Mechanical damage assessment of Polymer–Matrix Composites using active infrared thermography

The present work uses an active form of the infrared (IR) thermography technique for monitoring and characterization of the damage of glass fibers reinforced Polymer–Matrix Composites (PMCs) following an experimental protocol based on a monotonic tensile test with constant stress steps. The active form introduces a new approach using the cooling rate variation of the material after thermal stimulations during different constant stress levels. This study proves that the cooling speed increases when the damage state has accentuated due to the change of the applied stress. This new approach is original because it allows the auscultation of materials and structures at rest and in service under mechanical loadings without destroying them and with no contact.     

A characterization of the generalized spectral radius with Kronecker powers

Based on Turán’s power sum theory, we extend a recent result obtained by Blondel and Nesterov [Blondel, V. D., & Nesterov, Y. (2005). Computationally efficient approximations of the joint spectral radius, SIAM Journal on Matrix Analysis and Applications, 27, 256–272], by deriving a new characterization of the generalized spectral radius in terms of Kronecker powers.     

Computational analysis of a Markovian queueing system with geometric mean-reverting arrival process

In the queueing literature, an arrival process with random arrival rate is usually modeled by a Markov-modulated Poisson process (MMPP). Such a process has discrete states in its intensity and is able to capture the abrupt changes among different regimes of the traffic source. However, it may not be suitable for modeling traffic sources with smoothly (or continuously) changing intensity. Moreover, it is less parsimonious in that many parameters are involved but some are lack of interpretation. To cope with these issues, this paper proposes to model traffic intensity by a geometric mean-reverting (GMR) diffusion process and provides an analysis for the Markovian queueing system fed by this source. In our treatment, the discrete counterpart of the GMR arrival process is used as an approximation such that the matrix geometric method is applicable. A conjecture on the error of this approximation is developed out of a recent theoretical result, and is subsequently validated in our numerical analysis. This enables us to calculate the performance measures with high efficiency and precision. With these numerical techniques, the effects from the GMR parameters on the queueing performance are studied and shown to have significant influences.     

SCIHTBB: Sparsity constrained iterative hard thresholding with Barzilai-Borwein step size

Iterative hard thresholding (IHT) is a class of effective methods to compute sparse solution for underdetermined linear system. In this paper, an efficient IHT method with theoretical guarantee is proposed and named SCIHTBB with attractive features: (1) Monotone and Non-Monotone versions are presented with initial Barzilai-Borwein step size and finite step line search. (2) Convergence analysis has been developed based on the asymmetrical restricted isometry property. (3) An adaptive sparsity framework is provided to tackle the problem with unknown sparsity. (4) Some extensions are presented to handle group sparsity, non-negative sparsity and matrix rank minimization. Experimental comparisons with some state of the art methods verify that SCIHTBB is faster and more accurate for compressive sensing and matrix completion.     

Beam broadening synthesis for SAR antenna array based on Projection Matrix Algorithm

A new beam broadening synthesis technique for Synthetic Aperture Radar （SAR） antenna array, namely Projection Matrix Algorithm （PMA） is presented. The theory of PMA is introduced firstly, and then the iterative renewed manner is improved to resolve the unbalance problem under amplitude and phase control. In order to validate the algorithm correct and effective, an actual en- gineering application example is investigated. The beam synthesis results of 1.0-4.5 times broadening under the phase only control and the amplitude and phase control using improved PMA are given. The results show that the beam directivity, the beam broadening, and the side-lobe level requirements were met. It is demonstrated that the improved PMA was effective and feasible for SAR application.     

Auxiliary signal design for robust active fault detection of linear discrete-time systems

In this paper, algorithms are proposed to design auxiliary signals for active fault detection based on a multi-model formulation of discrete-time systems. Two different scenarios are considered for this problem; the first one assumes there is no a priori information on initial conditions and no exogenous input signal, while the second allows for having a priori information and the possibility of having a known input in addition to the test signal. Approaches are proposed for solving these two types of problems which are capable of solving the problems efficiently. This is achieved by using a recursive approach based on the use of special Riccati equations. These algorithms can be used for systems of higher dimension and on longer time horizons than the existing methods.     

Table matrix L systems

A new type of development array system called Table Matrix L system is studied. In any rectangular array derivation takes place row by row or column by column restricted by tables so as to make the resultant array rectangular. The motivation for this is to find a development type of system which could generate interesting picture classes. The properties of this system with and without coding and hierarchy are studied.     

一类变系数偏微分方程的精确解的求法及其计算机机械化实现

The variable-coe?cient partial differential equations are not only used in many physical models, but also fundamentally applied in the field of nonlinear science. In order to solve certain variable-coe?cient partial differential equations, the aux-iliary elliptic-like equation method is introduced in this article by means of the symbolic computation software. The basic idea of the new algorithm is that if certain variable-coe?cient partial differential equation can be converted into the form of elliptic equation, then its solutions are readily obtained. By taking the Kadomtsev-Petviashvili equation for an example, not only the effectiveness of the algorithm is demonstrated, but many new solutions are worked out, including dark solitary wave, bell profile solitary wave solutions and Jacobian elliptic function solutions, which may be useful for depicting nonlinear physical phenomena.     

Structure and Reactions of Aliphatic Bridged Bifunctional Radical Ions: Exploring Fine-Tuning in Radiation Chemistry

Bridged bifunctional molecules of general structure X (CH₂)_n Y are useful models for investigations into the effects of intra- and intermolecular interactions in primary radiation-induced processes, with a number of implications for radiation chemistry, radiobiology, and molecular electronics. This short Review presents an outline of recent studies on the structure and reactivity of aliphatic bifunctional radical ions in low-temperature matrices using EPR spectroscopy and quantum-chemical calculations. Both EPR data and DFT calculations for radical cations show that the delocalization of charge and spin density occurs if XY or X and Y have close electronic properties. If the difference in the ionization potentials between X and Y is large, localized radical cations are observed with ground-state properties close to those of the corresponding monofunctional species. Nevertheless, the remote second functional group may affect the photochemistry of such radical cations at a specific bridge length, probably due to intramolecular interactions in a certain conformation. The stabilization of bridged bifunctional radical anions containing two carbonyl groups was found to be very sensitive to the local environment, which may be described in terms of a microsolvation model at the MP2 level of theory. Two independent reactions pathways with excess electrons, yielding different types of localized radical anions, were demonstrated for asymmetrical bifunctional molecules. The obtained results and their implications are discussed in terms of fine-tuning effects in radiation-induced chemical processes in condensed phases.     

Behavioral clusters in dynamic graphs

This paper contributes a method for combining sparse parallel graph algorithms with dense parallel linear algebra algorithms in order to understand dynamic graphs including the temporal behavior of vertices. Our method is the first to cluster vertices in a dynamic graph based on arbitrary temporal behaviors. In order to successfully implement this method, we develop a feature based pipeline for dynamic graphs and apply Nonnegative Matrix Factorization (NMF) to these features. We demonstrate these steps with a sample of the Twitter mentions graph as well as a CAIDA network traffic graph. We contribute and analyze a parallel NMF algorithm presenting both theoretical and empirical studies of performance. This work can be leveraged by graph/network analysts to understand the temporal behavior cluster structure and segmentation structure of dynamic graphs.