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1.
This paper is the first attempt to successfully design efficient approximation algorithms for the single-machine weighted
flow-time minimization problem when jobs have different release dates and weights equal to their processing times under the
assumption that one job is fixed (i.e., the machine is unavailable during a fixed interval corresponding to the fixed job).
Our work is motivated by an interesting algorithmic application to the generation of valid inequalities in a branch-and-cut
method. Our analysis shows that the trivial FIFO sequence can lead to an arbitrary large worst-case performance bound. Hence,
we modify this sequence so that a new 2-approximation solution can be obtained for every instance and we prove the tightness
of this bound. Then, we propose a fully polynomial-time approximation algorithm with efficient running time for the considered
problem. Especially, the complexity of our algorithm is strongly polynomial. 相似文献
2.
This paper addresses the deadlock-free scheduling problem in Flexible Manufacturing Systems. An efficient deadlock-free scheduling algorithm was developed, using timed Petri nets, for a class of FMSs called Systems of Sequential Systems with Shared Resources (S 4 R). The algorithm generates a partial reachability graph to find the optimal or near-optimal deadlock-free schedule in terms of the firing sequence of the transitions of the Petri net model. The objective is to minimize the mean flow time (MFT). An efficient truncation technique, based on the siphon concept, has been developed and used to generate the minimum necessary portion of the reachability graph to be searched. It has been shown experimentally that the developed siphon truncation technique enhances the ability to develop deadlock-free schedules of systems with a high number of deadlocks, which cannot be achieved using standard Petri net scheduling approaches. It may be necessary, in some cases, to relax the optimality condition for large FMSs in order to make the search effort reasonable. Hence, a User Control Factor (UCF) was defined and used in the scheduling algorithm. The objective of using the UCF is to achieve an acceptable trade-off between the solution quality and the search effort. Its effect on the MFT and the CPU time has been investigated. Randomly generated examples are used for illustration and comparison. Although the effect of UCF did not affect the mean flow time, it was shown that increasing it reduces the search effort (CPU time) significantly. 相似文献
3.
Nazrin S. N. Umar S. A. Halimah M. K. Marian M. M. Najwa Z. W. Jufa M. S. Syahirah M. T. Zuhasanah Z. Azlan M. N. Geidam I. G. Boukhris Imed Kebaili Imen 《Journal of Inorganic and Organometallic Polymers and Materials》2022,32(7):2513-2526
Journal of Inorganic and Organometallic Polymers and Materials - Copper oxide doped TeO2–B2O3 glass system with empirical formula;... 相似文献
4.
Modeling of Particle Emission During Dry Orthogonal Cutting 总被引:2,自引:0,他引:2
Riad Khettabi Victor Songmene Imed Zaghbani Jacques Masounave 《Journal of Materials Engineering and Performance》2010,19(6):776-789
Because of the risks associated with exposure to metallic particles, efforts are being put into controlling and reducing them
during the metal working process. Recent studies by the authors involved in this project have presented the effects of cutting
speeds, workpiece material, and tool geometry on particle emission during dry machining; the authors have also proposed a
new parameter, named the dust unit (D
u), for use in evaluating the quantity of particle emissions relative to the quantity of chips produced during a machining
operation. In this study, a model for predicting the particle emission (dust unit) during orthogonal turning is proposed.
This model, which is based on the energy approach combined with the microfriction and the plastic deformation of the material,
takes into account the tool geometry, the properties of the worked material, the cutting conditions, and the chip segmentation.
The model is validated using experimental results obtained during the orthogonal turning of 6061-T6 aluminum alloy, AISI 1018,
AISI 4140 steels, and grey cast iron. A good agreement was found with experimental results. This model can help in designing
strategies for reducing particle emission during machining processes, at the source. 相似文献
5.
Ines Ben Said Adele Muscolo Imed Mezghani Mohamed Chaieb 《Water and Environment Journal》2023,37(3):549-560
The increasing aridity exacerbated by climatic changes is leading to loss of perennial herbaceous plants Cenchrus ciliaris, an apomictic, polyploid grass used as forage in hot and dry areas, and is currently under threat for the increased scarcity of water. In this study, treated municipal wastewater (TWW) was used to irrigate two ploidy levels of C. ciliaris for two consecutive years. The objectives were (1) to assess the possibility of using unconventional water for watering C. ciliaris and (2) to identify at what extent TWW irrigation affected growth and nutritive properties of C. ciliaris that differed for polyploidy level. TWW irrigation positively affected growth and physiological plant parameters. In leaves of TWW watered C. ciliaris, the concentration of Nt, P and K significantly increased. The tetraploid C. ciliaris showed a better growth and quality than the hexaploid ones, appearing the most suitable cultivar to be irrigated with TWW for feed uses. In short, TWW can be strategically used for irrigating forage species with the double output of ameliorating soil properties, recovering degraded area and improving the nutritive values of fodder species contributing to the promotion of a green and sustainable circular economy, more in climatically under pressure developing countries. 相似文献
6.
Narjes Hasni Centina Pinier Cheraief Imed Monêem Ouhichi Philippe Couzi Brahim Chermiti Brigitte Frérot Imen Saïd Didier Rochat 《Journal of chemical ecology》2017,43(7):631-643
Laboratory and field investigations to identify and evaluate plant co-attractants of the aggregation pheromone of the date palm pest Oryctes agamemnon are reported. Volatiles emitted by freshly cut palm core and palm core with feeding males, were collected, analyzed by gas chromatography coupled to mass spectrometry and evaluated in olfactometers alone or combined with synthetic pheromone. A collection of palm odor without male effluvia was attractive alone and enhanced attraction to synthetic pheromone in an olfactometer similar to that to a collection of palm odor emitted with feeding males and containing natural pheromone. Behavioral responses to collections of palm volatiles were correlated to the amount of volatiles material in them. Enhancement of the attractiveness of the pheromone was not correlated to chemicals specific to beetle feeding. The chemicals common to the active collections extracts were benzoate esters, mostly ethyl benzoate, anisole derivatives and sesquiterpenes. Blends of the most abundant components of the extracts were evaluated for enhancement of the attractiveness of pheromone (1 μg) in olfactometers at 1 or 10 μg doses. The mixtures were further evaluated by field trapping in Tunisia at 3–10 mg/day using reference (6 mg/day) or experimental pheromone formulations. A mixture of ethyl benzoate, 4-methylanisole and farnesol (1:1:1 w/w at 6.5 mg/day) enhanced captures in pheromone baited traps in 2014 and 2015 and this mixture was as active as the natural palm bait. The practical prospect of the result for the management for O. agamemnon, and other palm beetles is discussed. 相似文献
7.
Jacobian-based performance indices such as the manipulability ellipsoid, the condition number and the minimum singular value, have been very helpful tools both for mechanical manipulator design and for determining suitable manipulator postures to execute a given task. For a manipulator having complex degrees of freedom (translations and rotations), Jacobian matrix becomes non-homogeneous, i.e. it contains elements with different physical units; therefore, the evaluation of its determinant, eigenvalues or singular values needs the combination of quantities of different nature, which is physically inconsistent and moreover it corresponds to a noncommensurable system. In this paper, a new performance index of robot manipulators is proposed. It is fully homogeneous and it constitutes a physically consistent system whether the manipulator contains joints of different natures, or the task space combines both translation and rotation motion. The development is concerned with the study of power within the mechanism. Given that the power has the same physical units in translation and rotation, it can be used as a homogeneous or natural performance index of manipulators by examining the behaviour of its basic components namely, force and speed, at different kinematics configurations. Furthermore, the new concept of vectorial power is introduced, followed by to the quadrivector of apparent power, and leading to the final homogeneous performance index of the power manipulability (PM). This new approach matches perfectly with mechanisms having joints of different natures, as well as with a task space combining both translation and rotation. 相似文献
8.
Monia Bouktif Zarrouk Esrine Gharbi Imed Maatouk Jean-Charles Leblanc Ahmed Landoulsi 《Food additives & contaminants. Part A, Chemistry, analysis, control, exposure & risk assessment》2020,37(7):1165-1179
ABSTRACT Dietary exposure of the Tunisian adult population to pesticide residue was assessed using the Total Diet Study method. In the present study 170 pesticides were searched for in 42 aggregated foods characterised by 64 food samples representing the Tunisian diet. All the food samples were collected, prepared, and analysed for remains of pesticides including organochlorine, organophosphorous, carbamates and pyrethroids. The GC-MS analysis and the LC-MS/MS analysis and some other specific analytical methods were employed for the quantification of the pesticide residues in the food samples. Results revealed that21pesticides reached amounts greater than the LOQ(12.3%) and 149 pesticides reached amounts below the LOD (88%).For the 21 pesticides quantified, the ADI was not exceeded. For the 149 non-quantified pesticides, an interval defined by the lower and upper bounds was defined to assess the dietary exposure of the Tunisian adult population to those pesticides. We conclude that 8 pesticides theoretically exceed the ADI with the 95th percentile of exposure, those are: Diféthialone, Brodifacoum, Bromadiolone, Glufosinate, Heptachlor, Dieldrin Aldrin Oxydemeton-methyl. This study concludes that there is a low dietary exposure to pesticide residue of the Tunisian adult population. In fact, all the cases where the ADI was exceeded were theoretical due to the lower ADI value used. 相似文献
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