虚拟机和随机调度技术简化无线设计

一种新的无线设计方法使设计师们能将多种基于分组的标准融合到资源受限的手机硬件中.     

FRAM-单芯片全能存储技术

从事嵌入式系统的设计工程师通常会根据需要保存的内容来选择存储器类型。一个简单的区分办法就是在非易失性存储器中保存可执行代码,而在易失性存储器中保存数据(需要存档的数据除外)。近年,随着消费类电子的兴起,包含图像和音乐信息的数据也开始使用     

Temperature and Frequency Dependence of Electric Field‐Induced Phase Transitions in PMN–0.32PT

Single crystal (1 ? x)Pb(Mg_1/3 Nb_2/3)O₃–xPbTiO₃ [PMN–xPT] (x = 0.32) is a relaxor‐ferroelectric material known to exhibit ‘giant’ piezoelectric behavior, with achievable strains in excess of 1% for samples of certain particular crystallographic orientations and chemical compositions close to the morphotropic phase boundary. In this study, we investigate the electric field‐induced structural phase transitions in single crystal PMN–0.32PT with time‐of‐flight neutron diffraction and macroscopic electrical polarization measurements, and show that both the frequency of the applied ac field and the temperature of the sample are critical factors in determining these phase transition fields.     

Capillary study on geometrical dependence of shear viscosity of polymer melts

Geometrical dependence of viscosity of polymethylmethacrylate (PMMA) and high density polyethylene (HDPE) are studied by means of a twin‐bore capillary rheometer based on power‐law model. Contrary geometrical dependences of shear viscosity are observed for PMMA between 210 and 255°C, but similar geometrical dependences are revealed for HDPE between 190 and 260°C. The fact that wall slip can not successfully explain the irregular geometrical dependence of PMMA viscosity is found in this work. Then, pressure effect and dependence of fraction of free volume (FFV) on both pressure and temperature are proposed to be responsible for the geometrical dependence of capillary viscosity of polymers. The dependence of shear viscosity on applied pressure is first investigated based on the Barus equation. By introducing a shift factor, shear viscosity curves of PMMA measured under different pressures can be shifted onto a set of parallel plots by correcting the pressure effect and the less shear‐thinning then disappears, especially at high pressure. Meanwhile, the FFV and combining strength among molecular chains are evaluated for both samples based on molecular dynamics simulation, which implies that the irregular geometrical dependence of PMMA viscosity can not be attributed to the wall slip behavior. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39982.     

Compatibilization of polypropylene/polyamide 6 blends using new synthetic nanosized talc fillers: Morphology,thermal, and mechanical properties

New synthetic nanotalc and a commercially available natural fine talc (Luzenac© A3) were chosen in order to establish a comparative study in terms of their contributions on the improvement of the morphology as well as the final properties of PP/PA6 blends prepared by melt processing. At first, the TEM and SEM micrographs showed that both talc particles have a preferential affinity for the more hydrophilic polyamide 6 phase compared with the continuous PP matrix. Moreover, in both cases, the addition of talc fillers induces a significant decrease of the size of the PA6 domains but the better compatibilization efficiency was obtained in the presence of synthetic nanotalc particles. In this work, the positive change induced by the talc nanofillers on the crystallization kinetics and final morphology was highlighted. In addition, compared with natural talc, a highly level of dispersion of talc layers has been obtained with the synthetic nanotalc which is more hydrophilic. Thus, this better dispersion greatly improves the thermal stability of PP/PA6 blends and leads to better mechanical properties (+ 40% in Young's modulus). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40453.     

Isothermal and non-isothermal crystallization kinetics of hydroxyl-functionalized polypropylene

Hydroxyl-modified polypropylenes (PPOH) with side chains containing OH groups were synthesized by copolymerization of the propylene and undecenyloxytrimethylsilane monomers. The isothermal and non-isothermal crystallization behavior of the modified polypropylenes (PPOH) with side chains containing up to 6.8 mol% OH groups were compared with that of polypropylene (PP). The introduction of the OH-comonomer decreased the overall rate of isothermal crystallization compared with PP due to steric effects of the hydroxyl-containing side-chains that hindered packing of the PP backbone chains into a lamellar structure. However, a maximum reduction in the rate of crystallization occurred at an intermediate hydroxyl concentration as a consequence of a competition between the effects of the comonomer on the nuclei density and the thermodynamic barrier to crystallization. Steric hindrance by the comonomer side-chains also reduced the radial growth rate of the crystals in PPOH and produced a coarser crystal morphology than that for PP. PP and PPOH exhibited an identical α-monoclinic crystal structure, but the introduction of only ∼6.8 mol% comonomer reduced the fold-surface free energy of the crystals by 42%. For non-isothermal crystallization, the crystallization peak temperature (T_p) decreased for low concentrations of OH, but above a critical OH concentration, T_p increased, a result similar to the isothermal crystallization rate.     

Nanocomposites of polypropylene/titanate nanotubes: morphology,nucleation effects of nanoparticles and properties

High-quality titanate nanotubes (TiNT) were mixed with modified polypropylene (PP*) by a batch melt-mixing procedure. To improve compatibility between the nanofiller and the matrix, polypropylene (PP) was modified by electron beam irradiation. Effects of TiNT nanoparticles on crystallization, mechanical, thermal and rheological properties of the modified polypropylene were studied and compared with the analogous systems filled with commercial micro- (mTiO₂) and nano- (nTiO₂) titanium dioxide particles. Nucleation effects of the TiO₂-based fillers on PP* crystallization were investigated in detail. The microstructure of the PP*/TiNT nanocomposites shows well-dispersed TiNT sparse aggregates (clouds), penetrated by the polymer. A large-scale structure in the nanocomposite melts confirmed also rheology. In comparison to the matrix characteristics, the stiffness and microhardness of the TiNT nanocomposites increase by 27 and 33 %, respectively. The enhancement in mechanical properties demonstrates that the quality titanate nanotubes can be used as an efficient filler in non-polar polymers using the polymers modified by irradiation. In the case of the nanocomposites containing nTiO₂-anatase particles, the increase in these mechanical characteristics is lower. The investigated changes in the rate of crystallization indicate a marked nucleation effect of the nanotubes. The crystallization kinetics data, processed by the Avrami equation, suggest 3-dimensional crystal growth in the polypropylene matrix. The observed improvement in mechanical properties of the TiNT nanocomposites is induced not only by the nanofiller reinforcement but also by the changes of supermolecular structure of the polymer matrix due to nucleated crystallization.     

风景园林中的设计思维

风景园林师运用他们的创造力以及创造性的思维能力为世界上许多有关环境和社区的问题寻找解决途径。风景园林教育为保证学生通过学习掌握创造性解决问题的思维起到了重要的作用。而通过思考与映像体现出创造力的行为被称作"设计思维"。通过描述设计思维与设计思考者的特征,以及可视化的作用,探讨了设计思维在景观设计中的作用与地位。同时,展示了中国呼和浩特内蒙古农业大学林学院一群硕士研究生对自己设计思维能力的评估结果。这份自我评估结果凸显了将创造性与设计思维技巧正式纳入景观设计教学的必要性。