Joint production and setup control policies: an extensive study addressing implementation issues via quantitative and qualitative criteria

This paper addresses the production and setup control problem in unreliable multiproducts manufacturing system. Several decision criteria are considered in order to conduct an exhaustive comparative study of the two most complete control policies in the literature. The objective is to propose a production and setup control policy for the system under review. The first part of this work consists in analyzing the effect of the system parameters variation on the difference between the total costs of the two control policies studied. The best control policy in terms of cost will then be determined using a numerical example in the case of two identical product types and without the loss of generality of the problem. In the second part, two key performance indicators (KPIs): the cost and the customer satisfaction rate are simultaneously considered. The goal is to optimize the parameters of the policies studied, which minimize the total cost incurred while respecting customer satisfaction constraint. A discussion on the best control policy is conducted based on cost and customer satisfaction. An experimental resolution approach is used. It integrates combined discrete-continuous simulation models with statistical techniques of optimization such as design of experiments, analysis of variance, and response surface methodology. Finally, a discussion is conducted on the effects of other quantitative and qualitative criteria in order to determine the best control policy and to reach the best concerns of the company’s decision makers. These decision criteria are generally related to the storage space required constraint, the setups complexity, the implementation issue, and the complexity of the optimal control problem.     

Multitone power and intermodulation load-pull characterization ofmicrowave transistors suitable for linear SSPA's design

In this paper, an experimental load-pull characterization of microwave transistors operated under N-tone-excitations (2⩽N⩽32) is presented. Such characterization is very useful to investigate the linearity of high-power amplifiers via intermodulation distortion analysis. All the measurements were carried out using a newly developed multiline measurement system which uses an arbitrary waveform generator (AWG) to generate the spectrum of any N desired tones and a microwave transition analyzer (MTA) as a vector receiver. The measured intermodulation rejection (IMR) behavior, as the number of tones increases, is compared with previously published theoretical results. Constant output power contours and IMR contours in the Γ_L (f₀) plane for different number of tones are presented and discussed. The dependency of the IMR on the biasing conditions and the carriers' phase distribution is also investigated     

Use of prior bounds on time constants and steady‐state gain in recursive parameter bounding

Computation of parameter bounds of a linear dynamical system, given input–output observations and bounds on model‐output error, has been developed as an alternative to classical parameter estimation using least squares, maximum likelihood or the prediction error method. When bounds on time‐domain plant behaviour are known in advance, they can be used to develop prior parameter bounds for discrete‐time rational transfer‐function parameters. These bounds can be used to initialize standard parameter‐bounding algorithms which process input–output observations to update the exact polytope feasible set or one of its outer bounding approximations such as an ellipsoid, orthotope or parallelotope. This paper presents a method to compute such prior bounds from bounds on time constants and steady‐state (dc) gain, often available from the physics of the system or from previous experience. The method finds subsets making up the prior feasible parameter set, recursively in model order, for any configuration of the pole ranges. An analysis leading to measures of the value of prior bounds, in terms of their chances of remaining active when new bounds derived from observations are imposed, is presented. A simulation study compares polytope updating with and without such initial bounds. The simulations investigate the influence of the tightness of time‐constant and steady‐state‐gain bounds in reducing the volume of the feasible sets obtained as observations are processed. The effects of initial bound tightness and signal‐to‐noise ratio on survival time of the prior bounds are also examined. Copyright © 2002 John Wiley & Sons, Ltd.     

Ileal lipoma: a cause of severe lower digestive tract hemorrhage

We report a case of major lower digestive tract hemorrhage caused by an ileal lipoma. The main clinical signs of this uncommon pathology are presented together with the necessary paraclinical investigations. Ileal lipoma may be spontaneously complicated and requires surgical treatment.     

Delay-efficient MAC protocol with traffic differentiation and run-time parameter adaptation for energy-constrained wireless sensor networks

This paper presents an asynchronous cascading wake-up MAC protocol for heterogeneous traffic gathering in low-power wireless sensor networks. It jointly considers energy/delay optimization and switches between two modes, according to the traffic type and delay requirements. The first mode is high duty cycle, where energy is traded-off for a reduced latency in presence of realtime traffic (RT). The second mode is low duty cycle, which is used for non-realtime traffic and gives more priority to energy saving. The proposed protocol, DuoMAC, has many features. First, it quietly adjusts the wake-up of a node according to (1) its parent’s wake-up time and, (2) its estimated load. Second, it incorporates a service differentiation through an improved contention window adaptation to meet delay requirements. A comprehensive analysis is provided in the paper to investigate the effectiveness of the proposed protocol in comparison with some state-of-the-art energy-delay efficient duty-cycled MAC protocols, namely DMAC, LL-MAC, and Diff-MAC. The network lifetime and the maximum end-to-end packet latency are adequately modeled, and numerically analyzed. The results show that LL-MAC has the best performance in terms of energy saving, while DuoMAC outperforms all the protocols in terms of delay reduction. To balance the delay/energy objectives, a runtime parameter adaptation mechanism has been integrated to DuoMAC. The mechanism relies on a constrained optimization problem with energy minimization in the objective function, constrained by the delay required for RT. The proposed protocol has been implemented on real motes using MicaZ and TinyOS. Experimental results show that the protocol clearly outperforms LL-MAC in terms of latency reduction, and more importantly, that the runtime parameter adaptation provides additional reduction of the latency while further decreasing the energy cost.     

Electrical conductivity of 1 : 1 and 2 : 1 clay minerals

The A.C. impedance plots were used as tools to analyze the electrical response of two varieties of Tunisian halloysite 1: 1 and illitic samples 2: 1 as a function of frequency at different temperatures (80–800°C). The real and imaginary parts of the complex impedance trace semicircles in the complex plane. Except for the illite, It-1, the second sample analyzed in this study, these plots give evidence for the presence of both bulk and grain boundary effect, above 600°C onwards. The bulk resistance of the materials decreases with the rise in temperature. Impedance Spectroscopy data reveal a non-Debye type of dielectric relaxation. The Nyquist plots show the negative temperature coefficient of resistance of both pure Tunisian illite and halloysite samples. The results of bulk electrical conductivity and its activation energy are presented for the two mineral clay samples. For illite It-1, the activation energy values estimated from the AC conductivity pattern and modulus pattern are very similar and suggest a possibility of a long-range mobility of charge carriers (ions) via hopping mechanism of electrical transport processes at higher temperature. On the other hand, for the halloysite sample provided from kasserine, (Ha-Kass), the modulus analysis admit that the electrical transport processes of the material are very likely of electronic nature. Relaxation frequencies follow an Arrhenius behavior with the activation energy values not comparable to those found for the electrical conductivity.     

A transient model for insulated gate bipolar transistors (IGBTs)

In this paper, we present a physics-based model for the non punch-through (NPT) insulated gate bipolar transistor (IGBT) during transient turn off period. The steady state part of the model is derived from the solution of the ambipolar diffusion equation in the drift region of the NPT IGBT. The transient component of the model is based on the availability of a newly developed expression for the excess carrier concentration in the base. The transient voltage and current are obtained both numerically and analytically from this model. The theoretical predictions of both approaches are compared with experimental data and found to be in good agreement.     

Purification of silicon powder by the formation of thin porous layer followed by photo-thermal annealing

ABSTRACT: Porous silicon has been prepared using a vapor-etching based technique on a commercial silicon powder. Strong visible emission was observed in all samples. Obtained silicon powder with a thin porous layer at the surface was subjected to a photo-thermal annealing at different temperatures under oxygen atmosphere followed by a chemical treatment. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) results indicate that silicon purity is im-proved from 99.1 to 99.994 % after annealing at 900 degreesC.     

Purification of metallurgical-grade silicon powder via chemical attack by hydrofluoric and nitric acids followed by thermal treatment

We investigated a novel process for purifying metallurgical-grade silicon (MG-Si). MG-Si powder was first treated to form a thin porous silicon layer. This was heated at 900 °C under oxygen to weaken impurity–Si bonds. Samples were then chemically etched with dilute aqueous hydrofluoric acid. To understand the mechanisms in this purification process, structural, chemical composition and optical properties of MG-Si powder before and after treatment were characterized using Fourier-transform infrared (FTIR), inductively coupled plasma-atomic emission (ICP-AES), and photoluminescence (PL) spectroscopy techniques. FTIR studies of treated MG-Si powder revealed the formation of a thin porous silicon layer on the top surface, as evidenced by SiH_x vibration peaks. PL spectra show that 30-min HF etching of MG-Si led to an increase in red emission, indicating the formation of porous silicon and suggesting a decrease in impurities. ICP-AES revealed that the process led to significant decreases in the concentrations of 15 different elemental impurities.     

Structural properties of FeTe2 thin films synthesized by tellurization of amorphous iron oxide thin films

This paper deals with the structural properties of FeTe₂ thin films obtained using a simple and non-toxic experimental procedure. First, iron oxide thin films have been prepared by the spray pyrolysis technique from an aqueous solution containing FeCl₃6H₂O (0.03 M) as a precursor onto glass substrates heated at 623 K. Second, these films were subjected to a heat treatment under tellurium atmosphere at various temperatures (723–803 K) for 24 h. XRD analysis revealed that FeTe₂-ortorombic phase films were obtained at a heat treatment of the order of 773 K. This film has a good crystalline state with a preferential orientation of the crystallites along (111) direction. Moreover, AFM as well as SEM morphological observations show a relatively perturbed surface state.To date, this simple and low cost route process to obtained FeTe₂ thin films has not yet been used.