环路跟踪卡尔曼滤波算法的性能分析

基于卡尔曼滤波的环路跟踪算法多是通过一定仿真证明算法性能,没有系统性性能评估,难以较好指导工程应用。在原有算法基础上进行了优化,并系统性地对比分析、评估了基于卡尔曼环路滤波算法性能,以期为算法工程化提供指导。首先提出对跟踪环路反馈调整量进行预测,使之更符合系统实际,减小环路跟踪误差。而后基于卫星信号模拟器输出信号和自生产信号源,充分评估基于卡尔曼滤波环路跟踪算法的收敛时间和灵敏度。仿真结果表明,相比目前工程常用的二阶FFL辅助三阶PLL算法,基于卡尔曼滤波环路跟踪算法能够缩短环路所需稳定时间约90%,并能提升跟踪灵敏度约5 d B,有效改善弱信号场景中接收机输出信息的完好性和连续性。     

Determination of Ti-6242 α and β slip properties using micro-pillar test and computational crystal plasticity

The properties and behaviour of an α−β colony Ti-6242 alloy have been investigated at 20 °C utilising coupled micro-pillar stress relaxation tests and computational crystal plasticity. The β-phase slip strength and intrinsic slip system strain rate sensitivity have been determined, and the β-phase shown to have stronger rate sensitivity than that for the α phase. Close agreement of experimental observations and crystal plasticity predictions of micro-pillar elastic-plastic response, stress relaxation, slip activation in both α and β-phases, and strain localisation within the α−β pillars with differing test strain rate, β morphology, and crystal orientations is achieved, supporting the validity of the properties extracted. The β-lath thickness is found to affect slip transfer across the α−β−α colony, but not to significantly change the nature of the slip localisation when compared to pure α-phase pillars with the same crystallographic orientation. These results are considered in relation to rate-dependent deformation, such as dwell fatigue, in complex multiphase titanium alloys.     

Bayesian robustness under a skew-normal class of prior distribution

We develop a global sensitivity analysis to measure the robustness of the Bayesian estimators with respect to a class of prior distributions. This class arises when we consider multiplicative contamination of a base prior distribution. A similar structure was presented by van der Linde [12]. Some particular specifications for this multiplicative contamination class coincide with well known families of skewed distributions. In this paper, we explore the skew-normal multiplicative contamination class for the prior distribution of the location parameter of a normal model. Results of a Bayesian conjugation and expressions for some measures of distance between posterior means and posterior variance are obtained. We also elaborate on the behavior of the posterior means and of the posterior variances through a simulation study.     

Untersuchungen zur Empfindlichkeit der β-Rückstreumethode bei der Messung dünner Auftragsschichten mit einem 11C-Spezialpräparat

Die Bestimmung dünner Auftragsschichten auf bewegten Trāgermaterialien mit der β-Rūckstreumethode hängt wesentlich von der Empfindlichkeit der Messung und der Dynamik des Prozesses ab.

In diesem Beitrag wird für spezielle Stoffe der Einfluβ der Trāgermaterialien bei Mehrschichtproblemen auf die Empfindlichkeit untersucht.     

Modeling and testing of snow penetration

Penetration by a cone into snow is commonly used to characterize snow properties. However, the effects of the diameter and half-angle of the cone on the mechanical properties of snow have not been systematically studied. In addition, no estimation of material parameters in a physically-based model has been made such that the results from penetration provide only an index of snow properties. In this paper, modeling and experimental methods are used to examine the effects of cone geometry on the maximum penetration force and associated hardness, with penetrometers ranging from 2.5 to 4 mm in diameter, 15° to 45° in cone half-angle, and testing both fine-grained and coarse-grained snows. The material point method, in conjunction with the Drucker–Prager cap plasticity model, was used to obtain the theoretical penetration force-distance relationship. Global sensitivity studies were conducted that indicate that the cohesion accounts for 86% of the penetration force, followed distantly by friction angle which accounts for 27%. A general trend, for the simulation results was established: for a given half-angle, the penetration force increases with the increase of diameter which holds for most of the test data as well; for a given diameter, the penetration force decreases with the increase of half-angle, which holds for some of the test data. In addition, for a given half-angle, the hardness decreases with the increase of diameter; for a given diameter, the hardness decreases with the increase of half-angle. To take into consideration the uncertainty of test data, a simple interval-based metric was used to compare test data with simulation results; the comparison was satisfactory. The material parameters from the simulations can thus be considered as calibrated ones for the snow studied.     

Direct and adjoint global stability analysis of turbulent transonic flows over a NACA0012 profile

In this work, various turbulent solutions of the two‐dimensional (2D) and three‐dimensional compressible Reynolds averaged Navier–Stokes equations are analyzed using global stability theory. This analysis is motivated by the onset of flow unsteadiness (Hopf bifurcation) for transonic buffet conditions where moderately high Reynolds numbers and compressible effects must be considered. The buffet phenomenon involves a complex interaction between the separated flow and a shock wave. The efficient numerical methodology presented in this paper predicts the critical parameters, namely, the angle of attack and Mach and Reynolds numbers beyond which the onset of flow unsteadiness appears. The geometry, a NACA0012 profile, and flow parameters selected reproduce situations of practical interest for aeronautical applications. The numerical computation is performed in three steps. First, a steady baseflow solution is obtained; second, the Jacobian matrix for the RANS equations based on a finite volume discretization is computed; and finally, the generalized eigenvalue problem is derived when the baseflow is linearly perturbed. The methodology is validated predicting the 2D Hopf bifurcation for a circular cylinder under laminar flow condition. This benchmark shows good agreement with the previous published computations and experimental data. In the transonic buffet case, the baseflow is computed using the Spalart–Allmaras turbulence model and represents a mean flow where the high frequency content and length scales of the order of the shear‐layer thickness have been averaged. The lower frequency content is assumed to be decoupled from the high frequencies, thus allowing a stability analysis to be performed on the low frequency range. In addition, results of the corresponding adjoint problem and the sensitivity map are provided for the first time for the buffet problem. Finally, an extruded three‐dimensional geometry of the NACA0012 airfoil, where all velocity components are considered, was also analyzed as a Triglobal stability case, and the outcoming results were compared to the previous 2D limited model, confirming that the buffet onset is well detected. Copyright © 2014 John Wiley & Sons, Ltd.     

AN EFFICIENT SEQUENTIAL DESIGN FOR SENSITIVITY EXPERIMENTS

In sensitivity experiments, the response is binary and each experimental unit has a critical stimulus level that cannot be observed directly. It is often of interest to estimate extreme quantiles of the distribution of these critical stimulus levels over the tested products. For this purpose a new sequential scheme is proposed with some commonly used models. By using the bootstrap repeated-sampling principle, reasonable prior distributions based on a historic data set are specified. Then, a Bayesian strategy for the sequential procedure is provided and the estimator is given. Further, a high order approximation for such an estimator is explored and its consistency is proven. A simulation study shows that the proposed method gives superior performances over the existing methods.     

Quantum chemical studies on the structure and detonation properties of the fused polynitrodiazoles: New high energy density molecules

In this study, we explore the possibility that fused polynitrodiazoles act as high energy density materials. Density functional theory calculations at the B3LYP/aug‐cc‐pVDZ level were performed to predict the structure, energy of explosion (≈1.68 kcal g^?1), density (≈1.98 g cm^?3), detonation velocity (≈9.50 km s^?1), and detonation pressure (≈41.50 GPa) of model molecules. The predicted properties have been found to be promising compared with 3,4,5‐trinitro‐1H‐pyrazole, 1,3,5‐trinitro‐1,3,5‐triazinane, and octahydro‐1,3,5,7‐tetranitro‐l,3,5,7‐tetraazocane. The nature of azoles of the molecule presumably determines the geometry, stability, sensitivity, density, and detonation performance. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

仪器定量分析中几个问题的探讨

详细介绍了分析方法的评价指标,包括检出限、测定限、灵敏度、精密度、准确度、动态范围和线性范围、抗干扰能力等,单因素优化方法与加标回收实验评定测定结果准确度的可靠性,并就分析工作中遇到的一些实际问题进行了讨论.     

Strain rate sensitivity of polyurea coatings: Viscous and elastic contributions

Polyurea, a reaction product of isocyanates and an amine blend has been reported to be highly strain rate sensitive, which responds in its own unique way when subjected to increasing strain rates. The amine blend comprise of a long chain amine, forming the soft segments, chain extender, which brings the urea linkages closer and a crosslinker, which serves as a chemical bond between the chains. In this work, we attempt to tune the viscous contribution in polyurea, by increasing crosslinking density, while keeping the amount of chain extender more or less constant. The viscoelastic behavior and its effect on the time dependant behavior was established by extensive dynamic studies. Quasi-static tests and Split Hopkinson testing was performed over large deformation rates (10⁻⁴ to 10³ s⁻¹). It was observed that polyureas with larger viscous contribution (tan δ), were capable of exhibiting larger strain rate sensitivity.