Ionospheric effects on terrestrial communications :Working Group 3 overview

Telecommunications via ionospheric reflection of radio signals of ground-based transmitters are a traditional area. However, this technique is still in use in telecommunications, broadcasting, etc. Various problems have not yet been solved and some of them were studied in Working Group 3 (WG3). Structure of WG 3 and the terms of reference of its four working packages are described in the introductory paper by Zolesi and Cander (2004). Here we describe the main results achieved in COST 271 in the following areas: i) large-scale fluctuations of planetary and gravity waves; ii) development of a new type of HF channel simulator; iii) geomagnetic storm effects on the F1-region ionosphere; iv) the sporadic E-layer and spread-F phenomena; v) the HF radio wave propagation over northerly paths; vi) how to increase the bit rate in ionospheric radio links. In general, substantial progress was achieved but some problems remain open for future investigations

COST 296 MIERS: Mitigation of Ionospheric Effects on Radio Systems

The COST 296 Action MIERS (Mitigation of Ionospheric Effects on Radio Systems) within the ionospheric community has the objectives, embodied in the Memorandum of Understanding (MoU), to develop an increased knowledge of the effects imposed by the ionosphere on practical radio systems, and the development and implementation of techniques to mitigate the deleterious effects of the ionosphere on such systems. This introductory paper summarizes briefly the background and historical context of COST 296 and outlines the main objectives, working methods and structure. It also lists the participating countries and institutions, the Management Committee (MC) Meetings, the Workshops, Short-term Scientific Missions. In addition, the paper discusses the dissemination activities and the collaboration among the participating institutions and researchers, before outlining the content of the Final Report

COST 296 MIERS: conclusion

The need for more reliable and efficient communications services, especially those involving ionospheric HF communications and navigational systems, imposes increasing demand for a better knowledge of the effects imposed by the Earth’s upper atmosphere and ways to mitigate disturbing effects. Temporal and spatial changes in the upper atmosphere act to limit and degrade the performance of terrestrial and Earth-space radio systems in many different ways and this is why mitigation activities must involve several topics like ionospheric monitoring and modeling, development of new hardware for communication systems and new propagation simulator, measurements and modeling of ionospheric Total Electron Content (TEC) and ionospheric scintillations, using in particular the Global Positioning System (GPS). The European ionospheric community has long been aware that cooperation research on an international basis is essential to deal with such complex issues. In particular, international cooperation is required for the collection of data, in both the real-time and in retrospective modes, the development and verification of new methods to improve the performance of both operational and future terrestrial and Earth-space communication systems and the exchange of expertise on space plasma effects on Global Navigation Satellite Systems (GNSS). In this context the COST 296 Action MIERS on the «Mitigation of Ionospheric Effects on Radio Systems» has made a significant impact in a number of areas

Creation and pinning of vortex-antivortex pairs

Computer modeling is reported about the creation and pinning of a magnetic vortex-antivortex (V-AV) pair in a superconducting thin film, due to the magnetic field of a vertical magnetic dipole above the film, and two antidot pins inside the film. For film thickness $= 0.1\xi$, $\kappa = 2$, and no pins, we find the film carries two V-AV pairs at steady state in the imposed flux range $2.10\Phi_0 < \Phi^+ < 3.0\Phi_0$, and no pairs below. With two antidot pins suitably introduced into the film, a single V-AV pair can be stable in the film for $\Phi^+ \ge 1.3\Phi_0$. At pin separation $\ge 17\xi$, we find the V-AV pair remains pinned after the dipole field is removed, and, so can represent a 1 for a nonvolatile memory.Comment: 8 pages, 6 figure

Design and fabrication of a long-life Stirling cycle cooler for space application. Phase 3: Prototype model

A second-generation, Stirling-cycle cryocooler (cryogenic refrigerator) for space applications, with a cooling capacity of 5 watts at 65 K, was recently completed. The refrigerator, called the Prototype Model, was designed with a goal of 5 year life with no degradation in cooling performance. The free displacer and free piston of the refrigerator are driven directly by moving-magnet linear motors with the moving elements supported by active magnetic bearings. The use of clearance seals and the absence of outgassing material in the working volume of the refrigerator enable long-life operation with no deterioration in performance. Fiber-optic sensors detect the radial position of the shafts and provide a control signal for the magnetic bearings. The frequency, phase, stroke, and offset of the compressor and expander are controlled by signals from precision linear position sensors (LVDTs). The vibration generated by the compressor and expander is cancelled by an active counter balance which also uses a moving-magnet linear motor and magnetic bearings. The driving signal for the counter balance is derived from the compressor and expander position sensors which have wide bandwidth for suppression of harmonic vibrations. The efficiency of the three active members, which operate in a resonant mode, is enhanced by a magnetic spring in the expander and by gas springs in the compressor and counterbalance. The cooling was achieved with a total motor input power of 139 watts. The magnetic-bearing stiffness was significantly increased from the first-generation cooler to accommodate shuttle launch vibrations

A content-linking-context model for “notice-and-takedown” procedures

The US Digital Millennium Copyright Act (DMCA) of 1998 adopted a notice-and-take-down procedure to help tackle alleged online infringements through online service providers’ actions. The European Directive 2000/31/EC (e-Commerce Directive) introduced similar liability exemptions, but did not specify any take-down procedure. Many intermediary (host, and online search engine) service providers even in Europe have followed this notice-and-take-down procedure to enable copyright owners to issue notices to take down allegedly infringing Web resources. However, the accuracy of take-down is not known, and notice receivers do not reveal clear information about how they check the legitimacy of these requests, about whether and how they check the lawfulness of allegedly infringing content, or what criteria they use for these actions. In this paper, we use Google’s Transparency Report as the benchmark to investigate the information content of take-down notices and the accuracy of the resulting take-downs of allegedly infringing Web resources. The analysis of copyright infringement is limited to the five scenarios most frequently encountered in our study of Web resources. Based on our investigation, we propose a Content-Linking-Context (CLC) model of the criteria to be considered by intermediary service providers to achieve more accurate take-down

Mid-latitude <i>E</i>-region bulk motions inferred from digital ionosonde and HF radar measurements

In the mid-latitude <i>E</i>-region there is now evidence suggesting that neutral winds play a significant role in driving the local plasma instabilities and electrodynamics inside sporadic<i>E</i> layers. Neutral winds can be inferred from coherent radar backscatter measurements of the range-/azimuth-time-intensity (RTI/ATI) striations of quasi-periodic (QP) echoes, or from radar interferometer/imaging observations. In addition, neutral winds in the <i>E</i>-region can be estimated from angle-of-arrival ionosonde measurements of sporadic-<i>E</i> layers. In the present paper we analyse concurrent ionosonde and HF coherent backscatter observations obtained when a Canadian Advanced Digital Ionosonde (CADI) was operated under a portion of the field-of-view of the Valensole high frequency (HF) radar. The Valensole radar, a mid-latitude radar located in the south of France with a large azimuthal scanning capability of 82&deg; (24&deg; E to 58&deg; W), was used to deduce zonal bulk motions of QP echoing regions using ATI analysis. The CADI was used to measure angle-of-arrival information in two orthogonal horizontal directions and thus derive the motion of sporadic-<i>E</i> patches drifting with the neutral wind. This paper compares the neutral wind drifts of the unstable sporadic-<i>E</i> patches as determined by the two instruments. The CADI measurements show a predominantly westward aligned motion, but the measured zonal drifts are underestimated relative to those observed with the Valensole radar

A way to increase the bit ratein ionospheric radio links

The aim of this paper is to present a high data rate transmission system through the ionospheric channel in the HF-band (3-30 MHz). The applications expected in this study are image transmitting and real-time videoconferencing. Very high rates are required compared to the standard modems. Therefore, an array processing is performed with a set of antennas whose spatial response differs from one another arranged in a circular array or in a collocated sensor. Synchronization (Zero Crossing Detector) and source separation (LMS algorithm) resort to classical well-tested techniques involving training sequences. Experimental results are presented for both antenna configurations. These techniques improve data rate, reaching 20 kbits/s within the 6 kHz bandwidth (QAM 64) without coding or interleaving