On the possibility of radar echo detection of ultra-high energy cosmic ray- and neutrino-induced extensive air showers

We revisit and extend the analysis supporting a 60 year-old suggestion that cosmic rays air showers resulting from primary particles with energies above 10^{18} eV should be straightforward to detect with radar ranging techniques, where the radar echoes are produced by scattering from the column of ionized air produced by the shower. The idea has remained curiously untested since it was proposed, but if our analysis is correct, such techniques could provide a significant alternative approach to air shower detection in a standalone array with high duty cycle, and might provide highly complementary measurements of air showers detected in existing and planned ground arrays such as the Fly's Eye or the Auger Project. The method should be particularly sensitive to showers that are transverse to and relatively distant from the detector, and is thus effective in characterizing penetrating horizontal showers such as those that might be induced by ultra-high energy neutrino primaries.Comment: 29 pages, 16 figures, uses aas2pp4.sty. Final version, to appear in Astroparticle Physics. Contains new figs, better estimate of angular precision possibl

pH-Controlled Gas-Generating Mineralized Nanoparticles: A Theranostic Agent for Ultrasound Imaging and Therapy of Cancers

We report a theranostic nanoparticle that can express ultrasound (US) imaging and simultaneous therapeutic functions for cancer treatment. We developed doxorubicin-loaded calcium carbonate (CaCO₃) hybrid nanoparticles (DOX-CaCO₃-MNPs) through a block copolymer templated <i>in situ</i> mineralization approach. The nanoparticles exhibited strong echogenic signals at tumoral acid pH by producing carbon dioxide (CO₂) bubbles and showed excellent echo persistence. <i>In vivo</i> results demonstrated that the DOX-CaCO₃-MNPs generated CO₂ bubbles at tumor tissues sufficient for echogenic reflectivity under a US field. In contrast, the DOX-CaCO₃-MNPs located in the liver or tumor-free subcutaneous area did not generate the CO₂ bubbles necessary for US contrast. The DOX-CaCO₃-MNPs could also trigger the DOX release simultaneously with CO₂ bubble generation at the acidic tumoral environment. The DOX-CaCO₃-MNPs displayed effective antitumor therapeutic activity in tumor-bearing mice. The concept described in this work may serve as a useful guide for development of various theranostic nanoparticles for US imaging and therapy of various cancers