Simple self-assembly of SnS2 entrapped graphene aerogel and its enhanced lithium storage performance

In this work, SnS₂ nanoplates entrapped graphene aerogel has been successfully prepared by simple self-assembly of reduced graphene oxide obtained through mild chemical reduction. Structural and morphological investigations demonstrated that SnS₂ nanoplates are highly dispersed in the three dimensional (3D) porous graphene matrix. When served as anode material for lithium-ion batteries, the electrochemical properties of SnS₂/graphene aerogel (SnS₂/GA) were evaluated by galvanostatic discharge–charge tests, cyclic voltammetry and impedance spectroscopy measurement. Compared with pristine SnS₂, the SnS₂/GA nanocomposite achieved a much higher initial reversible capacity (1186 mAh g⁻¹), superior cyclic stability (1004 mAh g⁻¹ after 60 cycles, corresponding to 84.7% of the initial reversible capacity), as well as better rate capability (650 mAh g⁻¹ at a current density of 1000 mA g⁻¹). This significantly improved lithium storage performance can be attributed to the good integration of SnS₂ nanoplates with 3D porous graphene network, which can not only provide much more active sites and easy access for Li ions intercalation, but also prevent the aggregation of SnS₂ nanoplates and facilitate fast transportation of Li ions and surface electrons during the electrochemical process.     

Photoluminescent and electrical properties of novel Nd3+ doped ZnV2O6 and Zn2V2O7

Nd³⁺ doped ZnV₂O₆ and Zn₂V₂O₇ samples were synthetized by using melt-quenching method. X-ray diffraction patterns indicate that both samples are polycrystalline. The crystallinity was also verified by Raman scattering, from which the different vibrational modes of ZnV₂O₆ and Zn₂V₂O₇ were detected. Electron dispersive spectroscopy (EDS) analysis shows that the Nd³⁺ incorporation into the ZnV₂O₆ and Zn₂V₂O₇ hosts is around 0.9±0.1 and 0.2±0.1 at%, respectively. The micrographs obtained by Scanning Electron Microscopy, reveal that the Nd³⁺ doped ZnV₂O₆ sample is predominantly composed by micro-rods, whereas the Nd³⁺ doped Zn₂V₂O₇ one is only composed by irregular blocks. The band gap energies (E_g) were calculated from the diffuse reflectance spectra by the Kubelka–Munk equation; E_g values resulted to be 2.24 and 2.86 eV for the Nd³⁺ doped ZnV₂O₆ and Zn₂V₂O₇ samples, respectively. By means of two points dark conductivity measurements, conductivity values in the 10⁻⁴–10⁻⁶ and 10⁻⁶–10⁻⁸(Ω cm)⁻¹range for the Nd³⁺ doped ZnV₂O₆ and Zn₂V₂O₇ samples were measured, respectively. The conductivity as a function of the temperature indicated a semiconductor behavior. The photoluminescence spectra upon Ar⁺ laser excitation at 488 nm, exhibited the Nd³⁺ characteristics emissions. For instance, the Nd³⁺ doped ZnV₂O₆ sample displayed the Nd^{3+ 4}F_5/2→⁴I_9/2 and ⁴F_3/2→⁴I_9/2 emissions; while the Nd³⁺ doped Zn₂V₂O₇ one showed the Nd³⁺ characteristic emissions associated with the ⁴G_7/2, ⁴F_9/2, ⁴F_5/2 and ⁴F_3/2→⁴I_9/2 transitions. The lifetimes were 80 and 130 µs for the Nd³⁺ doped ZnV₂O₆ and Zn₂V₂O₇ samples, respectively. All these results suggest a successful synthesis of Nd³⁺ doped zinc vanadate compounds by the melt-quenching technique.     

雾霾治理的偏好性--以奥运期间首钢搬迁为例

中国在近些年的经济发展规划中提出经济转型计划--走资源节约型,环境友好型的发展道路,这说明环境治理工作是一项不可忽视的、对社会各方面进程均会产生影响的任务。但是,环境治理需要顶层设计和路径选择。本文主要以首钢搬迁为例,讨论在治理以雾霾为代表的环境治理中,偏好性事实的产生及其后果。     

Doubly thermo-responsive brush-linear diblock copolymers and formation of core-shell-corona micelles

Doubly thermo-responsive brush-linear diblock copolymer of poly[poly(ethylene glycol) methyl ether vinylphenyl]-block-poly(N-isopropylacrylamide) (PmPEGV-b-PNIPAM) is prepared by RAFT polymerization. The obtained brush-linear diblock copolymer exhibits two lower critical solution temperatures (LCSTs) corresponding to the linear poly(N-isopropylacrylamide) (PNIPAM) block and the brush poly[poly(ethylene glycol) methyl ether vinylphenyl] (PmPEGV) block in water. This brush-linear diblock copolymer undergoes a two-step temperature sensitive micellization. At temperature above the first LCST, the brush-linear diblock copolymer self-assembles into core-corona micelles with the dehydrated PNIPAM block forming the core and the solvated brush PmPEGV block forming the corona. When temperature increases above the second LCST, the polystyrene backbone in the brush PmPEGV block collapses onto the dehydrated PNIPAM core to form core-shell-corona micelles, in which the dehydrated PNIPAM block forms the core, the collapsed polystyrene backbone in the brush PmPEGV block forms the shell and the solvated poly(ethylene glycol) side-chains forms the corona. The effect of the length of the PNIPAM block and the length of the poly(ethylene glycol) side-chains on the thermo-responsive micellization and the size of core-shell-corona micelles is investigated.     

用支持向量机网络实现VBR视频通信量的预测

VBR(Variable Bit Rate)视频信号具有时变性、非线性和突发性等特点,实现该信号通信量的高精度预测是提高信息传输速度和提高网络带宽资源利用效率的重要手段.针对以上问题,本文提出了一种用于VBR视频通信量预测的差分输入支持向量机(SVM:Support Vector Machine)网络模型.该网络模型采用结构风险最小化准则,在最小化经验风险的同时,尽量缩小模型预测误差的上界,从而使网络模型具有更好的推广能力.实验结果表明:支持向量机网络模型的预测误差为0.0018,而梯度径向基函数(Gradient Radial Basis Function:GRBF)神经网络模型的预测误差为0.0029.可以看出,支持向量机网络模型的预测精度要比GRBF网络模型的预测精度高出大约40%.     

Polarization-dependent ultrafast optical nonlinearities of N,N-dimethylformamide at 400 nm

Ultrafast optical nonlinearities of N,N-dimethylformamide(DMF) are studied by using polarized light at 400 nm. Both nonlinear refraction(NLR) and stimulated Rayleigh-wing scattering(SRWS) depend on the polarization state of incident beam, while two-photon absorption(TPA) changes negligibly with polarization state. The polarization dependence of SRWS originates from that of NLR via self-focusing effect. Third-order susceptibility elements of DMF were determined, and a method to distinguish the mu...     

乙基红掺杂聚合物薄膜全光开关特性的研究

用偶氮染料乙基红(EthylRed,简称ER)掺杂到聚甲基丙烯酸甲酯(PMMA)并用重复旋涂法制成了聚合物薄膜。研究了在不同功率和不同调制频率的控制光(532nm,CW)激发下,不同掺杂浓度薄膜样品的全光开关特性。结果表明:在室温和8mW的控制光功率条件下,乙基红聚合物薄膜的开关响应时间少于2.5ms并且开关的调制深度在50%以上,最大的调制深度达72%,合适的掺杂浓度(质量分数)为2%~6%薄膜样品的开关特性较优。     

烟气脱硫技术研究进展

总结了近年来国内外应用的几种主要脱硫工艺和正在研究开发的新脱硫工艺。对其中发生的化学反应、技术特点及存在的问题进行了详细的分析,并从技术、经济分析角度评估各种工艺,提出适合我国燃煤电厂情况的脱硫方案。     

Banach空间中二阶周期边值问题的解

本文研究Banach空间中弱拓扑下二阶周期边值问题的解。在上解小于等于下解的假设条件下证明了二阶周期边值问题解的存在性。     

基于支持向量机函数逼近的性能研究

通过仿真分析比较支持向量机与前馈神经网络在非线性函数逼近的结果,得出在小样本下,SVM的样本依赖程度、抗噪声能力和泛化性能都优于前馈神经网络。