一种基于PCA和Hough变换的类星体自动识别方法

确定类星体的红移是类星体识别的一个重要目标。由于过去类星体发射谱的静止发射谱模板主要靠天文学家的先验知识得到 ,因此采用模板匹配的方法效果一般不太理想。本文的主要工作有以下二个方面 :(1 )选用了主分量分析方法构造类星体静止发射谱的模板 ,这样 ,模板来源于实际光谱 ,而不是依赖于天文学家的推断 ,因此更加接近实际情况 ;(2 )用二维Hough变换来自动确定红移值。尽管理论上来说 ,只有一个红移参数需要确定 ,但观测发现 ,在大多数情况下发射峰的强度同时发生了变化 ,故在Hough变换中加入强度比例因子作为另一个参数 ,这样可有效提高正确识别率。实验证明 ,本文所提出的方法是可行的 ,正确识别率可达 90 %左右。     

The Cosmic Time in Terms of the Redshift

In cosmology one labels the time t since the Big Bang in terms of the redshift of light emitted at t, as we see it now. In this Note we derive a formula that relates t to z which is valid for all redshifts. One can go back in time as far as one wishes, but not to the Big Bang at which the redshift tends to infinity.     

利用爱因斯坦转盘推求中心引力场中的光频红移--在普通物理教学中讲解等效原理的一种尝试

通过球对称引力场与爱因斯坦转盘上的惯性离心力场的对比，利用强等效原理导出光频的引力红移。     

共轭尺寸和表面氧化协同触发的红色荧光碳点用于有机溶剂中痕量水的检测

以邻苯二胺和盐酸多巴胺为前体,利用磷酸调节反应体系的pH值(pH=7, 3, 1),制备了荧光逐渐红移的碳点(CDs):CDs-7(绿光)、 CDs-3(橙光)和CDs-1(红光).通过透射电子显微镜(TEM)、拉曼光谱(Raman)、傅里叶变换红外光谱(FTIR)、 X射线电子能谱(XPS)、紫外-可见吸收光谱和荧光衰减曲线分析表明,反应体系pH值的减小促进了前体碳化交联,导致sp2共轭域尺寸和石墨化程度增加,从而使CDs的荧光红移.另外,酸性环境有利于使CDs表面氧化形成羧基,促进CDs荧光红移的同时改善了量子效率(QY).利用CDs-1量子产率高(14.8%)和发光的溶剂依赖特性,将其作为荧光探针分别检测了乙醇(EtOH)、 N,N-二甲基甲酰胺(DMF)和1,4-二氧六环(DIO)中的痕量水,检出限分别为0.86%, 0.123%和0.023%,表明CDs-1在痕量水的检测方面具有应用潜力.     

Difference in effect of temperature on absorption and Raman spectra between all-trans-β-carotene and all-trans-retinol

<正>Temperature dependencies(81℃-18℃) of visible absorption and Raman spectra of all-trans-β-carotene and all-trans-retinol extremely diluted in dimethyl sulfoxide are investigated in order to clarify temperature effects on different polyenes.Their absorption spectra are identified to be redshifted with temperature decreasing.Moreover, all-trans-β-carotene is more sensitive to temperature due to the presence of a longer length of conjugated system.The characteristic energy responsible for the conformational changes in all-trans-β-carotene is smaller than that in all-transretinol. Both of the Raman scattering cross sections increase with temperature decreasing.The results are explained with electron-phonon coupling theory and coherent weakly damped electron-lattice vibrations model.     

Conformations, energies, and intramolecular hydrogen bonds in dicarboxylic acids: implications for the design of synthetic dicarboxylic acid receptors

The various conformers of the dicarboxylic acids HO2C--(CH2)n--CO2H, n = 1-4, were obtained using density functional methods (DFT), both in the gas phase and in the aqueous phase using a polarized continuum model (PCM). Several new conformers were identified, particularly for the two larger molecules glutaric (n = 3) and adipic acid (n =4). The PCM results show that the stability of most conformers were affected, many becoming unstable in the aqueous phase; and the energy ordering of conformers is also different. The results suggest that conformational preferences could be important in determining the design and stability of appropriate synthetic receptors for glutaric and adipic acid. Geometry changes between gas and aqueous phases were most marked in those conformers containing an intramolecular hydrogen bond. Additional calculations have probed the strength of intramolecular hydrogen bonds in these dicarboxylic acids. In the cases of glutaric and adipic acid, the strength of the intramolecular hydrogen bond were estimated to be around 28-29 kJ/mol, without any vibrational energy correction. The intramolecular hydrogen bond energies in malonic and succinic acid were also estimated from the calculated H-bond distances using an empirical relationship. Intramolecular H-bond redshifts of 170-250 cm(-1) have been estimated from the results of the harmonic frequency analyses.     

飞秒光脉冲基于交叉相位调制的压缩脉冲对的产生

数值模拟了在喇曼散射效应影响下,波长位于反常色散区的高阶孤子泵浦脉冲与波长在正常色散区的信号脉冲通过交叉相位调制作用产生的压缩脉冲对.结果表明,由于受喇曼效应的影响,飞秒信号脉冲产生的脉冲对不再保持对称,滞后的蓝移脉冲峰值功率随传输距离的增加而减小,产生孤子红移.同时发现喇曼系数增大,超前红移脉冲峰值功率增加,滞后蓝移脉冲峰值功率降低.分析了孤子阶数和正、负走离效应对脉冲压缩对变化规律的影响.     

基于粒子群优化算法的测光红移回归预测

星系的红移在天文研究中极其重要,星系测光红移的预测对研究宇宙大尺度结构及演变有着重要的研究意义。利用斯隆巡天项目发布的SDSS DR13的150 000个星系的测光及光谱数据进行分析,首先根据颜色特征并基于聚类的方法对星系进行分类,由分类结果可知早型星系的占比较大。对比了三种不同的机器学习算法对早型星系进行测光红移回归预测实验,并找出最优的方法。实验中将星系样本中u, g, r, i, z五个波段的测光值以及两两做差得到的10个颜色特征作为输入数据,首先构建BP网络,使用BP算法对星系的测光红移进行回归预测;然后利用遗传算法（GA）优化BP网络各层参数,将优化后的GA-BP算法应用于早型星系的回归预测试验中。考虑到GA算法的复杂操作会影响预测效率,并且粒子群算法（PSO）不仅稳定性高且操作简单,因此将粒子群算法应用到星系样本中早型星系的测光红移回归预测实验中,进而采用粒子群算法优化BP网络（PSO-BP）。实验中将光谱红移作为期望值,采用均方差（MSE）作为误差分析指标来评判三种算法的精度,将PSO-BP回归预测结果与BP网络模型、GA-BP网络模型进行比较。由实验结果可知,BP网络的MSE值为0.001 92,GA-BP网络的MSE值0.001 728,PSO-BP网络的MSE值为0.001 708。实验结果表明,所用到的PSO-BP优化模型在精度上优于BP神经网络模型和GA-BP神经网络模型,分别提高了11.1%和1.2%;在效率上优于传统的K近邻（KNN）测光红移估计算法, 克服了KNN算法中遍历所有数据样本进行训练的缺点并且其泛化性能优于其它BP网络优化模型。     

Properties of hyperon stars rotating at Keplerian frequency

The structure and properties of a Keplerian rotating hyperon star with an equation of state (EOS) investigated using the relativistic σ--ω--ρ model are examined by employing an accurate numerical scheme. It is shown that there is a clear rotating effect on the structure and properties, and that hyperon star matter cannot support a star with a mass larger than 1.9 M_Θ, even a star rotating at the fastest allowed frequency. The constraints of the two known fastest rotating frequencies (716 Hz and 1122 Hz) on the mass and radius of a hyperon star are also explored. Furthermore, our results indicate that the imprint of the rapid rotation of a hyperon star on the moment of inertia is clear; the backward equatorial redshift, the forward equatorial redshift and the polar redshift can be distinguished clearly, the forward equatorial redshift is always negative; and its figuration is far from a spherical symmetric shape.