A subband Steiglitz‐McBride algorithm for automatic analysis of FID data

Fast, accurate, and automatic extraction of parameters of nuclear magnetic resonance free induction decay (FID) signal for chemical spectroscopy is a challenging problem. Recently, the Steiglitz‐McBride algorithm has been shown to exhibit superior performance in terms of speed, accuracy, and automation when applied to the extraction of T₂ relaxation parameters for myelin water imaging of brain. Applying it to FID data reveals that it falls short of the second objective, the accuracy. Especially, it struggles with the issue of missed spectral peaks when applied to chemical samples with relatively dense frequency spectra. To overcome this issue, a preprocessing stage of subband decomposition is proposed before the application of Steiglitz‐McBride algorithm to the FID signal. It is demonstrated that by doing so, a considerable improvement in accuracy is achieved. But this is not gained at the cost of the first objective, the speed. An adaptive subband decomposition is employed in conjunction with the Bayesian information criteria to carry out an efficient decomposition according to spectral content of the signal under investigation. Furthermore, adaptive subband decomposition and the Bayesian information criteria also serve to make the resulting algorithm independent of user input, which also fulfills the third objective, the automation. This makes the proposed algorithm favorable for fast, accurate, and automatic extraction of FID signal parameters.     

A method for the automatic selection and tuning of the parameters of a sparse SLE solver

A technique for the automatic selection of the method for solution of a sparse system of linear algebraic equations (SLE) and selection of the method parameters from the analysis of the SLE matrix of coefficients is presented. The parameters are selected so as to maximize the performance metric. A formal model of the performance of a SLE solver is presented and is used to formulate an algorithm for construction, precedent learning, and application of the proposed method. The method is approved for iterative SLE solvers from the PETSc parallel library of the MVS-100K supercomputer platform at the Interdepartmental Supercomputer Center of the Russian Academy of Sciences.     

Shape Optimization for 3D Turbulent Flows Using Automatic Differentiation

Abstract

We present through this paper some new results with our approach for optimal shape design based on a CAD-free framework for shape and unstructured mesh deformations, automatic differentiation by program for the gradient computation and mesh adaption by metric control. Automatic differentiation allows for an easy, reliable and fast discrete adjoint computation. We managed to get the Jacobian of our Navier-Stokcs solver including a k-e turbulence model and wall-laws. The CAD-free framework is shown to be particularly convenient for optimization when the mesh connectivities and the shape discretization arc variable during optimization. Using these ingredients constrained optimization for turbulent transonic flows has been investigated in both 2 and 3D.     

多壁碳纳米管/聚乙烯复合材料的制备及其导电行为

多壁碳纳米管/聚乙烯复合材料的制备及其导电行为;碳纳米管;高密度聚乙烯;渗流阈值;导电行为;V-PTC特性     

Measurement of stimulated Brillouin scattering （SBS） threshold based on waveform variation of SBS optical limiting

This paper proposes a method for measuring the stimulated Brillouin scattering (SBS) threshold based on waveform variation of SBS optical limiting. The output waveforms for different pump power densities are numerically simulated, and validated in the Nd:YAG seed-injected laser system. The results indicate that SBS does not take place in the case of a low pump power density and thus the output power scales up linearly with pump power. Once the pump power density exceeds the SBS threshold, SBS takes place and thereby the energies are transferred from pump to Stokes. As a result, a small shoulder appears in the trailing edge of the output waveform, which provides another method to determine the SBS threshold.     

基于回归相关模型的自动图像标注

如何挖掘基于语义的相关模型是当前自动图像标注技术中一项重要而迫切的研究课题。本文从相关概率模型的角度分析了回归技术解决自动图像标注任务的可行性,进而提出了基于回归相关模型(Regression RelevanceModel,RRM)的自动图像标注框架。RRM通过有效地建立了图像-关键词的相     

垂直裂缝气井生产动态预测及参数识别

为了摆脱分析解释水力压裂裂缝参数时选择图版的繁复工作和克服人为的误差,在引入非达西因子的基础上,考虑裂缝导流能力在生产过程中的变化,提出了垂直裂缝气井中真实气体在地层-裂缝系统中非达西渗流的数学模型和生产动态预测模型,建立了识别垂直裂缝气井水力裂缝参数的生产历史自动拟合模型,并给出了数值解法,为认识和了解气层、分析和评估气井压裂施工质量,提供了准确可靠的方法。     

KDP晶体激光损伤机理研究

大口径KDP晶体是唯一可用作激光约束核聚变(ICF)中Pockels盒和倍频器件的晶体材料,但是低的抗激光损伤阈值使其应用受到了限制.本文从电子-空穴对的产生及稳定机制、光伤实体的本质等方面总结了多年来人们对KDP晶体激光损伤机理的研究进展,尤其从多光子电离、碰撞电离、激光加热三个方面定性阐述了电子-空穴对的产生机制, 而电子-空位对的稳定机制是探讨光损伤的关键步骤.另外从晶体生长过程及后处理两个方面初步讨论了提高光伤阈值和光学均匀性的途径.     

Yb:GdVO4晶体的光谱及激光损伤阈值

采用提拉法(Czochralski)生长出优质的GdVO4和Yb:GdVO4晶体,其中纯GdVO4晶体具有较高的透过率,可达81;.晶体在室温下的偏振吸收光谱与非偏振荧光光谱表明,Yb:GdVO4晶体是一种具有较大的吸收半峰宽和荧光半峰宽的激光晶体,分别为44～52nm和40～46nm;随着掺杂浓度增大,π偏振吸收系数呈现饱和趋势,且荧光峰的位置出现了红移.此外,还采用Nd:YAG激光器测试了晶体的激光损伤阈值,实验表明,随着Yb3+掺杂浓度从4.1at;增加到22.9at;,激光损伤阈值也相应地从19.9×109W/cm2逐渐减小到2.79×109W/cm2.     

低温低剂量率下金属-氧化物-半导体器件的辐照效应

对金属氧化物半导体(MOS)器件在低剂量率γ射线辐照条件下的剂量率效应以及温度效应进行了研究.对不同剂量率、不同温度辐照后MOS器件的阈值电压漂移进行了比较.结果表明,低剂量率辐照下,感生界面态要受到辐照时间的长短以及生成的氢离子数目的影响,辐照时间越长,生成的氢离子越多,感生界面态密度越大;温度对界面态的影响与界面态建立的时间有关,低温辐照时,界面态建立的时间要加长 关键词： 辐照效应 阈值电压漂移 低剂量率 低温 界面态