标准摩尔吉布斯函数变化相同的原电池

有这样的一类反应，它可以被设计成不同的化学电池，在这些不同的化学电池中发生着相同的电池反应，而各个电池的标准电动势Ｅ０却又各不相等．这是由于相同的化学反应的标准摩尔吉布斯函数变化虽然相同，但可能有不同的电子得失数     

基于LDA模型的BBS话题演化

BBS(论坛)作为一种新兴的网络媒体,是网民获取信息和发表评论的主要渠道之一。怎样组织BBS上的话题,发现和跟踪新话题以及话题的演化成为了研究的热点。传统的方法更多的是去检测和跟踪话题,而没有考虑话题的演化。提出了基于LDA模型的话题演化方法,表示话题在时间上的演化情况,发现热门话题和冷门话题,能更好地指导网民了解正在发生的事情。实验证明有很好的效果。     

Numerical Simulation of Muzzle Flow Field Based on Calculation ofCombustion Productions in Bore

To improve the accuracy of numerical simulation of muzzle chemical flow field, and study the gunpowder combustion productions, the muzzle flow field is simulated coupled with the calculation of combustion productions in bore. The calculation in bore uses the gibbs free-energy minimization method and the classical interior ballistics model. The simulation of the muzzle flow field employs the multi-component ALE(Arbitrary Lagrange-Euler)equations. Computations are performed for a 12.7 mm gun. From 2.48 ms to 3.14 ms, the projectile moves in the gun barrel. CO and H₂O masses decrease by 3.37％ and 6.51％, and H₂ and CO₂ masses increase by 11.11％ and 10.58％. The changes conform to the fact that the water-gas equilibrium reaction of all reactions plays a dominant role in this phase. After the projectile leaves the barrel, the masses of H₂ and CO decrease, and the masses of H₂O and CO₂ increase. When it moves to 80d away from the muzzle, the decreases are 12.75％ and 8.05％, and the increases are 12.76％ and 36.26％, which tallies with the existence of muzzle flame. Further, CO and H₂ burn more and more fiercely with the muzzle pressure p_g increasing, and burn more and more weakly with the altitude rising. When two projectiles launch in series, the combustion of the second projectile muzzle flow field is fiercer than the first projectile. Analysis results have shown that the proposed method is effective for simulating the muzzle flow filed.     

基于在线消息传递的主题追踪方法

主题追踪因可以有效地汇集和组织分散在不同时间、地点的信息,并从主题层次的角度对某个主题相关事件的时效性、动态演化关系等得到比较全面的把握,成为当前数据挖掘领域的重要研究方向.现有基于概率主题模型的主题追踪方法主要以潜在狄利克雷分布(Latent Dirichlet allocation,LDA)模型为基础,采用在线吉布斯采样(Online Gibbs Sampling,OGS)和在线变分贝叶斯(Online Variational Bayesian,OVB)算法进行参数估计.OGS和OVB算法尽管解决了LDA模型中使用传统离线近似推理方法所需内存空间的大小随数据集的增长而不断增加,无法训练海量数据集以及数据流数据的问题,但训练的精度和速度均有待提高.该文基于LDA模型的改进因子图提出了一种在线消息传递(Online Belief Propagation,OBP)的主题追踪算法.该算法借助因子图中消息传递(BeliefPropagation,BP)算法的推理,通过切分海量数据集为段,并用前一段数据集训练后的参数计算当前段的梯度下降,使得主题追踪更加快速和准确.四组大规模文本数据集的实验对比表明,LDA模型中OBP算法在速度和精度上均优越于OGS和OVB算法,文中也从理论上进一步验证了OBP算法的收敛性,并给出了主题追踪的具体应用.     

超高清内容清晰度用户体验质量评价

针对多媒体行业对超高清内容清晰度用户体验评价的迫切需求,提出了一种有效的无参考质量评价算法,以预测目标内容的用户感知体验,并区分原始4K和伪4K内容。通过对目标内容进行分割,利用局部方差选择了3个代表性子块代替全局来提高计算效率。针对超高清内容的特性,提取了复杂度特征、频域特征和像素统计特征。采用支持向量回归的方法将这些提取的特征融合为一个质量指标,以预测目标内容的质量分数。实验结果表明,本模型可以有效地评估用户感知体验,并具有良好的辨别真假4K内容的能力。     

Synthesis of group IV and V metal diboride nanocrystals via borothermal reduction with sodium borohydride

The synthesis of early transition nanocrystals using NaBH₄ and the respective metal oxides at atmospheric pressure was studied at temperatures between 400 and 1000°C. Reaction products were analyzed by x‐ray diffraction, the crystallite size was determined after Rietveld refinement of diffraction patterns, while the morphology was analyzed by scanning and transmission electron microscopy. For all the investigated systems the lowest temperature to complete the synthesis was 700°C and the reaction occurred in three subsequent steps: (i) decomposition of NaBH₄, (ii) formation of crystalline ternary species Na–M–O and Na–B–O, (iii) conversion of intermediary species to MB₂ and NaBO₂. Syntheses carried out at T > 700°C only caused coarsening of the powders. The synthetized boride powders had the morphology of highly agglomerated nanocrystals. TiB₂ had a specific surface area of 33.5 m²/g and crystallite diameter of 12 nm. Both ZrB₂ and HfB₂ had a platelet‐like morphology with crystallite diameter around 45 nm and specific surface area of 25.0 and 36.4 m²/g, respectively. Finally, NbB₂ and TaB₂ powders had a crystallite diameter around 5 nm with specific surface area of 21.1 and 11.4 m²/g, respectively. The goal of this synthesis is the use of cheap raw materials and moderate temperature conditions.     

Phase content prediction in polymer-derived ceramics with metal additives

In this study, silicon oxycarbide (SiOC) is selected as the base polymer to derive a SiOC ceramic (PDC) matrix, and four transition metals M (M = Ni, Mo, Co, and Zr) are individually introduced into the SiOC base to form various SiOC/M systems. SiOC-Ni, SiOC-MoC_x, and SiOC-CoSi_x are obtained by pyrolysis at 1100°C, whereas SiOC-ZrO_x forms upon pyrolysis at 1400°C. The selected SiOC/M systems encompass four different types of phase separation pathways—pure metal, metal carbide, metal silicide, and metal oxide (SiC-SiO₂-C-Ni, SiC-SiO₂-C-MoC_x, SiC-SiO₂-C-CoSi_x, and SiC-SiO₂-C-ZrO_x). The driving force for crystallization has been analyzed using a Gibbs free energy minimization method and phase fractions of these different PDC systems are calculated based on the lever rule. This work also reveals the energetics related to the quaternary systems and provides guidance to synthesizing metal-containing PDCs with desired phase contents. In addition, we have examined the broad applicability of the phase content prediction method for a variety of other SiOC/M systems.     

嫦娥一号卫星CCD立体相机影像超分辨率重建算法

针对嫦娥一号卫星CCD立体相机空间分辨率不足的问题,运用最大后验概率估计法(MAP)实现了月表影像的超分辨率重建。介绍了嫦娥一号卫星CCD立体相机的成像模型,分析了图像获取过程中的主要影响因素,并建立了相应的超分辨率重建模型。基于该模型,首先采用误差-参数分析法估计嫦娥一号卫星CCD立体相机动态成像光学系统的点扩散函数(PSF);然后将估计的PSF应用到MAP算法所建立的目标函数中,采用共轭梯度法对目标函数进行最值求解;再通过VC软件平台编程实现了对单帧正视月表影像的超分辨率重建;最后从信息熵、清晰度和频谱等方面对重建图像进行评价,结果表明重建图像像质优良。     

一种新颖的异步多径CDMA信号的 贝叶斯多用户检测方法

马尔可夫链蒙特卡罗(MCMC)方法有效地解决了贝叶斯计算的问题,但是不容易将它应用于有未知干扰用户的异步多径CDMA系统.为了克服这一困难,本文提出一种新颖的贝叶斯多用户检测方法,它首先用线性群盲解相关器对接收信号做预处理,然后再用Gibbs采样(一种典型的MCMC算法)做贝叶斯多用户检测.仿真结果表明,该方法的检测性能明显地优于线性群盲多用户检测,其计算复杂度的增加与小区内用户数目呈线性关系.为了进一步提高本文方法的性能,我们使用两级Gibbs采样,根据第一级Gibbs采样的输出得到更精确的参数估计,并把它用于第二级Gibbs采样中.仿真结果证明,与只使用一级Gibbs采样的方法相比,两级Gibbs采样的检测性能明显地改善了.