Single‐crystal diffraction at the Extreme Conditions beamline P02.2: procedure for collecting and analyzing high‐pressure single‐crystal data

Fast detectors employed at third‐generation synchrotrons have reduced collection times significantly and require the optimization of commercial as well as customized software packages for data reduction and analysis. In this paper a procedure to collect, process and analyze single‐crystal data sets collected at high pressure at the Extreme Conditions beamline (P02.2) at PETRA III, DESY, is presented. A new data image format called `Esperanto' is introduced that is supported by the commercial software package CrysAlis^Pro (Agilent Technologies UK Ltd). The new format acts as a vehicle to transform the most common area‐detector data formats via a translator software. Such a conversion tool has been developed and converts tiff data collected on a Perkin Elmer detector, as well as data collected on a MAR345/555, to be imported into the CrysAlis^Pro software. In order to demonstrate the validity of the new approach, a complete structure refinement of boron‐mullite (Al₅BO₉) collected at a pressure of 19.4 (2) GPa is presented. Details pertaining to the data collections and refinements of B‐mullite are presented.     

基于DEMON线谱的轴频提取方法研究

目标的螺旋桨不同则轴频不相同。轴频是目标的特征之一,可以应用于目标识别当中。本文提出一种改进的高频噪声解调分析(DEMON)方法,能够得到具有明显线谱的DEMON谱;提出最大公约数算法,并给出提取轴频的具体步骤。海试数据实验结果验证了本文所提方法及算法的有效性和可行性。     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

轨道运动方程数值解的一种加速算法

针对卫星轨道受大气阻力摄动的运动方程,提出了一种数值加速算法,该算法实现简单、计算量小、精度高,适合于各类卫星轨道的方程的求解.     

反射式光纤传感器光纤参量对调制系数的影响

介绍了反射式强度型光纤传感器的光强调制原理,并以最简单的光纤对为基础,仿真研究了光纤参量对光强调制特性的影响规律.给出了这类传感器设计的指导原则.     

电光晶体正弦位相调制干涉技术

本文讨论了调制信噪比是如何影响正弦位相调制(SPM)干涉仪精度的。为了改善调制信噪比,本文提出一种新的SPM干涉仪,其中参考波和检测波由一加了正弦电压的LiNbO_3电光晶体所调制,这种方法的调制信噪比较振镜调制法高,因此能用电光调制器提高SPM干涉仪的测量精度。     

Measurements of retinal aerial image modulation (AIM) for white light based on wave-front aberration of human eye

The aerial image modulation (AIM) curve of retina under the condition of white light is obtained based on the wave-front aberration of human eye. According to the relationship between the wavelength and defocus, we modify the monochromatic wave-front aberration data to calculate the modulation transfer function (MTF) of human eye in the white-light illumination. Combined with the measurement of contrast sensitivity function (CSF) for complete eye and visual acuity (VA) under the same luminance condition, we deduce the AIM curve in natural light. We find that AIM varies slightly at lower and intermediate spatial frequencies among different eyes; at higher frequencies AIM is the predominant factor for VA when the wave-front aberration is not significant. In addition, retinal AIM is expressed in terms of neural contrast sensitivity function (NCSF) which is the clinical valuable for ophthalmologists. Considering the real illumination circumstance, it is of practical significance to obtain the AIM curve and NCSF curve under white-light condition.     

Analysis of modulation format in the 40 Gbit/s optical communication system

Three different modulation formats including nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed return-to-zero (CS-RZ) and the differential phase keying (DPSK) modulation format of each code are introduced in the article. A method of their modulated signal generation with computer is described, and a comparison of their spectra and waveforms is made. The 40 Gbps signal transmitted in 200 km G.652 fiber by way of single channel with erbium-doped-fiber-amplifier (EDFA) is simulated for these three formats. The ability of anti-dispersion and anti-PMD is analyzed. It is shown that RZ and CS-RZ formats are more tolerant than NRZ format in the same conditions.     

On algorithms for and computing with the tensor ring decomposition

Tensor decompositions such as the canonical format and the tensor train format have been widely utilized to reduce storage costs and operational complexities for high‐dimensional data, achieving linear scaling with the input dimension instead of exponential scaling. In this paper, we investigate even lower storage‐cost representations in the tensor ring format, which is an extension of the tensor train format with variable end‐ranks. Firstly, we introduce two algorithms for converting a tensor in full format to tensor ring format with low storage cost. Secondly, we detail a rounding operation for tensor rings and show how this requires new definitions of common linear algebra operations in the format to obtain storage‐cost savings. Lastly, we introduce algorithms for transforming the graph structure of graph‐based tensor formats, with orders of magnitude lower complexity than existing literature. The efficiency of all algorithms is demonstrated on a number of numerical examples, and in certain cases, we demonstrate significantly higher compression ratios when compared to previous approaches to using the tensor ring format.     

Annihilating sets for the short time Fourier transform

We obtain a class of subsets of R2d such that the support of the short time Fourier transform (STFT) of a signal f∈L²(Rd) with respect to a window g∈L²(Rd) cannot belong to this class unless f or g is identically zero. Moreover we prove that the L²-norm of the STFT is essentially concentrated in the complement of such a set. A generalization to other Hilbert spaces of functions or distributions is also provided. To this aim we obtain some results on compactness of localization operators acting on weighted modulation Hilbert spaces.