Sample records for radio propagation characteristics

  1. CME Propagation Characteristics from Radio Observations

    E-print Network

    S. Pohjolainen; L. van Driel-Gesztelyi; J. L. Culhane; P. K. Manoharan; H. A. Elliott

    2007-11-20

    We explore the relationship among three coronal mass ejections (CMEs), observed on 28 October 2003, 7 November 2004, and 20 January 2005, the type II burst-associated shock waves in the corona and solar wind, as well as the arrival of their related shock waves and magnetic clouds at 1 AU. Using six different coronal/interplanetary density models, we calculate the speeds of shocks from the frequency drifts observed in metric and decametric radio wave data. We compare these speeds with the velocity of the CMEs as observed in the plane-of-the-sky white-light observations and calculated with a cone model for the 7 November 2004 event. We then follow the propagation of the ejecta using Interplanetary Scintillation (IPS) measurements, which were available for the 7 November 2004 and 20 January 2005 events. Finally, we calculate the travel time of the interplanetary (IP) shocks between the Sun and Earth and discuss the velocities obtained from the different data. This study highlights the difficulties in making velocity estimates that cover the full CME propagation time.

  2. CME Propagation Characteristics from Radio Observations

    E-print Network

    Pohjolainen, S; Culhane, J L; Manoharan, P K; Elliott, H A

    2007-01-01

    We explore the relationship among three coronal mass ejections (CMEs), observed on 28 October 2003, 7 November 2004, and 20 January 2005, the type II burst-associated shock waves in the corona and solar wind, as well as the arrival of their related shock waves and magnetic clouds at 1 AU. Using six different coronal/interplanetary density models, we calculate the speeds of shocks from the frequency drifts observed in metric and decametric radio wave data. We compare these speeds with the velocity of the CMEs as observed in the plane-of-the-sky white-light observations and calculated with a cone model for the 7 November 2004 event. We then follow the propagation of the ejecta using Interplanetary Scintillation (IPS) measurements, which were available for the 7 November 2004 and 20 January 2005 events. Finally, we calculate the travel time of the interplanetary (IP) shocks between the Sun and Earth and discuss the velocities obtained from the different data. This study highlights the difficulties in making velo...

  3. Plasma plume propagation characteristics of pulsed radio frequency plasma jet

    SciTech Connect

    Liu, J. H.; Liu, X. Y.; Hu, K.; Liu, D. W.; Lu, X. P. [Advanced Electromagnetic Engineering and Technology Laboratory, Huazhong University of Science and Technology, WuHan, HuBei 430074 (China); Iza, F.; Kong, M. G. [Department of Electronic and Electrical Engineering, Loughborough University, Leicestershire LE11 3TU (United Kingdom)

    2011-04-11

    A 4 cm long helium cold atmospheric pressure plasma jet with pulsed radio frequency (rf) excitation was obtained by a copper electrode inside a quartz tube. The plasma bullet propagation characteristics common to the microseconds direct current pulse and kilohertz plasma jet is not observed in this case. The space-, time-, and wavelength-resolved optical emission profiles suggest the pulsed rf plasma channel out of the tube was strengthened by ions and metastables with longer life time than the rf period, and the plasma propagation was actually an illumination of the plasma channel caused by energetic electrons accelerated along the channel.

  4. Plasma plume propagation characteristics of pulsed radio frequency plasma jet

    NASA Astrophysics Data System (ADS)

    Liu, J. H.; Liu, X. Y.; Hu, K.; Liu, D. W.; Lu, X. P.; Iza, F.; Kong, M. G.

    2011-04-01

    A 4 cm long helium cold atmospheric pressure plasma jet with pulsed radio frequency (rf) excitation was obtained by a copper electrode inside a quartz tube. The plasma bullet propagation characteristics common to the microseconds direct current pulse and kilohertz plasma jet is not observed in this case. The space-, time-, and wavelength-resolved optical emission profiles suggest the pulsed rf plasma channel out of the tube was strengthened by ions and metastables with longer life time than the rf period, and the plasma propagation was actually an illumination of the plasma channel caused by energetic electrons accelerated along the channel.

  5. Propagation characteristics on microcellular urban mobile radio channels at 910 MHz

    Microsoft Academic Search

    ROBERT J. C. BULTITUDE; G. KEITH BEDAL

    1989-01-01

    The results of measurements made to determine propagation characteristics on urban mobile radio channels with low base-station antennas and line of sight between the base and mobile units are reported. Results show that multipath propagation conditions would be significantly less severe if small-celled systems were implemented. Root-mean-square delay spread averages computed by considering all multipath signal components with powers greater

  6. Tropospheric radio propagation assessment

    Microsoft Academic Search

    H. V. Hitney; J. H. Richter; R. A. Pappert; K. D. Anderson; G. B. Baumgartner Jr.

    1985-01-01

    An evaluation is made of the development status of tropospheric radio propagation assessments, with attention to recent advances and emphasis on anomalous propagation in a marine environment. Modeling and measurement methods for ducting phenomena due to the oceanic evaporation duct and elevated refractive layers are presented, together with the effects of sea surface roughness and horizontal inhomogeneity. A propagation assessment

  7. 910 MHz Urban Mobile Radio Propagation: Multipath Characteristics in New York City

    Microsoft Academic Search

    D. Cox

    1973-01-01

    Small scale statistics of multipath propagation in a heavily built-up urban mobile radio environment are presented. The statistics cover vehicle travel distances on the order of 30 m along streets. Measuring equipment time delay resolution is about 0.1 ?s. In some locations, paths with significant amplitudes are observed with excess delays of 9 to 10 ?s. The delay spreads (sqrt{second

  8. Radio propagation by reflection from meteor trails

    Microsoft Academic Search

    G. R. Sugar

    1964-01-01

    This paper is a survey of those characteristics of meteors, and of meteor propagation, which are important to the understanding and use of meteor ionization insofar as it provides a means of radio transmission. The subjects discussed include the utility of meteor bursts for intermittent radio communication, physical properties of meteors and meteor trails, reflection properties of individual trails, short-term

  9. Theoretical investigations on site attenuation - Propagation characteristics inside the measuring site for the radio interference

    Microsoft Academic Search

    T. Kawana; S. Miyajima

    1978-01-01

    Theoretical investigations are presented on the site attenuation of the measuring site in which radio interference waves radiated from electrical equipment are measured. The general formula for calculation of site attenuation was obtained from these investigations and the reference values were calculated by this formula. Comparing these values with the site attenuation values actually measured in an open field, good

  10. The indoor radio propagation channel

    Microsoft Academic Search

    HOMAYOUN HASHEMI

    1993-01-01

    In this tutorial survey the principles of radio propagation in indoor environments are reviewed. The channel is modeled as a linear time-varying filter at each location in the three-dimensional space, and the properties of the filter's impulse response are described. Theoretical distributions of the sequences of arrival times, amplitudes and phases are presented. Other relevant concepts such as spatial and

  11. Modeling UHF Radio Propagation in Buildings.

    NASA Astrophysics Data System (ADS)

    Honcharenko, Walter

    The potential implementation of wireless Radio Local Area Networks and Personal Communication Services inside buildings requires a thorough understanding of signal propagation within buildings. This work describes a study leading to a theoretical understanding of wave propagation phenomenon inside buildings. Covered first is propagation in the clear space between the floor and ceiling, which is modeled using Kirchoff -Huygens diffraction theory. This along with ray tracing techniques are used to develop a model to predict signal coverage inside buildings. Simulations were conducted on a hotel building, two office buildings, and a university building to which measurements of CW signals were compared, with good agreement. Propagation to other floors was studied to determine the signal strength as a function of the number of floors separating transmitter and receiver. Diffraction paths and through the floor paths which carry significant power to the receivers were examined. Comparisons were made to measurements in a hotel building and an office building, in which agreements were excellent. As originally developed for Cellular Mobile Radio (CMR) systems, the sector average is obtained from the spatial average of the received signal as the mobile traverses a path of 20 or so wavelengths. This approach has also been applied indoors with the assumption that a unique average could be obtained by moving either end of the radio link. However, unlike in the CMR environment, inside buildings both ends of the radio link are in a rich multipath environment. It is shown both theoretically and experimentally that moving both ends of the link is required to achieve a unique average. Accurate modeling of the short pulse response of a signal within a building will provide insight for determining the hardware necessary for high speed data transmission and recovery, and a model for determining the impulse response is developed in detail. Lastly, the propagation characteristics of concrete walls are examined. Theoretical and experimental studies were conducted to determine their transmission and reflections coefficients with respect to incidence angle. Furthermore, Floquet' s theory of periodic structures was used to compute the space harmonic modes introduced by the periodicity of concrete blocks.

  12. Variations of the tropospheric propagation range of ultrashort radio waves above the sea

    Microsoft Academic Search

    A. R. Gliner; S. N. Krivonozhkin; B. M. Shevtsov

    1988-01-01

    In connection with the development of beyond-the-horizon radar, communications and remote sensing of the atmosphere, the problem of predicting the tropospheric propagation range of ultrashort (US) radio waves has assumed great practical importance. Therefore, the dependence of radio signal characteristics on the propagation conditions has been investigated over different radio paths. Of special interest are routes over oceans, where the

  13. Wave propagation and earth satellite radio emission studies

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    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.

  14. Propagation Characteristics of Boolean Functions

    Microsoft Academic Search

    Bart Preneel; Werner Van Leekwijck; Luc Van Linden; René Govaerts; Joos Vandewalle

    1990-01-01

    The relation between the Walsh-Hadamard transform and the autocorrelation function of Boolean functions is used to study propagation characteristics of these functions. The Strict Avalanche Criterion and the Perfect Nonlinearity Crite- rion are generalized in a Propagation Criterion of degree k. New properties and constructions for Boolean bent functions are given and also the extension of the deflnition to odd

  15. Radio-wave propagation for space communications systems

    Microsoft Academic Search

    L. J. Ippolito

    1981-01-01

    The most recent information on the effects of Earth's atmosphere on space communications systems is reviewed. The design and reliable operation of satellite systems that provide the many applications in space which rely on the transmission of radio waves for communications and scientific purposes are dependent on the propagation characteristics of the transmission path. The presence of atmospheric gases, clouds,

  16. Radio Propagation at Frequencies above 30 Megacycles

    Microsoft Academic Search

    K. Bullington

    1947-01-01

    Radio propagation is affected by many factors, including the frequency, distance, antenna heights, curvature of the earth, atmospheric conditions, and the presence of hills and buildings. The influence of each of these factors at frequencies above about 30 megacycles is discussed, with most of the quantitative data being presented in a series of nomograms. By means of three or four

  17. The propagation of radio waves in the terrestrial environment

    Microsoft Academic Search

    L. Boithias

    1983-01-01

    The propagation of a radio wave from a transmitter to an antenna, with one of the two imbedded in the neutral or ionized earth atmosphere, is examined. Attention is given to the propagation of radio waves through an unobstructed space, such as occurs with microwave communications and radar. The theoretical basis for radio wave propagation is reviewed, as are the

  18. 1.2 GHz band wave propagation measurements in concrete building for indoor radio communications

    Microsoft Academic Search

    Jun Horikoshi; K. Tanaka; T. Morinaga

    1986-01-01

    For the design of indoor radio communication or a portable radio telephone system, 1.2 GHz band radio wave propagation characteristics are investigated in a concrete building. Penetration loss through a window, local median variations, and cumulative distributions of received signal levels in a room, reflection coefficient or equivalent dielectric constant and transmission loss of a wall\\/floor are discussed.

  19. Propagation of cosmic rays in extragalactic radio sources

    NASA Technical Reports Server (NTRS)

    Earl, J. A.

    1978-01-01

    A model of extragalactic radio sources is considered which assumes that relativistic electrons carry energy from the central galaxy to the radio lobes and also emit the radio waves. It is suggested that the radio emission is confined to an axis because electrons propagate parallel to the magnetic field more readily than perpendicular to it and that symmetric radio lobes appear on this axis because electrons are deposited at supercoherent transitions far from the central galaxy, where they propagate diffusively. The slow drift velocities that characterize this propagation are shown to explain the secondary structure between the main lobes and to establish a relationship between double sources and galactic radio trails.

  20. D region predictions. [effects on radio propagation

    NASA Technical Reports Server (NTRS)

    Thrane, E. V.; Chakrabarty, D. K.; Deshpande, S. D.; Doherty, R. H.; Gregory, J. B.; Hargreaves, J. K.; Lastovicka, J.; Morris, P.; Piggott, W. R.; Reagan, J. B.

    1979-01-01

    Present knowledge of D region phenomena is briefly reviewed and the status of current methods of predicting their effects on radio propagation considered. The ELF, VLF and LF navigational and timing systems depend on the stability of the lower part of the D layer where these waves are reflected, whereas MF and HF waves are absorbed as they penetrate the region, in most cases mainly in the upper part of the layer. Possible methods of improving predictions, warnings, and real time operations are considered with particular stress on those which can be implemented in the near future.

  1. Characteristics of radio halos, cosmic ray electron propagation, and the warm ionized medium as determined through observations of radio synchrotron emission from the Milky Way and edge-on spiral galaxies

    NASA Astrophysics Data System (ADS)

    Peterson, Jason Drew

    Observations of radio synchrotron emission from the Milky Way and other galaxies can be used as a powerful probe of the intrinsic properties and distribution of both the emitting material and absorbing material along the line of sight. In the case of our own Galaxy, low radio frequency measurements (˜100 kHz 100 MHz) exhibit the telltale signs of free-free absorption. By assuming a reasonable form of the cosmic ray electron (CRE) spectrum and its distribution with height above the galactic plane, propagation simulations imply that the warm ionized medium of the Galaxy is clumpy on scales of the order of a parsec with electron density of 0.225 cm-3, a filling factor of ˜0.1, and temperature of 7000 K. In order to explain the shape of the radio spectrum at the lowest end of the frequency range, the simulations further predict a “local cloud” with the same properties of the clumps in which the solar system is embedded. The radio synchrotron emission from edge-on galaxies proves to be useful in examining the vertical distribution of CREs above the galactic plane. Several methods have been proposed to extract as much information as possible from the outer halo of these galaxies, such as the multiscale clean algorithm employed in this project. For the seven sample galaxies chosen for this project, medium resolution observations reveal radio emission distributed exponentially above the galactic plane with a typical scale height of about 1 kpc. These halos are seen to extend up to ˜10 kpc from the plane, although these estimates appear to be affected by a distance related bias. Spectral index profiles derived from observations at 20 cm and 6 cm are compared with those predicted by cosmic ray propagation models to constrain the values of parameters governing the propagation of CREs throughout the galaxies, particularly: D, the diffusion coefficient (D ? 6.8 ą 5.1 cm 2/s), ?, the CRE injection spectral index (? ? 2.0 ą 0.2), and B, the magnetic field strength ( B ? 5.5 ą 1.8 ?G). These models are also consistent with a Gaussian source distribution in the galactic plane with a FWHM of 5.4 ą 1.4 kpc.

  2. Radio propagation at 900 MHz in underground coal mines

    Microsoft Academic Search

    Y. P. Zhang; G. X. Zheng; J. H. Sheng

    2001-01-01

    This paper reports on experimental results of radio propagation in two underground coal mines. Measurements were performed at 900 MHz on horizontal and vertical polarization in typical coal mine operational zones. Values of propagation loss in dB\\/100 m are derived. Additional losses due to coal mine curvatures and common coal mining equipment obstructions are also presented. A hybrid tunnel propagation

  3. Radio-wave propagation for space communications systems

    NASA Technical Reports Server (NTRS)

    Ippolito, L. J.

    1981-01-01

    The most recent information on the effects of Earth's atmosphere on space communications systems is reviewed. The design and reliable operation of satellite systems that provide the many applications in space which rely on the transmission of radio waves for communications and scientific purposes are dependent on the propagation characteristics of the transmission path. The presence of atmospheric gases, clouds, fog, precipitation, and turbulence causes uncontrolled variations in the signal characteristics. These variations can result in a reduction of the quality and reliability of the transmitted information. Models and other techniques are used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz have been reviewed. Particular emphasis has been placed on the effects of precipitation on the Earth/space path, including rain attenuation, and ice particle depolarization. Other factors are sky noise, antenna gain degradation, scintillations, and bandwidth coherence. Each of the various propagation factors has an effect on design criteria for communications systems. These criteria include link reliability, power margins, noise contribution, modulation and polarization factors, channel cross talk, error rate, and bandwidth limitations.

  4. Measurement and identification of mobile radio propagation channels

    Microsoft Academic Search

    R. S. Thoma; D. Hampicke; A. Richter; G. Sommerkorn

    2001-01-01

    MIMO vector radio channel sounding devices allow multidimensional analysis of wave propagation in mobile radio channels. 6-dimensions represent Doppler, TDOA, 2D DOD and 2D DOA. Antenna array architectures, calibration and K-D unitary ESPRIT parameter estimation are discussed. Parametric channel models can be derived from the estimated data

  5. Realistic radio propagation models (RPMs) for VANET simulations

    Microsoft Academic Search

    Francisco J. Martinez; Chai-Keong Toh; Juan-Carlos Cano; Carlos Miguel Tavares Calafate; Pietro Manzoni

    2009-01-01

    Deploying and testing vehicular ad hoc networks (VANETs) involves high cost and intensive labor. Hence simulation is a useful alternative prior to actual implementation. Most works found in the literature employ very simplistic radio propagation models (RPMs), ignoring the dramatic effects presented by buildings on radio signals. In this paper, we present three different RPMs that increase the level of

  6. Antarctic surface roughness effects on radio pulse propagation

    NASA Astrophysics Data System (ADS)

    Dookayka, Kamlesh

    2009-05-01

    Rough surface features on the Antarctic continent that are commensurate with radio wavelengths can affect transmission of such waves. This is especially more pronounced for incidence near the critical angle. We simulate such behavior for radio pulses propagating through Antarctic ice and analyze time-domain effects due to various surface roughness. These have ramifications for detectability by the ANITA neutrino experiment which detects radio Cerenkov emission from within the Antarctic ice sheet.

  7. Radio Propagation above 40 MC over Irregular Terrain

    Microsoft Academic Search

    John Egli

    1957-01-01

    Radio transmissions in the vhf and uhf frequency region over land areas always contend with the irregularities of the terrain and the presence thereon of dispersed quantities of trees, buildings, and other man-made structures, or wave propagation incumbrances. The determination of path attenuation is not easily satisfied by simple, curved, or plane earth calculations. However, quantitative wave propagation data are

  8. Exploring the Characteristics of "News Radio" Stations.

    ERIC Educational Resources Information Center

    Riffe, Daniel

    A descriptive mail survey extended two earlier studies done in the 1970s on "all-news" stations (or "news radio") and compared characteristics of stations using all-news with those of stations using extended news or news/information formats. Specifically, the previous studies were updated by exploration of how the following sets of characteristics…

  9. Theoretical and experimental studies of the specific features of the tropospheric propagation of UHF and EHF radio signals

    Microsoft Academic Search

    V. V. van'kevich; Iu. M. Galaev; V. T. Durasov; B. V. Zhukov; M. A. Ivanov; F. V. Kivva; S. V. Kozelkov; B. I. Makarenko

    1990-01-01

    The main radio-physical phenomena associated with the transmission of wideband ELF radio signals through the troposphere are systematized, and the specific character of their effect on the operating efficiency of ultrahigh-speed communications systems is indicated. The present analysis indicates the importance of taking into account the specific characteristics of the tropospheric propagation of wideband ELF signals in the design of

  10. Airyprime beams and their propagation characteristics

    NASA Astrophysics Data System (ADS)

    Zhou, Guoquan; Chen, Ruipin; Ru, Guoyun

    2014-02-01

    A type of Airyprime beam is introduced in this document. An analytical expression of Airyprime beams passing through a separable ABCD paraxial optical system is derived. The beam propagation factor of the Airyprime beam is proved to be 3.676. An analytical expression of the kurtosis parameter of an Airyprime beam passing through a separable ABCD paraxial optical system is also presented. The kurtosis parameter of the Airyprime beam passing through a separable ABCD paraxial optical system depends on the two ratios B/(Azrx) and B/(Azry). As a numerical example, the propagation characteristics of an Airyprime beam is demonstrated in free space. In the source plane, the Airyprime beam has nine lobes, one of which is the central dominant lobe. In the far field, the Airyprime beam becomes a dark-hollow beam with four uniform lobes. The evolvement of an Airyprime beam propagating in free space is well exhibited. Upon propagation, the intensity distribution of the Airyprime beam becomes flatter and the kurtosis parameter decreases from the maximum value 2.973 to a saturated value 1.302. The Airyprime beam is also compared with the second-order elegant Hermite–Gaussian beam. The novel propagation characteristics of Airyprime beams denote that they could have potential application prospects such as optical trapping.

  11. INVERSION ALGORITHM FOR ESTIMATING RADIO FREQUENCY INTERFERENCE CHARACTERISTICS BASED ON

    E-print Network

    Ruf, Christopher

    INVERSION ALGORITHM FOR ESTIMATING RADIO FREQUENCY INTERFERENCE CHARACTERISTICS BASED ON KURTOSIS to recover power and duty-cycle of incoming Radio Frequency Interference (RFI) signals from kurtosis using experimental data. Index terms ­ Microwave radiometry, radio frequency interference, Simulated

  12. APPLICATION OF SMALL SATELLITES FOR HIGH PRECISION MEASURING EFFECTS OF RADIO WAVE PROPAGATION

    Microsoft Academic Search

    K. Igarashi; N. A. Armand; A. G. Pavelyev; Ch. Reigber; J. Wickert; K. Hocke; G. Beyerle; S. S. Matyugov; O. I. Yakovlev

    The radio holography methodology may be applied in the scientific programs for future small satellite that will use radio signals emitted by radio navigation, radio communication satellites for precise measuring effects of radio waves propagation at low elevation angles and for global monitoring of radio communication channels passed through the atmosphere and ionosphere. Another task consists in monitoring of the

  13. Propagation Characteristics of Pseudochiral Microstrip Lines

    Microsoft Academic Search

    Hossein Hatefi Ardakani; Jalil Rashed-Mohassel; Abbas Akbarzadeh Jahromi; Mohammad Khalaj Amirhosseini

    2010-01-01

    This paper presents new detailed features of microstrip lines on a generic pseudochiral medium. A full-wave analysis is also proposed based on the spectral domain technique to extract the propagation characteristics of the new line in a straightforward way is compared to other methods in the literature. In addition, The Extended Method of Lines (E-MoL) is implemented to validate the

  14. Radio propagation for space communications systems

    Microsoft Academic Search

    L. J. Ippolito

    1981-01-01

    This paper presents a review of the most recent information on the effects of the earth's atmosphere on space communications systems. Models and techniques used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission are discussed. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30

  15. Coherence bandwidth loss in transionospheric radio propagation

    NASA Technical Reports Server (NTRS)

    Rino, C. L.; Gonzalez, V. H.; Hessing, A. R.

    1980-01-01

    In this report a theoretical model is developed that predicts the single-point, two-frequency coherence function for transionospheric radio waves. The theoretical model is compared to measured complex frequency correlation coefficients using data from the seven equispaced, phase-coherent UHF signals transmitted by the Wideband satellite. The theory and data are in excellent agreement. The theory is critically dependent upon the power-law index, and the frequency coherence data clearly favor the comparatively small spectral indices that have been consistently measured from the wideband satellite phase data. A model for estimating the pulse delay jitter induced by the coherence bandwidth loss is also developed and compared with the actual delay jitter observed on synthesized pulses obtained from the Wideband UFH comb. The results are in good agreement with the theory. The results presented in this report, which are based on an asymptotic theory, are compared with the more commonly used quadratic theory. The model developed and validated in this report can be used to predict the effects of coherence bandwidth loss in disturbed nuclear environments. Simple formulas for the resultant pulse delay jitter are derived that can be used in predictive codes.

  16. Propagation characteristics of acoustic waves in snow

    NASA Astrophysics Data System (ADS)

    Capelli, Achille; Kapil, Jagdish Chandra; Reiweger, Ingrid; Schweizer, Jürg; Or, Dani

    2015-04-01

    Acoustic emission analysis is a promising technique for monitoring snow slope stability with potential for application in early warning systems for avalanches. Current research efforts focus on identification and localization of acoustic emission features preceding snow failure and avalanches. However, our knowledge of sound propagation characteristics in snow is still limited. A review of previous studies showed that significant gaps exist and that the results of the various studies are partly contradictory. Furthermore, sound velocity and attenuation have been determined for the frequency range below 10 kHz, while recent snow failure experiments suggest that the peak frequency is in the ultrasound range between 30 kHz to 500 kHz. We therefore studied the propagation of pencil lead fracture (PLF) signals through snow in the ultrasound frequency range. This was achieved by performing laboratory experiments with columns of artificially produced snow of varying density and temperature. The attenuation constant was obtained by varying the size of the columns to eliminate possible influences of the snow-sensor coupling. The attenuation constant was measured for the entire PLF burst signal and for single frequency components. The propagation velocity was calculated from the arrival time of the acoustic signal. We then modelled the sound propagation for our experimental setup using Biot's model for wave propagation in porous media. The Model results were in good agreement with our experimental results. For the studied samples, the acoustic signals propagated as fast and slow longitudinal waves, but the main part of the energy was carried by the slow waves. The Young's modulus of our snow samples was determined from the sound velocity. This is highly relevant, as the elastic properties of snow are not well known.

  17. Radio Propagation in Rural Residential Areas withVegetation

    Microsoft Academic Search

    N. Blaunstein; D. Censor; A. Freedman; I. Matityahu

    2003-01-01

    Abstract—In this paper we describe radio wave propagation within mixed residential area consisting of vegetation and houses. We assume no specific knowledge of the houses and vegetation location,but only of their statistical parameters. A three-dimensional (3D) stochastic approach,which is based on the statistical description of the terrain features,houses and vegetation,and deterministic description of signal decay is presented. The scattering and

  18. Statistics of short time variations of indoor radio propagation

    Microsoft Academic Search

    Rajamani Ganesh; Kaveh Pahlavan

    1991-01-01

    In an indoor environment, channel variations which occur most frequently are due to the movement of personnel near the transmitting or receiving antennas and\\/or local movements of the terminals around a given location. Such short-time variations in the indoor radio channel are studied and determined by performing propagation experiments in line-of-sight and non-line-of-sight environments at 910 MHz. The database is

  19. Fade durations in satellite-path mobile radio propagation

    NASA Astrophysics Data System (ADS)

    Schmier, Robert G.; Bostian, Charles W.

    1986-12-01

    Fades on satellite to land mobile radio links are caused by several factors, the most important of which are multipath propagation and vegetative shadowing. Designers of vehicular satellite communications systems require information about the statistics of fade durations in order to overcome or compensate for the fades. Except for a few limiting cases, only the mean fade duration can be determined analytically, and all other statistics must be obtained experimentally or via simulation. This report describes and presents results from a computer program developed at Virginia Tech to simulate satellite path propagation of a mobile station in a rural area. It generates rapidly-fading and slowly-fading signals by separate processes that yield correct cumulative signal distributions and then combines these to simulate the overall signal. This is then analyzed to yield the statistics of fade duration.

  20. Fade durations in satellite-path mobile radio propagation

    NASA Technical Reports Server (NTRS)

    Schmier, Robert G.; Bostian, Charles W.

    1986-01-01

    Fades on satellite to land mobile radio links are caused by several factors, the most important of which are multipath propagation and vegetative shadowing. Designers of vehicular satellite communications systems require information about the statistics of fade durations in order to overcome or compensate for the fades. Except for a few limiting cases, only the mean fade duration can be determined analytically, and all other statistics must be obtained experimentally or via simulation. This report describes and presents results from a computer program developed at Virginia Tech to simulate satellite path propagation of a mobile station in a rural area. It generates rapidly-fading and slowly-fading signals by separate processes that yield correct cumulative signal distributions and then combines these to simulate the overall signal. This is then analyzed to yield the statistics of fade duration.

  1. Nondiffusive propagation of cosmic rays in the solar system and in extragalactic radio sources

    NASA Technical Reports Server (NTRS)

    Earl, J. A.

    1976-01-01

    If charged particles are scattered by random magnetic fields while they propagate along the diverging lines of force of a spatially inhomogeneous guiding field, the diffusive mode of transport, which occurs when adiabatic focusing is weak compared to scattering, gives way to novel coherent modes when focusing becomes dominant. This paper begins with a nonmathematical discussion of the higher-order transport phenomena that underlie these modes, and goes on to explore some astrophysical implications of their existence. In an interplanetary context, one of the new modes, the supercoherent mode, corresponds exactly to the 'scatter-free' propagation of kilovolt solar-flare electrons. Moreover, quasi-diffusive propagation in the presence of moderately strong focusing offers an explanation of several poorly understood aspects of solar cosmic-ray events. On a much larger scale, focused transport provides an interpretation of many observed characteristics of extragalactic radio sources. In particular, their double structure is explained in terms of basic transport phenomena.

  2. GPS radio occultations with CHAMP: A radio holographic analysis of GPS signal propagation in the troposphere and surface reflections

    NASA Astrophysics Data System (ADS)

    Beyerle, G.; Hocke, K.; Wickert, J.; Schmidt, T.; Marquardt, C.; Reigber, C.

    2002-12-01

    Within the first nine months following the activation of the GPS radio occultation experiment aboard the low Earth orbiting satellite CHAMP, more than 25,000 occultation events have been observed. A radio holographic analysis of 3783 occultation events, recorded between 14 May 2001 and 10 June 2001, reveals that in about 20-30% of these events the received signal contains contributions from components reflected at Earth's surface. On the basis of geometrical ray tracing and multiple phase screen calculations, characteristic frequency shifts in the radio holograms' power spectral densities are analyzed quantitatively. These frequency shifts are found to be dominated by surface elevation at the reflection point location and ground-level refractivity. Using temperature and pressure profiles from European Centre for Medium-Range Weather Forecasting (ECMWF) analyses, ground-level specific humidities are derived in good agreement with ECMWF values. Complex patterns found in radio hologram spectra within a subset of observations at low latitudes are interpreted in terms of multipath propagation caused by layered structures in the refractivity field.

  3. HF radio field strength and total propagation invariants

    NASA Astrophysics Data System (ADS)

    Tsedilina, E. E.

    1994-01-01

    This paper investigates the relationship between measured field strengths, observed over two midlatitude long-distance paths, and total adiabatic invariants calculated for all possible propagation channels, for equinoxes and for low and high solar activity. Communication channel invariants or channel volumes of all types of channels have been calculated for a frequency of 15 MHz using the EMI-81 ionospheric model for both simple channels (F, E, FE) made up of conventional hop trajectories (Fh, Eh) refracted by ionospheric layers, and ricochet, or chordal, trajectories (Fr, Er, FE) which propagate in stratification ducts within the ionospheric layers, or combinations of these channels. It is shown that under night and twilight (day-night) conditions the field strength, in general, is proportional to the total channel volume: E approximately = (I(sub Sigma))(sup n), where n = 0.5 to 2. This indicates the strong influence of multiple scattering by irregularities on the processes of capture, loss, and radio wave propagation in ionospheric waveguide channels. This is in accordance with the results of using ray diffusion theory and adiabatic approximation, where the horizontal character of the waveguide channel varies slowly in relation to the oscillation of the ray within the duct. Greater field strengths observed during sunset, when the terminator was moving along the path, are explained by the influence of the larger wave channel volumes at this time in comparison with other periods.

  4. Comparison between the measured and predicted parameters of HF radio signals propagating along the midlatitude trough and within the polar cap

    Microsoft Academic Search

    A. J. Stocker; E. M. Warrington; D. R. Siddle

    2007-01-01

    Prediction of the propagation characteristics of HF signals is an important aspect in the planning and operation of radio systems operating within that frequency band. Various computer codes have been developed by a number of organizations for this purpose. These prediction techniques assume that propagation is along the great circle path and ignore the effects of various large-scale ionospheric structures

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

    Microsoft Academic Search

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

    1975-01-01

    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

  6. Propagation Characteristics of International Space Station Wireless Local Area Network

    NASA Technical Reports Server (NTRS)

    Sham, Catherine C.; Hwn, Shian U.; Loh, Yin-Chung

    2005-01-01

    This paper describes the application of the Uniform Geometrical Theory of Diffraction (UTD) for Space Station Wireless Local Area Networks (WLANs) indoor propagation characteristics analysis. The verification results indicate good correlation between UTD computed and measured signal strength. It is observed that the propagation characteristics are quite different in the Space Station modules as compared with those in the typical indoor WLANs environment, such as an office building. The existing indoor propagation models are not readily applicable to the Space Station module environment. The Space Station modules can be regarded as oversized imperfect waveguides. Two distinct propagation regions separated by a breakpoint exist. The propagation exhibits the guided wave characteristics. The propagation loss in the Space Station, thus, is much smaller than that in the typical office building. The path loss model developed in this paper is applicable for Space Station WLAN RF coverage and link performance analysis.

  7. Military operations in urban terrain: indoor radio frequency propagation prediction methods

    Microsoft Academic Search

    Julia Andrusenko

    2004-01-01

    This paper investigates the applicability of two current military tactical communications technologies to military operations in urban terrain (MOUT): Single channel ground and airborne radio system (SINCGARS) and squad radios. Various existing radio frequency (RF) propagation prediction (or path loss) methods for urban environments were surveyed. The primary criterion for the selection of methods of consideration was that they must

  8. Characteristics of magnetospheric radio noise spectra

    NASA Technical Reports Server (NTRS)

    Herman, J. R.

    1976-01-01

    Magnetospheric radio noise spectra (30 kHz to 10 MHz) taken by IMP-6 and RAE-2 exhibit time varying characteristics which are related to spacecraft position and magnetospheric processes. In the midfrequency range (100-1000 kHz) intense noise peaks rise a factor of 100 or more above background; 80% of the peak frequencies are within the band 125 kHz to 600 kHz, and the peak occurs most often (18% of the time) at 280 kHz. Bandwidths of the peaks range from about 100 kHz to more than 500 kHz; most often the lower cutoff is at about 100 kHz and the upper at 380 kHz for a total bandwidth of 280 kHz. This intense mid-frequency noise was detected at radial distances from 1.3 Re to 60 Re on all sides of the earth (i.e., all local times) during magnetically quiet as well as disturbed periods. Maximum occurrence of the mid-frequency noise is in the evening to midnight hours where splash-type energetic particle precipitation takes place.

  9. Propagation characteristics of ground based urban communications in the military UHF band

    Microsoft Academic Search

    Jerry R. Hampton; Naim M. Merheb; William L. Lain; Douglas E. Paunil; Robert M. Shuford; Jason A. Abrahamson; William T. Kasch

    2005-01-01

    A series of experiments were conducted to characterize the propagation characteristics in an urban canyon setting between ground-based communicators operating within the military ultrahigh frequency band (225 to 450 MHz). The experiments were conducted over a two-day period in downtown Philadelphia. Profiles of received power versus distance were generated along a variety of straight and L-shaped paths for different radio

  10. Characteristics of a partially coherent Gaussian Schell-model beam propagating in slanted atmospheric turbulence

    Microsoft Academic Search

    Li Ya-Qing; Wu Zhen-Sen

    2012-01-01

    On the basis of the extended Huygens—Fresnel principle and the model of the refractive-index structure constant in the atmospheric turbulence proposed by the International Telecommunication Union-Radio Communication Sector, the characteristics of the partially coherent Gaussian Schell-model (GSM) beams propagating in slanted atmospheric turbulence are studied. Using the cross- spectral density function (CSDF), we derive the expressions for the effective beam

  11. Event-based Transmission Line Matrix Method for Simulating Site-Specific Multipath Propagation Characteristics

    SciTech Connect

    Kuruganti, Phani Teja [ORNL] [ORNL; Nutaro, James J [ORNL] [ORNL; Djouadi, Seddik M [ORNL] [ORNL

    2012-01-01

    Accurate radio channel modeling is essential for deploying advanced wireless sensors in harsh industrial and urban environments. Site-specific propagation modeling tools are required to understand the channel parameters with in these environments. Multipath delay spread determines the frequency-selective fading characteristics of the channel. This paper describes a novel computationally inexpensive technique to determine multipath delay spread. Event-based transmission line matrix-based method is used to simulate the channel.

  12. Observations of the characteristics of propagation of VLF signals during meridian transits by Sco X-1

    Microsoft Academic Search

    J. H. Beall; K. S. Wood; F. J. Kelly

    1990-01-01

    The authors have conducted a series of studies of the VLF propagation characteristics during coordinated radio, optical, ultraviolet, and X-ray observations of the X-ray star Sco X-1. The observations were taken from 9-12 March 1989, a period when Sco X-1 was particularly active, and during a time of intense day-side solar activity. VLF sites were used to obtain phase and

  13. Characteristics of vector propagation channels in dynamic mobile scenarios

    Microsoft Academic Search

    Adnan Kavak; Weidong Yang; Guanghan Xu; Wolfhard J. Vogel

    2001-01-01

    In wireless communications, the performance of a smart antenna system depends heavily upon vector channels describing channel propagation between an antenna array and a mobile subscriber. The smart antennas perform quite well in stationary mobile environments in which channel propagation characteristics are stable. However, in dynamic wireless environments where the mobile user is in motion, knowledge of how vector channels

  14. Fundamental Jupiter millisecond radio burst characteristics

    Microsoft Academic Search

    H. O. Rucker

    2003-01-01

    The development of high spectral resolution instrumentation, i.e. the digital spectropolarimeter (DSP) and waveform receiver (WFR) and their installation at large decameter band radio telescopes (UTR-2 at Kharkov, Ukraine and Nancay, France) opened new possibilities in the investigation of fast Jupiter radio emissions in the decametric range. The internal structure of a drifting millisecond (S-)burst, being analyzed by means of

  15. The Birth and Development of Radio Astronomy Studies of the Sun at the Siberian Institute of Terrestrial Magnetism, the Ionosphere and Radio-Wave Propagation

    NASA Astrophysics Data System (ADS)

    Smol'kov, G. Y.

    The history of the organisation of the Department of Radio Astronomy at the Siberian Institute of Terrestrial Magnetism, the Ionosphere and Radio-Wave Propagation (SibIZMIRAN) is described, together with the principles behind the construction of the Siberian Solar Radio Telescope and the results of observations of the solar radio emission at decimetre wavelengths using this telescope.

  16. Collaboration between URSI and CCIR in the study of tropospheric radio wave propagation problems

    Microsoft Academic Search

    J. A. Saxton

    1978-01-01

    Topics in tropospheric radio wave propagation addressed by the International Union of Radio Science and the International Radio Consultative Committee include clear-air phenomena, precipitation effects, improvements in centimeter-wavelength space and terrestrial communications, and planning for VHF and UHF services. An example of cochannel interference between earth-space and terrestrial links operating at 4 GHz is presented. In addition, interference by precipitation

  17. Handbook of radio wave propagation loss (100-10,000 MHz)

    Microsoft Academic Search

    W. E. Frazier

    1984-01-01

    This handbook is intended to assist in manual analysis techniques that must be used when an automated analysis is not possible. It provides estimates of radio wave propagation loss between transmitting and receiving antennas above the assumed smooth-earth surface that were calculated using the Integrated Propagation System (IPS) computer model. For many cases involving electromagnetic compatibility analysis, the included curves

  18. Study of long path VLF signal propagation characteristics as observed from Indian Antarctic station, Maitri

    NASA Astrophysics Data System (ADS)

    Sasmal, Sudipta; Chakrabarti, Sandip Kumar; Pal, Sujay

    To examine quality and propagation characteristics of radio waves in a very long propagation path, Indian Centre for Space Physics participated in the 27th Indian scientific expedition to Antarctica during 2007-2008. One Stanford University made AWESOME (Atmospheric Weather Educational System for Observation and Modeling of Effects) Very Low Frequency (VLF) receiving system was installed at the Indian Antarctic station Maitri and about five weeks of data was recorded successfully from the Indian transmitter VTX and several other transmitting stations worldwide. Signal quality of VTX was found to be very good and signal amplitude was highly stable. The signal showed evidences of round the clock solar radiation in Antarctic region during local summer. We compute elevation angle of the Sun theoretically during this period. We compute the spatial distribution of the signal by using the LWPC model during the all-day and all-night propagation conditions. We compute the attenuation coefficient of the different propagation modes and observe that different modes are dominating in different propagation conditions. We also observe effects of the Antarctic polar ice in the propagation modes.

  19. Study of long path VLF signal propagation characteristics as observed from Indian Antarctic station, Maitri

    NASA Astrophysics Data System (ADS)

    Sasmal, Sudipta; Pal, Sujay; Chakrabarti, Sandip K.

    2014-10-01

    To examine the quality and propagation characteristics of the Very Low Frequency (VLF) radio waves in a very long propagation path, Indian Centre for Space Physics, Kolkata, participated in the 27th Indian scientific expedition to Antarctica during 2007-2008. One Stanford University made AWESOME VLF receiving system was installed at the Indian Antarctic station Maitri and about five weeks of data were recorded successfully from the Indian transmitter VTX and several other transmitting stations worldwide. The quality of the signal from the VTX transmitter was found to be very good, consistent and highly stable in day and night. The signal shows the evidences of the presence of the 24 h solar radiation in the Antarctic region during local summer. Here we report the both narrow band and broadband VLF observations from this site. The diurnal variations of VTX signal (18.2 kHz) are presented systematically for Antarctica path and also compared the same with the variations for a short propagation path (VTX-Kolkata). We compute the spatial distribution of the VTX signal along the VTX-Antarctica path using the most well-known LWPC model for an all-day and all-night propagation conditions. The calculated signal amplitudes corresponding to those conditions relatively corroborate the observations. We also present the attenuation rate of the dominant waveguide modes corresponding to those propagation conditions where the effects of the Antarctic polar ice on the attenuation of different propagating waveguide modes are visible.

  20. Propagation characteristics of x ?? x 1 and Kloosterman sums

    Microsoft Academic Search

    Pascale Charpin; Tor Helleseth; Victor Zinoviev

    Abstract We study the inverse permutation ? : x ?? x, by means,of their com- ponent functions f?. We prove that the weights of derivatives of f? can be expressed in terms of Kloosterman sums. We are then able to compute,some,indicators of the propagation characteristics of ? . We can claim that ? , which is considered as a good

  1. Characteristics of Laser Beams Propagating in a Homogeneous Medium

    Microsoft Academic Search

    Ching-Yen Ho

    Characteristics of laser beams propagating in a homogeneous medium were investigated in this paper. The wavelength, refractive index, and beam waist radius specify the divergence angles of laser beams. Based on the viewpoints of geometrical and physical optics the properties of optics field near and far from beam waist are evidently different. The main aim of this study was to

  2. Analysis of electromagnetic wave propagation characteristics in rotating environments

    Microsoft Academic Search

    Yi Leng; Yingfeng Pan; Qingxia Li; Sheng Liu

    2008-01-01

    During the parameter acquisition of rotating components, wireless data transmission is an efficient way to resolve data transmission problem in rotating environments, and the design of wireless data transmission system is based on EMWP (electromagnetic wave propagation). In this paper, EMWP characteristics in rotating environments are preliminarily studied in order to provide a strong theoretical support for developing high-performance rotating

  3. Nonlinearity and Propagation Characteristics of Balanced Boolean Jennifer Seberry

    E-print Network

    Zheng, Yuliang

    of functions constructed are also discussed. Key Words Bent Functions, Boolean Functions, Cryptography, Data by Matsui (1994). It is well known that bent functions possess the highest nonlinearity and satisfyNonlinearity and Propagation Characteristics of Balanced Boolean Functions Jennifer Seberry Xian

  4. Long-Range Transhorizon Lunar Surface Radio Wave Propagation in the Presence of a Regolith and a Sparse Exospheric Plasma

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    2008-01-01

    Long-range, over-the-horizon (transhorizon) radio wave propagation is considered for the case of the Moon. In the event that relay satellites are not available or otherwise unwarranted for use, transhorizon communication provides for a contingency or backup option for non line-of-sight lunar surface exploration scenarios. Two potential low-frequency propagation mechanisms characteristic of the lunar landscape are the lunar regolith and the photoelectron induced plasma exosphere enveloping the Moon. Although it was hoped that the regolith would provide for a spherical waveguide which could support a trapped surface wave phenomena, it is found that, in most cases, the regolith is deleterious to long range radio wave propagation. However, the presence of the plasma of the lunar exosphere supports wave propagation and, in fact, surpasses the attenuation of the regolith. Given the models of the regolith and exosphere adopted here, it is recommended that a frequency of 1 MHz be considered for low rate data transmission along the lunar surface. It is also recommended that further research be done to capture the descriptive physics of the regolith and the exospheric plasma so that a more complete model can be obtained. This comprehensive theoretical study is based entirely on first principles and the mathematical techniques needed are developed as required; it is self-contained and should not require the use of outside resources for its understanding.

  5. Characteristics of Low-power Wireless Links and Radios Understanding the characteristics of low-power wireless links and radios is an essential step

    E-print Network

    Amir, Yair

    -power wireless links and radios is an essential step towards building robust, efficient and reliable wirelessCharacteristics of Low-power Wireless Links and Radios Understanding the characteristics of low Indication (RSSI), which the low-power radios use to measure the power of the wireless signal. This value

  6. Predictions and observations of HF radio propagation in the northerly ionosphere: The effect of the solar flares and a weak CME in early January 2014.

    NASA Astrophysics Data System (ADS)

    Hallam, Jonathan; Stocker, Alan J.; Warrington, Mike; Siddle, Dave; Zaalov, Nikolay; Honary, Farideh; Rogers, Neil; Boteler, David; Danskin, Donald

    2014-05-01

    We have previously reported on a significant new multi-national project to provide improved predictions and forecasts of HF radio propagation for commercial aircraft operating on trans-polar routes. In these regions, there are limited or no VHF air-traffic control facilities and geostationary satellites are below the horizon. Therefore HF radio remains important in maintaining communications with the aircraft at all times. Space weather disturbances can have a range of effects on the ionosphere and hence HF radio propagation - particularly in the polar cap. While severe space weather effects can lead to a total loss of communications (i.e. radio blackout), less intense events can still cause significant disruption. In this paper we will present the effect of a series of M and X class solar flares and a relatively weak CME on HF radio performance from 6 to 13 January 2014. This is an interesting interval from the point of view of HF radio propagation because while the solar effects on the ionosphere are significant, except for an interval of approximately 12 hours duration, they are not so intense as to produce a complete radio blackout on all paths. Observations of the signal-to-noise ratio, direction of arrival, and time of flight of HF radio signals on six paths (one entirely within the polar cap, three trans-auroral, and two sub-auroral) will be presented together with riometer measurements of the ionospheric absorption. Global maps of D-region absorption (D-region absorption prediction, DRAP) inferred from satellite measurements of the solar wind parameters will be compared with the HF and riometer observations. In addition, a ray-tracing model using a realistic background ionosphere and including localised features found in the ionospheric polar cap (e.g. polar patches and arcs) will be used to model the expected and observed HF radio propagation characteristics.

  7. The propagation of electromagnetic wave in random media and effects on radio astronomical observations

    Microsoft Academic Search

    Bao-Wei Lu; Zhen-Song Wang; Wen-Jun Han

    1990-01-01

    The multiple scattering propagation of electromagnetic waves is investigated through the momentum method. A complete set of the momentum equations with different wavenumbers at different positions are derived for the propagation of a wave in a random medium where the small-angle forward-scattering and Markov random process approximations are valid. The seeing angle in radio-astronomy observations is analyzed by using the

  8. The Scope Of Impedance Boundary Conditions In Radio Propagation

    Microsoft Academic Search

    JAMES R. WAIT

    1990-01-01

    The surface impedance boundary condition is a useful concept when dealing with the analysis of radio wave transmission over inhomogeneous surfaces. The justification for the method is not rig- orous but confidence is gained by examining a number of canonical problems where exact solutions are obtainable. The scope of the sur- face impedance postulate is reviewed, and its relevance in

  9. The Mechanism of Radiation and Propagation in Radio Communication

    Microsoft Academic Search

    F. Lowenstein

    1916-01-01

    The intensity of the electric field at a distance from a statically charged antenna is calculated from elementary considerations. The same quantity is derived for the case in which the charge is oscillating at a radio frequency. It is shown that the total charges acting on the receiver in the two cases have a ratio equal to the square of

  10. High-latitude ionospheric phenomena diagnostics by high-frequency radio wave propagation observations

    SciTech Connect

    Blagoveshchenskii, D.V.; Egorova, L.V.; Lukashkin, V.M. (Leningradskii Institut Aviatsionnogo Priborostroeniia, Leningrad (USSR) Arkticheskii i Antarkticheskii NII, Leningrad (USSR))

    1992-04-01

    A system of radio paths in the decameter wave band is used to experimentally solve the problem of diagnostics of high-latitude ionospheric phenomena. Either the statistical parameters of radio signals at radio channel output or the radio wave propagation parameter on the basis of data of oblique sounding of the ionosphere is used as a source of information on a phenomenon. The former approach is taken in the diagnostics of auroral substorms and the main ionization trough. Oblique sounding is used in daytime polar cusp diagnostics. The experimental observations were carried out by two systems of paths: one is situated north of eastern Siberia, and the other encompasses the area north of the European part of the former USSR. The range of corrected geomagnetic latitudes is 55-75 deg. It is concluded that this system of radio paths makes it possible to conduct qualitative short-time prediction of these ionospheric phenomena. 11 refs.

  11. Certain aspects of tropospheric propagation in planning of transhorizon radio-relay and space telecommunication systems

    Microsoft Academic Search

    M. K. Basu

    1975-01-01

    Characteristics of radio signal transmission in the troposphere are considered in the context of planning a radio communication system. Attention is given to the effects of refraction including ray bending, variation in the refractive index gradient, and amplitude, phase, and angular scintillations; the effects of diffraction; the effects of scattering; and the effects of absorption including absorption by oxygen and

  12. A propagation prediction tool for urban mobile radio systems

    Microsoft Academic Search

    Athanasios G. Kanatas; Philip Constantinou

    2000-01-01

    This paper presents a propagation prediction tool (PPT), developed mainly to facilitate the path loss computation in urban environments. Based on analytical methods-geometrical optics (GOs), physical optics (POs), and uniform theory of diffraction (UTD)-the tool incorporates an empirical factor, the path loss factor n, used in all unobstructed paths between two points to remedy the deficiencies of the analytical models.

  13. The propagation of stable radio frequency signals through the atmosphere

    Microsoft Academic Search

    Charles Naudet; Christopher Jacobs; Steve Keihm; Gabor Lanyi; George Resch; L. Riely; Hans Rosenberger; Alan Tanner

    2000-01-01

    The terrestrial troposphere and ionosphere are known to have strong effects on the radiation fields traversing them. The primary types of effects are refraction (deflection, polarization rotation, propagation velocity changes), absorption, and scattering by the turbulent structure in the media. In particular, the phase accuracy of interferometric measurements and spacecraft Doppler tracking at frequencies greater than 5 GHz are dominated

  14. Radio Wave Scattering from Lampposts in Microcell Urban Mobile Propagation Channel

    Microsoft Academic Search

    Mir Ghoraishi; Jun-ichi Takada; Tetsuro Imai

    2009-01-01

    The radio wave scattering from lampposts in ur- ban areas is analyzed. The lamppost is modeled as a flnite-length conducting cylinder and the approxi- mate theoretical values of its bistatic radar cross sec- tion (RCS) are compared to those experimental val- ues obtained from a propagation channel measure- ment campaign in two urban environments. In the theoretical derivation it is

  15. The Signal Propagation Effects on IEEE 802.15.4 Radio Link in Fire Environment

    E-print Network

    Halgamuge, Malka N.

    were carried out for further investigation of the above phenomenon, under stimulated fire conditionsThe Signal Propagation Effects on IEEE 802.15.4 Radio Link in Fire Environment Chinthaka M suppression crews in firegrounds. In this paper, we consider the effect of fire upon 2.4 GHz IEEE 802

  16. Effects of Birefringence Within Ice Sheets on Obliquely Propagating Radio Waves

    Microsoft Academic Search

    Kenichi Matsuoka; Larry Wilen; Shawn P. Hurley; Charles F. Raymond

    2009-01-01

    In this paper, effects of birefringence on radio waves obliquely propagating though polar ice sheets are examined to facilitate interpretations of bistatic and side-looking radar data. A formalism applicable for arbitrary radar configurations is developed to predict the returned power from within and beneath the ice sheets that have arbitrary alignments of ice crystals (ice fabrics). We applied this formalism

  17. An Enhanced AODV Protocol for VANETs with Realistic Radio Propagation Model Validation

    E-print Network

    Paris-Sud XI, Université de

    An Enhanced AODV Protocol for VANETs with Realistic Radio Propagation Model Validation Jonathan for Vehicular Ad-hoc NETworks (VANETs). V-AODV is designed to run with a complex cross layered metric based for VANETs simulations. We also show that when using a routing metric based on delay and BER, the first

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

    E-print Network

    Jenn, David C.

    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

  19. Radio Propagation over a Flat Earth across a Boundary Separating Two Different Media

    Microsoft Academic Search

    P. C. Clemmow

    1953-01-01

    A theoretical investigation is given of the phenomena arising when vertically polarized radio waves are propagated across a boundary between two homogeneous sections of the earth's surface which have different complex permittivities. The problem is treated in a two-dimensional form, but the results, when suitably interpreted, are valid for a dipole source. The earth's surface is assumed to be flat.

  20. Handbook of radio wave propagation loss (100-20,000 MHz), part 2

    Microsoft Academic Search

    William E. Frazier

    1989-01-01

    The handbook provides estimates of radio wave propagation loss between transmitting and receiving antennas of various heights and transmission frequencies above the assumed smooth earth surface calculated using the NLAMBDA computer model. For many cases involving electromagnetic compatibility analysis, the curves of predicted transmission losses may be used to estimate the transmission losses of the desired and undesired signals. These

  1. SUBMITTED TO IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION. c 2012 IEEE. 1 The LWA1 Radio Telescope

    E-print Network

    Ellingson, Steven W.

    SUBMITTED TO IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION. c 2012 IEEE. 1 The LWA1 Radio Telescope, F.K. Schinzel and K.W. Weiler Abstract-- LWA1 is a new radio telescope operating in the frequency Observatories" program. Contemporary radio telescopes which are also capable of operating in LWA1's 10­88 MHz

  2. Spacecraft VHF Radio Propagation Analysis in Ocean Environments Including Atmospheric Effects

    NASA Technical Reports Server (NTRS)

    Hwu, Shian; Moreno, Gerardo; Desilva, Kanishka; Jih, CIndy

    2010-01-01

    The Communication Systems Simulation Laboratory (CSSL) at the National Aeronautics and Space Administration (NASA)/Johnson Space Center (JSC) is tasked to perform spacecraft and ground network communication system simulations. The CSSL has developed simulation tools that model spacecraft communication systems and the space/ground environment in which they operate. This paper is to analyze a spacecraft's very high frequency (VHF) radio signal propagation and the impact to performance when landing in an ocean. Very little research work has been done for VHF radio systems in a maritime environment. Rigorous Radio Frequency (RF) modeling/simulation techniques were employed for various environmental effects. The simulation results illustrate the significance of the environmental effects on the VHF radio system performance.

  3. Computational strategy for modeling radio wave propagation in lossy circular waveguides

    SciTech Connect

    Moses, Ronald [Los Alamos National Laboratory; Cai, D Michael [Los Alamos National Laboratory

    2008-01-01

    The propagation of radio waves in lossy waveguides and tunnels has been researched extensively for many years as can be seen in the detailed book by Wait. The mathematics used to model waveguides for communications is essentially the same as that needed to model radio frequency (RF) propagation in simple tunnels. The presence or lack of conductors inside a waveguide or tunnel is a key driver in the nature of the solutions one will find for a particular application, Delogne. When there are conductors passing through a waveguide or tunnel, the simplest modes of propagation are surface-guided waves following the conductor and typically enabling long-range transmission. A tunnel containing a core conductor can act rather like a coaxial cable, propagating waves at a nearly constant speed, regardless of frequency. Conversely, a tunnel or waveguide without internal conductors is subject to very different wave patterns, resulting in a much more complex propagation analysis. Holloway et al. presented an exhaustive study of RF propagation in circular structures embedded in lossy surroundings. The work of Holloway et al. is the basis for this paper, where we discuss application of their computational techniques and present refinements gleaned from our work on similar problems.

  4. The magnetoionic modes and propagation properties of auroral radio emissions

    NASA Technical Reports Server (NTRS)

    Calvert, Wynne; Hashimoto, Kozo

    1990-01-01

    The nature of the magnetoionic wave modes which accompany the aurora is clarified here by a detailed analysis, using multiple techniques, of DE 1 auroral radio observations. All four of the possible magnetoionic wave modes are found to occur, apparently emitted from two different source regions on the same auroral field line. AKR originates primarily in the X mode near the electron cyclotron frequency, and is frequently also accompanied by a weaker O-mode component from the same location. The next most prominent auroral emission is the W-mode auroral hiss originating from altitudes always well below the DE 1 satellite at frequencies below the local cyclotron frequency. The previously reported Z-mode auroral radiation was also detected, but from sources also below the satellite at the poleward edge of the cavity, and not from the expected AKR source at the cyclotron frequency.

  5. Radio Characteristics of Cool Stars and the HRD Manuel Gudel and Marc Audard

    E-print Network

    Guedel, Manuel

    ? Does radio emission re ect fundamental properties of stellar atmospheres much like X-ray radiationRadio Characteristics of Cool Stars and the HRD Manuel Gudel and Marc Audard Paul Scherrer properties of non- aring radio emis- sion of a large sample of active stars and binaries. Various radio Hertz

  6. Characteristics of shock propagation in high-strength cement mortar

    Microsoft Academic Search

    Zhanjiang Wang; Xiaolan Li; Ruoqi Zhang

    2001-01-01

    Planar impact experiments have been performed on high-strength cement mortar to determine characteristics of shock propagation.The experiments were conducted on a light-gas gun,and permanent-magnet particle velocity gages were used to obtain the sand of 0.5 3.5mm size.A bulk density of 2.31g\\/cm^3,and a compressive and tensile strength of 82MPa and 7.8MPa,respectively,were determined.Three kinds of experimental techniques were used,including the reverse ballistic

  7. PREDICTION OF PROPAGATION CHARACTERISTICS IN INDOOR RADIO COMMUNICATION ENVIRONMENTS

    Microsoft Academic Search

    Nathalie Yarkoni; Nathan Blaunstein

    2006-01-01

    In this work, we present a semi empirical approach and the analytical model on howto predict the total path loss in various indoor communication links, taking into account the newanalytical methods of the derivation of the fading phenomenon between floors and along corridors, respectively. We take into account the stochastic method of slowand fast fading estimations, caused by diffraction and

  8. Numerical modelling of VLF radio wave propagation through earth-ionosphere waveguide and its application to sudden ionospheric disturbances

    E-print Network

    Pal, Sujay

    2015-01-01

    In this thesis, we theoretically predict the normal characteristics of Very Low Frequency (3~30 kHz) radio wave propagation through Earth-ionosphere waveguide corresponding to normal behavior of the D-region ionosphere. We took the VLF narrow band data from the receivers of Indian Centre for Space Physics (ICSP) to validate our models. Detection of sudden ionospheric disturbances (SIDs) are common to all the measurements. We apply our theoretical models to infer the D-region characteristics and to reproduce the observed VLF signal behavior corresponding to such SIDs. We develop a code based on ray theory to simulate the diurnal behavior of VLF signals over short propagation paths (2000~3000 km). The diurnal variation from this code are comparable to the variation obtained from a more general Long Wave Propagation Capability (LWPC) code which is based on mode theory approach. We simulate the observational results obtained during the Total Solar Eclipse of July 22, 2009 in India. We also report and simulate a h...

  9. A wide-band propagation model based on UTD for cellular mobile radio communications

    Microsoft Academic Search

    Wei Zhang

    1997-01-01

    The present wide-band propagation model based on uniform geometrical theory of diffraction (UTD) for cellular mobile radio communications includes two major contributions. First, a UTD-based narrow-band channel transfer function containing both the diffracted electric field and the reflection of diffracted electric fields is derived. Not only is it an important element of the wide-band modeling method, but it also leads

  10. Influence of tropical F region in ionosphere on propagation of short radio waves

    NASA Astrophysics Data System (ADS)

    Kolomiytsev, O. P.; Savchenko, P. P.

    1985-05-01

    Tropical ionospheric waveguides in the presence of stratification of the electron concentration maximum were studied. Under these conditions a specific form of vertical electron concentration profile is formed which to a great extent determines the nature and conditions of propagation of short radio waves in the low latitudes. The phase trajectories were computed for a spherically stratified ionosphere. Three approaches for description of the ionospheric waveguide were used: comparative, temporal, latitudinal. Examples of computations are given which show that in a wide spatial-temporal range in the tropical ionosphere there is an additional ionospheric waveguide in which radio waves can be propagated along ricochetting trajectories. At identical time there can be three types of phases trajectories or three types of adjacent channels, each of which is characterized by a definite working frequency and definite conditions for the propagation of radio waves in it. The computations presented give a qualitative representation of the influence of stratification of the electron concentration on the formation, dynamics and degeneration of the additional ionospheric waveguides in the tropical latitudes.

  11. Reversible Parallel Discrete Event Formulation of a TLM-based Radio Signal Propagation Model

    SciTech Connect

    Seal, Sudip K [ORNL; Perumalla, Kalyan S [ORNL

    2011-01-01

    Radio signal strength estimation is essential in many applications, including the design of military radio communications and industrial wireless installations. For scenarios with large or richly- featured geographical volumes, parallel processing is required to meet the memory and computa- tion time demands. Here, we present a scalable and efficient parallel execution of the sequential model for radio signal propagation recently developed by Nutaro et al. Starting with that model, we (a) provide a vector-based reformulation that has significantly lower computational overhead for event handling, (b) develop a parallel decomposition approach that is amenable to reversibility with minimal computational overheads, (c) present a framework for transparently mapping the conservative time-stepped model into an optimistic parallel discrete event execution, (d) present a new reversible method, along with its analysis and implementation, for inverting the vector-based event model to be executed in an optimistic parallel style of execution, and (e) present performance results from implementation on Cray XT platforms. We demonstrate scalability, with the largest runs tested on up to 127,500 cores of a Cray XT5, enabling simulation of larger scenarios and with faster execution than reported before on the radio propagation model. This also represents the first successful demonstration of the ability to efficiently map a conservative time-stepped model to an optimistic discrete-event execution.

  12. Characteristics of shock propagation in high-strength cement mortar

    NASA Astrophysics Data System (ADS)

    Wang, Zhanjiang; Li, Xiaolan; Zhang, Ruoqi

    2001-06-01

    Planar impact experiments have been performed on high-strength cement mortar to determine characteristics of shock propagation.The experiments were conducted on a light-gas gun,and permanent-magnet particle velocity gages were used to obtain the sand of 0.5 3.5mm size.A bulk density of 2.31g/cm^3,and a compressive and tensile strength of 82MPa and 7.8MPa,respectively,were determined.Three kinds of experimental techniques were used,including the reverse ballistic configuration.These techniques effectively averaged the measured dynamic compression state over a sensibly large volume of the test sample.The impact velocities were controlled over a range of approximately 80m/s to 0.83km/s.Hugoniot equation of state data were obtained for the material over a pressure range of approximately 0.2 2.0GPa,and its nonlinear constitutive relation were analyzed.The experiment results show that,in higher pressure range provided in the experiment,the shock wave in the material splits into two components of an elastic and a plastic,with the Hugoniot elastic limit 0.4 0.5GPa and the precursor velocity about 4.7km/s,and the material presents a very strong nonlinear dynamic response,and its shock amplitude will greatly decrease in propagation.

  13. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 48, NO. 3, MARCH 2000 345 Estimation of Radio Refractivity Structure Using

    E-print Network

    Buckingham, Michael

    in the troposphere at microwave frequencies due to terrain and refractive index effects is an important aspectIEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 48, NO. 3, MARCH 2000 345 Estimation of Radio of the underlying "marine layer" creates elevated trapping layers in the radio refractivity structure. While direct

  14. FDTD analysis of ELF radio waves propagating in the Earth-ionosphere waveguide

    NASA Astrophysics Data System (ADS)

    Marchenko, Volodymyr; Kulak, Andrzej; Mlynarczyk, Janusz

    2015-04-01

    We developed an FDTD model of electromagnetic wave propagation in the Earth-ionosphere cavity. We present the results of FDTD calculations assuming axisymmetric system with the source located at the north pole and with no dependence on azimuthal coordinate. Therefore we reduced the Maxwell equations to 2D spherical system of Maxwell equations. To model the conductivity profile of the Earth-ionosphere waveguide we used two models, namely one- and two-exponential profiles [Mushtak and Williams, 2002]. The day-night asymmetry was introduced by setting different model parameters for the north and south hemispheres. The ground was modeled as a perfect electric conductor. Also the upper boundary for the model was a perfect conductor but it was placed at a high enough altitude to make sure there is no reflection of the waves from this boundary. We obtained the results for the electric and magnetic field components of the propagating wave in the time and frequency domains and for various locations on Earth along the meridian. In the time domain we analyzed the evolution of the electric and magnetic field components of the radio wave generated by lighting for different probe position, the penetration of the ionosphere by the electromagnetic waves and the reflection of the waves on the terminator. In the frequency domain we analyzed the Schumann resonance spectra in different field components for different location in the computational space, the behavior of the Poynting vector and the wave impedance. We also calculated real and imaginary parts of the characteristic electric and magnetic altitudes for the daytime and nighttime ionosphere. The analysis in the frequency domain was performed up to 1 kHz. We compared the results of numerical calculations with our analytical model and found a reasonably good agreement between them. The results can be used in the analysis of global thunderstorm activity based on measurements of Schumann resonance spectra. Acknowledgements. This work has been supported by the National Science Centre grant 2012/04/M/ST10/00565. The numerical computations were done using the PL-Grid infrastructure.

  15. Radio wave propagation measurements in tunnel entrance environment for intelligent transportation systems applications

    Microsoft Academic Search

    A. V. B. da Silva; M. Nakagawa

    2001-01-01

    Underground environments are of great interest to intelligent transportation system (ITS) applications, since they occur frequently in both urban and rural situations, and have peculiar propagation characteristics. This investigation includes two of the major fields in ITS applications: road-to-vehicle, and vehicle-to-vehicle communications. Besides that, the propagation measurements presented also focus on the transition effects when moving between the regions outside

  16. Investigation of the Radio Frequency Characteristics of CMOS Electrostatic Discharge Protection Devices

    E-print Network

    Anlage, Steven

    1 Investigation of the Radio Frequency Characteristics of CMOS Electrostatic Discharge Protection junctions may also rectify radio-frequency signals coupled onto CMOS data lines from incidental or malicious in logic levels. This paper presents a theoretical, numerical and experimental investigation of the radio-frequency

  17. Radio Characteristics of Cool Stars and the HRD Manuel Gudel and Marc Audard

    E-print Network

    Audard, Marc

    and comprehensive way? Does radio emission reflect fundamental properties of stellar atmospheres much like XRadio Characteristics of Cool Stars and the HRD Manuel G¨udel and Marc Audard Paul Scherrer properties of non­flaring radio emis­ sion of a large sample of active stars and binaries. Various radio

  18. Tropopause Characteristics Obtained From Champ Radio Occultation Soundings

    NASA Astrophysics Data System (ADS)

    Marquardt, C.; Schöllhammer, K.; Wickert, J.; Schmidt, T.; Beyerle, G.; Galas, R.; König, R.; Köhler, W.; Reigber, Ch.

    The German satellite CHAMP (Challenging mini-satellite Payload), launched in mid- 2000, exploits radio signals from the GPS (Global Positioning System) satellite con- stellation for the remote sensing of upper tropospheric and stratospheric temperatures. Due to the limb sounding geometry of the measurements, CHAMP's radio occultation measurements provide a high vertical vertical resolution in the tropopause region. The accuracy of the temperature soundings is also highest in the vicinity of the tropopause. Since the first measurements taken in early 2001, CHAMP has collected more than 40000 vertical profiles of the temperature distribution around the tropopause, and sev- eral multi-week periods of continuous measurements are available during all seasons. We intercompare tropopause temperatures, heights, pressures, and water vapor sat- uration mixing ratios obtained from CHAMP soundings with data from the global network of radiosonde data as well as with tropopause characteristics obtained from NCEP reanalysis. Special emphasis is put on the rich longitudinal structure of the tropical tropopause that is seen in the CHAMP data.

  19. Propagation Characteristics and Correlation-Immunity of Highly Nonlinear Boolean Functions

    Microsoft Academic Search

    Anne Canteaut; Claude Carlet; Pascale Charpin; Caroline Fontaine

    2000-01-01

    We investigate the link between the nonlinearity of a Boolean function and its propagation characteristics. We prove that highly nonlin- ear functions usually have good propagation properties regarding dier- ent criteria. Conversely, any Boolean function satisfying the propagation criterion with respect to a linear subspace of codimension 1 or 2 has a high nonlinearity. We also point out that most

  20. Interference Characteristics Of Microwave Ovens in Indoor Radio Communications

    Microsoft Academic Search

    J. Y. C. Cheah

    1991-01-01

    The scarcity of suitable radio spectrum for indoor radio communications under the regulatory constraints has prompted endeavors to investigate means of utilizing the valuable channel bandwidths available within these constraints. The interference potential of the microwave oven is characterized in an attempt to render the ISM band it occupied useful for indoor radio communications. The Characterization process included an in-depth

  1. Twisted Gaussian Schell-model beams: II. Spectrum analysis and propagation characteristics

    Microsoft Academic Search

    K. Sundar; R. Simon; N. Mukunda

    1993-01-01

    Extending the work of part I of this series, the authors analyze the structure of the eigenvalue spectrum as well as the propagation characteristics of the twisted Gaussian Schell-model beams. The manner in which the twist phase affects the spectrum, and hence the positivity property of the cross-spectral density, is brought out. Propagation characteristics of these beams are simply deduced

  2. Stochastic relation between anomalous propagation in the line-of-sight VHF radio band and occurrences of earthquakes

    NASA Astrophysics Data System (ADS)

    Motojima, K.; Haga, N.

    2013-11-01

    This paper was intended to find out any relation between anomalous line-of-sight propagation on the VHF band and occurrences of earthquakes near the VHF propagation paths. The television and FM radio broadcasting waves on the VHF band were monitored continuously over the long term. For that purpose, a multidirectional VHF band monitoring system was established and utilized. Anomalous line-of-sight propagation on the VHF band was distinguished from the monitored wave by using a statistical analysis. After the stochastic consideration, it was found out that earthquakes associated with anomalous propagation were characterized by magnitude of earthquakes M ? 4.5, and distances from epicenters L ? 75 km. The anomalous propagation was monitored on the VHF band a few days earlier the associated earthquakes occurred. Moreover, the anomaly appeared on multidirectional propagation paths simultaneously. The anomaly on the line-of-sight propagation indicates possibility of narrow focusing the area of epicenter of earthquake.

  3. Stochastic relation between anomalous propagation in the line-of-sight VHF radio band and occurrences of earthquakes

    NASA Astrophysics Data System (ADS)

    Motojima, K.; Haga, N.

    2014-08-01

    This paper was intended to find out any relation between anomalous line-of-sight propagation on the very high frequency (VHF) band and occurrences of earthquakes near the VHF propagation paths. The television and FM radio broadcasting waves on the VHF band were monitored continuously over the long term. For that purpose, a multidirectional VHF band monitoring system was established and utilized. Anomalous line-of-sight propagation on the VHF band was distinguished from the monitored wave by using a statistical analysis. After the stochastic consideration, it was found out that earthquakes associated with anomalous propagation were characterized by magnitude of earthquakes M ? 4.5, and distances from epicenters L ? 75 km. The anomalous propagation was monitored on the VHF band a few days before the associated earthquakes occurred. Moreover, the anomaly appeared on multidirectional propagation paths simultaneously. The anomaly on the line-of-sight propagation indicates the possibility of narrowly focusing the area of the epicenter of earthquake.

  4. HF Radio Wave Propagation in the Ionosphere Observed with the ePOP RRI (Radio Receiver Instrument) -- SuperDARN Experiment

    NASA Astrophysics Data System (ADS)

    Hussey, G. C.; Gillies, R. G.; Ridley, C. G.; Yau, A. W.; McWilliams, K. A.; Sofko, G. J.

    2014-12-01

    The Radio Receiver Instrument (RRI) on the enhanced Polar Outflow Probe (ePOP) scientific payload of the recently launched CSA (Canadian Space Agency) CASSIOPE (Cascade Demonstrator Small-Sat and Ionospheric Polar Explorer) satellite mission and the Super Dual Auroral Radar Network (SuperDARN) of HF radars have successfully executed a number of experiments since the launch of ePOP in late September, 2013. This presentation investigates the propagation delays and timing associated with HF radio waves transversing the plasma in the terrestrial ionosphere. Both the relative and absolute timing of the co-ordinated SuperDARN-RRI experiments will be presented. This knowledge is essential for interpreting HF radio wave propagation effects such as range accuracy, mode-splitting and timing, Doppler shift, and delayed 'echo' signatures, for example.

  5. Characteristics of beyond-the-horizon radio transmission

    Microsoft Academic Search

    K. Bullington

    1955-01-01

    During the past five years, it has been definitely established that useful radio signals at all frequencies can be received consistently at distances far beyond the horizon. These facts have forced a considerable modification of the theories, concepts and charts found in most textbooks and handbooks. Even more important, these facts have opened up many interesting radio possibilities, particularly in

  6. Review on terrestrial propagation channel modelling

    Microsoft Academic Search

    M. S. Pontes; L. A. R. Silva Mello

    2010-01-01

    Design and implementation of wireless systems, comprising mobile and fixed radios, requires the knowledge of the propagation characteristics of the channel. The random nature of the radio channel parameters and the complexity of the propagation phenomena suggest that characterization of the channel can be achieved based on statistical analysis of field measurements. This approach leads to statistical and empirical models

  7. Investigating raindrop shapes, oscillation modes, and implications for radio wave propagation

    NASA Astrophysics Data System (ADS)

    Thurai, M.; Bringi, V. N.; Mani?, A. B.; Ĺ ekelji?, N. J.; Notaroš, B. M.

    2014-10-01

    Studies of raindrop shapes, oscillation modes, and implications for radio wave propagation are presented. Drop shape measurements in natural rain using 2-D video disdrometers (2DVDs) are discussed. As a representative exception to vast majority of the cases where the "most probable" shapes conform to the axisymmetric (2,0) oscillation mode, an event with a highly organized line convection embedded within a larger rain system is studied. Measurements using two collocated 2DVD instruments and a C-band polarimetric radar clearly show the occurrence of mixed-mode drop oscillations within the line, which in turn is attributed to sustained drop collisions. Moreover, the fraction of asymmetric drops determined from the 2DVD camera data increases with the calculated collision probability when examined as time series. Recent wind-tunnel experiments of drop collisions are also discussed. They show mixed-mode oscillations, with (2,1) and (2,2) modes dramatically increasing in oscillation amplitudes, in addition to the (2,0) mode, immediately upon collision. The damping time constant of the perturbation caused by the collision is comparable to the inverse of the collision frequency within the line convection. Scattering calculations using an advanced method of moments numerical technique are performed to accurately and efficiently determine the pertinent parameters of electrically large oscillating raindrops with asymmetric shapes needed for radio wave propagation. The simulations show that the scattering matrix and differential reflectivity of drops are dependent on the particular oscillation modes and different time instants within the oscillation cycle. The technique can be utilized in conjunction with 3-D reconstruction of drop shapes from 2DVD data.

  8. Propagation characteristics of magnetoelastic waves in amorphous wires

    SciTech Connect

    Masuda, S.; Yamada, T.; Mochida, H.; Kakuno, K. (Yokohama City Univ. (Japan))

    1988-06-01

    The authors previously reported that when magnetoelastic waves propagate in as quenched amorphous wires, the main wave (MW) propagating directly from the source is accompanied by an anomalous wave (AW) with an irregular waveform, and that this AW seems to occur as the result of scattering of the MW in the amorphous wire. In this paper they report the results of experimental studies on the mechanism of AW generation, as well as information on the internal structure of the amorphous wire obtained from the waveforms of the AW.

  9. Contrasting Characteristics between the Northward and Eastward Propagation of the Intraseasonal Oscillation during the Boreal Summer

    Microsoft Academic Search

    Huang-Hsiung Hsu; Chun-Hsiung Weng; Cheng-Han Wu

    2004-01-01

    This study investigates the structural and evolutionary characteristics of the eastward- and northward-propagating intraseasonal oscillation (ISO) in the Indian Ocean and western Pacific during the boreal summer. Along the equator, the near-surface moisture convergence located to the east of the deep convection region appears to result in the eastward propagation of the ISO, consistent with the frictional wave CISK (conditional

  10. Experimental studies of indoor propagation characteristics of a smart antenna system at 1.8 GHz

    Microsoft Academic Search

    Adnan Kavak; Weidong Yang; Sang-Youb Kim; Kapil R. Dandekar; Guanghan Xu

    1999-01-01

    Smart antenna systems are becoming practical for indoor applications such as wireless local area networks. However, the challenging indoor propagation environment is one of biggest obstacles for designing smart antenna wireless networks. In order to fully understand and characterize channel propagation characteristics or vector channels of smart antenna systems in indoor environments, experiments are conducted using a 1.8 GHz real-time

  11. SHS combustion characteristics of several ceramics and intermetallic compounds. [Self-propagating High-temperature Synthesis

    Microsoft Academic Search

    Atsushi Makino; C. K. Law

    1994-01-01

    Extensive comparisons have been conducted between experimental and theoretical results for the SHS combustion characteristics of a number of solid-solid systems. The heterogeneous flame propagation theory describes a premixed mode of bulk flame propagation supported by the nonpremixed reaction of dispersed nonmetal (or higher melting point metal) particles in the liquid metal, with finite-rate reaction at the particle surface and

  12. Statistical modeling of the indoor radio channel at 10 GHz through propagation measurements .I. Narrow-band measurements and modeling

    Microsoft Academic Search

    Ayman F. Abouraddy; Said M. Elnoubi

    2000-01-01

    The aim of this paper is to report the results of a propagation measurement experiment to reach a statistical model of the indoor radio channel at 10 GHz using directive antennas at both terminals. The measurements were conducted on a floor of a university building. The distribution of the received fading envelope was tested to fit the Rayleigh and Rician

  13. The effect of the troposphere on radio wave propagation in a ground-satellite-ground communications system

    Microsoft Academic Search

    S. Ogulewicz

    1979-01-01

    The principal effects of the troposphere on radio wave propagation at centimeter wavelengths are described, with emphasis on space communications systems operating at frequencies above 10 GHz. These effects include: absorption by atmospheric gases, absorption and scattering by hydrometeors, noise emission from absorbing media, antenna beam divergence due to normal refraction, slow fading due to large-scale variations of refractive index,

  14. Characteristics and Problems of the Gifted: neural propagation depth and

    E-print Network

    Toint, Philippe

    differences in potential achievement between men and women. The sociological observations of an "old boys to explain these traits: neural propagation depth. The hypothesis is that in more intelligent brains. However, it is much less obvious why such an exceedingly small number of women have reached the highest

  15. Nonlinearity and Propagation Characteristics of Balanced Boolean Functions

    E-print Network

    Seberry, Jennifer

    author by A49130102, and the third author by A49232172. 1 #12;Key Words Bent Functions, Boolean Function that bent functions possess the highest nonlinearity and satisfy the propagation criterion with respect to all non-zero vectors Dil72]. However two drawbacks of bent functions prohibit their direct

  16. Utilizing a TDRS satellite for direct broadcast satellite-radio propagation experiments and demonstrations

    NASA Technical Reports Server (NTRS)

    Hollansworth, James E.

    1993-01-01

    The NASA/VOA Direct Broadcast Satellite - Radio (DBS-R) Program will be using a NASA Tracking Data Relay Satellite (TDRS) at 62 deg West longitude to conduct live satellite S-band propagation experiments and demonstrations of satellite sound broadcasting over the next two years (1993-1994). The NASA/VOA DBS-R program has applied intensive effort to garner domestic and international support for the DBS-R concept. An S-band DBS-R allocation was achieved for Region 2 at WARC-92 held in Spain. With this allocation, the DBS-R program now needs to conduct S-band propagation experiments and systems demonstrations that will assist in the development of planning approaches for the use of Broadcast Satellite Service (Sound) frequency bands prior to the planning conference called for by WARC-92. These activities will also support receiver concept development applied to qualities ranging from AM to Monophonic FM, Stereophonic FM, Monophonic CD, and Stereophonic CD quality.

  17. Utilizing a TDRS satellite for direct broadcast satellite-radio propagation experiments and demonstrations

    NASA Technical Reports Server (NTRS)

    Hollansworth, James E.

    1993-01-01

    The NASA/VOA Direct Broadcast Satellite - Radio (DBS-R) Program will be using a NASA Tracking Data Relay Satellite (TDRS) satellite at 62 deg West longitude to conduct live satellite S-band propagation experiments and demonstrations of satellite sound broadcasting over the next two years (1993-1994). The NASA/VOA DBS-R program has applied intensive effort to garner domestic and international support for the DBS-R concept. An S-band DBS-R allocation was achieved for Region 2 at WARC-92 held in Spain. With this allocation, the DBS-R program now needs to conduct S-band propagation experiments and systems demonstrations that will assist in the development of planning approaches for the use of Broadcast Satellite Service (Sound) frequency bands prior to the planning conference called for by WARC-92. These activities will also support receiver concept development applied to qualities ranging from AM to Monophonic FM, Stereophonic FM, Monophonic CD, and Stereophonic CD quality.

  18. Full-wave computation of characteristics of VHF radio link over random and nonstationary irregular terrain

    Microsoft Academic Search

    M. Le Palud; CREE St-Cyr

    2002-01-01

    Previously we described a method, based on a parabolic equation algorithm, for the computation of the impulse response of stationary deterministic channels. We focus now on random and nonstationary situations, extending our former approach to give efficient predictions when the propagation environment is partially undetermined and\\/or fluctuating with time. In the case of a radio link over a random irregular

  19. Dynamic characteristic of intense short microwave propagation in an atmosphere

    SciTech Connect

    Yee, J.H.; Alvarez, R.A.; Mayhall, D.J.; Madsen, N.K.; Cabayan, H.S.

    1983-07-01

    The dynamic behavior of an intense microwave pulse which propagates through the atmosphere will be presented. Our theoretical results are obtained by solving Maxwell's equations, together with the electron fluid equations. Our calculations show that although large portions of the initial energy are absorbed by the electrons that are created through the avalanche process, a significant amount of energy is still able to reach the earth's surface. The amount of energy that reaches the earth's surface as a function of initial energy and wave shape after having propagated through 100 km in the atmosphere are investigated. Results for the air breakdown threshold intensity as a function of the pressure for different pulse widths and different frequencies will also be presented. In addition, we will present a comparison between the theoretical and the experimental results for the pulse shape of a short microwave pulse after it has traveled through a rectangular wave guide which contains a section of air. 23 references, 9 figures.

  20. Nonlinearly Balanced Boolean Functions and Their Propagation Characteristics (Extended Abstract)

    Microsoft Academic Search

    Jennifer Seberry; Xian-mo Zhang; Yuliang Zheng

    1993-01-01

    Three of the most important criteria for cryptographically strong Boolean functions are the balancedness, the nonlinearity\\u000a and the propagation criterion. This paper studies systematic methods for constructing Boolean functions satisfying some or\\u000a all of the three criteria. We show that concatenating, splitting, modifying and multiplying sequences can yield balanced Boolean\\u000a functions with a very high nonlinearity. In particular, we show

  1. RADIO BURSTS WITH EXTRAGALACTIC SPECTRAL CHARACTERISTICS SHOW TERRESTRIAL ORIGINS

    SciTech Connect

    Burke-Spolaor, S.; Bailes, Matthew [Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail H39, P.O. Box 218, Hawthorn VIC 3122 (Australia); Ekers, Ronald [CSIRO Australia Telescope National Facility, P.O. Box 76, Epping NSW 1710 (Australia); Macquart, Jean-Pierre [ICRAR/Curtin Institute of Radio Astronomy, GPO Box U1987, Perth WA 6845 (Australia); Crawford, Fronefield III, E-mail: sburke@astro.swin.edu.au [Department of Physics and Astronomy, Franklin and Marshall College, Lancaster, PA 17604 (United States)

    2011-01-20

    Three years ago, the report of a solitary radio burst was thought to be the first discovery of a rare, impulsive event of unknown extragalactic origin. The extragalactic interpretation was based on the swept-frequency nature of the event, which followed the dispersive delay expected from an extragalactic pulse. We report here on the detection of 16 pulses, the bulk of which exhibit a frequency sweep with a shape and magnitude resembling the Lorimer Burst. These new events were detected in a sidelobe of the Parkes Telescope and are of clearly terrestrial origin, with properties unlike any known sources of terrestrial broadband radio emission. The new detections cast doubt on the extragalactic interpretation of the original burst, and call for further sophistication in radio-pulse survey techniques to identify the origin of the anomalous terrestrial signals and definitively distinguish future extragalactic pulse detections from local signals. The ambiguous origin of these seemingly dispersed, swept-frequency signals suggests that radio-pulse searches using multiple detectors will be the only experiments able to provide definitive information about the origin of new swept-frequency radio burst detections.

  2. Spectral characteristic evolution: a new algorithm for gravitational wave propagation

    NASA Astrophysics Data System (ADS)

    Handmer, Casey J.; Szilágyi, Béla

    2015-01-01

    We present a spectral algorithm for solving the full nonlinear vacuum Einstein field equations in the Bondi framework. Developed within the Spectral Einstein Code, we demonstrate spectral characteristic evolution as a technical precursor to Cauchy characteristic extraction, a rigorous method for obtaining gauge-invariant gravitational waveforms from existing and future astrophysical simulations. We demonstrate the new algorithm's stability, convergence, and agreement with existing evolution methods. We explain how an innovative spectral approach enables a two orders of magnitude improvement in computational efficiency.

  3. Authentication of Radio Frequency Identification Devices Using Electronic Characteristics

    ERIC Educational Resources Information Center

    Chinnappa Gounder Periaswamy, Senthilkumar

    2010-01-01

    Radio frequency identification (RFID) tags are low-cost devices that are used to uniquely identify the objects to which they are attached. Due to the low cost and size that is driving the technology, a tag has limited computational capabilities and resources. This limitation makes the implementation of conventional security protocols to prevent…

  4. Automated Classification of Spatiotemporal Characteristics of Gastric Slow Wave Propagation

    PubMed Central

    Paskaranandavadivel, Niranchan; Gao, Jerry; Du, Peng; O'Grady, Gregory; Cheng, Leo K.

    2014-01-01

    Gastric contractions are underpinned by an electrical event called slow wave activity. High-resolution electrical mapping has recently been adapted to study gastric slow waves at a high spatiotemporal detail. As more slow wave data becomes available, it is becoming evident that the spatial organization of slow wave plays a key role in the initiation and maintenance of gastric dsyrhythmias in major gastric motility disorders. All of the existing slow wave signal processing techniques deal with the identification and partitioning of recorded wave events, but not the analysis of the slow wave spatial organization, which is currently performed visually. This manual analysis is time consuming and is prone to observer bias and error. We present an automated approach to classify spatial slow wave propagation patterns via the use of Pearson cross correlations. Slow wave propagations were grouped into classes based on their similarity to each other. The method was applied to high-resolution gastric slow wave recordings from four pigs. There were significant changes in the velocity of the gastric slow wave wavefront and the amplitude of the slow wave event when there was a change in direction to the slow wave wavefront during dsyrhythmias, which could be detected with the automated approach. PMID:24111441

  5. [Monitoring of Crack Propagation in Repaired Structures Based on Characteristics of FBG Sensors Reflecting Spectra].

    PubMed

    Yuan, Shen-fang; Jin, Xin; Qiu, Lei; Huang, Hong-mei

    2015-03-01

    In order to improve the security of aircraft repaired structures, a method of crack propagation monitoring in repaired structures is put forward basing on characteristics of Fiber Bragg Grating (FBG) reflecting spectra in this article. With the cyclic loading effecting on repaired structure, cracks propagate, while non-uniform strain field appears nearby the tip of crack which leads to the FBG sensors' reflecting spectra deformations. The crack propagating can be monitored by extracting the characteristics of FBG sensors' reflecting spectral deformations. A finite element model (FEM) of the specimen is established. Meanwhile, the distributions of strains which are under the action of cracks of different angles and lengths are obtained. The characteristics, such as main peak wavelength shift, area of reflecting spectra, second and third peak value and so on, are extracted from the FBGs' reflecting spectral which are calculated by transfer matrix algorithm. An artificial neural network is built to act as the model between the characteristics of the reflecting spectral and the propagation of crack. As a result, the crack propagation of repaired structures is monitored accurately and the error of crack length is less than 0.5 mm, the error of crack angle is less than 5 degree. The accurately monitoring problem of crack propagation of repaired structures is solved by taking use of this method. It has important significance in aircrafts safety improvement and maintenance cost reducing. PMID:26117887

  6. The Relation Between Large-Scale Coronal Propagating Fronts and Type II Radio Bursts

    NASA Astrophysics Data System (ADS)

    Nitta, Nariaki V.; Liu, Wei; Gopalswamy, Nat; Yashiro, Seiji

    2014-12-01

    Large-scale, wave-like disturbances in extreme-ultraviolet (EUV) and type II radio bursts are often associated with coronal mass ejections (CMEs). Both phenomena may signify shock waves driven by CMEs. Taking EUV full-disk images at an unprecedented cadence, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory has observed the so-called EIT waves or large-scale coronal propagating fronts (LCPFs) from their early evolution, which coincides with the period when most metric type II bursts occur. This article discusses the relation of LCPFs as captured by AIA with metric type II bursts. We show examples of type II bursts without a clear LCPF and fast LCPFs without a type II burst. Part of the disconnect between the two phenomena may be due to the difficulty in identifying them objectively. Furthermore, it is possible that the individual LCPFs and type II bursts may reflect different physical processes and external factors. In particular, the type II bursts that start at low frequencies and high altitudes tend to accompany an extended arc-shaped feature, which probably represents the 3D structure of the CME and the shock wave around it, and not just its near-surface track, which has usually been identified with EIT waves. This feature expands and propagates toward and beyond the limb. These events may be characterized by stretching of field lines in the radial direction and may be distinct from other LCPFs, which may be explained in terms of sudden lateral expansion of the coronal volume. Neither LCPFs nor type II bursts by themselves serve as necessary conditions for coronal shock waves, but these phenomena may provide useful information on the early evolution of the shock waves in 3D when both are clearly identified in eruptive events.

  7. Spectral Characteristic Evolution: A New Algorithm for Gravitational Wave Propagation

    E-print Network

    Casey J. Handmer; Béla Szilágyi

    2014-09-24

    We present a spectral algorithm for solving the full nonlinear vacuum Einstein field equations in the Bondi framework. Developed within the Spectral Einstein Code (SpEC), we demonstrate spectral characteristic evolution as a technical precursor to Cauchy Characteristic Extraction (CCE), a rigorous method for obtaining gauge-invariant gravitational waveforms from existing and future astrophysical simulations. We demonstrate the new algorithm's stability, convergence, and agreement with existing evolution methods. We explain how an innovative spectral approach enables a two orders of magnitude improvement in computational efficiency.

  8. Characteristics of Radio-Frequency Circuits Utilizing Ferroelectric Capacitors

    NASA Technical Reports Server (NTRS)

    Eskridge, Michael; Gui, Xiao; MacLeod, Todd; Ho, Fat D.

    2011-01-01

    Ferroelectric capacitors, most commonly used in memory circuits and variable components, were studied in simple analog radio-frequency circuits such as the RLC resonator and Colpitts oscillator. The goal was to characterize the RF circuits in terms of frequency of oscillation, gain, etc, using ferroelectric capacitors. Frequencies of oscillation of both circuits were measured and studied a more accurate resonant frequency can be obtained using the ferroelectric capacitors. Many experiments were conducted and data collected. A model to simulate the experimental results will be developed. Discrepancies in gain and frequency in these RF circuits when conventional capacitors are replaced with ferroelectric ones were studied. These results will enable circuit designers to anticipate the effects of using ferroelectric components in their radio- frequency applications.

  9. Fundamental Characteristics of Electromagnetic Wave Propagation in Non-reflection Coaxial Waveguide

    NASA Astrophysics Data System (ADS)

    Yuasa, Sadayuki; Fujihara, Hirotake; Okabe, Shigemitsu

    Recently, diagnosis of gas insulated switchgears (GIS) is important because number of aged GIS is increasing and maintenance method of GIS is changing from TBM (Time Based Maintenance) to CBM (Condition Based Maintenance). In this paper, the mechanism of electromagnetic wave propagation in a GIS tank is investigated for understanding of fundamental characteristics for partial discharge detection using UHF method. In this paper, the output characteristics of UHF sensor in non-reflection coaxial waveguide are obtained under the various parameters of installation and shape of UHF sensor. The mechanism of electromagnetic wave propagation is investigated with comparison of the experimental result and EMTP (Electro-Magnetic Transients Program) analysis of equivalent circuit. In consequence, it is found that the mechanism of electromagnetic wave propagation can be treated as an equivalent electric circuit in the frequency region below cutoff frequency of TE11 mode, and another mechanism of electromagnetic wave with higher mode dominantly propagates.

  10. Evaluation of the multipath characteristics of the impulse radio channel

    Microsoft Academic Search

    R. Jean-Marc Cramer; Moe Z. Win; Robert A. Scholtz

    1998-01-01

    In order to estimate the performance of impulse radio communication systems, a characterization of the channel is required. In particular, knowledge of the multipath angle and time-of-arrival distributions is useful for predicting the performance of diversity reception schemes. In this paper, the CLEAN algorithm is applied to ultra-wide bandwidth (UWB) signals received on an array of sensors in order to

  11. Characteristics of self-propagating reaction in TiN combustion synthesis

    Microsoft Academic Search

    Hiroshi Kudo; Osamu Odawara

    1989-01-01

    The characteristics of the combustion synthesis of TiN are investigated through a self-propagating reaction of titanium powder compacts of specific packing density (40% to 60% theoretical one) in the presence of flowing nitrogen gas (0.01 m3 min-1) under atmospheric pressure. It was found that the propagating velocity of the combustion wave became slower with increasing packing density. The conversion ratio

  12. Adaptation of model parameters of VLF radio signals phase variations on the Novosibirsk-Yakutsk propagation path

    NASA Astrophysics Data System (ADS)

    Korsakov, Alexey A.; Kozlov, Vladimir I.; Mullayarov, Viktor A.; Karimov, Rustam R.

    2014-11-01

    Phase variations and sudden phase anomalies (SPA) VLF signals registered in Yakutsk from Novosibirsk radio station (14.9 kHz) for summer and winter daytime propagation conditions are considered. The threshold SPA sensitivity by Xrays flux P depends on the season weakly. SPA magnitude at fixed solar zenith angle X and X-ray flux P from summer to winter on the Novosibirsk - Yakutsk path is increased, SPA dependence on averaged along the propagation path of the cosine solar zenith angle is sharper in summer. X-ray flux is estimated according to the phase variations of the Novosibirsk radio signals. A satisfactory agreement with the simulated flux data from the satellite has been obtained booth in SPA, and unperturbed daytime conditions.

  13. The directional propagation characteristics of elastic wave in two-dimensional thin plate phononic crystals

    NASA Astrophysics Data System (ADS)

    Wen, Jihong; Yu, Dianlong; Wang, Gang; Zhao, Honggang; Liu, Yaozong; Wen, Xisen

    2007-04-01

    The directional propagation characteristics of elastic wave during pass bands in two-dimensional thin plate phononic crystals are analyzed by using the lumped-mass method to yield the phase constant surface. The directions and regions of wave propagation in phononic crystals for certain frequencies during pass bands are predicted with the iso-frequency contour lines of the phase constant surface, which are then validated with the harmonic responses of a finite two-dimensional thin plate phononic crystals with 16×16 unit cells. These results are useful for controlling the wave propagation in the pass bands of phononic crystals.

  14. Low Altitude Propagation Effects — A Validation Study of the Advanced Propagation Model (APM) for Mobile Radio Applications

    Microsoft Academic Search

    Amalia E. Barrios; Kenneth Anderson; Gary Lindem

    2006-01-01

    VHF signal strength data from two NOAA weather radio transmitters, located in southern California and southwestern Arizona, were collected over a wide range of topography ranging from relatively flat to mountainous terrain. Signal strength data were collected using a mobile receiver traveling from 20 km to over 100 km, with the receiving antenna at a constant height of 2.2 meters

  15. Further Steps Towards the Development of a Hardware Simulator for MIMO Radio Channels

    E-print Network

    Paris-Sud XI, Université de

    of the radio propagation channel. Moreover, after the realization of a communication system, its experimental be used to compare the performance of various radio communication systems in a time-variant propagation The development of a radio communication system requires the knowledge of the main characteristics

  16. Fundamental Characteristics of Electromagnetic Wave Propagation in Non-reflection Coaxial Waveguide (2)

    Microsoft Academic Search

    Hirotake Fujihara; Sadayuki Yuasa; Shigemitsu Okabe

    2004-01-01

    It is necessary to consider the TEM-mode, the higher TE and TM-mode and resonance phenomena in GIS to describe the propagation and detection characteristics for partial discharge measured with the UHF-method. Measurements on the non-reflection coaxial wave-guide simulating GIS were carried out with changing installation and shape of UHF sensor and wave-guide length. This paper describes the output characteristics of

  17. Propagation characteristics of a Gaussian laser beam in plasma with modulated collision frequency

    SciTech Connect

    Wang Ying; Yuan Chengxun; Zhou Zhongxiang; Gao Ruilin [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); Li Lei; Du Yanwei [Shanghai Key Laboratory of Space Intelligent Control Technology, Shanghai 201108 (China)

    2012-08-15

    The propagation characteristics of a Gaussian laser beam in cold plasma with the electron collision frequency modulated by laser intensity are presented. The nonlinear dynamics of the ponderomotive force, which induce nonlinear self-focusing as opposed to spatial diffraction, are considered. The effective dielectric function of the Drude model and complex eikonal function are adopted in deriving coupled differential equations of the varying laser beam parameters. In the framework of ponderomotive nonlinearity, the frequency of electron collision in plasmas, which is proportional to the spatial electron density, is strongly interrelated with the laser beam propagation characteristics. Hence, the propagation properties of the laser beam and the modulated electron collision frequency distribution in plasma were studied and explained in depth. Employing this self-consistent method, the obtained simulation results approach practical conditions, which is of significance to the study of laser-plasma interactions.

  18. Complex-wall effect on propagation characteristics and MIMO capacities for an indoor wireless communication environment

    Microsoft Academic Search

    Zhengqing Yun; Magdy F. Iskander; Zhijun Zhang

    2004-01-01

    The effects of complex wall structures on the characteristics of fading and the capacity of multi-input multi-output (MIMO) wireless communication systems for some typical indoor propagation environments are investigated. Two cases of wall structures are examined in this paper. In the first case, the walls are considered to be homogenous solid slabs, while, in the second case, the walls are

  19. Fundamental Characteristics of Electromagnetic Wave Propagation in Non-reflection Coaxial Waveguide

    Microsoft Academic Search

    Sadayuki Yuasa; Hirotake Fujihara; Shigemitsu Okabe

    2004-01-01

    Recently, diagnosis of gas insulated switchgears (GIS) is important because number of aged GIS is increasing and maintenance method of GIS is changing from TBM (Time Based Maintenance) to CBM (Condition Based Maintenance). In this paper, the mechanism of electromagnetic wave propagation in a GIS tank is investigated for understanding of fundamental characteristics for partial discharge detection using UHF method.

  20. Measured path loss and multipath propagation characteristics in UHF and microwave frequency bands for urban mobile communications

    Microsoft Academic Search

    Yasuhiro Oda; Reiko Tsuchihashi; Kouichi Tsunekawa; Masaharu Hata

    2001-01-01

    This paper presents the frequency dependence of propagation loss and multipath propagation characteristics for urban mobile communications based on measurement results in Japanese urban areas. Path loss in reference frequencies from 457.2 MHz to 15.45 GHz increases according to the free space propagation power law in terms of frequency dependence for both macrocell and microcell environments. The standard deviation of

  1. Frequency characteristics of the action of powerful radio-frequency radiation on the ionospheric F layer

    SciTech Connect

    Erukhimov, L.M.; Ivanov, V.A.; Mityakov, N.A.; Uryadov, V.P.; Frolov, V.A.; Shumaev, V.V.

    1988-03-01

    The results of an investigation of the effect of artificial ionospheric nonuniformities on the characteristics of LFM signals with vertical and oblique sounding of the ionosphere are presented. A classification of the effects observed on ionograms from vertical and oblique-sounding LFM ionosonde, owing to the effect of artificial nonuniformities of different scale, is given. It was found that powerful beams of radio waves have a characteristic effect on the ionospheric plasma under conditions when moving ionospheric disturbances appear.

  2. The effect of radio frequency plasma processing reactor circuitry on plasma characteristics

    Microsoft Academic Search

    Shahid Rauf; Mark J. Kushner

    1998-01-01

    Past experiments have demonstrated that details of the external electrical circuitry can strongly influence the performance of radio frequency (rf) plasma processing reactors. Seemingly minor changes in the circuit, such as changing cable lengths, can lead to significantly different plasma characteristics. To investigate these couplings, a plasma equipment model has been developed which consists of a linked reactor simulation and

  3. Long-term statistics related to evaporation duct propagation of 2 GHz radio waves in the English Channel

    NASA Astrophysics Data System (ADS)

    Gunashekar, S. D.; Warrington, E. M.; Siddle, D. R.

    2010-12-01

    This paper presents long-term statistics additional to those previously published pertaining to evaporation duct propagation of UHF radio waves in the British Channel Islands, with particular focus on a completely over-sea 50 km transhorizon path. The importance of the evaporation duct as an anomalous propagation mechanism in marine and coastal regions is highlighted. In particular, the influence of various atmospheric parameters on the performance of a popular operational evaporation duct model is examined. The strengths and weaknesses of this model are evaluated under specific atmospheric conditions. The relationship between the continually varying evaporation duct height and transmitter-receiver antenna geometries is analyzed, and a range of statistics related to the implications of this relationship on the received signal strength is presented. The various issues under investigation are of direct relevance in the planning of long-range, over-sea radio systems operating in the UHF band, and have implications for the radio regulatory work carried out by organizations such as the International Telecommunication Union.

  4. Quantum propagator and characteristic equation in the presence of a chain of ?-potentials

    NASA Astrophysics Data System (ADS)

    Refaei, A.; Kheirandish, F.

    2015-04-01

    The quantum propagator and characteristic equation in the presence of a chain of ?-potentials are obtained in the rectangular, cylindrical and spherical coordinate systems. The simplicity and efficiency of the method is illustrated via examples. As an application, the characteristic equation of a quantum harmonic oscillator confined to an infinite box is obtained. The roots of the characteristic equation, determining the energy eigenvalues of the restricted oscillator, are calculated approximately and compared with the existing numerical data. Due to the similarity between Schrödinger and diffusion equations, the problem can be considered as exact solutions of the diffusion equation in the presence of a chain of ?-potentials as boundary.

  5. Characteristics of Small-scale Gravity Wave Propagation in the Mesopause Region over Alaska

    NASA Astrophysics Data System (ADS)

    Kubota, M.; Yamaguchi, Y.; Kawamura, S.; Murayama, Y.; Kita, K.

    2014-12-01

    We investigated characteristics of the atmospheric gravity waves (AGWs) propagation using sodium airglow images obtained by an all-sky imager installed at Poker Flat Research Range (65.1N, 147.4W, MLAT 65.6) in Alaska. In this study, we developed data analysis programs which automatically derive the unambiguous 2-D power spectrum from the sodium airglow images, using a method by Coble et al. (1998). The power spectrums of the AGWs which have horizontal wavelengths between 2 - 400 km and periods up to 8 hours were obtained by these programs. Statistical study of the AGW data and mesospheric wind data by an MF radar during two winter seasons from October 2000 to April 2002 indicates the following characteristics. - During these periods, the AGW dominantly propagated westward in the zonal direction. - The meridional propagation direction frequently changed. This change seems to be explained by filtering effect by the mesospheric wind. - Total power of the AGW increased in December and January. In this paper, we discuss the relationship between these characteristics of the AGW propagation and unique phenomena in high-latitude region such as auroral precipitation. Acknowledgements This work is conducted as a part of "Alaska Project", the cooperative research project between NICT and Geophysical Institute of University of Alaska. Reference Coble, M. R., G. C. Papen, and C. S. Gardner, Computing two-dimensional unambiguous horizontal wavenumber spectra from OH airglow images, IEEE Trans. Geosci. and Remote Sens., 36, 368--382, 1998.

  6. Research of the atmosphere propagation characteristics of solar-blind ultraviolet communication

    NASA Astrophysics Data System (ADS)

    Chen, Junhong; Yang, Xiaoli

    2009-07-01

    Solar-Blind Ultraviolet Optics Communication is a new type of communication system in atmosphere optics communication fields. Its excellent performances such as safety, 24-hour service, anti-interference, non-line-of-sight, make it different from infrared optics communication. Hence, the solar-blind ultraviolet optics communication gratified the need of special and confidential communication in army. The atmosphere propagation characteristics of the solar-blind ultraviolet is still a difficulty of the communication system. In order to solve this problem, this paper majored on the influences of the solar-blind ultraviolet propagation by the absorption of ozone, the scattering of atmospheric molecule and aerosol.

  7. Radiowave propagation, building databases, and GIS: anything in common? A radio engineer's viewpoint

    Microsoft Academic Search

    Jean-Frédéric Wagen; Karim Rizk

    2003-01-01

    Mobile cellular communication has already entered the mass market, and mobile Internet services will soon become a reality. The frequent use of mobile radio technologies wherever people are has a direct impact on the deployment of base stations or radio access points, including antennas. Put simply, to serve an increasing number of users requires an increasing number of base stations.

  8. Characteristics of multiple filaments generated by femtosecond laser pulses in air: Prefocused versus free propagation

    SciTech Connect

    Hao Zuoqiang; Zhang Jie; Zhang Zhe; Zheng Zhiyuan; Lu Xin; Jin Zhan; Wang Zhaohua; Liu Yunquan [Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); Yuan Xiaohui [Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); State Key Laboratory of Transient Optics and Photonics, Xi'an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi'an 710068 (China); Zhong Jiayong [Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080 (China); National Astronomical Observatories, Chinese Academy of Science, Beijing 100012 (China)

    2006-12-15

    The characteristics of the multiple filaments formed by prefocused and freely propagating femtosecond laser pulses are investigated and compared. It is shown in our experiments that the diameter, length, stability, and interaction for the two cases can be quite different. The filaments formed by prefocused beam indicate dynamic spatial evolution with higher laser intensity and electron density. They have a typical diameter of 100 {mu}m are of shorter length. In the free propagation case, the filaments exhibit interesting properties such as hundred-meter propagation distance and mm-size diameter. Moreover, only the interaction of the filaments with the energy background affects the evolution of the filaments. Filament-filament interactions such as the filament splitting and merging were not observed in this case.

  9. Educational software tool based on a geographical information system (GIS) for radio wave propagation analysis

    Microsoft Academic Search

    Francisco J. Ponce; Fernando Martí Pallarés; Leandro Juan-Llácer; Narcís Cardona

    2001-01-01

    A tool is presented to evaluate and represent path loss, delay-spread, and the direction of arrival in graph form of each contribution considered in the propagation over buildings in urban scenarios. A geographical information system (GIS) and a ray-tracing technique are used in order to facilitate the understanding of the main propagation mechanisms in a more realistic environment, and the

  10. Clear-air propagation on line-of-sight radio paths: A review

    Microsoft Academic Search

    Erik T. Stephansen

    1981-01-01

    Recent progress in theoretical and experimental work on clear air propagation on line-of-sight paths is reviewed. Descriptions of the physical mechanisms involved, illustrations of the variability in time and in space of the phenomena, and descriptions of the modeling of the propagation are addressed. Absorption by atmospheric gases is dealt with briefly. Refractive index structures are mentioned as background information.

  11. Enhancement of electromagnetic propagation through complex media for Radio Frequency Identification

    E-print Network

    Marti, Uttara P

    2005-01-01

    In this thesis, I present and examine the fundamental limitations involved in Radio Frequency Identification (RFID) as well as provide a means to improve reader-tag communication in ultra high frequency RFID systems. The ...

  12. Propagation characteristics of extratropical planetary waves observed in the ATSR global sea surface temperature record

    Microsoft Academic Search

    Katherine L. Hill; Ian S. Robinson; Paolo Cipollini

    2000-01-01

    This paper examines the characteristics of planetary wave signatures that have been found in the Along Track Scanning Radiometer averaged sea surface temperature (ASST) record for 1991-1996. Longitude-time plots for every latitude between 5° and 50°, north and south, reveal westward propagating wave-like patterns at many locations, whose speed decreases with latitude like baroclinic Rossby waves. A two-dimensional Radon transform

  13. Characteristics of the partially coherent Gaussian Schell-model beam propagating in atmospheric turbulence

    Microsoft Academic Search

    Yaqing. Li; Zhensen. Wu; Rui. Wu; Jinpeng. Zhang

    2011-01-01

    Based on the extended Huygens-Fresnel principle, the expressions for effective beam parameter, beam size, angle spread, the variance of the angle-of-arrival fluctuation, and average intensity of the Gaussian Schell-model beam propagating on the level path through atmospheric turbulence are derived with the cross spectral density function of the beam employed, and the numerical results of these characteristic variables are presented.

  14. Geometric Localization and Polarimetric Localization: Space Weather Tools to Calculate CME Propagation Characteristics

    Microsoft Academic Search

    V. J. Pizzo; C. A. de Koning

    2008-01-01

    The geometric localization technique [Pizzo and Biesecker, 2004] utilizes a series of lines of sight from two space-based coronagraphs to determine gross propagation characteristics of coronal mass ejections (CMEs) in three-dimensional space. The polarimetric localization technique [Moran and Davila, 2004] uses the percent polarization observed by a single coronagraph to obtain a three-dimensional reconstruction of a CME. Both techniques can

  15. Measured Propagation Characteristics of Finite Ground Coplanar Waveguide on Silicon with a Thick Polyimide Interface Layer

    Microsoft Academic Search

    George E. Ponchakl; Edan Dalton; Andrew Bacon; John Papapolymerou; Emmanouil M. Tentzeris

    2002-01-01

    Measured propagation characteristics of Finite Ground Coplanar (FGC) waveguide on silicon substrates with resistivities spanning 3 orders of magnitude (0.1 to 15.6 Ohm cm) and a 20 żm thick polyimide interface layer are presented as a function of the FGC geometry. Results show that there is an optimum FGC geometry for minimum loss, and silicon with a resistivity of 0.1

  16. CHARACTERISTICS OF ELECTROMAGNETIC WAVE PROPAGATION IN BIAXIAL ANISOTROPIC LEFT-HANDED MATERIALS

    Microsoft Academic Search

    Wei Ding; Liang Chen; H. Liang

    2007-01-01

    Abstract—This paper investigates the characteristics of electromag- netic wave propagation in biaxially anisotropic left-handed materials (BA-LHMs) theoretically and numerically. We discuss under what con- ditions the anomalous refraction or reflection will occur at the interface when a plane wave passes from one isotropic right-handed material into another BA-LHM. Meanwhile the refraction angle of the wave vector and that of the

  17. The characteristics of atmospheric radio frequency discharges with frequency increasing at a constant power density

    SciTech Connect

    Zhang Yuantao; Li Qingquan; Lou Jie; Li Qingmin [School of Electrical Engineering, Shandong University, Jinan, Shandong Province 250061 (China)

    2010-10-04

    A computational model is used to investigate the characteristics of atmospheric radio frequency discharges by increasing frequency from 20 to 100 MHz at a constant power density. The simulation results show that increasing frequency can effectively enhance electron density before the transition frequency but after it the ignition is quenched then the electron density decreases. However this simulation also indicates the maximum time-averaged electron energy reduces monotonically with the excitation frequency increasing at a constant power density.

  18. Characteristics of radio-frequency atmospheric pressure dielectric-barrier discharge with dielectric electrodes

    NASA Astrophysics Data System (ADS)

    Hussain, S.; Qazi, H. I. A.; Badar, M. A.

    2014-03-01

    An experimental investigation to characterize the properties and highlight the benefits of atmospheric pressure radio-frequency dielectric-barrier discharge (rf DBD) with dielectric electrodes fabricated by anodizing aluminium substrate is presented. The current-voltage characteristics and millisecond images are used to distinguish the ? and ? modes. This atmospheric rf DBD is observed to retain the discharge volume without constriction in ? mode. Optical emission spectroscopy demonstrates that the large discharge current leads to more abundant reactive species in this plasma source.

  19. Characteristics of radio-frequency atmospheric pressure dielectric-barrier discharge with dielectric electrodes

    SciTech Connect

    Hussain, S., E-mail: shussain@uos.edu.pk, E-mail: shussainuos@yahoo.com; Qazi, H. I. A.; Badar, M. A. [Department of Physics, University of Sargodha, 40100 Sargodha (Pakistan)] [Department of Physics, University of Sargodha, 40100 Sargodha (Pakistan)

    2014-03-15

    An experimental investigation to characterize the properties and highlight the benefits of atmospheric pressure radio-frequency dielectric-barrier discharge (rf DBD) with dielectric electrodes fabricated by anodizing aluminium substrate is presented. The current-voltage characteristics and millisecond images are used to distinguish the ? and ? modes. This atmospheric rf DBD is observed to retain the discharge volume without constriction in ? mode. Optical emission spectroscopy demonstrates that the large discharge current leads to more abundant reactive species in this plasma source.

  20. End-to-End Network Simulation Using a Site-Specific Radio Wave Propagation Model

    SciTech Connect

    Djouadi, Seddik M [ORNL] [ORNL; Kuruganti, Phani Teja [ORNL] [ORNL; Nutaro, James J [ORNL] [ORNL

    2013-01-01

    The performance of systems that rely on a wireless network depends on the propagation environment in which that network operates. To predict how these systems and their supporting networks will perform, simulations must take into consideration the propagation environment and how this effects the performance of the wireless network. Network simulators typically use empirical models of the propagation environment. However, these models are not intended for, and cannot be used, to predict a wireless system will perform in a specific location, e.g., in the center of a particular city or the interior of a specific manufacturing facility. In this paper, we demonstrate how a site-specific propagation model and the NS3 simulator can be used to predict the end-to-end performance of a wireless network.

  1. Electromagnetic noise and radio wave propagation below 100 kHz in the Jovian atmosphere. I - The equatorial region

    NASA Technical Reports Server (NTRS)

    Rinnert, K.; Axford, W. I.; Lanzerotti, L. J.; Krider, E. P.; Uman, M. A.; Dehmel, G.; Gliem, F. O.

    1979-01-01

    The Galileo satellite program includes the delivery of an entry probe to the Jovian equatorial atmosphere in mid-1985. Optical and RF sensors for a lightning detection system are included as a part of the probe experimental payload. In this paper, calculations of the RF wave propagation and reflection characteristics of the equatorial Jovian atmosphere and ionosphere for frequencies less than 100 kHz are presented. It is shown that wave propagation is limited to line-of-sight and one-hop from the ionosphere. Results are also presented of a statistical treatment of the RF wave power densities for the case of a finite number of events and for the case of a uniformly distributed source. The results can be applied to specific RF experiment configurations concerned with establishing the statistical characteristics of Jovian lightning.

  2. Multipath delay spread and path loss correlation for 910MHz urban mobile radio propagation

    Microsoft Academic Search

    D. C. Cox

    1977-01-01

    Performance of some mobile radio systems is limited both by multipath delay spread and average path loss. This paper presents data indicating a low correlation between delay spread and path loss at 910 MHz for 100 small areas within a 2 × 2 ˝-km region. Some small areas with low path loss have large delay spread. The region extends from

  3. Radial-pulse propagation and impedance characteristics of optically shuttered channel intensifier tubes

    SciTech Connect

    Detch, J.L. Jr.; Noel, B.W.

    1981-01-01

    Electrically gated proximity-focused channel intensifier tubes are often used as optical shutters. Optimum nanosecond shuttering requires both understanding the electrical pulse propagation across the device structure and proper impedance matching. A distributed-transmission-line model is developed that describes analytically the voltage- and current-wave propagation characteristics as functions of time for any point on the surface. The optical gain's spatial uniformity and shutter-open times are shown to depend on the electrical pulse width and amplitude, and on the applied bias. The driving-point impedance is derived from the model and is expressed as a function of an infinite sum of terms in the complex frequency. The synthesis in terms of lumped-constant network elements is realized in first- and second-Foster equivalent circuits. Experimental impedance data are compared with the model's predictions and deviations from the ideal model are discussed.

  4. SHS combustion characteristics of several ceramics and intermetallic compounds. [Self-propagating High-temperature Synthesis

    SciTech Connect

    Makino, Atsushi (Shizuoka Univ., Hamamatsu (Japan). Dept. of Energy and Mechanical Engineering); Law, C.K. (Princeton Univ., NJ (United States). Dept. of Mechanical and Aerospace Engineering)

    1994-03-01

    Extensive comparisons have been conducted between experimental and theoretical results for the SHS combustion characteristics of a number of solid-solid systems. The heterogeneous flame propagation theory describes a premixed mode of bulk flame propagation supported by the nonpremixed reaction of dispersed nonmetal (or higher melting point metal) particles in the liquid metal, with finite-rate reaction at the particle surface and temperature-sensitive Arrhenius-type condensed-phase mass diffusivity. Systems examined are those of borides (TiB[sub 2], ZrB[sub 2], and HfB[sub 2]) and intermetallic compounds (NiAl, TiCo, and TiNi). By using a consistent set of physico-chemical parameters for these systems, satisfactorily quantitative agreement is demonstrated for the effects of mixture ratio, degree of dilution, and particle size on the burning velocity. Experimental flammability limits are also predicted by the theory.

  5. Sparsity-inspired nonparametric probability characterization for radio propagation in body area networks.

    PubMed

    Yang, Xiaodong; Yang, Shuyuan; Abbasi, Qammer Hussain; Zhang, Zhiya; Ren, Aifeng; Zhao, Wei; Alomainy, Akram

    2015-05-01

    Parametric probability models are common references for channel characterization. However, the limited number of samples and uncertainty of the propagation scenario affect the characterization accuracy of parametric models for body area networks. In this paper, we propose a sparse nonparametric probability model for body area wireless channel characterization. The path loss and root-mean-square delay, which are significant wireless channel parameters, can be learned from this nonparametric model. A comparison with available parametric models shows that the proposed model is very feasible for the body area propagation environment and can be seen as a significant supplement to parametric approaches. PMID:25014979

  6. Analysis of the Fourier split-step method for resolution of radio propagation over the sea

    Microsoft Academic Search

    Maxime Cayer; BBatrice Philibert; Michel Lecours; Denis Dion

    1994-01-01

    This method of solving the parabolic equation of propagation over the sea has proved the most popular on account of its performance in terms of computation time, and is equally well adapted to analysis in the presence of atmospheric ducts. The authors present an analysis of the method starting from the parabolic equation. They then show their implementation of the

  7. Schlieren Visualization of Acoustic Propagation Characteristics in a One-Dimensional Phononic Crystal

    NASA Astrophysics Data System (ADS)

    Jiang, Xue-Ping; Qian, Meng-Lu; Cheng, Qian

    2013-08-01

    The acoustic propagation characteristics of a finite one-dimensional water-glass phononic crystal (PC) are studied using the Schlieren visualization method, which is fast and non-invasive. The band structures of this PC are measured experimentally with continuous acoustic waves incident on it using the Schlieren method, and the results are highly consistent with the theoretical calculations. The dynamic acoustic field in the PC at different frequencies is imaged and the resonance phenomena in the components of the PC are observed. The results show that the Schlieren method is an effective means of studying the interactions between acoustic waves and PCs.

  8. On meteor-generated infrasound. [propagation characteristics during entry into earth atmosphere

    NASA Technical Reports Server (NTRS)

    Revelle, D. O.

    1976-01-01

    The characteristics of generation and propagation of infrasonic pressure waves excited during meteor entry into the earth's atmosphere are studied. Existing line source blast wave theory is applied to infrasonic airwave data from four bright fire-balls. It is shown that the strong shock behavior of the blast wave is confined to a cylinderical region with a radius proportional to the product of the meteor Mach number and its diameter. A description of the wave form far from the source is provided. Infrasonic data reported elsewhere are analyzed. All the results should be considered as preliminary, and additional work is under way to refine the estimates obtained.

  9. The effect of tropospheric layer structures on long-range VHF radio propagation

    Microsoft Academic Search

    Hsi-Tien Chang

    1971-01-01

    Long-distance radio communication at VHF is investigated by the waveguide mode theory taking into account the strong gradient, layered structure of the troposphere. A linear-segmented numerical method for the squared refractive index profile is developed to calculate the wave modes. This method reduces the reflection error from the discontinuities that occur in the conventional step-function approximation. The frequency at which

  10. Radiowave - Propagation

    Microsoft Academic Search

    Martin P. M. Hall; Leslie W. Barclay

    1989-01-01

    The effects of the earth atmosphere on the radio-wave propagation (RWP) and their implications for telecommunication systems are discussed in reviews based on lectures presented at the Second IEE Vacation School on Radiowave Propagation, held at the University of Surrey in September 1986. A general overview of propagation phenomena is presented, and particular attention is given to the theory of

  11. The High Latitude Ionosphere and its Effects on Radio Propagation, R. D. Hunsucker and J. K. Hargreaves, Cambridge University Press, xix + 617pp, 2003

    E-print Network

    The High Latitude Ionosphere and its Effects on Radio Propagation, R. D. Hunsucker and J. K emphasis on the high latitude ionosphere, the book contains much more. Indeed, it is a veritable compendium of ionosphere lore, data, and experimental and theoretical developments over the decades. Studies of the Earth

  12. Effects of laser parameters on propagation characteristics of laser-induced stress wave for gene transfer

    NASA Astrophysics Data System (ADS)

    Ando, Takahiro; Sato, Shunichi; Terakawa, Mitsuhiro; Ashida, Hiroshi; Obara, Minoru

    2010-02-01

    Laser-based gene delivery is attractive as a new method for topical gene therapy because of the high spatial controllability of laser energy. Previously, we demonstrated that an exogenous gene can be transferred to cells both in vitro and in vivo by applying nanosecond pulsed laser-induced stress waves (LISWs) or photomechanical waves (PMWs). In this study, we investigated effects of laser parameters on the propagation characteristics of LISWs in soft tissue phantoms and depth-dependent properties of gene transfection. Temporal pressure profiles of LISWs were measured with a hydrophone, showing that with a larger laser spot diameter, LISWs can be propagated more efficiently in phantoms with keeping flat wavefront. Phantoms with various thicknesses were placed on the rat dorsal skin that had been injected with plasmid DNA coding for reporter gene, and LISWs were applied from the top of the phantom. Efficient gene expression was observed in the rat skin that had interacted with LISWs propagating through a 15-mm-thick phantom. These results would be useful to determine appropriate laser parameters for gene delivery to deep-located tissue by transcutaneous application of LISWs.

  13. Polarization diversity for urban millimetric mobile radio communications: comparison of initial propagation measurement results with prediction

    Microsoft Academic Search

    H J Thomast; G L Siqueirat; R. S. Cole

    1992-01-01

    An experimental study of the propagation of vertical and horizontal polarized 55-GHz millimeter waves from a fixed transmitter to a mobile receiver in an urban environment is described. Ranges up to 400 m were used and measurements were obtained in the presence of traffic. Components transmitted received on orthogonal polarizations are uncorrelated. Cross coupling components are on average 10-20 dB

  14. An Evaluation of a Numerical Prediction Method for Electric Field Strength of Low Frequency Radio Waves based on Wave-Hop Ionospheric Propagation

    NASA Astrophysics Data System (ADS)

    Kitauchi, H.; Nozaki, K.; Ito, H.; Kondo, T.; Tsuchiya, S.; Imamura, K.; Nagatsuma, T.; Ishii, M.

    2014-12-01

    We present our recent efforts on an evaluation of the numerical prediction method of electric field strength for ionospheric propagation of low frequency (LF) radio waves based on a wave-hop propagation theory described in Section 2.4 of Recommendation ITU-R P.684-6 (2012), "Prediction of field strength at frequencies below about 150 kHz," made by International Telecommunication Union Radiocommunication Sector (ITU-R). As part of the Japanese Antarctic Research Expedition (JARE), we conduct on-board measurements of the electric field strengths and phases of LF 40 kHz and 60 kHz of radio signals (call sign JJY) continuously along both the ways between Tokyo, Japan and Syowa Station, the Japanese Antarctic station, at 69° 00' S, 39° 35' E on East Ongul Island, Lützow-Holm Bay, East Antarctica. The measurements are made by a newly developed, highly sensitive receiving system installed on board the Japanese Antarctic research vessel (RV) Shirase. We obtained new data sets of the electric field strength up to approximately 13,000-14,000 km propagation of LF JJY 40 kHz and 60 kHz radio waves by utilizing a newly developed, highly sensitive receiving system, comprised of an orthogonally crossed double-loop antenna and digital-signal-processing lock-in amplifiers, on board RV Shirase during the 55th JARE from November 2013 to April 2014. We have made comparisons between those on-board measurements and the numerical predictions of field strength for long-range propagation of low frequency radio waves based on a wave-hop propagation theory described in Section 2.4 of Recommendation ITU-R P.684-6 (2012) to show that our results qualitatively support the recommended wave-hop theory for the great-circle paths approximately 7,000-8,000 km and 13,000-14,000 km propagations.

  15. Back-propagation operation for analog neural network hardware with synapse components having hysteresis characteristics.

    PubMed

    Ueda, Michihito; Nishitani, Yu; Kaneko, Yukihiro; Omote, Atsushi

    2014-01-01

    To realize an analog artificial neural network hardware, the circuit element for synapse function is important because the number of synapse elements is much larger than that of neuron elements. One of the candidates for this synapse element is a ferroelectric memristor. This device functions as a voltage controllable variable resistor, which can be applied to a synapse weight. However, its conductance shows hysteresis characteristics and dispersion to the input voltage. Therefore, the conductance values vary according to the history of the height and the width of the applied pulse voltage. Due to the difficulty of controlling the accurate conductance, it is not easy to apply the back-propagation learning algorithm to the neural network hardware having memristor synapses. To solve this problem, we proposed and simulated a learning operation procedure as follows. Employing a weight perturbation technique, we derived the error change. When the error reduced, the next pulse voltage was updated according to the back-propagation learning algorithm. If the error increased the amplitude of the next voltage pulse was set in such way as to cause similar memristor conductance but in the opposite voltage scanning direction. By this operation, we could eliminate the hysteresis and confirmed that the simulation of the learning operation converged. We also adopted conductance dispersion numerically in the simulation. We examined the probability that the error decreased to a designated value within a predetermined loop number. The ferroelectric has the characteristics that the magnitude of polarization does not become smaller when voltages having the same polarity are applied. These characteristics greatly improved the probability even if the learning rate was small, if the magnitude of the dispersion is adequate. Because the dispersion of analog circuit elements is inevitable, this learning operation procedure is useful for analog neural network hardware. PMID:25393715

  16. Back-Propagation Operation for Analog Neural Network Hardware with Synapse Components Having Hysteresis Characteristics

    PubMed Central

    Ueda, Michihito; Nishitani, Yu; Kaneko, Yukihiro; Omote, Atsushi

    2014-01-01

    To realize an analog artificial neural network hardware, the circuit element for synapse function is important because the number of synapse elements is much larger than that of neuron elements. One of the candidates for this synapse element is a ferroelectric memristor. This device functions as a voltage controllable variable resistor, which can be applied to a synapse weight. However, its conductance shows hysteresis characteristics and dispersion to the input voltage. Therefore, the conductance values vary according to the history of the height and the width of the applied pulse voltage. Due to the difficulty of controlling the accurate conductance, it is not easy to apply the back-propagation learning algorithm to the neural network hardware having memristor synapses. To solve this problem, we proposed and simulated a learning operation procedure as follows. Employing a weight perturbation technique, we derived the error change. When the error reduced, the next pulse voltage was updated according to the back-propagation learning algorithm. If the error increased the amplitude of the next voltage pulse was set in such way as to cause similar memristor conductance but in the opposite voltage scanning direction. By this operation, we could eliminate the hysteresis and confirmed that the simulation of the learning operation converged. We also adopted conductance dispersion numerically in the simulation. We examined the probability that the error decreased to a designated value within a predetermined loop number. The ferroelectric has the characteristics that the magnitude of polarization does not become smaller when voltages having the same polarity are applied. These characteristics greatly improved the probability even if the learning rate was small, if the magnitude of the dispersion is adequate. Because the dispersion of analog circuit elements is inevitable, this learning operation procedure is useful for analog neural network hardware. PMID:25393715

  17. Morphology and scaling characteristics of propagating drying fronts in porous media delineated by neutron radiography

    NASA Astrophysics Data System (ADS)

    Shokri, N.; Sahimi, M.; Or, D.

    2011-12-01

    Improved understanding of fluid interface displacement in porous media is of considerable interest for various applications ranging from enhanced oil recovery to modeling of soil water flow and infiltration. The formation of fluid interfaces, their roughening and dynamics in porous media are influenced by the properties of the fluids and the transport properties of porous media, among other factors. We analyzed wettability effects on the dynamics and morphology of a primary drying front receding into a porous medium during stage 1 evaporation (i.e., liquid flow from drying front to evaporation plane at the surface). Neutron radiography images obtained at 300 sec intervals and at spatial resolution of 0.1 mm enabled quantifying drying front roughening and fractal and scaling characteristics in Hele-Shaw cells packed with hydrophilic and hydrophobic sand (particle size 0.3-0.9 mm). Results indicate that wettability had a minor impact on the fractal characteristics of a drying front; however the configuration, velocity and pinning-depinning of the receding front were significantly affected by wettability. The roughness exponent of the drying front was estimated by averaging over all neutron radiography images. We observed no difference in roughness exponent values obtained from fronts propagating in hydrophilic and hydrophobic sand, suggesting that wettability is negligible relative to other driving forces. The experimentally-determined roughness exponent was higher than predicted by theory which may indicate that drying front roughening is dominated by quenched disorder (generated by random packing of the sand grains). We have also calculated the height-height front correlation function. These results show fronts propagating in hydrophilic and hydrophobic sands may not be characterized by a single Hurst exponent, thus exhibiting multiaffine properties. These were further investigated by calculating different orders of the correlation function. Our results provide new insights regarding drying front dynamics and morphology including roughening and scaling characteristics for fronts in drying of hydrophilic and hydrophobic porous media.

  18. Propagation characteristics of waves upstream and downstream of quasi-parallel shocks

    NASA Technical Reports Server (NTRS)

    Krauss-Varban, D.; Omidi, N.

    1993-01-01

    The propagation characteristics of waves upstream and downstream of quasi-parallel shocks are investigated by using 2D hybrid simulations. At low Alfven Mach numbers, M(A) below about 2, the shock is initially associated with upstream phase-standing whistlers. At later times, backstreaming ions excite longer-wavelength whistlers via the right-hand resonant ion/ion instability. These waves propagate along the magnetic field at a group velocity no smaller than the upstream flow speed, so that the waves remain in the upstream region. At higher MA (above about 3), these waves are convected back into the shock, causing its reformation and downstream perturbations. Shock transmitted waves mode-convert into Alfven/ion-cyclotron waves which have a wave vector along the shock normal (pointing upstream) and convect downstream. The 2D simulation results confirm our earlier suggestion that the upstream waves should be field aligned, and that their convection into the downstream is associated with linear mode conversion into the Alfven/ion-cyclotron branch.

  19. Effects of the troposphere on radio communication

    Microsoft Academic Search

    M. P. M. Hall

    1980-01-01

    The book is concerned primarily with the effects of the troposphere and the ground on wave propagation at frequencies greater than about 30 MHz, although reference is made also to ionospheric phenomena where these are relevant. Consideration is given to the nature of atmospheric refractive index variations and of hydrometeor characteristics and their effects on radio waves. The characteristics of

  20. Characteristics of sound propagation in shallow water over an elastic seabed with a thin cap-rock layer

    E-print Network

    Characteristics of sound propagation in shallow water over an elastic seabed with a thin cap over a lay- ered elastic seabed with a shear wave speed comparable to but lower than the water frequencies which in turn are governed primarily by the water depth and compressional wave speed in the seabed

  1. Study of partial discharge radiated electromagnetic wave propagation characteristics in an actual 154 kV model GIS

    Microsoft Academic Search

    Masayuki Hikita; Shinya Ohtsuka; Junichi Wada; Shigemitsu Okabe; Toshihiro Hoshino; Shiro Maruyama

    2012-01-01

    A method to detect partial discharge (PD) is considered effective for gas insulated switchgear (GIS) insulation diagnostics. In this paper, for a 154 kV model GIS, the influence of the enclosure diameter on PD propagation characteristics was initially investigated using model GIS by varying the enclosure size. Secondly, an experiment was conducted for metallic particles placed in different locations as

  2. Propagation loss prediction in the urban environment with rectangular grid-plan streets

    Microsoft Academic Search

    N. Blaunstein; M. Levin

    1997-01-01

    The prediction of propagation loss characteristics is an essential part of radio network planning in urban and suburban environments. To design the MultiGain Wireless system constructed by Tadiran Telecommunication successfully it is very important to investigate the propagation characteristics and cell coverage of urban\\/suburban radio channels. We propose a new two-dimensional crossing-waveguides model which is based on the preliminary results

  3. Spatial and temporal distribution of the VHF\\/UHF radio waves in built-up land communication links

    Microsoft Academic Search

    Nathan Blaunstein; Nathalie Yarkoni; Dmitry Katz

    2006-01-01

    We present a unified approach of the description of the spatial and temporal distribution of radio signals within built-up radio communication links. This approach is based on a multiparametric stochastic model, which takes into account the characteristic features of built-up terrain and peculiarities of radio wave propagation related with multiple reflections, diffraction and scattering phenomena caused by obstructions surrounding both

  4. Radio-electronic equipment

    NASA Astrophysics Data System (ADS)

    Boldin, Viktor A.; Gorgonov, Gennadii I.; Konovalov, Viktor D.; Kurilov, N. N.; Levonchuk, V. V.

    The fundamentals of radio electronics are first elaborated, with attention given to the principles of circuits and signals, semiconductor devices, computing techniques, radio transmitters and receivers, and wave propagation. The principles of operation of onboard radio-electronic devices are then described, with emphasis on radio communication systems, radar systems, radio navigation systems, radio control systems, and electronic countermeasures. The maintenance of radio-electronic devices is also discussed.

  5. Effect of the initial pressure on the characteristics of the flame propagation in hydrogen-propane-air mixtures

    NASA Astrophysics Data System (ADS)

    Cheng, Guanbing; Bauer, Pascal; Zitoun, Ratiba

    2014-08-01

    This paper is aimed at an experimental investigation on effects of initial pressure on flame propagation characteristics of binary fuels hydrogen-propane-air mixtures at room temperature. The experiments are performed in a square channel equipped with perforated orifice obstacles. Four initial pressures are examined. Based on pressure transducers along the channel, the flame velocity, maximum pressure of the front peak and characteristic distances are measured. Successive stages are observed as flame propagates: (i) a velocity increase at the beginning, (ii) a velocity equal to the sound speed of combustion products and (iii) a decrease of the velocity. When the initial pressure is more important, the flame velocity and the maximal pressure of the front peak are higher, which yields a shorter characteristic distance of flame propagation. By means of a Schlieren photography technique, the physical mechanisms of flame propagation are identified in its initial stage. The physical mechanisms such as flame surface area increase and combustion product expansion as well as delayed combustion between two adjacent plates are responsible for flame acceleration upon its initial stage. The oscillations of the centerline flame velocity are due to the constrained-expanded structure of flow in reactants ahead of flame when it crosses the plates.

  6. Statistical Characteristics of MF/HF Auroral Radio Emissions Emanating from the Topside Ionosphere

    NASA Astrophysics Data System (ADS)

    Sato, Y.; Kumamoto, A.; Katoh, Y.; Shinbori, A.

    2014-12-01

    The terrestrial auroral ionosphere is a natural emitter of electromagnetic waves in the MF/HF ranges (up to 6 MHz) as well as well-known intense auroral kilometric radiation (AKR) and auroral hiss in the VLF/LF ranges. We report on the statistical properties of Terrestrial Hectometric Radiation (THR), MF/HF auroral radio emissions emanating from the topside ionosphere, using a long-term data set obtained from the Plasma Waves and Sounder (PWS) experiment mounted on the Akebono satellite during 2 solar cycles. THR typically occurs in either or both of two frequency bands near 1.5-2.0 MHz and 3.0-4.0 MHz, whose polarization features correspond to the L-O and R-X mode. Statistical studies using the Akebono/PWS data reveal clear bimodality in the frequency distribution of THR with two broad peaks near 1.6 MHz and 3.6 MHz and the spatial distribution of occurrence rate of THR-L (lower than 2.5 MHz) and THR-H (higher than 2.5 MHz). In the morning to postnoon sectors (3h-15h MLT), the spatial distribution of both types of THR is confined to magnetic latitudes higher than 70 deg, while during nighttime (15h-3h MLT) it spreads to lower magnetic latitudes (~ 30 deg) at higher altitudes. The explanation of this distribution is that THR is generated in the night-side auroral latitudes near 1000-km altitude and propagation effect makes an emission cone. Occurrence rate of THR-L is higher than that of THR-H. The long-term Akebono/PWS data also show clear solar activity dependence and seasonal variations of THR appearance; THR occurrence rate drops from a few percent during solar maxima to 0.1 percent or less during solar minima and is the highest in summer and the lowest in winter.

  7. Influence of an inhomogeneous structure of the high-latitude ionosphere on the long-distance propagation of high-frequency radio waves

    NASA Astrophysics Data System (ADS)

    Uryadov, V. P.; Vertogradov, G. G.; Vertogradova, E. G.

    2012-09-01

    We present the results of experimental studies of the features of long-distance propagation of high-frequency radio waves on the large-extent subauroral Magadan-Rostov-on-Don and midlatitude Khabarovsk-Rostov-on-Don and Irkutsk-Rostov-on-Don paths, which were obtained using the ionosonde-finder with a chirp output signal. Anomalous (lateral) signals with delays of about 1-2 ms with respect to a direct signal, which arrive from the azimuths 10°-20°, are observed on the Magadan-Rostov-on-Don path. The lateral signals were observed in the morning and antemeridian hours in the time interval 08:00-10:40 MSK. In the evening and night hours, the lateral signals were not observed. During magnetic activity, the amplitude of the lateral signals was greater than that observed prior to a magnetic storm by 5-10 dB. Location of the ionospheric-perturbation regions responsible for the appearance of the lateral signals was determined as ?geogr ? 69°-71°N (?magn ? 65°-66°N), and ? ? 51°-58°E. The mechanisms of the lateral-signal propagation due to lateral refraction of radio waves on patches with enhanced electron number density and due to scattering of radio waves from small-scale irregularities are considered.

  8. Remote sensing and modeling of lightning caused long recovery events within the lower ionosphere using VLF/LF radio wave propagation

    NASA Astrophysics Data System (ADS)

    Schmitter, E. D.

    2014-11-01

    On the 4 November 2012 at 3:04:27 UT a strong lightning in the midst of the North Sea affected the propagation conditions of VLF/LF transmitter radio signals from NRK (Iceland, 37.5 kHz) and GBZ (UK, 19.58 kHz) received at 5246° N 8° E (NW Germany). The amplitude and phase dips show a recovery time of 6-12 min pointing to a LOng Recovery Early VLF (LORE) event. Clear assignment of the causative return stroke in space and time was possible with data from the WWLLN (Worldwide Lightning Location Network). Based on a return stroke current model the electric field is calculated and an excess electron density distribution which decays over time in the lower ionosphere is derived. Ionization, attachment and recombination processes are modeled in detail. Entering the electron density distribution in VLF/LF radio wave propagation calculations using the LWPC (Long Wavelength Propagation Capability) code allows to model the VLF/LF amplitude and phase behavior by adjusting the return stroke current moment. The results endorse and quantify the conception of lower ionosphere EMP heating by strong - but not necessarily extremely strong - return strokes of both polarities.

  9. Study on fatigue crack propagation characteristics around welded joint interface in complexed conditions

    NASA Astrophysics Data System (ADS)

    Ota, Akihiko; Suzuki, Naoyuki; Maeda, Yoshio; Mawari, Toshio; Matsuoka, Saburo; Nishijima, Satoshi

    1993-01-01

    Marine structures are often constructed by welding, and they are subject to repeated loading such as waves and mechanical vibrations which can create fatigue cracks and consequently break the structures. Fatigue crack propagation properties of welded joints are studied under random loading in the air, synthetic sea water, and compressive cycling. It was found that the most crucial factor that controls fatigue crack propagation was high tensile residual stress fields of welded joints. This stress constantly kept the cracks open, simplifying fatigue crack propagation, and therefore, the rate of crack propagation could be assessed with high accuracy. In the transverse matching welded joints with cracks in the center, crack closure did not occur due to the tensile residual stress constantly induced at the crack ends in the center of the test samples. Fatigue crack propagation was accelerated both in artificial sea water and in compressive cycling compared to that in the air, and the fatigue lowest values were about half. Serious crack closures occurred in compressive cycling in which dry hours exceeded 45 minutes, and the fatigue crack propagation rate deteriorated remarkably. Mean fatigue crack propagation rate under the random loading is estimated precisely using equivalent stress intensity factor limit.

  10. Propagation characteristics of Airy-Bessel wave packets in free space.

    PubMed

    Ren, Zhijun; Wu, Qiong; Mao, Hefa; Shi, Yile; Fan, Changjiang

    2013-02-25

    Airy-Bessel configuration wave packets are believed to be exotic localized linear light bullets (LLBs) without spatiotemporal spread during propagation in free space. By carefully studying the propagation of ideal Airy-Bessel wave packets (ABWs) in free space, several new results were obtained. Cubic spatially induced dispersion (SID) slightly broadens Airy pulses while quadratic SID cannot temporally change ABWs transmission modes. Hence, ABWs, although remaining as superior localized linear wave packets, cannot be regarded as absolute LLBs. Moreover, cubic SID also decreases the longitudinal acceleration of the Airy pulse peak during propagation. PMID:23481981

  11. Introducing probabilistic radio propagation models in OMNeT++ mobility framework and cross validation check with NS2

    Microsoft Academic Search

    A. Kuntz; Felix Schmidt-eisenlohr; O. Graute; Hannes Hartenstein; Martina Zitterbart

    2008-01-01

    When performing wireless network simulations, the lack of precise channel modeling in simulator frameworks becomes a serious problem. Often deterministic models are used for packet propagation, which describe real conditions insuf- ficiently. To close this gap we extended the OMNeT++ Mobility Framework to support probabilistic propagation models. We provide an implementation for the Log-Normal- Shadowing, Nakagami, Rayleigh and Rice wave

  12. Throughput--Delay Characteristics of Some Slotted-ALOHA Multihop Packet Radio Networks

    Microsoft Academic Search

    H. Takagi; L. Kleinrock

    1985-01-01

    A Markovian model is formulated to find the throughputdelay performance for slotted-ALOHA multihop packet radio networks with a fixed configuration of packet radio units (terminals and repeaters) and fixed source-to-link paths for packets. Improvements in performance which are obtained by the adjustment of transmission parameters (suppression\\/acceleration) according to the states of nearby units and\\/or by having repeaters equipped with multiple

  13. An experimental investigation of the impact of human shadowing on temporal variation of broadband indoor radio channel characteristics and system performance

    Microsoft Academic Search

    P. Hafezi; A. Nix; M. A. Beach

    2000-01-01

    This paper reports the results of extensive measurements and analysis of the temporal variations of the indoor radio propagation channel as a result of human traffic. The broadband measurements presented were taken at 5.2 GHz and were carried out in a large laboratory environment. Four antenna configurations were considered: for three sets of measurement the receiver used an omni-directional antenna

  14. Numerical computation of wave propagation in fractured media by applying the grid-characteristic method on hexahedral meshes

    NASA Astrophysics Data System (ADS)

    Golubev, V. I.; Petrov, I. B.; Khokhlov, N. I.; Shul'ts, K. I.

    2015-03-01

    Wave propagation in fractured rock in the course of seismic exploration is studied. The grid-characteristic method on hexahedral meshes is extended to the case of an elastic medium with empty and fluid-saturated cracks. The crack effect on wave propagation in the medium is taken into account by introducing cracks at the stage of grid generation with boundary conditions and conditions on the crack edges specified in explicit form. This method is used to obtain wave patterns near an extended inclined crack. The problem of numerically computing the seismic effect produced by a cluster of vertical and subvertical cracks is given in a complete three-dimensional formulation. The structure of the resulting pattern and the influence exerted by the crack-filling substance on the signal recorded on the surface are examined.

  15. Method of lines for the analysis of the propagation characteristics of curved optical rib waveguides

    Microsoft Academic Search

    Jing-Song Gu; P.-A. Besse; H. Melchior

    1991-01-01

    A numerical technique based on the method of lines is developed for the analysis of curved optical rib waveguides. The approach yields accurate solutions for the modes of both polarizations propagating along the curved waveguides. The values of the calculated bending losses are substantiated by experimental results. The method of lines has proven to be very efficient for the solution

  16. Propagation characteristics of a novel complementary-structure planar segmented waveguide

    Microsoft Academic Search

    Vipul Rastogi; V. Mahalakshmi; M. R Shenoy; K. Thyagarajan

    1998-01-01

    A new waveguide structure with periodically segmented cover and substrate regions and a uniform film region is proposed. This complementary segmented waveguide is analysed in terms of the effective index and the spot size of the guided mode, by expressing the propagating field as a linear combination of the local normal modes of the corresponding uniform slab waveguides in different

  17. Investigation of high frequency signal propagation characteristics on HV XLPE cables

    Microsoft Academic Search

    H. N. O. T. R. Blackburn; B. T. Phung; M. Vakilian; M. S. Naderi; H. Zhang

    2005-01-01

    The insulation lifetime of power cables is determined by several factors. One of the more important of these is the occurrence of partial discharge (PD) at the dielectric. The ability to detect and locate a PD source is limited by attenuation of the high frequency PD pulses as they propagate through the cable. Therefore it is necessary to understand the

  18. REPORT ON MICROWAVE PROPAGATION CHARACTERISTICS OF U 12E TUNNEL, NEVADA TEST SITE, MERCURY, NEVADA

    Microsoft Academic Search

    J. F. Barham; S. A. Ingham

    1959-01-01

    An experiment to determine the feasibillty of a tunnel microwave ; telemetry system is described. Telemetry signals, usirg carrier wave frequencies ; of 3.85 and 4.05 kmc, were propagated over a one-mile distance in the u12e tunnel ; at the Nevada Test Site. The average attenuation produced by the tunnel link was ; comparable to that of a free space

  19. Fundamental Characteristics of Electromagnetic Wave Propagation in Non-reflection Coaxial Waveguide

    Microsoft Academic Search

    Shuhei Kaneko; Tetsuhiko Yokoi; Shigemitsu Okabe

    2006-01-01

    Electromagnetic waves have come to be used for measuring partial discharge, which is indispensable for predictive maintenance for GIS. The UHF method, using the frequency band of 300MHz to 3GHz with generally less noise is one of the advanced technologies of insulation diagnosis of GIS. There are three categories of electromagnetic wave propagating in coaxial cylindrical structure like GIS, namely,

  20. Characteristics pertinent to propagation of pulsating pressure in the channels of turbine machines

    NASA Astrophysics Data System (ADS)

    Liu, Hong; Chen, Zuoyi

    2007-01-01

    A new model describing the propagation of the pressure pulsations in the intricately shaped channels of turbine machines is presented. The proposed model was successfully used to analyze two emergency events: a failure of a steam turbine’s cast diaphragm and a failure of a rocket engine’s oxygen pump booster stage.

  1. The AN\\/GSC10 (KATHRYN) Variable Rate Data Modem for HF Radio

    Microsoft Academic Search

    M. Zimmerman; A. Kirsch

    1967-01-01

    The AN\\/GSC-10 (KATHRYN) is a new modem equipment for digital data transmission on HF radio circuits. Its unique modulation technique provides a wide range of signal redundancy and data rate to allow optimum performance over the correspondingly wide range of propagation conditions characteristic of HF radio. Efficient detection is achieved at all levels of redundancy by utilizing a fully coherent

  2. Quench and Normal Zone Propagation Characteristics of RHQT-Processed Wires Under Cryocooler-Cooling Conditions

    Microsoft Academic Search

    Satoru Murase; M. Shimoyama; N. Nanato; S. B. Kim; G. Nishijima; K. Watanabe; A. Kikuchi; N. Banno; T. Takeuchi

    2009-01-01

    The minimum quench energy (MQE) and normal zone propagation velocity (NZPV) of three kinds of Nb3Al superconductors fabricated by the rapid heating, quenching and transformation (RHQT) process were measured under various conditions of applied magnetic field (10-14 T), temperature (7-11 K), and transport current (80-95% of the critical current), while cooled by a cryocooler for developing the over 20-T class

  3. On the propagation characteristics of ultra-wideband signal in aluminum

    Microsoft Academic Search

    Daniel Piscarreta; Sut Kam Ho; Kam Weng Tam

    2010-01-01

    The UWB reflected signal at 4.7 GHz is characterized and measured for the application of short-circuited reflection material analysis with aluminum backing the sample. The sub-pulse with 120-ps pulse width is used to characterize the UWB reflected wave propagation phenomenon in some aluminum plates with different thickness. It was found the normalized amplitude of principal sub-pulse that is generated by

  4. Temporal propagation characteristics of ultrashort space- time Gaussian pulses in a laser satellite communication system

    Microsoft Academic Search

    Deborah Eliza Tjin Tham Sjin Kelly

    1998-01-01

    Tractable analytic expressions are obtained for the temporal broadening and scintillations of a narrowband, space-time Gaussian pulse propagating through clear-air weak atmospheric turbulence in a laser satellite communication system. The temporal broadening is deduced from the 1\\/e2 point of the temporal mean intensity and calculation of the temporal scintillations involves the second moment of intensity. Integral representations for the first

  5. Propagation characteristics of 20\\/30 GHz links with a 40 deg masking angle

    Microsoft Academic Search

    Faramaz Davarian; Anil V. Kantak; Choung Le

    1994-01-01

    An effective means of reducing Ka-band propagation loss is the use of high elevation angle paths, i.e., a large masking angle, between earth stations and the space platform. Experimental data have shown that the signal loss associated with most atmospheric effects is inversely proportional to sin(theta), where theta denotes the path elevation angle. A large masking angle and a generous

  6. Propagation characteristics of 20/30 GHz links with a 40 deg masking angle

    NASA Astrophysics Data System (ADS)

    Davarian, Faramaz; Kantak, Anil V.; Le, Choung

    1994-08-01

    An effective means of reducing Ka-band propagation loss is the use of high elevation angle paths, i.e., a large masking angle, between earth stations and the space platform. Experimental data have shown that the signal loss associated with most atmospheric effects is inversely proportional to sin(theta), where theta denotes the path elevation angle. A large masking angle and a generous link margin are the primary tools used in the Teledesic Corporation network to minimize atmospheric-related signal outages. This report documents the results of a study sponsored by Teledesic Corporation to characterize the effect of radiowave propagation on Teledesic's links. The recent Olympus campaign in Europe and the U.S. has provided new information that is not included. Therefore, CCIR recommendations and NASA Propagation Handbook models constitute the base of this study, and, when applicable, data from other sources have been used to improve the predictions. Furthermore, attention has been given to data from the Olympus campaign. The effects investigated during this study include gas, rain, fog, sand, and cloud attenuation; diversity gain; scintillation; and depolarization.

  7. Characteristics of the SAR distributions in a head exposed to electromagnetic fields radiated by a hand-held portable radio

    SciTech Connect

    Watanabe, Soichi; Taki, Masao [Tokyo Metropolitan Univ. (Japan). Dept. of Electronics and Information Engineering] [Tokyo Metropolitan Univ. (Japan). Dept. of Electronics and Information Engineering; Nojima, Toshio [NTT Mobile Communications Network Inc., Yokosuka (Japan)] [NTT Mobile Communications Network Inc., Yokosuka (Japan); Fujiwara, Osamu [Nagoya Inst. of Tech. (Japan). Faculty of Engineering] [Nagoya Inst. of Tech. (Japan). Faculty of Engineering

    1996-10-01

    This paper presents characteristics of the specific absorption rate (SAR) distributions calculated by the finite-difference time-domain (FDTD) method using a heterogeneous and realistic head model and a realistic hand-held portable radio model. The difference between the SAR distributions produced by a 1/4-wavelength monopole antenna and those produced by a 1/2-wavelength dipole antenna is investigated. The dependence of the maximum local SAR on the distance d{sub a} between the auricle of the head and the antenna of the radio is evaluated. It is shown that the maximum local SAR decreases as the antenna length extends from 1/4 to 1/2 of the wavelength. The maximum local SAR`s in a head model with auricles are larger than those in one without auricles. The dependence of the SAR on the electrical inhomogeneity of the tissues in the head model is not significant with regard to the surface distribution and the maximum local SAR when the radio is near the head. It is also shown that the maximum local SAR is not strongly dependent on the position of the hand when the hand does not shade the antenna. Furthermore, the SAR`s experimentally measured in a homogeneous head phantom are compared with the calculated SAR`s.

  8. Modelling Radio-Wave Propagation in Buildings Solving 19th Century Physics with 21st Century Computers

    E-print Network

    Sun, Jing

    -wave propagation is governed by Maxwell's equations (formulated by James Clerk Maxwell in 1861). These equations, analytical solutions to Maxwell's equations are difficult, if not impossible, to obtain for anything other numerical solutions to Maxwell's equations. Contributions of this Research This research focuses on applying

  9. A measured delay-Doppler scattering function for multipath propagation at 910 MHz in an urban mobile radio environment

    Microsoft Academic Search

    D. C. Cox

    1973-01-01

    A delay-Doppler scattering function is presented for multipath propagation at 910 MHz from a vertical antenna 120 m above a street to a mobile vehicle on another street. The direct path between the transmitting antenna and the mobile vehicle was blocked by many tall (over 100 m) buildings. Major features of the scattering function correspond to gross features of the

  10. An experimental study of the propagation of 55 GHz millimeter waves in an urban mobile radio environment

    Microsoft Academic Search

    H. J. Thomas; R. S. Cole; G. L. Siqueira

    1994-01-01

    An experimental study of the propagation of 55 GHz millimeter waves between a fixed transmitter and a mobile receiver in an urban environment is described. Ranges up to 400 m are used and measurements of the received signal's “fast fading” envelope, “local mean,” signal versus distance power law, and coherence bandwidth are obtained in the presence of traffic

  11. Characteristics of a propagating, self-pulsing, constricted ‘?-mode-like’ discharge

    NASA Astrophysics Data System (ADS)

    Schröder, Daniel; Burhenn, Sebastian; de los Arcos, Teresa; Schulz-von der Gathen, Volker

    2015-02-01

    Investigations on the self-pulsing operation regime of a modified micro-scaled atmospheric pressure plasma jet (?-APPJ) are presented. Using a wedge-shaped electrode configuration, a self-pulsing behavior of the device is achieved, which is characterized by the repetitive ignition of a constricted ‘?-mode-like’ discharge at the gas inlet, which propagates with the gas flow towards the nozzle, where it extinguishes. The ‘?-mode-like’ feature coexists with the homogeneous alpha-glow. Synchronized voltage/current and optical emission measurements are presented in order to correlate the evolution of electrical quantities such as voltage, current, dissipated power and phase with changes in the discharge structure. First insights are gained into the underlying discharge dynamics responsible for a stable self-sustainment, propagation and extinction of the constricted discharge. The results indicate that processes induced by helium metastables play a major role. Maximal electron densities on the order of ne = 3.2 ˇ 1012 cm?3 and dissipated power of 18.9 W are achieved in this novel operation regime.

  12. Experiments Determining the Effect of Viscous Characteristics on Propagation of Pure Sine Waves in Liquids

    NASA Astrophysics Data System (ADS)

    Takabayashi, Kenneth; Raichel, Daniel R.

    1996-11-01

    When viscous behavior becomes affected by a chemical or a physical change in a fluid, the overtones or harmonics arising from the inherently nonlinear nature of acoustic propagation of a pure sine wave in the fluid will also undergo modification(D. R. Raichel and W. H. Kapfer, "Sound Propagation in non-Newtonian Fluids," J. Appl. Mech.) 40 (Series E), 1, March 1973, pp. 1-6.. An experiment was conducted with a 'sonic viscometer' feasibility prototype(D. R. Raichel, "The Operational Principles and Construction of a Sonic Viscometer," presented Nov. 1991 at the 44th Annual Meeting of DFD, Scottsdale, AZ.) by sending a series of sinewave pulses from a submersible loudspeaker at one end to a sensing hydrophone at the other end of a 2-m length (20 cm I.D.) cylinder filled with distilled water. The sinewave frequencies ranged octave-wise from 500 Hz to 8 kHz; and the experiment was repeated with the same set of signals sent though a 1% solution of polyethylene oxide in distilled water. The resulting FFT analyses for each sinewave input yielded spectra that changed appreciably as the result of adding polyethylene oxide to distilled water, as anticipated. From the application of successive inputs, the spectra also manifested extremely high repeatability.

  13. Low-frequency type II radio detections and coronagraph data to describe and forecast the propagation of 71 CMEs/shocks

    E-print Network

    Cremades, H; Cyr, O C St; Xie, H; Kaiser, M L; Gopalswamy, N

    2015-01-01

    The vulnerability of technology on which present society relies demands that a solar event, its time of arrival at Earth, and its degree of geoeffectiveness be promptly forecasted. Motivated by improving predictions of arrival times at Earth of shocks driven by coronal mass ejections (CMEs), we have analyzed 71 Earth-directed events in different stages of their propagation. The study is primarily based on approximated locations of interplanetary (IP) shocks derived from type II radio emissions detected by the Wind/WAVES experiment during 1997-2007. Distance-time diagrams resulting from the combination of white-light corona, IP type II radio, and in situ data lead to the formulation of descriptive profiles of each CME's journey toward Earth. Furthermore, two different methods to track and predict the location of CME-driven IP shocks are presented. The linear method, solely based on Wind/WAVES data, arises after key modifications to a pre-existing technique that linearly projects the drifting low-frequency type...

  14. The measurement of sonic boom waveforms and propagation characteristics - Techniques and challenges

    NASA Astrophysics Data System (ADS)

    Bedard, Alfred J., Jr.

    1990-10-01

    The measurement of sonic boom waveforms in a turbulent atmosphere with complex nonstationary profiles and three-dimensional structures of temperature, wind, and humidity presents a difficult challenge. Representative measurements are critical for the verification of not only numerical predictive models but also of concepts for sonic boom alleviation. Variations in aircraft flight paths and speed as well as organized atmospheric structures in the acoustic propagation path further complicate this measurement problem. This paper reviews past experimental approaches, pointing out measurement needs; suggests possibilities in the form of new instruments, processing, and concepts that could be applied; and indicates the opportunities that exist or are being planned for facilities and networks that could provide data for initializing predictive models on a nationwide basis, or provide sites for field experiments.

  15. Performance characteristics of qualified cell lines for isolation and propagation of influenza viruses for vaccine manufacturing.

    PubMed

    Donis, Ruben O; Davis, C Todd; Foust, Angie; Hossain, M Jaber; Johnson, Adam; Klimov, Alexander; Loughlin, Rosette; Xu, Xiyan; Tsai, Theodore; Blayer, Simone; Trusheim, Heidi; Colegate, Tony; Fox, John; Taylor, Beverly; Hussain, Althaf; Barr, Ian; Baas, Chantal; Louwerens, Jaap; Geuns, Ed; Lee, Min-Shi; Venhuizen, Odewijk; Neumeier, Elisabeth; Ziegler, Thedi

    2014-11-12

    Cell culture is now available as a method for the production of influenza vaccines in addition to eggs. In accordance with currently accepted practice, viruses recommended as candidates for vaccine manufacture are isolated and propagated exclusively in hens' eggs prior to distribution to manufacturers. Candidate vaccine viruses isolated in cell culture are not available to support vaccine manufacturing in mammalian cell bioreactors so egg-derived viruses have to be used. Recently influenza A (H3N2) viruses have been difficult to isolate directly in eggs. As mitigation against this difficulty, and the possibility of no suitable egg-isolated candidate viruses being available, it is proposed to consider using mammalian cell lines for primary isolation of influenza viruses as candidates for vaccine production in egg and cell platforms. To investigate this possibility, we tested the antigenic stability of viruses isolated and propagated in cell lines qualified for influenza vaccine manufacture and subsequently investigated antigen yields of such viruses in these cell lines at pilot-scale. Twenty influenza A and B-positive, original clinical specimens were inoculated in three MDCK cell lines. The antigenicity of recovered viruses was tested by hemagglutination inhibition using ferret sera against contemporary vaccine viruses and the amino acid sequences of the hemagglutinin and neuraminidase were determined. MDCK cell lines proved to be highly sensitive for virus isolation. Compared to the virus sequenced from the original specimen, viruses passaged three times in the MDCK lines showed up to 2 amino acid changes in the hemagglutinin. Antigenic stability was also established by hemagglutination inhibition titers comparable to those of the corresponding reference virus. Viruses isolated in any of the three MDCK lines grew reasonably well but variably in three MDCK cells and in VERO cells at pilot-scale. These results indicate that influenza viruses isolated in vaccine certified cell lines may well qualify for use in vaccine production. PMID:24975811

  16. Experimental investigation of ULF/VLF radio wave generation and propagation in the upper atmosphere and ionosphere during EISCAT heating experiment in 2012

    NASA Astrophysics Data System (ADS)

    Ryakhovskiy, Iliya; Gavrilov, Boris; Zetzer, Julius; Rietveld, Michael; Poklad, Yuriy; Blagoveshchenskaya, Nataly

    Powerful high frequency radio waves transmitted from high-power HF heating facilities modify the ionospheric plasma. The X-mode HF pump wave generates strong small-scale artificial field aligned irregularities in the F region of the ionosphere when the heater frequency is near or above the critical frequency of F2 layer [Blagoveshchenskaya et al]. One of the tasks of the Russian EISCAT heating campaign in February 2012 was an investigation of the generation and propagation of ULF/VLF signals generated as the result of HF radiation modulation. Despite the numerous attempts of long-range detection of such signals, there are a few successful results. The most reliable and important results were obtained by [Barr et al.] more than 20 years ago. They measured the VLF radio waves in Lindau, Germany at the distance of about 2000 km from EISCAT Heater. We present the results of the ULF/VLF registrations at the same distance during heating campaign of February 2012. The measurements were conducted at Mikhnevo Geohysical Observatory located in 80 km to the south of Moscow and at the distance of about 1900 km from Tromsř. For measurements were used a sensitive receivers with crossed air-coil loop antennas in the frequency range from 800 Hz to 30 kHz in the femtotesla amplitude range. We recorded the radial and azimuthal magnetic component of the signals and from their ratio obtained the mode polarization. The radiated heater frequency was modulated by 517, 1017, 2017, 3017, 4017 and 6017 Hz. It was shown the signals with frequency less than 2 kHz propagate in the QTEM mode, and signals at the frequency from 2 to 4 kHz are in the QTE mode. Observed magnetic field strengths and waveguide polarizations are found to be in line with the predictions of simple waveguide models. Qualitative coincidence of the signals polarization character and its dependence on the frequency specifies adequacy of numerical models and reliability of the data received in campaign 2012. Blagoveshchenskaya N. F., M. T. Rietveld et al. Artificial field-aligned irregularities in the high-latitude F region of the ionosphere induced by an X-mode HF heater wave. // Geophys. Res. Lett. - 2011. V. 38, doi: 10.1029/2011GL046724. Barr, R., P. Stubbe, and H. Kopka, 1991, Long-range detection of VLF radiation produced by heating the auroral electrojet. Radio Science, Volume 26, Number 4, Pages 871-879, July-August 1991

  17. Microwave characteristics of AlxGa1-xN\\/InxGa1-xN\\/GaN-based HEMT using propagation delay model

    Microsoft Academic Search

    T. R. Lenka; A. K. Panda

    2009-01-01

    A new GaN-based high electron mobility transistor (HEMT) structure is proposed to study DC, RF and microwave characteristics using TCAD tool and propagation delay model. The proposed device is embedded into the circuit and its circuit characteristics are also studied and presented in this paper. Apart from DC and small-signal characteristics, we have investigated various microwave parameters such as maximum

  18. Source and Propagation Characteristics of Kilometric Continuum Observed with Multiple Satellites

    NASA Technical Reports Server (NTRS)

    Hashimoto, K.; Anderson, R. R.; Green, J. L.; Matsumoto, H.

    2004-01-01

    Kilometric continuum radiation was first identified with the GEOTAIL Plasma Wave Instrument (PWI) as the high frequency extension of escaping continuum emissions in the frequency range from 100 kHz to 800 kHz. It consists of from a few to many narrow-band emissions. It was observed mainly near the magnetic equator, and its source was expected to be inside of the plasmapause and the topside equatorial region. Recently, data from the IMAGE Radio Plasma Imager (RPI) and Extreme ultraviolet (EUV) experiments have been used to show that kilometric continuum is generated at the plasmapause, in or near the magnetic equator, within a notch region, and have confirmed the expectation. Data from the CRRES PWI have also identified other sources from the equatorial density irregularities. An example of CRRES observations reveals a possibility that kilometric continuum has been radiated as a wide beam emission. The IMAGE and GEOTAIL simultaneous observations are not like the previous observations since they show it has been observed to have a very broad emission cone. It could also be the highest frequency continuum enhancement so far observed since it is associated with a high energy electron injection event.

  19. Performance Analysis of a Built-In Planar Inverted Antenna for 800 MHz Band Portable Radio Units

    Microsoft Academic Search

    TOKIO TAGA; KOUICHI TSUNEKAWA

    1987-01-01

    The pattern averaging gain (PAG) method to estimate the average gain of mobile antennas in a multipath propagation environment is proposed. By using this method and a wire-grid model, the radiation characteristics of the planar invertedFantenna (PIFA) mounted on a portable radio case is analyzed. In particular, the variation of the antenna gain with the radio case dimensions and inclination

  20. Characteristics of interplanetary type II radio emission and the relationship to shock and plasma properties

    NASA Technical Reports Server (NTRS)

    Lengyel-Frey, D.; Stone, R. G.

    1989-01-01

    A large sample of type II events is the basis of the present study of the properties of interplanetary type II bursts' radio-emission properties. Type II spectra seem to be composed of fundamental and harmonic components of plasma emission, where the intensity of the fundamental component increases relative to the harmonic as the burst evolves with heliocentric distance; burst average flux density increases as a power of the associated shock's average velocity. Solar wind density structures may have a significant influence on type II bandwidths.

  1. Spectral Cauchy Characteristic Extraction: A New Algorithm for Gravitational Wave Propagation

    NASA Astrophysics Data System (ADS)

    Handmer, Casey; Szilágyi, Béla

    2014-03-01

    We present a spectral algorithm for solving the full nonlinear vacuum Einstein field equations in the Bondi framework. Developed within the Spectral Einstein Code (SpEC), we demonstrate spectral Cauchy Characteristic Extraction (CCE), a thorough method for obtaining valid gravitational waveforms from existing and future astrophysical simulations. We demonstrate the new algorithm's stability, convergence, and agreement with existing CCE methods. We explain how an innovative spectral approach enables greatly improved computational efficiency.

  2. Propagation characteristics of a focused laser beam in a strontium barium niobate photorefractive crystal under reverse external electric field.

    PubMed

    Guo, Q L; Liang, B L; Wang, Y; Deng, G Y; Jiang, Y H; Zhang, S H; Fu, G S; Simmonds, P J

    2014-10-01

    The propagation characteristics of a focused laser beam in a SBN:75 photorefractive crystal strongly depend on the signal-to-background intensity ratio (R=Is/Ib) under reverse external electric field. In the range 20>R>0.05, the laser beam shows enhanced self-defocusing behavior with increasing external electric field, while it shows self-focusing in the range 0.03>R>0.01. Spatial solitons are observed under a suitable reverse external electric field for R=0.025. A theoretical model is proposed to explain the experimental observations, which suggest a new type of soliton formation due to "enhancement" not "screening" of the external electrical field. PMID:25322227

  3. Characterizing lower ionosphere forcing by a strong lightning stroke using VLF/LF radio wave remote sensing and propagation modeling

    NASA Astrophysics Data System (ADS)

    Schmitter, E. D.

    2013-09-01

    The direct and indirect effects of lightning strokes on the lower ionosphere seen with VLF signal propagation with regard to the generation of Trimpis are well known, e.g. [5]. Additionally to these events with recovery times of the order of seconds disturbance events with long recovery times of the order of minutes to half an hour are observed and related to direct lightning EMP heating of the lower ionosphere [2]. This work discusses remote sensing and modeling of such an event (4th of Nov. 2012, 3:04:27 UT, North Sea) allowing to characterize the disturbance conditions with regard to time development and space extension.

  4. Crack propagation through phase-separated glasses: effect of the characteristic size of disorder.

    PubMed

    Dalmas, Davy; Lelarge, Anne; Vandembroucq, Damien

    2008-12-19

    We perform fracture experiments on nanoscale phase-separated glasses and measure crack surface roughness by atomic force microscopy. The ability of tuning the phase domain size by thermal treatment allows us to test thoroughly the predictions of crack front depinning models about the scaling properties of crack surface roughness. It appears that, in the range of validity of these depinning models developed for the fracture of brittle materials, our experimental results show a quantitative agreement with theoretical predictions: Beyond the characteristic size of disorder, the roughness of crack surfaces obeys the logarithmic scaling early predicted by Ramanathan, Erta?, and Fisher [Phys. Rev. Lett. 79, 873 (1997)]. PMID:19113722

  5. Analytical and experimental procedures for determining propagation characteristics of millimeter-wave gallium arsenide microstrip lines

    NASA Technical Reports Server (NTRS)

    Romanofsky, Robert R.

    1989-01-01

    In this report, a thorough analytical procedure is developed for evaluating the frequency-dependent loss characteristics and effective permittivity of microstrip lines. The technique is based on the measured reflection coefficient of microstrip resonator pairs. Experimental data, including quality factor Q, effective relative permittivity, and fringing for 50-omega lines on gallium arsenide (GaAs) from 26.5 to 40.0 GHz are presented. The effects of an imperfect open circuit, coupling losses, and loading of the resonant frequency are considered. A cosine-tapered ridge-guide text fixture is described. It was found to be well suited to the device characterization.

  6. Flux pinning characteristics in cylindrical ingot niobium used in superconducting radio frequency cavity fabrication

    SciTech Connect

    Dhavale Ashavai, Pashupati Dhakal, Anatolii A Polyanskii, Gianluigi Ciovati

    2012-04-01

    We present the results of from DC magnetization and penetration depth measurements of cylindrical bulk large-grain (LG) and fine-grain (FG) niobium samples used for the fabrication of superconducting radio frequency (SRF) cavities. The surface treatment consisted of electropolishing and low temperature baking as they are typically applied to SRF cavities. The magnetization data were fitted using a modified critical state model. The critical current density Jc and pinning force Fp are calculated from the magnetization data and their temperature dependence and field dependence are presented. The LG samples have lower critical current density and pinning force density compared to FG samples which implies a lower flux trapping efficiency. This effect may explain the lower values of residual resistance often observed in LG cavities than FG cavities.

  7. Electrochemical characteristics of amorphous carbon nanorod synthesized by radio frequency magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Chang, Hsin-Yueh; Huang, Yung-Jui; Chang, Hsuan-Chen; Su, Wei-Jhih; Shih, Yi-Ting; Chen, John L.; Honda, Shin-ichi; Huang, Ying-Sheng; Lee, Kuei-Yi

    2015-01-01

    Amorphous carbon nanorods (CNRs) were deposited directly using radio frequency magnetron sputtering. The synthesized CNR electrochemical properties were investigated using graphene as the current collector for an electric double layer capacitor. The CNRs were vertically aligned to the graphene to achieve higher specific surface area. The capacitor performance was characterized using electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge testing in 1 M KOH electrolyte at 30°C, 40°C, 50°C, and 60°C. The CNR specific capacitance was observed to increase with increasing measurement temperature and could reach up to 830 F/g at 60°C. Even after extensive measurements, the CNR electrode maintained good adhesion to the graphene current collector thereby suggesting electrode material stability.

  8. Propagation characteristics of omega signals and their triggered emissions observed by EXOS-D satellite

    SciTech Connect

    Sawada, Akira; Kishi, Youji; Yamamoto, Masayuki; Sakurai, Akihiro; Kasahara, Yoshiya; Kimura, Iwane (Kyoto Univ. (Japan))

    1991-02-01

    Omega signals have been frequently observed by the Japanese satellite EXOS-D (Akebono) in the magnetosphere. The authors have statistically analyzed VLF-WBA (wide-band analyzer) data in a period of 6 months, which were acquired by Kagoshima (KSC) and Prince Albert (PA) satellite tracking stations. About a quarter of the data obtained at KSC contain Omega signals from Australia and about a sixth of the data at PA contain those from North Dakota. Ray tracing calculations for the Australian Omega signals are consistent with the results of observations. 10 cases of triggered emissions are also found in the analyzed data. Amplitude and phase characteristics along an Omega pulse are investigated for the triggering event and an apparent phase lead, corresponding to a frequency increase by about 10 Hz was found at the center frequency of signals after the triggering starts.

  9. Characteristics of vibrational wave propagation and attenuation in submarine fluid-filled pipelines

    NASA Astrophysics Data System (ADS)

    Yan, Jin; Zhang, Juan

    2015-04-01

    As an important part of lifeline engineering in the development and utilization of marine resources, the submarine fluid-filled pipeline is a complex coupling system which is subjected to both internal and external flow fields. By utilizing Kennard's shell equations and combining with Helmholtz equations of flow field, the coupling equations of submarine fluid-filled pipeline for n=0 axisymmetrical wave motion are set up. Analytical expressions of wave speed are obtained for both s=1 and s=2 waves, which correspond to a fluid-dominated wave and an axial shell wave, respectively. The numerical results for wave speed and wave attenuation are obtained and discussed subsequently. It shows that the frequency depends on phase velocity, and the attenuation of this mode depends strongly on material parameters of the pipe and the internal and the external fluid fields. The characteristics of PVC pipe are studied for a comparison. The effects of shell thickness/radius ratio and density of the contained fluid on the model are also discussed. The study provides a theoretical basis and helps to accurately predict the situation of submarine pipelines, which also has practical application prospect in the field of pipeline leakage detection.

  10. Analysis of propagation characteristics of flexural wave in honeycomb sandwich panel and design of loudspeaker for radiating inclined sound

    NASA Astrophysics Data System (ADS)

    Fujii, Ayaka; Wakatsuki, Naoto; Mizutani, Koichi

    2015-07-01

    A loudspeaker for an auditory guiding system is proposed. This loudspeaker utilizes inclined sound transformed from a flexural wave in a honeycomb sandwich panel. We focused on the fact that the inclined sound propagates extensively with uniform level and direction. Furthermore, sound can be generated without group delay dispersion because the phase velocity of the flexural wave in the sandwich panel becomes constant with increasing frequency. These characteristics can be useful for an auditory guiding system in public spaces since voice-guiding navigation indicates the right direction regardless of position on a pathway. To design the proposed loudspeaker, the behavior of the sandwich panel is predicted using a theoretical equation in which the honeycomb core is assumed as an orthotropic continuum. We calculated the phase velocity dispersion of the flexural wave in the sandwich panel and compared the results obtained using the equation with those of a simulation based on the finite element method and an experiment in order to confirm the applicability of the theoretical equation. It was confirmed that the phase velocities obtained using the theoretical equation and by the simulation were in good agreement with that obtained experimentally. The obtained results suggest that the behavior of the sandwich panel can be predicted using the parameters of the panel. In addition, we designed an optimized honeycomb sandwich panel for radiating inclined sound by calculating the phase velocity characteristics of various panels that have different parameters of core height and cell size using the theoretical equation. Sound radiation from the optimized panel was simulated and compared with that of a homogeneous plate. It was clear that the variance of the radiation angle with varying frequency of the optimized panel was smaller than that of the homogeneous plate. This characteristic of sound radiation with a uniform angle is useful for indicating the destination direction. On the basis of this fact, we established a design method of the flat-panel loudspeaker for generating inclined sound using a honeycomb sandwich panel.

  11. Polarization and propagation characteristics of switchable first-order azimuthally asymmetric beam generated in dual-mode fiber.

    PubMed

    Khan, Saba N; Chatterjee, Sudip K; Chaudhuri, Partha Roy

    2015-02-20

    We report here the controlled generation of a linearly polarized first-order azimuthally asymmetric beam (F-AAB) in a dual-mode fiber (DMF) by appropriate superposition of selectively excited zeroth-order vector modes that are doughnut-shaped azimuthally symmetric beams (D-ASBs). We first demonstrate continually switching polarization mode structures having an identical two-lobe intensity profile (i.e., intra-F-AAB conversion). Then, under a distinct launching state, we generate mode structures progressively toggling between the doughnut-shaped profile and two-lobe pattern having dissimilar polarization orientations (i.e., F-AAB to D-ASB conversion). Interestingly, a decentralized elliptical Gaussian beam possessing homogenous spatial polarization is obtained by enhancing the contribution of the fundamental mode (HE11/LP01) in selectively excited F-AAB. A smoothly varying azimuth of the input beam in this situation resulted in redistribution of transverse energy procuring a unique and exciting unconventional two-grain T-polarized beam having mutually orthogonal state of polarization (SOP). All of the above three were achieved under a given set of launching conditions (tilt/offset) of a Gaussian mode (TEM00) devised with changing SOP of the input beam. A strong modulation in the output beam characteristics was also observed with the variation in propagation distance (for a fixed input SOP) owing to the large difference in propagation constants of the participating modes (LP01 and one of the F-AABs). Finally, this particular study led to a design for a low-cost highly sensitive strain measuring device based on tracking the centroid movement of the output intensity pattern. Each of our experimentally observed intensity/polarization distributions is theoretically mapped on a one-to-one basis considering a linear superposition of appropriately excited LP basis modes of the waveguide toward a complete understanding of the polarization and mode propagation in the dual-mode structure. PMID:25968222

  12. Simulation of sudden phase anomalies of VLF signals of radio stations on the Novosibirsk - Yakutsk and Krasnodar - Yakutsk propagation paths

    NASA Astrophysics Data System (ADS)

    Korsakov, Alexey; Mullayarov, Viktor; Kozlov, Vladimir; Karimov, Rustam

    Sudden phase anomalies (SPA) of radiosignals VLF (3-30 kHz) dependence from X-ray flux and solar zenith angle is described by the expression: begin{center} begin{equation} phi?=B•Lg(P)+C•Lg(Cos(X))+A, where ? - a signal phase variation, reduced to a unit length of the path [degree/Mm]; P - a solar radiation (1 - 8 Ĺ) flux [W/m(2) ]; Cos(X) - averaged along the propagation path cosine of the solar zenith angle. Registered in Yakutsk SPA signal of stations Krasnodar and Novosibirsk (14.9 kHz) separately for summer and winter daytime conditions are considered. The threshold sensitivity of the SPA by the flux P is weakly dependent on the season. The SPA value for fixed P and X from summer to winter on the path Novosibirsk-Yakutsk increases, the SPA dependence from Cos(X) more distinct in the summer. On the Krasnodar-Yakutsk SPA clearly depends on Cos(X) in winter, due to the greater interval of the longitude and the path crosses higher latitudes.

  13. Case studies for solving the Saint-Venant equations using the method of characteristics: pipeline hydraulic transients and discharge propagation

    NASA Astrophysics Data System (ADS)

    Barros, R. M.; Tiago Filho, G. L.; dos Santos, I. F. S.; da Silva, F. G. B.

    2014-03-01

    Hydraulic transients occur during a change from one equilibrium state to another, for example, in flows. The pipeline project should provide the head and discharge in any operating states, e.g., sudden valve opening or closure. Among the various numerical approaches for the calculation of pipeline transients, the method of characteristics (MOC) is advantageous This study aims to present a hydraulic transitory study as MOC applications for solving the Saint- Venant equations in two case studies: 1) in a penstock of a small hydropower system as a simple pipeline in the case of valve-closure in the downstream boundary with a reservoir in the upstream boundary; and 2) for discharge propagation into a channel by velocity and depth of the flow channel along space evaluation. The main data for the first case study consisted of a design head that is 182 meters, a turbine discharge of 13.82 m3/s, a diameter of 4 meters and length pipe (penstock) of 2,152.50 meters. Regarding the second case study, the entry hydrogram was given to a rectangular channel with a width of 6.1 meters, length of 3,048 meters, slope of 0.0016 meters, and exhibited uniform flow with nominal depth of 2.44 meters. The characteristic curve of the discharge in the downstream extremity is Q = 158.(y – 3.25)32. The proposed methodology by Chaudry [5] concerning the development of hydrodynamic models was used. The obtained results for first case study showed that the simulated values for valve pressure while varying turning the valve between 4 and 12 seconds results in maximum values of pressures that oscillated between 219.97mca and 212.39 mca (4s) and 196.42mca and 190.86mca (12s). For the second case study, the values of discharge, velocity, and depth for x=0 and elapsed time of 850s were, respectively, 127.70m3/s, 3.87m/s, and 5.36m. For x=0 and an elapsed time of 1,230s, the values were 87.92m3/s, 4.49m/s, and 3.21m. Therefore, the MOC numerical approach has been confirmed to be useful for several engineering purposes, including cases of hydraulic transients and discharge propagation in hydraulic systems

  14. Space Telecommunications Radio System STRS Cognitive Radio

    NASA Technical Reports Server (NTRS)

    Briones, Janette C.; Handler, Louis M.

    2013-01-01

    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.

  15. Wideband Propagation Measurements and Channel Implications for Indoor Broadband Wireless Local Area Networks at the 60 GHz Band

    Microsoft Academic Search

    Andreas G. Siamarou

    2003-01-01

    This paper addresses some wideband propagation characteristics for Indoor Broadband Wireless LANs at the 60 GHz band. Important system design characteristics from measured results obtained from two wideband 60 GHz LOS radio links are presented. Measurements had been undertaken using the swept frequency channel sounding method. Analysis from the complex frequency responses in a worst-case scenario have yielded to a

  16. Radio stars.

    PubMed

    Hjellming, R M; Wade, C M

    1971-09-17

    Up to the present time six classes of radio stars have been established. The signals are almost always very faint and drastically variable. Hence their discovery has owed as much to serendipity as to the highly sophisticated equipment and techniques that have been used. When the variations are regular, as with the pulsars, this characteristic can be exploited very successfully in the search for new objects as well as in the detailed study of those that are already known. The detection of the most erratically variable radio stars, the flare stars and the x-ray stars, is primarily a matter of luck and patience. In the case of the novas, one at least knows where and oughly when to look for radio emission. A very sensitive interferometer is clearly the best instrument to use in the initial detection of a radio star. The fact that weak background sources are frequently present makes it essential to prove that the position of a radio source agrees with that of a star to within a few arc seconds. The potential of radio astronomy for the study of radio stars will not be realized until more powerful instruments than those that are available today can be utilized. So far, we have been able to see only the most luminous of the radio stars. PMID:17836594

  17. Characteristics of Arctic low-tropospheric humidity inversions based on radio soundings

    NASA Astrophysics Data System (ADS)

    Nygĺrd, T.; Valkonen, T.; Vihma, T.

    2014-02-01

    Humidity inversions have a high potential importance in the Arctic climate system, especially for cloud formation and maintenance, in wide spatial and temporal scales. Here we investigate the climatology and characteristics of humidity inversions in the Arctic, including their spatial and temporal variability, sensitivity to the methodology applied and differences from the Antarctic humidity inversions. The study is based on data of the Integrated Global Radiosonde Archive (IGRA) from 36 Arctic stations between the years 2000 and 2009. The results indicate that humidity inversions are present on multiple levels nearly all the time in the Arctic atmosphere. Almost half (48%) of the humidity inversions were found at least partly within the same vertical layer with temperature inversions, whereas the existence of the other half may, at least partly, be linked to uneven vertical distribution of horizontal moisture transport. A high atmospheric surface pressure was found to increase the humidity inversion occurrence, whereas relationships between humidity inversion properties and cloud cover were generally relatively weak, although for some inversion properties they were systematic. For example, humidity inversions occurred slightly more often and were deeper under clear sky than in overcast conditions for almost all stations. The statistics of Arctic humidity inversion properties, especially inversion strength, depth and base height, proved to be very sensitive to the instruments and methodology applied. For example, the median strength of the strongest inversion in a profile was twice as large as the median of all Arctic inversions. The most striking difference between the Arctic and Antarctic humidity inversions was the much larger range of the seasonal cycle of inversion properties in the Arctic. Our results offer a baseline for validation of weather prediction and climate models and also encourage further studies on humidity inversions due to the vital, but so far poorly understood, role of humidity inversions in Arctic cloud processes.

  18. Characteristics of Arctic low-tropospheric humidity inversions based on radio soundings

    NASA Astrophysics Data System (ADS)

    Nygĺrd, T.; Valkonen, T.; Vihma, T.

    2013-08-01

    Humidity inversions have a high potential importance in the Arctic climate system, especially for cloud formation and maintenance, in wide spatial and temporal scales. Here we investigate the climatology and characteristics of humidity inversions in the Arctic, including their spatial and temporal variability, sensitivity to the methodology applied and differences from the Antarctic humidity inversions. The study is based on data of the Integrated Global Radiosonde Archive (IGRA) from 36 Arctic stations between the years 2000-2009. The results indicate that humidity inversions are nearly all the time present on multiple levels in the Arctic atmosphere. Almost half (48%) of the humidity inversions were found at least partly within the same vertical layer with temperature inversions, whereas the existence of the other half may, at least partly, be linked to uneven vertical distribution of horizontal moisture transport. A high atmospheric surface pressure was found to increase the humidity inversion occurrence, whereas relationships between humidity inversion properties and cloud cover were generally relatively weak, although for some inversion properties systematic. The statistics of Arctic humidity inversion properties, especially inversion strength, depth and base height, proved to be very sensitive to the instruments and methodology applied. For example, the median strength of the strongest inversion in a profile was twice as large as the median of all Arctic inversions. The most striking difference between the Arctic and Antarctic humidity inversions was the much larger range of the seasonal cycle of inversion properties in the Arctic. Our results offer a baseline for validation of weather prediction and climate models and also encourage for further studies on humidity inversions due to the vital, but so far poorly understood, role of humidity inversions in Arctic cloud processes.

  19. Characteristics and Problems of the Gifted: neural propagation depth and flow motivation as a model of intelligence and creativity

    Microsoft Academic Search

    Francis HEYLIGHEN

    Giftedness, the potential for exceptional achievement, is characterized by high intelligence and creativity. Gifted people exhibit a complex of cognitive, perceptual, emotional, motivational and social traits. Extending neurophysiological hypotheses about the general intelligence (g) factor, a construct is proposed to explain these traits: neural propagation depth. The hypothesis is that in more intelligent brains, activation propagates farther, reaching less directly

  20. Propagation and stability characteristics of a 500-m-long laser-based fiducial line for high-precision alignment of long-distance linear accelerators.

    PubMed

    Suwada, Tsuyoshi; Satoh, Masanori; Telada, Souichi; Minoshima, Kaoru

    2013-09-01

    A laser-based alignment system with a He-Ne laser has been newly developed in order to precisely align accelerator units at the KEKB injector linac. The laser beam was first implemented as a 500-m-long fiducial straight line for alignment measurements. We experimentally investigated the propagation and stability characteristics of the laser beam passing through laser pipes in vacuum. The pointing stability at the last fiducial point was successfully obtained with the transverse displacements of ą40 ?m level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ą0.08 ?rad. This report contains a detailed description of the experimental investigation for the propagation and stability characteristics of the laser beam in the laser-based alignment system for long-distance linear accelerators. PMID:24089818

  1. Characteristics of anomalous skin effect and evolution of power absorption regions in a cylindrical radio frequency inductively coupled plasma

    NASA Astrophysics Data System (ADS)

    Ding, Z. F.; Sun, B.; Huo, W. G.

    2015-06-01

    In a low-pressure radio-frequency (13.56 MHz), inductively coupled argon plasma generated by a normal cylindrical rf coil, electric field, current density, and absorbed power density is calculated from magnetic field measured with a phase-resolved magnetic probe. The anomalous skin effect (ASE) for the cylindrical rf coil is compared to those previously reported for the planar and re-entrant cylindrical rf coils. Physical reasons for our observed characteristics of ASE are presented. With the increasing discharge power, the size and the number of negative and positive power absorption regions evolve into several distinct patterns. For the low discharge power (at 156.9 W), there is one area of positive and one area of negative power absorption in the radial direction. For the medium discharge power (279 W-683.5 W), there are two areas of negative and two areas of positive power absorption. For the even higher discharge power (above 803.5 W), the number of areas is the same as that of the medium discharge power, but the size of the inner positive and negative power absorption areas is approximately doubled and halved, respectively, while the outer positive and negative power absorption areas slightly shrinks. The evolution of positive and negative power absorption regions is explained as a result of electron thermal diffusion and the energy conversion between rf current and electric field. The spatial decays of electric field and current density are also elucidated by linking them with the positive and negative power absorption pattern.

  2. Characteristics' prediction in urban and suburban environments

    Microsoft Academic Search

    Nathan Blaunstein; Ran Giladi; Moshe Levin

    1998-01-01

    The characteristics of the propagation in the microcellular urban and suburban environments in the 902-928-MHz frequency band in line-of-sight (LOS) conditions is investigated both theoretically and experimentally for the purpose of wireless radio local loop (WRLL) prediction. The path-loss characteristics and the range of a break point, at which the polynomial character of field intensity decay along the street level

  3. Propagation characteristics of surface acoustic waves in perovskite-type ferroelectric films/MgO/GaAs structures

    NASA Astrophysics Data System (ADS)

    Shih, Wen-Ching; Wu, Mu-Shiang

    1997-01-01

    The propagation characteristics of surface acoustic waves (SAW) in perovskite-type ferroelectric films/MgO/GaAs structures were investigated theoretically. Phase velocities of the 0022-3727/30/2/001/img1 layered structure are larger than those of the 0022-3727/30/2/001/img2 and PZT/MgO/GaAs layered structures for the same hK value of the perovskite-type ferroelectric film. Large coupling coefficients 0022-3727/30/2/001/img3 can be obtained when the interdigital transducer (IDT) is on top of the perovskite-type ferroelectric film, with and without the floating-plane electrode at the perovskite-type ferroelectric film - MgO buffer layer interface; and peak values of the coupling coefficients 0022-3727/30/2/001/img4 of the PZT films (2.8 - 3.8%) are higher than those of the 0022-3727/30/2/001/img5 (1.9 - 2.5%) and 0022-3727/30/2/001/img6 films (1.5 - 2.3%). There exists a minor peak of the coupling coefficients for the PZT and 0022-3727/30/2/001/img5 films when the hK value of the perovskite-type ferroelectric film is about 0.5, but not for the 0022-3727/30/2/001/img6 films, if the IDT is on top of the perovskite-type ferroelectric film with the floating-plane electrode at the perovskite-type ferroelectric film - MgO buffer layer interface. The minor peak values of the coupling coefficients 0022-3727/30/2/001/img9 for both PZT/MgO/GaAs and 0022-3727/30/2/001/img1 layered structures all decrease when we increase the hK value of the MgO buffer layer from 0 to 0.25. The results could be beneficial for combining ferroelectric devices, semiconductor devices and SAW devices on the same GaAs substrate.

  4. Radio science investigations with Voyager

    NASA Technical Reports Server (NTRS)

    Eshleman, V. R.; Tyler, G. L.; Anderson, J. D.; Fjeldbo, G.; Levy, G. S.; Wood, G. E.; Croft, T. A.

    1977-01-01

    Radio links to and from the Voyager spacecraft will be used for occultation measurements of planetary and satellite atmospheres and ionospheres, the rings of Saturn, the solar corona, and the general-relativistic time delay for radio wave propagation through the solar gravity field. In addition, the radio link measurements may provide information on the gravity fields of the planets, the masses of the satellites, properties of the interplanetary medium, and long-wavelength gravitational radiation propagation in the solar system.

  5. Influence of geophysical factors on oblique-sounder ionospheric characteristics

    SciTech Connect

    Baranets, A.N.; Blagoveshchenskaya, N.F.; Borisova, T.D.; Bubnov, V.A.

    1988-10-01

    The purpose of this paper is to study the influence of geophysical factors, including magnetoionospheric disturbances, on decameter wave propagation over extended paths using oblique sounding (OS) data, and also to compare experimental and calculated OS ionograms for various conditions of radio waver propagation (season, time of day). Variations of oblique-sounder ionospheric characteristics along a 9000 km long subauroral path for various geophysical conditions are considered. A comparison is made of experimental and calculated ionograms of oblique sounding.

  6. Characteristics of 2-D Rupture Propagation of Stick-slip Events during Meter-sized Biaxial Friction Experiments

    NASA Astrophysics Data System (ADS)

    Tsuchida, K.; Kawakata, H.; Fukuyama, E.; Yamashita, F.; Mizoguchi, K.

    2014-12-01

    Using centimeter-sized rock specimens, friction experiments have been carried out. Ohnaka and Kuwahara (1990) showed a stably propagating shear strain drop (nucleation phase) followed by its accelerated propagation. Such process was reproduced by numerical simulations considering heterogeneous fault strength and the weakening (e.g., Dieterich, 1992; Matsu'ura et al., 1992). However, in previous studies, the rupture propagation was measured only with 1-D array of strain gauges along in-plane direction. In addition, very few nucleation phenomena were observed in natural earthquakes. We performed friction experiments using a pair of meter-sized Indian gabbro specimens. The fault plane was 1.5 m long and 0.5 m wide. The specimens were loaded at a speed as low as 0.0025 m/s. We continuously observed shear strains and elastic waves with 2-D array of piezoelectric sensors and strain gauges to improve our knowledge about rupture nucleation process. Sensors and gauges were installed at 24 sites located 60 mm below the fault plane at intervals of 150 mm and 75 mm for in-plane and anti-plane directions, respectively. The stick-slip events were extracted using wave amplitudes and the ratio of share and normal stresses. Two typical stable phases (nucleation phases) of decrease in shear strain were recognized followed by the dynamic rupture. The first decrease was initiated around the edge in anti-plane direction (northern side). The decreasing rate was lower than 10-6 s-1, and the decrease preferably propagated in anti-plane direction at a speed slower than 100 m/s. The second decrease was initiated about when the first one reached the opposite end (southern side). The decreasing rate was higher (~10-4 s-1) than that of the first one, and the decrease preferably propagated in anti-plane direction at a higher speed (an order of 100 m/s). About when the second phase got back to the northern end, the rapid decrease (~10-3 s-1) was initiated at the western edge, and two-dimensionally propagated faster than 1 km/s, which corresponded to dynamic rupture. Then, the rupture nucleation and dynamic rupture propagations in laboratory were suggested to be controlled by the sample edge.

  7. 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)

    2010-08-01

    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

  8. Experimental and theoretical investigation for temperature characteristics and propagation losses of SAWs on SiO2\\/Al\\/LiTaO3

    Microsoft Academic Search

    K. Asai; M. Hikita; A. Isobe; K. Sakiyama; T. Tada

    2002-01-01

    Improvement of temperature coefficients of frequency (TCFs) for LiTaO3 substrate was investigated. SAW resonators formed on SiO2\\/Al\\/36°Y-X LiTaO3 substrate with various kinds of SiO2 relative thickness were examined experimentally and theoretically. A zero TCF at fr was obtained for h\\/??0.31, while that at fa was obtained for h\\/??0.36 from experiments. Moreover, the experimental propagation losses revealed also different characteristics between

  9. Radio Galaxies.

    ERIC Educational Resources Information Center

    Downes, Ann

    1986-01-01

    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)

  10. Measurement and modeling of the effects of atmospheric turbulence on coherent laser propagation characteristics and FSO system performance

    NASA Astrophysics Data System (ADS)

    Zhou, Jian; Lu, Wei; Sun, Jianfeng; Liu, Liren

    2013-09-01

    We investigate the random phase fluctuations of coherent laser propagate through the turbulent atmosphere, and introduce a model of its impact on optical heterodyne reception free space coherent laser optical communication (FSO) system. A polarization based shearing interferometer is used to detect the distorted laser wave-front and reconstruct the wave-front after propagate through a 1Km near-ground atmospheric channel. Further, the heterodyne efficiency of the heterodyne reception system would be given under special consideration of the mismatch between the signal field and the local oscillator. By analyzing the heterodyne efficiency data and the real-time atmospheric coherence length data, a mathematical model of the effects of atmospheric turbulence on FSO system performance is given.

  11. Characteristics of VLF wave propagation in the Earth's magnetosphere in the presence of an artificial density duct

    NASA Astrophysics Data System (ADS)

    Pasmanik, Dmitry; Demekhov, Andrei

    We study the propagation of VLF waves in the Earth's ionosphere and magnetosphere in the presence of large-scale artificial plasma inhomogeneities which can be created by HF heating facilities like HAARP and ``Sura''. A region with enhanced cold plasma density can be formed due to the action of HF heating. This region is extended along geomagnetic field (up to altitudes of several thousand km) and has rather small size across magnetic field (about 1 degree). The geometric-optical approximation is used to study wave propagation. The plasma density and ion composition are calculated with the use of SAMI2 model, which was modified to take the effect of HF heating into account. We calculate ray trajectories of waves with different initial frequency and wave-normal angles and originating at altitudes of about 100 km in the region near the heating area. The source of such waves could be the lightning discharges, modulated HF heating of the ionosphere, or VLF transmitters. Variation of the wave amplitude along the ray trajectories due to refraction is considered and spatial distribution of wave intensity in the magnetosphere is analyzed. We show that the presence of such a density disturbances can lead to significant changes of wave propagation trajectories, in particular, to efficient guiding of VLF waves in this region. This can result in a drastic increase of the VLF-wave intensity in the density duct. The dependence of wave propagation properties on parameters of heating facility operation regime is considered. We study the variation of the spatial distribution of VLF wave intensity related to the slow evolution of the artificial inhomogeneity during the heating.

  12. Propagation characteristics of leaky surface acoustic waves for two thin metal layers on LiTaO3 substrate

    Microsoft Academic Search

    H. Meier; P. Russer

    1991-01-01

    Leaky surface acoustic waves (LSAWs) propagating in the crystalline X-direction of rotated Y-cuts of LiTaO3 substrates are investigated. The effect of two thin isotropic metallic films deposited on the substrate surface is rigorously taken into consideration. The relatively small bulk wave term in the partial wave solution has a phase velocity vector tilted towards the substrate at an angle of

  13. Sugarcane (Saccharum sp. Hybrid) Propagated in Headspace Renovating Systems Shows Autotrophic Characteristics and Develops Improved Anti-oxidative Response

    Microsoft Academic Search

    Carlos Aragón; Luísa C. Carvalho; Justo González; Maritza Escalona; Sara Amâncio

    2009-01-01

    Previous results have shown that sugarcane plantlets micropropagated in Temporary Immersion Bioreactors (TIB) demonstrated\\u000a a better morphology and physiological behaviour when compared to plantlets propagated in Gelled Medium (GM). The present work\\u000a focuses on the onset of oxidative stress symptoms at transfer to ex vitro and during acclimatization. The specific ROS being produced were identified and tissue-located by infiltrating leaves

  14. Acoustic characteristics and the underlying rules of intonation of the common Japanese used by radio and television announcers

    Microsoft Academic Search

    Hiroya Fujisaki; Keikichi Hirose; Noboru Takahashi; Hiroyoshi Morikawa

    1986-01-01

    Announcements and narrations broadcast over radio and television have been serving in recent years as the most effective means for spreading the spoken version of the common Japanese, especially in regards to intonation. No formal studies, however, seem to have been conducted on the objective analysis and formulation of the rules of intonation of the common Japanese. The present work

  15. Studies on characteristics of resistive power calculated with discrete Fourier transform in a pulse-modulated radio frequency discharge.

    PubMed

    Huo, W G; Zhang, H; Ding, Z F

    2015-02-01

    In a pulse-modulated (PM) radio-frequency (RF) capacitively coupled plasma, the DFT (Discrete Fourier Transform)-calculated RF power and the corresponding phase shift between voltage and current measured with calibrated voltage and current probes present oscillations in the pulse rising and falling edges. The oscillating phase shift between voltage and current obtained in the falling edge is outside the expected value for a resistive-capacitive RF discharge. Numerical simulation and analytical analysis are made to interpret these abnormal characteristics and seek an approach to obtaining the reliable resistive (active) RF power. The oscillation is proved to be originated from the oscillating non-zero reactive RF power of the capacitor(s) in the load. At the time instant when the reactive RF power within an integer RF period is not zero, the reactive RF power is mistakenly regarded as the active RF power in the DFT analysis, as a result, the corresponding phase is thus incorrect and even outside the expected value for a resistive-capacitive load. The resistive RF power and the phase can be only correctly calculated at the time instant when the reactive RF power is zero. For a series (or parallel) RC (resistor-capacitor) load and a combined RC load with the dominated series (or parallel) RC impedance, the time instant of the zero reactive RF power is calculated with one of the two proposed empirical formulae. In practice, the DFT-calculated resistive RF power is obtained according to the following procedures: (1) applying DFT to the measured RF voltage and current signals to obtain the power and time instants for minimal phase shifts between voltage and current; (2) selecting the empirical formula to calculate time instants of the zero reactive RF power; (3) getting resistive powers at time instants of the zero reactive RF power. In real PM RF capacitively coupled plasmas, the empirical formula for the series RC load is selected to calculate the resistive RF power. The accuracy of DFT-calculated resistive RF power is proved to be related to two kinds of errors. The first is the error of the time instant of the zero reactive RF power calculated using the empirical formula. This error is relatively lower when the requirement that the dominated parallel or series RC impedance is met and is almost independent of the impedance phase angle of a combined RC load. The second is the error of the DFT-calculated resistive RF power compared with the corresponding time integral RF power at the real zero reactive RF power. This error is independent of the load type or the load impedance but varies with the slope of PM RF voltage amplitude vs. time. The two kinds of errors both increase in the pulse rising and falling edges. PMID:25725843

  16. Radio Astronomy Radio astronomy

    E-print Network

    Metchev, Stanimir

    ;#12;Arecibo 300m telescope #12;Radio interferometer #12;Radio interferometer Very Large Array (VLA) (New;WestVirginia) #12;Centimeter radio astronomy HI 21cm line emission traces the distribution of atomic hydrogen. Dust: far-Infrared (60-240micron) map NASA/GSFC Atomic hydrogen (HI): 21cm emission-line Dickey & Lockman

  17. Considerations on an underground neutrino radio detector in salt

    NASA Astrophysics Data System (ADS)

    Badescu, A.-M.

    2013-03-01

    This article presents the possibility of in-salt radio detection of high energy neutrinos, and shows the implications that a heterogeneous propagating medium has on both antenna behaviour, and on constructing the detector. Based on several factors (propagation effects signal to noise ratio, minimum necessary number of triggers, etc.) it was found that observations are limited at a 1022 eV energy threshold. This higher limit allows both neutrino characteristics, and internal structure of the dome to be simultaneously determined. A total number of 40 to 200 events per year is expected when typical sedimentary layers of about 5cm are considered for the internal salt dome structure.

  18. Extragalactic Synchrotron Transients in the Era of Wide-field Radio Surveys. I. Detection Rates and Light Curve Characteristics

    NASA Astrophysics Data System (ADS)

    Metzger, Brian D.; Williams, P. K. G.; Berger, Edo

    2015-06-01

    The impending era of wide-field radio surveys has the potential to revolutionize our understanding of astrophysical transients. Here we evaluate the prospects of a wide range of planned and hypothetical radio surveys using the properties and volumetric rates of known and hypothetical classes of extragalactic synchrotron radio transients (e.g., on-axis and off-axis gamma-ray bursts (GRBs), supernovae, tidal disruption events, compact object mergers). Utilizing these sources and physically motivated considerations we assess the allowed phase space of radio luminosity and peak timescale for extragalactic transients. We also include for the first time effects such as redshift evolution of the rates, K-corrections, and non-Euclidean luminosity distance, which affect the detection rates of the most sensitive surveys. The number of detected events is calculated by means of a Monte Carlo method, using the various survey properties (depth, cadence, area) and realistic detection criteria that include a cut on the minimum variability of the transients during the survey and an assessment of host galaxy contamination. We find that near-term GHz frequency surveys (ASKAP/VAST, Very Large Array Sky Survey) will detect few events: ? 30-50 on- and off-axis long GRBs (LGRBs) and off-axis tidal disruption events, and ? 50-100 neutron star binary mergers if ? 0.5% of the mergers result in a stable millisecond magnetar. Low-frequency surveys (e.g., LOFAR) are unlikely to detect any transients, while a hypothetical large-scale mm survey may detect ?40 on-axis LGRBs. On the other hand, we find that SKA1 surveys at ? 0.1-1 GHz have the potential to uncover thousands of transients, mainly on-axis and off-axis LGRBs, on-axis short GRBs, off-axis TDEs, and neutron star binary mergers with magnetar remnants.

  19. The NASA radiowave propagation program

    Microsoft Academic Search

    Faramaz Davarian

    1990-01-01

    The objectives of the NASA radiowave Propagation Program are to enable new satellite communication applications and to enhance existing satellite communication networks. These objectives are achieved by supporting radio wave propagation studies and disseminating the study results in a timely fashion. Studies initiated by this program in the 1980s enabled the infant concept of conducting mobile communications via satellite to

  20. The propagation and scattering characteristics of a forest as measured by coherent ultra-wideband foliage penetration

    NASA Astrophysics Data System (ADS)

    Gwynne, John Scott

    Coherent polarimetric synthetic aperture radar (SAR) measurements of a central Ohio forest have been collected, and it is the objective of this research to document and analyze the results. The foliage data presented in this dissertation are unique in several aspects. Primarily, the data are Ultra-Wideband (UWB) in that the bandwidth (200-1600MHz) divided by center frequency is at least 25% and are of a wavelength selected to penetrate the forest canopy. Data of this bandwidth or resolution offer the opportunity to see for the first time at these frequencies scattering components such as branches, tree trunks, and ground-tree interaction terms. Secondly, coherent apertures were collected by precisely moving the antennas within a well-known coordinate system leading to absolute phase calibration and to the generation of fully coherent SAR imagery. Much of the past work performed on foliage propagation and scattering does not include phase information which is crucial for predicting the performance of radars of this type. The underlying goals of this research are to identify the fundamental scattering mechanisms associated with the forest backscatter at these frequencies and to assess UWB usage for the concealed target detection and identification problems. To this end, methods are developed to analyze the above measurements and extract modeling parameters such as the propagation loss, phase defect, and backscatter per unit area (sigmasp{o}). The analysis of these data provide the insight needed to statistically model the forest in both forward scatter and backscatter and to determine the ability of these UWB frequencies to penetrate the forest canopy.

  1. Adaptive ground implemented phased array. [evaluation to overcome radio frequency interference characteristics of TDRS VHF return link

    NASA Technical Reports Server (NTRS)

    Smith, J. M.

    1973-01-01

    Tests were conducted to determine the feasibility of using an adaptive ground implemented phased array (AGIPA) to overcome the limitations of the radio frequency interference limited low data Tracking and Data Relay Satellite VHF return link. A feasibility demonstration model of a single user channel AFIPA system was designed, developed, fabricated, and evaluated. By scaling the frequency and aperture geometry from VHF to S-band, the system performance was more easily demonstrated in the controlled environment of an anechoic chamber. The testing procedure employs an AGIPA in which received signals from each element of the array are processed on the ground to form an adaptive, independent, computer controlled beam for each user.

  2. Nonlinear Electrodynamics: Alternative Field Theory for Featuring Photon Propagation Over Weak Background Electromagnetic Fields and what Earth Receivers Read off Radio Signals from Interplanetary Spacecraft Transponders

    Microsoft Academic Search

    Herman J. Mosquera Cuesta

    2011-01-01

    A few observational and\\/or experimental results have dramatically pushed forward the research program on gravity as those from the radio-metric Doppler tracking received from the Pioneer 10 and 11 spacecrafts when the space vehicles were at heliocentric distances between 20 and 70 Astronomical Units (AU). These data have conclusively demonstrated the presence of an anomalous, tiny and blue-shifted frequency drift

  3. Engineering geological characteristics and the hydraulic fracture propagation mechanism of the sand-shale interbedded formation in the Xu5 reservoir

    NASA Astrophysics Data System (ADS)

    Lu, Cong; Li, Mei; Guo, Jian-Chun; Tang, Xu-Hai; Zhu, Hai-Yan; Yong-Hui, Wang; Liang, Hao

    2015-06-01

    In the Xu5 formation the sandstone reservoir and the shale reservoir are interbedded with each other. The average thickness of each formation is about 8?m, which increases the difficulty of the hydraulic fracturing treatment. The shale thickness ratio (the ratio of shale thickness to formation thickness) is 55–62.5%. The reservoir is characterized by ultra-low porosity and permeability. The brittleness index of sandstone is 0.5–0.8, and the brittleness index of shale is 0.3–0.8. Natural fractures are poorly developed and are mainly horizontal and at a low angle. The formation strength is medium and the reservoir is of the hybrid strike-slip fault and reverse fault stress regime. The difference between the minimum principal stress and the vertical stress is small, and the maximum horizontal principal stress is 20?MPa higher than the minimum horizontal principal stress and vertical stress. A mechanical model of a hydraulic fracture encountering natural fractures is built according to geological characteristics. Fracture mechanics theory is then used to establish a hydraulic fracturing model coupling the seepage–stress–damage model to simulate the initiation and propagation of a fracture. The hydraulic fracture geometry is mainly I-shaped and T-shaped, horizontal propagation dominates the extension, and vertical propagation is limited. There is a two to three meter stress diversion area around a single hydraulic fracture. The stress diversion between a hydraulic fracture and a natural fracture is advantageous in forming a complex fracture. The research results can provide theoretical guidance for tight reservoir fracturing design.

  4. Kinematics of ICMEs Deduced From Remote Radio Observations

    NASA Astrophysics Data System (ADS)

    Reiner, M. J.; MacDowall, R. J.

    2009-12-01

    Low-frequency radio emissions, generated at the driven shock wave at the fundamental and harmonic of the plasma frequency, can directly reveal the kinematics of ICMEs as they propagate through the inner heliosphere. The reason is that the frequency of the radio emissions varies in a predictable way as a function of heliocentric distance. Hence, the observed frequency drift of these radio emissions is essentially a plot of the height above the Sun as a function of time. The derivative of the observed frequency-time curve at each point then gives the instantaneous speed of the propagating interplanetary shock. We have used these remote radio observations to determine the speed profiles for some 40 fast CMEs observed during solar cycle 23. The speed profiles for these fast ICMEs were found to imply an initial rapid deceleration at a constant rate, followed by a constant propagation speed to 1 AU (Reiner et al. ApJ 663, 1369, 2007), consistent with some earlier Doppler scintillation measurements (Woo et al., JGR 90, 154, 1985). Because of the large number of CME events for which this analysis was carried out, we were further able to study the correlations of the deceleration parameters of the ICME speed profiles. For most of those remote radio observations, there were no corresponding white-light observations beyond the 32 Rs (0.15 AU) limit of the LASCO coronagraph. After 2003, the all-sky camera SMEI permitted the first direct comparison between the remote radio and the white-light observations in interplanetary space (Reiner et al. JGR 110, A09S14, 2005). The STEREO spacecraft, launched in October of 2006, provide a new and unique opportunity to make direct comparisons between the radio and white-light observations of the ICME kinematics. The STEREO observations also allow the locations of the radio sources along the shock front to be directly deduced from two or three spacecraft triangulation measurement from STEREO and Wind (Reiner et al. Solar Physics 10.1007/s11207-009-9404-z, 2009). However, due to solar minimum, to date no CMEs observed by STEREO were fast enough to produce measurable radio emissions. As we approach solar maximum that situation will surely change. Nevertheless, some height-time data for fast CMEs that were observed in the Heliospheric Imagers on STEREO do seem to confirm the general characteristics of the speed profile previously deduced from radio tracking (Wood et al., ApJ 694, 707, 2009). In this talk, we will summarize our previous remote radio results, and show how they can be used to provide improved algorithms for space weather predictions.

  5. The radio emission from pulsars

    Microsoft Academic Search

    F. Graham-Smith

    2003-01-01

    The basic observed properties of pulsar radio emission are reviewed with a view to guiding their interpretation. Particular attention is given to the location of the sources of emission both in normal and in gamma-ray pulsars, with brief reviews of radio propagation in the magnetosphere and of emission mechanisms.

  6. Analytical model of bistatic reflections and radio occultation signals

    NASA Astrophysics Data System (ADS)

    Pavelyev, A. G.; Zhang, K.; Matyugov, S. S.; Liou, Y. A.; Wang, C. S.; Yakovlev, O. I.; Kucherjavenkov, I. A.; Kuleshov, Y.

    2011-02-01

    The relationships between the Doppler frequencies, eikonal acceleration, and refractive attenuations of the direct and reflected signals are established for bistatic and radio occultation experiments. These connections allow recalculating the Doppler shifts and the phase delays to the refractive attenuation (reflectivity cross section) and open a new avenue for potentially measuring the total absorption in the atmosphere at low elevation angles. The fundamental characteristics of bistatic remote sensing of the atmosphere and Earth's surface such as the phase delay, reflection coefficient, reflectivity cross section, and Doppler shift of the reflected signals relative to the direct signals are obtained in analytical forms by taking into account the refraction and absorption effects in the atmosphere. Difference in the Doppler frequencies of the reflected and direct signals is proportional to the difference of the modified refractive index at the radio ray perigee and at the Earth's surface. The obtained analytical results are in good agreement with the measurements data obtained during the MIR/GEO (wavelengths 2 and 32 cm), and CHAMP (wavelengths 19 and 24 cm) radio occultation experiments. Detecting the reflected signals in radio occultation data has opened new perspectives for bistatic monitoring of the atmosphere and Earth's surface at low elevation angles. Experimental results of the propagation effects at low elevation angles are of great importance for fundamental theoretical investigation of radio waves propagation.

  7. The effect of adiabatic focusing upon charged particle propagation in random magnetic fields

    NASA Technical Reports Server (NTRS)

    Earl, J. A.

    1975-01-01

    Charged particles propagating along the diverging lines of force of a spatially inhomogeneous guiding field were considered as they are scattered by random fields. Their longitudinal transport is described in terms of the eigenfunctions of a Sturm-Liouville operator incorporating the effect of adiabatic focussing along with that of scattering. The relaxation times and characteristic velocities are graphed and tabulated. The particle density is evaluated as a function of space and time for two different regimes. In the first regime (relatively weak focussing), a diffusive mode of propagation is dominant but coherent modes are also dominant. In the second regime (strong focussing), diffusion does not occur and the propagation is purely coherent. This supercoherent mode corresponds exactly to the so-called scatter-free propagation of kilovolt solar flare electrons. On a larger scale, focussed transport provides an interpretation of many observed characteristics of extragalactic radio sources.

  8. A Study of Type II Radio Bursts to Map the Alfvén Speed Profile in the Inner Heliosphere

    NASA Astrophysics Data System (ADS)

    Bain, Hazel; Martinez Oliveros, Juan Carlos; Sundkvist, David; Bale, Stuart D

    2014-06-01

    It is well accepted that interplanetary Type II radio bursts are the manifestations of electron acceleration in shocks driven by propagating of coronal mass ejections (CMEs) traveling faster than the characteristic local fast magnetosonic speed. A prominent feature of type II radio bursts is the intermittency of the observed emission across the metric, decametric and kilometric frequency ranges, as the shock propagates to greater distances. This can be attributed to changes in both the shock driver and to the conditions in the ambient medium. We present results from a survey of coronal and interplanetary type II radio bursts using radio observations from STEREO/WAVES and WIND/WAVES to determine the distance of the observed type II emission and the speed of the associated shock. By establishing regions of the corona and interplanetary medium that are predisposed to shock formation, we map out the profile of the fast magnetosonic speed, and in turn infer the local Alfvén speed.

  9. NASA Lunar Base Wireless System Propagation Analysis

    NASA Technical Reports Server (NTRS)

    Hwu, Shian U.; Upanavage, Matthew; Sham, Catherine C.

    2007-01-01

    There have been many radio wave propagation studies using both experimental and theoretical techniques over the recent years. However, most of studies have been in support of commercial cellular phone wireless applications. The signal frequencies are mostly at the commercial cellular and Personal Communications Service bands. The antenna configurations are mostly one on a high tower and one near the ground to simulate communications between a cellular base station and a mobile unit. There are great interests in wireless communication and sensor systems for NASA lunar missions because of the emerging importance of establishing permanent lunar human exploration bases. Because of the specific lunar terrain geometries and RF frequencies of interest to the NASA missions, much of the published literature for the commercial cellular and PCS bands of 900 and 1800 MHz may not be directly applicable to the lunar base wireless system and environment. There are various communication and sensor configurations required to support all elements of a lunar base. For example, the communications between astronauts, between astronauts and the lunar vehicles, between lunar vehicles and satellites on the lunar orbits. There are also various wireless sensor systems among scientific, experimental sensors and data collection ground stations. This presentation illustrates the propagation analysis of the lunar wireless communication and sensor systems taking into account the three dimensional terrain multipath effects. It is observed that the propagation characteristics are significantly affected by the presence of the lunar terrain. The obtained results indicate the lunar surface material, terrain geometry and antenna location are the important factors affecting the propagation characteristics of the lunar wireless systems. The path loss can be much more severe than the free space propagation and is greatly affected by the antenna height, surface material and operating frequency. The results from this paper are important for the lunar wireless system link margin analysis in order to determine the limits on the reliable communication range, achievable data rate and RF coverage performance at planned lunar base work sites.

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

    NASA Astrophysics Data System (ADS)

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

    2006-08-01

    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 the impact site. As the plasma cloud expands away from the spacecraft it produces a voltage pulse on the RPWS electric field antennas, the amplitude of which is proportional to the mass of the impacting particle. Two types of measurements are made: waveform measurements from the x-axis dipole antenna, and spectrum measurements from the w-axis monopole antenna. The waveform measurements from the dipole antenna provide a determination of the impact rate and the relative mass distribution, and the spectrum measurements from the monopole antenna provide a determination of the root-mean-square particle mass. The impact rate at both ring plane crossings provides a good fit to the sum of two Gaussians, with an average impact rate of about 1200 per second (the exact value depends on the voltage threshold used), and a north-south thickness of about 300 km. The mass distribution depends on the distance from the ring plane, varying from about m-2 near the ring plane at z=0ą100km, where z is the north-south distance from the ring plane, to as steep as m-4 well away from the ring plane at z=500ą100km. The mechanisms involved in the impact detection are discussed and a formula relating the root-mean-square particle mass to the root-mean-square voltage on the w-axis monopole is derived. Using this formula, the root-mean-square mass is estimated to be 7.7×10 -11 g, which for water ice particles with a density of 0.92 g cm -3 gives a root-mean-square radius of about 2.6 ?m.

  11. Nonlinear Electrodynamics: Alternative Field Theory for Featuring Photon Propagation Over Weak Background Electromagnetic Fields and what Earth Receivers Read off Radio Signals from Interplanetary Spacecraft Transponders

    E-print Network

    Cuesta, Herman J Mosquera

    2011-01-01

    A few observational and/or experimental results have dramatically pushed forward the research program on gravity as those from the radio-metric Doppler tracking received from the Pioneer 10 and 11 spacecrafts when the space vehicles were at heliocentric distances between 20 and 70 Astronomical Units (AU). These data have conclusively demonstrated the presence of an anomalous, tiny and blue-shifted frequency drift that changes smoothly at a rate of $ \\sim 6 \\times 10^{-9}$ Hz s$^{-1}$. Those signals, if interpreted as a gravitational pull of the Sun on each Pioneer vehicle, translates into a deceleration of $a_P = (8.74\\pm 1.33) \\times 10^{-10}$ m s$^{-2}$. This Sunward acceleration appears to be a violation of Newton's inverse-square law of gravitation, and is referred to as the Pioneer anomaly, the nature of which remains still elusive to unveil. Within the theoretical framework of nonlinear electrodynamics (NLED) in what follows we will address this astrodynamics puzzle, which over the last fifteen years ha...

  12. Satellite observations of type 3 solar radio bursts at low frequencies

    NASA Technical Reports Server (NTRS)

    Fainberg, J.; Stone, R. G.

    1973-01-01

    Type III solar radio bursts were observed from 10 MHz to 10 KHz by satellite experiments above the terrestrial plasmasphere. Solar radio emission in this frequency range results from excitation of the interplanetary plasma by energetic particles propagating outward along open field lines over distances from 5 solar radii to at least 1 AU from the sun. This review summarizes the morphology, characteristics and analysis of individual as well as storms of bursts. Burst rise times are interpreted in terms of exciter length and dispersion while decay times refer to the radiation damping process. The combination of radio observations at the lower frequencies and in-situ measurements on nonrelativistic electrons at 1 AU provide data on the energy range and efficiency of the wave-particle interactions responsible for the radio emission.

  13. Nonlinear Electrodynamics: Alternative Field Theory for Featuring Photon Propagation Over Weak Background Electromagnetic Fields and what Earth Receivers Read off Radio Signals from Interplanetary Spacecraft Transponders

    E-print Network

    Herman J. Mosquera Cuesta

    2011-05-13

    A few observational and/or experimental results have dramatically pushed forward the research program on gravity as those from the radio-metric Doppler tracking received from the Pioneer 10 and 11 spacecrafts when the space vehicles were at heliocentric distances between 20 and 70 Astronomical Units (AU). These data have conclusively demonstrated the presence of an anomalous, tiny and blue-shifted frequency drift that changes smoothly at a rate of $ \\sim 6 \\times 10^{-9}$ Hz s$^{-1}$. Those signals, if interpreted as a gravitational pull of the Sun on each Pioneer vehicle, translates into a deceleration of $a_P = (8.74\\pm 1.33) \\times 10^{-10}$ m s$^{-2}$. This Sunward acceleration appears to be a violation of Newton's inverse-square law of gravitation, and is referred to as the Pioneer anomaly, the nature of which remains still elusive to unveil. Within the theoretical framework of nonlinear electrodynamics (NLED) in what follows we will address this astrodynamics puzzle, which over the last fifteen years has challenged in a fundamental basis our understanding of gravitational physics. To this goal we will first, and briefly, review the history of the Pioneers 10 and 11 missions. Then a synopsis of currently available Lagrangian formulations of NLED is given. And finally, we present our solution of this enigma by invoking a special class of NLED theories featuring a proper description of electromagnetic phenomena taking place in environments where the strength of the (electro)magnetic fields in the background is decidedly low.

  14. Radio telescopes

    Microsoft Academic Search

    J. Findlay

    1964-01-01

    A radio telescope is used in radio astronomy to measure the intensity of the radiation received from various parts of the sky. Such a telescope must be able both to detect and to locate faint radio sources of small angular size, and also to measure the brightness distribution across extended radio sources or over large sky areas. Ideally the telescope

  15. Near-Relativistic Solar Electrons and Type III Radio Bursts

    NASA Technical Reports Server (NTRS)

    Cane, H. V.

    2003-01-01

    Recently it has been found that the inferred injection times of greater than 25 keV electrons are up to 30 minutes later than the start times of the associated type III radio bursts at the Sun. Thus it has been suggested that the electrons that produce type III bursts do not belong to the same population as those observed above 25 keV. This paper examines the characteristics and circumstances of 79 solar electron beam events measured on the ACE spacecraft. Particular attention is paid to the very low frequency emissions of the associated radio bursts and the ambient conditions at the arrival times of the electrons at the spacecraft. It is found that the inferred greater than 25 keV electron injection delays are correlated with the times required for the associated radio bursts to drift to the lowest frequencies. This suggests that the electrons responsible for the radio emission and those observed above 25 keV are part of a single population, and that the electrons both above and below 25 keV are delayed in the interplanetary medium. Further evidence for a single population is the general correspondence between electron and local radio intensities and temporal profiles. It is found that the delays increase with the ambient solar wind density consistent with the propagation times of the electrons being determined by the characteristics of the interplanetary medium. However it is known that particle arrival times at 1 AU are a linear function of inverse particle speed. Conventionally such a relationship is taken to indicate scatter-free propagation when inferred path lengths lie close to 1.2 AU, as they do for the electron events studied here. These conflicting interpretations require further investigation.

  16. Radio channel measurement and modelling for future mobile radio systems

    NASA Astrophysics Data System (ADS)

    Guerdenli, E.; Huish, P. W.

    1989-12-01

    Digital mobile radio systems will require planning methods that provide accurate predictions of signal strength, distortion, and interference for situations ranging from very small cells in dense urban locations to large rural cells. Topographic and land usage data bases will find increasing use to enhance the accuracy of prediction models. The implications of these issues are discussed and the work in progress at British Telecommunications Research Laboratories on land mobile radio propagation modeling and wide-band channel measurements is presented.

  17. The surface acoustic wave propagation characteristics of 64° Y-X LiNbO3 and 36° Y-X LiTaO3 substrates with thin-film SiO2

    Microsoft Academic Search

    F. S. Hickemell; H. D. Knuth; R. C. Dablemont; T. S. Hickernell

    1995-01-01

    The SAW characteristics of thin-film sputtered silicon dioxide (SiO2) on substrates of 64° Y-X lithium niobate (LiNbO 3) and 36° Y-X lithium tantalate (LiTaO3) have been measured in the frequency range from 30 MHz to above 1.0 GHz. Silicon dioxide films in the 500 nm to 2000 nm thickness range were deposited by RF diode sputtering. The SAW velocity, propagation

  18. Modification of tropospheric propagation conditions

    Microsoft Academic Search

    H. Jeske

    1990-01-01

    The propagation mechanisms of ultra-short radio waves and microwaves are governed by the composition of the troposphere and their space-time structure of the refractive index field. Useful effects are obtained by chaff clouds concerning communication channels, masking of targets or meteorological research. A wide field of posiibilities seems to be within the scope of weather modification experiments. But due to

  19. Proceedings of the Thirteenth NASA Propagation Experimenters Meeting (NAPEX 13)

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz (editor)

    1989-01-01

    The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. The meeting was organized into three technical sessions: the first focused on mobile satellite propagation; the second examined the propagation effects for frequencies above 10 GHz; and the third addressed studies devoted exclusively to the Olympus/Advanced Communications Technology Satellite (ACTS) Program.

  20. Premixed Turbulent Flame Propagation in Microgravity

    NASA Technical Reports Server (NTRS)

    Menon, S.; Disseau, M.; Chakravarthy, V. K.; Jagoda, J.

    1997-01-01

    Papers included address the following topics: (1) Turbulent premixed flame propagation in microgravity; (2) The effect of gravity on turbulent premixed flame propagation - a preliminary cold flow study; and (3) Characteristics of a subgrid model for turbulent premixed combustion.

  1. Indoor radio communications for factories of the future

    Microsoft Academic Search

    Theodore S. Rappaport

    1989-01-01

    The need for reliable, real-time communication for automated factories is discussed. The ability of narrowband digital radio systems to meet that need is examined. The major problems encountered in multipath propagation, resulted from multiple reflections of the transmitted signal from the building structure and surrounding inventory. Radio wave propagation experiments at 1300 MHz, which were conducted by the author in

  2. Radio Astronomy

    NSDL National Science Digital Library

    Tenenbaum, David

    This article is a Why Files short piece on how astronomers use information from radio astronomy. Contrary to popular belief, large radio telescopes are not looking for signs of life outside our solar system, but are making images of black holes, centers of galaxies, and gamma ray bursts. These phenomena cannot be seen in visible light, but emit radio waves which can be translated into images. The article discusses how this process works, and the information gathered from radio waves.

  3. Radio Communication by Scattering from Meteoric Ionization

    Microsoft Academic Search

    Von Eshleman; Laurence Manning

    1954-01-01

    By a consideration of the amplitude and duration of echoes forward-scattered from individual meteor ionization trails, and of the probability of detecting randomly oriented trails over an oblique radio propagation path, an estimate of the contribution of meteoric ionization to extended range hf and vhf radio transmission has been obtained. It has been concluded that meteoric ionization alone would give

  4. A virus spreading model for cognitive radio networks

    NASA Astrophysics Data System (ADS)

    Hou, L.; Yeung, K. H.; Wong, K. Y.

    2012-12-01

    Since cognitive radio (CR) networks could solve the spectrum scarcity problem, they have drawn much research in recent years. Artificial intelligence(AI) is introduced into CRs to learn from and adapt to their environment. Nonetheless, AI brings in a new kind of attacks specific to CR networks. The most powerful one is a self-propagating AI virus. And no spreading properties specific to this virus have been reported in the literature. To fill this research gap, we propose a virus spreading model of an AI virus by considering the characteristics of CR networks and the behavior of CR users. Several important observations are made from the simulation results based on the model. Firstly, the time taken to infect the whole network increases exponentially with the network size. Based on this result, CR network designers could calculate the optimal network size to slow down AI virus propagation rate. Secondly, the anti-virus performance of static networks to an AI virus is better than dynamic networks. Thirdly, if the CR devices with the highest degree are initially infected, the AI virus propagation rate will be increased substantially. Finally, it is also found that in the area with abundant spectrum resource, the AI virus propagation speed increases notably but the variability of the spectrum does not affect the propagation speed much.

  5. Firefighters' Radios

    NASA Technical Reports Server (NTRS)

    1976-01-01

    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.

  6. Transparent boundary conditions application to the tropospheric ducting propagation simulation

    Microsoft Academic Search

    I. D. Sirkova

    2000-01-01

    Summary form only given. Methods based on parabolic equation (PE) approach have become the preferred propagation modeling technique for a number of electromagnetic propagation problems. In the case of tropospheric radio-wave propagation prediction and assessment these methods allow efficient and accurate numerical solutions for a complicated refractive environment (i. e. ducting) and underlying surfaces. In this report, the applicability of

  7. Effect of propagating media on wireless communication system

    Microsoft Academic Search

    M. M. Hossain

    2008-01-01

    Electronic communication system i.e. the radio wave propagation is completely depends on the medium. The signals of LF and VLF are rapidly alternated by the earth's surface. The medium and short wave signals are also affected by troposphere and ionosphere conditions. The line of sight propagation depend both the troposphere condition and ground conductivity. There are various propagation models currently

  8. Svetloe Radio Astronomical Observatory

    NASA Technical Reports Server (NTRS)

    Smolentsev, Sergey; Rahimov, Ismail

    2013-01-01

    This report summarizes information about the Svetloe Radio Astronomical Observatory activities in 2012. Last year, a number of changes took place in the observatory to improve some technical characteristics and to upgrade some units to their required status. The report provides an overview of current geodetic VLBI activities and gives an outlook for the future.

  9. Zelenchukskaya Radio Astronomical Observatory

    NASA Technical Reports Server (NTRS)

    Smolentsev, Sergey; Dyakov, Andrei

    2013-01-01

    This report summarizes information about Zelenchukskaya Radio Astronomical Observatory activities in 2012. Last year a number of changes took place in the observatory to improve some technical characteristics and to upgrade some units to the required status. The report provides an overview of current geodetic VLBI activities and gives an outlook for the future.

  10. Sound propagation

    Microsoft Academic Search

    Marinus M. Boone

    1992-01-01

    An overview is presented of our work on sound propagation models. These models are applied for the prediction of noise emission levels in the atmosphere as well as for studies on acoustic and elastic propagation through earth-layers for seismic exploration applications. The computational models that we use range from ray-tracing algorithms to finite difference techniques. Additionally, physical scale models are

  11. Global morphology of infrasound propagation

    NASA Astrophysics Data System (ADS)

    Drob, Douglas P.; Picone, J. M.; GarcéS, M.

    2003-11-01

    Atmospheric sound waves in the 0.02-10 Hz region, also known as infrasound, exhibit long-range global propagation characteristics. Measurable infrasound is produced around the globe on a daily basis by a variety of natural and man-made sources. As a result of weak classical attenuation (˜0.01 dB km-1 at 0.1 hz), these acoustic signals can propagate thousands of kilometers in tropospheric, stratospheric, and lower thermospheric ducts. To model this propagation accurately, detailed knowledge of the background atmospheric state variables, the global winds and temperature fields from the ground to ˜170 km, is required. For infrasound propagation calculations, we have developed a unique atmospheric specification system (G2S) that is capable of providing this information. Using acoustic ray tracing methods and detailed G2S atmospheric specifications, we investigate the major aspects of the spatiotemporal variability of infrasound propagation characteristics.

  12. Real-time numerical simulations and experimental research for the propagation characteristics of shock waves and gas flow during coal and gas outburst

    Microsoft Academic Search

    Kai Wang; Aitao Zhou; Jianfang Zhang; Pin Zhang

    When coal and gas outburst occurs, high-speed gas flow and air shock wave with high kinetic energy could be created. In this paper, the formation process of outburst shock waves and gas flow has been analyzed firstly. Afterwards, the numerical simulation models of the roadways with right-angled intersection have been established, by which real-time simulation of the propagation of outburst

  13. A body-shadowing model for indoor radio communication environments

    Microsoft Academic Search

    Shuichi Obayashi; Jens Zander

    1998-01-01

    Deterministic propagation prediction methods proposed for indoor radio are useful for estimating the average propagation loss in real environments, which usually have complicated geometries. On the other hand, these methods generally fail to accommodate human body shadowing, which is a significant propagation effect in indoor picocells. Several empirical models to describe body shadowing have been reported. However, to our knowledge,

  14. Propagation invariance and 3D light fields

    Microsoft Academic Search

    Joseph Shamir; Rafael Piestun; Yoav Y. Schechner

    1999-01-01

    Wave-fields that propagate in free space while maintaining invariant characteristics are important for technological applications and they are interesting from a fundamental point of view. Conditions for generalized propagation- invariant wave-fields are discussed and specific examples are presented. Propagation invariance in a limited region of space is considered as well.

  15. GNU radio is a free/open-source software toolkit for building software radios, in which software defines the

    E-print Network

    Wu, Dapeng Oliver

    , Python, , DBPSK/DQPSK, TCP socket I. INTRODUCTION The fundamental characteristic of software radio1 ABSTRACT GNU radio is a free/open-source software toolkit for building software radios, in which software defines the transmitted waveforms and demodulates the received waveforms. Software radio

  16. Structural exploration using longwave radio-clock time-signal

    NASA Astrophysics Data System (ADS)

    Yamazaki, S.; Mikada, H.; Onishi, K.; Konishi, N.

    2008-12-01

    VLF methods have been used for one dimensional survey that ties records of the single point measurement with subsurface structure. Since VLF electromagnetic wave is not stable due to various effects in the propagation, subsurface structural exploration using VLF methods has limitations in resolution and in the applicability depending on the place of surveys. To overcome some of the limitations, we propose to use standard-time longwaveelectromagnetic transmissions (JJY in Japan), that could be more stable than VLF, for the exploration of underground structure. Once radio time-signal receivers have become popular, we may distribute many receivers in a wide area to record continuous time signal simultaneously for estimating subsurface resistivity distribution. Continuous measurements, moreover, might improve measurement efficiency and S/N ratio. In our study, we applied numerical experiments to confirm the method to work. First, we created a test data set composed of air and heterogeneous half space earth for which JJY signal propagates. Then, we estimate the distortion of time signal on the surface of the half space to evaluate the characteristics of underground response to JJY and to see the availability of JJY standard electromagnetic wave for structural exploration as well as for a VLF method. We used electromagnetic wave of 20 kHz as a VLF wave and 40 and 60 kHz as JJY standard electromagnetic waves and evaluated the resolution of the methods derived from the skin depth and the influence of the geometry for various combination of the orientation of anomalous structure, the propagation direction of radio wave, and the orientation of two- dimentionally aligned receivers. To estimate the influence of the geometry between the orientations of structural anomaly and the propagation direction, we evaluated the characteristic response of the survey as a function of difference angle of the orientations. Our results show the following confirmation: (i) there are little influence on the attenuation of the electromagnetic radiation if observation point is located above the resistivity anomaly, (ii) - higher the frequency becomes, shallower layer the influences come from, and (iii) the smaller difference angle becomes, better the sensitivity of survey becomes. Therefore, we conclude that the structural anomaly runs in the direction of radio wave propagation, the most ideal survey would be conducted as known well for electromagnetic surveys. Our study suggests that JJY signal or any other continuous time signal could be used for the estimation of subsurface resistivity distribution. In the future, we try to extend the method to VLF-MT for subsurface structure and to apply it for field data.

  17. High amplitude propagated contractions.

    PubMed

    Bharucha, A E

    2012-11-01

    While most colonic motor activity is segmental and non-propulsive, colonic high amplitude propagated contractions (HAPC) can transfer colonic contents over long distances and often precede defecation. High amplitude propagated contractions occur spontaneously, in response to pharmacological agents or colonic distention. A subset of patients with slow transit constipation have fewer HAPC. In this issue of Neurogastroenterology and Motility, Rodriguez et al. report that anal relaxation during spontaneous and bisacodyl-induced HAPC exceeds anal relaxation during rectal distention in constipated children undergoing colonic manometry. Moreover, and consistent with a neural mechanism, anal relaxation often precedes arrival of HAPC in the left colon. High amplitude propagated contractions are also used to evaluate the motor response to a meal and pharmacological stimuli (e.g., bisacodyl, neostigmine) and to identify colonic inertia during colonic motility testing in chronic constipation. This editorial comprehensively reviews the characteristics, physiology and pharmacology of HAPC, their assessment by manometry, and relevance to constipation and diarrhea. PMID:23057554

  18. On Sun-to-Earth Propagation of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Liu, Ying D.; Luhmann, Janet G.; Lugaz, Noé; Möstl, Christian; Davies, Jackie A.; Bale, Stuart D.; Lin, Robert P.

    2013-05-01

    We investigate how coronal mass ejections (CMEs) propagate through, and interact with, the inner heliosphere between the Sun and Earth, a key question in CME research and space weather forecasting. CME Sun-to-Earth kinematics are constrained by combining wide-angle heliospheric imaging observations, interplanetary radio type II bursts, and in situ measurements from multiple vantage points. We select three events for this study, the 2012 January 19, 23, and March 7 CMEs. Different from previous event studies, this work attempts to create a general picture for CME Sun-to-Earth propagation and compare different techniques for determining CME interplanetary kinematics. Key results are obtained concerning CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of fast CMEs can be approximately formulated into three phases: an impulsive acceleration, then a rapid deceleration, and finally a nearly constant speed propagation (or gradual deceleration); (2) the CMEs studied here are still accelerating even after the flare maximum, so energy must be continuously fed into the CME even after the time of the maximum heating and radiation has elapsed in the corona; (3) the rapid deceleration, presumably due to interactions with the ambient medium, mainly occurs over a relatively short timescale following the acceleration phase; and (4) CME-CME interactions seem a common phenomenon close to solar maximum. Our comparison between different techniques (and data sets) has important implications for CME observations and their interpretations: (1) for the current cases, triangulation assuming a compact CME geometry is more reliable than triangulation assuming a spherical front attached to the Sun for distances below 50-70 solar radii from the Sun, but beyond about 100 solar radii we would trust the latter more; (2) a proper treatment of CME geometry must be performed in determining CME Sun-to-Earth kinematics, especially when the CME propagation direction is far away from the observer; and (3) our approach to comparing wide-angle heliospheric imaging observations with interplanetary radio type II bursts provides a novel tool in investigating CME propagation characteristics. Future CME observations and space weather forecasting are discussed based on these results.

  19. Plasma Diagnostics of the Interstellar Medium with Radio Astronomy

    E-print Network

    Haverkorn, Marijke

    2013-01-01

    We discuss the degree to which radio propagation measurements diagnose conditions in the ionized gas of the interstellar medium (ISM). The "signal generators" of the radio waves of interest are extragalactic radio sources (quasars and radio galaxies), as well as Galactic sources, primarily pulsars. The polarized synchrotron radiation of the Galactic non-thermal radiation also serves to probe the ISM, including space between the emitting regions and the solar system. Radio propagation measurements provide unique information on turbulence in the ISM as well as the mean plasma properties such as density and magnetic field strength. Radio propagation observations can provide input to the major contemporary questions on the nature of ISM turbulence, such as its dissipation mechanisms and the processes responsible for generating the turbulence on large spatial scales. Measurements of the large scale Galactic magnetic field via Faraday rotation provide unique observational input to theories of the generation of the ...

  20. Plasma Diagnostics of the Interstellar Medium with Radio Astronomy

    NASA Astrophysics Data System (ADS)

    Haverkorn, Marijke; Spangler, Steven R.

    2013-10-01

    We discuss the degree to which radio propagation measurements diagnose conditions in the ionized gas of the interstellar medium (ISM). The "signal generators" of the radio waves of interest are extragalactic radio sources (quasars and radio galaxies), as well as Galactic sources, primarily pulsars. The polarized synchrotron radiation of the Galactic non-thermal radiation also serves to probe the ISM, including space between the emitting regions and the solar system. Radio propagation measurements provide unique information on turbulence in the ISM as well as the mean plasma properties such as density and magnetic field strength. Radio propagation observations can provide input to the major contemporary questions on the nature of ISM turbulence, such as its dissipation mechanisms and the processes responsible for generating the turbulence on large spatial scales. Measurements of the large scale Galactic magnetic field via Faraday rotation provide unique observational input to theories of the generation of the Galactic field.

  1. Plasma Diagnostics of the Interstellar Medium with Radio Astronomy

    NASA Astrophysics Data System (ADS)

    Haverkorn, Marijke; Spangler, Steven R.

    We discuss the degree to which radio propagation measurements diagnose conditions in the ionized gas of the interstellar medium (ISM). The "signal generators" of the radio waves of interest are extragalactic radio sources (quasars and radio galaxies), as well as Galactic sources, primarily pulsars. The polarized synchrotron radiation of the Galactic non-thermal radiation also serves to probe the ISM, including space between the emitting regions and the solar system. Radio propagation measurements provide unique information on turbulence in the ISM as well as the mean plasma properties such as density and magnetic field strength. Radio propagation observations can provide input to the major contemporary questions on the nature of ISM turbulence, such as its dissipation mechanisms and the processes responsible for generating the turbulence on large spatial scales. Measurements of the large scale Galactic magnetic field via Faraday rotation provide unique observational input to theories of the generation of the Galactic field.

  2. Elements of Radio Waves

    E-print Network

    Frank G. Borg; Ismo Hakala; Jukka Määttälä

    2007-12-24

    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.

  3. Chamber propagation

    SciTech Connect

    Langdon, B.

    1991-01-16

    Propagation of a heavy ion beam to the target appears possible under conditions thought to be realizable by several reactor designs. Beam quality at the lens is believed to provide adequate intensity at the target -- but the beam must pass through chamber debris and its self fields along the way. This paper reviews present consensus on propagation modes and presents recent results on the effects of photoionization of the beam ions by thermal x-rays from the heated target. Ballistic propagation through very low densities is a conservative mode. The more-speculative self-pinched mode, at 1 to 10 Torr, offers reactor advantages and is being re-examined by others. 13 refs.

  4. Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Beskin, V. S.; Chernov, S. V.; Gwinn, C. R.; Tchekhovskoy, A. A.

    2015-06-01

    Almost 50 years after radio pulsars were discovered in 1967, our understanding of these objects remains incomplete. On the one hand, within a few years it became clear that neutron star rotation gives rise to the extremely stable sequence of radio pulses, that the kinetic energy of rotation provides the reservoir of energy, and that electromagnetic fields are the braking mechanism. On the other hand, no consensus regarding the mechanism of coherent radio emission or the conversion of electromagnetic energy to particle energy yet exists. In this review, we report on three aspects of pulsar structure that have seen recent progress: the self-consistent theory of the magnetosphere of an oblique magnetic rotator; the location, geometry, and optics of radio emission; and evolution of the angle between spin and magnetic axes. These allow us to take the next step in understanding the physical nature of the pulsar activity.

  5. Radio Pulsars

    E-print Network

    Beskin, V S; Gwinn, C R; Tchekhovskoy, A

    2015-01-01

    Almost 50 years after radio pulsars were discovered in 1967, our understanding of these objects remains incomplete. On the one hand, within a few years it became clear that neutron star rotation gives rise to the extremely stable sequence of radio pulses, that the kinetic energy of rotation provides the reservoir of energy, and that electromagnetic fields are the braking mechanism. On the other hand, no consensus regarding the mechanism of coherent radio emission or the conversion of electromagnetic energy to particle energy yet exists. In this review, we report on three aspects of pulsar structure that have seen recent progress: the self-consistent theory of the magnetosphere of an oblique magnetic rotator; the location, geometry, and optics of radio emission; and evolution of the angle between spin and magnetic axes. These allow us to take the next step in understanding the physical nature of the pulsar activity.

  6. Basic Study on the Radio Frequency Characteristics of the Transmission Lines Employing Periodically Perforated Ground Metal on GaAs Monolithic Microwave Integrated Circuit and Their Equivalent Ciruits

    Microsoft Academic Search

    Young Yun; Jeong-Gab Ju; Hong Seung Kim

    2011-01-01

    In this work, basic characteristics of transmission line employing periodically perforated ground metal (PPGM) were investigated using theoretical and experimental analysis. Concretely, bandwidth and impedance were investigated using theoretical analysis, and wavelength and effective permittivity were extracted from experimental results. In addition, insertion loss and isolation characteristics were investigated using equivalent circuit analysis. For simplification of design process, equivalent circuits

  7. On Sun-to-Earth Propagation of Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Liu, Y.; Luhmann, J. G.; Lugaz, N.; Moestl, C.; Bale, S. D.; Lin, R. P.

    2013-05-01

    We investigate how coronal mass ejections (CMEs) propagate through, and interact with, the inner heliosphere between the Sun and Earth, a key question in CME research and space weather forecasting. CME Sun-to-Earth kinematics are constrained by combining wide-angle heliospheric imaging observations, interplanetary radio type II bursts and in situ measurements from multiple vantage points. We select three events for this study, the 2012 January 19, 23, and March 7 CMEs, each of which has wide-angle imaging coverage from both STEREO A and B, a long-duration interplanetary type II burst and in situ signatures near the Earth. Key results are obtained concerning CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of fast CMEs can be formulated into three phases: an impulsive acceleration, then a rapid deceleration, and finally a nearly constant speed propagation (or gradual deceleration); (2) the CMEs studied here are still accelerating even after the flare maximum, so energy must be continuously fed into the CME even after the maximum heating and radiation have elapsed in the corona; (3) the rapid deceleration, presumably due to interactions with the ambient medium, mainly occurs within a relatively short time scale following the acceleration phase; (4) CME-CME interactions seem a common phenomenon close to solar maximum. Comparison between different techniques (and data sets) gives important implications for CME observations and interpretations: (1) for the current cases triangulation with the fixed ? approximation is more reliable than triangulation with the harmonic mean approximation below 50-70 solar radii from the Sun, but beyond about 100 solar radii we would trust the harmonic mean triangulation more; (2) a proper treatment of CME geometry must be performed in determining CME Sun-to-Earth kinematics, especially when the CME propagation direction is far away from the observer; (3) our approach in comparing wide-angle heliospheric imaging observations with interplanetary radio type II bursts provides a novel tool in investigating CME propagation characteristics. Future CME observations and space weather forecasting are discussed based on the results.

  8. Global morphology of infrasound propagation

    Microsoft Academic Search

    Douglas P. Drob; J. M. Picone; M. Garcés

    2003-01-01

    Atmospheric sound waves in the 0.02-10 Hz region, also known as infrasound, exhibit long-range global propagation characteristics. Measurable infrasound is produced around the globe on a daily basis by a variety of natural and man-made sources. As a result of weak classical attenuation (~0.01 dB km-1 at 0.1 hz), these acoustic signals can propagate thousands of kilometers in tropospheric, stratospheric,

  9. Global morphology of infrasound propagation

    Microsoft Academic Search

    Douglas P. Drob; J. M. Picone; M. Garcés

    2003-01-01

    Atmospheric sound waves in the 0.02–10 Hz region, also known as infrasound, exhibit long-range global propagation characteristics. Measurable infrasound is produced around the globe on a daily basis by a variety of natural and man-made sources. As a result of weak classical attenuation (?0.01 dB km?1 at 0.1 hz), these acoustic signals can propagate thousands of kilometers in tropospheric, stratospheric,

  10. CONTROL OF LASER RADIATION PARAMETERS: Simulation of the output characteristics and propagation of radiation from a CO laser with a selection cell

    NASA Astrophysics Data System (ADS)

    Dolinina, V. I.; Ivanov, S. V.; Kovsh, Ivan B.; Kucherov, Arkadii N.; Makashev, N. K.; Pen'kov, B. A.; Urin, B. M.; Shustov, A. V.

    1996-06-01

    An investigation was made of the influence of an intracavity absorption cell containing water vapour on the spectral and energy characteristics of an electron-beam-controlled discharge-pumped CO laser. The absorption coefficients of laser radiation travelling along a model path containing dried air were calculated. Perturbations of the optical beam along the path was considered under conditions of forced transverse motion of air in the case of unmodified radiation and of radiation with a selected spectrum.

  11. The effects of process conditions on the plasma characteristic in radio-frequency capacitively coupled SiH4/NH3/N2 plasmas: Two-dimensional simulations

    NASA Astrophysics Data System (ADS)

    Liu, Xiang-Mei; Song, Yuan-Hong; Jiang, Wei; Yi, Lin

    2013-04-01

    A two-dimensional (2D) fluid model is presented to study the behavior of silicon plasma mixed with SiH4, N2, and NH3 in a radio-frequency capacitively coupled plasma (CCP) reactor. The plasma-wall interaction (including the deposition) is modeled by using surface reaction coefficients. In the present paper we try to identify, by numerical simulations, the effect of variations of the process parameters on the plasma properties. It is found from our simulations that by increasing the gas pressure and the discharge gap, the electron density profile shape changes continuously from an edge-high to a center-high, thus the thin films become more uniform. Moreover, as the N2/NH3 ratio increases from 6/13 to 10/9, the hydrogen content can be significantly decreased, without decreasing the electron density significantly.

  12. Phenomenology of magnetospheric radio emissions

    NASA Technical Reports Server (NTRS)

    Carr, T. D.; Desch, M. D.; Alexander, J. K.

    1983-01-01

    Jupiter has now been observed over 24 octaves of the radio spectrum, from about 0.01 MHz to 300,000 MHz. Its radio emissions fill the entire spectral region where interplanetary electromagnetic propagation is possible at wavelengths longer than infrared. Three distinct types of radiation are responsible for this radio spectrum. Thermal emission from the atmosphere accounts for virtually all the radiation at the high frequency end. Synchrotron emission from the trapped high-energy particle belt deep within the inner magnetosphere is the dominant spectral component from about 4000 to 40 MHz. The third class of radiation consists of several distinct components of sporadic low frequency emission below 40 MHz. The decimeter wavelength emission is considered, taking into account the discovery of synchrotron emission, radiation by high-energy electrons in a magnetic field, and the present status of Jovian synchrotron phenomenology. Attention is also given to the decameter and hectometer wavelength emission, and emissions at kilometric wavelengths.

  13. Cutting line determination for plant propagation

    NASA Astrophysics Data System (ADS)

    Lo, Li-Yun; Hsia, Chi-Chun; Sun, Hua-Hong; Chen, Hsiang-Ju; Wu, Xin-Ting; Hu, Min-Chun

    2014-01-01

    Investigating an efficient method for plant propagation can help not only prevent extinction of plants but also facilitate the development of botanical industries. In this paper, we propose to use image processing techniques to determine the cutting-line for the propagation of two kinds of plants, i.e. Melaleuca alternifolia Cheel and Cinnamomum kanehirai Hay, which have quite different characteristics in terms of shape, structure, and propagation way (e.g. propagation by seeding and rooting, respectively). The proposed cutting line determination methods can be further applied to develop an automatic control system to reduce labor cost and increase the effectiveness of plant propagation.

  14. Spacecraft Radio Scintillation and Solar System Exploration

    NASA Technical Reports Server (NTRS)

    Woo, Richard

    1993-01-01

    When a wave propagates through a turbulent medium, scattering by the random refractive index inhomogeneities can lead to a wide variety of phenomena that have been the subject of extensive study. The observed scattering effects include amplitude or intensity scintillation, phase scintillation, angular broadening, and spectral broadening, among others. In this paper, I will refer to these scattering effects collectively as scintillation. Although the most familiar example is probably the twinkling of stars (light wave intensity scintillation by turbulence in the Earth's atmosphere), scintillation has been encountered and investigated in such diverse fields as ionospheric physics, oceanography, radio astronomy, and radio and optical communications. Ever since planetary spacecraft began exploring the solar system, scintillation has appeared during the propagation of spacecraft radio signals through planetary atmospheres, planetary ionospheres, and the solar wind. Early studies of these phenomena were motivated by the potential adverse effects on communications and navigation, and on experiments that use the radio link to conduct scientific investigations. Examples of the latter are radio occultation measurements (described below) of planetary atmospheres to deduce temperature profiles, and the search for gravitational waves. However,these concerns soon gave way to the emergence of spacecraft radio scintillation as a new scientific tool for exploring small-scale dynamics in planetary atmospheres and structure in the solar wind, complementing in situ and other remote sensing spacecraft measurements, as well as scintillation measurements using natural (celestial) radio sources. The purpose of this paper is to briefly describe and review the solar system spacecraft radio scintillation observations, to summarize the salient features of wave propagation analyses employed in interpreting them, to underscore the unique remote sensing capabilities and scientific relevance of the scintillation measurements, and to highlight some of the scientific results obtained to date. Special emphasis is placed on comparing the remote sensing features of planetary and terrestrial scintillation measurements, and on contrasting spacecraft and natural radio source scintillation measurements. I will first discuss planetary atmospheres and ionospheres, and then the solar wind.

  15. Radio astronomy

    NASA Technical Reports Server (NTRS)

    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

    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.

  16. Effect of Low pH and Aluminum Toxicity on the Photosynthetic Characteristics of Different Fast-Growing Eucalyptus Vegetatively Propagated Clones

    PubMed Central

    Yang, Mei; Tan, Ling; Xu, Yuanyuan; Zhao, Yihui; Cheng, Fei; Ye, Shaoming; Jiang, Weixin

    2015-01-01

    Knowing how acid soils and aluminum in soils may limit the growth of Eucalyptus trees in plantations is important because these plantations grow in many tropical and subtropical regions. Seedlings of four vegetatively propagated Eucalyptus clones, E. grandis × E. urophylla ‘GLGU9’(G9), E. grandis × E. urophylla ‘GLGU12’ (G12), E. urophylla × E. camaldulensis ‘GLUC3’ (G3) and E. urophylla ‘GLU4’(G4), were subjected to liquid culture with Hoagland nutrient solution for 40 days, then treated with four different treatments of acid and aluminum for 1 day. The four treatments used either pH 3.0 or 4.0 with or without added aluminum (4.4 mM) in all possible combinations; a control used no added aluminum at pH 4.8. Subsequently, the photosynthetic parameters and morphology of leaves from eucalypt seedlings were determined and observed. The results showed that the tested chlorophyll content, net photosynthetic rate, transpiration rate and water use efficiency were apparently inhibited by aluminum. Under uniform Al concentration (4.4 mM), the Al-induced limitation to photosynthetic parameters increased with pH, indicating acid stimulation to Al toxicity. Among all treatments, the most significant reduction was found in the combination of pH 3.0 and 4.4 mM Al. The photosynthetic and transpiration rates showed similar trends with G9 > G12 > G3 > G4, suggesting that G9 and G12 had higher Al-tolerance than other two clones. Microscopic observation revealed changes in leaf morphology when exposed to Al stress; for example, a reduced thickness of leaf epidermis and palisade tissue, the descendant palisade tissue/spongy tissue ratio and leaf tissue looseness. Overall, the acid and aluminum stress exerted negative effects on the photosynthetic activity of eucalypt seedlings, but the differences in tolerance to Al toxicity between the clones were favorable, offering potential to improve Eucalyptus plantation productivity by selecting Al tolerant clones. PMID:26090998

  17. Effect of Low pH and Aluminum Toxicity on the Photosynthetic Characteristics of Different Fast-Growing Eucalyptus Vegetatively Propagated Clones.

    PubMed

    Yang, Mei; Tan, Ling; Xu, Yuanyuan; Zhao, Yihui; Cheng, Fei; Ye, Shaoming; Jiang, Weixin

    2015-01-01

    Knowing how acid soils and aluminum in soils may limit the growth of Eucalyptus trees in plantations is important because these plantations grow in many tropical and subtropical regions. Seedlings of four vegetatively propagated Eucalyptus clones, E. grandis × E. urophylla 'GLGU9'(G9), E. grandis × E. urophylla 'GLGU12' (G12), E. urophylla × E. camaldulensis 'GLUC3' (G3) and E. urophylla 'GLU4'(G4), were subjected to liquid culture with Hoagland nutrient solution for 40 days, then treated with four different treatments of acid and aluminum for 1 day. The four treatments used either pH 3.0 or 4.0 with or without added aluminum (4.4 mM) in all possible combinations; a control used no added aluminum at pH 4.8. Subsequently, the photosynthetic parameters and morphology of leaves from eucalypt seedlings were determined and observed. The results showed that the tested chlorophyll content, net photosynthetic rate, transpiration rate and water use efficiency were apparently inhibited by aluminum. Under uniform Al concentration (4.4 mM), the Al-induced limitation to photosynthetic parameters increased with pH, indicating acid stimulation to Al toxicity. Among all treatments, the most significant reduction was found in the combination of pH 3.0 and 4.4 mM Al. The photosynthetic and transpiration rates showed similar trends with G9 > G12 > G3 > G4, suggesting that G9 and G12 had higher Al-tolerance than other two clones. Microscopic observation revealed changes in leaf morphology when exposed to Al stress; for example, a reduced thickness of leaf epidermis and palisade tissue, the descendant palisade tissue/spongy tissue ratio and leaf tissue looseness. Overall, the acid and aluminum stress exerted negative effects on the photosynthetic activity of eucalypt seedlings, but the differences in tolerance to Al toxicity between the clones were favorable, offering potential to improve Eucalyptus plantation productivity by selecting Al tolerant clones. PMID:26090998

  18. Acoustic Propagation Considerations for Underwater Acoustic Communications Network Development

    E-print Network

    Zhou, Shengli

    Acoustic Propagation Considerations for Underwater Acoustic Communications Network Development Woods Hole, MA 02543 jpreisig@whoi.edu ABSTRACT Underwater acoustic communications systems are challenged by the characteristics of acoustic propagation through the underwater environment

  19. Radio Astronomy in LSST Era

    E-print Network

    Lazio, T Joseph W; Barger, A J; Brandt, W N; Chatterjee, S; Clarke, T E; Condon, J J; Dickman, Robert L; Hunyh, M T; Jarvis, Matt J; Juric, Mario; Kassim, N E; Myers, S T; Nissanke, Samaya; Osten, Rachel; Zauderer, B A

    2014-01-01

    A community meeting on the topic of "Radio Astronomy in the LSST Era" was hosted by the National Radio Astronomy Observatory in Charlottesville, VA (2013 May 6--8). The focus of the workshop was on time domain radio astronomy and sky surveys. For the time domain, the extent to which radio and visible wavelength observations are required to understand several classes of transients was stressed, but there are also classes of radio transients for which no visible wavelength counterpart is yet known, providing an opportunity for discovery. From the LSST perspective, the LSST is expected to generate as many as 1 million alerts nightly, which will require even more selective specification and identification of the classes and characteristics of transients that can warrant follow up, at radio or any wavelength. The LSST will also conduct a deep survey of the sky, producing a catalog expected to contain over 38 billion objects in it. Deep radio wavelength sky surveys will also be conducted on a comparable time scale,...

  20. TRACKER: A 3-D radio ray tracing code

    Microsoft Academic Search

    R. E. Carlson; J. H. Ellison

    1987-01-01

    TRACKER is a 3-D radio ray tracing code which has been designed to simulate high frequency radio wave propagation through a perturbed ionosphere. It is the centerpiece of a family of codes written for the Cray-1 computer whose purpose is to model radar systems for use in detecting and identifying ionospheric perturbations. TRACKER accepts as input a perturbation file that

  1. Astrometry and geodesy with radio interferometry: experiments, models, results

    E-print Network

    Ojars J. Sovers; John L. Fanselow; Christopher S. Jacobs

    1997-12-17

    Summarizes current status of radio interferometry at radio frequencies between Earth-based receivers, for astrometric and geodetic applications. Emphasizes theoretical models of VLBI observables that are required to extract results at the present accuracy levels of 1 cm and 1 nanoradian. Highlights the achievements of VLBI during the past two decades in reference frames, Earth orientation, atmospheric effects on microwave propagation, and relativity.

  2. Satellite radio beacon monitoring of the troposphere

    Microsoft Academic Search

    Y. V. Somayajulu; T. R. Tyagi; A. B. Ghosh

    1975-01-01

    In this communication some effects of characteristic enhancements and\\/or fluctuations of the satellite radio beacon transmissions are described. It is convincingly shown that these effects are of tropospheric origin. The satellite radio beacon can thus be used for monitoring the tropospheric events.

  3. Structure-guided engineering of Anticalins with improved binding behavior and biochemical characteristics for application in radio-immuno imaging and/or therapy.

    PubMed

    Eggenstein, E; Eichinger, A; Kim, H-J; Skerra, A

    2014-02-01

    Modern strategies in radio-immuno therapy and in vivo imaging require robust, small, and specific ligand-binding proteins. In this context we have previously developed artificial lipocalins, so-called Anticalins, with high binding activity toward rare-earth metal-chelate complexes using combinatorial protein design. Here we describe further improvement of the Anticalin C26 via in vitro affinity maturation to yield CL31, which has a fourfold slower dissociation half-life above 2h. Also, we present the crystallographic analyses of both the initial and the improved Anticalin, providing insight into the molecular mechanism of chelated metal binding and the role of amino acid substitutions during the step-wise affinity maturation. Notably, one of the four structurally variable loops that form the ligand pocket in the lipocalin scaffold undergoes a significant conformational change from C26 to CL31, acting as a lid that closes over the accommodated metal-chelate ligand. A systematic mutational study indicated that further improvement of ligand affinity is difficult to achieve while providing clues on the contribution of relevant side chains in the engineered binding pocket. Unexpectedly, some of the amino acid replacements led to strong increases - more then 10-fold - in the yield of soluble protein from periplasmic secretion in Escherichia coli. PMID:23542582

  4. RESOLVE: Bayesian algorithm for aperture synthesis imaging in radio astronomy

    NASA Astrophysics Data System (ADS)

    Junklewitz, H.; Bell, M. A.; Ensslin, T.

    2015-05-01

    RESOLVE is a Bayesian inference algorithm for image reconstruction in radio interferometry. It is optimized for extended and diffuse sources. Features include parameter-free Bayesian reconstruction of radio continuum data with a focus on extended and weak diffuse sources, reconstruction with uncertainty propagation dependent on measurement noise, and estimation of the spatial correlation structure of the radio astronomical source. RESOLVE provides full support for measurement sets and includes a simulation tool (if uv-coverage is provided).

  5. Proceedings of the Twentieth NASA Propagation Experimenters Meeting (NAPEX XX) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

    NASA Technical Reports Server (NTRS)

    Golshan, Nassar (Editor)

    1996-01-01

    The NASA Propagation Experimenters (NAPEX) Meeting and associated Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop convene yearly to discuss studies supported by the NASA Propagation Program. Representatives from the satellite communications (satcom)industry, academia, and government with an interest in space-ground radio wave propagation have peer discussion of work in progress, disseminate propagation results, and interact with the satcom industry. NAPEX XX, in Fairbanks, Alaska, June 4-5, 1996, had three sessions: (1) "ACTS Propagation Study: Background, Objectives, and Outcomes," covered results from thirteen station-years of Ka-band experiments; (2) "Propagation Studies for Mobile and Personal Satellite Applications," provided the latest developments in measurement, modeling, and dissemination of propagation phenomena of interest to the mobile, personal, and aeronautical satcom industry; and (3)"Propagation Research Topics," covered a range of topics including space/ground optical propagation experiments, propagation databases, the NASA Propagation Web Site, and revision plans for the NASA propagation effects handbooks. The ACTS Miniworkshop, June 6, 1996, covered ACTS status, engineering support for ACTS propagation terminals, and the ACTS Propagation Data Center. A plenary session made specific recommendations for the future direction of the program.

  6. AURORAL RADIO EMISSION FROM STARS: THE CASE OF CU VIRGINIS

    SciTech Connect

    Trigilio, Corrado; Leto, Paolo; Umana, Grazia; Buemi, Carla S. [INAF-Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania (Italy); Leone, Francesco, E-mail: ctrigilio@oact.inaf.it [Dipartimento di Fisica e Astronomia, Universita di Catania, Via Santa Sofia 78, 95123 Catania (Italy)

    2011-09-20

    CU Virginis is a rapidly rotating Magnetic Chemically Peculiar star with at present unique characteristics as a radio emitter. The most intriguing one is the presence of intense, 100% circularly polarized radiation ascribed to a cyclotron maser. Each time the star rotates, this highly beamed emission points two times toward the Earth, like a pulsar. We observed CU Vir in 2010 April with the Expanded Very Large Array in two bands centered at 1450 and 1850 MHz. We covered nearly the whole rotational period, confirming the presence of the two pulses at a flux density up to 20 mJy. Dynamical spectra, obtained with unprecedented spectral and temporal sensitivity, allow us to clearly see the different time delays as a function of frequency. We interpret this behavior as a propagation effect of the radiation inside the stellar magnetosphere. The emerging scenario suggests interesting similarities with the auroral radio emission from planets, in particular with the Auroral Kilometric Radiation from Earth, which originates at few terrestrial radii above the magnetic poles and was only recently discovered to be highly beamed. We conclude that the magnetospheres of CU Vir, Earth, and other planets, maybe also exoplanets, could have similar geometrical and physical characteristics in the regions where the cyclotron maser is generated. In addition, the pulses are perfect 'markers' of the rotation period. This has given us for the first time the possibility to measure with extraordinary accuracy the spin-down of a star on or near the main sequence.

  7. HIGH AMPLITUDE PROPAGATED CONTRACTIONS

    PubMed Central

    Bharucha, Adil E.

    2012-01-01

    While most colonic motor activity is segmental and non-propulsive, colonic high amplitude propagated contractions (HAPC) can transfer colonic contents over long distances and often precede defecation. HAPC occur spontaneously, in response to pharmacological agents or colonic distention. In this issue of Neurogastroenterology and Motility, Rodriguez and colleagues report that anal relaxation during spontaneous and bisacodyl-induced HAPC exceeds anal relaxation during rectal distention in constipated children undergoing colonic manometry. Moreover, and consistent with a neural mechanism, anal relaxation often precedes arrival of HAPC in the left colon. This editorial comprehensively reviews the characteristics, physiology and pharmacology of HAPC, their assessment by manometry, and relevance to constipation and diarrhea. PMID:23057554

  8. Basic Study on the Radio Frequency Characteristics of the Transmission Lines Employing Periodically Perforated Ground Metal on GaAs Monolithic Microwave Integrated Circuit and Their Equivalent Ciruits

    NASA Astrophysics Data System (ADS)

    Yun, Young; Ju, Jeong-Gab; Kim, Hong Seung

    2011-01-01

    In this work, basic characteristics of transmission line employing periodically perforated ground metal (PPGM) were investigated using theoretical and experimental analysis. Concretely, bandwidth and impedance were investigated using theoretical analysis, and wavelength and effective permittivity were extracted from experimental results. In addition, insertion loss and isolation characteristics were investigated using equivalent circuit analysis. For simplification of design process, equivalent circuits for the PPGM cell were extracted, and all circuit parameters were expressed by closed-form equation. Above results indicate that the transmission line employing PPGM is a promising candidate for a development of matching and passive elements on monolithic microwave integrated circuit (MMIC) including wireless communication circuit and compound semiconducting devices such as high electron mobility transistor (HEMT), diamond field effect transistor (FET) and light emitting diode (LED).

  9. The 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC'06) 1-4244-0330-8/06/$20.00 c2006 IEEE

    E-print Network

    Boyer, Edmond

    The 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, coding, etc. for these communication systems is based on a reliable model of the radio propagation the performance of various radio communication systems in a time-variant propagation channel in the same test

  10. On the Connectivity and Multihop Delay of Ad Hoc Cognitive Radio Networks

    E-print Network

    Islam, M. Saif

    On the Connectivity and Multihop Delay of Ad Hoc Cognitive Radio Networks Wei Ren§, Qing Zhao cognitive radio networks, where the transmission delay of each hop consists of the propagation delay opportunities. Index Terms--Cognitive radio network, multihop delay, con- nectivity, intermittent connectivity

  11. Indoor propagation measurements at infrared frequencies for wireless local area networks applications

    Microsoft Academic Search

    Homayoun Hashemi; Gang Yun; Mohsen Kavehrad; Farbod Behbahani; Peter A. Galko

    1994-01-01

    In a combination tutorial and research paper, propagation aspects of transmission at infrared (IR) frequencies for wireless in-building communications are explored. The tutorial section of the paper presents basic principles of propagation at IR, a comparison with indoor radio propagation, and the derivation of the channel's baseband model. The research aspect of the paper reports on the results of recent

  12. Propagation of a fluidization - combustion wave

    SciTech Connect

    Pron, G.P.; Gusachenko, L.K.; Zarko, V.E. [Institute of Chemical Kinetics and Combustion, Novosibirsk (Russian Federation)] [and others

    1994-05-01

    A fluidization-combustion wave propagating through a fixed and initially cool bed was created by igniting coal at the top surface of the bed. The proposed physical interpretation of the phenomenon is in qualitative agreement with the experimental dependences of the characteristics of the process on determining parameters. A kindling regime with forced wave propagation is suggested.

  13. A Statistical Model for Urban Radio Propogation

    Microsoft Academic Search

    H. Suzuki

    1977-01-01

    A statistical model, based on extensive experimental data, was established to characterize the urban radio propagation medium in various urban environments. Describing the medium by a linear filter, the peaks of the multipath response were analyzed statistically concerning the distribution of the path strength and the path arrival time. The statistical properties of these quantities depend on the modulation delay

  14. IMT2000 standards: radio aspects

    Microsoft Academic Search

    R. D. Carsello; R. Meidan; S. Allpress; F. O'Brien; J. A. Tarallo; N. Ziesse; A. Arunachalam; J. M. Costa; E. Berruto; R. C. Kirby; A. Maclatchy; F. Watanabe; H. Xia

    1997-01-01

    One of the key characteristics of IMT-2000 is the advanced radio technologies that will offer a whole new range of capabilities to the users of international mobile telecommunications. This article starts by comparing the significant differences between second-generation mobile systems and the major objectives envisioned for IMT-2000, with particular emphasis on the satellite component. It also describes the flexible modular

  15. Radio Continuum Emission from FS CMa Stars

    E-print Network

    Rodriguez, L F; Miroshnichenko, A S

    2011-01-01

    The FS CMa stars exhibit bright optical emission-line spectra and strong IR excesses. Very little is known of their radio characteristics. We analyzed archive Very Large Array data to search for radio continuum emission in a sample of them. There are good quality data for seven of the $\\sim$40 known FS CMa stars. Of these seven stars, five turn out to have associated radio emission. Two of these stars, CI Cam and MWC 300, have been previously reported in the literature as radio emitters. We present and briefly discuss the radio detection of the other three sources: FS CMa (the prototype of the class), AS 381, and MWC 922. The radio emission is most probably of a free-free nature but additional observations are required to better characterize it.

  16. Over-the-Horizon Anomalous VHF Propagation and Earthquake Precursors

    NASA Astrophysics Data System (ADS)

    Devi, M.; Barbara, A. K.; Ruzhin, Ya. Yu.; Hayakawa, M.

    2012-09-01

    The purpose of this paper is to review current activities for the identification of earthquake (EQ) precursors and their epicentres. Starting with a brief description on the background to approaches using ultra-low (ULF), extremely low (ELF), very low/low (VLF/LF), medium (MF), high (HF), very high frequency (VHF) etc. radio waves for short-term EQ prediction, the paper concentrates on those characteristics of anomalous VHF reception from frequency-modulation (FM) radio transmissions and broadcast television (TV) signals in relation to EQ precursors. The possible ways to identify an impending EQ and its epicentre position as defined and observed by workers from a variety of studies fall within the purview of the paper. In attempts to find pre-EQ energy exchange and coupling processes between the lithosphere and atmosphere, the paper highlights some relevant observations of surface latent heat flux, sonic detection and ranging (SODAR) echograms and LF propagation. Explanations on possible causes leading to such anomalous reception are reviewed with reported results in association with pre-seismic induced modifications to tropospheric and ionospheric parameters.

  17. Powerful Extended Radio Sources as Tools to Estimate Ambient Gas Densities, Jet Luminosities, and Other Key Physical Parameters

    NASA Astrophysics Data System (ADS)

    Daly, Ruth A.

    1995-12-01

    It would be quite valuable if the radio properties of powerful, extended radio sources could be used to deduce key physical quantities such as the density of the ambient gas in the vicinity of a radio source. It is shown here that radio observations can be used to estimate the ambient gas density, the luminosity in directed kinetic energy, and other key physical parameters relevant to the radio source and its gaseous environment. The methods described are applied to radio galaxies and radio-loud quasars with redshifts from about 0 to 2. The ambient gas density in the vicinity of the radio lobes is estimated by applying the strong shock jump conditions across the forward edge of the radio bridge (referred to as the radio lobe); this requires that the lobe pressure and the lobe propagation velocity be known. The lobe pressure is estimated assuming minimum energy conditions, and the local propagation velocity is estimated from the effects of synchrotron and inverse Compton aging of relativistic electrons on the radio spectrum across the radio bridge. At present this appears to be the only method of estimating the ambient gas density (as a single parameter) in the vicinity of distant powerful radio sources, and this first application of the method indicates that it provides a good rough estimate of the ambient gas density. One interesting result is that galaxies and quasars are found to lie in similar gaseous environments. Another is that the composite density profile is similar to that of gas in clusters of galaxies and is normalized to Cygnus A, which is known to be in a cluster with a hot intracluster medium in place. This suggests that the powerful radio sources considered here are surrounded by extended gaseous halos like those in present-day galaxy clusters, with the radio source interior to the core of the gaseous halo. One interpretation is that the radio sources considered are in the cores of clusters of galaxies with their intracluster media in place, which would suggest that some clusters, or at least cluster cores, exist out to redshifts of about 2. The lobe propagation velocity, the rate at which energy is channeled from the central engine in the form of a collimated outflow (known as the luminosity in directed kinetic energy), and a time-independent characteristic source size, which provides a calibrated yardstick and hence is a useful cosmological tool, are also discussed. The basic assumptions adopted by Daly (1994) in the use of these sources as cosmological probes are empirically tested; it is found that the data are consistent with the assumptions adopted. Relations between different parameters are investigated and discussed in detail. This leads to a wide perspective and good understanding of the environments and nuclear properties of powerful extended radio sources. For example, a maximum value for the energy extraction rate is seen in the present data set and may imply an upper limit to this quantity. And the lobe propagation velocity may also have a maximum value, indicating that there may be an upper limit to the Mach number at which the radio lobe propagates into the ambient medium. The limited data set used here supports the idea that radio galaxies and radio-loud quasars are intrinsically similar but appear different due to different viewing angles, however, they may not be intrinsically identical. Perhaps the two types of active galactic nucleus (AGN) activity observed, highly collimated outflows and radiant energy from the nuclear region of the AGN, should be identified with the two ultimate energy sources associated with massive compact objects: the spin energy of the massive compact object and the gravitational energy of matter falling onto the object, respectively. Then, the three types of AGN observed may not be intrinsically identical: radio-quiet quasars result when only the gravitational energy is being tapped, radio-loud quasars result when both energy sources are being tapped, and radio galaxies result when the spin energy of the massive compact object is being tapped. Since the sources

  18. Radio Bridge Structure and Its Application to Estimate the Mach Number and Ambient Gas Temperature of Powerful Sources

    NASA Astrophysics Data System (ADS)

    Wellman, Greg F.; Daly, Ruth A.; Wan, Lin

    1997-05-01

    The radio bridge shape of very powerful extended (FR II) radio sources has been studied in detail; the sample used here includes 12 radio galaxies and six radio-loud quasars with redshifts between 0 and 1.8. Specifically, the width and radio surface brightness of the radio bridge are measured as a function of distance from the radio hot spot on each side of each source. The width as a function of distance from the hot spot agrees very well with theoretical predictions based on the standard model of bridge growth, in which the bridge expands laterally because of a blast wave driven by the large pressure difference between the relativistic plasma in the radio hot spot and surrounding radio lobe and the adjacent ambient gas. The simple assumptions that go into the theoretical prediction are that the lobe radio power and width (measured in the vicinity of the radio hot spot) are roughly constant over the lifetime of a given source, and that the rate at which the bridge lengthens, referred to as the lobe propagation velocity, is roughly constant over the lifetime of a source. These three assumptions appear to be consistent with other independent studies of very powerful extended radio sources of the type studied here, within the present (rather large) observational uncertainties. The radio surface brightness as a function of distance from the hot spot agrees surprisingly well with a simple model in which the radio bridge undergoes adiabatic expansion in the lateral direction, assuming that the initial lobe radio power and lobe width are time independent for a given source. That is, the observed lobe surface brightness and width, and the width as a function of position along the radio bridge, are used to predict the radio surface brightness as a function of position along the radio bridge, assuming adiabatic expansion of the bridge in the lateral direction. The predicted and observed surface brightness along the bridge agree surprisingly well. This suggests that there is little reacceleration of relativistic electrons within the radio bridge and that the backflow velocity of relativistic plasma within the bridge is small compared with the lobe advance velocity. These results are consistent with implications based on the bridge shape and structure discussed by Alexander & Leahy since we consider only very powerful FR II sources here. The Mach number with which the radio lobe propagates into the ambient medium can be estimated using the structure of the radio bridge; this Mach number is the ratio of the lobe propagation velocity to the sound speed of the ambient gas. The lateral expansion of the bridge is driven initially by a blast wave. When the velocity of the blast wave falls to a value of the order of the sound speed of the ambient medium, the character of the expansion changes, and the functional form of the bridge width as a function of position exhibits a break, which may be used to estimate the ratio of the lobe advance velocity to the sound speed of the ambient gas. We observe this break in several sources studied here. The Mach number of lobe advance depends only upon the ratio of the width to the length of the bridge as a function of position, which is purely geometric. Typical Mach numbers obtained range from about 2 to 10 and seem to be roughly independent of redshift and the total size (core-lobe separation) of the radio source. The Mach number can be used to estimate the temperature of the ambient gas if an independent estimate of the lobe propagation velocity is available. Lobe propagation velocities estimated using the effects of synchrotron and inverse Compton aging of the relativistic electrons that produce the radio emission are combined with the Mach numbers in order to estimate ambient gas temperatures. The temperature obtained for Cygnus A matches that indicated by X-ray data for this source. Typical temperatures obtained range from about 1 to 20 keV. This temperature is characteristic of gas in clusters of galaxies at low redshift, which is interesting since we show in a companion paper that the ambi

  19. Proceedings of the 16th NASA Propagation Experimenters Meeting (NAPEX 16) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz (editor)

    1992-01-01

    The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. NAPEX 16 was held on May 29, 1992 in Houston, Texas. The meeting was organized into two technical sessions. The first session was dedicated to slant path propagation studies and measurements. The second session focused on Olympus propagation measurements and results. Following NAPEX 16, the Advanced Communications Technology Satellite (ACTS) Miniworkshop was held to review ACTS propagation activities with emphasis on ACTS hardware development and experiment planning. Eight technical papers were presented by contributors from government agencies, private industry, and university research establishments.

  20. The Cubesat Radio Experiment (CURE) and Beyond: Cubesat-based Low Frequency Radio Interferometry

    NASA Astrophysics Data System (ADS)

    Saint-Hilaire, P.; Sundkvist, D. J.; Martinez Oliveros, J. C.; Sample, J. G.; Pulupa, M.; Maruca, B.; Bale, S. D.; Bonnell, J. W.; Mozer, F.; Hurford, G. J.

    2014-12-01

    We have proposed a 3U cubesat, to carry a low-frequency radio receiver into low-Earth orbit to study solar radio bursts induced by solar flares and Coronal Mass Ejections. Because of the reflective properties of the Earth's ionosphere, observations of radio waves around and below 10 MHz must be made from space. The measurements will allow continuous tracking of radio bursts and associated CMEs through the inner heliosphere. These observations are important since such events are the main cause for space weather disturbances. Data products from the mission will primarily be spectra and waveforms of solar radio type II and III bursts, and the direction to the radio source as it propagates through the inner heliosphere. These data products will be available to the community through an automated pipeline nominally within a few hours of downlink. Additional science data products will be sizes of radio sources obtained via lunar occultations, and local ionospheric plasma density and electron temperature. As a first cubesat with a scientific radio instrument at these frequencies, this project is also intended as a path-finder: the instrument and sub-systems can immediately be duplicated in other cubesats, with the goal of providing the first radio interferometric measurements below the ionospheric cutoff.

  1. 36 IEEE COMMUNICATIONS LETTERS, VOL. 2, NO. 2, FEBRUARY 1998 Impulse Radio: How It Works

    E-print Network

    Ha, Dong S.

    36 IEEE COMMUNICATIONS LETTERS, VOL. 2, NO. 2, FEBRUARY 1998 Impulse Radio: How It Works Moe Z. Win-range communications in dense multipath environments. This letter describes the characteristics of impulse radio using. A RATIONALE FOR IMPULSE RADIO IMPULSE RADIO communicates with baseband pulses of very short duration

  2. Graphene electrostatic microphone and ultrasonic radio.

    PubMed

    Zhou, Qin; Zheng, Jinglin; Onishi, Seita; Crommie, M F; Zettl, Alex K

    2015-07-21

    We present a graphene-based wideband microphone and a related ultrasonic radio that can be used for wireless communication. It is shown that graphene-based acoustic transmitters and receivers have a wide bandwidth, from the audible region (20?20 kHz) to the ultrasonic region (20 kHz to at least 0.5 MHz). Using the graphene-based components, we demonstrate efficient high-fidelity information transmission using an ultrasonic band centered at 0.3 MHz. The graphene-based microphone is also shown to be capable of directly receiving ultrasound signals generated by bats in the field, and the ultrasonic radio, coupled to electromagnetic (EM) radio, is shown to function as a high-accuracy rangefinder. The ultrasonic radio could serve as a useful addition to wireless communication technology where the propagation of EM waves is difficult. PMID:26150483

  3. Moon exploration: lunar radio observatory

    NASA Astrophysics Data System (ADS)

    Skalsky, Alexandre; Zelenyi, Lev; Rothkaehl, Hanna; Gurvits, Leonid; Sadovski, Andrei; Mogilevsky, Mikhail; Gotlib, Vladimir

    The Moon is an attractive base for fundamental scientific studies. The conducting ionosphere of Earth prevents propagation of radio emission coming from the outer space to the Earth’s surface at frequencies below a few MHz. In contrast, the Moon surrounded by a very thin atmosphere and ionosphere is a perfect site for an ultra-long-wavelength (ULW) facility for studies of cosmic radio emission at frequencies below the Earth’s ionosphere cut-off. This range of frequencies is the last unexplored window in the spectrum of the universe’s electromagnetic emission, The radio facility deployed on the Moon’s surface will be a multidisciplinary tool for addressing a wide range of scientific disciplines from cosmology to astrophysics to planetology, solar-terrestrial physics and geophysics. The Moon-based ULW observatory will be an experimental and observational facility for transformational science. One of the most intriguing objectives for the ULW science is a search for terrestrial-like planets in the exosolar systems, i.e. extra-solar planets possessing an intrinsic magnetic field and magnetospheres interacting with a stellar wind. Such the interaction generates radio emission similar to the Auroral Kilometric Radiation (AKR) of the terrestrial magnetosphere. The intrinsic magnetic field shielding the planetary surface from the cosmic radiation is one of the strong indicators of possible habitability of an exoplanet. ACKNOWLEDGMENTS: This work was supported by the PP RAS 22 grant.

  4. Radio tracking system

    NASA Technical Reports Server (NTRS)

    Breidenthal, J. C.; Komarek, T. A.

    1982-01-01

    The principles and techniques of deep space radio tracking are described along with the uses of tracking data in navigation and radio science. Emphasis is placed on the measurement functions of radio tracking.

  5. Uranus as a radio source

    NASA Technical Reports Server (NTRS)

    Desch, M. D.; Kaiser, M. L.; Zarka, P.; Lecacheux, A.; Leblanc, Y.; Aubier, M.; Ortega-Molina, A.

    1991-01-01

    The complex nature of the Uranus radio emissions, both magnetospheric and atmospheric, is reviewed, with emphasis on the identification of distinct components and the determination of their source locations. Seven radii components were discovered in addition to the RF signature of lightning in the planet's atmosphere. Six of the seven magnetospheric components are freely propagating emissions; one component, the nonthermal continuum, is trapped in the density cavity between the magnetopause and the dense inner magnetosphere. The radio components are divided into two types according to their emission signature: bursty emission and smooth emission. The inferred source location for the dominant nightside emission is above the nightside magnetic pole, largely overlapping the UV auroral region and the magnetic polar cap. The N-burst component appears to be associated with solar-wind enhancements at Uranus, consistent with the idea that the solar wind was triggering magnetospheric substormlike activity during the encounter.

  6. Characteristics of UWB antenna and wave propagation

    Microsoft Academic Search

    Guan-Yu Chen; Jwo-Shiun Sun; Sheng-Yi Huang; Y. D. Chen; Cheng-Hung Lin

    2005-01-01

    This paper proposes an omni-directional UWB antenna pattern in azimuth cut, low voltage standing wave ratio (VSWR), and easy to construct antenna for ultra wideband (UWB) systems. The designed antenna uses the multi circular blade configuration with a radiating element and on two different ground planes (square and circular ground shape). The multi-circular blades UWB antenna suitable for IEEE 802.15.3a

  7. Nonlinear Characteristics of Wave Propagation over Vegetation 

    E-print Network

    Venkattaramanan, Aravinda

    2014-04-28

    ) ........................................ 34 5 Evolution of HRMS for Test IR12WD44 from Dubi and Torum (1994) ..... 36 6 Evolution of HRMS for Test IR5WD63 from Dubi and Torum (1994) ....... 37 7 Evolution of Spectrum for Test IR12WD44 from Dubi and Torum (1994) 38 8 Evolution... of Spectrum for Test IR5WD63 from Dubi and Torum (1994) 39 9 Evolution of Spectrum for Test IR12WD44 using Linear Model .............. 40 10 Evolution of Spectrum for Test IR12WD44 through the test domain ....... 41 11 Profile of wave flume...

  8. What is Radio Astronomy?

    NSDL National Science Digital Library

    This website contains information on radio astronomy, the NRAO, how telescopes work, the history and discovery of radio astronomy, and the radio communication process. This website has activites like "Make your own Radio Image", and visual aids on topics such as: free-free emission, spectral lines, synchrotron emission, masers, and how radio communication works. The site is also a resource for blackbody radiation, the Cosmic Microwave Backround, and the mechanisms of radio wave emission.

  9. Technical evaluation report on the ElectromagneticWave Propagation Panel Symposium on Propagation Effects on Military Systems in the High Latitude Region

    NASA Astrophysics Data System (ADS)

    Hunsucker, R. D.

    1985-11-01

    Propagation effects on military systems in the high latitude region were examined. Topics discussed include: experimental studies of ionospheric irregularities and regular structure, results of ionospheric modification (HF heating) experiments,theoretical studies of ionospheric irregularity formation, global survey of ground conductivities,disturbance modeling studies, high latitude effects on HF radio communicaton, transionospheric communications, satellite synthetic aperture radar (SAR), MF radio broadcasting, spatially adaptive propagation, HF digital, Skywave HF sea state radar, and meteor burst communication.

  10. Learning radio astronomy by doing radio astronomy

    NASA Astrophysics Data System (ADS)

    Vaquerizo Gallego, J. A.

    2011-11-01

    PARTNeR (Proyecto Académico con el Radio Telescopio de NASA en Robledo, Academic Project with the NASA Radio Telescope at Robledo) is an educational program that allows high school and undergraduate students to control a 34 meter radio telescope and conduct radio astronomical observations via the internet. High-school teachers who join the project take a course to learn about the science of radio astronomy and how to use the antenna as an educational resource. Also, teachers are provided with learning activities they can do with their students and focused on the classroom implementation of the project within an interdisciplinary framework. PARTNeR provides students with firsthand experience in radio astronomy science. Thus, remote radio astronomical observations allow students to learn with a first rate scientific equipment the basics of radio astronomy research, aiming to arouse scientific careers and positive attitudes toward science. In this contribution we show the current observational programs and some recent results.

  11. Phenomenology of Neptune's radio emissions observed by the Voyager planetary radio astronomy experiment

    NASA Technical Reports Server (NTRS)

    Pedersen, B. M.; Lecacheux, A.; Zarka, P.; Aubier, M. G.; Kaiser, M. L.; Desch, M. D.

    1992-01-01

    The Neptune flyby in 1989 added a new planet to the known number of magnetized planets generating nonthermal radio emissions. We review the Neptunian radio emission morphology as observed by the planetary radio astronomy experiment on board Voyager 2 during a few weeks before and after closest approach. We present the characteristics of the two observed recurrent main components of the Neptunian kilometric radiation, i.e., the 'smooth' and the 'bursty' emissions, and we describe the many specific features of the radio spectrum during closest approach.

  12. Proceedings of the Twenty-First NASA Propagation Experiments Meeting (NAPEX XXI) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

    NASA Technical Reports Server (NTRS)

    Golshan, Nasser (Editor)

    1997-01-01

    The NASA Propagation Experimenters (NAPEX) meeting is convened each year to discuss studies supported by the NASA Propagation Program. Representatives from the satellite communications industry, academia and government who have an interest in space-ground radio wave propagation are invited to NAPEX meetings for discussions and exchange of information. The reports delivered at this meeting by program managers and investigators present recent activities and future plans. This forum provides an opportunity for peer discussion of work in progress, timely dissemination of propagation results, and close interaction with the satellite communications industry. NAPEX XXI took place in El Segundo, California on June 11-12, 1997 and consisted of three sessions. Session 1, entitled "ACTS Propagation Study Results & Outcome " covered the results of 20 station-years of Ka-band radio-wave propagation experiments. Session 11, 'Ka-band Propagation Studies and Models,' provided the latest developments in modeling, and analysis of experimental results about radio wave propagation phenomena for design of Ka-band satellite communications systems. Session 111, 'Propagation Research Topics,' covered a diverse range of propagation topics of interest to the space community, including overviews of handbooks and databases on radio wave propagation. The ACTS Propagation Studies miniworkshop was held on June 13, 1997 and consisted of a technical session in the morning and a plenary session in the afternoon. The morning session covered updates on the status of the ACTS Project & Propagation Program, engineering support for ACTS Propagation Terminals, and the Data Center. The plenary session made specific recommendations for the future direction of the program.

  13. Solar radio emission very near the plasma frequency

    SciTech Connect

    Wentzel, D.G.

    1983-07-01

    Plasma-frequency radio emission from the solar corona has been observed with very short duration and very narrow bandwidth. These observations imply an upper corona with a structured field-aligned density distribution. I evaluate the propagation characteristics of fundamental plasma radio emission when the bandwidth is small compared with the electron gyrofrequency (..cap omega..), which is small compared with the plasma frequency (..omega../sub p/). The ''normal'' group velocity, c(..cap omega../..omega../sub p/)/sup 1//sup ///sup 2/, applies only to radiation emitted nearly parallel to the magnetic field. Most of the radiation at first travels with a much lower group velocity and is delayed relative to the radiation emitted parallel to the magnetic field. Radiation emitted at one instant of time over a finite range of angles leaves the corona with a time profile of finite duration. Very short observed signals of about 20 ms duration may be explained in two ways. (1) We observe only rays from a small part of the cone of emission. Then the observed bandwidth may be small compared with the inherent bandwidth of emission. (2) The density scale height is substantially less than 10/sup 5/ km, and the direction of the density gradient is well outside the cone of emission. The shortest signals from the upper corona may indicate density variations across magnetic flux tubes with scale heights as small as 10/sup 4/ km.

  14. Transequatorial Propagation and Depletion Precursors

    NASA Astrophysics Data System (ADS)

    Miller, E. S.; Bust, G. S.; Kaeppler, S. R.; Frissell, N. A.; Paxton, L. J.

    2014-12-01

    The bottomside equatorial ionosphere in the afternoon and evening sector frequently evolves rapidly from smoothly stratified to violently unstable with large wedges of depleted plasma growing through to the topside on timescales of a few tens of minutes. These depletions have numerous practical impacts on radio propagation, including amplitude scintillation, field-aligned irregularity scatter, HF blackouts, and long-distance transequatorial propagation at frequencies above the MUF. Practical impacts notwithstanding, the pathways and conditions under which depletions form remain a topic of vigorous inquiry some 80 years after their first report. Structuring of the pre-sunset ionosphere---morphology of the equatorial anomalies and long-wavelength undulations of the isodensity contours on the bottomside---are likely to hold some clues to conditions that are conducive to depletion formation. The Conjugate Depletion Experiment is an upcoming transequatorial forward-scatter HF/VHF experiment to investigate pre-sunset undulations and their connection with depletion formation. We will present initial results from the Conjugate Depletion Experiment, as well as a companion analysis of a massive HF propagation data set.

  15. Jet propagation through energetic materials

    SciTech Connect

    Pincosy, P; Poulsen, P

    2004-01-08

    In applications where jets propagate through energetic materials, they have been observed to become sufficiently perturbed to reduce their ability to effectively penetrate subsequent material. Analytical calculations of the jet Bernoulli flow provides an estimate of the onset and extent of such perturbations. Although two-dimensional calculations show the back-flow interaction pressure pulses, the symmetry dictates that the flow remains axial. In three dimensions the same pressure impulses can be asymmetrical if the jet is asymmetrical. The 3D calculations thus show parts of the jet having a significant component of radial velocity. On the average the downstream effects of this radial flow can be estimated and calculated by a 2D code by applying a symmetrical radial component to the jet at the appropriate position as the jet propagates through the energetic material. We have calculated the 3D propagation of a radio graphed TOW2 jet with measured variations in straightness and diameter. The resultant three-dimensional perturbations on the jet result in radial flow, which eventually tears apart the coherent jet flow. This calculated jet is compared with jet radiographs after passage through the energetic material for various material thickness and plate thicknesses. We noted that confinement due to a bounding metal plate on the energetic material extends the pressure duration and extent of the perturbation.

  16. Technical evaluation report on the ElectromagneticWave Propagation Panel Symposium on Propagation Effects on Military Systems in the High Latitude Region

    Microsoft Academic Search

    R. D. Hunsucker

    1985-01-01

    Propagation effects on military systems in the high latitude region were examined. Topics discussed include: experimental studies of ionospheric irregularities and regular structure, results of ionospheric modification (HF heating) experiments,theoretical studies of ionospheric irregularity formation, global survey of ground conductivities,disturbance modeling studies, high latitude effects on HF radio communicaton, transionospheric communications, satellite synthetic aperture radar (SAR), MF radio broadcasting, spatially

  17. 18 Ghz propagation and rainfall intensity

    NASA Astrophysics Data System (ADS)

    Kuehn, U.

    1988-07-01

    Comparisons between the depth of the absorption fading at 18 Ghz and rainfall intensity along a 21 km path revealed information on how to reduce point rainfall intensity over a radio path in order to predict fading probability from point rainfall data. Simultaneous studies of 18 Ghz propagation on two radio paths, one running in the east-west and the other in the north-south direction, have been performed to get information about the influence of rain cells moving mostly from west to east in central Europe. Six rain recorders of the water-wheel type made it possible to distinguish between absorption and multipath fading. The fading probability was found to be higher on the east-west path as the rain cells remain over the radio link for a longer time compared with a north-south running path.

  18. The Frequency Spectrum Radio.

    ERIC Educational Resources Information Center

    Howkins, John, Ed.

    1979-01-01

    This journal issue focuses on the frequency spectrum used in radio communication and on the World Administrative Radio Conference, sponsored by the International Telecommunication Union, held in Geneva, Switzerland, in the fall of 1979. Articles describe the World Administrative Radio Conference as the most important radio communication conference…

  19. The Radio Amateur's Handbook.

    ERIC Educational Resources Information Center

    Blakeslee, Douglas, Ed.

    The objectives of this basic reference work for the radio amateur are to present radio theory and practice in terms of application and to reflect both the fundamentals and the rapidly-advancing technology of radio communications so that the radio amateur will have a guide to what is practical, meaningful, proven, and useful. Twenty-three chapters…

  20. Radio Controlled Clocks

    Microsoft Academic Search

    Michael A. Lombardi

    Radio controlled clocks have existed for decades, but have become far more common in the United States in recent years, due mainly to the explosion of new products that receive time signals from NIST radio station WWVB. This paper explores the history of radio controlled clocks, how they work, and the types of radio signals that control them.

  1. Theory of Type 3 and Type 2 Solar Radio Emissions

    NASA Technical Reports Server (NTRS)

    Robinson, P. A.; Cairns, I. H.

    2000-01-01

    The main features of some current theories of type III and type II bursts are outlined. Among the most common solar radio bursts, type III bursts are produced at frequencies of 10 kHz to a few GHz when electron beams are ejected from solar active regions, entering the corona and solar wind at typical speeds of 0.1c. These beams provide energy to generate Langmuir waves via a streaming instability. In the current stochastic-growth theory, Langmuir waves grow in clumps associated with random low-frequency density fluctuations, leading to the observed spiky waves. Nonlinear wave-wave interactions then lead to secondary emission of observable radio waves near the fundamental and harmonic of the plasma frequency. Subsequent scattering processes modify the dynamic radio spectra, while back-reaction of Langmuir waves on the beam causes it to fluctuate about a state of marginal stability. Theories based on these ideas can account for the observed properties of type III bursts, including the in situ waves and the dynamic spectra of the radiation. Type 11 bursts are associated with shock waves propagating through the corona and interplanetary space and radiating from roughly 30 kHz to 1 GHz. Their basic emission mechanisms are believed to be similar to those of type III events and radiation from Earth's foreshock. However, several sub-classes of type II bursts may exist with different source regions and detailed characteristics. Theoretical models for type II bursts are briefly reviewed, focusing on a model with emission from a foreshock region upstream of the shock for which observational evidence has just been reported.

  2. ATS-6 engineering performance report. Volume 5: Propagation experiments

    NASA Technical Reports Server (NTRS)

    Wales, R. O. (editor)

    1981-01-01

    Propagation experiments at 1550 MHz to 1650 MHz are reviewed, including the Integrated L-Band Experiments system and results, and the Mobile L-Band Terminals for Satellite Communication system. Experiments at 4 GHz to 6 GHz are reported, including the Radio Frequency Interferometer Measurements system and results, and Earth station antenna evaluations. Experiments above 10 GHz are discussed, including Comsat and ATS-6 millimeter wave propagation/experiments, and communication ATS-6 version at 20 and 30 GHz.

  3. Proceedings of the Fifteenth NASA Propagation Experimenters Meeting (NAPEX 15) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz (editor)

    1991-01-01

    The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. The meeting was organized into three technical sessions. The first session was dedicated to Olympus and ACTS studies and experiments, the second session was focused on the propagation studies and measurements, and the third session covered computer-based propagation model development. In total, sixteen technical papers and some informal contributions were presented. Following NAPEX 15, the Advanced Communications Technology Satellite (ACTS) miniworkshop was held on 29 Jun. 1991, to review ACTS propagation activities, with emphasis on ACTS hardware development and experiment planning. Five papers were presented.

  4. 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, â??â?Ś. is to promote young peopleâ??s 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.

  5. Radio frequency detection assembly and method for detecting radio frequencies

    DOEpatents

    Cown, Steven H. (Rigby, ID); Derr, Kurt Warren (Idaho Falls, ID)

    2010-03-16

    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.

  6. Application of radio holographic method for observation of altitude variations of the electron density in the mesosphere\\/lower thermosphere using GPS\\/MET radio occultation data

    Microsoft Academic Search

    K. Igarashi; A. Pavelyev; J. Wickert; K. Hocke; D. Pavelyev

    2002-01-01

    A radio holographic method for observation of wave phenomena in the upper atmosphere (height interval 60–120km) is described. The radio holography uses coherent properties of the rays propagating through the atmosphere. These properties arise due to the high stability of the GPS signal and its high sensitivity to layered structures in the atmosphere and ionosphere. High angular and vertical resolution

  7. Wave equations for pulse propagation

    SciTech Connect

    Shore, B.W.

    1987-06-24

    Theoretical discussions of the propagation of pulses of laser radiation through atomic or molecular vapor rely on a number of traditional approximations for idealizing the radiation and the molecules, and for quantifying their mutual interaction by various equations of propagation (for the radiation) and excitation (for the molecules). In treating short-pulse phenomena it is essential to consider coherent excitation phenomena of the sort that is manifest in Rabi oscillations of atomic or molecular populations. Such processes are not adequately treated by rate equations for excitation nor by rate equations for radiation. As part of a more comprehensive treatment of the coupled equations that describe propagation of short pulses, this memo presents background discussion of the equations that describe the field. This memo discusses the origin, in Maxwell's equations, of the wave equation used in the description of pulse propagation. It notes the separation into lamellar and solenoidal (or longitudinal and transverse) and positive and negative frequency parts. It mentions the possibility of separating the polarization field into linear and nonlinear parts, in order to define a susceptibility or index of refraction and, from these, a phase and group velocity. The memo discusses various ways of characterizing the polarization characteristics of plane waves, that is, of parameterizing a transverse unit vector, such as the Jones vector, the Stokes vector, and the Poincare sphere. It discusses the connection between macroscopically defined quantities, such as the intensity or, more generally, the Stokes parameters, and microscopic field amplitudes. The material presented here is a portion of a more extensive treatment of propagation to be presented separately. The equations presented here have been described in various books and articles. They are collected here as a summary and review of theory needed when treating pulse propagation.

  8. Astrometry and geodesy with radio interferometry: experiments, models, results

    Microsoft Academic Search

    Ojars J. Sovers; John L. Fanselow; Christopher S. Jacobs

    1998-01-01

    Summarizes current status of radio interferometry at radio frequencies\\u000abetween Earth-based receivers, for astrometric and geodetic applications.\\u000aEmphasizes theoretical models of VLBI observables that are required to extract\\u000aresults at the present accuracy levels of 1 cm and 1 nanoradian. Highlights the\\u000aachievements of VLBI during the past two decades in reference frames, Earth\\u000aorientation, atmospheric effects on microwave propagation,

  9. The nature of extragalactic radio-jets from high-resolution radio-interferometric observations

    NASA Astrophysics Data System (ADS)

    Perucho-Pla, M.

    2015-05-01

    Extragalactic jets are a common feature of radio-loud active galaxies. The nature of the observed jets in relation to the bulk flow is still unclear. In particular it is not clear whether the observations of parsec-scale jets using the very long baseline interferometric technique (VLBI) reveal wave-like structures that develop and propagate along the jet, or trace the jet flow itself. In this contribution I review the evidence collected during the last years showing that the ridge-lines of helical radio-jets do not correspond to observational artifacts. This conclusion was reached by studying a number of VLBI observations of the radio jet in the quasar S5 0836+710 at different frequencies and epochs. The ridge-line of the emission in the jet coincides at all frequencies within the errors. Moreover, small differences between the ridge-lines as observed at different epochs reveal wave-like motion transversal to the jet propagation axis. I also discuss similar results, albeit with different interpretations, obtained by other authors. The current challenge is to measure the propagation velocities of these waves and to try to characterise them in terms of simple perturbations or Kelvin-Helmholtz instability, which would help understanding the physical conditions of the flow where the waves develop. This problem can only be tackled by high-resolution observations such as those that can be achieved by the space radio-antenna Radioastron.

  10. Radio signatures of CME-streamer interaction and source diagnostics of type II radio burst

    E-print Network

    Feng, S W; Kong, X L; Li, G; Song, H Q; Feng, X S; Liu, Ying

    2012-01-01

    It has been suggested that type II radio bursts are due to energetic electrons accelerated at coronal shocks. Radio observations, however, have poor or no spatial resolutions to pinpoint the exact acceleration locations of these electrons. In this paper, we discuss a promising approach to infer the electron acceleration location by combining radio and white light observations. The key assumption is to relate specific morphological features (e.g. spectral bumps) of the dynamic spectra of type II radio bursts, to imaging features (e.g. CME going into a streamer) along the CME (and its driven shock) propagation. In this study, we examine the CME-streamer interaction for the solar eruption dated on 2003 November 1. The presence of spectral bump in the relevant type II radio burst is identified, which is interpreted as a natural result of the shock-radio emitting region entering the dense streamer structure. The study is useful for further determinations of the location of type II radio burst and the associated el...

  11. Parallel acceleration of diffuse scattering model for indoor radio prediction by CUDA

    NASA Astrophysics Data System (ADS)

    Meng, Xiao; Guo, Li-xin; Tao, Wei

    2013-10-01

    Radio wave propagation prediction is very important for the design of the mobile communication network. The raytracing algorithm is a commonly used computational method for site-specific prediction of the radio channel characteristics of wireless communication systems. However, it does not consider the diffuse scattering. Therefore, an indoor diffuse scattering model which based on diffuse scattering theory and FDTD is established. The diffuse scattering of indoor walls and ceiling and floor is calculated at a series of discrete time instance in this method. In recent years, the compute unified device architecture (CUDA) of NVIDIA takes advantage of the GPU for parallel computing, and greatly improve the speed of computation. Because there is a large number of data to deal with, in order to reduce the computation time, a GPU-based diffuse scattering model for indoor radio prediction is introduced in this paper, which fully utilizes the parallel processing capabilities of CUDA to further improve the computational efficiency. It can be found that good acceleration effect has been achieved.

  12. Spectral Structures and Their Generation Mechanisms for Solar Radio Type-I Bursts

    NASA Astrophysics Data System (ADS)

    Iwai, K.; Miyoshi, Y.; Masuda, S.; Tsuchiya, F.; Morioka, A.; Misawa, H.

    2014-07-01

    The fine spectral structures of solar radio type-I bursts were observed by the solar radio telescope AMATERAS. The spectral characteristics, such as the peak flux, duration, and bandwidth, of the individual burst elements were satisfactorily detected by the highly resolved spectral data of AMATERAS with the burst detection algorithm that is improved in this study. The peak flux of the type-I bursts followed a power-law distribution with a spectral index of 2.9-3.3, whereas their duration and bandwidth were distributed more exponentially. There were almost no correlations between the peak flux, duration, and bandwidth. That means there was no similarity in the shapes of the burst spectral structures. We defined the growth rate of a burst as the ratio between its peak flux and duration. There was a strong correlation between the growth rate and peak flux. These results suggest that the free energy of type-I bursts that is originally generated by nonthermal electrons is modulated in the subsequent stages of the generation of nonthermal electrons, such as plasma wave generation, radio wave emissions, and propagation. The variation of the timescale of the growth rate is significantly larger than that of the coronal environments. These results can be explained by the situation wherein the source region may have the inhomogeneity of an ambient plasma environment, such as the boundary of open and closed field lines, and the superposition of entire emitted bursts was observed by the spectrometer.

  13. Possible radio emission mechanism for pulsars

    NASA Technical Reports Server (NTRS)

    Kovalev, Y. A.

    1979-01-01

    A mathematical model is presented and discussed as a possible mechanism to describe radio emission from pulsars. The model determines that the magnetic field in the neutron proton electron (npe) layer of a neutron star results from a quasistationary eddy current of superconducting and normal protons relative to normal electrons, which generates radio emission by the Josephson effect. The radiation propagates in the magnetically active medium, from the optically thick npe layer to the magnetosphere through breaks in the crust. As a result, hot radio spots form on the surface of the star, and a radiation pattern forms near the magnetic poles, the cross section of which gives the observed pulse structure. Due to the specific properties of the mechanism, variations of the quasistationary current are converted to amplitude frequency variations of the radiation spectrum. Variations of the fine structure of the spectrum pulse amplitude and spectral index, as well as their correlation are discussed.

  14. Effect of interlayer on stress wave propagation in CMC\\/RHA multi-layered structure

    Microsoft Academic Search

    Yangwei Wang; Fuchi Wang; Xiaodong Yu; Zhuang Ma; Jubin Gao; Xiaopeng Kang

    2010-01-01

    Due to the significance of the propagation of stress wave in composite armor during projectile–target interaction, the characteristics of stress wave propagation in multi-layered composite structure under impact load were investigated by traditional Split Hopkinson Pressure Bar system in this study. The effect of interlayer characteristic on the stress wave propagation was discussed. The results show that the interlayer properties

  15. Analysis of fatigue crack propagation

    NASA Technical Reports Server (NTRS)

    Liu, H. W.

    1972-01-01

    The correlation between fatigue crack propagation and stress intensity factor is analyzed. When determining fatigue crack propagation rate, a crack increment, delta a, and its corresponding increment in load cycles, delta N, are measured. Fatigue crack propagation must be caused by a shear and/or a normal separation mode. Both of these two processes are discrete if one looks at the atomic level. If the average deformation and fracture properties over the crack increments, delta a, can be considered as homogeneous, if the characteristic discrete lengths of sigma a, if the plastic zone size is small, and if a plate is thick enough to insure a plane strain case, da/dN is proportional to delta K squared. Any deviation of empirical data from this relation must be caused by the fact that one or more of these conditions are not satisfied. The effects of plate thickness and material inhomogeneity are discussed in detail. A shear separation mode of fatigue crack propagation is described and is used to illustrate the effects of material inhomogeneity.

  16. A New Solar Broadband Radio Spectrometer (SBRS) in China

    Microsoft Academic Search

    Qijun Fu; Huirong Ji; Zihai Qin; Zhicai Xu; Zhiguo Xia; Hongao Wu; Yuying Liu; Yihua Yan; Guangli Huang; Zhijun Chen; Zhenyu Jin; Qijun Yao; Congling Cheng; Fuying Xu; Min Wang; Libei Pei; Shanhuai Chen; Guo Yang; Chenming Tan; Suobiao Shi

    2004-01-01

    A new radio spectrometer, Solar Broadband Radio Spectrometer (SBRS) with characteristics of high time resolution, high-frequency resolution, high sensitivity, and wide frequency coverage in the microwave region is described. Its function is to monitor solar radio bursts in the frequency range of 0.7–7.6 GHz with time resolution of 1–10 ms. SBRS consists of five `component spectrometers' which work in five different wave

  17. Electromagnetic waves in space plasma: Generation and propagation

    Microsoft Academic Search

    V. V. Zhelezniakov

    1977-01-01

    The aim of the book is to provide insight into the mechanisms of electromagnetic wave emission from space plasmas (interstellar medium, supernova remnants, magnetospheres of neutron stars, the solar corona, Jovian ionosphere, etc.), which is essential for interpreting the results of radio astronomic investigations. An attempt is made to outline systematically the general principles of wave generation and propagation in

  18. Propagation effects on handoff activity in a cellular system

    Microsoft Academic Search

    Wu Jianhui; Yuan Dongfeng

    1996-01-01

    The handoff performance is very important in a cellular radio system, especially in densely populated urban areas. This paper presents some statistical results of currently operating cellular system in Jinan city and through field measurements, we analyze propagation effects on intercell handoff and intracell handoff in the Jinan cellular system. We conclude that a new, practical handoff algorithm should be

  19. Signal Propagation Analysis and Signature Extraction for GNSS Indoor Positioning

    Microsoft Academic Search

    Marcus Andreotti; Marcio Aquino; Malcolm Woolfson; John Walker; Terry Moore

    2006-01-01

    The large popularization of GNSS (based on GPS, Glonass and forthcoming Galileo) receivers and the increased market interest for Location Based Services (LBS) have motivated interesting studies in modelling the radio channel propagation for dense urban and indoor geolocation, where two key problems need to be addressed: weak signal operation and multipath, both leading to receiver range errors and consequently

  20. Canal de Propagation 3me anne Tlcom-Rseaux

    E-print Network

    Dobigeon, Nicolas

    1 Canal de Propagation 3čme année Télécom-Réseaux 2007-2008 Martial COULON #12;2 #12;3 Chap. I VHF/UHF Pico-Cellules : qques m, haut débit. #12;5 I.2. Définition du Canal Radio Mobile ˇ Canal de ( entre 100km et 1mm) Canal montant (Reverse Channel ou Uplink Channel) Mobiles vers BS Transmissions

  1. Propagation Models for Multi-hop Wireless Networks in Ns2 Simulator

    Microsoft Academic Search

    Bing Qi; Fangyang Shen

    2011-01-01

    Due to the high cost of wireless network testbeds, most of initial research work in this field depends on different network simulation tools to verify their effectiveness. Among those simulators, Ns-2 is one of the most widely used one. In this paper, we described different radio propagation models implemented in Ns- 2 simulator in detail and applied two-ray ground propagation

  2. Radio Diaries on National Public Radio (NPR)

    NSDL National Science Digital Library

    Radio Diaries is a nonprofit radio production company which looks "to find extraordinary stories in ordinary places, to create original and moving first-person documentaries - true radio verite - from voices that are rarely heard." And that it does. Radio Diaries staff train all kinds of people -- from teenagers to the elderly -- to become reporters. These fledgling reporters create tapes about their area of interest, tell their stories, and send their product back to Radio Diaries. A collaborative editing process then ensues, and the end product is aired as part of National Public Radio's All Things Considered. The Radio Diaries site brings together an amazing range of recorded stories divided into adult and teen areas. Two examples of diaries on the site include a piece by a teenager from New York City with Tourette's Syndrome as well as the story of the last two known remaining Civil War widows whose husbands fought on opposing sides of the war. Users can listen to the recordings using RealPlayer, or they can read transcripts; other materials are occasionally included too. The site encourages users to send in their own story ideas and will provide even more support for creative ventures with their Handbook for Teen Reporters (available in January of 2000). The site also has a store section where tapes of various radio diaries are for sale.

  3. Fundamentals of Radio Telescopes

    Microsoft Academic Search

    Jingquan Cheng

    \\u000a In this chapter, a brief review of radio astronomical telescopes is provided. The fundamental concepts of radio antennas,\\u000a including radiation pattern, antenna gain, antenna temperature, antenna efficiency, and polarization, are introduced. These\\u000a concepts are important for readers outside the radio antenna field. The emphasis of this chapter is placed on the parameter\\u000a design of reflector radio telescope antennas. These parameter

  4. Triggered Jovian radio emissions

    NASA Technical Reports Server (NTRS)

    Calvert, W.

    1985-01-01

    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.

  5. Extra Low-Frequency Terrestrial Radio-Wave Field Calculations with the Zonal Harmonics Series

    Microsoft Academic Search

    J. Ralph Johler; Richard L. Lewis

    1969-01-01

    Use of the zonal harmonics series for calculating the terrestrial wave guide fields directly is described. The analysis is extended to include radio waves propagating into sea water or below the earth's surface. A sample calculation of ELF radio waves is analyzed into a direct wave and a wave that has traveled the circumference of the earth. The location of

  6. Simultaneous cancellation of cross interference and ISI in CDMA mobile radio communications

    Microsoft Academic Search

    A. Klein; P. W. Baier

    1992-01-01

    In this paper, data estimation in the uplink of a synchronous mobile radio system applying CDMA is considered. In mobile radio systems applying CDMA, multipath propagation leads on the one hand to ISI and on the other hand, together with time-variance, to cross interference between the signals of different users, regardless whether the user codes are chosen orthogonal or not.

  7. Simulation Platform for Wireless Sensor Networks Based on Impulse Radio Ultra Wide Band

    E-print Network

    Paris-Sud XI, Université de

    Simulation Platform for Wireless Sensor Networks Based on Impulse Radio Ultra Wide Band Abdoulaye Radio Ultra Wide Band (IR-UWB) is a promising technology to address Wireless Sensor Network (WSN into account the pulse collision by dealing with the pulse propagation delay. We also modelled MAC protocols

  8. Hybrid fibre-radio field experiment at 60 GHz

    Microsoft Academic Search

    Harald Schmuck; Rolf Heidemann

    1996-01-01

    For the first time we present the long distance transport of 60 GHz digital modulated radio signal over an installed link of 46 km standard fibre and optical distribution to 256 miniaturised remote antenna units which are serving pico-radio-cell. This concept is applicable to full service wireless local loops due to the broadband characteristic, the low bit error rate and

  9. Experimental radio frequency link for Ka-band communications applications

    NASA Technical Reports Server (NTRS)

    Fujikawa, Gene; Conray, Martin J.; Saunders, Alan L.; Pope, Dale E.

    1988-01-01

    An experimental radio frequency link has been demonstrated to provide two-way communication between a remote user ground terminal and a ground-based Ka-band transponder. Bit-error-rate performance and radio frequency characteristics of the communication link were investigated.

  10. Light-year scale radio cores in four LINER galaxies

    Microsoft Academic Search

    M. E. Filho; P. D. Barthel; L. C. Ho

    2002-01-01

    The LINER galaxies NGC 2911, NGC 3079, NGC 3998, and NGC 6500 were observed at 5 GHz with the European VLBI Network at a resolution of 5 milliarcsecond and found to possess flat-spectrum, variable, high-brightness temperature (TB > 108 K) radio cores. These radio characteristics reinforce the view that these LINERs host central engines associated with active galactic nuclei.

  11. Radio frequency spectrum management

    Microsoft Academic Search

    E. J. Sujdak Jr.

    1980-01-01

    This thesis is a study of radio frequency spectrum management as practiced by agencies and departments of the Federal Government. After a brief introduction to the international agency involved in radio frequency spectrum management, the author concentrates on Federal agencies engaged in frequency management. These agencies include the National Telecommunications and Information Administration (NTIA), the Interdepartment Radio Advisory Committee (IRAC),

  12. Extragalactic Radio Sources

    ERIC Educational Resources Information Center

    Kellerman, Kenneth I.

    1973-01-01

    Discusses new problems arising from the growing observational data through radio telescope arrays, involving the origin of radio sources, apparent superluminal velocities, conversion of radio sources to relativistic particles, and the nature of compact opaque and extended transparent sources. New physics may be needed to answer these cosmological…

  13. Universal portable radio communications

    Microsoft Academic Search

    D. C. Cox

    1985-01-01

    In our highly mobile society, the provision of voice and data communications to people away from their wireline telephones has become a major communications frontier. Some emerging radio systems, e.g., cellular mobile radio, cordless telephone, and radio paging, have begun to penetrate this frontier. However, each of these approaches only partially satisfies portable communication needs. That is, the approaches do

  14. Introduction Big Radio Data

    E-print Network

    Prodić, Aleksandar

    Introduction VLBI Pulsars Summary Big Radio Data Ue-Li Pen CITA, UofT, CIFAR July 3, 2014U. Pen Big Radio Data #12;Introduction VLBI Pulsars Summary Overview History VLBI Processing Future U. Pen Big signal processing U. Pen Big Radio Data #12;Introduction VLBI Pulsars Summary VLBI Current experiments

  15. Radio Continuum Surveys

    NASA Astrophysics Data System (ADS)

    Jonas, Justin L.; Baart, Eddie E.

    1995-08-01

    The Rhodes University radio astronomy group has been involved in radio continuum mapping of southern extended radio sources since 1976. We describe the various mapping projects undertaken with the HartRAO telescope, particularly the Rhodes/HartRAO 2300 MHz all-sky survey, and speculate on future projects.

  16. The software radio architecture

    Microsoft Academic Search

    J. Mitola

    1995-01-01

    As communications technology continues its rapid transition from analog to digital, more functions of contemporary radio systems are implemented in software, leading toward the software radio. This article provides a tutorial review of software radio architectures and technology, highlighting benefits, pitfalls, and lessons learned. This includes a closer look at the canonical functional partitioning of channel coding into antenna, RF,

  17. Radio AGN Surveys

    E-print Network

    Carlos De Breuck; Wil van Breugel; Huub Rottgering; Chris Carilli

    2001-11-13

    We present a short overview of radio surveys for AGN, including the `complete' flux limited surveys and `filtered' surveys. We also describe our ultra-steep spectrum search for the highest redshift radio galaxies, and our follow-up VLA and ATCA observations of the most distant (z=5.19) and the most luminous z<2 radio galaxy known.

  18. Global Ionosphere Radio Observatory

    NASA Astrophysics Data System (ADS)

    Galkin, I. A.; Reinisch, B. W.; Huang, X. A.

    2014-12-01

    The Global Ionosphere Radio Observatory (GIRO) comprises a network of ground-based high-frequency vertical sounding sensors, ionosondes, with instrument installations in 27 countries and a central Lowell GIRO Data Center (LGDC) for data acquisition and assimilation, including 46 real-time data streams as of August 2014. The LGDC implemented a suite of technologies for post-processing, modeling, analysis, and dissemination of the acquired and derived data products, including: (1) IRI-based Real-time Assimilative Model, "IRTAM", that builds and publishes every 15-minutes an updated "global weather" map of the peak density and height in the ionosphere, as well as a map of deviations from the classic IRI climate; (2) Global Assimilative Model of Bottomside Ionosphere Timelines (GAMBIT) Database and Explorer holding 15 years worth of IRTAM computed maps at 15 minute cadence;. (3) 17+ million ionograms and matching ionogram-derived records of URSI-standard ionospheric characteristics and vertical profiles of electron density; (4) 10+ million records of the Doppler Skymaps showing spatial distributions over the GIRO locations and plasma drifts; (5) Data and software for Traveling Ionospheric Disturbance (TID) diagnostics; and (6) HR2006 ray tracing software mated to the "realistic" IRTAM ionosphere. In cooperation with the URSI Ionosonde Network Advisory Group (INAG), the LGDC promotes cooperative agreements with the ionosonde observatories of the world to accept and process real-time data of HF radio monitoring of the ionosphere, and to promote a variety of investigations that benefit from the global-scale, prompt, detailed, and accurate descriptions of the ionospheric variability.

  19. Why are central radio relics so rare?

    NASA Astrophysics Data System (ADS)

    Vazza, F.; Brüggen, M.; van Weeren, R.; Bonafede, A.; Dolag, K.; Brunetti, G.

    2012-04-01

    In this paper, we address the question of why cluster radio relics that are connected to shock acceleration, so-called radio gischt relics, have preferentially been found in the outskirts of galaxy clusters. By identifying merger shock waves in cosmological grid simulations, we explore several prescriptions for relating the energy dissipated in shocks to the energy emitted in the radio band. None of the investigated models produces detectable radio relics within 100-200 kpc from the cluster centre. All models cause >50 per cent of the detectable relic emission at projected distances >800 kpc. Central radio relics caused by shocks that propagate along the line of sight are rare events for simple geometrical reasons, and they have a low surface brightness making them elusive for current instruments. Our simulations show that the radial distribution of observed relics can be explained by the radial trend of dissipated kinetic energy in shocks, which increases with distance from the cluster centre up until half of the virial radius.

  20. Time Domain Analysis Of Sound Propagation In Shallow Water With Transitional Layer

    Microsoft Academic Search

    T. Tsuchiya; S. Matsumoto; N. Endoh

    \\u000a The characteristics of sound propagation in shallow water are influenced by the bottom media because sound propagation is\\u000a affected by acoustic boundary conditions of the water-sediment interface. In order to investigate the characteristics of sound\\u000a propagating in shallow water, it is necessary to develop an accurate numerical method of sound propagation. The elastic finite\\u000a difference time domain (FDTD) method is

  1. Classification of neocortical interneurons using affinity propagation

    PubMed Central

    Santana, Roberto; McGarry, Laura M.; Bielza, Concha; Larrańaga, Pedro; Yuste, Rafael

    2013-01-01

    In spite of over a century of research on cortical circuits, it is still unknown how many classes of cortical neurons exist. In fact, neuronal classification is a difficult problem because it is unclear how to designate a neuronal cell class and what are the best characteristics to define them. Recently, unsupervised classifications using cluster analysis based on morphological, physiological, or molecular characteristics, have provided quantitative and unbiased identification of distinct neuronal subtypes, when applied to selected datasets. However, better and more robust classification methods are needed for increasingly complex and larger datasets. Here, we explored the use of affinity propagation, a recently developed unsupervised classification algorithm imported from machine learning, which gives a representative example or exemplar for each cluster. As a case study, we applied affinity propagation to a test dataset of 337 interneurons belonging to four subtypes, previously identified based on morphological and physiological characteristics. We found that affinity propagation correctly classified most of the neurons in a blind, non-supervised manner. Affinity propagation outperformed Ward's method, a current standard clustering approach, in classifying the neurons into 4 subtypes. Affinity propagation could therefore be used in future studies to validly classify neurons, as a first step to help reverse engineer neural circuits. PMID:24348339

  2. Radio frequency interference mitigation in radio astronomy

    NASA Astrophysics Data System (ADS)

    Boonstra, Albert-Jan

    2005-12-01

    The next generation of radio telescopes is expected to be one to two orders of magnitude more sensitive than the current generation. Examples of such new telescopes are the Low Frequency Array (LOFAR), currently under construction in the Netherlands, and the Square Kilometer Array (SKA), currently in a concept study phase. Another trend is that technological advances in the fields of electronics and communications systems have led to a vast increase in radio communication applications and systems, and also to an increasing demand for radio spectrum. These two trends, more sensitive telescopes and a much denser spectrum use, imply that radio astronomy will become more vulnerable to interference from radio transmitters. Although protection criteria exist for radio astronomy, it becomes increasingly difficult to keep the radio astronomy frequency bands free from interference. In order to mitigate interference in radio astronomical data, filtering techniques can be used. In this thesis, modern array signal processing techniques have been applied to narrow-band multichannel interference detection and excision, and to narrow-band spatial interference filtering. By investigating the subspace structure of the telescope array output covariance matrices, new results were found, such as upper limits on interference residuals after excision and spatial filtering. The effect of bandwidth, extendedness of the interfering sources, and multipath effects on the detection and spatial filter effectiveness were studied as well. The advantage of a multichannel approach over a single telescope approach was demonstrated by using experimental data from the Westerbork Synthesis Radio Telescope (WSRT). As the performance of mitigation algorithms can be improved by calibration of the telescope gains and noise powers, calibration algorithms were developed. These algorithms were verified both for single and dual polarised arrays. Finally, a LOFAR interference mitigation strategy was developed.

  3. The ghost propagator in Coulomb gauge

    NASA Astrophysics Data System (ADS)

    Watson, P.; Reinhardt, H.

    2011-05-01

    We present results for a numerical study of the ghost propagator in Coulomb gauge whereby lattice results for the spatial gluon propagator are used as input to solving the ghost Dyson-Schwinger equation. We show that in order to solve completely, the ghost equation must be supplemented by a boundary condition (the value of the inverse ghost propagator dressing function at zero momentum) which determines if the solution is critical (zero value for the boundary condition) or subcritical (finite value). The various solutions exhibit a characteristic behavior where all curves follow the same (critical) solution when going from high to low momenta until `forced' to freeze out in the infrared to the value of the boundary condition. The boundary condition can be interpreted in terms of the Gribov gauge-fixing ambiguity; we also demonstrate that this is not connected to the renormalization. Further, the connection to the temporal gluon propagator and the infrared slavery picture of confinement is discussed.

  4. ``Drifting tadpoles'' in wavelet spectra of decimetric radio emission of fiber bursts

    Microsoft Academic Search

    H. Mészárosová; M. Karlický; J. Rybák; K. Jiricka

    2009-01-01

    Aims: The solar decimetric radio emission of fiber bursts was investigated searching for the ``drifting tadpole'' structures proposed by theoretical studies. Methods: Characteristic periods with the tadpole pattern were searched for in the radio flux time series by wavelet analysis methods. Results: For the first time, we have found drifting tadpoles in the wavelet spectra of the decimetric radio emission

  5. Connectivity in a Multi-radio, Multichannel Heterogeneous Ad Hoc Network

    Microsoft Academic Search

    Dave Cavalcanti; Hrishikesh Gossain; Dharma Agrawal

    Future wireless networks are expected to integrate heterogeneous devices equipped with multiple radios and different characteristics. Nodes equipped with a single communication interface will co-exist with nodes equipped with multiple radios that can transmit and receive simultaneously. Therefore, it is important to understand how these heterogeneous radios can affect connectivity and overall multihop network performance. Maintaining connectivity in ad hoc

  6. The earth as a radio source. [noting auroral kilometric radiation

    NASA Technical Reports Server (NTRS)

    Gurnett, D. A.

    1975-01-01

    The primary characteristics of radio emission from the earth's magnetosphere are summarized, the origins of these missions are considered and similarities to other astronomical radio sources discussed. The auroral kilometric radiation has features very similar to Io-related decametric radiation from Jupiter and from Saturn. The radiation at fp and 2 fp upstream of the bow shock appears to be generated by the same mechanism as type III solar radio bursts. The beaming of the auroral kilometric radiation into a cone shaped region over the polar cap has some similarity to the angular distribution of radiation from Io and to the beaming of radio emission from pulsars.

  7. Geodesy by radio interferometry: Water vapor radiometry for estimation of the wet delay

    Microsoft Academic Search

    G. Elgered; J. L. Davis; T. A. Herring; I. I. Shapiro

    1991-01-01

    An important source of error in very-long-baseline interferometry (VLBI) estimates of baseline length is unmodeled variations of the refractivity of the neutral atmosphere along the propagation path of the radio signals. The authors present and discuss the method of using data from a water vapor readiometer (WVR) to correct for the propagation delay caused by atmospheric water vapor, the major

  8. Evaluation of the diffusion component around 7 GHz for a maritime radio relay link

    Microsoft Academic Search

    A. Bernardini; G. Meucci

    1974-01-01

    The effect of tropospheric scattering and sea reflection on wave propagation at 7 GHz in point to point communication radio relay link were studied using mathematical models to determine diffusion cross reactions and power spectra. For the tropospheric scattering two models were used; the first makes use of the existence of vortices even outside the propagation axis, the second uses

  9. Radiowave propagation measurements in Nigeria (preliminary reports)

    NASA Astrophysics Data System (ADS)

    Falodun, S. E.; Okeke, P. N.

    2013-07-01

    International conferences on frequency coordination have, in recent years, required new information on radiowave propagation in tropical regions and, in particular, on propagation in Africa. The International Telecommunications Union (ITU-R) initiated `radio-wave propagation measurement campaign' in some African countries some years back. However, none of the ITU-initiated experiments were mounted in Nigeria, and hence, there is lack of adequate understanding of the propagation mechanisms associated with this region of the tropics. The Centre for Basic Space Science (CBSS) of NASRDA has therefore embarked on propagation data collection from the different climatic zones of Nigeria (namely Coastal, Guinea Savannah, Midland, and Sahelian) with the aim of making propagation data available to the ITU, for design and prediction purposes in order to ensure a qualitative and effective communication system in Nigeria. This paper focuses on the current status of propagation data from Nigeria (collected by CBSS), identifying other parameters that still need to be obtained. The centre has deployed weather stations to different locations in the country for refractivity measurements in clear atmosphere, at the ground surface and at an altitude of 100 m, being the average height of communication mast in Nigeria. Other equipments deployed are Micro Rain Radar and Nigerian Environmental and Climatic Observing Program equipments. Some of the locations of the measurement stations are Nsukka (7.4° E, 6.9° N), Akure (5.12° E, 7.15° N), Minna (6.5° E, 9.6° N), Sokoto (5.25° E, 13.08° N), Jos (8.9° E, 9.86° N), and Lagos (3.35° E, 6.6° N). The results obtained from the data analysis have shown that the refractivity values vary with climatic zones and seasons of the year. Also, the occurrence probability of abnormal propagation events, such as super refraction, sub-refraction, and ducting, depends on the location as well as the local time. We have also attempted to identify and calculate the most important propagation factors and associated data, such as k factor, that are relevant in considerations of propagation in tropical regions like Nigeria.

  10. Plants 2: Plant Propagation

    NSDL National Science Digital Library

    Science Netlinks

    2001-10-20

    This is the second (and final) Science NetLinks lesson in a series on plants. In this lesson, students will do a project in which they choose a plant and try to propagate it. The project will take about 6 to 8 weeks to complete. During this time, students will research propagation, attempt to propagate a plant, keep a journal, and write a summary when the project is finished.

  11. Bidirectional Type III Solar Radio Bursts P. A. Robinson

    E-print Network

    Bidirectional Type III Solar Radio Bursts P. A. Robinson School of Physics, University of Sydney, NSW 2006, Australia Electronic mail: p.robinson@physics.usyd.edu.au A. O. Benz Institute of Astronomy. ROBINSON Figure 1. Geometries of beam propagation in (a) normal, (b) inverted­U or ­J, (c) reverse

  12. Variations in Radio and Television Interference from Transmission Lines

    Microsoft Academic Search

    H. H. Newell; F. W. Warburton

    1956-01-01

    Growth of power utility loads is steeply upward with the resulting requirement of higher transmission voltages. Radio interference (RI) influence has been reported1 to be a limiting factor in choice of size of transmission conductors. There are still large gaps in the present knowledge of generation, propagation, attenuation, and measurement of interference, and approaches toward a more complete understanding of

  13. Radio coverage and performance analysis for local area networks

    Microsoft Academic Search

    Cristian Androne; Tudor Palade

    2010-01-01

    The paper is concerned with the study of coverage and co-channel interference for local area networks operating at three different frequencies -2.4 GHz, 5 GHz and 60 GHz. The studies will be conducted in an indoor environment. The effects of the surrounding environment on the radio wave propagation are studied in detail for each of the three technologies. Advantages and

  14. Intermittent activity of radio sources. Accretion instabilities and jet precession

    Microsoft Academic Search

    M. Kunert-Bajraszewska; A. Janiuk; A. Siemiginowska; M. Gawronski

    2011-01-01

    We consider the radiation pressure instability operating on short timescales (103 - 106 years) in the accretion disk around a supermassive black hole as the origin of the intermittent activity of radio sources. We test whether this instability can be responsible for short ages (<104 years) of Compact Steep Spectrum sources measured by hot spots propagation velocities in VLBI observations

  15. On Asynchronous OFDM Implementation for Cognitive Radio

    Microsoft Academic Search

    Meng Wah Chia; Ying-Chang Liang

    2010-01-01

    There is an increasing need for a cognitive radio (CR) that is capable of observing its environment and modifying its transmission characteristics to transmit on unused frequency bands in ways that cause no harmful interference to the primary users (PU). In this paper, we assume that the PU transmits using a conventional OFDM system. We present a non-contiguous OFDM (NC-OFDM)

  16. Propagation measurements for satellite radio reception inside buildings

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1993-01-01

    Swept CW signals (from 700 to 1800 MHz) were received inside six buildings of brick, corrugated sheet-metal, wood-frame, mobile-home, and reinforced concrete-wall construction. A transmitter antenna was mounted outdoors on top of an 18 m tower to simulate a satellite, and a linearly scanned directional receiver antenna was used to probe the spatial, spectral, and temporal variability of the signal indoors. Levels were found to have much structure in the spatial and frequency domain, but were relatively stable in time. Typically, people moving nearby produced variations of less than 0.5 dB, whereas a person blocking the transmission path produced fades of 6 to 10 dB. Severe losses (17.5 dB) were observed in the concrete-wall building, which also exhibited the longest multipath delays (over 100 ns). Losses inside a mobile home were even larger (over 20 dB) and were independent of antenna orientation. The power-frequency distortion increased with the logarithm of the bandwidth, but could be reduced by moving to a position of higher power. Only the losses showed a clear frequency dependence, but they could be mitigated by moving the antenna.

  17. Further examples of seasonal variations of ELF radio propagation parameters

    NASA Astrophysics Data System (ADS)

    Bannister, Peter R.

    1999-01-01

    In this paper we use experimentally determined values of effective attenuation rate, excitation factor, and relative phase velocity, along with the theoretical expressions derived by C. and P. Greifinger, to establish the seasonal variation of representative ionospheric conductivity parameters. These parameters include the reflection heights h0 and h1 (or hE), inverse scale height ?, and reference height H. The basis for this analysis is provided by the 1990-1992 76-Hz field strength measurements taken at four land-based ELF monitoring sites established by the U.S. Navy. The source for these measurements was the U.S. Navy's dual-antenna transmitting system (WTF/MTF). The main conclusion of this paper is that the summertime and January nighttime attenuation rates are substantially lower than during other times of the year. This nighttime attenuation rate decrease appears to be mainly due to an increase in the inverse scale height ?, rather than to an increase in the reflection heights h0 and hE.

  18. Vertical laser beam propagation through the troposphere

    NASA Technical Reports Server (NTRS)

    Minott, P. O.; Bufton, J. L.; Schaefer, W. H.; Grolemund, D. A.

    1974-01-01

    The characteristics of the earth's atmosphere and its effects upon laser beams was investigated in a series of balloon borne, optical propagation experiments. These experiments were designed to simulate the space to ground laser link. An experiment to determine the amplitude fluctuation, commonly called scintillation, caused by the atmosphere was described.

  19. Data format and observational modes for the RadioAstron interferometer

    NASA Astrophysics Data System (ADS)

    Andreyanov, V. V.

    2015-05-01

    To transmit radio-astronomy and auxiliary data from a space radio telescope to a ground tracking station (and then to a correlator) via radio link it is necessary to use a special data format and coding and decoding procedures. Here, the format developed and successfully implemented in the RadioAstron ground-space radio interferometer is considered in detail. The goal of the paper is to present the characteristics necessary for astronomers, observers, designers of tracking stations, and management and planning workgroups, as well as for testing for compatibility of the space radio telescope and tracking stations.

  20. Hf propagation through actively modified ionospheres

    SciTech Connect

    Argo, P.E.; Fitzgerald, T.J.; Wolcott, J.H.; Simons, D.J. (Los Alamos National Lab., NM (USA)); Warshaw, S.; Carlson, R. (Lawrence Livermore National Lab., CA (USA))

    1990-01-01

    We have developed a computer modeling capability to predict the effect of localized electron density perturbations created by chemical releases or high-power radio frequency heating upon oblique, one-hop hf propagation paths. We have included 3-d deterministic descriptions of the depleted or enhanced ionization, including formation, evolution, and drift. We have developed a homing ray trace code to calculate the path of energy propagation through the modified ionosphere in order to predict multipath effects. We also consider the effect of random index of refraction variations using a formalism to calculate the mutual coherence functions for spatial and frequency separations based upon a path integral solution of the parabolic wave equation for a single refracted path through an ionosphere which contains random electron density fluctuations. 5 refs., 8 figs.

  1. Characteristics of pressure waves

    NASA Technical Reports Server (NTRS)

    1977-01-01

    Air blast characteristics generated by most types of explosions are discussed. Data cover both negative and positive blast load phases and net transverse pressure as a function of time. The effects of partial or total confinement, atmospheric propagation, absorption of energy by ground shock or cratering, and transmission over irregular terrain on blast wave properties were also considered.

  2. Effects on transionospheric HF propagation observed by ISIS at middle and auroral latitudes

    NASA Astrophysics Data System (ADS)

    James, H. G.

    2006-01-01

    In 1978, an experiment on transionospheric HF propagation was carried out using a transmitter at Ottawa and the sounder receivers of the ISIS-I and ISIS-II spacecraft. Over 100 ISIS-II passes were successfully recorded using a fixed frequency of 9.303 MHz. A survey of the data has allowed some reproducible characteristics of transionospheric propagation to be identified. A number of ISIS-II ionograms are published here to illustrate those characteristics. A systematic feature of the pulses is their partial splitting into ordinary (O) and extraordinary (X) parts, producing a tripartite compound pulse at the satellite. Equatorward pulses are comparatively sharp and occasionally exhibit periodic fades with beat frequencies between about 1 and 4 Hz. Features of the fades indicate that focussing of rays is a better explanation for the fades than diffraction. Rays near the limits of the reception zone can result in dispersed pulses, thought to indicate forward scattering. Swept-frequency ionograms interleaved with fixed-frequency measurements allowed two-dimensional density distributions to be modeled in altitude and latitude. Three-dimensional ray tracing plus a Newton’s-iteration algorithm were used to find rays that connected the transmitter with the position of the satellite at any time along its path. The latitudinal extent of the zone irradiated at ISIS-II altitude thus computed is approximately as observed, albeit sensitively dependent upon north south density gradients. Within this “iris” of accessibility, the maximum intensity of waves recorded at the spacecraft is within 10 dB of what is computed with a link calculation based on ray optics, but there are many dropouts of 20 30 dB below this maximum envelope. Toward the equator, propagation directions come to within about 10° of the magnetic-field axis. This research supports planning for coordinated ground-space radio experiments in the upcoming e-POP satellite mission.

  3. NASA Propagation Information Center

    NASA Technical Reports Server (NTRS)

    Smith, Ernest K.; Flock, Warren L.

    1989-01-01

    The NASA Propagation Information Center became formally operational in July 1988. It is located in the Department of Electrical and Computer Engineering of the University of Colorado at Boulder. The Center is several things: a communications medium for the propagation with the outside world, a mechanism for internal communication within the program, and an aid to management.

  4. Geometric Sound Propagation

    E-print Network

    North Carolina at Chapel Hill, University of

    methods[4] General pipeline is often variant of ray tracing Create many sound waves from source Propagate of sound d: path distance d1 d2 1 d #12;Sound output[4] Sound pipeline #12;Demo #12;Ray tracing[3] #12;Ray tracing Create many rays from sound source Propagate through scene Collect rays at listener #12;Ray

  5. Vegetative propagation of jojoba

    Microsoft Academic Search

    C. B. Low; W. P. Hackett

    1981-01-01

    Development of jojoba as an economically viable crop requires improved methods of propagation and culture. Rooting experiments were performed on cutting material collected from wild jojoba plants. A striking seasonal fluctuation in rooting potential was found. Jojoba plants can be successfully propagated from stem cuttings made during spring, summer, and, to some extent, fall. Variability among jojoba plants may also

  6. NASA propagation information center

    NASA Technical Reports Server (NTRS)

    Smith, Ernest K.; Flock, Warren L.

    1990-01-01

    The NASA Propagation Information Center became formally operational in July 1988. It is located in the Department of Electrical and Computer Engineering of the University of Colorado at Boulder. The center is several things: a communications medium for the propagation with the outside world, a mechanism for internal communication within the program, and an aid to management.

  7. Propagation of Significant Figures.

    ERIC Educational Resources Information Center

    Schwartz, Lowell M.

    1985-01-01

    Shows that the rules of thumb for propagating significant figures through arithmetic calculations frequently yield misleading results. Also describes two procedures for performing this propagation more reliably than the rules of thumb. However, both require considerably more calculational effort than do the rules. (JN)

  8. US Radio Broadcasting Past

    NSDL National Science Digital Library

    White, Thomas W.

    Thomas H. White discusses the history of United States radio in detail from the late 1800�s to the 1940�s in this informative site featuring a compilation of materials and articles. The site features 24 different sections arranged by title and year for users to browse, each section allows the user to discover the beginnings of radio in the United States. Sections include some that outline the changes of radio in relation to U.S. history, including but not limited to the World Wars, as well as discussions of big business and radio, and early government regulation to name only a few. For anyone interested in the history of radio and how radio got to where it is today, this site is an excellent resource.

  9. American RadioWorks

    NSDL National Science Digital Library

    Radio documentaries have been around almost since the beginning of regularly scheduled radio programming, but not all are created equal (or with great aplomb), and the American Radio Works is certainly one of the finer documentary production units in the field. Based at Minnesota Public Radio in St. Paul, Minnesota, Radio Works' primary themes include public affairs documentaries on major social and economic issues, investigative reporting, and the Living History series, which seeks to document the 20th century American experience "through the lives of those who witnessed it." The web-browsing public will be glad to know that all of the radio projects are available online here, and can be listened to in their entirety. Visitors can listen to close to 40 of their productions, including their most recent production which deals with the extensive phone conversations recorded by Presidents Johnson, Kennedy, and Nixon during their terms in the White House

  10. Propagation along azimuthally magnetized ferrite-loaded circular waveguides

    NASA Technical Reports Server (NTRS)

    Mueller, R. S.; Rosenbaum, F. J.

    1977-01-01

    The paper describes the modal dispersion characteristics of electromagnetic waves traveling along the azimuthally magnetized ferrite-loaded coaxial transmission line and the ferrite-loaded wire. The modal dispersion curves are used to determine the pass and stop bands of normal propagation. Boundary-value problems were solved with Bolle-Heller functions. The dispersion characteristics of transverse electric modes are presented as plots of the normalized propagation constant vs the normalized frequency.

  11. Radio continuum properties of luminous infrared galaxies. Identifying the presence of an AGN in the radio

    NASA Astrophysics Data System (ADS)

    Vardoulaki, E.; Charmandaris, V.; Murphy, E. J.; Diaz-Santos, T.; Armus, L.; Evans, A. S.; Mazzarella, J. M.; Privon, G. C.; Stierwalt, S.; Barcos-Muńoz, L.

    2015-02-01

    Context. Luminous infrared galaxies (LIRGs) are systems enshrouded in dust, which absorbs most of their optical/UV emission and radiates it again in the mid- and far-infrared. Radio observations are largely unaffected by dust obscuration, enabling us to study the central regions of LIRGs in an unbiased manner. Aims: The main goal of this project is to examine how the radio properties of local LIRGs relate to their infrared spectral characteristics. Here we present an analysis of the radio continuum properties of a subset of the Great Observatories All-sky LIRG Survey (GOALS), which consists of 202 nearby systems (z< 0.088). Our radio sample consists of 35 systems, containing 46 individual galaxies, that were observed at both 1.49 and 8.44 GHz with the VLA with a resolution of about 1 arcsec (FWHM). The aim of the project is to use the radio imagery to probe the central kpc of these LIRGs in search of active galactic nuclei (AGN). Methods: We used the archival data at 1.49 and 8.44 GHz to create radio-spectral-index maps using the standard relation between flux density S? and frequency ?, S? ~ ?- ?, where ? is the radio spectral index. By studying the spatial variations in ?, we classified the objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the presence of an active nucleus using the radio morphology, deviations from the radio/infrared correlation, and spatially resolved spectral index maps, and then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII] line ratios and equivalent width of the 6.2 ?m PAH feature) and optical (BPT diagram) AGN diagnostics. Results: We find that 21 out of the 46 objects in our sample (~45%) are radio-AGN, 9 out of the 46 (~20%) are classified as starbursts (SB) based on the radio analysis, and 16 (~35%) are AGN/SB. After comparing to other AGN diagnostics we find 3 objects out of the 46 (~7%) that are identified as AGN based on the radio analysis, but are not classified as such based on the mid-infrared and optical AGN diagnostics presented in this study. Appendix A is available in electronic form at http://www.aanda.orgVLA images as FITS files are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A4

  12. The software radio development system

    Microsoft Academic Search

    S. P. Reichhart; B. Youmans; R. Dygert

    1999-01-01

    This article focuses on the effort to advance the field of software reprogrammable radios and the building of a software radio testbed to develop advanced radio waveforms and techniques. The Air Force Research Laboratory has performed research on software reprogrammable radios since 1990 when the SPEAKeasy program was begun to determine if a multiband, multimode software radio was technically feasible.

  13. Radio-Locator

    NSDL National Science Digital Library

    Radio-Locator is a comprehensive database of radio stations throughout the United States and Canada. Stations can be searched by location and format, or even more specifically with the site's advanced search. Users can even search for vacant frequencies on the dial. The bulk of their information come from the FCC's public databases, but is also updated and corrected. Radio-Locator also provides links to individual stations website and internet streams if available.

  14. Radio Link Frequency Assignment

    Microsoft Academic Search

    Bertrand Cabon; Simon De Givry; Lionel Lobjois; Thomas Schiex; Joost P. Warners

    1999-01-01

    Abstract: The problem of radio frequency assignment is to provide communication channelsfrom limited spectral resources whilst keeping to a minimum the interference suered by thosewhishing to communicate in a given radio communication network. This problem is a combinatorial(NP-hard) optimization problem. In 1993, the CELAR (the French \\\\Centre d'Electronique del'Armement") built a suite of simplied versions of Radio Link Frequency Assignment

  15. Some radio meteor news

    NASA Astrophysics Data System (ADS)

    Rault, Jean-Louis

    2013-01-01

    Radio meteor observing for astronomy purposes is still alive, despite the fact that traditional TV transmitters used for decades tend to disappear. Radio observers are now starting to develop their own dedicated transmitters, and are using new kinds of transmitters, such as military and radio-navigation systems to continue their studies. Encouraging results are also obtained in the aeronomy/geophysics domain when searching for evidence of modifications of the Earth/ionosphere waveguide by discrete ionized meteor trails.

  16. Dominion Radio Astrophysical Observatory

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    The Dominion Radio Astrophysical Observatory began operating in 1959, and joined the NATIONAL RESEARCH COUNCIL in 1970. It became part of the Herzberg Institute of Astrophysics in 1975. The site near Penticton, BC has a 26 m radio telescope, a seven-antenna synthesis telescope on a 600 m baseline and two telescopes dedicated to monitoring the solar radio flux at 10.7 cm. This part of the Institu...

  17. STEM on the radio

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    2011-10-01

    Looking for an Internet radio station focusing on programing about science, technology, engineering, and math (STEM)? The U.S. National Science Foundation (NSF) announced on 26 September the launch of Science360 Radio, which it says is the first Internet radio stream dedicated to STEM programing. Science360 includes more than 100 radio shows and podcasts that are available on the Web as well as on iPhone and Android devices. The shows originate from a variety of sources, including NSF, other U.S. government agencies, science organizations, universities, and media outlets. For more information, see http://science360.gov/files/.

  18. Isotropization of the terrestrial low-frequency radio bursts

    NASA Astrophysics Data System (ADS)

    Steinberg, J.-L.; Lacombe, C.; Hoang, S.

    2000-09-01

    We analyze ISEE 3 radio data acquired in the solar wind. Using a new technique we measure the spectrum of the isotropic component ("tail" or isotropic terrestrial kilometric radiation (ITKR)) of low-frequency (LF) bursts which extends from ? fp.sw (the interplanetary (IP) medium plasma frequency) to an upper limit fmax which can reach 5×fp.sw. The relative intensities of the auroral kilometric radiation (AKR) burst, often associated with LF bursts, and of the ITKR are highly variable when observed from the Lagrange point Ll most probably because of propagation effects. In the range of frequencies 2fp.sw < f < 5fp.sw the AKR source angular radius measured from Ll is a few degrees, while that of the ITKR source is close to 90°: the radiation from these two sources must propagate through very different regions of the magneto sphere. The isotropization of the radiation from a magnetospheric source at fmax requires the presence of large overdense structures in the IP medium. For each event, such structures were identified and their peak plasma frequency fp.bump measured using ISEE 3 plasma density data acquired in the ecliptic. The frequency fmax is always larger than fp.bump and there is only a weak correlation between these quantities. Thus fp.bump cannot be taken as a characteristic of the three-dimensional IP structures needed to isotropize the radiation. These structures should be rough and capable of sending some radiation towards the Sun to reach IP regions where higher values of fp.sw will be encountered. The study of the isotropization of LF bursts requires a deeper knowledge of the dense structures of the IP medium.

  19. Seismic wave propagation in viscoelastic and saturated rock

    NASA Astrophysics Data System (ADS)

    Cai, Yuan-Qiang; Xu, Chang-Jie; Wu, Shi-Ming

    1998-05-01

    Considering engineering practice, the viscoelastic two-phase model is adopted, seismic wave propagation in saturated rock is studied. Not only the effect of the viscosity of rock skeleton but also the effect of ground water on the propagation of the seismic wave can be considered by this model, the propagation characteristics of seismic wave in saturated rock can be understood comprehensively and the model is more reasonable than other model by which seismic wave propagation is studied. The effect of frequency, water content and viscosity constant on the wave velocity and attenuation are studied by numerical examples and some valuable conclusions are drawn.

  20. A Study of Malware Propagation via Online Social Networking

    NASA Astrophysics Data System (ADS)

    Faghani, Mohammad Reza; Nguyen, Uyen Trang

    The popularity of online social networks (OSNs) have attracted malware creators who would use OSNs as a platform to propagate automated worms from one user's computer to another's. On the other hand, the topic of malware propagation in OSNs has only been investigated recently. In this chapter, we discuss recent advances on the topic of malware propagation by way of online social networking. In particular, we present three malware propagation techniques in OSNs, namely cross site scripting (XSS), Trojan and clickjacking types, and their characteristics via analytical models and simulations.

  1. Propagation of sound in turbulent media

    NASA Technical Reports Server (NTRS)

    Wenzel, A. R.

    1976-01-01

    Perturbation methods commonly used to study the propagation of acoustic waves in turbulent media are reviewed. Emphasis is on those techniques which are applicable to problems involving long-range propagation in the atmosphere and ocean. Characteristic features of the various methods are illustrated by applying them to particular problems. It is shown that conventional perturbation techniques, such as the Born approximation, yield solutions which contain secular terms, and which therefore have a relatively limited range of validity. In contrast, it is found that solutions obtained with the aid of the Rytov method or the smoothing method do not contain secular terms, and consequently have a much greater range of validity.

  2. HF Radio Wave Production of Artificial Ionospheres

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert

    In 1993 it was predicted that artificial ionospheres would be produced by high power HF radio waves, once HF transmitters approached a GWatt ERP. When that threshold was very recently achieved, such production was indeed detected and published at two high latitude high power HF facilities. Here we review: the first-principles logic behind that prediction, which aspects of such production are critically dependent on magnetic latitude, and which aspects of such production depend only on physical parameters independent of latitude. These distinctions follow directly from decomposition of the problem of ionization production into its components of: radio-wave propagation, wave-particle interactions, electron transport, and quantitative elastic/inelastic cross-sections. We outline this analysis to show that, within the context of early observations, the production of ionization is inevitable, and only a question of competing instability thresholds, and scale of ionization production. This illustrates complimentary aeronomy and plasma physics to advance understanding of both.

  3. Linear and Nonlinear Whistler Wave Propagation in the Magnetosphere Based on Plasma Density Models from IMAGE Spacecraft Data

    NASA Astrophysics Data System (ADS)

    Flores, Mauricio; Correa, Cynthia; Horton, Wendel

    2010-11-01

    From the radio plasma imager on the IMAGE satellite, spatial profiles of electron density in the inner magnetosphere were constructed [B.W. Reinisch et al, Geophys. Res. Lett., 28, 1167 (2001)]. We use these profiles and the dipolar magnetic field model to analyze the propagation of whistler waves. We compute the dispersion characteristics of wave packets from the 2D ?(kx,kz,n, B) dispersion function, showing wave energy focusing into low phase velocity regions. We add model growth rates from S. Sazhin, Whistler-mode waves in a hot plasma (Cambridge U. Press, Cambridge, 1993) and nonlinear terms from Horton et al [W. Horton et al, Nonlinear Dynamics of the Electromagnetic Ion Cyclotron Structures, Firehose and Whistlers, preprint, Nonlin. Processes Geophys.] to determine saturation levels of whistler chorus waves and associated coherent structures. We explore NLS, DNLS and vortex models, consistent with experiments by Stenzel et al [R.L. Stenzel et al, Plasma Phys. Control. Fusion 50 074009 (2008)].

  4. Stabilized radio frequency quadrupole

    DOEpatents

    Lancaster, Henry D. (Orinda, CA); Fugitt, Jock A. (Berkeley, CA); Howard, Donald R. (Danville, CA)

    1984-01-01

    A long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator.

  5. Radio Astronomy for Amateurs

    Microsoft Academic Search

    N. Quinn

    2003-01-01

    Karl Jansky is considered the father of RADIOASTRONOMY. During the 1930s, Jansky worked for the Bell Telephone Laboratories studying the origin of static noise from thunderstorms. During the course of this work he discovered that some signals had an extraterrestrial origin. However, it was Grote Reber, a professional radio engineer and radio amateur, who carried out further investigations. In 1937...

  6. Radio Astronomy for Amateurs

    NASA Astrophysics Data System (ADS)

    Quinn, N.; Murdin, P.

    2003-04-01

    Karl Jansky is considered the father of RADIOASTRONOMY. During the 1930s, Jansky worked for the Bell Telephone Laboratories studying the origin of static noise from thunderstorms. During the course of this work he discovered that some signals had an extraterrestrial origin. However, it was Grote Reber, a professional radio engineer and radio amateur, who carried out further investigations. In 1937...

  7. Radio spectrum surveillance station

    Microsoft Academic Search

    D. R. Hersey

    1979-01-01

    The paper presents a general and functional description of a low-cost surveillance station designed as the first phase of NASA's program to develop a radio spectrum surveillance capability for deep space stations for identifying radio frequency interference sources. The station described has identified several particular interferences and is yielding spectral signature data which, after cataloging, will serve as a library

  8. The Radio Transient Sky

    NASA Astrophysics Data System (ADS)

    Lazio, J.

    Radio transients are known on time scales from nanoseconds to years, from sources in the Galaxy and beyond, and with either coherent or incoherent emission mechanisms. Observations of this wide variety of sources are relevant to many of the highest profile questions in astronomy and astrophysics. As illustrations of the breadth of the radio transient sky, both coherent and incoherent radio emission has long been known from stars and stellar remnants and has informed topics ranging from stellar evolution to Galactic structure to relativistic jet dynamics to tests of fundamental physics. Coherent radio emission is now also known from brown dwarfs, and there are active programs to find similar emissions from extrasolar planets. Outside of the Galaxy, incoherent radio counterparts to supernovae, tidal disruption events, and gamma-ray bursts is well known and have contributed to topics such as understanding the cosmic star formation rate and the formation of relativistic jets. Excitingly, coherent radio bursts that appear to be at cosmological distances were recently discovered. I provide a survey of the radio transient sky, illustrating both how radio transients are part of the Hot-Wired Sky and are likely to help drive the Hot-Wiring. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

  9. A refracting radio telescope

    Microsoft Academic Search

    Paul Bernhardt; A. V. da Rosa

    1977-01-01

    Observations of extraterrestrial radio sources at the lower end of the radio frequency spectrum are limited by reflection of waves from the topside ionosphere and by the large size of antenna apertures necessary for the realization of narrow beamwidths. The use of the ionosphere as a lens is considered. The lens is formed by the release of chemicals such as

  10. Radio on the Internet.

    ERIC Educational Resources Information Center

    Raeder, Aggi

    1996-01-01

    Discusses the availability of radio "cybercasts" on the Internet, either in real time or on demand. Topics include problems and opportunities, copyright issues, equipment and software needed for listening, and searchability of sites. Provides an annotated list of radio-related Uniform Resource Locators (URLs), including music, news, talk, and…

  11. Amateur Radio Satellite Communications.

    ERIC Educational Resources Information Center

    Koch, David P.

    The Amateur Radio Satellite Communications project had, as its goal, the assembly of an amateur radio satellite station in a high school physics classroom. Specific objectives were to provide: (1) a special source of interest as a motivator for attracting students and building public relations; (2) a center of interest as a motivator for the study…

  12. The Radio Jove Project

    NASA Technical Reports Server (NTRS)

    Thieman, J. R.

    2010-01-01

    The Radio love Project is a hands-on education and outreach project in which students, or any other interested individuals or groups build a radio telescope from a kit, operate the radio telescope, transmit the resulting signals through the internet if desired, analyze the results, and share the results with others through archives or general discussions among the observers. Radio love is intended to provide an introduction to radio astronomy for the observer. The equipment allows the user to observe radio signals from Jupiter, the Sun, the galaxy, and Earth-based radiation both natural and man-made. The project was started through a NASA Director's Discretionary Fund grant more than ten years ago. it has continued to be carried out through the dedicated efforts of a group of mainly volunteers. Dearly 1500 kits have been distributed throughout the world. Participation can also be done without building a kit. Pre-built kits are available. Users can also monitor remote radio telescopes through the internet using free downloadable software available through the radiosky.com website. There have been many stories of prize-winning projects, inspirational results, collaborative efforts, etc. We continue to build the community of observers and are always open to new thoughts about how to inspire the observers to still greater involvement in the science and technology associated with Radio Jove.

  13. Stabilized radio frequency quadrupole

    DOEpatents

    Lancaster, H.D.; Fugitt, J.A.; Howard, D.R.

    1984-12-25

    Disclosed is a long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator. 5 figs.

  14. Smart Radio Spectrum Management for Cognitive Radio

    E-print Network

    Bhattacharya, Partha Pratim; Gera, Rishita; Agarwal, Anjali

    2011-01-01

    Today's wireless networks are characterized by fixed spectrum assignment policy. The limited available spectrum and the inefficiency in the spectrum usage necessitate a new communication paradigm to exploit the existing wireless spectrum opportunistically. Cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users. In this work, a fuzzy logic based system for spectrum management is proposed where the radio can share unused spectrum depending on some parameters like distance, signal strength, node velocity and availability of unused spectrum. The system is simulated and is found to give satisfactory results.

  15. Electric and magnetic fields of an intense pulse of relativistic electrons propagating through air

    Microsoft Academic Search

    K. A. Dreyer

    1979-01-01

    Since propagation characteristics of an electron beam traversing a neutral gas are determined by the response of the beam electrons to their self-fields, an accurate evaluation of the electric and magnetic (EM) fields is essential to any propagation analysis. We report here on theoretical models that were developed for the electromagnetic fields associated with an electron beam propagating in air.

  16. Electric and Magnetic Fields of AN Intense Pulse of Relativistic Electrons Propagating Through Air

    Microsoft Academic Search

    Kenneth Allen Dreyer

    1979-01-01

    Since propagation characteristics of an electron beam traversing a neutral gas are determined by the response of the beam electrons to their self-fields, an accurate evaluation of the electric and magnetic (EM) fields is essential to any propagation analysis. We report here on theoretical models that were developed for the electromagnetic fields associated with an electron beam propagating in air.

  17. Electric and magnetic fields of an intense pulse of relativistic electrons propagating through air. Final report

    Microsoft Academic Search

    Dreyer

    1979-01-01

    Since propagation characteristics of an electron beam traversing a neutral gas are determined by the response of the beam electrons to their self-fields, an accurate evaluation of the electric and magnetic (EM) fields is essential to any propagation analysis. We report here on theoretical models that were developed for the electromagnetic fields associated with an electron beam propagating in air.

  18. Planetary radio lasing

    NASA Technical Reports Server (NTRS)

    Calvert, W.

    1988-01-01

    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.

  19. UHECRs from the Radio Lobes of AGNs

    E-print Network

    F. Fraschetti; F. Melia

    2008-10-07

    We report a stochastic mechanism of particle acceleration from first principles in an environment having properties like those of Radio Lobes in AGNs. We show that energies $\\sim 10^{20}$ eV are reached in $\\sim 10^6$ years for protons. Our results reopen the question regarding the nature of the high-energy cutoff in the observed spectrum: whether it is due solely to propagation effects, or whether it is also affected by the maximum energy permitted by the acceleration process itself.

  20. Propagation of Environmental Noise

    ERIC Educational Resources Information Center

    Lyon, R. H.

    1973-01-01

    Solutions for environmental noise pollution lie in systematic study of many basic processes such as reflection, scattering, and spreading. Noise propagation processes should be identified in different situations and assessed for their relative importance. (PS)

  1. Radio efficiency of pulsars

    SciTech Connect

    Szary, Andrzej; Melikidze, George I.; Gil, Janusz [Kepler Institute of Astronomy, University of Zielona Góra, Lubuska 2, 65-265 Zielona Góra (Poland); Zhang, Bing [Department of Physics and Astronomy, University of Nevada, Las Vegas, NV 89154 (United States); Xu, Ren-Xin, E-mail: aszary@astro.ia.uz.zgora.pl, E-mail: zhang@physics.unlv.edu [School of Physics and Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)

    2014-03-20

    We investigate radio emission efficiency, ?, of pulsars and report a near-linear inverse correlation between ? and the spin-down power, E-dot , as well as a near-linear correlation between ? and pulsar age, ?. This is a consequence of very weak, if any, dependences of radio luminosity, L, on pulsar period, P, and the period derivative, P-dot , in contrast to X-ray or ?-ray emission luminosities. The analysis of radio fluxes suggests that these correlations are not due to a selection effect, but are intrinsic to the pulsar radio emission physics. We have found that, although with a large variance, the radio luminosity of pulsars is ?10{sup 29} erg s{sup –1}, regardless of the position in the P-- P-dot diagram. Within such a picture, a model-independent statement can be made that the death line of radio pulsars corresponds to an upper limit in the efficiency of radio emission. If we introduce the maximum value for radio efficiency into the Monte Carlo-based population syntheses we can reproduce the observed sample using the random luminosity model. Using the Kolmogorov-Smirnov test on a synthetic flux distribution reveals a high probability of reproducing the observed distribution. Our results suggest that the plasma responsible for generating radio emission is produced under similar conditions regardless of pulsar age, dipolar magnetic field strength, and spin-down rate. The magnetic fields near the pulsar surface are likely dominated by crust-anchored, magnetic anomalies, which do not significantly differ among pulsars, leading to similar conditions for generating electron-positron pairs necessary to power radio emission.

  2. Maximally symmetric vector propagator

    SciTech Connect

    Tsamis, N. C.; Woodard, R. P. [Department of Physics, University of Crete, GR-710 03 Heraklion (Greece); Department of Physics, University of Florida, Gainesville, Florida 32611 (United States)

    2007-05-15

    We derive the propagator for a massive vector field on a de Sitter background of arbitrary dimension. This propagator is de Sitter invariant and possesses the proper flat space-time and massless limits. Moreover, the retarded Green's function inferred from it produces the correct classical response to a test source. Our result is expressed in a tensor basis which is convenient for performing quantum-field-theory computations using dimensional regularization.

  3. Propagation of Ornamental Plants. 

    E-print Network

    DeWerth, A. F.

    1955-01-01

    Propagation of Ornamental Plants I A. I?. DEWERTH, Head Department of Floriculture and Landscape Architecture Texas A. & M. College System THE MULTIPLICATION of ornamental plants is After sterilizing, firm the soil to within 1; receiving more... larger see1 gardener to produce high-quality plants in a and add soil screened through fly screen until comparatively short time. the seed are barely hidden. Covering seed top deeply is a common error. Propagation by Seed For very fine seed, screen a...

  4. HOST GALAXIES OF X-SHAPED RADIO SOURCES

    SciTech Connect

    Springmann, A.; Cheung, C.

    2007-01-01

    Most radiation from galaxies containing active galactic nuclei (AGNs) is emitted not by the stars composing the galaxy, but from an active source at the galactic center, most likely a supermassive black hole. Of particular interest are radio galaxies, active galaxies that emit much of their radiation at radio wavelengths. Within each radio galaxy, an AGN powers a pair of collimated jets of relativistic particles, forming a pair of giant lobes at the end of the jets and thus giving a characteristic double-lobed appearance. A particular class of radio galaxies has an “X”-or winged-shaped morphology: in these, two pairs of lobes appear to originate from the galactic center, producing a distinctive X-shape. Two main mechanisms have been proposed to explain the X-shape morphology: one being a realignment of the black hole within the AGN and the second positing that the radio jets are expanding into an asymmetric medium, causing backflow and producing secondary wings. By analyzing radio host galaxy shapes, the distribution of the stellar mass is compared to the differing model expectations regarding the distribution of the surrounding gas and stellar material about the AGN. Results show elliptical host galaxies with an orthogonal offset between the semi-major axis of the host galaxy and the secondary radio wings, which lends support to the hydrodynamical model. However, results also show circular host galaxies with radio wings, making the realignment scenario a more likely model to describe the formation of these X-shaped radio sources.

  5. Statistics of optical intraday variability in a complete sample of radio-selected BL Lac objects

    E-print Network

    Jochen Heidt; Stefan J. Wagner

    1995-06-06

    We present a study of the intraday variability behaviour of a complete sample of radio-selected BL Lac objects taken from the 1 Jy catalogue. In 28 out of 34 BL Lac objects (82\\%) we detected intraday variability. 7 objects were observed during several campaigns. None of them changed its variability behaviour. The duty cycle in radio-loud BL Lac objects is very high, i.e. at least 0.8. The typical peak-to-peak amplitudes of the variability were 30\\%. By means of structure function and autocorrelation analyses we investigated the typical time-scales of the variability and determined the activity of the BL Lac objects. In 21 of the variable BL Lac objects we were able to measure a typical time-scale, which lies in the range between 0.5 and 3 days. In general, the results can be explained by the standard model, where shocks are propagating down a relativistic jet. However, in the two most densely sampled observations we found variability characteristics, which cannot easily be explained by the standard model alone, demonstrating that at least in these objects alternative models should be taken into account. Nevertheless, all models, which are able to explain variability on time-scales of days must be able to consider the high duty cycle of these BL Lac objects.

  6. 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)

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

    2014-12-01

    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.

  7. RADIO SIGNATURES OF CORONAL-MASS-EJECTION-STREAMER INTERACTION AND SOURCE DIAGNOSTICS OF TYPE II RADIO BURST

    SciTech Connect

    Feng, S. W.; Chen, Y.; Kong, X. L.; Li, G.; Song, H. Q. [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Shandong University at Weihai, Weihai 264209 (China); Feng, X. S. [SIGMA Weather Group, State Key laboratory for Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Liu Ying, E-mail: yaochen@sdu.edu.cn [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)

    2012-07-01

    It has been suggested that type II radio bursts are due to energetic electrons accelerated at coronal shocks. Radio observations, however, have poor or no spatial resolutions to pinpoint the exact acceleration locations of these electrons. In this paper, we discuss a promising approach to infer the electron acceleration location by combining radio and white light observations. The key assumption is to relate specific morphological features (e.g., spectral bumps) of the dynamic spectra of type II radio bursts to imaging features (e.g., coronal mass ejection (CME) going into a streamer) along the CME (and its driven shock) propagation. In this study, we examine the CME-streamer interaction for the solar eruption dated on 2003 November 1. The presence of spectral bump in the relevant type II radio burst is identified, which is interpreted as a natural result of the shock-radio-emitting region entering the dense streamer structure. The study is useful for further determinations of the location of type II radio burst and the associated electron acceleration by CME-driven shock.

  8. Population Studies of Radio and Gamma-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Harding, Alice K; Gonthier, Peter; Coltisor, Stefan

    2004-01-01

    Rotation-powered pulsars are one of the most promising candidates for at least some of the 40-50 EGRET unidentified gamma-ray sources that lie near the Galactic plane. Since the end of the EGRO mission, the more sensitive Parkes Multibeam radio survey has detected mere than two dozen new radio pulsars in or near unidentified EGRET sources, many of which are young and energetic. These results raise an important question about the nature of radio quiescence in gamma-ray pulsars: is the non-detection of radio emission a matter of beaming or of sensitivity? The answer is very dependent on the geometry of the radio and gamma-ray beams. We present results of a population synthesis of pulsars in the Galaxy, including for the first time the full geometry of the radio and gamma-ray beams. We use a recent empirically derived model of the radio emission and luminosity, and a gamma-ray emission geometry and luminosity derived theoretically from pair cascades in the polar slot gap. The simulation includes characteristics of eight radio surveys of the Princeton catalog plus the Parkes MB survey. Our results indicate that EGRET was capable of detecting several dozen pulsars as point sources, with the ratio of radio-loud to radio-quiet gamma-ray pulsars increasing significantly to about ten to one when the Parkes Survey is included. Polar cap models thus predict that many of the unidentified EGRET sources could be radio-loud gamma- ray pulsars, previously undetected as radio pulsars due to distance, large dispersion and lack of sensitivity. If true, this would make gamma-ray telescopes a potentially more sensitive tool for detecting distant young neutron stars in the Galactic plane.

  9. Imaging interplanetary CMEs at radio frequency from solar polar orbit

    NASA Astrophysics Data System (ADS)

    Wu, Ji; Sun, Weiying; Zheng, Jianhua; Zhang, Cheng; Liu, Hao; Yan, Jingye; Wang, Chi; Wang, Chuanbing; Wang, Shui

    2011-09-01

    Coronal mass ejections (CMEs) represent a great concentration of mass and energy input into the lower corona. They have come to be recognized as the major driver of physical conditions change in the Sun-Earth system. Consequently, observations of CMEs are important for understanding and ultimately predicting space weather conditions. This paper discusses a proposed mission, the Solar Polar Orbit Radio Telescope (SPORT) mission, which will observe the propagation of interplanetary CMEs to distances of near 0.35 AU from the Sun. The orbit of SPORT is an elliptical solar polar orbit. The inclination angle between the orbit and ecliptic plane should be about 90°. The main payload on board SPORT will be an imaging radiometer working at the meter wavelength band (radio telescope), which can follow the propagation of interplanetary CMEs. The images that are obtained by the radio telescope embody the brightness temperature of the objectives. Due to the very large size required for the antenna aperture of the radio telescope, we adopt interferometric imaging technology to reduce it. Interferometric imaging technology is based on indirect spatial frequency domain measurements plus Fourier transformation. The SPORT spacecraft will also be equipped with a set of optical and in situ measurement instruments such as a EUV solar telescope, a solar wind ion instrument, an energetic particle detector, a magnetometer, a wave detector and a solar radio burst spectrometer.

  10. Multiple Radios for Effective Rendezvous in Cognitive Radio Networks

    E-print Network

    Chu, Xiaowen

    Multiple Radios for Effective Rendezvous in Cognitive Radio Networks Lu Yu1 , Hai Liu1 , Yiu in cognitive radio networks (CRNs) for establishing a communication link on a commonly-available channel, we investigate the rendezvous problem in CRNs where cognitive users are equipped with multiple radios

  11. Multiple Radios for Fast Rendezvous in Cognitive Radio Networks

    E-print Network

    Chu, Xiaowen

    , Xiaowen Chu, and Zhiyong Lin Abstract--Rendezvous is a fundamental operation in cognitive radio networks1 Multiple Radios for Fast Rendezvous in Cognitive Radio Networks Lu Yu, Hai Liu, Yiu-Wing Leung. The existing work on rendezvous implicitly assumes that each cognitive user is equipped with one radio (i

  12. Radio-communications architectures 1 Radio-communications architectures

    E-print Network

    Paris-Sud XI, Université de

    Radio-communications architectures 1 X Radio-communications architectures Antoine Diet*, Martine Paris-Est, ESYCOM, ESIEE Paris France 1. Introduction Wireless communications, i.e. radio-communications of the architecture is that a transceiver is built with respect to the radio-communications signals. We classify them

  13. Long-term variability of the radio source J0010+1058 in 2000-2013

    NASA Astrophysics Data System (ADS)

    Gorshkov, A. G.; Konnikova, V. K.; Mingaliev, M. G.; Kratov, D. V.

    2015-04-01

    During thirteen-year monitoring of the source J0010+1058, four bursts have been observed with an amplitude greater than 1 Jy on a frequency of 21.7 GHz. Using autocorrelation functions, we determined the average characteristic burst time ? acf ? 1.55 ą 0.1 yr (max-min), identical at five frequencies: 2.3, 4.8, 7.7, 11.2, and 21.7 GHz, which provides the linear sizes of the emission region R ? c? acf ? 0.48 pc, and the angular ones—0.28 mas; the brightness temperature is 0.6-6.5 × 1011 K at the frequencies 21.7-2.3 GHz. Moreover, at frequencies higher than 2.3 GHz, there is one more characteristic time ? ? 0.6 yr. We estimated the average lag time of the bursts in relation to a frequency of 21.7 GHz as 150, 210, 270, and 390 days at 11.2, 7.7, 4.8, and 2.3 GHz respectively, and some other source characteristics. Spectra obtained in different periods of source activity confirm the model of the burst development as a result of the evolution of a shock wave propagating along the radio source jet.

  14. Multifractal identifying and characterization of ionospheric propagation modes

    Microsoft Academic Search

    A. Dziri; C. Goutelard; H. VU THIEN; C. Ammar BOUALLEGUE

    2003-01-01

    The dynamic nature of the high latitude ionosphere leads to the formation of small-scale ionospheric irregularities capable of scattering HF radio waves. The large-scale irregularities were identified by many models, however, small-scale irregularities are not well identified and characterized. The aim of this paper is to present a new wavelet-based multifractal approach to identify the ionospheric propagation modes and to

  15. OneWorldRadio

    NSDL National Science Digital Library

    A number of media commentators have been complaining lately about the lack of ideological viewpoints within the vast sea of radio programming, something that has not been lost on the people at OneWorldRadio. Funded by the Department for International Development, OneWorld Radio is part of an international network of over 1200 partner organizations that are utilizing the internet "to promote human rights and sustainable development worldwide." With online audio content from member organizations (such as radio stations) available in French, Spanish, and a number of other languages, visitors can listen or download any one of hundreds of programs archived here. Additionally, visitors can elect to search their impressive archive by language, region, or topic. Persons interested in the use of radio for development and human rights will want to examine the news and events section as it contains important updates about events dealing with conferences on media freedom throughout the world and links to important radio broadcasts of note. Finally, visitors (and all who sign up for the free membership) can elect to receive the helpful OneWorldRadio e-newsletter.

  16. Radio source evolution

    E-print Network

    Perucho, Manel

    2015-01-01

    Baldwin (1982) wrote that "the distribution of sources in the radio luminosity, P, overall physical size, D, diagram" could be considered as "the radio astronomer's H-R diagram". However, unlike the case of stars, not only the intrinsic properties of the jets, but also those of the host galaxy and the intergalactic medium are relevant to explain the evolutionary tracks of radio radio sources. In this contribution I review the current status of our understanding of the evolution of radio sources from a theoretical and numerical perspective, using the P-D diagram as a framework. An excess of compact (linear size < 10 kpc) sources could be explained by low-power jets being decelerated within the host galaxy, as shown by recent numerical simulations. These decelerated jets could also explain the population of the radio sources that have been recently classified as FR0. I will discuss the possible tracks that radio sources may follow within this diagram, and some of the physical processes that can explain the d...

  17. Propagation via lazy clause generation

    Microsoft Academic Search

    Olga Ohrimenko; Peter J. Stuckey; Michael Codish

    2009-01-01

    Finite domain propagation solvers eectively represent the possible values of variables by a set of choices which can be naturally modelled as Boolean variables. In this paper we describe how to mimic a nite domain propagation engine, by mapping propagators into clauses in a SAT solver. This immediately results in strong nogoods for nite domain propagation. But a naive static

  18. Multiple-site investigation of the properties of an HF radio channel and the ionosphere using Digital Radio Mondiale broadcasting

    NASA Astrophysics Data System (ADS)

    Mlynarczyk, Janusz; Koperski, Piotr; Kulak, Andrzej

    2012-01-01

    The Digital Radio Mondiale (DRM), one of the new digital radio broadcasting standards, has been designed to overcome typical short wave radio channel difficulties, such as the multipath propagation and fast temporal changes of the received signal level, both related to the properties of the ionosphere along the path of propagation. In particular, some of the RF carriers used in the applied COFDM transmission technique serve to estimate the current state of the radio channel to enable the proper demodulation of the received signal.We have been detecting such RF carriers on select frequency channels (standard DRM broadcast) using a network of recording stations located in different parts of Poland in order to collect data on the HF radio channel. We have been also evaluating the usefulness of this procedure in providing information on the current state of the ionosphere in the refraction region between the transmitter and receivers. When the DRM system becomes more widespread, this method can supplement data that comes from the ionosondes, since it does not require much financial resources and the receivers can be easily scattered over a large area. This paper presents a set of experimental data and its analysis.

  19. An Introduction to Radio Astronomy

    Microsoft Academic Search

    Bernard F. Burke; Francis Graham-Smith

    1996-01-01

    Radio astronomy uses unique observational techniques and offers the only way to investigate many phenomena in the Universe. This book, by two founders of the field, presents both a clear introduction to radio telescopes and techniques and a broad overview of the radio universe. In the first half of the book, we are shown clearly how radio telescopes work -

  20. Packet Radio for Library Automation.

    ERIC Educational Resources Information Center

    Brownrigg, Edwin B.; And Others

    1984-01-01

    This tutorial on packet radio (communication system using radio and digital packet-switching technology) highlights radio transmission of data, brief history, special considerations in applying packet radio to library online catalogs, technology, defining protocol at physical and network levels, security, geographic coverage, and components. (A…

  1. DROMO Propagator Revisited

    NASA Astrophysics Data System (ADS)

    Urrutxua, H.; Sanjurjo-Rivo, M.; Peláez, J.

    2013-12-01

    In year 2000 a house-made orbital propagator was developed by the SDGUPM (former Grupo de Dinámica de Tethers) based in a set of redundant variables including Euler parameters. This propagator was called DROMO. and it was mainly used in numerical simulations of electrodynamic tethers. It was presented for the first time in the international meeting V Jornadas de Trabajo en Mecánica Celeste, held in Albarracín, Spain, in 2002 (see reference 1). The special perturbation method associated with DROMO can be consulted in the paper.2 In year 1975, Andre Deprit in reference 3 proposes a propagation scheme very similar to the one in which DROMO is based, by using the ideal frame concept of Hansen. The different approaches used in references 3 and 2 gave rise to a small controversy. In this paper we carried out a different deduction of the DROMO propagator, underlining its close relation with the Hansen ideal frame concept, and also the similarities and the differences with the theory carried out by Deprit in 3. Simultaneously we introduce some improvements in the formulation that leads to a more synthetic propagator.

  2. Modeling Radio Networks

    E-print Network

    Lynch, Nancy

    2009-06-04

    We describe a modeling framework and collection of foundational composition results for the study of probabilistic distributed algorithms in synchronous radio networks. Existing results in this setting rely on informal ...

  3. Eratosthenes via Ham Radio

    ERIC Educational Resources Information Center

    Koser, John F.

    1975-01-01

    A secondary geology class used Eratosthenes' method for measuring the circumference of the earth by comparing their measurements of the shadow of a vertical rod to the measurements made by another person contacted by ham radio. (MLH)

  4. A Radio Theatre Laboratory.

    ERIC Educational Resources Information Center

    Potter, Doug

    1982-01-01

    Briefly discusses the potential of radio theater for high school drama. Sketches a modest equipment layout that will provide students with the fundamental combination of hardware and wires to produce audio drama. (PD)

  5. RADIO-SCIENTIFIQUE INTERNATIONALE

    E-print Network

    Goldberg, Bennett

    the Earths ionospherebeginningwiththelaunch of Sputnik, died peacefully in his sleep at his home in Newton at middle and auroral latitudes, first using radio starsandthensatellitebeacons,to define an equatorward

  6. Light-year Scale Radio Cores in Four LINER Galaxies

    Microsoft Academic Search

    Mercedes E. Filho; Peter D. Barthel; Luis C. Ho

    2002-01-01

    The LINER galaxies NGC 2911, NGC 3079, NGC 3998, and NGC 6500 were observed\\u000aat 5 GHz with the European VLBI Network at a resolution of 5 milliarcsecond and\\u000afound to possess flat-spectrum, variable, high-brightness temperature ($T_{\\\\rm\\u000aB} > 10^8$ K) radio cores. These radio characteristics reinforce the view that\\u000athese LINERs host central engines associated with active galactic nuclei.

  7. The effects of radio frequency radiation on the dc SQUID

    SciTech Connect

    Koch, R.H.; Foglietti, V.; Rozen, J.R.; Stawiasz, K.G.; Ketchen, M.B.; Lathrop, D.K.; Sun, J.Z.; Gallagher, W.J. [IBM Thomas J. Watson Research Center, Yorktown Heights, NY (United States)

    1994-12-31

    The effects of radio frequency radiation on the dc SQUID are examined. Simulations show how the shape of the SQUID transfer characteristic is distorted by radio frequency interference (RFI). How this affects three commonly used SQUID modulation methods is discussed, and the results explain why the authors experimentally observe the bias current reversing readout method to be the least susceptible to RFI. The commonly seen increase in the low frequency flux noise power spectrum of dc SQUIDs in unshielded environments is also explained.

  8. Elevated Temperature Crack Propagation

    NASA Technical Reports Server (NTRS)

    Orange, Thomas W.

    1994-01-01

    This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.

  9. Elevated temperature crack propagation

    SciTech Connect

    Orange, T.W.

    1994-02-01

    This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.

  10. Astrometry of southern radio sources

    NASA Technical Reports Server (NTRS)

    White, Graeme L.; Jauncey, David L.; Harvey, Bruce R.; Savage, Ann; Gulkis, Samuel; Preston, Robert A.

    1991-01-01

    An overview is presented of a number of astrometry and astrophysics programs based on radio sources from the Parkes 2.7 GHz catalogs. The programs cover the optical identification and spectroscopy of flat-spectrum Parkes sources and the determination of their milliarcsecond radio structures and positions. Work is also in progress to tie together the radio and Hipparcos positional reference frames. A parallel program of radio and optical astrometry of southern radio stars is also under way.

  11. A Database for Propagation Models and Conversion to C++ Programming Language

    NASA Technical Reports Server (NTRS)

    Kantak, Anil V.; Angkasa, Krisjani; Rucker, James

    1996-01-01

    In the past few years, a computer program was produced to contain propagation models and the necessary prediction methods of most propagation phenomena. The propagation model database described here creates a user friendly environment that makes using the database easy for experienced users and novices alike. The database is designed to pass data through the desired models easily and generate relevant results quickly. The database already contains many of the propagation phenomena models accepted by the propagation community and every year new models are added. The major sources of models included are the NASA Propagation Effects Handbook or the International Radio Consultive Committee (CCIR) or publications such as the Institute for Electrical and Electronic Engineers (IEEE).

  12. Gas and radio galaxies: a story of love and hate

    NASA Astrophysics Data System (ADS)

    Morganti, Rafaella

    2011-07-01

    Gas in radio galaxies is an important component that plays different roles. Gas can feed the AGN and make it active but dense gas can also be an obstacle for radio jets and (temporarily) destroy their flow. The characteristics of the different phases of gas in the circumnuclear regions of active nuclei hold clear signatures of the influences that the black hole activity has on its surroundings. I will review these effects based on some recent results obtained in the study of neutral hydrogen and CO. In particular, I will concentrate on the effects of radio jets in generating the strong negative feedback of the kind invoked in current scenarios for galaxy evolution.

  13. Radio Emission from Supernovae

    Microsoft Academic Search

    J. I. Katz

    2001-01-01

    I consider radio emission from the remarkable supernova (SN) 1998bw. Decay of 56Ni and 56Co produces a gamma-ray flux, whose Compton-scattered electrons naturally explain the observed mildly relativistic expansion of the radio source and its double-peaked history. Such models require a surrounding plasma, perhaps produced by the supernova progenitor, whose interaction with the nonrelativistic debris may account for the observed

  14. Effects on transionospheric HF propagation observed by ISIS at middle and auroral latitudes

    NASA Astrophysics Data System (ADS)

    James, G.

    During the months of May through July 1978, an experiment on transionospheric HF propagation was carried out using a transmitter at Ottawa and the sounder receivers of the ISIS-I and ISIS-II spacecraft. Fixed- and synchronous swept-frequency recordings were made. Over 100 ISIS-II passes were successfully recorded at 9.303 MHz, the highest fixed frequency of receiver operation. Several tens of these passes have been analyzed in an attempt to establish the salient characteristics of the propagation. From these characteristics, the goal is to improve understanding of the processes experienced by waves passing through the ionosphere, e.g., focusing or scattering. This research supports planning for coordinated ground-space radio experiments in the upcoming Enhanced Polar Outflow Probe satellite mission, to be flown for the Canadian Space Agency. Swept-frequency ionograms interleaved with the aforementioned fixed-frequency measurements allowed two-dimensional density distributions to be modeled in altitude and latitude. Computer code was developed for three-dimensional ray tracing. A Newton's-iteration algorithm was used for efficient searches for solution rays that connect the transmitter with the position of the satellite at any time along its path. The latitudinal extent of the zone irradiated at ISIS-II altitude thus computed is approximately as observed, albeit sensitively dependent upon north-south density gradients. Within this "iris" of accessibility, the peak intensity of waves recorded at the spacecraft is within 10 dB of that found with a link calculation based on ray optics. Density inhomogeneities influence the transmitted O and X mode waves, in various ways. Poleward rays result in dispersed pulses, indicating quasi-perpendicular propagation that is forward scattered. Toward the equator, propagation directions come to within about 10 of the magnetic-field axis. Equatorward pulses are comparatively sharp and occasionally exhibit periodic fades with beat frequencies between about 1 and 4 Hz. Features of the fades indicate that focusing of rays is a better explanation for the fades than diffraction.

  15. Dynamic crack propagation

    NASA Astrophysics Data System (ADS)

    Bolotin, V. V.

    1992-02-01

    The unified approach to the problems of the stability and quasi-static growth of cracks in solid bodies under cyclic and slowly varying loading, developed in earlier studies (Bolotin, 1983, 1987, 1985), is extended to the case of dynamic crack propagation. A system of equations is obtained which makes it possible to describe the dynamic behavior of bodies with cracks for fixed crack parameters, dynamic crack propagation, and transition of a body with cracks from one state to another (i.e., crack initiation and closure). The use of the method is illustrated by examples.

  16. Vegetative Propagation Project

    NSDL National Science Digital Library

    Nancy Iversen (Cooperstown High School REV)

    1995-06-30

    Students select a healthy plant to be propagated, do some reading about that plant, and determine what type of vegetative reproduction is suitable for that plant. Students vegetatively reproduce plant, keeping a journal of observations of the plant and the process. The journal entries should include a description of the procedure used to propagate, the amount of water given the plant, the date and numbers of roots that appear, when plant was transferred to soil, a description of soil and pot used and sketches drawn 'every so often' --the works!

  17. Turbofan Duct Propagation Model

    NASA Technical Reports Server (NTRS)

    Lan, Justin H.; Posey, Joe W. (Technical Monitor)

    2001-01-01

    The CDUCT code utilizes a parabolic approximation to the convected Helmholtz equation in order to efficiently model acoustic propagation in acoustically treated, complex shaped ducts. The parabolic approximation solves one-way wave propagation with a marching method which neglects backwards reflected waves. The derivation of the parabolic approximation is presented. Several code validation cases are given. An acoustic lining design process for an example aft fan duct is discussed. It is noted that the method can efficiently model realistic three-dimension effects, acoustic lining, and flow within the computational capabilities of a typical computer workstation.

  18. Modulation of Radio Frequency Signals by Nonlinearly Generated Acoustic Fields

    NASA Astrophysics Data System (ADS)

    Johnson, Spencer Joseph

    Acousto-electromagnetic scattering is a process in which an acoustic excitation is utilized to induce modulation on an electromagnetic (EM) wave. This phenomenon can be exploited in remote sensing and detection schemes whereby target objects are mechanically excited by high powered acoustic waves resulting in unique object characterizations when interrogated with EM signals. Implementation of acousto-EM sensing schemes, however, are limited by a lack of fundamental understanding of the nonlinear interaction between acoustic and EM waves and inefficient simulation methods in the determination of the radiation patterns of higher order scattered acoustic fields. To address the insufficient simulation issue, a computationally efficient mathematical model describing higher order scattered sound fields, particularly of third-order in which a 40x increase in computation speed is achieved, is derived using a multi-Gaussian beam (MGB) expansion that expresses the sound field of any arbitrary axially symmetric beam as a series of Gaussian base functions. The third-order intermodulation (IM3) frequency components are produced by considering the cascaded nonlinear second-order effects when analyzing the interaction between the first- and second-order frequency components during the nonlinear scattering of sound by sound from two noncollinear ultrasonic baffled piston sources. The theory is extended to the modeling of the sound beams generated by parametric transducer arrays, showing that the MGB model can be efficiently used to calculate both the second- and third-order sound fields of the array. Additionally, a near-to-far-field (NTFF) transformation method is developed to model the far-field characteristics of scattered sound fields, extending Kirchhoff's theorem, typically applied to EM waves, determining the far-field patterns of an acoustic source from amplitude and phase measurements made in the near-field by including the higher order sound fields generated by the nonlinear scattering of sound by sound as the acoustic waves propagate into the far-field. With improvements in the sensitivity of radio frequency (RF) receivers, spectral content previously below the measurable noise floor, such as the nonlinear content produced by acousto-EM scattering, can now be examined and analyzed. Through the use of a high dynamic range nonlinear measurement system based on analog cancellation, the ability to experimentally investigate the effects of nonlinear interaction between acoustic and EM waves previously unattainable is enabled. To further the understanding of the effects of acousto-EM scattering and verify experimental results, a mathematical description of the periodic change in the medium characteristics due to the propagation of a high powered acoustic wave through a medium that modulates an EM signal proportional to the acoustic frequency is developed.

  19. Constraints on cosmic ray propagation in the galaxy

    NASA Technical Reports Server (NTRS)

    Cordes, James M.

    1992-01-01

    The goal was to derive a more detailed picture of magnetohydrodynamic turbulence in the interstellar medium and its effects on cosmic ray propagation. To do so, radio astronomical observations (scattering and Faraday rotation) were combined with knowledge of solar system spacecraft observations of MHD turbulence, simulations of wave propagation, and modeling of the galactic distribution to improve the knowledge. A more sophisticated model was developed for the galactic distribution of electron density turbulence. Faraday rotation measure data was analyzed to constrain magnetic field fluctuations in the ISM. VLBI observations were acquired of compact sources behind the supernova remnant CTA1. Simple calculations were made about the energies of the turbulence assuming a direct link between electron density and magnetic field variations. A simulation is outlined of cosmic ray propagation through the galaxy using the above results.

  20. Characterization of HF Propagation for Digital Audio Broadcasting

    NASA Technical Reports Server (NTRS)

    Vaisnys, Arvydas

    1997-01-01

    The purpose of this presentation is to give a brief overview of some propagation measurements in the Short Wave (3-30 MHz) bands, made in support of a digital audio transmission system design for the Voice of America. This task is a follow on to the Digital Broadcast Satellite Radio task, during which several mitigation techniques would be applicable to digital audio in the Short Wave bands as well, in spite of the differences in propagation impairments in these two bands. Two series of propagation measurements were made to quantify the range of impairments that could be expected. An assessment of the performance of a prototype version of the receiver was also made.