A nonparametric spectrum estimation method for dispersion and attenuation analysis of borehole acoustic measurements

Dispersion and attenuation analysis can be used to determine formation anisotropy induced by fractures,or stresses.In this paper,we propose a nonparametric spectrum estimation method to get phase dispersion characteristics and attenuation coefficient.By designing an appropriate vector filter,phase velocity,attenuation coefficient and amplitude can be inverted from the waveform recorded by the receiver array.Performance analysis of this algorithm is compared with Extended Prony Method(EPM)and Forward and Backward Matrix Pencil(FBMP)method.Based on the analysis results,the proposed method is capable of achieving high resolution and precision as the parametric spectrum estimation methods.At the meantime,it also keeps high stability as the other nonparametric spectrum estimation methods.At last,applications to synthetic waveforms modeled using finite difference method and real data show its efficiency.The real data processing results show that the P-wave attenuation log is more sensitive to oil formation compared to S-wave;and the S-wave attenuation log is more sensitive to shale formation compared to P-wave.

High-Precision Vital Signs Detection Method Based on Spectrum Refinement and Extended DCMA

In this paper,the spectral estimation algorithm is extended to the detection of human vi-tal signs by mm-wave frequency modulated continuous wave(FMCW)radar,and a comprehensive algorithm based on spectrum refinement and the extended differentiate and cross multiply al-gorithm(DCMA)has been proposed.Firstly,the improved DFT algorithm is used to accurately obtain the distance window of human body.Secondly,phase ambiguity in phase extraction is avoided based on extended DCMA algorithm.Then,the spectrum range of refinement is determ-ined according to the peak position of the spectrum,and the respiratory and heartbeat frequency information is obtained by using chirp z-transform(CZT)algorithm to perform local spectrum re-finement.For verification,this paper has simulated the radar echo signal modulated by the simu-lated cardiopulmonary signal according to the proposed algorithm.By recovering the simulated car-diopulmonary signal,the high-precision respiratory and heartbeat frequency have been obtained.The results show that the proposed algorithm can effectively restore human breathing and heart-beat signals,and the relative error of frequency estimation is basically kept below 1.5%.

Supercontinuum spectra generation in the single-mode optical fibre with concave dispersion profile

In this paper, a new method is proposed to generate broad supercontinuum （SC） spectra in the single-mode optical fibre with concave dispersion profile, We numerically simulate pulse evolutions and discuss physics mechanism in detail for SC spectrum generation in the optical fibre with concave dispersion profile. Furthermore, general criteria are presented for specifying the shape of SC spectrum by introducing normalized parameters, which are related to the fibres and the initial pump pulses. The results show that the flat and broad SC spectra are indeed generated in our proposed optical fibre.

Quantitative energy-dispersive X-ray fluorescence analysis for unknown samples using full-spectrum least-squares regression

The full-spectrum least-squares(FSLS) method is introduced to perform quantitative energy-dispersive X-ray fluorescence analysis for unknown solid samples.Based on the conventional least-squares principle, this spectrum evaluation method is able to obtain the background-corrected and interference-free net peaks, which is significant for quantization analyses. A variety of analytical parameters and functions to describe the features of the fluorescence spectra of pure elements are used and established, such as the mass absorption coefficient, the Gi factor, and fundamental fluorescence formulas. The FSLS iterative program was compiled in the C language. The content of each component should reach the convergence criterion at the end of the calculations. After a basic theory analysis and experimental preparation, 13 national standard soil samples were detected using a spectrometer to test the feasibility of using the algorithm. The results show that the calculated contents of Ti, Fe, Ni, Cu, and Zn have the same changing tendency as the corresponding standard content in the 13 reference samples. Accuracies of 0.35% and 14.03% are obtained, respectively, for Fe and Ti, whose standard concentrations are 8.82% and 0.578%, respectively. However, the calculated results of trace elements (only tens of lg/g) deviate from the standard values. This may be because of measurement accuracy and mutual effects between the elements.

Taylor Dispersion of Contaminants by Dual-peak Spectral Random Waves

Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra. Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency.

An IR Study of the Dispersion Stability of Catalyst Powders Dispersed in Solutions of Linear Saturated Polyesters

The conformation of polymers at the solid-liquid interface has been the subject of considerable interest in the fundamental theory and applied practice. In paints and printing inks, dispersions of pigment or filler powders in polymeric binder solutions have to be maintained in the colloidal state. One of the stabilizing mechanisms for paint is the steric stabilization. On the other hand, in the formation reaction of polymer at the solid-liquid interface took place between monomer solutions and solid

Seismic energy dispersion compensation by multi-scale morphology

Seismic energy decays while propagating subsurface, which may reduce the resolution of seismic data. This paper studies the method of seismic energy dispersion compensation which provides the basic principles for multi-scale morphology and the spectrum simulation method. These methods are applied in seismic energy compensation. First of all, the seismic data is decomposed into multiple scales and the effective frequency bandwidth is selectively broadened for some scales by using a spectrum simulation method. In this process, according to the amplitude spectrum of each scale, the best simulation range is selected to simulate the middle and low frequency components to ensure the authenticity of the simulation curve which is calculated by the median method, and the high frequency component is broadened. Finally, these scales are reconstructed with reasonable coefficients, and the compensated seismic data can be obtained. Examples are shown to illustrate the feasibility of the energy compensation method.

Asymmetric W-shaped and M-shaped soliton pulse generated from a weak modulation in an exponential dispersion decreasing fiber

We study localized waves on continuous wave background in an exponential dispersion decreasing fiber with two orthogonal polarization states. We demonstrate that asymmetric W-shaped and M-shaped soliton pulse can be generated from a weak modulation on continuous wave background. The numerical simulation results indicate that the generated asymmetric soliton pulses are robust against small noise or perturbation. In particular, the asymmetric degree of the asymmetric soliton pulse can be effectively controlled by changing the relative frequency of the two components. This character can be used to generate other nonlinear localized waves, such as dark-antidark and antidark-dark soliton pulse pair, symmetric W-shaped and M-shaped soliton pulse. Furthermore, we find that the asymmetric soliton pulse possesses an asymmetric discontinuous spectrum.

Supercontinuum Generation Enhanced by Cross-phase Modulation in Dispersion-flattened and Decreasing Fiber

Supercontinuum spectrum generation in a dispersion-flattened and decreasing fiber with two orthogonally polarized pulses was simulated and calculated. The research results indicated that the supercontinuum spectrum generated by two orthogonally polarized pulses is wider and flatter than that generated by single polarized pulse due to cross-phase modulation. The cross-phase modulation effect can enhance the supercontinuum spectrum generation. When the pump power of the input pulse is lower, the enhancement of supercontinuum spectrum generation by cross-phase modulation effect is more significant.

Novel Biomaterial for NCT - “Rigid” Particles of (DNA-gadolinium) Liquid-Crystalline Dispersions

The formation and physico-chemical properties of biomaterial, based on double-stranded (ds) DNA molecules and bearing high concentration of gadolinium, is described. This “rigid” biomaterial demonstrate a few unique properties: (i) the ds DNA molecules forming complexes with gadolinium are fixed in the spatial structure of “rigid” particles, (ii) an abnormal negative band in the circular dichroism spectrum permits to follow the formation of this biomaterial;(iii) local concentration gadolinium in the content of biomaterial can reach 40%. These properties show that we are dealing with a novel type of biomaterial strongly enriched by gadolinium. This opens a gateway for practical application of this biomaterial for neutron-capture reactions. A first attempt to apply this material for neutron-capture reaction in combination with neutron generator of thermal neutron flux was performed. Positive result obtained at destruction of CHO cells allows one to state that the advantages of this biomaterial are a simple manipulation with it, a possibility to adjust its gadolinium content, long-term stability of its physico-chemical properties, as well as a reduced cost of neutron-capture experiment.

Effect of Initial Frequency Chirp on Supercontinuum Generation in Dispersion-flattened Fibers

Supercontinuum generation in dispersion-flattened fibers is studied theoretically.It is found that the flat spectral width of the supercontinuum generation in normal dispersion-flattened fiber can be increased from 66 nm to over 100 nm when the absolute value of the initial frequency chirps is increased from zero to 10.It is further found that initial frequency chirps are adverse to flat and wideband supercontinuum generation in anomalous dispersion-flattened fiber,and when the absolute value of the frequency chirps is increased to a certain degree,supercontinuum spectrum even can not be achieved.

一款紧凑型磁谱仪的特性参数分析与实验刻度研究

超短脉冲激光与靶相互作用可产生高能电子以及质子、离子、X/γ射线等次级粒子和射线,这些粒子和射线在惯性约束聚变、激光核物理、实验室天体物理、生物、医学以及材料科学等领域具有广泛的应用前景。高能电子的特征参数测量对理清激光等离子体相互作用过程、优化粒子参数和拓展其应用具有重要意义。本文研究设计了一款紧凑型矩形结构磁谱仪,在永磁铁均匀场中采用前、侧、后三面IP板布局,满足了几十keV到10 MeV的电子能谱测量需求,并对磁谱仪的特征参数如能量色散、能量色散梯度、能量分辨率、斜入射效应等进行详细分析。基于北京大学DC-SRF-Ⅱ射频超导光阴极电子枪开展了磁谱仪能量刻度实验,在真空条件下实验测量了0.7~1.8 MeV区间内多个能量的电子能谱,结果显示,磁谱仪的能量测量与监测系统结果基本符合。电子能谱的能量分辨率主要决定于磁谱仪自身分辨能力,为提高能量分辨率,需通过准直系统进一步减小入射孔径和电子发散角。

GaSe/ZnS异质结的结构和界面性质的第一性原理研究

本文设计了一种GaSe/ZnS范德瓦耳斯异质结构(vdWH),并用第一性原理计算系统地分析了该异质结构的几何、电子、输运性质。通过结合能、声子谱、从头算分子动力学(AIMD)模拟验证了所构建GaSe/ZnS范德瓦耳斯异质结构的稳定性。详细计算了GaSe/ZnS vdWH界面性质中的平面平均电子密度差和平均静电势。结果表明,GaSe/ZnS vdWH是一种直接带隙为2.19 eV,载流子迁移率较高的异质结构。其中,沿x方向的电子迁移率可达1394.63 cm^(2)·V^(-1)·s^(-1),而沿y方向的电子迁移率可达1913.18 cm^(2)·V^(-1)·s^(-1),性能优异,有望应用于电子纳米器件。

多途混响环境中声扩频信号线性与相关性分析

为分析浅海多途信道中声扩频信号的相关性和线性,建立了计入频率衰减与海底损耗的浅海Pekeris波导虚源法计算模型;对浅海中的脉冲信号与扩频信号进行了仿真计算,通过混响室试验初步研究了多途混响环境中扩频信号的线性。仿真结果显示:虚源法和简正波法的频域解一致,得到了与简正波理论相同的低频模式频散现象,验证了虚源法适用于浅海理想波导、Pekeris波导中的低频问题;当发生模式频散,低频扩频信号的相关性能强于同扩频参数的高频信号。试验结果表明:低频脉冲的时域波形发生畸变、展宽时,同频率的扩频信号能准确测出反射信号的几何时延,证明了低频多途效果仍可看作每个“路径”信号的线性叠加。

基于夹层氮化硅波导的可见-中红外超连续谱特性研究

提出一种低厚度氮化硅-蓝宝石-氮化硅夹层波导结构。利用其色散波辐射现象和中红外相位匹配条件,结合波导脉冲传输模型,讨论了夹层波导不同物理尺寸对相位匹配点和光谱展宽的影响,数值模拟获得了0.5~4μm的超连续谱展宽,并且在-40 dB水平下具有更远中红外色散波产生。通过该模型,详细解释了非线性波导脉冲传输的潜在机制。理论模型分析表明,通过优化氮化硅及蓝宝石夹层的物理尺寸,进而改变相位匹配条件,可以在较宽的波长范围内控制色散波的位置。

可见光-近红外伪装分散染料墨水的制备及其性能

针对当前分散染料墨水其喷墨印花织物仅能与背景环境“同色”而不能“同谱”,无法有效躲避现有侦察技术的问题,开发了一套可见光-近红外伪装分散染料墨水。通过模拟绿叶、土壤和枯叶的反射光谱特征,筛选了特定分散染料,探究了印花工艺对织物伪装及服用性能的影响,通过超细化加工制备了分散染料墨水并探究了其性能。结果表明:调控分散蓝60、分散深蓝SUBC 12、分散橙30、分散黄CPY 015、分散红CPM 011与炭黑复配比例及印花工艺制备的仿绿叶、土壤和枯叶印花织物,其伪装及服用性能良好;5种分散染料墨水的粒径均小于173.00 nm,离心、耐热、高温储存和常温储存稳定性均高于80%,过滤流速分别为200、375、188、428、167 g/min,喷墨印花性能良好。

扩散MRI技术在颞叶癫痫中的应用进展

癫痫是一种由于大脑神经元异常放电造成短暂性功能障碍的慢性神经系统疾病,严重影响着患者的身心健康和生活质量。其中,颞叶癫痫(temporal lobe epilepsy, TLE)是成年人常见的药物难治性癫痫,因此对其进行及时的诊断和治疗尤为重要。扩散MRI(diffusion MRI, dMRI)技术可以利用水分子的扩散反映TLE患者大脑组织微观结构的变化,dMRI主要包括扩散加权成像(diffusion weighted imaging, DWI)以及在其基础上衍生的各种扩散技术,如扩散张量成像(diffusion tensor imagin,DTI)、扩散峰度成像(diffusion kurtosis imaging, DKI)、扩散频谱成像(diffusion spectrum imaging, DSI)以及神经突方向离散度和密度成像(neurite orientation dispersion and density imaging, NODDI)等。本文简要总结了各种dMRI技术在TLE中的临床应用进展,并对其未来的研究前景进行了展望,旨在了解dMRI技术在TLE中的应用现状,为TLE的诊疗及扩散技术在相关领域的研究提供一定参考。

基于自适应光子和分层色散图的实时色散渲染方法

焦散是光线经过反射或折射后汇集形成的高亮区域现象,色散是由于折射焦散中不同波长的单色光折射率差异而出现的彩色光谱现象,是渲染逼真半透明物体时复杂和耗时的光照计算步骤。在渲染色散时,现有光线追踪技术必须依赖高端GPU硬件才能实现实时渲染。基于图像空间的焦散图技术,文中提出一种简洁、高效的实时色散渲染方法。提出了采样7个单色光并自适应调整7色光子尺寸的方法,用于近似整条色散光谱的渲染;并提出了分层色散图策略,避免了光子光栅化尺寸的增加,提高了渲染效率。实验结果表明,所提方法在个人电脑上可做到实时渲染,以离散采样光谱的7个单色光模拟了整条连续光谱,减少了渲染的计算量和存储量,并且改善了基于图像空间技术的噪点问题。

基于核磁共振技术测量研究锂电池正极导电浆料的分散性

采用核磁共振(NMR)技术研究了不同类型导电颗粒制备的锂电池正极导电浆料。通过测量导电浆料的弛豫时间和弛豫谱,发现了在同等研磨分散条件下炭黑浆料的弛豫时间与比表面积(BET)值呈负相关性,且炭黑浆料弛豫谱为单峰结构,说明炭黑更容易得到分散;而碳纳米管(CNT)浆料的弛豫谱全部为多峰结构,说明CNT的分散性较差。研究结果表明,CNT浆料的固含量越大,颗粒的比表面积越大,那么弛豫谱主峰的弛豫时间就越大,主峰信号占比就越低,说明CNT在溶剂中就越容易发生纠缠和团聚。

槽波地震勘探隐伏地质体探查研究及应用

在构造复杂矿井中,隐伏地质体是制约矿井安全生产的主要因素,如何准确、高效的查明隐伏地质异常体,是智慧化、透明化矿山建设必须解决的问题。本文以晋北煤业5-302工作面为例,采用槽波地震勘探技术对工作面内隐伏地质构造进行探测。通过频散分析、频谱分析、能量分析等槽波地震数据处理手段,可查明工作面内隐伏地质构造及其他异常体的分布情况,对同类型构造复杂矿井回采工作面探测有一定的借鉴指导意义。