Adaptive video protection in large scale peer‐to‐peer video streaming over mobile wireless mesh networks

Because video streaming over mobile handheld devices has been of great interest, the necessity of introducing new methods with low implementation cost and scalable infrastructures is a strong demand of the service. In particular, these requirements are present in popular wireless networks such as wireless mesh networks (WMN). Peer‐to‐peer (P2P) networks promise an efficient scalable network infrastructure for video streaming over wired and wireless networks. Limited resources of the peers in P2P networks and high error rate in wireless channels make it more challenging to run P2P streaming applications over WMNs. Therefore, it is necessary to design efficient and improved error protection methods in P2P video streaming applications over WMNs. In this paper, we propose a new adaptive unequal video protection method specially intended for large scale P2P video streaming over mobile WMNs. Using this method, different frames have different priorities in receivers along the recovery process. Moreover, we precisely and completely evaluate different aspects related to frame protection in these networks using five important performance metrics including video distortion, late arrival distortion, end‐to‐end delay, overhead and initial start‐up delay. The results obtained from a precise simulation in OMNeT++ show that the proposed adaptive method significantly outperforms other solutions by providing better video quality on mobile wireless nodes. Copyright © 2015 John Wiley & Sons, Ltd.     

Integrated methanol reforming and oxidation in wash-coated microreactors: A three-dimensional simulation

A microreactor consisting of two parallel channels is numerically simulated where methanol steam reforming takes place in one channel, and the required heat is supplied by methanol oxidation in the other channel. Effects of different parameters on methanol conversion, hydrogen yield and CO concentration are examined. Results from the parametric study are then used to propose conditions for high methanol conversion and hydrogen yield. A microreactor with enhanced output conditions is thus designed which is capable of producing a gas stream consisting of 74% hydrogen (dry). CO concentration in the generated synthesis gas stream is low enough to require only a PROX reactor for CO clean-up, eliminating the need for a bulky water–gas shift reactor. The produced hydrogen from an assembly of such microreactors can feed a low-power PEM fuel cell. A cluster of these microreactors would take a volume of about 91 cm³ to feed a typical 30-watt PEM fuel cell.     

A method for discriminating original pulses in online partial discharge measurement

Partial discharge (PD) measurement is a promising method for condition assessment of insulation systems in high voltage equipments. Conventional PD measuring systems have some difficulties in the measurements especially in online conditions and noisy environments. There is a growing tendency to use new measuring systems for separation of PD pulses from different sources and rejection of external noises. In this investigation a new ultra wideband PD measuring system and relevant methodology are discussed. The proposed system uses an efficient detection method for extracting PD pulses embedded in noisy signal, meanwhile, a wavelet multiresolution analysis is applied to reduce background and communication noise level. In this paper some new and modified features for pulse classification procedure have been proposed. The proposed system, methodology and features have been implemented on a hydrogenerator and also a power transformer. Finally performance of the system is discussed.     

Lean flammability limits for stable performance with a porous burner

Applications of porous burners are of high interest due to many advantages such as extended lean flammability limit in comparison with free flame structures. In this work, laminar premixed flame propagation of methane/air mixture in a porous medium is numerically investigated. An unsteady one-dimensional physical model of a porous burner is considered, in which the flame location is not predetermined. The computational domain is extended beyond either side of the porous medium to accurately model reactions close to the edges of the solid matrix. After validation of the model and performing a baseline simulation, a parametric study is carried out to investigate the lean flammability limits of the burner and the unstable flash-back/blow-out phenomena. Stable performance diagrams are given for two controlling parameters of turn–down ratio and porous medium porosity. The simulation results indicate that the stable performance range of the burner is extended when the equivalence ratio increases; however, the blow-out region expands with an increase in the firing rate. For constant values of porosity and firing rate, increasing the equivalence ratio can change the operating regime of the burner from blow-out to a stable condition. It is observed that by the variation of porosity in the range of 0.6–0.9, and for the equivalence ratios of more than 0.6, the flame flash-back cannot occur. An equivalence ratio of 0.43 is found to be the lower limit at which the flame stabilizes in the matrix.     

The effects of roof reflectance on air temperatures surrounding a rooftop condensing unit

Recent anecdotal information suggests that “cool” roofs might produce significant energy savings by reducing the temperature of air entering rooftop air-conditioner (RTU) condensers. Unfortunately, measurements to support this claim are not well documented. To overcome this problem, we carried out a set of six rigorous field experiments to determine the effects of roof reflectance on the heating of condenser inlet air by the roof, and to assess the effects of condenser fan operation on the potential recirculation of hot discharge air from the condenser. The experiments involved combinations of two roof conditions (a “hot” roof and then the same roof with a “cool” coating) and three RTU operation modes (condenser fan and compressor both operating, condenser fan operating without the compressor, and condenser fan and compressor both not operating). For each case, we continuously measured outdoor air temperature at 26 locations near and far from the RTU, as well as roof surface temperatures at 2 locations (1 near and 1 far from the RTU), wind speed and direction, and solar radiation.     

Synthesis of a novel fluorescent coloured copolymer based on 4‐butylthio‐1,8‐naphthalimide

A novel fluorescent coloured copolymer based on naphthalimide was prepared. Acenaphthene was brominated and oxidised to prepare 4‐bromo‐1,8‐naphthalic anhydride and further reacted with butanethiol, 2‐aminoethanol and acryloyl chloride, in order to obtain a new polymerisable fluorescent dye. The synthesised dyes were characterised by differential scanning calorimetry, absorption spectroscopy (Fourier Transform–infrared, proton and carbon nuclear magnetic resonance, ultraviolet–visible spectroscopy) and fluorimetry. Molar extinction coefficients and wavelength maxima were obtained by examining the dye solution in ethanol. The solvatochromic effects of the prepared dyes have also been investigated. Finally, the dye was copolymerised with methyl methacrylate and an intrinsically coloured copolymer was obtained. The photophysical characteristics of the obtained copolymer have also been considered. It is assumed that 99% of the copolymerised dye is chemically bonded to polymer chains. The fluorescent characteristics of the copolymer in the solid state were determined by fluorometer and it was found that it has relatively high fluorescent intensity. The physical properties of the synthesised copolymer have been evaluated by differential scanning calorimetry and gel permeation chromatography.     

Procedure for measuring the solar reflectance of flat or curved roofing assemblies

The widely used methods to measure the solar reflectance of roofing materials include ASTM standards E903 (spectrometer), C1549 (reflectometer), and E1918 (pyranometer). Standard E903 uses a spectrometer with an integrating sphere to measure the solar spectral reflectance of an area approximately 0.1 cm². The solar spectral reflectance is then weighted with a solar spectral irradiance to calculate the solar reflectance. Standard C1549 uses a reflectometer to measure the solar reflectance of an area approximately 5 cm². Both E903 and C1549 are best suited to measurement of the solar reflectance of flat, homogeneous surfaces. Standard E1918 uses a pyranometer to measure the solar reflectance of an area approximately 10 m², and is best applied to large surfaces that may also be rough and/or non-uniform.We describe a technique that uses a pyranometer to measure the solar reflectance of a uniform or variegated sample with diffusely reflective surface of an area of approximately 1 m², and use this technique (referred to as E1918A) to measure the solar reflectances of low- and high-profile tile assemblies. For 10 large (10 m²) tile assemblies whose E1918 solar reflectances ranged from 0.10 to 0.50, the magnitude of the difference between the E1918A and E1918 measurements did not exceed 0.02 for unicolor assemblies, and did not exceed 0.03 for multicolor assemblies.     

Effect of particle size and co-deposition technique on hardness and corrosion properties of Ni–Co/SiC composite coatings

Ni–Co/SiC alloy matrix composite coatings were electrodeposited in a modified Watt's bath containing micro and nano sized SiC particles by using conventional electro-co-deposition (CECD) and sediment co-deposition (SCD) techniques. The deposits were characterized using SEM, EDX and XRD analyses, and microhardness and potentiodynamic polarization measurements. The maximum incorporation of the SiC micro- and nano-particles was obtained using the SCD technique at deposition current densities of 2 and 3 A/dm², respectively. It was found that in the composite coatings, incorporation of SiC particles improves the microhardness of unalloyed Ni and Ni–Co alloy matrices. The nanocomposite coatings exhibit higher microhardness values than microcomposite ones. The potentiodynamic polarization measurements in 3.5% NaCl solution revealed that the corrosion resistance of the Ni–Co/SiC nanocomposite coatings is much higher than the Ni–Co alloy and Ni–Co/SiC microcomposite coatings. Moreover, corrosion resistance of Ni–Co/SiC nanocomposite coatings deposited by SCD technique is higher than the ones deposited by CECD technique. Corrosion resistance of the studied Ni–Co/SiC composite coatings was considerably affected by Co content, SiC particle size and content. Hardness enhancement was related to the structural features, and corrosion behavior was discussed based on the formation of corrosion micro cells, diminishing the effective metallic area, and increasing and hindering the corrosion paths.     

Free convective laminar flow within the Trombe wall channel

Free convective laminar heat transfer between the channel surfaces of the Trombe wall has been investigated. Considered in this study were the velocity profiles normal and parallel to the direction of fluid flow, the pressure drop due to flow acceleration at the channel entrance, and the effect of dissimilar but uniform channel surface temperatures for a wide range of flow rates and temperatures.A finite difference procedure was used to solve the governing equations in dimensionless form using air as the fluid. After comparison with available experimental data, results have been reduced, and several correlations developed to enable important performance characteristics to be estimated given the channel thickness, height, and surface temperatures.