Large electrostrictive effect and high energy storage performance of Pr3+-doped PIN-PMN-PT multifunctional ceramics in the ergodic relaxor phase

The photoluminescence, dielectric relaxation, ferroelectric hysteresis, and field-induced strain properties of Pr³⁺-doped 0.24Pb(In_1/2Nb_1/2)O₃-0.42Pb(Mg_1/3Nb_2/3)O₃-0.34PbTiO₃ (PIN-PMN-PT:Pr³⁺) multifunctional ceramics have been investigated. It was found that Pr³⁺ doping enhanced the dielectric diffuseness and relaxation behavior of PIN-PMN-PT ceramics. Slim P-E loops and S-E curves appear in PIN-PMN-PT:Pr³⁺ ceramics when the Pr³⁺ doping concentration reaches 1.4 mol%. Local domain configurations associated with phase transitions were investigated by piezoresponse force microscopy (PFM). Large electrostrictive coefficient Q₃₃ (?0.03 m⁴/C²) and high energy-storage efficiency η (92%) were obtained in 2 mol% Pr³⁺-doped PIN-PMN-PT ceramic in the ergodic relaxor (ER) phase at room temperature. The giant electrostrictive effect and excellent energy-storage performance are related to the field-induced dynamic behavior of polar nanoregions (PNRs). The results show that the PIN-PMN-PT:Pr³⁺ system is an excellent multifunctional material for making electromechanical and energy storage devices.     

Pore and compression characteristics of clay solidified by ionic soil stabilizer

It is of great significance to study the soil pore structure for soil reinforcement and ground treatment because it can be used to evaluate the solidification effect and explain the curing mechanism. The pore and compression characteristics of clay from Wuhan in China before and after solidification by ionic soil stabilizer (ISS) in different soil initial states were studied by the use of standard consolidation test, environmental scanning electron microscope analysis, specific surface area (SSA) test, and analysis by PCAS software. Results show that the influence sequence of soil initial states on the change of pore characteristics and ISS-solidification effectiveness was as follows: reducing initial water content + remolding soil > reducing initial water content > remolding soil > natural soil with high initial water content. Besides, loading can also increase the solidification effect. Compared to random and chaotic pore directions of natural clay, remolded solidified clay had a more certain direction after curing and compression. In addition, the total pore number and SSA decreased from 1190 to 756 by 36.47% and 109.690 m²/g to 87.837 m²/g by 19.92% respectively. Results indicate that ISS-clay solidification effect in practical engineering is closely related to the soil initial pre-curing state and can lead to the change of pore direction, decrease of pore number, reduction of pore size and porosity, and formation of larger aggregates.

     

故事性建构 ——Sky Joy Club早教中心空间设计

文章以Sky Joy Club早教中心设计为例,阐述如何突破对幼儿空间的片面化认知,避免幼稚化的表象设计.以建筑化设计手法介入幼儿空间,构建有故事可发生的空间结构,为幼儿创建符合成长规律的空间环境,让空间成为成长的一部分,成为教育的第三位老师.     

Application of bio-based dimer acid diglycidyl ester in paper-based copper clad laminate

Using dimer acid (DA) as raw material, DA diglycidyl ester (DADGE) was synthesized and used as reactive toughening agent to prepare paper-based copper clad laminate (p-CCL). The factors affecting the epoxy value of DADGE and the effect of the resin on the gelation time were studied. The effects of the epoxy value and the addition amount of DADGE on the solderleaching resistance, flammability, water absorption, bending strength, and impact strength of the p-CCL were discussed. The results showed when the molar ratio of DA to ECH was 1:8 and the molar ratio of DA to sodium hydroxide was 1:1.6, the epoxy value of DADGE reached the maximum value of 0.23 mol/100 g. The DADGE can shorten the gelation time of the glue. The p-CCL meets the performance of the IPC-TM-650 standard. And when the addition amount of DADGE is less than 12 wt %, the flammability of the p-CCL reaches UL94V-0 level. The p-CCL prepared by adding 6 wt % of DADGE with 0.08 mol/100 g epoxy value has the best comprehensive performance, its toughness and rigid are comparable to those of p-CCL with 12 wt % of commercially available high performance toughening agents and it has higher solderleaching resistance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47508.     

切向结构永磁同步电机磁钢径向并联组合研究

针对低速大转矩切向结构永磁同步电机中磁钢尺寸对性能的影响进行研究.提出一种"工"字形排布的磁钢径向并联组合优化方案.在保证电机磁钢轴向长度和体积不变前提下,分析磁钢磁化方向长度变化对电机性能的影响.分析表明:磁钢的磁化方向长度在一定范围内增加可降低磁钢漏磁、增大反电动势和降低转矩波动;但磁钢的磁化方向长度过度增加会大大降低电机磁通面积,使得电机反电动势不增反降.在此基础上,提出一种降低磁钢漏磁、增大反电动势和降低转矩波动的三块磁钢径向并联组合的"工"字形排布方案:近气隙侧和近隔磁槽侧磁钢槽内分别插入磁化方向长度短、径向宽度窄的磁钢以降低近气隙侧和近隔磁套侧磁钢漏磁;近气隙侧磁钢和近隔磁槽侧磁钢之间采用磁化方向长度较短的磁钢以保证磁钢磁通面积降低得不多.通过仿真实验验证所提方案的可行性.     

The effect of Nd3+ concentration on fabrication,microstructure, and luminescent properties of anisotropic S-FAP ceramics

Nd³⁺ doped strontium fluorophosphate (S-FAP), with chemical formula Sr₅(PO₄)₃F, nanopowders were prepared using the co-precipitation method. The prepared powders had no impurity phase with a grain size of about 30 nm and the doping limit of Nd³⁺ ions in strontium fluorophosphate is about 9 at.%. The morphology and particle size were determined by the doping concentration of Nd³⁺. Anisotropic Nd: S-FAP transparent ceramics with different Nd³⁺ doping concentrations were fabricated successfully by the simple hot-pressing method. The grain size of prepared S-FAP transparent ceramics decreased first and then increased with the increase of Nd³⁺ concentration. The 2 at.% Nd: S-FAP ceramic presented the highest optical transmittance at all wavelengths range. The characteristic transitions from the ground state to the excited states of Nd³⁺ ions were observed from the absorption spectra, and the absorption cross-section was calculated at 3.71 × 10^–20 cm². The influence of Nd³⁺ ion concentration on luminescence intensity and fluorescence lifetime was studied under 796 nm excitation. The strong emission of ⁴F_3/2→⁴I_9/2 transition in Nd: S-FAP was calculated by Judd–Ofelt (J-O) theory.     

Remarkable Antibacterial Activity of Reduced Graphene Oxide Functionalized by Copper Ions

Despite long-term efforts for exploring antibacterial agents or drugs, potentiating antibacterial activity and meanwhile minimizing toxicity to the environment remains a challenge. Here, it is experimentally shown that the functionality of reduced graphene oxide (rGO) through copper ions displays selective antibacterial activity that is significantly stronger than that of rGO itself and no toxicity to mammalian cells. Remarkably, this antibacterial activity is two-orders-of-magnitude greater than the activity of its surrounding copper ions. It is demonstrated that rGO is functionalized through the cation–π interaction to massively adsorb copper ions to form a rGO–copper composite and result in an extremely low concentration level of surrounding copper ions (less than ≈0.5 µm ). These copper ions on rGO are positively charged and strongly interact with negatively charged bacterial cells to selectively achieve antibacterial activity, while rGO exhibits the functionality to not only actuate rapid delivery of copper ions and massive assembly onto bacterial cells but also result in the valence shift in the copper ions from Cu²⁺ into Cu⁺, which greatly enhances the antibacterial activity. Notably, this rGO functionality through cation–π interaction with copper ions can similarly achieve algaecidal activity but does not exert cytotoxicity against neutrally charged mammalian cells.