Enhancing signal-to-noise ratio and resolution in low-field NMR relaxation measurements using post-acquisition digital filters

The traditional way to enhance signal-to-noise ratio (SNR) of nuclear magnetic resonance (NMR) signals is to increase the number of scans. However, this procedure increases the measuring time that can be prohibitive for some applications. Therefore, we have tested the use of several post-acquisition digital filters to enhance SNR up to one order of magnitude in time domain NMR (TD-NMR) relaxation measurements. The procedures were studied using continuous wave free precession (CWFP-T₁) signals, acquired with very low flip angles that contain six times more noise than the Carr–Purcell–Meiboom–Gill (CPMG) signal of the same sample and experimental time. Linear (LI) and logarithmic (LO) data compression, low-pass infinity impulse response (LP), Savitzky–Golay (SG), and wavelet transform (WA) post-acquisition filters enhanced the SNR of the CWFP-T₁ signals by at least six times. The best filters were LO, SG, and WA that have high enhancement in SNR without significant distortions in the ILT relaxation distribution data. Therefore, it was demonstrated that these post-acquisition digital filters could be a useful way to denoise CWFP-T₁, as well as CPMG noisy signals, and consequently reducing the experimental time. It was also demonstrated that filtered CWFP-T₁ method has the potential to be a rapid and nondestructive method to measure fat content in beef and certainly in other meat samples.     

一种全局运动的图像处理算法研究

在摄像机进行航拍的图像处理系统中,由摄像机运动所引起的视频运动,背景变化是主要特点。在进行图像采集时,每个像素都在变化,采用传统的图像编码方式进行图像压缩,压缩效果比较差。提出了基于块分割的精确运动估计算法,它是一种很好的图像压缩方法。     

超强脉冲激光在低密度等离子体中的相对论自导引效应

分析了相对论条件下激光超短脉冲在等离子体中的传输特性 ,在傍轴近似和慢变振幅近似条件下 ,推导了折射率、电子密度、静电场以及电子空腔尺度的表达式。当激光功率超过产生自导引阈值功率时 ,激光束斑沿着传输光轴方向振荡。在有质动力产生的压力非常强时 ,聚焦光束中央部分的电子被全部排开形成电子空腔。给出了电子空腔的尺寸以及在出现电子空腔时的处理方法。在超过形成电子空腔的阈值功率 (Pc≈ 2 .5TW )时 ,空腔的尺度几乎与激光功率无关 ,这意味着电子空腔阻止了激光脉冲的进一步聚焦。     

CsI(Tl)晶体中反冲Cs和I核Quenching?Factor的测量

许多实验对用CsI(Tl)闪烁晶体作为探测器来寻找和探测暗物质的可行性进行了研究.本工作利用8MeV单能中子轰击CsI(Tl)晶体探测器来研究Cs核和I核的QuenchingFactor.在数据处理中,运用脉冲形状甄别(PSD)方法来分辨反冲核信号和本底信号.实验结果表明,在7keV到132keV的能区中,Quench ingFactor随着反冲核能量的减少而增加.在探测暗物质的实验中,这一性质对于CsI(Tl)晶体探测器获得较低的能量阈值是很有利的.     

在不同激光脉宽下的高次谐波

用数值计算方法计算了不同强激光脉冲宽度下高次谐波的产生.我们发现对于激光场强度不高,不能有效电离初态的激光场,长脉冲宽度可以更有效产生高次谐波;而对于高场强的激光场,由于它能够在几个光学周期之内把原子的初态全部电离,所以短脉冲的激光场能够更有效产生高次谐波.     

用自适应脉冲微扰引导混沌系统到周期解

用自适应脉冲微扰方法控制的系统的某个系统变量作为驱动,设计了一种自适应控制器方法对两个或多个响应混沌系统进行脉冲微扰,引导这些系统从混沌运动到低周期运动,实现同时控制多个混沌系统到不同的周期态. 当选择相同的自适应控制器输入变量实施脉冲微扰时,还可控制两个或多个混沌系统达到不同的周期态同步. 通过对R?ssler混沌系统的仿真研究证实了方法的有效性. 关键词： 混沌控制 系统参量 自适应控制器 脉冲微扰 周期态同步     

直径对脉冲爆震发动机性能的影响

本文通过实验研究了脉冲爆震发动机的直径对其性能的影响．实验结果表明；当爆震室的直径增大时，爆震波压力波形相似，平均峰值压力比较接近，且比冲基本保持不变，而推力则随爆震室直径的增大而增大。实验曲线表明爆震室内的流动具有自相似性，从而为建立尺寸律提供了实验依据．本文中比冲和平均推力是利用摆动原理测量的，并与由作用在推力壁上的压力计算得出的比冲和平均推力的理论值和实验值进行了比较，结果基本吻合，说明该测量方法可行．     

离子交换富集-导数火焰原子吸收法测定自来水中Cu,Fe和Zn

本文研究了用 2 0 1× 7阳离子交换树脂对自来水中的微量元素进行交换富集 ,采用微量脉冲进样 导数火焰原子吸收法测定富集后溶液中的Cu ,Fe和Zn ,该方法灵敏度分别为 0 2 9,0 5 9和 0 0 6 μg·L- 1 ,精密度分别为 4 2 8% ,1 95 %和 2 2 8% ,检测限分别为 1 2 8,5 85和 0 6 8μg·L- 1 ,回收率分别为 91 13% ,10 1 34%和99 84 % ,本方法大大减少了需样量 ,简便快速 ,灵敏度高。     

Active long pulse shaping technique of pulsed CO2 laser using multi-pulse discharge control

We describe the pulse forming of pulsed CO₂ laser using multi-pulse superposition technique. Various pulse shapes, high duty cycle pulse forming network (PFN) are constructed by time sequence. This study shows a technology that makes it possible to make various long pulse shapes by activating SCRs of three PFN modules consecutively at a desirable delay time with the aid of a PIC one-chip microprocessor. The power supply for this experiment consists of three PFN modules. Each PFN module uses a capacitor, a pulse forming inductor, a SCR, a high voltage pulse transformer, and a bridge rectifier on each transformer secondary. The PFN modules operate at low voltage by driving the primary of HV pulse transformer. The secondary of the transformer has a full-wave rectifier, which passes the pulse energy to the load in a continuous sequence.We investigated various long pulse shapes as different trigger time intervals of SCRs among three PFN modules. As a result, we could obtain laser beam with various pulse shapes and durations from about 250 to 1000 μs.     

Acoustic Analysis of Pathological Voices Compressedwith MPEG System

The MPEG-1 Layer 3 compression schema of audio signal, commonly known as mp3, has caused a great impact in recent years as it has reached high compression rates while conserving a high sound quality. Music and speech samples compressed at high bitrates are perceptually indistinguishable from the original samples, but very little was known about how compression acoustically affects the voice signal. A previous work with normal voices showed a high fidelity at high-bitrate compressions both in voice parameters and the amplitude-frequency spectrum. In the present work, dysphonic voices were tested through two studies. In the first study, spectrograms, long-term average spectra (LTAS), and fast Fourier transform (FFT) spectra of compressed and original samples of running speech were compared. In the second study, intensities, formant frequencies, formant bandwidths, and a multidimensional set of voice parameters were tested in a set of sustained phonations. Results showed that compression at high bitrates (96 and 128 kbps) preserved the relevant acoustic properties of the pathological voices. With compressions at lower bitrates, fidelity decreases, introducing some important alterations. Results from both works, Gonzalez and Cervera and this paper, open up the possibility of using MPEG-compression at high bitrates to store or transmit high-quality speech recordings, without altering their acoustic properties.