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1

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

2

Propagation characteristics on microcellular urban mobile radio channels at 910 MHz  

Microsoft Academic Search

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

ROBERT J. C. BULTITUDE; G. KEITH BEDAL

1989-01-01

3

Radio propagation characteristics for line-of-sight microcellular and personal communications  

Microsoft Academic Search

To acquire a knowledge of radio propagation characteristics in the microcellular environments for personal communications services (PCS), a comprehensive measurement program was conducted by Telesis Technologies Laboratory (TTL) in the San Francisco Bay area using three base station antenna heights of 3.2 m, 8.7 m, and 13.4 m and two frequencies at 900 MHz and 1900 MHz. Five test settings

Howard H. Xia; Henry L. Bertoni; Leandro R. Maciel; Andrew Lindsay-Stewart; Robert Rowe

1993-01-01

4

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

Microsoft Academic Search

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

D. Cox

1973-01-01

5

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

6

Frequency characteristics of angular spread for radio wave propagation through foliage  

Microsoft Academic Search

This paper experimentally investigates the angular spread due to the propagation through the foliage. Assuming von Mises angular spectrum under Rayleigh fading condition, the theoretical coherence distance is related to the measured coherence distance to estimate the spread parameter. For the propagation range of about 100 m, the average angular spread was found to be about 25 degree within the

Chaymaly Phakasoum; Mir Ghoraishi; Jun-ichi Takada; Koshiro Kitao; Tetsuro Imai

2011-01-01

7

High-accuracy positioning method using public wireless network based on recorded radio propagation characteristics  

Microsoft Academic Search

By focusing on the Personal Handy-phone System (PHS) positioning service used in physical distribution logistics, a method that improves the positioning accuracy is developed. A disadvantage of PHS positioning is that measurement errors caused by the fluctuation of radio waves due to buildings around the terminal are large, ranging from several tens to several hundreds of meters. Therefore, in this

Naoaki Yokoi; H. Hosaka; Y. Kawahara; Kenji Sakata

2010-01-01

8

Theoretical predictions for VLF radio propagation  

NASA Astrophysics Data System (ADS)

The very low frequency (VLF, 3 to 30 kHz) part of the radio frequency spectrum is characterized by low attenuation rate, high phase and frequency stability, and high signal to noise ratio. Consequently, VLF radio propagation is used for many practical applications, e.g., frequency standardization, clock synchronization, and reliable long-distance radio communications. Because of the distinct advantages of VLF radio propagation, the U.S. Navy will be conducting a balloon-to-balloon-borne cross link communication experiment to study the characteristics of VLF altitude radio propagation. In this Technical Report, an attempt has been made to make theoretical computations of the vertical components of the individual and multimode field strengths as a function of distance based on mode theory. The variations of various ionospheric parameters, e.g., attenuation rates, the heights of the ionospheric reflection point, the height gain factors for an appropriate combination of the transmitting and receiving antenna elevations, along with the presence of the Earth's geomagnetic field, especially for the East-West propagation, have been duly considered.

Paul, M. P.

1983-08-01

9

Investigation of indoor WIFI radio signal propagation  

Microsoft Academic Search

The purpose of this study is to analyze the WIFI signal propagation, using IEEE 802.11g radio interface. In most cases, the WIFI radio interface is installed by the people who are not familiar with the system, especially when dealing with signal propagation at high frequency. Hence, there is a need to understand this signal behavior particularly in indoor scenarios. This

Abdul Halim Ali; M. R. A. Razak; M. Hidayab; S. A. Azman; M. Z. M. Jasmin; M. A. Zainol

2010-01-01

10

Modeling UHF Radio Propagation in Buildings.  

NASA Astrophysics Data System (ADS)

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

Honcharenko, Walter

11

Theoretical Predictions for VLF Radio Propagation.  

National Technical Information Service (NTIS)

The very low frequency (VLF, 3 to 30 kHz) part of the radio frequency spectrum is characterized by low attenuation rate, high phase and frequency stability, and high signal to noise ratio. Consequently, VLF radio propagation is used for many practical app...

M. P. Paul

1983-01-01

12

Propagation Issues for Cognitive Radio  

Microsoft Academic Search

Cognitive radios are expected to work in bands below about 3.5 GHz and may be used for a variety of applications, e.g., broadband fixed wireless access, mobile and nomadic access, etc. Cognitive radio system designers must have access to a wide range of channel models covering a wide span of operating frequencies, carrier bandwidths, deployment conditions, and environments. This paper

Andreas F. Molisch; Larry J. Greenstein; Mansoor Shafi

2009-01-01

13

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

14

Radio wave propagation in pulsar magnetospheres  

NASA Astrophysics Data System (ADS)

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

Gallant, Y. A.

15

Propagators from characteristic surfaces  

E-print Network

We study the Goursat or characteristic problem, i.e. a hyperbolic equation with given data on a surface (the half of the standard Cauchy problem), with some kind of dimensional regularization procedure to deal with the divergences that appear. We will also comment some possible relation with a holographic setup.

Jorge Conde

2005-01-17

16

Measurement of Radio Propagation Path Loss over the Sea for Wireless Multimedia  

Microsoft Academic Search

\\u000a In order to estimate the signal parameters accurately for wireless multimedia services, it is necessary to estimate a system’s\\u000a propagation characteristics through a medium. Propagation analysis provides a good initial estimate of the signal characteristics.\\u000a The ability to accurately predict radio propagation behavior for wireless multimedia services is becoming crucial to system\\u000a design. Since site measurements are costly, propagation models

Dong-you Choi

2006-01-01

17

Efficient Clustering of Cognitive Radio Networks Using Affinity Propagation  

Microsoft Academic Search

Cognitive radios must be able to form collaborative wireless network clusters in dynamically changing environments to achieve such desired objectives as interference resilience and low communications overhead. In this work, we explore the affinity propagation (AP) message-passing technique to efficiently group nodes in an ad hoc cognitive radio network (CRN). With the proposed approach, nodes exchange local messages with their

K. E. Baddour; O. Ureten; T. J. Willink

2009-01-01

18

The Ionizing Effect of Meteors in Relation to Radio Propagation  

Microsoft Academic Search

From a study of available meteor data it is concluded: (1) that meteors expend the larger part of their energy in the Kennelly-Heaviside regions, that is, in the regions of the upper atmosphere which control the propagation of all long-distance radio waves; (2) that the major portion of a meteor's energy goes into ionization of the gases around its path;

A. M. Skellett

1932-01-01

19

Nonlinear Ionospheric Propagation Effects on UHF and VLF Radio Signals  

Microsoft Academic Search

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

Keith Michael Groves

1991-01-01

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

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

22

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

23

Wideband radio propagation modeling for indoor geolocation applications  

Microsoft Academic Search

A framework for statistical modeling of the wideband characteristics of the frequency-selective fading multipath indoor radio channel for geolocation applications is presented. Multipath characteristics of the channel are divided into three classes according to availability and the strength of the direct line of sight (DLOS) path with respect to the other paths. Statistics of the error in estimating the time

Kaveh Pahlavan; Prashant Krishnamurthy; A. Beneat

1998-01-01

24

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

25

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

26

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

Microsoft Academic Search

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

Charles Burrows

1962-01-01

27

Modeling ELF radio atmospheric propagation and extracting lightning currents from ELF observations  

Microsoft Academic Search

Observations of extremely low freq uency (ELF) radio atmospherics (sferics) , the transient electromagnetic fields radiated by lightning discharges, are used to determine the current moment waveforms of vertical lightning discharges. In order to extract this information the propagation of radio atmospherics from source to receiver must be modeled accurately, especially in view of the. important role played by the

Steven A. Cummerl; Umran S. Inan

2000-01-01

28

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

29

Higher order ionospheric propagation effects on GPS radio occultation signals  

Microsoft Academic Search

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

M. Mainul Hoque; N. Jakowski

2010-01-01

30

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

31

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

NASA Astrophysics Data System (ADS)

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

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

32

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

33

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

NASA Astrophysics Data System (ADS)

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

Järveläinen, J.; Haneda, K.

2014-04-01

34

Propagation characteristics of power line harmonic radiation in the ionosphere  

NASA Astrophysics Data System (ADS)

Theoretical model and solutions on power line harmonic radiation (PLHR) propagating in the ground, air, and anisotropic homogeneous ionosphere are presented. The theoretical model is verified by the PLHR events observed by the DEMETER satellite. Some propagation characteristics of PLHR based on the model are obtained. This paper is beneficial to quantitatively interpret the formation mechanism of PLHR phenomenon.

Wu, Jing; Fu, Jing-Jing; Zhang, Chong

2014-03-01

35

Image transmission in tactical radio frequency shared network propagation environments  

Microsoft Academic Search

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

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

1997-01-01

36

UHF-radio Propagation Predictor for Temporal Variations in Populated Indoor Environments  

Microsoft Academic Search

Ray-tracing is often used for site-specific propagation predictions, but current methods generally fail to accommodate shadowing and reflections caused by the movement of people: these represent significant effects in indoor radio environments. The method presented here improves site-specific indoor propagation predictions by including multiple, moving human bodies. The model, based on a hybrid image and ray-shooting approach, alto takes into

F. Villanese; W. G. Scanlon; N. E. Evans

37

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

38

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.

39

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

E-print Network

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

Boyer, Edmond

40

Mobile radio propagation in built-up areas: a numerical model of slow fading  

Microsoft Academic Search

A model of mobile radio propagation over buildings is proposed, enabling prediction of sector median field strength and its variability with varying building setups. The model predicts diffraction over building rooftops by combining ray methods with a novel method of multiple knife edge diffraction calculation suitable for applications requiring rapid computation. This technique is rapid and flexible enough to permit

S. R. Saunders; F. R. Bonar

1991-01-01

41

Measurements of LF and MF radio propagation over irregular, inhomogeneous terrain  

Microsoft Academic Search

Measurements of radio propagation path loss and local ground conductivity were made over four paths in the 100 to 2000 kHz band. The paths were of lengths up to 50 km and were chosen to represent both extreme and typical topography and conductivity conditions to the U.S. The measurements were made near Canyonlands National Park in Utah, at Highland Range

W. A. Kissick; E. J. Haakinson; G. H. Stonehocker

1978-01-01

42

The magnetoionic modes and propagation properties of auroral radio emissions  

NASA Technical Reports Server (NTRS)

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

Calvert, Wynne; Hashimoto, Kozo

1990-01-01

43

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

44

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

E-print Network

Characteristics of Low-power Wireless Links and Radios Understanding the characteristics of low-power Indication (RSSI), which the low-power radios use to measure the power of the wireless signal. This value. Calibrating RSSI Values Reported by 802.15.4 Radios 1 / 3 #12;Characteristics of Low-power Wireless Links

Amir, Yair

45

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

NASA Astrophysics Data System (ADS)

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

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

1985-12-01

46

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

47

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

48

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

Microsoft Academic Search

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

LÓRÁNT FARKAS; LAJOS NAGY; ANDREA FARKASVÖLGYI

2008-01-01

49

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

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

50

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

Microsoft Academic Search

The NASA\\/VOA Direct Broadcast Satellite - Radio (DBS-R) Program will be using a NASA Tracking Data Relay Satellite (TDRS) satellite at 62 deg West longitude to conduct live satellite S-band propagation experiments and demonstrations of satellite sound broadcasting over the next two years (1993-1994). The NASA\\/VOA DBS-R program has applied intensive effort to garner domestic and international support for the

James E. Hollansworth

1993-01-01

51

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

52

Analysis of quench propagation characteristics of the YBCO coated conductor  

NASA Astrophysics Data System (ADS)

Hot spot may emerge in a local region if the critical current is not uniform along the high temperature superconducting (HTS) tape, and the hot spot will cause serious damage to the HTS tape in some cases. However, under the present processing techniques, it is hard to make a long-length YBCO tape with uniform critical current density. Therefore, examining the thermal stability characteristic of the YBCO tape for the quench protection is very important. In this paper, the quench propagation velocities of YBCO tapes with insulating sheath materials were measured in liquid nitrogen (77 K) immersion. A heater is installed at the center of the tape to produce a normal zone to examine the propagation characteristics of the normal zone in the longitudinal direction. The quench characteristics were obtained by measuring the voltages between two nodes at different locations. Two different YBCO tapes produced by SuperPower Inc. and American Superconductor Corporation (AMSC) were tested under different currents respectively. The velocities both of them are under 3 cm/s and the results are discussed in detail. Based on the results, special attentions concerning the problems of stability in the power applications were discussed.

Liu, S.; Ren, L.; Li, J.; Tang, Y.

2011-11-01

53

Light propagation characteristics of high-purity polystyrene  

NASA Astrophysics Data System (ADS)

Organic scintillation materials involve short wavelength light emitted from polymers containing aromatic ring moieties. We have characterized high-purity (>99.9%) polystyrene (PS) as a potential scintillator. It emits ultraviolet light with a 310-nm emission maximum. We demonstrate that the effective refractive index (1.67) for PS is a function of the emission spectrum. Light yield distributions generated by 137Cs and 207Bi radioactive sources were also characterized. The light attenuation length is 41.6 ± 0.5 mm, which is ten times than expected. These results demonstrate that high-purity PS has important light propagation characteristics needed for organic scintillation materials.

Nakamura, Hidehito; Shirakawa, Yoshiyuki; Kitamura, Hisashi; Sato, Nobuhiro; Shinji, Osamu; Saito, Katashi; Takahashi, Sentaro

2013-10-01

54

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

55

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

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

56

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

57

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

58

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

NASA Technical Reports Server (NTRS)

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

Hollansworth, James E.

1993-01-01

59

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

NASA Technical Reports Server (NTRS)

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

Hollansworth, James E.

1993-01-01

60

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

NASA Technical Reports Server (NTRS)

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

Hollansworth, James E.

1993-01-01

61

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 2012. 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. Furthermore, global coverage is reached on a monthly basis, allowing to examine both temporal and spatial characteristics thoroughly. 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 monthly mean and median for 10° zonal bands. The latitudinal structure of first tropopauses shows the well-known distribution with high (cold) tropical tropopauses and low (warm) extratropical tropopauses. In the transition zones (20° N/S to 40° N/S), individual profiles reveal varying tropopause altitudes from 7 km to 17 km due to the influence of the subtropical jets. 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) and atmospheric dynamics (such as the very strong polar vortex in southern hemispheric winter). Inter-annual anomalies of tropopause parameters show signatures of El Niño-Southern Oscillation, the Quasi-Biennial Oscillation, and the varying strength of the polar vortex, including sudden stratospheric warming events.

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

2014-05-01

62

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

63

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

64

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

E-print Network

Large-scale, wave-like disturbances in extreme-ultraviolet (EUV) and type II radio bursts are often associated with coronal mass ejections (CMEs). Both phenomena may signify shock waves driven by CMEs. Taking EUV full-disk images at an unprecedented cadence, the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory has observed the so-called EIT waves or large-scale coronal propagating fronts (LCPFs) from their early evolution, which coincides with the period when most metric type II bursts occur. This article discusses the relation of LCPFs as captured by AIA with metric type II bursts. We show examples of type II bursts without a clear LCPF and fast LCPFs without a type II burst. Part of the disconnect between the two phenomena may be due to the difficulty in identifying them objectively. Furthermore, it is possible that the individual LCPFs and type II bursts may reflect different physical processes and external factors. In particular, the type II bursts that start at low frequencies an...

Nitta, Nariaki V; Gopalswamy, Nat; Yashiro, Seiji

2014-01-01

65

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

E-print Network

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

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

2002-02-13

66

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

E-print Network

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

Chandran, B D G

2002-01-01

67

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

68

Regional wave propagation characteristics and velocity structure in Asia  

Microsoft Academic Search

One of the most tectonically active continental regions in the world is in east Asia where continental collision occurs. In this dissertation an extensive study of seismic wave propagation recorded from earthquakes and nuclear explosions in China and its surrounding regions is presented. High-frequency Sn and Lg wave amplitude ratios are used to map lateral variations of shear wave attenuation.

Richard Ronald Rapine

2000-01-01

69

Failure initiation and propagation characteristics of honeycomb sandwich composites  

Microsoft Academic Search

The energy absorbed during the failure of a variety of structural shapes is influenced by material, geometry and the failure mode. Failure initiation and propagation of the honeycomb sandwich under loading involves not only non-linear behavior of the constituent materials, but also complex interactions between various failure mechanisms. Therefore, there is a need for an improved understanding of the material

A. R. Othman; D. C. Barton

2008-01-01

70

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

71

The characteristic polarized radio continuum distribution of cluster spiral galaxies  

NASA Astrophysics Data System (ADS)

Deep observations are presented of the 6 cm polarized radio continuum emission of 8 Virgo spiral galaxies. All galaxies show strongly asymmetric distributions of polarized intensity with elongated ridges located in the outer galactic disk. These features are not found in existing observations of polarized radio continuum emission of field spiral galaxies, where the distribution of 6 cm polarized intensity is generally relatively symmetric and strongest in the interarm regions. We therefore conclude that most Virgo spiral galaxies and, most probably, the majority of cluster spiral galaxies show asymmetric distributions of polarized radio continuum emission due to their interaction with the cluster environment. The polarized continuum emission is sensitive to compression and shear motions in the plane of the sky and thus contains important information about the velocity distortions caused by these interactions.

Vollmer, B.; Soida, M.; Beck, R.; Urbanik, M.; Chy?y, K. T.; Otmianowska-Mazur, K.; Kenney, J. D. P.; van Gorkom, J. H.

2007-03-01

72

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

73

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

74

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

75

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

Microsoft Academic Search

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

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

2003-01-01

76

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

77

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

2014-06-26

78

Propagation characteristics of coupled surface plasmon polaritons in PVDF slab waveguides at terahertz frequencies  

NASA Astrophysics Data System (ADS)

We present the propagation characteristics of y-polarized coupled surface plasmon polariton (SPP) modes supported by ferroelectric polyvinylidene fluoride (PVDF) slab waveguides at terahertz (THz) frequencies. Employing a two-dimensional (2D) finite-element method, four y-polarized coupled SPP modes are obtained, where two modes exhibit long propagation lengths (˜700 ?m) and the others provide subwavelength confinement. It is shown that PVDF is a promising material for plasmon-like excitation in the terahertz regime and results in strong confinement of THz wave propagation in SPP-based coupled waveguides.

Shruti; Sinha, Ravindra Kumar; Srivastava, Triranjita; Bhattacharyya, Ragunath

2013-03-01

79

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

SciTech Connect

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

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

2013-01-01

80

Propagation Path Visibility Estimation for Radio Local Distribution Systems in Built-Up Areas  

Microsoft Academic Search

For the design of radio local distribution systems in densely built-up areas, estimating how many subscribers are in sight from a nodal station is important. This paper proposes a method for estimating probability of success of line-of-sight paths termed visibility. Method validity is confirmed bypractical field examinations.

E. Ogawa; AKIO SATOH

1986-01-01

81

Radio propagation measurements at microwave frequencies for microcellular mobile and personal communications  

Microsoft Academic Search

The design and results of a propagation experiment at 900 MHz and 11 GHz to characterize microcell channels at two distinct frequencies in various environments, from rural to dense urban, are presented. The measurements were made by transmitting a continuous-wave (CW) signal from a mobile source to a fixed base and recording the signal envelope variations as a function of

N. Amitay; R. S. Owens; R. S. Roman

1989-01-01

82

Interstellar Weather -- Radio Wave Propagation Through the Turbulent Ionized Interstellar Medium  

NASA Astrophysics Data System (ADS)

Turbulence, or turbulent-like structures, in the interstellar medium when combined with motions of the medium and the pulsar-Earth line of sight lead to observable changes in pulse arrival time via both dispersion measure changes and multipath propagation or pulse broadening. In the Crab (PSR B0531+21) and Vela (PSR B0833-45) pulsars the column density variations are dominated by structures within the high-density material associated with the surrounding supernova remnants and pre-stellar matter. The Crab pulsar propagation parameters have been particularly disturbed during the past two years -- including a dispersion measure ``glitch'' with an amplitude of 0.1 pc cm(-3) in 1997 October. In the millisecond pulsar B1937+21 variable propagation effects are much smaller and are associated with the general intervening interstellar medium. Daily monitoring with small telescopes at NRAO Green Bank and at Jodrell Bank allow detailed inspection of the development of these propagation effects. We learn about structures in thermal plasma, ``interstellar weather'' along the line of sight, and can assess the impact of these effects on less frequently sampled precision timing programs.

Backer, D.; Wong, T.; Valanju, J.; Lyne, A.

1998-09-01

83

Effects of sandstorms and explosion-generated atmospheric dust on radio propagation  

Microsoft Academic Search

Suspended particulate matter in the atmosphere, generated by natural phenomena such as dust and sandstorms or by man-made near-surface explosions, has been suspected as a cause of microwave and millimeter-wave communications systems outages. An analysis carried out on the radio-frequency and optical effects of such dust clouds and the results, coupled with available information on particle-size distributions and suspended mass,

R. P. Rafuse

1981-01-01

84

Receiver operating characteristics of RadioVisioGraphy.  

PubMed

The diagnostic utility of intra-oral images obtained from the RVG second generation digital imaging system are compared with standard film images with the use of receiver operating characteristic analysis. Ten phantoms were constructed, each with 8 extracted teeth that had 12 approximal surfaces per phantom with holes drilled randomly to simulate approximal caries. Three images of each phantom were tested: a conventional film image, a thermal paper print, and a screen image. The images were rated by 26 dentists at separate sessions according to their confidence in the visibility of the simulated caries. A series of receiver operating characteristics curves were computed from the resulting 3120 decisions that indicate consistently greater success at detection of the holes on the film images. A full statistical analysis is given, and recommendations are made with respect to the use of this unit. PMID:7614189

Dagenais, M E; Clark, B G

1995-02-01

85

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

SciTech Connect

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

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

2012-08-15

86

NON-LINEAR PROPAGATION CHARACTERISTICS IN THE EVOLUTION OF BRASS MUSICAL INSTRUMENT DESIGN  

E-print Network

NON-LINEAR PROPAGATION CHARACTERISTICS IN THE EVOLUTION OF BRASS MUSICAL INSTRUMENT DESIGN PACS: 43 02138, USA; rpyle@post.harvard.edu ABSTRACT The capacity of brass instruments to generate sounds of the various kinds of brass instrument. INTRODUCTION Pyle and Myers 1 suggested a parameter related to non

Paris-Sud XI, Université de

87

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

E-print Network

Crack propagation through phase separated glasses: effect of the characteristic size of disorder of length scales, these objects obey a self-affine symmetry: they are left statistically invariant rescaling with different ratios depending on the direction. More specifically, self-affinity implies that the typical

Paris-Sud XI, Université de

88

UWB Characteristics of RF Propagation for Body Mounted and Implanted Sensors Submitted to the Faculty  

E-print Network

the human body to another sensor on the body surface or external. From the image data provided1 UWB Characteristics of RF Propagation for Body Mounted and Implanted Sensors by Jin Chen A Thesis of Department #12;2 Abstract Body Area Network (BAN) technology is related to many applications inside

Pahlavan, Kaveh

89

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

Microsoft Academic Search

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

Yasuhiro Oda; Reiko Tsuchihashi; Kouichi Tsunekawa; Masaharu Hata

2001-01-01

90

Fading characteristics of a 2.3 GHz radio telemetry channel in a hospital building.  

PubMed

This paper reports on radio path attenuation measurements made in a hospital complex at a spot frequency of 2.340 GHz. Power loss figures for fixed path propagation in a variety of building types have been determined for proposed telemetry use in operational ward situations. Throughout the hospital, the radio paths assessed all exhibited a loss in excess of that calculated for free-space communications. Modern buildings had external wall losses of 10-25 dB, with dividing walls in wards contributing an additional 5 dB. Received signal strength levels indicated a Rayleigh distribution for obstructed paths. Temporal testing was used to find the rate and depth of signal fades caused by the movement of personnel and equipment during normal ward usage; signal level reductions of greater than 35 dB were common during busy periods. PMID:7795861

Wang, L Q; Evans, N E; Burns, J B; Matthews, J G

1995-04-01

91

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

92

Theoretical and experimental investigation of feedforward signal regeneration as a means of combating multipath propagation effects in pilot-based SSB mobile radio systems  

Microsoft Academic Search

A technique is described, feedforward signal regeneration (FFSR), to combat the effects of multipath propagation on VHF and UHF pilot tone single sideband (SSB) mobile radio systems. Unlike feedforward automatic gain control (FFAGC), FFSR suppresses both the random amplitude and phase fluctuations in the received signal. Extensive laboratory and field tests have shown that the operation of SSB at UHF

J. P. McGeehan; AKD ANDREW J. BATEMAN

1983-01-01

93

Checking of communications and radio navigation systems  

Microsoft Academic Search

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

H. Maidment

1980-01-01

94

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

NASA Astrophysics Data System (ADS)

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

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

2004-09-01

95

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

Microsoft Academic Search

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

Wei Ding; Liang Chen; H. Liang

2007-01-01

96

Provision of the required navigation characteristics of satellite radio navigation systems in unfavorable helio-geophysical conditions  

Microsoft Academic Search

A detailed review of domestic and foreign scientific publications, dedicated to the influence of geomagnetic disturbances\\u000a and powerful bursts of the Sun’s radio radiation on the operation quality of satellite radio navigation systems (SRNS) and\\u000a their functional additions, is performed. It is shown that existing methods of providing the required radio navigation characteristics\\u000a during operation of the SRNS user’s device

V. V. Demyanov; E. L. Afraimovich; A. M. Alesshechkin

2009-01-01

97

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

SciTech Connect

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

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

2010-10-04

98

Characteristics of radio transmission over polymer optical fiber for indoor wireless coverage  

Microsoft Academic Search

The characteristics of radio over polymer optical fiber (RoPOF) are evaluated for indoor or in-building wireless coverage. The frequency responses and the third order intermodulation distortion products of the RoPOF link are investigated. The eye diagrams and EVM values of signals carrying quadrature-phase-shift-keyed (QPSK) data and global system for mobile (GSM) signals are measured to evaluate the transmission performance. The

Tao Jia; Shilie Zheng; Xianmin Zhang; Xinyu Jin; Xicheng Ai; Jian Xu

2006-01-01

99

Estimating the propagation characteristics of large-scale traveling ionospheric disturbances using ground-based and satellite data  

NASA Astrophysics Data System (ADS)

In this article, the propagation characteristics of large-scale traveling ionospheric disturbances (LS TIDs) are estimated during the geomagnetic storm periods of 14-16 May 2005 and 25-27 September 2011 over South Africa. One and two GPS arrays have been independently considered for the storms of 15 May 2005 and 26 September 2011, respectively. The average periods of dominant modes (? 2.5-3.5h) in the time series data were determined by applying wavelet analysis on both ionosonde and GPS data. The consideration of diurnal GPS total electron content (TEC) variability from receivers along three different longitude sectors showed a time shift in TEC enhancement with increasing latitude, the first indication of equatorward motion of the traveling ionospheric disturbances (TIDs). The statistical method (based on GPS radio interferometry) employed shows that these TIDs were mostly propagating nearly equatorward (for both storm periods), which is consistent with the existing literature about storm-induced TIDs. On storm days, TID horizontal velocities have been determined in the range of ?200-500m/s. The analysis of diurnal TEC response from different stations confirmed that the positive storm effect observed on 15 May 2005 was a result of the large-scale TIDs of wavelength ?4000 km. On the other hand, the estimated wavelengths of LS TIDs on 26 September 2011 were ?2400-3400km between 10 and 17 UT. A time lag is observed between the times at which enhancements in TEC, ionosonde foF2, and hmF2 data are revealed, and this has been attributed to the passage of the TID.

Habarulema, John Bosco; Katamzi, Zama Thobeka; McKinnell, Lee-Anne

2013-12-01

100

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

101

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

102

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

NASA Technical Reports Server (NTRS)

Measured propagation characteristics of Finite Ground Coplanar (FGC) waveguide on silicon substrates with resistivities spanning 3 orders of magnitude (0.1 to 15.5 Ohm cm) and a 20 micron thick polyimide interface layer is presented as a function of the FGC geometry. Results show that there is an optimum FGC geometry for minimum loss, and silicon with a resistivity of 0.1 Ohm cm has greater loss than substrates with higher and lower resistivity. Lastly, substrates with a resistivity of 10 Ohm cm or greater have acceptable loss.

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

2002-01-01

103

Nonlinear programming analysis of multi-mode wave propagating characteristics in ion-beam plasma system  

NASA Astrophysics Data System (ADS)

Propagating characteristics of multimode waves are analyzed in an ion-beam plasma system by means of nonlinear programming techniques. A fine structure of each wave mode such as a wavenumber, damping rate, a wave amplitude, a wave peak point, and a phase relation among the waves is obtained from the observed interferometer traces of multimode waves. The wave pattern assembled with the separated patterns into each wave mode is confirmed to be quite similar to the observed one. A qualitative agreement of wave dispersion relation is obtained between the values analyzed by the present method and calculated by the plasma kinetic theory.

Yagura, Shinya; Fujita, Hiroharu; Kankubo, Kouichi

1989-08-01

104

Eigenvalue Analysis of sound propagation characteristics in a circular duct lined with poroelastic foams  

NASA Astrophysics Data System (ADS)

An effective method for eigenvalue analysis of a circular duct lined with poroelastic foams is presented using axisymmetric finite element models based on Biot's theory and Helmholtz equation. Complex dispersion relations in a cylindrical foam-lined duct are successfully identified using an iterative Prony series method. It is shown that the numerical results obtained by the proposed method agree well with those obtained by measurements and direct forced response simulations. The influences of thickness and boundary conditions of the poroelastic foam on the sound propagation characteristics in a duct are also investigated. Furthermore, the damping effect due to viscosity of the foam on dispersion curves is discussed at a theoretical level.

Son, Myung Seob; Lee, Seung Yeop; Kang, Yeon June

2014-03-01

105

Low-Complexity Adaptive Transmission for Cognitive Radios in Dynamic Spectrum Access Networks  

Microsoft Academic Search

Cognitive radios that are employed in a network with dynamic frequency assignments must operate efficiently in the presence of uncertainties and variations in the propagation characteristics of the network's communication links. A low-complexity adaptive transmission protocol is described and evaluated for use in cognitive radio networks whose links have unknown and possibly time-varying propagation losses as a result of such

Michael B. Pursley; Thomas C. Royster Iv

2008-01-01

106

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

107

Modal propagation and imaging characteristics of a custom designed coherent fiberbundle for endomicroscopy  

NASA Astrophysics Data System (ADS)

In recent years, several groups have investigated the use of Proximal Spatial Light modulation (PSML) as an alternative fiber optic imaging technique. In PSLM, the light exiting the distal end of the fiber optic endoscope can be focused, without any distal micro-optics or micro-mechanics, on any point within the Field Of View (FOV) via spatial modulation of the light before it is coupled in at the endoscope's proximal end. In previous work, we reported on the custom design of a Coherent Fiber Bundle made with soft glasses (as opposed to the commercially available optical fibers used by other groups) to be used with PSLM. In this paper we present the results of the numerical characterization of the Coherent Fiber Bundle fabricated according to our design. We investigate the CFB's modal propagation characteristics as well as its imaging properties (FOV and point spread function). Our numerical characterization also takes into account fabrication induced defects such as variations in core size, core shape (ellipticity) and lattice constant. Realistic values for the defects were obtained via SEM images of the fabricated CFB's cross section. We find that noise on the wave front of the field exiting the distal end of the CFB causes a much larger deterioration of the point spread function than amplitude noise. And while we find that variations in core shape have the largest impact on the CFB's propagation characteristics, our results indicate that this negative impact could be negated if the elliptical cores were aligned along a common axis.

Heyvaert, S.; Ottevaere, H.; Kujawa, I.; Buczynski, R.; Raes, M.; Terryn, H.; Thienpont, H.

2014-05-01

108

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

109

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

110

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

PubMed Central

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

111

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

112

Propagation characteristics of guided waves in a rod surrounded by an infinite solid medium  

NASA Astrophysics Data System (ADS)

The dispersion and excitation characteristics of the guided waves in a rod surrounded by an infinite solid medium (cladding) are investigated. First, the bisection technique is employed to find all the roots of the dispersion function on the basis of theoretical analysis and to obtain the complex phase and group velocity dispersion curves of the guided modes. Second, according to their different dispersion characteristics, the guided modes are divided into two categories: normal modes and Stoneley modes. And it is concluded that the normal modes merely exist in the “hard cladding” model in which the cladding’s shear velocity is larger than the rod’s; while the Stoneley modes in cylindrical interface are highly dispersive and merely exist in the model whose acoustical parameters satisfied the existence condition of the Stoneley waves. Third, the seldom discussed issue, the excitation mechanisms of the guided waves, excited by three source models: symmetric point source, axial and radial force sources, are simulated respectively. Attention is paid on the dominant mode which has better excitation sensitivity and the suitable excitation frequency range. Moreover, the propagation characteristics of the Stoneley modes, ignored in previous references, are analyzed and compared with those of the normal modes.

Cui, Hanyin; Zhang, Bixing; Ji, Shunxin

2010-07-01

113

Normal zone propagation characteristics of the HTS wires by heat energy applied  

NASA Astrophysics Data System (ADS)

With the successful commercialization of Bi-2223 powder-in-tube wire, various attempts in the R&D of the high- Tc superconducting (HTS) magnets for high magnetic field applications are being implemented actively. Operating temperature of HTS magnet has to be maintained at the designed level but the magnetic energy and mechanical disturbance can cause unstable operational temperature of HTS magnet. Especially, the generated heat energy of inner HTS winding is apt to be accumulated, so the normal region appears in HTS winding. This paper deals with the quenching characteristics of three kinds of selected Bi-2223 wires: the high current density wire (HC-A) and the high strength wire (HS-A) made by AMSC and HTS wire (HW-I) made by Innost. The Innost wire has the highest minimum quench energy (MQE). The high current density wire has the highest normal zone propagation velocity (NZPV).

Bae, Duck Kweon; Kang, Hyoungku; Ahn, Min Cheol; Sim, Kideok; Kim, Yeong Sik; Yoon, Yong Soo; Ko, Tae Kuk

2006-05-01

114

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

115

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

116

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

Microsoft Academic Search

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

Mohammed A. Alhaider

1986-01-01

117

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

118

Simulation of Effervescent Atomization and Nanoparticle Characteristics in Radio Frequency Suspension Plasma Spray  

NASA Astrophysics Data System (ADS)

In this paper, a comprehensive model was developed to investigate the suspension spray for a radio frequency (RF) plasma torch coupled with an effervescent atomizer. Firstly, the RF plasma is simulated by solving the thermo-fluid transport equations with electromagnetic Maxwell equation. Secondly, primary atomization of the suspension is solved by a proposed one-dimensional breakup model and validated with the experimental data. Thirdly, the suspension droplets and discharged nanoparticles are modeled in Lagrangian manner, to calculate each particle tracking, acceleration, heating, melting and evaporation. Saffman lift force, Brownian force and non-continuum effect are considered for nanoparticle momentum transfer, as well as the effects of evaporation on heat transfer. This model predicts the nanoparticle trajectory, velocity, temperature and size in the RF suspension plasma spray. Effects of the torch and atomizer operating conditions on the particle characteristics are investigated. Such operating conditions include gas-to-liquid flow ratio, atomizer orifice diameter, injection pressure, power input level, plasmas gas flow rate, and powder material. The statistical distributions for the multiple particles are also discussed for different cases.

Xiong, Hong-Bing; Qian, Li-Juan; Lin, Jian-Zhong

2012-03-01

119

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

120

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

NASA Astrophysics Data System (ADS)

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

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

121

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

NASA Technical Reports Server (NTRS)

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

1975-01-01

122

Radio Ghosts  

E-print Network

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

Torsten A. Ensslin

1999-06-11

123

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

Microsoft Academic Search

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

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

2000-01-01

124

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

NASA Astrophysics Data System (ADS)

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

Schmitter, E. D.

2013-09-01

125

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

Microsoft Academic Search

When viscous behavior becomes affected by a chemical or a physical change in a fluid, the overtones or harmonics arising from the inherently nonlinear nature of acoustic propagation of a pure sine wave in the fluid will also undergo modification(D. R. Raichel and W. H. Kapfer, \\

Kenneth Takabayashi; Daniel R. Raichel

1996-01-01

126

Spatial and temporal variations in acoustic propagation characteristics at the New England shelfbreak front  

Microsoft Academic Search

The spatial and temporal variability of the acoustic field in the region of a strong coastal shelfbreak front are examined, using the high-resolution environmental data from the 1996-1997 New England shelfbreak PRIMER experiment to provide input to acoustic propagation models. Specifically, the \\

J. F. Lynch; A. E. Newhall; B. Sperry; G. Gawarkiewicz; A. Fredricks; P. Tyack; C. S. Chiu; P. Abbot

2003-01-01

127

Propagation characteristics of historical tsunamis that attacked the east coast of Korea  

Microsoft Academic Search

In this study, a numerical modeling system based on the dispersion–correction finite difference scheme equipped with a grid-nesting\\u000a scheme is constructed. The model is applied to simulate the propagation of three historical tsunami events that attacked the\\u000a east coast of Korea. The calculated free-surface displacements for the cases of the 1983 Akita and the 1993 Okushiri tsunamis\\u000a are compared with

Chae Ho Lim; Jae Seok Bae; Jong In Lee; Sung Bum Yoon

2008-01-01

128

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

129

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

130

The Long-term Characteristics of Radio Flares from V711 Tau, ? Per and UX Ari  

NASA Astrophysics Data System (ADS)

We have studied the long-term behavior of radio flares from three binary systems: V711 Tau, ? Per and UX Ari. The radio flares were collected with the Green Bank Interferometer continuously from 1995 to 2000 at frequencies of 2.3 GHz and 8.3 GHz (see Richards, Waltman, and Ghigo, these proceedings). Many strong flares were detected from the three systems. We found that flaring activity in ? Per was nearly continuous, while V711 Tau and UX Ari were usually quiescent for 50 - 100 days before a large flare event. Long-term monitoring permitted us to discover both active and quiescent flaring epochs in V711 Tau and ? Per which apparently last for more than 500 days in both systems. This work was supported by NSF grant AST-0074586.

Soinski, T. L.; Richards, M. T.

2002-05-01

131

On-Body Antennas and Propagation: Recent Development  

Microsoft Academic Search

The paper reviews recent advances in on-body antennas and propagation under a joint UK EPSRC research project between Queen Mary College, University of London and University of Birmingham. The study of on-body radio propagation has been extended by using various small antennas. The effect of antenna size, gain and radiation patterns on on-body channel characteristics has been studied. A practical

Yang Hao; Peter S. Hall

2008-01-01

132

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

NASA Astrophysics Data System (ADS)

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

Takabayashi, Kenneth; Raichel, Daniel R.

1996-11-01

133

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

PubMed

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

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

2012-01-01

134

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

135

Space Telecommunications Radio System STRS Cognitive Radio  

NASA Technical Reports Server (NTRS)

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

Briones, Janette C.; Handler, Louis M.

2013-01-01

136

Vertical propagation characteristics of internal gravity waves around the mesopause observed by the Arecibo UHF radar  

NASA Astrophysics Data System (ADS)

A high resolution wind observation of the mesosphere and lower thermosphere (73-95 km) was conducted with the aid of the high power UHF Doppler radar at Arecibo (18.4 deg N, 66.8 deg W). Zonal wind velocities were continuously observed during day-time hours on Aug. 1-15, 1980. The observed wind fluctuations with periods of 1-4 h are discussed in the light of internal gravity waves. The phase propagation associated with these fluctuations is, on average, shown to be downward, indicating an upward energy flux. A space-time spectral analysis shows that waves with vertical wavelengths shorter than 10 km disappear around the mesopause (about 85 km), while those with longer vertical wavelengths exist throughout the observational height. This result is explained in terms of wave absorption at a critical layer where the mean zonal wind has a westerly shear with height. This feature is consistent with the behavior required for internal gravity waves around the summer mesopause in order to explain general circulation models.

Maekawa, Yasuyuki; Fukao, Shoichiro; Kato, Susumu

1987-01-01

137

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

SciTech Connect

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

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

2012-04-01

138

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

139

A Prony Technique for Prediction of Ground Multipath Parameters in LOS Radio Links Using Field-height Data  

Microsoft Academic Search

Multipath propagation is a major cause of impairment in LOS link performance. With the advent of high capacity digital radio and development of high level modulation schemes both a high bit rate and wide bandwidth are required to accommodate the transmitted signal. Such requirements are highly affected by the frequency selective fading, which is a typical characteristic of multipath propagation.

Khalil H. Sayidmarie; Sinan K. Shanshal

140

Radio Wave Propagation over Salem  

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

141

Statistical characteristics of AGW wave packet propagation in the lower atmosphere observed by the MU radar  

NASA Astrophysics Data System (ADS)

We study the horizontal structure of the atmospheric gravity waves (AGW) in the height ranges between 6 and 22 km observed using the MU radar at Shigaraki in Japan, during a 3 day period in January and a 4 day period in August 1988. The data were divided by double Fourier transformation into a data set of upward moving waves and a data set of downward moving waves for independent analysis. The phase and group velocity tracing technique was applied to measure the vertical group and phase velocity as well as the characteristic period of the gravity wave packet. Then the dispersion equation of the linear theory of AGW was solved to obtain its intrinsic wave period - horizontal wavelength and horizontal group velocity - and the vertical flux of horizontal momentum associated with each wave packet was estimated to help determine the direction of the characteristic horizontal wave vector. The results showed that the waves with periods in the range of 30 min~6 h had horizontal scales ranging from 20 km to 1500 km, vertical scales from 4 km to 15 km, and horizontal phase velocities from 15 m/s to 60 m/s. The upward moving wave packets of wave period of 2 h~6 h had horizontal group velocities mainly toward east-south-east and northeast in winter, and mainly in the section between the directions of west-north-west and north in summer.

Kuo, F. S.; Lue, H. Y.; Fern, C. L.; Röttger, J.; Fukao, S.; Yamamoto, M.

2009-10-01

142

The carbon nanotube radio  

Microsoft Academic Search

The characteristics of the nanotube radio are improved considering new configurations based on quantum tunneling. In this way, the new invented nanotube radio could be tuned electrically in the entire FM or AM bands and biased with miniaturized batteries.

M. Dragoman; D. Dragoman

2008-01-01

143

Lunar Surface Propagation Modeling and Effects on Communications  

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

144

Interference Characteristics and Success Probability at the Primary User in a Cognitive Radio Network  

E-print Network

) devices in the ultra high frequency (UHF) television (TV) bands under the condition that they do not cause harmful interference to the operation of the primary users [1], [2]. This paper assesses the effect harmful interference at the PU. Using the concepts of stochastic geometry, we study the characteristics

Boyer, Edmond

145

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

146

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

147

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

Microsoft Academic Search

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

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

2008-01-01

148

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

149

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

150

Radio Observations of Weak Coronal Transients  

NASA Astrophysics Data System (ADS)

In this review we discuss radio observations of weak coronal transients. We concentrate on the transient events observed primarily by Yohkoh/SXT and to a smaller extent by SOHO/EIT. The radio observations are those obtained with the Very Large Array (VLA) in microwaves, the Nancay (France) metric radioheliograph at 150 - 450 MHz and the Nobeyama RadioHeliograph (NRH) at 17 GHz. We discuss the observational characteristics of X-ray bright point flares at meter wavelengths and in microwaves, and provide evidence that both thermal and nonthermal processes occur in these small scale flaring events. Similarly, radio observations of X-ray jets in microwaves and at meter wavelengths provide evidence for both thermal and nonthermal processes in these dynamic coronal phenomena. Nonthermal radio emission in the form of metric type III bursts is produced by electron beams propagating along the jet, whereas microwave emission comes mostly from the jet base. We discuss active region transient brightenings (ARTB's) and show that their radio emission can be purely thermal, thermal gyro- resonance or nonthermal gyrosynchrotron radiation. We discuss one form (radio-selected) of quiet Sun transient brightenings located far from active regions. We provide evidence that weak plasma ejections following flares is observed at metric wavelengths in the form of transient continuum emission. Finally, we discuss the time-varying polar brightenings at 17 GHz, and their relationship to polar erupting plumes observed by SOHO-EIT.

Kundu, M. R.

1999-12-01

151

Radio frequency strain monitor  

NASA Technical Reports Server (NTRS)

A radio frequency strain monitor includes a voltage controlled oscillator for generating an oscillating signal that is input into a propagation path. The propagation path is preferably bonded to the surface of a structure to be monitored and produces a propagated signal. A phase difference between the oscillating and propagated signals is detected and maintained at a substantially constant value which is preferably a multiple of 90.degree. by changing the frequency of the oscillating signal. Any change in frequency of the oscillating signal provides an indication of strain in the structure to which the propagation path is bonded.

Heyman, Joseph S. (Inventor); Rogowski, Robert S. (Inventor); Holben, Jr., Milford S. (Inventor)

1989-01-01

152

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

153

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

154

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

NASA Astrophysics Data System (ADS)

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

2010-08-01

155

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

156

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

157

Statistical study of Pc1–2 wave propagation characteristics in the high-latitude ionospheric waveguide  

Microsoft Academic Search

ULF wave propagation in the ionospheric waveguideAntarctic ground magnetometer array observed poleward wave power attenuationFrequency cutoff in the waveguide is dependent on the ionospheric conductivity

H. Kim; M. R. Lessard; M. J. Engebretson; M. A. Young

2011-01-01

158

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

PubMed

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. PMID:24089818

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

2013-09-01

159

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

160

Temperature Effects on the Propagation Characteristics of Love Waves along Multi-Guide Layers of Sio2/Su-8 on St-90?X Quartz  

PubMed Central

Theoretical calculations have been performed on the temperature effects on the propagation characteristics of Love waves in layered structures by solving the coupled electromechanical field equations, and the optimal design parameters were extracted for temperature stability improvement. Based on the theoretical analysis, excellent temperature coefficient of frequency (Tcf) of the fabricated Love wave devices with guide layers of SU-8/SiO2 on ST-90°X quartz substrate is evaluated experimentally as only 2.16 ppm. PMID:22969349

Xu, Fangqian; Wang, Wen; Hou, Jiaoli; Liu, Minghua

2012-01-01

161

The present state of continental and intercontinental ionospheric radio communications  

NASA Astrophysics Data System (ADS)

Ionospheric characteristics which affect radio wave propagation are discussed, with an emphasis on techniques for using the ionosphere to extend the range of radio links. Interference has been proven highly correlated with the onset of solar disturbances. The ionosphere, however, by bending and reflecting radio signals, is useful for beyond-the-horizon radio links. ELF frequencies permit communication with submerged submarines. HF bands are employed for mobile surface communications around 75 MHz. The VLF bands from 3-30 kHz are applied for long-range links and radionavigation, and with controlled polarization furnish a high SNR. Continuity of broadcasts from earth-earth and earth-satellite depends on constant monitoring of ionospheric conditions and the spectra of the disturbances.

Silleni, S.

162

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

163

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

Microsoft Academic Search

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

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

2006-01-01

164

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

165

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

NASA Astrophysics Data System (ADS)

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

Pasmanik, Dmitry; Demekhov, Andrei

166

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

Microsoft Academic Search

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

H. Meier; P. Russer

1991-01-01

167

Effects of H{sub 2} enrichment on the propagation characteristics of CH{sub 4}-air triple flames  

SciTech Connect

The effects of H{sub 2} enrichment on the propagation of laminar CH{sub 4}-air triple flames in axisymmetric coflowing jets are numerically investigated. A comprehensive, time-dependent computational model, which employs a detailed description of chemistry and transport, is used to simulate the transient ignition and flame propagation phenomena. Flames are ignited in a jet-mixing layer far downstream of the burner. Following ignition, a well-defined triple flame is formed that propagates upstream along the stoichiometric mixture fraction line with a nearly constant displacement velocity. As the flame approaches the burner, it transitions to a double flame, and subsequently to a burner-stabilized nonpremixed flame. Predictions are validated using measurements of the displacement flame velocity. As the H{sub 2} concentration in the fuel blend is increased, the displacement flame velocity and local triple flame speed increase progressively due to the enhanced chemical reactivity, diffusivity, and preferential diffusion caused by H{sub 2} addition. In addition, the flammability limits associated with the triple flames are progressively extended with the increase in H{sub 2} concentration. The flame structure and flame dynamics are also markedly modified by H{sub 2} enrichment, which substantially increases the flame curvature and mixture fraction gradient, as well as the hydrodynamic and curvature-induced stretch near the triple point. For all the H{sub 2}-enriched methane-air flames investigated in this study, there is a negative correlation between flame speed and stretch, with the flame speed decreasing almost linearly with stretch, consistent with previous studies. The H{sub 2} addition also modifies the flame sensitivity to stretch, as it decreases the Markstein number (Ma), implying an increased tendency toward diffusive-thermal instability (i.e. Ma {yields} 0). These results are consistent with the previously reported experimental results for outwardly propagating spherical flames burning a mixture of natural gas and hydrogen. (author)

Briones, Alejandro M.; Aggarwal, Suresh K. [Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, Chicago, IL 60607 (United States); Katta, Viswanath R. [Innovative Scientific Solutions, Inc., 2766 Indian Ripple Road, Dayton, OH 45440 (United States)

2008-05-15

168

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

169

One-to-one relationship between low latitude whistlers and conjugate source lightning discharges and their propagation characteristics  

NASA Astrophysics Data System (ADS)

One-to-one relation with its causative lightning discharges and propagation features of night-time whistlers recorded at low-latitude station, Allahabad (geomag. lat. 16.05°N, L = 1.08), India, from continuous observations made during 1-7 April, 2011 have been studied. The whistler observations were made using the Automatic Whistler Detector (AWD) system and AWESOME VLF receiver. The causative lightning strikes of whistlers were checked in data provided by World-Wide Lightning Location Network (WWLLN). A total of 32 whistlers were observed out of which 23 were correlated with their causative lightnings in and around the conjugate location (geom. lat. 9.87°S) of Allahabad. A multi-flash whistler is also observed on 1 April with dispersions 15.3, 17.5 and 13.6 s1/2. About 70% (23 out of 32) whistlers were correlated with the WWLLN detected causative lightnings in the conjugate region which supports the ducted mode of propagation at low latitude. The multi-flash and short whistlers also propagated most likely in the ducted mode to this station.

Srivastava, Prateek R.; Gokani, Sneha A.; Maurya, Ajeet K.; Singh, Rajesh; Kumar, Sushil; Veenadhari, B.; Selvakumaran, R.; Singh, Abhay K.; Siingh, Devendraa; Lichtenberger, Janos

2013-12-01

170

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

Microsoft Academic Search

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

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

2002-01-01

171

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

172

Propagation research in Japan  

NASA Technical Reports Server (NTRS)

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

Wakana, Hiromitsu

1991-01-01

173

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

174

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

175

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

SciTech Connect

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

He, H.-Q.; Qin, G. [State Key Laboratory of Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Zhang, M., E-mail: hqhe@spaceweather.ac.cn, E-mail: gqin@spaceweather.ac.cn, E-mail: mzhang@fit.edu [Department of Physics and Space Science, Florida Institute of Technology, Melbourne, FL 32901 (United States)

2011-06-20

176

VLF Phase Characteristics Deduced from Atmospheric Wave Forms  

Microsoft Academic Search

The wave forms of the electric field of atmospherics recorded at four widely separated stations are analyzed to yield the phase characteristics of radio waves at very low frequencies. It is indicated that the relative phase velocity for propagation to great distances is about 3 per cent greater than c (velocity of light in a vacuum) at 4 kc\\/s. Above

A. Glenn Jean; William L. Taylor; James R. Wait

1960-01-01

177

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

E-print Network

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

Herman J. Mosquera Cuesta

2011-05-13

178

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

PubMed

Measurements of low-frequency sound propagation over the areas of the Australian continental shelf, where the bottom sediments consist primarily of calcarenite, have revealed that acoustic transmission losses are generally much higher than those observed over other continental shelves and remain relatively low only in a few narrow frequency bands. This paper considers this phenomenon and provides a physical interpretation in terms of normal modes in shallow water over a layered elastic seabed with a shear wave speed comparable to but lower than the water-column sound speed. A theoretical analysis and numerical modeling show that, in such environments, low attenuation of underwater sound is expected only in narrow frequency bands just above the modal critical frequencies which in turn are governed primarily by the water depth and compressional wave speed in the seabed. In addition, the effect of a thin layer of harder cap-rock overlaying less consolidated sediments is considered. Low-frequency transmission loss data collected from an offshore seismic survey in Bass Strait on the southern Australian continental shelf are analyzed and shown to be in broad agreement with the numerical predictions based on the theoretical analysis and modeling using an elastic parabolic equation solution for range-dependent bathymetry. PMID:23862798

Duncan, Alec J; Gavrilov, Alexander N; McCauley, Robert D; Parnum, Iain M; Collis, Jon M

2013-07-01

179

Radio Journalism.  

ERIC Educational Resources Information Center

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

Bittner, John R.; Bittner, Denise A.

180

Prediction of propagation characteristics of photonic crystal fibers by a simpler, more complete and versatile formulation of their effective cladding indices  

NASA Astrophysics Data System (ADS)

We present a simpler, more complete and versatile formulation for the effective cladding index of a solid-core photonic crystal fiber (PCF) with a triangular lattice of air holes in the cladding region. This index depends on two fundamental geometrical parameters: the air hole diameters and their separation in the endlessly single mode region of the PCF corresponding to a prescribed upper limit of relative air hole size as well as the wavelength of the light used. Our earlier available formulation for the normalized propagation constants of the infinite cladding region of the same PCF and hence its effective cladding index takes care only of the dependence on the relative air hole size and wavelength at a particular hole pitch. Now, the hole pitch dependence is also taken into account to make the formulation complete in all senses. The proposed new formulation is shown to be accurate on the basis of a comparison of our results with those obtained by available techniques. Further, to check its validity in different problems of practical interest, we apply our new formulation to evaluate various propagation characteristics of the PCF. On comparison with the previously available results, our results are seen to agree excellently with them. The formulation should find wide use for simple verification by system designers and users.

Kundu, Dipankar; Sarkar, Somenath

2014-05-01

181

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

182

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

NASA Astrophysics Data System (ADS)

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

Huebner, Christof; Kottmeier, Christoph; Brandelik, Alexander

2011-06-01

183

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

184

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

185

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

186

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

187

Educational Radio.  

ERIC Educational Resources Information Center

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

Arafeh, Sousan

1999-01-01

188

Distinct propagating fast wave trains associated with flaring energy releases  

NASA Astrophysics Data System (ADS)

Context. Large-scale fast waves with perturbation of the EUV emission intensity are well resolved in both temporal and spatial scale by SDO/AIA. These waves are prone to propagate along the magnetic field line. Aims: We aim to probe the link between propagating fast wave trains and flaring energy releases. By measuring the wave parameters, we reveal their nature and investigate the potential to diagnose the energy source and waveguide. Methods: The spatial and temporal evolution of the wave amplitude and propagating speed are studied. The correlation of individual wave trains with flare-generated radio bursts is tested. Results: The propagating wave pattern comprises distinct wave trains with varying periods and wavelengths. This characteristic signature is consistent with the patterns formed by waveguide dispersion, when different spectral components propagate at different phase and group speeds. The wave train releases are found to be highly correlated in start time with the radio bursts emitted by the non-thermal electrons that were accelerated in bursty energy releases. The wave amplitude is seen to reach the maximum midway during its course. This can be caused by a combined effect of the waveguide spread in the transverse direction and density stratification. The transverse amplitude distribution perpendicular to the wave vector is found to follow approximately a Gaussian profile. The spatial structure is consistent with the kink mode that is polarised along the line-of-sight. The propagating speed is subject to deceleration from ~735-845 km s-1 to ~600 km s-1. This could be caused by the decrease in the local Alfvén speed and/or the projection effect.

Yuan, D.; Shen, Y.; Liu, Y.; Nakariakov, V. M.; Tan, B.; Huang, J.

2013-06-01

189

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

190

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

191

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

SciTech Connect

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

Kuruganti, Phani Teja [ORNL

2007-01-01

192

Research on simulation of sound propagation system  

Microsoft Academic Search

The basic design idea of sound propagation system simulation is introduced, and the sound propagation characteristics in enclosure are analyzed. Establish a two-dimension space mathematic model of sound propagation system. Present the general process and methods of sound propagation system simulation, based on which the system simulation was realized. According to the similar principle, simulation can be extended to three-dimensional

Feng Yuan; Cai Zeng-yu; Jiang Ya-ping; Gan Yong

2010-01-01

193

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

194

Implementation of Digital Radio Mondiale receiver-part I  

Microsoft Academic Search

Radio communications possessing high signal quality and long-distance propagation have traditionally been difficult to achieve reliably over shortwave bands (up to 30 MHz). This is due to the analog modulation schemes in use and the vulnerability of shortwave radio to atmospheric disturbances. The development of the Digital Radio Mondiale (DRM) standard in 2001 provided digital coding methods, audio compression, and

Donald E. Willcox; Joonwan Kim; Chris Loewen; John Wineman

2010-01-01

195

A Stream-Based Configurable Computing Radio Testbed  

Microsoft Academic Search

Software radios have emerged as important tools in the development of new signal processing algorithms, networking protocols, and propagation experiments in wireless environments. With a software radio, the signal processing and modem management can be changed in a timely matter. This enables users to explore a variety of domains before committing a design to silicon. Contemporary DSP-based software radios have

Steven Swanchara; Scott J. Harper; Peter M. Athanas

1998-01-01

196

Broadcasting in Unreliable Radio Networks  

E-print Network

Practitioners agree that unreliable links, which fluctuate between working and not working, are an important characteristic of wireless networks. In contrast, most theoretical models of radio networks fix a static set of ...

Oshman, Rotem

2010-06-08

197

Broadcasting in unreliable radio networks  

E-print Network

Practitioners agree that unreliable links, which sometimes deliver messages and sometime do not, are an important characteristic of wireless networks. In contrast, most theoretical models of radio networks fix a static set ...

Kuhn, Fabian

198

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

199

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

Microsoft Academic Search

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

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

1995-01-01

200

Radio Telescopes  

NASA Astrophysics Data System (ADS)

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

Ekers, Ron; Wilson, Thomas L.

201

Elements of Radio Waves  

E-print Network

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

Frank G. Borg; Ismo Hakala; Jukka Määttälä

2007-12-24

202

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

203

Why Radio?  

ERIC Educational Resources Information Center

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

Josephson, Larry

1979-01-01

204

CB Radios  

ERIC Educational Resources Information Center

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

Martin, Dick

1977-01-01

205

Satellite radio  

Microsoft Academic Search

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

S. Rangarajan

2002-01-01

206

Chamber propagation  

SciTech Connect

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

Langdon, B.

1991-01-16

207

Plasma Diagnostics of the Interstellar Medium with Radio Astronomy  

NASA Astrophysics Data System (ADS)

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

Haverkorn, Marijke; Spangler, Steven R.

208

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

SciTech Connect

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

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

2013-05-31

209

On the Propagation of a Reaction Front Through a Porous Fuel in the Presence of an Opposed Forced Flow: Application to Mixtures Characteristic of Municipal Waste  

Microsoft Academic Search

An expression for the propagation velocity of a reaction front in a porous solid material is obtained by using a one-dimensional energy conservation equation. The reaction is divided in two distinct fronts.an ignition front where gasification of large part of the fuel occursand a flamingfront where gas phase oxidation takes place. Forced flow and reaction move in opposite directions, so,

X. ZHOU; J. L. TORERO; J. C. GOUDEAU; B. BREGEON

1995-01-01

210

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

211

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

212

Radio astronomy  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

213

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

NASA Technical Reports Server (NTRS)

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

Baumeister, K. J.

1979-01-01

214

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

215

Characteristic investigation of 2D photonic crystals with full material anisotropy under out-of-plane propagation and liquid-crystal-filled photonic-band-gap-fiber applications using finite element methods.  

PubMed

To effectively investigate the fundamental characteristics of two-dimensional (2D) photonic crystals (PCs) with arbitrary 3D material anisotropy under the out-of-plane wave propagation, we establish a full-vectorial finite element method based eigenvalue algorithm to perform related analysis correctly. The band edge diagrams can be conveniently constructed from the band structures of varied propagation constants obtained from the algorithm, which is helpful for the analysis and design of photonic ban gap (PBG) fibers. Several PCs are analyzed to demonstrate the correctness of this numerical model. Our analysis results for simple PCs are checked with others' ones using different methods, including the transfer matrix method, the finite-difference frequency-domain (FDFD) method, and the plane-wave expansion method. And the validity of those for the most complex PC with arbitrary 3D anisotropy is supported by related liquid-crystal-filled PBG fiber mode analysis, which demonstrates the dependence of transmission properties on the PBGs, employing a full-vectorial finite element beam propagation method (FE-BPM). PMID:19104565

Hsu, Sen-ming; Chang, Hung-chun

2008-12-22

216

Physics-based modeling of wave propagation for terrestrial and space communications  

Microsoft Academic Search

This dissertation investigates the solutions to two important and challenging problems of radio wave propagation in wireless communication. The first problem pertains to modeling of wave propagation in foliage. The second problem involves a comprehensive study in enhancing the radio uplink between a ground station and a spacecraft using an array of reflector antennas. Solutions are developed using physics-based modeling

Feinian Wang

2006-01-01

217

CORONAL MAGNETOGRAPHY FROM QUASI -TRANSVERSE PROPAGATION  

E-print Network

magnetography for the microwave wavelength range: - quantitative analysis of the circularly polarized free the radio maps of a microwave source at a set of wavelengths (Brosius et al., 1997); - field measurements of quasi-transverse (QT-) propagation of microwaves in the low solar corona and some coronal magnetograms

Ryabov, Boris I.

218

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

219

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

220

Radio and space research at Slough 1920-1981  

Microsoft Academic Search

The investigations conducted are concerned with problems of radio propagation and upper atmosphere research, dating back to the formation in 1920 of the Radio Research Board of the Department of Scientific and Industrial Research. The years from 1925 to 1927 were of great importance to the science of geophysics because it was in that period that the existence of a

G. W. Gardiner; H. Rishbeth

1982-01-01

221

Robust Nonparametric Cyclic Correlation Based Spectrum Sensing for Cognitive Radio  

Microsoft Academic Search

Cognitive radios sense the radio spectrum in order to find underutilized spectrum and then exploit it in an agile man- ner. Spectrum sensing has to be performed reliably in challeng- ing propagation environments characterized by shadowing and fading effects as well as heavy-tailed noise distributions. In this paper a robust computationally efficient nonparametric cyclic correlation estimator based on the multivariate

Jarmo Lunden; Saleem A. Kassam; Visa Koivunen

2009-01-01

222

Radio refractive index investigations over Bass Strait, Southern Australia  

Microsoft Academic Search

Radio refractive index profile measurements between 500 and 5000 feet were made over Bass Strait (Australia) during January and March 1966, using a microwave refractometer car-tied in a light aircraft. During these flights continuous radio propagation measurements at 173 MHz and 1.9 GHz were made over paths at points along which the profiles were measured. Supporting meteorological observations were also

G. Jenkinson; M. Van Dijk

1969-01-01

223

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

224

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

225

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

226

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

227

Radio Variability of Radio Quiet and Radio Loud Quasars  

E-print Network

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

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

2004-09-22

228

Radio astronomy and spectrum management - The impact of WARC-79  

NASA Astrophysics Data System (ADS)

The characteristics of radio astronomy are considered, taking into account broad-band and narrow-band cosmic radiation, the evolution of equipment and techniques of the radio astronomer toward better sensitivity and better angular resolution, and the three general classes into which radio telescopes can be divided. Attention is given to the extraordinary interference problems faced by radio astronomers, the location of radio-astronomy observatories in secluded locations, the preparation by radio astronomers and space scientists for WARC-79, the actions taken at WARC-79, and the WARC impact. It is pointed out that radio astronomy has emerged from WARC-79 in a better position in the International Radio Regulations than it has ever enjoyed in the past. Radio astronomers can be satisfied that the requirements of their radio service are generally being given serious consideration. Most of the requests for allocations have been granted at frequencies above 20 GHz.

Pankonin, V.; Price, R. M.

1981-08-01

229

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

Microsoft Academic Search

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

Young Yun; Jeong-Gab Ju; Hong Seung Kim

2011-01-01

230

A Statistical Model for Urban Radio Propogation  

Microsoft Academic Search

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

H. Suzuki

1977-01-01

231

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

NASA Technical Reports Server (NTRS)

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

Golshan, Nassar (Editor)

1996-01-01

232

Low Power Radio Transmitters for Broadcasting  

Microsoft Academic Search

This paper discusses the place of low powered installations in the existing radio broadcast system, and the importance of apparatus for such stations meeting the present-day requirements pertaining to frequency stability, modulation capability, fidelity, and radio-frequency harmonics. The characteristics and more interesting features of a new line of transmitters covering the range of output from 100 to 1000 watts are

A. W. Kishpaugh; R. E. Coram

1933-01-01

233

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

234

Radio Occultation Measurements of Jupiter's Multilayered Lower Ionosphere: New Results from Voyager and Galileo  

Microsoft Academic Search

Radio occultation measurements with Pioneer 10 provided the first evidence for the multilayered structure of Jupiter's lower ionosphere (Fjeldbo et al., Astron. Astrophys. 39, 91-96, 1975). However, radio occultation studies of this region are inherently difficult for the following reason. Radio signals propagating from spacecraft to Earth can follow a variety of paths through the ionosphere, refracting off the top

D. P. Hinson; E. T. Karayel; J. D. Twicken

1996-01-01

235

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

E-print Network

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

Islam, M. Saif

236

Radio Jove: Jupiter Radio Astronomy for Citizens  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

237

Graphical Processing Units (GPUs) in Radio Astronomy  

E-print Network

purpose computing on GPUs (GPGPU): History, motivations, device characteristics. How GPUs fit into radio exist for NVIDIA, AMD, Intel, Apple. First release Dec 2008, currently at v1.2 #12;CUDA vs OpenCL CUDA

Groppi, Christopher

238

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

239

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

PubMed

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

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

2014-02-01

240

High-power test and thermal characteristics of a new radio-frequency quadrupole cavity for the Japan Proton Accelerator Research Complex linac  

NASA Astrophysics Data System (ADS)

We performed a high-power test of a new radio-frequency quadrupole (RFQ II) for the J-PARC linac. RFQ II was developed as a spare RFQ because the operating J-PARC RFQ has suffered from a sparking problem. First, the conditioning of RFQ II was carried out; after 50 h of conditioning, RFQ II became very stable with a nominal power and duty of 330 kW and 3%, respectively. Next the thermal properties were measured because the resonant frequency of RFQ II is tuned by changing the temperature of the cooling water. The frequency response was measured and compared to finite-element method simulation results, confirming that the simple two-dimensional model reproduces the experimental data well. The differences in the field distribution with changes in the rf loading and the cooling-water temperature were also measured, and no serious field distortion was observed. Therefore, we conclude that RFQ II can perform well as a high-power rf cavity.

Kondo, Yasuhiro; Morishita, Takatoshi; Hasegawa, Kazuo; Chishiro, Etsuji; Hirano, Koichiro; Hori, Toshihiko; Oguri, Hidetomo; Sato, Fumiaki; Shinozaki, Shinichi; Sugimura, Takashi; Kawamata, Hiroshi; Naito, Fujio; Fukui, Yuji; Futatsukawa, Kenta; Nanmo, Kesao

2013-04-01

241

Transionospheric propagation predictions  

NASA Technical Reports Server (NTRS)

The current status and future prospects of the capability to make transionospheric propagation predictions are addressed, highlighting the effects of the ionized media, which dominate for frequencies below 1 to 3 GHz, depending upon the state of the ionosphere and the elevation angle through the Earth-space path. The primary concerns are the predictions of time delay of signal modulation (group path delay) and of radio wave scintillation. Progress in these areas is strongly tied to knowledge of variable structures in the ionosphere ranging from the large scale (thousands of kilometers in horizontal extent) to the fine scale (kilometer size). Ionospheric variability and the relative importance of various mechanisms responsible for the time histories observed in total electron content (TEC), proportional to signal group delay, and in irregularity formation are discussed in terms of capability to make both short and long term predictions. The data base upon which predictions are made is examined for its adequacy, and the prospects for prediction improvements by more theoretical studies as well as by increasing the available statistical data base are examined.

Klobucher, J. A.; Basu, S.; Basu, S.; Bernhardt, P. A.; Davies, K.; Donatelli, D. E.; Fremouw, E. J.; Goodman, J. M.; Hartmann, G. K.; Leitinger, R.

1979-01-01

242

Radio-Frequency Strain Monitor  

NASA Technical Reports Server (NTRS)

Radio-frequency (RF) strain monitor developed to measure lengths of objects. RF waveguide or cable bonded to structure monitored. Propagation of RF signal along waveguide results in phase shift proportional to length of path traveled. Impedance mismatches placed in RF cable at nodes of structure. Records mismatches and detects overall length of line and lengths of intervals between nodes. Used to detect changes in elements of large structure with single cable. Monitor has potential for many applications, including monitoring stability of such large structures as aircraft, bridges, and buildings in Earthquake zones.

Heyman, Joseph S.; Rogowski, Robert S.; Holben, Milford S., Jr.

1988-01-01

243

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

244

S-Band propagation measurements  

NASA Technical Reports Server (NTRS)

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.

1994-01-01

245

Radio frequency plasma power dependence of the moisture permeation barrier characteristics of Al{sub 2}O{sub 3} films deposited by remote plasma atomic layer deposition  

SciTech Connect

In the present study, we investigated the gas and moisture permeation barrier properties of Al{sub 2}O{sub 3} films deposited on polyethersulfone films (PES) by capacitively coupled plasma (CCP) type Remote Plasma Atomic Layer Deposition (RPALD) at Radio Frequency (RF) plasma powers ranging from 100 W to 400 W in 100 W increments using Trimethylaluminum [TMA, Al(CH{sub 3}){sub 3}] as the Al source and O{sub 2} plasma as the reactant. To study the gas and moisture permeation barrier properties of 100-nm-thick Al{sub 2}O{sub 3} at various plasma powers, the Water Vapor Transmission Rate (WVTR) was measured using an electrical Ca degradation test. WVTR decreased as plasma power increased with WVTR values for 400 W and 100 W of 2.6 × 10{sup ?4} gm{sup ?2}day{sup ?1} and 1.2 × 10{sup ?3} gm{sup ?2}day{sup ?1}, respectively. The trends for life time, Al-O and O-H bond, density, and stoichiometry were similar to that of WVTR with improvement associated with increasing plasma power. Further, among plasma power ranging from 100 W to 400 W, the highest power of 400 W resulted in the best moisture permeation barrier properties. This result was attributed to differences in volume and amount of ion and radical fluxes, to join the ALD process, generated by O{sub 2} plasma as the plasma power changed during ALD process, which was determined using a plasma diagnosis technique called the Floating Harmonic Method (FHM). Plasma diagnosis by FHM revealed an increase in ion flux with increasing plasma power. With respect to the ALD process, our results indicated that higher plasma power generated increased ion and radical flux compared with lower plasma power. Thus, a higher plasma power provides the best gas and moisture permeation barrier properties.

Jung, Hyunsoo [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of) [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Samsung Display Co. Ltd., Tangjeong, Chungcheongnam-Do 336-741 (Korea, Republic of); Choi, Hagyoung; Lee, Sanghun [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)] [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Jeon, Heeyoung [Department of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)] [Department of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Jeon, Hyeongtag [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of) [Division of Materials Science and Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of); Department of Nano-scale Semiconductor Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)

2013-11-07

246

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

NASA Astrophysics Data System (ADS)

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

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

1997-05-01

247

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

248

Youth Radio  

NSDL National Science Digital Library

With an impressive headquarters in downtown Oakland, Youth Radio is fast becoming a compelling and insightful media phenomenon that should be watched closely. Their mission is a laudable one, and as their website puts it, âÂÂâ¦. is to promote young peopleâÂÂs intellectual creative and professional growth through training and access to media and to produce the highest quality original media for local and national outlets.â Of course, the real heart of the site contains the actual programming, which is streamed 24 hours a day, 7 days a week. Along with unique mix of music, individuals can listen to a host of stories reported by young people. Visitors can also browse a list of recently added stories by topic, which include relationships, society, sports, poetry, and health. Those who are hoping to get some of the basic flavor of the offerings here would do well to take a look at the story featuring reporting from a group of Berkeley High School students at the World Social Forum in Caracas, or by listening to the commentary offered by Lauryn Silverman on the modern conundrum of multi-tasking.

249

Recent radio studies of SNR  

NASA Astrophysics Data System (ADS)

Current radio data on supernova remnants (SNR) are examined for clues to the physical characteristics of SNR. Continuum observations of young SNR such as Tycho reveal an amorphous shell. Brightest emissions arise from filaments, i.e., denser areas of the interstellar medium that have encountered the shock. Radio observations of older SNR, such as IC443 and the Cygnus Loop, are begining to reveal individual filaments composed of cool, dense sheets that form after thermal instabilities have been caused by shock-heating of the interstellar medium. Data on Crab-like SNR and plerions suggest the presence of a neutron star in a spin down phase. Cas A and CTB80 (which displays jets) are as yet unresolved objects. Extragalactic SNR are not presently amenable to radio surveys due to instrumental limitations.

Dickel, J. R.

250

Jet propagation through energetic materials  

SciTech Connect

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

Pincosy, P; Poulsen, P

2004-01-08

251

Industrial interference and radio astronomy  

NASA Astrophysics Data System (ADS)

The interferer - victim scenario is described for the case of industrial interference affecting radio astronomical observatories. The sensitivity of radio astronomical receivers and their interference limits are outlined. EMC above 30 MHz is a serious problem for Radio Astronomy. Interferer (CISPR) and victim (ITU-R RA 769) standards are not harmonised. The emissions from the interferer and their spectral characteristics are not defined sufficiently well by CISPR standards. The required minimum coupling losses (MCL) between an industrial device and radio astronomical antenna depends on device properties but is shown to exceed 140 dB in most cases. Spatial separation of a few km is insufficient on its own, the terrain must shield > 30-40 dB, additional mitigations such as extra shielding or suppression of high frequency emissions may be necessary. A case by case compatibility analysis and tailored EMC measures are required for individual installations. Aggregation of many weak rfi emitters can become serious problem. If deployment densities are high enough, the emission constraints can even exceed those for a single interferer at a short distance from the radio observatory. Compatibility studies must account not only for the single interferer but also for many widely distributed interference sources.

Jessner, A.

2013-07-01

252

Galactic Magnetic Turbulence from Radio data  

E-print Network

Fluctuations in the Galactic synchrotron emission can be traced by the angular power spectrum of radio maps at low multipoles. At frequencies below few GHz, large-scale anisotropies are mainly induced by magnetic field turbulence. By performing an analysis of five radio maps, we extract constraints on turbulence spectral index and halo scale. Results favour a power spectrum significantly flatter than for 3D Kolmogorov-like turbulence, and a thin halo. This can be interpreted as an indication supporting non-conventional models of propagation of cosmic-ray particles in the Galaxy, or as a suggestion of a spectral-index break in the observed magnetic turbulence power spectrum.

Marco Regis

2011-01-28

253

Galactic Magnetic Turbulence from Radio data  

E-print Network

Fluctuations in the Galactic synchrotron emission can be traced by the angular power spectrum of radio maps at low multipoles. At frequencies below few GHz, large-scale anisotropies are mainly induced by magnetic field turbulence. By performing an analysis of five radio maps, we extract constraints on turbulence spectral index and halo scale. Results favour a power spectrum significantly flatter than for 3D Kolmogorov-like turbulence, and a thin halo. This can be interpreted as an indication supporting non-conventional models of propagation of cosmic-ray particles in the Galaxy, or as a suggestion of a spectral-index break in the observed magnetic turbulence power spectrum.

Regis, Marco

2011-01-01

254

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

255

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

256

Midlatitude propagation of VLF to MF waves through nighttime ionosphere above powerful VLF transmitters  

NASA Astrophysics Data System (ADS)

nighttime observations made by the DEMETER satellite in the very low frequency (VLF) to medium frequency (MF) bands (3 kHz to 3 MHz) have demonstrated the propagation of radio waves from the bottom of ionosphere up to the satellite altitude (~700 km). Propagation characteristics derived from the magneto-ionic theory [Budden, ] are used to explain the absence of wave observations between ~1 and 2 MHz. Under hypotheses made for the Appleton and Hartree (or Appleton and Lassen) formula, studies of the vertical variations of the real and imaginary parts of the refractive index are performed to point out modifications in the propagation characteristics of the waves: (i) at the crossing of the plasma cutoffs regions, (ii) at the crossing of the ordinary and extraordinary mode resonance regions, and (iii) in the region where the product of the collision frequency (?) and the electronic density (Ne) is maximum. It is shown that enhancements in the collision frequencies, produced by powerful VLF transmitters in the region where the product of ? and Ne is maximum, open the half angle of the MF wave transmission cones and increase the power densities of those waves at the DEMETER altitude.

Lefeuvre, F.; PinçOn, J. L.; Parrot, M.

2013-03-01

257

Propagation of Big Island eddies  

NASA Astrophysics Data System (ADS)

Using satellite altimetry data, we have observed a series of anticyclonic eddies as they form at the Big Island of Hawaii and have tracked them as they move away from the island. While similar eddies have been observed near the Hawaiian Islands in previous studies, the fate of the anticyclonic eddies has previously been unclear. The eddies that we observed initially propagated to the southwest but consistently changed propagation direction to the northwest later in their lifetimes. This was intriguing to us, as theoretically, the decay of isolated anticyclonic eddies on a ? plane should cause them to continually move toward the southwest. Such isolated eddy dynamics are unable to account for the observed change to northwestward eddy propagation, and the presence of the westward flowing North Equatorial Current turns out to be important to the Big Island eddy dynamics. The eddies are not passively advected by the North Equatorial Current; rather, the mean flow changes the propagation characteristics of the eddies. An existing theory that includes meridionally varying, purely zonal mean flow is shown to account for the observed propagation of the Big Island eddies if the zonal variation of the mean flow is considered.

Holland, Christina L.; Mitchum, Gary T.

2001-01-01

258

ON THE RELATION BETWEEN COMPLEX MODES AND WAVE PROPAGATION PHENOMENA  

Microsoft Academic Search

This paper discusses the well-known, but often misunderstood, concept of complex modes of dynamic structures. It shows how complex modes can be interpreted in terms of wave propagation phenomena caused by either localized damping or propagation to the surrounding media. Numerical simulation results are presented for different kinds of structures exhibiting modal and wave propagation characteristics: straight beams, an L-shaped

K. M. AHMIDA; J. R. F. ARRUDA

2002-01-01

259

On the Relation Between Complex Modes and Wave Propagation Phenomena  

Microsoft Academic Search

This paper discusses the well-known, but often misunderstood, concept of complex modes of dynamic structures. It shows how complex modes can be interpreted in terms of wave propagation phenomena caused by either localized damping or propagation to the surrounding media. Numerical simulation results are presented for different kinds of structures exhibiting modal and wave propagation characteristics: straight beams, an L-shaped

K. M. Ahmida; J. R. F. Arruda

2002-01-01

260

Quark propagator, instantons and gluon propagator  

E-print Network

The Schwinger-Dyson formalism is used to check the consistency of instanton model solutions for the quark propagator with recent models of confining gluon propagators. We find that the models are not consistent. A major discrepancy is the absence of a vector condensate in the instanton model that is present in the solutions with nonperturbative confining gluons.

L. S. Kisslinger; M. Aw; A. Harey; O. Linsuain

1999-06-22

261

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

NASA Technical Reports Server (NTRS)

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

Wales, R. O. (editor)

1981-01-01

262

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

263

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

264

The Crab Nebula's Wisps in Radio and Optical  

E-print Network

We present four new, high-resolution VLA radio images of the Crab nebula, taken between 2001 Feb. and Apr. The radio images show systematic variability in the Crab's radio emission throughout the region near the pulsar. The principal geometry of the variable features is that of elliptical ripples very similar to the optical wisps. The radio wisps are seen to move systematically outward with projected speeds of up to 0.3c. Comparing the new radio images to our earlier ones from 1998 and 2000, we show there are also more slowly moving features somewhat farther away from the pulsar. In particular, there is a prominent moving feature to the northwest of the pulsar which has a projected speed of order 10,000 km/s. Striation is seen throughout the nebula, suggesting the presence of wave-like disturbances propagating through the synchrotron bubble. The radio images were taken simultaneously with HST optical observations. Comparing the radio to the optical images, we find that the radio wisps are sometimes displaced from the optical ones or have no optical counterparts. We also find that some optical wisps in particular, the brightest optical wisps near the pulsar, do not seem to have radio counterparts. In the exterior of the nebula, by contrast, there is generally a good correspondence between the radio and optical features.

M. F. Bietenholz; J. J. Hester; D. A. Frail; N. Bartel

2004-08-03

265

Low Frequency Radio Emissions: Remote Sensing of the Energetic Heliosphere  

NASA Astrophysics Data System (ADS)

Low frequency radio emissions (below about 50 MHz) are tracers of energetic plasma instabilities. Their observation provides us with a unique proxy for instable energetic electron populations. In the solar wind, two types of emissions can be monitored: Type II and Type III radio bursts. The former are related to interplanetary shocks, while the latter are linked to energetic electron beams going out from the solar corona. The magnetized planets are also producing low frequency radio emissions linked to the auroral activity, and thus to the interaction between the planet and the solar wind. These radio emission are non-thermal emissions. They are very powerful (Jupiter is as intense as the Sun in this frequency range). Furthermore, the low frequency radio instrumentation in space has the advantage to be quasi-isotropic. The antenna systems have no intrinsic directivity. However, goniopolarimetric inversions have been developed to derive the observed radio waves parameters (assuming we see a single source at a given time). Hence, the low frequency radio systems can monitor the whole sky at once and provide direction of arrival for each event. We will present the various emission mechanisms involved for the low frequency radio emissions in the solar system, the various propagation effects along the wave path and the radio instrumentation necessary to derived all relevant wave parameters. We will discuss how these radio emissions can be used in a space weather perspective. We will finally overview the possible future steps in terms of instrumentation for this frequency range.

Cecconi, Baptiste

2014-05-01

266

Theory of Type 3 and Type 2 Solar Radio Emissions  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

267

The Use of Extraterrestrial Radio Sources in the Measurement of Antenna Parameters  

Microsoft Academic Search

Extraterrestrial radio sources, whose emission characteristics (flux density, spectrum, angular size) and coordinates have been firmly established by careful observations, have application in the measurement of the effective area (aperture efficiency and gain) of an antenna and its radiation pattern. The radio-emission characteristics of the strong discrete (celestial) radio sources, of the sun, and of the moon are presented. Problems

D. A. Guidice; J. P. Castelli

1971-01-01

268

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

SciTech Connect

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

Sirothia, S. K.; Gopal-Krishna [National Centre for Radio Astrophysics, TIFR, Post Bag No. 3, Pune University Campus, Ganeshkhind, Pune 411 007 (India); Wiita, Paul J., E-mail: sirothia@ncra.tifr.res.in, E-mail: krishna@ncra.tifr.res.in, E-mail: wiitap@tcnj.edu [Department of Physics, College of New Jersey, P.O. Box 7718, Ewing, NJ 08628 (United States)

2013-03-01

269

Global Ionospheric Radio Observatory (GIRO): Status and prospective  

Microsoft Academic Search

The Global Ionospheric Radio Observatory (GIRO), http:\\/\\/giro.uml.edu, acquires and disseminates HF ionospheric sounding data from 64 Digisonde locations in 27 countries. GIRO publishes its 30+ million record holdings over the Internet, provides an interactive read\\/write environment to experts of data interpretation, and forwards real-time data for measurement assimilation and radio propagation and space weather forecast. Of importance to the ionospheric

Ivan A. Galkin; Bodo W. Reinisch

2011-01-01

270

Triggered Jovian radio emissions  

NASA Technical Reports Server (NTRS)

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

Calvert, W.

1985-01-01

271

Affinity Propagation Brendan Frey  

E-print Network

Affinity Propagation Brendan Frey University of Toronto Where is the exemplar? An interpretation of affinity propagation by Marc Mezard, Laboratoire de Physique Théorique et Modeles Statistique, Paris Number of clusters, k Squared error #12;Let's close the gap! Source: MSNBC #12;Affinity Propagation

Haykin, Simon

272

Wave equations for pulse propagation  

SciTech Connect

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

Shore, B.W.

1987-06-24

273

Cognitive Radio Architecture Evolution  

Microsoft Academic Search

The radio research community has aggressively embraced cognitive radio for dynamic radio spectrum management to enhance spectrum usage, e.g., in ISM bands and as secondary users in unused TV bands, but the needs of the mobile wireless user have not been addressed as thoroughly on the question of high quality of information (QoI) as a function of place, time, and

Joseph Mitola

2009-01-01

274

Educational Radio 1972.  

ERIC Educational Resources Information Center

A synopsis of educational radio in this country today includes a brief history, figures on the growth of educational radio, rules and regulations governing it, procedures for filing an application for a station, suggestions for financing, and lists of organizations and government agencies concerned with educational radio. (JK)

Federal Communications Commission, Washington, DC.

275

Who's Running College Radio?  

ERIC Educational Resources Information Center

While management styles and theories differ among administrators of college radio stations, the views concerning the operation of college radio tend to be consistent. Common elements present in varying degrees in every college radio stations include public broadcasting philosophy, community needs, management and staff, financing, school relations,…

Sauls, Samuel J.

276

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

277

Commercial Radio as Communication.  

ERIC Educational Resources Information Center

Compares the day-to-day work routines of commercial radio with the principles of a theoretical communication model. Illuminates peculiarities of the conduct of communication by commercial radio. Discusses the application of theoretical models to the evaluation of practicing institutions. Offers assessments of commercial radio deriving from…

Rothenbuhler, Eric W.

1996-01-01

278

Electromagnetic Wave Propagation In The Plasma Layer of A Reentry Vehicle  

E-print Network

The ability to simulate a reentry vehicle plasma layer and the radio wave interaction with that layer, is crucial to the design of aerospace vehicles when the analysis of radio communication blackout is required. Results of aerothermal heating, plasma generation and electromagnetic wave propagation over a reentry vehicle are presented in this paper. Simulation of a magnetic window radio communication blackout mitigation method is successfully demonstrated.

Kundrapu, Madhusudhan; Beckwith, Kris; Stoltz, Peter; Shashurin, Alexey; Keidar, Michael

2014-01-01

279

A theory of solar type 3 radio bursts  

NASA Technical Reports Server (NTRS)

Energetic electrons propagating through the interplanetary medium are shown to excite the one dimensional oscillating two stream instability (OTSI). The OTSI is in turn stabilized by anomalous resistivity which completes the transfer of long wavelength Langmuir waves to short wavelengths, out of resonance with the electrons. The theory explains the small energy losses suffered by the electrons in propagating to 1 AU, the predominance of second harmonic radiation, and the observed correlation between radio and electron fluxes.

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

1979-01-01

280

Refractive effects from VHF to EHF. Part A: Propagation Mechanisms  

NASA Astrophysics Data System (ADS)

Radio wave propagation in the very high frequency (VHF) to extremely high frequency (EHF) bands at low elevation angles and near the earth's surface is almost always affected by refraction. This lecture details these effects and the various methods used to model them, from simple effective-earth-radius factors for standard refraction to parabolic-equation methods for range-dependent ducting environments. Refraction and Snell's law are discussed and standard and nonstandard propagation mechanisms are defined. To establish the significance of nonstandard propagation effects, some statistics on the occurrence of ducting around the world are presented.

Hitney, Herbert V.

1994-09-01

281

Studies of Space Weather Using Solar Radio Bursts  

NASA Astrophysics Data System (ADS)

High quality observations of solar radio bursts in the frequency range 14-1 MHz have been possible since late 1994 with the launch of the Wind spacecraft. However the standard solar patrols typically commence observations above 25 MHz leaving a small, but important, gap in the frequency coverage. This gap is filled by the Bruny Island Radio Spectrometer. In this paper we describe the studies that have been made using this extended frequency range. Our main interest has been the role of radio bursts in diagnosing energetic particle acceleration and propagation in the inner heliosphere.

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

2005-12-01

282

Propagation of radio waves through the lower atmosphere of Venus  

NASA Technical Reports Server (NTRS)

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

Richter, K. R.

1972-01-01

283

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

284

Practical modeling and prediction of radio coverage of indoor sensor networks  

Microsoft Academic Search

The robust operation of many sensor network applications depends on deploying relays to ensure wireless coverage. Radio mapping aims to predict network coverage based on a small number of link measurements. This problem is particularly challenging in complex indoor environments where walls significantly affect radio signal propagation. Nevertheless, we show that it is feasible to accurately predict coverage through a

Octav Chipara; Gregory Hackmann; Chenyang Lu; William D. Smart; Gruia-Catalin Roman

2010-01-01

285

Features of the Digital Block of a Hardware Simulator for MIMO Radio Channels  

E-print Network

Features of the Digital Block of a Hardware Simulator for MIMO Radio Channels Sylvie Picol, is the realization of a hardware simulator of MIMO propagation channels for UMTS and WLAN applications. The simulator-media services. MIMO (Multiple-Input Multiple-Output) systems make use of antenna arrays at both sides of a radio

Paris-Sud XI, Université de

286

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

E-print Network

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

Royer, Dana

287

High Energy Astrophysics: Radio Galaxies Geoffrey V. Bicknell Radio Galaxies  

E-print Network

High Energy Astrophysics: Radio Galaxies © Geoffrey V. Bicknell Radio Galaxies 1 Fanaroff Laing #12;High Energy Astrophysics: Radio Galaxies 2/56 The prototype FR 2 radio galaxy, Cygnus A Energy Astrophysics: Radio Galaxies 3/56 Cygnus A at 850 microns. Only the hot spots and core are visible

Bicknell, Geoff

288

Hypersonic phonon propagation in one-dimensional surface phononic crystal  

NASA Astrophysics Data System (ADS)

Hypersonic, thermally activated surface acoustic waves propagating in the surface of crystalline silicon patterned with periodic stripes were studied by Brillouin light scattering. Two characteristic directions (normal and parallel to the stripes) of surface acoustic waves propagation were examined exhibiting a distinctive propagation behavior. The measured phononic band structure exhibits diverse features, such as zone folding, band gap opening, and hybridization to local resonance for waves propagating normal to the stripes, and a variety of dispersive modes propagating along the stripes. Experimental results were supported by theoretical calculations performed using finite element method.

Graczykowski, B.; Sledzinska, M.; Kehagias, N.; Alzina, F.; Reparaz, J. S.; Sotomayor Torres, C. M.

2014-03-01

289

ATS6-satellite radio beacon measurements at Ootacamund, India  

Microsoft Academic Search

In August 1975 the ATS6 was repositioned at 35 deg E. Radio beacon measurements of time delay, Faraday rotation and signal amplitude, made at Ootacamund, India in October 1975, are discussed with emphasis on the problem of determining the Faraday content under essentially transverse propagation conditions. It is shown that at the low geomagnetic latitude of Ootacamund the use of

K. Davies; R. F. Donnelly; R. N. Grubb; P. V. S. Rama Rao; R. G. Rastogi; M. R. Deshpande; H. Chandra; H. O. Vats; G. Sethia

1978-01-01

290

Ray Tracing Jupiter`s HOM Radio Emission  

Microsoft Academic Search

Cassini, Galileo, and Voyager spacecraft observations show well-defined attenuation features in the hectometer (HOM) spectrum of Jupiter's radio emission. The features are best displayed as frequency versus time spectrograms of HOM intensity between 500 - 3000 kHz. The bands have been shown by Gurnett et al. (1998) to be the result of propagation processes involving these emissions from opposite hemispheres.

C. Higgins

2007-01-01

291

Computer Modeling of the MX Simulcast Radio Network  

Microsoft Academic Search

Nodes of the MX system can communicate effectively in a trans-or post-attack environment by using a simulcast network that employs groundwave propagation. For a sufficiently dense original network, the simulcast approach is relatively insensitive to degrading channel conditions and loss of nodes and links. Network performance is a complicated function of the radio and antenna designs, terrain in the deployment

D. Brown; S. Lee; H. Sunkenberg; H. dePedro

1982-01-01

292

A multifunctional antenna for terrestrial and satellite radio applications  

Microsoft Academic Search

A multifunctional antenna is presented for the application in terrestrial radio services like GSM 900 MHz, DCS 1800 MHz as well as for satellite radio services like GPS 1575 MHz. At the terrestrial frequency bands GSM 900 MHz and DCS 1800 MHz the antenna exhibits omnidirectional radiation characteristics in horizontal plane for vertical polarized waves. At the frequency bands of

S. Lindenmeier; J. F. Luy; P. Russer

2001-01-01

293

An advanced low power radio 1 chip IC  

Microsoft Academic Search

A low-power single chip FM\\/AM radio IC capable of extending the battery life of a radio has been developed. Decreasing the current consumption is realized solely by new circuit design techniques without making changes to the conventional processes in IC fabrication. The characteristics of this IC is not degraded even though the current consumption is decreased, but instead, operating time

Taiwa Okanobu; Hitoshi Tomiyama

1994-01-01

294

Power efficient MAC protocol for multihop radio networks  

Microsoft Academic Search

In this paper we develop a new multi-access protocol for multi-hop radio networks. The unique feature of our protocol is that it is energy conserving. Radios that are not actively transmitting or receiving a packet power themselves off. The manner in which nodes power themselves off does not influence the delay or throughput characteristics of our protocol. Simulation results indicate

Suresh Singh; C. S. Raghavendra

1998-01-01

295

Propagation of tropospheric gravity waves into the upper atmosphere of Mars  

NASA Astrophysics Data System (ADS)

We study the propagation of gravity waves in the martian atmosphere using a linearized one-dimensional full-wave model. Calculations are carried out for atmospheric parameters characteristic of Mars Orbiter Laser Altimeter (on Mars Global Surveyor MGS) observations of apparent gravity waves in high latitude clouds and MGS radio occultation measurements of temperature variations with height suggestive of gravity wave activity. Waves that reach the thermosphere produce fluctuations in density comparable in amplitude with the density variations detected in Mars Odyssey aerobraking data. Gravity waves of modest amplitude are found to deposit momentum and generate significant heating and cooling in the martian atmosphere. The largest heating and cooling effects occur in the thermosphere, at altitudes between about 130 and 150 km, with heating occurring at the lower altitudes and cooling taking place above.

Parish, Helen F.; Schubert, Gerald; Hickey, Michael P.; Walterscheid, Richard L.

2009-09-01

296

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

297

Radio Properties of AGN  

NASA Astrophysics Data System (ADS)

To study the radio properties of AGN, we cross-correlate and investigate Veron-Cetty & Veron catalog of QSOs and Active Galaxies (v.13, 2010) with a number of radio catalogs: NVSS, FIRST, GB6, 87GB, SUMSS, WISH, WENSS, and 7C. This catalog contains 168,940 objects with positional accuracy of mostly 1 arcsec, though many positions have larger errors. We use new cross-correlation software based on accuracy of each object independently. In this software we take into account errors for each source and take identifications with errors within 3 sigma. Altogether, we find ~16,000 AGN having radio detection in any of the listed catalogs. Using all data from radio catalogs, we derive a homogeneous sample of radio AGN. The sample allows accomplish several tasks, including study of the distribution of radio sources by activity types, differences in physical properties of radio-loud and radio-quiet AGN, luminosity functions for various types of radio AGN, study of the q parameter by AGN types and its evolution, etc.

Abrahamyan, Hayk V.; Mickaelian, Areg M.

2014-07-01

298

75 FR 66709 - Commercial Radio Operators Rules  

Federal Register 2010, 2011, 2012, 2013

...General Radiotelephone Operator License, GMDSS Radio Maintainer's License). (2) Six Months...Endorsement, Six Months Service Endorsement, GMDSS Radio Operator's License, Restricted GMDSS Radio Operator's License, GMDSS Radio...

2010-10-29

299

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

300

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

301

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; Kovacic, Stanislav; Kristan, Matej; Pers, Janez

2013-01-01

302

NASA propagation information center  

NASA Technical Reports Server (NTRS)

The NASA Propagation Information Center became formally operational in July 1988. It is located in the Department of Electrical and Computer Engineering of the University of Colorado at Boulder. The center is several things: a communications medium for the propagation with the outside world, a mechanism for internal communication within the program, and an aid to management.

Smith, Ernest K.; Flock, Warren L.

1990-01-01

303

NASA Propagation Information Center  

NASA Technical Reports Server (NTRS)

The NASA Propagation Information Center became formally operational in July 1988. It is located in the Department of Electrical and Computer Engineering of the University of Colorado at Boulder. The Center is several things: a communications medium for the propagation with the outside world, a mechanism for internal communication within the program, and an aid to management.

Smith, Ernest K.; Flock, Warren L.

1989-01-01

304

A generalized photon propagator  

E-print Network

A covariant gauge independent derivation of the generalized dispersion relation of electromagnetic waves in a medium with local and linear constitutive law is presented. A generalized photon propagator is derived. For Maxwell constitutive tensor, the standard light cone structure and the standard Feynman propagator are reinstated.

Yakov Itin

2007-05-07

305

Analysis of flame propagation  

Microsoft Academic Search

We develop a mathematical theory of flame propagation and analyze the stability of a flame front. We consider a premixed, combustible fluid and model the front between the burnt and unburnt regions as an infinitely thin curve propagating in a direction normal to itself at a constant speed. We assume that the specific volume of a fluid particle increases by

J. A. Sethian

1982-01-01

306

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

307

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

308

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

309

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

310

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

311

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; Larranaga, Pedro; Yuste, Rafael

2013-01-01

312

Smart Radio Spectrum Management for Cognitive Radio  

E-print Network

Today's wireless networks are characterized by fixed spectrum assignment policy. The limited available spectrum and the inefficiency in the spectrum usage necessitate a new communication paradigm to exploit the existing wireless spectrum opportunistically. Cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users. In this work, a fuzzy logic based system for spectrum management is proposed where the radio can share unused spectrum depending on some parameters like distance, signal strength, node velocity and availability of unused spectrum. The system is simulated and is found to give satisfactory results.

Bhattacharya, Partha Pratim; Gera, Rishita; Agarwal, Anjali

2011-01-01

313

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

314

Film, Radio, and Television.  

ERIC Educational Resources Information Center

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

Hardesty, Carolyn, Ed.

1990-01-01

315

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.

316

Early Cambridge radio astronomy  

Microsoft Academic Search

Radio astronomy started in Cambridge immediately after the hostilities of the World War II have ceased. Martin Ryle was the inspiring leader of a small group that started to develop interferometry techniques at the Cavendish Laboratory. From this development came the numerous Cambridge radio source surveys culminating in the Nobel prize awarded to Martin Ryle for invention of aperture synthesis.

F. G. Smith

2007-01-01

317

Radio determination satellite service  

Microsoft Academic Search

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

Robert D. Briskman

1990-01-01

318

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

319

Radio Emission from Exoplanets  

E-print Network

We present results from new low frequency observations of two extrasolar planetary systems (Epsilon Eridani and HD128311) taken at 150 MHz with the Giant Metrewave Radio Telescope (GMRT). We do not detect either system, but are able to place tight upper limits on their low frequency radio emission.

Samuel J. George; Ian R. Stevens

2008-04-24

320

Amateur Radio Satellite Communications.  

ERIC Educational Resources Information Center

The Amateur Radio Satellite Communications project had, as its goal, the assembly of an amateur radio satellite station in a high school physics classroom. Specific objectives were to provide: (1) a special source of interest as a motivator for attracting students and building public relations; (2) a center of interest as a motivator for the study…

Koch, David P.

321

Division x: Radio Astronomy  

Microsoft Academic Search

Division X provides a common theme for astronomers using radio techniques to study a vast range of phenomena in the Universe, from exploring the Earth's ionosphere or making radar measurements in the Solar System, via mapping the distribution of gas and molecules in our own Galaxy and in other galaxies, to study the vast explosive processes in radio galaxies and

Luis F. Rodriguez; Ren-Dong Nan; Lucia Padrielli; Philip J. Diamond; Gloria M. Dubner; Michael Garrett; W. Miller Goss; Anne Green; Masato Ishiguro; A. Pramesh Rao; Russell A. Taylor; Jose M. Torrelles; Jean L. Turner

2007-01-01

322

Radio efficiency of pulsars  

E-print Network

We investigate radio emission efficiency $\\xi$ of pulsars and report a near linear inverse correlation between $\\xi$ and the spindown power $\\dot E$, as well as a near linear correlation between $\\xi$ and pulsar age $\\tau$. This is a consequence of very weak, if any, dependences of radio luminosity $L$ on pulsar period $P$ and period derivative $\\dot{P}$, in contrast to X-ray or $\\gamma$-ray emission luminosities. The analysis of radio fluxes suggests that these correlations are not due to a selection effect, but are intrinsic to the pulsar radio emission physics. We have found that, although with a large variance, the radio luminosity of pulsars is $\\left\\approx 10^{29} \\,{\\rm erg/s}$, regardless of the position in the $P-\\dot P$ diagram. Within such a picture, a model-independent statement can be made that the death line of radio pulsars corresponds to an upper limit in the efficiency of radio emission. If we introduce the maximum value for a radio efficiency into Monte Carlo-based population syntheses we c...

Szary, Andrzej; Melikidze, George; Gil, Janusz; Xu, Ren-Xin

2014-01-01

323

Planetary radio lasing  

NASA Technical Reports Server (NTRS)

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

Calvert, W.

1988-01-01

324

Solar radio continuum storms  

NASA Technical Reports Server (NTRS)

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

1974-01-01

325

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

326

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

327

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

328

Talk Radio: Predictors of Use and Effects on Attitudes about Government  

Microsoft Academic Search

Early studies portrayed the talk radio listener, and the caller in particular, as more alienated and less politically and socially active. The research here, using national survey data, finds that the portrait of the talk radio audience has changed to one more positive in terms of socio-demographic characteristics and political participation. However, talk radio is also found to be associated

Barry A. Hollander

1996-01-01

329

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

330

Radio emission of RRAT pulsars at 111 MHz  

NASA Astrophysics Data System (ADS)

Observations of the RRAT pulsars J0627+16, J0628+09, J1819-1458, J1826-1419, J1839-01, J1840-1419, J1846-0257, J1848-12, J1850+15, J1854+0306, J1919+06, J1913+1330, J1919+17, J1946+24, and J2033+00 observed earlier on the 64-m Parkes telescope (Australia) and the 300-m Arecibo radio telescope (Puerto Rico) at 1400 MHz were conducted at 111 MHz on the LSA radio telescope of the Pushchino Radio Astronomy observatory in 2010-2012. A characteristic feature of these pulsars is their sporadic radio emission during rare active epochs and the absence of radio emission during long time intervals. No appreciable flare activity of these pulsars was detected in the Pushchino observations. However, processing the observations using the Fast Folding Algorithm taking into account known information about the pulsar dispersion measures and periods shows that, even during quiescent intervals, the majority of the studied pulsars generate weak radio pulses with a period corresponding to that of the radio emission of the sporadic pulses observed at active epochs. The flux of this radio emission does not exceed 100 mJy at the pulse peak, even at the low frequency of 111 MHz. This considerably hinders detection of the radio emission of RRAT pulsars at high frequencies, since the radio fluxes of RRAT pulsars decreases with increasing frequency.

Losovsky, B. Ya.; Dumsky, D. V.

2014-08-01

331

Propagation of Singularities for Weak KAM Solutions and Barrier Functions  

NASA Astrophysics Data System (ADS)

This paper studies the structure of the singular set (points of nondifferentiability) of viscosity solutions to Hamilton-Jacobi equations associated with general mechanical systems on the n-torus. First, using the level set method, we characterize the propagation of singularities along generalized characteristics. Then, we obtain a local propagation result for singularities of weak KAM solutions in the supercritical case. Finally, we apply such a result to study the propagation of singularities for barrier functions.

Cannarsa, Piermarco; Cheng, Wei; Zhang, Qi

2014-10-01

332

Propagation of sound beams behind sonic crystals  

Microsoft Academic Search

A theoretical and experimental study of the propagation of sound beams in and behind two-dimensional sonic crystals at frequencies close to the band edges is presented. Beam focusing is predicted and discussed. We evaluate, by analytical numerical methods, the main focusing characteristics, such as the focal distance, the width of beam waist, and the beam quality at the waist. The

V. J. Sánchez-Morcillo; K. Staliunas; V. Espinosa; I. Pérez-Arjona; J. Redondo; E. Soliveres

2009-01-01

333

On the complete characterization of the physical observables of radio emissions from arbitrary sources  

NASA Astrophysics Data System (ADS)

Like all forms of electromagnetic radiation, radio emissions of cosmic origin contain a diversity of physical observables that are constants of motion. Each of these observables carry unique information about the physics of the source(s) from which the radiation emanates and the medium through which it propagates. While the electromagnetic observables used in present-day radio and radar studies of space are limited to the energy (radiometry) and the linear momentum (radio astronomy, space radio and radar applications), the angular momentum and the boost momentum of the radiation are typically discarded and thereby important information wasted. We show how all electromagnetic observables can be measured and analysed, yielding information about vorticity and other topological properties as well as turbulence of radio sources and propagation media. Both theoretical predictions and experimental results confirming these predictions will be presented.

Thidé, Bo; Tamburini, Fabrizio

2014-05-01

334

Encoding many channels in the same frequency through radio vorticity: first experimental test  

E-print Network

We have shown experimentally that it is possible to propagate and use the properties of twisted non-monochromatic incoherent radio waves to simultaneously transmit to infinity more radio channels on the same frequency band by encoding them in different orbital angular momentum states. This novel radio technique allows the implementation of, at least in principle, an infinite number of channels on one and the same frequency, even without using polarization or dense coding techniques. An optimal combination of all these physical properties and techniques represents a solution for the problem of radio band congestion. Our experimental findings show that the vorticity of each twisted electromagnetic wave is preserved after the propagation, paving the way for entirely new paradigms in radio communication protocols.

Tamburini, Fabrizio; Sponselli, Anna; Romanato, Filippo; Thidé, Bo; Bianchini, Antonio; Palmieri, Luca; Someda, Carlo G

2011-01-01

335

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

336

Relative characteristics of TE/TM waves excited by airborne VLF/LF transmitters  

NASA Astrophysics Data System (ADS)

Studies of the characteristics of long radio waves excited by airborne VLF/LF transmitting antennas are described. These antennas provide a source of both conventionally used transverse magnetic (TM) waves and heretofore unused transverse electric (TE) waves. A variety of experimental and theoretical studies are described. Included are discussions of TE/TM signal and atmospheric noise data obtained using balloon, rocket and aircraft platforms, and theoretical studies on the propagation of TE/TM waves under both normal and disturbed ionospheric conditions. The exploitation of the TE polarization for improving the range and reliability of VLF/LF air-to-air communications is also considered.

Kossey, P. A.; Lewis, E. A.; Field, E. C., Jr.

1982-02-01

337

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

338

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

339

Multiple Radios for Effective Rendezvous in Cognitive Radio Networks  

E-print Network

Multiple Radios for Effective Rendezvous in Cognitive Radio Networks Lu Yu1 , Hai Liu1 , Yiu in cognitive radio networks (CRNs) for establishing a communication link on a commonly-available channel, we investigate the rendezvous problem in CRNs where cognitive users are equipped with multiple radios

Chu, Xiaowen

340

A fluid model for error propagation characterization in video coding  

Microsoft Academic Search

An error corruption model (ECM) to describe the interframe error propagation phenomenon in a motion-compensated predictive video codec using fluid flow characteristics is proposed. First, we derive a diffusion differential equation and discuss its solution, which captures the damping effect of error propagation. Then, we propose a tracking quadrilateral (TQ) mechanism to capture the shaping and drilling effects of error

Xiaoming Sun; C.-C. Jay Kuo

2004-01-01

341

Radio Relics (Type A)  

NASA Astrophysics Data System (ADS)

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

Murray, Stephen

2012-09-01

342

Radio Frequency (RF) strain monitor  

NASA Technical Reports Server (NTRS)

This invention relates to an apparatus for measuring strain in a structure. In particular, the invention detects strain in parts per million to over ten percent along an entire length (or other dimension) of a structure measuring a few millimeters to several kilometers. By using a propagation path bonded to the structure, the invention is not limited by the signal attenuation characteristics of the structure and thus frequencies in the megahertz to gigahertz range may be used to detect strain in part per million to over ten percent with high precision.

Heyman, Joseph S. (inventor); Rogowski, Robert S. (inventor); Holben, Milford S., Jr. (inventor)

1988-01-01

343

The Sardinia Radio Telescope  

NASA Astrophysics Data System (ADS)

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

D'Amico, Nichi

2011-08-01

344

Structuring Unreliable Radio Networks  

E-print Network

In this paper we study the problem of building a connected dominating set with constant degree (CCDS) in the dual graph radio network model [4,9,10]. This model includes two types of links: reliable, which always deliver ...

Censor-Hillel, Keren

2011-01-01

345

Structuring Unreliable Radio Networks  

E-print Network

In this paper we study the problem of building a connected dominating set with constant degree (CCDS) in the dual graph radio network model. This model includes two types of links: reliable links, which

Censor-Hillel, Keren

2011-12-22

346

BEA Symposium: Research in Radio.  

ERIC Educational Resources Information Center

The seven articles in this journal issue examine trends and topics related to radio and other broadcast media. The articles discuss the following: (1) current trends in radio audience measurement, (2) the policy implications of radio research, (3) a research study of the relationships between age and radio usage, (4) the role of the part-time…

Finney, Robert G., Ed.; Neckowitz, Alan, Ed.

1980-01-01

347

Packet Radio for Library Automation.  

ERIC Educational Resources Information Center

This tutorial on packet radio (communication system using radio and digital packet-switching technology) highlights radio transmission of data, brief history, special considerations in applying packet radio to library online catalogs, technology, defining protocol at physical and network levels, security, geographic coverage, and components. (A…

Brownrigg, Edwin B.; And Others

1984-01-01

348

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

NASA Technical Reports Server (NTRS)

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

Davarian, Faramaz (editor)

1995-01-01

349

Early Cambridge radio astronomy  

NASA Astrophysics Data System (ADS)

Radio astronomy started in Cambridge immediately after the hostilities of the World War II have ceased. Martin Ryle was the inspiring leader of a small group that started to develop interferometry techniques at the Cavendish Laboratory. From this development came the numerous Cambridge radio source surveys culminating in the Nobel prize awarded to Martin Ryle for invention of aperture synthesis. The history of this early development is the subject of the present paper.

Smith, F. G.

2007-06-01

350

The Radio JOVE Project  

NASA Astrophysics Data System (ADS)

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

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

1999-09-01

351

Conceptual Background to Radio  

NASA Astrophysics Data System (ADS)

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

Ponsonby, J. E. B.

2004-06-01

352

Radio Signatures of Coronal-mass-ejection-Streamer Interaction and Source Diagnostics of Type II Radio Burst  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

353

RADIO SIGNATURES OF CORONAL-MASS-EJECTION-STREAMER INTERACTION AND SOURCE DIAGNOSTICS OF TYPE II RADIO BURST  

SciTech Connect

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

Feng, S. W.; Chen, Y.; Kong, X. L.; Li, G.; Song, H. Q. [Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Physics, Shandong University at Weihai, Weihai 264209 (China); Feng, X. S. [SIGMA Weather Group, State Key laboratory for Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Liu Ying, E-mail: yaochen@sdu.edu.cn [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)

2012-07-01

354

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

355

Imaging interplanetary CMEs at radio frequency from solar polar orbit  

NASA Astrophysics Data System (ADS)

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

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

2011-09-01

356

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

357

HOST GALAXIES OF X-SHAPED RADIO SOURCES  

SciTech Connect

Most radiation from galaxies containing active galactic nuclei (AGNs) is emitted not by the stars composing the galaxy, but from an active source at the galactic center, most likely a supermassive black hole. Of particular interest are radio galaxies, active galaxies that emit much of their radiation at radio wavelengths. Within each radio galaxy, an AGN powers a pair of collimated jets of relativistic particles, forming a pair of giant lobes at the end of the jets and thus giving a characteristic double-lobed appearance. A particular class of radio galaxies has an “X”-or winged-shaped morphology: in these, two pairs of lobes appear to originate from the galactic center, producing a distinctive X-shape. Two main mechanisms have been proposed to explain the X-shape morphology: one being a realignment of the black hole within the AGN and the second positing that the radio jets are expanding into an asymmetric medium, causing backflow and producing secondary wings. By analyzing radio host galaxy shapes, the distribution of the stellar mass is compared to the differing model expectations regarding the distribution of the surrounding gas and stellar material about the AGN. Results show elliptical host galaxies with an orthogonal offset between the semi-major axis of the host galaxy and the secondary radio wings, which lends support to the hydrodynamical model. However, results also show circular host galaxies with radio wings, making the realignment scenario a more likely model to describe the formation of these X-shaped radio sources.

Springmann, A.; Cheung, C.

2007-01-01

358

Radio magazines and the development of broadcasting: Radio broadcast and radio news, 1922–1930  

Microsoft Academic Search

This paper explores the development of two early popular radio magazines: Radio Broadcast and Radio News. The two magazines developed along with the emerging broadcast industry during the 1920s. The historical review and content analysis of the magazines revealed that they enjoyed a great deal of success in the early 1920s by appealing to amateur radio enthusiasts. Both started as

Michael Brown

1998-01-01

359

Population Studies of Radio and Gamma-Ray Pulsars  

NASA Technical Reports Server (NTRS)

Rotation-powered pulsars are one of the most promising candidates for at least some of the 40-50 EGRET unidentified gamma-ray sources that lie near the Galactic plane. Since the end of the EGRO mission, the more sensitive Parkes Multibeam radio survey has detected mere than two dozen new radio pulsars in or near unidentified EGRET sources, many of which are young and energetic. These results raise an important question about the nature of radio quiescence in gamma-ray pulsars: is the non-detection of radio emission a matter of beaming or of sensitivity? The answer is very dependent on the geometry of the radio and gamma-ray beams. We present results of a population synthesis of pulsars in the Galaxy, including for the first time the full geometry of the radio and gamma-ray beams. We use a recent empirically derived model of the radio emission and luminosity, and a gamma-ray emission geometry and luminosity derived theoretically from pair cascades in the polar slot gap. The simulation includes characteristics of eight radio surveys of the Princeton catalog plus the Parkes MB survey. Our results indicate that EGRET was capable of detecting several dozen pulsars as point sources, with the ratio of radio-loud to radio-quiet gamma-ray pulsars increasing significantly to about ten to one when the Parkes Survey is included. Polar cap models thus predict that many of the unidentified EGRET sources could be radio-loud gamma- ray pulsars, previously undetected as radio pulsars due to distance, large dispersion and lack of sensitivity. If true, this would make gamma-ray telescopes a potentially more sensitive tool for detecting distant young neutron stars in the Galactic plane.

Harding, Alice K; Gonthier, Peter; Coltisor, Stefan

2004-01-01

360

Hierarchical Affinity Propagation  

E-print Network

Affinity propagation is an exemplar-based clustering algorithm that finds a set of data-points that best exemplify the data, and associates each datapoint with one exemplar. We extend affinity propagation in a principled way to solve the hierarchical clustering problem, which arises in a variety of domains including biology, sensor networks and decision making in operational research. We derive an inference algorithm that operates by propagating information up and down the hierarchy, and is efficient despite the high-order potentials required for the graphical model formulation. We demonstrate that our method outperforms greedy techniques that cluster one layer at a time. We show that on an artificial dataset designed to mimic the HIV-strain mutation dynamics, our method outperforms related methods. For real HIV sequences, where the ground truth is not available, we show our method achieves better results, in terms of the underlying objective function, and show the results correspond meaningfully to geographi...

Givoni, Inmar; Frey, Brendan J

2012-01-01

361

Elevated Temperature Crack Propagation  

NASA Technical Reports Server (NTRS)

This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.

Orange, Thomas W.

1994-01-01

362

Liouvillian propagators, Riccati equation and differential Galois theory  

NASA Astrophysics Data System (ADS)

In this paper a Galoisian approach to building propagators through Riccati equations is presented. The main result corresponds to the relationship between the Galois integrability of the linear Schrödinger equation and the virtual solvability of the differential Galois group of its associated characteristic equation. As the main application of this approach we solve Ince’s differential equation through the Hamiltonian algebrization procedure and the Kovacic algorithm to find the propagator for a generalized harmonic oscillator. This propagator has applications which describe the process of degenerate parametric amplification in quantum optics and light propagation in a nonlinear anisotropic waveguide. Toy models of propagators inspired by integrable Riccati equations and integrable characteristic equations are also presented.

Acosta-Humánez, Primitivo; Suazo, Erwin

2013-11-01

363

Magnetic-azimuth dependence of D-layer radio reflectivity, using lightning sferics as radio transmitters  

NASA Astrophysics Data System (ADS)

The Very Low Frequency (3-30 kHz) and Low-Frequency (30-300 kHz) radiation from lightning strokes provides a convenient intense source for studying radio propagation in the ionospheric D-region [Cheng and Cummer, 2005; Cheng et al., 2006; Cheng et al., 2007; Cummer et al., 1998; Jacobson et al., 2010; Shao and Jacobson, 2009]. In this poster we present a new study of the magnetic-azimuth dependence of D-layer radio reflectivity at relatively short ranges (r < 1000 km). This range regime is poorly adapted to a waveguide approach but is well treated by our discrete-reflection approach [Jacobson et al., 2009]. We use cloud-to-ground strokes, which are ~100X more numerous than the Narrow Bipolar Pulse sferics to which our method had previously been confined. Cheng, Z., and S. A. Cummer (2005), Broadband VLF measurements of lightning-induced ionospheric perturbations, Geophys. Res. Lett., 32, L08804, doi:08810.01029/02004GL022187. Cheng, Z., S. A. Cummer, D. N. Baker, and S. G. Kanekal (2006), Nighttime D region electron density profiles and variabilities inferred from broadband measurements using VLF radio emissions from lightning, J. Geophys. Res., 111, A05302, doi:05310.01029/02005JA011308. Cheng, Z., S. A. Cummer, H.-T. Su, and R.-R. Hsu (2007), Broadband very low frequency measurement of D region ionospheric perturbations caused by lightning electromagnetic pulses, J. Geophys. Res., 112, A06318. Cummer, S. A., U. S. Inan, and T. F. Bell (1998), Ionospheric D region remote sensing using VLF radio atmospherics, Radio Sci., 33, 1781-1792. Jacobson, A. R., X. Shao, and R. H. Holzworth (2009), Full-wave reflection of lightning long-wave radio pulses from the ionospheric D-region: Numerical model, J. Geophys. Res.- Space, 114, A03303, doi:03310.01029/02008JA013642. Jacobson, A. R., R. Holzworth, and X.-M. Shao (2010), Full-wave reflection of lightning long-wave radio pulses from the ionospheric D-region: Comparison with midday observations of broadband lightning signals, J. Geophys. Res. -Space, 115, A00E27, doi:10.1029/2009JA014540. Shao, X.-M., and A. R. Jacobson (2009), Model simulation of Very-Low-Frequency and Low-Frequency lightning signal propagation over intermediate ranges, IEEE Trans. Electromag. Compat., 51(3), 519-525.

Jacobson, A. R.; Shao, X.; Holzworth, R. H.; Lay, E. H.

2011-12-01

364

Turbofan Duct Propagation Model  

NASA Technical Reports Server (NTRS)

The CDUCT code utilizes a parabolic approximation to the convected Helmholtz equation in order to efficiently model acoustic propagation in acoustically treated, complex shaped ducts. The parabolic approximation solves one-way wave propagation with a marching method which neglects backwards reflected waves. The derivation of the parabolic approximation is presented. Several code validation cases are given. An acoustic lining design process for an example aft fan duct is discussed. It is noted that the method can efficiently model realistic three-dimension effects, acoustic lining, and flow within the computational capabilities of a typical computer workstation.

Lan, Justin H.; Posey, Joe W. (Technical Monitor)

2001-01-01

365

Vegetative Propagation Project  

NSDL National Science Digital Library

Students select a healthy plant to be propagated, do some reading about that plant, and determine what type of vegetative reproduction is suitable for that plant. Students vegetatively reproduce plant, keeping a journal of observations of the plant and the process. The journal entries should include a description of the procedure used to propagate, the amount of water given the plant, the date and numbers of roots that appear, when plant was transferred to soil, a description of soil and pot used and sketches drawn 'every so often' --the works!

BEGIN:VCARD VERSION:2.1 FN:Nancy Iversen N:Iversen;Nancy ORG:Cooperstown High School REV:2005-04-13 END:VCARD

1995-06-30

366

Characteristic 0 Positive characteristic  

E-print Network

Characteristic 0 Positive characteristic Unlikely formal intersections Piotr Kowalski Instytut Matematyczny Uniwersytetu Wroclawskiego June 14, 2012 Kowalski Unlikely formal intersections #12;Characteristic(A) + dim(V ) - dim(W). Kowalski Unlikely formal intersections #12;Characteristic 0 Positive characteristic

Kowalski, Piotr

367

Wave propagation into the middle atmosphere  

NASA Technical Reports Server (NTRS)

Recent observations of various types of waves propagating into the middle atmosphere are reviewed. Emphasis is made on the excitation processes in the lower atmosphere and their vertical propagation through the background flow as a function of the latitude, height and season. The following subjects are discussed: (1) Vertical propagation of quasi-stationary forced Rossby waves into the winter stratosphere in connection with the sudden warming; (2) Spectral distribution and seasonal characteristics of normal mode (free) Rossby waves and the asymmetry of the Northern and Southern Hemispheres; and (3) Seasonal variation of internal gravity waves in the middle atmosphere. Further discussions are presented for future studies based on accumulated observational data during the MAP period.

Hirota, I.

1989-01-01

368

Educational Radio. Information Bulletin 21-B.  

ERIC Educational Resources Information Center

The term "Educational Radio" includes all radio stations licensed for noncommercial operation. A history of educational radio begins with the first domestic law for control of radio in general, The Radio Act of 1912. Federal Communication Commission (FCC) regulations pertaining to educational radio or "public radio" deal with channel assignments,…

Federal Communications Commission, Washington, DC.

369

Coronal Mass Ejections and Solar Radio Emissions  

NASA Technical Reports Server (NTRS)

Coronal mass ejections (CMEs) have important connections to various types of radio emissions from the Sun. The persistent noise storm radiation (type I storm at metric wavelengths, type III storms at longer wavelengths) can be clearly interrupted by the occurrence of a CME in the active region that produces the storm. Sometimes the noise storm completely disappears and other times, it reappears in the active region. Long-lasting type III bursts are associated with CME eruption, thought to be due to the reconnection process taking place beneath the erupting CME. Type II bursts are indicative of electron acceleration in the CME-driven shocks and hence considered to be the direct response of the CME propagation in the corona and interplanetary medium. Finally type IV bursts indicate large-scale post-eruption arcades containing trapped electrons that produce radio emission. This paper summarizes some key results that connect CMEs to various types of radio emission and what we can learn about particle acceleration in the corona) and interplanetary medium. Particular emphasis will be placed on type If bursts because of their connection to interplanetary shocks detected in situ.

Gopalswamy, Nat

2010-01-01

370

Polarized radio emission from a magnetar  

NASA Astrophysics Data System (ADS)

We present polarization observations of the radio emitting magnetar AXPJ1810-197. Using simultaneous multifrequency observations performed at 1.4, 4.9 and 8.4 GHz, we obtained polarization information for single pulses and the average pulse profile at several epochs. We find that in several respects this magnetar source shows similarities to the emission properties of normal radio pulsars while simultaneously showing striking differences. The emission is nearly 80-95 per cent polarized, often with a low but significant degree of circular polarization at all frequencies which can be much greater in selected single pulses. The position angle swing has a low average slope of only 1 deg deg-1, deviating significantly from an S-like swing as often seen in radio pulsars which is usually interpreted in terms of a rotating vector model and a dipolar magnetic field. The observed position angle is consistent at all frequencies while showing significant secular variations. On average, the interpulse is less linearly polarized but shows a higher degree of circular polarization. Some epochs reveal the existence of non-orthogonal emission modes in the main pulse and systematic wiggles in the PA swing, while the interpulse shows a large variety of position angle values. We interpret many of the emission properties as propagation effects in a non-dipolar magnetic field configuration where emission from different multipole components is observed.

Kramer, M.; Stappers, B. W.; Jessner, A.; Lyne, A. G.; Jordan, C. A.

2007-05-01

371

UNIVERSAL ERROR PROPAGATION LAW  

Microsoft Academic Search

As an ubiquitous statistical theory, Gaussian Distribution (GD) or Gaussian Error Propagation Law (GEPL) has been widely used for modelling random errors in many engineering and application fields since 1809. In recent years, this theory has been extended to handle the uncertainties of spatial data in GIS, such as positional error modelling. But most of the results for spatial error

Xiaoyong CHEN; Shunji MURAI

372

COBE nonspinning attitude propagation  

NASA Technical Reports Server (NTRS)

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

Chu, D.

1989-01-01

373

PROPAGATION 1. Introduction  

E-print Network

, guiding vanes, fans and diffusers which not only reflect but also scatter sound. It is here beyond. Therein, the shape of the sound source set the scene and the waves emanating were assumed to propagate for certain kl µ !. One can furthermore infer from this derivation that the sound field will have a build- up

Berlin,Technische Universität

374

Generalized Belief Propagation  

Microsoft Academic Search

Belief propagation (BP) was only supposed to work for tree-like networks but works surprisingly well in many applications involving networks with loops, including turbo codes. However, there has been little understanding of the algorithm or the nature of the solutions it finds for general graphs. We show that BP can only converge to a stationary point of an approximate free

Jonathan S. Yedidia; William T. Freeman; Yair Weiss

2000-01-01

375

Spherical shock-wave propagation in three-dimensional granular packings  

Microsoft Academic Search

We investigate numerically the spherical shock-wave propagation in an open dense granular packing perturbed by the sudden expansion of a spherical intruder in the interior of the pack, focusing on the correlation between geometrical fabrics and propagating properties. The measurements of the temporal and spatial variations in a variety of propagating properties define a consistent serrated wave substructure with characteristic

Kun Xue; Chun-Hua Bai

2011-01-01

376

New American Radio  

NSDL National Science Digital Library

It's quite unusual that a long-defunct radio program would garner a new website, but this is the case with the New American Radio (NAR) show. During its 10-year run, NAR commissioned and distributed over 300 original works, including conceptual new drama works, language explorations, sonic meditations, and works that "pioneer new dimensions in acoustic space." On the site's homepage, visitors can peruse a list of full-length works, excerpts, and even a set of meditative essays on the creative process. A good work to start with here is "O Little Town of East New York" by Shelley Hirsch. It's a compelling autobiographical "docu-musical" about growing up in this diverse neighborhood in the 1960s. The site could be used by any number of students studying communication, drama, theater, radio production, and related subjects.

377

Radio-emitting electrons and cosmic ray confinement  

NASA Technical Reports Server (NTRS)

Evidence from radio data obtained at frequencies of 10 to 8000 MHz for steepening of the observed background-radio-continuum spectra in the directions of the galactic Anticenter (A) and Halo Minimum (H) is used to deduce quantitative information on the variation of the magnetic field with distance from the galactic plane. The radio data are analyzed in the framework of the cosmic-ray diffusion model developed by Bulanov and Dogel (1975), and some inferences are drawn regarding the injection spectrum of cosmic-ray electrons as well as their propagation in the Galaxy. The results indicate that: (1) radio-spectrum steepening is centered around 200 MHz in the direction of H and around 330 MHz in the direction of A, implying a lower mean magnetic field toward H and supporting the existence of a radio halo; (2) an injection electron spectrum with a single power law up to the lowest energies cannot explain the radio observations satisfactorily in terms of the diffusion model; and (3) the observed spectral steepening can be satisfactorily understood as being due partly to the deviation from a power-law injection spectrum below a few GeV and partly to the first break arising from electron energy losses in approximately the same energy region.

Badhwar, G. D.; Daniel, R. R.; Stephens, S. A.

1977-01-01

378

Ray Tracing Jupiter`s HOM Radio Emission  

NASA Astrophysics Data System (ADS)

Cassini, Galileo, and Voyager spacecraft observations show well-defined attenuation features in the hectometer (HOM) spectrum of Jupiter's radio emission. The features are best displayed as frequency versus time spectrograms of HOM intensity between 500 - 3000 kHz. The bands have been shown by Gurnett et al. (1998) to be the result of propagation processes involving these emissions from opposite hemispheres. Enhancements in the HOM intensity and occurrence are seen along the edges of the observed attenuation features which may indicate caustic surfaces due to refraction along the propagation path. Using magnetic field and density models of the Jovian magnetosphere, we present some ray tracing analyses to show that radio wave refraction from density enhancements in the Io flux tube can produce the attenuation structures seen in the observations. This can provide boundaries to the electron density within the Io flux tube.

Higgins, C.; West, C.

2007-05-01

379

Radio Interference at the Molonglo Radio Observatory.  

NASA Astrophysics Data System (ADS)

In conjunction with the local Spectrum Management Agency, field trials have been carried out to determine the susceptibility of the Molonglo Observatory Synthesis Telescope (MOST) to interference from terrestrial transmitters. The MOST operates at a frequency of 843 MHz with a 3 dB bandwidth of 3 MHz. The entire band from 825 to 845 MHz has been allocated for mobile telephone use and is soon to be sold to commercial users. Even though 843 MHz is not an internationally recognised radio astronomy frequency, since the MOST began operation in 1980, the band has been locally respected after consultation with Telecom Australia. Normal operation of the MOST requires 12 hours observation to synthesise an image of ~1-5 sq. degrees of sky. In-band interference with irradiance exceeding -172 dBWm^-2 (which confirms our theoretical predictions) causes noticable degradation of MOST images, although occasional bursts stronger than that are tolerable. The damage to MOST images caused by interference depends on the type of modulation and duration of the transmission and the type of observation. The telescope has recently been funded to carry out a deep radio survey of the southern sky. The viability of this survey is now being seriously threatened.

Davidson, G.; Campbell-Wilson, D.; Large, M. I.

380

eRadio : empowerment through community Web radio  

E-print Network

The eRadio project proposes to be an effective aid to increase interaction and reduce alienation among the members of dispersed communities by using a holistic approach to participatory and interactive web radio-production, ...

Gomez-Monroy, Carla, 1977-

2004-01-01

381

The cosmic evolution of radio-AGN feedback to z = 1  

NASA Astrophysics Data System (ADS)

This paper presents the first measurement of the radio luminosity function of `jet-mode' (radiatively inefficient) radio-AGN out to z = 1, in order to investigate the cosmic evolution of radio-AGN feedback. Eight radio source samples are combined to produce a catalogue of 211 radio-loud AGN with 0.5 < z < 1.0, which are spectroscopically classified into jet-mode and radiative-mode (radiatively efficient) AGN classes. Comparing with large samples of local radio-AGN from the Sloan Digital Sky Survey, the cosmic evolution of the radio luminosity function of each radio-AGN class is independently derived. Radiative-mode radio-AGN show an order of magnitude increase in space density out to z ? 1 at all luminosities, consistent with these AGN being fuelled by cold gas. In contrast, the space density of jet-mode radio-AGN decreases with increasing redshift at low radio luminosities (L1.4 GHz ? 1024 W Hz-1) but increases at higher radio luminosities. Simple models are developed to explain the observed evolution. In the best-fitting models, the characteristic space density of jet-mode AGN declines with redshift in accordance with the declining space density of massive quiescent galaxies, which fuel them via cooling of gas in their hot haloes. A time delay of 1.5-2 Gyr may be present between the quenching of star formation and the onset of jet-mode radio-AGN activity. The behaviour at higher radio luminosities can be explained either by an increasing characteristic luminosity of jet-mode radio-AGN activity with redshift (roughly as (1 + z)3) or if the jet-mode radio-AGN population also includes some contribution of cold-gas-fuelled sources seen at a time when their accretion rate was low. Higher redshifts measurements would distinguish between these possibilities.

Best, P. N.; Ker, L. M.; Simpson, C.; Rigby, E. E.; Sabater, J.

2014-11-01

382

Radio Observations of Supernovae  

E-print Network

Study of radio supernovae over the past 25 years includes two dozen detected objects and more than 100 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the stellar system, to detect clumpiness of the circumstellar material, and to put useful constraints on the progenitors of undetected Type Ia supernovae.

Panagia, N; Van Dyk, S D; Sramek, R A; Stockdale, C J; Panagia, Nino; Weiler, Kurt W.; Dyk, Schuyler D. Van; Sramek, Richard A.; Stockdale, Christopher J.

2007-01-01

383

Radio Observations of Supernovae  

E-print Network

Study of radio supernovae over the past 25 years includes two dozen detected objects and more than 100 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the stellar system, to detect clumpiness of the circumstellar material, and to put useful constraints on the progenitors of undetected Type Ia supernovae.

Nino Panagia; Kurt W. Weiler; Schuyler D. Van Dyk; Richard A. Sramek; Christopher J. Stockdale

2007-03-15

384

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

385

Problems in contemporary radio engineering and electronics  

NASA Astrophysics Data System (ADS)

Papers are presented on such topics as the radar mapping of Venus, the attenuation and scattering of millimeter waves in the earth's atmosphere, radio probing of the turbulent structure of the interplanetary and circumsolar plasma, and the characteristics of fiber-optic communication systems and sensors. Consideration is also given to an analysis of natural VLF noise, semiconductor components in millimeter-wave radiation detectors, the design of acoustoelectronic devices for data processing, and superconducting radiation detectors.

Kotel'Nikov, V. A.

386

Coherent Mechanisms of Pulsar Radio Emission  

E-print Network

Relativistic plasma masers operating on the anomalous cyclotron-Cherenkov resonance and the Cherenkov-drift resonance are capable of explaining the main observational characteristics of pulsar radio emission. Both electromagnetic instabilities are due to the interaction of the fast particles from the primary beam and from the tail of the secondary pairs distribution with the normal modes of a strongly magnetized one-dimensional electron-positron plasma. In a typical pulsar both resonances occur in the outer parts of magnetosphere .

Maxim Lyutikov; Roger Blandford; George Machabeli

1999-10-14

387

Adaptive radio frequency interference mitigation for HF surface wave radar  

Microsoft Academic Search

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

Wan Xianrong; Wen Biyang; Ke Hengyu

2004-01-01

388

A Database for Propagation Models and Conversion to C++ Programming Language  

NASA Technical Reports Server (NTRS)

In the past few years, a computer program was produced to contain propagation models and the necessary prediction methods of most propagation phenomena. The propagation model database described here creates a user friendly environment that makes using the database easy for experienced users and novices alike. The database is designed to pass data through the desired models easily and generate relevant results quickly. The database already contains many of the propagation phenomena models accepted by the propagation community and every year new models are added. The major sources of models included are the NASA Propagation Effects Handbook or the International Radio Consultive Committee (CCIR) or publications such as the Institute for Electrical and Electronic Engineers (IEEE).

Kantak, Anil V.; Angkasa, Krisjani; Rucker, James

1996-01-01

389

Constraints on cosmic ray propagation in the galaxy  

NASA Technical Reports Server (NTRS)

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

Cordes, James M.

1992-01-01

390

CURVATURE-DRIFT INSTABILITY FAILS TO GENERATE PULSAR RADIO EMISSION  

SciTech Connect

The curvature-drift instability has long been considered as a viable mechanism for pulsar radio emission. We reconsidered this mechanism by finding an explicit solution describing the propagation of short electromagnetic waves in a plasma flow along curved magnetic field lines. We show that even though the waves could be amplified, the amplification factor remains very close to unity; therefore, this mechanism is unable to generate high brightness temperature emission from initial weak fluctuations.

Kaganovich, Alexander; Lyubarsky, Yuri [Physics Department, Ben-Gurion University, P.O. Box 653, Beer-Sheva 84105 (Israel)

2010-10-01

391

Evolutionary algorithms for radio resource management in cognitive radio network  

Microsoft Academic Search

Cognitive radio (CR) technology employing dynamic spectrum access (DSA) improves spectrum utilization by exploiting its unused portions and provides a solution to the apparent spectrum scarcity problem. In this paper we present binary particle swarm optimization (BPSO) and genetic algorithm (GA) for radio resource management (RRM) in OFDMA-based cognitive radio network (CRN). The simulation results show that BPSO-based RRM performs

Muhammad Waheed; Anni Cai

2009-01-01

392

Sirius Satellite Radio: Radio entertainment in the sky  

Microsoft Academic Search

Satellite broadcasting of radio programs is an effective means of serving large and distributed markets. A space-based radio system can provide about 100 high quality music, voice, and data channels to users spread over a vast geographic area. Employing digital technology and an elaborate system design, this approach significantly outperforms traditional AM and FM radio broadcasting in signal quality, program

F. Davarian

2002-01-01

393

Simulation studies of GPS radio occultation measurements  

NASA Astrophysics Data System (ADS)

The atmospheric propagation of GPS signals under multipath conditions and their detection are simulated. Using the multiple phase screen method, C/A-code modulated L1 signals are propagated through a spherically symmetric refractivity field derived from a high-resolution radio sonde observation. The propagated signals are tracked by a GPS receiver implemented in software and converted to refractivity profiles by the canonical transform technique and the Abel inversion. Ignoring noise and assuming an ideal receiver tracking behavior, the true refractivity profile is reproduced to better than 0.1% at altitudes above 2 km. The nonideal case is simulated by adding between 14 and 24 dB of Gaussian white noise to the signal and tracking the signal with a receiver operating at 50 and 200 Hz sampling frequency using two different carrier phase detectors. In the upper troposphere and stratosphere the fractional refractivity retrieval error is below 0.3% for 50 Hz sampling and below 0.15% for 200 Hz sampling. In the midtroposphere down to altitudes of about 2 km, phase-locked loop tracking induces negative fractional refractivity biases on the order of -1 to -2% at 50 Hz sampling frequency. Modifications to the receiver tracking algorithm significantly improve the retrieval results. In particular, replacing the carrier loop's two-quadrant phase extractor with a four-quadrant discriminator reduces the refractivity biases by a factor of 5; increasing the sampling frequency from 50 to 200 Hz gains another factor of 2.

Beyerle, G.; Gorbunov, M. E.; Ao, C. O.

2003-10-01

394

Low Frequency Radio Signals from Sprite Streamers  

NASA Astrophysics Data System (ADS)

Sprites are mesospheric discharges that carry significant electrical currents and produce radio signals observed typically in the extremely low (ELF) to very low (VLF) frequency bands [Cummer et al., GRL, 25, 1281, 1998]. Recently, Low-Frequency (LF) radio observations of sprite-producing lightning discharges have shown the existence of consecutive broadband pulses exhibiting EM radiation that spans in the LF range, and it has been suggested that this LF radio signals may stem from non-luminous relativistic electron beams above thunderstorms [Fullekrug et al., JGR, 115, A00E09, 2010]. In this talk, we present the first theoretical estimates of the radio signals produced by individual sprite streamers using simulation results from a plasma fluid model. It is demonstrated that the spectral content of the radiation produced by sprite streamers is a function of the air density N and the lightning-induced quasi-static ambient electric field E in the regions of space where the sprite streamers are propagating. We demonstrate that the exponential growth of the current in sprite streamers at 75 km would be preferentially associated with electromagnetic radiation in the frequency range from 0 and up to ˜3 kHz, whereas the growth of the streamer current at 40 km could produce radiation with frequencies up to ˜300 kHz, consistently with the scaling of atmospheric air density [Kosar et al., JGR, 117, A08328, 2012]. We further conjecture that the periodic branching of streamers may lead to a radiation spectrum enhancement in the VLF to LF range. The present study shows that sprite streamers could be responsible for at least part of the LF radiation associated with sprite-producing lightning discharges that was detected recently by Fullekrug et al. [2010].

Qin, J.; Celestin, S. J.; Pasko, V. P.

2013-12-01

395

The auroral radio emissions from planetary magnetospheres - What do we know, what don't we know, what do we learn from them?  

Microsoft Academic Search

This overview examines the current observational data regarding the planetary radio emissions of the earth, Jupiter, Saturn, Uranus, and Neptune and examines the fundamental characteristics of the planets. Auroral radio emissions are studied in terms of their relation to important magnetospheric regions with attention given to their observational limitations. The primary observationally deduced characteristics of planetary radio emissions are listed

Philippe Zarka

1992-01-01

396

Talk Radio as Interpersonal Communication.  

ERIC Educational Resources Information Center

Examines whether talk radio serves different purposes for listeners who phone in, compared to those who do not. Finds that talk radio provides callers with an accessible and nonthreatening alternative to interpersonal communication. (MS)

Armstrong, Cameron B.; Rubin, Alan M.

1989-01-01

397

Speakeasy: the military software radio  

Microsoft Academic Search

The Speakeasy Phase II radio will use programmable processing to emulate more than 15 existing military radios. Speakeasy is a challenge, even with recent advancements in DSP technologies. The benefits, however, make the challenge highly worthwhile

R. I. Lackey; D. W. Upmal

1995-01-01

398

Uncertainty and its propagation in dynamics models  

SciTech Connect

The purpose of this paper is to bring together some characteristics due to uncertainty when we deal with dynamic models and therefore to propagation of uncertainty. The respective role of uncertainty and inaccuracy is examined. A mathematical formalism based on Chapman-Kolmogorov equation allows to define a {open_quotes}subdynamics{close_quotes} where the evolution equation takes the uncertainty into account. The problem of choosing or combining models is examined through a loss function associated to a decision.

Devooght, J. [Universite Libre de Bruxelles, Brussels (Belgium)

1994-10-01

399

Variation of Flow Propagation Velocity with Age  

Microsoft Academic Search

Flow propagation velocity is a new color Doppler M-mode measurement of left ventricular filling characteristics. This study was designed to establish normal values for this measurement in healthy individuals and to compare these findings with pulsed Doppler transmitral velocities. Complete M-mode, two-dimensional, and Doppler echocardiographic studies were performed on 64 volunteers between 21 and 79 years of age. Significant negative

David M. Mego; Vincent S. DeGeare; Sheri Y. Nottestad; Vernadette P. Lamanna; Lori C. Oneschuk; Bernard J. Rubal; Miguel Zabalgoitia

1998-01-01

400

CHARACTERIZING COSMIC-RAY PROPAGATION IN MASSIVE STAR-FORMING REGIONS: THE CASE OF 30 DORADUS AND THE LARGE MAGELLANIC CLOUD  

SciTech Connect

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

Murphy, E. J. [Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Porter, T. A.; Moskalenko, I. V. [Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States); Helou, G. [California Institute of Technology, MC 100-22, Pasadena, CA 91125 (United States); Strong, A. W., E-mail: emurphy@obs.carnegiescience.edu, E-mail: tporter@stanford.edu, E-mail: imos@stanford.edu, E-mail: gxh@ipac.caltech.edu, E-mail: aws@mpe.mpg.de [Max-Planck-Institut fuer extraterrestrische Physik, Postfach 1312, D-85741 Garching (Germany)

2012-05-10

401

Radio science investigations by VeRa onboard the Venus Express spacecraft  

Microsoft Academic Search

The Venus Express Radio Science Experiment (VeRa) uses radio signals at wavelengths of 3.6 and 13cm (“X”- and “S”-band, respectively) to investigate the Venus surface, neutral atmosphere, ionosphere, and gravity field, as well as the interplanetary medium. An ultrastable oscillator (USO) provides a high quality onboard reference frequency source; instrumentation on Earth is used to record amplitude, phase, propagation time,

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

2006-01-01

402

Radio fiber bursts and fast magnetoacoustic wave trains  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

403

Preventing Unofficial Information Propagation  

NASA Astrophysics Data System (ADS)

Digital copies are susceptible to theft and vulnerable to leakage, copying, or manipulation. When someone (or some group), who has stolen, leaked, copied, or manipulated digital documents propagates the documents over the Internet and/or distributes those through physical distribution channels many challenges arise which document holders must overcome in order to mitigate the impact to their privacy or business. This paper focuses on the propagation problem of digital credentials, which may contain sensitive information about a credential holder. Existing work such as access control policies and the Platform for Privacy Preferences (P3P) assumes that qualified or certified credential viewers are honest and reliable. The proposed approach in this paper uses short-lived credentials based on reverse forward secure signatures to remove this assumption and mitigate the damage caused by a dishonest or honest but compromised viewer.

Le, Zhengyi; Ouyang, Yi; Xu, Yurong; Ford, James; Makedon, Fillia

404

Radio's regulatory roadblocks  

Microsoft Academic Search

Great news! Your team has come up with a new radio technology - one that may have the same impact as Wi-Fi or Bluetooth. Management loves it, funding is in place, patent applications are ' filed, production is lined up, and marketing is ready to go. This will be huge. Or maybe not. Your invention could be illegal in the

M. Lazarus

2009-01-01

405

Japanese Radio Exercises. Revised.  

ERIC Educational Resources Information Center

This unit focuses on Japanese radio exercises which became popular in Japan just after World War II and are still used among students and workers in companies to help raise morale and form group unity. The exercises reflect the general role of exercise in Japanese culture--to serve as a symbol of unity and cooperation among the Japanese, as well…

Young, Jocelyn

406

RECONFIGURABILITY FACILITATING COMPOSITE RADIO  

Microsoft Academic Search

The key objective of End-to-End Reconfigurability (E²R) is to devise, develop and trial architectural design of reconfigurable devices and supporting system functions to offer an expanded set of operational choices to the different actors of the value chain in the context of heterogeneous mobile radio systems.

Jijun Luo; Klaus Moessner; David Grandblaise; Karim El-Khazen; Didier Bourse; Eiman Mohyeldin; Panagiotis Demestichas

407

Radio and Biography  

Microsoft Academic Search

Scholars and authors sometimes lament that broadcast versions of written biographies are inaccurate or simplistic. This essay considers the intellectual dilemmas of presenting lives in broadcast formats, particularly radio, focusing on audience, function, and representation. How much fiddling with facts and milieu is permissible in the adaptive process? How can writers ensure integrity of their material when broadcast?

David King Dunaway

1997-01-01

408

Radio and Biography  

Microsoft Academic Search

:Scholars and authors sometimes lament that broadcast versions of written biographies are inaccurate or simplistic. This essay considers the intellectual dilemmas of presenting lives in broadcast formats, particularly radio, focusing on audience, function, and representation. How much fiddling with facts and milieu is permissible in the adaptive process? How can writers ensure integrity of their material when broadcast?

David King Dunaway

1997-01-01

409

NationalRadio Observatory  

E-print Network

-on learning about the incredible space science we do! WestVirginia's SpacePlace www.nrao.edu/VisitGB 304-456-2150 Check out the Green Bank Science Center on Facebook for updated events & specials! W VTOURISM.COM 800 exhibits and displays in our exhibit hall where you will discover what radio astronomers are learning about

Groppi, Christopher

410

Educational Broadcasting--Radio.  

ERIC Educational Resources Information Center

This manual is intended for those who must conduct educational radio broadcasting training courses in Asia-Pacific countries without the resources of experienced personnel, as well as for individuals to use in self-learning situations. The selection of material has been influenced by the need to use broadcasting resources effectively in programs…

Ahamed, Uvais; Grimmett, George

411

Division X: Radio Astronomy  

Microsoft Academic Search

There have been important advances in radio astronomy in the last three years. New discoveries both at the galactic and extragalactic scale have been reported over this period and we highlight here several of them. The outstanding results of the Wilkinson Microwave Anisotropy Probe satellite, allowing an accurate determination of the main cosmological constants, are certainly among the most important.

Luis F. Rodríguez; Ren-Dong Nan; Philip J. Diamond; Gloria Dubner; Michael Garrett; Anne Green; Masato Ishiguro; W. Miller Goss; Russ Taylor; Lucia Padrielli; A. Pramesh Rao; José M. Torrelles; Jean L. Turner

2007-01-01

412

Some Fundamental Limitations for Cognitive Radio  

E-print Network

' & $ % Some Fundamental Limitations for Cognitive Radio Anant Sahai Wireless Foundations, UCB EECS program November 1 at BWRC Cognitive Radio Workshop #12;' & $ % Outline 1. Why cognitive radios? 2 November 1 at BWRC Cognitive Radio Workshop #12;' & $ % Apparent spectrum allocations · Traditional

Sahai, Anant

413

The ACTS propagation program  

NASA Technical Reports Server (NTRS)

The success or failure of the ACTS experiment will depend on how accurately the rain-fade statistics and fade dynamics can be predicted in order to derive an appropriate algorithm that will combat weather vagaries, specifically for links with small terminals, such as very small aperture terminals (VSAT's) where the power margin is a premium. The planning process and hardware development program that will comply with the recommendations of the ACTS propagation study groups are described.

Chakraborty, D.; Davarian, Faramaz

1992-01-01

414

Florida's propagation report  

NASA Technical Reports Server (NTRS)

One of the key goals of the Florida Center is to obtain a maximum of useful information on propagation behavior unique to its subtropical weather and subtropical climate. Such weather data is of particular interest when it is (or has the potential to become) useful for developing and implementing techniques to compensate for adverse weather effects. Also discussed are data observations, current challenges, CDF's, sun movement, and diversity experiments.

Helmken, Henry; Henning, Rudolf

1994-01-01

415

Propagation of Oscillation  

Microsoft Academic Search

\\u000a A series of simple harmonic oscillators, which represents masses connected by springs, is a good conceptual medium in which\\u000a sound travels as a wave. This chapter focusses on oscillation propagating via connected oscillators as a wave that originated\\u000a in initial disturbance in a local portion of a medium. A sound wave travels by a process in which the kinetic energy

Mikio Tohyama

416

Adaptive Affinity Propagation Clustering  

Microsoft Academic Search

Affinity propagation clustering (AP) has two limitations: it is hard to know\\u000awhat value of parameter 'preference' can yield an optimal clustering solution,\\u000aand oscillations cannot be eliminated automatically if occur. The adaptive AP\\u000amethod is proposed to overcome these limitations, including adaptive scanning\\u000aof preferences to search space of the number of clusters for finding the\\u000aoptimal clustering solution,

Kaijun Wang; Junying Zhang; Dan Li; Xinna Zhang; Tao Guo

2008-01-01

417

CRAF Handbook for Radio Astronomy  

E-print Network

CRAF Handbook for Radio Astronomy EUROPEAN SCIENCE FOUNDATION Committee on Radio Astronomy forum for science. The ESF Expert Committee on Radio Astronomy Frequencies, CRAF, was established Astronomy Service and other passive applications. Cover: The 76-m diameter Lovell Telescope at Jodrell Bank

Rodriguez, Luis F.

418

Microwave instrumentation for radio astronomy  

Microsoft Academic Search

Radio astronomy is a branch of science that allows observation of natural radio signals from cosmic sources. Microwave techniques are employed in large radio telescope systems in diverse ways. Starting with early vacuum tube receivers at meter wavelengths, low-noise receivers have pushed the leading edge of technology, culminating in present-day receivers employing HFET amplifiers, superconducting tunnel junctions, and other advanced

John C. Webber; Marian W. Pospieszalski

2002-01-01

419

Radio disturbance warning issuance system  

NASA Technical Reports Server (NTRS)

A radio disturbance warning issuance system was introduced in the Hiraiso Branch of the Radio Research Laboratories in 1972 to reconstruct the current radio disturbance warning service as a social information service. A description of the new ideas which were experimentally systematized by means of an electronic computer is presented.

Maeda, R.; Inuki, H.

1979-01-01

420

Spectrum Sensing for Cognitive Radio  

Microsoft Academic Search

Spectrum sensing is the very task upon which the entire operation of cognitive radio rests. For cognitive radio to fulfill the potential it offers to solve the spectrum underutilization problem and do so in a reliable and computationally feasible manner, we require a spectrum sensor that detects spectrum holes (i.e., underutilized subbands of the radio spectrum), provides high spectral-resolution capability,

Simon Haykin; David J. Thomson; Jeffrey H. Reed

2009-01-01

421

Intelligence artificielle et radio cognitive  

E-print Network

Intelligence artificielle et radio cognitive Badr Benmammar badr.benmammar@gmail.com cel-00680196,version2-25Mar2012 #12;2 Plan Intelligence artificielle et radio cognitive Algorithmes intelligents Réseaux de neurones Logique floue Processus de décision de Markov Langages de la radio cognitive Domaines

Paris-Sud XI, Université de

422

Mathematical Foundations of Cognitive Radios  

E-print Network

Mathematical Foundations of Cognitive Radios Romain Couillet and M´erouane Debbah Abstract. In this paper, we intro- duce a fundamental vision of cognitive radios from a physical layer viewpoint -- Recently, much interest has been directed towards software defined radios and embedded intelligence

Paris-Sud XI, Université de

423

Cognitive Radio: Fundamentals and Opportunities  

E-print Network

Cognitive Radio: Fundamentals and Opportunities Robert H. Morelos-Zaragoza Department of Electrical Engineering San Jose State University October 12, 2007 #12;Cognitive Radio - RHMZ - 2007 Slide 2 of 18 Outline. Cognitive radio (CR) a) Definition and overview (Mitola) b) CR features (FCC) 3. Unlicensed TV spectrum

Morelos-Zaragoza, Robert H.

424

Language Issues for Cognitive Radio  

E-print Network

INVITED P A P E R Language Issues for Cognitive Radio Computer languages that may be useful for expressing cognitive radio concepts are identified and evaluated in this tutorial paper. By Mieczyslaw M aspects of formal languages in the context of cognitive radio. A bottom up approach is taken in which

Kokar, Mieczyslaw M.

425

John E. Hibbard National Radio  

E-print Network

John E. Hibbard National Radio Astronomy Observatory The Antennae Galaxies: Archetype for Colliding Galaxies #12;The Antennae: A Merger Prototype J. Hibbard, NRAO 203rd AAS Jan 9 2004 Talk Outline of radio galaxiesUsed to support collisional origin of radio galaxies (Baade & Minkowski 1954, ApJ, 119

Hibbard, John

426

Imaging Interplanetary CMEs at Radio Frequency From Solar Polar Orbit  

NASA Astrophysics Data System (ADS)

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

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

427

Collaborative Beamfocusing Radio (COBRA)  

NASA Astrophysics Data System (ADS)

A Ziva team has recently demonstrated a novel technique called Collaborative Beamfocusing Radios (COBRA) which enables an ad-hoc collection of distributed commercial off-the-shelf software defined radios to coherently align and beamform to a remote radio. COBRA promises to operate even in high multipath and non-line-of-sight environments as well as mobile applications without resorting to computationally expensive closed loop techniques that are currently unable to operate with significant movement. COBRA exploits two key technologies to achieve coherent beamforming. The first is Time Reversal (TR) which compensates for multipath and automatically discovers the optimal spatio-temporal matched filter to enable peak signal gains (up to 20 dB) and diffraction-limited focusing at the intended receiver in NLOS and severe multipath environments. The second is time-aligned buffering which enables TR to synchronize distributed transmitters into a collaborative array. This time alignment algorithm avoids causality violations through the use of reciprocal buffering. Preserving spatio-temporal reciprocity through the TR capture and retransmission process achieves coherent alignment across multiple radios at ~GHz carriers using only standard quartz-oscillators. COBRA has been demonstrated in the lab, aligning two off-the-shelf software defined radios over-the-air to an accuracy of better than 2 degrees of carrier alignment at 450 MHz. The COBRA algorithms are lightweight, with computation in 5 ms on a smartphone class microprocessor. COBRA also has low start-up latency, achieving high accuracy from a cold-start in 30 ms. The COBRA technique opens up a large number of new capabilities in communications, and electronic warfare including selective spatial jamming, geolocation and anti-geolocation.

Rode, Jeremy P.; Hsu, Mark J.; Smith, David; Husain, Anis

2013-05-01

428

Beam propagation in atomic waveguides  

Microsoft Academic Search

We perform modal analysis and ultracold atomic beam propagation in hollow optical fibers. The eigenmodes and modal propagation constants of the atomic waveguide are determined by numerical solution of the Schrodinger equation for the center-of-mass motion. The existence of a threshold de Broglie wavelength for the fundamental mode is predicted. Beam propagation is performed by modal expansion of the wavefunction

E. Arevalo; Angela M. Guzman

1999-01-01

429

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

430

Shock Wave Propagation Process in Epoxy Syntactic Foams  

Microsoft Academic Search

The Shock Wave Propagation Process [SWPP] in epoxy syntatctic foams (Hollow Glass Micro Spheres [HGMS] within an epoxy binder), with a nano-second temporal and micrometer spatial resolution, is presented and discussed. Samples with three different characteristic pore sizes were studied (40; 90 and 130 mum). For the samples with characteristic pore size of 90 mum, the effects of different densities

Jose Ribeiro; Jose Campos; Igor Plaksin; Ricardo Mendes

2001-01-01

431

Shock Wave Propagation Process in Epoxy Syntactic Foams  

Microsoft Academic Search

The Shock Wave Propagation Process SWPP in epoxy syntactic foams SF (Hollow Glass Micro Spheres HGMS within an epoxy binder) with a nano-second temporal and micrometer spatial resolution is presented and discussed. Samples with three different characteristic HGMS sizes were studied (42, 92 and 135 mum). For the samples with characteristic HGMS size of 92 mum, the effects of the

J. Ribeiro; J. Campos; I. Plaksin; R. Mendes

2002-01-01

432

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

Microsoft Academic Search

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

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

2009-01-01

433

Audience participation in radio development programmes: A study of radio seremban, a Malaysian local radio station  

Microsoft Academic Search

Among the methods adopted to accelerate rural quality of life in Malaysia is a continuous dissemination of development messages to the people. The local radio stations in the country are expected to be effective sources for the rural population's participation in radio for development. To what extent do the rural audience participate in the local radio development programmes? What factors

Adam Tanko Zakariah

1993-01-01

434

Prediction of received signal power and propagation path loss in open\\/rural environments using modified Free-Space loss and Hata models  

Microsoft Academic Search

This paper describes a modification of the Free-Space and Hata formulae for the prediction of received signal power, PR and propagation path loss, LP, in two cellular mobile radio systems (CMRS), in the Northern Nigeria. Measurements of PRs were taken with a Cellular Mobile Radio test Receiver (Sagem OT 160), in some selected open\\/rural environments, when the receiver was being

W. A. Shittu; B. G. Bajoga; F. Anwar; M. J. E. Salami

2008-01-01

435

Liouvillian Propagators, Riccati Equation and Differential Galois Theory  

E-print Network

In this paper a Galoisian approach to build propagators through Riccati equations is presented. The main result corresponds to the relationship between the Galois integrability of the linear Schr\\"odinger equation and the virtual solvability of the differential Galois group of its associated characteristic equation. As main application of this approach we solve the Ince's differential equation through Hamiltonian Algebrization procedure and Kovacic Algorithm to find the propagator for a generalized harmonic oscillator that has applications describing the process of degenerate parametric amplification in quantum optics and the description of the light propagation in a nonlinear anisotropic waveguide. Toy models of propagators inspired by integrable Riccati equations and integrable characteristic equations are also presented.

Primitivo B. Acosta-Humánez; Erwin Suazo

2013-04-21

436

Temporal scaling in information propagation  

NASA Astrophysics Data System (ADS)

For the study of information propagation, one fundamental problem is uncovering universal laws governing the dynamics of information propagation. This problem, from the microscopic perspective, is formulated as estimating the propagation probability that a piece of information propagates from one individual to another. Such a propagation probability generally depends on two major classes of factors: the intrinsic attractiveness of information and the interactions between individuals. Despite the fact that the temporal effect of attractiveness is widely studied, temporal laws underlying individual interactions remain unclear, causing inaccurate prediction of information propagation on evolving social networks. In this report, we empirically study the dynamics of information propagation, using the dataset from a population-scale social media website. We discover a temporal scaling in information propagation: the probability a message propagates between two individuals decays with the length of time latency since their latest interaction, obeying a power-law rule. Leveraging the scaling law, we further propose a temporal model to estimate future propagation probabilities between individuals, reducing the error rate of information propagation prediction from 6.7% to 2.6% and improving viral marketing with 9.7% incremental customers.

Huang, Junming; Li, Chao; Wang, Wen-Qiang; Shen, Hua-Wei; Li, Guojie; Cheng, Xue-Qi

2014-06-01

437

Temporal scaling in information propagation.  

PubMed

For the study of information propagation, one fundamental problem is uncovering universal laws governing the dynamics of information propagation. This problem, from the microscopic perspective, is formulated as estimating the propagation probability that a piece of information propagates from one individual to another. Such a propagation probability generally depends on two major classes of factors: the intrinsic attractiveness of information and the interactions between individuals. Despite the fact that the temporal effect of attractiveness is widely studied, temporal laws underlying individual interactions remain unclear, causing inaccurate prediction of information propagation on evolving social networks. In this report, we empirically study the dynamics of information propagation, using the dataset from a population-scale social media website. We discover a temporal scaling in information propagation: the probability a message propagates between two individuals decays with the length of time latency since their latest interaction, obeying a power-law rule. Leveraging the scaling law, we further propose a temporal model to estimate future propagation probabilities between individuals, reducing the error rate of information propagation prediction from 6.7% to 2.6% and improving viral marketing with 9.7% incremental customers. PMID:24939414

Huang, Junming; Li, Chao; Wang, Wen-Qiang; Shen, Hua-Wei; Li, Guojie; Cheng, Xue-Qi

2014-01-01

438

Introduction to special section on Mitigation of Radio Frequency Interference in Radio Astronomy  

E-print Network

Introduction to special section on Mitigation of Radio Frequency Interference in Radio Astronomy presented at the Workshop on the Mitigation of Radio Frequency Interference in Radio Astronomy (RFI2004), Introduction to special section on Mitigation of Radio Frequency Interference in Radio Astronomy, Radio Sci

Ellingson, Steven W.

439

Development of a curved ray tracing method for modeling of phase paths from GPS radio occultation: A two-dimensional study  

NASA Astrophysics Data System (ADS)

A two-dimensional curved ray tracer (CRT) is developed to study the propagation path of radio signals across a heterogeneous planetary atmosphere. The method, designed to achieve improvements in both computational efficiency and accuracy over conventional straight-line methods, takes rays' first-order bending into account to better describe curved raypaths in the stratified atmosphere. CRT is then used to simulate the phase path from GPS radio occultation (RO). The merit of the ray tracing approach in GPS RO is explicit consideration of horizontal variation in the atmosphere, which may lead to a sizable error but is disregarded in traditional retrieval schemes. In addition, direct modeling of the phase path takes advantage of simple error characteristics in the measurement. With provision of ionospheric and neutral atmospheric refractive indices, in this effort, rays are traced along the full range of GPS-low Earth orbiting (LEO) radio links just as the measurements are made in real life. Here, ray shooting is employed to realize the observed radio links with controlled accuracy. CRT largely reproduces the very measured characteristics of GPS signals. When compared, the measured and simulated phases show remarkable agreement. The cross validation between CRT and GPS RO has confirmed not only the strength of CRT but also the high accuracy of GPS RO measurements. The primary motivation for this study is enabling effective quality control for GPS RO data, overcoming a complicated error structure in the high-level data. CRT has also shown a great deal of potential for improved utilization of GPS RO data for geophysical research.

Wee, Tae-Kwon; Kuo, Ying-Hwa; Lee, Dong-Kyou

2010-12-01

440

Millisecond solar radio spikes.  

NASA Astrophysics Data System (ADS)

Currently available models of one of the most intriguing types of unsteady RF solar emission, millisecond solar radio spikes, are discussed. A comparative analysis of the models' implications and of the body of existing data yields an outline of the most realistic radio spike model possible. The spikes are produced by the cyclotron maser mechanism. The cyclotron cone instability is caused by fast electrons distributed over energies according to a (piecewise) power law. The angular part of the distribution function (whose exact form is, as yet, undetermined) suffers fluctuations due to the magnetic field inhomogeneities that arise in the burst loop as a consequence of the original energy release. In some portions of the loop the distribution is not anisotropic enough to secure the development of a cyclotron instability; it is in these 'microtraps' where individual spikes form. Key areas of future theoretical and experimental research are suggested with a view to verifying the adequacy and realizing the diagnostic potential of the model.

Fleishman, G. D.; Mel'Nikov, V. F.

1998-12-01

441

Pecan Propagation in Texas.  

E-print Network

PECAN PROPAGATION IN TEXAS I SOIL AND CLIMATIC REQ:UIREMENTS The ideal condition for pecan production is to have the roots of the tree in perpetual, moderate moisture and the top in constant sunshine. Good pecan land should be fertile, deep, loose... it should be much deeper. Shallow soils cannot be relied upon to pro­ duce regular crops. Tight land prevents the growth of an extended root system, and is too uneven in its moisture content. The wood growing period of a pecan tree extends froInt the opening...

Swallow, A. P.

1924-01-01

442

Adaptive Affinity Propagation Clustering  

E-print Network

Affinity propagation clustering (AP) has two limitations: it is hard to know what value of parameter 'preference' can yield an optimal clustering solution, and oscillations cannot be eliminated automatically if occur. The adaptive AP method is proposed to overcome these limitations, including adaptive scanning of preferences to search space of the number of clusters for finding the optimal clustering solution, adaptive adjustment of damping factors to eliminate oscillations, and adaptive escaping from oscillations when the damping adjustment technique fails. Experimental results on simulated and real data sets show that the adaptive AP is effective and can outperform AP in quality of clustering results.

Wang, Kaijun; Li, Dan; Zhang, Xinna; Guo, Tao

2008-01-01

443

Attenuation of wave propagation in a novel periodic structure  

Microsoft Academic Search

A novel periodic mount was presented. A theoretical model was developed to describe the dynamics of wave propagation in the\\u000a novel periodic mount. The model was derived using Hamilton’s energy conservation principle. The characteristics of wave propagation\\u000a in unit cell were analyzed by transfer matrix formulation. Numerical examples were given to illustrate the effectiveness of\\u000a the periodic mount. The experiments

Ling Zheng; Yi-nong Li; A. Baz

2011-01-01

444

Modeling Information Propagation Along Traffic on Two Parallel Roads  

E-print Network

that the developed approximation works well. This work further identifles a Markov property for instantaneous information propagation along two parallel roads based on two types of transmission regions. Communication capable vehicles are assumed to follow two.... The developed formulas enable numerical calculation of the characteristics of propagation process. We hope this research will shed light on studies of vehicular ad hoc networks on more general discrete roadway networks. v To my parents for their love...

Yin, Kai

2010-10-12

445

Cognitive Adaptive Radio Teams  

Microsoft Academic Search

Cognitive adaptive radio teams (CART) is a new platform developed by our group in support of collaborative mapping of complex communications-challenged environments, for example in support of search and rescue operations in environments lacking an adequate communications infrastructure. Experience during the 9\\/11 terrorist attacks, Asian tsunami, Kashmir earthquake, and post-Katrina Gulf Coast make it clear that rescue workers cannot count

Richard Lau; Stephanie Demers; Yibei Ling; B. Siegel; E. Voliset; K. Birman; R. van Renesse; H. Shrobe; J. Bachrach Lester Foster

2006-01-01

446

A Waveguide Model for UHF Propagation in Streets Dana Porrat and Donald C. Cox  

E-print Network

@wireless.stanford.edu, dcox@nova.stanford.edu Stanford University, Stanford, CA 94305-9515, USA Abstract Radio frequency propagation [3, 8, 15], and in this paper we develop this approach more rigorously. Our model is based;ects of the ground and any objects within the waveguide (such as people, cars and trees

Porrat, Dana

447

The Askaryan Radio Array  

NASA Astrophysics Data System (ADS)

Ultra high energy cosmogenic neutrinos could be most efficiently detected in dense, radio frequency (RF) transparent media via the Askaryan effect. Building on the expertise gained by RICE, ANITA and IceCube's radio extension in the use of the Askaryan effect in cold Antarctic ice, we are currently developing an antenna array known as ARA (The Askaryan Radio Array) to be installed in boreholes extending 200 m below the surface of the ice near the geographic South Pole. The unprecedented scale of ARA, which will cover a fiducial area of ~ 100 square kilometers, was chosen to ensure the detection of the flux of neutrinos suggested by the observation of a drop in high energy cosmic ray flux consistent with the GZK cutoff by HiRes and the Pierre Auger Observatory. Funding to develop the instrumentation and install the first prototypes has been granted, and the first components of ARA were installed during the austral summer of 2010-2011. Within 3 years of commencing operation, the full ARA will exceed the sensitivity of any other instrument in the 0.1-10 EeV energy range by an order of magnitude. The primary goal of the ARA array is to establish the absolute cosmogenic neutrino flux through a modest number of events. This information would frame the performance requirements needed to expand the array in the future to measure a larger number of neutrinos with greater angular precision in order to study their spectrum and origins.

Hoffman, Kara D.

2013-01-01

448

Radio Bubbles in Clusters  

E-print Network

We extend our earlier work on cluster cores with distinct radio bubbles, adding more active bubbles, i.e. those with Ghz radio emission, to our sample, and also investigating ``ghost bubbles,'' i.e. those without GHz radio emission. We have determined k, which is the ratio of the total particle energy to that of the electrons radiating between 10 MHz and 10 GHz. Constraints on the ages of the active bubbles confirm that the ratio of the energy factor, k, to the volume filling factor, f lies within the range 1 bubbles present in the current sample to be able to determine the shape of the population. An analysis of the ghost bubbles in our sample showed that on the whole they have higher upper limits on k/f than the active bubbles, especially when compared to those in the same cluster. A study of the Brightest 55 cluster sample shows that 17, possibly 20, clusters required some form of heating as they have a short central cooling time, t_cool bubbles. This indicates that the duty cycle of bubbles is large in such clusters and that they can play a major role in the heating process.

R. J. H. Dunn; A. C. Fabian; G. B. Taylor

2005-10-06

449

AIDS radio triggers.  

PubMed

In April 1991, the Ethnic Communities' Council of NSW was granted funding under the Community AIDS Prevention and Education Program through the Department of Community Services and Health, to produce a series of 6x50 second AIDS radio triggers with a 10-second tag line for further information. The triggers are designed to disseminate culturally-sensitive information about HIV/AIDS in English, Italian, Greek, Spanish, Khmer, Turkish, Macedonian, Serbo-Croatian, Arabic, Cantonese, and Vietnamese, with the goal of increasing awareness and decreasing the degree of misinformation about HIV/AIDS among people of non-English-speaking backgrounds through radio and sound. The 6 triggers cover the denial that AIDS exists in the community, beliefs that words and feelings do not protect one from catching HIV, encouraging friends to be compassionate, compassion within the family, AIDS information for a young audience, and the provision of accurate and honest information on HIV/AIDS. The triggers are slated to be completed by the end of July 1991 and will be broadcast on all possible community, ethnic, and commercial radio networks across Australia. They will be available upon request in composite form with an information kit for use by health care professionals and community workers. PMID:12179698

Elias, A M

1991-07-01

450

Radio Emission from Supernovae  

E-print Network

I consider radio emission from the remarkable SN1998bw. Ni-56 and Co-56 decays produce a gamma-ray flux whose Compton-scattered electrons naturally explain the observed mildly relativistic exapnsion of the radio source and its double- peaked history. Such models require a surrounding plasma, perhaps produced by the supernova progenitor, whose interaction with the nonrelativistic debris may account for the observed X-ray source. The radio spectrum appears to be self- absorbed. This interpretation determines the brightness temperature, and hence the energy of the radiating electrons, implying a surprisingly large magnetic field. Attempts to avoid this conclusion by interpreting the spectrum as the result of inverse bremsstrahlung absorption do not lead to significantly lower fields. The large inferred field may have several explanations: radiation from a central pulsar, a turbulent hydrodynamic dynamo or an aspherical Compton current, but a frozen-in field from the supernova progenitor is not adequate. The electron-ion and particle-field equipartition problems are discussed. Compton electrons also explain the inferred expansion speed of SN1987A's spots.

J. I. Katz

1999-04-04

451

MULTIMOMENT RADIO TRANSIENT DETECTION  

SciTech Connect

We present a multimoment technique for signal classification and apply it to the detection of fast radio transients in incoherently dedispersed data. Specifically, we define a spectral modulation index in terms of the fractional variation in intensity across a spectrum. A signal whose intensity is distributed evenly across the entire band has a lower modulation index than a spectrum whose intensity is localized in a single channel. We are interested in broadband pulses and use the modulation index to excise narrowband radio frequency interference by applying a modulation index threshold above which candidate events are removed. The technique is tested both with simulations and using data from known sources of radio pulses (RRAT J1928+15 and giant pulses from the Crab pulsar). The method is generalized to coherent dedispersion, image cubes, and astrophysical narrowband signals that are steady in time. We suggest that the modulation index, along with other statistics using higher order moments, should be incorporated into signal detection pipelines to characterize and classify signals.

Spitler, L. G.; Cordes, J. M.; Chatterjee, S. [Astronomy Department and NAIC, Cornell University, Ithaca, NY 14853 (United States); Stone, J., E-mail: lspitler@astro.cornell.edu [Department of Physics and Astronomy, Barnard College, New York, NY 10027 (United States)

2012-04-01

452

The brightness and spatial distributions of terrestrial radio sources  

NASA Astrophysics Data System (ADS)

Faint undetected sources of radio-frequency interference (RFI) might become visible in long radio observations when they are consistently present over time. Thereby, they might obstruct the detection of the weak astronomical signals of interest. This issue is especially important for Epoch of Reionization (EoR) projects that try to detect the faint redshifted H I signals from the time of the earliest structures in the Universe. We explore the RFI situation at 30-163 MHz by studying brightness histograms of visibility data observed with Low-Frequency Array (LOFAR), similar to radio-source-count analyses that are used in cosmology. An empirical RFI distribution model is derived that allows the simulation of RFI in radio observations. The brightness histograms show an RFI distribution that follows a power-law distribution with an estimated exponent around -1.5. With several assumptions, this can be explained with a uniform distribution of terrestrial radio sources whose radiation follows existing propagation models. Extrapolation of the power law implies that the current LOFAR EoR observations should be severely RFI limited if the strength of RFI sources remains strong after time integration. This is in contrast with actual observations, which almost reach the thermal noise and are thought not to be limited by RFI. Therefore, we conclude that it is unlikely that there are undetected RFI sources that will become visible in long observations. Consequently, there is no indication that RFI will prevent an EoR detection with LOFAR.

Offringa, A. R.; de Bruyn, A. G.; Zaroubi, S.; Koopmans, L. V. E.; Wijnholds, S. J.; Abdalla, F. B.; Brouw, W. N.; Ciardi, B.; Iliev, I. T.; Harker, G. J. A.; Mellema, G.; Bernardi, G.; Zarka, P.; Ghosh, A.; Alexov, A.; Anderson, J.; Asgekar, A.; Avruch, I. M.; Beck, R.; Bell, M. E.; Bell, M. R.; Bentum, M. J.; Best, P.; Bîrzan, L.; Breitling