Autonomous and adaptive beaconing strategy for multi‐interfaced wireless mobile nodes

Ad hoc wireless communications rely on beaconing to manage and maintain several network operations and to share relevant network parameters among network nodes. Beacon frames are sent at the start of each beacon interval. The frequency of beaconing depends on whether beacon intervals are fixed size or may be adapted and regulated according to the perceived network and workload conditions. On the other hand, current mobile nodes usually embed several heterogeneous wireless interfaces that urge the design of an adaptive beaconing strategy. In this paper, we propose an autonomous and adaptive beaconing strategy for multi‐interfaced mobile wireless nodes that is capable of regulating the beacon interval size dynamically according to the perceived network conditions. The proposed strategy is based on a joint dynamic estimation of both the announcement traffic indication message (ATIM) window and the beyond‐ATIM window sizes for each beacon interval. Extensive simulations were conducted using OMNeT++ to ascertain the improvements achieved by autonomously regulating the entire beacon interval to take into account the network and workload conditions. Obtained results showed that the two proposed approaches improve significantly the efficiency of the network in terms of throughput, end‐to‐end delay, and power consumption. The proposed fixed beacon interval (fixed‐BI) approach stands as an enhanced version of the power‐saving multi‐channel MAC protocol (PSM‐MMAC). The proposed variable beacon interval (variable‐BI) approach, which regulates dynamically both of the ATIM and the beyond‐ATIM windows, outperforms both the fixed‐BI and the PSM‐MMAC. In particular, under nominal traffic loads, the end‐to‐end delay of the variable‐BI is much lower than those provided by the fixed‐BI and PSM‐MMAC. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization and modeling of sintering of polymer particles

An experimental study of simultaneous sintering of several particles has been carried out using spherical polymer grains. Considering rotational molding condition, coalescence of several grains in contact, happens simultaneously on internal surface of the mould. Theoretical model based on the effect of surface tension and viscosity can accurately predict the coalescence of a pairs of grains. However, it was observed in this study that coalescence rate changes with presence of neighboring grains and their position and the theoretical model proposed for two grains, is not able to predict the coalescence rate of mutli‐grains. Based on this finding, we have modified this model with taking into account the effect of neighboring particles in the sintering rate of multi‐grains. Obtained modified model is capable of predicting the multi‐grains sintering rate observed in this study. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A comparative in-process monitoring of temperature profile in fused filament fabrication

Fused filament fabrication (FFF), an additive manufacturing technique, is used to produce prototypes and a gradually more important processing route to get final products. Due to the layer-by-layer deposition mechanism involved, bonding between adjacent layers is controlled by the thermal energy of the material being printed. Thus, it is strongly in conjunction with the temperature development of the filaments during the deposition sequence. This study gives out an in-process set-up enabling to record temperature profile of two adjacent filaments or a sequence of deposition in various locations during FFF process. The main characteristic of the presented procedure is the possibility of obtaining a global temperature profile resulted from an IR-camera; parallel to those recorded using a K-type thermocouple. Needless to say that a K-type thermocouple accurately records the local temperature at the interface of adjacent filaments. Conversely, an IR-camera signifies the temperature profile on the captured surface. The obtained results showed that there is a remarkable difference between the cooling rate and re-heating peaks. The primary outcome of this study is the consideration of results accuracy and the possibility of working on optimization of the obtained temperature profile. Altogether it helps optimize inter-layer strength while assessing the temperature evolution.     

Microstructure and microtexture evolution with aging treatment in an Al–Mg–Si alloy severely deformed by HPT

Experiments were conducted on an Al–0.6 % Mg–0.4 % Si alloy to evaluate the effect of different preliminary thermal treatments on the evolution of microstructure and microtexture during processing by High-Pressure Torsion (HPT). Disks of the alloy were solution-treated, then some disks were briefly aged at 473 K, and other disks were briefly aged at 523 K before processing by HPT for up to 20 complete revolutions. The processing by HPT refined the microstructure to an average grain size as small as ~0.25 μm in the solution-treated alloy after 20 turns but preliminary aging led to slightly larger average grain sizes of ~0.35–0.40 μm after 20 turns. For all processing conditions, there was a high fraction of high-angle grain boundaries after HPT and it is shown that aging introduces changes in the microtexture intensities.     

Posidonia oceanica (L.) fibers as a potential low-cost adsorbent for the removal and recovery of orthophosphate

Adsorption efficiency of orthophosphate from aqueous solution onto Posidonia oceanica fibers (POF) as a raw, natural and abundant material was investigated and compared with other common natural materials. A series of batch tests were undertaken to assess the effect of the system variables, i.e. initial aqueous orthophosphate concentration, contact time, adsorbent dosage, pH and temperature. Results indicate that orthophosphate uptake increased with increasing initial orthophosphate concentration, temperature and adsorbent dosage and decreased with increasing pH values. The maximum adsorption capacity (Q(m)) determined from the Langmuir isotherm was calculated to be 7.45 mg g(-1) for the studied orthophosphates concentration range of 15-100 mg L(-1), pH 7; adsorbent dosage of 2 g L(-1) and temperature of 20±2°C. The adsorption data were very well described by the pseudo-second order model predicting a chemisorption process. The energy dispersive spectroscopy (EDS) and FTIR analysis before and after adsorption of orthophosphate onto POF showed that the main involved mechanisms are ligand exchange between orthophosphate and Cl(-), SO(4)(2-) and OH(-) and precipitation with calcium. In comparison with other natural adsorbents, raw POF could be considered as one of the most efficient natural materials for the removal of orthophosphate with the possibility of agronomic reuse.     

Optimal Power Flow Using Differential Search Algorithm

—In this article, a new nature-inspired metaheuristic technique called the differential search algorithm is proposed to solve the optimal power flow problem. The proposed differential search algorithm has been developed and tested under normal and contingency power system conditions. To show the effectiveness of the proposed method, it has been demonstrated on the standard IEEE 30-bus and IEEE 118-bus test systems with different objectives that reflect performance indices of the power system. Obtained results using the proposed technique indicate that the proposed differential search algorithm provides an effective, a robust, and a high-quality solution for the optimal power flow problem. The comparisons of the proposed differential search algorithm results with those reported in the literature reveal the potential and superiority of the proposed algorithm in terms of the optimal solution quality and robustness.     

A perceptual metric for stereoscopic image quality assessment based on the binocular energy

Stereoscopic imaging is becoming very popular and its deployment by means of photography, television, cinema. . .is rapidly increasing. Obviously, the access to this type of images imposes the use of compression and transmission that may generate artifacts of different natures. Consequently, it is important to have appropriate tools to measure the quality of stereoscopic content. Several studies tried to extend well-known metrics, such as the PSNR or SSIM, to 3D. However, the results are not as good as for 2D images and it becomes important to have metrics dealing with 3D perception. In this work, we propose a full reference metric for quality assessment of stereoscopic images based on the binocular fusion process characterizing the 3D human perception. The main idea consists of the development of a model allowing to reproduce the binocular signal generated by simple and complex cells, and to estimate the associated binocular energy. The difference of binocular energy has shown a high correlation with the human judgement for different impairments and is used to build the Binocular Energy Quality Metric (BEQM). Extensive experiments demonstrated the performance of the BEQM with regards to literature.     

Database design and querying within the fuzzy semantic model

Fuzzy semantic model (FSM) is a data model that uses basic concepts of semantic modeling and supports handling fuzziness, uncertainty and imprecision of real-world at the attribute, entity and class levels. The paper presents the principles and constructs of the FSM. It proposes ways to define the membership functions within all the constructs of the FSM. In addition, it provides a proposal for specifying FSM schema and introduce a query language adapted to FSM-based databases.