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排序方式: 共有85条查询结果,搜索用时 22 毫秒
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.
Hamza Saidi Walid Aloui Abdelaziz Bouazizi 《Journal of Materials Science: Materials in Electronics》2018,29(21):18051-18058
The electrical proprieties of poly (3-hexylthiophene): Silicon nanowires (P3HT: SiNWs) nanocomposite was investigated by impedance spectroscopy technique. The effect of bias voltage under and without illumination was discussed. Indeed, the imaginary part of the impedance shows a high relaxation frequency related to Maxwell–Wagner–Sillars (MWS) polarization. The relaxation time was found in the range of ms and it was shifted towards high frequency with increasing the bias voltage especially at 0.6 V At bias voltage equal to Vth and under illumination, the conductivity increases because the trapped charges acquire the necessary energy to escape from the interface and the hopping time found was reduced. This indicates a change of the conduction mechanism. The Cole–Cole diagram was excellently fitted through an equivalent circuit including a chemical capacitance Cµ, a contact electrical resistance Rs and recombination resistance Rp. 相似文献
6.
Amal Bouazizi Ghada Zaibi Amjad Iqbal Abdul Basir Mounir Samet Abdennaceur Kachouri 《国际射频与微波计算机辅助工程杂志》2019,29(8)
In this article, a novel 3D meandered planar inverted‐F antenna (PIFA) is proposed for dual band application targeting Wireless Body Area Network (WBAN). The proposed antenna is printed on the casing of a 3D‐base‐station model having a size of 88 × 95 × 10.2 mm3. The proposed PIFA covers two bands including medical implant communication service (MICS) (402‐405 MHz), as well as the industrial, scientific, and medical (ISM) (2.4‐2.48 GHz) bands. Each of the two bands can be controlled independently. The 3D configuration contains two linked meandered resonators to downsize the structure. Due to its conformal shape, omnidirectional radiation pattern, and low‐profile nature, the proposed PIFA is a potential candidate for targeting the WBAN applications. The proposed antenna, covering the MICS and ISM bands, works with an optimally matching (VSWR<2) at the aforementioned bands. The design concept was validated by fabricating the antenna prototype and measuring its characteristics. 相似文献
7.
Charguia Raihane Hcini Sobhi Hcini Fakher Bouazizi Mohamed Lamjed 《Journal of Superconductivity and Novel Magnetism》2022,35(2):603-613
Journal of Superconductivity and Novel Magnetism - In this work, the thermal, microstructural, magnetic, and optical studies for both La0.7Ca0.3CoO3 (LCCO) and La0.7Pb0.3CoO3 (LPCO) cobaltite... 相似文献
8.
Rejaiba Omar Hcini Fakher Nasri Maria Alzahrani Bandar Bouazizi Mohamed Lamjed Hlil E. K. Khelifi Jabeur Khirouni Kamel Dhahri Essebti 《Journal of Materials Science》2021,56(28):16044-16058
Journal of Materials Science - The CuFeCr0.5Ni0.5O4 (CFO) compound was synthesized using sol–gel reaction combustion technic. The structural analysis showed that the obtained composites have... 相似文献
9.
Metal-organoclays (MOC) were prepared through incorporation of Boltorn polyol dendrimer H30 in Na+-exchanged montmorillonite (NaMt), followed by in-situ dispersion of Cu0 and Pd0 nanoparticles (CuNPs and PdNPs). The organoclays displayed high CO2 retention capacity (CRC) of 3.6–11.1 μmol/g, but metal incorporation induced a significant increase of hydrogen uptake up to 51.8–508.2 micmol/g at the expense of the CRC. Thermal programmed desorption and FT-IR investigations revealed strong interactions with CO2 before metal incorporation. These interactions markedly depleted in the presence of CuNPs and PdNPs. This was regarded as a precise indicator of the appreciable metal stabilization within the organic entanglement, due to enhancements of HO:Cu0 and HO:Pd0 interactions at the expense of HO:CO2 carbonate-like association. The CO2 and H2 retention capacities (CRC and HRC, respectively) were found to strongly correlate to the number of OH groups of the dendritic moiety incorporated. Hydrogen retention appears to involve mainly physical interactions as supported by easy gas release between 20 °C and 75 °C or even at room temperature under vacuum. This demonstrates unequivocally the reversible capture of hydrogen. The increase of the hydrogen uptake with increasing contact time provides evidence of the occurrence of diffusion phenomena. This was not observed with CO2 before metal incorporation, suggesting a structure compaction that improves metal stabilization. This opens new prospects for hydrogen storage via truly reversible capture on low cost clay materials and biodegradable hyperbranched macromolecules deriving from plants. 相似文献
10.
Generally, textile dyeing is based on a mixture of several dyestuffs used in different proportions to achieve the desired-colors. The dyes used in a mixture should react with the fiber similarly; thus they must be compatible among themselves. So, to realize mixtures it is indispensable to study the compatibility of dyes, in order to ensure optimal dyeing formulation. This paper describes the characterization and studies the compatibility of three cold bifunctionnal reactive dyes (C.I. Reactive Yellow 145, C.I. Reactive Red 238, and C.I. Reactive Blue 235) in order to explore the possibility to use them in mixtures. The dye compatibility was studied based on several criteria such as dye extinction coefficients, exhaustion and fixation yield rates, adsorption kinetics, and adsorption isotherms. The exhaustion and fixation yield rates of all three dyes was compared between them and their adsorption kinetics and adsorption isotherms models were drawn and discussed. Between the different studied models, the Elovich model presents the best model describing the kinetics of different dyes, and Freundlich model presents the best model for analyzing the adsorption isotherms. The obtained results show that the analyzed dyes are perfectly compatible and have the same dyeing properties. They present close extinction coefficients as well as similar exhaustion and fixation yield rates. 相似文献