Design of intelligent distributed control systems: a dependability point of view

The use of fieldbuses and the emergence of intelligent sensors and actuators are opening up new possibilities for distributed control systems, but are also introducing additional constraints in terms of achieving dependability objectives. The type of production environment will greatly determine the predominant criterion for an automatic control system, i.e. reliability, availability, maintainability, safety, etc. On the other hand, the choice of a fieldbus system will also depend on factors such as application size, data throughput, and integration of time considerations. Other important criteria include cost, confidentiality, and compatibility with existing equipment. Therefore, it appears essential that designers be given the means to assess dependability at each design step by integrating feedback from experience. Assessing dependability is too often limited to an evaluation at the end of the design process, which often involves reselecting previous choices. The main topic of this paper is to focus on the communication function which is a pivotal of intelligent distributed control systems. So this article is a synthesis of different aspects linked to the design of fieldbus based applications thanks to the contributors, who come from various fields. Consequently it highlights the main problem and give some ways to solve them.     

Development of biodegradable coatings for covered horizontal bunker‐stored silage

The addition of different plasticizers, thickeners and hydrophobic compounds such as fatty acids in biodegradable coatings has been evaluated using pH values and dry matter content as criteria in silage during one month of storage at room temperature under laboratory conditions. A base coating solution was prepared with whey protein concentrate, calcium caseinate and carboxymethylcellulose. From the base coating solution, derivative coating solutions were developed to evaluate the effect of plasticizers by incorporating glycerol at different concentrations and different ratios of sorbitol and glycerol. Thickening agents were also evaluated by adding fine silage powder, coarse silage powder, hay powder, or cornstarch. Derivative coating solutions were studied to evaluate the effect of fat constituents. Canola oil, beef fat, shortening, bees wax or candellila wax were added to the base solution following various procedures. Results showed that the addition of glycerol (320 g kg^?1) in the coating formulation resulted in a pH value of 5.21 after 31 days of storage without visible spoilage under the coating. The presence of plasticizer compounds avoids the appearance of cracking in the coating during the early stage of conservation. The pH of silage coated with formulations containing coarse or fine silage powder was preserved below 5 until day 17 as compared to the other formulations where the pH was preserved below 5 only for 10 days. The incorporation of beef fat in the coating formulation resulted in the lowest pH as compared to all the other fat compounds evaluated, showing a value of 4.61 at the end of storage. The addition of glycerol, coarse silage and beef fat in the same coating formulation recovered by a hydrophobic layer of zein stabilized the pH to 4.47 for 28 days of storage with a final dry matter content at 344.3 g kg^?1 without visible spoilage under the coating during all of the storage at room temperature. Copyright © 2004 Society of Chemical Industry     

Dislocation structure behind a shock front in fcc perfect crystals: Atomistic simulation results

Large-scale molecular dynamics simulations are used to investigate the dislocation structure behind a shock front in perfect fcc crystals. Shock compression in both the 〈100〉 and 〈111〉 directions induces dislocation loop formation via a sequential emission of partial dislocations, but in the 〈100〉 case, this process is arrested after the first partial, resulting in stacking-fault loops. The large mobility of the bounding partial dislocations results in a plastic wave that is always overdriven in the 〈100〉 direction; the leading edges of the partials are traveling with the plastic front, as in the models of Smith and Hornbogen. In contrast, both partials are emitted in 〈111〉 shock compression, resulting in perfect dislocation loops bounded only by thin stacking fault ribbons due to the split partial dislocations. These loops grow more slowly than the plastic shock velocity, so new loops are periodically nucleated at the plastic front, as suggested by Meyers. This article is based on a presentation given in the symposium “Dynamic Deformation: Constitutive Modeling, Grain Size, and Other Effects: In Honor of Prof. Ronald W. Armstrong,” March 2–6, 2003, at the 2003 TMS/ASM Annual Meeting, San Diego, California, under the auspices of the TMS/ASM Joint Mechanical Behavior of Materials Committee.     

The modified count and weigh method: an improved procedure for assessing weight loss in stored maize cobs

This paper describes a modification of the well-known count and weigh (gravimetric) method for assessing losses due to insect pests in stored maize cobs. The modification involves counting the destroyed grains on each cob and using an adjusted calculation. Data are presented to show that the precision of the modified method is similar to that of the conventional count and weigh method. No systematic bias was detected with the modified method, in contrast to the conventional method which is shown to underestimate true weight loss by up to half. The main justification given for the use of the modified method is that the conventional method underestimates loss to an unpredictable extent, depending on the degree to which pest-damaged grains retain a separate, countable identity. For example, it is shown that the degree to which the conventional method underestimated loss was much greater for a floury, small-grained variety, in which many insect-damaged grains were reduced to powder, than for a large-grained variety in which most damaged grains retained their identity. This implies that comparisons of weight losses based on the conventional method should be interpreted with great caution in studies with significant amounts of destroyed grains.     

Filters in topology optimization

In this article, a modified (‘filtered’) version of the minimum compliance topology optimization problem is studied. The direct dependence of the material properties on its pointwise density is replaced by a regularization of the density field by the mean of a convolution operator. In this setting it is possible to establish the existence of solutions. Moreover, convergence of an approximation by means of finite elements can be obtained. This is illustrated through some numerical experiments. The ‘filtering’ technique is also shown to cope with two important numerical problems in topology optimization, checkerboards and mesh dependent designs. Copyright © 2001 John Wiley & Sons, Ltd.     

Group-average covariance matrices for the hafnium isotopes of interest for light water reactor applications

A consistent set of covariance matrices for the neutron cross-sections of ¹⁷⁴Hf, ¹⁷⁶Hf, ¹⁷⁷Hf, ¹⁷⁸Hf, ¹⁷⁹Hf and ¹⁸⁰Hf has been generated with results of a recent shape analysis performed on transmission data measured at the GELINA facility. The focus of this work is to propagate the Hf nuclear data uncertainties in specific reactivity worth measurements performed in the EOLE critical facility of the CEA Cadarache and to draw useful trends on the quality of the latest version of the European library JEFF-3.1.1.     

Energy Levels of Singly-Ionized Platinum

The analysis of Pt II is extended by using accurate wavelength measurements by Sansonetti et al. Forty-three new even and 104 new odd levels have been found. The Slater-Condon parametric method is used for the interpretation of the 5d⁹, 5d⁸6s, and 5d⁷6s² low even configurations and the 5d⁸(7s+6d) high even configurations with root mean square deviations smaller than 80 cm⁻¹. The importance of the 5d⁸–5d⁷6s core interaction in interpreting the even-parity levels is stressed.