arXiv subjects

Yuki Osada

Publications and source records attributed to Yuki Osada.

4 recordsLinked to original sources

arXiv2026

Standing waves for defocusing nonlinear Schr\"odinger equations with point interaction

We consider standing waves of the nonlinear Schr\"odinger equation $i\partial_t u = -\Delta_\alpha u + |u|^{p-1}u$ in the defocusing case in dimensions $N=2$ and $N=3$. Here, $-\Delta_\alpha$ denotes the Laplacian with a point interaction. This operator is bounded from below by a negative constant; consequently, unlike in the free case, the associated energy functional admits non-trivial minimizers. We establish existence and uniqueness of standing waves, and prove further qualitative properties, including radial symmetry, positivity, and stability. Moreover, we build an appropriate functional space for the zero-mass case and establish sharp decay estimates in this case.

math.AP↗

arXiv2025

Coupled nonlinear Schr\"odinger equations with point interaction: existence and asymptotic behaviour

In this paper we deal with the following weakly coupled nonlinear Schr\"{o}dinger system \begin{align*} \begin{cases} - \Delta_\alpha u + \omega u = |u|^2 u + \beta u |v|^2&\quad \mathrm{in}\ \mathbb{R}^2,\\ - \Delta v + \tilde{\omega} v = |v|^2 v + \beta |u|^2 v&\quad \mathrm{in}\ \mathbb{R}^2, \end{cases} %\tag{$\mathcal{P}_\beta$} \end{align*} where $-\Delta_\alpha$ denotes the Laplacian operator with a point interaction, $\omega$ greater then a suitable positive constant, $\tilde{\omega}>0$, and $\beta\ge 0$. For any $\beta\ge 0$ this system admits the existence of a ground state solution which can have only one nontrivial component or two nontrivial components and which could be regular or singular. We analyse this phenomenon showing how this depends strongly on the parameters. Moreover we study the asymptotic behaviour of ground state solutions whenever $\beta\to \infty$.

math.AP↗

arXiv2024

Giant Seebeck Effect in PEDOT Materials with Molecular Strain

Poly 3,4-ethylenedioxythiophene (PEDOT) has been attracting attention as a thermoelectric material for room-temperature use due to its flexibility and non-toxicity. However, PEDOT reportedly generates insufficient thermoelectric power for practical use. This work tried to improve the Seebeck coefficient by introducing molecular strain to PEDOT molecules by loading a Polystyrene sulfonate (PSS)-free PEDOT on a Polyethyleneterephthalate (PET) fiber. Raman spectroscopy revealed the PEDOT materials with significant compression in the C{\alpha}-C{\alpha} bond and extension in the C{\alpha}=C\b{eta} bond exhibit Seebeck coefficients two orders of magnitude larger than usual. Furthermore, strain in the C\b{eta}-C\b{eta} bond strongly correlated with the Seebeck coefficient that varied in a broad range from -2100 to 3100 {\mu}V K-1. This variation indicated that the molecular strain formed a sharp peak or valley around the Fermi level in the density of state (DOS) function, which gradually shifts along with the C\b{eta}-C\b{eta} strain. This molecular strain-induced giant Seebeck effect is expected to be an applicable technique for other polythiophene molecules.

cond-mat.mtrl-sci↗

arXiv2014

Hourglass Automata

In this paper, we define the class of hourglass automata, which are timed automata with bounded clocks that can be made to progress backwards as well as forwards at a constant rate. We then introduce a new clock update for timed automata that allows hourglass automata to be expressed. This allows us to show that language emptiness remains decidable with this update when the number of clocks is two or less. This is done by showing that we can construct a finite untimed graph using clock regions from any timed automaton that use this new update.

cs.FL↗