HF-START: A Regional Radio Propagation Simulator

NASA Astrophysics Data System (ADS)

Hozumi, K.; Maruyama, T.; Saito, S.; Nakata, H.; Rougerie, S.; Yokoyama, T.; Jin, H.; Tsugawa, T.; Ishii, M.

2017-12-01

HF-START (HF Simulator Targeting for All-users' Regional Telecommunications) is a user-friendly simulator developed to meet the needs of space weather users. Prediction of communications failure due to space weather disturbances is of high priority. Space weather users from various backgrounds with high economic impact, i.e. airlines, telecommunication companies, GPS-related companies, insurance companies, international amateur radio union, etc., recently increase. Space weather information provided by Space Weather Information Center of NICT is, however, too professional to be understood and effectively used by the users. To overcome this issue, I try to translate the research level data to the user level data based on users' needs and provide an immediate usable data. HF-START is positioned to be a space weather product out of laboratory based truly on users' needs. It is originally for radio waves in HF band (3-30 MHz) but higher frequencies up to L band are planned to be covered. Regional ionospheric data in Japan and southeast Asia are employed as a reflector of skywave mode propagation. GAIA (Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy) model will be used as ionospheric input for global simulation. To evaluate HF-START, an evaluation campaign for Japan region will be launched in coming months. If the campaign successes, it will be expanded to southeast Asia region as well. The final goal of HF-START is to provide the near-realtime necessary radio parameters as well as the warning message of radio communications failure to the radio and space weather users.

Effects of the 2017 Solar Eclipse on HF Radio Propagation and the D-Region Ionosphere: Citizen Science Investigation

NASA Technical Reports Server (NTRS)

Fry, C. D.; Rawlins, L.; Krause, L. H.; Suggs, R. M.; McTernan, J. K.; Adams, M. L.; Gallagher, D. L.; Anderson, Scott; Allsbrooks, Robert IV

2017-01-01

August 21, 2017 provided a unique opportunity to investigate the effects of the total solar eclipse on high frequency (HF) radio propagation and ionospheric variability. In Marshall Space Flight Center's partnership with the US Space and Rocket Center (USSRC) and Austin Peay State University (APSU), we engaged students and citizen scientists in an investigation of the eclipse effects on the mid-latitude ionosphere. Activities included implementing and configuring software, monitoring the HF Amateur Radio frequency bands and collecting radio transmission data on days before, the day of, and days after the eclipse to build a continuous record of changing propagation conditions as the moon's shadow marched across the United States. Post-eclipse radio propagation analysis provided insights into ionospheric variability due to the eclipse. We report on results, interpretation, and conclusions of these investigations.

Radio Wave Propagation: A Handbook of Practical Techniques for Computing Basic Transmission Loss and Field Strength

DTIC Science & Technology

1982-09-01

MARK A. WEISSBEGU KALLE R. XONTSON Project Msnaqer, IUTRZ Assistant Director Contractor Operations Approved by CRARLES L. FLYNN, 001, us A. M. MESSE...34 BSTJ, 1946. 2-4priis, H.T., "Introduction to Radio and Antennas," IEEE Spectrum, April, 1971 . RADIO WAVE PROPAGATION: A HANDBOOK OF PRACTICAL...Propagation Tests, TR-0177-71.01, Gautney & Jones Communications, Inc., Falls Church, VA, June 1971 . 3 -7 Comparison of Predicted VLF/LF Signal

Plasma and radio waves from Neptune: Source mechanisms and propagation

NASA Astrophysics Data System (ADS)

Wong, H. K.

1994-03-01

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.

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.

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.

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.

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.

The effect of various parameters of large scale radio propagation models on improving performance mobile communications

NASA Astrophysics Data System (ADS)

Pinem, M.; Fauzi, R.

2018-02-01

One technique for ensuring continuity of wireless communication services and keeping a smooth transition on mobile communication networks is the soft handover technique. In the Soft Handover (SHO) technique the inclusion and reduction of Base Station from the set of active sets is determined by initiation triggers. One of the initiation triggers is based on the strong reception signal. In this paper we observed the influence of parameters of large-scale radio propagation models to improve the performance of mobile communications. The observation parameters for characterizing the performance of the specified mobile system are Drop Call, Radio Link Degradation Rate and Average Size of Active Set (AS). The simulated results show that the increase in altitude of Base Station (BS) Antenna and Mobile Station (MS) Antenna contributes to the improvement of signal power reception level so as to improve Radio Link quality and increase the average size of Active Set and reduce the average Drop Call rate. It was also found that Hata’s propagation model contributed significantly to improvements in system performance parameters compared to Okumura’s propagation model and Lee’s propagation model.

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.

Types of propagation of radio waves of the decameter range, according to observations by the OBS method on Cuba--Soviet Union paths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berdeyans, D.; Bocharov, V.I.; Lobachevskii, L.A.

Ionosphere observations by the OBS method were performed to study ionospheric conditions under which radio waves in the decameter range propagate on Cuba--Soviet Union paths. The results of observations in the summer of 1973 are reported. The distance--frequency and distance--time characteristics of back-scattered signals in the sounding direction for each day of observation are discussed. (JFP)

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

NASA Astrophysics Data System (ADS)

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

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

Propagation of radio frequency waves through density fluctuations

NASA Astrophysics Data System (ADS)

Valvis, S. I.; Papagiannis, P.; Papadopoulos, A.; Hizanidis, K.; Glytsis, E.; Bairaktaris, F.; Zisis, A.; Tigelis, I.; Ram, A. K.

2017-10-01

On their way to the core of a tokamak plasma, radio frequency (RF) waves, excited in the vacuum region, have to propagate through a variety of density fluctuations in the edge region. These fluctuations include coherent structures, like blobs that can be field aligned or not, as well as turbulent and filamentary structures. We have been studying the effect of fluctuations on RF propagation using both theoretical (analytical) and computational models. The theoretical results are being compared with those obtained by two different numerical codes ``a Finite Difference Frequency Domain code and the commercial COMSOL package. For plasmas with arbitrary distribution of coherent and turbulent fluctuations, we have formulated an effective dielectric permittivity of the edge plasma. This permittivity tensor is then used in numerical simulations to study the effect of multi-scale turbulence on RF waves. We not only consider plane waves but also Gaussian beams in the electron cyclotron and lower hybrid range of frequencies. The analytical theory and results from simulations on the propagation of RF waves will be presented. Supported in part by the Hellenic National Programme on Controlled Thermonuclear Fusion associated with the EUROfusion Consortium and by DoE Grant DE-FG02-91ER-54109.

Radio-loud AGN Variability from Propagating Relativistic Jets

NASA Astrophysics Data System (ADS)

Li, Yutong; Schuh, Terance; Wiita, Paul J.

2018-06-01

The great majority of variable emission in radio-loud AGNs is understood to arise from the relativistic flows of plasma along two oppositely directed jets. We study this process using the Athena hydrodynamics code to simulate propagating three-dimensional relativistic jets for a wide range of input jet velocities and jet-to-ambient matter density ratios. We then focus on those simulations that remain essentially stable for extended distances (60-120 times the jet radius). Adopting results for the densities, pressures and velocities from these propagating simulations we estimate emissivities from each cell. The observed emissivity from each cell is strongly dependent upon its variable Doppler boosting factor, which depends upon the changing bulk velocities in those zones with respect to our viewing angle to the jet. We then sum the approximations to the fluxes from a large number of zones upstream of the primary reconfinement shock. The light curves so produced are similar to those of blazars, although turbulence on sub-grid scales is likely to be important for the variability on the shortest timescales.

Crowdsourcing-Assisted Radio Environment Database for V2V Communication.

PubMed

Katagiri, Keita; Sato, Koya; Fujii, Takeo

2018-04-12

In order to realize reliable Vehicle-to-Vehicle (V2V) communication systems for autonomous driving, the recognition of radio propagation becomes an important technology. However, in the current wireless distributed network systems, it is difficult to accurately estimate the radio propagation characteristics because of the locality of the radio propagation caused by surrounding buildings and geographical features. In this paper, we propose a measurement-based radio environment database for improving the accuracy of the radio environment estimation in the V2V communication systems. The database first gathers measurement datasets of the received signal strength indicator (RSSI) related to the transmission/reception locations from V2V systems. By using the datasets, the average received power maps linked with transmitter and receiver locations are generated. We have performed measurement campaigns of V2V communications in the real environment to observe RSSI for the database construction. Our results show that the proposed method has higher accuracy of the radio propagation estimation than the conventional path loss model-based estimation.

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.

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

Crowdsourcing-Assisted Radio Environment Database for V2V Communication †

PubMed Central

Katagiri, Keita; Fujii, Takeo

2018-01-01

In order to realize reliable Vehicle-to-Vehicle (V2V) communication systems for autonomous driving, the recognition of radio propagation becomes an important technology. However, in the current wireless distributed network systems, it is difficult to accurately estimate the radio propagation characteristics because of the locality of the radio propagation caused by surrounding buildings and geographical features. In this paper, we propose a measurement-based radio environment database for improving the accuracy of the radio environment estimation in the V2V communication systems. The database first gathers measurement datasets of the received signal strength indicator (RSSI) related to the transmission/reception locations from V2V systems. By using the datasets, the average received power maps linked with transmitter and receiver locations are generated. We have performed measurement campaigns of V2V communications in the real environment to observe RSSI for the database construction. Our results show that the proposed method has higher accuracy of the radio propagation estimation than the conventional path loss model-based estimation. PMID:29649174

Characteristics of shocks in the solar corona, as inferred from radio, optical, and theoretical investigations

NASA Technical Reports Server (NTRS)

Maxwell, A.; Dryer, M.

1982-01-01

Solar radio bursts of spectral type II provide one of the chief diagnostics for the propagation of shocks through the solar corona. Radio data on the shocks are compared with computer models for propagation of fast-mode MHD shocks through the solar corona. Data on coronal shocks and high-velocity ejecta from solar flares are then discussed in terms of a general model consisting of three main velocity regimes.

Forecasts of geomagnetic activities and HF radio propagation conditions made at Hiraiso/Japan

NASA Technical Reports Server (NTRS)

Marubashi, K.; Miyamoto, Y.; Kidokoro, T.; Ishii, T.

1979-01-01

The Hiraiso Branch of RRL prediction techniques are summarized separately for the 27 day recurrent storm and the flare-associated storm. The storm predictions are compared with the actual geomagnetic activities in two ways. The first one is the comparison on a day to day basis. In the second comparison, the accuracy of the storm predictions during 1965-1976 are evaluated. In addition to the storm prediction, short-term predictions of HF radio propagation conditions are conducted at Hiraiso. The HF propagation predictions are briefly described as an example of the applications of the magnetic storm prediction.

Characteristics of worst hour rainfall rate for radio wave propagation modelling in Nigeria

NASA Astrophysics Data System (ADS)

Osita, Ibe; Nymphas, E. F.

2017-10-01

Radio waves especially at the millimeter-wave band are known to be attenuated by rain. Radio engineers and designers need to be able to predict the time of the day when radio signal will be attenuated so as to provide measures to mitigate this effect. This is achieved by characterizing the rainfall intensity for a particular region of interest into worst month and worst hour of the day. This paper characterized rainfall in Nigeria into worst year, worst month, and worst hour. It is shown that for the period of study, 2008 and 2009 are the worst years, while September is the most frequent worst month in most of the stations. The evening time (LT) is the worst hours of the day in virtually all the stations.

Programming an Artificial Neural Network Tool for Spatial Interpolation in GIS - A Case Study for Indoor Radio Wave Propagation of WLAN.

PubMed

Sen, Alper; Gümüsay, M Umit; Kavas, Aktül; Bulucu, Umut

2008-09-25

Wireless communication networks offer subscribers the possibilities of free mobility and access to information anywhere at any time. Therefore, electromagnetic coverage calculations are important for wireless mobile communication systems, especially in Wireless Local Area Networks (WLANs). Before any propagation computation is performed, modeling of indoor radio wave propagation needs accurate geographical information in order to avoid the interruption of data transmissions. Geographic Information Systems (GIS) and spatial interpolation techniques are very efficient for performing indoor radio wave propagation modeling. This paper describes the spatial interpolation of electromagnetic field measurements using a feed-forward back-propagation neural network programmed as a tool in GIS. The accuracy of Artificial Neural Networks (ANN) and geostatistical Kriging were compared by adjusting procedures. The feedforward back-propagation ANN provides adequate accuracy for spatial interpolation, but the predictions of Kriging interpolation are more accurate than the selected ANN. The proposed GIS ensures indoor radio wave propagation model and electromagnetic coverage, the number, position and transmitter power of access points and electromagnetic radiation level. Pollution analysis in a given propagation environment was done and it was demonstrated that WLAN (2.4 GHz) electromagnetic coverage does not lead to any electromagnetic pollution due to the low power levels used. Example interpolated electromagnetic field values for WLAN system in a building of Yildiz Technical University, Turkey, were generated using the selected network architectures to illustrate the results with an ANN.

Global ionospheric effects of geomagnetic storm on May 2-3, 2010 and their influence on HF radio wave propagation

NASA Astrophysics Data System (ADS)

Kotova, Daria; Klimenko, Maxim; Klimenko, Vladimir; Zakharov, Veniamin

2013-04-01

In this work we have investigated the global ionospheric response to geomagnetic storm on May 2-3, 2010 using GSM TIP (Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere) simulation results. In the GSM TIP storm time model runs, several input parameters such as cross-polar cap potential difference and R2 FAC (Region 2 Field-Aligned Currents) varied as a function of the geomagnetic activity AE-index. Current simulation also uses the empirical model of high-energy particle precipitation by Zhang and Paxton. In this model, the energy and energy flux of precipitating electrons depend on a 3 hour Kp-index. We also have included the 30 min time delay of R2 FAC variations with respect to the variations of cross-polar cap potential difference. In addition, we use the ground-based ionosonde data for comparison our model results with observations. We present an analysis of the physical mechanisms responsible for the ionospheric effects of geomagnetic storms. The obtained simulation results are used by us as a medium for HF radio wave propagation at different latitudes in quiet conditions, and during main and recovery phase of a geomagnetic storm. To solve the problem of the radio wave propagation we used Zakharov's (I. Kant BFU) model based on geometric optics. In this model the solution of the eikonal equation for each of the two normal modes is reduced using the method of characteristics to the integration of the six ray equation system for the coordinates and momentum. All model equations of this system are solved in spherical geomagnetic coordinate system by the Runge-Kutta method. This model was tested for a plane wave in a parabolic layer. In this study, the complex refractive indices of the ordinary and extraordinary waves at ionospheric heights was calculated for the first time using the global first-principal model of the thermosphere-ionosphere system that describes the parameters of an inhomogeneous anisotropic medium during a

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.

Airyprime beams and their propagation characteristics

NASA Astrophysics Data System (ADS)

Zhou, Guoquan; Chen, Ruipin; Ru, Guoyun

2014-02-01

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

Programming an Artificial Neural Network Tool for Spatial Interpolation in GIS - A Case Study for Indoor Radio Wave Propagation of WLAN

PubMed Central

Şen, Alper; Gümüşay, M. Ümit; Kavas, Aktül; Bulucu, Umut

2008-01-01

Wireless communication networks offer subscribers the possibilities of free mobility and access to information anywhere at any time. Therefore, electromagnetic coverage calculations are important for wireless mobile communication systems, especially in Wireless Local Area Networks (WLANs). Before any propagation computation is performed, modeling of indoor radio wave propagation needs accurate geographical information in order to avoid the interruption of data transmissions. Geographic Information Systems (GIS) and spatial interpolation techniques are very efficient for performing indoor radio wave propagation modeling. This paper describes the spatial interpolation of electromagnetic field measurements using a feed-forward back-propagation neural network programmed as a tool in GIS. The accuracy of Artificial Neural Networks (ANN) and geostatistical Kriging were compared by adjusting procedures. The feedforward back-propagation ANN provides adequate accuracy for spatial interpolation, but the predictions of Kriging interpolation are more accurate than the selected ANN. The proposed GIS ensures indoor radio wave propagation model and electromagnetic coverage, the number, position and transmitter power of access points and electromagnetic radiation level. Pollution analysis in a given propagation environment was done and it was demonstrated that WLAN (2.4 GHz) electromagnetic coverage does not lead to any electromagnetic pollution due to the low power levels used. Example interpolated electromagnetic field values for WLAN system in a building of Yildiz Technical University, Turkey, were generated using the selected network architectures to illustrate the results with an ANN. PMID:27873854

Propagation effects on radio range and noise in earth-space telecommunications

NASA Technical Reports Server (NTRS)

Flock, W. L.; Slobin, S. D.; Smith, E. K.

1982-01-01

Attention is given to the propagation effects on radio range and noise in earth-space telecommunications. The use of higher frequencies minimizes ionospheric effects on propagation, but tropospheric effects often increase or dominate. For paths of geostationary satellites, and beyond, the excess range delay caused by the ionosphere and plasmasphere is proportional to the total electron content along the path and inversely proportional to frequency squared. The delay due to dry air is usually of the order of a few meters while the delay due to water vapor (a few tens of centimeters) is responsible for most of the temporal variation in the range delay for clean air. For systems such as that of the Voyager spacecraft, and for attenuation values up to about 10 dB, increased sky noise degrades the received signal-to-noise ratio more than does the reduction in signal level due to attenuation.

International Conference on Antennas and Propagation (ICAP 89), 6th, University of Warwick, Coventry, England, Apr. 4-7, 1989, Proceedings. Part 1 - Antennas. Part 2 - Propagation

NASA Astrophysics Data System (ADS)

Various papers on antennas and propagation are presented. The general topics addressed include: phased arrays; reflector antennas; slant path propagation; propagation data for HF radio systems performance; satellite and earth station antennas; radio propagation in the troposphere; propagation data for HF radio systems performance; microstrip antennas; rain radio meteorology; conformal antennas; horns and feed antennas; low elevation slant path propagation; radio millimeter wave propagation; array antennas; propagation effects on satellite mobile, satellite broadcast, and aeronautical systems; ionospheric irregularities and motions; adaptive antennas; transient response; measurement techniques; clear air radio meteorology; ionospheric and propagation modeling; millimeter wave and lens antennas; electromagnetic theory and numerical techniques; VHF propagation modeling, system planning methods; radio propagation theoretical techniques; scattering and diffraction; transhorizon rain scatter effects; ELF-VHF and broadcast antennas; clear air millimeter propagation; scattering and frequency-selective surfaces; antenna technology; clear air transhorizon propagation.

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.

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

NASA Astrophysics Data System (ADS)

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

2014-10-01

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

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…

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.

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

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

Analysis of ELF Radio Atmospherics Radiated by Rocket-Triggered Lightning

NASA Astrophysics Data System (ADS)

Dupree, N. A.; Moore, R. C.; Pilkey, J. T.; Uman, M. A.; Jordan, D. M.; Caicedo, J. A.; Hare, B.; Ngin, T. K.

2014-12-01

Experimental observations of ELF radio atmospherics produced by rocket-triggered lightning flashes are used to analyze Earth-ionosphere waveguide excitation and propagation characteristics. Rocket-triggered lightning experiments are performed at the International Center for Lightning Research and Testing (ICLRT) located at Camp Blanding, Florida. Long-distance ELF observations are performed in California, Greenland, and Antarctica. The lightning current waveforms directly measured at the base of the lightning channel (at the ICLRT) along with pertinent Lightning Mapping Array (LMA) data are used together with the Long Wavelength Propagation Capability (LWPC) code to predict the radio atmospheric (sferic) waveform observed at the receiver locations under various ionospheric conditions. We identify fitted exponential electron density profiles that accurately describe the observed propagation delays, phase delays, and signal amplitudes. The ability to infer ionospheric characteristics using distant ELF observations greatly enhances ionospheric remote sensing capabilities, especially in regard to interpreting observations of transient luminous events (TLEs) and other ionospheric effects associated with lightning.

Ionospheric Radio Propagation

DTIC Science & Technology

1948-06-25

fluctuation According to this method the noise figure of a radio noise, generated either in the receiving sys - receiver is a quotient of the ratio of available...Ibmaity @" nabe ) adal 38. So"&UJ Malabo u~aIS. 5 a"), il61 Sudde io o ,disturbances (OLD). 6; absorption elects. 111. &e d"a hashed ~ ~ ~ ~ ~~( Saim. kuiy1

Numerical simulations of particle acceleration and low frequency radio emission in stellar environments

NASA Astrophysics Data System (ADS)

Paraskevi Moschou, Sofia; Sokolov, Igor; Cohen, Ofer; Drake, Jeremy J.; Borovikov, Dmitry; Alvarado-Gomez, Julian D.; Garraffo, Cecilia

2018-06-01

Due to their favorable atmospheric window radio waves are a useful tool for ground-based observations of astrophysical systems throughout a plethora of scales, from cosmological down to planetary ones. A wide range of physical mechanisms, from thermal processes to eruptive events linked to magnetic reconnection, can generate emission in radio frequencies. Radio waves have the distinct characteristic that they follow curved paths as they propagate in stratified environments, such as the solar corona, due to their dependence on the refraction index. Low frequency radio rays in particular are affected the most by refraction.Solar radio observations are of particular importance, since it is possible to spatially resolve the Sun and its corona and gain insights on highly dynamic and complex radio-emitting phenomena. The multi-scale problem of particle acceleration and energy partition between CMEs, flares and SEPs requires both MHD and kinetic considerations to account for the emission and mass propagation through the interplanetary space.Radio observations can play a significant role in the rapidly developing area of exoplanetary research and provide insights on the stellar environments of those systems. Even though a large number of flares has been observed for different stellar types, nevertheless there is a lack of stellar CME observations. Currently, the most promising method to incontrovertibly observe stellar CMEs is through Type II radio bursts. Low frequency radio emission can also be produced by the interaction of a magnetized planet with the stellar wind of the host star.The above mentioned characteristics of radio-waves make their integration into numerical simulations imperative for capturing and disentangling the complex radio emitting processes along the actual radio paths and provide the observers with detection limits for future Earth- and space-based missions. Radio synthetic imaging tools incorporated in realistic computational codes are already

Propagation Characteristics of Two Coronal Mass Ejections from the Sun Far into Interplanetary Space

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Xiaowei; Liu, Ying D.; Hu, Huidong

Propagation of coronal mass ejections (CMEs) from the Sun far into interplanetary space is not well understood, due to limited observations. In this study we examine the propagation characteristics of two geo-effective CMEs, which occurred on 2005 May 6 and 13, respectively. Significant heliospheric consequences associated with the two CMEs are observed, including interplanetary CMEs (ICMEs) at the Earth and Ulysses , interplanetary shocks, a long-duration type II radio burst, and intense geomagnetic storms. We use coronagraph observations from SOHO /LASCO, frequency drift of the long-duration type II burst, in situ measurements at the Earth and Ulysses , and magnetohydrodynamicmore » propagation of the observed solar wind disturbances at 1 au to track the CMEs from the Sun far into interplanetary space. We find that both of the CMEs underwent a major deceleration within 1 au and thereafter a gradual deceleration when they propagated from the Earth to deep interplanetary space, due to interactions with the ambient solar wind. The results also reveal that the two CMEs interacted with each other in the distant interplanetary space even though their launch times on the Sun were well separated. The intense geomagnetic storm for each case was caused by the southward magnetic fields ahead of the CME, stressing the critical role of the sheath region in geomagnetic storm generation, although for the first case there is a corotating interaction region involved.« less

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.

New Phenomena in Propagation of Radio Polarizations due to Magnetic Fields on Cosmological Scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ralston, J.P.; Jain, P.; Nodland, B.

1998-07-01

We discuss a new mechanism which could cause a rotation of polarization of electromagnetic waves due to magnetic fields on cosmological scales. The effect hinges on the geometrical phase of Pancharatnam and Berry, and causes a corkscrew twisting of the plane of polarization. The new effect represents an additional tool that allows possible intergalactic and cosmological magnetic fields to be studied using radio propagation. {copyright} {ital 1998} {ital The American Physical Society}

Detection of Propagating Fast Sausage Waves through Detailed Analysis of a Zebra-pattern Fine Structure in a Solar Radio Burst

NASA Astrophysics Data System (ADS)

Kaneda, K.; Misawa, H.; Iwai, K.; Masuda, S.; Tsuchiya, F.; Katoh, Y.; Obara, T.

2018-03-01

Various magnetohydrodynamic (MHD) waves have recently been detected in the solar corona and investigated intensively in the context of coronal heating and coronal seismology. In this Letter, we report the first detection of short-period propagating fast sausage mode waves in a metric radio spectral fine structure observed with the Assembly of Metric-band Aperture Telescope and Real-time Analysis System. Analysis of Zebra patterns (ZPs) in a type-IV burst revealed a quasi-periodic modulation in the frequency separation between the adjacent stripes of the ZPs (Δf ). The observed quasi-periodic modulation had a period of 1–2 s and exhibited a characteristic negative frequency drift with a rate of 3–8 MHz s‑1. Based on the double plasma resonance model, the most accepted generation model of ZPs, the observed quasi-periodic modulation of the ZP can be interpreted in terms of fast sausage mode waves propagating upward at phase speeds of 3000–8000 km s‑1. These results provide us with new insights for probing the fine structure of coronal loops.

Drought propagation and its relation with catchment biophysical characteristics

NASA Astrophysics Data System (ADS)

Alvarez-Garreton, C. D.; Lara, A.; Garreaud, R. D.

2016-12-01

Droughts propagate in the hydrological cycle from meteorological to soil moisture to hydrological droughts. To understand the drivers of this process is of paramount importance since the economic and societal impacts in water resources are directly related with hydrological droughts (and not with meteorological droughts, which have been most studied). This research analyses drought characteristics over a large region and identify its main exogenous (climate forcing) and endogenous (biophysical characteristics such as land cover type and topography) explanatory factors. The study region is Chile, which covers seven major climatic subtypes according to Köppen system, it has unique geographic characteristics, very sharp topography and a wide range of landscapes and vegetation conditions. Meteorological and hydrological droughts (deficit in precipitation and streamflow, respectively) are characterized by their durations and standardized deficit volumes using a variable threshold method, over 300 representative catchments (located between 27°S and 50°S). To quantify the propagation from meteorological to hydrological drought, we propose a novel drought attenuation index (DAI), calculated as the ratio between the meteorological drought severity slope and the hydrological drought severity slope. DAI varies from zero (catchment that attenuates completely a meteorological drought) to one (the meteorological drought is fully propagated through the hydrological cycle). This novel index provides key (and comparable) information about drought propagation over a wide range of different catchments, which has been highlighted as a major research gap. Similar drought indicators across the wide range of catchments are then linked with catchment biophysical characteristics. A thorough compilation of land cover information (including the percentage of native forests, grass land, urban and industrial areas, glaciers, water bodies and no vegetated areas), catchment physical

Propagation characteristics of electromagnetic waves in dusty plasma with full ionization

NASA Astrophysics Data System (ADS)

Dan, Li; Guo, Li-Xin; Li, Jiang-Ting

2018-01-01

This study investigates the propagation characteristics of electromagnetic (EM) waves in fully ionized dusty plasmas. The propagation characteristics of fully ionized plasma with and without dust under the Fokker-Planck-Landau (FPL) and Bhatnagar-Gross-Krook (BGK) models are compared to those of weakly ionized plasmas by using the propagation matrix method. It is shown that the FPL model is suitable for the analysis of the propagation characteristics of weakly collisional and fully ionized dusty plasmas, as is the BGK model. The influence of varying the dust parameters on the propagation properties of EM waves in the fully ionized dusty plasma was analyzed using the FPL model. The simulation results indicated that the densities and average radii of dust grains influence the reflection and transmission coefficients of fully ionized dusty plasma slabs. These results may be utilized to analyze the effects of interaction between EM waves and dusty plasmas, such as those associated with hypersonic vehicles.

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.

A Method of the UMTS-FDD Network Design Based on Universal Load Characteristics

NASA Astrophysics Data System (ADS)

Gajewski, Slawomir

In the paper an original method of the UMTS radio network design was presented. The method is based on simple way of capacity-coverage trade-off estimation for WCDMA/FDD radio interface. This trade-off is estimated by using universal load characteristics and normalized coverage characteristics. The characteristics are useful for any propagation environment as well as for any service performance requirements. The practical applications of these characteristics on radio network planning and maintenance were described.

Medium frequency propagation characteristics of different transmission lines in an underground coal mine

PubMed Central

Li, Jingcheng; Waynert, Joseph A.; Whisner, Bruce G.

2015-01-01

A medium frequency (MF) communication system operating in an underground coal mine couples its signals to a long conductor, which acts as an MF transmission line (TL) in a tunnel to permit communications among transceivers along the line. The TL is generally the longest signal path for the system, and its propagation characteristics will have a major impact on the performance of the MF communication system. In this study, the propagation characteristics of three types of MF TLs in two layouts—on the roof and on the floor of a coal mine tunnel—were obtained in an effort to understand the propagation characteristics of different TLs in different locations. The study confirmed a low MF signal loss on all of these TLs. The study also found that the TLs in different layouts had substantially different propagation characteristics. The propagation characteristics of these different TLs in different layouts are presented in the paper. PMID:26203349

Optical Characteristics of Astrometric Radio Sources OCARS

NASA Astrophysics Data System (ADS)

Malkin, Z.

2013-04-01

In this paper, the current status of the catalog of Optical Characteristics of Astrometric Radio Sources OCARS is presented. The catalog includes radio sources observed in various astrometric and geodetic VLBI programs in 1979-2012. For these sources the physical object type, redshift and visual or infrared magnitude is given when available. Detailed comments are provided when some problems with published data were encountered. Since the first version created in December 2007, the catalog is continuously developed and expanded in respect to inclusion of new radio sources and addition of new or correction of old astrophysical data. Several sources of information are used for OCARS. The main of them are the NASA/IPAC Extragalactic Database (NED) and SIMBAD astronomical databases. Besides several astronomical journals and arXiv depository are regularly monitored, so that new data is included in OCARS just after publication. The redshift for about 150 sources have been determined from dedicated optical spectroscopic observations. As of October 2012, OCARS catalog includes 7173 radio sources. 3898 sources have known redshift, and 4860 sources have known magnitude. In 2009, it was used as a supplement material to the ICRF2. The list of radio sources with a good observational history but lacking astrophysical information is provide for planning of optical observations of the most important astrometric sources. The OCARS catalog is updated, in average every several weeks and is available at http://www.gao.spb.ru/english/as/ac_vlbi/ocars.txt.

Electromagnetic Measurements Conducted by the Central Radio Propagation Laboratory During Operation Upshot-Knothole (Redacted)

DTIC Science & Technology

1954-03-31

b . ABSTRACT c. THIS PAGE 19b. TELEPHONE NUMBER (include area code) Standard Form 298 (Re . 8-98) v Prescribed by ANSI Std. Z39.18 31...March 1954 Final report Electromagnetic Measurements Conducted by the Central Radio Propagation Laboratory During Operation Upshot-Knothole B /216/E...Vubington 25, D. C. COD fw 5 U.S.C. § 552 ( b )( 6) O££ice (or AtOIIIie Fnergy, DCS/0 r r T l A . O!tp1rtment o£ the 1\\ir force \\ ·-’ . If

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.

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.

Wave propagation characteristics of a magnetic granular chain

NASA Astrophysics Data System (ADS)

Leng, Dingxin; Liu, Guijie; Sun, Lingyu; Wang, Xiaojie

2017-10-01

We investigate the wave propagation characteristics of a horizontal alignment of magnetic grains under a non-uniform magnetic field. The magnetic force of each grain is obtained using Maxwell's principle. The contact interaction of grains is based on Hertz potential. The effects of magnetic field strength on the dynamic responses of a granular chain under strong, intermediate, and weak amplitudes of incident impulses in comparison with static precompression force are studied. Different wave propagation modes induced by the magnetic field are observed. The applied field strength demonstrably reinforces the granular-position-dependent behaviors of decreasing amplitude and increasing wave propagation velocity. The magnetic field-induced features of a magnetic granular chain have potential applications in adaptive structures for shock attenuation.

Characteristics of diving in radio-marked Xantus's Murrelets

USGS Publications Warehouse

Hamilton, C.D.; Golightly, R.T.; Takekawa, John 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.

Design and Calibration of the US Army Research Laboratory (ARL) Closed Loop Laboratory Radio Frequency (RF) Propagation Section

DTIC Science & Technology

2016-10-01

ARL-TR-7860 ● OCT 2016 US Army Research Laboratory Design and Calibration of the US Army Research Laboratory (ARL) Closed Loop ...ARL-TR-7860 ● OCT 2016 US Army Research Laboratory Design and Calibration of the US Army Research Laboratory (ARL) Closed Loop Laboratory...Design and Calibration of the US Army Research Laboratory (ARL) Closed Loop Laboratory Radio Frequency (RF) Propagation Section 5a. CONTRACT NUMBER

N V Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of the Russian Academy of Sciences (IZMIRAN) yesterday, today, tomorrow

NASA Astrophysics Data System (ADS)

Kuznetsov, V. D.

2015-06-01

This paper describes the basic and applied research rationale for the organization of IZMIRAN and provides insight into the 75 years of the Institute's activities and development. Historically, early magnetic measurements in Russia were developed largely to meet the Navy's navigation needs and were, more generally, stimulated by the Peter the Great decrees and by the foundation of the St. Petersburg Academy of Sciences in 1724. The paper examines the roles of the early Academicians in developing geomagnetism and making magnetic measurements a common practice in Russia. The need for stable radio communications prompted ionospheric and radio wave propagation research. The advent of the space era and the 1957-1958 International Geophysical Year Project greatly impacted the development of IZMIRAN and spurred the creation of a number of geophysical research institutes throughout the country. Currently, the research topics at IZMIRAN range widely from geomagnetism to solar-terrestrial physics to the ionosphere and radio wave propagation, and its primary application areas are the study and forecast of space weather, an increasingly important determining factor in ever-expanding ground- and space-based technologies (space navigation and communications, space activities, etc.).

Using IRI and GSM TIP model results as environment for HF radio wave propagation model during the geomagnetic storm occurred on September 26-29, 2011

NASA Astrophysics Data System (ADS)

Kotova, D. S.; Klimenko, M. V.; Klimenko, V. V.; Zakharov, V. E.; Ratovsky, K. G.; Nosikov, I. A.; Zhao, B.

2015-11-01

This paper analyses the geomagnetic storm on September 26-29, 2011. We compare the calculation results obtained using the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) and IRI-2012 (Bilitza et al., 2014) model with ground-based ionosonde data of stations at different latitudes and longitudes. We examined physical mechanisms responsible for the formation of ionospheric effects during the main phase of geomagnetic storm that occurred at the rising phase of the 24th solar cycle. We used numerical results obtained from IRI-2012 and GSM TIP models as propagation environment for HF signals from an equatorial transmitter during quiet and disturbed conditions. We used the model of HF radio wave propagation developed in I. Kant Baltic Federal University (BFU) that is based on the geometrical optics approximation. We compared the obtained radio paths in quiet conditions and during the main and recovery storm phases and evaluated radio wave attenuation in different media models.

Managing Data From Signal-Propagation Experiments

NASA Technical Reports Server (NTRS)

Kantak, A. V.

1989-01-01

Computer programs generate characteristic plots from amplitudes and phases. Software system enables minicomputer to process data on amplitudes and phases of signals received during experiments in ground-mobile/satellite radio propagation. Takes advantage of file-handling capabilities of UNIX operating system and C programming language. Interacts with user, under whose guidance programs in FORTRAN language generate plots of spectra or other curves of types commonly used to characterize signals. FORTRAN programs used to process file-handling outputs into any of several useful forms.

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.

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

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

Finite-difference time-domain modelling of through-the-Earth radio signal propagation

NASA Astrophysics Data System (ADS)

Ralchenko, M.; Svilans, M.; Samson, C.; Roper, M.

2015-12-01

This research seeks to extend the knowledge of how a very low frequency (VLF) through-the-Earth (TTE) radio signal behaves as it propagates underground, by calculating and visualizing the strength of the electric and magnetic fields for an arbitrary geology through numeric modelling. To achieve this objective, a new software tool has been developed using the finite-difference time-domain method. This technique is particularly well suited to visualizing the distribution of electromagnetic fields in an arbitrary geology. The frequency range of TTE radio (400-9000 Hz) and geometrical scales involved (1 m resolution for domains a few hundred metres in size) involves processing a grid composed of millions of cells for thousands of time steps, which is computationally expensive. Graphics processing unit acceleration was used to reduce execution time from days and weeks, to minutes and hours. Results from the new modelling tool were compared to three cases for which an analytic solution is known. Two more case studies were done featuring complex geologic environments relevant to TTE communications that cannot be solved analytically. There was good agreement between numeric and analytic results. Deviations were likely caused by numeric artifacts from the model boundaries; however, in a TTE application in field conditions, the uncertainty in the conductivity of the various geologic formations will greatly outweigh these small numeric errors.

Propagation Characteristics Of Weakly Guiding Optical Fibers

NASA Technical Reports Server (NTRS)

Manshadi, Farzin

1992-01-01

Report discusses electromagnetic propagation characteristics of weakly guiding optical-fiber structures having complicated shapes with cross-sectional dimensions of order of wavelength. Coupling, power-dividing, and transition dielectric-waveguide structures analyzed. Basic data computed by scalar-wave, fast-Fourier-transform (SW-FFT) technique, based on numerical solution of scalar version of wave equation by forward-marching fast-Fourier-transform method.

Spatial Characterization of Radio Propagation Channel in Urban Vehicle-to-Infrastructure Environments to Support WSNs Deployment

PubMed Central

Granda, Fausto; Azpilicueta, Leyre; Vargas-Rosales, Cesar; Lopez-Iturri, Peio; Aguirre, Erik; Astrain, Jose Javier; Villandangos, Jesus; Falcone, Francisco

2017-01-01

Vehicular ad hoc Networks (VANETs) enable vehicles to communicate with each other as well as with roadside units (RSUs). Although there is a significant research effort in radio channel modeling focused on vehicle-to-vehicle (V2V), not much work has been done for vehicle-to-infrastructure (V2I) using 3D ray-tracing tools. This work evaluates some important parameters of a V2I wireless channel link such as large-scale path loss and multipath metrics in a typical urban scenario using a deterministic simulation model based on an in-house 3D Ray-Launching (3D-RL) algorithm at 5.9 GHz. Results show the high impact that the spatial distance; link frequency; placement of RSUs; and factors such as roundabout, geometry and relative position of the obstacles have in V2I propagation channel. A detailed spatial path loss characterization of the V2I channel along the streets and avenues is presented. The 3D-RL results show high accuracy when compared with measurements, and represent more reliably the propagation phenomena when compared with analytical path loss models. Performance metrics for a real test scenario implemented with a VANET wireless sensor network implemented ad-hoc are also described. These results constitute a starting point in the design phase of Wireless Sensor Networks (WSNs) radio-planning in the urban V2I deployment in terms of coverage. PMID:28590429

Spatial Characterization of Radio Propagation Channel in Urban Vehicle-to-Infrastructure Environments to Support WSNs Deployment.

PubMed

Granda, Fausto; Azpilicueta, Leyre; Vargas-Rosales, Cesar; Lopez-Iturri, Peio; Aguirre, Erik; Astrain, Jose Javier; Villandangos, Jesus; Falcone, Francisco

2017-06-07

Vehicular ad hoc Networks (VANETs) enable vehicles to communicate with each other as well as with roadside units (RSUs). Although there is a significant research effort in radio channel modeling focused on vehicle-to-vehicle (V2V), not much work has been done for vehicle-to-infrastructure (V2I) using 3D ray-tracing tools. This work evaluates some important parameters of a V2I wireless channel link such as large-scale path loss and multipath metrics in a typical urban scenario using a deterministic simulation model based on an in-house 3D Ray-Launching (3D-RL) algorithm at 5.9 GHz. Results show the high impact that the spatial distance; link frequency; placement of RSUs; and factors such as roundabout, geometry and relative position of the obstacles have in V2I propagation channel. A detailed spatial path loss characterization of the V2I channel along the streets and avenues is presented. The 3D-RL results show high accuracy when compared with measurements, and represent more reliably the propagation phenomena when compared with analytical path loss models. Performance metrics for a real test scenario implemented with a VANET wireless sensor network implemented ad-hoc are also described. These results constitute a starting point in the design phase of Wireless Sensor Networks (WSNs) radio-planning in the urban V2I deployment in terms of coverage.

Refraction of Radio Waves on the Radio-Occultation Satellite-to-Satellite Paths as a Characteristic of the Atmospheric State

NASA Astrophysics Data System (ADS)

Matyugov, S. S.; Yakovlev, O. I.; Pavelyev, A. G.; Pavelyev, A. A.; Anufriev, V. A.

2017-10-01

We present the results of analyzing the radio-wave refractive characteristics measured on the radio-occultation paths between the GPS navigation satellites and the FORMOSAT-3 research satellites in the central region of the European territory of Russia in 2007-2013. The diurnal, seasonal, and annual variations in the refraction angle at altitudes of 2 to 25 km are discussed. It is shown that the refraction angle can be used as an independent characteristic of the atmospheric state and its long-term variation trends. Diurnal and nocturnal variations in the refraction angle in the winter and summer seasons are analyzed. Trends in the atmospheric refraction variations over seven years are discussed.

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

2014-12-10

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.

Laboratory investigations into fracture propagation characteristics of rock material

NASA Astrophysics Data System (ADS)

Prasad, B. N. V. Siva; Murthy, V. M. S. R.

2018-04-01

After Industrial Revolution, demand of materials for building up structures have increased enormously. Unfortunately, failures of such structures resulted in loss of life and property. Rock is anisotropic and discontinuous in nature with inherent flaws or so-called discontinuities in it. Rock is apparently used for construction in mining, civil, tunnelling, hydropower, geothermal and nuclear sectors [1]. Therefore, the strength of the structure built up considering rockmass as the construction material needs proper technical evaluation during designing stage itself to prevent and predict the scenarios of catastrophic failures due to these inherent fractures [2]. In this study, samples collected from nine different drilling sites have been investigated in laboratory for understanding the fracture propagation characteristics in rock. Rock material properties, ultrasonic velocities through pulse transmission technique and Mode I Fracture Toughness Testing of different variants of Dolomites and Graywackes are determined in laboratory and the resistance of the rock material to catastrophic crack extension or propagation has been determined. Based on the Fracture Toughness values and the rock properties, critical Energy Release Rates have been estimated. However further studies in this direction is to be carried out to understand the fracture propagation characteristics in three-dimensional space.

The Role of Quasi-Transverse Propagation in Observed Polarization of Flare Loop Microwave Radiation

NASA Astrophysics Data System (ADS)

Shain, A. V.; Melnikov, V. F.; Morgachev, A. S.

2017-12-01

The ordinary mode of gyrosynchrotron radiation was identified to be predominant in some segments of flare loops in solar flares of July 19, 2012, and October 22, 2014. These events were studied by investigation of the quasi-transverse propagation effect on the observed polarization. The analysis involved reconstruction of the magnetic field topology at the linear force-free approximation based on the data of the SDO HMI space telescope and the subsequent simulation of radio emission of flare loops with the GX Simulator software package. The quasi-transverse propagation effect was established to be characteristic for both events, but its influence on the radio emission polarization at a frequency of 17 GHz was observed only in the October 22, 2014 flare.

Crowd-Sourced Radio Science at Marshall Space Flight Center

NASA Technical Reports Server (NTRS)

Fry, C. D.; McTernan, J. K.; Suggs, R. M.; Rawlins, L.; Krause, L. H.; Gallagher, D. L.; Adams, M. L.

2018-01-01

August 21, 2017 provided a unique opportunity to investigate the effects of the total solar eclipse on high frequency (HF) radio propagation and ionospheric variability. In Marshall Space Flight Center's partnership with the US Space and Rocket Center (USSRC) and Austin Peay State University (APSU), we engaged citizen scientists and students in an investigation of the effects of an eclipse on the mid-latitude ionosphere. Activities included fieldwork and station-based data collection of HF Amateur Radio frequency bands and VLF radio waves before, during, and after the eclipse to build a continuous record of changing propagation conditions as the moon's shadow marched across the United States. Post-eclipse radio propagation analysis provided insights into ionospheric variability due to the eclipse.

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

Study of the solar flares effect on VLF radio signal propagating along NRK-ALG path using LWPC code

NASA Astrophysics Data System (ADS)

Bouderba, Y.; NaitAmor, S.; Tribeche, M.

2016-07-01

The X-ray solar flare emissions penetrate down into the D region of the ionosphere (60-90 km of altitude) and affect the propagating very low frequency (VLF) radio signal. In this paper, we will present the effect of the solar flares on the signal mode composition of the NRK-ALG path during the period from 2007 to 2013. In the Long Wave Propagating Capability (LWPC) code theory, the VLF signal is a sum of discrete modes that propagate to the receiver with different attenuation coefficients. Therefore, an interest is given to the behavior of these coefficients under solar flares. Effectively, from the simulation, we give more explanations about the role of the signal mode composition on the fading displacement since this later is a consequence of the destructive modes interferences. Thus, the sign (positive or negative) of the perturbed signal parameters (amplitude and phase) is found to be depending on the distance between the transmitter and the receiver. Finally, we give the Wait parameters and the electron density variations as a function of solar flares.

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

Wiggles and knots in radio jets

NASA Astrophysics Data System (ADS)

Trussoni, E.; Ferrari, A.; Zaninetti, L.

Dynamical effects in binary nuclei inside parent galactic cores, gravitational interactions with companion galaxies, and Kelvin-Helmholtz instabilities in the flow propagation have been proposed as mechanism responsible for the formation of the low amplitude morphologies, wiggles and knots, observed in radio jets. Here the basic characteristics and implications of these models are discussed with reference to the limited sample of existing data. In conclusion it will be shown that present observations cannot discriminate definitely these theories; conversely, different mechanisms may be at work together in any jet at the same time.

Galileo radio science investigations

NASA Technical Reports Server (NTRS)

Howard, H. T.; Eshleman, V. R.; Hinson, D. P.; Kliore, A. J.; Lindal, G. F.; Woo, R.; Bird, M. K.; Volland, H.; Edenhoffer, P.; Paetzold, M.

1992-01-01

Galileo radio-propagation experiments are based on measurements of absolute and differential propagation time delay, differential phase delay, Doppler shift, signal strength, and polarization. These measurements can be used to study: the atmospheric and ionospheric structure, constituents, and dynamics of Jupiter; the magnetic field of Jupiter; the diameter of Io, its ionospheric structure, and the distribution of plasma in the Io torus; the diameters of the other Galilean satellites, certain properties of their surfaces, and possibly their atmospheres and ionospheres; and the plasma dynamics and magnetic field of the solar corona. The spacecraft system provides linear rather than circular polarization on the S-band downlink signal, the capability to receive X-band uplink signals, and a differential downlink ranging mode. A highly-stable, dual-frequency, spacecraft radio system is developed that is suitable for simultaneous measurements of all the parameters normally attributed to radio waves.

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.

[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.

Integrating uncertainty propagation in GNSS radio occultation retrieval: from excess phase to atmospheric bending angle profiles

NASA Astrophysics Data System (ADS)

Schwarz, Jakob; Kirchengast, Gottfried; Schwaerz, Marc

2018-05-01

Global Navigation Satellite System (GNSS) radio occultation (RO) observations are highly accurate, long-term stable data sets and are globally available as a continuous record from 2001. Essential climate variables for the thermodynamic state of the free atmosphere - such as pressure, temperature, and tropospheric water vapor profiles (involving background information) - can be derived from these records, which therefore have the potential to serve as climate benchmark data. However, to exploit this potential, atmospheric profile retrievals need to be very accurate and the remaining uncertainties quantified and traced throughout the retrieval chain from raw observations to essential climate variables. The new Reference Occultation Processing System (rOPS) at the Wegener Center aims to deliver such an accurate RO retrieval chain with integrated uncertainty propagation. Here we introduce and demonstrate the algorithms implemented in the rOPS for uncertainty propagation from excess phase to atmospheric bending angle profiles, for estimated systematic and random uncertainties, including vertical error correlations and resolution estimates. We estimated systematic uncertainty profiles with the same operators as used for the basic state profiles retrieval. The random uncertainty is traced through covariance propagation and validated using Monte Carlo ensemble methods. The algorithm performance is demonstrated using test day ensembles of simulated data as well as real RO event data from the satellite missions CHAllenging Minisatellite Payload (CHAMP); Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC); and Meteorological Operational Satellite A (MetOp). The results of the Monte Carlo validation show that our covariance propagation delivers correct uncertainty quantification from excess phase to bending angle profiles. The results from the real RO event ensembles demonstrate that the new uncertainty estimation chain performs robustly. Together

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

Convective Propagation Characteristics Using a Simple Representation of Convective Organization

NASA Astrophysics Data System (ADS)

Neale, R. B.; Mapes, B. E.

2016-12-01

Observed equatorial wave propagation is intimately linked to convective organization and it's coupling to features of the larger-scale flow. In this talk we a use simple 4 level model to accommodate vertical modes of a mass flux convection scheme (shallow, mid-level and deep). Two paradigms of convection are used to represent convective processes. One that has only both random (unorganized) diagnosed fluctuations of convective properties and one with organized fluctuations of convective properties that are amplified by previously existing convection and has an explicit moistening impact on the local convecting environment We show a series of model simulations in single-column, 2D and 3D configurations, where the role of convective organization in wave propagation is shown to be fundamental. For the optimal choice of parameters linking organization to local atmospheric state, a broad array of convective wave propagation emerges. Interestingly the key characteristics of propagating modes are the low-level moistening followed by deep convection followed by mature 'large-scale' heating. This organization structure appears to hold firm across timescales from 5-day wave disturbances to MJO-like wave propagation.

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.

Electromagnetic Propagation Problems in the Tactical Environment

DTIC Science & Technology

1982-04-01

Radio Consultative Committee of the International Telecommunications Union , Geneva 1-9 Table I Frequency Ranges Frequency Band Typical Tactical... Union , Geneva, 1978. 4. Bradley, P. A., AGARD Lecture Series No. 99, Propagation at medium and high frequencies: Practical radio systems and...International Radio Consultative Committee, Antenna Diagrams, International Telecommunication Union , Geneva, 1978. 7. Barghausen, A. F., J. W. Finney, L. L

Effects of the turbulent ISM on radio observations of quasars

NASA Astrophysics Data System (ADS)

Gabányi, Krisztina; Britzen, S.; Krichbaum, T. P.; Bach, U.; Fuhrmann, L.; Kraus, A.; Witzel, A.; Zensus, J. A.

In radio bands, the study of compact radio sources can be affected by propagation effects introduced by the interstellar medium, usually attributed to the presence of turbulent intervening plasma along the line of sight. Here, two of such effects are presented. The line of sight of B 2005+403 passes through the heavily scattered region of Cygnus causing substantial angular broadening of the source images obtained at frequencies between 0.6 GHz and 8 GHz. At higher frequencies, however, the intrinsic source structure shines through. Therefore, multi-frequency VLBI observations allow to study the characteristics of the intervening material, the source morphology and the interplay between them in forming the observed image.

What makes a good voice for radio: perceptions of radio employers and educators.

PubMed

Warhurst, Samantha; McCabe, Patricia; Madill, Catherine

2013-03-01

To inform vocal training and management of voice disorders of professional radio performers in Australia by determining radio employers' and educators' qualitative perceptions on (1) what makes a good voice for radio and (2) what communication characteristics are important when employing radio performers. Radio employers and educators (n=9) participated in semistructured interviews. Interview transcripts were coded line-by-line and analyzed for qualitative themes using principles of grounded theory. Radio performers sound easy-on-the-ear, natural, and have an ability to read and produce voices that suit the station. Many of these characteristics make them sound different to radio voices in the past. Content and personality are now also more significant than voice characteristics. A multidimensional model of these characteristics is presented. The model has implications for the training and management of voice disorders in radio performers and will guide future quantitative research on the vocal features of this population. Copyright © 2013 The Voice Foundation. Published by Mosby, Inc. All rights reserved.

Internal gravity waves in Titan's atmosphere observed by Voyager radio occultation

NASA Technical Reports Server (NTRS)

Hinson, D. P.; Tyler, G. L.

1983-01-01

The radio scintillations caused by scattering from small-scale irregularities in Titan's neutral atmosphere during a radio occultation of Voyager 1 by Titan are investigated. Intensity and frequency fluctuations occurred on time scales from about 0.1 to 1.0 sec at 3.6 and 13 cm wavelengths whenever the radio path passed within 90 km of the surface, indicating the presence of variations in refractivity on length scales from a few hundred meters to a few kilometers. Above 25 km, the altitude profile of intensity scintillations closely agrees with the predictions of a simple theory based on the characteristics of internal gravity waves propagating with little or no attenuation through the vertical stratification in Titan's atmosphere. These observations support a hypothesis of stratospheric gravity waves, possibly driven by a cloud-free convective region in the lowest few kilometers of the stratosphere.

FLARE-GENERATED SHOCK WAVE PROPAGATION THROUGH SOLAR CORONAL ARCADE LOOPS AND AN ASSOCIATED TYPE II RADIO BURST

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Pankaj; Cho, Kyung-Suk; Innes, D. E., E-mail: pankaj@kasi.re.kr

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{sup −1} and it accelerated to ∼1490 km s{supmore » −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{sup −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.« less

A Short Open Calibration (SOC) Technique to Calculate the Propagation Characteristics of Substrate Integrated Waveguide

DTIC Science & Technology

2015-07-01

integrated with the commercial electromagnetic software for accurate extraction of propagation constant of substrate integrated waveguide ( SIW ) with...respectively. After three distinctive equivalent circuit networks are described for SOC de-embedding procedure. The propagation constants of SIW with...final, the phase and attenuation constants of SIW are derived to demonstrate the propagation and leakage characteristics of SIW . Index Terms

Estimation of the parameters of disturbances on long-range radio-communication paths

NASA Astrophysics Data System (ADS)

Gerasimov, Iu. S.; Gordeev, V. A.; Kristal, V. S.

1982-09-01

Radio propagation on long-range paths is disturbed by such phenomena as ionospheric density fluctuations, meteor trails, and the Faraday effect. In the present paper, the determination of the characteristics of such disturbances on the basis of received-signal parameters is considered as an inverse and ill-posed problem. A method for investigating the indeterminacy which arises in such determinations is proposed, and a quantitative analysis of this indeterminacy is made.

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

Fish-Eye Observing with Phased Array Radio Telescopes

NASA Astrophysics Data System (ADS)

Wijnholds, S. J.

The radio astronomical community is currently developing and building several new radio telescopes based on phased array technology. These telescopes provide a large field-of-view, that may in principle span a full hemisphere. This makes calibration and imaging very challenging tasks due to the complex source structures and direction dependent radio wave propagation effects. In this thesis, calibration and imaging methods are developed based on least squares estimation of instrument and source parameters. Monte Carlo simulations and actual observations with several prototype show that this model based approach provides statistically and computationally efficient solutions. The error analysis provides a rigorous mathematical framework to assess the imaging performance of current and future radio telescopes in terms of the effective noise, which is the combined effect of propagated calibration errors, noise in the data and source confusion.

Propagation and spatiotemporal coupling characteristics of ultra-short Gaussian vortex pulse

NASA Astrophysics Data System (ADS)

Nie, Jianye; Liu, Guodong; Zhang, Rongzhu

2018-05-01

Based on Collins diffraction integral formula, the propagation equation of ultra-short Gaussian vortex pulse beam has been derived. Using the equation, the intensity distribution variations of vortex pulse in the propagation process are calculated. Specially, the spatiotemporal coupling characteristics of ultra-short vortex beams are discussed in detail. The results show that some key parameters, such as transverse distance, transmission distance, pulse width and topological charge number will influence the spatiotemporal coupling characteristics significantly. With the increasing of transverse distance, the waveforms of the pulses distort obviously. And when transmission distance is far than 50 mm, the distribution curve of transverse intensity gradually changes into a Gaussian type. In addition, initial pulse width will affect the distribution of light field, however, when initial pulse width is larger than 3 fs, the spatiotemporal coupling effect will be insignificant. Topological charge number does not affect the time delay characteristics, since with the increasing of topological charge number, the waveform of the pulse distorts gradually but the time delay does not occur.

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.

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.

Modelling and mitigating refractive propagation effects in precision pulsar timing observations

NASA Astrophysics Data System (ADS)

Shannon, R. M.; Cordes, J. M.

2017-01-01

To obtain the most accurate pulse arrival times from radio pulsars, it is necessary to correct or mitigate the effects of the propagation of radio waves through the warm and ionized interstellar medium. We examine both the strength of propagation effects associated with large-scale electron-density variations and the methodology used to estimate infinite frequency arrival times. Using simulations of two-dimensional phase-varying screens, we assess the strength and non-stationarity of timing perturbations associated with large-scale density variations. We identify additional contributions to arrival times that are stochastic in both radio frequency and time and therefore not amenable to correction solely using times of arrival. We attribute this to the frequency dependence of the trajectories of the propagating radio waves. We find that this limits the efficacy of low-frequency (metre-wavelength) observations. Incorporating low-frequency pulsar observations into precision timing campaigns is increasingly problematic for pulsars with larger dispersion measures.

HF propagation results from the Metal Oxide Space Cloud (MOSC) experiment

NASA Astrophysics Data System (ADS)

Joshi, Dev; Groves, Keith M.; McNeil, William; Carrano, Charles; Caton, Ronald G.; Parris, Richard T.; Pederson, Todd R.; Cannon, Paul S.; Angling, Matthew; Jackson-Booth, Natasha

2017-06-01

With support from the NASA sounding rocket program, the Air Force Research Laboratory launched two sounding rockets in the Kwajalein Atoll, Marshall Islands in May 2013 known as the Metal Oxide Space Cloud experiment. The rockets released samarium metal vapor at preselected altitudes in the lower F region that ionized forming a plasma cloud. Data from Advanced Research Project Agency Long-range Tracking and Identification Radar incoherent scatter radar and high-frequency (HF) radio links have been analyzed to understand the impacts of the artificial ionization on radio wave propagation. The HF radio wave ray-tracing toolbox PHaRLAP along with ionospheric models constrained by electron density profiles measured with the ALTAIR radar have been used to successfully model the effects of the cloud on HF propagation. Up to three new propagation paths were created by the artificial plasma injections. Observations and modeling confirm that the small amounts of ionized material injected in the lower F region resulted in significant changes to the natural HF propagation environment.

Evaluation of Propagation Characteristics Using the Human Body as an Antenna

PubMed Central

Li, Jingzhen; Liu, Yuhang; Hao, Yang

2017-01-01

In this paper, an inhomogeneous human body model was presented to investigate the propagation characteristics when the human body was used as an antenna to achieve signal transmission. Specifically, the channel gain of four scenarios, namely, (1) both TX electrode and RX electrode were placed in the air, (2) TX electrode was attached on the human body, and RX electrode was placed in the air, (3) TX electrode was placed in the air, and RX electrode was attached on the human body, (4) both the TX electrode and RX electrode were attached on the human body, were studied through numerical simulation in the frequency range 1 MHz to 90 MHz. Furthermore, the comparisons of input efficiency, accepted efficiency, total efficiency, absorption power of human body, and electric field distribution of different distances of four aforementioned scenarios were explored when the frequency was at 44 MHz. In addition, the influences of different human tissues, electrode position, and the distance between electrode and human body on the propagation characteristics were investigated respectively at 44 MHz. The results showed that the channel gain of Scenario 4 was the maximum when the frequency was from 1 MHz to 90 MHz. The propagation characteristics were almost independent of electrode position when the human body was using as an antenna. However, as the distance between TX electrode and human body increased, the channel gain decreased rapidly. The simulations were verified by experimental measurements. The results showed that the simulations were in agreement with the measurements. PMID:29232905

Evaluation of Propagation Characteristics Using the Human Body as an Antenna.

PubMed

Li, Jingzhen; Nie, Zedong; Liu, Yuhang; Wang, Lei; Hao, Yang

2017-12-11

In this paper, an inhomogeneous human body model was presented to investigate the propagation characteristics when the human body was used as an antenna to achieve signal transmission. Specifically, the channel gain of four scenarios, namely, (1) both TX electrode and RX electrode were placed in the air, (2) TX electrode was attached on the human body, and RX electrode was placed in the air, (3) TX electrode was placed in the air, and RX electrode was attached on the human body, (4) both the TX electrode and RX electrode were attached on the human body, were studied through numerical simulation in the frequency range 1 MHz to 90 MHz. Furthermore, the comparisons of input efficiency, accepted efficiency, total efficiency, absorption power of human body, and electric field distribution of different distances of four aforementioned scenarios were explored when the frequency was at 44 MHz. In addition, the influences of different human tissues, electrode position, and the distance between electrode and human body on the propagation characteristics were investigated respectively at 44 MHz. The results showed that the channel gain of Scenario 4 was the maximum when the frequency was from 1 MHz to 90 MHz. The propagation characteristics were almost independent of electrode position when the human body was using as an antenna. However, as the distance between TX electrode and human body increased, the channel gain decreased rapidly. The simulations were verified by experimental measurements. The results showed that the simulations were in agreement with the measurements.

Type II Radio Bursts Observed by STEREO/Waves and Wind/Waves instruments

NASA Astrophysics Data System (ADS)

Krupar, V.; Magdalenic, J.; Zhukov, A.; Rodriguez, L.; Mierla, M.; Maksimovic, M.; Cecconi, B.; Santolik, O.

2013-12-01

Type II radio bursts are slow-drift emissions triggered by suprathermal electrons accelerated on shock fronts of propagating CMEs. We present several events at kilometric wavelengths observed by radio instruments onboard the STEREO and Wind spacecraft. The STEREO/Waves and Wind/Waves have goniopolarimetric (GP, also referred to as direction finding) capabilities that allow us to triangulate radio sources when an emission is observed by two or more spacecraft. As the GP inversion has high requirements on the signal-to-noise ratio we only have a few type II radio bursts with sufficient intensity for this analysis. We have compared obtained radio sources with white-light observations of STEREO/COR and STEREO/HI instruments. Our preliminary results indicate that radio sources are located at flanks of propagating CMEs.

Overview of Solar Radio Bursts and their Sources

NASA Astrophysics Data System (ADS)

Golla, Thejappa; MacDowall, Robert J.

2018-06-01

Properties of radio bursts emitted by the Sun at frequencies below tens of MHz are reviewed. In this frequency range, the most prominent radio emissions are those of solar type II, complex type III and solar type IV radio bursts, excited probably by the energetic electron populations accelerated in completely different environments: (1) type II bursts are due to non-relativistic electrons accelerated by the CME driven interplanetary shocks, (2) complex type III bursts are due to near-relativistic electrons accelerated either by the solar flare reconnection process or by the SEP shocks, and (3) type IV bursts are due to relativistic electrons, trapped in the post-eruption arcades behind CMEs; these relativistic electrons probably are accelerated by the continued reconnection processes occurring beneath the CME. These radio bursts, which can serve as the natural plasma probes traversing the heliosphere by providing information about various crucial space plasma parameters, are also an ideal instrument for investigating acceleration mechanisms responsible for the high energy particles. The rich collection of valuable high quality radio and high time resolution in situ wave data from the WAVES experiments of the STEREO A, STEREO B and WIND spacecraft has provided an unique opportunity to study these different radio phenomena and understand the complex physics behind their excitation. We have developed Monte Carlo simulation techniques to estimate the propagation effects on the observed characteristics of these low frequency radio bursts. We will present some of the new results and describe how one can use these radio burst observations for space weather studies. We will also describe some of the non-linear plasma processes detected in the source regions of both solar type III and type II radio bursts. The analysis and simulation techniques used in these studies will be of immense use for future space based radio observations.

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.

Characteristics of magnetospheric radio noise spectra

NASA Technical Reports Server (NTRS)

Herman, J. R.

1976-01-01

Magnetospheric radio noise spectra (30 kHz to 10 MHz) taken by IMP-6 and RAE-2 exhibit time-varying characteristics which are related to spacecraft position and magnetospheric processes. In the mid-frequency range (100-1,000 kHz) intense noise peaks rise by a factor of 100 or more above background; 80% of the peak frequencies are within the band 125 kHz to 600 kHz, and the peak occurs most often (18% of the time) at 280 kHz. This intense mid-frequency noise has been detected at radial distances from 1.3 Re to 60 Re on all sides of the Earth during magnetically quiet as well as disturbed periods. Maximum occurrence of the mid-frequency noise is in the evening to midnight hours where splash-type energetic particle precipitation takes place. ""Magnetospheric lightning'' can be invoked to explain the spectral shape of the observed spectra.

Subionospheric VLF Propagation Modelling During a solar flares

NASA Astrophysics Data System (ADS)

Akel, A. F.

2013-05-01

This work aims to present a preliminary study of the behavior of the lower ionosphere under transient regimes of ionization through the technique of wave propagation of VLF (Very Low Frequency). For this, we characterized the lower ionosphere by two traditional (wait) parameters H' and β which are found by VLF radio modelling using the computational code of subionospheric radio propagation LWPC(Long Wave Propagation Capability). The main effects and behaviors investigated in this study was due to a solar flare 2M class near solar minimum at 03/25/2008. We changed Solar zenith angle dependence of the ionospheric parameters H' and β for diurnal time by a polynomial equation. For this study we used the available data the South America VLF Network (SAVNET) and show the results between modeling and data

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.

ELF/VLF propagation measurements in the Atlantic during 1989

NASA Astrophysics Data System (ADS)

Nickolaenko, A. P.

1995-06-01

The vertical electric field component was measured by a group of the Ukrainian Insitute of Radio Astronomy on board the Professor Zubov scientific vessel during April 1989 at latitudes from 30 deg S to 50 deg N. Results of the amplitude measurements in the Atlantic of natural ELF radio signals and those from the VLF navigation system 'Omega' at its lowest frequency of 10.2 kHz are given. Characteristics were obtained of the moving ship as the field-site for the ELF observations. Variations in the ELF radio noise amplitude recorded at tropical latitudes agree with the computed data for the model of three continental centers of lightning activity. The VLF results were obtained by the 'beat' technique providing the simplest narrow-band amplitude registration. Range dependencies of the field amplitudes from A (Norway), B (Liberia) and F (Argentina) stations have been analyzed. The VLF attentuation factor was estimated for the ambient day conditions along the four cardinal directions. This allowed the detection of a statistically significant attenuation difference between the east-west and west-east propagation paths. The VLF radio signal was also used as a probe to evaluate the effective height of the vertical electric antenna and to calibrate the ELF noise amplitudes.

Measurement and analysis of time-domain characteristics of corona-generated radio interference from a single positive corona source

NASA Astrophysics Data System (ADS)

Li, Xuebao; Li, Dayong; Chen, Bo; Cui, Xiang; Lu, Tiebing; Li, Yinfei

2018-04-01

The corona-generated electromagnetic interference commonly known as radio interference (RI) has become a limiting factor for the design of high voltage direct current transmission lines. In this paper, a time-domain measurement system is developed to measure the time-domain characteristics of corona-generated RI from a single corona source under a positive corona source. In the experiments, the corona current pulses are synchronously measured through coupling capacitors. The one-to-one relationship between the corona current pulse and measured RI voltage pulse is observed. The statistical characteristics of pulse parameters are analyzed, and the correlations between the corona current pulse and RI voltage pulse in the time-domain and frequency-domain are analyzed. Depending on the measured corona current pulses, the time-domain waveform of corona-generated RI is calculated on the basis of the propagation model of corona current on the conductor, the dipolar model for electric field calculation, and the antenna model for inducing voltage calculation. The well matched results between measured and simulated waveforms of RI voltage can show the validity of the measurement and calculation method presented in this paper, which also further show the close correlation between corona current and corona-generated RI.

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.

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.

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.

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.

47 CFR 32.2231 - Radio systems.

Code of Federal Regulations, 2010 CFR

2010-10-01

... costs. This account shall also include the original cost of earth stations and spare parts, material or..., amplification, propagation, reception, modulation, and demodulation of radio waves in free space over which...

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.

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

Analysis of foliage effects on mobile propagation in dense urban environments

NASA Astrophysics Data System (ADS)

Bronshtein, Alexander; Mazar, Reuven; Lu, I.-Tai

2000-07-01

Attempts to reduce the interference level and to increase the spectral efficiency of cellular radio communication systems operating in dense urban and suburban areas lead to the microcellular approach with a consequent requirement to lower antenna heights. In large metropolitan areas having high buildings this requirement causes a situation where the transmitting and receiving antennas are both located below the rooftops, and the city street acts as a type of a waveguiding channel for the propagating signal. In this work, the city street is modeled as a random multislit waveguide with randomly distributed regions of foliage parallel to the building boundaries. The statistical propagation characteristics are expressed in terms of multiple ray-fields approaching the observer. Algorithms for predicting the path-loss along the waveguide and for computing the transverse field structure are presented.

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.

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.

Experimental study on flame propagation characteristics of Hydrogen premixed gas in gas pipeline

NASA Astrophysics Data System (ADS)

Ma, Danzhu; Li, Zhuang; Jia, Fengrui; Li, Zhou

2018-06-01

Hydrogen is the cleanest high-energy gas fuel, and also is the main industrial material. However, hydrogen is more explosive and more powerful than conventional gas fuels, which restricts its application. In particular, the expansion of premixed combustion under a strong constraint is more complicated, the reaction spreads faster. The flame propagation characteristics of premixed hydrogen/air were investigated by experiment. The mechanism of reaction acceleration is discussed, and then the speed of the flame propagation and the reaction pressure were tested and analysed.

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.

Pervasive Radio Mapping of Industrial Environments Using a Virtual Reality Approach

PubMed Central

Nedelcu, Adrian-Valentin; Machedon-Pisu, Mihai; Talaba, Doru

2015-01-01

Wireless communications in industrial environments are seriously affected by reliability and performance issues, due to the multipath nature of obstacles within such environments. Special attention needs to be given to planning a wireless industrial network, so as to find the optimum spatial position for each of the nodes within the network, and especially for key nodes such as gateways or cluster heads. The aim of this paper is to present a pervasive radio mapping system which captures (senses) data regarding the radio spectrum, using low-cost wireless sensor nodes. This data is the input of radio mapping algorithms that generate electromagnetic propagation profiles. Such profiles are used for identifying obstacles within the environment and optimum propagation pathways. With the purpose of further optimizing the radio planning process, the authors propose a novel human-network interaction (HNI) paradigm that uses 3D virtual environments in order to display the radio maps in a natural, easy-to-perceive manner. The results of this approach illustrate its added value to the field of radio resource planning of industrial communication systems. PMID:26167533

Pervasive Radio Mapping of Industrial Environments Using a Virtual Reality Approach.

PubMed

Nedelcu, Adrian-Valentin; Machedon-Pisu, Mihai; Duguleana, Mihai; Talaba, Doru

2015-01-01

Wireless communications in industrial environments are seriously affected by reliability and performance issues, due to the multipath nature of obstacles within such environments. Special attention needs to be given to planning a wireless industrial network, so as to find the optimum spatial position for each of the nodes within the network, and especially for key nodes such as gateways or cluster heads. The aim of this paper is to present a pervasive radio mapping system which captures (senses) data regarding the radio spectrum, using low-cost wireless sensor nodes. This data is the input of radio mapping algorithms that generate electromagnetic propagation profiles. Such profiles are used for identifying obstacles within the environment and optimum propagation pathways. With the purpose of further optimizing the radio planning process, the authors propose a novel human-network interaction (HNI) paradigm that uses 3D virtual environments in order to display the radio maps in a natural, easy-to-perceive manner. The results of this approach illustrate its added value to the field of radio resource planning of industrial communication systems.

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.

Project Radio JOVE: Hands-On Radio Astronomy for the Classroom

NASA Astrophysics Data System (ADS)

Thieman, J. R.; Higgins, C. A.

2000-10-01

Radio Jove is a relatively new educational project to involve secondary school students in collecting and analyzing observations of the natural radio emissions of the planet Jupiter and the Sun. Participating students get hands-on experience in gathering and working with space science data. They obtain the data by either building a radio receiver and antenna and making observations with their equipment, or by remotely using professional radio telescopes through the web. They can then compare their results with other schools who had also observed and come to conclusions concerning the nature of the radio sources and how the radio waves propagate to Earth. Thus, they fully follow the method of scientific inquiry used by radio astronomers to study our solar system. (National Science Content Standard A: Science as Inquiry) More than 200 kits have been distributed thus far to schools and individuals as a result of the project. With the coming Cassini flyby of Jupiter we will be advocating a campaign in which many of the schools involved in the project will be observing at times of scientific interest. While Galileo and Cassini are monitoring Jovian radio emissions at lower frequencies, the schools will be observing at frequencies of 20.1 MHz (kit-based observations) or the frequencies available through the professional radio telescopes connected on-line. The aim will be to get a thorough picture of the levels of activity at Jupiter during the flyby period and how the radio signals are received at different observing stations around the world. An archive of observations submitted by the schools will be maintained at Goddard Space Flight Center and there will also be an archive of the professional telescopes data at the University of Florida. We hope that many students will have the feeling of being a part of the planetary exploration program as a result.

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.

A propagation method with adaptive mesh grid based on wave characteristics for wave optics simulation

NASA Astrophysics Data System (ADS)

Tang, Qiuyan; Wang, Jing; Lv, Pin; Sun, Quan

2015-10-01

Propagation simulation method and choosing mesh grid are both very important to get the correct propagation results in wave optics simulation. A new angular spectrum propagation method with alterable mesh grid based on the traditional angular spectrum method and the direct FFT method is introduced. With this method, the sampling space after propagation is not limited to propagation methods no more, but freely alterable. However, choosing mesh grid on target board influences the validity of simulation results directly. So an adaptive mesh choosing method based on wave characteristics is proposed with the introduced propagation method. We can calculate appropriate mesh grids on target board to get satisfying results. And for complex initial wave field or propagation through inhomogeneous media, we can also calculate and set the mesh grid rationally according to above method. Finally, though comparing with theoretical results, it's shown that the simulation result with the proposed method coinciding with theory. And by comparing with the traditional angular spectrum method and the direct FFT method, it's known that the proposed method is able to adapt to a wider range of Fresnel number conditions. That is to say, the method can simulate propagation results efficiently and correctly with propagation distance of almost zero to infinity. So it can provide better support for more wave propagation applications such as atmospheric optics, laser propagation and so on.

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.

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.

A model of fast radio bursts: collisions between episodic magnetic blobs

NASA Astrophysics Data System (ADS)

Li, Long-Biao; Huang, Yong-Feng; Geng, Jin-Jun; Li, Bing

2018-06-01

Fast radio bursts (FRBs) are bright radio pulses from the sky with millisecond durations and Jansky-level flux densities. Their origins are still largely uncertain. Here we suggest a new model for FRBs. We argue that the collision of a white dwarf with a black hole can generate a transient accretion disk, from which powerful episodicmagnetic blobs will be launched. The collision between two consecutive magnetic blobs can result in a catastrophic magnetic reconnection, which releases a large amount of free magnetic energy and forms a forward shock. The shock propagates through the cold magnetized plasma within the blob in the collision region, radiating through the synchrotron maser mechanism, which is responsible for a non-repeating FRB signal. Our calculations show that the theoretical energetics, radiation frequency, duration timescale and event rate can be very consistent with the observational characteristics of FRBs.

Wave-optics uncertainty propagation and regression-based bias model in GNSS radio occultation bending angle retrievals

NASA Astrophysics Data System (ADS)

Gorbunov, Michael E.; Kirchengast, Gottfried

2018-01-01

A new reference occultation processing system (rOPS) will include a Global Navigation Satellite System (GNSS) radio occultation (RO) retrieval chain with integrated uncertainty propagation. In this paper, we focus on wave-optics bending angle (BA) retrieval in the lower troposphere and introduce (1) an empirically estimated boundary layer bias (BLB) model then employed to reduce the systematic uncertainty of excess phases and bending angles in about the lowest 2 km of the troposphere and (2) the estimation of (residual) systematic uncertainties and their propagation together with random uncertainties from excess phase to bending angle profiles. Our BLB model describes the estimated bias of the excess phase transferred from the estimated bias of the bending angle, for which the model is built, informed by analyzing refractivity fluctuation statistics shown to induce such biases. The model is derived from regression analysis using a large ensemble of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) RO observations and concurrent European Centre for Medium-Range Weather Forecasts (ECMWF) analysis fields. It is formulated in terms of predictors and adaptive functions (powers and cross products of predictors), where we use six main predictors derived from observations: impact altitude, latitude, bending angle and its standard deviation, canonical transform (CT) amplitude, and its fluctuation index. Based on an ensemble of test days, independent of the days of data used for the regression analysis to establish the BLB model, we find the model very effective for bias reduction and capable of reducing bending angle and corresponding refractivity biases by about a factor of 5. The estimated residual systematic uncertainty, after the BLB profile subtraction, is lower bounded by the uncertainty from the (indirect) use of ECMWF analysis fields but is significantly lower than the systematic uncertainty without BLB correction. The systematic and

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

Polarization Characteristics of Zebra Patterns in Type IV Solar Radio Bursts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaneda, K.; Misawa, H.; Tsuchiya, F.

The polarization characteristics of zebra patterns (ZPs) in type IV solar bursts were studied. We analyzed 21 ZP events observed by the Assembly of Metric-band Aperture Telescope and Real-time Analysis System between 2010 and 2015 and identified the following characteristics: a degree of circular polarization (DCP) in the range of 0%–70%, a temporal delay of 0–70 ms between the two circularly polarized components (i.e., the right- and left-handed components), and dominant ordinary-mode emission in about 81% of the events. For most events, the relation between the dominant and delayed components could be interpreted in the framework of fundamental plasma emissionmore » and depolarization during propagation, though the values of DCP and delay were distributed across wide ranges. Furthermore, it was found that the DCP and delay were positively correlated (rank correlation coefficient R = 0.62). As a possible interpretation of this relationship, we considered a model based on depolarization due to reflections at sharp density boundaries assuming fundamental plasma emission. The model calculations of depolarization including multiple reflections and group delay during propagation in the inhomogeneous corona showed that the DCP and delay decreased as the number of reflections increased, which is consistent with the observational results. The dispersive polarization characteristics could be explained by the different numbers of reflections causing depolarization.« less

User needs for propagation data

NASA Technical Reports Server (NTRS)

Sullivan, Thomas M.

1993-01-01

New and refined models of radio signal propagation phenomena are needed to support studies of evolving satellite services and systems. Taking an engineering perspective, applications for propagation measurements and models in the context of various types of analyses that are of ongoing interest are reviewed. Problems that were encountered in the signal propagation aspects of these analyses are reviewed, and potential solutions to these problems are discussed. The focus is on propagation measurements and models needed to support design and performance analyses of systems in the Mobile-Satellite Service (MSS) operating in the 1-3 GHz range. These systems may use geostationary or non-geostationary satellites and Frequency Division Multiple Access (FDMA), Time Division Multiple Access Digital (TDMA), or Code Division Multiple Access (CDMA) techniques. Many of the propagation issues raised in relation to MSS are also pertinent to other services such as broadcasting-satellite (sound) at 2310-2360 MHz. In particular, services involving mobile terminals or terminals with low gain antennas are of concern.

Characteristics of the Lower Atmosphere Influencing Radio Wave Propagation: Conference Proceedings Symposium of the Electromagnetic Wave Propagation Panel (33rd) Held at Spatind, Norway on 4-7 October 1983

DTIC Science & Technology

1984-02-01

selecting the most appropriate model is constrained by the problem faced by the system designer and/or system user, funding available, ability to collect...before new systems are designed . Propagation studies are somewhat cyclic in nature. When sufficient knowledge of a particular phenomenon for the...phenomena are continuing to be better understood in terms of absorption, attenuation, and forecasting. This leads to better system design . o Propagation

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.

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

INSPIRE - Premission. [Interactive NASA Space Physics Ionosphere Radio Experiment

NASA Technical Reports Server (NTRS)

Taylor, William W. L.; Mideke, Michael; Pine, William E.; Ericson, James D.

1992-01-01

The Interactive NASA Space Physics Ionosphere Radio Experiment (INSPIRE) designed to assist in a Space Experiments with Particle Accelerators (SEPAC) project is discussed. INSPIRE is aimed at recording data from a large number of receivers on the ground to determine the exact propagation paths and absorption of radio waves at frequencies between 50 Hz and 7 kHz. It is indicated how to participate in the experiment that will involve high school classes, colleges, and amateur radio operators.

First Joint Observations of Radio Aurora by the VHF and HF Radars of the ISTP SB RAS

NASA Astrophysics Data System (ADS)

Berngardt, O. I.; Lebedev, V. P.; Kutelev, K. A.; Kushnarev, D. S.; Grkovich, K. V.

2018-01-01

Two modern radars for diagnosis of the ionosphere by the radio-wave backscattering method, namely, the Irkutsk incoherent scatter radar at VHF (IISR, 154-162 MHz) and the Ekaterinburg coherent radar at HF (EKB, 8-20 MHz) are operated at the Institute of Solar-Terrestrial Physics, Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS). The paper analyzes the results of joint observations of strong scattering (radio aurora) on June 8, 2015. To determine the geographical position of the radio aurora, we developed original methods that take into account both the features of the radio-wave propagation and the features of the radar antenna systems. It is shown that there are areas where the spatial position of the HF and VHF radio aurora can coincide. This permits using the radars as a single complex for diagnosis of the characteristics of small-scale high-latitude irregularities in the ionospheric E and F layers. A comparative analysis of the characteristics and temporal dynamics of the radio-aurora region in the HF and VHF ranges is performed. Using the DMSP satellite data, it has been shown that the radio aurora dynamics during this experiment with the EKB radar can be related with the spatial dynamics of the localized area with high electric field, which moves from high to equatorial latitudes. It is found that due to the broader field of view, radio aurora at the HF radar was stably observed 6-12 min earlier than at the VHF radar. This permits using the EKB radar data for prediction of the radio-aurora detection by the IISR radar.

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.

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoffman, Adam J., E-mail: adamhoff@umich.edu; Lee, John C., E-mail: jcl@umich.edu

2016-02-15

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 Sourcemore » 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.« less

A Study of Solar Flare Effects on Mid and High Latitude Radio Wave Propagation using SuperDARN.

NASA Astrophysics Data System (ADS)

Ruohoniemi, J. M.; Chakraborty, S.; Baker, J. B.

2017-12-01

Over the Horizon (OTH) communication is strongly dependent on the state of the ionosphere, which is sensitive to solar X-ray flares. The Super Dual Auroral Radar Network (SuperDARN), whose working principle is dependent on trans-ionospheric radio communication, uses HF radio waves to remotely sense the ionosphere. The backscatter returns from the terrestrial surface (also known as ground-scatter) transit the ionosphere four times and simulate the operation of an HF communications link. SuperDARN backscatter signal properties are altered (strongly attenuated and changes apparent phase) during a sudden ionospheric disturbance following a solar flare, commonly known as Short-Wave Fadeout or SWF. During an SWF the number of SuperDARN backscatter echoes drops suddenly (≈1 min) and sharply, often to near zero, and recovers within 30 minutes to an hour. In this study HF propagation data (SuperDARN backscatter) obtained during SWF events are analyzed for the purpose of validating and improving the performance of HF absorption models, such as, Space Weather Prediction Center (SWPC) D-region Absorption model (DRAP) and CCMC physics based AbbyNormal model. We will also present preliminary results from a physics based model for the mid and high latitude ionospheric response to flare-driven space weather anomalies, which can be used to estimate different physical parameters of the ionosphere such as electron density, collision frequency, absorption coefficients, response time of D-region etc.

Past and future of radio occultation studies of planetary atmospheres

NASA Technical Reports Server (NTRS)

Eshleman, Von R.; Hinson, David P.; Tyler, G. Leonard; Lindal, Gunnar F.

1987-01-01

Measurements of radio waves that have propagated through planetary atmospheres have provided exploratory results on atmospheric constituents, structure, dynamics, and ionization for Venus, Mars, Titan, Jupiter, Saturn, and Uranus. Highlights of past results are reviewed in order to define and illustrate the potential of occultation and related radio studies in future planetary missions.

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.

Optically reconfigurable patterning for control of the propagation characteristics of a planar waveguide

NASA Astrophysics Data System (ADS)

Wang, Y.; Klittnick, A.; Clark, N. A.; Keller, P.

2008-10-01

We demonstrate an easily fabricated all-optical and freely reconfigurable method of controlling the propagating characteristics of the optic path within a planar waveguide with low insertion losses by employing the optical patterning of the refractive index of an erasable and rewriteable photosensitive liquid crystal polymer cladding layer.

Coronal mass ejection kinematics deduced from white light (Solar Mass Ejection Imager) and radio (Wind/WAVES) observations

NASA Astrophysics Data System (ADS)

Reiner, M. J.; Jackson, B. V.; Webb, D. F.; Mizuno, D. R.; Kaiser, M. L.; Bougeret, J.-L.

2005-09-01

White-light and radio observations are combined to deduce the coronal and interplanetary kinematics of a fast coronal mass ejection (CME) that was ejected from the Sun at about 1700 UT on 2 November 2003. The CME, which was associated with an X8.3 solar flare from W56°, was observed by the Mauna Loa and Solar and Heliospheric Observatory (SOHO) Large-Angle Spectrometric Coronograph (LASCO) coronagraphs to 14 R⊙. The measured plane-of-sky speed of the LASCO CME was 2600 km s-1. To deduce the kinematics of this CME, we use the plane-of-sky white light observations from both the Solar Mass Ejection Imager (SMEI) all-sky camera on board the Coriolis spacecraft and the SOHO/LASCO coronagraph, as well as the frequency drift rate of the low-frequency radio data and the results of the radio direction-finding analysis from the WAVES experiment on the Wind spacecraft. In agreement with the in situ observations for this event, we find that both the white light and radio observations indicate that the CME must have decelerated significantly beginning near the Sun and continuing well into the interplanetary medium. More specifically, by requiring self-consistency of all the available remote and in situ data, together with a simple, but not unreasonable, assumption about the general characteristic of the CME deceleration, we were able to deduce the radial speed and distance time profiles for this CME as it propagated from the Sun to 1 AU. The technique presented here, which is applicable to mutual SMEI/WAVES CME events, is expected to provide a more complete description and better quantitative understanding of how CMEs propagate through interplanetary space, as well as how the radio emissions, generated by propagating CME/shocks, relate to the shock and CME. This understanding can potentially lead to more accurate predictions for the onset times of space weather events, such as those that were observed during this unique period of intense solar activity.

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

EFFECT OF A SAUSAGE OSCILLATION ON RADIO ZEBRA-PATTERN STRUCTURES IN A SOLAR FLARE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Sijie; Yan, Yihua; Nakariakov, V. M., E-mail: sjyu@nao.cas.cn

2016-07-20

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 valuesmore » 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.« less

e-POP RRI provides new opportunities for space-based, high-frequency radio science experiments

NASA Astrophysics Data System (ADS)

Burrell, Angeline G.

2017-04-01

Perry et al. (2016, https://doi.org/10.1002/2017JG003855) present the first results of the Radio Receiver Instrument (RRI), a part of the enhanced Polar Outflow Probe (e-POP) that flies on board the CAScade, Smallsat and IOnospheric Polar Explorer satellite. Using a matched filter technique, e-POP RRI was able to observe individual radio pulses transmitted by a ground-based radar. These results were used to examine the temporal variations in the dispersion, polarization, and power of the pulses, demonstrating the capacity for e-POP RRI to contribute to studies of radio propagation at high-frequency (HF) ranges. Understanding radio propagation in the presence and absence of ionospheric irregularities is crucial for ionospheric physics, as well as commercial and military radio applications. Conjunctions between e-POP RRI and ground- or space-based HF transmitters offer a new opportunity for coherent scatter experiments.

Solar polar orbit radio telescope for space weather forecast

NASA Astrophysics Data System (ADS)

Wu, J.; Wang, C.; Wang, S.; Wu, J.; Sun, W.; Cai, J.; Yan, Y.

Radio emission from density plasma can be detected at low radio frequencies. An image of such plasma clouds of the entire inner interplanetary space is always a wanted input for space weather forecast and ICME propagation studies. To take such an image within the ecliptic plane may not fully explore what is happening around the Sun not only because of the blockage of the Sun, also because most of the ICMEs are propagating in the low-latitude of the Sun, near the ecliptic plane. It is then proposed to launch a solar polar orbit radio telescope to acquire high density plasma cloud images from the entire inner interplanetary space. Low radio frequency images require a large antenna aperture in space. It is, therefore, proposed to use the existing passive synthetic aperture radiometer technology to reduce mass and complicity of the deployment system of the big antenna. In order to reduce the mass of the antenna by using minimum number of elements, a zero redundant antenna element design can be used with a rotating time-shared sampling system. A preliminary assessment study shows the mission is feasible.

Azimuthal propagation and frequency characteristic of compressional Pc 5 waves observed at geostationary orbit

NASA Astrophysics Data System (ADS)

Takahashi, K.; Higbie, P. R.; Baker, D. N.

1985-02-01

Properties of compressional Pc 5 waves as deduced from multiple-satellite observations at geosynchronous orbit are presented. The occurrence characteristics of the waves are determined, and the relation between variations in particle fluxes and magnetic field is examined. The spatiotemporal structure of the waves is considered, including the propagation perpendicular to the ambient magnetic field and the relation of the frequency characteristics to harmonic waves. It is demonstrated that the waves have large azimuthal wave numbers from 40 to 120, westward propagation at a typical velocity of 10 km/s, frequency roughly 25 percent of the second harmonic of the poloidal wave, and phase lag of 180 deg between the parallel and radial components of the wave magnetic field and + or -90 deg between the parallel and azimuthal components. These features are discussed in the light of existing theories of instabilities in the ring current plasma.

Characteristics of shock propagation in high-strength cement mortar

NASA Astrophysics Data System (ADS)

Wang, Zhanjiang; Li, Xiaolan; Zhang, Ruoqi

2001-06-01

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

In-Body to On-Body Ultrawideband Propagation Model Derived From Measurements in Living Animals.

PubMed

Floor, Pål Anders; Chávez-Santiago, Raúl; Brovoll, Sverre; Aardal, Øyvind; Bergsland, Jacob; Grymyr, Ole-Johannes H N; Halvorsen, Per Steinar; Palomar, Rafael; Plettemeier, Dirk; Hamran, Svein-Erik; Ramstad, Tor A; Balasingham, Ilangko

2015-05-01

Ultrawideband (UWB) radio technology for wireless implants has gained significant attention. UWB enables the fabrication of faster and smaller transceivers with ultralow power consumption, which may be integrated into more sophisticated implantable biomedical sensors and actuators. Nevertheless, the large path loss suffered by UWB signals propagating through inhomogeneous layers of biological tissues is a major hindering factor. For the optimal design of implantable transceivers, the accurate characterization of the UWB radio propagation in living biological tissues is indispensable. Channel measurements in phantoms and numerical simulations with digital anatomical models provide good initial insight into the expected path loss in complex propagation media like the human body, but they often fail to capture the effects of blood circulation, respiration, and temperature gradients of a living subject. Therefore, we performed UWB channel measurements within 1-6 GHz on two living porcine subjects because of the anatomical resemblance with an average human torso. We present for the first time, a path loss model derived from these in vivo measurements, which includes the frequency-dependent attenuation. The use of multiple on-body receiving antennas to combat the high propagation losses in implant radio channels was also investigated.

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.

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

NASA Astrophysics Data System (ADS)

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

2014-03-01

An experimental investigation to characterize the properties and highlight the benefits of atmospheric pressure radio-frequency dielectric-barrier discharge (rf DBD) with dielectric electrodes fabricated by anodizing aluminium substrate is presented. The current-voltage characteristics and millisecond images are used to distinguish the 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.

Characterizing cosmic-ray propagation in massive star-forming regions: The case of 30 Doradus and the large Magellanic cloud

DOE PAGES

Murphy, E. J.; Porter, T. A.; Moskalenko, I. V.; ...

2012-04-24

We investigate the propagation characteristics of cosmic-ray (CR) electrons and nuclei in the 30 Doradus (30 Dor) star-forming region in the Large Magellanic Cloud (LMC) using infrared, radio, and γ-ray data and a phenomenological model based on the radio-far-infrared correlation within galaxies. By employing a correlation analysis, we derive an average propagation length of ~100-140 pc for ~3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed γ-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and γ-ray data, wemore » estimate a ~20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for ~3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is ~4 times higher, scaling as (R/GV) δ with δ ≈ 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include ~70 GeV CR nuclei traced by the 3-10 GeV γ-ray data (δ ≈ 0.66 ± 0.23). Using the mean age of the stellar populations in 30 Dor and the results from our correlation analysis, we estimate a diffusion coefficient D R ≈ (0.9-1.0) × 10 27(R/GV) 0.7 cm 2 s –1. We also compare the values of the CR electron propagation length and surface brightness for 30 Dor and the LMC as a whole with those of entire disk galaxies. We find that the trend of decreasing average CR propagation distance with increasing disk-averaged star formation activity holds for the LMC, and extends down to single star-forming regions, at least for the case of 30 Dor.« less

Empirical Modeling of the Statistical Structure of Radio Signals from Satellites Moving over Mid- and High-Latitude Trajectories in the Southern Hemisphere

NASA Astrophysics Data System (ADS)

Fatkullin, M. N.; Solodovnikov, G. K.; Trubitsyn, V. M.

2004-01-01

The results of developing the empirical model of parameters of radio signals propagating in the inhomogeneous ionosphere at middle and high latitudes are presented. As the initial data we took the homogeneous data obtained as a result of observations carried out at the Antarctic ``Molodezhnaya'' station by the method of continuous transmission probing of the ionosphere by signals of the satellite radionavigation ``Transit'' system at coherent frequencies of 150 and 400 MHz. The data relate to the summer season period in the Southern hemisphere of the Earth in 1988-1989 during high (F > 160) activity of the Sun. The behavior of the following statistical characteristics of radio signal parameters was analyzed: (a) the interval of correlation of fluctuations of amplitudes at a frequency of 150 MHz (τkA) (b) the interval of correlation of fluctuations of the difference phase (τkϕ) and (c) the parameter characterizing frequency spectra of amplitude (PA) and phase (Pϕ) fluctuations. A third-degree polynomial was used for modeling of propagation parameters. For all above indicated propagation parameters, the coefficients of the third-degree polynomial were calculated as a function of local time and magnetic activity. The results of calculations are tabulated.

Effects of large-scale irregularities of the ionosphere in the propagation of decametric radio waves

NASA Astrophysics Data System (ADS)

Kerblai, T. S.; Kovalevskaia, E. M.

1985-12-01

A numerical experiment is used to study the simultaneous influence of regular space-time gradients and large-scale traveling ionospheric disturbances (TIDs) as manifested in the angular and Doppler characteristics of decametric-wave propagation. Conditions typical for middle latitudes are chosen as the ionospheric models: conditions under which large-scale TIDs in the F2-layer evolve on the background of winter or equinox structures of the ionosphere. Certain conclusions on the character of TID effects for various states of the background ionosphere are drawn which can be used to interpret experimental results.

Measurement of radio emission from extensive air showers with LOPES

NASA Astrophysics Data System (ADS)

Hörandel, J. R.; Apel, W. D.; Arteaga, J. C.; Asch, T.; Badea, F.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Brüggemann, M.; Buchholz, P.; Buitink, S.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Ender, M.; Engel, R.; Falcke, H.; Finger, M.; Fuhrmann, D.; Gemmeke, H.; Ghia, P. L.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Horneffer, A.; Huege, T.; Isar, P. G.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Krömer, O.; Kuijpers, J.; Lafebre, S.; Link, K.; Łuczak, P.; Ludwig, M.; Mathes, H. J.; Mayer, H. J.; Melissas, M.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Nigl, A.; Oehlschläger, J.; Over, S.; Palmieri, N.; Petcu, M.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F.; Sima, O.; Singh, K.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.; Zensus, J. A.

2011-02-01

A new method is explored to detect extensive air showers: the measurement of radio waves emitted during the propagation of the electromagnetic shower component in the magnetic field of the Earth. Recent results of the pioneering experiment LOPES are discussed. It registers radio signals in the frequency range between 40 and 80 MHz. The intensity of the measured radio emission is investigated as a function of different shower parameters, such as shower energy, angle of incidence, and distance to shower axis. In addition, new antenna types are developed in the framework of LOPESstar and new methods are explored to realize a radio self-trigger algorithm in real time.

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.

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.

A theory of solar type 3 radio bursts

NASA Technical Reports Server (NTRS)

Goldstein, M. L.; Papadopoulos, K.; Smith, R. A.

1979-01-01

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.

Radio Receiver Instrument (RRI) ePOP transionospheric observations from an HF transmitter in Ottawa (45N, 75W)

NASA Astrophysics Data System (ADS)

Hussey, G. C.; Danskin, D. W.; Gillies, R. G.; James, H. G.; Yau, A. W.; Hird, F. C.; Fairbairn, D. T.

2016-12-01

A ground-based HF transmitter operating at 10.422 MHz in Ottawa, Canada (45.4N, 75.6W) was the radio source for reception by the satellite-based Radio Receiver Instrument (RRI) for 5 passes in late April, 2016. The RRI is one of eight instruments on the enhanced Polar Outflow Probe (ePOP) scientific payload portion of the CSA (Canadian Space Agency) CASSIOPE (Cascade Demonstrator Small-Sat and Ionospheric Polar Explorer) satellite mission launched in September, 2013. The crossed-dipole configuration of the RRI allows for complete polarization observations. Initial analysis of the passes indicates reception of a highly polarized signal. South of the transmitter the signal clearly exhibits Faraday rotation of an essentially linearly polarized radio wave in agreement with modeling by Gillies et al. [2007]. This propagation is characterized as quasi-longitudinal (QL) by the Appleton-Hartree equation (electromagnetic wave propagation in a cold magnetized plasma) as the radio waves travel in a direction more along the magnetic field of the Earth. When the satellite moves north of the Ottawa transmitter the radio wave propagation transitions into quasi-transverse (QT). The data indicates favoring circular polarization dependent on the geometry with respect to the transmitter. Surprisingly the Faraday rotation effect is still very pronounced reversing in direction roughly 1000 km north of the transmitter. The model of Gillies et al. [2007] has been extended to explain these observations. This is the first direct observation, by polarimetry, of HF radio wave propagation in near-Earth space plasmas.Gillies, R.G., G.C. Hussey, H.G. James, G.J. Sofko, and D. Andre, Modelling and observation of transionospheric propagation results from ISIS II in preparation for ePOP, Ann. Geophys. 25, 87-97, 2007.

Phase Retrieval for Radio Telescope and Antenna Control

NASA Technical Reports Server (NTRS)

Dean, Bruce

2011-01-01

Phase-retrieval is a general term used in optics to describe the estimation of optical imperfections or "aberrations." The purpose of this innovation is to develop the application of phase retrieval to radio telescope and antenna control in the millimeter wave band. Earlier techniques do not approximate the incoherent subtraction process as a coherent propagation. This approximation reduces the noise in the data and allows a straightforward application of conventional phase retrieval techniques for radio telescope and antenna control. The application of iterative-transform phase retrieval to radio telescope and antenna control is made by approximating the incoherent subtraction process as a coherent propagation. Thus, for systems utilizing both positive and negative polarity feeds, this approximation allows both surface and alignment errors to be assessed without the use of additional hardware or laser metrology. Knowledge of the antenna surface profile allows errors to be corrected at a given surface temperature and observing angle. In addition to imperfections of the antenna surface figure, the misalignment of multiple antennas operating in unison can reduce or degrade the signal-to-noise ratio of the received or broadcast signals. This technique also has application to the alignment of antenna array configurations.

Imaging interplanetary CMEs at radio frequency from solar polar orbit

NASA Astrophysics Data System (ADS)

Wu, Ji; Sun, Weiying; Zheng, Jianhua; Zhang, Cheng; Liu, Hao; Yan, Jingye; Wang, Chi; Wang, Chuanbing; Wang, Shui

2011-09-01

Coronal mass ejections (CMEs) represent a great concentration of mass and energy input into the lower corona. They have come to be recognized as the major driver of physical conditions change in the Sun-Earth system. Consequently, observations of CMEs are important for understanding and ultimately predicting space weather conditions. This paper discusses a proposed mission, the Solar Polar Orbit Radio Telescope (SPORT) mission, which will observe the propagation of interplanetary CMEs to distances of near 0.35 AU from the Sun. The orbit of SPORT is an elliptical solar polar orbit. The inclination angle between the orbit and ecliptic plane should be about 90°. The main payload on board SPORT will be an imaging radiometer working at the meter wavelength band (radio telescope), which can follow the propagation of interplanetary CMEs. The images that are obtained by the radio telescope embody the brightness temperature of the objectives. Due to the very large size required for the antenna aperture of the radio telescope, we adopt interferometric imaging technology to reduce it. Interferometric imaging technology is based on indirect spatial frequency domain measurements plus Fourier transformation. The SPORT spacecraft will also be equipped with a set of optical and in situ measurement instruments such as a EUV solar telescope, a solar wind ion instrument, an energetic particle detector, a magnetometer, a wave detector and a solar radio burst spectrometer.

Radio Frequency Electromagnetic Radiation From Streamer Collisions

NASA Astrophysics Data System (ADS)

Luque, Alejandro

2017-10-01

We present a full electromagnetic model of streamer propagation where the Maxwell equations are solved self-consistently together with electron transport and reactions including photoionization. We apply this model to the collision of counter-propagating streamers in gaps tens of centimeters wide and with large potential differences of hundreds of kilovolts. Our results show that streamer collisions emit electromagnetic pulses that, at atmospheric pressure, dominate the radio frequency spectrum of an extended corona in the range from about 100 MHz to a few gigahertz. We also investigate the fast penetration, after a collision, of electromagnetic fields into the streamer heads and show that these fields are capable of accelerating electrons up to about 100 keV. By substantiating the link between X-rays and high-frequency radio emissions and by describing a mechanism for the early acceleration of runaway electrons, our results support the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges.

Radio Frequency Electromagnetic Radiation From Streamer Collisions.

PubMed

Luque, Alejandro

2017-10-16

We present a full electromagnetic model of streamer propagation where the Maxwell equations are solved self-consistently together with electron transport and reactions including photoionization. We apply this model to the collision of counter-propagating streamers in gaps tens of centimeters wide and with large potential differences of hundreds of kilovolts. Our results show that streamer collisions emit electromagnetic pulses that, at atmospheric pressure, dominate the radio frequency spectrum of an extended corona in the range from about 100 MHz to a few gigahertz. We also investigate the fast penetration, after a collision, of electromagnetic fields into the streamer heads and show that these fields are capable of accelerating electrons up to about 100 keV. By substantiating the link between X-rays and high-frequency radio emissions and by describing a mechanism for the early acceleration of runaway electrons, our results support the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges.

50 CFR 21.30 - Raptor propagation permits.

Code of Federal Regulations, 2012 CFR

2012-10-01

... method to condition raptors. You may hack a raptor that you produce under your propagation permit. (1) You may need permission from your State or tribal wildlife agency to hack a raptor you possess under... hacking is allowed. (2) Any hybrid you hack must have two attached functioning radio transmitters during...

50 CFR 21.30 - Raptor propagation permits.

Code of Federal Regulations, 2014 CFR

2014-10-01

... method to condition raptors. You may hack a raptor that you produce under your propagation permit. (1) You may need permission from your State or tribal wildlife agency to hack a raptor you possess under... hacking is allowed. (2) Any hybrid you hack must have two attached functioning radio transmitters during...

50 CFR 21.30 - Raptor propagation permits.

Code of Federal Regulations, 2013 CFR

2013-10-01

... method to condition raptors. You may hack a raptor that you produce under your propagation permit. (1) You may need permission from your State or tribal wildlife agency to hack a raptor you possess under... hacking is allowed. (2) Any hybrid you hack must have two attached functioning radio transmitters during...

50 CFR 21.30 - Raptor propagation permits.

Code of Federal Regulations, 2011 CFR

2011-10-01

... method to condition raptors. You may hack a raptor that you produce under your propagation permit. (1) You may need permission from your State or tribal wildlife agency to hack a raptor you possess under... hacking is allowed. (2) Any hybrid you hack must have two attached functioning radio transmitters during...

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.

76 FR 29665 - Migratory Bird Permits; Changes in the Regulations Governing Raptor Propagation

Federal Register 2010, 2011, 2012, 2013, 2014

2011-05-23

... hack a raptor that you produce under your propagation permit. (1) You may need permission from your State or tribal wildlife agency to hack a raptor you possess under your propagation permit. Check with... you hack must have two attached functioning radio transmitters during hacking. (3) You may not hack a...

Ionospheric Caustics in Solar Radio Observations

NASA Astrophysics Data System (ADS)

Koval, A.; Chen, Y.; Stanislavsky, A.

2016-12-01

The Earth ionosphere possesses by natural focusing and defocusing effects on radio waves due to presence of variable ionospheric irregularities which could act like convergent and divergent lenses on incident radiation. In particular, the focusing of emission from the Sun was firstly detected on the Nançay Decameter Array dynamic spectra in the 1980s. On time-frequency spectrograms the intensity variations form specific structures different from well-known solar radio bursts and clearly distinguishing on a background of solar radiation. Such structures have been identified as ionospheric caustics (ICs) and considered to be the result of radio waves refraction on medium scale travelling ionospheric disturbances (MSTIDs). Although nowadays the ICs are registered by different radio observatories due to augmentation of low-frequency radio telescopes, the most recent papers devoted to ICs in solar radio records date back to the 1980s. In this study, we revisit the ICs issue with some new results by conducting a statistical analysis of occurrence rate of ICs in solar dynamic spectra in meter-decameter wavelength range for long continuous period (15 years). The seasonal variations in ICs appearance have been found for the first time. Besides, we report the possible solar cycle dependence of ICs emergence. The radio waves propagation in the ionosphere comprising MSTIDs will be considered. The present research renews the subject of ICs in the low-frequency solar radio astronomy after about 35-year letup.

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.

Amplitude and Phase Characteristics of Signals at the Output of Spatially Separated Antennas for Paths with Scattering

NASA Astrophysics Data System (ADS)

Anikin, A. S.

2018-06-01

Conditional statistical characteristics of the phase difference are considered depending on the ratio of instantaneous output signal amplitudes of spatially separated weakly directional antennas for the normal field model for paths with radio-wave scattering. The dependences obtained are related to the physical processes on the radio-wave propagation path. The normal model parameters are established at which the statistical characteristics of the phase difference depend on the ratio of the instantaneous amplitudes and hence can be used to measure the phase difference. Using Shannon's formula, the amount of information on the phase difference of signals contained in the ratio of their amplitudes is calculated depending on the parameters of the normal field model. Approaches are suggested to reduce the shift of phase difference measured for paths with radio-wave scattering. A comparison with results of computer simulation by the Monte Carlo method is performed.

Propagation characteristic of THz wave in camouflage net material

NASA Astrophysics Data System (ADS)

Dong, Hailong; Wang, Jiachun; Chen, Zongsheng; Lin, Zhidan; Zhao, Dapeng; Liu, Ruihuang

2017-10-01

Terahertz (THz) radar system, with excellent potentials such as high-resolution and strong penetration capability, is promising in the field of anti-camouflage. Camouflage net is processed by cutting the camouflage net material, which is fabricated on pre-processing substrate by depositing coatings with camouflage abilities in different bands, such as visible, infrared and radar. In this paper, we concentrate on the propagation characteristic of THz wave in camouflage net material. Firstly, function and structure of camouflage net were analyzed. Then the advantage and appliance of terahertz time-domain spectroscopy (THz-TDS) was introduced. And the relevant experiments were conducted by utilizing THz-TDS. The results obtained indicate that THz wave has better penetration capacity in camouflage net material, which demonstrates the feasibility of using THz radar to detect those targets covered with camouflage net.

Measurements on wave propagation characteristics of spiraling electron beams

NASA Technical Reports Server (NTRS)

Singh, A.; Getty, W. D.

1976-01-01

Dispersion characteristics of cyclotron-harmonic waves propagating on a neutralized spiraling electron beam immersed in a uniform axial magnetic field are studied experimentally. The experimental setup consisted of a vacuum system, an electron-gun corkscrew assembly which produces a 110-eV beam with the desired delta-function velocity distribution, a measurement region where a microwave signal is injected onto the beam to measure wavelengths, and a velocity analyzer for measuring the axial electron velocity. Results of wavelength measurements made at beam currents of 0.15, 1.0, and 2.0 mA are compared with calculated values, and undesirable effects produced by increasing the beam current are discussed. It is concluded that a suitable electron beam for studies of cyclotron-harmonic waves can be generated by the corkscrew device.

Higher order contribution to the propagation characteristics of low frequency transverse waves in a dusty plasma

NASA Astrophysics Data System (ADS)

Misra, A. P.; Chowdhury, A. Roy; Paul, S. N.

2004-09-01

Characteristic features of low frequency transverse wave propagating in a magnetised dusty plasma have been analysed considering the effect of dust-charge fluctu- ation. The distinctive behaviours of both the left circularly polarised and right circularly polarised waves have been exhibited through the analysis of linear and non-linear disper- sion relations. The phase velocity, group velocity, and group travel time for the waves have been obtained and their propagation characteristics have been shown graphically with the variations of wave frequency, dust density and amplitude of the wave. The change in non-linear wave number shift and Faraday rotation angle have also been exhibited with respect to the plasma parameters. It is observed that the effects of dust particles are significant only when the higher order contributions are considered. This may be referred to as the `dust regime' in plasma.

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.

Four Decades of Space-Borne Radio Sounding

NASA Technical Reports Server (NTRS)

Benson, Robert F.

2010-01-01

A review is given of the 38 rocket, satellite, and planetary payloads dedicated to ionospheric/magnetospheric radio sounding since 1961. Between 1961 and 1995, eleven sounding-rocket payloads from four countries evolved from proof-of-concept flights to sophisticated instruments. Some involved dual payloads, with the sounder transmitter on one and the sounder receiver on the other. The rocket sounders addressed specific space-plasma-wave questions, and provided improved measurements of ionospheric electron-density (N(sub e)) field-aligned irregularities (FAI). Four countries launched 12 ionospheric topside-sounder satellites between 1962 and 1994, and an ionospheric sounder was placed on the Mir Space Station in 1998. Eleven magnetospheric radio sounders, most of the relaxation type, were launched from 1977 to 2000. The relaxation sounders used low-power transmitters, designed to stimulate plasma resonances for accurate local Ne determinations. The latest magnetospheric sounder designed for remote sensing incorporated long antennas and digital signal processing techniques to overcome the challenges posed by low Ne values and large propagation distances. Three radio sounders from three countries were included on payloads to extraterrestrial destinations from 1990 to 2003. The scientific accomplishments of space-borne radio sounders included (1) a wealth of global N(sub e) information on the topside ionosphere and magnetosphere, based on vertical and magnetic-field-aligned N(sub e) profiles; (2) accurate in-situ N(sub e) values, even under low-density conditions; and (3) fundamental advances in our understanding of the excitation and propagation of plasma waves, which have even led to the prediction of a new plasma-wave mode.

Characterization of HF Propagation for Digital Audio Broadcasting

NASA Technical Reports Server (NTRS)

Vaisnys, Arvydas

1997-01-01

The purpose of this presentation is to give a brief overview of some propagation measurements in the Short Wave (3-30 MHz) bands, made in support of a digital audio transmission system design for the Voice of America. This task is a follow on to the Digital Broadcast Satellite Radio task, during which several mitigation techniques would be applicable to digital audio in the Short Wave bands as well, in spite of the differences in propagation impairments in these two bands. Two series of propagation measurements were made to quantify the range of impairments that could be expected. An assessment of the performance of a prototype version of the receiver was also made.

Solitonic characteristics of Airy beam nonlinear propagation

NASA Astrophysics Data System (ADS)

Bouchet, Thomas; Marsal, Nicolas; Sciamanna, Marc; Wolfersberger, Delphine

2018-05-01

We analyze the nonlinear propagation of a one-dimensional Airy beam. Under nonlinear focusing conditions, the Airy beam splits into a weak accelerating structure and a beam that has been named an "off-shooting soliton." Experimental measurements and numerical results related to the off-shooting Airy beam are compared to soliton theoretical profiles and a good agreement is found in terms of transverse shape, width, and amplitude. We identify the different parameters to generate an Airy beam off-shooting soliton and demonstrate that its profile is also preserved through propagation over long distances.

Static current-voltage characteristics for radio-frequency induction discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 ofmore » 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.« less

Propagation characteristics of pulverized coal and gas two-phase flow during an outburst.

PubMed

Zhou, Aitao; Wang, Kai; Fan, Lingpeng; Tao, Bo

2017-01-01

Coal and gas outbursts are dynamic failures that can involve the ejection of thousands tons of pulverized coal, as well as considerable volumes of gas, into a limited working space within a short period. The two-phase flow of gas and pulverized coal that occurs during an outburst can lead to fatalities and destroy underground equipment. This article examines the interaction mechanism between pulverized coal and gas flow. Based on the role of gas expansion energy in the development stage of outbursts, a numerical simulation method is proposed for investigating the propagation characteristics of the two-phase flow. This simulation method was verified by a shock tube experiment involving pulverized coal and gas flow. The experimental and simulated results both demonstrate that the instantaneous ejection of pulverized coal and gas flow can form outburst shock waves. These are attenuated along the propagation direction, and the volume fraction of pulverized coal in the two-phase flow has significant influence on attenuation of the outburst shock wave. As a whole, pulverized coal flow has a negative impact on gas flow, which makes a great loss of large amounts of initial energy, blocking the propagation of gas flow. According to comparison of numerical results for different roadway types, the attenuation effect of T-type roadways is best. In the propagation of shock wave, reflection and diffraction of shock wave interact through the complex roadway types.

Propagation characteristics of pulverized coal and gas two-phase flow during an outburst

PubMed Central

Zhou, Aitao; Wang, Kai; Fan, Lingpeng; Tao, Bo

2017-01-01

Coal and gas outbursts are dynamic failures that can involve the ejection of thousands tons of pulverized coal, as well as considerable volumes of gas, into a limited working space within a short period. The two-phase flow of gas and pulverized coal that occurs during an outburst can lead to fatalities and destroy underground equipment. This article examines the interaction mechanism between pulverized coal and gas flow. Based on the role of gas expansion energy in the development stage of outbursts, a numerical simulation method is proposed for investigating the propagation characteristics of the two-phase flow. This simulation method was verified by a shock tube experiment involving pulverized coal and gas flow. The experimental and simulated results both demonstrate that the instantaneous ejection of pulverized coal and gas flow can form outburst shock waves. These are attenuated along the propagation direction, and the volume fraction of pulverized coal in the two-phase flow has significant influence on attenuation of the outburst shock wave. As a whole, pulverized coal flow has a negative impact on gas flow, which makes a great loss of large amounts of initial energy, blocking the propagation of gas flow. According to comparison of numerical results for different roadway types, the attenuation effect of T-type roadways is best. In the propagation of shock wave, reflection and diffraction of shock wave interact through the complex roadway types. PMID:28727738

EclipseMob: Results from a nation-wide citizen science experiment on the effects of the 2017 Solar Eclipse on Low-frequency (LF) Radio Propagation

NASA Astrophysics Data System (ADS)

Liles, W. C.; Lukes, L.; Nelson, J.; Henry, J.; Oputa, J.; Kerby-Patel, K. C.

2017-12-01

Early experiments to study the effects of a solar eclipse on radio wave propagation were done with either a limited number of sites before any theory of the ionosphere had been confirmed or involved collecting data that proved to be unusable because submissions were missing critical information such as date, time or location. This study used the 2017 solar eclipse over the continental U.S. to conduct the first wide-area (across the U.S.) low-frequency (LF) propagation study. The data collection process was crowdsourced through the engagement of students/educators, citizens, ham radio enthusiasts, and the scientific community. In order to accomplish data collection by geographically dispersed citizen scientists, the EclipseMob team designed and shared a low cost, low tool/skill DIY receiver system to collect LF data that leveraged existing cell phone technology and made the experiment more accessible to students and people with no prior experience constructing electronic systems. To support engagement, in addition to web guides (eclipsemob..org), EclipseMob supplied 150 DIY kits and provided build/Q&A webinars and events. For the experiment, participants constructed a simple receiver system consisting of a homemade antenna, a simple homemade receiver to convert the radio frequency (RF) signals to audio frequencies, and a smart phone app. Before, during, and after the eclipse, participants used their receiver systems to record transmitter signal data from WWVB located near Fort Collins, Colorado on 60.000 kHz (a U.S. frequency standard that is operated by NIST and transmits time codes). A second frequency, 55.500 kHz transmitted by a LF station in Dixon, CA was also used. By using the time, date and location features of the smart phone, the problems experienced in earlier experiments could be minimized. By crowdsourcing the observation sites across the U.S., data from a number of different short, medium and long- paths could be obtained as the total eclipse crossed

Interplanetary Radio Transmission Through Serial Ionospheric and Material Barriers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fields, David; Kennedy, Robert G; Roy, Kenneth I

2013-01-01

A usual first principle in planning radio astronomy observations from the earth is that monitoring must be carried out well above the ionospheric plasma cutoff frequency (~5 MHz). Before space probes existed, radio astronomy was almost entirely done above 6 MHz, and this value is considered a practical lower limit by most radio astronomers. Furthermore, daytime ionization (especially D-layer formation) places additional constraints on wave propagation, and waves of frequency below 10-20 MHz suffer significant attenuation. More careful calculations of wave propagation through the earth s ionosphere suggest that for certain conditions (primarily the presence of a magnetic field) theremore » may be a transmission window well below this assumed limit. Indeed, for receiving extraterrestrial radiation below the ionospheric plasma cutoff frequency, a choice of VLF frequency appears optimal to minimize loss. The calculation, experimental validation, and conclusions are presented here. This work demonstrates the possibility of VLF transmission through the ionosphere and various subsequent material barriers. Implications include development of a new robust communications channel, communications with submerged or subterranean receivers / instruments on or offworld, and a new approach to SETI.« less

A general method for radio spectrum efficiency defining

NASA Astrophysics Data System (ADS)

Ramadanovic, Ljubomir M.

1986-08-01

A general method for radio spectrum efficiency defining is proposed. Although simple it can be applied to various radio services. The concept of spectral elements, as information carriers, is introduced to enable the organization of larger spectral spaces - radio network models - characteristic for a particular radio network. The method is applied to some radio network models, concerning cellular radio telephone systems and digital radio relay systems, to verify its unified approach capability. All discussed radio services operate continuously.

A database for propagation models

NASA Technical Reports Server (NTRS)

Kantak, Anil V.; Suwitra, Krisjani; Le, Choung

1993-01-01

The NASA Propagation Program supports academic research that models various propagation phenomena in the space research frequency bands. NASA supports such research via school and institutions prominent in the field. The products of such efforts are particularly useful for researchers in the field of propagation phenomena and telecommunications systems engineers. The systems engineer usually needs a few propagation parameter values for a system design. Published literature on the subject, such as the Cunsultative Committee for International Radio (CCIR) publications, may help somewhat, but often times, the parameter values given in such publications use a particular set of conditions which may not quite include the requirements of the system design. The systems engineer must resort to programming the propagation phenomena model of interest and to obtain the parameter values to be used in the project. Furthermore, the researcher in the propagation field must then program the propagation models either to substantiate the model or to generate a new model. The researcher or the systems engineer must either be a skillful computer programmer or hire a programmer, which of course increases the cost of the effort. An increase in cost due to the inevitable programming effort may seem particularly inappropriate if the data generated by the experiment is to be used to substantiate the already well-established models, or a slight variation thereof. To help researchers and the systems engineers, it was recommended by the participants of NASA Propagation Experimenters (NAPEX) 15 held in London, Ontario, Canada on 28-29 June 1991, that propagation software should be constructed which will contain models and prediction methods of most propagation phenomenon. Moreover, the software should be flexible enough for the user to make slight changes to the models without expending a substantial effort in programming.

Analysis of an Interplanetary Coronal Mass Ejection by a Spacecraft Radio Signal: A Case Study

NASA Astrophysics Data System (ADS)

Molera Calvés, G.; Kallio, E.; Cimo, G.; Quick, J.; Duev, D. A.; Bocanegra Bahamón, T.; Nickola, M.; Kharinov, M. A.; Mikhailov, A. G.

2017-11-01

Tracking radio communication signals from planetary spacecraft with ground-based telescopes offers the possibility to study the electron density and the interplanetary scintillation of the solar wind. Observations of the telemetry link of planetary spacecraft have been conducted regularly with ground antennae from the European Very Long Baseline Interferometry Network, aiming to study the propagation of radio signals in the solar wind at different solar elongations and distances from the Sun. We have analyzed the Mars Express spacecraft radio signal phase fluctuations while, based on a 3-D heliosphere plasma simulation, an interplanetary coronal mass ejection (ICME) crossed the radio path during one of our observations on 6 April 2015. Our measurements showed that the phase scintillation indices increased by a factor of 4 during the passage of the ICME. The method presented here confirms that the phase scintillation technique based on spacecraft signals provides information of the properties and propagation of the ICMEs in the heliosphere.

3D relativistic MHD numerical simulations of X-shaped radio sources

NASA Astrophysics Data System (ADS)

Rossi, P.; Bodo, G.; Capetti, A.; Massaglia, S.

2017-10-01

Context. A significant fraction of extended radio sources presents a peculiar X-shaped radio morphology: in addition to the classical double lobed structure, radio emission is also observed along a second axis of symmetry in the form of diffuse wings or tails. In a previous investigation we showed the existence of a connection between the radio morphology and the properties of the host galaxies. Motivated by this connection we performed two-dimensional numerical simulations showing that X-shaped radio sources may naturally form as a jet propagates along the major axis a highly elliptical density distribution, because of the fast expansion of the cocoon along the minor axis of the distribution. Aims: We intend to extend our analysis by performing three-dimensional numerical simulations and investigating the role of different parameters in determining the formation of the X-shaped morphology. Methods: The problem is addressed by numerical means, carrying out three-dimensional relativistic magnetohydrodynamic simulations of bidirectional jets propagating in a triaxial density distribution. Results: We show that only jets with power ≲ 1044 erg s-1 can give origin to an X-shaped morphology and that a misalignment of 30° between the jet axis and the major axis of the density distribution is still favourable to the formation of this kind of morphology. In addition we compute synthetic radio emission maps and polarization maps. Conclusions: In our scenario for the formation of X-shaped radio sources only low power FRII can give origin to such kind of morphology. Our synthetic emission maps show that the different observed morphologies of X-shaped sources can be the result of similar structures viewed under different perspectives.

Detection of Propagating Fast Sausage Waves through a Detailed Analysis of a Zebra Pattern Fine Structure in a Solar Radio Burst

NASA Astrophysics Data System (ADS)

Kaneda, K.; Misawa, H.; Iwai, K.; Masuda, S.; Tsuchiya, F.; Katoh, Y.; Obara, T.

2017-12-01

Recent observations have revealed that various modes of magnetohydrodynamic (MHD) waves are ubiquitous in the corona. In imaging observations in EUV, propagating fast magnetoacoustic waves are difficult to observe due to the lack of time resolution. Quasi-periodic modulation of radio fine structures is an important source of information on these MHD waves. Zebra patterns (ZPs) are one of such fine structures in type IV bursts, which consist of several parallel stripes superimposed on the background continuum. Although the generation mechanism of ZPs has been discussed still, the most favorable model of ZPs is so-called double plasma resonance (DPR) model. In the DPR model, the frequency separation between the adjacent stripes (Δf) is determined by the plasma density and magnetic field in their source. Hence, the variation of Δf in time and frequency represents the disturbance in their source region in the corona. We report the detection of propagating fast sausage waves through the analysis of a ZP event on 2011 June 21. The variation of Δf in time and frequency was obtained using highly resolved spectral data from the Assembly of Metric-band Aperture Telescope and Real-time Analysis System (AMATERAS). We found that Δf increases with the increase of emission frequency as a whole, which is consistent with the DPR model. Furthermore, we also found that irregularities in Δf are repetitively drifting from the high frequency side to the low frequency side. Their frequency drift rate was 3 - 8 MHz/s and the repetitive frequency was several seconds. Assuming the ZP generation by the DPR model, the drifting irregularities in Δf correspond to propagating disturbances in plasma density and magnetic field with speeds of 3000 - 8000 km/s. Taking account of these facts, the observed modulations in Δf can be explained by fast sausage waves propagating through the corona. We will also discuss the plasma conditions in the corona estimated from the observational results.

Imaging Interplanetary CMEs at Radio Frequency From Solar Polar Orbit

NASA Astrophysics Data System (ADS)

Wu, Ji; Sun, Weiying; Zheng, Jianhua; Zhang, Cheng; Wang, Chi; Wang, C. B.; Wang, S.

Coronal mass ejections (CMEs) are violent discharges of plasma and magnetic fields from the Sun's corona. They have come to be recognized as the major driver of physical conditions in the Sun-Earth system. Consequently, the detection of CMEs is important for un-derstanding and ultimately predicting space weather conditions. The Solar Polar Orbit Radio Telescope (SPORT) is a proposed mission to observe the propagation of interplanetary CMEs from solar polar orbit. The main payload (radio telescope) on board SPORT will be an in-terferometric imaging radiometer working at the meter wavelength band, which will follow the propagation of interplanetary CMEs from a distance of a few solar radii to near 1 AU from solar polar orbit. The SPORT spacecraft will also be equipped with a set of optical and in situ measurement instruments such as a EUV solar telescope, a solar wind plasma experiment, a solar wind ion composition instrument, an energetic particle detector, a wave detector, a mag-netometer and an interplanetary radio burst tracker. In this paper, we first describe the current shortage of interplanetary CME observations. Next, the scientific motivation and objectives of SPORT are introduced. We discuss the basic specifications of the main radio telescope of SPORT with reference to the radio emission mechanisms and the radio frequency band to be observed. Finally, we discuss the key technologies of the SPORT mission, including the con-ceptual design of the main telescope, the image retrieval algorithm and the solar polar orbit injection. Other payloads and their respective observation objectives are also briefly discussed. Key words: Interplanetary CMEs; Interferometric imaging; Solar polar orbit; Radiometer.

Characteristics of the anomalous refractive conditions in Nigeria

NASA Astrophysics Data System (ADS)

Emmanuel, I.; Adeyemi, B.; Ogolo, E. O.; Adediji, A. T.

2017-11-01

The thirty six years (1979-2014) meteorological data needed to calculate refractivity gradient is obtained from Era interim build on IFS CY31r2 model. Diurnal cycle of ducting occurrence for four seasons in Nigeria were analysed from refractivity gradient. Percentage occurrence of anomalous propagation in thirty locations across Nigeria were estimated. It is discovered that ducting is more frequent at mid night and early morning which also vary seasonally and regionally across the country. Highest percentage of 94 % of ducting and zero occurrence of sub refractive is obtained in Lagos. Highest percentage of 34.24 % and 45.62 % of super refractive and sub refractive are obtained in Sapele and Oban hill, respectively. Minimum percentage of 21.9 % and 4.33 % of ducting and super refractive were obtained for Calabar and Gashua, respectively. The minimum frequency for a radio wave to be trapped within Nigeria troposphere varies between 0.045 GHz and 0.11 GHz. The occurrence of anomalous propagation condition, such as ducts, super refractive and sub refractive provide valuable information about the propagation of radio waves over Nigeria, which will assist the radio engineer in their planning and designing of radio circuitry.

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.

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

NASA Technical Reports Server (NTRS)

Revelle, D. O.

1976-01-01

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

VHF electromagnetic wave propagation

NASA Astrophysics Data System (ADS)

Gole, P.

Theoretical and experimental study of large-scale VHF propagation characteristics is presented. Certain phenomena that are difficult to model, such as the effects of ground near the antenna, are examined from a purely experimental point of view. The characteristics of electromagnetic waves over a spherical surface and through a medium having a certain refractive index, such as is the case for waves propagated over the earth's surface, are analytically described. Two mathematical models are used, one for the case of the receiver being within the radioelectric horizon of the transmitter and the other for when it is not. Propagation phenomena likely to increase the false alarm probability of an air surveillance radar are briefly considered.

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.

Propagation of a radio-frequency pulsed signal over the Earth. The JOLLY programs

NASA Astrophysics Data System (ADS)

Carroll, D.; Detch, J. L.; Malik, J.

1983-07-01

The interpretation of observed radioflash/electromagnetic pulse (emp) observed signals from nuclear detonations in terms of theoretical models or extrapolation to signals expected at military systems involves correction for ground-wave propagation effects. For most applications, previously developed programs have been adequate. There have been problems when these techniques have been tried for situations in the near tangent regime where a considerable concern exists. It has been found that the problem of predicting propagation response functions in the near tangent regime has been the inconsistent derivation of the equations. Resolution of this problem has evolved into a program to better predict ground-wave propagation. The description of the method and detailed description of the programs are described for both propagation over realistic earth and sea-water paths. Results can be given in terms of amplitude and phase as a function of the frequency or as amplitude versus time, the usual Green's or resolution function.

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.

ULF radio monitoring network in a seismic area

NASA Astrophysics Data System (ADS)

Toader, Victorin; Moldovan, Iren-Adelina; Ionescu, Constantin; Marmureanu, Alexandru

2017-04-01

ULF monitoring is a part of a multidisciplinary network (AeroSolSys) located in Vrancea (Curvature Carpathian Mountains). Four radio receivers (100 kHz - microwave) placed on faults in a high seismic area characterized by deep earthquakes detect fairly weak radio waves. The radio power is recorded in correlation with many other parameters related to near surface low atmosphere phenomena (seismicity, solar radiation, air ionization, electromagnetic activity, radon, CO2 concentration, atmospheric pressure, telluric currents, infrasound, seismo-acoustic emission, meteorological information). We follow variations in the earth's surface propagate radio waves avoiding reflection on ionosphere. For this reason the distance between stations is less than 60 km and the main source of emission is near (Bod broadcasting transmitter for long- and medium-wave radio, next to Brasov city). In the same time tectonic stress affects the radio propagation in air and it could generates ULF waves in ground (LAI coupling). To reduce the uncertainty is necessary to monitor a location for extended periods of time to outline local and seasonal fluctuations. Solar flares do not affect seismic activity but they produce disturbances in telecommunications networks and power grids. Our ULF monitoring correlated with two local magnetometers does not indicate this so far with our receivers. Our analysis was made during magnetic storms with Kp 7 and 8 according to NOAA satellites. To correlate the results we implemented an application that monitors the satellite EUTELSAT latency compared to WiMAX land communication in the same place. ULF band radio monitoring showed that our receiver is dependent on temperature and that it is necessary to introduce a band pass filter in data analysis. ULF data acquisition is performed by Kinemetrics and National Instruments digitizers with a sampling rate of 100 Hz in Miniseed format and then converted into text files with 1 Hz rate for analysis in very low

Transequatorial Propagation and Depletion Precursors

NASA Astrophysics Data System (ADS)

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

2014-12-01

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

Radio Occultation Experiments with Venus Express and Mars Express using the Planetary Radio Interferometry and Doppler Experiment (PRIDE) Technique

NASA Astrophysics Data System (ADS)

Bocanegra Bahamon, T.; Gurvits, L.; Molera Calves, G.; Cimo, G.; Duev, D.; Pogrebenko, S.; Dirkx, D.; Rosenblatt, P.

2017-12-01

The Planetary Radio Interferometry and Doppler Experiment (PRIDE) is a technique that can be used to enhance multiple radio science experiments of planetary missions. By 'eavesdropping' on the spacecraft signal using radio telescopes from different VLBI networks around the world, the PRIDE technique provides precise open-loop Doppler and VLBI observables to able to reconstruct the spacecraft's orbit. The application of this technique for atmospheric studies has been assessed by observing ESA's Venus Express (VEX) and Mars Express (MEX) during multiple Venus and Mars occultation events between 2012 and 2014. From these observing sessions density, temperature and pressure profiles of Venus and Mars neutral atmosphere and ionosphere have been retrieved. We present an error propagation analysis where the uncertainties of the atmospheric properties measured with this technique have been derived. These activities serve as demonstration of the applicability of the PRIDE technique for radio occultation studies, and provides a benchmark against the traditional Doppler tracking provided by the NASA's DSN and ESA's Estrack networks for these same purposes, in the framework of the upcoming ESA JUICE mission to the Jovian system.

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.

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

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.

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

Atmospheric Models for Over-Ocean Propagation Loss

DTIC Science & Technology

2015-05-15

Atmospheric Models For Over-Ocean Propagation Loss Bruce McGuffin1 MIT Lincoln Laboratory Introduction Air -to-surface radio links differ from...from radiosonde profiles collected along the Atlantic coast of the United States, in order to accurately estimate high-reliability SHF/EHF air -to...predict required link performance to achieve high reliability at different locations and times of year. Data Acquisition Radiosonde balloons are

Analysis of heating, ventilation, and air conditioning ducts as a radio frequency communication channel

NASA Astrophysics Data System (ADS)

Nikitin, Pavel Viktorovich

2002-01-01

A typical HVAC duct system is a network of interconnected hollow metal pipes which can serve as waveguides and carry electromagnetic waves. This work presents an analysis of this system as a radio frequency communication channel. Two main parts of the analysis include channel modelling and antenna design. The propagation modelling approach used here is based on the waveguide mode theory and employs the transfer matrix method to describe propagation through various cascaded HVAC elements. This allows one to model the channel response in the frequency domain. Impulse response characteristics of the ducts are also analyzed in this work. The approximate transfer matrices of cylindrical straight sections, bends, and tapers are derived analytically. The transforming properties of cylindrical T-junctions are analyzed experimentally. Antenna designs in waveguides and free-space are different. In waveguides, mode excitation characteristics are important as well as the impedance match. The criteria for antenna design in waveguides are presented here. Antennas analyzed in this work are monopole antennas, dipole antennas, and antenna arrays. The developed model can predict both channel response and antenna characteristics for a given geometry and dimensions of the duct system and the antennas. The model is computationally efficient and can potentially be applied to duct systems of multiple story buildings. The accuracy of the model has been validated with extensive experimental measurements on real HVAC ducts.

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.

The 40 and 50 GHz propagation experiments at the Rutherford Appleton Laboratory, UK, using the ITALSAT beacons

NASA Technical Reports Server (NTRS)

Woodroffe, J. M.; Davies, P. G.; Ladd, D. N.; Norbury, John R.

1994-01-01

This paper describes the current experimental program and future plans for the reception of transmissions from the 18.7, 39.6, and 49.5 GHz beacons from the ITALSAT satellite by the Radio Communications Research Unit at Rutherford Appleton Laboratory, UK. The Radio Communications Research Unit, which has had considerable experience in developing experimental millimetric equipment for propagation studies, has initiated the development of a single-channel receiver and a triple-channel receiver to measure propagation effects at 49.5 GHz and 39.6 GHz respectively. The initial location of the receivers will be at Chilbolton, Hampshire, UK.

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.

Radio Frequency Compatibility of an RFID Tag on Glideslope Navigation Receivers

NASA Technical Reports Server (NTRS)

Nguyen, Truong X.; Mielnik, John J.

2008-01-01

A process is demonstrated to show compatibility between a radio frequency identification (RFID) tag and an aircraft glideslope (GS) radio receiver. The particular tag chosen was previously shown to have significant peak spurious emission levels that far exceeded the emission limits in the GS aeronautical band. The spurious emissions are emulated in the study by capturing the RFID fundamental transmission and playing back the signal in the GS band. The signal capturing and playback are achieved with a vector signal generator and a spectrum analyzer that can output the in-phase and quadrature components (IQ). The simulated interference signal is combined with a desired GS signal before being injected into a GS receiver s antenna port for interference threshold determination. Minimum desired propagation loss values to avoid interference are then computed and compared against actual propagation losses for several aircraft.

Radio Frequency Compatibility of an RFID Tag on Glideslope Navigation Receivers

NASA Technical Reports Server (NTRS)

Nguyen, Truong X.; Mielnik, John J.

2008-01-01

A process is demonstrated to show compatibility between a radio frequency identification (RFID) tag and an aircraft glideslope (GS) radio r eceiver. The particular tag chosen was previously shown to have significant spurious emission levels that exceeded the emission limit in th e GS aeronautical band. The spurious emissions are emulated in the study by capturing the RFID fundamental transmission and playing back th e signal in the GS band. The signal capturing and playback are achiev ed with a vector signal generator and a spectrum analyzer that can output the in-phase and quadrature components (IQ). The simulated interf erence signal is combined with a GS signal before being injected into a GS receiver#s antenna port for interference threshold determination . Minimum desired propagation loss values to avoid interference are then computed and compared against actual propagation losses for severa l aircraft.

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.

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.

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.

Theoretical analysis of SAW propagation characteristics in (100) oriented AlN/diamond structure.

PubMed

Ro, Ruyen; Chiang, Yuan-Feng; Sung, Chia-Chi; Lee, Ruyue; Wu, Sean

2010-01-01

In this study, the finite element method is employed to calculate SAW characteristics in (100) AlN/diamond based structures with different electrical interfaces; i.e., IDT/ AlN/diamond, AlN/IDT/diamond, IDT/AlN/thin metal film/ diamond, and thin metal film/AlN/IDT/diamond. The effects of Cu and Al electrodes as well as the thickness of electrode on phase velocity, coupling coefficient, and reflectivity of SAWs are illustrated. Propagation characteristics of SAWs in (002) AlN/diamond-based structures are also presented for comparison. Simulation results show that to retain a large reflectivity for the design of RF filters and duplexers, the Cu IDT/(100) AlN/diamond structure possesses the highest phase velocity and largest coupling coefficient at the smallest AlN film thickness- to-wavelength ratio.

HF Propagation Effects Caused by an Artificial Plasma Cloud in the Ionosphere

NASA Astrophysics Data System (ADS)

Joshi, D. R.; Groves, K. M.; McNeil, W. J.; Caton, R. G.; Parris, R. T.; Pedersen, T. R.; Cannon, P. S.; Angling, M. J.; Jackson-Booth, N. K.

2014-12-01

In a campaign carried out by the NASA sounding rocket team, the Air Force Research Laboratory (AFRL) launched two sounding rockets in the Kwajalein Atoll, Marshall Islands, in May 2013 known as the Metal Oxide Space Cloud (MOSC) experiment to study the interactions of artificial ionization and the background plasma and measure the effects on high frequency (HF) radio wave propagation. The rockets released samarium metal vapor in the lower F-region of the ionosphere that ionized forming a plasma cloud that persisted for tens of minutes to hours in the post-sunset period. Data from the experiments has been analyzed to understand the impacts of the artificial ionization on HF radio wave propagation. Swept frequency HF links transiting the artificial ionization region were employed to produce oblique ionograms that clearly showed the effects of the samarium cloud. Ray tracing has been used to successfully model the effects of the ionized cloud. Comparisons between observations and modeled results will be presented, including model output using the International Reference Ionosphere (IRI), the Parameterized Ionospheric Model (PIM) and PIM constrained by electron density profiles measured with the ALTAIR radar at Kwajalein. Observations and modeling confirm that the cloud acted as a divergent lens refracting energy away from direct propagation paths and scattering energy at large angles relative to the initial propagation direction. The results confirm that even small amounts of ionized material injected in the upper atmosphere can result in significant changes to the natural propagation environment.

Constraints on cosmic ray propagation in the galaxy

NASA Technical Reports Server (NTRS)

Cordes, James M.

1992-01-01

The goal was to derive a more detailed picture of magnetohydrodynamic turbulence in the interstellar medium and its effects on cosmic ray propagation. To do so, radio astronomical observations (scattering and Faraday rotation) were combined with knowledge of solar system spacecraft observations of MHD turbulence, simulations of wave propagation, and modeling of the galactic distribution to improve the knowledge. A more sophisticated model was developed for the galactic distribution of electron density turbulence. Faraday rotation measure data was analyzed to constrain magnetic field fluctuations in the ISM. VLBI observations were acquired of compact sources behind the supernova remnant CTA1. Simple calculations were made about the energies of the turbulence assuming a direct link between electron density and magnetic field variations. A simulation is outlined of cosmic ray propagation through the galaxy using the above results.

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.

Fine Structures of Solar Radio Type III Bursts and Their Possible Relationship with Coronal Density Turbulence

NASA Astrophysics Data System (ADS)

Chen, Xingyao; Kontar, Eduard P.; Yu, Sijie; Yan, Yihua; Huang, Jing; Tan, Baolin

2018-03-01

Solar radio type III bursts are believed to be the most sensitive signatures of near-relativistic electron beam propagation in the corona. A solar radio type IIIb-III pair burst with fine frequency structures, observed by the Low Frequency Array (LOFAR) with high temporal (∼10 ms) and spectral (12.5 kHz) resolutions at 30–80 MHz, is presented. The observations show that the type III burst consists of many striae, which have a frequency scale of about 0.1 MHz in both the fundamental (plasma) and the harmonic (double plasma) emission. We investigate the effects of background density fluctuations based on the observation of striae structure to estimate the density perturbation in the solar corona. It is found that the spectral index of the density fluctuation spectrum is about ‑1.7, and the characteristic spatial scale of the density perturbation is around 700 km. This spectral index is very close to a Kolmogorov turbulence spectral index of ‑5/3, consistent with a turbulent cascade. This fact indicates that the coronal turbulence may play the important role of modulating the time structures of solar radio type III bursts, and the fine structure of radio type III bursts could provide a useful and unique tool to diagnose the turbulence in the solar corona.

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.

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.

HamSCI: The Ham Radio Science Citizen Investigation

NASA Astrophysics Data System (ADS)

Frissell, N. A.; Moses, M. L.; Earle, G. D.; McGwier, R. W.; Miller, E. S.; Kaeppler, S. R.; Silver, H. W.; Ceglia, F.; Pascoe, D.; Sinanis, N.; Smith, P.; Williams, R.; Shovkoplyas, A.; Gerrard, A. J.

2016-12-01

Amateur (or "ham") radio operators are individuals with a non-pecuniary interest in radio technology, engineering, communications, science, and public service. They are licensed by their national governments to transmit on amateur radio frequencies. In many jurisdictions, there is no age requirement for a ham radio license, and operators from diverse backgrounds participate. There are more than 740,000 hams in the US, and over 3 million (estimated) worldwide. Many amateur communications are conducted using transionospheric links and thus affected by space weather and ionospheric processes. Recent technological advances have enabled the development of automated ham radio observation networks (e.g. the Reverse Beacon Network, www.reversebeacon.net) and specialized operating modes for the study of weak-signal propagation. The data from these networks have been shown to be useful for the study of ionospheric processes. In order to connect professional researchers with the volunteer-based ham radio community, HamSCI (Ham Radio Science Citizen Investigation, www.hamsci.org) has been established. HamSCI is a platform for publicizing and promoting projects that are consistent with the following objectives: (1) Advance scientific research and understanding through amateur radio activities. (2) Encourage the development of new technologies to support this research. (3) Provide educational opportunities for the amateur community and the general public. HamSCI researchers are working with the American Radio Relay League (ARRL, www.arrl.org) to publicize these objectives and recruit interested hams. The ARRL is the US national organization for amateur radio with a membership of over 170,000 and a monthly magazine, QST. HamSCI is currently preparing to support ionospheric research connected to the 21 Aug 2017 Total Solar Eclipse by expanding coverage of the Reverse Beacon Network and organizing a large-scale ham radio operating event ("QSO Party") to generate data during the

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, J. M., E-mail: jschmidt@physics.usyd.edu.au; Cairns, Iver H.

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 andmore » 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 ≈ 10{sup 6} and ≈ 10{sup 3}, 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.« less

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.

The Sub-Parsec Radio Jet in NGC 4151

NASA Astrophysics Data System (ADS)

Roy, A. L.; Ulvestad, J. S.; Colbert, E. J. M.; Wilson, A. S.

1997-05-01

We are surveying eight nearby Seyfert galaxies (four Sy1s and four Sy2s) that have compact radio cores, using the VLBA. We are interested in parsec-scale morphology and low-frequency absorption effects, and so are observing three frequencies per galaxy (1.6, 4.8, and 8.4 or 15 GHz) to get spectral-index diagnostics. VLBA imaging of NGC 4151 at 1.6 and 4.8 GHz reveals the following results: * NGC 4151 contains a remarkable chain of knots strongly resembling a jet, emerging in component C4 and extending for 0.8 pc. * The jet propagates NNE for 0.5 pc then turns sharply eastward and becomes the known MERLIN jet. * Curiously, by propagating northwards at first, the jet initially makes an angle of 60d with the axis of the ionization cones seen by HST. This breaks the cylindrical symmetry required by orientation unification, and may indicate that the BLR and torus have a symmetry axis unrelated to the axis of the NLR. * The nucleus looks to be in the C4 eastern component from our radio continuum morphology and from limited radio spectral information, rather than being in the C4 western component as Mundell et al. (1995, MNRAS, 272, 355) infer from HI absorbing columns. * The components located at 6 and 30 pc from the C4 eastern component have apparent speeds relative to that component of < 0.1 c to 0.2 c.

Effects of storage temperature on the physiological characteristics and vegetative propagation of desiccation-tolerant mosses

NASA Astrophysics Data System (ADS)

Guo, Yuewei; Zhao, Yunge

2018-02-01

Mosses, as major components of later successional biological soil crusts (biocrusts), play many critical roles in arid and semiarid ecosystems. Recently, some species of desiccation-tolerant mosses have been artificially cultured with the aim of accelerating the recovery of biocrusts. Revealing the factors that influence the vegetative propagation of mosses, which is an important reproductive mode of mosses in dry habitats, will benefit the restoration of moss crusts. In this study, three air-dried desiccation-tolerant mosses (Barbula unguiculata, Didymodon vinealis, and Didymodon tectorum) were hermetically sealed and stored at five temperature levels (0, 4, 17, 25, and 30 °C) for 40 days. Then, the vegetative propagation and physiological characteristics of the three mosses were investigated to determine the influence of storage temperature on the vegetative propagation of desiccation-tolerant mosses and the mechanism. The results showed that the vegetative propagation of the three mosses varied with temperature. The most variation in vegetative propagation among storage temperatures was observed in D. tectorum, followed by the variation observed in B. unguiculata. In contrast, no significant difference in propagation among temperatures was found in D. vinealis. The regenerative capacity of the three mosses increased with increasing temperature from 0 to 17 °C, accompanied by a decrease in malondialdehyde (MDA) content, and decreased thereafter. As the temperature increased, the chlorophyll and soluble protein contents increased in B. unguiculata but decreased in D. vinealis and D. tectorum. As to storage, the MDA and soluble sugar contents increased after storage. The MDA content of the three mosses increased at each of the investigated temperatures by more than 50 % from the initial values, and the soluble sugar content became higher than before in the three mosses. The integrity of cells and cell membranes is likely the most important factor influencing the

Radiolocation Techniques (Les Techniques de Radiolocalisation). Papers Presented at the Electromagnetic Wave Propagation Panel Symposium Held in London, England on 1-5 Jun 92

DTIC Science & Technology

1992-11-01

coivergence. PROPAGATION CHARACTERISTICS OF THE IONOSPHERIC TRANSMISSION WINDOW RELATING TO LONG WAVE RADIO LOCATION ISSUES Paul A. Kossey Phillips...aý iteil wed as tt~onthi. ’o~ar li: i i~e froiti Janitarx 1:1hiý t brotuli FeI,riiar% 󈧕l, withi 1\\: trott I) o~ .- o ; , ::tr--t’rh -li- axitnuti...the great circle path at the midpoint. meters on a leg. Both arrays are in an "L" Experimental evidence ( Paul , 1985)indicates configuration using seven

Wearable ECG Based on Impulse-Radio-Type Human Body Communication.

PubMed

Wang, Jianqing; Fujiwara, Takuya; Kato, Taku; Anzai, Daisuke

2016-09-01

Human body communication (HBC) provides a promising physical layer for wireless body area networks (BANs) in healthcare and medical applications, because of its low propagation loss and high security characteristics. In this study, we have developed a wearable electrocardiogram (ECG) which employs impulse radio (IR)-type HBC technology for transmitting vital signals on the human body in a wearable BAN scenario. The HBC-based wearable ECG has two excellent features. First, the wideband performance of the IR scheme contributed to very low radiation power so that the transceiver is easy to satisfy the extremely weak radio laws, which does not need a license. This feature can provide big convenience in the use and spread of the wearable ECG. Second, the realization of common use of sensing and transmitting electrodes based on time sharing and capacitive coupling largely simplified the HBC-based ECG structure and contributed to its miniaturization. To verify the validity of the HBC-based ECG, we evaluated its communication performance and ECG acquisition performance. The measured bit error rate, smaller than 10 -3 at 1.25 Mb/s, showed a good physical layer communication performance, and the acquired ECG waveform and various heart-rate variability parameters in time and frequency domains exhibited good agreement with a commercially available radio-frequency ECG and a Holter ECG. These results sufficiently showed the validity and feasibility of the HBC-based ECG for healthcare applications. This should be the first time to have realized a real-time ECG transmission by using the HBC technology.

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.

LF/MF Propagation Modeling for D-Region Ionospheric Remote Sensing

NASA Astrophysics Data System (ADS)

Higginson-Rollins, M. A.; Cohen, M.

2017-12-01

The D-region of the ionosphere is highly inaccessible because it is too high for continuous in-situ measurement techniques and too low for satellite measurements. Very-Low Frequency (VLF) signals have been developed and used as a diagnostic tool for this region of the ionosphere and are favorable because of the low ionospheric attenuation rates, allowing global propagation - but this also creates an ill-posed multi-mode propagation problem. As an alternative, Low-Frequency (LF) and Medium-Frequency (MF) signals could be used as a diagnostic tool of the D-region. These higher frequencies have a higher attenuation rate, and thus only a few modes propagate in the Earth-ionosphere waveguide, creating a much simpler problem to analyze. The United States Coast Guard (USCG) operates a national network of radio transmitters that serve as an enhancement to the Global Positioning System (GPS). This network is termed Differential Global Positioning System (DGPS) and uses fixed reference stations as a method of determining the error in received GPS satellite signals and transmits the correction value using low frequency and medium frequency radio signals between 285 kHz and 385 kHz. Using sensitive receivers, we can detect this signal many hundreds of km away. We present modeling of the propagation of these transmitters' signals for use as a diagnostic tool for characterizing the D-region. The Finite-Difference Time-Domain (FDTD) method is implemented to model the groundwave radiated by the DGPS beacons and account for environmental effects, such as changing soil conductivities and terrain. A full wave numerical solver is used to model the skywave component of the propagating signal and specifically to ascertain the reflection coefficients for various ionospheric conditions. Preliminary results are shown and discussed, and comparisons with collected data are presented.

About the Modeling of Radio Source Time Series as Linear Splines

NASA Astrophysics Data System (ADS)

Karbon, Maria; Heinkelmann, Robert; Mora-Diaz, Julian; Xu, Minghui; Nilsson, Tobias; Schuh, Harald

2016-12-01

Many of the time series of radio sources observed in geodetic VLBI show variations, caused mainly by changes in source structure. However, until now it has been common practice to consider source positions as invariant, or to exclude known misbehaving sources from the datum conditions. This may lead to a degradation of the estimated parameters, as unmodeled apparent source position variations can propagate to the other parameters through the least squares adjustment. In this paper we will introduce an automated algorithm capable of parameterizing the radio source coordinates as linear splines.

Phase synchronization between tropospheric radio refractivity and rainfall amount in a tropical region

NASA Astrophysics Data System (ADS)

Fuwape, Ibiyinka A.; Ogunjo, Samuel T.; Dada, Joseph B.; Ashidi, Gabriel A.; Emmanuel, Israel

2016-11-01

This study investigated linear and nonlinear relationship between the amount of rainfall and radio refractivity in a tropical country, Nigeria using forty seven locations scattered across the country. Correlation and Phase synchronization measures were used for the linear and nonlinear relationship respectively. Weak correlation and phase synchronization was observed between seasonal mean rainfall amount and radio refractivity while strong phase synchronization was found for the detrended data suggesting similar underlying dynamics between rainfall amount and radio refractivity. Causation between rainfall and radio refractivity in a tropical location was studied using Granger causality test. In most of the Southern locations, rainfall was found to Granger cause radio refractivity. Furthermore, it was observed that there is strong correlation between mean rainfall amount and the phase synchronization index over Nigeria. Coupling between rainfall and radio refractivity has been found to be due to water vapour in the atmosphere. Frequency planning and budgeting for microwave propagation during periods of high rainfall should take into consideration this nonlinear relationship.

Propagation Characteristics of CMEs Associated with Magnetic Clouds and Ejecta

NASA Astrophysics Data System (ADS)

Kim, R.-S.; Gopalswamy, N.; Cho, K.-S.; Moon, Y.-J.; Yashiro, S.

2013-05-01

We have investigated the characteristics of magnetic cloud (MC) and ejecta (EJ) associated coronal mass ejections (CMEs) based on the assumption that all CMEs have a flux rope structure. For this, we used 54 CMEs and their interplanetary counterparts (interplanetary CMEs: ICMEs) that constitute the list of events used by the NASA/LWS Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We considered the location, angular width, and speed as well as the direction parameter, D. The direction parameter quantifies the degree of asymmetry of the CME shape in coronagraph images, and shows how closely the CME propagation is directed to Earth. For the 54 CDAW events, we found the following properties of the CMEs: i) the average value of D for the 23 MCs (0.62) is larger than that for the 31 EJs (0.49), which indicates that the MC-associated CMEs propagate more directly toward the Earth than the EJ-associated CMEs; ii) comparison between the direction parameter and the source location shows that the majority of the MC-associated CMEs are ejected along the radial direction, while many of the EJ-associated CMEs are ejected non-radially; iii) the mean speed of MC-associated CMEs (946 km s-1) is faster than that of EJ-associated CMEs (771 km s-1). For seven very fast CMEs (≥ 1500 km s-1), all CMEs with large D (≥ 0.4) are associated with MCs and the CMEs with small D are associated with EJs. From the statistical analysis of CME parameters, we found the superiority of the direction parameter. Based on these results, we suggest that the CME trajectory essentially determines the observed ICME structure.

A Constant Envelope OFDM Implementation on GNU Radio

DTIC Science & Technology

2015-02-02

more advanced schemes like Decision Feedback Equalization or Turbo Equalization must be implemented to avoid the noise enhancement that all linear...block is coded in C++, and uses the phase unwrapping algorithm similar to MATLABs unwrap() function. To avoid false wraps propagating throughout the...outperform the real-time GNU radio implementation at higher SNR’s. While the unequalized experiment with the Matlab processor usually stayed within 5

FOREWORD: Radio and Antenna Days of the Indian Ocean (RADIO 2012)

NASA Astrophysics Data System (ADS)

Monebhurrun, Vikass; Lesselier, Dominique

2013-04-01

It was an honor and a great pleasure for all those involved in its organization to welcome the participants to the 'Radio and Antenna Days of the Indian Ocean' (RADIO 2012) international conference that was held from 24th to 27th September 2012 at the Sugar Beach Resort, Wolmar, Flic-en-Flac, Mauritius. RADIO 2012 is the first of a series of conferences that is to be regularly organized in the Indian Ocean region. The aim is to discuss recent developments, theories and practical applications covering the whole scope of radio-frequency engineering, including radio waves, antennas, propagation, and electromagnetic compatibility. Following discussions with engineers and scientists from the countries of the Indian Ocean as well as from other parts of the world, a need was felt for the organization of such an international event in this region. The Island of Mauritius, worldwide known for its white sandy beaches and pleasant tropical atmosphere, provided an excellent environment for the organization of the 1st RADIO international conference. The Local Organizing Committee consisted of scientists from SUPELEC, the University of Mauritius, and the University of Technology, Mauritius. Various members of staff of the University of Mauritius provided help for the organization of the conference. The International Union of Radio Science (URSI) made available technical and financial sponsorship for partial support of young scientists. A number of companies also supported RADIO 2012 ('Platinum': GSMA, ICTA & MMF, 'Gold': CST & FEKO). The event itself was organized in a premier hotel on Mauritius. In this foreword, we would like to take the opportunity again to thank all the people, institutions and companies that made the event such a success. More than 120 abstracts were submitted to the conference and were peer-reviewed by an international scientific committee. RADIO 2012 overall featured six oral sessions, one poster session and two workshops. Three internationally recognized

Phase fluctuations model for EM wave propagation through solar scintillation at superior solar conjunction

NASA Astrophysics Data System (ADS)

Xu, Guanjun; Song, Zhaohui

2017-04-01

Traveling solar wind disturbances have a significant influence on radio wave characteristics during the superior solar conjunction communication. This paper considers the impact of solar scintillation on phase fluctuations of electromagnetic (EM) wave propagation during the superior solar conjunction. Based on the Geometric Optics approximation, the close-form approximation model for phase fluctuations is developed. Both effects of anisotropic temporal variations function of plasma irregularities and their power spectrum are presented and analyzed numerically. It is found that phase fluctuations rapidly decrease with increasing Sun-Earth-Probe angle and decrease with increasing frequency at the rate of 1/f2. Moreover, the role of various features of the solar wind irregularities and their influence on the EM wave characteristic parameters is studied and discussed. Finally, we study the phase fluctuations of typical cases in order to better understand the impact of phase fluctuations in future deep space communication scenarios during solar conjunction periods.

Premixed Turbulent Flame Propagation in Microgravity

NASA Technical Reports Server (NTRS)

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

1997-01-01

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

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

PubMed Central

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

2014-01-01

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

Propagation characteristics of ultrasonic guided waves in continuously welded rail

NASA Astrophysics Data System (ADS)

Yao, Wenqing; Sheng, Fuwei; Wei, Xiaoyuan; Zhang, Lei; Yang, Yuan

2017-07-01

Rail defects cause numerous railway accidents. Trains are derailed and serious consequences often occur. Compared to traditional bulk wave testing, ultrasonic guided waves (UGWs) can provide larger monitoring ranges and complete coverage of the waveguide cross-section. These advantages are of significant importance for the non-destructive testing (NDT) of the continuously welded rail, and the technique is therefore widely used in high-speed railways. UGWs in continuous welded rail (CWR) and their propagation characteristics have been discussed in this paper. Finite element methods (FEMs) were used to accomplish a vibration modal analysis, which is extended by a subsequent dispersion analysis. Wave structure features were illustrated by displacement profiles. It was concluded that guided waves have the ability to detect defects in the rail via choice of proper mode and frequency. Additionally, thermal conduction that is caused by temperature variation in the rail is added into modeling and simulation. The results indicated that unbalanced thermal distribution may lead to the attenuation of UGWs in the rail.

Roost sites of radio-marked Mexican spotted owls in Arizona and New Mexico: sources of variability and descriptive characteristics

Treesearch

Joseph L. Ganey; William M. Block; Rudy M. King

2000-01-01

To increase understanding of roosting habitat of Mexican Spotted Owls (Strix occidentalis lucida) and factors that influence use of roosting habitat, we sampled habitat characteristics at 1790 sites used for roosting by 28 radio-marked Mexican Spotted Owls in three study areas in Arizona and New Mexico. We explored potential patterns of variation in...

Propagational characteristics in a warm hybrid plasmonic waveguide

NASA Astrophysics Data System (ADS)

Mahmodi Moghadam, M.; Shahmansouri, M.; Farokhi, B.

2017-12-01

We theoretically analyze the properties of guided modes in a warm planar conductor-gap-dielectric (CGD) system. The latter consists of a high index dielectric, separated from a warm metallic plasma with a low index nano-sized dielectric layer (gap) by using the hydrodynamic model coupled to Maxwell's equations. The effects of thermal pressure on the confinement and the propagation losses of Hybrid Plasmon Polariton (HPP) modes are studied. We found that the thermal effect leads to a reduction in the effective refractive index as well as in the propagation losses of the HPP mode. Furthermore, the cutoff thickness in the warm CGD waveguide is found to be smaller than that in a cold CGD waveguide. The results may be useful in understanding the essential physics of active/passive Plasmonic devices and chip-scale systems.

Effects on transionospheric HF propagation observed by ISIS at middle and auroral latitudes

NASA Astrophysics Data System (ADS)

James, G.

During the months of May through July 1978, an experiment on transionospheric HF propagation was carried out using a transmitter at Ottawa and the sounder receivers of the ISIS-I and ISIS-II spacecraft. Fixed- and synchronous swept-frequency recordings were made. Over 100 ISIS-II passes were successfully recorded at 9.303 MHz, the highest fixed frequency of receiver operation. Several tens of these passes have been analyzed in an attempt to establish the salient characteristics of the propagation. From these characteristics, the goal is to improve understanding of the processes experienced by waves passing through the ionosphere, e.g., focusing or scattering. This research supports planning for coordinated ground-space radio experiments in the upcoming Enhanced Polar Outflow Probe satellite mission, to be flown for the Canadian Space Agency. Swept-frequency ionograms interleaved with the aforementioned fixed-frequency measurements allowed two-dimensional density distributions to be modeled in altitude and latitude. Computer code was developed for three-dimensional ray tracing. A Newton's-iteration algorithm was used for efficient searches for solution rays that connect the transmitter with the position of the satellite at any time along its path. The latitudinal extent of the zone irradiated at ISIS-II altitude thus computed is approximately as observed, albeit sensitively dependent upon north-south density gradients. Within this "iris" of accessibility, the peak intensity of waves recorded at the spacecraft is within 10 dB of that found with a link calculation based on ray optics. Density inhomogeneities influence the transmitted O and X mode waves, in various ways. Poleward rays result in dispersed pulses, indicating quasi-perpendicular propagation that is forward scattered. Toward the equator, propagation directions come to within about 10 of the magnetic-field axis. Equatorward pulses are comparatively sharp and occasionally exhibit periodic fades with beat

2nd Radio and Antenna Days of the Indian Ocean (RADIO 2014)

NASA Astrophysics Data System (ADS)

2014-10-01

It was an honor and a great pleasure for all those involved in its organization to welcome the participants to the ''Radio and Antenna Days of the Indian Ocean'' (RADIO 2014) international conference that was held from 7th to 10th April 2014 at the Sugar Beach Resort, Wolmar, Flic-en-Flac, Mauritius. RADIO 2014 is the second of a series of conferences organized in the Indian Ocean region. The aim of the conference is to discuss recent developments, theories and practical applications covering the whole scope of radio-frequency engineering, including radio waves, antennas, propagation, and electromagnetic compatibility. The RADIO international conference emerged following discussions with engineers and scientists from the countries of the Indian Ocean as well as from other parts of the world and a need was felt for the organization of such an event in this region. Following numerous requests, the Island of Mauritius, worldwide known for its white sandy beaches and pleasant tropical atmosphere, was again chosen for the organization of the 2nd RADIO international conference. The conference was organized by the Radio Society, Mauritius and the Local Organizing Committee consisted of scientists from SUPELEC, France, the University of Mauritius, and the University of Technology, Mauritius. We would like to take the opportunity to thank all people, institutions and companies that made the event such a success. We are grateful to our gold sponsors CST and FEKO as well as URSI for their generous support which enabled us to partially support one PhD student and two scientists to attend the conference. We would also like to thank IEEE-APS and URSI for providing technical co-sponsorship. More than hundred and thirty abstracts were submitted to the conference. They were peer-reviewed by an international scientific committee and, based on the reviews, either accepted, eventually after revision, or rejected. RADIO 2014 brought together participants from twenty countries spanning

System of the optic-electronic sensors for control position of the radio telescope elements

NASA Astrophysics Data System (ADS)

Konyakhin, Igor; Stepashkin, Ivan; Petrochenko, Andrey

2016-04-01

A promising area of modern astronomy is the study of the field of millimeter waves. The use of this band is due to a large extent the spectrum characteristics of the propagation of waves in the atmosphere, short wavelength. Currently, Russia jointly with Uzbekistan is implementing a project to build a radio astronomy observatory on the Suffa plateau (Uzbekistan). The main instrument of the observatory is fully steerable radio telescope RT-70 type. Main mirror telescope is a fragment of an axisymmetric parabolic with a focal length of 21 m, consisting of 1200 reflecting panels; main mirror diameter - 70 m; diameter of counter reflector - 3 m. A feature of the radio telescope as a means of research in the millimeter wavelength range are high for the quality requirements parabolic surface of the primary mirror (standard deviation of points on the surface of the theoretical parabolic is not more than 0.05 mm), to the stability of the mutual arrangement of the primary mirror and the counter reflector (not more than 0, 07 mm) for precision guidance in the corners of the mirror system azimuth and elevation (margin of error 1.5-2"). Weight of structure, temperature changes and air shock result in significant deformation elements radio telescope construction (progressive linear displacements of points of the surface of the main mirror), reaching in the marginal zone of 30 mm; counter reflector shift of up to 60 mm; Unlike the angular position of the axis of the beam pattern of the radio telescope of the measured angle transducers can reach 10 ". Therefore, to ensure the required quality of the reflective elements RT-70 systems, as well as the implementation of precision-guided munitions needs complex measuring deformation elements telescope design. This article deals with the construction of opto-electronic system of remote optoelectronic displacement sensor control elements mirror telescope system.

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.

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.

Effects on transionospheric HF propagation observed by ISIS at middle and auroral latitudes

NASA Astrophysics Data System (ADS)

James, H. G.

2006-01-01

In 1978, an experiment on transionospheric HF propagation was carried out using a transmitter at Ottawa and the sounder receivers of the ISIS-I and ISIS-II spacecraft. Over 100 ISIS-II passes were successfully recorded using a fixed frequency of 9.303 MHz. A survey of the data has allowed some reproducible characteristics of transionospheric propagation to be identified. A number of ISIS-II ionograms are published here to illustrate those characteristics. A systematic feature of the pulses is their partial splitting into ordinary (O) and extraordinary (X) parts, producing a tripartite compound pulse at the satellite. Equatorward pulses are comparatively sharp and occasionally exhibit periodic fades with beat frequencies between about 1 and 4 Hz. Features of the fades indicate that focussing of rays is a better explanation for the fades than diffraction. Rays near the limits of the reception zone can result in dispersed pulses, thought to indicate forward scattering. Swept-frequency ionograms interleaved with fixed-frequency measurements allowed two-dimensional density distributions to be modeled in altitude and latitude. Three-dimensional ray tracing plus a Newton’s-iteration algorithm were used to find rays that connected the transmitter with the position of the satellite at any time along its path. The latitudinal extent of the zone irradiated at ISIS-II altitude thus computed is approximately as observed, albeit sensitively dependent upon north south density gradients. Within this “iris” of accessibility, the maximum intensity of waves recorded at the spacecraft is within 10 dB of what is computed with a link calculation based on ray optics, but there are many dropouts of 20 30 dB below this maximum envelope. Toward the equator, propagation directions come to within about 10° of the magnetic-field axis. This research supports planning for coordinated ground-space radio experiments in the upcoming e-POP satellite mission.

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.

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.

Characteristics of type III exciters derived from low frequency radio observations

NASA Technical Reports Server (NTRS)

Evans, L. G.; Fainberg, J.; Stone, R. G.

1973-01-01

Low-frequency radio observations (2.8 MHz to 67 kHz) from the RAE-1 and IMP-6 satellites allow the tracking of type III solar burst exciters out to large distances from the sun (of the order of 1 AU). A study of the interaction processes between the exciter and the interplanetary medium was made using the time-intensity profiles of the radio emission. The change in exciter length with distance from the sun, and the resulting exciter velocity dispersion which can be deduced from this change are investigated. From detailed measurements on 35 simple bursts it is found that the exciter length increases at a faster rate than a constant velocity dispersion would give. The damping of the radio emission is also investigated, and it is concluded that some current theories of the damping mechanism give results which are not consistent with the low-frequency observations.

Radio variability in complete samples of extragalactic radio sources at 1.4 GHz

NASA Astrophysics Data System (ADS)

Rys, S.; Machalski, J.

1990-09-01

Complete samples of extragalactic radio sources obtained in 1970-1975 and the sky survey of Condon and Broderick (1983) were used to select sources variable at 1.4 GHz, and to investigate the characteristics of variability in the whole population of sources at this frequency. The radio structures, radio spectral types, and optical identifications of the selected variables are discussed. Only compact flat-spectrum sources vary at 1.4 GHz, and all but four are identified with QSOs, BL Lacs, or other (unconfirmed spectroscopically) stellar objects. No correlation of degree of variability at 1.4 GHz with Galactic latitude or variability at 408 MHz has been found, suggesting that most of the 1.4-GHz variability is intrinsic and not caused by refractive scintillations. Numerical models of the variability have been computed.

Regional propagation characteristics and source parameters of earthquakes in northeastern North America

USGS Publications Warehouse

Boatwright, John

1994-01-01

The vertical components of the S wave trains recorded on the Eastern Canadian Telemetered Network (ECTN) from 1980 through 1990 have been spectrally analyzed for source, site, and propagation characteristics. The data set comprises some 1033 recordings of 97 earthquakes whose magnitudes range from M ≈ 3 to 6. The epicentral distances range from 15 to 1000 km, with most of the data set recorded at distances from 200 to 800 km. The recorded S wave trains contain the phases S, SmS, Sn, and Lg and are sampled using windows that increase with distance; the acceleration spectra were analyzed from 1.0 to 10 Hz. To separate the source, site, and propagation characteristics, an inversion for the earthquake corner frequencies, low-frequency levels, and average attenuation parameters is alternated with a regression of residuals onto the set of stations and a grid of 14 distances ranging from 25 to 1000 km. The iteration between these two parts of the inversion converges in about 60 steps. The average attenuation parameters obtained from the inversion were Q = 1997 ± 10 and γ = 0.998 ± 0.003. The most pronounced variation from this average attenuation is a marked deamplification of more than a factor of 2 at 63 km and 2 Hz, which shallows with increasing frequency and increasing distance out to 200 km. The site-response spectra obtained for the ECTN stations are generally flat. The source spectral shape assumed in this inversion provides an adequate spectral model for the smaller events (Mo < 3 × 1021 dyne-cm) in the data set, whose Brune stress drops range from 5 to 150 bars. For the five events in the data set with Mo ≧ 1023 dyne-cm, however, the source spectra obtained by regressing the residuals suggest that an ω2 spectrum is an inadequate model for the spectral shape. In particular, the corner frequencies for most of these large events appear to be split, so that the spectra exhibit an intermediate behavior (where |ü(ω)| is roughly proportional to ω).

Measurement of RF propagation around corners in underground mines and tunnels.

PubMed

Jacksha, R; Zhou, C

2016-01-01

This paper reports measurement results for radio frequency (RF) propagation around 90° corners in tunnels and underground mines, for vertically, horizontally and longitudinally polarized signals. Measurements of signal power attenuation from a main entry into a crosscut were performed at four frequencies - 455, 915, 2450 and 5800 MHz - that are common to underground radio communication systems. From the measurement data, signal power loss was determined as a function of signal coupling from the main entry into the crosscut. The resultant power loss data show there are many factors that contribute to power attenuation from a main entry into a crosscut, including frequency, antenna polarization and cross-sectional entry dimensions.

3D numerical study of the propagation characteristics of a consequence of coronal mass ejections in a structured ambient solar wind

NASA Astrophysics Data System (ADS)

Zhou, Y.; Feng, X. S.

2015-12-01

CMEs have been identified as a prime causal link between solar activity and large, nonrecurrent geomagnetic storm. In order to improve geomagnetic storm predictions, a careful study of CME's propagation characteristics is important. Here, we analyze and quantitatively study the evolution and propagation characteristics of coronal mass ejections (CMEs) launched at several positions into a structured real ambient solar wind by using a three-dimensional (3D) numerical magnetohydrodynamics (MHD) simulation. The ambient solar wind structure during Carrington rotation 2095 is selected, which is an appropriate around activity minimum and declining phase. The CME is initiated by a simple spherical plasmoid model: a spheromak magnetic structure with high speed, high pressure and high plasma density plasmoid. We present a detailed analysis of the plasma, magnetic field, geoeffectiveness, and composition signatures of these CMEs. Results show that the motion and local appearance of a CME in interplanetary space is strongly affected by its interaction with the background solar wind structure, including its velocity, density, and magnetic structures. The simulations show that the initial launched position substantially affects the IP evolution of the CMEs influencing the propagation velocity, the shape, the trajectory and even the geo-effectiveness

Outer heliospheric radio emissions. II - Foreshock source models

NASA Technical Reports Server (NTRS)

Cairns, Iver H.; Kurth, William S.; Gurnett, Donald A.

1992-01-01

Observations of LF radio emissions in the range 2-3 kHz by the Voyager spacecraft during the intervals 1983-1987 and 1989 to the present while at heliocentric distances greater than 11 AU are reported. New analyses of the wave data are presented, and the characteristics of the radiation are reviewed and discussed. Two classes of events are distinguished: transient events with varying starting frequencies that drift upward in frequency and a relatively continuous component that remains near 2 kHz. Evidence for multiple transient sources and for extension of the 2-kHz component above the 2.4-kHz interference signal is presented. The transient emissions are interpreted in terms of radiation generated at multiples of the plasma frequency when solar wind density enhancements enter one or more regions of a foreshock sunward of the inner heliospheric shock. Solar wind density enhancements by factors of 4-10 are observed. Propagation effects, the number of radiation sources, and the time variability, frequency drift, and varying starting frequencies of the transient events are discussed in terms of foreshock sources.

A Study of Nonthermal X-Ray and Radio Emission from the O Star 9 Sgr

NASA Technical Reports Server (NTRS)

Waldron, Wayne L.; Corcoran, Michael F.; Drake, Stephen A.

1999-01-01

The observed X-ray and highly variable nonthermal radio emission from OB stars has eluded explanation for more than 18 years. The most favorable model of X-ray production in these stars (shocks) predicts both nonthermal radio and X-ray emission. The nonthermal X-ray emission should occur above 2 keV and the variability of this X-ray component should also be comparable to the observed radio variability. To test this scenario, we proposed an ASC/VLA monitoring program to observe the OB star, 9 Sgr, a well known nonthermal, variable radio source and a strong X-ray source. We requested 625 ks ASCA observations with a temporal spacing of approximately 4 days which corresponds to the time required for a density disturbance to propagate to the 6 cm radio free-free photosphere. The X-ray observations were coordinated with 5 multi-wavelength VLA observations. These observations represent the first systematic attempt to investigate the relationship between the X-ray and radio emission in OB stars.

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.

Characterization of Impulse Radio Intrabody Communication System for Wireless Body Area Networks.

PubMed

Cai, Zibo; Seyedi, MirHojjat; Zhang, Weiwei; Rivet, Francois; Lai, Daniel T H

2017-01-01

Intrabody communication (IBC) is a promising data communication technique for body area networks. This short-distance communication approach uses human body tissue as the medium of signal propagation. IBC is defined as one of the physical layers for the new IEEE 802.15.6 or wireless body area network (WBAN) standard, which can provide a suitable data rate for real-time physiological data communication while consuming lower power compared to that of radio-frequency protocols such as Bluetooth. In this paper, impulse radio (IR) IBC (IR-IBC) is examined using a field-programmable gate array (FPGA) implementation of an IBC system. A carrier-free pulse position modulation (PPM) scheme is implemented using an IBC transmitter in an FPGA board. PPM is a modulation technique that uses time-based pulse characteristics to encode data based on IR concepts. The transmission performance of the scheme was evaluated through signal propagation measurements of the human arm using 4- and 8-PPM transmitters, respectively. 4 or 8 is the number of symbols during modulations. It was found that the received signal-to-noise ratio (SNR) decreases approximately 8.0 dB for a range of arm distances (5-50 cm) between the transmitter and receiver electrodes with constant noise power and various signal amplitudes. The SNR for the 4-PPM scheme is approximately 2 dB higher than that for the 8-PPM one. In addition, the bit error rate (BER) is theoretically analyzed for the human body channel with additive white Gaussian noise. The 4- and 8-PPM IBC systems have average BER values of 10 -5 and 10 -10 , respectively. The results indicate the superiority of the 8-PPM scheme compared to the 4-PPM one when implementing the IBC system. The performance evaluation of the proposed IBC system will improve further IBC transceiver design.

Social Media Propagation of Content Promoting Risky Health Behavior.

PubMed

Park, Mina; Sun, Yao; McLaughlin, Margaret L

2017-05-01

While social media have been found useful in providing social support and health information, they have also been home to content advocating risky health behavior. This study focused on how content defending and even celebrating anorexia as a lifestyle are circulated among social media users, and investigates the characteristics that promote wide propagation of such messages. We captured anorexia-related content on Tumblr, a popular blog for talking about eating disorders, during a one-month period. Among the 35,432 posts collected, we examined the most highly propagated posts and coded them for message characteristics. Our findings revealed that posts in which the source of a narrative ("testimony") was identified (was either from an anorexic poster or about another's anorexia) and which were positive toward the pro-anorexia perspective were more likely to be propagated on Tumblr. In addition, posts containing content that references an anorexic person and contains an affective tone were more likely to be propagated. We also found that underweight bodies and bodies with a high degree of exposure were associated with propagation of posts. The present study suggested practical implications by focusing on the characteristics of highly propagated but potentially harmful content in social media.

Experimental investigation of starting characteristics and wave propagation from a shallow open cavity and its acoustic emission at supersonic speed

NASA Astrophysics Data System (ADS)

Pandian, S.; Desikan, S. L. N.; Niranjan, Sahoo

2018-01-01

Experiments were carried out on a shallow open cavity (L/D = 5) at a supersonic Mach number (M = 1.8) to understand its transient starting characteristics, wave propagation (inside and outside the cavity) during one vortex shedding cycle, and acoustic emission. Starting characteristics and wave propagation were visualized through time resolved schlieren images, while acoustic emissions were captured through unsteady pressure measurements. Results showed a complex shock system during the starting process which includes characteristics of the bifurcated shock system, shock train, flow separation, and shock wave boundary layer interaction. In one vortex shedding cycle, vortex convection from cavity leading edge to cavity trailing edge was observed. Flow features outside the cavity demonstrated the formation and downstream movement of a λ-shock due to the interaction of shock from the cavity leading edge and shock due to vortex and generation of waves on account of shear layer impingement at the cavity trailing edge. On the other hand, interesting wave structures and its propagation were monitored inside the cavity. In one vortex shedding cycle, two waves such as a reflected compression wave from a cavity leading edge in the previous vortex shedding cycle and a compression wave due to the reflection of Mach wave at the cavity trailing edge corner in the current vortex shedding cycle were visualized. The acoustic emission from the cavity indicated that the 2nd to 4th modes/tones are dominant, whereas the 1st mode contains broadband spectrum. In the present studies, the cavity feedback mechanism was demonstrated through a derived parameter coherence coefficient.

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

Empirical radio propagation model for DTV applied to non-homogeneous paths and different climates using machine learning techniques

PubMed Central

Gomes, Herminio Simões; Cavalcante, Gervásio Protásio dos Santos

2018-01-01

The establishment and improvement of transmission systems rely on models that take into account, (among other factors), the geographical features of the region, as these can lead to signal degradation. This is particularly important in Brazil, where there is a great diversity of scenery and climates. This article proposes an outdoor empirical radio propagation model for Ultra High Frequency (UHF) band, that estimates received power values that can be applied to non-homogeneous paths and different climates, this last being of an innovative character for the UHF band. Different artificial intelligence techniques were chosen on a theoretical and computational basis and made it possible to introduce, organize and describe quantitative and qualitative data quickly and efficiently, and thus determine the received power in a wide range of settings and climates. The proposed model was applied to a city in the Amazon region with heterogeneous paths, wooded urban areas and fractions of freshwater among other factors. Measurement campaigns were conducted to obtain data signals from two digital TV stations in the metropolitan area of the city of Belém, in the State of Pará, to design, compare and validate the model. The results are consistent since the model shows a clear difference between the two seasons of the studied year and small RMS errors in all the cases studied. PMID:29596503

Empirical radio propagation model for DTV applied to non-homogeneous paths and different climates using machine learning techniques.

PubMed

Gomes, Igor Ruiz; Gomes, Cristiane Ruiz; Gomes, Herminio Simões; Cavalcante, Gervásio Protásio Dos Santos

2018-01-01

The establishment and improvement of transmission systems rely on models that take into account, (among other factors), the geographical features of the region, as these can lead to signal degradation. This is particularly important in Brazil, where there is a great diversity of scenery and climates. This article proposes an outdoor empirical radio propagation model for Ultra High Frequency (UHF) band, that estimates received power values that can be applied to non-homogeneous paths and different climates, this last being of an innovative character for the UHF band. Different artificial intelligence techniques were chosen on a theoretical and computational basis and made it possible to introduce, organize and describe quantitative and qualitative data quickly and efficiently, and thus determine the received power in a wide range of settings and climates. The proposed model was applied to a city in the Amazon region with heterogeneous paths, wooded urban areas and fractions of freshwater among other factors. Measurement campaigns were conducted to obtain data signals from two digital TV stations in the metropolitan area of the city of Belém, in the State of Pará, to design, compare and validate the model. The results are consistent since the model shows a clear difference between the two seasons of the studied year and small RMS errors in all the cases studied.

Radio Spectral Imaging of Reflective MHD Waves during the Impulsive Phase of a Solar Flare

NASA Astrophysics Data System (ADS)

Yu, S.; Chen, B.; Reeves, K.

2017-12-01

We report a new type of coherent radio bursts observed by the Karl G. Jansky Very Large Array (VLA) in 1-2 GHz during the impulsive phase of a two-ribbon flare on 2014 November 1, which we interpret as MHD waves reflected near the footpoint of flaring loops. In the dynamic spectrum, this burst starts with a positive frequency drift toward higher frequencies until it slows down near its highest-frequency boundary. Then it turns over and drifts toward lower frequencies. The frequency drift rate in its descending and ascending branch is between 50-150 MHz/s, which is much slower than type III radio bursts associated with fast electron beams but close to the well-known intermediate drift bursts, or fiber bursts, which are usually attributed to propagating whistler or Alfvenic waves. Thanks to VLA's unique capability of imaging with spectrometer-like temporal and spectral resolution (50 ms and 2 MHz), we are able to obtain an image of the radio source at every time and frequency in the dynamic spectrum where the burst is present and trace its spatial evolution. From the imaging results, we find that the radio source firstly moves downward toward one of the flaring ribbons before it "bounces off" at the lowest height (corresponding to the turnover frequency in the dynamic spectrum) and moves upward again. The measured speed in projection is at the order of 1-2 Mm/s, which is characteristic of Alfvenic or fast-mode MHD waves in the low corona. We conclude that the radio burst is emitted by trapped nonthermal electrons in the flaring loop carried along by a large-scale MHD wave. The waves are probably launched during the eruption of a magnetic flux rope in the flare impulsive phase.

Characteristics of shock-associated fast-drift kilometric radio bursts

NASA Technical Reports Server (NTRS)

Macdowall, R. J.; Kundu, M. R.; Stone, R. G.

1987-01-01

The existence of a class of fast-drift, shock-associated (SA), kilometric radio bursts which occur at the time of metric type II emission and which are not entirely the kilometric continuation of metric type III bursts has been reported previously (Cane et al., 1981). In this paper unambiguous SA event criteria are established for the purpose of statistically comparing SA events with conventional kilometric type III bursts. Applying these criteria to all long-duration, fast-drift bursts observed by the ISEE-3 spacecraft during a 28-month interval, it is found that more than 70 percent of the events satisfying the criteria are associated with the radio signatures of coronal shocks. If a given event is associated with a metric type II or type IV burst, it is 13 times more likely to satisfy the SA criteria than an event associated only with metric type III activity.

Analysis of the Metal Oxide Space Clouds (MOSC) HF Propagation Environment

NASA Astrophysics Data System (ADS)

Jackson-Booth, N.; Selzer, L.

2015-12-01

Artificial Ionospheric Modification (AIM) attempts to modify the ionosphere in order to alter the high frequency (HF) propagation environment. It can be achieved through injections of aerosols, chemicals or radio (RF) signals into the ionosphere. The Metal Oxide Space Clouds (MOSC) experiment was undertaken in April/May 2013 to investigate chemical AIM. Two sounding rockets were launched from the Kwajalein Atoll (part of the Marshall Islands) and each released a cloud of vaporized samarium (Sm). The samarium created a localized plasma cloud, with increased electron density, which formed an additional ionospheric layer. The ionospheric effects were measured by a wide range of ground based instrumentation which included a network of high frequency (HF) sounders. Chirp transmissions were made from three atolls and received at five sites within the Marshall Islands. One of the receive sites consisted of an 18 antenna phased array, which was used for direction finding. The ionograms have shown that as well as generating a new layer the clouds created anomalous RF propagation paths, which interact with both the cloud and the F-layer, resulting in 'ghost traces'. To fully understand the propagation environment a 3D numerical ray trace has been undertaken, using a variety of background ionospheric and cloud models, to find the paths through the electron density grid for a given fan of elevation and azimuth firing angles. Synthetic ionograms were then produced using the ratio of ray path length to speed of light as an estimation of the delay between transmission and observation for a given frequency of radio wave. This paper reports on the latest analysis of the MOSC propagation environment, comparing theory with observations, to further understanding of AIM.

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.

Space-Time Localization of Plasma Turbulence Using Multiple Spacecraft Radio Links

NASA Technical Reports Server (NTRS)

Armstrong, John W.; Estabrook, Frank B.

2011-01-01

Space weather is described as the variability of solar wind plasma that can disturb satellites and systems and affect human space exploration. Accurate prediction requires information of the heliosphere inside the orbit of the Earth. However, for predictions using remote sensing, one needs not only plane-of-sky position but also range information the third spatial dimension to show the distance to the plasma disturbances and thus when they might propagate or co-rotate to create disturbances at the orbit of the Earth. Appropriately processed radio signals from spacecraft having communications lines-of-sight passing through the inner heliosphere can be used for this spacetime localization of plasma disturbances. The solar plasma has an electron density- and radio-wavelength-dependent index of refraction. An approximately monochromatic wave propagating through a thin layer of plasma turbulence causes a geometrical-optics phase shift proportional to the electron density at the point of passage, the radio wavelength, and the thickness of the layer. This phase shift is the same for a wave propagating either up or down through the layer at the point of passage. This attribute can be used for space-time localization of plasma irregularities. The transfer function of plasma irregularities to the observed time series depends on the Doppler tracking mode. When spacecraft observations are in the two-way mode (downlink radio signal phase-locked to an uplink radio transmission), plasma fluctuations have a two-pulse response in the Doppler. In the two-way mode, the Doppler time series y2(t) is the difference between the frequency of the downlink signal received and the frequency of a ground reference oscillator. A plasma blob localized at a distance x along the line of sight perturbs the phase on both the up and down link, giving rise to two events in the two-way tracking time series separated by a time lag depending the blob s distance from the Earth: T2-2x/c, where T2 is the

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.

Propagation of a fluidization - combustion wave

DOE Office of Scientific and Technical Information (OSTI.GOV)

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.

Compact radio sources in luminous infrared galaxies

NASA Astrophysics Data System (ADS)

Parra, Rodrigo

2007-08-01

Radio interferometry is an observational technique of high sensitivity and incomparably high spatial resolution. Moreover, because radio waves can freely propagate through interstellar dust and gas, it allows the study of regions of the universe completely obscured at other wavelengths. This thesis reports the observational and theoretical results of my research during the past four years which are mostly based on interferometric radio data. The COLA sample is an infrared selected sample of active star forming galaxies. We conducted 6 cm VLA and VLBI snapshot observations of the northern half of this sample. The radio emission seen at VLA scales is consistent with being powered by star formation activity because it follows the far infrared to radio correlation. We detect 22% of the sample sources in our VLBI snapshots. Based on luminosity arguments, we argue that these sub-parsec VLBI sources are powered by AGN activity. Furthermore, we find that VLBI detections are preferentially found in sources whose VLA scale structures have the highest peak brightnesses suggesting a strong correlation between compact starburst and AGN activity. This observational result is consistent with the theoretical picture of an Eddington-limited nuclear starburst acting as the last valve in the pipeline transporting the gas from kiloparsec scales onto the accretion disc of a buried AGN. Arp 220 is the archetypical ultra luminous infrared galaxy. For many years this source has been known to harbour a compact (~100 pc) cluster of unresolved 18 cm bright sources believed to be bright core collapse supernovae. Using multiwavelength VLBI observations, we obtained for the first time radio spectra for 18 of these sources. We find that over a half of them have spectra consistent with young supernovae. The rest can be better explained as older supernova remnants interacting with the high density starburst ISM. This finding allowed us to constrain the number of possible scenarios for the Arp 220

Autonomous robotic platforms for locating radio sources buried under rubble

NASA Astrophysics Data System (ADS)

Tasu, A. S.; Anchidin, L.; Tamas, R.; Paun, M.; Danisor, A.; Petrescu, T.

2016-12-01

This paper deals with the use of autonomous robotic platforms able to locate radio signal sources such as mobile phones, buried under collapsed buildings as a result of earthquakes, natural disasters, terrorism, war, etc. This technique relies on averaging position data resulting from a propagation model implemented on the platform and the data acquired by robotic platforms at the disaster site. That allows us to calculate the approximate position of radio sources buried under the rubble. Based on measurements, a radio map of the disaster site is made, very useful for locating victims and for guiding specific rubble lifting machinery, by assuming that there is a victim next to a mobile device detected by the robotic platform; by knowing the approximate position, the lifting machinery does not risk to further hurt the victims. Moreover, by knowing the positions of the victims, the reaction time is decreased, and the chances of survival for the victims buried under the rubble, are obviously increased.

Network-Based Analysis of Software Change Propagation

PubMed Central

Wang, Rongcun; Qu, Binbin

2014-01-01

The object-oriented software systems frequently evolve to meet new change requirements. Understanding the characteristics of changes aids testers and system designers to improve the quality of softwares. Identifying important modules becomes a key issue in the process of evolution. In this context, a novel network-based approach is proposed to comprehensively investigate change distributions and the correlation between centrality measures and the scope of change propagation. First, software dependency networks are constructed at class level. And then, the number of times of cochanges among classes is minded from software repositories. According to the dependency relationships and the number of times of cochanges among classes, the scope of change propagation is calculated. Using Spearman rank correlation analyzes the correlation between centrality measures and the scope of change propagation. Three case studies on java open source software projects Findbugs, Hibernate, and Spring are conducted to research the characteristics of change propagation. Experimental results show that (i) change distribution is very uneven; (ii) PageRank, Degree, and CIRank are significantly correlated to the scope of change propagation. Particularly, CIRank shows higher correlation coefficient, which suggests it can be a more useful indicator for measuring the scope of change propagation of classes in object-oriented software system. PMID:24790557

Network-based analysis of software change propagation.

PubMed

Wang, Rongcun; Huang, Rubing; Qu, Binbin

2014-01-01

The object-oriented software systems frequently evolve to meet new change requirements. Understanding the characteristics of changes aids testers and system designers to improve the quality of softwares. Identifying important modules becomes a key issue in the process of evolution. In this context, a novel network-based approach is proposed to comprehensively investigate change distributions and the correlation between centrality measures and the scope of change propagation. First, software dependency networks are constructed at class level. And then, the number of times of cochanges among classes is minded from software repositories. According to the dependency relationships and the number of times of cochanges among classes, the scope of change propagation is calculated. Using Spearman rank correlation analyzes the correlation between centrality measures and the scope of change propagation. Three case studies on java open source software projects Findbugs, Hibernate, and Spring are conducted to research the characteristics of change propagation. Experimental results show that (i) change distribution is very uneven; (ii) PageRank, Degree, and CIRank are significantly correlated to the scope of change propagation. Particularly, CIRank shows higher correlation coefficient, which suggests it can be a more useful indicator for measuring the scope of change propagation of classes in object-oriented software system.

Measurement of RF propagation around corners in underground mines and tunnels

PubMed Central

Jacksha, R.; Zhou, C.

2017-01-01

This paper reports measurement results for radio frequency (RF) propagation around 90° corners in tunnels and underground mines, for vertically, horizontally and longitudinally polarized signals. Measurements of signal power attenuation from a main entry into a crosscut were performed at four frequencies — 455, 915, 2450 and 5800 MHz — that are common to underground radio communication systems. From the measurement data, signal power loss was determined as a function of signal coupling from the main entry into the crosscut. The resultant power loss data show there are many factors that contribute to power attenuation from a main entry into a crosscut, including frequency, antenna polarization and cross-sectional entry dimensions. PMID:28626351

Radiowave propagation measurements in Nigeria (preliminary reports)

NASA Astrophysics Data System (ADS)

Falodun, S. E.; Okeke, P. N.

2013-07-01

International conferences on frequency coordination have, in recent years, required new information on radiowave propagation in tropical regions and, in particular, on propagation in Africa. The International Telecommunications Union (ITU-R) initiated `radio-wave propagation measurement campaign' in some African countries some years back. However, none of the ITU-initiated experiments were mounted in Nigeria, and hence, there is lack of adequate understanding of the propagation mechanisms associated with this region of the tropics. The Centre for Basic Space Science (CBSS) of NASRDA has therefore embarked on propagation data collection from the different climatic zones of Nigeria (namely Coastal, Guinea Savannah, Midland, and Sahelian) with the aim of making propagation data available to the ITU, for design and prediction purposes in order to ensure a qualitative and effective communication system in Nigeria. This paper focuses on the current status of propagation data from Nigeria (collected by CBSS), identifying other parameters that still need to be obtained. The centre has deployed weather stations to different locations in the country for refractivity measurements in clear atmosphere, at the ground surface and at an altitude of 100 m, being the average height of communication mast in Nigeria. Other equipments deployed are Micro Rain Radar and Nigerian Environmental and Climatic Observing Program equipments. Some of the locations of the measurement stations are Nsukka (7.4° E, 6.9° N), Akure (5.12° E, 7.15° N), Minna (6.5° E, 9.6° N), Sokoto (5.25° E, 13.08° N), Jos (8.9° E, 9.86° N), and Lagos (3.35° E, 6.6° N). The results obtained from the data analysis have shown that the refractivity values vary with climatic zones and seasons of the year. Also, the occurrence probability of abnormal propagation events, such as super refraction, sub-refraction, and ducting, depends on the location as well as the local time. We have also attempted to identify

Analysis of the Capability and Limitations of Relativistic Gravity Measurements Using Radio Astronomy Methods

NASA Technical Reports Server (NTRS)

Shapiro, I. I.; Counselman, C. C., III

1975-01-01

The uses of radar observations of planets and very-long-baseline radio interferometric observations of extragalactic objects to test theories of gravitation are described in detail with special emphasis on sources of error. The accuracy achievable in these tests with data already obtained, can be summarized in terms of: retardation of signal propagation (radar), deflection of radio waves (interferometry), advance of planetary perihelia (radar), gravitational quadrupole moment of sun (radar), and time variation of gravitational constant (radar). The analyses completed to date have yielded no significant disagreement with the predictions of general relativity.

The detectability of radio emission from exoplanets

NASA Astrophysics Data System (ADS)

Lynch, C. R.; Murphy, Tara; Lenc, E.; Kaplan, D. L.

2018-05-01

Like the magnetised planets in our Solar System, magnetised exoplanets should emit strongly at radio wavelengths. Radio emission directly traces the planetary magnetic fields and radio detections can place constraints on the physical parameters of these features. Large comparative studies of predicted radio emission characteristics for the known population of exoplanets help to identify what physical parameters could be key for producing bright, observable radio emission. Since the last comparative study, many thousands of exoplanets have been discovered. We report new estimates for the radio flux densities and maximum emission frequencies for the current population of known exoplanets orbiting pre-main sequence and main-sequence stars with spectral types F-M. The set of exoplanets predicted to produce observable radio emission are Hot Jupiters orbiting young stars. The youth of these system predicts strong stellar magnetic fields and/or dense winds, which are key for producing bright, observable radio emission. We use a new all-sky circular polarisation Murchison Widefield Array survey to place sensitive limits on 200 MHz emission from exoplanets, with 3σ values ranging from 4.0 - 45.0 mJy. Using a targeted Giant Metre Wave Radio Telescope observing campaign, we also report a 3σ upper limit of 4.5 mJy on the radio emission from V830 Tau b, the first Hot Jupiter to be discovered orbiting a pre-main sequence star. Our limit is the first to be reported for the low-frequency radio emission from this source.

Land mobile satellite propagation measurements in Japan using ETS-V satellite

NASA Technical Reports Server (NTRS)

Obara, Noriaki; Tanaka, Kenji; Yamamoto, Shin-Ichi; Wakana, Hiromitsu

1993-01-01

Propagation characteristics of land mobile satellite communications channels have been investigated actively in recent years. Information of propagation characteristics associated with multipath fading and shadowing is required to design commercial land mobile satellite communications systems, including protocol and error correction method. CRL (Communications Research Laboratory) has carried out propagation measurements using the Engineering Test Satellite-V (ETS-V) at L band (1.5 GHz) through main roads in Japan by a medium gain antenna with an autotracking capability. This paper presents the propagation statistics obtained in this campaign.

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…

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.

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.

The South Pole, Antarctica, Solar Radio Telescope (SPASRT) System

NASA Astrophysics Data System (ADS)

Gerrard, A. J.; Weatherwax, A. T.; Gary, D. E.; Kujawski, J. T.; Nita, G. M.; Melville, R.; Stillinger, A.; Jeffer, G.

2014-12-01

The study of the sun in the radio portion of the electromagnetic spectrum furthers our understanding of fundamental solar processes observed in the X-ray, UV, and visible regions of the spectrum. For example, the study of solar radio bursts, which have been shown to cause serious disruptions of technologies at Earth, are essential for advancing our knowledge and understanding of solar flares and their relationship to coronal mass ejections and solar energetic particles, as well as the underlying particle acceleration mechanisms associated with these processes. In addition, radio coverage of the solar atmosphere could yield completely new insights into the variations of output solar energy, including Alfven wave propagation through the solar atmosphere and into the solar wind, which can potentially modulate and disturb the solar wind and Earth's geospace environment. In this presentation we discuss the development, construction, and testing of the South Pole, Antarctica, Solar Radio Telescope that is planned for installation at South Pole. The system will allow for 24-hour continuous, long-term observations of the sun across the 1-18 GHz frequency band and allow for truly continuous solar observations. We show that this system will enable unique scientific investigations of the solar atmosphere.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suwada, Tsuyoshi; Satoh, Masanori; Telada, Souichi

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 detailedmore » 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.« less

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.

Received signal strength and local terrain profile data for radio network planning and optimization at GSM frequency bands.

PubMed

Popoola, Segun I; Atayero, Aderemi A; Faruk, Nasir

2018-02-01

The behaviour of radio wave signals in a wireless channel depends on the local terrain profile of the propagation environments. In view of this, Received Signal Strength (RSS) of transmitted signals are measured at different points in space for radio network planning and optimization. However, these important data are often not publicly available for wireless channel characterization and propagation model development. In this data article, RSS data of a commercial base station operating at 900 and 1800 MHz were measured along three different routes of Lagos-Badagry Highway, Nigeria. In addition, local terrain profile data of the study area (terrain elevation, clutter height, altitude, and the distance of the mobile station from the base station) are extracted from Digital Terrain Map (DTM) to account for the unique environmental features. Statistical analyses and probability distributions of the RSS data are presented in tables and graphs. Furthermore, the degree of correlations (and the corresponding significance) between the RSS and the local terrain parameters were computed and analyzed for proper interpretations. The data provided in this article will help radio network engineers to: predict signal path loss; estimate radio coverage; efficiently reuse limited frequencies; avoid interferences; optimize handover; and adjust transmitted power level.

Laser-Generated Rayleigh Waves Propagating in Transparent Viscoelastic Adhesive Coating/Metal Substrate Systems

NASA Astrophysics Data System (ADS)

Guan, Yi-jun; Sun, Hong-xiang; Yuan, Shou-qi; Zhang, Shu-yi; Ge, Yong

2016-10-01

We have established numerical models for simulating laser-generated Rayleigh waves in coating/substrate systems by a finite element method and investigated the propagation characteristics of Rayleigh waves in systems concerning the viscoelasticity and transparency of adhesive coatings. In this way, we have studied the influence of the mechanical properties of the coating, such as the elastic moduli, viscoelastic moduli, coating thickness, transparency, and coating material, on the propagation characteristics of the Rayleigh waves. The results show that the propagation characteristics of the Rayleigh waves can be divided into low- and high-frequency parts. The high-frequency propagation characteristics of the Rayleigh wave are closely related to the properties of the adhesive coating.

Radio physics of the sun; Proceedings of the Symposium, University of Maryland, College Park, Md., August 7-10, 1979

NASA Technical Reports Server (NTRS)

Kundu, M. R. (Editor); Gergely, T. E.

1980-01-01

Papers are presented in the areas of the radio characteristics of the quiet sun and active regions, the centimeter, meter and decameter wavelength characteristics of solar bursts, space observations of low-frequency bursts, theoretical interpretations of solar active regions and bursts, joint radio, visual and X-ray observations of active regions and bursts, and the similarities of stellar radio characteristics to solar radio phenomena. Specific topics include the centimeter and millimeter wave characteristics of the quiet sun, radio fluctuations arising upon the transit of shock waves through the transition region, microwave, EUV and X-ray observations of active region loops and filaments, interferometric observations of 35-GHz radio bursts, emission mechanisms for radio bursts, the spatial structure of microwave bursts, observations of type III bursts, the statistics of type I bursts, and the numerical simulation of type III bursts. Attention is also given to the theory of type IV decimeter bursts, Voyager observations of type II and III bursts at kilometric wavelengths, radio and whitelight observations of coronal transients, and the possibility of obtaining radio observations of current sheets on the sun.

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)

Intercomparisons of radiosondes and an airborne refractometer for measuring radio ducts

NASA Astrophysics Data System (ADS)

Morrissey, J. F.; Izumi, Y.; Cote, O. R.

1986-07-01

The capabilities of two types of radiosondes and an aircraft refractometer to measure radio ducting conditions were compared in a series of flights in September 1985 at Chatham, Mass., on Cape Cod. The tests were part of a program studying radio propagation on Air Force communication links. The intercomparisons were made between data from a refractometer mounted on a small single engine aircraft (Cessna 172) and data from an operational National Weather Service synoptic sounding system. The synoptic sonde and the portable sonde were often on the same balloon train. The comparisons show that the aircraft refractometer data indicate the highest number of ducts and the synoptic data the least number of ducts.

Propagation characteristics of partially coherent anomalous elliptical hollow Gaussian beam propagating through atmospheric turbulence along a slant path

NASA Astrophysics Data System (ADS)

Tian, Huanhuan; Xu, Yonggen; Yang, Ting; Ma, Zairu; Wang, Shijian; Dan, Youquan

2017-02-01

Based on the extended Huygens-Fresnel principal and the Wigner distribution function, the root mean square (rms) angular width and propagation factor (M2-factor) of partially coherent anomalous elliptical hollow Gaussian (PCAEHG) beam propagating through atmospheric turbulence along a slant path are studied in detail. Analytical formulae of the rms angular width and M2-factor of PCAEHG beam are derived. Our results show that the rms angular width increases with increasing of wavelength and zenith angle and with decreasing of transverse coherence length, beam waist sizes and inner scale. The M2-factor increases with increasing of zenith angle and with decreasing of wavelength, transverse coherence length, beam waist sizes and inner scale. The saturation propagation distances (SPDs) increase as zenith angle increases. The numerical calculations also indicate that the SPDs of rms angular width and M2-factor for uplink slant paths with zenith angle of π/12 are about 0.2 and 20 km, respectively.

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09

NASA Astrophysics Data System (ADS)

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.; Mitra, D.; Rankin, J. M.; Stappers, B. W.; Wright, G. A. E.; Basu, R.; Szary, A.; van Leeuwen, J.

2017-04-01

We report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09 with ESA's XMM-Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822-09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2-1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ˜0.15 at 0.3 keV to ˜0.6 at 1 keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ˜0.96 × 106 K, hotspot radius R ˜2.0 km) and a hot component (T ˜2.2 × 106 K, R ˜100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822-09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055-52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822-09, which might be a pulsar wind nebula.

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822$-$09

DOE PAGES

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.; ...

2016-12-05

Here, we report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822–09 with ESA's XMM–Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822–09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2–1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ~0.15 at 0.3 keV to ~0.6 at 1more » keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ~0.96 × 10 6 K, hotspot radius R ~2.0 km) and a hot component (T ~2.2 × 10 6 K, R ~100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822–09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055–52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822–09, which might be a pulsar wind nebula.« less

Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822$-$09

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hermsen, W.; Kuiper, L.; Hessels, J. W. T.

Here, we report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822–09 with ESA's XMM–Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822–09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2–1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ~0.15 at 0.3 keV to ~0.6 at 1more » keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ~0.96 × 10 6 K, hotspot radius R ~2.0 km) and a hot component (T ~2.2 × 10 6 K, R ~100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822–09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055–52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822–09, which might be a pulsar wind nebula.« less

Research and application of self - propagating welding technology

NASA Astrophysics Data System (ADS)

Ma, Yunhe; Li, Zhizun; Wang, Jianjiang; Sun, Liming

2018-04-01

Self-propagating welding is an important application area of self-propagating high-temperature synthesis technology (SHS technology), suitable for special environment and special materials welding. This paper briefly introduces the principle of self - propagating welding and its technical characteristics, and briefly summarizes the current research and application of SHS welding around three aspects of thin film welding, welding of refractory welding and emergency welding of battlefield.

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.

Investigation on Characteristic Variation of the FBG Spectrum with Crack Propagation in Aluminum Plate Structures

PubMed Central

Jin, Bo; Zhang, Weifang; Zhang, Meng; Ren, Feifei; Dai, Wei; Wang, Yanrong

2017-01-01

In order to monitor the crack tip propagation of aluminum alloy, this study investigates the variation of the spectrum characteristics of a fiber Bragg grating (FBG), combined with an analysis of the spectrum simulation. The results identify the location of the subordinate peak as significantly associated with the strain distribution along the grating, corresponding to the different plastic zones ahead of the crack tip with various crack lengths. FBG sensors could observe monotonic and cyclic plastic zones ahead of the crack tip, with the quadratic strain distribution along the grating at the crack tip-FBG distance of 1.2 and 0.7 mm, respectively. FBG sensors could examine the process zones ahead of the crack tip with the cubic strain distribution along the grating at the crack tip-FBG distance of 0.5 mm. The spectrum oscillation occurs as the crack approaches the FBG where the highly heterogeneous strain is distributed. Another idea is to use a finite element method (FEM), together with a T-matrix method, to analyze the reflection intensity spectra of FBG sensors for various crack sizes. The described crack propagation detection system may apply in structural health monitoring. PMID:28772949

Investigation on Characteristic Variation of the FBG Spectrum with Crack Propagation in Aluminum Plate Structures.

PubMed

Jin, Bo; Zhang, Weifang; Zhang, Meng; Ren, Feifei; Dai, Wei; Wang, Yanrong

2017-05-27

In order to monitor the crack tip propagation of aluminum alloy, this study investigates the variation of the spectrum characteristics of a fiber Bragg grating (FBG), combined with an analysis of the spectrum simulation. The results identify the location of the subordinate peak as significantly associated with the strain distribution along the grating, corresponding to the different plastic zones ahead of the crack tip with various crack lengths. FBG sensors could observe monotonic and cyclic plastic zones ahead of the crack tip, with the quadratic strain distribution along the grating at the crack tip-FBG distance of 1.2 and 0.7 mm, respectively. FBG sensors could examine the process zones ahead of the crack tip with the cubic strain distribution along the grating at the crack tip-FBG distance of 0.5 mm. The spectrum oscillation occurs as the crack approaches the FBG where the highly heterogeneous strain is distributed. Another idea is to use a finite element method (FEM), together with a T -matrix method, to analyze the reflection intensity spectra of FBG sensors for various crack sizes. The described crack propagation detection system may apply in structural health monitoring.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dowla, Farid; Nekoogar, Faranak

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 accordingmore » 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.« less

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.

AN IMAGING STUDY OF A COMPLEX SOLAR CORONAL RADIO ERUPTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feng, S. W.; Chen, Y.; Song, H. Q.

2016-08-10

Solar coronal radio bursts are enhanced radio emission excited by energetic electrons accelerated during solar eruptions. Studying these bursts is important for investigating the origin and physical mechanism of energetic particles and further diagnosing coronal parameters. Earlier studies suffered from a lack of simultaneous high-quality imaging data of the radio burst and the eruptive structure in the inner corona. Here we present a study on a complex solar radio eruption consisting of a type II burst and three reversely drifting type III bursts, using simultaneous EUV and radio imaging data. It is found that the type II burst is closelymore » associated with a propagating and evolving CME-driven EUV shock structure, originated initially at the northern shock flank and later transferred to the top part of the shock. This source transfer is coincident with the presence of shock decay and enhancing signatures observed at the corresponding side of the EUV front. The electron energy accelerated by the shock at the flank is estimated to be ∼0.3 c by examining the imaging data of the fast-drifting herringbone structure of the type II burst. The reverse-drifting type III sources are found to be within the ejecta and correlated with a likely reconnection event therein. The implications for further observational studies and relevant space weather forecasting techniques are discussed.« less

Improvement of technical purpose materials performance characteristics with the radio frequency low pressure plasma

NASA Astrophysics Data System (ADS)

Makhotkina, L. Yu; Khristoliubova, V. I.

2017-11-01

The main aim of the work is to solve the actual problem of increasing the competitiveness of tanning products by reducing the prime cost and improving the quality of finished products due to the increased durability of the working elements of tanneries. The impact of the low pressure radio frequency (RF) plasma in the processes of treating for modification of the materials for special purposes is considered in the article. The results of working elements of tanneries and the materials for special purposes sample processing by a RF low pressure plasma are described. As a result of leather materials nano structuring and nano modifying physical, mechanical and hygienic characteristics were increased. Processing of the technical purpose materials allows to increase operational performance of products and extend their lifespan.

New challenges in propagation research in the US

NASA Technical Reports Server (NTRS)

Davarian, Faramaz

1993-01-01

Earth/space propagation research in the U.S. is tied to new developments in satellite communications. In spite of the fiber optics competition for trunked point-to-point communications, a host of emerging services are discovering the great potential of satellites for wireless communications. The application of satellites for radio communications appears to grow with a rapid pace in the areas of thin-route and mobile/personal communications. An important factor influencing the future of satellite communications is the congestion of the spectral slots at Ku- and lower bands. This heavy usage of the spectrum gives rise to conflicts among the users and consequently forces regulatory organizations to relocate frequency assignments, a decision that, for obvious reasons, is unpopular with the relocated service. Because of this frequency shortage, frequencies in Ka- and higher spectral bands are currently viewed as good candidates for Earth/space communications in the future. Therefore, new challenges in propagation research in the U.S. include the characterization of mobile/personal links and the investigation of higher bands for satellite communications. The plans and the challenges of the propagation research in the U.S. are briefly reviewed.

Radio frequency communication system utilizing radiating transmission lines

DOEpatents

Struven, Warren C.

1984-01-01

A radio communication system for use in tunnels, mines, buildings or other shielded locations in which a pair of radiating transmission lines (30), (31) extend through such location in spaced coextensive relation to each other. Each transmission line (30), (31) has at least one unidirectional amplifier (32), (33) interposed therein with the sense of the unidirectional amplifier (32) of one transmission line (30) being opposite to the sense of the unidirectional amplifier (33) of the other transmission line (31). Each of the amplifiers (32), (33) has a gain which is less than the coupling loss between the transmission lines (30), (31). Two or more mobile transceivers (35) in the location served by the system are coupled to the transmission lines (30), (31) by electromagnetic wave propagation in space in order to communicate directly with each other at a given radio frequency within the frequency range of the system.

Observations of Nonthermal Radio Emission from Early-type Stars

NASA Technical Reports Server (NTRS)

Abbott, D. C.; Bieging, J. H.; Churchwell, E.

1985-01-01

As a part of a wider survey of radio emission from O, B, and Wolf-Rayet (WR) stars, five new stars whose radio emission is dominated by a nonthermal mechanism of unknown origin were discovered. From statistics of distance-limited samples of stars, it is estimated that the minimum fraction of stars which are nonthermal emitters is 25% for the OB stars and 10% for the WR stars. The characteristics of this new class of nonthermal radio emitter are investigated.

Imaging spectroscopy of type U and J solar radio bursts with LOFAR

NASA Astrophysics Data System (ADS)

Reid, Hamish A. S.; Kontar, Eduard P.

2017-10-01

Context. Radio U-bursts and J-bursts are signatures of electron beams propagating along magnetic loops confined to the corona. The more commonly observed type III radio bursts are signatures of electron beams propagating along magnetic loops that extend into interplanetary space. Given the prevalence of solar magnetic flux to be closed in the corona, why type III bursts are more frequently observed than U-bursts or J-bursts is an outstanding question. Aims: We use Low-Frequency Array (LOFAR) imaging spectroscopy between 30-80 MHz of low-frequency U-bursts and J-bursts, for the first time, to understand why electron beams travelling along coronal loops produce radio emission less often. Radio burst observations provide information not only about the exciting electron beams but also about the structure of large coronal loops with densities that are too low for standard extreme ultraviolet (EUV) or X-ray analysis. Methods: We analysed LOFAR images of a sequence of two J-bursts and one U-burst. The different radio source positions were used to model the spatial structure of the guiding magnetic flux tube and then deduce the energy range of the exciting electron beams without the assumption of a standard density model. We also estimated the electron density along the magnetic flux rope and compared it to coronal models. Results: The radio sources infer a magnetic loop that is 1 solar radius in altitude with the highest frequency sources starting around 0.6 solar radii. Electron velocities were found between 0.13 c and 0.24 c with the front of the electron beam travelling faster than the back of the electron beam. The velocities correspond to energy ranges within the beam from 0.7-11 keV to 0.7-43 keV. The density along the loop is higher than typical coronal density models and the density gradient is smaller. Conclusions: We found that a more restrictive range of accelerated beam and background plasma parameters can result in U-bursts or J-bursts, causing type III

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…

High Frequency Propagation modeling in a disturbed background ionosphere: Results from the Metal Oxide Space Cloud (MOSC) experiment

NASA Astrophysics Data System (ADS)

Joshi, D. R.; Groves, K. M.

2015-12-01

The Air Force Research Laboratory (AFRL) launched two sounding rockets in the Kwajalein Atoll, Marshall Islands, in May 2013 known as the Metal Oxide Space Cloud (MOSC) experiment to study the interactions of artificial ionization and the background plasma. The rockets released samarium metal vapor in the lower F-region of the ionosphere that ionized forming a plasma cloud. A host of diagnostic instruments were used to probe and characterize the cloud including the ALTAIR incoherent scatter radar, multiple GPS and optical instruments, satellite radio beacons, and a dedicated network of high frequency (HF) radio links. Data from ALTAIR incoherent scatter radar and HF radio links have been analyzed to understand the impacts of the artificial ionization on radio wave propagation. During the first release the ionosphere was disturbed, rising rapidly and spread F formed within minutes after the release. To address the disturbed conditions present during the first release, we have developed a new method of assimilating oblique ionosonde data to generate the background ionosphere that can have numerous applications for HF systems. The link budget analysis of the received signals from the HF transmitters explains the missing low frequencies in the received signals along the great circle path. Observations and modeling confirm that the small amounts of ionized material injected in the lower-F region resulted in significant changes to the natural propagation environment.

Voltage tunable plasmon propagation in dual gated bilayer graphene

NASA Astrophysics Data System (ADS)

Farzaneh, Seyed M.; Rakheja, Shaloo

2017-10-01

In this paper, we theoretically investigate plasmon propagation characteristics in AB and AA stacked bilayer graphene (BLG) in the presence of energy asymmetry due to an electrostatic field oriented perpendicularly to the plane of the graphene sheet. We first derive the optical conductivity of BLG using the Kubo formalism incorporating energy asymmetry and finite electron scattering. All results are obtained for room temperature (300 K) operation. By solving Maxwell's equations in a dual gate device setup, we obtain the wavevector of propagating plasmon modes in the transverse electric (TE) and transverse magnetic (TM) directions at terahertz frequencies. The plasmon wavevector allows us to compare the compression factor, propagation length, and the mode confinement of TE and TM plasmon modes in bilayer and monolayer graphene sheets and also to study the impact of material parameters on plasmon characteristics. Our results show that the energy asymmetry can be harnessed to increase the propagation length of TM plasmons in BLG. AA stacked BLG shows a larger increase in the propagation length than AB stacked BLG; conversely, it is very insensitive to the Fermi level variations. Additionally, the dual gate structure allows independent modulation of the energy asymmetry and the Fermi level in BLG, which is advantageous for reconfiguring plasmon characteristics post device fabrication.

Dry and wet arc track propagation resistance testing

NASA Technical Reports Server (NTRS)

Beach, Rex

1995-01-01

The wet arc-propagation resistance test for wire insulation provides an assessment of the ability of an insulation to prevent damage in an electrical environment. Results of an arc-propagation test may vary slightly due to the method of arc initiation; therefore a standard test method must be selected to evaluate the general arc-propagation resistance characteristics of an insulation. This test method initiates an arc by dripping salt water over pre-damaged wires which creates a conductive path between the wires. The power supply, test current, circuit resistances, and other variables are optimized for testing 20 guage wires. The use of other wire sizes may require modifications to the test variables. The dry arc-propagation resistance test for wire insulation also provides an assessment of the ability of an insulation to prevent damage in an electrical arc environment. In service, electrical arcs may originate form a variety of factors including insulation deterioration, faulty installation, and chafing. Here too, a standard test method must be selected to evaluate the general arc-propagation resistance characteristics of an insulation. This test method initiates an arc with a vibrating blade. The test also evaluates the ability of the insulation to prevent further arc-propagation when the electrical arc is re-energized.

On High and Low Starting Frequencies of Type II Radio Bursts

NASA Astrophysics Data System (ADS)

Sharma, J.; Mittal, N.

2017-06-01

We have studied the characteristics of type II radio burst during the period May 1996 to March 2015, for the solar cycle 23 and 24, observed by WIND/WAVES radio instrument. A total of 642 events were recorded by the instrument during the study period. We have divided the events with two starting frequency range (high > 1 MHz; low ≤ 1MHz) as type II1 (i.e., 1-16 MHz) radio burst and type II2 (i.e., 20 KHz - 1020 KHz) radio burst which constitute the DH and km type II radio burst observed by WIND spacecraft, and determined their time and frequency characteristics. The mean drift rate of type II1 and type II2 radio bursts is 29.76 × 10-4 MHz/s and 0.17 × 10-4 MHz/s respectively, which shows that type II1 with high start frequency hase larger drift rate than the type II2 with low starting frequencies. We have also reported that the start frequency and the drift rate of type II1 are in good correlation, with a linear correlation coefficient of 0.58.

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.

[Community types, phenology and propagation characteristics of Taxus mairei in north Guangdong].

PubMed

Liao, Wenbo; Zhang, Zhiqian; Chen, Zhiming; Tang, Changgen; Deng, Shifu

2002-07-01

Community types, phenology and propagation characteristics of Taxus mairei in north Guangdong were studied. The results showed that in north Guangdong province, Taxus mairei mainly distributed in the typical ever-green broad-leaf forest of lower and mid-subtropics dispersedly. Terminal bud of Taxus mairei was formed in late October and begun to grow foliages in mid-April, male flower bud was appeared in mid-May and the efflorescence was from late July to late November, female flower bud was formed in late August and the efflorescence was from late October to late January of second year, and the fruit mature period was in early October of second year. Under natural condition, the seed germination needed 2-3 years. Under experimental condition, the germination rate could be up to 82.2%. The effect of cuttage was better by taking mature annual twig and pretreatment by ABT1(100 mg.L-1) from October to November every year, and the rooting rate could be up to 95%.

CCIR paper on the radiocommunications requirements for systems to search for extraterrestrial life

NASA Technical Reports Server (NTRS)

Nightingale, D.

1978-01-01

The allocation and propagation of radio frequency bands to be used in the search for extraterrestrial intelligence is considered. Topics discussed include: propagation factors; preferred frequency bands; system characteristics and requirements; and interference.

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.

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.

ATS-5 millimeter wave propagation measurements

NASA Technical Reports Server (NTRS)

Ippolito, L. J.

1973-01-01

Long term experimental measurements to determine the propagation characteristics of 15 and 32 GHz earth-space links and to evaluate performance characteristics of operational millimeter wave systems are reported. The ATS 5 millimeter wave experimental link experienced attenuation and fading characteristics as a function of rainfall rate and other meteorological parameters. A method of site selection for the lowest attenuation rainfall rate improved reception tremendously.

Sea Turtles Geolocalization in the Indian Ocean: An Over Sea Radio Channel framework integrating a trilateration technique

NASA Astrophysics Data System (ADS)

Guegan, Loic; Murad, Nour Mohammad; Bonhommeau, Sylvain

2018-03-01

This paper deals with the modeling of the over sea radio channel and aims to establish sea turtles localization off the coast of Reunion Island, and also on Europa Island in the Mozambique Channel. In order to model this radio channel, a framework measurement protocol is proposed. The over sea measured channel is integrated to the localization algorithm to estimate the turtle trajectory based on Power of Arrival (PoA) technique compared to GPS localization. Moreover, cross correlation tool is used to characterize the over sea propagation channel. First measurement of the radio channel on the Reunion Island coast combine to the POA algorithm show an error of 18 m for 45% of the approximated points.

Directional Statistics for Polarization Observations of Individual Pulses from Radio Pulsars

NASA Astrophysics Data System (ADS)

McKinnon, M. M.

2010-10-01

Radio polarimetry is a three-dimensional statistical problem. The three-dimensional aspect of the problem arises from the Stokes parameters Q, U, and V, which completely describe the polarization of electromagnetic radiation and conceptually define the orientation of a polarization vector in the Poincaré sphere. The statistical aspect of the problem arises from the random fluctuations in the source-intrinsic polarization and the instrumental noise. A simple model for the polarization of pulsar radio emission has been used to derive the three-dimensional statistics of radio polarimetry. The model is based upon the proposition that the observed polarization is due to the incoherent superposition of two, highly polarized, orthogonal modes. The directional statistics derived from the model follow the Bingham-Mardia and Fisher family of distributions. The model assumptions are supported by the qualitative agreement between the statistics derived from it and those measured with polarization observations of the individual pulses from pulsars. The orthogonal modes are thought to be the natural modes of radio wave propagation in the pulsar magnetosphere. The intensities of the modes become statistically independent when generalized Faraday rotation (GFR) in the magnetosphere causes the difference in their phases to be large. A stochastic version of GFR occurs when fluctuations in the phase difference are also large, and may be responsible for the more complicated polarization patterns observed in pulsar radio emission.

Modeling Amateur Radio Soundings of the Ionospheric Response to the 2017 Great American Eclipse

NASA Astrophysics Data System (ADS)

Frissell, N. A.; Katz, J. D.; Gunning, S. W.; Vega, J. S.; Gerrard, A. J.; Earle, G. D.; Moses, M. L.; West, M. L.; Huba, J. D.; Erickson, P. J.; Miller, E. S.; Gerzoff, R. B.; Liles, W.; Silver, H. W.

2018-05-01

On 21 August 2017, a total solar eclipse traversed the continental United States and caused large-scale changes in ionospheric densities. These were detected as changes in medium- and high-frequency radio propagation by the Solar Eclipse QSO Party citizen science experiment organized by the Ham Radio Science Citizen Investigation (hamsci.org). This is the first eclipse-ionospheric study to make use of measurements from a citizen-operated, global-scale HF propagation network and develop tools for comparison to a physics-based model ionosphere. Eclipse effects were observed ±0.3 hr on 1.8 MHz, ±0.75 hr on 3.5 and 7 MHz, and ±1 hr on 14 MHz and are consistent with eclipse-induced ionospheric densities. Observations were simulated using the PHaRLAP raytracing toolkit in conjunction with the eclipsed SAMI3 ionospheric model. Model results suggest 1.8, 3.5, and 7 MHz refracted at h≥125 km altitude with elevation angles θ≥22°, while 14 MHz signals refracted at h < 125 km with elevation angles θ < 10°.

Radio-frequency characteristic variation of interdigital capacitor having multilayer graphene of various widths

NASA Astrophysics Data System (ADS)

Lee, Hee-Jo; Hong, Young-Pyo

2018-03-01

In this paper, a radio-frequency circuit model of an interdigital capacitor (IDC) with a multilayer graphene (MLG) width variation is proposed. The circuit model with three sample configurations, i.e., a bare IDC, IDC-MLG with a width of 5 μm, and IDC-MLG with a width of 20 μm, is constructed via a fitted method based on the measured samples. The simulated results of the circuit model are validated through the RF characteristics, e.g., the capacitance and the self-resonance frequency, of the measured samples. From the circuit model, all samples show not only a similar capacitance behavior but also an identical self-resonance frequency of 10 GHz. Moreover, the R, L, and C values of MLG with a 5 μm width (MLG with a 20 μm width) alone are approximately 0.8 kΩ (0.5 kΩ), 0.5 nH (0.9 nH), and 0.3 pF (0.1 pF), respectively. As a result, we find that the simulated results are in good agreement with RF characteristics of the measured samples. In the future, we expect that the proposed circuit model of an IDC with MLG will offer assistance with performance predictions of diverse IDC-based 2D material applications, such as biosensors and gas sensors, as well as supercapacitors.

The Gamma-Ray Emitting Radio-Loud Narrow-Line Seyfert 1 Galaxy PKS 2004-447 II. The Radio View

NASA Technical Reports Server (NTRS)

Schulz, R.; Kreikenbohm, A.; Kadler, M.; Ojha, R.; Ros, E.; Stevens, J.; Edwards, P. G.; Carpenter, B.; Elsaesser, D.; Gehrels, N.;

Comparison between model predictions and observations of ELF radio atmospherics generated by rocket-triggered lightning

NASA Astrophysics Data System (ADS)

Dupree, N. A.; Moore, R. C.

2011-12-01

Model predictions of the ELF radio atmospheric generated by rocket-triggered lightning are compared with observations performed at Arrival Heights, Antarctica. The ability to infer source characteristics using observations at great distances may prove to greatly enhance the understanding of lightning processes that are associated with the production of transient luminous events (TLEs) as well as other ionospheric effects associated with lightning. The modeling of the sferic waveform is carried out using a modified version of the Long Wavelength Propagation Capability (LWPC) code developed by the Naval Ocean Systems Center over a period of many years. LWPC is an inherently narrowband propagation code that has been modified to predict the broadband response of the Earth-ionosphere waveguide to an impulsive lightning flash while preserving the ability of LWPC to account for an inhomogeneous waveguide. ELF observations performed at Arrival Heights, Antarctica during rocket-triggered lightning experiments at the International Center for Lightning Research and Testing (ICLRT) located at Camp Blanding, Florida are presented. The lightning current waveforms directly measured at the base of the lightning channel (at the ICLRT) are used together with LWPC to predict the sferic waveform observed at Arrival Heights under various ionospheric conditions. This paper critically compares observations with model predictions.

A New Signaling Architecture THREP with Autonomous Radio-Link Control for Wireless Communications Systems

NASA Astrophysics Data System (ADS)

Hirono, Masahiko; Nojima, Toshio

This paper presents a new signaling architecture for radio-access control in wireless communications systems. Called THREP (for THREe-phase link set-up Process), it enables systems with low-cost configurations to provide tetherless access and wide-ranging mobility by using autonomous radio-link controls for fast cell searching and distributed call management. A signaling architecture generally consists of a radio-access part and a service-entity-access part. In THREP, the latter part is divided into two steps: preparing a communication channel, and sustaining it. Access control in THREP is thus composed of three separated parts, or protocol phases. The specifications of each phase are determined independently according to system requirements. In the proposed architecture, the first phase uses autonomous radio-link control because we want to construct low-power indoor wireless communications systems. Evaluation of channel usage efficiency and hand-over loss probability in the personal handy-phone system (PHS) shows that THREP makes the radio-access sub-system operations in a practical application model highly efficient, and the results of a field experiment show that THREP provides sufficient protection against severe fast CNR degradation in practical indoor propagation environments.

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

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.

Afterglow model for the radio emission from the jetted tidal disruption candidate Swift J1644+57

NASA Astrophysics Data System (ADS)

Metzger, Brian D.; Giannios, Dimitrios; Mimica, Petar

2012-03-01

The recent transient event Swift J1644+57 has been interpreted as emission from a collimated relativistic jet, powered by the sudden onset of accretion on to a supermassive black hole following the tidal disruption of a star. Here we model the radio-microwave emission as synchrotron radiation produced by the shock interaction between the jet and the gaseous circumnuclear medium (CNM). At early times after the onset of the jet (t≲ 5-10 d) a reverse shock propagates through and decelerates the ejecta, while at later times the outflow approaches the Blandford-McKee self-similar evolution (possibly modified by additional late energy injection). The achromatic break in the radio light curve of Swift J1644+57 is naturally explained as the transition between these phases. We show that the temporal indices of the pre- and post-break light curve are consistent with those predicted if the CNM has a wind-type radial density profile n∝r-2. The observed synchrotron frequencies and self-absorbed flux constrain the fraction of the post-shock thermal energy in relativistic electrons ɛe≈ 0.03-0.1, the CNM density at 1018 cm n18≈ 1-10 cm-3 and the initial Lorentz factor Γj≈ 10-20 and opening angle ? of the jet. Radio modelling thus provides robust independent evidence for a narrowly collimated outflow. Extending our model to the future evolution of Swift J1644+57, we predict that the radio flux at low frequencies (ν≲ few GHz) will begin to brighten more rapidly once the characteristic frequency νm crosses below the radio band after it decreases below the self-absorption frequency on a time-scale of months (indeed, such a transition may already have begun). Our results demonstrate that relativistic outflows from tidal disruption events provide a unique probe of the conditions in distant, previously inactive galactic nuclei, complementing studies of normal active galactic nuclei.

Methode des Rayons avec Calcul d’Intensite Appliquee a la Propagation Anormale (Method of Ray Intensity Calculation as Applied to Anomalous Propagation),

DTIC Science & Technology

1986-06-01

D’INTENSITE 0 APPLIQUEE A LA PROPAGATION "ANORNALE" par D. Dion DEFENCE RESEARCH ESTABLISHMENT CENTRE DE RECHERCHES POUR LA DEFENSE VALCARTI ER 6- Tel: (418...faqon ils sont reli~s aux conditions atmosph~riques. Les ph~no- manes les plus importants A signaler sont les conduits et les "trous radio". En effet...6tant tr~s fr~quents en mer, 11 est d’int&rt pour la marine de rechercher des m~thodes simples permettant de les caract~riser. Des 6quations d’int

Radio continuum properties of luminous infrared galaxies. Identifying the presence of an AGN in the radio

NASA Astrophysics Data System (ADS)

Vardoulaki, E.; Charmandaris, V.; Murphy, E. J.; Diaz-Santos, T.; Armus, L.; Evans, A. S.; Mazzarella, J. M.; Privon, G. C.; Stierwalt, S.; Barcos-Muñoz, L.

2015-02-01

Context. Luminous infrared galaxies (LIRGs) are systems enshrouded in dust, which absorbs most of their optical/UV emission and radiates it again in the mid- and far-infrared. Radio observations are largely unaffected by dust obscuration, enabling us to study the central regions of LIRGs in an unbiased manner. Aims: The main goal of this project is to examine how the radio properties of local LIRGs relate to their infrared spectral characteristics. Here we present an analysis of the radio continuum properties of a subset of the Great Observatories All-sky LIRG Survey (GOALS), which consists of 202 nearby systems (z< 0.088). Our radio sample consists of 35 systems, containing 46 individual galaxies, that were observed at both 1.49 and 8.44 GHz with the VLA with a resolution of about 1 arcsec (FWHM). The aim of the project is to use the radio imagery to probe the central kpc of these LIRGs in search of active galactic nuclei (AGN). Methods: We used the archival data at 1.49 and 8.44 GHz to create radio-spectral-index maps using the standard relation between flux density Sν and frequency ν, Sν ~ ν- α, where α is the radio spectral index. By studying the spatial variations in α, we classified the objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the presence of an active nucleus using the radio morphology, deviations from the radio/infrared correlation, and spatially resolved spectral index maps, and then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII] line ratios and equivalent width of the 6.2 μm PAH feature) and optical (BPT diagram) AGN diagnostics. Results: We find that 21 out of the 46 objects in our sample (~45%) are radio-AGN, 9 out of the 46 (~20%) are classified as starbursts (SB) based on the radio analysis, and 16 (~35%) are AGN/SB. After comparing to other AGN diagnostics we find 3 objects out of the 46 (~7%) that are identified as AGN based on the radio analysis, but are not classified as such based on

Interplanetary scintillation observations with the Cocoa Cross radio telescope

NASA Technical Reports Server (NTRS)

Cronyn, W. M.; Shawhan, S. D.; Erskine, F. T.; Huneke, A. H.; Mitchell, D. G.

1976-01-01

Physical and electrical parameters for the 34.3-MHz Cocoa Cross radio telescope are given. The telescope is dedicated to the determination of solar-wind characteristics in and out of the ecliptic plane through measurement of electron-density irregularity structure as determined from IPS (interplanetary scintillation) of natural radio sources. The collecting area (72,000 sq m), angular resolution (0.4 deg EW by 0.6 deg NS), and spatial extent (1.3 km EW by 0.8 km NS) make the telescope well suited for measurements of IPS index and frequency scale for hundreds of weak radio sources without serious confusion effects.

Quasi-periodic Radio Bursts Associated with Fast-mode Waves near a Magnetic Null Point

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Pankaj; Nakariakov, Valery M.; Cho, Kyung-Suk, E-mail: pankaj.kumar@nasa.gov

This paper presents an observation of quasi-periodic rapidly propagating waves observed in the Atmospheric Image Assembly (AIA) 171/193 Å channels during the impulsive phase of an M1.9 flare that occurred on 2012 May 7. The instant period was found to decrease from 240 to 120 s, and the speed of the wavefronts was in the range of ∼664–1416 km s{sup −1}. Almost simultaneously, quasi-periodic bursts with similar instant periods, ∼70 and ∼140 s, occur in the microwave emission and in decimetric type IV and type III radio bursts, and in the soft X-ray emission. The magnetic field configuration of themore » flare site was consistent with a breakout topology, i.e., a quadrupolar field along with a magnetic null point. The quasi-periodic rapidly propagating wavefronts of the EUV emission are interpreted as a fast magnetoacoustic wave train. The observations suggest that the fast-mode waves are generated during the quasi-periodic magnetic reconnection in the cusp region above the flare arcade loops. For the first time, we provide evidence of a tadpole wavelet signature at about 70–140 s in decimetric (245/610 MHz) radio bursts, along with the direct observation of a coronal fast-mode wave train in EUV. In addition, at AIA 131/193 Å we observed quasi-periodic EUV disturbances with periods of 95 and 240 s propagating downward at apparent speeds of 172–273 km s{sup −1}. The nature of these downward propagating disturbances is not revealed, but they could be connected to magnetoacoustic waves or periodically shrinking loops.« less

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.

Seventy Years of Radio Science, Technology, Standards, and Measurement at the National Bureau of Standards

NASA Astrophysics Data System (ADS)

Gillmor, C. Stewart

This large volume describes all the forms of radio research done at the National Bureau of Standards (now, National Institute of Standards and Technology) from its founding in 1901 until about 1980. The volume truly reflects its subtitle; it describes in great detail research in radio propagation and all its connections with geophysics and geospace, but also radio as instrument for discovery and application in meteorology, navigation, and in standards of measurement and testing in electronics.The book is a bit unwieldy and some of its chapters will be of most interest to former NBS employees. For example, there is a lengthy chapter on the transfer of radio research work from Washington, D.C, to Boulder, Colo., in the early 1950s, complete with photostat of the quit claim deed to NBS from the Boulder Chamber of Commerce. On the other hand, radio research developed and flourished in this country in the early days at industrial (Bell Telephone, General Electric, Westinghouse) and government (NBS, Naval Research Laboratory) labs more than in academia, and it is very interesting to learn how the labs interacted and to read details of the organizational structure. I can attest personally to the great difficulties in locating materials concerning radio history. While we have numerous volumes devoted to certain popular radio heroes, little is available concerning government radio pioneers such as L. W. Austin, who directed the U.S. Navy's radio research for many years while situated physically at the Bureau of Standards, or J. H. Dellinger, long-time chief of the Radio Section and head spokesman on radio for the U.S. government until the 1930s.

Atmospheric sound propagation

NASA Technical Reports Server (NTRS)

Cook, R. K.

1969-01-01

The propagation of sound waves at infrasonic frequencies (oscillation periods 1.0 - 1000 seconds) in the atmosphere is being studied by a network of seven stations separated geographically by distances of the order of thousands of kilometers. The stations measure the following characteristics of infrasonic waves: (1) the amplitude and waveform of the incident sound pressure, (2) the direction of propagation of the wave, (3) the horizontal phase velocity, and (4) the distribution of sound wave energy at various frequencies of oscillation. Some infrasonic sources which were identified and studied include the aurora borealis, tornadoes, volcanos, gravity waves on the oceans, earthquakes, and atmospheric instability waves caused by winds at the tropopause. Waves of unknown origin seem to radiate from several geographical locations, including one in the Argentine.

Source Regions of the Type II Radio Burst Observed During a CME-CME Interaction on 2013 May 22

NASA Technical Reports Server (NTRS)

Makela, P.; Gopalswamy, N.; Reiner, M. J.; Akiyama, S.; Krupar, V.

2016-01-01

We report on our study of radio source regions during the type II radio burst on 2013 May 22 based on direction finding analysis of the Wind/WAVES and STEREO/WAVES (SWAVES) radio observations at decameter-hectometric wavelengths. The type II emission showed an enhancement that coincided with the interaction of two coronal mass ejections (CMEs) launched in sequence along closely spaced trajectories. The triangulation of the SWAVES source directions posited the ecliptic projections of the radio sources near the line connecting the Sun and the STEREO-A spacecraft. The WAVES and SWAVES source directions revealed shifts in the latitude of the radio source, indicating that the spatial location of the dominant source of the type II emission varies during the CME-CME interaction. The WAVES source directions close to 1MHz frequencies matched the location of the leading edge of the primary CME seen in the images of the LASCO/C3 coronagraph. This correspondence of spatial locations at both wavelengths confirms that the CME-CME interaction region is the source of the type II enhancement. Comparison of radio and white-light observations also showed that at lower frequencies scattering significantly affects radio wave propagation.

Radio-Frequency Emissions from Streamer Collisions: Implications for High-Energy Processes.

NASA Astrophysics Data System (ADS)

Luque, A.

2017-12-01

The production of energetic particles in a discharge corona is possibly linked to the collision of streamers of opposite polarities [Cooray et al. (2009), Kochkin et al. (2012), Østgaard et al. (2016)]. There is also experimental evidence linking it to radio-frequency emissions in the UHF frequency range (300 MHz-3 GHz) [Montanyà et al. (2015), Petersen and Beasley (2014)]. Here we investigate these two links by modeling the radio-frequency emissions emanating from an encounter between two counter-propagating streamers. Our numerical model combines self-consistently a conservative, high-order Finite-Volume scheme for electron transport with a Finite-Difference Time-Domain (FDTD) method for electromagnetic propagation. We also include the most relevant reactions for streamer propagation: impact ionization, dissociative attachment and photo-ionization. Our implementation benefits from massive parallelization by running on a General-Purpose Graphical Processing Unit (GPGPU). With this code we found that streamer encounters emit electromagnetic waves predominantly in the UHF range, supporting the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges. References Cooray, V., et al., J. Atm. Sol.-Terr. Phys., 71, 1890, doi:10.1016/j.jastp.2009.07.010 (2009). Kochkin, P. O., et al., J. Phys. D, 45, 425202, doi: 10.1088/0022-3727/45/42/425202 (2012). Montanyà, J., et al., J. Atm. Sol.-Terr. Phys., 136, 94, doi:10.1016/j.jastp.2015.06.009, (2015). Østgaard, N., et al., J. Geophys. Res. (Atmos.), 121, 2939, doi:10.1002/2015JD024394 (2016). Petersen, D., and W. Beasley, Atmospheric Research, 135, 314, doi:10.1016/j.atmosres.2013.02.006 (2014).

A theory for narrow-banded radio bursts at Uranus - MHD surface waves as an energy driver

NASA Technical Reports Server (NTRS)

Farrell, W. M.; Curtis, S. A.; Desch, M. D.; Lepping, R. P.

1992-01-01

A possible scenario for the generation of the narrow-banded radio bursts detected at Uranus by the Voyager 2 planetary radio astronomy experiment is described. In order to account for the emission burstiness which occurs on time scales of hundreds of milliseconds, it is proposed that ULF magnetic surface turbulence generated at the frontside magnetopause propagates down the open/closed field line boundary and mode-converts to kinetic Alfven waves (KAW) deep within the polar cusp. The oscillating KAW potentials then drive a transient electron stream that creates the bursty radio emission. To substantiate these ideas, Voyager 2 magnetometer measurements of enhanced ULF magnetic activity at the frontside magnetopause are shown. It is demonstrated analytically that such magnetic turbulence should mode-convert deep in the cusp at a radial distance of 3 RU.

Analysis of Characteristics and Requirements for 5G Mobile Communication Systems

NASA Astrophysics Data System (ADS)

Ancans, G.; Stafecka, A.; Bobrovs, V.; Ancans, A.; Caiko, J.

2017-08-01

One of the main objectives of the fifth generation (5G) mobile communication systems, also known as IMT-2020, is to increase the current data rates up to several gigabits per second (Gbit/s) or even up to 10 Gbit/s and higher. One of the possibilities to consider is the use of higher frequencies in order to enlarge the available bandwidth. Wider bandwidth is necessary to achieve much higher data rates. It should be noted that wireless broadband transmission technologies require frequencies for their development. The main goal of the research is to investigate the characteristics and requirements of 5G mobile communication systems. The paper provides an insight into deployment scenario and radio wave propagation in frequencies above 24 GHz of IMT-2020.

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.

Vertically Propagating Waves in the Upper Atmosphere of Saturn From Cassini Radio Occultations

NASA Astrophysics Data System (ADS)

Schinder, P. J.; Flasar, F. M.; Kliore, A. J.; French, R. G.; Marouf, E. A.; Nagy, A.; Rappaport, N.; Anabtawi, A.; Asmar, S.; Barbinis, E.; Fleischman, D. U.; Goltz, G. L.; Johnston, D. V.; Rochblatt, D.; McGhee, C. A.

2005-12-01

We present results from 12 ingress and egress soundings done within 10 degrees of Saturn's equator. Above the 100-mbar level, near the tropopause, the vertical profiles of temperature are marked by undulatory structure that may be associated with vertically propagating waves. We determine the properties and spectra of these waves, and speculate on their origins and their dynamical effects on the upper atmosphere.

Accurate Estimate of Some Propagation Characteristics for the First Higher Order Mode in Graded Index Fiber with Simple Analytic Chebyshev Method

NASA Astrophysics Data System (ADS)

Dutta, Ivy; Chowdhury, Anirban Roy; Kumbhakar, Dharmadas

2013-03-01

Using Chebyshev power series approach, accurate description for the first higher order (LP11) mode of graded index fibers having three different profile shape functions are presented in this paper and applied to predict their propagation characteristics. These characteristics include fractional power guided through the core, excitation efficiency and Petermann I and II spot sizes with their approximate analytic formulations. We have shown that where two and three Chebyshev points in LP11 mode approximation present fairly accurate results, the values based on our calculations involving four Chebyshev points match excellently with available exact numerical results.

Low frequency spectra of type III solar radio bursts

NASA Technical Reports Server (NTRS)

Weber, R. R.

1978-01-01

Flux density spectra have been determined for 91 simple type III solar bursts observed by the Goddard Space Flight Center radio astronomy experiment on the IMP-6 spacecraft during 1971 and 1972. Spectral peaks were found to occur at frequencies ranging from 44 kHz up to 2500 kHz. Half of the bursts peaked between 250 kHz and 900 kHz, corresponding to emission at solar distances of about 0.3 to 0.1 AU. Maximum burst flux density sometimes exceeds 10 to the -14th W/sq m/Hz. The primary factor controlling the spectral peak frequency of these bursts appears to be a variation in intrinsic power radiated by the source as the exciter moves outward from the sun, rather than radio propagation effects between the source and IMP-6. Thus, a burst spectrum strongly reflects the evolution of the properties of the exciting electron beam, and according to current theory, beam deceleration could help account for the observations.

Propagation characteristics of two-color laser pulses in homogeneous plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 withmore » 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.« less

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.

I. S. Shklovsky and Low-Frequency Radio Astronomy

NASA Astrophysics Data System (ADS)

Konovalenko, A. A.

2017-03-01

Purpose: Proving of the high astrophysical significance of the low-frequency radio astronomy (decameter and adjacent hectometer and meter wavelengths), demonstration of the priority results of the Ukrainian low-frequency radio astronomy as well as significant contribution of I. S. Shklovsky to its development. Design/methodology/approach: The requirements to characteristics of high efficiency radio telescopes UTR-2, URAN, GURT and to sensitive and interference immune observational methods at low frequencies are formulated by using the theoretical analysis and astrophysical predictions including those I. S. Shklovsky’s. Findings: New generation radio telescopes UTR-2, URAN, GURT are created and modernized. New observational methods at low frequencies are introduced. Large-scale investigations of the Solar system, Galaxy and Methagalaxy are carried out. They have allowed to detect new objects and phenomena for the continuum, monochromatic, pulse and sporadic cosmic radio emission. The role of I. S. Shklovsky in the development of many low-frequency radio astronomy directions is noted, too. Conclusions: The unique possibilities of the low-frequency radio astronomy which gives new information about the Universe, inaccessible with the other astrophysical methods, are shown. The progress of the low-frequency radio astronomy opens the impressive possibilities for the future. It includes modernization of the largest radio telescopes UTR-2, URAN, NDA and creation of new instruments GURT, NenuFAR, LOFAR, LWA, MWA, SKA as well as making multi-antenna and ground-space experiments. The contribution of outstanding astrophysicist of the XX century I. S. Shklovsky to this part of actual astronomical science is evident, claiming for attention and will never be forgotten.

X-ray Properties and the Environment of Compact Radio Sources.

NASA Astrophysics Data System (ADS)

Siemiginowska, Aneta; Sobolewska, Malgorzata; Guainazzi, Matteo; Hardcastle, Martin; Migliori, Giulia; Ostorero, Luisa; Stawarz, Lukasz

2018-01-01

Compact extragalactic radio sources provide important insights into the initial stages of radio source evolution and probe states of a black hole activity at the time of the formation of the relativistic outflow. Such outflows propagate out to hundreds kpc distances from the origin and impact environment on many scales, and thus influence evolution of structures in the universe. These compact sources show radio features typically observed in large-scale radio galaxies (jets, lobes, hot spots), but contained within the central 1 kpc region of the host galaxy. Compact Symmetric Objects (CSOs, a subclass of GigaHertz Peaked spectrum radio sources) are symmetric and not affected by beaming. Their linear radio size can be translated into a source age if one measures the expansion velocity of the radio structures. Such ages has been measured for a small sample of CSOs. Using the Chandra X-ray Observatory and XMM-Newton we observed a pilot samples of 16 CSOs in X-rays (6 for the first time). Our results show heterogeneous nature of the CSOs X-ray emission indicating a range of AGN luminosities and a complex environment. In particular, we identified four Compton Thick sources with a dense medium (equivalent column > 1e24 cm^-2) capable of disturbing/slowing down the jet and confining the jet to a small region. Thus for the first time we gain the observational evidence in X-ray domain in favor of the hypothesis that in a sub-population of CSOs the radio jets may be confined by the dense X-ray obscuring medium. As a consequence, the kinematic ages of these CSOs may be underestimated.. We discuss the implications of our results on the emission models of CSOs, the earliest stages of the radio source evolution, jet interactions with the ISM, diversity of the environments in which the jets expand, and jet-galaxy co-evolution.Partial support for this work was provided by the NASA grants GO1-12145X, GO4-15099X, NNX10AO60G, NNX17AC23G and XMM AO15 project 78461. This work supported

Experimental investigation of outdoor propagation of finite-amplitude noise. [aircraft noise

NASA Technical Reports Server (NTRS)

Webster, D. A.; Blackstock, D. T.

1978-01-01

The outdoor propagation of finite amplitude acoustic waves was investigated using a conventional electroacoustic transmitter which was mounted on the ground and pointed upward in order to avoid ground reflection effects. The propagation path was parallel to a radio tower 85 m tall, whose elevator carried the receiving microphone. The observations and conclusions are as follows: (1) At the higher source levels nonlinear propagation distortion caused a strong generation of high frequency noise over the propagation path. For example, at 70 m for a frequency 2-3 octaves above the source noise band, the measured noise was up to 30 dB higher than the linear theory prediction. (2) The generation occurred in both the nearfield and the farfield of the transmitter. (3) At no measurement point was small-signal behavior established for the high requency noise. Calculations support the contention that the nonlinearity generated high frequency noise never becomes small-signal in its behavior, regardless of distance. (4) When measured spectra are scaled in frequency and level to make them comparable with spectra of actual jet noise, they are found to be well within the jet noise range. It is therefore entirely possible that nonlinear distortion affects jet noise.

Ir A.H. de Voogt: life and career of a radio pioneer

NASA Astrophysics Data System (ADS)

Strom, R. G.

2007-06-01

There are probably few radio astronomers who would be able to recall A.H. de Voogt, which is unfortunate, but at the same time unsurprising: for he published no original astronomical research, never carried out pioneering observations, nor is his name linked to either theoretical or instrumental breakthroughs. Yet he was described by the man who first observed the 21 cm hydrogen line from the Netherlands as a radio astronomy pioneer, at the very birth of the Dutch effort. He was, moreover, a trail blazer at the cutting edge of radio, not once but twice in his career. Without him it is unlikely that the 21 cm line would have been observed in the Netherlands in 1951, and arguably the H I mapping of the Milky Way under Jan Oort's leadership would have taken place much later, if at all. Radio astronomy observing itself might well have been compromised by interference had it not been for De Voogt's foresight. \\ Anthonet Hugo de Voogt (1892-1969) built, while still a teenager, one of the very first amateur radio stations (call letters VO: *** -/- - -) in Holland, earned the radio-telegrapher's diploma during his student days, and was intimately involved in the foundation of the Dutch Society for Radio-Telegraphy in 1916. Until the 1920s, he was very active in amateur radio and astronomy circles. Trained in electrical engineering at Delft, he joined the PTT (Post Office) as a telegraph engineer in 1919, worked his way through the ranks to become head of the telephone district of Breda in 1939, and was promoted to head the PTT Radio Service just days after the end of the war. As his department was responsible for overseas radio communication, he initiated a research effort to study radio propagation in the ionosphere and the effects of solar activity. To this end, he rescued a number of Würzburg-Riese 7.5-m radar antennas abandoned at the end of the war, made one available for Jan Oort's H I work, and launched a series of radio astronomical initiatives. His group also

Radio Jove: Citizen Science for Jupiter Radio Astronomy

NASA Astrophysics Data System (ADS)

Higgins, C. A.; Thieman, J.; Reyes, F. J.; Typinski, D.; Flagg, R. F.; Greenman, W.; Brown, J.; Ashcraft, T.; Sky, J.; Cecconi, B.; Garcia, L. N.

2016-12-01

The Radio Jove Project (http://radiojove.gsfc.nasa.gov) has been operating as an educational activity for 18 years to introduce radio astronomy activities to students, teachers, and the general public. Participants may build a simple radio telescope kit, make scientific observations, and interact with radio observatories in real-time over the Internet. Recently some of our dedicated citizen science observers have upgraded their systems to better study radio emission from Jupiter and the Sun by adding dual-polarization spectrographs and wide-band antennas in the frequency range of 15-30 MHz. Some of these observations are being used in conjunction with professional telescopes such as the Long Wavelength Array (LWA), the Nancay Decametric Array, and the Ukrainian URAN2 Radio Telescope. In particular, there is an effort to support the Juno Mission radio waves instrument at Jupiter by using citizen science ground-based data for comparison and polarization verification. These data will be archived through a Virtual European Solar and Planetary Access (VESPA) archive (https://voparis-radiojove.obspm.fr/radiojove/welcome) for use by the amateur and professional radio science community. We overview the program and display recent observations that will be of interest to the science community.

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.

The ghost propagator in Coulomb gauge

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 lowmore » 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.« less

Nanosats for a Radio Interferometer Observatory in Space

NASA Astrophysics Data System (ADS)

Cecconi, B.; Katsanevras, S.; Puy, D.; Bentum, M.

2015-10-01

During the last decades, astronomy and space physics changed dramatically our knowledge of the evolution of the Universe. However, our view is still incomplete in the very low frequency range (1- 30 MHz), which is thus one of the last unexplored astrophysical spectral band. Below 30 MHz, ionospheric fluctuations severely perturb groundbased observations. They are impossible below 10 MHz due to the ionospheric cutoff. In addition, man made radio interferences makes it even more difficult to observe from ground at low frequencies. Deploying a radio instrument in space is the only way to open this new window on the Universe. Among the many science objectives for such type of instrumentations, we can find cosmological studies such as the Dark Ages of the Universe, the remote astrophysical objects, pulsars and fast transients, the interstellar medium. The following Solar system and Planetary objectives are also very important: - Sun-Earth Interactions: The Sun is strongly influencing the interplanetary medium (IPM) and the terrestrial geospatial environment. The evolution mechanisms of coronal mass ejections (CME) and their impact on solar system bodies are still not fully understood. This results in large inaccuracies on the eruption models and prediction tools, and their consequences on the Earth environment. Very low frequency radio imaging capabilities (especially for the Type II solar radio bursts, which are linked with interplanetary shocks) should allow the scientific community to make a big step forward in understanding of the physics and the dynamics of these phenomena, by observing the location of the radio source, how they correlate with their associated shocks and how they propagate within the IPM. - Planets and Exoplanets: The Earth and the fourgiant planets are hosting strong magnetic fields producing large magnetospheres. Particle acceleration are very efficient therein and lead to emitting intense low frequency radio waves in their auroral regions. These

Fluctuations of radio occultation signals in sounding the Earth's atmosphere

NASA Astrophysics Data System (ADS)

Kan, Valery; Gorbunov, Michael E.; Sofieva, Viktoria F.

2018-02-01

We discuss the relationships that link the observed fluctuation spectra of the amplitude and phase of signals used for the radio occultation sounding of the Earth's atmosphere, with the spectra of atmospheric inhomogeneities. Our analysis employs the approximation of the phase screen and of weak fluctuations. We make our estimates for the following characteristic inhomogeneity types: (1) the isotropic Kolmogorov turbulence and (2) the anisotropic saturated internal gravity waves. We obtain the expressions for the variances of the amplitude and phase fluctuations of radio occultation signals as well as their estimates for the typical parameters of inhomogeneity models. From the GPS/MET observations, we evaluate the spectra of the amplitude and phase fluctuations in the altitude interval from 4 to 25 km in the middle and polar latitudes. As indicated by theoretical and experimental estimates, the main contribution into the radio signal fluctuations comes from the internal gravity waves. The influence of the Kolmogorov turbulence is negligible. We derive simple relationships that link the parameters of internal gravity waves and the statistical characteristics of the radio signal fluctuations. These results may serve as the basis for the global monitoring of the wave activity in the stratosphere and upper troposphere.

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.

Full vector modal analysis of microstructured optical fiber propagation characteristics

NASA Astrophysics Data System (ADS)

Zghal, Mourad; Bahloul, Faouzi; Chatta, Rihab; Attia, Rabah; Pagnoux, Dominique; Roy, Philippe; Melin, Gilles; Gasca, Laurent

2004-10-01

Microstructured optical fibers (MOFs) are optical fibers having a periodic air-silica cross-section. The air holes extend along the axis of the fiber for its entire length. The core of the fiber is formed by a missing hole in the periodic structure. Remarkable properties of MOFs have recently been reported. This paper presents new work in the modeling of the propagation characteristics of MOFs using the Finite Element Method (FEM) and the Galerkin Method (GM). This efficient electromagnetic simulation package provides a vectorial description of the electromagnetic fields and of the associated effective index. This information includes accurate determination of the spectral extent of the modes, cutoff properties and mode-field distributions. We show that FEM is well adapted for describing the fields at abrupt transitions of the refractive index while GM has the advantage to accurately analyze MOFs of significant complexity using only modest computational resources. This presentation will focus on the specific techniques required to determine single mode operation, dispersion properties and effective area through careful choice of the geometrical parameters of the fibers. We demonstrate that with suitable geometrical parameters, the zero dispersion wavelength can be shifted. This tool can also provide design criteria for fabricating MOFs and a corresponding map of effective area. This approach is validated by comparison with experimental results and measurements on actual MOFs fabricated at IRCOM and at Alcatel Research and Innovation Center.

Firefighters' Radios

NASA Technical Reports Server (NTRS)

1976-01-01

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

Attenuation characteristics of the fundamental modes that propagate in buried iron water pipes.

PubMed

Long, R; Lowe, M; Cawley, P

2003-09-01

The attenuation of the fundamental non-torsional modes that propagate down buried iron water pipes has been studied. The mode shapes, mode attenuation due to leakage into the surrounding medium and the scattering of the modes as they interact with pipe joints and fittings have been investigated. In the low frequency region the mode predicted to dominate over significant propagation distances approximates a plane wave in the water within the pipe. The established acoustic technique used to locate leaks in buried iron water pipes assumes that leak noise propagates as a single non-dispersive mode at a velocity related to the low frequency asymptote of this water borne mode. Experiments have been conducted on buried water mains at test sites in the UK to verify the attenuation and velocity dispersion predictions.

Using Solar Radio Burst Integrated Fluxes to Predict Energetic Proton Flux Increases.

DTIC Science & Technology

1982-08-31

Energy Density, ET, of the radio burst, an integration across the frequency interval of the time-integrated radio fluxes at each frequency, was found to...integrated flux or energy at five frequencies in the 600- to 8800-MHz frequency interval and related them to the peak proton flux of the associated... energy of the burst normalized to its peak flux. One other characteristic of the radio burst to which Croom 13 referred was the total energy density, ET

Speckle-field propagation in 'frozen' turbulence: brightness function approach

NASA Astrophysics Data System (ADS)

Dudorov, Vadim V.; Vorontsov, Mikhail A.; Kolosov, Valeriy V.

2006-08-01

Speckle-field long- and short-exposure spatial correlation characteristics for target-in-the-loop (TIL) laser beam propagation and scattering in atmospheric turbulence are analyzed through the use of two different approaches: the conventional Monte Carlo (MC) technique and the recently developed brightness function (BF) method. Both the MC and the BF methods are applied to analysis of speckle-field characteristics averaged over target surface roughness realizations under conditions of 'frozen' turbulence. This corresponds to TIL applications where speckle-field fluctuations associated with target surface roughness realization updates occur within a time scale that can be significantly shorter than the characteristic atmospheric turbulence time. Computational efficiency and accuracy of both methods are compared on the basis of a known analytical solution for the long-exposure mutual correlation function. It is shown that in the TIL propagation scenarios considered the BF method provides improved accuracy and requires significantly less computational time than the conventional MC technique. For TIL geometry with a Gaussian outgoing beam and Lambertian target surface, both analytical and numerical estimations for the speckle-field long-exposure correlation length are obtained. Short-exposure speckle-field correlation characteristics corresponding to propagation in 'frozen' turbulence are estimated using the BF method. It is shown that atmospheric turbulence-induced static refractive index inhomogeneities do not significantly affect the characteristic correlation length of the speckle field, whereas long-exposure spatial correlation characteristics are strongly dependent on turbulence strength.

Speckle-field propagation in 'frozen' turbulence: brightness function approach.

PubMed

Dudorov, Vadim V; Vorontsov, Mikhail A; Kolosov, Valeriy V

2006-08-01

Speckle-field long- and short-exposure spatial correlation characteristics for target-in-the-loop (TIL) laser beam propagation and scattering in atmospheric turbulence are analyzed through the use of two different approaches: the conventional Monte Carlo (MC) technique and the recently developed brightness function (BF) method. Both the MC and the BF methods are applied to analysis of speckle-field characteristics averaged over target surface roughness realizations under conditions of 'frozen' turbulence. This corresponds to TIL applications where speckle-field fluctuations associated with target surface roughness realization updates occur within a time scale that can be significantly shorter than the characteristic atmospheric turbulence time. Computational efficiency and accuracy of both methods are compared on the basis of a known analytical solution for the long-exposure mutual correlation function. It is shown that in the TIL propagation scenarios considered the BF method provides improved accuracy and requires significantly less computational time than the conventional MC technique. For TIL geometry with a Gaussian outgoing beam and Lambertian target surface, both analytical and numerical estimations for the speckle-field long-exposure correlation length are obtained. Short-exposure speckle-field correlation characteristics corresponding to propagation in 'frozen' turbulence are estimated using the BF method. It is shown that atmospheric turbulence-induced static refractive index inhomogeneities do not significantly affect the characteristic correlation length of the speckle field, whereas long-exposure spatial correlation characteristics are strongly dependent on turbulence strength.

The slant path atmospheric refraction calibrator - An instrument to measure the microwave propagation delays induced by atmospheric water vapor

NASA Technical Reports Server (NTRS)

Walter, Steven J.; Bender, Peter L.

1992-01-01

The water vapor-induced propagation delay experienced by a radio signal traversing the atmosphere is characterized by the Slant Path Atmospheric Refraction Calibrator (SPARC), which measures the difference in the travel times between an optical and a microwave signal propagating along the same atmospheric path with an accuracy of 15 picosec or better. Attention is given to the theoretical and experimental issues involved in measuring the delay induced by water vapor; SPARC measurements conducted along a 13.35-km ground-based path are presented, illustrating the instrument's stability, precision, and accuracy.

DEEP CHANDRA X-RAY IMAGING OF A NEARBY RADIO GALAXY 4C+29.30: X-RAY/RADIO CONNECTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Siemiginowska, Aneta; Aldcroft, Thomas L.; Burke, D. J.

2012-05-10

We report results from our deep Chandra X-ray observations of a nearby radio galaxy, 4C+29.30 (z = 0.0647). The Chandra image resolves structures on sub-arcsec to arcsec scales, revealing complex X-ray morphology and detecting the main radio features: the nucleus, a jet, hotspots, and lobes. The nucleus is absorbed (N{sub H} {approx_equal} 3.95{sup +0.27}{sub -0.33} Multiplication-Sign 10{sup 23} cm{sup -2}) with an unabsorbed luminosity of L{sub 2-10keV} {approx_equal} (5.08 {+-} 0.52) Multiplication-Sign 10{sup 43} erg s{sup -1} characteristic of Type 2 active galactic nuclei. Regions of soft (<2 keV) X-ray emission that trace the hot interstellar medium (ISM) are correlatedmore » with radio structures along the main radio axis, indicating a strong relation between the two. The X-ray emission extends beyond the radio source and correlates with the morphology of optical-line-emitting regions. We measured the ISM temperature in several regions across the galaxy to be kT {approx_equal} 0.5 keV, with slightly higher temperatures (of a few keV) in the center and in the vicinity of the radio hotspots. Assuming that these regions were heated by weak shocks driven by the expanding radio source, we estimated the corresponding Mach number of 1.6 in the southern regions. The thermal pressure of the X-ray-emitting gas in the outermost regions suggests that the hot ISM is slightly underpressured with respect to the cold optical-line-emitting gas and radio-emitting plasma, which both seem to be in a rough pressure equilibrium. We conclude that 4C+29.30 displays a complex view of interactions between the jet-driven radio outflow and host galaxy environment, signaling feedback processes closely associated with the central active nucleus.« less

Radio Galaxy Zoo: A Search for Hybrid Morphology Radio Galaxies

NASA Astrophysics Data System (ADS)

Kapińska, A. D.; Terentev, I.; Wong, O. I.; Shabala, S. S.; Andernach, H.; Rudnick, L.; Storer, L.; Banfield, J. K.; Willett, K. W.; de Gasperin, F.; Lintott, C. J.; López-Sánchez, Á. R.; Middelberg, E.; Norris, R. P.; Schawinski, K.; Seymour, N.; Simmons, B.

2017-12-01

Hybrid morphology radio sources (HyMoRS) are a rare type of radio galaxy that display different Fanaroff-Riley classes on opposite sides of their nuclei. To enhance the statistical analysis of HyMoRS, we embarked on a large-scale search of these sources within the international citizen science project, Radio Galaxy Zoo (RGZ). Here, we present 25 new candidate hybrid morphology radio galaxies. Our selected candidates are moderate power radio galaxies ({L}{median}=4.7× {10}24 W Hz-1 sr-1) at redshifts 0.14< z< 1.0. Hosts of nine candidates have spectroscopic observations, of which six are classified as quasars, one as high- and two as low-excitation galaxies. Two candidate HyMoRS are giant (> 1 Mpc) radio galaxies, one resides at the center of a galaxy cluster, and one is hosted by a rare green bean galaxy. Although the origin of the hybrid morphology radio galaxies is still unclear, this type of radio source starts depicting itself as a rather diverse class. We discuss hybrid radio morphology formation in terms of the radio source environment (nurture) and intrinsically occurring phenomena (nature; activity cessation and amplification), showing that these peculiar radio galaxies can be formed by both mechanisms. While high angular resolution follow-up observations are still necessary to confirm our candidates, we demonstrate the efficacy of the RGZ in the pre-selection of these sources from all-sky radio surveys, and report the reliability of citizen scientists in identifying and classifying complex radio sources.

IRAS observations of radio-quiet and radio-loud quasars

NASA Technical Reports Server (NTRS)

Neugebauer, G.; Soifer, B. T.; Miley, G.; Habing, H. J.; Young, E.; Low, F. J.; Beichman, C. A.; Clegg, P. E.; Harris, S.; Rowan-Robinson, M.

1984-01-01

Observations from 12 to 100 microns are presented of two radio-quiet and three radio-loud quasars. Over this wavelength range, all five have grossly similar continuum energy distributions. The continua of the radio-loud quasars are consistent with synchrotron radiation. There is an indication, however, of excess 100 micron emission in the two radio-quiet quasars.

Calibration of Solar Radio Spectrometer of the Purple Mountain Observatory

NASA Astrophysics Data System (ADS)

Lei, LU; Si-ming, LIU; Qi-wu, SONG; Zong-jun, NING

2015-10-01

Calibration is a basic and important job in solar radio spectral observations. It not only deduces the solar radio flux as an important physical quantity for solar observations, but also deducts the flat field of the radio spectrometer to display the radio spectrogram clearly. In this paper, we first introduce the basic method of calibration based on the data of the solar radio spectrometer of Purple Mountain Observatory. We then analyze the variation of the calibration coefficients, and give the calibrated results for a few flares. These results are compared with those of the Nobeyama solar radio polarimeter and the hard X-ray observations of the RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) satellite, it is shown that these results are consistent with the characteristics of typical solar flare light curves. In particular, the analysis on the correlation between the variation of radio flux and the variation of hard X-ray flux in the pulsing phase of a flare indicates that these observations can be used to study the relevant radiation mechanism, as well as the related energy release and particle acceleration processes.

Magnetic Field Effects and Electromagnetic Wave Propagation in Highly Collisional Plasmas.

NASA Astrophysics Data System (ADS)

Bozeman, Steven Paul

The homogeneity and size of radio frequency (RF) and microwave driven plasmas are often limited by insufficient penetration of the electromagnetic radiation. To investigate increasing the skin depth of the radiation, we consider the propagation of electromagnetic waves in a weakly ionized plasma immersed in a steady magnetic field where the dominant collision processes are electron-neutral and ion-neutral collisions. Retaining both the electron and ion dynamics, we have adapted the theory for cold collisionless plasmas to include the effects of these collisions and obtained the dispersion relation at arbitrary frequency omega for plane waves propagating at arbitrary angles with respect to the magnetic field. We discuss in particular the cases of magnetic field enhanced wave penetration for parallel and perpendicular propagation, examining the experimental parameters which lead to electromagnetic wave propagation beyond the collisional skin depth. Our theory predicts that the most favorable scaling of skin depth with magnetic field occurs for waves propagating nearly parallel to B and for omega << Omega_{rm e} where Omega_{rm e} is the electron cyclotron frequency. The scaling is less favorable for propagation perpendicular to B, but the skin depth does increase for this case as well. Still, to achieve optimal wave penetration, we find that one must design the plasma configuration and antenna geometry so that one generates primarily the appropriate angles of propagation. We have measured plasma wave amplitudes and phases using an RF magnetic probe and densities using Stark line broadening. These measurements were performed in inductively coupled plasmas (ICP's) driven with a standard helical coil, a reverse turn (Stix) coil, and a flat spiral coil. Density measurements were also made in a microwave generated plasma. The RF magnetic probe measurements of wave propagation in a conventional ICP with wave propagation approximately perpendicular to B show an increase in

Radio evidence for shock acceleration of electrons in the solar corona

NASA Technical Reports Server (NTRS)

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

1981-01-01

It is pointed out that the new class of kilometer-wavelength solar radio bursts observed with the ISEE-3 Radio Astronomy Experiment occurs at the reported times of type II events, which are indicative of a shock wave. An examination of records from the Culgoora Radio Observatory reveals that the associated type II bursts have fast drift elements emanating from them; that is, a herringbone structure is formed. It is proposed that this new class of bursts is a long-wavelength continuation of the herringbone structure, and it is thought probable that the electrons producing the radio emission are accelerated by shocks. These new events are referred to as shock-accelerated events, and their characteristics are discussed.

Radio Frequency Interference Mitigation

NASA Astrophysics Data System (ADS)

An, T.; Chen, X.; Mohan, P.; Lao, B. Q.

2017-09-01

The observational facilities of radio astronomy keep constant upgrades and developments to achieve better capabilities including increasing the time of the data recording and frequency resolutions, and increasing the receiving and recording bandwidth. However in contrast, only a limited spectrum resource has been allocated to radio astronomy by the International Telecommunication Union, resulting in that the radio observational instrumentations are inevitably exposed to undesirable radio frequency interference (RFI) signals which originate mainly from the terrestrial human activity and are becoming stronger with time. RFIs degrade the quality of data and even lead to invalid data. The impact of RFIs on scientific outcome becomes more and more serious. In this article, the requirement for RFI mitigation is motivated, and the RFI characteristics, mitigation techniques, and strategies are reviewed. The mitigation strategies adopted at some representative observatories, telescopes, and arrays are also introduced. The advantages and shortcomings of the four classes of RFI mitigation strategies are discussed and presented, applicable at the connected causal stages: preventive, pre-detection, pre-correlation, and post-correlation. The proper identification and flagging of RFI is the key to the reduction of data loss and improvement in data quality, and is also the ultimate goal of developing RFI mitigation technique. This can be achieved through a strategy involving a combination of the discussed techniques in stages. The recent advances in the high speed digital signal processing and high performance computing allow for performing RFI excision of the large data volumes generated from large telescopes or arrays in both real time and offline modes, aiding the proposed strategy.

Low frequency wave propagation in a cold magnetized dusty plasma

NASA Astrophysics Data System (ADS)

Sarkar, S.; Ghosh, S.; Khan, M.

1998-12-01

In this paper several characteristics of low frequency waves in a cold magnetized dusty plasma propagating parallel and perpendicular to the static background magnetic field have been investigated. In the case of parallel propagation the negatively charged dust particles resonate with the right circularly polarized (RCP) component of em waves when the wave frequency equals the dust cyclotron frequency. It has been shown that an RCP wave in dusty plasma consists of two branches and there exists a region where an RCP wave propagation is not possible. Dispersion relation, phase velocity and group velocity of RCP waves have been obtained and propagation characteristics have been shown graphically. Poynting flux and Faraday rotation angles have been calculated for both lower and upper branches of the RCP wave. It has been observed that sense of rotation of the plane of polarization of the RCP wave corresponding to two distinct branches are opposite. Finally, the effect of dust particles on the induced magnetization from the inverse Faraday effect (IFE) due to the interaction of low frequency propagating and standing em waves with dusty plasmas has been evaluated.

Radio morphology and parent population of X-ray selected BL Lacertae objects

NASA Technical Reports Server (NTRS)

Laurent-Muehleisen, S. A.; Kollgaard, R. I.; Moellenbrock, G. A.; Feigelson, E. D.

1993-01-01

High-dynamic range (typically 1700:1) radio maps of 15 X-ray BL Lac (XBL) objects from the HEAO-1 Large Area Sky Survey are presented. Morphological characteristics of these sources are compared with Fanaroff-Riley (FR) class I radio galaxies in the context of unified schemes, with reference to one-sided kiloparsec-scale emission. Evidence that cluster membership of XBLs is significantly higher than previously thought is also presented. It is shown that the extended radio powers, X-ray emission, core-to-lobe ratios, and linear sizes of the radio selected BL Lac (RBL) and XBL populations are consistent with an FR I radio galaxy parent population. A source list and VLA observing log and map parameters are provided.

Reproducing continuous radio blackout using glow discharge plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Kai; Li, Xiaoping; Liu, Donglin

2013-10-15

A novel plasma generator is described that offers large-scale, continuous, non-magnetized plasma with a 30-cm-diameter hollow structure, which provides a path for an electromagnetic wave. The plasma is excited by a low-pressure glow discharge, with varying electron densities ranging from 10{sup 9} to 2.5 × 10{sup 11} cm{sup −3}. An electromagnetic wave propagation experiment reproduced a continuous radio blackout in UHF-, L-, and S-bands. The results are consistent with theoretical expectations. The proposed method is suitable in simulating a plasma sheath, and in researching communications, navigation, electromagnetic mitigations, and antenna compensation in plasma sheaths.

Oscillations in the 45 - 5000 MHz Radio Spectrum of the 18 April 2014 Flare

NASA Astrophysics Data System (ADS)

Karlický, Marian; Rybák, Ján; Monstein, Christian

2017-07-01

Using a new type of oscillation map, made from the radio spectra by the wavelet technique, we study the 18 April 2014 M7.3 flare (SOL2014-04-18T13:03:00L245C017). We find a quasi-periodic character of this flare with periods in the range 65 - 115 seconds. At the very beginning of this flare, in connection with the drifting pulsation structure (plasmoid ejection), we find that the 65 - 115 s oscillation phase slowly drifts towards lower frequencies, which indicates an upward propagating wave initiated at the start of the magnetic reconnection. Many periods (1 - 200 seconds) are found in the drifting pulsation structure, which documents multi-scale and multi-periodic processes. On this drifting structure, fiber bursts with a characteristic period of about one second are superimposed, whose frequency drift is similar to that of the drifting 65 - 115 s oscillation phase. We also checked periods found in this flare by the EUV Imaging Spectrometer (EIS)/ Hinode and Interface Region Imaging Spectrograph (IRIS) observations. We recognize the type III bursts (electron beams) as proposed, but their time coincidence with the EIS and IRIS peaks is not very good. The reason probably is that the radio spectrum is a whole-disk record consisting of all bursts from any location, while the EIS and IRIS peaks are emitted only from locations of slits in the EIS and IRIS observations.

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.

Characteristics and climatology of mid-latitude F-region ionospheric irregularities observed by COSMIC radio occultation measurements

NASA Astrophysics Data System (ADS)

Watson, C.; Pedatella, N. M.

2017-12-01

Small-medium scale ( 1-50 km) ionospheric plasma irregularities are a ubiquitous feature of the earth's F region ionosphere. COSMIC radio occultation measurements provide a valuable opportunity to improve upon the incomplete global observational picture of irregularity occurrence and characteristics. A climatological database of ionospheric irregularities and their characteristics (e.g. magnitude, scale size, gradient, and associated scintillation) has been developed through detection of total electron content (TEC) perturbations by COSMIC precise orbit determination (POD) antennas and associated receivers. Vertical scale sizes ranging from 1 to 50 km were resolved from 1 Hz TEC measurements stored in podTec files. Amplitude scintillation index (S4) of ScnLv1 files was used as a proxy for the occurrence of smaller scale (<1 km) scintillation producing structures. Four years of processed data (2007-2008 and 2012-2013) has revealed interesting climatological features of irregularity occurrence and characteristics. The presentation will focus on the results at mid-latitudes. One interesting mid-latitude feature is a high occurrence of irregularities in regions corresponding to the solar terminator. Perturbations larger than 0.1 TEC units (TECU) were observed 50%-80% of the time in terminator regions, with higher occurrence and more intense perturbations around sunset and during years of high solar activity. Altitude of peak occurrence of terminator irregularities was about 150 km, with a sharp upper-altitude cut-off of 250 km. The occurrence and characteristics of these irregularities are modified according to proximity to solar terminator location. A possible link to thermospheric neutral density perturbations also associated with the solar terminator will be discussed. The climatology of non-terminator mid-latitude irregularities is consistent with previous observations of mid-latitude field-aligned irregularities (FAIs), including a local-time dependent altitude

Numerical simulation of the structure of the high-latitude ionospheric F region during meridional HF propagation

NASA Astrophysics Data System (ADS)

Andreev, M. Yu.; Mingaleva, G. I.; Mingalev, V. S.

2007-08-01

A previously developed model of the high-latitude ionosphere is used to calculate the distribution of the ionospheric parameters in the polar region. A specific method for specifying input parameters of the mathematical model, using the experimental data obtained by the method of satellite radio tomography, is used in this case. The spatial distributions of the ionospheric parameters characterized by a complex inhomogeneous structure in the high-latitude region, calculated with the help of the mathematical model, are used to simulate the HF propagation along the meridionally oriented radio paths extending from middle to high latitudes. The method for improving the HF communication between a midlatitude transmitter and a polar-cap receiver is proposed.

Satellite Ka-band propagation measurements in Florida

NASA Technical Reports Server (NTRS)

Helmken, Henry; Henning, Rudolf

1995-01-01

Commercial growth of interactive, high data rate communication systems is expected to focus on the use of the Ka-band (20/30 GHz) radio spectrum. The ability to form narrow spot beams and the attendant small diameter antennas are attractive features to designers of mobile aeronautical and ground based satellite communication systems. However, Ka-band is strongly affected by weather, particularly rain, and hence systems designs may require a significant link margin for reliable operations. Perhaps the most stressing area in North America, weatherwise, is the Florida sub-tropical climatic region. As part of the NASA Advanced Communications Technology Satellite (ACTS) propagation measurements program, beacon and radiometer data have been recorded since December 1993 at the University of South Florida (USF), Tampa, Florida.

T he Faint Drifting Decameter Radio Bursts From The Solar Corona

NASA Astrophysics Data System (ADS)

Briand, C.; Zaslavsky, A.; Lecacheux, A.; Zarka, P.; Maksimovic, M.; Mangeney, A.

2007-01-01

The radio observations of solar corona at decameter wavelengths reveal the presence of numerous faint, frequency drifting structures. We analyse observations performed on July 13th , 2002 with the DSP wideband spectrometer instrument implemented at the UTR-2 radiote- lescope. The main characteristics of these structures are statistically studied. Three populations of bursts are iden- tifies. The largest one presents negative frequency drifts of about -0.89 MHz.s-1 and a lifetime extending up to 11 sec (median value 2.72 sec). A second one shows positive frequency drifts of about +0.95 MHz.s-1 and a life- time extending up to 3 sec. The last population consists in structures with very small frequency drifts of about -0.1 MHz.s-1 and a shorter lifetime (about 1 sec). Assuming that those emissions are the signature of elec- tron beams propagating through the solar corona, we deduce that they have a velocity of about 3-5 times the electron thermal velocity. A new mechanism is proposed to explain the formation of plasma waves with such low beam velocity: spatially localized, temporal fluctuations of the electron distribution function width (heating).

Characterization of electrophysiological propagation by multichannel sensors

PubMed Central

Bradshaw, L. Alan; Kim, Juliana H.; Somarajan, Suseela; Richards, William O.; Cheng, Leo K.

2016-01-01

Objective The propagation of electrophysiological activity measured by multichannel devices could have significant clinical implications. Gastric slow waves normally propagate along longitudinal paths that are evident in recordings of serosal potentials and transcutaneous magnetic fields. We employed a realistic model of gastric slow wave activity to simulate the transabdominal magnetogastrogram (MGG) recorded in a multichannel biomagnetometer and to determine characteristics of electrophysiological propagation from MGG measurements. Methods Using MGG simulations of slow wave sources in a realistic abdomen (both superficial and deep sources) and in a horizontally-layered volume conductor, we compared two analytic methods (Second Order Blind Identification, SOBI and Surface Current Density, SCD) that allow quantitative characterization of slow wave propagation. We also evaluated the performance of the methods with simulated experimental noise. The methods were also validated in an experimental animal model. Results Mean square errors in position estimates were within 2 cm of the correct position, and average propagation velocities within 2 mm/s of the actual velocities. SOBI propagation analysis outperformed the SCD method for dipoles in the superficial and horizontal layer models with and without additive noise. The SCD method gave better estimates for deep sources, but did not handle additive noise as well as SOBI. Conclusion SOBI-MGG and SCD-MGG were used to quantify slow wave propagation in a realistic abdomen model of gastric electrical activity. Significance These methods could be generalized to any propagating electrophysiological activity detected by multichannel sensor arrays. PMID:26595907

The importance of Radio Quiet Zone (RQZ) for radio astronomy

NASA Astrophysics Data System (ADS)

Umar, Roslan; Abidin, Zamri Zainal; Ibrahim, Zainol Abidin

2013-05-01

Most of radio observatories are located in isolated areas. Since radio sources from the universe is very weak, astronomer need to avoid radio frequency interference (RFI) from active spectrum users and radio noise produced by human made (telecommunication, mobile phone, microwave user and many more. There are many observatories around the world are surrounded by a Radio Quiet Zone (RQZ), which is it was set up using public or state laws. A Radio Quiet Zone normally consists of two areas: an exclusive area in which totally radio emissions are forbidden, with restrictions for residents and business developments, and a larger (radius up to 100 km above) coordination area where the power of radio transmission limits to threshold levels. Geographical Information System (GIS) can be used as a powerful tool in mapping large areas with varying RQZ profiles. In this paper, we report the initial testing of the usage of this system in order to identify the areas were suitable for Radio Quiet Zone. Among the important parameters used to develop the database for our GIS are population density, information on TV and telecommunication (mobile phones) transmitters, road networks (highway), and contour shielding. We will also use other information gathered from on-site RFI level measurements on selected 'best' areas generated by the GIS. The intention is to find the best site for the purpose of establishing first radio quiet zones for radio telescope in Malaysia.

Software-Defined Radio Global System for Mobile Communications Transmitter Development for Heterogeneous Network Vulnerability Testing

DTIC Science & Technology

2013-12-01

AbdelWahab, “ 2G / 3G Inter-RAT Handover Performance Analysis,” Second European Conference on Antennas and Propagation, pp. 1, 8, 11–16, Nov. 2007. [19] J...RADIO GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS TRANSMITTER DEVELOPMENT FOR HETEROGENEOUS NETWORK VULNERABILITY TESTING by Carson C. McAbee... MOBILE COMMUNICATIONS TRANSMITTER DEVELOPMENT FOR HETEROGENEOUS NETWORK VULNERABILITY TESTING 5. FUNDING NUMBERS 6. AUTHOR(S) Carson C. McAbee

Stern-Gerlach dynamics with quantum propagators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsu, Bailey C.; Berrondo, Manuel; Van Huele, Jean-Francois S.

2011-01-15

We study the quantum dynamics of a nonrelativistic neutral particle with spin in inhomogeneous external magnetic fields. We first consider fields with one-dimensional inhomogeneities, both unphysical and physical, and construct the corresponding analytic propagators. We then consider fields with two-dimensional inhomogeneities and develop an appropriate numerical propagation method. We propagate initial states exhibiting different degrees of space localization and various initial spin configurations, including both pure and mixed spin states. We study the evolution of their spin densities and identify characteristic features of spin density dynamics, such as the spatial separation of spin components, and spin localization or accumulation. Wemore » compare our approach and our results with the coverage of the Stern-Gerlach effect in the literature, and we focus on nonstandard Stern-Gerlach outcomes, such as radial separation, spin focusing, spin oscillation, and spin flipping.« less

Q/V-band communications and propagation experiments using ALPHASAT

NASA Astrophysics Data System (ADS)

Koudelka, O.

2011-12-01

The lower satellite frequency bands become more and more congested; therefore it will be necessary to exploit higher frequencies for satellite communications. New broadband applications (e.g. 3D-TV, fast Internet access) will require additional spectrum in the future. The Ku-band is highly utilised nowadays and Ka-band systems, which have been extensively studied in the 1990s, are already in commercial use. The next frontier is the Q/V-band. At millimetre waves the propagation effects are significant. The traditional approach of implementing large fade margins is impractical, since this leads to high EIRP and G/ T figures for the ground stations, resulting in unacceptable costs. Fade mitigation techniques by adaptive coding and modulation (ACM) offer a cost-effective solution to this problem. ESA will launch the ALPHASAT satellite in 2012. It will carry experimental Ka- and Q/V-band propagation and communications payloads, enabling propagation measurements throughout Europe and communications experiments. Three communications spot beams will be covering Northern Italy, Southern Italy and Austria with some overlap. Joanneum Research and Graz University of Technology are preparing for communications and propagation experiments using these new payloads of ALPHASAT in close cooperation with ESA, the Italian Space Agency ASI, Politecnico di Milano and Università Tor Vergata. The main focus of the communications experiments is on ACM techniques. The paper describes the design of the planned Q/V-band ground station with the planned ACM tests and investigations as well as the architecture of the communications terminal, based on a versatile software-defined radio platform.

Propagating elastic vibrations dominate thermal conduction in amorphous silicon

NASA Astrophysics Data System (ADS)

Moon, Jaeyun; Latour, Benoit; Minnich, Austin J.

2018-01-01

The thermal atomic vibrations of amorphous solids can be distinguished by whether they propagate as elastic waves or do not propagate due to lack of atomic periodicity. In a -Si, prior works concluded that nonpropagating waves are the dominant contributors to heat transport, with propagating waves being restricted to frequencies less than a few THz and scattered by anharmonicity. Here, we present a lattice and molecular dynamics analysis of vibrations in a -Si that supports a qualitatively different picture in which propagating elastic waves dominate the thermal conduction and are scattered by local fluctuations of elastic modulus rather than anharmonicity. We explicitly demonstrate the propagating nature of waves up to around 10 THz, and further show that pseudoperiodic structures with homogeneous elastic properties exhibit a marked temperature dependence characteristic of anharmonic interactions. Our work suggests that most heat is carried by propagating elastic waves in a -Si and demonstrates that manipulating local elastic modulus variations is a promising route to realize amorphous materials with extreme thermal properties.

Application of the nudged elastic band method to the point-to-point radio wave ray tracing in IRI modeled ionosphere

NASA Astrophysics Data System (ADS)

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

2017-07-01

Point-to-point ray tracing is an important problem in many fields of science. While direct variational methods where some trajectory is transformed to an optimal one are routinely used in calculations of pathways of seismic waves, chemical reactions, diffusion processes, etc., this approach is not widely known in ionospheric point-to-point ray tracing. We apply the Nudged Elastic Band (NEB) method to a radio wave propagation problem. In the NEB method, a chain of points which gives a discrete representation of the radio wave ray is adjusted iteratively to an optimal configuration satisfying the Fermat's principle, while the endpoints of the trajectory are kept fixed according to the boundary conditions. Transverse displacements define the radio ray trajectory, while springs between the points control their distribution along the ray. The method is applied to a study of point-to-point ionospheric ray tracing, where the propagation medium is obtained with the International Reference Ionosphere model taking into account traveling ionospheric disturbances. A 2-dimensional representation of the optical path functional is developed and used to gain insight into the fundamental difference between high and low rays. We conclude that high and low rays are minima and saddle points of the optical path functional, respectively.

An introduction to wave propagation in pavements and soils : theory and practice

DOT National Transportation Integrated Search

1999-02-01

This paper introduces the physics and analyst of wave propagation in pavement and soils. The study of wave propagation in soils can yield useful results to engineers concerned with resilient characteristics of a particular site, dynamic soils structu...

Juno Radio Science Observations and Gravity Science Calibrations of Plasma Electron Content in Io Plasma Torus

NASA Astrophysics Data System (ADS)

Yang, Y. M.; Buccino, D.; Folkner, W. M.; Oudrhiri, K.; Phipps, P. H.; Parisi, M.; Kahan, D. S.

2017-12-01

Interplanetary and Earth ionosphere plasma electrons can have significant impacts on radio frequency signal propagation such as telecommunication between spacecraft and the Deep Space Network (DSN). On 27 August 2016, the first closest approach of The Juno spacecraft (Perijove 1) provided an opportunity to observe plasma electrons inside of the Io plasma torus using radio science measurements from Juno. Here, we report on the derivations of plasma electron content in the Io plasma torus by using two-way coherent radio science measurements made from Juno's Gravity Science Instrument and the Deep Space Network. During Perijove 1, Juno spacecraft passed through the inner region (perijove altitude of 1.06 Jovian Radii) between Jupiter and the Io plasma torus. Significant plasma electron variations of up to 30 TEC units were observed while the radio link between Juno and the DSN traveled through the Io plasma torus. In this research, we compare observations made by open-loop and closed-loop processes using different frequency radio signals, corresponding Io plasma torus model simulations, and other Earth ionosphere observations. The results of three-dimensional Io plasma model simulations are consistent with observations with some discrepancies. Results are shown to improve our understanding of the Io plasma torus effect on Juno gravity science measurements and its calibrations to reduce the corresponding (non-gravity field induced) radio frequency shift.

Wave optics-based LEO-LEO radio occultation retrieval

NASA Astrophysics Data System (ADS)

Benzon, Hans-Henrik; Høeg, Per

2016-06-01

-Range Weather Forecasts analysis model. This model is used in a forward propagator that simulates the electromagnetic field amplitudes and phases at the receiver on board the LEO satellite. LEO-LEO cross-link radio occultations using high frequencies are a relatively new technique, and the possibilities and advantages of the technique still need to be investigated. The retrieval of this type of radio occultations is considerably more complicated than standard GPS to LEO radio occultations, because the attenuation of the probing radio waves is used in the retrieval and the atmospheric parameters are found using a least squares solver. The best algorithms and the number of probing frequencies that is economically viable must also be determined. This paper intends to answer some of these questions using end-to-end simulations.

Radio and television use in Butte County, California: application to fire prevention

Treesearch

William S. Folkman

1975-01-01

A sample of Butte County residents were interviewed about their radio and television use habits. Their responses were analyzed in terms of demographic, social, and economic characteristics. The findings can be used in developing more effective fire prevention programs. Most people in Butte County listen to the radio or watch television but they differ widely in the way...

Improving Thermal Ablation Delineation With Electrode Vibration Elastography Using a Bidirectional Wave Propagation Assumption

PubMed Central

DeWall, Ryan J.; Varghese, Tomy

2013-01-01

Thermal ablation procedures are commonly used to treat hepatic cancers and accurate ablation representation on shear wave velocity images is crucial to ensure complete treatment of the malignant target. Electrode vibration elastography is a shear wave imaging technique recently developed to monitor thermal ablation extent during treatment procedures. Previous work has shown good lateral boundary delineation of ablated volumes, but axial delineation was more ambiguous, which may have resulted from the assumption of lateral shear wave propagation. In this work, we assume both lateral and axial wave propagation and compare wave velocity images to those assuming only lateral shear wave propagation in finite element simulations, tissue-mimicking phantoms, and bovine liver tissue. Our results show that assuming bidirectional wave propagation minimizes artifacts above and below ablated volumes, yielding a more accurate representation of the ablated region on shear wave velocity images. Area overestimation was reduced from 13.4% to 3.6% in a stiff-inclusion tissue-mimicking phantom and from 9.1% to 0.8% in a radio-frequency ablation in bovine liver tissue. More accurate ablation representation during ablation procedures increases the likelihood of complete treatment of the malignant target, decreasing tumor recurrence. PMID:22293748

Improving thermal ablation delineation with electrode vibration elastography using a bidirectional wave propagation assumption.

PubMed

DeWall, Ryan J; Varghese, Tomy

2012-01-01

Thermal ablation procedures are commonly used to treat hepatic cancers and accurate ablation representation on shear wave velocity images is crucial to ensure complete treatment of the malignant target. Electrode vibration elastography is a shear wave imaging technique recently developed to monitor thermal ablation extent during treatment procedures. Previous work has shown good lateral boundary delineation of ablated volumes, but axial delineation was more ambiguous, which may have resulted from the assumption of lateral shear wave propagation. In this work, we assume both lateral and axial wave propagation and compare wave velocity images to those assuming only lateral shear wave propagation in finite element simulations, tissue-mimicking phantoms, and bovine liver tissue. Our results show that assuming bidirectional wave propagation minimizes artifacts above and below ablated volumes, yielding a more accurate representation of the ablated region on shear wave velocity images. Area overestimation was reduced from 13.4% to 3.6% in a stiff-inclusion tissue-mimicking phantom and from 9.1% to 0.8% in a radio-frequency ablation in bovine liver tissue. More accurate ablation representation during ablation procedures increases the likelihood of complete treatment of the malignant target, decreasing tumor recurrence. © 2012 IEEE

Ideal Magnetohydrodynamic Simulations of Magnetic Bubble Expansion as a Model for Extragalactic Radio Lobes

NASA Astrophysics Data System (ADS)

Liu, Wei; Hsu, Scott; Li, Hui; Li, Shengtai; Lynn, Alan

2009-05-01

Recent astronomical observations indicate that radio lobes are gigantic relaxed magnetized plasmas with kilo-to-megaparsec scale jets providing a source of magnetic energy from the galaxy to the lobes. Therefore we are conducting a laboratory plasma experiment, the Plasma Bubble Expansion Experiment (PBEX) in which a higher pressure magnetized plasma bubble (i.e., the lobe) is injected into a lower pressure background plasma (i.e., the intergalactic medium) to study key nonlinear plasma physics issues. Here we present detailed ideal magnetohydrodynamic (MHD) three-dimensional simulations of PBEX. First, the direction of bubble expansion depends on the ratio of the bubble toroidal to poloidal magnetic field, with a higher ratio leading to expansion predominantly in the direction of propagation and a lower ratio leading to expansion predominantly normal to the direction of propagation. Second, a leading MHD shock and a trailing slow-mode compressible MHD wave front are formed ahead of the bubble as it propagates into the background plasma. Third, the bubble expansion and propagation develop asymmetries about its propagation axis due to reconnection arising from numerical resistivity and to inhomogeneous angular momentum transport due to the background magnetic field. These results will help guide the initial experiments and diagnostic measurements on PBEX.

A transient, flat spectrum radio pulsar near the Galactic Centre

NASA Astrophysics Data System (ADS)

Dexter, J.; Degenaar, N.; Kerr, M.; Deller, A.; Deneva, J.; Lazarus, P.; Kramer, M.; Champion, D.; Karuppusamy, R.

2017-06-01

Recent studies have shown possible connections between highly magnetized neutron stars ('magnetars'), whose X-ray emission is too bright to be powered by rotational energy, and ordinary radio pulsars. In addition to the magnetar SGR J1745-2900, one of the radio pulsars in the Galactic Centre (GC) region, PSR J1746-2850, had timing properties implying a large magnetic field strength and young age, as well as a flat spectrum. All characteristics are similar to those of rare, transient, radio-loud magnetars. Using several deep non-detections from the literature and two new detections, we show that this pulsar is also transient in the radio. Both the flat spectrum and large amplitude variability are inconsistent with the light curves and spectral indices of three radio pulsars with high magnetic field strengths. We further use frequent, deep archival imaging observations of the GC in the past 15 yr to rule out a possible X-ray outburst with a luminosity exceeding the rotational spin-down rate. This source, either a transient magnetar without any detected X-ray counterpart or a young, strongly magnetized radio pulsar producing magnetar-like radio emission, further blurs the line between the two categories. We discuss the implications of this object for the radio emission mechanism in magnetars and for star and compact object formation in the GC.

The Influence of The Galilean Satellites on Radio Emissions From The Jovian System

NASA Technical Reports Server (NTRS)

Kurth, W. S.; Gurnett, D. A.; Menietti, J. D.

2000-01-01

The Galilean satellites influence radio emissions from the Jovian system in a variety of ways. The best and most familiar example of these is the Io control of decametric radiation discovered in 1964 by Bigg. Voyager observations of broadband kilometric radiation revealed a low-latitude shadow zone cast by the Io torus at frequencies between a few tens of kHz and about 1 MHz. Voyager also discovered narrowband kilometric radio emissions emanating from the outer edge of the torus. In this paper we will discuss expansions in the suite of satellite influences based on new observations by Galileo. These include the discovery of Ganymede's magnetosphere and evidence of radio emissions generated via mode conversion from upper hybrid waves in the frequency range of about 20 - 100 kHz. There is evidence that Ganymede may control some of the hectometric or low-frequency decametric radio emissions based on occultation measurements and statistical studies of radio emission occurrence as a function of Ganymede phase. Direction-finding measurements in the vicinity of Io suggest that a portion of the hectometric emissions may be generated near the lo L-shell. A rotationally modulated attenuation band in the hectometric emission appears to be the result of scattering at or near the Io L-shell where the waves propagate nearly parallel to the magnetic field. There is even a tantalizing hint of a Europa connection to the source of narrowband kilometric radiation.

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

PubMed

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.

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

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, S.; Chen, Z. Y.; Wang, X. H., E-mail: xhw@mail.xjtu.edu.cn

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 instantaneousmore » 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.« less

Wave propagation in pulsar magnetospheres - Refraction of rays in the open flux zone

NASA Technical Reports Server (NTRS)

Barnard, J. J.; Arons, J.

1986-01-01

The propagation of waves through a relativistically outflowing electron-positron plasma in a very strong dipolar magnetic field, conditions expected in pulsar magnetospheres, is investigated. Halmilton's equations is derived for the propagation of rays through a plasma which is inhomogeneous in density, magnetic field directions, and Lorentz factor. These equations are solved for rays propagating through the plasmas outflowing along the 'open' dipolar field lines in which the density decreases inversely as the radius cubed and in the case where gradients transverse to the radial direction exist. In the radial case, the effects of refraction on pulse profiles, spectrum, and polarization are examined, and the effects of a transverse gradient are indicated. Attention is given to models in which the observed broad bandwidth in the radio emission has its origin in a radius to frequency map. Models with broad-band emission at a single radius are also studied. These are compared to observations of pulse width and pulse component separation as a function of frequency. The origin of 'orthogonal modes' is discussed.

Radio refractivity gradients in the lowest 100m of the atmosphere over Lagos, Nigeria in the rainy-harmattan transition phase

NASA Astrophysics Data System (ADS)

Dairo, O. F.; Kolawole, L. B.

2018-01-01

Radio engineers and researchers in conjunction with the International Telecommunication Union (ITU) have established the pivotal role of radio refractivity to the propagation of electromagnetic energy in the troposphere. In particular, the refractivity gradient statistics for the lowest 100m in the troposphere are used to determine the probability of occurrence of anomalous propagation conditions known as ducting. The major challenge to characterising the propagation condition over any environment is accessing the data of the lowest boundary layer of the atmosphere, which is highly dynamic and turbulent in evolution. High resolution radiosonde data from the Nigerian Meteorological Agency (NiMet) were used for a synoptic study of the rain-harmattan transition phase. The rain-harmattan transition phase marks the onset of the dry season due to the movement of the intertropical convergence zone interplay between (north-easterly and south-westerly) trade winds and monsoonal circulation. The lowest 100m data were analysed to determine the frequency of ducting per month. Progressive increase in the occurrence of ducting was observed during the rain-harmattan transition phase, which coincides with the West African Monsoon retreat. The results show significant divergence from previous studies, which reported that the tropospheric condition over Lagos (Geo. 6 . 5 °N, 3 . 3 °E), Nigeria, is predominantly super-refractive.

Effects of the major sudden stratospheric warming event of 2009 on the subionospheric very low frequency/low frequency radio signals

NASA Astrophysics Data System (ADS)

Pal, S.; Hobara, Y.; Chakrabarti, S. K.; Schnoor, P. W.

2017-07-01

This paper presents effects of the major sudden stratospheric warming (SSW) event of 2009 on the subionospheric very low frequency/low frequency (VLF/LF) radio signals propagating in the Earth-ionosphere waveguide. Signal amplitudes from four transmitters received by VLF/LF radio networks of Germany and Japan corresponding to the major SSW event are investigated for possible anomalies and atmospheric influence on the high- to middle-latitude ionosphere. Significant anomalous increase or decrease of nighttime and daytime amplitudes of VLF/LF signals by ˜3-5 dB during the SSW event have been found for all propagation paths associated with stratospheric temperature rise at 10 hPa level. Increase or decrease in VLF/LF amplitudes during daytime and nighttime is actually due to the modification of the lower ionospheric boundary conditions in terms of electron density and electron-neutral collision frequency profiles and associated modal interference effects between the different propagating waveguide modes during the SSW period. TIMED/SABER mission data are also used to investigate the upper mesospheric conditions over the VLF/LF propagation path during the same time period. We observe a decrease in neutral temperature and an increase in pressure at the height of 75-80 km around the peak time of the event. VLF/LF anomalies are correlated and in phase with the stratospheric temperature and mesospheric pressure variation, while minimum of mesospheric cooling shows a 2-3 day delay with maximum VLF/LF anomalies. Simulations of VLF/LF diurnal variation are performed using the well-known Long Wave Propagating Capability (LWPC) code within the Earth-ionosphere waveguide to explain the VLF/LF anomalies qualitatively.

Occurrence statistics and ray tracing study of Jovian quasiperiodic radio bursts observed from low latitudes

NASA Astrophysics Data System (ADS)

Kimura, Tomoki; Tsuchiya, Fuminori; Misawa, Hiroaki; Morioka, Akira; Nozawa, Hiromasa

2010-05-01

The occurrence characteristics of Jovian quasiperiodic (QP) bursts at a VLF range (<10 kHz) were statistically investigated using data from the Galileo spacecraft at low latitudes in the Jovian magnetosphere. The results confirmed that the occurrence of QP bursts is significantly dependent on the phase of planetary rotation rather than the central meridian longitude of the observer seen from Jupiter. It was revealed that the meridional distribution of QP bursts forms a shadow zone in the equatorial region of <30 Jovian radii from Jupiter, similar to that of hectometric radio emissions, where QP bursts are quenched. Based on the ray tracing method, we surveyed the source parameters, which can reproduce the observed shadow zone. It was suggested that the wave mode, source location, and directivity of the radio emissions are as follows: the extraordinary mode is reasonable for QP bursts observed at low latitudes, the source is located around an altitude of ˜10-20 Jovian radii above the polar region, the L value of the source field line is in a range of L > ˜20, and QP bursts could have beaming angles like “filled cone” in a restricted L value range or have a large source L value range with beaming angles like “hollow cones.” These results imply that QP bursts observed at low latitudes are generated at fRX surfaces in the polar region and propagate to the equatorial region.

A Reverse Shock and Unusual Radio Properties in GRB 160625B

NASA Astrophysics Data System (ADS)

Alexander, K. D.; Laskar, T.; Berger, E.; Guidorzi, C.; Dichiara, S.; Fong, W.; Gomboc, A.; Kobayashi, S.; Kopac, D.; Mundell, C. G.; Tanvir, N. R.; Williams, P. K. G.

2017-10-01

We present multi-wavelength observations and modeling of the exceptionally bright long γ-ray burst GRB 160625B. The optical and X-ray data are well fit by synchrotron emission from a collimated blastwave with an opening angle of {θ }j≈ 3\\buildrel{\\circ}\\over{.} 6 and kinetic energy of {E}K≈ 2× {10}51 erg, propagating into a low-density (n≈ 5× {10}-5 cm-3) medium with a uniform profile. The forward shock is sub-dominant in the radio band; instead, the radio emission is dominated by two additional components. The first component is consistent with emission from a reverse shock, indicating an initial Lorentz factor of {{{Γ }}}0≳ 100 and an ejecta magnetization of {R}B≈ 1{--}100. The second component exhibits peculiar spectral and temporal evolution and is most likely the result of scattering of the radio emission by the turbulent Milky Way interstellar medium (ISM). Such scattering is expected in any sufficiently compact extragalactic source and has been seen in GRBs before, but the large amplitude and long duration of the variability seen here are qualitatively more similar to extreme scattering events previously observed in quasars, rather than normal interstellar scintillation effects. High-cadence, broadband radio observations of future GRBs are needed to fully characterize such effects, which can sensitively probe the properties of the ISM and must be taken into account before variability intrinsic to the GRB can be interpreted correctly.

SOURCE REGIONS OF THE TYPE II RADIO BURST OBSERVED DURING A CME–CME INTERACTION ON 2013 MAY 22

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mäkelä, P.; Reiner, M. J.; Akiyama, S.

2016-08-20

We report on our study of radio source regions during the type II radio burst on 2013 May 22 based on direction-finding analysis of the Wind /WAVES and STEREO /WAVES (SWAVES) radio observations at decameter–hectometric wavelengths. The type II emission showed an enhancement that coincided with the interaction of two coronal mass ejections (CMEs) launched in sequence along closely spaced trajectories. The triangulation of the SWAVES source directions posited the ecliptic projections of the radio sources near the line connecting the Sun and the STEREO-A spacecraft. The WAVES and SWAVES source directions revealed shifts in the latitude of the radiomore » source, indicating that the spatial location of the dominant source of the type II emission varies during the CME–CME interaction. The WAVES source directions close to 1 MHz frequencies matched the location of the leading edge of the primary CME seen in the images of the LASCO/C3 coronagraph. This correspondence of spatial locations at both wavelengths confirms that the CME–CME interaction region is the source of the type II enhancement. Comparison of radio and white-light observations also showed that at lower frequencies scattering significantly affects radio wave propagation.« less

Chromospheric evaporation and decimetric radio emission in solar flares

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.; Benz, Arnold O.

1995-01-01

We have discovered decimetric signatures of the chromospheric evaporation process. Evidence for the radio detection of chromospheric evaporation is based on the radio-inferred values of (1) the electron density, (2) the propagation speed, and (3) the timing, which are found to be in good agreement with statistical values inferred from the blueshifted Ca XIX soft X-ray line. The physical basis of our model is that free-free absorption of plasma emission is strongly modified by the steep density gradient and the large temperature increase in the upflowing flare plasma. The steplike density increase at the chromospheric evaporation front causes a local discontinuity in the plasma frequency, manifested as almost infinite drift rate in decimetric type III bursts. The large temperature increase of the upflowing plasma considerably reduces the local free-free opacity (due to the T(exp -3/2) dependence) and thus enhances the brightness of radio bursts emitted at the local plasma frequency near the chromospheric evaporation front, while a high-frequency cutoff is expected in the high-density regions behind the front, which can be used to infer the velocity of the upflowing plasma. From model calculations we find strong evidence that decimetric bursts with a slowly drifting high-frequency cutoff are produced by fundamental plasma emission, contrary to the widespread belief that decimetric bursts are preferentially emitted at the harmonic plasma level. We analyze 21 flare episodes from 1991-1993 for which broadband (100-3000 MHz) radio dynamic spectra from Pheonix, hard X-ray data from (BATSE/CGRO) and soft X-ray data from Burst and Transient Source Experiment/Compton Gamma Ray Observatory (GOES) were available.

Radio emission of energetic cosmic ray air showers: Polarization measurements with LOPES

NASA Astrophysics Data System (ADS)

Lopes Collaboration; Isar, P. G.; Apel, W. D.; Arteaga, J. C.; Asch, T.; Auffenberg, J.; Badea, F.; Bähren, L.; Bekk, K.; Bertaina, M.; Biermann, P. L.; Blümer, J.; Bozdog, H.; Brancus, I. M.; Brüggemann, M.; Buchholz, P.; Buitink, S.; Cantoni, E.; Chiavassa, A.; Cossavella, F.; Daumiller, K.; de Souza, V.; di Pierro, F.; Doll, P.; Engel, R.; Falcke, H.; Finger, M.; Fuhrmann, D.; Gemmeke, H.; Ghia, P. L.; Glasstetter, R.; Grupen, C.; Haungs, A.; Heck, D.; Hörandel, J. R.; Horneffer, A.; Huang, X.; Huege, T.; Kampert, K.-H.; Kang, D.; Kickelbick, D.; Kolotaev, Y.; Krömer, O.; Kuijpers, J.; Lafebre, S.; Łuczak, P.; Mathes, H. J.; Mayer, H. J.; Milke, J.; Mitrica, B.; Morello, C.; Navarra, G.; Nehls, S.; Nigl, A.; Oehlschläger, J.; Over, S.; Petcu, M.; Pierog, T.; Rautenberg, J.; Rebel, H.; Roth, M.; Saftoiu, A.; Schieler, H.; Schmidt, A.; Schröder, F.; Sima, O.; Singh, K.; Stümpert, M.; Toma, G.; Trinchero, G. C.; Ulrich, H.; Walkowiak, W.; Weindl, A.; Wochele, J.; Wommer, M.; Zabierowski, J.; Zensus, J. A.; LOPES Collaboration

2009-06-01

LOPES is a radio antenna array co-located with the Karlsruhe Shower Core and Array DEtector, KASCADE-Grande in Forschungszentrum Karlsruhe, Germany, which provides well-calibrated trigger information and air shower parameters for primary energies up to 10eV. By the end of 2006, the radio antennas were re-configured to perform polarization measurements of the radio signal of cosmic ray air showers, recording in the same time both, the East-West and North-South polarization directions of the radio emission. The main goal of these measurements is to reconstruct the polarization characteristics of the emitted signal. This will allow a detailed comparison with theoretical predictions. The current status of these measurements is reported here.

Generation of spirally polarized propagation-invariant beam using fiber microaxicon.

PubMed

Philip, Geo M; Viswanathan, Nirmal K

2011-10-01

We present here a fiber microaxicon (MA)based method to generate spirally polarized propagation-invariant optical beam. MA chemically etched in the tip of a two-mode fiber efficiently converts the generic cylindrically polarized vortex fiber mode into a spirally polarized propagation-invariant (Bessel-type) beam via radial dependence of polarization rotation angle. The combined roles of helico-conical phase and nonparaxial propagation in the generation and characteristics of the output beam from the fiber MA are discussed. © 2011 Optical Society of America

Geodesy by radio interferometry - Water vapor radiometry for estimation of the wet delay

NASA Technical Reports Server (NTRS)

Elgered, G.; Davis, J. L.; Herring, T. A.; Shapiro, I. I.

1991-01-01

An important source of error in VLBI estimates of baseline length is unmodeled variations of the refractivity of the neutral atmosphere along the propagation path of the radio signals. This paper presents and discusses the method of using data from a water vapor radiomete (WVR) to correct for the propagation delay caused by atmospheric water vapor, the major cause of these variations. Data from different WVRs are compared with estimated propagation delays obtained by Kalman filtering of the VLBI data themselves. The consequences of using either WVR data or Kalman filtering to correct for atmospheric propagation delay at the Onsala VLBI site are investigated by studying the repeatability of estimated baseline lengths from Onsala to several other sites. The repeatability obtained for baseline length estimates shows that the methods of water vapor radiometry and Kalman filtering offer comparable accuracies when applied to VLBI observations obtained in the climate of the Swedish west coast. For the most frequently measured baseline in this study, the use of WVR data yielded a 13 percent smaller weighted-root-mean-square (WRMS) scatter of the baseline length estimates compared to the use of a Kalman filter. It is also clear that the 'best' minimum elevationi angle for VLBI observations depends on the accuracy of the determinations of the total propagation delay to be used, since the error in this delay increases with increasing air mass.

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

PubMed

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

2015-02-20

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

Recent Advances in Radio and Optical Propagation for Modern Communications, Navigation and Detection Systems

DTIC Science & Technology

1978-04-01

of coherent detection techniques (e.g. laser and optical heterodyning, sensitive to phase fluctuations caused by atmospheric turbulence). The...ATMOSPHERIC OPTICAL EFFECTS 2.1 Atmospheric Refraction The index of refraction n = c/v, with c = velocity of propagation in a vacuum and v ’n air , is... oscillating electrons reradiate and the net effect is to change the phase of the advancing wave. When sufficient molecules are present the moving electrons

An Experimental Study of the Effects of Radio upon the Rural Indian Audience.

ERIC Educational Resources Information Center

Sitaram, Kondavagil Suryanarayana

This study focused on whether radio increases the awareness level of the rural population in India, whether increases in awareness vary by the type of subject matter broadcast, and what the characteristics are (including media habits and community awareness) of the rural radio listeners. Ten villages in Hassan District, Mysore State, were…

An Analysis of Characteristics of Magnetostatic Waves Propagating in Nonhomogeneous Fields Across the Ferrospinel Film Thickness

NASA Astrophysics Data System (ADS)

Velikanova, Yu. V.; Vinogradova, M. R.; Mitlina, L. A.

2018-06-01

The amplitude-frequency characteristics (AFCs) of magnetostatic waves in the films of magnesium-manganese ferrospinels with nanostructured inhomogeneities are discussed. A common effect, observed in the film AFCs under different process conditions, is the `oscillations of propagation' of magnetostatic waves as a function of the frequency. The oscillation pattern is thought to depend on the inhomogeneous exchange parameters and the surface anisotropy constants. The wave instability is characterized by the resonant interaction of the dipole magnetostatic waves with the surface spin waves. It is shown that the ferrospinel films with periodic nanostructured inhomogeneities of 30-40 nm could be treated as magnon crystals. An inclusion of the inhomogeneity into consideration allows one to provide reasoning for the formation of the rejection bands within the range 9-12 GHz, whose frequencies correspond to Bragg frequencies.

Ultra-wideband radios for time-of-flight-ranging and network position estimation

DOEpatents

Hertzog, Claudia A [Houston, TX; Dowla, Farid U [Castro Valley, CA; Dallum, Gregory E [Livermore, CA; Romero, Carlos E [Livermore, CA

2011-06-14

This invention provides a novel high-accuracy indoor ranging device that uses ultra-wideband (UWB) RF pulsing with low-power and low-cost electronics. A unique of the present invention is that it exploits multiple measurements in time and space for very accurate ranging. The wideband radio signals utilized herein are particularly suited to ranging in harsh RF environments because they allow signal reconstruction in spite of multipath propagation distortion. Furthermore, the ranging and positioning techniques discussed herein directly address many of the known technical challenges encountered in UWB localization regarding synchronization and sampling. In the method developed, noisy, corrupted signals can be recovered by repeating range measurements across a channel, and the distance measurements are combined from many locations surrounding the target in a way that minimizes the range biases associated to indirect flight paths and through-wall propagation delays.

Technique to determine location of radio sources from measurements taken on spinning spacecraft

NASA Technical Reports Server (NTRS)

Fainberg, J.

1979-01-01

The procedure developed to extract average source direction and average source size from spin-modulated radio astronomy data measured on the IMP-6 spacecraft is described. Because all measurements are used, rather than just finding maxima or minima in the data, the method is very sensitive, even in the presence of large amounts of noise. The technique is applicable to all experiments with directivity characteristics. It is suitable for onboard processing on satellites to reduce the data flow to Earth. The application to spin-modulated nonpolarized radio astronomy data is made and includes the effects of noise, background, and second source interference. The analysis was tested with computer simulated data and the results agree with analytic predictions. Applications of this method with IMP-6 radio data have led to: (1) determination of source positions of traveling solar radio bursts at large distances from the Sun; (2) mapping of magnetospheric radio emissions by radio triangulation; and (3) detection of low frequency radio emissions from Jupiter and Saturn.

HOMOLOGOUS SOLAR EVENTS ON 2011 JANUARY 27: BUILD-UP AND PROPAGATION IN A COMPLEX CORONAL ENVIRONMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pick, M.; Démoulin, P.; Zucca, P.

2016-05-20

In spite of the wealth of imaging observations at the extreme-ultraviolet (EUV), X-ray, and radio wavelengths, there are still relatively few cases where all of the imagery is available to study the full development of a coronal mass ejection (CME) event and its associated shock. The aim of this study is to contribute to the understanding of the role of the coronal environment in the development of CMEs and the formation of shocks, and their propagation. We have analyzed the interactions of a couple of homologous CME events with ambient coronal structures. Both events were launched in a direction farmore » from the local vertical, and exhibited a radical change in their direction of propagation during their progression from the low corona into higher altitudes. Observations at EUV wavelengths from the Atmospheric Imaging Assembly instrument on board the Solar Dynamic Observatory were used to track the events in the low corona. The development of the events at higher altitudes was followed by the white-light coronagraphs on board the Solar and Heliospheric Observatory . Radio emissions produced during the development of the events were well recorded by the Nançay solar instruments. Thanks to their detection of accelerated electrons, the radio observations are an important complement to the EUV imaging. They allowed us to characterize the development of the associated shocks, and helped to unveil the physical processes behind the complex interactions between the CMEs and ambient medium (e.g., compression, reconnection).« less

Shock Wave Propagation in Layered Planetary Interiors: Revisited

NASA Astrophysics Data System (ADS)

Arkani-Hamed, J.; Monteux, J.

2017-12-01

The end of the terrestrial planet accretion is characterized by numerous large impacts. About 90% of the mass of a large planet is accreted while the core mantle separation is occurring, because of the accretionary and the short-lived radio-isotope heating. The characteristics of the shockwave propagation, hence the existing scaling laws are poorly known within the layered planets. Here, we use iSALE-2D hydrocode simulations to calculate shock pressure in a differentiated Mars type body for impact velocities of 5-20 km/s, and impactor sizes of 100-400 km. We use two different rheologies for the target interior, an inviscid model ("no-stress model") and a pressure and damage-dependent strength model ("elaborated model"). To better characterize the shock pressure within the whole mantle as a function of distance from the impact site, we propose the following distribution: (1) a near field zone larger than the isobaric core that extends to 7-15 times the projectile radius into the target, where the peak shock pressure decays exponentially with increasing distance, (2) a far field zone where the pressure decays with distance following a power law. The shock pressure decreases more rapidly with distance in the near field for the elaborated model than for the no-stress model because of the influence of acoustic fluidization and damage. However to better illustrate the influence of the rheology on the shock propagation, we use the same expressions to fit the shock pressure with distance for both models. At the core-mantle boundary, CMB, the peak shock pressure jumps as the shock wave enters the core. We derived the boundary condition at CMB for the peak shock pressure. It is less sensitive to the impact velocity or the impactor size, but strongly depends on the rheology of the planet's mantle. Because of the lower shock wave velocity in the core compared to that in the mantle, the refracted shockwave propagates toward the symmetry axis of the planet, and the shock

Magnetospheric Radio Tomography: Observables, Algorithms, and Experimental Analysis

NASA Technical Reports Server (NTRS)

Cummer, Steven

2005-01-01

This grant supported research towards developing magnetospheric electron density and magnetic field remote sensing techniques via multistatic radio propagation and tomographic image reconstruction. This work was motivated by the need to better develop the basic technique of magnetospheric radio tomography, which holds substantial promise as a technology uniquely capable of imaging magnetic field and electron density in the magnetosphere on large scales with rapid cadence. Such images would provide an unprecedented and needed view into magnetospheric processes. By highlighting the systems-level interconnectedness of different regions, our understanding of space weather processes and ability to predict them would be dramatically enhanced. Three peer-reviewed publications and 5 conference presentations have resulted from this work, which supported 1 PhD student and 1 postdoctoral researcher. One more paper is in progress and will be submitted shortly. Because the main results of this research have been published or are soon to be published in refereed journal articles listed in the reference section of this document, we provide here an overview of the research and accomplishments without describing all of the details that are contained in the articles.

Pulsar B0329+54: scattering disk resolved by RadioAstron interferometer at 324 MHz

NASA Astrophysics Data System (ADS)

Popov, M.

Propagation of pulsar radio emission through the interstellar plasma is accompanied with scattering by inhomogeneities of the plasma. The scattering produces a range of effects: angular broadening, pulse broadening, intensity modulation (scintillations), and distortion of radio spectra (diffraction pattern). In this presentation, we will primarily deal with scattering effects affecting interferometric measurements. Pulsars are point like radio sources at angular resolution provided by space VLBI even at largest baseline projections. Therefore, any structure, observed by the space-ground interferometer, is due to scattering effects. The objective of our study was to measure parameters of a scattering disk for the PSR B0329+54 at a frequency of 324 MHz with the space-ground interferometer RadioAstron. Observations were conducted on November 26-29 2012 in four sessions, one hour duration each, with progressively increasing baseline projections of 70, 90,175, and 235 thousand kilometers correspondingly. Only one ground radio telescope observed the pulsar together with the space radio telescope (SRT); it was 100-m telescope in Green Bank (GBT). Notable visibility amplitudes were detected at all baseline projections at a maximum level of 0.05 with the SNR of about 20. It was found that visibility function in delay consists of many isolated unresolved spikes. The overall spread of such spikes in delay corresponds to the scattering disk of about 4 mas at a half wide. Fine structure of the visibility amplitude in delay domain corresponds to a model of amplitude modulated noise (AMN). Fringe rate behavior with time indicates on dominant influence of refraction on traveling ionospheric disturbances (TID).

Geospace ionosphere research with a MF/HF radio instrument on a cubesat

NASA Astrophysics Data System (ADS)

Kallio, E. J.; Aikio, A. T.; Alho, M.; Fontell, M.; van Gijlswijk, R.; Kauristie, K.; Kestilä, A.; Koskimaa, P.; Makela, J. S.; Mäkelä, M.; Turunen, E.; Vanhamäki, H.

2016-12-01

Modern technology provides new possibilities to study geospace and its ionosphere, using spacecraft and and computer simulations. A type of nanosatellites, CubeSats, provide a cost effective possibility to provide in-situ measurements in the ionosphere. Moreover, combined CubeSat observations with ground-based observations gives a new view on auroras and associated electromagnetic phenomena. Especially joint and active CubeSat - ground based observation campaigns enable the possibility of studying the 3D structure of the ionosphere. Furthermore using several CubeSats to form satellite constellations enables much higher temporal resolution. At the same time, increasing computation capacity has made it possible to perform simulations where properties of the ionosphere, such as propagation of the electromagnetic waves in the medium frequency, MF (0.3-3 MHz) and high frequency, HF (3-30 MHz), ranges is based on a 3D ionospheric model and on first-principles modelling. Electromagnetic waves at those frequencies are strongly affected by ionospheric electrons and, consequently, those frequencies can be used for studying the plasma. On the other hand, even if the ionosphere originally enables long-range telecommunication at MF and HF frequencies, the frequent occurrence of spatiotemporal variations in the ionosphere disturbs communication channels, especially at high latitudes. Therefore, study of the MF and HF waves in the ionosphere has both a strong science and technology interests. We present computational simulation results and measuring principles and techniques to investigate the arctic ionosphere by a polar orbiting CubeSat whose novel AM radio instrument measures HF and MF waves. The cubesat, which contains also a white light aurora camera, is planned to be launched in 2017 (http://www.suomi100satelliitti.fi/eng). We have modelled the propagation of the radio waves, both ground generated man-made waves and space formed space weather related waves, through the 3D

The spatial variation of the infrared-to-radio ratio in spiral galaxies

NASA Technical Reports Server (NTRS)

Marsh, K. A.; Helou, G.

1995-01-01

We have produced two-dimensional maps of the intensity ratio, Q(sub 60), of 60 micron infrared to 20 cm radio continuum emission, for a set of 25 nearby galaxies, mostly spirals. The ratio maps were obtained from infrared images made using IRAS data with the maximum correlation method, and radio images made using VLA data. Before taking the ratio, the radio images were processed so as to have the same resolution properties as the infrared images; the final spatial resolution in all cases is approximately 1 min, corresponding to 1 - 2 kpc for most galaxies. This resolution represents a significant improvement over previous studies. Our new high-resolution maps confirm the slow decrease of Q(sub 60) with increasing radial distance from the nucleus, but show additional structure which is probably associated with separate sites of active star formation in the spiral arms. The maps show Q(sub 60) to be more closely related to infrared surface brightness than to the radial distance r in the galaxy disk. We note also that the Q(sub 60) gradients are absent (or at least reduced) for the edge-on galaxies, a property which can be attributed to the dilution of contrast due to the averaging of the additional structure along the line of sight. The results are all in qualitative agreement with the suggestion that the radio image represents a smeared version of the infrared image, as would be expected on the basis of current models in which the infrared-radio correlation is driven by the formation of massive stars, and the intensity distribution of radio emission is smeared as a result of the propagation of energetic electrons accelerated during the supernova phase.

A Radio-Map Automatic Construction Algorithm Based on Crowdsourcing

PubMed Central

Yu, Ning; Xiao, Chenxian; Wu, Yinfeng; Feng, Renjian

2016-01-01

Traditional radio-map-based localization methods need to sample a large number of location fingerprints offline, which requires huge amount of human and material resources. To solve the high sampling cost problem, an automatic radio-map construction algorithm based on crowdsourcing is proposed. The algorithm employs the crowd-sourced information provided by a large number of users when they are walking in the buildings as the source of location fingerprint data. Through the variation characteristics of users’ smartphone sensors, the indoor anchors (doors) are identified and their locations are regarded as reference positions of the whole radio-map. The AP-Cluster method is used to cluster the crowdsourced fingerprints to acquire the representative fingerprints. According to the reference positions and the similarity between fingerprints, the representative fingerprints are linked to their corresponding physical locations and the radio-map is generated. Experimental results demonstrate that the proposed algorithm reduces the cost of fingerprint sampling and radio-map construction and guarantees the localization accuracy. The proposed method does not require users’ explicit participation, which effectively solves the resource-consumption problem when a location fingerprint database is established. PMID:27070623

Galaxy-wide radio-induced feedback in a radio-quiet quasar

NASA Astrophysics Data System (ADS)

Villar-Martín, M.; Emonts, B.; Cabrera Lavers, A.; Tadhunter, C.; Mukherjee, D.; Humphrey, A.; Rodríguez Zaurín, J.; Ramos Almeida, C.; Pérez Torres, M.; Bessiere, P.

2017-12-01

We report the discovery of a radio-quiet type 2 quasar (SDSS J165315.06+234943.0 nicknamed the 'Beetle' at z = 0.103) with unambiguous evidence for active galactic nucleus (AGN) radio-induced feedback acting across a total extension of ∼46 kpc and up to ∼26 kpc from the AGN. To the best of our knowledge, this is the first radio-quiet system where radio-induced feedback has been securely identified at ≫several kpc from the AGN. The morphological, ionization and kinematic properties of the extended ionized gas are correlated with the radio structures. We find along the radio axis (a) enhancement of the optical line emission at the location of the radio hotspots (b) turbulent gas kinematics (FWHM ∼ 380-470 km s-1) across the entire spatial range circumscribed by them (c) ionization minima for the turbulent gas at the location of the hot spots, (d) high temperature Te ≳ 1.9 × 104 K at the NE hotspot. Turbulent gas is also found far from the radio axis, ∼25 kpc in the perpendicular direction. We propose a scenario in which the radio structures have perforated the interstellar medium of the galaxy and escaped into the circumgalactic medium. While advancing, they have interacted with in situ gas modifying its properties. Our results show that jets of modest power can be the dominant feedback mechanism acting across huge volumes in radio-quiet systems, including highly accreting luminous AGNs, where radiative mode feedback may be expected.

Propagation of sound in turbulent media

NASA Technical Reports Server (NTRS)

Wenzel, A. R.

1976-01-01

Perturbation methods commonly used to study the propagation of acoustic waves in turbulent media are reviewed. Emphasis is on those techniques which are applicable to problems involving long-range propagation in the atmosphere and ocean. Characteristic features of the various methods are illustrated by applying them to particular problems. It is shown that conventional perturbation techniques, such as the Born approximation, yield solutions which contain secular terms, and which therefore have a relatively limited range of validity. In contrast, it is found that solutions obtained with the aid of the Rytov method or the smoothing method do not contain secular terms, and consequently have a much greater range of validity.

Stable radio-frequency transfer over optical fiber by phase-conjugate frequency mixing.

PubMed

He, Yabai; Orr, Brian J; Baldwin, Kenneth G H; Wouters, Michael J; Luiten, Andre N; Aben, Guido; Warrington, R Bruce

2013-08-12

We demonstrate long-distance (≥100-km) synchronization of the phase of a radio-frequency reference over an optical-fiber network without needing to actively stabilize the optical path length. Frequency mixing is used to achieve passive phase-conjugate cancellation of fiber-length fluctuations, ensuring that the phase difference between the reference and synchronized oscillators is independent of the link length. The fractional radio-frequency-transfer stability through a 100-km "real-world" urban optical-fiber network is 6 × 10(-17) with an averaging time of 10(4) s. Our compensation technique is robust, providing long-term stability superior to that of a hydrogen maser. By combining our technique with the short-term stability provided by a remote, high-quality quartz oscillator, this system is potentially applicable to transcontinental optical-fiber time and frequency dissemination where the optical round-trip propagation time is significant.