Determination of ionization conditions characterizing the breakdown threshold of a point-plane air interval using fuzzy logic

The objective of this paper is to study the discharge phenomenon for a point-plane air interval using an original fuzzy logic system. Firstly, a physical model based on streamer theory with consideration of the space charge fields due to electrons and positive ions is proposed. To test this model we have calculated the breakdown threshold voltage for a point-plane air interval. The same model is used to determine the discharge steps for different configurations as an inference data base. Secondly, using results obtained by the numerical simulation of the previous model, we have introduced the fuzzy logic technique to predict the breakdown threshold voltage of the same configurations used in the numerical model and make estimation on the insulating state of the air interval. From the comparison of obtained results, we can conclude that they are in accordance with the experimental ones obtained for breakdown discharges in different point-plane air gaps collected from the literature. The proposed study using fuzzy logic technique shows a good performance in the analysis of different discharge steps of the air interval.     

Activity Awareness as an Enabler for Communication and Network Building in Construction Design Teams

The paper reports on ongoing research into the facilitation of communication in distributed design teams of the type typically encountered in the construction sector. Ideas around social aspects in such design teams are discussed followed by our previous research efforts as an evolutionary process that has led us to develop in this direction. It is argued that facilitating timely and contextually grounded communication in a distributed environment can help to build the social networks and associated social capital common in collocated design teams but often absent in distributed ones. We describe our framework for providing such facilitation through monitoring and awareness of the information “space” of a construction project. We believe that by leveraging the relationships in the information space, we can go some way to identifying those individuals who would benefit from developing interpersonal relations in their work and further by exploiting those relationships in real time we can accelerate the formation of personal social networks and social capital between those individuals.     

Effect of different starches on rheological and microstructural properties of (II) commercial processed cheese

A range of commercial processed cheese samples containing starch were prepared on a Rapid Visco Analyser (RVA) and on a pilot plant scale. This work clearly demonstrated that it was possible to manufacture processed cheese with part of the protein replaced with potato starch, while maintaining similar rheological attributes (firmness) to those of the control and an acceptable melt index. Sensory evaluation showed that, although the reduced‐protein cheese samples had a good, clean, fresh flavour that was comparable with that of the control, at high starch concentrations the starch‐containing processed cheese had a pasty texture and tended to stick to the wrapper.     

Improving the performance of retail stores subject to execution errors: coordination versus RFID technology

This paper analyzes a Newsvendor type inventory model in which a manufacturer sells a single product to a retailer store whose inventory is subject to errors stemming from execution problems. Hence, within the store, all of the products are not available on shelf for sales either because the replenishment of the shelf from the backroom is subject to execution errors that mainly result in products lost in the backroom or products misplaced on the other shelves of the store. We compare two situations: in the first situation, the two supply chain actors are aware of errors and optimize their ordering decisions by taking into account this issue. The second situation deals with the case where an advanced automatic identification system such as the Radio Frequency Identification technology is deployed in order to eliminate errors. Each situation is developed for three scenarios: in the centralized scenario, we consider a single decision-maker who is concerned with maximizing the entire supply chain’s profit; in the decentralized uncoordinated scenario, the retailer and the manufacturer act as different parties and do not cooperate. The third scenario is the decentralized coordinated scenario where we give conditions for coordinating the channel by designing a buyback contract. The authors would like to thank the editor, Prof. Dr. Hans-Otto Guenther, and two anonymous referees for their constructive comments to improve this article.     

Material response characterization of a low-density carbon composite ablator in high-enthalpy plasma flows

Future space exploration missions beyond Earth’s orbit, such as sample returns from Mars, will use ablative materials for the thermal protection system in order to shield the spacecraft from the severe heating during reentry. In this paper, we present the results of an elaborate test campaign on a lightweight carbon composite ablator with the aim of defining a procedure for material response characterization in a 1.2-MW inductively heated Plasmatron facility, suitable to reproduce the hypersonic flight boundary layer environment. Three different test gases were used, air, nitrogen, and argon, at surface temperatures exceeding 3300 K. A comprehensive experimental setup was developed including a nonintrusive technique to measure surface recession by means of a high-speed camera. Surface degradation was strongly test gas dependent, while mass loss was mainly driven by in-depth decomposition of phenolic resin. Emission spectroscopy helped us identify C₂ as a product of dissociating hydrocarbons, as well as cyanogen, suggesting surface nitridation. Melt flow at the surface and silicon emission indicated degradation of the glass microspheres used as additional filler. In air plasma, oxidation was inferred to be the main mechanism for ablation.     

Une nouvelle architecture de gestion de réseaux DiffServ basée sur la technologie de réseau actif et la gestion à base de règles

The objective of this work is to propose an architectural solution to the very complex problem of DiffServ network management and control. Despite the fact that DiffServ offers a scalable QoS provisioning solution, it introduces a high complexity in term of its deployment due to the number of complex configurations to perform in the highly distributed and heterogeneous network environment. The proposed solution aims to take benefit from the scalability and flexibility properties of Active Network technology for distributing the control in large scale as well as the autonomic property of Policy Based Management to automate the distribution of these tasks in the operator network. This solution constitutes an alternative to the client/server approach generally used.     

Regular Random k-SAT: Properties of Balanced Formulas

We consider a model for generating random k-SAT formulas, in which each literal occurs approximately the same number of times in the formula clauses (regular random and k-SAT). Our experimental results show that such regular random k-SAT instances are much harder than the usual uniform random k-SAT problems. This is in agreement with other results that show that more balanced instances of random combinatorial problems are often much more difficult to solve than uniformly random instances, even at phase transition boundaries. There are almost no formal results known for such problem distributions. The balancing constraints add a dependency between variables that complicates a standard analysis. Regular random 3-SAT exhibits a phase transition as a function of the ratio α of clauses to variables. The transition takes place at approximately α = 3.5. We show that for α > 3.78 with high probability (w.h.p.) random regular 3-SAT formulas are unsatisfiable. Specifically, the events hold with high probability if Pr when n → ∞. We also show that the analysis of a greedy algorithm proposed by Kaporis et al. for the uniform 3-SAT model can be adapted for regular random 3-SAT. In particular, we show that for formulas with ratio α < 2.46, a greedy algorithm finds a satisfying assignment with positive probability.     

Control of Morphological and Rheological Properties of Carrot Cell Wall Particle Dispersions through Processing

A range of thermal and mechanical processes were used to create dispersions with different particle morphologies, i.e., systems that contain primarily plant cell wall clusters with an average particle size (d(0.5)) of ～200 µm, single cells ((d(0.5)?=?～70 µm) or cell fragments (d(0.5)?=?～40 µm). The small and large deformation rheology (viscoelastic properties and flow properties) of these dispersions, with a range of total solid contents covering textures varying from a fluid to a paste, were determined. The particle dispersions showed weak gel-like behaviour. Their elastic modulus (G′) as a function of total solid content exhibited three regions of different rheological behaviours. The particles formed particulate colloidal networks at relatively low solid content. The interaction of particles contributed to the sharp increase in the elastic modulus of the dispersion in the concentrated region. Further packing of particles beyond the critical packing volume fraction, caused the G′ for the ‘cluster-cell’ and the ‘single-cell’ dispersions to reach a plateau value. This is due to particle deformation resulting in changes in their microstructure and their ability to pack closely. Plant particle dispersions displayed abrupt yielding at the critical stress with a 3–4 order decrease in viscosity and high yield stress at low solids due to the formation of particulate colloidal network.     

Small-deformation rheology investigation of rehydrated cell wall particles–xanthan mixtures

The rheological behaviour and microstructural properties of rehydrated cell wall particle (CWP) dispersions and CWP–xanthan mixtures were investigated using small-deformation rheology and confocal laser scanning microscopy. Dispersions with two different CWP particle sizes were used. CWP dispersions were found to be elastic with a weak-gel type behaviour. The elastic modulus was a function of the CWP concentration c_p and depended on the particle size of the CWP. The addition of xanthan to the CWP dispersions was found to affect the rheological behaviour of the CWP–xanthan mixtures at low CWP concentration (c_p ≤ 1 wt%), due to the increase in the viscoelastic properties of the continuous phase. At high CWP concentrations (c_p ≥ 3%), the effect of xanthan on the rheological behaviour of the CWP–xanthan mixtures was marginal, as the viscoelastic behaviour of the mixtures was dominated by the CWP particle network, with xanthan molecules entrapped in the interstitial voids. However, at intermediate CWP volume fractions (e.g. at a CWP concentration c_p = 2%) both xanthan and CWP phases contributed to the viscoelastic behaviour of the CWP–xanthan mixtures.