液态聚碳硅烷的结构及固化行为对其陶瓷化的影响

液态聚碳硅烷作为一种新型陶瓷先驱体,可通过先驱体浸渍裂解工艺(PIP)制备陶瓷基复合材料(CMC),也可通过包覆有机纤维来提高柔性绝热层的耐烧蚀性能。文中通过红外光谱和核磁共振表征了3种液态聚碳硅烷先驱体VHPCS,VHPCS-S和AHPCS的结构组成,在150℃前的固化反应主要通过C═C键以多种方式进行,与AHPCS相比,VHPCS和VHPCS-S中双键与硅氢键的摩尔比提高了约18.2%;采用非等温差示扫描量热分析(DSC)法研究了3种先驱体及其在交联剂过氧化二异丙苯体系时的固化反应动力学,发现固化反应温度和表观活化能均有所降低,先驱体可以在低温下实现快速交联反应;利用同步热分析和X射线衍射分析了先驱体的陶瓷化过程及裂解产物的结晶行为,VHPCS-S在1200℃时的陶瓷产率高于其余2种先驱体VHPCS与AHPCS。对于DCP/VHPCS-S交联体系,在150℃固化后陶瓷产率达到89.82%。此外,DCP的加入可以有效抑制β-SiC结晶。

Atmospheric Disturbance Characteristics in the Lower-middle Stratosphere Inferred from Observations by the Round-Trip Intelligent Sounding System(RTISS)in China

Through multi-order structure function analysis and singularity measurement,the Hurst index and intermittent parameter are obtained to quantitatively describe the characteristics of atmospheric disturbance based on the round-trip intelligent sounding system(RTISS)in the lower-middle stratosphere.According to the third-order structure function,small-scale gravity waves are classified into three states:stable,unstable,and accompanied by turbulence.The evolution of gravity waves is reflected by the variation of the third-order structure function over time,and the generation of turbulence is also observed.The atmospheric disturbance intensity parameter RT is defined in this paper and contains both wave disturbance(H_(1))and random intermittency(C_(1)).RT is considered to reflect the characteristics of atmospheric disturbance more reasonably than either of the above two alone.In addition,by obtaining the horizontal wavenumber spectrum from the flat-floating stage and the vertical wavenumber spectrum from the ascending and descending stages at the height range of18-24 km,we found that when the gravity wave activity is significantly enhanced in the horizontal direction,the amplitude of the vertical wavenumber spectrum below is significantly larger,which shows a significant impact of gravity wave activity on the atmospheric environment below.

Learning Dual-Domain Calibration and Distance-Driven Correlation Filter:A Probabilistic Perspective for UAV Tracking

Unmanned Aerial Vehicle(UAV)tracking has been possible because of the growth of intelligent information technology in smart cities,making it simple to gather data at any time by dynamically monitoring events,people,the environment,and other aspects in the city.The traditional filter creates a model to address the boundary effect and time filter degradation issues in UAV tracking operations.But these methods ignore the loss of data integrity terms since they are overly dependent on numerous explicit previous regularization terms.In light of the aforementioned issues,this work suggests a dual-domain Jensen-Shannon divergence correlation filter(DJSCF)model address the probability-based distance measuring issue in the event of filter degradation.The two-domain weighting matrix and JS divergence constraint are combined to lessen the impact of sample imbalance and distortion.Two new tracking models that are based on the perspectives of the actual probability filter distribution and observation probability filter distribution are proposed to translate the statistical distance in the online tracking model into response fitting.The model is roughly transformed into a linear equality constraint issue in the iterative solution,which is then solved by the alternate direction multiplier method(ADMM).The usefulness and superiority of the suggested strategy have been shown by a vast number of experimental findings.

A Deep Neural Collaborative Filtering Based Service Recommendation Method with Multi-Source Data for Smart Cloud-Edge Collaboration Applications

Service recommendation provides an effective solution to extract valuable information from the huge and ever-increasing volume of big data generated by the large cardinality of user devices.However,the distributed and rich multi-source big data resources raise challenges to the centralized cloud-based data storage and value mining approaches in terms of economic cost and effective service recommendation methods.In view of these challenges,we propose a deep neural collaborative filtering based service recommendation method with multi-source data(i.e.,NCF-MS)in this paper,which adopts the cloud-edge collaboration computing paradigm to build recommendation model.More specifically,the Stacked Denoising Auto Encoder(SDAE)module is adopted to extract user/service features from auxiliary user profiles and service attributes.The Multiple Layer Perceptron(MLP)module is adopted to integrate the auxiliary user/service features to train the recommendation model.Finally,we evaluate the effectiveness of the NCF-MS method on three public datasets.The experimental results show that our proposed method achieves better performance than existing methods.

Porous carbon microspheres assembled by defective nitrogen and sulfur co-doped nanosheets as anode materials for lithium-/sodium-ion batteries

Carbon-based anode materials are widely used in various battery energy storage systems due to their low cost,wide source,high conductivity and easy morphology control.However,current commercially available anode materials as active materials for lithium-/sodium-ion batteries generally suffer from large volume changes and poor rate performance.In response,we synthesized defect-rich N,S co-doped two dimensional(2D)nanosheet-assembled porous carbon microspheres(N,S-PCS)via simple hydrothermal,carbonization and etching process based on the principle of Schiff base reaction.The N,S-PCS structure is thus constructed by removing Fe7S8 nanoparticles from the carbon skeleton to form porous microspheres with N,S doping.Therefore,the micromorphology characteristic,pore structure and electroconductivity of carbon materials are effectively optimized via heteroatom doping and surface engineering.As expected,the prepared N,S-PCS electrodes exhibit excellent electrochemical performance in both lithium-ion and sodium-ion batteries.For lithium-ion batteries,it achieves reversible capacities of 1045 and 237 mAh g^(-1) at 0.1 and 20 A g^(-1),respectively.For sodium-ion batteries,it shows good cycling stability with a capacity of 157 mAh g^(-1) after 500 cycles at 1 A g^(-1).Experimental and theoretical calculation results confirm that the N,S co-doping strategies help to improve the structural stability,shorten the ion diffusion paths,and promote the reaction kinetics,thus achieving excellent electrochemical performance.This work is instructive for the practical application of nonmetal doping functionalized porous carbon structures for metal-ion batteries.

具有三维传输通道的化学键合Ti_(3)C_(2) MXene@C复合材料促进混合电容器中的锂离子存储

锂离子电容器(LICs)是一种很有前途的储能装置,因为它们同时具有锂离子电池的高能量密度和超级电容器的高功率密度的特点.然而,由于锂离子电容器中阳极和阴极之间电化学反应动力学的不匹配使得探索具有快速离子扩散和电子转移通道的阳极材料面临挑战.在此,通过静电纺丝策略将具有可控末端基团的二维Ti_(3)C_(2)MXene引入一维碳纳米纤维中,形成三维导电网络.在这种Ti_(3)C_(2)MXene和碳基复合材料(称为KTi-400@CNFs)中,二维纳米片结构赋予了Ti_(3)C_(2)MXene更多Li+存储活性位点,而碳骨架则有利于提高复合材料的导电性.更值得一提的是,在Ti_(3)C_(2)MXene和碳骨架的界面上形成了Ti–O–C键.复合材料中的这种化学键为电子的快速传输和离子在层与层之间纵向的快速扩散建立了桥梁.因此,优化后的KTi-400@CNFs复合材料在电流密度为5 A g-1的情况下,500次循环后仍保持235 mA h g-1的良好容量.由KTi-400@CNFs//AC组成的锂离子电容器实现了高能量密度(114.3 W h kg-1)和高功率密度(12.8 kW kg-1).KTi-400@CNFs的这种独特结构和优异的电化学性能为二维材料制备提供了参考.

Atomic scale visualizations of low-angle grain boundary mediated plasticity by coupled dislocation climb and glide in nanoporous gold

Grain boundaries(GBs),as a prevalent structural characteristic,play a crucial role in the deformation of nanoporous metals with nanosized grains and ligaments.However,the fundamental understanding of GB-mediated deformation is still lacking because the plastic behavior of discrete ligaments involving GBs remains to be unknown.Here,we report atomic scale visualizations of coupled GB dislocation climb and glide in nanoporous gold ligaments with low-angle GBs via in situ tensile straining inside a Cs-corrected transmission electron microscope.The zig-zag motion paths of GB dislocations are precisely determined by real-time tracking of the movements of dislocation cores.The concurrent climb and glide of the dislocation arrays are confined to a narrow GB region,greatly enhancing GB diffusion in the bicrystal ligament.Our findings of coupled dislocation climb and glide shine a light on the room-temperature deformation of nanoporous metals and provide a time-dependent atomic-level physical image for GB engineering.

Shifts in the BCFW method for QED

We study the application of BCFW recursion relations to the QED process 0→e^(-)e^(+)nγ.Based on 6-point amplitudes(both MHVA and NMHVA)computed from Feynman diagrams in the Berends-Giele gauge,we conduct a comprehensive study on different shifts.Subsequently,we propose a new shift(LLYZ shift),which can lead to the full amplitudes of these processes and have several realistic computational advantages.We compare the number of terms and independent amplitudes of this novel shift with those of a few typical shifts.