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排序方式: 共有150条查询结果,搜索用时 216 毫秒
1.
Sadok Rezig Zied Achour Mohamed-Ali Kammoun 《International journal of systems science》2016,47(14):3425-3435
This paper addresses the synthesis of Petri net (PN) controller for the forbidden state transition problem with a new utilisation of the theory of regions. Moreover, as any method of control synthesis based on a reachability graph, the theory of regions suffers from the combinatorial explosion problem. The proposed work minimises the number of equations in the linear system of theory of regions and therefore one can reduce the computation time. In this paper, two different approaches are proposed to select minimal cuts in the reachability graph in order to synthesise a PN controller. Thanks to a switch from one cut to another, one can activate and deactivate the corresponding?PNcontroller. An application is implemented in a flexible manufacturing system to illustrate the present method. Finally, comparison with previous works with experimental results in obtaining a maximally permissive controller is presented. 相似文献
2.
A new approach to 3D reconstruction without camera calibration 总被引:2,自引:0,他引:2
In this paper, we present a new approach for 3D scene reconstruction based on projective geometry without camera calibration. Previous works use at least six points to build two projective reference planes. Our contribution is to reduce the number of reference points to four by exploiting some geometrical shapes contained in the scene. The first implemented algorithm allows the reconstruction of a fourth point on each reference plane. The second algorithm is devoted to the 3D reconstruction. We obtained the expected good results and the proposed method is to equip a mobile robot moving in a structured environment. 相似文献
3.
Emna B. Saafi‐Ben Salah Guido Flamini Amira El Arem Manel Issaoui Samia Dabbou Leila BenYahia Ali Ferchichi Mohamed Hammami Lotfi Achour 《International Journal of Food Science & Technology》2012,47(9):1903-1908
This paper reports a discrimination study based on the physico‐chemical characteristics, fatty acids and profile of volatile compounds of the seeds from seven date palm varieties (Phoenix dactylifera L.) grown in Tunisia. Date seeds contained 10.49–14.76% moisture; 6.28–11.2% fat (on a dry weight basis); 2.67–12.85% protein; 0.91–6.06% reducing sugar; 0.61–2.98% sucrose and 0.97–1.17% ash. Gas liquid chromatography revealed that the oil fraction of the date palm seeds contained eighteen fatty acids, with oleic acid (30.77–42.50%) and lauric acid (18.51–27.48%) as the main unsaturated and saturated ones. Volatile profile showed differences among varieties. In total, forty‐five compounds were identified, mainly alcohols, aldehydes and unsaturated hydrocarbons ones. This study provides evidence that the seeds of date may be a potential source of valuable nutrients with interesting functionality. 相似文献
4.
In this paper an algorithm for the probabilistic analysis of concrete structures is proposed which considers material uncertainties and failure due to cracking. The fluctuations of the material parameters are modeled by means of random fields and the cracking process is represented by a discrete approach using a coupled meshless and finite element discretization. In order to analyze the complex behavior of these nonlinear systems with low numerical costs a neural network approximation of the performance functions is realized. As neural network input parameters the important random variables of the random field in the uncorrelated Gaussian space are used and the output values are the interesting response quantities such as deformation and load capacities. The neural network approximation is based on a stochastic training which uses wide spanned Latin hypercube sampling to generate the training samples. This ensures a high quality approximation over the whole domain investigated, even in regions with very small probability. 相似文献
5.
6.
Thomas Most 《Computers & Structures》2011,89(17-18):1664-1672
In this paper several methods for model assessment considering uncertainties are discussed. Sensitivity analysis is performed to quantify the influence of the individual model input parameters. In addition to the well-known analysis of a single model, a new procedure for quantifying the influence of the model choice on the uncertainty of the model prediction is proposed. Furthermore, a procedure is presented which can be used to estimate the model framework uncertainty and which enables the selection of the optimal model with the best compromise between model input and framework uncertainty. Finally Bayesian methods for model selection are extended for model assessment without measurements using model averaging as reference. 相似文献
7.
The control of a permanent-magnet synchronous motor is a nontrivial issue in AC drives, because of its nonlinear dynamics and time-varying parameters. Within this paper, a new passivity-based controller designed to force the motor to track time-varying speed and torque trajectories is presented. Its design avoids the use of the Euler–Lagrange model and destructuring since it uses a flux-based dq modelling, independent of the rotor angular position. This dq model is obtained through the three-phase abc model of the motor, using a Park transform. The proposed control law does not compensate the model’s workless force terms which appear in the machine’s dq model, as they have no effect on the system’s energy balance and they do not influence the system’s stability properties. Another feature is that the cancellation of the plant’s primary dynamics and nonlinearities is not done by exact zeroing, but by imposing a desired damped transient. The effectiveness of the proposed control is illustrated by numerical simulation results. 相似文献
8.
Yoram Bouhnik Lotfi Achour Damien Paineau Michel Riottot Alain Attar Francis Bornet 《Nutrition journal》2007,6(1):42
Background
Short-chain fructo-oligosaccharides (scFOS) are increasingly used in human diet for their prebiotic properties. We aimed at investigating the effects of scFOS ingestion on the colonic microflora and oro-fecal transit time in elderly healthy humans. 相似文献9.
10.
Sonia Ben Salem Zahra Ben Achour Kamel Thamri Oualid Touayar 《Nanoscale research letters》2014,9(1):577
The aim of this work is to optimize the different parameters for realization of an absorbing cavity to measure the incident absolute laser energy. Electrochemical oxidation is the background process that allowed the copper blackening. A study of the blackened surface quality was undertaken using atomic force microscopy (AFM) analysis and ultraviolet-visible-infrared spectrophotometry using a Shimadzu spectrophotometer. A two-dimensional and three-dimensional visualization by AFM of the formed oxide coating showed that the copper surfaces became porous after electrochemical etching with different roughness. This aspect is becoming more and more important with decreasing current density anodization. In a 2 mol L
-1 of NaOH solution, at a temperature of 90°C, and using a 16 mA cm2 constant density current, the copper oxide formed has a reflectivity of around 3% in the spectral range between 300 and 1,800 nm. Using the ‘mirage effect’ technique, the obtained Cu2O diffusivity and thermal conductivity are respectively equal to (11.5 ± 0.5) 10 to 7 m2 s-1 and (370 ± 20) Wm-1 K-1. This allows us to consider that our Cu2O coating is a good thermal conductor. The results of the optical and thermal studies dictate the choice of the cavity design. The absorbing cavity is a hollow cylinder machined to its base at an angle of 30°. If the included angle of the plane is 30° and the interior surface gives specular reflection, an incoming ray parallel to the axis will undergo five reflections before exit. So the absorption of the surface becomes closely near 0.999999. 相似文献