摘要：
Purpose This paper is concerned with the H-infinity optimization design of passive and active dynamic vibration absorbers (DVAs) attached to an undamped or damped primary system.Methods The proposed optimization method is an efficient non-smooth H-infinity-synthesis algorithm that is utilized to solve structured H-infinity-synthesis in control engineering. This method can conveniently achieve the optimal design for the amplitude magnification factors of both the absolute and the relative displacements of a DVA using the proposed dual H-infinity design, and implement co-design of H-infinity-optimal proportional-integral-differential controllers and passive parameters of an active DVA.Results Two active DVAs and two variant passive DVAs reported in the literature are taken as examples for design improvement. The optimization results indicate that the proposed method has significant advantages over the conventional fixed points-theory-based methods and many numerical global optimization methods.Conclusions The proposed H-infinity optimization design yields much better vibration suppression result for proportional-integral differential control based active DVAs and variant passive DVAs with complicated structures. It is directly based on their equations of motion in state-space forms, and explicit formulations of various amplitude magnification factors, such as those on the absolute and the relative displacements and active force, need not be derived in the MATLAB environment. A possible situation of occurrence of large amplitude of the relative displacement in DVAs rarely considered in the literature can be handled by using the proposed dual H-infinity design.
摘要：
adipate terephthalate (PBAT) as matrix and zinc oxide nanoparticles (ZnONPs) and silver nanoparticles (AgNPs) as antibacterial agents, a series of antibacterial PLA/PBAT films were prepared by melt blending. The weight ratio of PLA, PBAT and nanoparticles in composite films was 70:900:10 (lower loading) or 70:900:20 (higher loading). The results showed that comparing with the PLA/PBAT films, the hydrophilicity, oxygen barrier properties, mechanical performance and antibacterial activities of PLA/PBAT/nanoparticles films were significantly improved (P < 0.05), and influenced by the content and type of nanoparticles. After the addition of nanoparticles, the maximum change of films performance was from 71.3 degrees to 35.8 degrees for water contact angle, from 7.4 x 10(-14) cm(3) cm.cm(-2). s(-1). Pa-1 to 5.5 x 10(-14) cm(3) cm.cm(-2). s(-1). Pa-1 for oxygen transmission permeability, from 26.4 MPa to 31.4 MPa for tensile strength, and from 0% to 57.8% (Escherichia coli) or 58.6% (Staphylococcus aureus) for antibacterial ratio. The films with higher loading content of nanoparticles showed a better antibacterial activity. For the same nanoparticles content, the antibacterial activity of PLA/PBAT/AgNPs was better than PLA/PBAT/ZnONPs. The overall migration in food simulants involving acetic acid (3%) ethanol (10% and 95%) was below 10 mg/dm(2) for most films, however, the overall migration for the films with higher content of AgNPs exceeded the limit value. The fresh noodles packaged by PLA/PBAT/AgNPs films showed the significant lowest total viable count with 4.6 lg (CFU/g) and the best appearance color characterized by L* (lightness), a*(red-green) and b*(yellow-blue) at storage time of 7 d in contrast with PLA/PBAT and PLA/PBAT/ZnONPs films, indicating the potential application of prepared films in active packaging to prolong the shelf life of food.
通讯机构：
[Shen, SN ; Li, H ; Li, H] W;Wuhan Univ, Sch Power & Mech Engn, Wuhan 430072, Peoples R China.;Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430048, Peoples R China.
关键词：
Laser powder bed fusion;Laser ultrasonic detection;Surface roughness;Internal holes;Longitudinal wave
摘要：
In view of the non-destructive and non-contact features, laser ultrasonic (LU) technology has long been the effective method to detect tiny defects for laser powder bed fusion (LPBF) additive manufactured specimens. Of larger concern is the variation and the corresponding mechanism on tested results of LU detection as the property of LPBF additive manufactured specimen is changed. Aiming at the property of surface roughness, this work investigated the propagation characteristics of excited ultrasonic waves in LPBF additive manufactured 316L stainless steel with different surface roughness, as well as the interaction between ultrasonic waves and artificial submillimeter holes. Both numerical simulated and experimental study were conducted. Simulated results revealed that the amplitudes of longitudinal wave (L wave) and its echo wave L1 at the holes exhibited a discernible increase as the surface was coarser. The increase in surface roughness was detrimental to the resolution of defect detection as was expected from the increased amount of noise. LPBF fabrication and the subsequent LU pulse-echo detection were conducted for 316L stainless steel. Both B-scan and C-scan were able to detect the holes with the diameter of 0.6 mm. The speckle phenomenon deriving from the increase in surface roughness emerged, corresponding to the increased ultrasonic signal energy but deteriorated resolution of detected images. It is feasible to optimize LU detected effect by minimize the surface roughness of tested specimens.
摘要：
Anthocyanin extracts from purple tomato (PTA) were incorporated with polyvinyl alcohol (PVA), resulting in a series of colorimetric PVA/PTA films with PTA concentrations of 0%, 1%, 3%, and 5% (based on PVA). The role of anthocyanin on color response, Fourier-transform infrared (FTIR), thickness, water content, mechanical properties, antioxidant activity, and water vapor permeability (WVP) through the films was examined. In addition, its application in smart packaging to assess the freshness of shrimp was studied. It was found that the tensile strength, contact angle and WVP of PVA/PTA films increases with the addition of more PTA, while the elongation at break and water content decreased. FTIR analysis showed that there are interactions between PTA and the PVA matrix. The addition of anthocyanins caused significant improvement in the antioxidant properties of PVA films. Furthermore, the total volatile alkaline nitrogen (TVB-N), total plate count (TPC), and pH value of shrimp were monitored after 4 days of refrigeration, and the color change of the indexes was recorded. The PVA/PTA films changed color from purple to yellow-green during the storage time of 0-4 days for shrimp. This suggests that the film could be used in smart packaging as a real-time freshness indicator for shrimp.
关键词：
Beam shaping;Femtosecond lasers;Lithium niobate;Nonlinear frequency conversion;Nonlinear photonic crystals;Ultrafast lasers
摘要：
We experimentally extend the nonlinear Gaussian to flattop beam shaping from one to two dimensions through a three-dimensional nonlinear photonic crystal. Employing a near -infrared femtosecond laser, we induce a modification inside lithium niobate to achieve a second -order nonlinear optical coefficient modulation in three dimensions. The flat-topped truncation of wavefront has been adjusted in a mutual perpendicular coordinate separately. Among the generated flat-topped beams, the optimal flatness is 97.1%, and the nonlinear conversion efficiency is 10-2 at the peak power of 37 kW with the interaction length of 630 mu m. By adding an extra dimension, our work simultaneously enables full-wavefront flat -top distribution and nonlinear frequency conversion. (c) 2024 Optica Publishing Group
通讯机构：
[Li, B ] W;Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430023, Hubei, Peoples R China.
摘要：
Deep eutectic solvents (DES) were prepared using urea (U) and acrylamide (AM) as hydrogen bond donors (HBD) and choline chloride (ChCl) as hydrogen bond acceptor (HBA), and polyethylene glycol (PEG) was selected as a filler and uniformly dispersed in DES to prepare PEG/P(U-AM-ChCl) composite hydrogels by light polymerization. The composite hydrogels were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The effects of the content of PEG on the swelling properties, mechanical properties and fatigue resistance of the composite hydrogels were investigated. The results showed that the compressive strength and fatigue strength of the composite hydrogels were gradually enhanced with the increase of the PEG content in the composite hydrogels, in which the maximum compressive strength of the hydrogels with 1 wt% PEG added was increased by 1.86 times. The composite hydrogel had excellent swelling properties, and the equilibrium swelling degree of the hydrogel with 1 wt% PEG added reached 10.15. Meanwhile, the PEG/P(U-AM-ChCl) composite hydrogel had excellent self-healing properties, and the self-healing rate of the composite hydrogel with a PFG content of 1 wt% could reach 91.93% after 48 hours of healing. This study provides a convenient and efficient method to prepare composite hydrogels with superior swelling properties and self-healing properties. Deep eutectic solvents (DES) were prepared using urea (U) and acrylamide (AM) as hydrogen bond donors and choline chloride (ChCl) as hydrogen bond acceptor. Polyethylene glycol (PEG) was selected as a filler and uniformly dispersed in DES to prepare PEG/P(U-AM-ChCl) composite hydrogels.
摘要：
Selective laser melting (SLM) additive manufacturing technology with different oxygen contents leads to the appearance of spherical solids of different sizes on the surface of the part, which affects the mechanical properties of the part, surface roughness, etc. In this study, the SLM molding technique was applied using three different 316L metal powders with different oxygen contents. The spheroidization properties and morphology of the samples were observed using a Quanta 200 environmental scanning electron microscope (ESEM), and the samples were observed microscopically and subjected to EDX spectroscopy using metallographic microscopy, and the mechanical properties were investigated. The results of the study showed that when using gas atomized powders, no spheroidization occurred when the oxygen content of the powders was 5.44 +/- 0.01% in all cases, whereas using water atomized powders produced spherical structures with larger dimensions. This observation was closely related to the shape and particle size of the powder. When 316L metal powder with an oxygen content of 4.52 +/- 0.01% was used for molding, small spherical structures appeared on the surface of the samples. When metal powder with an oxygen content of 5.44 +/- 0.01% was used for the molding, larger spherical structures appeared on the surface of the samples. When the powder with an oxygen content of 5.90 +/- 0.01% was used for the molding, more small spherical structures and some large spherical structures appeared on the surface of the samples. This suggests that higher oxygen levels may inhibit the occurrence of spheroidization. EDX spectroscopic analysis revealed that the white matter on the surface of the samples without spheroidization was mainly composed of Fe and Cr, whereas the white matter on the surface of the large-sized spherical structures was mainly composed of Si and Mn, which may be related to the oxygenophilicity of the various substances. Selective laser melting (SLM) additive manufacturing technology with different oxygen contents leads to the appearance of spherical solids of different sizes on the surface of the part, which affects the mechanical properties of the part, surface roughness, etc.
关键词：
Freshwater fish;head and tail;ICNet;image segmentation;manipulator
摘要：
Pre-treatment processing technology plays a crucial role in the overall freshwater fish processing procedure, and automatic head and tail cutting stands out as a significant pre-treatment technique within the industry. The system for removing the head and tail of freshwater fish comprised a Cartesian coordinate manipulator, a fish transfer device, a control system, and an image acquisition device. In the vision system, five image segmentation methods were utilized for fish head and tail image segmentation comparison tests. These methods include U-Net (U-shaped Deep Neural Network), DeeplabV3, PSPNet (Pyramid Scene Parsing Network), FastSCNN (Fast Semantic Segmentation Network), and ICNet (Image Cascade Network), all of which were employed to evaluate their performance. Among the tested segmentation methods, the ICNet demonstrated the most excellent segmentation capability. The experimental results indicated a segmentation accuracy of 99.01%, a mean intersection over union (MIoU) of 82.50%, and an image processing time of 15.25 ms. The results showed that the fish head and tail were successfully cut off using this model for recognition with a circular knife. Consequently, the segmentation model employed in the machine vision system within this study has demonstrated successful applicability in automatically cutting the heads and tails of freshwater fish of various sizes.
摘要：
PurposeThis paper aims to identify the optimal forming angle for the selective laser melting (SLM) process and evaluate the mechanical properties of the SLM-formed GH3536 alloy in the aero-engine field.Design/methodology/approachForming the samples with optimized parameters and analyzing the microstructure and properties of the block samples in different forming angles with scanning electron microscope, XRD, etc. so as to analyze and reveal the laws and mechanism of the block samples in different forming angles by SLM.FindingsThere are few cracks on the construction surface of SLM formed samples, and the microstructure shows columnar subgrains and cellular subgrains. The segregation of metal elements was not observed in the microstructure. The pattern shows strong texture strength on the (111) crystal plane. In the sample, the tensile strength of 60 degrees sample is the highest, the plasticity of 90 degrees forming sample is the best, the comprehensive property of 45 degrees sample is the best and the fracture mode is plastic fracture. The comprehensive performance of the part is the best under the forming angle of 45 degrees. To ensure the part size, performance and support structure processing, additional dimensions are added to the part structure.Originality/valueIn this paper, how to make samples with different forming angles is described. Combined with the standard of forged GH3536 alloy, the microstructure and properties of the samples are analyzed, and the optimal forming angle is obtained.
通讯机构：
[Shen, SN ; Li, H] W;Wuhan Univ, Inst Technol Sci, Wuhan 430072, Peoples R China.
关键词：
Laser powder bed fusion;Laser ultrasonic;Thermo-elastic regime;Internal defect
摘要：
In the development of additive manufacturing (AM) technology, laser powder bed fusion (LPBF) is one of the important processing methods. However, the hole defects in the fabricated samples limit the development. Laser ultrasonic (LU) technology plays a major role in the detection of LPBF parts with tiny defects, which has the advantages of non-contact and non-destructive. In this work, the detection of submillimeter internal defects in four typical LPBF alloys by LU technology is studied numerically and experimentally. A multiphysics simulation model of LU detection is established to investigate the propagation characteristics of excited ultrasonic waves in different LPBF alloys and their interaction with submillimeter artificial defects. Simulation results show that the amplitude of longitudinal (L) wave at the defect is the largest in AlSi10Mg alloy, and the amplitude of L wave in the 316L alloy, Ti6Al4V alloy and In718 alloy are very close, but their phases are slightly different. The amplitude of L wave tends to decrease nearly linearly with the increase in defect diameter. Then, four typical LPBF alloys are fabricated and measured by the LU through-transmission detection. The geometric information of artificial holes with a diameter larger than 0.2 mm are clearly characterized by the LU C-scan results, indicating the prominent applicability and feasibility of LU detection on different materials fabricated by LPBF.
关键词：
Near -Infrared spectroscopy;Rapid non-destructive detection;Grass carp fillets;Total volatile basic nitrogen;Machine learning;Orthogonal signal correction (OSC);Particle swarm optimization algorithm;optimized BP neural network (PSO-BP)
摘要：
This research aims to accurately forecast the freshness indicators (TVB-N) of skinned and skinless grass carp fillets by integrating near-infrared spectroscopy (NIR) with machine learning algorithms. By comparing the predictive accuracy of machine learning models for the two types of grass carp fillets, the most effective modeling method is identified. Methodologically, the study first applies orthogonal signal correction (OSC) and the first derivative among other algorithms for spectral pre-processing. Subsequently, competitive adaptive reweighted sampling (CARS), moving window partial least squares (MWPLS), and random frog (RF) are used for the selection of variables. Lastly, partial least squares regression (PLSR), support vector regression (SVR), backpropagation neural networks (BPNN), and particle swarm optimization-enhanced BP neural networks (PSO-BP) are employed to quantitatively analyze the NIR data. The most relevant results reveal that the (OSC+D1)-CARS-PSO-BP model exhibits superior predictive capabilities. Especially when applied to skin-on fish fillets (R2P =0.988, RMSEP=0.092), this model surpasses that for skinless fish fillet data (R2P =0.987, RMSEP=0.096). Therefore, combining near-infrared with machine learning to predict the freshness (TVB-N) of grass carp fillets based on skin-on samples is a more effective non-destructive testing method.
期刊：
Journal of Cleaner Production,2024年440:140972 ISSN：0959-6526
通讯作者：
Wang, JJ
作者机构：
[Cao, Rui; Wang, Jiaojiao] Zhoukou Normal Univ, Coll Mech & Elect Engn, Zhoukou 466001, Peoples R China.;[Wang, Qiaohua] Huazhong Agr Univ, Coll Engn, Wuhan 430070, Peoples R China.;[Ma, Meihu] Huazhong Agr Univ, Natl Res & Dev Ctr Egg Proc, Wuhan 430070, Peoples R China.;[Fu, Dandan] Wuhan Polytech Univ, Coll Mech Engn, Wuhan 430048, Peoples R China.
通讯机构：
[Wang, JJ ] Z;Zhoukou Normal Univ, Coll Mech & Elect Engn, Zhoukou 466001, Peoples R China.
关键词：
Egg;Respiration;Reutilization of unfertilized eggs;Dead embryo;Classification and identification
摘要：
Respiration plays a crucial role in the physiological development of embryos throughout the entire incubation process and serves as a vital indicator for discerning unfertilized eggs and embryos that have stopped development. This article explores the relationship between egg respiration, fertilization status, and chicken embryo viability. First, it studied the changes in respiration of fertilized and unfertilized eggs during the early stages of incubation (Day 1–3) and found that the CO2 production of fertilized eggs gradually increased, while those of unfertilized eggs gradually decreased. Moreover, significant differences in respiration between fertilized and unfertilized eggs were observed on the second day of incubation. Next, we employed Random Forest (RF), Logistic Regression (LR), and Support Vector Machine (SVM) models to differentiate between fertilized and unfertilized eggs. Notably, the SVM algorithm exhibited exceptional performance in discriminating between fertilized and unfertilized eggs, achieving a remarkable test set accuracy of 98.41 %. Finally, a Bayesian algorithm was applied to classify embryos as either dead, weak, or viable in middle and later stages of incubation. Bayesian discriminant analysis yielded compelling results, achieving a 100 % detection rate for deceased embryo eggs. The outcomes of this study provide a robust theoretical foundation and empirical data to advance non-destructive testing methodologies for poultry eggs.
摘要：
This study utilises the transfer matrix method (TMM) to address the acoustic characteristics of multilayered cylindrical shells lined with porous materials. The TMM theoretical model for the sound transmission loss of composite cylindrical shells with internal porous materials is derived by establishing transfer matrices for the air/composite material interface, composite material/foam interface, foam/air interface and boundary interfaces. The accuracy of the TMM model is validated through a comparison and analysis with experimental results. Building upon this, the impact of porous foam material parameters and types on the structural sound transmission loss is discussed. The results indicate that the use of TMM accurately reflects the acoustic performance of composite structures. Additionally, this model allows for the determination of the influence patterns of porous foam material parameters and types on the acoustic performance of composite structures. In the frequency range of 100-10,000 Hz, the sound transmission loss of the melamine foam-lined composite structure increases with the increase in flow resistance and porosity and the decrease of the tortuosity factor. The use of the porous lining material significantly enhances the structural sound insulation performance.
摘要：
Edge -dependent states in electronic and synthetic graphenes have stimulated extensive research interests in recent years. The orbital degree of freedom (ODOF), facilitating the understanding of exotic phenomena in condensed matter, supplies a powerful base to explore boundary topological properties, which has not yet been investigated extensively in classical -wave realms such as acoustic systems. Here, we experimentally demonstrate orbital -dependent acoustic twig edge states in multi-ODOF systems as degenerate -orthogonal p orbitals are introduced. We analyze and discuss the band structures of orbital strip supercell lattices with the twig and zigzag edges by using the tight -binding method (TBM) and full -wave simulation (FWS). We visualize fourfold zero -energy orbital twig edge states that form the complete flat band across the Brillouin zone, characterized by nontrivial topological windings. Moreover, we unravel the selective excitation of the orbital twig edge states in experiments. Our findings advance the field for understanding the interplay between graphene edge states and acoustic orbitals as well as broaden the potential application opportunities of Dirac materials such as trapping and sensing.
摘要：
As an advanced time-frequency (TF) decomposition (TFD) method, variational nonlinear chirplet mode decomposition (VNCMD) decomposes the original signal into a series of nonlinear chirplet modes (NCMs), such that the inherent characteristic information contained in the signal can be revealed effectively. However, the decomposition ability of VNCMD is largely affected by the prior instantaneous frequency (IF) and the pre-set parameters. In practical engineering applications, the presence of noise and interference components often complicates the accurate determination of prior IFs and appropriate decomposition parameters. Considering the above issues, in order to precisely extract the NCMs and realize the effective analysis of mechanical vibration signals, this paper mainly focuses on the drawbacks of accurate prior IF and the decomposition parameters of VNCMD, and proposed an improved version via local maximum synchrosqueezing transform and a recursive mode extracting scheme. The performance of the proposed method is evaluated through simulation cases, and the results demonstrate its effectiveness. Finally, the proposed method is successfully applied to bearing data analysis and rub-impact fault detection.
摘要：
During the rice milling process, single and continuous compression occurs between brown rice and the processing parts. When the external load exceeds the yield limit of brown rice, brown rice kernels are damaged; with an increase in compression deformation or the extent of compression, the amount of damage to the kernels expands and accumulates, ultimately leading to the fracture and breakage of kernels. In order to investigate the mechanical compression damage characteristics of brown rice kernels under real-world working conditions, this study constructs an elastic-plastic compression model and a continuous damage model of brown rice kernels based on Hertz theory and continuous damage theory; the accuracy of this model is verified through experiments, and the relevant processing critical parameters are calculated. In this study, three varieties of brown rice kernels are taken as the research object, and mechanical compression tests are carried out using a texture apparatus; finally, the test data are analysed and calculated by combining them with the theoretical model to obtain the relevant critical parameters of damage. The results of the single compression crushing test of brown rice kernels showed that the maximum destructive forces F(c) in the single compression of Hunan Early indica 45, Hunan Glutinous 28, and Southern Japonica 518 kernels were 134.77 ± 11.20 N, 115.64 ± 4.35 N, and 115.84 ± 5.89 N, respectively; the maximum crushing deformations α(c) in the single compression crushing test were 0.51 ± 0.04 mm, 0.43 ± 0.01 mm, and 0.48 ± 0.17 mm, respectively; and the critical average deformations α(s) of elasticity-plasticity deformation were 0.224 mm, 0.267 mm, and 0.280 mm, respectively. The results of the continuous compression crushing test of brown rice kernels showed that the critical deformations α(d) of successive compression damage formation were 0.224 mm, 0.267 mm, and 0.280 mm, and the deformation ratios δ of compression damage were 12.24%, 14.35%, and 12.84%. From the test results, it can be seen that the continuous application of compression load does not result in the crushing of kernels if the compression deformation is less than α(d) during mechanical compression. The continuous application of compressive loads can lead to fragmentation of the kernels if the compressive deformation exceeds α(d); the larger the compression variant, the less compression is required for crushing. If the compression deformation exceeds α(c), then a single compressive load can directly fragment the kernels. Therefore, the load employed during rice milling should be based on the variety of brown rice used in order to prevent brown rice deformation, which should be less than α(d), and the maximum load should not exceed F(c). The results of this study provide a theoretical reference for the structure and parameter optimisation of a rice milling machine.
摘要：
This study explores the influence of various ultrasound treatment parameters and microwave drying parameters on the quality and drying characteristics of rice. The rice was treated in an ultrasound water bath (200W) for 30 min, 40 min, and 50 min, followed by microwave drying (210W) for 10 min. The influence of ultrasound treatment time on the moisture content variation of rice was found to be significant through correlation analysis. The time required for the 50 -min ultrasound treatment to reach the safe moisture level (15 %) was approximately 20 % shorter than the time required for the 30 -min ultrasound treatment. Due to the combined ultrasoundmicrowave treatment, changes occur in the constituents of rice (Starch gelatinization, Maillard reaction, etc.), and the variations in rice quality can be reflected by the changes in CIE Lab color parameters. The differences in characteristic peaks of Fourier Transform Infrared Spectroscopy (FTIR) can reflect the variations in flavor and aroma of rice, as well as the significant disruption of the ordered structure of starch molecules. Additionally, response surface experiments based on Box-Behnken design were conducted to obtain the optimal conditions for ultrasound-microwave combined treatment (240W, 46min, 3min). Moreover, ultrasound-microwave combined treatment leads to a significant reduction in rice hardness and an increase in elasticity.
期刊：
Journal of Materials Science,2024年59(2):715-727 ISSN：0022-2461
通讯作者：
Li, B
作者机构：
[Wu, Aolin; Li, B; Li, Bin; Su, Lihua; Liu, Haiying; Du, Li; Zhou, Mengjing] Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430023, Hubei, Peoples R China.
通讯机构：
[Li, B ] W;Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430023, Hubei, Peoples R China.
摘要：
Preparation of composite hydrogels by in situ polymerization (SP) using choline chloride (ChCl), acrylamide (AM), and urea (U) as raw materials for deep eutectic solvent (DES), with the introduction of PVA and PVDF as fillers into DES. Characterization of the composite hydrogels was conducted using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). This study analyzed the pressure sensitivity, piezoelectricity, swelling behavior, and mechanical properties of the composite hydrogels. The results indicate that due to the dipole–dipole interactions between PVA and PVDF, the composite hydrogels exhibit excellent pressure sensitivity and piezoelectric performance. When the ratio of PVA to PVDF is 1:1, the composite hydrogels exhibit optimal performance, with a 3.37-fold increase in pressure sensitivity and a 6.49-fold increase in piezoelectricity compared to other ratios. This research provides a method for preparing composite hydrogels with excellent piezoelectric performance and pressure sensitivity.
通讯机构：
[Pei, HC ] W;Wuhan Polytech Univ, Sch Mech Engn, Wuhan 430048, Peoples R China.
关键词：
Air-cooled PEMFC stack;Temperature distribution;Cathode air intake mode;Ambient temperature
摘要：
Open-cathode air-cooled proton exchange membrane fuel cells (PEMFCs) simplify conventional cell stacks' cooling and air supply systems, effectively reducing additional energy consumption and improving portability and reliability. As an air fan provides the cathode reaction gas, different air supply conditions significantly influence the output performance of the air-cooled PEMFC stack. This study used a cathode air supply with exhaust and blow modes to investigate the stack performance under different operating conditions. Compared with the exhaust air supply mode, the stack output voltage in the blow-flow mode increased by 5.5 %, and both voltage and temperature uniformities were improved, with 43.0 % and 23.9 % reductions in standard deviation, respectively, when the current density was 300 mA/cm2. In addition, the effect of ambient temperature on stack performance was investigated. Comparing the stack's performance at 15 degrees C and 30 degrees C ambient temperatures, the higher ambient temperature increased the stack's voltage, but led to worsening non-uniform temperature distribution. In the air-cooled PEMFC stack, the influence of the heat generated by the fan on the air-cooled stack temperature could not be ignored. The air supply in the blow-flow mode transfers heat to the stack. At a lower ambient temperature, the temperature increase in the stack was more evident under the exhaust air supply mode.
通讯机构：
[Yang, L ] W;Wuhan Polytech Univ, Coll Mech Engn, Wuhan 430048, Hubei, Peoples R China.
关键词：
Rice starch gel;Crosslink network structure;Rheological property;Direct-write 3D printing
摘要：
Amylopectin and amylose components are natural polymers within rice starch granules, intertwined in specific conditions to form gel polymerized with pore crosslink network, has potential printing properties. In this study, a rice starch gel preparation scheme is proposed for stable properties, and starch granule phase transition mechanism is analyzed based on RVA test during preparation, it can be divided into four-stage, swelling, reacting, homogenizing and self-assembling stages. Gel surface tension and contact angle tested with starch concentration effect, a correlation is developed, reflecting a competition result to gel droplet macro-morphology between the intermolecular cohesion and crosslink network. SEM is used to reveal typical crosslink structures of different starch molecular component proportions, providing objective support for starch gel rheologic property change. Results indicate gel interior crosslink network formed under concentration 12%, the gel with amylose 4.475% presents better printing accuracy. Gel shear modulus positively correlated with amylose proportion. Japonica gel under 20% is of higher viscosity and rapid reassembly ability after interior crosslink network is broken. Max dynamic viscosity is positively correlated with starch concentration. The study aims to provide theoretical and practical support for in-depth analysis of rice starch material application in direct-write 3D printing.
