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1

Radio wave scintillations at equatorial regions  

NASA Technical Reports Server (NTRS)

Radio waves, passing through the atmosphere, experience amplitude and phase fluctuations know as scintillations. A characterization of equatorial scintillation, which has resulted from studies of data recorded primarily in South America and equatorial Africa, is presented. Equatorial scintillation phenomena are complex because they appear to vary with time of day (pre-and postmidnight), season (equinoxes), and magnetic activity. A wider and more systematic geographical coverage is needed for both scientific and engineering purposes; therefore, it is recommended that more observations should be made at earth stations (at low-geomagnetic latitudes) to record equatorial scintillation phenomena.

Poularikas, A. D.

1972-01-01

2

Multistation analysis of VHF radio wave scintillations at low latitudes  

NASA Astrophysics Data System (ADS)

Simultaneous observations of VHF-ionospheric scintillations at Bhopal, Varanasi and Agra, during the period (January 1991-December 1991) have been reported. Nocturnal variation of occurrence of scintillations is found to be higher at Bhopal as compared to that at Varanasi and Agra. Under the geomagnetic disturbances the scintillations are suppressed in pre-midnight period at all the three stations. Severity of suppression is found to be more at Bhopal. The storms with the D(sub st) value below -100nT, reaching in local nighttime or in very early morning hours are found to be most effective in giving rise to the scintillations in post-midnight period. The results have been interpreted in terms of (1) F-region irregularities associated with spread-F and (2) coupling of high latitude and magnetospheric current systems with equatorial electric field.

Kumar, Sushil; Singh, A. K.; Chauhan, Pawan; Gwal, A. K.; Singh, Birbal; Singh, R. P.

1993-08-01

3

New systems for space based monitoring of ionospheric irregularities and radio wave scintillations  

NASA Astrophysics Data System (ADS)

The ionosphere has long been known to be the primary source of amplitude and phase fluctuations for VHF, UHF, and L-Band radio waves. Monitoring ionospheric irregularities that affect radio propagation is currently being implemented using in situ, radio and optical sensors on satellites in low-earth orbit (LEO). The remote sensing instruments provide observations of extreme ultraviolet (EUV) emissions or total electron content (TEC) to reconstruct images of electron densities. The GPS MET satellite has provided a global description of the ionosphere using GPS occultation from space. The ARGOS satellite launched in February 1999 has produced new images of the ionosphere using both EUV limb scanning and computerized ionospheric tomography (CIT) techniques. Recent measurements from the ARGOS satellite have provided data for improved modeling of both global scale and small-scale structures in the ionosphere. Future satellite sensors will be launched with EUV limb scanners, GPS occultation receivers, radio beacons for CIT, and beacon receivers for global mapping of ionospheric scintillations. These satellites will be placed in a variety of orbit inclinations to cover the equatorial, mid-latitude, and polar ionospheres.

Bernhardt, P. A.; Huba, J. D.; Selcher, C. A.; Dymond, K. F.; Carruthers, G. R.; Bust, G.; Rocken, C.; Beach, T. L.

4

Some new results on the statistics of radio wave scintillation. I - Empirical evidence for Gaussian statistics  

NASA Technical Reports Server (NTRS)

This paper presents an analysis of ionospheric scintillation data which shows that the underlying statistical structure of the signal can be accurately modeled by the additive complex Gaussian perturbation predicted by the Born approximation in conjunction with an application of the central limit theorem. By making use of this fact, it is possible to estimate the in-phase, phase quadrature, and cophased scattered power by curve fitting to measured intensity histograms. By using this procedure, it is found that typically more than 80% of the scattered power is in phase quadrature with the undeviated signal component. Thus, the signal is modeled by a Gaussian, but highly non-Rician process. From simultaneous UHF and VHF data, only a weak dependence of this statistical structure on changes in the Fresnel radius is deduced. The signal variance is found to have a nonquadratic wavelength dependence. It is hypothesized that this latter effect is a subtle manifestation of locally homogeneous irregularity structures, a mathematical model proposed by Kolmogorov (1941) in his early studies of incompressible fluid turbulence.

Rino, C. L.; Livingston, R. C.; Whitney, H. E.

1976-01-01

5

A decametric wavelength radio telescope for interplanetary scintillation observations  

NASA Technical Reports Server (NTRS)

A phased array, electrically steerable radio telescope (with a total collecting area of 18 acres), constructed for the purpose of remotely sensing electron density irregularity structure in the solar wind, is presented. The radio telescope is able to locate, map, and track large scale features of the solar wind, such as streams and blast waves, by monitoring a large grid of natural radio sources subject to rapid intensity fluctuation (interplanetary scintillation) caused by the irregularity structure. Observations verify the performance of the array, the receiver, and the scintillation signal processing circuitry of the telescope.

Cronyn, W. M.; Shawhan, S. D.

1975-01-01

6

Radio scintillations observed during atmospheric occultations of Voyager: Internal gravity waves at Titan and magnetic field orientations at Jupiter and Saturn. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

The refractive index of planetary atmospheres at microwave frequencies is discussed. Physical models proposed for the refractive irregularities in the ionosphere and neutral atmosphere serve to characterize the atmospheric scattering structures, and are used subsequently to compute theoretical scintillation spectra for comparison with the Voyager occultation measurements. A technique for systematically analyzing and interpreting the signal fluctuations observed during planetary occultations is presented and applied to process the dual-wavelength data from the Voyager radio occultations by Jupiter, Saturn, and Titan. Results concerning the plasma irregularities in the upper ionospheres of Jupiter and Saturn are reported. The measured orientation of the irregularities is used to infer the magnetic field direction at several locations in the ionospheres of these two planets; the occultation measurements conflict with the predictions of Jovian magnetic field models, but generally confirm current models of Saturn's field. Wave parameters, including the vertical fluxes of energy and momentum, are estimated, and the source of the internal gravity waves discovered in Titan's upper atmosphere is considered.

Hinson, D. P.

1983-01-01

7

The Bubbler and Radio Scintillation  

NSDL National Science Digital Library

This is a lesson about the formation of plasma bubbles in Earth's ionosphere. Plasma bubbles cause stars to twinkle and radio signals from satellites to distort. Learners will build a model ionosphere in order to demonstrate and understand this process. This activity requires special materials including a laser pointer and silicon-based glue.

8

Looking for radio waves with a simple radio wave detector  

NASA Astrophysics Data System (ADS)

I created a simple device that can detect radio waves in a classroom. In physics classes I tell students that we live in a sea of radio waves. They come from TV, radio, and cell phone signals as well as other sources. Students don't realize this because those electromagnetic waves are invisible. So, I wondered if I could come up with a way to detect the waves and help students to understand them better. Electromagnetic wave meters, which measure intensity of radio waves quantitatively, are commercially available. However, to students most of these are black boxes, and at the introductory level it is more effective to detect radio waves in a simpler way. This paper describes my device and how I have used it in my classes.

Sugimoto (Stray Cats), Norihiro

2011-11-01

9

Elements of Radio Waves  

E-print Network

We present a summary of the basic properties of the radio wave generation, propagation and reception, with a special attention to the gigahertz bandwidth region which is of interest for wireless sensor networks. We also present some measurement results which use the so-called RSSI indicator in order to track how the field strength varies with position and distance of the transceivers. We hope the paper may be useful to anyone who looks for a quick review of the fundamentals of electromagnetic theory with application to antennas.

Frank G. Borg; Ismo Hakala; Jukka Määttälä

2007-12-24

10

THE ORIGIN OF RADIO SCINTILLATION IN THE LOCAL INTERSTELLAR MEDIUM Jeffrey L. Linsky,1  

E-print Network

be explained by scintillation in a local region whose electron density has much greater rms variation than OF FAST RADIO SCINTILLATION Interstellar scintillation (ISS) is the apparent variation in flux density of very compact radio sources due to propagation through the irregular refractive index of the ionized

Royer, Dana

11

Radio wave propagation in pulsar magnetospheres  

NASA Astrophysics Data System (ADS)

The collective plasma processes responsible for the radio emission of pulsars remain an unsolved question. While several models have been proposed for the emission mechanism, little has appeared thus far to relate them to discriminating observational tests. I suggest that refractive interstellar scintillation measurements, as first analysed by Wolszczan and Cordes (1987), coupled with the expected propagation properties of radio waves in pulsar magnetospheres, can provide important clues to the location of the emission region and the propertiesof the polar cap plasma. The conventional geometrical interpretation of observed pulse widths in terms of emission altitude relies on the assumption of straight-line propagation of the observed radio waves from the point where they are emitted parallel to the local dipolar magnetic field. Interstellar interferometric observations, however, reveal a projected displacement of the emission region as a function of pulse phase which is much too large to be explained in this model. I propose that this can be reconciled with the observed pulse widths by taking into account the propagation properties of waves in the dense, relativistic and strongly magnetised plasma present above the polar cap. As shown by Barnard and Arons (1986), the subluminous branch of the O-mode polarisation in this situation propagates such that the ray is ``ducted'' along the magnetic field, while the initial k--vector direction is preserved to lowest order. This propagation regime holds up to the radius at which the frequency becomes comparable to the proper plasma frequency, omega ~= 2 square root ? omega_p, which depends on the bulk Lorentz factor gamma and the density of the polar cap plasma. This radius can be large enough, for reasonable multiplicities and flow Lorentz factors, to explain the observed displacements, assuming that the O-mode converts to the escaping branch beyond that point.

Gallant, Y. A.

12

VLF Radio Waves from Meteors  

NASA Astrophysics Data System (ADS)

To find the origin of electrophonic sounds produced by fireballs [1,2], a great number of project started, but only a few relevant data till now exist [3]. The effort to finding VLF emission from weak meteors with our group was inconclusive [4], probably because all the produced VLF radio waves of the meteors were at altitudes above the ionosphere, so the emitted radio waves were reflected towards space. There also exists the possibility that the signal to noise ratio was too small, or perhaps that some technical problems occurred [5]. The VLF emissions detected in some situations after faint meteors by others seem to be of dubious provenance [6,7]. Many open questions exist here, and to collect the necessary data in the search for the solutions, a planned new electronic equipment is described.

Korlevic, K.

13

The Cassini Radio and Plasma Wave Investigation  

Microsoft Academic Search

The Cassini radio and plasma wave investigation is designed to study radio emissions, plasma waves, thermal plasma, and dust in the vicinity of Saturn. Three nearly orthogonal electric field antennas are used to detect electric fields over a frequency range from 1 Hz to 16 MHz, and three orthogonal search coil magnetic antennas are used to detect magnetic fields over

D. A. Gurnett; W. S. Kurth; D. L. Kirchner; G. B. Hospodarsky; T. F. Averkamp; P. Zarka; A. Lecacheux; R. Manning; A. Roux; P. Canu; N. Cornilleau-Wehrlin; P. Galopeau; A. Meyer; R. Boström; G. Gustafsson; J.-E. Wahlund; L. Åhlen; H. O. Rucker; H. P. Ladreiter; W. Macher; L. J. C. Woolliscroft; H. Alleyne; M. L. Kaiser; M. D. Desch; W. M. Farrell; C. C. Harvey; P. Louarn; P. J. Kellogg; K. Goetz; A. Pedersen

2004-01-01

14

OVERCOMING IONOSPHERIC SCINTILLATION FOR WORLDWIDE GPS AVIATION  

E-print Network

in the equatorial area, including Brazil and India, is ionospheric scintillation. Due to electron density irregularities inside the ionosphere, transionospheric radio waves interfere constructively and de- structively

Stanford University

15

Wavelength dependence of radio scintillation: ionosphere and interplanetary irregularities  

Microsoft Academic Search

Recent in situ measurements and scintillation spectra suggest a power law irregularity spectrum in the F region ionosphere with a large outer-scale dimension (100 km). This result is consistent with the 'near-field' scintillation approximation, since Fresnel filtering attenuates irregularity structure larger than (rXz) v2, about 1 km. Consequently, the observed scintillation scale ( 1 km) is much smaller than the

Clifford L. Rufenach

1974-01-01

16

Ionospheric irregularities causing scintillation of GHz frequency radio signals  

NASA Technical Reports Server (NTRS)

Consideration of the recently observed phenomenon of scintillation of satellite signals at GHz frequency range. Based on the scintillation data and results from in situ measurements, several ionospheric irregularity models with different power spectra are studied. Scintillation index is computed for the various models and compared with observed results. Both magnitude and frequency dependence of the scintillation index are investigated. It is found that a thick irregularity slab of the order of 200 km with an electron density fluctuation of about 20 per cent of its background value and with a nonmonotonic power spectrum may account for the maximum observed values of the scintillation index as well as its frequency dependence. Some future observations and measurements are suggested.

Wernik, A. W.; Liu, C. H.

1974-01-01

17

Information Content in Radio Waves: Student Investigations in Radio Science  

NASA Astrophysics Data System (ADS)

We describe an inquiry-based instructional unit on information content in radio waves, created in the summer of 2013 as part of a MIT Haystack Observatory (Westford, MA) NSF Research Experiences for Teachers (RET) program. This topic is current and highly relevant, addressing science and technical aspects from radio astronomy, geodesy, and atmospheric research areas as well as Next Generation Science Standards (NGSS). Projects and activities range from simple classroom demonstrations and group investigations, to long term research projects incorporating data acquisition from both student-built instrumentation as well as online databases. Each of the core lessons is applied to one of the primary research centers at Haystack through an inquiry project that builds on previously developed units through the MIT Haystack RET program. In radio astronomy, students investigate the application of a simple and inexpensive software defined radio chip (RTL-SDR) for use in systems implementing a small and very small radio telescope (SRT and VSRT). Both of these systems allow students to explore fundamental principles of radio waves and interferometry as applied to radio astronomy. In ionospheric research, students track solar storms from the initial coronal mass ejection (using Solar Dynamics Observatory images) to the resulting variability in total electron density concentrations using data from the community standard Madrigal distributed database system maintained by MIT Haystack. Finally, students get to explore very long-baseline interferometry as it is used in geodetic studies by measuring crustal plate displacements over time. Alignment to NextGen standards is provided for each lesson and activity with emphasis on HS-PS4 'Waves and Their Applications in Technologies for Information Transfer'.

Jacobs, K.; Scaduto, T.

2013-12-01

18

Wave-wave interactions in solar type III radio bursts  

NASA Astrophysics Data System (ADS)

The high time resolution observations from the STEREO/WAVES experiment show that in type III radio bursts, the Langmuir waves often occur as localized magnetic field aligned coherent wave packets with durations of a few ms and with peak intensities well exceeding the strong turbulence thresholds. Some of these wave packets show spectral signatures of beam-resonant Langmuir waves, down- and up-shifted sidebands, and ion sound waves, with frequencies, wave numbers, and tricoherences satisfying the resonance conditions of the oscillating two stream instability (four wave interaction). The spectra of a few of these wave packets also contain peaks at fpe, 2fpe and 3 fpe (fpe is the electron plasma frequency), with frequencies, wave numbers and bicoherences (computed using the wavelet based bispectral analysis techniques) satisfying the resonance conditions of three wave interactions: (1) excitation of second harmonic electromagnetic waves as a result of coalescence of two oppositely propagating Langmuir waves, and (2) excitation of third harmonic electromagnetic waves as a result of coalescence of Langmuir waves with second harmonic electromagnetic waves. The implication of these findings is that the strong turbulence processes play major roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation in type III radio bursts.

Thejappa, G.; MacDowall, R. J.

2014-02-01

19

Theory of thin screen scintillations for a spherical wave  

NASA Technical Reports Server (NTRS)

A thin screen scintillation theory for a spherical wave is presented under the 'quasi-optical' approximation. We calculate the 'scattering angle', the 'observed angle', the intensity correlation function and the temporal pulse broadening for the random wave. It is found that as the wave propagates outward away from the phase screen, the correlation scale of the intensity fluctuation increases linearly while the 'observed angle' decreases linearly. The calculations are carried out for both Gaussian and power-law spectra of the turbulent medium.

Lee, L. C.

1976-01-01

20

Development and use of a GPS ionospheric scintillation monitor  

Microsoft Academic Search

Global Positioning System (GPS) satellite signals provide convenient radio beacons for ionospheric studies. Among other propagation phenomena, the ionosphere affects GPS signal propagation through amplitude scintillations that develop after radio waves propagate through ionospheric electron density irregularities. This paper outlines the design, testing, and operation of a specialized GPS receiver to monitor L-band amplitude scintillations: the Cornell scintillation monitor. The

Theodore L. Beach; Paul M. Kintner

2001-01-01

21

Effect of blowing snow and ground blizzards on millimeter wave scintillation spectra  

Microsoft Academic Search

We describe the effect of ground blizzards and blowing snow on millimeter wave scintillation spectra at 116 and 230 GHz. During snowstorms, multipath propagation can occur for various reasons. Whatever the reason for the multipath, it will affect the scintillation spectrum. Enhancement of the scintillation spectrum is observed at both low and high temporal frequencies. In some cases, two additional

A. D. Sarma; R. J. Hill

1991-01-01

22

Constraining the Vela Pulsar's Radio Emission Region Using Nyquist-limited Scintillation Statistics  

NASA Astrophysics Data System (ADS)

Using a novel technique, we achieve ~100 picoarcsec resolution and set an upper bound of less than 4 km for the characteristic size of the Vela pulsar's emission region. Specifically, we analyze flux-density statistics of the Vela pulsar at 760 MHz. Because the pulsar exhibits strong diffractive scintillation, these statistics convey information about the spatial extent of the radio emission region. We measure both a characteristic size of the emission region and the emission sizes for individual pulses. Our results imply that the radio emission altitude for the Vela pulsar at this frequency is less than 340 km.

Johnson, M. D.; Gwinn, C. R.; Demorest, P.

2012-10-01

23

Strong scintillations during atmospheric occultations Theoretical intensity spectra. [radio scattering during spacecraft occultations by planetary atmospheres  

NASA Technical Reports Server (NTRS)

Each of the two Voyager spacecraft launched in 1977 has completed a reconnaissance of the Jovian and Saturnian systems. In connection with occultation experiments, strong scintillations were observed. Further theoretical work is required before these scintillations can be interpreted. The present study is, therefore, concerned with the derivation of a theory for strong scattering during atmospheric occultation experiments, taking into account as fundamental quantity of interest the spatial spectrum (or spectral density) of intensity fluctuations. Attention is given to a theory for intensity spectra, and numerical calculations. The new formula derived for Phi-i accounts for strong scattering of electromagnetic waves during atmospheric occultations.

Hinson, D. P.

1986-01-01

24

Radio-wave propagation through a medium containing electron-density fluctuations described by an anisotropic Goldreich-Sridhar spectrum  

E-print Network

We study the propagation of radio waves through a medium possessing density fluctuations that are elongated along the ambient magnetic field and described by an anisotropic Goldreich-Sridhar power spectrum. We derive general formulas for the wave phase structure function, visibility, angular broadening, diffraction-pattern length scales, and scintillation time scale for arbitrary distributions of turbulence along the line of sight, and specialize these formulas to idealized cases.

B. D. G. Chandran; D. C. Backer

2002-02-13

25

Radio-wave propagation through a medium containing electron-density fluctuations described by an anisotropic Goldreich-Sridhar spectrum  

E-print Network

We study the propagation of radio waves through a medium possessing density fluctuations that are elongated along the ambient magnetic field and described by an anisotropic Goldreich-Sridhar power spectrum. We derive general formulas for the wave phase structure function, visibility, angular broadening, diffraction-pattern length scales, and scintillation time scale for arbitrary distributions of turbulence along the line of sight, and specialize these formulas to idealized cases.

Chandran, B D G

2002-01-01

26

Detection Of Cosmic Rays Air Showers Using Radio Antenna Arrays And Scintillation Counters  

NASA Astrophysics Data System (ADS)

In this progress report we describe a test bench developed in order to evaluate the performance of radio antennas and other gaseous detectors in detecting air showers initiating by cosmic rays. This test bench is based on an array of HELYCON scintillation counters and is used to operate a digital radio telescope. The results of this research and development activity will be applied in developing a sea top calibration array of an underwater neutrino telescope. We also describe the performance of a single HELYCON station in detecting and reconstructing showers as well as on the pilot operation of a single low frequency radio antenna in order to develop techniques to suppress the contribution of the anthropogenic RF background originated from human activities.

Papageorgiou, K.; Tzamarias, S.; Gkialas, I.; Tsirigotis, A.; Bourlis, G.; Manthos, I.; Avgitas, G.

2014-06-01

27

Near-Sun solar wind consequences of solar structure and dynamic phenomena observed by radio scintillation measurements  

NASA Technical Reports Server (NTRS)

Since radio propagation measurements using either natural or spacecraft radio signals are used for probing the solar wind in the vicinity of the sun, they represent a key tool for studying the interplanetary consequences of solar structure and dynamic phenomena. New information on the near sun consequences was obtained from radio scintillation observations of coherent spacecraft signals. The results covering density fluctuations, fractional density fluctuations, coronal streamers, heliospheric current sheets, coronal mass ejections and interplanetary shocks are reviewed. A joint ICE S-band (13 cm wavelength) Doppler scintillation measurement with the SOHO white-light coronograph (LASCO) is described.

Woo, Richard

1994-01-01

28

Advances in magnetospheric radio wave analysis and tomography  

Microsoft Academic Search

A number of experiments have been accomplished in which the Radio Plasma Imager (RPI) on the IMAGE spacecraft was used as a low frequency radio wave transmitter and the WAVES instrument on WIND and the Wide-band instruments on all four CLUSTER spacecraft as receivers. These transmissions\\/receptions provide a unique opportunity to test a number of important magnetospheric measurement techniques. For

J. Green; S. Cummer; B. Reinisch; S. Fung; M. Kaiser; R. Mutel; J. Pickett; I. Christopher; D. Gurnett

2002-01-01

29

Evidence for nonlinear wave-wave interactions in solar type III radio bursts  

Microsoft Academic Search

Evidence is presented that nonlinear wave-wave interactions occur in type III solar radio bursts. Intense, spiky Langmuir waves are observed to be driven by electron beams associated with type III solar radio bursts in the interplanetary medium. Bursts of 30-300 Hz (in the spacecraft frame) waves are often observed coincident in time with the most intense spikes of the Langmuir

R. P. Lin; W. K. Levedahl; W. Lotko; D. A. Gurnett; F. L. Scarf

1986-01-01

30

Effect of blowing snow and ground blizzards on millimeter wave scintillation spectra  

NASA Astrophysics Data System (ADS)

We describe the effect of ground blizzards and blowing snow on millimeter wave scintillation spectra at 116 and 230 GHz. During snowstorms, multipath propagation can occur for various reasons. Whatever the reason for the multipath, it will affect the scintillation spectrum. Enhancement of the scintillation spectrum is observed at both low and high temporal frequencies. In some cases, two additional corner frequencies are evident at the high-frequency end of the scintillation spectrum. The method of obtaining the cross-path wind component fails when the wind is nearly parallel to the propagation path.

Sarma, A. D.; Hill, R. J.

1991-09-01

31

HF produced ionospheric electron density irregularities diagnosed by UHF radio star scintillations  

NASA Technical Reports Server (NTRS)

Three observations of radio star intensity fluctuations at UHF are reported for HF ionospheric modification experiments carried out at the Arecibo Observatory. Two observations at 430 MHz and one at 1400 MHz suggest that the the thin phase screen theory is a good approximation to the observed power spectra. It is noted, however, that the theory has to be extended to include antenna filtering. This type of filtering is important for UHF radio star scintillations since the antenna usually has a narrow beamwidth. HF power densities of less than 37 microwatts/sq m incident on the ionosphere give rise to electron density irregularities larger than 13% of the ambient density (at 260 km) having scale sizes of approximately 510 m perpendicular to the geomagnetic field. The irregularities are found to form within 20-25 s after the HF power is turned on. The drift velocities of the irregularities can be estimated from the observed power spectra.

Frey, A.; Gordon, W. E.

1982-01-01

32

Plasma distribution of Comet ISON (C/2012 S1) observed using the radio scintillation method  

E-print Network

We report the electron density in a plasma tail of Comet ISON (C/2012 S1) derived from interplanetary scintillation (IPS) observations during November 1--28, 2013. Comet ISON showed a well-developed plasma tail (longer than 2.98 x 10^{7} km) before its perihelion passage on November 28. We identified a radio source whose line-of-sight approached the ISON's plasma tail in the above period and obtained its IPS data using the Solar Wind Imaging Facility at 327 MHz. We used the Heliospheric Imager onboard the Solar-Terrestrial Relation Observatory to distinguish between the cometary tail and solar eruption origins of their enhanced scintillation. From our examinations, we confirmed three IPS enhancements of a radio source 1148-00 on November 13, 16, and 17, which could be attributed to the disturbance in the cometary tail. They showed no appreciable change of fluctuation power spectra during the occultation by the plasma tail of Comet ISON. We estimated the electron density in the ISON's plasma tail and found 84 ...

Iju, Tomoya; Tokumaru, Munetoshi; Fujiki, Ken'ichi

2014-01-01

33

Making Waves: Pirate Radio and Popular Music.  

ERIC Educational Resources Information Center

The history of pirate radio--radio broadcasts offered by unlicensed broadcasters as alternatives to licensed, commercial radio programming--is difficult to trace, both in America and the United Kingdom (UK) since mention of pirate broadcasts of a less-then-thrilling nature are rarely found. Also, until 1927, the U.S. government did not formally…

Jones, Steve

34

Polarization of Radio Waves Reflected from the Inhomogeneous Ionosphere.  

National Technical Information Service (NTIS)

Calculations show that there is a very small difference between the true mean field polarization of radio waves reflected from the inhomogeneous ionosphere and that calculated using Stokes parameters. A Stokes parameter system is derived, from which the w...

Y. V. Morozov

1973-01-01

35

Radio and Plasma Waves Synergistic Science Opportunities with EJSM  

Microsoft Academic Search

The radio and plasma wave (RPW) diagnostics provide a unique access to critical parameters of space plasma, in particular in planetary and satellite environments. Concerning giant planets, this has been demonstrated by major results obtained by the radio investigation on the Galileo and Cassini spacecraft, but also during the Ulysses, Voyager, and Pioneer flybys of Jupiter. Several other missions, past

Baptiste Cecconi; Nicolas André; Jean-Louis Bougeret

2010-01-01

36

Plasma and radio waves from Neptune: Source mechanisms and propagation  

NASA Technical Reports Server (NTRS)

This report summarizes results obtained through the support of NASA Grant NAGW-2412. The objective of this project is to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as if flew by Neptune. This study has included data analysis, theoretical and numerical calculations, ray tracing, and modeling to determine the possible source mechanism(s) and locations of the Neptune radio emissions. We have completed four papers, which are included in the appendix. The paper 'Modeling of Whistler Ray Paths in the Magnetosphere of Neptune' investigated the propagation and dispersion of lighting-generated whistler in the magnetosphere of Neptune by using three dimensional ray tracing. The two papers 'Numerical Simulations of Bursty Radio Emissions from Planetary Magnetospheres' and 'Numerical Simulations of Bursty Planetary Radio Emissions' employed numerical simulations to investigate an alternate source mechanism of bursty radio emissions in addition to the cyclotron maser instability. We have also studied the possible generation of Z and whistler mode waves by the temperature anisotropic beam instability and the result was published in 'Electron Cyclotron Wave Generation by Relativistic Electrons.' Besides the aforementioned studies, we have also collaborated with members of the PRA team to investigate various aspects of the radio wave data. Two papers have been submitted for publication and the abstracts of these papers are also listed in the appendix.

Wong, H. K.

1994-01-01

37

Stellar scintillations as a remote atmospheric wave-front sensor.  

PubMed

Stellar scintillations are considered noise in adaptive-optics sensors and are measured for calibration purposes only. We propose to use scintillations to provide direct instantaneous information about the structure of the atmosphere. As a result it will be possible to increase the field of view provided by adaptive optics. The scintillation pattern is created when stellar light is diffracted by high-altitude turbulence. Alternatively, this pattern can be viewed as a Laplacian of this turbulence and can thus be inverted to estimate it. The measurement is limited by the intensity and the angular size of the reference star, by the height distribution of the atmospheric turbulence, and by the detector resolution and spectral response. PMID:19865430

Ribak, E N; Gershnik, E; Cheselka, M

1996-03-15

38

Adaptive radio frequency interference mitigation for HF surface wave radar  

Microsoft Academic Search

The paper analyses the characteristics of radio frequency interference (RFI) in HF surface wave radar (HFSWR) which adopt the linear frequency modulated interrupted continuous wave (FMICW). RFI will influence all the range cells including all the positive and negative frequency, and that the negative frequency range cells contain only the interference information. Based on the above characteristics, we introduce and

Wan Xianrong; Wen Biyang; Ke Hengyu

2004-01-01

39

Interpretation of gravity wave signatures in GPS radio occultations  

Microsoft Academic Search

The horizontal averaging of global positioning system radio occultation retrievals produces an amplitude attenuation and phase shift in any plane gravity wave, which may lead to significant discrepancies with respect to the original values. In addition, wavelengths cannot be straightforwardly inferred due to the observational characteristics. If the waves produce small departures from spherical symmetry in the background atmosphere and

P. Alexander; A. de la Torre; P. Llamedo

2008-01-01

40

A Water Surface Wave-Height Radio Telemeter  

Microsoft Academic Search

This paper discusses the evolution of a telemetric device that enables the remote measurement of surface wave height on a freshwater lake. The basic instrumentation package uses an anchored, insulated metal probe as a capacitive sensor element to determine peak wave amplitudes up to 1 m; the probe also serves as the mechanical support for a lightweight UHF radio-link antenna.

Noel E. Evans

1987-01-01

41

Roles Played by Electrostatic Waves in Producing Radio Emissions  

NASA Technical Reports Server (NTRS)

Processes in which electromagnetic radiation is produced directly or indirectly via intermediate waves are reviewed. It is shown that strict theoretical constraints exist for electrons to produce nonthermal levels of radiation directly by the Cerenkov or cyclotron resonances. In contrast, indirect emission processes in which intermediary plasma waves are converted into radiation are often favored on general and specific grounds. Four classes of mechanisms involving the conversion of electrostatic waves into radiation are linear mode conversion, hybrid linear/nonlinear mechanisms, nonlinear wave-wave and wave-particle processes, and radiation from localized wave packets. These processes are reviewed theoretically and observational evidence summarized for their occurrence. Strong evidence exists that specific nonlinear wave processes and mode conversion can explain quantitatively phenomena involving type III solar radio bursts and ionospheric emissions. On the other hand, no convincing evidence exists that magnetospheric continuum radiation is produced by mode conversion instead of nonlinear wave processes. Further research on these processes is needed.

Cairns, Iver H.

2000-01-01

42

Evidence for nonlinear wave-wave interactions in solar type III radio bursts  

NASA Technical Reports Server (NTRS)

Evidence is presented that nonlinear wave-wave interactions occur in type III solar radio bursts. Intense, spiky Langmuir waves are observed to be driven by electron beams associated with type III solar radio bursts in the interplanetary medium. Bursts of 30-300 Hz (in the spacecraft frame) waves are often observed coincident in time with the most intense spikes of the Langmuir waves. These low-frequency waves appear to be long-wavelength ion acoustic waves, with wavenumber approximately equal to the beam resonant Langmuir wavenumber. Three possible interpretations of these observations are considered: modulational instability, parametric decay of the parent Langmuir waves to daughter ion acoustic and Langmuir waves, and decay to daughter electromagnetic waves and ion acoustic waves.

Lin, R. P.; Levedahl, W. K.; Lotko, W.; Gurnett, D. A.; Scarf, F. L.

1986-01-01

43

First experimental evidence of HF produced electron density irregularities in the polar ionosphere, diagnosed by UHF radio star scintillations  

Microsoft Academic Search

Observations made on May 10 and September 9, 1983, during which large scale irregularities in the ionosphere were excited by the HF facility at Tromso, Norway, are discussed. The observations were detected using radio star scintillations at 933 MHz, and the HF-beam was pointed 10-15 deg south. Observations made on September 9 showed the HF-power density threshold to be 22

A. Frey; P. Stubbe; H. Kopka

1984-01-01

44

Synopsis of Mid-latitude Radio Wave Absorption in Europe  

NASA Technical Reports Server (NTRS)

Radio wave absorption data covering almost two years from Europe to Central Asia are presented. They are normalized by relating them to a reference absorption. Every day these normalized data are fitted to a mathematical function of geographical location in order to obtain a daily synopsis of radio wave absorption. A film of these absorption charts was made which is intended to reveal movements of absorption or absorption anomaly. In addition, radiance (temperature) data from the lower D-region are also plotted onto these charts.

Torkar, K. M.; Friedrich, M.

1984-01-01

45

Trajectories of radio waves in linear layer with isometric inhomogeneities  

NASA Astrophysics Data System (ADS)

The trajectories of radio waves in a statistically nonhomogeneous medium such as a linear ionospheric layer are estimated, taking into account their perturbation by local inhomogeneities. Assuming that the trajectories do remain in the plane of incidence, the deviation of the most probable trajectory from its unperturbed path in accordance with Snell's law is calculated for three models of wave diffusion as a Markov process (D- diffusion). The results are useful for design and operation of radio communication lines, calculation of the maximum usable frequency, and other applications.

Golynskiy, S. M.; Khlybov, G. N.

1984-05-01

46

Radio emission from a shock wave in the solar wind  

SciTech Connect

It is shown that the region of increased electron temperature in a shock wave front propagating along the magnetic field at large distances from the sun can be bounded by a sharp jump in temperature (collisionless electron thermal wave); the width of this temperature-jump region is determined by the ion-acoustic turbulence developing in the opposing streams of hot and cool electrons. Energetic electrons moving away from the thermal wave front excite plasma waves, which are then converted into radio emission. 26 references.

Ledenev, V.G.

1985-12-01

47

Adaptive radio frequency interference mitigation for HF surface wave radar  

Microsoft Academic Search

The paper analyses the characteristics of radio frequency interference (RFI) in HF surface wave radar (HF-SWR) which adopts\\u000a the linear frequency modulated interrupted continuous wave (FMICW). RFI will influence all the range cells including all the\\u000a positive frequency and negative frequency, and the negative frequency range cells contain only the interference information.\\u000a Based on the above characteristics, we introduce and

Wan Xian-rong; Ke Heng-yu; Cheng Feng

2005-01-01

48

Effect of small ionospheric irregularities on radio wave absorption  

NASA Technical Reports Server (NTRS)

The ionospheric absorption of a radio wave caused by small-scale irregularities with a gaussian autocorrelation function is calculated for various values of the linear scale height, the radio frequency, the scale size of the irregularities, and the mean-square fractional electron density fluctuations. The absorption is due to scattering of the radio wave into plasma oscillations by the irregularities. It is concluded that the absorption due to such irregularities with a mean-square fractional electron density deviation greater than about 0.000001 exceeds the normal collisional height-integrated absorption. Absorption of this type could play a significant part in heating experiments or in an ionosphere containing naturally occurring irregularities.

Chen, H. C.; Fejer, J. A.

1975-01-01

49

Plasma Diagnostics of the Solar Corona Using Decimetric Radio Waves  

E-print Network

process may have different forms. Are they enough to heat the solar corona? The answer seems to become electric currents, must also be con­ sidered. The heating problem of the solar corona can only be solved. Plasma Diagnostics of the Solar Corona Using Decimetric Radio Waves (Review) Arnold O. Benz

50

Improved spacecraft radio science using an on-board atomic clock: application to gravitational wave searches  

E-print Network

Recent advances in space-qualified atomic clocks (low-mass, low power-consumption, frequency stability comparable to that of ground-based clocks) can enable interplanetary spacecraft radio science experiments at unprecedented Doppler sensitivities. The addition of an on-board digital receiver would allow the up- and down-link Doppler frequencies to be measured separately. Such separate, high-quality measurements allow optimal data combinations that suppress the currently-leading noise sources: phase scintillation noise from the Earth's atmosphere and Doppler noise caused by mechanical vibrations of the ground antenna. Here we provide a general expression for the optimal combination of ground and on-board Doppler data and compute the sensitivity such a system would have to low-frequency gravitational waves (GWs). Assuming a plasma scintillation noise calibration comparable to that already demonstrated with the multi-link CASSINI radio system, the space-clock/digital-receiver instrumentation enhancements would give GW strain sensitivity of $2.0 \\times 10^{-17}$ for randomly polarized, monochromatic GW signals over a two-decade ($\\sim0.0001-0.01$ Hz) region of the low-frequency band. This is about an order of magnitude better than currently achieved with traditional two-way coherent Doppler experiments. The utility of optimally combining simultaneous up- and down-link observations is not limited to GW searches. The Doppler tracking technique discussed here could be performed at minimal incremental cost to also improve other radio science experiments (i.e. tests of relativistic gravity, planetary and satellite gravity field measurements, atmospheric and ring occultations) on future interplanetary missions.

Massimo Tinto; George J. Dick; John D. Prestage; J. W. Armstrong

2008-12-13

51

Improved spacecraft radio science using an on-board atomic clock: Application to gravitational wave searches  

SciTech Connect

Recent advances in space-qualified atomic clocks (low-mass, low power-consumption, frequency stability comparable to that of ground-based clocks) can enable interplanetary spacecraft radio science experiments at unprecedented Doppler sensitivities. The addition of an on-board digital receiver would allow the up- and down-link Doppler frequencies to be measured separately. Such separate, high-quality measurements allow optimal data combinations that suppress the currently leading noise sources: phase scintillation noise from the Earth's atmosphere and Doppler noise caused by mechanical vibrations of the ground antenna. Here we provide a general expression for the optimal combination of ground and on-board Doppler data and compute the sensitivity such a system would have to low-frequency gravitational waves (GWs). Assuming a plasma scintillation noise calibration comparable to that already demonstrated with the multilink CASSINI radio system, the space-clock/digital-receiver instrumentation enhancements would give GW strain sensitivity of 3.7x10{sup -14} Hz{sup -1/2} for randomly polarized, monochromatic GW signals isotropically distributed over the celestial sphere, over a two-decade ({approx}0.0001-0.01 Hz) region of the low-frequency band. This is about an order of magnitude better than currently achieved with traditional two-way coherent Doppler experiments. The utility of optimally combining simultaneous up- and down-link observations is not limited to GW searches. The Doppler tracking technique discussed here could be performed at minimal incremental cost to improve also other radio science experiments (i.e., tests of relativistic gravity, planetary and satellite gravity field measurements, atmospheric and ring occultations) on future interplanetary missions.

Tinto, Massimo; Dick, George J.; Prestage, John D.; Armstrong, J. W. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)

2009-05-15

52

Characteristics of layers, waves and turbulence in the atmosphere and ionosphere as estimated by GPS space radio-holography  

NASA Astrophysics Data System (ADS)

The spatial, seasonal and geographical distrubutions of the intensity of layers, turbulence and internal waves at different altitudes in the atmosphere and ionosphere of the Earth are presented. The results have been obtained on the base of locality principle using a new phase acceleration-intensity method for analysis of the GPS radio occultation signals. This methodology has been applied to mesearements of the inclination and altitude of ionospheric layers. Obtained information has been used for estimation of the front orientation, internal frequency and phase speed of the internal waves in the ionosphere and neutral atmosphere. A new index of the ionospheric activity as measured from the phase of radio waves passed through the ionosphere is introduced and its high correlation with S4 scintillation index is established. This correlation indicates the significant influence of ionospheric layers on variations of characteristics of radio waves in transionospheric communication links. Specially for the troposphere the geographical distribution of the weak total absorption (about of 1-2 db) of the radio waves at GPS frequencies in the Earth atmosphere corresponding to influence of the oxygen and water vapor in the troposphere is measured with accuracy better than 0.1 db. Obtained results expanded the applicable domain of the GPS space radio-holography for global investigation of the natural processes in the atmosphere and ionosphere as function of solar activity and space weather effects. The new phase acceleration-intensity method is also a basic tool which can be applied for data analysis of future planetary radio occultation missions

Pavelyev, Alexander; Gubenko, Vladimir; Matyugov, Stanislav; Pavelyev, Alexey

53

Dynamics of wave scintillation in random media Guillaume Bal  

E-print Network

and on the size of the "array of detectors" where the wave fields are measured. In many practical settings, we Villeurbanne Cedex, France; pinaud@math.univ-lyon1.fr 1 #12;[23] for acoustic, electromagnetic and elastic

Bal, Guillaume

54

Dynamics of wave scintillation in random media Guillaume Bal  

E-print Network

and on the size of the "array of detectors" where the wave fields are measured. In many practical settings, we Villeurbanne Cedex, France; pinaud@math.univ-lyon1.fr 1 #12;[24] for acoustic, electromagnetic and elastic

Pinaud, Olivier

55

Twisted Radio Waves and Twisted Thermodynamics  

PubMed Central

We present and analyze a gedanken experiment and show that the assumption that an antenna operating at a single frequency can transmit more than two independent information channels to the far field violates the Second Law of Thermodynamics. Transmission of a large number of channels, each associated with an angular momenta ‘twisted wave’ mode, to the far field in free space is therefore not possible. PMID:23424647

Kish, Laszlo B.; Nevels, Robert D.

2013-01-01

56

WAVES: The radio and plasma wave investigation on the wind spacecraft  

Microsoft Academic Search

The WAVES investigation on the WIND spacecraft will provide comprehensive measurements of the radio and plasma wave phenomena which occur in Geospace. Analyses of these measurements, in coordination with the other onboard plasma, energetic particles, and field measurements will help us understand the kinetic processes that are important in the solar wind and in key boundary regions of the Geospace.

J.-L. Bougeret; M. L. Kaiser; P. J. Kellogg; R. Manning; K. Goetz; S. J. Monson; N. Monge; L. Friel; C. A. Meetre; C. Perche; L. Sitruk; S. Hoang

1995-01-01

57

Density Waves in Saturn's Rings from Cassini Radio Occultations  

NASA Astrophysics Data System (ADS)

The Cassini Radio Science Team conducted a set of optimized diametric occultations by Saturn and its rings from May to September 2005, providing 11 separate probes of Saturn's ionosphere and atmosphere, and 12 optical depth profiles of the complete ring system. Each event was observed by the stations of the Deep Space Net (DSN) at three radio frequencies (S, X, Ka bands, with corresponding wavelengths of ? = 13, 3.6, and 0.9 cm). Very accurate pointing by the spacecraft and ground antennas resulted in stable baseline signal levels, and the relatively large ring opening angle (B=19-25°) permitted us to probe even quite dense ring regions with excellent SNR. The RSS occultation technique enables us to recover very fine detailed radial structure by correcting for diffraction effects. Multiple occultation chords, covering a variety of ring longitudes and ring opening angles, reveal the structure of the rings in remarkable detail, including density and bending waves, satellite wakes, and subtle variations at the 100-m radius scale. Janus and Epimetheus are responsible for a particularly rich set of density waves, and their coorbital interactions result in a complex interplay of time-variable ring structure over the 8-year libration period of the two satellites. We compare the first-order 2:1, 4:3, 5:4, and 6:5 coorbital density waves from multiple occultation chords to linear density wave models based on a dynamical model of the orbital exchange between the moons. From the observed dispersion relation of the wave crests, we infer the surface mass density and eccentricity gradient of particle streamlines, and match the detailed shapes of the wave crests using a non-linear analysis. Second-order coorbital features are also evident, and there are even hints of third-order density waves in the high SNR radio occultation data.

French, R. G.; Rappaport, N. J.; Marouf, E. A.; McGhee, C. A.

2005-12-01

58

Data compression for the Cassini radio and plasma wave instrument  

NASA Technical Reports Server (NTRS)

The Cassini Radio and Plasma Wave Science experiment will employ data compression to make effective use of the available data telemetry bandwidth. Some compression will be achieved by use of a lossless data compression chip and some by software in a dedicated 80C85 processor. A description of the instrument and data compression system are included in this report. Also, the selection of data compression systems and acceptability of data degradation is addressed.

Farrell, W. M.; Gurnett, D. A.; Kirchner, D. L.; Kurth, W. S.; Woolliscroft, L. J. C.

1993-01-01

59

Progress in millimeter-wave fiber-radio access networks  

Microsoft Academic Search

\\u000a Abstract  Future radio access networks operating at millimeter-wave frequencies have the capacity to offer broadband interactive services\\u000a to a customer base requiring untethered access. Optical fiber-feed networks incorporating wavelength division multiplexing\\u000a have been proposed as a backbone network providing full-duplex interconnectivity between multiple remote antenna basestations\\u000a and a central office implementing a variety of switching and routing functions. Rapid developments in

A. Nirmalathas; C. Lim; D. Novak; R. B. Waterhouse

2001-01-01

60

Radio fiber bursts and fast magnetoacoustic wave trains  

NASA Astrophysics Data System (ADS)

Aims: We present a model for dm-fiber bursts that is based on assuming fast sausage magnetoacoustic wave trains that propagate along a dense vertical filament or current sheet. Methods: Eight groups of dm-fiber bursts that were observed during solar flares were selected and analyzed by the wavelet analysis method. To model these fiber bursts we built a semi-empirical model. We also did magnetohydrodynamic simulations of a propagation of the magnetoacoustic wave train in a vertical and gravitationally stratified current sheet. Results: In the wavelet spectra of the fiber bursts computed at different radio frequencies we found the wavelet tadpoles, whose head maxima have the same frequency drift as the drift of fiber bursts. It indicates that the drift of these fiber bursts can be explained by the propagating fast sausage magnetoacoustic wave train. Using new semi-empirical and magnetohydrodynamic models with a simple radio emission model we generated the artificial radio spectra of the fiber bursts, which are similar to the observed ones.

Karlický, M.; Mészárosová, H.; Jelínek, P.

2013-02-01

61

An Overview of Recent Results from the Cassini Radio and Plasma Wave Science Investigation  

Microsoft Academic Search

The Radio and Plasma Wave Science (RPWS) investigation on the Cassini spacecraft provides measurements of radio emissions, plasma waves, and thermal plasma parameters in the vicinity of Saturn. This paper gives an overview of recent results from the RPWS. These include the most recent measurements of the rotational modulation period of radio emissions from Saturn (Saturn Kilometric Radiation), of impulsive

D. Gurnett; W. Kurth; G. Hospodarsky; A. Persoon; T. Averkamp; B. Cecconi; A. Lecacheux; P. Zarka; P. Canu; N. Cornilleau-Wehrlin; P. Galopeau; A. Roux; C. Harvey; P. Louarn; R. Bostrom; G. Gustafsson; J.-E. Wahlund; M. Desch; W. Farrell; M. Kaiser; P. Kellogg; K. Goetz; G. Fischer; H.-P. Ladreiter; H. Rucker; H. Alleyne; A. Pedersen

2005-01-01

62

On Microwave Radio Scintillation Effects and Space Weather Impacts on Electric Power Supply Systems in Middle Latitudes  

NASA Astrophysics Data System (ADS)

In this paper results of morphological studies and investigations on revealing of main characteristics of ionospheric scintillation effects experienced for microwave radio signals for the Space-Earth path, its impacts on navigation and communication systems, dependence on the solar and geomagnetic activity, geophysical and other processes/factors are briefly provided to help system designers who are involved in the activities related to the development and functioning of systems, particularly, for consumers in middle geographical latitudes. Ionospheric propagation model computer code was applied for studying of scintillation effects on microwave radio signals used in the area of Azerbaijan for worst case scenario of main space weather and ionosphere parameters. Part of main results of the complex investigations on possible impact of geomagnetic disturbances of various strengths on electric power supply systems in middle latitudes is described. Daily data on power failures and breakdowns that occurred in Baku capital city (Azerbaijan) and surrounded big urban area in years of descending phase of solar 11-year activity cycle was investigated and analyzed.

Babayev, E. S.; Hashimov, A. M.; Asgarov, A. B.; Yusifbeyli, N. A.; Shustarev, P. N.

2006-12-01

63

Scattering of radio frequency waves by blobs in tokamak plasmasa)  

NASA Astrophysics Data System (ADS)

The density fluctuations and blobs present in the edge region of magnetic fusion devices can scatter radio frequency (RF) waves through refraction, reflection, diffraction, and coupling to other plasma waves. This, in turn, affects the spectrum of the RF waves and the electromagnetic power that reaches the core of the plasma. The usual geometric optics analysis of RF scattering by density blobs accounts for only refractive effects. It is valid when the amplitude of the fluctuations is small, of the order of 10%, compared to the background density. In experiments, density fluctuations with much larger amplitudes are routinely observed, so that a more general treatment of the scattering process is needed. In this paper, a full-wave model for the scattering of RF waves by a blob is developed. The full-wave approach extends the range of validity well beyond that of geometric optics; however, it is theoretically and computationally much more challenging. The theoretical procedure, although similar to that followed for the Mie solution of Maxwell's equations, is generalized to plasmas in a magnetic field. Besides diffraction and reflection, the model includes coupling to a different plasma wave than the one imposed by the external antenna structure. In the model, it is assumed that the RF waves interact with a spherical blob. The plasma inside and around the blob is cold, homogeneous, and imbedded in a uniform magnetic field. After formulating the complete analytical theory, the effect of the blob on short wavelength electron cyclotron waves and longer wavelength lower hybrid waves is studied numerically.

Ram, Abhay K.; Hizanidis, Kyriakos; Kominis, Yannis

2013-05-01

64

Scattering of radio frequency waves by blobs in tokamak plasmas  

SciTech Connect

The density fluctuations and blobs present in the edge region of magnetic fusion devices can scatter radio frequency (RF) waves through refraction, reflection, diffraction, and coupling to other plasma waves. This, in turn, affects the spectrum of the RF waves and the electromagnetic power that reaches the core of the plasma. The usual geometric optics analysis of RF scattering by density blobs accounts for only refractive effects. It is valid when the amplitude of the fluctuations is small, of the order of 10%, compared to the background density. In experiments, density fluctuations with much larger amplitudes are routinely observed, so that a more general treatment of the scattering process is needed. In this paper, a full-wave model for the scattering of RF waves by a blob is developed. The full-wave approach extends the range of validity well beyond that of geometric optics; however, it is theoretically and computationally much more challenging. The theoretical procedure, although similar to that followed for the Mie solution of Maxwell's equations, is generalized to plasmas in a magnetic field. Besides diffraction and reflection, the model includes coupling to a different plasma wave than the one imposed by the external antenna structure. In the model, it is assumed that the RF waves interact with a spherical blob. The plasma inside and around the blob is cold, homogeneous, and imbedded in a uniform magnetic field. After formulating the complete analytical theory, the effect of the blob on short wavelength electron cyclotron waves and longer wavelength lower hybrid waves is studied numerically.

Ram, Abhay K. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)] [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Hizanidis, Kyriakos; Kominis, Yannis [School of Electrical and Computer Engineering, National Technical University of Athens, Association EURATOM-Hellenic Republic, Athens, GR-15773 (Greece)] [School of Electrical and Computer Engineering, National Technical University of Athens, Association EURATOM-Hellenic Republic, Athens, GR-15773 (Greece)

2013-05-15

65

Interpretation of gravity wave signatures in GPS radio occultations  

NASA Astrophysics Data System (ADS)

The horizontal averaging of global positioning system radio occultation retrievals produces an amplitude attenuation and phase shift in any plane gravity wave, which may lead to significant discrepancies with respect to the original values. In addition, wavelengths cannot be straightforwardly inferred due to the observational characteristics. If the waves produce small departures from spherical symmetry in the background atmosphere and under the assumption that the refractivity kernel may be represented by a delta function, an analytical expression may be derived in order to find how the retrieved amplitudes become weakened (against the original ones). In particular, we study the range of waves that may be detected and the consequent reduction in variance calculation, which is found to be around 19%. A larger discrepancy was obtained when comparing an occultation variance with the one computed from a numerical simulation of that case. Wave amplitudes can be better resolved when the fronts are nearly horizontal or when the angle between the occultation line of sight and the horizontal component of the wave vector approaches ?/2. Short horizontal scale waves have a high probability of becoming attenuated or of not being detected at all. We then find geometrical relations in terms of the relative orientation between waves and sounding, so as to appropriately interpret wavelengths extracted from the acquired data. Only inertio-gravity waves, which exhibit nearly horizontal fronts, will show small differences between detected and original vertical wavelengths. Last, we analyze the retrieval effect on wave phase and find a shift between original and detected wave that generally is nonzero and approaches ?/4 for the largest horizontal wavelengths.

Alexander, P.; de la Torre, A.; Llamedo, P.

2008-08-01

66

TURBULENCE IN THE IONOSPHERE WITH APPLICATIONS TO METEOR-TRAILS, RADIO-STAR SCINTILLATION, AURORAL RADAR ECHOES, AND OTHER PHENOMENA  

Microsoft Academic Search

The irregularities in electron-density responsible for incoherent scattering of radio waves in the ionosphere are discussed on the assumption of isotropic turbulence in the neutral molecules, with allowance made for the effect of the earth's magnetic field on the associated irregularities in the density of the charges particles. The atmospheric model used is based on rocket observations, extrapolated upwards in

H. G. Booker

1956-01-01

67

Recovery of radioisotopes from nuclear waste for radio-scintillator-luminescence energy applications  

E-print Network

Extraction of the light weight radioisotopes (LWR) 89Sr/90Sr, from the expended nuclear bars in the Fukushima reactor, should have decreased the extent of contamination during the course of the accident. 89Sr applications could pay for the extraction of 89Sr/90Sr from nuclear residues. Added value could be obtained by using 89Sr for cancer treatments. Known technologies could be used to relate into innovative ways LWR, to obtain nuclear energy at battery scale. LWR interact by contact with scintillators converting \\beta-radiation into light-energy. This would lead to manufacturing scintillator lamps which operate independently of other source of energy. These lamps could be used to generate photoelectric energy. Engineering of radioisotopes scintillator photovoltaic cells, would lead to devices without moving parts.

Bennun, Alfred

2012-01-01

68

Recovery of radioisotopes from nuclear waste for radio-scintillator-luminescence energy applications  

E-print Network

Extraction of the light weight radioisotopes (LWR) 89Sr/90Sr, from the expended nuclear bars in the Fukushima reactor, should have decreased the extent of contamination during the course of the accident. 89Sr applications could pay for the extraction of 89Sr/90Sr from nuclear residues. Added value could be obtained by using 89Sr for cancer treatments. Known technologies could be used to relate into innovative ways LWR, to obtain nuclear energy at battery scale. LWR interact by contact with scintillators converting \\beta-radiation into light-energy. This would lead to manufacturing scintillator lamps which operate independently of other source of energy. These lamps could be used to generate photoelectric energy. Engineering of radioisotopes scintillator photovoltaic cells, would lead to devices without moving parts.

Alfred Bennun

2012-08-16

69

An Overview of Cassini Radio, Plasma Wave, and Langmuir Probe Observations in the Vicinity of Saturn  

Microsoft Academic Search

The Cassini Radio and Plasma Wave Science (RPWS) instrument detected a wide variety of radio and plasma wave phenomena during the approach and first flyby of Saturn. These include Saturn kilometric radiation (SKR), Saturn electrostatic discharges (SEDs), upstream electrostatic waves, the bow shock, trapped continuum radiation, whistler-mode chorus emissions, electrostatic upper-hybrid emissions, impulsive signals from dust impacts, narrowband electromagnetic emissions

D. Gurnett; W. Kurth; G. Hospodarsky; A. Persoon; M. Desch; W. Farrell; M. Kaiser; K. Goetz; B. Cecconi; A. Lecacheux; P. Zarka; C. Harvey; P. Louarn; P. Canu; N. Cornilleau-Wehrlin; P. Galopeau; A. Roux; G. Fischer; H. Ladreiter; H. Rucker; H. Alleyne; R. Bostrom; G. Gustafsson; J. Wahlund; A. Pedersen

2004-01-01

70

Cassini radio and plasma wave investigation - Data compression and scientific applications  

Microsoft Academic Search

The Radio and Plasma Wave Science (RPWS) experiment being built for the Cassini spacecraft will study a wide range of plasma and radio wave phenomena in the magnetosphere of Saturn and will also make valuable measurements during the cruise phase and at other encounters. A feature of data from wave receivers is the capability of producing vastly more data than

L. J. C. Woolliscroft; W. M. Farrell; H. St. C. Alleyne; D. A. Gurnett; D. L. Kirchner; W. S. Kurth; J. A. Thompson

1993-01-01

71

Cassini radio and plasma wave investigation: Data compression and scientific applications  

Microsoft Academic Search

The Radio and Plasma Wave Science (RPWS) experiment being built for the Cassini spacecraft will study a wide range of plasma and radio wave phenomena in the magnetosphere of Saturn and will also make valuable measurements during the cruise phase and at other encounters. A feature of data from wave receivers is the capability of producing vastly more data than

L. J. C. Woolliscroft; W. M. Farrell; H. St. C. Alleyne; D. A. Gurnett; D. L. Kirchner; W. S. Kurth; J. A. Thompson

1993-01-01

72

Regimes of ionospheric turbulence from fractal analysis of satellite radio signal scintillations  

NASA Astrophysics Data System (ADS)

The paper describes a fractal analysis of the amplitude scintillations of signals from a geostationary satellite which can be used to characterize ionospheric turbulence and turbulence in the turbopause. The algorithm by Grassberger and Procaccia (1983) is employed to analyze the scintillations, and the drift velocity of the diffraction pattern and the spectral characteristics of the signal are calculated. Fractal dimensionality is estimated at 3.26-4.36 for three of the seven calculations, and the results are interpreted as evidence of two regimes of ionospheric turbulence at midlatitudes. Localized turbulent regions or sources are inferred in regimes for which reliable estimates of low dimensionality are determined. This and the high dimensionality of the second regime are consistent with the notion of horizontally homogeneous ionospheric turbulence.

Zvezdin, V. N.; Fridman, S. V.

1992-08-01

73

Optical detection of radio waves through a nanomechanical transducer.  

PubMed

Low-loss transmission and sensitive recovery of weak radio-frequency and microwave signals is a ubiquitous challenge, crucial in radio astronomy, medical imaging, navigation, and classical and quantum communication. Efficient up-conversion of radio-frequency signals to an optical carrier would enable their transmission through optical fibres instead of through copper wires, drastically reducing losses, and would give access to the set of established quantum optical techniques that are routinely used in quantum-limited signal detection. Research in cavity optomechanics has shown that nanomechanical oscillators can couple strongly to either microwave or optical fields. Here we demonstrate a room-temperature optoelectromechanical transducer with both these functionalities, following a recent proposal using a high-quality nanomembrane. A voltage bias of less than 10?V is sufficient to induce strong coupling between the voltage fluctuations in a radio-frequency resonance circuit and the membrane's displacement, which is simultaneously coupled to light reflected off its surface. The radio-frequency signals are detected as an optical phase shift with quantum-limited sensitivity. The corresponding half-wave voltage is in the microvolt range, orders of magnitude less than that of standard optical modulators. The noise of the transducer--beyond the measured 800 pV Hz-1/2 Johnson noise of the resonant circuit--consists of the quantum noise of light and thermal fluctuations of the membrane, dominating the noise floor in potential applications in radio astronomy and nuclear magnetic imaging. Each of these contributions is inferred to be 60 pV Hz-1/2 when balanced by choosing an electromechanical cooperativity of ~150 with an optical power of 1?mW. The noise temperature of the membrane is divided by the cooperativity. For the highest observed cooperativity of 6,800, this leads to a projected noise temperature of 40 mK and a sensitivity limit of 5 pV Hz-1/2. Our approach to all-optical, ultralow-noise detection of classical electronic signals sets the stage for coherent up-conversion of low-frequency quantum signals to the optical domain. PMID:24598636

Bagci, T; Simonsen, A; Schmid, S; Villanueva, L G; Zeuthen, E; Appel, J; Taylor, J M; Sørensen, A; Usami, K; Schliesser, A; Polzik, E S

2014-03-01

74

Tran-spectral searches for transient radio pulses and gravitational waves  

Microsoft Academic Search

The detection of radio wavelength transients from astrophysical sources can provide external triggers for gravitational wave (GW) searches within LIGO\\/Virgo data. There are a variety of sources of GWs that should also produce a radio transient, such as compact object inspirals and mergers, core- collapse super- novae, and the cusps or kinks of superconducting cosmic strings. Radio polarization and spectral

Megan Torpey

2010-01-01

75

The History of Radio Wave Propagation up to the End of World War I  

Microsoft Academic Search

Hertz in the 1880's demonstrated electromagnetic wave propagation predicted by Maxwell from his equations in 1864. Heaviside and Kennelly postulated the ionosphere to explain Marconi's historical transatlantic reception of radio waves in 1901. Austin derived the first formula for radio propagation in 1911 from experimental data in the kilometer wavelength range taken in the daytime. Much theoretical effort was expended

Charles Burrows

1962-01-01

76

Ulysses observations of wave activity at interplanetary shocks and implications for type II radio bursts  

Microsoft Academic Search

We present the first quantitative investigation of interplanetary type II radio emission in which in situ waves measured at interplanetary shocks are used to compute radio wave intensities for comparison with type II observations. This study is based on in situ measurements of 42 in-ecliptic forward shocks as well as 10 intervals of type II emission observed by the Ulysses

D. Lengyel-Frey; G. Thejappa; R. J. MacDowall; R. G. Stone; J. L. Phillips

1997-01-01

77

Initial results from the Cassini radio and plasma wave science investigation at Saturn  

Microsoft Academic Search

On July 1, 2004, the Cassini spacecraft will arrive at Saturn and is expected to be injected into orbit around Saturn. This talk will report the initial results from the Radio and Plasma Wave Science (RPWS) investigation. The RPWS is designed to study radio emissions, plasma waves, thermal plasma, and dust in the vicinity of Saturn. Three nearly orthogonal electric

D. Gurnett

2004-01-01

78

Walkie-Talkie Measurements for the Speed of Radio Waves in Air  

ERIC Educational Resources Information Center

A handheld emitter-receiver device suitable for the direct estimation of the velocity of radio waves in air is presented. The velocity of radio waves is measured using the direct time-of-flight method, without the need for any tedious and precise settings. The results for two measurement series are reported. Both sets of results give an estimate…

Dombi, Andra; Tunyagi, Arthur; Neda, Zoltan

2013-01-01

79

HF produced ionospheric electron density irregularities diagnosed by UHF radio star scintillations  

Microsoft Academic Search

Three observations of radio star intensity fluctuations at UHF are reported for HF ionospheric modification experiments carried out at the Arecibo Observatory. Two observations at 430 MHz and one at 1400 MHz suggest that the the thin phase screen theory is a good approximation to the observed power spectra. It is noted, however, that the theory has to be extended

Alfred Frey; W. E. Gordon

1982-01-01

80

Structure of the Electric Field of a High-Power Radio Wave in the Outer Ionosphere  

NASA Astrophysics Data System (ADS)

The electric field of a high-power HF radio wave radiated by the Sura facility was measured using onboard instruments of the French microsatellite DEMETER at altitudes of 670 km. The data analysis shows that the high-power radio wave passes to the outer ionosphere under conditions where the difference between the cutoff frequency and the pump-wave frequency does not exceed 0.5-0.7 MHz in the undisturbed ionosphere. Energy and spatial characteristics of the high-power radio wave transmitted through the ionosphere are determined. A possible mechanism explaining such a penetration to the supercritical plasma is discussed.

Frolov, V. L.; Mityakov, N. A.; Shorokhova, E. A.; Parrot, M.

2013-11-01

81

Jupiter's low-frequency radio spectrum from Cassini\\/Radio and Plasma Wave Science (RPWS) absolute flux density measurements  

Microsoft Academic Search

We apply the calibration method developed by Dulk et al. [2001] to the data from the Cassini\\/Radio and Plasma Wave Science (RPWS) High-Frequency Receiver in order to derive flux density measurements of six components of the Jovian low-frequency radio spectrum over the full frequency range of the instrument (3.5 kHz to 16.1 MHz). The estimated accuracy is better than 50%,

P. Zarka; B. Cecconi; W. S. Kurth

2004-01-01

82

Scattering of Radio Frequency Waves by Edge Density Blobs in Tokamak Plasmas  

SciTech Connect

The density blobs and fluctuations present in the edge region of magnetic fusion devices can scatter radio frequency (RF) waves through refraction and diffraction. The scattering can diffuse the rays in space and in wave-vector space. The diffusion in space can make the rays miss their intended target region, while the diffusion in wave-vector space can broaden the wave spectrum and modify the wave damping and current profile.

Ram, A. K. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States); Hizanidis, K.; Kominis, Y. [National Technical University of Athens, Association EURATOM-Hellenic Republic, Zografou, Athens 15773 (Greece)

2011-12-23

83

Relations among low ionosphere parameters and A3 radio wave absorption  

NASA Technical Reports Server (NTRS)

Charged particle conductivities measured in the very low ionosphere are compared with atmospheric parameters and high-frequency radio wave absorption measurements. Between 33 and 58 km, positive conductivity is well correlated with neutral atmospheric temperature. Good correlations are found also between high-frequency radio wave absorption and negative conductivity at altitudes as low as 53 km, this fact suggesting that day-to-day variations in absorption may be principally due to variations in electron loss rate. These correlations do not apply to some days of very low or very high radio wave absorption, for which the effects of transport on nitric oxide appear to be important.

Cipriano, J. P.; Hale, L. C.; Mitchell, J. D.

1974-01-01

84

Radio and Plasma Wave Science Opportunities Afforded by the Jupiter Icy Moons Orbiter  

Microsoft Academic Search

The Galileo mission demonstrated the extensive and varied interactions between the Jovian magnetosphere and the icy Galilean satellites. In particular, the Galileo plasma wave investigation showed the surprisingly complex array of plasma and radio wave phenomena accompanying Ganymede's magnetosphere, evidence of an extensive magnetospheric interaction at Europa, and a weaker yet highly variable interaction at Callisto. The plasma wave observations

W. S. Kurth; D. A. Gurnett; W. M. Farrell; M. D. Desch; M. L. Kaiser; P. Zarka; A. Lecacheux; P. Canu; S. J. Bolton; J. E. Wahlund; L. G. Blomberg; S. D. Bale; M. Moncuquet

2003-01-01

85

Radio wave remote sensing by Cluster and Regatta  

NASA Technical Reports Server (NTRS)

A coordinated Cluster/Regatta mission provides unique opportunities for remote sensing studies of terrestrial radio emissions. The scientific questions that can be addressed by remote radio measurements from Cluster and Regatta are described and the technical issues involved are discussed. The radio emission of primary interest is Auroral Kilometric Radiation (AKR) which is a powerful radio emission generated over the Earth's auroral zones at frequencies from 100 to 500 kHz.

Gurnett, Donald A.

1990-01-01

86

Chapter 7: Radio-Frequency Wave Physics in the FTU  

SciTech Connect

This chapter reports the main physics results obtained with three radio-frequency-injection systems. The frequency of 8 GHz for the lower hybrid (LH) current drive (CD) (LHCD) system was chosen to explore CD at high density: full CD has been demonstrated for central densities up to 1.4 x 10{sup 20} m{sup -3} at 0.5 MA with an applied power up to 2.0 MW. The Frascati Tokamak Upgrade (FTU) database shows CD efficiencies from 0.1 to 0.3 x 10{sup 20} AW{sup -1} m{sup -2}. In combined experiments with electron cyclotron (EC) waves (140 GHz, up to 1.2 MW), a suprathermal absorption by the fast electron tail generated by LHCD has been observed in both downshifted and upshifted interaction regimes, with the resulting electron cyclotron current drive (ECCD) ranging from 20 to 100 kA, depending on experimental conditions. With pure EC resonance heating, the narrowness of the radial power deposition profile has been exploited, resulting in strong local electron heating. Results in high-density regimes are also presented. The third system (433 MHz, 0.5 MW) is the first to test ion Bernstein wave (IBW) coupling with a waveguide antenna. The experiment operates at high frequency, avoiding the occurrence of nonlinear phenomena at the edge. Improved confinement regimes resulting in a central peaking of the pressure profiles have been achieved with P{sub IBW} up to 0.4 MW. Modeling and experimental results are summarized.

Granucci, G. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Airoldi, A. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Barbato, E. [Associazione EURATOM-ENEA sulla Fusione (Italy); Bruschi, A. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Cardinali, A. [Associazione EURATOM-ENEA sulla Fusione (Italy); Castaldo, C. [Associazione EURATOM-ENEA sulla Fusione (Italy); Cesario, R. [Associazione EURATOM-ENEA sulla Fusione (Italy); Cirant, S. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Esposito, B. [Associazione EURATOM-ENEA sulla Fusione (Italy); Farina, D. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Gandini, F. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Giruzzi, G. [Association EURATOM-CEA sur la Fusion (France); Gormezano, C. [Associazione EURATOM-ENEA sulla Fusione (Italy); Leigheb, M. [Associazione EURATOM-ENEA sulla Fusione (Italy); Marinucci, M. [Associazione EURATOM-ENEA sulla Fusione (Italy); Mirizzi, F. [Associazione EURATOM-ENEA sulla Fusione (Italy); Nowak, S. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Panaccione, L. [Associazione EURATOM-ENEA sulla Fusione (Italy); Pericoli-Ridolfini, V. [Associazione EURATOM-ENEA sulla Fusione (Italy); Podda, S. [Associazione EURATOM-ENEA sulla Fusione (Italy); Ramponi, G. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Ravera, G.L. [Associazione EURATOM-ENEA sulla Fusione (Italy); Saveliev, A.N. [A. F. Ioffe Physico-Technical Institute (Russian Federation); Simonetto, A. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Sozzi, C. [Associazione EURATOM-ENEA-CNR sulla Fusione (Italy); Tuccillo, A.A. [Associazione EURATOM-ENEA sulla Fusione (Italy); Zonca, F. [Associazione EURATOM-ENEA sulla Fusione (Italy)

2004-05-15

87

Jupiter: As a planet. [its physical characteristics and radio waves emitted from Jupiter  

NASA Technical Reports Server (NTRS)

The planet Jupiter, its planetary mass and atmosphere, radio waves emitted from Jupiter, thermal radiation, internal structure of Jupiter, and the possibility of life on Jupiter are discussed. Educational study projects are included.

1975-01-01

88

Radio-over-fiber distribution using an optical millimeter-wave\\/DWDM overlay  

Microsoft Academic Search

We demonstrate an optical MM-wave\\/DWDM overlay using optical suppressed-carrier modulation to simultaneously upconvert multi-wavelength subcarriers to 35 GHz. Performance of the system is analyzed for radio-over-fiber distribution

R. A. Griffin; J. J. O'Reilly

1999-01-01

89

Energetic electrons and plasma waves associated with a solar type III radio burst  

Microsoft Academic Search

We present detailed in situ observations from the ISEE 3 spacecraft of energetic electrons, plasma waves, and radio emission for the type III solar radio burst of 1979 February 17. The reduced one-dimensional distribution function f (v) of the electrons is constructed as a function of time. Since the faster electrons arrive before the slower ones, a bump on tail

R. P. Lin; D. W. Potter; D. A. Gurnett; F. L. Scarf

1981-01-01

90

Energetic electrons and plasma waves associated with a solar type III radio burst  

Microsoft Academic Search

Detailed in situ observations from the ISEE 3 spacecraft of energetic electrons, plasma waves, and radio emission for the type II solar radio burst of February 17, 1979, are presented. The reduced, one-dimensional electron distribution function is constructed as a function of time. Since the faster electrons arrive before the slower ones, a bump on tail distribution forms which is

R. P. Lin; D. W. Potter; D. A. Gurnett; F. L. Scarf

1981-01-01

91

Relations Among Low Ionosphere Parameters and A3 Radio Wave Absorption  

Microsoft Academic Search

Charged particle conductivities measured in the very low ionosphere are compared with atmospheric parameters and high-frequency radio wave absorption measurements. Between 33 and 58 km, positive conductivity is well correlated with neutral atmospheric temperature. Good correlations are found also between high-frequency radio wave absorption and negative conductivity at altitudes as low as 53 km, this fact suggesting that day-to-day variations

J. P. Cipriano; L. C. Hale; J. D. Mitchell

1974-01-01

92

The Effects of Langmuir Wave Evolution on Type III Radio Emission  

NASA Astrophysics Data System (ADS)

High energy electron beams are produced during solar flares and propagate through the inhomogeneous plasma of the solar corona, generating high levels of Langmuir waves which can produce Type III radio bursts. We consider the effects of long length-scale density fluctuations on these Langmuir waves using a diffusive approximation, and calculate the diffusion coefficients. We use 1-D simulations to follow the time-evolution of the Langmuir waves, and the subsequent effects on the electron beam. In addition, we simulate the Type III radio emission from the Langmuir waves, and consider the modification of brightness and spectrum due to inhomogeneities.

Ratcliffe, H.; Kontar, E. P.; Bian, N.

2012-12-01

93

Expressions of the scintillation index for optical waves propagating through weak non-Kolmogorov turbulence based on the generalized atmospheric spectral model  

NASA Astrophysics Data System (ADS)

The high frequency "bump" which occurs in the turbulence spectral model just prior to the turbulence cell dissipation is important for the analysis of the irradiance scintillation for optical wave propagating through atmospheric turbulence. In this study, expressions of the irradiance scintillation index are developed from the generalized modified atmospheric spectral model for optical waves propagating through weak non-Kolmogorov turbulence. Compared with the expressions of the irradiance scintillation index derived from the general non-Kolmogorov spectral model, the new expressions can consider the influences of finite turbulence inner and outer scales and the influence of finite diameter aperture receiver. As the irradiance scintillation is caused mainly by the small scale turbulence cells' diffractive effects for weak turbulence, the turbulence outer scale's influence can be ignored. Numerical simulations show that variable inner scale values produce obvious effects on the irradiance scintillation for non-Kolmogorov turbulence.

Cui, Linyan; Xue, Bindang; Xue, Wenfang; Bai, Xiangzhi; Cao, Xiaoguang; Zhou, Fugen

2012-11-01

94

The wave expansion approach to broadcasting in multihop radio networks  

Microsoft Academic Search

An algorithm for efficient communication between neighbours in multihop radio networks is proposed. The algorithm guarantees a bound on the transmission efficiency in a radio channel for arbitrary topology. The algorithm can be embedded in protocols for solving basic network problems such as broadcast, multicast, leader election, or finding shortest paths. The problem of bounded-time broadcasting utilizing the proposed algorithm

Imrich Chlamtac; Orly Weinstein

1991-01-01

95

Ulysses observations of wave activity at interplanetary shocks and implications for type II radio bursts  

SciTech Connect

We present the first quantitative investigation of interplanetary type II radio emission in which in situ waves measured at interplanetary shocks are used to compute radio wave intensities for comparison with type II observations. This study is based on in situ measurements of 42 in-ecliptic forward shocks as well as 10 intervals of type II emission observed by the Ulysses spacecraft between 1 AU and 5 AU. The analysis involves comparisons of statistical properties of type II bursts and in situ waves. Most of the 42 shocks are associated with the occurrence of electrostatic waves near the time of shock passage at Ulysses. These waves, which are identified as electron plasma waves and ion acoustic-like waves, are typically most intense several minutes before shock passage. This suggests that wave-wave interactions might be of importance in electromagnetic wave generation and that type II source regions are located immediately upstream of the shocks. We use the in situ wave measurements to compute type II brightness temperatures, assuming that emission at the fundamental of the electron plasma frequency is generated by the merging of electron plasma waves and ion acoustic waves or the decay of electron plasma waves into ion acoustic and transverse waves. Second harmonic emission is assumed to be produced by the merging of electron plasma waves. The latter mechanism requires that a portion of the electron plasma wave distribution is backscattered, presumably by density inhomogeneities in regions of observed ion acoustic wave activity. The computed type II brightness temperatures are found to be consistent with observed values for both fundamental and second harmonic emission, assuming that strong ({approx_equal}10{sup {minus}4}V/m) electron plasma waves and ion acoustic waves are coincident and that the electron plasma waves have phase velocities less than about 10 times the electron thermal velocity. (Abstract Truncated)

Lengyel-Frey, D. [Department of Astronomy, University of Maryland, College Park, Maryland (United States)] [Department of Astronomy, University of Maryland, College Park, Maryland (United States); [Computer Sciences Corporation, Suitland, Maryland (United States); Thejappa, G. [Department of Astronomy, University of Maryland, College Park, Maryland (United States)] [Department of Astronomy, University of Maryland, College Park, Maryland (United States); MacDowall, R.J.; Stone, R.G. [NASA Goddard Space Flight Center, Greenbelt, Maryland (United States)] [NASA Goddard Space Flight Center, Greenbelt, Maryland (United States); Phillips, J.L. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico (United States); [NASA Johnson Space Flight Center, Houston, Texas (United States)

1997-02-01

96

Observations of chorus at Saturn using the Cassini Radio and Plasma Wave Science instrument  

Microsoft Academic Search

Observations at Saturn of whistler mode chorus emissions have been obtained by the Cassini Radio and Plasma Wave Science instrument. Data from the first 45 orbits are analyzed, and the characteristics of the chorus emissions are discussed. Wave normal and Poynting vector measurements from the five-channel waveform receiver are used to examine the propagation characteristics of the chorus, and high-resolution

G. B. Hospodarsky; T. F. Averkamp; W. S. Kurth; D. A. Gurnett; J. D. Menietti; O. Santolik; M. K. Dougherty

2008-01-01

97

Density waves in Saturn's rings probed by radio and optical occultation - Observational tests of theory  

NASA Technical Reports Server (NTRS)

A parallel examination is conducted of Voyager radio and photopolarimeter occultation observations of the Saturn A ring's density waves. The radio instrument waves exhibit an average -90 deg offset from the dynamical phase. A warping height of about 100-m amplitude can qualtitatively reproduce this phase shift, while preserving the overall model wave shape. These results may be profoundly relevant for satellite-ring torque calculations in Saturn's rings, given the deposition of all of the net torque of the standard model in the first wavelength.

Brophy, Thomas G.; Rosen, Paul A.

1992-01-01

98

Cassini radio and plasma wave investigation - Data compression and scientific applications  

NASA Technical Reports Server (NTRS)

The Radio and Plasma Wave Science (RPWS) experiment being built for the Cassini spacecraft will study a wide range of plasma and radio wave phenomena in the magnetosphere of Saturn and will also make valuable measurements during the cruise phase and at other encounters. A feature of data from wave receivers is the capability of producing vastly more data than the spacecraft telemetry link is capable of transmitting back to the Earth. Thus, techniques of on-board data compression and data reduction are important. The RPWS instrument has one processor dedicated to data compression tasks.

Woolliscroft, L. J. C.; Farrell, W. M.; Alleyne, H. St. C.; Gurnett, D. A.; Kirchner, D. L.; Kurth, W. S.; Thompson, J. A.

1993-01-01

99

Cassini radio and plasma wave investigation: Data compression and scientific applications  

NASA Technical Reports Server (NTRS)

The Radio and Plasma Wave Science (RPWS) experiment being built for the Cassini spacecraft will study a wide range of plasma and radio wave phenomena in the magnetosphere of Saturn and will also make valuable measurements during the cruise phase and at other encounters. A feature of data from wave receivers is the capability of producing vastly more data than the spacecraft telemetry link is capable of transmitting back to the Earth. Thus, techniques of on-board data compression and data reduction are important. The RPWS instrument has one processor dedicated to data compression tasks.

Woolliscroft, L. J. C.; Farrell, W. M.; Alleyne, H. St. C.; Gurnett, D. A.; Kirchner, D. L.; Kurth, W. S.; Thompson, J. A.

1993-01-01

100

Wave propagation and earth satellite radio emission studies  

NASA Technical Reports Server (NTRS)

Radio propagation studies of the ionosphere using satellite radio beacons are described. The ionosphere is known as a dispersive, inhomogeneous, irregular and sometimes even nonlinear medium. After traversing through the ionosphere the radio signal bears signatures of these characteristics. A study of these signatures will be helpful in two areas: (1) It will assist in learning the behavior of the medium, in this case the ionosphere. (2) It will provide information of the kind of signal characteristics and statistics to be expected for communication and navigational satellite systems that use the similar geometry.

Yeh, K. C.; Liu, C. H.; Flaherty, B. J.

1974-01-01

101

Approach warning system for snowplow using aerial-high-power ultrasonic wave with radio wave  

NASA Astrophysics Data System (ADS)

An approach warning system for a snowplow and guide was developed by using aerial-high-power ultrasonic transducer. To be robust against some serious factors in winter, ultrasonic signal and radio one were combined on the system, and the flat face side of stepped circular vibrating plate was utilized as a radiation plate. The ultrasonic wave radiated from the flat face side still had a better directivity, and the flat face had advantage to prevent bad influences from water, snow or ice. From experiment results, when double transducers were set on both sides of roof of snowplow, this system was able to be measure distance between a guide and snowplow in whole of controlled area.

Manabu, Aoyagi; Yuta, Amagi; Hiroaki, Miura; Okeya, Ryota; Hideki, Tamura; Takehiro, Takano

2012-05-01

102

Double layers and plasma-wave resistivity in extragalactic jets: Cavity formation and radio-wave emission  

NASA Astrophysics Data System (ADS)

For estimated values of the currents carried by extragalactic jets, current-driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur. Strong plasma double layers, however, may exist within self-maintained density cavities, the relativistic double-layer-emitted electron, and ion beams driving plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layer-emitted electron beams may also emit polarized radio waves via a collective bremsstrahlung process mediated by electrostatic two-stream instabilities.

Borovsky, Joseph E.

1987-05-01

103

Double layers and plasma-wave resistivity in extragalactic jets: Cavity formation and radio-wave emission  

NASA Technical Reports Server (NTRS)

For estimated values of the currents carried by extragalactic jets, current-driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur. Strong plasma double layers, however, may exist within self-maintained density cavities, the relativistic double-layer-emitted electron, and ion beams driving plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layer-emitted electron beams may also emit polarized radio waves via a collective bremsstrahlung process mediated by electrostatic two-stream instabilities.

Borovsky, Joseph E.

1987-01-01

104

Double layers and plasma-wave resistivity in extragalactic jets - Cavity formation and radio-wave emission  

NASA Astrophysics Data System (ADS)

Current driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur in extragalactic jets for estimated values of the carried currents. Strong plasma double layers, however, may exist within self-maintained density cavities. The relativistic double-layer-emitted electron and ion beams drive plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layer-emitted electron beams may also emit polarized radio waves via a collective bremsstrahlung process mediated by electrostatic two-stream instabilities.

Borovsky, Joseph E.

1987-05-01

105

Comparison of LaBr3:Ce and NaI(Tl) Scintillators for Radio-Isotope Identification Devices  

SciTech Connect

Lanthanum halide (LaBr3:Ce) scintillators offer significantly better resolution (<3 percent at 662 kilo-electron volt [keV]) relative to sodium iodide (NaI(Tl)) and have recently become commercially available in sizes large enough for the hand-held radio-isotope identification device (RIID) market. There are drawbacks to lanthanum halide detectors, however. These include internal radioactivity that contributes to spectral counts and a low-energy response that can cause detector resolution to be lower than that of NaI(Tl) below 100 keV. To study the potential of this new material for RIIDs, we performed a series of measurements comparing a 1.5?1.5 inch LaBr?3:Ce detector with an Exploranium GR 135 RIID, which contains a 1.5-2.2 inch NaI(Tl) detector. Measurements were taken for short time frames, as typifies RIID usage. Measurements included examples of naturally occurring radioactive material (NORM), typically found in cargo, and special nuclear materials. Some measurements were noncontact, involving short distances or cargo shielding scenarios. To facilitate direct comparison, spectra from the different detectors were analyzed with the same isotope identification software (ORTEC ScintiVision TM). In general, the LaBr3:Ce detector was able to find more peaks and find them faster than the NaI(Tl) detector. To the same level of significance, the LaBr3:Ce detector was usually two to three times faster. The notable exception was for 40K containing NORM where interfering internal contamination in the LaBr3:Ce detector exist. NaI(Tl) consistently outperformed LaBr3:Ce for this important isotope. LaBr3:Ce currently costs much more than NaI(Tl), though this cost-difference is expected to diminish (but not completely) with time. As is true of all detectors, LaBr3:Ce will need to be gain-stabilized for RIID applications. This could possibly be done using the internal contaminants themselves. It is the experience of the authors that peak finding software in RIIDs needs to be improved, regardless of the detector material.

Milbrath, Brian D.; Choate, Bethany J.; Fast, Jim E.; Hensley, Walter K.; Kouzes, Richard T.; Schweppe, John E.

2006-07-31

106

Wave Normal Calculations of Chorus at Saturn Using the Cassini Radio and Plasma Wave Science Five-Channel Waveform Receiver  

Microsoft Academic Search

The Cassini spacecraft has completed the first year of its four-year prime mission to study the Saturnian system. The Cassini Radio and Plasma Wave Science (RPWS) Five-Channel Waveform Receiver (WFR) provides simultaneous waveforms from up to five separate sensors in passbands of either 1 Hz to 26 Hz, or 3 Hz to 2.5 kHz. The wave normal and Poynting vector

G. B. Hospodarsky; T. F. Averkamp; W. S. Kurth; D. A. Gurnett; M. K. Dougherty

2005-01-01

107

System capacity for millimeter-wave radio-over-fiber distribution employing an optically supported PLL  

Microsoft Academic Search

We consider the performance of a hybrid radio-over-fiber distribution system with a remote phase-locked loop (PLL) providing the local oscillator for upconversion to millimeter (mm)-wave frequencies. The reference signal for the PLL is transmitted together with digitally modulated subcarriers over a fiber link, allowing centralization of radio processing. Through analysis and simulation, we identify the relationship between the phase noise

Robert A. Griffin; H. M. Salgado; J. J. O'Reilly

1999-01-01

108

High-frequency radio-wave ablation of osteoid osteoma in the lumbar spine  

Microsoft Academic Search

The authors report on the first known application in the spine of percutaneous ablation of osteoid osteoma using radio-frequency\\u000a waves. The technique involves a CT-guided biopsy of the lesion followed by introduction of a 1-mm probe connected to a radio-frequency\\u000a lesion generator. The procedure was performed on an outpatient basis and the patient experienced immediate relief of his symptoms.\\u000a No

O. L. Osti; R. Sebben

1998-01-01

109

Signatures in a Giant Radio Galaxy of a Cosmological Shock Wave at Intersecting Filaments of Galaxies  

E-print Network

Sensitive images of low-level, Mpc-sized radio cocoons offer new opportunities to probe large scale intergalactic gas flows outside clusters of galaxies. New radio images of high surface brightness sensitivity at strategically chosen wavelengths of the giant radio galaxy NGC 315 (Mack et al. 1997,1998) reveal significant asymmetries and particularities in the morphology, radio spectrum and polarization of the ejected radio plasma. We argue that the combination of these signatures provides a sensitive probe of an environmental shock wave. Analysis of optical redshifts in NGC 315 vicinity confirms its location to be near, or at a site of large-scale flow collisions in the 100 Mpc sized Pisces-Perseus Supercluster region. NGC 315 resides at the intersection of several galaxy filaments, and its radio plasma serves there as a `weather station' (Burns 1998) probing the flow of the elusive and previously invisible IGM gas. If our interpretation is correct, this is the first indication for a shock wave in flows caused by the cosmological large scale structure formation, which is located in a filament of galaxies. The possibility that the putative shock wave is a source of gamma-rays and ultra high energy cosmic rays is briefly discussed.

Torsten A. Ensslin; Patrick Simon; Peter L. Biermann; Ulrich Klein; Sven Kohle; Philipp P. Kronberg; Karl-Heinz Mack

2000-12-19

110

Radio Detection of Cosmic Rays with LOPES  

E-print Network

electron & muon scintillator detector huts LOPES30: 30 radio antennas KASCADE Grande: expansion of KASCADE Frequency Array) ... #12;12 KASCADE measures electron component Ne muon component Nµ hadron component/(m MHz) variation of the frequency in 1 MHz 5 MHz 10 MHz steps sine wave signal calibration factor

Siegen, Universität

111

Relations among low ionosphere parameters and high frequency radio wave absorption  

NASA Technical Reports Server (NTRS)

Charged particle conductivities measured in the very low ionosphere at White Sands Missile Range, New Mexico, and Wallops Island, Virginia, are compared with atmospheric parameters and high frequency radio wave absorption measurements. Charged particle densities are derived from the conductivity data. Between 33 and 58 km, positive conductivity correlated well with neutral atmospheric temperature, with temperature coefficients as large as 4.6%/deg K. Good correlations were also found between HF radio wave absorption and negative conductivity at altitudes as low as 53 km, indicating that the day-to-day absorption variations were principally due to variations in electron loss rate.

Cipriano, J. P.

1973-01-01

112

Study of the Radio-Wave Absorbing Properties of a Lithium-Zinc Ferrite Based Composite  

NASA Astrophysics Data System (ADS)

Results are presented of a study of the radio-wave absorbing properties of a composite material based on lithium-zinc ferrite with composition Li0.4Fe2.4Zn0.2O4, synthesized by heating a mechanically activated mixture of the initial reagents Li2CO3-ZnO-Fe2O3 in a high-energy electron beam. It has been shown that a composite based on this material is promising as a radio-wave absorbing coating in the frequency range up to 12 GHz.

Surzhikov, A. P.; Lysenko, E. N.; Malyshev, A. V.; Vlasov, V. A.; Suslyaev, V. I.; Zhuravlev, V. A.; Korovin, E. Yu.; Dotsenko, O. A.

2014-09-01

113

Hybrid Support Vector Regression and GA\\/TS for Radio-Wave Path-Loss Prediction  

Microsoft Academic Search

\\u000a This paper presents support vector regression with hybrid genetic algorithms and tabu search (GA\\/TS) algorithms (SVRGA\\/TS)\\u000a models for the prediction of radio-wave path-loss in suburban environment. The support vector regression (SVR) model is a\\u000a novel forecasting approach and has been successfully used to solve time series problems. However, the application of SVR model\\u000a in a radio-wave path-loss forecasting has not

Kuo-Chen Hung; Kuo-Ping Lin; Gino K. Yang; Yuan-Cheng Tsai

2010-01-01

114

Goniopolarimetric study of the revolution 29 perikrone using the Cassini Radio and Plasma Wave Science instrument high-frequency radio receiver  

Microsoft Academic Search

We present goniopolarimetric (also known as direction finding) results of the Saturn kilometric radiation (SKR), using the Cassini Radio and Plasma Wave Science instrument high-frequency radio receiver data. Tools to retrieve the characteristics of the SKR sources have been developed that allow us to measure their 3-D location and beaming angle relative to the magnetic field in the source and,

B. Cecconi; L. Lamy; P. Zarka; R. Prangé; W. S. Kurth; P. Louarn

2009-01-01

115

Radio-wave oscillations of molecular-chain resonators.  

PubMed

We report a new type of nanomechanical resonator system based on one-dimensional chains of only 4 to 7 weakly coupled small molecules. Experimental characterization of the truly nanoscopic resonators is achieved by means of a novel radio-frequency scanning tunneling microscopy detection technique at cryogenic temperatures. Above 20 K we observe concerted oscillations of the individual molecules in chains, reminiscent of the first and second eigenmodes of a one-dimensional harmonic resonator. Radio-frequency scanning tunneling microscopy based frequency measurement reveals a characteristic length dependence of the oscillation frequency (between 51 and 127 MHz) in reasonable agreement with one-dimensional oscillator models. Our study demonstrates a new strategy for investigating and controlling the resonance properties of nanomechanical oscillators. PMID:24702407

Müllegger, Stefan; Rashidi, Mohammad; Mayr, Karlheinz; Fattinger, Michael; Ney, Andreas; Koch, Reinhold

2014-03-21

116

Broadband Metric-Range Radio Emission Associated with a Moreton/EIT Wave  

NASA Astrophysics Data System (ADS)

We present the evolution and kinematics of a broadband radio source that propagated collaterally with an H?/EIT wave, linking it with the type II burst that was excited higher up in the corona. The NRH wave emission extended from the frequency f~327 to f<151 MHz and was considerably weaker than the flare-related type IV burst. The emission centroid propagated at a height of 0-200 Mm above the solar limb and was intensified when the disturbance passed over enhanced coronal structures. We put forward the ad hoc hypothesis that the NRH wave signature is optically thin gyrosynchrotron emission excited by the passage of the coronal MHD fast-mode shock. The identification of radio emission associated with the coronal wave front is important since it offers us new diagnostic information that could provide us with better insight into the physical conditions in the disturbance itself.

Vršnak, B.; Magdaleni?, J.; Temmer, M.; Veronig, A.; Warmuth, A.; Mann, G.; Aurass, H.; Otruba, W.

2005-05-01

117

Results of refraction-angle measurement of radio waves in the Venus atmosphere on the basis of bistatic radar data  

NASA Astrophysics Data System (ADS)

Improved measurements of refraction in the Venus atmosphere using bistatic radar data have been obtained. To describe the refraction effects, a theoretical model is developed that makes it possible to determine the parameters for calculating radio communication lines in the Venus troposphere from the height dependence of the refractive index. Expressions are obtained relating the phase path length of radio waves and the integral absorption of radio waves in the atmosphere to the parameters of the theoretical model.

Salimzyanov, R. R.; Pavel'Ev, D. A.

1993-08-01

118

Ulysses observations of wave activity at interplanetary shocks and implications for type II radio bursts  

NASA Astrophysics Data System (ADS)

We present the first quantitative investigation of interplanetary type II radio emission in which in situ waves measured at interplanetary shocks are used to compute radio wave intensities for comparison with type II observations. This study is based on in situ measurements of 42 in-ecliptic forward shocks as well as 10 intervals of type II emission observed by the Ulysses spacecraft between 1 AU and 5 AU. The analysis involves comparisons of statistical properties of type II bursts and in situ waves, since the type II events are not related to particular shock passages at Ulysses. Most of the 42 shocks are associated with the occurrence of electrostatic waves near the time of shock passage at Ulysses. These waves, which are identified as electron plasma waves and ion acoustic-like waves, are typically most intense several minutes before shock passage. This suggests that wave-wave interactions might be of importance in electromagnetic wave generation and that type II source regions are located immediately upstream of the shocks. We use the in situ wave measurements to compute type II brightness temperatures, assuming that emission at the fundamental of the electron plasma frequency is generated by the merging of electron plasma waves and ion acoustic waves or the decay of electron plasma waves into ion acoustic and transverse waves. Second harmonic emission is assumed to be produced by the merging of electron plasma waves. The latter mechanism requires that a portion of the electron plasma wave distribution is backscattered, presumably by density inhomogeneities in regions of observed ion acoustic wave activity. The computed type II brightness temperatures are found to be consistent with observed values for both fundamental and second harmonic emission, assuming that strong (~=10-4V/m) electron plasma waves and ion acoustic waves are coincident and that the electron plasma waves have phase velocities less than about 10 times the electron thermal velocity. Thus a single conversion mechanism provides a plausible scenario for generation of both fundamental and harmonic interplanetary type II emission.

Lengyel-Frey, D.; Thejappa, G.; MacDowall, R. J.; Stone, R. G.; Phillips, J. L.

1997-02-01

119

A New Approach Towards Large Scale Soil Moisture Mapping by Radio Waves  

NASA Astrophysics Data System (ADS)

A new approach for obtaining integrated estimates of soil moisture content over larger regions of typically 10-50 km is described. It is based on a known correlation between propagation characteristics of low frequency radio surface waves and surface soil moisture, and provides valuable new benefits especially for meteorological prognostic models and for soil water estimation in agriculture. The paper consists of (1) a description of the theory of radio wave propagation with an extension of the classical theory of Norton (Proceedings of the Institute of Radio Engineers, Vol. 24, 1936), specifically the exploitation of the phase information, (2) demonstration of a method which guarantees the selection of reliable results from a large measurement data set, (3) a presentation of a new low cost measurement device to detect the amplitude and phase changes, and (4) results from initial measurements providing evidence that theoretical calculations are consistent with the measured change of electromagnetic signal properties due to soil moisture change.

Huebner, Christof; Kottmeier, Christoph; Brandelik, Alexander

2011-06-01

120

First experimental evidence of HF produced electron density irregularities in the polar ionosphere; Diagnosed by UHF radio star scintillations  

Microsoft Academic Search

HF-produced electron density irregularities with scale sizes of several hundred meters were observed in the polar ionosphere by means of UHF-scintillations using the new facilities at Tromsø. HF-power densities as low as 20 µW\\/m² excited irregularities during over-dense (HF < penetration frequency) modification.

A. Frey; P. Stubbe; H. Kopka

1984-01-01

121

EFFECTS OF RADIO WAVE PROPAGATION IN URBANIZED AREAS ON UAV-GCS COMMAND AND CONTROL  

E-print Network

EFFECTS OF RADIO WAVE PROPAGATION IN URBANIZED AREAS ON UAV-GCS COMMAND AND CONTROL Lock Wai Lek In an urban environment, the linkage between UAVs and ground control stations are subjected to multipath multipath can result in a nearly complete loss of command signals, which can limit the UAV's operational

Jenn, David C.

122

Radio and Plasma Waves in the Magnetosphere of Saturn: Similarities to Earth and Jupiter  

Microsoft Academic Search

With a few notable exceptions, most of the radio and plasma waves observed in the magnetosphere of Saturn are remarkably similar to those observed in the magnetospheres of Earth and Jupiter. For example, Saturn kilometric radiation, terrestrial kilometric radiation, and Jovian decametric radiation have many characteristics in common and are all generated by the same basic plasma mechanism, namely the

D. Gurnett; W. Kurth; G. Hospodarsky; A. Persoon; B. Cecconi; M. Desch; W. Farrell; M. Kaiser; P. Kellogg; K. Goetz; A. Lecacheux; P. Zarka; C. Harvey; P. Louarn; P. Canu; N. Cornilleau-Wehrlin; P. Galopeau; A. Roux; G. Fischer; H. Ladreiter; H. Rucker; H. Alleyne; R. Bostrom; G. Gustafsson; J. Wahlund; A. Pedersen

2005-01-01

123

An overview of observations by the Cassini radio and plasma wave investigation at earth  

Microsoft Academic Search

On August 18, 1999, the Cassini spacecraft flew by Earth at an altitude of 1186 km on its way to Saturn. Although the flyby was performed exclusively to provide the spacecraft with sufficient velocity to get to Saturn, the radio and plasma wave science (RPWS) instrument, along with several others, was operated to gain valuable calibration data and to validate

W. S. Kurth; G. B. Hospodarsky; D. A. Gurnett; M. L. Kaiser; J.-E. Wahlund; A. Roux; P. Canu; P. Zarka; Y. Tokarev

2001-01-01

124

Cassini Observations of Radio and Plasma Wave Phenomena Associated with the Saturn's Rings  

Microsoft Academic Search

During the Cassini passage through the inner region of the Saturnian system, the Radio and Plasma Wave Science (RPWS) instrument observed several effects associated with the rings. First, during both the inbound and outbound ring plane crossings, which were between the F and G rings, numerous impulsive signals with durations of several hundred microseconds were detected by the RPWS electric

D. A. Gurnett; W. S. Kurth; G. B. Hospodarsky; A. M. Persoon; L. Xin; W. Farrell; A. Lecacheux; J.-E. Wahlund

2004-01-01

125

A Radiance Model for Predicting Radio Wave Propagation in Irregular Dense Urban Areas  

E-print Network

to establish links that represent radiance transfers that include diffraction and free space losses based interest in the simulation and prediction of radio wave propagation in urban environments. Path-loss can accurate path loss predictions [4][5][6][7][8][9][10][11]. Deterministic models use detailed 2D or 3D

Boyer, Edmond

126

Incoherent Scattering of Radio Waves by Free Electrons with Applications to Space Exploration by Radar  

Microsoft Academic Search

Free electrons in an ionized medium scatter radio waves weakly. Under certain conditions only incoherent scattering exists. A powerful radar can detect the incoherent backscatter from the free electrons in and above the earth's ionosphere. The received signal is spread in frequency by the Doppler shifts associated with the thermal motion of the electrons. On the basis of incoherent backscatter

W. E. Gordon

1958-01-01

127

Radio Science, Volume ???, Number , Pages 110, Time Reversal of Electromagnetic Waves and  

E-print Network

Radio Science, Volume ???, Number , Pages 1­10, Time Reversal of Electromagnetic Waves that the techniques developed for ultrasound might be used for the electromagnetic case. It could be an interesting 10 and 30 cm are scattered off ob- jects such as walls, desks, cars and so on, which produces

Paris 7 - Denis Diderot, Université

128

A Simple Demonstration for Exploring the Radio Waves Generated by a Mobile Phone  

ERIC Educational Resources Information Center

Described is a simple low cost home-made device that converts the radio wave energy from a mobile phone signal into electricity for lighting an LED. No battery or complex circuitry is required. The device can form the basis of a range of interesting experiments on the physics and technology of mobile phones. (Contains 5 figures.)

Hare, Jonathan

2010-01-01

129

MEETING REPORT: SRP Meeting: Radio Wave Exposures - A Cause for Concern? (Preston, June 2002)  

Microsoft Academic Search

The purpose of the meeting was to explore issues raised concerning exposures to radio waves arising from radiofrequency and microwave communication technologies. The meeting was held at Ribby Hall Conference Centre, near Preston, on 27 June 2002 and was attended by 72 delegates. After an introduction by Ian MacDiarmid (BAE SYSTEMS), Tim Cooper (NRPB) gave the first presentation of the

Raj Bunger

2002-01-01

130

Radio and plasma wave observations at Saturn from Cassini's approach and first orbit.  

PubMed

We report data from the Cassini radio and plasma wave instrument during the approach and first orbit at Saturn. During the approach, radio emissions from Saturn showed that the radio rotation period is now 10 hours 45 minutes 45 +/- 36 seconds, about 6 minutes longer than measured by Voyager in 1980 to 1981. In addition, many intense impulsive radio signals were detected from Saturn lightning during the approach and first orbit. Some of these have been linked to storm systems observed by the Cassini imaging instrument. Within the magnetosphere, whistler-mode auroral hiss emissions were observed near the rings, suggesting that a strong electrodynamic interaction is occurring in or near the rings. PMID:15604362

Gurnett, D A; Kurth, W S; Hospodarsky, G B; Persoon, A M; Averkamp, T F; Cecconi, B; Lecacheux, A; Zarka, P; Canu, P; Cornilleau-Wehrlin, N; Galopeau, P; Roux, A; Harvey, C; Louarn, P; Bostrom, R; Gustafsson, G; Wahlund, J-E; Desch, M D; Farrell, W M; Kaiser, M L; Goetz, K; Kellogg, P J; Fischer, G; Ladreiter, H-P; Rucker, H; Alleyne, H; Pedersen, A

2005-02-25

131

Radio-wave emission due to hypervelocity impacts and its correlation with optical observations  

NASA Astrophysics Data System (ADS)

This paper describes the most interesting phenomena of radio-wave emission due to hypervelocity impacts. A projectile of polycarbonate with 1.1 g weight was accelerated by a rail gun to 3.8 km/sec, and hit two targets which are a 2 mm thick aluminum plate upstream and a 45 mm diameter aluminum column downstream, respectively. The projectile first breaks wires to give a triggering signal to a data recorder, then penetrates the aluminum plate, and finally hit the column, The emitted radio-waves propagate through the chamber window, and are received by antennas at each frequency band. The receivers in 22 GHz- and 2 GHz-bands consist of a low noise amplifier, a mixer, a local oscillator and an IF amplifier , respectively. The receiver in 1 MHz-band is a simple RF amplifier. The outputs of all receivers are fed to a data recorder which is actually a high-speed digital oscilloscope with a large amount of memory. The radio-waves were successfully recorded in 22 GHz-band with 500 MHz bandwidth, in 2 GHz-band with 300 MHz bandwidth, and in 1MHz-band. The waveforms in 22 GHz- and 2 GHz-bands coincide well each other, and are composed of two groups of sharp impulses with a separation of about 20 micro seconds. The width of an impulse is less than 2 n sec. which is the resolution limit of the data recorder. We carried out optical observations using an ultra-high speed camera simultaneously through another window of the chamber. The time interval between scenes is 2 micro sec. We can see a faint light of the projectile before the first impact to the plate, and then a brilliant gas exploding backward from the plate and forward to the column. After hitting the column target, the brilliant gas flows to the chamber wall and is reflected back to make a mixture with dark gas in the chamber. Excellent correlation between radio-wave emission and the observed optical phenomena was obtained in the experiment. It is easily conceived that the radio-waves consist of quite a wide frequency spectrum because of the spiky waveforms. The emission of the radio-waves is delayed from the optical events by several micro seconds. The optical phenomena are said to be mostly attributed to Bremstrahlung. The radio-wave phenomena are esteemed to be partially due to Bremstrahlung, but mainly due to other causes such as the heating effects of the targets or energy release from broken lattices of the targets.

Takano, T.; Maki, K.; Yamori, A.

132

Combined evidence for four- and three-wave interactions in solar type III radio bursts  

NASA Astrophysics Data System (ADS)

The high time resolution observations obtained by the STEREO/WAVES experiment show that in solar type III radio bursts, Langmuir waves often occur as intense one-dimensional or three-dimensional wave packets. We present the observations of one of the 1d wave packets as well as one of the 3d wave packets, whose short durations and peak intensities satisfy the threshold conditions for the oscillating two-stream instability (OTSI) and formation of collapsing envelope solitons. The depths, widths and temporal coincidences of the density cavities, observed during these wave packets indicate that they probably correspond to cavitons, generated by the ponderomotive force of the collapsing wave packets. The spectrum of each of the parallel and perpendicular components of the 3d wave packet as well as the spectrum of the parallel component of the 1d wave packet show similar characteristics, namely, each of them contains a primary peak at fpe, two secondary peaks at fpe×fS and a low-frequency enhancement below fS, which, as indicated by the frequency and wave number resonance conditions, and the fast Fourier transform (FFT)-based tricoherence spectral peak at (fpe, fpe, fpe+fS, fpe- fS) are coupled to each other by the OTSI type of four-wave interaction (fpe is the local electron plasma frequency and fS is the frequency of ion sound waves). In addition to the primary peak at fpe, each of these spectra also contains a peak at 2fpe, which as indicated by the frequency and wave number resonance conditions, and the waveletbased bicoherence spectral peak at (fpe, fpe), appears to correspond to the second harmonic electromagnetic waves generated as a result of coalescence of oppositely propagating sidebands excited by the OTSI. Additionally, the spectrum of the 1d wave packet also contains a peak at 3fpe, which as indicated by the bispectral analysis probably corresponds to electromagnetic waves excited as a result of merging of Langmuir waves with second harmonic electromagnetic waves. Thus, these observations for the first time provide combined evidence that (1) the OTSI and related strong turbulence processes play a significant role in the stabilization of the electron beam, (2) the coalescence of the oppositely propagating up- and down-shifted daughter Langmuir waves excited by the OTSI probably is the emission mechanism of the second harmonic radiation, and (3) the Langmuir collapse follows the route of OTSI in some of the type III radio bursts.

Golla, T.; MacDowall, R. J.

2013-12-01

133

Kilometric radio waves generated along auroral field lines observed by ground facilities - A theoretical model  

NASA Technical Reports Server (NTRS)

A theory of generation of radio waves observed by ground-based facilities in the frequency range 150-700 kHz is discussed. This work is a continuation of an earlier discussion (Wu et al., 1989) in which it was proposed that the trapped electrons along the auroral field lines can lead to a cyclotron instability which amplifies the whistler waves observed at ground level. The objective of the present study is to investigate the propagation effect on the wave amplification and to examine whether the proposed mechanism is indeed viable.

Ziebell, L. F.; Wu, C. S.; Yoon, Peter H.

1991-01-01

134

In-flight calibration of the Cassini-Radio and Plasma Wave Science (RPWS) antenna system for direction-finding and polarization measurements  

Microsoft Academic Search

One major objective of the Cassini mission is the analysis of Saturnian radio emissions of magnetospheric (auroral) as well as atmospheric (lightning) origin. The Radio and Plasma Wave Science (RPWS) experiment is designed to measure the full polarization and the wave vector of the incoming radio waves, allowing us to retrieve information on source locations and emission modes. For that

Dieter F. Vogl; Baptiste Cecconi; Wolfgang Macher; Philippe Zarka; Hans Peter Ladreiter; Pierre Fédou; Alain Lecacheux; Terry Averkamp; Georg Fischer; Helmut O. Rucker; Donald A. Gurnett; William S. Kurth; George B. Hospodarsky

2004-01-01

135

NONLINEAR WAVE INTERACTIONS AS EMISSION PROCESS OF TYPE II RADIO BURSTS  

SciTech Connect

The emission of fundamental and harmonic frequency radio waves of type II radio bursts are assumed to be products of three-wave interaction processes of beam-excited Langmuir waves. Using a particle-in-cell code, we have performed simulations of the assumed emission region, a coronal mass ejection foreshock with two counterstreaming electron beams. Analysis of wavemodes within the simulation shows self-consistent excitation of beam-driven modes, which yield interaction products at both fundamental and harmonic emission frequencies. Through variation of the beam strength, we have investigated the dependence of energy transfer into electrostatic and electromagnetic modes, confirming the quadratic dependence of electromagnetic emission on electron beam strength.

Ganse, Urs; Kilian, Patrick; Spanier, Felix [Lehrstuhl fuer Astronomie, Universitaet Wuerzburg, Wuerzburg (Germany); Vainio, Rami, E-mail: uganse@astro.uni-wuerzburg.de [Department of Physics, University of Helsinki, Helsinki (Finland)

2012-06-01

136

Cluster Radio Relics as a Tracer of Shock Waves of the Large-Scale Structure Formation  

E-print Network

We present evidence for the existence of shock waves caused by the formation of the large-scale structure. In some clusters of galaxies peripherally located sources of extended diffuse radio emission exist, the so-called cluster radio relics. They have steep radio spectra but no apparent cutoff, as old remnants of radio galaxies usually have. Therefore particle acceleration has to take place within them. We propose that shock structures of the cosmological large-scale matter flows are responsible for the acceleration of relativistic electrons: cluster accretion shocks and bow shocks of merger events. We develop a theory of radio plasma having traversed these shocks and compare it to observational data of nine radio relics (0038-096, 0917+75, 1140+203, 1253+275, 1712+64, 1706+78, 2006-56, 2010-57, 1401-33) and their host clusters (A85, A786, A1367, Coma, A2255, A2256, A3667, S753). The necessary accretion power, the spectral index of the radio spectrum, the acceleration efficiency of the shock, the diffusion coefficient in the post-shock region, and the predicted radio polarization in all of our examples fit into a coherent interpretation of the observational data. Since polarization measurements are available only for four sources, the predictions of our theory can be independently checked using other examples. The predicted values of the shock compression ratio, density and temperature of the infalling gas, magnetic field strength of the shocked and unshocked radio plasma are discussed within the frame of structure formation theory.

Torsten A. Ensslin; Peter L. Biermann; Ulrich Klein; Sven Kohle

1997-12-22

137

Nonlinear nonresonant forces by radio-frequency waves in plasmas  

SciTech Connect

Nonresonant forces by applied rf waves in plasmas are analyzed. Along the background dc magnetic field, the force arises from the gradient of the ponderomotive potential. Only when the dc magnetic field is straight, however, is this parallel force completely consistent with that from the single particle picture, where the ponderomotive force depends on the gradients of rf fields only. Across the dc magnetic field, besides the ponderomotive force from the particle picture, additional Reynolds stress and polarization stress contribute to the total force. For waves with frequency much lower than the cyclotron frequency, the perpendicular forces from the particle and fluid pictures can have opposite signs. In plasmas with a symmetry angle (e.g., toroidal systems), nonresonant forces cannot drive net flow or current in the flux surface, but the radial force may influence macroscopic behavior of plasma. Moreover, nonresonant forces may drive flow or current in linear plasmas or in a localized region of toroidal plasmas.

Gao Zhe; Fisch, Nathaniel J.; Qin, Hong; Myra, J. R. [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543 (United States); Lodestar Research Corporation, Boulder, Colorado 80301 (United States)

2007-08-15

138

Anomalous Radio-Wave Scattering from Interstellar Plasma Structures  

NASA Astrophysics Data System (ADS)

This paper considers scattering screens that have arbitrary spatial variations of scattering strength transverse to the line of sight, including screens that are spatially well confined, such as disks and filaments. We calculate the scattered image of a point source and the observed pulse shape of a scattered impulse. The consequences of screen confinement include (1) source image shapes that are determined by the physical extent of the screen rather than by the shapes of much smaller diffracting microirregularities (these include image elongations and orientations that are frequency dependent); (2) variation with frequency of angular broadening that is much weaker than the trademark ?-2 scaling law (for a cold, unmagnetized plasma), including frequency-independent cases; and (3) similar departure of the pulse-broadening time from the usually expected ?-4 scaling law. We briefly discuss applications that include scattering of pulses from the Crab pulsar by filaments in the Crab Nebula; image asymmetries from Galactic scattering of the sources Cyg X-3, Sgr A*, and NGC 6334B; and scattering of background active galactic nuclei by intervening galaxies. We also address the consequences for inferences about the shape of the wavenumber spectrum of electron density irregularities, which depend on scaling laws for the image size and the pulse broadening. Future low-frequency (<100 MHz) array observations will also be strongly affected by the Galactic structure of scattering material. Our formalism is derived in the context of radio scattering by plasma density fluctuations. It is also applicable to optical, UV, and X-ray scattering by grains in the interstellar medium.

Cordes, J. M.; Lazio, T. Joseph W.

2001-03-01

139

Thunderstorms, lightning, sprites and magnetospheric whistler-mode radio waves  

E-print Network

Thunderstorms and the lightning that they produce are inherently interesting phenomena that have intrigued scientists and mankind in general for many years. The study of thunderstorms has rapidly advanced during the past century and many efforts have been made towards understanding lightning, thunderstorms and their consequences. Recent observations of optical phenomena above an active lightning discharge along with the availability of modern technology both for data collection and data analysis have renewed interest in the field of thunderstorms and their consequences in the biosphere. In this paper, we review the electrification processes of a thunderstorm, lightning processes and their association with global electric circuit and climate. The upward lightning discharge can cause sprites, elves, jets, etc. which are together called transient luminous events. Their morphological features and effects in the mesosphere are reviewed. The wide spectrum of electromagnetic waves generated during lightning discharg...

Siingh, Devendraa; Patel, R P; Singh, Rajesh; Singh, R P; Veenadhari, B; Mukherjee, M

2009-01-01

140

Storm time, short-lived bursts of relativistic electron precipitation detected by subionospheric radio wave propagation  

NASA Astrophysics Data System (ADS)

In this study we report on ground-based observations of short bursts of relativistic electron precipitation (REP), detected by a subionospheric propagation sensor in Sodankylä, Finland during 2005. In two ˜4 hour case study periods from L = 5.2, around local midnight, several hundred short-lived radio wave perturbations were observed, covering a wide range of arrival azimuths. The vast majority (˜99%) of these perturbations were not simultaneous with perturbations on other paths, consistent with a precipitation "rainstorm" producing ionospheric changes of small spatial sizes around the Sodankylä receiver. The recovery time of these radio wave perturbations are ˜1.2 s, which is consistent with the modeled effects of a burst of >2 MeV precipitating electrons. This agrees with satellite observations of the microburst energy spectrum. The energetic nature of the precipitation which produces the FAST perturbations suggests that they should be observable in both day and night conditions. While it is widely assumed that satellite-detected REP microbursts are due to wave-particle interactions with very low-frequency chorus waves, the energy spectra predicted by our current models of chorus propagation and wave-particle interaction are not consistent with the experimentally observed radio wave perturbations presented here or previously reported satellite observations of REP microbursts. The results inferred from both the satellite and subionospheric observations, namely the absence of a large, dominant component of <100 keV precipitating electrons, fundamentally disagrees with a mechanism of chorus-driven precipitation. Nonetheless, further work on the modeling of chorus-driven precipitation is required.

Rodger, Craig J.; Clilverd, Mark A.; Nunn, David; Verronen, Pekka T.; Bortnik, Jacob; Turunen, Esa

2007-07-01

141

An Overview of Observations by the Cassini Radio and Plasma Wave Investigation at Earth  

NASA Technical Reports Server (NTRS)

On August 18, 1999, the Cassini spacecraft flew by Earth at an altitude of 1186 km on its way to Saturn. Although the flyby was performed exclusively to provide the spacecraft with sufficient velocity to get to Saturn, the radio and plasma wave science (RPWS) instrument, along with several others, was operated to gain valuable calibration data and to validate the operation of a number of capabilities. In addition, an opportunity to study the terrestrial radio and plasma wave environment with a highly capable instrument on a swift fly-through of the magnetosphere was afforded by the encounter. This paper provides an overview of the RPWS observations, at Earth, including the identification of a number of magnetospheric plasma wave modes, an accurate measurement of the plasma density over a significant portion of the trajectory using the natural wave spectrum in addition to a relaxation sounder and Langmuir probe, the detection of natural and human-produced radio emissions, and the validation of the capability to measure the wave normal angle and Poynting flux of whistler-mode chorus emissions. The results include the observation of a double-banded structure at closest' approach including a band of Cerenkov emission bounded by electron plasma and upper hybrid frequencies and an electron cyclotron harmonic band just above the second harmonic of the electron cyclotron frequency. In the near-Earth plasma sheet, evidence for electron phase space holes is observed, similar to those first reported by Geotail in the magnetotail. The wave normal analysis confirms the Polar result that chorus is generated very close to the magnetic equator and propagates to higher latitudes. The integrated power flux of auroral kilometric radiation is also used to identify a series of substorms observed during the outbound passage through the magnetotail.

Kurth, W. S.; Hospodarsky, G. B.; Gurnett, D. A.; Kaiser, M. L.; Wahlund, J.-E.; Roux, A.; Canu, P.; Zarka, P.; Tokarev, Y.

2001-01-01

142

Global mapping of ionospheric HF/VHF radio wave absorption due to solar energetic protons  

NASA Astrophysics Data System (ADS)

Simple, one-parameter algorithms are applied to the observed energetic proton flux as provided by instruments aboard the GOES series of satellites to yield estimates of the high-latitude HF and VHF radio wave absorption for day and night, respectively. These results are extended to full daily coverage by treating the effects of solar illumination, geomagnetic cutoff variation, and frequency dependence over the entire earth. Validation calculations of the polar cap absorption of HF radio waves have been performed for 11 larger solar energetic particle events during the period from 1992 to 2002 and the results are compared to observations of 30 MHz riometers operated by the Air Force Geophysics Laboratory and located at Thule, Greenland. Prediction of the minimum event duration from current flux level is also obtained, and a specimen presentation of the north and south polar caps illustrates the graphical output of the model for the peak of the 6 December 2006 solar proton event.

Sauer, Herbert H.; Wilkinson, Daniel C.

2008-12-01

143

On the determination of gravity wave momentum flux from GPS radio occultation data  

NASA Astrophysics Data System (ADS)

Global Positioning System (GPS) radio occultation (RO) is a well-established technique for obtaining global gravity wave (GW) information. RO uses GPS signals received by low Earth-orbiting satellites for atmospheric limb sounding. Temperature profiles are derived with high vertical resolution and provide a global coverage under any weather conditions, offering the possibility of global monitoring of the vertical temperature structure and atmospheric wave parameters. The six-satellite constellation COSMIC/FORMOSAT-3 delivers approximately 2000 temperature profiles daily. In this study, we use a method to obtain global distributions of horizontal gravity wave wavelengths, to be applied in the determination of the vertical flux of horizontal momentum transported by gravity waves. Here, a method for the determination of the real horizontal wavelength from three vertical profiles is applied to the COSMIC data. The horizontal and vertical wavelength, the specific potential energy (Ep), and the vertical flux of horizontal momentum (MF) are calculated and their global distribution is discussed.

Faber, A.; Llamedo, P.; Schmidt, T.; de la Torre, A.; Wickert, J.

2013-11-01

144

Phase shift keying using optical delay modulation for millimeter-wave fiber-optic radio links  

Microsoft Academic Search

We propose a novel phase shift keying technique that uses optical delay modulation for fiber optic radio links. Using only a 2×1 switch and a delay line, this technique enables modulation of a millimeter-wave carrier at bit rates of several gigabits per second or higher, where high-speed devices are not needed. Binary phase shift keying (BPSK) was experimentally demonstrated, 2-Gb\\/s

Yoshiyuki Doi; Seiji Fukushima; Tetsuichiro Ohno; Yutaka Matsuoka; Hiroaki Takeuchi

2000-01-01

145

Z mode waves as the source of Saturn narrowband radio emissions  

Microsoft Academic Search

We report 5 kHz narrowband Z mode emissions observed by the Cassini Radio and Plasma Waves Science (RPWS) instrument during high latitude perikrone passes. The narrowband emissions observed below the local electron cyclotron frequency (fce) are >20 dB more intense than the usual L-O mode narrowband emissions observed above local fce. Polarization measurements show that the narrowband emissions observed below

Sheng-Yi Ye; J. D. Menietti; G. Fischer; Z. Wang; B. Cecconi; D. A. Gurnett; W. S. Kurth

2010-01-01

146

Silicon Millimeter-Wave Radio Circuits at 60-100 GHz  

Microsoft Academic Search

This paper reviews silicon millimeter-wave radio circuits operating between 60 and 100GHz. Transmitter and receiver chips operating in the 60-GHz ISM band are highlighted, where the packaged chipset has shown data rates as high as 2 Gb\\/s over 5m for a wireless high-definition video link. In addition, a 60GHz PA with 23dBm output power and a class-E 60GHz PA with

B. Floyd; U. Pfeiffer; S. Reynolds; A. Valdes-Garcia; C. Haymes; Y. Katayamat; D. Nakano; T. Beukema; B. Gaudier; M. Soyuer

2007-01-01

147

High resolution of electromagnetic waves in time-varying radio channels  

Microsoft Academic Search

The applicability of the SAGE (space-alternating generalized expectation-maximization) algorithm to the estimation of time variant radio channels is demonstrated. This algorithm allows one to separate the complex multi-dimensional optimization problem required to compute the estimate of the parameters characterizing the impinging waves, i.e. their delay, incidence azimuth, Doppler frequency, and complex amplitude, into separate one dimensional optimization processes that can

Klaus I. Pedersen; Bernard H. Fleury; Preben E. Mogensen

1997-01-01

148

A Minimal Radio and Plasma Wave Investigation For a Mercury Orbiter Mission  

NASA Technical Reports Server (NTRS)

The primary thrust of the effort at The University of Iowa for the definition of an orbiter mission to Mercury is a minimum viable radio and plasma wave investigation. While it is simple to add sensors and capability to any payload, the challenge is to do reasonable science within limited resources; and viable missions to Mercury are especially limited in payload mass. For a wave investigation, this is a serious concern, as the sensor mass often makes up a significant fraction of the instrumentation mass.

Kurth, W. S.

2001-01-01

149

Higher order moments used in ionospheric scintillation description  

NASA Astrophysics Data System (ADS)

Ionospheric scintillations, caused by small scale fluctuations in the electron density structure, presents one of the most influential factor in transionospheric radio wave propagation and important topic for the mitigation of its effects. Initiating disturbances and distortion in phase and amplitude of the propagating signal, scintillation can significantly affect the GNSS accuracy and cause serious problems to commercial navigation systems. Decades of investigations of the probability distribution of the scintillating signals brought a lot of possible solutions, several of them are widely adopted and are in use this days. Solutions like joint Gaussian distribution of complex signal and Rytov solution seems to work for weak scintillating signals, but still there is not an easy way to derive satisfactory results, leading to need for further investigations [Yeh and Liu, 1982]. The focus of this paper is on the statistical analysis of ionospheric scintillation. We analyze various probability distribution functions of scintillating signals using simulated and real data. The analysis results are presented through higher order moments, dependent on various parameters (scintillation index, phase variance, season, time of the day and solar/magnetic activity). Implementation of higher order moments, skewness and kurtosis, could give more information about the ionospheric irregularities influence on the propagating signal and relation to the time delay of the signal.

Stevanovic, D.; Wernik, A. W.

2013-12-01

150

Phase Coupling in Langmuir Wave Packets: Evidence for Four Wave Interactions in Solar Type III Radio Bursts  

NASA Technical Reports Server (NTRS)

The four wave interaction process, known as the oscillating two stream instability (OTSI) is considered as one of the mechanisms responsible for stabilizing the electron beams associated with solar type III radio bursts. It has been reported that (1) an intense localized Langmuir wave packet associated with a type III burst contains the spectral characteristics of the OTSI: (a) a resonant peak at the local electron plasma frequency, f(sub pe), (b) a Stokes peak at a frequency slightly lower than f(sub pe), (c) anti-Stokes peak at a frequency slightly higher than f(sub pe), and (d) a low frequency enhancement below a few hundred Hz, (2) the frequencies and wave numbers of these spectral components satisfy the resonance conditions of the OTSI, and (3) the peak intensity of the wave packet is well above the thresholds for the OTSI as well as spatial collapse of envelope solitons. Here, for the first time, applying the trispectral analysis on this wave packet, we show that the tricoherence, which measures the degree of coherent four-wave coupling amongst the observed spectral components exhibits a peak. This provides an additional evidence for the OTSI and related spatial collapse of Langmuir envelope solitons in type III burst sources.

Thejappa, G.; MacDowall, R. J.; Bergamo, M.

2012-01-01

151

Fokker-Planck description of the scattering of radio frequency waves at the plasma edge  

SciTech Connect

In magnetic fusion devices, radio frequency (rf) waves in the electron cyclotron (EC) and lower hybrid (LH) range of frequencies are being commonly used to modify the plasma current profile. In ITER, EC waves are expected to stabilize the neoclassical tearing mode (NTM) by providing current in the island region [R. Aymar et al., Nucl. Fusion 41, 1301 (2001)]. The appearance of NTMs severely limits the plasma pressure and leads to the degradation of plasma confinement. LH waves could be used in ITER to modify the current profile closer to the edge of the plasma. These rf waves propagate from the excitation structures to the core of the plasma through an edge region, which is characterized by turbulence--in particular, density fluctuations. These fluctuations, in the form of blobs, can modify the propagation properties of the waves by refraction. In this paper, the effect on rf due to randomly distributed blobs in the edge region is studied. The waves are represented as geometric optics rays and the refractive scattering from a distribution of blobs is formulated as a Fokker-Planck equation. The scattering can have two diffusive effects--one in real space and the other in wave vector space. The scattering can modify the trajectory of rays into the plasma and it can affect the wave vector spectrum. The refraction of EC waves, for example, could make them miss the intended target region where the NTMs occur. The broadening of the wave vector spectrum could broaden the wave generated current profile. The Fokker-Planck formalism for diffusion in real space and wave vector space is used to study the effect of density blobs on EC and LH waves in an ITER type of plasma environment. For EC waves the refractive effects become important since the distance of propagation from the edge to the core in ITER is of the order of a meter. The diffusion in wave vector space is small. For LH waves the refractive effects are insignificant but the diffusion in wave vector space is important. The theoretical model is general enough to study the effect of density blobs on all propagating cold plasma waves.

Hizanidis, Kyriakos; Kominis, Yannis; Tsironis, Christos [School of Electrical and Computer Engineering, National Technical University of Athens, Athens GR 15773 (Greece); Ram, Abhay K. [Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2010-02-15

152

Circular Polarization Induced by Scintillation in a Magnetized Medium  

E-print Network

A new theory is presented for the development of circular polarization as radio waves propagate through the turbulent, birefringent interstellar medium. The fourth order moments of the wavefield are calculated and it is shown that unpolarized incident radiation develops a nonzero variance in circular polarization. A magnetized turbulent medium causes the Stokes parameters to scintillate in a non-identical manner. A specific model for this effect is developed for the case of density fluctuations in a uniform magnetic field.

J. -P. Macquart; D. B. Melrose

2000-06-30

153

Effect exerted by a radio wave electromagnetic field on the rheological properties of water and portland-cement systems  

NASA Astrophysics Data System (ADS)

We have studied the effect of the regimes of high-frequency (radio wave) electromagnetic treatment of gauging water on the process of structurization and on the technological characteristics of portland-cement systems. It has been established that the radio wave electromagnetic activation of water leads to a reduction in its surface tension, dynamic viscosity, and shear stress, as well as intensifies the formation of coagulation structures in a portlandcement slurry and aids in increasing the mobility of cement-sand mixtures.

Azharonok, V. V.; Belous, N. Kh.; Rodtsevich, S. P.; Koshevar, V. D.; Shkadretsova, V. G.; Goncharik, S. V.; Chubrik, N. I.; Orlovich, A. I.

2013-09-01

154

Monitoring the solar-terrestrial environment using interplanetary scintillation  

NASA Astrophysics Data System (ADS)

Before being detected on Earth, radio waves from a celestial source pass through the interplanetary medium, where they undergo diffraction by plasma density variations in the solar wind, making them appear to scintillate. The amount of scintillation observed can be used to infer the electron density along the line-of-sight to the source. Therefore, when observing many sources across the sky, the solar wind can be mapped out daily. Observations taken over a 5 year period (1990-94) with the Cambridge IPS array are now being analysed at Glasgow. Man-made interference, from sources such as domestic appliances and car engines, is a significant problem in much of these data. Obviously, to get the most out of the data, this noise must be dealt with properly. Another problem is caused by scintillation in the ionosphere. We must be able to distinguish between scintillation caused by the ionosphere, and that caused by the interplanetary medium. Using a model for the expected scintillation profile and timescale for each radio source, it is possible to cut out noise, and to identify periods of ionospheric scintillation in the data. The fitting procedure returns an estimate of both the scintillating power of the source, and the scintillation frequency, which can in turn be used to measure both the density and speed of the solar wind over the whole sky. From this, it's possible to track transient events in the interplanetary medium, such as Coronal Mass Ejections. This whole-sky picture has several advantages over a localised measurement given by an in-situ spacecraft.

Daly, N.

155

Scintillation Monitoring Using Asymmetry Index  

NASA Astrophysics Data System (ADS)

Variation in electron density can have significant effect on GNSS signals in terms of propagation delay. Ionospheric scintillation can be caused by rapid change of such delay, specifically, when they last for a longer period of time. Ionospheric irregularities that account for scintillation may vary significantly in spatial range and drift with the background plasma at speeds of 45 to 130 m/sec. These patchy irregularities may occur several times during night, e.g. in equatorial region, with the patches move through the ray paths of the GNSS satellite signals. These irregularities are often characterized as either ‘large scale’ (which can be as large as several hundred km in East-West direction and many times that in the North-South direction) or ‘small scale’ (which can be as small as 1m). These small scale irregularities are regarded as the main cause of scintillation [1,2]. In normal solar activity conditions, the mid-latitude ionosphere is not much disturbed. However, during severe magnetic storms, the aurora oval extends towards the equator and the equator anomaly region may stretched towards poles extending the scintillation phenomena more typically associated with those regions into mid-latitudes. In such stormy conditions, the predicted TEC may deviate largely from the true value of the TEC both at low and mid-latitudes due to which GNSS applications may be strongly degraded. This work is an attempt to analyze ionospheric scintillation (S4 index) using ionospheric asymmetry index [3]. The asymmetry index is based on trans-ionospheric propagation between GPS and LEO satellites in a radio occultation (RO) scenario, using background ionospheric data provided by MIDAS [4]. We attempted to simulate one of the recent geomagnetic storms (NOAA scale G4) occurred over low/mid-latitudes. The storm started on 26 September 2011 at UT 18:00 and lasted until early hours of 27 September 2011. The scintillation data for the storm was taken from an ionospheric station in Cairo, Egypt (lat= 29.8641 °, long= 31.3172 °). It was observed that the level of asymmetry was significantly increased during the main phase of the geomagnetic storm. This was due to the changes in ionization, which in turn produced large gradients along occulted ray path in the ionosphere. A very good correlation was found between the evaluated ionospheric asymmetry index and the S4 scintillation index. Additionally, the correlation between evaluated ionospheric asymmetry and errors related to the RO inversion products such as peak electron density (delta NmF2) and Vertical TEC (delta VTEC) estimates also showed promising results. This work is carried out under the framework of the TRANSMIT project (Training Research and Applications Network to Support the Mitigation of Ionospheric Threats - www.transmit-ionosphere.net). [1]Basu Sa. and Basu Su., (1981), ‘Equatorial Scintillation - A Review’, Journal of Atmospheric and Solar-Terrestrial Physics, 43, p. 473. [2]Davies K., (1990), ‘Ionospheric Radio’, IEEE Electromagnetic Waves Series 31, Peter Peregrinus Ltd. [3]Spencer, P., Mitchell, C.N., (2007) ‘Imaging of fast moving electron-density structures in the polar cap’, Annals of Geophysics, vol. 50, no. 3, pp. 427-434. [4]Shaikh, M.M., Notarpietro, R., Nava, B., (2013) ‘The Impact of Spherical Symmetry Assumption on Radio Occultation Data Inversion in the Ionosphere: An Assessment Study’, Advances in Space Research, doi: http://dx.doi.org/10.1016/j.asr.2013.10.025.

Shaikh, Muhammad Mubasshir; Mahrous, Ayman; Abdallah, Amr; Notarpietro, Riccardo

156

High power water load for microwave and millimeter-wave radio frequency sources  

DOEpatents

A high power water load for microwave and millimeter wave radio frequency sources has a front wall including an input port for the application of RF power, a cylindrical dissipation cavity lined with a dissipating material having a thickness which varies with depth, and a rear wall including a rotating reflector for the reflection of wave energy inside the cylindrical cavity. The dissipation cavity includes a water jacket for removal of heat generated by the absorptive material coating the dissipation cavity, and this absorptive material has a thickness which is greater near the front wall than near the rear wall. Waves entering the cavity reflect from the rotating reflector, impinging and reflecting multiple times on the absorptive coating of the dissipation cavity, dissipating equal amounts of power on each internal reflection.

Ives, R. Lawrence (Saratoga, CA); Mizuhara, Yosuke M. (Palo Alto, CA); Schumacher, Richard V. (Sunnyvale, CA); Pendleton, Rand P. (Saratoga, CA)

1999-01-01

157

Prospects for joint radio telescope and gravitational wave searches for astrophysical transients  

E-print Network

The radio skies remain mostly unobserved when it comes to transient phenomena. The direct detection of gravitational waves will mark a major milestone of modern astronomy, as an entirely new window will open on the universe. Two apparently independent phenomena can be brought together in a coincident effort that has the potential to boost both searches. In this paper we will outline the scientific case that stands behind these future joint observations and will describe the methods that might be used to conduct the searches and analyze the data. The targeted sources are binary systems of compact objects, known to be strong candidate sources for gravitational waves. Detection of transients coincident in these two channels would be a significant smoking gun for first direct detection of gravitational waves, and would open up a new field for characterization of astrophysical transients involving massive compact objects.

V. Predoi; J. Clark; T. Creighton; E. Daw; S. Fairhurst; I. S. Heng; J. Kanner; T. Regimbau; P. Shawhan; X. Siemens; P. Sutton; A. Vecchio; D. White; G. Woan

2009-12-02

158

Self-compensated standing wave probe for characterization of radio-frequency plasmas  

NASA Astrophysics Data System (ADS)

A simple self-compensated Langmuir probe using the character of a standing wave is developed for characterization of radio-frequency (RF) discharge plasmas. This probe is based on a concept that the interference of RF field is eliminated at the node of a standing wave which exists ideally at one-fourth of the RF wavelength (?/4) away from the probe tip in the plasma. The fluctuation of plasma space potential is suppressed as confirmed by comparison with a non-compensated probe and a self-compensated probe using an inductor-capacitor (LC) resonant circuit. The plasma parameters obtained with the standing wave probe are in agreement with those with the LC resonant probe within discrepancy of 15% indicating high reliability of the results.

Sung, Ta-Lun; Matsumura, Shosaku; Teii, Kungen; Teii, Shinriki

2014-06-01

159

An Experiment Study of the Propagation of Radio Waves in a Scaled Model of Long-Wall Coal Mining Tunnels  

SciTech Connect

A long-wall coal mining tunnel is the most important working area in a coal mine. It has long been realized that radio communications can improve both productivity and safety in this dangerous area. Hence, many attempts to use radio communications in such an environment have been made. Unfortunately, no radio system has satisfactorily provided communication services there, which, we believe, is partially due to poor understanding of the propagation characteristics of radio waves in the long-wall mining tunnel. To have deeper physical insight into the propagation problem, a scaled model of the long-wall mining tunnel was built, and the propagation characteristics of UHF radio waves were measured. The experiment and the measured results are presented and discussed.

Han, G.R.; Zhang, W.M.; Zhang, Y.P. [Shanxi University, Taiyuan (China)

2009-07-01

160

Radio and Plasma Wave Observations From the Cassini and Galileo Spacecraft During the Cassini Flyby of Jupiter  

Microsoft Academic Search

During the Cassini flyby of Jupiter, which occurred on December 30, 2000, simultaneous data were collected from the Galileo spacecraft, which is in orbit around Jupiter, and from the Cassini spacecraft. In this paper we report results from the Radio and Plasma Wave Science (RPWS) instrument on the Cassini spacecraft and from the Plasma Wave Science (PWS) instrument on the

D. Gurnett; W. Kurth; G. Hospodarsky; A. Persoon; H. Alleyne; S. Bolton; R. Bostrom; P. Canu; N. Cornilleau-Wehrlin; M. Desch; W. Farrell; P. Galopeau; K. Goetz; G. Gustafsson; C. Harvey; M. Kaiser; P. Kellogg; H. P. Ladreiter; A. Lecacheux; P. Louarn; A. Pedersen; A. Roux; H. Rucker; J. Wahlund; P. Zarka

2001-01-01

161

Coordinated Radio, Electron, and Waves Experiment (CREWE) for the NASA Comet Rendezvous and Asteroid Flyby (CRAF) instrument  

Microsoft Academic Search

The Coordinated Radio, Electron, and Waves Experiment (CREWE) was designed to determine density, bulk velocity and temperature of the electrons for the NASA Comet Rendezvous and Asteroid Flyby Spacecraft, to define the MHD-SW IMF flow configuration; to clarify the role of impact ionization processes, to comment on the importance of anomalous ionization phenomena (via wave particle processes), to quantify the

Jack D. Scudder

1992-01-01

162

Science Sampler: Radio-wave inquiry with web-controlled receivers  

NSDL National Science Digital Library

This article describes a web-enhanced investigation of radio waves suitable for upper middle school science students that correlates with the National Science Education Standards. In this engaging lesson, students are involved in science inquiry using internet-linked instruments to observe and study electromagnetic radiation, one of the fundamental forces of nature. It follows the learning cycle phases of exploring, inventing or introducing, and applying a concept (Abraham 1997). This investigation builds on previous work by incorporating the unique twist of having students use high-quality, web-controlled receivers (Wise 2006, 2007).

Wise, Kevin

2007-04-01

163

Wave activity at ionospheric heights above the Andes Mountains detected from FORMOSAT-3/COSMIC GPS radio occultation data  

NASA Astrophysics Data System (ADS)

estimation of the ionospheric wave activity, derived from 4 years of FORMOSAT-3/ COSMIC GPS (Taiwan's Formosa Satellite Mission 3/Constellation Observing System for Meteorology—Global Positioning System) radio occultation electron density data, is presented. A systematic enhancement at the eastern side of the Andes range with respect to the western side is observed. A fitting method to remove the wavelike component from each measured profile and estimate the wave activity is described. The differential effect introduced by the action of orography on the generation, to the eastern side of the Andes, of mountain waves, deep convection waves, or even secondary waves aloft after momentum deposition in the middle atmosphere, is suggested.

Torre, A.; Alexander, P.; Llamedo, P.; Hierro, R.; Nava, B.; Radicella, S.; Schmidt, T.; Wickert, J.

2014-03-01

164

Satellite radio occultation investigations of internal gravity waves in the planetary atmospheres  

NASA Astrophysics Data System (ADS)

Internal gravity waves (IGWs) modulate the structure and circulation of the Earth’s atmosphere, producing quasi-periodic variations in the wind velocity, temperature and density. Similar effects are anticipated for the Venus and Mars since IGWs are a characteristic of stably stratified atmosphere. In this context, an original method for the determination of IGW parameters from a vertical temperature profile measurement in a planetary atmosphere has been developed [Gubenko et al., 2008, 2011, 2012]. This method does not require any additional information not contained in the profile and may be used for the analysis of profiles measured by various techniques. The criterion for the IGW identification has been formulated and argued. In the case when this criterion is satisfied, the analyzed temperature fluctuations can be considered as wave-induced. The method is based on the analysis of relative amplitudes of the wave field and on the linear IGW saturation theory in which these amplitudes are restricted by dynamical (shear) instability processes in the atmosphere. When the amplitude of an internal wave reaches the shear instability threshold, energy is assumed to be dissipated in such a way that the IGW amplitude is maintained at the instability threshold level as the wave propagates upwards. We have extended the developed technique [Gubenko et al., 2008] in order to reconstruct the complete set of wave characteristics including such important parameters as the wave kinetic and potential energy per unit mass and IGW fluxes of the energy and horizontal momentum [Gubenko et al., 2011]. We propose also an alternative method to estimate the relative amplitudes and to extract IGW parameters from an analysis of perturbations of the Brunt-Vaislala frequency squared [Gubenko et al., 2011]. An application of the developed method to the radio occultation (RO) temperature data has given the possibility to identify the IGWs in the Earth's, Martian and Venusian atmospheres and to determine the magnitudes of key wave parameters such as the intrinsic frequency, amplitudes of vertical and horizontal wind velocity perturbations, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase (and group) speeds, kinetic and potential energy per unit mass, vertical fluxes of the wave energy and horizontal momentum. Vertical profiles of temperature retrieved from RO measurements of the CHAMP (Earth), Mars Global Surveyor (Mars), Magellan and Venus Express (Venus) missions are used and analyzed to identify discrete or “narrow spectral” wave events and to determine IGW characteristics in the Earth’s, Martian and Venusian atmospheres. This work was partially supported by the RFBR grant 13-02-00526-? and Program 22 of the RAS Presidium. References. Gubenko V.N., Pavelyev A.G., Andreev V.E. Determination of the intrinsic frequency and other wave parameters from a single vertical temperature or density profile measurement // J. Geophys. Res. 2008. V. 113. No.D08109, doi:10.1029/2007JD008920. Gubenko V.N., Pavelyev A.G., Salimzyanov R.R., Pavelyev A.A. Reconstruction of internal gravity wave parameters from radio occultation retrievals of vertical temperature profiles in the Earth’s atmosphere // Atmos. Meas. Tech. 2011. V. 4. No.10. P. 2153-2162, doi:10.5194/amt-4-2153-2011. Gubenko V.N., Pavelyev A.G., Salimzyanov R.R., Andreev V.E. A method for determination of internal gravity wave parameters from a vertical temperature or density profile measurement in the Earth’s atmosphere // Cosmic Res. 2012. V. 50. No.1. P. 21-31, doi: 10.1134/S0010952512010029.

Kirillovich, Ivan; Gubenko, Vladimir; Pavelyev, Alexander

165

A millimeter-wave full-duplex fiber-radio star-tree architecture incorporating WDM and SCM  

Microsoft Academic Search

We propose a full-duplex millimeter-wave fiber-radio network for providing wireless customer access to broadband services. It consists of a hybrid star-tree architecture connecting remote antenna base stations to a central control office (CO) by incorporating wavelength-division multiplexing (WDM) of the optical signals and subcarrier multiplexing (SCM) of the radio signals. These multiplexing schemes allow the sharing of equipment at the

G. H. Smith; D. Novak; C. Lim

1998-01-01

166

Interplanetary dust detection by radio antennas: Mass calibration and fluxes measured by STEREO/WAVES  

NASA Astrophysics Data System (ADS)

We analyze dust impacts recorded by the S/WAVES radio instrument onboard the two STEREO spacecraft near 1 A.U. during the period 2007-2010. The impact of a dust particle on a spacecraft produces a plasma cloud whose associated electric field can be detected by on-board electric antennas. For this study we use the electric potential time series recorded by the waveform sampler of the instrument. The high time resolution and long sampling times of this measurement enable us to deduce considerably more information than in previous studies based on the dynamic power spectra provided by the same instrument or by radio instruments onboard other spacecraft. The large detection area compared to conventional dust detectors provides flux data with a better statistics. We show that the dust-generated signals are of two kinds, corresponding to impacts of dust from distinctly different mass ranges. We propose calibration formulas for these signals and show that we are able to use S/WAVES as a dust detector with convincing results both in the nanometer and micrometer size ranges. In the latter, the orbital motion of the spacecraft enables us to distinguish between interstellar and interplanetary dust components. Our measurements cover the mass intervals ˜10-22-10-20 kg and ˜10-17 - 5 × 10-16 kg. The flux of the larger dust agrees with measurements of other instruments on different spacecraft.

Zaslavsky, A.; Meyer-Vernet, N.; Mann, I.; Czechowski, A.; Issautier, K.; Le Chat, G.; Pantellini, F.; Goetz, K.; Maksimovic, M.; Bale, S. D.; Kasper, J. C.

2012-05-01

167

A new approach to global gravity wave momentum flux determination from GPS radio occultation data  

NASA Astrophysics Data System (ADS)

GPS Radio Occultation (RO) is a well-established technique for obtaining global gravity wave (GW) information. RO uses GPS signals received aboard low Earth orbiting satellites for atmospheric limb sounding. Temperature profiles are derived with high vertical resolution and provide a global coverage under any weather conditions offering the possibility for global monitoring of the vertical temperature structure and atmospheric wave parameters. The six satellites constellation COSMIC/FORMOSAT-3 delivers approximately 2000 temperature profiles daily. In this study, we use a method to obtain global distributions of horizontal gravity wave wavelengths, to be applied in the determination of the vertical flux of horizontal momentum transported by gravity waves. The horizontal wavenumber is derived by the ratio of the phase shift and the spatial distance between adjacent temperature fluctuation profiles at a given altitude, following the method by Ern et al. (2004). A new method for the determination of the real horizontal wavelength from triads of vertical profiles is presented and applied to the COSMIC data. The horizontal and vertical wavelength, the specific potential energy (Ep) and the vertical flux of horizontal momentum (MF) are calculated and their global distribution is discussed.

Faber, A.; Llamedo, P.; Schmidt, T.; de la Torre, A.; Wickert, J.

2013-03-01

168

Standing wave pattern of HF radio waves in the ionospheric reflection region. I - General formulas  

NASA Astrophysics Data System (ADS)

General formulas for the accurate computing of the field strength near the reflection point of an electromagnetic wave impinging vertically upon a horizontally stratified ionosphere are derived by means of a uniform approximation valid throughout the whole reflection region. Smoothly varying profiles of general shape but with the gross features determined by the presence of one or two transition points are assumed. Coupling and nonlinear effects are not explicitly included. Since the uniform approximation method is analytic in its essence, it is in many respects more versatile than existing brute force numerical methods.

Lundborg, B.; Thide, B.

1985-08-01

169

Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Radio Flux Density Variations with Frequency  

E-print Network

We have performed a statistical study of $152$ Type III radio bursts observed by Solar TErrestrial RElations Observatory (STEREO)/Waves between May 2007 and February 2013. We have investigated the flux density between $125$kHz and $16$MHz. Both high- and low-frequency cutoffs have been observed in $60\\,%$ of events suggesting an important role of propagation. As already reported by previous authors, we observed that the maximum flux density occurs at $1$MHz on both spacecraft. We have developed a simplified analytical model of the flux density as a function of radial distance and compared it to the STEREO/Waves data.

Krupar, V; Santolik, O; Kontar, E P; Cecconi, B; Hoang, S; Kruparova, O; Soucek, J; Reid, H; Zaslavsky, A

2014-01-01

170

Experimental Study of Radio Frequency Sheaths Created by Fast Wave Antennae  

NASA Astrophysics Data System (ADS)

There is a great deal of interest in radio frequency (RF) sheaths as the result of ion cyclotron resonant frequency heating (ICRF). During high power operation in fusion devices, large RF sheaths on the order of several kV can form on the RF antenna or at the machine wall. These large sheaths are detrimental because of impurity generation, local heating, arcing, etc. A series of experiments at the Large Plasma Device (LAPD) at UCLA is underway to study the generation of RF sheaths on conductors both in the near field and in the far field of the fast wave antenna. A fast wave antenna has been constructed for LAPD and has been shown to launch fast waves. The potential in the RF sheath near a metallic conductor will be probed with Langmuir probes and emissive probes. These probes can be positioned with an accuracy of ten micron perpendicular to the metallic plate, and can thus probe the sheath and pre-sheath over a distance of several cm. The design and first tests of the probe system will be presented as well as antenna coupling studies for different plasma conditions.

Martin, Michael; van Compernolle, Bart; Carter, Troy; Gekelman, Walter; Pribyl, Patrick; D'Ippolito, Daniel A.; Myra, James R.

2011-11-01

171

In-flight calibration of the Cassini-Radio and Plasma Wave Science (RPWS) antenna system for direction-finding and  

E-print Network

In-flight calibration of the Cassini-Radio and Plasma Wave Science (RPWS) antenna system) as well as atmospheric (lightning) origin. The Radio and Plasma Wave Science (RPWS) experiment is designed information on source locations and emission modes. For that purpose, RPWS uses a two-channel receiver

Gurnett, Donald A.

172

GNSS Phase Scintillation and Cycle Slips Occurrence at High Latitudes: Climatology and Forecasting  

NASA Astrophysics Data System (ADS)

Space weather impacts the operation of modern technology that relies on Global Navigation Satellite Systems (GNSS). Ionospheric scintillation (rapid fluctuation of radio wave amplitude and phase) degrades GPS positional accuracy and causes cycle slips leading to loss of lock that affects performance of radio communication and navigation systems. At high latitudes, GPS scintillation and total electron content has been monitored by the Canadian High Arctic Ionospheric Network (CHAIN). GPS phase scintillation and cycle slips, as a function of magnetic latitude and local time, occur on the dayside in the ionospheric cusp, in the nightside auroral oval, and in the polar cap. Interplanetary coronal mass ejections and corotating interaction regions on the leading edge of high-speed streams are closely correlated with the occurrence of scintillation at high latitudes. Results of a superposed epoch analysis of time series of phase scintillation and cycle slips occurrence keyed by arrival times of high speed solar wind streams and interplanetary coronal mass ejections are presented. Based on these results, a method of probabilistic forecasting of high-latitude phase scintillation occurrence is proposed.

Prikryl, Paul; Jayachandran, Periyadan T.; Chadwick, Richard; Kelly, Todd D.

2014-05-01

173

Radio-wave heating of iron oxide nanoparticles can regulate plasma glucose in mice.  

PubMed

Medical applications of nanotechnology typically focus on drug delivery and biosensors. Here, we combine nanotechnology and bioengineering to demonstrate that nanoparticles can be used to remotely regulate protein production in vivo. We decorated a modified temperature-sensitive channel, TRPV1, with antibody-coated iron oxide nanoparticles that are heated in a low-frequency magnetic field. When local temperature rises, TRPV1 gates calcium to stimulate synthesis and release of bioengineered insulin driven by a Ca(2+)-sensitive promoter. Studying tumor xenografts expressing the bioengineered insulin gene, we show that exposure to radio waves stimulates insulin release from the tumors and lowers blood glucose in mice. We further show that cells can be engineered to synthesize genetically encoded ferritin nanoparticles and inducibly release insulin. These approaches provide a platform for using nanotechnology to activate cells. PMID:22556257

Stanley, Sarah A; Gagner, Jennifer E; Damanpour, Shadi; Yoshida, Mitsukuni; Dordick, Jonathan S; Friedman, Jeffrey M

2012-05-01

174

Thermal response of the F region ionosphere in artificial modification experiments by HF radio waves  

NASA Technical Reports Server (NTRS)

The thermal response of the nighttime F region ionosphere to local heating by HF radio waves has been observed with the incoherent scatter radar at Arecibo, Puerto Rico. The observations consist of high-resolution space and time variation of the electron temperature as a high-power HF transmitter is switched on and off with a period 240 s. As soon as the HF transmitter is turned on, the electron temperature begins to rise rapidly in a narrow altitude region near 300 km, below the F2 layer peak. The electron temperature perturbation subsequently spreads over a broader altitude region. The observations are compared with the anticipated thermal response of the ionosphere based on numerical solutions of the coupled time-dependent heat conduction equations for the electron and composite ion gases and are found to be in good agreement over the entire altitude region covered by the observations.

Mantas, G. P.; Lahoz, C. H.; Carlson, H. C., Jr.

1981-01-01

175

Modeling Ionospheric HF/VHF Radio-Wave Absorption due to Solar Energetic Proton Events  

NASA Astrophysics Data System (ADS)

Simple, one-parameter, algorithms have been applied to the observed energetic proton flux as provided by the GOES series of satellites to yield estimates of the high latitude HF and VHF radio-wave absorption for both day and night respectively. The twilight response is obtained as a bi-linear function of the solar zenith angle at the observation positions, and the latitude dependence of the absorption region near the edge of the absorbing region (the polar caps) are estimated from extant models of geomagnetic cut-offs and their dependence on geomagnetic activity. The approximate inverse square frequency dependence of ionospheric absorption is used to translate across the HF/VHF range and predictions of the minimum duration of events are determined. Calculations of the polar cap absorption of HF radio waves have been performed for eleven larger Solar Energetic Proton (SEP) events during the period from 1992 through 2002 and the results compared to observations of 30 MHz Riometers operated by the AFGL and located at Thule, Greenland. While discrepancies between the estimated and observed absorption using these procedures occur, especially at low absorption levels, this model has operational value in view of its simplicity and its being the only extant model, to our knowledge, which treats solar-illumination, geomagnetic cutoff variation, and frequency effects, at least to first order. Specimen graphical representations of the north and south polar caps illustrate the output of the model for the peak of the 12 December 2006 solar proton event. Given sufficient interest, improvements to the methodology used here are practicable and could be expected to achieve accuracies to the order of 25% or better.

Sauer, H. H.; Wilkinson, D. C.

2007-12-01

176

Modeling Ionospheric Radio-Wave Absorption due to Solar Energetic Proton Events  

NASA Astrophysics Data System (ADS)

Simple, one-parameter, algorithms have been applied to the observed energetic proton flux as provided by the GOES series of satellites to yield estimates of the high latitude HF and VHF radio-wave absorption for both day and night respectively. The twilight response is obtained as a bi-linear function of the solar zenith angle at the observation positions, and the latitude dependence of the absorption region near the edge of the absorbing region (the polar caps) are estimated from extant models of geomagnetic cut-offs and their dependence on geomagnetic activity. The approximate inverse square frequency dependence of ionospheric absorption is used to translate across the HF/VHF range and predictions of the minimum duration of events are determined. Calculations of the polar cap absorption of HF radio waves have been performed for eleven larger Solar Energetic Proton (SEP) events during the period from 1992 through 2002 and the results compared to observations of 30 MHz Riometers operated by the AFGL and located at Thule, Greenland. While discrepancies between the estimated and observed absorption using these procedures occur, especially at low absorption levels, this model has operational value in view of its simplicity and its being the only extant model which treats solar- illumination, geomagnetic cutoff variation, and frequency effects, at least to first order. A specimen presentation of the northern and southern polar caps illustrates the output of the model for the peak of the 6 December 2006 solar proton event. Given motivation, improvements to the methodology used here are practicable and could be expected to achieve accuracies to the order of 25%.

Sauer, H. H.

2007-05-01

177

EFFECTS OF ALFVEN WAVES ON ELECTRON CYCLOTRON MASER EMISSION IN CORONAL LOOPS AND SOLAR TYPE I RADIO STORMS  

SciTech Connect

Solar type I radio storms are long-lived radio emissions from the solar atmosphere. It is believed that these type I storms are produced by energetic electrons trapped within a closed magnetic structure and are characterized by a high ordinary (O) mode polarization. However, the microphysical nature of these emissions is still an open problem. Recently, Wu et al. found that Alfven waves (AWs) can significantly influence the basic physics of wave-particle interactions by modifying the resonant condition. Taking the effects of AWs into account, this work investigates electron cyclotron maser emission driven by power-law energetic electrons with a low-energy cutoff distribution, which are trapped in coronal loops by closed solar magnetic fields. The results show that the emission is dominated by the O mode. It is proposed that this O mode emission may possibly be responsible for solar type I radio storms.

Zhao, G. Q.; Chen, L.; Wu, D. J. [Purple Mountain Observatory, CAS, Nanjing 210008 (China); Yan, Y. H., E-mail: djwu@pmo.ac.cn [Key Laboratory of Solar Activity, National Astronomical Observatories, CAS, Beijing 100012 (China)

2013-06-10

178

Characteristics of dust particles detected near Saturn's ring plane with the Cassini Radio and Plasma Wave instrument  

Microsoft Academic Search

During the inbound and outbound passes of the Cassini spacecraft through Saturn's ring plane on July 1, 2004, the Radio and Plasma Wave Science (RPWS) instrument detected many small particles striking the spacecraft. When a small particle strikes the spacecraft at a high velocity, it is instantly vaporized and produces a small cloud of plasma that expands radially outward from

Z. Wang; D. A. Gurnett; T. F. Averkamp; A. M. Persoon; W. S. Kurth

2006-01-01

179

In-flight calibration of the Cassini Radio and Plasma Wave Science (RPWS) antennas after the Huygens probe release  

Microsoft Academic Search

The RPWS instrument on board the Cassini spacecraft orbiting Saturn includes three 10 m long monopole antennas for studying dust, plasma and wave phenomena, including Saturnian radio emissions. Due to the presence of the spacecraft body, the electric antenna directions and lengths, represented by the effective length vectors, deviate from their physical directions and lengths. In order to provide accurate

R. L. Karlsson; W. Macher; U. Taubenschuss; H. O. Rucker

2006-01-01

180

Applications of a travelling wave-based radio-frequency-only stacked ring ion guide.  

PubMed

The use of radio-frequency (RF)-only ion guides for efficient transport of ions through regions of a mass spectrometer where the background gas pressure is relatively high is widespread in present instrumentation. Whilst multiple collisions between ions and the background gas can be beneficial, for example in inducing fragmentation and/or decreasing the spread in ion energies, the resultant reduction of ion axial velocity can be detrimental in modes of operation where a rapidly changing influx of ions to the gas-filled ion guide needs to be reproduced at the exit. In general, the RF-only ion guides presently in use are based on multipole rod sets. Here we report investigations into a new mode of ion propulsion within an RF ion guide based on a stack of ring electrodes. Ion propulsion is produced by superimposing a voltage pulse on the confining RF of an electrode and then moving the pulse to an adjacent electrode and so on along the guide to provide a travelling voltage wave on which the ions can surf. Through appropriate choice of the travelling wave pulse height, velocity and gas pressure it will be shown that the stacked ring ion guide with the travelling wave is effective as a collision cell in a tandem mass spectrometer where fast mass scanning or switching is required, as an ion mobility separator at pressures around 0.2 mbar, as an ion delivery device for enhancement of duty cycle on an orthogonal acceleration time-of-flight (oa-TOF) mass analyser, and as an ion fragmentation device at higher wave velocities. PMID:15386629

Giles, Kevin; Pringle, Steven D; Worthington, Kenneth R; Little, David; Wildgoose, Jason L; Bateman, Robert H

2004-01-01

181

Radio frequency CD by LH waves in the reversed field experiment  

SciTech Connect

We present a feasibility study for the active control of the poloidal current density profile in the RFX (reversed field pinch) experiment using radio frequency in the range of lower hybrid waves. The main goal of the rf current drive is to reduce the magnetic fluctuations and the magnetic stochasticity, so as to improve the energy confinement. The compelling constraints of accessibility and damping of the slow waves due to the present and extrapolated RFX plasma parameters are investigated; they have been used to fix the frequency ({approx_equal}1.3 GHz) and the best n{sub parallel} values ({approx_equal}8), and therefore the antenna size (Grill). A modified version of the FELICE code, which takes into account the strong shear of the magnetic field of the RFP plasmas, has been developed and used to estimate the antenna-plasma coupling: the reflected power for the proposed antenna is found to be less than 30% for a quite wide range of plasma parameters. In order to estimate the current drive profile and efficiency a one dimensional Fokker-Planck code has been used: an additional crucial contribution to the driven current is due to the enhancement of the plasma conductivity as consequence of the suprathermal electron population increase. Although the total estimated CD efficiency is promising, the rf-power required to drive the current necessary to produce a significant reduction of the magnetic fluctuations is found to be in the MW range.

Bilato, R. [Consorzio RFX, Corso Stati Uniti 4, 35127 Padova (Italy); Istituto Nazionale di Fisica della Materia, Padova (Italy); Brambilla, M. [Maz Planck Institute fuer Plasmaphysik, EURATOM Ass., D-85748 Garching (Germany)

1999-09-20

182

Nanodust detection near 1 AU from spectral analysis of Cassini/Radio and Plasma Wave Science data  

NASA Astrophysics Data System (ADS)

Nanodust grains of a few nanometers in size are produced near the Sun by collisional breakup of larger grains and picked up by the magnetized solar wind. They have so far been detected at 1 AU by only the two STEREO spacecraft. Here we analyze the spectra measured by the radio and plasma wave instrument onboard Cassini during the cruise phase close to Earth orbit; they exhibit bursty signatures similar to those observed by the same instrument in association with nanodust stream impacts on Cassini near Jupiter. The observed wave level and spectral shape reveal impacts of nanoparticles at about 300 km/s, with an average flux compatible with that observed by the radio and plasma wave instrument onboard STEREO and with the interplanetary flux models.

Schippers, P.; Meyer-Vernet, N.; Lecacheux, A.; Kurth, W. S.; Mitchell, D. G.; André, N.

2014-08-01

183

Some results of night-time scintillations at low latitude  

NASA Astrophysics Data System (ADS)

Ionospheric scintillation observations of VHF radio signals from FLEETSAT satellite (73 deg E longitude) at Bhopal from January 1990 to December 1990 are used to study the characteristic variations of scintillation activity. It is found that scintillation occurrence is essentially a nighttime phenomenon and daytime scintillations are very rare. Annual average nocturnal variation of percentage occurrence of scintillations shows maximum at around 2100-2200 h LT. Seasonally, scintillations are most prominent during equinoxes and least during summer. Geomagnetic disturbances tend to decrease the occurrence of scintillations in the pre-midnight period.

Kumar, Sushil; Vijay, S. K.; Gwal, A. K.

1993-06-01

184

Halide Scintillators  

Microsoft Academic Search

Scintillators have been used for decades to make ionising radiation visible. Either by direct observation of the light flash produced by the material when it is exposed to radiation, or indirect by use of a photomultiplier tube or photodiode.\\u000aDespite the enormous amount of commercially available scintillators, the ideal scintillator that combines a high light yield, a high density, a

E. V. D. Van Loef

2003-01-01

185

Scintillator material  

DOEpatents

An improved scintillator material comprising cerium fluoride is disclosed. Cerium fluoride has been found to provide a balance of good stopping power, high light yield and short decay constant that is superior to known scintillator materials such as thallium-doped sodium iodide, barium fluoride and bismuth germanate. As a result, cerium fluoride is favorably suited for use as a scintillator material in positron emission tomography. 4 figs.

Anderson, D.F.; Kross, B.J.

1992-07-28

186

Scintillator material  

DOEpatents

An improved scintillator material comprising cerium fluoride is disclosed. Cerium fluoride has been found to provide a balance of good stopping power, high light yield and short decay constant that is superior to known scintillator materials such as thallium-doped sodium iodide, barium fluoride and bismuth germanate. As a result, cerium fluoride is favorably suited for use as a scintillator material in positron emission tomography.

Anderson, David F. (Batavia, IL); Kross, Brian J. (Aurora, IL)

1992-01-01

187

Scintillator material  

DOEpatents

An improved scintillator material comprising cerium fluoride is disclosed. Cerium fluoride has been found to provide a balance of good stopping power, high light yield and short decay constant that is superior to known scintillator materials such as thallium-doped sodium iodide, barium fluoride and bismuth germanate. As a result, cerium fluoride is favorably suited for use as a scintillator material in positron emission tomography.

Anderson, David F. (Batavia, IL); Kross, Brian J. (Aurora, IL)

1994-01-01

188

Scintillator material  

DOEpatents

An improved scintillator material comprising cerium fluoride is disclosed. Cerium fluoride has been found to provide a balance of good stopping power, high light yield and short decay constant that is superior to known scintillator materials such as thallium-doped sodium iodide, barium fluoride and bismuth germanate. As a result, cerium fluoride is favorably suited for use as a scintillator material in positron emission tomography. 4 figs.

Anderson, D.F.; Kross, B.J.

1994-06-07

189

Spatial structure of auroral day-time ionospheric electron density irregularities generated by a powerful HF-wave  

Microsoft Academic Search

We describe an experiment in satellite radio- wave probing of the ionosphere, modified by powerful waves from the HF heating facility at Tromsø (Norway) in May 1995. Amplitude scintillations and variations of the phase of VHF signals from Russian navigational satellites passing over the heated region were observed. We show that both large-scale electron density irregu- larities (several tens of

E. D. Tereshchenko; B. Z. Khudukon; M. T. Rietveld; A. Brekke

1998-01-01

190

Spatial structure of auroral day-time ionospheric electron density irregularities generated by a powerful HF-wave  

Microsoft Academic Search

We describe an experiment in satellite radio-wave probing of the ionosphere, modified by powerful waves from the HF heating facility at Tromsø (Norway) in May 1995. Amplitude scintillations and variations of the phase of VHF signals from Russian navigational satellites passing over the heated region were observed. We show that both large-scale electron density irregularities (several tens of kilometers in

E. D. Tereshchenko; B. Z. Khudukon; M. T. Rietveld; A. Brekke

1998-01-01

191

Radio-Frequency Wave Excitation and Damping on a High Beta Plasma Column.  

NASA Astrophysics Data System (ADS)

Azimuthally symmetric (m = 0) radio-frequency (RF) waves for zero and for finite axial wave number k(,z) are investigated on the High-Beta Q Machine, a two-meter, 20 cm-diameter, low-compression linear theta pinch (T (GREATERTHEQ) 200 eV, n (DBLTURN) 10('15)cm('-3)) fast rising (0.4 (mu)s) compression field. The (k(,z) = 0) modes occur spontaneously following the implosion phase of the discharge. A novel 100-MWatt, 1 to 1.3-MHz, short wavelength current drive excites the plasma column in the vicinity of the lowest fast magnetoacoustic mode at various filling pressures. This current drive is designed as an integral part of the compression coil, which is segmented with a 20-cm axial wavelength (k(,z) = 0.314 cm('-1)). The electron density oscillations along major and minor chords at various positions are measured by interferometry perpendicular to the pinch axis. The oscillatory radial magnetic field component between pinch wall and hot plasma edge is measured by probes. Phases, amplitudes and radial mode structure are studied for the free (k = 0) modes and the externally driven (k (NOT=) 0) modes for various filling pressures of deuterium. In the first case, the damping is determined from the e-folding time of the decaying oscillations. In the latter case, the phases and amplitudes indicate a broad resonance structure, from which we extract the damping constant. The energy deposition from the externally driven RF wave leads to a radial expansion of the plasma column, as observed by axial interferometry and by excluded flux measurements. We compare these experimental results with damping phenomena as predicted by MHD-like collisional (viscous) and collisionless (ion-Landau and cyclotron) damping models. It is found that the viscous model overestimates the observed (k = 0) damping by at least an order of magnitude, while both the viscous and kinetic models underestimate the (k (NOT=) 0) damping by at least an order of magnitude. The characteristic and resonant frequencies, as well as the oscillatory radial mode structure, can be understood within the ideal MHD description. The experimentally observed damping and wave-energy deposition are consistent with the magnitude of the density oscillations. The efficiency of the RF energy deposition is at least 27%, somewhat exceeding that observed in other high-beta magnetoacoustic experiments.

Meuth, Hermann

192

LETTER doi:10.1038/nature13029 Optical detection of radio waves through a  

E-print Network

is sufficient to induce strong coupling4,6,7 be- tween the voltage fluctuations ina radio-frequency resonance electronic signals sets the stage for coherent up-conversion of low- frequency quantum signals to the optical recovery of weak radio- frequency and microwave signals is a ubiquitous challenge, crucial in radio

Cai, Long

193

Horizontal Wave Analysis using COSMIC/FORMOSAT-3 Radio Occultation Data  

NASA Astrophysics Data System (ADS)

We discuss vertical and horizontal gravity wave (GW) parameters in the lower stratosphere (20-30km) derived from GPS radio occultation (RO) data for selected case studies in different geographical regions. Available satellite data give global pictures of GW parameters, but each seen through an individual observational window depending on the used measurement characteristics. The RO technique is a limb sounding method sensitive to GWs with small ratios of vertical to horizontal wavelengths. Due to the horizontal averaging within the RO retrieval the measuring geometry between the Line-of-Sight (LOS) and the wave propagation direction get important for the interpretation of the results with respect to GWs.For our case studies we apply the method from Ern et al. (2004) to derive horizontal wavelengths between adjacent temperature profiles from the early COSMIC mission (April-October 2006) whereas only profiles measured within a time window of ten minutes and with the same LOS were considered. A cross-wavelet analysis was applied to pairs of temperature fluctuation profiles to detect phase shifts. Finally, the horizontal wavenumber in the direction of the connecting line between the pairs of profiles is the ratio of the phase shift and the distance between them. By using a combination of at least three occultation events the horizontal wavenumber (wavelength) can be determined. To validate the results we compare our findings with results from the mesoscale Weather Research and Forecasting Model. For a global analysis of the horizontal wavelength the prior discribed restrictions in time and space are loosened up. Results for August and December 2006 are displayed. Additionally the potential energy for the considerated profiles is shown. A first look negative correlation of those two variables can be found.

Haser, A.; Schmidt, T.; de la Torre, A.; Fischer, J.

2010-12-01

194

Day-fo-day Monitoring of the Comparisons Between UHF Scintillation Forecasts and GNSS Observations  

NASA Astrophysics Data System (ADS)

When trans-ionospheric radio waves propagate through an irregular ionosphere with plasma depletions or 'bubbles', they are subject to sporadic enhancement and fading which is referred to as scintillation. Communication and navigation systems may be subject to these detrimental effects if the scintillation is strong enough. It is critical to have knowledge of the current ionospheric conditions so that system operators can distinguish between the natural radio environment and system-induced failures. In this paper, we present and describe a proven technique for forecasting UHF scintillation activity in the equatorial region after sunset and compare these forecasts with observed global navigation satellite systems (GNSS) L-band scintillation activity at Jicamarca, Peru, on a night-to-night basis. The UHF scintillation forecasting technique is described in a paper by Redmon et al. (Space Weather, Vol 8, 2010) entitled 'A Forecasting Ionospheric Real-time Scintillation Tool (FIRST).' The technique utilizes the observed characteristic parameter h'F from a ground-based, ionospheric sounder near the magnetic equator. This paper demonstrated that there exists an excellent correlation (R2 ~ 0.91) between h'F (1930LT) and the pre-reversal enhancement in vertical ExB drift velocity after sunset which is the prime driver for creating plasma depletions and bubbles. In addition, there exists a 'threshold' in the h'F value at 1930 LT, h'Fthr, such that, on any given evening if h'F is significantly above h'Fthr then scintillation activity is likely to occur and if it is below h'Fthr, scintillation activity is unlikely to occur. The digital sounder at Jicamarca, Peru provides the h'F values between 1830 and 2000 LT. A multi-constellation GNSS receiver at Jicamarca provides 50Hz navigation signal observables continuously since December 2012. S4 index and detrended carrier phase standard deviation, two commonly used amplitude and phase scintillation indices are computed from these observables during the equinox months in 2013. An unprecedented number of open signals from GPS, GLONASS, Galileo, Beidou, and SBAS satellites are included in the observations, providing high spatial and temporal resolution of scintillation indices measurements. In addition to the statistical analysis between the UHF scintillation forecast and observed GNSS receiver S4 index values, detailed quantitative relationships between the vertical ExB drift velocity, prompt penetration magnetic storm disturbances, and the intensity, duration, and spatial distributions of amplitude and phase scintillation will be presented.

Anderson, D. N.; Morton, Y.; Jiao, Y.; Redmon, R. J.

2013-12-01

195

Generation of Acoustic Gravity Waves by Periodic Radio Transmissions from a High-Power Ionospheric Heater  

NASA Astrophysics Data System (ADS)

The Radiophysical Research Institute (Nizhny Novgorod, Russia) and Kharkiv V. N. Karazin National University (Kharkiv, Ukraine) have studied opportunities for the effective generation of acoustic gravity waves (AGWs) in 3 - 180-min period range. The excitation of such waves was conducted for the last several years using the SURA heating facility (Nizhny Novgorod). The detection of the HF-induced AGWs was carried out in the Radiophysical Observatory located near Kharkiv City at a distance of about 960 km from the SURA. A coherent radar for vertical sounding, an ionosonde, and magnetometer chains were used in our measurements. The main results are the following (see [1-5]): 1. Infrasound oscillation trains with a period of 6 min are detected during periodic SURA heater turn-on and -off. Similar oscillation trains are detected after long time pumping, during periodic transmissions with a period of 20 s, as well as after pumping turn-off. The train recordings begin 28 - 54 min after the heater turn-on or -off, and the train propagation speeds are about 300 - 570 m/s, the value of which is close to the sound speed at upper atmospheric altitudes. The amplitude of the Doppler shift frequency is of 10 - 40 mHz, which fits to the 0.1 - 0.3% electron density disturbances at ionospheric altitudes. The amplitude of the infrasound oscillations depends on the SURA mode of operation and the state of the upper atmosphere and ionosphere. 2. High-power radio transmissions stimulate the generation (or enhancement) of waves at ionospheric altitudes in the range of internal gravity wave periods. The HF-induced waves propagate with speeds of 360 - 460 m/s and produce changes in electron density with amplitudes of 2 - 3%. The generation of such periodic perturbations is more preferable with periods of 10 - 60 minutes. Their features depend significantly on the heater mode of operation. It should be stressed that perturbation intensity increases when a pumping wave frequency approaches the F _{_2} layer critical frequency. High-power periodic radio transmissions are capable of enhancing/damping natural wave perturbations generated by the solar terminator. 3. The study has demonstrated that the generation and propagation of AGWs with periods close to the natural oscillation periods of the atmosphere is possible. The duration of AGW oscillation trains does not dependent on the duration of turn-on/-off trains, but it is determined by changes in the current state of the atmosphere-ionosphere-magnetosphere system in general. The period of the AGW oscillation trains is determined by the period or semi-period of the pumping. It means that the mechanism of AGW generation in this case is distinct from the agreed-upon mechanism developed earlier. The AGWs, whose periods are 5 - 10% greater than the Brunt-Vaisala period, exhibit group velocities less than the speed of sound that is of about 80 - 160 m/s. They induce electron density perturbations of about 1.1 - 1.5%. The AGW generation has the following features. When the effective radiated power (ERP) is 50 MW or less, AGWs are not detected; they are reliably observed when the ERP is equal or larger than about 100 MW. Geomagnetic storms play a dual role in the AGW generation because they: (i) increase amplitudes of AGWs with 4 - 6-min and 8 - 12-min periods and (ii) yet enhance background oscillations. The latter hampers the identification of the HF-induced oscillations. Moderate magnetic storms do not markedly exert an influence on the amplitudes of oscillations with 13 - 17-min periods. 4. The quasi-periodic variations in the horizontal components of the geomagnetic field with 8 - 12-min periods become observable near Kharkiv 35 - 45 min after the beginning of pumping. Their speeds are 355 - 460 m/s, and they form trains 40 - 90 min in duration when the [5-min on, 5-min off] or [10-min on, 10-min off] heater timing is used. The 12 - 18-min period variations become observable 35 - 45 min after the beginning of pumping. Their speeds are 355 - 460 m/s, and they form trains 55 - 90 min in duration when the

Frolov, Vladimir; Chernogor, Leonid; Rozumenko, Victor

196

On the Relation between Auroral ``Scintillation'' and ``Phase Without Amplitude'' Scintillation: Initial Investigations  

NASA Astrophysics Data System (ADS)

The ionosphere, being a plasma, affects any radio signal passing through it by introducing a phase advance and a group delay in the signal. Occasionally, due to electron density irregularities in the ionosphere, the radio signal can experience rapid amplitude and phase fluctuations called scintillation. Scintillation can sometimes be intense enough to cause a Global Positioning System (GPS) receiver to lose lock on a signal, thus making it a significant aspect to consider in GPS-based positioning, navigation, and timing systems. Quantitative information about scintillation is usually obtained from parameters called the scintillation indices. The most commonly used GPS scintillation indices are S _{4} and sigma{phi} that quantify scintillation in power and phase of the GPS signal, respectively. Recent studies have shown that at high latitudes, the probability of occurrence of phase scintillation is greater than amplitude scintillation. These events are called “phase without amplitude” scintillation. In this study, the relation between these events and auroral scintillation is analyzed. As an initial step, data from the Canadian High Arctic Ionospheric Network and 10 more GPS stations located in Canada was used simultaneously along with data from 11 Canadian THEMIS all-sky imagers. Preliminary investigations reveal that phase fluctuations associated with aurora can be the main reason behind “phase without amplitude” scintillation. Spectral studies of differential-carrier-phase TEC were also performed.

Mushini, Sajan; Spanswick, Emma; Jayachandran, Thayyil; Donovan, Eric; Langley, R.; Prikryl, Paul

197

The Standing Wave Phenomenon in Radio Telescopes; Frequency Modulation of the WSRT Primary Beam  

E-print Network

Inadequacies in the knowledge of the primary beam response of current interferometric arrays often form a limitation to the image fidelity. We hope to overcome these limitations by constructing a frequency-resolved, full-polarization empirical model for the primary beam of the Westerbork Synthesis Radio Telescope (WSRT). Holographic observations, sampling angular scales between about 5 arcmin and 11 degrees, were obtained of a bright compact source (3C147). These permitted measurement of voltage response patterns for seven of the fourteen telescopes in the array and allowed calculation of the mean cross-correlated power beam. Good sampling of the main-lobe, near-in, and far-side-lobes out to a radius of more than 5 degrees was obtained. A robust empirical beam model was detemined in all polarization products and at frequencies between 1322 and 1457 MHz with 1 MHz resolution. Substantial departures from axi-symmetry are apparent in the main-lobe as well as systematic differences between the polarization properties. Surprisingly, many beam properties are modulated at the 5 to 10% level with changing frequency. These include: (1) the main beam area, (2) the side-lobe to main-lobe power ratio, and (3) the effective telescope aperture. These semi-sinusoidsal modulations have a basic period of about 17 MHz, consistent with the natural 'standing wave' period of a 8.75 m focal distance. The deduced frequency modulations of the beam pattern were verified in an independent long duration observation using compact continuum sources at very large off-axis distances. Application of our frequency-resolved beam model should enable higher dynamic range and improved image fidelity for interferometric observations in complex fields. (abridged)

Attila Popping; Robert Braun

2007-12-14

198

Investigation of ionospheric irregularities and scintillation using TEC at high latitude  

NASA Astrophysics Data System (ADS)

The occurrence of ionospheric irregularities at high latitudes, with dimensions of several kms down to decameter scale size shows strong correlation with geomagnetic disturbance, season and solar activity. Transionospheric radio waves propagating through these irregularities experience rapid random fluctuations in phase and/or amplitude of the signal at the receiver, termed scintillation, which can degrade GNSS services. Thus, investigation and prediction of this scintillation effect is very important. To investigate such scintillation effects, a GISTM (GPS Ionospheric Scintillation and TEC Monitoring) NovAtel dual frequency (L1/L2) GPS receiver has been installed at Trondheim, Norway (63.41° N, 10.4° E), capable of collecting scintillation indices at a 1 min rate as well as the raw data (phase and intensity) of the satellite signals at a 50 Hz sampling rate and TEC (Total Electron Content) at a 1 Hz rate. Many researchers have reported that both phase and amplitude scintillation is closely associated with TEC fluctuations or associated with a significant developing enhancement or depletion in the TEC. In this study, a novel analogous phase index is developed which provides samples at a 1 min rate. Generally the scintillation indices can help in estimating the irregularity scintillation effect at a one minute rate, but such procedures are time consuming if DFTs of the phase and/or amplitude at a 50 Hz data are required. In this study, instead, this analogous phase index is estimated from 1 Hz rate TEC values obtained from the raw signals and is then compared for weak, moderate and strong scintillation at Trondheim for one year of data collected from the installed GPS receiver. The spectral index of the irregularities (that is the inverse power law of their spatial spectrum) is determined from the resultant phase scintillation psd. The correlations of the scintillation indices and spectral indices with the analogous phase index have been investigated under different geomagnetic conditions (represented by the Kp index) and an approximate linear correlation of phase scintillation with the analogous phase index was found. Then a principal advantage of this index is that it achieves this correlation without requiring a high sampling data rate and the need for DFTs. Thus, the index seems a good candidate for developing a simple means of ionospheric scintillation prediction which could also be utilized in the development of alerts using regional mappings.

Tiwari, R.; Strangeways, H. J.; Tiwari, S.; Ahmed, A.

2013-09-01

199

Determination of internal radio frequency electric field profiles via millimeter wave reflectometry in the DIII-D Tokamak  

SciTech Connect

Millimeter wave reflectometry was employed to determine radio frequency wave electric field profiles in the DIII-D Tokamak. The method utilizes spatially localized X-mode reflectometer measurements in the 65{endash}73 GHz frequency range to detect coherent fluctuations in magnetic field and density driven at the fast magnetosonic wave (FW) frequency (60 MHz). The FW electric field profiles were determined by adopting a geometric optics approach, which is appropriate for interpreting reflectometer data where the perturbing wavelength is longer than the probing wavelength. Successful measurements from this system were utilized to investigate FW propagation effects on DIII-D. The FW launch directionality necessary for current drive was confirmed at a position toroidally close to the FW antenna. {copyright} {ital 1997 American Institute of Physics.}

Lee, J.H.; Doyle, E.J. [Department of Electrical Engineering and Institute of Plasma and Fusion Research, University of California, Los Angeles, California 90095 (United States)] [Department of Electrical Engineering and Institute of Plasma and Fusion Research, University of California, Los Angeles, California 90095 (United States); Luhmann, N.C. [Department of Applied Science, University of California, Davis, California 95616 (United States)] [Department of Applied Science, University of California, Davis, California 95616 (United States); Peebles, W.A. [Department of Electrical Engineering and Institute of Plasma and Fusion Research, University of California, Los Angeles, California 90095 (United States)] [Department of Electrical Engineering and Institute of Plasma and Fusion Research, University of California, Los Angeles, California 90095 (United States); Petty, C.C.; Pinsker, R.I. [General Atomics, San Diego, California 92186 (United States)] [General Atomics, San Diego, California 92186 (United States); Rhodes, T.L. [Department of Electrical Engineering and Institute of Plasma and Fusion Research, University of California, Los Angeles, California 90095 (United States)] [Department of Electrical Engineering and Institute of Plasma and Fusion Research, University of California, Los Angeles, California 90095 (United States)

1997-01-01

200

Theory of the propagation of UHF radio waves in coal mine tunnels  

Microsoft Academic Search

The theoretical study of UHF radio communication in coal mines, with particular reference to the rate of loss of signal strength along a tunnel, and from one tunnel to another around a corner is the concern of this paper. Of prime interest are the nature of the propagation mechanism and the prediction of the radio frequency that propagates with the

ALFRED G. EMSLIE; ROBERT L. LAGACE; PETER F. STRONG

1975-01-01

201

Radio wave propagation measurements for land-mobile satellite systems at 2.33 GHz  

Microsoft Academic Search

The performance of a mobile satellite communications link is dominated by roadside attenuation due to vegetation or manmade structures. Previous measurement campaigns characterized land-mobile satellite channels at UHF and L bands. In 1997, the FCC allocated S-band spectrum to the Digital Audio Radio Satellite (DARS) service to provide nationwide radio services to the North American continent via satellite. This article

L. Mousselon; R. M. Barts; S. Licul; G. Joshi

2003-01-01

202

Coorelation between VHF scintillation and spread F  

NASA Astrophysics Data System (ADS)

The VHF scintillation observed over Bhopal, a station near the northern crest of the equatorial anomaly region, using the 244 MHz radio signal from FLEETSAT (730). The data use to study the occurrence characteristics of scintillation are recorded from March to April 2001 and then September to October 2001. The occurrences of scintillation are compared with the occurrence of spread-F over Delhi as observed by the modern digital ionosonde. The scintillation events are closely associated with the range type spread-F. In this paper the parameters of geomagnetic activity like Kp and Ap are used to study the association of the amplitude scintillation and spread-F. It is observed that an increase in magnetic activity suppressed the occurrence of scintillation and spread-F.

Smita, S.; Rashmi, R.; Gwal, G.

2003-04-01

203

Addressing the Emerging Wireless Bandwidth Crisis and the Need for Power-Efficient Bandwidth: Prospects for mm-Wave Radio Technology  

E-print Network

crisis. The main promise of mm-wave radio is that it offers a route to power-efficient bandwidth of high-bandwidth, low power mm-wave networks. Short Biography of the Presenter Dr. Daniel Foty has some processing, wired/wireless communications, and ultra-low-power design. A serial entrepreneur, he is currently

204

Applicability of radio astronomy techniques to the processing and interpretation of aperture synthesis passive millimetre-wave applications  

NASA Astrophysics Data System (ADS)

This PhD programme is contributing to the development of Passive Millimetre-Wave Imagers (PMMWI) using the principles of interferometric aperture synthesis and digital signal processing. The principal applications are security screening, all-weather flight aids and earth observation. To enhance the cost-effectiveness of PMMWI systems the number of collecting elements must be minimised whilst maintaining adequate image fidelity. A wide range of techniques have been developed by the radio astronomy community for improving the fidelity of sparse interferometric array imagery. This paper brings to the attention of readers these techniques and discusses how they may be applied to imaging using software packages publicly available from the radio astronomy community. The intention of future work is to adapt these algorithms to process experimental data from a range of realistic simulations and real-world targets.

Taylor, Christopher T.; Wilkinson, Peter N.; Salmon, Neil A.; Cameron, Colin D.

2012-06-01

205

SiOx Ink-Repellent Layer Deposited by Radio Frequency (RF) Plasmas in Continuous Wave and Pulse Mode  

NASA Astrophysics Data System (ADS)

Low surface energy layers, proposed application for non-water printing in computer to plate (CTP) technology, are deposited in both continuous wave and pulse radio frequency (13.56 MHz) plasma with hexamethyldisiloxane (HMDSO) as precursor. It is found that the plasma mode dominates the polymer growth rate and the surface composition. Derived from the spectra of X-ray photoelectron spectroscopy (XPS) and combined with printable test it is concluded that concentration of Si in coatings plays an important role for the ink printability and the ink does not adhere on the surface with high silicon concentration.

Chen, Qiang; Fu, Yabo; Pang, Hua; Zhang, Yuefei; Zhang, Guangqiu

2007-12-01

206

Generation of 40-GHz millimeter-wave signals based on radio-over-fiber system employing optical frequency quadrupling scheme  

NASA Astrophysics Data System (ADS)

This Letter proposes a low-cost Optical Frequency Multiplication (OFM) scheme based on dual drive Mach-Zehnder Modulator (DD-MZM) to generate 40-GHz millimeter-Wave (mmW) signals and 32Gbps 64QAM-OFDM signal at the center frequency of 35GHz occupying 5.6GHz bandwidth applied to Radio-over-Fiber (RoF) system. The optimal driving power of Intensity Modulator (IM) is also discovered to achieve the smallest EVM (Error Vector Magnitude) for the RoF system.

Guo, Xiaxia; Chen, Jian; Chen, Xiang; Li, Haining; Fu, Lei; Zou, Shihuan

2011-12-01

207

Scintillating Stars  

NSDL National Science Digital Library

Often, a bright planet that is visible over the horizon will be mistaken for a star. Some believe they can tell the difference between a star and a planet because stars twinkle, or scintillate , and planets do not. In actuality however, both will twinkle because any light that passes through our atmosphere, whether it be reflected from a planet or generated by a star, will be interfered with by the atmospheric elements. This month's column sheds light on this "scintillating" subject and engages students in a research activity that revolves around the question: Is Pluto a planet?

Riddle, Bob

2003-02-01

208

Results of Experimental and Theoretical Studies of the Atmospheric Turbulence, Internal Gravity Waves and Sporadic-E Layers by Resonant Scattering of Radio Waves on Artificial Periodic Irregularities  

NASA Astrophysics Data System (ADS)

Artificial periodic irregularities (API) formed by the powerful standing radio waves in the ionospheric plasma give the good chance for the lower ionosphere comprehensive studies. In this paper we present some applications of the API technique for experimental studies of sporadic E-layers (E _{s}), internal gravity waves and turbulent events in the lower ionosphere. API are formed in the field of the standing radio wave produced by interference of the incident wave and reflected one from the ionosphere (in more details about the API technique one can see in the book Belikovich et al., Ionospheric Research by Means of Artificial Periodic Irregularities - Katlenburg-Lindau, Germany. 2002. Copernicus GmbH. ISBN 3-936586-03-9). The spatial period of the irregular structure is equal to the standing wavelength Lambda or one-half the powerful wavelength lambda/2. API diagnostics are carried out at the API relaxation or decay stage by their sounding of probing radio pulses. Based on the measurement of an amplitude and a phase of the API scattered signal their relaxation time and regular vertical plasma velocity are measured. In the E-region of the ionosphere API are formed as a result of the diffusion redistribution of the non-uniformly heated plasma. The relaxation of the periodic structure is specified by the ambipolar diffusion process. The diffusion time is tau=(K (2) D _{a}) (-1) where K=2pi/Lambda and D _{a} is the ambipolar diffusion rate. The atmospheric turbulence causes reduction of the API relaxation time in comparison the diffusion time. Determination of the turbulent velocity is based on this fact. The vertical plasma velocity is determined by measuring the phase of the scattered signal. Atmospheric waves having the periods from 5-10 minutes to 5-6 hours give the contribution to temporal variations of the velocity. Parameters and effects of atmospheric waves and the turbulence on the API relaxation process are presented. Determination of the masses of the predominant metallic ions at the E _{s}-layer height is one of the API applications (Bakhmetieva N.V. and Belikovich V.V. Radiophys. Quantum Electron., 2008, Vol. 51, No 11, pp. 956-969). It is based on the observed fact of the local maximum of the API relaxation time at the sporadic E-layer location. The long-lived metallic ions cause the growth of the API relaxation time tau? at the E _{s}-layer height. It is shown by API technique the sporadic E-layers contain Mg (+) , Ca (+) and Fe (+) ions predominantly at heights of 95-110 km. The new applications are based on the so-called two-frequency method of the API creation and their diagnostics. The method allows one to define the neutral atmosphere and the ionosphere parameters with high accuracy. The main results of the lower ionosphere studies carried out in 2006-2012 by the API technique using the SURA heating facility (56,1 N; 46,15 E) are presented and discussed. We aslo discuss the studies of the HF pumping effects on the formation and parameters of the sporadic E-layers and the modification of the semitransparent E _{s}-layer by the powerful radio wave and diagnostics by the API technique. The work was supported by Russian Foundation for Basic Research under project No 13-02-97067, 13-02-12074 and 13-05-00511.

Bakhmetieva, Nataliya V.; Grigoriev; Tolmacheva, Ariadna V.

209

Prospects for GMRT to Observe Radio Waves from UHE Particles Interacting with the Moon  

E-print Network

Ultra high energy (UHE) particles of cosmic origin impact the lunar regolith and produce radio signals through Askaryan effect, signals that can be detected by Earth based radio telescopes. We calculate the expected sensitivity for observation of such events at the Giant Metrewave Radio Telescope (GMRT), both for UHE cosmic rays (CR) and UHE neutrino interactions. We find that for 30 days of observation time a significant number of detectable events is expected above $10^{20}$ eV for UHECR or neutrino fluxes close to the current limits. Null detection over a period of 30 days will lower the experimental bounds on UHE particle fluxes by magnitudes competitive to both present and future experiments at the very highest energies.

Sukanta Panda; Subhendra Mohanty; Padmanabhan Janardhan; Oscar Stål

2007-08-13

210

Prospects for GMRT to Observe Radio Waves from UHE Particles Interacting with the Moon  

E-print Network

Ultra high energy (UHE) particles of cosmic origin impact the lunar regolith and produce radio signals through Askaryan effect, signals that can be detected by Earth based radio telescopes. We calculate the expected sensitivity for observation of such events at the Giant Metrewave Radio Telescope (GMRT), both for UHE cosmic rays (CR) and UHE neutrino interactions. We find that for 30 days of observation time a significant number of detectable events is expected above $10^{20}$ eV for UHECR or neutrino fluxes close to the current limits. Null detection over a period of 30 days will lower the experimental bounds on UHE particle fluxes by magnitudes competitive to both present and future experiments at the very highest energies.

Panda, Sukanta; Janardhan, Padmanabhan; Stål, Oscar

2007-01-01

211

Conference on the Ionosphere and Radio Wave Propagation, 3rd, University of Sydney, Australia, February 11-15, 1985, Proceedings  

NASA Astrophysics Data System (ADS)

Various papers on the ionosphere and radio wave propagation are presented. The subjects discussed include: day-to-day variability in foF2 at low latitudes over a solar cycle; semiempirical, low-latitude ionospheric model; remote sensing with the Jindalee skywave radar; photographic approach to irregularities in the 80-100 km region; interference of radio waves in a CW system; study of the F-region characteristics at Waltair; recent developments in the international reference ionosphere; research-oriented ionosonde with directional capabilities; and ionospheric forecasting for specific applications. Also addressed are: experimental and theoretical techniques for the equatorial F region; empirical models of ionospheric electron concentration; the Jindalee ionospheric sounding system; a semiempirical midlatitude ionospheric model; Es structure using an HF radar; short-term variations in f0F2 and IEC; nonreciprocity in Omega propagation observed at middle latitudes; propagation management for no acknowledge HF links; new techniques in ionospheric sounding and studies; and lunar effects in the ionospheric F region.

Cole, D. G.; McNamara, L. F.

1985-12-01

212

Characteristics of atmospheric gravity waves observed using the MU (Middle and Upper atmosphere) radar and GPS (Global Positioning System) radio occultation  

PubMed Central

The wind velocity and temperature profiles observed in the middle atmosphere (altitude: 10–100 km) show perturbations resulting from superposition of various atmospheric waves, including atmospheric gravity waves. Atmospheric gravity waves are known to play an important role in determining the general circulation in the middle atmosphere by dynamical stresses caused by gravity wave breaking. In this paper, we summarize the characteristics of atmospheric gravity waves observed using the middle and upper atmosphere (MU) radar in Japan, as well as novel satellite data obtained from global positioning system radio occultation (GPS RO) measurements. In particular, we focus on the behavior of gravity waves in the mesosphere (50–90 km), where considerable gravity wave attenuation occurs. We also report on the global distribution of gravity wave activity in the stratosphere (10–50 km), highlighting various excitation mechanisms such as orographic effects, convection in the tropics, meteorological disturbances, the subtropical jet and the polar night jet. PMID:24492645

TSUDA, Toshitaka

2014-01-01

213

Space-Borne Radio-Sounding Investigations Facilitated by the Virtual Wave Observatory (VWO)  

NASA Technical Reports Server (NTRS)

The goal of the Virtual Wave Observatory (VWO) is to provide userfriendly access to heliophysics wave data. While the VWO initially emphasized the vast quantity of wave data obtained from passive receivers, the VWO infrastructure can also be used to access active sounder data sets. Here we use examples from some half-million Alouette-2, ISIS-1, and ISIS-2 digital topside-sounder ionograms to demonstrate the desirability of such access to the actual ionograms for investigations of both natural and sounder-stimulated plasma-wave phenomena. By this demonstration, we wish to encourage investigators to make other valuable space-borne sounder data sets accessible via the VWO.

Benson, Robert F.; Fung, Shing F.; Bilitza,Dieter; Garcia, Leonard N.; Shao, Xi; Galkin, Ivan A.

2011-01-01

214

The First Wave: The Beginnings of Radio in Canadian Distance Education  

ERIC Educational Resources Information Center

This article describes one of the first developments and deployment of radio for distance learning and education in Canada, beginning in the early 1920s. Anticipating a recent initiative of public-private partnerships, the impetus, infrastructure, and initial programs were provided by a large corporation. Description of the system, its purpose,…

Buck, George H.

2006-01-01

215

Radio-wave propagation for emerging wireless personal-communication systems  

Microsoft Academic Search

The present survey paper summarizes radio-propagation measurements and models for emerging wireless personal-communication systems. Both indoor and microcell-propagation environments are considered, and the problem of RF penetration into buildings is identified as an important area of research for emerging wireless-communication systems

Theodore S. Rappaport; S. Sandhu

1994-01-01

216

Interplanetary phase scintillation and the search for very low frequency gravitational radiation  

NASA Technical Reports Server (NTRS)

Observations of radio-wave phase scintillation are reported which used the Viking spacecraft having an earth-spacecraft link very similar to that which will be used in very low-frequency (VLF) gravitational-wave searches. The phase power-spectrum level varies by seven orders of magnitude as the sun-earth-spacecraft (elongation) angle changes from 1 to 175 deg. It is noteworthy that a broad minimum in the S-band (2.3 GHz) phase fluctuation occurs in the antisolar direction; the corresponding fractional frequency stability (square root Allan variance) is about 3 x 10 to the -14th for 1000-s integration times. A simultaneous two-frequency two-station observation indicates that the contribution to the phase fluctuation from the ionosphere is significant but dominated by the contribution from the interplanetary medium. Nondispersive tropospheric scintillation was not detected (upper limit to fractional frequency stability about 5 x 10 to the -14th). Evidently, even observations in the antisolar direction will require higher radio frequencies, phase scintillation calibration, and correlation techniques in the data processing, for detection of gravitational bursts at the anticipated strain amplitude levels of no more than 10 to the -15th.

Armstrong, J. W.; Woo, R.; Estabrook, F. B.

1979-01-01

217

Wave propagation channel simulation by satellite-to-indoor radio link  

Microsoft Academic Search

In our paper we present the simulation of the propagation characteristics of the satellite-to-indoor propagation channel. Our first aim has been to find a correct description of the polarization state of the received inside wave. The result of our first in- vestigations is that the polarization state of the indoor wave signigicantly changes as we move further away from the

LÓRÁNT FARKAS; LAJOS NAGY; ANDREA FARKASVÖLGYI

2008-01-01

218

Radio Ghosts  

E-print Network

We investigate the possibility that patches of old radio plasma (`radio ghosts') of former radio galaxies form a second distinct phase of the inter-galactic medium (IGM), not mixed with the thermal gas. The separation of this phase from the ambient gas and its resistance against eroding turbulent forces is given by magnetic fields, which are expected to be roughly in pressure equilibrium with the surrounding medium. Since patches of this plasma are largely invisible in the radio we use the term `radio ghost' to characterize their nature. Possibilities and difficulties of different detection strategies of ghosts are discussed. These involve radio emission, cosmic microwave background (CMB) and starlight Comptonization, and Faraday rotation. Re-activation of the electron population in shock waves of cosmological structure formation, which seems to lead to the cluster radio relic phenomena. We discuss the role radio ghosts can have: They are able to store relativistic particles for cosmological times, but are also able to release them under the influence of very strong turbulence. This might happen during a major merger event of clusters of galaxies. The released relativistic proton population could produce the observed radio halos of some cluster of galaxies via hadronic reactions with the background gas leading to the production of secondary electrons and positrons. Destroyed ghosts, mixed with the IGM can help to magnetize it. Finally, the strong field strength within ghosts should have a significant impact on the propagation of extragalactic high energy cosmic rays.

Torsten A. Ensslin

1999-06-11

219

Internal wave activity in the polar atmospheric regions during 2006 - 2009 revealed by COSMIC radio occultation data  

NASA Astrophysics Data System (ADS)

The satellite mission Formosat-3/COSMIC (Constellation Observing System for Meteorology, Ionosphere and Climate) consists of six micro-satellites, and each of them has four GPS-antennas. It was launched in April 2006, orbiting around the Earth at approximately 800 km. The primary scientific goal of the mission is to demonstrate the value of near-real-time radio occultation (RO) observations in improving operational numerical weather predictions (NWP). The goal is readily shown by assimilating the measurements of atmospheric parameters into used NWP-models. These parameters include density, temperature, pressure and relative humidity fields in the atmosphere. An analysis of their geographic and seasonal distributions is necessary to the understanding of the energy and momentum transfer and the reaction of the polar atmosphere in response to global warming. This task is especially important as the Polar Regions are very sensitive to the change in global temperature and it may be a major cause of global sea level rising. In this work, a statistical analysis of the internal gravity wave (IGW) activity in polar atmospheric regions (latitudes more than 60º) using Formosat-3/COSMIC RO temperature data collected from July 2006 to March 2009 has been performed. Geographic and seasonal distributions of the IGW potential energy (wave activity indicator) in the altitude interval from 15 to 35 km have been determined and analyzed. The obtained results show that the wave activity in the polar atmosphere is strong in winter and spring. The potential energy of IGWs in spring is largest in Antarctic atmospheric region, while it is largest in winter in Arctic region. The wave potential energy increases with altitude up to 35 km in the atmosphere of both Earth’s hemispheres. In Antarctic region, internal waves with high potential energy occur in the atmosphere over the Antarctic Peninsula. In Arctic region, a high wave activity is mainly observed over North Atlantic Ocean (Iceland) and Scandinavian Peninsula. In this work, the results of an analysis of the wave activity and factors influencing upon it in the polar stratosphere of Arctic and Antarctic have been presented and discussed. A statistical analysis of the IGW activity in Polar Regions (latitudes more than 60º) of the Earth’s atmosphere using Formosat-3/COSMIC RO temperature data collected from July 2006 to March 2009 is performed. Geographic and seasonal distributions of the IGW potential energy per unit mass (wave activity indicator) in the altitude interval from 15 to 35 km are determined and analyzed. This work was partially supported by the RFBR grant 13-02-00526-? and Program 22 of the RAS Presidium.

Kirillovich, Ivan; Gubenko, Vladimir; Pavelyev, Alexander; Liou, Yuei-An

220

The large adaptive reflector: a 200-m diameter wideband centimeter- to meter-wave radio telescope  

Microsoft Academic Search

The Large Adaptive Reflector (LAR) is a concept for a low- cost, large aperture, wideband, radio telescope, designed to operate over the wavelength range from 2 m to 1.4 cm. It consists of a 200-m diameter actuated-surface parabolic reflector with a focal length of 500 m, mounted flat on the ground. The feed is held in place by a tension-structure,

Brent Carlson; Luc Bauwens; Leonid Belostotski; Elizabeth Cannon; Ya-Ying Chang; Xiaohui Deng; Peter E. Dewdney; Joeleff T. Fitzsimmons; David Halliday; Kai Kuerschner; Gerard Lachapelle; David Lo; Pedram Mousavi; Meyer Nahon; Lot Shafai; Sigfried F. Stiemer; Russell Taylor; Bruce Veidt

2000-01-01

221

Radio-wave trajectories in a linear layer with isomerous irregularities  

NASA Astrophysics Data System (ADS)

A numerical analysis is made of deviations of the most probable trajectory of rays in a linear ionospheric layer with isomerous irregularities from the undisturbed trajectory described by the Snellius law. It is shown that the presence of scattering irregularities in the medium leads to an increase in the length of the radio path and to a change in the inclination angle of the trajectory at the exit from the layer.

Golynskii, S. M.; Khlybov, G. N.

1983-12-01

222

External heating of stents by radio waves Pilot studies in rabbit aorta  

SciTech Connect

Purpose: This experiment was designed to assess the feasibility of radio frequency energy delivered by a prototype radio frequency generator inductive heating device (REVAX) positioned external to the body, for transient heating of stents after arterial implant. Methods and Materials: Twenty-one New Zealand White rabbits underwent stenting of their infrarenal aorta. Nine rabbits were stented and immediately placed in the REVAX for external stent heating with internal temperature probes in place. Twelve rabbits were stented and 3 days later either heated or placed in the generator as a sham for 20 min. The animals were terminated 28 days later. Results: The REVAX was able to heat the aortic stents in a controlled fashion; in Phase II experiments, the stent temperature was raised to 42 deg. C for 20 min. In Phase I mild necrosis was noted at the stent struts. In Phase II, necrosis and mineralization of the media was seen at the stent struts, and evidence of neointimal suppression was observed. Conclusion: This study demonstrated that external heating of stents in a blood vessel in a live animal via radio frequency energy is feasible. Further studies will be needed to assess whether any specific heating regimen might inhibit fibrocellular neointimal hyperplasia.

Levitt, Adam B.; Robinson, Keith; Chronos, Nicolas A.F.; Daum, Wolfgang

2003-09-01

223

Onboard Signal Processing: Wave of the Future for Planetary Radio Science?  

NASA Technical Reports Server (NTRS)

Future spacecraft-based radio observations of planetary surfaces, rings, and atmospheres could significantly benefit from recent technological advances in real-time digital signal processing (DSP) hardware. Traditionally, the radio observations have been carried out in a 'down link' configuration in which about 20-W spacecraft transmitted RF power illuminates the target of interest and the perturbed signal is collected at an Earth receiving station. The down link configuration was dictated by the large throughput of received data, corresponding to a relatively large recording band width (about 50 kHz) needed to capture the coherent and scattered signal components in the presence of trajectory, ephemeris, and measurement uncertainties. An alternative 'up link' configuration in which powerful Earth-based radio transmitters (20-200 kW) are used to illuminate the target and data are recorded on board a spacecraft could enhance the measurements' signal-to-noise ratio by a factor of about 1000, allowing a quantum leap in scientific capabilities. Various aspects of alternative signal processing technologies are discussed.

Marouf, E. A.

1993-01-01

224

Plastic scintillation dosimetry: Optimal selection of scintillating fibers and scintillators  

SciTech Connect

Scintillation dosimetry is a promising avenue for evaluating dose patterns delivered by intensity-modulated radiation therapy plans or for the small fields involved in stereotactic radiosurgery. However, the increase in signal has been the goal for many authors. In this paper, a comparison is made between plastic scintillating fibers and plastic scintillator. The collection of scintillation light was measured experimentally for four commercial models of scintillating fibers (BCF-12, BCF-60, SCSF-78, SCSF-3HF) and two models of plastic scintillators (BC-400, BC-408). The emission spectra of all six scintillators were obtained by using an optical spectrum analyzer and they were compared with theoretical behavior. For scintillation in the blue region, the signal intensity of a singly clad scintillating fiber (BCF-12) was 120% of that of the plastic scintillator (BC-400). For the multiclad fiber (SCSF-78), the signal reached 144% of that of the plastic scintillator. The intensity of the green scintillating fibers was lower than that of the plastic scintillator: 47% for the singly clad fiber (BCF-60) and 77% for the multiclad fiber (SCSF-3HF). The collected light was studied as a function of the scintillator length and radius for a cylindrical probe. We found that symmetric detectors with nearly the same spatial resolution in each direction (2 mm in diameter by 3 mm in length) could be made with a signal equivalent to those of the more commonly used asymmetric scintillators. With augmentation of the signal-to-noise ratio in consideration, this paper presents a series of comparisons that should provide insight into selection of a scintillator type and volume for development of a medical dosimeter.

Archambault, Louis; Arsenault, Jean; Gingras, Luc; Sam Beddar, A.; Roy, Rene; Beaulieu, Luc [Departement de Radio-Oncologie et Centre de Recherche en Cancerologie, Hotel-Dieu de Quebec, 11 cote du palais, Quebec, Quebec G1R 2J6 (Canada) and Departement de Physique, de Genie Physique et d'Optique, Universite Laval, Quebec, Quebec (Canada); Department of Radiation Physics, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030 (United States); Department de Physique, de Genie Physique et d'Optique, Universite Laval, Quebec, Quebec (Canada); Departement de Radio-Oncologie et Centre de Recherche en Cancerologie, Hotel-Dieu de Quebec, 11 cote du palais, Quebec, Quebec G1R 2J6 (Canada) and Departement de Physique, de Genie Physique et d'Optique, Universite Laval, Quebec, Quebec (Canada)

2005-07-15

225

Plastic scintillation dosimetry: optimal selection of scintillating fibers and scintillators.  

PubMed

Scintillation dosimetry is a promising avenue for evaluating dose patterns delivered by intensity-modulated radiation therapy plans or for the small fields involved in stereotactic radiosurgery. However, the increase in signal has been the goal for many authors. In this paper, a comparison is made between plastic scintillating fibers and plastic scintillator. The collection of scintillation light was measured experimentally for four commercial models of scintillating fibers (BCF-12, BCF-60, SCSF-78, SCSF-3HF) and two models of plastic scintillators (BC-400, BC-408). The emission spectra of all six scintillators were obtained by using an optical spectrum analyzer and they were compared with theoretical behavior. For scintillation in the blue region, the signal intensity of a singly clad scintillating fiber (BCF-12) was 120% of that of the plastic scintillator (BC-400). For the multiclad fiber (SCSF-78), the signal reached 144% of that of the plastic scintillator. The intensity of the green scintillating fibers was lower than that of the plastic scintillator: 47% for the singly clad fiber (BCF-60) and 77% for the multiclad fiber (SCSF-3HF). The collected light was studied as a function of the scintillator length and radius for a cylindrical probe. We found that symmetric detectors with nearly the same spatial resolution in each direction (2 mm in diameter by 3 mm in length) could be made with a signal equivalent to those of the more commonly used asymmetric scintillators. With augmentation of the signal-to-noise ratio in consideration, this paper presents a series of comparisons that should provide insight into selection of a scintillator type and volume for development of a medical dosimeter. PMID:16121582

Archambault, Louis; Arsenault, Jean; Gingras, Luc; Beddar, A Sam; Roy, René; Beaulieu, Luc

2005-07-01

226

A study of electron density profiles in relation to ionization sources and ground-based radio wave absorption measurements, part 1  

NASA Technical Reports Server (NTRS)

An extensive set of ground-based measurements of the diurnal variation of medium frequency radio wave adsorption and virtual height is analyzed in terms of current understanding of the D- and lower E-region ion production and loss process. When this is done a gross discrepancy arises, the source of which is not known.

Gnanalingam, S.; Kane, J. A.

1973-01-01

227

Gigahertz surface acoustic wave generation on ZnO thin films deposited by radio frequency magnetron sputtering on III-V semiconductor  

E-print Network

Gigahertz surface acoustic wave generation on ZnO thin films deposited by radio frequency magnetron-beam lithography on a thin ZnO piezoelectric film deposited on an InP substrate. The highly oriented, dense- conductors may be found by depositing a thin film of a highly piezoelectric material such as ZnO on the III

Ham, Donhee

228

Optical multiple millimeter-wave signal generation using frequency quadrupling for radio-over-fiber systems  

NASA Astrophysics Data System (ADS)

In this work, we propose and investigate a novel modulation technique for the generation of multiple millimeter wave (mm-wave) signals using high-order harmonic generation with a dual-electrode Mach-Zehnder modulator (MZM). The laser output is split into two branches by the use of a polarization beam splitter. We use polarization multiplexing to avoid the inter-symbol interference between multiple mm-wave signals. The proposed technique is comprised of two parallel MZMs. As an example, we consider an RF1 at 7.5 GHz and RF2 at 8.125 GHz, each of which carries its own data signal and drives each MZM, respectively; and mm-wave signals at 30 GHz and 32.5 GHz, i.e. a frequency quadrupler, are obtained after photomixing. The performance of the system is evaluated in terms of Q-factor. Simulation results show that data signal at 625 Mb/s is successfully transmitted over 50 km of single mode fiber. The generated mm-wave signal is robust to chromatic dispersion.

Mohamed, Mohmoud; Zhang, Xiupu; Kuwairi, Salah

229

Solar gravitational deflection of radio waves measured by very-long-baseline interferometry  

NASA Technical Reports Server (NTRS)

Utilizing a four-antenna technique, simultaneous observations were made, at each end of an 845-km baseline, of the radio sources 3C279 and 3C273B, which are 10 deg apart in the sky. Differences in interferometric phases at 3.7-cm wavelength monitored near the time of the 1972 occultation of 3C279 by the sun, yielded a gravitational deflection of 0.99 plus or minus 0.03 times the value predicted by general relativity, corresponding to gamma = 0.98 plus or minus 0.06 (standard error).

Counselman, C. C., III; Kent, S. M.; Knight, C. A.; Shapiro, I. I.; Clark, T. A.; Hinteregger, H. F.; Rogers, A. E. E.; Whitney, A. R.

1974-01-01

230

Scintillation is an indicator of astrometric stability  

NASA Astrophysics Data System (ADS)

We examine the relationship between astrometric stability and astrophysical properties in flat-spectrum radio-loud quasars making up the celestial reference frame. We use position determinations from geodetic very long baseline interferometry measurements and develop a new metric for source position stability. We then compare this quantity to two measures of source compactness: structure index, which probes structure on milliarcsecond scales and the presence of interstellar scintillation associated with the quasar, which probes scales of tens of ?as. We find that persistent scintillators have greater position stability than episodic scintillators, which are in turn more stable than non-scintillators. Scintillators are also more likely to be compact on milliarcsecond scales, as measured by the structure index. Persistent scintillators are therefore excellent candidates for inclusion in any future realization of the celestial reference frame. A list of these sources is presented in Appendix A. We find that slow (characteristic time-scale >3 d) scintillators have more stable positions than rapid scintillators, suggesting that they are more compact. High-cadence, long-term monitoring is therefore required to identify other members of this population of compact, high brightness temperature quasars.

Schaap, R. G.; Shabala, S. S.; Ellingsen, S. P.; Titov, O. A.; Lovell, J. E. J.

2013-09-01

231

Plasma ionization through wave-particle interaction in a capacitively coupled radio-frequency discharge  

SciTech Connect

Phase resolved optical emission spectroscopy, with high temporal resolution, shows that wave-particle interactions play a fundamental role in sustaining capacitively coupled rf plasmas. The measurements are in excellent agreement with a simple particle-in-cell simulation. Excitation and ionization mechanisms are dominated by beam-like electrons, energized through the advancing and retreating electric fields of the rf sheath. The associated large-amplitude electron waves, driven by a form of two-stream instability, result in power dissipation through electron trapping and phase mixing.

O'Connell, D.; Gans, T.; Vender, D.; Czarnetzki, U.; Boswell, R. [Institute for Plasma and Atomic Physics, CPST, Ruhr-University Bochum (Germany); Port Arthur, Tasmania (Australia); Institute for Plasma and Atomic Physics, CPST, Ruhr-University Bochum (Germany); SP3/RSPhysSE, ANU, Canberra (Australia)

2007-03-15

232

Global estimates of gravity wave parameters from GPS radio occultation temperature data  

Microsoft Academic Search

Gravity waves (GWs) play critical roles in the global circulation and the temperature and constituent structures in the middle atmosphere. They also play significant roles in the dynamics and transport and mixing processes in the upper troposphere and lower stratosphere and can affect tropospheric weather. Despite significant advances in our understanding of GWS and their effects in different regions of

L. Wang; M. J. Alexander

2010-01-01

233

Z mode waves as the source of Saturn narrowband radio emissions  

E-print Network

observed at 5 kHz are mode converted from the Z mode waves at a density gradient or density irregularity. The Z mode to LO mode conversion via scattering off of density irregularities can also account perikrone passes. The narrowband emissions observed below the local electron cyclotron frequency ( fce

Gurnett, Donald A.

234

Spatial observations by the CUTLASS coherent scatter radar of ionospheric modication by high power radio waves  

E-print Network

excite plasma density irregularities in regions where the wave frequency is close to the local upper nature of electron transport in the ionosphere. Small-scale ®eld- aligned irregularities (FAI) with scale Sys- tem) coherent scatter radar was employed to observe arti®cial ®eld aligned irregularities (FAI

Paris-Sud XI, Université de

235

Radio Telescopes  

NASA Astrophysics Data System (ADS)

``Radio Telescopes" starts with a brief historical introduction from Jansky's1931 discovery of radio emission from the Milky Way through the development ofradio telescope dishes and arrays to aperture synthesis imaging. It includessufficient basics of electromagnetic radiation to provide some understanding of thedesign and operation of radio telescopes. The criteria such as frequencyrange, sensitivity, survey speed, angular resolution, and field of view thatdetermine the design of radio telescopes are introduced. Because it is soeasy to manipulate the electromagnetic waves at radio frequencies, radiotelescopes have evolved into many different forms, sometimes with "wire"structures tuned to specific wavelengths, which look very different from anykind of classical telescope. To assist astronomers more familiar with otherwavelength domains, the appendix A.1. includes a comparison of radioand optical terminology. Some of the different types of radio telescopesincluding the filled aperture dishes, electronically steered phased arrays, andaperture synthesis radio telescopes are discussed, and there is a sectioncomparing the differences between dishes and arrays. Some of the morerecent developments including hierarchical beam forming, phased arrayfeeds, mosaicing, rotation measure synthesis, digital receivers, and longbaseline interferometers are included. The problem of increasing radiofrequency interference is discussed, and some possible mitigation strategies areoutlined.

Ekers, Ron; Wilson, Thomas L.

236

Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/ Waves Instruments: Goniopolarimetric Properties and Radio Source Locations  

NASA Astrophysics Data System (ADS)

We have performed a statistical analysis of a large number of Type III radio bursts observed by STEREO between May 2007 and February 2013. Only intense, simple, and isolated cases have been included in our data set. We focused on the goniopolarimetric (GP, also referred to as direction-finding) properties at frequencies between 125 kHz and 2 MHz. The apparent source size ? is very extended (? 60?) for the lowest analyzed frequencies. Observed apparent source sizes ? expand linearly with a radial distance from the Sun at frequencies below 1 MHz. We show that Type III radio bursts statistically propagate in the ecliptic plane. The calculated positions of radio sources indicate that scattering of the primary beam pattern plays an important role in the propagation of Type III radio bursts in the interplanetary medium.

Krupar, V.; Maksimovic, M.; Santolik, O.; Cecconi, B.; Kruparova, O.

2014-12-01

237

Potential Spacecraft-to-Spacecraft Radio Observations with EJSM: Wave of the Future? (Invited)  

NASA Astrophysics Data System (ADS)

Future active radio observations of planetary and satellite atmospheres and surfaces could significantly benefit form the presence of two or more spacecraft in orbit around a target object. Traditionally, radio occultation and bistatic surface scattering experiments have been conducted using a single spacecraft operating in the Downlink (DL) configuration, with the spacecraft transmitting and at least one Earth-based station receiving. The configuration has the advantage of using powerful ground-based receivers for down-conversion, digitization, and digital recording of large bandwidth data for later off-line processing and analysis. It has the disadvantage of an available free-space signal-to-noise ratio (SNR) limited by the relatively small carrier power (10-20 W) a spacecraft can practically transmit. Recent technological advances in designing small-mass and small-power spacecraft-based digital receivers capable of on-board signal processing could open the door for significant performance improvement compared with the DL configuration. For example, with two spacecraft in orbit instead of one, the smaller distance D between the two spacecraft compared with the distance to Earth can boost achievable free-space SNR by one to three orders of magnitude, depending on D. In addition, richer variability in observation geometry can be captured using spacecraft-to-spacecraft (SC-to-SC) radio occultations and surface scattering. By their nature, traditional DL occultations are confined to the morning and evening terminators. Availability of on-board processing capability also opens the door for conducting Uplink (UL) occultation and bistatic observations, where very large power (> 20 kW) can be transmitted from an Earth-based station, potentially boasting achievable free-space SNR by orders of magnitude, comparable to the SC-to-SC case and much higher than the DL case. The Europa Jupiter System Mission (EJSM) will likely be the first planetary mission to benefit from the unprecedented opportunity of having two highly capable spacecraft orbiting Jupiter in concert and during the same time window. The strawman payload of the American Jupiter Europa Orbiter (JEO) and the European Jupiter Ganymede Orbiter (JGO) envisions at least one spacecraft (JGO) hosting an on-board digital receiving and processing capability. The receiver is specifically designed to allow for synergistic SC-to-SC observations, as well as Earth-to-JGO UL observations. In principle, each spacecraft can host an on-board digital receiver for rich combinations of high-performance synergistic or individual observations, depending on the opportunity. For the envisioned EJSM strawman payload and example tour, we examine achievable performance for potential observations that include SC-to-SC, UL, and DL occultations of Jupiter’s ionosphere and neutral atmosphere, the ionospheres and thin atmospheres of the large Jovian satellites, and of the tenuous Jovian Rings. We also consider potential bistatic scattering (bistatic-radar) observation opportunities of the surfaces of Europa and Ganymede.

Marouf, E. A.; Tortora, P.; Asmar, S. W.; Folkner, W. M.; Hinson, D.; Iess, L.; Linscott, I. R.; Lorenz, R. D.; Mueller-Wodarg, I. C.

2010-12-01

238

Radio wave diffraction during the passage of an acoustic shock through a sporadic E layer  

SciTech Connect

Bistatic HF Doppler measurements of the ionospheric disturbance arising from a large ground-level chemical explosion have revealed a peculiar HF return which begins at large positive Doppler (greater than +5 Hz) and linearly evolves to large negative Doppler (less than -5 Hz). Various pieces of evidence in the data suggest that an HF wave which is diffracted from the intersection of the acoustic shock and an extensive plane of sporadic E ionization at 110 km was observed. From these measurements the horizontal trace velocity of the locus of intersection is estimated. 16 references.

Jacobson, A.R.; Carlos, R.C.; Argo, P.E.; Rickel, D.G.

1986-08-01

239

Sixty gigahertz indoor radio wave propagation prediction method based on full scattering model  

NASA Astrophysics Data System (ADS)

In radio system deployment, the main focus is on assuring sufficient coverage, which can be estimated with path loss models for specific scenarios. When more detailed performance metrics such as peak throughput are studied, the environment has to be modeled accurately in order to estimate multipath behavior. By means of laser scanning we can acquire very accurate data of indoor environments, but the format of the scanning data, a point cloud, cannot be used directly in available deterministic propagation prediction tools. Therefore, we propose to use a single-lobe directive model, which calculates the electromagnetic field scattering from a small surface and is applicable to the point cloud, and describe the overall field as fully diffuse backscattering from the point cloud. The focus of this paper is to validate the point cloud-based full diffuse propagation prediction method at 60 GHz. The performance is evaluated by comparing characteristics of measured and predicted power delay profiles in a small office room and an ultrasonic inspection room in a hospital. Also directional characteristics are investigated. It is shown that by considering single-bounce scattering only, the mean delay can be estimated with an average error of 2.6% and the RMS delay spread with an average error of 8.2%. The errors when calculating the azimuth and elevation spreads are 2.6° and 0.6°, respectively. Furthermore, the results demonstrate the applicability of a single parameter set to characterize the propagation channel in all transmit and receive antenna locations in the tested scenarios.

Järveläinen, J.; Haneda, K.

2014-04-01

240

Ionospheric observations of F region artificial plasma turbulence, modified by powerful X-mode radio waves  

NASA Astrophysics Data System (ADS)

We study the influence of additional X-mode heating of the ionospheric plasma on the features of artificial ionospheric turbulence, induced in the ionospheric F region by O-mode waves over the ``Sura'' heating facility (Nizhny Novgorod, Russia). The X heating is shown to suppress the generation of HF plasma turbulence resulting from the development of both the parametric decay and thermal parametric instabilities. Typical times of variations in the turbulence intensity change from <=0.1 s to ~10 s, strongly depending on the heating scheme. Aftereffects of the X heating last up to 30-60 s. We distinguish at least three types of phenomena, according to the observed typical times of the processes, and discuss possible reasons for each of them.

Frolov, V. L.; Kagan, L. M.; Sergeev, E. N.; Komrakov, G. P.; Bernhardt, P. A.; Goldstein, J. A.; Wagner, L. S.; Selcher, C. A.; Stubbe, P.

1999-06-01

241

A High-Resolution Study of Quasiperiodic Radio Emissions Observed by the Galileo Plasma Wave Instrument  

NASA Technical Reports Server (NTRS)

We have conducted a study of quasiperiodic emission observed by the plasma wave instrument on board the Galileo spacecraft. These emissions appear as broadband bursts with dominant periods ranging from 10 min to over 40 min. For these emissions we have explicitly analyzed the high-resolution (waveform) data to determine the presence of impulsive, solitary signatures. Our investigations have indicated that the broadband bursts, as well as the background more narrowband continuum emission, are composed of a highly turbulent spectrum. Within the broadband burst, however, there are higher-frequency components present, but no impulsive electrostatic signatures. Also significantly, the broadband bursts show no low-frequency dispersion. We conclude that the bursts are consistent with a distant, electromagnetic source, probably in the near-Jupiter vicinity.

Menietti, J. D.; Christopher, I.; Granroth, L. J.

2001-01-01

242

Triggered Jovian radio emissions  

NASA Technical Reports Server (NTRS)

Certain Jovian radio emissions seem to be triggered from outside, by much weaker radio waves from the sun. Recently found in the Voyager observations near Jupiter, such triggering occurs at hectometric wavelengths during the arrival of solar radio bursts, with the triggered emissions lasting sometimes more than an hour as they slowly drifted toward higher frequencies. Like the previous discovery of similar triggered emissions at the earth, this suggests that Jupiter's emissions might also originate from natural radio lasers.

Calvert, W.

1985-01-01

243

Electron-ion temperature ratio estimations in the summer polar mesosphere when subject to HF radio wave heating  

NASA Astrophysics Data System (ADS)

We have inferred the electron temperature enhancements above mesospheric altitudes under Polar Mesospheric Summer Echoes (PMSE) conditions when the ionosphere is exposed to artificial HF radio wave heating. The proposed method uses the dependence of the radar cross section on the electron-to-ion temperature ratio to infer the heating factor from incoherent scatter radar (ISR) power measurements above 90 km. Model heating temperatures match our ISR estimations between 90 and 130 km with 0.94 Pearson correlation index. The PMSE strength measured by the MORRO MST radar is about 50% weaker during the heater-on period when the modeled electron-to-ion mesospheric temperature is approximately 10 times greater than the unperturbed value. No PMSE weakening is found when the mesospheric temperature enhancement is by a factor of three or less. The PMSE weakening and its absence are consistent with the modeled mesospheric electron temperatures. This consistency supports to the proposed method for estimating mesospheric electron temperatures achieved by independent MST and ISR radar measurements.

Pinedo, H.; La Hoz, C.; Havnes, O.; Rietveld, M.

2014-10-01

244

Study of effects of radio-wave frequency radiation emitted from cellular telephones on embryonic development of danio rerio  

NASA Astrophysics Data System (ADS)

Radio wave frequency (RF) radiation emitted from cellular telephones has become increasingly ubiquitous as a result of the popularity of these phones. With the increasing and unavoidable exposure to RF radiation a reality, it is imperative that the effects of such radiation on living tissue be well understood. In particular, it is critical to understand any effects that RF radiation may have as a carcinogen and on embryonic development, as pregnant women are not exempt from such exposure. As a model organism, zebrafish (Danio rerio) have been studied extensively, and their value in studies of gene expression cannot be overstated. This study observed the effects of RF radiation on the embryonic development of zebrafish. The expression of two genes, shha and hoxb9a, that are key to the early development of the fish was examined. Both genes have homologs in humans as well as in other model organisms. Preliminary results suggest that exposure to cell phone radiation might have an effect on the expression of shha in zebrafish embryos, causing under expression. More trials are necessary to validate these results.

Vagula, Mary; Harkless, Ryan

2013-05-01

245

Schemes of generating M-ASK signals and remote local oscillator at millimeter-wave band in radio over fiber system  

NASA Astrophysics Data System (ADS)

This paper introduces two schemes to generate millimeter-wave (mm-wave) BPSK and M-ASK signals in Base Station in Radio over Fiber (RoF) system based on cascaded Dual-Drive Mach-Zehnder modulators (DD-MZM). A BPSKmodulated mm-wave RoF system is proposed by controlling the amplitudes of baseband digital signal. Another scheme to generate M-ASK-modulated mm-wave in BS is based on commanding the power of Intermediated Frequency (IF) signal. Both schemes can make the remote local reference signal available in the BS, which makes the system costefficient. The proposed schemes are verified by theoretical derivation and simulation.

Chen, Haoshuo; Lin, Rujian; Ye, Jianjun

2009-11-01

246

Effect of large-amplitude perpendicularly propagating radio frequency waves on the interchange instability  

SciTech Connect

Results are presented from hybrid 2-D quasineutral Darwin simulations of the interchange instability in the presence of a large rf wave in the ion-cyclotron frequency range. The simulation models the plane perpendicular to the background magnetic field using cold particle ions and a cold E x B electron fluid. Related theory is also discussed. Fluid equations appropriate to the simulation model are derived and their properties demonstrated and compared to simulation. A method for solving for the rf-modified growth rates from the fluid equations is described. It is generally expected that the current component associated with the mean, rf-induced ion drift is capable of influencing the stability of the interchange mode; however, no modification of the mean ion drift is observed in simulations in which rf is present. Instead, in both the theory and simulation, an electron rf-field oscillation current dominates the modification to the gravitational current. As a result, even in the presence of large rf fields (B/sub rf//B/sub 0/ = 15%), only modest corrections to the interchange growth rates are observed. The effect is stabilizing for kL/sub n/approx. <0.8--0.9, apparently for both signs of the square-electric-field gradient, and is destabilizing for larger values of kL/sub n/, although the credibility of the simulation begins to become suspect here.

Otani, N.F.; Cohen, B.I.

1988-01-01

247

Fine Structure of Solar Radio Bursts Observed at Decametric and Hectometric Waves  

NASA Astrophysics Data System (ADS)

The analysis of WIND/WAVES RAD2 spectra with fine structure in the form of different fibers in 14 events covering 1997 2005 is carried out. A splitting of broad bands of the interplanetary (IP) type II bursts into narrow band fibers of different duration is observed. The instantaneous-frequency bandwidth of fibers is stable: 200 300 kHz for slow-drifting fibers in type II bursts, and 700 1000 kHz for fast-drifting fibers in type II + IV (continuum). Intermediate drift bursts (IDB or fiber bursts) and zebra patterns with variable frequency drift of stripes, typical for the metric range, were not found. Comparison of spectra with the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph (SOHO/LASCO C2) images shows a connection of the generation of the fiber structures with the passage of shock fronts through narrow jets in the wake of Coronal Mass Ejections (CME). Therefore the most probable emission mechanism of fibers in IP type II bursts appears to be resonance transition radiation (RTR) of fast particles at the boundary of two media with different refractive indices. The same mechanism is also valid for striae in the type III bursts. Taking into account a high-density contrast in the CME wake and the actually observed small-scale inhomogeneities, the effectiveness of the RTR mechanism in IP space must be considerably higher than in the meter or decimeter wavelengths. For the most part the fibers in the type IV continuum at frequencies of 14 8 MHz were seen as the direct expansion of similar fine structure (as fibers or “herringbone” structure) in the decametric range observed with the Nançay and IZMIRAN spectrographs.

Chernov, G. P.; Kaiser, M. L.; Bougeret, J.-L.; Fomichev, V. V.; Gorgutsa, R. V.

2007-03-01

248

Hyperstrong Radio-Wave Scattering in the Galactic Center. II. A Likelihood Analysis of Free Electrons in the Galactic Center  

NASA Astrophysics Data System (ADS)

The scattering diameters of Sgr A* and several nearby OH masers (~1" at 1 GHz) indicate that a region of enhanced scattering is along the line of sight to the Galactic center. We combine radio-wave scattering data and free-free emission and absorption measurements in a likelihood analysis that constrains the following parameters of the GC scattering region: The GC-scattering region separation, ?GC the angular extent of the region, ?l and ?b the outer scale on which density fluctuations occur, l0; and the gas temperature, Te. The maximum likelihood estimates of these parameters are ?GC=133+200-80 pc, 0.5d<=?l<~1deg, and (l0/1 pc)2/3T-1/2e=10-7+/-0.8. The parameter ?b was not well constrained, and we adopt ?b = 0.5d. The close correspondence between ?GC and ?lDGC suggests that the scattering region encloses the GC. As host media for the scattering, we consider the photoionized surface layers of molecular clouds and the interfaces between molecular clouds and the 107 K ambient gas. We are unable to make an unambiguous determination, but we favor the interface model in which the scattering medium is hot (Te ~ 106 K) and dense (ne ~ 10 cm-3). The GC scattering region produces a 1 GHz scattering diameter for an extragalactic source of 90", if the region is a single screen, or 180", if the region wraps around the GC, as appears probable. We modify the Taylor-Cordes model for the Galactic distribution of free electrons in order to include an explicit GC component. We predict that pulsars seen through this region will have a dispersion measure of approximately 2000 pc cm-3, of which approximately 1500 pc cm-3 arises from the GC component itself. We stress the uniqueness of the GC scattering region, probably resulting from the high-pressure environment in the GC.

Lazio, T. Joseph W.; Cordes, James M.

1998-10-01

249

Multi-PSPMT scintillation camera  

SciTech Connect

Gamma ray imaging is usually accomplished by the use of a relatively large scintillating crystal coupled to either a number of photomultipliers (PMTs) (Anger Camera) or to a single large Position Sensitive PMT (PSPMT). Recently the development of new diagnostic techniques, such as scintimammography and radio-guided surgery, have highlighted a number of significant limitations of the Anger camera in such imaging procedures. In this paper a dedicated gamma camera is proposed for clinical applications with the aim of improving image quality by utilizing detectors with an appropriate size and shape for the part of the body under examination. This novel scintillation camera is based upon an array of PSPMTs (Hamamatsu R5900-C8). The basic concept of this camera is identical to the Anger Camera with the exception of the substitution of PSPMTs for the PMTs. In this configuration it is possible to use the high resolution of the PSPMTs and still correctly position events lying between PSPMTs. In this work the test configuration is a 2 by 2 array of PSPMTs. Some advantages of this camera are: spatial resolution less than 2 mm FWHM, good linearity, thickness less than 3 cm, light weight, lower cost than equivalent area PSPMT, large detection area when coupled to scintillating arrays, small dead boundary zone (< 3 mm) and flexibility in the shape of the camera.

Pani, R.; Pellegrini, R.; Trotta, G.; Scopinaro, F. [Univ. of Rome (Italy). Dept. of Experimental Medicine] [Univ. of Rome (Italy). Dept. of Experimental Medicine; Soluri, A.; Vincentis, G. de [CNR (Italy). Inst. of Biomedical Technologies] [CNR (Italy). Inst. of Biomedical Technologies; Scafe, R. [ENEA-INN, Rome (Italy)] [ENEA-INN, Rome (Italy); Pergola, A. [PSDD, Rome (Italy)] [PSDD, Rome (Italy)

1999-06-01

250

Lead carbonate scintillator materials  

DOEpatents

Improved radiation detectors containing lead carbonate or basic lead carbonate as the scintillator element are disclosed. Both of these scintillators have been found to provide a balance of good stopping power, high light yield and short decay constant that is superior to other known scintillator materials. The radiation detectors disclosed are favorably suited for use in general purpose detection and in medical uses.

Derenzo, Stephen E. (Pinole, CA); Moses, William W. (Berkeley, CA)

1991-01-01

251

Scintillator materials for calorimetry  

SciTech Connect

Requirements for fast, dense scintillator materials for calorimetry in high energy physics and approaches to satisfying these requirements are reviewed with respect to possible hosts and luminescent species. Special attention is given to cerium-activated crystals, core-valence luminescence, and glass scintillators. The present state of the art, limitations, and suggestions for possible new scintillator materials are presented.

Weber, M.J. [Lawrence Berkeley Lab., CA (United States). Life Sciences Div.

1994-09-01

252

Scintillator manufacture at Fermilab  

SciTech Connect

A decade of research into plastic scintillation materials at Fermilab is reviewed. Early work with plastic optical fiber fabrication is revisited and recent experiments with large-scale commercial methods for production of bulk scintillator are discussed. Costs for various forms of scintillator are examined and new development goals including cost reduction methods and quality improvement techniques are suggested.

Mellott, K.; Bross, A.; Pla-Dalmau, A.

1998-08-01

253

A Challenging Solar Eruptive Event of 18 November 2003 and the Causes of the 20 November Geomagnetic Superstorm. II. CMEs, Shock Waves, and Drifting Radio Bursts  

NASA Astrophysics Data System (ADS)

We continue our study (Grechnev et al., 2013, doi:10.1007/s11207-013-0316-6; Paper I) on the 18 November 2003 geoffective event. To understand possible impact on geospace of coronal transients observed on that day, we investigated their properties from solar near-surface manifestations in extreme ultraviolet, LASCO white-light images, and dynamic radio spectra. We reconcile near-surface activity with the expansion of coronal mass ejections (CMEs) and determine their orientation relative to the earthward direction. The kinematic measurements, dynamic radio spectra, and microwave and X-ray light curves all contribute to the overall picture of the complex event and confirm an additional eruption at 08:07 - 08:20 UT close to the solar disk center presumed in Paper I. Unusual characteristics of the ejection appear to match those expected for a source of the 20 November superstorm but make its detection in LASCO images hopeless. On the other hand, none of the CMEs observed by LASCO seem to be a promising candidate for a source of the superstorm being able to produce, at most, a glancing blow on the Earth's magnetosphere. Our analysis confirms free propagation of shock waves revealed in the event and reconciles their kinematics with "EUV waves" and dynamic radio spectra up to decameters.

Grechnev, V. V.; Uralov, A. M.; Chertok, I. M.; Slemzin, V. A.; Filippov, B. P.; Egorov, Y. I.; Fainshtein, V. G.; Afanasyev, A. N.; Prestage, N. P.; Temmer, M.

2014-04-01

254

Monitoring and Forecasting Ionospheric Scintillation at High Latitudes (Invited)  

NASA Astrophysics Data System (ADS)

Ionospheric scintillation (rapid signal amplitude fading and phase fluctuation) poses a threat to reliable and safe operation of modern technology that relies on Global Navigation Satellite Systems (GNSS). Ionospheric scintillation of GNSS signal severely degrades positional accuracy, causes cycle slips leading to loss of lock that affects performance of radio communication and navigation systems. At high latitudes, the scintillation is caused by ionospheric irregularities produced through coupling between solar wind plasma and the magnetosphere. Climatology of GPS scintillation at high latitudes in both hemispheres shows that phase scintillation occurs predominantly on the dayside in the cusp and in the nightside auroral oval. Solar wind disturbances, in particular the co-rotating interaction regions (CIR) on the leading edge of high-speed streams (HSS) and interplanetary coronal mass ejections (ICME), have been closely correlated with the occurrence of scintillation at high latitudes. These results demonstrated a technique of probabilistic forecast of high-latitude phase scintillation occurrence relative to arrival times of HSS and ICME. The Canadian High Arctic Ionospheric Network (CHAIN) has been monitoring GPS ionospheric scintillation and total electron content (TEC) since November 2007. One-minute amplitude and phase scintillation indices from L1 GPS signals and TEC from L1 and L2 GPS signals are computed from amplitude and phase data sampled at 50 Hz. Since 2012, significant expansion of CHAIN has begun with installation of new receivers, each capable of tracking up to 30 satellites including GLONASS and Galileo. The receivers log the raw phase and amplitude of the signal up to a 100-Hz rate for scintillation measurements. We briefly review observations of ionospheric scintillation and highlight new results from CHAIN, including the climatology of scintillation occurrence, collocation with aurora and HF radar backscatter, correlation with CIRs and ICMEs, and the method of probabilistic forecasting of phase scintillation at high latitudes.

Prikryl, P.; Jayachandran, P. T.; Chadwick, R.; Kelly, T.

2013-12-01

255

Scintillator reflective layer coextrusion  

DOEpatents

A polymeric scintillator has a reflective layer adhered to the exterior surface thereof. The reflective layer comprises a reflective pigment and an adhesive binder. The adhesive binder includes polymeric material from which the scintillator is formed. A method of forming the polymeric scintillator having a reflective layer adhered to the exterior surface thereof is also provided. The method includes the steps of (a) extruding an inner core member from a first amount of polymeric scintillator material, and (b) coextruding an outer reflective layer on the exterior surface of the inner core member. The outer reflective layer comprises a reflective pigment and a second amount of the polymeric scintillator material.

Yun, Jae-Chul (Naperville, IL); Para, Adam (St. Charles, IL)

2001-01-01

256

Radio Galaxies.  

ERIC Educational Resources Information Center

Provides background information on radio galaxies. Topic areas addressed include: what produces the radio emission; radio telescopes; locating radio galaxies; how distances to radio galaxies are found; physics of radio galaxies; computer simulations of radio galaxies; and the evolution of radio galaxies with cosmic time. (JN)

Downes, Ann

1986-01-01

257

CIGALA: an FP7 innovative activity to tackle the threat of Ionospheric Scintillation to GNSS operations in Latin America  

NASA Astrophysics Data System (ADS)

Drifting ionospheric electron density irregularities may lead to the scintillation of transionospheric radio waves, as in the case of signals broadcast from artificial satellites. Scintillations can not only degrade signal quality but also cause receiver loss of lock on GNSS satellites, therefore posing a major threat to GNSS based applications demanding high levels of accuracy, availability and integrity, including EGNOS-based applications notably in low latitude areas. The problem is particularly acute in Latin America and will be further amplified with the next solar maximum, predicted for 2013. The CIGALA (Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America) project, led by Septentrio NV and co-funded by the European GNSS Supervisory Authority (GSA) through the European 7th Framework Program, will tackle this problem. The aim of the CIGALA project is to develop ionospheric scintillation mitigation countermeasures to be implemented in Septentrio's professional multi-frequency multi-constellation GNSS receivers and tested in Latin America. The project will leverage research and development activities coordinated between European and Brazilian experts and will involve a wide scale ionospheric measurement and test campaigns that will be conducted in Brazil with the support of several local academic and industrial partners. Details on the objectives, current status, and workflow of the project will be presented and discussed.

Francisco Galera Monico, João.; Bougard, Bruno; Sleewaegen, Jean-Marie; Willems, Tom; Saüt, Carine; Aquino, Marcio; de Franceschi, Giorgiana; Ferreira da Silva, Elcia; Forte, Biagio; Wernik, Andrzej W.

2010-05-01

258

Low/Mid-latitude Ionospheric irregularities and scintillation climatology  

NASA Astrophysics Data System (ADS)

Ionospheric scintillation occur when radio signals propagate through an irregular ionosphere (e.g., plasma bubbles). Since plasma bubbles are regions of depleted ion and electron densities, a plasma bubble located on the satellite-to-ground signal path will cause radio signals to fluctuate in phase and amplitude. Ionospheric scintillation data were analyzed in the magnetic latitudinal field-of-view 29° N -13.4° N, observed by a stand-alone SCINDA (Scintillation Network Decision Aid) - GPS receiver at Helwan, Egypt (29.86° N, 31.32° E). A minimum 20° elevation cut off angle has been set in order to minimize the multipath effect. During the enhancing phase of the current solar cycle 24 (years 2010, 2011, 2012 and 2013), the behaviour of the scintillation occurrence were characterized. The seasonal, annual and solar cycle variation of scintillation occurrence is investigated together with the Total Electron Content (TEC), to put in evidence the relation between the electron density gradients and the ionospheric irregularities causing scintillation. This study considers a first step to develop a scintillation climatology over Northern Africa.

Abdallah, Amr; Groves, K. M.; Mahrous, Ayman; Hussein, Fayrouz

259

Lead carbonate scintillator materials  

DOEpatents

Improved radiation detectors containing lead carbonate or basic lead carbonate as the scintillator element are disclosed. Both of these scintillators have been found to provide a balance of good stopping power, high light yield and short decay constant that is superior to other known scintillator materials. The radiation detectors disclosed are favorably suited for use in general purpose detection and in medical uses. 3 figures.

Derenzo, S.E.; Moses, W.W.

1991-05-14

260

The detection of coronal mass ejections in the interplanetary medium using scintillation observations  

NASA Astrophysics Data System (ADS)

Daily observations of scintillating radio sources obtained from July 2011 through June 2012 on the Big Scanning Antenna of the P.N. Lebedev Physical Institute at 111 MHz using a 16 beams system are analyzed. Variations in the observed scintillation indices are compared with data on solar X-ray flares and geomagnetic disturbances. Comparison of the observed scintillation indices on successive days enables the detection of most propagating disturbances associated with coronal events of class M5.0 and higher.

Glyantsev, A. V.; Tyul'bashev, S. A.; Chashei, I. V.; Shishov, V. I.

2014-09-01

261

A multi-instrument technique for localization of scintillation-causing regions in the equatorial ionosphere  

Microsoft Academic Search

Scintillation of transionospheric radio signals is a phenomenon of great practical consequence for users of satellite communication and navigation systems, often rendering these systems inaccurate or simply useless for periods of time. In order to understand the occurrence and underlying physics of the plasma instabilities that generate scintillation-causing irregularities, it is necessary to study the scale and velocity of these

E. S. Miller; J. J. Makela

2008-01-01

262

Statistics of ionospheric scintillation occurrence over European high latitudes  

NASA Astrophysics Data System (ADS)

Rapid fluctuation in the amplitude and phase of transionospheric radio signals caused by small scale ionospheric plasma density irregularities is known as scintillation. Over the high latitudes, irregularities causing scintillation are associated with large scale plasma structures and scintillation occurrence is mainly enhanced during geomagnetic storms. This paper presents a statistical analysis of scintillation occurrence on GPS L1C/A signal at a high latitude station located in Bronnoysund (geographic latitude 65.5°N, geographic longitude 12.2°E; corrected geomagnetic (CGM) latitude 62.77°N), Norway, during the periods around the peaks of solar cycles 23 (2002-2003) and 24 (2011-2013). The analysis revealed that the scintillation occurrence at Bronnoysund during both the solar maximum periods maximises close to the midnight magnetic local time (MLT) sector. A higher occurrence of scintillation is observed on geomagnetically active days during both the solar maximum periods. The seasonal pattern of scintillation occurrence indicated peaks during the summer and equinoctial months. A comparison with the interplanetary magnetic field (IMF) components By and Bz showed an association of scintillation occurrence with the southward IMF Bz conditions.

Sreeja, V.; Aquino, M.

2014-12-01

263

Radio wave propagation into sandstorms-system design based on ten-years visibility data in Riyadh, Saudi Arabia  

Microsoft Academic Search

Reliability analysis for millimetric radio links is presented in this paper. Based on 10-years visibility data for VXyadh City, Saudi Arabia, the expected outage caused by sandstorms is estimated. It is shown that an extended hop length of i0 to 20 km can be achieved with high reliability for dry conditions and small particle size. The present analysis is limited

Mohammed A. Alhaider

1986-01-01

264

An alternative to the plasma emission model: Particle-in-cell, self-consistent electromagnetic wave emission simulations of solar type III radio bursts  

SciTech Connect

High-resolution (sub-Debye length grid size and 10 000 particle species per cell), 1.5D particle-in-cell, relativistic, fully electromagnetic simulations are used to model electromagnetic wave emission generation in the context of solar type III radio bursts. The model studies generation of electromagnetic waves by a super-thermal, hot beam of electrons injected into a plasma thread that contains uniform longitudinal magnetic field and a parabolic density gradient. In effect, a single magnetic line connecting Sun to Earth is considered, for which five cases are studied. (i) We find that the physical system without a beam is stable and only low amplitude level electromagnetic drift waves (noise) are excited. (ii) The beam injection direction is controlled by setting either longitudinal or oblique electron initial drift speed, i.e., by setting the beam pitch angle (the angle between the beam velocity vector and the direction of background magnetic field). In the case of zero pitch angle, i.e., when v-vector{sub b{center_dot}}E-vector{sub perpendicular}=0, the beam excites only electrostatic, standing waves, oscillating at local plasma frequency, in the beam injection spatial location, and only low level electromagnetic drift wave noise is also generated. (iii) In the case of oblique beam pitch angles, i.e., when v-vector{sub b{center_dot}}E-vector{sub perpendicular}=0, again electrostatic waves with same properties are excited. However, now the beam also generates the electromagnetic waves with the properties commensurate to type III radio bursts. The latter is evidenced by the wavelet analysis of transverse electric field component, which shows that as the beam moves to the regions of lower density and hence lower plasma frequency, frequency of the electromagnetic waves drops accordingly. (iv) When the density gradient is removed, an electron beam with an oblique pitch angle still generates the electromagnetic radiation. However, in the latter case no frequency decrease is seen. (v) Since in most of the presented results, the ratio of electron plasma and cyclotron frequencies is close to unity near the beam injection location, in order to prove that the electromagnetic emission, generated by the non-zero pitch angle beam, oscillates at the plasma frequency, we also consider a case when the magnetic field (and the cyclotron frequency) is ten times smaller. Within the limitations of the model, the study presents the first attempt to produce synthetic (simulated) dynamical spectrum of the type III radio bursts in the fully kinetic plasma model. The latter is based on 1.5D non-zero pitch angle (non-gyrotropic) electron beam that is an alternative to the plasma emission classical mechanism for which two spatial dimensions are needed.

Tsiklauri, David [Astronomy Unit, School of Mathematical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS (United Kingdom)

2011-05-15

265

Modification of the high latitude F region of the ionosphere by X-mode powerful HF radio waves: Experimental results from multi-instrument diagnostics  

NASA Astrophysics Data System (ADS)

We present the experimental results for strong plasma modifications induced by the X-mode powerful HF radio waves injected towards the magnetic zenith into the high latitude F region of the ionosphere. A large number of experiments in the course of Russian EISCAT heating campaigns were conducted in 2009 - 2013 under different background conditions in a wide heater frequency range from 4 to 8 MHz. The EISCAT UHF incoherent scatter radar at Tromsø, the CUTLASS (SuperDARN) HF coherent radar in Finland, SEE receiver at Tromsø, the HF Doppler equipment near St. Petersburg, and the EISCAT ionosonde (dynasonde) were used as diagnostic instruments. The results show that the X-mode HF pump wave can generate: (1) strong small-scale artificial field aligned irregularities (AFAIs); (2) HF-induced plasma and HF-enhanced ion lines (HFPLs and HFILs) from UHF radar spectra; (3) strong electron density enhancements along magnetic field line in a wide altitude range; (4) spectral components (few tens of Hz) in the Doppler spectra of the heater signal measured at a distance of 1200 km from the Tromsø HF heating facility. The experimental results obtained points to the strong magnetic zenith effect due to self-focusing powerful HF radio wave with X-mode polarization. For heater frequencies in the range of about 4 - 6 MHz the mentioned above phenomena are generated when the heater frequency is equal or above the ordinary-mode critical frequency (foF2). Under high background electron density and the heater frequencies used of 6.5 - 8.0 MHz, the strong X-mode HF-induced phenomena were observed both when the heater frequency is equal or above the foF2 and the heater frequency is below the foF2.

Blagoveshchenskaya, Nataly; Rietveld, Michael; Haggstrom, Ingemar; Borisova, Tatiana; Yeoman, Tim

266

An Introduction to Radio Astronomy  

NASA Astrophysics Data System (ADS)

Preface; 1. Introduction; 2. The nature of the radio signal; 3. Signals, noise, radiometers and spectrometers; 4. Single-aperture radio telescopes; 5. The two-element interferometer; 6. Aperture synthesis; 7. Radiation, propagation and absorption of radio waves; 8. The local universe; 9. The interstellar medium; 10. Galactic dynamics; 11. Stars; 12. Pulsars; 13. Radio galaxies and quasars; 14. Cosmology fundamentals; 15. The angular structure of the CMB; 16. Cosmology: discrete radio sources and gravitational lensing; 17. The future of radio astronomy; Appendixes; References; Index.

Burke, Bernard F.; Graham-Smith, Francis

2014-02-01

267

A novel radio over fiber system with DWDM mm-wave generation and wavelength reuse for upstream data connection.  

PubMed

We proposed and experimentally demonstrated a novel radio-over-fiber architecture using an electrical mixer and an optical intensity modulator based on double side-band modulation scheme to generate dense wavelength-division multiplexing (DWDM) optical millimeter for carrying downstream data and centralized lightwave for carrying upstream data. Since the remaining optical carriers with high power have been reused, the optical power is effectively utilized; therefore the system cost can be reduced. PMID:19532849

Chen, Lin; Lei, Xiaoyan; Wen, Shuangchun; Yu, Jianguo

2007-04-30

268

Excitation of guided ELF-VLF waves through modification of the F{sub 2} ionospheric layer by high-power radio waves  

SciTech Connect

The possibility of controlled excitation of ELF-VLF electromagnetic waves through modification of the F{sub 2} ionospheric layer by high-power high-frequency emission is demonstrated in a natural experiment by using the Sura midlatitude heating facility. The excited low-frequency waves can be used to explore the near-Earth space and stimulate the excitation of a magnetospheric maser.

Markov, G. A.; Belov, A. S.; Komrakov, G. P. [Lobachevsky State University (Russian Federation); Parrot, M. [Environmental Physics and Chemistry Laboratory (France)

2012-03-15

269

Plasma radio emission from inhomogeneous collisional plasma  

NASA Astrophysics Data System (ADS)

We consider the production of radio waves via plasma emission involving Langmuir waves from a flare-accelerated electron beam in a dense plasma with density perturbations. We numerically solve the system of nonlinear kinetic equations for the particles, Langmuir waves and electromagnetic waves. We include the effects of collisions on electrons and waves, and of random fluctuations in the plasma density on Langmuir waves. We follow the temporal evolution of the system, and obtain an estimate of the radio emission produced.

Ratcliffe, Heather

2011-07-01

270

Interstellar scintillation of extragalactic radiosources and Local Interstellar Medium  

NASA Astrophysics Data System (ADS)

In the past tens of years a rich material was collected on variability of extragalactic radio sources over a wide frequency range. At frequencies exceeding 1000 MHz the flux variability is supposed to be due to activity of quasars and/or galactic nuclear. At low frequencies the variability in the flux of cosmic radio sources is caused by scintillations in the interstellar medium caused by electron density inhomogeneties. The model of anisotropic structure of the Local Interstellar Medium LISM developed by Bochkarev 1987 is compared with the results of investigation of extragalactic radio sources scintillation of the southern sky at 80 and 160 MHz Slee, Siegmen, 1988. In the direction where scintillation indices increase, regions of interaction of interstellar wind with large scale structure of LISM are located. Decrease region of scintillation indices are observed wherein on towards the third galactic quadrant near 1 is 240 grad., there is a gas free tunnel. In 1998, systematic observations of compact extragalactic radio sources will be performed with the radiotelescope DKR-1000 Pushino Radioastronomical Observatory Astro Space Center FIAN at 112 MHz with the aim of detecting the turbulent LISM region in the Northern Hemisphere. The observational programm and expected result are considered.

Ryabov, M. I.

271

All-optical frequency downconversion technique utilizing a four-wave mixing effect in a single semiconductor optical amplifier for wavelength division multiplexing radio-over-fiber applications.  

PubMed

An all-optical frequency downconversion utilizing a four-wave mixing effect in a single semiconductor optical amplifier (SOA) was experimentally demonstrated for wavelength division multiplexing (WDM) radio-over-fiber (RoF) applications. Two WDM optical radio frequency (RF) signals having 155 Mbps differential phase shift keying (DPSK) data at 28.5 GHz were simultaneously down-converted to two WDM optical intermediate frequency (IF) signals having an IF frequency of 4.5 GHz by mixing with an optical local oscillator (LO) signal having a LO frequency of 24 GHz in the SOA. The bit-error-rate (BER) performance of the RoF up-links with different optical fiber lengths employing all-optical frequency downconversion was investigated. The receiver sensitivity of the RoF up-link with a 6 km single mode fiber and an optical IF signal in an optical double-sideband format was approximately -8.5 dBm and the power penalty for simultaneous frequency downconversion was approximately 0.63 dB. The BER performance showed a strong dependence on the fiber length due to the fiber dispersion. The receiver sensitivity of the RoF up-link with the optical IF signal in the optical single-sideband format was reduced to approximately -17.4 dBm and showed negligible dependence on the fiber length. PMID:22453476

Kim, Hyoung-Jun; Song, Jong-In

2012-03-26

272

Improving the sensitivity of gravitational wave detection by applying a magnetic field evolution model to high cadence observational data of millisecond radio pulsars  

NASA Astrophysics Data System (ADS)

Radio pulsars are the most stable natural clocks in the universe, yet their timing noises can still be substantial when the times of arrivals of their pulses are fitted with some well accepted spin-down models or templates of pulsars. We have recently developed a model of the magnetic field evolution of neutron stars, which includes a long-term power-law decay modulated by periodic oscillations of the surface magnetic fields of neutron stars. Our model can explain the statistical properties of their timing noises. We find that the spin-down evolutions of young and old pulsars are dominated by the power-law decay and periodic oscillations, respectively. By applying this model to fit the high cadence observational data of millisecond radio pulsars with the Monte-Carlo Markov Chain method, we are able to improve the sensitivity of gravitational wave detection, because their timing residuals are reduced substantially. In the mean time, accurate parameters of pulsars' spi-down and magnetic fields are also obtained.

Zhang, Shuang-Nan; Yi, Shuxu

273

Extended ionospheric amplitude scintillation model for GPS receivers  

NASA Astrophysics Data System (ADS)

scintillation is a phenomenon that occurs after sunset, especially in the low-latitude region, affecting radio signals that propagate through the ionosphere. Depending on geophysical conditions, ionospheric scintillation may cause availability and precision problems to Global Navigation Satellite System users. The present work is concerned with the development of an extended model for describing the effects of the amplitude ionospheric scintillation on GPS receivers. Using the ?-? probabilistic model, introduced by previous authors in different contexts, the variance of GPS receiver tracking loop error may be estimated more realistically. The proposed model is developed with basis on the ?-? parameters and also considering correlation between amplitude and phase scintillation. Its results are interpreted to explain how a receiver may experience different error values under the influence of ionospheric conditions leading to a fixed scintillation level S4. The model is applied to a large experimental data set obtained at São José dos Campos, Brazil, near the peak of the equatorial anomaly during high solar flux conditions, between December 2001 and January 2002. The results from the proposed model show that depending on the ?-? pair, moderate scintillation (0.5 ? S4 ? 0.7) may be an issue for the receiver performance. When S4 > 0.7, the results indicate that the effects of scintillation are serious, leading to a reduction in the receiver availability for providing positioning solutions in approximately 50% of the cases.

Oliveira Moraes, Alison; Costa, Emanoel; Paula, Eurico Rodrigues; Perrella, Waldecir João.; Monico, João. Francisco Galera

2014-05-01

274

Using the dressed test particle approach to deduce the scattering power spectrum of radio waves by a quasi-equilibrium ionized gas in the presence of an external magnetic field  

Microsoft Academic Search

The dressed test particle approach of Rosenbluth and Rostoker (1962), with a different mathematical technique, is used to obtain an identical result for the expression of the scattering power spectrum of radio waves by a quasi-equilibrium plasma in the presence of a magnetic field. Starting from the Vlasov and Poisson equations, the differential equation is solved by repeatedly taking the

Z.-Y. Chen

1982-01-01

275

Characterization of ionospheric amplitude scintillations using wavelet entropy detrended GNSS data  

NASA Astrophysics Data System (ADS)

The extensive monitoring networks of Global Navigation Satellite System (GNSS) ionospheric scintillation have been established to continuously log observation data. Further, the amplitude scintillation index and the phase scintillation index, which are derived from scintillation observations, are anticipated to accommodate the accuracy requirement of both the user level and the monitoring station level. However, raw scintillation observations essentially measure superposed waveform impairments of GNSS signals propagating through ionosphere and troposphere. It implies that fluctuations of raw scintillation observations are caused by multiple factors from the entire radio propagation environment. Hence, it is crucial to characterize ionospheric scintillations from GNSS observation data. And the characterization is implemented through extracting fluctuations of raw observations merely induced by ionospheric scintillations. Designed to address this problem by means of Fourier filtering detrending, the present work investigates the influence of varying detrending cutoff frequencies on wavelet statistical energy and wavelet entropy distributions of scintillation data. It consequently derives criteria on the optimum detrending cutoff frequency for three types of raw amplitude scintillation data, which are classified by their wavelet energy distributions. Results of the present work verify that detrending with specific optimum cutoff frequencies rather than the fixed and universally applicable one renders the validity and credibility of characterizing ionospheric scintillations as the part of GNSS observation fluctuations purely induced by ionosphere electron density irregularities whose scale sizes are comparable with or smaller than the Fresnel scale.

Su, Yongqing; Liu, Hao; Yue, Jiguang; Yang, Yunfan

2014-12-01

276

Recent developments in scintillator research  

SciTech Connect

Some results of recent scintillator research are presented. A description of the scintillation mechanisms of BaF/sub 2/, and of the influence of Pb/sup 2/ and La/sup 3/+ doping on the scintillation characteristics is given. Furthermore, the UV scintillation properties of LaF/sub 3/:Nd/sup 3/+ are discussed. Scintillation light (lambda=173 nm) emitted by this crystal can be detected in a photosensitive MWPC. The decay time of the emission is 6 ns.

Schotanus, P.; Dorenbos, P.; Von Eijk, C.W.E.; Hollander, R.W.

1989-02-01

277

Report on the ESO Workshop ''mm-wave VLBI with ALMA and Radio Telescopes around the World''  

NASA Astrophysics Data System (ADS)

Very long baseline interferometry at millimetre/submillimetre wavelengths (mm-VLBI) offers the highest achievable spatial resolution at any wavelength in astronomy and the inclusion of ALMA into a global network will bring unprecedented sensitivity. The workshop on mm-VLBI reviewed the broad range of science topics, from imaging the event horizon of the black hole at the centre of the Galaxy, through masers in the Milky Way and distant galaxies to jets in radio galaxies. Plans were laid to develop a science case and a European organisation to promote mm-VLBI including ALMA.

Falcke, H.; Laing, R.; Testi, L.; Zensus, A.

2012-09-01

278

Liquid scintillator sampling calorimetry  

E-print Network

LIQUID SCINTILLATOR SAMPLING CALORIMETRY A Thesis by R. GREG DUDGEON Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August 1994 Major... Subject: Physics LIQUID SCINTILLATOR SAMPLING CALORIMETRY A Thesis by R. GREG DUDGEON Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved...

Dudgeon, R. Greg

2012-06-07

279

The wavelet transform function to analyze interplanetary scintillation observations  

NASA Astrophysics Data System (ADS)

Interplanetary scintillation (IPS) observations are useful to remotely sense the inner heliosphere. We present a new technique to analyze IPS observations using a wavelet transform (WT) function. This technique allows us to derive, in a straightforward way, a simple method to obtain the scintillation index (m). We tested this WT technique to analyze IPS observations obtained by the Solar-Terrestrial Environment Laboratory (STEL) radio telescope. The analysis of the m index of the radio source 3C48 detected by STEL over the year 2012 shows the expected decrease with solar elongation reported in previous studies. The WT technique has a great potential for future solar wind studies using IPS observations from contemporary radio telescopes.

Aguilar-Rodriguez, E.; Rodriguez-Martinez, M.; Romero-Hernandez, E.; Mejia-Ambriz, J. C.; Gonzalez-Esparza, J. A.; Tokumaru, M.

2014-05-01

280

Optical generation of millimeter-wave signals for fiber-radio systems using a dual-mode DFB semiconductor laser  

Microsoft Academic Search

This paper presents a new approach to the optical generation of millimeter-wave signals using a dual-mode multisection distributed feedback semiconductor laser. This simple device is capable of generating high power signals between 40 and 60 GHz with extremely high spectral purity and stability. The two optical modes produced by this laser are heterodyned on an ultrafast photodiode to give a

David Wake; Claudio R. Lima; Phillip A. Davies

1995-01-01

281

On the formation of cluster radio relics  

NASA Astrophysics Data System (ADS)

In several merging clusters of galaxies so-called cluster radio relics have been observed. These are extended radio sources which do not seem to be associated with any radio galaxies. Two competing physical mechanisms to accelerate the radio-emitting electrons have been proposed: (i) diffusive shock acceleration and (ii) adiabatic compression of fossil radio plasma by merger shock waves. Here the second scenario is investigated. We present detailed three-dimensional magneto-hydrodynamical simulations of the passage of a radio plasma cocoon filled with turbulent magnetic fields through a shock wave. Taking into account synchrotron, inverse Compton and adiabatic energy losses and gains, we evolved the relativistic electron population to produce synthetic polarization radio maps. On contact with the shock wave the radio cocoons are first compressed and finally torn into filamentary structures, as is observed in several cluster radio relics. In the synthetic radio maps the electric polarization vectors are mostly perpendicular to the filamentary radio structures. If the magnetic field inside the cocoon is not too strong, the initially spherical radio cocoon is transformed into a torus after the passage of the shock wave. Very recent, high-resolution radio maps of cluster radio relics seem to exhibit such toroidal geometries in some cases. This supports the hypothesis that cluster radio relics are fossil radio cocoons that have been revived by a shock wave. For a late-stage relic the ratio of its global diameter to the filament diameter should correlate with the shock strength. Finally, we argue that the total radio polarization of a radio relic should be well correlated with the three-dimensional orientation of the shock wave that produced the relic.

Enßlin, T. A.; Brüggen, M.

2002-04-01

282

Planetary radio lasing  

NASA Technical Reports Server (NTRS)

Both the Earth's auroral kilometric radiation (AKR) and Jupiter's decametric radio S-bursts are attributed to natural radio lasing. Presumably consisting of self-excited, closed-loop wave feedback oscillations between local irregularities of the source plasma density, this radio lasing is comparable to that which occurs in man-made optical lasers, although at radio, rather than optical wavelengths. As a result, it should produce a multiple discrete emission spectrum and intense, coherent beams. Recent observations of the AKR's discreteness and coherence have clearly ruled out the previous open-loop amplifier model for such emissions, and recent observations of the Jovian S-bursts have shown the expected, regularly-spaced, longitudinal laser modes. These new observations thus confirm the proposed planetary cyclotron radio lasing at both planets.

Calvert, W.

1988-01-01

283

Solar radio continuum storms  

NASA Technical Reports Server (NTRS)

Radio noise continuum emission observed in metric and decametric wave frequencies is discussed. The radio noise is associated with actively varying sunspot groups accompanied by the S-component of microwave radio emissions. It is shown that the S-component emission in microwave frequencies generally occurs several days before the emission of the noise continuum storms of lower frequencies. It is likely that energetic electrons, 10 to 100 Kev, accelerated in association with the variation of sunspot magnetic fields, are the sources of the radio emissions. A model is considered to explain the relation of burst storms on radio noise. An analysis of the role of energetic electrons on the emissions of both noise continuum and type III burst storms is presented. It is shown that instabilities associated with the electrons and their relation to their own stabilizing effects are important in interpreting both of these storms.

1974-01-01

284

Radio Relics (Type A)  

NASA Astrophysics Data System (ADS)

Galaxy clusters grow by mergers with other clusters and groups. These mergers create shocks within the ICM that accelerate particles which then emit radio waves. We have compiled a sample of clusters with such shocks using radio observations and WHT/INT optical imaging. We propose Chandra observations to determine the conditions under which radio relics form. Modelling of the X-ray data can yield the mass ratio and the impact parameter of the merger. This permits a unique reconstruction of the cluster merger events. Simulations make specific prediction about the location of the relics and the dynamical state of the cluster which can now be tested.

Murray, Stephen

2012-09-01

285

Self consistent radio-frequency wave propagation and peripheral direct current plasma biasing: Simplified three dimensional non-linear treatment in the 'wide sheath' asymptotic regime  

SciTech Connect

A minimal two-field fluid approach is followed to describe the radio-frequency (RF) wave propagation in the bounded scrape-off layer plasma of magnetic fusion devices self-consistently with direct current (DC) biasing of this plasma. The RF and DC parts are coupled by non-linear RF and DC sheath boundary conditions at both ends of open magnetic field lines. The physical model is studied within a simplified framework featuring slow wave (SW) only and lateral walls normal to the straight confinement magnetic field. The possibility is however kept to excite the system by any realistic 2D RF field map imposed at the outer boundary of the simulation domain. The self-consistent RF + DC system is solved explicitly in the asymptotic limit when the width of the sheaths gets very large, for several configurations of the RF excitation and of the target plasma. In the case of 3D parallelepipedic geometry, semi-analytical results are proposed in terms of asymptotic waveguide eigenmodes that can easily be implemented numerically. The validity of the asymptotic treatment is discussed and is illustrated by numerical tests against a quantitative criterion expressed from the simulation parameters. Iterative improvement of the solution from the asymptotic result is also outlined. Throughout the resolution, key physical properties of the solution are presented. The radial penetration of the RF sheath voltages along lateral walls at both ends of the open magnetic field lines can be far deeper than the skin depth characteristic of the SW evanescence. This is interpreted in terms of sheath-plasma wave excitation. Therefore, the proper choice of the inner boundary location is discussed as well as the appropriate boundary conditions to apply there. The asymptotic scaling of various quantities with the amplitude of the input RF excitation is established.

Colas, L.; Jacquot, J.; Hillairet, J.; Goniche, M. [CEA, IRFM, F-13108 Saint-Paul-lez-Durance (France); Heuraux, S.; Faudot, E. [IJL-P2M UMR 7198 CNRS, F-54506 Vandoeuvre les Nancy (France); Crombe, K. [Department of Applied Physics, Ghent University, B-9000 Ghent (Belgium); Kyrytsya, V. [LPP-ERM/KMS, Association Euratom-'Belgian State', TEC Partner, Brussels (Belgium)

2012-09-15

286

Laboratory Studies on the Removal of Radon-Born Lead from KamLAND's Organic Liquid Scintillator  

E-print Network

The removal of radioactivity from liquid scintillator has been studied in preparation of a low background phase of KamLAND. This paper describes the methods and techniques developed to measure and efficiently extract radon decay products from liquid scintillator. We report the radio-isotope reduction factors obtained when applying various extraction methods. During this study, distillation was identified as the most efficient method for removing radon daughters from liquid scintillator.

G. Keefer; C. Grant; A. Piepke; T. Ebihara; H. Ikeda; Y. Kishimoto; Y. Kibe; Y. Koseki; M. Ogawa; J. Shirai; S. Takeuchi; C. Mauger; C. Zhang; G. Schweitzer; B. E. Berger; S. Dazeley; M. P. Decowski; J. A. Detwiler; Z. Djurcic; D. A. Dwyer; Y. Efremenko; S. Enomoto; S. J. Freedman; B. K. Fujikawa; K. Furuno; A. Gando; Y. Gando; G. Gratta; S. Hatakeyama; K. M. Heeger; L. Hsu; K. Ichimura; K. Inoue; T. Iwamoto; Y. Kamyshkov; H. J. Karwowski; M. Koga; A. Kozlov; C. E. Lane; J. G. Learned; J. Maricic; D. M. Marko; S. Matsuno; D. McKee; R. D. McKeown; T. Miletic; T. Mitsui; M. Motoki; K. Nakajima; K. Nakajima; K. Nakamura; T. O'Donnell; H. Ogawa; F. Piquemal; J. -S. Ricol; I. Shimizu; F. Suekane; A. Suzuki; R. Svoboda; O. Tajima; Y. Takemoto; K. Tamae; K. Tolich; W. Tornow; Hideki Watanabe; Hiroko Watanabe; L. A. Winslow; S. Yoshida; for the KamLAND Collaboration

2013-12-03

287

Millisecond Pulsar Scintillation Studies with LOFAR: Initial Results  

NASA Astrophysics Data System (ADS)

High-precision timing of millisecond pulsars (MSPs) over years to decades is a promising technique for direct detection of gravitational waves at nanohertz frequencies. Time-variable, multi-path scattering in the interstellar medium is a significant source of noise for this detector, particularly as timing precision approaches 10 ns or better for MSPs in the pulsar timing array. For many MSPs, the scattering delay above 1 GHz is at the limit of detectability; therefore, we study it at lower frequencies. Using the LOw-Frequency ARray (LOFAR) radio telescope, we have analyzed short (5-20 minutes) observations of 3 MSPs in order to estimate the scattering delay at 110-190 MHz, where the number of scintles is large and, hence, the statistical uncertainty in the scattering delay is small. We used cyclic spectroscopy, still relatively novel in radio astronomy, on baseband-sampled data to achieve unprecedented frequency resolution while retaining adequate pulse-phase resolution. We detected scintillation structure in the spectra of the MSPs PSR B1257+12, PSR J1810+1744, and PSR J2317+1439 with diffractive bandwidths of 6 ± 3, 2.0 ± 0.3, and ~7 kHz, respectively, where the estimate for PSR J2317+1439 is reliable to about a factor of two. For the brightest of the three pulsars, PSR J1810+1744, we found that the diffractive bandwidth has a power-law behavior ??dvprop??, where ? is the observing frequency and ? = 4.5 ± 0.5, consistent with a Kolmogorov inhomogeneity spectrum. We conclude that this technique holds promise for monitoring the scattering delay of MSPs with LOFAR and other high-sensitivity, low-frequency arrays like the low-frequency component of the Square Kilometre Array.

Archibald, Anne M.; Kondratiev, Vladislav I.; Hessels, Jason W. T.; Stinebring, Daniel R.

2014-08-01

288

Non-Thermal Radio and Gamma-Ray Emissions from a Supernova Remnant by Blast Wave Breaking Out of the Circumstellar Matter  

NASA Astrophysics Data System (ADS)

We calculated synchrotron radio emission and ?-ray emission due to bremsstrahlung, inverse-Compton scattering, and ?0-decay from the remnant of supernova that exploded in the circumstellar matter (CSM) formed by the progenitor's stellar wind. This sort of situation is a possible origin of mixed-morphology supernova remnants (SNRs), like W 49B, which exhibit recombination-radiation spectra in X-ray emission. We assumed that the CSM of 1.5 M? exists at 0.07-3 pc away from the supernova in the interstellar medium (ISM) of density 0.016 cm-3. When the blast wave breaks out of the CSM into the ISM, its velocity rapidly increases, and hence particle acceleration is enhanced. The maximum energy of protons reaches ˜1300 TeV just after the break-out with ˜0.5% of the explosion energy. We considered the non-thermal emission from the blast-shocked ISM shell after the break-out. Synchrotron radio flux at 1 GHz is tens of Jy, comparable to that observed from mixed-morphology SNRs. Because of low density, the ?-ray luminosity is dominated by inverse-Compton scattering, which is higher than the ?0-decay luminosity by an order of magnitude. The total ?-ray luminosity, including bremsstrahlung, is on the order of 1033 erg s-1 lower than the typical value of 1035-1036 erg s-1 observed from mixed-morphology SNRs. However, if, e.g., ˜10% of accelerated protons interact with some matter of density of 100 cm-3, the ?0-decay ?-ray luminosity would be enhanced to be comparable with the observed value.

Shimizu, Takafumi; Masai, Kuniaki; Koyama, Katsuji

2013-06-01

289

Radio Journalism.  

ERIC Educational Resources Information Center

This book, a how-to-do-it guide for the novice and the professional alike, deals with several aspects of radio journalism: producing documentaries, preparing and announcing radio news, ethics and responsibility, regulation of radio journalism, and careers. It traces the history and growth of radio news, shows its impact on the public, and…

Bittner, John R.; Bittner, Denise A.

290

Interplanetary plasma scintillation parameters measurements retrieved from the spacecraft observations.  

NASA Astrophysics Data System (ADS)

Measurement of the Interplanetary Scintillations (IPS) of radio signals propagating through the plasma in the Solar System by the radio astronomical instruments is a powerful tool to characterise and study the spatial and temporal variation of the electron density in the Solar wind. Several techniques based on the observation of natural and artificial radio sources have been developed during the last 50 years. Here we report our results of the IPS parameters measurement based on the multi-station observations of the planetary mission spacecraft. The ESA Venus Express spacecraft was observed at X-band (8.4 GHz) by several European VLBI stations - Metsähovi Radio Observatory (Aalto University , FI), Medicina (INAF-RA, IT), Matera (ASI, IT), Wettzell (BKG, DE), Noto (INAF-IRA, IT) and Yebes (OAN-IGN, ES) during a 2008-2010 campaign in a framework of the PRIDE (Planetary Radio Interferometry and Doppler Experiments) project as a preparatory stage for the European Radio Astronomy VLBI facilities participation in the planned ESA planetary missions (EJSM, TESM, EVE and others). Observational data were processed at Metsähovi Radio Observatory with the on-purpose developed high performance, ultra-high spectral resolution and spacecraft tracking capable software spectrometer-correlator and analysed at the Joint Institute for VLBI in Europe (JIVE, NL). High quality of acquired and analysed data enables us to study and define several parameters of the S/C signal and accompanying "ranging" tones with milli-Hz accuracy, among which the phase fluctuations of the spacecraft signal carrier line can be used to characterise the interplanetary plasma density fluctuations along the signal propagation line at different spatial and temporal scales at different Solar elongations and which exhibits a near-Kolmogorov spectrum. Such essential parameters as the phase scintillation index and bandwidth of scintillations and their dependence on the solar elongation, distance to the target, positions of the source in the Solar system and Solar activity index were retrieved from our measurements and are reported. This study is focused on the technique of the measurements and data analysis, leaving the physical interpretation of the measurement results to the upcoming studies when more observational data is collected. Our measurements of the phase scintillations from the sources within the Solar system are complementary to the classical measurements of the power level scintillations of signals from the natural radio sources. The results presented in this paper are promising and observations will continue during 2010.

Molera Calvés, Guifré; Pogrebenko, S. V.; Wagner, J.; Maccaferri, G.; Colucci, G.; Kronschnabl, G.; Scilliro, F.; Bianco, G.; Pérez Ayúcar, M.; Cosmovici, C. B.

2010-05-01

291

Iterative addition of parallel temperature effects to finite-difference simulation of radio-frequency wave propagation in plasmas  

NASA Astrophysics Data System (ADS)

Accurate simulations of how radio frequency (RF) power is launched, propagates, and absorbed in a magnetically confined plasma is a computationally challenging problem that for which no comprehensive approach presently exists. The underlying physics is governed by the Vlasov-Maxwell equations, and characteristic length scales can vary by three orders of magnitude. Present algorithms are, in general, based on finding the constituative relation between the induced RF current and the RF electric field and solving the resulting set of Maxwell’s equations. These linear equations use a Fourier basis set that is not amenable to multi-scale formulations and have a large dense coefficient matrix that requires a high-communications overhead factorization technique. Here the use of operator splitting to separate the current and field calculations, and a low-overhead iterative solver leads to an algorithm that avoids these issues and has the potential to solve presently intractable problems due to its data-parallel and favorable scaling characteristics. We verify the algorithm for the iterative addition of parallel temperature effects for a 1D electron Langmuir by reproducing the solution obtained with the existing Fourier kinetic RF code AORSA (Jaeger et al., 2008).

Green, D. L.; Berry, L. A.

2014-03-01

292

Guided radio-wave propagation in the equatorial ionosphere according to the Intercosmos-19 and Alouette/ISIS satellites  

NASA Astrophysics Data System (ADS)

In addition to normal vertical-incident ionogram traces, strongly remote (up to 2000 km), traces of HF-radio-signal reflections observed on topside-sounder ionograms of the Interkosmos-19 satellite obtained in the equatorial ionosphere are presented. Such traces are connected with waveguides (ducts). These waveguides are field-aligned irregularities of ionospheric plasma with electron density depletion of a few percent and cross-field dimension of a few to several kilometers. Ray tracing confirms this supposition and allows an estimate of the typical parameters of the waveguides. The waveguide traces usually start at the cutoff frequency of the main trace. However, sometimes they begin at much lower frequencies which indicate the waveguides are located in plasma bubbles. Only one ducted trace is usually observed on the Interkosmos-19 ionograms; a second conjugate trace is rarely recorded. Waveguides are observed at all heights of Interkosmos-19 (500-1000 km) inside the equatorial anomaly region (from -40 to +40 degrees DipLat). Ducted-echo characteristics observed with the Interkosmos-19 are different from those observed earlier with the Alouette and ISIS satellites. This difference is discussed. It is shown that the ionospheric plasma irregularities responsible for the waveguides are observed much more often during nighttime than during daytime.

Karpachev, Alexander; Zhbankov, Gennadii; Telegin, Viktor; Kuleshova, Valentina

293

Scintillation-Induced Intermittency in SETI  

E-print Network

We consider interstellar scintillations as a cause of intermittency in radio signals from extraterrestrial intelligence (ETI). We demonstrate that scintillations are very likely to allow initial detections of narrowband signals from distant sources (> 100 pc), while making redetections improbable. We consider three models in order to assess the non-repeating, narrowband events found in recent SETI and to analyze large surveys in general: (I) Radiometer noise; (II) A population of constant Galactic sources undergoing interstellar scintillation,; and (III) Real, transient signals (or hardware errors) of either terrestrial or ET origin. We apply likelihood and Bayesian tests of the models to The Planetary Society/Harvard META data. We find that Models II and III are both highly preferred to Model I, but that Models II and III are about equally likely. Ruling out Model II in favor of Model III requires many more reobservations than were conducted in META *or* the reobservation threshold must be much lower than was used in META. *We cannot rule out the possibility that META events are real, intrinsically steady ETI signals.* We recommend that future surveys use thresholds far below the typical false-alarm threshold to lessen the effects of intermittency. The threshold level is best defined in terms of the recording and computational technology that is available at a cost commensurate with other survey costs.

James M. Cordes; T. Joseph W. Lazio; Carl Sagan

1997-07-02

294

Guided radio-wave propagation in the equatorial ionosphere according to the topside sounding onboard Interkosmos-19  

NASA Astrophysics Data System (ADS)

In addition to normal vertical-incident ionogram traces, strongly remote (up to 2000 km) traces of HF-radio-signal reflections observed on topside-sounder ionograms of the Interkosmos-19 satellite obtained in the equatorial ionosphere are presented. Such traces are connected with waveguides (ducts). These waveguides are field-aligned irregularities of the ionospheric plasma with electron density depletions of a few percent and cross-field dimension of a few to several kilometers. Ray tracing confirms this supposition and allows an estimate of typical waveguide parameters: diameter ?10-15 km and amplitude |?N/N|?10%, where N is the electron density. The waveguide traces usually start at the cutoff frequencies of the main traces. However, sometimes they begin at much lower frequencies which indicates the satellite was transitioning through an equatorial plasma bubble during the recording of the ionogram. The X-mode of ducted echoes is more distinct then the O-mode. Only one ducted trace is usually observed on the Interkosmos-19 ionograms; a second conjugate trace is rarely recorded. The same is true for combination modes which is a combination of an oblique-incidence and guided propagation. Waveguides are observed at all heights of Interkosmos-19 (500-1000 km) inside the equatorial anomaly region (from -40° to +40° Dip). Waveguides are usually associated with other irregularities of various sizes in the equatorial ionosphere, some of which cause additional traces and spread F on the topside-sounding ionograms. Ducted-echo characteristics observed with Interkosmos-19 are different from those observed earlier with the Alouette and ISIS satellites. This difference is discussed. It is shown that the ionospheric plasma irregularities responsible for the waveguides are observed much more often during nighttime than during daytime.

Karpachev, A. T.; Zhbankov, G. A.; Kuleshova, V. P.; Telegin, V. A.

2014-12-01

295

High Efficiency Traveling-Wave Tube Power Amplifier for Ka-Band Software Defined Radio on International Space Station-A Platform for Communications Technology Development  

NASA Technical Reports Server (NTRS)

The design, fabrication and RF performance of the output traveling-wave tube amplifier (TWTA) for a space based Ka-band software defined radio (SDR) is presented. The TWTA, the SDR and the supporting avionics are integrated to forms a testbed, which is currently located on an exterior truss of the International Space Station (ISS). The SDR in the testbed communicates at Ka-band frequencies through a high-gain antenna directed to NASA s Tracking and Data Relay Satellite System (TDRSS), which communicates to the ground station located at White Sands Complex. The application of the testbed is for demonstrating new waveforms and software designed to enhance data delivery from scientific spacecraft and, the waveforms and software can be upgraded and reconfigured from the ground. The construction and the salient features of the Ka-band SDR are discussed. The testbed is currently undergoing on-orbit checkout and commissioning and is expected to operate for 3 to 5 years in space.

Simons, Rainee N.; Force, Dale A.; Kacpura, Thomas J.

2013-01-01

296

Waves  

E-print Network

WAVES BY Mari LaCure Submitted to the graduate degree program in Visual Art and the Graduate Faculty of the University of Kansas in partial fulfillment of the requirements for the degree of Master’s of Fine Arts. Yoonmi Nam Chairperson... Committee members: Shawn Bitters Michael Krueger Date Defended: March 10, 2010 2 The Thesis Committee for Mari LaCure certifies that this is the approved Version of the following thesis: WAVES...

LaCure, Mari Mae

2010-04-29

297

Polysiloxane scintillator composition  

DOEpatents

A plastic scintillator useful for detecting ionizing radiation comprising a matrix which comprises an optically transparent polysiloxane having incorporated therein at least one ionizing radiation-hard fluor capable of converting electromagnetic energy produced in the polysiloxane upon absorption of ionizing radiation to detectable light.

Walker, James K. (Gainesville, FL)

1992-01-01

298

Liquid Scintillation Counting Technique  

Microsoft Academic Search

3 INCDIE ICPE- CA, 313 Splaiul Unirii, 030138, Bucharest, Romania The method applied to the evaluation of radiation activities implies sample preparation, liquid scintillation cocktail choosing, quench standard curve constructing and implementation, and results verification. We have constructed the quench curve using interpolation method by polynomial spline functions of three degree. In order to evaluate the measurement efficiencies of tritium

MAGDALENA DIANU; CORNELIU PODINA; TRAIAN ZAHARESCU

299

Scintillator Waveguide For Sensing Radiation  

DOEpatents

The present invention is an apparatus for detecting ionizing radiation, having: a waveguide having a first end and a second end, the waveguide formed of a scintillator material wherein the therapeutic ionizing radiation isotropically generates scintillation light signals within the waveguide. This apparatus provides a measure of radiation dose. The apparatus may be modified to permit making a measure of location of radiation dose. Specifically, the scintillation material is segmented into a plurality of segments; and a connecting cable for each of the plurality of segments is used for conducting scintillation signals to a scintillation detector.

Bliss, Mary (West Richland, WA); Craig, Richard A. (West Richland, WA); Reeder; Paul L. (Richland, WA)

2003-04-22

300

Scintillator requirements for medical imaging  

SciTech Connect

Scintillating materials are used in a variety of medical imaging devices. This paper presents a description of four medical imaging modalities that make extensive use of scintillators: planar x-ray imaging, x-ray computed tomography (x-ray CT), SPECT (single photon emission computed tomography) and PET (positron emission tomography). The discussion concentrates on a description of the underlying physical principles by which the four modalities operate. The scintillator requirements for these systems are enumerated and the compromises that are made in order to maximize imaging performance utilizing existing scintillating materials are discussed, as is the potential for improving imaging performance by improving scintillator properties.

Moses, William W.

1999-09-01

301

The Sardinia Radio Telescope  

NASA Astrophysics Data System (ADS)

We present the status of the Sardinia Radio Telescope (SRT) project, a new general purpose, fully steerable 64 m diameter parabolic radio telescope under construction in Sardinia. The instrument is funded by Italian Ministry of University and Research (MIUR), by the Sardinia Regional Government (RAS), and by the Italian Space Agency (ASI), and it is charge to three research structures of the National Institute for Astrophysics (INAF): the Institute of Radio Astronomy of Bologna, the Cagliari Astronomical Observatory (in Sardinia), and the Arcetri Astrophysical Observatory in Florence. The radio telescope has a shaped Gregorian optical configuration with a 8 m diameter secondary mirror and additional Beam-Wave Guide (BWG) mirrors. One of the most challenging feature of SRT is the active surface of the primary reflector which provides good efficiency up to about 100 GHz. This paper reports on the most recent advances of the construction.

D'Amico, Nichi

2011-08-01

302

From Maxwell's Equations to Cognitive Radio  

Microsoft Academic Search

Maxwell's equations that were published around 1865 caused Heinrich Hertz to prove the existence of electromagnetic waves. He succeeded in 1887\\/88. Around 1900, Marconi established the first long distance radio communication connections. During the following five decades, analog radio communication was brought to perfection. A big change in radio development was launched by Shannon with the publication of the sampling

Friedrich K. Jondral

2008-01-01

303

27/10/2010 12:48AGU: Highlatitude geomagnetically induced current events observed on very low frequency radio wave receiver systems Page 1 of 2http://europa.agu.org/?view=article&uri=/journals/rs/rs1002/2009RS004215/2009RS004215.xml&t=  

E-print Network

27/10/2010 12:48AGU: Highlatitude geomagnetically induced current events observed on very low Abstract Highlatitude geomagnetically induced current events observed on very low frequency radio wave. Kavanagh (2010), Highlatitude geomagnetically induced current events observed on very low frequency radio

Ulich, Thomas

304

A multidisciplinary study of planetary, solar and astrophysical radio emissions  

NASA Technical Reports Server (NTRS)

Combination of the related fields of planetary, solar, and astrophysical radio emissions was attempted in order to more fully understand the radio emission processes. Topics addressed include: remote sensing of astrophysical plasma turbulence; Alfven waves; astrophysical shock waves; surface waves; very long base interferometry results; very large array observations; solar magnetic flux; and magnetohydrodynamic waves as a tool for solar corona diagnostics.

Gurnett, D. A.; Calvert, W.; Fielder, R.; Goertz, C.; Grabbe, C.; Kurth, W.; Mutel, R.; Sheerin, J.; Mellott, M.; Spangler, S.

1986-01-01

305

Educational Radio.  

ERIC Educational Resources Information Center

Examines the effectiveness of the radio in education and the crucial role of the radio in distance education in first half of the 20th century; dramatic social changes in the 1960s that led to a review of educational institutions and of educational media; and the radio today as a neglected but inexpensive medium of communication that should be…

Arafeh, Sousan

1999-01-01

306

Scintillation-induced Intermittency in SETI  

NASA Astrophysics Data System (ADS)

We use scattering theory, simulations, and empirical constraints on interstellar scintillations to discuss the intermittency of radio signals from extraterrestrial intelligence (ETI). The number of ETI sources in the Galaxy has a direct influence on the expected dynamic range of fluxes in a survey, through inverse square-law effects and, equally importantly, by the number of independent statistical trials made on modulations caused by interstellar scintillations. We demonstrate that scintillations are very likely to allow initial detections of narrowband signals, while making redetections extremely improbable, a result that follows from the skewed, exponential distribution of the modulation. This conclusion holds for relatively distant sources but does not apply to radio SETI toward nearby stars (<~100 pc). Recent SETI has found nonrepeating, narrowband events that are largely unexplained. We consider three models in order to assess these events and to analyze large surveys in general: (model I) radiometer noise fluctuations; (model II) a population of constant Galactic sources that undergo deep fading and amplification due to interstellar scintillation, consistent with ETI transmissions; and (model III) real, transient signals (or hardware errors) of either terrestrial or extraterrestrial origin. We derive likelihood and Bayesian tests of the models for individual events and globally on entire surveys. Applying them to The Planetary Society/Harvard META data, we find that models II and III are both highly preferred to model I, but that models II and III are about equally likely. In the context of model II, the likelihood analysis indicates that candidate events above threshold (~32 ?) are combinations of large amplitude noise fluctuations and scintillation gains, making it highly probable that events seen once will only very rarely be seen again. Ruling out model II in favor of model III is difficult--to do so, many more reobservations (e.g., thousands) are needed than were conducted in META (hundreds) or the reobservation threshold must be much lower than was used in META. We cannot, therefore, rule out the possibility that META events are real, intrinsically steady ETI signals. Our formalism can be used to analyze any SETI program. We estimate the number of reobservations required to rule out model II in favor of model III, taking into account that reobservations made promptly sample the same scintillation gain as in the original detection, while delayed reobservations sample a decorrelated scintillation modulation. The required number is a strong function of the thresholds used in the original survey and in reobservations. We assess optimal methods for applying statistical tests in future SETI programs that use multiple site and multiple beam observations as well as single site observations. We recommend that results be recorded on many more events than have been made to date. In particular, we suggest that surveys use thresholds that are far below the false-alarm threshold that is usually set to yield a small number of noise-induced ``detections'' in a massive survey. Instead, large numbers of events should be recorded in order to (1) demonstrate that background noise conforms to the distribution expected for it; and (2) investigate departures from the expected noise distribution as due to interference or to celestial signals. In this way, celestial signals can be investigated at levels much smaller than the false-alarm threshold. The threshold level for archiving candidate intensities and their corresponding sky positions is best defined in terms of the recording and computational technology that is available at a cost commensurate with other survey costs.

Cordes, James M.; Lazio, Joseph W.; Sagan, Carl

1997-10-01

307

The AT20G view of Swift/BAT selected AGN: high-frequency radio waves meet hard X-rays  

NASA Astrophysics Data System (ADS)

We cross-matched the 6-year Swift/Burst Alert Telescope (BAT) survey of active galactic nuclei (AGN) with the AT20G radio survey of the southern sky, which is one of the largest high-frequency radio surveys available. With these data we investigated the possible correlation between the radio and the X-ray emission at the highest radio and X-ray frequencies. We found 37 AGN with a high probability of association (>80 per cent), among which 19 are local Seyfert galaxies (with median redshift z = 0.03) and 18 blazars. We found that ?20 per cent of the AGN detected in hard X-rays are also bright radio sources at 20 GHz, but the apparent correlation between the radio and hard X-ray luminosity is completely driven by the different median redshifts of the two subgroups of AGN. When we consider only the local Seyfert sample we find no evidence of a correlation between their 20 GHz and 15-55 keV power. Therefore it appears that at high frequencies the radio-X connection, which had been previously observed at lower frequencies, disappears. The disappearance of the radio-X correlation at high radio and X-ray frequencies could be tested through Very Long Baseline Interferometry and the use of the Nuclear Spectroscopic Telescope Array (NuSTAR) satellite.

Burlon, D.; Ghirlanda, G.; Murphy, T.; Chhetri, R.; Sadler, E.; Ajello, M.

2013-05-01

308

Firefighters' Radios  

NASA Technical Reports Server (NTRS)

Public Technology Inc. asked for NASA assistance to devise the original firefighter's radio. Good short-range radio communications are essential during a fire to coordinate hose lines, rescue victims, and otherwise increase efficiency. Useful firefighting tool is lower cost, more rugged short range two-way radio. Inductorless electronic circuit replaced inductances and coils in radio circuits with combination of transistors and other low-cost components. Substitution promises reduced circuit size and cost. Enhanced electrical performance made radio more durable and improved maintainability by incorporating modular construction.

1976-01-01

309

On the second order statistics for GPS ionospheric scintillation modeling  

NASA Astrophysics Data System (ADS)

ionospheric scintillation is a phenomenon that occurs frequently, typically during nighttime, affecting radio signals that propagate through the ionosphere. Depending on the temporal and spatial distribution, ionospheric scintillation can represent a problem in the availability and precision for the Global Navigation Satellite System's users. This work is concerned with the statistical evaluation of the amplitude ionospheric scintillation fading events, namely, level crossing rate (LCR) and average fading duration (AFD). Using ?-? model, the LCR and AFD are validated against experimental data obtained in São José dos Campos (23.1°S; 45.8°W; dip latitude 17.3°S), Brazil, a station located near the southern crest of the ionospheric equatorial ionization anomaly. The amplitude scintillation data were collected between December 2001 and January 2002, a period of high solar flux conditions. The obtained results with the proposed model fitted quite well with the experimental data and performed better when compared to the widely used Nakagami-m model. Additionally, this work discusses the estimation of ? and ? parameters, and the best fading coefficients found in this analysis are related to scintillation severity. Finally, for theoretical situations in which no set of experimental data are available, this work also presents parameterized equations to describe these fading statistics properly.

Oliveira Moraes, Alison; Paula, Eurico Rodrigues; Assis Honorato Muella, Marcio Tadeu; Perrella, Waldecir João.

2014-02-01

310

Scintillations of Laguerre Gaussian beams  

Microsoft Academic Search

By using the Rytov method, we formulate and numerically evaluate the scintillations of Laguerre Gaussian beams in weak atmospheric\\u000a turbulence. Our results indicate that at on-axis positions, Laguerre Gaussian beams with zero angular mode number will have\\u000a less scintillations than fundamental Gaussian beams, where the amount of scintillations will further decrease with rising\\u000a radial mode number. When off-axis positions are

H. T. Eyyubo?lu; Y. Baykal; X. Ji

2010-01-01

311

Model-based prediction of amplitude scintillation variance due to clear-air tropospheric turbulence on Earth-satellite microwave links  

Microsoft Academic Search

A statistical method to predict tropospheric amplitude scintillation parameters along Earth-space microwave links from meteorological data is proposed. The evaluation of the mean value and the variance of the refractive-index structure constant and of the scintillation power (i.e. the variance of the log-amplitude fluctuations of the received electromagnetic field) is carried out from conventional radio-sounding measurements. A large radio-sounding data

Frank S. Marzano; Giovanni d'Auria

1998-01-01

312

Magnetohydrodynamic solitons and radio knots in jets  

NASA Technical Reports Server (NTRS)

Weakly nonlinear surface waves are examined in the context of the beam model for jetlike radio sources. By introducing a finite scale length, viz. the beam radius, geometrical dispersion can act to balance nonlinear wave growth and thereby produce solitons, localized wave packets of stable waveform. A method for obtaining a soliton equation from the MHD equations is presented and then applied to radio knots in jets.

Fiedler, R.

1986-01-01

313

Liquid xenon scintillation spectrometer  

NASA Astrophysics Data System (ADS)

A liquid xenon scintillation detector has been worked out. Liquid xenon fills up a volume 27 mm diameter by 12-30 mm long inside a quartz cylinder with a teflon reflector. Both ends of the cylinder are sealed with photomultipliers with quartz windows. The energy resolution of the detector was found to be of the same order of magnitude as NaI(Tl) crystals for the energy 120 KeV. However, the resolution increases for the higher energies and comes up to 15% for 662 KeV. The reasons of such deterioration of resolution with increasing energy are discussed.

Barabanov, I. R.; Gavrin, V. N.; Pshukov, A. M.

1987-02-01

314

Radio Wave Propagation over Salem  

NASA Astrophysics Data System (ADS)

In this paper study of rainfall has been carried out over Salem, a place in Southern India. Rainfall rate values have been recorded using a fast response rain gauge installed at Sona College of Technology. The derived rainfall rates have been used to estimate attenuation in the 10-100 GHz frequency range. Using the estimated co-polar attenuation cross polar discriminations (XPD) have been computed using ITU-R(2002) model in the 10-35 GHz range. The study shows that attenuation and cross polarization vary with frequency, elevation angle and rainfall rate. The study also depicts the cumulative distribution of rainfall rate, attenuation and XPD.

Jaiswal, R. S.; Uma, S.; Raj, M. V. A.

2007-07-01

315

Radio wave scattering in the interstellar medium; Proceedings of the AIP Conference, University of California, San Diego, CA, Jan. 18, 19, 1988  

NASA Astrophysics Data System (ADS)

Recent observational and theoretical investigations of ISM electromagnetic scattering are discussed in reviews and reports. Topics addressed include scintillation phenomena and theory, the physics of scattering media, turbulence in the solar wind, and diffraction phenomena and the interstellar electron-density power spectrum. Consideration is given to refraction phenomena and large-scale structure, the Galactic distribution of scattering material, imaging techniques and pulsar studies, and the agendas of previous interstellar-scattering conferences.

Cordes, James M.; Rickett, Barney J.; Backer, Donald C.

316

Development of radiation hard scintillators  

SciTech Connect

The authors have demonstrated that the radiation stability of scintillators made from styrene polymer is very much improved by compounding with pentaphenyltrimethyltrisiloxane (DC 705 vacuum pump oil). The resulting scintillators are softer than desired, so they decided to make the scintillators directly from monomer where the base resin could be easily crosslinked to improve the mechanical properties. They can now demonstrate that scintillators made directly from the monomer, using both styrene and 4-methyl styrene, are also much more radiation resistant when modified with DC705 oil. In fact, they retain from 92% to 95% of their original light output after gamma irradiation to 10 Mrads in nitrogen with air annealing. When these scintillators made directly from monomer are compared with scintillators of the same composition made from polymer the latter have much higher light outputs. They commonly reach 83% while those made form monomer give only 50% to 60% relative to the reference, BC408. When oil modified scintillators using both p-terphenyl and tetraphenylbutadiene are compared with identical scintillators except that they use 3 hydroxy-flavone as the only luminophore the radiation stability is the same. However the 3HF system gives only 30% as much light as BC408 instead of 83% when both are measured with a green extended Phillips XP2081B phototube.

Markley, F.; Davidson, M.; Keller, J.; Foster, G.; Pla-Dalmau, A. [Fermi National Accelerator Lab., Batavia, IL (United States); Harmon, J.; Biagtan, E.; Schueneman, G. [Univ. of Florida, Gainesville, FL (United States). Physics Dept.; Senchishin, V. [Inst. for Single Crystals, Kharkov (Ukraine); Gustfason, H.; Rivard, M. [Univ. of Michigan, Ann Arbor, MI (United States)

1993-11-01

317

Free liquid scintillation counting bibliography  

SciTech Connect

Packard Instrument Company announces the availability of its newly updated Bibliography of Packard Tri-Carb Liquid Scintillation Analyzers. This unique new booklet lists 628 references in which Packard Tri-Carb{reg_sign} liquid scintillation analyzers have been used in life science, environmental, nuclear power and archaeological measurements. All listings are cross-referenced by radionuclide, specific field of study and author.

NONE

1996-12-31

318

CONFERENCES AND SYMPOSIA: Seventy years of the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Waves Propagation (IZMIRAN) (Scientific session of the Physical Sciences Division of the Russian Academy of Sciences, 25 November 2009)  

NASA Astrophysics Data System (ADS)

A scientific session of the Physical Sciences Division of the Russian Academy of Sciences dedicated to the 70th anniversary of the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN) (Troitsk, Moscow region) was held in the conference hall of IZMIRAN on 25 November 2009. The following reports were put on the session agenda posted on the web site www.gpad.ac.ru of the Physical Sciences Division, RAS: (1) Gurevich A V (Lebedev Physical Institute RAS, Moscow) "The role of cosmic rays and runaway electron breakdown in atmospheric lightning discharges"; (2) Aleksandrov E B (Ioffe Physical Technical Institute, RAS, St. Petersburg) "Advances in quantum magnetometry for geomagnetic research"; (3) Dorman L I (IZMIRAN, Troitsk, Moscow region, CR & SWC, Israel) "Cosmic ray variations and space weather"; (4) Mareev E A (Institute of Applied Physics, RAS, Nizhnii Novgorod) "Global electric circuit research: achievements and prospects"; (5) Tereshchenko E D, Safargaleev V V (Polar Geophysical Institute, Kola Research Center, RAS, Murmansk) "Geophysical research in Spitsbergen Archipelago: status and prospects"; (6) Gulyaev Yu V, Armand N A, Efimov A I, Matyugov S S, Pavelyev A G, Savich N A, Samoznaev L N, Smirnov V V, Yakovlev O I (Kotel'nikov Institute of Radio Engineering and Electronics RAS, Fryazino Branch, Fryazino, Moscow region) "Results of solar wind and planetary ionosphere research using radiophysical methods"; (7) Kunitsyn V E (Lomonosov Moscow State University, Moscow) "Satellite radio probing and the radio tomography of the ionosphere"; (8) Kuznetsov V D (IZMIRAN, Troitsk, Moscow region) "Space Research at the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences." Papers based on reports 2-8 are published below. The main contents of report 1 are reproduced in A V Gurevich's review, "Nonlinear effects in the ionosphere" [Phys. Usp. 50 1091 (2007)] and in the paper by A V Gurevich et al., "Nonlinear phenomena in the ionospheric plasma. Effects of cosmic rays and runaway breakdown on thunderstorm discharges" [Phys. Usp. 52 735 (2009)]. • Advances in quantum magnetometry for geomagnetic research , E B Aleksandrov Physics-Uspekhi, 2010, Volume 53, Number 5, Pages 487-496 • Cosmic ray variations and space weather, L I Dorman Physics-Uspekhi, 2010, Volume 53, Number 5, Pages 496-503 • Global electric circuit research: achievements and prospects, E A Mareev Physics-Uspekhi, 2010, Volume 53, Number 5, Pages 504-511 • Geophysical research in Spitsbergen Archipelago: status and prospects, V V Safargaleev, E D Tereshchenko Physics-Uspekhi, 2010, Volume 53, Number 5, Pages 511-517 • Results of solar wind and planetary ionosphere research using radiophysical methods, N A Armand, Yu V Gulyaev, A L Gavrik, A I Efimov, S S Matyugov, A G Pavelyev, N A Savich, L N Samoznaev, V M Smirnov, O I Yakovlev Physics-Uspekhi, 2010, Volume 53, Number 5, Pages 517-523 • Satellite radio probing and radio tomography of the ionosphere, V E Kunitsyn, E D Tereshchenko, E S Andreeva, I A Nesterov Physics-Uspekhi, 2010, Volume 53, Number 5, Pages 523-528 • Space research at the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences , V D Kuznetsov Physics-Uspekhi, 2010, Volume 53, Number 5, Pages 528-534

2010-08-01

319

AN OVERVIEW OF SATURN NARROWBAND RADIO EMISSIONS OBSERVED BY CASSINI  

E-print Network

., 1981a; Scarf et al., 1982]. Since 2004, the Radio and Plasma Wave Science (RPWS) instrument onboard emissions are detected between 3 and 70 kHz, with occurrence probability and wave intensity peaking around 5 of the Cassini mission and the improved capabilities of the Radio and Plasma Wave Science (RPWS) instrument have

Gurnett, Donald A.

320

Adaptive photonic-assisted M2-QAM millimeter-wave synthesis in multi-antenna radio-over-fiber system using M-ASK modulation.  

PubMed

A novel method for generating an adaptive photonic-assisted M2-quadrature amplitude modulation (M2-QAM) millimeter-wave signal in a multiantenna radio-over-fiber system using M-ray amplitude-shift keying (M-ASK) modulation is proposed and experimentally demonstrated. It takes full advantage of high-density small cells without introducing additional complexity into remote antenna units (RAUs) or mobile users. The 4, 8, and 12 Gb/s 4QAM millimeter-wave signals are obtained from two independent 2, 4, and 6 Gb/s on-off-keying 40 GHz channels, respectively. The experimental results show that a double bit rate can be received without additional digital signal processing in RAUs and mobile users. The results, including the constellation diagrams and bit error rate, show that the transmitted signals are received successfully. PMID:25361290

Zhang, Qi; Yu, Jianjun; Li, Xinying; Xin, Xiangjun

2014-11-01

321

GPS Carrier Tracking Loop Performance in the presence of Ionospheric Scintillations  

E-print Network

, and developing GPS instru- ments for space science. He is a Fellow of the APS. ABSTRACT The performance filter reduces the car- rier lock threshold by more than 7 dB compared to a 15-Hz constant-bandwidth loop with radio-frequency scintillations.1­6 Proposals for future work call for large arrays of GPS re- ceivers

Psiaki, Mark L.

322

Proton recoil scintillator neutron rem meter  

DOEpatents

A neutron rem meter utilizing proton recoil and thermal neutron scintillators to provide neutron detection and dose measurement. In using both fast scintillators and a thermal neutron scintillator the meter provides a wide range of sensitivity, uniform directional response, and uniform dose response. The scintillators output light to a photomultiplier tube that produces an electrical signal to an external neutron counter.

Olsher, Richard H. (Los Alamos, NM); Seagraves, David T. (Los Alamos, NM)

2003-01-01

323

Evidence for refractive scintillation of two extragalactic sources seen through the galactic disk  

SciTech Connect

Extragalactic radio sources were qualitatively examined to determine if there are any cases in which apparent variations at 2.7 GHz are uncorrelated with variations at 8.1 GHz, as might be expected for extrinsically induced refractive scintillation. Two sources exhibiting this behavior were identified, NRAO 150 and 2013 + 370, both of which happen to lie within 2 deg of the Galactic plane. The calculated refractive scintillation properties, based on intrinsic VLBI sizes and scattering measurements in the Galactic disk, are in reasonable agreement with the observed fluctuations. The light curves of these sources are interpreted as significantly affected by refractive scintillation in the interstellar medium. The findings suggest that extragalactic sources seen through extended paths in the Galactic disk may be modulated by refractive scintillation even at gigahertz frequencies. 25 references.

Dennison, B.; Fiedler, R.; Johnston, K.J.; Spencer, J.H.; Waltman, E.B.

1987-02-01

324

Total electron content and scintillation in the vicinity of the main ionospheric trough over Northern Europe. Final report, 1 Jul 90-30 Jun 91  

SciTech Connect

A receiving system for NNSS satellites located at Lerwick (60.1N, 1.2W) has been used to make differential carrier phase measurements in the vicinity of the main ionospheric trough. The observations have been calibrated to obtain absolute total electron content using measurements from a co-located GPS receiver for two months near solar maximum. Mapping techniques, developed to study the changes in night-time total electron content as a function of both latitude and time, are described. Examples are given of characteristic trough behaviour for different levels of geomagnetic activity. A new feature of the work is the limited extent of the poleward wall of the trough for moderate geomagnetic conditions. The mapping techniques can also be applied to measurements of radio-wave scintillation allowing comparison between small-scale irregularity behaviour and the larger-scale changes in total electron content.

Kersley, L.; Walker, I.K.

1991-06-30

325

A multi-instrument case study of high-latitude ionospheric GNSS scintillation due to drifting plasma irregularities  

NASA Astrophysics Data System (ADS)

For this study, GPS receiver scintillation and Total Electron Content (TEC) data from high-latitude locations on Svalbard have been combined with several other data sets, including the EISCAT Svalbard Radar (ESR) and allsky cameras, to perform a multi-instrument case study of high-latitude GPS ionospheric scintillations in relation to drifting plasma irregularities at night over Svalbard on 31 October 2011. Scintillations are rapid amplitude and phase fluctuations of electromagnetic signals. GNSS-based systems may be disturbed by ionospheric plasma irregularities and structures such as plasma patches (areas of enhanced electron density in the polar cap) and plasma gradients. When the GNSS radio signals propagate through such areas, in particular gradients, the signals experience scintillations that at best increases positioning errors and at worst may break the receiver's signal lock, potentially resulting in the GNSS receiver losing track of its position. Due to the importance of many GNSS applications, it is desirable to study the scintillation environment to understand the limitations of the GNSS systems. We find scintillation mainly localised to plasma gradients, with predominantly phase scintillation at the leading edge of patches and both phase and amplitude scintillation at the trailing edge. A single edge may also contain different scintillation types at different locations.

van der Meeren, C.; Oksavik, K.; Moen, J. I.; Romano, V.

2013-12-01

326

Scintillator materials containing lanthanum fluorides  

DOEpatents

An improved radiation detector containing a crystalline mixture of LaF[sub 3] and CeF[sub 3] as the scintillator element is disclosed. Scintillators made with from 25% to 99.5% LaF[sub 3] and the remainder CeF[sub 3] have been found to provide a balance of good stopping power, high light yield and short decay constant that is equal to or superior to other known scintillator materials, and which may be processed from natural starting materials containing both rare earth elements. The radiation detectors disclosed are favorably suited for use in general purpose detection and in positron emission tomography. 2 figures.

Moses, W.W.

1991-05-14

327

Scintillator materials containing lanthanum fluorides  

DOEpatents

An improved radiation detector containing a crystalline mixture of LaF.sub.3 and CeF.sub.3 as the scintillator element is disclosed. Scintillators made with from 25% to 99.5% LaF.sub.3 and the remainder CeF.sub.3 have been found to provide a balance of good stopping power, high light yield and short decay constant that is equal to or superior to other known scintillator materials, and which may be processed from natural starting materials containing both rare earth elements. The radiation detectors disclosed are favorably suited for use in general purpose detection and in positron emission tomography.

Moses, William W. (Berkeley, CA)

1991-01-01

328

In situ detection of interplanetary and Jovian nanodust with radio and plasma  

E-print Network

the radio (Warwick et al., 1982) nor the plasma wave (Scarf et al., 1982) instrument was designed to do soIn situ detection of interplanetary and Jovian nanodust with radio and plasma wave instruments Nicole Meyer-Vernet and Arnaud Zaslavsky Abstract Radio and plasma wave instruments in space can detect

Demoulin, Pascal

329

In situ detection of interplanetary and Jovian nanodust with radio and plasma  

E-print Network

Voyager, despite the fact that neither the radio (Warwick et al., 1982) nor the plasma wave (Scarf et alIn situ detection of interplanetary and Jovian nanodust with radio and plasma wave instruments Nicole Meyer-Vernet and Arnaud Zaslavsky Abstract Radio and plasma wave instruments in space can detect

Demoulin, Pascal

330

Simultaneous observations of Jovian quasi-periodic radio emissions by the Galileo and Cassini spacecraft  

E-print Network

by Kurth et al. [1989] using the Voyager plasma wave wideband instrument [Scarf and Gurnett, 1977 of many Jovian plasma wave and radio emissions. One of these emissions is Jovian type III radio emissions); 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 6984 Radio Science: Waves in plasma

Gurnett, Donald A.

331

Waves and instabilities in the three-dimensional heliosphere  

NASA Astrophysics Data System (ADS)

Contents: 1. Introduction. Wave modes in the solar wind. Instrumentation for wave observations: Ulysses overview. 2. Radio bursts caused by solar flares. Type III radio burst theory and observations. Applications in remote studies of the IPM. 3. Waves associated with IP shocks. Low-frequency electromagnetic waves. Ion acoustic waves. Langmuir waves. Radio waves. 4. Waves in coronal mass ejections and magnetic clouds. 5. Waves at IP discontinuities and magnetic holes. 6. The "quiet" solar wind. Whistler waves and heat-flux regulation. VLF waves associated with expanding regions of the solar wind. More ion acoustic waves. Thermal noise.

MacDowall, Robert J.; Kellogg, Paul J.

332

Why Radio?  

ERIC Educational Resources Information Center

Addresses such broad issues as the function of public radio in contemporary American culture, and how its public service justifies the public money it now receives, or any increased amounts it might receive in the future. (Author/CMV)

Josephson, Larry

1979-01-01

333

CB Radios  

ERIC Educational Resources Information Center

Citizen band radios keep trucking across the American scene, and no doubt your students are caught in the folk craze. Provides some suggestions for channeling students' interests with a unit on CBs. (Author/RK)

Martin, Dick

1977-01-01

334

Ionospheric Irregularities at High Latitudes During Geomagnetic Storms and Substorms: Simultaneous Observations of Magnetic Field Perturbations and GPS Scintillations  

NASA Astrophysics Data System (ADS)

Plasma instability in the ionosphere is often observed as disturbance and distortion of the amplitude and phase of radio signals, which are known as ionospheric scintillations. High-latitude ionospheric plasma, closely connected to solar wind and magnetospheric dynamics, produce very dynamic and short-lived GPS scintillations, making it challenging to characterize them. This study reports simultaneous observations of geomagnetic pulsations and GPS signal scintillations during geomagnetic storms and substorms using a newly designed Autonomous Adaptive Low-Power Instrument Platform (AAL-PIP) installed at the South Pole. A statistical investigation of the AAL-PIP data recorded from January through May 2012 is presented to study local time distribution of scintillation events and a correlation between GPS scintillation and magnetic field perturbations. This report discusses a possible connection between magnetic field perturbations associated with the ionospheric currents and the creation of plasma instability by examining relative contribution of storm/substorm activity to ionospheric irregularities.

Kim, H.; Deshpande, K.; Clauer, C. R.; Bust, G. S.; Crowley, G.; Humphreys, T. E.; Kim, L.; Lessard, M.; Weatherwax, A. T.; Zachariah, T. P.

2012-12-01

335

Satellite radio  

Microsoft Academic Search

Satellites have been a highly effective platform for multi-form broadcasts. This has led to a revival of the radio era. The\\u000a satellite radio is a natural choice to bridge the digital gap. It has several novel features like selective addressing and\\u000a error control. The value-added services from such systems are of particular interest.

S. Rangarajan

2002-01-01

336

LORA: A scintillator array for LOFAR to measure extensive air showers  

E-print Network

The measurement of the radio emission from extensive air showers, induced by high-energy cosmic rays is one of the key science projects of the LOFAR radio telescope. The LOfar Radboud air shower Array (LORA) has been installed in the core of LOFAR in the Netherlands. The main purpose of LORA is to measure the properties of air showers and to trigger the read-out of the LOFAR radio antennas to register extensive air showers. The experimental set-up of the array of scintillation detectors and its performance are described.

S. Thoudam; S. Buitink; A. Corstanje; J. E. Enriquez; H. Falcke; W. Frieswijk; J. R. Hörandel; A. Horneffer; M. Krause; A. Nelles; P. Schellart; O. Scholten; S. ter Veen; M. van den Akker

2014-08-19

337

LORA: A scintillator array for LOFAR to measure extensive air showers  

E-print Network

The measurement of the radio emission from extensive air showers, induced by high-energy cosmic rays is one of the key science projects of the LOFAR radio telescope. The LOfar Radboud air shower Array (LORA) has been installed in the core of LOFAR in the Netherlands. The main purpose of LORA is to measure the properties of air showers and to trigger the read-out of the LOFAR radio antennas to register extensive air showers. The experimental set-up of the array of scintillation detectors and its performance are described.

Thoudam, S; Corstanje, A; Enriquez, J E; Falcke, H; Frieswijk, W; Hörandel, J R; Horneffer, A; Krause, M; Nelles, A; Schellart, P; Scholten, O; ter Veen, S; Akker, M van den

2014-01-01

338

LORA: A scintillator array for LOFAR to measure extensive air showers  

NASA Astrophysics Data System (ADS)

The measurement of the radio emission from extensive air showers, induced by high-energy cosmic rays, is one of the key science projects of the LOFAR radio telescope. The LOfar Radboud air shower Array (LORA) has been installed in the core of LOFAR in the Netherlands. The main purpose of LORA is to measure the properties of air showers and to trigger the read-out of the LOFAR radio antennas to register extensive air showers. The experimental set-up of the array of scintillation detectors and its performance are described.

Thoudam, S.; Buitink, S.; Corstanje, A.; Enriquez, J. E.; Falcke, H.; Frieswijk, W.; Hörandel, J. R.; Horneffer, A.; Krause, M.; Nelles, A.; Schellart, P.; Scholten, O.; ter Veen, S.; van den Akker, M.

2014-12-01

339

Comparisons of COSMIC and C/NOFS GPS Occultation Ionospheric Scintillation Measurements with Ground-based Radar and VHF Measurements  

NASA Astrophysics Data System (ADS)

Ionospheric irregularities are known to cause scintillation of trans-ionospheric radio signals and can affect space-based UHF/VHF communications, causing outages, and degrading GPS accuracy and precision. Current capability for characterizing and predicting ionospheric scintillation utilizes a network of ground-based receivers to detect scintillation and then extrapolate for short-term forecasts. Practical limits on deploying the ground receivers limits the accuracy and spatial coverage one can achieve with this approach. A more global approach is to use a set of space-based satellites equipped with GPS receivers, such as the COSMIC satellite constellation, to measure scintillations observed during so-called occultations with GPS satellites. In this paper the signal-to-noise values of GPS L1 signals received on the COSMIC and C/NOFS satellites for the portions of the occultations that are not affected by the terrestrial atmosphere are examined to help identify areas of ionospheric scintillation. Three years of S4 scintillation index values from COSMIC occultations are compared with near-zenith ground-based VHF S4 scintillation measurements from the AFRL SCIntillation Network Decision Aid (SCINDA) network stations. The data are correlated to ascertain the viability of using space-based scintillation measurements to characterize and predict scintillation to ground-based receivers. Several days of COSMIC and C/NOFS data are compared with each other and the ALTAIR radar located on Kwajalein Atoll, Marshall Islands to examine how occultation geometry affects observed scintillation and also to verify techniques that provide an upper bound on the spatial location of the ionospheric irregularities contributing to scintillations observed in the occultations.

Ruggiero, F. H.; Groves, K. M.; Straus, P. R.; Caton, R. G.; Starks, M. J.; Tanyi, K. L.; Verlinden, M.

2009-12-01

340

The Production of Free Electrons in the Ionospheric D Layer by Solar and Galactic Cosmic Rays and the Resultant Absorption of Radio Waves  

Microsoft Academic Search

The behavior of the D layer under bombardment by solar and galactic cosmic rays of energy greater than a few Mev is discussed. In particular, the variation with incident particle flux of the ionospheric parameters that determine the equilibrium electron density is deduced by means of the measurements of mid-day and mid-night absorption of cosmic radio noise corre- sponding to

William Webber

1962-01-01

341

Radio science investigations by VeRa onboard the Venus Express spacecraft  

NASA Astrophysics Data System (ADS)

The Venus Express Radio Science Experiment (VeRa) uses radio signals at wavelengths of 3.6 and 13 cm ("X"- and "S"-band, respectively) to investigate the Venus surface, neutral atmosphere, ionosphere, and gravity field, as well as the interplanetary medium. An ultrastable oscillator (USO) provides a high quality onboard reference frequency source; instrumentation on Earth is used to record amplitude, phase, propagation time, and polarization of the received signals. Simultaneous, coherent measurements at the two wavelengths allow separation of dispersive media effects from classical Doppler shift. VeRa science objectives include the following: Determination of neutral atmospheric structure from the cloud deck (approximately 40 km altitude) to 100 km altitude from vertical profiles of neutral mass density, temperature, and pressure as a function of local time and season. Within the atmospheric structure, search for, and if detected, study of the vertical structure of localized buoyancy waves, and the presence and properties of planetary waves. Study of the H 2SO 4 vapor absorbing layer in the atmosphere by variations in signal intensity and application of this information to tracing atmospheric motions. Scintillation effects caused by radio wave diffraction within the atmosphere can also provide information on small-scale atmospheric turbulence. Investigation of ionospheric structure from approximately 80 km to the ionopause (<600 km), allowing study of the interaction between solar wind plasma and the Venus atmosphere. Observation of forward-scattered surface echoes obliquely reflected from selected high-elevation targets with anomalous radar properties (such as Maxwell Montes). More generally, such bistatic radar measurements provide information on the roughness and density of the surface material on scales of centimeters to meters. Detection of gravity anomalies, thereby providing insight into the properties of the Venus crust and lithosphere. Measurement of the Doppler shift, propagation time, and frequency fluctuations along the interplanetary ray path, especially during periods of superior conjunction, thus enabling investigation of dynamical processes in the solar corona.

Häusler, B.; Pätzold, M.; Tyler, G. L.; Simpson, R. A.; Bird, M. K.; Dehant, V.; Barriot, J.-P.; Eidel, W.; Mattei, R.; Remus, S.; Selle, J.; Tellmann, S.; Imamura, T.

2006-11-01

342

Geophysical properties of the ionospheric irregularities responsible for radio scintillation  

NASA Technical Reports Server (NTRS)

The properties of F-region ionospheric irregularities are described based on in-situ measurements of the actual waveforms of ion concentration. The spectral properties of the irregularities are discussed. In high, middle and low latitudes most of the irregularities observed fall into a single 'noiselike' category having power spectra which can be approximated by f to the negative n-th power and S to the n-th power, where S is the irregularity scale size and n is approximately 2. Thus the spectral components have a maximum gradient which is almost independent of their size. Other categories of irregularities are also observed occasionally.

Mcclure, J. P.

1974-01-01

343

Need a Classroom Stimulus? Introduce Radio Astronomy  

ERIC Educational Resources Information Center

Silently, invisibly, ceaselessly, our planet Earth is showered by radio waves from every direction and from every region of space. This radio energy originates in our solar system, throughout the Milky Way galaxy, and far beyond, out to the remotest reaches of the universe. Detecting and unraveling the origins of these invisible signals is what…

Derman, Samuel

2010-01-01

344

Checking of communications and radio navigation systems  

Microsoft Academic Search

The testing of aircraft communications and radio navigation systems is addressed. Limited assessments need to take account of variations in ground station performance, and uncertainty regarding radio wave propagation conditions. Antenna performance can vary markedly in different aircraft to affect the radial coverage of all systems, or the accuracy achieved by direction finding equipment. Aircraft transmitting antenna characteristics can be

H. Maidment

1980-01-01

345

Flux tube analysis of L-band ionospheric scintillation  

NASA Astrophysics Data System (ADS)

This manuscript presents magnetic flux tube analysis of L-band signal scintillation in the nighttime equatorial and low-latitude ionosphere. Residues of the scintillation index S4 estimated from the L-band signals received from Geostationary Earth Orbit (GEO) satellites are employed in the analysis. The S4 estimates have been shown to be associated with simultaneous GPS VTEC variations derived from JPL's GIPSY-GIM package. We have applied the wavelet decomposition technique simultaneously on the S4 time series in a flux tube over the equatorial and low-latitude regions. The technique decomposes the S4 signal to identify the dominant mode of variabilities and the temporal variations of scintillation-producing irregularities in the context of a flux tube. Statistically significant regions of the wavelet power spectra considered in our study have mainly shown that (a) dominant plasma irregularities associated with S4 variabilities in a flux tube have periods of about 4 to 15 minutes (horizontal irregularity scales of about 24 to 90 km). These periods match short period gravity waves, (b) scintillation-producing irregularities are anisotropic along the flux tube and in the east-west direction, and (c) the occurrences of scintillation-producing irregularities along the flux tube indicate that the entire flux tube became unstable. However, plasma instability occurrences were not simultaneous in most cases along the flux tube, there were time delays of various orders. Understanding the attributes of L-band scintillation-producing irregularities could be important for developing measures to mitigate L-band signal degradation.

Shume, E. B.; Mannucci, A. J.; Butala, M. D.; Pi, X.; Valladares, C. E.

2013-06-01

346

Encapsulated scintillation detector  

SciTech Connect

An encapsulated scintillation detector is disclosed in which a detector crystal or the like is encapsulated in a hermetically sealed housing having a light-transmitting window at one end. In some instances, the window is mounted in a window assembly by a compression seal established by the differential coefficient of expansion and contraction during the cooling of the assembly. In other instances, the window is chemically bonded to the ring with or without a compression seal. The window is mounted within a ring, which is in turn welded to the end of a tubular body portion of the housing along thin weld flanges to reduce the amount of weld heat which must be applied. A thermal barrier is provided to resist the flow of welding heat from the weld to the seal between the ring and the window. Such thermal barrier includes a zone of relatively thin section located between the weld zone and the seal through which weld heat must flow. The zone of relatively thin cross section is, in some embodiments, provided by a groove cut partially through the wall of the ring. A layer of low friction material such as teflon is positioned between the tubular body and the crystal to minimize friction resisting relative axial movement created by differential coefficients of thermal expansion.

Toepke, I.L.

1983-05-10

347

Radio astronomy  

NASA Technical Reports Server (NTRS)

The following subject areas are covered: (1) scientific opportunities (millimeter and sub-millimeter wavelength astronomy; meter to hectometer astronomy; the Sun, stars, pulsars, interstellar masers, and extrasolar planets; the planets, asteroids, and comets; radio galaxies, quasars, and cosmology; and challenges for radio astronomy in the 1990's); (2) recommendations for new facilities (the millimeter arrays, medium scale instruments, and small-scale projects); (3) continuing activities and maintenance, upgrading of telescopes and instrumentation; (4) long range programs and technology development; and (5) social, political, and organizational considerations.

Kellermann, Kenneth I.; Heeschen, David; Backer, Donald C.; Cohen, Marshall H.; Davis, Michael; Depater, Imke; Deyoung, David; Dulk, George A.; Fisher, J. R.; Goss, W. Miller

1991-01-01

348

From Mechanical Objectivity to Instrumentalizing Theory: Inventing Radio Ionospheric Sounders  

Microsoft Academic Search

While the discovery of the ionosphere through wireless communications technology in the mid-1920s had built a close connection between atmospheric science and radio, the full-fledged use of radio waves as a geophysical probe did not start until an instrumental development occurred a few years later. This article examines this advance, which centered on the invention of radio sounders of the

Chen-Pang Yeang

2012-01-01

349

The search for Titan lightning radio emissions G. Fischer1  

E-print Network

The search for Titan lightning radio emissions G. Fischer1 and D. A. Gurnett2 Received 1 March 2011­detection of radio emissions indicative of Titan lightning by the Cassini RPWS (Radio and Plasma Wave Science) instrument. A previous study by Fischer et al. (2007) investigated the first 35 Titan flybys, and here we

Gurnett, Donald A.

350

Full-wave consistent MDS-based simulation of a beam-waveguide circuit fragment for a deep space communication or radio astronomy antenna  

Microsoft Academic Search

In this paper we perform full-wave two-dimensional (2-D) simulation of the e-polarized beam wave guidance and scattering by a chain of four finite-size reflectors and mirrors modelling a typical fragment of quasioptical feeding circuit of a deep-space communication antenna. Elementary geometry tuning aimed at the maximum circuit transmission is also demonstrated. The feed beam generated by the aperture of a

Andrey A. Nosich; Ronan Sauleau; Yuriy V. Gandel

2008-01-01

351

IPS limits on very low frequency VLBI. [Interplanetary Scintillation  

NASA Technical Reports Server (NTRS)

The ability of a space-based radio interferometer array to make high resolution images at frequencies of only a few MHz will be limited by interplanetary scintillation. Numerical simulations have been used to study the severity of interferometer phase fluctuations caused by the density fluctuations in the solar wind over a range of frequencies and solar elongation angles. The impact of these fluctuations on the quality of radio images produced has also been investigated. The results show that, for baselines up to 100 km, accurate imaging should be possible when nu sin (epsilon/2) is equal to or greater than 2.5, where nu is the observing frequency in MHz and epsilon is the solar elongation angle.

Jones, Dayton L.; Williamson, Robert S., III

1990-01-01

352

Nanophosphor composite scintillator with a liquid matrix  

DOEpatents

An improved nanophosphor scintillator liquid comprises nanophosphor particles in a liquid matrix. The nanophosphor particles are optionally surface modified with an organic ligand. The surface modified nanophosphor particle is essentially surface charge neutral, thereby preventing agglomeration of the nanophosphor particles during dispersion in a liquid scintillator matrix. The improved nanophosphor scintillator liquid may be used in any conventional liquid scintillator application, including in a radiation detector.

McKigney, Edward Allen (Los Alamos, NM); Burrell, Anthony Keiran (Los Alamos, NM); Bennett, Bryan L. (Los Alamos, NM); Cooke, David Wayne (Santa Fe, NM); Ott, Kevin Curtis (Los Alamos, NM); Bacrania, Minesh Kantilal (Los Alamos, NM); Del Sesto, Rico Emilio (Los Alamos, NM); Gilbertson, Robert David (Los Alamos, NM); Muenchausen, Ross Edward (Los Alamos, NM); McCleskey, Thomas Mark (Los Alamos, NM)

2010-03-16

353

3D Printing of Scintillating Materials  

E-print Network

We demonstrate, for the first time, the applicability of 3D printing technique to the manufacture of scintillation detectors. We report of a formulation, usable in stereolithographic printing, that exhibits scintillation efficiency on the order of 30\\% of that of commercial polystyrene based scintillators. We discuss the applicability of these techniques and propose future enhancements that will allow tailoring the printed scintillation detectors to various application.

Y. Mishnayot; M. Layani; I. Cooperstein; S. Magdassi; G. Ron

2014-06-15

354

3D Printing of Scintillating Materials  

E-print Network

We demonstrate, for the first time, the applicability of 3D printing technique to the manufacture of scintillation detectors. We report of a formulation, usable in stereolithographic printing, that exhibits scintillation efficiency on the order of 30\\% of that of commercial polystyrene based scintillators. We discuss the applicability of these techniques and propose future enhancements that will allow tailoring the printed scintillation detectors to various application.

Mishnayot, Y; Cooperstein, I; Magdassi, S; Ron, G

2014-01-01

355

Characterization of liquid scintillation detectors  

NASA Astrophysics Data System (ADS)

Five scintillation detectors of different scintillator size and type were characterized. The pulse height scale was calibrated in terms of electron light output units using photon sources. The response functions for time-of-flight (TOF)-selected monoenergetic neutrons were experimentally determined and also simulated with the NRESP code over a wide energy range. A comparison of the measured and calculated response functions allows individual characteristics of the detectors to be determined and the response matrix to be reliably derived. Various applications are discussed.

Schmidt, D.; Asselineau, B.; Böttger, R.; Klein, H.; Lebreton, L.; Neumann, S.; Nolte, R.; Pichenot, G.

2002-01-01

356

Scintillator Cosmic Ray Super Telescope  

NASA Astrophysics Data System (ADS)

The Scintillator Cosmic Ray Super Telescope (SciCRST) is a new experiment to detect solar neutrons, and also it is expected to work as a muon and cosmic ray detector. The SciCRST consist of 14,848 plastic scintillator bars, and it will be installed at the top of Sierra Negra volcano, Mexico, 4580 m.a.s.l. We use a prototype, called as miniSciBar, to test the hardware and software of the final experiment. In this paper, we present the status and details of the experiment, and results of the prototype.

González, L. X.; Valdés-Galicia, J. F.; Matsubara, Y.; Nagai, Y.; Itow, Y.; Sako, T.; López, D.; Mitsuka, G.; Munakata, K.; Kato, C.; Yasue, S.; Kosai, M.; Tsurusashi, M.; Nakamo, Y.; Shibata, S.; Takamaru, H.; Kojima, H.; Tsuchiya, H.; Watanabe, K.; Koi, T.; Fragoso, E.; Hurtado, A.; Musalem, O.

2013-04-01

357

Nonlinear Ionospheric Propagation Effects on UHF and VLF Radio Signals  

Microsoft Academic Search

An investigation of nonlinear wave-plasma interactions in the ionosphere causing significant propagation effects on VLF and UHF radio waves has been conducted. Nonlinear scattering of VLF waves off existing density irregularities is shown to be responsible for the observed spectral broadening. When the irregularity scale size does not exceed a few tens of meters, the scattered wave is found to

Keith Michael Groves

1991-01-01

358

Composite scintillators for detection of ionizing radiation  

SciTech Connect

Applicant's present invention is a composite scintillator having enhanced transparency for detecting ionizing radiation comprising a material having optical transparency wherein said material comprises nano-sized objects having a size in at least one dimension that is less than the wavelength of light emitted by the composite scintillator wherein the composite scintillator is designed to have selected properties suitable for a particular application.

Dai, Sheng (Knoxville, TN) [Knoxville, TN; Stephan, Andrew Curtis (Knoxville, TN) [Knoxville, TN; Brown, Suree S. (Knoxville, TN) [Knoxville, TN; Wallace, Steven A. (Knoxville, TN) [Knoxville, TN; Rondinone, Adam J [Knoxville, TN

2010-12-28

359

A new list of extra-galactic radio jets  

E-print Network

A catalogue of extra-galactic jets is very useful both in observational and theoretical studies of active galaxies. With the use of new powerful radio instruments, the detailed structures of very compact or weak radio sources are investigated observationally and many new radio jets are detected. In this paper, we give a list of 661 radio sources with detected radio jets known to us prior to the end of December 2000. All references are collected for the observations of jets in radio, IR, optical, UV and X-ray wave-bands.

F. K. Liu; Y. H. Zhang

2002-12-20

360

Synthesis of plastic scintillation microspheres: Evaluation of scintillators  

NASA Astrophysics Data System (ADS)

The use of plastic scintillation microspheres (PSm) appear to be an alternative to liquid scintillation for the quantification of alpha and beta emitters because it does not generate mixed wastes after the measurement (organic and radioactive). In addition to routine radionuclide determinations, PSm can be used for further applications, e.g. for usage in a continuous monitoring equipment, for measurements of samples with a high salt concentration and for an extractive scintillation support which permits the separation, pre-concentration and measurement of the radionuclides without additional steps of elution and sample preparation. However, only a few manufacturers provide PSm, and the low number of regular suppliers reduces its availability and restricts the compositions and sizes available. In this article, a synthesis method based on the extraction/evaporation methodology has been developed and successfully used for the synthesis of plastic scintillation microspheres. Seven different compositions of plastic scintillation microspheres have been synthesised; PSm1 with polystyrene, PSm2 with 2,5-Diphenyloxazol(PPO), PSm3 with p-terphenyl (pT), PSm4 with PPO and 1,4-bis(5-phenyloxazol-2-yl) (POPOP), PSm5 pT and (1,4-bis [2-methylstyryl] benzene) (Bis-MSB), PSm6 with PPO, POPOP and naphthalene and PSm7 with pT, Bis-MSB and naphthalene. The synthesised plastic scintillation microspheres have been characterised in terms of their morphology, detection capabilities and alpha/beta separation capacity. The microspheres had a median diameter of approximately 130 ?m. Maximum detection efficiency values were obtained for the PSm4 composition as follows 1.18% for 3H, 51.2% for 14C, 180.6% for 90Sr/90Y and 76.7% for 241Am. Values of the SQP(E) parameter were approximately 790 for PSm4 and PSm5. These values show that the synthesised PSm exhibit good scintillation properties and that the spectra are at channel numbers higher than in commercial PSm. Finally, the addition of naphthalene modifies the shape of the pulses produced by alpha and beta particles leading to better alpha/beta separation.

Santiago, L. M.; Bagán, H.; Tarancón, A.; Garcia, J. F.

2013-01-01

361

The Radio JOVE Project - Shoestring Radio Astronomy  

NASA Technical Reports Server (NTRS)

Radio JOVE is an education and outreach project intended to give students and other interested individuals hands-on experience in learning radio astronomy. They can do this through building a radio telescope from a relatively inexpensive kit that includes the parts for a receiver and an antenna as well as software for a computer chart recorder emulator (Radio Skypipe) and other reference materials

Thieman, J.; Flagg, R.; Greenman, W.; Higgins, C.; Reyes, F.; Sky, J.

2010-01-01

362

SNO+ Scintillator Purification and Assay  

NASA Astrophysics Data System (ADS)

We describe the R&D on the scintillator purification and assay methods and technology for the SNO+ neutrino and double-beta decay experiment. The SNO+ experiment is a replacement of the SNO heavy water with liquid scintillator comprised of 2 g/L PPO in linear alkylbenzene (LAB). During filling the LAB will be transported underground by rail car and purified by multi-stage distillation and steam stripping at a flow rate of 19 LPM. While the detector is operational the scintillator can be recirculated at 150 LPM (full detector volume in 4 days) to provide repurification as necessary by either water extraction (for Ra, K, Bi) or by functional metal scavenger columns (for Pb, Ra, Bi, Ac, Th) followed by steam stripping to remove noble gases and oxygen (Rn, O2, Kr, Ar). The metal scavenger columns also provide a method for scintillator assay for ex-situ measurement of the U and Th chain radioactivity. We have developed "natural" radioactive spikes of Pb and Ra in LAB and use these for purification testing. Lastly, we present the planned operating modes and purification strategies and the plant specifications and design.

Ford, R.; Chen, M.; Chkvorets, O.; Hallman, D.; Vázquez-Jáuregui, E.

2011-04-01

363

An interplanetary scintillation activity index  

Microsoft Academic Search

Using interplanetary scintillation (IPS) data obtained from the Cambridge 81.5 MHz array, an activity index is developed in which it is possible to identify (1) discrete structures, most likely relating to transient density enhancements, and (2) periodic activity, relating to corotating interplanetary structure. Significant, yet weak correlations are found between the index and geomagnetic activity. Results suggest that the pursuit

R. A. Harrison; M. A. Hapgood; V. Moore; E. A. Lucek

1992-01-01

364

Scintillating fiber ribbon --- tungsten calorimeter  

SciTech Connect

We describe an ultra-high density scintillating fiber and tungsten calorimeter used as an active beam-dump for electrons. Data showing the calorimeter response to electrons with momenta between 50 and 350 GeV/c are presented. 9 figs.

Bross, A.; Crisler, M.; Kross, B.; Wrbanek, J.

1989-07-14

365

SNO+ Scintillator Purification and Assay  

SciTech Connect

We describe the R and D on the scintillator purification and assay methods and technology for the SNO+ neutrino and double-beta decay experiment. The SNO+ experiment is a replacement of the SNO heavy water with liquid scintillator comprised of 2 g/L PPO in linear alkylbenzene (LAB). During filling the LAB will be transported underground by rail car and purified by multi-stage distillation and steam stripping at a flow rate of 19 LPM. While the detector is operational the scintillator can be recirculated at 150 LPM (full detector volume in 4 days) to provide repurification as necessary by either water extraction (for Ra, K, Bi) or by functional metal scavenger columns (for Pb, Ra, Bi, Ac, Th) followed by steam stripping to remove noble gases and oxygen (Rn, O{sub 2}, Kr, Ar). The metal scavenger columns also provide a method for scintillator assay for ex-situ measurement of the U and Th chain radioactivity. We have developed ''natural'' radioactive spikes of Pb and Ra in LAB and use these for purification testing. Lastly, we present the planned operating modes and purification strategies and the plant specifications and design.

Ford, R.; Vazquez-Jauregui, E. [SNOLAB, Creighton Mine, Lively, P3Y 1N2 (Canada); Chen, M. [Department of Physics, Queen's University, Kingston, K7L 3N6 (Canada); Chkvorets, O.; Hallman, D. [Department of Physics, Laurentian University, Sudbury, P3E 2C6 (Canada)

2011-04-27

366

Method of making a scintillator waveguide  

DOEpatents

The present invention is an apparatus for detecting ionizing radiation, having: a waveguide having a first end and a second end, the waveguide formed of a scintillator material wherein the therapeutic ionizing radiation isotropically generates scintillation light signals within the waveguide. This apparatus provides a measure of radiation dose. The apparatus may be modified to permit making a measure of location of radiation dose. Specifically, the scintillation material is segmented into a plurality of segments; and a connecting cable for each of the plurality of segments is used for conducting scintillation signals to a scintillation detector.

Bliss, Mary (West Richland, WA); Craig, Richard A. (West Richland, WA); Reeder, Paul L. (Richland, WA)

2000-01-01

367

Space Telecommunications Radio System STRS Cognitive Radio  

NASA Technical Reports Server (NTRS)

Radios today are evolving from awareness toward cognition. A software defined radio (SDR) provides the most capability for integrating autonomic decision making ability and allows the incremental evolution toward a cognitive radio. This cognitive radio technology will impact NASA space communications in areas such as spectrum utilization, interoperability, network operations, and radio resource management over a wide range of operating conditions. NASAs cognitive radio will build upon the infrastructure being developed by Space Telecommunication Radio System (STRS) SDR technology. This paper explores the feasibility of inserting cognitive capabilities in the NASA STRS architecture and the interfaces between the cognitive engine and the STRS radio. The STRS architecture defines methods that can inform the cognitive engine about the radio environment so that the cognitive engine can learn autonomously from experience, and take appropriate actions to adapt the radio operating characteristics and optimize performance.

Briones, Janette C.; Handler, Louis M.

2013-01-01

368

Comparisons of Space-based GPS Occultation Ionospheric Scintillation Measurements with Ground-based VHF Measurements  

NASA Astrophysics Data System (ADS)

Ionospheric irregularities are known to cause scintillation of transionospheric radio signals and can affect space-based UHF/VHF communications, causing outages, and degrade GPS accuracy and precision. Current capability for characterizing and predicting ionospheric scintillation utilizes a network of ground- based receivers to detect scintillation and then extrapolate for short-term forecasts. Practical limits on deploying the ground receivers limits the accuracy and spatial coverage one can achieve with this approach. A more global approach is to use a set of space-based satellites equipped with GPS receivers, such as the COSMIC satellite constellation, to measure scintillations observed during so-called occultations with GPS satellites. The term occultation refers to the geometry where the clear line-of-sight path between the space- based GPS receiver and the GPS satellite is ultimately blocked, or occulted, by the earth's surface. Before or after occultation the ray-path passes through the lower atmosphere and ionosphere providing information on the total electron content (TEC) and irregularities between the transmitter and the receiver. In this paper the signal-to-noise values of GPS L1 signals received on the COSMIC (and possibly C/NOFS if available) satellites are examined to help identify areas of ionospheric scintillation. The S4 scintillation index values from these occultations are compared with ground-based VHF S4 scintillation measurements from several equatorial stations. Preliminary results show that while there are cases where both the occultation and ground measurements indicate enhanced scintillation, there are also a number of cases where the occultation GPS S4 is significantly larger than the ground-based VHF S4, somewhat contrary to expectations given that scintillation effects generally increase with decreasing frequency. Reasons for high GPS S4 in the presence of relatively low VHF S4 include geometry differences between space- and ground-based observations, possible signal processing problems, and physical non-scintillation ionospheric features characterized by relatively short intense spikes in the signal-to-noise. We examine these parameters and look at developing algorithms to filter out non-related cases so that we develop an improved correlation between the space-based and ground-based scintillation values.

Ruggiero, F. H.; Groves, K. M.; Starks, M. J.; Beach, T. L.

2008-12-01

369

Radio Variability of Radio Quiet and Radio Loud Quasars  

E-print Network

The majority of quasars are weak in their radio emission, with flux densities comparable to those in the optical, and energies far lower. A small fraction, about 10%, are hundreds to thousands of times stronger in the radio. Conventional wisdom holds that there are two classes of quasars, the radio quiets and radio louds, with a deficit of sources having intermediate power. Are there really two separate populations, and if so, is the physics of the radio emission fundamentally different between them? This paper addresses the second question, through a study of radio variability across the full range of radio power, from quiet to loud. The basic findings are that the root mean square amplitude of variability is independent of radio luminosity or radio-to-optical flux density ratio, and that fractionally large variations can occur on timescales of months or less in both radio quiet and radio loud quasars. Combining this with similarities in other indicators, such as radio spectral index and the presence of VLBI-scale components, leads to the suggestion that the physics of radio emission in the inner regions of all quasars is essentially the same, involving a compact, partially opaque core together with a beamed jet.

Richard Barvainis; Joseph Lehar; Mark Birkinshaw; Heino Falke; Katherine M. Blundell

2004-09-22

370

Slow-Wave Phase Shifters, Based on Thin Ferroelectric Films, for Reflectarray Antennas. Frequency-Agile Radio: Systems and Technlogies, WMG 139  

NASA Technical Reports Server (NTRS)

We have developed relatively broadband K- and Ka-band phase shifters using synthetic (slow-wave) transmission lines employing coupled microstripline "varactors". The tunable coupled microstripline circuits are based on laser ablated BaSrTiO films on lanthanum aluminate substrates. A model and design criteria for these novel circuits will be presented, along with measured performance including anomalous phase delay characteristics. The critical role of phase shifter loss and transient response in reflectarray antennas will be emphasized.

Romanofsky, Robert R.

2006-01-01

371

A multi-instrument study of high-latitude ionospheric irregularities and their effects on GPS ionospheric scintillation  

NASA Astrophysics Data System (ADS)

Scintillations are rapid amplitude and phase fluctuations of electromagnetic signals. GNSS-based systems may be disturbed by plasma irregularities and structures such as plasma patches (areas of enhanced electron density) and plasma gradients in the ionosphere. When the GNSS radio signals propagate through such areas, in particular gradients, the signals experience scintillations that at best increases positioning errors and at worst may break the receiver's signal lock, potentially resulting in the GNSS receiver losing track of its position. Due to the importance of many GNSS applications, it is desirable to study the scintillation environment to understand the limitations of the GNSS systems. For this study, GPS receiver scintillation and Total Electron Content (TEC) data from high-latitude locations will be combined with several other data sets, including the EISCAT Svalbard Radar (ESR) and allsky cameras to perform a multi-instrument case study of GPS ionospheric scintillations. The EISCAT data provides a means to determine the altitude and density of the F layer, which can then be used to calibrate allsky projections as well as coordinates of ionospheric piercing points of the GPS signals. The focus will be studying any connection between scintillations and polar cap patches; however, other interesting and related findings will also be presented, herein statistical long-timespan studies of GPS TEC and/or scintillation data.

van der Meeren, Christer; Oksavik, Kjellmar; Moen, Jøran; Romano, Vincenzo

2013-04-01

372

Cosmic ray scintillations. II - General theory of interplanetary scintillations  

NASA Technical Reports Server (NTRS)

The motion of charged particles in a stochastic magnetic field with nonzero mean is considered via a generalized quasi-linear expansion of Liouville's equation. The general result is an equation relating cosmic ray scintillations to magnetic fluctuations and to cosmic ray gradients. The resonant interaction between particles and the random magnetic field is considered in detail, and the effect of nonlinear terms in the equations is considered. The nonlinear terms are important in damping out initial conditions and in determining conditions near cyclotron resonances. The application of the theory to the propagation of cosmic rays during quiet times in interplanetary space is considered. It is concluded that cosmic ray scintillations in interplanetary space may provide useful information about interplanetary particles and fields and also about nonlinear plasma interactions.

Owens, A. J.

1974-01-01

373

Results from a study of scintillation behavior at 12, 20, and 30 GHz using the results from the Virginia Tech Olympus receivers  

NASA Technical Reports Server (NTRS)

Tropospheric scintillations are rapid fluctuations of signal caused by multiple scattering from the small scale turbulent refractive index inhomogeneities in the troposphere. They can strongly impair satellite communications links operating at frequency above 10 GHz. The VA Tech OLYMPUS propagation experiment which includes 12, 20, and 30 GHz beacon receivers at an elevation angle of 14 degrees provides us with valuable multifrequency scintillation data. A long term analysis of tropospheric scintillation results from the VA Tech OLYMPUS experiment is presented. It includes statistics of both the scintillation intensity and the attenuation relative to clear air as well as seasonal, diurnal and meteorological trends. A comparison with the Consultative Committee for International Radio (CCIR) predictive model for scintillation fading is presented.

Pratt, Timothy; Haidara, F.

1993-01-01

374

BL LAC OBJECT PKS B1144-379: AN EXTREME SCINTILLATOR  

SciTech Connect

Rapid variability in the radio flux density of the BL Lac object PKS B1144-379 has been observed at four frequencies, ranging from 1.5 to 15 GHz, with the Very Large Array and the University of Tasmania's Ceduna antenna. Intrinsic and line-of-sight effects were examined as possible causes of this variability, with interstellar scintillation best explaining the frequency dependence of the variability timescales and modulation indices. This scintillation is consistent with a compact source 20-40 {mu}as or 0.15-0.3 pc in size. The inferred brightness temperature for PKS B1144-379 (assuming that the observed variations are due to scintillation) is 6.2 Multiplication-Sign 10{sup 12} K at 4.9 GHz, with approximately 10% of the total flux in the scintillating component. We show that scintillation surveys aimed at identifying variability timescales of days to weeks are an effective way to identify the active galactic nuclei with the highest brightness temperatures.

Turner, R. J.; Ellingsen, S. P.; Shabala, S. S.; Blanchard, J.; Lovell, J. E. J.; McCallum, J. N. [School of Mathematics and Physics, Private Bag 37, University of Tasmania, Hobart, TAS 7001 (Australia); Cimo, G. [Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo (Netherlands)

2012-08-01

375

Jupiter plasma wave observations: an initial Voyager 1 overview  

Microsoft Academic Search

The Voyager 1 plasma wave instrument detected low-frequency radio emissions, ion acoustic waves, and electron plasma oscillations for a period of months before encountering Jupiter's bow shock. In the outer magnetosphere, measurements of trapped radio waves were used to derive an electron density profile. Near and within the Io plasma torus the instrument detected high-frequency electrostatic waves, strong whistler mode

F. L. Scarf; D. A. Gurnett; W. S. Kurth

1979-01-01

376

Jupiter plasma wave observations - an initial Voyager 1 overview  

Microsoft Academic Search

The Voyager 1 plasma wave instrument detected low-frequency radio emissions, ion acoustic waves, and electron plasma oscillations for a period of months before encountering Jupiter's bow shock. In the outer magnetosphere, measurements of trapped radio waves were used to derive an electron density profile. Near and within the Io plasma torus the instrument detected high-frequency electrostatic waves, strong whistler mode

F. L. Scarf; D. A. Gurnett; W. S. Kurth

1979-01-01

377

Detecting scintillations in liquid helium  

NASA Astrophysics Data System (ADS)

We review our work in developing a tetraphenyl butadiene (TPB)-based detection system for a measurement of the neutron lifetime using magnetically confined ultracold neutrons (UCN). As part of the development of the detection system for this experiment, we studied the scintillation properties of liquid helium itself, characterized the fluorescent efficiencies of different fluors, and built and tested three detector geometries. We provide an overview of the results from these studies as well as references for additional information.

Huffman, P. R.; McKinsey, D. N.

2013-09-01

378

Echo scintillation index affected by cat-eye target's caliber in FSO communication  

NASA Astrophysics Data System (ADS)

Cat-eye effect has been widely used in active laser detection, optical target identification and free space optical (FSO) communication, but atmospheric turbulence makes laser beam fluctuate, which limits the use of cat-eye effect. The optical aperture has the aperture averaging effect to the detecting laser, which can be used to identify optical targets. Using the flashing theory of spherical wave in the weak atmospheric turbulence, the circular aperture filter function and the Kolmogorov power spectrum, the analytic expression of the echo scintillation index of the cat-eye target of the horizontal path two-way transmission was given in which the cat-eye target were equivalent to a combination of two circular apertures and the detector of cat-eye target was equivalent to a reflecting plane with the reflectivity ? when the light is normal incidence. Then the impact of turbulence inner and outer scales to the echo scintillation index and the analytic expression of the echo scintillation index at the receiving aperture were presented using the modified Hill spectrum and the modified Von Karman spectrum. The simulation results show that scintillation index of considering the inner scale is larger compared with that of without considering the inner and outer scales and considering the inner and outer scales. Echo scintillation index shows the tendency of decreasing with the target aperture increases. The echo scintillation index increases with the transmission distance increasing.

Shan, Cong-miao; Sun, Hua-yan; Zhang, Lai-xian

2013-08-01

379

Radio Jove: Jupiter Radio Astronomy for Citizens  

NASA Astrophysics Data System (ADS)

Radio JOVE is a hands-on educational activity that brings the radio sounds of the Sun, Jupiter, the Milky Way Galaxy, and terrestrial radio noise to students, teachers, and the general public. Participants may build a simple radio telescope kit, make scientific observations, and interact with professional radio observatories in real-time over the Internet. Our website (http://radiojove.gsfc.nasa.gov) includes science information, construction manuals, observing guides, and education resources for teachers and students. Radio Jove is continually expanding its participants with over 1800 kits sold to more than 70 countries worldwide. Recently some of our most dedicated observers have upgraded their Radio Jove antennas to semi-professional observatories. We have spectrographs and wide band antennas, some with 8 MHz bandwidth and some with dual polarization capabilities. In an effort to add to the science literature, these observers are coordinating their efforts to pursue some basic questions about Jupiter’s radio emissions (radio source locations, spectral structure, long term changes, etc.). We can compare signal and ionosphere variations using the many Radio Jove observers at different locations. Observers are also working with members of the Long Wavelength Array Station 1 (LWA1) radio telescope to coordinate observations of Jupiter; Radio Jove is planning to make coordinated observations while the Juno Mission is active beginning in 2015. The Radio Jove program is overviewed, its hardware and software are highlighted, recent sample observations are shown, and we demonstrate that we are capable of real citizen science.

Higgins, Charles; Thieman, J. R.; Flagg, R.; Reyes, F. J.; Sky, J.; Greenman, W.; Brown, J.; Typinski, D.; Ashcraft, T.; Mount, A.

2014-01-01

380

In ecliptic observations of Jovian radio emissions by Ulysses - Comparison with Voyager results  

NASA Technical Reports Server (NTRS)

During the Ulysses inbound cruise to Jupiter the Unified Radio and Plasma Wave (URAP) experiment observed a variety of the planet's radio components in the frequency range below 1 MHz. Most of these emissions were already detected by the Voyager Radio Astronomy and Plasma Wave experiments, however, with much less sensitivity and different spectral coverage. These different radio components within the URAP dynamic spectra are identified, and their appearance with the previous Voyager observations are compared.

Lecacheux, A.; Pedersen, B. M.; Zarka, PH.; Aubier, M. G.; Desch, M. D.; Farrell, W. M.; Kaiser, M. L.; Macdowall, R. J.; Stone, R. G.

1992-01-01

381

Temperature dependence of CsI(Tl) gamma-ray excited scintillation characteristics  

Microsoft Academic Search

The gamma-ray excited, temperature dependent scintillation characteristics of CsI(Tl) are reported over the temperature range of -100 to +50°C. The modified Bollinger-Thomas and shaped square wave methods were used to measure the rise and decay times. Emission spectra were measured using a monochromator and corrected for monochromator and photocathode spectral efficiencies. The shaped square wave method was also used to

John D. Valentine; William W. Moses; Stephen E. Derenzo; David K. Wehe; Glenn F. Knoll

1993-01-01

382

Small-scale variations in the galactic magnetic field - The rotation measure structure function and birefringence in interstellar scintillations  

NASA Technical Reports Server (NTRS)

The structure function of rotation measures of extragalactic sources and birefringence in interstellar scintillations are used to investigate variations in the interstellar magnetic field on length scales of about 0.01-100 pc and 10 to the 11th cm, respectively. Model structure functions are derived for the case of a power-law power spectrum of irregularities in the quantity (n(e)B), and an estimate for the structure function is computed for several regions of the sky using data on extragalactic sources. The results indicate an outer angular scale for rotation measure (RM) variations of not less than about 5 deg (a linear scale of about 9-90 pc at a distance of 0.1-1 kpc). There is also evidence for RM variations on angular scales as small as 1 arcmin, but it cannot be determined whether these are intrinsic to the source or caused by the interstellar medium. The effect of a random, Faraday-active medium on the diffraction of radio waves is derived, and an upper limit to the variations in n(e)B on a length scale of 10 to the 11th cm is obtained from available observations.

Simonetti, J. H.; Cordes, J. M.; Spangler, S. R.

1984-01-01

383

Low-cost extruded plastic scintillator  

NASA Astrophysics Data System (ADS)

Motivated by a need for lower cost plastic scintillation detectors, we have tested commercially available polystyrene pellets in order to produce scintillating materials that can be extruded into various shapes. Selection of the raw materials is discussed. Two techniques are described that add wavelength shifting dopants to polystyrene pellets and extrude plastic scintillating bars using these materials. Data on light yield and transmittance are presented.

Pla-Dalmau, Anna; Bross, Alan D.; Mellott, Kerry L.

2001-07-01

384

Deep Field Surveys - A Radio View  

E-print Network

I present an introductory review text, focusing on recent deep field studies using radio telescopes, including high-resolution, wide-field VLBI observations. The nature of the faint radio source population is discussed, taking into account complimentary data and results that are now available via the sub-mm, IR, optical and X-ray wave-bands. New developments regarding the increased sensitivity of VLBI and an expansion in the instruments field-of-view are also presented. VLBI may be an important tool in recognising distant, obscured AGN from the ``contaminant'' star forming galaxies that now dominate lower-resolution, sub-arcsecond and arcsecond radio observations.

M. A. Garrett

2004-09-08

385

Constraining Solar Coronal Turbulence with Radio Data  

NASA Astrophysics Data System (ADS)

The best available models for density turbulence and density profiles in the corona and Solar wind are used to predict the scattering of radio waves. Predictions for the mean square scattering angle < ?sc2 > are then compared with the small angular sizes (< 60'') of Solar noise storms recently observed at 327 MHz by the Giant Metrewave Radio Telescope (GMRT) and the Nancay Radio Heliograph (NRH). We find that the predicted values of ? = < ?sc2 >1/2 can exceed the minimum observed source sizes by up to 2-3 orders of magnitude. We discuss the implications of this surprising result.

Subramanian, P.; Cairns, I.

2009-09-01

386

LOFAR Transients and the Radio Sky Monitor  

E-print Network

The study of transient and variable low-frequency radio sources is a key goal for LOFAR, with an extremely broad science case ranging from relativistic jets sources to pulsars, exoplanets, radio bursts at cosmological distances, the identification of gravitational wave sources and even SETI. In this paper we will very briefly summarize the science of the LOFAR Transients key science project, will outline the capabilities of LOFAR for transient studies, and introduce the LOFAR Radio Sky Monitor, a proposed mode in which LOFAR regularly scans 2 pi radians of sky.

Rob Fender; Ralph Wijers; Ben Stappers; the LOFAR Transients Key Science Project

2008-05-28

387

AM Radio Ionosphere Station: Teacher's Guide  

NSDL National Science Digital Library

In this activity students will monitor the ionosphere by using an amplitude modulated (AM) radio to track solar storms and other changes in ionosphere reflectivity. They will discover that above the earth's surface a layer of charged particles called the ionosphere is capable of reflecting radio waves and that the reflectivity properties of the ionosphere can be changed dramatically by solar activity. In order to detect and study some of these changes, students will use the radio to listen for changes in background noise and the appearance of distant stations, learning that a simple everyday device can let them detect invisible changes in their environment caused by solar activity.

388

Waveshifters and Scintillators for Ionizing Radiation Detection  

SciTech Connect

Scintillation and waveshifter materials have been developed for the detection of ionizing radiation in an STTR program between Ludlum Measurements, Inc. and the University of Notre Dame. Several new waveshifter materials have been developed which are comparable in efficiency and faster in fluorescence decay than the standard material Y11 (K27) used in particle physics for several decades. Additionally, new scintillation materials useful for fiber tracking have been developed which have been compared to 3HF. Lastly, work was done on developing liquid scintillators and paint-on scintillators and waveshifters for high radiation environments.

B.Baumgaugh; J.Bishop; D.Karmgard; J.Marchant; M.McKenna; R.Ruchti; M.Vigneault; L.Hernandez; C.Hurlbut

2007-12-11

389

Divalent fluoride doped cerium fluoride scintillator  

DOEpatents

The use of divalent fluoride dopants in scintillator materials comprising cerium fluoride is disclosed. The preferred divalent fluoride dopants are calcium fluoride, strontium fluoride, and barium fluoride. The preferred amount of divalent fluoride dopant is less than about two percent by weight of the total scintillator. Cerium fluoride scintillator crystals grown with the addition of a divalent fluoride have exhibited better transmissions and higher light outputs than crystals grown without the addition of such dopants. These scintillators are useful in radiation detection and monitoring applications, and are particularly well suited for high-rate applications such as positron emission tomography (PET).

Anderson, David F. (630 Sylvan Pl., Batavia, IL 60510); Sparrow, Robert W. (28 Woodlawn Dr., Sturbridge, MA 01566)

1991-01-01

390

Modernized GPS Signals and Ionospheric Scintillation  

NASA Astrophysics Data System (ADS)

One of the major threats to accurate and reliable navigation, positioning, and timing (PNT) using the L1 CA code is scintillation produced by ionospheric irregularities. The introduction of new civilian PRN codes on L2 and L5 promise more accurate and reliable PNT, but these new signals are also vulnerable to scintillation. Recently we have developed GPS software receivers for examining the details of amplitude and phase scintillations on L1 and L2. These software receivers demonstrate that on L1, amplitude and phase scintillations are not independent and are strongly correlated. That is, the fastest phase shifts occur during the deepest fades. This leads to a similar question, are scintillations independent on L1 and L2? An experiment to address this question was conducted in January 2007. Signals were collected from the L1CA code and the L2C code during moderate scintillations using a software receiver located at Natal, Brazil. The answer to the question is that scintillations are strongly correlated between L1 and L2 for this example. The consequence of this strong correlation is that tracking will be unable to switch between the L1 and L2 signals when one of the signals is challenged by a fade for at least moderate scintillation levels. Earlier experiments at L band frequencies suggest that during strong scintillation fading may be less well correlated between L1 and L2. We present simulations to examine this hypothesis.

Kintner, P. M.; Cerruti, A.; O'Hanlon, B.; Humphreys, T.; Psiaki, M.

2008-12-01

391

Low Frequency Radio Emissions: Remote Sensing of the Energetic Heliosphere  

NASA Astrophysics Data System (ADS)

Low frequency radio emissions (below about 50 MHz) are tracers of energetic plasma instabilities. Their observation provides us with a unique proxy for instable energetic electron populations. In the solar wind, two types of emissions can be monitored: Type II and Type III radio bursts. The former are related to interplanetary shocks, while the latter are linked to energetic electron beams going out from the solar corona. The magnetized planets are also producing low frequency radio emissions linked to the auroral activity, and thus to the interaction between the planet and the solar wind. These radio emission are non-thermal emissions. They are very powerful (Jupiter is as intense as the Sun in this frequency range). Furthermore, the low frequency radio instrumentation in space has the advantage to be quasi-isotropic. The antenna systems have no intrinsic directivity. However, goniopolarimetric inversions have been developed to derive the observed radio waves parameters (assuming we see a single source at a given time). Hence, the low frequency radio systems can monitor the whole sky at once and provide direction of arrival for each event. We will present the various emission mechanisms involved for the low frequency radio emissions in the solar system, the various propagation effects along the wave path and the radio instrumentation necessary to derived all relevant wave parameters. We will discuss how these radio emissions can be used in a space weather perspective. We will finally overview the possible future steps in terms of instrumentation for this frequency range.

Cecconi, Baptiste

2014-05-01

392

The Galileo Plasma wave investigation  

Microsoft Academic Search

The purpose of the Galileo plasma wave investigation is to study plasma waves and radio emissions in the magnetosphere of Jupiter. The plasma wave instrument uses an electric dipole antenna to detect electric fields, and two search coil magnetic antennas to detect magnetic fields. The frequency range covered is 5 Hz to 5.6 MHz for electric fields and 5 Hz

D. A. Gurnett; W. S. Kurth; R. R. Shaw; A. Roux; R. Gendrin; C. F. Kennel; F. L. Scarf; S. D. Shawhan

1992-01-01

393

Aperture averaging of optical scintillations in CO{sub 2} DIAL  

SciTech Connect

Atmospheric turbulence causes several effects on a propagating laser beam. The authors have previously studied the effects of beam spreading and beam wander, and feel they have a good understanding of their impact on CO{sub 2} DIAL. Another effect is scintillation where atmospheric turbulence causes irradiance fluctuations within the envelope of the beam profile. They believe that scintillation at the target plays an important role in LIDAR return statistics. A Huygens-Fresnel wave optics computer simulation for propagating beams through atmospheric optical turbulence has been previously developed. They modify this simulation to include the effects of reflective speckle and examine its application in comparison with experimental data.

Nelson, D.H.; Petrin, R.R.; Schmitt, M.J.; Whitehead, M.C. [Los Alamos National Lab., NM (United States); Walters, D.L. [Naval Postgraduate School, Monterey, CA (United States)

1997-10-01

394

Science Priorities of the RadioAstron Space VLBI Mission  

NASA Astrophysics Data System (ADS)

The main scientific goal of the RadioAstron Space VLBI mission is study of Active Galactic Nuclei (AGN), Masers and other astronomical objects with unprecedented angular resolution, up to few millionths of an arc-second. The resolution achieved with RadioAstron will allow study the following phenomena and problems: * Central engine of AGN and physical processes near super massive black holes providing an acceleration of cosmic rays size, velocity and shape of emitting region in the core, spectrum, polarization and variability of emitting components; * Cosmological models, dark matter and dark energy by studying dependence of above mentioned AGN's parameters with redshift, and by observing gravitational lensing; * Structure and dynamics of star and planets forming regions in our Galaxy and in AGN by studying maser and Mega maser radio emission; * Neutron (quark?) stars and black holes in our Galaxy, their structure and dynamics by VLBI and measurements of visibility scintillations, proper motions and parallaxes; * Structure and distribution of interstellar and interplanetary plasma by fringe visibility scintillations of pulsars; The RadioAstron mission uses the satellite SPECTR (astrophysical module), developed by Lavochkin Association of Russian Aviation and Space Agency (RASA). This module will be used in several other scientific missions. The total mass of the scientific payload is about 2500 kg, of which the unfolding parabolic 10-m radio astronomy antenna's mass is about 1500 kg, and scientific package holding the receivers, power supply, synthesizers, control units, frequency standards and data transmission radio system. The mass of the whole system (satellite and scientific payload) to be carried into orbit by the powerful "Zenit-2SB"-"Fregat-2CB" launcher is about 5000 kg. The RadioAstron project is an international collaboration between RASA and ground radio telescope facilities around the world.

Langston, Glen; Kardashev, N.; International Space VLBI Collaboration

2006-12-01

395

Scintillation properties of lead sulfate  

SciTech Connect

We report on the scintillation properties of lead sulfate (PbSO{sub 4}), a scintillator that show promise as a high energy photon detector. It physical properties are well suited for gamma detection, as its has a density of 6.4 gm/cm{sup 3}, a 1/e attenuation length for 511 keV photons of 1.2 cm, is not affected by air or moisture, and is cut and polished easily. In 99.998% pure PbSO{sub 4} crystals at room temperature excited by 511 keV annihilation photons, the fluorescence decay lifetime contains significant fast components having 1.8 ns (5%) and 19 ns (36%) decay times, but with longer components having 95 ns (36%) and 425 ns (23%) decays times. The peak emission wavelength is 335 nm, which is transmitted by borosilicate glass windowed photomultiplier tubes. The total scintillation light output increases with decreasing temperature fro 3,200 photons/MeV at +45{degrees}C to 4, 900 photons/MeV at room temperature (+25{degrees}C) and 68,500 photons/MeV at {minus}145{degrees}C. In an imperfect, 3 mm cube of a naturally occurring mineral form of PbSO{sub 4} (anglesite) at room temperature, a 511 keV photopeak is seen with a total light output of 60% that BGO. There are significant sample to sample variations of the light output among anglesite samples, so the light output of lead sulfate may improve when large synthetic crystals become available. 10 refs.

Moses, W.W.; Derenzo, S.E. [Lawrence Berkeley Lab., CA (United States); Shlichta, P.J. [Crystal Research, San Pedro, CA (United States)

1991-11-01

396

Youth Radio  

NSDL National Science Digital Library

With an impressive headquarters in downtown Oakland, Youth Radio is fast becoming a compelling and insightful media phenomenon that should be watched closely. Their mission is a laudable one, and as their website puts it, âÂÂâ¦. is to promote young peopleâÂÂs intellectual creative and professional growth through training and access to media and to produce the highest quality original media for local and national outlets.â Of course, the real heart of the site contains the actual programming, which is streamed 24 hours a day, 7 days a week. Along with unique mix of music, individuals can listen to a host of stories reported by young people. Visitors can also browse a list of recently added stories by topic, which include relationships, society, sports, poetry, and health. Those who are hoping to get some of the basic flavor of the offerings here would do well to take a look at the story featuring reporting from a group of Berkeley High School students at the World Social Forum in Caracas, or by listening to the commentary offered by Lauryn Silverman on the modern conundrum of multi-tasking.

397

A study of intense ionospheric scintillation observed during a quiet day in the East African low-latitude region  

NASA Astrophysics Data System (ADS)

Ionospheric plasma density irregularities are a common feature of the equatorial and low-latitude ionosphere. These irregularities are known to cause fading and phase fluctuation (scintillation) of L-band radio navigation signals such as those used by Global Navigation Satellite Systems. This study investigates the occurrence of intense ionospheric scintillation in the postsunset period during a geomagnetically quiet day on 8 April 2011. In particular, we use Global Positioning System (GPS) derived observations, i.e., total electron content (TEC) and amplitude scintillation intensity index, S4, to examine the occurrence of intense scintillations at two low-latitude stations in the East African sector. Deep TEC depletions, in some cases roughly 40 TECU, are observed consistently with the occurrence of intense scintillations. In addition, we compare the GPS-based observations to the Communication/Navigation Outage Forecasting System (C/NOFS) satellite plasma data. The intense scintillation events also correspond well with plasma depletion structures present on the C/NOFS observations and can be attributed to strong plasma bubble activity. The C/NOFS data also provide evidence of strong upward drift velocities (> 60 m/s) associated with the depletions, which may have contributed to the generation of the strong irregularities.

Ngwira, Chigomezyo M.; Klenzing, Jeff; Olwendo, Joseph; D'ujanga, Florence M.; Stoneback, Russell; Baki, Paul

2013-07-01

398

Generation of Artificial Ionospheric Irregularities by the Modification of the Earth's Middle-Latitude Ionosphere by X-Mode Powerful HF Radio Waves  

NASA Astrophysics Data System (ADS)

Basing on experimental data obtained at the SURA heating facility by modification of the Earth’s middle-latitude ionosphere, we consider in the report some peculiarities of the generation of artificial plasma density irregularities when X-mode powerful waves (PW) are used for ionosphere pumping [1]. Experiments were carried out during 2008 - 2012 under quite ionospheric conditions (Sigma K_p = 10 - 30). Analysis of obtained experimental data has shown that: 1) In our measurements the generation of small-scale irregularities with l{_?} {?} 10 - 20 m is not observed in contrast to analogous measurements conducted at the EISCAT-heater [2,3]. 2) The generation of irregularities with l{_?} {?} 50 m - 3 km is mainly observed in evening and night hours. In these conditions their intensity is by 3 to 4 times below in comparison with the O-mode pumping. During day hours these irregularities are not detected due to both strong PW energy absorption in the lower ionosphere and forming a defocusing lens at altitudes of 130 - 150 km [4]. 3) The generation of irregularities with l{_?} {?} 5 - 10 km is only observed in evening and night hours. In these conditions their intensity is by 10 times below in comparison with the O-mode pumping. 4) The generation of the irregularities with l{_?} {?} 50 m is observed only when the PW reflects in the ionospheric F _{2} region. 5) Under day-time conditions the defocusing lens is forming at altitudes of about of 130 - 150 km when the ionosphere is pumping both X- and O- mode powerful waves [4]. Its horizontal size is determined by the HF beam. In our experiments [1] it was revealed that the stronger generation of irregularities with scale-lengths l{_?} {?} 5 - 10 km is observed at the HF beam edge where the effective radiated power is of about 0.1 P _{max}. Such a “beam-edge” effect is also observed when the ionosphere is modified by O-mode PW. The enhancement of irregularity generation at the HF beam edge was considered in [5]. The work was supported by RFBR grants (## 12-05-00312, 13-02-12074, 13-02-12241, 14-05-31445, 14-05-00855, 14-05-10069), grant MK-2670.2014.5, and by the scientific program “Geophysics”. References: 1. Frolov et al. // Radiophys. Quant. Electron., Engl. Transl., 2013 (submitted for publication). 2. Blagovethshenskaya N.F., et al. // Geophys. Res. Lett., 2011. Vol. 38, L08802, doi:10.1029/2011GL046724. 3. Blagoveshchensraya N.F. et al. // J. Atmos. Sol.-Terr. Phys., 2013. Vol. 105-106, p. 231. 4. Boiko G.N. et al. // Radiophys. Quant. Electron., Engl. Transl., 1985. Vol. 28, No. 8, p. 960. 5. Kuo S., et al. // Geophys. Res. Lett., 2010. Vol. 37, L01101, doi:10.1029/2009GL041471.

Frolov, Vladimir; Padokhin, Artem; Kunitsyn, Viacheslav; Akchurin, Adel; Bolotin, Ilya; Zykov, Evgeniy; Vertogradov, Gennadiy

399

Twenty and thirty GHz millimeter wave experiments with the ATS-6 satellite  

NASA Technical Reports Server (NTRS)

Studies at 11 locations in the continental United States were directed at an evaluation of rain attenuation effects, scintillations, depolarization, site diversity, coherence bandwidth, and analog and digital communications techniques using the Applications Technology Satellite-6(ATS-6). In addition to direct measurements on the 20- and 30-GHz links, methods of attenuation prediction with radars, rain gages, and radiometers were developed and compared with the directly measured attenuation. Initial data results of the ATS-6 millimeter wave experiment were presented. The first section describes the experiment objectives, flight hardware, and modes of operation. The remaining six sections present papers prepared by the major participating organizations in the experiment. The papers present a comprehensive summary of the significant results of the initial 11 months of ATS-6 experiment measurements and related radiometric, radar, and radio-meteorology studies.

Ippolito, L. J.

1976-01-01

400

Binderless composite scintillator for neutron detection  

DOEpatents

Composite scintillator material consisting of a binderless sintered mixture of a Lithium (Li) compound containing .sup.6Li as the neutron converter and Y.sub.2SiO.sub.5:Ce as the scintillation phosphor, and the use of this material as a method for neutron detection. Other embodiments of the invention include various other Li compounds.

Hodges, Jason P [Knoxville, TN; Crow, Jr; Lowell, M [Oak Ridge, TN; Cooper, Ronald G [Oak Ridge, TN

2009-03-10

401

Wind effects on scintillation decorrelation times  

Microsoft Academic Search

The effects of wind on scintillation decorrelation times are well known only for winds transverse to the propagation path. Therefore, we have investigated such effects using laser scintillation and sonic anemometer data obtained at an outdoor test site at DRDC-Valcartier. The data were taken during both day and night periods in May and June 2003. Meteorological data were also taken

Guy Potvin; Denis Dion Jr.; J. L. Forand

2005-01-01

402

Luminescence and Scintillation Properties at the Nanoscale  

Microsoft Academic Search

This contribution is a review of the luminescence and scintillation properties of nanoparticles (NP), particularly doped insulators. Luminescence spectroscopy is an appropriate tool to probe matter at the nanoscale. Luminescence is also the last stage of the scintillation process. Specific surface and structural effects occurring in NP are reported. Their consequences on the NP luminescence properties are discussed. Parts of

Christophe Dujardin; David Amans; Andrei Belsky; Frederic Chaput; Gilles Ledoux; Anne Pillonnet

2010-01-01

403

The most powerful scintillator supernovae detector: LVD  

Microsoft Academic Search

Summary The Large Volume Detector (LVD) in the Gran Sasso underground Laboratory is a multipurpose detector consisting of a large volume of liquid scintillator interleaved with limited streamer tubes. In this paper we discuss its power to study low-energy cosmic neutrinos. The results show that the first LVD tower (368 tons of liquid scintillator) is well suited to detect neutrinos

M. Aglietta; B. Alpat; E. D. Alyea; P. Antonioli; G. Anzivino; G. Badino; Y. Ban; G. Bari; M. Basile; A. Benelli; V. S. Berezinsky; L. Bergamasco; S. Bianco; A. Bizzetti; G. Bruni; Y. Cao; G. Cara Romeo; R. Casaccia; C. Castagnoli; A. Castellina; K. Chen; R. Chen; J. A. Chinellato; L. Cifarelli; G. Cini; S. Cong; A. Contin; V. L. Dadikin; M. Dardo; A. De Silva; M. Deutsch; L. G. Dos Santos; R. I. Enikeev; F. L. Fabbri; W. Fulgione; P. Galeotti; P. L. Ghia; P. Giusti; F. Grianti; S. Gu; E. S. Hafen; P. Haridas; G. Iacobucci; N. Inoue; F. F. Khalchukov; E. V. Korolkova; P. V. Kortchaguin; V. B. Kortchaguin; V. A. Kudryavtsev; G. Landi; K. Lau; X. Lin; L. Lu; J. Ma; Z. Ma; G. Maccarrone; A. S. Malguin; Z. Mao; M. A. Markov; T. Massam; B. Mayes; N. Mengotti Silva; A. Misaki; G. H. Mo; B. Monteleoni; C. Morello; J. Moromisato; R. Nania; G. Navarra; L. Panaro; D. Parks; P. G. Pelfer; L. Periale; P. Picchi; P. Pinna; L. Pinsky; I. A. Pless; M. Pu; J. Pyrlyk; J. Qiu; V. G. Ryasny; O. G. Ryazhskaya; O. Saavedra; K. Saitoh; D. Sanders; G. Sartorelli; S. Sarwar; D. Shen; V. P. Talochkin; H. Tang; J. Tang; W. Tian; G. C. Trinchero; A. Turtelli; I. Uman; P. Vallania; S. Vernetto; E. von Goeler; L. Votano; T. Wada; F. Wang; H. Wang; S. Wang; R. Weathers; R. Weinstein; M. Widgoff; L. Xu; Z. Xu; V. F. Yakushev; I. Yamamoto; G. Yi; A. Zallo; G. T. Zatsepin; X. Zhou; Q. Zhu; X. Zhu; B. Zhuan; A. Zichichi

1992-01-01

404

Auroral kilometric radiation triggered by type II solar radio bursts  

NASA Technical Reports Server (NTRS)

The previously-reported triggering of auroral kilometric radiation (AKR) during type III solar radio bursts was attributed to the incoming radio waves rather than other aspects of the burst's causative solar flare. This conclusion has now been confirmed by ISEE-1 and ISEE-3 observations showing AKR which seems to have been triggered also by a subsequent type II solar radio burst, up to eleven hours after the flare.

Calvert, W.

1985-01-01

405

INSPIRE - Premission. [Interactive NASA Space Physics Ionosphere Radio Experiment  

NASA Technical Reports Server (NTRS)

The Interactive NASA Space Physics Ionosphere Radio Experiment (INSPIRE) designed to assist in a Space Experiments with Particle Accelerators (SEPAC) project is discussed. INSPIRE is aimed at recording data from a large number of receivers on the ground to determine the exact propagation paths and absorption of radio waves at frequencies between 50 Hz and 7 kHz. It is indicated how to participate in the experiment that will involve high school classes, colleges, and amateur radio operators.

Taylor, William W. L.; Mideke, Michael; Pine, William E.; Ericson, James D.

1992-01-01

406

Extruded scintillator for the Calorimetry applications  

SciTech Connect

An extrusion line has been installed and successfully operated at FNAL (Fermi National Accelerator Laboratory) in collaboration with NICADD (Northern Illinois Center for Accelerator and Detector Development). This new Facility will serve to further develop and improve extruded plastic scintillator. Recently progress has been made in producing co-extruded plastic scintillator, thus increasing the potential HEP applications of this Facility. The current R and D work with extruded and co-extruded plastic scintillator for a potential ALICE upgrade, the ILC calorimetry program and the MINERvA experiment show the attractiveness of the chosen strategy for future experiments and calorimetry. We extensively discuss extruded and co-extruded plastic scintillator in calorimetry in synergy with new Solid State Photomultipliers. The characteristics of extruded and co-extruded plastic scintillator will be presented here as well as results with non-traditional photo read-out.

Dyshkant, A.; Rykalin, V.; Pla-Dalmau, A.; Beznosko, D. [Northern Illinois Center for Accelerator and Detector Development (NICADD), Northern Illinois University, DeKalb, IL 60115 (United States); Fermi Nationa Acceleratorl Laboratory, Batavia, IL 60510 (United States); State University of New York at Stony Brook, Stony Brook, NY 11790 (United States)

2006-10-27

407

Scintillation proximity assay using polymeric membranes  

SciTech Connect

Liquid scintillation counting (LSC) is typically used to quantify electron emitting isotopes. In LSC, radioactive samples are dissolved in an organic fluor solution (scintillation cocktail) to ensure that the label is close enough to the fluor molecules to be detected. Although efficient, scintillation cocktail is neither specific or selective for samples labeled with the same radioisotope. Scintillation cocktail is flammable posing significant health risks to the user and is expensive to purchase and discard. Scintillation Proximity Assay (SPA) is a radioanalytical technique where only those radiochemical entities (RCE's) bound to fluor containing matrices are detected. Only bound RCE's are in close enough proximity the entrapped fluor molecules to induce scintillations. Unbound radioligands are too far removed from the fluor molecules to be detected. The research in this dissertation focused on the development and evaluation of fluor-containing membranes (scintillation proximity membranes, SP membranes) to be used for specific radioanalytical techniques without using scintillation cocktail. Polysulfone and PVC SP membranes prepared in our laboratory were investigated for radioimmunossay (RIA) where only bound radioligand is detected, thereby eliminating the separation step impeding the automation of RIA. These SP membranes performed RIA where the results were nearly identical to commercial SP microbeads. SP membranes functionalized with quaternary ammonium hydroxide moieties were able to trap and quantify [sup 14]CO[sub 2] without using liquid scintillation cocktail. RCE's bound in the pore structure of SP membranes are intimate with the entrapped fluor providing the geometry needed for high detection efficiencies. Absorbent SP membranes were used in radiation surveys and were shown to be as effective as conventional survey techniques using filter paper and scintillation cocktail.

Mansfield, R.K.

1992-01-01

408

DEMONSTRATION BULLETIN: RADIO FREQUENCY HEATING - IIT RESEARCH INSTITUTE  

EPA Science Inventory

Radio frequency heating (RFH) is a process that uses electromagnetic energy generated by radio waves to heat soil in situ, thereby potentially enhancing the performance of standard soil vapor extraction (SVE) technologies. An RFH system developed by the IIT Research Institute ...

409

A multifunctional antenna for terrestrial and satellite radio applications  

Microsoft Academic Search

A multifunctional antenna is presented for the application in terrestrial radio services like GSM 900 MHz, DCS 1800 MHz as well as for satellite radio services like GPS 1575 MHz. At the terrestrial frequency bands GSM 900 MHz and DCS 1800 MHz the antenna exhibits omnidirectional radiation characteristics in horizontal plane for vertical polarized waves. At the frequency bands of

S. Lindenmeier; J. F. Luy; P. Russer

2001-01-01

410

Source locations of narrowband radio emissions detected at Saturn  

Microsoft Academic Search

Since Cassini's arrival at Saturn in 2004, the Radio and Plasma Wave Science instrument has detected numerous narrowband (NB) radio emission events. These emissions, mostly detected around 5 and 20 kHz, usually occur periodically for several days after intensifications of Saturn kilometric radiation. We present calculations based on an electron density profile of Saturn's plasma torus and a dipole magnetic

Sheng-Yi Ye; D. A. Gurnett; G. Fischer; B. Cecconi; J. D. Menietti; W. S. Kurth; Z. Wang; G. B. Hospodarsky; P. Zarka; A. Lecacheux

2009-01-01

411

IS TITAN A RADIO SOURCE? W. S. Kurth  

E-print Network

IS TITAN A RADIO SOURCE? W. S. Kurth , B. Cecconi , D. A. Gurnett , M. L. Kaiser , P. Zarka , and A. Lecacheux Abstract Voyager 1 observations near Titan suggested that radio emissions near 60 kHz were generated via mode conversion from upper hybrid waves on the density gradient associated with Titan

Gurnett, Donald A.

412

Construction of 21cm Cosmic Radio Antenna  

Microsoft Academic Search

We made a pyramidal horn antenna system for 21cm cosmic radio wave. The antenna system has a rectangular waveguide with TE10 mode and a copper probe to detect the electromagnetic wave in waveguide. The parameters of the probe are obtained by experiments using two waveguides. Pyramidal horn antenna is designed to get a gain of 20dB. The size of the

Jong Ae Park; Jong-Man Yang; Seog Tae Han; Yong Sun Park

1993-01-01

413

Problems in contemporary radio engineering and electronics  

NASA Astrophysics Data System (ADS)

Papers are presented on such topics as the radar mapping of Venus, the attenuation and scattering of millimeter waves in the earth's atmosphere, radio probing of the turbulent structure of the interplanetary and circumsolar plasma, and the characteristics of fiber-optic communication systems and sensors. Consideration is also given to an analysis of natural VLF noise, semiconductor components in millimeter-wave radiation detectors, the design of acoustoelectronic devices for data processing, and superconducting radiation detectors.

Kotel'Nikov, V. A.

414

Waves in Space Plasmas (WISP)  

NASA Technical Reports Server (NTRS)

Activities under this project have included participation in the Waves in Space Plasmas (WISP) program, a study of the data processing requirements for WISP, and theoretical studies of radio sounding, ducting, and magnetoionic theory. An analysis of radio sounding in the magnetosphere was prepared.

Calvert, Wynne

1994-01-01

415

Radio frequency detection assembly and method for detecting radio frequencies  

DOEpatents

A radio frequency detection assembly is described and which includes a radio frequency detector which detects a radio frequency emission produced by a radio frequency emitter from a given location which is remote relative to the radio frequency detector; a location assembly electrically coupled with the radio frequency detector and which is operable to estimate the location of the radio frequency emitter from the radio frequency emission which has been received; and a radio frequency transmitter electrically coupled with the radio frequency detector and the location assembly, and which transmits a radio frequency signal which reports the presence of the radio frequency emitter.

Cown, Steven H. (Rigby, ID); Derr, Kurt Warren (Idaho Falls, ID)

2010-03-16

416

Remote Sensing of Solar Wind Velocities using Interplanetary Scintillation with MEXART and STELab Stations  

NASA Astrophysics Data System (ADS)

Radio signals from compact radio sources are scattered by electron density irregularities in the solar wind. This effect is registered by radio telescopes as intensity fluctuations of the observed radio source amplitude and known as Interplanetary Scintillation (IPS). The Mexican Array Radio Telescope (MEXART) and the antennas of Solar Terrestrial Environment Laboratory (STELab) are instruments dedicated to studies of IPS signals. In this work we present a technique (Manoharan and Ananthakrishnan, 1990) used to estimate solar wind velocities applied to observations of MEXART and STELab using single station spectra. Currently STELab uses a multi-station IPS technique to determinate solar wind speeds. Here we compare velocities obtained with a single station to those obtained using the multi-station technique for a few strong radio sources using both techniques and with both instruments. At the Center for Astrophysics and Space Sciences - University of California, San Diego (CASS-UCSD), a tomography program is able to reconstruct the dynamics of the inner heliosphere globally using IPS measurements to give solar wind densities and velocities. We show the incorporation of velocities provided by MEXART into this program that has been used successfully for over a decade with STELab IPS measurements.

Mejia-Ambriz, J. C.; Jackson, B. V.; Gonzalez-Esparza, A.; Tokumaru, M.; Yu, H.; Buffington, A.; Hick, P.

2013-05-01

417

Small-area fiber-coupled scintillation camera for imaging beta-ray distributions intraoperatively  

NASA Astrophysics Data System (ADS)

A small area, imaging, scintillation probe is being developed for locating small amounts of radio-labeled malignant tissue during surgery. Preliminary in brain surgery, avoiding the removal of excess tissue is a priority. It is possible to locate the main body of a brain tumor both before and during surgery, but once the bulk of the tumor is excised the identification of residual malignant tissue is difficult. A probe that covers an area of 1-2 cm(superscript 2) with an intrinsic resolution of 1-2 mm could locate small tumor masses that pose a threat of recurrence of the disease, and prevent removal of healthy tissue. A pre-operative injection of tumor seeking, beta emitting radiopharmaceutical (e.g. (superscript 18)fluorodeoxyuridine-FDUR-) will label the tumor. The limited range of beta-rays ensures proximity upon successful detection. Plastic scintillators are used for beta detection, and visible light photon counters (VLPCs) detect the scintillation light. For maneuverability in and around the surgical cavity, the scintillators are coupled to the VLPCs via 2 m of optical fiber. An imaging device can cover the tissue bed in a time compatible with surgery, as opposed to a single element detector on the order of 1-2 mm in size with comparable resolution. An imager also distinguishes high background rates (such as from annihilation gammas in FDUR) and concentrations of activity.

MacDonald, L. R.; Tornai, Martin P.; Levin, C. S.; Park, J.; Atac, Muzaffer; Cline, David B.; Hoffman, Eric G.

1995-09-01

418

Explore. Learn. Inspire. National Radio Astronomy Observatory  

E-print Network

of Education endorses HOU as a means of integrating relevant technology into the science curriculum Size: 20 Suitable for all ages. Duration: 40 minutes per group. · Students search the Science Center for sources of man-made radio waves ­ fun! Exploring Our Solar System Group Size: 20 Suitable for all ages

Groppi, Christopher

419

Scintillation Breakdowns in Chip Tantalum Capacitors  

NASA Technical Reports Server (NTRS)

Scintillations in solid tantalum capacitors are momentarily local breakdowns terminated by a self-healing or conversion to a high-resistive state of the manganese oxide cathode. This conversion effectively caps the defective area of the tantalum pentoxide dielectric and prevents short-circuit failures. Typically, this type of breakdown has no immediate catastrophic consequences and is often considered as nuisance rather than a failure. Scintillation breakdowns likely do not affect failures of parts under surge current conditions, and so-called "proofing" of tantalum chip capacitors, which is a controllable exposure of the part after soldering to voltages slightly higher than the operating voltage to verify that possible scintillations are self-healed, has been shown to improve the quality of the parts. However, no in-depth studies of the effect of scintillations on reliability of tantalum capacitors have been performed so far. KEMET is using scintillation breakdown testing as a tool for assessing process improvements and to compare quality of different manufacturing lots. Nevertheless, the relationship between failures and scintillation breakdowns is not clear, and this test is not considered as suitable for lot acceptance testing. In this work, scintillation breakdowns in different military-graded and commercial tantalum capacitors were characterized and related to the rated voltages and to life test failures. A model for assessment of times to failure, based on distributions of breakdown voltages, and accelerating factors of life testing are discussed.

Teverovsky, Alexander

2008-01-01

420

Crab pulsar giant pulses: Simultaneous radio and GRO observations  

NASA Technical Reports Server (NTRS)

Observations are reported of the Crab pulsar made at radio frequencies concurrent with Oriented Scintillation Spectrometer Experiment (OSSE) observations from 15 to 27 May 1991. Using the 43 m telescope at Green Bank at 0.8 and 1.4 GHz, samples were made continuously for 10 hrs/day at intervals of 100 to 300 microsecs. The analysis of the radio data includes calculation of histograms of pulse intensities, absolute timing to about 20 microsec precision, and characterization of intensity variations on time scales from the 33 ms spin period to days. The most detailed analysis is presented made of giant pulses. The ultimate goal is to bin the radio data into giant and nongiant pulses and to form average waveforms of OSSE data for the corresponding pulse periods. A test is done to see whether the violet radio fluctuations (which are not seen in other radio pulsars to the same degree) are correlated with low energy gamma rays, yielding constraints on the radio coherence mechanism and the steadiness of the electron-positron outflow in the magnetosphere. Timing analysis of the radio data provides a well defined ephemeris over the specified range of epochs. The gamma ray pulse phase was predicted with an error of less than 70 microsecs.

Lundgren, Scott C.; Cordes, James M.; Foster, Roger; Hankins, Tim; Ulmer, Mel; Garasi, Chris

1992-01-01

421

Crab pulsar giant pulses: Simultaneous radio and GRO observations  

NASA Astrophysics Data System (ADS)

Observations are reported of the Crab pulsar made at radio frequencies concurrent with Oriented Scintillation Spectrometer Experiment (OSSE) observations from 15 to 27 May 1991. Using the 43 m telescope at Green Bank at 0.8 and 1.4 GHz, samples were made continuously for 10 hrs/day at intervals of 100 to 300 microsecs. The analysis of the radio data includes calculation of histograms of pulse intensities, absolute timing to about 20 microsec precision, and characterization of intensity variations on time scales from the 33 ms spin period to days. The most detailed analysis is presented made of giant pulses. The ultimate goal is to bin the radio data into giant and nongiant pulses and to form average waveforms of OSSE data for the corresponding pulse periods. A test is done to see whether the violet radio fluctuations (which are not seen in other radio pulsars to the same degree) are correlated with low energy gamma rays, yielding constraints on the radio coherence mechanism and the steadiness of the electron-positron outflow in the magnetosphere. Timing analysis of the radio data provides a well defined ephemeris over the specified range of epochs. The gamma ray pulse phase was predicted with an error of less than 70 microsecs.

Lundgren, Scott C.; Cordes, James M.; Foster, Roger; Hankins, Tim; Ulmer, Mel; Garasi, Chris

1992-02-01

422

Coherent emission in fast radio bursts  

NASA Astrophysics Data System (ADS)

The fast (ms) radio bursts reported by Lorimer et al. Science 318, 777 (2007) and Thornton et al. Science 341, 53 (2013) have extremely high brightness temperatures if at the inferred cosmological distances. This implies coherent emission by "bunches" of charges. Fast radio bursts, like the giant pulses of the Crab pulsar, display banded spectra that may be harmonics of plasma frequency emission by plasma turbulence and are inconsistent with emission by charge distributions moving relativistically. We model the emission region as a screen of half-wave dipole radiators resonant around the frequencies of observation, the maximally bright emission mechanism of nonrelativistic charges, and calculate the implied charge bunching. From this we infer the minimum electron energy required to overcome electrostatic repulsion. If fast radio bursts are the counterparts of Galactic events, their Galactic counterparts may be detected from any direction above the horizon by radio telescopes in their far sidelobes or by small arrays of dipoles.

Katz, J. I.

2014-05-01

423

Radio Supernovae in the Local Universe  

E-print Network

In the last three decades, about 50 radio supernovae have been detected as a result of targeted searches of optically discovered supernovae in the local universe. Despite this relatively small number some diversity among them has already been identified which is an indication of the underlying richness of radio supernovae waiting to be discovered. For example, comparison of star formation and supernova discovery rate imply that as many as half of the supernovae remain undetected in the traditional optical searches, either because of intrinsic dimness or due to dust obscuration. This has far reaching consequences to the models of stellar and galaxy evolution. A radio sky survey would be ideal to uncover larger supernova population. Transient radio sky would benefit significantly from such a survey. With the advent of advanced gravitational wave detectors a new window is set to open on the local Universe. Localization of these gravitational detectors is poor to identify electromagnetic counterparts of the gravi...

Kamble, Atish; Berger, Edo; Zauderer, Ashley; Chakraborti, Sayan; Williams, Peter

2014-01-01

424

Non-WKB Alfven Wave Reflection from the Solar Photosphere to the Distant Heliosphere  

NASA Astrophysics Data System (ADS)

Magnetohydrodynamic (MHD) turbulence has been considered for several decades as a possibly substantial heat source for the solar chromosphere, corona, and heliosphere. However, it is still not well understood how the turbulent fluctuations are generated and how they evolve in frequency and wavenumber. Although the dominant population of Alfvén waves near the Sun must be propagating outwards, one also needs waves propagating inwards in order to ``seed'' a turbulent cascade. As a part of an ongoing study of various aspects of solar MHD turbulence, we present a model of linear, non-WKB reflection of Alfvén waves that propagate in both directions along an open magnetic flux tube. Our work differs from previous models in the following ways. (1) The background plasma density, magnetic field, and flow velocity are constrained empirically from below the photosphere to distances past 1 AU. The successive merging of flux tubes on granular and supergranular scales is described using a two-dimensional magnetostatic model of a magnetic network element in the stratified solar atmosphere. (2) The amplitudes of horizontal wave motions are specified only at the photosphere, based on previous analyses of G-band bright point motions. Everywhere else in the model the amplitudes of outward and inward propagating waves are computed self-consistently. We compare the resulting wave properties with observed nonthermal motions in the chromosphere and corona, radio scintillation measurements, and in-situ fluctuation spectra. Quantities such as the MHD turbulent heating rate and the non-WKB wave pressure are computed, and the need for other sources of inward waves (e.g., nonlinear reflection or scattering off density inhomogeneities) will also be discussed. This work is supported by the National Aeronautics and Space Administration under grants NAG5-11913 and NAG5-12865 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the Swiss contribution to the ESA PRODEX program.

Cranmer, S. R.; van Ballegooijen, A.

2003-12-01

425

Cerium oxidation state in LSO:Ce scintillators  

Microsoft Academic Search

Trivalent cerium ions form the luminescence centers in several important families of scintillation materials including the rare earth oxyorthosilicates, pyrosilicates, and aluminates. When comparing the experimentally determined scintillation properties of cerium-doped scintillators to theoretical models of scintillation mechanisms, there is often speculation regarding the fraction of the total cerium that exists in the radiative trivalent charge state (Ce3+) rather than

Charles L. Melcher; Stephan Friedrich; Stephen P. Cramer; Merry A. Spurrier; Piotr Szupryczynski; Ron Nutt

2005-01-01

426

Problems in the further improvement of the efficiency of radio telescopes having A diameter of 64 to 128 m in the short-wave portion of the centimeter range  

Microsoft Academic Search

As is well known, prospective problems in radio astronomy require the creation of the most varied instruments having ultrahigh sensitivity and resolving power for their solution. The principal obstacle along this path lies in the high cost of equipment and engineering difficulties in realizing high accuracy. The realization of ultralarge radio telescopes becomes especially complicated in the centimeter and millimeter

A. F. Bogomolov; B. A. Poperechenko

1973-01-01

427

A sociabilidade em ondas sonoras: as audiências e o rádio dos anos 50 e 60 em Fortaleza The sociability in sonorous waves: the audience and the radio of years 50 and 60 in Fortaleza  

Microsoft Academic Search

The present study reflects on the meanings of the sociabilities mediated for the radio from two distinct perspectives: of the producers of the radio in the fifties and sixty of century XX and of its listeners in the same period, in the city of Fortaleza, located in the Northeast region of Brazil. This period of time presents itself as extremely

Roberta Manuel; Barros de Andrade; Erotilde Honório Silva

428

Estimating the radiative activation characteristics of a Gd3Al2Ga3O12:Ce scintillator in low earth orbit  

NASA Astrophysics Data System (ADS)

Gd3Al2Ga3O12:Ce (GAGG:Ce) is a recently developed inorganic scintillator. With excellent characteristics of high density and high light yield, GAGG:Ce could be potentially applied as a gamma-ray detector for astrophysical experiments on satellite missions. We report the characteristics of GAGG:Ce for radiation dose by irradiating 150 MeV protons up to 100 Gy, as compared with GSO:Ce, CsI:Tl and GYSO:Ce scintillators. We investigated the radio-activated intrinsic background count rates due to spallation within an energy range of 30–400 keV for each scintillator, and then estimated the background count rates for a satellite experiment conducted in low earth orbit. The results showed that the background count rate of GAGG:Ce was the lowest per day or in a longer timescale than the other scintillators.

Sakano, M.; Nakamori, T.; Gunji, S.; Katagiri, J.; Kimura, S.; Otake, S.; Kitamura, H.

2014-10-01

429

DIFFUSIVE SHOCK ACCELERATION SIMULATIONS OF RADIO RELICS  

SciTech Connect

Recent radio observations have identified a class of structures, so-called radio relics, in clusters of galaxies. The radio emission from these sources is interpreted as synchrotron radiation from GeV electrons gyrating in {mu}G-level magnetic fields. Radio relics, located mostly in the outskirts of clusters, seem to associate with shock waves, especially those developed during mergers. In fact, they seem to be good structures to identify and probe such shocks in intracluster media (ICMs), provided we understand the electron acceleration and re-acceleration at those shocks. In this paper, we describe time-dependent simulations for diffusive shock acceleration at weak shocks that are expected to be found in ICMs. Freshly injected as well as pre-existing populations of cosmic-ray (CR) electrons are considered, and energy losses via synchrotron and inverse Compton are included. We then compare the synchrotron flux and spectral distributions estimated from the simulations with those in two well-observed radio relics in CIZA J2242.8+5301 and ZwCl0008.8+5215. Considering that CR electron injection is expected to be rather inefficient at weak shocks with Mach number M {approx}< a few, the existence of radio relics could indicate the pre-existing population of low-energy CR electrons in ICMs. The implication of our results on the merger shock scenario of radio relics is discussed.

Kang, Hyesung [Department of Earth Sciences, Pusan National University, Pusan 609-735 (Korea, Republic of); Ryu, Dongsu [Department of Astronomy and Space Science, Chungnam National University, Daejeon 305-764 (Korea, Republic of); Jones, T. W., E-mail: kang@uju.es.pusan.ac.kr, E-mail: ryu@canopus.cnu.ac.kr, E-mail: twj@msi.umn.edu [School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)

2012-09-01

430

The Borexino scintillator and solvent procurement  

NASA Astrophysics Data System (ADS)

The Borexino experiment for solar neutrino physics and other rare phenomena requires an extremely low radioactive background to disentangle the very few events due to neutrino interactions. Therefore, the Borexino scintillator has to satisfy the most stringent radiopurity requirements, being about eight orders of magnitude less radioactive than an ordinary material. This was achieved by means of scintillator purification techniques and of a special care during all the production, handling and procurement of the scintillator solvent. This paper describes the methodology and the quality control procedures that were employed during the production, handling and shipping of the solvent.

Giammarchi, Marco

2014-05-01

431

Large volume flow-through scintillating detector  

DOEpatents

A large volume flow through radiation detector for use in large air flow situations such as incinerator stacks or building air systems comprises a plurality of flat plates made of a scintillating material arranged parallel to