The coexistence of cognitive radio and radio astronomy

An increase of the efficiency of spectrum usage requires the development of new communication techniques. Cognitive radio may be one of those new technique, which uses unoccupied frequency bands for communications. This will lead to more power in the bands and therefore an increasing level of Radio Frequency Interference (RFI), which would cause loss of operation particularly for passive users of the spectrum, such as radio astronomy. This paper will address this issue and will present calculations indicating that the impact of cognitive radio on radio astronomy observations is considerable. The signal levels resulting from cognitive radio systems indicate that spectral bands used for cognitive radio applications cannot be used for radio astronomical research

Assessment of rfi measurements for lofar

In the North-Western part of Europe, ASTRON is building the world-largest largest low-frequency radio telescope. The telescope is based on phased array principles and is known as the LOw Frequency ARray (LOFAR). LOFAR is optimized for detecting astronomical signals in the 30-80 MHz and 120-240 MHz frequency windows. Since this part of the spectrum is in extensive use by others, special care must be taken in the selection of possible out-station sites for LOFAR. RFI measurements were made to be sure that the radio spectrum at the potential out-station locations is suitable for LOFAR operations. An assessment procedure is presented here and specific issues are discussed, such as the impact of Digital Video Broadcast, and wind turbines. The results of\ud the RFI observations has generated a list of specifications for (international) LOFAR out-stations

A novel astronomical application for formation flying small satellites

OLFAR, Orbiting Low Frequency Antennas for Radio Astronomy, will be a space mission to observe the universe frequencies below 30 MHz, as it was never done before with an orbiting telescope. Because of the ionospheric scintillations below 30 MHz and the opaqueness of the ionosphere below 15 MHz, a space mission is the only opportunity for this as yet unexplored frequency range in radio astronomy. The frequency band is scientifically very interesting for exploring the early cosmos at high hydrogen redshifts, the so-called dark-ages and the epoch of reionization, the discovery of planetary and solar bursts in other solar systems, for obtaining a tomographic view of space weather, ultra-high energy cosmic rays and for many other astronomical areas of interest. Because of the low observing frequency the aperture size of the instrument must be in the order of 100 km. This requires a distributed space mission which is proposed to be implemented using formation flying of small satellites. The individual satellites are broken down in five major subsystems: the spacecraft bus, the antenna design, the frontend, backend and data transport. One of the largest challenges is the inter-satellite communication. In this paper the concept and design considerations of OLFAR are presented

Daris, a low-frequency distributed aperture array for radio astronomy in space

DARIS (Distributed Aperture Array for Radio Astronomy in Space) is a radio astronomy space mission concept aimed at observing the low-frequency radio sky in the range 1-10 MHz. Because of the Earth's ionospheric disturbances and opaqueness, this frequency range can only be observed from space. The astronomical science cases include sensitive extragalactic surveys, radio transients such as Jupiter-like burst and Crab-like pulses, and coronal mass ejection tracking. The focus of the DARIS concept study is on feasibility aspects of a distributed aperture synthesis array in space, consisting of small satellite nodes and a mother-ship. The study selected suitable science cases, antenna concepts, communications, signal processing, orbital design, and mission analysis. With current-day technologies a satellite cluster can be built consisting of at least eight satellite nodes and a mother-ship, which could be launched with a Soyuz rocket from Kourou. Such a satellite cluster would open up the last unexplored frequency range for astronomy

SKA antenna systems; outlook for non-astronomy applications

The globally endorsed Square Kilometre Array project primarily aims to advance high sensitivity radio astronomy using a distributed collection of radio telescope stations spiraling outward from the core along three to five arms out to 3000km. This planned highly sensitive instrument covering a frequency range from 70MHz up to 10GHz will be used as wideband, high resolution, wide observing field interferometer of which the first phase will be realized this decade. With these SKA telescope capabilities and with the underlying technologies, there are many space related applications outside the immediate radio astronomy domain especially in the ground segment area. Examples are tracking space debris, precision orbit determination, simultaneous deep space tracking of multiple spacecrafts, GNSS and for other ground segment applications such as search and rescue tracking. After a brief introduction to the SKA, this paper will explore these potential application areas using the SKA based on its underlying approaches in the antenna and receiving subsystems

Generalized Conformal Quantum Mechanics of D0-brane

We study the generalized conformal quantum mechanics of the probe D0-brane in the near horizon background of the bound state of source D0-branes. We elaborate on the relationship of such model to the M theory in the light cone frame.Comment: 14 pages, RevTeX, revised version with added references to appear in Phys. Rev.

SKA antenna systems; Outlook for non-astronomy applications

The globally endorsed Square Kilometre Array project primarily aims to advance high sensitivity radio astronomy using a distributed collection of radio telescope stations spiraling outward from the core along three to five arms out to 3000km. This planned highly sensitive instrument covering a frequency range from 70MHz up to 10GHz will be used as wideband, high resolution, wide observing field interferometer of which the first phase will be realized this decade. With the SKA telescope capabilities and with the underlying technologies, there are many space related applications outside the immediate radio astronomy domain. Examples are tracking space debris, precision orbit determination, simultaneous deep space tracking of multiple spacecrafts, GNSS and other ground segment applications, such as search and rescue tracking. After a brief introduction to the SKA, this paper will explore these potential application areas using the SKA based on its underlying approaches in the antenna and receiving subsystems

Evaluating changes in functioning and psychological distress in visitors of the @ease youth mental health walk-in centres

Background:Highly accessible youth initiatives worldwide aim to prevent worsening of mental health problems, but research into outcomes over time is scarce. Aims:This study aimed to evaluate outcomes and support use in 12- to 15-year-old visitors of the @ease mental health walk-in centres, a Dutch initiative offering free counselling by trained and supervised peers.Method:Data of 754 visitors, collected 2018-2022, included psychological distress (Clinical Outcomes in Routine Evaluation 10 (CORE-10)), social and occupational functioning (Social and Occupational Functioning Assessment Scale (SOFAS)), school absenteeism and support use, analysed with change indicators (first to last visit), and mixed models (first three visits).Results:Among return visitors, 50.5% were female, 79.4% were in tertiary education and 36.9% were born outside of The Netherlands (one-time visitors: 64.7%, 72.9% and 41.3%, respectively). Moreover, 29.9% of return visitors presented with suicidal ideations, 97.1% had clinical psychological distress levels, and 64.1% of the latter had no support in the previous 3 months (one-time visitors: 27.2%, 90.7% and 71.1%, respectively). From visit 1 to 3, psychological distress decreased (β = -3.79, 95% CI -5.41 to -2.18; P &lt; 0.001) and social and occupational functioning improved (β = 3.93, 95% CI 0.51-7.36; P = 0.025). Over an average 3.9 visits, 39.6% improved reliably and 28.0% improved clinically significantly on the SOFAS, which was 28.4% and 8.8%, respectively, on the CORE-10, where 43.2% improved in clinical category. Counselling satisfaction was rated 4.5/5. Conclusions:Reductions in psychological distress, improvements in functioning and high counselling satisfaction were found among @ease visitors, forming a basis for future research with a control group.</p

Evaluating changes in functioning and psychological distress in visitors of the @ease youth mental health walk-in centres

Background:Highly accessible youth initiatives worldwide aim to prevent worsening of mental health problems, but research into outcomes over time is scarce. Aims:This study aimed to evaluate outcomes and support use in 12- to 15-year-old visitors of the @ease mental health walk-in centres, a Dutch initiative offering free counselling by trained and supervised peers.Method:Data of 754 visitors, collected 2018-2022, included psychological distress (Clinical Outcomes in Routine Evaluation 10 (CORE-10)), social and occupational functioning (Social and Occupational Functioning Assessment Scale (SOFAS)), school absenteeism and support use, analysed with change indicators (first to last visit), and mixed models (first three visits).Results:Among return visitors, 50.5% were female, 79.4% were in tertiary education and 36.9% were born outside of The Netherlands (one-time visitors: 64.7%, 72.9% and 41.3%, respectively). Moreover, 29.9% of return visitors presented with suicidal ideations, 97.1% had clinical psychological distress levels, and 64.1% of the latter had no support in the previous 3 months (one-time visitors: 27.2%, 90.7% and 71.1%, respectively). From visit 1 to 3, psychological distress decreased (β = -3.79, 95% CI -5.41 to -2.18; P &lt; 0.001) and social and occupational functioning improved (β = 3.93, 95% CI 0.51-7.36; P = 0.025). Over an average 3.9 visits, 39.6% improved reliably and 28.0% improved clinically significantly on the SOFAS, which was 28.4% and 8.8%, respectively, on the CORE-10, where 43.2% improved in clinical category. Counselling satisfaction was rated 4.5/5. Conclusions:Reductions in psychological distress, improvements in functioning and high counselling satisfaction were found among @ease visitors, forming a basis for future research with a control group.</p