无序非厄密系统中的体-边对应

尽管广义布里渊区理论已经被提出,但考虑到广泛应用的非布洛赫能带理论往往只适用于干净体系,对于无序系统的体-边对应及其相关理论一直没有得到恰当的处理.本文提出无平移对称性体系的普适体-边对应方案.该方案建议通过最小化F=|det[E-HOBC]-det[E-HPBC]|以求重建体-边对应,并给出了无序作用下的广义布里渊区理论.基于该理论,作者不仅阐明了无序系统中缠绕数与非厄密趋肤效应的内在一致性的起源,而且给出的解析结果准确地刻画体系非厄密趋肤效应的强度与方向随参数的演化趋势,并预言了无序调控的非厄密趋肤效应以及耦合诱导非厄米趋肤效应反转等多种现象.

Tailoring the multiscale mechanics of tunable decellularized extracellular matrix (dECM) for wound healing through immunomodulation

With the discovery of the pivotal role of macrophages in tissue regeneration through shaping the tissue immune microenvironment, various immunomodulatory strategies have been proposed to modify traditional biomaterials. Decellularized extracellular matrix (dECM) has been extensively used in the clinical treatment of tissue injury due to its favorable biocompatibility and similarity to the native tissue environment. However, most reported decellularization protocols may cause damage to the native structure of dECM, which undermines its inherent advantages and potential clinical applications. Here, we introduce a mechanically tunable dECM prepared by optimizing the freeze-thaw cycles. We demonstrated that the alteration in micromechanical properties of dECM resulting from the cyclic freeze-thaw process contributes to distinct macrophage-mediated host immune responses to the materials, which are recently recognized to play a pivotal role in determining the outcome of tissue regeneration. Our sequencing data further revealed that the immunomodulatory effect of dECM was induced via the mechnotrasduction pathways in macrophages. Next, we tested the dECM in a rat skin injury model and found an enhanced micromechanical property of dECM achieved with three freeze-thaw cycles significantly promoted the M2 polarization of macrophages, leading to superior wound healing. These findings suggest that the immunomodulatory property of dECM can be efficiently manipulated by tailoring its inherent micromechanical properties during the decellularization process. Therefore, our mechanics-immunomodulation-based strategy provides new insights into the development of advanced biomaterials for wound healing.

Moiréflat bands of twisted few-layer graphite

We report that the twisted few layer graphite(tFL-graphite)is a new family of moiréheterostructures(MHSs),which has richer and highly tunable moiréflat band structures entirely distinct from all the known MHSs.A tFL-graphite is composed of two few-layer graphite(Bernal stacked multilayer graphene),which are stacked on each other with a small twisted angle.The moiréband structure of the tFL-graphite strongly depends on the layer number of its composed two van der Waals layers.Near the magic angle,a tFL-graphite always has two nearly flat bands coexisting with a few pairs of narrowed dispersive(parabolic or linear)bands at the Fermi level,thus,enhances the DOS at EF.This coexistence property may also enhance the possible superconductivity as been demonstrated in other multiband superconductivity systems.Therefore,we expect strong multiband correlation effects in tFL-graphite.Meanwhile,a proper perpendicular electric field can induce several isolated nearly flat bands with nonzero valley Chern number in some simple tFL-graphites,indicating that tFL-graphite is also a novel topological flat band system.

Nb元素对Mar-M246合金力学性能的影响研究

高温合金中含有多种战略性金属资源,如Nb及稀土元素等,合理利用高温合金返回料是实现金属资源高效回收利用的关键。但是高温合金返回料在利用时可能会引人其他合金元素,本文以Mar-M246合金返回料在利用过程中可能引人Nb元素为出发点,采用真空感应熔炼炉冶炼了不同Nb元素含量的Mar-M246合金。采用热力学计算软件、三维光学显微镜(3DM)、扫描电镜(SEM)和万能试验机对不同Nb元素含量的Mar-M246合金进行了组织和性能分析。结果表明,在Mar-M246合金中添加≤0.25w.t.%含量的Nb元素会扩大相和MC碳化物的析出温度区间,但不改变合金的析出相类型。Nb元素的添加对Mar-M246合金强度影响不大,随着Nb元素含量的增加合金强度降低在100MPa以内,同时合金塑性得到改善.

Advances in the Application of Molecular Diagnostic Techniques to Brucellosis

Brucellosis is a zoonotic infectious and allergic disease caused by Brucella bacteria.Brucellosis occurs worldwide and has had a huge economic impact on the livestock industry in many countries and regions.It has become a major public health problem.Brucella is an endoparasitic,non-motile Gram-negative bacterium capable of surviving within a diverse range of domestic animal hosts.

基于新型SRLR结构的双通带超导平衡滤波器研制

本文提出了一种新型多模SRLR (square ring loaded resonators)结构,并基于该谐振结构设计了一款具有高共模噪声抑制的双通带超导平衡滤波器.此外,本文详细地给出了该谐振器的差共模谐振机理,拓扑结构,模拟仿真结果.基于上述分析,使用0.5 mm厚度的氧化镁(MgO)基片上的钇钡铜氧(YBCO)高温超导薄膜设计制作一款四阶双通带平衡滤波器,该滤波器的两个通带的中心频率分别为2.2 GHz和3.5 GHz,带内的损耗分别为0.1 d B和0.12 dB,两个通带内的共模抑制分别为74.9 d B和67.4 dB.其测试曲线、模拟仿真曲线、理论计算具有良好的吻合度,验证了所提出滤波器的设计方法的正确性.

Impact of 1.5°C and 2.0°C global warming on aircraft takeoff performance in China

Associated with global warming, climate extremes such as extreme temperature will significantly increase. Understanding how climate change will impact the airflights is important to the planning of future flight operations. In this study, the impacts of 1.5 and 2 degree's global warming on the aircraft takeoff performance in China are investigated using a unique climate projection data from an international collaboration project named HAPPI. It is found that the mean summer daily maximum temperature, which is a major factor that affects the flight through changing the aircraft's takeoff weight, will increase significantly with magnitude less than 1.5℃ over most parts of China except for the Tibetan Plateau. The half a degree additional global warming will lead to higher extreme temperature in the arid and semi-arid western China, the Tibetan Plateau and the northeastern China, while the change in eastern China is weak. Five airports including Beijing, Shanghai, Kunming, Lasa and Urumqi will see ～1.0°-2.0℃(1.4°-3.0℃) higher daily maximum temperature under 1.5℃(2.0℃) scenario. The half-degree additional warming will lead to a shift toward higher extreme temperature in these five sites. For both1.5° and 2.0℃ scenarios, the number of weight-restriction days will increase significantly at 3 airports including Beijing, Shanghai, and Lasa. Urumqi will witness an increase of weight-restriction days only in 2.0℃ future.

Amplification of the Solar Signal in the Summer Monsoon Rainband in China by Synergistic Actions of Different Dynamical Responses

A rainband meridional shift index （RMSI） is defined and used to statistically prove that the East Asian summer monsoon rainband is usually significantly more northward in the early summer of solar maximum years than that of solar minimum years. By applying continuous wavelet transform, cross wavelet transform, and wavelet coherence, it is found that throughout most of the 20th century, the significant decadal oscillations of sunspot number （SSN） and the RMSI are phase-locked and since the 1960s, the SSN has led the RMSI slightly by approximately 1.4 yr. Wind and Eliassen-Palm （EP） flux analysis shows that the decadal meridional oscillation of the June rainband likely re- sults from both a stronger or earlier onset of the tropical monsoon and poleward shift of the subtropical westerly jet in high-solar months of May and June. The dynamical responses of the lower tropical monsoon and the upper subtropical westerly jet to the 11-yr solar cycle transmit bottom-up and top-down solar signals, respectively, and the synergistic actions between the monsoon and the jet likely amplify the solar signal at the northern boundary of the monsoon to some extent.

Deterministic Approach to Achieve Full-Polarization Cloak

Achieving full-polarization(σ)invisibility on an arbitrary three-dimensional(3D)platform is a long-held knotty issue yet extremely promising in real-world stealth applications.However,state-of-the-art invisibility cloaks typically work under a specific polarization because the anisotropy and orientation-selective resonant nature of artificial materials made theσ-immune operation elusive and terribly challenging.Here,we report a deterministic approach to engineer a metasurface skin cloak working under an arbitrary polarization state by theoretically synergizing two cloaking phase patterns required,respectively,at spin-up(σ+)and spin-down(σ−)states.Therein,the wavefront of any light impinging on the cloak can be well preserved since it is a superposition ofσ+andσ−wave.To demonstrate the effectiveness and applicability,several proof-of-concept metasurface cloaks are designed to wrap over a 3D triangle platform at microwave frequency.Results show that our cloaks are essentially capable of restoring the amplitude and phase of reflected beams as if light was incident on a flat mirror or an arbitrarily predesigned shape under full polarization states with a desirable bandwidth of~17.9%,conceiving or deceiving an arbitrary object placed inside.Our approach,deterministic and robust in terms of accurate theoretical design,reconciles the milestone dilemma in stealth discipline and opens up an avenue for the extreme capability of ultrathin 3D cloaking of an arbitrary shape,paving up the road for real-world applications.

High-efficiency broadband polarization-independent superscatterer using conformal metasurfaces

Safe detection of an arbitrarily shaped platform is critical for survivability, rescue, or navigation safety in a remote region. Metasurfaces afford great potential due to their strong electromagnetic(EM) wave control. However,studies have mainly focused on the physics and design of metasurfaces on planar plates, which does not satisfy the current requirements of aerodynamics and aesthetics. Herein, we propose a sophisticated strategy to design a metasurface that can wrap over arbitrarily shaped objects with moderate curvature on which optical aberrations are commonly introduced. By designing each meta-atom on the basis of the required position and phase compensation, exact EM wavefronts are restored. For verification, several conformal metasurfaces were designed and numerically studied on metallic cylinders at the microwave spectrum. A proof-of-concept device is fabricated and is experimentally characterized. The results demonstrate the availability of the desirable dual-beam superscatterer with strong backscattering enhancement toward two directions, thus indicating that the distortions induced by an arbitrary platform can be efficiently corrected. Our method affords an efficient alternative for designing highperformance multifunctional optoelectronic devices equipped on a moderately curved platform.

A Case Study on the Rapid Rain-to-Snow Transition in Late Spring 2018 over Northern China:Effects of Return Flows and Topography

Phase changes in the precipitation processes of early winter and late spring in midlatitude regions represent challenges when forecasting the timing and magnitude of snowfall.On 4 April 2018,a heavy snow process occurred in Beijing and northwestern Hebei Province,becoming the most delayed occurrence of heavy spring snow ever recorded over Beijing in the last 30 years.This paper uses observational and numerical simulation data to investigate the causes for the rapid rain-to-snow(RRTS)phase transition during this process.The following results are obtained.(1)Return flows(RFs),an interesting type of easterly wind,including those at 1000,925,and 800 hPa,played an important role in this heavy snow process and presented a characteristic"sandwich"structure.The RFs,complex topography,and snow particles that dominated the clouds,were the three key factors for the RRTS transition.(2)The RRTS transition in the plains was directly related to the RF at 925 hPa,which brought about advective cooling initiated approximately 4-6 h before the onset of precipitation.Then,the RF played a role of diabatic cooling when snow particles began to fall at the onset of precipitation.(3)The RRTS transition in the northern part of the Taihang Mountains was closely related to the relatively high altitude that led to a lower surface temperature owing to the vertical temperature lapse rate.Both immediately before and after the onset of precipitation,the snow particles in clouds entrained the middle-level cold air downward,causing the melting layer(from surface to the 0℃-isotherm level)to become very thin;and thus the snow particles did not have adequate time to melt before falling to the ground.(4)The rapid RRTS over the Yanqing mountainous area in the northwest of Beijing could have involved all the three concurrent mechanisms:the advective cooling of RF,the melting cooling of cloud snow particles,and the high-altitude effect.Compared with that in the plain area with less urbanization the duration of the RRTS in the plain area with significant urbanization was extended by approximately 2 h.

基于简并p轨道的平带模型及其二维材料实现

作为一种无色散且态密度发散的电子结构,平带为研究相互作用、实现新奇物理性质提供了理想平台.设计理论模型并寻找相应的材料实现受到了广泛关注.当前,基于现有理论模型寻找和制备具有理想平带的二维材料仍存在不同程度的挑战.本文提出了一种可以在一系列二维材料中实现平带的新型理论模型.以结构稳定的硫化钾(K2S)二维单层为例,其平带的色散仅为50毫电子伏左右.在硫化钾单层与石墨烯构成的异质结中,层间的电荷转移可以调节平带的部分填充.该平带模型还可以在一些1T结构的三元化合物中实现.例如,已经被实验室合成的Gd2CCl2.第一性原理计算表明,在铁磁态的Gd2CCl2单层中,还可以实现自旋极化的平带.此文提出的理论模型与二维材料为平带以及相关新奇物理性质的研究提供了理想的且可实现的平台.

Dephasing eflfects in topological insulators

Topological insulators,a class of typical topological materials in both two dimensions and three dimensions,are insulating in bulk and metallic at surface.The spin-momentum locked surface states and peculiar transport properties exhibit promising potential applications on quantum devices,which generate extensive interest in the last decade.Dephasing is the process of the loss of phase coherence,which inevitably exists in a realistic sample.In this review,we focus on recent progress in dephasing effects on the topological insulators.In general,there are two types of dephasing processes:normal dephasing and spin dephasing.In two-dimensional topological insulators,the phenomenologically numerical investigation shows that the longitudinal resistance plateaus is robust against normal dephasing but fragile with spin dephasing.Several microscopic mechanisms of spin dephasing are then discussed.In three-dimensional topological insulators,the helical surface states exhibit a helical spin texture due to the spin-momentum locking mechanism.Thus,normal dephasing has close connection to spin dephasing in this case,and gives rise to anomalous "gap-like" feature.Dephasing effects on properties of helical surface states are investigated.

基于非对称耦合阶跃阻抗谐振器的高阶窄带超导平衡式滤波器设计

本文研究了一款基于非对称耦合阶跃阻抗谐振器SIR(stepped-impedance resonator)设计的6阶窄带超导平衡式带通滤波器,该滤波器具有高的频率选择性以及宽阻带特性.本文首先研究了3种具有不同耦合特性的SIR耦合对,分析了其差模DM(differential mode)相位移、耦合系数,以及共模CM(common mode)抑制水平.通过适当选取SIR的阻抗比以及使用具有分散谐波分量的不同尺寸的SIR,其高次频得以远离基频,从而拓宽阻带.同时,由于其DM和CM等效电路具有不同的谐振频率,其带内的共模噪声可以得到天然的抑制.研究表明,电磁耦合对可在不增加电路面积的情况下获得小的耦合系数以利于窄带设计,电耦合对结构有利于高阶电路的互连,而磁耦合对具有最佳的CM抑制水平.此外,3类SIR对的弱耦合特性均可用于窄带设计.为了验证,本文采用所述3类SIR对设计了一款6阶平衡式带通滤波器,并在此基础上引入交叉耦合结构产生传输零点以提高通带选择性.其零点的产生机理通过传输路径的幅度及相位移分析进行了说明.最终,本文利用高温超导HTS(high-temperature superconducting)技术实现了所设计的具有交叉耦合结构的滤波器,以降低插入损耗.该电路在77 K温度下进行了测量,测试结果表明:通带的相对带宽FBW(fractional bandwidth)为1.6%,带内插损约为0.37 dB,带内CM抑制度优于40 dB.其-60 dB带宽/-3 dB带宽的矩形系数小于1.45,同时-20 dB DM阻带达到约5倍f_(0)^(d)(f_(0)^(d)代表DM基波频率).

Effective spin dephasing mechanism in confined two-dimensional topological insulators

A Kramers pair of helical edge states in quantum spin Hall effect(QSHE) is robust against normal dephasing but not robust to spin dephasing. In our work, we provide an effective spin dephasing mechanism in the puddles of two-dimensional(2D) QSHE, which is simulated as quantum dots modeled by 2D massive Dirac Hamiltonian. We demonstrate that the spin dephasing effect can originate from the combination of the Rashba spin-orbit coupling and electron-phonon interaction, which gives rise to inelastic backscattering in edge states within the topological insulator quantum dots, although the time-reversal symmetry is preserved throughout. Finally,we discuss the tunneling between extended helical edge states and local edge states in the QSH quantum dots, which leads to backscattering in the extended edge states. These results can explain the more robust edge transport in In As/Ga Sb QSH systems.

Log-periodic quantum oscillations in topological or Dirac materials

As a manifestation of the underlying physical nature, quailtum oscillations with the applied magnetic field (B) are one of the most important topics in condensed matter physics. The research history can be tracked to 1930 when Lev Shubnikov and W. J. de Haas observed Shubnikov-de Haas (SdH) oscillations in the magnetoresistance (MR) of bismuth crystals. Since then, researchers have observed quantum oscillations in diverse materials, including metals, metallic compounds, semimetals, semiconductors and even insula tors, as well as in artificial mesoscopic microstructures . Nowadays, quantum oscillation detec ted by magneto transport investigation has been a powerful tool to detect the physical properties in solid-state systems.

超导β-W薄膜中厚度调控的普适类

本文使用磁控溅射生长了不同厚度的超导β-W薄膜.在具有不同无序强度不同厚度的β-W薄膜中观察到可调控的超导普适类(TUC),它们对应完全不同的临界行为,在面内磁场和面外磁场中均显示出显著的TUC性质.具体来说,超导金属相变的普适类会随着β-W薄膜厚度不同而变化2次:当厚度达到8 nm时,普适类将从量子格里菲斯奇异性(QGS)变到多重量子临界性;而当厚度进一步达到16 nm时,多重量子临界性将转变为单量子临界性.值得一提的是,通过有限尺度缩放方法可得到2 nm样品中具有超高的量子临界指数zv~30 (0.05 K温度下).这个数值是目前报道最高的,同时,超导金属相变在面内磁场下也被观察到,并具有相似的TUC性质.

Quantum to classical crossover under dephasing effects in a two-dimensional percolation model

Scaling theory predicts complete localization in d = 2 in quantum systems belonging to the orthogonal class(i.e., with timereversal symmetry and spin-rotation symmetry). The conductance g behaves as g^exp(-L/l) with system size L and localization length l in the strong disorder limit. However, classical systems can always have metallic states in which Ohm’s law shows a constant g in d=2. We study a two-dimensional quantum percolation model by controlling dephasing effects. The numerical investigation of g aims at simulating a quantum-to-classical percolation evolution. An unexpected metallic phase, where g increases with L, generates immense interest before the system becomes completely classical. Furthermore, the analysis of the scaling plot of g indicates a metal-insulator crossover.