Synthesizing active and durable cubic ceria catalysts(<6 nm)for fast dehydrogenation of bio-polyols to carboxylic acids coproducing green H_(2)

Dehydrogenation is considered as one of the most important industrial applications for renewable energy.Cubic ceria-based catalysts are known to display promising dehydrogenation performances in this area.Large particle size(>20 nm)and less surface defects,however,hinder further application of ceria materials.Herein,an alternative strategy involving lactic acid(LA)assisted hydrothermal method was developed to synthesize active,selective and durable cubic ceria of<6 nm for dehydrogenation reactions.Detailed studies of growth mechanism revealed that,the carboxyl and hydroxyl groups in LA molecule synergistically manipulate the morphological evolution of ceria precursors.Carboxyl groups determine the cubic shape and particle size,while hydroxyl groups promote compositional transformation of ceria precursors into CeO_(2) phases.Moreover,enhanced oxygen vacancies(Vo)on the surface of CeO_(2) were obtained owing to continuous removal of O species under reductive atmosphere.Cubic CeO_(2) catalysts synthesized by the LA-assisted method,immobilized with bimetallic PtCo clusters,exhibit a record high activity(TOF:29,241 h^(-1))and Vo-dependent synergism for dehydrogenation of bio-derived polyols at 200℃.We also found that quenching Vo defects at air atmosphere causes activity loss of PtCo/CeO_(2) catalysts.To regenerate Vo defects,a simple strategy was developed by irradiating deactivated catalysts using hernia lamp.The outcome of this work will provide new insights into manufacturing durable catalyst materials for aqueous phase dehydrogenation applications.

Layer-Valley Hall Effect under Inversion and Time-Reversal Symmetries

Hall effects have been the central paradigms in modern physics,materials science and practical applications,and have led to many exciting breakthroughs,including the discovery of topological Chern invariants and the revolution of metrological resistance standard.To date,the Hall effects have mainly focused on a single degree of freedom(Do F),and most of them require the breaking of spatial-inversion and/or time-reversal symmetries.Here we demonstrate a new type of Hall effect,i.e.,layer-valley Hall effect,based on a combined layer-valley Do F characterized by the product of layer and valley indices.The layer-valley Hall effect has a quantum origin arising from the layer-valley contrasting Berry curvature,and can occur in nonmagnetic centrosymmetric crystals with both spatial-inversion and time-reversal symmetries,transcending the symmetry constraints of single Do F Hall effect based on the constituent layer or valley index.Moreover,the layer-valley Hall effect is highly tunable and shows a W-shaped pattern in response to the out-of-plane electric fields.Additionally,we discuss the potential detection approaches and material-specific design principles of layer-valley Hall effect.Our results demonstrate novel Hall physics and open up exotic paradigms for new research direction of layer-valleytronics that exploits the quantum nature of the coupled layer-valley DoF.

Design and In Situ Additive Manufacturing of Multifunctional Structures

Multifunctional structures(MFSs)integrate diverse functions to achieve superior properties.However,conventional design and manufacturing methods—which generally lack quality control and largely depend on complex equipment with multiple stations to achieve the integration of distinct materials and devices—are unable to satisfy the requirements of MFS applications in emerging industries such as aerospace engineering.Motivated by the concept of design for manufacturing,we adopt a layer regulation method with an established optimization model to design typical MFSs with load-bearing,electric,heat-conduction,and radiation-shielding functions.A high-temperature in situ additive manufacturing(AM)technology is developed to print various metallic wires or carbon fiber-reinforced high-meltingpoint polyetheretherketone(PEEK)composites.It is found that the MFS,despite its low mass,exceeds the stiffness of the PEEK substrate by 21.5%.The embedded electrics remain functional after the elastic deformation stage.Compared with those of the PEEK substrate,the equivalent thermal conductivity of the MFS beneath the central heat source area is enhanced by 568.0%,and the radiation shielding is improved by 27.9%.Moreover,a satellite prototype with diverse MFSs is rapidly constructed as an illustration.This work provides a systematic approach for high-performance design and advanced manufacturing,which exhibits considerable prospects for both the function expansion and performance enhancement of industrial equipment.

Hydrothermal conversion of fructose to lactic acid and derivatives:Synergies of metal and acid/base catalysts

With increasing strict regulation on single-use plastics,lactic acid(LA)and alkyl lactates,as essential monomers for bio-degradable polylactic acid(PLA)plastic products,have gained worldwide attention in both academia and industry.While LA is still dominantly produced through fermentation processes from start,chemical synthesis from cellulosic biomass remains a grand challenge,owing to poor selectivity in activating CAH and CAC bonds in sugar molecules.To our best knowledge,recent publications have been focused on hydrothermal conversion of glucose to LA,while this review summarizes the highlights on direct thermal conversion of fructose as starting material to LA and derivatives.In particular,the synergies of metal/metal cations and acid/base catalysts will be critically revised on retro-aldol and dehydration reactions.This work will provide insights into rational design of active and selective catalysts for the production of carboxylic acids from biomass feedstocks.

Reputation-Based Cooperative Spectrum Sensing Algorithm for Mobile Cognitive Radio Networks

Identifying malicious users accurately in cognitive radio networks(CRNs) is the guarantee for excellent detection performance. However, existing algorithms fail to take the mobility of secondary users into consideration. If applied directly in mobile CRNs, those conventional algorithms would overly punish reliable users at extremely bad or good locations, leading to an obvious decrease in detection performance. To overcome this problem, we divide the whole area of interest into several cells to consider the location diversity of the network. Each user's reputation score is updated after each sensing slot and is used for identifying whether it is malicious or not. If so, it would be removed away. And then our algorithm assigns users in cells with better channel conditions, i.e. larger signal-to-noise ratios(SNRs), with larger weighting coefficients, without requiring the prior information of SNR. Detailed analysis about the validity of our algorithm is presented. The simulation results show that in a CRN with 60 mobile secondary users, among which, 18 are malicious, our solution has an improvement of detection probability by 0.97-d B and 3.57-d B when false alarm probability is 0.1, compared with a conventional trust-value-based algorithm and a trusted collaborative spectrum sensing for mobile CRNs, respectively.

A review of experimental advances in twisted graphene moiré superlattice

Twisted moirésuperlattice receives tremendous interests since the discovery of correlated insulating states and superconductivity in magic angle twist bilayer graphene(MA-TBG)[Nature 55680(2018),Nature 55643(2018)],even gives arise to a new field"twistronics"[Science 361690(2018)].It is a new platform hosting strong electron correlations,providing an alternative for understanding unconventional superconductivity.In this article,we provide a review of recent experimental advances in the twisted moirésuperlattice,from MA-TBG to twisted double bilayer graphene and other two-dimensional materials based moirésuperlattice,covering correlated insulating states,superconductivity,magnetism,et al.

Emergence of Chern Insulating States in Non-Magic Angle Twisted Bilayer Graphene

Twisting two layers into a magic angle(MA) of ~1.1°is found essential to create low energy flat bands and the resulting correlated insulating,superconducting,and magnetic phases in twisted bilayer graphene(TBG).While most of previous works focus on revealing these emergent states in MA-TBG,a study of the twist angle dependence,which helps to map an evolution of these phases,is yet less explored.Here,we report a magnetotransport study on one non-magic angle TBG device,whose twist angle θ changes from 1.25° at one end to 1.43°at the other.For θ=1.25° we observe an emergence of topological insulating states at hole side with a sequence of Chern number |C|=4-|v|,where v is the number of electrons(holes) in moire unite cell.When θ> 1.25°,the Chern insulator from flat band disappears and evolves into fractal Hofstadter butterfly quantum Hall insulator where magnetic flux in one moire unite cell matters.Our observations will stimulate further theoretical and experimental investigations on the relationship between electron interactions and non-trivial band topology.

Influence of Heavy Metals on Seed Germination and Early Seedling Growth in Crambe abyssinica, a Potential Industrial Oil Crop for Phytoremediation

The influence of essential (Cu, Ni and Zn) and non-essential heavy metals (Hg, Cr, Pb and Cd) on seed germination and early seedling growth in industrial oil crop Crambe abyssinica was evaluated under laboratory conditions. Our results indicated that among the 7 heavy metals tested only Cu and Hg significantly (P < 0.01) decreased Crambe seed germination in a dose-dependent manner at higher concentrations while certain Cr concentrations significantly increased the seed germination (P < 0.05). All the 7 heavy metals decreased significantly relative root length, shoot length and fresh seedling weight in a dose-dependent manner (P < 0.01). The heavy metals except Ni decreased relative root length first, then shoot length or fresh seedling weight, and finally seed germination. Ni seemed to influence the relative fresh seedling weight first, then shoot length, root length and finally seed germination at lower concentrations, but the decrease in relative root length became faster when the Ni concentrations were increased. Our results indicated that Crambe is tolerant or moderately tolerant to the heavy metals tested except Ni and can be improved for phytoremediation of soils contaminated by heavy metals.

Information Collection System of Crop Growth Environment Based on the Internet of Things

Based on the technology of Internet of things, for the issues of large amount data acquisition and difficult real time transport in the data acquisition of crop growth environment, this paper designs one information collection system for crop growth environment. Utilizing the range free location mechanism which defines the node position and GEAR routing mechanism give solutions to the problems of node location, routing protocol applications and so on. This system can realize accurate and automatic real time collection, aggregation and transmission of crop growth environment information, and can achieve the automation of agricultural production, to the maximum extent.

“双师双能型”青年教师培养路径浅析

随着新兴产业的不断发展,加快培养应用技术性人才,促进地方普通高校向应用型大学转型已经是大势所趋。如何建立一支结构完备,具有本校特色的“双师双能型”队伍是每一个应用型本科院校和正在转型的高校所面临的问题。

Pressure-mediated contact quality improvement between monolayer MoS_2 and graphite

Two-dimensional(2D) materials and their heterostructures have attracted a lot of attention due to their unique electronic and optical properties. MoS_2 as the most typical 2D semiconductors has great application potential in thin film transistors, photodetector, hydrogen evolution reaction, memory device, etc. However, the performance of MoS_2 devices is limited by the contact resistance and the improvement of its contact quality is important. In this work, we report the experimental investigation of pressure-enhanced contact quality between monolayer MoS_2 and graphite by conductive atom force microscope(C-AFM). It was found that at high pressure, the contact quality between graphite and MoS_2 is significantly improved. This pressure-mediated contact quality improvement between MoS_2 and graphite comes from the enhanced charge transfer between MoS_2 and graphite when MoS_2 is stretched. Our results provide a new way to enhance the contact quality between MoS_2 and graphite for further applications.

Direct visualization of structural defects in 2D semiconductors

Direct visualization of the structural defects in two-dimensional(2D)semiconductors at a large scale plays a significant role in understanding their electrical/optical/magnetic properties,but is challenging.Although traditional atomic resolution imaging techniques,such as transmission electron microscopy and scanning tunneling microscopy,can directly image the structural defects,they provide only local-scale information and require complex setups.Here,we develop a simple,non-invasive wet etching method to directly visualize the structural defects in 2D semiconductors at a large scale,including both point defects and grain boundaries.Utilizing this method,we extract successfully the defects density in several different types of monolayer molybdenum disulfide samples,providing key insights into the device functions.Furthermore,the etching method we developed is anisotropic and tunable,opening up opportunities to obtain exotic edge states on demand.

Precisely controlling the twist angle of epitaxial MoS_(2)/graphene heterostructure by AFM tip manipulation

Two-dimensional(2D)moirématerials have attracted a lot of attention and opened a new research frontier of twistronics due to their novel physical properties.Although great progress has been achieved,the inability to precisely and reproducibly manipulate the twist angle hinders the further development of twistronics.Here,we demonstrated an atomic force microscope(AFM)tip manipulation method to control the interlayer twist angle of epitaxial MoS_(2)/graphene heterostructure with an ultra-high accuracy better than 0.1°.Furthermore,conductive AFM and spectroscopic characterizations were conducted to show the effects of the twist angle on moirépattern wavelength,phonons and excitons.Our work provides a technique to precisely control the twist angle of 2D moirématerials,enabling the possibility to establish the phase diagrams of moiréphysics with twist angle.

Observation of quadratic magnetoresistance in twisted double bilayer graphene

Magnetoresistance(MR) provides rich information about Fermi surface, carrier scatterings, and exotic phases for a given electronic system. Here, we report a study of the magnetoresistance for the metallic states in twisted double bilayer graphene(TDBG). We observe quadratic magnetoresistance in both Moiré valence band(VB) and Moiré conduction band(CB). The scaling analysis shows validity of Kohler's rule in the Moiré valence band. On the other hand, the quadratic magnetoresistance appears near the halo structure in the Moiré conduction band, and it violates Kohler's rule, demonstrating the MR scaling related to band structure in TDBG. We also propose an alternative scaling near the halo structure. Further analysis implies that the observed quadratic magnetoresistance and alternative scaling in conduction band are related to the halo boundary. Our results may inspire investigation on MR in twisted 2D materials and provide new knowledge for MR study in condensed matter physics.

Electronic synapses based on ultrathin quasi-two-dimensional gallium oxide memristor

Synapse emulation is very important for realizing neuromorphic computing, which could overcome the energy and throughput limitations of today's computing architectures. Memristors have been extensively studied for using in nonvolatile memory storage and neuromorphic computing. In this paper, we report the fabrication of vertical sandwiched memristor device using ultrathin quasi-two-dimensional gallium oxide produced by squeegee method. The as-fabricated two-terminal memristor device exhibited the essential functions of biological synapses, such as depression and potentiation of synaptic weight, transition from short time memory to long time memory, spike-timing-dependent plasticity, and spike-rate-dependent plasticity. The synaptic weight of the memristor could be tuned by the applied voltage pulse, number,width, and frequency. We believe that the injection of the top Ag cations should play a significant role for the memristor phenomenon. The ultrathin of medium layer represents an advance to integration in vertical direction for future applications and our results provide an alternative way to fabricate synaptic devices.

Low-Frequency Reciprocating Fretting Wear Testing System Design and Experiment Research

The fretting wear is resulted from different or same sample's surfaces by the small variationand leads to mechanism failures. The main factors consist of the variation of normal load and oscillation frequencies,among which surface topography of different materials are the main factors to the problems of the fretting wear.Therefore,a novel low-frequency reciprocating fretting wear test system is designed upon the principle of Friction coefficient measurement. Four metal and non-metallic samples are measured under various normal load and oscillation frequencies to obtain the instantaneous friction coefficient in the repeat experiments. In fact,the experimental results show that Co F curves of different samples with the increase of the normal load are the similar exponential decay or parabolic shapes,which are consistent with the literatures to verify the rational design and reliable-operation of the system under the conditions of different frequencies.

Numerical investigation on seismic performance of a shallow buried underground structure with isolation devices

A design procedure for improving the seismic performance of unequal-span underground structures by installing isolation devices at the top end of columns is proposed based on the seismic failure mode of frame-type underground structures and the design concept of critical support columns.A two-dimensional finite element model(FEM)for a soil-underground structure with an unequal-span interaction system was established to shed light on the effects of a complex subway station with elastic sliding bearings(ESB)and lead rubber bearings(LRB)on seismic mitigation.It was found that the stiffness and internal force distribution of the underground structure changed remarkably with the installation of isolation devices at the top end of the columns.The constraints of the beam-column joints were significantly weakened,resulting in a decrease in the overall lateral stiffness and an increase in the structural lateral displacement.The introduction of the isolation device effectively reduces the internal force and seismic damage of the frame column;however,the tensile damage to the isolation structure,such as the roof,bottom plate,and sidewall,significantly increased compared to those of the non-isolation structure.Although the relative slip of the ESB remains within a controllable range under strong earthquake excitation as well as frame columns with stable vertical support and self-restoration functions,the LRB shows a better performance during seismic failure and better lateral displacement response of the unequal-span underground structure.The analysis results provide new ideas and references for promoting the application of seismic isolation technology in underground structures.

Theoretical model of azimuthal combustion instability subject to non-trivial boundary conditions

The problem of evaluating the sensitivity of non-trivial boundary conditions to the onset of azimuthal combustion instability is a longstanding challenge in the development process of mod-ern gas turbines.The difficulty lies in how to describe three-dimensional in-and outlet boundary conditions in an artificial computational domain.To date,the existing analytical models have still failed to quantitatively explain why the features of the azimuthal combustion instability of a com-bustor in laboratory environment are quite different from that in a real gas turbine,making the sta-bility control devices developed in laboratory generally lose the effectiveness in practical applications.To overcome this limitation,we provide a novel theoretical framework to directly include the effect of non-trivial boundary conditions on the azimuthal combustion instability.A key step is to take the non-trivial boundary conditions as equivalent distributed sources so as to uniformly describe the physical characteristics of the inner surface in an annular enclosure along with different in-and outlet configurations.Meanwhile,a dispersion relation equation is established by the application of three-dimensional Green's function approach and generalized impedance con-cept.Results show that the effects of the generalized modal reflection coefficients on azimuthal unstable modes are extremely prominent,and even prompt the transition from stable to unstable mode,thus reasonably explaining why the thermoacoustic instability phenomena in a real gas tur-bine are difficult to observe in an isolated combustion chamber.Overall,this work provides an effective tool for analysis of the azimuthal combustion instability including various complicated boundary conditions.

模块化局域元素供应技术批量制备12英寸过渡金属硫族化合物

二维过渡金属二硫族化合物(TMDs)因其原子级厚度、高载流子迁移率和超快电荷转移等优点而被认为是下一代半导体器件的核心材料.与传统半导体工业类似,晶圆级TMDs材料的批量生产是其集成电路发展的先决条件.然而,由于生长过程中需要严格满足多种前驱体的有效传输,TMDs晶圆的制备能力通常局限在每批次单片和小片(主要尺寸为2~4英寸).本研究开发了一种用于批量生产晶圆级TMDs的模块化生长策略,可以制造从2英寸(每批15片)到突破性的12英寸(每批3片)的TMDs晶圆.其中,每个模块包括供应TMDs晶圆生长的自充足的局域前驱体供应单元,通过将多个模块堆叠组装形成阵列可实现批量化制备.利用包括光谱学、电子显微镜和电学测量在内的多种表征技术,可以证明制得的单层薄膜具有高结晶度和大面积均匀性.此外,该模块化单元可以将制备的晶圆级MoS_(2)取代转换为多种结构,例如,Janus型MoSSe结构,MoS_(2(1-x))Se_(2x)合金以及MoS_(2)-MoSe_(2)平面异质结等,充分体现了本制备策略的可扩展性.本研究展现了高质量和高产量的晶圆批量生产能力,有望推动二维半导体从实验室规模到工业化规模的无缝过渡,实现与传统硅基技术的互补.

Regulating electronic structure of porous nickel nitride nanosheet arrays by cerium doping for energy-saving hydrogen production

Water electrolysis for energy-efficient H_(2)production coupled with hydrazine oxidation reaction(HzOR)is prevailing,while the sluggish electrocatalysts are strongly hindering its scalable application.Herein,we schemed a novel porous Ce-doped Ni3N nanosheet arrays grown on nickel foam(Ce-Ni3N/NF)as a remarkable bifunctional catalyst for both hydrogen evolution reaction and HzOR.Significantly,the overall hydrazine splitting system can achieve low cell voltages of 0.156 and 0.671 V at 10 and 400 mA·cm^(−2),and the system is remarkably stable to operate over 100 h continuous test at the high-current-density of 400 mA·cm^(−2).Various characterizations prove that the porous nanosheet arrays expose more active sites,and more excellent diffusion kinetics and lower charge-transfer resistance,therefore boosting catalytic performance.Furthermore,density functional theory calculation reveals that the incorporation of Ce can effectively optimize the free energy of hydrogen adsorption and promote intrinsic catalytic activity of Ni_(3)N.