股票收益率的组合分布研究

股票收益率等金融时间序列具有尖峰厚尾性,因而不适于用正态分布来描述.建立在极端事件风险的理论基础上,提出了由原始分布和尾分布组成的组合分布模型.并对深证成分A指的收益率进行了组合分布拟合.结果显示组合分布不仅比原始分布和正态分布在效率上有明显的提高,而且能较准确地估测股票的风险价值.     

Electrophoretic deposition of ZnCo2O4 spinel and its electrocatalytic properties for oxygen evolution reaction

In this paper, ZnCo₂O₄ was deposited on nickel substrate by electrophoretic deposition (EPD) method as electrocatalyst for the oxygen evolution reaction. The effect of electrophoresis variables including the deposition time, the applied voltages was discussed. XRD, SEM, and electrochemical measurement techniques were used to characterize the deposit and ZnCo₂O₄/Ni electrode. Compared with the ZnCo₂O₄ electrode prepared by nitrate decomposition method, the electrophoretic ZnCo₂O₄ electrodes exhibit better electrocatalytic properties and higher mechanical stability. And the electrode prepared at 10 V for 5 min has the best electrocatalytic properties with the overpotential of only 0.203 V at current density of 100 mA cm⁻².     

Lamellar Thickness of a Syndiotactic Polystyrene Determined from Small-angle X-ray Scattering and Transmission Electron Microscopy

Extensive morphological studies on a syndiotactic polystyrene (sPS) sample prepared from compression molding were carried out using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). SAXS was conducted at 25C as well as at 150C to enhance the scattering contrast in order to obtain more reliable morphological parameters. The compression-molded sample was crystallized into a orthorhombic crystal lattice characterized by wide-angle X-ray diffraction (WAXD). A similar weight fraction of crystallinity, ca. 0.37, was obtained from both WAXD and differential scanning calorimetry measurements.In addition to the scattering peak at a scattering vector of ca. 0.36 nm^–1 attributable to the presence of lamellar/amorphous layers, anomalous scattering at the zero angle was found from the SAXS intensity profiles. Based on the Debye–Bueche theory, the scattering profile of this peculiar zero-angle scattering was deduced and was subtracted from the raw intensity profile to obtain the intensity profile exclusively associated with the lamellar/amorphous structure. A consistent long period was obtained for SAXS measured either at 25 or 150C, provided that the appropriate subtraction of intensities due to the zero-angle scattering was conducted. Moreover, the lamellar thickness deduced from the one-dimensional correlation function was in good agreement with TEM results. A difference scattering pattern derived from SAXS measured at 150 and 25C was obtained and a comparison of the morphological parameters was provided as well.     

氰戊菊酯和甲氰菊酯对棉铃虫的亚致死效应

本文通过饲喂法测定了氰戊菊酯、甲氰菊酯两种拟除虫菊酯杀虫剂亚致死剂量(LC1与LC50)对棉铃虫3龄幼虫拒食、体重、生长发育以及驱避作用的影响。结果表明,各处理棉铃虫3龄幼虫,取食量均低于对照。处理后48h,LC50剂量以氰戊菊酯拒食活性较高,拒食率为38.65%,且LC50剂量的各处理与对照差异显著。所有处理对棉铃虫幼虫—蛹、蛹—成虫的存活率都有影响。药剂处理后,幼虫的历期延长,幼虫的化蛹也受到影响,出现畸蛹,但各处理畸蛹率均低于15%。亚致死剂量杀虫剂对棉铃虫的生长发育、幼虫体重及蛹重都有抑制作用。在LC1与LC50剂量下,两种药剂对棉铃虫也表现出驱避作用。处理48h,氰戊菊酯LC1与LC50剂量的驱避率分别为76.25%与98.75%。这些研究结果显示,低剂量的拟除虫菊酯对棉铃虫生物学方面存在不良影响。     

A comprehensive study on the droplet formation processes and its influencing factors of a tubular piezoelectric print head

Abstract

Various inks with different properties are widely used in the printed electronic industry. In order to obtain high quality inkjet printing, it is necessary to study the droplet formation process and its influencing factors comprehensively. Only in this way, the incentive conditions and liquid physical parameters of droplet ejection can be obtained and optimized. Firstly, the calculation model of the droplet ejection process is established for a tubular print head and the boundary conditions are set according to the driving characteristics. Secondly, the free surface flow is calculated in the simulation software and sequential pictures of the droplet formation processes are captured to validate the availability of the numerical algorithm. Finally, the droplet formation processes of the tubular piezoelectric print head are simulated under different incentive conditions, different viscosities and different surface tensions. Too small a driving energy is insufficient to cause the head to eject droplets. Excessive excitation energy will result in larger or multiple satellite droplets. Additionally, the thinning process of the liquid neck is examined carefully in this paper. Results show that surface tension and viscosity have a significant effect on the thinning speed of the liquid neck, but the effect is not as significant as previous studies.     

基于Windows平行文件系统下的平行I/O

近年来,平行档案系统被广泛的用来解决这个问题,除此之外,由于电脑被使用于平行处理平台的普及率逐步上升,造成使用于电脑上的平行处理软体需求量持续增加,但是,却有可能缺乏平行I/O的系统。因此,文章旨在研究与分析Windows平行文件系统下的平行I/O的特点与实现方式。     

专用丁苯胶乳对混凝土的改性

用自制的专用丁苯胶乳对混凝土进行改性,考察了聚合物与混凝土质量比(简称聚灰比)、水与混凝土质量比(简称水灰比)、消泡剂用量、养护条件和胶乳稳定性对改性混凝土性能的影响。结果表明,当聚灰比为12%、水灰比为35%、消泡剂质量分数为丁苯胶乳的3%时,且在混凝土浇铸后干养28d的条件下,改性混凝土的抗压强度、抗折强度、黏结强度及抗渗性比未改性混凝土分别提高了6%,9%,85%,50%。稳定性越好的胶乳对改性混凝土的性能提高幅度越大。     

塔里木河“二源一干”生态供水潜力研究

为解决塔里木河干流水资源短缺、流域损失水量过大、用水效率低下、农业灌溉用水挤占生态用水等问题,基于“节水优先”的治水方针,以塔里木河二源流(阿克苏河、叶尔羌河)及其干流(“二源一干”)的山区水库群和平原水库群为研究对象,兼顾塔里木河干流的农业灌溉用水、生态用水、工业用水、生活用水等多目标,构建并求解了现状水平年和远景规划年的山区与平原水库群联合调度优化模型,分析了塔里木河干流的生态供水潜力和山区水库群联合调度的贡献。结果表明：仅通过干流平原水库群联合调度,农业灌溉用水和生态用水的供水保证率难以满足设计要求;通过山区与平原水库群优化调度,在远景规划年各行业均满足设计保证率要求,体现了山区水库群显著的调控性能和“节水优先”治水方针的合理性和可靠性;远景规划年塔里木河干流的生态供水潜力为2.84亿m³,可为塔里木河下游生态保护与修复提供了坚实的水量基础。     

A low‐profile antenna with circularly polarized reconfigurable and omnidirectional radiation patterns

A low profile circularly polarized (CP) antenna with reconfigurable polarization is designed and presented, which can radiate omnidirectional patterns that can be switched between left‐hand circularly polarized (LHCP) and right‐hand circularly polarized (RHCP). A pair of arc‐shaped complementary dipoles is acted as reconfigurable elements by bridging four pin diodes at the dipole arced arms. A meander phase shift line is employed to connected the arc dipole arms and plate cavity to adjust the phase relationship of two sources. The proposed antenna exhibits the omnidirectional radiation pattern by combining six identical elements placed in a circular array configuration. 24 p‐i‐n diodes are exploited to six elements, by manipulating the dc bias voltage across the diodes, the polarization state of the antenna can be switched. The patterns of the antenna are similar to that of a dipole, but its size is only about Φ0.87 × 0.029λ₀ at 5.8 GHz. The overlapped bandwidth of measured 3‐dB axial ratio (AR) and 10‐dB return loss is 5.724‐5.87 and 5.738‐5.91 GHz for two polarization states, which are right on the target of ISM band. It can be well adapted to medical diagnosis systems.     

空气质量细粒度数据内联关系可视分析系统

随着数据观测和数字计算技术的快速发展,空气质量数据粒度越来越细致,为研究空气质量的细粒度数据内联关系可视化、辅助理解空气污染物的转化规律提供了数据基础.针对蕴含丰富内联特征的大气质量细粒度数据开发了一个内联关系可视分析系统.首先,基于大气质量数据多维属性设计时空数据维度模型增强数据的时空表达,并提出一种基于深度学习的特征提取方法,将空气质量数据从高维空间映射到支持交互可视分析的低维特征空间;然后,设计了一套多视图联动的可视化系统,帮助用户发现空气污染传输中的细粒度内联关系,理解污染传输途径的数据分布特征.用户实例和用户评价结果表明,该系统是有效的.