The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was address...The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets（GNPs） using two types of surfactant： anionic（sodium dodecyl benzene sulfate（SDBS）） and non-ionic polymeric（ethyl cellulose（EC））. After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures（550 and 620°C）. The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5 wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620°C, while a 22% increase in hardness with reduced wear rate of 96.98% at 550°C was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.展开更多
In this study, the multistep method is applied to the STF system. This method has been tested on the STF system, which is a three-dimensional system of ODE with quadratic nonlinearities. A computer based Matlab progra...In this study, the multistep method is applied to the STF system. This method has been tested on the STF system, which is a three-dimensional system of ODE with quadratic nonlinearities. A computer based Matlab program has been developed in order to solve the STF system. Stable and unstable position of the system has been analyzed graphically and finally a comparison as well as accuracy between two-step sizes with detail. Newton’s method has been applied to show the best convergence of this system.展开更多
Saving the electrical power system in stable condition is considered as one of important challenges to avoid any failure of high voltage equipment. Additionally, with the increasing off the critical loads, it’s very ...Saving the electrical power system in stable condition is considered as one of important challenges to avoid any failure of high voltage equipment. Additionally, with the increasing off the critical loads, it’s very important to use the accurate protection system that can deal with any abnormal condition. This paper studies one of critical cases that can effect on the coordination of the protection system with the faults during fuse fail condition. Over Head transmission line (OHTL) is the most part in the power system that faces the disturbances, which can be protected by multi-protection functions as line differential function, distance protection function, over current, earth fault, over/under voltage etc. The distance protection function is depending on the line voltage and the load current to calculate the load zone. This paper aims to prevent the falls operation of distance protection function during voltage transformer fuse failure condition.展开更多
The article presents a miniaturized monopole antenna dedicated to modern flexible electronic systems.The antenna combines three fundamental properties in a single structure.Firstly,it is characterized by a compact siz...The article presents a miniaturized monopole antenna dedicated to modern flexible electronic systems.The antenna combines three fundamental properties in a single structure.Firstly,it is characterized by a compact size compared to the state-of-the-art literature with an overall size of 18×18×0.254 mm3,secondly,the proposed antenna integrates the reconfigurability function of frequency,produced by means of a Positive-IntrinsicNegative(PIN)diode introduced into the radiating element.Thus,the antenna is able to switch between different frequencies and different modes,making it suitable to meet the ever-changing demands of communication systems.third,the antenna is equipped by the property of flexibility.In fact,a conformability test is performed and has demonstrated the stability of the antenna performance under normal and bending conditions.Finally,in order to demonstrate the potential of the proposed antenna,a comparison between the simulated and measured results is made and turned out to be a strong agreement,making the antenna an excellent candidate for future miniaturized rigid and conformal devices.展开更多
Concentrating solar power technology is one of the most promising alternative energy technologies.In recent past,Linear Fresnel Reflector systems have received great attention and novel designs have been proposed keep...Concentrating solar power technology is one of the most promising alternative energy technologies.In recent past,Linear Fresnel Reflector systems have received great attention and novel designs have been proposed keeping in view the objective to enhance its functionality and performance.For achieving the same objective,this study presents a novel concept where a conventional LFR is enclosed in a greenhouse called greenhouse-LFR.It was expected that such an enclosure can:(1)increase the incoming solar radiation,(2)further improve the overall efficiency due to simplified cleaning process and(3)reduce the capital cost for the construction of LFR support system.A complete thermal and optical analysis was presented for modeling and performance evaluation of the solar field of both conventional-LFR and novel greenhouse-LFR.Sets of non-linear equations for each system were solved using Newton-Raphson method.More detailed optical analysis was further performed for conventional-LFR considering the seasonal variations.The results concluded that the greenhouse-LFR is better than the conventional-LFR as it had higher efficiency and useful heat with lesser heat losses.For greenhouse-LFR,the maximum thermal efficiency was 73.2%whereas for conventional-LFR it was 37.2%.Also,there was an average increase of useful heat by 3 times in the month of February and 4.7 times in the month of September.SolTrace^(TM) analysis indicated significant spillage loss when a conventional-LFR was used without a secondary reflector or slight curvature of the mirrors.展开更多
Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explore...Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explored for various tip clearance levels,axial spacings and circumferential clockings.Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle,meridional gas passage and camber distributions in order to have a true comparison with conventional design.Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance.Linear-equation models for correlating stage characteristics with tip clearance are proposed.Comparing two designs,it is clearly evident that the conventional design shows better performance at moderate flow rates.However;near choke flow,tandem design gives better results primarily because of the increase in throat area.Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.展开更多
Expanding the structural diversity of crystalline two-dimensional polymers(2DPs) is highly desired but remains a considerable challenge. Herein we report the first synthesis of novel crystalline secondary amine-linked...Expanding the structural diversity of crystalline two-dimensional polymers(2DPs) is highly desired but remains a considerable challenge. Herein we report the first synthesis of novel crystalline secondary amine-linked triazine-based 2DPs(SAT-2DPs) by using benzidine or 4, 4′′-diamino-p-terphenyl and cyanuric chloride under solvothermal conditions. We find the structures of diamine-based monomers play a crucial role in deciding whether the synthesized material is crystalline 2DPs nanosheets or amorphous nanoparticles, which is unexpected and provides an important understanding of the 2D polymerization mechanism.The obtained SAT-2DPs not only show a lateral size of micrometers and an ultrathin thickness of a few nanometers, but also demonstrate high crystallinity with a unique ABC stacking configuration, excellent solvent dispersibility and superior thermal stability. In addition, the resultant SAT-2DPs are used to guide uniform lithium-ion deposition due to their abundant nitrogen atoms and ordered open channels. The assembled asymmetric coin cells(Li|Cu) with SAT-2DPs realize the average coulombic efficient up to 99.3% during discharge-charge cycles. This work provides valuable insights into the synthesis of new 2DPs for various applications.展开更多
文摘The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets（GNPs） using two types of surfactant： anionic（sodium dodecyl benzene sulfate（SDBS）） and non-ionic polymeric（ethyl cellulose（EC））. After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures（550 and 620°C）. The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5 wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620°C, while a 22% increase in hardness with reduced wear rate of 96.98% at 550°C was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.
文摘In this study, the multistep method is applied to the STF system. This method has been tested on the STF system, which is a three-dimensional system of ODE with quadratic nonlinearities. A computer based Matlab program has been developed in order to solve the STF system. Stable and unstable position of the system has been analyzed graphically and finally a comparison as well as accuracy between two-step sizes with detail. Newton’s method has been applied to show the best convergence of this system.
文摘Saving the electrical power system in stable condition is considered as one of important challenges to avoid any failure of high voltage equipment. Additionally, with the increasing off the critical loads, it’s very important to use the accurate protection system that can deal with any abnormal condition. This paper studies one of critical cases that can effect on the coordination of the protection system with the faults during fuse fail condition. Over Head transmission line (OHTL) is the most part in the power system that faces the disturbances, which can be protected by multi-protection functions as line differential function, distance protection function, over current, earth fault, over/under voltage etc. The distance protection function is depending on the line voltage and the load current to calculate the load zone. This paper aims to prevent the falls operation of distance protection function during voltage transformer fuse failure condition.
基金This work is supported by Taif University Researchers Supporting Project Number TURSP-2020/34,Taif University,Taif,Saudi Arabia.Also,this work is supported by Antenna and Wireless Propagation Group(https://sites.google.com/view/awpgrp)。
文摘The article presents a miniaturized monopole antenna dedicated to modern flexible electronic systems.The antenna combines three fundamental properties in a single structure.Firstly,it is characterized by a compact size compared to the state-of-the-art literature with an overall size of 18×18×0.254 mm3,secondly,the proposed antenna integrates the reconfigurability function of frequency,produced by means of a Positive-IntrinsicNegative(PIN)diode introduced into the radiating element.Thus,the antenna is able to switch between different frequencies and different modes,making it suitable to meet the ever-changing demands of communication systems.third,the antenna is equipped by the property of flexibility.In fact,a conformability test is performed and has demonstrated the stability of the antenna performance under normal and bending conditions.Finally,in order to demonstrate the potential of the proposed antenna,a comparison between the simulated and measured results is made and turned out to be a strong agreement,making the antenna an excellent candidate for future miniaturized rigid and conformal devices.
基金The authors extend their appreciation to the Deputyship for Research&Innovation,“Ministry of Education”in Saudi Arabia for funding this research work through the project number IFKSURG-2020-200.
文摘Concentrating solar power technology is one of the most promising alternative energy technologies.In recent past,Linear Fresnel Reflector systems have received great attention and novel designs have been proposed keeping in view the objective to enhance its functionality and performance.For achieving the same objective,this study presents a novel concept where a conventional LFR is enclosed in a greenhouse called greenhouse-LFR.It was expected that such an enclosure can:(1)increase the incoming solar radiation,(2)further improve the overall efficiency due to simplified cleaning process and(3)reduce the capital cost for the construction of LFR support system.A complete thermal and optical analysis was presented for modeling and performance evaluation of the solar field of both conventional-LFR and novel greenhouse-LFR.Sets of non-linear equations for each system were solved using Newton-Raphson method.More detailed optical analysis was further performed for conventional-LFR considering the seasonal variations.The results concluded that the greenhouse-LFR is better than the conventional-LFR as it had higher efficiency and useful heat with lesser heat losses.For greenhouse-LFR,the maximum thermal efficiency was 73.2%whereas for conventional-LFR it was 37.2%.Also,there was an average increase of useful heat by 3 times in the month of February and 4.7 times in the month of September.SolTrace^(TM) analysis indicated significant spillage loss when a conventional-LFR was used without a secondary reflector or slight curvature of the mirrors.
基金the Deanship of Scientific Research,Research Center of College of Engineering, King Saud University for the financial support
文摘Extensive numerical investigations of the performance and flow structure in an unshrouded tandem-bladed centrifugal compressor are presented in comparison to a conventional compressor.Stage characteristics are explored for various tip clearance levels,axial spacings and circumferential clockings.Conventional impeller was modified to tandem-bladed design with no modifications in backsweep angle,meridional gas passage and camber distributions in order to have a true comparison with conventional design.Performance degradation is observed for both the conventional and tandem designs with increase in tip clearance.Linear-equation models for correlating stage characteristics with tip clearance are proposed.Comparing two designs,it is clearly evident that the conventional design shows better performance at moderate flow rates.However;near choke flow,tandem design gives better results primarily because of the increase in throat area.Surge point flow rate also seems to drop for tandem compressor resulting in increased range of operation.
基金support by the National Natural Science Foundation of China (51873039, 51673042)the Young Elite Scientist Sponsorship Program by CAST (2017QNRC001)。
文摘Expanding the structural diversity of crystalline two-dimensional polymers(2DPs) is highly desired but remains a considerable challenge. Herein we report the first synthesis of novel crystalline secondary amine-linked triazine-based 2DPs(SAT-2DPs) by using benzidine or 4, 4′′-diamino-p-terphenyl and cyanuric chloride under solvothermal conditions. We find the structures of diamine-based monomers play a crucial role in deciding whether the synthesized material is crystalline 2DPs nanosheets or amorphous nanoparticles, which is unexpected and provides an important understanding of the 2D polymerization mechanism.The obtained SAT-2DPs not only show a lateral size of micrometers and an ultrathin thickness of a few nanometers, but also demonstrate high crystallinity with a unique ABC stacking configuration, excellent solvent dispersibility and superior thermal stability. In addition, the resultant SAT-2DPs are used to guide uniform lithium-ion deposition due to their abundant nitrogen atoms and ordered open channels. The assembled asymmetric coin cells(Li|Cu) with SAT-2DPs realize the average coulombic efficient up to 99.3% during discharge-charge cycles. This work provides valuable insights into the synthesis of new 2DPs for various applications.
