Modern Physics Letters B

In this paper, an efficient approach for traffic sign detection, classification, and localization is introduced. An integration of the tiling technique with the RetinaFace model and the MobileNetV1-SSD was proposed for traffic detection and classification. The combination of the extraction of the region of interest with a depth estimation model, namely the AANet+, was introduced for the traffic sign localization task. All models were developed based on the transfer learning technique and existing datasets, including the Zalo and ApolloScape datasets. The accuracy and the computational efficiency of the approach are evaluated. Experimental results show that the novel traffic sign detection and classification method outperform the existing ones with an average precision of 77.2%. Moreover, the computing performance achieved is 5 FPS on Jetson Nano and 50 FPS on Jetson Xavier. For the traffic sign localization, the relative error can be reduced to 3.78%, and the computing time is 1.965 s/pair on Jetson Nano and 0.128 s/pair on Jetson Xavier, while the existing method has lower accuracy and is more time-consuming.

In this study, pure polyethylene terephthalate (PET) fabric was coated with polyaniline (PANI) doped with hydrochloric acid (HCl) by in situ chemical oxidation polymerization to form conductive PET/PANIHCl fabric. The surface morphology, chemical, structural, and electrical conductivity of the conductive PET/PANIHCl fabric are examined by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), and a four-point probe, respectively. FE-SEM images showed that PANIHCl was successfully coated on the PET fabric. According to the four-point probe test, the electrical conductivity of pure PET and PET/PANIHCl fabrics were $6.71\times 10^{-9}$ and $2.18\times 10^{-3}$ S/cm, respectively. The electrical conductivity of PET/PANIHCl fabric is about 10⁶ higher than that of pure PET fabric. The conductive PET/PANIHCl fabric can be used as antistatic and electrostatic discharge material, and even anti-electromagnetic interference material.

This study presented an innovative concept to develop a home-made equipment to make a 2D circular-shaped polyvinylidene fluoride (PVDF) fiber piezoelectric sensor. The fibers spun by direct-write near-field electrospinning can be collected orderly to enhance the orientation of dipole moments and the piezoelectric effect. The electrospinning system mainly consists of a high voltage power supply system, a digitally controlled $X$–$Y$ table, a solution injection system, and a rotating flat disc collector system. PVDF piezoelectric fibers were spun for the sensing element of the sensor with a diameter of $\sim$16 $\mu$m under a high electric field ($\sim 1.6\times 10^7$ V/m). The optimal parameters of electrospinning process were investigated and determined by the uniform design (UD) method in terms of the working high voltage, feeding rate, and gap distance between the needle and collector. In addition, a prototype of this newly designed rotating flat disc collector system was utilized to make 2D circular-shaped PVDF piezoelectric fibers. Besides, the newly-designed radial electrodes were used to characterize multi-directional sensing ability. The 2D circular-shaped fibers were then packaged with this radial electrodes and polyethylene terephthalate (PET) film together to measure the dynamic behavior characteristics.

This study investigates the influence of heat treatment on the hardness and material structure of SKD61 steel. The study focused on the influence of quenching temperature and tempering temperature on the hardness distribution of SKD61 steel. The equations representing the relationship between hardness and tempering temperature were derived based on the results. By the results of the analysis of the material structure, the appropriate process conditions for machining molds at high temperature were determined. We concluded that the steel should be heated to 1050${}^{\circ }$C. The heat was maintained for 2 h and the steel then quenched in oil media. It was further annealed at 580${}^{\circ }$C, with the heat maintained for 2 h and then cooled in the same furnace. With the above heat treatment process, an average hardness of 52HRC was obtained and the structure of the steel was sufficiently stable to ensure the success of subsequent heat treatment processes.

Ultrasonication is a simple way to cut carbon nanotubes in suspension. The length of fragmented carbon nanotubes is made shorter by iterating ultrasonication but approaches a critical aspect ratio. The critical aspect ratio is determined by the tensile strength of the carbon nanotube, the viscosity of the solvent, and physical properties of the cavitation bubbles produced by ultrasonication. Thus, it is possible to evaluate the tensile strength of carbon nanotubes from the critical aspect ratio. In this study, the tensile strengths of multi-walled carbon nanotubes with different diameters were evaluated using sonication-induced fragmentation. The results confirmed the strong dependency of tensile strength on diameter.

High-performance poly-ether-ketone-ketone (PEKK) thermoplastic (TP) composites, which are beginning to gain interest in the aerospace industry, require a joining procedure to integrate the individual parts. Amorphous TP bonding has been recently proposed to address the limitations of commonly used joining techniques for composites, such as mechanical fastening and adhesive bonding. In this study, we investigated the adhesive properties of a polyetherimide (PEI) film applied by hot press welding as an amorphous polymer interlayer of PEKK laminate. The temperature range of the bonding process was determined via differential scanning calorimetry analysis. The bonding strength was evaluated through single-lap shear tests. The effect of process temperature on the bonding strength was qualitatively analyzed via fracture surface morphology analysis. The interface between PEKK and PEI was analyzed via optical microscopy. The adhesive strength was as low as about 5 MPa up to the bonding temperature of 280${}^{\circ }$C but then started to improve as the temperature increased, which is attributed to the interdiffusion of the PEKK matrix and PEI adhesive film. The maximum bonding strength of 23 MPa was confirmed at a bonding temperature of 340${}^{\circ }$C. A mixed failure mode consisting of a relatively high ratio of fiber-tear failure to light-fiber-tear failure is observed at this process temperature. This failure mode can be attributed to the bonding temperature condition at which PEKK begins to melt.

This paper aims to develop an automatic 3D object segmentation method for the large-scale point clouds. Given a range image, the preprocessing is first applied to get the optimal 3D point cloud. A $k$-nearest neighbor is built, and a segmentation algorithm based on the conditional angular clustering technique is used to segment the objects from the point cloud. The algorithm is tested on the real point cloud datasets. The experiment results demonstrated that the developed segmentation method can be used to localize the object with the relative uncertainty of 0.27%.

In this work, polyvinylidene fluoride (PVDF) and graphene oxide (GO) composite membranes were fabricated using electrospinning technology for particulate matter (PM) filtration. The preparation conditions like GO oxidation time, electrospinning solution composition, and GO content in the composite film, and the basic properties and filtration performance of PVDF–GO films were systematically analyzed. It was found that GO with lamellar structure was of great benefit to endow the membrane with excellent mechanical properties and particle capture capacity. The as-prepared PVDF–GO membranes with GO addition of 0.6 wt.% exhibited the highest tensile strength and PM filtration efficiency. This work demonstrated that blending GO in PVDF is a feasible modification to fabricate an effective PM filtration membrane.

This paper presents a model for producing nano-microparticles by ultrasound-aided electric discharge. After machining, scanning electron microscopy (SEM) was used to check the shape and size of the nickel particles; they were found to be distributed in a few micrometers to 80 $\mu$m range. The nickel particles were regular spherical shaped, and the grain sizes of the particles were different. In addition, many small particles were attached to the surface. Various methods such as inlay polishing, nitric acid etching, and direct SEM imaging were employed to determine the hollow nickel particles such as very thin particles, large thickness grains, hollow sponge-like structures, and solid particles.

Herein, coating diamonds on WC–Co by using the hot filament chemical vapor deposition (HFCVD) method are discussed. CVD was performed for 8 h under a deposition pressure of 40 torr using various doping gases such as boron, nitrogen, and argon to control the particle size of the diamond thin films, the surface was then analyzed through scanning electron microscopy (SEM) and Raman spectroscopy. The SEM images confirmed that the diamond crystal size was reduced upon boron and argon doping. In contrast, nitrogen doping promoted the growth of diamond crystals. In the Raman spectra, the D and G bands were observed at 1332 and 1580 cm${}^{-1}$, respectively. Thus, the surface roughness can be controlled using a variety of doping gases, which may be used in tools.