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Yuta Suzuki

Publications and source records attributed to Yuta Suzuki.

At least 37 records · Page 2Linked to original sources
arXiv2024

Environments around quasars at $z\sim$3 revealed by wide-field imaging with Subaru HSC and CFHT

We examine the local density environments around 67 quasars at $z\sim3$, by combining the imaging data of Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) and Canada-France-Hawaii Telescope Large Area U-band Survey (CLAUDS) over about 20 deg$^{2}$. Our measurements exploit $U$-dropout galaxies in the vicinities of quasars taken from Sloan Digital Sky Survey (SDSS). We find that the quasars have the indistinguishable surrounding density distribution from the $U$-dropout galaxies, and that three quasars are associated with protocluster candidates within a projected separation of 3 arcmin. According to a halo evolutionary model, our results suggest that quasars at this epoch occupy haloes with a typical mass of $1.3^{+1.4}_{-0.9} \times 10^{13} h^{-1} \mathrm{M_{\odot}}$. We also investigate the dependence of the local galaxy overdensity on ultraviolet (UV) luminosities, black hole (BH) masses, and proximity zone sizes of the quasars, but no statistically-significant correlation was found. Finally, we find that the local density of faint $U$-dropout galaxies are lower than that of bright $U$-dropout galaxies within a projected distance of $0.51\pm0.05$ physical Mpc, where the quasar UV radiation is 30 times intenser than backgroung UV radiation. We argue that photoevaporation may suppress galaxy formation at short distances where the quasar UV intensity is strong, even in massive haloes.

astro-ph.GA↗
arXiv2024

On Telhcirid's theorem on arithmetic progressions

In this paper, we study the distribution of the digital reverses of prime numbers, which we call the "reversed primes". We prove the infinitude of reversed primes in any arithmetic progression satisfying straightforward necessary conditions provided the base is sufficiently large. We indeed prove an effective Siegel--Walfisz type result for reversed primes, which has a larger admissible level of modulus than the classical case.

math.NT↗
arXiv2024

Crystalformer: Infinitely Connected Attention for Periodic Structure Encoding

Predicting physical properties of materials from their crystal structures is a fundamental problem in materials science. In peripheral areas such as the prediction of molecular properties, fully connected attention networks have been shown to be successful. However, unlike these finite atom arrangements, crystal structures are infinitely repeating, periodic arrangements of atoms, whose fully connected attention results in infinitely connected attention. In this work, we show that this infinitely connected attention can lead to a computationally tractable formulation, interpreted as neural potential summation, that performs infinite interatomic potential summations in a deeply learned feature space. We then propose a simple yet effective Transformer-based encoder architecture for crystal structures called Crystalformer. Compared to an existing Transformer-based model, the proposed model requires only 29.4% of the number of parameters, with minimal modifications to the original Transformer architecture. Despite the architectural simplicity, the proposed method outperforms state-of-the-art methods for various property regression tasks on the Materials Project and JARVIS-DFT datasets.

cs.LG↗
arXiv2024

Relatively prime pairs in the Piatetski-Shapiro sequences

In this paper, we prove an asymptotic formula for the number of relatively prime pairs in the Piatetski-Shapiro sequence of arbitrarily large order. This improves the result of Pimsert, Srichan and Tangsupphathawat (2023), the order of which was restricted to be $<\frac{3}{2}$. The key ingredients of the proof are a simple averaging trick and an extension of Deshouillers' result on the distribution of the Piatetski-Shapiro sequence in arithmetic progressions.

math.NT↗
arXiv2024

Counting relatively prime pairs of palindromes

For a given base $g\ge2$, a positive integer is called a palindrome if its base $g$ expansion reads the same backwards as forwards. In this paper, we give an asymptotic formula for the number of relatively prime pairs of palindromes of a fixed odd length and of any base $g\ge2$, which solves an open problem proposed by Banks and Shparlinski (2005).

math.NT↗
arXiv2024

Transport through a monolayer-tube junction: sheet-to-tube spin current in silicene

A method is developed to calculate the electron flow between an atomic monolayer sheet and a tube with use of tunneling matrix elements between monolayer sheets and applied to the spin current from monolayer silicene with sublattice-staggered current-induced spin polarization to silicene tube. Calculated sheet-to-tube spin current exhibits an oscillation as a function of the tube circumferential length since the Fermi points in the tube cross the Fermi circle in the sheet. It is also shown that the spin current with spin in the out-of-plane direction, which is absent in the sheet-sheet junction (including twisted sheets) with the $C_3$ rotational symmetry, appears in an oscillating form owing to the broken $C_3$ symmetry in the tube-sheet junction.

cond-mat.mes-hall↗
arXiv2023

Some remarks on the $[x/n]$-sequence

After the work of Bordellès, Dai, Heyman, Pan and Shparlinki (2018) and Heyman (2019), several authors studied the averages of arithmetic functions over the sequence $[x/n]$ and the integers of the form $[x/n]$. In this paper, we give three remarks on this topic. Firstly, we improve the result of Wu and Yu (2022) on the distribution of the integers of the form $[x/n]$ in arithmetic progressions by using a variant of Dirichlet's hyperbola method. Secondly, we prove an asymptotic formula for the number of primitive lattice points with coordinates of the form $[x/n]$, for which we introduce a certain averaging trick. Thirdly, we study a certain "multiplicative" analog of the Titchmarsh divisor problem. We derive asymptotic formulas for such "multiplicative" Titchmarsh divisor problems for "small" arithmetic functions and the Euler totient function with the von Mangoldt function. However, it turns out that the average of the Euler totient function over the $[x/p]$-sequence seems rather difficult and we propose a hypothetical asymptotic formula for this average.

math.NT↗
arXiv2023

Neural Structure Fields with Application to Crystal Structure Autoencoders

Representing crystal structures of materials to facilitate determining them via neural networks is crucial for enabling machine-learning applications involving crystal structure estimation. Among these applications, the inverse design of materials can contribute to explore materials with desired properties without relying on luck or serendipity. We propose neural structure fields (NeSF) as an accurate and practical approach for representing crystal structures using neural networks. Inspired by the concepts of vector fields in physics and implicit neural representations in computer vision, the proposed NeSF considers a crystal structure as a continuous field rather than as a discrete set of atoms. Unlike existing grid-based discretized spatial representations, the NeSF overcomes the tradeoff between spatial resolution and computational complexity and can represent any crystal structure. We propose an autoencoder of crystal structures that can recover various crystal structures, such as those of perovskite structure materials and cuprate superconductors. Extensive quantitative results demonstrate the superior performance of the NeSF compared with the existing grid-based approach.

cond-mat.mtrl-sci↗
arXiv2023

Antiparallel spin polarization and spin current induced by thermal current and locally-broken inversion symmetry in a double-quantum-well structure

Generating a nonequilibrium spin polarization with a driving force has been first realized by the electric current in a system with broken inversion symmetry and extended to that induced by the thermal current and that appearing in an inversion-symmetric system with locally-broken inversion symmetry. This paper theoretically explores the spin polarization generated by the thermal current and the locally-broken inversion symmetry in a symmetric double-quantum-well structure (DQWS). This thermally-induced spin polarization (TISP) appears in the antiparallel configuration with the TISP of two wells in opposite directions. The calculation using the Boltzmann equation in the relaxation-time approximation under the condition of zero charge current shows that the local TISP exhibits the maximum at a finite Rashba spin-orbit interaction when the electron density is fixed. This is because the local TISP in the DQWS is enhanced at the chemical potential near the bottom of the first-excited subband. This enhancement also occurs in a single quantum well with globally-broken inversion symmetry. Another finding is that the maximum of the local TISP appears at a nonzero interwell coupling. The spin current by the diffusion of the local TISP into an adjacent electrode is also calculated.

cond-mat.mes-hall↗
arXiv2023

Distribution of rational points on random Fano hypersurfaces

We prove an asymptotic formula for the average number of rational points on Fano hypersurfaces that are contained in a small ball centered at a given adelic point. We also prove an asymptotic formula for the number of hypersurfaces admitting adelic points that are contained in a small ball.

math.NT↗
arXiv2023

Quantum state tomography for Kerr parametric oscillators

Kerr parametric oscillators (KPOs) implemented in the circuit QED architecture can operate as qubits. Their applications to quantum annealing and universal quantum computation have been studied intensely. For these applications, the readout of the state of KPOs is of practical importance. We develop a scheme of state tomography for KPOs with reflection measurement. Although it is known that the reflection coefficient depends on the state of the KPO, it is unclear whether tomography of a qubit encoded into a KPO can be performed in a practical way mitigating decoherence during the measurement, and how accurate it is. We show that the reflection coefficient has a one-to-one correspondence with a diagonal element of the density matrix of the qubit when a probe frequency is properly chosen and an additional single-photon-drive is introduced. Thus, our scheme offers a novel way to readout the qubit along an axis of the Bloch sphere, and therefore the reflection measurement and single-qubit gates can constitute state tomography.

quant-ph↗
arXiv2023

Sum formulas for Schur multiple zeta values

In this paper, we study sum formulas for Schur multiple zeta values and give a generalization of the sum formulas for multiple zeta(-star) values. We show that for ribbons of certain types, the sum over all admissible Young tableaux of this shape evaluates to a rational multiple of the Riemann zeta value. For arbitrary ribbons with $n$ corners, we show that these can be always expressed in terms of multiple zeta values of depth $\leq n$. In particular, when $n=2$, we give explicit, what we call, bounded type sum formulas for these ribbons. Finally, we show how to evaluate the sum over all admissible Young tableaux with exactly one corner and also prove bounded type sum formulas for them. This will also lead to relations among sums of Schur multiple zeta values over all admissible Young tableaux of different shapes.

math.NT↗
arXiv2022

Spin Relaxation, Diffusion and Edelstein Effect in Chiral Metal Surface

We study electron spin transport at spin-splitting surface of chiral-crystalline-structured metals and Edelstein effect at the interface, by using the Boltzmann transport equation beyond the relaxation time approximation. We first define spin relaxation time and spin diffusion length for two-dimensional systems with anisotropic spin--orbit coupling through the spectrum of the integral kernel in the collision integral. We then explicitly take account of the interface between the chiral metal and a nonmagnetic metal with finite thickness. For this composite system, we derive analytical expressions for efficiency of the charge current--spin current interconversion as well as other coefficients found in the Edelstein effect. We also develop the Onsager's reciprocity in the Edelstein effect along with experiments so that it relates local input and output, which are respectively defined in the regions separated by the interface. We finally provide a transfer matrix corresponding to the Edelstein effect through the interface, with which we can easily represent the Onsager's reciprocity as well as the charge--spin conversion efficiencies we have obtained. We confirm the validity of the Boltzmann transport equation in the present system starting from the Keldysh formalism in the supplemental material. Our formulation also applies to the Rashba model and other spin-splitting systems.

cond-mat.mes-hall↗
arXiv2022

Measurement-based state preparation of Kerr parametric oscillators

Kerr parametric oscillators (KPOs) have attracted increasing attention in terms of their application to quantum information processing and quantum simulations. The state preparation and measurement of KPOs are typical requirements when they are used as qubits. The methods previously proposed for state preparations of KPOs utilize modulation of a pump field or an auxiliary drive field. We study the stochastic state preparation of a KPO based on homodyne detection, which does not require modulation of a pump field nor an auxiliary drive field, and thus can exclude unwanted effects of possible imperfection in control of these fields. We quantitatively show that the detection data, if averaged over a proper time to decrease the effect of measurement noise, has a strong correlation with the state of the KPO, and therefore can be used to estimate the state of the KPO (stochastic state preparation). We examine the success probability of the state estimation taking into account the effect of the measurement noise and bit flips. Moreover, the proper range of the averaging time to realize a high success probability is obtained by developing a binomial-coherent-state model, which describes the stochastic dynamics of the KPO under homodyne detection.

quant-ph↗
arXiv2021

Tunneling spin current in a system with spin degeneracy

We study theoretically spin current generation from a band insulator with PT symmetry, which is associated with Zener tunneling in strong dc electric fields. Each band in this system is doubly degenerate with opposite spins, but spin rotational symmetry is not preserved in general. We consider the condition for spin current generation in connection with the nature of the wave function, which ultimately depends on a geometric quantity known as the shift vector. From an analysis of a two-band model, we find that the shift vector is necessary for spin current generation in a PT symmetric system. We also present zigzag chain models that have shift vectors, and confirm from numerical calculations that a nonzero tunneling spin current occurs in spin-degenerate systems.

cond-mat.mes-hall↗
arXiv2020

Heart Rate Variability as a Predictive Biomarker of Thermal Comfort

Thermal comfort is an assessment of one's satisfaction with the surroundings; yet, most mechanisms that are used to provide thermal comfort are based on approaches that preclude physiological, psychological, and personal psychophysics that are precursors to thermal comfort. This leads to many people feeling either cold or hot in an environment that was supposed to be thermally comfortable to most users. To address this problem, this paper proposes to use heart rate variability (HRV) as an alternative indicator of thermal comfort status. Since HRV is linked to homeostasis, we conjectured that people's thermal comfort could be more accurately estimated based on their heart rate variability (HRV). To test our hypothesis, we analyzed statistical, spectral, and nonlinear HRV indices of 17 human subjects doing light office work in a cold, neutral, and hot environment. The resulting HRV indices were used as inputs to machine learning classification algorithms. We observed that HRV is distinctively different depending on the thermal environment and that it is possible to reliably predict each subject's thermal state (cold, neutral, and hot) with up to 93.7% accuracy. The result of this study suggests that it could be possible to design automatic real-time thermal comfort controllers based on people's HRV.

eess.SP↗
arXiv2020

Heart Rate Variability as an Indicator of Thermal Comfort State

Thermal comfort is a personal assessment of one's satisfaction with the surroundings. Yet, most thermal comfort delivery mechanisms preclude physiological and psychological precursors to thermal comfort. Accordingly, many people feel either cold or hot in an environment that is supposedly thermally comfortable to most people. To address this issue, this paper proposes to use people's heart rate variability (HRV) as an alternative indicator of thermal comfort. Since HRV is linked to homeostasis, we hypothesize that it could be used to predict people's thermal comfort status. To test our hypothesis, we analyzed statistical, spectral, and nonlinear HRV indices of 17 human subjects doing light office work in a cold, a neutral, and a hot environment. The resulting HRV indices were used as inputs to machine learning classification algorithms. We observed that HRV is distinctively altered depending on the thermal environment and that it is possible to steadfastly predict each subject's thermal environment (cold, neutral, and hot) with up to a 93.7% prediction accuracy. The result of this study implies that it could be possible to design automatic real-Time thermal comfort controllers based on people's HRV.

q-bio.OT↗