Fairness-related challenges in mobile opportunistic networking

The fundamental challenge in opportunistic networking, regardless of the application, is when and how to forward a message. Rank-based forwarding techniques currently represent one of the most promising methods for addressing this message forwarding challenge. While these techniques have demonstrated great efficiency in performance, they do not address the rising concern of fairness amongst various nodes in the network. Higher ranked nodes typically carry the largest burden in delivering messages, which creates a high potential of dissatisfaction amongst them. In this paper, we adopt a real-trace driven approach to study and analyze the trade-offs between efficiency, cost, and fairness of rank-based forwarding techniques in mobile opportunistic networks.Our work comprises three major contributions. First, we quantitatively analyze the trade-off between fair and efficient environments. Second, we demonstrate how fairness coupled with efficiency can be achieved based on real mobility traces. Third, we propose FOG, a real-time distributed framework to ensure efficiency–fairness trade-off using local information. Our framework, FOG, enables state-of-the-art rank-based opportunistic forwarding algorithms to ensure a better fairness–efficiency trade-off while maintaining a low overhead. Within FOG, we implement two real-time distributed fairness algorithms; Proximity Fairness Algorithm (PFA), and Message Context Fairness Algorithm (MCFA). Our data-driven experiments and analysis show that mobile opportunistic communication between users may fail with the absence of fairness in participating high-ranked nodes, and an absolute fair treatment of all users yields inefficient communication performance. Finally our analysis shows that FOG-based algorithms ensure relative equality in the distribution of resource usage among neighbor nodes while keeping the success rate and cost performance near optimal.     

Investigation of the liquid crystal alignment layer: effect on electrical properties

We investigate the electrical behavior of a symmetric liquid crystal (LC) cell: elecrode-silane-LC-silane-electrode. The silane (chlorodimethyloctadecyl-silane) layer induces a homeotropic orientation of the nematic liquid crystal (NLC) molecules. The wettability technique is used to detect the change of the surface energy of the electrode upon cleaning and silane layer deposition. We report on the dynamic impedance measurements of the nematic liquid crystal cell. It is found that the silane alignment layer has a blocking effect on the liquid crystal (LC) cell. We also study the relaxation behavior of the cell which is later assimilated as an electrical equivalent circuit.     

Formation of silicon nanowire packed films from metallurgical-grade silicon powder using a two-step metal-assisted chemical etching method

In this work, we use a two-step metal-assisted chemical etching method to produce films of silicon nanowires shaped in micrograins from metallurgical-grade polycrystalline silicon powder. The first step is an electroless plating process where the powder was dipped for few minutes in an aqueous solution of silver nitrite and hydrofluoric acid to permit Ag plating of the Si micrograins. During the second step, corresponding to silicon dissolution, we add a small quantity of hydrogen peroxide to the plating solution and we leave the samples to be etched for three various duration (30, 60, and 90 min). We try elucidating the mechanisms leading to the formation of silver clusters and silicon nanowires obtained at the end of the silver plating step and the silver-assisted silicon dissolution step, respectively. Scanning electron microscopy (SEM) micrographs revealed that the processed Si micrograins were covered with densely packed films of self-organized silicon nanowires. Some of these nanowires stand vertically, and some others tilt to the silicon micrograin facets. The thickness of the nanowire films increases from 0.2 to 10 μm with increasing etching time. Based on SEM characterizations, laser scattering estimations, X-ray diffraction (XRD) patterns, and Raman spectroscopy, we present a correlative study dealing with the effect of the silver-assisted etching process on the morphological and structural properties of the processed silicon nanowire films.     

Architectured Materials to Improve the Reliability of Power Electronics Modules: Substrate and Lead-Free Solder

Power electronics modules (>100 A, >500 V) are essential components for the development of electrical and hybrid vehicles. These modules are formed from silicon chips (transistors and diodes) assembled on copper substrates by soldering. Owing to the fact that the assembly is heterogeneous, and because of thermal gradients, shear stresses are generated in the solders and cause premature damage to such electronics modules. This work focuses on architectured materials for the substrate and on lead-free solders to reduce the mechanical effects of differential expansion, improve the reliability of the assembly, and achieve a suitable operating temperature (<175°C). These materials are composites whose thermomechanical properties have been optimized by numerical simulation and validated experimentally. The substrates have good thermal conductivity (>280 W m^?1 K^?1) and a macroscopic coefficient of thermal expansion intermediate between those of Cu and Si, as well as limited structural evolution in service conditions. An approach combining design, optimization, and manufacturing of new materials has been followed in this study, leading to improved thermal cycling behavior of the component.     

An enhanced MSU-TSCH scheduling algorithms for industrial wireless sensor networks

The reliability and latency requirements of wireless sensor network-based smart grid communications are met in large part by MAC protocols. Developed by IEEE, time slotted channel hopping (TSCH), a method that is effective, dependable, and predictable. However, the TSCH standard does not enable mobility and does not offer any solution for scheduling, especially in IEEE 802.15.4 TSCH, the most recent generation of extremely dependable and low-power MAC protocols. Recently, MSU-TSCH a time-frequency communication schedule was proposed to provide mobility to TSCH. Despite its distinctive qualities, MSU-TSCH has the drawback of computing the TSCH schedule at each node independently of its traffic load, which can significantly increase the communication delay. Due to this limitation, MSU-TSCH is not suitable for some delay-sensitive smart grid applications. In this article, we provide an improved MSU-TSCH-based TSCH protocol, called Mobility-TSCH, that dynamically adjusts time slot assignments based on traffic volume and latency requirement. Moreover, the protocol Mobility-TSCH adapts to topology changes and supports mobility. Additionally, it optimizes time slot allocation by prioritizing nodes closest to the sink. The performance and evaluation analysis of Mobility-TSCH compared to the original MSU-TSCH, reveal that the communication delay is greatly reduced, decreases the average end-to-end latency, the high packet delivery ratio (PDR), Increase the performance of both metrics, parent connectivity ratio (PCR) and convergence time (CT), while maintaining a minimal overhead signaling.     

CAF: Community aware framework for large scale mobile opportunistic networks

The fundamental challenge in opportunistic networking is when and how to forward a message. Rank-based forwarding, one of the most promising methods for addressing this challenge, ranks nodes based on their social profiles or contact history in order to identify the most suitable forwarders. While these forwarding techniques have demonstrated great performance trends, we observe that they fail to efficiently forward messages in large scale networks. In this paper, we demonstrate using real mobility traces, the weakness of existing rank-based forwarding algorithms in large scale communities. We propose strategies for partitioning large communities into sub-communities based on geographic locality or social interests. We also propose exploiting particular nodes, named MultiHomed nodes, in order to disseminate messages across these sub-communities. We introduce CAF, a Community Aware Forwarding framework, which is designed to be integrated with state-of-the-art rank-based forwarding algorithms, in order to improve their performance in large scale networks. We use real mobility traces to evaluate our proposed techniques. Our results empirically show a delivery success rate increase of up to 40%, along with 5% to 30% improved success delivery rates compared to state-of-the-art rank-based forwarding algorithms; these results are obtained while incurring a marginal increase in cost which is less than 10%. We finally propose an extension of the original framework called Community Destination Aware Framework (CDAF). Assuming that the source node can determine the destination’s community, CDAF further reduces the cost of CAF by a factor of 2 while maintaining similar success rates.     

A survey on wireless sensor network databases

Wireless Networks - In recent years, the use of wireless sensors has increased drastically in most fields. Wireless Sensor Networks (WSNs) have attracted the interest of industries and they have...     

γ-Alkylsulfide phosphonates through the thia-Michael strategy

The formation of γ-alkylsulfide phosphonates is described from allylphosphonates under mild conditions using thiols through the thia-Michael strategy. A series of new phosphonates, bisphosphonates were cleanly prepared in high yields. The methodology developed allowed further preparing γ-alkylsulfide phosphonates bearing valuable esters groups in β and δ positions with respect to the phosphonate moiety.     

Industrial pressure sensitive adhesives suitable for physicochemical microencapsulation

The main objective of this investigation is to characterize several industrial pressure sensitive adhesives (PSA) for their microencapsulation. The adhesive selected must remain stable within the variations of the microencapsulation conditions. Thanks to its encapsulation, the adhesive will be self protected into the microcapsule's shell, and its release will be then controlled applying a light pressure. First, physicochemical microencapsulation processes were selected, and three industrial water-based acrylic adhesives were consequently chosen. The adhesive main characteristics (composition, particle size distribution and peel strength) were determined. Then, particle size stability was tested under ranges of pH (from 2 to 9), temperature (from 5 to 85 °C) and electrical conductivity variations (up to 12 mS/cm), within an interval of values encountered in the physicochemical processes of microencapsulation. Finally, the compatibility with various solvents (acetone, ethanol and ethyl acetate) was also tested.