Showing papers by "John Morgan published in 2023"

Probing Gas Kinematics towards the High-mass Protostellar Object G358.46−0.39

Abstract: We investigated the nature of protostellar objects in G358.46−0.39 and their gas kinematics using ALMA data, with the aim of understanding the ongoing star formation activities in the region. The dust continuum map reveals multiple cores (MM1a, MM1b, MM1c and MM2) dominated by MM1a, with no detectable free-free emission. We calculated the masses and the column densities of the various objects (MM1a, MM1b, MM1c and MM2). A total of 33, 10, 10 and 9 molecular transitions are detected towards MM1a, MM1b, MM1c and MM2, respectively. The differences in the number of molecular lines detected towards each of the cores support different excitation conditions at different positions. We derived the kinetic temperature ranges of MM1a, MM1b, MM1c and MM2 to be ∼ 96 − 118 K, 96 − 114 K, 72 − 74 K and 80 − 84 K, respectively. A highly collimated bipolar outflow traced by 12CO emission is observed to be associated with MM1a, with knots along the outflow lobes, which could be an indication of episodic ejection. The C17O emission is observed to be likely tracing a slowly rotating envelope of gas around MM1a. The velocity field map of CH3OH (22, 1 − 31, 2) emission suggests the presence of a rotating structure, possibly a disk. The physical and kinematic properties of MM1a are strong indication of a massive young stellar object, with ongoing outflow activity and accretion in its early stage of formation.

Transmitter Design Considerations for a Small Satellite Multi-Frequency Antenna

Abstract: This paper presents a transmitter design strategy for integrating several high efficiency Class-E RF amplifiers for small satellite subsystems operating at different frequencies to a single antenna. An electrically small monopole/dipole type antenna is preferred for small satellites. However, integrating Class-E RF amplifiers to the low antenna resistance and high capacitive reactance of this class of antenna presents two challenges. First, matching networks with large impedance transformation ratios that are impractically sensitive to circuit and antenna port variations are necessary to achieve the high optimum load resistance of conventional low power Class-E design solutions. Second, a low antenna resistance results in comparatively significant real circuit and components resistive losses which means that the Class-E amplifier efficiency becomes a strong function of the dissipative losses as well as the Class-E waveforms. We propose a transmitter design that is based on a novel Class-E amplifier design strategy, and a multiplexer design technique that builds impedance matching into each multiplexer branch that can be adjusted without altering the multiplexers filtering characteristics. We reduce the impedance transformation ratio required by introducing a Class-E amplifier design strategy that tailors the optimum fundamental load impedance of the amplifier to the antenna impedance by varying three Class-E design parameters which control the transistor voltage and current waveforms. To realize high power added efficiency, we propose utilizing the adjustable impedance matching within each multiplexer branch to predictably and independently optimize each Class-E amplifiers load impedance for real circuit and components in the multiplexer configuration without causing an unwanted deviation in the performance of the remaining Class-E amplifiers multiplexed to the common antenna port. This is achieved because the independence of each impedance match to the multiplexers filtering characteristics ensures that optimizing each amplifiers load impedance does not alter how each amplifier loads the common antenna port. To demonstrate the transmitter design strategy, an example transmitter design operating at 144.2 MHz, 432.6 MHz, and 1297.8 MHz was synthesized and simulated for a tri-band 3U CubeSat antenna which has been designed for Ionospheric remote sensing. The simulation results show that the transmitter design strategy can achieve a power added efficiency and power gain of greater than 54.9% and 13.1 dB respectively for an antenna exhibiting a resistance as low as 1.07Ω.

Detection and Characterization of a Coronal Mass Ejection Using Interplanetary Scintillation Measurements From the Murchison Widefield Array

Abstract: We have shown previously that the Murchison Widefield Array (MWA), can detect 100s of Interplanetary Scintillation (IPS) sources simultaneously across a field of view (FoV) ∼30° in extent. To test if we can use this capability to track heliospheric structures, we undertook a search of 88 hr of MWA IPS data, and identified an observation likely to have a significant Coronal Mass Ejection (CME) in the FoV. We demonstrate that in a single 5‐min MWA observation we are able to localize and image a CME ∼33 hr after launch at an elongation of ∼37° from the Sun. We use IPS observables to constrain the kinematics of the CME, and describe how MWA IPS observations can be used in the future to make a unique contribution to heliospheric modeling efforts.