A survey of wireless technologies coexistence in WBAN: analysis and open research issues

Wireless Body Area Network (WBAN) is the most convenient, cost-effective, accurate, and non-invasive technology for e-health monitoring. The performance of WBAN may be disturbed when coexisting with other wireless networks. Accordingly, this paper provides a comprehensive study and in-depth analysis of coexistence issues and interference mitigation solutions in WBAN technologies. A thorough survey of state-of-the art research in WBAN coexistence issues is conducted. The survey classified, discussed, and compared the studies according to the parameters used to analyze the coexistence problem. Solutions suggested by the studies are then classified according to the followed techniques and concomitant shortcomings are identified. Moreover, the coexistence problem in WBAN technologies is mathematically analyzed and formulas are derived for the probability of successful channel access for different wireless technologies with the coexistence of an interfering network. Finally, extensive simulations are conducted using OPNET with several real-life scenarios to evaluate the impact of coexistence interference on different WBAN technologies. In particular, three main WBAN wireless technologies are considered: IEEE 802.15.6, IEEE 802.15.4, and low-power WiFi. The mathematical analysis and the simulation results are discussed and the impact of interfering network on the different wireless technologies is compared and analyzed. The results show that an interfering network (e.g., standard WiFi) has an impact on the performance of WBAN and may disrupt its operation. In addition, using low-power WiFi for WBANs is investigated and proved to be a feasible option compared to other wireless technologies.     

Complex Envelope Second-Order Statistics in High-Altitude Platforms Communication Channels

High-altitude platforms are one of the most promising alternative infrastructures for realizing next generation high data rate wireless networks. This paper presents a three-dimensional (3-D) scattering model for land mobile stratospheric multipath-fading channel with its complex faded envelope. From the scattering model and the complex envelope second-order statistics are derived for a 3-D non-isotropic scattering environment. When we discuss on the second-order statistics we refer to the level crossing rate and the average fade duration, whichare two main parameters in describing the fading severity over time and are very important in assess system characteristics such as hand off, velocities of the transmitter and receiver and fading rate. Numerical calculations have been carried out to demonstrate theoretical derivations and the utility of the proposed model.     

Designed spiro-bicyclic analogues targeting the ribosomal decoding center

The bacterial ribosome represents the confirmed biological target for many known antibiotics that interfere with bacterial protein synthesis. Aminoglycosides represent a lead paradigm in RNA molecular recognition and constitute ideal starting points for the design and synthesis of novel RNA binders. Previous rational design approaches of RNA-targeting small molecules have been mainly concentrated on direct functionalization of aminoglycosidic substructures. Herein, we successfully designed and synthesized rigid spirocyclic scaffolds locked in a predicted ribosome-bound "bioactive" conformation. These analogues are able to mimic many of the interactions of the natural products for the A-site, as proven by their obtained binding affinities. The development of an optimized approach for their synthesis and their potential to inhibit protein production in vitro are presented. Our results could be further utilized for the development of analogues with improved antibiotic profiles.     

Evaluation of channel dependent bandwidth allocation in wireless access networks: centralized and distributed approach

The problem of bandwidth allocation in wireless access networks is studied in this paper, investigating the performance of two approaches. Firstly, we use centralized algorithms, such as bankruptcy division rules and Nash bargaining. Secondly, a distributed algorithm is proposed in order to find the optimal solution of the bandwidth allocation problem. In both approaches, the allocation rules are properly modified to incorporate the influence of the channel state resulting in a more efficient and fair bandwidth allocation. The channel dependent centralized and distributed schemes are compared in terms of efficiency and fairness with a view to highlighting the advantages and disadvantages of every approach.     

Numerical optimisation of laser assisted friction stir welding of structural steel

ABSTRACT

Significant progress has been made on the implementation of friction stir welding (FSW) in the industry for aluminium alloys. However, steel FSW and other high-temperature alloys is still the subject of considerable research, mainly because of the short life and high cost of the FSW tool. Different auxiliary energies have been considered as a means of optimising the FSW process and reducing the forces on the tool during the plunge and traverse stages, but numerical studies on steel are particularly limited. Building on the state-of-art, laser-assisted steel FSW has been numerically developed and analysed as a viable process amendment. Laser-assisted FSW increased the traverse speed up to 1500?mm?min^?1, significantly higher than conventional steel FSW. The application of laser assistance with a distance of 20?mm from the rotating tool reduced the reaction force on the tool probe tip up to 55% when compared to standard FSW.     

Effect of friction stir welding tool design on welding thermal efficiency

ABSTRACT

Enhancing the heat transfer to the material being welded, instead of the tool, will improve the welding thermal efficiency. Friction stir welding of 5?mm thick 6061-T6 aluminium alloy plates was carried out with the newly produced tools. It was found that the thermal efficiency increased by 4.2% using a tool with all the new design features (i.e. hollow, fluted and thermally insulated) compared to the conventional tool for aluminium welding. To assess the benefits of the new tool design on steel FSW, a finite element numerical simulation study was undertaken. In this case, the simulation results yielded a welding thermal efficiency increase of 10–15% using a thermally coated tool, thereby offering potential productivity gains.     

Failure Investigation of Cold-Rolled ZnTiCu Alloy Fracture During Bending Under Ambient Temperature Conditions

Bending ductility is an important quality parameter of the ZnTiCu rolled sheet for the fabrication of specially formed members in construction industry. Fabrication of such components is usually realized under severe loading conditions (i.e., high strain rate forming using manual tools or press brake machinery) and even sometimes under low temperature environment in the construction field, which is very often close to or less than 0 °C. Bending orientation is also an important parameter, since texture-sensitive Zn alloy cold-worked strip affects ductility performance in direction transverse to the rolling direction. A failure analysis process was implemented on a ZnTiCu bent sheet possessing cracks on outer bent areas. Light optical metallography, and scanning electron microscopy coupled with energy dispersive spectrometry, along with mechanical testing were the principal investigation techniques employed to evaluate the failure. The presence of pronounced elongated grain structure combined with coarse and continuous Ti-rich intermetallic phase, likely reduces the fracture resistance against the transverse stress field imposed by bending, stimulating, thus crack initiation and propagation.     

Predicting returns on Canadian exchange rates with artificial neural networks and EGARCH-M models

This paper investigates the problem of predicting daily returns based on five Canadian exchange rates using artificial neural networks and EGARCH-M models. First, the statistical properties of five daily exchange rate series (US Dollar, German Mark, French Franc, Japanese Yen and British Pound) are analysed. EGARCH-M models on the Generalised Error Distribution (GED) are fitted to the return series, and serve as comparison standards, along with random walk models. Second, backpropagation networks (BPN) using lagged returns as inputs are trained and tested. Estimated volatilities from the EGARCH-M models are used also as inputs to see if performance is affected. The question of spillovers in interrelated markets is investigated with networks of multiple inputs and outputs. In addition, Elman-type recurrent networks are also trained and tested. Comparison of the various methods suggests that, despite their simplicity, neural networks are similar to the EGARCH-M class of nonlinear models, but superior to random walk models, in terms of insample fit and out-of-sample prediction performance.     

Wall factor for acceleration and terminal velocity of falling spheres at high reynolds numbers

The wall factor for spheres in the acceleration and terminal velocity ranges was determined experimentally for very high Reynolds numbers (13 500 < Re < 70 000). Experiments were performed with 12, 15, 18, 21, 25 and 31.75 mm spheres, falling in water inside cylinders 3.4, 4.9, 7, 10, 14 and 19 cm in diameter. A published empirical equation was found to yield good results for the terminal velocity wall factor in the range of studied Reynolds numbers.