On the low cycle fatigue behaviour of an Al-Zn-Mg-Cu alloy processed via non-isothermal ageing

The low cycle fatigue behaviour of an Al-Zn-Mg-Cu alloy processed via non-isothermal ageing(NIA)was examined at different strain amplitudes.We showed that NIA improved the low cycle fatigue life(more than 7000 cycles)by optimising the precipitate configuration within 5.5 h while maintaining comparable mechanical properties(570 MPa for tensile strength)and conductivity(nearly 39%IACS)to conventional isothermal ageing,simultaneously.Experimental observation combined with molecular dynamic simula-tion revealed that precipitation configuration manipulated by NIA had a crucial effect on fatigue resis-tance.A great number of repeatedly sheared and locally destructed GP zones enhanced co-planar slip and slip localisation in the under-aged alloy during the early stage of NIA,responsible for the dramatic displacement steps on the surface and resultant poor fatigue performance.As the NIA further proceeded,moderately coarsened precipitates with an average dimension of 6.0 nm and elevated number density ef-fectively impeded the dislocation movement and weaken the slip localisation to a great extent,improving the fatigue performance within a few hours.

Low-temperature and flexible strategy to in-situ fabricate ZrSiO_(4)-based ceramic composites via doping and tuning solid-state reaction

Synthetic zircon(ZrSiO_(4))ceramics are typically fabricated at elevated temperatures(over 1500℃),which would lead to high manufacturing cost.Meanwhile,reports about preparing ZrSiO_(4)-based ceramic composites via controlling the solid-state reaction between zirconia(ZrO_(2))and silica(SiO_(2))are limited.In this work,we proposed a low-temperature strategy to flexibly design and fabricate ZrSiO_(4)-based ceramic composites via doping and tuning the solid-state reaction.Two ceramic composites and ZrSiO_(4) ceramics were in-situ prepared by reactive fast hot pressing(FHP)at approximately 1250℃ based on the proposed strategy,i.e.,a ZrSiO_(4)-SiO_(2) dual-phase composite with bicontinuous interpenetrating and hierarchical microstructures,a ZrSiO_(4)-ZrO_(2) dual-phase composite with a microstructure of ZrO_(2) submicron-and nano-particles embedded in a micron ZrSiO_(4) matrix,and ZrSiO_(4) ceramics with a small amount of residual ZrO_(2) nanoparticles.The results showed that the phase compositions,microstructure configurations,mechanical properties,and wear resistance of the materials can be flexibly regulated by the proposed strategy.Hence,ZrSiO_(4)-based ceramic composites with different properties can be easily fabricated based on different application scenarios.These findings would offer useful guidance for researchers to flexibly fabricate ZrSiO_(4)-based ceramic composites at low temperatures and tailor their microstructures and properties through doping and tuning the solid-state reaction.

非绝热和乐量子计算研究进展

量子计算的实际应用依赖于高保真度的量子门,而获得高保真度量子门所面临的两个主要挑战是克服系统的控制误差和环境噪声.几何相仅依赖于系统的演化路径而与演化速度等细节无关,因此基于几何相设计的量子门具有对控制误差的鲁棒性.特别是,基于非绝热非阿贝尔几何相设计的非绝热和乐(holonomic)门具有完全的几何性质并且不受绝热条件的限制,受到了人们的广泛关注.自2012年首次提出以来,非绝热和乐量子计算取得了很大的进展:人们逐步改进了非绝热和乐量子计算的设计理论,使得非绝热和乐门的设计不断优化;发展了抗退相干的非绝热和乐量子计算,使得量子门既能抵抗控制误差又能抵抗退相干;构建了基于各种具体物理系统的非绝热和乐量子计算方案,并且在实验上成功演示了非绝热和乐门.本文回顾了非绝热和乐量子计算的主要理论进展,并简要介绍了物理实现和实验工作.

基于增大碳层间距和增强电容行为的协同效应提升碳材料储钾性能

本文通过简易高效的碳化工艺,构建了一种具有大碳层间距(0.407 nm)、高比表面积(681.15 m2 g-1)以及丰富电化学活性位点的N/S共掺杂碳材料(NSC)用作钾离子电池负极材料.研究结果发现,基于增大碳层间距和增强电容行为的协同效应, NSC表现出了较高的储钾容量(在0.1和0.5 A g-1电流密度下,可逆容量分别为302.8和206.7 mA h g-1)和优异的长循环稳定性(在2 A g-1电流密度下循环600圈之后,可逆容量能够保持在105.2 mA h g-1).同时,通过与单一硫掺杂碳材料(SC)和商用硬碳(HC)材料的储钾性能对比,作者发现单一硫原子掺杂尽管能够最大限度地增大碳层间距、提升储钾容量,但也会加剧碳材料结构的不稳定性,导致较差的循环性能和倍率性能.因此,作者强调了氮原子的引入不仅能够增强碳材料的导电性和电容吸附行为,而且有助于保持碳材料微观结构的稳定性.

Dispersion-limited versus power-limited terahertz communication links using solid core subwavelength dielectric fibers

Terahertz(THz)band(0.1–10 THz)is the next frontier for ultra-high-speed communication systems.Currently,most of communications research in this spectral range is focused on wireless systems,while waveguide/fiber-based links have been less explored.Although free space communications have several advantages such as convenience in mobility for the end user,as well as easier multi-device interconnectivity in simple environments,fiber-based communications provide superior performance in certain short-range communication applications such as multi-device connectivity in complex geometrical environments(ex.,intra-vehicle connectivity)and secure communications with low probability of eavesdropping,as well as secure signal delivery to hard-to-reach or highly protected environments.In this work,we present an in-depth experimental and numerical study of the short-range THz communications links that use subwavelength dielectric fibers for information transmission and define the main challenges and trade-offs in the link implementation.Particularly,we use air or foam-cladded polypropylene-core subwavelength dielectric THz fibers of various diameters(0.57–1.75 mm)to study link performance as a function of the link length of up to∼10 m,and data bit rates of up to 6 Gbps at the carrier frequency of 128 GHz(2.34 mm wavelength).We find that depending on the fiber diameter,the quality of the transmitted signal is mostly limited either by the modal propagation loss or by the fiber velocity dispersion(GVD).An error-free transmission over 10 m is achieved for the bit rate of 4 Gbps using the fiber of smaller 0.57 mm diameter.Furthermore,since the fields of subwavelength fibers are weakly confined and extend deep into the air cladding,we study the modal field extent outside of the fiber core,as well as fiber bending loss.Finally,the power budget of the rod-in-air subwavelength THz fiber-based links is compared to that of free space communication links,and we demonstrate that fiber links offer an excellent solution for various short-range applications.

A bridge between acoustic metamaterials and quantum computation

Acoustic waves are one necessary ingredient for many useful tasks.To complete these tasks,acoustic waves need to be transmitted in certain ways,and sometimes,people would like them to be transmitted in ways that are unnatural through passive devices.The latter seemingly unrealistic wish became true with the advent of acoustic metamaterials,which sunrises people very much.Acoustic metamaterials are artificial materials made of well-designed microstructures[1].

Nonadiabatic holonomic quantum computation based on nitrogen-vacancy centers

Because of quantum superposition,quantum computation can solve many problems,such as factoring large integers[1]and searching unsorted databases[2,3],much faster than classical computation.To realize practical quantum computation and then gain the desired advantages,a universal set of quantum gates with sufficiently high fidelities are needed.However,various inevitable errors reduce the gate fidelities and finally collapse the computation results,which makes the realizations of quantum computation very challenging.To