Dyeing wastewater poses a serious threat to environmental protection and industrial development. The piezoelectric effect can be used to optimize the band structure of semiconductors and improve the photon efficiency of photocatalysts. Bi2Fe4O9, a narrow gap semiconductor with piezoelectric effect, was prepared by a hydrothermal synthesis method for the degradation of reactive dye KN-R. The results show that the degradation efficiency of KN-R can be significantly improved by piezophotocatalysis, and the degradation rate constant of piezophotocatalysis kpi-phis about 3. 4 times as large as the degradation rate constant of piezoelectric catalysis kpiand about 2. 6 times as large as the degradation rate constant of photocatalysis kph. At a pH value of 3 and a lower KN-R mass concentration(60 mg/L), a higher degradation efficiency(98. 5%) is achieved. CO32-and cationic surfactant(CTAB) inhibit the degradation of KN-R. It is proved that the contributions of different active species to the degradation of KN-R follow the order: ·OH, ·O2~-, h+,and ~1O2. The possible mechanism of piezo-photocatalytic degradation of KN-R was discussed. The photoexcitation generates a large amount of free charges, and the piezoelectric effect modulates the energy band structure of Bi2Fe4O9 and promotes the separation of photogenerated electron-hole pairs. The synergistic effect of the two factors significantly improves the degradation efficiency of KN-R.
The research, fabrication and development of piezoelectric nanofibrous materials offer effective solutions to the challenges related to energy consumption and non-renewable resources. However, enhancing their electrical output still remains a significant challenge. Here, a strategy of inducing constrained phase separation on single nanofibers via shear force was proposed. Employing electrospinning technology, a polyacrylonitrile/polyvinylidene difluoride(PAN/PVDF) nanofibrous membrane was fabricated in one step, which enabled simultaneous piezoelectric and triboelectric conversion within a single-layer membrane. Each nanofiber contained independent components of PAN and PVDF and exhibited a rough surface. The abundant frictional contact points formed between these heterogeneous components contributed to an enhanced endogenous triboelectric output, showcasing an excellent synergistic effect of piezoelectric and triboelectric response in the nanofibrous membrane. Additionally, the component mass ratio influenced the microstructure, piezoelectric conformation and piezoelectric performance of the PAN/PVDF nanofibrous membranes. Through comprehensive performance comparison, the optimal mass ratio of PAN to PVDF was determined to be 9 ∶1. The piezoelectric devices made of the optimal PAN/PVDF nanofibrous membranes with rough nanofiber surfaces generated an output voltage of 20 V, which was about 1. 8 times that of the smooth one at the same component mass ratio. The strategy of constrained phase separation on the surface of individual nanofibers provides a new approach to enhance the output performance of single-layer piezoelectric nanofibrous materials.
MXene is an emerging class of two-dimensional (2D) layered transition metal carbides or nitrides. Due to the highly tunable components and surface functional groups, it holds great potential in electrocatalytic hydrogen evolution reaction (HER). However, MXene nanosheet suffers from a strong tendency to restack and a lack of active edge sites. In this work, the porous Ti3C2Tx was synthesized by an oxidation and etching two-step strategy and then characterized by a series of spectroscopic techniques. The obtained porous Ti3C2Tx possesses a large number of in-plane pores. This not only creates abundant active edge sites but also enhances the mass transfer and increases the accessibility of the active sites. Compared with Ti3C2Tx, in a 0. 5 mol/L H2SO4 electrolyte, the porous Ti3C2Tx shows a 65. 6% higher electrochemical surface area (ECSA) (440 mF/cm2), a 95. 2% lower charge transfer resistance (12. 8 Ω), and a 69. 8% lower Tafel slope (144 mV/dec), and thus exhibits lower overpotential with good stability at a current density of 10 mA/cm2. At the same time, the HER performance of the porous Ti3C2Tx can be further enhanced by near-infrared laser irradiation based on the localized surface plasmon resonance effect.
A new suspension gravity compensation system has been developed to alleviate the gravity effects on a twodimensional(2D)deployable mechanism for ground verification. Considering the rigid-flexible coupling of both the rotating servo and the suspension system, a multi-body dynamic model simulating their integration is established using Lagrange's equation. To mitigate instantaneous impact forces due to significant non-plumb effects from passive following in the horizontal direction, an elastic element is added in series with the rope in the vertical suspension system. The dynamic response of this elastic element relative to the rotating servo system is analyzed by the ADAMS software. Simulation results show that the compensating error decreases significantly from 45% to 0. 31% when incorporating elastic elements compared to scenarios without such elements. Additionally, low-stiffness elastic elements demonstrate a higher compensating error than high-stiffness ones. A spring with a stiffness coefficient of 6 N/mm is selected in the experiment, ensuring that compensating error meets the design specification of 5%.
The agitated thin-film evaporator(ATFE) plays a crucial role in evaporation and concentration processes.The design of the scraper for processing high-viscosity non-Newtonian fluids in the ATFE is complex. The intricate scraping action of the scraper introduces gas into the liquid film, leading to the formation of a gas ring along the wall.This process subsequently reduces wall heat flow, thereby affecting heat transfer. Computational fluid dynamics(CFD) is used to simulate the flow field of the non-Newtonian fluid in the ATFE. The investigation focuses on understanding the mechanism behind the formation of gas rings in the liquid film and proposes methods to prevent their formation. The results demonstrate a transition of the gas from a gas ring suspended in the liquid to a gas ring attached to the wall after entering the liquid film. The scraping action around the circumference of the scraper helps to expel gas rings, indicating the necessity of adjusting the scraper arrangement and increasing the frequency of scraping to enhance gas ring expulsion. The spiral motion of the bow wave serves as the source of gas entry into the liquid film. Therefore, the rotation speed can appropriately increase to reduce the size of the bow wave, thereby inhibiting the formation of the gas ring from the source.This research investigates the mechanism of gas ring generation and expulsion, offering theoretical guidance for processing high-viscosity non-Newtonian materials in the flow field of the ATFE.
A small quasi-zero stiffness(QZS) vibration isolator is designed to be mounted on the roof of an agricultural vehicle for the working environment and vibration frequency of the inertial navigation system. By using the principle that the Euler beam has a negative stiffness in the critical state, the dynamic stiffness of the loaded QZS vibration isolator in the balance position tends to be close to zero by connecting a vertical spring in parallel. Firstly, the stiffness of the QZS vibration isolation system at the balance position is analyzed statically, and the material parameters and properties of the Euler beam are determined. Then, the dynamic equations are established,and the harmonic equilibrium method is used to solve the dynamic response under sinusoidal excitation to obtain the force transmissibility of the QZS vibration isolation system,and to make a comparison with that of the linear isolation system. Finally, the modal simulation, harmonic response simulation and random vibration simulation of the QZS vibration isolator are carried out through the finite element analysis, and the results show that the QZS vibration isolator has a lower initial isolation frequency and a larger isolation range, and the peak vibration isolation can reach about 11. 58 dB.
The active sound absorption technique excels in mitigating low-frequency sound waves, yet it falls short when dealing with medium and high-frequency sound waves. To enhance the sound-absorbing effect of medium and high-frequency sound waves, a novel semi-active sound absorption method has been introduced. This method modulates the surface impedance of a loudspeaker positioned behind the sound-absorbing material, thereby altering the sound absorption coefficient. The theoretical sound absorption coefficient is calculated using MATLAB and compared with the experimental one. Results show that the method can effectively modulates the absorption coefficient in response to varying incident sound wave frequencies,ensuring that it remains at its peak value.
To enhance the hydrophilicity and antistatic properties of the polyethylene terephthalate(PET) fabric,the lawsone dye was employed in dyeing the PET fabric. It was dissolved in ethanol/deionized water mixture and deionized water separately, forming different lawsone dye solutions(LDSs). The study investigated how the compounds in the LDS improve the surface properties and color durability of the PET fabric, resulting in increased dye uptake. An infrared dyeing machine was utilized to expedite the reactions between the lawsone dye and the PET fabric.Additionally, the chemical composition of the dyed PET fabric was verified using techniques such as Fourier transform infrared(FTIR)spectroscopy,X-ray photoelectron spectroscopy(XPS), X-ray diffraction(XRD) and ultraviolet-visible(UV-Vis) spectrophotometry.The K/S value was measured to assess color durability.After dyeing, the PET fabric exhibited high hydrophilicity which improved the hygroscopicity of the PET fabric and thus the conductivity of the PET fabric surface increased,thereby providing an antistatic effect.
Pulmonary nodules represent an early manifestation of lung cancer. However, pulmonary nodules only constitute a small portion of the overall image, posing challenges for physicians in image interpretation and potentially leading to false positives or missed detections. To solve these problems, the YOLOv8 network is enhanced by adding deformable convolution and atrous spatial pyramid pooling(ASPP), along with the integration of a coordinate attention(CA) mechanism. This allows the network to focus on small targets while expanding the receptive field without losing resolution. At the same time, context information on the target is gathered and feature expression is enhanced by attention modules in different directions. It effectively improves the positioning accuracy and achieves good results on the LUNA16 dataset. Compared with other detection algorithms, it improves the accuracy of pulmonary nodule detection to a certain extent.
Video classification is an important task in video understanding and plays a pivotal role in intelligent monitoring of information content. Most existing methods do not consider the multimodal nature of the video, and the modality fusion approach tends to be too simple, often neglecting modality alignment before fusion. This research introduces a novel dual stream multimodal alignment and fusion network named DMAFNet for classifying short videos. The network uses two unimodal encoder modules to extract features within modalities and exploits a multimodal encoder module to learn interaction between modalities. To solve the modality alignment problem, contrastive learning is introduced between two unimodal encoder modules.Additionally, masked language modeling(MLM) and video text matching(VTM) auxiliary tasks are introduced to improve the interaction between video frames and text modalities through backpropagation of loss functions.Diverse experiments prove the efficiency of DMAFNet in multimodal video classification tasks. Compared with other two mainstream baselines, DMAFNet achieves the best results on the 2022 WeChat Big Data Challenge dataset.
End-to-end object detection Transformer(DETR) successfully established the paradigm of the Transformer architecture in the field of object detection. Its end-to-end detection process and the idea of set prediction have become one of the hottest network architectures in recent years. There has been an abundance of work improving upon DETR. However, DETR and its variants require a substantial amount of memory resources and computational costs, and the vast number of parameters in these networks is unfavorable for model deployment. To address this issue, a greedy pruning(GP) algorithm is proposed, applied to a variant denoising-DETR(DN-DETR), which can eliminate redundant parameters in the Transformer architecture of DN-DETR. Considering the different roles of the multi-head attention(MHA) module and the feed-forward network(FFN) module in the Transformer architecture, a modular greedy pruning(MGP) algorithm is proposed. This algorithm separates the two modules and applies their respective optimal strategies and parameters. The effectiveness of the proposed algorithm is validated on the COCO 2017 dataset. The model obtained through the MGP algorithm reduces the parameters by 49% and the number of floating point operations(FLOPs) by 44% compared to the Transformer architecture of DN-DETR. At the same time, the mean average precision(m AP) of the model increases from 44. 1% to 45. 3%.