreover, the magnetic characteristics at the substituted sites are also the same as in the bulk. These results suggest that the observed magnetic properties may not be due to the geometrical frustration but the importance of disorder.

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., 27pages

We have performed $^{1}\mathrm{H}$ NMR and $^{13}\mathrm{C}$ NMR measurements to investigate the coupling between molecular dynamics and the electronic state of ${\ensuremath{\beta}}^{\ensuremath{'}}$-(BEDT-TTF)${}_{2}{\mathrm{ICl}}_{2}$. From the $^{1}\mathrm{H}$ NMR measurements, we observed a frequency-dependent anomaly in the nuclear spin-lattice relaxation rate $^{1}\mathrm{T}_{1}^{\ensuremath{-}1}$ that originates from the slowing down of the ethylene motion. In the $^{13}\mathrm{C}$ 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 $(^{13}\mathrm{T}_{2})$ anomaly. The magnitudes of the anomalies in the linewidth and in $^{13}\mathrm{T}_{2}^{\ensuremath{-}1}$ 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 ${\ensuremath{\beta}}^{\ensuremath{'}}$-(BEDT-TTF)${}_{2}{\mathrm{ICl}}_{2}$.

The electronic state of (TMTTF) 2 SbF 6 was investigated by the 1 H and 13 C NMR measurements. The temperature dependence of T 1 −1 in 1 H NMR shows a sharp peak associated with the antiferromagnetic transition at T AF =6 K. The temperature dependence of T 1 −1 is described by the power law T 2.4 below T AF . This suggests the nodal gapless spin wave excitation in antiferromagnetic phase. In 13 C NMR, two sharp peaks at high temperature region, associated with the inner and the outer carbon sites in TMTTF dimer, split into four peaks below 150 K. It indicates that the charge disproportionation occurs. The degree of charge disproportionation Δ ρ is estimated as (0.25±0.09) e from the chemical shift difference. This value of Δ ρ is consistent with that obtained from the infrared spectroscopy. In the antiferromagnetic state (AFI), the observed line shape is well fitted by eight Lorentzian peaks. This suggests that the charge order with the same degree still remains in the AF state. From the line assignment, the AF staggered spin amplitude is obtained as 0.70 μ B and 0.24 μ B at the charge rich and the poor sites, respectively. These values corresponding to almost 1 μ B per dimer are quite different from 0.11 μ B of another AF (AFII) state in (TMTTF) 2 Br with effective higher pressure. As a result, it is understood that the antiferromagnetic staggered spin order is stabilized on the CO state in the AFI phase of (TMTTF) 2 SbF 6 .

We performed $^{13}\mathrm{C}$ NMR measurements on the unconventional organic superconductor $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ to clarify its electronic properties in the paramagnetic state. We found that the spin-lattice relaxation rate divided by temperature $1/{T}_{1}T$ shows Curie-like enhancement above 55 K that arises from an antiferromagnetic fluctuation. In addition, we found additional enhancement of $1/{T}_{1}T$ below 10 K, where the Knight shift decreases and the linewidth of NMR spectra is broadened. The result could be understood by the magnetic fluctuation induced by the nesting of the Fermi surface. We discovered that $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ salt inherently exhibits the two different types of magnetic fluctuations.

A general topology optimization method, which is capable of simultaneous design of density and orientation of anisotropic material, is proposed by introducing orientation design variables in addition to the density design variable. In this work, the Cartesian components of the orientation vector are utilized as the orientation design variables. The proposed method supports continuous orientation design, which is out of the scope of discrete material optimization approaches, as well as design using discrete angle sets. The advantage of this approach is that vector element representation is less likely to fail into local optima because it depends less on designs of former steps, especially compared with using the angle as a design variable (Continuous Fiber Angle Optimization) by providing a flexible path from one angle to another with relaxation of orientation design space. An additional advantage is that it is compatible with various projection or filtering methods such as sensitivity filters and density filters because it is free from unphysical bound or discontinuity such as the one at theta = 2 pi and theta = 0 seen with direct angle representation. One complication of Cartesian component representation is the point-wise quadratic bound of the design variables; that is, each pair of element values has to reside in a given circular bound. To overcome this issue, we propose an isoparametric projection method, which transforms box bounds into circular bounds by a coordinate transformation with isoparametric shape functions without having the singular point that is seen at the origin with polar coordinate representation. A new topology optimization method is built by taking advantage of the aforementioned features and modern topology optimization techniques. Several numerical examples are provided to demonstrate its capability. Copyright (C) 2014 John Wiley & Sons, Ltd.