Concordia University

About: Concordia University is a education organization based out in Montreal, Quebec, Canada. It is known for research contribution in the topics: Context (language use) & Control theory. The organization has 13565 authors who have published 31084 publications receiving 783525 citations. The organization is also known as: Sir George Williams University & Loyola College, Montreal.

Trajectory-Tracking Control of Mobile Robot Systems Incorporating Neural-Dynamic Optimized Model Predictive Approach

Abstract: Mobile robots tracking a reference trajectory are constrained by the motion limits of their actuators, which impose the requirement for high autonomy driving capabilities in robots This paper presents a model predictive control (MPC) scheme incorporating neural-dynamic optimization to achieve trajectory tracking of nonholonomic mobile robots (NMRs) By using the derived tracking-error kinematics of nonholonomic robots, the proposed MPC approach is iteratively transformed as a constrained quadratic programming (QP) problem, and then a primal–dual neural network is used to solve this QP problem over a finite receding horizon The applied neural-dynamic optimization can make the cost function of MPC converge to the exact optimal values of the formulated constrained QP Compared with the existing fast MPC, which requires repeatedly calculating the Hessian matrix of the Langragian and then solves a quadratic program The computation complexity reaches ${O}({n}^{{3}})$ , while the proposed neural-dynamic optimization contains ${O}({n}^{{2}})$ operations Finally, extensive experiments are provided to illustrate that the MPC scheme has an effective performance on a real mobile robot system

Twinning, dynamic recovery and recrystallization in hot worked Mg–Al–Zn alloy

Abstract: The AZ31 Mg alloy was hot torsion tested from 180 to 450 °C and from 0.01 to 1.0 s −1 . The flow curves showed a peak and a decline towards a steady-state regime which were lower as temperature T rose and strain rate declined; however, the fracture strain increased to about 1.9 at 0.1 s −1 . In transmission electron microscopy, twins were observed from 180 to 360 °C (in declining numbers). At low T , they had sharp walls and contrasting transverse bands; while the matrix showed indistinct linear streaks. As T rose, the twin bands developed cells with tangled walls and finally subgrains (∼360 °C), while the twin walls became tangles of dislocations and finally serrated boundaries. The matrix developed elongated dislocation walls and subgrains at higher T . The twin intersections at 180 and 240 °C consisted of diamond-shaped cells with a duplex set of orientations but at 300 and 360 °C, these had developed into polygonal cells with high misorientations in dark field. The first very small dynamically recrystallized grains were observed at these intersections, slightly larger than the cells. At 360–450 °C, as observed by optical microscopy, small dynamically recrystallized grains formed at the original grain boundaries, probably related to multiple slip. Since twinning and other features described at low T were also found at high ones, albeit with decreasing frequency, the microstructures showed severe heterogeneity which accounted for the limited ductility.

Scheduling fixed-priority tasks with preemption threshold

Abstract: In the context of fixed-priority scheduling, feasibility of a task set with non-preemptive scheduling does not imply the feasibility with preemptive scheduling and vice versa. We use the notion of preemption threshold, first introduced by Express Logic, in their ThreadX real-time operating system, to develop a scheduling model that subsumes both preemptive and non-preemptive fixed priority scheduling. Preemption threshold allows a task to only disable preemption of tasks up to a specified threshold priority. Tasks having priorities higher than the threshold are still allowed to preempt. With this new scheduling model, we show that schedulability is improved as compared to both the preemptive and nonpreemptive scheduling models. We develop the equations for computing the worst-case response times, using the concept of level-i busy period. Some useful results about the generalized model are presented and an algorithm for optimal assignment of priority and preemption threshold is designed based on these results.

Comparative genomics of citric-acid-producing Aspergillus niger ATCC 1015 versus enzyme-producing CBS 513.88

Abstract: The filamentous fungus Aspergillus niger exhibits great diversity in its phenotype. It is found globally, both as marine and terrestrial strains, produces both organic acids and hydrolytic enzymes in high amounts, and some isolates exhibit pathogenicity. Although the genome of an industrial enzyme-producing A. niger strain (CBS 513.88) has already been sequenced, the versatility and diversity of this species compel additional exploration. We therefore undertook whole-genome sequencing of the acidogenic A. niger wild-type strain (ATCC 1015) and produced a genome sequence of very high quality. Only 15 gaps are present in the sequence, and half the telomeric regions have been elucidated. Moreover, sequence information from ATCC 1015 was used to improve the genome sequence of CBS 513.88. Chromosome-level comparisons uncovered several genome rearrangements, deletions, a clear case of strain-specific horizontal gene transfer, and identification of 0.8 Mb of novel sequence. Single nucleotide polymorphisms per kilobase (SNPs/kb) between the two strains were found to be exceptionally high (average: 7.8, maximum: 160 SNPs/kb). High variation within the species was confirmed with exo-metabolite profiling and phylogenetics. Detailed lists of alleles were generated, and genotypic differences were observed to accumulate in metabolic pathways essential to acid production and protein synthesis. A transcriptome analysis supported up-regulation of genes associated with biosynthesis of amino acids that are abundant in glucoamylase A, tRNA-synthases, and protein transporters in the protein producing CBS 513.88 strain. Our results and data sets from this integrative systems biology analysis resulted in a snapshot of fungal evolution and will support further optimization of cell factories based on filamentous fungi.