公务员招聘问题的研究

建立了不符合度、失望度、不满意度等概念,将公务员招聘问题转化为求不满意度总和最小的0—1规划模型,很好地解决了在不考虑和考虑应聘人员意愿的两种情形下公务员招聘的问题.充分体现了录取的公平公正性和对人才的充分利用.     

Variable Energy Positron Annihilation Spectroscopy of GaN Grown on Sapphire Substrates with MOCVD

Depth profiled Doppler broadening of positron annihilation spectroscopy (DBPAS), which is also called the variable energy positron annihilation spectroscopy (VEPAS), is used in characterization of GaN grown on sapphire substrates with metal-organic chemical vapour deposition (MOCVD). The GaN film and the film/substrate interface are investigated. The VEPFIT (variable energy positron fit) software was used for analysing the data,and the positron diffusion length of the sapphire is obtained. The results suggest that there is a highly defected region near the GaN/sapphire interface. This thin dislocated region is generated at the film/substrate interface to relieve the strain. Effects of implantation dose on defect formation, for the GaN/Sapphire samples, which implanted by Al^ ions, are also investigated. Studies on AI implanted GaN films (not including the interface and sapphire) have revealed that there are two different regions of implantation damage. For the low Al^ implantation dose samples, in the region close to the surface, defects are mainly composed of vacancy pairs with small amount of vacancy clusters, and in the interior region of the film the positron traps are vacancy clusters without micro-voids. For the highest dose sample, however, some positron trap centres are in the form of micro-voids in the second region.     

Nanoporous Structure in Low-Dielectric Films with Positronium Annihilation Lifetime Spectroscopy

We investigate nano-porous structures in thin low-dielectric films, i.e. the pore sizes, distributions, and interconnectivity, by using depth profiled positronium annihilation lifetime spectroscopy (PALS). It is found that PALS has good sensitivity to probe both interconnected and closed pores in the range from 0.3nm to 3Onto, even in the film buried beneath a diffusion barrier. A series of low dielectric constant films of organosilicon-silsequioxane with different weight percentages of porogen have been comparatively investigated. The PALS technique can be used to distinguish the open porosity from the closed one, to determine the pore size, and to detect the percolation threshold with the increasing porosity that represents the transition from closed pores to interconnected pores.Furthermore, the pore percolation length can be derived.     

基于电磁-压电混合结构的超声波穿金属通信系统

在密闭金属腔体内外间进行通信时,超声波由于没有金属屏蔽效应而是一种良好的信号传输载体。在基于超声波的通信系统中超声换能器主要有压电式和电磁式两类结构,在同一通信系统中用于超声波发射和接收的一对换能器往往为相同类型的压电式或电磁式结构。考虑到压电式和电磁式换能器的各自优点和不足,本研究提出一种电磁-压电混合结构的超声波穿金属通信系统,该系统使用电磁式结构作为发射换能器,使用压电式结构作为接收换能器。其中所采用的电磁式超声换能器由永磁铁和绕制线圈组成,该换能器易于制作且成本较低。在此基础上,以现场可编程门阵列（Field programmable gate array, FPGA）和实验室自制电路为信号处理模块,进行穿越60mm厚铝板的信号和图像无线传输试验。系统采用通断键控(On-off keying, OOK)进行信号调制,通过自适应判决反馈均衡器（Decision feedback equalization,DFE）进行信道回波消除,在500kHz的载波下实现了100kbit/s的通信速率。在此基础上,本研究还进一步开展了穿金属图像无线传输的研究,恢复后的图像相对于原始图像达到了94.02%的相似度。     

磷化钴封装在磷富集的三维多孔碳及其双功能氧电催化性能研究

能源和环境问题是制约人类延续和发展的首要问题,高效便宜的能源存储和转换装置吸引着广泛注意。基于便携式,功率密度高,无污染等,可充放电锌-空气电池(ZAB)被大量研究。然而,阴极的氧还原(ORR)和氧析出反应(OER)缓慢的动力学限制了ZAB的实际应用。开发电催化高效,便宜,高稳定性的双功能电催化剂至关重要,而其中将过渡金属和碳基材料复合是明智的决定。磷化钴(Co₂P)化合物已经广泛研究用作高效的OER催化剂,但是对于催化剂的ORR活性很少研究。在此,本论文通过简单热处理钴盐和植酸掺杂的k-卡拉胶复合物制备出磷化钴封装在磷掺杂的多孔碳(Co₂P-PCA-800)纳米催化剂。该催化剂具有3D分级多孔结构,表现出具有与商用Pt/C相当的半波电位(E_1/2) 0.84 V,从而满足了可充放电锌-空电池需求。同时,我们还制备了磷掺杂的多孔碳(PCA)和钴掺杂的多空碳(Co-CA),对比了结构形貌对性能的影响。结果表明,具有完整的多孔结构,在每个位点的阻抗更一致,从而会有更多的有效活性位点。高效的ORR和OER活性主要归功于3D蜂窝分层多孔结构和正电荷磷化钴(Co₂P)纳米颗粒的协同作用。此外,蜂窝状3D孔结构不仅利于传质和加快电子传输也保护了磷化钴,让其更稳定。最后,我们组装了可充放电锌-空气电池用Co₂P-PCA-800作空气阴极催化剂。相比贵金属,该催化剂组装的ZAB具有接近的充放电性能和能量密度以及更高的比容量和更好的稳定性。这项工作也为解决能源和环境问题提供了新思路。     

Probing Cu Diffusion Barrier Layers on Porous Low-Dielectric-Constant Films by Posireonium Annihilation Lifetime Spectroscopy

Two kinds of Cu diffusion barrier layers, sealed films and capped films, on nanoporous low-dielectric-constant films are investigated by positronium annihilation lifetime spectroscopy （PALS）. We have found that the minimum thickness of Ta to form an effective diffusion barrier is affected by the pore size. The films with large pores require thick barrier layers to form effective diffusion barriers. In addition, a possible ultra-thin diffusion barrier, i.e. a plasma-induced densification layer, has also been investigated. The PALS data confirm that a porous low-dielectric-constant thin film can be shrunk by exposure to plasma. This shrinkage is confined to a surface layer of collapsed pores and forms a dense layer. The dense layer tends to behave as Ps （positronium） diffusion barriers. Indeed, the controlled thin “skin” layer could prevent Cu diffusion into the underlying dielectrics.     

Rectifying barrier at GaN/SiC hetero-junction studied with positron annihilation spectroscopy

Positron annihilation spectroscopy on GaN films grown on SiC substrate with MBE are presented. It is shown that the GaN/SiC interface is rectifying towards positrons, such that positrons can only travel from SiC to GaN and not vice versa. Potential steps seen by the positron at the GaN/SiC interface are calculated from experimental values of electron and positron work function. This “rectifying” effect has been successfully mimicked by inserting a thin region of very high electric field in the Variable Energy Positron Fit （VEPF） analysis. The built-in electric field is attributed to different positron affinities, dislocation and/or interface defects at the GaN/SiC interface.     

Dielectric Performance of Porous Methyl Silsesquioxane/Triacetyl-β-Cyclodextrin Thin Films

Porous methyl silsesquioxane thin films with low dielectric constant are successfully synthesized by means of the sol-gel spin-coating method. The precursor solutions are prepared by properly mixing the polymer as a matrix with different contents of triacetyl-β-cyclodextrin （TABCD） as a porogen. The chemical structure, dielectric constants, optical constants and void fraction are investigated by the ellipsometric porosimetry, Fourier transform infrared （FTIR） spectroscopy, and other methods. Influences of TABCD and methyl trimethoxysilane （MTMS） on the dielectric properties are discussed. For those samples with higher porogen loading, orientation and electronic polarizations are lower in low and high frequency regions, respectively, because of a considerably smaller number of polar molecules. The FTIR results suggest that high R value （molar ratio of H2 O to MTMS） is more advantageous for formation of cage structures and the cage/network structural ratio increases with the increasing R value.