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Sample records for radio propagation characteristics

  1. The seasonal variation of the D region as inferred from propagation characteristics of LF radio waves

    NASA Technical Reports Server (NTRS)

    Ishimine, T.; Ishii, T.; Echizenya, Y.

    1985-01-01

    The propagation data of JG2AS 40 kHz (Japanese Standard Frequency), Loran C 100 kHz radio waves, and meteorological data were analyzed to study the association of propagation characteristics of LF radio waves with the atmospheric circulation in the mesosphere. The monthly averaged electric fields were depicted on the complex plane for typical summer and winter months, June and November. The locus traced out by the electric field vector during daytime is nearly circular. This is because during daytime the amplitude of the sky wave remains nearly constant while its phase changes in accord with the height change of the reflection layer, and thus the electric field vector traces out a circular locus with its center at the tip of the supposed ground wave vector. The locus has a loop during the sunrise or sunset period, which seems to arise from interference of two waves reflected by two different layers. In June the amplitude of the sky wave decreases rapidly before the dawn or increases after the dusk. In November such rapid change is not observed. During nighttime, the sky wave phase changes in such a way as to suggest that the reflection height moves upwards with time before midnight or lowers after midnight in November. In June it changes similarly before midnight, but after midnight it varies erratically. These characteristics are closely related to the structure of the D region, which is clearly shown by simulating the loci traced out by electric fields.

  2. Radio wave propagation and acoustic sounding

    NASA Astrophysics Data System (ADS)

    Singal, S. P.

    Radio wave propagation of the decimetric and centimetric waves depends to a large extent on the boundary layer meteorological conditions which give rise to severe fadings, very often due to multipath propagation. Sodar is one of the inexpensive remote sensing techniques which can be employed to probe the boundary layer structure. In the paper a historical perspective has been given of the simultaneously conducted studies on radio waves and sodar at various places. The radio meteorological information needed for propagation studies has been clearly spelt out and conditions of a ray path especially in the presence of a ducting layer have been defined as giving rise to fading or signal enhancement conditions. Finally the potential of the sodar studies to obtain information about the boundary layer phenomena has been stressed, clearly spelling out the use of acoustic sounding in radio wave propagation studies.

  3. Antenna Construction and Propagation of Radio Waves.

    ERIC Educational Resources Information Center

    Marine Corps Inst., Washington, DC.

    Developed as part of the Marine Corps Institute (MCI) correspondence training program, this course on antenna construction and propagation of radio waves is designed to provide communicators with instructions in the selection and/or construction of the proper antenna(s) for use with current field radio equipment. Introductory materials include…

  4. Probing geomagnetic storm-driven magnetosphere-ionosphere dynamics in D-region via propagation characteristics of very low frequency radio signals

    NASA Astrophysics Data System (ADS)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip K.; Ogunmodimu, Olugbenga

    2016-07-01

    The amplitude and phase of VLF/LF radio signals are sensitive to changes in electrical conductivity of the lower ionosphere which imprints its signature on the Earth-ionosphere waveguide. This characteristic makes it useful in studying sudden ionospheric disturbances, especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbance and storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region of the ionosphere. In this paper, using the data of three propagation paths at mid-latitudes (40-54°), we analyse the trend in variation of aspects of VLF diurnal signal under varying solar and geomagnetic space environmental conditions in order to identify possible geomagnetic footprints on the D region characteristics. We found that the trend of variations generally reflected the prevailing space weather conditions in various time scales. In particular, the 'dipping' of mid-day signal amplitude peak (MDP) occurs after significant geomagnetic perturbed or storm conditions in the time scale of 1-2 days. The mean signal amplitude before sunrise (MBSR) and mean signal amplitude after sunset (MASS) also exhibit storm-induced dipping, but they appear to be influenced by event's exact occurrence time and the highly variable conditions of dusk-to-dawn ionosphere. We also observed few cases of the signals rise (e.g., MDP, MBSR or MASS) following a significant geomagnetic event. This effect may be related to storms associated phenomena or effects arising from sources other than solar origin. The magnitude of induced dipping (or rise) significantly depends on the intensity and duration of event(s), as well as the propagation path of the signal. The post-storm day signal (following a main event, with lesser or significantly reduced geomagnetic activity) exhibited a tendency of recovery to pre-storm day level. In the

  5. Effects of D region ionization on radio wave propagation

    NASA Technical Reports Server (NTRS)

    Larsen, T. R.

    1979-01-01

    The effects of anomalous D region ionization upon radio wave propagation are described for the main types of disturbances: sudden ionospheric disturbances, relativistic electron events, magnetic storms, auroral disturbances, polar cap events, and stratospheric warmings. Examples of radio wave characteristics for such conditions are given for the frequencies between the extremely low (3-3000 Hz) and high (3-30 MHz) frequency domains. Statistics on the disturbance effects and radio wave data are given in order to contribute towards the evaluation of possibilities for predicting the radio effects.

  6. 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.

  7. 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.

  8. Subionospheric VLF/LF radio waves propagation characteristics before, during and after the Sofia, Bulgaria Mw=5.6 earthquake occurred on 22 May 2012

    NASA Astrophysics Data System (ADS)

    Moldovan, Iren Adelina; Emilian Toader, Victorin; Nenovski, Petko; Biagi, Pier Francesco; Maggipinto, Tommaso; Septimiu Moldovan, Adrian; Ionescu, Constantin

    2013-04-01

    In 2009, INFREP, a network of VLF (20-60 kHz) and LF (150-300 kHz) radio receivers, was put into operation in Europe having as principal goal, the study of disturbances produced by the earthquakes on the propagation properties of these signals. On May 22nd, 2012 an earthquake with Mw=567 occurred in Bulgaria, near Sofia, inside the "sensitive" area of the INFREP VLF/LF electromagnetic network. The data collected on different frequencies, during April-May 2012 were studied using different methods of analysis: daily correlation methods, spectral approaches and terminator time techniques, in order to find out possible connections between the seismic activity and the subionospheric propagation properties of radio waves. The studies were performed with the help of a specially designed LabVIEW application, which accesses the VLF/LF receiver through internet. This program opens the receiver's web-page and automatically retrieves the list of data files to synchronize the user-side data with the receiver's data. Missing zipped files are also automatically downloaded. The application performs primary, statistical correlation and spectral analysis, appends daily files into monthly and annual files and performs 3D colour-coded maps with graphic representations of VLF and LF signals' intensities versus the minute-of-the-day and the day-of-the-month, facilitating a near real-time observation of VLF and LF electromagnetic waves' propagation. Another feature of the software is the correlation of the daily recorded files for the studied frequencies by overlaying the 24 hours radio activity and taking into account the sunrise and sunset. Data are individually processed (spectral power, correlations, differentiation, filtered using bandpass, lowpass, highpass). JTFA spectrograms (Cone-Shaped Distribution CSD, Gabor, Wavelet, short-time Fourier transform STFT, Wigner-Ville Distribution WVD, Choi-Williams Distribution CWD) are used, too.

  9. Radio-wave propagation for space communications systems

    NASA Astrophysics Data System (ADS)

    Ippolito, L. J.

    1981-02-01

    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.

  10. 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.

  11. Multipath propagation of low-frequency radio waves inferred from high-resolution array analysis

    NASA Astrophysics Data System (ADS)

    Füllekrug, Martin; Smith, Nathan; Mezentsev, Andrew; Watson, Robert; Astin, Ivan; Gaffet, Stéphane; Evans, Adrian; Rycroft, Michael

    2015-11-01

    The low-frequency radio sky shows the locations of electromagnetic radio sources with a characteristic dilution of precision. Here we report a thorough high-resolution analysis of radio waves from low-frequency (˜20-150 kHz) radio communication transmitters which are recorded with a small aperture array of radio receivers during the day. It is found that the observed dilution of precision results from the array geometry of the radio receivers, a birefringent wave propagation, and the correlated multipath propagation of low-frequency radio waves. The influence of the array geometry on the dilution of precision is reduced by taking into account the impulse response of the array. This procedure reveals for the very first time the splitting of one single radio source into two distinct source locations separated by ˜0.2°-1.9° which result from a birefringent wave propagation. The two locations are yet more clearly identified by using the polarity of the modulated wave number vectors of the radio waves. This polarity is also used to quantify the dilution of precision arising from correlated multipath propagation which is discriminated against wave number fluctuations arising from the timing accuracy of the radio receivers. It is found that ˜69% of the wave number variability is of natural origin and ˜31% originates from the timing accuracy of the receivers. The wave number variability from correlated multipath propagation results in a standard deviation ˜2-8% relative to the source location. This compact measurement of correlated multipath propagation is used to characterize the uncertainty of source locations in the radio sky. The identification of correlated multipath propagation strongly suggests the existence of very fast processes acting on time scales <1 ms in the D region ionosphere with physically meaningful effects on low-frequency radio wave propagation. This important result has implications for practical applications in that the observed multipath

  12. Relationship Between the Radio Bursts from the Sun and Ionospheric Propagation

    NASA Astrophysics Data System (ADS)

    West, Mary Lou; Frissell, N.; Papalos, M.

    2006-12-01

    We are monitoring the sun’s radio activity at 20.1 MHz with a Radio Jove rig, and have begun to monitor the Earth’s ionosphere for HF radio propagation using the worldwide network of beacons set up by the Northern California DX Foundation. These 18 beacons transmit at 14.1, 18.11, 21.15, 24.93, and 28.2 MHz on a 3 minute cadence and allow ham radio operators to judge the radio propagation characteristics to distant lands easily. Although the solar activity cycle is now near its bottom, there are occasional outbursts, some spectacular. August 29, 2006, was such a day, prompting the Radio Jove community to post ten times the usual number of reports to the archive at Goddard Space Flight Center. The next day the Earth’s ionosphere suddenly blossomed with HF openings without any X-ray flares reported. The delay time of 26 hours from the most energetic radio event indicated a velocity of 1600 km/s, normal for a coronal mass ejection. Several other events have also shown delays of about 24 hours from the radio sun to the ionosphere, and are especially noticeable at the higher frequency bands and on the events list of the Space Environment Center of NOAA. The 20.1 MHz monitors may serve as a method to predict radio propagation properties of the ionosphere more quickly than previous methods.

  13. 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.

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

    SciTech Connect

    Han, G.R.; Zhang, W.M.; Zhang, Y.P.

    2009-07-01

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

  15. Plasma and radio waves from Neptune: Source mechanisms and propagation

    NASA Technical Reports Server (NTRS)

    Wong, H. K.

    1994-01-01

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

  16. Radio Wave Propagation Handbook for Communication on and Around Mars

    NASA Technical Reports Server (NTRS)

    Ho, Christian; Golshan, Nasser; Kliore, Arvydas

    2002-01-01

    This handbook examines the effects of the Martian environment on radio wave propagation on Mars and in the space near the planet. The environmental effects include these from the Martian atmosphere, ionosphere, global dust storms, aerosols, clouds, and geomorphologic features. Relevant Martian environmental parameters were extracted from the measurements of Mars missions during the past 30 years, especially from Mars Pathfinder and Mars Global Surveyor. The results derived from measurements and analyses have been reviewed through an extensive literature search. The updated parameters have been theoretically analyzed to study their effects on radio propagation. This handbook also provides basic information about the entire telecommunications environment on and around Mars for propagation researchers, system engineers, and link analysts. Based on these original analyses, some important recommendations have been made, including the use of the Martian ionosphere as a reflector for Mars global or trans-horizon communication between future Martian colonies, reducing dust storm scattering effects, etc. These results have extended our wave propagation knowledge to a planet other than Earth; and the tables, models, and graphics included in this handbook will benefit telecommunication system engineers and scientific researchers.

  17. Radio propagation through solar and other extraterrestrial ionized media

    NASA Technical Reports Server (NTRS)

    Smith, E. K.; Edelson, R. E.

    1980-01-01

    The present S- and X-band communications needs in deep space are addressed to illustrate the aspects which are affected by propagation through extraterrestrial plasmas. The magnitude, critical threshold, and frequency dependence of some eight propagation effects for an S-band propagation path passing within 4 solar radii of the Sun are described. The theory and observation of propagation in extraterrestrial plasmas are discussed and the various plasma states along a near solar propagation path are illustrated. Classical magnetoionic theory (cold anisotropic plasma) is examined for its applicability to the path in question. The characteristics of the plasma states found along the path are summarized and the errors in some of the standard approximations are indicated. Models of extraterrestrial plasmas are included. Modeling the electron density in the solar corona and solar wind, is emphasized but some cursory information on the terrestrial planets plus Jupiters is included.

  18. The prediction of radio-path characteristics

    NASA Astrophysics Data System (ADS)

    Gitina, G. M.; Kalinin, Iu. K.

    The paper examines algorithms for the long-term prediction of radio-path characteristics in the ionosphere, the main characteristic being the MUF at a given distance. The proposed approach is based on long-term memories called DATA BANKS. Attention is given to the characteritics of the various banks, including the BANK OF CITIES, the BANK OF RADIO PATHS, the REFERENCE DATA BANK, and the OUTPUT DATA BANK.

  19. 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.

  20. Annual report 1992/93, FOA 38. Radio systems and wave propagation

    NASA Astrophysics Data System (ADS)

    Mildh, I. M.

    1994-01-01

    The main objective of the division of Radio Systems and Wave Propagation is to carry out research and development in the field of secure and robust radio communications for Sweden's national defense. This is the Annual Report for fiscal year 1992/93 of the Division of Radio Systems and Wave Propagation. The division is responsible for research and development of secure radio communication for information transmission. We are also responsible for wave propagation research within a frequency range from LF to SHF. We carry out applied research in fields like antijamming systems, modulation, error correcting codes, wave propagation and digital signal processing. The wave propagation research is carried out by basic research so the demands from new techniques and new radio systems for accurate propagation models can be achieved.

  1. Discrete Method of Images for 3D Radio Propagation Modeling

    NASA Astrophysics Data System (ADS)

    Novak, Roman

    2016-09-01

    Discretization by rasterization is introduced into the method of images (MI) in the context of 3D deterministic radio propagation modeling as a way to exploit spatial coherence of electromagnetic propagation for fine-grained parallelism. Traditional algebraic treatment of bounding regions and surfaces is replaced by computer graphics rendering of 3D reflections and double refractions while building the image tree. The visibility of reception points and surfaces is also resolved by shader programs. The proposed rasterization is shown to be of comparable run time to that of the fundamentally parallel shooting and bouncing rays. The rasterization does not affect the signal evaluation backtracking step, thus preserving its advantage over the brute force ray-tracing methods in terms of accuracy. Moreover, the rendering resolution may be scaled back for a given level of scenario detail with only marginal impact on the image tree size. This allows selection of scene optimized execution parameters for faster execution, giving the method a competitive edge. The proposed variant of MI can be run on any GPU that supports real-time 3D graphics.

  2. 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.

  3. Propagation characteristics of superconducting microstrip lines

    SciTech Connect

    Mao, S.G.; Ke, J.Y.; Chen, C.H.

    1996-01-01

    The modified spectral-domain approach is applied to study the propagation characteristics of high temperature superconducting microstrip lines whose signal strip and ground plane are of arbitrary thickness. In this study, numerical results for effective dielectric constant, attenuation constant, and strip current distribution are presented to discuss the effects due to frequency, temperature, strip thickness, and substrate loss tangent. In particular, the conductor and dielectric attenuation constants of superconducting microstrip line are depicted separately to discuss the mechanism of the line losses. A comparison with published theoretical and experimental results is also included to check the accuracy of the new approach`s results.

  4. Propagation from ground transmitters to the ePOP/Radio Receiver Instrument

    NASA Astrophysics Data System (ADS)

    James, Gordon

    2016-07-01

    Since its launch in 2013 as part of the Enhanced Polar Outflow Probe (ePOP) payload on the Canadian CASSIOPE small satellite, the Radio Receiver Instrument (RRI) has been successfully commanded to participate in a number of transionospheric collaborative electromagnetic-wave experiments. The RRI is a digital receiver connected to two orthogonal 6-m dipoles and operating in the frequency range from 10 Hz to 18 MHz. The elliptical (325 km - 1500 km) high-inclination (81°) orbit has presented a variety of experimental opportunities in plasma-wave studies. These have involved the reception of EM signals from coordinated ground transmitters in the very-low-frequency to high-frequency range, such as VLF communication transmitters, HF ionospheric heaters, HF over-the-horizon radars, HF coherent-backscatter radars, ionosondes, and amateur radio sources. At the front of this list are powerful sources presenting the RRI with high signal-to-noise transmissions; in these cases, the characteristics of transionospheric propagation observed by the RRI in the ionosphere may be used to test interpretive assumptions about such propagation that hitherto may have been observed only when reflected or scattered back to the ground. In some cases, the RRI measurements are part of studies exploiting simultaneous coordinated measurements by instruments on the ground.

  5. Plasma and radio waves from Neptune: Source mechamisms and propagation

    NASA Technical Reports Server (NTRS)

    Menietti, J. Douglas

    1994-01-01

    The purpose of this project was to conduct a comprehensive investigation of the radio wave emission observed by the planetary radio astronomy (PRA) instrument on board Voyager 2 as it flew by Neptune. The study has included data analysis, theoretical and numerical calculations, and ray tracing to determine the possible source mechanisms and locations of the radiation, including the narrowband bursty and smooth components of the Neptune radio emission.

  6. 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.

  7. Radio jet propagation and wide-angle tailed radio sources in merging galaxy cluster environments

    NASA Technical Reports Server (NTRS)

    Loken, Chris; Roettiger, Kurt; Burns, Jack O.; Norman, Michael

    1995-01-01

    The intracluster medium (ICM) within merging clusters of galaxies is likely to be in a violent or turbulent dynamical state which may have a significant effect on the evolution of cluster radio sources. We present results from a recent gas + N-body simulation of a cluster merger, suggesting that mergers can result in long-lived, supersonic bulk flows, as well as shocks, within a few hundred kiloparsecs of the core of the dominant cluster. These results have motivated our new two-dimensional and three-dimensional simulations of jet propagation in such environments. The first set of simulations models the ISM/ICM transition as a contact discontinuity with a strong velocity shear. A supersonic (M(sub j) = 6) jet crossing this discontinuity into an ICM with a transverse, supersonic wind bends continuously, becomes 'naked' on the upwind side, and forms a distended cocoon on the downwind side. In the case of a mildly supersonic jet (M(sub j) = 3), however, a shock is driven into the ISM and ISM material is pulled along with the jet into the ICM. Instabilities excited at the ISM/ICM interface result in the jet repeatedly pinching off and reestablishing itself in a series of 'disconnection events.' The second set of simulations deals with a jet encountering a shock in the merging cluster environment. A series of relatively high-resolution two-dimensional calculations is used to confirm earlier analysis predicting that the jet will not disrupt when the jet Mach number is greater than the shock Mach number. A jet which survives the encounter with the shock will decrease in radius and disrupt shortly thereafter as a result of the growth of Kelvin-Helmholtz instabilities. We also find, in disagreement with predictions, that the jet flaring angle decreases with increasing jet density. Finally, a three-dimensional simulation of a jet crossing an oblique shock gives rise to a morphology which resembles a wide-angle tailed radio source with the jet flaring at the shock and

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

    NASA Astrophysics Data System (ADS)

    Li, Ya-Qing; Wu, Zhen-Sen

    2012-05-01

    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 radius, the spreading angle, and the average intensity. The variance of the angle-of-arrival fluctuation and the wander effect of the GSM beam in the turbulence are calculated numerically. The influences of the coherence degree, the propagation distance, the propagation height, and the waist radius on the propagation characteristics of the partially coherent beams are discussed and compared with those of the fully coherent Gaussian beams.

  9. Observation of quasi-periodic solar radio bursts associated with propagating fast-mode waves

    NASA Astrophysics Data System (ADS)

    Goddard, C. R.; Nisticò, G.; Nakariakov, V. M.; Zimovets, I. V.; White, S. M.

    2016-10-01

    Aims: Radio emission observations from the Learmonth and Bruny Island radio spectrographs are analysed to determine the nature of a train of discrete, periodic radio "sparks" (finite-bandwidth, short-duration isolated radio features) which precede a type II burst. We analyse extreme ultraviolet (EUV) imaging from SDO/AIA at multiple wavelengths and identify a series of quasi-periodic rapidly-propagating enhancements, which we interpret as a fast wave train, and link these to the detected radio features. Methods: The speeds and positions of the periodic rapidly propagating fast waves and the coronal mass ejection (CME) were recorded using running-difference images and time-distance analysis. From the frequency of the radio sparks the local electron density at the emission location was estimated for each. Using an empirical model for the scaling of density in the corona, the calculated electron density was used to obtain the height above the surface at which the emission occurs, and the propagation velocity of the emission location. Results: The period of the radio sparks, δtr = 1.78 ± 0.04 min, matches the period of the fast wave train observed at 171 Å, δtEUV = 1.7 ± 0.2 min. The inferred speed of the emission location of the radio sparks, 630 km s-1, is comparable to the measured speed of the CME leading edge, 500 km s-1, and the speeds derived from the drifting of the type II lanes. The calculated height of the radio emission (obtained from the density) matches the observed location of the CME leading edge. From the above evidence we propose that the radio sparks are caused by the quasi-periodic fast waves, and the emission is generated as they catch up and interact with the leading edge of the CME. The movie associated to Fig. 2 is available at http://www.aanda.org

  10. Radio wave propagation at frequencies exceeding MUF-F2 in the short wave band

    NASA Technical Reports Server (NTRS)

    Ashkaliyev, Y. F.; Bocharov, V. I.

    1972-01-01

    The results of measurements of field strength and signal/noise ratio on experimental ionospheric-scattering short wave radio links are presented. It is shown that the seasonal and diurnal variations of field strength are determined by features of solar and meteoric activity. The role of the sporadic E-layer in propagation of short radio waves at frequencies exceeding MUF-F2 is noted.

  11. The influence of polarization on millimeter wave propagation through rain. [radio signals

    NASA Technical Reports Server (NTRS)

    Bostian, C. W.; Stutzman, W. L.; Wiley, P. H.; Marshall, R. E.

    1973-01-01

    The measurement and analysis of the depolarization and attenuation that occur when millimeter wave radio signals propagate through rain are described. Progress was made in three major areas: the processing of recorded 1972 data, acquisition and processing of a large amount of 1973 data, and the development of a new theoretical model to predict rain cross polarization and attenuation. Each of these topics is described in detail along with radio frequency system design for cross polarization measurements.

  12. A computer simulation study of type III radio burst propagation through the solar corona

    NASA Astrophysics Data System (ADS)

    Itkina, M. A.; Levin, B. N.

    1992-01-01

    Type III solar radio burst propagation through large-scale coronal structure is numerically simulated. It is shown that radio wave refraction in an overdense streamer results in an increase of the apparent radial distance of the type III fundamental source and produces a broadening of the radiation polar diagram in agreement with the observations. It is also verified that the well-known fine frequency structure of type IIIb emission can be due to the fibrous character of the streamer.

  13. Propagation Characteristics in an Underground Shopping Area for 5GHz-band Wireless Access Systems

    NASA Astrophysics Data System (ADS)

    Itokawa, Kiyohiko; Kita, Naoki; Sato, Akio; Matsue, Hideaki; Mori, Daisuke; Watanabe, Hironobu

    5-GHz band wireless access systems, such as the RLAN (Radio Local Area Network) system of IEEE802.11a, HiperLAN/2, HiSWANa and AWA, are developed and provide transmission rates over 20 Mbps for indoor use. Those 5-GHz access systems are expected to extend service areas from the office to the so-called “hot-spot" in public areas. Underground shopping malls are one of the anticipated service areas for such a nomadic wireless access service. Broadband propagation characteristics are required for radio zone design in an underground mall environment despite previous results obtained by narrow band measurements. This paper presents results of an experimental study on the propagation characteristics for broadband wireless access systems in an underground mall environment. First, broadband propagation path loss is measured and formulated considering human body shadowing. A ray trace simulation is used to clarify the basic propagation mechanism in such a closed environment. Next, a distance dependency of the delay spread during a crowded time period, rush hour, is found to be at most 65 nsec, which is under the permitted maximum value of the present 5-GHz systems. Finally, above propagation characteristics support the result of transmission test carried out by using AWA equipment.

  14. Morphology of solar wind fluctuations and structure in the vicinity of the Sun from radio propagation measurements

    NASA Technical Reports Server (NTRS)

    Woo, R.

    1995-01-01

    Radio propagation measurements represent a powerful means for remote probing of electron density and solar wind speed in the acceleration region of the solar wind not yet explored by in situ measurements. Recent investigations based on radio propagation measurements have led to considerable progress in our knowledge of the general morphology of solar wind fluctuations and structure, especially in terms of their relationship to solar wind properties that have been observed directly by fields and particles measurements, and to coronal features observed in white-light measurements. The purpose of this paper is to present an overview of the latest results on quasi-stationary structure covering the large scale variation of solar wind speed over the streamer belt and coronal hole regions, coronal streamers (source of slow solar wind) and their associated small-scale electron density structure, plumes, density and fractional or relative density fluctuations, and the spectral characteristics of the electron density fluctuations. The radio propagation measurements not only reveal new information on the structure near the Sun, but also show that the structure appears to undergo substantial evolution on its way to 0.3 AU, the closest radial distance for which direct in situ spacecraft measurements are available.

  15. Preliminary Study on Active Modulation of Polar Mesosphere Summer Echoes with the Radio Propagation in Layered Space Dusty Plasma

    NASA Astrophysics Data System (ADS)

    Zhou, Shengguo; Li, Hailong; Fu, Luyao; Wang, Maoyan

    2016-06-01

    Radar echoes intensity of polar mesosphere summer echoes (PMSE) is greatly affected by the temperature of dusty plasma and the frequency of electromagnetic wave about the radar. In this paper, a new method is developed to explain the active experiment results of PMSE. The theory of wave propagation in a layered media is used to study the propagation characteristics of an electromagnetic wave at different electron temperatures. The simulation results show that the variation tendency of the reflected power fraction almost agrees with the results observed by radar in the European Incoherent Scatter Scientific Association (EISCAT). The radar echoes intensity of PMSE greatly decreases with the increase of the radio frequency and the enhancement of the electron temperature. supported by National Natural Science Foundation of China (Nos. 41104097 and 41304119) and by the National Key Laboratory of Electromagnetic Environment, China Research Institute of Radiowave Propagation (CRIRP)

  16. 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.

  17. 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.

  18. Radio wave propagation experiments to probe the ionosphere

    NASA Technical Reports Server (NTRS)

    Schmid, P. E.

    1972-01-01

    Ionospheric bias corrections associated with radio tracking of spacecraft depend on the following measuring techniques for integrated electron content: (1) Faraday rotation measurements from an earth synchronous satellite; (2) ranging measurements at two frequencies; and (3) group and phase velocity measurements obtained from tracking data. The extraction of the integrated electron content directly from tracking data is achieved by comparison of range-rate measurements based on Doppler shift with differentiated range measurements based on tone delay. This method is most desirable because the measured corrections pertain directly to the spacecraft whose orbit is being determined and can be used in near earth as well as deep space tracking data.

  19. Propagation of radio frequency waves through density filaments

    NASA Astrophysics Data System (ADS)

    Ram, Abhay K.; Hizanidis, Kyriakos

    2015-12-01

    In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments are routinely observed in the scrape-off layer. In this paper we develop an analytical formalism for the scattering of radio frequency waves by filaments which are cylindrical with their major axis aligned along the toroidal magnetic field lines. Since the magnitude of the ratio of the density inside the filaments to the background density is generally of order 1, the geometric optics approximation cannot be used to describe the scattering. A full-wave model is formulated which assumes that the plasma is cold and that the plasma in the cylindrical filament has uniform density. The background plasma, in which the filament is present, is also assumed to be cold and uniform. The theoretical framework applies to the scattering of any plasma wave.

  20. Propagation of radio frequency waves through density filaments

    SciTech Connect

    Ram, Abhay K.; Hizanidis, Kyriakos

    2015-12-10

    In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments are routinely observed in the scrape-off layer. In this paper we develop an analytical formalism for the scattering of radio frequency waves by filaments which are cylindrical with their major axis aligned along the toroidal magnetic field lines. Since the magnitude of the ratio of the density inside the filaments to the background density is generally of order 1, the geometric optics approximation cannot be used to describe the scattering. A full-wave model is formulated which assumes that the plasma is cold and that the plasma in the cylindrical filament has uniform density. The background plasma, in which the filament is present, is also assumed to be cold and uniform. The theoretical framework applies to the scattering of any plasma wave.

  1. 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.

  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; Cai, D Michael

    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. Solar Type III Radio Bursts: Directivity Characteristics

    NASA Astrophysics Data System (ADS)

    Thejappa, G.; MacDowall, R. J.

    2015-09-01

    Type III radio bursts are a group of fast drifting radio emissions associated with solar flares. These radio emissions are believed to be excited at the fundamental and second harmonic of the electron plasma frequency, fpe by the electron beam excited Langmuir waves through a mechanism called the plasma mechanism. This mechanism attributes the dipole and quadrupole beam patterns for the fundamental and harmonic emissions. To verify these predictions, we analyze the simultaneous observations of type III radio bursts by the STEREO A, B and Wind spacecraft located at different vantage points in the ecliptic plane, and determine their normalized peak intensities (directivity factors) at each spacecraft using their time profiles. Assuming that the sources of these bursts are located on the Parker spiral magnetic field lines emerging from the associated active regions, we estimate the angles between the magnetic field directions and the lines connecting the sources to the spacecraft (viewing angles). Based on the plots of the directivity factors versus the viewing angles, one can divide these bursts into (1) intense bursts emitted into a narrow cone centered around the tangent to the magnetic field, and (2) relatively weaker bursts emitting into a wider cone centered around the tangent to the magnetic field. We compute the distributions of ray trajectories emitted by an isotropic point source and show that the refraction focuses the fundamental and harmonic emissions into narrow and wider cones, respectively. The comparison of these distributions with observations indicates that the intense bursts visible to a narrow range of angles around the tangent to the magnetic field probably correspond to the fundamental, and the relatively weaker bursts visible to a wide range of angles probably are the harmonic emissions.

  5. Radio Wave Propagation for Communication on and around Mars. Part 1; Highlights: Propagation Through Mars Environment

    NASA Technical Reports Server (NTRS)

    Ho, Christian; Golshan, Nasser

    1999-01-01

    We recommend to use the dayside Martian ionosphere as a reflector for global communication, because the dayside ionosphere has stable density peak and usable critic frequency. This is very crucial for the future Mars ground to around communication. The dayside ionosphere has been well modeled as a Chapman layer. We suggest to perform the Martian nightside ionospheric modeling study. Because the nightside ionosphere has very little measurements available, we propose to drop a digital ionosond instrument into the Mars surface for data collection. Even though the Martian tropospheric radio refractivity has small value, it still can cause the ray bending and multipath effects. We recommend to perform an accurate calculation on excess phase and group delays (range and time delays). Other effects, such as range rate errors, appearance angle deviation, defocusing loss on Mars, etc. are also needed to be estimated. Ice depolarization effects due to Martian clouds on radio waves is unknown yet, which is expected to be small, because lower optical depth and thinner layer of cloud: Total Martian atmospheric gaseous attenuation is expected to be less than 1 dB on microwaves band, because the Martian atmosphere has very low concentration in uncondensed H2O and O2. An accurate calculation for zenith opacity requires the information about scale heights of H2O and O2 distribution. An accurate water vapor altitude profile at Mars is not available yet. Under the normal condition, CO2 and N2 gases do not have electric or magnetic dipoles and do not absorb electromagnetic energy from the waves. However, they may generate the dipoles through a collision and interact with waves under a high density condition and absorb electromagnetic waves in the infrared and visible band. Dust storm is most dominant factor to the radio wave attenuation. Large Martian dust storm can cause at least 3 dB or higher loss to Ka band wave. For a normal dust storm, the attenuation is about 1 dB. The

  6. Remote sensing of the turbulence characteristics of a planetary atmosphere by radio occultation of a space probe.

    NASA Technical Reports Server (NTRS)

    Woo, R.; Ishimaru, A.

    1973-01-01

    The purpose of this paper is to analyze the effects of small-scale turbulence on radio waves propagating through a planetary atmosphere. The analysis provides a technique for inferring the turbulence characteristics of a planetary atmosphere from the radio signals received from a spacecraft as it is occulted by the planet. The planetary turbulence is assumed to be localized and smoothly varying, with the structure constant varying exponentially with altitude. Rytov's method is used to derive the variance of log-amplitude and phase fluctuations of a wave propagating through the atmosphere.

  7. Characteristics of Electromagnetic Pulse Propagation in Metal

    NASA Technical Reports Server (NTRS)

    Namkung, M.; Wincheski, B.; Nath, S.; Fulton, J. P.

    2004-01-01

    It is well known that the solution of the diffusion equation for an electromagnetic field with a time harmonic term, e(sup iwt), is in the form of a traveling wave whose amplitude attenuates over distance into a conducting medium. As the attenuation is an increasing function of frequency, the high frequency components attenuate more rapidly than those of low ones upon entering a well conducting object. At the same time, the phase velocity of an individual component is also an increasing function of frequency causing a broadening of the pulse traveling inside a conductor. In the results of our previous study of numerical simulations, the problem of using a gaussian input pulse was immediately clear. First, having the dominant frequency components distributed around zero, the movement of the peak was not well defined. Second, with the amplitude of fourier components varying slowly over a wide range, the dispersion-induced blurring of the peak position was seen to be severe. For the present study, we have used a gaussian modulated single frequency sinusoidal wave, i. e., the carrier, as an input pulse in an effort to improve the issues related to the unclear movement of peak and dispersion as described above. This was based on the following two anticipated advantages: First, the packet moves in a conductor at the group velocity calculated at the carrier frequency, which means it is well controllable. Second, the amplitude of frequency components other than that of the carrier can be almost negligible, such that the effect of dispersion can be significantly reduced. A series of experiments of transmitting electromagnetic pulses through aluminum plates of various thickness was performed to test the validity of the above points. The results of numerical simulation based on wave propagation are discussed with respect to the experimental results. Finally, a simple simulation was performed based on diffusion of a continuous sine wave input and the results are compared with

  8. Detection of long-term trends in the meso-/lower thermosphere from ground-based radio propagation measurements

    NASA Astrophysics Data System (ADS)

    Bremer, J.

    Long-term observations of different ground based ionospheric radio propagation experiments have been used to get information about trends in the mesosphere and lower thermosphere. Ionospheric reflection height observations (measurements of phase height in the LF range as well as of the peak height of the ionospheric E layer) suggest a shrinking of the meso-/lower thermosphere. This result is in agreement with model calculations of an increasing atmospheric greenhouse effect. From data series of different ionospheric absorption measurements in the LF, MF, and HF ranges trends have been derived with characteristic differences in dependence on the reflection height of the measuring paths. These trends in the absorption as well as in foE data from ionosonde observations cannot be explained by a simple atmospheric shrinking but confirm the prediction of different model results of a decrease of the density of nitric oxide and of changes the effective recombination coefficient in the mesosphere as well as in the lower thermosphere. In different data series of radio propagation experiments there are indications of changing trends in the MLT region before and after the year 1979 as firstly remarked by Labitzke in stratospheric temperature trends. The shrinking of the MLT region seems to be stronger after this time than before. Comparisons with ozone variations suggest that this behaviour seems to be caused by a steeper ozone decrease after 1979.

  9. Ionospheric disturbances during November 30-December 1, 1988. XI - Abnormal propagations of HF and VHF radio waves

    NASA Astrophysics Data System (ADS)

    Ichinose, Masaru; Kamata, Mitsuhiro

    1992-07-01

    Unusual propagations of HF and VHF radio waves associated with a geomagnetic storm during the period from November 30 to December 1, 1988 are investigated using ionospheric data collected from Japan, China, and Taiwan. The increased field strength of the Japanese frequency standard signals (JJY 2.5 MHz and 5 MHz) which were received at Akita Radio Wave Observatory on the night of November 30 seem to have been caused by increased MUFs and/or scattering due to the disturbed ionosphere. The VHF-TV radio waves propagated from China were received at Kokubunji in Tokyo. One of the most probable mechanisms explaining this unusual propagation of VHF is a one-hop-F2 mode of propagation created by an ionosphere with an anomalously high f0F2. It was found out that these unusual HF and VHF propagations were attributed to unusual ionospheric conditions associated with these geomagnetic disturbances.

  10. 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

  11. A Lightweight Radio Propagation Model for Vehicular Communication in Road Tunnels.

    PubMed

    Qureshi, Muhammad Ahsan; Noor, Rafidah Md; Shamim, Azra; Shamshirband, Shahaboddin; Raymond Choo, Kim-Kwang

    2016-01-01

    Radio propagation models (RPMs) are generally employed in Vehicular Ad Hoc Networks (VANETs) to predict path loss in multiple operating environments (e.g. modern road infrastructure such as flyovers, underpasses and road tunnels). For example, different RPMs have been developed to predict propagation behaviour in road tunnels. However, most existing RPMs for road tunnels are computationally complex and are based on field measurements in frequency band not suitable for VANET deployment. Furthermore, in tunnel applications, consequences of moving radio obstacles, such as large buses and delivery trucks, are generally not considered in existing RPMs. This paper proposes a computationally inexpensive RPM with minimal set of parameters to predict path loss in an acceptable range for road tunnels. The proposed RPM utilizes geometric properties of the tunnel, such as height and width along with the distance between sender and receiver, to predict the path loss. The proposed RPM also considers the additional attenuation caused by the moving radio obstacles in road tunnels, while requiring a negligible overhead in terms of computational complexity. To demonstrate the utility of our proposed RPM, we conduct a comparative summary and evaluate its performance. Specifically, an extensive data gathering campaign is carried out in order to evaluate the proposed RPM. The field measurements use the 5 GHz frequency band, which is suitable for vehicular communication. The results demonstrate that a close match exists between the predicted values and measured values of path loss. In particular, an average accuracy of 94% is found with R2 = 0.86.

  12. Radio and X-ray diagnostics of electron acceleration and propagation in the solar atmosphere

    NASA Astrophysics Data System (ADS)

    Vilmer, N.; Reid, H.

    2015-12-01

    Efficient particle acceleration is observed in association with solar flares. X-ray and radio emissions provide valuable information on the properties of electron acceleration, interaction and propagation. In particular, type III radio bursts observed in a whole frequency band from several hundred MHz to tens of MHz allow to diagnose the propagation of electron beams from the flare acceleration site in the corona to the outer solar atmosphere. We will present here the results of a study based on ten years of data (2002-2011) starting with a list of coronal type III bursts. We will reexamine long-standing questions on the connections between type III bursts and HXR flares using combined data from RHESSI, the Phoenix 2 and Blein 7M radiospectrometers, the NRH and Wind/Waves: -Do all coronal type III bursts have X-ray counterparts? -What kind of correlation between X-ray and radio intensities? -Do all coronal type III bursts have an Interplanetary component? We will further describe how these kind of studies can be continued in the future using the combination of ground-based measurements with Solar Orbiter and Solar Probe + observations.

  13. A Lightweight Radio Propagation Model for Vehicular Communication in Road Tunnels.

    PubMed

    Qureshi, Muhammad Ahsan; Noor, Rafidah Md; Shamim, Azra; Shamshirband, Shahaboddin; Raymond Choo, Kim-Kwang

    2016-01-01

    Radio propagation models (RPMs) are generally employed in Vehicular Ad Hoc Networks (VANETs) to predict path loss in multiple operating environments (e.g. modern road infrastructure such as flyovers, underpasses and road tunnels). For example, different RPMs have been developed to predict propagation behaviour in road tunnels. However, most existing RPMs for road tunnels are computationally complex and are based on field measurements in frequency band not suitable for VANET deployment. Furthermore, in tunnel applications, consequences of moving radio obstacles, such as large buses and delivery trucks, are generally not considered in existing RPMs. This paper proposes a computationally inexpensive RPM with minimal set of parameters to predict path loss in an acceptable range for road tunnels. The proposed RPM utilizes geometric properties of the tunnel, such as height and width along with the distance between sender and receiver, to predict the path loss. The proposed RPM also considers the additional attenuation caused by the moving radio obstacles in road tunnels, while requiring a negligible overhead in terms of computational complexity. To demonstrate the utility of our proposed RPM, we conduct a comparative summary and evaluate its performance. Specifically, an extensive data gathering campaign is carried out in order to evaluate the proposed RPM. The field measurements use the 5 GHz frequency band, which is suitable for vehicular communication. The results demonstrate that a close match exists between the predicted values and measured values of path loss. In particular, an average accuracy of 94% is found with R2 = 0.86. PMID:27031989

  14. A Lightweight Radio Propagation Model for Vehicular Communication in Road Tunnels

    PubMed Central

    Shamim, Azra; Shamshirband, Shahaboddin; Raymond Choo, Kim-Kwang

    2016-01-01

    Radio propagation models (RPMs) are generally employed in Vehicular Ad Hoc Networks (VANETs) to predict path loss in multiple operating environments (e.g. modern road infrastructure such as flyovers, underpasses and road tunnels). For example, different RPMs have been developed to predict propagation behaviour in road tunnels. However, most existing RPMs for road tunnels are computationally complex and are based on field measurements in frequency band not suitable for VANET deployment. Furthermore, in tunnel applications, consequences of moving radio obstacles, such as large buses and delivery trucks, are generally not considered in existing RPMs. This paper proposes a computationally inexpensive RPM with minimal set of parameters to predict path loss in an acceptable range for road tunnels. The proposed RPM utilizes geometric properties of the tunnel, such as height and width along with the distance between sender and receiver, to predict the path loss. The proposed RPM also considers the additional attenuation caused by the moving radio obstacles in road tunnels, while requiring a negligible overhead in terms of computational complexity. To demonstrate the utility of our proposed RPM, we conduct a comparative summary and evaluate its performance. Specifically, an extensive data gathering campaign is carried out in order to evaluate the proposed RPM. The field measurements use the 5 GHz frequency band, which is suitable for vehicular communication. The results demonstrate that a close match exists between the predicted values and measured values of path loss. In particular, an average accuracy of 94% is found with R2 = 0.86. PMID:27031989

  15. Propagation measurements on a line-of-sight over-water radio link in Norway

    NASA Astrophysics Data System (ADS)

    Thorvaldsen, Per; Henne, Ingvar

    2014-07-01

    Propagation measurements have been carried out on a 43 km long 13 GHz 128 QAM (quadrature amplitude modulation) over-water path in the coastal regions of Norway. The measurements lasted for 18 months. The intention with the measurements on this in-service radio link was to compare results with models given by the (Recommendation International Telecommunication Union) Rec. ITU-R P. 530-15. The attenuation due to combined rain and wet snow was of special interest, since the radio link is situated in an area—Trondheimsfjorden—that has a significant amount of wet snow in winter. The radio link experienced outages due to multipath, rain and wet snow, where the latter were the predominant outage cause. The fading due to combined rain and wet snow resembled the shape of the model given in Rec. ITU-R P. 530-15, but the model underpredicts the amount of fading. In addition to outages (performance degradation and unavailability) and fading, various other parameters such as fading speed, enhancement, average fade duration, and number of fade events have been measured and compared to Rec. ITU-R P. 530-15. The radio link activity has also been compared to the weather conditions at the time for the most severe fading incidents.

  16. Probing geomagnetic storm-driven magnetosphere-ionosphere dynamics in D-region ionosphere using VLF signal propagation characteristics

    NASA Astrophysics Data System (ADS)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip Kumar; Ogunmodimu, Olugbenga

    2016-07-01

    When propagating in the Earth-ionosphere waveguide, the amplitude and phase of VLF/LF radio signals are sensitive to changes in the electrical conductivity of the lower ionosphere. This characteristic makes it useful in studying sudden ionospheric disturbances, especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbances and/or storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region ionosphere. Diurnal VLF signature may also convey other important information, especially those related to geomagnetic disturbance/storm induced ionospheric changes. In this paper, using the data of three propagation paths (at latitudes 40-54º), we analyze in detail the trend of anomalies of VLF diurnal signal under varying solar and geomagnetic space environmental conditions to identify possible geomagnetic footprints on the D region ionosphere.

  17. Radio wave propagation in arch-shaped tunnels: Measurements and simulations by asymptotic methods

    NASA Astrophysics Data System (ADS)

    Masson, E.; Combeau, P.; Cocheril, Y.; Berbineau, M.; Aveneau, L.; Vauzelle, R.

    2010-01-01

    Several wireless communication systems are developed for communication needs between train and ground and between trains in the railway or mass transit domains. They are developed for operational needs for security and comfort. In order to deploy these systems in specific environments, such as tunnels, straight or curved, rectangular or arch-shaped section, specific propagation models have to be developed. A modelisation of the radio wave propagation in straight arch-shaped tunnels is realized by using asymptotic methods, such as Ray Tracing and Ray Launching, combined with the tessellation of the arched section. A method of interpolation of the facets' normals was implemented in order to minimize the error made when using the tessellation. Results obtained are validated by comparison to the literature and to measurement results.

  18. Type III radio bursts in the interplanetary medium - The role of propagation

    NASA Technical Reports Server (NTRS)

    Steinberg, J. L.; Hoang, S.; Lecacheux, A.; Aubier, M. G.; Dulk, G. A.

    1984-01-01

    Interplanetary type III radio burst observations are analyzed in order to ascertain the role played by propagation effects between the true source and the observer. Large source altitudes are noted, together with an increasing angular size of sources with increasing angular distance from the sun's center. These and other observations furnish strong evidence for the theory that propagation effects, group delays, ducting and/or scattering significantly affect the observed heights, sizes, and brightness temperatures of interplanetary type III bursts. This would be true irrespective of whether the bursts are due to plasma radiation at the fundamental or at the harmonic, and the effects would extend to the arrival times of the radiation to a greater or lesser extent, depending on the path from the source to the observer.

  19. A 3-D Propagation Model for Emerging Land Mobile Radio Cellular Environments.

    PubMed

    Ahmed, Abrar; Nawaz, Syed Junaid; Gulfam, Sardar Muhammad

    2015-01-01

    A tunable stochastic geometry based Three-Dimensional (3-D) scattering model for emerging land mobile radio cellular systems is proposed. Uniformly distributed scattering objects are assumed around the Mobile Station (MS) bounded within an ellipsoidal shaped Scattering Region (SR) hollowed with an elliptically-cylindric scattering free region in immediate vicinity of MS. To ensure the degree of expected accuracy, the proposed model is designed to be tunable (as required) with nine degrees of freedom, unlike its counterparts in the existing literature. The outer and inner boundaries of SR are designed as independently scalable along all the axes and rotatable in horizontal plane around their origin centered at MS. The elevated Base Station (BS) is considered outside the SR at a certain adjustable distance and height w.r.t. position of MS. Closed-form analytical expressions for joint and marginal Probability Density Functions (PDFs) of Angle-of-Arrival (AoA) and Time-of-Arrival (ToA) are derived for both up- and down-links. The obtained analytical results for angular and temporal statistics of the channel are presented along with a thorough analysis. The impact of various physical model parameters on angular and temporal characteristics of the channel is presented, which reveals the comprehensive insight on the proposed results. To evaluate the robustness of the proposed analytical model, a comparison with experimental datasets and simulation results is also presented. The obtained analytical results for PDF of AoA observed at BS are seen to fit a vast range of empirical datasets in the literature taken for various outdoor propagation environments. In order to establish the validity of the obtained analytical results for spatial and temporal characteristics of the channel, a comparison of the proposed analytical results with the simulation results is shown, which illustrates a good fit for 10(7) scattering points. Moreover, the proposed model is shown to degenerate

  20. A 3-D Propagation Model for Emerging Land Mobile Radio Cellular Environments

    PubMed Central

    Ahmed, Abrar; Nawaz, Syed Junaid; Gulfam, Sardar Muhammad

    2015-01-01

    A tunable stochastic geometry based Three-Dimensional (3-D) scattering model for emerging land mobile radio cellular systems is proposed. Uniformly distributed scattering objects are assumed around the Mobile Station (MS) bounded within an ellipsoidal shaped Scattering Region (SR) hollowed with an elliptically-cylindric scattering free region in immediate vicinity of MS. To ensure the degree of expected accuracy, the proposed model is designed to be tunable (as required) with nine degrees of freedom, unlike its counterparts in the existing literature. The outer and inner boundaries of SR are designed as independently scalable along all the axes and rotatable in horizontal plane around their origin centered at MS. The elevated Base Station (BS) is considered outside the SR at a certain adjustable distance and height w.r.t. position of MS. Closed-form analytical expressions for joint and marginal Probability Density Functions (PDFs) of Angle-of-Arrival (AoA) and Time-of-Arrival (ToA) are derived for both up- and down-links. The obtained analytical results for angular and temporal statistics of the channel are presented along with a thorough analysis. The impact of various physical model parameters on angular and temporal characteristics of the channel is presented, which reveals the comprehensive insight on the proposed results. To evaluate the robustness of the proposed analytical model, a comparison with experimental datasets and simulation results is also presented. The obtained analytical results for PDF of AoA observed at BS are seen to fit a vast range of empirical datasets in the literature taken for various outdoor propagation environments. In order to establish the validity of the obtained analytical results for spatial and temporal characteristics of the channel, a comparison of the proposed analytical results with the simulation results is shown, which illustrates a good fit for 107 scattering points. Moreover, the proposed model is shown to degenerate to

  1. Study of the propagation characteristics of Very Low Frequency Signal as observed from Indian Permanent station Maitri and Bharati

    NASA Astrophysics Data System (ADS)

    Sasmal, Sudipta; Chakrabarti, Sandip Kumar; Pal, Sujay; Palit, Sourav; Chakraborty, Suman

    2016-07-01

    Propagation of Very Low Frequency (VLF) radio signal through the Earth-ionosphere waveguide strongly depends on the plasma properties of the ionospheric D layer. Solar extreme ultraviolet radiation plays the central role in controlling physical and chemical properties of the lower ionospheric layers and hence determining the quality and propagation characteristics of a VLF signal. The nature of interference among different propagating modes varies widely with the length of the propagation path. For a very long path, exposure of solar radiation and thus the degree of ionization vary by a large amount along the path. Study of radio signal characteristics in the Antarctic region during summer period in the Southern Hemisphere gives us a unique opportunity to explore such a possibility. In addition, there is an extra feature in this path - the presence of solar radiation and hence the D region for the whole day during summer in at least some sections of the path. We present long-distance propagation characteristics of VLF signals transmitted from VTX (18.2 kHz) and NWC (19.8 kHz) transmitters recorded simultaneously at Indian permanent stations Maitri (latitude 70 ^{o}45 ^{'}S, longitude 11 ^{o}40 ^{'}E) and Bharati (69 ^{o}24 ^{'}S, 76 ^{o}10 ^{'}E). A very stable diurnal variation of the signal (both amplitude and phase) has been obtained with no signature of nighttime fluctuation due the presence of 24 h of sunlight for both the stations. We 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. VLF signals show the effects of high energetic solar events. Using ion production and recombination profiles by solar irradiance and incorporating D region ion chemistry processes, we calculate the electron density profile at different heights. Using this profile in the Long Wavelength Propagation Capability

  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. On the mean profiles of radio pulsars - I. Theory of propagation effects

    NASA Astrophysics Data System (ADS)

    Beskin, V. S.; Philippov, A. A.

    2012-09-01

    We study the influence of propagation effects on the mean profiles of radio pulsars using the method of wave propagation in inhomogeneous media described by Kravtsov & Orlov. This approach allows us first to take into consideration the transition from geometrical optics to vacuum propagation, the cyclotron absorption and the wave refraction simultaneously. In addition, the non-dipole magnetic field configuration, the drift motion of plasma particles and their realistic energy distribution are taken into account. It is confirmed that, for ordinary pulsars (period P ˜ 1 s, surface magnetic field B0 ˜ 1012 G) and typical plasma generation near the magnetic poles (multiplicity parameter λ = ne/nGJ ˜ 103), the polarization is formed inside the light cylinder at a distance resc ˜ 1000 R from the neutron star, the circular polarization being 5-20 per cent which is in agreement with observational data. A one-to-one correspondence between the signs of circular polarization and position angle (PA) derivative along the profile for both ordinary and extraordinary waves is predicted. Using numerical integration we now can model the mean profiles of radio pulsars. It is shown that the standard S-shape form of the PA swing can be realized for small enough multiplicity λ and large enough bulk Lorentz factor γ only. It is also shown that the value of the maximum derivative of PA, which is often used for determination of the angle between magnetic dipole and rotation axis, depends on the plasma parameters and could differ from the rotation vector model (RVM) prediction.

  4. Antenna system characteristics and solar radio burst observations

    NASA Astrophysics Data System (ADS)

    Li, Sha; Yan, Yi-Hua; Chen, Zhi-Jun; Wang, Wei; Liu, Dong-Hao

    2015-11-01

    The Chinese Spectral Radio Heliograph (CSRH) is an advanced aperture synthesis solar radio heliograph, independently developed by National Astronomical Observatories, Chinese Academy of Sciences. It consists of 100 reflector antennas, which are grouped into two antenna arrays (CSRH-I and CSRH-II) for low and high frequency bands respectively. The frequency band of CSRH-I is 0.4-2 GHz and that for CSRH-II is 2-15 GHz. In the antenna and feed system, CSRH uses eleven feeds to receive signals coming from the Sun. The radiation pattern has a lower side lobe and the back lobe of the feed is well illuminated. The characteristics of gain G and antenna noise temperature T affect the quality of solar radio imaging. For CSRH, the measured G is larger than 60 dBi and T is less than 120 K. After CSRH-I was established, we successfully captured a solar radio burst between 1.2-1.6 GHz on 2010 November 12 using this instrument and this event was confirmed through observations with the Solar Broadband Radio Spectrometer at 2.84 GHz and the Geostationary Operational Environmental Satellite. In addition, an image obtained from CSRH-I clearly revealed the profile of the solar radio burst. The other observational work involved the imaging the Fengyun-2E geosynchronous satellite which is assumed to be a point source. Results indicate that the data processing method applied in this study for deleting errors in a noisy image could be used for processing images from other sources.

  5. Source characteristics of Jovian narrow-band kilometric radio emissions

    NASA Astrophysics Data System (ADS)

    Reiner, M. J.; Fainberg, J.; Stone, R. G.; Kaiser, M. L.; Desch, M. D.; Manning, R.; Zarka, P.; Pedersen, B.-M.

    1993-07-01

    New observations of Jovian narrow-band kilometric (nKOM) radio emissions were made by the Unified Radio and Plasma Wave (URAP) experiment on the Ulysses spacecraft during the Ulysses-Jupiter encounter in early February 1992. These observations have demonstrated the unique capability of the URAP instrument for determining both the direction and polarization of nKOM radio sources. An important result is the discovery that nKOM radio emission originates from a number of distinct sources located at different Jovian longitudes and at the inner and outermost regions of the Io plasma torus. These sources have been tracked for several Jovian rotations, yielding their corotational lags, their spatial and temporal evolution, and their radiation characteristics at both low latitudes far from Jupiter and at high latitudes near the planet. Both right-hand and left-hand circularly polarized nKOM sources were observed. The polarizations observed for sources in the outermost regions of the torus seem to favor extraordinary mode emission.

  6. Testing radio bursts observed on the nightside of Venus for evidence of whistler mode propagation from lightning

    NASA Technical Reports Server (NTRS)

    Sonwalkar, Vikas S.; Carpenter, D. L.; Strangeway, R. J.

    1991-01-01

    Results are presented from a series of tests of radio bursts on the nightside of Venus (observed by an orbiting electric field detector on board the Pioneer Venus Orbiter), which were conducted as a search for the evidence of whistler mode propagation from lightning. Preliminary results suggest that there are at least two main categories of bursts: one that exhibits one or more properties consistent with whistler mode propagation from subionospheric lightning sources, and another that is not.

  7. Radio wave propagation studies along an Earth-space satellite link

    NASA Astrophysics Data System (ADS)

    Albert, Jacques

    1990-03-01

    The use of superhigh microwave frequencies for satellite communications has many advantages, but its major drawback lies in the effects of atmospheric hydrometeors on electromagnetic wave propagation. One research effort under way to investigate this problem is being conducted by the European Space Agency, which will launch the Olympus-1 communications satellite in June 1989. One of this satellite's four payloads is a 12.5/20/30 GHz beacon package which will enable 17 countries, including Canada, to conduct propagation experiments. The main objective of the Canadian participation is to study propagation during adverse weather conditions. The present thesis provides a model of the propagation path so that the system induced depolarization impurities can be removed from the received beacon signals. The overall system configuration and requirements are given. A system polarization matrix which incorporates all effects existing on the satellite link is described. Analyses needed to obtain the medium propagation characteristics from measured data at 12.5, 20, and 30 GHz are presented. The development of software to perform data acquisition and control of the equipment is reviewed and program listings are included. The preprocessing of the data using the mathematical model will be integrated into the software, as well as other needed mathematical analysis.

  8. Estimation of the propagation characteristics of elastic waves propagating through a partially saturated sand soil

    NASA Astrophysics Data System (ADS)

    Nakayama, M.; Kawakata, H.; Doi, I.; Takahashi, N.

    2015-12-01

    Recently, landslides due to heavy rain and/or earthquakes have been increasing and severe damage occurred in Japan in some cases (e.g., Chigira et al., 2013, Geomorph.). One of the principle factors activating landslides is groundwater. Continuous measurements of moisture in soil and/or pore pressure are performed to investigate the groundwater behavior. However, such measurements give information on only local behavior of the groundwater. To monitor the state of target slope, it is better to measure signals affected by the behavior of groundwater in a widely surrounding region. The elastic waves propagating through the medium under the target slope are one of candidates of such signals. In this study, we measure propagating waves through a sand soil made in laboratory, injecting water into it from the bottom. We investigate the characteristics of the propagating waves. We drop sand particles in a container (750 mm long, 300 mm wide and 400 mm high) freely and made a sand soil. The sand soil consists of two layers. One is made of larger sand particles (0.2-0.4 mm in diameter) and the other is made of smaller sand particles (0.05-0.2 mm in diameter). The dry density of these sand layers is about 1.45 g/cm3. We install a shaker for generating elastic waves, accelerometers and pore pressure gauges in the sand soil. We apply small voltage steps repeatedly, and we continuously measure elastic waves propagating through the sand soil at a sampling rate of 51.2 ksps for a period including the water injection period. We estimate the spatio-temporal variation in the maximum cross-correlation coefficients and the corresponding time lags, using template waveforms recorded in the initial period as references. The coefficient for the waveforms recorded at the accelerometer attached to the tip of the shaker is almost stable in high values with a slight decrease down to 0.94 in the period when the sand particles around the shaker are considered to become wet. On the other hand

  9. Investigation of the UHF mobile-radio propagation channel in a temperate-zone forested environment

    NASA Astrophysics Data System (ADS)

    White, Kenneth J.

    1986-08-01

    Experimental verification of the stochastic power-spectral-density theory of radio propagation, as applied to a mobile receiver in a forested environment, is presented. Using a novel technique to achieve fractional-hertz resolution of the diffuse and direct wave components of the Doppler-spread received spectrum, the resultant data taken at 432 MHz shows that the angle of arrival of the diffuse component of the incident energy at the receive antenna is described by an uniform probability density function for both vertical and horizontal polarizations. Given an 8.8 km transmission path with the signal penetrating 1.3 km of forest just before reaching the receiver, the ratio of coherent (direct wave) intensity to total received signal power is 42% for horizontal polarization and 5% for vertical polarization. The results of the research indicate that long transmission paths in foliage are better characterized by a forward-scattering mechanism than by a lateral wave model.

  10. The coherer: with simple demonstrations of the generation, propagation and detection of radio waves

    NASA Astrophysics Data System (ADS)

    Mills, Allan

    2010-03-01

    A coherer is a bistable device based on metal filings loosely confined between solid metal electrodes. This granular material normally exhibits a very high electrical resistance (tens of kilohms), but passage of the high-frequency current generated by reception of a radio signal causes it to 'cohere' into a comparatively low resistance condition (tens of ohms). This state persists until the device is mechanically disturbed, whereupon the high resistance state is restored. This characteristic was employed by scientists in the 1890s to detect radio waves, and applied commercially by Marconi in his 'wireless' telegraph. It is easy to make a working coherer and directions are given for operating it from a distance with a spark transmitter based on a piezoelectric gas igniter. Incorporation of an 'aerial' and 'earth' enable a range of 7 m to be achieved and simple signals may be transmitted.

  11. Study of Temperature Wave Propagation in Superfluid Helium Focusing on Radio-Frequency Cavity Cooling

    NASA Astrophysics Data System (ADS)

    Koettig, T.; Peters, B. J.; Avellino, S.; Junginger, T.; Bremer, J.

    2015-12-01

    Oscillating Superleak Transducers (OSTs) can be used to localize quenches of superconducting radio-frequency cavities. Local hot spots at the cavity surface initiate temperature waves in the surrounding superfluid helium that acts as cooling fluid at typical temperatures in the range of 1.6 K to 2 K. The temperature wave is characterised by the properties of superfluid helium such as the second sound velocity. For high heat load densities second sound velocities greater than the standard literature values are observed. This fast propagation has been verified in dedicated small scale experiments. Resistors were used to simulate the quench spots under controlled conditions. The three dimensional propagation of second sound is linked to OST signals. The aim of this study is to improve the understanding of the OST signal especially the incident angle dependency. The characterised OSTs are used as a tool for quench localisation on a real size cavity. Their sensitivity as well as the time resolution was proven to be superior to temperature sensors glued to the surface of the cavity.

  12. 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.

  13. 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.

  14. 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.

  15. Antenna Construction & Propagation of Radio Waves, 5-1. Military Curriculum Materials for Vocational and Technical Education.

    ERIC Educational Resources Information Center

    Marine Corps, Washington, DC.

    These military-developed curriculum materials consist of five individualized, self-paced chapters dealing with antenna construction and propagation of radio waves. Covered in the individual lessons are the following topics: basic electricity; antenna transmission-line fundamentals; quarter-wave antennas, half-wave antennas, and associated radio…

  16. Long-term integrated radiophysical studies of the ionosphere, near space, and the propagation of radio waves from space objects

    NASA Technical Reports Server (NTRS)

    Misyura, V. A.

    1974-01-01

    The radiophysical studies reported consist of direct measurements of certain effects induced in the propagation of radio waves from space objects. From measured effects and from data on the motion and position of space objects, physical parameters of the medium and bodies are determined.

  17. Longitudinal elastic wave propagation characteristics of inertant acoustic metamaterials

    NASA Astrophysics Data System (ADS)

    Kulkarni, Prateek P.; Manimala, James M.

    2016-06-01

    Longitudinal elastic wave propagation characteristics of acoustic metamaterials with various inerter configurations are investigated using their representative one-dimensional discrete element lattice models. Inerters are dynamic mass-amplifying mechanical elements that are activated by a difference in acceleration across them. They have a small device mass but can provide a relatively large dynamic mass presence depending on accelerations in systems that employ them. The effect of introducing inerters both in local attachments and in the lattice was examined vis-à-vis the propagation characteristics of locally resonant acoustic metamaterials. A simple effective model based on mass, stiffness, or their combined equivalent was used to establish dispersion behavior and quantify attenuation within bandgaps. Depending on inerter configurations in local attachments or in the lattice, both up-shift and down-shift in the bandgap frequency range and their extent are shown to be possible while retaining static mass addition to the host structure to a minimum. Further, frequency-dependent negative and even extreme effective-stiffness regimes are encountered. The feasibility of employing tuned combinations of such mass-delimited inertant configurations to engineer acoustic metamaterials that act as high-pass filters without the use of grounded elements or even as complete longitudinal wave inhibitors is shown. Potential device implications and strategies for practical applications are also discussed.

  18. Generation and Upper Atmospheric Propagation of Acoustic Gravity Waves according to Numerical Modeling and Radio Tomography

    NASA Astrophysics Data System (ADS)

    Vorontsov, Artem; Andreeva, Elena; Nesterov, Ivan; Padokhin, Artem; Kurbatov, Grigory

    2016-04-01

    The acoustic-gravity waves (AGW) in the upper atmosphere and ionosphere can be generated by a variety of the phenomena in the near-Earth environment and atmosphere as well as by some perturbations of the Earth's ground or ocean surface. For instance, the role of the AGW sources can be played by the earthquakes, explosions, thermal heating, seisches, tsunami waves. We present the examples of AGWs excited by the tsunami waves traveling in the ocean, by seisches, and by ionospheric heating by the high-power radio wave. In the last case, the gravity waves are caused by the pulsed modulation of the heating wave. The AGW propagation in the upper atmosphere induces the variations and irregularities in the electron density distribution of the ionosphere, whose structure can be efficiently reconstructed by the method of the ionospheric radio tomography (RT) based on the data from the global navigational satellite systems (GNSS). The input data for RT diagnostics are composed of the 150/400 MHz radio signals from the low-orbiting (LO) satellites and 1.2-1.5 GHz radio signals from the high-orbiting (HO) satellites with their orbits at ~1000 and ~20000 km above the ground, respectively. These data enable ionospheric imaging on different spatiotemporal scales with different spatiotemporal resolution and coverage, which is suitable, inter alia, for tracking the waves and wave-like features in the ionosphere. In particular, we demonstrate the maps of the ionospheric responses to the tornado at Moore (Oklahoma, USA) of May 20, 2013, which are reconstructed from the HO data. We present the examples of LORT images containing the waves and wavelike disturbances associated with various sources (e.g., auroral precipitation and high-power heating of the ionosphere). We also discuss the results of modeling the AGW generation by the surface and volumetric sources. The millihertz AGW from these sources initiate the ionospheric perturbation with a typical scale of a few hundred km at the

  19. Characteristics of diving in radio-marked Xantus's Murrelets

    USGS Publications Warehouse

    Hamilton, C.D.; Golightly, R.T.; Takekawa, J.Y.

    2005-01-01

    We monitored diving activity of radio-marked Xantus's Murrelets Synthliboramphus hypoleucus near Anacapa Island, California, during the breeding season. Thirteen radio-marked murrelets were remotely monitored from Anacapa Island with a handheld antenna and radio receiver for 29 hours in three sample periods in April and May 2003. Mean dive durations in the sample periods were 18 s ?? 2 s, 28 s ?? 2 s, and 24 s ?? 4 s, suggesting that dives were less than 21 m from the surface. Dive duration and subsequent time on the surface differed between the sample periods. Dive duration and subsequent time on the surface were not correlated in observations stratified by individual bird or by sample period. Further, dive duration and subsequent time on the surface were not correlated within foraging bouts. Dive characteristics measured near Anacapa Island suggested that Xantus's Murrelets have the ability to capture prey found at varying depths, but will feed on prey that is most available near the surface of the water.

  20. Results of a study of the effect of high-power short-wave emissions on the propagation of radio waves on the Kiev-Ioshkar-Ola path

    NASA Astrophysics Data System (ADS)

    Boguta, N. M.; Ivanov, V. A.; Katkov, E. V.; Maksimenko, O. I.; Mitiakova, E. E.; Uriadov, V. P.; Frolov, V. A.; Erm, R..

    Experiments were performed during March-April 1982 and April-June 1983 to study the effect of ionospheric disturbances caused by high-power radio transmissions on the propagation of decameter waves on the Kiev-Ioshkar-Ola path. Sounding waves were emitted at four fixed frequencies: 10.8, 16.6, 18.2, and 19.85 MHz; and high-power (50 MW) heating waves were emitted at 5.8-9.3 MHz. An analysis of the data shows that the degree of the effect of high-power radio emissions on the decameter-signal characteristics depends on ionospheric conditions, e.g., the effect was strongest when the critical frequencies on the path were highest, the effect being observed most frequently at 10.8 MHz.

  1. Vibration and wave propagation characteristics of multisegmented elastic beams

    NASA Technical Reports Server (NTRS)

    Nayfeh, Adnan H.; Hawwa, Muhammad A.

    1990-01-01

    Closed form analytical solutions are derived for the vibration and wave propagation of multisegmented elastic beams. Each segment is modeled as a Timoshenko beam with possible inclusion of material viscosity, elastic foundation and axial forces. Solutions are obtained by using transfer matrix methods. According to these methods formal solutions are first constructed which relate the deflection, slope, moment and shear force of one end of the individual segment to those of the other. By satisfying appropriate continuity conditions at segment junctions, a global 4x4 matrix results which relates the deflection, slope, moment and shear force of one end of the beam to those of the other. If any boundary conditions are subsequently invoked on the ends of the beam one gets the appropriate characteristic equation for the natural frequencies. Furthermore, by invoking appropriate periodicity conditions the dispersion relation for a periodic system is obtained. A variety of numerical examples are included.

  2. Ionosphere-magnetosphere studies using ground based VLF radio propagation technique: an Indian example

    NASA Astrophysics Data System (ADS)

    Chakravarty, Subhas

    Since IGY period (1957-58), natural and artificially produced Very Low Frequency (VLF) elec-tromagnetic radiations are being recorded at large number of ground stations all over the world and on-board satellites to study various radio wave-thermal/energetic plasma interactive pro-cesses related to earth's ionosphere-plasmasphere-magnetosphere environment. The terrestrial propagation of these VLF radio waves are primarily enabled through the earth ionosphere wave guide (EIWG) mode to long horizontal distances around the globe and ducted along the ge-omagnetic field lines into the conjugate hemisphere through the plasmasphere-magnetosphere regions. The time frequency spectra of the received signals indicate presence of dispersion (wave/group velocities changing with frequency) and various cut-off frequencies based on the width of the EIWG, electron gyro and plasma frequencies etc., providing several types of received signals like whistlers, chorus, tweeks, hiss and hisslers which can be heard on loud-speakers/earphones with distinguishing audio structures. While the VLF technique has been a very effective tool for studying middle and high latitude phenomena, the importance of the similar and anomalous observations over the Indian low latitude stations provide potentially new challenges for their scientific interpretation and modelling. The ducted and non-ducted magnetospheric propagation, pro-longitudinal (PL) mode, low latitude TRIMPI/TLE (Tran-sient Luminous Emissions) or other effects of wave-particle/wave-wave interactions, effects due to ionospheric irregularities and electric fields, full wave solutions to D-region ionisation per-turbations due to solar and stellar energetic X-and γ ray emissions during normal and flaring conditions are a few problems which have been addressed in these low latitude studies over India. Since the conjugate points of Indian stations lie over the Indian oceanic region, the VLF propagation effects would be relatively free from

  3. Tracker: A three-dimensional raytracing program for ionospheric radio propagation

    SciTech Connect

    Argo, P.E.; DeLapp, D.; Sutherland, C.D.; Farrer, R.G.

    1994-12-01

    TRACKER is an extension of a three-dimensional Hamiltonian raytrace code developed some thirty years ago by R. Michael Jones. Subsequent modifications to this code, which is commonly called the {open_quotes}Jones Code,{close_quotes} were documented by Jones and Stephensen (1975). TRACKER incorporates an interactive user`s interface, modern differential equation integrators, graphical outputs, homing algorithms, and the Ionospheric Conductivity and Electron Density (ICED) ionosphere. TRACKER predicts the three-dimensional paths of radio waves through model ionospheres by numerically integrating Hamilton`s equations, which are a differential expression of Fermat`s principle of least time. By using continuous models, the Hamiltonian method avoids false caustics and discontinuous raypath properties often encountered in other raytracing methods. In addition to computing the raypath, TRACKER also calculates the group path (or pulse travel time), the phase path, the geometrical (or {open_quotes}real{close_quotes}) pathlength, and the Doppler shift (if the time variation of the ionosphere is explicitly included). Computational speed can be traded for accuracy by specifying the maximum allowable integration error per step in the integration. Only geometrical optics are included in the main raytrace code; no partial reflections or diffraction effects are taken into account. In addition, TRACKER does not lend itself to statistical descriptions of propagation -- it requires a deterministic model of the ionosphere.

  4. A Probe of Magnetosphere-Ionosphere Coupling using the Propagation Characteristics of Very Low Frequency Signal

    NASA Astrophysics Data System (ADS)

    Nwankwo, V. U. J.; Chakrabarti, S. K.; Ogunmodimu, O. A.

    2015-12-01

    The amplitude and phase of VLF/LF radio signal are sensitive to changes in the electrical conductivity of the lower ionosphere when propagated in the Earth-ionosphere waveguide. This unique characteristic makes it useful in studying sudden ionospheric disturbances and/or anomaly especially those related to prompt X-ray flux output from solar flares and gamma ray bursts (GRBs). However, strong geomagnetic disturbances and/or storm conditions are known to produce large and global ionospheric disturbances, which can significantly affect VLF radio propagation in the D region ionosphere. Other than X-ray flux enhancement of amplitude and phase, diurnal VLF signature may convey other important information especially those related to geomagnetic disturbance/storm induced ionospheric changes. In this paper, using the data of three propagation paths (at latitudes 40-54), we performed detail analysis of the trend of variations of aspects VLF diurnal signal under varying solar and/or geomagnetic space environmental conditions for identification of possible geomagnetic footprint on the ionosphere. We found that trend of variations significantly reflected the prevailing space weather conditions of various time scales. The `dipping' of the signal diurnal amplitude have shown noteworthy consistency with significantly geomagnetic perturbed and/or storm conditions in the time scale of 1-2 days. We also found that dipping of most MDP signal occurred irrespective of the time (of the day), which an event happened, while those of MBSR, MASS, SRT and SST appear to largely depend on event occurrence time and/or duration. Pre-sunset event had more influence on the SST and MASS (dusk signal), while pre-sunrise event had more influence on the SRT and MBSR (dawn signal), and depending on the duration of the event, impact could be extended to the neighbouring point/component in succession. The induced dipping varied with geomagnetic activity/event intensity and/or duration, as well as the

  5. Analyses of Impedance Microstructure and Wave Propagation Characteristics in Rocks

    NASA Astrophysics Data System (ADS)

    Prasad, M.; Mukerji, T.

    2002-12-01

    Seismic methods are our primary tools to image subsurface structures and to derive information about microstructural properties at subsurface that are pertinent to exploration. However, velocity - physical property transforms are mostly empirical or qualitative in nature, mainly because microstructural descriptions are qualitative. Although, sedimentary systems produce distinctive textures that influence physical properties and seismic signatures, these textures are not quantified in terms comparable to seismic. We present a method to quantify microsctructure in terms of acoustic impedance and show how these microstructural impedance maps can be used to analyze wave propagation characteristics in rocks. Using image analyses techniques, the texture of the calibrated scanned images is quantified by spatial autocorrelation functions and binary morphological operations. Parametric modeling of the empirical autocorrelation functions is used to estimate the textural anisotropy. We quantify microstructural impedance anisotropy and compare these textural maps to ultrasonic velocity anisotropy measurements. Inclusion based effective medium theory is used to upscale the impedances at the microstructural scale to the core plug scale. In the example of optically opaque kerogen-rich shales, we find that 1. Acoustic impedance in kerogen shales increases with shale maturity, 2. Impedance measured on a micrometer scale and centimeter scale match well, indicating that seismic wave propagation are controlled by the microtexture 3. With increasing maturity, there is a transition from kerogen supported to grain supported framework We thank the Fraunhofer Institute for Nondestructive Testing (IZfP) for use of AM facilities, Walter Arnold (IZfP) for discussions about acoustic microscopy, ARCO and SRB Project for support. This work was performed under the auspices of National Science Foundation (Grant No. EAR 0074330) and Department of Energy (Award No. DE-FC26-01BC15354).

  6. 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.

  7. Formulation of Multiple Diffraction by Trees and Buildings for Radio Propagation Predictions for Local Multipoint Distribution Service

    PubMed Central

    Zhang, Wei

    1999-01-01

    This paper presents a closed-form expression for multiple forward diffraction by rows of tree canopies and buildings applicable to the propagation predictions at centimeter and millimeter wavelengths for local multipoint distribution service (LMDS). The expression is derived from the uniform geometrical theory of diffraction and physical optics, as well as from some existing models for vegetation and buildings. When the transmitter antennas are sufficiently high, the attenuation of the buildings varies around the value of free space and the building effect is negligible, because a line-of-sight (LOS) propagation path between transmitter and over building-rooftop receiver antennas exists and plays a major role. The tree canopies which extend above the building rooftop heights block the LOS propagation path and cause additional signal attenuation. An existing study of the LMDS radio channel based on measurements came to the same conclusion. The attenuation effect of the buildings is significant if the transmitter antennas are not high enough.

  8. Characteristic of laser diode beam propagation through a collimating lens.

    PubMed

    Xu, Qiang; Han, Yiping; Cui, Zhiwei

    2010-01-20

    A mathematical model of a laser diode beam propagating through a collimating lens is presented. Wave propagation beyond the paraxial approximation is studied. The phase delay of the laser diode wave in passing through the lens is analyzed in detail. The propagation optical field after the lens is obtained from the diffraction integral by the stationary phase method. The model is employed to predict the light intensity at various beam cross sections, and the computed intensity distributions are in a good agreement with the corresponding measurements.

  9. Turbulent Flame Propagation Characteristics of High Hydrogen Content Fuels

    SciTech Connect

    Seitzman, Jerry; Lieuwen, Timothy

    2014-09-30

    This final report describes the results of an effort to better understand turbulent flame propagation, especially at conditions relevant to gas turbines employing fuels with syngas or hydrogen mixtures. Turbulent flame speeds were measured for a variety of hydrogen/carbon monoxide (H2/CO) and hydrogen/methane (H2/CH4) fuel mixtures with air as the oxidizer. The measurements include global consumption speeds (ST,GC) acquired in a turbulent jet flame at pressures of 1-10 atm and local displacement speeds (ST,LD) acquired in a low-swirl burner at atmospheric pressure. The results verify the importance of fuel composition in determining turbulent flame speeds. For example, different fuel-air mixtures having the same unstretched laminar flame speed (SL,0) but different fuel compositions resulted in significantly different ST,GC for the same turbulence levels (u'). This demonstrates the weakness of turbulent flame speed correlations based simply on u'/SL,0. The results were analyzed using a steady-steady leading points concept to explain the sensitivity of turbulent burning rates to fuel (and oxidizer) composition. Leading point theories suggest that the premixed turbulent flame speed is controlled by the flame front characteristics at the flame brush leading edge, or, in other words, by the flamelets that advance farthest into the unburned mixture (the so-called leading points). For negative Markstein length mixtures, this is assumed to be close to the maximum stretched laminar flame speed (SL,max) for the given fuel-oxidizer mixture. For the ST,GC measurements, the data at a given pressure were well-correlated with an SL,max scaling. However the variation with pressure was not captured, which may be due to non-quasi-steady effects that are not included in the current model. For the ST,LD data, the leading points model again faithfully captured the variation of turbulent flame speed over a wide range of fuel-compositions and turbulence intensities. These results provide

  10. Type 2 solar radio events observed in the interplanetary medium. Part 1: General characteristics

    NASA Technical Reports Server (NTRS)

    Cane, H. V.; Stone, R. G.; Fainberg, J.; Steinberg, J. L.; Hoang, S.

    1980-01-01

    Twelve type 2 solar radio events were observed in the 2 MHz to 30 kHz frequency range by the radio astronomy experiment on the ISEE-3 satellite over the period from September 1978 to December 1979. These data provide the most comprehensive sample of type 2 radio bursts observed at kilometer wavelengths. Dynamic spectra of a number of events are presented. Where possible, the 12 events were associated with an initiating flare, ground based radio data, the passage of a shock at the spacecraft, and the sudden commencement of a geomagnetic storm. The general characteristics of kilometric type 2 bursts are discussed.

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

    SciTech Connect

    Djouadi, Seddik M; Kuruganti, Phani Teja; Nutaro, James J

    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.

  12. Analysis of radio wave propagation for ISM 2.4 GHz Wireless Sensor Networks in inhomogeneous vegetation environments.

    PubMed

    Azpilicueta, Leire; López-Iturri, Peio; Aguirre, Erik; Mateo, Ignacio; Astrain, José Javier; Villadangos, Jesús; Falcone, Francisco

    2014-01-01

    The use of wireless networks has experienced exponential growth due to the improvements in terms of battery life and low consumption of the devices. However, it is compulsory to conduct previous radio propagation analysis when deploying a wireless sensor network. These studies are necessary to perform an estimation of the range coverage, in order to optimize the distance between devices in an actual network deployment. In this work, the radio channel characterization for ISM 2.4 GHz Wireless Sensor Networks (WSNs) in an inhomogeneous vegetation environment has been analyzed. This analysis allows designing environment monitoring tools based on ZigBee and WiFi where WSN and smartphones cooperate, providing rich and customized monitoring information to users in a friendly manner. The impact of topology as well as morphology of the environment is assessed by means of an in-house developed 3D Ray Launching code, to emulate the realistic operation in the framework of the scenario. Experimental results gathered from a measurement campaign conducted by deploying a ZigBee Wireless Sensor Network, are analyzed and compared with simulations in this paper. The scenario where this network is intended to operate is a combination of buildings and diverse vegetation species. To gain insight in the effects of radio propagation, a simplified vegetation model has been developed, considering the material parameters and simplified geometry embedded in the simulation scenario. An initial location-based application has been implemented in a real scenario, to test the functionality within a context aware scenario. The use of deterministic tools can aid to know the impact of the topological influence in the deployment of the optimal Wireless Sensor Network in terms of capacity, coverage and energy consumption, making the use of these systems attractive for multiple applications in inhomogeneous vegetation environments. PMID:25513820

  13. Analysis of Radio Wave Propagation for ISM 2.4 GHz Wireless Sensor Networks in Inhomogeneous Vegetation Environments

    PubMed Central

    Azpilicueta, Leire; López-Iturri, Peio; Aguirre, Erik; Mateo, Ignacio; Astrain, José Javier; Villadangos, Jesús; Falcone, Francisco

    2014-01-01

    The use of wireless networks has experienced exponential growth due to the improvements in terms of battery life and low consumption of the devices. However, it is compulsory to conduct previous radio propagation analysis when deploying a wireless sensor network. These studies are necessary to perform an estimation of the range coverage, in order to optimize the distance between devices in an actual network deployment. In this work, the radio channel characterization for ISM 2.4 GHz Wireless Sensor Networks (WSNs) in an inhomogeneous vegetation environment has been analyzed. This analysis allows designing environment monitoring tools based on ZigBee and WiFi where WSN and smartphones cooperate, providing rich and customized monitoring information to users in a friendly manner. The impact of topology as well as morphology of the environment is assessed by means of an in-house developed 3D Ray Launching code, to emulate the realistic operation in the framework of the scenario. Experimental results gathered from a measurement campaign conducted by deploying a ZigBee Wireless Sensor Network, are analyzed and compared with simulations in this paper. The scenario where this network is intended to operate is a combination of buildings and diverse vegetation species. To gain insight in the effects of radio propagation, a simplified vegetation model has been developed, considering the material parameters and simplified geometry embedded in the simulation scenario. An initial location-based application has been implemented in a real scenario, to test the functionality within a context aware scenario. The use of deterministic tools can aid to know the impact of the topological influence in the deployment of the optimal Wireless Sensor Network in terms of capacity, coverage and energy consumption, making the use of these systems attractive for multiple applications in inhomogeneous vegetation environments. PMID:25513820

  14. The Coherer: With Simple Demonstrations of the Generation, Propagation and Detection of Radio Waves

    ERIC Educational Resources Information Center

    Mills, Allan

    2010-01-01

    A coherer is a bistable device based on metal filings loosely confined between solid metal electrodes. This granular material normally exhibits a very high electrical resistance (tens of kilohms), but passage of the high-frequency current generated by reception of a radio signal causes it to "cohere" into a comparatively low resistance condition…

  15. 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…

  16. Enhanced MUF propagation of HF radio waves in the auroral zone

    NASA Astrophysics Data System (ADS)

    Milan, S. E.; Jones, T. B.; Warrington, E. M.

    1997-01-01

    Four high frequency propagation paths were monitored from a transmitter located within the polar cap by four receivers located variously within the polar cap and at sub-auroral latitudes. Of these paths, one was contained entirely within the polar cap at all times, two were trans-auroral at all times, and one varied from trans-auroral during the day to polar cap during the night. Fourteen frequencies within the HF band were transmitted each hour for the duration of two 24 day experimental campaigns during the summer of 1988 and the winter of 1989. From an analysis of the received signals the confidence of signal recognition and signal strength were determined. During geomagnetically undisturbed periods the propagation behaviour resembled that of mid-latitude paths. During geomagnetically disturbed times, however, night-time propagation occurred on frequencies up to and sometimes over 10 MHz above the undisturbed night-time MUF, for periods of 2 to 6 h. These features appeared on the trans-auroral paths only and were attributed to E region (and occasionally F region) enhancement by auroral precipitation. APEs (auroral E propagation events) occurred on over 50% of nights. The occurrence of APEs also coincided with ionospheric storm periods when the HF band available for propagation was otherwise significantly narrowed due to a depletion of the F region electron density.

  17. Characteristics of lightning leader propagation and ground attachment

    NASA Astrophysics Data System (ADS)

    Jiang, Rubin; Qie, Xiushu; Wang, Zhichao; Zhang, Hongbo; Lu, Gaopeng; Sun, Zhuling; Liu, Mingyuan; Li, Xun

    2015-12-01

    The grounding process and the associated leader behavior were analyzed by using high-speed video record and time-correlated electric field change for 37 natural negative cloud-to-ground flashes. Weak luminous grounded channel was recognized below the downward leader tip in the frame preceding the return stroke, which is inferred as upward connecting leader considering the physical process of lightning attachment, though not directly confirmed by sequential frames. For stepped leader-first return strokes, the upward connecting leaders tend to be induced by those downward leader branches with brighter luminosity and lower channel tip above ground, and they may accomplish the attachment with great possibility. The upward connecting leaders for 2 out of 61 leader-subsequent stroke sequences were captured in the frame prior to the return stroke, exhibiting relatively long channel lengths of 340 m and 105 m, respectively. The inducing downward subsequent leaders were of the chaotic type characterized by irregular electric field pulse train with duration of 0.2-0.3 ms. The transient drop of the high potential difference between stepped leader system and ground when the attachment occurred would macroscopically terminate the propagation of those ungrounded branches while would not effectively prevent the development of the existing space stem systems in the low-conductivity streamer zone apart from the leader tip. When the ungrounded branches are of poor connection with the main stroke channel, their further propagation toward ground would be feasible. These two factors may contribute to the occurrence of multiple grounding within the same leader-return stroke sequence.

  18. Communication interference/jamming and propagation analysis system and its application to radio location

    NASA Astrophysics Data System (ADS)

    Kuzucu, H.

    1992-11-01

    Modern defense systems depend on comprehensive surveillance capability. The ability to detect and locate the radio signals is a major element of a surveillance system. With the increasing need for more mobile surveillance systems in conjunction with the rapid deployment of forces and the advent of technology allowing more enhanced use of small aperture systems, tactical direction finding (DF) and radiolocation systems will have to be operated in diverse operational conditions. A quick assessment of the error levels expected and the evaluation of the reliability of the fixes on the targeted areas bears crucial importance to the effectiveness of the missions relying on DF data. This paper presents a sophisticated, graphics workstation based computer tool developed for the system level analysis of radio communication systems and describes its use in radiolocation applications for realizing such accurate and realistic assessments with substantial money and time savings.

  19. 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.

  20. Galactic synchrotron radiation from radio to microwaves, and its relation to cosmic-ray propagation models: past, present and future

    NASA Astrophysics Data System (ADS)

    Orlando, Elena

    2016-04-01

    Galactic synchrotron radiation observed from radio to microwaves is produced by cosmic-ray (CR) electrons propagating in magnetic fields (B-fields). The low-frequency foreground component separated maps by WMAP and Planck depend on the assumed synchrotron spectrum. The synchrotron spectrum varies for different line of sights as a result of changes on the CR spectrum due to propagation effects and source distributions. Our present knowledge of the CR spectrum at different locations in the Galaxy is not sufficient to distinguish various possibilities in the modeling. As a consequence uncertainties on synchrotron emission models complicate the foreground component separation analysis with Planck and future microwave telescopes. Hence, any advancement in synchrotron modeling is important for separating the different foreground components.The first step towards a more comprehensive understanding of degeneracy and correlation among the synchrotron model parameters is outlined in our Strong et al. 2011 and Orlando et al. 2013 papers. In the latter the conclusion was that CR spectrum, propagation models, B-fields, and foreground component separation analysis need to be studied simultaneously in order to properly obtain and interpret the synchrotron foreground. Indeed for the officially released Planck maps, we use only the best spectral model from our above paper for the component separation analysis.Here we present a collections of our latest results on synchrotron, CRs and B-fields in the context of CR propagation, showing also our recent work on B-fields within the Planck Collaboration. We underline also the importance of using the constraints on CRs that we obtain from gamma ray observations. Methods and perspectives for further studies on the synchrotron foreground will be addressed.

  1. [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.

  2. Method of Transverse Displacements Formulation for Calculating the HF Radio Wave Propagation Paths. Statement of the Problem and Preliminary Results

    NASA Astrophysics Data System (ADS)

    Nosikov, I. A.; Bessarab, P. F.; Klimenko, M. V.

    2016-06-01

    Fundamentals of the method of transverse displacements for calculating the HF radio-wave propagation paths are presented. The method is based on the direct variational principle for the optical path functional, but is not reduced to solving the Euler—Lagrange equations. Instead, the initial guess given by an ordered set of points is transformed successively into a ray path, while its endpoints corresponding to the positions of the transmitter and the receiver are kept fixed throughout the entire iteration process. The results of calculation by the method of transverse displacements are compared with known analytical solutions. The importance of using only transverse displacements of the ray path in the optimization procedure is also demonstrated.

  3. Multi-flare study of acceleration region characteristics using combined X-ray and Radio Observations

    NASA Astrophysics Data System (ADS)

    Reid, Hamish; Kontar, Eduard; Vilmer, Nicole

    2012-07-01

    Using emission in X-ray and radio wavelengths, we infer properties of accelerated electrons to indirectly obtain estimates about flare acceleration regions. We have selected a list of events using the RHESSI flare catalogue and the PHOENIX 2 radio burst list that show temporally correlated X-ray and radio emission. We find some events show a very good anti-correlation between the hard X-ray spectral index and the starting frequency of type III bursts. We use this information to constrain the distance an outwardly propagating electron beam can travel before it undergoes the bump-in-tail instability. By assuming the height dependence of the background electron density we are able to observationally estimate the height and vertical extent of a variety of different solar flare acceleration regions. We verify the feasibility of these predictions by using kinetic simulations to check the Langmuir wave-particle instability distance for electron beam.

  4. Unstructured grid finite volume analysis for acoustic and pulsed wave propagation characteristics in exhaust silencer systems

    SciTech Connect

    Kim, J.T.; Kim, Y.M.; Maeng, J.S.; Lyu, M.S.; Ku, Y.G.

    1996-10-01

    The unstructured grid finite volume method has been applied to predict the linear and nonlinear attenuation characteristics of the expansion chamber type silencer system. In order to achieve grid flexibility and a solution adaptation for geometrically complex flow regions associated with the actual silencers, the unstructured mesh algorithm in context with the node-centered finite volume method has been employed. The validation cases for the linear and nonlinear wave propagation characteristics include the acoustic field of the concentric expansion chamber and the axisymmetric blast flow field with the open end. Effects of the chamber geometry on the nonlinear wave propagation characteristics are discussed in detail.

  5. Radio polarization characteristics of two RS CVn binaries

    NASA Technical Reports Server (NTRS)

    Mutel, R. L.; Lestrade, J.-F.; Doiron, D. J.

    1985-01-01

    The results of multifrequency epoch VLA observations of polarized radio emission from the nearby active RS CVn binaries UX Arietis and HR 1099 are reported. For both systems, there is an excellent correlation between handedness of circular polarization and frequency. Helicity reversal is almost always seen between 1.4 and 5.0 GHz, possibly due to optical depth effects. There may also be an anticorrelation between total intensity and fractional circular polarization, especially at 5 GHz. This is consistent with models in which intense flares are associated with compact selfabsorbed synchrotron sources, while the quiescent emission arises from larger gyrosynchrotron-emitting plasma.

  6. Flare-generated Shock Wave Propagation through Solar Coronal Arcade Loops and an Associated Type II Radio Burst

    NASA Astrophysics Data System (ADS)

    Kumar, Pankaj; Innes, D. E.; Cho, Kyung-Suk

    2016-09-01

    This paper presents multiwavelength observations of a flare-generated type II radio burst. The kinematics of the shock derived from the type II burst closely match a fast extreme ultraviolet (EUV) wave seen propagating through coronal arcade loops. The EUV wave was closely associated with an impulsive M1.0 flare without a related coronal mass ejection, and was triggered at one of the footpoints of the arcade loops in active region NOAA 12035. It was initially observed in the 335 Å images from the Atmospheric Image Assembly with a speed of ˜800 km s‑1 and it accelerated to ˜1490 km s‑1 after passing through the arcade loops. A fan–spine magnetic topology was revealed at the flare site. A small, confined filament eruption (˜340 km s‑1) was also observed moving in the opposite direction to the EUV wave. We suggest that breakout reconnection in the fan–spine topology triggered the flare and associated EUV wave that propagated as a fast shock through the arcade loops.

  7. Flare-generated Shock Wave Propagation through Solar Coronal Arcade Loops and an Associated Type II Radio Burst

    NASA Astrophysics Data System (ADS)

    Kumar, Pankaj; Innes, D. E.; Cho, Kyung-Suk

    2016-09-01

    This paper presents multiwavelength observations of a flare-generated type II radio burst. The kinematics of the shock derived from the type II burst closely match a fast extreme ultraviolet (EUV) wave seen propagating through coronal arcade loops. The EUV wave was closely associated with an impulsive M1.0 flare without a related coronal mass ejection, and was triggered at one of the footpoints of the arcade loops in active region NOAA 12035. It was initially observed in the 335 Å images from the Atmospheric Image Assembly with a speed of ˜800 km s-1 and it accelerated to ˜1490 km s-1 after passing through the arcade loops. A fan-spine magnetic topology was revealed at the flare site. A small, confined filament eruption (˜340 km s-1) was also observed moving in the opposite direction to the EUV wave. We suggest that breakout reconnection in the fan-spine topology triggered the flare and associated EUV wave that propagated as a fast shock through the arcade loops.

  8. Diagnostic study of coupled solar wind-magnetosphere-ionosphere dynamics in D-region ionosphere via VLF signal propagation characteristic

    NASA Astrophysics Data System (ADS)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip Kumar

    2016-07-01

    Geomagnetic disturbances and storms are known to produce significant global disturbances in the ionosphere, including the middle atmosphere and troposphere. There is little understanding about the mechanism and dynamics that drive these processes in lower ionosphere. The ionosphere is also thought to be sensitive to seismic events, and it is believed that it exhibits precursory characteristics as reported in studies via characteristic anomalies in VLF signal. However, distinguishing or separating seismically induced ionospheric fluctuations from those of other origins (e.g., Solar activity, planetary and tidal waves, stratospheric warming etc.) remain vital to robust conclusion, and challenging too. The unique propagation characteristic of VLF radio signal makes it an ideal tool for the study and diagnosis of variability of D-region ionosphere. In this work, we present the analysis of solar wind-magnetosphere-ionosphere coupling dynamics in D-region ionosphere using VLF signal characteristics, and performed an investigation of previously reported 'ionospheric precursors' to understand the true origins of measured anomalies.

  9. A new model of amplitude fluctuations for radio propagation in solar corona during superior solar conjunction

    NASA Astrophysics Data System (ADS)

    Xu, Guanjun; Song, Zhaohui

    2016-02-01

    Radio communication links through the solar corona are disturbed by electron density fluctuations caused by coronal turbulence. This has become a problem for deep space exploration when the spacecraft is near superior conjunction with the Sun. With a forecast of the signal fluctuations the link could be adapted to compensate for these impairments in real time. Motivated by this need, we present a theoretical study of the signal fluctuations including an analytical expression for the amplitude fluctuations. The proposed model includes an anisotropic spectrum of density fluctuations, the solar wind "outer scale," and the spectral exponent. The performance of this analytical solution is demonstrated by comparison with published data from spacecraft and with other existing analytical methods.

  10. Propagation influences on the performance of a reduced bandwidth quadrature phase shift keyed digital radio system

    NASA Astrophysics Data System (ADS)

    Doble, J. E.

    1984-10-01

    British Telecom is running a field trial of a spectrally efficient (4.2 bits/Hz) reduced bandwidth quadrature phase shift keyed digital radio system for the lower 6 GHz and 4 GHz bands in a part of the UK that is subject to above average multipath activity. Some of the observations made during a two-year period are described together with the improvements made to the antennas and the methods likely to be used in predicting system performance in other locations. The current method of predicting multipath fading is examined and found wanting in its application to digital system planning. An alternative is put forward and an example of its use is given.

  11. Effect of Seasonal Variation of Anomalous Condition on Radio Propagation in Nigeria

    NASA Astrophysics Data System (ADS)

    Emmanuel, Israel; Adeyemi, Babatunde; Ogolo, Emmanuel; Adediji, Adekunle

    Daily variation of effective earth radius factor and seasonal variation of refractivity gradients from surface to around 1000 m above ground level in the tropospheric layer are presented based on observation from the meteorological data obtain from ECMWF database. Thirty four years (1979 -2014) of data from surface and profile of Era Interim of the temperature and relative humidity are used to determine the surface anomalous propagation over some selected location I Nigeria. Estimation of anomalous propagation are observed for onset and peak of rainy and dry seasons. The occurrence of anomalous strongly depends on the local time and synoptic weather conditions which have an appreciable on the refractivity vertical profile, especially the seasonal north - south movement of inter tropical Convergence Zone (ITCD) which provide wet and dry seasonal variations of anomalous were also determined. Spatial distribution of refractivity gradient for both wet and dry seasons are also obtained. The highest occurrence of duct were noticed in the night and morning (00:00 UTC and 06:00UTC) across the country though it was low in the northern part of the country, while low or no occurrence of duct were observed in the afternoon and evening (12:00 UTC and 18:00 UTC). Also percentage occurrence of duct were also high and low during the wet and dry seasons respectively.

  12. Cascaded neural networks for sequenced propagation estimation, multiuser detection, and adaptive radio resource control of third-generation wireless networks for multimedia services

    NASA Astrophysics Data System (ADS)

    Hortos, William S.

    1999-03-01

    A hybrid neural network approach is presented to estimate radio propagation characteristics and multiuser interference and to evaluate their combined impact on throughput, latency and information loss in third-generation (3G) wireless networks. The latter three performance parameters influence the quality of service (QoS) for multimedia services under consideration for 3G networks. These networks, based on a hierarchical architecture of overlaying macrocells on top of micro- and picocells, are planned to operate in mobile urban and indoor environments with service demands emanating from circuit-switched, packet-switched and satellite-based traffic sources. Candidate radio interfaces for these networks employ a form of wideband CDMA in 5-MHz and wider-bandwidth channels, with possible asynchronous operation of the mobile subscribers. The proposed neural network (NN) architecture allocates network resources to optimize QoS metrics. Parameters of the radio propagation channel are estimated, followed by control of an adaptive antenna array at the base station to minimize interference, and then joint multiuser detection is performed at the base station receiver. These adaptive processing stages are implemented as a sequence of NN techniques that provide their estimates as inputs to a final- stage Kohonen self-organizing feature map (SOFM). The SOFM optimizes the allocation of available network resources to satisfy QoS requirements for variable-rate voice, data and video services. As the first stage of the sequence, a modified feed-forward multilayer perceptron NN is trained on the pilot signals of the mobile subscribers to estimate the parameters of shadowing, multipath fading and delays on the uplinks. A recurrent NN (RNN) forms the second stage to control base stations' adaptive antenna arrays to minimize intra-cell interference. The third stage is based on a Hopfield NN (HNN), modified to detect multiple users on the uplink radio channels to mitigate multiaccess

  13. Trends in Performance and Characteristics of Ultra-Stable Oscillators for Deep Space Radio Science Experiments

    NASA Technical Reports Server (NTRS)

    Asmar, Sami

    1997-01-01

    Telecommunication systems of spacecraft on deep space missions also function as instruments for Radio Science experiments. Radio scientists utilize the telecommunication links between spacecraft and Earth to examine very small changes in the phase/frequency, amplitude, and/or polarization of radio signals to investigate a host of physical phenomena in the solar system. Several missions augmented the radio communication system with an Ultra-Stable Oscillator (USO) in order to provide a highly stable reference signal for oneway downlink. This configuration is used in order to enable better investigations of the atmospheres of the planets occulting the line-of-sight to the spacecraft; one-way communication was required and the transponders' built-in auxiliary oscillators were neither sufficiently stable nor spectrally pure for the occultation experiments. Since Radio Science instrumentation is distributed between the spacecraft and the ground stations, the Deep Space Network (DSN) is also equipped to function as a world-class instrument for Radio Science research. For a detailed account of Radio Science experiments, methodology, key discoveries, and the DSN's historical contribution to the field, see Asmar and Renzetti (1993). The tools of Radio Science can be and have also been utilized in addressing several mission engineering challenges; e.g., characterization of spacecraft nutation and anomalous motion, antenna calibrations, and communications during surface landing phases. Since the first quartz USO was flown on Voyager, the technology has advanced significantly, affording future missions higher sensitivity in reconstructing the temperature pressure profiles of the atmospheres under study as well as other physical phenomena of interest to Radio Science. This paper surveys the trends in stability and spectral purity performance, design characteristics including size and mass, as well as cost and history of these clocks in space.

  14. Radio propagation at 900 MHz in urban areas: Models with a fixed frequency and experimental results

    NASA Astrophysics Data System (ADS)

    Olivier, P.; Tiffon, J.

    1984-09-01

    Models which describe multipath propagation are examined in order to design a 900 MHz mobile communication system adapted to urban areas. A justification of the experimental data treatment is derived from this analysis. The measurements were made at a fixed 855 MHz frequency, transmitting from three locations. The fast fluctuations of the received signals are well represented by a Rayleigh process, which means that there are practically no paths of direct transmission. The coherence length is 1 m. The statistical distribution of the average field is Gaussian and the normal deviation decreases with the distance emitter-receiver. The empiric Okumura-Hata prediction model agrees well with the experimental results, giving an average cell field decreasing with distance with a logarithmic law.

  15. Simultaneous observation of VHF radio wave transmission anomaly propagated beyond line of site prior to earthquakes in multiple sites

    NASA Astrophysics Data System (ADS)

    Yamashita, H.; Mogi, T.; Moriya, T.; Takada, M.; Morisada, M.

    2010-12-01

    The VHF radio wave transmission anomalies propagated beyond line of site prior to earthquakes (M>4), (hereafter termed EQ-echo) have been observed more than 20 times from 2004 at the Erimo observatory (ERM) in Hokkaido, Northern Japan. A statistical relationship between magnitude of preceding earthquake and total duration time of the EQ-echo has been proposed (Moriya et al.2009). To confirm a region where the EQ-echo simultaneously observed for each earthquake, we installed another 3 observatory with approximately 5 km spacing in the surroundings of ERM. The EQ-echoes have been observed simultaneously at two observatories prior to four earthquakes since 2008. The initial time and duration of each EQ echo were same time in several cases but different at some minutes each other in other cases. The wave forms of the EQ-echoes were similar in both records. In the Fuyushima observatory (FYS, 10km away from ERM) , three-way antennas were installed at every 120 degree to detect an arrival direction of EQ-echoes. Simultaneous observations of EQ-echoes at ERM and FYS for the preceding EQ (M=4.7) that occurred in the Hidaka mountains revealed that this EQ-echo came from direction of the epicenter based on the FYS observation and this direction was consistent with that of EQ-echo observed simultaneously in ERM. Although some of simultaneous observed EQ-echoes were observed in same time completely at both observatories, but some of them were with time rag of duration of each EQ-echo between multiple observed sites. We discussed what these time rags mean by considering possibilities of moving of scattering objects, generation of a radio duct, and so on, as in response to this fact.

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

    SciTech Connect

    Wang Ying; Yuan Chengxun; Zhou Zhongxiang; Gao Ruilin; Li Lei; Du Yanwei

    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.

  17. Delay time measurements of the propagation of radio waves in the atmosphere

    NASA Technical Reports Server (NTRS)

    Rohde, F.

    1972-01-01

    The characteristics and operation of the Geodetic Secor System are described. The precision of the ionospheric radiation measurements was determined by a collocation experiment. The EGRS-13 satellite, which was used in the experiment, is discussed. The geodetic network is shown in a diagram form. Conclusions resulting from the experiments are reported.

  18. Propagation properties and dispersion characteristics of the tapered gap plasmonic waveguides

    NASA Astrophysics Data System (ADS)

    Sheikhi, Kamran; Granpayeh, Nosrat; Ahmadi, Vahid

    2016-08-01

    In this study, we numerically analyse the propagation properties and dispersion characteristics of the tapered gap plasmonic waveguides (TGPWs). Using the finite element method, the waveguide parameters such as modal field distribution and complex propagation constant are calculated for different geometrical parameters over a wide spectral range. Moreover, using a kind of active medium with appropriate gain, the required gains for lossless propagation are obtained. Results show that the propagation properties and dispersion characteristics of the waveguide along with the value of required gain for achieving lossless propagation can be well controlled by adjusting the geometrical parameters of the waveguide. The simulation results indicate that the calculated gain values are obtainable using the existing semiconductor technology such as InGaAsP-InGaAlAs multi-quantum well and InAs/GaAs quantum dot active medium at the wavelength of 1550 nm. The strong mode confinement of the TGPWs can be used for achieving strong nonlinear effects. Furthermore, due to optical energy confinement in nanoscale, optical nanofocusing devices based on TGPWs are attainable. TGPWs can be utilized in the field of nanotechnology to fulfil the photonic devices integration.

  19. Numerical investigation of fast-wave propagation and radio-frequency sheath interaction with a shaped tokamak wall

    SciTech Connect

    Kohno, H.; Myra, J. R.; D'Ippolito, D. A.

    2015-07-15

    Interactions between propagating fast waves and radio-frequency (RF) sheaths in the ion cyclotron range of frequencies are numerically investigated based on a cold fluid plasma model coupled with a sheath boundary condition. In this two-dimensional study, the capability of the finite element code rfSOL, which was developed in previous numerical work, is extended to analyze self-consistent RF sheath-plasma interaction problems in a tokamak with a non-circular cross-section. It is found that a large sheath voltage is generated near the edges of the limiter-shaped deformation as a result of the conversion from fast to slow waves on the sheaths. The sheath voltage associated with this conversion is particularly significant in the localized region where the contact angle between the magnetic field line and the conducting wall varies rapidly along the curved sheath surface, which is consistent with the results in previous one-dimensional theoretical work. The dependences of the RF sheaths on various parameters in plasma such as the toroidal wavenumber, edge plasma density, and the degree of the RF wave absorption in the core region are also examined in detail.

  20. 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.

  1. Characteristics of radio-frequency, atmospheric-pressure glow discharges with air using bare metal electrodes

    SciTech Connect

    Wang Huabo; Sun Wenting; Li Heping; Bao Chengyu; Zhang Xiaozhang

    2006-10-16

    In this letter, an induced gas discharge approach is proposed and described in detail for obtaining a uniform atmospheric-pressure glow discharge with air in a {gamma} mode using water-cooled, bare metal electrodes driven by radio-frequency (13.56 MHz) power supply. A preliminary study on the discharge characteristics of the air glow discharge is also presented in this study. With this induced gas discharge approach, radio-frequency, atmospheric-pressure glow discharges using bare metal electrodes with other gases which cannot be ignited directly as the plasma working gas, such as nitrogen, oxygen, etc., can also be obtained.

  2. Solar longitude dependence of some characteristics of type III radio bursts from metric to hectometric wavelengths

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1974-01-01

    Using the observed data for metric and hectometric type III radio bursts, the dependence of burst characteristics on the solar longitude has been examined over a wide frequency range. It is found that there exists and east-west asymmetry for the extension of metric type III bursts into the hectometric wavelength range. In particular, hectometric bursts are rarely observed for solar flares associated with metric bursts east of 60 E solar longitude. Furthermore, for east longitudes, the low-frequency radio observations show a large dispersion in drift time interval.

  3. Propagation characteristics of the magnetostatic surface wave in the YBCO-YIG film-layered structure

    SciTech Connect

    Tsutsumi, M.; Fukusako, T.; Yoshida, S.

    1996-08-01

    Propagation characteristics of the magnetostatic surface wave (MSSW) in a YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} (YBCO)-yttrium iron garnet (YIG) multilayered structure are investigated. Effects of the superconductor on the MSSW are discussed with regard to the dispersion characteristics of both the phase and attenuation constants as a function of the air gap between YIG and YBCO, taking into consideration the magnetic line-width of the YIG film. It was found that the nonreciprocity of MSSW is enhanced significantly by the superconductivity and depends on the magnetic line-width of the YIG film. To examine the effect of a YBCO on the MSSW propagation, experiments are carried out using a commercially available YIG film. Magnetic losses at low temperature are briefly discussed with experimentally observed nonreciprocity.

  4. Energetic Particle Propagation in the Inner Heliosphere as Deduced from Low Frequency (less than 100 kHz) Observations of Type III Radio Bursts

    NASA Technical Reports Server (NTRS)

    Cane, H. V.; Erickson, W. C.

    2003-01-01

    Solar energetic particle (SEP) events are well-associated with solar flares. It is observed that the delay between the time of the flare and the first-arriving particles at a spacecraft increases with increasing difference between the flare longitude and the footpoint of the field line on which the spacecraft is located. This difference we call the "connection angle" and can be as large as approximately 120 deg. Recently it has been found that all SEP events are preceded by type III radio bursts. These bursts are plasma emission caused by the propagation of 2-50 keV flare electrons through the solar corona and into the solar wind. The drift of these type III radio bursts to lower and lower frequencies enables the propagation of the flare electrons to be traced from the Sun to about 1 AU. We have made an extensive analysis of the type III bursts associated with greater than 20 MeV proton events and find that, in most cases, the radio emission extends to the local plasma frequency when the energetic particles arrive within a few hours of the flare. We conclude that this emission at the lowest possible frequency is generated close to the spacecraft. We then use the time from when the burst started at the Sun to when it reached the local plasma frequency to infer the time it took the radio producing electrons to travel to the spacecraft. We find that these delay times are organized by the connection angle and correlate with the proton delay times. We also find that the differences between the radio delays at Wind and Ulysses are matched by differences in the relative arrival times of the energetic particles at the two spacecraft. The consistent timing between the relative arrival times of energetic electrons and protons and the start of the lowest frequency radio emissions suggests that the first arriving particles of both species are accelerated as part of the flare process and that they propagate to the spacecraft along trajectories similar to those of the lower

  5. Propagation characteristics of decentered annular beams through non-Kolmogorov turbulence.

    PubMed

    Li, Xiaoqing; Ji, Xiaoling

    2014-01-01

    This paper studies the propagation characteristics related to higher-order moments of decentered annular beams through non-Kolmogorov turbulence. The analytical expressions for the mean-squared beam width w, the skewness parameter A, and the kurtosis parameter K are derived. The analytical expression for the non-Kolmogorov turbulence parameter T' is also derived, and the differences between two non-Kolmogorov turbulence parameters T' and T are examined. It is shown that K depends on both T and T', but w and A only depend on T. K decreases monotonically as the spectral power law exponent α increases, but there exist a maximum of w and a minimum of A when α=3.112. When propagation distance z is long enough, A reaches zero, i.e., the intensity distribution is perfectly symmetric about the centroid position axis. In free space, both A>0 and A<0 may appear on propagation. However, it is always A>0 or A<0 on propagation when turbulence is not weak. On the other hand, in turbulence, the maximum of K increases as the decentered parameter increases and the obscure ratio decreases. In particular, when z is long enough, the beam spot is elliptical in free space, but it becomes circular in turbulence.

  6. Study of performance and propagation characteristics of wire and planar structures around human body.

    PubMed

    Aroul, A L Praveen; Bhatia, Dinesh

    2011-01-01

    Continued miniaturization of electronic devices and technological advancements in wireless communications has made wearable body-centric telemedicine systems viable. Antennas play a crucial role in characterizing the efficiency and reliability of these systems. The performance characteristics such as the radiation pattern, gain, efficiency of the antennas get adversely affected due to the presence of lossy human body tissues. In this paper we investigate the above mentioned performance parameters and radio frequency transmission properties of wire and planar structures operating at ISM frequency band of 2.40-2.50 GHz in the proximity of human body.

  7. Turbid media optical properties derived from the characteristics of propagating laser radiation beams

    NASA Astrophysics Data System (ADS)

    Gurdev, Ljuan; Dreischuh, Tanja; Vankov, Orlin; Bliznakova, Irina; Avramov, Lachezar; Stoyanov, Dimitar

    2014-06-01

    The possibility is studied to develop a straightforward analytical approach to the determination of the optical properties of liquid turbid media having forward-peaked scattering indicatrices. The approach is based on investigating the in-depth behavior of the radius and the axial intensity of a laser radiation beam propagating through the turbid medium. Based on the small-angle approximation, the detected forward-propagating light power spatial distribution, at relatively small or large optical depths along the beam axis, is obtained asymptotically in analytical form allowing one to derive relatively simple expressions of the extinction, reduced-scattering and absorption coefficients and the anisotropy factor of the medium through the characteristics of the propagating light beam. Preliminary experiments have also been performed, using Intralipid dilutions of different relatively low concentrations and measuring the cross-sectional radial distribution of the detected light power at different depths along the beam axis. The corresponding on-axis detected light power profiles have been measured independently as well. The experimental results are consistent with the analytical expressions obtained that allow one to estimate the optical coefficients and the anisotropy factor of the investigated media on the basis of the measured beam characteristics. The values obtained are near those predicted by other researchers.

  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. Discharge characteristics of atmospheric-pressure radio-frequency glow discharges with argon/nitrogen

    SciTech Connect

    Wang Huabo; Sun Wenting; Li Heping; Bao Chengyu; Gao Xing; Luo Huiying

    2006-10-16

    In this letter, atmospheric-pressure glow discharges in {gamma} mode with argon/nitrogen as the plasma-forming gas using water-cooled, bare copper electrodes driven by radio-frequency power supply at 13.56 MHz are achieved. The preliminary studies on the discharge characteristics show that, induced by the {alpha}-{gamma} coexisting mode or {gamma} mode discharge of argon, argon-nitrogen mixture with any mixing ratios, even pure nitrogen, can be employed to generate the stable {gamma} mode radio-frequency, atmospheric-pressure glow discharges and the discharge voltage rises with increasing the fraction of nitrogen in the argon-nitrogen mixture for a constant total gas flow rate.

  10. VLF Waveguide Propagation: The Basics

    NASA Astrophysics Data System (ADS)

    Lynn, Kenneth J. W.

    2010-10-01

    In recent times, research has moved towards using VLF radio transmissions propagating in the earth-ionosphere waveguide as a detector of a variety of transient geophysical phenomena. A correct interpretation of such results depends critically on understanding the propagation characteristics of the path being monitored. The observed effects will vary depending on time of day, path length, path orientation, magnetic latitude and VLF frequency. This paper provides a brief tutorial of the relevant propagation dependencies for medium to long VLF paths best understood in terms of waveguide mode theory together with results either not previously published, not published in the open scientific literature or whose significance has been little recognised.

  11. A time-dependent neutron transport method of characteristics formulation with time derivative propagation

    NASA Astrophysics Data System (ADS)

    Hoffman, Adam J.; Lee, John C.

    2016-02-01

    A new time-dependent Method of Characteristics (MOC) formulation for nuclear reactor kinetics was developed utilizing angular flux time-derivative propagation. This method avoids the requirement of storing the angular flux at previous points in time to represent a discretized time derivative; instead, an equation for the angular flux time derivative along 1D spatial characteristics is derived and solved concurrently with the 1D transport characteristic equation. This approach allows the angular flux time derivative to be recast principally in terms of the neutron source time derivatives, which are approximated to high-order accuracy using the backward differentiation formula (BDF). This approach, called Source Derivative Propagation (SDP), drastically reduces the memory requirements of time-dependent MOC relative to methods that require storing the angular flux. An SDP method was developed for 2D and 3D applications and implemented in the computer code DeCART in 2D. DeCART was used to model two reactor transient benchmarks: a modified TWIGL problem and a C5G7 transient. The SDP method accurately and efficiently replicated the solution of the conventional time-dependent MOC method using two orders of magnitude less memory.

  12. Multi-Band (K- Q- and E-Band) Multi-Tone Millimeter-Wave Frequency Synthesizer for Radio Wave Propagation Studies

    NASA Technical Reports Server (NTRS)

    Simons, Rainee N.; Wintucky, Edwin G.

    2014-01-01

    This paper presents the design and test results of a multi-band multi-tone millimeter-wave frequency synthesizer, based on a solid-state frequency comb generator. The intended application of the synthesizer is in a space-borne transmitter for radio wave atmospheric studies at K-band (18 to 26.5 GHz), Q-band (37 to 42 GHz), and E-band (71 to 76 GHz). These studies would enable the design of robust multi-Gbps data rate space-to-ground satellite communication links. Lastly, the architecture for a compact multi-tone beacon transmitter, which includes a high frequency synthesizer, a polarizer, and a conical horn antenna, has been investigated for a notional CubeSat based space-to-ground radio wave propagation experiment.

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

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Papapolymerou, John; Tentzeris, Emmanouil M.; Williams, W. O. (Technical Monitor)

    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 15.5 Ohm cm) and a 20 micron thick polyimide interface layer is 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 Ohm cm has greater loss than substrates with higher and lower resistivity. Lastly, substrates with a resistivity of 10 Ohm cm or greater have acceptable loss.

  14. The use of the spectral matrix in analyzing the propagation characteristics of electromagnetic emissions

    NASA Astrophysics Data System (ADS)

    Lefeuvre, F.; Parrot, M.

    1984-09-01

    Estimations of all or part of the power spectra of the wave field components of an electromagnetic emission, observed on GEOS and ISEE satellites are used to obtain information on the wave field, and to determine the wave distribution function (WDF). Knowledge of 3 X 3 spectral matrix of the magnetic wave field components provides information on the degree of polarization of the wave and on the validity of the plane wave approximation. Full information on the propagation characteristics of a sum of waves, or of random wave fields, is also obtained from the spectral matrix using either multiplane wave models or WDF models.

  15. Error propagation characteristic analysis of halo orbit based on condition number of state transition matrix

    NASA Astrophysics Data System (ADS)

    Sun, Yu; Zhang, Jin

    2016-09-01

    The error propagation characteristics of different points of a halo orbit are studied in this paper. The condition number of state transition matrix after a period is used to estimate the sensitivity of different positions on a halo orbit to the state errors. Then the covariance propagation method is applied to compute the error covariance matrix under the initial state errors, and the results are validated by Monte Carlo simulation. The variations of the position error are compared with the variations of the condition number. The results show that the variation trend of the position error after a period of that halo orbit is the same as the variation trend of the condition number. Moreover, this identified property is verified by testing the halo orbits with different amplitudes and the halo orbits in systems with different mass ratios. Finally, the variation trends of the condition numbers against propagation time corresponding to different points on the halo orbit are analyzed. It is shown that the largest point in the negative z direction of the north halo orbit and its vicinity are more sensitive to state errors than other positions on the halo orbit, and they should not be selected as the injection point.

  16. Propagation characteristics and guiding of a high-power microwave in plasma waveguide.

    PubMed

    Ito, H; Rajyaguru, C; Yugami, N; Nishida, Y; Hosoya, T

    2004-06-01

    The propagation characteristics of a high-power microwave [electromagnetic (em) wave] in a plasma waveguide are reported. The plasma waveguide is formed by expanding plasmas via the ponderomotive force of the high-power microwave and the microwave pulse remains trapped within the plasma waveguide and is guided in it. With the increase of the incident microwave power, the width of the plasma waveguide increases and the half width of the radial electric field distribution decreases. This shows that the em wave modifies the refractive index of the plasma waveguide area. For a plasma waveguide with narrower width, the microwave propagates along the plasma waveguide at the fundamental TE mode, while as the waveguide width increases the higher mode component starts appearing. Analytical treatment to the propagation of the electromagnetic wave in a dielectric waveguide having a step-index profile and the numerical calculations for the radial distribution of the electric field show fairly good agreement with the results observed in the present experiments.

  17. 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.

  18. The effect of nitrogen on biogas flame propagation characteristic in premix combustion

    NASA Astrophysics Data System (ADS)

    Anggono, Willyanto; Suprianto, Fandi D.; Hartanto, Tan Ivan; Purnomo, Kenny; Wijaya, Tubagus P.

    2016-03-01

    Biogas is one of alternative energy and categorized as renewable energy. The main sources of biogas come from animal waste, garbage, and household waste that are organic waste. Primarily, over 50% of this energy contains methane (CH4). The other substances or inhibitors are nitrogen and carbon dioxide. Previously, carbon dioxide effect on biogas combustion is already experimented. The result shows that carbon dioxide reduces the flame propagation speed of biogas combustion. Then, nitrogen as an inhibitor obviously also brings some effects to the biogas combustion, flame propagation speed, and flame characteristics. Spark ignited cylinder is used for the premixed biogas combustion research. An acrylic glass is used as the material of this transparent cylinder chamber. The cylinder is filled with methane (CH4), oxygen (O2), and nitrogen (N2) with particular percentage. In this experiment, the nitrogen composition are set to 0%, 5%, 10%, 20%, 30%, 40%, and 50%. The result shows that the flame propagation speed is reduced in regard to the increased level of nitrogen. It can also be implied that nitrogen can decrease the biogas combustion rate.

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

    SciTech Connect

    Hussain, S. E-mail: shussainuos@yahoo.com; Qazi, H. I. A.; Badar, M. A.

    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 α and γ modes. This atmospheric rf DBD is observed to retain the discharge volume without constriction in γ mode. Optical emission spectroscopy demonstrates that the large discharge current leads to more abundant reactive species in this plasma source.

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

    NASA Astrophysics Data System (ADS)

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

    2000-09-01

    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 method is used to measure the wave speed and its variation with location and time, which broadly matches the Rossby wave speeds predicted by the most recent theory and those measured by TOPEX altimetry, although there are some discrepancies. At low latitudes the thermally detected speeds are slower than expected, a possible consequence of sampling limitations. Wave signatures are clearest between 25° and 40°S, where the meridional temperature gradient is strongest. Here observed speeds are 20-30% greater than theoretical predictions. Planetary wave speed varies considerably with longitude. In general, it increases toward the west of ocean basins, and distinct differences between ocean basins are evident. The propagation characteristics of the waves appear to change abruptly at locations consistent with latitudinal variations in seafloor bathymetry, particularly midocean ridges. In addition, eastward propagating signatures are found in the Southern Ocean. The results demonstrate the value of the ASST data set as a tool for studying basin-scale wave processes as a complement to the use of altimetry. By observing the thermal signature of Rossby waves the method has the potential to clarify their influence on air-sea interaction processes and to contribute to climate modeling studies.

  1. Characteristics of annular beams propagating through atmospheric turbulence along a downlink path and an uplink path

    NASA Astrophysics Data System (ADS)

    Ji, Xiaoling; Chen, Hong; Ji, Guangming

    2016-08-01

    Characteristics of annular beams propagating through atmospheric turbulence along a downlink path and an uplink path are studied in detail by using numerical simulation method. It is found that in downlink the influence of atmospheric turbulence on the characteristics is quite different from that in uplink because of the altitude-dependent index structure constant. It is shown that, when the zenith angle θ is not large enough, it is always σ_{{I {{up}}}}2 > σ_{{I {{down}}}}2 on propagation whatever the value of the obscure ratio ɛ is, where σ_{{I {{up}}}}2 and σ_{{I {{down}}}}2 are the on-axis scintillation index in uplink and downlink, respectively. However, when θ is large enough, σ_{{I {{down}}}}2 is close to σ_{{I {{up}}}}2 as the propagation distance z increases, and σ_{{I {{up}}}}2 and σ_{{I {{down}}}}2 overlap each other as ɛ increases. Furthermore, as z increases, σ_{{I {{up}}}}2 approaches an asymptotical value when θ is not large enough, and the saturation phenomenon of σ_{{I {{up}}}}2 appears when θ is large enough. But the asymptotical value and the saturation phenomenon of σ_{{I {{down}}}}2 never appear. On the other hand, the energy focusability in downlink is better than that in uplink, and the difference of energy focusability between a downlink and an uplink increases with increasing θ or decreasing ɛ. In addition, in downlink there may exist sidelobes of intensity distributions when θ is not large enough, but the sidelobes never appear in uplink.

  2. Propagation characteristics of optical fiber structures with arbitrary shape and index variation

    NASA Technical Reports Server (NTRS)

    Manshadi, F.

    1990-01-01

    The application of the scalar wave-fast Fourier transform (SW-FFT) technique to the computation of the propagation characteristics of some complex optical fiber structures is presented. The SW-FFT technique is based on the numerical solution of the scalar wave equation by a forward-marching fast Fourier transform method. This solution yields the spatial configuration of the fields as well as its modal characteristics in and around the guiding structure. The following are treated by the SW-FFT method: analysis of coupled optical fibers and computation of their odd and even modes and coupling length; the solution of tapered optical waveguides (transitions) and the study of the effect of the slope of the taper on mode conversion; and the analysis of branching optical fibers and demonstration of their mode-filtering and/or power-dividing properties.

  3. Technique for measurement of characteristic impedance and propagation constant for porous materials

    NASA Astrophysics Data System (ADS)

    Jung, Ki Won; Atchley, Anthony A.

    2005-09-01

    Knowledge of acoustic properties such as characteristic impedance and complex propagation constant is useful to characterize the acoustic behaviors of porous materials. Song and Bolton's four-microphone method [J. Acoust. Soc. Am. 107, 1131-1152 (2000)] is one of the most widely employed techniques. In this method two microphones are used to determine the complex pressure amplitudes for each side of a sample. Muehleisen and Beamer [J. Acoust. Soc. Am. 117, 536-544 (2005)] improved upon a four-microphone method by interchanging microphones to reduce errors due to uncertainties in microphone response. In this paper, a multiple microphone technique is investigated to reconstruct the pressure field inside an impedance tube. Measurements of the acoustic properties of a material having square cross-section pores is used to check the validity of the technique. The values of characteristic impedance and complex propagation constant extracted from the reconstruction agree well with predicted values. Furthermore, this technique is used in investigating the acoustic properties of reticulated vitreous carbon (RVC) in the range of 250-1100 Hz.

  4. On wave propagation characteristics in fluid saturated porous materials by a nonlocal Biot theory

    NASA Astrophysics Data System (ADS)

    Tong, Lihong; Yu, Yang; Hu, Wentao; Shi, Yufeng; Xu, Changjie

    2016-09-01

    A nonlocal Biot theory is developed by combing Biot theory and nonlocal elasticity theory for fluid saturated porous material. The nonlocal parameter is introduced as an independent variable for describing wave propagation characteristics in poroelastic material. A physical insight on nonlocal term demonstrates that the nonlocal term is a superposition of two effects, one is inertia force effect generated by fluctuation of porosity and the other is pore size effect inherited from nonlocal constitutive relation. Models for situations of excluding fluid nonlocal effect and including fluid nonlocal effect are proposed. Comparison with experiment confirms that model without fluid nonlocal effect is more reasonable for predicting wave characteristics in saturated porous materials. The negative dispersion is observed theoretically which agrees well with the published experimental data. Both wave velocities and quality factors as functions of frequency and nonlocal parameter are examined in practical cases. A few new physical phenomena such as backward propagation and disappearance of slow wave when exceeding critical frequency and disappearing shear wave in high frequency range, which were not predicted by Biot theory, are demonstrated.

  5. A time-dependent method of characteristics formulation with time derivative propagation

    NASA Astrophysics Data System (ADS)

    Hoffman, Adam J.

    We developed a new time-dependent neutron transport method for nuclear reactor kinetics using method of characteristics (MOC) with angular flux time derivative propagation. In contrast to conventional time integration methods which use local finite difference approximations to treat the time derivative, the new method solves for the spatially-dependent angular flux time derivative by propagation along characteristics in space. This results in the angular flux time derivative being recast in terms of the neutron source time derivatives, and thus the new method is called Source Derivative Propagation (SDP). We developed three SDP methods using different approximations, and they require much less memory than the conventional methods. For SDP, we approximate the source derivatives using backward differences. This is analogous to the backward differentiation formula (BDF), and our results confirmed that the high-order SDP approximations reproduced the high-order angular flux derivative approximation of equivalent order BDF. We assessed SDP by comparison to conventional time-dependent MOC methods. This included both a reference method (RBDC) which stored the angular flux and a popular approximate method (IBDC). We performed error analysis for SDP, RBDC, and IBDC. This informed the refinement of the SDP methods, and clarified when SDP will be accurate. We tested SDP using the computer code DeCART, which was used to model three transients based on the TWIGL and C5G7 benchmarks. A fine time step reference solution was generated using RBDC. The SDP methods converged to the reference when the time step was refined and the BDF order increased. In addition, we observed that SDP accurately replicated the RBDC solution when the same time step and BDF order was used. This indicates that the propagated angular flux time derivative of SDP reproduced the RBDC angular flux derivative. SDP was much more accurate than the IBDC. We assessed the efficiency of SDP by comparing the run

  6. Multiple signal propagation at the tropopause of the Venusian atmosphere: new insights from the Radio Science Experiment (VeRa) onboard Venus Express

    NASA Astrophysics Data System (ADS)

    Herrmann, Maren; Oschlisniok, Janusz; Remus, Stefan; Tellmann, Silvia; Häusler, Bernd; Pätzold, Martin

    2016-10-01

    The rapid change of the refractive index over a short altitude range in a planetary atmosphere can lead to multi-path effects when sounding the atmosphere with radio waves. The Radio Science Experiment (VeRa) [1,2] onboard Venus Express sounded the Venusian atmosphere from 90 km downward to 40 km altitude[3,4]. More than 800 profiles of temperature, pressure and neutral number density could be retrieved which cover almost all local times and latitudes. A specially developed analysis method based on the VeRa open loop receiving technique deciphers the multi-path effect and identifies an inversion layer near the tropopause at an altitude of about 60km. This layer is of particular interest - it separates the stratified troposphere from the highly variable mesosphere and can be a likely location for the formation of gravity waves [5]. The new retrieval method shows an inversion layer up to 15 K colder than commonly thought. Local time and latitude dependence including the influence of the spacecraft trajectory on this effect will be discussed. These results will contribute to a consistent picture of the Venus' thermal atmosphere structure and therefore help to improve atmospheric models.[1] Häusler, B. et al: 'Radio science investigations by VeRa onboard the Venus Express spacecraft' Planetary and Space Science 54, 2006[2] Häusler, B. et al, 'Venus Atmospheric, Ionospheric, Surface and Interplanetery Radio-Wave Propagation Studies with the VeRa Radio Science experiment' Eur. Space Agencys, Spec. Publ., ESA SP 1295, 2007[3] Pätzold, M. et al: 'The structure of Venus' middle atmosphere and ionosphere', Nature 450, 2007[4] Tellmann, S. et al : 'Structure of the Venus neutral atmosphere as observed by the Radio Science experiment VeRa on Venus Express', Journal of Geophysical Research 114, 2009[5] Tellmann, S. et al: 'Small-scale temperature fluctuations seen by the VeRa Radio Science Experiment on Venus Express' Icarus 221, 2012.

  7. 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

  8. Transmit-reference methods in software defined radio platforms for communication in harsh propagation environments and systems thereof

    DOEpatents

    Dowla, Farid U; Nekoogar, Faranak

    2015-03-03

    A method for adaptive Radio Frequency (RF) jamming according to one embodiment includes dynamically monitoring a RF spectrum; detecting any undesired signals in real time from the RF spectrum; and sending a directional countermeasure signal to jam the undesired signals. A method for adaptive Radio Frequency (RF) communications according to another embodiment includes transmitting a data pulse in a RF spectrum; and transmitting a reference pulse separated by a predetermined period of time from the data pulse; wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated. A method for adaptive Radio Frequency (RF) communications according to yet another embodiment includes receiving a data pulse in a RF spectrum; and receiving a reference pulse separated in time from the data pulse, wherein the data pulse is modulated with data, wherein the reference pulse is unmodulated; and demodulating the pulses.

  9. A Statistical Study on the Dependence of Characteristics of VLF/LF Terminator Times on the Propagation Direction

    NASA Astrophysics Data System (ADS)

    Maekawa, Shinko; Hayakawa, Masashi

    We present a detailed statistical study over two years on the times of amplitude minima (so-called terminator times) observed for the VLF/LF transmitters NPM/NWC/JJY as received at three sites. We analyzed three paths: East-West long propagation path, North-South long propagation path and North-South short propagation path. In this paper we examine the statistical behavior on the dependence of VLF/LF terminator time characteristics on the propagation direction and also we focus on the short-term terminator time (TT) characteristics. We found from the data analysis that TT behavior is regularly influenced by the lower-ionospheric condition which depends on the sunrise/sunset transition and season.

  10. Self-configurable radio receiver system and method for use with signals without prior knowledge of signal defining characteristics

    NASA Technical Reports Server (NTRS)

    Hamkins, Jon (Inventor); Simon, Marvin K. (Inventor); Divsalar, Dariush (Inventor); Dolinar, Samuel J. (Inventor); Tkacenko, Andre (Inventor)

    2013-01-01

    A method, radio receiver, and system to autonomously receive and decode a plurality of signals having a variety of signal types without a priori knowledge of the defining characteristics of the signals is disclosed. The radio receiver is capable of receiving a signal of an unknown signal type and, by estimating one or more defining characteristics of the signal, determine the type of signal. The estimated defining characteristic(s) is/are utilized to enable the receiver to determine other defining characteristics. This in turn, enables the receiver, through multiple iterations, to make a maximum-likelihood (ML) estimate for each of the defining characteristics. After the type of signal is determined by its defining characteristics, the receiver selects an appropriate decoder from a plurality of decoders to decode the signal.

  11. 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.

  12. Propagation characteristics of silver nanorods based compact waveguides for plasmonic circuitry

    NASA Astrophysics Data System (ADS)

    Dillu, Venus; Shruti; Srivastava, Triranjita; Sinha, Ravindra Kumar

    2013-02-01

    We propose ultra-compact waveguides for plasmonic circuitry based on silver nanorods array embedded vertically into silicon on insulator (SOI) substrate for nanoscale guidance of optical frequencies. Silver nanorods array palisade silicon to form core of SOI waveguide and is theoretically modeled for the first time. Propagation characteristics of the structure are obtained using finite difference time domain (FDTD) computations, exposing bandgap in the visible regime for transverse magnetic modes and are verified by the plane wave expansion (PWE) method. Narrow transmission bandwidth of ∼10 nm with quality factor and confinement factor of 97.5% and 92% is achieved respectively, confirming strong confinement of the propagating mode at 633 nm and the losses calculated in decible per micrometer (dB/μm) for the waveguide is found to be .75 dB/μm for straight waveguide. Further, Y-splitter designed from the basis equally bifurcate power and the outputs received at the two ends are in phase yielding a viable 50-50 power splitter. Bend design routing light in nano-dimensions is also implemented successfully, offering components for high density plasmonic circuitry.

  13. Characteristics of the propagation of radioactive pollutants near a radiation-hazardous object

    SciTech Connect

    Romanov, V.I.

    1995-09-01

    It is well known that the radiation effect of nuclear enterprises on the environment is due mainly to gas-aerosol emissions which emanate from the object in the form of a jet flow. A characteristic feature of the propagation of radioactive impurities near such structures is that they depend on the local thermal and wind conditions at the location of the source of contamination. Transferring directly the results of laboratory investigations of the propagation and diffusion of fluxes to objects in the environment and neglecting the peculiarities of the wind and thermal interference with the underlying surface and other buildings can lead to incorrect conclusions. In this paper, we examine two examples: (1) emissions through the plant stack or other ventilation system openings, and (2) leakage of radioactive pollutants into the reactor building and from there to the atmosphere. A mathematical description on each example is provided, and data on the Archimedes number for a convective jet is given as a function of the deflecting wind velocity.

  14. Propagation characteristics of atmospheric-pressure He+O2 plasmas inside a simulated endoscope channel

    NASA Astrophysics Data System (ADS)

    Wang, S.; Chen, Z. Y.; Wang, X. H.; Li, D.; Yang, A. J.; Liu, D. X.; Rong, M. Z.; Chen, H. L.; Kong, M. G.

    2015-11-01

    Cold atmospheric-pressure plasmas have potential to be used for endoscope sterilization. In this study, a long quartz tube was used as the simulated endoscope channel, and an array of electrodes was warped one by one along the tube. Plasmas were generated in the inner channel of the tube, and their propagation characteristics in He+O2 feedstock gases were studied as a function of the oxygen concentration. It is found that each of the plasmas originates at the edge of an instantaneous cathode, and then it propagates bidirectionally. Interestingly, a plasma head with bright spots is formed in the hollow instantaneous cathode and moves towards its center part, and a plasma tail expands through the electrode gap and then forms a swallow tail in the instantaneous anode. The plasmas are in good axisymmetry when [O2] ≤ 0.3%, but not for [O2] ≥ 1%, and even behave in a stochastic manner when [O2] = 3%. The antibacterial agents are charged species and reactive oxygen species, so their wall fluxes represent the "plasma dosage" for the sterilization. Such fluxes mainly act on the inner wall in the hollow electrode rather than that in the electrode gap, and they get to the maximum efficiency when the oxygen concentration is around 0.3%. It is estimated that one can reduce the electrode gap and enlarge the electrode width to achieve more homogenous and efficient antibacterial effect, which have benefits for sterilization applications.

  15. On the statistical characteristics of radio-loud and radio-quiet halo coronal mass ejections and their associated flares during solar cycles 23 and 24

    NASA Astrophysics Data System (ADS)

    Mittal, Nishant; Sharma, Joginder; Verma, Virendar Kumar; Garg, Vijay

    2016-08-01

    We have studied the characteristics of radio-loud (RL) and radio-quiet (RQ) front side halo coronal mass ejections (HCMEs) (angular width 360°) observed between the time period years 1996-2014. RL-HCMEs are associated with type II radio bursts, while RQ-HCMEs are not associated with type II radio bursts. CMEs near the Sun in the interplanetary medium associated with radio bursts also affect the magnetosphere. The type II radio burst data was observed by WIND/WAVES instrument and HCMEs were observed by LASCO/ SOHO instruments. In our study, we have examined the properties of RL-HCMEs and RQ-HCMEs and found that RL-HCMEs follow the solar cycle variation. Our study also shows that the 26% of slow speed HCMEs and 82% of fast speed HCMEs are RL. The average speed of RL-HCMEs and RQ-HCMEs are 1370 km/s and 727 km/s, respectively. Most of the RQ-HCMEs occur around the solar disc center while most of RL-HCMEs are uniformly distributed across the solar disc. The mean value of acceleration of RL-HCMEs is more than twice that of RQ-HCMEs and mean value of deceleration of RL- HCMEs is very small compare to RQ-HCMEs events. It is also found that RQ-HCMEs events are associated with C- and M-class of SXR flares, while RL-HCMEs events are associated with M and X-class of SXR flares, which indicates that the RQ-HCMEs are less energetic than the RL-HCMEs. We have also discussed the various results obtained in present investigation in view of recent scenario of solar physics.

  16. Propagation characteristics of dust-acoustic waves in presence of a floating cylindrical object in the DC discharge plasma

    NASA Astrophysics Data System (ADS)

    Choudhary, Mangilal; Mukherjee, S.; Bandyopadhyay, P.

    2016-08-01

    The experimental observation of the self-excited dust acoustic waves (DAWs) and its propagation characteristics in the absence and presence of a floating cylindrical object is investigated. The experiments are carried out in a direct current (DC) glow discharge dusty plasma in a background of argon gas. Dust particles are found levitated at the interface of plasma and cathode sheath region. The DAWs are spontaneously excited in the dust medium and found to propagate in the direction of ion drift (along the gravity) above a threshold discharge current at low pressure. Excitation of such a low frequency wave is a result of the ion-dust streaming instability in the dust cloud. Characteristics of the propagating dust acoustic wave get modified in the presence of a floating cylindrical object of radius larger than that of the dust Debye length. Instead of propagation in the vertical direction, the DAWs are found to propagate obliquely in the presence of the floating object (kept either vertically or horizontally). In addition, a horizontally aligned floating object forms a wave structure in the cone shaped dust cloud in the sheath region. Such changes in the propagation characteristics of DAWs are explained on the basis of modified potential (or electric field) distribution, which is a consequence of coupling of sheaths formed around the cylindrical object and the cathode.

  17. Calculated characteristics of radio-frequency plasma display panel cells including the influence of xenon metastables

    NASA Astrophysics Data System (ADS)

    Pitchford, L. C.; Kang, J.; Punset, C.; Boeuf, J. P.

    2002-12-01

    Although alternating-current plasma display panels (ac PDPs) are now produced by several companies, improvements are still necessary. In particular, the overall efficiency of the discharge in the standard configuration is low, on the order of 1 lm/W i.e., about 0.5% of the power dissipated in the discharge is transformed into useful visible photons. One way to substantially improve the efficiency of PDPs is to use radio-frequency (rf) excitation because, when compared to ac PDPs, less of the electrical energy input is dissipated by ions in the sheath and relatively more power is deposited in excitation of the xenon, which produces the ultraviolet photons used to excite the phosphors. In this article, we show calculated discharge characteristics for typical rf PDP conditions and pay particular attention to the role of the xenon metastable atoms in the ionization balance. Our discussion is limited to the sustaining regime, the "on-state," of a PDP cell.

  18. Statistical study of propagation characteristics of Pc1 pearl structures using conjugate ground-satellite observations

    NASA Astrophysics Data System (ADS)

    Jun, C. W.; Shiokawa, K.; Takahashi, K.; Paulson, K. W.; Schofield, I.; Connors, M. G.; Poddelskiy, I.; Shevtsov, B.; Kletzing, C.; Wygant, J. R.

    2015-12-01

    We investigated statistical characteristics of pearl structures (amplitude modulation) of Pc1 pulsations using conjugate observations with the ground induction magnetometers located at Athabasca (ATH, L = 4.3) in Canada and Magadan (MGD, L = 2.7) in Russia and the Van Allen Probes (RBSP-A and B) satellites located in the inner magnetosphere for a 1-year period (August 2012 to August 2013). We consider a ground magnetometer and a satellite to be conjugate when the satellite footprint is located within 1000 km of the ground magnetometer. From a survey of data acquired during the conjunction periods, we found 42 pearl Pc1events. These events were classified into four categories: structured Pc1 waves observed at both locations (9 events), structured Pc1 waves observed only on the ground (22 events) or in space (0 events), and unstructured Pc1 waves at both locations (11 events). We describe the spatial and temporal distributions of Pc1 pearl structures and their dependence on geomagnetic conditions. We also compare the frequency, the power ratio between space and ground, and the polarization among the four categories of events. In addition, we verified the similarity of Pc1 pearl structures between ground and space observations in order to investigate propagation and polarization characteristics of Pc1 pearl structures from the magnetosphere to the ionosphere.

  19. Study of propagation characteristics of very low latitude whistlers by means of three-dimensional ray-tracing computations

    NASA Astrophysics Data System (ADS)

    Ohta, Kenji; Nishimura, Yasuhiro; Kitagawa, Tomomi; Hayakawa, Masashi

    1997-04-01

    The propagation mechanism of very low latitude (geomagnetic latitudes of less than 10-15°) whistlers is poorly understood. There is a controversy on their propagation; some workers using the observational facts have suggested field-aligned propagation, but some theoretical (ray tracing) works have all indicated nonducted propagation. This paper reexamines the propagation characteristics of nonducted propagation, but we use three-dimensional ray tracing (different from previous works) for realistic ionosphere/magnetosphere models (the electron density profile with latitudinal and longitudinal gradients and the International Geomagnetic Reference Field (IGRF) magnetic field model instead of the conventional dipole model). By assuming small possible tilts (in the latitudinal and longitudinal direction) of the initial wave normal angle in the input southern hemisphere, we have found that it is possible for us to detect simultaneously, at a very low latitude position in the northern ionosphere, one-hop whistler rays started from slightly spaced locations in the south with different initial wave normal angles and that some of them can penetrate through the ionosphere, but some others cannot. On the basis of systematic analysis of important parameters, we come to the general conclusion that it is possible for us to find a closely spaced set of paths to reproduce the one-hop and three-hop whistlers in the north and to have the dispersion ratio of 1:3. The echo train whistlers, as were often observed by Hayakawa et al. [1990], are realized also by this nonducted propagation without any serious requirements.

  20. Characteristics of meter-scale surface electrical discharge propagating along water surface at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Hoffer, Petr; Sugiyama, Yuki; Hosseini, S. Hamid R.; Akiyama, Hidenori; Lukes, Petr; Akiyama, Masahiro

    2016-10-01

    This paper reports physical characteristics of water surface discharges. Discharges were produced by metal needle-to-water surface geometry, with the needle electrode driven by 47 kV (FWHM) positive voltage pulses of 2 µs duration. Propagation of discharges along the water surface was confined between glass plates with 2 mm separation. This allowed generation of highly reproducible 634 mm-long plasma filaments. Experiments were performed using different atmospheres: air, N2, and O2, each at atmospheric pressure. Time- and spatially-resolved spectroscopic measurements revealed that early spectra of discharges in air and nitrogen atmospheres were dominated by N2 2nd positive system. N2 radiation disappeared after approx. 150 ns, replaced by emissions from atomic hydrogen. Spectra of discharges in O2 atmosphere were dominated by emissions from atomic oxygen. Time- and spatially-resolved emission spectra were used to determine temperatures in plasma. Atomic hydrogen emissions showed excitation temperature of discharges in air to be about 2  ×  104 K. Electron number densities determined by Stark broadening of the hydrogen H β line reached a maximum value of ~1018 cm-3 just after plasma initiation. Electron number densities and temperatures depended only slightly on distance from needle electrode, indicating formation of high conductivity leader channels. Direct observation of discharges by high speed camera showed that the average leader head propagation speed was 412 km · s-1, which is substantially higher value than that observed in experiments with shorter streamers driven by lower voltages.

  1. Wave propagation characteristics of helically orthotropic cylindrical shells and resonance emergence in scattered acoustic field. Part 2. Numerical results

    NASA Astrophysics Data System (ADS)

    Rajabi, Majid

    2016-09-01

    In the present work as the second part of the research work on wave propagation characteristics of helically orthotropic cylindrical shells, the main aim is to use the developed solution for resonance isolation and identification of an air-filled and water submerged Graphite/Epoxy cylindrical shell and quantitative sensitivity analysis of excited resonance frequencies to the perturbation in the material's elastic constants. The physical justifications are presented for the singular features associated with the stimulated resonance frequencies according to their style of propagation and polarization, induced stress-strain fields and wave type. For evaluation purposes, the wave propagation characteristics of the anisotropic shell and the far-field form function amplitude of a limiting case are considered and good agreement with the solutions available in the literature is established.

  2. 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 Tromsø. 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

  3. Static current-voltage characteristics for radio-frequency induction discharge

    SciTech Connect

    Budyansky, A.; Zykov, A.

    1995-12-31

    The aim of this work was to obtain experimentally such characteristic of Radio-Frequency Induction Discharge (RFID) that can play the role of its current-voltage characteristic (CVC) and to explain the nature of current and voltage jumps arising in RF coils at exciting of discharge. Experiments were made in quartz 5.5, 11, 20 cm diam tubes with outer RF coil at pressures 10--100 mTorr, at frequency 13.56 MHz and discharge power to 500 W. In case of outer coil as analogue of discharge voltage it`s convenient to use the value of the RF voltage U{sub R}, induced around outer perimeter of discharge tube. It is evident that current and voltage jumps arising at exciting of discharge are due to low output resistance of standard generators and negative slope of initial part of CVC. Three sets of such dependencies for different pressures were obtained for each diameter of tubes. The influence of different metal electrodes placed into discharge volume on CVC`s shape has been studied also. Experimental results can explain the behavior of HFI discharge as a load of RF generator and give data for calculation of RF circuit.

  4. Feedback control of wave propagation in a rectangular panel, Part 1: Theoretical investigation of fundamental characteristics

    NASA Astrophysics Data System (ADS)

    Iwamoto, Hiroyuki; Tanaka, Nobuo; Hill, Simon G.

    2013-08-01

    This study presents the feedback control of flexural waves propagating in a rectangular panel. The objective of this paper (part 1) is to theoretically investigate the fundamental properties of the feedback wave control system. First, a transfer matrix method in the Laplace domain is introduced which is based on a wave solution of a rectangular panel. This is followed by the derivation of the characteristic equation and the feedback control laws for absorbing the reflected waves. Then, from a viewpoint of numerical simulations, the control performance of the proposed method is clarified. It is found that the reflected wave absorbing control enables inactivation of vibration modes since standing waves which cause resonant phenomena disappear from the structural vibration. Finally, the stability verification of the proposed control system is conducted using Nyquist diagram. It is shown that although the controller has unstable poles in some cases, the nominal control system is stable irrespective of whether the collocation holds or not. Furthermore, it is clarified that a wave-absorbing control system becomes robust for the parameter fluctuation if the uncontrolled region does not exist.

  5. 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.

  6. On the propagation of concentration polarization from microchannel-nanochannel interfaces. Part I: Analytical model and characteristic analysis.

    PubMed

    Mani, Ali; Zangle, Thomas A; Santiago, Juan G

    2009-04-01

    We develop two models to describe ion transport in variable-height micro- and nanochannels. For the first model, we obtain a one-dimensional (unsteady) partial differential equation governing flow and charge transport through a shallow and wide electrokinetic channel. In this model, the effects of electric double layer (EDL) on axial transport are taken into account using exact solutions of the Poisson-Boltzmann equation. The second simpler model, which is approachable analytically, assumes that the EDLs are confined to near-wall regions. Using a characteristics analysis, we show that the latter model captures concentration polarization (CP) effects and provides useful insight into its dynamics. Two distinct CP regimes are identified: CP with propagation in which enrichment and depletion shocks propagate outward, and CP without propagation where polarization effects stay local to micro- nanochannel interfaces. The existence of each regime is found to depend on a nanochannel Dukhin number and mobility of the co-ion nondimensionalized by electroosmotic mobility. Interestingly, microchannel dimensions and axial diffusion are found to play an insignificant role in determining whether CP propagates. The steady state condition of propagating CP is shown to be controlled by channel heights, surface chemistry, and co-ion mobility instead of the reservoir condition. Both models are validated against experimental results in Part II of this two-paper series.

  7. Characteristics of coronal shock waves and solar type 2 radio bursts

    NASA Technical Reports Server (NTRS)

    Mann, G.; Classen, H.-T.

    1995-01-01

    In the solar corona shock waves generated by flares and/or coronal mass ejections can be observed by radio astronomical methods in terms of solar type 2 radio bursts. In dynamic radio spectra they appear as emission stripes slowly drifting from high to low frequencies. A sample of 25 solar type 2 radio bursts observed in the range of 40 - 170 MHz with a time resolution of 0.1 s by the new radiospectrograph of the Astrophvsikalisches Institut Potsdam in Tremsdorf is statistically investigated concerning their spectral features, i.e, drift rate, instantaneous bandwidth, and fundamental harmonic ratio. In-situ plasma wave measurements at interplanetary shocks provide the assumption that type 2 radio radiation is emitted in the vicinity of the transition region of shock waves. Thus, the instantaneous bandwidth of a solar type 2 radio burst would reflect the density jump across the associated shock wave. Comparing the inspection of the Rankine-Hugoniot relations of shock waves under coronal circumstances with those obtained from the observational study, solar type 2 radio bursts should be regarded to be generated by weak supercritical, quasi-parallel, fast magnetosonic shock waves in the corona.

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

    NASA Astrophysics Data System (ADS)

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

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

  9. Comparison of pulse propagation and gain saturation characteristics among different input pulse shapes in semiconductor optical amplifiers

    NASA Astrophysics Data System (ADS)

    Barua, Suchi; Das, Narottam; Nordholm, Sven; Razaghi, Mohammad

    2016-01-01

    This paper presents the pulse propagation and gain saturation characteristics for different input optical pulse shapes with different energy levels in semiconductor optical amplifiers (SOAs). A finite-difference beam propagation method (FD-BPM) is used to solve the modified nonlinear Schrödinger equation (MNLSE) for the simulation of nonlinear optical pulse propagation and gain saturation characteristics in the SOAs. In this MNLSE, the gain spectrum dynamics, gain saturation are taken into account those are depend on the carrier depletion, carrier heating, spectral hole-burning, group velocity dispersion, self-phase modulation and two photon absorption. From this simulation, we obtained the output waveforms and spectra for different input pulse shapes considering different input energy levels. It has shown that the output pulse shape has changed due to the variation of input parameters, such as input pulse shape, input pulse width, and input pulse energy levels. It also shown clearly that the peak position of the output waveforms are shifted toward the leading edge which is due to the gain saturation of the SOA. We also compared the gain saturation characteristics in the SOA for different input pulse shapes.

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

    NASA Technical Reports Server (NTRS)

    1975-01-01

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

  11. Midwest Radio Survey: Management Identification of Vocational Needs and Perceptions of Entry-Level Skills and Long-Term Success Characteristics.

    ERIC Educational Resources Information Center

    Parcells, Frank E.

    To help with the curriculum development of college broadcasting programs, a survey was administered to 375 radio station managers in major, medium, and small midwest markets. Designed to establish the vocational needs of radio stations, determine and prioritize entry level broadcasting skills, and identify characteristics of success for long-term…

  12. 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.

  13. Propagation characteristics of Bessel beams generated by continuous, incoherent light sources.

    PubMed

    Altıngöz, Ceren; Yalızay, Berna; Akturk, Selcuk

    2015-08-01

    We investigate the propagation behavior of Bessel beams generated by incoherent, continuous light sources. We perform experiments with narrowband and broadband light emitting diodes, and, for comparison, with a laser diode. We observe that the formation of Bessel beams is affected minimally by temporal coherence, while spatial coherence determines the longitudinal evolution of the beam profile. With spatially incoherent beams, the fringe contrast is comparable to the coherent case at the beginning of the Bessel zone, while it completely fades away by propagation, turning into a cylindrical light pipe. Our results show that beam shaping methods can be extended to cases of limited spatial coherence, paving the way for potential new uses and applications of such sources.

  14. Propagation characteristics of two-color laser pulses in homogeneous plasma

    SciTech Connect

    Hemlata,; Saroch, Akanksha; Jha, Pallavi

    2015-11-15

    An analytical and numerical study of the evolution of two-color, sinusoidal laser pulses in cold, underdense, and homogeneous plasma has been presented. The wave equations for the radiation fields driven by linear as well as nonlinear contributions due to the two-color laser pulses have been set up. A variational technique is used to obtain the simultaneous equations describing the evolution of the laser spot size, pulse length, and chirp parameter. Numerical methods are used to graphically analyze the simultaneous evolution of these parameters due to the combined effect of the two-color laser pulses. Further, the pulse parameters are compared with those obtained for a single laser pulse. Significant focusing, compression, and enhanced positive chirp is obtained due to the combined effect of simultaneously propagating two-color pulses as compared to a single pulse propagating in plasma.

  15. Propagation characteristics of Bessel beams generated by continuous, incoherent light sources.

    PubMed

    Altıngöz, Ceren; Yalızay, Berna; Akturk, Selcuk

    2015-08-01

    We investigate the propagation behavior of Bessel beams generated by incoherent, continuous light sources. We perform experiments with narrowband and broadband light emitting diodes, and, for comparison, with a laser diode. We observe that the formation of Bessel beams is affected minimally by temporal coherence, while spatial coherence determines the longitudinal evolution of the beam profile. With spatially incoherent beams, the fringe contrast is comparable to the coherent case at the beginning of the Bessel zone, while it completely fades away by propagation, turning into a cylindrical light pipe. Our results show that beam shaping methods can be extended to cases of limited spatial coherence, paving the way for potential new uses and applications of such sources. PMID:26367302

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

    NASA Technical Reports Server (NTRS)

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

    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 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.

  17. Hermite-cosine-Gaussian laser beam and its propagation characteristics in turbulent atmosphere.

    PubMed

    Eyyuboğlu, Halil Tanyer

    2005-08-01

    Hermite-cosine-Gaussian (HcosG) laser beams are studied. The source plane intensity of the HcosG beam is introduced and its dependence on the source parameters is examined. By application of the Fresnel diffraction integral, the average receiver intensity of HcosG beam is formulated for the case of propagation in turbulent atmosphere. The average receiver intensity is seen to reduce appropriately to various special cases. When traveling in turbulence, the HcosG beam initially experiences the merging of neighboring beam lobes, and then a TEM-type cosh-Gaussian beam is formed, temporarily leading to a plain cosh-Gaussian beam. Eventually a pure Gaussian beam results. The numerical evaluation of the normalized beam size along the propagation axis at selected mode indices indicates that relative spreading of higher-order HcosG beam modes is less than that of the lower-order counterparts. Consequently, it is possible at some propagation distances to capture more power by using higher-mode-indexed HcosG beams.

  18. 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.

  19. Field observation of low-to-mid-frequency acoustic propagation characteristics of an estuarine salt wedge.

    PubMed

    Reeder, D Benjamin

    2016-01-01

    The estuarine environment often hosts a salt wedge, the stratification of which is a function of the tide's range and speed of advance, river discharge volumetric flow rate, and river mouth morphology. Competing effects of temperature and salinity on sound speed in this stratified environment control the degree of acoustic refraction occurring along an acoustic path. A field experiment was carried out in the Columbia River Estuary to test the hypothesis: the estuarine salt wedge is acoustically observable in terms of low-to-mid-frequency acoustic propagation. Linear frequency-modulated acoustic signals in the 500-2000 Hz band were transmitted during the advance and retreat of the salt wedge during May 27-29, 2013. Results demonstrate that the salt wedge front is the dominant physical mechanism controlling acoustic propagation in this environment: received signal energy is relatively stable before and after the passage of the salt wedge front when the acoustic path consists of a single medium (either entirely fresh water or entirely salt water), and suffers a 10-15 dB loss and increased variability during salt wedge front passage. Physical parameters and acoustic propagation modeling corroborate and inform the acoustic observations. PMID:26827001

  20. Propagation characteristics of young hot flow anomalies near the bow shock: Cluster observations

    NASA Astrophysics Data System (ADS)

    Xiao, T.; Zhang, H.; Shi, Q. Q.; Zong, Q.-G.; Fu, S. Y.; Tian, A. M.; Sun, W. J.; Wang, S.; Parks, G. K.; Yao, S. T.; Rème, H.; Dandouras, I.

    2015-06-01

    Based on Cluster observations, the propagation velocities and normal directions of hot flow anomaly (HFA) boundaries upstream the Earth's bow shock are calculated. Twenty-one young HFAs, which have clear leading and trailing boundaries, were selected, and multispacecraft timing method considering errors was employed for the investigation. According to the difference in the propagation velocity of the leading and trailing edges, we categorized these events into three groups, namely, contracting, expanding, and stable events. The contraction speed is a few tens of kilometers per second for the contracting HFAs, and the expansion speed is tens to more than hundred kilometers per second for expanding events. For the stable events, the leading and trailing edges propagate at almost the same speed within the error range. We have further investigated what causes them to contract, expand, or stay stable by carefully calculating the thermal pressure of the young HFAs which have two distinct ion populations (solar wind beam and reflected flow). It is found that the extreme value of the sum of the magnetic and thermal pressure inside the HFAs compared with that of the nearest point outside of the leading edges is higher for expanding events and lower for contracting events, and there is no significant difference for the stable events, and the total pressure (sum of thermal, magnetic, and dynamic pressure) variation has a significant effect on the evolution for most (70%) of the HFAs, which implies that the pressure plays an important role in the evolution of young HFAs.

  1. 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.

  2. The influences of soil and nearby structures on dispersion characteristics of wave propagating along buried plastic pipes

    NASA Astrophysics Data System (ADS)

    Liu, Shuyong; Jiang, J.; Parr, Nicola

    2016-09-01

    Water loss in distribution systems is a global problem for the water industry and governments. According to the international water supply association (IWSA), as a result of leaks from distribution pipes, 20% to 30% of water is lost while in transit from treatment plants to consumers. Although governments have tried to push the water industry to reduce the water leaks, a lot of experts have pointed out that a wide use of plastic pipes instead of metal pipes in recent years has caused difficulties in the detection of leaks using current acoustic technology. Leaks from plastic pipes are much quieter than traditional metal pipes and comparing to metal pipes the plastic pipes have very different coupling characteristics with soil, water and surrounding structures, such as other pipes, road surface and building foundations. The dispersion characteristics of wave propagating along buried plastic pipes are investigated in this paper using finite element and boundary element based models. Both empty and water- filled pipes were considered. Influences from nearby pipes and building foundations were carefully studied. The results showed that soil condition and nearby structures have significant influences on the dispersion characteristics of wave propagating along buried plastic pipes.

  3. Numerical study of wave propagation in porous media with the use of the grid-characteristic method

    NASA Astrophysics Data System (ADS)

    Kvasov, I. E.; Leviant, V. B.; Petrov, I. B.

    2016-09-01

    Elastic wave propagation in a porous medium is numerically studied by applying the grid-characteristic method. On the basis of direct measurements of reflected and transmitted wave amplitudes, the reflection and decay coefficients are investigated as depending on the degree of porosity (percentage of the pore volume) and on the type of the filling substance (solid, liquid, or nothing). The reflection and decay coefficients are shown to be closely related to the porosity of the medium, which can be used in geological applications (estimation of porosity) and engineering applications (acoustic response attenuation).

  4. Propagation Characteristics of Finite Ground Coplanar Waveguide on Si Substrates With Porous Si and Polyimide Interface Layers

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Itotia, Isaac K.; Drayton, Rhonda Franklin

    2003-01-01

    Measured and modeled propagation characteristics of Finite Ground Coplanar (FGC) waveguide fabricated on a 15 ohm-cm Si substrate with a 23 micron thick, 68% porous Si layer and a 20 micron thick polyimide interface layer are presented for the first time. Attenuation and effective permittivity as function of the FGC geometry and the bias between the center conductor and the ground planes are presented. It is shown that the porous Si reduces the attenuation by 1 dB/cm compared to FGC lines with only polyimide interface layers, and the polyimide on porous silicon demonstrates negligible bias dependence.

  5. A Study on Propagation Characteristic of One-dimensional Stress Wave in Functionally Graded Armor Composites

    NASA Astrophysics Data System (ADS)

    Yang, S. Y.; Liu, X.; Cao, D. F.; Mei, H.; Lei, Z. T.; Liu, L. S.

    2013-03-01

    The development of Functionally Graded Materials (FGM) for energy-absorbing applications requires understanding of stress wave propagation in these structures in order to optimize their resistance to failure. One-dimensional stress wave in FGM composites under elastic and plastic wave loading have been investigated. The stress distributions through the thickness and stress status have been analyzed and some comparisons have been done with the materials of sharp interfaces (two-layered material). The results demonstrate that the gradient structure design greatly decreases the severity of the stress concentrations at the interfaces and there are no clear differences in stress distribution in FGM composites under elastic and plastic wave loading.

  6. 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

  7. 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.

  8. Physics of radio emission in gamma-ray pulsars

    NASA Astrophysics Data System (ADS)

    Petrova, S. A.

    2016-04-01

    > Propagation of radio emission in a pulsar magnetosphere is reviewed. The effects of polarization transfer, induced scattering and reprocessing to high energies are analysed with a special emphasis on the implications for the gamma-ray pulsars. The possibilities of the pulsar plasma diagnostics based on the observed radio pulse characteristics are also outlined. As an example, the plasma number density profiles obtained from the polarization data for the Vela and the gamma-ray millisecond pulsars J1446-4701, J1939+2134 and J1744-1134 are presented. The number densities derived tend to be the highest/lowest when the radio pulse leads/lags the gamma-ray peak. In the PSR J1939+2134, the plasma density profiles for the main pulse and interpulse appear to fit exactly the same curve, testifying to the origin of both radio components above the same magnetic pole and their propagation through the same plasma flow in opposite directions. The millisecond radio pulse components exhibiting flat position angle curves are suggested to result from the induced scattering of the main pulse by the same particles that generate gamma rays. This is believed to underlie the wide-sense radio/gamma-ray correlation in the millisecond pulsars. The radio quietness of young gamma-ray pulsars is attributed to resonant absorption, whereas the radio loudness to the radio beam escape through the periphery of the open field line tube.

  9. Effect of Radio Frequency Plasma Treatment on Evaporation Behavior and Characteristics of RuCr Alloy Powder.

    PubMed

    Jung, Taek-Kyun; Lim, Sung-Chul; Kwon, Hyouk-Chon; Park, Soo-Keun; Hon, Jong-Whan; Jung, Seung-Boo; Baek, Jong-Jin; Jang, Kyu-Bong

    2015-11-01

    The evaporation behavior and characteristics of jet milled RuCr alloy powders processed by radio-frequency (RF) plasma treatment were evaluated during this study. RF plasma treatment was found to be effective in eliminating internal pores and in manufacturing spherical powder. However, the RF plasma treatment resulted in the evaporation of Cr. The degree of evaporation of Cr was significantly affected by the powder feeding rate. As a result, it was found that controlling the torch power was more effective than controlling the powder feeding rate for obtaining desirable RuCr alloy powders. PMID:26726528

  10. Effects of nonlinear sound propagation on the characteristic timbres of brass instruments.

    PubMed

    Myers, Arnold; Pyle, Robert W; Gilbert, Joël; Campbell, D Murray; Chick, John P; Logie, Shona

    2012-01-01

    The capacity of a brass instrument to generate sounds with strong high-frequency components is dependent on the extent to which its bore profile supports nonlinear sound propagation. At high dynamic levels some instruments are readily sounded in a "cuivré" (brassy) manner: this phenomenon is due to the nonlinear propagation of sound in ducts of the proportions typical of labrosones (lip-reed aerophones). The effect is also evident at lower dynamic levels and contributes to the overall tonal character of the various kinds of brass instrument. This paper defines a brassiness potential parameter derived from the bore geometries of brass instruments. The correlation of the brassiness potential parameter with spectral enrichment as measured by the spectral centroid of the radiated sound is examined in playing tests using musicians, experiments using sine-wave excitation of instruments, and simulations using a computational tool. The complementary effects of absolute bore size on spectral enrichment are investigated using sine-wave excitation of cylindrical tubes and of instruments, establishing the existence of a trade-off between bore size and brassiness potential. The utility of the brassiness potential parameter in characterizing labrosones is established, and the graphical presentation of results in a 2D space defined by bore size and brassiness potential demonstrated. PMID:22280689

  11. A RANS simulation toward the effect of turbulence and cavitation on spray propagation and combustion characteristics

    NASA Astrophysics Data System (ADS)

    Taghavifar, Hadi; Khalilarya, Shahram; Jafarmadar, Samad; Taghavifar, Hamid

    2016-08-01

    A multidimensional computational fluid dynamic code was developed and integrated with probability density function combustion model to give the detailed account of multiphase fluid flow. The vapor phase within injector domain is treated with Reynolds-averaged Navier-Stokes technique. A new parameter is proposed which is an index of plane-cut spray propagation and takes into account two parameters of spray penetration length and cone angle at the same time. It was found that spray propagation factor (SPI) tends to increase at lower r/ d ratios, although the spray penetration tends to decrease. The results of SPI obtained by empirical correlation of Hay and Jones were compared with the simulation computation as a function of respective r/ d ratio. Based on the results of this study, the spray distribution on plane area has proportional correlation with heat release amount, NO x emission mass fraction, and soot concentration reduction. Higher cavitation is attributed to the sharp edge of nozzle entrance, yielding better liquid jet disintegration and smaller spray droplet that reduces soot mass fraction of late combustion process. In order to have better insight of cavitation phenomenon, turbulence magnitude in nozzle and combustion chamber was acquired and depicted along with spray velocity.

  12. Simulations and Characteristics of Large Solar Events Propagating Throughout the Heliosphere and Beyond (Invited)

    NASA Astrophysics Data System (ADS)

    Intriligator, D. S.; Sun, W.; Detman, T. R.; Dryer, Ph D., M.; Intriligator, J.; Deehr, C. S.; Webber, W. R.; Gloeckler, G.; Miller, W. D.

    2015-12-01

    Large solar events can have severe adverse global impacts at Earth. These solar events also can propagate throughout the heliopshere and into the interstellar medium. We focus on the July 2012 and Halloween 2003 solar events. We simulate these events starting from the vicinity of the Sun at 2.5 Rs. We compare our three dimensional (3D) time-dependent simulations to available spacecraft (s/c) observations at 1 AU and beyond. Based on the comparisons of the predictions from our simulations with in-situ measurements we find that the effects of these large solar events can be observed in the outer heliosphere, the heliosheath, and even into the interstellar medium. We use two simulation models. The HAFSS (HAF Source Surface) model is a kinematic model. HHMS-PI (Hybrid Heliospheric Modeling System with Pickup protons) is a numerical magnetohydrodynamic solar wind (SW) simulation model. Both HHMS-PI and HAFSS are ideally suited for these analyses since starting at 2.5 Rs from the Sun they model the slowly evolving background SW and the impulsive, time-dependent events associated with solar activity. Our models naturally reproduce dynamic 3D spatially asymmetric effects observed throughout the heliosphere. Pre-existing SW background conditions have a strong influence on the propagation of shock waves from solar events. Time-dependence is a crucial aspect of interpreting s/c data. We show comparisons of our simulation results with STEREO A, ACE, Ulysses, and Voyager s/c observations.

  13. Effects of nonlinear sound propagation on the characteristic timbres of brass instruments.

    PubMed

    Myers, Arnold; Pyle, Robert W; Gilbert, Joël; Campbell, D Murray; Chick, John P; Logie, Shona

    2012-01-01

    The capacity of a brass instrument to generate sounds with strong high-frequency components is dependent on the extent to which its bore profile supports nonlinear sound propagation. At high dynamic levels some instruments are readily sounded in a "cuivré" (brassy) manner: this phenomenon is due to the nonlinear propagation of sound in ducts of the proportions typical of labrosones (lip-reed aerophones). The effect is also evident at lower dynamic levels and contributes to the overall tonal character of the various kinds of brass instrument. This paper defines a brassiness potential parameter derived from the bore geometries of brass instruments. The correlation of the brassiness potential parameter with spectral enrichment as measured by the spectral centroid of the radiated sound is examined in playing tests using musicians, experiments using sine-wave excitation of instruments, and simulations using a computational tool. The complementary effects of absolute bore size on spectral enrichment are investigated using sine-wave excitation of cylindrical tubes and of instruments, establishing the existence of a trade-off between bore size and brassiness potential. The utility of the brassiness potential parameter in characterizing labrosones is established, and the graphical presentation of results in a 2D space defined by bore size and brassiness potential demonstrated.

  14. NASA Propagation Studies Website

    NASA Technical Reports Server (NTRS)

    Angkasa, Krisjani S.

    1996-01-01

    The NASA propagation studies objective is to enable the development of new commercial satellite communication systems and services by providing timely data and models about propagation of satellite radio signals through the intervening environment and to support NASA missions. In partnership with industry and academia, the program leverages unique NASA assets (currently Advanced Communications Technology Satellite) to obtain propagation data. The findings of the study are disseminated through referred journals, NASA reference publications, workshops, electronic media, and direct interface with industry.

  15. Electromagnetically induced transparency and steady-state propagation characteristics in Doppler broadened diamond systems

    NASA Astrophysics Data System (ADS)

    Baig Mirza, Azeem; Singh, Suneel

    2015-01-01

    We explore the feasibility of attaining simultaneous electromagnetically induced transparency (EIT) and efficient nonlinear generation in different configurations of Doppler broadened diamond (double-cascade) systems such as, the frequency up-conversion, nearly degenerate and degenerate scheme. We show that EIT and nonlinear generation efficiency depend critically on the type of residual Doppler broadening present in each of the two cascade subsystems constituting the diamond system. Furthermore, it is observed that nonlinear generation with perfect EIT simultaneously in both subsystems is not possible as the process of nonlinear generation actually tends to oppose EIT. Yet in an extended medium, on resonance field propagation under matched conditions for probe and generated signal can occur when a balance (equilibrium) is established between these two competing processes.

  16. Electrochemical characteristics of a self-propagating molecular-based assembly.

    PubMed

    Motiei, Leila; Lahav, Michal; Gulino, Antonino; Iron, Mark A; van der Boom, Milko E

    2010-11-18

    The electrochemical properties of a metallosupramolecular network that undergoes reversible redox chemistry on indium-tin oxide (ITO)-coated glass substrates have been investigated. The redox-active osmium complexes are electrochemically accessible even for films with a thickness > 15 nm. The electrochemical data correlates well with our previously observed self-propagating growth process, for which the electron density for the assemblies remains constant during film growth. Electron-transfer rate constants obtained by potential step chronoamperometry experiments suggest an exceptionally low attenuation factor, β, of 0.013 ± 0.001 Å(-1). However, the intrinsically porous nature of the assembly could be to a large extent or even entirely responsible for such a low value. PMID:20088551

  17. Characteristics in the jet region of helium radio-frequency atmospheric-pressure glow discharge with array generators

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-Bin; Nie, Qiu-Yue

    2015-09-01

    The two-dimensional spatially extended atmospheric plasma arrays by many parallel radio-frequency glow discharge plasma jets packed densely, represent a feature option of large-scale low-temperature atmospheric plasma technologies with distinct capability of directed delivery of reactive species and good insusceptibility to sample variations. However, it is still a challenge to form plasma jet with large area of uniform active species on a downstream substrate due to the complex interactions between individual jets. This paper proposes to numerically study the strategy and mechanism of control/modulation for the array discharge to produce two-dimensional plasma uniformity in the downstream working area. In this work, a two dimensional fluid model is employed to investigate the characteristics in the jet region of helium radio-frequency atmospheric-pressure glow discharge (RF APGD) with array generators. The influences of upstream discharge characteristics, gas flow and their cooperative effects on the distribution of species densities, gas temperatures and the uniformity of active species in the material treating area is studied, and the essential strategy for the modulation method is acquired. The results will be significant for deep understanding of coupling behaviors of multiple plasma plumes in the RF APGD array and applications of the technology.

  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. Lunar Surface Propagation Modeling and Effects on Communications

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

    This paper analyzes the lunar terrain effects on the signal propagation of the planned NASA lunar wireless communication and sensor systems. It is observed that the propagation characteristics are significantly affected by the presence of the lunar terrain. The obtained results indicate that the terrain geometry, antenna location, and lunar surface material are important factors determining the propagation characteristics of the lunar wireless communication systems. The path loss can be much more severe than the free space propagation and is greatly affected by the antenna height, operating frequency, and surface material. The analysis results from this paper are important for the lunar communication link margin analysis in determining the limits on the reliable communication range and radio frequency coverage performance at planned lunar base worksites. Key Words lunar, multipath, path loss, propagation, wireless.

  20. Atmospheric Propagation

    NASA Technical Reports Server (NTRS)

    Embleton, Tony F. W.; Daigle, Gilles A.

    1991-01-01

    Reviewed here is the current state of knowledge with respect to each basic mechanism of sound propagation in the atmosphere and how each mechanism changes the spectral or temporal characteristics of the sound received at a distance from the source. Some of the basic processes affecting sound wave propagation which are present in any situation are discussed. They are geometrical spreading, molecular absorption, and turbulent scattering. In geometrical spreading, sound levels decrease with increasing distance from the source; there is no frequency dependence. In molecular absorption, sound energy is converted into heat as the sound wave propagates through the air; there is a strong dependence on frequency. In turbulent scattering, local variations in wind velocity and temperature induce fluctuations in phase and amplitude of the sound waves as they propagate through an inhomogeneous medium; there is a moderate dependence on frequency.

  1. Theoretical Analysis of the Optical Propagation Characteristics in a Fiber-Optic Surface Plasmon Resonance Sensor

    PubMed Central

    Liu, Linlin; Yang, Jun; Yang, Zhong; Wan, Xiaoping; Hu, Ning; Zheng, Xiaolin

    2013-01-01

    Surface plasmon resonance (SPR) sensor is widely used for its high precision and real-time analysis. Fiber-optic SPR sensor is easy for miniaturization, so it is commonly used in the development of portable detection equipment. It can also be used for remote, real-time, and online detection. In this study, a wavelength modulation fiber-optic SPR sensor is designed, and theoretical analysis of optical propagation in the optical fiber is also done. Compared with existing methods, both the transmission of a skew ray and the influence of the chromatic dispersion are discussed. The resonance wavelength is calculated at two different cases, in which the chromatic dispersion in the fiber core is considered. According to the simulation results, a novel multi-channel fiber-optic SPR sensor is likewise designed to avoid defaults aroused by the complicated computation of the skew ray as well as the chromatic dispersion. Avoiding the impact of skew ray can do much to improve the precision of this kind of sensor. PMID:23748170

  2. Characteristics and Propagation of Airgun Pulses in Shallow Water with Implications for Effects on Small Marine Mammals

    PubMed Central

    Hermannsen, Line; Tougaard, Jakob; Beedholm, Kristian; Nabe-Nielsen, Jacob; Madsen, Peter Teglberg

    2015-01-01

    Airguns used in seismic surveys are among the most prevalent and powerful anthropogenic noise sources in marine habitats. They are designed to produce most energy below 100 Hz, but the pulses have also been reported to contain medium-to-high frequency components with the potential to affect small marine mammals, which have their best hearing sensitivity at higher frequencies. In shallow water environments, inhabited by many of such species, the impact of airgun noise may be particularly challenging to assess due to complex propagation conditions. To alleviate the current lack of knowledge on the characteristics and propagation of airgun pulses in shallow water with implications for effects on small marine mammals, we recorded pulses from a single airgun with three operating volumes (10 in3, 25 in3 and 40 in3) at six ranges (6, 120, 200, 400, 800 and 1300 m) in a uniform shallow water habitat using two calibrated Reson 4014 hydrophones and four DSG-Ocean acoustic data recorders. We show that airgun pulses in this shallow habitat propagated out to 1300 meters in a way that can be approximated by a 18log(r) geometric transmission loss model, but with a high pass filter effect from the shallow water depth. Source levels were back-calculated to 192 dB re µPa2s (sound exposure level) and 200 dB re 1 µPa dB Leq-fast (rms over 125 ms duration), and the pulses contained substantial energy up to 10 kHz, even at the furthest recording station at 1300 meters. We conclude that the risk of causing hearing damage when using single airguns in shallow waters is small for both pinnipeds and porpoises. However, there is substantial potential for significant behavioral responses out to several km from the airgun, well beyond the commonly used shut-down zone of 500 meters. PMID:26214849

  3. Characteristics of the flare acceleration region derived from simultaneous hard X-ray and radio observations

    NASA Astrophysics Data System (ADS)

    Reid, H. A. S.; Vilmer, N.; Kontar, E. P.

    2011-05-01

    We investigate the type III radio bursts and X-ray signatures of accelerated electrons in a well-observed solar flare in order to find the spatial properties of the acceleration region. Combining simultaneous RHESSI hard X-ray flare data and radio data from Phoenix-2 and the Nançay radioheliograph, the outward transport of flare accelerated electrons is analysed. The observations show that the starting frequencies of type III bursts are anti-correlated with the HXR spectral index of solar flare accelerated electrons. We demonstrate both analytically and numerically that the type III burst starting location is dependent upon the accelerated electron spectral index and the spatial acceleration region size, but weakly dependent on the density of energetic electrons for relatively intense electron beams. Using this relationship and the observed anti-correlation, we estimate the height and vertical extent of the acceleration region, giving values of around 50 Mm and 10 Mm, respectively. The inferred acceleration height and size suggest that electrons are accelerated well above the soft X-ray loop-top, which could be consistent with the electron acceleration between 40 Mm and 60 Mm above the flaring loop.

  4. 75th anniversary of the N V Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN) (Scientific session of the Physical Sciences Division of the Russian Academy of Sciences, 25 February 2015)

    NASA Astrophysics Data System (ADS)

    2015-06-01

    A scientific session of the Physical Sciences Division of the Russian Academy of Sciences (RAS) celebrating the 75th anniversary of the N V Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation of the RAS (IZMIRAN) was held in the IZMIRAN conference hall on 25 February 2015. The agenda of the session announced on the website http://www.gpad.ac.ru of the RAS Physical Sciences Division contained the following reports: (1) Kuznetsov V D (IZMIRAN, Moscow) "N V Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN) yesterday, today, and tomorrow"; (2) Gvishiani A D (Geophysical Center, Moscow) "Studies of the terrestrial magnetic field and the network of Russian magnetic laboratories"; (3) Sokoloff D D (Faculty of Physics, Lomonosov Moscow State University, Moscow) "Magnetic dynamo questions"; (4) Petrukovich A A (Space Research Institute, RAS, Moscow) "Some aspects of magnetosphere-ionosphere relations"; (5) Lukin D S (Moscow Institute of Physics and Technology (State University), Dolgoprudnyi, Moscow region) "Current problems of ionospheric radio wave propagation"; (6) Safargaleev V V (Polar Geophysical Institute, Kola Scientific Center, RAS, Murmansk), Sergienko T I (Swedish Institute of Space Physics (IRF), Sweden), Kozlovskii A E (Sodankyl \\ddot a Geophysical Observatory, Finland), Safargaleev A V (St. Petersburg State University, St. Petersburg), Kotikov A L (St. Petersburg Branch of IZMIRAN, St. Petersburg) "Magnetic and optical measurements and signatures of reconnection in the cusp and vicinity"; (7) Kuznetsov V D (IZMIRAN, Moscow) "Space solar research: achievements and prospects". Papers written on the basis of oral reports 1, 3, 4, 6, and 7 are given below. • N V Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN) yesterday, today, tomorrow, V D Kuznetsov Physics-Uspekhi, 2015

  5. Investigation on broadband propagation characteristic of terahertz electromagnetic wave in anisotropic magnetized plasma in frequency and time domain

    SciTech Connect

    Tian, Yuan; Han, Yiping; Ai, Xia; Liu, Xiuxiang

    2014-12-15

    In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.

  6. 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.

  7. Investigation on broadband propagation characteristic of terahertz electromagnetic wave in anisotropic magnetized plasma in frequency and time domain

    NASA Astrophysics Data System (ADS)

    Tian, Yuan; Ai, Xia; Han, Yiping; Liu, Xiuxiang

    2014-12-01

    In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.

  8. Signatures and Characteristics of Internal Gravity Waves in the Venus' and Mars' Atmospheres as Revealed by the Radio Occultation Temperature Data Analysis

    NASA Astrophysics Data System (ADS)

    Gubenko, Vladimir; Pavelyev, Alexander; Andreev, Vitali; Salimzyanov, Rishat; Pavelyev, Alexey

    2012-07-01

    It is well known that internal gravity waves (IGWs) affect the structure and mean circulation of the Earth' middle and upper atmosphere by transporting energy and horizontal momentum upward from the lower atmosphere. The IGWs modulate the background atmospheric structure, producing a periodic pattern of spatial and temporal variations in the wind velocity, temperature and density. Similar effects are anticipated for the Venus and Mars since IGWs are a characteristic of stably stratified atmosphere. For instance, Yakovlev et al. (1991) and Gubenko et al. (2008a) used the radio occultation (RO) data from Venera 15 and 16 missions to investigate the thermal structure and layering of the Venus' middle atmosphere. They noted that a wavelike periodic structure commonly appears in retrieved vertical profiles at altitudes above 60 km in the atmosphere where the static stability is large. Through comparisons between Magellan RO observations in the Venus' atmosphere, Hinson and Jenkins (1995) have demonstrated that small scale variations in retrieved temperature profiles at altitudes from 60 to 90 km are caused by a spectrum of vertical propagating IGWs. Temperature profiles from the Mars Global Surveyor (MGS) measurements reveal vertical wavelike structures assumed to be atmospheric IGWs in the Mars' lower atmosphere (Creasey et al., 2006). The very large IGW amplitudes inferred from MGS RO data imply a very significant role for IGWs in the atmospheric dynamics of Mars as well. There is one general problem inherent to all measurements of IGWs. Observed wavelike variations may alternatively be caused by the IGWs, turbulence or persistent layers in the atmosphere, and it is necessary to have an IGW identification criterion for the correct interpretation of obtained results. In this context, we have developed an original method for the determination of internal gravity wave parameters from a single vertical temperature profile measurement in a planetary atmosphere (Gubenko et

  9. 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.

  10. Observational Characteristics of Langmuir Turbulence Associated with Solar Type III Radio Bursts

    NASA Astrophysics Data System (ADS)

    Golla, T.; MacDowall, R. J.

    2015-12-01

    Solar flares present the most dramatic energy releases from the Sun. The solar flares accelerate electrons, which form bump-on-tail distributions, and excite electrostatic waves called Langmuir waves, which are subsequently converted into escaping radiation at the fundamental and second harmonic of the electron plasma frequency by some nonlinear processes. These radio emissions are called the type III radio bursts. The sources of these bursts represent natural laboratories of beam-plasma systems. The WAVES experiment on the STEREO spacecraft contains an improved Time Domain Sampler (TDS), improved over that of all similar high time resolution receivers flown in earlier spacecraft. It is primarily intended for the study of Langmuir waves. These in situ high time resolution wave measurements enable us to identify and understand the physical processes associated with beam-plasma systems, as well as for conversion of Langmuir waves into escaping radiation at the fundamental and second harmonic of the electron plasma frequency. The waveforms captured by the TDS usually contain a variety of distortions caused by various nonlinear processes. The normalized peak intensities, wave numbers and spectral widths of these wave packets determine the nonlinear processes, which control the evolution of these wave packets. We have analyzed the in situ high time resolution measurements of Langmuir wave packets and determined their three dimensional relative peak intensities, spectral components and spectral widths. Using the frequency drifts of the type III bursts, we have estimated the velocities of the electron beams which in turn yielded the corresponding wave numbers. We will present the distributions of these important physical quantities and their implications for the theoretical models.

  11. 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.

  12. Determination of the time delay in the case of two-path propagation on the basis of the attenuation characteristics for two adjacent frequencies

    NASA Technical Reports Server (NTRS)

    Gilroi, H. G.

    1979-01-01

    Pronounced fading occurring in the line of sight radio links at frequencies below 10 GHz can be traced to the effects of multipath propagation. Modulation disturbances depend on travel time differences between the direct wave and the wave which is reflected at atmospheric layers. A method described for the determination of the time delay is based on an indirect approach which utilizes the difference in fading at various frequencies. The method was employed in measurements involving a distance of 181 km. The results obtained in the measurement are discussed.

  13. 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

  14. Electrical and optical emission characteristics of radio-frequency-driven hollow slot microplasmas operating in open air

    NASA Astrophysics Data System (ADS)

    Yalin, A. P.; Yu, Z. Q.; Stan, O.; Hoshimiya, K.; Rahman, A.; Surla, V. K.; Collins, G. J.

    2003-10-01

    We employ hollow slot electrodes, with pd values of ˜10 Torr cm and average E/N values of ˜70 Td, to create plasmas in open air. We measure the 13.56 MHz Irf-Vrf electrical characteristics of the plasma. Stable discharges, with sinusoidal currents, are obtained up to power densities of 14 kW/cm3, and root-mean-square radio-frequency (rf) currents of 1.5 A/cm of slot length, before nonsinusoidal currents and rf glow-to-arc transitions occur. We report the absolute optical emission in the vacuum ultraviolet region located between 110 and 155 nm, with a focus on the 149 nm atomic nitrogen line. For this atomic N line alone, we find an emitter efficiency of 0.0024.

  15. 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)

  16. 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.

  17. Theoretical investigation of surface acoustic wave propagation characteristics in periodic (AlN/ZnO)N /diamond multilayer structures

    NASA Astrophysics Data System (ADS)

    Qian, Lirong; Li, Cuiping; Li, Mingji; Wang, Fang; Yang, Baohe

    2014-11-01

    Propagation characteristics of surface acoustic wave (SAW) in periodic (AlN/ZnO)N/diamond multilayer structures were theoretically investigated using effective permittivity method. The phase velocity Vp, electromechanical coupling coefficient K2, and temperature coefficient of frequency (TCF) of the Sezawa mode are analyzed for different thicknesses-to-wavelength H/λ, thickness ratios of AlN to ZnO Rh, and periods of alternating ZnO and AlN layers N. Results show that, comparing with AlN/ZnO/diamond multilayer structure, the periodic (AlN/ZnO)N/diamond multilayer structure (N ≥ 2) shows excellent electromechanical coupling and temperature stable characteristics with significantly improved K2 and TCF. The largest coupling coefficient of 3.0% associated with a phase velocity of 5726 m/s and a TCF of -29.2 ppm/°C can be reached for Rh = 0.2 and N = 2. For a low TCF of -24.4 ppm/°C, a large coupling coefficient of 2.0% associated with a phase velocity of 7058 m/s can be obtained for Rh = 1.0 and N = 5. The simulated results can be used to design the low loss and good temperature stability SAW devices of gigahertz-band application.

  18. Asymptotic limits of some models for sound propagation in porous media and the assignment of the pore characteristic lengths.

    PubMed

    Horoshenkov, Kirill V; Groby, Jean-Philippe; Dazel, Olivier

    2016-05-01

    Modeling of sound propagation in porous media requires the knowledge of several intrinsic material parameters, some of which are difficult or impossible to measure directly, particularly in the case of a porous medium which is composed of pores with a wide range of scales and random interconnections. Four particular parameters which are rarely measured non-acoustically, but used extensively in a number of acoustical models, are the viscous and thermal characteristic lengths, thermal permeability, and Pride parameter. The main purpose of this work is to show how these parameters relate to the pore size distribution which is a routine characteristic measured non-acoustically. This is achieved through the analysis of the asymptotic behavior of four analytical models which have been developed previously to predict the dynamic density and/or compressibility of the equivalent fluid in a porous medium. In this work the models proposed by Johnson, Koplik, and Dashn [J. Fluid Mech. 176, 379-402 (1987)], Champoux and Allard [J. Appl. Phys. 70(4), 1975-1979 (1991)], Pride, Morgan, and Gangi [Phys. Rev. B 47, 4964-4978 (1993)], and Horoshenkov, Attenborough, and Chandler-Wilde [J. Acoust. Soc. Am. 104, 1198-1209 (1998)] are compared. The findings are then used to compare the behavior of the complex dynamic density and compressibility of the fluid in a material pore with uniform and variable cross-sections. PMID:27250142

  19. Characteristics of radio frequency-sputtered ZnS on the flexible polyethylene terephthalate (PET) substrate.

    PubMed

    Yoo, Dongjun; Choi, Moon-Suk; Chung, Chulwon; Heo, Seung Chan; Kim, Dohyung; Choi, Changhwan

    2013-12-01

    Zinc sulfide (ZnS) thin film was deposited on the flexible polyethylene-terephtalate (PET) polymer substrate by radio frequency (RF) magnetron sputtering system. ZnS film has a critical thickness range affecting crystal structure where it shows preferred orientation with intensity peak of X-ray diffractometer at 28.4 degrees for ZnS thinner than 200 nm while hexagonal wurtzite and cubic zinc-blend (101) are co-existed for film thicker than 200 nm. Optical band gap energy (Eg) decreases with increasing RF-powers, resulting from increase in film thickness. Eg of ZnS films on PET is 3.68-3.86 eV, which is lower than that of ZnS on the rigid substrate by 0.27-0.28 eV. This is attributed to amount of incorporated oxygen to ZnS material as well as residual strain and disorder of grain boundary. Transmittance of ZnS on PET degrades due to surface defects and complex internal structure. Energy dispersive spectroscopy reveals out that ZnS film does not have a unity of Zn to S ratio, but it is close to stoichiometric composition with increasing thickness. PMID:24266145

  20. Propagation characteristics of atmospheric-pressure He+O{sub 2} plasmas inside a simulated endoscope channel

    SciTech Connect

    Wang, S.; Chen, Z. Y.; Wang, X. H. Li, D.; Yang, A. J.; Liu, D. X.; Rong, M. Z.; Chen, H. L.; Kong, M. G.

    2015-11-28

    Cold atmospheric-pressure plasmas have potential to be used for endoscope sterilization. In this study, a long quartz tube was used as the simulated endoscope channel, and an array of electrodes was warped one by one along the tube. Plasmas were generated in the inner channel of the tube, and their propagation characteristics in He+O{sub 2} feedstock gases were studied as a function of the oxygen concentration. It is found that each of the plasmas originates at the edge of an instantaneous cathode, and then it propagates bidirectionally. Interestingly, a plasma head with bright spots is formed in the hollow instantaneous cathode and moves towards its center part, and a plasma tail expands through the electrode gap and then forms a swallow tail in the instantaneous anode. The plasmas are in good axisymmetry when [O{sub 2}] ≤ 0.3%, but not for [O{sub 2}] ≥ 1%, and even behave in a stochastic manner when [O{sub 2}] = 3%. The antibacterial agents are charged species and reactive oxygen species, so their wall fluxes represent the “plasma dosage” for the sterilization. Such fluxes mainly act on the inner wall in the hollow electrode rather than that in the electrode gap, and they get to the maximum efficiency when the oxygen concentration is around 0.3%. It is estimated that one can reduce the electrode gap and enlarge the electrode width to achieve more homogenous and efficient antibacterial effect, which have benefits for sterilization applications.

  1. e-POP Radio Science Using Amateur Radio Transmissions

    NASA Astrophysics Data System (ADS)

    Frissell, N. A.; Perry, G. W.; Miller, E. S.; Shovkoplyas, A.; Moses, M. L.; James, H. G.; Yau, A. W.

    2015-12-01

    A major component of the enhanced Polar Outflow Probe (e-POP) Radio Receiver Instrument (RRI) mission is to utilize artificially generated radio emissions to study High Frequency (HF) radio wave propagation in the ionosphere. In the North American and European sectors, communications between amateur radio operators are a persistent and abundant source source of HF transmissions. We present the results of HF radio wave propagation experiments using amateur radio transmissions as an HF source for e-POP RRI. We detail how a distributed and autonomously operated amateur radio network can be leveraged to study HF radio wave propagation as well as the structuring and dynamics of the ionosphere over a large geographic region. In one case, the sudden disappearance of nearly two-dozen amateur radio HF sources located in the midwestern United States was used to detect a enhancement in foF2 in that same region. We compare our results to those from other more conventional radio instruments and models of the ionosphere to demonstrate the scientific merit of incorporating amateur radio networks for radio science at HF.

  2. 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

  3. Nanosecond Pulsed Discharge in Water without Bubbles: A Fundamental Study of Initiation, Propagation and Plasma Characteristics

    NASA Astrophysics Data System (ADS)

    Seepersad, Yohan

    The state of plasma is widely known as a gas-phase phenomenon, but plasma in liquids have also received significant attention over the last century. Generating plasma in liquids however is theoretically challenging, and this problem is often overcome via liquid-gas phase transition preceding the actual plasma formation. In this sense, plasma forms in gas bubbles in the liquid. Recent work at the Drexel Plasma Institute has shown that nanosecond pulsed electric fields can initiate plasma in liquids without any initial cavitation phase, at voltages below theoretical direct-ionization thresholds. This unique regime is poorly understood and does not fit into any current descriptive mechanisms. As with all new phenomena, a complete fundamental description is paramount to understanding its usefulness to practical applications. The primary goals of this research were to qualitatively and quantitatively understand the phenomenon of nanosecond pulsed discharge in liquids as a means to characterizing properties that may open up niche application possibilities. Analysis of the plasma was based on experimental results from non-invasive, sub-nanosecond time-resolved optical diagnostics, including direct imaging, transmission imaging (Schlieren and shadow), and optical emission spectroscopy. The physical characteristics of the plasma were studied as a function of variations in the electric field amplitude and polarity, liquid permittivity, and pulse duration. It was found that the plasma size and emission intensity was dependent on the permittivity of the liquid, as well as the voltage polarity, and the structure and dynamics were explained by a 'cold-lightning' mechanism. The under-breakdown dynamics at the liquid-electrode interface were investigated by transmission imaging to provide evidence for a novel mechanism for initiation based on the electrostriction. This mechanism was proposed by collaborators on the project and developed alongside the experimental work in this

  4. An Introduction to Radio Astronomy

    NASA Astrophysics Data System (ADS)

    Burke, Bernard F.; Graham-Smith, Francis

    2009-09-01

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

  5. An Introduction to Radio Astronomy

    NASA Astrophysics Data System (ADS)

    Burke, Bernard F.; Graham-Smith, Francis

    2014-02-01

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

  6. 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

  7. NASA Propagation Studies Website

    NASA Technical Reports Server (NTRS)

    Angkasa, Krisjani S.

    1996-01-01

    This paper describes an Internet website which provides information to enable the development of new commerical satellite systems and services by providing timely data and models about the propagation of satellite radio signals. In partnership with industry and academia, the program leverages NASA assets, currently the Advanced Communications Technology Satellite (ACTS), to obtain propagation data. The findings of the study are disseminated through refereed journals, NASA reference publications, workshops, electronic media, and direct interface with industry.

  8. Characteristics of tropical cyclones and overshooting from GPS radio occultation data

    NASA Astrophysics Data System (ADS)

    Biondi, Riccardo; Rieckh, Therese; Steiner, Andrea; Kirchengast, Gottfried

    2014-05-01

    Tropical cyclones (TCs) are extreme weather events causing every year huge damages and several deaths. In some countries they are the natural catastrophes accounting for the major economic damages. The thermal structure of TCs gives important information on the cloud top height allowing for a better understanding of the troposphere-stratosphere transport, which is still poorly understood. The measurement of atmospheric parameters (such as temperature, pressure and humidity) with high vertical resolution and accuracy in the upper troposphere and lower stratosphere (UTLS) is difficult especially during severe weather events (e.g TCs). Satellite remote sensing has improved the TC forecast and monitoring accuracy. In the last decade the Global Positioning Systems (GPS) Radio Occultation (RO) technique contributed to improve our knowledge especially at high troposphere altitudes and in remote regions of the globe thanks to the high vertical resolution, avoiding temperature smoothing issues (given by microwave and infrared instruments) in the UTLS and improving the poor temporal resolution and global coverage given by lidars and radars. We selected more than twenty-thousand GPS RO profiles co-located with TC best tracks for the period 2001 to 2012 and computed temperature anomaly profiles relative to a RO background climatology in order to detect TC cloud tops. We characterized the thermal structure for different ocean basins and for different TC intensities, distinguishing between tropical and extra-tropical cases. The analysis shows that all investigated storms have a common feature: they warm the troposphere and cool the UTLS near the cloud top. This behavior is amplified in the extra-tropical areas. Results reveal that the storms' cloud tops in the southern hemisphere basins reach higher altitudes and lower temperatures than in the northern hemisphere basins. We furthermore compared the cloud top height of each profile with the mean tropopause altitude (from the RO

  9. A Study of the Short-Term Stability of Energy Characteristics of the Ionospheric Radio Channel

    NASA Astrophysics Data System (ADS)

    Barabashov, B. G.; Ogar, A. S.; Pelevin, O. Yu.; Radio, L. P.

    2015-04-01

    On the basis of the results of long-term measurements on the calibrated mid-latitude highfrequency paths, it is concluded that the processes responsible for the energy characteristics of the high-frequency wave field have inertial properties. Slow (one-hour) absolute variations in the average signal and effective-noise levels in the daytime and the night-time hours do not exceed 2 .0 dB. Similar variations in the average signal levels in the twilight hours after removal of the trend, which is caused by the diurnal variation in the ionospheric characteristics, are also below 2 .0 dB. Analysis of the time behavior of the relative error-appearance frequency during transmission of the binary sequences with the amplitude manipulation indicates that the above frequency varies in the range 20 -75 % for an hour if the reception results are averaged for 20 min.

  10. Characteristics of atmospheric-pressure, radio-frequency glow discharges operated with argon added ethanol

    NASA Astrophysics Data System (ADS)

    Sun, Wen-Ting; Li, Guo; Li, He-Ping; Bao, Cheng-Yu; Wang, Hua-Bo; Zeng, Shi; Gao, Xing; Luo, Hui-Ying

    2007-06-01

    Rf, atmospheric-pressure glow discharge (APGD) plasmas with bare metal electrodes have promising prospects in the fields of plasma-aided etching, thin film deposition, disinfection and sterilization, etc. In this paper, the discharge characteristics are presented for the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes. The experimental results show that the breakdown voltage can be reduced significantly when a small amount of ethanol is added into argon, probably due to the fact that the Penning ionization process is involved, and a pure α-mode discharge can be produced more easily with the help of ethanol. The uniformity of the rf APGDs of pure argon or argon-ethanol mixtures using bare metallic electrodes is identified with the aid of the intensified charge coupled device images.

  11. Characteristics of atmospheric-pressure, radio-frequency glow discharges operated with argon added ethanol

    SciTech Connect

    Sun Wenting; Li Guo; Li Heping; Bao Chengyu; Wang Huabo; Zeng Shi; Gao Xing; Luo Huiying

    2007-06-15

    Rf, atmospheric-pressure glow discharge (APGD) plasmas with bare metal electrodes have promising prospects in the fields of plasma-aided etching, thin film deposition, disinfection and sterilization, etc. In this paper, the discharge characteristics are presented for the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes. The experimental results show that the breakdown voltage can be reduced significantly when a small amount of ethanol is added into argon, probably due to the fact that the Penning ionization process is involved, and a pure {alpha}-mode discharge can be produced more easily with the help of ethanol. The uniformity of the rf APGDs of pure argon or argon-ethanol mixtures using bare metallic electrodes is identified with the aid of the intensified charge coupled device images.

  12. GPS radio interferometry of travelling ionospheric disturbances

    NASA Astrophysics Data System (ADS)

    Afraimovich, E. L.; Palamartchouk, K. S.; Perevalova, N. P.

    1998-01-01

    This paper presents some results investigating the new possibilities of radio interferometry of Travelling Ionospheric Disturbances (TIDs) that are based on exploiting standard measurements of transionospheric radio signal characteristics and coordinate-time measurements using dual-frequency multichannel receivers of the Global Positioning System (GPS). A Statistical Angle-of-arrival and Doppler Method for GPS radio interferometry (SADM-GPS) is proposed for determining the characteristics of the TIDs dynamics by measuring variations of GPS phase derivatives with respect to time and spatial coordinates. These data are used to calculate corresponding values of the velocity vector, in view of a correction for satellite motions based on the current information available regarding the angular coordinates of the satellites. Subsequently, velocity and direction distributions are constructed and analyzed to verify the hypothesis of whether there is a predominant displacement. If it exists, then the pattern can be considered to be travelling, and the mean travel velocity can be determined from the velocity distribution. Through a computer simulation it was shown that multi-satellite GPS radio interferometry in conjunction with the SADM-GPS algorithm allows the detection and measurement of the velocity vector of TIDs in virtually the entire azimuthal range of possible TID propagation directions. The use of the proposed method is exemplified by an investigation of TIDs during the solar eclipse of 9 March 1997, using the GPS-radio interferometer GPSINT at Irkutsk.

  13. Satellite sound broadcast propagation measurements and system impairments

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.; Golshan, Nasser

    1992-01-01

    An evaluation of the operational characteristics of indoor portable reception of satellite sound reception has identified the nature of UHF and L-band signals' penetration loss in the cases of buildings having intricate spectral and spatial signal structures. These propagation impairments must be mitigated by resort to a combination of link margin, diversity techniques, and/or the efforts of a listener to place the radio (or its antenna) in an advantageous location. Attention is given to cost/performance tradeoffs for a mix of these measures, with a view to Direct Broadcast Satellite Radio system design.

  14. Particle model analyses of N2O dilution with He on electrical characteristics of radio-frequency discharges

    NASA Astrophysics Data System (ADS)

    Younis, G.; Yousfi, M.; Despax, B.

    2009-05-01

    The electrical characteristics (voltage, electric field, charged particle densities, dissipated power, particle energy, etc.) are analyzed in the case of low pressure (0.5 and 1 Torr) radio-frequency (rf) discharges in nitrous oxide (N2O)/Helium (He) mixtures. An optimized and validated particle model has been used for these analyses in the case of gradual dilutions of N2O with He buffer gas. A specific care is carried on the power density evolution and variation which show a complex behavior as a function of He proportion (up to 85%). These analyses are based on a microscopic approach enabling one to show the contribution of the different inelastic processes mainly between electrons and respectively N2O and He gases. This approach enables also one to show the discharge region (the positive column or the plasma region) where the power is preferentially dissipated. The power density variation is found to be mainly proportional to the electron density variation. The latter is dependent on the different processes occurring between the charged particles [i.e., electrons, negative ions (O- and NO-), and positive ions (N2O+ and He+)] and the neutral gas mixture (N2O and He). Furthermore, the particle model shows the role of the electron-He collisions on the variation in the electron energy and distribution. This allows more particularly explaining the effects of N2O dilution with He on the dissipated power variation in terms of creation and loss of electrons through collision processes.

  15. Photocatalytic characteristic and photodegradation kinetics of toluene using N-doped TiO2 modified by radio frequency plasma.

    PubMed

    Shie, Je-Lueng; Lee, Chiu-Hsuan; Chiou, Chyow-San; Chen, Yi-Hung; Chang, Ching-Yuan

    2014-01-01

    This study investigates the feasibility of applications of the plasma surface modification of photocatalysts and the removal of toluene from indoor environments. N-doped TiO2 is prepared by precipitation methods and calcined using a muffle furnace (MF) and modified by radio frequency plasma (RF) at different temperatures with light sources from a visible light lamp (VLL), a white light-emitting diode (WLED) and an ultraviolet light-emitting diode (UVLED). The operation parameters and influential factors are addressed and prepared for characteristic analysis and photo-decomposition examination. Furthermore, related kinetic models are established and used to simulate the experimental data. The characteristic analysis results show that the RF plasma-calcination method enhanced the Brunauer Emmett Teller surface area of the modified photocatalysts effectively. For the elemental analysis, the mass percentages of N for the RF-modified photocatalyst are larger than those of MF by six times. The aerodynamic diameters of the RF-modifiedphotocatalyst are all smaller than those of MF. Photocatalytic decompositions of toluene are elucidated according to the Langmuir-Hinshelwood model. Decomposition efficiencies (eta) of toluene for RF-calcined methods are all higher than those of commercial TiO2 (P25). Reaction kinetics ofphoto-decomposition reactions using RF-calcined methods with WLED are proposed. A comparison of the simulation results with experimental data is also made and indicates good agreement. All the results provide useful information and design specifications. Thus, this study shows the feasibility and potential use of plasma modification via LED in photocatalysis.

  16. Photocatalytic characteristic and photodegradation kinetics of toluene using N-doped TiO2 modified by radio frequency plasma.

    PubMed

    Shie, Je-Lueng; Lee, Chiu-Hsuan; Chiou, Chyow-San; Chen, Yi-Hung; Chang, Ching-Yuan

    2014-01-01

    This study investigates the feasibility of applications of the plasma surface modification of photocatalysts and the removal of toluene from indoor environments. N-doped TiO2 is prepared by precipitation methods and calcined using a muffle furnace (MF) and modified by radio frequency plasma (RF) at different temperatures with light sources from a visible light lamp (VLL), a white light-emitting diode (WLED) and an ultraviolet light-emitting diode (UVLED). The operation parameters and influential factors are addressed and prepared for characteristic analysis and photo-decomposition examination. Furthermore, related kinetic models are established and used to simulate the experimental data. The characteristic analysis results show that the RF plasma-calcination method enhanced the Brunauer Emmett Teller surface area of the modified photocatalysts effectively. For the elemental analysis, the mass percentages of N for the RF-modified photocatalyst are larger than those of MF by six times. The aerodynamic diameters of the RF-modifiedphotocatalyst are all smaller than those of MF. Photocatalytic decompositions of toluene are elucidated according to the Langmuir-Hinshelwood model. Decomposition efficiencies (eta) of toluene for RF-calcined methods are all higher than those of commercial TiO2 (P25). Reaction kinetics ofphoto-decomposition reactions using RF-calcined methods with WLED are proposed. A comparison of the simulation results with experimental data is also made and indicates good agreement. All the results provide useful information and design specifications. Thus, this study shows the feasibility and potential use of plasma modification via LED in photocatalysis. PMID:24645445

  17. Empirical relations to determine the normalized spot size of a single-mode trapezoidal index fiber and computation of its propagation characteristics

    NASA Astrophysics Data System (ADS)

    Mallick, Aswini Kumar; Sarkar, Somenath

    2014-07-01

    Simple and complete empirical relations are presented here to determine a normalized spot size in terms of normalized frequencies over a long range and aspect ratio of a trapezoidal index single-mode fiber considering Gaussian approximation of the fundamental mode following the Marcuse method for the first time. After verification of their validity for arbitrary values of aspect ratio and normalized frequency, we calculate various propagation characteristics viz. dispersion and splice loss by using our formulations. Upon comparison, we observe an excellent match and the validity of our results with exact values and other results available in the literature. These formulas should attract the attention of experimentalists as a simple alternative to the rigorous methods of estimating the propagation characteristics of such fibers.

  18. 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 ±40 μm level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ±0.08 μrad. 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.

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

    SciTech Connect

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

    2013-09-15

    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 ±40 μm level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ±0.08 μrad. 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.

  20. Experimental investigations of the characteristics of short-wave signals on short paths during modification of the ionosphere by powerful short-wave radio emission

    NASA Astrophysics Data System (ADS)

    Blagoveshchenskaia, N. F.; Bubnov, V. A.; Shelukhin, V. I.

    1992-01-01

    Results of experimental investigations of the fine structure and parameters of aspect-scattered short-wave signals are presented. The results are based on experimental observations obtained by a Doppler technique and the ionospheric oblique sounding technique. Measurement data of the Doppler and angular characteristics of shortwave signals during modification of the ionosphere by powerful short-wave radio emission are presented. The seasonal and diurnal variations of the short-wave scattering frequency range are considered.

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

    SciTech Connect

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

    2015-06-15

    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. Particle model analyses of N{sub 2}O dilution with He on electrical characteristics of radio-frequency discharges

    SciTech Connect

    Younis, G.; Yousfi, M.; Despax, B.

    2009-05-01

    The electrical characteristics (voltage, electric field, charged particle densities, dissipated power, particle energy, etc.) are analyzed in the case of low pressure (0.5 and 1 Torr) radio-frequency (rf) discharges in nitrous oxide (N{sub 2}O)/Helium (He) mixtures. An optimized and validated particle model has been used for these analyses in the case of gradual dilutions of N{sub 2}O with He buffer gas. A specific care is carried on the power density evolution and variation which show a complex behavior as a function of He proportion (up to 85%). These analyses are based on a microscopic approach enabling one to show the contribution of the different inelastic processes mainly between electrons and respectively N{sub 2}O and He gases. This approach enables also one to show the discharge region (the positive column or the plasma region) where the power is preferentially dissipated. The power density variation is found to be mainly proportional to the electron density variation. The latter is dependent on the different processes occurring between the charged particles [i.e., electrons, negative ions (O{sup -} and NO{sup -}), and positive ions (N{sub 2}O{sup +} and He{sup +})] and the neutral gas mixture (N{sub 2}O and He). Furthermore, the particle model shows the role of the electron-He collisions on the variation in the electron energy and distribution. This allows more particularly explaining the effects of N{sub 2}O dilution with He on the dissipated power variation in terms of creation and loss of electrons through collision processes.

  3. ACTS propagation experiment discussion: Ka-band propagation measurements using the ACTS propagation terminal and the CSU-CHILL and Space Communications Technology Center Florida propagation program

    NASA Technical Reports Server (NTRS)

    Bringi, V. N.; Chandrasekar, V.; Mueller, Eugene A.; Turk, Joseph; Beaver, John; Helmken, Henry F.; Henning, Rudy

    1993-01-01

    Papers on Ka-band propagation measurements using the ACTS propagation terminal and the Colorado State University CHILL multiparameter radar and on Space Communications Technology Center Florida Propagation Program are discussed. Topics covered include: microwave radiative transfer and propagation models; NASA propagation terminal status; ACTS channel characteristics; FAU receive only terminal; FAU terminal status; and propagation testbed.

  4. Wave propagation characteristics of helically orthotropic cylindrical shells and resonance emergence in scattered acoustic field. Part 1. Formulations

    NASA Astrophysics Data System (ADS)

    Rajabi, Majid

    2016-05-01

    The method of wave function expansion is adopted to study the three dimensional scattering of a plane progressive harmonic acoustic wave incident upon an arbitrarily thick-walled helically filament-wound composite cylindrical shell submerged in and filled with compressible ideal fluids. An approximate laminate model in the context of the so-called state-space formulation is employed for the construction of T-matrix solution to solve for the unknown modal scattering coefficients. Considering the nonaxisymmetric wave propagation phenomenon in anisotropic cylindrical components and following the resonance scattering theory which determines the resonance and background scattering fields, the stimulated resonance frequencies of the shell are isolated and classified due to their fundamental mode of excitation, overtone and style of propagation along the cylindrical axis (i.e., clockwise or anticlockwise propagation around the shell) and are identified as the helically circumnavigating waves.

  5. The correlation between the characteristics of seismic wave propagation in Western Caucasus and the geological-tectonic features of the region

    NASA Astrophysics Data System (ADS)

    Kharazova, Yu. V.; Pavlenko, O. V.; Dudinskii, K. A.

    2016-05-01

    The relationship between the characteristics of seismic waves in the Western Caucasus and the geological-tectonic structure of the region is studied for identifying the specificity of seismic propagation in the mountainous regions with a complicated geological structure and forecasting the characteristics of the propagation from the geological and tectonic data. The interpretation is presented for the estimates of the Q-factor of the medium ( Q( f) ~ 55 f 0.9 in the region of Sochi and Q( f) ~ 90 f 0.7 in the region of Anapa), seismic wave enhancement in the upper crustal layers ( A( f) ~ 1), and peak ground acceleration residuals, which were previously determined from the records of the local earthquakes and show the distributions of local variations in the parameters of seismic wave radiation and propagation. The obtained characteristics are interpreted in the context of the up-to-date information about the tectonic, geological, and deep structure of the epicentral zones in the Western Caucasus and neighboring territory of the Black Sea. The discrepancies revealed in the low-frequency behavior of the Q-factor in the vicinities of Sochi and Anapa is accounted for by the spatial scale and character of tectonic dislocations of the rocks in these regions. The local variations in the parameters of seismic radiation and propagation are probably related to the geological features of the region such as the fault structures, including the thrusts, shatter zones, oblique seismic boundaries, variations in the thickness and consolidation of the sedimentary cover, as well as the peculiarities in the structure and material composition of the basement.

  6. Horizontal structure and propagation characteristics of mesospheric gravity waves observed by Antarctic Gravity Wave Imaging/Instrument Network (ANGWIN), using a 3-D spectral analysis technique

    NASA Astrophysics Data System (ADS)

    Matsuda, Takashi S.; Nakamura, Takuji; Murphy, Damian; Tsutsumi, Masaki; Moffat-Griffin, Tracy; Zhao, Yucheng; Pautet, Pierre-Dominique; Ejiri, Mitsumu K.; Taylor, Michael

    2016-07-01

    ANGWIN (Antarctic Gravity Wave Imaging/Instrument Network) is an international airglow imager/instrument network in the Antarctic, which commenced observations in 2011. It seeks to reveal characteristics of mesospheric gravity waves, and to study sources, propagation, breaking of the gravity waves over the Antarctic and the effects on general circulation and upper atmosphere. In this study, we compared distributions of horizontal phase velocity of the gravity waves at around 90 km altitude observed in the mesospheric airglow imaging over different locations using our new statistical analysis method of 3-D Fourier transform, developed by Matsuda et al. (2014). Results from the airglow imagers at four stations at Syowa (69S, 40E), Halley (76S, 27W), Davis (69S, 78E) and McMurdo (78S, 156E) out of the ANGWIN imagers have been compared, for the observation period between April 6 and May 21 in 2013. In addition to the horizontal distribution of propagation and phase speed, gravity wave energies have been quantitatively compared, indicating a smaller GW activity in higher latitude stations. We further investigated frequency dependence of gravity wave propagation direction, as well as nightly variation of the gravity wave direction and correlation with the background wind variations. We found that variation of propagation direction is partly due to the effect of background wind in the middle atmosphere, but variation of wave sources could play important role as well. Secondary wave generation is also needed to explain the observed results.

  7. Radio Channel Simulator (RCSM)

    2007-01-31

    This is a simulation package for making site specific predictions of radio signal strength. The software computes received power at discrete grid points as a function of the transmitter location and propagation environment. It is intended for use with wireless network simulation packages and to support wireless network deployments.

  8. Solar Power Satellite (SPS) pilot beam and communication link subsystem investigation study, phase 1. [ionospheric propagation, radio frequency interference, and microwave transmission

    NASA Technical Reports Server (NTRS)

    1979-01-01

    A preliminary engineering model of ionospheric interactions with the pilot beam was established and used to demonstrate that the dual frequency baseline pilot beam system might not be viable in the presence of an unstable transmission path. Alternate approaches to remove this difficulty are described. Although ionospheric fluctuations will not significantly degrade beam pointing or raise the sidelobe levels, they will reduce transmission efficiency by upwards of 25%. Mitigating strategies to substantially reduce this effect are proposed. Based on the Klystron noise spectrum, the pilot beam transmitter power was determined as a function of frequency offset from the power beam carrier frequency. The RFI from the pilot beam, on the ground and at geosynchronous orbit is shown. Noise levels on the earth's surface due to the SPS are presented as a function of frequency and the number of SPS systems. Analysis of the communication subsystem indicates that a standard telemetry line of 1.544 MB/s would satisfy both voice and data link requirements. Additional links would be required for TV and radio transmissions.

  9. Light propagation characteristics in photonic crystal fibers with α-power profiles of air hole diameter distributions and their application to fiber collimator

    NASA Astrophysics Data System (ADS)

    Yokota, Hirohisa; Higuchi, Keiichi; Imai, Yoh

    2016-08-01

    Light propagation characteristics in photonic crystal fibers (PCFs) with α-power profiles of air hole diameter distributions were theoretically investigated. It was clarified that the intensity peak of the beam propagating in the PCF with Gaussian beam excitation varied periodically with little power attenuation. It was found that the envelope of the periodic intensity variation depended on α. We theoretically demonstrated that the PCF with the α-power profile of the air hole diameter distribution could be applied to a collimator for a conventional PCF with uniform air holes in Gaussian beam excitation to reduce coupling loss, where a PCF of appropriate length with the α-power air hole diameter distribution was spliced to a conventional PCF. It was also found that the coupling efficiency was higher for a larger α.

  10. 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.

  11. Locating Radio Noise from Sprites

    NASA Astrophysics Data System (ADS)

    Fullekrug, M.; Mezentsev, A.; Watson, R.; Gaffet, S.; Astin, I.; Evans, A.

    2014-12-01

    Sprites are composed of individual streamer discharges (e.g., Pasko, 2010) which split into exponentially growing streamer tips (McHarg et al., 2010). The acceleration of the electrons to a few eV results in the radiation of a small amount of electromagnetic energy. The incoherent superposition of many streamers causes the low frequency radio noise from sprites near ~40 km height (Qin et al., 2012). The presence of this theoretically predicted radiation was recently confirmed by low frequency radio noise measurements during dancing sprites with a very sensitive radio receiver (Fullekrug et al., 2013). To locate the radio noise from sprites in the sky, an interferometric network of low frequency radio receivers was developed (Mezentsev and Fullekrug, JGR, 2013). The key parameter for the interferometric signal processing is the frequency dependent wave propagation velocity of the radio waves within the Earth's atmosphere. This wave propagation velocity is determined by the wave number vector which needs to be inferred from the measurements. Here we adapt and subsequently apply array analyses which have been developed for seismic and infrasound arrays to determine the horizontal wave number vectors of ~20-24 kHz radio waves measured with an array of ten radio receivers distributed over an area of ~1 km × 1 km. It is found that the horizontal slowness of ~20-24 kHz radio waves ranges from ~2.7 ns/m to ~4.1 ns/m depending on the arrival azimuth of the radio wave. For comparison, an electromagnetic wave in vacuum has a slowness of ~3.34 ns/m. A larger slowness indicates an apparent velocity which is smaller than the speed of light and a smaller slowness indicates that the radio wave arrives at the array from an elevation angle. The observed variability of the observed slowness almost certainly results from the distance dependent superposition of the transverse electric and magnetic TEn and TMn radio wave propagation modes.

  12. Propagation research in Japan

    NASA Technical Reports Server (NTRS)

    Wakana, Hiromitsu

    1991-01-01

    L-band propagation measurements for land-mobile, maritime, and aeronautical satellite communications have been carried out by using the Japanese Engineering Test Satellite-Five (ETS-5) which was launched in Aug. 1987. This paper presents propagation characteristics for each of the mobile satellite communication channels.

  13. Energetic electrons from solar flares and associated type 3 radio bursts from metric to hectometric wave frequencies

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1972-01-01

    Distinct Kev electron events as observed by satellites near the earth are, in general, associated with solar flares which are accompained by the emission of both metric and hectometric type 3 radio bursts. The positions of these flares are mainly on the western hemisphere of the sun. These results show that Kev electrons propagate under the control of the magnetic field in the interplanetary space and that, while propagating through this space, these electrons excite type 3 radio bursts from metric to hectometric wave frequencies. Emission characteristics of hectometric type 3 bursts are briefly considered in relation to the positions of associated flares.

  14. Microplasma mode transition and corresponding propagation characteristics controlled by manipulating electric field strength in a microchannel-cavity hybrid structure device

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Ni, J. H.; Zhong, S.; Zhang, X.; Liang, Z.; Liu, C.; Park, S.-J.; Eden, J. G.

    2016-10-01

    Plasma redistribution in a symmetric microchannel-cavity hybrid structure device has been investigated by modulating the applied electric field strength. The device array has been operated in 200 Torr of argon, driven by a 20 kHz bipolar waveform. With the existence of the intervening microchannel between microcavities, several stable modes of operation of the microplasma have been observed, including cavity mode, hybrid mode and channel mode. Transition between the modes occurs with modulation of the applied voltage from 800 to 1100 V. The characteristics of microplasma propagation in different modes are investigated and the propagation speed along diagonal direction of the device in cavity mode, hybrid and channel mode are calculated to be ~48, ~29 and ~32 km s-1, respectively. Nonhomogeneous electric field strength distribution and plasma interaction have been discussed to explain these experimental results. Emission intensity and propagation speed differences in the cavity mode between the polarities of the applied voltage are interpreted through spatially resolved measurements of the emission profile in a partial channel-cavity array.

  15. Radio Journalism.

    ERIC Educational Resources Information Center

    Bittner, John R.; Bittner, Denise A.

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

  16. The NASA radiowave propagation program

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz

    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 reach a state of relative maturity in 1990. The program also supported the satellite communications community by publishing and revising two handbooks dealing with radio wave propagation effects for frequencies below and above 10 GHz, respectively. The program has served the international community through its support of the International Telecommunications Union. It supports state of the art work at universities. Currently, the program is focusing on the Advanced Communications Technology Satellite (ACTS) and its propagation needs. An overview of the program's involvement in the ACTS project is given.

  17. The NASA radiowave propagation program

    NASA Astrophysics Data System (ADS)

    Davarian, Faramaz

    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 reach a state of relative maturity in 1990. The program also supported the satellite communications community by publishing and revising two handbooks dealing with radio wave propagation effects for frequencies below and above 10 GHz, respectively. The program has served the international community through its support of the International Telecommunications Union. It supports state of the art work at universities. Currently, the program is focusing on the Advanced Communications Technology Satellite (ACTS) and its propagation needs. An overview of the program's involvement in the ACTS project is given.

  18. Measured Propagation Characteristics of Coplanar Waveguide on Semi-Insulating 4H-SiC Through 800 K

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Alterovitz, Samuel A.; Downey, Alan N.; Freeman, Jon C.; Schwartz, Zachary D.

    2003-01-01

    Wireless sensors for high temperature industrial applications and jet engines require RF transmission lines and RF integrated circuits (RFICs) on wide bandgap semiconductors such as SiC. In this paper, the complex propagation constant of coplanar waveguide fabricated on semiinsulating 4H-SiC has been measured through 813 K. It is shown that the attenuation increases 3.4 dB/cm at 50 GHz as the SiC temperature is increased from 300 K to 813 K. Above 500 K, the major contribution to loss is the decrease in SiC resistivity. The effective permittivity of the same line increases by approximately 5 percent at microwave frequencies and 20 percent at 1 GHz.

  19. PROPAGATION OF SOLAR ENERGETIC PARTICLES IN THREE-DIMENSIONAL INTERPLANETARY MAGNETIC FIELDS: IN VIEW OF CHARACTERISTICS OF SOURCES

    SciTech Connect

    He, H.-Q.; Qin, G.; Zhang, M. E-mail: gqin@spaceweather.ac.cn

    2011-06-20

    In this paper, a model of solar energetic particle (SEP) propagation in the three-dimensional Parker interplanetary magnetic field is calculated numerically. We study the effects of the different aspects of particle sources on the solar surface, which include the source location, coverage of latitude and longitude, and spatial distribution of source particle intensity, on propagation of SEPs with both parallel and perpendicular diffusion. We compute the particle flux and anisotropy profiles at different observation locations in the heliosphere. From our calculations, we find that the observation location relative to the latitudinal and longitudinal coverage of particle source has the strongest effects on particle flux and anisotropy profiles observed by a spacecraft. When a spacecraft is directly connected to the solar sources by the interplanetary magnetic field lines, the observed particle fluxes are larger than when the spacecraft is not directly connected. This paper focuses on the situations when a spacecraft is not connected to the particle sources on the solar surface. We find that when the magnetic footpoint of the spacecraft is farther away from the source, the observed particle flux is smaller and its onset and maximum intensity occur later. When the particle source covers a larger range of latitude and longitude, the observed particle flux is larger and appears earlier. There is east-west azimuthal asymmetry in SEP profiles even when the source distribution is east-west symmetric. However, the detail of particle spatial distribution inside the source does not affect the profile of the SEP flux very much. When the magnetic footpoint of the spacecraft is significantly far away from the particle source, the anisotropy of particles in the early stage of an SEP event points toward the Sun, which indicates that the first arriving particles come from outside of the observer through perpendicular diffusion at large radial distances.

  20. 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

  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. NASA Propagation Program Status and Propagation Needs of Satcom Industry

    NASA Technical Reports Server (NTRS)

    Golshan, Nassar

    1996-01-01

    The program objective is to enable the development of new commercial satellite systems and services and to support NASA's programs by providing timely data and models about propagation of satellite radio signals though the intervening environment. Provisions include new services, higher frequencies, higher data rates, different environments (mobile, indoors, fixed), and different orbits (geostationary, low earth orbit).

  3. Noise characteristics of CT perfusion imaging: how does noise propagate from source images to final perfusion maps?

    NASA Astrophysics Data System (ADS)

    Li, Ke; Chen, Guang-Hong

    2016-03-01

    Cerebral CT perfusion (CTP) imaging is playing an important role in the diagnosis and treatment of acute ischemic strokes. Meanwhile, the reliability of CTP-based ischemic lesion detection has been challenged due to the noisy appearance and low signal-to-noise ratio of CTP maps. To reduce noise and improve image quality, a rigorous study on the noise transfer properties of CTP systems is highly desirable to provide the needed scientific guidance. This paper concerns how noise in the CTP source images propagates to the final CTP maps. Both theoretical deviations and subsequent validation experiments demonstrated that, the noise level of background frames plays a dominant role in the noise of the cerebral blood volume (CBV) maps. This is in direct contradiction with the general belief that noise of non-background image frames is of greater importance in CTP imaging. The study found that when radiation doses delivered to the background frames and to all non-background frames are equal, lowest noise variance is achieved in the final CBV maps. This novel equality condition provides a practical means to optimize radiation dose delivery in CTP data acquisition: radiation exposures should be modulated between background frames and non-background frames so that the above equality condition is satisïnAed. For several typical CTP acquisition protocols, numerical simulations and in vivo canine experiment demonstrated that noise of CBV can be effectively reduced using the proposed exposure modulation method.

  4. 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.

  5. Radio broadcasting via satellite

    NASA Astrophysics Data System (ADS)

    Helm, Neil R.; Pritchard, Wilbur L.

    1990-10-01

    Market areas offering potential for future narrowband broadcast satellites are examined, including international public diplomacy, government- and advertising-supported, and business-application usages. Technical issues such as frequency allocation, spacecraft types, transmission parameters, and radio receiver characteristics are outlined. Service and system requirements, advertising revenue, and business communications services are among the economic issues discussed. The institutional framework required to provide an operational radio broadcast service is studied, and new initiatives in direct broadcast audio radio systems, encompassing studies, tests, in-orbit demonstrations of, and proposals for national and international commercial broadcast services are considered.

  6. 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.

  7. Quasar feedback and the origin of radio emission in radio-quiet quasars

    NASA Astrophysics Data System (ADS)

    Zakamska, Nadia L.; Greene, Jenny E.

    2014-07-01

    We analyse Sloan Digital Sky Survey spectra of 568 obscured luminous quasars. The [O III] λ5007 Å emission line shows blueshifts and blue excess, indicating that some of the narrow-line gas is undergoing an organized outflow. The velocity width containing 90 per cent of line power ranges from 370 to 4780 km s-1, suggesting outflow velocities up to ˜2000 km s-1, and is strongly correlated with the radio luminosity among the radio-quiet quasars. We propose that radio emission in radio-quiet quasars is due to relativistic particles accelerated in the shocks within the quasar-driven outflows; star formation in quasar hosts is insufficient to explain the observed radio emission. The median radio luminosity of the sample of νLν[1.4 GHz] = 1040 erg s-1 suggests a median kinetic luminosity of the quasar-driven wind of Lwind = 3 × 1044 erg s-1, or about 4 per cent of the estimated median bolometric luminosity Lbol = 8 × 1045 erg s-1. Furthermore, the velocity width of [O III] is positively correlated with mid-infrared luminosity, which suggests that outflows are ultimately driven by the radiative output of the quasar. Emission lines characteristic of shocks in quasi-neutral medium increase with the velocity of the outflow, which we take as evidence of quasar-driven winds propagating into the interstellar medium of the host galaxy. Quasar feedback appears to operate above the threshold luminosity of Lbol ˜ 3 × 1045 erg s-1.

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

    PubMed Central

    TSUDA, Toshitaka

    2014-01-01

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

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

    PubMed

    Tsuda, Toshitaka

    2014-01-01

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

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

    PubMed

    Tsuda, Toshitaka

    2014-01-01

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

  11. 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.

  12. 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.

  13. Fast, Accurate RF Propagation Modeling and Simulation Tool for Highly Cluttered Environments

    SciTech Connect

    Kuruganti, Phani Teja

    2007-01-01

    As network centric warfare and distributed operations paradigms unfold, there is a need for robust, fast wireless network deployment tools. These tools must take into consideration the terrain of the operating theater, and facilitate specific modeling of end to end network performance based on accurate RF propagation predictions. It is well known that empirical models can not provide accurate, site specific predictions of radio channel behavior. In this paper an event-driven wave propagation simulation is proposed as a computationally efficient technique for predicting critical propagation characteristics of RF signals in cluttered environments. Convincing validation and simulator performance studies confirm the suitability of this method for indoor and urban area RF channel modeling. By integrating our RF propagation prediction tool, RCSIM, with popular packetlevel network simulators, we are able to construct an end to end network analysis tool for wireless networks operated in built-up urban areas.

  14. Radio wave.

    PubMed

    Elkin, V

    1992-01-01

    In developing countries with high rates of poverty and illiteracy, radio is emerging as an excellent medium for delivering information on health issues, family planning, nutrition, and agricultural development. Since radio does not require wired electricity, it can reach remote rural populations. Surveys have found that between 50-75% of poor rural households in developing countries own radios, and the majority listen to educational radio at least once a week. A program that reaches the urban poor outside of Lima, Peru, has been instrumental in controlling the spread of cholera. A Bolivian station broadcasts 8 hours of literacy, health, agricultural, and cultural programming a day to an audience of more than 2 million Aymara Indians. Small village radio stations with a broadcast range of 15 miles can be established for under US$400 and can generally achieve sustainability through local fundraising events such as raffles. In many cases, listeners have become broadcasters at their local radio stations.

  15. Radio sociology

    NASA Astrophysics Data System (ADS)

    Swenson, George W., Jr.

    1996-04-01

    A work was conducted, using radio telemetry, to locate a migrating, radio-tagged, sharp-shinned hawk. The hawk was monitored through the noise radiation it created. The hawk was found. During this study, it was found that the concentration of population corresponds with areas of increased noise temperature. Through this study, a bigger study was planned. The study would involved the relationship between a place's radiation signature and its other attributes, such as economic type, population, geographic concentration. The method of radio sociology would be used to track the sources of radio noise.

  16. The back-diffusion effect of air on the discharge characteristics of atmospheric-pressure radio-frequency glow discharges using bare metal electrodes

    NASA Astrophysics Data System (ADS)

    Sun, Wen-Ting; Liang, Tian-Ran; Wang, Hua-Bo; Li, He-Ping; Bao, Cheng-Yu

    2007-05-01

    Radio-frequency (RF), atmospheric-pressure glow discharge (APGD) plasmas using bare metal electrodes have promising prospects in the fields of plasma-aided etching, deposition, surface treatment, disinfection, sterilization, etc. In this paper, the discharge characteristics, including the breakdown voltage and the discharge voltage for sustaining a stable and uniform α mode discharge of the RF APGD plasmas are presented. The experiments are conducted by placing the home-made planar-type plasma generator in ambient and in a vacuum chamber, respectively, with helium as the primary plasma-forming gas. When the discharge processes occur in ambient, particularly for the lower plasma-working gas flow rates, the experimental measurements show that it is the back-diffusion effect of air in atmosphere, instead of the flow rate of the gas, that results in the obvious decrease in the breakdown voltage with increasing plasma-working gas flow rate. Further studies on the discharge characteristics, e.g. the luminous structures, the concentrations and distributions of chemically active species in plasmas, with different plasma-working gases or gas mixtures need to be conducted in future work.

  17. Population and movement characteristics of radio-collared striped skunks in North Dakota during an epizootic of rabies

    USGS Publications Warehouse

    Greenwood, Raymond J.; Newton, Wesley E.; Pearson, Gary L.; Schamber, George J.

    1997-01-01

    We observed a total of 102 striped skunks (Mephitis mephitis) from March to July of both 1991 and 1992 in Stutsman County, North Dakota (USA) during an experiment with food supplementation. Twenty-three apparently healthy skunks in 1991 and 56 in 1992 were equipped with radio-collars. In 1991, one of the 23 was tested and found to be rabid. In 1992, 50 of 56 were tested; 35 (70%) were rabid. Of skunks with ages estimated, 19 (66%) of 29 were first year animals in 1991 compared with nine (22%) of 41 first year animals in 1992. All 18 females captured in 1991 were pregnant or parous compared with 21 (60%) of 35 in 1992. The estimated survival rate of skunks was 0.85 during April to June 1991, but only 0.17 during April to July 1992. In 1992, the survival rate of first year skunks was 0.08, compared with 0.35 for older animals. Eleven (31%) of 36 skunks found dead of rabies or in late clinical stage were located below ground. We detected no differences in 1992 between healthy and rabid skunks in estimated mean (±SE) rate of travel (232 ± 14 m/hr), distance traveled (2,047 ± 141 m/night), or home range size (1.6 ± 0.4 km2) during half-month periods from April through June. Among rabid skunks, mean rate of travel tended to decrease from 298 ± 48 m/hr during the 14 days preceding the clinical period of rabies (pre-clinical) to 174 ± 48 m/hr during the clinical period of rabies (14 days immediately before death). Similar decrease occurred in distance traveled in a night (2,318 ± 281 m, pre-clinical; 1,497 ± 281 m, clinical). Mean home range size of males (2.8 ± 0.4) was greater than of females (1.2 ± 0.4) during the pre-clinical period, but during the clinical period home range sizes of males (1.8 ± 0.4) and females (1.8 ± 0.4) were similar. Mean home range size of females did not differ between pre-clinical (1.2 ± 0.4) and clinical (1.8 ± 0.4) periods (P= 0.22). Deaths of skunks from rabies in 1992 tended to be more spatially clumped than expected had they

  18. Population and movement characteristics of radio-collared striped skunks in North Dakota during an epizootic of rabies

    USGS Publications Warehouse

    Greenwood, R.J.; Newton, W.E.; Pearson, G.L.; Schamber, G.J.

    1997-01-01

    We observed a total of 102 striped skunks (Mephitis mephitis) from March to July of both 1991 and 1992 in Stutsman County, North Dakota (USA) during an experiment with food supplementation. Twenty-three apparently healthy skunks in 1991 and 56 in 1992 were equipped with radio-collars. In 1991, one of 23 was tested and found to be rabid. In 1992, 50 of 56 were tested; 35 (69%) were rabid. Of skunks with ages estimated, 19 (66%) of 29 were first year animals in 1991 compared with nine (22%) of 41 first year animals in 1992. All 18 females captured in 1991 were pregnant or parous compared with 21 (60%) of 35 in 1992. The estimated survival rate of skunks was 0.85 during April to June 1991, but only 0.17 during April to July 1992. In 1992, the survival rate of first year skunks was 0.08, compared with 0.35 for older animals. Eleven (31%) of 36 skunks found dead of rabies or in late clinical stage were located below ground. We detected no differences in 1992 between healthy and rabid skunks in estimated mean (i?? SE) rate of travel (232 i?? 14 m/hr), distance traveled (2047 i?? 141 m/night), or home range size (1.6 i?? 0.4 km2) during half-month periods from April through June. Among rabid skunks, mean (i?? SE) rate of travel tended to decrease from 298 i?? 48 m/hr during the 14 days preceding the clinical period of rabies (pre-clinical) to 174 i?? 48 m/hr during the clinical period of rabies (14 days immediately before death). Similar decrease occurred in mean (i?? SE) distance traveled in a night (2318 i?? 281 m, pre-clinical; 1497 i?? 281 m, clinical). Mean (i?? SE) home range size of males (2.8 i?? 0.4) was greater than of females (1.2 i?? 0.4) during the pre-clinical period, but during the clinical period home range sizes of males (1.8 i?? 0.4) and females (1.8 i?? 0.4) were similar. Mean (i?? SE) home range size of females did not differ between pre-clinical (1.2 i?? 0.4) and clinical (1.8 i?? 0.4) periods (P = 0.22). Deaths of skunks from rabies in 1992 tended to

  19. Low Pressure Radio-Frequency Oxygen Plasma Induced Oxidation of Titanium – Surface Characteristics and Biological Effects

    PubMed Central

    Tseng, Wan-Yu; Hsu, Sheng-Hao; Huang, Chieh-Hsiun; Tu, Yu-Chieh; Tseng, Shao-Chin; Chen, Hsuen-Li; Chen, Min-Huey; Su, Wei-Fang; Lin, Li-Deh

    2013-01-01

    Objective This research was designed to investigate the effects of low pressure radio-frequency (RF) oxygen plasma treatment (OPT) on the surface of commercially pure titanium (CP-Ti) and Ti6Al4V. Surface topography, elemental composition, water contact angle, cell viability, and cell morphology were surveyed to evaluate the biocompatibility of titanium samples with different lengths of OP treating time. Materials and Methods CP-Ti and Ti6Al4V discs were both classified into 4 groups: untreated, treated with OP generated by using oxygen (99.98%) for 5, 10, and 30 min, respectively. After OPT on CP-Ti and Ti6Al4V samples, scanning probe microscopy, X-ray photoelectron spectrometry (XPS), and contact angle tests were conducted to determine the surface topography, elemental composition and hydrophilicity, respectively. The change of surface morphology was further studied using sputtered titanium on silicon wafers. 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and F-actin immunofluorescence stain were performed to investigate the viability and spreading behavior of cultivated MG-63 cells on the samples. Results The surface roughness was most prominent after 5 min OPT in both CP-Ti and Ti6Al4V, and the surface morphology of sputtered Ti sharpened after the 5 min treatment. From the XPS results, the intensity of Ti°, Ti2+, and Ti3+ of the samples’ surface decreased indicating the oxidation of titanium after OPT. The water contact angles of both CP-Ti and Ti6Al4V were increased after 5 min OPT. The results of MTT assay demonstrated MG-63 cells proliferated best on the 5 min OP treated titanium sample. The F-actin immunofluorescence stain revealed the cultivated cell number of 5 min treated CP-Ti/Ti6Al4V was greater than other groups and most of the cultivated cells were spindle-shaped. Conclusions Low pressure RF oxygen plasma modified both the composition and the morphology of titanium samples’ surface. The CP-Ti/Ti6Al4V treated with 5 min

  20. College Radio.

    ERIC Educational Resources Information Center

    Sauls, Samuel J.

    As with commercial stations, the underlying premise of the college radio station is to serve the community, whether it be the campus community or the community at large, but in unique ways often geared to underserved niches of the population. Much of college radio's charm lies in its unpredictable nature and constant mutations. The stations give…

  1. Radio Astronomy

    NASA Technical Reports Server (NTRS)

    Shaffer, R. D.; Wolken, P. R.; Niell, A. E.

    1981-01-01

    The activities of the DSN in support of Radio and Radar Astronomy Operations during September through December 1980 are described. Emphasis is on a report of an experiment selected for use of the DSN by the radio Astronomy Experiment Selection Panel: that of VLBI observations of the energetic galactic object SS-433.

  2. Radio astronomy

    NASA Technical Reports Server (NTRS)

    Wolken, P. R.; Schaffer, R. D.; Gorenstein, M. V.

    1981-01-01

    The activities of the Deep Space Network in support of Radio Astronomy Operations during April and May 1981 are reported. Work in progres in support of an experiment selected for use of the DSN by the Radio Astronomy Experiment Selection Panel, Twin Quasi-Stellar Object VLBI, is reported.

  3. Radio astronomy

    NASA Technical Reports Server (NTRS)

    Shaffer, R. D.; Wolken, P. R.; Gulkis, S.

    1981-01-01

    The activities of the Deep Space Network in support of radio astronomy operations during the first quarter of 1981 are reported. Results of the use of a low noise maser are presented, as well as updates in DSN support of experiments sanctioned by the Radio Astronomy Experiment Selection Panel.

  4. Radio astronomy

    NASA Technical Reports Server (NTRS)

    Taylor, R. M.; Manchester, R. N.

    1980-01-01

    The activities of the Deep Space Network in support of radio and radar astronomy operations during July and August 1980 are reported. A brief update on the OSS-sponsored planetary radio astronomy experiment is provided. Also included are two updates, one each from Spain and Australia on current host country activities.

  5. Rosetta Radio Science Investigations (RSI)

    NASA Astrophysics Data System (ADS)

    Pätzold, Martin; Häusler, Bernd; Aksnes, Kaare; Anderson, John D.; Asmar, Sami W.; Barriot, Jean-Pierre; Bird, Michael K.; Boehnhardt, Hermann; Eidel, Werner; Grün, Eberhardt; Ip, Wing H.; Marouf, Essam; Morley, Trevor; Neubauer, Fritz M.; Rickman, Hans; Thomas, Nicolas; Tsurutani, Bruce T.; Wallis, Max K.; Wickramasinghe, N. C.; Mysen, Eirik; Olson, Oystein; Remus, Stefan; Tellmann, Silvia; Andert, Thomas; Carone, Ludmila; Fels, Markus; Stanzel, Christina; Audenrieth-Kersten, Iris; Gahr, Alexander; Müller, Anna-Liane; Stupar, Dusan; Walter, Christina

    2007-02-01

    The Rosetta spacecraft has been successfully launched on 2nd March 2004 to its new target comet 67 P/Churyumov-Gerasimenko. The science objectives of the Rosetta Radio Science Investigations (RSI) experiment address fundamental aspects of cometary physics such as the mass and bulk density of the nucleus, its gravity field, its interplanetary orbit perturbed by nongravitational forces, its size and shape, its internal structure, the composition and roughness of the nucleus surface, the abundance of large dust grains, the plasma content in the coma and the combined dust and gas mass flux. The masses of two asteroids, Steins and Lutetia, shall be determined during flybys in 2008 and 2010, respectively. Secondary objectives are the radio sounding of the solar corona during the superior conjunctions of the spacecraft with the Sun during the cruise phase. The radio carrier links of the spacecraft Telemetry, Tracking and Command (TT&C) subsystem between the orbiter and the Earth will be used for these investigations. An Ultrastable oscillator (USO) connected to both transponders of the radio subsystem serves as a stable frequency reference source for both radio downlinks at X-band (8.4 GHz) and S-band (2.3 GHz) in the one-way mode. The simultaneous and coherent dual-frequency downlinks via the High Gain Antenna (HGA) permit separation of contributions from the classical Doppler shift and the dispersive media effects caused by the motion of the spacecraft with respect to the Earth and the propagation of the signals through the dispersive media, respectively. The investigation relies on the observation of the phase, amplitude, polarization and propagation times of radio signals transmitted from the spacecraft and received with ground station antennas on Earth. The radio signals are affected by the medium through which the signals propagate (atmospheres, ionospheres, interplanetary medium, solar corona), by the gravitational influence of the planet on the spacecraft and

  6. Radio properties of Compact Steep Spectrum and GHz-Peaked Spectrum radio sources

    NASA Astrophysics Data System (ADS)

    Orienti, M.

    2016-02-01

    Compact steep spectrum (CSS) and GHz-peaked spectrum (GPS) radio sources represent a large fraction of the extragalactic objects in flux density-limited samples. They are compact, powerful radio sources whose synchrotron peak frequency ranges between a few hundred MHz to several GHz. CSS and GPS radio sources are currently interpreted as objects in which the radio emission is in an early evolutionary stage. In this contribution I review the radio properties and the physical characteristics of this class of radio sources, and the interplay between their radio emission and the ambient medium of the host galaxy.

  7. Radio emissions from RHESSI TGFs

    NASA Astrophysics Data System (ADS)

    Mezentsev, Andrey; Østgaard, Nikolai; Gjesteland, Thomas; Albrechtsen, Kjetil; Cummer, Steven

    2016-04-01

    The discovery of bursts of energetic photons coming out to space from the Earth's atmosphere, referred to as terrsetrial gamma-ray flashes (TGFs), has stimulated research activity investigating different aspects of the TGF generation and accompanying processes. Two models of the TGF production are nowadays competing to explain the observations of the TGFs and related phenomena. One of the models involves the feedback mechanism enhancing the production rate of the runaway electrons in the ambient electric field of a thundercloud. Another model considers runaway electrons accelerated in the strong local electric field in front of the upward propagating negative leader of the +IC. We performed a detailed analysis of RHESSI TGFs detected between August 2004 and September 2015. It was reported that the RHESSI satellite clock has a systematic error of ˜ 1.8 ms, but the exact value remained unknown, also it was unclear if this systematic clock error is changing with time or not. We compared RHESSI TGFs with the world wide lightning location network (WWLLN) database and found the distribution of the time delays between the TGF peak times and associated WWLLN detections. This distribution allowed us to find the value of the RHESSI systematic clock offset with the microsecond accuracy level. Also we found that this offset experienced two changes: in August 2005 and in October 2013, which was confirmed by two independent ways. We found that in case of double TGFs WWLLN detection corresponds to the second TGF of the pair. VLF magnetic field recordings from the Duke University also attribute radio sferics to the second TGF, exhibiting no detectable radio emission during the first TGFs of the TGF pairs. We have proposed a possible scenario that is consistent with the observations. This scenario supports the leader-based model of the TGF generation. Spectral characteristics of 77 sferics recorded by the Duke University VLF sensors and related to the RHEESI TGFs show that maximal

  8. 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.

  9. 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.

  10. Radio emision from supernova remnants

    NASA Astrophysics Data System (ADS)

    Dubner, G.

    2016-06-01

    The vast majority of supernova remnants (SNRs) in our Galaxy and nearby galaxies have been discovered through radio observations, and only a very small number of the SNRs catalogued in the Milky Way have not been detected in the radio band, or are poorly defined by current radio observations. The study of the radio emission from SNRs is an excellent tool to investigate morphological characteristics, marking the location of shock fronts and contact discontinuities; the presence, orientation and intensity of the magnetic field; the energy spectrum of the emitting particles; and the dynamical consequences of the interaction with the circumstellar and interstellar medium. I will review the present knowledge of different important aspects of radio remnants and their impact on the interstellar gas. Also, new radio studies of the Crab Nebula carried out with the Karl Jansky Very Large Array (JVLA) at 3 GHz and with ALMA at 100 GHz, will be presented.

  11. Satellite observations of type III solar radio bursts at low frequencies

    NASA Technical Reports Server (NTRS)

    Fainberg, J.; Stone, R. G.

    1974-01-01

    Type III solar radio bursts have been 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 earth 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. Substantial evidence is available to show that the radio emission is observed at the second harmonic instead of the fundamental of the plasma frequency. This brings the density scale derived by radio observations into better agreement with direct solar wind density measurements at 1 AU and relaxes the requirement for type III propagation along large density-enhanced regions. This density scale with the measured direction of arrival of the radio burst allows the trajectory of the exciter path to be determined from 10 earth radii to 1 AU.

  12. Radio Telescopes

    NASA Astrophysics Data System (ADS)

    Ekers, Ron; Wilson, Thomas L.

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

  13. 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.

  14. Estimate of a D region ionospheric electron density profile from MF radio wave observations by the S-310-37 rocket

    NASA Astrophysics Data System (ADS)

    Ashihara, Y.; Ishisaka, K.; Miyake, T.

    2016-01-01

    The S-310-37 rocket, launched at 11:20 (JST) on 16 January 2007, was equipped with a radio receiver to observe the medium-frequency (MF) radio wave propagation characteristics in the ionosphere. The radio receiver measured the intensity and the waveform of the radio wave at 873 kHz from the NHK Kumamoto broadcasting station. The polarized mode waves' intensity characteristics were obtained by analyzing the observed waveform. In this study, the S-310-37 rocket-observed polarized mode waves' propagation characteristics are analyzed in order to estimate the electron density profile in the ionospheric D region. These observations become better measurement approach because the electron density profile in the ionospheric D region is difficult to be observed by other equipment such as a Langmuir probe. A Langmuir probe can measure in the ionospheric D region; however, the absolute values may be off by the influence of wake effects around the sounding rocket. It is demonstrated that the propagation characteristics of the polarized mode waves can be successfully used to derive the electron density profile in the ionospheric D region.

  15. 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.

  16. Physical modeling of direct current and radio frequency characteristics for InP-based InAlAs/InGaAs HEMTs

    NASA Astrophysics Data System (ADS)

    Sun, Shu-Xiang; Ji, Hui-Fang; Yao, Hui-Juan; Li, Sheng; Jin, Zhi; Ding, Peng; Zhong, Ying-Hui

    2016-10-01

    Direct current (DC) and radio frequency (RF) performances of InP-based high electron mobility transistors (HEMTs) are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shockley-Read-Hall recombination, Auger recombination, radiative recombination, density gradient model and high field-dependent mobility are used to characterize the devices. The simulated results and measured results about DC and RF performances are compared, showing that they are well matched. However, the slight differences in channel current and pinch-off voltage may be accounted for by the surface defects resulting from oxidized InAlAs material in the gate-recess region. Moreover, the simulated frequency characteristics can be extrapolated beyond the test equipment limitation of 40 GHz, which gives a more accurate maximum oscillation frequency (f max) of 385 GHz. Project supported by the National Natural Science Foundation of China (Grant Nos. 61404115 and 61434006), the Postdoctoral Science Foundation of Henan Province, China (Grant No. 2014006), and the Development Fund for Outstanding Young Teachers of Zhengzhou University (Grant No. 1521317004).

  17. Characteristics of high-purity Cu thin films deposited on polyimide by radio-frequency Ar/H{sub 2} atmospheric-pressure plasma jet

    SciTech Connect

    Zhao, P.; Zheng, W.; Meng, Y. D.; Nagatsu, M.

    2013-03-28

    With a view to fabricating future flexible electronic devices, an atmospheric-pressure plasma jet driven by 13.56 MHz radio-frequency power is developed for depositing Cu thin films on polyimide, where a Cu wire inserted inside the quartz tube was used as the evaporation source. A polyimide substrate is placed on a water-cooled copper heat sink to prevent it from being thermally damaged. With the aim of preventing oxidation of the deposited Cu film, we investigated the effect of adding H{sub 2} to Ar plasma on film characteristics. Theoretical fitting of the OH emission line in OES spectrum revealed that adding H{sub 2} gas significantly increased the rotational temperature roughly from 800 to 1500 K. The LMM Auger spectroscopy analysis revealed that higher-purity Cu films were synthesized on polyimide by adding hydrogen gas. A possible explanation for the enhancement in the Cu film deposition rate and improvement of purity of Cu films by H{sub 2} gas addition is that atomic hydrogen produced by the plasma plays important roles in heating the gas to promote the evaporation of Cu atoms from the Cu wire and removing oxygen from copper oxide components via reduction reaction.

  18. Effects of the shielding cylinder and substrate on the characteristics of an argon radio-frequency atmospheric glow discharge plasma jet

    SciTech Connect

    Li Guo; Le Peisi; Li Heping; Bao Chengyu

    2010-05-15

    With unique features of low breakdown voltages, large and uniform discharge areas and high concentrations of chemically reactive species, radio-frequency, atmospheric-pressure glow discharge (rf APGD) plasma sources produced with bare-metallic electrodes have shown promising prospects in the field of materials processing. In this paper, the spatial distributions (i.e., the directly measured integrated axial distribution and the radial distribution by using the inverse Abel transform) of the emission intensities of the Ar I 696.5 nm line are studied for the argon rf APGD plasma jet under different operation conditions, including variations of the rf power input or the argon flow rate, the existence of the solid shielding cylinder or the substrate. The experimental results show that, with other parameters being unchanged, the emission intensities of the Ar I 696.5 nm line increase with increasing the rf power input or the argon flow rate; and the solid shielding cylinder has more significant influences on the characteristics of the plasma impinging jet by reducing the mass flow rate of the ambient air entrained into the plasma jet region than those for the cases without the existence of the substrate at the downstream of the plasma torch nozzle exit.

  19. Radio studies of extragalactic supernovae.

    PubMed

    Weiler, K W; Sramek, R A; Panagia, N

    1986-03-14

    Some exploding stars (supernovae) are powerful emitters of centimeter radio radiation. Detailed observations have shown that these supernovae quickly become detectable in the radio range, first at shorter wavelengths (higher frequencies) and later at progressively longer and longer wavelengths (lower frequencies). This part of the phenomenon appears to be well explained by a monotonic decrease in the amount of ionized material surrounding the radio-emitting regions as the shock from the explosion travels outward. The radio emission itself is of a nonthermal, synchrotron origin, as is the case in most bright cosmic radio sources. Once the absorption effects become negligible, the radio intensity declines with time until reaching the detection limit of the telescope. Models suggest that the absorbing material originates in a dense wind of matter lost by the supernova progenitor star, or by its companion if it is in a binary system, in the last stages of evolution before the explosion. The synchrotron radio emission can be generated either externally by the shock wave from the explosion propagating through this same high density stellar wind or internally by a rapidly rotating neutron star, which is the collapsed core of the exploded star. Present results appear to favor the former model for at least the first several years after the supernova explosion, although the latter model remains viable.

  20. SPEAKING IN LIGHT - Jupiter radio signals as deflections of light-emitting electron beams in a vacuum chamber

    NASA Astrophysics Data System (ADS)

    Petrovic, K.

    2015-10-01

    Light emitting electron beam generated in a vacuum chamber is used as a medium for visualizing Jupiter's electromagnetic radiation. Dual dipole array antenna is receiving HF radio signals that are next amplified to radiate a strong electromagnetic field capable of influencing the propagation of electron beam in plasma. Installation aims to provide a platform for observing the characteristics of light emitting beam in 3D, as opposed to the experiments with cathode ray tubes in 2-dimensional television screens. Gas giant 'speaking' to us by radio waves bends the light in the tube, allowing us to see and hear the messages of Jupiter - God of light and sky.

  1. Radio Astronomy

    NASA Technical Reports Server (NTRS)

    Wolken, P. R.; Shaffer, R. D.

    1983-01-01

    Deep Space Network (DSN) 26- and 64-meter antenna stations were utilized in support of Radio Astronomy Experiment Selection Panel experiments. Within a time span of 10 days, in May 1983 (267.75 hours total), nine RAES experiments were supported. Most of these experiments involved multifacility interferometry using Mark 3 data recording terminals and as many as six non-DSN observatories. Investigations of black holes, quasars, galaxies, and radio sources are discussed.

  2. Radio triangulation - mapping the 3D position of the solar radio emission

    NASA Astrophysics Data System (ADS)

    Magdalenic, Jasmina

    2016-04-01

    Understanding the relative position of the sources of the radio emission and the associated solar eruptive phenomena (CME and the associated shock wave) has always been a challenge. While ground-based radio interferometer observations provide us with the 2D position information for the radio emission originating from the low corona (up to 2.5 Ro), this is not the case for the radio emission originating at larger heights. The radio triangulation measurements (also referred to as direction-finding or goniopolarimetric measurements) from two or more widely separated spacecraft can provide information on the 3D positions of the sources of the radio emission. This type of interplanetary radio observations are currently performed by STEREO WAVES and WIND WAVES instruments, providing a unique possibility for up to three simultaneous radio triangulations (using up to three different pairs of spacecraft). The recent results of the radio triangulation studies bring new insight into the causal relationship of the solar radio emission and CMEs. In this presentation I will discuss some of the most intriguing results on the source positions of: a) type III radio bursts indicating propagation of the fast electrons accelerated along the open field lines, b) type II radio bursts indicating interaction of the CME-driven shocks and other coronal structures e.g. streamers and c) type IV-like radio bursts possibly associated with CME-CME interaction.

  3. Planetary radio waves

    NASA Technical Reports Server (NTRS)

    Goertz, C. K.

    1986-01-01

    Three planets, the earth, Jupiter and Saturn are known to emit nonthermal radio waves which require coherent radiation processes. The characteristic features (frequency spectrum, polarization, occurrence probability, radiation pattern) are discussed. Radiation which is externally controlled by the solar wind is distinguished from internally controlled radiation which only originates from Jupiter. The efficiency of the externally controlled radiation is roughly the same at all three planets (5 x 10 to the -6th) suggesting that similar processes are active there. The maser radiation mechanism for the generation of the radio waves and general requirements for the mechanism which couples the power generator to the region where the radio waves are generated are briefly discussed.

  4. Shaping propagation invariant laser beams

    NASA Astrophysics Data System (ADS)

    Soskind, Michael; Soskind, Rose; Soskind, Yakov

    2015-11-01

    Propagation-invariant structured laser beams possess several unique properties and play an important role in various photonics applications. The majority of propagation invariant beams are produced in the form of laser modes emanating from stable laser cavities. Therefore, their spatial structure is limited by the intracavity mode formation. We show that several types of anamorphic optical systems (AOSs) can be effectively employed to shape laser beams into a variety of propagation invariant structured fields with different shapes and phase distributions. We present a propagation matrix approach for designing AOSs and defining mode-matching conditions required for preserving propagation invariance of the output shaped fields. The propagation matrix approach was selected, as it provides a more straightforward approach in designing AOSs for shaping propagation-invariant laser beams than the alternative technique based on the Gouy phase evolution, especially in the case of multielement AOSs. Several practical configurations of optical systems that are suitable for shaping input laser beams into a diverse variety of structured propagation invariant laser beams are also presented. The laser beam shaping approach was applied by modeling propagation characteristics of several input laser beam types, including Hermite-Gaussian, Laguerre-Gaussian, and Ince-Gaussian structured field distributions. The influence of the Ince-Gaussian beam semifocal separation parameter and the azimuthal orientation between the input laser beams and the AOSs onto the resulting shape of the propagation invariant laser beams is presented as well.

  5. ON SUN-TO-EARTH PROPAGATION OF CORONAL MASS EJECTIONS

    SciTech Connect

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

    2013-05-20

    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.

  6. Proceedings of the Seventeenth NASA Propagation Experimenters Meeting (NAPEX 17) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz (Editor)

    1993-01-01

    The NASA Propagation Experimenters Meeting (NAPEX) is convened annually to discuss studies made on radio wave propagation by investors from domestic and international organizations. NAPEX 17 was held on 15 June 1993. The meeting was organized into two technical sessions. The first session was dedicated to slant path propagation studies and experiments. The second session focused on propagation studies for mobile and personal communications. Preceding NAPEX 17, the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop was held on 14 June 1993 to review ACTS propagation activities with emphasis on ACTS experiments status and data collection, processing, and exchange.

  7. 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.

  8. Features of Superlong-Distance and Round-the-World Propagation of HF Waves

    NASA Astrophysics Data System (ADS)

    Ponyatov, A. A.; Vertogradov, G. G.; Uryadov, V. P.; Vertogradova, E. G.; Shumaev, V. V.; Chernov, A. G.; Chaika, E. G.

    2014-11-01

    We present the results of the experimental studies of the features of superlong-distance and round-the-world propagation of the HF waves in the radio lines with different orientation and length, which were obtained in 2012-2014 using a new method of oblique ionospheric sounding. The frequency-time travel intervals of the direct round-the-world signals, their amplitude-frequency and angular-frequency characteristics are determined. The mechanism of propagation and transformation of the round-the-world signals due to the radio-wave refraction by the transverse electron-density gradients in the region of approach of two optimal paths passing via the transmitter and receiver so that each path forms the smallest angle with the terminator. It is shown that the proposed mechanism is in good agreement with the experimentally observed variation of the azimuth of the direct round-the-world signal on the Cyprus-Rostov-on-Don path and on the Alice Springs (Australia)-Rostov-on-Don path in the absence of variation of the direct round-the-world signal azimuth. For the superlong-distance propagation of the HF waves on the Virginia (USA)-Yoshkar-Ola and Puerto Rico-Yoshkar-Ola (the distances about 8000-10000 km) paths, the best propagation conditions are observed when the entire path is in the illuminated ionosphere near the terminator boundary making a small angle of 10°-25° with the terminator.

  9. Influence of the axicon characteristics and beam propagation parameter M{sup 2} on the formation of Bessel beams from semiconductor lasers

    SciTech Connect

    Sokolovskii, G S; Dyudelev, V V; Losev, S N; Butkus, M; Soboleva, K K; Sobolev, A I; Deryagin, A G; Kuchinskii, V I; Sibbet, V; Rafailov, E U

    2013-05-31

    We study the peculiarities of the formation of Bessel beams in semiconductor lasers with a high propagation parameter M{sup 2}. It is shown that the propagation distance of the Bessel beam is determined by the divergence of the quasi-Gaussian beam with high M{sup 2} rather than the geometric parameters of the optical scheme. It is demonstrated that technologically inevitable rounding of the axicon tip leads to a significant increase in the transverse dimension of the central part of the Bessel beam near the axicon. (semiconductor lasers. physics and technology)

  10. Numerical characterization and modeling of subject-specific ultrawideband body-centric radio channels and systems for healthcare applications.

    PubMed

    Abbasi, Qammer Hussain; Sani, Andrea; Alomainy, Akram; Hao, Yang

    2012-03-01

    The paper presents a subject-specific radio propagation study and system modeling in wireless body area networks using a simulation tool based on the parallel finite-difference time-domain technique. This technique is well suited to model the radio propagation around complex, inhomogeneous objects such as the human body. The impact of different digital phantoms in on-body radio channel and system performance was studied. Simulations were performed at the frequency of 3-10 GHz considering a typical hospital environment, and were validated by on-site measurements with reasonably good agreement. The analysis demonstrated that the characteristics of the on-body radio channel and system performance are subject-specific and are associated with human genders, height, and body mass index. Maximum variations of almost 18.51% are observed in path loss exponent due to change of subject, which gives variations of above 50% in system bit error rate performance. Therefore, careful consideration of subject-specific parameters are necessary for achieving energy efficient and reliable radio links and system performance for body-centric wireless network.

  11. 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

  12. UHF Radio Wave Attenuation Factor Database

    NASA Astrophysics Data System (ADS)

    Khomenko, S. I.; Kostina, V. L.; Mytsenko, I. M.; Roenko, A. N.

    2007-07-01

    As is known each sea-going vessel is equipped with navigation, communication and other radio engineering facilities that serve to secure the safety of navigation and are chiefly operated at UHF-wave band. In developing these systems and calculating the energy potential for a necessary coverage range one should be well aware of the radio signal attenuation processes on a propagation path. The key parameter of this path is the (radio) wave attenuation factor V and its distance dependence V(R). A diversity of factors influencing the radio signal attenuation over the oceanic expanses, especially well pronounced and quite stable tropospheric ducts, and the lack of experimental data were the compelling reasons why the researchers of the Institute for Radiophysics and Electronics, NASU, had spent many years on comprehensive radiophysical investigations carried out in different regions of the Atlantic, Indian, Arctic and Pacific Oceans. The experimental data obtained allow creating the database of radio wave attenuation factor V.

  13. The Radio JOVE Project - Shoestring Radio Astronomy

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  14. A time dependent difference theory for sound propagation in ducts with flow. [characteristic of inlet and exhaust ducts of turbofan engines

    NASA Technical Reports Server (NTRS)

    Baumeister, K. J.

    1979-01-01

    A time dependent numerical solution of the linearized continuity and momentum equation was developed for sound propagation in a two dimensional straight hard or soft wall duct with a sheared mean flow. The time dependent governing acoustic difference equations and boundary conditions were developed along with a numerical determination of the maximum stable time increments. A harmonic noise source radiating into a quiescent duct was analyzed. This explicit iteration method then calculated stepwise in real time to obtain the transient as well as the steady state solution of the acoustic field. Example calculations were presented for sound propagation in hard and soft wall ducts, with no flow and plug flow. Although the problem with sheared flow was formulated and programmed, sample calculations were not examined. The time dependent finite difference analysis was found to be superior to the steady state finite difference and finite element techniques because of shorter solution times and the elimination of large matrix storage requirements.

  15. EVA Radio DRATS 2011 Report

    NASA Technical Reports Server (NTRS)

    Swank, Aaron J.; Bakula, Casey J.

    2012-01-01

    In the Fall of 2011, National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) participated in the Desert Research and Technology Studies (DRATS) field experiments held near Flagstaff, Arizona. The objective of the DRATS outing is to provide analog mission testing of candidate technologies for space exploration, especially those technologies applicable to human exploration of extra- terrestrial rocky bodies. These activities are performed at locations with similarities to extra-terrestrial conditions. This report describes the Extravehicular Activity (EVA) Dual-Band Radio Communication System which was demonstrated during the 2011 outing. The EVA radio system is designed to transport both voice and telemetry data through a mobile ad hoc wireless network and employs a dual-band radio configuration. Some key characteristics of this system include: 1. Dual-band radio configuration. 2. Intelligent switching between two different capability wireless networks. 3. Self-healing network. 4. Simultaneous data and voice communication.

  16. 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.

  17. Radio-relay and satellite transmission systems

    NASA Astrophysics Data System (ADS)

    Nemirovskii, A. S.

    The present work is a handbook on the design and analysis of radio-relay, tropospheric, and satellite transmission systems. Particular consideration is given to the propagation of decimeter and centimeter waves; antenna and feed devices for relay and satellite systems; noise and distortions; the signal fading problem; EMC; and the optimization of the transmission systems.

  18. RADIO ALTIMETERS

    DOEpatents

    Bogle, R.W.

    1960-11-22

    A radio ranging device is described which utilizes a superregenerative oscillator having alternate sending and receiving phases with an intervening ranging interval between said phases, means for varying said ranging interval, means responsive to an on-range noise reduction condition for stopping said means for varying the ranging interval and indicating means coupled to the ranging interval varying means and calibrated in accordance with one-half the product of the ranging interval times the velocity of light whereby the range is indicated.

  19. Ionospheric wave and irregularity measurements using passive radio astronomy techniques

    NASA Technical Reports Server (NTRS)

    Erickson, W. C.; Mahoney, M. J.; Jacobson, A. R.; Knowles, S. H.

    1988-01-01

    The observation of midlatitude structures using passive radio astronomy techniques is discussed, with particular attention being given to the low-frequency radio telescope at the Clark Lake Radio Observatory. The present telescope operates in the 10-125-MHz frequency range. Observations of the ionosphere at separations of a few kilometers to a few hundreds of kilometers by the lines of sight to sources are possible, allowing the determination of the amplitude, wavelength, direction of propagation, and propagation speed of ionospheric waves. Data are considered on large-scale ionospheric gradients and the two-dimensional shapes and sizes of ionospheric irregularities.

  20. Indoor radio measurement and planning for UMTS/HSDPA with antennas

    NASA Astrophysics Data System (ADS)

    Eheduru, Marcellinus

    and some important properties of antennas which must be considered when choosing an antenna for indoor radio propagation. The challenges of in-building network coverage and also the objectives of this thesis are also mentioned in this chapter. The evolution and standardization, network architecture, radio features and most importantly, the radio resource management features of UMTS/HSDPA are given in chapter two. In this chapter, the reason why Wideband Code Division Multiple Access (WCDMA) was specified and selected for 3G (UMTS) systems would be seen. The architecture of the radio access network, interfaces with the radio access network between base stations and radio network controllers (RNC), and the interface between the radio access network and the core network are also described in this chapter. The main features of HSDPA are mentioned at the end of the chapter. In chapter three the principles of the WCDMA air interface, including spreading, Rake reception, signal fading, power control and handovers are introduced. The different types and characteristics of the propagation environments and how they influence radio wave propagation are mentioned. UMTS transport, logical and physical channels are also mentioned, highlighting their significance and relationship in and with the network. Radio network planning for UMTS is discussed in chapter four. The outdoor planning process which includes dimensioning, detailed planning, optimization and monitoring is outlined. Indoor radio planning with distributed antenna systems (DAS), which is the idea and motivation behind this thesis work, is also discussed. The various antennas considered and the antenna that was selected for this thesis experiment was discussed in chapter five. The antenna radiation pattern, directivity, gain and input impedance were the properties of the antenna that were taken into consideration. The importance of the choice of the antenna for any particular type of indoor environment is also mentioned

  1. Radio Jove: Jupiter Radio Astronomy for Citizens

    NASA Astrophysics Data System (ADS)

    Higgins, Charles; Thieman, J. R.; Flagg, R.; Reyes, F. J.; Sky, J.; Greenman, W.; Brown, J.; Typinski, D.; Ashcraft, T.; Mount, A.

    2014-01-01

    Radio JOVE is a hands-on educational activity that brings the radio sounds of the Sun, Jupiter, the Milky Way Galaxy, and terrestrial radio noise to students, teachers, and the general public. Participants may build a simple radio telescope kit, make scientific observations, and interact with professional radio observatories in real-time over the Internet. Our website (http://radiojove.gsfc.nasa.gov) includes science information, construction manuals, observing guides, and education resources for teachers and students. Radio Jove is continually expanding its participants with over 1800 kits sold to more than 70 countries worldwide. Recently some of our most dedicated observers have upgraded their Radio Jove antennas to semi-professional observatories. We have spectrographs and wide band antennas, some with 8 MHz bandwidth and some with dual polarization capabilities. In an effort to add to the science literature, these observers are coordinating their efforts to pursue some basic questions about Jupiter’s radio emissions (radio source locations, spectral structure, long term changes, etc.). We can compare signal and ionosphere variations using the many Radio Jove observers at different locations. Observers are also working with members of the Long Wavelength Array Station 1 (LWA1) radio telescope to coordinate observations of Jupiter; Radio Jove is planning to make coordinated observations while the Juno Mission is active beginning in 2015. The Radio Jove program is overviewed, its hardware and software are highlighted, recent sample observations are shown, and we demonstrate that we are capable of real citizen science.

  2. Solar radio continuum storms

    NASA Technical Reports Server (NTRS)

    Sakurai, K.

    1976-01-01

    The paper reviews the current status of research on solar radio continuum emissions from metric to hectometric wave frequencies, emphasizing the role of energetic electrons in the 10-100 keV range in these emissions. It is seen that keV-energy electrons generated in active sunspot groups must be the sources of radio continuum storm emissions for wide frequency bands. These electrons excite plasma oscillations in the medium, which in turn are converted to electromagnetic radiation. The radio noise continuum sources are usually associated with type III burst activity observed above these sources. Although the mechanism for the release of the energetic electrons is not known, it seems they are ejected from storm source regions in association with rapid variation of associated sunspot magnetic fields due to their growth into complex types. To explain some of the observed characteristics, the importance of two-stream instability and the scattering of ambient plasma ions on energetic electron streams is pointed out.

  3. 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.

  4. Electron Exciter Speeds Associated with Interplanetary Type III Solar Radio Bursts

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    This article provides a comprehensive quantitative investigation of the kinematics of the electron exciters associated with interplanetary type III solar radio bursts. Detailed multispacecraft analyses of the radio and plasma wave data from the widely separated Wind and STEREO spacecraft are provided for five interplanetary type III bursts that illustrate different aspects of the problems involved in establishing the electron exciter speeds. The exciter kinematics are determined from the observed frequency drift and in-situ radiation characteristics for each type III burst. The analysis assumes propagation of the electron exciters along a Parker spiral, with origin at the associated solar active region, and curvature determined by the measured solar wind speed. The analyses take fully into account the appropriate light-propagation-time corrections from the radio source to the observing spacecraft as the exciters propagate along the Parker spiral path. For the five in-situ type III bursts analyzed in detail here, we found that their initial exciter speeds, near the Sun, ranged from 0.2c to 0.38c, where c is the speed of light. This is significantly higher than the exciter speeds derived from other recent analyses. The results presented here further suggest that the type III electron exciters normally decelerate as they propagate through the interplanetary medium. We argue based on the observations by the widely separated spacecraft that the initial part of the type III radiation usually occurs at the fundamental of the plasma frequency. Finally, we compare the results for the exciter speeds to all previous determinations and provide quantitative arguments to explain the differences.

  5. 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.

  6. 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.

  7. S-Band propagation measurements

    NASA Technical Reports Server (NTRS)

    Briskman, Robert D.

    1994-01-01

    A geosynchronous satellite system capable of providing many channels of digital audio radio service (DARS) to mobile platforms within the contiguous United States using S-band radio frequencies is being implemented. The system is designed uniquely to mitigate both multipath fading and outages from physical blockage in the transmission path by use of satellite spatial diversity in combination with radio frequency and time diversity. The system also employs a satellite orbital geometry wherein all mobile platforms in the contiguous United States have elevation angles greater than 20 deg to both of the diversity satellites. Since implementation of the satellite system will require three years, an emulation has been performed using terrestrial facilities in order to allow evaluation of DARS capabilities in advance of satellite system operations. The major objective of the emulation was to prove the feasibility of broadcasting from satellites 30 channels of CD quality programming using S-band frequencies to an automobile equipped with a small disk antenna and to obtain quantitative performance data on S-band propagation in a satellite spatial diversity system.

  8. S-Band propagation measurements

    NASA Astrophysics Data System (ADS)

    Briskman, Robert D.

    1994-08-01

    A geosynchronous satellite system capable of providing many channels of digital audio radio service (DARS) to mobile platforms within the contiguous United States using S-band radio frequencies is being implemented. The system is designed uniquely to mitigate both multipath fading and outages from physical blockage in the transmission path by use of satellite spatial diversity in combination with radio frequency and time diversity. The system also employs a satellite orbital geometry wherein all mobile platforms in the contiguous United States have elevation angles greater than 20 deg to both of the diversity satellites. Since implementation of the satellite system will require three years, an emulation has been performed using terrestrial facilities in order to allow evaluation of DARS capabilities in advance of satellite system operations. The major objective of the emulation was to prove the feasibility of broadcasting from satellites 30 channels of CD quality programming using S-band frequencies to an automobile equipped with a small disk antenna and to obtain quantitative performance data on S-band propagation in a satellite spatial diversity system.

  9. 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.

  10. Radio emission from supernova remnants

    NASA Astrophysics Data System (ADS)

    Dubner, Gloria; Giacani, Elsa

    2015-09-01

    The explosion of a supernova releases almost instantaneously about 10^{51} ergs of mechanic energy, changing irreversibly the physical and chemical properties of large regions in the galaxies. The stellar ejecta, the nebula resulting from the powerful shock waves, and sometimes a compact stellar remnant, constitute a supernova remnant (SNR). They can radiate their energy across the whole electromagnetic spectrum, but the great majority are radio sources. Almost 70 years after the first detection of radio emission coming from an SNR, great progress has been achieved in the comprehension of their physical characteristics and evolution. We review the present knowledge of different aspects of radio remnants, focusing on sources of the Milky Way and the Magellanic Clouds, where the SNRs can be spatially resolved. We present a brief overview of theoretical background, analyze morphology and polarization properties, and review and critically discuss different methods applied to determine the radio spectrum and distances. The consequences of the interaction between the SNR shocks and the surrounding medium are examined, including the question of whether SNRs can trigger the formation of new stars. Cases of multispectral comparison are presented. A section is devoted to reviewing recent results of radio SNRs in the Magellanic Clouds, with particular emphasis on the radio properties of SN 1987A, an ideal laboratory to investigate dynamical evolution of an SNR in near real time. The review concludes with a summary of issues on radio SNRs that deserve further study, and analysis of the prospects for future research with the latest-generation radio telescopes.

  11. 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

  12. Graphene electrostatic microphone and ultrasonic radio

    PubMed Central

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

    2015-01-01

    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

  13. Statistical Angle-of-Arrival and Doppler Method for GPS Radio Interferometry of TIDS

    NASA Astrophysics Data System (ADS)

    Afraimovich, E. L.; Palamartchouk, K. S.; Perevalova, N. P.

    A Statistical Angle-of-arrival and Doppler Method for GPS radio interferometry (SADM-GPS) is proposed for determining the characteristics of the Travelling Ionospheric Disturbances (TIDs) by measuring variations of GPS phase derivatives with respect to time and spatial coordinates. These data are used to calculate corresponding values of the velocity vector, in view of a correction for satellite motion based on current information available regarding the angular coordinates of the satellites. Through a computer simulation it was shown that multi satellite GPS radio interferometry in conjunction with the SADM-GPS algorithm allows for detecting and measuring the velocity vector of TIDs in virtually the entire azimuthal range of possible TID propagation directions

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

    SciTech Connect

    Trigilio, Corrado; Leto, Paolo; Umana, Grazia; Buemi, Carla S.; Leone, Francesco

    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.

  15. WIND/WAVES observations of man-made radio transmissions

    NASA Astrophysics Data System (ADS)

    Kaiser, M. L.; Desch, M. D.; Bougeret, J.-L.; Manning, R.; Meetre, C. A.

    The WAVES radio and plasma wave instrument on the Wind spacecraft, launched on November 1, 1994, has detected copious shortwave radio transmissions from broadcast stations on Earth. WAVES can easily detect signals consisting of only a few kW of transmitted power, suggesting that useful ionospheric propagation research can be accomplished with very modest equipment. We also conclude that the terrestrial radio spectrum is quite “non natural” so that any extraterrestrial radio astronomer should easily deduce that Earth is populated with a civilization with technical capabilities.

  16. Decimetric radio dot emissions

    NASA Astrophysics Data System (ADS)

    Mészárosová, H.; Karlický, M.; Sawant, H. S.; Fernandes, F. C. R.; Cecatto, J. R.; de Andrade, M. C.

    2008-11-01

    Context: We study a rare type of solar radio bursts called decimetric dot emissions. Aims: In the period 1999-2001, 20 events of decimetric dot emissions observed by the Brazilian Solar Spectroscope (BSS) in the frequency range 950-2640 MHz are investigated statistically and compared with radio fine structures of zebras and fibers. Methods: For the study of the spectral characteristics of the dot emissions we use specially developed Interactive Data Language (IDL) software called BSSView and basic statistical methods. Results: We have found that the dm dot emissions, contrary to the fine structures of the type IV bursts (i.e. zebras, fibers, lace bursts, spikes), are not superimposed on any background burst emission. In the radio spectrum, in most cases the dot emissions form chains that appear to be arranged in zebra patterns or fibers. Because some zebras and fibers, especially those observed with high time and high spectral resolutions, also show emission dots (but superimposed on the background burst emission), we compared the spectral parameters of the dot emissions with the dots being the fine structure of zebras and fibers. For both these dots, similar spectral characteristics were found. Some similarities of the dot emissions can be found also with the lace bursts and spikes. For some events the dot emissions show structural evolution from patterns resembling fibers to patterns resembling zebras and vice versa, or they evolve into fully chaotic patterns. Conclusions: For the first time, we present decimetric dot emissions that appear to be arranged in zebra patterns or fibers. We propose that these emissions are generated by the plasma emission mechanism at the locations in the solar atmosphere where the double resonance condition is fulfilled.

  17. 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.

  18. Propagation of a fluidization - combustion wave

    SciTech Connect

    Pron, G.P.; Gusachenko, L.K.; Zarko, V.E.

    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.

  19. Proceedings of the Eighteenth NASA Propagation Experimenters Meeting (NAPEX 18) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz (Editor)

    1994-01-01

    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. Participants included representatives from Canada, the Netherlands, England, and the United States, including researchers from universities, government agencies, and private industry. The meeting was organized into two technical sessions. The first session was dedicated to slant path propagation studies and experiments. The second session focused on propagation studies for mobile, personal, and sound broadcast systems. In total, 14 technical papers and some informal contributions were presented. Preceding NAPEX_17, the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop was held to review ACTS propagation activities.

  20. 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

    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

  1. 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.

  2. Proceedings of the Twentieth NASA Propagation Experimenters Meeting (NAPEX 20) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

    NASA Technical Reports Server (NTRS)

    Golshan, Nasser (Editor)

    1996-01-01

    The NASA Propagation Experimenters (NAPEX) Meeting is convened each year to discuss studies supported by the NASA Propagation Program. Representatives from the satellite communications (satcom) 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 these meetings 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 satcom industry.

  3. 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.

  4. Evaluation of quadrature-phase-shift-keying signal characteristics in W-band radio-over-fiber transmission using direct in-phase/quadrature-phase conversion technique

    NASA Astrophysics Data System (ADS)

    Suzuki, Meisaku; Kanno, Atsushi; Yamamoto, Naokatsu; Sotobayashi, Hideyuki

    2016-02-01

    The effects of in-phase/quadrature-phase (IQ) imbalances are evaluated with a direct IQ down-converter in the W-band (75-110 GHz). The IQ imbalance of the converter is measured within a range of +/-10 degrees in an intermediate frequency of DC-26.5 GHz. 1-8-G-baud quadrature phase-shift keying (QPSK) signals are transmitted successfully with observed bit error rates within a forward error correction limit of 2×10-3 using radio over fiber (RoF) techniques. The direct down-conversion technique is applicable to next-generation high-speed wireless access communication systems in the millimeter-wave band.

  5. Detection of traveling ionospheric disturbances by medium-frequency Doppler sounding using AM radio transmissions

    NASA Astrophysics Data System (ADS)

    Chilcote, M.; LaBelle, J.; Lind, F. D.; Coster, A. J.; Miller, E. S.; Galkin, I. A.; Weatherwax, A. T.

    2015-03-01

    Nighttime traveling ionosphere disturbances (TIDs) propagating in the lower F region of the ionosphere have been detected by measuring time variations in the Doppler shifts of commercial AM radio broadcast signals. Three receivers, components of the Intercepted Signals for Ionospheric Science (ISIS) Array software radio instrumentation network in the northeastern United States, recorded signals from two radio stations during 11 nights in March-April, 2012. By combining these measurements, TIDs were detected as approximately 40min periodic variations in the frequencies of the received signals resulting from Doppler shifts produced by the ionosphere. The variations had amplitudes of up to a few tenths of a hertz and were correlated across the array. For one study interval, 0000-0400 UT on 13 April 2012, simultaneous GPS total electron content, Digisonde®, and Super Dual-Auroral Radar Network coherent backscatter radar measurements confirmed the detection of TIDs with the same characteristics. Besides TIDs, the receiver network often detected large (nearly 1 Hz) upward (downward) Doppler shifts of the AM broadcast signals at the dawn (dusk) terminator. These results demonstrate that AM radio signals can be used for detection and monitoring of nighttime TIDs and related effects.

  6. 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.

  7. Updated galactic radio constraints on Dark Matter

    NASA Astrophysics Data System (ADS)

    Cirelli, Marco; Taoso, Marco

    2016-07-01

    We perform a detailed analysis of the synchrotron signals produced by dark matter annihilations and decays. We consider different set-ups for the propagation of electrons and positrons, the galactic magnetic field and dark matter properties. We then confront these signals with radio and microwave maps, including Planck measurements, from a frequency of 22 MHz up to 70 GHz. We derive two sets of constraints: conservative and progressive, the latter based on a modeling of the astrophysical emission. Radio and microwave constraints are complementary to those obtained with other indirect detection methods, especially for dark matter annihilating into leptonic channels.

  8. Tracking the CME-driven shock wave on 2012 March 5 and radio triangulation of associated radio emission

    SciTech Connect

    Magdalenić, J.; Marqué, C.; Mierla, M.; Zhukov, A. N.; Rodriguez, L.; Krupar, V.; Maksimović, M.; Cecconi, B.

    2014-08-20

    We present a multiwavelength study of the 2012 March 5 solar eruptive event, with an emphasis on the radio triangulation of the associated radio bursts. The main points of the study are reconstruction of the propagation of shock waves driven by coronal mass ejections (CMEs) using radio observations and finding the relative positions of the CME, the CME-driven shock wave, and its radio signatures. For the first time, radio triangulation is applied to different types of radio bursts in the same event and performed in a detailed way using goniopolarimetric observations from STEREO/Waves and WIND/Waves spacecraft. The event on 2012 March 5 was associated with a X1.1 flare from the NOAA AR 1429 situated near the northeast limb, accompanied by a full halo CME and a radio event comprising long-lasting interplanetary type II radio bursts. The results of the three-dimensional reconstruction of the CME (using SOHO/LASCO, STEREO COR, and HI observations), and modeling with the ENLIL cone model suggest that the CME-driven shock wave arrived at 1 AU at about 12:00 UT on March 7 (as observed by SOHO/CELIAS). The results of radio triangulation show that the source of the type II radio burst was situated on the southern flank of the CME. We suggest that the interaction of the shock wave and a nearby coronal streamer resulted in the interplanetary type II radio emission.

  9. 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

  10. 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

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

    DOEpatents

    Cown, Steven H.; Derr, Kurt Warren

    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.

  12. Testing for clonal propagation.

    PubMed

    Gregorius, H-R

    2005-02-01

    The conceptual basis for testing clonal propagation is reconsidered with the result that two steps need to be distinguished clearly: (1) specification of the characteristics of multilocus genotype frequencies that result from sexual reproduction together with the kinds of deviations from these characteristics that are produced by clonal propagation, and (2) a statistical method for detecting these deviations in random samples. It is pointed out that a meaningful characterization of sexual reproduction reflects the association of genes in (multilocus) genotypes within the bounds set by the underlying gene frequencies. An appropriate measure of relative gene association is developed which is equivalent to a multilocus generalization of the standardized gametic disequilibrium (linkage disequilibrium). Its application to the characterization of sexually produced multilocus genotypes is demonstrated. The resulting hypothesis on the frequency of a sexually produced genotype is tested with the help of the (significance) probability of obtaining at least two copies of the genotype in question in a random sample of a given size. If at least two copies of the genotype are observed in a sample, and if the probability is significant, then the hypothesis of sexual reproduction is rejected in favor of the assumption that all copies of the genotype belong to the same clone. Common testing approaches rest on the hypothesis of completely independent association of genes in genotypes and on the (significance) probability of obtaining at least as many copies of a genotype as observed in a sample. The validity of these approaches is discussed in relation to the above considerations and recommendations are set out for conducting appropriate tests.

  13. 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.

  14. 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.

  15. Tgf Pulse and Radio Properties Detected at Close Range

    NASA Astrophysics Data System (ADS)

    Cohen, M.; Gross, N. C.; Zoghzoghy, F. G.; Briggs, M. S.; Stanboro, M.; Fitzpatrick, G.

    2014-12-01

    Terrestrial Gamma-ray Flashes (TGFs) are short (10s to 100s of us) energetic (100s to 10000s of keV) discharges originating from the tops of thunderclouds. TGFs have long been associated with radio pulses detected at VLF receivers, but recent evidence indicates that the radio pulse may be from the TGF itself, rather than from a stroke or pulse that either precedes or follows the TGFs. Unfortunately, subionospheric propagation of VLF/LF smooths the radio pulse and destroys in particular the high frequency content, so that the radio signal looks similar to those from ordinary lightning strokes. Since TGFs have a broad range of durations as detected by satellites, these variations should be apparent in the LF radio pulse from the TGF, which may confirm that the TGF is the dominant source of the associated radio pulse and identify a distinguishing feature of TGF-associated pulses. We report on an effort to detect and characterize the LF radio pulses associated with TGFs at close range (<1000 km) with a high sensitivity LF receiver in the Caribbean. This requires some luck and time since TGFs, at least those detectable by satellites, are not especially common. We directly compare the temporal shape of the TGF source to the radio source, after accounting for dead time and Compton scattering to interpret the satellite TGF data, as well as propagation of the LF pulse along the ground to the receiver.

  16. Propagation Regime of Iron Dust Flames

    NASA Technical Reports Server (NTRS)

    Tang, Francois-David; Goroshin, Samuel; Higgins, Andrew J.

    2012-01-01

    A flame propagating through an iron-dust mixture can propagate in two asymptotic regimes. When the characteristic time of heat transfer between particles is much smaller than the characteristic time of particle combustion, the flame propagates in the continuum regime where the heat released by reacting particles can be modelled as a space-averaged function. In contrast, when the characteristic time of heat transfer is much larger than the particle reaction time, the flame can no longer be treated as a continuum due to dominating effects associated with the discrete nature of the particle reaction. The discrete regime is characterized by weak dependence of the flame speed on the oxygen concentration compared to the continuum regime. The discrete regime is observed in flames propagating through an iron dust cloud within a gas mixture containing xenon, while the continuum regime is obtained when xenon is substituted with helium.

  17. 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.

  18. Proceedings of the Fourteenth NASA Propagation Experimenters Meeting (NAPEX 14) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz (Editor)

    1990-01-01

    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 XIV was held on May 11, 1990, at the Balcones Research Centers, University of Texas, Austin, Texas. The meeting was organized into two technical sessions: Satellite (ACTS) and the Olympus Spacecraft, while the second focused on the fixed and mobile satellite propagation studies and experiments. Following NAPEX XIV, the ACTS Miniworkshop was held at the Hotel Driskill, Austin, Texas, on May 12, 1990, to review ACTS propagation activities since the First ACTS Propagation Studies Workshop was held in Santa Monica, California, on November 28 and 29, 1989.

  19. Characteristics of second-order residual ionospheric error in GNSS radio occultation and its impact on inversion of neutral atmospheric parameters

    NASA Astrophysics Data System (ADS)

    Qu, Xiaochuan; Li, Zhenghang; An, Jiachun; Ding, Wenwu

    2015-08-01

    In Global Navigation Satellite Systems (GNSS) radio occultation (RO), one of the most significant error sources is the ionospheric error, which is largely eliminated by dual-frequency linear combination. However, second-order residual ionospheric error (RIE) in excess phase still remains and affects the retrievals of neutral atmospheric parameters in RO. Second-order RIE varies with RO azimuth in a sinusoidal pattern for a set of simulated RO events occurring in the same location at different azimuths. The amplitude of the sinusoidal curve below 60 km is at the order of sub-centimeter under moderate solar activity level. The retrieval biases of the neutral atmospheric parameters induced by second-order RIE also have sinusoidal features with RO azimuth, but have opposite variation trends to that of the second-order RIE. The RO azimuths of the maximum positive and negative retrieval biases correspond approximately to the azimuths of maximum negative and positive second-order RIEs, respectively. The order of the maximum bending angle bias induced by the second-order RIE is about 10-8 rad under moderate solar activity level. However, the retrieval errors at low latitude are larger than those at high and middle latitudes, and the maximum temperature bias at low latitude could be 0.35 K at 40 km. Based on the sinusoidal variation of second-order RIE, it is shown that even at the same RO point and under the same solar activity level, the second-order RIEs at different RO azimuths still have different effects on the retrieval precision of atmospheric parameters. This should be considered carefully when many RO profiles are averaged for climate trend detection, especially at low latitude.

  20. The universal propagator

    NASA Technical Reports Server (NTRS)

    Klauder, John R.

    1993-01-01

    For a general Hamiltonian appropriate to a single canonical degree of freedom, a universal propagator with the property that it correctly evolves the coherent-state Hilbert space representatives for an arbitrary fiducial vector is characterized and defined. The universal propagator is explicitly constructed for the harmonic oscillator, with a result that differs from the conventional propagators for this system.

  1. A review of ionospheric effects on Earth-space propagation

    NASA Technical Reports Server (NTRS)

    Klobuchar, J. A.

    1984-01-01

    A short description is given of each ionospheric total electron content (TEC) effect upon radio waves, along with a representative value of the magnitude of each of these effects under normal ionospheric conditions. A discussion is given of the important characteristics of average ionospheric TEC behavior and the temporal and spatial variability of TEC. Radio waves undergo several effects when they pass through the Earth's ionosphere. One of the most important of these effects is a retardation, or group delay, on the modulation or information carried on the radio wave that is due to its encounter with the free, thermal electrons in the Earth's ionosphere. Other effects the ionosphere has on radio waves include: radio frequency (RF) carrier phase advance; Doppler shift of the RF carrier of the radio wave; Faraday rotation of the plane of polarization of linearly polarized waves; angular refraction or bending of the radio wave path as it travels through the ionosphere; and amplitude and phase scintillations.

  2. Effects of propagation phenomena and frequency allocation on the growth of satellite communications

    NASA Technical Reports Server (NTRS)

    Freibaum, J.

    1976-01-01

    The development of new allocations and new frequency and orbit sharing criteria for satellite communications below 10 GHz is discussed. These criteria are dependent on the outcome of current spectrum and orbit utilization and propagation studies addressing such problems as intersystem interference, satellite spacing, positioning, and repositioning, spillover of radio signals across geographic boundaries, and the adverse effects of propagation phenomena. These problems are discussed in relation to preparations for the 1979 General World Administrative Radio Conference.

  3. Calculating Sonic-Boom Propagation

    NASA Technical Reports Server (NTRS)

    Darden, C. M.; Ting, L.

    1987-01-01

    Nonlinear effects included, enabling more-realistic modeling. Modified Method of Characteristics Sonic Boom Extrapolation Program (MMOC) is computer program for sonic-boom propagation that includes shock coalescence and incorporates effects of asymmetries due to volume and lift. Numerically integrates nonlinear governing equations using data on initial data line approximately one body length from aircraft and yields sonic-boom pressure at ground as function of time or of position at given time. MMOC written in FORTRAN IV.

  4. Resonance and Radio

    ERIC Educational Resources Information Center

    Starrett, Malin J.

    2008-01-01

    The science and technology of radio receives little attention in contemporary education. This article discusses ways to explore the basic operating principles of radio. (Contains 4 figures, 3 footnotes, and 2 notes.)

  5. DISCOVERY OF GIANT RELIC RADIO LOBES STRADDLING THE CLASSICAL DOUBLE RADIO GALAXY 3C452

    SciTech Connect

    Sirothia, S. K.; Gopal-Krishna; Wiita, Paul J. E-mail: krishna@ncra.tifr.res.in

    2013-03-01

    We report the discovery of a pair of megaparsec size radio lobes of extremely steep spectrum straddling the well-known classical double radio source 3C452. The existence of such fossil lobes was unexpected since for the past several decades this powerful radio galaxy has been regarded as a textbook example of an edge-brightened double radio source of Fanaroff-Riley type II (FR II), which we now show to be a bona fide ''double-double'' radio galaxy (DDRG). Thus, 3C452 presents a uniquely robust example of recurrent nuclear activity in which the restarted jets are expanding non-relativistically within the relic synchrotron plasma from an earlier active phase and hence the inner double fed by them has evolved into a perfectly normal FR II radio source. This situation contrasts markedly with the strikingly narrow inner doubles observed in a few other DDRGs that have been interpreted in terms of compression of the synchrotron plasma of the relic outer lobes at the relativistic bow-shocks driven by the near ballistic propagation of the two inner jets through the relic plasma. A key ramification of this finding is that it cautions against the currently widespread use of FR II classical double radio sources for testing cosmological models and unification schemes for active galactic nuclei.

  6. Rosetta Radio Science Investigations (RSI)

    NASA Astrophysics Data System (ADS)

    Tellmann, Silvia; Pätzold, M.; Häusler, B.; Bird, M. K.

    2006-09-01

    In March 2004 the ROSETTA spacecraft started its journey to the comet P/Churyumov-Gerasimenko. The very ambitious mission will escort the comet for several months in 2015 as it heads towards the sun. The ROSETTA Radio Science Experiment (RSI) uses the radio carrier links of the spacecraft Telemetry, Tracking and Command subsystem at X-band and S-band. The spacecraft is specially equipped with an Ultra-Stable Oscillator (USO) that stabilizes the radio links for a significant improvement of the sensitivity and accuracy of the measurement. RSI is interested in dispersive frequency shifts due to the propagation of the radio signals through ionized media as well as non-dispersive frequency shifts caused by other perturbing forces acting on the spacecraft (gravity field, gas and dust mass flux from the comet). These observations will allow the investigation of the comet's nucleus, its size and shape and the lower harmonics of its gravity field, and the dielectric properties of its surface. In addition the electron content of the cometary coma and the abundance of large dust grains can be determined. The mass and bulk density of the asteroid will be determined during the flyby at asteroid Lutetia in 2010 First results from the commissioning phase and regularly performed measurements allow to assess the sensitivity of the experiment and the ageing of the USO quartz oscillator. These results are compared with the coherent two-way-measurements also recorded during commissioning. Between March and May 2006 ROSETTA moved into superior conjunction with the Sun. This allowed the investigation of the solar corona to derive electron density profiles in the structured corona, solar wind speed and to detect, identify and describe the spatial and temporal evolution of the shockfronts of coronal mass ejections.

  7. Ionospheric Stimulation By High Power Radio Waves

    NASA Astrophysics Data System (ADS)

    Minami, S.; Nishino, M.; Suzuki, Y.; Sato, S.; Tanikawa, T.; Nakamura, Y.; Wong, A. Y.

    1999-01-01

    We have performed an experiment to artificially stimulate the ionosphere using higher power radio waves at the HIPAS (High Power Auroral Stimulation) facility in Alaska. A radio transmission of 2.85 MHz was made at 80 MW (ERP). Diagnostics were made at the other site located 35 km from the transmission site. The results of cross-correlating the excited HF wave and observed with an 8 channel, 30 MHz scanning cosmic radio noise absorption records revealed the excited height of 90 km. Also atmospheric pressure waves observed on the ground show evident propagation of pressure waves which are generated in the ionosphere by the high-power HF wave. The results determine the excitation height of 90 km in the ionosphere and show evidence of the pressure wave coupling between the ionosphere and the lower atmosphere for periods of 10 min

  8. 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.

  9. POLARIZATION OF THE THERMAL RADIO EMISSION FROM OUTER SOLAR CORONA

    SciTech Connect

    Sastry, Ch. V.

    2009-06-01

    The Haselgrove equations for radio-ray propagation in an anisotropic medium are used to determine the degree of circular polarization (dcp) of the low-frequency thermal radio emission from the outer solar corona with a magnetic field. The variation of dcp with frequency and magnetic field strength is investigated. It is found that weak magnetic fields can be detected by measuring the dcp at low frequencies.

  10. Speckles in interstellar radio-wave scattering

    NASA Technical Reports Server (NTRS)

    Desai, K. M.; Gwinn, C. R.; Reynolds, J.; King, E. A.; Jauncey, D.; Nicholson, G.; Flanagan, C.; Preston, R. A.; Jones, D. L.

    1991-01-01

    Observations of speckles in the scattering disk of the Vela pulsar are presented and speckle techniques for studying and circumventing scattering of radio waves by the turbulent interstellar plasma are discussed. The speckle pattern contains, in a hologrammatic fashion, complete information on the structure of the radio source as well as the distribution of the scattering material. Speckle observations of interstellar scattering of radio waves are difficult because of their characteristically short timescales and narrow bandwidths. Here, first observations are presented, taken at 13 cm wavelength with elements of the SHEVE VLBI network, of speckles in interstellar scattering.

  11. Propagation of model and forcing uncertainty into hydrological drought characteristics in a multi-model century-long experiment in continental river basins

    NASA Astrophysics Data System (ADS)

    Samaniego, L. E.; Kumar, R.; Schaefer, D.; Huang, S.; Yang, T.; Mishra, V.; Eisner, S.; Vetter, T.; Pechlivanidis, I.; Liersch, S.; Flörke, M.; Krysanova, V.

    2015-12-01

    Droughts are creeping hydro-meteorological events that bring societiesand natural systems to their limits and inducing considerablesocio-economic losses. Currently it is hypothesized that climate changewill exacerbate current trends leading a more severe and extendeddroughts, as well as, larger than normal recovery periods. Currentassessments, however, lack of a consistent framework to deal withcompatible initial conditions for the impact models and a set ofstandardized historical and future forcings. The ISI-MIP project provides an unique opportunity to understand thepropagation of model and forcing uncertainty into century-long timeseries of drought characteristics using an ensemble of model predictionsacross a broad range of climate scenarios and regions. In the presentstudy, we analyze this issue using the hydrologic simulations carriedout with HYPE, mHM, SWIM, VIC, and WaterGAP3 in seven large continentalriver basins: Amazon, Blue Nile, Ganges, Niger, Mississippi, Rhine,Yellow. All models are calibrated against observed streamflow duringthe period 1971-2001 using the same forcings based on the WATCH datasets. These constrained models were then forced with bias correctedoutputs of five CMIP-5 GCMs under four RCP scenarios (i.e. 2.6, 4.5,6.0, and 8.5 W/m2) for the period 1971-2099. A non-parametric kernel density approach is used to estimate thetemporal evolution of a monthly runoff index based on simulatedstreamflow. Hydrologic simulations corresponding to each GCM during thehistoric period of 1981-2010 serve as reference for the estimation ofthe basin specific monthly probability distribution functions. GCMspecific reference pdfs are then used to recast the future hydrologicmodel outputs from different RCP scenarios. Based on these results,drought severity and duration are investigated during periods: 1)2006-2035, 2) 2036-2065 and 3) 2070-2099. Two main hypothesis areinvestigated: 1) model predictive uncertainty of drought indices amongdifferent hydrologic

  12. 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).

  13. 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…

  14. 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.

  15. A Kinetic Model for the Radio CME

    NASA Astrophysics Data System (ADS)

    Lee, Jeongwoo; Gary, D. E.

    2009-05-01

    Current studies on Coronal Mass Ejections (CMEs) are mostly concentrated on their macroscopic properties as measured on White-Light images. On the other hand, radio emissions from CMEs carry the information of high energy particles associated with them, but usually without spatial information. In this regard, the rare radio maps of the 1998 April 20 CME obtained with the Nancay radioheliograph between 164 and 432 MHz (called a radio CME by Bastian et al. in 2001) offer an exceptional opportunity to explore the spatial distribution of high energy electrons inside the CME loop. We present a detailed kinetic model for the radio CME employing the lower hybrid (LH) waves excited by the CME shock as the primary electron acceleration mechanism, and magnetic mirroring and Coulomb collisions as the propagation effects inside the expanding loop. The main constraint in this modeling comes from the fact that the LH waves accelerate electrons parallel to the magnetic field and the accelerated electrons should gain, during propagation, sufficient amount of the perpendicular momentum to emit the synchrotron radiation as observed. The relative magnetic field variation responsible for the magnetic mirroring is inferred from the geometrical shape of the CME on the images of the Large Angle and Spectrometric Coronagraph Experiment (LASCO), and the field strength and the amplitude of the LH waves are determined from the observed radio spectra. The modeling is focused on the spatial distribution of the LH waves most plausible to explain the radio maps, and the result is discussed in relation to the associated shock property.

  16. Report from the Symposia on Antennas and Propagation

    NASA Astrophysics Data System (ADS)

    Mattsson, S.

    1985-12-01

    Communications including shortwave; mobile radio; radiolink; satellite networks; and array, microstrip, adaptive, and reflector type antennas; surface and underground antennas; and waves were treated. Rain attenuation was discussed. Multipath propagation on radiolinks, and the interference between terrestrial links and satellite links were considered.

  17. Radio propagation experiments in the outer solar system with Voyager

    NASA Technical Reports Server (NTRS)

    Tyler, G. Leonard

    1987-01-01

    The outer solar system's planetary atmospheres, ionospheres, rings, and magnetic fields are under study in light of microwave telecommunications from the two Voyager spacecraft. The use of the hydrogen maser frequency standards on the ground, in conjunction with thermally controlled quartz oscillators aboard the spacecraft, ensures long coherence intervals and allows the application of novel signal processing methods. On this basis, studies of atmospheric structure and scintillation parameters, planetary ring structure, and magnetic control of small ionospheric irregularities have been undertaken; information concerning planetary evolution, composition, and dynamics is thereby obtained.

  18. Propagation of radio waves through the lower atmosphere of Venus

    NASA Technical Reports Server (NTRS)

    Richter, K. R.

    1972-01-01

    A simplified model of the Venus atmosphere is developed providing the loss factor profile of the atmosphere. With this profile the atmospheric attenuation as it depends upon the incidence angle is calculated for wavelengths between 2 cm and 20 cm. It is shown that the signal-to-noise ratios for a real aperture radar, a synthetic aperture radar, and communication links between a satellite and a landing probe achieve maximum values by the proper choice of the wavelengths. Furthermore, it turns out that the wavelength dependence is less crucial for the synthetic aperture radar compared to the other cases.

  19. Scintillation effects on radio wave propagation through solar corona

    NASA Technical Reports Server (NTRS)

    Ho, C. M.; Sue, M. K.; Bedrossian, A.; Sniffin, R. W.

    2002-01-01

    When RF waves pass through the solar corona and solar wind regions close to the Sun, strong scintillation effects appear at their amplitude, frequency and phase, especially in the regions very close to the Sun (less than 4 solar radius).

  20. 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 β, 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 β, rather than to an increase in the reflection heights h0 and hE.

  1. Planetary radio astronomy observations during the Voyager 1 Titan flyby

    NASA Technical Reports Server (NTRS)

    Daigne, G.; Pedersen, B. M.; Kaiser, M. L.; Desch, M. D.

    1982-01-01

    During the Voyager 1 Titan flyby, unusual radio emissions were observed by the planetary radio astronomy experiment in the 20- to 97-kHz frequency range. It is shown that Titan itself is not the source of the observed radio emission. The emission features are attributed to modification of the normal Saturn kilometric radiation by propagation effects in enhanced density structures within the Titan wake. Furthermore, spiky emissions observed in the magnetic wake of Titan are interpreted in terms of local electrostatic instabilities at the electron plasma frequency. From these measurements a range of electron densities in the wake region is derived, and the consistency of the results is discussed.

  2. The new class of FR 0 radio galaxies

    NASA Astrophysics Data System (ADS)

    Baldi, R. D.; Capetti, A.; Giovannini, G.

    2016-02-01

    Are the FRI and FRII radio galaxies representative of the radio-loud (RL) AGN population in the local Universe? Recent studies on the local low-luminosity radio sources cast lights on an emerging population of compact radio galaxies which lack extended radio emission. In a pilot JVLA project, we study the high-resolution images of a small but representative sample of this population. The radio maps reveal compact unresolved or slightly resolved radio structures on a scale of 1-3 kpc. We find that these RL AGN live in red massive early-type galaxies, with large black hole masses (≳ 108 M⊙), and spectroscopically classified as Low Excitation Galaxies, all characteristics typical of FRI radio galaxies which they also share the same nuclear luminosity with. However, they are more core dominated (by a factor of ˜ 30) than FRIs and show a clear deficit of extended radio emission. We call these sources ``FR0'' to emphasize their lack of prominent extended radio emission. A posteriori, other compact radio sources found in the literature fulfill the requirements for a FR0 classification. Hence, the emerging FR0 population appears to be the dominant radio class of the local Universe. Considering their properties we speculate on their possible origins and the possible cosmological scenarios they imply.

  3. Demonstration of a viable quantitative theory for interplanetary type II radio bursts

    NASA Astrophysics Data System (ADS)

    Schmidt, J. M.; Cairns, Iver H.

    2016-03-01

    Between 29 November and 1 December 2013 the two widely separated spacecraft STEREO A and B observed a long lasting, intermittent, type II radio burst for the extended frequency range ≈ 4 MHz to 30 kHz, including an intensification when the shock wave of the associated coronal mass ejection (CME) reached STEREO A. We demonstrate for the first time our ability to quantitatively and accurately simulate the fundamental (F) and harmonic (H) emission of type II bursts from the higher corona (near 11 solar radii) to 1 AU. Our modeling requires the combination of data-driven three-dimensional magnetohydrodynamic simulations for the CME and plasma background, carried out with the BATS-R-US code, with an analytic quantitative kinetic model for both F and H radio emission, including the electron reflection at the shock, growth of Langmuir waves and radio waves, and the radiations propagation to an arbitrary observer. The intensities and frequencies of the observed radio emissions vary hugely by factors ≈ 106 and ≈ 103, respectively; the theoretical predictions are impressively accurate, being typically in error by less than a factor of 10 and 20 %, for both STEREO A and B. We also obtain accurate predictions for the timing and characteristics of the shock and local radio onsets at STEREO A, the lack of such onsets at STEREO B, and the z-component of the magnetic field at STEREO A ahead of the shock, and in the sheath. Very strong support is provided by these multiple agreements for the theory, the efficacy of the BATS-R-US code, and the vision of using type IIs and associated data-theory iterations to predict whether a CME will impact Earth's magnetosphere and drive space weather events.

  4. Low-Frequency Radio Bursts and Space Weather

    NASA Technical Reports Server (NTRS)

    Gopalswamy, N.

    2016-01-01

    Low-frequency radio phenomena are due to the presence of nonthermal electrons in the interplanetary (IP) medium. Understanding these phenomena is important in characterizing the space environment near Earth and other destinations in the solar system. Substantial progress has been made in the past two decades, because of the continuous and uniform data sets available from space-based radio and white-light instrumentation. This paper highlights some recent results obtained on IP radio phenomena. In particular, the source of type IV radio bursts, the behavior of type III storms, shock propagation in the IP medium, and the solar-cycle variation of type II radio bursts are considered. All these phenomena are closely related to solar eruptions and active region evolution. The results presented were obtained by combining data from the Wind and SOHO missions.

  5. The Transient Radio Sky

    NASA Astrophysics Data System (ADS)

    Keane, E. F.

    2010-11-01

    the discovery of 19 new sources. Of these, 12 have been re-detected on multiple occasions, whereas the others have not been seen to re-emitsince the initial discovery observations, and may be very low burst-rate RRATs, or, isolated burst events. These discoveries suggest that the initial population estimate was not over-estimated -- RRATs, though not a distinct population, are indeed numerous.In addition to finding new sources, characterisation of their properties is vital. To this end, a campaign of regular radio observations of the newly discovered sources, was mounted, at theParkes Observatory, in Australia. In addition, some of the initially identified RRATs were observed with the Lovell Telescope at Jodrell Bank. These have revealed glitches in J1819-1458, with anomalous post-glitch recovery of the spin-down rate. If such glitches werecommon, it would imply that the source was once a magnetar, neutron stars with the strongest known magnetic fields of up to 10^{15} gauss. The observations have also been used to perform`timing' observations of RRATs, i.e. determination of their spin-down characteristics. At the beginning of this thesis, 3 of the original sources had `timing solutions' determined. This has since risen to 7, and furthermore, 7 of the newly discovered sources now also have timing solutions. With this knowledge, we can see where RRATs lie in period-period derivative space. The Parkes RRATs seem to be roughly classifiable into three groupings, with high observed nulling fractions -- normal pulsars, high magnetic field pulsars and old,`dying' pulsars.It seems that RRATs and pulsars are one and the same. When a pulsar is more easily detected in searches for single bright pulses, as opposed to in periodicity searches, we label it a RRAT. Such searches impart a selection effect on the parameter space of possible sources, in bothnulling fraction and rotation period. In this sense, an observational setup could be designed to make any pulsar appear as a RRAT

  6. Equatorial ionospheric disturbance observed through a transequatorial HF propagation experiment

    NASA Astrophysics Data System (ADS)

    Maruyama, T.; Kawamura, M.

    2006-07-01

    A transequatorial radio-wave propagation experiment at shortwave frequencies (HF-TEP) was done between Shepparton, Australia, and Oarai, Japan, using the radio broadcasting signals of Radio Australia. The receiving facility at Oarai was capable of direction finding based on the MUSIC (Multiple Signal Classification) algorithm. The results were plotted in azimuth-time diagrams (AT plots). During the daytime, the propagation path was close to the great circle connecting Shepparton and Oarai, thus forming a single line in the AT plots. After sunset, off-great-circle paths, or satellite traces in the AT plot, often appeared abruptly to the west and gradually returned to the great circle direction. However, there were very few signals across the great circle to the east. The off-great-circle propagation was very similar to that previously reported and was attributed to reflection by an ionospheric structure near the equator. From the rate of change in the direction, we estimated the drift velocity of the structure to range mostly from 100 to 300 m/s eastward. Multiple instances of off-great-circle propagation with a quasi-periodicity were often observed and their spatial distance in the east-west direction was within the range of large-scale traveling ionospheric disturbances (LS-TIDs). Off-great-circle propagation events were frequently observed in the equinox seasons. Because there were many morphological similarities, the events were attributed to the onset of equatorial plasma bubbles.

  7. Effect of a Sausage Oscillation on Radio Zebra-pattern Structures in a Solar Flare

    NASA Astrophysics Data System (ADS)

    Yu, Sijie; Nakariakov, V. M.; Yan, Yihua

    2016-07-01

    Sausage modes that are axisymmetric fast magnetoacoustic oscillations of solar coronal loops are characterized by variation of the plasma density and magnetic field, and hence cause time variations of the electron plasma frequency and cyclotron frequency. The latter parameters determine the condition for the double plasma resonance (DPR), which is responsible for the appearance of zebra-pattern (ZP) structures in time spectra of solar type IV radio bursts. We perform numerical simulations of standing and propagating sausage oscillations in a coronal loop modeled as a straight, field-aligned plasma slab, and determine the time variation of the DPR layer locations. Instant values of the plasma density and magnetic field at the DPR layers allowed us to construct skeletons of the time variation of ZP stripes in radio spectra. In the presence of a sausage oscillation, the ZP structures are shown to have characteristic wiggles with the time period prescribed by the sausage oscillation. Standing and propagating sausage oscillations are found to have different signatures in ZP patterns. We conclude that ZP wiggles can be used for the detection of short-period sausage oscillations and the exploitation of their seismological potential.

  8. Radio Astronomy Explorer (RAE) 1 observations of terrestrial radio noise

    NASA Technical Reports Server (NTRS)

    Herman, J. R.; Caruso, J. A.

    1971-01-01

    Radio Astonomy Explorer (RAE) 1 data are analyzed to establish characteristics of HF terrestrial radio noise at an altitude of about 6000 km. Time and frequency variations in amplitude of the observed noise well above cosmic noise background are explained on the basis of temporal and spatial variations in ionospheric critical frequency coupled with those in noise source distributions. It is shown that terrestrial noise regularly breaks through the ionosphere and reaches RAE with magnitudes 15 or more db higher than cosmic noise background. Maximum terrestrial noise is observed when RAE is over the dark side of the Earth in the neighborhood of equatorial continental land masses where thunderstorms occur most frequently. The observed noise level is 30-40 db lower with RAE over oceans.

  9. The OPEX project and standard processing of propagation data

    NASA Astrophysics Data System (ADS)

    Brussaard, G.

    1989-05-01

    The Olympus Propagation Package, (OPEX), its mission, and main characteristics, are described. The voluntary participation of experimenters on the OPEX project, and their preparation of detailed handbooks for the design of hardware, data preprocessing and analysis are described. The main characteristics of the standard software developed for propagation data treatment are described.

  10. Voyager planetary radio astronomy studies

    NASA Technical Reports Server (NTRS)

    Staelin, David H.; Eikenberry, Stephen S.

    1993-01-01

    Analysis of nonthermal radio emission data obtained by the Planetary Radio Astronomy (PRA) spectrometers on the Voyager 1 and 2 spacecraft was performed. This PRA data provided unique insights into the radio emission characteristics of the outer planets because of PRA's unique spectral response below the terrestrial ionospheric plasma frequency and its unprecedented proximity to the source. Of those results which were documented or published, this final report surveys only the highlights and cites references for more complete discussions. Unpublished results for Uranus, Neptune, and theoretical Ionian current distributions are presented at greater length. The most important conclusion to be drawn from these observations is that banded spectral emission is common to the radio emission below 1-2 MHz observed from all four Jovian planets. In every case multiple spectral features evolve on time scales of seconds to minutes. To the extent these features drift in frequency, they appear never to cross one another. The Neptunian spectral features appear to drift little or not at all, their evolution consisting principally of waxing and waning. Since other evidence strongly suggests that most or all of this radio emission is occurring near the local magnetospheric electron cyclotron frequency, this implies that this emission preferentially occurs at certain continually changing planetary radii. It remains unknown why certain radii might be favored, unless radial electric field components or other means serve to differentiate radially the magnetospheric plasma density, particle energy vectors, or particle coherence. Calculation of the spatial distribution and intensity of the Io-generated magnetospheric currents are also presented; these currents may be limited principally by wave impedance and local field strengths.

  11. Direct imaging in radio of CME development

    NASA Astrophysics Data System (ADS)

    Maia, D.; Pick, M.; Kerdraon, A.; Mercier, C.

    2003-04-01

    On April 15 2001, the Nançay Radioheliograph observed fast moving, expanding loops, in images taken in the wavelength range between 164 and 432 MHz. We were able to follow the progression of the radio loops, starting from a few tenth to almost one solar radii above the solar limb, with a time cadence on the order of the second. The loops seen in radio agree very well with the features of the coronal mass ejection (CME) seen later, more than 1.5 solar radii above the limb, in white light images by the Large-Angle Spectrometric Coronagraph (LASCO) experiment, on board the Solar and Heliospheric Observatory (SOHO) spacecraft. This is the first time that a "radio CME" is seen so low in the corona, making possible a detailed study on the initiation and main characteristics of the "radio CME" phenomenon. Quite remarkable in this event is the fact that, simultaneous with the radio loops, the Nançay Radioheliograph imaged also strong radio bursts, seen only at the lowest frequencies. This events provides thus a unique opportunity to directly compare the positions, and timing, of the electron acceleration sites, associated with the radio bursts, to the progression, and development, of the CME.

  12. The Giant Metrewave Radio Telescope

    NASA Astrophysics Data System (ADS)

    Nityananda, R.

    2003-05-01

    The Giant Metrewave Radio Telescope (GMRT) of the National Centre of Radio Astrophysics (NCRA) of the Tata Institute of Fundamental Research (TIFR) at Khodad, India, has been operational in the band 0.2 to 2 metres for the last two and a half years. The system characteristics and performance and recent results from the group will be presented. Details of use over the last six months by scientists from other observatories under the GMRT Time Allocation Committee (GTAC) and future plans will be also be reviewed in this paper. Areas which have been studied include observations made in the GMRT band of neutral hydrogen, nearby galaxies, supernova remnants, the Galactic Centre, pulsars, the Sun and others.

  13. Spectral structures and their generation mechanisms for solar radio type-I bursts

    SciTech Connect

    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.

  14. 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.

  15. Radio source evolution

    NASA Astrophysics Data System (ADS)

    Perucho, M.

    2016-02-01

    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. Finally, I discuss the possible tracks that radio sources may follow within this diagram, and the physical processes that can explain the different tracks.

  16. The Sardinia Radio Telescope

    NASA Astrophysics Data System (ADS)

    Grueff, G.; Alvito, G.; Ambrosini, R.; Bolli, P.; D'Amico, N.; Maccaferri, A.; Maccaferri, G.; Morsiani, M.; Mureddu, L.; Natale, V.; Olmi, L.; Orfei, A.; Pernechele, C.; Poma, A.; Porceddu, I.; Rossi, L.; Zacchiroli, G.

    We describe the Sardinia Radio Telescope (SRT), a new general purpose, fully steerable antenna of the National Institute for Astrophysics. The radio telescope is under construction near Cagliari (Sardinia). With its large aperture (64m diameter) and its active surface, SRT is capable of operations up to ˜100GHz, it will contribute significantly to VLBI networks and will represent a powerful single-dish radio telescope for many science fields. The radio telescope has a Gregorian optical configuration with a supplementary beam-waveguide (BWG), which provides additional focal points. The Gregorian surfaces are shaped to minimize the spill-over and standing wave. After the start of the contract for the radio telescope structural and mechanical fabrication in 2003, in the present year the foundation construction will be completed. The schedule foresees the radio telescope inauguration in late 2006.

  17. Earth-Space Propagation Data Bases

    NASA Technical Reports Server (NTRS)

    Smith, Ernest K.

    1996-01-01

    This paper, designed for the newcomer rather than the expert, will take a rather broad view of what is meant by 'propagation data bases' in that it will take the term to mean both the actual measurements and models of Earth-space paths. The text will largely be drawn from International Radio Consultative Committee (CCIR) reports, now annexed to the Recommendations of the International Telecommunications Union-R Study Group 3, plus some experience with a course taught at the University of Colorado.

  18. The radio luminosity function and redshift evolution of radio-mode and quasar-mode AGN

    NASA Astrophysics Data System (ADS)

    Pracy, Mike

    2016-08-01

    The properties of the AGN population indicate that there are two fundamentally different accretion modes operating. In the quasar-mode, material is accreted onto the supermassive black hole via a small, thin, optically luminous accretion disc. Accretion in this mode is recognisable by emission lines in the optical spectrum. However, there is a population of AGN observable only by their radio emission and without optical emission lines. These radio-mode AGN are likely powered by radiatively inefficient accretion from a hot gas halo. I will describe the cosmic evolution of these two populations via radio luminosity functions. The radio luminosity functions are constructed from a new survey of over 4000 radio galaxies out to z=1, all with confirmed redshifts and their accretion mode classified from their optical spectra. This is 20 times larger than the only other survey used to make such a measurement. The radio-mode AGN population displays no statistically significant evolution in space density out to redshift z=1. In contrast the quasar mode AGN exhibits rapid evolution in space density, increasing by a factor of 8 over the same redshift range. The characteristic break in the radio luminosity function occurs at a significantly higher power for the quasar-mode AGN in comparison to the radio-mode AGN and we demonstrate this is consistent with the two populations representing fundamentally different accretion modes. The radio luminosity function is used to estimate the total amount of mechanical energy available for radio mode feedback as a function of redshift, and is found to be in good agreement with cosmological models and previous measurements. Again, by separating by accretion mode, the previously estimated increase in available mechanical energy per unit volume out to z=1 (approximately a factor of 2) can be attributed to the rapid evolution of the quasar-mode AGN, while for the classical radio-mode AGN the total mechanical energy output remains roughly

  19. Radio for formal education and for development communication.

    PubMed

    Jamison, D T

    1978-09-01

    A substantial body of literature documents the successful use of open radio broadcasting, radio campaigns, and radio-listening groups in nonformal education and other aspects of development communication. The 4 alternative strategies for using radio in formal education -- using radio to enrich learning, direct instruction, extending in-school education, and distance learning -- need to be assessed in terms of users' needs. The use of radio to enrich in-school education holds little promise for major improvements, but the potential for the use of radio in direct instruction in 1 or more subjects is promising and presents a strong challenge to educators. Case studies of 2 Mexican projects to extend school in order to expand the rural population's access to information and schools were disappointing. Both projects showed that radio could teach about as effectively as traditional elementary school teachers, but neither expanded beyond the pilot stage. Better financing and a firmer government commitment might have made a difference. The use of radio in formal education as a component of a distance-learning system has been successful in Kenya and the Dominican Republic, among other places. The best use of open broadcast is to transmit an interesting message; the most appropriate use of listening-group strategies -- radio schools, farm forums, and radio animation -- are to promote more complex and longterm changes. Communication planners need to be aware that radio can be used in numerous ways in response to a variety of goals. 4 projects are reviewed to illustrate instances in which radio has realized its goals with special success -- the Kenyan health broadcasts, the radio program that used nutrition "ads," the Guatemalan agricultural information programs, and the Tanzania radio campaigns. These projects show that the development goals being promoted and the special characteristics of the project determine the strategy, its effects, and its transferability.

  20. Limitations in scatter propagation

    NASA Astrophysics Data System (ADS)

    Lampert, E. W.

    1982-04-01

    A short description of the main scatter propagation mechanisms is presented; troposcatter, meteor burst communication and chaff scatter. For these propagation modes, in particular for troposcatter, the important specific limitations discussed are: link budget and resulting hardware consequences, diversity, mobility, information transfer and intermodulation and intersymbol interference, frequency range and future extension in frequency range for troposcatter, and compatibility with other services (EMC).

  1. 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.

  2. NASA propagation information center

    NASA Astrophysics Data System (ADS)

    Smith, Ernest K.; Flock, Warren L.

    1990-07-01

    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.

  3. Propagation data bases

    NASA Astrophysics Data System (ADS)

    1981-12-01

    Existing data bases accumulated as the result of experiments to gather propagation data on millimeter wave Earth-space links are described. The satellites used are described and results of the significant experiments conducted in the United States are summarized. The data bases consist primarily of cumulative attenuation statistics, though some depolarization measurements are included. Additional summaries of propagation data are cited.

  4. Wave propagation, scattering and emission in complex media

    NASA Astrophysics Data System (ADS)

    Jin, Ya-Qiu

    I. Polarimetric scattering and SAR imagery. EM wave propagation and scattering in polarimetric SAR interferometry / S. R. Cloude. Terrain topographic inversion from single-pass polarimetric SAR image data by using polarimetric stokes parameters and morphological algorithm / Y. Q. Jin, L. Luo. Road detection in forested area using polarimetric SAR / G. W. Dong ... [et al.]. Research on some problems about SAR radiometric resolution / G. Dong ... [et al.]. A fast image matching algorithm for remote sensing applications / Z. Q. Hou ... [et al.]. A new algorithm of noised remote sensing image fusion based on steerable filters / X. Kang ... [et al.]. Adaptive noise reduction of InSAR data based on anisotropic diffusion models and their applications to phase unwrapping / C. Wang, X. Gao, H. Zhang -- II. Scattering from randomly rough surfaces. Modeling tools for backscattering from rough surfaces / A. K. Fung, K. S. Chen. Pseudo-nondiffracting beams from rough surface scattering / E. R. Méndez, T. A. Leskova, A. A. Maradudin. Surface roughness clutter effects in GPR modeling and detection / C. Rappaport. Scattering from rough surfaces with small slopes / M. Saillard, G. Soriano. Polarization and spectral characteristics of radar signals reflected by sea-surface / V. A. Butko, V. A. Khlusov, L. I. Sharygina. Simulation of microwave scattering from wind-driven ocean surfaces / M. Y. Xia ... [et al.]. HF surface wave radar tests at the Eastern China Sea / X. B. Wu ... [et al.] -- III. Electromagnetics of complex materials. Wave propagation in plane-parallel metamaterial and constitutive relations / A. Ishimaru ... [et al.]. Two dimensional periodic approach for the study of left-handed metamaterials / T. M. Grzegorczyk ... [et al.]. Numerical analysis of the effective constitutive parameters of a random medium containing small chiral spheres / Y. Nanbu, T. Matsuoka, M. Tateiba. Wave propagation in inhomogeneous media: from the Helmholtz to the Ginzburg -Landau equation / M

  5. Millimeter wavelength propagation studies

    NASA Technical Reports Server (NTRS)

    Hodge, D. B.

    1974-01-01

    The investigations conducted for the Millimeter Wavelength Propagation Studies during the period December, 1966, to June 1974 are reported. These efforts included the preparation for the ATS-5 Millimeter Wavelength Propagation Experiment and the subsequent data acquisition and data analysis. The emphasis of the OSU participation in this experiment was placed on the determination of reliability improvement resulting from the use of space diversity on a millimeter wavelength earth-space communication link. Related measurements included the determination of the correlation between radiometric temperature and attenuation along the earth-space propagation path. Along with this experimental effort a theoretical model was developed for the prediction of attenuation statistics on single and spatially separated earth space propagation paths. A High Resolution Radar/Radiometer System and Low Resolution Radar System were developed and implemented for the study of intense rain cells in preparation for the ATS-6 Millimeter Wavelength Propagation Experiment.

  6. Wave propagation phenomena

    NASA Astrophysics Data System (ADS)

    Groenenboom, P. H. L.

    The phenomenon of wave propagation is encountered frequently in a variety of engineering disciplines. It has been realized that for a growing number of problems the solution can only be obtained by discretization of the boundary. Advantages of the Boundary Element Method (BEM) over domain-type methods are related to the reduction of the number of space dimensions and of the modelling effort. It is demonstrated how the BEM can be applied to wave propagation phenomena by establishing the fundamental relationships. A numerical solution procedure is also suggested. In connection with a discussion of the retarded potential formulation, it is shown how the wave propagation problem can be cast into a Boundary Integral Formulation (BIF). The wave propagation problem in the BIF can be solved by time-successive evaluation of the boundary integrals. The example of pressure wave propagation following a sodium-water reaction in a Liquid Metal cooled Fast Breeder Reactor steam generator is discussed.

  7. 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/.

  8. Modeling and Simulation for Realistic Propagation Environments of Communications Signals at SHF Band

    NASA Technical Reports Server (NTRS)

    Ho, Christian

    2005-01-01

    In this article, most of widely accepted radio wave propagation models that have proven to be accurate in practice as well as numerically efficient at SHF band will be reviewed. Weather and terrain data along the signal's paths can be input in order to more accurately simulate the propagation environments under particular weather and terrain conditions. Radio signal degradation and communications impairment severity will be investigated through the realistic radio propagation channel simulator. Three types of simulation approaches in predicting signal's behaviors are classified as: deterministic, stochastic and attenuation map. The performance of the simulation can be evaluated under operating conditions for the test ranges of interest. Demonstration tests of a real-time propagation channel simulator will show the capabilities and limitations of the simulation tool and underlying models.

  9. Radio data transmission for SCADA

    SciTech Connect

    Frasier, W.E. )

    1989-09-01

    Enron has used such wireless systems as meteor burst radio, 952 MHz multiple address radio, VSAT and L-band satellite, cellular radio and ACSB radio. The company's experience with meteor burst radio communications is discussed in this paper. It indicates good system reliability and consequently all back-up telephone lines have been removed from sites using this system.

  10. Tracking by Identification Using Computer Vision and Radio

    PubMed Central

    Mandeljc, Rok; Kovačič, Stanislav; Kristan, Matej; Perš, Janez

    2013-01-01

    We present a novel system for detection, localization and tracking of multiple people, which fuses a multi-view computer vision approach with a radio-based localization system. The proposed fusion combines the best of both worlds, excellent computer-vision-based localization, and strong identity information provided by the radio system, and is therefore able to perform tracking by identification, which makes it impervious to propagated identity switches. We present comprehensive methodology for evaluation of systems that perform person localization in world coordinate system and use it to evaluate the proposed system as well as its components. Experimental results on a challenging indoor dataset, which involves multiple people walking around a realistically cluttered room, confirm that proposed fusion of both systems significantly outperforms its individual components. Compared to the radio-based system, it achieves better localization results, while at the same time it successfully prevents propagation of identity switches that occur in pure computer-vision-based tracking. PMID:23262485

  11. Proceedings of the Twenty-First NASA Propagation Experimenters 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.

  12. Gear crack propagation investigations

    NASA Technical Reports Server (NTRS)

    Lewicki, David G.; Ballarini, Roberto

    1996-01-01

    Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture ANalysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modeling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gages in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.

  13. Impact of the magnetic superstorm on March 17-19, 2015 on subpolar HF radio paths: Experiment and modeling

    NASA Astrophysics Data System (ADS)

    Blagoveshchensky, D. V.; Maltseva, O. A.; Anishin, M. M.; Sergeeva, M. A.; Rogov, D. D.

    2016-09-01

    The ionospheric phenomena which significantly influenced radio propagation during March 17-19, 2015 are considered in the study. The data of oblique ionospheric sounding (OIS) were analyzed at six radio paths. These paths are located in the zone of North Siberia in Russia and have different lengths: from 1000 to 5000 km. The results are the following. The magnetic storm drastically changed the character of radio propagation at all the considered paths: in most cases the reflections from the ionospheric F2-layer were changed by the reflections only from the sporadic Es-layer. The parameters of movement of the disturbance front were estimated on the basis of OIS data of the paths. The average velocity of the front movements from east to west was about V = 440 m/s. Even the moderate growth of riometer absorption within the region of radio paths' locations, resulted in loss of multihop modes in the signal reflections from sporadic layers. It also resulted in a sharp decrease of signal strength at the paths. Real distance-frequency characteristics (DFC) of the paths were compared to DFC calculated on the basis of International Reference Ionosphere (IRI) model. It was revealed that on a quiet day of March, 15th, the real and the calculated DFC are similar or coincide in the majority of cases. During the disturbed days of March, 17-19, most commonly observed are the significant differences between the calculated and the experimental data. The most pronounced difference is revealed while estimating the character of OIS signals' reflections from Es-layers.

  14. Using TEC and radio scintillation data from the CITRIS radio beacon receiver to study low and midlatitude ionospheric irregularities

    NASA Astrophysics Data System (ADS)

    Siefring, Carl L.; Bernhardt, Paul A.; Koch, Douglas E.; Galysh, Ivan J.

    2011-12-01

    Unique data on ionospheric plasma irregularities from the Naval Research Laboratory Scintillation and TEC Receiver in Space (CITRIS) instrument is presented. CITRIS is a multiband receiver that recorded Total Electron Content (TEC) and radio scintillations from Low-Earth Orbit (LEO) on STPSat1. The 555 ± 5 km altitude 35° inclination orbit covers low and midlatitudes. The measurements require propagation from a transmitter to a receiver through the F region plasma. CITRIS used both 1) satellite beacons in LEO and 2) the French sponsored global network of ground-based Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) beacons. This paper is both a brief review of the CITRIS experiment and the first combined TEC and scintillation study of ionospheric irregularities using a satellite-borne beacon receiver. It primarily focuses on CITRIS/DORIS observations and is a case study of the ionospheric irregularities and associated scintillation characteristics at 401.25 MHz during the 2008 equinox solar minimum. In addition, CITRIS was operated in a complementary fashion with the Communication/Navigations Outages Forecasting System (C/NOFS) satellite during C/NOFS' first year of operations and comparison with measured C/NOFS irregularity characteristics are made. Several types of irregularities have been studied including Spread-F and the newly discovered dawn-side depletions.

  15. The ghost propagator in Coulomb gauge

    SciTech Connect

    Watson, P.; Reinhardt, H.

    2011-05-23

    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.

  16. 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.

  17. Solar radio astronomy at low frequencies

    NASA Technical Reports Server (NTRS)

    Dulk, George A.

    1990-01-01

    The characteristics of solar radio emissions at decametric to kilometric wavelengths are reviewed. Special attention is given to the radiation of the quiet sun at several metric and decametric wavelengths and to nonthermal radiation from the active sun, including radio bursts of type III (electron beams), type-III bursts from behind the sun, storms of type III bursts, the flare-associated radio bursts, type II bursts (shock waves), and shock-associated bursts. It is pointed out that almost no observations have been made so far of solar radiation between about 20 MHz and about 2 MHz. Below about 2 MHz, dynamic spectra of flux densities of solar burst have been recorded in space and observations were made of the directions of centroids and characteristic sizes of the emitting sources.

  18. 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.

  19. Film, Radio, and Television.

    ERIC Educational Resources Information Center

    Hardesty, Carolyn, Ed.

    1990-01-01

    This journal issue covers the history of film, radio, and television in Iowa. The first article, "When Pictures and Sound Came to Iowa," summarizes the origin of movies and radio and their early beginnings in Iowa. Using old photographs and measurement charts, the viewing, reading, and listening habits of young people in 1950 and 1958 are…

  20. Writing for Radio.

    ERIC Educational Resources Information Center

    Tupper, Marianna S.

    1995-01-01

    Describes a 24-hour commercial radio station simulation class project for eighth-grade language arts. Students wrote their own scripts, chose music and were disc jockeys on their own music and talk shows, and prepared news and traffic reports. Guest speakers from actual commercial radio came in to discuss issues such as advertising, censorship,…

  1. Frequencies for radio astronomy.

    PubMed

    Smith, F G

    1970-10-31

    At present the scope of research in radio astronomy is limited by the allocation of frequencies, some of which have to be shared with other radio services. When the International Telecommunications Union reconsiders all frequency allocations next year, astronomers are hoping for an improvement.

  2. 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.

  3. Stabilized radio frequency quadrupole

    DOEpatents

    Lancaster, Henry D.; Fugitt, Jock A.; Howard, Donald R.

    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.

  4. Classification of neocortical interneurons using affinity propagation

    PubMed Central

    Santana, Roberto; McGarry, Laura M.; Bielza, Concha; Larrañaga, 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

  5. Classification of neocortical interneurons using affinity propagation.

    PubMed

    Santana, Roberto; McGarry, Laura M; Bielza, Concha; Larrañaga, 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.

  6. Classification of neocortical interneurons using affinity propagation.

    PubMed

    Santana, Roberto; McGarry, Laura M; Bielza, Concha; Larrañaga, 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

  7. Radio efficiency of pulsars

    SciTech Connect

    Szary, Andrzej; Melikidze, George I.; Gil, Janusz; Zhang, Bing; Xu, Ren-Xin E-mail: zhang@physics.unlv.edu

    2014-03-20

    We investigate radio emission efficiency, ξ, of pulsars and report a near-linear inverse correlation between ξ and the spin-down power, E-dot , as well as a near-linear correlation between ξ and pulsar age, τ. 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 γ-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.

  8. 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)

  9. Solar Radio Bursts and Space Weather

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Natchimuthuk,

    2012-01-01

    Radio bursts from the Sun are produced by electron accelerated to relativistic energies by physical processes on the Sun such as solar flares and coronal mass ejections (CMEs). The radio bursts are thus good indicators of solar eruptions. Three types of nonthermal radio bursts are generally associated with CMEs. Type III bursts due to accelerated electrons propagating along open magnetic field lines. The electrons are thought to be accelerated at the reconnection region beneath the erupting CME, although there is another view that the electrons may be accelerated at the CME-driven shock. Type II bursts are due to electrons accelerated at the shock front. Type II bursts are also excellent indicators of solar energetic particle (SEP) events because the same shock is supposed accelerate electrons and ions. There is a hierarchical relationship between the wavelength range of type /I bursts and the CME kinetic energy. Finally, Type IV bursts are due to electrons trapped in moving or stationary structures. The low frequency stationary type IV bursts are observed occasionally in association with very fast CMEs. These bursts originate from flare loops behind the erupting CME and hence indicate tall loops. This paper presents a summary of radio bursts and their relation to CMEs and how they can be useful for space weather predictions.

  10. Wave Propagation Program

    SciTech Connect

    McCandless, Kathleen; Petersson, Anders; Nilsson, Stefan; Sjogreen, Bjorn

    2007-01-08

    WPP is a massively parallel, 3D, C++, finite-difference elastodynamic wave propagation code. Typical applications for wave propagation with WPP include: evaluation of seismic event scenarios and damage from earthquakes, non-destructive evaluation of materials, underground facility detection, oil and gas exploration, predicting the electro-magnetic fields in accelerators, and acoustic noise generation. For more information, see User’s Manual [1].

  11. Database for propagation models

    NASA Technical Reports Server (NTRS)

    Kantak, Anil V.

    1991-01-01

    A propagation researcher or a systems engineer who intends to use the results of a propagation experiment is generally faced with various database tasks such as the selection of the computer software, the hardware, and the writing of the programs to pass the data through the models of interest. This task is repeated every time a new experiment is conducted or the same experiment is carried out at a different location generating different data. Thus the users of this data have to spend a considerable portion of their time learning how to implement the computer hardware and the software towards the desired end. This situation may be facilitated considerably if an easily accessible propagation database is created that has all the accepted (standardized) propagation phenomena models approved by the propagation research community. Also, the handling of data will become easier for the user. Such a database construction can only stimulate the growth of the propagation research it if is available to all the researchers, so that the results of the experiment conducted by one researcher can be examined independently by another, without different hardware and software being used. The database may be made flexible so that the researchers need not be confined only to the contents of the database. Another way in which the database may help the researchers is by the fact that they will not have to document the software and hardware tools used in their research since the propagation research community will know the database already. The following sections show a possible database construction, as well as properties of the database for the propagation research.

  12. 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.

  13. Correlation of radio and gamma emissions in lightning initiation.

    PubMed

    Gurevich, A V; Antonova, V P; Chubenko, A P; Karashtin, A N; Mitko, G G; Ptitsyn, M O; Ryabov, V A; Shepetov, A L; Shlyugaev, Yu V; Thu, W M; Vildanova, L I; Zybin, K P

    2013-10-18

    The results of simultaneous radio and gamma emission measurements during thunderstorms are presented. A gamma detector situated at the height 3840 m and two radio detectors of Tien-Shan Mountain Scientific Station (altitude 3340 m) registered intensive gamma flashes and radio pulses during the time of lightning initiation. The radio-gamma correlation grows abruptly at the initial moment (a few hundred microseconds), and the correlation coefficient reaches 0.9-0.95. The gamma-energy spectrum measured during lightning initiation is close to the characteristic spectrum of runaway breakdown. Radio pulses observed at the same time have highest amplitudes. Combined observation of gamma and radio emissions confirm the conception of lightning initiation due to multiple simultaneous electric discharges at hydrometeors stimulated and synchronized by low-energy electrons generated in the runaway breakdown process. PMID:24182272

  14. Future changes in propagating and non-propagating diurnal rainfall over East Asia

    NASA Astrophysics Data System (ADS)

    Huang, Wan-Ru; Wang, S.-Y. Simon

    2016-09-01

    The characteristics of diurnal rainfall in the East Asian continent consist of a propagating regime over the Yangtze River and a non-propagating regime in southeast China. Simulations of these two diurnal rainfall regimes by 18 CMIP5 models were evaluated from the historical experiment of 1981-2005. The evaluation led to the identification of one model, the CMCC-CM that replicated the key characteristics of diurnal rainfall regimes including the propagation of moisture convergence. Using the CMCC-CM to assess the future (2076-2100) change of diurnal evolution and propagation projected by the RCP4.5 experiment, it was found that propagating diurnal rainfall will enhance and expand southward into the non-propagating regime in southeast China. This change in diurnal rainfall is attributed to the intensification of diurnal land-sea thermal contrast over eastern China and the southward shift of the upper-level jet stream over 20°-30°N. Similar projected changes in diurnal rainfall and associated large-scale dynamical mechanisms were also depicted by four other models (GFDL-ESM2G, GFDL-ESM2M, MRI-CGCM3, and MRI-ESM1) showing a higher skill in representing the diurnal rainfall regimes over East Asia. If such model projection holds true, southeast China will experience an increase in the eastward propagating diurnal rainfall, which could further impact Taiwan.

  15. The new class of FR0 radio galaxies

    NASA Astrophysics Data System (ADS)

    Baldi, Ranieri D.

    2016-08-01

    I present my recent project aimed at studying the bulk of the radio-emitting AGN population. In previous works (Baldi & Capetti 2009, 2010) we provide evidences of an emerging population of compact radio galaxies which lack of extended radio emission. In a pilot JVLA project, we observe a small but representative sub-sample of this population. The radio maps reveal compact unresolved or slightly resolved radio structures on a scale of 1-3 kpc. We find that these radio-loud AGN live in red massive early-type galaxies, with large black hole masses ( 10^{8} solar mass), and spectroscopically classified as Low Excitation Galaxies, all characteristics typical of FRI radio galaxies which they also share the same nuclear luminosity with. However, they are more core dominated (by a factor of 30) than FRIs and show a clear deficit of extended radio emission. We call these sources 'FR0' to emphasize their lack of prominent extended radio emission (Baldi et al 2015). The emerging FR0 population appears to be the dominant radio class of the local Universe. Considering their properties I peculate their possible origins and the possible cosmological scenarios they imply.

  16. VLF Radio Observations and Modeling of the Ionospheric Effects of SGR 1550-5418

    NASA Astrophysics Data System (ADS)

    Carlson, B. E.; Lehtinen, N. G.; Cohen, M.; Fishman, G. J.; Kouveliotou, C.; van der Horst, A.; Chaplan, V.; Inan, U. S.

    2010-12-01

    Cosmic gamma-ray bursts ionize the upper atmosphere, affecting sub-ionospheric propagation of very-low-frequency (VLF) radio waves. Perturbations of VLF radio signals can therefore be used to study gamma-ray burst effects on the ionosphere. We present observations of VLF radio signal perturbations coincident with bursts observed by the Fermi satellite to be produced by soft gamma-ray repeater (SGR) 1550-5418 on January 22, 2009. Massive VLF signal amplitude perturbations as large as 15 dB are seen coincident with the gamma-ray events. Models of gamma-ray ionization and chemical recovery of the upper atmosphere are then used to drive simulations of VLF radio propagation. Simulation results are compared to the observed radio data and to Fermi gamma-ray observations and are used to constrain the properties of the ionosphere and the gamma-ray events.

  17. Experimental study on flames propagating through zirconium particle clouds.

    PubMed

    Yin, Yi; Sun, Jinhua; Ding, Yibin; Guo, Song; He, Xuechao

    2009-10-15

    To reveal the mechanisms of flame propagation through the hardly volatile metal dust clouds clearly, the flame propagating through zirconium particle clouds has been examined experimentally. A high-speed video camera was used to record the propagation process of the flame. Combustion zone temperature was detected by a fine thermocouple. Based on the experimental results, structure of flame and combustion courses of zirconium particles were analyzed, the combustion propagation in zirconium dust was investigated, and the velocity and temperature characteristics of the combustion zone were also elucidated. The combustion zone propagating through zirconium particle clouds consists of luminous particles. Particle concentration plays an important role in the combustion zone propagation process. With the increase of zirconium particle concentration, the maximum temperature of the combustion zone increases at the lower concentration, takes a maximum value, and then decreases at the higher concentration. It is also found that the propagation velocity of the combustion zone has a linear relationship with its maximum temperature.

  18. The Deep Space Network as an instrument for radio science research

    NASA Technical Reports Server (NTRS)

    Asmar, S. W.; Renzetti, N. A.

    1993-01-01

    Radio science experiments use radio links between spacecraft and sensor instrumentation that is implemented in the Deep Space Network. The deep space communication complexes along with the telecommunications subsystem on board the spacecraft constitute the major elements of the radio science instrumentation. Investigators examine small changes in the phase and/or amplitude of the radio signal propagating from a spacecraft to study the atmospheric and ionospheric structure of planets and satellites, planetary gravitational fields, shapes, masses, planetary rings, ephemerides of planets, solar corona, magnetic fields, cometary comae, and such aspects of the theory of general relativity as gravitational waves and gravitational redshift.

  19. 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.

  20. Features of the Electromagnetic and Plasma Disturbances Induced at the Altitudes of the Earth's Outer Ionosphere by Modification of the Ionospheric F 2 Region Using High-Power Radio Waves Radiated by the SURA Heating Facility

    NASA Astrophysics Data System (ADS)

    Frolov, V. L.; Rapoport, V. O.; Schorokhova, E. A.; Belov, A. S.; Parrot, M.; Rauch, J.-L.

    2016-08-01

    In this paper we systematize the results of studying the characteristics of the plasma-density ducts, which was conducted in 2005-2010 during the DEMETER-satellite operation. The ducts are formed at altitudes of about 700 km as a result of the ionospheric F 2 region modification by high-power high-frequency radio waves radiated by the midlatitude SURA heating facility. All the performed measurements are used as the basis for determining the formation conditions for such ducts, the duct characteristics are studied, and the opportunities for the duct influence on the ionosphere-magnetosphere coupling and propagation of radio waves of various frequency ranges are demonstrated. The results of numerical simulation of the formation of such ducts are presented.

  1. Propagation study of 850nm/58 GHz hybrid municipal system

    NASA Astrophysics Data System (ADS)

    Wilfert, Otakar; Kvicera, Vaclav; Kolka, Zdenek; Grabner, Martin; Fiser, Ondrej

    2010-08-01

    The paper deals with the results of a propagation study on a fixed hybrid Free Space Optical (FSO) and Radio Frequency (RF) system operating in 850 nm / 58 GHz bands. Propagation models for the availability assessment of both FSO and RF links were examined against a comprehensive database of meteorological attenuation events. The influences of individual hydrometeors were analyzed and the availability performances of the simulated FSO/MMW hybrid link were evaluated. The study pointed out that visibility and rainfall measurements can be only used for the raw assessment of availability performance due to the concurrent occurrence of different attenuation effect.

  2. 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.

  3. Proceedings of the 19th NASA Propagation Experimenters Meeting (NAPEX 19) and the 7th Advanced Communications Technology Satellite (ACTS) Propagation Studies Workshop (APSW 7)

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz (Editor)

    1995-01-01

    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 19 was held on 14 Jun. 1995, in Fort Collins, Colorado. Participants included representatives from Canada, Japan, and the United States, including researchers from universities, government agencies, and private industry. The meeting focused on mobile personal satellite systems and the use of 20/30-GHz band for fixed and mobile satellite applications. In total, 18 technical papers were presented. Following NAPEX 19, the Advanced Communications Technology Satellite (ACTS) Propagation Studies Workshop 7 (APSW 7) was held on 15-16 Jun. 1995, to review ACTS propagation activities with emphasis on the experimenters' status reports and dissemination of propagation data to industry.

  4. 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)

  5. The Sardinia Radio Telescope

    NASA Astrophysics Data System (ADS)

    D'Amico, Nichi

    2011-08-01

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

  6. 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.; Feng, X. S.; Liu Ying

    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.

  7. Conceptual Background to Radio

    NASA Astrophysics Data System (ADS)

    Ponsonby, J. E. B.

    2004-06-01

    The International Telecommunications Union (ITU) conceives the radio spectrum as primarily a resource for telecommunications. Indeed most applications of radio are for communications and other radio services, particularly the Radio Astronomy Service, are deemed to be `pretend'communication serviceas for spectrum amnagement purposes. The language of Radio Spectrum Management is permeated by the terminology ofcommunications, some derived from the physics of radio and some from aspects of information theory. This contribution touches on all the essential concepts of radiocommunications which the author thinks should be the common mental equipment of the Spectrum Manager. The fundamental capacity of a communication channel is discussed in terms of the degrees of freedom and bandwidth of a signal, and the signal to noise ratio. It is emphasized that an information bearing signal is inherently unpredictable, and must, at some level, be discontinuous. This has important consequences for the form of its power spectrum. The effect of inserting filters is discussed particularly with regard to constant amplitude signals and, in the context of non-linear power amplifiers, the phenomenon of`sideband recovery'. All the common generic forms of modulation are discussed including the very different case of `no-modulation' which applies in all forms of passive remote sensing. Whilst all are agreed that the radio spectrum should be used `efficiently', there is no quantitative measure of spectral efficiency which embraces all relevant aspects of spectral usage. These various aspects are dicussed. Finally a brief outline of some aspects of antennae are reviewed. It is pointed out that the recent introduction of so-called `active antennnae', which have properties unlike traditional passive antennae, has confused the interpretation of those ITU Radio Regulations which refer to antennae.

  8. The Radio JOVE Project

    NASA Astrophysics Data System (ADS)

    Garcia, L.; Thieman, J.; Higgins, C.

    1999-09-01

    Radio JOVE is an interactive educational activity which brings the radio sounds of Jupiter and the Sun to students, teachers, and the general public. This is accomplished through the construction of a simple radio telescope kit and the use of a real-time radio observatory on the Internet. Our website (http://radiojove.gsfc.nasa.gov/) will contain science information, instruction manuals, observing guides, and education resources for students and teachers. Our target audience is high school science classes, but subjects can be tailored to college undergraduate physics and astronomy courses or even to middle school science classes. The goals of the project are: 1) Educate people about planetary and solar radio astronomy, space physics, and the scientific method 2) Provide teachers and students with a hands-on radio astronomy exercise as a science curriculum support activity by building and using a simple radio telescope receiver/antenna kit 3) Create the first ever online radio observatory which provides real-time data for those with internet access 4) Allow interactions among participating schools by facilitating exchanges of ideas, data, and observing experiences. Our current funding will allow us to impact 100 schools by partially subsidizing their participation in the program. We expect to expand well beyond this number as publicity and general interest increase. Additional schools are welcome to fully participate, but we will not be able to subsidize their kit purchases. We hope to make a wide impact among the schools by advertising through appropriate newsletters, space grant consortia, the INSPIRE project (http://image.gsfc.nasa.gov/poetry/inspire/), electronic links, and science and education meetings. We would like to acknoledge support from the NASA/GSFC Director's Discretionary Fund, the STScI IDEAS grant program and the NASA/GSFC Space Science Data Operations Office.

  9. 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 γ is very extended (≈ 60∘) for the lowest analyzed frequencies. Observed apparent source sizes γ 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.

  10. Automatic crack propagation tracking

    NASA Technical Reports Server (NTRS)

    Shephard, M. S.; Weidner, T. J.; Yehia, N. A. B.; Burd, G. S.

    1985-01-01

    A finite element based approach to fully automatic crack propagation tracking is presented. The procedure presented combines fully automatic mesh generation with linear fracture mechanics techniques in a geometrically based finite element code capable of automatically tracking cracks in two-dimensional domains. The automatic mesh generator employs the modified-quadtree technique. Crack propagation increment and direction are predicted using a modified maximum dilatational strain energy density criterion employing the numerical results obtained by meshes of quadratic displacement and singular crack tip finite elements. Example problems are included to demonstrate the procedure.

  11. Astrometry of southern radio sources.

    PubMed

    White, G L; Jauncey, D L; Harvey, B R; Savage, A; Gulkis, S; Preston, R A; Peterson, B A; Reynolds, J E; Nicolson, G D; Malin, D F

    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 catalogues. The programs cover the optical identification and spectroscopy of flat-spectrum Parkes sources and the determination of their milliarc-second 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.

  12. Slow-Slip Propagation Speeds

    NASA Astrophysics Data System (ADS)

    Rubin, A. M.; Ampuero, J.

    2007-12-01

    Combined seismic and geodetic data from subduction zones and the Salton Trough have revealed slow slip events with reasonably well-defined propagation speeds. This in turn is suggestive of a more-or-less well- defined front separating nearly locked regions outside the slipping zone from interior regions that slide much more rapidly. Such crack-like nucleation fronts arise naturally in models of rate-and-state friction for lab-like values of a/b, where a and b are the coefficients of the velocity- and state-dependence of the frictional strength (with the surface being velocity-neutral for a/b=1). If the propagating front has a quasi-steady shape, the propagation and slip speeds are kinematically tied via the local slip gradient. Given a sufficiently sharp front, the slip gradient is given dimensionally by Δτp- r/μ', where Δτp-r is the peak-to-residual stress drop at the front and μ' the effective elastic shear modulus. Rate-and-state simulations indicate that Δτp-r is given reasonably accurately by bσ\\ln(Vmaxθi/Dc), where σ is the effective normal stress, Vmax is the maximum slip speed behind the propagating front, θi is the the value of "state" ahead of the propagating front, and Dc is the characteristic slip distance for state evolution. Except for a coefficient of order unity, Δτp-r is independent of the evolution law. This leads to Vprop/Vmax ~μ'/[bσ\\ln(Vmaxθi/Dc)]. For slip speeds a few orders of magnitude above background, \\ln(Vmaxθi/Dc) can with reasonable accuracy be assigned some representative value (~4-5, for example). Subduction zone transients propagate on the order of 10 km/day or 10-1 m/s. Geodetic data constrain the average slip speed to be a few times smaller than 1 cm/day or 10-7 m/s. However, numerical models indicate that the maximum slip speed at the front may be several times larger than the average, over a length scale that is probably too small to resolve geodetically, so a representative value of Vprop/Vmax may be ~106

  13. Pancreatic pseudocyst propagating into retroperitoneum and mediastinum.

    PubMed

    Baranyai, Z; Jakab, F

    1997-01-01

    The extrahepatic pseudocysts of pancreatic origin sometimes propagate into mediastinum and retroperitoneum. A large pseudocyst of pancreatic origin propagating into the mediastinum up to the aortic arch is published. The surgical intervention has been urged by the dislocation of the heart, by the danger of autodigestion of the mediastinal aorta and by the danger of rupture. Attention is directed to the external drainage operation which is suitable for emptying of the pseudocyst not independently from the ripeness of pseudocyst wall and the characteristics of the pseudocyst content. Should the time short after the exacerbation and should the amylase content high in the cyst, the immediate result of external drainage better and reliable safe.

  14. Observations and interpretation of solar decameter type IIIb radio bursts

    NASA Astrophysics Data System (ADS)

    Krishan, V.; Subramanian, K. R.; Sastry, C. V.

    1980-06-01

    Observations on the time structure of short duration, narrow band solar decameter type IIIb radio bursts are presented along with a theoretical model accounting for various features of the bursts. In contrast to the theory of Smith and de la Noe (1976), the electromagnetic modes of the plasma are immersed in the electric and magnetic fields in the presented theory, and the electric field enters at the single particle level and thus is accounted for in a more exact manner. In addition, the direction of propagation of the type IIIb radio burst is more clearly indicated by this theory than by Smith and de la Noe (1976).

  15. 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.

  16. Radio plasma imager simulations and measurements

    NASA Astrophysics Data System (ADS)

    Green, J. L.; Benson, R. F.; Fung, S. F.; Taylor, W. W. L.; Boardsen, S. A.; Reinisch, B. W.; Haines, D. M.; Bibl, K.; Cheney, G.; Galkin, I. A.; Huang, X.; Myers, S. H.; Sales, G. S.; Bougeret, J.-L.; Manning, R.; Meyer-Vernet, N.; Moncuquet, M.; Carpenter, D. L.; Gallagher, D. L.; Reiff, P. H.

    2000-01-01

    The Radio Plasma Imager (RPI) will be the first-of-its kind instrument designed to use radio wave sounding techniques to perform repetitive remote sensing measurements of electron number density (N_e) structures and the dynamics of the magnetosphere and plasmasphere. RPI will fly on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission to be launched early in the year 2000. The design of the RPI is based on recent advances in radio transmitter and receiver design and modern digital processing techniques perfected for ground-based ionospheric sounding over the last two decades. Free-space electromagnetic waves transmitted by the RPI located in the low-density magnetospheric cavity will be reflected at distant plasma cutoffs. The location and characteristics of the plasma at those remote reflection points can then be derived from measurements of the echo amplitude, phase, delay time, frequency, polarization, Doppler shift, and echo direction. The 500 m tip-to-tip X and Y (spin plane) antennas and 20 m Z axis antenna on RPI will be used to measures echoes coming from distances of several R_E. RPI will operate at frequencies between 3 kHz to 3 MHz and will provide quantitative N_e values from 10^-1 to 10^5 cm^-3. Ray tracing calculations, combined with specific radio imager instrument characteristics, enables simulations of RPI measurements. These simulations have been performed throughout an IMAGE orbit and under different model magnetospheric conditions. They dramatically show that radio sounding can be used quite successfully to measure a wealth of magnetospheric phenomena such as magnetopause boundary motions and plasmapause dynamics. The radio imaging technique will provide a truly exciting opportunity to study global magnetospheric dynamics in a way that was never before possible.

  17. 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.

  18. Burst propagation in Texas Helimak

    NASA Astrophysics Data System (ADS)

    Pereira, F. A. C.; Toufen, D. L.; Guimarães-Filho, Z. O.; Caldas, I. L.; Gentle, K. W.

    2016-05-01

    We present investigations of extreme events (bursts) propagating in the Texas Helimak, a toroidal plasma device in which the radial electric field can be changed by application of bias. In the experiments analyzed, a large grid of Langmuir probes measuring ion saturation current fluctuations is used to study the burst propagation and its dependence on the applied bias voltage. We confirm previous results reported on the turbulence intermittency in the Texas Helimak, extending them to a larger radial interval with a density ranging from a uniform decay to an almost uniform value. For our analysis, we introduce an improved procedure, based on a multiprobe bidimensional conditional averaging method, to assure precise determination of burst statistical properties and their spatial profiles. We verify that intermittent bursts have properties that vary in the radial direction. The number of bursts depends on the radial position and on the applied bias voltage. On the other hand, the burst characteristic time and size do not depend on the applied bias voltage. The bias voltage modifies the vertical and radial burst velocity profiles differently. The burst velocity is smaller than the turbulence phase velocity in almost all the analyzed region.

  19. DROMO propagator revisited

    NASA Astrophysics Data System (ADS)

    Urrutxua, Hodei; Sanjurjo-Rivo, Manuel; Peláez, Jesús

    2016-01-01

    In the year 2000 an in-house orbital propagator called DROMO (Peláez et al. in Celest Mech Dyn Astron 97:131-150, 2007. doi: 10.1007/s10569-006-9056-3) was developed by the Space Dynamics Group of the Technical University of Madrid, based in a set of redundant variables including Euler-Rodrigues parameters. An original deduction of the DROMO propagator is carried out, underlining its close relation with the ideal frame concept introduced by Hansen (Abh der Math-Phys Cl der Kon Sachs Ges der Wissensch 5:41-218, 1857). Based on the very same concept, Deprit (J Res Natl Bur Stand Sect B Math Sci 79B(1-2):1-15, 1975) proposed a formulation for orbit propagation. In this paper, similarities and differences with the theory carried out by Deprit are analyzed. Simultaneously, some improvements are introduced in the formulation, that lead to a more synthetic and better performing propagator. Also, the long-term effect of the oblateness of the primary is studied in terms of DROMO variables, and new numerical results are presented to evaluate the performance of the method.

  20. COBE nonspinning attitude propagation

    NASA Technical Reports Server (NTRS)

    Chu, D.

    1989-01-01

    The Cosmic Background Explorer (COBE) spacecraft will exhibit complex attitude motion consisting of a spin rate of approximately -0.8 revolution per minute (rpm) about the x-axis and simultaneous precession of the spin axis at a rate of one revolution per orbit (rpo) about the nearly perpendicular spacecraft-to-Sun vector. The effect of the combined spinning and precession is to make accurate attitude propagation difficult and the 1-degree (3 sigma) solution accuracy goal problematic. To improve this situation, an intermediate reference frame is introduced, and the angular velocity divided into two parts. The nonspinning part is that which would be observed if there were no rotation about the X-axis. The spinning part is simply the X-axis component of the angular velocity. The two are propagated independently and combined whenever the complete attitude is needed. This approach is better than the usual one-step method because each of the two angular velocities look nearly constant in their respective reference frames. Since the angular velocities are almost constant, the approximations made in discrete time propagation are more nearly true. To demonstrate the advantages of this nonspinning method, attitude is propagated as outlined above and is then compared with the results of the one-step method. Over the 100-minute COBE orbit, the one-step error grows to several degrees while the nonspinning error remains negligible.

  1. Radio emission from supernovae.

    NASA Astrophysics Data System (ADS)

    Weiler, K. W.; Panagia, N.; Sramek, R. A.; Van Dyk, S. D.; Stockdale, C. J.; Williams, C. L.

    Study of radio supernovae over the past 30 years includes more than three dozen detected objects and more than 150 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. Along with reviewing these general properties of the radio emission from supernovae, we present our extensive observations of the radio emission from supernova (SN) 1993J in M 81 (NGC 3031) made with the Very Large Array and other radio telescopes. The SN 1993J radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-supernova stellar wind describes the observations rather well considering the complexity of the phenomenon. However: 1) The highest frequency measurements at 85 - 110 GHz at early times (<40 days) are not well fitted by the parameterization which describes the cm wavelength measurements. 2) At a time ˜3100 days after shock breakout, the decline rate of the radio emission steepens from (t+beta ) beta ˜ -0.7 to beta ˜ -2.7 without change in the spectral index (nu +alpha ; alpha ˜ -0.81). This decline is best described not as a power-law, but as an exponential decay with an e-folding time of ˜ 1100 days. 3) The best overall fit to all of the data is a model including both non-thermal synchrotron self-absorption (SSA) and a thermal free-free absorbing (FFA) components at early times, evolving to a constant spectral index, optically thin decline rate, until a break in that decline rate at day ˜3100, as mentioned above.

  2. Wave Normal and Poynting Vector Calculations using the Cassini Radio and Plasma Wave Instrument

    NASA Technical Reports Server (NTRS)

    Hospodarsky, G. B.; Averkamp, T. F.; Kurth, W. S.; Gurnett, D. A.; Dougherty, M.; Inan, Umran; Wood, Troy

    2001-01-01

    Wave normal and Poynting vector measurements from the Cassini radio and plasma wave instrument (RPWS) are used to examine the propagation characteristics of various plasma waves during the Earth flyby on August 18, 1999. Using the five-channel waveform receiver (WFR), the wave normal vector is determined using the Means method for a lightning-induced whistler, equatorial chorus, and a series of low-frequency emissions observed while Cassini was in the magnetosheath. The Poynting vector for these emissions is also calculated from the five components measured by the WFR. The propagation characteristics of the lightning-induced whistler were found to be consistent with the whistler wave mode of propagation, with propagation antiparallel to the magnetic field (southward) at Cassini. The sferic associated with this whistler was observed by both Cassini and the Stanford VLF group at the Palmer Station in Antarctica. Analysis of the arrival direction of the sferic at the Palmer Station suggests that the lightning stroke is in the same sector as Cassini. Chorus was observed very close (within a few degrees) to the magnetic equator during the flyby. The chorus was found to propagate primarily away from the magnetic equator and was observed to change direction as Cassini crossed the magnetic equator. This suggests that the source region of the chorus is very near the magnetic equator. The low-frequency emission in the magnetosheath has many of the characteristics of lion roars. The average value of the angle between the wave normal vector and the local magnetic field was found to be 16 degrees, and the emissions ranged in frequency from 0. 19 to 0.75 f(sub ce), where f(sub ce) is the electron cyclotron frequency. The wave normal vectors of these waves were primarily in one direction for each individual burst (either parallel or antiparallel to the local field) but varied in direction throughout the magnetosheath. This suggests that the sources of the emissions are far from

  3. Magnetohydrodynamic Characteristic Boundary Conditions

    NASA Astrophysics Data System (ADS)

    Schaffenberger, Werner; Stein, R.

    2009-05-01

    We implemented MHD characteristic boundary conditions for a non-ideal plasma in the "stagger-code" (Gudiksen and Nordlund, 2005, ApJ 618, 1020). The aim of these boundary conditions is to reduce reflection at the boundaries which is important for the simulation of wave propagation. We present some test simulations of propagating waves demonstrating the capability of these boundary conditions.

  4. RF propagation simulator to predict location accuracy of GSM mobile phones for emergency applications

    NASA Astrophysics Data System (ADS)

    Green, Marilynn P.; Wang, S. S. Peter

    2002-11-01

    Mobile location is one of the fastest growing areas for the development of new technologies, services and applications. This paper describes the channel models that were developed as a basis of discussion to assist the Technical Subcommittee T1P1.5 in its consideration of various mobile location technologies for emergency applications (1997 - 1998) for presentation to the U.S. Federal Communication Commission (FCC). It also presents the PCS 1900 extension to this model, which is based on the COST-231 extended Hata model and review of the original Okumura graphical interpretation of signal propagation characteristics in different environments. Based on a wide array of published (and non-publicly disclosed) empirical data, the signal propagation models described in this paper were all obtained by consensus of a group of inter-company participants in order to facilitate the direct comparison between simulations of different handset-based and network-based location methods prior to their standardization for emergency E-911 applications by the FCC. Since that time, this model has become a de-facto standard for assessing the positioning accuracy of different location technologies using GSM mobile terminals. In this paper, the radio environment is described to the level of detail that is necessary to replicate it in a software environment.

  5. Flame propagation in partially premixed conditions

    NASA Astrophysics Data System (ADS)

    Ruetsch, G.; Poinsot, T.; Veynante, D.; Trouvé, A.

    1996-11-01

    Turbulent flame propagation is studied under inhomogenously premixed conditions via data from direct numerical simulations. Departures from the premixed case are studied using four different configurations, ranging from one dimensional unsteady flames to turbulent three-dimensional simulations. Simulations are performed in these cases with various values of the mean equivalence ratio, fluctuations about the mean equivlalence ratio, correlation length scales, and probability denisty functions of the mixture composition. Propagation characteristics are described in terms of the flamelet approach, where the the main contribution of partial premixing on flame propagation is due to flame wrinkling relative to modification of the mean flamelet structure. This behavior is consistent over a broad range of conditions, with the exception being extreme departures from stoichiometric conditions where flamability limits are exceeded and flame quenching is observed.

  6. Wave propagation into the middle atmosphere

    NASA Technical Reports Server (NTRS)

    Hirota, I.

    1989-01-01

    Recent observations of various types of waves propagating into the middle atmosphere are reviewed. Emphasis is made on the excitation processes in the lower atmosphere and their vertical propagation through the background flow as a function of the latitude, height and season. The following subjects are discussed: (1) Vertical propagation of quasi-stationary forced Rossby waves into the winter stratosphere in connection with the sudden warming; (2) Spectral distribution and seasonal characteristics of normal mode (free) Rossby waves and the asymmetry of the Northern and Southern Hemispheres; and (3) Seasonal variation of internal gravity waves in the middle atmosphere. Further discussions are presented for future studies based on accumulated observational data during the MAP period.

  7. Liouvillian propagators, Riccati equation and differential Galois theory

    NASA Astrophysics Data System (ADS)

    Acosta-Humánez, Primitivo; Suazo, Erwin

    2013-11-01

    In this paper a Galoisian approach to building propagators through Riccati equations is presented. The main result corresponds to the relationship between the Galois integrability of the linear Schrödinger equation and the virtual solvability of the differential Galois group of its associated characteristic equation. As the main application of this approach we solve Ince’s differential equation through the Hamiltonian algebrization procedure and the Kovacic algorithm to find the propagator for a generalized harmonic oscillator. This propagator has applications which describe the process of degenerate parametric amplification in quantum optics and light propagation in a nonlinear anisotropic waveguide. Toy models of propagators inspired by integrable Riccati equations and integrable characteristic equations are also presented.

  8. PHYSICAL CONSTRAINTS ON FAST RADIO BURSTS

    SciTech Connect

    Luan, Jing; Goldreich, Peter

    2014-04-20

    Fast radio bursts (FRBs) are isolated, ms radio pulses with dispersion measure (DM) of order 10{sup 3} pc cm{sup –3}. Galactic candidates for the DM of high latitude bursts detected at GHz frequencies are easily dismissed. DM from bursts emitted in stellar coronas are limited by free-free absorption and those from H II regions are bounded by the nondetection of associated free-free emission at radio wavelengths. Thus, if astronomical, FRBs are probably extragalactic. FRB 110220 has a scattering tail of ∼5.6 ± 0.1 ms. If the electron density fluctuations arise from a turbulent cascade, the scattering is unlikely to be due to propagation through the diffuse intergalactic plasma. A more plausible explanation is that this burst sits in the central region of its host galaxy. Pulse durations of order ms constrain the sizes of FRB sources implying high brightness temperatures that indicates coherent emission. Electric fields near FRBs at cosmological distances would be so strong that they could accelerate free electrons from rest to relativistic energies in a single wave period.

  9. A theory of solar type III radio bursts

    NASA Technical Reports Server (NTRS)

    Goldstein, M. L.; Papadopoulos, K.; Smith, R. A.

    1979-01-01

    A theory of type III bursts is reviewed. Energetic electrons propagating through the interplanetary medium are shown to excite the one dimensional oscillating two stream instability (OTSI). The OTSI is in turn stabilized by anomalous resistivity which completes the transfer of long wavelength Langmuir waves to short wavelengths, out of resonance with the electrons. The theory explains the small energy losses suffered by the electrons in propagating to 1 AU, the predominance of second harmonic radiation, and the observed correlation between radio and electron fluxes.

  10. Theories of radio emissions and plasma waves. [in Jupiter magnetosphere

    NASA Technical Reports Server (NTRS)

    Goldstein, M. L.; Goertz, C. K.

    1983-01-01

    The complex region of Jupiter's radio emissions at decameter wavelengths, the so-called DAM, is considered, taking into account the basic theoretical ideas which underly both the older and newer theories and models. Linear theories are examined, giving attention to direct emission mechanisms, parallel propagation, perpendicular propagation, and indirect emission mechanisms. An investigation of nonlinear theories is also conducted. Three-wave interactions are discussed along with decay instabilities, and three-wave up-conversio. Aspects of the Io and plasma torus interaction are studied, and a mechanism by which Io can accelerate electrons is reviewed.

  11. Fluid-Mud Gravity Current Propagation through Aquatic Vegetation

    NASA Astrophysics Data System (ADS)

    Testik, F. Y.; Yilmaz, N. A.

    2012-12-01

    This study aims to elucidate the effects of aquatic vegetation on the propagation of constant-flux non-Newtonian gravity currents. The motivation of this study is related to the formation of fluid-mud gravity currents, which exhibit non-Newtonian rheology, in the vegetated coastal zones during shallow-water dredge disposal operations. Although the propagation dynamics and phase transitions of non-Newtonian gravity currents over horizontal bottoms have been previously studied both experimentally and theoretically, the effects of stiff aquatic vegetation on the propagation characteristics have not been studied yet. During its propagation, a gravity current is under the influence of three main forces: inertia, buoyancy and viscous forces. Based upon the balance among these forces, the gravity currents may propagate in three distinct phases: slumping (for constant-volume gravity currents) or jet (for constant-flux gravity currents), inertia-buoyancy and viscous-buoyancy phase. Propagation characteristics of gravity currents differ for each of these phases. Presence of aquatic vegetation, which is typical in shallow coastal waters, disturbs the form and propagation characteristics of the gravity currents. In this present study, the effects of emerged stiff aquatic vegetation (such as the Spartina Alterniflora, also known as smooth cordgrass that exist in salt marshes) on the propagation characteristics of fluid-mud gravity currents are studied experimentally. A laboratory tank (4.3m x 0.25m x 0.5m) is used to generate constant-flux gravity currents that propagate over a 2.0m long perforated plate with stiff plastic rods that simulate emerged stiff aquatic vegetation. Experiments have been conducted with different concentrations of fluid-mud mixtures that are prepared by mixing Kaolinite clay and tap water. In the experiments, different vegetation densities have been considered. For each of the experimental runs with the vegetation, an experimental run without vegetation

  12. Saturn's variable radio period

    NASA Astrophysics Data System (ADS)

    Kurth, W. S.; Lecacheux, A.; Zarka, P.; Gurnett, D. A.; Cecconi, B.

    Temporal modulations in radio emissions are often used to determine the rotation rate of the emitting body. The rotation period (presumably) of Jupiter's interior was established in this way [Burke et al., 1962] and has recently been refined by Higgins et al. [1997]. Rotation periods for the remainder of the outer planet gas giants were determined from Voyager planetary radio astronomy observations. Similar techniques have been applied to astrophysical objects, including pulsars, for which the radio period is assumed to be the rotation period of the neutron star. In 2001, however, this simple relation between the radio period and rotation period became suspect, at least for the case of Saturn. Galopeau and Lecacheux [2001] reported that the radio period of Saturn had changed by as much as 1% from that determined by Voyager and, further, exhibited variations on time scales of years. More recently, Cassini observations indicate that the Saturn kilometric radiation is modulated with a period longer than that observed by Voyager and that this period is variable on a time scale of a year or less. The recent Higgins et al. result suggests that Jupiter's period is steady, within measurement accuracy. There are no additional measurements from Uranus or Neptune with which to look for time variations in their radio periods. For conservation of energy and angular momentum reasons, true variations of the rotation period of Saturn's deep interior are not believed to be a viable explanation for the variation in radio period, hence, it would appear that there is some disconnection of the radio period from the rotation period in the case of Saturn. One possible contributing factor may be that since Saturn's magnetic field is very accurately aligned with its rotational axis, there is no first-order beaming effect caused by the wobbling of the magnetic field, contrary to the situation at the other magnetized planets. Another explanation suggested by Galopeau and Lecacheux [2001] and

  13. Comets at radio wavelengths

    NASA Astrophysics Data System (ADS)

    Crovisier, Jacques; Bockelée-Morvan, Dominique; Colom, Pierre; Biver, Nicolas

    2016-11-01

    Comets are considered as the most primitive objects in the Solar System. Their composition provides information on the composition of the primitive solar nebula, 4.6 Gyr ago. The radio domain is a privileged tool to study the composition of cometary ices. Observations of the OH radical at 18 cm wavelength allow us to measure the water production rate. A wealth of molecules (and some of their isotopologues) coming from the sublimation of ices in the nucleus have been identified by observations in the millimetre and submillimetre domains. We present an historical review on radio observations of comets, focusing on the results from our group, and including recent observations with the Nançay radio telescope, the IRAM antennas, the Odin satellite, the Herschel space observatory, ALMA, and the MIRO instrument aboard the Rosetta space probe. xml:lang="fr"

  14. Radio coverage statistics.

    PubMed

    Lynn, W

    1984-01-01

    The Clearinghouse on Development Communication surveyed 135 countries in Asia, Africa, Europe, North and South America, for U.S.A.I.D., to determine the number of radio and television broadcast stations and receivers. Some of the data were obtained from the World Factbook, the World Radio and TV Handbook, and the World Radio and T.V. Facts and Figures, from 1979 to 1981. In those countries where stations are privately owned, audience surveys are often available. In 2 out of 3 developing countries, however, stations are government owned, and no such information is available. Numbers of receivers can sometimes be ascertained from receiver license applications. There is a need for more complete information on broadcast demographics, listening and viewing patterns by the community of world development program personnel.

  15. High redshift radio galaxies

    NASA Technical Reports Server (NTRS)

    Mccarthy, Patrick J.

    1993-01-01

    High redshift galaxies that host powerful radio sources are examined. An overview is presented of the content of radio surveys: 3CR and 3CRR, 4C and 4C/USS, B2/1 Jy, MG, MRC/1Jy, Parkes/PSR, B3, and ESO Key-Project. Narrow-line radio galaxies in the visible and UV, the source of ionization and excitation of the emission lines, emission-line luminosities, morphology of the line-emitting gas, physical properties and energetics, kinematics of the line-emitting gas, and implications from the emission lines are discussed. The morphologies and environments of the host galaxies, the alignment effect, and spectral energy distributions and ages are also examined.

  16. On the speed and acceleration of electron beams triggering interplanetary type III radio bursts

    NASA Astrophysics Data System (ADS)

    Krupar, V.; Kontar, E. P.; Soucek, J.; Santolik, O.; Maksimovic, M.; Kruparova, O.

    2015-08-01

    Aims: Type III radio bursts are intense radio emissions triggered by beams of energetic electrons often associated with solar flares. These exciter beams propagate outwards from the Sun along an open magnetic field line in the corona and in the interplanetary (IP) medium. Methods: We performed a statistical survey of 29 simple and isolated IP type III bursts observed by STEREO/Waves instruments between January 2013 and September 2014. We investigated their time-frequency profiles in order to derive the speed and acceleration of exciter electron beams. Results: We show these beams noticeably decelerate in the IP medium. Obtained speeds range from ~0.02c up to ~0.35c depending on initial assumptions. It corresponds to electron energies between tens of eV and hundreds of keV, and in order to explain the characteristic energies or speeds of type III electrons (~0.1c) observed simultaneously with Langmuir waves at 1 au, the emission of type III bursts near the peak should be predominately at double plasma frequency. Derived properties of electron beams can be used as input parameters for computer simulations of interactions between the beam and the plasma in the IP medium. Appendix A is available in electronic form at http://www.aanda.org

  17. 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).

  18. Digital signal processing for ionospheric propagation diagnostics

    NASA Astrophysics Data System (ADS)

    Rino, Charles L.; Groves, Keith M.; Carrano, Charles S.; Gunter, Jacob H.; Parris, Richard T.

    2015-08-01

    For decades, analog beacon satellite receivers have generated multifrequency narrowband complex data streams that could be processed directly to extract total electron content (TEC) and scintillation diagnostics. With the advent of software-defined radio, modern digital receivers generate baseband complex data streams that require intermediate processing to extract the narrowband modulation imparted to the signal by ionospheric structure. This paper develops and demonstrates a processing algorithm for digital beacon satellite data that will extract TEC and scintillation components. For algorithm evaluation, a simulator was developed to generate noise-limited multifrequency complex digital signal realizations with representative orbital dynamics and propagation disturbances. A frequency-tracking procedure is used to capture the slowly changing frequency component. Dynamic demodulation against the low-frequency estimate captures the scintillation. The low-frequency reference can be used directly for dual-frequency TEC estimation.

  19. Sensors Locate Radio Interference

    NASA Technical Reports Server (NTRS)

    2009-01-01

    After receiving a NASA Small Business Innovation Research (SBIR) contract from Kennedy Space Center, Soneticom Inc., based in West Melbourne, Florida, created algorithms for time difference of arrival and radio interferometry, which it used in its Lynx Location System (LLS) to locate electromagnetic interference that can disrupt radio communications. Soneticom is collaborating with the Federal Aviation Administration (FAA) to install and test the LLS at its field test center in New Jersey in preparation for deploying the LLS at commercial airports. The software collects data from each sensor in order to compute the location of the interfering emitter.

  20. Radio astronomy with microspacecraft

    NASA Technical Reports Server (NTRS)

    Collins, D.

    2001-01-01

    A dynamic constellation of microspacecraft in lunar orbit can carry out valuable radio astronomy investigations in the frequency range of 30kHz--30MHz, a range that is difficult to explore from Earth. In contrast to the radio astronomy ivestigations that have flown on individual spacecraft, the four microspacecraft together with a carrier spacecraft, which transported them to lunar orbit, form an interferometer with far superior angular resolution. Use of microspacecraft allows the entire constellation to be launched with a Taurus-class vehicle. Also distinguishing this approach is that the Moon is used as needed to shield the constellation from RF interference from the Earth and Sun.

  1. Radio Emission from Supernovae

    NASA Astrophysics Data System (ADS)

    Weiler, Kurt W.; Panagia, Nino; Sramek, Richard A.; van Dyk, Schuyler D.; Williams, Christopher L.; Stockdale, Christopher J.; Kelley, Matthew T.

    2007-10-01

    Study of radio supernovae over the past 27 years includes more than three dozen detected objects and more than 150 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the presupernova stellar system, and to detect clumpiness of the circumstellar material. Along with reviewing these general properties of the radio emission from supernovae, we present our extensive observations of the radio emission from supernova (SN) 1993J in M 81 (NGC 3031) made with the Very Large Array and other radio telescopes. The SN 1993J radio emission evolves regularly in both time and frequency, and the usual interpretation in terms of shock interaction with a circumstellar medium (CSM) formed by a pre-supernova stellar wind describes the observations rather well considering the complexity of the phenomenon. However: 1) The highest frequency measurements at 85-110 GHz at early times (<40 days) are not well fitted by the parameterization which describes the cm wavelength measurements rather well. 2) At mid-cm wavelengths there is often deviation from the fitted radio light curves, particularly near the peak flux density, and considerable shorter term deviations in the declining portion when the emission has become optically thin. 3) At a time ~3100 days after shock breakout, the decline rate of the radio emission steepens from (t+β)β~-0.7 to β~-2.7 without change in the spectral index (ν+αα~-0.81). However, this decline is best described not as a power-law, but as an exponential decay starting at day ~3100 with an e-folding time of ~1100 days. 4) The best overall fit to all of the data is

  2. Radio Emission from Supernovae

    SciTech Connect

    Weiler, Kurt W.; Panagia, Nino; Sramek, Richard A.; Van Dyk, Schuyler D.; Stockdale, Christopher J.; Kelley, Matthew T.

    2009-05-03

    Study of radio supernovae over the past 27 years includes more than three dozen detected objects and more than 150 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the presupernova stellar system, and to detect dumpiness of the circumstellar material.

  3. Transionospheric Propagation Code (TIPC)

    SciTech Connect

    Roussel-Dupre, R.; Kelley, T.A.

    1990-10-01

    The Transionospheric Propagation Code is a computer program developed at Los Alamos National Lab to perform certain tasks related to the detection of vhf signals following propagation through the ionosphere. The code is written in Fortran 77, runs interactively and was designed to be as machine independent as possible. A menu format in which the user is prompted to supply appropriate parameters for a given task has been adopted for the input while the output is primarily in the form of graphics. The user has the option of selecting from five basic tasks, namely transionospheric propagation, signal filtering, signal processing, DTOA study, and DTOA uncertainty study. For the first task a specified signal is convolved against the impulse response function of the ionosphere to obtain the transionospheric signal. The user is given a choice of four analytic forms for the input pulse or of supplying a tabular form. The option of adding Gaussian-distributed white noise of spectral noise to the input signal is also provided. The deterministic ionosphere is characterized to first order in terms of a total electron content (TEC) along the propagation path. In addition, a scattering model parameterized in terms of a frequency coherence bandwidth is also available. In the second task, detection is simulated by convolving a given filter response against the transionospheric signal. The user is given a choice of a wideband filter or a narrowband Gaussian filter. It is also possible to input a filter response. The third task provides for quadrature detection, envelope detection, and three different techniques for time-tagging the arrival of the transionospheric signal at specified receivers. The latter algorithms can be used to determine a TEC and thus take out the effects of the ionosphere to first order. Task four allows the user to construct a table of delta-times-of-arrival (DTOAs) vs TECs for a specified pair of receivers.

  4. Florida's propagation report

    NASA Technical Reports Server (NTRS)

    Helmken, Henry; Henning, Rudolf

    1994-01-01

    One of the key goals of the Florida Center is to obtain a maximum of useful information on propagation behavior unique to its subtropical weather and subtropical climate. Such weather data is of particular interest when it is (or has the potential to become) useful for developing and implementing techniques to compensate for adverse weather effects. Also discussed are data observations, current challenges, CDF's, sun movement, and diversity experiments.

  5. Pilot study of the radio-emitting AGN population: the emerging new class of FR 0 radio-galaxies

    NASA Astrophysics Data System (ADS)

    Baldi, Ranieri D.; Capetti, Alessandro; Giovannini, Gabriele

    2015-04-01

    We present the results of a pilot JVLA project aimed at studying the bulk of the radio-emitting AGN population, that was unveiled by the NVSS/FIRST and SDSS surveys. The key questions are related to the origin of their radio-emission and to its connection with the properties of their hosts. We obtained A-array observations at the JVLA at 1.4, 4.5, and 7.5 GHz for 12 sources, a small but representative subsample. The radio maps reveal compact unresolved or only slightly resolved radio structures on a scale of 1-3 kpc, with the one exception of a hybrid FR I/FR II source extended over ~40 kpc. Thanks to either the new high-resolution maps or to the radio spectra, we isolated the radio core component in most of them. We split the sample into two groups. Four sources have low black hole (BH) masses (mostly ~107 M⊙) and are hosted by blue galaxies, often showing evidence of a contamination from star formation to their radio emission, and are associated with radio-quiet (RQ) AGN. The second group consists in seven radio-loud (RL) AGN, which are located in red massive (~1011 M⊙) early-type galaxies, have high BH masses (≳108 M⊙), and are spectroscopically classified as low excitation galaxies (LEG). These are all characteristics typical of FR I radio galaxies. They also lie on the correlation between radio core power and [O III] line luminosity defined by FR Is. However, they are more core-dominated (by a factor of ~30) than FR Is and show a deficit of extended radio emission. We dub these sources "FR 0" to emphasize their lack of prominent extended radio emission, which is their single distinguishing feature with respect to FR Is. The differences in radio properties between FR 0s and FR Is might be ascribed to an evolutionary effect, with the FR 0 sources undergoing rapid intermittency that prevents the growth of large-scale structures. However, this contrasts with the scenario in which low-luminosity radio-galaxies are fed by continuous accretion of gas from

  6. 75 FR 10439 - Cognitive Radio Technologies and Software Defined Radios

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-08

    ... Order 1. On March 17, 2005, the Commission adopted the Cognitive Radio Report and Order, 70 FR 23032... Memorandum Opinion and Order (MO&O), 72 FR 31190, June 6, 2007, which responded to two petitions filed in... COMMISSION 47 CFR Part 2 Cognitive Radio Technologies and Software Defined Radios AGENCY:...

  7. Relationship of Solar Radio Emission at λ=1.43m and Optical Processes in the Sun

    NASA Astrophysics Data System (ADS)

    Makandarashvili, Sh.; Oghrapishvili, N.; Japaridze, D.; Maghradze, D.

    2016-09-01

    Radio frequency observations supplement optical studies and in some cases they are the only way of obtaining information on the physical conditions for radio waves and their propagation. Solar radio emission appears in two forms, "quiescent" and "sporadic." Their distinctive features are well known. Solar radio observations at meter wavelengths (λ = 1.43 m, ν = 210 MHz) have been made at the Abastumani Astrophysical Observatory using a solar radio telescope throughout five solar cycles (since 1957). This article is a study of the long-term observations of solar radio bursts and sunspots. It is found that there is a correlation between the amplitudes of the radio bursts, the number of spots, and the regions of the spots.

  8. CURVATURE-DRIFT INSTABILITY FAILS TO GENERATE PULSAR RADIO EMISSION

    SciTech Connect

    Kaganovich, Alexander; Lyubarsky, Yuri

    2010-10-01

    The curvature-drift instability has long been considered as a viable mechanism for pulsar radio emission. We reconsidered this mechanism by finding an explicit solution describing the propagation of short electromagnetic waves in a plasma flow along curved magnetic field lines. We show that even though the waves could be amplified, the amplification factor remains very close to unity; therefore, this mechanism is unable to generate high brightness temperature emission from initial weak fluctuations.

  9. Escaping radio emission from pulsars: Possible role of velocity shear

    SciTech Connect

    Mahajan, S.M. |; Machabeli, G.Z.; Rogava, A.D. |

    1997-01-01

    It is demonstrated that the velocity shear, intrinsic to the e{sup +}e{sup {minus}} plasma present in the pulsar magnetosphere, can efficiently convert the nonescaping longitudinal Langmuir waves (produced by some kind of a beam or stream instability) into propagating (escaping) electromagnetic waves. It is suggested that this shear induced transformation may be the basic mechanism needed for the eventual generation of the observed pulsar radio emission.

  10. Birth and Evolution of Isolated Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Faucher-Giguère, Claude-André; Kaspi, Victoria M.

    2008-02-01

    We investigate the birth and evolution of isolated radio pulsars using a population synthesis method, modeling the birth properties of the pulsars, their time evolution, and their detection in the Parkes and Swinburne Multibeam (MB) surveys. Together, the Parkes and Swinburne MB surveys [1, 2] have detected nearly 2/3 of the known pulsars and provide a remarkably homogeneous sample to compare with simulations. New proper motion measurements [3, 4] and an improved model of the distribution of free electrons in the interstellar medium, NE2001 [5], also make revisiting these issues particularly worthwhile. We present a simple population model that reproduces the actual observations well, and consider others that fail. We conclude that: pulsars are born in the spiral arms, with the birthrate of 2.8+/-0.5 pulsars/century peaking at a distance ~3 kpc from the Galactic centre, and with mean initial speed of 380-60+40 km s-1 the birth spin period distribution extends to several hundred milliseconds, with no evidence of multimodality, implying that characteristic ages overestimate the true ages of the pulsars by a median factor >2 for true ages <30,000 yr models in which the radio luminosities of the pulsars are random generically fail to reproduce the observed P-Ṗ diagram, suggesting a relation between intrinsic radio luminosity and (P,Ṗ) radio luminosities L~Ė provides a good match to the observed P-Ṗ diagram; for this favored radio luminosity model, we find no evidence for significant magnetic field decay over the lifetime of the pulsars as radio sources (~100 Myr).

  11. Prism beamswitch for radio telescopes.

    PubMed

    Payne, J M; Ulich, B L

    1978-12-01

    A dielectric prism and switching mechanism have been constructed for beamswitching a Cassegrain radio telescope. Spatially extended radio sources may be mapped without significant confusion utilizing the sensitivity and stability inherent in the conventional Dicke radiometer.

  12. Low Frequency Radio Signals from Sprite Streamers

    NASA Astrophysics Data System (ADS)

    Qin, J.; Celestin, S. J.; Pasko, V. P.

    2013-12-01

    Sprites are mesospheric discharges that carry significant electrical currents and produce radio signals observed typically in the extremely low (ELF) to very low (VLF) frequency bands [Cummer et al., GRL, 25, 1281, 1998]. Recently, Low-Frequency (LF) radio observations of sprite-producing lightning discharges have shown the existence of consecutive broadband pulses exhibiting EM radiation that spans in the LF range, and it has been suggested that this LF radio signals may stem from non-luminous relativistic electron beams above thunderstorms [Fullekrug et al., JGR, 115, A00E09, 2010]. In this talk, we present the first theoretical estimates of the radio signals produced by individual sprite streamers using simulation results from a plasma fluid model. It is demonstrated that the spectral content of the radiation produced by sprite streamers is a function of the air density N and the lightning-induced quasi-static ambient electric field E in the regions of space where the sprite streamers are propagating. We demonstrate that the exponential growth of the current in sprite streamers at 75 km would be preferentially associated with electromagnetic radiation in the frequency range from 0 and up to ˜3 kHz, whereas the growth of the streamer current at 40 km could produce radiation with frequencies up to ˜300 kHz, consistently with the scaling of atmospheric air density [Kosar et al., JGR, 117, A08328, 2012]. We further conjecture that the periodic branching of streamers may lead to a radiation spectrum enhancement in the VLF to LF range. The present study shows that sprite streamers could be responsible for at least part of the LF radiation associated with sprite-producing lightning discharges that was detected recently by Fullekrug et al. [2010].

  13. Propagation Effects of Wind and Temperature on Acoustic Ground Contour Levels

    NASA Technical Reports Server (NTRS)

    Heath, Stephanie L.; McAninch, Gerry L.

    2006-01-01

    Propagation characteristics for varying wind and temperature atmospheric conditions are identified using physically-limiting propagation angles to define shadow boundary regions. These angles are graphically illustrated for various wind and temperature cases using a newly developed ray-tracing propagation code.

  14. Community Radio in Canada.

    ERIC Educational Resources Information Center

    Canadian Broadcasting Corp., Ottawa (Ontario).

    Results are presented of a survey of 20 community radio organizations operating in Canada. For each of the 20 agencies, information is provided relating to: (1) the name and address of the organization; (2) the name and population of the community served; (3) the station's call letters, frequency, and power; (4) the date of the station's license;…

  15. RADIO RANGING DEVICE

    DOEpatents

    Nieset, R.T.

    1961-05-16

    A radio ranging device is described. It utilizes a super regenerative detector-oscillator in which echoes of transmitted pulses are received in proper phase to reduce noise energy at a selected range and also at multiples of the selected range.

  16. Educational Broadcasting--Radio.

    ERIC Educational Resources Information Center

    Ahamed, Uvais; Grimmett, George

    This manual is intended for those who must conduct educational radio broadcasting training courses in Asia-Pacific countries without the resources of experienced personnel, as well as for individuals to use in self-learning situations. The selection of material has been influenced by the need to use broadcasting resources effectively in programs…

  17. Telling It by Radio

    ERIC Educational Resources Information Center

    Milander, Henry M.

    1975-01-01

    Olympic College purchased eight one-minute advertising spots per day for use seven days a week at a local independent radio station. Ten sample spots are presented. This economical approach was successful in increasing over-all enrollment and the number of FTE students; it also attracted many adults to the college. (DC)

  18. A Radio Station Project.

    ERIC Educational Resources Information Center

    Geva, Edna

    2002-01-01

    Describes a radio program in an English-as-a-Foreign-Language classroom in Israel. Classrooms of English students listen carefully to daily broadcasts, waiting to solve the brain teaser. Personal messages and catchy music follow the program. The project has encouraged students to use English actively and purposefully. Evaluation of the broadcasts…

  19. Japanese Radio Exercises. Revised.

    ERIC Educational Resources Information Center

    Young, Jocelyn

    This unit focuses on Japanese radio exercises which became popular in Japan just after World War II and are still used among students and workers in companies to help raise morale and form group unity. The exercises reflect the general role of exercise in Japanese culture--to serve as a symbol of unity and cooperation among the Japanese, as well…

  20. Torun Radio Astronomy Observatory

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    Torun Center for Astronomy is located at Piwnice, 15 km north of Torun, Poland. A part of the Faculty of Physics and Astronomy of the Nicolaus Copernicus University, it was created by the union of Torun Radio Astronomy Observatory (TRAO) and the Institute of Astronomy on 1 January 1997....