磁力可控电磁超声换能器设计及特性

电磁超声换能器一般采用具有超强磁力的稀土永磁制作,在实际检测中由于磁力不可控,存在偏置磁场不够强导致换能效率过低和磁力过强造成操作不方便等问题.提出一种偏置磁场磁力可控的电磁超声换能器,采用电磁铁与永磁铁相结合的方式,达到偏置磁场磁力可控的目的.通过有限元仿真和试验得出,提出的偏置磁场磁力可控的电磁超声换能器,在电磁铁处于关闭模式下,永磁铁能够提供基础磁场;采用增强模式或减弱模式,无被测物时,换能器下表面平均垂直磁通最大分别增强78.58％和减弱19.36％,而提离2 mm检测钢板时,换能器下方钢板表面平均垂直磁通最大分别增强52.99％和减弱38.02％;得出3种模式下,探头磁力随着提离距离缩小而增强的试验曲线;通过增强模式对铝板和钢板进行测厚试验,将检测信号幅值分别提高46.91％和62.01％.所设计的磁力可控电磁超声换能器不仅具有磁力可控的功能,还能够提高检测信号幅值.     

Customization of ZrO2 loose/tight bilayer ultrafiltration membranes by reverse micelles-mediated aqueous sol-gel process for wastewater treatment

Two types of spherical zirconyl oxalate aqueous sols were successfully customized by a reverse micelles-mediated aqueous sol-gel process, and the sols were sequentially spin-coated on porous supports to prepare ZrO₂ loose/tight bilayer ultrafiltration membranes. After three times of spin-coating process, a defect-free ZrO₂ loose ultrafiltration membrane with pure water permeability of 110.5 ± 2.25 L m^?2 h^-1 bar^-1, molecular weight cut-off (MWCO) of 16.5 kDa and excellent rejection of up to 97.5 % for bovine serum albumin was fabricated. Then, the loose ultrafiltration membrane was used as a substrate to prepare ZrO₂ tight ultrafiltration membrane. Performances of tight ultrafiltration membrane regarding to permeability, retention of polyethylene glycol and treatment of dyes wastewater were evaluated. The tight ultrafiltration membrane with a thickness of 200 nm exhibited a pure water permeability of 22.5 ± 0.3 L m^-2 h^-1 bar^-1 and MWCO of 1150 Da. Additionally, the rejections of methyl red and methyl orange by the tight ultrafiltration membrane were both <65 %, while of alizarin red, direct red, bromocresol green and methyl blue achieved maximum values of 98.5 %, 99.2 %, 99.5 % and 99.6 %, respectively. The fouled membranes could restore the virgin performance for reuse by cleaning and low-temperature calcination.     

Characteristics of Preferential Flow Paths in Reservoirs After Polymer Flooding and an Adaptive Compound Flooding Method

Chemistry and Technology of Fuels and Oils - When a reservoir is subjected to long-term water and polymer flooding, the formed preferential flow paths are widely distributed in the formation, and...     

Effects of Different Short-Term UV-B Radiation Intensities on Metabolic Characteristics of Porphyra haitanensis

The effects of ultraviolet (UV) radiation, particularly UV-B on algae, have become an important issue as human-caused depletion of the protecting ozone layer has been reported. In this study, the effects of different short-term UV-B radiation on the growth, physiology, and metabolism of Porphyra haitanensis were examined. The growth of P. haitanensis decreased, and the bleaching phenomenon occurred in the thalli. The contents of total amino acids, soluble sugar, total protein, and mycosporine-like amino acids (MAAs) increased under different UV-B radiation intensities. The metabolic profiles of P. haitanensis differed between the control and UV-B radiation-treated groups. Most of the differential metabolites in P. haitanensis were significantly upregulated under UV-B exposure. Short-term enhanced UV-B irradiation significantly affected amino acid metabolism, carbohydrate metabolism, glutathione metabolism, and phenylpropane biosynthesis. The contents of phenylalanine, tyrosine, threonine, and serine were increased, suggesting that amino acid metabolism can promote the synthesis of UV-absorbing substances (such as phenols and MAAs) by providing precursor substances. The contents of sucrose, D-glucose-6-phosphate, and beta-D-fructose-6-phosphate were increased, suggesting that carbohydrate metabolism contributes to maintain energy supply for metabolic activity in response to UV-B exposure. Meanwhile, dehydroascorbic acid (DHA) was also significantly upregulated, denoting effective activation of the antioxidant system. To some extent, these results provide metabolic insights into the adaptive response mechanism of P. haitanensis to short-term enhanced UV-B radiation.     

Microstructure and electric properties of Pr-doped Pb(Zr0.52Ti0.48)O3 ceramics

Improving the piezoelectric activity of lead zirconate titanate (PZT) ceramics is of great importance for practical applications. In this study, the influence of Pr³⁺ doping on the ferroelectric phase composition, microstructure, and electric properties on the A-site of (Pb_1-1.5xPr_x)(Zr_0.52Ti_0.48)O₃ is extensively investigated. A dense and fine microstructural sample is obtained with the introduction of Pr³⁺. The results show that the morphotropic phase boundary (MPB) moves to the rhombohedral phase region. The rhombohedral and tetragonal phases exhibit an ideal coexistence in the 4 mol.% Pr³⁺ doped (PPZT4) samples. Lead vacancy and the reduction of the potential energy barrier are considered to be the key mechanisms for donor doping, which is upheld by the Pr³⁺ doping. Combining the I-E hysteresis loops with the P-E hysteresis loops, it becomes apparent that both contribution maximums of the domain switching and residual polarisation are in PPZT4. Moreover, the thermal aging resistance of PZT is improved by doping, and the temperature stability is optimised from 83% in PZT to 96% in PPZT4. Hence, an appropriate amount of Pr³⁺ doping can effectively improve the piezoelectric activity of PZT ceramics in the MPB area and optimise the performance stability of the material under application temperatures.     

Mechanical properties and wear behavior of Tin+1(Al,A)Cn (A = Ga,In, Sn,n = 1, 2) via quasi-high-entropy of single atomic thick A layer

The strengthening method of multi-element M-site solid solution is a common approach to improve mechanical properties of MAX phase ceramic. However, the research on capability of multi-element A-site solid solution to improve mechanical properties has rarely been reported. Thereupon, quasi-high-entropy MAX phase ceramic bulks of Ti₂(Al_1?xA_x)C and Ti₃(Al_1?xA_x)C₂ (A = Ga, In, Sn, x = 0.2, 0.3, 0.4) were successfully synthesized by in situ vacuum hot pressing via multi-elements solid solution. The multi-elements solid solution in single-atom thick A layer was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy as well as by energy dispersive X-ray spectroscopy mappings. Effects of doped multi-elements contents on the phase, microstructure, mechanical properties, and high temperature tribological behaviors were studied. Results demonstrated that the Vickers hardness, anisotropic flexural strength, fracture toughness, and tribological properties of Ti–Al–C based MAX ceramics could be remarkably improved by constitution of quasi-high-entropy MAX phase in A layers. Moreover, the strengthening and wear mechanisms were also discussed in detail. This method of multi-element solid solution at A-site provides new way to enhance mechanical properties of other MAX phase ceramics.     

Freeze-drying and mechanical redispersion of aqueous PEDOT:PSS

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films are attracting famous applications in antistatic coating, energy storage and conversion, printed electronics, and biomedical fields due to their conductivity, optical transparency and flexibility. However, PEDOT:PSS has poor dispersion stability during long-term storage and transport. Moreover, the dried PEDOT:PSS films are insoluble in any solvent and cannot be redispersed again. In comparison to bake drying, here, a feasible strategy to achieve mechanically redispersed PEDOT:PSS with the help of freeze-drying process was reported. The redispersed PEDOT:PSS can recover not only the initial characters such as pH, chemical composition, viscosity, and particle size under similar solid contents, but also conductivity and surface morphology of treated films. In addition, the treated film exhibits self-healing properties similar to pristine film in terms of mechanical and electrical properties. This technology enables reuse and overcomes the technical problems of PEDOT:PSS dispersion, realizing real-time processing to meet variable applications.     

Contribution of Invariant Natural Killer T Cells to the Clearance of Pseudomonas aeruginosa from Skin Wounds

Chronic infections are considered one of the most severe problems in skin wounds, and bacteria are present in over 90% of chronic wounds. Pseudomonas aeruginosa is frequently isolated from chronic wounds and is thought to be a cause of delayed wound healing. Invariant natural killer T (iNKT) cells, unique lymphocytes with a potent regulatory ability in various inflammatory responses, accelerate the wound healing process. In the present study, we investigated the contribution of iNKT cells in the host defense against P. aeruginosa inoculation at the wound sites. We analyzed the re-epithelialization, bacterial load, accumulation of leukocytes, and production of cytokines and antimicrobial peptides. In iNKT cell–deficient (Jα18KO) mice, re-epithelialization was significantly decreased, and the number of live colonies was significantly increased, when compared with those in wild-type (WT) mice on day 7. IL-17A, and IL-22 production was significantly lower in Jα18KO mice than in WT mice on day 5. Furthermore, the administration of α-galactosylceramide (α-GalCer), a specific activator of iNKT cells, led to enhanced host protection, as shown by reduced bacterial load, and to increased production of IL-22, IL-23, and S100A9 compared that of with WT mice. These results suggest that iNKT cells promote P. aeruginosa clearance during skin wound healing.     

基于电沉积法回收废水中铝离子的最佳工艺参数分析

基于电沉积法,针对某铝箔生产企业所产生的高含铝离子废水,通过不同峰值电流密度下形成的电沉积试样的相关电化学曲线测试结果和镀层中的Al质量分数分析,确定所采用电沉积法的最佳峰值电流密度为9 A·dm-2,此时沉积层中铝质量分数为33.21％,原子数量占比为24.69％.