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581.
Songlin Ran Shuigen G. Huang Omer Van der Biest Jef Vleugels 《Journal of the European Ceramic Society》2012,32(10):2537-2543
Fully densified ZrB2-based ceramic composites were produced by reactive pulsed electric current sintering (PECS) of ZrB2–ZrH2 powders within a total thermal cycle time of only 35 min. The composition of the final composite was directly influenced by the initial ZrH2 content in the starting powder batch. With increasing ZrH2 content, ZrB2–ZrO2, ZrB2–ZrB–ZrO2 and ZrB2–ZrB–Zr3O composites were obtained. The ZrB2–ZrB–ZrO2 composite derived from a 9.8 wt% ZrH2 starting powder exhibited an excellent flexural strength of 1382 MPa combined with a Vickers hardness of 17.1 GPa and a fracture toughness of 5.0 MPa m1/2. The high strength was attributed to a fine grain size and the removal of B2O3 through reaction with Zr. Higher ZrH2 content starting powders were densified through solution-reprecipitation resulting in the formation of coarser angular ZrB2–ZrB composites with a Zr3O grain boundary phase with a fracture toughness of 5.0 MPa m1/2 and an acceptable strength in the 852–939 MPa range. 相似文献
582.
Omer MusicJulian M. Allwood 《Journal of Materials Processing Technology》2012,212(5):1139-1156
A novel test method for the characterisation of flexible forming processes is proposed and applied to four flexible forming processes: Incremental Sheet Forming (ISF), conventional spinning, the English wheel and power hammer. The proposed method is developed in analogy with time-domain control engineering, where a system is characterised by its impulse response. The spatial impulse response is used to characterise the change in workpiece deformation created by a process, but has also been applied with a strain spectrogram, as a novel way to characterise a process and the physical effect it has on the workpiece. Physical and numerical trials to study the effects of process and material parameters on spatial impulse response lead to three main conclusions. Incremental sheet forming is particularly sensitive to process parameters. The English wheel and power hammer are strongly similar and largely insensitive to both process and material parameters. Spinning develops in two stages and is sensitive to most process parameters, but insensitive to prior deformation. Finally, the proposed method could be applied to modelling, classification of existing and novel processes, product-process matching and closed-loop control of flexible forming processes. 相似文献
583.
Fahrettin Sarcan Omer Donmez Mustafa Gunes Ayse Erol Mehmet Cetin Arikan Janne Puustinen Mircea Guina 《Nanoscale research letters》2012,7(1):529
In this study, we investigate the effect of annealing and nitrogen amount on electronic transport properties in n- and p-type-doped Ga0.68In0.32NyAs1 − y/GaAs quantum well (QW) structures with y = 0%, 0.9%, 1.2%, 1.7%. The samples are thermal annealed at 700°C for 60 and 600 s, and Hall effect measurements have been performed between 10 and 300 K. Drastic decrease is observed in the electron mobility of n-type N-containing samples due to the possible N-induced scattering mechanisms and increasing effect mass of the alloy. The temperature dependence of electron mobility has an almost temperature insensitive characteristic, whereas for p-type samples hole mobility is decreased drastically at T > 120 K. As N concentration is increased, the hole mobility also increased as a reason of decreasing lattice mismatch. Screening effect of N-related alloy scattering over phonon scattering in n-type samples may be the reason of the temperature-insensitive electron mobility. At low temperature regime, hole mobility is higher than electron mobility by a factor of 3 to 4. However, at high temperatures (T > 120 K), the mobility of p-type samples is restricted by the scattering of the optical phonons. Because the valance band discontinuity is smaller compared to the conduction band, thermionic transport of holes from QW to the barrier material, GaAs, also contributes to the mobility at high temperatures that results in a decrease in mobility. The hole mobility results of as-grown samples do not show a systematic behavior, while annealed samples do, depending on N concentration. Thermal annealing does not show a significant improvement of electron mobility. 相似文献
584.
Seed mediated aqueous chemical growth (ACG) route was used for the growth of ZnO nanostructures on Si substrate in four different growth mediums. The growth medium has shown to affect the morphology and the size of the different nanostructures. We observed that the medium containing zinc nitrate anions yields the nanorods, in a medium containing zinc acetate anions nano-candles are obtained. While in a medium containing zinc chloride anions ZnO nano-discs were obtained and in a medium containing zinc sulfate anions nano-flakes are achieved. Growth in these different mediums has also shown effect on the optical emission characteristics of the different ZnO nanostructures. 相似文献
585.
Muhammad Jaseemuddin Junaid Ahmed Zubairi Omer Mahmoud 《Wireless Communications and Mobile Computing》2002,2(4):339-356
There is a growing interest in providing Internet services to the mobile nodes. When mobile nodes travel from one router's service area to another, the time‐sensitive applications may see degradation in service. We investigate into the effects of handoff on service quality of mobile nodes. Several experiments are conducted using various packet metering and marking schemes with or without transferring profiles to the new router. Results indicate the relative instability period following handoff, loss of packets and delay encountered by packets in profiled or un‐profiled handoffs, leading to determining suitable mix of metering and marking schemes with or without context transfer. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献