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991.
Wanis Alfitouri Hasan Sharul Kamal Abdul Rahim Zaid Ahmed Shamsan Kim Geok Tan 《International Journal of Electronics》2013,100(12):1721-1731
World Radio Conference WRC-1992 has allocated the frequency band 21.4–22.0?GHz to regions 1 and 3 to be utilised to carry direct broadcasting satellite (DBS) services. This high-frequency band is more susceptible to rain attenuation, leading to degradation of the signal quality. Moreover, this frequency band is assigned to two different services, i.e. satellite broadcasting and fixed mobile services at the same regions; hence, the impact of intersystem interference in a depredated signal is a critical issue in the DBS receiver. In this study, the effects of rain attenuation on the DBS downlink signals as well as the impact of the potential interference on the reception quality will be estimated. An interference scenario will be introduced to investigate the system performance in both propagation mechanisms of clear-sky and rain conditions. 相似文献
992.
Sr2La3Nb1?x Ta x Ti4O17 (0 ≤ x ≤ 1) ceramics were processed via a solid-state mixed oxide route. Sr2La3Nb1?x Ta x Ti4O17 (0 ≤ x ≤ 1) solid solutions were single phase in the whole range of x values within the x-ray diffraction (XRD) detection limit. The microstructure comprised elongated and needle-shaped grains. The ceramics exhibit relative permittivity (ε r) of 73 to 68.6, product of unloaded quality factor and resonant frequency (Q u f 0) of 7100 GHz to 9500 GHz, and temperature coefficient of resonant frequency (τ f) of 78.6 ppm/°C to 56.6 ppm/°C. 相似文献
993.
Andrej Mihailovic Apostolos Kousaridas Alexandre Jaron Paul Pangalos Nancy Alonistioti Hamid A. Aghvami 《Wireless Personal Communications》2013,72(1):343-374
A key challenge for the management systems of future networks is the reduction of human interventions in the fundamental management functions. These include mechanisms that render the networks capable to configure, optimize, heal and protect itself, but also handle the emerging complexity. Demands for the future internet networks mandate the rapid assessment of the feasibility of such cognitive management architectures that shall bridge the gap between conceptual design and practical network deployments. In this paper, a novel architecture is introduced, based on organized distribution of control feedback cycles at locations allocated across network’s operational elements. Two realisations of self-management in the operations of wired and wireless access network segments are presented. The first one is focused on organization of the wireless access regions in networks by the use of compartments of access points for enabling coverage optimization. A compartment-based approach facilitates the more efficient usage of network resources, exploiting local situation awareness and local optimisation features, according to the varying traffic needs. The second realization shows the control of mobility management processes in wired parts of access networks for balancing utilization of network resources. A dynamic deployment and re-configuration of mobility agents permit to tackle the problem of congestion induced by mobility agents in mobile protocols and combined with a dynamic access router assignment, network resources are efficiently balanced within the network. The paper concludes with findings and recommendations on how common principles of self-management evolve from design theory to practice. 相似文献
994.
Nafiseh Masaeli Hamid Haj Seyed Javadi Elham Noori 《Wireless Personal Communications》2013,72(4):2721-2740
Cluster-based routing protocols are one of the most favorable approaches for energy management in wireless sensor networks. The selection of the best cluster heads (CHs), as well as the formation of optimal clusters, is an NP-hard problem. The present study proposes an optimal solution for CHs selection to generate a network topology with optimized network performance. The problem is formulated as facility location problem and a linear programming model is used to solve the optimization problem. Results of analysis o the network simulator (NS2) indicate that applying this method in cluster-based routing protocols prolongs 16 % of the network lifetime, increases 15.5 % of data transmission and improves 5.5 % of throughput, as compared to the results of current heuristic methods such as LEACH, DEEC and EDFCM protocols. 相似文献
995.
F. S. Qureshi S. H. Hamid A. G. Maadhah Mohamad B. Amin 《Polymer-Plastics Technology and Engineering》2013,52(7-8):663-670
A number of plastic materials, such as unplasticized poly(viny1 chloride) (uPVC), acrylonitrile-butadiene-styrene (ABS), high-density polyethylene (HDPE), poly-(vinylidene fluoride) (PVDF), and chlorinated poly(viny1 chloride) (cPVC), are available for numerous applications. uPVC and HDPE pipes are used in pressurized piping systems in Saudi Arabia for industrial, agricultural, domestic, and general-purpose applications. Some studies have been carried out to investigate the causes of failure in plastic pipes, which is very high in the area. In this chapter an overview of the failure of plastic pipes is presented, with emphasis given to failure of pipes due to severe weather conditions in Saudi Arabia. 相似文献
996.
Hamid Shaikh Syed K. H. Gulrez Arfat Anis Anesh M. Poulose Patrick E. H. Qua Mukesh K. Yadav 《Polymer-Plastics Technology and Engineering》2013,52(17):1845-1860
Due to their lightweight and excellent toughness, carbon fiber (CF) and its reinforced thermoplastic composites are suitable for high-performance applications such as aerospace, aviation, automotive and sport equipments. In this study, comprehensive detail is provided on the production of carbon fiber, its various forms and geometry and their corresponding effects on the mechanical properties of CF and its reinforced polypropylene (PP) and polyethylene (PE) composites. Here we discuss extensively various methods reported in literature on improving the interfacial fiber-matrix adhesion and dispersion in order to achieve better mechanical properties for such composites. 相似文献
997.
Iqbal Mokhtar Mohd Yazid Yahya Mohammed Rafiq Abdul Kadir Mohd Faisal Kambali 《Polymer-Plastics Technology and Engineering》2013,52(11):1140-1146
The aim of this study was to investigate the performance of UHMWPE/HDPE-reinforced kenaf, basalt and hybrid kenaf/basalt composites. Mechanical testing of these samples was carried out such as tensile, flexural (three-point bending) and an impact test (Charpy). Pure resin (UHMWPE/HDPE) samples were tested and compare with reinforced 10% weight fraction of kenaf, basalt and hybrid kenaf/basalt samples to identifying their contribution and potential in this new composite material. UHMWPE/ HDPE sample was produced in constant ratio 60:40 respectively via extrusion process. Basalt reinforced UHMWPE/HDPE generates the highest elastic modulus result compared to kenaf and hybrid kenaf/basalt as a reinforcement material. The tensile results of kenaf reinforcement UHMWPE/HDPE samples are significantly higher (20%) than pure blend resin, which is an indication for good performance of kenaf, basalt and hybrid kenaf/basalt to be used in UHMWPE/HDPE-blend polymers. The flexural and Charpy strengths show the drawback results, where performance of polymer is reduced 5% with the absence of kenaf. It can be concluded that kenaf, basalt and hybrid kenaf/basalt fiber successfully increase the UHMWPE/HDPE blends performance especially under tensile loading. 相似文献
998.
Hamid Ghanbari Henrik Saxén Ignacio E. Grossmann 《American Institute of Chemical Engineers》2013,59(10):3659-3670
A process integration approach has been applied to integrate a traditional steelmaking plant with a polygeneration system to increase energy efficiency and suppress carbon dioxide emissions from the system. Using short‐cut models and empirical equations for different units and available technologies for gas separation, methane gasification, and methanol synthesis, a mixed integer nonlinear model is applied to find the optimal design of the polygeneration plant and operational conditions of the system. Due to the complexity of the blast furnace (BF) operation, a surrogate model technique is chosen based on an existing BF model. The results show that from an economic perspective, the pressure swing adsorption process with gas‐phase methanol unit is preferred. The results demonstrate that integration of conventional steelmaking with a polygeneration system could decrease the specific emissions by more than 20 percent. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3659–3670, 2013 相似文献
999.
Peng Hu Hamid Rismani‐Yazdi Gregory Stephanopoulos 《American Institute of Chemical Engineers》2013,59(9):3176-3183
Anaerobic bacteria such as Moorella thermoacetica have the capacity of fixing carbon dioxide with carbon monoxide and hydrogen for the production of ethanol, acetic acid, and other useful chemicals. In this study, we evaluated the fixation of CO2 for the production of acetic acid, as a product in its own right but also as precursor for lipid synthesis by oleaginous organisms. We achieved maximum cell optical density of 11.3, acetic acid titer of 31 g/L, and productivity of 0.55 g/L‐h at CO mass‐transfer rate of 83 mM/h. We also showed electron availability by CO mass transfer limited the process at CO mass transfer rates lower than 30 mM/h. Further enhancement of mass‐transfer rate removed such limitations in favor of biological kinetics as main limitation. This work underlines the potential of microbial processes for converting syngas to fuel and chemical products in processes suitable for distributed feedstock utilization. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3176–3183, 2013 相似文献
1000.
AbstractAccurate machining in small-radius paths is a challenge associated with Wire Electrical Discharge Machining (WEDM). This article experimentally and theoretically analyzes the machining errors of the arced paths through successive machining stages. The machining errors of a three-stage WEDM on both straight and arced paths are first experimentally analyzed. Mathematical expressions are derived to relate new theoretical concepts, including spark angle and spark density, for each finishing stage on both straight and arced paths. Then, the effects of these concepts on machining errors of the finishing stages are determined. The causes of the machining errors of the first and second finishing stages on male and female arced paths are theoretically analyzed, and a novel mathematical methodology for the prediction of these errors is developed. The experimental machining errors of the first and second finishing stages on the different arced paths are compared and evaluated with related theoretical ones. Results reveal that the mathematical methodology predicts and compensates the machining errors of the first finishing stage with the accuracy of 78% and of the second finishing stage with the accuracy of 83%. There is a good improvement which can be employed in WEDM applications and to increase the wire electrical discharge (WED) machine capability. 相似文献