Tracking of an electron beam through the solar corona with LOFAR

© ESO 2018. The Sun's activity leads to bursts of radio emission, among other phenomena. An example is type-III radio bursts. They occur frequently and appear as short-lived structures rapidly drifting from high to low frequencies in dynamic radio spectra. They are usually interpreted as signatures of beams of energetic electrons propagating along coronal magnetic field lines. Here we present novel interferometric LOFAR (LOw Frequency ARray) observations of three solar type-III radio bursts and their reverse bursts with high spectral, spatial, and temporal resolution. They are consistent with a propagation of the radio sources along the coronal magnetic field lines with nonuniform speed. Hence, the type-III radio bursts cannot be generated by a monoenergetic electron beam, but by an ensemble of energetic electrons with a spread distribution in velocity and energy. Additionally, the density profile along the propagation path is derived in the corona. It agrees well with three-fold coronal density model by (1961, ApJ, 133, 983)

Gender differences in the use of cardiovascular interventions in HIV-positive persons; the D:A:D Study

Peer reviewe

LOFAR 144-MHz follow-up observations of GW170817

ABSTRACT We present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by Advanced LIGO–Virgo. These data, with a central frequency of 144 MHz, were obtained with LOFAR, the Low-Frequency Array. The maximum elevation of the target is just 13${_{.}^{\circ}}$7 when observed with LOFAR, making our observations particularly challenging to calibrate and significantly limiting the achievable sensitivity. On time-scales of 130–138 and 371–374 d after the merger event, we obtain 3σ upper limits for the afterglow component of 6.6 and 19.5 mJy beam−1, respectively. Using our best upper limit and previously published, contemporaneous higher frequency radio data, we place a limit on any potential steepening of the radio spectrum between 610 and 144 MHz: the two-point spectral index $\alpha ^{610}_{144} \gtrsim$ −2.5. We also show that LOFAR can detect the afterglows of future binary neutron star merger events occurring at more favourable elevations.</jats:p

NOIRE study report : towards a low frequency radio interferometer in space

Ground based low frequency radio interferometers have been developed in the last decade and are providing the scientific community with high quality observations. Conversely, current radioastronomy instruments in space have a poor angular resolution with single point observation systems. Improving the observation capabilities of the low frequency range (a few kHz to 100 MHz) requires to go to space and to set up a space based network of antenna that can be used as an interferometer. \u3cbr/\u3eWe present the outcome of the NOIRE (Nanosatellites pour un Observatoire Interf\'erom\'etrique Radio dans l'Espace / Nanosatellites for a Radio Interferometer Observatory in Space) study which assessed, with help of CNES PASO (Architecture Platform for Orbital Systems is CNES' cross-disciplinary team in charge of early mission and concept studies), the feasibility of a swarm of nanosatellites dedicated to a low frequency radio observatory. With such a platform, space system engineering and instrument development must be studied as a whole: each node is a sensor and all sensors must be used together to obtain a measurement. The study was conducted on the following topics: system principle and concept (swarm, node homogeneity); Space and time management (ranging, clock synchronization); Orbitography (Moon orbit, Lagrange point options); Telecommunication (between nodes and with ground) and networking; Measurements and processing; Propulsion; Power; Electromagnetic compatibility. \u3cbr/\u3eNo strong show-stopper was identified during the preliminary study, although the concept is not yet ready. Several further studies and milestones are identified. The NOIRE team will collaborate with international teams to try and build this next generation of space systems

NOIRE study report : towards a low frequency radio interferometer in space

\u3cp\u3eGround based low frequency radio interferometers have been developed in the last decade and are providing the scientific community with high quality observations. Conversely, current radioastronomy instruments in space have a poor angular resolution with single point observation systems. Improving the observation capabilities of the low frequency range (a few kHz to 100 MHz) requires to go to space and to set up a space based network of antenna that can be used as an interferometer. We present the outcome of the NOIRE (Nanosatellites pour un Observatoire Interférométrique Radio dans l'Espace / Nanosatellites for a Radio Interferometer Observatory in Space) study which assessed, with help of CNES' PASO \u3csup\u3e2\u3c/sup\u3e, the feasibility of a swarm of nanosatellites dedicated to a low frequency radio observatory. With such a platform, space system engineering and instrument development must be studied as a whole: each node is a sensor and all sensors must be used together to obtain a measurement. The study was conducted on the following topics: system principle and concept (swarm, node homogeneity); Space and time management (ranging, clock synchronization); Orbitography (Moon orbit, Lagrange point options); Telecommunication (between nodes and with ground) and networking; Measurements and processing; Propulsion; Power; Electromagnetic compatibility. No strong show-stopper was identified during the preliminary study, although the concept is not yet ready. Several further studies and milestones are identified. The NOIRE team will collaborate with international teams to try and build this next generation of space systems. \u3c/p\u3

Design of an ultra low frequency CubeSat antenna payload for radio astronomy in space:state of the art

This paper presents a brief overview of the state of the art for the design of an ultra low frequency antenna (80 kHz-30 MHz) as a payload for a CubeSat used for radio astronomy in space. Current ultra low frequency radio astronomy antenna designs are shown along with a discussion about the basis for future research. One of the designs, the spiral antenna is discussed in more detail

System design of a low-power wireless link for neural recording in a visual prosthesis

Restoring visual function in blind people through technology can be challenging but very beneficial in improving the quality of life. For most cases of blindness, the only option is to stimulate the visual cortex directly. Such a system requires external cameras, image processing and implanted electrodes. Powering, stimulating the brain, and recording neural activity is preferably done wirelessly to avoid infections. The wireless link for sending the neural activity (uplink) out of the brain is vital as the neural recording is for calibration and monitoring. Uplink requirements on (low-power) consumption at the implanted transmitter and a high data rate lead us to compare two promising wireless link options. A system-level analysis is carried out on the feasibility of impulse radio ultrawideband (IR-UWB) by a worst-case link budget. A low power CMOS IR-UWB transmitter consisting of an on-off keying (OOK) modulator and an impulse generator is proposed closely, fulfilling low-power and high data rate requirements

Low-power communication for an implanted intracortical visual prosthesis

Assisting visually impaired people to see again using technology is quite challenging, especially for cases where most of the visual pathway is damaged. The only viable option is to stimulate the visual cortex directly. Sending the stimulation data to electrodes on the visual cortex is preferably done wirelessly to avoid infections and to ease mobility. The receiver on the implant poses a challenge in design, as the power supply is limited. In this paper, vital system requirements for this communication link are discussed. A low power system-level approach is presented which seeks to avoid power hungry components. This leads to the consideration of a bandpass sampled phase shift keying scheme via an inductive link. We propose a non-coherent digital demodulator, which relaxes the need for low phase noise oscillators which consume more power and, also avoids the use of phase locks loops. The overall communication system has a potential to deliver stimulation data to the implant side in the presence of simultaneous power transfer and reception of recorded data from the brain. Index Terms—Low-power, Inductive link, Non-coherent digital demodulator, Phase shift keying, Intracortical Visual Prosthesi

Low-power BPSK inductive data link for an implanted intracortical visual prosthesis

In making visually impaired people see again, for most cases the only option is to stimulate the visual cortex. In building such a system, it is desired that the communication to/from the implant and powering be done wirelessly to avoid infections. For the downlink, which is sending stimulation data to the implanted electrode, bandpass-sampled binary phase shift keying (BPSK) is chosen due to its potential for low-power consumption at its digital receiver. However, since an inductive link is most suited, designing practical inductive links with a flat band region to avoid poor phase transition and also refining the reset timing for imperfect transition times as well as designing low-power custom 1- bit Analog-to-digital converter is crucial. The bandpass-sampled BPSK system is designed and simulated at circuit level in Cadence using 180 nm CMOS technology at data rates of 0.5-4 Mbps and carrier frequency of 5-12 MHz. The improved bandpass-sampled BPSK system meets the requirements on data-rate, low-power consumption and robustness and is an integral part of the overall wireless communication and powering of the implanted intracortical visual prosthesis