Sampling of fractional bandlimited signals associated with fractional Fourier transform

Fractional Fourier transform (FRFT) plays an important role in many fields of optics and signal processing. This paper considers the problem of reconstructing a fractional bandlimited signal with FRFT. We propose a novel reconstruction method for fractional bandlimited signals using the fractional Fourier series (FRFS). The advantage is that the sampling expansion can be deduced directly not based on the Shannon theorem. By utilizing the generalized form of Parseval’s relation for complex FRFS, we obtain the sampling expansion for fractional bandlimited signals with FRFT. We show that the sampling expansion for fractional bandlimited signals with FRFT is a special case of Parseval’s relation for complex FRFS.     

融合引导概率的语音识别解码算法研究

语音帧在声学特征空间中的位置信息可以辅助解码器对潜在路径进行筛选。传统的语音识别系统缺乏利用这种位置信息。针对这种不足,本文提出一种引导概率模型,用于描述语音帧属于声学特征空间不同局部的概率,并将其用于识别。使用引导概率后,解码器更强调对声学特征空间中最有希望的局部进行搜索,保留并扩展通过此局部空间的路径,同时弱化不经过此局部空间的路径。实验结果显示,融合引导概率的解码算法在不显著增加解码复杂度的情形下,使汉字相对错误率下降10.95%。结果分析表明,融合了语音帧声学位置信息的解码方法能够更有效地鉴别潜在路径,从而降低误识率。     

Low-temperature electrolytic coloration and spectral property of ammonium alum crystals

Ammonium alum crystals are colored electrolytically using a pointed cathode and a flat anode at low temperatures and under various voltages. SO₃^?, SO₂^? and O₃^? hole-trapped centers are produced in colored ammonium alum crystals. Characteristic absorption bands of SO₃^?, SO₂^? and O₃^? hole-trapped centers are observed in absorption spectra of colored ammonium alum crystals. Production and conversion of hole-trapped centers are explained. Current–time curves for electrolytic coloration of ammonium alum crystal and their relationship with electrolytic coloration process are given.     

基于非色散紫外算法的一氧化氮气体检测与分析

提出了一种基于非色散紫外(NDUV)算法,利用光电二极管阵列(PDA)探测器和光谱仪检测一氧化氮气体的分析方法。通过对比分析不同积分次数下一氧化氮吸收谱和无吸收谱内不同波长宽度的总光强,引入光源影响因子F和吸收谱因子B,得到吸光度与浓度的拟合方程及相关系数。结果表明,采用合适的拟合阶数、拟合波长宽度和分析方法,吸光度与浓度的二阶拟合相关系数可达0.999 9以上, 通过拟合方程所获得的待测气体浓度与标准值浓度的误差在3%以内。     

Preparation and Mechanical Properties of Fe3Al Nanostructured Intermetallics

Nanostructured Fe₃Al intermetallic compounds were produced by using hydrogen arc plasma method. The transmission electron microscopy experiments showed that the average particle size of the as-synthesized was about 40-nm. The change in hardness of Fe₃Al nanostructured intermetallic compounds with annealing temperatures was observed and evaluated.     

Li and K NMR relaxation study of a LiKSO4 single crystal

The ⁷Li and ³⁹K NMR relaxations in a LiKSO₄ single crystal grown by the slow evaporation method were investigated by employing a pulse NMR spectrometer. From the experimental data, the quadrupole coupling constant and asymmetry parameter were determined at the temperatures of 180 and 300 K. The relaxation processes of ⁷Li and ³⁹K were studied for the LiKSO₄ crystal, and the relaxation times for the ⁷Li and ³⁹K nuclei exhibit remarkable changes near T_c2 (=190 K). The activation energies for ⁷Li and ³⁹K were determined in phases I and III. The large change in the activation energy at 190 K indicates that the Li and K ions are significantly affected during this transition. The correlation time of the ⁷Li calculated from the spin-lattice relaxation time and quadrupole parameters was larger than that of the ³⁹K calculated using the same method. The reason for this is that the Li ion undergoes molecular motion as in the LiO₄ groups.     

Atomic force microscopy investigation of growth process of organic TCNQ aggregates on SiO2 and mica substrates

<正>Deposition patterns of tetracyanoquinodimethane(TCNQ) molecules on different surfaces are investigated by atomic force microscopy.A homemade physical vapour deposition system allows the better control of molecule deposition. Taking advantage of this system,we investigate TCNQ thin film growth on both SiO_2 and mica surfaces.It is found that dense island patterns form at a high deposition rate,and a unique seahorse-like pattern forms at a low deposition rate.Growth patterns on different substrates suggest that the fractal pattern formation is dominated by molecule-molecule interaction.Finally,a phenomenal "two-branch" model is proposed to simulate the growth process of the seahorse pattern.     

Cs 39D态Rydberg原子Stark光谱的实验研究

本文从理论和实验上对Cs39D态Rydberg原子在弱电场作用下的Stark效应做了详细研究. 理论上利用数值方法计算了Cs原子39D态的Stark结构;实验上,采用两步激发超冷基态原子获得超冷Rydberg原子,通过场电离的方法获得了39D态的Stark光谱,测量获得α^5/2₂,α^5/2₀,α^3/2₂和α^3/2₀相应的极化率分别为：62(7),－146(13), 73(6) 和－106(20) MHz·V^-2cm²,实验结果与理论相符合.     

Integrated modeling of insect flight: From morphology,kinematics to aerodynamics

An integrated and rigorous model for the simulation of insect flapping flight is addressed. The method is very versatile, easily integrating the modeling of realistic wing–body morphology, realistic flapping-wing and body kinematics, and unsteady aerodynamics in insect flight. A morphological model is built based on an effective differential geometric method for reconstructing geometry of and a specific grid generator for the wings and body; and a kinematic model is constructed capable to mimic the realistic wing–body kinematics of flapping flight. A fortified FVM-based NS solver for dynamically moving multi-blocked, overset-grid systems is developed and verified to be self-consistent by a variety of benchmark tests; and evaluation of flapping energetics is established on inertial and aerodynamic forces, torques and powers. Validation of this integrated insect dynamic flight simulator is achieved by comparisons of aerodynamic force-production with measurements in terms of the time-varying and mean lift and drag forces. Results for three typical insect hovering flights (hawkmoth, honeybee and fruitfly) over a wide rang of Reynolds numbers from O(10²) to O(10⁴) demonstrate its feasibility in accurately modeling and quantitatively evaluating the unsteady aerodynamic mechanisms in insect flapping flight.     

基于经验模态分解和小波阈值的冲击信号去噪

冲击信号是非线性的并且容易受到噪声污染。为研究冲击信号去噪的问题,本文针对经验模态分解(Empirical Mode Decomposition,EMD)去噪和小波阈值去噪方法存在的不足,提出了基于EMD的小波阈值去噪方法。单纯的EMD去噪方法会在去除高频噪声的同时压制高频的有效信息。本文将EMD与小波阈值去噪相结合,利用连续均方误差准则确定含噪较多的高频固有模态函数(Intrinsic Mode Function, IMF),对高频IMF分量进行小波阈值去噪,以分离并保留这些分量中的有效信息,同时保持低频IMF分量不变。对模拟数据和实际冲击信号进行去噪处理,结果表明,基于EMD的小波阈值去噪方法的去噪效果优于单纯的EMD去噪方法和小波阈值去噪方法。