新型异面结构高功率Vivaldi天线

Vivaldi天线属于非频变天线,充分利用该天线超宽的工作频带、辐射定向性良好、输入阻抗稳定、效率高、结构简单、造价低廉、平面易集成的特点进行新结构高功率天线的设计。高功率器件必须解决的难点是部件之间的放电问题。将Vivaldi天线的两个辐射面分置于介质衬底的两侧,得到一种具有耐高压特性好、相对对带宽达196%的新型异面结构高功率天线。为解决异面结构的馈电问题,将天线交错设计,采用平行板波导过波结构馈电,得到了相对带宽达180%的带宽。

空间异面弯扭结构密集胎架支撑施工与卸载技术

研究的内容为某城市当代艺术馆与城市规划展览馆项目钢结构密集胎架支撑施工与卸载技术。本项目为空间异面弯扭结构,弯扭钢结构截面大,外表皮钢结构作为屋盖的一部分覆盖、包裹整栋建筑物,安装难度极大。主要采用密集胎架支撑,地面拼装,单元整体吊装的方法安装技术、分区域分级卸载技术、全站仪多点实时监测技术等。通过本文的研究以及现场的实时反馈结果将形成空间异面弯扭结构的施工及卸载关键技术,为后续类似空间异面结构的施工提供宝贵的施工经验。同时以实际工程再次验证了有限元理论分析的重要性和精确性。

基于JRC的结构面双面剪切强度经验公式

为揭示岩体结构面单、双面剪切强度差异,更好评估层状岩体的稳定性,选择4条Barton标准剖面线建立结构面模型,制作含单、双结构面的类岩试样进行剪切试验。基于试验结果,分析3种法向应力(σ_(n))下单、双结构面的峰值剪切强度(τ_(p))的差异及其原因。基于颗粒流模拟结果,推导出同JRC双结构面的峰值剪切强度经验公式,引入组合节理粗糙系数(JRC_(c))表征异JRC双结构面的粗糙度,构造JRC_(c)与低、高粗糙度系数(JRC_(xx),JRC_(yy))的相关关系,建立了综合考虑JRC_(xx),JRC_(yy)对异JRC双结构面峰值剪切强度影响的经验公式,然后分析同JRC双结构面与异JRC双结构面的τ_(p)随混合节理粗糙系数变化的规律,最终建立了估算任意JRC组合双结构面峰值剪切强度的经验公式。研究表明:在τ_(p)-JRC曲线的增长趋势随σ_(n)增大而增大的阶段,σ_(n)一定时,双结构面的τ_(p)随上、下结构面的JRC之和增大而增大;对于JRC之和较小的异JRC双结构面,其τ_(p)由JRC较低的结构面控制,但这种控制作用随JRC之和增大而减弱,逐渐转换为由JRC较高的结构面控制。

超快响应GaN半导体光导开关的研制

半导体光导开关(PCSS)利用半导体材料的高耐压、快速响应与高迁移率等特性,可产生大功率超窄脉冲信号。利用半绝缘GaN材料制备了异面斜对电极PCSS,通过去除芯片侧边金属化合物来减小暗态电阻,提升了PCSS暗态耐压并降低暗态漏电,采用绝缘导热封装提升器件的耐压与可靠性,研制了快拆式测试电路与夹具,实现储能、触发与低寄生同轴输出功能,提升了高频测试准确度与高频响应能力。搭建了高压宽带PCSS测试系统,测量开关线性工作特性,在5 kV偏置电压、触发激光脉冲波长为532 nm、能量为5 mJ下,GaN PCSS在50Ω负载上输出超快脉冲信号电压峰峰值大于2 kV,脉冲信号上升沿小于88 ps。

Al/GaSb Contact with Slow Positron Beam

Annealing study of the Al/GaSb system was performed by using a slow positron beam and the measurement of X-ray diffraction. The S parameter against positron energy data were fitted by a three layer model （Al/interface/GaSb）. It was found there was a ～5 nm interfacial at the region between the Al layer and bulk in the sample of as-deposited. After the 400 ℃ annealing, this interfacial region extends to over 40 nm and S parameter dramatically drops. This is possibly due to a new phase formation induced by the atoms＇inter-diffusion at the interface. The annealing out of the open volume defects in the Al layer was revealed by the decrease of the S parameter and the increase of the effective diffusion length of the Al layer. Annealing behaviors of Sb and Lb of the GaSb bulk showed the annealing out of positron traps at 250 ℃. However,further annealing at 400 ℃ induces formation of positron traps, which are possibly another kind of VGarelated defect and the positron shallow trap GaSb anti-site. The results of the X-ray diffraction experiment verified the conclusion of obtained by using positron technology.

Yielding and fracture behaviors of coarse-grain/ultrafine-grain heterogeneous-structured copper with transitional interface

Heterogeneous-structured Cu samples composed of coarse-grained(CG) and ultrafine-grained(UFG) domains with a transitional interface were fabricated by friction stir processing, in order to investigate the effect of interface constraint on the yielding and fracture behaviors. Tensile test revealed that the synergetic strengthening induced by elastic/plastic interaction between incompatible domains increases with increasing the area of constraint interface. The strain distribution near interface and the fracture morphology were characterized using digital image correlation technique and scanning electron microscopy, respectively. Fracture dimples preferentially formed at the interface, possibly due to extremely high triaxial stress and strain accumulation near the interface. Surprisingly, the CG domain was fractured by pure shear instead of the expected voids growth caused by tensile stress.

Enhancing hydrogen electrocatalytic oxidation on Ni_(3)N/MoO_(2)in-plane heterostructures in alkaline solution

Nickel(Ni)-based materials act as one of the most promising candidates as platinum-group-metal-free(PGM-free)electrocatalysts for hydrogen oxidation reaction(HOR)in alkaline solution.Nevertheless,the electrocatalytic activity of pure Ni is significantly limited due to the sluggish kinetics under alkaline condition.To accelerate the kinetics,constructing heterostructures and nitride structures have been developed as two representative strategies.Here,we combined the two methods and presented a facile synthesis of the sheet-like Ni_(3)N/MoO_(2)in-plane heterostructures for enhanced HOR in alkaline electrolytes.Relative to Ni or Ni_(3)N,the Ni_(3)N/MoO_(2)in-plane heterostructures exhibited a significantly increased mass activity by 8.6-fold or 4.4-fold,respectively.Mechanistic studies revealed that the enhanced activity of Ni_(3)N/MoO_(2)could be attributed to the weakened hydrogen adsorption and strengthened hydroxyl adsorption.This work provides a facile approach to design high-efficiency catalysts for hydrogen-oxidation catalysis and beyond.

Surface assembly of cobalt species for simultaneous acceleration of interfacial charge separation and catalytic reactions on Cd_(0.9)Zn_(0.1)S photocatalyst

Although photocatalytic water splitting has excellent potential for converting solar energy into chemical energy,the challenging charge separation process and sluggish surface catalytic reactions significantly limit progress in solar energy conversion using semiconductor photocatalysts.Herein,we demonstrate a feasible strategy involving the surface assembly of cobalt oxide species(CoO_(x))on a visible-light-responsive Cd_(0.9)Zn_(0.1)S(CZS)photocatalyst to fabricate a hierarchical CZS@CoO_(x) heterostructure.The unique hierarchical structure effectively accelerates the directional transfer of photogenerated charges,reducing charge recombination through the smooth interfacial heterojunction between CZS and CoO_(x),as evidenced by photoluminescence(PL)spectroscopy and various electrochemical characterizations.The surface cobalt species on the CZS material also act as efficient cocatalysts for photocatalytic hydrogen production,with activity even higher than that of noble metals.The well-defined CZS@CoO_(x) heterostructure not only enhances the interfacial separation of photoinduced charges,but also improves surface catalytic reactions.This leads to superior photocatalytic performances,with an apparent quantum efficiency of 20%at 420 nm for visible-light-driven hydrogen generation,which is one of the highest quantum efficiencies measured among noble-metal-free photocatalysts.Our work presents a potential pathway for controlling complex charge separation and catalytic reaction processes in photocatalysis,guiding the practical development of artificial photocatalysts for successful transformation of solar to chemical energy.

Analysis of structural hot-spot stress in orthotropic plates

On the basis of the actual steel deck structure of Taizhou Bridge, this paper carries out hot-spot stress analysis on some key spots by using the finite element model which simulates local structure of orthotropic steel bridge decks. A finite element model is established for local structure of orthotropic steel bridge decks, and in the analysis of linear elasticity of the structure, face load is employed to simulate the loads from vehicle wheels. Analysis results show that main stresses are relatively heavy at the joints between diaphragm plates, top plates and U-shaped ribs and the joints between diaphragm plates and U-shaped ribs. These joints shall be regarded as key points for hot-spot stress analysis. Different mesh densities are adopted in the finite element model and the main stresses at different hot spots are contrasted and linear extrapolation is carried out using extrapolation formulae. Results show that different mesh densities have different influences on the hot-spot stresses at the welded seams of U-shaped ribs. These influences shall be considered in calculation and analysis.

Effects of Non-specific and Specific Solvation on Adsorption of BPTI on Au Surface： Insight from Molecular Dynamics Simulation

Proteins adsorption at solid surfaces are of paramount important for many natural processes. However, the role of specific water in influencing the adsorption process has not been well understood. We used molecular dynamics simulation to study the adsorption of BPTI on Au surface in three water environments （dielectric constant model, partial and full solvation models）. The result shows that a fast and strong adsorption can occur in the dielectric environment, which leads to significant structure changes, as confirmed by great deviation from the crystal structure, largely spreading along the Au surface, rapid lose in all secondary structures and the great number of atoms in contact with the surface. Compared to the dielectric model, slower adsorption and fewer changes in the calculated properties above are observed in the partial solvation system since the specific water layer weakens the adsorption effects. However, in the partial solvation system, the adsorption of polar Au surface causes a significant decrease in the specific hydration around the protein, which still results in large structure changes similar to the dielectric system, but with much less adsorption extent. Enough water molecules in the full solvation system could allow the protein to rotate, and to large extent preserve the protein native structure, thus leading to the slowest and weakest adsorption. On the whole, the effects of non-specific and specific solvation on the protein structure and adsorption dynamics are significantly different, highlighting the importance of the specific water molecule in the protein adsorption.

The development of MOFs-based nanomaterials in heterogeneous organocatalysis

Metal-organic framework(MOF) is a class of inorganic-organic hybrid material assembled periodically with metal ions and organic ligands. MOFs have always been the focuses in a variety of frontier fields owing to the advantageous properties, such as large BET surface areas, tunable porosity and easyfunctionalized surface structure. Among the various application areas, catalysis is one of the earliest application fields of MOFs-based materials and is one of the fastest-growing topics. In this review, the main roles of MOFs in heterogeneous organocatalysis have been systematically summarized, including used as support materials(or hosts), independent catalysts, and sacrificial templates. Moreover, the application prospects of MOFs in photocatalysis and electrocatalysis frontiers were also mentioned.Finally, the key issues that should be conquered in future were briefly sketched in the final parts of each item. We hope our perspectives could be beneficial for the readers to better understand these topics and issues, and could also provide a direction for the future exploration of some novel types of MOFs-based nanocatalysts with stable structures and functions for heterogeneous catalysis.

Interface engineering of heterostructured electrocatalysts towards efficient alkaline hydrogen electrocatalysis

Boosting the alkaline hydrogen evolution and oxidation reaction(HER/HOR)kinetics is vital to practicing the renewable hydrogen cycle in alkaline media.Recently,intensive research has demonstrated that interface engineering is of critical significance for improving the performance of heterostructured electrocatalysts particularly toward the electrochemical reactions involving multiple reaction intermediates like alkaline hydrogen electrocatalysis,and the research advances also bring substantial non-trivial fundamental insights accordingly.Herein,we review the current status of interface engineering with respect to developing efficient heterostructured electrocatalysts for alkaline HER and HOR.Two major subjects—how interface engineering promotes the reaction kinetics and what fundamental insights interface engineering has brought into alkaline HER and HOR—are discussed.Specifically,heterostructured electrocatalysts with abundant interfaces have shown substantially accelerated alkaline hydrogen electrocatalysis kinetics owing to the synergistic effect from different components,which could balance the adsorption/desorption behaviors of the intermediates at the interfaces.Meanwhile,interface engineering can effectively tune the electronic structures of the active sites via electronic interaction,interfacial bonding,and lattice strain,which would appropriately optimize the binding energy of targeted intermediates like hydrogen.Furthermore,the confinement effect is critical for delivering high durability by sustaining high density of active sites.At last,our own perspectives on the challenges and opportunities toward developing efficient heterostructured electrocatalysts for alkaline hydrogen electrocatalysis are provided.

Interface of transition metal oxides at the atomic scale

Remarkable phenomena arise at well-defined heterostructures, composed of transition metal oxides, which is absent in the bulk counterpart, providing us a paradigm for exploring the various electron correlation effects. The functional properties of such heterostructures have attracted much attention in the microelectronic and renewable energy fields. Exotic and unexpected states of matter could arise from the reconstruction and coupling among lattice, charge, orbital and spin at the interfaces. Aberration-corrected scanning transmission electron microscopy （STEM） is a powerful tool to visualize the lattice structure and electronic structure at the atomic scale. In the present study some novel phenomena of oxide heterostructures at the atomic scale are summarized and pointed out from the perspective of electron microscopy.

Temperature-controlled synthesis of heterostructured Ru-Ru_(2)P nanoparticles embedded in carbon nanofibers for highly efficient hydrogen production

Developing highly efficient,cost-effective,and stable electrocatalysts for hydrogen evolution reaction(HER)is of considerable importance but remains challenging.Herein,we report the fabrication of a robust Ru-based electrocatalyst,which comprises heterostructured Ru-Ru_(2)P nanoparticles that are embedded in the N,P-codoped carbon nanofibers(CNFs),through a synthetic strategy involving electrospinning and temperature-controlled pyrolysis treatment.The as-prepared Ru-Ru_(2)P catalyst(Ru-Ru_(2)P@CNFs)shows excellent HER catalytic activities with low overpotentials of 11 and 14 mV in acidic and alkaline media,respectively,to achieve a current density of 10 mA cm^(−2),which are superior to the individual components of pure Ru and Ru_(2)P catalysts.Density functional theory calculations demonstrate the existence of electronic coupling effect between Ru and Ru_(2)P at the heterointerfaces,leading to a well-modulated electronic structure with optimized hydrogen adsorption strength and enhanced electrical conductivity for efficient HER electrocatalysis.In addition,the overall synthetic strategy can be generalized for the synthesis of a series of transitional metal phosphide-based nanofibers,thereby holding a remarkable capacity for various potential applications.

Interface energetics and engineering of organic heterostructures in organic photovoltaic cells

The reliable information about interface energetics of organic materials, especially the energy level alignment at organic heterostructures is of pronounced importance for unraveling the photon harvesting and charge separation process in organic photovoltaic(OPV) cells. This article provides an overview of interface energetics at typical planar and mixed donor-acceptor heterostructures, perovskite/organic hybrid interfaces, and their contact interfaces with charge collection layers. The substrate effect on energy level offsets at organic heterostructures and the processes that control and limit the OPV operation are presented. Recent efforts on interface engineering with electrical doping are also discussed.

High interfacial-energy heterostructure facilitates large-sized lithium nucleation and rapid Li+desolvation process

High interfacial energy Li^(0)-electrolyte interface contributes to larger Li^(0) nucleation embryos and a more stable interface,so the interfacial energy is essential for highly reversible Li^(0) deposition/stripping.Herein,a high interfacial-energy artificial solid electrolyte interphase(SEI)with rich LiF embedded in lithiated poly-2-acrylamido-2-methylpropane sulfonic acid(PAMPS-Li)network is designed to realize favorable Li^(0) nucleation and rapid desolvation of Li+simultaneously.The Li-F bonds in LiF(001)exhibit stronger ion-dipole interactions with Li atoms,offering higher interfacial energies.When the growth surface energy and total interfacial energy of Li^(0) are balanced,the high interfacial energy SEI with abundant LiF can promote the formation of larger Li^(0) nucleation embryos.In addition,the PAMPS-Li with immobilized anions presents weaker interaction with Li^(0) and possesses higher polymer-Li interfacial energy,and its amide and sulfonic acid groups exhibit higher binding energies with Li^(+).Therefore,PAMPS-Li can easily promote the Li+to escape from the solvent sheath and weaken the desolvation energy barrier.The highly reversible Li^(0) deposition behavior with restricted side reactions is achieved based on the synergistic modification of high interfacial energy SEI with heterostructure.Most importantly,lifespan of multi-layered Li^(0) pouch cell(330 Wh kg-1)with a low N/P ratio(1.67)is over 100 cycles,verifying its potential practical application.

Phase-field crystal modeling of shape transition of strained islands in heteroepitaxy

The phase-field crystal(PFC) model is employed to study the shape transition of strained islands in heteroepitaxy on vicinal substrates.The influences of both substrate vicinal angles β and the lattice mismatch ξ are discussed.The increase of substrate vicinal angles is found to be capable of significantly changing the surface nanostructures of epitaxial films.The surface morphology of films undergoes a series of transitions that include Stranski-Krastonov(SK) islands,the couple growth of islands and the step flow as well as the formation of step bunching.In addition,the larger ξ indicates an increased strained island density after coarsening,and results in the incoherent growth of strained islands with the creation of misfit dislocations.Coarsening,coalescence and faceting of strained islands are also observed.Some facets in the shape transition of strained islands are found to be stable and can be determined by β and crystal symmetry of the film.

Contracted interlayer distance in graphene/sapphire heterostructure

Direct growth of graphene on insulators is expected to yield significant improvements in performance of graphene-based electronic and spintronic devices. In this study, we successfully reveal the atomic arrangement and electronic properties of a coherent heterostructure of single-layer graphene and α-Al2O3（0001）. The analysis of the atomic arrangement of single-layer graphene on α-Al2O3（0001） revealed an apparentcontradiction. The in-plane analysis shows that single-layer graphene grows not in a single-crystalline epitaxial manner, but rather in polycrystalline form, with two strongly pronounced preferred orientations. This suggests relatively weak interfacial interactions are operative. However, we demonstrate that unusually strong physical interactions between graphene and α-Al2O3（0001） exist, as evidenced by the small separation between the graphene and the α-Al2O3（0001） surface. The interfacial interaction is shown to be dominated by the electrostatic forces involved in the graphene n-system and the unsaturated electrons of the topmost O layer of α-Al2O3（0001）, rather than the van der Waals interactions. Such features causes graphene hole doping and enable the graphene to slide on the α-Al2O3（0001） surface with only a small energy barrier despite the strong interfacial interactions.