MHz VHF Research Articles

Prevention of septic ventilatory depression with naloxone

TARA (Telescope Array Radar) is a cosmic ray radar detection experiment colocated with Telescope Array, the conventional surface scintillation detector (SD) and fluorescence telescope detector (FD) near Delta, Utah, U.S.A. The TARA detector combines a 40 kW, 54.1 MHz VHF transmitter and high-gain transmitting antenna which broadcasts the radar carrier over the SD array and within the FD field of view, towards a 250 MS/s DAQ receiver. TARA has been collecting data since 2013 with the primary goal of observing the radar signatures of extensive air showers (EAS). Simulations indicate that echoes are expected to be short in duration (∼ 10 µs) and exhibit rapidly changing frequency, with rates on the order 1 MHz/µs. The EAS radar cross-section (RCS) is currently unknown although it is the subject of over 70 years of speculation. A novel signal search technique is described in which the expected radar echo of a particular air shower is used as a matched filter template and compared to waveforms obtained by triggering the radar DAQ using the Telescope Array fluorescence detector. No evidence for the scattering of radio frequency radiation by EAS is obtained to date. We report the first quantitative RCS upper limits using EAS that triggered the Telescope Array Fluorescence Detector.

VHF amplitude scintillations and associated electron content depletions as observed at Arequipa, Peru

Results of observations on occurrences and behavior of 137 MHz VHF amplitude scintillations and associated ionospheric electron content depletions obtained at Arequipa, Peru (16.4°S, 71.5°W, geogr.; 9°S dip) during the recent solar maximum period 1979–1980 are presented. The seasonal variation of scintillations shows the usual deep minimum during May–July and a prominent maximum in December, when scintillations also persist for a long period of time, sometimes even beyond sunrise. Ionospheric irregularities have been found to occur in distinct patches whose extent varies with season. During the December solstice the average VHF scintillation patch duration is about 6 h, while numerous patches of much shorter duration are observed in equinoctial months. The depletions in the height integrated ionospheric electron content associated with scintillations have a typical duration of 10–15 min and amplitude less than 5 × 10 16 el m −2, although depletions with an amplitude as large as 20 × 10 16 elm −2 and with a duration of more than 30 min are sometimes encountered. The pre-midnight amplitude scintillations and associated electron content depletions could be identified with range type spread- F, as established earlier, while the association of post-midnight VHF scintillations with frequency type spread- F is found to be a special feature observed during years of very high solar activity. The seasonal dependence of irregularity patch dimensions is examined in terms of variations of drifts in the post-sunset equatorial ionosphere.