Arm symmetrical PbS dendrite （ASD-PbS） nanostructures can be prepared on a large scale by a solvothermal process. The ASD-PbSs exhibit a three-dimensional symmetrical structure, and each dendrite grows multiple branches on the main trunk. Such unique ASD-PbSs can be combined with polyvinylidene fluoride （PVDF） to prepare a composite material with enhanced dielectric and microwave-absorption properties. A detailed investigation of the dependence of the dielectric properties on the frequency and temperature shows that the ASD-PbS/PVDF composite has an ultrahigh dielectric constant and a low percolation threshold. The dielectric permittivity is as high as 1,548 when the concentration of the ASD-PbS filler reaches 13.79 vol.% at 102 Hz, which is 150 times larger than that of pure PVDF, while the composite is as flexible as pure PVDF. Furthermore, the maximum reflection loss can reach -36.69 dB at 16.16 GHz with a filler content of only 2 wt.%, which indicates excellent microwave absorption. The loss mechanism is also elucidated. The present work demonstrates that the addition of metal sulfide microcrystals to polymer matrix composites provides a useful method for improving the dielectric and microwave-absorption properties.
Mass production of high-quality silver nanowires （Ag NWs） is of significant importance because of its potential applications in flexible transparent conductive devices. Halogen ions have been widely used for the synthesis of Ag NWs; however, owing to the lack of a deep insight into heterogeneous nucleation processes, usually a trace feeding amount （e.g. [Cl^-] 〈 0.25 mM） is used, which in turn lowers the concentration of precursor （[Ag^＋]）. Here we systematically investigated the nucleation and growth behavior of Ag NWs and concluded that the number of heterogeneous nucleation sites was determined by the total surface area of AgCl seeds, which indicated a linear relationship between the concentrations of Ag^＋ and Cl^- during precipitation. Based on this mechanism, we successfully produced high-quality Ag NWs with Ag^＋ concentrations which were 20 times higher for a polyol system and 5 times higher for an aqueous system as compared to that in the previously reported strategies. Besides, by tailoring the heterogeneous nucleation sites by controlling the size of the AgCl seeds, the diameters of the final Ag NWs could be well controlled even at high Ag^＋ concentration. Based on the mechanistic understandings, this synthetic strategy could be extended to other AgX-seeds （X = Br^-, F and SO4^2-） and the basic principles can be applied to help rational synthesis of other high-yield metal NWs with tunable sizes.
Cheng WangBaisong ChengHaichuan ZhangPengbo WanLiang LuoYun KuangXiaoming Sun
Polydimethylsiloxane （PDMS） is an excellent material for investigating the mechanism of triboelectricity as it can easily be used to construct various microstructures. In this study, micro-capacitors （MCs） and variable microcapacitors （VMCs） were embedded in PDMS by filling PDMS with silver nanoparticles （NPs） and constructing an internal cellular structure. The output performance of the triboelectric nanogenerators （TENGs） based on MCs@PDMS and VMCs@PDMS films was systematically investigated, with variation of the filling content of silver NPs and the pore ratio and size. The microstructure, permittivity, dielectric loss, and capacitance of the VMCs@PDMS films were well characterized. The output current of the TENG based on the VMCs@PDMS film was respectively 4.0 and 1.6 times higher than that of the TENGs based on the pure PDMS film and MCs@PDMS film, and the output power density of the former reached 6 W·m-2. This study sheds light on the physical nature of conductive nanoparticle fillings and cellular structures in dielectric triboelectric polymers.
Xiaona XiaJie ChenHengyu GuoGuanlin LiuDapeng WeiYi XiXue WangChenguo Hu
Long-term loosening is the major cause of failure of arthroplasty. One of the major causes is stress shielding, initiated by the large stiffness difference between prosthesis and bone tissue. Therefore, prosthesis with reduced stiffness properties to match those of the bone tissue may be able to minimize such a problem. Design with porous structure is believed to reduce the stiffness of the prosthesis, however at the cost of decreased strength. In this study, a patient-specific bone-implant finite element model was developed for contact mechanics study of hip joint, and algorithms were developed to adjust the elastic modulus of elements in certain regions of the femoral stem, until optimal properties were achieved according to the pre-defined criterions of the strength and stability of the system. The global safety factor of the optimized femoral stem was 11.3, and 26.4% of elements were designed as solid. The bone volume with density loss was reduced by 40% compared to the solid stem. The methodology developed in this study provides a universal method to design a patient-specific prosthesis with a gradient modulus distribution for the purposes of minimizing the stress shielding effect and extending the lifespan of the implant.
Changning SunLing WangJianfeng KangDichen LiZhongmin Jin
Large-intergenic noncoding RNAs （lincRNAs） cooperate with core transcription factors to coordinate the pluripotency network of embryonic stem cells. The mechanisms by which lincRNAs affect chromatin structure and gene transcription remain mostly unknown. Here, we identified that a UncRNA （linc1614）, occupied by pluripotency factors at its promoter, was indispensable for both maintenance and acquisition of pluripotency. Linc1614 sewed as a specific partner of core factor Sox2 in maintaining pluripotency, primarily by mediating the function of Sox2 in the repression of developmental genes. Moreover, Ezh2, an essential subunit of polycomb repressive complex 2 （PRC2）, physically interacted with linc1614 and contributed to lincRNA-mediated transcriptional silencing. Thus, we propose that the interplay of linc1614 with Sox2 implicates this lincRNA as a recruitment platform that mediates transcriptional silencing by guiding the PRC2 complex to the loci of developmental genes.
Xudong GuoZikang WangChenqi LuWujun HongGuiying WangYanxin XuZhongmin LiuJiuhong Kang
Optimization of hybrid ultrahigh frequency pulse variable polarity gas tungsten arc welding （HPVP-GTAW） process was carried out to obtain the optimum weld characteristics of 5AO6-HX4 aluminum-magnesium alloy sheets of 3 mm thickness. The square butt joints were produced by HPVP-GTA W process, the microstructure and mechanical properties were systematically investigated. It is observed that the process parameters influence the weld microstructure and mechanical properties significantly. Weld microstructure is mainly composed of grid a （A1） solid solution, with a large number of intermetallic （ Mg2Al3 ） precipitates distributed in the matrix. The amount of ~ （ Mg2Al3 ） precipitates has an obvious difference with different parameters. Compared with that of the base material, tensile strength of 5AO6-HX4 alloy welded joints has a certain reduction, as well as the elongation and reduction of area. The optimized welding process parameters for 5A06-HX4 alloy sheets are presented.
We study optomechanically induced amplification and perfect transparency in a double-cavity op- tomechanical system. We find that if two control lasers with appropriate amplitudes and detunings are applied to drive the system, optomechanically induced amplification of a probe laser can occur. In addition, perfect optomechanieally induced transparency, which is robust to mechanical dissipation, can be realized by the same type of driving. These results indicate important progress toward signal amplification, light storage, fast light, and slow light in quantum information processes.
ZnFe2O4（ZFO） was synthesized via a sol-gel method firstly, then the ZFO was irradiated with microwave treatment to obtain M-ZFO using NH4C1 as dispersant for 10 min to improve the photocatalytic activity. Large par- tides of ZFO were broken into small and uniform particles by the gases of hydrogen chlorine and ammonia during the decomposition of NH4Cl. Compared to ZnFe2O4 without microwave treatment（ZFO）, M-ZFO exhibits smaller particle size, higher surface area and larger saturation magnetization. More importantly, the photocatalytic activity of M-ZFO for methylene blue was increased by 25% compared with that of ZFO.
FENG Jing WANG Yuting ZOU Linyi LI Bowen HE Xiaofeng Lü Shengna CHEN Tingting
Urbanization processes affect the ecosystem through alterations in ecological functions and landscape patterns. Currently, analysis of the total ecosystem services value （ESV） has targeted the overall benefits which human beings obtain from the regional ecosystem but does not generally include information regarding ecological struc- tures and patterns. Therefore, the results cannot reflect the comprehensive state of the local ecosystem. We propose a new, integrative ecosystem quality indicator based on the ESV and landscape metrics for evaluating the quality of the regional ecosystem. We adopted the method of a coupled degree of coordination for evaluating the interrelationship between urbanization and ecosystem quality in Lianyun- gang City from 1985 to 2010. The coupling degree of coordination between urbanization and ecosystem quality showed an inverse U-shaped curve. At the primary stage of urbanization （1985-1995）, the degree of coupling of urbanization and the ecosystem was just barely balanced. From 1995 until 2000, the coupling system reached a balanced condition, in which the urbanization level increased. Since 2000, the urbanization process has accelerated. The coordination between urbanization and the ecosystem achieved the optimum condition in 2005. A turning point appeared at the same time, and the degree of coupling coordination began falling from the optimum. Subsequently, the coupled system once more entered a barely balanced state. Overall, the comprehensive level of ecosystem quality decreased since 1985 and degraded sharply after 2005, suggesting an overall degradation of the local ecosystem quality.
Junyong AILan FENGXiaowei DONGXiaodong ZHUYangfan LI
