一种新的X射线脉冲星信号模拟方法

由于无法在地面直接观测到X射线脉冲星信号, 且空间飞行探测耗时长, 成本高, 模拟具有真实物理特征的X射线脉冲星信号对X射线脉冲星信号处理方法及导航方案的验证具有重要意义. 本文提出了一种利用太阳系质心处脉冲星信号模型和航天器轨道信息, 建立航天器处实时光子到达速率函数, 再利用尺度变换法产生光子到达时间序列的脉冲星信号模拟新方法. 该方法真实还原了脉冲星信号的频率缓变特性, 考虑了动态探测环境下的相对论效应, 且避免了现有模拟航天器处光子序列方法中的迭代过程, 产生非齐次泊松光子到达时间序列的运算量也低于常用的齐次泊松过程筛选法和反函数递推法. 数值仿真从频率特性、流量特性、轮廓相似度及与实测数据的接近程度四个方面验证了该模拟方法的正确性.     

一种脉冲星信号模拟新方法

在脉冲星导航地面实验中,为解决地面无法接收脉冲星辐射的X射线信号的问题,必须在实验系统中模拟脉冲星辐射信号. 本文提出两种全新脉冲星信号模拟方法. 第一种方法基于统计物理模型,该方法克服了常用泊松模型模拟方法中仿真适应性窄、仿真速度慢和时间分辨率低等不足,实现了对任意随机过程的脉冲信号进行快速高时间分辨率的仿真;第二种方法基于优化统计模型,该方法针对非齐次泊松过程信号的特性进行优化,仿真速度比常用泊松模型模拟方法提高至少30 倍,对于低流量脉冲星,甚至提高4个数量级,可实现纳秒级时间分辨率仿真. 关键词： 脉冲星导航 非齐次泊松过程 X射线光子信号     

A new dilute gas transport phenomenon

A new transport phenomenon is deduced by arguments based on the existence of nonequilibrium long-range pair correlations which persist even in a dilute gas.     

Shifted identical bands: A new phenomenon

The levels in ¹⁶²Gd were identified in spontaneous fission studies. Its transition energies are remarkably similar to those in ¹⁶⁰Gd. From that work, an analysis of yrast bands in even-even proton to neutron-rich Ba to Pb nuclei led to the discovery of a new phenomenon, shifted identical bands (SIB). SIBs are yrast bands in neighboring nuclei (a, b) with moments of inertia which are identical when shifted by a constant amount κ, so J _1a (1+κ)=J _1b , from 2⁺ to 8⁺ and higher to 16⁺. Out of over 700 comparisons, 55 SIBs were found from stable to the most neutron-rich Ce-W nuclei with $\left| {\bar k} \right|$ between 1.5% and 13%, where the spread in κ is less than ±1%, and only four identical bands ( $\bar k \cong 0$ ). As examples, we found for ¹⁵⁸Sm-¹⁶⁰Gd, $\bar k = \left( { - 3.2_{ - 0.2}^{ + 0.1} } \right)\%$ (where the ± is the total spread in κ from ?3.1 to ?3.4); ¹⁵⁶Nd-¹⁶⁰Gd, (?10.6 _?0.2 ^+0.4 )%; ¹⁵⁸Sm-¹⁶⁰Sm, (3.4 _?0.3 ^+0.5 )%. The J ₁ values were fitted to a variable moment of inertia model with parameters J ₀ and C whose values correlate with the SIB J ₁ values. The SIBs are not correlated either with deformation or with the N _p N _n product of the IBA model.     

脉冲星脉冲轮廓累积的最小熵方法

获取脉冲星辐射信号累积轮廓的传统方法是先识别信号周期,再按周期对信号进行折叠累加,这种方法依赖于周期识别的准确性,对累积轮廓质量也无评价标准.本文分析了脉冲星累积轮廓和周期的强相关性,提出了周期未知时直接进行轮廓累积的最小熵方法,并对其进行证明,在此基础上,讨论了该方法在周期识别中的作用.利用仿真数据和RXTE卫星的实测数据实验验证了该方法的有效性. 关键词： 脉冲星 最小熵 累积轮廓 周期识别     

A fully vectorial effective index method to analyse the propagation properties of microstructured fiber

Based on numerical simulation, we theoretically study the linear and nonlinear properties of microstructured fiber. Using the fully vectorial effective index method, we calculate the effective refractive index for different air hole size. We show how the linear properties such as spot size, numerical aperture, splice loss and bend loss can be controled by changing the air hole size. We also propose the same method for analysing effective area and self-phase modulation of microstructured fiber for different designing parameters. We compare all our results with other numerical methods.     

多谐波脉冲星信号时延估计方法

针对脉冲星导航技术中延时估计这一关键问题, 提出了频域上直接使用脉冲星信号测量到达时间集合进行时延估计的方法——多谐波脉冲星信号时延估计(MHSPE)方法. 该方法建立在频域上相位时延的极大似然估计的基础上, 通过高次谐波对脉冲星观测信号提取出各谐波相位的极大似然估计, 然后取频谱上各谐波的幅值进行归一化作为各谐波相位的权值, 最后取各谐波相位的加权平均作为该时刻的相位估计. 理论上证得MHSPE算法对相位的估计是无偏、一致的, 相比于频域上一次谐波的极大似然估计, MHSPE方法的信噪比随谐波数m的增加而增加, 当各谐波幅值相同时, 信噪比可提高m_1/2倍; 与脉冲星信号时延的克拉美罗界比较, 脉冲星信号时域的导数在频域上的反映就是各谐波分量的数量, 因此随着谐波次数的增加脉冲星信号时延估计可极大趋近克拉美罗界. 采用RXTE航天器对Crab脉冲星的实测数据检验MHSPE方法的性能, 实验结果表明, 针对低信噪比的脉冲星信号, MHSPE可获得高精度的相位估计, 随观测时间增加, 估计精度快速收敛于克拉美罗界.     

一种测量高精度角度误差的新方法

本文严格从折射定律出发,给出了适合于任意大入射角的棱镜光学平行差的计算公式,据此提出了一种以大入射角光路测量平面光学件角度误差的新方法,并讨论了几个实例,最后分析了入射角的误差对测量精度的影响及入射角的选定原则,得出了一些有价值的结论。     

A pulsar inside the Sun?

The Crimean observation of solar oscillations in 1974–1982 showed that the basic period of pulsation of the Sun hidden in its deep interior was equal to P ₀=160.0101±0.0001min. More recently, the period was changed to the new value P ₁=159.9662±0.0006min, which almost coincided with the annual sidelobe of the former period P ₀. The amplitude of the P₁ oscillation has increased considerably over 1994–1995. We substantiate the hypothesis that a) the change in the period was caused by the interaction of the P₀ oscillation with the rapid rotation of the solar core and that b) the latter has the form of a compact, highly magnetized object like a neutron star rotating with sidereal period P₁.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 10, pp. 1210–1214, October, 1996.The author expresses his gratitude to the referee for his honest and useful comments to this paper. The author is also thankful to V. I. Haneychuk and T. T. Tsap for their active participation in the solar observations at the CrAO which were used in the present paper. This work was supported in part by the International Science Foundation under Grants No. UCU000 and UCU200.     

A new method to calculate phonons in superlattices

The crystalline structure of the superlattice can be described by a suitably chosen supercell. From the known dynamical matrices of the constituent compounds, two large matrices are derived in the multi-dimensional space of the supercell using a similarity transformation. An appropriate combination of the elements of these two matrices results in the desired dynamical matrix for the supperlattice. A numerical example for a 4×4 GaAs-AlAs superlattice and a discussion concerning experimental results are also given.     

A new method to measure the neutron skin

Dipole resonances have been excited in ^121?124Sn isotopes using (³He,t) charge exchange reaction at E ³ _He=177 MeV and the cross sections were related to the neutron-skin thicknesses. The well understood correlation may be used to determine the neutron-skin thicknesses in the future.     

A new method to test virtual photon spectra

Millisecond isomers in¹⁴⁶Tb,¹⁴⁸Ho and¹⁵⁰Tm, observed in⁶⁰Ni reactions on³⁹Y,⁹⁰Zr, and⁹²Mo targets, are interpreted as (πh_11/2 vh_11/2 ^?1) 10⁺ isomers predicted by the shell model. Their decays are characterized.     

提高PCA识别率的新算法

针对基于主元分析(PCA)的识别算法不能最优区分不同种类样本的缺点,提出了一种新的多主元分析(Multi-PCA)识别算法。该算法为每类样本构造单独特征空间,用各个空间的特征向量重建待识别样本。特征空间是基于某类样本图像的共性建立,因此重建该类样本图像时将得到较小重建误差,而重建其它类图像时的误差较大。可以根据重建误差的大小来识别样本图像,将待识别样本分类到具有最小重建误差的特征空间。在ORL、YALE人脸库和标牌压印字符库上的实验结果显示,Multi-PCA的识别率比PCA有较大提高。     

非线性波方程求解的新方法

从Legendre椭圆积分和Jacobi椭圆函数的定义出发，得到了新的变换，并把它用于非线性演化方程的求解.用三个具体的例子，如非线性Klein-Gordon方程、Boussinesq方程和耦合的mKdV方程组，说明了具体的求解步骤.比较方便地得到非线性演化方程或方程组的新解析解，如周期解、孤子解等. 关键词： Jacobi椭圆函数 非线性方程 周期解 孤子解     

Practical limitations to accuracy in a nulling automatic wavelength-scanning ellipsometer

The limits of accuracy in an automatic wavelength-scanning ellipsometer are defined on the basis of measured mechanical properties of the instrument and the geometrical and optical defects of the optical components. A computational procedure is described for obtaining accurate Δ and ψ values by using a matrix model of the instrument, and the areás in which the greatest improvements in accuracy can be achieved are identified.     

A generalized Ohm law for pulsar magnetospheres

A generalized Ohm law is obtained for relativistically streaming plasmas.     

安培环路定理的一种证明方法

一般地证明了安培环路定理，证明方法简明易懂，直观且不失普遍性，适合在普通物理和电磁学中使用。     

A new graphical method relating to optical fiber attenuation

A new graphical method is presented for separating the causes of optical fiber losses. Some examples are given showing the use of this technique and some results derived from this technique are presented.