A new simple magnetic electrospinning setup was devised to manufacture partially aligned nanofiber in the paper. Compared with the traditional electrospinning setup, a U-shaped permanent magnet was employed and applied with a slide rheostat. Polyvinyl alcohol (PVA) and PVA/Fe 3 O 4 fibers were prepared by the magnetic electrospinning, respectively. The morphology and alignment of the fibers were characterized by the use of scanning electron microscopy (SEM). Results showed that the magnetic field could decrease the diameter of fibers and enhance the crystal conditions of fibers, and the addition of Fe 3 O 4 nanoparticles improved the alignment of nanofibers.
Hollow silica spheres (HSS) are prepared via soft template method. The morphology, internal structure, phase composition, particle size distribution and porosity of HSSs are characterized. It is found that the amorphous HSSs with thin shell thickness and density of around 0.41 g/cm3 have good sphericity and are relatively uniform in size. Most importantly, the size of the synthesized spheres is controlled successfully via stirring rate, and the linear fitting equation is described as d50 = -0.45 × R + 206. This research provides a facile way to produce HSS with low density which has promising application in many fields.
Dispersed Y2O3-MgO nanopowder was synthesized by calcining the stearate. XRD, TG-DTA, FT-IR, BET and FE-SEM were employed to analyze The formation mechanism of the precursor and the Y2O3-MgO nanopowder. Pure and dispersed Y2O3-MgO nanopowder with an average particle size of 40 nm was produced by calcining the precursor at 600 °C. The particle size increases to about 70 nm with the increase of the calcination temperature to 700 °C. In the preparation of Y2O3-MgO from stearate, no water medium is involved, thus capillarity force and bridging of adjacent particles by hydrogen bonds can be avoided, resulting in good dispersion of the particles. The dispersed Y2O3-MgO nanopowder prepared in this work has potential application in infrared transparent ceramic materials.
In this paper, a model of FH spread spectrum communication system has been built in Matlab/Simulink platform. Theoretical analysis of repeater jamming are derived. These limitations arise because of the geometry and so on. Then, we analyze the bit error rate performance in FH communication system under repeater jamming. The benefits of frequency hopping are potentially neutralized by a repeater jammer.
Effect of grain boundary morphology on ductility dip cracking (DDC) sensitivity of nickel base alloy inconel52 deposited metal was researched by welding thermal simulation method and high temperature tensile test. The sample was hold at 1300 °C for 2S ~ 10s and then stretched at its DDC sensitive temperature 1050 °C at different tensile rates. The DDC sensitivity was compared by reduction of area (VoA) of tensile test sample. The results show that straight grain boundary reduces VoA, precipitates in grain boundaries increases VoA, and VoA increases with the increase of tensile rate. Straight grain boundary causes stress concentration and strain localization at the trigeminal grain boundary, curved grain boundary decreases the maximum Mises stress which make more uniform stress distribution. Precipitates on the grain boundary can play a role of locking the grain boundary migration and disperse the strain concentration at the trigeminal grain boundary. The lower the strain rate, the longer the deformation time, which will lead to decrease of dislocation movement rate. The smaller the critical shear stress of grain boundary sliding, the smaller the deformation resistance, and the full progress of dislocation movement and climbing. Effect of strain rate on DDC needs more research.
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