Accurate and robust adaptive mesh refinement for aerodynamic simulation with multi‐block structured curvilinear mesh

A multi‐block curvilinear mesh‐based adaptive mesh refinement (AMR) method is developed to satisfy the competing objectives of improving accuracy and reducing cost. Body‐fitted curvilinear mesh‐based AMR is used to capture flow details of various length scales. A series of efforts are made to guarantee the accuracy and robustness of the AMR system. A physics‐based refinement function is proposed, which is proved to be able to detect both shock wave and vortical flow. The curvilinear mesh is refined with cubic interpolation, which guarantees the aspect ratio and smoothness. Furthermore, to enable its application in complex configurations, a sub‐block‐based refinement strategy is developed to avoid generating invalid mesh, which is the consequence of non‐smooth mesh lines or singular geometry features. A newfound problem of smaller wall distance, which negatively affects the stability and is never reported in the literature, is also discussed in detail, and an improved strategy is proposed. Together with the high‐accuracy numerical scheme, a multi‐block curvilinear mesh‐based AMR system is developed. With a series of test cases, the current method is verified to be accurate and robust and be able to automatically capture the flow details at great cost saving compared with the global refinement. Copyright © 2015 John Wiley & Sons, Ltd.     

Robustness Screen in Enantioselective Catalysis Enabled Generation of Enantioenriched Heterocyclic Scaffolds in One Pot

Enantioselective catalysis has emerged as a powerful synthetic paradigm and has accelerated the development of new methods to make diverse chiral molecules. Generally, these reactions are very sensitive to the steric and electronic environment present in the catalyst as well as the substrates. With this scenario, the presence of an additional component in the reaction mixture is expected to add complexity in achieving the enantioselective variants. Herein, we report that various enantioenriched molecules could be obtained from multiple starting materials in one pot. The reaction of aminoaromatics A with alkynols B₁, B₂, B₃…?B_n with a Au^I/chiral Brønsted acid catalyst afforded AB₁*, AB₂*, AB₃*…AB_n*; while, the reaction of alkynols B with aminoaromatics A₁, A₂, A₃…A_n under the same reaction conditions gave A₁B*, A₂B*, A₃B*…A_nB * .     

A hybrid multi-degree-of-freedom vibration isolation platform for spacecrafts by the linear active disturbance rejection control

The hybrid vibration isolation, which takes advantages of both the passive and active approaches, has been an important solution for space missions. The objective of this paper is to design a vibration isolation platform for payloads on spacecrafts with the robust, wide bandwidth, and multi-degree-of-freedom(MDOF). The proposed solution is based on a parallel mechanism with six voice-coil motors(VCMs) as the actuators. The linear active disturbance resistance control(LADRC) algorithm is used for the active control. Numerical simulation results show that the vibration isolation platform performs effectively over a wide bandwidth, and the resonance introduced by the passive isolation is eliminated. The system robustness to the uncertainties of the structure is also verified by simulation.     

Minimization of artifact protein aggregation using tetradecyl sulfate and hexadecyl sulfate in capillary gel electrophoresis under reducing conditions

In the biopharmaceutical industry, CE-SDS assesses the purity, heterogeneity, and stability of therapeutic proteins. However, for mAb-1 and mAb-2, typical CE-SDS under reducing conditions produced atypical protein peak profiles, which led to biased purity results, thus were not acceptable for biologics manufacturing. This bias was caused by the formation of method-induced higher molecular weight artifacts, the levels of which correlated with protein concentration. Here we show that adding sodium tetradecyl and hexadecyl sulfates to the sample and the sieving gel buffer solutions was required to prevent formation of aggregate artifacts and to maintain detergent:protein uniformity, suggesting their importance during the sample preparation steps of heat denaturation and subsequent cooling as well as during capillary migration. For these proteins, we show that this uniformity was likely due to the ability of these detergents to bind proteins with markedly higher affinities compared to SDS. “CE-SC_XS” methods (where CE-SC_XS is CGE using detergent composed of a sodium sulfate head group and a hydrocarbon tail, with “C_X” representing various tail lengths), were developed with a sodium tetradecyl sulfate sample buffer and a sodium hexadecyl sulfate containing sieving gel buffer that minimized artifacts and provided robust characterization and release results for mAb-1 and mAb-2.     

一般生长曲线模型中最优预测的稳健性

研究了一般生长曲线模型中最优线性无偏预测的稳健性,得到了线性可预测变量的这种预测关于协方差阵具有稳健性的充要条件.     

A model of the effects of authority on consensus formation in adaptive networks: Impact on network topology and robustness

Opinions of individuals in real social networks are arguably strongly influenced by external determinants, such as the opinions of those perceived to have the highest levels of authority. In order to model this, we have extended an existing model of consensus formation in an adaptive network by the introduction of a parameter representing each agent’s level of ‘authority’, based on their opinion relative to the overall opinion distribution. We found that introducing this model, along with a randomly varying opinion convergence factor, significantly impacts the final state of converged opinions and the number of interactions required to reach that state. We also determined the relationship between initial and final network topologies for this model, and whether the final topology is robust to node removals. Our results indicate firstly that the process of consensus formation with a model of authority consistently transforms the network from an arbitrary initial topology to one with distinct measurements in mean shortest path, clustering coefficient, and degree distribution. Secondly, we found that subsequent to the consensus formation process, the mean shortest path and clustering coefficient are less affected by both random and targeted node disconnection. Speculation on the relevance of these results to real world applications is provided.     

An image encryption scheme based on rotation matrix bit-level permutation and block diffusion

This paper proposes a novel image encryption scheme based on rotation matrix bit-level permutation and block diffusion. Firstly, divide plain image into non-overlapping 8 × 8 pixels blocks with a random matrix, then transform each block into an 8 × 8 × 8 three-dimensional (3-D) binary matrix, which has six directions just as a cube. Permutation is performed by multiplying the 3-D matrix by the rotation matrix that relies on plain image according to different direction. Secondly, use block diffusion to further change the statistical characteristics of the image after confusion. Experiment results and analysis show that the scheme can not only achieve a satisfactory security performance, but also have the suitability for a parallel mode and the robustness against noise in communication system.     

Robustness of F-tests in singular linear models

F-test is the most popular test in the general linear model. However, there is few discussions on the robustness of F-test under the singular linear model. In this paper, the necessary and sufficient conditions of robust F-test statistic are given under the general linear models or their partition models, which allows that the design matrix has deficient rank and the covariance matrix of error is a nonnegative definite matrix with parameters. The main results obtained in this paper include the existing findings of the general linear model under the definite covariance matrix. The usage of the theorems is illustrated by an example.