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1

CME Propagation Characteristics from Radio Observations  

E-print Network

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

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

2007-11-20

2

CME Propagation Characteristics from Radio Observations  

E-print Network

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

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

2007-01-01

3

Plasma plume propagation characteristics of pulsed radio frequency plasma jet  

SciTech Connect

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

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

2011-04-11

4

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

5

Radio Wave Propagation  

Microsoft Academic Search

Electromagnetic radio waves traveling within earth's atmosphere are called terrestrial waves, and communications between two or more points on earth is called terrestrial radio communications. Terrestrial waves are influenced by the atmosphere and earth itself. In terrestrial radio communications, waves can be propagated in several ways, depending on the type of system and the environment. Electromagnetic waves also travel in

S. Venkatesh

2007-01-01

6

Radio wave propagation aspects for future digital mobile radio systems  

Microsoft Academic Search

The authors investigate the possibility of using frequencies around 1700 MHz for mobile radio communication, focusing on a comparison of the characteristics of 900 MHz and 1700 MHz radio wave propagation. Radio-wave propagation for mobile radio is broken down into large-scale and small-scale effects. The large-scale variations depend on the BS (base station) to MS (mobile station) distance and also

Mats Nilson; Sven Nordin; M. Mizuno

1988-01-01

7

Radio-wave propagation in space  

NASA Astrophysics Data System (ADS)

The characteristics of radio waves propagating in space are discussed, with attention given to their astronomical applications. Physical phenomena influencing the propagation of radio waves in the earth's atmospheres are considered, including atmospheric absorption, attenuation and refraction effects. The uses of radar interferometry in interstellar and interplanetary astronomy are described and radar data are presented concerning coronal scattering; interplanetary scintillations; relativistic time delay measurements; and gravitational lens effects. The effect of the gravitational field of interstellar space on the propagation of radio waves is also discussed.

Iakovlev, O. I.

8

Radio propagation by reflection from meteor trails  

Microsoft Academic Search

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

G. R. Sugar

1964-01-01

9

The indoor radio propagation channel  

Microsoft Academic Search

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

HOMAYOUN HASHEMI

1993-01-01

10

Method for calculating certain characteristics of radio-wave propagation using inclination angles of plasma-frequency isolines  

Microsoft Academic Search

The paper describes a method for calculating azimuthal deviations and Doppler frequency shifts in the ionosphere on the basis of inclination angles of plasma-frequency isolines. The method is applicable to ionospheric radio lines under the effect of traveling ionospheric disturbances moving at an angle of 90 deg to the radio-line direction.

G. N. Nosova

1985-01-01

11

Antenna Construction and Propagation of Radio Waves.  

ERIC Educational Resources Information Center

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

Marine Corps Inst., Washington, DC.

12

Wave propagation and earth satellite radio emission studies  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

13

A basic atlas of radio-wave propagation  

NASA Astrophysics Data System (ADS)

Basic concepts in radio-wave propagation and system design are brought together in this volume along with all of the essential design elements required for VHF, UHF, and SHF radio. The basic topics addressed include free-space propagation path, reflection interference propagation path, diffraction propagation path, troposcatter propagation path, absorption propagation path, passive-relay propagation path, noise and S/N, fading estimation and system evaluation, and astronomy and geography.

Shibuya, Shigekazu

14

VHF and Microwave Propagation Characteristics of Ducts  

Microsoft Academic Search

Observations from many years of amateur radio operations together with commercial microwave propagation studies and are used to illustrate the nature of the VHF propagation in ducts. Recently developed formula for characterizing VHF and microwave propagation in ducts are used and modified to reconcile the observations with theory. Measurements from a high resolution SODAR are used to show the complex

Andrew L. Martin

2007-01-01

15

a Study on the Radio Propagation in the Korean Ionosphere  

Microsoft Academic Search

The effects of the ionosphere on the radio wave propagation are scattering of radio waves, attenuation, angle error, ranging error, and time delay. If ionospheric conditions are suitable, the charged particles can remove energy from radio waves and thus attenuate the signal. Also, a radio wave traveling a path along which the electron density is not constant undergoes changes in

Seok-Hee Bae; Kyu-Hong Choi; Jai-Rim Yuk; Hong-Ik Kim; Kyoung W. Min

1992-01-01

16

Radio propagation for space communications systems  

NASA Technical Reports Server (NTRS)

This paper presents a review of the most recent information on the effects of the earth's atmosphere on space communications systems. Models and techniques used in the prediction of atmospheric effects as influenced by frequency, geography, elevation angle, and type of transmission are discussed. Recent data on performance characteristics obtained from direct measurements on satellite links operating to above 30 GHz are reviewed. Particular emphasis is placed on the effects of precipitation on the earth-space path, including rain attenuation, and rain and ice-particle depolarization. Sky noise, antenna gain degradation, scintillations, and bandwidth coherence are also discussed. The impact of the various propagation factors on communications system design criteria is presented. These criteria include link reliability, power margins, noise contributions, modulation and polarization factors, channel crosstalk, error-rate, and bandwidth limitations.

Ippolito, L. J.

1981-01-01

17

Radio-wave propagation for space communications systems  

NASA Technical Reports Server (NTRS)

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

Ippolito, L. J.

1981-01-01

18

Radio-wave propagation in a statistically inhomogeneous medium  

Microsoft Academic Search

The Helmholtz equation describing the propagation of radio waves in an inhomogeneous atmosphere is solved in the framework of geometrical optics with consideration of the existence of traveling waves. The analysis has application to the scattering of radio waves in the ionosphere.

V. D. Gusev

1978-01-01

19

The TIR system - A two-frequency interferometer for the investigation of transionospheric radio-wave propagation  

Microsoft Academic Search

The design and characteristics of a radio interferometer (the TIR system) for investigating transionospheric radio-wave propagation at frequencies of 136 and 714 MHz are described. Measured radio-signal field parameters will be used to determine the characteristics of the space-time variability of the ionosphere, from traveling ionospheric disturbances that are responsible for signal refraction to the spectrum of small-scale irregularities that

E. L. Afraimovich; V. N. Zvezdin; N. P. Min'ko; A. N. Shapovalov

1989-01-01

20

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

SciTech Connect

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

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

2009-07-01

21

Propagation characteristics of satellite links  

NASA Astrophysics Data System (ADS)

Lower and upper atmospheric effects on signal characteristics of satellite transmissions are reviewed. The effects of importance produced by the ionosphere are the fading, caused by irregularities in the equatorial and high latitude ionospheres, the time delay errors produced by the passage of radiowaves through the ionospheric electrons, and absorption of the lower ionosphere at auroral and polar cap latitudes. The tropospheric effects include absorption by constituents and the problem of scattering of energy into unwanted polarizations. In some applications low angle effects of refraction and scintillation are also of importance.

Aarons, J.

1982-04-01

22

Multipath characteristics of impulse radio channels  

Microsoft Academic Search

We investigate the multipath characteristics of the impulse radios (IR) which have drawn much attention for future high-speed wireless communication services. For this objective, we observe the characteristics of bit error rates through computer simulations for the deterministic two-path model and the statistical indoor multipath model of Saleh and Valenzuela (1987). The simulation results indicate that the performance of the

Hojoon Lee; Byungchil Han; Yoan Shin; Sungbin Imt

2000-01-01

23

Mitigation of Effects of the Atmosphere on Radio Wave Propagation  

Microsoft Academic Search

Radio waves traveling through free space have little or no external influence on them. But when such signals are traversed through the atmosphere, their effective propagation will be determined by atmospheric factors. Some of these atmospheric factors are variations in geographic height, differences in geographic locations, and changes in time (day, night, season, etc.). This paper has critically looked into

A. S. Adegoke

24

Impulse Response Modeling of Indoor Radio Propagation Channels  

Microsoft Academic Search

If indoor radio propagation channels are modeled as linear filters, they can be characterized by reporting the parameters of their equivalent impulse response functions. The measurement and modeling of estimates for such functions in two different office buildings are reported. The resulting data base consists of 12000 impulse response estimates of the channel that were obtained by inverse Fourier transforming

Homayoun Hashemi

1993-01-01

25

Coplanar stripline propagation characteristics and bandpass filter  

Microsoft Academic Search

In this paper, a coplanar stripline bandpass filter is developed. The propagation characteristics of the coplanar stripline used for the construction of the filter are presented in the form of phase constant and attenuation constant. The filter is characterized experimentally as well as theoretically by use of the finite-difference time-domain (FDTD) technique. The agreement between the measured and modeled filter

Kavita Goverdhanam; Rainee N. Simons; Linda P. B. Katehi

1997-01-01

26

Radio propagation prediction services in Japan  

NASA Technical Reports Server (NTRS)

Japanese prediction services for HF radio communications are outlined in relation to prediction method, performance and evaluation. The current prediction is based on the CCIR interim method with some modifications matching to a computer system. The principal service is the monthly median prediction issued regularly three months in advance for various communication circuits. A daily prediction for short distance circuits is being prepared by using real time ionospheric sounding data. An evaluation theory and practice is expected to be introduced in the future prediction service.

Maeda, R.

1979-01-01

27

Plasma and radio waves from Neptune: Source mechanisms and propagation  

NASA Technical Reports Server (NTRS)

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

Wong, H. K.

1994-01-01

28

Coherence bandwidth loss in transionospheric radio propagation  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

29

Ionospheric HF radio propagation in problems and computer assignments  

E-print Network

The book's purpose is to introduce the HF ionospheric radio-propagation, through the solution of problems and computer assignments. The problems and computer assignments are used primarily as a check and deepening of the theoretical part, which however is essential. Secondly, they are used to introduce the reader to new subjects in a natural way. The text proposes the main objective of bringing the reader which has a background similar to a master degree in physics or engineering, to an operative level in the field of ionospheric radio-propagation. The material covers the fundamentals of plasma physics, the Appleton-Hartree equation, its interpretation and discussion, and group refractive indices. The applications presented include ionograms simulation, ray tracing, and ionospheric absorption.

Scotto, Carlo

2013-01-01

30

The effect of radio-wave propagation conditions in the solar corona on the properties of observed type III radio bursts  

Microsoft Academic Search

Geometrical optics is used to perform a ray-tracing analysis of radio waves in the solar corona in the presence of large-scale ducts. It is shown that some of the characteristic features of type III bursts can be explained by taking into account the effects of radio-wave propagation in the inhomomgenous coronal plasma. In particular, it is possible to explain the

M. A. Itkina; V. A. Yashnov

1989-01-01

31

Radio Wave Propagation Handbook for Communication on and Around Mars  

NASA Technical Reports Server (NTRS)

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

Ho, Christian; Golshan, Nasser; Kliore, Arvydas

2002-01-01

32

Radio propagation through solar and other extraterrestrial ionized media  

NASA Technical Reports Server (NTRS)

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.

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

1980-01-01

33

Fade durations in satellite-path mobile radio propagation  

NASA Astrophysics Data System (ADS)

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.

Schmier, Robert G.; Bostian, Charles W.

1986-12-01

34

Fade durations in satellite-path mobile radio propagation  

NASA Technical Reports Server (NTRS)

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.

Schmier, Robert G.; Bostian, Charles W.

1986-01-01

35

General Theory on the Propagation of Radio Waves in the Ionized Layer of the Upper Atmosphere  

Microsoft Academic Search

1. Theories on the propagation of radio waves in the entire range of frequencies used in communications are treated together with discussions on the applicable limit of the theory of geometrical optics to wave propagation. 2. Definitions of the \\

S. Namba

1933-01-01

36

HF radio field strength and total propagation invariants  

NASA Astrophysics Data System (ADS)

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

Tsedilina, E. E.

1994-01-01

37

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

Microsoft Academic Search

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

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

1975-01-01

38

Lightning-induced effects on VLF/LF radio propagation  

NASA Technical Reports Server (NTRS)

In recent years, at least two different ways in which energy from lightning discharges couples into the lower ionosphere and the radiation belts have come to the fore. In this paper, we briefly review these recent results especially from the point of view of their effects on VLF/LF radio propagation in the earth-ionosphere wave guide. We separately discuss two different mechanisms of coupling, namely lightning-induced electron precipitation, and lightning-induced heating and ionization of the lower ionosphere. We also discuss a planned active VLF wave-injection experiment designed to investigate ionospheric heating by VLF waves under controlled conditions and to generate ELF waves by modulated VLF heating.

Inan, U. S.; Rodriguez, J. V.

1993-01-01

39

Characteristics of magnetospheric radio noise spectra  

NASA Technical Reports Server (NTRS)

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.

Herman, J. R.

1976-01-01

40

Propagation Characteristics of International Space Station Wireless Local Area Network  

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

41

Microwave Propagation Characteristics in the MMDS Frequency Band  

Microsoft Academic Search

This report presents the results of measurements to characterize MMDS band radio propagation in a suburban environment for a system using a directional base antenna and either a directional or an omni-directional fixed subscriber antenna. Channel sounding measurements were made using three subscriber antenna heights at representative locations throughout residential and commercial areas. Path loss and delay spread are reported

Jeffrey W. Porter; John A. Thweatt

2000-01-01

42

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

SciTech Connect

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

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

2012-01-01

43

Characteristics and Problems of the Gifted: neural propagation depth and  

E-print Network

- 1 - Characteristics and Problems of the Gifted: neural propagation depth and flow motivation. Gifted people exhibit a complex of cognitive, perceptual, emotional, motivational and social traits skills and challenges. Gifted people, being more cognitively skilled, will seek out more difficult

Toint, Philippe

44

The effect of radio-wave propagation conditions in the solar corona on the properties of observed type III radio bursts  

NASA Astrophysics Data System (ADS)

Geometrical optics is used to perform a ray-tracing analysis of radio waves in the solar corona in the presence of large-scale ducts. It is shown that some of the characteristic features of type III bursts can be explained by taking into account the effects of radio-wave propagation in the inhomomgenous coronal plasma. In particular, it is possible to explain the fact that the radial coordinates of the point of radio-wave emergence from the corona exceed the level of the fundamental plasma frequency, and the fact that the bursts of decametric storms are observed at the fundamental frequency near the central meridian and at the second harmonic near the solar limb.

Itkina, M. A.; Yashnov, V. A.

1989-10-01

45

Analysis of tropospheric propagation characteristics based on regional meteorological data  

NASA Astrophysics Data System (ADS)

Meteorological data has been processed to investigate RF (radio frequency) propagation efforts of the tropospheric region from ground to 28 km in space. A data base has been developed to provide enough information for analyzing many different phenomena of the troposphere in terms of lapse rate, refractivity, range error, angle error, slant range, and interrelationships among these parameters. Based on preliminary analysis, the results are very distinguishable from the values arrived at through the application of conventional data for analysis of RF propagation patterns. This implies that the seasonal average value provides better indications of the current atmospheric variation than the annual global average value which most users have adopted for convenience.

Choi, Junho; Melton, Mara; Donohue, John; Fryland, Albert

1995-02-01

46

Parallel Simulation of Wireless Networks with TED: Radio Propagation, Mobility and Protocols  

Microsoft Academic Search

We describe the , a parallel simulation testbed for mobile wireless networks. In this article we emphasize the techniques for modeling of radio propagation (long- and short-scale fading and interference) and protocols for integrated radio resource management in mobile wireless voice networks. The testbed includes the standards-based AMPS, NA-TDMA and GSM protocols, and several research-oriented protocol families.

Jignesh Panchal; Owen Kelly; Jie Lai; Narayan B. Mandayam; Andarew T. Ogielski; Roy D. Yates

1998-01-01

47

Impulse radio multipath characteristics and diversity reception  

Microsoft Academic Search

Delay-and-sum beamforming is applied to both ideal and measured ultra-wideband (UWB) signals. The results of propagation measurements are also used directly to estimate the performance of an UWB communication system and to characterize design tradeoffs

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

1998-01-01

48

Empirical formula for propagation loss in land mobile radio services  

Microsoft Academic Search

An empirical formula for propagation loss is derived from Okumura's report in order to put his propagation prediction method to computational use. The propagation loss in an urban area is presented in a simple form: A + B log10R, where A and B are frequency and antenna height functions and R is the distance. The introduced formula is applicable to

M. Hata

1980-01-01

49

Radio-wave propagation for emerging wireless personal-communication systems  

Microsoft Academic Search

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

Theodore S. Rappaport; S. Sandhu

1994-01-01

50

Normal transition and propagation Characteristics of YBCO tape  

Microsoft Academic Search

YBCO tape is expected to be used in future HTS applications, because it has better Jc characteristic in high temperatures and in high applied magnetic fields. It is important to consider the stability in superconducting applications. To establish the stability criterion for coated conductors, the characteristics of the transition to the normal state and normal-zone propagation in YBCO sample tapes

Atsushi Ishiyama; Masahiro Yanai; Toru Morisaki; Hiroshi Ueda; Yuh Shiohara; Teruo Izumi; Yasuhiro Iijima; Takashi Saitoh

2005-01-01

51

Plasma and radio waves from Neptune: Source mechamisms and propagation  

NASA Technical Reports Server (NTRS)

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.

Menietti, J. Douglas

1994-01-01

52

URSI workshop report - Effects of the lower atmosphere on radio propagation at frequencies above 1 GHz  

NASA Astrophysics Data System (ADS)

The URSI workshop which investigated the effects of the lower atmosphere on radio propagation at frequencies above 1 GHz is summarized. Topics of the workshop include scattering from hydrometeors, predicting attenuation due to rainfall on terrestrial links, clear air propagation on line-of-sight radio paths, cross polarization on terrestrial and earth-space links, and transhorizon propagation. Exact calculations of electromagnetic wave scattering by single hydrometeors are given, and recommendations are made to develop a better characterization of cross polarization in clear-air and precipitation conditions.

Holt, A. R.; Hall, M. P. M.; Boithias, L.; Strickland, J.; Paraboni, A.; Bostian, C.; Ochs, A.

1981-10-01

53

Source and Propagation Characteristics of Explosive and Other Seismic Sources  

SciTech Connect

Understanding of the source and propagation characteristics of seismic events of different types including earthquakes, explosions and mining-induced events is essential for successful discrimination of nuclear explosions. We are compiling a data set of mining related seismic events in east Eurasia. Natural earthquake data in the same region are also collected for comparison study between mining related events and earthquakes. The ground-truth data set will provide a unique and valuable resource for monitoring research. We will utilize the data set to investigate the source and propagation characteristics of seismic sources of different types including mine blasts, tremors, collapses and earthquakes. We will use various seismological techniques including spectral analysis, and waveform modeling to conduct the investigation. The research will improve our understanding of the S-wave excitation and propagation characteristics of chemical explosions and other source types.

Ni, X; Chan, W; Wagner, R; Walter, W R; Matzel, E M

2005-07-14

54

Characteristics of Electromagnetic Pulse Propagation in Metal  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

55

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

NASA Technical Reports Server (NTRS)

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

Woo, R.; Ishimaru, A.

1973-01-01

56

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

57

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

NASA Technical Reports Server (NTRS)

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 disrupting to form a long, turbulent tail which is dragged downstream by the preshock wind.

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

1995-01-01

58

Channel propagation characteristics of wireless MICAz sensor nodes  

Microsoft Academic Search

Wireless sensor nodes are envisioned to be deployed in the urban and indoor environments. With the advancement of technologies, such as nano-wires and molecular circuits, sensor nodes will become small, cheap and power efficient. At present, many researchers are implementing and developing protocols with MICAz motes. Thus, it is important to understand the propagation characteristics of the MICAz motes. Antenna

Weilian Su; Mohamad Alzaghal

2009-01-01

59

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

NASA Technical Reports Server (NTRS)

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.

Manning, Robert M.

2008-01-01

60

Parallel simulations of wireless networks with TED: radio propagation, mobility and protocols  

Microsoft Academic Search

We describe the TeD\\/C++ implementation of WiPPET, a parallel simulation testbed for mobile wireless networks. In this article we emphasize the techniques for modeling of radio propagation (long- and short-scale fading and interference) and protocols for integrated radio resource management in mobile wireless voice networks. The testbed includes the standards-based AMPS, NA-TDMA and GSM protocols, and several research-oriented protocol families.

Jignesh Panchal; Owen Kelly; Jie Lai; Narayan Mandayam; Andarew T. Ogielski; Roy Yates

1998-01-01

61

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

Microsoft Academic Search

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

Subhas Chakravarty

2010-01-01

62

38 GHz wideband point-to-multipoint radio wave propagation study for a campus environment  

Microsoft Academic Search

This article presents the results of a fixed millimeter-wave short-hop radio wave propagation study at 38 GHz. A wideband measurement campaign was performed using three cross-campus radio links from April to August 1998 at Virginia Tech. 73,963 power delay profiles (PDPs) were recorded during different weather events such as clear sky, rain, and hail. Rain\\/hail attenuation, short-term signal variation, and

Hao Xut; T. S. Rappaport; R. J. Boyle; J. H. Schaffner

1999-01-01

63

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

64

Millimeter wave radio telescopes: Gain and pointing characteristics  

Microsoft Academic Search

The basic gain and pointing characteristics of millimeter-wave radio telescopes are described in this paper. Formal definitions of relevant telescope parameters are given. Performance limits set by conventional technology are discussed and compared with measurements of existing telescopes. Methods are also suggested for minimizing pointing errors.

B. L. Ulich

1981-01-01

65

Millimeter wave radio telescopes - Gain and pointing characteristics  

Microsoft Academic Search

The basic gain and pointing characteristics of millimeter-wave radio telescopes are described in this paper. Formal definitions of relevant telescope parameters are given. Performance limits set by conventional technology are discussed and compared with measurements of existing telescopes. Methods are also suggested for minimizing pointing errors.

B. L. Ulich

1981-01-01

66

Radio emission characteristics of Pulsars and their magnetic dipole angle  

Microsoft Academic Search

We have made a statistical analysis on the subpulse width, the mean pulse width and the rate of change of polarization angle in pulsars. We obtained a number of empirical relations showing how these radio emission characteristics are related to the magnetic inclination and discussed the physical implications of the relations.

Zhen-Ru Wang; Yi Chu

1981-01-01

67

Radio-thermal radiation of the atmosphere during waveguide propagation  

NASA Astrophysics Data System (ADS)

The invariant submersion method is used to conduct a spectral analysis of the Green function and calculate the loss coefficient of electromagnetic waves in a tropospheric waveguide. The diffraction problem of thermal atmospheric radiation during waveguide propagation is solved on the basis of this method.

Shevtsov, B. M.; Shishkarev, A. A.

1992-01-01

68

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

E-print Network

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

Jenn, David C.

69

Radio-Wave Propagation in the Non-Gaussian Interstellar Medium  

Microsoft Academic Search

Radio waves propagating from distant pulsars in the interstellar medium (ISM) are refracted by electron density inhomogeneities, so the intensity of observed pulses fluctuates with time. The observed pulse shapes are used to diagnose electron density distribution in the ISM. The theory relating the observed pulse time shapes to the electron density correlation function has developed for 30 years; however,

Stanislav Boldyrev; Carl R. Gwinn

2005-01-01

70

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

E-print Network

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

Ellingson, Steven W.

71

Higher order ionospheric propagation effects on GPS radio occultation signals  

NASA Astrophysics Data System (ADS)

With the increasing number of remote sensing satellites using the GPS radio occultation technique for atmospheric sounding, the estimation of higher order ionospheric effects and their mitigation have become relevant and important. Due to long ionospheric limb paths, GPS signals are strongly affected by ionospheric refraction during radio occultation. Standard dual-frequency GPS measurements may be used to estimate the first order term of the refractive index. However, non-linear terms such as the second and third order ionospheric terms and ray path bending effects are not considered in occultation measurements so far. Analysing selected CHAMP-GPS occultation events different higher order ionospheric terms are estimated and their effects on dual-frequency range estimation and total electron content (TEC) estimation are discussed. We have found that the separation between the GPS L1 and L2 ray paths exceeds the kilometer level during occultation for a vertical TEC level of more than 160 TEC units. Corresponding errors in the GPS dual-frequency range estimation and TEC estimation are found to exceed the meter and 10 TEC units level, respectively.

Hoque, M. Mainul; Jakowski, N.

2010-07-01

72

Spacecraft VHF Radio Propagation Analysis in Ocean Environments Including Atmospheric Effects  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

73

Computational strategy for modeling radio wave propagation in lossy circular waveguides  

SciTech Connect

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

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

2008-01-01

74

Experimental comparison of indoor UHF and EHF radio channel characteristics  

Microsoft Academic Search

This paper reports experimental results obtained for narrowband and wideband indoor radio channels at 893 MHz and 37.2 GHz, respectively. Under LOS conditions and same scenarios, the multipath channel characteristics for both frequency bands are compared in terms of distance-power law exponents and cumulative distribution functions (CDF) of the CW measurement data, and root-mean-square (RMS) delay spreads of the impulse

Larbi Talbi

2000-01-01

75

Image transmission in tactical radio frequency shared network propagation environments  

NASA Astrophysics Data System (ADS)

The need to transmit images across tactical radio frequency (rf) links has been identified in army digitization applications. For example, military doctrine requires that tactical functions like identification of battlefield entities as potential targets and battle damage assessment be performed by the soldier. Currently, a key input to these processes is imagery. Therefore, the quality and timeliness of the image directly impact tactical performance. The military is investigating the employment of remote sensors and advanced communications systems to meet this requirement as part of its digitization effort. Army communications systems exist that partially meet this requirement. However, many existing solutions employ these legacy systems in the context of a point-to-point communications architecture. Solutions to the problem of transmitting images across a rf network have not been fully explored. The term network implies that the rf transmission media is common to and shared by multiple subscribers. It is a suite of capabilities that collectively manage media access and information transfer for its subscribers thus providing substantial improvements in effectiveness, efficiency, and robustness. This paper discusses the challenges of transmitting images using one army legacy communications system in a tactical rf network, presents a conceptual framework for attacking the problem, and discusses one solution.

White, Kent H.; Wagner, Kerry A.; O'Hanian, Scott

1997-06-01

76

Source characteristics of Jovian narrow-band kilometric radio emissions  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

77

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

NASA Technical Reports Server (NTRS)

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 attenuation much depends on dust mass loading, dust size distribution, etc. Most large dust storm occur in the southern hemisphere during later spring and early summer when the southern hemisphere become suddenly hot.

Ho, Christian; Golshan, Nasser

1999-01-01

78

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

ERIC Educational Resources Information Center

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

Marine Corps, Washington, DC.

79

Characteristics of diving in radio-marked Xantus's Murrelets  

USGS Publications Warehouse

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.

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

2005-01-01

80

Some characteristics of wave propagation observed during T-REX  

NASA Astrophysics Data System (ADS)

T-Rex observation campaign took place in Owens Valley during March and April 2006. The radiosondes launched during this campaign include profiles of the horizontal wind components, temperature, humidity and pressure. The observations are used together with analysis from the European Center of Medium Weather Forecast (ECMWF), and simulations from the Weather Research and Forecasting Model (WRF) to extend the field data to regions that were not covered by measurements. These data are then used to study some characteristics of waves observed during T-Rex. We found cases where waves are modified as they approach critical levels, or as they propagate through refractive regions. We also present cases where waves are reflected at breaking levels, and other cases which show secondary wave generation by shear instability.

Teitelbaum, Hector; Moustaoui, Mohamed; Mahalov, Alex

2010-05-01

81

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

Microsoft Academic Search

This paper presents long-term statistics additional to those previously published pertaining to evaporation duct propagation of UHF radio waves in the British Channel Islands, with particular focus on a completely over-sea 50 km transhorizon path. The importance of the evaporation duct as an anomalous propagation mechanism in marine and coastal regions is highlighted. In particular, the influence of various atmospheric

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

2010-01-01

82

Analysis of radio-frequency radiation from a propagating electron beam. Master's Thesis  

SciTech Connect

An experiment was conducted which measured the Radio Frequency (RF) radiation from the PHERMEX accelerator, capable of 30 MeV and 600 A. This was accomplished by placing TEM horn antennae at varying angles from the path of the electron beam. The signals received by the antennae were then recorded by using a Digitizing Camera System (DCS). Measurements were taken of the radiation from propagating and non-propagating beams, beams with energy above and below Cherenkov threshold, and beams with varied currents. The captured RF signals and their corresponding frequency spectra were then analyzed. This analysis showed that the radio frequency radiation from the beams below the cherenkov threshold contained primarily transition radiation; when above, diffracted Cherenkov radiation was observed. Non-propagating beams produced larger-angle radiation and had less definition in their spectrum. All electric fields measured were proportional to the beam current. Lastly, the electron beam pulse width and separation were determined by both the received signals and their spectrum.

Lally, R.W.

1990-06-01

83

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

NASA Astrophysics Data System (ADS)

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

Motojima, K.; Haga, N.

2013-11-01

84

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

NASA Astrophysics Data System (ADS)

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

Motojima, K.; Haga, N.

2014-08-01

85

The propagation path for line-of-sight radio with diversity reception  

NASA Astrophysics Data System (ADS)

Multipath propagation in line-of-sight radio relay links is frequency selective and causes substantial additional attenuation. It is possible to reduce these effects by diversity reception, using two antennas mounted one above the other. The ratio of the time in which the attenuation with single reception exceeds a given threshold to the corresponding time with diversity reception is called improvement factor. Measurements at a single frequency were performed to investigate in which way this factor depends on the antenna spacing. With the improvement factor being known, it is possible to evaluate the reduction of the outage time of FM/FDM radio. High-capacity systems with digital modulation are much more sensitive to frequency-selective fading than those with frequency modulation. The transfer functions of the propagation channels for three antennas were then measured in a 43-MHz bandwidth, and the improvement was calculated as the ratio of time in which the bit error rate did not exceed a given treshold with single and with diversity reception.

Giloi, Hans-Georg; Metzger, Kurt; Valentin, Rolf

86

Characteristics of tropopause parameters as observed with GPS radio occultation  

NASA Astrophysics Data System (ADS)

Characteristics of the lapse rate tropopause are analyzed globally for tropopause altitude and temperature using global positioning system (GPS) radio occultation (RO) data from late 2001 to the end of 2013. RO profiles feature high vertical resolution and excellent quality in the upper troposphere and lower stratosphere, which are key factors for tropopause determination, including multiple ones. RO data provide measurements globally and allow examination of both temporal and spatial tropopause characteristics based entirely on observational measurements. To investigate latitudinal and longitudinal tropopause characteristics, the mean annual cycle, and inter-annual variability, we use tropopauses from individual profiles as well as their statistical measures for zonal bands and 5° × 10° bins. The latitudinal structure of first tropopauses shows the well-known distribution with high (cold) tropical tropopauses and low (warm) extra-tropical tropopauses. In the transition zones (20 to 40° N/S), individual profiles reveal varying tropopause altitudes from less than 7 km to more than 17 km due to variability in the subtropical tropopause break. In this region, we also find multiple tropopauses throughout the year. Longitudinal variability is strongest at northern hemispheric mid latitudes and in the Asian monsoon region. The mean annual cycle features changes in amplitude and phase, depending on latitude. This is caused by different underlying physical processes (such as the Brewer-Dobson circulation - BDC) and atmospheric dynamics (such as the strong polar vortex in the southern hemispheric winter). Inter-annual anomalies of tropopause parameters show signatures of El Niño-Southern Oscillation (ENSO), the quasi-biennial oscillation (QBO), and the varying strength of the polar vortex, including sudden stratospheric warming (SSW) events. These results are in good agreement with previous studies and underpin the high utility of the entire RO record for investigating latitudinal, longitudinal, and temporal tropopause characteristics globally.

Rieckh, T.; Scherllin-Pirscher, B.; Ladstädter, F.; Foelsche, U.

2014-11-01

87

Waveguide radio-wave propagation in the equatorial ionosphere according to the Interkosmos-19 data  

NASA Astrophysics Data System (ADS)

Additional strongly remote (up to 2000 km) radio-signal reflection traces on Intercosmos-19 ionograms obtained in the equatorial ionosphere have been considered. These traces, as a rule, begin at frequencies slightly lower than the main trace cutoff frequencies, which indicates that an irregularity with a decreased plasma density exists here. The waveguide stretched along the magnetic-field line is such an inhomogeneity in the equatorial ionosphere. The ray tracing confirm that radio waves propagate in a waveguide and make it possible to determine the typical waveguide parameters: -? N e ? 10%, with a diameter of 15-20 km. Since the waveguide walls are smooth, an additional trace is always recorded distinctly even in the case in which main traces were completely eroded by strong diffusivity. Only one additional trace (of the radio signal X mode) is usually observed one more multiple trace is rarely recorded. Waveguides can be observed at all altitudes of the equatorial ionosphere at geomagnetic latitudes of ±40°. The formation of waveguides is usually related to the formation of different-scale irregularities in the nighttime equatorial ionosphere, which result in the appearance of other additional traces and spread F.

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

2014-03-01

88

A parametric study of the propagation of auroral radio emissions through auroral cavities  

NASA Astrophysics Data System (ADS)

Auroral Kilometric Radiation is the radio counterpart of the Earth's auroral radiations, observed in a large domain of wavelength, from Infrared to UV and obviously in visible. It is generated at high latitude (~70°), mostly along the nightside magnetic field lines connecting to the Earth's magnetospheric tail. In-situ observations by numerous spacecraft show that the radio sources are embedded inside depleted cavities. The auroral cavities contain a hot tenuous plasma (ne~1 cm-3, Te~5 keV) in a strong ambient magnetic field (fp/fc < 0.1). The mechanism of emission, the Cyclotron Maser Instability (CMI), predicts an intense X mode emission near gyromagnetic frequency preferentially perpendicular to the local magnetic field. But as the radio waves are generated inside a depleted cavity, they are refracted. The apparent beaming of the source is different from that predicted by the CMI. The characteristics of the apparent beaming of the source outside of the cavity depends on several geometrical and physical parameters of the surrounding medium, as well as the frequency of the radio wave. A ray tracing code (ARTEMIS-P), which computes the trajectories of electromagnetic waves in magnetized plasma, is use to compute the path of radio ray from the source inside the hot tenuous plasma of the cavity to the outside. We model a cylindrical plasma cavity characterized by a few parameters (width, edge and parallel gradients) and we study the effect of the cavity geometry on the beaming of AKR for several frequencies. We draw conclusions about the deterministic nature of the beaming angle of the radio emissions generated in cavities. We then extend our study to emissions from giant planets.

Gautier, A.; Hess, S.; Cecconi, B.; Zarka, P. M.

2013-12-01

89

The Distortion Characteristics of a Pulse Wave Propagating through Fog Medium at Millimeter Wave Band  

Microsoft Academic Search

When a pulse wave propagates through fog, the effects of distortion, being severer at millimeter wave band, is caused by fog\\u000a because of its dispersive property. The transfer function of a pulse signal is obtained by the theory of radio wave propagation;\\u000a the complex envelope is deduced by the solution of Fourier integral. The broadening and compressing effects of a

Jiying Huang; Wang He; Shuhong Gong

2007-01-01

90

Scalable parallel simulations of wireless networks with WiPPET: Modeling of radio propagation, mobility and protocols  

Microsoft Academic Search

We review the design, selected applications and performance of WiPPET (Wireless Propagation and Protocol Evaluation Testbed), a general parallel simulation testbed for various types of wireless networks. WiPPET has been written in TeD\\/C++, an object-oriented modeling framework that isolates network modeling from the underlying parallel discrete event simulator. We describe the techniques for modeling radio propagation (long and short-scale fading

O. E. Kelly; J. Lai; N. B. Mandayam; A. T. Ogielski; J. Panchal; R. D. Yates

2000-01-01

91

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

Microsoft Academic Search

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

T. S. Kerblai; E. M. Kovalevskaia

1985-01-01

92

Source characteristics of Jovian narrow-band kilometric radio emissions  

Microsoft Academic Search

New observations of Jovian narrow-band kilometric (nKOM) radio emissions were made by the Unified Radio and Plasma Wave (URAP) experiment on the Ulysses spacecraft during the Ulysses-Jupiter encounter in early February 1992. These observations have demonstrated the unique capability of the URAP instrument for determining both the direction and polarization of nKOM radio sources. An important result is the discovery

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

1993-01-01

93

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

94

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

NASA Technical Reports Server (NTRS)

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

Misyura, V. A.

1974-01-01

95

Radio Frequency Characteristics of Printed Meander Inductors and Interdigital Capacitors  

NASA Astrophysics Data System (ADS)

Radio frequency (RF) characterizations of printed silver ink inductors manufactured at low (150 °C) and high (850 °C) temperatures and interdigital capacitors manufactured at high (850 °C) temperatures were carried out in the 500 MHz to 6 GHz range. The S-parameter responses of the components were measured with a probe station and an Agilent 8510C network analyzer. Electrical parameters such as inductance, capacitance, and a quality factor were estimated from experimental results and numerical calculation. Component parameters are dependent on physical dimensions and material properties. The components were created in a 4 ×4 mm2 area with line widths/gaps of 500/500, 250/250, and 200/200 µm. Windings in the coils varied from 2 to 5 turns and finger counts in the capacitors, from 5 to 11 within the defined area and line widths. As a result, low-T-cured (150 °C) silver ink meander line inductors achieved 8 to 18 nH inductances at 1 and 2 GHz with a quality value of 10-25. High-T-cured (850 °C) silver ink meander line inductors had 6-15 nH inductances and quality values were around 100, indicating a conductivity challenge with low-T-cured inks. Interdigital capacitors with 1 to 4 pF capacitances and sufficient quality values were created. A low-loss BaTiO3 coating was printed over the interdigital capacitors; they exhibited suitable electrical characteristics to allow decreasing the physical size of the component.

Myllymaki, Sami; Teirikangas, Merja; Nelo, Mikko; Tulppo, Joel; Soboci?ski, Maciej; Juuti, Jari; Jantunen, Heli; Sloma, Marcin; Jakubowska, Malgorzata

2013-05-01

96

Dynamic characteristic of intense short microwave propagation in an atmosphere  

SciTech Connect

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

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

1983-07-01

97

Dispersion characteristics of optically excited coplanar striplines: pulse propagation  

Microsoft Academic Search

The propagation of optically excited picosecond electrical pulses on coplanar striplines is analyzed. A full-wave analysis method that includes dispersion and losses over terahertz bandwidths is outlined. Results of the full-wave analysis are interpreted in terms of the underlying physical phenomena. The full-wave analysis reveals the existence of peaks in the dispersion curve of the coplanar stripline. These are interpreted

D. S. Phatak; A. P. Defonzo

1990-01-01

98

Sunward propagation characteristics of Pc5 ULF waves at dayside magnetosphere  

NASA Astrophysics Data System (ADS)

The waveforms power spectra and polarization characteristics of Pc5 ULF waves observed in the ACE satellite and the GEOS12 satellite at synchronous orbit at dayside during a geomagnetic storm on November 9 2004 show the good correlation oscillation spectral peaks simultaneously and the similar polarization ellipses respectively In CANOPUS MACCS and GREENLAND magnetometers chain the Pc5 waves propagate toward sun and propagate from higher latitude region to lower latitude The polarization and propagation characteristics of the Pc5 waves indicate that the shear Alfven waves and the compression waves are coupled together simultaneously

Du, A.; Xu, W.

99

An Investigation of the Effects of Vegetation on Radio Signal Propagation Through a Corn Field  

NASA Astrophysics Data System (ADS)

As part on of an ongoing research effort, seven rain gauge platforms are deployed in a 1×1-km corn field, near Ames, Iowa. Each site transmits its data to The University of Iowa via a cellular modem operating at 2.4 GHz, at 15-minunte intervals. To monitor communications quality, the system records the received signal at each site in the field every 15 minutes. Though not collected for this purpose, the signal strength data, gathered between mid May and the end of October 2007 provide an opportunity to investigate how vegetation and water moisture in the atmospheric boundary layer affect radio signal propagation. The signal strength data are quite noisy, yet one can clearly identify a long-term trend where the signal strength decreases as the growing season progresses and the plants progressively obscure the radios' view to the cell towers. At the end of the growing season, as the plants dry out and are finally harvested, the signal strength recovers. One can explain this recovery in terms of the water-content in the plants. This is supported by the measured plant water content at different times and selected locations in the field. Spectral and other analysis of the signal strength data also reveal a subtle, yet clear diurnal variation where the signal strength from all sites in the field reaches a minimum between 1 p.m. and 2 p.m. local time. This may be explained by water vapor in the atmospheric boundary layer, probably driven by plant transpiration. However, the maximum signal strength occurs at night, but at different times for different stations. This is still being investigated.

Hunt, K. P.; Kruger, A.; Cunha, L. K.

2008-12-01

100

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

NASA Astrophysics Data System (ADS)

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 ? 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 sferics at least in some seasons providing a noise free environment for observing rare and new phenomena requiring better SNR to detect such changes, The VLF signals from the active seismic zones or other electro-geological sources would require high sensitivities of the system and suitable network of transmitting and receiv-ing stations designed for targeted data and applications. Some new results over Indian and other regions show evidences of earthquake related seismo-geological VLF emissions with the potential of being used as a prognostic tool, change in ozone and ion production in the night time middle atmosphere due to transit of stellar x-ray/? ray sources. Results obtained on whistlers and related studies from a number of Indian stations covering geomagnetic latitude range between 13-24 N will be mentioned and reviewed in the background of theoretical understanding of the lightning return stroke signal elements, VLF propagation through cold plasma, ionospheric wave guide mode, electron precipitation due to cyclotron resonance and production of atomic oxygen O (3 P) and ionisation in the mesosphere due to solar/stellar UV/X/?rays. Use of future VLF techniques in terms of improving ground based observations, critical analysis of available satellite data in the context and real time moni-toring/modelling of earth's geosphere and space weather conditions will be considered for a possible programme of a developing country.

Chakravarty, Subhas

101

RADIO BURSTS WITH EXTRAGALACTIC SPECTRAL CHARACTERISTICS SHOW TERRESTRIAL ORIGINS  

SciTech Connect

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

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

2011-01-20

102

Radio Bursts with Extragalactic Spectral Characteristics Show Terrestrial Origins  

E-print Network

Three years ago, the report of a solitary radio burst was thought to be the first discovery of a rare, impulsive event of unknown extragalactic origin (Lorimer et al. 2007). The extragalactic interpretation was based on the swept-frequency nature of the event, which followed the dispersive delay expected from an extragalactic pulse. We report here on the detection of 16 pulses, the bulk of which exhibit a frequency sweep with a shape and magnitude resembling the Lorimer Burst. These new events were detected in a sidelobe of the Parkes Telescope and are of clearly terrestrial origin, with properties unlike any known sources of terrestrial broad-band radio emission. The new detections cast doubt on the extragalactic interpretation of the original burst, and call for further sophistication in radio-pulse survey techniques to identify the origin of the anomalous terrestrial signals and definitively distinguish future extragalactic pulse detections from local signals. The ambiguous origin of these seemingly disper...

Burke-Spolaor, Sarah; Ekers, Ronald; Macquart, Jean-Pierre; Crawford, Fronefield

2010-01-01

103

Spectral characteristic evolution: a new algorithm for gravitational wave propagation  

NASA Astrophysics Data System (ADS)

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

Handmer, Casey J.; Szilágyi, Béla

2015-01-01

104

Experimental simulation of beam propagation over long path lengths using radio-frequency and magnetic traps  

NASA Astrophysics Data System (ADS)

An overview is given of the novel beam-dynamics experiments based on compact non-neutral plasma traps at Hiroshima University. We have designed and constructed two different classes of trap systems, one of which uses a radio-frequency electric field (Paul trap) and the other uses an axial magnetic field (Penning trap) for transverse plasma confinement. These systems are called "S-POD" (Simulator for Particle Orbit Dynamics). The S-POD systems can approximately reproduce the collective motion of a charged-particle beam propagating through long alternating-gradient (AG) quadrupole focusing channels using the Paul trap and long continuous focusing channels using the Penning trap. This allows us to study various beam-dynamics issues in compact and inexpensive experiments without relying on large-scale accelerators. So far, the linear Paul traps have been applied for the study of resonance-related issues including coherent-resonance-induced stop bands and their dependence on AG lattice structures, resonance crossing in fixed-field AG accelerators, ultralow-emittance beam stability, etc. The Penning trap with multi-ring electrodes has been employed primarily for the study of beam halo formation driven by initial distribution perturbations. In this paper, we briefly overview the S-POD systems, and then summarize recent experimental results on resonance effects and halo formation.

Okamoto, H.; Endo, M.; Fukushima, K.; Higaki, H.; Ito, K.; Moriya, K.; Yamaguchi, S.; Lund, S. M.

2014-01-01

105

Authentication of Radio Frequency Identification Devices Using Electronic Characteristics  

ERIC Educational Resources Information Center

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…

Chinnappa Gounder Periaswamy, Senthilkumar

2010-01-01

106

Spectral Characteristic Evolution: A New Algorithm for Gravitational Wave Propagation  

E-print Network

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

Casey J. Handmer; Béla Szilágyi

2014-09-24

107

Scalable parallel simulations of wireless networks with WiPPET: Modeling of radio propagation, mobility and protocols  

Microsoft Academic Search

We review the design, selected applications and parallelperformance of WiPPET, a general parallel simulationtestbed for various types of wireless networks. WiPPEThas been written in TeD\\/C++, a new object-oriented modelingframework that isolates network modeling from theunderlying parallel discrete event simulator. We describethe techniques for modeling radio propagation (long andshort-scale fading and interference) and protocols thatpromote scalability of parallel simulations at session

Owen Kelly; Jie Lai; Narayan B. Mandayam; Andrew T. Ogielski; Jignesh Panchal; Roy D. Yates

2000-01-01

108

FURTHER STUDY OF RAINFALL EFFECT ON VHF FORESTED RADIO-WAVE PROPAGATION WITH FOUR-LAYERED MODEL  

Microsoft Academic Search

In this paper, rainfall efiect on the VHF radio-wave propagation in a tropical forest is further studied in details. Theoretical study and experimental investigations are performed with the help of a four-layered model for forested environment. It is found that the lateral wave traveling along the air-canopy interface, the direct waves, and the ground re?ected waves are the main modes

Yu Song Meng; Yee Hui Lee; Boon Chong Ng

2009-01-01

109

Down the Block and Around the Corner The Impact of Radio Propagation on Inter-vehicle Wireless Communication  

Microsoft Academic Search

Vehicular networks are emerging as a new distributed system environment with myriad possible applications. Most studies on vehicular networks are carried out via simulation, given the logistical and economical problems with large- scale deployments. This paper investigates the impact of realistic radio propagation settings on the evaluation of VANET-based systems. Using a set of instrumented cars, we collected IEEE 802.11b

John S. Otto; Fabián E. Bustamante; Randall A. Berry

2009-01-01

110

Temporal and spatial characteristics of intracerebral seizure propagation: predictive value in surgery for temporal lobe epilepsy.  

PubMed

We examined the prognostic value of spatial and temporal characteristics of intracerebral propagation of seizures during temporal lobe epilepsy (TLE) surgery. Seven TLE patients resistant to standard anterotemporal lobectomy who had no known causes of resistance [e.g., extratemporal (ET), lesions, multifocal epilepsy] were matched with 7 seizure-free patients and 7 others who were almost seizure-free after operation. Intracerebral ictal propagation pathways were not different in the three groups. Propagation was multidirectional, most frequently to the frontal lobes and sometimes to the contralateral temporal lobe (CTL). ET propagation delays were significantly shorter in resistant patients than in markedly improved patients. The resistant group also had more frequent propagation delays < 1.0 s, but propagation times > 1.0 s were equally likely in all groups. The extent of ET propagation and frequency of focal onsets were not different among the groups. Results suggest that very short propagation times predict reduced efficacy of operation, and that long propagation times are not related to surgical success. PMID:7925153

Adam, C; Saint-Hilaire, J M; Richer, F

1994-01-01

111

Formation of zebra patterns of solar microwave bursts as a result of propagation of radio waves through the inhomogeneous corona  

NASA Astrophysics Data System (ADS)

The geoefficiency of solar bursts is diagnosed using the dynamic radio emission spectrum. At certain time intervals, the spectrum exhibits nearly parallel narrow-band emission strips termed the zebra pattern. Although there are many hypotheses of its origin, all of them do not take into account changes in the signal parameters upon signal propagation through the solar corona. Our analysis shows that the propagation effects form a dynamic spectrum that contains a zebra pattern. The properties of the modeled spectrum are shown to coincide with the basic properties of the observed spectrum. It is clarified that the spike structure of strips is a natural consequence of the interference of radio waves, and the occurrence of this structure is considered to be evidence in favor of the interference nature of the zebra pattern formation. Consequently, the zebra pattern can be formed not in the radiation source itself, but rather can arise as a result of propagation of radio waves through an inhomogeneous refracting medium of the solar corona.

Yurovsky, Yu. F.

2008-06-01

112

Characteristics of Radio-Frequency Circuits Utilizing Ferroelectric Capacitors  

NASA Technical Reports Server (NTRS)

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.

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

2011-01-01

113

Evaluation of the multipath characteristics of the impulse radio channel  

Microsoft Academic Search

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

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

1998-01-01

114

Fundamental analysis on throughput characteristics of orthogonal frequency division multiple access (OFDMA) in multipath propagation environments  

Microsoft Academic Search

This paper describes an image of radio access method: OFDMA, which is based on OFDM modulation realizing reliable data transmission under frequency selective fading, and analyzes its transmission characteristics. In this method, the whole frequency band is shared with all users and a given number of subcarriers with higher order in CNR are selected by each user. Then the adaptive

Jianyu Fu; Yoshio Karasawa

2002-01-01

115

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

116

Radio polarization characteristics of two RS CVn binaries  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

117

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

NASA Astrophysics Data System (ADS)

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

Reid, Hamish; Kontar, Eduard; Vilmer, Nicole

2012-07-01

118

Predictions of HF system performance for propagation through disturbed ionospheres measured using low-Earth-orbit satellite radio beacon tomography  

NASA Astrophysics Data System (ADS)

CERTO radio beacon on the C/NOFS satellite sends VHF/UHF radio signals at 150 and 400 MHz to provide measurements of integrated electron density or Total Electron Content (TEC) by an east-west chain of ground receivers in Peru. Computerized Ionospheric Tomography (CIT) is used to convert the TEC data into two-dimensional images of electron densities with maximum 5 × 5 km resolution in Longitude-Altitude space. These images are updated every 95 min as the C/NOFS satellite passes over the receiver network in its low-latitude orbit with an inclination of 12°. The 2-D, high-resolution images of the ionosphere are used to predict the impact of equatorial plasma structures on HF propagation of radar and radio signals. Electron density measurements from the NRL radio tomography chain across Peru are used for simulations of the performance by HF one-way links. HF rays from transmitter to receiver are traced through the electron density images produced by radio beacon tomography. Eight separate paths are found between a transmitter and ground receiver separated by 2000 km. A total of 36 backscatter echoes are found with unique group delay, Doppler frequency shift, phase delay, and echo amplitude. This multipath effect explains the range and Doppler spreading of observations for HF monostatic radar propagation through F layer irregularities. This type of analysis is useful for prediction and interpretation of range and Doppler observations from HF systems including over-the-horizon and SuperDARN radars, HF Geolocation Arrays, and HF communications networks.

Bernhardt, Paul A.; Hei, Matthew A.; Siefring, Carl L.; Wilkens, Matthew R.

2014-07-01

119

The high-frequency characteristics of solar radio bursts  

NASA Technical Reports Server (NTRS)

The millimeter, microwave, and soft X-ray emission from a number of solar flares is compared in order to determine the properties of the HF radio emission of flares. The millimeter observations use a sensitive interferometer at 86 GHz which offers much better sensitivity and spatial resolution than most previous high-frequency observations. The 86-GHz emission onset appears often to be delayed with respect to the microwave onset. Even in large flares the millimeter-wavelength emission can arise in sources of only a few arc sec dimension. The millimeter emission in the impulsive phase does not correlate with the soft X-ray emission, and thus is unlikely to contain any significant thermal bremsstrahlung component. The electron energy distributions implied by the millimeter observations are much flatter (spectral indices of 2.5 to 3.6) than is usual for microwave or hard X-ray observations.

Lim, J.; White, S. M.; Kundu, M. R.; Gary, D. E.

1992-01-01

120

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

Microsoft Academic Search

Deep-space missions and radio navigation satellite operations place high requirements upon the precision of range and Doppler frequency measurements and may be sensitive to even small increases in radio noise. For paths to geostationary satellites and beyond, the excess range delay due to the ionosphere and plasmasphere is proportional to the total electron content along the path and inversely proportional

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

1982-01-01

121

The winter anomaly as seen in the propagation of low frequency 40 kHz radio waves  

NASA Astrophysics Data System (ADS)

An analysis of propagation data for LF 40 kHz radio waves shows that the field strength of the sky wave is enhanced during day-time on winter anomaly days (WAD), in striking contrast to the severe attenuation of HF radio waves. This peculiar enhancement of the field strength may be ascribed to an increase in the reflection coefficient. The analysis also demonstrates that the reflection height is lower on WAD, which seems to be associated with enhancements of ionization in the D-region. Moreover, it was found that WAD are characterized by an earlier occurrence in the morning and a delayed occurrence in the evening of pronounced interference maxima and minima, respectively.

Ishimine, T.; Echizenya, Y.

1986-12-01

122

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

NASA Technical Reports Server (NTRS)

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.

Asmar, Sami

1997-01-01

123

Propagation characteristics of the fundamental symmetric Lamb wave in thin aluminum nitride membranes with infinite gratings  

NASA Astrophysics Data System (ADS)

A theoretical approach for the analysis of Lamb waves in grating configurations based on the Floquet-Bloch theorem is developed. Subsequently, it is applied for the prediction of the propagation characteristics of the fundamental symmetric Lamb wave (S0) propagating in thin c-oriented aluminum nitride (AlN) membranes with different types of aluminum grating configurations. The calculations indicate the existence of a frequency stop band exhibiting a complex behavior. The proposed analysis is to be used for the design and optimization of high velocity thin-film Lamb wave resonators. It can easily be adapted for the analysis of arbitrary Lamb waves in periodic gratings.

Yantchev, Ventsislav M.; Katardjiev, Ilia V.

2005-10-01

124

Propagation characteristics considering modulation and type of wavefront in free-space laser communications  

NASA Astrophysics Data System (ADS)

Conventional circuit designs have considered only visibility distance and transmission power. However, these are part of circuit design variables. There are a variety of other variables such as modulation method, carrier wave length, type of wavefront. Communication circuits should be designed appropriately depending on the installation environment. This study has performed an evaluation of the propagation characteristics of combinations of each modulation method and carrier waves, and considered indexes for communication circuit designs that suit the installation environment. As a result, the result has been obtained that modulation method needs to be selected depending on the CNR, and the wave length and wavefront of carrier waves depending on the propagation distance.

Sakamoto, Maiko; Ogawa, Kayo

2013-05-01

125

RAKE reception evaluation for microwave mobile propagation using characteristic function method  

Microsoft Academic Search

Delay profiles measured in metropolitan Tokyo are used to evaluate the improvement that RAKE reception has on radio transmission performance. Frequencies of 3.35, 8.45 and 15.75 GHz, and a spread rate of 50 Mchip\\/s were used for the estimation. A novel stochastic method based on the characteristic function method is introduced to estimate the transmission performance from only amplitudes of

Satoshi Takahashi; Koichi Takahashi; Hironari Masui; Kouzou Kage; Takehiko Kobayashi

1999-01-01

126

Enhancement of electromagnetic propagation through complex media for Radio Frequency Identification  

E-print Network

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

Marti, Uttara P

2005-01-01

127

Estimating channel fading statistics based on radio wave propagation predicted with deterministic MRFDPF method  

Microsoft Academic Search

The MR-FDPF (Multi-Resolution Frequency-Domain Partial Flow) method has proved to be an efficient tool for the indoor radio coverage prediction (1). In this paper, a new approach is proposed allowing extracting the fading statistics for indoor radio channels based on the electric field strength predicted with the MR-FDPF method. The performance of the proposed approach is verified both by simulations

Meiling Luo; Dmitry Umansky; Guillaume Villemaud; Marc Lafort; Jean-Marie Gorce

2011-01-01

128

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

PubMed

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

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

2014-01-01

129

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

PubMed Central

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

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

2014-01-01

130

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

PubMed Central

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.

?en, Alper; Gümü?ay, M. Ümit; Kavas, Aktül; Bulucu, Umut

2008-01-01

131

SAW propagation characteristics and fabrication technology of piezoelectric thin film\\/diamond structure  

Microsoft Academic Search

The authors report a theoretical analysis of the surface-acoustic wave (SAW) propagation characteristics of ZnO\\/diamond and AlN\\/diamond structures. The analysis shows about 12000 m\\/s and a large electromechanical coupling coefficient K2 of 0.03 for AlN thin film. The numerical analysis for the ZnO\\/diamond structure shows that there exists a coupling between the Rayleigh wave and the Sezawa wave at H\\/?=0.2

K. Yamanouchi; N. Sakurai; T. Satoh

1989-01-01

132

Effects of microstructure on the short fatigue crack initiation and propagation characteristics of biomedical ?\\/? titanium alloys  

Microsoft Academic Search

This article presents the results of a study of the effects of microstructure on the fatigue strength and the short fatigue\\u000a crack initiation and propagation characteristics of a biomedical ?\\/? titanium alloy, Ti-6Al-7Nb. The results are compared to those obtained from a Ti-6Al-4V extra-low interstitial (ELI) alloy.\\u000a Fatigue crack initiation occurs mainly at primary ? grain boundaries in an equiaxed

Toshikazu Akahori; Mitsuo Niinomi; Kei-Ichi Fukunaga; Ikuhiro Inagaki

2000-01-01

133

Effects of the power atmosphere on radio propagation at frequencies above 1 GHz; Proceedings of the Symposium, Lennoxville, Quebec, Canada, May 26-30, 1980  

NASA Astrophysics Data System (ADS)

Scattering from hydrometeors, prediction of attenuation due to rainfall on terrestrial links, and clear-air propagation on line-of-sight radio paths are the topics that are discussed. Particular consideration is given to analytical models for cross polarization on earth-space radio paths for frequency range distribution, application of synthetic storm data to evaluate simpler techniques for the prediction of rain attenuation statistics, and low elevation angle measurements of the ATS-6 beacons at 4 and 30 GHz.

1980-12-01

134

Non-detection at Venus of High-Frequency Radio Signals Characteristic of Terrestrial Lightning  

NASA Technical Reports Server (NTRS)

The detection of impulsive low-frequency (10 to 80 kHz) radio signals, and separate very-low-frequency (approx. 100 Hz) radio 'whistler' signals provided the first evidence for lightning in the atmosphere of Venus. Later, a small number of impulsive high- frequency (100 kHz to 5.6 MHz) radio signals, possibly due to lightning, were also detected. The existence of lightning at Venus has, however, remained controversial. Here we report the results of a search for high-frequency (0.125 to 16 MHz) radio signals during two close fly-bys of Venus by the Cassini spacecraft. Such signals are characteristic of terrestrial lightning, and are commonly heard on AM (amplitude-modulated) radios during thunderstorms. Although the instrument easily detected signals from terrestrial lightning during a later fly-by of Earth (at a global flash rate estimated to be 70/s, which is consistent with the rate expected for terrestrial lightning), no similar signals were detected from Venus. If lightning exists in the venusian atmosphere, it is either extremely rare, or very different from terrestrial lightning.

Gurnett, D. A.; Zarka, P.; Manning, R.; Kurth, W. S.; Hospodarsky, G. B.; Averkamp, T. F.; Kaiser, M. L.; Farrell, W. M.

2001-01-01

135

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

NASA Astrophysics Data System (ADS)

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

Thorvaldsen, Per; Henne, Ingvar

2014-07-01

136

Effect of space diversity technique in UHF band radio indoor propagation  

Microsoft Academic Search

In order to clarify the receiving condition in the whole room, in this paper, the received level contour map is created based on the measured data of the UHF band radio wave in the indoor environment. Moreover, this paper investigates the effects of applying the space diversity technique that have been well known to be effective techniques to improve the

Masahiro NISHI; A. Yabuki; T. Yoshida

2003-01-01

137

Measurements of radio propagation in rock salt for the detection of high-energy neutrinos  

Microsoft Academic Search

We present measurements of the transmission of radio\\/microwave pulses through salt in the Cote Blanche salt mine operated by the North American Salt Company in St. Mary Parish, Louisiana. These results are from data taken in the southwestern region of the 1500ft (457m) deep level of the mine on our third and most recent visit to the mine. We transmitted

Amy Connolly; Abigail Goodhue; Christian Miki; Ryan Nichol; David Saltzberg

2009-01-01

138

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

ERIC Educational Resources Information Center

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…

Mills, Allan

2010-01-01

139

Microwave indoor radio propagation measurements and modeling at 5 GHz for future wireless LAN systems  

Microsoft Academic Search

Wide-band frequency domain measurement and modeling of indoor radio channels at 5 GHz, for future HIPERLAN system are presented. Vector network analyzer is used to measure the frequency response of the channel. Impulse response profiles are obtained by using inverse Fourier transform. Empirical values of the RMS delay spread and number of multipath values are tested for normal distribution using

S. P. T. Kumar; B. Farhang-Boroiijeny; S. Uysal; C. S. Ng

1999-01-01

140

Vertical and lateral propagation characteristics of intraseasonal oscillation from the tropical lower troposphere to upper mesosphere  

NASA Astrophysics Data System (ADS)

Using a mesosphere-stratosphere-troposphere (MST) radar and a Rayleigh lidar collocated at the Indian tropical station, Gadanki (13.5°N, 79.2°E), European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis data and the horizontal wind velocities measured by the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED Doppler Interferometer (TIDI) instrument onboard the TIMED satellite, the present study makes a report on the lateral and vertical propagation characteristics of an intraseasonal oscillation (ISO, 20-40 day period band), propagating from the lower troposphere to the upper mesosphere region during the winter (November, December, January, and February) months of the years 2004-2005. It is found that the ISO had its origin in the tropical lower troposphere and propagated laterally and vertically to the upper mesosphere through the subtropical latitudes by partial refraction and reflection processes about the subtropical westerly jet. Corresponding enhancements in the wavelet spectrum of outgoing long-wave-radiation (OLR, NOAA interpolated) indicate that convective forces in the lower troposphere are one of the main sources for the generation of the ISO. From the phase of the ISO in the horizontal winds, as observed by the MST radar, it is found that the ISO propagated upward from the lower troposphere up to near the tropopause, where it got sharply attenuated. From the ECMWF data, it is observed that the ISO was refracted to the subtropical latitudes, through the tropical tropopause, from where it got radiated upward into the stratosphere. The phase propagation of the filtered winds shows that the ISO arched back toward the tropical latitudes and propagated to the mesospheric region.

Niranjankumar, K.; Ramkumar, T. K.; Krishnaiah, M.

2011-11-01

141

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

SciTech Connect

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

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

2014-03-15

142

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

143

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

PubMed

This paper studies the propagation characteristics related to higher-order moments of decentered annular beams through non-Kolmogorov turbulence. The analytical expressions for the mean-squared beam width w, the skewness parameter A, and the kurtosis parameter K are derived. The analytical expression for the non-Kolmogorov turbulence parameter T' is also derived, and the differences between two non-Kolmogorov turbulence parameters T' and T are examined. It is shown that K depends on both T and T', but w and A only depend on T. K decreases monotonically as the spectral power law exponent ? increases, but there exist a maximum of w and a minimum of A when ?=3.112. When propagation distance z is long enough, A reaches zero, i.e., the intensity distribution is perfectly symmetric about the centroid position axis. In free space, both A>0 and A<0 may appear on propagation. However, it is always A>0 or A<0 on propagation when turbulence is not weak. On the other hand, in turbulence, the maximum of K increases as the decentered parameter increases and the obscure ratio decreases. In particular, when z is long enough, the beam spot is elliptical in free space, but it becomes circular in turbulence. PMID:24561953

Li, Xiaoqing; Ji, Xiaoling

2014-01-01

144

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

NASA Astrophysics Data System (ADS)

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.

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

145

Effect of local inhomogeneity of the ionosphere on the propagation of ULF radio waves  

Microsoft Academic Search

The Stratton-Chu integral equation is used to solve the electrodynamic problem concerning the propagation of ULF waves in an inhomogeneous spherical earth-ionosphere cavity. The effect of the local inhomogeneity of the ionosphere is taken into account in the framework of the Born approximation of perturbation theory. An analysis is made of perturbation variations of the vertical electric component of the

A. P. Nikolaenko

1984-01-01

146

Internal Microwave Propagation and Distortion Characteristics of Travelling-Wave Amplifiers Studied by Electro-Optic Sampling  

Microsoft Academic Search

The internal signal propagation and saturation characteristics of two monolithic microwave travelling-wave amplifiers (TWA) are measured by electro-optic sampling. Gate and drainline responses are compared with theory and simulation, leading to revisions in the FET models. Drain voltage frequency dependence and harmonic current propagation together lead to more complex saturation behavior than is discussed in the literature.

M. J. W. Rodwell; M. Riaziat; K. J. Weingarten; D. M. Bloom

1986-01-01

147

Design considerations and propagation characteristics of channel Bragg-plasmon-coupled-waveguides  

NASA Astrophysics Data System (ADS)

We present a detailed design principle and propagation characteristics of channel Bragg-plasmon-coupled-waveguide. We have found that there is a significant change in the slope of the phase-velocity dispersion curve leading to an ultranarrow interaction bandwidth (˜765 pm) and group-velocity dispersion (GVD˜±4.5×104 ps/km-nm) that is an appreciably large GVD using a waveguide mode-coupling geometry in any region of the optical spectrum. The effect of waveguide parameters such as channel width, number of bilayers, etc. on a mode-coupling mechanism is also studied with significant emphasis on the propagation loss suffered by the supermodes of the structure. The proposed waveguide exhibits sensitivity as high as 7500 nm/RIU, thereby opening a route for biochemical sensing.

Srivastava, Triranjita; Das, Ritwick; Jha, Rajan

2010-11-01

148

Experimental study on pulse propagation characteristics at normal dispersion region in dispersion flatted fibers  

NASA Astrophysics Data System (ADS)

Pulse propagation characteristics at normal-dispersion region in dispersion-flatted-fibers are experimentally investigated by employing the second-harmonic generation frequency-resolved optical gating (SHG-FROG) method. It is found that the experimental results are consistent with the theoretical prediction. The initial optical pulse with negative chirp is compressed for nonlinear effect in the normal-dispersion fiber, and it evolves into near Gaussian pulse. Temporal width of the optical pulse decreases with the increase of the input power and propagation distance. The output pulse width for small dispersion is less than that for great dispersion at the same input power. The spectrum of the output pulse is still symmetrical about the central wavelength, and is broadened with the increase of input power. The spectral width of the output pulse is much wider than the input spectral width.

Zheng, Hongjun; Liu, Shanliang; Wu, Chongqing; Yu, Huishan; Li, Xin; Wang, Weitao; Tian, Zhen

2012-06-01

149

The effect of solar-flare X-rays on radio-wave propagation  

NASA Astrophysics Data System (ADS)

Model calculations of variations of ionospheric electron density profiles in relation to variations of the solar X-ray spectrum are analyzed. It is shown that the season, the time of day, the geographic latitude, and the solar-flare spectrum all have an effect on the type of field-strength variations of long-wave radio signals, determined by variations of electron density profile. The strength of each of these factors is determined by the magnitude of the difference between the actual vertical profile of electron density and the summer midday level.

Turkeeva, B. A.

150

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

SciTech Connect

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

Wang Huabo; Sun Wenting; Li Heping; Bao Chengyu; Gao Xing; Luo Huiying [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); School of Public Health and Family Medicine, Capital University of Medical Sciences, Beijing 100069 (China); Beijing Center for Diseases Control and Prevention, Beijing 100013 (China)

2006-10-16

151

Measurements of radio propagation in rock salt for the detection of high-energy neutrinos  

E-print Network

We present measurements of the transmission of radio/microwave pulses through salt in the Cote Blanche salt mine operated by the North American Salt Company in St. Mary Parish, Louisiana. These results are from data taken in the southwestern region of the 1500 ft. (457 m) deep level of the mine on our third and most recent visit to the mine. We transmitted and received a fast, high-power, broadband pulse from within three vertical boreholes that were drilled to depths of 100 ft. (30 m) and 200 ft. below the 1500 ft. level using three different pairs of dipole antennas whose bandwidths span 125 to 900 MHz. By measuring the relative strength of the received pulses between boreholes with separations of 50 m and 169 m, we deduce the attenuation of the signal attributed to the salt medium. We fit the frequency dependence of the attenuation to a power law and find the best fit field attenuation lengths to be 93 \\pm 7 m at 150 MHz, 63 \\pm 3 m at 300 MHz, and 36 \\pm 2 m at 800 MHz. This is the most precise measurement of radio attenuation in a natural salt formation to date. We assess the implications of this measurement for a future neutrino detector in salt.

Amy Connolly; Abigail Goodhue; Christian Miki; Ryan Nichol; David Saltzberg

2008-06-12

152

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

PubMed

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

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

2014-01-01

153

Measurements of radio propagation in rock salt for the detection of high-energy neutrinos  

E-print Network

We present measurements of the transmission of radio/microwave pulses through salt in the Cote Blanche salt mine operated by the North American Salt Company in St. Mary Parish, Louisiana. These results are from data taken in the southwestern region of the 1500 ft. (457 m) deep level of the mine on our third and most recent visit to the mine. We transmitted and received a fast, high-power, broadband pulse from within three vertical boreholes that were drilled to depths of 100 ft. (30 m) and 200 ft. below the 1500 ft. level using three different pairs of dipole antennas whose bandwidths span 125 to 900 MHz. By measuring the relative strength of the received pulses between boreholes with separations of 50 m and 169 m, we deduce the attenuation of the signal attributed to the salt medium. We fit the frequency dependence of the attenuation to a power law and find the best fit field attenuation lengths to be 93 \\pm 7 m at 150 MHz, 63 \\pm 3 m at 300 MHz, and 36 \\pm 2 m at 800 MHz. This is the most precise measuremen...

Connolly, Amy; Miki, Christian; Nichol, Ryan; Saltzberg, David

2008-01-01

154

Propagation characteristics of Pi 2 magnetic pulsations observed at ground high latitudes  

NASA Astrophysics Data System (ADS)

In order to investigate the characteristics of Pi 2 propagation observed in the high-latitude region, ground magnetometer data obtained at high-latitude CPMN stations were analyzed. The power of magnetic perturbation, (?H)2 + (?D)2, were calculated for Pi 2 events observed at four stations from 11 February through 20 April 1996 and for Pi 2s observed at two stations from 1 January through 27 March 1997. The times when the power of Pi 2s reached the maximum and the maximum amplitudes were compared among stations. The results are as follows. Pi 2s observed at Kotel'nyy (KTN: MLAT = 69.94°, MLON = 201.02°) reached the maximum amplitude earlier than those at lower-latitude station Tixie (TIK: MLAT = 65.67°, MLON = 196.88°), though the amplitudes were smaller at KTN than at TIK on average. The time lag from KTN to TIK has two peaks in its distribution; the primary and the secondary peaks are located around 10 s and 35 s, respectively. The mean value of the whole distribution of the time lag from KTN to TIK is about 20 s. Ultra Violet Image (UVI) data obtained by the Polar satellite was available during the second period; the UVI data indicate that it was when the auroral oval was located equatorward to KTN that the Pi 2 amplitude tended to reach the maximum earlier at KTN than at TIK. This observational result is important because Pi 2 was observed earlier in the polar cap region rather than in the auroral region. That is to say, Pi 2 was observed earlier in the polar cap region, which is not directly connected with the source region of Pi 2 via the magnetic field line. Longitudinal characteristics of Pi 2 propagation were derived by using data from longitudinally separated stations TIK, Chokurdakh (CHD: MLAT = 64.67°, MLON = 212.12°) and Kotzebue (KOT: MLAT = 64.52°, MLON = 249.72°). The result indicates the existence of the longitudinal center of Pi 2 propagation. The average magnetic local time of the center is estimated to have been ˜22.5 MLT; eastward (westward) of the center, Pi 2 exhibited an eastward (westward) propagation. The temporal and spatial developments of the Pi 2 propagation along the auroral zone were derived in an empirical manner. That is, the MLT (set to zero at the propagation center) dependence of the maximum amplitude time and the maximum amplitude itself of Pi 2 were derived in an empirical manner. As a result it is concluded that in the premidnight sector (i.e., around 22.5 MLT), KTN is the most probable location that observes the maximum amplitude of Pi 2 earliest among the CPMN stations located along 210° magnetic meridian. Our results show that the low-latitude Pi 2, which has often been used as a time indicator of substorm onset, is often delayed from the Pi 2 observed in the premidnight polar cap region. The present results imply that the consideration of high-latitude Pi 2s in addition to low-latitude Pi 2s can provide a new insight into the substorm onset timing. Thus it is necessary to consider the global features, especially Pi 2s observed in higher-latitude region, for studying substorm onset timing issues.

Uozumi, Teiji; Yumoto, K.; Kawano, H.; Yoshikawa, A.; Ohtani, S.; Olson, J. V.; Akasofu, S.-I.; Solovyev, S. I.; Vershinin, E. F.; Liou, K.; Meng, C.-I.

2004-08-01

155

Characteristics of Frontal Waves Propagating Along the Kuroshio Near the Separation Point From the Western Boundary  

NASA Astrophysics Data System (ADS)

Direct current measurements were conducted from April 2003 to March 2004 to investigate the characteristics of frontal waves propagating along the Kuroshio near the separation point from the western boundary. During the study period, the main stream of the Kuroshio flowed northeastward in the upper layer slightly offshore from the array of four mooring systems, while a southwestward current was observed in the intermediate layer on the coastal side of the array. Downstream-propagating waves detected as significant extended empirical orthogonal functions (EEOFs) are predominant over velocity fluctuations of periods shorter than 50~days, explaining 67% of the total variance. The five apparent wave groups have periods of 7--18~days, wavelengths of 220--380~km, and phase velocities of 22--30~cm~s-1, respectively, similar to the values reported in previous studies of upstream regions. Although the phase velocity at a given wavelength in the Kuroshio is lower than that in the Gulf Stream, the dispersion tendency (i.e., that phase velocity increases with decreasing period and wavelength) is the same for both currents. The relatively low phase velocity of the Kuroshio is considered to reflect its relatively low background velocity. Data regarding growth rate, vertical phase lags, and energetics suggest that kinetic energy in this region is transferred from small to large scales mainly via eddies resulting from baroclinic instability, which is possibly related to synoptic-scale path variability and the penetration of areas of high kinetic energy into the Kuroshio Extension.

Itoh, S.; Sugimoto, T.; Yasuda, I.

2008-12-01

156

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

SciTech Connect

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

Romanov, V.I.

1995-09-01

157

Spatiotemporal propagation characteristics based on the exact solutions of the generalized nonlinear Schrödinger equation by intensity moments  

NASA Astrophysics Data System (ADS)

Based on the exact solutions of the (3 + 1)-dimensional ((3 + 1)D) generalized nonlinear Schrödinger equation (GNLSE), we analyze the spatiotemporal propagation characteristics by intensity moments when a laser propagates in an inhomogeneous nonlinear medium. The different order intensity moment can describe the characteristics of a laser, and in the paper, the beam width (BW), the pulse width (PW), the skewness and the kurtosis parameter are calculated. The spatiotemporal propagation stability of the exact solutions is analyzed in detail by the second-order intensity moment. We find that when the diffraction and dispersion coefficients are the identical distributed functions, the BW and PW of the exact solutions are constants or vary periodically during nonlinear propagation. So, the spatiotemporal propagation of the exact solutions is stable. When the diffraction and dispersion coefficients are other coefficients, the BW and PW of the exact solutions vary irregularly due to the effect of a chirp. Thus the spatiotemporal propagation of the exact solutions is unstable. The results are helpful to the extendable investigation of nonlinear propagation and control of a laser pulse.

Deng, Yangbao; Fu, Xiquan; Tan, Chao

2012-06-01

158

A hybrid technique based on combining ray tracing and FDTD methods for site-specific modeling of indoor radio wave propagation  

Microsoft Academic Search

The paper presents a hybrid technique based on combining ray tracing and finite-difference time-domain (FDTD) methods for site-specific modeling of indoor radio wave propagation. Ray tracing is used to analyze the wide area and FDTD is used to study areas close to complex discontinuities where ray-based solutions are not sufficiently accurate. The hybrid technique ensures improved accuracy and practicality in

Ying Wang; Safieddin Safavi-Naeini; Sujeet K. Chaudhuri

2000-01-01

159

Low-frequency radio wave propagation in the earth-ionosphere waveguide disturbed by a large-scale three-dimensional irregularity  

Microsoft Academic Search

In this paper, we develop further the analytical and numerical method of solving three-dimensional problems in the theory\\u000a of radio wave propagation, including three-dimensional local inhomogeneities (ionospheric disturbances or Earth’s surface\\u000a irregularities). To model the Earth-ionosphere waveguide, we use the surface impedance concept, by which the irregularity\\u000a extending beyond one waveguide wall has an arbitrary smooth shape, and its surface

O. V. Soloviev

1998-01-01

160

Ultra-short-wave propagation in the jungle  

Microsoft Academic Search

The predominant characteristic of propagation in the VHF frequency range is the presence of a reflected wave which tends to cancel the direct wave and results in the received field being proportional to the product of the antenna heights, and inversely proportional to the square of the distance; and the radio gain being independent of frequency. For propagation in the

C. Burrows

1966-01-01

161

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

SciTech Connect

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

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

2012-09-15

162

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)

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 energy flare electrons. To be detected by observers at locations distant from the nominal field lines originating in the flaring regions the particles must undergo lateral transport. The continuity of the radio bursts suggests that the cross-field transport may occur in the interplanetary medium.

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

2003-01-01

163

1238 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009 Mode-Based Analysis of Resonant Characteristics  

E-print Network

1238 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 8, 2009 Mode-Based Analysis of Resonant Abstract--This letter proposes a new approach for estimating resonant characteristics of near-field coupled using the addition theorem of spherical modes. Using the proposed method, the splitting of the resonant

Nam, Sangwook

164

Propagation through nonlinear time-dependent bubble clouds and the estimation of bubble populations from measured acoustic characteristics  

Microsoft Academic Search

For several decades the propagation characteristics of acoustic pulses (attenuation and sound speed) have been inverted in attempts to measure the size distributions of gas bubbles in liquids. While this has biomedical and industrial applications, most notably it has been attempted in the ocean for defence and environmental purposes, where the bubbles are predominantly generated by breaking waves. Such inversions

T. G. Leighton; S. D. Meers; P. R. White

2004-01-01

165

Radio-electronic equipment  

NASA Astrophysics Data System (ADS)

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

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

166

Study of Characteristics of the Radio-Frequency Sheath over a Substrate with a Circular Trench  

NASA Astrophysics Data System (ADS)

Since processed substrates usually exhibit nonplanar surface structures in micro-electro-mechanical-systems (MEMS) etching, a two-dimensional (2D) fluid model is developed to simulate the characteristics of the sheath near a conductive substrate with a circular trench, which is placed in an argon discharge powered by a radio-frequency (RF) current source. The model consists of 2D time-dependent fluid equations, the Poisson equation, and a current balance equation that can self-consistently determine the instantaneous voltage on the substrate placed on a powered electrode. The effects of both the aspect ratio (depth/width) and the structure of the trench on the characteristics of the sheath are simulated. The time-averaged potential and electric field in the sheath are calculated and compared for different discharge parameters. The results show that the radial sheath profile is not uniform and always tends to adapt to the contour of the substrate, which is believed to be the moulding effect. Affected by the structure of the substrate surface, the potential and electric field near the inner and outer sidewalls of the trench exhibit obvious non-uniformity, which will inevitably lead to non-uniformity in etching, such as notching. Furthermore, with a fixed amplitude of the RF current source, the potential drops and the sheath thickness decrease with an increase in aspect ratio.

Dai, Zhongling; Hao, Meilan; Wang, Younian

2011-02-01

167

Static current-voltage characteristics for radio-frequency induction discharge  

SciTech Connect

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

Budyansky, A.; Zykov, A. [Kharkov Univ. (Ukraine). Scientific Center of Physical Technologies

1995-12-31

168

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

NASA Astrophysics Data System (ADS)

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

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

169

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

NASA Astrophysics Data System (ADS)

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

Cheng, Guanbing; Bauer, Pascal; Zitoun, Ratiba

2014-08-01

170

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)

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.

Schmitter, E. D.

2014-11-01

171

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

NASA Technical Reports Server (NTRS)

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.

Simons, Rainee N.; Wintucky, Edwin G.

2014-01-01

172

Microwave propagation characteristics depending on base-station antenna height in an urban area  

Microsoft Academic Search

We have conducted propagation experiments assuming the environment of low base station antenna height and, hence, microcells in an urban area and have reported their results. In this report, we report the results of a propagation experiment in the microwave band that is conducted with transmission base station antennas installed at height sufficiently higher or lower than the surrounding building

K. Sakawa; H. Masui; M. Ishii; H. Shimizu; T. Kobayashi

2001-01-01

173

Galileo radio science investigations  

Microsoft Academic Search

The radio science investigations planned for Galileo's 6-year flight to and 2-year orbit of Jupiter use as their instrument the dual-frequency radio system on the spacecraft operating in conjunction with various US and German tracking stations on Earth. The planned radio propagation experiments are based on measurements of absolute and differential propagation time delay, differential phase delay, Doppler shift, signal

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

1992-01-01

174

Philippe Zarka Recherche de transitoires radio associs  

E-print Network

TO GW EVENTS · RADIO PROPAGATION · TRANSIENT RADIO SKY · LOFAR TELESCOPE & OPERATING MODES · LOFAR EARLY · REFERENCES #12;· RADIO COUNTERPARTS TO GW EVENTS · RADIO PROPAGATION · TRANSIENT RADIO SKY · LOFAR TELESCOPEPhilippe Zarka LESIA Recherche de transitoires radio associés à des ondes gravitationnelles avec

Demoulin, Pascal

175

The role of the atmosphere in satellite geodesy, radio astronomy and other applications of trans-atmospheric propagation of radio waves  

Microsoft Academic Search

The influence of the atmosphere on radio waves relevant to technological applications is investigated theoretically, and the associated errors are classified and defined. Range errors are defined as the length of the phase path minus the geometric distance, and range errors are divided into those related to the troposphere and those related to the ionosphere. Ground-path error and group delay

R. Leitinger

1990-01-01

176

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

NASA Astrophysics Data System (ADS)

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

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

1993-01-01

177

New field of application of the IRI modeling - Determination of ionosphere transfer characteristic for radio astronomical signals  

NASA Astrophysics Data System (ADS)

We suggest a new field of application of IRI modeling - determination of ionosphere transfer characteristic (ITC) for radio astronomical signals (RAS). VHF and HF RAS are widely used for observations of the Sun and pulsars. It is necessary to take into account possible distortions of RAS in the Earth ionosphere. However, in contrast to modern navigation systems (GPS, GLONASS, GALILEO), where very accurate reconstruction of ionosphere parameters is a built-in function, in present-day radio astronomy a retrieve of ITC has not been appropriately worked out yet. It collides with increasing requirements to accuracy of the analysis of RAS amplitude profile and to the angular and polarizing resolution of radio telescopes of new generation. We have developed a method and software for calculation of the ionosphere measure of rotation (RM) and the measure of dispersion (DM). We used the ionosphere model IRI-2001, magnetic-field model IGRF-10 and values of ionosphere total electron content as deduced from GPS measurements. The obtained values of the ionosphere DM and RM were recalculated into characteristics of phase delay, Faraday amplitude modulation and polarization changes. We made calculations for different levels of geomagnetic activity and for different angular position of radio sources as well.

Afraimovich, E. L.; Yasukevich, Yu. V.

2009-06-01

178

Near-Earth wave propagation characteristics of electric dipole in presence of vegetation or snow layer  

Microsoft Academic Search

The problem of near-earth wave propagation in the presence of a dielectric layer such as a vegetation or snow covering is considered in this paper by modeling the propagation environment as a homogeneous two-layer medium (air\\/dielectric\\/ground). A number of studies have demonstrated the relevancy of the lateral wave for the case when both the transmitter and receiver are located within

DaHan Liao; Kamal Sarabandi

2005-01-01

179

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

Microsoft Academic Search

Presents characteristics of the specific absorption rate (SAR) distributions calculated by the finite-difference time-domain (FDTD) method using a heterogeneous and realistic head model and a realistic hand-held portable radio model. The difference between the SAR distributions produced by a 1\\/4-wavelength monopole antenna and those produced by a 1\\/2-wavelength dipole antenna is investigated. The dependence of the maximum local SAR on

Soichi Watanabe; H. Taki; Toshio Nojima; Osamu Fujiwara

1996-01-01

180

Frequency characteristics of modification effects of high-power radio waves on the ionospheric F-layer  

Microsoft Academic Search

The paper presents experimental results concerning the effect of artificial ionospheric irregularities on the characteristics of linear-FM signals for vertical and oblique sounding of the ionosphere. The radio-transmitting facility operated at a frequency of 4.8 MHz with a power of 200 MW. The effects observed on the linear-FM ionograms are classified according to the effects of artificial irregularities of different

L. M. Erukhimov; V. A. Ivanov; N. A. Mitiakov; V. P. Uriadov; V. A. Frolov

1987-01-01

181

Characteristics of coronal shock waves and solar type 2 radio bursts  

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

182

Characteristics of coronal shock waves and solar type 2 radio bursts  

NASA Astrophysics Data System (ADS)

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.

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

1995-06-01

183

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

NASA Astrophysics Data System (ADS)

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

Liu, Hong; Chen, Zuoyi

2007-01-01

184

Radiation Characteristics of Photonic Antenna for Optical Wireless Communication using Beam Propagation Method  

Microsoft Academic Search

The optical wireless communication is the only solution to the emerging next generation wireless communication. The photonic antennas play major role in the development of optical wireless communications. This photonic antenna transfers light energy from optical waveguide to free-space with high directionality and act as a matching device between optical source and channel (atmosphere). The analysis of light propagation through

L. R. D. Suresh; S. Sundaravadivelu

2007-01-01

185

ESTABLISHMENT OF BESNOITIA DARLINGI FROM OPOSSUMS (DIDELPHIS VIRGINIANA) IN EXPERIMENTAL INTERMEDIATE AND DEFINITIVE HOSTS, PROPAGATION IN CELL CULTURE, AND DESCRIPTION OF ULTRASTRUCTURAL AND GENETIC CHARACTERISTICS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Besnoitia darlingi from naturally infected opossums (Didelphis virginiana) from Mississippi, USA, was propagated experimentally in mice, cats, and cell culture and was characterised according to ultrastructural, genetic, and life-history characteristics. Cats fed tissue cysts from opossums ...

186

Propagation considerations for the design of an indoor broad-band communications system at EHF  

Microsoft Academic Search

This paper reports the measurement and analysis of wideband propagation data for indoor radio channels at 40 GHz. Propagation characteristics are reported for two open-concept office areas of different sizes in two different buildings. Also, the results of measurements in one building are compared for system configurations in which either an omnidirectional or a narrowbeam antenna is employed at a

Robert J. C. Bultitude; Robert F. Hahn; Robert J. Davies

1998-01-01

187

Diagnostics of magnetic flux tube oscillations on the Sun based on fine-structure characteristics of the radio spectrum  

NASA Astrophysics Data System (ADS)

The possibility of obtaining information about oscillation processes in magnetic flux tubes on the Sun by analyzing the undulating frequency drift of the zebra pattern in the dynamic spectrum of solar radio emission is discussed. It is shown that the oscillatory variation in the frequency of zebra stripes can be associated with fast magnetoacoustic (FMA) oscillations in a flux tube, which lead to oscillations in the magnetic field strength and electron number density. The October 25, 1994 event recorded by the radio spectrograph of the Astrophysical Institute Potsdam is used as an example to demonstrate the possibility of determining the parameters of FMA oscillations and the physical conditions in coronal magnetic loops from the observed zebra-pattern characteristics.

Zlotnik, E. Ya.; Zaitsev, V. V.; Aurass, H.

2011-07-01

188

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

Microsoft Academic Search

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

M. Zimmerman; A. Kirsch

1967-01-01

189

The Physical Reality of Space and Surface Waves in the Radiation Field of Radio Antennas  

Microsoft Academic Search

Evidence is presented which indicates that, notwithstanding the change in sign made by Sommerfeld in his 1926 paper on radio wave propagation, the radiation field of a vertical electric dipole may be separated into space and surface wave components. Sommerfeld's original concepts as to the characteristics of two such waves in radio transmission are largely substantiated. It is shown that

K. A. Norton

1937-01-01

190

Propagation characteristics of finite-width conductor-backed coplanar waveguides with periodic electromagnetic bandgap cells  

Microsoft Academic Search

Wave propagation along the finite-width conductor-backed coplanar waveguide (FW-CBCPW) with periodically loaded one-dimensional electromagnetic bandgap (EBG) cells proposed earlier by the authors is investigated theoretically and experimentally in this paper. The full-wave simulation in conjunction with Floquet's theorem is employed to find the dispersion diagram for characterizing the guided and leaky waves over a wide frequency range. For examining the

Shau-Gang Mao; Ming-Yi Chen

2002-01-01

191

Nearfield aerodynamics and optical propagation characteristics of a large-scale turret model  

NASA Astrophysics Data System (ADS)

Measurements of the unsteady flow field affecting optical propagation quality have been made with both aerodynamic and direct optical instrumentation. Properties affecting degradation of coherent radiation beams propagated from within the turret have been investigated. These properties include both the magnitude and scale sizes of the fluctuating index-of-refraction field present in the turbulent shear layers and separation regions of the turret flow field. Direct optical degradation information was obtained by holographic interferometry and quantified through techniques presented here. Aerodynamic measurements were made with hot-wire anemometry and multiple-port probes. Comparisons between the aerodynamically and optically deduced data are presented. These data can be used directly to estimate trends in expected loss of optical quality of a coherent beam for various flight speeds, altitudes, wavelengths and azimuthal turret angles. More data are now available for estimating the effects of unsteady aerodynamic flow fields on optical propagation quality. Data were obtained for Reynolds numbers near those occurring at full-scale flight conditions over a range of Mach number from 0.55 to 0.75. Investigation results generally agree with those obtained previously on smaller scale models and indicate that severe optical degradation can be present at aft-looking azimuth angles.

Rose, W. C.; Craig, J. E.; Raman, K. R.

1982-02-01

192

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

193

Acoustic propagation and atmosphere characteristics derived from infrasonic waves generated by the Concorde.  

PubMed

Infrasonic signals generated by daily supersonic Concorde flights between North America and Europe have been consistently recorded by an array of microbarographs in France. These signals are used to investigate the effects of atmospheric variability on long-range sound propagation. Statistical analysis of wave parameters shows seasonal and daily variations associated with changes in the wind structure of the atmosphere. The measurements are compared to the predictions obtained by tracing rays through realistic atmospheric models. Theoretical ray paths allow a consistent interpretation of the observed wave parameters. Variations in the reflection level, travel time, azimuth deviation and propagation range are explained by the source and propagation models. The angular deviation of a ray's azimuth direction, due to the seasonal and diurnal fluctuations of the transverse wind component, is found to be approximately 5 degrees from the initial launch direction. One application of the seasonal and diurnal variations of the observed phase parameters is the use of ground measurements to estimate fluctuations in the wind velocity at the reflection heights. The simulations point out that care must be taken when ascribing a phase velocity to a turning height. Ray path simulations which allow the correct computation of reflection heights are essential for accurate phase identifications. PMID:11837968

Le, Pichon Alexis; Garcés, Milton; Blanc, Elisabeth; Barthélémy, Maud; Drob, Doug P

2002-01-01

194

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

E-print Network

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

Sun, Jing

195

Performance of UWB Impulse Radio With Planar Monopoles Over On-Human-Body Propagation Channel for Wireless Body Area Networks  

Microsoft Academic Search

Ultrawideband (UWB) is a promising technology for wireless body area networks (WBANs). This paper studied the impacts of 3.1-10.6 GHz on-human-body UWB channel on the impulse radio WBAN system. A performance evaluation method is presented for the realistic UWB WBAN systems, which observes the waveform distortion along the signal path. The measurement and characterization of the 3.1-10.6 GHz on-human-body UWB

Yue Ping Zhang; Qiang Li

2007-01-01

196

Propagation Characteristics of Surface Acoustic Waves in AlN/128° Y-X LiNbO3 Structures  

NASA Astrophysics Data System (ADS)

In this study, propagation characteristics of surface acoustic waves in a layered piezoelectric structure (AlN/128° Y-X LiNbO3) are investigated. The phase velocity and coupling coefficient of the layered structure with interdigital transducers (IDTs) and/or thin metal films deposited at various interfaces are calculated numerically. The effects of the polarity of 128° Y-X LiNbO3 on SAW characteristics are illustrated. The calculated phase velocity and coupling coefficient of SAWs in the IDT/ZnO/128° Y-X LiNbO3 structure are also demonstrated for comparison. The simulation results obtained in this study can be applied to the design of SAW devices using AlN/128° Y-X LiNbO3 structures.

Ro, Ruyen; Lee, Ruyue; Wu, Sean; Lin, Zhi-Xun; Lee, Maw-Shung

2009-04-01

197

Rupture propagation and seismic energy radiation along fault surfaces of fractal characteristics  

NASA Astrophysics Data System (ADS)

We study rupture propagation in a 2D/3D infinite elastic medium with a slip-weakening friction law and heterogeneous distribution of slip-weakening distance, Dc. Ide and Aochi (2005 JGR) numerically demonstrated statistically self-similar rupture growths in a 3D space using a set of circular patches that obey a power-law size statistics. They showed that the rupture propagation velocity was sub-shear in average, but it could exceed S-wave velocity locally. Moment rate functions of most events had initial phases, but these were useless to predict the final event size. Seismic energy radiation from each model scaled linearly with seismic moment as expected from the self-similarity. We present a simple 2D model of shear crack growth to further investigate the effects of fractal property and Dc scaling. We define the local values of Dc to be proportional to the size of asperities, which is measured on a randomly generated fractal surface in the macroscopic slip direction, and calculate the Dc distribution multiplying a proportionality constant A. The initial, yield, and residual stresses are homogeneous over entire model area except within an initial nucleation area where Dc value is a local minimum. Changing the values of Dc and A, we simulate spontaneous rupture propagation from numerous local minimums. Each rupture is calculated till it stops spontaneously (stopped event) or breaks the entire model space (non-stopping event). We use a boundary integration equation method with a renormalization technique developed by Aochi and Ide (2004). When D = 1, most ruptures naturally stop and the probability of rupture arrest is almost constant at any size. The ratio of non-stopping events increases as A decreases and D increases. At the limit to D = 2, where the topography becomes white noise, it is natural that such high irregularity acts as a spatially uniform Dc and no rupture stops once starts. For these non-stopping events, the final rupture area should be determined by other factor such as stress heterogeneity that is not considered in the present model. For many stopped events, we observe dynamic behavior similar to those visible in our 3D circular patch simulation, such as average sub-shear rupture propagation, local acceleration and deceleration of rupture front, and initial phase in radiated seismograms. The ratio between seismic energy and seismic moment is almost constant for the stopped events except for very small ones.

Ide, S.; Aochi, H.

2005-12-01

198

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

199

Microwave propagation in multi-room buildings for PCS  

Microsoft Academic Search

A key technical issue in providing personal communication services is the reliability of radio interface. Successful implementation of radio interface depends on the knowledge of the propagation characteristics of the service area. This paper reports a novel indoor multi-room slow fading model which used an exponential probability function to explain the dB-per-distance loss caused by shadowing effects of randomly located

Yuqiang Tang; Harold Sobol

1993-01-01

200

Polarization characteristics of VHF radio waves reflected by the E\\/sub s\\/-layer  

Microsoft Academic Search

Interference in VHF-TVs caused by the radio waves reflected from the ionosphere is a very serious problem in the area around Japan. The polarization rotation of the waves reflected by an Es-layer are clarified by the measurement of a VHF television signal. Two types of polarization rotation are observed. In one case, the more common of the two, the polarization

Masaru Ichinose; Syoji Kainuma

1996-01-01

201

Propagation prediction inside a B767 in the 2.4 GHz and 5 GHz radio bands  

Microsoft Academic Search

A signal strength prediction model was developed for a B767-300ER using Wireless Valley's EnterprisePlanner, which is commercial grade software intended for predictions within office buildings. The performance of the model was validated through a comparison with test data measurements taken on the aircraft. It was concluded that the model can accurately predict power propagation throughout the cabin. This model can

G. Hankins; L. Vahala; J. H. Beggs

2005-01-01

202

THE TERMINATOR-TIME METHOD AND 3D PROBLEM OF SUBIONOSPHERIC RADIO WAVE PROPAGATION ACROSS THE SOLAR TERMINATOR  

Microsoft Academic Search

This paper presents a mathematical model, an asymptotic theory and an appropriate numerical algorithm to study, in the scalar approximation, VLF point source field propagation problem within the non-uniform Earth-ionosphere waveguide allowing for 3D local ionosphere inhomogeneity upon a ground of the solar terminator transition. The local ionosphere inhomogeneity, which centre is situated above the model earthquake, is simulated by

O. V. Soloviev; M. Hayakawa; O. A. Molchanov

203

Characteristics of the pulsed emission of the peculiar pulsar B1822-09 at low radio frequencies  

NASA Astrophysics Data System (ADS)

The pulse structure of the pulsar B1822-09 has been studied at 112, 62, and 42 MHz. The observations were conducted in 2010 on the Large Scanning Antenna and the DKR-1000 radio telescope of the Pushchino Radio Astronomy Observatory. The shape of the main pulse and interpulse undergo considerable changes at low radio frequencies. In the main pulse, the precursor disappears and is replaced by a new component that trails 50 ms behind the main component. At 62 MHz, the interpulse acquires a pronounced two-peaked shape. At 62 and 112 MHz, as well as at higher frequencies, the brighter second component of the interpulse follows the main pulse at 185° and has a relative amplitude of about 5%. The main pulse width changes with frequency according to the power law W 0.5 ˜ ? -0.15 in the frequency range 42-4750-MHz. The interpulse width follows this law only in the range 325-4750 MHz; at 112, 102, and 62 MHz, the interpulse is almost a factor of three broader than themain pulse. The parameters of the pulse's scattering on interstellar plasma inhomogeneities and the initial pulse width before it enters the scattering medium have been measured at 62 and 42 MHz. The frequency dependence of the characteristic scale for scattering of the pulses of B1822-09 corresponds to a Kolmogorov spectrum for the electron-density fluctuations in the interstellar medium in the direction toward this pulsar.

Suleymanova, S. A.; Logvinenko, S. V.; Smirnova, T. V.

2012-03-01

204

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

205

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

NASA Astrophysics Data System (ADS)

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

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

206

Propagation characteristics of lightning stepped leaders developing in charge regions and descending out of charge regions  

NASA Astrophysics Data System (ADS)

We conducted lightning observation campaign using VHF broadband digital interferometers (DITFs) in Darwin, Australia. We divided a stepped leader into two parts; the first part is a stepped leader propagating almost horizontally in the charge regions (ICR) of thunderclouds and the last part is a stepped leader descending out of the charge region (OCR). The VHF observation indicates that the channels of the stepped leaders OCR located by the DITFs were clearly broader than the channels of the stepped leaders ICR and dart leaders, indicating that the stepped leaders OCR descended in a heavily branched manner. High speed video camera images of a CG flash support the idea that stepped leaders OCR descend in a heavily branched manner.

Yoshida, Satoru; Akita, Manabu; Morimoto, Takeshi; Ushio, Tomoo; Kawasaki, Zen

2012-03-01

207

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

PubMed

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

Donis, Ruben O

2014-11-12

208

Difference of break-point characteristics due to mobile antenna heights in microwave urban LOS propagation  

Microsoft Academic Search

This paper discusses microwave path-loss characteristics as a function of mobile antenna height in an urban line-of-sight environment. Comparing daytime and midnight measurements, we reveal that the break points shift to the near side because of the existence of effective heights of the road and the sidewalk

Hironari Masui; Masanon Ishii; Satoshi Takahashi; H. Shimizu; T. Kobayashi

2000-01-01

209

Source and Propagation Characteristics of Kilometric Continuum Observed with Multiple Satellites  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

210

On Polarization and Frequency Dependence of Diffuse Indoor Propagation  

Microsoft Academic Search

The room electromagnetics (RE) theory describes the radio propagation in a single room assuming diffuse scattering. A main characteristic is the exponential power-delay profile (PDP) decaying with the so-called reverberation time (RT) parameter, depending only on the wall area, the volume of the room and an absorption coefficient. The PDP is independent on the location in the room, except for

Jesper Ødum Nielsen; Jorgen Bach Andersen; Gert Frolund Pedersen; Mauro Pelosi

2011-01-01

211

Propagation characteristics of coastally trapped waves on the Australian Continental Shelf  

NASA Astrophysics Data System (ADS)

Coastally trapped waves (CTWs) are investigated around the Australian coast based on their signature in the sea surface height (SSH) field, using independent data from coastal tide gauge observations and the Bluelink ocean forecasting system from 2009. A high correlation (correlation coefficients from 0.6 to 0.9) between the model and observational data is demonstrated for locations between Hillarys, in the south-west of the continent, and Cape Ferguson, in the north-east. This justifies the use of Bluelink data for the rest of the investigation and enables coastal locations between tide gauge stations to be included. Spectrum analysis shows that CTWs have periods of between 10 and 25 days, with the 10 day period dominating along the south coast, and greater energy around the 20 day period on the east coast. The greatest spectral power is located around the Great Australian Bight. After filtering to isolate these CTW frequencies, phase speeds are estimated using two methods and are consistent with earlier studies. There is a close correlation between the standard deviation of the filtered SSH data and the width of the continental shelf, indicating that CTW amplitudes are strongly modulated by the local shelf width. Contrary to earlier studies, a complex empirical orthogonal function analysis shows that the majority of the variance propagates as continuous features between the south-west and north-east, and although modulated by the shelf width, it is unaffected by the sharply changing coastline orientation, shallow Bass Strait, or wind forcing regions.

Woodham, Robert; Brassington, Gary B.; Robertson, Robin; Alves, Oscar

2013-09-01

212

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

PubMed

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

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

2014-10-01

213

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

214

Characteristics of rainfall queues for rain attenuation studies over radio links at subtropical and equatorial Africa  

NASA Astrophysics Data System (ADS)

due to precipitation remains an important design factor in the future deployment of terrestrial and earth-space communication radio links. Largely, there are concerted efforts to understand the dynamics of precipitation in attenuation occurrence at subtropical, tropical, and equatorial region of Africa. In this deliberate approach, rainfall spikes pertaining to rain cells are conceptualized as distinct rain spike traffic over radio links, by applying queueing theory concepts. The queue distributions at Durban (29°52'S, 30°58'E) and Butare (2°36'S, 29°44'E)—respectively, of subtropical and equatorial climates—are investigated from distrometer measurements. The data sets at both sites are observed over four rain regimes: drizzle, widespread, shower, and thunderstorm. The queue parameters of service time and inter-arrival of rain spikes traffic at both regions are found to be Erlang-k distributed (Ek) and exponentially distributed (M), respectively. It is established that the appearance of rain rates over radio links invariably follows a First Come, First Served (FCFS), multi-server (s), infinite queue, and semi-Markovian process, designated as M/Ek/s/?/FCFS discipline. Modeled queue parameters at both regions are found to vary significantly over different regimes. However, these queue parameters over the entire data set suggest similar queue patterns at both sites. More importantly, power law relationships describing other queue-related parameters are formulated. The paper concludes by demonstrating an application of queueing theory for rainfall synthesis. The proposed technique will provide an alternative method of estimating rain cell sizes and rain attenuation over satellite and terrestrial links.

Alonge, Akintunde A.; Afullo, Thomas J.

2014-08-01

215

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

NASA Astrophysics Data System (ADS)

It is well known that internal gravity waves (IGWs) affect the structure and mean circulation of the Earth' middle and upper atmosphere by transporting energy and horizontal momentum upward from the lower atmosphere. The IGWs modulate the background atmospheric structure, producing a periodic pattern of spatial and temporal variations in the wind velocity, temperature and density. Similar effects are anticipated for the Venus and Mars since IGWs are a characteristic of stably stratified atmosphere. For instance, Yakovlev et al. (1991) and Gubenko et al. (2008a) used the radio occultation (RO) data from Venera 15 and 16 missions to investigate the thermal structure and layering of the Venus' middle atmosphere. They noted that a wavelike periodic structure commonly appears in retrieved vertical profiles at altitudes above 60 km in the atmosphere where the static stability is large. Through comparisons between Magellan RO observations in the Venus' atmosphere, Hinson and Jenkins (1995) have demonstrated that small scale variations in retrieved temperature profiles at altitudes from 60 to 90 km are caused by a spectrum of vertical propagating IGWs. Temperature profiles from the Mars Global Surveyor (MGS) measurements reveal vertical wavelike structures assumed to be atmospheric IGWs in the Mars' lower atmosphere (Creasey et al., 2006). The very large IGW amplitudes inferred from MGS RO data imply a very significant role for IGWs in the atmospheric dynamics of Mars as well. There is one general problem inherent to all measurements of IGWs. Observed wavelike variations may alternatively be caused by the IGWs, turbulence or persistent layers in the atmosphere, and it is necessary to have an IGW identification criterion for the correct interpretation of obtained results. In this context, we have developed an original method for the determination of internal gravity wave parameters from a single vertical temperature profile measurement in a planetary atmosphere (Gubenko et al., 2008b, 2011). This method does not require any additional information not contained in the profile and may be used for the analysis of profiles measured by various techniques. The criterion for the IGW identification has been formulated and argued. In the case when this criterion is satisfied, the analyzed temperature fluctuations can be considered as wave-induced. The method is based on the analysis of relative amplitude thresholds of the wave temperature field and on the linear IGW saturation theory in which amplitude thresholds are restricted by dynamical (shear) instability processes in the atmosphere. When the amplitude of an internal wave reaches the shear instability limit, energy is assumed to be dissipated in such a way that the amplitude is maintained at the instability limit as the wave propagates upwards. An application of the developed method to the RO temperature data has given the possibility to identify the IGWs in the Venus' and Mars' atmospheres and to determine the magnitudes of key wave parameters such as the intrinsic frequency, amplitudes of vertical and horizontal perturbations of the wind velocity, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase (and group) speeds, kinetic and potential energy, vertical fluxes of the wave energy and horizontal momentum. The obtained results of internal wave studies in the Venus' and Mars' atmospheres deduced from the Magellan and MGS RO temperature profiles are presented and discussed. This work was partially supported by the RFBR Grant (No. 10-02-01015-a) and program OFN-15 of the Russian Academy of Sciences. References Creasey, J. E., Forbes, J. M., and Hinson, D. P.: Global and seasonal distribution of gravity wave activity in Mars' lower atmosphere derived from MGS radio occultation data, Geophys. Res. Lett., 33, L01803, doi: 10.1029/2005GL024037, 2006. Gubenko, V.N., Andreev, V.E., and Pavelyev, A.G.: Detection of layering in the upper cloud layer of Venus northern polar atmosphere observed from radio occultation data, J. Geophys. Res., 113, E03001, doi:10.1029/2007

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

2012-07-01

216

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

NASA Technical Reports Server (NTRS)

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

Romanofsky, Robert R.

1989-01-01

217

Radio Wave Characterization and Modeling in Underground Mine Tunnels  

Microsoft Academic Search

Results are presented on wideband radio propagation measurements and statistical modeling at 2.4 GHz and 5.8 GHz in real underground mine tunnels. This peculiar type of confined environment is characterized by very rough surfaces and a frequent absence of a line-of-sight between transmitting and receiving antennas. The resulting propagation characteristics differ from those frequently encountered in more typical indoor environments

Mathieu Boutin; Ahmed Benzakour; Charles L. Despins; Sofiène Affes

2008-01-01

218

Propagation characteristics of some novel coplanar waveguide transmission lines on GaAs at MM-wave frequencies  

NASA Technical Reports Server (NTRS)

Three new Coplanar Waveguide (CPW) transmission lines, namely, Suspended CPW (SCPW), Stripline-like Suspended CPW (SSCPW) and Inverted CPW (ICPW), are proposed and also analyzed for their propagation characteristics. The substrate thickness, permittivity and dimensions of housing are assumed to be arbitrary. These structures have the following advantages over conventional CPW. Firstly, the ratio of guide wavelength to free space wavelength is closer to unity which results in larger dimensions and hence lower tolerances. Secondly, the effective dielectric constant is lower and hence the electromagnetic field energies are concentrated more in the air regions which should reduce attenuation. Thirdly, for a prescribed impedance level, the above structures have a wider slot width for identical strip width. Thus, low impedance lines can be achieved with reasonable slot dimensions. Fourthly, in an inverted CPW shunt mounting of active devices, such as Gunn and IMPATT diodes, between the strip and the metal trough is possible. This feature further enhances the attractiveness of the above structures. Lastly, an E-plane probe type transition from a rectangular waveguide to suspended CPW can also be easily realized. The computed results for GaAs at Ka-band illustrate the variation of normalized guide wavelength, effective dielectric constant and the characteristic impedance as a function of the: (1) frequency; (2) distance of separation between the trough side walls; (3) normalized strip and slot widths; and (4) normalized air gap.

Simons, Rainee N.

1986-01-01

219

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

220

Inverting ionospheric radio occultation measurements using maximum entropy  

Microsoft Academic Search

Practical aspects of the inversion of ionospheric radio occultation data using the Abel transform and its inverse are discussed. The linear inverse transform exhibits poor error propagation characteristics, producing significant artifacts preferentially at low altitudes where they might easily be mistaken for intermediate or sporadic layers in the ionosphere. Tikhonov regularization, which can be viewed as fixed linear filtering, reduces

D. L. Hysell

2007-01-01

221

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)

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.

Gilroi, H. G.

1979-01-01

222

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

223

Establishment of Besnoitia darlingi from opossums ( Didelphis virginiana) in experimental intermediate and definitive hosts, propagation in cell culture, and description of ultrastructural and genetic characteristics  

Microsoft Academic Search

Besnoitiadarlingi from naturally infected opossums (Didelphisvirginiana) from Mississippi, USA, was propagated experimentally in mice, cats, and cell culture and was characterised according to ultrastructural, genetic, and life-history characteristics. Cats fed tissue cysts from opossums shed oocysts with a prepatent period of nine or 11 days. Oocysts, bradyzoites, or tachyzoites were infective to outbred and interferon-gamma gene knockout mice. Tachyzoites were

J. P Dubey; D. S Lindsay; B. M Rosenthal; C Sreekumar; D. E Hill; S. K Shen; O. C. H Kwok; L. G Rickard; S. S Black; A Rashmir-Raven

2002-01-01

224

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

Microsoft Academic Search

Rf, atmospheric-pressure glow discharge (APGD) plasmas with bare metal electrodes have promising prospects in the fields of plasma-aided etching, thin film deposition, disinfection and sterilization, etc. In this paper, the discharge characteristics are presented for the rf APGD plasmas generated with pure argon or argon-ethanol mixture as the plasma-forming gas and using water-cooled, bare copper electrodes. The experimental results show

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

2007-01-01

225

Tuning characteristics of a long erbium doped fiber external cavity semiconductor laser for radio-over fibre applications  

NASA Astrophysics Data System (ADS)

Measurements and analysis of electrical and temperature tuning characteristics of a 1490 nm erbium doped fiber external cavity semiconductor laser (DFECL) are presented. The laser has a long piece of doped fiber in the external cavity. The standing wave in the external cavity causes spatial hole-burning and absorption modulation in the saturable absorber, and forms a long dynamic grating. In this paper, we show that the wavelength of DFECL can be tuned within the bandwidth of the FBG (~100 pm), by tuning the semiconductor laser temperature. The wavelength of the laser can also be tuned smoothly and continuously over 60 pm by controlling the current over 160 mA; the equivalent optical frequency tuning rate is ~50MHz/mA. The results indicate that the peak wavelength of the dynamic grating can be tuned with the dominant mode within the bandwidth of the fiber Bragg grating. This fine tuning characteristic is very attractive for microwave optical generation in Radio over Fiber applications.

Liu, Runnan; Kostko, Irina; Wu, Ke; Kashyap, Raman

2006-09-01

226

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

PubMed Central

Objective This research was designed to investigate the effects of low pressure radio-frequency (RF) oxygen plasma treatment (OPT) on the surface of commercially pure titanium (CP-Ti) and Ti6Al4V. Surface topography, elemental composition, water contact angle, cell viability, and cell morphology were surveyed to evaluate the biocompatibility of titanium samples with different lengths of OP treating time. Materials and Methods CP-Ti and Ti6Al4V discs were both classified into 4 groups: untreated, treated with OP generated by using oxygen (99.98%) for 5, 10, and 30 min, respectively. After OPT on CP-Ti and Ti6Al4V samples, scanning probe microscopy, X-ray photoelectron spectrometry (XPS), and contact angle tests were conducted to determine the surface topography, elemental composition and hydrophilicity, respectively. The change of surface morphology was further studied using sputtered titanium on silicon wafers. 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay and F-actin immunofluorescence stain were performed to investigate the viability and spreading behavior of cultivated MG-63 cells on the samples. Results The surface roughness was most prominent after 5 min OPT in both CP-Ti and Ti6Al4V, and the surface morphology of sputtered Ti sharpened after the 5 min treatment. From the XPS results, the intensity of Ti°, Ti2+, and Ti3+ of the samples’ surface decreased indicating the oxidation of titanium after OPT. The water contact angles of both CP-Ti and Ti6Al4V were increased after 5 min OPT. The results of MTT assay demonstrated MG-63 cells proliferated best on the 5 min OP treated titanium sample. The F-actin immunofluorescence stain revealed the cultivated cell number of 5 min treated CP-Ti/Ti6Al4V was greater than other groups and most of the cultivated cells were spindle-shaped. Conclusions Low pressure RF oxygen plasma modified both the composition and the morphology of titanium samples’ surface. The CP-Ti/Ti6Al4V treated with 5 min OPT displayed the roughest surface, sharpest surface profile and best biocompatibility. PMID:24386433

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

2013-01-01

227

Characteristics of tropical cyclones and overshooting from GPS radio occultation data  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

228

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.

229

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

NASA Astrophysics Data System (ADS)

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

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

2007-06-01

230

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

SciTech Connect

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

Sun Wenting; Li Guo; Li Heping; Bao Chengyu; Wang Huabo; Zeng Shi; Gao Xing; Luo Huiying [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); School of Public Health and Family Medicine, Capital University of Medical Sciences, Beijing 100069 (China); Beijing Center for Diseases Control and Prevention, Beijing 100013 (China)

2007-06-15

231

Electrical switching dynamics and broadband microwave characteristics of VO2 radio frequency devices  

NASA Astrophysics Data System (ADS)

Vanadium dioxide (VO2) is a correlated electron system that features a metal-insulator phase transition (MIT) above room temperature and is of interest in high speed switching devices. Here, we integrate VO2 into two-terminal coplanar waveguides and demonstrate a large resistance modulation of the same magnitude (>103) in both electrically (i.e., by bias voltage, referred to as E-MIT) and thermally (T-MIT) driven transitions. We examine transient switching characteristics of the E-MIT and observe two distinguishable time scales for switching. We find an abrupt jump in conductivity with a rise time of the order of 10 ns followed by an oscillatory damping to steady state on the order of several ?s. We characterize the RF power response in the On state and find that high RF input power drives VO2 further into the metallic phase, indicating that electromagnetic radiation-switching of the phase transition may be possible. We measure S-parameter RF properties up to 13.5 GHz. Insertion loss is markedly flat at 2.95 dB across the frequency range in the On state, and sufficient isolation of over 25 dB is observed in the Off state. We are able to simulate the RF response accurately using both lumped element and 3D electromagnetic models. Extrapolation of our results suggests that optimizing device geometry can reduce insertion loss further and maintain broadband flatness up to 40 GHz.

Ha, Sieu D.; Zhou, You; Fisher, Christopher J.; Ramanathan, Shriram; Treadway, Jacob P.

2013-05-01

232

Structural characteristics of phosphorus-doped C60 thin film prepared by radio frequency-plasma assisted thermal evaporation technique.  

PubMed

Phosphorus doped C60 (P:C60) thin films were prepared by a radio frequency plasma assisted thermal evaporation technique using C60 powder as a carbon source and a mixture of argon and phosphine (PH3) gas as a dopant precursor. The effects of the plasma power on the structural characteristics of the as-prepared films were then studied using Raman spectroscopy, Auger electron spectroscopy (AES) and X-ray photo-electrons spectroscopy (XPS). XPS and Auger analysis indicated that the films were mainly composed of C and P and that the concentration of P was proportional to the plasma power. The Raman results implied that the doped films contained a more disordered carbon structure than the un-doped samples. The P:C60 films were then used as a coating layer for the Si anodes of lithium ion secondary batteries. The cyclic voltammetry (CV) analysis of the P:C60 coated Si electrodes demonstrated that the P:C60 coating layer might be used to improve the transport of Li-ions at the electrode/electrolyte interface. PMID:22630023

Arie, Arenst Andreas; Lee, Joong Kee

2012-02-01

233

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

SciTech Connect

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 ?m level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ±0.08 ?rad. This report contains a detailed description of the experimental investigation for the propagation and stability characteristics of the laser beam in the laser-based alignment system for long-distance linear accelerators.

Suwada, Tsuyoshi; Satoh, Masanori [Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan)] [Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Telada, Souichi; Minoshima, Kaoru [Length Standards Section, Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563 (Japan)] [Length Standards Section, Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8563 (Japan)

2013-09-15

234

Packet Switching in Radio Channels: Part I--Carrier Sense Multiple-Access Modes and Their Throughput-Delay Characteristics  

Microsoft Academic Search

Radio communication is considered as a method for providing remote terminal access to computers. Digital byte streams from each terminal are partitioned into packets (blocks) and transmitted in a burst mode over a shared radio channel. When many terminals operate in this fashion, transmissions may conflict with and destroy each other. A means for controlling this is for the terminal

LEONARD KLEINROCK; FOUAD A. TOBAGI

1975-01-01

235

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

Microsoft Academic Search

Radio-frequency (RF), atmospheric-pressure glow discharge (APGD) plasmas using bare metal electrodes have promising prospects in the fields of plasma-aided etching, deposition, surface treatment, disinfection, sterilization, etc. In this paper, the discharge characteristics, including the breakdown voltage and the discharge voltage for sustaining a stable and uniform alpha mode discharge of the RF APGD plasmas are presented. The experiments are conducted

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

2007-01-01

236

Radio science investigations with Voyager  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

237

IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 4, 2005 31 Comparison Between Two Different Antennas for  

E-print Network

the propagation channel characteristics, radio system compat- ibility, and the effect of the human body. On-body BODY-CENTRIC wireless networks are aiming to provide communication systems with constant availability. more realistic representation of the human body behavior such as different body positions and movements

Hao, Yang

238

Results of Microwave Propagation Tests on a 40Mile Overland Path  

Microsoft Academic Search

This paper gives the results of a series of microwave radio propagation tests over an unobstructed 40-mile overland path. The purpose of the tests was to investigate the transmission characteristics of such a path at centimeter wavelengths over a long period of time. Statistics on the transmission results at wavelengths ranging from 1.25 to 42 cm. are given. The tests

A. L. Durkee

1948-01-01

239

The impact of propagation environment and traffic load on the performance of routing protocols in ad hoc networks  

E-print Network

Wireless networks are characterized by a dynamic topology triggered by the nodes mobility. Thus, the wireless multi-hops connection and the channel do not have a determinist behaviour such as: interference or multiple paths. Moreover, the nodes' invisibility makes the wireless channel difficult to detect. This wireless networks' behaviour should be scrutinized. In our study, we mainly focus on radio propagation models by observing the evolution of the routing layer's performances in terms of the characteristics of the physical layer. For this purpose, we first examine and then display the simulation findings of the impact of different radio propagation models on the performance of ad hoc networks. To fully understand how these various radio models influence the networks performance, we have compared the performances of several routing protocols (DSR, AODV, and DSDV) for each propagation model. To complete our study, a comparison of energy performance based routing protocols and propagation models are presente...

Rhattoy, A; 10.5121/ijdps.2012.3106

2012-01-01

240

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

E-print Network

The impending era of wide-field radio surveys has the potential to revolutionize our understanding of astrophysical transients. Here we evaluate the prospects of a wide range of planned and hypothetical radio surveys using the properties and volumetric rates of known and hypothetical classes of extragalactic synchrotron radio transients (e.g., on- and off-axis gamma-ray bursts [GRB], supernovae, tidal disruption events [TDE], compact object mergers). Utilizing these sources and physically motivated considerations we assess the allowed phase-space of radio luminosity and peak timescale for extragalactic transients. We also include for the first time effects such as redshift evolution of the rates, K-corrections, and non-Euclidean luminosity distance, which affect the detection rates of the most sensitive surveys. The number of detected events is calculated by means of a Monte Carlo method, using the various survey properties (depth, cadence, area) and realistic detection criteria that include a cut on the mini...

Metzger, Brian D; Berger, Edo

2015-01-01

241

Radio Astronomy Radio astronomy  

E-print Network

Effelsberg 100m telescope (Germany) Green Bank 100m telescope (National Radio Astronomy ObservatoryExperiment -10m (Chile, Europe) #12;Submillimeter radio astronomy #12;Size of telescope Snow sweep at Nobeyama 45;#12;Arecibo 300m telescope #12;Radio interferometer #12;Radio interferometer Very Large Array (VLA) (New

Metchev, Stanimir

242

An Introduction to Radio Astronomy  

NASA Astrophysics Data System (ADS)

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

Burke, Bernard F.; Graham-Smith, Francis

2014-02-01

243

Radio Galaxies.  

ERIC Educational Resources Information Center

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

Downes, Ann

1986-01-01

244

New space-time perspectives on the propagation characteristics of the Black Death epidemic and its relation to bubonic plague  

Microsoft Academic Search

This work presents, for the first time, a series of detailed space-time maps of Black Death mortality and infected area propagation\\u000a throughout the fourteenth century AD Europe. The maps integrate a variety of interdisciplinary knowledge bases about the devastating\\u000a epidemic and provide researchers and the interested public with an informative description of the Black Death dynamics (temporal\\u000a evolution, local and

George Christakos; Ricardo A. Olea

2005-01-01

245

Multielement system design in astronomy and radio science  

NASA Astrophysics Data System (ADS)

This book deals with multielement systems representing a set of interdependent identical elements of a comparatively small size. Such systems are widely used in various fields of astronomy and radio science, their classical examples being radio telescopes, optical and radio interferometers, orbital X-ray and gamma-ray telescopes, and phased antenna arrays for radio communication and radar facilities. Here the problems of the optimal arrangement of elements of such systems are investigated to provide their high-performance characteristics such as resolution, sensitivity, and robustness to the statistically inhomogeneous propagation medium. The distinctive feature of the book is the use of the combinatorial approach to system optimization that proves especially useful for systems with a very large number of elements. The book is addressed to research physicists and engineers who are concerned with the development of astronomical instruments and large antenna arrays, and to graduate students learning about these subjects.

Kopilovich, Lazarus E.; Sodin, Leonid G.

246

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)

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.

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

1993-01-01

247

Amplitude fluctuations of decimeter and centimeter radio waves emmitted by the Venera-15 and Venera-16 space probes during propagation through the solar plasma  

Microsoft Academic Search

Results are presented of investigations into the fluctuations of centimeter and decimeter radio waves in the solar plasma. The experimental dependence of the scintillation index on distance of closest point of approach in the range 2.3-100 solar radii is given. Dependence of the scintillation index on wavelength and solar activity is discussed. The dependence of the variance of the fluctuations

O. I. Yakovlev; A. I. Efimov; E. P. Molotov; S. N. Rubtsov; V. P. Yakubov; A. I. Kucheryavenkov; A. S. Kaftonov

1988-01-01

248

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

NASA Astrophysics Data System (ADS)

We analyse Sloan Digital Sky Survey spectra of 568 obscured luminous quasars. The [O III] ?5007 Å emission line shows blueshifts and blue excess, indicating that some of the narrow-line gas is undergoing an organized outflow. The velocity width containing 90 per cent of line power ranges from 370 to 4780 km s-1, suggesting outflow velocities up to ˜2000 km s-1, and is strongly correlated with the radio luminosity among the radio-quiet quasars. We propose that radio emission in radio-quiet quasars is due to relativistic particles accelerated in the shocks within the quasar-driven outflows; star formation in quasar hosts is insufficient to explain the observed radio emission. The median radio luminosity of the sample of ?L?[1.4 GHz] = 1040 erg s-1 suggests a median kinetic luminosity of the quasar-driven wind of Lwind = 3 × 1044 erg s-1, or about 4 per cent of the estimated median bolometric luminosity Lbol = 8 × 1045 erg s-1. Furthermore, the velocity width of [O III] is positively correlated with mid-infrared luminosity, which suggests that outflows are ultimately driven by the radiative output of the quasar. Emission lines characteristic of shocks in quasi-neutral medium increase with the velocity of the outflow, which we take as evidence of quasar-driven winds propagating into the interstellar medium of the host galaxy. Quasar feedback appears to operate above the threshold luminosity of Lbol ˜ 3 × 1045 erg s-1.

Zakamska, Nadia L.; Greene, Jenny E.

2014-07-01

249

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

250

Refractive effects from VHF to EHF. Part B: Propagation models  

NASA Astrophysics Data System (ADS)

This lecture describes and discusses propagation models used to assess radio propagation effects, and uses examples from propagation assessment systems and other propagation software to illustrate many of the effects. Frequencies from about 30 MHz to 100 GHz are considered. Both standard and nonstandard propagation models are described. A brief description of three propagation assessment systems that include the various models is given, and several application examples are presented to illustrate both the propagation effects and the applicability of the models.

Hitney, Herbert V.

1994-09-01

251

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

NASA Technical Reports Server (NTRS)

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

Smith, J. M.

1973-01-01

252

Effect of source-gate spacing on direct current and radio frequency characteristic of graphene field effect transistor  

NASA Astrophysics Data System (ADS)

The effect of source-gate spacing on graphene filed effect transistors has been investigated. Reducing the source gate spacing allows for a significant improvement on both the direct current and radio frequency (RF) performances. Instead of the generally considered output conductance, our results suggest that the access resistances at the un-gated region contribute more to the maximum oscillation frequency (fmax). Further analysis reveals that the ratio of cut off frequency (fT) to fmax is also sensitive to the resistances at source-gate spacing. This work can be used to guide the further optimization of graphene-based RF devices.

Peng, Song-ang; Jin, Zhi; Zhang, Da-yong; Shi, Jing-yuan; Wang, Xuan-yun; Wang, Shao-qing; Liu, Xin-yu; Yu, Guang-hui

2015-01-01

253

Kinematics of ICMEs Deduced From Remote Radio Observations  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

254

Three-dimensional propagation characteristics of the upward connecting leaders in six negative tall-object flashes in Guangzhou  

NASA Astrophysics Data System (ADS)

Six downward negative flashes terminated on tall structures in Guangzhou are analyzed. The three-dimensional (3-D) lightning channels are reconstructed from dual-station optical observations. For each reconstructed 3-D upward connecting leader (UCL) channel, its 3-D length and speed are calculated. The 3-D length values of the six positive UCLs range from 180 to 818 m. There are 38 3-D speed values which are calculated combining the 3-D UCL channel and the high-speed images for the six UCLs. The 3-D speed values range from 0.8 to 14.3 × 105 m s- 1 and four of them (11%, 4/38) are on the order of 106 m s- 1. For comparison, the corresponding two-dimensional (2-D) parameters are calculated using the single-station high-speed images. The values of the 2-D length and 2-D speed range from 147 to 610 m and 0.3 to 10.6 × 105 m s- 1, respectively. From the statistical analysis, we determine that the average value of the 3-D speed is 1.3 times that of the 2-D speed. When the time is approaching the return stroke (RS), the propagation speed of the UCL is increasing. All of the four 3-D speed values on the order of 106 m s- 1 occur less than 0.2 ms prior to the RS. When the 3-D length is shorter than 300 m, 77% (20/26) of the corresponding 3-D speed values are smaller than 5 × 105 m s- 1. When the 3-D length is longer than 300 m or the UCL tip height is higher than 650 m, all of the corresponding 3-D speed values are faster than 5 × 105 m s- 1.

Gao, Yan; Lu, Weitao; Ma, Ying; Chen, Luwen; Zhang, Yang; Yan, Xu; Zhang, Yijun

2014-11-01

255

Characteristics of a rocket-triggered lightning flash with large stroke number and the associated leader propagation  

NASA Astrophysics Data System (ADS)

negative lightning flash with 16 leader-return stroke sequences, triggered in the summer of 2013 using the classical rocket-and-wire triggering technique, was examined with simultaneous two-dimensional (2D) imaging of very high-frequency (VHF) radiation sources, channel-base current measurement, broadband electric field waveforms and high-speed video images. A total of 28.0 C negative charge was transferred to ground during the whole flash, and the charge transferred during the initial stage was 4.9 C, which is the weakest among the triggered lightning flashes at the SHandong Artificially Triggering Lightning Experiment (SHATLE). The peak current of 16 return strokes ranged from 5.8 to 32.5 kA with a geometric mean of 14.1 kA. The progression of upward positive leader and downward negative (dart or dart-stepped) leaders was reproduced visually by using an improved short-baseline VHF lightning location system with continuous data recording capability. The upward positive leader was mapped immediately from the tip of the metal wire during the initial stage, developing at a speed of about 104 m/s without branches. The upward positive leader and all the 14 negative leaders captured by the 2D imaging system propagated along the same channel with few branches inside the cloud, which might be the reason for the relatively small charge transfer. The 2D imaging results also show that dart leaders may transform into dart-stepped leaders after a long time interval between successive strokes.

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

2014-12-01

256

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

257

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

PubMed Central

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

TSUDA, Toshitaka

2014-01-01

258

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

PubMed

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

Tsuda, Toshitaka

2014-01-01

259

Galileo radio science investigations  

NASA Technical Reports Server (NTRS)

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.

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

260

NASA Lunar Base Wireless System Propagation Analysis  

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

261

A Detailed Investigation of Radio Power Selection Effects Relevant to the Study of Classical Double Radio Sources  

NASA Astrophysics Data System (ADS)

A sample of powerful classical double radio sources, also known as FR II sources, has been assembled to study the properties of the radio sources and their gaseous environments, as well as the redshift evolution of these properties. The possibility that the observed redshift dependences of various parameters of interest are caused by radio power selection effects is investigated here using statistical tools such as two-parameter fitting and partial rank correlation analysis. It is found that the Mach number of lobe advance, the lobe propagation velocity, and the ambient gas density of the FR II sources are unlikely to be significantly affected by radio power selection effects. Hence, the observed redshift dependences of these parameters are likely to reflect real redshift evolution. A previous study by Wellman, Daly, & Wan indicates that the powerful FR II sources in this sample lie in cluster-like gaseous environments. The fact that the ambient gas density of the FR II sources is not affected by radio power selection means that these sources can be used to probe the evolution of their environments. Specifically, the observed decrease of the ambient gas density with redshift is likely to reflect real redshift evolution rather than being caused by radio power selection effects. It is interesting to note that the current data suggest that the Mach number of lobe advance is independent of redshift, while the lobe propagation velocity increases with redshift, as summarized in the final table in this paper. Radio power selection effects are likely to be quite weak, if present at all, in the study of the nonthermal pressure inside a classical double source, and the study of the characteristic size of a source. The two-parameter fitting and partial rank correlation analysis applied to the ambient gas temperature and luminosity in directed kinetic energy of the jet yield inconclusive results, so these direct analyses do not clearly indicate whether the redshift evolution of each of these two parameters is due to radio power selection effects. However, each parameter is estimated using other parameters such as the Mach number of lobe advance, the lobe propagation velocity, and the nonthermal pressure inside the radio lobe, which do not suffer significant radio power selection effects.

Wan, Lin; Daly, Ruth A.

262

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

NASA Technical Reports Server (NTRS)

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

1979-01-01

263

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

264

The NASA radiowave propagation program  

NASA Technical Reports Server (NTRS)

The objectives of the NASA radiowave Propagation Program are to enable new satellite communication applications and to enhance existing satellite communication networks. These objectives are achieved by supporting radio wave propagation studies and disseminating the study results in a timely fashion. Studies initiated by this program in the 1980s enabled the infant concept of conducting mobile communications via satellite to reach a state of relative maturity in 1990. The program also supported the satellite communications community by publishing and revising two handbooks dealing with radio wave propagation effects for frequencies below and above 10 GHz, respectively. The program has served the international community through its support of the International Telecommunications Union. It supports state of the art work at universities. Currently, the program is focusing on the Advanced Communications Technology Satellite (ACTS) and its propagation needs. An overview of the program's involvement in the ACTS project is given.

Davarian, Faramaz

1990-01-01

265

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

USGS Publications Warehouse

We observed a total of 102 striped skunks (Mephitis mephitis) from March to July of both 1991 and 1992 in Stutsman County, North Dakota (USA) during an experiment with food supplementation. Twenty-three apparently healthy skunks in 1991 and 56 in 1992 were equipped with radio-collars. In 1991, one of 23 was tested and found to be rabid. In 1992, 50 of 56 were tested; 35 (69%) were rabid. Of skunks with ages estimated, 19 (66%) of 29 were first year animals in 1991 compared with nine (22%) of 41 first year animals in 1992. All 18 females captured in 1991 were pregnant or parous compared with 21 (60%) of 35 in 1992. The estimated survival rate of skunks was 0.85 during April to June 1991, but only 0.17 during April to July 1992. In 1992, the survival rate of first year skunks was 0.08, compared with 0.35 for older animals. Eleven (31%) of 36 skunks found dead of rabies or in late clinical stage were located below ground. We detected no differences in 1992 between healthy and rabid skunks in estimated mean (i?? SE) rate of travel (232 i?? 14 m/hr), distance traveled (2047 i?? 141 m/night), or home range size (1.6 i?? 0.4 km2) during half-month periods from April through June. Among rabid skunks, mean (i?? SE) rate of travel tended to decrease from 298 i?? 48 m/hr during the 14 days preceding the clinical period of rabies (pre-clinical) to 174 i?? 48 m/hr during the clinical period of rabies (14 days immediately before death). Similar decrease occurred in mean (i?? SE) distance traveled in a night (2318 i?? 281 m, pre-clinical; 1497 i?? 281 m, clinical). Mean (i?? SE) home range size of males (2.8 i?? 0.4) was greater than of females (1.2 i?? 0.4) during the pre-clinical period, but during the clinical period home range sizes of males (1.8 i?? 0.4) and females (1.8 i?? 0.4) were similar. Mean (i?? SE) home range size of females did not differ between pre-clinical (1.2 i?? 0.4) and clinical (1.8 i?? 0.4) periods (P = 0.22). Deaths of skunks from rabies in 1992 tended to be more spatially clumped than expected had they been random, mostly due to deaths detected before 8 May. We detected no correlation between locations of animals found dead of rabies and dates of death.

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

1997-01-01

266

Establishment of Besnoitia darlingi from opossums (Didelphis virginiana) in experimental intermediate and definitive hosts, propagation in cell culture, and description of ultrastructural and genetic characteristics.  

PubMed

Besnoitia darlingi from naturally infected opossums (Didelphis virginiana) from Mississippi, USA, was propagated experimentally in mice, cats, and cell culture and was characterised according to ultrastructural, genetic, and life-history characteristics. Cats fed tissue cysts from opossums shed oocysts with a prepatent period of nine or 11 days. Oocysts, bradyzoites, or tachyzoites were infective to outbred and interferon-gamma gene knockout mice. Tachyzoites were successfully cultivated and maintained in vitro in bovine monocytes and African green monkey cells and revived after an 18-month storage in liquid nitrogen. Schizonts were seen in the small intestinal lamina propria of cats fed experimentally-infected mouse tissues. These schizonts measured up to 45 x 25 microm and contained many merozoites. A few schizonts were present in mesenteric lymph nodes and livers of cats fed tissue cysts. Ultrastructurally, tachyzoites and bradyzoites of B. darlingi were similar to other species of Besnoitia. A close relationship to B. besnoiti and an even closer relationship to B. jellisoni was indicated for B. darlingi on the basis of the small subunit and ITS-1 portions of nuclear ribosomal DNA. PMID:12076634

Dubey, J P; Lindsay, D S; Rosenthal, B M; Sreekumar, C; Hill, D E; Shen, S K; Kwok, O C H; Rickard, L G; Black, S S; Rashmir-Raven, A

2002-07-01

267

Radio telescopes  

Microsoft Academic Search

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

J. Findlay

1964-01-01

268

Indoor radio measurement and planning for UMTS/HSDPA with antennas  

NASA Astrophysics Data System (ADS)

Over the last decade, mobile communication networks have evolved tremendously with a key focus on providing high speed data services in addition to voice. The third generation of mobile networks in the form of Universal Mobile Telecommunications System (UMTS) is already offering revolutionary mobile broadband experience to its users by deploying High Speed Downlink Packet Access (HSDPA) as its packet-data technology. With data speeds up to 14.4 Mbps and ubiquitous mobility, HSDPA is anticipated to become a preferred broadband access medium for end-users via mobile phones, laptops etc. While majority of these end-users are located indoors most of the time, approximately 70-80% of the HSDPA traffic is estimated to originate from inside buildings. Thus for network operators, indoor coverage has become a necessity for technical and business reasons. Macro-cellular (outdoor) to indoor coverage is a natural inexpensive way of providing network coverage inside the buildings. However, it does not guarantee sufficient link quality required for optimal HSDPA operation. On the contrary, deploying a dedicated indoor system may be far too expensive from an operator's point of view. In this thesis, the concept is laid for the understanding of indoor radio wave propagation in a campus building environment which could be used to plan and improve outdoor-to-indoor UMTS/HSDPA radio propagation performance. It will be shown that indoor range performance depends not only on the transmit power of an indoor antenna, but also on the product's response to multipath and obstructions in the environment along the radio propagation path. An extensive measurement campaign will be executed in different indoor environments analogous to easy, medium and hard radio conditions. The effects of walls, ceilings, doors and other obstacles on measurement results would be observed. Chapter one gives a brief introduction to the evolution of UMTS and HSDPA. It goes on to talk about radio wave propagation 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. In chapter six, the design and fabrication of the monopole antennas used for the experimental m

Eheduru, Marcellinus

269

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

Microsoft Academic Search

A new approach for obtaining integrated estimates of soil moisture content over larger regions of typically 10–50 km is described.\\u000a It is based on a known correlation between propagation characteristics of low frequency radio surface waves and surface soil\\u000a moisture, and provides valuable new benefits especially for meteorological prognostic models and for soil water estimation\\u000a in agriculture. The paper consists of

Christof Huebner; Christoph Kottmeier; Alexander Brandelik

2011-01-01

270

NASA Propagation Program Status and Propagation Needs of Satcom Industry  

NASA Technical Reports Server (NTRS)

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

Golshan, Nassar

1996-01-01

271

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

SciTech Connect

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

Li Guo; Le Peisi; Li Heping; Bao Chengyu [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)

2010-05-15

272

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

SciTech Connect

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

Zhao, P. [Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561 (Japan); Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031 (China); Zheng, W. [Research and Technology Center, Yazaki Corp., 1500 Misyuuku, Susono 410-1194 (Japan); Meng, Y. D. [Institute of Plasma Physics, Chinese Academy of Sciences, P.O. Box 1126, Hefei 230031 (China); Nagatsu, M. [Graduate School of Science and Technology, Shizuoka University, 3-5-1 Johoku, Naka-ku, Hamamatsu 432-8561 (Japan)

2013-03-28

273

Characteristics of high-purity Cu thin films deposited on polyimide by radio-frequency Ar/H2 atmospheric-pressure plasma jet  

NASA Astrophysics Data System (ADS)

With a view to fabricating future flexible electronic devices, an atmospheric-pressure plasma jet driven by 13.56 MHz radio-frequency power is developed for depositing Cu thin films on polyimide, where a Cu wire inserted inside the quartz tube was used as the evaporation source. A polyimide substrate is placed on a water-cooled copper heat sink to prevent it from being thermally damaged. With the aim of preventing oxidation of the deposited Cu film, we investigated the effect of adding H2 to Ar plasma on film characteristics. Theoretical fitting of the OH emission line in OES spectrum revealed that adding H2 gas significantly increased the rotational temperature roughly from 800 to 1500 K. The LMM Auger spectroscopy analysis revealed that higher-purity Cu films were synthesized on polyimide by adding hydrogen gas. A possible explanation for the enhancement in the Cu film deposition rate and improvement of purity of Cu films by H2 gas addition is that atomic hydrogen produced by the plasma plays important roles in heating the gas to promote the evaporation of Cu atoms from the Cu wire and removing oxygen from copper oxide components via reduction reaction.

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

2013-03-01

274

Near-Relativistic Solar Electrons and Type III Radio Bursts  

NASA Technical Reports Server (NTRS)

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

Cane, H. V.

2003-01-01

275

Radio channel measurement and modelling for future mobile radio systems  

NASA Astrophysics Data System (ADS)

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

Guerdenli, E.; Huish, P. W.

1989-12-01

276

HF propagation at high latitudes  

Microsoft Academic Search

A review of problems associated with HF propagation at high latitudes is presented. Disturbances and electron densities are greater in the ionosphere in the auroral oval than in other parts of the polar ionosphere. The high latitude ionosphere is characterized by a marked absorption of radio waves traveling through the region, particularly during geomagnetically disturbed periods. In a high latitude

T. B. Jones

1987-01-01

277

2-dimensional FDTD simulations of plasma wave propagations in the ionosphere  

NASA Astrophysics Data System (ADS)

We developed a 2-dimensional FDTD simulation code which can treat wave propagations in magnetized plasma. Though we need to perform full particle simulations in order to recognize accurate characteristics of waves propagating in space plasma, FDTD simulations can be performed with much less computer resources than those necessary for full particle simulations, in memories as well as cpu times. Since space plasma is magnetized, it is necessary to incorporate the dielectric tensor with anisotropy and dispersibility in FDTD simulation code, in order to calculate the electromagnetic field in space plasma. We use PLRC method to formulization FDTD scheme to reduce numerical errors. In FDTD simulations, it is essential that how to realize an effective absorbing boundary. We developed PML absorbing boundary condition with anisotropy and dispersibility, and succeeded to realize very effective absorbind boundary. According to the rocket observations, we can receive MF radio wave above the dense ionospheric layer whose density is larger than those corresponding to cutoff frequency of MF radio wave. We consider that this is because the thickness of the ionopheric layer is smaller than the wavelength of MF radio wave, the density of ionospheric layer is not constant in the horizontal plane. We have been analyzing the characteristics of MF wave propagation in the ionospher with Full-wave method. In the Full-wave method, since the electron density profile is assumed to change in one-dimensional corrsponding to the alititude, we can only treat one-dimensional electron density profiles. In this study, therefore, we performed a series of FDTD simulations of MF wave propagations in ionospheres with several types of electron density distributions in the horizontal plane, such as electron dense cloud, sporadic layer, etc., and studied the relation between spatial scale of ionospheric layer and MF radio wavelength. In addition, we performed a FDTD simulation of MF radio wave propagations with the ionospheric layer model which is estimated by Full-wave analysis of S-310-37 sounding rocket observations. S-310-37 sonding rocket was launched at USC (Uchinoura Space Center, Kagoshima) in Jan. 2007. We are going to compare FDTD simulation results, Full-wave analysis and rocket observations, and study the influence of electron density profile on the propagation characterictics of MF radio wave in the ionosphere.

Miyake, T.; Yoshino, S.; Okada, T.; Ishisaka, K.

2007-12-01

278

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

NASA Technical Reports Server (NTRS)

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.

Davarian, Faramaz (editor)

1989-01-01

279

Radio Astronomy  

NSDL National Science Digital Library

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

Tenenbaum, David

280

Effect of surface modification of high-density polyethylene by direct current and radio frequency glow discharge on wetting and adhesion characteristics  

NASA Astrophysics Data System (ADS)

The present investigation aims to optimize the process parameters of Direct Current (DC) and Radio Frequency (RF) glow discharge treatment through air in terms of discharge power and time of exposure for the surface modification of high-density polyethylene (HDPE) sheet, for attaining best adhesive joint of the polymer to mild steel. In order to estimate the extent of surface modification, the surface energies of the polymer surfaces exposed to glow discharge have been determined by measuring contact angles using two standard test liquids of known surface energies. It is observed that at a given power level of DC glow discharge, surface energy and its polar component increase with increasing exposure time, attaining a maximum and then decreasing. In the case of RF glow discharge, surface energy and its polar component increase with increasing exposure time and then saturate. Surface modification by DC glow discharge increases the surface energy of HDPE relatively more at a lower power compared to that observed for RF glow discharge. The dispersion component of surface energy remains almost unaffected. The surfaces have also been studied by electron spectroscopy for chemical analysis (ESCA) and energy-dispersive spectra (EDS). A significant oxygen peak is observed for surface-modified polymer as detected by ESCA and EDS. Lap shear tensile test of an adhesive (Araldite AY 105) joint of HDPE with mild steel has been carried out in optimizing the parameters of DC and RF glow discharge for maximum joint strength. When HDPE is exposed to DC glow discharge, improvement of adhesive joint strength of HDPE to mild steel is found to be by a factor more than 7. On the other hand, when HDPE is exposed to RF glow discharge, results in improvement of adhesive joint strength of HDPE to mild steel by a factor nearer to 7 are found. Thus, DC glow discharge is more capable for increasing wetting and adhesion characteristics of the polymer.

Bhowmik, S.; Chaki, T. K.; Ray, S.; Hoffman, F.; Dorn, L.

2004-03-01

281

Cognitive radio: Making software radios more personal  

Microsoft Academic Search

Software radios are emerging as platforms for multiband multimode personal communications systems. Radio etiquette is the set of RF bands, air interfaces, protocols, and spatial and temporal patterns that moderate the use of the radio spectrum. Cognitive radio extends the software radio with radio-domain model-based reasoning about such etiquettes. Cognitive radio enhances the flexibility of personal services through a Radio

Joseph Mitola; Gerald Quentin Maguire Jr.

1999-01-01

282

Propagation characteristics of Po/So in the lithosphere of the Eastern Atlantic ocean revealed from automatic incoherent ocean bottom array processing  

NASA Astrophysics Data System (ADS)

Contrary to continental lithosphere, the seismic shear wave anisotropy of the uppermost oceanic mantle is rarely sampled at local scales. Local anisotropy information from ocean bottom stations are often difficult to obtain because of the rare deployments and because of poor signal to noise (SNR) ratio at these stations. In a pilot study in the North Atlantic between Portugal mainland, Madeira and the Azores, we demonstrate that an ocean bottom mid-aperture array at 4-5 km depth allows for automatic retrieval of SHo, SVo and Po velocities from data filtered between 4 and 25 Hz from regional weak earthquakes with Ml < 3 in up to 500 km distance, even if the SNR is poor. We use incoherent array analysis applied to short-term average / long-term average (STA/LTA) characteristic functions. Contrary to conventional methods the array analysis reveals local, absolute velocities beneath the array that are not averages over long travelpaths. Additionally, earthquakes can be located using the backazimuth and So-Po difference times. For instance, we observe seismicity at an aseismic segment of the Gloria transform fault. For our pilot array at 38.4 N 18.38 W we detect and study more than 900 suited earthquakes over a period of 10 months, and retrieve a strong azimuthal anisotropy of SH and SV waves of about 8% with a fast direction striking 90E in accord with the direction of plate motion. Unexpectedly, the azimuthal anisotropy of P waves is small or even absent. We study furthermore the different propagation paths and find strong attenuation of Po and So for paths crossing the Azores hotspot region and attenuation of So only for the region directly west of Portugal. This indicates that Po and So phases are blocked or not generated in the hot upper mantle of active spreading zones The project is funded by the German Research Foundation (Da478/21-1, Kr1935/13-1). DEPAS (AWI, GFZ) and University of Hamburg supported the OBS deployment.

Dahm, T.; Krueger, F.; Hannemann, K.

2013-12-01

283

UHF Radio Wave Attenuation Factor Database  

Microsoft Academic Search

As is known each sea-going vessel is equipped with navigation, communication and other radio engineering facilities that serve to secure the safety of navigation and are chiefly operated at UHF-wave band. In developing these systems and calculating the energy potential for a necessary coverage range one should be well aware of the radio signal attenuation processes on a propagation path.

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

2007-01-01

284

Circular Polarization of Solar Radio Noise  

Microsoft Academic Search

IN two recent communications to these columns1,2 we have reported the existence of powerful radio emissions in the 5-metre wave-length band from sunspot areas. Since such radio waves must travel through regions of considerable ionization in escaping from the sun, it occurred to us that the magneto-ionic theory of radio wave propagation3, which has proved so useful in elucidating phenomena

E. V. Appleton; J. S. Hey

1946-01-01

285

Firefighters' Radios  

NASA Technical Reports Server (NTRS)

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

1976-01-01

286

Modelling evaporation duct effects on microwave propagation with experiment validation  

Microsoft Academic Search

Microwave propagation is adversely affected by evaporation duct, which can occur as often as 85% of the time in the sea of the world. Evaporation duct propagation is the abnormal bending and diversion of electromagnetic radiation from the intended paths, that resulting in the problems of extended propagation of microwave signals well beyond the radio horizon, radar holes, and anomalous

Pan Yue; Ma Yuanliang

2006-01-01

287

7 IMPULSE RADIO Robert A. Scholtz  

E-print Network

7 IMPULSE RADIO Robert A. Scholtz and Moe Z. Win Communication Sciences Institute Department@milly.usc.edu win@milly.usc.edu Abstract: Impulse radio, a form of ultra-wide band signaling, has properties describes the characteristics of impulse radio, gives analytical estimates of its multiple access capability

Ha, Dong S.

288

Case studies of the propagation characteristics of auroral TIDS with EISCAT CP2 data using maximum entropy cross-spectral analysis  

E-print Network

south-eastwards and a vertical phase speed of 55 m/s for a height of about 300 km. The other example propagation) 1 Introduction Considerable progress has been gained in recent years in the investigation; Crowley and McCrea, 1988; Rice et al., 1988; Williams et al., 1988, 1993). An important quantity

Paris-Sud XI, Université de

289

The Deep Space Network as an instrument for radio science research  

Microsoft Academic Search

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

S. W. Asmar; N. A. Renzetti

1993-01-01

290

Virtual radios  

Microsoft Academic Search

Conventional software radios take advantage of vastly improved analog to digital converters (ADCs) and digital signal processing (DSP) hardware. Our approach, which we refer to as virtual radios, also depends upon high performance ADCs. However, rather than use DSPs, we have chosen to ride the curve of rapidly improving workstation hardware. We use wideband digitization and then perform all of

Vanu Bose; Michael Ismert; Matt Welborn; John Guttag

1999-01-01

291

College Radio.  

ERIC Educational Resources Information Center

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

Sauls, Samuel J.

292

Learning by Radio: The First Step to Literacy  

ERIC Educational Resources Information Center

Suggests a basic-education radio program as an alternative to traditional literacy education programs. One advantage of radio as an instructional medium is that it is available to most rural poor people. Stresses the need for creating innovative radio programs which are suited to radio's special characteristics. (Author/DB)

Allen, Dwight W.; Anzalone, Stephen

1978-01-01

293

ON SUN-TO-EARTH PROPAGATION OF CORONAL MASS EJECTIONS  

SciTech Connect

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

Liu, Ying D. [State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing (China); Luhmann, Janet G.; Moestl, Christian; Bale, Stuart D.; Lin, Robert P. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Lugaz, Noe [Space Science Center, University of New Hampshire, Durham, NH 03824 (United States); Davies, Jackie A., E-mail: liuxying@ssl.berkeley.edu [Space Science and Technology Department, Rutherford Appleton Laboratory, Didcot (United Kingdom)

2013-05-20

294

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

295

Structural exploration using longwave radio-clock time-signal  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

296

Reaction-Diffusion Equations In Narrow Tubes and Wave Front Propagation  

E-print Network

propagation is any of the ways in which waves travel through a medium. Wavefront is the locus (a line, or is Wave Front Propagation ? Examples Radio propagation and electromagnetic waves. Signal transmissionOutlines Reaction-Diffusion Equations In Narrow Tubes and Wave Front Propagation Konstantinos

Spiliopoulos, Konstantinos

297

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 50, NO. 5, MAY 2002 759 Iterative Site-Based Modeling for  

E-print Network

propagation behavior than those at radio or microwave frequencies. At radio and microwave frequenciesIEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 50, NO. 5, MAY 2002 759 Iterative Site Identifier S 0018-926X(02)05453-4. the propagation of light to the transmitter's room. Furthermore, for most

Carruthers, Jeffrey

298

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)

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.

Davarian, Faramaz (editor)

1993-01-01

299

Illustrative propagation  

E-print Network

with one example: wave equation with variable speed of propagation Direct Problem: Find the solution #8; given c(x) and g. Inverse Problem: Start with one example: wave equation with variable speed of the algorithm #15; limited data (#12;nite set of measurements) #12; ITLA MAR 2001 (part 1) 15 Slide 14

Zubelli, Jorge Passamani

300

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

Microsoft Academic Search

With unique features of low breakdown voltages, large and uniform discharge areas and high concentrations of chemically reactive species, radio-frequency, atmospheric-pressure glow discharge (rf APGD) plasma sources produced with bare-metallic electrodes have shown promising prospects in the field of materials processing. In this paper, the spatial distributions (i.e., the directly measured integrated axial distribution and the radial distribution by using

Guo Li; Pei-Si Le; He-Ping Li; Cheng-Yu Bao

2010-01-01

301

Consideration on the scatter of cod and fatigue crack propagation characteristics of heavy section C-Mn-V forged steel for offshore structure  

SciTech Connect

A 197-mm thick C-Mn-V forged steel plate including welds was subjected to mechanical and corrosion-fatigue tests and several engineering data useful for the design of offshore structures were obtained. The chemical and mechanical properties of base metal and welds satisfy typical current requirements in the North Sea projects and the heavy wall forged tubular is proved to be applicable to the offshore structures. The scatter of critical cod in the transition temperature range was studied and a new statistical method was presented for estimating the lowest critical cod value. Corrosion-fatigure tests in seawater were conducted on the base metal and heat affected zone (HAZ) of submerged arc welding at a cyclic frequency corresponding to sea wave frequency. No difference in fatigue crack propagation rate was observed between the base metal and HAZ.

Fukuda, T.; Iwadate, T.; Shimazaki, M.

1982-01-01

302

Cosmic Radio Jets  

E-print Network

Extragalactic radio sources, including quasars, are now typically understood as being produced by a pair of nearly symmetric, oppositely directed relativistic jets. While some these sources span megaparsecs, and are thus the largest physically connected structures in the universe, emitting regions identified as jets have now been found on all scales down to fractions of a parsec, and jets appear to be a common element of most (maybe all) types of active galactic nuclei (AGN). We first summarize key observations of different classes of cosmic radio jets, and describe how they may be connected. Theoretical models for the launching and propagation of extragalactic jets are briefly described. All of these models assume a magnetized plasma, which typically amounts to only a small fraction of the accreted gas, is ejected from the vicinity of a supermassive black hole. The extreme complexity of the relevant physics has demanded numerical simulations to examine non-linear effects on the stability of propagating jets, and some recent results from these efforts are summarized.

Paul J. Wiita

2001-03-01

303

Impulse radio: how it works  

Microsoft Academic Search

Impulse radio, a form of ultra-wide bandwidth (UWB) spread-spectrum signaling, has properties that make it a viable candidate for short-range communications in dense multipath environments. This paper describes the characteristics of impulse radio using a modulation format that can be supported by currently available impulse signal technology and gives analytical estimates of its multiple-access capability under ideal multiple-access channel conditions

Moe Z. Win; Robert A. Scholtz

1998-01-01

304

Coherent Cherenkov radio pulses from hadronic showers up to EeV energies  

NASA Astrophysics Data System (ADS)

The Cherenkov radio pulse emitted by hadronic showers of energies in the EeV range in ice is calculated for the first time using full three dimensional simulations of both shower development and the coherent radio pulse emitted as the excess charge develops in the shower. A Monte Carlo, ZHAIRES, has been developed for this purpose combining the high energy hadronic interaction capabilities of AIRES, and the dense media propagation capabilities of TIERRAS, with the precise low energy tracking and specific algorithms developed to calculate the radio emission in ZHS. A thinning technique is implemented to allow the simulation of radio pulses induced by showers up to 10 EeV in ice. The code is validated comparing the results for electromagnetic and hadronic showers to those obtained with GEANT4 and ZHS codes. The contribution to the pulse of other shower particles in addition to electrons and positrons, mainly protons, pions and muons, is found to be below 3% for 10 PeV and above proton induced showers. The characteristics of hadronic showers and the corresponding Cherenkov frequency spectra are compared with those from purely electromagnetic showers. The dependence of the spectra on shower energy and high-energy hadronic model is addressed and parameterizations for the radio emission in hadronic showers in ice are given for practical applications.

Alvarez-Muñiz, Jaime; Carvalho, Washington R.; Tueros, Matías; Zas, Enrique

2012-01-01

305

Phenomenology of magnetospheric radio emissions  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

306

Innovative Antennas and Propagation Studies for MIMO Systems  

Microsoft Academic Search

SUMMARY This paper reviews our recent antennas and propagation studies for MIMO systems. First we introduce a MIMO propagation chan- nel model in which an interesting nature can be found in eigenvalue statis- tics from a practical viewpoint. Then we introduce multi-keyhole model which is an efficient tool for designing a MIMO repeater systems, or MIMO radio-relay systems. For realization

Yoshio Karasawa

2007-01-01

307

Spacecraft Radio Scintillation and Solar System Exploration  

NASA Technical Reports Server (NTRS)

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

Woo, Richard

1993-01-01

308

Ray trace calculation of ionospheric propagation at lower frequencies  

Microsoft Academic Search

The Raytrace\\/Ionospheric Conductivity and Electron Density-Bent-Gallagher model has been revised to make it applicable to ionospheric propagation at low radio frequencies (0.5-5.0 MHz), where the ionosphere and magnetic anisotropy drastically alter propagation paths and provide a severe test of propagation model algorithms. The necessary revisions are discussed, and the model is applied to the problem of ionospheric penetration from a

Michael H. Reilly

2006-01-01

309

Ray trace calculation of ionospheric propagation at lower frequencies  

Microsoft Academic Search

The Raytrace\\/Ionospheric Conductivity and Electron Density–Bent-Gallagher model has been revised to make it applicable to ionospheric propagation at low radio frequencies (0.5–5.0 MHz), where the ionosphere and magnetic anisotropy drastically alter propagation paths and provide a severe test of propagation model algorithms. The necessary revisions are discussed, and the model is applied to the problem of ionospheric penetration from a

Michael H. Reilly

2006-01-01

310

Acoustic Propagation Considerations for Underwater Acoustic Communications Network Development  

E-print Network

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

Zhou, Shengli

311

Multi-lane Vehicle-to-Vehicle Networks with Time-Varying Radio Ranges  

E-print Network

Multi-lane Vehicle-to-Vehicle Networks with Time-Varying Radio Ranges: Information Propagation propagation speed in multi-lane vehicle-to-vehicle networks such as roads or highways. We focus on the impact of time-varying radio ranges and of multiple lanes of vehicles, varying in speed and in density. We assess

Paris-Sud XI, Université de

312

HIGH AMPLITUDE PROPAGATED CONTRACTIONS  

PubMed Central

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

Bharucha, Adil E.

2012-01-01

313

Probing the solar plasma with Mariner radio tracking data  

NASA Technical Reports Server (NTRS)

The range and Doppler radio tracking close to the sun made it possible to measure solar plasma dynamics. These were measured by means of a method known as differenced range versus integrated Doppler, which exploits the opposite change of group and phase velocity as the plasma density changes along the radio raypath. A simple solar plasma propagation model is proposed.

Macdoran, P. F.; Callahan, P. S.; Zygielbaum, A. I.

1971-01-01

314

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

E-print Network

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

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

1997-12-17

315

AUTOMATED RADIO NETWORK DESIGN USING ANT COLONY OPTIMIZATION  

E-print Network

AUTOMATED RADIO NETWORK DESIGN USING ANT COLONY OPTIMIZATION by Jeffrey Allen Sharkey A thesis by each member of the thesis committee and has been found to be satisfactory regarding content, English help as I learned about radio systems and propagation algorithms. I would like to thank Dr. John Paxton

Dyer, Bill

316

Models and solutions for radio irregularity in wireless sensor networks  

Microsoft Academic Search

In this paper, we investigate the impact of radio irregularity on wireless sensor networks. Radio irregularity is a common phenomenon which arises from multiple factors, such as variance in RF sending power and dieren t path losses depending on the direction of propagation. From our experiments, we discover that the variance in received signal strength is largely random; however, it

Gang Zhou; Tian He; Sudha Krishnamurthy; John A. Stankovic

2006-01-01

317

Impact of radio irregularity on wireless sensor networks  

Microsoft Academic Search

In this paper, we investigate the impact of radio irregularity on the communication performance in wireless sensor networks. Radio irregularity is a common phenomenon which arises from multiple factors, such as variance in RF sending power and different path losses depending on the direction of propagation. From our experiments, we discover that the variance in received signal strength is largely

Gang Zhou; Tian He; Sudha Krishnamurthy; John A. Stankovic

2004-01-01

318

EVA Radio DRATS 2011 Report  

NASA Technical Reports Server (NTRS)

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.

Swank, Aaron J.; Bakula, Casey J.

2012-01-01

319

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

320

A low cost multi-media radio system  

Microsoft Academic Search

An alternative, or supplemental, approach to automatic link establishment (ALE) radios is to combine modern, commercially available packet radio technology with an understanding of channel requirements to produce a low-cost multimedia radio (MMR). A prototype unit has been demonstrated to provide two-way, half-duplex packetized message communication via skywave propagation when the operating frequency is below the maximum usable frequency (MUF)

Steven C. Merrill; Anne K. McDonough; S. W. Symes; Robert I. Desourdis Jr

1991-01-01

321

A Study of Type II Radio Bursts to Map the Alfvén Speed profile in the Inner Heliosphere  

NASA Astrophysics Data System (ADS)

It is well accepted that interplanetary Type II radio bursts are the manifestations of electron acceleration in shocks driven by propagating of coronal mass ejections (CMEs) traveling faster than the characteristic local plasma speed. The slow solar wind (in the equatorial plane) becomes super-Alfvénic at the so-called 'Alfvén point', which is thought to occur at a distance of around 10 Rsun. However, observationally this has not been confirmed and furthermore, it is likely that the Alfvén point will vary considerably due to the changing conditions of the ambient medium, over the solar cycle. We present results from an investigation of coronal and interplanetary type II radio bursts to probe the changing plasma parameters in the ambient medium. A prominent feature of type II radio bursts, is the intermittency of the observed emission across the metric, decametric and kilometric frequency ranges, as the shock propagates to greater distances. This can be attributed to changes in both the shock driver and to the conditions in the ambient medium. Using radio observations from e.g. STEREO/WAVES and WIND/WAVES we will determine the distance of the observed type II emission and the speed of the associated shock. By establishing regions of the corona and interplanetary medium that are predisposed to shock formation, we map out the profile of the local Alfvén speed.

Martinez Oliveros, J.; Bain, H. M.; Sundkvist, D. J.; Bale, S. D.; Krucker, S.

2013-12-01

322

Universal scaling of forest fire propagation  

E-print Network

In this paper we use a variant of the Watts-Strogatz small-world model to predict wildfire behavior near the critical propagation/nonpropagation threshold. We find that forest fire patterns are fractal and that critical exponents are universal, which suggests that the propagation/nonpropagation transition is a second-order transition. Universality tells us that the characteristic critical behaviour of propagation in real (amorphous) forest landscapes can be extracted from the simplest network model.

Bernard, Porterie; Pierre, Clerc Jean; Nouredine, Zekri; Zekri, Lotfi

2008-01-01

323

HF groundwave and skywave propagation  

NASA Astrophysics Data System (ADS)

The principles of HF ground- and skywave propagation are reviewed with regard to regular conditions as well as anomalous phenomena which may effect the signal characteristics and thus may have an influence on the performance of digital communication systems. Particular consideration is given to the statistics of signal fading as a basis for system design.

Hortenbach, Klaus-Juergen

1986-10-01

324

HF groundwave and skywave propagation  

Microsoft Academic Search

The principles of HF ground- and skywave propagation are reviewed with regard to regular conditions as well as anomalous phenomena which may effect the signal characteristics and thus may have an influence on the performance of digital communication systems. Particular consideration is given to the statistics of signal fading as a basis for system design.

Klaus-Juergen Hortenbach

1986-01-01

325

AURORAL RADIO EMISSION FROM STARS: THE CASE OF CU VIRGINIS  

SciTech Connect

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

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

2011-09-20

326

The Radio JOVE Project - Shoestring Radio Astronomy  

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

327

RADIO ASTRONOMY OBSERVATORYNAT IONA TI TLE: VANE TYPE POLARIZATION CONVERTER  

E-print Network

RADIO ASTRONOMY OBSERVATORYNAT IONA TI TLE: VANE TYPE POLARIZATION CONVERTER AUTHOR (S) C1 BROCKWAY perpendicular to vanes Propagation direction #12;= c= 1)(2. 2 2. Phase Shift (1)1_ = d = (w/vc) d (radians) (1 spacing so v > v c ). = radian frequency. = propagation constant (Pi- (P11 E Acp = wd (l/vc - 1/v). Acp

Groppi, Christopher

328

Linearized Zverev Transform and its application for modeling radio occultations  

Microsoft Academic Search

The multiple phase screens technique is often used for modeling wave propagation and radio occultation sounding of the atmosphere. The last step of this procedure is the propagation from the last phase screen to the observation orbit of the spaceborne receiver. This step was formerly performed by the computation of multiple diffractive integrals, which impairs the numerical efficiency of the

M. E. Gorbunov; K. B. Lauritsen

2007-01-01

329

Cassini/RPWS: A low frequency radio imager at Saturn  

NASA Astrophysics Data System (ADS)

The High Frequency Receiver (HFR) of the Radio and Plasma Waves Science experiment (RPWS) onboard Cassini is a sensitive, and versatile radio instrument. Although the radio antenna connected to this instrument have no intrinsic directivity, the HFR measurements can provide instantaneous direction of arrival, flux density and polarization degree of the observed radio waves. Hence, the HFR can be described as an full-sky radio imager. As the instrument provides direction of arrival, radio sources can be located with some assumption on the propagation between the source and the observer. Hence, it is possible to produce radio source maps and correlate them with observations at other wavelengths, such as UV or IR observations of the auroral regions of Saturn. The flux and polarization measurements together with the time-frequency shape of the radio emissions can also be used to identify the radio emission processes. We present a review of the results of the Cassini/RPWS/HFR observations since its arrival at Saturn in 2004: interpretation of the radio arc shapes and equatorial shadow zones; in-situ observations in the radio source region; comparison with other wavelengths and particle measurements; confirmation of the Cyclotron Maser Instability (CMI) as the main emission mechanism for auroral radio emissions; monitoring of the radio emission variability in time and location, etc.

Cecconi, Baptiste; Lamy, Laurent; Zarka, Philippe

2014-05-01

330

INVITED PAPER, IEEE PIMRC'97 HELSINKI, FINLAND. 0 Impulse Radio  

E-print Network

INVITED PAPER, IEEE PIMRC'97 ­ HELSINKI, FINLAND. 0 Impulse Radio Robert A. Scholtz and Moe Z. Win, Los Angeles, CA 90089-2565 USA Abstract Impulse radio, a form of ultra-wide band signaling, has. This paper describes the characteristics of impulse radio, gives analytical estimates of its multiple access

Southern California, University of

331

Ionospheric wave and irregularity measurements using passive radio astronomy techniques  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

332

Measurement techniques for UMTS signals radiated by radio base stations.  

PubMed

In the most European countries radio coverage for the third radio mobile generation. i.e, the UMTS (Universal Mobile Telecommunications System), will soon be started. In the past few years, national laws specifying limits on exposure to electromagnetic fields have drawn much attention on electromagnetic test bed and measurement procedures for radio mobile equipment/systems. An overview is given of the UMTS system, showing the main characteristics of the radio access network UTRAN (UMTS Terrestrial Radio Access Network). An analysis is also provided as to the measurement techniques and related instrumentation for the electric field intensity radiated by a UMTS radio station. PMID:11878424

Buscaglia, F; Gianola, P

2001-01-01

333

Over-the-Horizon Anomalous VHF Propagation and Earthquake Precursors  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

334

Characteristics and Time-Dependent Instability of Ga-Doped ZnO Thin Film Transistor Fabricated by Radio Frequency Magnetron Sputtering  

Microsoft Academic Search

We report on the fabrication and electrical characteristics of Ga-doped ZnO thin film transistors (TFTs). Low Ga-doped (0.7wt%) ZnO thin films were deposited on SiO2\\/p-Si substrates by rf magnetron sputtering. The GZO TFTs show a mobility of 1.76 cm2\\/V·s, an on\\/off ratio of 1.0 × 106, and a threshold voltage of 35 V. The time-dependent instability of the TFT is

Huang Hai-Qin; Sun Jian; Liu Feng-Juan; Zhao Jian-Wei; Hu Zuo-Fu; Li Zhen-Jun; Zhang Xi-Qing; Wang Yong-Sheng

2011-01-01

335

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)

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.

Davarian, Faramaz (editor)

1992-01-01

336

Mesoscale characteristics  

Microsoft Academic Search

The spatial length, time, and propagation characteristics of the ocean mesoscale variability are examined throughout the globe. Sea surface height (SSH) variations from a combination of the Geosat Exact Repeat Mission, ERS-1, ERS-2, and TOPEX\\/Poseidon altimeter satellites are used to compute the observed covariance of the mesoscale. The mesoscale is defined as the residual SSH after removing a filtered large-scale

G. A. Jacobs; C. N. Barron; R. C. Rhodes

2001-01-01

337

S-Band propagation measurements  

NASA Astrophysics Data System (ADS)

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.

Briskman, Robert D.

1994-08-01

338

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)

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.

Davarian, Faramaz (editor)

1994-01-01

339

Moon exploration: lunar radio observatory  

NASA Astrophysics Data System (ADS)

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

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

340

Radio pulsars: the search for truth  

E-print Network

It was as early as the 1980s that A V Gurevich and his group proposed a theory to explain the magnetosphere of radio pulsars and the mechanism by which they produce coherent radio emission. The theory has been sharply criticized and is currently rarely mentioned when discussing the observational properties of radio pulsars, even though all the criticisms were in their time disproven in a most thorough and detailed manner. Recent results show even more conclusively that the theory has no internal inconsistencies. New observational data also demonstrate the validity of the basic conclusions of the theory. Based on the latest results on the effects of wave propagation in the magnetosphere of a neuron star, we show that the developed theory does indeed allow quantitative predictions of the evolution of neutron stars and the properties of the observed radio emission.

Beskin, V S; Philippov, A A

2013-01-01

341

Radio tracking of solar energetic particles through interplanetary space.  

NASA Technical Reports Server (NTRS)

Satellite observations of traveling solar radio bursts provide information about the propagation of energetic solar particles through interplanetary space. This information leads to data on the solar wind density and gross magnetic field configuration over distances of 1 AU. By placing a radio telescope well above the ionosphere it is possible to observe the radio emission down to frequencies that correspond to emission at distances of the order of 1 AU. The observations reported provide the first 'radio picture' over 1 AU of the spiral magnetic field configuration in interplanetary space.

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

1972-01-01

342

The radio lighthouse CU Virginis: the spindown of a single main sequence star  

E-print Network

The fast rotating star CU Virginis is a magnetic chemically peculiar star with an oblique dipolar magnetic field. The continuum radio emission has been interpreted as gyrosyncrotron emission arising from a thin magnetospheric layer. Previous radio observations at 1.4 GHz showed that a 100% circular polarized and highly directive emission component overlaps to the continuum emission two times per rotation, when the magnetic axis lies in the plane of the sky. This sort of radio lighthouse has been proposed to be due to cyclotron maser emission generated above the magnetic pole and propagating perpendicularly to the magnetic axis. Observations carried out with the Australia Telescope Compact Array at 1.4 and 2.5 GHz one year after this discovery show that this radio emission is still present, meaning that the phenomenon responsible for this process is steady on a timescale of years. The emitted radiation spans at least 1 GHz, being observed from 1.4 to 2.5 GHz. On the light of recent results on the physics of the magnetosphere of this star, the possibility of plasma radiation is ruled out. The characteristics of this radio lighthouse provides us a good marker of the rotation period, since the peaks are visible at particular rotational phases. After one year, they show a delay of about 15 minutes. This is interpreted as a new abrupt spinning down of the star. Among several possibilities, a quick emptying of the equatorial magnetic belt after reaching the maximum density can account for the magnitude of the breaking. The study of the coherent emission in stars like CU Vir, as well as in pre main sequence stars, can give important insight into the angular momentum evolution in young stars. This is a promising field of investigation that high sensitivity radio interferometers such as SKA can exploit.

C. Trigilio; P. Leto; G. Umana; C. S. Buemi; F. Leone

2007-11-21

343

Uranus as a radio source  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

344

Decimetric radio dot emissions  

NASA Astrophysics Data System (ADS)

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

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

2008-11-01

345

Nonlinear Characteristics of Wave Propagation over Vegetation  

E-print Network

The attenuation of wave energy by submerged or near-emergent coastal vegetation is one of the prominent methods of energy dissipation in areas with significant presence of wetlands. In this thesis, the nature of this dissipation in nearshore random...

Venkattaramanan, Aravinda

2014-04-28

346

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)

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.

Golshan, Nasser (Editor)

1997-01-01

347

Understanding tropscatter propagation  

NASA Astrophysics Data System (ADS)

Although troposcatter communications systems have shortcomings, this transmission scheme has found consistent use in several applications. Troposcatter propagation is discussed with emphasis on theory, characteristics, and prediction tools. Theoretical understanding of the troposcatter propagation mechanism is rooted in atmospheric phenomena, specifically--refractivity and turbulence. Two modes of transmission exist: incoherent scatter, if refractivity irregularities exist as turbulent blobs, and quasi-coherent scatter, if irregularities arrange themselves in layers. Frequency and meteorological parameters define the dominant mechanism. One can expect received signal levels to exhibit distance and frequency dependence; short and long-term fading; aperture-to-medium coupling loss; and diurnal, seasonal, climatic, and meteorological variations. Diversity techniques are indispensable in thwarting short-term fading. Atmospheric multipath is known to limit analog system bandwidths yet digital systems are prone to the related delay spread phenomenon which causes intersymbol interference. Adaptive processing is used to overcome this problem and can further improve digital performance through implicit diversity. Most troposcatter prediction methods are rooted in empirical expressions. Unfortunately, all the methods suffer shortcomings with reliance on surface refractivity and incorrect coupling loss calculations topping the list.

Reynolds, Joseph Henderson

348

13 Edgar Nett Mobile Computer Communication SS'10 Signal propagation ranges  

E-print Network

Multiplexing medium characteristics Basic schemes Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM) #12;17 Edgar Nett Mobile Computer Communication SS'10 Modulation and demodulation synchronization decision digital dataanalog demodulation radio carrier analog baseband signal 101101001 radio

349

Wave propagation in the magnetosphere of Jupiter  

NASA Technical Reports Server (NTRS)

A systematic procedure is developed for identifying the spatial regimes of various modes of wave propagation in the Jupiter magnetosphere that may be encountered by flyby missions. The Clemmow-Mullaly-Allis (CMA) diagram of plasma physics is utilized to identify the frequency regimes in which different modes of propagation occur in the magnetoplasma. The Gledhill model and the Ioannidis and Brice model of the magnetoplasma are summarized, and configuration-space CMA diagrams are constructed for each model for frequencies from 10 Hz to 1 MHz. The distinctive propagation features, the radio noise regimes, and the wave-particle interactions are discussed. It is concluded that the concentration of plasma in the equatorial plane makes this region of vital importance for radio observations with flyby missions. Local radio noise around the electron cyclotron frequency will probably differ appreciably from its terrestrial counterpart due to the lack of field-line guidance. Hydromagnetic wave properties at frequencies near the ion cyclotron frequency and below will probably be similar to the terrestrial case.

Liemohn, H. B.

1972-01-01

350

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

351

Perpendicular propagation of magnetosonic waves  

NASA Astrophysics Data System (ADS)

Azimuthal and radial propagation characteristics of perpendicularly propagating fast magnetosonic waves in an axis-symmetrical medium with the presence of plasmapause is investigated analytically based on Snell's law. We find that Q = nr sin ? is conserved during the propagation, where n is wave refractive index, r is geo-centered distance, and ? is wave azimuthal angle with zero pointing radially outward. The radial range of wave propagation can be determined by comparing Q and the radial profile of nr.Trapped waves, which are bounded in a narrow radial range but migrate azimuthally and even circularly, are identified inside the plasmapause over a broad range of wave azimuthal angles and over a broad range of wave frequencies from the proton gyrofrequency to the lower hybrid resonance frequency. In contrast untrapped waves launched inside and outside the plasmasphere can travel azimuthally 0-4 hrs and 0-7 hrs in local times respectively. The substantial radial and azimuthal propagation may account for the presence of magnetosonic waves away from the source region.

Chen, Lunjin; Thorne, Richard M.

2012-07-01

352

X-ray Dips Followed by Superluminal Ejections as Evidence for An Accretion Disc Feeding the Jet in A Radio Galaxy  

NASA Technical Reports Server (NTRS)

Accretion onto black holes is thought to power the relativistic jets and other high-energy phenomena in both active galactic nuclei (AGNs) and the "microquasar" binary systems located in our Galaxy. However, until now there has been insufficient multifrequency monitoring to establish a direct observational link between the black hole and the jet in an AGE. This contrasts with the case of microquasars, in which superluminal features appear and propagate down the radio jet shortly after sudden decreases in the X-ray flux. Such an X-ray dip is most likely caused by the disappearance of a section of the inner accretion disc, part of which falls past the event horizon and the remainder of which is injected into the jet. This infusion of energy generates a disturbance that propagates down the jet, creating the appearance of a superluminal bright spot. Here we report the results of three years of intensive monitoring of the X-ray and radio emission of the Seyfert-like radio galaxy 3C 120. As in the case of microquasars, dips in the X-ray emission are followed by ejections of bright superluminal knots in the radio jet. Comparison of the characteristic length and time scales allows us to infer that the rotational states of the black holes in these two objects are different.

Marscher, Alan P.; Jorstad, Svetlana G.; Gomez, Jose-Luis; Aller, Margo F.; Terasranta, Harri; Lister, Matthew L.; Stirling, Alastair, M.

2002-01-01

353

An Emergency Message Propagation Method in Highway Traffic  

Microsoft Academic Search

This paper presents an intelligent vehicle safety system, constructed by exchanging emergency-related information such as\\u000a urgency stop, traffic accident, and obstacles between vehicles. In the majority of vehicle safety communication applications,\\u000a an emergency message is propagated in the form of broadcasts. However, this causes numerous problems, such as massive radio\\u000a collision, multi-hop propagation and fast relay. This paper presents a

Sukdea Yu; Moonkun Lee; Gihwan Cho

2006-01-01

354

A review of ionospheric effects on Earth-space propagation  

NASA Technical Reports Server (NTRS)

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.

Klobuchar, J. A.

1984-01-01

355

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)

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.

Davarian, Faramaz (editor)

1991-01-01

356

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)

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.

Davarian, Faramaz (editor)

1990-01-01

357

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 49, NO. 12, DECEMBER 2001 1683 Atmospheric Transmission at Microwaves (ATM)  

E-print Network

that improves in many respects widely used older models such as the microwave propagation model (MPM) [1 suitable for submillimeter astronomy. Index Terms--Atmospheric measurements, microwave radio propagationIEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 49, NO. 12, DECEMBER 2001 1683 Atmospheric

Pardo-Carrión, Juan R.

358

Propagating shocks in the corona  

NASA Astrophysics Data System (ADS)

High resolution observations performed with the Decimeter spectrograph and the multichannel receiver at Nancay were analyzed in the range of 25-75 MHz. Sixty Type II bursts were selected. In this frequency range, type II events are generally associated with other radio emissions (such as storms of type III-U-I bursts); they are preceeded or followed by groups of U-bursts. One third of type II events show a nonuniform frequency drift, usually a steep decrease followed by an abrupt increase. This phenomenon can be explained by the propagation of an extended disturbance through the ambient corona when the density gradient is enhanced. An empirical coronal model is proposed to interpret these observations. The observations at fixed frequency of Type II bursts including fundamental and harmonic components are analyzed. It is shown that the spectrum of the intensity fluctuations differs with the fundamental and the harmonic components. The origin of these differences is discussed.

Leblanc, Yolanda

1987-09-01

359

Radio frequency detection assembly and method for detecting radio frequencies  

DOEpatents

A radio frequency detection assembly is described and which includes a radio frequency detector which detects a radio frequency emission produced by a radio frequency emitter from a given location which is remote relative to the radio frequency detector; a location assembly electrically coupled with the radio frequency detector and which is operable to estimate the location of the radio frequency emitter from the radio frequency emission which has been received; and a radio frequency transmitter electrically coupled with the radio frequency detector and the location assembly, and which transmits a radio frequency signal which reports the presence of the radio frequency emitter.

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

2010-03-16

360

Compatibility analysis of in-band digital radio systems in interference channel environment  

Microsoft Academic Search

Many countries today face converting their analog radio broadcasting to digital service. Since the in-band digital radio systems are used in the existing analog FM frequency band, compatibility and robustness is very important characteristics of the digital radio systems. In this paper, we evaluate the performances of HD-Radio and DRM+ which are in-band digital radio broadcasting techniques in the various

Myung-Sun Baek; So-Ra Park; Yong-Hoon Lee; Gun Kim; Seokhyun Yoon; Kyung-Tek Lee; Sang-Woon Lee; Soo-In Lee; Yong-Tae Lee

2010-01-01

361

A review of ionospheric effects on Earth-space propagation  

Microsoft Academic Search

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

J. A. Klobuchar

1984-01-01

362

The universal propagator  

NASA Technical Reports Server (NTRS)

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

Klauder, John R.

1993-01-01

363

Propagation modeling of moist air and suspended water/ice particles at frequencies below 1000 GHz  

NASA Astrophysics Data System (ADS)

Propagation characteristics of the atmosphere are modeled for the frequency range from 1 to 1000 GHz (1 THz) by the modular millimeter-wave propagation model MPM. Refractivity spectra of the main natural absorbers (i.e., oxygen, water-vapor, suspended droplets and ice particles) are computed from known meteorological variables. The primary contributions of dry air come from 44 O2 lines. Results from extensive 60-GHz laboratory measurements of the pressure-broadened O3 spectrum were applied to update the line data base. The water-vapor module considers 34 local H2O lines plus continuum contributions from the H2O spectrum above 1 THz, which are formulated as wing response of a pseudo-line centered at 1.8 THz Cloud/fog effects are treated with the Rayleigh approximation employing revised formulations for the permittivities of water and ice. The influence of the Earth's magnetic field on O2 absorption line becomes noticeable at altitudes between 30 and 120 km. Anisotropic medium properties result, which are computed by the Zeema propagation model ZPM. Here the elements of a complex refractivity tensor are determined in the vicinity (plus or minus 10 MHz) of O2 line centers and their effect on the propagation of plane, polarized radiowaves is evaluated. A spherically stratified (0-130 km) atmosphere provides the input for the codes MPM and ZPM in order to analyze transmission and emission properties of radio paths. Height profiles of air and water vapor densities and of the geocoded magnetic field are specified. ZPM predicts polarization- and direction-dependent propagation through the mesosphere. Emission spectra of the 9+ line (61150 plus or minus 3 MHz) for paths with tangential heights ranging from 30 to 125 km are consistent with data measured by the shuttle-based millimeter-wave limb sounder MAS.

Liebe, H. J.; Hufford, G. A.; Cotton, M. G.

1993-11-01

364

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

Microsoft Academic Search

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

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

1998-01-01

365

An Introduction to Radio Frequency Engineering  

NASA Astrophysics Data System (ADS)

Using an easily understood approach combined with numerous worked examples, illustrations and homework problems, this textbook focuses on minimizing the mathematics needed to grasp radio frequency engineering. The book includes broad coverage of RF systems, circuit design, antennas, propagation and digital techniques. Written for upper level undergraduate courses, it will also provide an excellent introduction to the subject for graduate students, researchers and practicing engineers.

Coleman, Christopher

2004-06-01

366

Improved Estimation Of Delays In Radio Interferometry  

NASA Technical Reports Server (NTRS)

Report describes status of mathematical model of delays in propagation of radio signals that originate at extra-galactic or other distant sources and received at widely separated terrestrial antennas engaged in very-long-baseline interferometry. Implemented in multiparameter estimation computer program MODEST. Needed, in applications as geodynamics and astronomy, to extract significant parameters from observed signal delays. Program and present report are updated versions of MASTERFIT program and accompanying report.

Sovers, Ojars J.

1993-01-01

367

Possible radio emission mechanism for pulsars  

NASA Technical Reports Server (NTRS)

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

Kovalev, Y. A.

1979-01-01

368

Propagation Constraints in Elephant Localization Using an Acoustic Sensor Network  

E-print Network

. Recently, technological progression leads to use radio and Global Positioning Systems (GPS) collars carried out have shown that these elephant calls travel over a range of at least two kilometres [5 as longitudinal waves and the propagation is affected by the properties of the medium. For instance

Halgamuge, Malka N.

369

“Real world” FTTH optical-to-radio interface performance for bi-directional multi-format OFDM wireless signal transmission  

Microsoft Academic Search

The optical-to-radio and radio-to-optical interfaces in fiber-to-the-home access networks were evaluated for LTE, WiMAX and UWB simultaneous distribution. Successful bi- directional transmission was achieved after 20.2 km standard single mode fiber and 3 m radio propagation. OCIS codes: (060.0060) Fiber optics and optical communications; (060.5625) Radio frequency photonics

Maria Morant; Terence Quinlan; Stuart Walker; Roberto Llorente

2011-01-01

370

Energy Efficient Radio Resource  

E-print Network

Energy Efficient Radio Resource Management in a Coordinated Multi-Cell Distributed Antenna System Omer HALILOGLU Introduction System Model Performance Evaluation Conclusion References Energy Efficient Hacettepe University 5 September 2014 Omer HALILOGLU (Hacettepe University) Energy Efficient Radio Resource

Yanikomeroglu, Halim

371

Resonance and Radio  

ERIC Educational Resources Information Center

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

Starrett, Malin J.

2008-01-01

372

Radio Diaries on National Public Radio (NPR)  

NSDL National Science Digital Library

Radio Diaries is a nonprofit radio production company which looks "to find extraordinary stories in ordinary places, to create original and moving first-person documentaries - true radio verite - from voices that are rarely heard." And that it does. Radio Diaries staff train all kinds of people -- from teenagers to the elderly -- to become reporters. These fledgling reporters create tapes about their area of interest, tell their stories, and send their product back to Radio Diaries. A collaborative editing process then ensues, and the end product is aired as part of National Public Radio's All Things Considered. The Radio Diaries site brings together an amazing range of recorded stories divided into adult and teen areas. Two examples of diaries on the site include a piece by a teenager from New York City with Tourette's Syndrome as well as the story of the last two known remaining Civil War widows whose husbands fought on opposing sides of the war. Users can listen to the recordings using RealPlayer, or they can read transcripts; other materials are occasionally included too. The site encourages users to send in their own story ideas and will provide even more support for creative ventures with their Handbook for Teen Reporters (available in January of 2000). The site also has a store section where tapes of various radio diaries are for sale.

373

Radio Detection of Radio-Quiet Galaxies  

E-print Network

We investigate the radio emission of ~185,000 quiescent (optically unclassifiable) galaxies selected from the Sloan Digital Sky Survey (SDSS). By median-stacking FIRST cutouts centered on the optically-selected sources, we are able to reach flux densities down to the 10s of microJy. The quiescent galaxy sample is composed of two subgroups inhabiting vastly different regimes: those targeted for the SDSS MAIN Galaxy Sample (~55%), and those targeted for the Luminous Red Galaxy (LRG) sample (~45%). To investigate the star-formation rates (SFRs) of these quiescent galaxies, we calibrate a radio-SFR conversion using a third sample of star-forming galaxies. Comparing this SFR-indicator with indicators in the optical and UV, we derive conflicting SFR estimates for the MAIN sample quiescent galaxies. These radio-derived SFRs intersect those calculated using the 4000-Angstrom break (D4000) around an SFR of 1 Msun/yr and agree to within a factor of 3 over the range of SFRs. However, we find that the radio-derived SFRs are too high relative to the SFRs estimated for similar populations of galaxies using analysis of UV emission, implying either contamination of the radio by Active Galactic Nuclei (AGN) or incomplete dust modeling. If AGN activity is dominant in these galaxies, then a relation between AGN radio luminosity and galaxy mass is required to explain the observed trends. For the LRGs, on the other hand, we find the radio luminosity to be independent of SFR as derived from D4000, indicating an AGN component dominates their radio emission. AGN-based radio emission often implies the existence of radio jets, providing evidence of a mechanism for low-level feedback in these quiescent LRGs. (Abridged)

J. A. Hodge; R. H. Becker; R. L. White; W. H. de Vries

2008-06-25

374

The software radio architecture  

Microsoft Academic Search

As communications technology continues its rapid transition from analog to digital, more functions of contemporary radio systems are implemented in software, leading toward the software radio. This article provides a tutorial review of software radio architectures and technology, highlighting benefits, pitfalls, and lessons learned. This includes a closer look at the canonical functional partitioning of channel coding into antenna, RF,

J. Mitola

1995-01-01

375

Radio search for exoplanets  

E-print Network

Radio search for exoplanets Philippe Zarka LESIA, Observatoire de Paris/CNRS, Meudon philippe.zarka) [Zarka et al., 1997; Zarka, , 2004, 2007] #12;· Low-frequency radio observations of exoplanets;Aurorae #12;Aurorae #12;Magnetospheric (auroral) radio emissions [Zarka, 1998] #12;Properties of auroral

Demoulin, Pascal

376

Introduction Big Radio Data  

E-print Network

Introduction VLBI Pulsars Summary Big Radio Data Ue-Li Pen CITA, UofT, CIFAR July 3, 2014U. Pen Big Radio Data #12;Introduction VLBI Pulsars Summary Overview History VLBI Processing Future U. Pen Big signal processing U. Pen Big Radio Data #12;Introduction VLBI Pulsars Summary VLBI Current experiments

Prodiæ, Aleksandar

377

Extragalactic Radio Sources  

ERIC Educational Resources Information Center

Discusses new problems arising from the growing observational data through radio telescope arrays, involving the origin of radio sources, apparent superluminal velocities, conversion of radio sources to relativistic particles, and the nature of compact opaque and extended transparent sources. New physics may be needed to answer these cosmological…

Kellerman, Kenneth I.

1973-01-01

378

Effect of magnetic storms (substorms) on HF propagation: A review  

NASA Astrophysics Data System (ADS)

The manifestations of the so-called main ionospheric effect during geomagnetic storms (substorms) in the character of decameter-wave propagation are analyzed. On HF radio paths, the main effect is observed as variations in the signal amplitude and the MOF-LOF working frequency band similarly to the critical frequency of the ionospheric F2 layer. Specifically, these parameters increase before the disturbance active phase, decrease during the active phase, and increase again after this phase. The propagation outside the great circle arc, the change in the propagation processes, and the HF radio noise behavior were also considered on these paths during storms (substorms). It is assumed that the storm (substorm) development onset can be predicted.

Blagoveshchenskii, D. V.

2013-07-01

379

Ray trace calculation of ionospheric propagation at lower frequencies  

NASA Astrophysics Data System (ADS)

The Raytrace/Ionospheric Conductivity and Electron Density-Bent-Gallagher model has been revised to make it applicable to ionospheric propagation at low radio frequencies (0.5-5.0 MHz), where the ionosphere and magnetic anisotropy drastically alter propagation paths and provide a severe test of propagation model algorithms. The necessary revisions are discussed, and the model is applied to the problem of ionospheric penetration from a source below the ionosphere to a receiver above the ionosphere. It is necessary to include the electron collision frequency in the Appleton-Hartree index of refraction in order to permit ionospheric penetration for radio frequencies below the maximum plasma frequency (e.g., whistler modes). The associated reformulation of the ray trace equations for a complex index of refraction is straightforward. Difficulties with numerical methods are cited for the lowest frequencies, and future improvements are indicated.

Reilly, Michael H.

2006-10-01

380

Sub-Fresnel-scale vertical resolution in atmospheric profiles from radio occultation  

Microsoft Academic Search

We have investigated the vertical resolution that can be achieved in atmospheric profiles retrieved from radio occultation measurements. The results are based on forward simulations of radio wave propagation through model atmospheres using the multiple phase-screen method. We find that profiles retrieved through Abel inversion, the standard algorithm derived from geometrical optics, have a vertical resolution that is diffraction-limited, as

E. Tuna Karayel; David P. Hinson

1997-01-01

381

Extra Low-Frequency Terrestrial Radio-Wave Field Calculations with the Zonal Harmonics Series  

Microsoft Academic Search

Use of the zonal harmonics series for calculating the terrestrial wave guide fields directly is described. The analysis is extended to include radio waves propagating into sea water or below the earth's surface. A sample calculation of ELF radio waves is analyzed into a direct wave and a wave that has traveled the circumference of the earth. The location of

J. Ralph Johler; Richard L. Lewis

1969-01-01

382

Multi-spacecraft Observations of type III radio bursts and their associated Langmuir waves  

Microsoft Academic Search

The radio signatures of flare accelerated electron beams in the corona and interplanetary medium are the fast drifting emission features called type III radio bursts. The production of these bursts involves the generation of high levels of Langmuir waves excited by the flare accelerated electron beams propagating along open field lines, and their subsequent conver-sion into electromagnetic radiation at the

Thejappa Golla; Robert MacDowall

2010-01-01

383

Atmospheric sounding by GNSS radio occultation: An analysis of the negative refractivity bias using CHAMP observations  

Microsoft Academic Search

Abstract. Validation studies of current GPS radio occultation experiments using meteorological analyses consistently report on a negative refractivity bias in the lower troposphere. It is shown that refractivity profiles obtained from Doppler-inverted bending angle profiles not only deviate significantly within zones of multipath propagation but also depend on the selected end point of the occultation signal in the Earth’s radio

G. Beyerle; S. Sokolovskiy; J. Wickert; T. Schmidt

384

The Giant Metrewave Radio Telescope  

NASA Astrophysics Data System (ADS)

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

Nityananda, R.

2003-05-01

385

Voyager planetary radio astronomy studies  

NASA Technical Reports Server (NTRS)

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.

Staelin, David H.; Eikenberry, Stephen S.

1993-01-01

386

Low-frequency radio emissions at Neptune  

NASA Technical Reports Server (NTRS)

The Voyager 2 plasma wave receiver detected weak radio emissions from Neptune's magnetosphere in the frequency range of 3 - 60 kHz. The emissions occurred in bursts lasting for typically 1.5 hours, often occurring twice per planetary rotation. Most of these radio bursts were detected within several degrees of the magnetic equatorial plane. During the passage through the magnetosphere, electrostatic upper hybrid resonance bands were observed close to the magnetic equator in conjunction with intensifications of the radio emissions at frequencies close to and above the upper hybrid bands. Further, near closest approach, the radio emissions were observed to cross the right-hand cutoff frequency with no apparent attenuation. It is concluded that the Neptunian radio emissions below about 60 kHz are produced by mode conversion from the upper hybrid waves and propagate in the ordinary mode into beams within about 12 deg of the magnetic equator. There is also evidence of an extraordinary mode emission at about 60 kHz which is apparently generated by an entirely different source from the escaping continuum radiation.

Kurth, W. S.; Gurnett, D. A.; Cairns, I. H.; Barbosa, D. D.; Poynter, R. L.

1990-01-01

387

Classification of neocortical interneurons using affinity propagation  

PubMed Central

In spite of over a century of research on cortical circuits, it is still unknown how many classes of cortical neurons exist. In fact, neuronal classification is a difficult problem because it is unclear how to designate a neuronal cell class and what are the best characteristics to define them. Recently, unsupervised classifications using cluster analysis based on morphological, physiological, or molecular characteristics, have provided quantitative and unbiased identification of distinct neuronal subtypes, when applied to selected datasets. However, better and more robust classification methods are needed for increasingly complex and larger datasets. Here, we explored the use of affinity propagation, a recently developed unsupervised classification algorithm imported from machine learning, which gives a representative example or exemplar for each cluster. As a case study, we applied affinity propagation to a test dataset of 337 interneurons belonging to four subtypes, previously identified based on morphological and physiological characteristics. We found that affinity propagation correctly classified most of the neurons in a blind, non-supervised manner. Affinity propagation outperformed Ward's method, a current standard clustering approach, in classifying the neurons into 4 subtypes. Affinity propagation could therefore be used in future studies to validly classify neurons, as a first step to help reverse engineer neural circuits. PMID:24348339

Santana, Roberto; McGarry, Laura M.; Bielza, Concha; Larrañaga, Pedro; Yuste, Rafael

2013-01-01

388

Classification of neocortical interneurons using affinity propagation.  

PubMed

In spite of over a century of research on cortical circuits, it is still unknown how many classes of cortical neurons exist. In fact, neuronal classification is a difficult problem because it is unclear how to designate a neuronal cell class and what are the best characteristics to define them. Recently, unsupervised classifications using cluster analysis based on morphological, physiological, or molecular characteristics, have provided quantitative and unbiased identification of distinct neuronal subtypes, when applied to selected datasets. However, better and more robust classification methods are needed for increasingly complex and larger datasets. Here, we explored the use of affinity propagation, a recently developed unsupervised classification algorithm imported from machine learning, which gives a representative example or exemplar for each cluster. As a case study, we applied affinity propagation to a test dataset of 337 interneurons belonging to four subtypes, previously identified based on morphological and physiological characteristics. We found that affinity propagation correctly classified most of the neurons in a blind, non-supervised manner. Affinity propagation outperformed Ward's method, a current standard clustering approach, in classifying the neurons into 4 subtypes. Affinity propagation could therefore be used in future studies to validly classify neurons, as a first step to help reverse engineer neural circuits. PMID:24348339

Santana, Roberto; McGarry, Laura M; Bielza, Concha; Larrañaga, Pedro; Yuste, Rafael

2013-01-01

389

The Transient Radio Sky  

NASA Astrophysics Data System (ADS)

The high time-resolution radio sky represents unexplored astronomical territory where the discovery potential is high. In this thesis I have studied the transient radio sky, focusing on millisecond scales. As such, this work is concerned primarily with neutron stars, the mostpopulous member of the radio transient parameter space. In particular, I have studied the well known radio pulsars and the recently identified group of neutron stars which show erratic radio emission, known as RRATs, which show radio bursts every few minutes to every few hours. When RRATs burst onto the scene in 2006, it was thought that they represented a previously unknown, distinct class of sporadically emitting sources. The difficulty in their identification implies a large underlying population, perhaps larger than the radio pulsars. The first question investigated in this thesis was whether the large projected population of RRATs posed a problem, i.e. could the observed supernova rate account for so many sources. In addition to pulsars and RRATs, the various other known neutron star manifestations were considered, leading to the conclusion that distinct populations would result in a `birthrate problem'. Evolution between the classes could solve this problem -- the RRATs are not a distinct population ofneutron stars.Alternatively, perhaps the large projected population of RRATs is an overestimate. To obtain an improved estimate, the best approach is to find more sources. The Parkes Multi-beam Pulsar Survey, wherein the RRATs were initially identified, offered an opportunity to do just this. Abouthalf of the RRATs showing bursts during the survey were thought to have been missed, due to the deleterious effects of impulsive terrestrial interference signals. To remove these unwanted signals, so that we could identify the previously shrouded RRATs, we developed newinterference mitigation software and processing techniques. Having done this, the survey was completely re-processed, resulting in the discovery of 19 new sources. Of these, 12 have been re-detected on multiple occasions, whereas the others have not been seen to re-emitsince the initial discovery observations, and may be very low burst-rate RRATs, or, isolated burst events. These discoveries suggest that the initial population estimate was not over-estimated -- RRATs, though not a distinct population, are indeed numerous.In addition to finding new sources, characterisation of their properties is vital. To this end, a campaign of regular radio observations of the newly discovered sources, was mounted, at theParkes Observatory, in Australia. In addition, some of the initially identified RRATs were observed with the Lovell Telescope at Jodrell Bank. These have revealed glitches in J1819-1458, with anomalous post-glitch recovery of the spin-down rate. If such glitches werecommon, it would imply that the source was once a magnetar, neutron stars with the strongest known magnetic fields of up to 10^{15} gauss. The observations have also been used to perform`timing' observations of RRATs, i.e. determination of their spin-down characteristics. At the beginning of this thesis, 3 of the original sources had `timing solutions' determined. This has since risen to 7, and furthermore, 7 of the newly discovered sources now also have timing solutions. With this knowledge, we can see where RRATs lie in period-period derivative space. The Parkes RRATs seem to be roughly classifiable into three groupings, with high observed nulling fractions -- normal pulsars, high magnetic field pulsars and old,`dying' pulsars.It seems that RRATs and pulsars are one and the same. When a pulsar is more easily detected in searches for single bright pulses, as opposed to in periodicity searches, we label it a RRAT. Such searches impart a selection effect on the parameter space of possible sources, in bothnulling fraction and rotation period. In this sense, an observational setup could be designed to make any pulsar appear as a RRAT. For realistic survey parameters however, this is not the case, and the groups mentioned above s

Keane, E. F.

2010-11-01

390

The ghost propagator in Coulomb gauge  

NASA Astrophysics Data System (ADS)

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.

Watson, P.; Reinhardt, H.

2011-05-01

391

The ghost propagator in Coulomb gauge  

SciTech Connect

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.

Watson, P.; Reinhardt, H. [Institut fuer Theoretische Physik, Universitaet Tuebingen, Auf der Morgenstelle 14, D-72076 Tuebingen (Germany)

2011-05-23

392

Studies of High-Frequency Radio Wave Propagation  

Microsoft Academic Search

Studies of multiple signals of high frequency have been made upon a quantitative basis with reference not only to the round-the-world signals (sometimes called echo signals) but to nearby echoes which have a very much shorter time of arrival. A method of predicting in advance the the likelihood of round-the-world echoes occurring between any two different stations has been worked

A. H. Taylor; L. C. Young

1928-01-01

393

Radio pulse propagation in a smoothly bent oversized waveguide  

Microsoft Academic Search

An efficient method to calculate EM pulse dynamics in a wide nonuniform waveguide is proposed. Fourier transformation of the adiabatic approximation into time domain results in a series of traveling pulsed modes whose group velocities depend on the mode number, waveguide cross section and axis curvature. Parabolic equation can be used for numerical implementation of the asymptotic solution.

Alexei V. Popov

2003-01-01

394

Measurement of mobile radio propagation channel in ruins  

Microsoft Academic Search

Within a running project, I-LOV1, wireless communication channel model for mobile communications is developed based on measurements in reconstructed disaster and salvage scenarios. Due to complex environment in ruins, great multipath interference can take place, which strongly impacts communication quality and localization accuracy. Besides numerous measurements investigated in environments such as urban, outdoor-to-indoor or indoor, only a few are in

Ling Chen; Thomas Ostertag; Marc Loschonsky; Leonhard M. Reindl

2010-01-01

395

Microwave propagation measurements for mobile digital radio application  

Microsoft Academic Search

Measurements over a variety of urban and terrain conditions were made using a spread-spectrum waveform centered at 1370 MHz. Chip rates of 10 and 20 MHz were used, giving high time-delay resolution. The transmitter end of the measurement link was elevated and fixed while the receiver was mobile. A detailed analysis of the multipath structure was made for various terrain

D. L. Nielson

1978-01-01

396

Propagation measurements for satellite radio reception inside buildings  

NASA Technical Reports Server (NTRS)

Swept CW signals (from 700 to 1800 MHz) were received inside six buildings of brick, corrugated sheet-metal, wood-frame, mobile-home, and reinforced concrete-wall construction. A transmitter antenna was mounted outdoors on top of an 18 m tower to simulate a satellite, and a linearly scanned directional receiver antenna was used to probe the spatial, spectral, and temporal variability of the signal indoors. Levels were found to have much structure in the spatial and frequency domain, but were relatively stable in time. Typically, people moving nearby produced variations of less than 0.5 dB, whereas a person blocking the transmission path produced fades of 6 to 10 dB. Severe losses (17.5 dB) were observed in the concrete-wall building, which also exhibited the longest multipath delays (over 100 ns). Losses inside a mobile home were even larger (over 20 dB) and were independent of antenna orientation. The power-frequency distortion increased with the logarithm of the bandwidth, but could be reduced by moving to a position of higher power. Only the losses showed a clear frequency dependence, but they could be mitigated by moving the antenna.

Vogel, Wolfhard J.; Torrence, Geoffrey W.

1993-01-01

397

Radio Loud and Radio Quiet Quasars  

NASA Astrophysics Data System (ADS)

It has been half a century since the population of radio quiet quasars has been recognized. Although all quasars are thought to contain a supper massive black hole which powers their extraordinary optical luminosity, it is still not clear why only a small fraction of optically selected quasars are strong radio sources. Using 5 GHz VLA observations, we compare the radio and optical properties of 179 quasars selected from the SDSS with absolute magnitude brighter than -23 and contained within a volume limited sample defined by redshifts between 0.2 and 0.3.

Kellermann, Kenneth I.; Kimball, Amy E.; Condon, James J.; Perley, Richard A.; Ivezic, Zeljko

2015-01-01

398

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)

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.

Golshan, Nasser (Editor)

1997-01-01

399

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

Microsoft Academic Search

An important source of error in very-long-baseline interferometry (VLBI) estimates of baseline length is unmodeled variations of the refractivity of the neutral atmosphere along the propagation path of the radio signals. The authors present and discuss the method of using data from a water vapor readiometer (WVR) to correct for the propagation delay caused by atmospheric water vapor, the major

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

1991-01-01

400

CORONAL MAGNETOGRAPHY OF SOLAR ACTIVE REGION 8365 WITH THE SSRT AND NoRH RADIO HELIOGRAPHS  

E-print Network

-) propagation of microwave emission described by Ryabov et al., 1999 (hereafter Paper I). Our present paper to the line of sight. Theoretically the quasi- transverse propagation of microwaves is well understood 88349, USA Abstract. The microwave radio maps of solar active region NOAA 8365 are used to derive

Ryabov, Boris I.

401

Intermittent activity of radio sources. Accretion instabilities and jet precession  

Microsoft Academic Search

We consider the radiation pressure instability operating on short timescales (103 - 106 years) in the accretion disk around a supermassive black hole as the origin of the intermittent activity of radio sources. We test whether this instability can be responsible for short ages (<104 years) of Compact Steep Spectrum sources measured by hot spots propagation velocities in VLBI observations

M. Kunert-Bajraszewska; A. Janiuk; A. Siemiginowska; M. Gawronski

2011-01-01

402

Numerical methods for SAW propagation characterization  

Microsoft Academic Search

Due to more and more stringent requirements on SAW filter performance, it is mandatory to precisely characterize the SAW propagation characteristics as a function of manufacturing variations (metal thickness, mark-to-space ratio, etc.). Several authors have already proposed experimental characterizations using sets of test devices. One of the main difficulties of this experimental approach is the accuracy of both the geometrical

P. Ventura; J. M. Hode; M. Solal; J. Desbois; J. Ribbe

1998-01-01

403

The earth as a radio source. [noting auroral kilometric radiation  

NASA Technical Reports Server (NTRS)

The primary characteristics of radio emission from the earth's magnetosphere are summarized, the origins of these missions are considered and similarities to other astronomical radio sources discussed. The auroral kilometric radiation has features very similar to Io-related decametric radiation from Jupiter and from Saturn. The radiation at fp and 2 fp upstream of the bow shock appears to be generated by the same mechanism as type III solar radio bursts. The beaming of the auroral kilometric radiation into a cone shaped region over the polar cap has some similarity to the angular distribution of radiation from Io and to the beaming of radio emission from pulsars.

Gurnett, D. A.

1975-01-01

404

Ultrasound Monitoring of InVitro Radio Frequency Ablation by Echo  

E-print Network

characteristic nterstitial thermal ablation methods, including radio frequency and laser approaches, haveUltrasound Monitoring of InVitro Radio Frequency Ablation by Echo Decorrelation Imaging T. Douglas imaging for mapping and characterization of tissue effects caused by radio frequency ablation (RFA

Mast, T. Douglas

405

Uncertainties and Error Propagation  

NSDL National Science Digital Library

This item is a tutorial on Uncertainties and Error Propagation. Topics covered include Systematic versus Random Error, Determining Random Errors, Relative and Absolute error, Propagation of errors, Rounding answers properly, and Significant figures. A list of well illustrated problems are embedded throughout the tutorial.

Lindberg, Vern

2008-07-22

406

Theory of flame propagation  

NASA Technical Reports Server (NTRS)

The mechanism of flame propagation has been qualitatively formulated. In accordance with this formulation, the chemical reaction initiated in some layer brings about an increase in the temperature; because of the heat conduction, the temperature is raised in the neighboring layer where in turn the chemical reaction is initiated. In this manner the flame is propagated.

Zeldovich, Y B

1951-01-01

407

Propagation of Significant Figures.  

ERIC Educational Resources Information Center

Shows that the rules of thumb for propagating significant figures through arithmetic calculations frequently yield misleading results. Also describes two procedures for performing this propagation more reliably than the rules of thumb. However, both require considerably more calculational effort than do the rules. (JN)

Schwartz, Lowell M.

1985-01-01

408

PC software for SAW propagation in anisotropic multilayers  

Microsoft Academic Search

A software package that provides an interactive and graphical environment for surface acoustic wave (SAW) and plate-mode propagation studies in arbitrarily oriented anisotropic and piezoelectric multilayers is described. The software, which runs on an IBM PC with math coprocessor, is based on a transfer-matrix formulation for calculating the characteristics of SAW propagation in multilayers that was originally written for a

E. L. Adler; J. K. Slaboszewicz; G. W. Farnell; C. K. Jen

1990-01-01

409

Ray-tracing techniques to assess the electromagnetic field radiated by radio base stations: application and experimental validation in an urban environment.  

PubMed

This paper aims to validate a ray-tracing model for electromagnetic field calculation, which is used in urban environments to predict irradiation from radio base stations for population exposure evaluation. Validation was carried out through a measurement campaign by choosing measurement points in order to test different propagation environments and analysing broadcast control channels through narrow band measurements. Comparison of the calculated and measured fields indicates that the ray-tracing model used calculates electric field with good accuracy, in spite of the fact that the propagation environment is not described in detail, because of difficulties in modelling the geometrical and electrical characteristics of urban areas. Differences between the calculated and measured results remain below 1.5 dB, with a mean value of 1 dB. PMID:15550698

Adda, S; Anglesio, L; d'Amore, G; Mantovan, M; Menegolli, M

2004-01-01

410

Architecture of an Autonomous Radio Receiver  

NASA Technical Reports Server (NTRS)

A program to develop an autonomous radio receiver compatible with a variety of digital communication schemes is underway. The proposed receiver, to be implemented largely in software, would configure itself to receive an incoming signal without much a priori knowledge of defining characteristics of the signal. The proposed receiver would include estimating and classifying modules that would analyze the incoming signal to determine its defining characteristics and would then configure itself on the basis of the outputs of these modules.

Hamkins, Jon; Simon, Marvin; Divsalar, Dariush; Dolinar, Samuel

2007-01-01

411

Tracking by Identification Using Computer Vision and Radio  

PubMed Central

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

Mandeljc, Rok; Kova?i?, Stanislav; Kristan, Matej; Perš, Janez

2013-01-01

412

Spectrum agile radio: radio resource measurements for opportunistic spectrum usage  

Microsoft Academic Search

Radio spectrum allocation is undergoing radical rethinking. Regulators, government agencies, industry, and the research community have recently established many initiatives for new spectrum policies and seek approaches to more efficiently manage the radio spectrum. In this paper, we examine new approaches, namely, spectrum agile radios, for opportunistic spectrum usage. Spectrum agile radios use parts of the radio spectrum that were

Stefan Mangold; Zhun Zhong; Kiran Challapali; Chun-Ting Chou

2004-01-01

413

Ionospheric Sounding Using Real-Time Amateur Radio Reporting Networks  

NASA Astrophysics Data System (ADS)

Amateur radio reporting networks, such as the Reverse Beacon Network (RBN), PSKReporter, and the Weak Signal Propagation Network, are powerful tools for remote sensing the ionosphere. These voluntarily constructed and operated networks provide real-time and archival data that could be used for space weather operations, forecasting, and research. The potential exists for the study of both global and localized effects. The capability of one such network to detect space weather disturbances is demonstrated by examining the impacts on RBN-observed HF propagation paths of an X2.9 class solar flare detected by the GOES 15 satellite. Prior to the solar flare, the RBN observed strong HF propagation conditions between multiple continents, primarily Europe, North America, and South America. Immediately following the GOES 15 detection of the solar flare, the number of reported global RBN propagation paths dropped to less than 35% that of prior observations. After the flare, the RBN showed the gradual recovery of HF propagation conditions.

Frissell, N. A.; Miller, E. S.; Kaeppler, S. R.; Ceglia, F.; Pascoe, D.; Sinanis, N.; Smith, P.; Williams, R.; Shovkoplyas, A.

2014-12-01

414

Correlation of radio and gamma emissions in lightning initiation.  

PubMed

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

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

2013-10-18

415

Correlation of Radio and Gamma Emissions in Lightning Initiation  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

416

American RadioWorks  

NSDL National Science Digital Library

Radio documentaries have been around almost since the beginning of regularly scheduled radio programming, but not all are created equal (or with great aplomb), and the American Radio Works is certainly one of the finer documentary production units in the field. Based at Minnesota Public Radio in St. Paul, Minnesota, Radio Works' primary themes include public affairs documentaries on major social and economic issues, investigative reporting, and the Living History series, which seeks to document the 20th century American experience "through the lives of those who witnessed it." The web-browsing public will be glad to know that all of the radio projects are available online here, and can be listened to in their entirety. Visitors can listen to close to 40 of their productions, including their most recent production which deals with the extensive phone conversations recorded by Presidents Johnson, Kennedy, and Nixon during their terms in the White House

417

Radio determination satellite service  

NASA Astrophysics Data System (ADS)

The capabilities and measured performance of a geosynchronous satellite-based service called the radio determination satellite service (RDSS), which operates at radio frequencies allocated by the International Telecommunications Union (ITU) and is licensed in the United States by the Federal Communications Commission (FCC), are discussed. Plans for both improvement in capability and expansion to nearly global coverage are described. Since RDSS can also provide radio navigation, some comparisons of this service with the Global Positioning System (GPS) are made.

Briskman, Robert D.

1990-07-01

418

Radio-Locator  

NSDL National Science Digital Library

Radio-Locator is a comprehensive database of radio stations throughout the United States and Canada. Stations can be searched by location and format, or even more specifically with the site's advanced search. Users can even search for vacant frequencies on the dial. The bulk of their information come from the FCC's public databases, but is also updated and corrected. Radio-Locator also provides links to individual stations website and internet streams if available.

419

Dominion Radio Astrophysical Observatory  

NASA Astrophysics Data System (ADS)

The Dominion Radio Astrophysical Observatory began operating in 1959, and joined the NATIONAL RESEARCH COUNCIL in 1970. It became part of the Herzberg Institute of Astrophysics in 1975. The site near Penticton, BC has a 26 m radio telescope, a seven-antenna synthesis telescope on a 600 m baseline and two telescopes dedicated to monitoring the solar radio flux at 10.7 cm. This part of the Institu...

Murdin, P.

2000-11-01

420

National Radio Observatory  

NSDL National Science Digital Library

The National Radio Astronomy Observatory (NRAO) "operates powerful, advanced radio telescopes spanning the western hemisphere." The website is nicely divided into information for the general public, astronomers, and teachers and students. Users can learn all about NRAO's many telescopes located throughout the United States. Researchers can find out about meetings, conferences, software resources, and surveys. Amateur radio astronomers can find links describing how to build antennas and interferometers. Everyone will enjoy the numerous images of astronomical phenomena and NRAO's telescopes and facilities.

421

Predictions for Radio Emission from Extrasolar Planets  

NASA Astrophysics Data System (ADS)

LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot; 5 Place Jules Janssen, 92190 Meudon, France E-mail: jean-mathias.griessmeier@obspm.fr LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris Diderot; 5 Place Jules Janssen, 92190 Meudon, France E-mail: philippe.zarka@obspm.fr Close-in giant extrasolar planets ("Hot Jupiters") are believed to be strong emitters in the decametric radio range. We present the expected characteristics of the low-frequency magnetospheric radio emission of all currently known extrasolar planets, including the maximum emission frequency and the expected radio flux. We compare the different predictions obtained with all four existing analytical models for all currently known exoplanets. We also take care to use realistic values for all input parameters. The four different models for planetary radio emission lead to very different results. The largest fluxes are found for the magnetic energy model, followed by the CME model and the kinetic energy model (for which our results are found to be much less optimistic than those of previous studies). The unipolar interaction model does not predict any observable emission for the present exoplanet census. Our results show that observations of exoplanetary radio emission are feasible, but that the number of promising targets is not very high. The catalog of targets will be particularly useful for current and future radio observation campaigns (e.g. with the VLA, GMRT, UTR-2 and with LOFAR).

Spreeuw, H.; Griessmeier, J. M.; Zarka, P.

422

Radio data transmission for SCADA  

SciTech Connect

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

Frasier, W.E. (Enron Corp., Houston, TX (US))

1989-09-01

423

Vector wave propagation method.  

PubMed

In this paper, we extend the scalar wave propagation method (WPM) to vector fields. The WPM [Appl. Opt.32, 4984 (1993)] was introduced in order to overcome the major limitations of the beam propagation method (BPM). With the WPM, the range of application can be extended from the simulation of waveguides to simulation of other optical elements like lenses, prisms and gratings. In that reference it was demonstrated that the wave propagation scheme provides valid results for propagation angles up to 85 degrees and that it is not limited to small index variations in the axis of propagation. Here, we extend the WPM to three-dimensional vectorial fields (VWPMs) by considering the polarization dependent Fresnel coefficients for transmission in each propagation step. The continuity of the electric field is maintained in all three dimensions by an enhanced propagation vector and the transfer matrix. We verify the validity of the method by transmission through a prism and by comparison with the focal distribution from vectorial Debye theory. Furthermore, a two-dimensional grating is simulated and compared with the results from three-dimensional RCWA. Especially for 3D problems, the runtime of the VWPM exhibits special advantage over the RCWA. PMID:20360813

Fertig, M; Brenner, K-H

2010-04-01

424

Propagation along azimuthally magnetized ferrite-loaded circular waveguides  

NASA Technical Reports Server (NTRS)

The paper describes the modal dispersion characteristics of electromagnetic waves traveling along the azimuthally magnetized ferrite-loaded coaxial transmission line and the ferrite-loaded wire. The modal dispersion curves are used to determine the pass and stop bands of normal propagation. Boundary-value problems were solved with Bolle-Heller functions. The dispersion characteristics of transverse electric modes are presented as plots of the normalized propagation constant vs the normalized frequency.

Mueller, R. S.; Rosenbaum, F. J.

1977-01-01

425

STEM on the radio  

NASA Astrophysics Data System (ADS)

Looking for an Internet radio station focusing on programing about science, technology, engineering, and math (STEM)? The U.S. National Science Foundation (NSF) announced on 26 September the launch of Science360 Radio, which it says is the first Internet radio stream dedicated to STEM programing. Science360 includes more than 100 radio shows and podcasts that are available on the Web as well as on iPhone and Android devices. The shows originate from a variety of sources, including NSF, other U.S. government agencies, science organizations, universities, and media outlets. For more information, see http://science360.gov/files/.

Showstack, Randy

2011-10-01

426

Apparent Faster-Than-Light Pulse Propagation in Interstellar Space: A New Probe of the Interstellar Medium  

Microsoft Academic Search

Radio pulsars emit regular bursts of radio radiation that propagate through the interstellar medium (ISM), the tenuous gas and plasma between the stars. Previously known dispersive properties of the ISM cause low-frequency pulses to be delayed in time with respect to high frequency ones. This effect can be explained by the presence of free electrons in the medium. The ISM

F. A. Jenet; D. Fleckenstein; A. Ford; A. Garcia; R. Miller; J. Rivera; K. Stovall

2010-01-01

427

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

NASA Astrophysics Data System (ADS)

Context. Luminous infrared galaxies (LIRGs) are systems enshrouded in dust, which absorbs most of their optical/UV emission and radiates it again in the mid- and far-infrared. Radio observations are largely unaffected by dust obscuration, enabling us to study the central regions of LIRGs in an unbiased manner. Aims: The main goal of this project is to examine how the radio properties of local LIRGs relate to their infrared spectral characteristics. Here we present an analysis of the radio continuum properties of a subset of the Great Observatories All-sky LIRG Survey (GOALS), which consists of 202 nearby systems (z< 0.088). Our radio sample consists of 35 systems, containing 46 individual galaxies, that were observed at both 1.49 and 8.44 GHz with the VLA with a resolution of about 1 arcsec (FWHM). The aim of the project is to use the radio imagery to probe the central kpc of these LIRGs in search of active galactic nuclei (AGN). Methods: We used the archival data at 1.49 and 8.44 GHz to create radio-spectral-index maps using the standard relation between flux density S? and frequency ?, S? ~ ?- ?, where ? is the radio spectral index. By studying the spatial variations in ?, we classified the objects as radio-AGN, radio-SB, and AGN/SB (a mixture). We identified the presence of an active nucleus using the radio morphology, deviations from the radio/infrared correlation, and spatially resolved spectral index maps, and then correlated this to the usual mid-infrared ([NeV]/[NeII] and [OIV]/[NeII] line ratios and equivalent width of the 6.2 ?m PAH feature) and optical (BPT diagram) AGN diagnostics. Results: We find that 21 out of the 46 objects in our sample (~45%) are radio-AGN, 9 out of the 46 (~20%) are classified as starbursts (SB) based on the radio analysis, and 16 (~35%) are AGN/SB. After comparing to other AGN diagnostics we find 3 objects out of the 46 (~7%) that are identified as AGN based on the radio analysis, but are not classified as such based on the mid-infrared and optical AGN diagnostics presented in this study. Appendix A is available in electronic form at http://www.aanda.orgVLA images as FITS files are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A4

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

428

Simulation of EHF propagation through the atmosphere  

NASA Astrophysics Data System (ADS)

The effect of the clear, nonturbulent air mass on the propagation of extremely high frequency radio waves at various slant path angles is examined. Molecular absorption spectra (principly of O2 and H2O) cause frequency dependent signal attenuation, phase delay, ray bending, and medium noise. The interaction between the physical environment and the traversing radiation is expressed by a complex refractivity Nc, which is a function of frequency f, total pressure p, partial water vapor pressure Pw, and temperature T. The Earth's magnetic field strength, which enters into Zeeman splitting of the absorption lines at high altitudes, is regarded as a nearly negligible background parameter. The means of calculating Nc utilizes a recent spectroscopic data base for the 60 GHz oxygen band and the 22.235 GHz water vapor line. In addition to the 183 GHz water vapor line, 6 higher frequency lines plus a nonresonant term are included. A distribution of the gas variables P, Pw, and T for the neutral air (surface to 80 km) leads to a profile of Nc which provides the basis for calculating the various propagation effects along a specified radio path (ground to ground, aircraft, or spacecraft. The distribution of atmospheric data may be obtained from in situ soundings (e.g., radiosonde) or from standard atmospheric models. The computer model assumes a symmetric, spherically stratified atmosphere in which the layers need not be regarded as homogeneous, as a consequence of the interpolation methods developed for Nc. Noise integrals are detailed.

Hopponen, J. D.

1980-08-01

429

Radio Frequency Interference and the National Radio Astronomy Observatory  

NASA Astrophysics Data System (ADS)

Radio frequency interference (RFI) and radio astronomy have been closely linked since the emergence of radio astronomy as a scientific discipline in the 1930s. Even before the official establishment of the National Radio Astronomy Observatory, protection against contemporary and future radio noise levels was seen as crucial to ensure success of any new observatory. My talk will examine the various local, regional, national, and international efforts enacted to protect NRAO and other American radio astronomy sites from RFI.

Smith, Sierra

2014-01-01

430

A Study of Malware Propagation via Online Social Networking  

NASA Astrophysics Data System (ADS)

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.

Faghani, Mohammad Reza; Nguyen, Uyen Trang

431

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

NASA Technical Reports Server (NTRS)

Wave normal and Poynting vector measurements from the Cassini radio and plasma wave instrument (RPWS) are used to examine the propagation characteristics of various plasma waves during the Earth flyby on August 18, 1999. Using the five-channel waveform receiver (WFR), the wave normal vector is determined using the Means method for a lightning-induced whistler, equatorial chorus, and a series of low-frequency emissions observed while Cassini was in the magnetosheath. The Poynting vector for these emissions is also calculated from the five components measured by the WFR. The propagation characteristics of the lightning-induced whistler were found to be consistent with the whistler wave mode of propagation, with propagation antiparallel to the magnetic field (southward) at Cassini. The sferic associated with this whistler was observed by both Cassini and the Stanford VLF group at the Palmer Station in Antarctica. Analysis of the arrival direction of the sferic at the Palmer Station suggests that the lightning stroke is in the same sector as Cassini. Chorus was observed very close (within a few degrees) to the magnetic equator during the flyby. The chorus was found to propagate primarily away from the magnetic equator and was observed to change direction as Cassini crossed the magnetic equator. This suggests that the source region of the chorus is very near the magnetic equator. The low-frequency emission in the magnetosheath has many of the characteristics of lion roars. The average value of the angle between the wave normal vector and the local magnetic field was found to be 16 degrees, and the emissions ranged in frequency from 0. 19 to 0.75 f(sub ce), where f(sub ce) is the electron cyclotron frequency. The wave normal vectors of these waves were primarily in one direction for each individual burst (either parallel or antiparallel to the local field) but varied in direction throughout the magnetosheath. This suggests that the sources of the emissions are far from the spacecraft and that there are multiple source regions.

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

2001-01-01

432

Propagation of Environmental Noise  

ERIC Educational Resources Information Center

Solutions for environmental noise pollution lie in systematic study of many basic processes such as reflection, scattering, and spreading. Noise propagation processes should be identified in different situations and assessed for their relative importance. (PS)

Lyon, R. H.

1973-01-01

433

On 3D detection of lightning discharges and associated events with a small scale interferometric network of radio receivers  

NASA Astrophysics Data System (ADS)

Lightning discharges cause different phenomena in the atmosphere such as sprites, gigantic jets and runaway electron beams. Lightning discharges and their associated events exhibit characteristic electromagnetic signatures in a wide range of frequencies. These electromagnetic signatures are detected and recorded with radio receivers for a detailed investigation. This work uses a small scale network of wide band digital radio receivers, which record vertical electric field strengths in the frequency range from ~ 4 Hz to ~ 400 KHz, with a sampling frequency of 1 MHz, an amplitude resolution of ~ 35 ?V/m and a timing accuracy of ~ 12 ns. The small scale interferometric network consists of eight radio receivers, which are separated by distances ranging from 1 km up to 30 km. The network was deployed in Southern France from July to September 2011. Three additional receivers served as remote reference measurements at distances from 300 km up to 1000 km. The small scale interferometric network enables the detection of lightning discharges and associated events in three dimensions for nearby thunderstorms which are less than 500 km away. The network operated successfully during several nearby sprite producing thunderstorms. The recorded waveforms are very consistent and exhibit small time delays which reflect the propagation of the electromagnetic waves across the network. These time delays are used to determine the bearing and elevation angle of the arriving electromagnetic energy. The first results obtained with the interferometric network are presented.

Mezentsev, A.; Fullekrug, M.

2012-04-01

434

Solar Radio Bursts and Space Weather  

NASA Technical Reports Server (NTRS)

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.

Gopalswamy, Natchimuthuk,

2012-01-01

435

Radio variability of the blazar AO 0235 + 164  

NASA Technical Reports Server (NTRS)

The high-redshift blazar A0 0235 + 164 exhibits flux-density variations which are primarily of the less common variety in which low-frequency flux-density variations track the high-frequency variations but are delayed and of smaller amplitude. Observational results based on five years of monitoring are presented which are correlated over at least a factor of 50 frequency range in the sense expected for an expanding synchrotron component: outbursts propagating toward lower frequencies with diminishing amplitudes. A simple, semiempirical jet model is developed which accounts reasonably well for the radio properties of the object. The predictions of the model are compared with observations, examining the radio flux-density histories, the radio spectral evolution, the radio structure, and evidence for relativistic bulk motion.

O'Dell, S. L.; Dennison, B.; Broderick, J. J.; Altschuler, D. R.; Condon, J. J.; Payne, H. E.; Mitchell, K. J.

1988-01-01

436

Database for propagation models  

NASA Technical Reports Server (NTRS)

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

Kantak, Anil V.

1991-01-01

437

Outer heliospheric radio emissions. II - Foreshock source models  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

438

Topside plasma scale height retrieved from radio occultation measurements  

NASA Astrophysics Data System (ADS)

The plasma scale height is one of the important ionospheric characteristics due to its intrinsic connection to the ionospheric plasma temperature and composition and also, to the altitudinal profile of the electron density. Therefore, the knowledge of the plasma scale height is of crucial importance when addressing several open scientific and technological issues such as the upper ionosphere temperature balance and ion composition, the estimation and correction of propagation delays in Global Navigation Satellite Systems (GNSS), the nowcast and forecast of space-weather effects on telecommunications, etc. While the plasma scale height value in the bottomside ionosphere can be deduced directly and reliably enough by vertical incidence sounding, the plasma scale height in the topside ionosphere is quite difficult to obtain. The ionospheric radio occultation (IRO) technique employed by the Low-Earth-Orbiting (LEO) satellites can deliver the valuable information on the topside plasma scale height behaviour and can provide a rich database for consequent development of new empirical models of the plasma scale height and density. Reported here is a procedure for post-processing retrieval of the topside plasma scale height values from IRO measurements by the LEO satellite CHAMP (CHAllenging Minisatellite Payload). Described also is the accumulated data base of such values. Further, presented are first results from the analysis of the topside plasma scale height's temporal and spatial variations. These preliminary results are compared with corresponding estimates from the International Reference Ionosphere (IRI) model calculations.

Stankov, S.; Jakowski, N.

439

RF propagation simulator to predict location accuracy of GSM mobile phones for emergency applications  

NASA Astrophysics Data System (ADS)

Mobile location is one of the fastest growing areas for the development of new technologies, services and applications. This paper describes the channel models that were developed as a basis of discussion to assist the Technical Subcommittee T1P1.5 in its consideration of various mobile location technologies for emergency applications (1997 - 1998) for presentation to the U.S. Federal Communication Commission (FCC). It also presents the PCS 1900 extension to this model, which is based on the COST-231 extended Hata model and review of the original Okumura graphical interpretation of signal propagation characteristics in different environments. Based on a wide array of published (and non-publicly disclosed) empirical data, the signal propagation models described in this paper were all obtained by consensus of a group of inter-company participants in order to facilitate the direct comparison between simulations of different handset-based and network-based location methods prior to their standardization for emergency E-911 applications by the FCC. Since that time, this model has become a de-facto standard for assessing the positioning accuracy of different location technologies using GSM mobile terminals. In this paper, the radio environment is described to the level of detail that is necessary to replicate it in a software environment.

Green, Marilynn P.; Wang, S. S. Peter

2002-11-01

440

Radio Frequency Interference: Radio Astronomy's Biggest Enemy  

NASA Astrophysics Data System (ADS)

As technology progresses, the demand for the usage of the electromagnetic spectrum increases with it. The development is so fast and prolific that clean band space for passive users such as Radio Astronomy is becoming ever so scarce. Even though, several spectral bands have been protected for Radio Astronomy by Federal Communication Commission (in the USA) under the recommendations of the International Telecommunication Union (ITU), pressure for making more spectral space commercially usable is extreme. Although these commercial usages make our modern living at all possible, often the extreme vulnerability of passive users are are not fully appreciated, resulting in unwanted emissions (RFI) in the Radio Astronomy Bands. Another source of RFI is the fact that many of the electronic devices used in the observatories themselves generate radio waves. If proper precautions are not taken, these can be received back through the Radio Telescope itself. This problem is referred to as internal RFI. The focus of this paper is the search and diminution of internal RFI in the Arecibo Observatory in Arecibo, Puerto Rico. Using a simple setup of a log-periodic antenna and a Spectrum Analyzer, spectra spanning a frequency range of 100 - 1800 MHZ were recorded in some areas of the Observatory and the new Visitor Center (AOVEF). The measurements disclosed sources of radio emission among some of the digital electronic equipment in the Equipment room and a few displays in the AOVEF. Most prominent of these was a 2.5 MHz comb spanning the entire range of the measurements emitted from the SRENDIP and AOFTM machines. The respective groups were informed and corrective shielding & isolations were implemented immediately. In AOVEF, three displays, some audio-visual equipment, and video/digital cameras used by the visitors were found to be "leaky". In future, the use of such cameras will be prohibited and the exhibits will be screened appropriately.

Acevedo, F.; Ghosh, Tapasi

1997-12-01

441

The Radio Universe  

NSDL National Science Digital Library

The Radio Universe website provides a brief introduction the electromagnetic radiation, HII regions, the structure of the Milky Way galaxy, and quasars as seen by radio wave observations. The site also contains an expliantion of the doppler effect and 21 cm line.

2005-06-07

442

Stabilized radio frequency quadrupole  

DOEpatents

Disclosed is a long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator. 5 figs.

Lancaster, H.D.; Fugitt, J.A.; Howard, D.R.

1984-12-25

443

Imaging the Radio Universe  

E-print Network

-rays, and microwaves, etc). · Sound waves are pressure waves. Require a medium (air, water, etc.) to travel through. · Sound is created by a pressure wave moving a membrane in your ear. Your brain turns the vibration of this membrane into "sound". MediumEar Sound Radio Waves are not Sound Waves #12;You do not listen to radio waves

Groppi, Christopher

444

Radio astronomy receivers  

Microsoft Academic Search

A general survey of the principles of radio astronomy receivers is presented. System noise temperature, the sensitivity of different receiver types, and the calibration of receivers are studied. A total-power receiver is analyzed as a basic radio telescope receiver and the results are used to obtain the performance of other receiver types such as the Dicke receiver, Graham's receiver, correlation

M. Tiuri

1964-01-01

445

Pulsating Solar Radio Emission  

NASA Astrophysics Data System (ADS)

A status report of current research on pulsating radio emission is given, based on working group discussions at the CESRA 2004 workshop. Quasi-periodic pulsations have been observed at all wavelength ranges of the radio band. Usually, they are associated with flare events; however since the late 90s, pulsations of the slowly-varying component of the Sun’s radio emission have also been observed. Radio pulsations show a large variety in their periods, bandwidths, amplitudes, temporal and spatial signatures. Most of them have been attributed to MHD oscillations?dex waves!MHD waves in coronal loops, while alternative interpretations consider intrinsic oscillations of a nonlinear regime of kinetic plasma instabilities or modulation of the electron acceleration. Combined radio spectroscopic observations with radio imaging and X-ray/EUV data have revived interest in the subject. We summarize recent progress in using radio pulsations as a powerful tool for coronal plasma and magnetic field diagnostics. Also the latest developments on the study of the physical processes leading to radio emission modulation are summarized.

Nindos, Alexander; Aurass, Henry

446

The Radio Transient Sky  

Microsoft Academic Search

Transient radio sources are necessarily compact and usually are the locations of explosive or dynamic events, therefore offering unique opportunities for probing fundamental physics and astrophysics. In addition, short-duration transients are powerful probes of intervening media owing to dispersion, scattering, and Faraday rotation that modify the signals. While radio astronomy has an impressive record obtaining high time resolution, usually it

J. Lazio; P. S. Ray; S. Ellingson; S. Close; P. Crane; S. D. Hyman; B. A. Jacoby; W. Junor; N. E. Kassim; S. R. Kulkarni; Y. M. Pihlstrom; G. B. Taylor; D. Werthimer

2006-01-01

447

Radio Transmission Measurements  

Microsoft Academic Search

The paper divides naturally into three sections. The first section briefly analyses the radio transmission circuit into (a) the sending or radiating portion, (b) the transmitting portion consisting of the ether path thru which the radiated waves travel, and (c) the receiving portion. The relation of these from the standpoint of the radio transmission engineer is discussed, pointing out the

R. Bown; C. R. Englund; H. T. Friis

1923-01-01

448

The Radio Jove Project  

NASA Technical Reports Server (NTRS)

The Radio love Project is a hands-on education and outreach project in which students, or any other interested individuals or groups build a radio telescope from a kit, operate the radio telescope, transmit the resulting signals through the internet if desired, analyze the results, and share the results with others through archives or general discussions among the observers. Radio love is intended to provide an introduction to radio astronomy for the observer. The equipment allows the user to observe radio signals from Jupiter, the Sun, the galaxy, and Earth-based radiation both natural and man-made. The project was started through a NASA Director's Discretionary Fund grant more than ten years ago. it has continued to be carried out through the dedicated efforts of a group of mainly volunteers. Dearly 1500 kits have been distributed throughout the world. Participation can also be done without building a kit. Pre-built kits are available. Users can also monitor remote radio telescopes through the internet using free downloadable software available through the radiosky.com website. There have been many stories of prize-winning projects, inspirational results, collaborative efforts, etc. We continue to build the community of observers and are always open to new thoughts about how to inspire the observers to still greater involvement in the science and technology associated with Radio Jove.

Thieman, J. R.

2010-01-01

449

Stabilized radio frequency quadrupole  

DOEpatents

A long-vane stabilized radio frequency resonator for accelerating charged particles and including means defining a radio frequency resonator cavity, a plurality of long vanes mounted in the defining means for dividing the cavity into sections, and means interconnecting opposing ones of the plurality of vanes for stabilizing the resonator.

Lancaster, Henry D. (Orinda, CA); Fugitt, Jock A. (Berkeley, CA); Howard, Donald R. (Danville, CA)

1984-01-01

450

World Ocean Radio  

NSDL National Science Digital Library

World Ocean Radio is a weekly series of five-minute audio essays on a wide range of ocean issues hosted by W2O's own Peter Neill. Available for RSS feed (bottom of page), podcast, and syndicated use at no cost by community radio stations worldwide.

451

A refracting radio telescope  

Microsoft Academic Search

Observations of extraterrestrial radio sources at the lower end of the radio frequency spectrum are limited by reflection of waves from the topside ionosphere and by the large size of antenna apertures necessary for the realization of narrow beamwidths. The use of the ionosphere as a lens is considered. The lens is formed by the release of chemicals such as

Paul Bernhardt; A. V. da Rosa

1977-01-01

452

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

Microsoft Academic Search

The Slant Path Atmospheric Refraction Calibrator (SPARC) has been developed to measure the water-vapor-induced propagation delay experienced by a radio signal traversing the atmosphere. SPARC measures the difference in the travel times between an optical and a microwave signal propagating along the same atmospheric path. Since the refractivity of dry air is similar for both the microwave and optical signals,

Steven J. Walter; Peter L. Bender

1992-01-01

453

Receiver design using the dependence between quadrature components of impulsive radio noise  

Microsoft Academic Search

A new BPSK receiver based on the statistical characteristics of impulsive radio noise is proposed. First, the statistical characteristics of impulsive radio noise are investigated, and it is proved that the quadrature components of impulsive noise are dependent. Next, with the consideration of the dependence between these components, a new BPSK receiver designed for impulsive noise is proposed, and it

S. Miyamoto; M. Katayama; N. Morinaga

1995-01-01

454

Design and evaluation of optical antenna module suitable for radio-on free-space optics link system for ubiquitous wireless  

NASA Astrophysics Data System (ADS)

We present initial results on research and development of an optical antenna module suitable for Radio-on Free-Space Optics (RoFSO) links. This new optical communication system is envisaged to be an effective means of realizing a ubiquitous society and therefore eliminating the digital divide. The RoFSO system is a trial system applying Radio on Fiber (RoF) technology for transmission through free space. Based on the results of research of next generation high-speed free-space optical communication system conducted in the past two years at Waseda University, we have developed an optical antenna module with efficient laser receiving characteristics as well as simple adjustment. The tracking system adopts two phases including rough tracking by the beacon light at 0.85 ?m wavelength and fine tracking using communication light at 1.55 ?m wavelength to improve compensation precision for the atmospheric turbulence at the time of beam propagation. We present results on the evaluation of performance characteristics (static characteristics) of the separate functions for RoFSO antenna module we have developed and confirmed the coupling efficiency and fine tracking characteristics which were set as goals at the beginning.

Takahashi, Koichi; Higashino, Takeshi; Nakamura, Takuya; Aburakawa, Yuji; Tsukamoto, Katsutoshi; Komaki, Shozo; Wakamori, Kazuhiko; Suzuki, Toshiji; Kazaura, Kamugisha; Shah, Alam Mohammad; Omae, Kazunori; Matsumoto, Mitsuji; Miyamoto, Yuichi

2008-02-01

455

47 CFR 90.185 - Multiple licensing of radio transmitting equipment in the mobile radio service.  

Code of Federal Regulations, 2013 CFR

...of radio transmitting equipment in the mobile radio service. 90.185 Section 90...SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Policies Governing the...of radio transmitting equipment in the mobile radio service. Two or more...

2013-10-01

456

47 CFR 90.185 - Multiple licensing of radio transmitting equipment in the mobile radio service.  

Code of Federal Regulations, 2012 CFR

...of radio transmitting equipment in the mobile radio service. 90.185 Section 90...SPECIAL RADIO SERVICES PRIVATE LAND MOBILE RADIO SERVICES Policies Governing the...of radio transmitting equipment in the mobile radio service. Two or more...

2012-10-01

457

The cluster environments of radio loud quasars  

E-print Network

We have carried out multi-colour imaging of the fields of a statistically complete sample of low-frequency selected radio loud quasars at 0.6characteristics of their environments. The largest radio sources are located in the field, and smaller steep-spectrum sources are more likely to be found in richer environments, from compact groups through to clusters. This radio-based selection (including source size) of high redshift groups and clusters is a highly efficient method of detecting rich environments at these redshifts. Although our single filter clustering measures agree with those of other workers, we show that these statistics cannot be used reliably on fields individually, colour information is required for this.

J. M. Barr; M. N. Bremer; J. C. Baker; M. D. Lehnert

2001-09-28

458

Project CLEA: Radio Astronomy of Pulsars  

NSDL National Science Digital Library

This software for Windows, from Project CLEA -- Contemporary Laboratory Experiences In Astronomy, presents students with a radio telescope. The default operating characteristics (beam width, receiver noise, steerability) can be set by the instructor. Students can point the telescope at a source in the sky, viewing the output of the radio receiver on a graphic display that resembles a digital oscilloscope. The student manual describes exercises in which students acquaint themselves with the operation of the radio telescope, measure the signals from several pulsars at various frequencies, learn about pulsar signals, and then estimate the distance to the pulsar. The site includes student and instructor manuals as well as a pre- and posttest. The software is available for Windows only.

459

A new method for studying remote type II radio emissions from coronal mass ejection-driven shocks  

Microsoft Academic Search

Some interplanetary shocks associated with coronal mass ejections (CMEs) generate type II radio emissions at the local plasma frequency and\\/or its harmonic. These type II radio emissions provide a means of remotely studying and tracking CMEs from the solar corona to 1 AU and beyond. New analysis techniques that inherently reveal the dynamics of a CME as it propagates through

M. J. Reiner; M. L. Kaiser; J. Fainberg; R. G. Stone

1998-01-01

460

Comparison of HF groundwave propagation models  

NASA Astrophysics Data System (ADS)

The groundwave component of high frequency (HF) radio propagation is utilized in both civilian and military applications. A variety of groundwave propagation models exist to predict field strength loss over the transmission path. In this thesis, groundwave field strength predictions were compared for programs which employ such models: GRWAVE, MIXPATH, and ADVANCED PROPHET. A range of parameter values was used to generate predictions for comparison. HF groundwave field strength predictions by PROPHET were 3 to 10 dB stronger than those of the other programs. GRWAVE and MIXPATH field strength predictions were in close agreement, the difference generally being less than 1 or 2 dB. Field measurements of path loss for two AM broadcast frequencies were evaluated by comparison with estimates provided by ADVANCED PROPHET. The measured groundwave field strengths were found to be from 8 dB weaker at short distances to 18 dB stronger at large distances it is recommended that future efforts be directed toward improving and validating the accuracy of the groundwave propagation models used in these programs. It is also recommended that more extensive documentation be developed for GRWAVE.

Davila, Celso V.

1993-06-01