Structural, magnetic and dielectric properties of La2−xCaxNiO4+δ (x = 0, 0.1, 0.2, 0.3)

The synthesis, structural, magnetic and dielectric properties of a new type of high permittivity materials La_2−xCa_xNiO_4+δ (x = 0, 0.1, 0.2, 0.3) (abbreviated as LCNs) were reported. The samples were prepared through conventional solid state reaction route. Detailed structural information was retrieved by Rietveld refinement; normalized bond length and bond valence was calculated to investigate the compression/dilation effect of bonds and atoms in unit cell. It can be found all samples belong to K₂NiF₄ structure with space group I4/mmm. Doping of Ca in La₂NiO_4+δ shrinks the unit cell and makes the structure tend to become instable. Three types of (La, Ca)-O bonds, and two kinds of Ni-O bonds exist in LCNs. Along c axis there are alternately compressed (La,Ca)O₉ dodecahedra and lengthened NiO₆ octahedra. Room temperature magnetic measurements show that the materials are paramagnetic and Ca doping can improve the spontaneous magnetization. Furthermore, all samples have colossal values of the dielectric constant (?) at frequencies lower than 1 kHz. Interestingly, La_1.8Ca_0.2NiO_4+δ maintains its high permittivity at frequencies up to 1 MHz while La_1.7Ca_0.3NiO_4+δ has the lowest dielectric loss (tan δ). Calcium doping can effectively enhance ? and inhibit tan δ. The distortion of (La,Ca)O₉ dodecahedra can well explain their dielectric properties.     

Microfiber SMPU film affords quicker shape recovery than the bulk one

Comparing to the bulk SMPU (shape memory polyurethane) film, microfiber SMPU film afforded much quicker and sharper shape recovery when heated in water bath. The shape recovery of the microfiber film only took ~ 1/4 time of that needed for the bulk film from R_r (shape recovery ratio) = 10% to R_r = 90%. The final R_r and R_f (shape fix ratio) of the microfiber film was also enhanced. The microfiber film was fabricated by electrospinning with the fiber diameter of 200 nm to 1 μm. DSC and DMA results indicate that the formation of microfiber has very limited effect on the T_trans (switching temperature) of the SMPU. The quick shape recovery of the microfiber SMPU film is considered due to the higher surface area of microfiber film that is favorable for quicker heating/cooling of the sample and quicker diffusion of water. This study offers a possible way to improve the shape recovery speed without changing the chemical composition, which may meet special needs for sensors or actuators of biomedical devices and others.     

利用量子比特间交换衰减实现无退纠缠的量子信息传输

在量子信息传输过程中,环境的作用会导致退相干与退纠缠。利用不同类型量子比特的优点,构成杂化量子比特系统是克服退相干效应,实现量子信息传输的一个有效方案。本文指出：将耦合量子比特之间信息交换过程中存在的能量损耗(量子比特间的交换衰减),与外部环境的退相干效应有机的结合起来,可以实现无退纠缠效应的量子信息传输。给出了实现无退纠缠效应信息传输,交换衰减率与退相干时间匹配的约束关系。     

基于描述特征的人脸识别研究

针对基于主成分分析识别人脸存在计算复杂、不能准确地估计训练图像的协方差矩阵等问题,提出了一种基于描述特征的人脸识别算法(Expressive feature face recognitionalgorithm, EFFRA).该算法用训练图像的右奇异向量代替PCA求解的子空间的基向量,避免了将人脸图像转换成图像向量,明显降低了计算复杂性.进一步研究发现,EFFRA提取的每一个主成分向量中含有冗余,在此基础上,利用PCA实现了EFFRA的简化算法(MEFFRA),在ORL和Essex数据库上的实验结果表明,EFFRA及MEFFRA明显优于特征脸算法,MEFFRA的识别精度略好于EFFRA,但明显减少了对存储空间的需求.     

基于模型切换的自适应背景建模方法

提出了一种基于模型切换的背景建模方法 (MSBM). 该方法以熵图像为纽带, 实现了不同精细程度的背景模型在空间上的自适应选取和在时间上的自适应切换. 对于亮度分布复杂度高的背景区域采用精细的模型以保证运动目标检测的精度, 反之采用简单的模型以降低计算量. 通过模型结构自适应结合参数自适应, 很好地兼顾了检测精度和计算代价. 基于高斯混合模型和时间平均模型的双模型切换式运动目标检测算法被用于实验研究, 结果表明这种算法的检测效果和单独采用高斯混合模型的检测效果相当, 而计算速度却比后者提高很多.     

碳包覆纳米SnO2锂离子电池负极材料合成及其性能研究

采用热解Sn(OH)₄和淀粉混合物制备碳包覆纳米SnO₂的方法合成了无定形碳包覆纳米SnO₂.采用XRD、SEM、TEM、STEM-EDX以及充放电测试等手段对其结构、形貌和性能进行表征.结果表明,样品材料中无定形碳呈薄片状,被包覆的纳米SnO₂（20~50nm）均匀分布在片状无定形碳中.产物中SnO₂与碳的不同比例影响了产物的性能,样品（SnO₂∶C＝1∶1）首次循环的可逆比容量达到404mAh·g^-1, 20次循环内无明显衰减.     

微型热管在台式电脑中的应用设计

本文根据热管导热速度很快的工作特征,在具体情况下热管可制作成可大可小的、可长可短的、可自由弯曲的结构。提出了在计算机核心部件上应用微型热管散热,将热量引出到专用风道内集中散热。机箱可制作成较封闭的结构的设计方案,从而解决了计算机中用传统风扇散热效果差,与外界对流又带来灰尘沉集在主板上,对主板带来安全隐患的问题。     

Modification on crystallization of poly(vinylidene fluoride) (PVDF) by solvent extraction of poly(methyl methacrylate) (PMMA) in PVDF/PMMA blends

The crystallization modification of poly(vinylidene fluoride) (PVDF) was investigated for the blend films of PVDF and poly(methyl methacrylate) (PMMA). The mass crystallinity (χ_c) and further, the β-phase content (F_(β)) of PVDF, were studied for the as-prepared blend films with different mass ratios. In addition, the variations of χ_c and F_(β) were systematically probed once the PMMA component was removed from the related blend systems. DSC, FTIR and XRD measurements all indicated that 1) χ_c, F_(β) and even the content of α-phase (F_(α)) decreased with the addition of PMMA; 2) with the extraction of PMMA, both χ_c and F_(β) increased while F_(α) decreased. It is worth noting that the increase of χ_c and F_(β) depended on the relative amount of extracted PMMA (E_PMMA), i.e., the more PMMA was removed, the more χ_c and F_(β) increased. These results reveal the hindrance effect from the PMMA constituent to the crystallization of PVDF, and consequently, this restriction would be released when the PMMA was extracted.     

气井泡沫排水起泡剂NJS的研制与应用

针对中原油田地层水矿化度高、温度高、井深的情况,研制了泡沫排水起泡剂NJS.NJS分子中碳链长度为12-14,含有OCC,C=N和SO     

烤烟间作草木樨对土壤养分的影响

利用生物多样性作用机理进行不同作物间作套种是目前养分利用、生物抗病、化感作用和信息交换的研究热点。采用盆栽和田间小区试验方法,研究了烤烟间作草木樨对土壤养分的影响,结果表明,烤烟间作草木樨后对植烟土壤碱解氮和土壤速效磷含量的影响间作处理与单作处理比较没有显著差异,而在烤烟成熟中后期间作体系能不同程度地增加植烟土壤的速效钾含量,对平衡和协调土壤养分有积极的作用。