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Aiming at the problem of false detection and missed detection in the traffic sign detection task, an improved YOLOv4 detection algorithm is proposed. Based on the YOLOv4 algorithm, the Efficient Channel Attention Module (ECA) and the Convolutional Block Attention Module (CBAM) are added to form YOLOv4-A algorithm. At the same time, the global K-means clustering algorithm is used to regenerate smaller anchors, which makes the network converge faster and reduces the error rate. The YOLOv4-A algorithm re-calibrates the detection branch features in the two dimensions of channel and space, so that the network can focus and enhance the effective features, and suppress the interference features, which improves the detection ability of the algorithm. Experiments on the TT100K traffic sign dataset show that the proposed algorithm has a particularly significant improvement in the performance of small target detection. Compared with the YOLOv4 algorithm, the precision and mAP@0.5 of the proposed algorithm are increased by 5.38% and 5.75%. &nbsp

Multi-wall carbon nanotube (MWNT)-reinforced alumina composites were prepared by a sol-spray process combined with a vacuum hot press process. The relative densities of all the samples were higher than 97%. Scanning electron microscopy (SEM) results showed that the MWNTs were well-dispersed in the alumina matrix; specifically, most of them were distributed along the grain boundaries in the form of networks, whereas the others were located in the grains. For 0.5 wt.% MWNTs, the Vicker hardness and fracture toughness were 32.1% and 75.6% higher than those of pure alumina, and the average increment of the thermal diffusivity under different test temperatures is ~ 26.2%. When the content of MWNTs is higher than 0.5 wt.%, the composites showed conductor properties. Moreover, the percolation threshold of the prepared composites was 0.37 wt.% with the nonlinear fitting of conductivity data, which indicates that the MWNTs were well dispersed in the alumina matrix.

Additional file 3: Table S3. GC/MS detailed experimental steps.

The combination of active materials and carbon nanotubes (CNTs) provides an effective way to enhance battery capacity and optimize cycle performance. In the present study, the powder electrodeposition technology is employed to synthesize the NiO-Ni/CNTs composite for the first time. This technique contains the following steps. The CNTs are negatively charged by pre-discharge in lithium-ion batteries. Then, the negatived CNTs are uniformly dispersed in the NiCl2 plating solution by electrostatic repulsion, and the Ni ions are in situ reduced and deposited onto the CNTs. The close combination of CNTs and NiO-Ni improves the overall conductivity and structural stability. As electrode of lithium-ion battery, the reversible capacity is improved due to the coordination of the Ni metal in the mixture of the composite electrode. Besides, the reversible capacity of the composite electrode is 851 mAh g-1 at 50 mA g-1 after 50 cycles. The “Powder Electrodeposition” method in the current work provides a new way for the preparation of other similar powder composite materials. Furthermore, the problem that the traditional electrodeposition process is difficult to apply in the powder materials will be solved.

Interface between carbon nanotubes (CNTs) and copper matrix is generally weak mechanical bonding due to the lack of wetting and interaction between them. In the present study, the homogeneous distribution of CNTs in copper matrix was realized through a novel mixing method and spark plasma sintering (SPS). The interface structures of CNTs/Cu composites were optimized by using decorated CNTs. Transmission electron microscopy (TEM) observation revealed the formation of interfacial products, amorphous transition areas and interfacial stress zones at the decorated-CNT/Cu interfaces. The compressive tests showed that the composite containing 2 vol% of Ni-coated CNTs has a maximum compression yield strength of 554 MPa, which was increased by 55% and 30% compared with that of pure Cu and the composite reinforced with pristine CNTs, respectively. The strong strengthening effects of the decorated CNTs can be attributed to their interaction with Cu matrix. The strengthening mechanisms, load transfer efficiency and interfacial shear strength were also discussed from the point of interface structure. This work underscores the importance of the surface state of CNTs on the interface structure in metal matrix composites, and may provide insights into the composites where reinforcements and matrix are lack of wetting and interactions.

In this study, a novel mixing method that combines wet mixing and conventional ball milling followed by spark plasma sintering (SPS) was used to fabricate carbon nanotube (CNT)-reinforced Cu-matrix composites. The samples were characterized using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. In the CNT/Cu composites produced, the CNTs were uniformly dispersed whilst maintaining their integrity. Consequently, a combination of high strength, ductility, and electrical conductivity was achieved by a 2.5 vol% CNT/Cu composites (ultimate tensile strength 280 MPa, elongation 41.7%, and electrical conductivity (IACS%) 91.6%). These results could potentially be used to effectively ameliorate the issue of strength-ductility and strength-conductivity trade-offs in metal-matrix composites.

Carbon nanotubes reinforced silver composites (CNTs-Ag composites) are considered as a promising candidate for high-performance contact materials with the potential properties of low contact resistance, high thermal conductivity and excellent mechanical performance. While at present the dispersion of CNTs in silver matrix and the interfacial bonding of the composites remain problems to be resolved or enhanced. In this study, silver nanoparticles coated carbon nanotubes (Ag@CNTs) were synthesized through an improved electroless plating method assisted by ultrasonic spray atomization, which inhibited excessive growth of silver particles and led to much more uniform nanometer grain-sized coating. The Ag@CNTs were solution ball-milled (SBM) with Ag powders and then were densified by spark plasma sintering (SPS). The composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The results showed the CNTs dispersion in Ag matrix was improved benefitting from the homogeneous Ag nanoparticles distribution on CNTs, and correspondingly, the hardness and electrical conductivity were significantly improved. The mechanism may result from the combination of more homogeneous CNTs dispersion and tighter interface bonding in composite materials.

Silica/Cu composites generally fail to achieve the high strength due to the weak interfacial bonding between SiO2 and Cu. In the current work, the first use of silica quantum dots (SiO2 QDs) as a copper-based composite reinforcement. Silicon quantum dots (Si QDs) and copper acetate are employed as raw materials for spray pyrolysis to obtain an interconnected structure of SiO2 QDs/Cu2O, which achieve well-dispersion of the reinforcement and good interface combination in one step. The SiO2 QDs/Cu2O composite block is obtained by ball milling, hydrogen reduction, and SPS sintering. Micro interface structure and strengthening mechanism of the composites are investigated and presented in detail. Microstructural analysis discovers the Cu2O transition layer between SiO2 QDs and Cu matrix and well-dispersed SiO2 QDs in the Cu matrix. The good bonding of grain interface can significantly enhance the mechanical properties. The 1.2 wt% SiO2 QDs/Cu composite block exhibits an excellent ultimate tensile strength of 456.63 MPa, which is 101.68% higher than that of unreinforced Cu (227.39 MPa). Furthermore, the composite block maintains the high conductivity (83.27% IACS) and elongation (8.86%). Moreover, this work can promote the development of Cu matrix composites using ceramic reinforcement with an improved interface bonding.

Microlaminated carbon nanotubes (CNTs) reinforced Cu matrix composites were prepared by combination of composite electrodeposition and spark plasma sintering (SPS). Interdiffusion transition regions formed between CNTs and Cu matrix under high sintering temperature, which were responsible for the balanced strength and ductility of the composites.

Micron-sized CNTs/Cu 2 O composite powder prepared by Molecular Level Mixing (MLM) was mixed with flaked Cu-1.0 wt% Ti (Cu-1.0 Ti) matrix powders by low-energy ball milling. After reduction and hot pressing, CNTs/Cu-Ti composites were fabricated. Microstructure and mechanical properties of the composites were characterized by SEM, EDS, HRTEM, hardness and tensile tests, etc. The results showed that mechanical properties of the CNTs/Cu-Ti composites were enhanced compared with alloy matrix, which were ascribed to the well-distributed of CNTs and strong bonding interface with the matrix by the formation of a transition layer of TiC. Finally, strengthening mechanisms were discussed.

CNT/Cu composite was fabricated by using copper powders within small amounts of titanium nanometer powder via balling milling and followed by spark plasma sintering. Microstructure analysis by SEM, FETEM and EDS shows that laminar grain shape of the composite is inherited from the starting flake powder, and some CNT aggregates are observed at the edge of copper grains. TiC nanoprecipitation, as a transition phase from CNT to metal matrix, is formed in the composites; this phase shows a typical orientation relationship with the Cu matrix, that is Cu (002)//TiC (002). The coherent relationship between TiC and Cu grain reveals the formation mechanism of titanium carbide. Besides, TiC nanostructures contribute to the load transfer of the interface and then the enhancement of the mechanical strength. Furthermore, low angle grain boundary is also revealed by deflecting Moire fringes. It improves the dislocation carrying capacity of the interface.

A novel carbonized polymer dots (CPD)/copper (Cu) composite was successfully synthesized via molecular level mixing (MLM) and spark plasma sintering (SPS) process. Microstructure analysis shows that the CPD clusters are well dispersed at the Cu grain interfaces by forming an amorphous carbon (AC) network with a large number of inserted graphene carbon dots (some of them show the typical graphene microstructure). Mechanical properties of the CPD/Cu composite are remarkably higher than that of pure Cu sample, which increases initially with CPD wt.% and then decreases. 0.4 wt% CPD/Cu composite obtains ~47% higher strength than that of pure Cu matrix. Meanwhile, the thermal conductivity is improved from 305 W/m·K to 360 W/m·K without any adverse impact on the mechanical properties. This study provides new insights into the preparation of the advanced Cu composite with enhanced comprehensive performance.

The present study investigated the effect of co-doping with elemental crystal Ge or/and GeO 2 on the TiO 2 –Ta 2 O 5 –BaCO 3 varistor ceramic. Results showed that with the doping content of Ta 2 O 5 and BaCO 3 of 0.3 mol% and 0.2 mol%, respectively, the optimum doping content of 0.4 mol% Ge and 1.2 mol% GeO 2 exhibited the highest α value ( α = 12.1), lower breakdown voltage E B ( E B = 20.8 V mm − 1 ), lesser leakage current J L ( J L = 11.5 μA cm − 2 ), and highest grain boundary barrier Φ B ( Φ B = 0.93 eV). The microstructural analyses indicated that Ge–GeO 2 co-doping notably changed the TiO 2 –Ta 2 O 5 –BaCO 3 ceramic microstructure, increased α , and decreased E B . In addition, Ge and GeO 2 , which function as sintering aids, reduced the sintering temperature caused by the low melting point; the best sintering temperature was 1280 °C for TiO 2 –Ta 2 O 5 –BaCO 3 –Ge–GeO 2 ceramic.