Effects of internal bremsstrahlung of tritium β-decay and surface roughness in the BIXS method

We have studied the effects of the internal bremsstrahlung of tritium β-decay, sample surface roughness and tritium content as well on the tritium β-decay induced X-ray spectroscopy (BIXS) for tritium measurements based on Monte Carlo simulations. The Knipp-Uhlenbeck-Bloch theoretical model was adopted for the internal bremsstrahlung. It is found that the contributions of internal bremsstrahlung of tritium β-decays are approximately 30%, 10%, 4% and 2% of the corresponding external bremsstrahlung for C, Ti, Mo and W materials, respectively, and the sample surface roughness may cause an error of several percent in the BIXS method if the surface roughness of a sample is in a reasonable range. Moreover, the effect of tritium content should be taken into account when a sample contains a large amount of tritium, otherwise, the tritium contents measured by the BIXS method will be underestimated, for example, by up to ∼15% for Ti metal.     

基于贝叶斯理论的神经网络算法研究

本文研究了基于贝叶斯理论的神经网络算法,采用贝叶斯方法来确定超参数,使得神经网络在训练过程中能自适应地调节超参数的大小,得出目标函数的最优化参数,从而达到提高神经网络泛化能力的目的.还编制仿真软件,验证了该算法的可行性.     

双向防水型数字缆的设计及开发

本文重点介绍了江苏亨通线缆科技有限公司结合目前特殊场合布线的需求,并从产品性能及成本角度出发,开发出了一种双向防水型数字电缆,并简单阐述了该产品的工艺设计、电气性能特点和生产过程中关键开发技术的控制。     

Representation of High Resolution Images from Low Sampled Fourier Data: Applications to Dynamic MRI

In this work we propose the use of B-spline functions for the parametric representation of high resolution images from low sampled data in the Fourier domain. Traditionally, exponential basis functions are employed in this situation, but they produce artifacts and amplify the noise on the data. We present the method in an algorithmic form and carefully consider the problem of solving the ill-conditioned linear system arising from the method by an efficient regularization method. Two applications of the proposed method to dynamic Magnetic Resonance images are considered. Dynamic Magnetic Resonance acquires a time series of images of the same slice of the body; in order to fasten the acquisition, the data are low sampled in the Fourier space. Numerical experiments have been performed both on simulated and real Magnetic Resonance data. They show that the B-splines reduce the artifacts and the noise in the representation of high resolution Magnetic Resonance images from low sampled data. This work was supported by the Italian MIUR project Inverse Problems in Medical Imaging 2004–2006 (grant no 2004015818). Germana Landi received the BS degree in Mathematics from the University of Bologna in 1997 and the Ph.D. degree in Computational Mathematics from the University of Padova in 2000. She is currently a postdoctoral researcher in Numerical Analysis at the Department of Mathematics of the University of Bologna. Her research interests include medical imaging and inverse ill-posed problems. Elena Loli Piccolomini received the BS degree in Mathematics from the University of Bologna in 1988. She is an associate professor in Numerical Analysis at the Department of Mathematics of the University of Bologna. Her research interests include numerical methods for the regularization of discrete ill-posed problems with application to medical imaging (MR, TAC, SPECT, PET).     

非线性时域识别方程的不适定性与正则化方法研究

研究了非线性时域识别方程的不适定性及其正则化求解方法。雅可比矩阵的性态能够反映非线性识别方程的性态，因此雅可比矩阵的条件数是非线性识别方程的不适定性的度量。阻尼最小二乘法只是一种强迫正定的计算方法，其识别结果仍然对测试噪声很敏感，解决该问题的有效途径是将阻尼最小二乘法与正则化方法两者结合使用。算例表明，将先验的参数预估值引入Tikhonov镇定泛函可以得到稳定的参数解，且识别误差与原始数据的测试噪声基本保持在同一水平。     

反射型超声衍射CT迭代重建算法

本文以傅立叶衍射定理为基础,将非均匀傅立叶变换和迭代法相结合,用正则化方法处理迭代的收敛问题,建立了反射型超声衍射成像算法。数据直接在频域中的非均匀频率点上比较,避免了频域内插引入的误差。本算法也减少了采样数据量,降低了运算的复杂度。实验结果表明,在迭代次数不多情况下,重建图像可以达到较好的视觉效果。     

A Full Curvature Based Algorithm for Image Registration

Image registration, i.e., finding an optimal displacement field u which minimizes a distance functional D(u) is known to be an ill-posed problem. In this paper a novel variational image registration method is presented, which matches two images acquired from the same or from different medical imaging modalities. The approach proposed here is also independent of the image dimension. The proposed variational penalty against oscillations in the solutions is the standard H²(Ω) Sobolev semi-inner product for each component of the displacement. We investigate the associated Euler-Lagrange equation of the energy functional. Furthermore, we approach the solution of the underlying system of biharmonic differential equations with higher order boundary conditions as the steady-state solution of a parabolic partial differential equation (PDE). One of the important aspects of this approach is that the kernel of the Euler-Lagrange equation is spanned by all rigid motions. Hence, the presented approach includes a rigid alignment. Experimental results on both synthetic and real images are presented to illustrate the capabilities of the proposed approach. Stefan Henn obtained his diploma (1997) and his Ph.D. in mathematics (2001), both from the Heinrich-Heine University (HHU) of Düsseldorf (Germany). From 1997–1999 he had a researcher position at the Institute for Brain Research at the HHU Düsseldorf. Since 1999 he is a research assistant at the Institute of Mathematics at the HHU Düsseldorf. He received the SIAM outstanding paper prize in 2003 for the paper (Iterative Multigrid Regularization Techniques for Image Matching, SIAM Journal on Scientific Computing, 23(4), pp. 1077-1093). His research interests include Multiscale methods in Scientific Computing and Image Processing, nonlinear large-scale optimization, and numerical analysis of partial differential equations.     

考虑二次受力碳纤维布加固短柱的抗震试验

基于结构加固存在二次受力的特性，对碳纤维布加固钢筋混凝土短柱在反复荷载作用下的受力性能进行了对比试验研究。探讨了二次受力对碳纤维布加固钢筋混凝土短柱的受力性能、破坏特征及破坏机理的影响。试验表明，采用不考虑构件二次受力特性的加固加载方案，会过高地评估加固构件的承载力提高值和抗震性能改善的相关指标，将对指导实际加固工程产生不利影响。     

双相介质二维波动方程孔隙率反演的扰动方法

本文考虑在双相介质的二维波动方程中，应用扰动方法对其中的参数孔隙率进行反演，并应用正则化方法解反演中出现的不稳定问题，方法简洁，迭代过程稳定，收敛效率高，文中给出的算例说明此方法是可行的。     

An entropic optimization approach for a parameter identification problem in quasibrittle fracture

The cohesive crack model is a widely used idealization to represent simply and reliably the quasibrittle fracture behavior of concrete-like materials. However, knowledge of the parameters characterizing this model is of prime importance and cannot all be obtained directly from experiments. Typically, recourse is made to some inverse numerical approach. Our particular formulation can be elegantly cast as an instance of a challenging optimization problem known as a mathematical program with equilibrium (or, more precisely in our case, complementarity) constraints (MPEC). The present paper investigates application of an entropic optimization approach to solve the MPEC, and compares its performance with our previously proposed Fischer–Burmeister smoothing scheme. We use actual experimental data for the comparison.