The 3D creep and dynamic displacements and stresses of the suddenly pressurized “finite-length” thick visco-hyperelastic cylinders with fixed ends are investigated here for the first time, employing ...a hybrid semi-analytical approach. By incorporating the incompressibility condition of the material and the hierarchical Prony-series-type Mooney–Rivlin constitutive model, the dynamic 3D visco-hyperelasticity equations of the vessel are interpreted in terms of the instantaneous axial and radial time variations of the radii. The heredity integral is written in terms of the time-derivative of the relaxation kernel rather than the time derivatives of the stresses, for the first time. The resulting nonlinear integrodifferential governing equations whose number of terms grows with time are solved by an iterative solution that uses a point-collocation technique, the time-domain trapezoidal technique, and the Runge–Kutta time-marching method. Comprehensive parametric studies are performed to evaluate the effects of various geometric, hyperelastic, and viscous/creep material properties on the creep and dynamic/vibration responses of the structure. Results show that (1) in comparison with the traditional structures, the effects of the superimposed higher vibration modes and damping are much more notable in visco-hyperelastic structures, (2) the displacement and stress components are affected by not only radial inflation but also the time-dependent magnitude and sign of the bending-inspired curvatures, (3) the largest hoop and axial stresses occur in regions located about the mid-length section and in the vicinity of the fixed ends, respectively, and (4) the displacements and stresses increase but the thickness reduction decreases by increasing the cylinder length. The creep results show while the slopes of the creep curves are larger for longer cylinders, the shorter cylinder reaches the steady state earlier.
This paper considers the problem of hybrid flowshop scheduling. First, we review the shortcoming of the available model in the literature. Then, four different mathematical models are developed in ...form of mixed integer linear programming models. A complete experiment is conducted to compare the models for performance based on the size and computational complexities. Besides the models, the paper proposes a novel hybrid particle swarm optimization algorithm equipped with an acceptance criterion and a local search heuristic. The features provide a fine balance of diversification and intensification capabilities for the algorithm. Using Taguchi method, the algorithm is fine tuned. Then, two numerical experiments are performed to evaluate the performance of the proposed algorithm with three particle swarm optimization algorithms available in the scheduling literature and one well-known iterated local search algorithm in the hybrid flowshop literature. All the results show the high performance of the proposed algorithm.
While there have been recent reports of brain retention of gadolinium following gadolinium-based contrast agent administration in adults, a retrospective series of pediatric patients has not ...previously been reported, to our knowledge. We investigated the relationship between the number of prior gadolinium-based contrast agent doses and increasing T1 signal in the dentate nucleus on unenhanced T1-weighted MR imaging. We hypothesized that despite differences in pediatric physiology and the smaller gadolinium-based contrast agent doses that pediatric patients are typically administered based on weighted-adjusted dosing, the pediatric brain would also demonstrate dose-dependent increasing T1 signal in the dentate nucleus.
We included children with multiple gadolinium-based contrast agent administrations at our institution. A blinded reader placed ROIs within the dentate nucleus and adjacent cerebellar white matter. To eliminate reader bias, we also performed automated ROI delineation of the dentate nucleus, cerebellar white matter, and pons. Dentate-to-cerebellar white matter and dentate-to pons ratios were compared with the number of gadolinium-based contrast agent administrations.
During 20 years at our institution, 280 patients received at least 5 gadolinium-based contrast agent doses, with 1 patient receiving 38 doses. Sixteen patients met the inclusion/exclusion criteria for ROI analysis. Blinded reader dentate-to-cerebellar white matter ratios were significantly associated with gadolinium-based contrast agent doses (r
= 0.77, P = .001). The dentate-to-pons ratio and dentate-to-cerebellar white matter ratios based on automated ROI placement were also significantly correlated with gadolinium-based contrast agent doses (t = 4.98, P < .0001 and t = 2.73, P < .02, respectively).
In pediatric patients, the number of prior gadolinium-based contrast agent doses is significantly correlated with progressive T1-weighted dentate hyperintensity. Definitive confirmation of gadolinium deposition requires tissue analysis. Any potential clinical sequelae of gadolinium retention in the developing brain are unknown. Given this uncertainty, we suggest taking a cautious stance, including the use, in pediatric patients, of higher stability, macrocyclic agents, which in both human and animal studies have been shown to be associated with lower levels of gadolinium deposition, and detailed documentation of dosing. Most important, a patient should not be deprived of a well-indicated contrasted MR examination.
Flexible job-shop scheduling problem (FJSP) is an extension of the classical job-shop scheduling problem. FJSP is NP-hard and mainly presents two difficulties. The first one is to assign each ...operation to a machine out of a set of capable machines, and the second one deals with sequencing the assigned operations on the machines. This paper proposes a parallel variable neighborhood search (PVNS) algorithm that solves the FJSP to minimize makespan time. Parallelization in this algorithm is based on the application of multiple independent searches increasing the exploration in the search space. The proposed PVNS uses various neighborhood structures which carry the responsibility of making changes in assignment and sequencing of operations for generating neighboring solutions. The results obtained from the computational study have shown that the proposed algorithm is a viable and effective approach for the FJSP.
Periodic solutions and their existence are one of the most important subjects in dynamical systems. Fractional order systems like integer ones are no exception to this rule.
Tavazoei and Haeri (2009) ...have shown that a time-invariant fractional order system does not have any periodic solution. In this article, this claim has been investigated and it is shown that although in any finite interval of time the solutions do not show any periodic behavior, when the steady state responses of fractional order systems are considered, periodic orbits can be detected.
•This paper considers the problem of multi factory parallel machine problems.•We analyzed the available model and algorithm and showed that they suffer from serious shortcomings.•We propose three ...intelligent mathematical models for makespan and total completion time objectives.•We propose effective metaheuristics based on artificial bee colony algorithm.•The proposed models and algorithm significantly outperform the available model and algorithm.
This paper considers the problem of multi factory parallel machine problems. This problem is already studied in the literature and there is a mathematical model and a genetic algorithm for the problem. We analyzed the model and algorithm, and showed that they suffer from serious shortcomings. Then, we propose three mathematical models for makespan and total completion time objectives. The proposed models are compared with the available model in both size and computational complexities. The available model is significantly outperformed. Moreover, we propose three effective metaheuristics based on artificial bee colony algorithms. The proposed metaheuristics are compared against the four available algorithms on both small and large instances. The proposed metaheuristics perform much more effectively.
•Considering a three-echelon location-inventory problem with correlated demand.•Proposing a new coordinated location-inventory model with shortages and periodic review system.•Formulating the ...management problem as an MINLP.•Solving the model using a genetic algorithm and simulated annealing with the decoding scheme.•Demonstrating the presented model and solution methods effectively.
This paper considers a location-inventory problem in the three-level supply chain where demand across the retailers is assumed to be correlated and inventory shortages are allowed. For better monitoring the stock status, a periodic review of inventory level is taken into account. In order to overcome the joint location-inventory problem, this paper proposes an optimization model based on a mixed integer non-linear programming (MINLP) whose objective function is the minimization of the total supply chain costs. To solve the designed MINLP model, two meta-heuristic algorithms are presented, including genetic algorithm (GA) and simulated annealing (SA) with an appropriate decoding scheme. Since the performance of meta-heuristic algorithms depends on setting the parameters; therefore, the Taguchi method is used to set parameters of the developed solving algorithms. Finally, the proposed algorithms have been used to several numerical test problems that indicate the higher performance of the GA compared with the SA in terms of objective function.
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