Twisted Yangian Y(sp_(2))的单权模

讨论了Twisted Yangian Y(sp_(N))的权模问题,构造了Y(sp_(2))的一类无限维单权模,分类了具有一个一维权空间的Y(sp_(2))单权模.

Twisted Yangian Y(sp^(2))的一类单权模

研究了Twisted Yangian Y(g_(N))的权模问题,构造了Y(sp^(2))的一类权空间维数均为2的无限维权模,给出了该权模不可约的充分条件.

Visualizing the Local Twist Angle Variation within and between Domains of Twisted Bilayer Graphene

Moirésuperlattices in twisted two-dimensional materials have emerged as ideal platforms for engineering quantum phenomena,which are highly sensitive to twist angles,including both the global value and the spatial inhomogeneity.However,only a few methods provide spatial-resolved information for characterizing local twist angle distribution.

Valley-dependent transport in a mescoscopic twisted bilayer graphene device

We study the valley-dependent electron transport in a four-terminal mesoscopic device of the two monolayer graphene nanoribbons vertically stacked together, where the intersection forms a bilayer graphene lattice with a controllable twist angle. Using a tight-binding lattice model, we show that the longitudinal and transverse conductances exhibit significant valley polarization in the low energy regime for small twist angles. As the twist angle increases, the valley polarization shifts to the high energy regime. This arises from the regrouping effect of the electron band in the twisted bilayer graphene region. But for relatively large twist angles, no significant valley polarization is observed. These results are consistent with the spectral densities of the twisted bilayer graphene.

Twisted Integration of Complex Oxide Magnetoelectric Heterostructures via Water‑Etching and Transfer Process

Manipulating strain mode and degree that can be applied to epitaxial complex oxide thin films have been a cornerstone of strain engineering.In recent years,lift-off and transfer technology of the epitaxial oxide thin films have been developed that enabled the integration of heterostructures without the limitation of material types and crystal orientations.Moreover,twisted integration would provide a more interesting strategy in artificial magnetoelectric heterostructures.A specific twist angle between the ferroelectric and ferromagnetic oxide layers corresponds to the distinct strain regulation modes in the magnetoelectric coupling process,which could provide some insight in to the physical phenomena.In this work,the La_(0.67)Sr_(0.33)MnO_(3)(001)/0.7Pb(Mg_(1/3)Nb_(2/3))O_(3)-0.3PbTiO_(3)(011)(LSMO/PMN-PT)heterostructures with 45.and 0.twist angles were assembled via water-etching and transfer process.The transferred LSMO films exhibit a fourfold magnetic anisotropy with easy axis along LSMO<110>.A coexistence of uniaxial and fourfold magnetic anisotropy with LSMO[110]easy axis is observed for the 45°Sample by applying a 7.2 kV cm^(−1)electrical field,significantly different from a uniaxial anisotropy with LSMO[100]easy axis for the 0°Sample.The fitting of the ferromagnetic resonance field reveals that the strain coupling generated by the 45°twist angle causes different lattice distortion of LSMO,thereby enhancing both the fourfold and uniaxial anisotropy.This work confirms the twisting degrees of freedom for magnetoelectric coupling and opens opportunities for fabricating artificial magnetoelectric heterostructures.

Wafer-scale 30°twisted bilayer graphene epitaxially grown on Cu_(0.75)Ni_(0.25)(111)

Twisted bilayer graphene(TBG) has been extensively studied because of its novel physical properties and potential application in electronic devices.Here we report the synthesis and characterization of 300 TBG naturally grown on Cu_(0.75)Ni_(0.25)(111) film and investigate the electronic structure by angle-resolved photoemission spectroscopy.Compared with other substrates,our TBG with a wafer scale is acquired with a shorter growth time.The Fermi velocity and energy gap of Dirac cones of TBG are comparable with those of a monolayer on Cu_(0.85)Ni_(0.15)(111).The signature of moré lattices has not been observed in either the low-energy electron diffraction patterns or the Fermi surface map within experimental resolution,possibly due to different Cu and Ni contents in the substrates enhancing the different couplings between the substrate and the first/second layers and hindering the formation of a quasiperiodic structure.

Tubular Heat Enhancement Using Twisted Tape Inserts with Large Holes

Heat augmentation techniques play a vital role in the heating and cooling processes in industries,including solar collectors and many applications that utilize heat exchangers.Several studies are based on inserting fillers inside the tubes to enhance heat transfer.This investigation considered the effects of twisted tapes with large holes on a tubular heat exchanger’s(HX)heat transmission,pressure drop,and thermal boosting factor.In the experimental section,counter-swirl flow generators used twisted tapes with pairs of 1.0 cm-diameter holes and changes in porosity(Rp)at 1.30%and 2.70%.In the experiments,air was utilized as a working fluid in a tube with a circular cross-section.The turbulent flow was considered,with Reynolds numbers(Re)domain from 4800 to 9500,and a boundary condition with a uniform wall heat flux was constructed.The findings expound that when the number of holes rose,the Nusselt number(Nu),the factor of friction(f),and the thermal enhancement factor(η)all increased as well.Additionally,as the friction factor increased,the Nusselt number of the tape-equipped tube was noticeably higher.Additionally,it was discovered that the friction factor was between 70%and 94%lower than the values of the tube without tape,while the(Nu)was between 87%and 97%higher than the conventional tube values.The maximum value ofηis 89%.According to the experimental results,empirical correlations for Nu,f,andηwere also generated.

Linear Functional Equations and Twisted Polynomials

A certain variety of non-switched polynomials provides a uni-figure representation for a wide range of linear functional equations. This is properly adapted for the calculations. We reinterpret from this point of view a number of algorithms.

基于Super-Twisting滑模S面的无人机路径跟踪控制

针对小型固定翼无人机在执行任务时跟踪精度低以及容易受外界风影响的问题,设计基于Super-Twisting滑模S面(STSM S-Plane)的路径跟踪控制器,同时采用内外双环控制模式。外环即速度环采用Super-Twisting滑模控制,内环即姿态环采用S面控制。考虑到S面控制求导易导致积分爆炸的问题引入了二阶微分器,并对外界风组成进行建模研究。最后通过空间特殊曲线来验证所设计算法的控制性能。仿真结果表明,所设计的算法可以实现固定翼无人机对期望路径的精确跟踪,并具有良好的鲁棒性和抗干扰性能。

基于改进型Super-twisting的双馈感应发电机直接功率控制

为提高双馈感应发电机(DFIG)直接功率控制的鲁棒性和抗干扰能力,提出一种改进型超螺旋滑模(STSMC)的直接功率控制(DPC)。首先,建立参数摄动下的DFIG最大功率捕获模型和定子磁场定向的双馈感应发电机模型;然后,将非奇异快速终端滑模面(NFTSM)与一种改进型超螺旋(Super-twisting)优化算法结合,设计DFIG直接功率控制器(IST-NFTSMC)。其中所设计的非奇异滑模面能有效避免传统滑模控制(SMC)的奇异现象,且改进超螺旋控制律能有效削弱NFTSMC抖振,提高功率控制精度;最后,通过仿真和实验,与PI控制和传统SMC控制相比,该控制能削弱DFIG功率与电流抖振问题,加快其收敛速度,提高DFIG直接功率控制稳态精度。

Preface to Special Topic on Twisted van der Waals Heterostructures

Twisted van der Waals heterostructures are becoming the building blocks for engineering new device structures, in which their electronic, optical and mechanical properties can be tuned by changing the “twist” angle between layers of 2D materials. Such twisted 2D heterostructures offer a unique opportunity to create a new field of “twistronics” by mechanically stacking different 2D van der Waals materials together.

Optical Tunable MoiréExcitons in Twisted Hexagonal GaTe Bilayers

Optical fine-tunable layer-hybridized Moiréexcitons are highly in demand for emerging many-body states in two-dimensional semiconductors.We report naturally confined layer-hybridized bright Moiréexcitons with long lifetimes in twisted hexagonal GaTe bilayers,using ab initio many-body perturbation theory and the Bethe–Salpeter equation.Due to the hybridization of electrons and holes between layers,which enhances the brightness of excitons,the twisted bilayer system becomes attractive for optical applications.We find that in both R and H-type stacking Moirésuperlattices,more than 200 meV lateral quantum confinements occur on exciton energies,which results in two scenarios:(1)The ground state bright excitons XA are found to be trapped at two high-symmetry points,with opposite electric dipoles in the R-stacking Moirésupercell,forming a honeycomb superlattice of nearest-neighbor dipolar attraction.(2)For H-stacking case,the XA is found to be trapped at only one high-symmetry point exhibiting a triangular superlattice.Our results suggest that twisted h-GaTe bilayer is one of the promising systems for optical fine-tunable excitonic devices and provide an ideal platform for realizing strong correlated Bose–Hubbard physics.

Coupled Ferroelectricity and Correlated States in a Twisted Quadrilayer MoS_(2) Moiré Superlattice

Moiré superlattices have emerged as a highly controllable quantum platform for exploration of various fascinating phenomena,such as Mott insulator states,ferroelectric order,unconventional superconductivity and orbital ferromagnetism.Although remarkable progress has been achieved,current research in moiré physics has mainly focused on the single species properties,while the coupling between distinct moiré quantum phenomena remains elusive.Here we demonstrate,for the first time,the strong coupling between ferroelectricity and correlated states in a twisted quadrilayer MoS2moiré superlattice,where the twist angles are controlled in sequence to be ~57°,~0°,and ~-57°.Correlated insulator states are unambiguously established at moiré band filling factors v = 1,2,3 of twisted quadrilayer MoS_(2).Remarkably,ferroelectric order can occur at correlated insulator states and disappears quickly as the moiré band filling deviates from the integer fillings,providing smoking gun evidences of the coupling between ferroelectricity and correlated states.Our results demonstrate the coupling between different moiré quantum properties and will hold great promise for new moiré physics and applications.

TFF3依赖TWIST1上调TRIB3促结直肠癌转移的机制

目的探讨TFF3基因过表达对结直肠癌HT29细胞增殖、迁移和侵袭能力的影响,以及与癌转移相关的机制。方法构建TFF3过表达的HT29细胞系,qRT-PCR和Western blot法检测TFF3、TWIST1/TRIB3信号通路及上皮间质转化过程中相关mRNA和蛋白的表达,CCK-8法检测HT29细胞增殖能力,细胞划痕实验和Transwell实验评估细胞迁移和侵袭能力,透射电子显微镜观察TFF3过表达前后细胞形态的变化。结果pIRES2-TFF3质粒转染HT29细胞后,相较于对照组,TFF3 mRNA和蛋白表达水平显著升高(P<0.01),细胞增殖、迁移和侵袭能力显著增强(P<0.01),且TWIST1、TRIB3、Vimentin、Snail的表达也显著上升,而E-cadherin的表达则明显下降(P<0.05)。TFF3过表达后的HT29细胞出现了多种变化,如细胞间连接减少、绒毛脱落、伪足形成,以及形态上梭形细胞增多等。结论TFF3过表达可能通过Twist1/TRIB3信号通路促进结直肠癌细胞的EMT过程,从而提高其转移潜力,加速癌症的恶性进展。

Emergence of correlations in twisted monolayer-trilayer graphene heterostructures

Twisted bilayer graphene heterostructures have recently emerged as a well-established platform for studying strongly correlated phases,such as correlated insulating,superconducting,and topological states.Extending this notion to twisted multilayer graphene heterostructures has exhibited more diverse correlated phases,as some fundamental properties related to symmetry and band structures are correspondingly modified.Here,we report the observations of correlated states in twisted monolayer-trilayer(Bernal stacked)graphene heterostructures.Correlated phases at integer fillings of the moire unit cell are revealed at a high displacement field and stabilized with a moderate magnetic field on the electron-doping side at a twist angle of 1.45°,where the lift of degeneracy at the integer fillings is observed in the Landau fan diagram.Our results demonstrate the effectiveness of moire engineering in an extended structure and provide insights into electric-field tunable correlated phases.

Large valley Nernst effect in twisted multilayer graphene systems

Valley Nernst effect is a newly proposed and experimentally confirmed effect,which could be used to design novel thermoelectric devices.We study the valley Nernst effect in(M+N)-layer twisted multilayer graphene systems by a simple low-energy effective model.It is found that the total valley Nernst coefficient(VNC)is three orders of magnitude larger than that in monolayer group-Ⅵdichalcogenides.The total VNC increases with the increase of layer numbers.It is shown that the total VNC exhibits a structure with three peaks as a function of the Fermi energy.We identify that the central peak is always negative stemming from the flat band.Two shoulder peaks are positively induced by the conduction and valence bands,respectively.These predicted features can be tested experimentally.The present work would shed more light on valley caloritronics.

Machine learning of theΓ-point gap and flat bands of twisted bilayer graphene at arbitrary angles

The novel electronic properties of bilayer graphene can be fine-tuned via twisting,which may induce flat bands around the Fermi level with nontrivial topology.In general,the band structure of such twisted bilayer graphene(TBG)can be theoretically obtained by using first-principles calculations,tight-binding method,or continuum model,which are either computationally demanding or parameters dependent.In this work,by using the sure independence screening sparsifying operator method,we propose a physically interpretable three-dimensional(3D)descriptor which can be utilized to readily obtain theΓ-point gap of TBG at arbitrary twist angles and different interlayer spacings.The strong predictive power of the descriptor is demonstrated by a high Pearson coefficient of 99%for both the training and testing data.To go further,we adopt the neural network algorithm to accurately probe the flat bands of TBG at various twist angles,which can accelerate the study of strong correlation physics associated with such a fundamental characteristic,especially for those systems with a larger number of atoms in the unit cell.

Correlated states in alternating twisted bilayer–monolayer–monolayer graphene heterostructure

Highly controlled electronic correlation in twisted graphene heterostructures has gained enormous research interests recently,encouraging exploration in a wide range of moirésuperlattices beyond the celebrated twisted bilayer graphene.Here we characterize correlated states in an alternating twisted Bernal bilayer–monolayer–monolayer graphene of~1.74°,and find that both van Hove singularities and multiple correlated states are asymmetrically tuned by displacement fields.In particular,when one electron per moiréunit cell is occupied in the electron-side flat band,or the hole-side flat band(i.e.,three holes per moiréunit cell),the correlated peaks are found to counterintuitively grow with heating and maximize around 20 K–a signature of Pomeranchuk effect.Our multilayer heterostructure opens more opportunities to engineer complicated systems for investigating correlated phenomena.

Tunable correlation in twisted monolayer–trilayer graphene

Flat-band physics of moirésuperlattices,originally discovered in the celebrated twisted bilayer graphene,have recently been intensively explored in multilayer graphene systems that can be further controlled by electric field.In this work,we experimentally find the evidence of correlated insulators at half filling of the electron moiréband of twisted monolayer–trilayer graphene with a twist angle around 1.2°.Van Hove singularity(VHS),manifested as enhanced resistance and zero Hall voltage,is observed to be distinct in conduction and valence flat bands.It also depends on the direction and magnitude of the displacement fields,consistent with the asymmetric crystal structure.While the resistance ridges at VHS can be enhanced by magnetic fields,when they cross commensurate fillings of the moirésuperlattice in the conduction band,the enhancement is so strong that signatures of correlated insulator appear,which may further develop into an energy gap depending on the correlation strength.At last,Fermi velocity derived from temperature coefficients of resistivity is compared between conduction and valence bands with different displacement fields.It is found that electronic correlation has a negative dependence on the Fermi velocity,which in turn could be used to quantify the correlation strength.

Pipes with Trapezoidal Cut Twisted Tape Inserts in the Laminar Flow Regime:Nusselt Number and Friction Coefficient Analysis

The thermal behavior of pipes with a twisted tape inside(used to enhance heat transfer through the tube wall)is studied in the laminar flow regime.Oil is used as the work fluid with the corresponding Reynolds Number spanning the interval 200–2000.It is found that in such conditions the‘Nusselt Number’(Nu)gradually increases with reducing the tape twist ratio,whereas the friction factor is detrimentally affected by the presence of the tape(as witnessed by the comparison with the companion case where a plain tube is considered).In particular,it is shown that the heat transfer efficiency can be improved by nearly 69%if tape inserts with a relatively low twist ratio are used.On the basis of these findings,it is concluded that loose fit tape inserts are superior to tight fit tapes in terms of heat transfer and ease of replacement.