PEEK modified PLA shape memory blends: towards enhanced mechanical and deformation properties

Polylactic acid (PLA) is one of the most promising shape memory polymers with outstanding biocompatibility, while poly(ether ether ketone) (PEEK) is a special engineering plastic with excellent mechanical performance. In this work, PEEK was selected to modify PLA, and a series of PLA blended with different PEEK contents (PLA/PEEK blends) were obtained. The effects of PEEK on thermodynamic, mechanical and shape memory properties of PLA/PEEK blends were investigated. The results showed that the thermal stability of the PLA/PEEK blend was improved with the PEEK content increase. The tensile strength reached the highest value of 20.6 MPa when the PEEK content was 10%. While the best shape memory performance occurred with the PEEK content of 15%, the shape recovery time was less than 2 s, and the shape fixation/recovery ratio was more than 99%. Furthermore, the programmable mimetic flower opening process was achieved by using PLA/PEEK blends with different PEEK content ratios. The above results indicated that the blend of an appropriate proportion of PEEK had positive effects on mechanical and deformation performances of PLA.     

Ultrafast Photoinduced Multimode Antiferromagnetic Spin Dynamics in Exchange‐Coupled Fe/RFeO3 (R = Er or Dy) Heterostructures

Antiferromagnetic spin dynamics is important for both fundamental and applied antiferromagnetic spintronic devices; however, it is rarely explored by external fields because of the strong exchange interaction in antiferromagnetic materials. Here, the photoinduced excitation of ultrafast antiferromagnetic spin dynamics is achieved by capping antiferromagnetic RFeO₃ (R = Er or Dy) with an exchange‐coupled ferromagnetic Fe film. Compared with antiferromagnetic spin dynamics of bare RFeO₃ orthoferrite single crystals, which can be triggered effectively by ultrafast laser heating just below the phase transition temperature, the ultrafast photoinduced multimode antiferromagnetic spin dynamic modes, for exchange‐coupled Fe/RFeO₃ heterostructures, including quasiferromagnetic resonance, impurity, coherent phonon, and quasiantiferromagnetic modes, are observed in a temperature range of 10–300 K. These experimental results not only offer an effective means to trigger ultrafast antiferromagnetic spin dynamics of rare‐earth orthoferrites, but also shed light on the ultrafast manipulation of antiferromagnetic magnetization in Fe/RFeO₃ heterostructures.     

Allyl ether‐modified unsaturated polyesters for UV/air dual‐curable coatings. I: Synthesis and characterization of the oligomers and their cured films

Allyl ether (AE)‐modified unsaturated polyester oligomers were synthesized from polyethylene glycol (PEG), maleic anhydride (MAH), and trimethylolpropane mono allyl ether (TMPAE), and characterized by Fourier transform infrared (FTIR) spectra. The UV/air dual‐curable coatings were prepared from the oligomers using vinyl ether (VE) as a reactive diluent. FTIR spectra showed that C?C bonds in the coating composition had polymerized partially after cured by UV or air. The investigation of rheological behavior of the dual curable composition suggested that all the systems belonged to pseudoplastic fluid, and the increasing allyloxy content in oligomer resulted in a higher viscosity. Differential scanning calorimetry (DSC) analysis showed that the increasing TMPAE‐PEG molar ratio resulted in lower T_g, and all samples had the same glass transition temperature irrespective of the type of curing. The results of TGA for cured films indicated that UV‐cured film had better thermal stability than the air‐cured one. The air‐cured film showed superior pencil hardness, impact strength, and flexibility to the UV‐cured counterpart. However, the air‐cured film had poor adhesion and electric resistance properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2765–2770, 2004     

Acidity and catalytic activity of the mesoporous aluminosilicate molecular sieve MCM-41

The acidity and catalytic properties of aluminosilicate mesoporous molecular sieves with the MCM-41 structure and bulk Si/Al ratios in the 10–60 range have been investigated. The incorporation of 4-coordinate aluminium into the structure of MCM-41 generates both BrØnsted and Lewis acid sites in amounts increasing with the degree of incorporation. However, the BrØnsted/Lewis acid population ratio is independent of the content of aluminium. The number and strength of acid sites generated are comparable to those of a pillared acid-activated clay and lower than in zeolite H-Y with Si/Al=3.65. Aluminosilicate MCM-41 is a moderate catalyst for the conversion of cumene which proceeds predominantly via catalytic cracking to propene and benzene. The sample of MCM-41 with the highest content of framework aluminium (Si/Al=10) has the largest number of BrØnsted acid sites and exhibits highest catalytic activity.     

高效填料塔成套分离工程技术

以总体方案、模拟计算、工艺流程、汽液传质设备、安装开车等５个基本工程步骤为线索，从工业应用角度，综述性地介绍高效填料塔成套分离工程技术的国内应用水平和发展趋势。     

Linux下以太网网络监听技术研究

随着网络技术的飞速发展,自由操作系统Linux的普及越来越迅速,Linux下的网络管理迫在眉睫,网络监听是网络管理的重要技术手段之一。本文介绍以太网环境中Linux系统下网络监听技术的原理、检测网络侦听的方法和网络监听技术在网络测试中的应用,重点介绍网络监听程序的设计。     

Effect of superabsorbent polymer on the shrinkage and crack resistance of concrete at early age

The superabsorbent polymer (SAP) with different volumes and modes of entrained water is incorporated into concrete to study the effect of SAP on the compressive strength, flexural strength, shrinkage, plastic cracking and electrical resistivity of concrete at early age. The result indicated that the influence of SAP with different modes of entrained water on the early strength of concrete is relatively obvious. It is beneficial for the early strength of concrete to add pre-absorbed SAP whose internal curing (IC) is detracted from mixing water and unabsorbed SAP. But the early strength of concrete is decreased by adding pre-absorbed SAP. The effect of pre-absorbed SAP is limited on shrinkage of concrete when IC water is detracted from mixing water. The unabsorbed SAP gradually decreases the concrete shrinkage with its volume increase. The moderate volume of pre-absorbed SAP can decrease the early concrete shrinkage. In addition, SAP can effectively alleviate the early appearance and development of concrete cracks. Furthermore, the pre-absorbed SAP can efficiently enhance the crack resistance of concrete. When the unabsorbed SAP is added, the cracking of concrete is reduced with the increase of volume. The longer the curing age, the more obvious would be the influence of SAP on the internal humidity of concrete, which effectively delays the increase of concrete resistivity.     

A power management circuit with 50% efficiency and large load capacity for triboelectric nanogenerator

Recently, triboelectric nanogenerators (TENGs), as a collection technology with characteristics of high reliability, high energy density and low cost, has attracted more and more attention. However, the energy coming from TENGs needs to be stored in a storage unit effectively due to its unstable ac output. The traditional energy storage circuit has an extremely low energy storage efficiency for TENGs because of their high internal impedance. This paper presents a new power management circuit used to optimize the energy using efficiency of TENGs, and realize large load capacity. The power management circuit mainly includes rectification storage circuit and DC-DC management circuit. A rotating TENG with maximal energy output of 106 mW at 170 rpm based on PCB is used for the experimental verification. Experimental results show that the power energy transforming to the storage capacitor reach up to 53 mW and the energy using efficiency is calculated as 50%. When different loading resistances range from 0.82 to 34.5 kΩ are connected to the storage capacitor in parallel, the power energy stored in the storage capacitor is all about 52.5 mW. Getting through the circuit, the power energy coming from the TENGs can be used to drive numerous conventional electronics, such as wearable watches.     

建筑施工企业项目管理机制系统演化规律研究

把建筑施工企业项目管理机制看作一个系统,首先阐述系统的构成要素、结构和系统演化的变量空间、演化轨迹,并指出企业项目管理机制系统本质上是一种生产关系。然后根据生产力和生产关系基本原理分析指出,建筑施工企业生产力的状况和发展决定了企业项目管理机制系统的形态和演化;企业项目管理机制系统形态又能动地反作用于建筑施工企业的生产力;最后得出企业项目管理机制系统形态一定要适合建筑施工企业的生产力状况的结论。