Effect of electrodeposition current density on the microstructure and the degradation of electroformed iron for degradable stents

Pure iron has become one of the most interesting candidate materials for degradable metallic stents due to its high mechanical properties and moderate degradation. In this work we studied the effect of electrodeposition current density on microstructure and degradation of pure iron films electrodeposited on Ti alloy substrate for degradable metallic stent application. Iron sheets were produced by electrodeposition using four different current densities 1, 2, 5 and 10 A dm⁻². The films were then studied by SEM (scanning electron microscope) and EBSD (electron backscatter diffraction) to observe the surface morphology, grain size and orientation. Potentiodynamic polarization and static immersion tests were used to determine the corrosion rate and to study the degradation behavior of iron films, respectively. The current density was found to significantly influence the texture, the grain size and the grain shape of the electrodeposited iron. At current densities of 1, 5 and 10 A dm⁻², weak textures corresponding to 〈1 0 1〉, 〈1 1 1〉 and 〈1 1 2〉 in the normal (electrodeposition) direction were obtained, respectively. At these current densities, average grain sizes smaller than 3 μm were also obtained. However, at 2 A dm⁻², a strong 〈1 1 1〉//ND texture with density of 7.4 MUD was obtained with larger average grain size of 4.4 μm. The microstructure of iron samples changed after annealing at 550 °C because of the induced recrystallization. Different corrosion rates were obtained from potentiodynamic polarization curves of iron films deposited at different current densities because of their microstructures. Fe-2 showed the lowest corrosion rate due to its larger grains size and its texture. The corrosion rates of all iron samples decreased after annealing. Static degradation showed lower corrosion rates for iron because of the formation of a degradation layer on samples surface which reduced the degradation reaction rate. The degradation morphology was uniform for Fe-2 due to its strong texture. On the other hand, microscopic pits were found for Fe-1, Fe-5 and Fe-10.     

Experimental and numerical assessment of using coconut oil as a phase-change material for unconditioned buildings

The efficacy of integrating organic coconut oil (co-oil) phase-change material (PCM) into an unconditioned building with a lightweight envelope is explored experimentally and numerically for heat gain reduction. In what we think is the first test of its kind for co-oil PCM, twin side-by-side single-room buildings (with and without PCM) are constructed and studied experimentally under ambient weather conditions. The effects of the co-oil on the thermal performance of the buildings are investigated with respect to the window orientation (east, west, north and south). Furthermore, numerical simulation of the buildings is carried out to evaluate the contribution of the co-oil to their thermal performance and to determine the effect of the co-oil layer thickness on the heat storage capacity. Moreover, by employing a simplified heat transfer analysis, an approximate relation for the optimal thickness of co-oil PCM layer is developed. Experimental and numerical results show that co-oil PCM can be a promising solution to improve the indoor thermal environment. It is found that with a south-facing window equipped with co-oil PCM, the indoor temperature is lowered by 23.8% compared to the case without PCM, when an optimal PCM layer of ~4 cm in thickness is embedded in the wall.     

Single-ended parametric voicing-aware models for live assessment of packetized VoIP conversations

The perceptual quality of VoIP conversations depends tightly on the pattern of packet losses, i.e., the distribution and duration of packet loss runs. The wider (resp. smaller) the inter-loss gap (resp. loss gap) duration, the lower is the quality degradation. Moreover, a set of speech sequences impaired using an identical packet loss pattern results in a different degree of perceptual quality degradation because dropped voice packets have unequal impact on the perceived quality. Therefore, we consider the voicing feature of speech wave included in lost packets in addition to packet loss pattern to estimate speech quality scores. We distinguish between voiced, unvoiced, and silence packets. This enables to achieve better correlation and accuracy between human-based subjective and machine-calculated objective scores.     

Fuzzy control of a swells canal system

This work forms a part of the research undertaken on the maritime developments behaviour submitted to the action of sea waves. To succeed in this objective, we have conceived and achieved a system of artificial wave generation in a swells channel (channel of 37.5 m of length, 1 m of width and 1 m of depth). Indeed, the simulation of swells on scale model has many advantages. We can mention the construction of dykes for the protection of ports, the didactic interest of conception and generation of new models of waves and the construction of boat shells. The installed canal has to achieve tests of developments stability in the domain of the maritime hydraulics. Every work or scale model is constituted of several layers of ripraps of shapes and well-determined relative density. Thus, the survey of stability consists in reproducing in similitude (scale 1/20) in the swells canal to observe their effects on the holding of riprap (accumulation of boulder) or the artificial blocks of the scale model. Otherwise, the modelling of the process of swell generation is described by complicated physical laws and requires important means of computation. To solve this problem, we have conceived a system based on fuzzy logic permitting to assure the generation of coherent command data with the statistical parameters characterizing the oceanic waves, and to guarantee its conformity to the model of Pierson Moskowich spectrum.     

Joint optimisation of maintenance and production policies considering random demand and variable production rate

This paper deals with a randomly failing manufacturing system M1 which has to satisfy a random demand during a finite horizon given a required service level. To help meet this demand, subcontracting is used through another production system M2. M1 operates with a variable production rate and its failure rate depends on both time and the production rate. In these conditions, as a first step, we establish a preliminary production plan corresponding to a given service level. In a second stage, we integrate the effect of the machine degradation introducing a unitary degradation cost. The optimal production plan is then obtained by minimising the sum of the production, the inventory and the degradation costs. In the final stage, we propose another optimal plan combined with a preventive maintenance policy aiming at reducing the machine degradation while minimising the total cost including the production, inventory and maintenance costs.     

Adaptive playout scheduling algorithm tailored for real-time packet-based voice conversations over wireless ad-hoc networks

The effective provision of real-time, packet-based voice conversations over multi-hop wireless ad-hoc networks faces several stringent constraints not found in conventional packet-based networks. Indeed, MANETs (mobile ad-hoc networks) are characterized by mobility of all nodes, bandwidth-limited channel, unreliable wireless transmission medium, etc. This environment will surely induce a high delay variation and packet loss rate impairing dramatically the user experienced quality of conversational services such as VoIP. Indeed, such services require the reception of each media unit before its deadline to guarantee a synchronous playback process. This requirement is typically achieved by artificially delaying received packets inside a de-jitter buffer. To enhance the perceptual quality the buffering delay should be adjusted dynamically throughout the vocal conversation.In this work, we describe the design of a playout algorithm tailored for real-time, packet-based voice conversations delivered over multi-hop wireless ad-hoc networks. The designed playout algorithm, which is denoted MAPA (mobility aware playout algorithm), adjusts the playout delay according to node mobility, which characterizes mobile ad-hoc networks, and talk-spurt, which is an intrinsic feature of voice signals. The detection of mobility is done in service passively at the receiver using several metrics gathered at the application layer. The perceptual quality is estimated using an augmented assessment approach relying on the ITU-T E-Model paradigm while including the time varying impairments observed by users throughout a packet-based voice conversation. Simulation results show that the tailored playout algorithm significantly outperforms conventional playout algorithms, specifically over a MANET with a high degree of mobility.     

Optimal integrated maintenance/production policy for randomly failing systems with variable failure rate

This article deals with the combined production and maintenance plans for a manufacturing system satisfying a random demand. We first establish an optimal production plan which minimises the average total inventory and production cost. Second, using this optimal production plan, and taking into account the deterioration of the machine according to its production rate, we derive an optimal maintenance schedule which minimises the maintenance cost. A numerical example illustrates the proposed approach, this analytical approach, based on a stochastic optimisation model and using the operational age concept, reveals the significant influence of the production rate on the deterioration of the manufacturing system and consequently on the integrated production/maintenance policy.     

Optimization of textile parameters of plain woven vascular prostheses

This paper investigates and reports the effect of some textile parameters (yarn and fabric parameters) on the main performances of plain woven vascular prostheses in order to enhance their overall quality. We weaved tubular structures with different fabric densities using texturized Dacron® polyester filament yarns with different linear densities and filament counts, in warp and weft directions. The performances of the manufactured samples, such as wall porosity, water permeability and mechanical features, have been tested. By adopting a two‐level fractional factorial design of experiments, the responses were fitted to predictive models using a multiple linear regression method. The models were tested by variance analysis and validated by correlation between measured and predicted values. We determined the optimum settings of main textile parameters enhancing plain woven vascular prosthesis quality by contour plots method.     

Joint optimisation of maintenance and production policies with subcontracting and product returns

This paper, an extension of our previous research, deals with the problem of jointly optimizing maintenance, production and inventory costs considering subcontracting and product returns. The manufacturing system, which fails randomly, has to satisfy a random product demand during a finite planning horizon under a required service level. The portion of products returned by the customers that are still in saleable condition are collected in the principle store from which customer demand is filled, while the portion that are non-conformal are collected in a second store and then remanufactured by a subcontractor. This study is validated by a real industrial case presented in this paper.