基于单频GPS的单点测浪方法的研究

介绍一种用单频单台GPS接收机解算其相对位置变化的算法—PVD算法的基本原理,针对它在海浪测量应用中的特点,提出基于海浪谱估计的自适应PVD算法。实测数据的处理结果表明,用自适应PVD算法解算出的浪高可达厘米级精度。     

Dark energy,co-evolution of massive black holes with galaxies,and ASTROD-GW

The detection of low frequency band (100 nHz–100 mHz) and very low frequency band (300 pHz–100 nHz) gravitational waves (GWs) is important for exploration of the equation of state of dark energy and the co-evolution of massive black holes (MBHs) with galaxies. Most galaxies are believed to have a massive black hole in the galactic core. In the formation of these black holes, merging and accretion are the two main processes. Merging of massive black holes generate GWs which could be detected by space GW detectors and Pulsar Timing Arrays (PTAs) to cosmological distances. LISA (Laser-Interferometric Space Antenna) is most sensitive to the frequency band 1 mHz–100 mHz, ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical Devices] optimized for Gravitational Wave detection) is most sensitive to the frequency band 100 nHz–1 mHz and PTAs are most sensitive to the frequency band 300 pHz–100 nHz. In this paper, we discuss the sensitivities and outlooks of detection of GWs from binary massive black holes in these frequency bands with an emphasis on ASTROD-GW. The GWs generated by the inspirals, merging and subsequent ringdowns of binary black holes are standard sirens to the cosmological distance. Using GW observations, we discuss the methods for determining the equation of state of dark energy and for testing the co-evolution models of massive black holes. ASTROD-GW is an optimization of ASTROD to focus on the goal of detection of GWs. The mission orbits of the 3 spacecraft forming a nearly equilateral triangular array are chosen to be near the Sun-Earth Lagrange points L3, L4 and L5. The 3 spacecraft range interferometrically with one another with arm length about 260 million kilometers. With 52 times longer in arm length compared to that of LISA, the strain detection sensitivity is 52 times better toward larger wavelength. The scientific aim is focused for gravitational wave detection at low frequency. The science goals include detection of GWs from MBHs, and Extreme-Mass-Ratio Black Hole Inspirals (EMRI), and using these observations to find the evolution of the equation of state of dark energy and to explore the co-evolution of massive black holes with galaxies.     

KrF激光对高速飞片的驱动特性研究

利用诱导空间非相干技术平滑的KrF准分子（248nm）激光驱动带有烧蚀层的平面靶，研究激光空间均匀性对产生完整飞片的影响，结果表明激光不均匀性在2％以下，能够产生完整的高速飞片，且完整飞片能够维持20ns以上不破裂；当激光不均匀性达到5％，激光引入流体力学不稳定性种子应很强，冲击波在靶内输运过程中不稳定性不断发展增强，到靶背时强到足以使飞片解体甚至气化，不能产生完整的飞片。为了获得尽可能高的飞片速度，采用激光与烧蚀层参数不匹配方法，使冲击波对飞片作多次加速。利用功率密度为1012 W/cm2的KrF激光与含50μm Kapton烧蚀层的5μm铝飞片作用，得到速度约10km/s的高速飞片，与模拟结果吻合得很好。     

声波激振破坏的机理及条件研究

从微观层面而言,物体在声波激励共振中发生了失效破坏,显然是因为出现了破坏物质微观粒子之间结合力的因素。在大气中运动传播的声波进入物质体后转换为应力波,这种应力波(能量)的传导、扩散和聚集交合方式会对物质微观粒子结合薄弱之处的结合力产生影响。这是因为当声波作为外激励源能量作用于物质粒子并大到一定程度时,特别是在两个纵波对撞或在变向结构交汇处出现回波激振效应时,会使粒子间出现异常的能量变化,从而破坏了粒子间相对稳定的平衡状态。如果物体中的粒子大量失衡,就会对物体产生整体结构性破坏作用,使物体结构强度下降、出现裂纹,甚至完全失效。     

粒子拖尾长度对高频DPIV测量误差的影响

基于连续激光源的高采样频率DPIV系统在进行曝光时可能会产生粒子拖尾现象。明渠湍流试验和数值模拟试验结果显示，粒子拖尾长度的增加会导致平均流速减小和湍流强度增大。分析表明，导致平均流速误差的原因之一是诊断窗口边缘局部粒子图像的缺失，且图像缺失程度会随着粒子拖尾长度增加而增大，从而使平均速度随粒子拖尾长度增加而减小；粒子拖尾的另一个直接后果是增大了粒子图像的有效粒径，从而导致湍流强度增大。通过增大第二个诊断窗口的尺寸，进行相关函数标准化和相关系数补偿等方法，可以消除粒子拖尾长度引起的误差。     

A method to test HF ray tracing algorithm in the ionosphere by means of the virtual time delay

It is well known that a 3D ray tracing algorithm furnishes the ray’s coordinates, the three components of the wave vector and the calculated group time delay of the wave along the path. The latter quantity can be compared with the measured group time delay to check the performance of the algorithm. Simulating a perfect reflector at an altitude equal to the virtual height of reflection, the virtual time delay is assumed as a real time delay. For a monotonic electronic density profile we find a very small relative difference between the calculated and the virtual delay for both analytic and numerical 3D electronic density models.     

Numerical simulation of time delay interferometry for a LISA-like mission with the simplification of having only one interferometer

In order to attain the requisite sensitivity for LISA, laser frequency noise must be suppressed below the secondary noises such as the optical path noise, acceleration noise etc. In a previous paper (Dhurandhar, S.V., Nayak, K.R., Vinet, J.-Y. Time delay interferometry for LISA with one arm dysfunctional. Class. Quantum Grav. 27, 135013, 2010), we have found a large family of second-generation analytic solutions of time delay interferometry with one arm dysfunctional, and we also estimated the laser noise due to residual time-delay semi-analytically from orbit perturbations due to Earth. Since other planets and solar-system bodies also perturb the orbits of LISA spacecraft and affect the time delay interferometry (TDI), we simulate the time delay numerically in this paper for all solutions with the generation number n ? 3. We have worked out a set of 3-year optimized mission orbits of LISA spacecraft starting at January 1, 2021 using the CGC2.7 ephemeris framework. We then use this numerical solution to calculate the residual optical path differences in the second-generation solutions of our previous paper, and compare with the semi-analytic error estimate. The accuracy of this calculation is better than 1 cm (or 30 ps). The maximum path length difference, for all configuration calculated, is below 1 m (3 ns). This is well below the limit under which the laser frequency noise is required to be suppressed. The numerical simulation in this paper can be applied to other space-borne interferometers for gravitational wave detection with the simplification of having only one interferometer.     

Interaction of oblique wave beam with ionospheric layer F2

Interaction of a powerful obliquely incident wave beam of decameter radio waves with the ionospheric F2 layer is analyzed. Much like the linear case, propagation through the natural anti-waveguide layer F2 splits the initial beam. Some part of its energy leaks through the ionospheric layer, the other part goes back along a downward trajectory. However, nonlinearity leads to further stratification of the ionospheric layer. A new feature, in comparison with the linear case, is appearing a narrow waveguide beneath the F2 layer maximum which traps a small part of the beam energy. We study the relationship between these parts of the wave field in a simplified model of parabolic F2 layer, with nonlinearity caused by thermal plasma expulsion from the high field intensity region. Analytical results are supplemented with numerical estimates of the effects.     

Evaluation of uncertainty in gravity wave potential energy calculations through GPS radio occultation measurements

The application of the Global Positioning System (GPS) radio occultation (RO) method to the atmosphere enables the determination of height profiles of temperature, among other variables. From these measurements, gravity wave activity is usually quantified by calculating the potential energy through the integration of the ratio of perturbation and background temperatures between two given altitudes in each profile. The uncertainty in the estimation of wave activity depends on the systematic biases and random errors of the measured temperature, but also on additional factors like the selected vertical integration layer and the separation method between background and perturbation temperatures. In this study, the contributions of different parameters and variables to the uncertainty in the calculation of gravity wave potential energy in the lower stratosphere are investigated and quantified. In particular, a Monte Carlo method is used to evaluate the uncertainty that results from different GPS RO temperature error distributions. In addition, our analysis shows that RO data above 30 km height becomes dubious for gravity waves potential energy calculations.     

基于功率复用的椭圆球面波函数非正交调制方法

围绕如何降低基于椭圆球面波函数的非正交调制（PSWF-NPSM）系统误码率，降低信号检测复杂度，引入调制信号功率复用思想，提出基于功率复用的椭圆球面波函数非正交调制（PD-PSWF-NPSM）方法。该方法对载波信号按子波带进行功率分配，增加了调制信号最小欧式距离，降低了系统误码率；在接收端，提出基于检测统计量的串行干扰相消信号检测方法，依据不同支路信号间功率差异，对信号进行分离、检测。理论与仿真分析表明，该方法在不降低系统频带利用率、调制信号功率谱、峰均功率比特性前提下，能够有效提高系统误码性能，降低调制信号检测复杂度；与原非正交调制方法相比，当误比特率（BER）为10^-5时，所提方法系统误码性能提升约1.7 dB。