RESUMEN
Dark photons can be the ultralight dark matter candidate, interacting with Standard Model particles via kinetic mixing. We propose to search for ultralight dark photon dark matter (DPDM) through the local absorption at different radio telescopes. The local DPDM can induce harmonic oscillations of electrons inside the antenna of radio telescopes. It leads to a monochromatic radio signal and can be recorded by telescope receivers. Using the observation data from the FAST telescope, the upper limit on the kinetic mixing can already reach 10^{-12} for DPDM oscillation frequencies at 1-1.5 GHz, which is stronger than the cosmic microwave background constraint by about one order of magnitude. Furthermore, large-scale interferometric arrays like LOFAR and SKA1 telescopes can achieve extraordinary sensitivities for direct DPDM search from 10 MHz to 10 GHz.
RESUMEN
The effect of scanning angle and region of interest (ROI) depth on shear-wave velocity (SWV) was investigated in this study. Shear-wave velocity of ox liver ex vivo was measured with different approaches. Region of interest was set underneath the liver capsule at depths of 1, 2, 3, 4, and 5 cm. Three groups of measurements were performed at different scanning angles. One group of measurement was conducted with a scanning angle of 0 to 15 degrees from the midline, and the other 2 groups were performed with scanning angles of 15 to 30 degrees and 30 to 45 degrees. The data on SWV from different scan angles and ROI depths were analyzed statistically. Scanning angle and ROI depth were found to be the 2 factors that affect SWV. Interaction was observed between the scan angle and ROI depth. The data at different depths within 0- to 15-degree scanning angles exhibited no significant difference. However, the reliability of SWV decreased with the increase in ROI depth. In the groups of 15 to 30 degrees and 30 to 45 degrees, a significant difference was found between the 2 different measured depths. Scanning angle and ROI depth affected the reliability of SWV measurement. The scanning angle should be confined within 15 degrees from the midline. Therefore, SWV from shallow ROI is more reliable than that at deep ROI.