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In recent years, with the rapid development of unmanned aerial vehicles (UAV) technology and swarm intelligence technology, hundreds of small-scale and low-cost UAV constitute swarms carry out complex combat tasks in the form of ad hoc networks, which brings great threats and challenges to low-altitude airspace defense. Security requirements for low-altitude airspace defense, using visual detection technology to detect and track incoming UAV swarms, is the premise of anti-UAV strategy. Therefore, this study first collected many UAV swarm videos and manually annotated a dataset named UAVSwarm dataset for UAV swarm detection and tracking; thirteen different scenes and more than nineteen types of UAV were recorded, including 12,598 annotated images—the number of UAV in each sequence is 3 to 23. Then, two advanced depth detection models are used as strong benchmarks, namely Faster R-CNN and YOLOX. Finally, two state-of-the-art multi-object tracking (MOT) models, GNMOT and ByteTrack, are used to conduct comprehensive tests and performance verification on the dataset and evaluation metrics. The experimental results show that the dataset has good availability, consistency, and universality. The UAVSwarm dataset can be widely used in training and testing of various UAV detection tasks and UAV swarm MOT tasks. [ABSTRACT FROM AUTHOR]

This paper proposes a novel single‐feed filtering dielectric resonator antenna (FDRA) using fusion design method and the microstrip‐slot coupled feeding structure. Two pairs of slotlines are elaborately designed and perpendicularly loaded on the coupling slot to provide two radiation nulls at the edges of the passband. Therefore, a compact DRA with a quasi‐elliptic function bandpass response is constructed without extra filter circuits. Furthermore, two radiation nulls can be individually controlled through changing the length of the corresponding slotlines. For proving the effectiveness of the design, a prototype FDRA operation at 3.45 GHz is fabricated and measured. The measured results show that the peak realized gain is 5.84 dBi and the ‐10dB impedance bandwidth is 10.29% (3.29 ‐ 3.65 GHz). The proposed FDRA not only has good performance, but also has simple design. [ABSTRACT FROM AUTHOR]

In this letter, a wideband circularly polarized (CP) dielectric resonator antenna (DRA) with flat gain is proposed. The antenna consists of two layers of DRs (the lower part DR 1 , the upper part DR 2), conformal microstrip on DR, and a dielectric substrate. Partitioning the DR into upper and lower sections with different dielectric constants is to equalize the gain within passband. Moreover, the conformal microstrips on both sides of the DR serve as feeders to excite the fundamental TEy 111 and TEx 111 modes, and high-order TEy 113 and TEx 113 modes of the DR. In addition, the 90° phase difference between the two resonant modes of each orthogonal pair is achieved by varying the corresponding conformal microstrip heights to improve circular polarization performance. For demonstration, a wideband CP DRA prototype was manufactured and measured. The measurements illustrate that the antenna achieves a wide impedance bandwidth of 38.5 % (3.48–5.14 GHz), an axial ratio (AR) bandwidth of 26.7 % (3.38–4.42 GHz) for left-hand circular polarization (LHCP), and a flat gain reaching 7.2 dBi in the passband. [ABSTRACT FROM AUTHOR]

In this paper, a wideband filtering power divider (FPD) based on dual-composite left–right-handed (D-CRLH) resonator is proposed. The D-CRLH filter unit, featuring a parallel stepped impedance resonator (SIR), is used to replace the λ/4 transmission line of the Wilkinson power divider, which can make the FPD more compact. Due to the inherent characteristics of D-CRLH resonator, two transmission zeros can be generated on both sides of the passband, so the proposed power divider based on the D-CRLH resonator can achieve a quasi-elliptic filtering response. To further enhance anti-interference ability at low frequencies, a pair of open stubs is added to the output feedline to introduce an additional transmission zero on the low-frequency side of the power divider passband. Finally, isolation resistors are introduced on the input and output feedlines to improve the isolation between the output ports. For validation, a prototype with a center frequency of 3.6 GHz is fabricated and measured, with −10 dB fractional bandwidths (FBWs) of 58.3 %(2.55–4.65 GHz). The measurement results are basically consistent with the simulation results, and its isolation in the passband is all more than 13.8 dB. [ABSTRACT FROM AUTHOR]

Infrared image and visible light image fusion is widely used in night vision, surveillance, military and other fields. The focus of the fusion task is to integrate complementary information in visible and infrared light images and eliminate redundant information. In addition, most of the fusion tasks are performed in the harsh environment of low light, and it is worth studying how to maintain the lighting information of the fusion results. In order to solve the problems existing, firstly, we designs a multi-level feature module to fusion multi-source information. Different from the parallel layer fusion strategy of the traditional network, we proposed a fusion strategy combine parallel layers and depth layers. Secondly, we add attention computing to the feature extraction network to improve the performance of the feature extraction network. Thirdly, in order to make the fusion image have good illumination information, we design the area illumination retention module, improved the performance of the fusion algorithm in low-light environments. A large number of experiments show that the proposed method has excellent performance and will perform better in low light environment. In addition, the proposed algorithm also shows great potential in multi modal object detection. • We propose a multi-level feature fusion network with region illumination retention for infrared and visible image fusion. • We optimise the traditional convolution to improve the feature extraction capability of the network. • Ours algorithm performs better in low-light environments. • It has the ability to integrate information from multiple sources at multiple levels. • It has shown great potential in the field of multi-modal target detection. [ABSTRACT FROM AUTHOR]

To improve the long-term ablation resistance of the C/C composite, the C f -reinforced ZrC-SiC coated C/C-ZrC-SiC composite is fabricated by thermal gradient chemical vapor infiltration (TGCVI) technology and the subsequent polymer infiltration and pyrolysis (PIP) process. The coating shares the same carbon fiber felt with the matrix, which can strengthen the bond between the coating and the matrix. Results show that the composite has excellent long-term anti-ablation performance (the linear ablation rate of the composite is −0.64 µm/s after ablated for 120 s (3 × 40 s), and the coating can withstand ablation for 160 s (4 × 40 s) without destruction). With the reinforcement of carbon fibers, the coating is peeled layer by layer rather than destructed in the whole coating, and the coating still works in the subsequent ablation cycles (the linear ablation rate of the composite is 2.40 µm/s after ablated for 280 s (7 × 40 s)). [ABSTRACT FROM AUTHOR]

Abstract A novel vertically aligned carbon nanotube/dense SiC (VACNT/SiC) composite was fabricated by cyclic precursor infiltration and pyrolysis technique. It exhibits ultrahigh Young's modulus, hardness and compressive strength thanks to the dense microstructure, which surpass the values ever reported in literature. The VACNT/SiC composite is always stronger at 0° loading direction than at 90° direction with respect to CNT orientation due to the stronger axial property of individual CNT, despite that different deformation mechanisms were demonstrated at the two loading directions. Specifically, interfacial debonding occurred during fracture of the VACNT/SiC composite, which suggests a weak bonding nature of the VACNT/SiC interface. Graphical abstract Mechanical anisotropy of a novel nanostructured composite made up by high-density vertically aligned CNT arrays and dense SiC matrix. Unlabelled Image [ABSTRACT FROM AUTHOR]

We introduced a strategic "Kinetic Diffusion Multiple" (KDM) that undergoes interdiffusion annealing followed by realistic thermal treatment. The blended spectra of phases and microstructures subjected to treatment in deeply grooved composition gradients enables the microstructure and micromechanical properties of structural materials to be surveyed by high-spatially resolved micro-analysis along the composition arrays. The KDM was demonstrated as a robust high-throughput methodology that enables rapid screening of the composition-microstructure-micromechanical/properties relationships for different metallic materials. It has also proven great success at elucidating the lasting effects of alloying elements and diffusion flux on microstructure, micromechanical properties, phase transformation, and their interrelationships as a whole. [ABSTRACT FROM AUTHOR]

Addressing the problems of moving small target detection in infrared image sequence caused by background clutter and target size variation with time, an approach for moving small target detection is proposed under a pipeline framework with an optimization strategy based on reinforcement learning. The pipeline framework is composed by pipeline establishment, target-background images separation, and target confirmation, in which the pipeline is established by designating several successive images with temporal sliding window, target-background images separation is dealt with low-rank and sparse matrix decomposition via robust principal component analysis, and target confirmation is achieved by employing a voting mechanism over more than one separated target images of the same input image. For unremitting optimization of target-background images separation, the weighting parameter of low-rank and sparse matrix decomposition is dynamically regulated by the way of reinforcement learning in consecutive detection, in which the complexity evaluation from sequential infrared images and results assessment of moving small target detection are integrated. The experiment results over four infrared small target image sequences with different cloudy sky backgrounds demonstrate the effectiveness and advantages of the proposed approach in both background clutter suppression and small target detection. ©2016 SPIE and IS&T [DOI: 10.1117/1.JEI.25.5.053032] [ABSTRACT FROM AUTHOR]

The dynamical nucleation of martensite in polycrystals is simulated by means of Lagrange–Rayleigh dynamics with Landau energetics, which is capable of obtaining the local stress as a result of the interplay of the potential of transformation and external loadings. By monitoring the spatio-temporal distribution of the strain in response to the local stress, we demonstrate that the postcursors, high angle grain boundaries and triple junctions act as favorable heterogeneous nucleation sites corresponding to different loading and cooling conditions, and predict the phase diagram of the nucleation mode of martensite. [ABSTRACT FROM AUTHOR]

Motivated by the robust principal component analysis, infrared small target image is regarded as low-rank background matrix corrupted by sparse target and noise matrices, thus a new target-background separation model is designed, subsequently, an adaptive detection method of infrared small target is presented. Firstly, multi-scale transform and patch transform are used to generate an image patch set for infrared small target detection; secondly, target-background separation of each patch is achieved by recovering the low-rank and sparse matrices using adaptive weighting parameter; thirdly, the image reconstruction and fusion are carried out to obtain the entire separated background and target images; finally, the infrared small target detection is realized by threshold segmentation of template matching similarity measurement. In order to validate the performance of the proposed method, three experiments: target-background separation, background clutter suppression and infrared small target detection, are performed over different clutter background with real infrared small targets in single-frame or sequence images. A series of experiment results demonstrate that the proposed method can not only suppress background clutter effectively even if with strong noise interference but also detect targets accurately with low false alarm rate. [ABSTRACT FROM AUTHOR]

Vertically aligned carbon nanotubes (VACNTs)/silicon carbide (SiC) nanocomposites (VSNs) present remarkably anisotropic mechanical properties originated from their intrinsic heterogeneous microstructures. However, the studies related to tensile mechanical behaviors and failure mechanisms of VSNs are still suspended so far. In this work, the tensile mechanical properties of VSNs were investigated by an in-situ transmission electron microscopy (TEM) tensile test combined with classic molecular dynamics (MD) simulation. The testing results show that the fracture strength and Young's modulus of VSNs along CNT-axis (∥ direction) are higher than those perpendicular to CNT-axis (⊥ direction). In addition, the fracture surface along ∥ direction is uneven whereas it is flat along ⊥ direction. The MD simulation reveals that the stronger behavior along ∥ direction is mainly benefited by the excellent tensile mechanical properties of CNTs, however, the relatively weak van der Waals interaction between CNTs and SiC matrix dominates the tensile performances of VSNs along ⊥ direction. Finally, the remarkable mechanical anisotropy of VSNs is explained by pulling-out and peeling-off failures of CNTs based on MD simulation. This work provides experimental and theoretical insights into the dominant mechanisms of mechanical anisotropy in typical VACNT/ceramic nanocomposites. In this work, the anisotropic tensile mechanical properties of Vertically aligned carbon nanotubes (VSNs) were investigated by an in-situ transmission electron microscopy (TEM) tensile test combined with classic molecular dynamics (MD) simulation. [Display omitted] [ABSTRACT FROM AUTHOR]

In this article, we propose a new particle swarm optimization–based satellite selection algorithm for BeiDou Navigation Satellite System/Global Positioning System receiver, which aims to reduce the computational complexity of receivers under the multi-constellation Global Navigation Satellite System. The influences of the key parameters of the algorithm—such as the inertia weighting factor, acceleration coefficient, and population size—on the performance of the particle swarm optimization satellite selection algorithm are discussed herein. In addition, the algorithm is improved using the adaptive simulated annealing particle swarm optimization (ASAPSO) approach to prevent converging to a local minimum. The new approach takes advantage of the adaptive adjustment of the evolutionary parameters and particle velocity; thus, it improves the ability of the approach to escape local extrema. The theoretical derivations are discussed. The experiments are validated using 3-h real Global Navigation Satellite System observation data. The results show that in terms of the accuracy of the geometric dilution of precision error of the algorithm, the ASAPSO satellite selection algorithm is about 86% smaller than the greedy satellite selection algorithm, and about 80% is less than the geometric dilution of precision error of the particle swarm optimization satellite selection algorithm. In addition, the speed of selecting the minimum geometric dilution of precision value of satellites based on the ASAPSO algorithm is better than that of the traditional traversal algorithm and particle swarm optimization algorithm. Therefore, the proposed ASAPSO algorithm reduces the satellite selection time and improves the geometric dilution of precision using the selected satellite algorithm. [ABSTRACT FROM AUTHOR]

Addressing the problems of visual surveillance for anti-UAV, a new flying small target detection method is proposed based on Gaussian mixture background modeling in a compressive sensing domain and low-rank and sparse matrix decomposition of local image. First of all, images captured by stationary visual sensors are broken into patches and the candidate patches which perhaps contain targets are identified by using a Gaussian mixture background model in a compressive sensing domain. Subsequently, the candidate patches within a finite time period are separated into background images and target images by low-rank and sparse matrix decomposition. Finally, flying small target detection is achieved over separated target images by threshold segmentation. The experiment results using visible and infrared image sequences of flying UAV demonstrate that the proposed methods have effective detection performance and outperform the baseline methods in precision and recall evaluation. [ABSTRACT FROM AUTHOR]

A dual mode square‐ring defected ground waveguide (SR‐DGW) with defected square patch is first proposed to excite a single‐feed dual mode circularly polarized (CP) patch antenna, which can improve the impedance bandwidth and achieve the CP radiation pattern. The defected square patch is called the perturbation element. By optimizing the size of the perturbation, the degenerate modes of the dual mode SR‐DGW are split and their orthogonal modes can be excited simultaneously. Due to the dual mode of the SR‐DGW, the TM01 mode, and TM10 mode of the square patch antenna are excited simultaneously, which can improve the impedance bandwidth of the antenna. Meanwhile, owing to the orthogonal modes, CP radiation pattern of the antenna is obtained. Then, for a better impedance matching, an L‐shaped spurline embedded in the feedline is introduced. The simulated and measured results show a good performance of the proposed antenna. The measured −10 dB impedance bandwidth is 10.4% (3.56 GHz‐3.95 GHz). The measured 3 dB axial ratio bandwidth is 5.36% (3.63 GHz‐3.83 GHz). Detailed designs and experiments are described and discussed. [ABSTRACT FROM AUTHOR]

The effect of carbon nanotube (CNT) orientation on the mechanical properties and fracture mechanisms of a vertically aligned CNT/C composite was studied in this work by a combination of nanoindentation and micropillar compression techniques. The results suggest stronger response of the composite when loading parallel to the CNT orientation. This led to higher Young's modulus and hardness (≈34 GPa and ≈3.75 GPa) at this direction than those at perpendicular direction (≈19 GPa and ≈2.6 GPa). The mechanical anisotropy led to fracture mechanisms that were also dependent on the CNT orientation. At 0° direction, the composite was fractured into segments by splitting of the micropillar. While at 90° direction, the composite was much brittle and was fractured by dual shearing, implying a strong CNT/C interface. [ABSTRACT FROM AUTHOR]

• SiO 2 oxide scale formed inside plasma wind tunnel maintains an amorphous microstructure. • Young's modulus and hardness of SiC/SiO 2 evolved linearly with penetration depth. • Compressive residual stress in SiO 2 may increase's its nanoindentation hardness. • SiO 2 delamination has a negligible effect on the nanoindentation response of SiC/SiO 2. Mechanical strain and delamination of surface oxide from substrate are important mechanisms leading to failure of thermal protection systems in hypersonic vehicles. In this work, the deformation and fracture mechanisms of a thermally oxidized SiC/SiO 2 , formed by dynamic oxidations inside a plasma wind tunnel, are studied by nanoindentation experiments and finite element modeling. The results show an amorphous and uniform SiO 2 formation on β-SiC at 1200∼1400 °C in the plasma flow (pressure ≈6.5 kPa), after long-term single/repeated oxidations. In the plasma environment the passive oxidation of SiC is slow, as a result the as-formed SiO 2 is very thin. The SiO 2 thickness is only ≈680 nm after 8 × 500 s dynamic oxidation. SiC/SiO 2 exhibits a strong depth dependent indentation behavior, and at a critical indentation depth, delamination of SiO 2 oxide scale is triggered. Finite element modeling helps decouple the effects of SiC substrate, residual thermal stress and interfacial delamination on the nanoindentation response of SiC/SiO 2. The results evidence that delamination has a negligible effect on the nanoindentation response, and the main contributions are the SiC substrate and residual thermal stress. This work may forward the fundamental understanding of deformation and fracture mechanisms of oxide scales on thermal protection materials in response to localized loading conditions. [ABSTRACT FROM AUTHOR]

Mechanical performance of ceramic/ceramic nanolaminates at elevated temperatures is a main concern when they are applied as protective coatings on compressed blades of aeroengines. In this work, the deformation mechanism and mechanical properties of physical vapor deposited TiN/ZrN nanolaminates are studied by instrumented nanoindentation at 25–450 °C. The effects of layer thickness and temperature are highlighted, with the help of detailed microstructural characterizations. The results show a cracking activity of individual layers for nanolaminates with 50 nm thick layers at 25 °C, which is detrimental to the mechanical performance and arises a strong indentation size effect. In addition, due to nanocrystalline structures of both TiN and ZrN layers, reduction of layer thickness is not effective to strengthen the nanolaminate. As a result, 'the thinner, the stronger' rule that works for most nanolaminates does not hold for the specific TiN/ZrN system. The indentation cracking activity is prohibited at elevated temperature due to thermally activated plasticity of both layers. An approximate linear softening in modulus and hardness, as determined by nanoindentation, is observed. Based on the high temperature data, 'apparent' activation energy for TiN/ZrN nanolaminate is finally quantified. The work may forward the advance of novel ceramic/ceramic nanolaminates in hot-section components of aeroengines. [Display omitted] • Cracking of individual layers in TiN/ZrN is responsible for indentation pop-ins at 25 °C. • 'The thinner, the strong' rule does not hold for TiN/ZrN due to nanocrystalline structure. • TiN/ZrN experiences softening at elevated temperatures due to thermal activated plasticity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Diverse strength sensitivity of Ni/Al is acquired by variation of Al or Ni layer thickness. • Compressive deformation of Ni/Al is dominated by the constrained plasticity in Al layers. • Yield strength of Al nano-layer versus grain size is determined by an inverse methodology. • Strengthening of Al nano-layer in Ni/Al is well described by a confined layer slip model. This work focuses on the mechanical properties and strengthening mechanism of Ni/Al nanolaminates, where dislocation strengthening and constraint dominate in the soft Al nanolayers. Nanoindentation and micropillar compression experiments highlight a constrained plasticity of Al nanolayers, which endows Ni/Al nanolaminates with a strain hardened behavior. Plasticity of Ni/Al nanolaminate begins with yielding of Al, and the Al yield strength depends on the individual layer thickness. Based on an inverse methodology, the Al yield strength as a function of Al grain size is determined. The results evidence a significant strengthening in the Al nanolayers. Specially, when Al layer thickness decreases from ≈110 nm to ≈16 nm, its yield strength is increased for ≈68 %, from ≈0.69 GPa to ≈1.16 GPa. The strengthening rule follows a confined layer slip model that is developed based on confining of single dislocation loops in nanolayers. Both the dislocation strengthening and the constraint effects in the Al layers contribute to a more sensitivity of Ni/Al strength with the variation of Al layer thickness, instead of Ni layer thickness. The work may forward the fundamental understanding in the strengthening mechanism and mechanical behavior of metallic nanolaminates with large elastoplastic mismatch. [ABSTRACT FROM AUTHOR]

The experimental data in the literature for the hcp phase of the Mg–Al–Zn ternary system have been critically reviewed. Based on the concentration profiles from the literature, the diffusion coefficients have been re-extracted using the Hall method for the impurity diffusion, and the Sauer–Freise and the Whittle–Green strategies for interdiffusion coefficients in binary and ternary systems, respectively. Moreover, extra interdiffusion coefficients were obtained from the “Darken-type” couples, which present relative maxima or/and minima at the concentration profiles. This information was assessed to obtain an atomic mobility database, by means of DICTRA software in conjunction with the CALPHAD thermodynamic description that is able to reproduce the diffusion couple experiments. Comprehensive comparisons between the calculated results and experimental values show an excellent agreement not only for the diffusion coefficient data, but also for the concentration profiles and the diffusion paths. [ABSTRACT FROM AUTHOR]

A differential dual‐polarized patch antenna with broadband, high isolation, and low cross‐polarization level for 5G base station is presented. The antenna is composed of the radiating element, feeding structure, and reflector. The radiating element is designed with four identical smaller quasi‐trapezoidal patches to achieve a wider bandwidth, which is capacitively driven by two trapezoidal feeding patches. Impedance matching of antennas can be adjusted by tuning the size of quasi‐trapezoidal patches in the feeding portion. Finally, a prototype antenna is fabricated based on the simulated model. The measured bandwidth of the proposed antenna is about 27.8% (3.19–4.22 GHz) with VSWR<1.5, and the port isolation is better than 39.5 dB over the whole operating band. Furthermore, the proposed antenna has a stable gain of 8.55 ± 0.8 dBi and a low cross‐polarization level (<−33 dB) within the operating band. [ABSTRACT FROM AUTHOR]

The compressive deformation behaviors were investigated in metastable β Ti–7Mo–3Al–3Cr–3Nb alloy single crystal micropillars oriented to [011] β and [001] β. The study demonstrates that the metastable β titanium single crystal oriented to [001] β exhibits nonlinear elastic behavior with hysteresis, which is attributed to reverse β to α″ transformation. Furthermore, the yield strength of the single crystal oriented to [011] β is almost twice as of the single crystal oriented to [001] β , which is influenced by the different roles of ω ath in both pillars due to differences in shear modulus G, in addition to being determined by the deformation mechanism at yielding. The continuous impedance to dislocation motion of ω and α″ phase in the pillar oriented to [011] β leads to a stable plastic flow behavior, but reverse β to ω phase transformation facilitating the formation of massive SIMα″ results in a sudden strain burst in the pillar oriented to [001] β. Finally, we find that the pillar oriented to [011] β is dominated by dislocation slip but SIMα″ occupies a dominant position in the pillar oriented to [001] β in the early deformation stage, which is same as predicted based on the martensitic transformation theory in metastable β titanium alloys. [ABSTRACT FROM AUTHOR]

• High-temperature "Inverse" Hall-Petch behavior was found in TA15 alloy. • Grain boundary-mediated deformation is the main mechanism of high temperature deformation. • By designing the grain size of specimen and distribution of the second phase, it is expected to fully exploit the high-temperature mechanical properties of the material. The Hall-Petch relationship is important for material design at room temperature. However, it is not well studied at high temperatures. In this work, the influence of different microstructures on the high-temperature mechanical behavior and corresponding softening mechanisms of high-temperature titanium alloy TA15 (Ti-6.5Al-2Zr-1Mo-1 V, wt.%) were studied. Specimens with duplex, Widmanstätten, and coarse Widmanstätten microstructures were obtained through powder metallurgy. High-temperature tensile tests were carried out between 500 and 650°C. It was found that the fracture mode of the Widmanstätten microstructure was transgranular at 500 °C and 550 °C, but intergranular at 600 °C and 650 °C. EBSD analysis revealed that the high-temperature deformation was facilitated by several mechanisms including GB softening, GB migration, grains rotation, and activation of multiple slip systems. High temperature nanoindentation indicated sofenting of individual grains with increasing temperature. In-situ tensile testing under SEM revealed deformation was primarily in grain interior at room temperature, and GBs played a significant role at 650℃. The GB behavior at high temperatures is believed responsible for the inverse Hall-Petch relationship. These findings provide a new perspective for improving the high-temperature mechanical properties and microstructure control of titanium and its alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

• Mechanical properties of partially recrystallized HEAs stay the same. • A new hetero-deformation between heterogeneous precipitate regions is identified. • Origins of the similar ductility and strength are discussed in details. • Discontinuous coarsening contributes to the formation of heterogeneous precipitates. Heterogeneous microstructure alloys provide a possibility for the combination of strength and ductility. As a typical heterogeneous microstructure, partially recrystallized microstructure is attractive because of the convenient processing route and great potential for industrial applications. However, the mechanical properties of this microstructure vary dramatically with different morphology factors, especially the recrystallization fraction, which restricts the processing window and the property consistency. In this study, we found that the yield strength (∼1.3 GPa) and ductility (∼20 %) of the partially recrystallized Ni 2 CoCrFeTi 0.24 Al 0.2 do not change when the recrystallization fraction increases from 21 % to 72 %. This novel phenomenon is attributed to an additional hetero-deformation induced (HDI) strain hardening effect produced by heterogeneous precipitates. With the increased recrystallization fraction, this additional HDI stress keeps the ductility unchanged by offsetting the decreased HDI stress arising from the hetero-deformation between recrystallized (RX) and non-recrystallized (NRX) areas. The unchanged yield strength comes from the increased strengthening effects of the lamellar precipitates and grain boundaries. We also confirmed that the discontinuous coarsening contributes to the formation of heterogeneous precipitates. These findings would open a new pathway for enhancing the consistency and processability of hetero-structured alloys and thus promote their broader industrial applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, a high-selectivity equal-ripple wideband balanced bandpass filter (BPF) is proposed. Comprising two parallel coupled lines (PCLs) linking the 50-Ohm input and output feedlines, a pair of branch lines connecting the respective differential input and output ports, and a transverse transmission line interconnecting the left and right branch lines within the symmetrical plane SS ', this design configuration yields a bandpass characteristic under differential-mode (DM) excitation, while also inherently achieving bandstop performance under common-mode (CM) excitation. The optimization objective function employs the ideal Chebyshev transfer function to attain equal-ripple DM filtering responses. Additionally, to bolster selectivity, a PCL structure replaces the left branch line, generating additional transmission zeros (TZs) positioned on both sides of the DM passband. For validation, simulation and measurement of an equal-ripple wideband balanced BPF operating at 3.7 GHz demonstrate close agreement between the simulated, measured, and synthesized results. [ABSTRACT FROM AUTHOR]

Eight‐element dual‐band multiple‐input multiple‐output (MIMO) antenna covering 3400–3600 MHz and 4800–5000 MHz for fifth‐generation (5G) smartphone is presented. The proposed MIMO antenna is constituted by four sets of dual‐band hybrid antenna pairs and the distance between two elements of each antenna pairs is only 0.045λg. Short‐circuited stub is loaded to the feedline of slot antenna for improving isolation. Desired isolation greater than 12 dB for the lower band and 15 dB for the higher band are realized. The proposed dual‐band eight‐element antenna array is fabricated and measured, and a good agreement between the simulation and measurement is achieved. [ABSTRACT FROM AUTHOR]

Micropillar compression technique was employed to study the microscale deformation mechanisms of basal slip, twinning and non-basal slips at selected grains in a Mg-2 wt.% Y alloy. The results suggest a critical resolved shear stress (τCRSS) for basal slip 12.5 ± 1.7 MPa, and for twin nucleation and twin growth 38.5 ± 1.2 MPa and 33.8 ± 0.7 MPa, respectively. The higher values compared to those in pure Mg suggests a more balanced deformation in Mg alloy with Y addition. The activation of dislocations in the twinned orientation is highlighted, which leads to strong work hardening in twinned favorable orientation [ 10 1 ‾ 0 ]. In addition, at prismatic-slip favorable orientation [ 11 2 ‾ 0 ] , a twinning-to-prismatic slip transition was observed when elevating temperature from 25 °C to 100 °C and 250 °C. Specially at 250 °C, twinning was completely prohibited, and pure prismatic slip was triggered. The measured τ CRSS for prismatic slip at 250 °C was 39.7 ± 0.3 MPa, much higher than that for pure Mg at the same temperature. Finally, at pyramidal-slip favorable orientation [ 0001 ] , an abnormal strengthening was observed at 100 °C and 250 °C due to activation of pyramidal slips. Decompositions of dislocations and Y segregation at stacking faults are the main mechanisms leading to the high-temperature strengthening in Mg–Y alloy. [ABSTRACT FROM AUTHOR]

Energetic multilayers are peculiarized by their self-propagation reactions when giving them a thermal pulse. This work reports the chemical reactions of Ni/Al energetic multilayers can be triggered upon ultrahigh compressive load (stress >1 GPa) at ambient temperature, which is realized by micro-compressions of Ni/Al micropillars with equal molar ratio. Detailed microscopic characterizations evidence monolayer reactions of Ni20Al30 and Ni110Al140 (NixAly: x and y are average thickness of individual layers in nanometer) are triggered, forming a stoichiometric NiAl phase after micropillar compression. The as-observed reactions must be triggered by ultrahigh compressive loads, which aid for nucleation of NiAl grains at atomic intermixing zones of Ni-Al interfaces. Once occurrence, the grain growth is self-sustained by the released heat during NiAl formation. The grain textures depend strongly on the deformation extent. The self-sustained process is terminated until the whole micropillar is reacted. Analogous chemical reactions are not observed in the thickest Ni450Al620 micropillar where atomic intermixing is absent. The comparison highlights the critical role of ultrahigh compressive load to trigger monolayer reactions of Ni/Al multilayers, and could forward the advance of Ni/Al energetic multilayers for diffusion welding purpose. • Chemical reactions of energetic multilayers can be triggered upon ultrahigh compressive load at ambient temperature. • Under ultrahigh compressive load, NiAl intermetallic is nucleated and is grown in self-sustained manner. • Chemical reactions are easier to trigger in Ni/Al micropillars with reduced monolayer thickness. • Severe compressive deformation benefits for NiAl nucleation, leading to evident grain growth in NiAl micropillars. [ABSTRACT FROM AUTHOR]

A novel C/C-ZrC-SiC gradient composite (GGC/C-ZS) is prepared via thermal gradient chemical vapor infiltration (TGCVI) technology combined with polymer infiltration and pyrolysis (PIP). And ablation tests are carried out to evaluate the thermal shock and ablation resistance. Results show that the GGC/C-ZS exhibits excellent anti-ablation performance (linear ablation rate is −2.12 μm/s) after ablation for 2 × 40 s (under 2500 °C). The high ZrC-SiC content in the surface region of GGC/C-ZS ensures a dense ZrO 2 scale of the ablation center and helps withstand the high thermal stress induced by the ablation. During the ablation, the compact ZrO 2 scale can block heat transfer from the surface to the matrix of GGC/C-ZS because of its low thermal conductivity, which can relieve the thermal etching and the massive loss of SiO 2 beneath the ZrO 2 scale. Besides, the gradient structure can also reduce heat mismatch between the ZrC-SiC ceramics and the C/C matrix, which can avoid the peeling off of the ZrO 2 scale after a second ablation process. • Gradient C/C-ZrC-SiC composite can be prepared by TGCVI technology combined with PIP method. • The rich-ceramic surface of the gradient C/C-ZrC-SiC composite can decrease the thermal etching of the whole composite. • The low C/C content in the surface region of the gradient C/C-ZrC-SiC composite helps withstand the high thermal stress. [ABSTRACT FROM AUTHOR]

In this paper, a newly composite right-/left-handed (CRLH) resonator is presented and applied to constitute a compact dual-band balanced bandpass filter (BPF). The proposed CRLH resonator contains two spiral coupled line segments. By imposing the differential-mode (DM) and common-mode (CM) excitation, the DM and CM equivalent circuits of the presented resonator and their lumped-element circuit models are built for investigating the resonant property. The CRLH resonator has two DM resonances and are adopted to design two DM passbands. Also, the CM resonances are all far away from DM resonances, achieved intrinsic desirable CM rejection within DM frequency range without any auxiliary elements. Attributing to the mixed electric and magnetic coupling between two coupled resonators and the introduced source-loaded coupling, multiple transmission zeros are obtained and therefore enhance the selectivity and attenuation in stopband. Finally, a well-designed dual-band balanced BPF is fabricated. Verification of the presented structure and design method's validity is evidenced by the measured results, which are in agreement with the simulations. [ABSTRACT FROM AUTHOR]

This work focuses on the anisotropic deformation and fracture mechanisms of a typical physical vapor deposited TiN/ZrN multilayer, employing novel nanoindentation and micropillar compression techniques. The results highlight a stronger nanoindentation response of the multilayer when loaded perpendicular (90°) to the layer orientation, and the deformation was mainly controlled by the plasticity of ZrN layers. In comparison, at parallel (0°) orientation, the kink banding and the induced cracking may weaken the constraint beneath the indenter, thus leading to degraded hardness. By considering the anisotropic deformation mechanisms, nanoindentation finite element modeling was further performed to give reliable predictions on the strength at the inclined orientation. The modeling results suggest a dominant deformation mechanism that occurred mainly in the ZrN layers, with minor contribution from the stiff TiN layers. As a result, a minimized hardness was predicted at 45° loading direction with respect to layer orientation. Finally, the micropillar compressions show a brittle nature of both 90° and 0° oriented micropillars, and a higher fracture strain was obtained at 90°, due to the observed crack termination mechanism at this orientation. [ABSTRACT FROM AUTHOR]

Abnormal event detection, also known as anomaly detection, is one challenging task in security video surveillance. It is important to develop effective and robust movement representation models for global and local abnormal event detection to fight against factors such as occlusion and illumination change. In this paper, a new algorithm is proposed. It can locate the abnormal events on one frame, and detect the global abnormal frame. The proposed algorithm employs a sparse measurement matrix designed to represent the movement feature based on optical flow efficiently. Then, the abnormal detection mission is constructed as a one-class classification task via merely learning from the training normal samples. Experiments demonstrate that our algorithm performs well on the benchmark abnormal detection datasets against state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Nanolaminates made up by alternative Ni and Al nanolayers are widely applied to solder structural materials, due to abundant heat releases when supplied with an energetic input. This work studies the microstructural evolution and mechanical properties of Ni/Al nanolaminates with a wide mole ratio of Ni (M Ni , 0.18–0.53), to ascertain the role of Ni x Al y intermetallic phases during heat-treatment. To this end, 3 nanolaminates with Al thickness fixed at ≈110 nm and Ni thickness varying 15–75 nm are fabricated and are heat-treated at 400 °C, to trigger formations of NiAl 3 , Ni 2 Al 3 and NiAl intermetallic phases. The results suggest an enhanced strength of Ni/Al after heat-treatment. However, their evolution with M Ni is complex. The nanolaminate with M Ni ≈0.18 is the softest after heat-treatment, due to the dominant plasticity of residual Al phases. The maximized strength is achieved when M Ni ≈0.40, in which a novel NiAl 3 /Ni 2 Al 3 nanolaminate structure is formed. Owing to the brittleness of both phases, the nanolaminate after heat-treatment is fractured by shearing upon uniaxial compression. The best strength-ductility synergy is achieved when Ni mole ratio ≈0.53. In the heat-treated nanolaminate a homogenous nanocrystalline NiAl phase is formed. As a result, the nanolaminate exhibits excellent ductility and intermediate strength among the 3 nanolaminates. [ABSTRACT FROM AUTHOR]

To lower the cost and preparation period of C/C-ZrC-SiC composites, the uneven-density C/C composites (with a high density in the inner region and low density in the surface region) are designed and prepared by thermal gradient CVI process, followed by local modification of ZrC-SiC composite ceramics by precursor infiltration-pyrolysis (PIP) mothed to improve the anti-ablation performance. The ablation tests show that the SiC contents have a great influence on the microstructure of ZrO 2 grains at the ablation center by adjusting the ablation temperature and the melting point of ZrO 2 grains. Results prove that about 20 wt% SiC is optimum for the ZrC-SiC composite ceramics to perform best during the ablation and modify the uneven C/C composites prepared in this work. Besides, the dense C/C matrix would stop the liquid ZrO 2 -SiO 2 phase from running off, and in return, the dense ZrO 2 -SiO 2 phase would sink into the surface within the ablated region, which could protect the carbon fibers of the surface region and the dense C/C matrix beneath. • C/C composite with porous surface. • ZrC-SiC composite coating prepared by PIP. • SiO 2 affects the ablation property of ZrO 2. [ABSTRACT FROM AUTHOR]

The microscopic deformation behavior is always been of significant interest in revealing the mechanism of the dwell fatigue effect. This study systematically characterized the deformation system activation in Ti–6Al–3Nb–2Zr–1Mo (Ti6321) alloy using in situ tensile and quasi-in situ dwell fatigue tests. The critical resolved shear stresses of the basal and prismatic slip systems in the Ti6321alloy were first calculated using the slip trace analysis method. The study demonstrated that, under dwell fatigue, basal and prismatic slips consist of major microscopic deformation modes. Most of the slip deformation occurred rapidly during the early stage of dwell fatigue and was independent of the dwell loading. The basal slip was found to be the predominant slip mode regardless of the dwell conditions. The results suggested that the elastic anisotropy of the hexagonal-closed-packed (HCP) structure could lead to heterogeneous microscopic stress, thus activating more basal slip activities. Such activities were found to participate in the crack initiation through two unique cracking modes: basal plane crack and (0001) twist boundary crack. [Display omitted] • The critical resolved shear stress was quantitatively evaluated through in situ tensile tests. • Dwell fatigue deformation modes were revealed by the crystallographic characteristics. • Basal slip deformation was proved to be the predominant slip mode and highly participated in the crack initiation. [ABSTRACT FROM AUTHOR]

The anisotropy of the mechanical properties of high-performance titanium-alloy plates has always been a key challenge in the fabrication of alloy plates and the application of components in service. In this work, the room-temperature creep behavior and microstructural crystallography of Ti6321 alloy plates along the rolling direction (RD), 45°, and transverse direction (TD) have been thoroughly investigated and discussed. The study demonstrates that the plates exhibit significantly different room-temperature creep characteristics along the three sampling directions. Among them, the creep strain along the 45° direction was the largest, whereas the creep strain along the TD was the smallest. Such anisotropic deformation was associated with the global Schmid factor variation caused by the T-type microtexture. Both the basal and prismatic slips occur easily along 45°, whereas it was hard to activate along the TD. In addition, the basal and prismatic slips were the main contributors to creep deformation, which also showed strong crystallographic orientation dependence. Among them, the basal slip was found to be more easily activated than prismatic slip, especially in the high Schmid factor range. The study also discusses the potential influence of elastic anisotropy on the activation of basal slip. [ABSTRACT FROM AUTHOR]

Although the bulk mechanical properties of materials are critically sensitive towards oxygen doping, the effect of oxygen on single prismatic slip is rarely reported. The current study systematically investigates the mechanical response and deformation mechanism of the prismatic slip in single-crystal Ti micropillars with respect to varying oxygen concentrations. The findings show that the prismatic slip is activated intrinsically regardless of oxygen content, while deformation twinning is evidently suppressed at the high oxygen content. Visible strain hardening behavior for the micropillars at the low oxygen content is witnessed and attributed to the interaction between dislocations and twin/stacking faults. Finally, an anomalous loss of strain rate sensitivity of the prismatic slip in highly oxygen-doped single-crystal Ti micropillars is interestingly observed, which is discussed carefully by correlating it with the metastable mechanical shuffling mechanism of oxygen. [ABSTRACT FROM AUTHOR]

A strain-transformable microstructure was successfully designed in a metastable β Ti–7Mo–3Nb–3Cr–3Al alloy with enhanced mechanical properties, by introducing ∼28% α precipitates coupled with the TRIP effect, overcoming the traditional trade-off dilemma between strength and ductility in most metastable β-Ti alloys. The as-designed lamellar microstructure was predominantly deformed by stress-induced martensitic (SIM α") phase transformations, martensitic twinning and dislocation slip of the parent β grains and α laths. The β→α" transformation followed the [113] β //[112] α" //[-310] α" //[1-21] α" orientation relationship, with the {133} β habit plane predicted by the Phenomenological Theory of Martensite Crystallography (PTMC). A novel <211> α" type II martensitic twinning mode was also found, in addition to the {111} α" type I mode at SIM α"/α impinging region. The results show that, not only the lamellar α precipitates play a major role in precipitation strengthening, but they can also effectively block SIM α" propagation at the initial stages of deformation. However, SIM α" transmission across the α laths was also observed for large strains. Moreover, < c + a > pyramidal slip and shear of the α laths also contributed to the accommodation of internal stresses. Therefore, the origin of the enhanced tensile mechanical properties can be attributed to the combined effects of α precipitation strengthening coupled with the TRIP softening effect and the extra interaction stresses introduced by the α laths and other deformation products, validating the design concept. The current investigation may provide a novel strategy for designing new high-performance metastable β-Ti alloys. • A strain-transformable microstructure was successfully designed in a metastable β-Ti alloy. • The designed microstructure is deformed by stress-induced martensitic (SIM α") phase transformation and dislocation slip. • The β→α" transformation follows [113] β //[112] α" //[-310] α" //[1-21] α" orientation relationship and {133} β habit plane. • A novel <211> α" type II twinning mode has been observed at SIM α"/α impinging region for the first time. • The α precipitates could deform compatibly with the SIM α". [ABSTRACT FROM AUTHOR]

The fretting behaviors of a metastable β titanium alloy with three kinds of microstructures were studied. Special attentions have been paid to the underlying wear mechanism mediated by fretting conditions and microstructural features. The wear volume is more sensitive to the stroke amplitude rather than the normal loading. The mixed abrasive-adhesive wear is dominated in all fretting samples. The microstructural features make a significant contribution to the difference in the wear resistance and subsurface microstructure stability. Due to a large difference in the grain size and the ability of plastic deformation in adjacent grains, the SM (single-phase microstructure) sample is more favorable to initiation and propagation of cracks. The DM (duplex microstructure) and BM (basketweave microstructure) samples, however, have a high resistance ability to fretting wear and subsurface microstructure stability. This can be attributed to the large amounts of the β/α interfaces and the dispersed orientation distribution of α precipitates. The present work offers valuable experimental data for the prediction of fatigue life after fretting. • The fretting behaviors are evidenced to connect with coupling effect of microstructural features and fretting conditions. • The fretting wear volume is more sensitive to the stroke amplitude rather than the normal loading. • The microstructural origins of fretting wear mechanisms are illustrated systematically. • Microstructure features dependence on the subsurface microstructure stability is revealed in detail. [ABSTRACT FROM AUTHOR]

Interleaved multichannel power factor correction (PFC) converter is very popular today because of its ability to reduce input and output current ripples. In this paper, the common-mode (CM) electromagnetic interference noise emission model of the multichannel PFC converter is studied. A balance technique is introduced to reduce CM noise emission. To improve the high-frequency balance, a novel topology with coupled-inductor structure is proposed. Its CM noise model is derived and balance condition for minimizing CM noise is calculated. Effects of phase shift and channel shedding on this solution are also studied. The proposed topology has effectively reduced CM noise under any phase shift and channel shedding conditions. A two-channel PFC converter is built to verify the proposed balance technique. Experimental results show that CM noise can be reduced up to 20 dB between 150 kH and 7 MHz. [ABSTRACT FROM AUTHOR]

The stress-induced martensitic (SIM) β→α″ phase transformation and SIM α″ twinning in the fully-β Ti–7Mo–3Nb–3Cr–3Al (Ti-7333) alloy was investigated as a function of strain, following a surface-to-bulk methodology assisted by electron backscatter diffraction (EBSD), focused ion beam (FIB) milling and transmission electron microscopy (TEM). The results indicate that the Ti-7333 alloy is predominantly deformed by SIM and SIM α″ twinning. At the onset of deformation, the lattice correspondent SIM α″ martensite variant that produces the maximum transformation strain along the tensile direction is activated firstly, which follows the <-110> β //<001> α″ orientation relationship. As the strain increases, the SIM α″ laths deform by twinning, predominantly through the {130}<310> α″ compound twinning and {111} α″ type Ⅰ twinning modes. Their activation can be rationalized in terms of the magnitude of the shear and the complexity of the atomic shuffle using the Bilby-Crocker deformation twinning theory. The prevalence of {130}<310> α″ compound twinning in this alloy is attributed to the comparatively small shear (0.1872) and the simple shuffle (q = 2, Δ Ⅰa = 0.3257) mechanism involved. During the last stages of deformation, secondary microtwinning takes place within the primary twins due to the reduced mobility of the intervariant boundaries. The evolution of such hierarchical microstructure with strain accounts for the complex microstructural features that developed with deformation, responsible for the high work hardening displayed by this alloy. • Metastable β-Ti alloy deforms by stress-induced martensitic phase transformation (SIM α″) and SIM twinning. • The α″ variant producing the maximum transformation strain along tensile direction was preferentially activated. • The origin of the {130}<310> α″ compound twinning was rationalized. • The prevalence of this peculiar twinning mode in metastable β-Ti alloys was first explained comprehensively. [ABSTRACT FROM AUTHOR]

Deep learning has attracted extensive attention in the field of hyperspectral images (HSIs) classification. However, supervised deep learning methods heavily rely on a large amount of label information. To address this problem, in this paper, we propose a two-stage deep domain adaptation method for hyperspectral image classification, which can minimize the data shift between two domains and learn a more discriminative deep embedding space with very few labeled target samples. A deep embedding space is first learned by minimizing the distance between the source domain and the target domain based on Maximum Mean Discrepancy (MMD) criterion. The Spatial–Spectral Siamese Network is then exploited to reduce the data shift and learn a more discriminative deep embedding space by minimizing the distance between samples from different domains but the same class label and maximizes the distance between samples from different domains and class labels based on pairwise loss. For the classification task, the softmax layer is replaced with a linear support vector machine, in which learning minimizes a margin-based loss instead of the cross-entropy loss. The experimental results on two sets of hyperspectral remote sensing images show that the proposed method can outperform several state-of-the-art methods. [ABSTRACT FROM AUTHOR]