1,404 research outputs found
Solar and Heliospheric Physics with the Square Kilometre Array
The fields of solar radiophysics and solar system radio physics, or radio
heliophysics, will benefit immensely from an instrument with the capabilities
projected for SKA. Potential applications include interplanetary scintillation
(IPS), radio-burst tracking, and solar spectral radio imaging with a superior
sensitivity. These will provide breakthrough new insights and results in topics
of fundamental importance, such as the physics of impulsive energy releases,
magnetohydrodynamic oscillations and turbulence, the dynamics of post-eruptive
processes, energetic particle acceleration, the structure of the solar wind and
the development and evolution of solar wind transients at distances up to and
beyond the orbit of the Earth. The combination of the high spectral, time and
spatial resolution and the unprecedented sensitivity of the SKA will radically
advance our understanding of basic physical processes operating in solar and
heliospheric plasmas and provide a solid foundation for the forecasting of
space weather events.Comment: 15 pages, Proceedings of Advancing Astrophysics with the Square
Kilometre Array (AASKA14). 9 -13 June, 2014. Giardini Naxos, Italy. Online at
http://pos.sissa.it/cgi-bin/reader/conf.cgi?confid=215, id.16
Potential for Solar System Science with the ngVLA
Radio wavelength observations of solar system bodies are a powerful method of
probing many characteristics of those bodies. From surface and subsurface, to
atmospheres (including deep atmospheres of the giant planets), to rings, to the
magnetosphere of Jupiter, these observations provide unique information on
current state, and sometimes history, of the bodies. The ngVLA will enable the
highest sensitivity and resolution observations of this kind, with the
potential to revolutionize our understanding of some of these bodies. In this
article, we present a review of state-of-the-art radio wavelength observations
of a variety of bodies in our solar system, varying in size from ring particles
and small near-Earth asteroids to the giant planets. Throughout the review we
mention improvements for each body (or class of bodies) to be expected with the
ngVLA. A simulation of a Neptune-sized object is presented in Section 6.
Section 7 provides a brief summary for each type of object, together with the
type of measurements needed for all objects throughout the Solar System
Millimeter-Wave Beam-Formed Array Antenna for Connected Driving Scenarios
Connected vehicles are the next frontier in massive mobile communications. The automotive industry is pursuing the exchange of essential information between vehicles, road infrastructure and all kind of external agents (V2X) for improving safety and traffic efficiency. Sharing data such as the position or kinematics, for example, can be used by other road participants to make a better prediction of hazardous situations. Even though, to meet the automotive-grade requirements, such as reliability during information exchange, or to support highly-automated applications such as platooning, high levels of reliability during information exchange are required. These cannot be sustained by the sub-6 GHz V2X band so it is therefore necessary to relocate to other bands such as the millimeter- Wave (mmWave) Frequency Range 2 (FR2) band, where larger bandwidths are available. The goal of this project is to develop a mmWave beam-formed array antenna for connected driving scenarios. With this framework, it will be possible to obtain metrics and understand how channel measurements can be used to improve V2X communications, by using for instance, di?erent antenna setups or combining di?erent beamforming strategies i.e. beam steering or beam shaping in diverse down-scaled urban scenarios. Based on this, it is largely intended to use physical layer measurements as a promising first barrier to improve the quality of V2X communications. MmWave communications for advanced connected and automated vehicle driving scenarios have drawn significant attention for their adaptability in a wide variety of applications. However, when Line-Of-Sight (LOS) and link stability cannot be assured in urban scenarios, the exchange of information between two vehicles becomes more complex and sometimes even dangerous if the information sent through the channel is not reliable. In this thesis, an improved mmWave beamforming method based on array antenna beam steering is presented. By using a channel-aware imaging algorithm, it aims to solve in large part the above-mentioned problematic by finding the most reliable path in non Line-Of- Sight (NLOS) scenarios. Thus, link stability over road infrastructures might be potentially improved besides enhancing safe-channel communications and traffic efficiency
SKA Weak Lensing II: Simulated Performance and Survey Design Considerations
We construct a pipeline for simulating weak lensing cosmology surveys with
the Square Kilometre Array (SKA), taking as inputs telescope sensitivity
curves; correlated source flux, size and redshift distributions; a simple
ionospheric model; source redshift and ellipticity measurement errors. We then
use this simulation pipeline to optimise a 2-year weak lensing survey performed
with the first deployment of the SKA (SKA1). Our assessments are based on the
total signal-to-noise of the recovered shear power spectra, a metric that we
find to correlate very well with a standard dark energy figure of merit. We
first consider the choice of frequency band, trading off increases in number
counts at lower frequencies against poorer resolution; our analysis strongly
prefers the higher frequency Band 2 (950-1760 MHz) channel of the SKA-MID
telescope to the lower frequency Band 1 (350-1050 MHz). Best results would be
obtained by allowing the centre of Band 2 to shift towards lower frequency,
around 1.1 GHz. We then move on to consider survey size, finding that an area
of 5,000 square degrees is optimal for most SKA1 instrumental configurations.
Finally, we forecast the performance of a weak lensing survey with the second
deployment of the SKA. The increased survey size (3\,steradian) and
sensitivity improves both the signal-to-noise and the dark energy metrics by
two orders of magnitude.Comment: 15 pages, 11 figures, 1 table. Comments welcome. Updated to match
published versio
Millimeter-wave and terahertz imaging techniques
This thesis presents the development and assessment of imaging techniques in the millimeterwave (mmW) and terahertz frequency bands. In the first part of the thesis, the development of a 94 GHz passive screener based on a total-power radiometer (TPR) with mechanical beamscanning is presented. Several images have been acquired with the TPR screener demonstrator, either in indoor and outdoor environments, serving as a testbed to acquire the know-how required to perform the research presented in the following parts of the thesis.
In the second part of the thesis, a theoretical research on the performance of near-field passive screeners is described. This part stands out the tradeoff between spatial and radiometric resolutions taking into account the image distortion produced by placing the scenario in
the near-field range of the radiometer array. In addition, the impact of the decorrelation effect in the image has been also studied simulating the reconstruction technique of a synthetic aperture radiometer. Guidelines to choose the proper radiometer depending on the application, the
scenario, the acquisition speed and the tolerated image distortion are given in this part.
In the third part of the thesis, the development of a correlation technique with optical processing applicable to millimeter-wave interferometric radiometers is described. The technique is capable of correlating wide-bandwidth signals in the optical domain with no loss of radiometric sensitivity. The theoretical development of the method as well as measurements validating the suitability to correlate radiometric signals are presented in this part.
In the final part of the thesis, the frequency band of the imaging problem is increased to frequencies beyond 100 GHz, covering the THz band. In this case the research is centered in tomographic techniques that include spectral information of the samples in the reconstructed
images. The tomographic algorithm can provide detection and identification of chemical compounds that present a certain spectral footprint in the THz frequency band.Postprint (published version
High-resolution radio observations of SNR 1987A at high frequencies
We present new imaging observations of the remnant of Supernova (SN) 1987A at
44 GHz, performed in 2011 with the Australia Telescope Compact Array (ATCA).
The 0\farcs35\times0\farcs23 resolution of the diffraction-limited image is
the highest achieved to date in high-dynamic range. We also present a new ATCA
image at 18 GHz derived from 2011 observations, which is super-resolved to
0\farcs25. The flux density is 402 mJy at 44 GHz and 816 mJy at 18
GHz. At both frequencies, the remnant exhibits a ring-like emission with two
prominent lobes, and an east-west brightness asymmetry that peaks on the
eastern lobe. A central feature of fainter emission appears at 44 GHz. A
comparison with previous ATCA observations at 18 and 36 GHz highlights higher
expansion velocities of the remnant eastern side. The 18-44 GHz spectral index
is (). The spectral index map
suggests slightly steeper values at the brightest sites on the eastern lobe,
whereas flatter values are associated with the inner regions. The remnant
morphology at 44 GHz generally matches the structure seen with contemporaneous
X-ray and H observations. Unlike the H emission, both the radio
and X-ray emission peaks on the eastern lobe. The regions of flatter spectral
index align and partially overlap with the optically-visible ejecta. Simple
free-free absorption models suggest that emission from a pulsar wind nebula or
a compact source inside the remnant may now be detectable at high frequencies,
or at low frequencies if there are holes in the ionised component of the
ejecta.Comment: References updated. High resolution version may be found at
http://ict.icrar.org/store/staff/gio/Papers/Zanardo_2013.pd
Wireless sensor systems in indoor situation modeling II (WISM II)
fi=vertaisarvioimaton|en=nonPeerReviewed
Radio emission from Supernova Remnants
The explosion of a supernova releases almost instantaneously about 10^51 ergs
of mechanic energy, changing irreversibly the physical and chemical properties
of large regions in the galaxies. The stellar ejecta, the nebula resulting from
the powerful shock waves, and sometimes a compact stellar remnant, constitute a
supernova remnant (SNR). They can radiate their energy across the whole
electromagnetic spectrum, but the great majority are radio sources. Almost 70
years after the first detection of radio emission coming from a SNR, great
progress has been achieved in the comprehension of their physical
characteristics and evolution. We review the present knowledge of different
aspects of radio remnants, focusing on sources of the Milky Way and the
Magellanic Clouds, where the SNRs can be spatially resolved. We present a brief
overview of theoretical background, analyze morphology and polarization
properties, and review and critical discuss different methods applied to
determine the radio spectrum and distances. The consequences of the interaction
between the SNR shocks and the surrounding medium are examined, including the
question of whether SNRs can trigger the formation of new stars. Cases of
multispectral comparison are presented. A section is devoted to reviewing
recent results of radio SNRs in the Magellanic Clouds, with particular emphasis
on the radio properties of SN 1987A, an ideal laboratory to investigate
dynamical evolution of an SNR in near real time. The review concludes with a
summary of issues on radio SNRs that deserve further study, and analyzing the
prospects for future research with the latest generation radio telescopes.Comment: Revised version. 48 pages, 15 figure
Very long baseline interferometry with the SKA
Adding VLBI capability to the SKA arrays will greatly broaden the science of the SKA, and is feasible within the current specifications. SKA-VLBI can be initially implemented by providing phased-array outputs for SKA1-MID and SKA1-SUR and using these extremely sensitive stations with other radio telescopes, and in SKA2 by realising a distributed configuration providing baselines up to thousands of km, merging it with existing VLBI networks. The motivation for and the possible realization of SKA-VLBI is described in this paper
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