arXiv subjects

Yohei Sato

Publications and source records attributed to Yohei Sato.

8 recordsLinked to original sources

arXiv2026

Normalized solutions for a class of gradient-type Schr\"odinger systems under Neumann boundary conditions in bounded domains

We investigate the existence of normalized solutions to the gradient-type Schr\"odinger system \begin{equation*} \begin{cases} -\Delta u+ V_1(x)u+\lambda u= uv^2 & \text{ in } \Omega,\\ -\Delta v+ V_2(x)v+\lambda v= u^2v & \text{ in } \Omega %\frac{\partial u}{\partial \nu}=\frac{\partial v}{\partial \nu}=0 \, & \text{ on } \partial \Omega \end{cases} \end{equation*} subject to the mass constraint $\int_{\Omega}\left(|u|^2+|v|^2 \right)dx=a>0$ and Neumann boundary conditions, where $\Omega\subset \mathbb{R}^3$ is a smooth bounded domain, each $V_i$ is continuous, and $\lambda$ is a Lagrange multiplier. Applying a minimax principle that incorporates Morse index information, we establish the existence of nontrivial normalized solutions of mountain pass type. The proof is based on a refined blow-up analysis adapted to such gradient-type systems, together with new Liouville-type theorems for finite Morse index solutions of the associated limit systems in $\mathbb{R}^3$ and $\mathbb{R}^3_+$.

math.AP↗

arXiv2026

Existence of Kelvin-Invariant Positive Solutions for Critical Elliptic Equations with Variable Coefficients via Profile Decomposition

In this paper, we consider the following critical nonlinear elliptic equation: \[ - \Delta u = a(x) |u|^{2^*-2}u \quad \text{in } \mathbb{R}^N, \quad u \in \mathcal{D}^{1,2}(\mathbb{R}^N) \] where $N \ge 3$, $2^* = \frac{2N}{N - 2}$, $a(x) \in C(\mathbb{R}^N, \mathbb{R})$ is a positive function that is invariant under the map $x \to -\frac{x}{|x|^2}$. Under some assumptions on $a(x)$, we show the existence of a positive solution to the equation that is invariant under the Kelvin transform. The symmetry condition imposed here is substantially weaker than the invariance under a noncompact symmetry group that is typically assumed in the literature. The key to the proof is a classification of the Palais--Smale sequences of the associated energy functional. To this end, we establish a new abstract profile decomposition theorem incorporating symmetries such as the Kelvin transform.

math.AP↗

arXiv2026

Sharp-interface VOF method for phase-change simulations on unstructured meshes

Unstructured meshes are among the most versatile approaches for capturing non-canonical geometries in fluid dynamics simulations. Despite this, most high-fidelity first-principles phase-change models are developed and applied on structured meshes. We present a phase-change simulation method for unstructured meshes that combines the algebraic Volume-of-Fluid (VOF) technique with geometric interface reconstruction, implemented in an in-house open-source CFD code. Phase-change rates are computed from local temperature gradients evaluated at the reconstructed interface, without empirical closure models, using a reconstruction procedure that operates on arbitrary polyhedral cells. Because the method relies on the standard finite-volume framework, it can be integrated into other cell-centred codes supporting unstructured meshes. The approach is validated against the one-dimensional Stefan and Sucking problems and the three-dimensional Scriven bubble growth on both hexahedral and polyhedral meshes, showing good agreement with analytical solutions in all three cases. A detailed analysis of the Scriven problem reveals that the interface-modified least-squares gradient stencil on Cartesian meshes overestimates the interfacial temperature gradient, producing a persistent overshoot of the analytical bubble radius and a coherent four-fold anisotropy that elongates the bubble along grid diagonals. On polyhedral meshes, the irregular face orientations eliminate both effects, yielding isotropic growth and monotonic convergence. Finally, we demonstrate the framework on turbulent upward co-current annular boiling flow, where early transient results are qualitatively consistent with a previous LES study and experimental observations of wave-modulated evaporation.

physics.comp-ph↗

arXiv2021

Selective crystal growth of indium selenide compounds from saturated solutions grown in a selenium vapor

Indium selenide compounds are promising materials for energy conversion, spintronic applications, and chemical sensing. However, it is difficult to grow stoichiometric indium selenide crystals due to the high equilibrium selenium vapor pressure and the complicated phase equilibrium system of indium selenide compounds. In this paper, we apply a novel and convenient crystal growth method, in which the saturated solution is grown by the application of a selenium vapor. In this method, selenium vapor at a pressure higher than the saturated vapor pressure is applied to molten indium, such that the selenium continuously dissolves into the indium solution until the solubility at the growth temperature is reached; then a slow cooling process results in crystallization. The selenium dose is matched to its solubility so that indium selenide compounds can be selectively grown just by controlling the temperature without the need to consider the chemical ratio in the solution. The pressure of the vapor is controlled during the whole growth process so that any deviation from a stoichiometric composition in the crystal can be controlled. Both InSe and In2Se3 were successfully grown using this method, and we have investigated the growth mechanism and found the growth window for each compound. This study presents a novel and convenient approach to fabricating transitional metal chalcogenides without deficiencies in the chalcogen element.

cond-mat.mtrl-sci↗

arXiv2018

Superconductivity at 38 K in an electrochemical interface between ionic liquid and Fe(Se0.8Te0.2) on various substrates

Superconducting FeSe0.8Te0.2 thin films on SrTiO3, LaAlO3 and CaF2 substrates were electrochemically etched in an ionic liquid DEME-TFSI electrolyte with a gate bias of 5 V. Superconductivity at 38 K was commonly observed on all substrates after etching the films with a thickness above 30 nm, in spite of different Tc of 8 K, 12 K and 19 K before the etching on SrTiO3, LaAlO3 and CaF2 substrates, respectively. Tc returned to the original value by removing the gate bias. The Tc enhancement on the thick film indicates no relationship between the Tc enhancement and any interface effects between the film and the substrate. The sheet resistance and the Hall coefficient of the surface conducting layer were estimated from the gate bias dependence of the transport properties. The sheet resistance of the surface conducting layer of the films on LaAlO3 and CaF2 showed an identical temperature dependence, and the Hall coefficient is almost temperature independent and -0.05 to -0.2 m2/C, corresponding to 4-17 electrons per one FeSe0.8Te0.2 unit cell area in two dimension. These common transport properties on various substrates suggest that the superconductivity at 38 K appeared in the surface conducting layer produced by electrochemical reaction between the surface of the FeSe0.8Te0.2 thin film and the ionic liquid electrolyte.

cond-mat.supr-con↗

arXiv2018

Data-driven modeling for boiling heat transfer: using deep neural networks and high-fidelity simulation results

Boiling heat transfer occurs in many situations and can be used for thermal management in various engineered systems with high energy density, from power electronics to heat exchangers in power plants and nuclear reactors. Essentially, boiling is a complex physical process that involves interactions between heating surface, liquid, and vapor. For engineering applications, the boiling heat transfer is usually predicted by empirical correlations or semi-empirical models, which has relatively large uncertainty. In this paper, a data-driven approach based on deep feedforward neural networks is studied. The proposed networks use near wall local features to predict the boiling heat transfer. The inputs of networks include the local momentum and energy convective transport, pressure gradients, turbulent viscosity, and surface information. The outputs of the networks are the quantities of interest of a typical boiling system, including heat transfer components, wall superheat, and near wall void fraction. The networks are trained by the high-fidelity data processed from first principle simulation of pool boiling under varying input heat fluxes. State-of-the-art algorithms are applied to prevent the overfitting issue when training the deep networks. The trained networks are tested in interpolation cases and extrapolation cases which both demonstrate good agreement with the original high-fidelity simulation results.

cs.CE↗

arXiv2015

A non-intrusive measurement technique applying CARS for concentration measurement in a gas mixing flow

Coherent anti-Stokes Raman scattering (CARS) microscope system was built and applied to a non-intrusive gas concentration measurement of a mixing flow in a millimeter-scale channel. Carbon dioxide and nitrogen were chosen as test fluids and CARS signals from the fluids were generated by adjusting the wavelengths of the Pump and the Stokes beams. The generated CARS signals, whose wavelengths are different from those of the Pump and the Stokes beams, were captured by an EM-CCD camera after filtering out the excitation beams. A calibration experiment was performed in order to confirm the applicability of the built-up CARS system by measuring the intensity of the CARS signal from known concentrations of the samples. After confirming that the measured CARS intensity was proportional to the second power of the concentrations as was theoretically predicted, the CARS intensities in the gas mixing flow channel were measured. Ten different measurement points were set and concentrations of both carbon dioxide and nitrogen at each point were obtained. Consequently, it was observed that the mixing of two fluids progressed as the measurement point moved downstream. The results show the applicability of CARS to the non-intrusive concentration measurement of gas flows without any preprocess such as gas absorption into liquid or solid.

physics.flu-dyn↗

arXiv2014

Van der Waals epitaxial growth of topological insulator Bi$_{2-x}$Sb$_x$Te$_{3-y}$Se$_y$ ultrathin nanoplate on electrically insulating fluorophlogopite mica

We report the growth of high quality Bi$_{2-x}$Sb$_x$Te$_{3-y}$Se$_y$ ultrathin nanoplates (BSTS-NPs) on an electrically insulating fluorophlogopite mica substrate using a catalyst-free vapor solid method. Under an optimized pressure and suitable Ar gas flow rate, we control the thickness, the size and the composition of BSTS-NPs. Raman spectra showing systematic change indicate that the thicknesses and compositions of BSTS-NPs are indeed accurately controlled. Electrical transport demonstrates that a robust Dirac cone carrier transport in BSTS-NPs. Since BSTS-NPs provide superior dominant surface transport of the tunable Dirac cone surface states with negligible contribution of the conduction of the bulk states, BSTS-NPs provide an ideal platform to explore intrinsic physical phenomena as well as technological applications of 3-dimensional topological insulators in the future.

cond-mat.mtrl-sci↗