arXiv subjects

Yusuke Doi

Publications and source records attributed to Yusuke Doi.

11 recordsLinked to original sources

arXiv2025

Floquet breathers in a modulated nonlinear lattice

In this work, we study a space-time modulated electro-mechanical system, consisting of an array of coupled cantilevers with their on-site potential provided by electromagnets driven by AC currents. Model equations are derived, and the effect of the modulation on the dispersion bands is examined. The theory of breather existence and stability is extended to include space-time modulation. We perform numerical simulations in a time-modulated system, showing three types of breather response depending on the driving frequency: (i) the modulation frequency is an integer multiple of the breather frequency or, in other words, this phenomenon corresponds to period doubling, tripling, etc.; (ii) the opposite, that is, the breather frequency is an integer multiple of the modulation frequency, corresponding to period-halving, etc. (iii) the breather and modulation frequencies are commensurate in a different form. We use for all of them the term {\em Floquet breathers} in analogy with Floquet solitons in photonic systems. As there is no dissipation, but periodic forcing, the energy is generally conserved but only at discrete times. There exists in this system a huge variety of breathers, either site-centered, symmetric and antisymmetric, bond centered, in-phase or in-quadrature with the modulation, and we analyze the evolution of stability of some of them as a function of the modulation frequency. The construction of a similar system would be of interest to study the properties of dynamic metamaterials.

nlin.PS↗

arXiv2025

Construction of cubic nonlinear lattice free from umklapp processes

We propose a novel type of umklapp-free lattice (UFL), where umklapp processes are completely absent. The proposed UFL incorporates cubic long-range nonlinearity, a feature not addressed in previous studies. In this paper, we derive an analytical expression for the cubic nonlinear coupling constants by imposing mathematical conditions such that the nonlinear coupling strength between particle pairs decays inversely with their separation distance. The absence of umklapp processes in the proposed lattice is confirmed through numerical comparisons with the Fermi-Pasta-Ulam-Tsingou (FPUT) lattice. Furthermore, molecular dynamics simulations are performed to investigate the thermal conductivity of the proposed lattice in the non-equilibrium steady state. Compared to the original FPUT lattice, the proposed UFL is closer to ballistic transport. Our results demonstrate that the umklapp processes induced by cubic nonlinearity are suppressed in the proposed UFL. Moreover, compared to the UFL with only quartic nonlinearity, truncation of long-range interactions plays a significant role in the proposed lattice.

nlin.CD↗

arXiv2024

Nonlinear bandgap transmission by discrete rogue waves induced in a pendulum chain

We study numerically a discrete, nonlinear lattice, which is formed by a chain of pendula submitted to a harmonic-driving source with constant amplitude and parametrical excitation. A supratransmission phenomenon is obtained after the derivation of the homoclinic threshold for the case when the lattice is driven at one edge. The lattice traps gap solitons when the chain is subjected to a periodic horizontal displacement of the pivot. Discrete rogue waves are generated for the case when the pendulum is simultaneously driven and shaken. This work may pave the way for experimental generation of discrete rogue waves within simple devices.

nlin.PS↗

arXiv2023

A semiclassical model for charge transfer along ion chains in silicates

It has been observed in fossil tracks and experiments in the layered silicate mica muscovite the transport of charge through the cation layers sandwiched between the layers of tetrahedra-octahedra-tetrahedra. A classical model for the propagation of anharmonic vibrations along the cation chains has been proposed based on first principles and empirical functions. In that model, several propagating entities have been found as kinks or crowdions and breathers, both with or without wings, the latter for specific velocities and energies. Crowdions are equivalent to moving interstitials and transport electric charge if the moving particle is an ion, but they also imply the movement of mass, which was not observed in the experiments. Breathers, being just vibrational entities, do not transport charge. In this work, we present a semiclassical model obtained by adding a quantum particle, electron or hole to the previous model. We present the construction of the model based on the physics of the system. In particular, the strongly nonlinear vibronic interaction between the nuclei and the extra electron or hole is essential to explain the localized charge transport, which is not compatible with the adiabatic approximation. The formation of vibrational localized charge carriers breaks the lattice symmetry group in a similar fashion to the Jahn-Teller Effect, providing a new stable dynamical state. We study the properties and the coherence of the model through numerical simulations from initial conditions obtained by tail analysis and other means. We observe that although the charge spreads from an initial localization in a lattice at equilibrium, it can be confined basically to a single particle when coupled to a chaotic quasiperiodic breather. This is coherent with the observation that experiments imply that a population of charge is formed due to the decay of potassium unstable isotopes.

cond-mat.mtrl-sci↗

arXiv2021

Classification of URL bitstreams using Bag of Bytes

Protecting users from accessing malicious web sites is one of the important management tasks for network operators. There are many open-source and commercial products to control web sites users can access. The most traditional approach is blacklist-based filtering. This mechanism is simple but not scalable, though there are some enhanced approaches utilizing fuzzy matching technologies. Other approaches try to use machine learning (ML) techniques by extracting features from URL strings. This approach can cover a wider area of Internet web sites, but finding good features requires deep knowledge of trends of web site design. Recently, another approach using deep learning (DL) has appeared. The DL approach will help to extract features automatically by investigating a lot of existing sample data. Using this technique, we can build a flexible filtering decision module by keep teaching the neural network module about recent trends, without any specific expert knowledge of the URL domain. In this paper, we apply a mechanical approach to generate feature vectors from URL strings. We implemented our approach and tested with realistic URL access history data taken from a research organization and data from the famous archive site of phishing site information, PhishTank.com. Our approach achieved 2~3% better accuracy compared to the existing DL-based approach.

cs.NI↗

arXiv2021

Construction of nonlinear lattice with potential symmetry for smooth propagation of discrete breather

We construct a nonlinear lattice that has a particular symmetry in its potential function consisting of long-range pairwise interactions. The symmetry enhances smooth propagation of discrete breathers, and it is defined by an invariance of the potential function with respect to a map acting on the complex normal mode coordinates. Condition of the symmetry is given by a set of algebraic equations with respect to coefficients of the pairwise interactions. We prove that the set of algebraic equations has a unique solution, and moreover we solve it explicitly. We present an explicit Hamiltonian for the symmetric lattice, which has coefficients given by the solution. We demonstrate that the present symmetric lattice is useful for numerically computing traveling discrete breathers in various lattices. We propose an algorithm using it.

nlin.PS↗

arXiv2021

Heat transport in nonlinear lattices free from the Umklapp process

We construct one-dimensional nonlinear lattices having the special property such that the Umklapp process vanishes and only the normal processes are included in the potential functions. These lattices have long-range quartic nonlinear and nearest neighbor harmonic interactions with/without harmonic on-site potential. We study heat transport in two cases of the lattices with and without harmonic on-site potential by non-equilibrium molecular dynamics simulation. It is shown that the ballistic heat transport occurs in both cases, i.e., the scaling law $\kappa\propto N$ holds between the thermal conductivity $\kappa$ and the lattice size $N$. This result directly validates Peierls's hypothesis that only the Umklapp processes can cause the thermal resistance while the normal one do not.

nlin.CD↗

arXiv2020

Plasmonic Nanoslit Arrays Fabricated by Serial Bideposition: Optical and Surface-Enhanced Raman Scattering Study

Recently, studies have been carried out on attempts to combine surface-enhanced Surface-enhanced Raman spectroscopy (SERS) substrates that can be based on either localized surface plasmon (LSP) or surface plasmon polaritons (SPP) structures. By combining these two systems, the drawbacks of each other can be solved. However, the manufacturing methods involved so far are sophisticated, labor-intensive, expensive, and also technically demanding. We propose a facile method for the fabrication of a flexible plasmonic nanoslit SERS sensor. We utilized the pattern on periodic optical disks (DVD-R) as a cheap substitute for printing the periodic pattern on PDMS with soft imprint lithography. Ag nanoslit (AgNS) was fabricated by serial bideposition using a dynamic oblique angle deposition (DOD) technique. The nanoslit structures were physically and optically characterized, and the experimental results were compared to the numerical simulation studies; Monte Carlo and the finite-difference time-domain (FDTD) simulation. The Ag nanoslit structure showed an excellent SERS enhancement, and its biosensing capability was demonstrated by the sensing of bilirubin.

cond-mat.mtrl-sci↗

arXiv2018

Nonlinear waves in a model for silicate layers

Some layered silicates are composed of positive ions, surrounded by layers of ions with opposite sign. Mica muscovite is a particularly interesting material, because there exist fossil and experimental evidence for nonlinear excitations transporting localized energy and charge along the cation rows within the potassium layers. This evidence suggest that there are different kinds of excitations with different energies and properties. Some of the authors proposed recently a one-dimensional model based in physical principles and the silicate structure. The main characteristic of the model is that it has a hard substrate potential and two different repulsion terms, between ions and nuclei. In a previous work with this model, it was found the propagation of crowdions, i.e., lattice kinks in a lattice with substrate potential that transport mass and charge. They have a single specific velocity and energy coherent with the experimental data. In the present work we perform a much more thorough search for nonlinear excitations in the same model using the pseudospectral method to obtain exact nanopteron solutions, which are single kinks with tails, crowdions and bi-crowdions. We analyze their velocities, energies and stability or instability and the possible reasons for the latter. We relate the different excitations with their possible origin from recoils from different beta decays and with the fossil tracks. We explore the consequences of some variation of the physical parameters because their values are not perfectly known. Through a different method, we also have found stationary and moving breathers, that is, localized nonlinear excitations with an internal vibration. Moving breathers have small amplitude and energy, which is also coherent with the fossil evidence.

nlin.PS↗

arXiv2017

Low-frequency discrete breathers in long-range systems without on-site potential

We propose a new mechanism of long-range coupling to excite low-frequency discrete breathers without the on-site potential. This mechanism is universal in long-range systems irrespective of the spatial boundary conditions, of topology of the inner degree of freedom, and of precise forms of the coupling functions. The limit of large population is theoretically discussed for the periodic boundary condition. Existence of discrete breathers is numerically demonstrated with stability analysis.

nlin.PS↗

arXiv2015

Maximum Likelihood based Multihop Localization in Wireless Sensor Networks

For data sets retrieved from wireless sensors to be insightful, it is often of paramount importance that the data be accurate and also location stamped. This paper describes a maximum-likelihood based multihop localization algorithm called kHopLoc for use in wireless sensor networks that is strong in both isotropic and anisotropic network deployment regions. During an initial training phase, a Monte Carlo simulation is utilized to produce multihop connection density functions. Then, sensor node locations are estimated by maximizing local likelihood functions of the hop counts to anchor nodes. Compared to other multihop localization algorithms, the proposed kHopLoc algorithm achieves higher accuracy in varying network configurations and connection link-models.

cs.NI↗