基于CZT的基波频率测量—更小运算量算法研究

由于周期信号的频谱是线谱,用FFT计算频谱时,需要设置采样频率是基波频率的整数倍,才能采样一个基波周期以最小运算量精确的计算出谐波幅度及相位.本文把CZT算法用于周期信号基波测量,提出了一种小点数多次CZT的运算方法,用4倍的基波频率采样,采样16点施加汉宁窗,合理设置计算路径,在估计的频率范围内求10点CZT,把求频谱的运算量集中在真实谱线附近,多次循环从粗测到细测逐步缩小计算范围提高精度,将计算误差控制在要求的范围内,最后把计算结果经过换算得到基波的频率.仿真结果说明该算法精度高,运算量小,优于直接FFT算法.     

弱n次积分半群拓扑

利用n次积分半群及连续线性泛函的概念,引入一新的局部凸向量拓扑,并对其基本性质进行研究。     

On the moments of some first passage times and the associated processes

First passage problems for exponenetial class of random processes are discussed     

Potential Well in Poincaré Recurrence

From a physical/dynamical system perspective, the potential well represents the proportional mass of points that escape the neighbourhood of a given point. In the last 20 years, several works have shown the importance of this quantity to obtain precise approximations for several recurrence time distributions in mixing stochastic processes and dynamical systems. Besides providing a review of the different scaling factors used in the literature in recurrence times, the present work contributes two new results: (1) For ϕ-mixing and ψ-mixing processes, we give a new exponential approximation for hitting and return times using the potential well as the scaling parameter. The error terms are explicit and sharp. (2) We analyse the uniform positivity of the potential well. Our results apply to processes on countable alphabets and do not assume a complete grammar.     

Control charts with random interarrival times between successive samplings

In the classical setup used in process monitoring, the times between the collection of successive plotted samples are considered as nonrandom. However, in several real‐life applications, it seems plausible to assume that the time needed to collect the necessary information for plotting a point in the control chart has a stochastic nature. Under this scenario, instead of focusing on the number of points plotted on the chart until an out‐of‐control signal is initiated, the appropriate statistic to look at is the total time until a signal is generated. If we denote by L the run length of a control chart and by Y_t,t = 1,2,…, the times between successive plotted points, then the compound random variable expresses the time to signal of a monitoring scheme, under a particular sampling policy. In this paper, we illustrate how S_L can be exploited to study various charts that are suitable for monitoring Poisson observations. We provide some results for the exact distribution of S_L that may facilitate the task of the performance assessment of a control chart with random plotting times; illustrations and several numerical comparisons that are useful for quality control experts who wish to practice them are presented, and finally, an illustrative example elucidating the implementation of the proposed model is also provided.     

Toward a constitutive model for cure-dependent modulus of a high temperature epoxy during the cure

A constitutive model, based on Kohlrausch-Williams-Watts (KWW) equations, was developed to simulate the evolution of the dynamic relaxation modulus during the cure of a ‘high temperature’ epoxy. The basic assumption of the modelling methodology proposed is the equivalence of the mechanisms underlying the evolution of the glass transition temperature and the relaxation time shift during the cure, leading to the use of a common potential function. This assumption is verified by the comparison of normalized glass transition data and principal relaxation times, which have been found to follow a single master curve. Results show satisfactory agreement between experimental data and model prediction over the range of chemical conversion considered.     

Analysis of bacterial fatty acids by flow modulated comprehensive two-dimensional gas chromatography with parallel flame ionization detector/mass spectrometry

Comprehensive two-dimensional gas chromatography (GC × GC) offers an interesting tool for profiling bacterial fatty acids. Flow modulated GC × GC using a commercially available system was evaluated, different parameters such as column flows and modulation time were optimized. The method was tested on bacterial fatty acid methyl esters (BAMEs) from Stenotrophomonas maltophilia LMG 958^T by using parallel flame ionization detector (FID)/mass spectrometry (MS). The results are compared to data obtained using a thermal modulated GC × GC system. The data show that flow modulated GC × GC-FID/MS method can be applied in a routine environment and offers interesting perspectives for chemotaxonomy of bacteria.     

Characteristic energy band values and electron attenuation length of a chemical-vapor-deposition diamond (0 0 1)2 × 1 surface

The characteristic energy band values such as the Fermi-level position with respect to valence band top for a boron-doped p-type hydrogen-terminated chemical-vapor-deposition (CVD) diamond (0 0 1)2 × 1 surface and for a clean CVD diamond (0 0 1)2 × 1 surface have been determined by a new method with an accuracy of ±0.02 eV. The electron attenuation length for the clean diamond (0 0 1)2 × 1 surface for the electron kinetic energy of C 1s X-ray photoemission peak by Mg Kα excitation is experimentally determined to be 2.1-2.2 nm. These values are compared and discussed with the previously reported experimental and simulation values.