Thermoelectricity in B80-based single-molecule junctions: First-principles investigation

Thermoelectricity is a thermorelated property that is of great importance in single-molecule junctions. The electrical conductance (σ), electron-derived thermal conductance (κ_el) and Seebeck coefficient (S) of B₈₀-based single-molecule junctions are investigated by using density functional theory in combination with non-equilibrium Green’s function. When the distance between the left/right electrodes is 11.4 Å, the relationship between σ and κ_el obeys the Wiedemann–Franz law very well because of the strong hybridization between B₈₀ molecular orbitals and the surface states of Au electrodes. Furthermore, the calculated Lorenz number is close to the famous value in metal or degenerate semiconductors. In addition, S is only –19.09 μV/K at 300 K, thus leading to the smaller electron’s thermoelectric figure of merit (Z_elT = S²σT/κ_el). Interestingly, the strain and chemical potential can modulate B₈₀-based single-molecule junctions from n-type to p-type when the compressive strain reaches –0.6 Å or the chemical potential shifts to –0.16 eV. This might be attributed that S reflects the asymmetry in the electrical conductance with respect to the chemical potential and is proportional to the slopes of the transmission spectrum.     

Entanglement measures of a new type pseudo-pure state in accelerated frames

In this work we analyze the characteristics of quantum entanglement of the Dirac field in noninertial reference frames in the context of a new type pseudo-pure state, which is composed of the Bell states. This will help us to understand the relationship between the relativity and quantum information theory. Some states will be changed from entangled states into separable ones around the critical value F = 1/4, but there is no such a critical value for the variable y related to acceleration a. We find that the negativity N_ABI (ρ^TA_ABI) increases with F but decreases with the variable y, while the variation of the negativity N_BIBII(ρ^TA_ABI) is opposite to that of the negativity N_ABI (ρ^TA_ABI). We also study the von Neumann entropies S(ρ_ABI) and S(ρ_BIBII). We find that the S(ρ_ABI) increases with variable y but S(ρ_BIBII) is independent of it. However, both S(ρ_ABI) and S(ρ_BIBII) first decreases with F and then increases with it. The concurrences C(ρ_ABI) and C(ρ_BIBII) are also discussed. We find that the former decreases with y while the latter increases with y but both of them first increase with F and then decrease with it.     

On the existence of N*(890) resonance in S11 channel of πN scatterings

Low-energy partial-wave πN scattering data is reexamined with the help of the production representation of partial-wave S matrix, where branch cuts and poles are thoroughly under consideration. The left-hand cut contribution to the phase shift is determined, with controlled systematic error estimates, by using the results of O(p³) chiral perturbative amplitudes obtained in the extended-onmass- shell scheme. In S₁₁ and P₁₁ channels, severe discrepancies are observed between the phase shift data and the sum of all known contributions. Statistically satisfactory fits to the data can only be achieved by adding extra poles in the two channels. We find that a S₁₁ resonance pole locates at \sqrt{z_r} = (0.895±0.081)−(0.164±0.023)i GeV, on the complex s-plane. On the other hand, a P₁₁ virtual pole, as an accompanying partner of the nucleon bound-state pole, locates at \sqrt{z_v} = (0.966±0.018) GeV, slightly above the nucleon pole on the real axis below threshold. Physical origin of the two newly established poles is explored to the best of our knowledge. It is emphasized that the O(p³) calculation greatly improves the fit quality comparing with the previous O(p²) one.     

串列对转双圆柱的多块LB模拟

结合格子玻尔兹曼方法(Lattice Boltzmann Method,简称LBM)和多块网格(Multi-Block Grid)技术,数值研究较小雷诺数(Re=100)下均匀来流绕串列对转双圆柱问题,综合分析圆柱中心间距比S/D和圆柱无量纲旋转速度α对流场结构的影响,考察前、后圆柱的涡脱落形态和升阻力特性.结果表明:当间距比为1.2时存在一临界旋转比α_c,转速超过这一值后前圆柱产生负Magnus效应;间距比为2时,流场出现类似单旋转圆柱时的第二不稳定模态;当间距比较大(S/D=4、6)时,前、后柱之间存在涡脱落,后柱尾涡中出现2S、2S^*、2P、P+S等多种形态.     

一类演化方程的高稳定性的差分格式

考虑一类演化方程u_t=au∂_2k+1(其中a是常数,u∂_2k+1=∂^2k+1u/∂x^2k+1,k=1,2……)的有限差分解法。构造了两类具有高稳定性的显式差分格式。并用引入耗散项的方法建立了两类半显式差分格式,它们是无条件稳定的且可显式地进行计算。     

Large magnetocaloric effect in van der Waals crystal CrBr3

We study the magnetocaloric effect (MCE) in van der Waals (vdW) crystal CrBr₃. Bulk CrBr₃ exhibits a second-order paramagnetic-ferromagnetic phase transition with T_C = 33 K. The maximum magnetic entropy change −ΔS_M near T_C is about 7.2 J·kg⁻¹·K⁻¹ with the maximum adiabatic temperature change ΔT^max_ad = 2.37 K and the relative cooling power RCP= 191.5 J·kg⁻¹ at μ₀H = 5 T, all of which are remarkably larger than those in CrI₃. These results suggest that the vdW crystal CrBr₃ is a promising candidate for the low-dimensional magnetic refrigeration in low temperature region.     

How does the S11 N*(890) state emerge from a naive K-matrix fit?

We give a pedagogical analysis on K-matrix models describing the πN scattering amplitude, in S₁₁ channel at low energies. We show how the correct use of analyticity in the s-channel and crossing symmetry in t- and u-channels leads to a much improved analytic behavior in the negative s region, in agreement with the prediction from chiral perturbation amplitudes in its validity region. The analysis leads again to the conclusion that a genuine N*(890) resonance exists.     

Resource reduction for simultaneous generation of two types of continuous variable nonclassical states

We demonstrate experimentally the simultaneous generation and detection of two types of continuous variable nonclassical states from one type-0 phase-matching optical parametric amplification (OPA) and subsequent two ring filter cavities (RFCs). The output field of the OPA includes the baseband ω₀ and sideband modes ω₀±nω_fsubjects to the cavity resonance condition, which are separated by two cascaded RFCs. The first RFC resonates with half the pump wavelength ω₀ and the transmitted baseband component is a squeezed state. The reflected fields of the first RFC, including the sideband modes ω₀±ω_f, are separated by the second RFC, construct Einstein–Podolsky–Rosen entangled state. All freedoms, including the filter cavities for sideband separation and relative phases for the measurements of these sidebands, are actively stabilized. The noise variance of squeezed states is 10.2 dB below the shot noise limit (SNL), the correlation variances of both quadrature amplitude-sum and quadrature phase-difference for the entanglement state are 10.0 dB below the corresponding SNL.     

Black ring entropy from the Weyl tensor

A black ring is an asymptotically flat vacuum solution of the n-dimensional Einstein equations with an event horizon of topology S¹×Sⁿ⁻³. In this study, a connection between the black ring entropy and the Weyl tensor C_μνλρ is explored by interpreting the Weyl scalar invariant C_μνλρC^μνλρ as the entropy density in five-dimensional space-time. It is shown that the proper volume integral of C_μνλρC^μνλρ for a neutral black ring is proportional to the black ring entropy in the thin-ring limit. Similar calculations are extended to more general cases: a black string, a black ring with two angular momenta, and a black ring with a cosmological constant. The proportionality is also found to be valid for these complex black objects at the leading order.     

QCD sum rules for nucleon-nucleon and hyperon-nucleon interactions

The QCD sum rules for spin-dependent nucleon-nucleon (N N) and hyperon-nucleon (Y N) interactions are formulated and their physical implications are clarified. A dispersion integral around the nucleon threshold can be identified as a measure of interaction strength. Calculating the operator product expansion (OPE) of the correlation function, we have found that the spin-dependent operators are related to the axial and tensor charges. The obtained sum rules relate the interaction strengths to the nucleon matrix elements of the quark-gluon operators. The spin-dependent parts are smaller than the spin-independent parts in the N N and the Y N channels. The spin-independent N N interaction strength is greater than the spin-independent Y N interaction strengths. The results are consistent with the empirical result in the N N channel.     

N00N态的Wigner函数及N00N态作为输入的量子干涉

根据量子力学相干态表象下的Wigner函数公式, 推导了N00N态在相空间的Wigner分布函数的解析表达式. 基于相空间方法, 研究N00N态作为输入的量子干涉. 推导了与输入光场参数和干涉仪参数相关的输出端探测光子概率的解析表达式, 并进行了数值分析. 从分析结果发现, 当相移参数φ取0和π时, 输出量子态仍为N00N态. 当输入2002态时, 输出结果总是2002态, 与相移参数无关. 随着N的增加, 条件概率随相位的分布峰数一般只有一个, 两个, 三个或四个, 且峰变得更窄. 这些结果可以为实验提供理论指导. 关键词： N00N态 Wigner函数 相空间 量子干涉     

Crossover from thermally activated flux creep to quantum tunneling of vortices in a YBa2Cu3O7−x film

We present the results of a study of flux creep in a ring-shaped epitaxial superconducting YBa₂Cu₃O_7−x film at low temperatures. Measurements between 2 and 20 K have been made and it is confirmed that the flux creep is a thermally activated process at temperatures exceeding 10 K. The low-temperature data are analyzed by assuming a crossover to quantum tunneling of the vortex lines. Using the fact that the critical current in our sample is almost independent of temperature below 20 K, we establish the temperature dependence of the Euclidian action S directly from the experimental data without any a priori assumptions. Our results imply that at temperatures below 8.5 K S(T)=S(0)(1−T²/T_qc²), with approximately the same value of T_qc≈15 K for the case of the remnant magnetization as well as in an external magnetic field of 1 kOe.     

Prospective study on observations of γ-ray sources in the Galaxy using the HADAR experiment

The High Altitude Detection of Astronomical Radiation (HADAR) experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique. It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energy γ-rays and cosmic rays. With the advantages of a large field-of-view (FOV) and low energy threshold, the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources. This study presents the prospects of using the HADAR experiment for the sky survey of TeV γ-ray sources from TeVCat and provids a one-year survey of statistical significance. Results from the simulation show that a total of 23 galactic point sources, including five supernova remnant sources and superbubbles, four pulsar wind nebula sources, and 14 unidentified sources, were detected in the HADAR FOV with a significance greater than 5 standard deviations (σ). The statistical significance for the Crab Nebula during one year of operation reached 346.0 σ and the one-year integral sensitivity of HADAR above 1 TeV was ~1.3%–2.4% of the flux from the Crab Nebula.     

Entangled chimeras in nonlocally coupled bicomponent phase oscillators: From synchronous to asynchronous chimeras

Chimera states, a symmetry-breaking spatiotemporal pattern in nonlocally coupled identical dynamical units, have been identified in various systems and generalized to coupled nonidentical oscillators. It has been shown that strong heterogeneity in the frequencies of nonidentical oscillators might be harmful to chimera states. In this work, we consider a ring of nonlocally coupled bicomponent phase oscillators in which two types of oscillators are randomly distributed along the ring: some oscillators with natural frequency ω₁ and others with ω₂ . In this model, the heterogeneity in frequency is measured by frequency mismatch |ω₁−ω₂| between the oscillators in these two subpopulations. We report that the nonlocally coupled bicomponent phase oscillators allow for chimera states no matter how large the frequency mismatch is. The bicomponent oscillators are composed of two chimera states, one supported by oscillators with natural frequency ω₁ and the other by oscillators with natural frequency ω₂. The two chimera states in two subpopulations are synchronized at weak frequency mismatch, in which the coherent oscillators in them share similar mean phase velocity, and are desynchronized at large frequency mismatch, in which the coherent oscillators in different subpopulations have distinct mean phase velocities. The synchronization–desynchronization transition between chimera states in these two subpopulations is observed with the increase in the frequency mismatch. The observed phenomena are theoretically analyzed by passing to the continuum limit and using the Ott-Antonsen approach.     

多通道心磁系统标定方法研究

在多通道超导量子干涉器件（SQUID）磁探测系统中,磁场电压转换系数（∂ B/∂ V）是系统的一个重要参数由于SQUID器件和读出电路之间不可避免地存在差异性因此对传感器系统进行系统标定（每个通道的单独标定）显得十分重要本文采用（PCB） 板印制圆形线圈对36通道心磁系统进行标定,并与传统的亥姆霍兹方形线圈产生均匀场的标定方法进行比较结果显示PCB圆形线圈的标定结果 在1.46–1.73 pT·mV^-1 之间,亥姆霍兹方形线圈标定的结果大都在1.56–1.64 pT·mV^-1之间,结果基本一致. 关键词： 超导量子干涉器件 磁探测 磁场-电压转换系数 系统标定     

悬链曲面上的点粒子动力学及扩展空间约束系统量子化

扩张型正则量子化方案的核心内容是位置、动量以及哈密顿量同时量子化. 通过分析悬链面上粒子的扩张型正则量子化方案, 并且与薛定谔理论进行比较, 发现内禀几何中二维悬链面给不出与薛定谔理论相一致的结果, 而考虑将二维悬链面嵌入在三维欧氏空间之后, 还需要将正则量子化方案进行扩张, 可以得到体系的几何势能和几何动量, 并与薛定谔理论相一致.     

Influence of the velocity barrier on the massive Dirac electron transport in a monolayer MoS2 quantum structure

Using the transfer matrix method, spin- and valley-dependent electron transport properties modulated by the velocity barrier were studied in the normal/ferromagnetic/normal monolayer MoS₂ quantum structure. Based on Snell’s Law in optics, we define the velocity barrier as ξ=v₂/v₁ by changing the Fermi velocity of the intermediate ferromagnetic region to obtain a deflection condition during the electron transport process in the structure. The results show that both the magnitude and the direction of spin- and valley-dependent electron polarization can be regulated by the velocity barrier. –100% polarization of spin- and valley-dependent electron can be achieved for ξ>1, while 100% polarization can be obtained for ξ<1. Furthermore, it is determined that perfect spin and valley transport always occur at a large incident angle. In addition, the spin- and valley-dependent electron transport considerably depends on the length k_FL and the gate voltage U(x) of the intermediate ferromagnetic region. These findings provide an effective method for designing novel spin and valley electronic devices.     

Experimental review of the ϒ(1S, 2S, 3S) physics at e+e− colliders and the LHC

The three lowest-lying \mathrm{\Upsilon } states, i.e., \mathrm{\Upsilon }(1S), \mathrm{\Upsilon }(2S), and \mathrm{\Upsilon }(3S), composed of bb¯ pairs and below the BB ¯ threshold, provide a good platform for the researches of hadronic physics and physics beyond the Standard Model. They can be produced directly in e⁺e⁻ colliding experiments, such as CLEO, Babar, and Belle, with low continuum backgrounds. In these experiments, many measurements of the exclusive \mathrm{\Upsilon }(1S) and \mathrm{\Upsilon }(2S) decays into light hadrons, which shed light on the “80% rule” for the Okubo–Zweig–Iizuka suppressed decays in the bottomonium sector, were carried out. Meanwhile, many studies of the charmonium and bottomonium productions in \mathrm{\Upsilon }(1S, 2S, 3S) decays were performed, to distinguish different Quantum Chromodynamics (QCD) models. Besides, exotic states and new physics were also extensively explored in \mathrm{\Upsilon }(1S, 2S, 3S) decays at CLEO, BaBar, and Belle. The \mathrm{\Upsilon }(1S, 2S, 3S) states can also be produced in pp collisions and in collisions involving heavy ions. The precision measurements of their cross sections and polarizations at the large hadron collider (LHC), especially in the CMS, ATLAS, and LHCb experiments, help to understandΥproduction mechanisms in pp collisions. The observation of the sequentialΥsuppression in heavy ion collisions at CMS, LHCb, and ALICE is of great importance for verifying the quark–gluon plasma predicted by QCD. In this article, we review the experimental results on \mathrm{\Upsilon }(1S, 2S, 3S) at e⁺e⁻ colliders and the LHC, and summarize their prospects at Belle II and the LHC.     

Effects of the initial perturbations on the Rayleigh–Taylor–Kelvin–Helmholtz instability system

The effects of initial perturbations on the Rayleigh–Taylor instability (RTI), Kelvin–Helmholtz instability (KHI), and the coupled Rayleigh–Taylor–Kelvin–Helmholtz instability (RTKHI) systems are investigated using a multiple-relaxation-time discrete Boltzmann model. Six different perturbation interfaces are designed to study the effects of the initial perturbations on the instability systems. It is found that the initial perturbation has a significant influence on the evolution of RTI. The sharper the interface, the faster the growth of bubble or spike. While the influence of initial interface shape on KHI evolution can be ignored. Based on the mean heat flux strength D_3,1, the effects of initial interfaces on the coupled RTKHI are examined in detail. The research is focused on two aspects: (i) the main mechanism in the early stage of the RTKHI, (ii) the transition point from KHI-like to RTI-like for the case where the KHI dominates at earlier time and the RTI dominates at later time. It is found that the early main mechanism is related to the shape of the initial interface, which is represented by both the bilateral contact angle θ₁ and the middle contact angle θ₂. The increase of θ₁ and the decrease of θ₂ have opposite effects on the critical velocity. When θ₂ remains roughly unchanged at 90 degrees, if θ₁ is greater than 90 degrees (such as the parabolic interface), the critical shear velocity increases with the increase of θ₁, and the ellipse perturbation is its limiting case; If θ₁ is less than 90 degrees (such as the inverted parabolic and the inverted ellipse disturbances), the critical shear velocities are basically the same, which is less than that of the sinusoidal and sawtooth disturbances. The influence of inverted parabolic and inverted ellipse perturbations on the transition point of the RTKHI system is greater than that of other interfaces: (i) For the same amplitude, the smaller the contact angle θ₁, the later the transition point appears; (ii) For the same interface morphology, the disturbance amplitude increases, resulting in a shorter duration of the linear growth stage, so the transition point is greatly advanced.