介孔碳有序度对其负载的CuCoCe催化剂催化合成气制低碳醇性能的影响

采用软模板法,通过调变碳源甲醛和间苯二酚的摩尔比,制备了3种不同有序度的介孔碳;并以其为载体,采用超声辅助等体积浸渍法制备了Cu Co Ce/介孔碳催化剂;考察了孔道结构有序度对其催化合成气制低碳醇性能的影响.采用X射线衍射(XRD)分析、N2吸附-脱附实验、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等对催化剂进行了表征.实验结果表明,随着介孔碳有序度的提高,催化活性呈增加趋势.以高度有序的介孔碳作为载体时,低碳醇的时空收率和选择性分别达到849.96 mg·g-1cat·h-1和50.48%,醇产物中C2+OH比例达到90.31%.研究表明,孔道结构影响了活性金属在载体上的分布及存在状态.规整有序的二维六方直通孔结构有利于活性组分Cu Co的均匀分散并使其紧密结合,促进了二者之间的电子转移,进而有效抑制了碳链的持续增长,使催化剂的活性明显提高,并缩窄了醇产物的分布.     

一例基于{PMo_6}单元的杂多钼酸盐的合成、结构及表征

采用常规水溶液合成法成功制备了一例新颖的有机-无机杂化的杂多钼酸盐(C3N2H5)4H[HPMo6O21(O2CC6H4NH2)3]·6H2O (1),并通过X射线单晶衍射、红外光谱、紫外光谱、热失重分析等方法对该化合物的结构进行表征.结构分析表明,化合物1属于三斜晶系,P-1空间群,晶胞参数a=1.319 1(9) nm,b=2.068 8(15) nm,c=2.322 2(16) nm,V=5.701(7) nm3.化合物1包含1个[HPMo6O21(O2CC6H4NH2)3]5-阴离子,4个[C3N2H5]+阳离子,1个H+质子和6个结晶水.化合物1聚阴离子结构中包含一个{PMo6}结构单元,3个对氨基苯甲酸配体通过羧基上的两个氧原子以近乎垂直的方式连接在{PMo6}单元同一侧.紫外光谱研究表明,化合物1在水溶液中6 h内保持相对稳定,能够稳定存在的pH范围大致是7.5～10.5.     

信息熵在产品设计中的应用研究

在设计中抓住痛点,提取用户需求是产品创新设计的重中之重,为了寻找出一种能有效提取及整合用户需求的方程式,帮助更好地进行用户需求模型的构建,先利用情境分析法获取用户需求,再利用KJ法对用户需求进行整合归类,然后利用信息熵法对需求项进行熵权值求解排序,求得需求重要度排序,并以此来构造精确的用户需求模型.最终,通过小型多功能...     

一个与Toda格相关的微分差分方程族及其反散射变换

By combined power evolution laws of the spectral parameter and the initial constants of integration,a new differential-difference hierarchy is presented from the Toda spectral problem.The hierarchy contains the classic Toda lattice equation,the nonisospectral Toda lattice equation and the mixed Toda lattice equation as reduced cases.The evolution of the scattering data in the inverse scattering transform is analyzed in detail and exact soliton solutions are computed through the corresponding inverse scattering transform.     

超低温摩擦学研究进展

近年来,随着深空探测、超导和量子计算等技术的发展,越来越多的装备需要在极端低温工况下服役,超低温引起的润滑问题日益显现.目前超低温摩擦学研究相对较少,主要集中在材料摩擦学性能的变化研究方面,对其背后作用机制的研究并不深入.超低温下大多数固体润滑材料的耐磨性能变差,难以满足长时间服役需求;材料的摩擦学行为受环境、制备方法以及材料种类等众多因素影响,摩擦学性能变化趋势和程度有所不同,难以形成统一的认识.本文作者从超低温对材料原子和电子运动抑制作用的本质出发,归纳分析了超低温对润滑材料摩擦学性能的影响机制,从超低温引起力学性能变化、摩擦界面间的化学反应活性变化、相结构及界面结构变化以及电子-声子耦合等微观能量耗散形式等4个方面的影响机制进行了介绍,并对未来超低温摩擦学的发展方向和亟需解决的问题进行了展望.     

基于优化的离散空间轨迹规划算法

针对无人车离散空间轨迹规划时存在路径不平滑、速度不平稳、动态规划运算时间长等问题,提出一种基于优化的离散空间轨迹规划算法。将无人车所需搜索的空间解耦为纵向-横向空间（S-L空间）和纵向-时间空间（S-T空间）,在S-L空间根据静态避障和路径平滑程度的要求设计代价函数进行动态规划,进而利用二次规划对动态规划结果进行优化;在S-T空间提出一种改进的动态规划方法,根据道路速度限制和不可倒车约束优化搜索,并引入启发函数加快对规划终点的搜索速度,减少算法计算量,提高运行效率。仿真实验结果表明,在静态避障和动态避障环境中,所提算法规划出的轨迹曲率更小、速度变化更平滑、运行时间更快,相比于传统动态规划算法单次规划时间减少了77.13%。     

矩生成函数与广义Feller算子

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Near-field lithography on the azobenzene polymer liquid crystal films

In this article, we reported near-field research on azobenzene polymer liquid crystal films using scanning near-field optical microscopy (SNOM). Optical writing and subsequently topographic reading of the patterns with subwavelength resolution were carried out in our experiments. Nanometer scale dots and lines were successfully fabricated on the films and the smallest dot diameter is about 120 nm. The width of the line fabricated is about 250 nm. This method is also a choice for nanolithography. The mechanism of the surface deformation on the polymer films was briefly analyzed from the viewpoint of gradient force in the optical near field. The intensity distribution of the electric field near the tip aperture was numerically simulated using finite-difference time-domain (FDTD) method and the numerical simulation results were consistent with the experimental results.     

Local thermal conductivity of polycrystalline AlN ceramics measured by scanning thermal microscopy and complementary scanning electron microscopy techniques

The local thermal conductivity of polycrystalline aluminum nitride (AlN) ceramics is measured and imaged by using a scanning thermal microscope (SThM) and complementary scanning electron microscope (SEM) based techniques at room temperature.The quantitative thermal conductivity for the AlN sample is gained by using a SThM with a spatial resolution of sub-micrometer scale through using the 3ω method.A thermal conductivity of 308 W/m·K within grains corresponding to that of high-purity single crystal AlN is obtained.The slight differences in thermal conduction between the adjacent grains are found to result from crystallographic misorientations,as demonstrated in the electron backscattered diffraction.A much lower thermal conductivity at the grain boundary is due to impurities and defects enriched in these sites,as indicated by energy dispersive X-ray spectroscopy.     

Wavelength tunable ultra-short pulses based on a flat broadband spectrum generated in a nonlinear ytterbium-doped fiber amplifier

We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pump power.Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum(center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges.Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm,the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around1200 nm, and its output power and pulse width are 40 m W and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.