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61.
62.
Molka Attia Hili Tahar Fakhfakh Lotfi Hammami Mohamed Haddar 《The International Journal of Advanced Manufacturing Technology》2005,26(5):615-622
The inherent problems of the rotating machine dysfunction are often caused by shaft misalignment. This defect generates some important loads and vibrations, and can lead to a premature failure of the bearing, the shaft, or the coupling. This work deals with the development of a theoretical model describing this phenomenon. This allows obtaining and analysing the vibration response as well as the reaction in bearings. 相似文献
63.
In this paper, we propose a new wavelet-based lossless image coder that is based on a state-of-the-art algorithm, namely SPIHT (set partitioning in hierarchical trees). An algorithmic modification is introduced in order to increase its efficiency. This consists of adding a new test on direct descendants in the sets of type A to process the parent coefficients that are significant due to their nondirect descendants. Also, new sets of type C are defined to perform a separate sorting of the sets that have insignificant children. The idea behind the second proposition is to remove all tests over the entries (A, B and C) since the number of significant sets is much higher than that of insignificant sets. A number of experiments, carried out on various test images, demonstrates significant improvement over the conventional SPIHT for both greyscale and colour images. 相似文献
64.
Low-temperature processing and characterization of single-phase PZT powders by sol-gel method 总被引:1,自引:0,他引:1
Radhouane Bel Hadj Tahar Noureddine Bel Hadj Tahar Abdelhamid Ben Salah 《Journal of Materials Science》2007,42(23):9801-9806
A new sol-gel system using acetoin was developed and employed for the fabrication of PZT powders and films with compositions
near the morphotropic phase boundary Pb(Zr0.52Ti0.48)O3. Acetoin was used as chelating agent to replace the highly toxic methoxyethanol used in previous formulations. This route
simplified the chemical processing of PZT-based solutions. Powders were completely crystallized by about 450 °C and contained
the ferroelectric perovskite single phase. The firing temperature and time were to be the most important variables. Metallic
lead formed only when excess Pb was incorporated. The precursor and the heat-treated powders have been characterized by using
thermal analysis and X-ray diffractometry (XRD) studies. The average particle size, as measured from X-ray line broadening,
was ∼35 nm. 相似文献
65.
In real manufacturing environments, variations in production factors (i.e. processing time, demand, due-dates) are inevitable facts. All these dynamic changes, together with random disturbances (e.g. machine breakdowns) can seriously affect the system performance. In this paper we focus on load, processing time and due date variation and analyse their impacts on a scheduling system. Specifically, we investigate the impact of variation on dispatching policies in a job shop environment via simulation. The statistical analysis of the results leads to two major conclusions: first, the relative performance of rules is not threatened much by PV (processing time variation), LV (load variation) or DDV (due date variation) -- a result that can be a consolation for practitioners in the field. Secondly, the performance of the rules deteriorates, in particular at high levels of PV, LV and DDV -- a result that can provide new insights into the problem and produces useful information for researchers in their continuous effort to develop better dispatching rules. 相似文献
66.
ATTIA HILI Molka BOUAZIZ Slim MAATAR Mohamed FAKHFAKH Tahar HADDAR Mohamed 《水动力学研究与进展(B辑)》2010,22(2):155-163
In this article, the effect of the bearing elastic deformation on the performance characteristics of a cylindrical journal bearing is analyzed. The variety of simulation models covers hydrodynamic (HD) and elastohydrodynamic (EHD) lubrication theories. The Reynolds equations governing the flow in the clearance space of the journal bearing are obtained by considering the effect of mass transfer across the fluid film. The finite element method with an iteration scheme was employed to solve both the Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell. The converged solutions for the lubricant flow and elastic deformation vector are obtained. Dynamic characteristics of the journal bearing are computed for HD and EHD theories. Numerical simulation results show that the flexibility of bearing liner has a significant influence on the performance of a cylindrical journal bearing. Indeed, the elastic deformations of the bearing liner extend the pressure area in the bearing and increase the minimum film thickness. Although, dynamic coefficient, load capacity and attitude angle decrease. 相似文献
67.
We have evaluated the effect of the long-term intake of a cocoa powder, with high concentration of polyphenols, named CocoanOX (CCX), on the development of hypertension of spontaneously hypertensive rats (SHR). Systolic blood pressure was measured weekly in the rats, from the 6th to 24th week of life, by the tail cuff method. The development of hypertension was attenuated in the groups treated with captopril or CCX. The antihypertensive effect was more accentuated in the group treated with captopril, and it was paradoxically more accentuated in the group treated with the lowest dose of CCX than in the other CCX groups. The arterial blood pressure increased in the treated SHR when the corresponding antihypertensive treatment was removed. Both, CCX and the standard cocoa, improved the aorta endothelial function in the SHR. In conclusion, CCX could be used as a functional food ingredient with antihypertensive activity. 相似文献
68.
The purpose of the present paper is to investigate the effect of elastic deformation of bearing liner on the acoustic behavior of oil lubricated journal bearings.Analysis is performed for hydrodynamic(HD) and elasto-hydrodynamic (EHD) lubrications.Dynamic behavior and acoustical properties are investigated through an analysis of pressure fluctuation calculated from the Reynolds equation governing the flow in the clearance space of the journal bearing.This is solved numerically using the finite difference method with the successive over relaxation technique.In elasto-hydrodynamic lubrication,the finite element method with in iteration scheme is adopted to solve both Reynolds equation and the three-dimensional elasticity equation representing the displacement field in the bearing shell.The results show that the sound pressure level of the bearing is markedly influenced by the flexibility of the bearing liner,the viscosity of lubricant and the load applied to journal.HD analysis shows that the journal centre’s orbit,from a disturbed position,converges to the static equilibrium position faster than EHD lubrication.The results of the present paper could aid in the design of low-noise rotor-bearing systems supported by oil lubricated journal bearings. 相似文献
69.
Mohamed Slim Abbes Tahar Fakhfakh Mohamed Haddar Aref Maalej 《The International Journal of Advanced Manufacturing Technology》2007,34(3-4):211-218
The dynamic response of gearbox remains a paramount concern because of noise generation. This work is concerned with numerical
simulation of the overall dynamic behaviour of a parallel helical gear transmission. A dynamic sub-structuring method using
different types of substructure (carrying and slave) is made to determine the natural frequencies and the corresponding mode
shapes. The structure to be investigated is subdivided into components or sub-structures, which are then analyzed independently
for natural frequencies and mode shapes. A numerical model taking into account the elastic coupling between the various components
of a gearbox was developed. It allows studying and analyzing the dynamic behaviour of elastic housing in the presence of gear
process. The static transmission error is introduced as a vibratory excitation source and it is represented by time-varying
mesh stiffness. The discretization of the housing deformation energy and the kinetic energy expressions using plate finite
elements leads to constructions of the stiffness and the mass matrixes. In dynamic analyses, time-discretization based on
the Newmark method is used. The different equations governing movement of gearbox are established in a truncated modal base
deduced from the average characteristics of the structure. A gearbox example is presented, and analyzed. A presentation and
discussion of the numerical results was emphasized. The numerical results allow us to conclude on the dominant phenomena of
the overall dynamic behaviour of the gear transmission. 相似文献
70.
The Hand Gestures Recognition (HGR) System can be employed to facilitate communication between humans and computers instead of using special input and output devices. These devices may complicate communication with computers especially for people with disabilities. Hand gestures can be defined as a natural human-to-human communication method, which also can be used in human-computer interaction. Many researchers developed various techniques and methods that aimed to understand and recognize specific hand gestures by employing one or two machine learning algorithms with a reasonable accuracy. This work aims to develop a powerful hand gesture recognition model with a 100% recognition rate. We proposed an ensemble classification model that combines the most powerful machine learning classifiers to obtain diversity and improve accuracy. The majority voting method was used to aggregate accuracies produced by each classifier and get the final classification result. Our model was trained using a self-constructed dataset containing 1600 images of ten different hand gestures. The employing of canny's edge detector and histogram of oriented gradient method was a great combination with the ensemble classifier and the recognition rate. The experimental results had shown the robustness of our proposed model. Logistic Regression and Support Vector Machine have achieved 100% accuracy. The developed model was validated using two public datasets, and the findings have proved that our model outperformed other compared studies. 相似文献