scholarly journals New results from LOFAR

2012 ◽  
Vol 8 (S291) ◽  
pp. 47-52
Author(s):  
Vladislav Kondratiev
Keyword(s):  
The Netherlands ◽  
Radio Telescope ◽  
Low Frequency ◽  
Next Generation ◽  
Frequency Range ◽  
High Quality ◽  
Pulsar Emission ◽  
Science Projects ◽  
Rapid Changes ◽  
Future Science

AbstractThe LOw Frequency Array, LOFAR, is a next generation radio telescope with its core in the Netherlands and elements distributed throughout Europe. It has exceptional collecting area and wide bandwidths at frequencies from 10 MHz up to 250 MHz. It is in exactly this frequency range where pulsars are brightest and also where they exhibit rapid changes in their emission profiles. Although LOFAR is still in the commissioning phase it is already collecting data of high quality. I will present highlights from our commissioning observations which will include: unique constraints on the site of pulsar emission, individual pulse studies, observations of millisecond pulsars, using pulsars to constrain the properties of the magneto-ionic medium and pilot pulsars surveys. I will also discuss future science projects and advances in the observing capabilities.

LOFAR4SW – Space Weather Science and Operations with LOFAR

2021 ◽  
Author(s):  
Hanna Rothkaehl ◽  
Barbara Matyjasiak ◽  
Carla Baldovin ◽  
Mario Bisi ◽  
David Barnes ◽  
...  
Keyword(s):  
The Netherlands ◽  
Radio Telescope ◽  
Space Weather ◽  
Low Frequency ◽  
Point Of View ◽  
Current Status ◽  
Civic Society ◽  
Horizon 2020 ◽  
Final Design ◽  
Areas Of Interest

<p>Space Weather (SW) research is a very important topic from the scientific, operational and civic society point of view. Knowledge of interactions in the Sun-Earth system, the physics behind observed SW phenomena, and its direct impact on modern technologies were and will be key areas of interest.  The LOFAR for Space Weather (LOFAR4SW) project aim is to prepare a novel tool which can bring new capabilities into this domain. The project is realised in the frame of a Horizon 2020 INFRADEV call.  The base for the project is the Low Frequency Array (LOFAR) - the worlds largest low frequency radio telescope, with a dense core near Exloo in The Netherlands and many stations distributed both in the Netherlands and Europe wide with baselines up to 2000 km.  The final design of LOFAR4SW will provide a full conceptual and technical description of the LOFAR upgrade, to enable simultaneous operation as a radio telescope for astronomical research as well as an infrastructure working for Space Weather studies.  In this work we present the current status of the project, including examples of the capabilities of LOFAR4SW and the project timeline as we plan for the Critical Design Review later in 2021.</p>

scholarly journals Pre-selection of the candidate fields for deep imaging of the epoch of reionization with SKA1-low

2020 ◽  
Vol 499 (3) ◽  
pp. 3434-3444
Author(s):  
Qian Zheng ◽  
Xiang-Ping Wu ◽  
Quan Guo ◽  
Melanie Johnston-Hollitt ◽  
Huanyuan Shan ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Low Frequency ◽  
Far Field ◽  
Frequency Range ◽  
High Quality ◽  
Average Surface ◽  
Square Kilometre Array ◽  
Broad Frequency Range ◽  
Deep Imaging ◽  
Selection Of

ABSTRACT The Square Kilometre Array (SKA) will be the first low-frequency instrument with the capability to directly image the structures of the epoch of reionization (EoR). Indeed, deep imaging of the EoR over five targeted fields of 20 sq deg each has been selected as the highest priority science objective for SKA1. Aiming at preparing for this highly challenging observation, we perform an extensive pre-selection of the ‘quietest’ and ‘cleanest’ candidate fields in the southern sky to be suited for deep imaging of the EoR using existing catalogues and observations over a broad frequency range. The candidate fields should meet a number of strict criteria to avoid contaminations from foreground structures and sources. The candidate fields should also exhibit both the lowest average surface brightness and smallest variance to ensure uniformity and high-quality deep imaging over the fields. Our selection eventually yields a sample of 7 ‘ideal’ fields of 20 sq deg in the southern sky that could be targeted for deep imaging of the EoR. Finally, these selected fields are convolved with the synthesized beam of SKA1-low stations to ensure that the effect of sidelobes from the far-field bright sources is also weak.

scholarly journals 21. The low-frequency spectrum of Cygnus A and Cassiopeia A

1957 ◽  
Vol 4 ◽  
pp. 145-147
Author(s):  
R. J. Lamden ◽  
A. C. B. Lovell
Keyword(s):  
Lower Limit ◽  
Radio Telescope ◽  
Low Frequency ◽  
Radio Sources ◽  
Pencil Beam ◽  
Frequency Range ◽  
Present Communication ◽  
Cassiopeia A ◽  
Cygnus A ◽  
Radio Transmitters

The published measurements of the intensity of the radio sources cover a frequency range down to a lower limit of 22·6 Mc./s., at which measurements have been made on Cygnus and Cassiopeia by Hey and Hughes (1954)[1]. Information about the spectrum at still lower frequencies is difficult to obtain because of interference arising from ionospheric reflexion of distant radio transmitters. Some of this trouble can be alleviated by using a narrow pencil-beam radio telescope for reception and the present communication describes measurements made on frequencies of 16·5, 19·0, 22·6 and 30·0 Mc./s. using the 218 ft. transit radio telescope at Jodrell Bank.

LOFAR4SpaceWeather (LOFAR4SW) – Increasing European Space-Weather Capability with Europe’s Largest Radio Telescope: Beyond the Detailed Design Review (DDR)

2020 ◽  
Author(s):  
Mario M. Bisi ◽  
Mark Ruiter ◽  
Richard A. Fallows ◽  
René Vermeulen ◽  
Stuart C. Robertson ◽  
...  
Keyword(s):  
The Netherlands ◽  
Radio Telescope ◽  
Space Weather ◽  
Low Frequency ◽  
Regular Space ◽  
The Sun ◽  
Weather System ◽  
Design Review ◽  
Detailed Design ◽  
Horizon 2020

<p>The Low Frequency Array (LOFAR) is an advanced phased-array radio-telescope system based across Europe.  It is capable of observing over a wide radio bandwidth of ~10-250 MHz at both high spatial and temporal resolutions.  LOFAR has capabilities that enable studies of many aspects of what we class as space weather (from the Sun to the Earth and afar) to be progressed beyond today’s state-of-the-art.   However, with the present setup and organisation behind the operations of the telescope, it can only be used for space-weather campaign studies with limited triggering availability.  This severely limits our ability to effectively use LOFAR to contribute to space-weather monitoring/forecast beyond its core strength of enabling world-leading scientific research.  LOFAR itself is made up of a dense core of 24 stations near Exloo in The Netherlands with an additional 14 stations spread across the northeast Netherlands.  In addition to those, there are a further 13 stations based internationally across Europe.  These international stations are, currently, six in Germany, three in northern Poland, and one each in France, Ireland, Latvia, Sweden, and the UK.  Further sites are under preparations (for example, in Italy).</p><p> </p><p>We are undertaking a Horizon 2020 (H2020) INFRADEV design study to undertake investigations into upgrading LOFAR to allow for regular space-weather science/monitoring observations in parallel with normal radio-astronomy/scientific operations.  This project is called the LOFAR For Space Weather (LOFAR4SW) project (see: http://lofar4sw.eu/).  Our work involves all aspects of scientific and engineering work along with end-user and political engagements with various stakeholders.  This is with the full recognition that space weather is a worldwide threat with varying local, regional, continent-wide impacts, and also global impacts – and hence is a global concern.</p><p> </p><p>Here, we summarise the most-recent key aspects of the LOFAR4SW progress including outputs/progress following the Detailed Design Review (DDR) that took place at ASTRON, The Netherlands, in March 2020, as well as the implementation of recommendations from the earlier Preliminary Design Review (PDR) with an outlook to the LOFAR4SW User Workshop the week following EGU 2020.  We also aim to briefly summarise a key set of the longer-term goals envisaged for LOFAR to become one of Europe’s most-comprehensive space-weather observing systems capable of shedding new light on several aspects of the space-weather system, from the Sun to the solar wind to Jupiter and Earth’s ionosphere.</p>

scholarly journals Radio spectra of millisecond pulsars

2017 ◽  
Vol 13 (S337) ◽  
pp. 358-359
Author(s):  
Vladislav Kondratiev ◽  
Anna Bilous ◽  
Keyword(s):  
Low Frequency ◽  
Flux Measurement ◽  
Power Laws ◽  
Published Data ◽  
Frequency Range ◽  
Pulsar Emission ◽  
Millisecond Pulsars ◽  
Pulsar Radio ◽  
Broadband Radio ◽  
Timing Data

AbstractBoth the physics of the pulsar emission mechanism and free-free absorption in the intervening interstellar medium can be tested with the pulsar radio spectra. We have built on our previous work on describing LOFAR population of millisecond pulsars (MSPs; Kondratiev et al. 2016) and HBA census of slow pulsars (Bilous et al. 2016) and present the study of radio spectra of the MSPs with a special attention on the low-frequency turnover. Using LOFAR timing data allowed us to measure flux densities of many MSPs over time span of up to three years in the frequency range 110–188 MHz. This provided more reliable estimates of mean flux densities and spectra reducing the influence of refractive scintillation, ionosphere and other factors on a single flux measurement. Together with published data at other radio frequencies we constructed pulsars’ spectra and fitted them with single or broken power-laws. We discuss the obtained spectra and their fits, paying special attention to the low-frequency turnover, and compare broadband radio spectra of MSPs to those of normal pulsars.

scholarly journals LOFAR in Germany

2007 ◽  
Vol 5 ◽  
pp. 407-412
Author(s):  
W. Reich
Keyword(s):  
The Netherlands ◽  
Radio Telescope ◽  
Low Frequency ◽  
Digital Radio ◽  
Long Wavelength ◽  
Basic Properties

Abstract. The LOw Frequency ARray – LOFAR – is a new fully digital radio telescope designed for frequencies between 30 MHz and 240 MHz centered in the Netherlands. In May 2006 ten German institutes formed the German LOng Wavelength consortium – GLOW – to coordinate its contributions and scientific interests to the LOFAR project. The first LOFAR station CS1 was installed in summer 2006 near Exloo/Netherlands. The second station IS-G1 is presently been placed in the immediate vicinity of the Effelsberg 100-m radio telescope near Bad Münstereifel/Germany. This contribution briefly describes the basic properties and aims of LOFAR, the aims of the GLOW consortium and the actual activities to install a LOFAR station at the Effelsberg site.

The Llanherne Low Frequency Radio Telescope

1972 ◽  
Vol 2 (3) ◽  
pp. 135-137 ◽  
Author(s):  
G. R. A. Ellis
Keyword(s):  
Lower Limit ◽  
Radio Telescope ◽  
Radio Astronomy ◽  
Angular Resolution ◽  
Low Frequency ◽  
Earth Satellite ◽  
The Sun ◽  
Frequency Range ◽  
Interstellar Absorption ◽  
The Galaxy

A large proportion of the easily accessible radio astronomy spectrum lies between 50 MHz and a lower limit of about 1 MHz set by interstellar absorption. The features of the spectrum in this frequency range, from sources such as the galaxy, extragalactic sources, pulsars, the Sun and Jupiter, remain only partially explored mainly owing to the large sizes of telescopes necessary to obtain adequate angular resolution and sensitivity. In addition, below 20 MHz, interference from man-made radiation and from the ionosphere severely hinders observations. At the lowest frequencies, the effects of the ionosphere can be overcome by using earth satellite telescopes at the expense of greatly increased difficulty in attaining sufficient telescope aperture.

scholarly journals Cosmic Microwave Background at Low Frequencies

2002 ◽  
Vol 199 ◽  
pp. 58-65 ◽  
Author(s):  
R. Subrahmanyan
Keyword(s):  
Cosmic Microwave Background ◽  
Radio Telescope ◽  
Low Frequency ◽  
Cosmological Models ◽  
Large Element ◽  
Radio Telescopes ◽  
Next Generation ◽  
Microwave Background ◽  
Low Frequencies

The next generation low-frequency radio telescopes may probe cosmological models by means of observations of the cosmic microwave background (CMB). I discuss the prospects for observations of CMB imprints —- recombination lines from the epoch of recombination, μ distortions and angular temperature anisotropies —- at low frequencies. A future low-frequency radio telescope, like the proposed SKA, may be capable of attempting some difficult CMB measurements because of the large collecting area and large element numbers; however, this will require a telescope design that will allow specialized calibration strategies and will give emphasis to the control of spurious responses.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

Dynamic Damping and Stiffness Characteristics of the Rolling Tire

2001 ◽  
Vol 29 (4) ◽  
pp. 258-268 ◽  
Author(s):  
G. Jianmin ◽  
R. Gall ◽  
W. Zuomin
Keyword(s):  
Dynamic Behavior ◽  
Variable Parameter ◽  
Low Frequency ◽  
Vertical Load ◽  
Frequency Range ◽  
Inflation Pressure ◽  
Vehicle Simulation ◽  
Dynamic Damping ◽  
Speed Range ◽  
Stiffness Characteristics

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

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