arXiv subjects

Bin Wei

Publications and source records attributed to Bin Wei.

28 records · Page 2Linked to original sources

arXiv2021

Giant Anisotropic in-Plane Thermal Conduction Induced by Anomalous Phonons in Nearly-Equilaterally Structured PdSe2

In two-dimensional materials, structure difference induces the difference in phonon dispersions, leading to the anisotropy of in-plane thermal transport. Here, we report an exceptional case in layered PdSe2, where the bonding, force constants, and lattice constants are nearly-equal along the in-plane crystallographic axis directions. The phonon dispersions show significant differences between the Gamma-X and Gamma-Y directions, leading to the anisotropy of in-plane thermal conductivity with a ratio up to 1.8. Such anisotropy is not only unexpected in equilaterally structured (in-plane) materials but also comparable to the record in the non-equilaterally structured material reported to date. By combining inelastic X-ray scattering and first-principles calculations, we attribute such anisotropy to the low-energy phonons along Gamma-X, in particular, their lower group velocities and "avoided-crossing" behavior. The different bucking structures between a- (zigzag-type) and b-axis (flat-type) are mainly responsible for the unique phonon dynamics properties of PdSe2. The present results illustrate the unusual thermal conduction mechanism of the equilaterally structured materials and provide valuable insights on thermal management in electronic devices.

cond-mat.mtrl-sci↗

arXiv2021

Matryoshka Phonon Twinning in alpha-GaN

Understanding lattice dynamics is crucial for effective thermal management in high-power electronic devices because phonons dominate thermal transport in most semiconductors. This study utilizes complementary inelastic X-ray and neutron scattering techniques and reports the temperature-dependent phonon dynamics of alpha-GaN, one of the most important third-generation power semiconductors. A prominent Matryoshka phonon dispersion is discovered with the scattering tools and confirmed by the first-principles calculations. Such Matryoshka twinning throughout the three-dimension reciprocal space is demonstrated to amplify the anharmonicity of the related phonon modes through creating abundant three-phonon scattering channels and cutting the phonon lifetime of affected modes by more than 50%. Such phonon topology effectively contributes to the reduction of the in-plane thermal transport, thus the anisotropic thermal conductivity of alpha-GaN. The results not only have significant implications for engineering the thermal performance and other phonon-related properties of alpha-GaN, but also offer valuable insights on the role of anomalous phonon topology in thermal transport of other technically important semiconductors.

cond-mat.mtrl-sci↗

arXiv2020

FeatherTTS: Robust and Efficient attention based Neural TTS

Attention based neural TTS is elegant speech synthesis pipeline and has shown a powerful ability to generate natural speech. However, it is still not robust enough to meet the stability requirements for industrial products. Besides, it suffers from slow inference speed owning to the autoregressive generation process. In this work, we propose FeatherTTS, a robust and efficient attention-based neural TTS system. Firstly, we propose a novel Gaussian attention which utilizes interpretability of Gaussian attention and the strict monotonic property in TTS. By this method, we replace the commonly used stop token prediction architecture with attentive stop prediction. Secondly, we apply block sparsity on the autoregressive decoder to speed up speech synthesis. The experimental results show that our proposed FeatherTTS not only nearly eliminates the problem of word skipping, repeating in particularly hard texts and keep the naturalness of generated speech, but also speeds up acoustic feature generation by 3.5 times over Tacotron. Overall, the proposed FeatherTTS can be $35$x faster than real-time on a single CPU.

eess.AS↗

arXiv2020

Hybrid plasmonic nano-emitters with controlled single quantum emitter positioning on the local excitation field

Hybrid plasmonic nanoemitters based on the combination of quantum dot emitters (QD) and plasmonic nanoantennas open up new perspectives in the control of light. However, precise positioning of any active medium at the nanoscale constitutes a challenge. Here, we report on the optimal overlap of antenna's near-field and active medium whose spatial distribution is controlled via a plasmon-triggered 2-photon polymerization of a photosensitive formulation containing QDs. Au nanoparticles of various geometries are considered. The response of these hybrid nano-emitters is shown to be highly sensitive to the light polarization. Different light emission states are evidenced by photoluminescence measurements. These states correspond to polarization-sensitive nanoscale overlap between the exciting local field and the active medium distribution. The decrease of the QD concentration within the monomer formulation allows trapping of a single quantum dot in the vicinity of the Au particle. The latter objects show polarization-dependent switching in the single-photon regime.

physics.optics↗

arXiv2019

Few-shot machine learning in the three-dimensional Ising model

We investigate theoretically the phase transition in three dimensional cubic Ising model utilizing state-of-the-art machine learning algorithms. Supervised machine learning models show high accuracies (~99\%) in phase classification and very small relative errors ($< 10^{-4}$) of the energies in different spin configurations. Unsupervised machine learning models are introduced to study the spin configuration reconstructions and reductions, and the phases of reconstructed spin configurations can be accurately classified by a linear logistic algorithm. Based on the comparison between various machine learning models, we develop a few-shot strategy to predict phase transitions in larger lattices from trained sample in smaller lattices. The few-shot machine learning strategy for three dimensional(3D) Ising model enable us to study 3D ising model efficiently and provides a new integrated and highly accurate approach to other spin models.

cond-mat.dis-nn↗

arXiv2018

Generalized Lambert Series Identities and Applications in Rank Differences

In this article, we prove two identities of generalized Lambert series. By introducing what we call $\mathcal{S}$-series, we establish relationships between multiple generalized Lambert series and multiple infinite products. Compared with Chan's work, these new identities are useful in generating various formulas for generalized Lambert series with the same poles. Using these formulas, we study the 3-dissection properties of ranks for overpartitions modulo 6. In this case, $-1$ appears as a unit root, so that double poles occur. We also relate these ranks to the third order mock theta functions $ω(q)$ and $ρ(q)$

math.CO↗

arXiv2018

Probing the R-parity violating supersymmetric effects in $B_c\to J/ψ\ell^-\barν_{\ell},η_c\ell^-\barν_{\ell}$ and $Λ_b\toΛ_c\ell^-\barν_{\ell}$ decays

Motivated by recent $R_D$, $R_{D^*}$ and $R_{J/ψ}$ anomalies in $B\to D\ell^- \barν_{\ell}$, $B\to D^*\ell^- \barν_{\ell}$ and $B_c\to J/ψ\ell^- \barν_{\ell}$ decays, respectively, we study possible R-parity violating supersymmetric effects in $B_c\to J/ψ\ell^- \barν_{\ell},η_c\ell^- \barν_{\ell}$ and $Λ_b \to Λ_c \ell^- \barν_{\ell}$ decays, which are also induced by $b\to c \ell^- \barν_{\ell}$ at quark level. We find that (I) the constrained slepton exchange couplings $λ_{i33}\tildeλ'^*_{i23}$ involving in $b\to c τ^- \barν_τ$ transition from relevant latest experimental data still have quite large effects on all (differential) branching ratios and the normalized forward-backward asymmetries of the exclusive semileptonic $b\to c τ^- \barν_τ$ decays as well as the ratios of the (differential) branching ratios; (II) after satisfying the data of $R_D$ and $R_{D^*}$, the upper limit of $R_{J/ψ}$, $R_{η_c}$ and $R_{Λ_c}$ could be increased by 10%, 112% and 24%, respectively, from their upper limits of the Standard Model predictions by the $λ_{i33}\tildeλ'^*_{i23}$ couplings. The results in this work could be used to probe R-parity violating effects and will correlate with searches for direct supersymmetric signals at the running LHCb and the forthcoming Belle-II.

hep-ph↗

arXiv2017

Study of $\mathbf{\boldsymbol{D \rightarrow a_0 (980) e^+ ν_e}}$ decay in the light-cone sum rules approach

Within the QCD light-cone sum rule (LCSR) approach, we investigate the transition form factors of $D\rightarrow a_0(980)$ up to the twist-3 light-cone distribution amplitudes (LCDAs) of the scalar meson $a_0(980)$ in the two-quark picture. Using these form factors, we calculate the differential decay widths and branching ratios of the $D\rightarrow a_0(980) e^+ ν_e$ semileptonic decays. We obtain ${\mathcal B}(D^0\rightarrow a_0^- (980) e^+ ν_e)=(4.08^{+1.37}_{-1.22})\times 10^{-4}$ and ${\mathcal B}(D^+\rightarrow a_0^0 (980) e^+ ν_e)=(5.40^{+1.78}_{-1.59})\times 10^{-4}$. The results are sensitive to the $a_0(980)$ inner structure. These decays can be searched for at BESIII experiment, and any experimental observations will be useful to identify internal quark contents of the $a_0(980)$ meson, which will shed light on understanding theoretical models.

hep-ph↗

arXiv2014

On Sums of Powers of Almost Equal Primes

We investigate the Waring-Goldbach problem of representing a positive integer $n$ as the sum of $s$ $k$th powers of almost equal prime numbers. Define $s_k=2k(k-1)$ when $k\ge 3$, and put $s_2=6$. In addition, put $θ_2=\frac{19}{24}$, $θ_3=\frac{4}{5}$ and $θ_k=\frac{5}{6}$ $(k\ge 4)$. Suppose that $n$ satisfies the necessary congruence conditions, and put $X=(n/s)^{1/k}$. We show that whenever $s>s_k$ and $\varepsilon>0$, and $n$ is sufficiently large, then $n$ is represented as the sum of $s$ $k$th powers of prime numbers $p$ with $|p-X|\le X^{θ_k+\varepsilon}$. This conclusion is based on a new estimate of Weyl-type specific to exponential sums having variables constrained to short intervals.

math.NT↗

arXiv2014

Rationality and power

We produce an infinite family of transcendental numbers which, when raised to their own power, become rational. We extend the method, to investigate positive rational solutions to the equation $x^x = α$, where $α$ is a fixed algebraic number. We then explore the consequences of $x^{P(x)}$ being rational, if $x$ is rational and $P(x)$ is a fixed integer polynomial.

math.NT↗