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排序方式: 共有421条查询结果,搜索用时 15 毫秒
61.
In this paper a new protocol using fuzzy logic control has been proposed. The protocol is based on Stable Election Protocol (SEP). Fuzzy logic control based on three variables, distance of nodes form base station, density of nodes and the battery level of nodes along with the traditional threshold values used in SEP are used to enhance the process of cluster head election in the existing SEP protocol and improve the lifetime and throughput of the Wireless Sensor Network. The result of the simulation which has been done in MATLAB simulator indicates that Stable Election Protocol based on fuzzy logic is more energy efficient and improves the lifetime and throughput of the network by 73.2 and 68.54 % respectively comparing with the existing SEP protocol. 相似文献
62.
Oktar FN Agathopoulos S Ozyegin LS Gunduz O Demirkol N Bozkurt Y Salman S 《Journal of materials science. Materials in medicine》2007,18(11):2137-2143
Biologically derived hydroxyapatite from calcinated (at 850 °C) bovine bones (BHA) was doped with 5 wt% and 10 wt% of SiO2, MgO, Al2O3 and ZrO2 (stabilized with 8% Y2O3). The aim was to improve the sintering ability and the mechanical properties (compression strength and hardness) of the resultant
BHA-composites. Cylindrical samples were sintered at several temperatures between 1,000 and 1,300 °C for 4 h in air. The experimental
results showed that sintering generally occurs at 1,200 °C. The BHA–MgO composites showed the best sintering performance.
In the BHA–SiO2 composites, extended formation of glassy phase occurred at 1,300 °C, resulting in structural degradation of the resultant
samples. No sound reinforcement was achieved in the case of doping with Al2O3 and zirconia probably due to the big gap between the optimum sintering temperatures of BHA and these two oxides. 相似文献
63.
High-Frequency Fatigue Behavior of Woven-Fiber-Fabric-Reinforced Polymer-Derived Ceramic-Matrix Composites 总被引:3,自引:0,他引:3
Nikhilesh Chawla Yahya K. Tur John W. Holmes James R. Barber y Szweda 《Journal of the American Ceramic Society》1998,81(5):1221-1230
The monotonic and high-frequency (100 Hz) fatigue behavior of two Nicalon-fabric-reinforced SiCON matrix composites was investigated at room temperature. The matrix composition was varied by the addition of BN and SiC particulate fillers, to contain shrinkage from processing by polymer infiltration and pyrolysis (PIP). The composites had strong fiber/matrix bonding, which resulted in substantially less frictional heating than observed with weakly bonded composites. Both composites exhibited fatigue runout at 107 cycles at ∼80% of the monotonic strength. Comparison with existing fatigue data in the literature (for the same composites) at 1 Hz shows no change in fatigue life; i.e., no frequency effect was observed. Most of the stiffness reduction in the composites occurred in the first fatigue cycle, whereas subsequent decreases in moduli were attributed to limited fiber cracking. The major driving force for failure was the localized debonding of transverse and longitudinal plies at the crossover points in the fabric, which, when linked, resulted in interlaminar damage and failure in the composite. 相似文献
64.
Poornima Ramburrun Pradeep Kumar Elias Ndobe Yahya E. Choonara 《International journal of molecular sciences》2021,22(21)
Optimal levels of functional recovery in peripheral nerve injuries remain elusive due to the architectural complexity of the neuronal environment. Commercial nerve repair conduits lack essential guidance cues for the regenerating axons. In this study, the regenerative potential of a biosimulated nerve repair system providing three types of regenerative cues was evaluated in a 10 mm sciatic nerve-gap model over 4 weeks. A thermo-ionically crosslinked gellan-xanthan hydrogel conduit loaded with electrospun PHBV-magnesium oleate-N-acetyl-cysteine (PHBV-MgOl-NAC) nanofibers was assessed for mechanical properties, nerve growth factor (NGF) release kinetics and PC12 viability. In vivo functional recovery was based on walking track analysis, gastrocnemius muscle mass and histological analysis. As an intraluminal filler, PHBV-MgOl-NAC nanofibers improved matrix resilience, deformation and fracture of the hydrogel conduit. NGF release was sustained over 4 weeks, governed by Fickian diffusion and Case-II relaxational release for the hollow conduit and the nanofiber-loaded conduit, respectively. The intraluminal fibers supported PC12 proliferation by 49% compared to the control, preserved up to 43% muscle mass and gradually improved functional recovery. The combined elements of physical guidance (nanofibrous scaffolding), chemical cues (N-acetyl-cysteine and magnesium oleate) and therapeutic cues (NGF and diclofenac sodium) offers a promising strategy for the regeneration of severed peripheral nerves. 相似文献
65.
F.A. Halim Yap M.S. Yahya M. Ismail 《International Journal of Hydrogen Energy》2017,42(33):21096-21104
In this work, we have investigated the hydrogen release and uptake pathways storage properties of the MgH2Na3AlH6 with a molar ratio of 4:1 and doped with 10 wt% of TiF3 using a mechanical alloying method. The doped composite was found to have a significant reduction on the hydrogen release temperature compared to the un-doped composite based on the temperature-programme-desorption result. The first stage of the onset desorption temperature of MgH2Na3AlH6 was reduced from 170 °C to 140 °C with the addition of the TiF3 additive. Three dehydrogenation steps with a total of 5.3 wt% of released hydrogen were observed for the 4MgH2Na3AlH6-10 wt% TiF3 composite. The re/dehydrogenation kinetics of 4MgH2Na3AlH6 system were significantly improved with the addition of TiF3. Kissinger analyses showed that the apparent activation energy, EA, of the 4MgH2Na3AlH6 doped composite was 124 kJ/mol, 16 kJ/mol and 34 kJ/mol lower for un-doped composite and the as-milled MgH2, respectively. It was believed that the enhancements of the MgH2Na3AlH6 hydrogen storage properties with the addition of TiF3 were due to formation of the NaF, the AlF3 and the Al3Ti species. These species may played a synergetic catalytic role in improving the hydrogenation properties of the MgH2Na3AlH6 system. 相似文献
66.
Zhen Wang Junbo Wang Zhenpeng Xu Ryan Hensleigh Haotian Lu Mack Sowers Marcus A. Worsley Yahya Rahmat-Samii Xiaoyu Zheng 《Advanced functional materials》2024,34(18):2313839
Charge-programmed 3D printing enables the fabrication of 3D electronics with lightweight and high precision via selective patterning of metals. This selective metal deposition is catalyzed by Pd nanoparticles that are specifically immobilized onto the charged surface and promises to fabricate a myriad of complex electronic devices with self-sensing, actuation, and structural elements assembled in a designed 3D layout. However, the achievable property space and the material-performance correlation of the charge-programmed printing remain unexplored. Herein, a series of photo-curable resins are designed for unveiling how the charge and crosslink densities synergistically impact the nanocatalyst-guided selective deposition in catalytic efficiency and properties of the 3D printed charge-programmed architectures, leading to high-quality 3D patterning of solid and liquid metals. The findings offer a wide tunability of the structural properties of the printed electronics, ranging from stiff to extreme flexibility. Capitalizing on these results, the printing and successful application of an ultralight-weight and deployable 3D multi-layer antenna system operating at an ultrahigh-frequency of 19 GHz are demonstrated. 相似文献
67.
Power management is an important issue in wireless sensor networks (WSNs) because wireless sensor nodes are usually battery powered, and an efficient use of the available battery power becomes an important concern specially for those applications where the system is expected to operate for long durations. This necessity for energy efficient operation of a WSN has prompted the development of new protocols in all layers of the communication stack. Provided that, the radio transceiver is the most power consuming component of a typical sensor node, large gains can be achieved at the link layer where the medium access control (MAC) protocol controls the usage of the radio transceiver unit. MAC protocols for sensor networks differ greatly from typical wireless networks access protocols in many issues. MAC protocols for sensor networks must have built‐in power conservation, mobility management, and failure recovery strategies. Furthermore, sensor MAC protocols should make performance trade‐off between latency and throughput for a reduction in energy consumption to maximize the lifetime of the network. This is in general achieved through duty cycling the radio transceiver. Many MAC protocols with different objectives were proposed for wireless sensor networks in the literature. Most of these protocols take into account the energy efficiency as a main objective. There is much more innovative work should be done at the MAC layer to address the hard unsolved problems. In this paper, we first outline and discuss the specific requirements and design trade‐offs of a typical wireless sensor MAC protocol by describing the properties of WSN that affect the design of MAC layer protocols. Then, a typical collection of wireless sensor MAC protocols presented in the literature are surveyed, classified, and described emphasizing their advantages and disadvantages whenever possible. Finally, we present research directions and identify open issues for future medium access research. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
68.
S. Ismail A. K. Yahya Nawazish A. Khan 《Journal of Superconductivity and Novel Magnetism》2012,25(6):1849-1856
Ce substituted Tl0.9Bi0.1Sr2?x Ce x Ca0.9Y0.1Cu1.99Fe0.01O7??? (x=0?C0.20) samples were synthesized to determine the effects of the higher valence ion substitution on superconductivity and structure of the Fe-doped Tl1212 derivatives. The normal state behavior for x=0 showed semiconductor-like behavior which gradually turned to metallic behavior with increasing Ce at x=0.05?C0.15. However, further substitution of Ce for x>0.15 turned the normal state to insulating behavior. The zero critical temperature, T c zero increased from 65.4?K (x=0.05) to 71.0?K (x=0.10), but slightly decreased for x>0.10 indicating the optimum value of average copper valence was achieved at x=0.10. Excess conductivity analysis using the Aslamazov Larkin, AL and Lawrence?CDoniach, LD models revealed two-dimensional, 2D to three-dimensional, 3D transition of superconducting fluctuation behavior, SFB with the highest transition temperature, $T_{\mathrm{2D}\mbox{-}\mathrm{3D}}$ at x=0.10. FTIR analysis in conjunction with XRD results showed softening of FeO2/CuO2 planar oxygen mode from 610.5?cm?1(x=0) to 605?cm?1(x=0.20) which is suggested to be related to possible increase of inter plane coupling, J and this is supported by computed results based on the LD model. The enhanced J increases superconducting coherence length along c-axis, ?? c (0), and hence lowers anisotropy, ?? resulting in enhanced superconducting properties. 相似文献
69.
The search for alternative fuels and new fuel resources is a top priority for Turkey, as is the case in the majority of countries throughout the world. The fuel policies pursued by governmental or civil authorities are of key importance in the success of alternative fuel use, especially for widespread and efficient use. Following the 1973 petroleum crisis, many users in Turkey, especially in transportation sector, searched for alternative fuels and forms of transportation. Gasoline engines were replaced with diesel engines between the mid-1970s and mid-1980s. In addition, natural gas was introduced to the Turkish market for heating in the early 1990s. Liquid petroleum gas was put into use in the mid-1990s, and bio-diesel was introduced into the market for transportation in 2003. However, after long periods of indifference governmental action, guidance and fuel policies were so weak that they did not make sense. Entrepreneurs and users experienced great economical losses and lost confidence in future attempts to search for other possible alternatives. In the present study, we will look at the history of alternative fuel use in the recent past and investigate the alternative engine fuel potential of Turkey, as well as introduce possible future policies based on experience. 相似文献
70.
F.A. Halim Yap N.S. Mustafa M.S. Yahya A.A. Mohamad M. Ismail 《International Journal of Hydrogen Energy》2018,43(17):8365-8374
In this work, the hydrogen storage properties of different molar ratio (in mole of 1:3 and 1:4) Na3AlH6LiBH4 system is investigated for the first time. X-ray diffraction and Fourier transform infrared results show that the Na3AlH6LiBH4 with molar ratio of 1:3 and 1:4 composite was transformed to Li3AlH6 and NaBH4 phases via a metathesis reaction during a ball-milling process for 6 h. Temperature-programmed-desorption (TPD) results show three stages of decomposition for the Na3AlH6LiBH4 (in mole ratio of 1:3 and 1:4) composite resulting from Li3AlH6 and NaBH4 phases. From the TPD graph, the Na3AlH6LiBH4 composite with molar ratio of 1:4 had showed better performance of hydrogenation properties compared to with molar ratio of 1:3. The composite began to release hydrogen at 180 °C in relation to decomposition of the Li3AlH6 stage into LiH and Al. The NaBH4 stage then began to decompose at approximately 380 °C, after reacting with Al to form an intermetallic phase, AlB2, which occurred at 100 °C lower than as-milled NaBH4. At 430 °C, the un-reacted NaBH4 was decomposed after catalysing with AlB2. Kissinger analysis shows the apparent activation energy of NaBH4 decomposition in the hydrides composite was reduced by about 75 kJ/mol compared to the as-milled NaBH4. The rehydrogenation process evidenced the reversibility of NaBH4. Based on these results, the intermetallic phase, AlB2, is considered to have played an important role by lowering the operating temperature and providing access to the full hydrogen content in the Na3AlH6LiBH4 composite system. 相似文献