An optimal boundary fair scheduling algorithm for multiprocessor real-time systems

With the emergence of multicore processors, the research on multiprocessor real-time scheduling has caught more researchers’ attention recently. Although the topic has been studied for decades, it is still an evolving research field with many open problems. In this work, focusing on periodic real-time tasks with quantum-based computation requirements and implicit deadlines, we propose a novel optimal scheduling algorithm, namely boundary fair (Bfair), which can achieve full system utilization as the well-known Pfair scheduling algorithms. However, different from Pfair algorithms that make scheduling decisions and enforce proportional progress (i.e., fairness) for all tasks at each and every time unit, Bfair makes scheduling decisions and enforces fairness to tasks only at tasks’ period boundaries (i.e., deadlines of periodic tasks). The correctness of the Bfair algorithm to meet the deadlines of all tasks’ instances is formally proved and its performance is evaluated through extensive simulations. The results show that, compared to that of Pfair algorithms, Bfair can significantly reduce the number of scheduling points (by up to 94%) and the overhead of Bfair at each scheduling point is comparable to that of the most efficient Pfair algorithm (i.e., PD²). Moreover, by aggregating the time allocation of tasks for the time interval between consecutive period boundaries, the resulting Bfair schedule can dramatically reduce the number of required context switches and task migrations (as much as 82% and 85%, respectively) when compared to those of Pfair schedules, which in turn reduces the run-time overhead of the system.     

A hierarchy of LMI inner approximations of the set of stable polynomials

Exploiting spectral properties of symmetric banded Toeplitz matrices, we describe simple sufficient conditions for the positivity of a trigonometric polynomial formulated as linear matrix inequalities (LMIs) in the coefficients. As an application of these results, we derive a hierarchy of convex LMI inner approximations (affine sections of the cone of positive definite matrices of size m) of the nonconvex set of Schur stable polynomials of given degree n<m. It is shown that when m tends to infinity the hierarchy converges to a lifted LMI approximation (projection of an LMI set defined in a lifted space of dimension quadratic in n) already studied in the technical literature. An application to robust controller design is described.     

A simple method to test the existence of 2-D partial fraction decomposition

In this paper we give a simple method to test the existence of the decomposition of the form

$\text{A(Z}{}_1\text{, Z}{}_2\text{) A(Z}{}_1{}^{\mathrm{?1}}\text{, Z}{}_2{}^{\mathrm{?1}}\text{B(Z}{}_1\text{, Z}{}_2\text{B(Z}{}_1{}^{\mathrm{?1}}\text{, Z}{}_2{}^{\mathrm{?1}}\text{=}\text{(Z}{}_1\text{, Z}{}_2\text{)}\text{B(Z}{}_1\text{, Z}{}_2\text{+}\text{P(Z}{}_1{}^{\mathrm{?1}}\text{, Z}{}_2{}^{\mathrm{?1}}\text{)}\text{B(Z}{}_1{}^{\mathrm{?1}}\text{, Z}{}_1{}^{\mathrm{?1}}\text{)}$

for a stable two-dimensional transfer function of a recursive filter H(Z₁, Z₂) = A(Z₁, Z₂)/B(Z₁, Z₂).     

Mobility-aware clustering algorithms with interference constraints in wireless mesh networks

One of the major concerns in wireless mesh networks (WMNs) is the radio resource utilization efficiency, which can be enhanced by managing efficiently the mobility of users as well as the interference effect among neighboring links. To achieve this, we propose in this paper the use of clustering and a new interference-aware routing metric, called INX. Specifically, we first propose two mobility-aware clustering algorithms that take into consideration the mobility properties of users in order to improve the WMN performance. Then, we propose the use of INX in the clustering process in order to maximize the total network throughput. We prove through simulations that both clustering schemes can achieve significant gains in terms of radio resource utilization and load balancing, especially when using the INX metric. Hence, and as a main contribution, we show that by taking into account the interference effect between links, we can improve the performance of our clustering algorithms and increase the gain initially observed with the conventional hop-count metric.     

A Geometric Approach for Regularization of the Data Term in Stereo-Vision

Every stereovision application must cope with the correspondence problem. The space of the matching variables, often consisting of spatial coordinates, intensity and disparity, is commonly referred as the data term (space). Since the data is often noisy a-priori, preference is required to result a smooth disparity (or piecewise smooth). To this end, each local method (e.g. window correlation techniques) performs a regularization of the data space. In this paper we propose a geometric framework for anisotropic regularization of the data space seeking to preserve the discontinuities in this space when filtering out the noise. On the other hand, the global methods consider a non-regularized data term with a smoothing constraint imposed directly on the disparity. This paper also proposes a new idea where the data space is regularized in a global method prior to the disparity evaluation. The idea is implemented on the state of the art variational method. Experimental results on the Middlebury real images demonstrate the advantages of the proposed approach.

Well-posedness and attainability of indefinite stochastic linear quadratic control in infinite time horizon

This paper is concerned with a stochastic linear-quadratic (LQ) problem in an infinite time horizon with multiplicative noises both in the state and the control. A distinctive feature of the problem under consideration is that the cost weighting matrices for the state and the control are allowed to be indefinite. A new type of algebraic Riccati equation – called a generalized algebraic Riccati equation (GARE) – is introduced which involves a matrix pseudo-inverse and two additional algebraic equality/inequality constraints. It is then shown that the well-posedness of the indefinite LQ problem is equivalent to a linear matrix inequality (LMI) condition, whereas the attainability of the LQ problem is equivalent to the existence of a “stabilizing solution” to the GARE. Moreover, all possible optimal controls are identified via the solution to the GARE. Finally, it is proved that the solution to the GARE can be obtained via solving a convex optimization problem called semidefinite programming.     

A two-stage Ant Colony optimization algorithm to minimize the makespan on unrelated parallel machines—part II: enhancements and experimentations

In a previous paper (Arnaout et al in J Intell Manuf 21:693–701, 2010), an Ant Colony optimization (ACO I) algorithm was introduced for minimizing the schedule’s makespan on unrelated parallel machines with sequence-dependent setup times. Optimal solutions for small instances of this problem were obtained by solving a mixed integer program. However, for larger instances (up to 10 machines and 120 jobs), heuristic and approximate algorithms were necessary to reach solutions in reasonable computational times. ACO I’s performance was evaluated by comparing its solutions to solutions obtained using Tabu Search and MetaRaPS (metaheuristic for Randomized Priority Search). While the results indicated that ACO I outperformed the other heuristics, it also showed that MetaRaPS had a better performance when all ratios of N/M (jobs to machines ratio) were considered. In this paper, we introduce an enhanced ACO which will be referred to as ACO II and compare its performance to other existing and new algorithms including ACO I, MetaRaPS, and SA. The extensive and expanded experiments conducted prove the superiority of the enhanced ACO II.     

Wax and Fatty Acids from Rice Bran Oil Sludges

Sludges obtained as tank settlings from solvent-extracted rice bran oil have been shown to be rich sources of wax and fatty acids. The wax content is variable, being about 18% in one sample and about 39% in a second sample of sludge. The wax was bleached to light colour. The crude wax shows good compatibility with other types of waxes. The oil fraction of sludges is high in free fatty acids (over 70%), about three fourth of which could be vacuum-distilled directly to yield light-coloured fatty acids.     

Cohesive fracture modeling of crack growth in thick-section composites

This paper presents a combined method for modeling the mode-I and II crack growth behavior in thick-section fiber reinforced polymeric composites having a nonlinear material response. The experimental part of this study includes crack growth tests of a thick composite material system manufactured using the pultrusion process. It consists of alternating layers of E-glass unidirectional roving and continuous filament mats in a polymeric matrix. Integrated micromechanical and cohesive finite element (FE) models are used to simulate the crack growth response in eccentrically loaded single-edge-notch, (tension), ESE(T) and notched butterfly specimens. Micromechanical constitutive models for the mat and the roving layers are used to generate the effective nonlinear material behavior from the in situ fiber and matrix responses. The validity of the numerical modeling approach before the onset of crack growth is investigated using an infrared thermal method. Cohesive FE models are calibrated and used to simulate the complete crack growth behavior for different crack configurations. The proposed integrated framework of multi-scale material models with cohesive fracture models is shown to be an effective method for predicting the structural and material responses including failure load and crack growth in thick-section fiber reinforced polymeric composites.     

Synthesis,characterization and liquid crystalline properties of polyacrylates and polymethacrylates containing aryl ester pendant unit

Aryloxycarbonylphenyl acrylates and methacrylates were prepared by reacting 4‐acryloyloxybenzoyl chloride and 4‐methacryloyloxybenzoyl chloride with different phenols. They were homopolymerized using benzoyl peroxide as the initiator at 65°C in dimethylformamide. The polymers were characterized by IR and ¹H–NMR spectra and size exclusion chromatography. Differential scanning calorimetry and polarizing optical microscopy studies revealed that the phenyl esters of poly(4‐acryloyloxybenzoic acid) and poly(4‐methacryloyloxybenzoic acid) did not show any liquid crystalline properties, but, the para‐aryl–substituted phenyl esters did exhibit mesophase properties in the temperature range of 98–265°C depending on the nature of the aryl substituent. Polymethacrylates exhibit higher T_g, and lower T_m and T_i than the polyacrylates having the same pendant mesogen. Thermogravimetric analyses have shown that the initial decomposition temperatures of the polymers are above 230°C. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 465–474, 2000