Robust and intrinsic type-Ⅲnodal points in a diamond-like lattice

An ideal type-Ⅲnodal point is generated by crossing a completely flat band and a dispersive band along a certain momentum direction.To date,the type-Ⅲnodal points found in two-dimensional(2D)materials have been mostly accidental and random rather than ideal cases,and no one mentions what kind of lattice can produce ideal nodal points.Here,we propose that ideal type-Ⅲnodal points can be obtained in a diamond-like lattice.The flat bands in the lattice originate from destructive interference of wavefunctions,and thus are intrinsic and robust.Moreover,the specific lattice can be realized in some 2D carbon networks,such as T-graphene and its derivatives.All the carbon structures possess type-ⅢDirac points.In two of the structures,consisting of triangular carbon rings,the type-ⅢDirac points are located just on the Fermi level and the Fermi surface is very clean.Our research not only opens a door to finding the ideal type-ⅢDirac points,but also provides 2D materials for exploring their physical properties experimentally.

Type-Ⅲ数字补偿器在双Buck逆变器中的实现

开关电源环路设计、补偿与参数整定一直是研究的焦点,本文所研究的典型双Buck逆变器是由2个Buck电路组成的。首先分析电流连续控制模式(CCM)下考虑寄生参数的单Buck电路系统模型,通过分析波特图采用经典的PI控制器无法降低系统静态误差和提高动态响应能力;然后设计了基于零极点补偿的Type-Ⅲ数字补偿器,在MathCad软件下搭建数学模型进行理论分析,并使用双线性变换法实现数字化转换;最后制作实验样机验证控制模型及环路补偿参数的合理性。结果表明,CCM下考虑寄生参数的双Buck逆变器采用所建立的Type-Ⅲ补偿器,具有良好的抗负载扰动性能。

Realization of low-energy type-Ⅱ Dirac fermions in(Ir_(1-x)Pt_x)Te_2 superconductors

Topological Dirac semimetals(DSMs) present a kind of topologically nontrivial quantum state of matter, which has massless Dirac fermions in the bulk and topologically protected states on certain surfaces. In superconducting DSMs, the effects of their nontrivial topology on superconducting pairing could realize topological superconductivity in the bulk or on the surface. As superconducting pairing takes place at the Fermi level E_F, to make the effects possible, the Dirac points should lie in the vicinity of E_F so that the topological electronic states can participate in the superconducting paring. Here,we show using angle-resolved photoelectron spectroscopy that in a series of(Ir_(1-x)Pt_x)Te_2 compounds, the type-Ⅱ Dirac points reside around E_F in the superconducting region, in which the bulk superconductivity has a maximum T_c of ～ 3 K.The realization of the coexistence of bulk superconductivity and low-energy Dirac fermions in(Ir_(1-x)Pt_x)Te_2 paves the way for studying the effects of the nontrivial topology in DSMs on the superconducting state.

联合H.264和多码率Turbo码的无线视频传输

提出了一种无线视频流联合信源信道编码传输的具体方案,结合H.264视频编码,对其进行合理数据分割后采用UEP技术,并联合信道设计了一个支持信道UEP的多码率Turbo编解码器,同时把Turbo编码与type-Ⅲ HARQ混合自动重传请求机制结合以达到更可靠的数据传输保证。通过仿真实验证明,这种设计方法可进一步优化系统在恶劣的无线信道下的链路吞吐量和取得更好的视频重建质量。

Nonlinear topological valley Hall edge states arising from type-Ⅱ Dirac cones

A Dirac point is a linear band crossing point originally used to describe unusual transport properties of materials like graphene.In recent years,there has been a surge of exploration of type-II Dirac/Weyl points using various engineered platforms including photonic crystals,waveguide arrays,metasurfaces,magnetized plasma and polariton micropillars,aiming toward relativistic quantum emulation and understanding of exotic topological phenomena.Such endeavors,however,have focused mainly on linear topological states in real or synthetic Dirac/Weyl materials.We propose and demonstrate nonlinear valley Hall edge(VHE)states in laserwritten anisotropic photonic lattices hosting innately the type-Ⅱ Dirac points.These self-trapped VHE states,manifested as topological gap quasi-solitons that can move along a domain wall unidirectionally without changing their profiles,are independent of external magnetic fields or complex longitudinal modulations,and thus are superior in comparison with previously reported topological edge solitons.Our finding may provide a route for understanding nonlinear phenomena in systems with type-Ⅱ Dirac points that violate the Lorentz invariance and may bring about possibilities for subsequent technological development in light field manipulation and photonic devices.

Efficiently band-tailored type-Ⅲ van der Waals heterostructure for tunnel diodes and optoelectronic devices

Broken-gap(type-Ⅲ)two-dimensional(2D)van der Waals heterostructures(vdWHs)offer an ideal platform for interband tunneling devices due to their broken-gap band offset and sharp band edge.Here,we demonstrate an efficient control of energy band alignment in a typical type-ⅢvdWH,which is composed of vertically-stacked molybdenum telluride(MoTe2)and tin diselenide(SnSe2),via both electrostatic and optical modulation.By a single electrostatic gating with hexagonal boron nitride(hBN)as the dielectric,a variety of electrical transport characteristics including forward rectifying,Zener tunneling,and backward rectifying are realized on the same heterojunction at low gate voltages of±1 V.In particular,the heterostructure can function as an Esaki tunnel diode with a room-temperature negative differential resistance.This great tunability originates from the atomicallyflat and inert surface of h-BN that significantly suppresses the interfacial trap scattering and strain effects.Upon the illumination of an 885 nm laser,the band alignment of heterojunction can be further tuned to facilitate the direct tunneling of photogenerated charge carriers,which leads to a high photocurrent on/off ratio of>105 and a competitive photodetectivity of 1.03×1012 Jones at zero bias.Moreover,the open-circuit voltage of irradiated heterojunction can be switched from positive to negative at opposite gate voltages,revealing a transition from accumulation mode to depletion mode.Our findings not only promise a simple strategy to tailor the bands of type-ⅢvdWHs but also provide an in-depth understanding of interlayer tunneling for future low-power electronic and optoelectronic applications.

A bacterial effector protein uncovers a plant metabolic pathway involved in tolerance to bacterial wilt disease

Bacterial wilt caused by the soil-borne plant pathogen Ralstonia solanacearum is a devastating disease worldwide.Upon plant colonization,R.solanacearum replicates massively,causing plant wilting and death;collapsed infected tissues then serve as a source of inoculum.In this work,we show that the plant metabolic pathway mediated by pyruvate decarboxylases(PDCs)contributes to plant tolerance to bacterial wilt disease.Arabidopsis and tomato plants resp ond to R.solanacearum infection by in creasing PDC activity,and plants with deficient PDC activity are more susceptible to bacterial wilt.Treatment with either pyruvic acid or acetic acid(substrate and product of the PDC pathway,respectively)enhances plant tolerance to bacterial wilt disease.An effector protein secreted by R.solanacearum,RipAK,interacts with PDCs and inhibits their oligomerization and enzymatic activity.Collectively,our work reveals a metabolic pathway involved in plant resistance to biotic and abiotic stresses,and a bacterial virulence strategy to promote disease and the completion of the pathogenic life cycle.

Influence of serum adiponectin level and SNP +45 polymorphism of adiponectin gene on myocardial fibrosis

Adiponectin plays an important role in the development of hypertension, atherosclerosis, and cardio- myocyte hypertrophy, but very little was known about the influence of serum adiponectin or the adiponectin gene polymorphism on myocardial fibrosis. Our study investigates the influence of the SNP ＋45 polymorphism of the adi- ponectin gene and serum levels of adiponectin on myocardial fibrosis in patients with essential hypertension. A case-control study was conducted on 165 hypertensive patients and 126 normotensive healthy controls. The geno- types of adiponectin gene polymorphisms were detected by the polymerase chain reaction （PCR） method. Serum concentrations of procollagen were measured by a double antibody sandwich enzyme-linked immunosorbent assay （ELISA） in all subjects. The integrated backscatter score （IBS） was measured in the left ventricular myocardium using echocardiography. The serum levels of adiponectin in hypertensive patients were significantly lower than those in the normal control group （（2.69±1.0） μg/ml vs. （4.21±2.89） μg/ml, respectively, P〈0.001）. The serum levels of type-Ⅰ procoilagen carboxyl end peptide （PiCP） and type-Ⅲprocollagen ammonia cardinal extremity peptide （PIIINP） in the hypertension group were significantly higher than those in the control group. In the hypertension group, serum levels of adiponectin were significantly and negatively related to the average acoustic intensity and corrected acoustic intensity of the myocardium （t=0.46 and 0.61, respectively, P〈0.05 for both）. The serum levels of PICP and PIIINP were sig- nificantly different among the three genotypes of SNP ＋45 （P〈0.01）. Logistic regression analyses showed that sex and genotype （GG＋GT） were the major risk factors of myocardial fibrosis in hypertensive patients （OR=5.343 and 3.278, respectively, P〈0.05）. These data suggest that lower levels of adiponectin and SNP ＋45 polymorphism of the adi- ponectin gene are likely to play an important role in myocardial fibrosis in hypertensive patients.