Search

Additive manufacturing (AM) of ceramic particle reinforced aluminum alloy has drawn increasing attention due to the refined microstructure and improved mechanical properties in as-deposited condition. However, it is still challenging to make defect-free ceramic particle reinforced aluminum alloy deposit with desirable surface finish using wire-based AM technique because of the special thermophysical properties of the incorporated ceramic particles. In this work, a novel oscillating laser-arc hybrid additive manufacturing (OLHAM) technique was developed to fabricate TiC nanoparticles reinforced 2219 aluminum alloy deposit. The surface finish and porosity were evaluated using optical microscope and 3D XCT, respectively. Compared with wire-arc additively manufactured (WAAMed) deposit, the surface roughness and volume porosity of OLHAMed deposit decreased by 46.0 % and 88.3 %, respectively. In-situ high-speed photography was used to observe the arc and molten pool behaviors to understand the mechanism of enhanced surface finish and reduced porosity. The enhanced surface finish was attributed to smaller layer width fluctuation and higher arc stability, which resulted from the action of the hybrid heat source. The elimination of large droplet transfer, which caused pores in the WAAMed deposit, and the promotion of molten pool fluidity resulted in much lower porosity of the OLHAMed deposit.

In this work, TiC nanoparticles (TiCps) reinforced 7075 aluminium alloy was fabricated via an oscillating laser-arc hybrid additive manufacturing process. To show the beneficial effect of TiCpsaddition on microstructure and mechanical properties, a conventional 7075 aluminium alloy was also manufactured for comparison. Upon the addition of TiCps, remarkable grain refinement was achieved with a decrease in average grain size from 111.8 to 12.5 µm, and grain boundary segregation was alleviated. It was also found that many secondary phases precipitated at the grain interior in the deposit with TiCps. Owing to the refined microstructure and favourable precipitation, as-deposited 7075 aluminium alloy with TiCpsshowed enhanced tensile properties of ultimate tensile strengths of 346 and 355 MPa along scanning and build directions.

In this work, TiC nanoparticles (TiCps) reinforced 7075 aluminium alloy was fabricated via an oscillating laser-arc hybrid additive manufacturing process. To show the beneficial effect of TiCpsaddition on microstructure and mechanical properties, a conventional 7075 aluminium alloy was also manufactured for comparison. Upon the addition of TiCps, remarkable grain refinement was achieved with a decrease in average grain size from 111.8 to 12.5 µm, and grain boundary segregation was alleviated. It was also found that many secondary phases precipitated at the grain interior in the deposit with TiCps. Owing to the refined microstructure and favourable precipitation, as-deposited 7075 aluminium alloy with TiCpsshowed enhanced tensile properties of ultimate tensile strengths of 346 and 355 MPa along scanning and build directions.

The accurate assessment of hydraulic transmissivity in rock fractures filled with particles is not only a scientific challenge but also a critical need for various industrial applications. However, the intricate dynamics of particle erosion and pore clogging that govern transmissivity evolution remain largely unexplored. In this study, we experimentally examine the fluid‐driven particle migration behavior in filled fractures and its consequent impact on fracture transmissivity under various hydraulic gradients, normal stresses, and fracture apertures. We find that escalating hydraulic gradients not only intensify particle erosion through amplified fluid drag forces and hydro‐mechanical coupling effects but also lead to an increase in the size of migrating particles, thereby augmenting pore clogging. The dynamics of erosion and clogging define four distinct migration phases within the filled fractures. Variations in normal stress and initial fracture aperture significantly alter the particle arrangement and the soil structure stability within the fractures, thereby modulating the progress of particle migration in response to hydraulic gradients. The pattern of particle migration in filled fractures dictates the development of the internal pore structure and normal deformation, ultimately affecting fracture transmissivity. We propose an empirical expression to encapsulate the comprehensive evolution of fracture transmissivity across different particle migration patterns. Our research advances the understanding of fluid‐driven particle migration within filled fractures and provides a practical tool for the precise determination of hydraulic properties of fractured rocks amidst complex geological settings. Filled fractures in rock masses, serving as dominant flow channels and potential failure planes, are typically perceived to exhibit constant hydraulic transmissivity. However, this perspective oversimplifies the dynamic nature of filled fractures, where fluid flow can greatly change the hydraulic characteristics by either eroding or accumulating the internal particles. Understanding how these filling particles respond to water flow and affect fracture transmissivity is vital for many geological processes and human activities. Here, we experimentally uncover four distinct phases of particle migration within a filled fracture, instigated by the dynamics of erosion and clogging under elevated hydraulic gradients. Variations in normal stress and fracture aperture significantly influence the particle arrangement and the soil structure stability within fractures, thereby affecting particle migration characteristics across phases. On this basis, we delve into how the patterns of particle migration impact the geometric structure of the filled fracture and, thus, the fracture transmissivity. Finally, we quantitatively portray the evolution in fracture transmissivity across various particle migration scenarios using an empirical model. Our findings enhance the understanding of fluid‐driven particle migration in filled fractures and provide a path forward for accurately assessing the hydraulic properties of fractured rocks in complex geological environments. Erosion and clogging dynamics, modulated by hydraulic gradients, define four particle migration phases in stressed‐filled fracturesParticle migration patterns dictate pore structure and normal deformation, impacting fracture transmissivityAn empirical model encapsulates fracture transmissivity evolution across different particle migration patterns Erosion and clogging dynamics, modulated by hydraulic gradients, define four particle migration phases in stressed‐filled fractures Particle migration patterns dictate pore structure and normal deformation, impacting fracture transmissivity An empirical model encapsulates fracture transmissivity evolution across different particle migration patterns

In robot skill learning, the higher accuracy of trajectory reproduction, the smaller difference between the trajectory reproduced by the robot and the expected trajectory, and the higher accuracy and reliability of the robot’s task execution. In robot skill learning methods based on dynamic movement primitives, the problems are found that the tail exponential decay of Gaussian kernel function and the number of shape parameters have a great influence on the accuracy of trajectory reproduction, a high precision trajectory learning method is proposed. A novel truncation processing method is proposed to eliminate the impact of tail exponential decay, and the optimization on the number of shape parameters is used to improve the approximation of the local gradient of the target forcing term, which are combined to improve trajectory reproduction accuracy. The principle of the proposed method is described in detail. The simulation and comparison experiments are performed to verify the effectiveness of the proposed method in improving trajectory reproduction accuracy. This paper makes contributions to the field of robot skill trajectory learning and provides a promising method for improving trajectory reproduction accuracy.

Frequency-modulated continuous-wave lidar realizes 4D (three-dimensional space and velocity) imaging of the scene by emitting positive and negative frequency sweep laser signals. The premise of it is to identify the frequency points corresponding to the same target in the positive and negative sweep echo signals. For dechirp receiving, there is usually one peak in the frequency spectrum of the positive and negative sweep signals, respectively. Therefore, it is easy to identify and match the peaks. But in a complex environment, the laser beam will irradiate multiple targets at the same time. In addition, beam scanning and target motion cause the echo spectrum to broaden. The above reasons make it extremely difficult to identify and match peaks in practice. To solve this problem, the waveform-matching algorithm based on the skeleton tree is first applied to multitarget echo pairing. The basic idea of the algorithm is to quantify the target echo hierarchically to generate a skeleton tree. The generation of nodes is based on the relative amplitude of waveform peaks and reflects the characteristics of wave crests nesting. Then the similarity of the signal is determined by comparing the distance between the two signal waveform feature trees. Finally, the waveforms are matched in terms of similarity. To further substantiate the role of the proposed algorithm, imaging experiments and related comparative data for different targets have been completed. The results show that the accuracy of matching processed by the algorithm exceeds 90%, which is improved by about 50% compared with not using the algorithm for the target whose overlapping part accounts for a large proportion of itself.

We have developed cyclodextrin-catalyzed lipid exchange methods to prepare large unilamellar vesicles (LUVs) with asymmetric charge distributions, i.e., with different net charges on the lipids in the inner and outer leaflets. LUVs contained a mixture of a zwitterionic lipid (phosphatidylcholine), cholesterol, and various cationic lipids (O-ethyl phosphatidylcholine or dioleoyl-3-trimethylammonium propane) or anionic lipids (phosphatidylglycerol, phosphatidylserine, or phosphatidic acid). Symmetric and asymmetric LUVs with a wide variety of lipid combinations were prepared. The asymmetric LUVs contained cationic or anionic outer leaflets and inner leaflets that had either the opposite charge or were uncharged. The behavior of symmetric LUVs prepared with zwitterionic, anionic, or cationic leaflets was compared to those of asymmetric LUVs. Lipid exchange was confirmed by quantitative thin-layer chromatography, and lipid asymmetry by a novel assay measuring binding of a cationic fluorescent probe to the LUV outer leaflet. For both symmetric and asymmetric LUVs, the level of entrapment of the cationic drug doxorubicin was controlled by the charge on the inner leaflet, with the greatest entrapment and slowest leakage in vesicles with an anionic inner leaflet. This shows that it is possible to choose inner leaflet lipids to maximize liposomal loading of charged drugs independently of the identity of outer-leaflet lipids. This implies that it should also be possible to independently vary outer-leaflet lipids to, for example, impart favorable bioavailability and biodistribution properties to lipid vesicles.

In space defense, utilizing the micromotion features to distinguish real targets from interfering targets and decoys is effective. Due to the imaging of the high-speed precession target by microwave radar consisting of isolated scattering centers, there are many difficulties in using inverse synthetic aperture radar (ISAR) images for feature extraction. On the other hand, the inverse synthetic aperture ladar (ISAL) image is relatively continuous because of the short wavelength of laser, and the image sequence contains information about the variation in image length and Doppler width caused by target precession, which can be used for inverse motion parameters. By establishing an observation model of the precession target and performing image processing on the obtained ISAL image at different times, the image length sequence and Doppler width sequence can be obtained. Using the ellipse fitting method to process the obtained sequence, the precession parameters of the target can be obtained. The algorithm does not require prior information such as the radius and speed of the target motion, effectively improving the practicability of the algorithm. Finally, the effectiveness of the algorithm is verified by experimental results, and the error is controlled within 2%.

New types of diodes, such as molecular and ionic diodes, have drawn considerable attention because of their advantages from the viewpoint of potential applications such as the downscaling of electronic devices, ionic circuits, and biological systems. Researchers are motivated to develop a simple, scalable, and promising system that can overcome the existing limitations because this can enable their application in various devices. This study proposes a system that not only integrates the advantages of ionic and single-molecule diodes but also avoids their disadvantages, denoting the rectification behavior due to ionic charge-selective electron transfer between two redox species, i.e., Fe(CN)63–and Ru(NH3)63+, on the polyelectrolyte multilayer (PEM)-modified flexible indium tin oxide (ITO) electrodes. Flexible current rectification devices were easily prepared by sandwiching an electrolytic solution of ionic redox species using bare and PEM-modified plastic ITO electrodes. An ionic bilayer was initially formed via Coulombic interactions on a PEM-modified charge-selective ITO surface. The ionic bilayer was analogous to a conventional single-molecule diode’s monolayer with consecutive molecular orbitals of two ionic redox species. Furthermore, the rectification ratio (RR) was increased from ∼6 to ∼10 using a conducting polymer to construct PEMs.

A sensitive and selective electrochemical biosensor was fabricated for polynucleotide kinase (PNK) activity assay and inhibitor screening based on phos-tag-biotin mediated double signal amplification, where streptavidin and alkaline phosphatase-conjugated biotin (biotin-ALP) were used as the signal amplification units. After the immobilization of probe DNA on the electrode surface, it was hybridized with complementary DNA containing the 5′-OH terminal, the OH can be phosphorylated under the catalytic effect of PNK in the presence of ATP. The generated phosphate group at the 5′-terminal can be further recognized by phos-tag-biotin, where phos-tag-biotin was not only used as the specific recognition reagent for the phosphate group, but also the capture reagent for streptavidin to induce the further assembly of biotin-ALP. Under the catalytic effect of ALP, the substrate of p-nitrophenyl phosphate disodium salt hexahydrate (PNPP) can be hydrolyzed to produce p-nitrophenol (PNP). According to the relationship between the electrochemical response of PNP and the logarithmic value of PNK concentration, a linear range of 0.01–5 units per mL and a low detection limit of 0.0027 unit per mL were achieved. The developed method showed high selectivity. The inhibition effect of (NH4)2SO4and Na2HPO4was also evaluated and the IC50values were calculated.