288 publications from this institution
Silica aerogels (SAs) present great application prospects especially on thermal insulation, but their flammability is usually ignored. A combined study on the combustion behaviors and oxidation kinetics of hydrophobic silica aerogels prepared by ambient pressure drying (SA-apd) and supercritical drying (SA-sd) was performed by employing cone calorimeter and thermal analysis. The whole combustion process for SAs could be divided into three stages in which a fire propagation phenomenon was observed with the radial propagation velocity of 6.6⿿8.3cms⿿1. Current investigations forcefully demonstrated that hydrophobic SAs were combustible and easy to flashover when exposed to a heat flux higher than 25kWm⿿2. Compared between the two SAs, the SA-sd owned a less fire risk with presenting a less fire hazard and a lower smoke toxicity than those of SA-apd. The oxidation kinetics by Ozawa-Flynn-Wall method revealed that SA-sd had larger apparent activation energies than those of SA-apd which conformed to the thermal stability analysis by TG-DSC. Furthermore, a two-step combustion mechanism was proposed to explain the combustion behaviors of SAs.
A frequency reconfigurable microstrip antenna is proposed. A circular patch and a C-shaped ring are used for different frequency bands and the two parts are connected by the PIN diode. The two parts can be one resonator when the PIN diode is shorted, otherwise to make the two parts independent. Because the main resonators are different for the different bands, the beam widths can be tuned to be similar for both bands. Simulated results show that the proposed antenna can cover frequency bands of 4.64–4.7GHz and 7.77–7.9GHz with reflection coefficient below −10 dB. The 3dB beam widths are between ± 40° to ±47°.
