The response of the contact point of the vehicle with the bridge, rather than the vehicle itself, is proposed for modal identification of bridges by a moving test vehicle. To begin, approximate closed-form solutions were derived for the vehicle and contact-point responses, and they were verified by finite element solutions. The contact-point acceleration is born to be free of the vehicle frequency, an annoying effect that may overshadow the bridge frequencies in case of rough surface. From the frequency response function (FRF) of the vehicle with respect to the contact point, it was shown that the contact-point response generally outperforms the vehicle response in extracting the bridge frequencies because it could identify more frequencies. In the numerical simulations, the contact-point response was compared with the vehicle response for various scenarios. It is concluded that in each case, say, for varying vehicle speeds or frequencies, for smooth or rough road surfaces, with or without existing traffic, the contact-point response outperforms the vehicle response in extracting either the frequencies or mode shapes of the bridge.

In the present study, direct Z-scheme Si/TiO 2 photocatalyst was synthesized via a facile hydrothermal reaction using tetrabutyl titanate and Si powder prepared from magnesiothermic reduction of SiO 2 nanospheres. The Si/TiO 2 nanospheres were composed of porous Si nanospheres with a diameter of $300 nm and TiO 2 nanosheets with a diameter of 50 nm and thickness of 10 nm, and demonstrated superior visible light harvesting ability to either Si nanospheres or TiO 2 nanosheets. CO 2 photocatalytic reduction proved that Si/TiO 2 nanocomposites exhibit high activity in conversion of CO 2 to methanol with the maximum photonic efficiency of 18.1%, while pure Si and TiO 2 catalyst are almost inactive, which can be ascribed to the integrated suitable band composition in the Si/TiO 2 Z-scheme system for CO 2 reduction. The enhanced photocatalytic property of Z-scheme Si/TiO 2 nanospheres was ascribed to the formation of Si/TiO 2 Z-scheme system, which improved the separation efficiency of the photogenerated carriers, prolonged their longevity, and therefore boosted their photocatalytic activity.

No abstract

The aero-optical effects of an optical seeker with a supersonic jet for hypersonic vehicles in near space were investigated by three suites of cases, in which the altitude, angle of attack, and Mach number were varied in a large range. The direct simulation Monte Carlo based on the Boltzmann equation was used for flow computations and the ray-tracing method was used to simulate beam transmission through the nonuniform flow field over the optical window. Both imaging displacement and phase deviation were proposed as evaluation parameters, and along with Strehl ratio they were used to quantitatively evaluate aero-optical effects. The results show that aero-optical effects are quite weak when the altitude is greater than 30 km, the imaging displacement is related to the incident angle of a beam, and it is minimal when the incident angle is approximately 15°. For reducing the aero-optical effects, the optimal location of an aperture should be in the middle of the optical window.