Design and evaluation of an abbreviated pixelwise dynamic contrast enhancement analysis protocol for early extracellular volume fraction estimation

IntroductionT1-based method is considered as the gold standard for extracellular volume fraction (ECV) mapping. This technique requires at least a 10 min delay after injection to acquire the post injection T1 map. Quantitative analysis of Dynamic Contrast Enhancement (DCE) images could lead to an earlier estimation of an ECV like parameter (2 min). The purpose of this study was to design a quantitative pixel-wise DCE analysis workflow to assess the feasibility of an early estimation of ECV.MethodsFourteen patients with mitral valve prolapse were included in this study. The MR protocol, performed on a 3 T MR scanner, included MOLLI sequences for T1 maps acquisition and a standard SR-turboFlash sequence for dynamic acquisition. DCE data were acquired for at least 120 s. We implemented a full DCE analysis pipeline with a pre-processing step using an innovative motion correction algorithm (RC-REG algorithm) and a post-processing step using the extended Tofts Model (ECV_ETM). Estimated ECV_ETM maps were compared to standard T1-based ECV maps (ECV_T1) with both a Pearson correlation analysis and a group-wise analysis.ResultsImage and map quality assessment showed systematic improvements using the proposed workflow. Strong correlation was found between ECV_ETM, and ECV_T1 values (r-square = 0.87).ConclusionA DCE analysis workflow based on RC-REG algorithm and ETM analysis can provide good quality parametric maps. Therefore, it is possible to extract ECV values from a 2 min-long DCE acquisition that are strongly correlated with ECV values from the T1 based method.     

Transient deformation and heat generation of solid polyurethane under impact compression

This investigation examines the transient deformation and heat generation of a solid polyurethane subjected to dynamic compression. A special method is presented to prepare the solid polyurethane from raw materials which are commonly used to make polyurethane foams. Testing methods including infrared spectrum, differential scanning calorimetry, quasi-static and dynamic compression were applied to study the basic physical properties of the solid polyurethane. High-speed optical and infrared imaging systems are used to obtain visual and thermo-graphic images during impact tests. Under quasi-static compression, the solid polyurethane presents a good performance in toughness. This is confirmed by its Poisson's ratio. Under impact compression, the adiabatic heat generation are identified statistically. Temperature distribution confirms the fact of transient heat generation in specimens. Adiabatic self-heating mechanism provides a consideration to understand the negative strain-rate effect and post-yield softening effect found in the solid polyurethane. Mechanical properties including quasi-static and dynamic responses are related with the composition of molecular and structure of polymer.     

Application of fractional calculus methods to asymmetric dynamical response of CB-Filled rubber

Frequency-sweep tests at various temperatures were conducted to study the asymmetric dynamic response of carbon black (CB) filled rubber. The master curves of storage modulus were constructed by use of time-temperature superposition (TTS), and the dynamic response of the material over a wide range of frequencies covering about 20 decades exhibits asymmetry. Based on the experimental results, the fractional Zener model and Prony series are verified to be unsuitable to reproduce the dynamicviscoelastic behavior. Therefore, a modified model by adding a spring-pot into the fractional Zener model is presented. The applicability of the modified model in describing the dynamic behavior of the CB-filled rubber is validated by the experimental results.     

On necessary precautions when measuring solid polymer linear viscoelasticity with dynamic analysis in torsion

Solid polymer linear viscoelasticity in shear is often characterized by applying torsion and using the Saint-Venant solution when rectangular prismatic specimens are considered. It is shown that experimental dynamic torsion tests can show a dependency of the storage modulus and damping factor on the dimensions of the rectangular prismatic specimen when linear temperature ramps are applied. While the discrepancy of damping factor is explained by temperature heterogeneities and can be corrected easily by applying temperature steps, the inconsistency of storage modulus is due to an invalid application of the Saint-Venant solution. Finite element simulations allowed definition of the sample dimensions for which the Saint-Venant solution provides a good approximation, and a coefficient is given to correct the results obtained with commercial instruments when other sample dimensions are used.     

On strong ellipticity for isotropic hyperelastic materials based upon logarithmic strain

This paper discusses various constitutive restrictions on the strain energy function for an isotropic hyperelastic material derived from the condition of strong ellipticity. The strain energy function is assumed to be a function of a novel set of invariants of the Hencky (logarithmic or natural) strain tensor introduced by Criscione et al. (J. Mech. Phys. Solids 48 (2000) 2445). A key step in the analysis is the derivation of an expression for the Fréchet derivative of the Hencky strain with respect to the deformation gradient that is convenient for analyzing the quadratic form over the space of second order tensors central to establishing strong ellipticity. The theory is illustrated by applying the restrictions to a model for rubber proposed by Criscione et al. (J. Mech. Phys. Solids 48 (2000) 2445) It is shown that while that model can be made to violate strong ellipticity, it does so only for very large strains.     

磁性纳米结构中由激光引起的超快自旋动力学研究

以单个磁性中心的NiO以及由Co和Ni等元素构成的双磁性中心的纳米结构为例,总结了近年所做的主要工作.为了在理论上实现磁性纳米结构中的超快自旋翻转和转移,提出了一种称为Λ进程(Λ process)的超快自旋转换机理.在实际计算中,首先采用量子化学第一性原理计算得到磁性纳米结构中精确的隙间d电子态,然后考虑外加磁场和自旋轨道耦合分析磁性原子中的自旋局域化程度,最后引入激光脉冲项,研究在其作用下材料的自旋态经由Λ进程实现转换的时间历程.研究结果表明自旋翻转和转移可以在线偏振光的作用下在亚皮秒的时间尺度内完成. 关键词： 超快自旋动力学 第一性原理计算 Λ进程 磁性纳米结构     

Analysis of a modified two-lane lattice model by considering the density difference effect

In this paper, a modified lattice hydrodynamic model of traffic flow is proposed by considering the density difference between leading and following lattice for two-lane system. The effect of density difference on the stability of traffic flow is examined through linear stability analysis and shown that the density difference term can significantly enlarge the stability region on the phase diagram. To describe the phase transition of traffic flow, the Burgers equation and mKdV equation near the critical point are derived through nonlinear analysis. To verify the theoretical findings, numerical simulation is conducted which confirms that traffic jam can be suppressed efficiently by considering the density difference effect in the modified lattice model for two-lane traffic.     

Reissner–Mindlin plate model with uncertain input data

A Reissner–Mindlin model of a plate resting on unilateral rigid piers and a unilateral elastic foundation is considered. Since the material coefficients of the orthotropic plate, stiffness of the foundation, and the lateral loading are uncertain, a method of the worst scenario (anti-optimization) is employed to find maximal values of some quantity of interest.The state problem is formulated in terms of a variational inequality with a monotone operator. Using mixed-interpolated finite elements, approximations are proposed for the state problem and for the worst scenario problem. The solvability of the problems and a convergence of approximations is proved.     

A new nonlinear blind source separation method with chaos indicators for decoupling diagnosis of hybrid failures: A marine propulsion gearbox case with a large speed variation

The normal operation of propulsion gearboxes ensures the ship safety. Chaos indicators could efficiently indicate the state change of the gearboxes. However, accurate detection of gearbox hybrid faults using Chaos indicators is a challenging task and the detection under speed variation conditions is attracting considerable attentions. Literature review suggests that the gearbox vibration is a kind of nonlinear mixture of variant vibration sources and the blind source separation (BSS) is reported to be a promising technique for fault vibration analysis, but very limited work has addressed the nonlinear BSS approach for hybrid faults decoupling diagnosis. Aiming to enhance the fault detection performance of Chaos indicators, this work presents a new nonlinear BSS algorithm for gearbox hybrid faults detection under a speed variation condition. This new method appropriately introduces the kernel spectral regression (KSR) framework into the morphological component analysis (MCA). The original vibration data are projected into the reproducing kernel Hilbert space (RKHS) where the instinct nonlinear structure in the original data can be linearized by KSR. Thus the MCA is able to deal with nonlinear BSS in the KSR space. Reliable hybrid faults decoupling is then achieved by this new nonlinear MCA (NMCA). Subsequently, by calculating the Chaos indicators of the decoupled fault components and comparing them with benchmarks, the hybrid faults can be precisely identified. Two specially designed case studies were implemented to evaluate the proposed NMCA-Chaos method on hybrid gear faults decoupling diagnosis. The performance of the NMCA-Chaos was compared with state of art techniques. The analysis results show high performance of the proposed method on hybrid faults detection in a marine propulsion gearbox with large speed variations.