Sand–rubber mixtures undergoing isotropic loading: derivation and experimental probing of a physical model

The volume of scrap tyres, an undesired urban waste, is increasing rapidly in every country. Mixing sand and rubber particles as a lightweight backfill is one of the possible alternatives to avoid stockpiling them in the environment. This paper presents a minimal model aiming to shed light on the relevant physical parameters governing the evolution of the void ratio of sand–rubber mixtures undergoing an isotropic compression loading, where the mixtures consist of various volume ratios of rubber. It is based on the idea that, when pressure is applied, the rubber particles deform and partially fill the porous space of the system, leading to a decrease of the void ratio with increasing pressure. We show that our simple approach is capable of reproducing experimental data obtained with sand and rubber of similar particle size distributions up to mixtures composed of 50% of rubber. The effect of the particle shape and size on the model parameters is discussed.     

Contribution of gallium oxide content to the crystallization characteristics and chemical stability of sodium phlogopite glasses

The effect of gallium oxide content on the crystallization characteristics and chemical durability of a sodium phlogopite based glass-ceramic of the stoichiometric phase formula NaMg₃(Si₃[Al_1−X,Ga_x]O₁₀)F₂ where X=0.0, 0.25, 0.5, 0.75 and 1.0 was investigated. The Ga₂O₃/Al₂O₃ replacement and heat treatment have an effect on the crystalline phases developed and their microstructure. Forsterite ss, enstatite, and sodium phlogopite phases were mostly detected in the crystallized glasses. There is a preferential tendency for forsterite to accommodate sodium phlogopite ions in its structure forming olivine solid solution of forsterite type. At low Ga₂O₃/Al₂O₃ replacement an increase in the crystallization temperature led to the decomposition of the sodium phlogopite phase to form forsterite ss phase, while at high Ga₂O₃ replacement increasing the heat-treatment temperature led to the development of forsterite ss at the expense of enstatite phase. The chemical stability of the crystallized materials was better in acidic than in alkaline media. The present data provides valuable information about the role played by the glass oxide constituent in determining the nature of the crystalline phases and solid solution formed in the materials especially in the field of preparation of glass-ceramic substrate used for magnetic information storage.     

Speech compression and encryption based on discrete wavelet transform and chaotic signals

Multimedia Tools and Applications - To increase transfer and storage efficiencies of the information, data compression has emerged as a significant issue in the communication environments. This...     

Millimeter-wave antenna of a travelling-wave long sinusoidal slot in the broad face of a rectangular waveguide

A travelling-wave long sinusoidal slot in the broad face of a millimeter-wave (Ka-Band) rectangular waveguide is investigated. Similarities and differences with a same-shaped slot, but in the narrow face of the waveguide, which was investigated in a former study [1], are also discussed. It is observed that the most important difference between two antenna structures is the applied analytical model. It is found in measurements that the antenna with a broad face can only be described by an electric current model unlike the antenna with a narrow face where the magnetic current model agrees with measurements. In experimental study, some antenna parameters of the structure are demonstrated. The sinusoidal slot antenna investigated in this study has also a cross-polarized beam like the one in the narrow face of rectangular waveguide and a similar metallic grid polarizer is used like in the previous study to suppress this cross polarized beam. A suppression level up to 12 dB is reached. Antenna efficiency is calculated using S-parameters measurement and a remarkable increment is obtained after the polarizer is applied.     

A novel noncooperative game competing model using generalized simple additive weighting method to perform network selection in heterogeneous wireless networks

Network selection mechanisms have a significant role in guaranteeing the QoS for users in a heterogeneous wireless networks environment. These mechanisms allow the selection of an optimal wireless network to satisfy the needs of users. Users are provided with the opportunity to select from multiple connectivity opportunities available all over various wireless networks. Furthermore, the network operators themselves can execute active selection strategies that facilitate proper decision making, in which user preferences are considered. This study proposes a new noncooperative competing game‐theoretic model and strategy space based on user preference. This model can solve network selection problems and capture the inter‐linkages of decisions taken by various networks. A generalized simple additive weighting method is incorporated into the framework of noncooperative game theory. In addition, the utility function is employed to assess the usefulness of the system. Simulation results and analysis illustrate the efficacy of the suggested model in attaining optimum network utility for heterogeneous wireless networks while optimizing user satisfaction. Copyright © 2014 John Wiley & Sons, Ltd.     

Validation of leading point concept in RANS simulations of highly turbulent lean syngas-air flames with well-pronounced diffusional-thermal effects

While significant increase in turbulent burning rate in lean premixed flames of hydrogen or hydrogen-containing fuel blends is well documented in various experiments and can be explained by highlighting local diffusional-thermal effects, capabilities of the vast majority of available models of turbulent combustion for predicting this increase have not yet been documented in numerical simulations. To fill this knowledge gap, a well-validated Turbulent Flame Closure (TFC) model of the influence of turbulence on premixed combustion, which, however, does not address the diffusional-thermal effects, is combined with the leading point concept, which highlights strongly perturbed leading flame kernels whose local structure and burning rate are significantly affected by the diffusional-thermal effects. More specifically, within the framework of the leading point concept, local consumption velocity is computed in extremely strained laminar flames by adopting detailed combustion chemistry and, subsequently, the computed velocity is used as an input parameter of the TFC model. The combined model is tested in RANS simulations of highly turbulent, lean syngas-air flames that were experimentally investigated at Georgia Tech. The tests are performed for four different values of the inlet rms turbulent velocities, different turbulence length scales, normal and elevated (up to 10 atm) pressures, various H₂/CO ratios ranging from 30/70 to 90/10, and various equivalence ratios ranging from 0.40 to 0.80. All in all, the performed 33 tests indicate that the studied combination of the leading point concept and the TFC model can predict well-pronounced diffusional-thermal effects in lean highly turbulent syngas-air flames, with these results being obtained using the same value of a single constant of the combined model in all cases. In particular, the model well predicts a significant increase in the bulk turbulent consumption velocity when increasing the H₂/CO ratio but retaining the same value of the laminar flame speed.     

Catalytic coprocessing of coal and petroleum residues with waste plastics to produce transportation fuels

Coprocessing reactions with waste plastics, petroleum residues and coal were performed to determine the individual and blended behavior of these materials using lower pressure and cheaper catalysts. The plastic used in this study was polypropylene. The thermodegradative behavior of polypropylene (PP) and PP/petroleum residues/coal blends were investigated in the presence of solid hydrocracking (HC) catalysts. A comparison among various catalysts has been performed on the basis of observed temperatures. The higher temperatures of initial weight loss of PP shifted to lower values by the addition of petroleum residues and coal. The catalysts were also tested in a fixed-bed micro reactor for the pyrolysis of polypropylene, petroleum residues and coal, alone and blended together in nitrogen and hydrogen atmosphere. High yields of liquid fuels in the boiling range 100-480 °C and gases were obtained along with a small amount of heavy oils and insoluble material such as gums and coke. The results obtained on the coprocessing of polypropylene with coal and petroleum residues are very encouraging as this method appears to be quite feasible to convert plastic materials into liquefied coal products and to upgrade the petroleum residues and waste plastics.     

Analysis of resource splitting scheme with cognitive based admission control for femto-WiFi wireless networks

The coexistence of femtocell and WiFi networks in a heterogeneous spectrum environment with licensed and unlicensed bands will support multi-mode femtocell users (FUs) to simultaneously transmit on both licensed and unlicensed bands. The efficient integration of both femtocell and WiFi technologies is seen as crucial for supporting the offloading of femtocell traffic to WiFi networks. To successfully deploy these integrated technologies, the overall licensed and unlicensed spectrum usage must be efficiently managed. Thus, we propose a new cognitive-based connection-level admission control with access retrial for a femtocell network that operates under a mixed spectrum of unlicensed and licensed bands. By deploying cognitive radio concepts, the FUs will utilize the unused spectrum of the existing unlicensed spectrum of the WiFi network in an opportunistic manner in addition to using the licensed spectrum. By using the retrial phenomenon policy, the blocked FUs can retry the access, which can reduce their loss probability. An analytical model using a three-dimensional continuous time Markov chain with a level-dependent quasi birth-and-death structure was developed to evaluate and study the performance of the proposed scheme. The matrix analytic method was used to obtain the steady state probability and performance measures. The result shows that the performance of FUs for integrated femtocell-WiFi networks using the proposed scheme significantly improved in terms of FUs throughput and loss probability. The results also show that the retrial phenomenon of FUs enhances their performance.