Fitting of two-tensor models without ad hoc assumptions to detect crossing fibers using clinical DWI data

Analysis of crossing fibers is a challenging topic in recent diffusion-weighted imaging (DWI). Resolving crossing fibers is expected to bring major changes to present tractography results based on the standard tensor model. Model free approaches, like Q-ball or diffusion spectrum imaging, as well as multi-tensor models are used to unfold the different diffusion directions mixed in a voxel of DWI data. Due to its seeming simplicity, the two-tensor model (TTM) is applied frequently to provide two positive-definite tensors and the relative population fraction modeling two crossing fiber branches. However, problems with uniqueness and noise instability are apparent. To stabilize the fit, several of the 13 physical parameters are fixed ad hoc, before fitting the model to the data. Our analysis of the TTM aims at fitting procedures where ad hoc parameters are avoided. Revealing sources of instability, we show that the model's inherent ambiguity can be reduced to one scalar parameter which only influences the fraction and the eigenvalues of the TTM, whereas the diffusion directions are not affected. Based on this, two fitting strategies are proposed: the parsimonious strategy detects the main diffusion directions without extra parameter fixation, to determine the eigenvalues and the population fraction an empirically motivated condition must be added. The expensive strategy determines all 13 physical parameters of the TTM by a fit to DWIs alone; no additional assumption is necessary. Ill-posedness of the model in case of noisy data is cured by denoising of the data and by L-curve regularization combined with global minimization performing a least-squares fit of the full model. By model simulations and real data applications, we demonstrate the feasibility of our fitting strategies and achieve convincing results. Using clinically affordable diffusion acquisition paradigms (encoding numbers: 21, 2*15, 2*21) and b values (b = 500–1500 s/mm²), this methodology can place the TTM parameters involved in crossing fibers on a more empirical basis than fitting procedures with technical assumptions.     

Data for scaling-up hydrothermal waste water treatment process

Abstract

Hydrothermal oxidation of wastes is developed as an alternative technique in order to limit the toxic end-product formation, the waste volume and the energy supply. We are now working on the transfer of this technology, and so on the determination of data for scaling-up the hydrothermal oxidation process. The main data concern the knowledge of reactive pathway, the determination of reaction kinetic and thermal parameter. Kinetic and thermal data have been determined for the hydrothermal oxidation of acetic acid as well as the reactive pathway of hydrothermal oxidation of a C, H, O, N compound, the fenuron (C₆H₅-NH-CO-N(CH₃)₂).     

SN-分子离子的势能函数和光谱常数研究

采用耦合簇CCSD(T)方法结合系列相关一致基组aug-cc-pVXZ (X=D,T,Q,5) 对基态SN^-分子离子(X³∑^-) 进行了结构优化和单点能扫描计算. 用四种方法进行基组外推得到该体系的平衡核间距R_e=0.15852 nm, 谐振频率ω_e=948.05 cm^-1, 离解能D_e=3.934 eV均与实验数据符合得很好. 对单点能扫描结果用9参数Murrell-Sorbie势能函数进行了最小二乘拟合, 得到了体系的解析势能函数表达式, 并进一步推导出了体系的力常数和光谱常数. 拟合所得势能曲线准确地再现了SN^-分子离子的离解能和平衡结构特征. 通过求解核运动的径向薛定谔方程, 得到了无转动SN^- (X³∑^-) 的全部振动态, 并进一步计算出了各振动能级相应的分子常数. 与实验结果及其他理论研究结果的对比表明, 本文关于SN^-分子离子平衡常数和光谱常数的计算结果达到了较高的精度, 能为进一步的实验探测和理论研究提供参考依据. 关键词： 势能曲线 解析势能函数 光谱常数 振动能级     

近地面三阵子天线估计电磁波到达角和极化参数

从自由空间中的三阵子天线求入射电磁波极角和方位角的基本原理出发, 结合电场各个分量与极化方式之间的关系给出了左手极化波计算波达角的公式, 及地球表面上方三阵子天线判断入射波极化方向的方法; 本文提出了一种新颖的滤除地面反射波的方法, 保证了波达角的求解精度; 利用获得的高精度的波达角和测得的电场强度, 计算出了电磁波的各种极化参数, 这些极化参数可以作为电离层研究和电磁波在电离层中传播研究的参考. 关键词： 地球表面 三阵子天线 波达角 极化参数     

Comparison of a fractal analysis and debye relaxation for the structural relaxation in amorphous metals

Abstract

Magnetic After-Effect isotherms have been measured on a metallic glass pre-annealed for different times. The results have been analyzed simultaneously by Debye relaxation functions leading to spectra of activation enthalpies and by extended exponential functions leading to a unique effective activation enthalpy. The thermodynamic activation parameters issued from both analyses compare well. The average values of the enthalpy spectra determined by assuming Debye relaxations are equal to the effective enthalpies resulting from the non-Debye relaxation.

Magnetische Nachwirkungs-Isothermen wurden an amorphen Legierungen gemessen, die mit verschiedenen Anlasszeiten vorbehandelt wurden. Die Ergebnisse wurden sowohl unter der Annahme von Debye-Relaxationsprozessen analysiert, die mit Aktivierungsspektren beschrieben wurden, als auch mit gestreckten Exponentialfunktionen, die zu einer einheitlichen effektiven Aktivierungsenthalpie führt. Die thermodynamischen Parameter von beiden Analysen sind gut vergleichbar. Die Mittelwerte der Aktivierungsenthalpie-Spektren, welche sich bei Zugrundelegung der Debye-Relaxationsprozesse ergeben, entsprechen den effektiven Enthalpien, die sich bei Anwendung der gestreckten Exponentialfunktionen ergeben.

Des isothermes de trainage magnétique ont été réalisées sur des echantillons de verres métalliques ayant subi des traitements thermiques de différentes durées. Les résultats ont été simultanément analysés par des processus de relaxation de Debye engendrant des distributions d'enthalpies d'activation, et par des exponentielles etirées possédant des enthalpies effectives. Les paramètres thermodynamiques issus des deux analyses sont cohérents et comparables. Les valeurs moyennes des distributions d'enthalpies résultant de la relaxation de Debye sont identiques aux enthalpies effectives qui découlent des exponentielles etirées.     

Theoretical investigation of the spin-Hamiltonian parameters and optical spectra for the doped Cu2+ in ZnCdO nanopowder

The spin-Hamiltonian (SH) parameters (g factors g_||, g_⊥ and hyperfine structure constants A_||, A_⊥) and d–d transitions for ZnCdO:Cu²⁺ are calculated based on the perturbation formulas for a 3d⁹ ion in tetragonally elongated octahedra. Good agreement between the calculated results (four SH parameters and three optical absorption bands) and the experimental results can be obtained. Since the SH parameters are sensitive to the local structure of a paramagnetic impurity center, the tetragonal distortion (characterized by the relative elongation ratio ρ ≈ 3.5% along the C₄ axis) of the impurity center due to the Jahn–Teller effect is also acquired from the calculations. The negative and positive signs of hyperfine structure constants A_|| and A_⊥ for ZnCdO:Cu²⁺, respectively, are also suggested in the discussions.     

EPR and optical spectra of cupric ions doped in powder strontium maleate tetrahydrate and magnesium Bis (hydrogen maleate) hexahydrate

Abstract

EPR spectra of Cu²⁺ ions doped in a strontium maleate tetrahydrate and magnesium bis (hydrogen maleate) hexahydrate have been studied in X-band at room temperature and at liquid nitrogen temperature. Spin-Hamiltonian parameters have been calculated. Molecular orbital coefficients are obtained by correlating optical absorption data with EPR results.     

The etching and structural response of Makrofol-N and Makrofol-KG polycarbonate to γ-irradiation

In order to estimate the damage densities produced by γ-rays to Makrofol-N and Makrofol-KG, some structural, optical and etching studies have been performed. It is found that both polymers are insensitive to low γ-doses (up to 10³ krad) but are influenced at higher doses. The changes in etching parameters have been noticed along with the changes in the FTIR and UV–VIS spectra. The results have been discussed on the basis of some basic mechanisms of radiation interactions with organic materials.     

Theoretical explanation of optical absorption spectra and covalent effect of Ni2+ ions in octahedral sites of Ca3Sc2Ge3O12 crystal

The optical absorption spectra (d-d transition bands) and covalent effect of Ni²⁺ ions in octahedral sites of Ca₃Sc₂Ge₃O₁₂ crystal have been investigated by the full energy matrix based on the two spin–orbit coupling parameters model. The bond length of octahedral site is R_i?=?2.19 Å, which can be determined by the cubic crystal-field parameter and optical spectral data. The lattice distortion of the Ni²⁺ center in Ca₃Sc₂Ge₃O₁₂ crystal is also obtained from the calculations. In addition, the result has shown that the covalent effect of Ni²⁺ ion in the octahedral site of Ga₃Sc₂Ge₃O₁₂ is obvious and cannot be ignored. The calculated d-d transition bands agree well with that of the experimental findings, suggesting that the present methods can explain reasonably the optical spectral data and covalent effect of 3d⁸ ions in octahedral lattices.     

基于卷积神经网络气动力降阶模型的翼型优化方法

针对非线性大扰动翼型气动力优化问题,提出了基于卷积神经网络气动力降阶模型的优化方法.该方法用不同形状参数下翼型的气动力数据作为训练信号,训练卷积神经网络翼型气动力降阶模型.采用该气动力降阶模型,以最大升阻比为目标,对翼型进行优化,结果表明该方法可用于大扰动下翼型气动力的预测和优化.该文同时还讨论了池化法和径向基法的训练...