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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

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

3

Transient Characteristics of Wearable Antennas and Radio Propagation Channels for Ultrawideband Body-Centric Wireless Communications  

Microsoft Academic Search

This paper presents transient characterization of ultrawideband (UWB) body-worn antennas and on-body radio propagation channels for body-centric wireless communications. A novel miniaturized CPW-fed tapered slot antenna is proposed and used for transient measurements of UWB radio channels for body area network (BAN) and personal area network (PAN) scenarios. Unlike conventional UWB CPW-fed antennas, the proposed antenna employs two diverging tapered

Akram Alomainy; Andrea Sani; Atiqur Rahman; Jaime G. Santas; Yang Hao

2009-01-01

4

Propagation characteristics of the ionospheric transmission window relating to long wave radio location issues  

NASA Astrophysics Data System (ADS)

Most applications of long radio waves (ELF/VLF/LF/MF) are ground-based and exploit the fact that such signals can propagate to great distances via reflections from the lower ionosphere. It is known however that, owing to the influence of the earth's magnetic field, long wave signals can penetrate through the ionosphere as well; at times, the waves penetrate with relatively little loss, depending on ionospheric conditions and other propagation factors. This has prompted investigations of the long wave 'ionospheric transmission window' as part of efforts to assess the feasibility of deploying long wave emitters in space for terrestrial applications and/or for exploiting, in space, signals emanating from ground-based long wave transmitters. This paper outlines results of theoretical and experimental investigations of the ionospheric transmission window over the frequency range from about 100 Hz to 500 kHz, with emphasis on directional issues associated with long wave penetration of the ionosphere.

Kossey, Paul A.; Lewis, Edward A.

1992-11-01

5

Radio Wave Propagation in Tunnels.  

National Technical Information Service (NTIS)

This report examines the radio propagation model for narrow and long tunnels. Modal analysis is used to model the path gain in 2-D and 3-D rectangular tunnels and the coupling loss of L, T and cross tunnels. Modal attenuation is determined by the waveleng...

J. Lee, H. L. Bertoni

2000-01-01

6

The indoor radio propagation channel  

Microsoft Academic Search

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

HOMAYOUN HASHEMI

1993-01-01

7

LUMPED PARAMATER RADIO WAVE PROPAGATION MODEL FOR STORM DRAIN PIPES  

Microsoft Academic Search

We conducted a measurement campaign to examine narrowband radio wave propagation characteristics of storm drain pipes (SDPs). The SDPs behave as multimode leaky waveguides for radio wave transmissions at higher frequencies. We derive a model for radio frequency (RF) propagation through concrete SDPs. We also observe attenuation in RF transmissions at 2.4 - 2.5 GHz and at 5.2 GHz by

Ivan Howitt; Jumanah Khan; Safeer Khan

8

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

9

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

10

Radio Propagation at Frequencies above 30 Megacycles  

Microsoft Academic Search

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

K. Bullington

1947-01-01

11

D region predictions. [effects on radio propagation  

NASA Technical Reports Server (NTRS)

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

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

1979-01-01

12

The propagation time of a radio pulse  

Microsoft Academic Search

The propagation of the ground-wave pulse between points on the ground is of considerable practical importance, particularly in the application of the Loran-C navigation system to the absolute time synchronization of geographically separated clocks. Thus, the envelope of the pulse is frequently used to remove ambiguities which would otherwise result from the pulse synchronization at the characteristic or carrier frequency

J. Johler

1963-01-01

13

A wideband propagation simulator for high speed mobile radio communications  

NASA Astrophysics Data System (ADS)

Multipath, jamming, listening and detection are the main limitations for mobile radio communications. Spread spectrum techniques, especially frequency hopping, can be used to avoid these problems. Therefore, a wideband simulation for multipath mobile channels appeared the most appropriate evaluation technique. It also gives useful indications for system characteristic improvements. This paper presents the design and realization of a new UHF-VHF propagation simulator, which can be considered as an extended version of Bussgang's one. This frequency hopping simulator (up to 100,000 hops per second) is wideband thus capable to deal with spread spectrum signals. As it generates up to 16 paths, it can be used in almost all mobile radio propagation situations. Moreover, it is also able to simulate high mobile relative speeds up to 2000km/h such as air-air communication systems. This simulator can reproduce, in laboratory, 16 rays Rician or Rayleigh fading channels with a maximum time delay of about 15 ms. At the highest frequency of 1200 MHz, Doppler rates up to 2 kHz can be generated corresponding to vehicle speeds up to 2000 km/h. Let note that the Bussgang simulator was defined for narrowband and fixed radio communications. In both equipments, in-phase and quadrature signals are obtained using two numerical transversal filters. Simulation results were derived in various situations especially in terrestrial urban and suburban environments, where they could be compared with measurements. The main advantage of the simulator lies in its capacity to simulate the high speed and wideband mobile radio communication channels.

Busson, P.; Lejannic, J. C.; Elzein, G.; Citerne, J.

1994-07-01

14

Imaging of indoor multipath radio propagation for 18 GHz band wireless LAN systems: applied radio holography  

Microsoft Academic Search

Development of high-speed wireless LANs is a major goal of telecommunications industry. We propose a dual-frequency continuous wave (CW) radio holography method for evaluating radio wave propagation environments for such LANs. Our method images the propagation environment with higher resolution (1 ns or less) and higher sensitivity (10 dB ?V\\/m) than conventional techniques which use frequency-modulated CWs (FMCWs), pseudonoise (PN)

H. Kitayoshi

1994-01-01

15

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

16

The prediction of radio-path characteristics  

NASA Astrophysics Data System (ADS)

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

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

17

ITS Wireless Transmission Technology. Technologies of Millimeter-Wave Inter-Vehicle Communications: Propagation Characteristics  

Microsoft Academic Search

In this paper, we introduce developed technologies for millimeter-wave inter-vehicle communication (IVC) system in intelligent transport systems (ITS), especially propagation characteristics of 60 GHz band for the system design of IVC. First we introduce the outline of an IVC system using millimeter wave and its research subjects. Next we show experimental results of propagation characteristics of radio wave at 60

Akihito Kato; Katsuyoshi Sato; Masayuki Fujise

2001-01-01

18

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

19

Radio Propagation Measurements and Modeling in Railway Viaduct Area  

Microsoft Academic Search

A network with high quality of service (QoS) is required for railway wireless communication and control systems. Research on radio-wave propagation in railway environment has great significance for the design and optimization of the railway wireless network. In this paper, measurements are taken in railway viaduct area using track side base stations of the GSM-R network. Comparison between the measured

Jinghui Lu; Gang Zhu; Bo Ai

2010-01-01

20

Morphology and characteristics of radio pulsars  

NASA Astrophysics Data System (ADS)

This review describes the observational properties of radio pulsars, fast rotating neutron stars, emitting radio waves. After the introduction we give a list of milestones in pulsar research. The following chapters concentrate on pulsar morphology: the characteristic pulsar parameters such as pulse shape, pulsar spectrum, polarization and time dependence. We give information on the evolution of pulsars with frequency since this has a direct connection with the emission heights, as postulated in the radius to frequency mapping (RFM) concept. We deal successively with the properties of normal (slow) pulsars and of millisecond (fast-recycled) pulsars. The final chapters give the distribution characteristics of the presently catalogued 1300 objects.

Seiradakis, John H.; Wielebinski, Richard

2004-12-01

21

Fundamental Jupiter millisecond radio burst characteristics  

NASA Astrophysics Data System (ADS)

The development of high spectral resolution instrumentation, i.e. the digital spectropolarimeter (DSP) and waveform receiver (WFR) and their installation at large decameter band radio telescopes (UTR-2 at Kharkov, Ukraine and Nancay, France) opened new possibilities in the investigation of fast Jupiter radio emissions in the decametric range. The internal structure of a drifting millisecond (S-)burst, being analyzed by means of the wavelet transform, reveals microsecond modulations which are visible as a train of signal bunches in the scalogram. Spectral characteristics of these superfine burst structures could be obtained from recent observations, and their implications are estimated with regard to radio source size and configuration. After decades of continuous Jupiter S-burst observations and investigations the physical fundamentals of this fast radio phenomenon seems to be unveiled.

Rucker, H. O.

2003-04-01

22

Space Weather Effects on Radio Propagation: Study of the CEDAR, GEM and ISTP Storm Events  

NASA Astrophysics Data System (ADS)

On three high-latitude HF radio paths of North-west Russia, impact of 14 geomagnetic storms from a list of CEDAR, GEM and ISTP storms within 1997-99 on radio propagation conditions have been investigated. These conditions were estimated through variations o the MOF and LOF (the maximum and lowestf operation frequencies) on each path before, during and after a storm. Geophysical data of Dst, Bz, AE as well as some riometer data by observatory Sodankyla, Finland, were attracted for an analysis. It was shown that the storm impact on the ionosphere and radio propagation for each storm has an individual character. Nevertheless, there are common tendencies in variation of the propagation parameters for all storms. Thus, the frequency range ? = MOF - LOF is getting wider several hours before a storm, then it is sharply narrow during a storm-time and further it is expanded again several hours after storm ending. These regularities may be useful for the HF radio communication organization at the high latitudes. On the radio path with a reflection point at the geomagnetic latitude F? = 66o , the full time interval when the path is destroyed throughout a storm depends on a local time LT. For the day-time storms an average value td e s is 30%, for the night storm t des is only 20%. The fact is established that the ionization increase in the F2 layer several hours (4 hours during the day-time and 2 hours during the night) before the storm expansion phase onset may be considered as a reliable forerunner of the storm expansion phase development. By present experimental data, it was revealed that at the high latitudes not only the traditional mechanism of the solar energy transfer into the upper atmosphere through the magnetosphere tail, plasma sheet and auroral ionosphere operates but a quite another mechanism also exists - through the diurnal cusp and enter sheet of the magnetosphere. Thus, considered CEDAR, GEM and ISTP storms are distinguished essentially one from the other by their main parameters. Impacts of these storms on the ionosphere and radio propagation on the high-latitude HF radio paths are distinguished too. Nevertheless, the common character of the certain manifestations during storm-time was revealed: in variations of the frequency range on the paths, in correlation between the LOF and the riometer absorption (A, dB), in absence of the signals due to absorption during mighty disturbances, in similarity of behaviour of the ionospheric parameters and propagation characteristics for day-time storms and separately for the night storms.

Blagoveshchensky, D.

23

ITS Wireless Transmission Technology. Technologies of Millimeter-Wave Inter-Vehicle Communications: Propagation Characteristics  

NASA Astrophysics Data System (ADS)

In this paper, we introduce developed technologies for millimeter-wave inter-vehicle communication (IVC) system in intelligent transport systems (ITS), especially propagation characteristics of 60 GHz band for the system design of IVC. First we introduce the outline of an IVC system using millimeter wave and its research subjects. Next we show experimental results of propagation characteristics of radio wave at 60 GHz between running vehicles. The propagation model and mechanism of fading propagation are argued. The joint research activity of IVC system in Yokosuka Research Park (YRP) is also introduced.

Kato, Akihito; Sato, Katsuyoshi; Fujise, Masayuki

2001-12-01

24

Optical propagation characteristics of positive dart leaders  

NASA Astrophysics Data System (ADS)

Optical propagation characteristics of negative dart leaders have been documented and studied by many authors before. In contrast, to the best of authors' knowledge, positive dart leaders have never been reported. Using a high speed video camera, we have documented two positive dart leaders, one occurring along a pre-channeled upward negative lightning and another propagating along the path of a downward positive first stroke. Both dart leaders exhibited bright channels with one extending at least 300 m and another one over 100 m. Their propagation speeds are estimated to be around 3*10^7 m/s, similar to that of their counterpart. In the presentation, we will report the detailed video of these two dart leaders as well as some interesting discharges associated with two leaders.

Wang, D.; Takagi, N.

2013-12-01

25

Lightning-induced effects on VLF/LF radio propagation  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

26

Propagation of Radio Frequency Waves in a Weakly Ionized Gas  

NASA Astrophysics Data System (ADS)

Long distance communication and diagnostics of the space environment rely on an understanding of the refraction, phase alteration and attenuation of electromagnetic waves in the ionosphere and plasmasphere. The nature of wave propagation in a spatially inhomogeneous plasma was explored using a numerical implementation of the eikonal approach(L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media), (Pergamon Press 1960), pp. 269-279. . The calculation was validated by comparing numerical results with analytic solutions( K. G. Budden, Radio Waves In the Ionosphere), (Cambridge University Press, 1966), pp. 179-182. for a horizontally stratified plasma with linear and exponential variations in the density. The treatment was extended to treat arbitrary plasma distributions. Ray trajectories and attentuation are presented for typical ionospheric profiles, exhibiting non-monotonic density variations, and profiles associated with a plasma generated by injection of a relativistic electron beam. USE ONLY)

Lockwood, Nathaniel P.; Bailey, Wm. F.

2000-10-01

27

The Black Hole Mass and Radio Characteristics of Radio Quasars  

NASA Astrophysics Data System (ADS)

In this paper, we collect the redshift, bolometric luminosity, full-width at half maximum (FWHM), monochromatic luminosity at 5100&:Aring;, radio loudness of 117 quasars, including 20 radio quiet quasars and 97 radio loud quasars. Then we calculate the black hole mass and Eddington ratio with the reverberation mapping method, and calculate the radio luminosity using total 5 GHz flux density. By analyzing the relations among them, our conclusions are as follows: (1) there are weak correlations between black hole mass and bolometric luminosity, between black hole mass and radio loudness, and between black hole mass and radio luminosity for radio quiet quasars (RQQs), while there are strong correlations between black hole mass and bolometric luminosity, between black hole mass and radio loudness, and between black hole mass and radio luminosity for radio loud quasars (RLQs); (2) there are weak correlations between bolometric luminosity and radio luminosity, and between bolometric luminosity and monochromatic luminosity at 5100Å for RQQs, while there are strong correlations between bolometric luminosity and radio luminosity, and between bolometric luminosity and monochromatic luminosity at 5100Å for RLQs; (3) the distributions of black hole mass, FWHM and Eddington ratio between RQQs and RLQs are different. From these results we suggest that the difference in black hole mass between RQQs and RLQs is predominantly due to the difference in FWHM between RQQs and RLQs; the difference between RQQs and RLQs is not due to the difference in orientation, but due to the difference in intrinsic property; the black hole mass, spin of black hole, Eddington ratio and morphology of host galaxy play an important role in explaining the origin of radio loudness and the radio loudness "bimodality"; there is a close link between the disk accretion rate and the generation of the relativistic radio jet.

Xiong, D. R.; Zhang, X.; Zheng, Y. G.; Huang, B. R.; Mao, L. S.; Liu, W. G.

2012-09-01

28

Extremely Low Frequency (ELF) Ionospheric Radio Propagation Studies Using Natural Sources  

Microsoft Academic Search

The purpose of this paper is to describe methods of studying the propagation of radio waves over the earth's surface in the extremely low frequency (ELF) frequency band (3 Hz-3 kHz) using natural (as distinct from \\

D. LLANWYN JONES

1974-01-01

29

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

NASA Astrophysics Data System (ADS)

This is a summary report of the workshops convened at the URSI Commission F Open Symposium, ‘Effects of the Lower Atmosphere on Radio Propagation at Frequencies above 1 GHz,’ Lennoxville, Quebec, Canada, May 26-30, 1980, prepared by URSI Commission F for CCIR Study Group 5. Document 5/120, Period 1978-1982, International Radio Consultative Committee (CCIR).

URSI Workshop Session Chairmen

30

Empirical formula for propagation loss in land mobile radio services  

Microsoft Academic Search

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

M. Hata

1980-01-01

31

Propagation Effects at Radio Frequencies on Satellite Navigation Systems.  

National Technical Information Service (NTIS)

The report discusses the effects of the neutral and ionized atmosphere on radio frequency signals used in satellite navigation systems. Knowledge of the signal velocity along the transmission path is necessary to properly interpret the navigation measurem...

V. L. Pisacane M. M. Feen

1974-01-01

32

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

NASA Astrophysics Data System (ADS)

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 (Mj = 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 (Mj = 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

1995-05-01

33

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

34

Proton Event Time Characteristics and Radio Burst Data.  

National Technical Information Service (NTIS)

Various studies undertaken for relating the proton event time characteristics to radio burst data are described. Eastern hemispheric events generally have a much larger onset time compared to the Western events. For western hemispheric events, the rise ti...

P. Bakshi T. Nguyen

1981-01-01

35

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

36

Propagation characteristics of thunderstorms in southern Germany.  

National Technical Information Service (NTIS)

The propagation of thunderstorms in southern Germany was investigated. The thunderstorms were observed by a lightning position system during the summer months of the years 1992 to 1996. On average every second day thunderstorms were observed anywhere in s...

M. Hagen B. Bartenschlager U. Finke

1998-01-01

37

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

38

Propagation Characteristics of Geo-Effective CMES  

Microsoft Academic Search

The expansion speeds of halo CMEs observed by LASCO aboard SoHO duirng 1996-2002 which were geo-effective (Dst <-100 nT) have been measured. The radial propagation profiles of these CMEs have been inferred from the measured expansion speeds. We also investigate if the propagation profiles of these geoeffective CMEs is of blast wave nature. It is found that the profiles of

Nandita Srivastava; P. Venkatakrishnan

2003-01-01

39

Space Weather Effects on Radio Propagation: Study of the CEDAR, GEM and ISTP Storm Events  

Microsoft Academic Search

On three high-latitude HF radio paths of North-west Russia, impact of 14 geomagnetic storms from a list of CEDAR, GEM and ISTP storms within 1997-99 on radio propagation conditions have been investigated. These conditions were estimated through variations o the MOF and LOF (the maximum and lowestf operation frequencies) on each path before, during and after a storm. Geophysical data

D. Blagoveshchensky

2002-01-01

40

Characteristics of a digital mobile radio channel  

Microsoft Academic Search

A field test has been made in order to better understand the digital mobile radio channel. At the mobile receiver (450 MHz, 1200 bits\\/s) recordings were made of the digital signal and the field strength. These recordings were later analyzed by a computer. Some existing models for digital channels have been tested. Theoretically motivated probability density functions for the fading

TOR AULIN

1981-01-01

41

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

42

Source and Propagation Characteristics of Explosive and Other Seismic Sources.  

National Technical Information Service (NTIS)

Understanding of the source and propagation characteristics of seismic events of different types including earthquakes, explosions and mining-induced events is essential for successful discrimination of nuclear explosions. We are compiling a data set of m...

X. Ni W. Chan R. Wagner W. R. Walter E. M. Matzel

2005-01-01

43

Predicting proton event time characteristics from radio burst data  

SciTech Connect

For events originating on the Western hemisphere, the delay before onset of the solar flare protons is shown to be well correlated (r about 0.80) with the rise time of the associated radio-burst at 2-3 GHz or the rise time of the H sub alpha flare. The peak flux time of the protons is shown to be very well correlated (r about 0.90) with the delay before onset, and fairly well correlated (r about 0.70) with the flare or radio rise time. These results allow a prediction of the proton event time characteristics from real time radio burst data.

Bakshi, P.; Nguyen, T.

1981-06-01

44

Excitation and Propagation of Jovian Quasi-Periodic Radio Bursts  

NASA Astrophysics Data System (ADS)

We discussed the source location, directivity, and propagation process of QP bursts based on the ray tracing analysis, comparing with the observation results, especially with the latitudinal beaming and shadow zone [Kimura et al., 2010]. The parametric survey indicated that QP bursts observed at high and low latitudes have the source region at 2-10 Rj altitude along high-latitudinal field lines (L>20). It was suggested that these QP bursts have significantly broadened beaming patterns like a "filled cone".

Kimura, T.; Misawa, H.; Morioka, A.; Tsuchiya, F.; Kasaba, Y.; Cecconi, B.; Zarka, P.; MacDowall, R. J.; Hess, R. A.

2011-10-01

45

Ultrasonic wave propagation characteristics of green ceramics  

SciTech Connect

Propagation of ultrasonic waves in green (unfired) ceramics is studied, and the effectiveness of ultrasonic methods for nondestructive evaluation is assessed. The objective is to obtain useful information on defects, cracking, delaminations, agglomerates, inclusions, regions of high porosity, and anisotropy. Conventional ultrasonic techniques are difficult to apply to flaw detection in green ceramics because of the high attenuation, fragility, and couplant-absorbing properties of these materials. However, velocity, attenuation, and spectral data were obtained with pressure-coupled transducers and provided useful information related to density variations and the presence of agglomerates and elastic anisotropy.

Kupperman, D.S.; Karplus, H.B.

1984-12-01

46

Magnetospheric propagation of very long radio waves in geomagnetic waveguides  

NASA Astrophysics Data System (ADS)

The conditions of the propagation of VLF waves along geomagnetic waveguides in the earth magnetosphere are investigated theoretically, and the results are compared with satellite data. It is shown that VLF signals emitted from the earth surface are captured by geomagnetic waveguides at heights of approximately 500-2000 km above the earth surface when charged particle concentration in the waveguide exceeds that in the ambient plasma by at least 10 percent. A criterion for the capture of VLF signals by a geomagnetic waveguide is formulated. The results obtained are consistent with satellite measurements of VLF signals from ground transmitters.

Aksenov, V. I.; Moshkov, A. V.

47

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

48

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

49

Confinement and propagation characteristics of subwavelength plasmonic modes  

NASA Astrophysics Data System (ADS)

We have studied subwavelength confinement of the surface plasmon polariton modes of various plasmonic waveguides and examined their relative merits using a graphical parametric representation of their confinement and propagation characteristics. While the same plasmonic phenomenon governs mode confinement in all these waveguides, the various architectures can exhibit distinctive behavior in terms of effective mode area and propagation distance. We found that the waveguides based on metal and one dielectric material show a similar trade-off between energy confinement and propagation distance. However, a hybrid plasmon waveguide, incorporating metal, low index and high index dielectric materials, exhibits longer propagation distances for the same degree of confinement. We also point out that plasmonic waveguides with sharp features can provide an extremely strong local field enhancement, which is not necessarily accompanied by strong confinement of the total electromagnetic energy. In these waveguides, a mode may couple strongly to nearby atoms, but suffer relatively low propagation losses due to weak confinement.

Oulton, R. F.; Bartal, G.; Pile, D. F. P.; Zhang, X.

2008-10-01

50

Source and Propagation Characteristics of Explosive and Other Seismic Sources  

SciTech Connect

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

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

2005-07-14

51

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

52

Three-dimensional modeling of 900MHz and 2.44GHz radio propagation in corridors  

Microsoft Academic Search

A three-dimensional (3-D) propagation model, combined with a patched-wall model, has been developed to predict radio loss in a corridor environment. The ray-tracing technique is used and combined with the ray-fixed coordinate system to simplify the computations of transmission, reflection, and diffraction coefficients in 3-D space. The computed path loss is compared with the measured value of 900-MHz and 2.44-GHz

J. H. Tarng; W. R. Chang; B. J. Hsu

1997-01-01

53

RADIO FREQUENCY AND SCATTERING ANGLE DEPENDENCE OF IONOSPHERIC SCATTER PROPAGATION AT VHF  

Microsoft Academic Search

The weak and fluctuating radio signals observed at distances of 1,500 km on VHF are attributed to scattering from E-region turbulence. It is noted that propagation constan'rs k = 4w\\/X sin (0\\/2), corresponding to the experimental frequencies (28 to 108 Mc), just straddle the viscosity cutoff wave-number k8 = (2 meters) - of the region, thereby giving a qualitative explanation

Albert D. Wheelon

1957-01-01

54

Radio propagation measurements of the solar corona and gravitational fields: Applications to Mariner 6 and 7  

NASA Technical Reports Server (NTRS)

Results from interferometric measurements of the apparent angular deflection of quasi-stellar object are examined. Some preliminary results from Mariner 6 and 7 experiments, particularly from the plasma effect viewpoint, are discussed, along with future experiments and plasma scintillation. Ray bending studies, plasma relativity separation for Mariner 6 and 7, and radio propagation test of general relativity are reviewed. First order approximations and time delay studies are appended, as well as Doppler velocity effect investigations.

Muhleman, D. O.; Anderson, J. D.; Esposito, P. B.; Martin, W. L.

1971-01-01

55

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

SciTech Connect

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

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

2011-01-01

56

Propagation characteristics of substrate integrated waveguide based on LTCC  

Microsoft Academic Search

The substrate integrated waveguide (SIW) is a new type of guided wave structure fabricated with periodic metallic via holes in a multilayered LTCC substrate. The SIW takes the advantages of both waveguide and microstrip structures, like the high-Q factor, high power capacity, small size, and the possibility of integration. In this paper, the propagation characteristics of the SIW are investigated,

Hao Li; Wei Hong; Tie Jun Cui; Ke Wu; Yu Lin Zhang; Li Yan

2003-01-01

57

Experimental comparison of indoor UHF and EHF radio channel characteristics  

Microsoft Academic Search

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

Larbi Talbi

2000-01-01

58

Propagation characteristics of plasma sheet oscillations during a small storm  

NASA Astrophysics Data System (ADS)

On 24 March 2007, the THEMIS spacecraft were in a string-of-pearls configuration through the dusk plasma sheet at the recovery phase of a small storm. Large undulations of the plasma sheet were observed that brought the five probes from one lobe to another. Each neutral sheet crossing was accompanied by bursty bulk flows and Pi2 oscillations. In this paper we focus on the low frequency (~10 min) large scale plasma sheet undulations and determine their propagation characteristics, origin, and properties in the presence of storm-time substorms. As the first case of ``flapping waves'' observed and analyzed during storm-time, it is interesting to find their characteristics coincide with those described by previous quiet-time observations. These characteristics include flankward propagation of the undulations with velocities generally between ~40-130 km/s.

Gabrielse, C.; Angelopoulos, V.; Runov, A.; Kepko, L.; Glassmeier, K. H.; Auster, H. U.; McFadden, J.; Carlson, C. W.; Larson, D.

2008-06-01

59

Source characteristics of Jovian narrow-band kilometric radio emissions  

NASA Astrophysics Data System (ADS)

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

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

1993-07-01

60

Observational Evidence for Solar Radio Microflares with Unusual Characteristics  

NASA Astrophysics Data System (ADS)

A very rare type of solar radio microflares occurred during 0645 - 0720 UT on Jan. 5, 1994 is introduced in this paper. The radio and optical characteristics of the solar microflares of a short decimetric wave (1.42 GHz) are discussed. This event contains 53 radio fast fine structures (FFS), that is 53 intermittently periodic impulse trains with similar morphologies superimposed on the continuum radiation background. The intensities of the pulses lie within 150 - 200 s.f.u. and the durations (half power width) are of the order of 10 - 20 milliseconds. 18 out of 53 FFSs are doublepeak- separating structures. There are two newly emerged small sunspot groups on Jan. 5 presenting complex polarities and it seems that there existed small multiple-cross magnetic flux loops in Figure 2. The multiple reconnections also might have occurred. In this paper we try to discuss the generation mechanism qualitatively and find it is in consistence with the model of current loop explosive coalescence (Sakai and De Jager, 1989a, 1989b; De Jager and Sakai, 1991; Tajima, et al., 1987): the explosive coalescense of the multiple of cross magnetic flux loops causes the plasma disturbance and so rapidly transform the magnetic energy into the kinetic energy of electrons. The radio emission can be generated by the stimulated plasma waves or the instability of electron cyclotron masers.

Xie, R. X.; Wang, M.

61

Mercury: heat transport and thermal radio emission propagation in structurally inhomogeneous regolith  

Microsoft Academic Search

We present the results of the theoretical study of the dependence of thermal radio emission from Mercury regolith on its structure and composition. By employing different models for a regolith structure we have shown that the radiative component of the heat flux influences strongly on the effective temperature and its spectral characteristics. It is shown also that electromagnetic inhomogeneities of

O. B. Shchuko; D. V. Kartashov

2002-01-01

62

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

Microsoft Academic Search

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

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

2001-01-01

63

Radio and magnetic field constraints on SEP propagation from the Sun to Earth  

NASA Astrophysics Data System (ADS)

Energetic particles accelerated in the solar corona can be detected in space provided an appropriate magnetic connection exists The interplanetary magnetic field is usually described by an Archimedian spiral Parker spiral starting at a source surface sim 2 5 R odot from the Sun s centre While statistically speaking impulsive solar energetic particle events SEP events are associated with flares at longitudes close to the root of the Parker spiral in the western solar hemisphere there is some scatter sometimes deviations of more than 10 heliocentric degrees We present a sample of impulsive electron events where we identify coronal and interplanetary paths of the particles through their type III radio emission We identify flux tubes into which electrons are injected at the Sun by imaging their radio emission with the Nan c c ay Radioheliograph below 0 5 R footnotesize odot above the photosphere The arrival of the electrons at Earth is traced by kilometric radio emission and Langmuir waves detected by the WAVES radio receiver aboard the it Wind mission and by the 3DP particle detector We compare the propagation paths of the electrons with the nominal Parker spiral and with the magnetic field below the source surface inferred from the potential field and source surface model developed by Schrijver DeRosa 2003 whose results are available within the SolarSoft package First results suggest that the type III emission is a reliable tracer of the magnetic field topology below the source surface even in cases when the parent flare

Klein, K.-L.; Krucker, S.; Hoang, S.; Lointier, G.

64

Propagation characteristics of picosecond electrical transients on coplanar striplines  

SciTech Connect

Using a cryogenic electro-optic sampling technique, we have studied the transient propagation characteristics of superconducting and normal indium lines in the picosecond regime. Transient dispersion effects, including increased rise time and increased pulse width, the introduction of ringing on the waveform, and a novel ''pulse sharpening'' were observed. A model that takes into consideration the effects of modal dispersion and superconducting complex conductivity was established, and an algorithm was developed that accurately describes all of the experimental findings.

Hsiang, T.Y.; Whitaker, J.F.; Sobolewski, R.; Dykaar, D.R.; Mourou, G.A.

1987-11-09

65

M 82 - A radio continuum and polarisation study. I. Data reduction and cosmic ray propagation  

NASA Astrophysics Data System (ADS)

Context. The potential role of magnetic fields and cosmic ray propagation for feedback processes in the early Universe can be probed by studies of local starburst counterparts with an equivalent star-formation rate. Aims: In order to study the cosmic ray propagation and determine the magnetic field strength and dominant loss processes in the nearby prototypical starbursting galaxy M 82, a multi-frequency analysis at four radio wavelengths is presented. Methods: Archival data from the Westerbork Synthesis Radio Telescope (WSRT) was reduced and a new calibration technique introduced to reach the high dynamic ranges needed for the complex source morphology. These data were combined with archival Very Large Array (VLA) data, yielding total power maps at ?3 cm, ?6 cm, ?22 cm, and ?92 cm. Results: The data show a confinement of the emission at wavelengths of ?3/?6 cm to the core region and a largely extended halo reaching up to 4 kpc away from the galaxy midplane at wavelengths of ?22/?92 cm up to a sensitivity limit of 90 ?Jy and 1.8 mJy respectively indicating different physical processes in the core and halo regions. The results are used to calculate the magnetic field strength to 98 ?G in the core region and to 24 ?G in the halo regions. From the observation of ionisation losses, the filling factor of the ionised medium could be estimated to 2%. This leads to a revised view of the magnetic field distribution in the core region and the propagation processes from the core into the halo regions. Conclusions: We find that the radio emission from the core region is dominated by very dense H ii-regions and supernova remnants, while the surrounding medium is filled with hot X-ray and neutral gas. Cosmic rays radiating at frequencies higher than 1.4 GHz suffer from high synchrotron and inverse Compton losses in the core region and are not able to reach the halo. Even the cosmic rays radiating at longer wavelengths are only able to build up the observed kpc-sized halo, when several starbursting periods are assumed where the far-infrared and radio luminosity vary by an order of magnitude. These findings, together with the strong correlation between H?, ionised polycyclic aromatic hydrocarbons (PAH+), and our radio continuum data, suggest a magnetic field which is frozen into the ionised medium and driven out of the galaxy kinematically. FITS files of the images are available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/555/A23

Adebahr, B.; Krause, M.; Klein, U.; We?gowiec, M.; Bomans, D. J.; Dettmar, R.-J.

2013-07-01

66

Ionospheric effects of X-ray source Scorpius XR-1. [on terrestrial radio propagation  

NASA Technical Reports Server (NTRS)

A simple two-ion model was employed to evaluate the ionospheric effects of various nocturnal ionization sources. The model was used to calculate the decay of the electron number density at 90 km with and without illumination by Scorpius XR-1 X rays. Reflection parameters for the determination of the effect of cosmic x-ray sources on radio wave propagation were also obtained. The results obtained in the investigation do not support the proposal made by Anathakrishnan and Ramanathan (1969) that the X-ray source in Scorpius XR-1 affects the nighttime lower ionosphere of the earth.

Poppoff, I. G.; Whitten, R. C.; Willoughby, D. S.

1975-01-01

67

Propagation of singularities along characteristics of Maxwell's equations  

NASA Astrophysics Data System (ADS)

We give a new proof that electromagnetic waves predict geometry, based on studying the propagation of singularities in first-order derivatives of generalized solutions \\left( \\mathbf{E},\\mathbf{H} \\right) to Maxwell's equations. As a byproduct, the growth of the intensity of the jumps in \\left( \\partial \\mathbf{E}/\\partial t,\\partial \\mathbf{H}/\\partial t \\right) across a characteristic hypersurface is shown to be homogeneous of degree -1. We determine generalized solutions (whose first-order derivatives have jumps across a fixed characteristic line) to the initial value problem for Maxwell's equations in one space variable.

Barletta, Elisabetta; Dragomir, Sorin

2014-06-01

68

Measurement-based investigations of radio wave propagation: An expose on building corner diffraction  

NASA Astrophysics Data System (ADS)

Predicting performance metrics for the next-generation of multi-mode and multi-antenna wireless communication systems demands site-specific knowledge of the wireless channels underlying radio wave propagation mechanisms. This thesis describes the first measurement system capable of characterizing individual propagation mechanisms in situ. The measurement system merges a high-resolution spatio-temporal wireless channel sounder with a new field reconstruction technique to provide complete knowledge of the wireless channels impulse response throughout a 2-dimensional region. This wealth of data may be combined with space-time filtering techniques to isolate and characterize individual propagation mechanisms. The utility of the spatio-temporal measurement system is demonstrated through a measurement-based investigation of diffraction around building corners. These measurements are combined with space-time filtering techniques and a new linear wedge diffraction model to extract the first semi-empirical diffraction coefficient. Specific contributions of this thesis are: (1) The first ultra-wideband single-input multiple-output (SIMO) channel sounder based upon the sliding correlator architecture. (2) A quasi 2-dimensional field reconstruction technique based upon a conjoint cylindrical wave expansion of coherent perimeter measurements. (3) A wireless channel "filming" technique that records the time-domain evolution of the wireless channel throughout a 2-dimensional region. (4) High-resolution measurements of the space-time wireless channel near a right-angled brick building corner. (5) The application of space-time filtering techniques to isolate the edge diffraction problem from the overall wireless channel. (6) An approximate uniform geometrical theory of diffraction (UTD)-style linear model describing diffraction by an impedance wedge. (7) The first-ever semi-empirical diffraction coefficient extracted from in situ measurement data. This thesis paves the way for several new avenues of research. The comprehensive measurement data provided by channel "filming" will enable researchers to develop and implement powerful space-time filtering techniques that facilitate measurement-based investigations of radio wave propagation. The measurement procedure described in this thesis may be adapted to extract realistic reflection and rough-surface scattering coefficients. Finally, exhaustive measurements of individual propagation mechanisms will enable the first semi-empirical propagation model that integrates empirical descriptions of propagation mechanisms into a UTD-style mechanistic framework.

Pirkl, Ryan J.

69

Characteristics of diving in radio-marked Xantus's Murrelets  

USGS Publications Warehouse

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

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

2005-01-01

70

The Relation between Type II Radio Bursts and Large-scale Coronal Propagating Fronts  

NASA Astrophysics Data System (ADS)

Both type II radio bursts and chromospheric Moreton-Ramsey waves are believed to signify shock waves that propagate in the solar corona. Large-scale coronal propagating fronts (LCPFs), which are also called EIT waves, EUV waves or coronal bright fronts in the literature, were initially thought to be coronal counterparts of Moreton-Ramsey waves, and thus they were expected to be correlated with type II bursts. At present, the prevailing view seems to be that both type II bursts and LCPFs are more closely linked with CMEs than with flares. Here we revisit the relation between type II bursts and LCPFs, by examining radio dynamic spectra (180-25 MHz) as obtained by USAF/RSTN and analyzing EUV and white-light data from SDO and STEREO. In the sample of about 140 type II bursts and LCPFs between April 2010 and January 2013, we find the correlation of 50-60 %. Type II bursts could be associated with eruptions without significant lateral expansion, and fast LCPFs could show no presence in the metric radio spectral range. Using data from STEREO COR-1 that observed the CME as a limb event, in 42 cases we directly measure the height of the CME at the onset of the type II burst. As expected, the height tends to be lower when the type II burst starts at a higher frequency. It is found that those type II bursts that start at higher altitudes and lower frequencies tend to have weaker EUV fronts. This may indicate multiple ways of how LCPFs and type II bursts are related with CMEs.

Nitta, Nariaki

2014-06-01

71

Identification of spectral radio interference characteristics in switching transistor converters  

NASA Astrophysics Data System (ADS)

Methods for the identification of spectral radio interference characteristics in switching transistor converters which make it possible to determine the smoothed estimates for peak and average values as well as to separate certain spectrum components on the basis of the discrete spectrum are proposed. The methods are based on the elements of homomorphic filtering and autoregression (AR) estimation. The investigation of the converter spectral characteristics has been performed, and techniques of rational filtering which make it possible to decrease the interference levels at the converter input terminals down to the values specified have been developed. For the optimum AR models, the parameters of damping circuits are determined which make it possible to decrease the maximum interference levels at the terminals of the converters by 5-15 dB, thus avoiding the application of external interference suppression filters.

Turin, L.; Shirokov, V.

72

Radio wave propagation in the Martian polar deposits: models and implications for radar sounding.  

NASA Astrophysics Data System (ADS)

In the present study the propagation of electromagnetic waves in the northern polar ice sheet of Mars is considered Several different scenarios of the structure of the polar deposits and composition of the ice compatible with previously published observational data are proposed Both analytical and numerical simulations of ultra wide band chirp radar pulse propagating through the cap are performed Approximate approach based on the non-coherent theory of the radiative transfer in layered media has been applied to the problem of the propagation of radar pulses in the polar caps Both 1D and 2D and 3D geometry applicable to the orbital and landed radar instruments are studied The side clutter and phase distortions of the signal are also addressed analyzed The possibilities of retrieval of the geological information depending on transparency of the polar cap for radio waves are discussed If the polar cap is relatively transparent the echo from the base of the sheet should be clearly distinctive and interpretable in terms of basal topography of the cap In the case of moderate optical thickness coherent basal echo is corrupted by strong multiple scattering in the layered structure However some conclusions about basal conditions could be made from the signals for example the subglacial lakes may be detected Finally optically thick polar caps prevent any sounding of the base so only the medium itself can be characterized by GPR measurements e g the impurity content in the ice can be found Ilyushin Y A R Seu

Ilyushin, Ya. A.

73

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

74

A survey of various propagation models for mobile communication  

Microsoft Academic Search

In order to estimate the signal parameters accurately for mobile systems, it is necessary to estimate a system's propagation characteristics through a medium. Propagation analysis provides a good initial estimate of the signal characteristics. The ability to accurately predict radio-propagation behavior for wireless personal communication systems, such as cellular mobile radio, is becoming crucial to system design. Since site measurements

Tapan K. Sarkar; Zhong Ji; Kyungiung Kim; A. Medouri; Magdalena Salazar-Palma

2003-01-01

75

Radio propagation measurements and prediction using three-dimensional ray tracing in urban environments at 908 MHz and 1.9 GHz  

Microsoft Academic Search

There is an explosive growth in the market of wireless communications services in urban areas. New regulatory environments as well as competition in the communications industry require that these systems be deployed quickly and at low cost. Computer-based radio propagation prediction tools are strong candidates for this goal. We introduce an outdoor radio propagation prediction tool using a ray tracing

Seong-Cheol Kim; Bernard J. Guarino; Thomas M. Willis III; Vinko Erceg; Steven J. Fortune; Reinaldo A. Valenzuela; Louis W. Thomas; Jonathan Ling; J. Don Moore

1999-01-01

76

UHF propagation prediction for wireless personal communications  

Microsoft Academic Search

Propagation characteristics of radio signals in the UHF band place fundamental limits on the design and performance of wireless personal communications systems, such as cellular mobile radio (CMR), wireless LANs, and personal communication services (PCS). Because the radio link is direct to each subscriber, the prediction of signal characteristics is most important in urban areas where subscriber density is high,

HENRY L. BERTONI; WALTER HONCHARENKO; L. R. Macel; HOWARD H. XIA

1994-01-01

77

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

NASA Astrophysics Data System (ADS)

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.

78

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

NASA Astrophysics Data System (ADS)

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.

1993-06-01

79

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

80

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

81

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

82

Measurements on wave propagation characteristics of spiraling electron beams  

NASA Technical Reports Server (NTRS)

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

Singh, A.; Getty, W. D.

1976-01-01

83

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

84

The High-Latitude Ionosphere and Its Effects on Radio Propagation  

NASA Astrophysics Data System (ADS)

The ionosphere is indeed the place where Earth and space come together. Correspondingly, the ionosphere is subject to the details and complexities of both Earth and space. If one is to develop a logical understanding of even a limited portion of the ionosphere, that knowledge will be constructed on a foundation of many facts of nature. Awareness of those facts will in turn be supported by a vast historical array of scientific effort to ascertain the fundamentals of Earth and space that combine to form the ionosphere as we know it. Fortunately for us, R. D. Hunsucker and J. K. Hargreaves have written a book that goes from the Earth up and comes from the Sun down to arrive at a remarkably detailed physical description of the ionosphere and its impact on human activities, especially radio-frequency (RF) communications. The High-Latitude Ionosphere and its Effects on Radio Propagation is a bit of a misnomer, because the book covers many more topics than its title suggests. The authors set the stage by developing a detailed picture of the density, temperature, chemical, neutral, and charge states of the atmosphere-ionosphere system. Basic models of the ionization and recombination processes are presented with supporting mathematics and graphical examples. Concepts such as the Chapman production function are introduced and applied, whereby ionizing solar radiation produces electron-ion pairs. One can then grasp how the so-called D, E, and F layers of the ionosphere are related to the ionization of specific molecular species. Along the way, the authors are careful to introduce the extensive nomenclature of ionospheric descriptors. There is a comfortable relationship of prose, mathematics, and graphical material. Reading this book is a pleasure for the scientifically curious mind.

Moses, Ronald W., Jr.

2004-05-01

85

Propagation Characteristics of CMEs Associated with Magnetic Clouds and Ejecta  

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

86

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

87

The characteristic polarized radio continuum distribution of cluster spiral galaxies  

Microsoft Academic Search

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

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

2007-01-01

88

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

SciTech Connect

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

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

1994-12-01

89

RADIO BURSTS WITH EXTRAGALACTIC SPECTRAL CHARACTERISTICS SHOW TERRESTRIAL ORIGINS  

SciTech Connect

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

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

2011-01-20

90

Computation of the key parameters of radio signals propagating through a perturbed ionosphere in the land-satellite channel  

NASA Astrophysics Data System (ADS)

An analysis of the key parameters of HF/UHF radio signals was carried out for land-satellite radio channels, which determine the effects of fading in a perturbed ionosphere. Using the parameters of the perturbed plasma, the effects of the absorption and phase fluctuations of radio signals are analyzed for a channel with fading. For the evaluation of the effect of scattering of a radio signal by ionospheric inhomogeneities in an approximation of small-scale scintillations, expressions for the root-mean-square (RMS) magnitude of signal intensity and phase scintillations are presented. Scintillation index ?{/I 2} that corresponds to variations in a signal under the conditions of multipath propagation with fading is investigated by using experimental data. It is shown that roughly ˜10% of inhomogeneities of the electron concentration in the F region of the ionosphere, perturbed during a magnetic storm, yield strong quickly fading radio signals in the VHF/UHF range with significant fluctuations (up to 1%) in the intensity of the signal and phase fluctuations (up to hundreds of radians). The calculated magnitudes of the scintillation index are in good agreement with experimentally observed data.

Blaunstein, N.; Pulinets, S. A.; Cohen, Y.

2013-04-01

91

Partial Halo CMEs on 29 May and 11 August 2011 - Initiation and Propagation Characteristics  

NASA Astrophysics Data System (ADS)

We report a study on two partial halo coronal mass ejections (CMEs) occurred on May 29 and August 11, 2011, respectively, near east and west limbs of the Sun. The initiation characteristics of these CME events are studied using images from SDO/EUV instrument, H-alpha measurements and radio data. In the case of May 29 event, before the onset of the flare, the destabilization and expansion of overlying large-scale loop systems above the eruption site was observed and some of these loops were twisted. As these loops expanded, they interacted with each other and observed as a partial halo CME in the LASCO field of view. The expansion speed of loops increased from ˜ 250 to 500 km/s within about a solar radius above Sun's limb. The timing and location of type II radio burst indicates the formation of the shock in front of the expanding loops in the distance range of ˜2-3 solar radii. Another interesting point is that the propagation speed of the white-light CME within about 12 solar radii is ˜500 -- 600 km/s and however, at larger heights in the LASCO C3 field of view, the CME has been accelerated from 500 to 1000 km/s. The CME event on August 11, 2011, is also associated with the expansion of large-scale system of loops, in which some of them are twisted. The white-light CME, at distances below 15 solar radii and at larger distance, respectively, show nearly constant speed ˜1200 km/s and acceleration of speed between 1200 and 1700 km/s. We discuss the kinematics of these CME events in the inner heliosphere.

Mahalakshmi, K.; Manoharan, P. K.

2012-07-01

92

Demonstration of Transverse Electric (TE) Mode Radio Propagation in the Earth-Ionosphere Waveguide.  

National Technical Information Service (NTIS)

An investigation was made of the use of Transverse Electric (TE) Modes of propagation rather than the conventional Transverse Magnetic (TM) Modes at Very Low Frequencies. Theoretical comparisons show that TE waves should propagate better then TM waves in ...

R. P. Harrison

1974-01-01

93

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

94

Predicting Proton Event Time Characteristics from Radio Burst Data.  

National Technical Information Service (NTIS)

For events originating on the Western hemisphere, the delay before onset of the solar flare protons is shown to be well correlated (r about 0.80) with the rise time of the associated radio-burst at 2-3 GHz or the rise time of the h sub alpha flare. The pe...

P. Bakshi T. Nguyen

1981-01-01

95

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

96

Validation of a novel radio location technique by a deterministic propagation model  

Microsoft Academic Search

A radio location system operates by measuring physical quantities related to radio signals traveling between a mobile terminal (MT) and a set of fixed base stations (BSs). In order to reduce the implementation complexity and the signalling overhead, the solution presented makes use of a single BS to locate unmodified MTs. The novel algorithm applies a triangulation technique supported by

M. Porretta; P. Nepa; G. Manara; F. Giannetti; A. H. Aghvami; M. Dohler

2003-01-01

97

Some Characteristics of a Propagating Brittle Tensile Crack.  

National Technical Information Service (NTIS)

A numerical technique was used to formulate the two-dimensional equations of motion for an elastic continuum. A brittle tensile crack was simulated to form and propagate in the continuum. The stress field in front of the fracture tip was found to become i...

A. R. Sanford M. E. Hanson

1970-01-01

98

Characteristics of Radio-Frequency Circuits Utilizing Ferroelectric Capacitors  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

99

Characteristics of electromagnetic wave propagation in uniaxially anisotropic left-handed materials  

Microsoft Academic Search

We investigate the characteristics of electromagnetic wave propagation in uniaxially anisotropic left-handed media. We discuss mainly under what conditions anomalous reflection or refraction shall occur at the interface when propagating waves pass from one isotropic regular medium into another uniaxially anistotropic left-handed medium and under what conditions anomalous transmission shall occur when an evanescent wave is transmitted through a slab

Liangbin Hu; S. T. Chui

2002-01-01

100

An implicit FDTD scheme for the propagation of VLF-LF radio waves in the Earth-ionosphere waveguide  

NASA Astrophysics Data System (ADS)

A new finite-difference time-domain scheme is presented for the propagation of VLF-LF radio waves in the Earth-ionosphere waveguide. The new scheme relies on the implicit solution of the auxiliary equation that governs the current density in the ionosphere. The advantages and drawbacks of the new scheme are discussed. Its main advantage is its stability condition, which is the same as that of the FDTD method in a vacuum. This permits the time step of the calculation to be increased and then the overall computational time to be reduced. Numerical experiments demonstrate the accuracy of the new scheme and the reduction of the computational time.

Bérenger, Jean-Pierre

2014-05-01

101

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

102

Estimation methods for propagation characteristics on earth-satellite links in microwave and millimeter wavebands  

NASA Astrophysics Data System (ADS)

This paper describes estimation methods for propagation characteristics, such as rain attenuation distributions (ten year average, the worst-month and worst-year for a ten year period etc.), rain attenuation duration time distributions, site diversity effect and frequency band diversity effect etc. on earth-satellite links using frequencies above 10 GHz. This paper also shows estimation formulas for these propagation characteristics, and estimation formula parameters, such as satellite elevation angles, rain rate distributions and raindrop layer heights at 20 locations in Japan. In addition, each concrete method and each estimation example are shown for the propagation characteristic estimation. By making use of this paper, it will be possible to estimate, without difficulty, the above-mentioned propagation characteristics on earth-satellite links using frequencies above 10 GHz.

Morita, K.

1980-06-01

103

Characteristics of coronal mass ejections associated with long-wavelength type II radio bursts  

Microsoft Academic Search

We investigated the characteristics of' coronal mass ejections (CMEs) associated with long-wavelength type II radio bursts in tim near-Sun interplanetary medium. Type II radio bursts in the decameter-hectometric (DH) wavelengths indicate powerful MHD shocks leaving the inner solar corona and entering the interplanetary medium. Almost all of these bursts are associated with wider and faster than average CMEs. A large

N. Gopalswamy; S. Yashiro; M. L. Kaiser; R. A. Howard; J.-L. Bougeret

2001-01-01

104

Characteristics of coronal mass ejections associated with long-wavelength type II radio bursts  

Microsoft Academic Search

We investigated the characteristics of coronal mass ejections (CMEs) associated with long-wavelength type II radio bursts in the near-Sun interplanetary medium. Type II radio bursts in the decameter-hectometric (DH) wavelengths indicate powerful MHD shocks leaving the inner solar corona and entering the interplanetary medium. Almost all of these bursts are associated with wider and faster than average CMEs. A large

N. Gopalswamy; S. Yashiro; M. L. Kaiser; R. A. Howard; J.-L. Bougeret

2001-01-01

105

Analysis of Propagation Characteristics of Circular Corrugated Waveguides Using Coupled Integral Equation Technique  

Microsoft Academic Search

The circular corrugated waveguides are useful as slow-wave circuits in traveling-wave tube amplifiers, linear accelerators, and backward-wave oscillators. The study of propagation characteristic of TM waves in circular corrugated waveguides is important for applications such as those above and is the focus of this paper. The propagation characteristics are computed using the coupled integral equation technique (CIET). Both infinitesimally thin

V. Latha Christie; Lalit Kumar; N. Balakrishnan

2007-01-01

106

Propagation characteristics of THz radiation in hollow rectangle metal waveguide  

NASA Astrophysics Data System (ADS)

The secular equation of medium coating were obtained by considering the particularity of THz, which had some reference value in designing of THz waveguides. The attenuation of medium coating metal hallow waveguides were theoretically calculated, the conclusion is that the power loss is less than the metal waveguides. Also we obtained the mode characters and attenuation in metal waveguides, and we noted that there exists an absorption peak. And we studied the affection of shape and size on propagation and got some useful conclusion. The split rectangular waveguide (SRW) is suitable for THz transmission which is confirmed by experiment. Our secular equation can be considered to be a theoretically discussion on it.

Zhang, Y.; Zhang, Y. Z.; Lu, D. M.; Wang, D. Y.; Liu, M.; Wang, S. Y.; Zhao, P. D.; Zhang, Z. D.; Yao, J. Q.

2011-02-01

107

Radio-Frequency Propagation Measurements in Confined Ship Spaces Aboard the ex-USS Shadwell.  

National Technical Information Service (NTIS)

Understanding the propagation of RF energy in confined naval shipboard environments is extremely important to the operability and effectiveness of communication systems used by the Navy. Single-frequency communication systems are known to suffer from mult...

E. L. Mokole M. Parent S. N. Samaddar E. Tomas B. T. Gold

2000-01-01

108

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

NASA Technical Reports Server (NTRS)

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

Asmar, Sami

1997-01-01

109

An Approximate Model of Radio Wave Propagation for Inter-Vehicles Communication Simulation Systems  

Microsoft Academic Search

In development of inter-vehicles com- munication (IVC) systems, simulation technologies are very essential to verify the correctness of proto- cols. We focus on a model of radio wave propaga- tion for IVC simulation systems and approximate the model. As a land mobile communication model, we adopt Kaji model. In our model, a distance be- tween vehicles, a building density, and

Junya Oishi; Koichi Asakura; Toyohide Watanabe

2006-01-01

110

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

Microsoft Academic Search

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

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

2009-01-01

111

Characterizing atmospheric multipath propagation in dense atmospheres for radio occultation measurements  

Microsoft Academic Search

In a dense planetary atmosphere, atmospheric multipath is caused by inflections with vertical extent larger than the first Fresnel zone in the refractivity with height profile. When using Abelian inversion to retrieve atmospheric profiles from radio occultation measurements, atmospheric multipath effects can cause unrecoverable errors unless they are detected correctly and mapped into the ray asymptote structure. In order to

K. Kusza; G. L. Tyler

2003-01-01

112

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

ERIC Educational Resources Information Center

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

Mills, Allan

2010-01-01

113

Reversed Temperature-Dependent Propagation Delay Characteristics in Nanometer CMOS Circuits  

Microsoft Academic Search

The supply voltage to threshold voltage ratio is reduced with each new technology generation. The gate overdrive variation with temperature plays an increasingly important role in determining the speed characteristics of CMOS integrated circuits. The temperature-dependent propagation delay characteristics, as shown in this brief, will experience a complete reversal in the near future. Contrary to the older technology generations, the

Ranjith Kumar; Volkan Kursun

2006-01-01

114

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

NASA Astrophysics Data System (ADS)

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

1980-12-01

115

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

116

High frequence and automatic link establishment (HF and ALE) radio propagation test to Antarctica  

NASA Astrophysics Data System (ADS)

Recent federal/military standards in the area of automatic link establishment (ALE) for HF radios have been developed that coordinate frequency selection between communicating terminals, allowing them to adapt to skywave conditions. This study focused on evaluating the utility of these state-of-the-art radios in the polar environment. A quick-look evaluation of this technology was demonstrated over a radio circuit between Christchurch, New Zealand, and McMurdo Station, Antarctica. This transauroral link, operated by the U.S. Navy for the National Science Foundation, is the primary link for all operational, logistical, and emergency communications for U.S. operations between the Antarctic and the outside world. Daily plots of the measured signal to noise ratio, probability of bit error, and channel quality are presented and analyzed. Because of the initial success of this technology demonstration, additional experiments were designed for deployment in FY 1993 to answer not only operational issues, but also to collect data for further scientific studies and engineering improvements.

Gilles, P. E.; Katan, J. R.; Pease, B. L.

1994-02-01

117

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

118

Non-detection at Venus of high-frequency radio signals characteristic of terrestrial lightning.  

PubMed

The detection of impulsive low-frequency (10 to 80 kHz) radio signals, and separate very-low-frequency (approximately 100 Hz) radio 'whistler' signals provided the first evidence for lightning in the atmosphere of Venus. Later, a small number of impulsive high-frequency (100 kHz to 5.6 MHz) radio signals, possibly due to lightning, were also detected. The existence of lightning at Venus has, however, remained controversial. Here we report the results of a search for high-frequency (0.125 to 16 MHz) radio signals during two close fly-bys of Venus by the Cassini spacecraft. Such signals are characteristic of terrestrial lightning, and are commonly heard on AM (amplitude-modulated) radios during thunderstorms. Although the instrument easily detected signals from terrestrial lightning during a later fly-by of Earth (at a global flash rate estimated to be 70 s(-1), which is consistent with the rate expected for terrestrial lightning), no similar signals were detected from Venus. If lightning exists in the venusian atmosphere, it is either extremely rare, or very different from terrestrial lightning. PMID:11201733

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

2001-01-18

119

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

120

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

NASA Astrophysics Data System (ADS)

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; Li, Lei; Du, Yanwei

2012-08-01

121

Research on propagation characteristics of leaky waveguide for train-ground information transmission in CBTC  

Microsoft Academic Search

The reliability and safety of information transmission can be improved when leaky waveguide is used as transmission medium of train-ground wireless communication in CBTC (Communication Based Train Control). Based on the theory of leaky waveguide, this paper studies the propagation characteristics of leaky waveguide by means of magnetic dipole, and compares the simulation results with field tests performed in Beijing

Qingwen Yang; Bing Bu; Hongwei Wang; Qianwen Yang

2011-01-01

122

Semiconducting Layer impedance and its effect on cable wave-propagation and transient Characteristics  

Microsoft Academic Search

This paper has derived an impedance formula for conductor's semiconducting layer based on a conventional circuit theory. The formula is confirmed to be identical to an accurate one derived by solving Maxwell's equation. A wave-propagation characteristic and a transient voltage on a cable having the semiconducting layer on the conductor's surface are evaluated by applying the derived formula, and are

Akihiro Ametani; Yukata Miyamoto; Naoto Nagaoka

2004-01-01

123

Microwave measurements of the propagation characteristics in a multi-beam waveguide system  

Microsoft Academic Search

The main heating method for the stellarator W7-X which is currently under construction is Electron Cyclotron Resonance Heating (ECRH) at 140 GHz. To meet the physical and technical demands of the W7-X machine a 10 MW ECRH system with CW capabilities has been constructed. To test the performance of the system and to measure the beam propagation characteristics, a prototype

G. Gantenbein; L. Empacher; F. Hollmann; W. Kasparek; P. G. Schuller; K. Schworer; V. Erckmann; M. Weissgerber

2000-01-01

124

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

125

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

NASA Astrophysics Data System (ADS)

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

Olivier, P.; Tiffon, J.

1984-09-01

126

Study on propagation characteristics of electromagnetic wave in underground, part 1  

NASA Astrophysics Data System (ADS)

Electromagnetic wave is used for underground survey, but underground is very non-uniform and attenuant. This paper proposed a new measuring method concerning the propagation characteristics of electromagnetic wave. This method used the balanced stripline (BS) which was composed of two wide outer conductors, shallow central conductor and supporting medium. Planar sample was inserted into BS to use as the transmitting medium for electromagnetic wave. The propagating time and attenuation of electromagnetic wave were measured. Propagating speed and attenuation constant were determined from measurements and dielectric constant and conductivity of the rock were calculated from the equation giving the propagation constant. This measuring method does not result the inferior contact between the conductors and sample and the error is small. The change of the width of the central conductor can reduce the mismatch reflection of characteristic impedance. This method was applied to rocks such as granite, andesite, tuff and sandstone in the frequency range of 13 to 500 MHz and the measurements were compared with measured values by impedance-analyzer to verify the effectiveness of this method.

Amano, Y.; Tanabe, K.

1990-05-01

127

Some common characteristics of the basic components of the solar radio emission and confirmation of a fourth basic component  

NASA Astrophysics Data System (ADS)

Our high-time resolution data observed with fast sampling radio telescopes in three periods were processed. It is found that there is a rapidly varying component(RVC) in the radio emission source on the Sun. After investigating some common characteristics of the basic components of the solar radio emission, we discover that RVC is different in nature from the known three basic components: the quiet Sun, the slowly varying component (SVC), and the radio burst. It has a character superimposed on the radio burst: short duration, high brightness temperature and small dimension. For this reason, it is presented as a fourth basic component. Up to now, we have observed five typoes of RVC. Among them four types can be confirmed, another is yet in dispute. Finally, the five categories of observational characteristics of RVC are given.

Ji, S. C.; Cao, W. D.; Chen, G. Q.; Yang, K. P.

1994-06-01

128

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

129

Discharge ignition characteristics of pulsed radio-frequency glow discharges in atmospheric helium  

NASA Astrophysics Data System (ADS)

An experimental study of radio-frequency (15 MHz) glow discharges in atmospheric helium modulated by pulses with repetition frequency of 500 kHz and duty cycle of 6% and 8% is presented in this paper. In each discharge burst, the discharge is restricted to operate in ignition phase with duration of one or two radio-frequency cycles. The ignition characteristics in terms of spatial-temporal evolution of discharge interelectrode structure and optical emission intensity are investigated by time resolved imaging. Optical emission intensities at lines of 706 and 777 nm are used to capture clearly the temporal evolution of energetic electrons and active specie of atom oxygen generated in discharge.

Shi, Jianjun; Cai, Yeqing; Zhang, Jie; Ding, Ke; Zhang, Jing

2009-07-01

130

Propagation characteristics of surface acoustic waves in single-electron transport devices and the electrical measurement.  

PubMed

We focused on investigating the propagation characteristics of surface acoustic waves (SAWs) in SAW-based single-electron-transport (SAW/SET) devices. SAW/SET devices operating in the gigahertz frequency range were fabricated on a GaAs/Al(x)Ga(1-x)As heterostructure. The transmittance and reflection performances of SAW/SET devices were obtained via the electrical measurement. Modeling based on coupling-of-modes theory was introduced to analyze SAW/ SET devices. Based on this model, many second-order effects such as propagation loss and the mechanical and electrical loadings caused by electrode perturbation of the surface were taken into account. Multiple-transit reflections of SAWs were also contained in the calculation. The calculated transmittance and reflection performances were in good agreement with the measured data. Furthermore, we proposed four interference types which could satisfactorily explain the periodic oscillations presented in the acoustoelectric current versus frequency characteristics. PMID:21768029

Zhang, Chuan-Yu; Gao, Jie; Li, Hong; Song, Li; Lu, Chuan

2011-07-01

131

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

SciTech Connect

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

Tsutsumi, M.; Fukusako, T.; Yoshida, S. [Kyoto Inst. of Tech. (Japan). Faculty of Engineering and Design] [Kyoto Inst. of Tech. (Japan). Faculty of Engineering and Design

1996-08-01

132

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

Microsoft Academic Search

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

K. Yamanouchi; N. Sakurai; T. Satoh

1989-01-01

133

Propagation Characteristics of Lamb Wave in Nematic Liquid-Crystal Cell  

Microsoft Academic Search

Propagation characteristics of a Lamb wave in a nematic liquid-crystal cell are examined by numerical analysis and experimental investigation. The directional dependence of the viscosity coefficients of the nematic liquid-crystal is taken into account for both compressional and shear vertical components of the Lamb wave in the numerical analysis. Higher order modes of Lamb wave are dispersive and the 6th

Masaru Inoue; Katsumi Yoshino; Hiroshi Moritake; Kohji Toda

2002-01-01

134

Propagation Characteristics of Power Line Communication Signals Along a Power Cable Having Semiconducting Layers  

Microsoft Academic Search

The propagation characteristics of power line communication (PLC) signals along a single-core power cable having two 3-mm-thick semiconducting layers are studied using the finite-difference time-domain method for solving Maxwell's equations. It turns out that a PLC signal of frequency 30 MHz suffers significant attenuation particularly when the conductivity of the semiconducting layers is around ? = 0.001 and 1000 S\\/m,

N. Okazima; Y. Baba; N. Nagaoka; A. Ametani; K. Temma; T. Shimomura

2010-01-01

135

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

NASA Astrophysics Data System (ADS)

The topics covered include the prediction of attenuation due to rainfall on earth-space satellite links, cross-polarization on terrestrial links, cross-polarization on earth-space links, and transhorizon propagation. Papers are presented on new radar studies of slant-path attenuation, multipath depolarization theory, model-oriented approaches to measure rain-induced cross-polarization, and rainfall scatter interference between terrestrial and satellite radio links.

1981-02-01

136

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

PubMed

Continued miniaturization of electronic devices and technological advancements in wireless communications has made wearable body-centric telemedicine systems viable. Antennas play a crucial role in characterizing the efficiency and reliability of these systems. The performance characteristics such as the radiation pattern, gain, efficiency of the antennas get adversely affected due to the presence of lossy human body tissues. In this paper we investigate the above mentioned performance parameters and radio frequency transmission properties of wire and planar structures operating at ISM frequency band of 2.40-2.50 GHz in the proximity of human body. PMID:22255220

Aroul, A L Praveen; Bhatia, Dinesh

2011-01-01

137

Propagation characteristics of photomechanical waves and their application to gene delivery into deep tissue.  

PubMed

Targeted gene transfection can be achieved by the use of photomechanical waves (PMWs) generated by irradiating a solid material with high-power nanosecond laser pulses. To examine the treatable tissue depth, we investigated propagation characteristics of PMWs and depth-dependent properties of gene transfection with different laser fluences and spot diameters. Pressure characteristics of PMWs were measured at different propagation distances using tissue phantoms and their propagation was imaged by shadowgraphing. Phantoms with various thicknesses were placed on rat dorsal skin that had been injected with plasmid DNA coding for a reporter gene and three pulses of PMWs were applied from the top of each phantom. Significant gene expression was observed in the skin even under a 15-mm-thick tissue phantom and the depth-dependent relationships between PMW parameters and gene expression level were revealed. The data obtained will be useful for determining appropriate laser parameters for PMW-based gene transfer into deep-located tissue. PMID:22104529

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

2012-01-01

138

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

139

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

140

Propagation Characteristics of Coronal Mass Ejections as Determined by Geometric Localization  

NASA Astrophysics Data System (ADS)

The geometric localization technique [Pizzo and Biesecker, 2004] utilizes a series of lines of sight from two space-based observatories in order to determine gross propagation characteristics of coronal mass ejections (CMEs). This technique was developed to meet the need within the space weather community for a means to accurately determine the gross properties of Earth-directed CMEs from a near-real-time data stream, such as the one provided by the STEREO (Solar TErrestrial RElations Observatory) Space Weather Beacon. This tool works with all STEREO coronagraph observations, including COR1 and COR2. Here, we employ the geometric localization technique to the CME of 31 December 2007 and present results on the speed and direction of propagation for this CME.

de Koning, C. A.; Pizzo, V. J.; Biesecker, D. A.

2008-05-01

141

Propagation Characteristics of the 2007 August 21 Coronal Mass Ejection as Determined by Geometric Localization  

NASA Astrophysics Data System (ADS)

The geometric localization technique [Pizzo and Biesecker, 2004] utilizes a series of lines of sight from two space-based observatories in order to determine gross propagation characteristics of coronal mass ejections (CMEs). We have set up this tool to work specifically with STEREO (Solar TErrestrial RElations Observatory) coronagraph observations. Here, we employ this technique to the CME of 21 August 2007 and present results on the speed and direction of propagation for this CME. This technique meets a need within the space weather community for a means to accurately determine the gross properties of Earth-directed CMEs from a near-real- time data stream, such as the one provided by the STEREO Space Weather Beacon.

de Koning, C. A.; Pizzo, V. J.; Biesecker, D. A.

2007-12-01

142

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

NASA Astrophysics Data System (ADS)

The geometric localization technique [Pizzo and Biesecker, 2004] utilizes a series of lines of sight from two space-based coronagraphs to determine gross propagation characteristics of coronal mass ejections (CMEs) in three-dimensional space. The polarimetric localization technique [Moran and Davila, 2004] uses the percent polarization observed by a single coronagraph to obtain a three-dimensional reconstruction of a CME. Both techniques can be used in near-real-time within an operational space weather forecast center. When these two independent techniques are used in conjunction with each other to analyze STEREO/Secchi/COR2 beacon data, they can provide significant constraints on the three-dimensional location and velocity, including speed and direction, for any Earth-directed CME. Here, we employ these techniques to the CME of 31 December 2007 and compare results on the speed and direction of propagation for this CME.

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

2008-12-01

143

Propagation Characteristics of Lamb Wave in Nematic Liquid-Crystal Cell  

NASA Astrophysics Data System (ADS)

Propagation characteristics of a Lamb wave in a nematic liquid-crystal cell are examined by numerical analysis and experimental investigation. The directional dependence of the viscosity coefficients of the nematic liquid-crystal is taken into account for both compressional and shear vertical components of the Lamb wave in the numerical analysis. Higher order modes of Lamb wave are dispersive and the 6th mode of Lamb wave is most sensitive to the director-orientation change of the nematic liquid crystal in the examined frequency region. The electric field dependences of the acoustic phase delay and the propagation loss are measured for three kinds of initial orientations of the nematic liquid crystal. The director orientation in the nematic liquid-crystal cell is evaluated from the phase velocity of the Lamb wave, which is related to the acoustic phase-delay change.

Inoue, Masaru; Yoshino, Katsumi; Moritake, Hiroshi; Toda, Kohji

2002-05-01

144

Observed structure and propagation characteristics of tropical summertime synoptic scale disturbances  

SciTech Connect

Twice daily global analyses for the 1980-1987 period are used here to study the three-dimensional structure and propagation characteristics of tropical synoptic scale transients during the northern summer. Regions of enhanced variability in relative vorticity at 850 mb are found in the western and eastern Pacific, Bay of Bengal, northern India, eastern Atlantic, and western Africa. Lag-correlation and regression analyses show strong teleconnectivity and temporal coherence over all of the active sites with enhanced vorticity variance, as well as over the western Atlantic/Caribbean and the Indochinese Peninsula. A substantial amount of the synoptic scale variability in the tropics is associated with propagating wavelike disturbances that remain coherent over several days and tend to travel west/northwestward. An extended empirical orthogonal function (EOF) technique is used to show that the leading EOF modes in the tropical zone within the 3- to 10-day band are these wavelike disturbances. 43 refs.

Lau, K.; Lau, N. (Princeton Univ., NJ (USA) NOAA, Geophysical Fluid Dynamics Laboratory, Princeton, NJ (USA))

1990-09-01

145

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

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

146

Route Construction Based on Measured Characteristics of Radio Propagation in Wireless Sensor Networks  

Microsoft Academic Search

There are many constraints on electrical power and communication in wireless sensor networks since sensor nodes can only be equipped with poor devices. Therefore, it is important to construct an effective communication route in terms of energy-efficiency and quality of communication. Many studies have been conducted to address this issue. In particular, controlling the transmission power of each individual node

Yasuhiro Nose; Akimitsu Kanzaki; Takahiro Hara; Shojiro Nishio

2009-01-01

147

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

NASA Technical Reports Server (NTRS)

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

Revelle, D. O.

1976-01-01

148

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

149

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

150

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

NASA Astrophysics Data System (ADS)

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

Jung, Ki Won; Atchley, Anthony A.

2005-09-01

151

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

NASA Astrophysics Data System (ADS)

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

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

2002-12-01

152

Propagation characteristics of silver nanorods based compact waveguides for plasmonic circuitry  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

153

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

154

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

155

The radio spectrum of Vela supernova and its implication on the propagation of cosmic rays from sources  

NASA Technical Reports Server (NTRS)

A detailed analysis of the radio spectrum of the Vela supernova remnant has been carried out to show that the positive spectral shape below 80 MHz can be understood on the basis of Razin effect. This result requires most of the gas in the remnant to be stratified into high density clumps with intense magnetic fields and large cosmic ray densities. The free-free emission is found to be partly responsible for the observed flat radio spectrum. In order to account for both the gamma ray flux above 100 MeV and the radio spectrum, the equipartition between the cosmic ray density and magnetic field seems to break down. The total cosmic ray energy residing in the supernova is found to be about ten to the forty-ninth ergs, which is much smaller than the value obtained without taking into account the stratification of gas.

Stephens, S. A.

1975-01-01

156

Nearfield Aerodynamics and Optical Propagation Characteristics of a Large-Scale Turret Model.  

National Technical Information Service (NTIS)

Measurements of the unsteady flow field affecting optical propagation quality have been made with both aerodynamic and direct optical instrumentation. Properties affecting degradation of coherent radiation beams propagated from within the turret have been...

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

1982-01-01

157

Theory of Localized Synfire Chain: Characteristic Propagation Speed of Stable Spike Patterns  

Microsoft Academic Search

Repeated spike patterns have often been taken as evidence for the synfire chain, a phenomenon that a stable spike synchrony propagates through a feedforward network. Inter-spike intervals which represent a repeated spike pattern are influenced by the propagation speed of a spike packet. However, the relation between the propagation speed and network struc- ture is not well understood. While it

Kosuke Hamaguchi; Masato Okada; Kazuyuki Aihara

158

Theory of localized synfire chain: characteristic propagation speed of stable spike pattern  

Microsoft Academic Search

Abstract Repeated spike patterns have often been taken as evidence for the synfire chain, a phenomenon that a stable spike synchrony propagates through a feedforward network. Inter-spike intervals which represent a repeated spike pattern are influenced by the propagation speed of a spike packet. However, the relation between the propagation speed and network struc- ture is not well understood. While

Kosuke Hamaguchi; Masato Okada; Kazuyuki Aihara

2004-01-01

159

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

SciTech Connect

The authors present preliminary two-dimensional hybrid simulation results from modeling wave propagation behavior from quasi-parallel shocks. The question of concern is whether the waves formed propagate along the normal to the shock front or along the magnetic field vector. For low Alfven mach number shocks, they are initially associated with upstream phase-standing waves. Later, longer wavelength waves are excited by backstreaming ions via instabilities, and these seem to propagate along field lines. At higher mach numbers the backward propagating waves can reach the shock front, interacting with it and propagating downstream. Mode conversion is also observed between modes in these waves.

Krauss-Varban, D.; Omidi, N. (Univ. of California, San Diego (United States))

1993-06-07

160

Generation and Propagation Characteristics of Dual-Band Chorus Emissions Observed by Geotail  

NASA Astrophysics Data System (ADS)

We analyze the generation and propagation characteristics of chorus emissions observed by the wave form capture (WFC) and the sweep frequency analyzer (SFA) onboard the Geotail spacecraft in the dayside outer magnetosphere (L from 9 to 10). We examine any observational evidence, which may validate the nonlinear growth theory of the chorus emissions [1]. In the nonlinear growth theory a rising-tone element is initially generated continuously in the frequency range from 0.1 to 0.7 fce, where fce is the gyrofrequency in the generation region. Because of the nonlinear damping mechanism the rising-tone element is separated into upper and lower bands at half the local gyrofrequency (1/2 fce) through propagation [2]. As the rising-tone emissions are generated in the minimum-B region and propagate toward the larger-B regions along the geomagnetic field line, the upper cutoff of the lower-band chorus corresponds to 1/2 fce in the generation region, and the lower cutoff of the upper-band chorus corresponds to 1/2 fce at the observation point. In this study, we analyze the SFA spectrum data (consecutively over several hours) and WFC waveform data (several seconds) of the dual-band chorus emissions observed by Geotail. As a result, it is found that the upper cutoff of the lower-band chorus coincides with 1/2 fce at the minimum-B region estimated from the geomagnetic field line connecting to the Geotail position by using the Tsyganenko geomagnetic field model (TS04 model), whereas the lower cutoff of the upper-band chorus coincides with 1/2 fce locally at the observation point. We also examine the amplitude of a rising-tone emission using the WFC waveform data on the basis of the nonlinear growth theory. The amplitude at the generation region is estimated from the observed frequency sweep rate of the emission, and the nonlinear growth of the amplitude through propagation toward the observation point is calculated from the nonlinear growth rate, which is found consistent with the observed amplitude. We will also discuss the observational evidence for the threshold amplitudes and the optimum amplitudes required for triggering rising-tone chorus emissions in the generation region. [1] Omura Y., Y. Katoh and D. Summers (2008), Theory and simulation of the generation of whistler-mode chorus, J. Geophys. Res., 113, A04223, doi:10.1029/2007JA012622. [2] Omura Y., M. Hikishima, Y. Katoh, D. Summers, and S. Yagitani (2009), Nonlinear mechanisms of lower-band and upper-band VLF chorus emissions in the magnetosphere, J.Geophys. Res., 114, A07217, doi:10.1029/2009JA014206. [3] Omura Y., and D. Nunn (2011), Triggering process of whistler mode chorus emissions in the magnetosphere, J. Geophys. Res., 116, A05205, doi:10.1029/2010JA016280.

Yagitani, S.; Habagishi, T.; Mori, S.; Omura, Y.; Kojima, H.

2012-12-01

161

Numerical Analysis of Wave Propagation Characteristics on a Buried Horizontal Conductor by an FDTD Method  

NASA Astrophysics Data System (ADS)

Fundamental characteristics of a 34-m long horizontal conductor buried at a depth of 1m have been studied with an FDTD method. An equivalent radius of a buried thin wire is shown to be 0.23 times the side of cells employed, which is the same as that of an aerial thin wire. The rate of current dissipating from each section of the buried conductor to the injected current is roughly equal to that of the section length to the total length although it is somewhat influenced by the direction of a current lead. As the conductivity of the ground is higher, the wavefronts of a voltage and a current become less steep. The high permittivity distorts wavefronts of a voltage and a current with their propagation. However, its influence appears only initially and the response at the injection point is little influenced by it. The transient grounding resistance at 5?s calculated by the FDTD method is 10 to 20% lower than the resistance calculated by Sunde’s formula.

Baba, Yoshihiro; Nayel, Mohamed; Nagaoka, Naoto; Ametani, Akihiro; Sekioka, Shozo

162

Error propagation in time-dependent probability of occurrence for characteristic earthquakes in Italy  

NASA Astrophysics Data System (ADS)

Time-dependent models for seismic hazard and earthquake probabilities are at the leading edge of research nowadays. In the framework of a 2-year national Italian project (2005-2007), we have applied the Brownian passage time (BPT) renewal model to the recently released Database of Individual Seismogenic Sources (DISS) to compute earthquake probability in the period 2007-2036. Observed interevent times on faults in Italy are absolutely insufficient to characterize the recurrence time. We, therefore, derived mean recurrence intervals indirectly. To estimate the uncertainty of the results, we resorted to the theory of error propagation with respect to the main parameters: magnitude and slip rate. The main issue concerned the high variability of slip rate, which could hardly be reduced by exploiting geodetic constraints. We did some validation tests, and interesting considerations were derived from seismic moment budgeting on the historical earthquake catalog. In a time-dependent perspective, i.e., when the date of the last event is known, only 10-15% of the 115 sources exhibit a probability of a characteristic earthquake in the next 30 years higher than the equivalent Poissonian probabilities. If we accept the Japanese conventional choice of probability threshold greater than 3% in 30 years to define “highly probable sources,” mainly intermediate earthquake faults with characteristic M < 6, having an elapsed time of 0.7-1.2 times the recurrence interval are the most “prone” sources. The number of highly probable sources rises by increasing the aperiodicity coefficient (from 14 sources in the case of variable ? ranging between 0.22 and 0.36 to 31 sources out of 115 in the case of an ? value fixed at 0.7). On the other hand, in stationary time-independent approaches, more than two thirds of all sources are considered probabilistically prone to an impending earthquake. The performed tests show the influence of the variability of the aperiodicity factor in the BPT renewal model on the absolute probability values. However, the influence on the relative ranking of sources is small. Future developments should give priority to a more accurate determination of the date of the last seismic event for a few seismogenic sources of the DISS catalog and to a careful check on the applicability of a purely characteristic model.

Peruzza, Laura; Pace, Bruno; Cavallini, Fabio

2010-01-01

163

Transfer function of multimode fiber links using an electric field propagation model: Application to Radio over Fibre Systems  

NASA Astrophysics Data System (ADS)

We present a closed-form expression for the evaluation of the transfer function of a multimode fiber (MMF) link based on the electric field propagation model. After validating the result we investigate the potential for broadband transmission in regions far from baseband. We find that MMFs offer the potential for broadband ROF transmission in the microwave and millimetre wave regions in short and middle reach distances.

Gasulla, I.; Capmany, J.

2006-10-01

164

A UHF channel simulator for digital mobile radio  

Microsoft Academic Search

A device to simulate the channel propagation characteristics of the ground mobile environment at UHF has been designed, built, and characterized. This device provides a flexible, easily changed set of simulated channel characteristics, which allows the performance of a mobile radio unit to be evaluated in the laboratory under controlled conditions. The channel simulator was designed to simulate mobile platform

EDGAR L. CAPLES; KHALIL E. MASSAD; TIMOTHY R. MINOR

1980-01-01

165

Propagation Modes, Equivalent Circuits, and Characteristic Terminations for Multiconductor Transmission Lines with Inhomogeneous Dielectrics  

Microsoft Academic Search

The theory of wave propagation on Iossless multiconductor transmission lines with inhomogeneous dielectrics is developed using matrix analysis. The treatment is concise and complete and has the advantage of identifying propagation modes in a way that permits straightforward physical interpretation. The equivalent circuit for the general line is derived and its application to the solution of wave problems with reflections

KENNETH D. MARX

1973-01-01

166

Model interpretation of type III radio burst characteristics. II - Temporal aspects  

NASA Technical Reports Server (NTRS)

A model of the radio emission region for kilometric type II bursts is used to interpret systematic variations observed in the temporal behavior of the burst parameters. The temporal behavior of the burst parameters observed by the ISEE-3 spacecraft is reviewed, and it is pointed out that the phase and modulation of the antenna signal vary in a systematic way with both time and observing frequency. The source azimuth is observed to drift with time, with the magnitude and sense of the drift depending on the location of the radio source relative to the observer. The modulation factor usually decreases uniformly with time and is frequently peaked near the burst onset. The model of the radio emission region is developed and used to obtain the intensity, phase, and modulation of the radio signal. Model results are used to show how the behavior of the burst parameters are related to attributes of the source region. It is shown that the temporal behavior of the radio parameters for an observed type II burst is well represented by the model.

Reiner, M. J.; Stone, R. G.

1989-01-01

167

A new radio propagation model at 2.4 GHz for wireless medical body sensors in outdoor environment.  

PubMed

This study investigates the effect of antenna height, receive antenna placement on human body, and distance between transmitter and receiver on the loss of wireless signal power in order to develop a wireless propagation model for wireless body sensors. Although many studies looked at the effect of distance, few studies were found that investigated methodically the effect of antenna height and antenna placement on the human body. Transmit antenna heights of 1, 2, and 3 meters, receive antenna heights of 1 and 1.65 meters, "on-body" and "off-body" placements of receive antenna, and a total of 11 distances ranging from 1 to 45 meters are tested in relation to received power in dBm. Multiple regression is used to analyze the data. Significance of a variable is tested by comparing its p-value with alpha, and model fit is assessed using adjusted R(2) and s of residuals. It is found that an increase in antenna height would increase power-but only for transmit antenna. The receive antenna height has a surprising, opposite effect in the on-body case and an insignificant effect in the off-body case. To formalize the propagation model, coefficient values from multiple regression are incorporated in an extension of the log-distance model to produce a new empirical model for on-body and off-body cases, and the new empirical model could conceivably be utilized to design more reliable wireless links for medical body sensors. PMID:24110426

Yang, Daniel S

2013-01-01

168

Frequency-Dependent Characteristics of Regional Seismic Phases: Propagation of Pn in Western China.  

National Technical Information Service (NTIS)

The propagation of Pn waves has been investigated over a large region in western China using regional events recorded by the Hi-CLIMB array. Seismic attributes, including arrival times, Hilbert envelope amplitudes, and pulse frequencies, are modeled to in...

R. L. Nowack W. Chen

2011-01-01

169

Characteristics of Acoustic Emission for A537 Structural Steel during Fatigue Crack Propagation.  

National Technical Information Service (NTIS)

The acoustic emission (AE) technique can be used to investigate the initiation and propagation processes of fatigue crack. The decrease in AE susceptibility with the yield strength decreasing of alloys makes AE monitoring more difficult, and AE investigat...

Z. F. Wang J. Li W. Ke Z. Zhu

1995-01-01

170

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

SciTech Connect

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

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

1996-10-01

171

The characteristics of the forced stationary planetary wave propagations in summer Northern Hemisphere  

Microsoft Academic Search

The three-dimensional propagations of the forced stationary planetary waves in a realistic summer current, in which the vertical\\u000a and horizontal wind shears are included, are discussed by using the refractive index squared of waves in a spherical coordinate\\u000a system.\\u000a \\u000a \\u000a The results show that there is no polar wave guide in stationary planetary wave propagations in summer. Thus, stationary planetary\\u000a waves

Huang Ronghui

1984-01-01

172

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

173

Calculation of Electrical Parameters for Studies on Propagation Characteristic of PD along Transformer Winding  

Microsoft Academic Search

In order to investigate the propagation of partial discharge pulses in transformer winding, the simulation model of a 180 turns continuous disc type transformer winding based on multi-conductor transmission line (MTL) theory is constructed. According to the symmetry of windings, a 2D equivalent finite element model is set up under ANSYS environment. A modified method is proposed to calculate the

Zhiye Du; Ling Ruan; Chun Zhao; Jiangjun Ruan; Yunfei Wu; Tao Wang

2008-01-01

174

Observed characteristics of ionospherically propagated HF atmospherics from normal and severe thunderstorms  

Microsoft Academic Search

Using a directional HF antenna with a nominal beamwidth of 0.51 deg, atmospherics from midwestern thunderstorms classified as severe, and thus likely to produce tornadoes, were studied in California. The antenna was scanned across regions within a one-hop propagation distance likely to develop tornadoes at the time of the test. These regions were selected on the basis of National Weather

W. B. Zavoli

1977-01-01

175

Parsec-Scale Radio Jet Characteristics of MOJAVE Hard-Spectrum Gamma-Ray Blazars  

NASA Astrophysics Data System (ADS)

MOJAVE is a long term VLBA key project to probe the structure and evolution of parsec-scale radio jets associated with active galactic nuclei (AGN). Our program has found that apparent superluminal motion is common in compact radio-selected AGN, indicating Lorentz factors up to ~50 in outflows oriented at a few degrees from the line of sight. Recently we have begun regularly obtaining 2 cm VLBA full polarization images of a new AGN sample selected on the basis of hard-spectrum gamma-ray flux. Only about 10% of these AGN have previously been monitored with VLBA, and they show slow apparent jet speeds that appear to be inconsistent with the very high Doppler factors inferred from emission modelling and rapid variability at high photon energies. We discuss the first-epoch radio jet properties of our sample, and the detection of superluminal motion in the jet associated with the hard-spectrum TeV blazar 1ES 1011+496.

Lister, Matthew L.

2014-06-01

176

Numerical study on the propagation characteristics of forward smoldering in a cellulosic packed bed  

Microsoft Academic Search

Based on a three-step kinetic mechanism, a one-dimensional, time dependent, numerical model is presented for the smoldering\\u000a propagation in a horizontally packed bed of cellulosic material. The kinetic processes include pyrolysis and oxidation degradation\\u000a of fuel and oxidation of char. Heat transfer between solid and gas is taken into account, and the diffusion coefficient varies\\u000a with the temperature. Radiative heat

Bao-shan Jia; Mao-zhao Xie; Hong Liu

2008-01-01

177

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

178

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

179

Influence of radio-frequency electromagnetic field on optical characteristics of cast-iron surface  

NASA Astrophysics Data System (ADS)

Variations in spectral coefficients of specular reflection and Raman scattering spectra were detected during exposure of a cast-iron surface to an electromagnetic field in the radio-wave range. The observed variations were supposed to be caused by both field-induced changes in the surface morphological structure, density, and crystalline state and ordering of the carbon structures accompanied by a reduction in the amount of defects. Spectral reflectometry and Raman scattering methods were shown to be applicable to nondestructive remote monitoring of the morphological state of the cast-iron surface and changes in the structure and size of its microcrystalline graphite inclusions.

Azharonok, V. V.; Krat'koa, L. E.; Anisovich, A. G.; Bislukb, L. V.

2012-11-01

180

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

181

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

182

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

183

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

184

Propagation characteristics of Pc 3 compressional waves generated at the dayside magnetopause  

NASA Technical Reports Server (NTRS)

New, 3D ray tracing of Pc 3 compressional waves from the magnetosheath reveals that the magnetosphere can present a major propagation barrier to the penetration of these waves to the plasmasphere. This barrier is the ion-ion cutoff between the He(+) and O(+) gyroresonances. As a result of the frequency-dependent location of this cutoff, the magnetosphere behaves like a filter for Pc 3 compressional waves, and only low-frequency components of Pc 3 compressional waves can penetrate to inner magnetosphere. Results are in agreement with previous satellite observations. This 'filter action' strongly depends on the relative concentration of He(+) and O(+) and is therefore sensitive to solar and magnetic activity. Ray-tracing results are based on a cold plasma dispersion relation, a semiempirical model of plasma density, and the Mead-Fairfield (1975) magnetic field model.

Zhang, X.; Comfort, R. H.; Musielak, Z. E.; Moore, T. E.; Gallagher, D. L.; Green, J. L.

1993-01-01

185

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

PubMed

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

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

2010-11-18

186

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

187

Propagation Characteristics of Pc 1-2 Waves at High Latitude Ionospheric Waveguide  

NASA Astrophysics Data System (ADS)

ULF Pc1 geomagnetic pulsations have been observed from a ground array of search-coil magnetometers predominantly in the pre-noon to post-noon sector of Antarctica. With extensive coverage from geomagnetic latitudes of 62° to 87° and good alignment along the magnetic meridian, the five search-coil magnetometers operating aboard American Automated Geophysical Observatories (AGOs) and British Antarctic Survey (BAS) showed very clear ducting with spectral power attenuation of the waves in the waveguide. Halley Station, located at the lowest latitude, typically observed the highest spectral wave power and well-defined band-limited signatures with the same wave event, showing less wave power, found at the other four remote stations at higher latitudes. This is a clear implication of the ducting of the electromagnetic ion cyclotron (EMIC) waves in the ionospheric waveguide, which are generated from the equatorial magnetosphere along the geomagnetic field lines and transmitted to the ionosphere. Since the wave event was observed over a very wide range in latitude, the observation of the wave propagation will provide significant information on the ULF wave ducting in the waveguide and the source region. This study presents the observations of over 100 Pc1 events showing spectral power attenuation in the waveguide. The changes of the polarization properties such as ellipticity and polarization ellipse major axis direction during the propagation are also shown. It is shown both qualitatively and quantitatively how these behaviors are affected by specific ionospheric conditions (i.e. conductivity) and geomagnetic activity. In addition, CHAMP satellite data obtained in the ionosphere is also presented to validate the wave ducting.

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

2009-12-01

188

Source and Propagation Characteristics of Kilometric Continuum Observed with Multiple Satellites  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

189

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

190

Neutron noise transmission characteristics of multiplying media and neutron noise source localization in liquid-metal fast breeder reactors by using the neutron wave propagation technique  

Microsoft Academic Search

The results of a theoretical study of noise transmission characteristics of multiplying media and neutron noise source localization in liquid-metal fast breeder reactors (LMFBRs) by using the neutron wave propagation technique is reported. The study was carried out using one-group as well as multigroup diffusion theory. Both theories show that the noise transmission characteristics are quite sensitive to the multiplication

T. M. John; O. P. Singh

1983-01-01

191

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

PubMed

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

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

2013-12-01

192

Some characteristics of Yakutat Eddies propagating along the continental slope of the northern Gulf of Alaska  

NASA Astrophysics Data System (ADS)

Data from array for real-time geostrophic oceanography (ARGO) profiling floats, oil tanker thermosalinographs, shipboard ADCP and towed-CTD surveys, and satellite altimetry are used to examine properties of two ˜200 km diameter, anticyclonic Yakutat Eddies that propagated westward at ˜1.5 km day -1 along the continental slope of the northern Gulf of Alaska (GOA) in 2001 and 2003. The eddies had lifetimes of up to 5 years, remained close to the shelfbreak, and had relatively constant size and strength until they encountered the Alaskan Stream where they appeared to spawn smaller, shorter-lived anticyclones. The azimuthal velocity field was vigorous (25-40 cm s -1) and in gradient wind balance with Rossby numbers of ˜0.05. Conservation of salt and azimuthal mass transports (between 20 m and the depth of the 32.2 isohaline) from shipboard surveys in May and August 2003 suggest little mass exchange occurred between the surface layers of the eddy and ambient waters. Chlorophyll concentrations were greater in the eddy than in ambient waters in both May and August. In May, the chlorophyll was patchily distributed, while in August dense chlorophyll concentrations occurred in and beneath the seasonal thermocline within 50 km of the eddy center. The high August chlorophyll concentrations might have been fostered by a broad and shallow (<˜150 m) upwelling of the eddy center between May and August. It appears likely that as Yakutat Eddies approach the shelfbreak non-linear processes will modify the slope flow field (and the stability and structure of the shelfbreak front), leading to cross-slope flows and flow reversals. This interaction may induce ˜30 km-wide streamers of shelf water to flow around the trailing edge of the anticyclone. The role of streamers in the freshwater and nutrient budgets of the GOA shelf and basin is unknown, but their contribution to these budgets will depend on the trajectory of a Yakutat Eddy, especially its proximity to the shelfbreak as the eddy propagates along the GOA continental slope.

Janout, Markus A.; Weingartner, Thomas J.; Okkonen, Stephen R.; Whitledge, Terry E.; Musgrave, David L.

2009-12-01

193

Ka-band propagation characteristics of microstrip lines on GaAs substrates at cryogenic temperatures  

Microsoft Academic Search

Effective permitivity and loss characteristics of gold microstrip lines on GaAs substrates were obtained by characterizing GaAs linear resonators at cryogenic temperatures (300 to 20 K) from 30-40 GHz. A slight decrease in effective permittivity and a significant reduction in loss were observed with lower temperatures.

R. R. Romanofsky; J. C. Martinez; B. J. Viergutz; K. B. Bhasin

1990-01-01

194

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

195

Propagation Characteristics of Shear-Horizontal-Type Surface Acoustic Wave on Langasite with Au or Ta2O5 Thin Film  

NASA Astrophysics Data System (ADS)

The propagation characteristics, mainly the propagation loss and bulk wave radiation loss, of a pure shear-horizontal-type surface acoustic wave on (0°, ?, 90°)-cut langasite with a high-density thin film such as a gold (Au) film or a tantalum pentoxide (Ta2O5) dielectric film were investigated experimentally. The cut angles ? of 0°, 10° and 20° were chosen because a coupling factor of 1.0% and a zero temperature coefficient of delay (TCD) can both be expected at approximately these cut angles. For the Au film, the propagation loss and bulk wave radiation loss were small at ?=10°.

Kakio, Shoji; Nozawa, Masaya; Nakagawa, Yasuhiko

2005-06-01

196

Propagation Characteristics and Mode Utilizability of Electromagnetic RF and Optical Surface Waves Travelling between a Pair of Metal Sheets  

NASA Astrophysics Data System (ADS)

Several characteristic features of electromagnetic (EM) surface waves propagating between a pair of planar conductors are disclosed analytically along with the other normal EM modes. The solutions are obtained on the basis of electron plasma oscillation in metals. The results are summarized as follows: (I) there exist primarily two independent surface waves (or optical surface waves), even and odd surface modes; (II) the odd surface mode (SWo) becomes a pure transverse electromagnetic (TEM) wave in the limiting case of an infinite value of electron density in metals; and (III) the even surface mode (SWe) will smoothly change to the even TM1e mode at a certain point of the dispersion curve. Utilizability of the lower modes is discussed for very-high-frequency RF and optical wave transmission lines and for long or large-area plasma production between planar electrodes.

Nonaka, Shigehiko

1993-06-01

197

Solitary waves and shocks in suprathermal plasmas modelled by the kappa distribution: existence and propagation characteristics from first principles (Invited)  

NASA Astrophysics Data System (ADS)

Space plasmas are often characterized by the presence of energetic particles in the background, e.g. due to various electron acceleration mechanisms [1]. This phenomenon is associated with a power-law dependence at high (superthermal) velocity values, modeled by a kappa-type distribution function, which reproduces observed data more efficiently that the standard Maxwellian distribution approach [2]. It has been shown from first principles that this ubiquitous superthermal feature of plasmas may alter the propagation characteristics of plasma modes, and modify the plasma screening properties [3]. We review, from first principles, of the effect of excess superthermality on the characteristics of electrostatic nonlinear plasma modes. We employ a kappa distribution function [1] to model the deviation of a plasma constituent (electrons, in general) from Maxwellian equlibrium. An excess in superthermal propulation modifies the charge screening mechanism, affecting the dispersion laws of both low- and higher frequency modes substantially. Various experimental observations may thus be interpreted as manifestations of excess superthermality [2]. Focusing on the features of nonlinear excitations (shocks, solitons), we investigate the role of superthermality in their propagation dynamics (existence laws, stability profile) and dynamical profile [3]. The relation to other nonthermal plasma theories is briefly discussed. [1] See V.M. Vasyliunas, J. Geophys. Res. 73, 2839 (1968), for a historical reference; also, V. Pierrard and M. Lazar, Solar Phys. 267, 153 (2010), for a more recent review. [2] M. Hellberg et al, J. Plasma Physics 64, 433 (2000). [3] S. Sultana, I. Kourakis, N.S. Saini, M.A. Hellberg, Phys. Plasmas 17, 032310 (2010); S. Sultana and I. Kourakis, Plasma Phys. Cont. Fus. 53, 045003 (2011); S. Sultana, G. Sarri and I. Kourakis, Phys. Plasmas 19, 012310 (2012); I. Kourakis, S. Sultana and M.A. Hellberg, Plasma Phys. Cont. Fusion, 54, 124001 (2012); G. Williams and I. Kourakis, Plasma Physics and Controlled Fusion 55, 055005/1-13 (2013).

Kourakis, I.; Hellberg, M. A.

2013-12-01

198

NASA Propagation Studies Website  

NASA Technical Reports Server (NTRS)

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

Angkasa, Krisjani S.

1996-01-01

199

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.

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

200

Characteristics of tropical cyclones and overshooting from GPS radio occultation data  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

201

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

NASA Technical Reports Server (NTRS)

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

Romanofsky, Robert R.

1989-01-01

202

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

203

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

204

Crack Propagation through Phase-Separated Glasses: Effect of the Characteristic Size of Disorder  

NASA Astrophysics Data System (ADS)

We perform fracture experiments on nanoscale phase-separated glasses and measure crack surface roughness by atomic force microscopy. The ability of tuning the phase domain size by thermal treatment allows us to test thoroughly the predictions of crack front depinning models about the scaling properties of crack surface roughness. It appears that, in the range of validity of these depinning models developed for the fracture of brittle materials, our experimental results show a quantitative agreement with theoretical predictions: Beyond the characteristic size of disorder, the roughness of crack surfaces obeys the logarithmic scaling early predicted by Ramanathan, Erta?, and Fisher [Phys. Rev. Lett. 79, 873 (1997)PRLTAO0031-900710.1103/PhysRevLett.79.873].

Dalmas, Davy; Lelarge, Anne; Vandembroucq, Damien

2008-12-01

205

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

206

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

207

Evaluation of Wave Propagation Properties during a True-Triaxial Rock Fracture Experiment using Acoustic Emission Frequency Characteristics  

NASA Astrophysics Data System (ADS)

A true-triaxial deformation experiment was conducted to study the evolution of wave propagation properties by using frequency characteristics of AE waveforms to diagnose the state of fracturing in a sample of sandstone. Changes in waveform frequency content has been interpreted as either the generation of progressively larger fractures or the relative attenuation of high-frequency wave components as a result of micro-crack formation. A cubic sample of Fontainebleau sandstone was initially loaded to a stress state of ?1 = ?2 = 35 MPa, ?3 = 5 MPa at which point ?1¬ was increased until failure. Acoustic emission (AE) activity was monitored by 18 PZT transducers, three embedded in each platen. The sensor amplitude response spectrum was determined by following an absolute source calibration procedure and showed a relatively constant sensitivity in the frequency range between 20 kHz and 1200 kHz. Amplified waveforms were continuously recorded at a sampling rate of 10 MHz and 12-bit resolution. Continuous acoustic emission waveforms were harvested to extract discrete events. Using a time-varying transverse isotropic velocity model, 48,502 events were locatable inside the sample volume. Prior to peak-stress, AE activity was associated with stable quasi-static growth of fractures coplanar with ?1 and ?2 located near the platen boundaries. In the post peak-stress regime, fracture growth displays unstable ¬dynamic propagation. Analysis of waveform frequency characteristics was limited to the pre peak-stress regime. Analysis of AE frequency characteristics was conducted on all 48,502 located AE events; each event file containing 18 waveforms of varied quality. If the signal to noise ratio was greater than 5, the waveforms power spectrum was estimated and the source-receiver raypath vector was calculated. The power spectrum of each waveform was divided into three frequency bands (Low: 100 - 300 kHz, Medium: 300 - 600 kHz and High: 600 - 1000 kHz) and the power in each band was calculated as a percentage of the total power within the 100-1000 kHz frequency band. The frequency band limits were carefully chosen to ensure that the component of power in each band was approximately equal in the early stages of the experiment. Next, issues related to the aperture effect were addressed. The frequency limit, above which there is azimuthal dependency, is a function of the sensing element diameter, the raypath azimuth (phi) and the P-wave velocity. Calculations indicated no significant aperture effect for 0 ? phi ? 60. All raypaths fitting these criteria were projected on a stereonet with the ratio of power held in the high frequency band (HF) to that held in the low frequency band (LF). Results show some underlying structure meaning that the HF/LF ratio is strongly dependent on raypath orientation. Transducer distortions and directionality effects were removed and source spectra corner frequencies were estimated to be above the frequency band of interest, suggesting the observed temporal and spatial changes in waveform frequency characteristics are a result of changing wave propagation properties (attenuation field) caused by progressive micro-crack formation.

Goodfellow, S. D.; Ghofrani Tabari, M.; Nasseri, M. B.; Young, R.

2013-12-01

208

The dispersion characteristics of the waves propagating in a spinning single-walled carbon nanotube  

NASA Astrophysics Data System (ADS)

As the nano-motor becomes a mechanical reality, its prototype can be envisaged as nano-sized rotating machinery at a situation, albeit for different purposes, like that in the first half of the 20th century during which rotor dynamics has contributed to boosting machine power capacity. Accordingly, we take the benefit of hindsight to develop a classical framework of vibration analysis. Essentially, the equations of motion are formulated to cope with both the special carbon-nanotube properties and the first author's previously developed spinning beam formalism, establishing a model satisfactorily verified by some available molecular dynamics (MD) data and classical spinning beam results extracted from the literature. The model is inexpensive based on continuum mechanics as an alternative to the less-flexible MD method for simulating wave motion of the spinning single-walled carbon nanotube, yielding several interesting phenomena, including the fall-off and splitting of the wave characteristic curves and the unexpected gyroscopic phase property. Potential applications are proposed.

Chan, K. T.; Zhao, Yapu

2011-10-01

209

The Mondrian Propagation Simulation Model  

Microsoft Academic Search

We present a propagation simulation model developed at TELECOM-ParisTech to assess performance of mobile radio networks. This model is consistent with the typical propagation model OSLN (one slope with log normal shadowing propagation model) considered by most authors. The new scheme, called Mondrian model, presents several interesting features: (i) it introduces correlations between powers measured on two nearby points, (ii)

Philippe Godlewski

2011-01-01

210

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

211

Characteristics of CMEs associated with solar flares and DH type II radio bursts based on source position  

NASA Astrophysics Data System (ADS)

We studied the characteristics of Coronal Mass Ejections (CMEs) associated with solar flares and Deca-Hectometric (DH) type II radio bursts, based on source position during 23rd solar cycle (1997-2007). We classified these CME events into three groups using solar flare locations as, (i) disk events (0-30?); (ii) intermediate events (31-60?) and (iii) limb events (61-90?). Main results from this studies are, (i) the number of CMEs associated with solar flares and DH-type IIs decreases as the source position approaches from disk to limb, (ii) most of the DH CMEs are halo (72%) in disk events and the number of occurrence of halo CMEs decreases from disk to limb, (iii) the average width and speed of limb events (164? and 1447 km s-1) are higher than those of disk events (134? and 1035 km s-1) and intermediate events (146? and 1170 km s-1) and (iv) the average accelerations for disk, intermediate and limb events are -8.2 m s-2, -10.3 m s-2 and -4.5 m s-2 respectively. These analysis of CMEs properties show more dependency on longitude and it gives strong evidence for projection effect.

Lakshmi, M. Anna; Umapathy, S.

2012-04-01

212

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

PubMed

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

Arie, Arenst Andreas; Lee, Joong Kee

2012-02-01

213

A comparison of conventional and radio frequency defrosting of lean beef meats: Effects on water binding characteristics  

Microsoft Academic Search

The effect of defrosting rate (slow conventional air vs. fast radio frequency (RF) method) on water holding properties of lean beef meat (whole, minced and comminuted) was investigated using a conventional centrifugation method (drip loss), nuclear magnetic resonance relaxometry (NMR) and dielectric spectroscopy. Tempering by radio frequency (RF) or a conventional air method had no subsequent effect (P?0.05) on drip

K. W. Farag; E. Duggan; D. J. Morgan; D. A. Cronin; J. G. Lyng

2009-01-01

214

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

Microsoft Academic Search

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

LEONARD KLEINROCK; FOUAD A. TOBAGI

1975-01-01

215

Research on propagation characteristic of radial array beams generated by radial array laser through misalignment optical system  

NASA Astrophysics Data System (ADS)

The analytical formula of radial array beams generated by radial array laser through misalignment of optical system is derived by using the diffraction integral equation. The propagation characteristics of radial array beams converged by the convergent optical system are studied. As the numerical examples, the influences of the two main parameters (the misalignment line deviation and angle deviation) on the light intensity are analyzed in detail. It is shown that the misalignment will lead to the increase of the light intensity of longitudinal lower-order Hermite-Gaussian beams (for example m=1, n=0), and the maximum light intensity (MLI) of the big misalignment (line deviation is 2 mm) is about 2 times higher than the small misalignment (line deviation is 1 mm). However, it will decrease for the transversal lower-order Hermite-Gaussian beams (for example m=0, n=1), and MLI of the small misalignment (line deviation is 1 mm) is about 2 times higher than the big misalignment (line deviation is 2 mm). The results are important for the laser rapid processing and high precision machining.

Xu, Yonggen

2014-06-01

216

Characteristics of carbon coatings on optical fibers prepared by radio-frequency plasma enhanced chemical vapor deposition with different H 2\\/C 2H 2 ratios  

Microsoft Academic Search

Characteristics of carbon coatings on optical fibers prepared by radio-frequency plasma enhanced chemical vapor deposition with different H2\\/C2H2 ratios are investigated. Five kinds of carbon coatings are prepared with H2\\/C2H2 ratios of 2, 4, 6, 8, and 10. Experimental results show that the deposition rate and surface roughness of carbon coatings decrease as the H2\\/C2H2 ratio increases. When the H2\\/C2H2

Hung-Chien Lin; Jen-Feng Yu; Sham-Tsong Shiue; Hung-Yi Lin

2010-01-01

217

Examination of Sub-Grid Technique for Simulation of Sound Wave Propagation Using Constrained Interpolation Profile Method with Method of Characteristics  

NASA Astrophysics Data System (ADS)

The constrained interpolation profile (CIP) method is a novel low-dispersive numerical scheme. It is a kind of method of characteristics (MOC). In our past study, we applied the CIP method to numerical analyses of sound wave propagation. For simulations of complicated heterogeneous media or large-scale simulations of wave propagation, a new grid system is indispensable. In this study, we examined a sub-grid technique for the CIP acoustic wave simulation. It is clarified that this technique has the advantages of its small memory requirements and less calculation time.

Ara, Yuta; Okubo, Kan; Tagawa, Norio; Tsuchiya, Takao; Ishizuka, Takashi

2011-07-01

218

Radar Characteristics of Precipitation of Different Nature, Spectra, Intensity and Temperatures in the Centimeter and Millimeter Ranges of Radio Waves.  

National Technical Information Service (NTIS)

The specific effective area of retrograde scattering and attenuation factors of radio waves in the centimeter and millimeter range, by rainfall at various temperatures and intensities were calculated. This quantitative data on the attenuating and reflecti...

N. P. Krasyuk V. I. Rozenberg D. A. Chistyakov

1969-01-01

219

Observations of beam propagation  

NASA Astrophysics Data System (ADS)

The observational evidence for propagating electron distributions in the solar corona as obtained from type III observations are discussed. The location of the beam acceleration region together with the effects of the ambient medium on beam propagation are discussed in the framework of recent observational and theoretical developments. The results of combined X-ray and radio observations obtained during and after the Solar Maximum Year are summarized. Special attention is paid to the effect of the small-scale structure of the corona on the observed radio emission. Various desirable developments which are necessary to improve the understanding of the behavior of charged particle beams in magnetized plasmas are outlined.

Pick, M.; van den Oord, G. H. J.

1990-12-01

220

Satellite sound broadcast propagation measurements and system impairments  

NASA Astrophysics Data System (ADS)

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

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

1992-03-01

221

Satellite sound broadcast propagation measurements and system impairments  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

222

NASA Propagation Studies Website  

NASA Technical Reports Server (NTRS)

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

Angkasa, Krisjani S.

1996-01-01

223

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

NASA Astrophysics Data System (ADS)

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

Zakamska, Nadia L.; Greene, Jenny E.

2014-07-01

224

Impulsiveness and energetics in solar flares with and without type II radio bursts - A comparison of hard X-ray characteristics for over 2500 solar flares  

NASA Technical Reports Server (NTRS)

The hard X-ray characteristics of more than 2500 solar flares are used to study the relative size, impulsiveness, and energetics of flares with and without type II radio bursts. A quantitative definition of the hard X-ray impulsiveness is introduced, which may be applied to a large number of events unambiguously. It is found that the flares with type II bursts are generally not significantly larger, more impulsive, or more energetic than those without type II bursts. Also, no evidence is found to suggest a simple classification of the flares as either 'impulsive' or 'gradual'. Because type II bursts are present even in small flares with relatively unimpulsive energy releases, it is concluded that changes in the ambient conditions of the solar atmosphere causing an unusually low Alfven speed may be important in the generation of the shock wave that produces type II radio bursts.

Pearson, Douglas H.; Nelson, Robert; Kojoian, Gabriel; Seal, James

1989-01-01

225

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

226

Study of the neutron noise transmission characteristics of nonmultiplying media in liquid-metal fast breeder reactors by neutron wave propagation technique  

Microsoft Academic Search

In this paper, an attempt has been made to investigate the noise transmission characteristics of nonmultiplying media of liquid-metal fast breeder reactors (LMFBRs) and study its implications on the detection of malfunctions in LMFBR cores by using out-of-core detectors and noise analysis methods. Neutron wave propagation technique has been used to study the problem by employing different approximations such as

T. M. John; C. P. Reddy; O. P. Singh

1982-01-01

227

Temperature effects on the propagation characteristics of Love waves along multi-guide layers of Sio2/Su-8 on St-90°X quartz.  

PubMed

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/SiO(2) 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

228

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.

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

2012-01-01

229

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

Microsoft Academic Search

In this paper case studies of propagation characteristics of two TIDs are presented which are induced by atmospheric gravity waves in the auroral F-region on a magnetic quiet day. By means of maximum entropy cross-spectral analysis of EISCAT CP2 data, apparent full wave-number vectors of the TIDs are obtained as a function of height. The analysis results show that the

S. Y. Ma; K. Schlegel; J. S. Xu

1998-01-01

230

Kinematics of ICMEs Deduced From Remote Radio Observations  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

231

Morphological and technological characteristics of silicon nitride powder prepared by self-propagating high-temperature synthesis  

Microsoft Academic Search

Silicon nitride produced by self-propagating high-temperature synthesis is ground in planetary and ball mills successively in both devices. The size distribution of particles, specific surface, shape factor, structure, and bulk density are evaluated. The behavior of powder pelletized with synthetic rubber under compaction and sintering in a nitrogen atmosphere in a charge containing magnesium oxide is studied. Powder after ball

S. Yu. Sharivker; I. P. Borovinskaya; G. A. Vishnyakova; Yu. N. Barinov; A. S. Mukas'yan; A. M. Knyazik

1992-01-01

232

Design optimization of tunneling field-effect transistor based on silicon nanowire PNPN structure and its radio frequency characteristics  

Microsoft Academic Search

Recently, a number of semiconductor devices have been widely researched in order to make breakthroughs from the short-channel effects (SCEs) and high standby power dissipation of the conventional metal-oxide-semiconductor field-effect transistors (MOSFETs). In this paper, a design optimization for the silicon nanowire tunneling field-effect transistor (SNW TFET) based on PNPN multi-junction structure and its radio frequency (RF) performances are presented

Seongjae Cho; In Man Kang

233

Characteristics of a compression wave propagating over porous plate wall in a high-speed railway tunnel  

NASA Astrophysics Data System (ADS)

A pressure wave is generated ahead of a high-speed train, while entering a tunnel. This pressure wave propagates to the tunnel exit and spouts as a micro-pressure wave, which causes an exploding sound. From the fact that the ballast track tunnel has smaller noise than the slab track tunnel, we have suggested a new inner tunnel model to decrease the noise of the micro-pressure wave, using the ballast effect. Experimental and numerical investigations are carried out to clarify the attenuation and distortion of propagating compression wave over porous plate wall in a model tunnel. Data shows that the strength of the compression wave and a maximum pressure gradient of the compression wave was weakened. These data shows the possibility of the present alleviative method using the porous plate wall in a tunnel.

Aoki, T.; Yamamoto, J.; Nagatani, K.

2008-09-01

234

Effect of auxin treatments, cuttings’ collection date and initial characteristics on Paeonia ‘Yang Fei Chu Yu’ cutting propagation  

Microsoft Academic Search

Paeonia ‘Yang Fei Chu Yu’ is one of the most popular and commercially valuable cultivars of herbaceous peony. The study was performed to explore propagation techniques by cuttings for the nursery industry. Results showed that the stem cuttings pretreated with 2000mgL?1 indole-3-butyric acid (IBA) in quick-dip method got the best rooting traits (rooting percentage is 86.7%, root number is 23.1

XianFeng Guo; XiLing Fu; DeKui Zang; Yan Ma

2009-01-01

235

Propagation characteristics of Pi 2 pulsations observed at high- and low-latitude MAGDAS\\/CPMN stations: A statistical study  

Microsoft Academic Search

The objective of this study is to understand better the propagation of Pi 2 waves in the nighttime region. We examined Pi 2 oscillations that showed high correlation between high- and low-latitude Magnetic Data Acquisition System\\/Circum Pan-Pacific Magnetometer Network stations (correlation coefficient: ??? ? 0.75). For each horizontal component (H and D) we examined the magnetic local time (MLT) dependence

Teiji Uozumi; S. Abe; K. Kitamura; T. Tokunaga; A. Yoshikawa; H. Kawano; R. Marshall; R. J. Morris; B. M. Shevtsov; S. I. Solovyev; D. J. McNamara; K. Liou; S. Ohtani; M. Itonaga; K. Yumoto

2009-01-01

236

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

237

A comparison of conventional and radio frequency defrosting of lean beef meats: Effects on water binding characteristics.  

PubMed

The effect of defrosting rate (slow conventional air vs. fast radio frequency (RF) method) on water holding properties of lean beef meat (whole, minced and comminuted) was investigated using a conventional centrifugation method (drip loss), nuclear magnetic resonance relaxometry (NMR) and dielectric spectroscopy. Tempering by radio frequency (RF) or a conventional air method had no subsequent effect (P?0.05) on drip loss. However, thawing by RF resulted in a significant decrease in drip loss (P<0.05) when compared to air thawing. Micronutrient loss (?g/mL of drip) was also greater in air thawed samples (P<0.05). NMR T(2) distributions did not show any marked difference between thawing methods. The dielectric properties of lean beef, measured from 0.01-20GHz at 5°C, were higher following RF thawing. Increased comminution reduced dielectric values, while fine comminution gave an additional fraction in the NMR T(2) distribution. These results provide valuable information on water binding in meat following RF tempering/thawing. PMID:20416737

Farag, K W; Duggan, E; Morgan, D J; Cronin, D A; Lyng, J G

2009-10-01

238

Frequency Correlation in Tropospheric Propagation.  

National Technical Information Service (NTIS)

The theoretical correlation of signals with varying frequency spacing for propagation through the troposphere is considered. It seems that certain conclusions on the signal propagation paths can be drawn from the correlation characteristics. The report th...

L. Jonasson

1971-01-01

239

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

240

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.

TSUDA, Toshitaka

2014-01-01

241

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

PubMed

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

Tsuda, Toshitaka

2014-01-01

242

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

243

Aperture Antenna Effects After Propagation through Strongly Disturbed Random Media.  

National Technical Information Service (NTIS)

A strongly disturbed layer of ionization irregularities that is used as a propagation channel for radio waves can degrade the propagating wave and thereby affect the resulting measurements at the receiving antenna. The antenna aperture itself also affects...

D. L. Knepp

1984-01-01

244

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

245

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

NASA Technical Reports Server (NTRS)

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

Earl, J. A.

1975-01-01

246

Simple instruments in radio astronomy  

NASA Astrophysics Data System (ADS)

Radio astronomy has a major role in the study of the universe. The spiral structure of our Galaxy and the cosmic background radiation were first detected, and the dense component of interstellar gas is studied, at radio wavelengths. COBE revealed very weak temperature fluctuations in the microwave background, considered to be the seeds of galaxies and clusters of galaxies. Most electromagnetic radiation from outer space is absorbed or reflected by the Earth's atmosphere, except in two narrow spectral windows: the visible-near-infrared and the radio, which are nearly transparent. Centimetre and longer radio waves propagate almost freely in space; observations of them are practically independent of weather. Turbulence in our atmosphere does not distort the wavefront, which simplifies the building of radio telescopes, because no devices are needed to correct for it. Observations at these wavelengths can be made in high atmospheric humidity, or where the sky is not clear enough for optical telescopes. Simple instruments operating at radio wavelengths can be built at low cost in tropical countries, to teach students and to familiarize them with radio astronomy. We describe a two-antennae radio interferometer and a single-dish radio telescope operating at centimetre wavelengths. The Sun and strong synchrotron radio-sources, like Cassiopeia A and Cygnus A, are potential targets.

Nguyen-Quang-Rieu

247

Radio broadcasting via satellite  

NASA Astrophysics Data System (ADS)

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

Helm, Neil R.; Pritchard, Wilbur L.

1990-10-01

248

Propagation characteristics of an optoelectronically reconfigurable waveguide with an infinite periodic slot array with an eletcrically short period  

Microsoft Academic Search

In this study, propgation characteristics of electromagnetic waves in a dielectric waveguide with an infinite periodic slot array with an elecrically shot period are analyzed using mode matching technique, when the apertures of the slot array are filled with a semiconductor illuminated with light at an interval of an integer time the period of the slot array. Bragg Interaction and

Kazuo Nishimura

2011-01-01

249

[Water cultured propagation of Polygonum multiflorum and dynamic changes of physiological and biochemical characteristics during adventitious roots formation].  

PubMed

Water cultured propagation technology of Polygonum multiflorum was investigated with Rooting Powder No. 2 (ABT 2) comparison experiments, and the dynamic changes of endogenous hormones including indole acetic acid (IAA), abscisic acid (ABA), zeatin riboside (ZRs) contents and activities of indoleacetic acid oxidase (IAAO), polyphenol oxidase (PPO) were analyzed during rooting period. The results showed that rooting percentage of softwood cutting with 50 mg x L(-1) ABT2 and 10 mg x L(-1) ABT2 + 0.2% Urea + 0.2% KH2PO4 treatments was 94%, rooting percentage of softwood cuttings of control was 46% only. The adventitious rooting displayed three distinct phases i. e. root-inducing, root formation and root-elongating phases. The dynamic changes of contents of endogenous plant hormones (IAA, ABA, ZRs) and activities of IAAO, PPO tested were tightly related to the rooting process of soft-wood cuttings in P. multiflorum. During root-inducing phase the contents of IAA, ABA and ZRs decreased sharply, whereas ZRs content and IAAO activity kept higher level. IAA content reached the peak and PPO activity increased obviously during root formation phase, while IAAO activities and ABA, ZRs contents declined to minimum. During root-elongating phase PPO, IAAO activities were higher and IAA, ABA, ZRs contents kept steady. During rooting ABT2 (50 mg x L(-1)) treatment increased the content of IAA and PPO activity in cuttings, while the opposite result occurred in contents of ZRs, ABA and IAAO activity. PMID:21585047

Gao, Jie; Liu, Xiaohui; Yuan, Yike

2011-02-01

250

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

251

Characteristics of atmospheric gravity wave activity in the polar regions revealed by GPS radio occultation data with CHAMP  

NASA Astrophysics Data System (ADS)

Using GPS radio occultation data during 2001-2005, we studied the climatological behavior of atmospheric gravity waves in the polar stratosphere. We calculated temperature fluctuations with vertical wavelengths shorter than 7 km and then determined the wave potential energy, E p , every month in a longitude-latitude cell of 20° × 10° between 12 km and 33 km. In the Arctic region (50-90°N), E p shows an annual variation with maximum in winter, consistent with the zonal mean horizontal wind, V, and the Eliassen-Palm (E-P) flux, F z . The large F z values indicate higher planetary wave activity, resulting in distortion of the polar vortex. The unbalanced flow can then excite gravity waves through geostrophic adjustment. In the Antarctic region (50-90°S), E p gradually increases during winter and reaches its maximum in spring before decreasing rapidly. The time derivative of V coincides with the E p peak and the horizontal distribution of E p has a similar structure to V, suggesting that the E p enhancement is closely related to the decay of the polar vortex. During major warming events over the Arctic, the divergence of E-P flux, ?F, was enhanced, coinciding with large E p . In the Antarctic, ?F strongly correlates with E p in spring. Gravity waves seem to be effectively generated through planetary wave transience and/or breaking. Orographic generation of gravity waves seems to be important in limited areas only, such as Scandinavia and the Antarctic Peninsula, showing that it is less important than the polar night jet in determining the climatological behavior of gravity waves.

Hei, Hayato; Tsuda, Toshitaka; Hirooka, Toshihiko

2008-02-01

252

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

253

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

254

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

255

Study of the spectral characteristics of a femtosecond Ti:sapphire laser after propagation of its radiation through a tapered fibre  

SciTech Connect

The method and results of precision measurements of the intermode frequency of a Ti:sapphire laser after the propagation of its radiation through a tapered optical fibre are described. It is shown that the stability of the intermode frequency is impaired by half at short averaging times (10 s) and by a factor of 1.1 at long averaging times (1000 s). The results of investigations of the spectrum of a femtosecond Ti:sapphire laser, which is broadened in a tapered optical fibre are presented. It is shown that, by varying the fibre parameters and the characteristics of input pulses, the envelope of the broadened spectrum can be profiled, which is important for practical applications. (control of laser radiation parameters)

Bagayev, S N; Denisov, V I; Zakharyash, Valerii F; Klementyev, Vasilii M; Korel', I I; Kuznetsov, Sergei A; Pivtsov, V S; Chepurov, S V [Institute of Laser Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk (Russian Federation)

2003-10-31

256

CONTROL OF LASER RADIATION PARAMETERS: Study of the spectral characteristics of a femtosecond Ti:sapphire laser after propagation of its radiation through a tapered fibre  

NASA Astrophysics Data System (ADS)

The method and results of precision measurements of the intermode frequency of a Ti:sapphire laser after the propagation of its radiation through a tapered optical fibre are described. It is shown that the stability of the intermode frequency is impaired by half at short averaging times (10 s) and by a factor of 1.1 at long averaging times (1000 s). The results of investigations of the spectrum of a femtosecond Ti:sapphire laser, which is broadened in a tapered optical fibre are presented. It is shown that, by varying the fibre parameters and the characteristics of input pulses, the envelope of the broadened spectrum can be profiled, which is important for practical applications.

Bagayev, S. N.; Denisov, V. I.; Zakharyash, Valerii F.; Klementyev, Vasilii M.; Korel', I. I.; Kuznetsov, Sergei A.; Pivtsov, V. S.; Chepurov, S. V.

2003-10-01

257

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

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

258

Radio-Frequency Characteristics of the Coaxial Step-Disk-Loaded Slow-Wave Structure for Relativistic Travelling Wave Tubes  

Microsoft Academic Search

We present a new periodic all-metal slow wave structure, a coaxial step-disc-loaded system and the dispersion characteristics of the structure. By using the field-matching method, the dispersion equation and the coupling impedance of this structure are obtained. The coaxial structure makes the bandwidth broader than that of the non-coaxial one. Compared with the coaxial disc-loaded and ridged-disc-loaded structures, the pass-band

Ling-Na Yue; Wen-Xiang Wang; Yan-Yu Wei; Yu-Bin Gong

2005-01-01

259

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

260

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

USGS Publications Warehouse

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

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

1997-01-01

261

A crack initiation and propagation simulation and the fatigue characteristics of solder joints considering the material property changes  

NASA Astrophysics Data System (ADS)

The re-working of the manufacturing process from the reliability evaluation after the production process is a significant cost and loss of energy. In-vehicle electronic devices are exposed to multiple environmental loads such as thermal and vibrational loads. The effects of the material property changes in the thermal cycle load on the fatigue life of solder joints were estimated with our fatigue simulation for the purpose of constructing a design method considering the fatigue characteristic changes in the thermal cycle. The fatigue lives were estimated with and without considering the creep property changes measured by indentation tests. The fatigue ductility index and the coefficients increased toward the reported values by considering the creep property changes.

Matsushima, M.; Shishihara, Y.; Matsunami, H.; Fukumoto, S.; Fujimoto, K.

2012-08-01

262

NASA Propagation Program Status and Propagation Needs of Satcom Industry  

NASA Technical Reports Server (NTRS)

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

Golshan, Nassar

1996-01-01

263

Compatible Radio Controlled Clock Technology for Radio Broadcasting Data Transceiver  

Microsoft Academic Search

Radio controlled clock (RCC) is a kind of time measuring technique that uses wireless radio to transmit time signals, purposing on synchronizing the signals of wireless receivers and solving the precision and synchronization problems of clocks between different ranges. This paper has thoroughly analyzed the transmitting characteristics and the encoding principle of RCC and based on the existing technique, a

Kuang-Hao Lin; Kuang-Hui Tang; Shi-Yan Huang; Jan-Dong Tseng

2012-01-01

264

Indoor radio communications for factories of the future  

Microsoft Academic Search

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

Theodore S. Rappaport

1989-01-01

265

Complex Experimental Evaluation of the Characteristics of Propagation of HF Signals Along Midlatitude Paths of Different Length and Orientation  

NASA Astrophysics Data System (ADS)

We outline a complex approach for measuring distance-frequency, angular, spectral, and statistical characteristics of HF signals and present the results of experimental studies of the turbidity coefficient, frequency-spread bandwidth, variations in the Doppler frequency shift, bearing, and elevation angle in a wide frequency range for the Khabarovsk-Rostov-on-Don, Moscow-Rostov-on-Don, and Cyprus-Rostov-on-Don sounding paths under various geophysical conditions. It is shown that the most probable values of the turbidity coefficient for one-hop paths in the afternoon range from 2 to 4. The turbidity coefficient decreases to about 0.6 in the twilight hours. The turbidity coefficient tends to decrease with the path length. The average frequency-spread bandwidth at the 95% level of the received signal power is found to be minimal for illuminated path and does not exceed a value from 0.1 to 0.3 Hz. The frequency-spread bandwidth increases in the sunset hours or under nonuniform illumination, but does not exceed 4 Hz. We estimated the range of Doppler frequency shift variations which are due mainly to the influence of medium-scale traveling ionospheric disturbances and do not exceed 2 Hz in the experiments. The method of one-position location of a radiation source is tested by the results of angular measurements on the basis of the IRI-2001 ionospheric model.

Vertogradov, G. G.; Myatezhnikov, Yu. P.; Uryadov, V. P.; Rozanov, S. V.

2004-01-01

266

Modification of Tropospheric Propagation Conditions.  

National Technical Information Service (NTIS)

The propagation mechanisms of ultra-short radio waves and microwaves (10 m - 1 mm) are governed by the composition of the troposphere and their space-time structure of the refractive index field. After a short discussion of the natural environmental param...

H. Jeske

1990-01-01

267

Radio sociology  

NASA Astrophysics Data System (ADS)

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

Swenson, George W., Jr.

1996-04-01

268

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

SciTech Connect

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

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

2010-05-15

269

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

270

Characteristic study of a radio-photoluminescence glass rod detector for clinical usages: Skin and inner body in-vivo verification  

NASA Astrophysics Data System (ADS)

Recently, the radio-photoluminescence glass dosimeter (RPLGD) was introduced as a substitute for the thermo-luminescence dosimeter, which had been commonly used for in-vivo measurements. In this study, a new RPLGD was introduced and its characteristics as a dosimeter for clinical usage. were evaluated. The reproducibility, dose linearity, angular dependency, small-field response, and energy dependency were estimated using an RPLGD. Furthermore, the uncertainties with the RPLGD for clinical usages (head and neck, and prostate cases) were evaluated with both phantoms and actual patients. We measured -1.1 ± 2.4, 1.9 ± 2.3, 2.3 ± 0.5, and 2.2 ± 3.0% as the uncertainties of dose linearity, accumulate dose linearity, reproducibility, and detector response, respectively. We found that the uncertainty of the dose response increased rapidly for sizes smaller than 1.4 × 1.4 cm2 and that when used for surface dosimetry, the RPLGD had an angular dependency. We measured -1.2 ± 2.7% and -1.7 ± 2.7% dose differences for silicon and for poly(methyl methacrylate) phantoms. The dose differences on the surface of the tongue for tongue cancer, and on the wall of the rectum wall, for prostate cancer, were measured as 3.7 ± 3.1% and 2.7 ± 4.4%, respectively.

Chung, Weon Kuu; Kim, Dong Wook

2013-02-01

271

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

272

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

273

Density Structure of the Solar Corona From Radio Occultation Measurements  

Microsoft Academic Search

Starting with angular broadening measurements five decades ago, a wide variety of radio propagation and scattering phenomena have been observed when natural radio sources or spacecraft radio signals happened to pass behind or were occulted by the solar corona. While yielding information on density, velocity and magnetic fields, these unique measurements probe density most directly, and with unprecedented sensitivity, spatial

R. Woo

2003-01-01

274

College Radio.  

ERIC Educational Resources Information Center

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

Sauls, Samuel J.

275

Radio Memories  

NSDL National Science Digital Library

The "Golden Age of Radio" that arguably lasted until the early 1950s may be hard to imagine today in an era of swirling iPod playlists and other genre-bending devices and technologies, but during this time the radio reigned supreme. People tuned in every week to hear the exploits of Flash Gordon, Sam Spade, and Amos n' Andy. Thanks to the Radio Memories website, many of these memories can be relived, or just experienced for the first time. Started in May 2005, the site contains a host of compelling programs, including episodes from the Interplanetary Adventures of Flash Gordon and a number of original episodes of the fabled Radio Detective Story Hour. If those types of programs fail to pique the interest of the casual visitor, the site also contains archived shows that explore the world of radio soap operas from the 1940s and the musical worlds of such stars as Tommy Dorsey and Harry James.

276

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

277

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

278

Simulation studies of GPS radio occultation measurements  

Microsoft Academic Search

Abstract. 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 spheri- cally symmetric refractivity field derived from a high-resolution radio sonde observation. The propagated signals are tracked by GPS receivers implemented in software and converted to refractivity profiles by the canonical

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

2002-01-01

279

Simulation studies of GPS radio occultation measurements  

Microsoft Academic Search

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

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

2003-01-01

280

Specific features of variations in the characteristics of VLF signals when the lunar shadow propagated along the path during the solar eclipse of March 29, 2006  

Microsoft Academic Search

The effects of the solar eclipse of March 29, 2006, in the signals of ULF radio stations, in the intensity of regular radio\\u000a noise at frequencies of 0.3–10 kHz, and in the number of atmospherics received in Yakutsk mostly from the west have been considered.\\u000a The observations were performed using a multichannel parallel analyzer-recorder (11 channels in the frequency band

R. R. Karimov; V. I. Kozlov; V. A. Mullayarov

2008-01-01

281

On-Body Antennas and Propagation: Recent Development  

NASA Astrophysics Data System (ADS)

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 wearable sensor antenna design is presented and it is demonstrated that a global simulation including sensor environment and human body is needed for accurate antenna characterisation. A 3D animation design software, POSER 6 has been used together with XFDTD to predict the on-body path loss variation due to changes in human postures and human motion. Finally, a preliminary study on the feasibility of a diversity scheme in an on-body environment has been carried out.

Hao, Yang; Hall, Peter S.

282

Propagation without wave equation toward an urban area model  

Microsoft Academic Search

Propagation in random media is a topic of great interest, whose application fields include, among others, the so-called last mile problem as well as the modeling of dense urban area radio communication channels. A simple scenario for this issue is considered, with an optical-ray propagation across a medium of disordered lossless scatterers. The propagation medium behaves like a percolating lattice

Giorgio Franceschetti; Stefano Marano; Francesco Palmieri

1999-01-01

283

The Deep Space Network as an instrument for radio science research  

Microsoft Academic Search

Radio science experiments use radio links between spacecraft and sensor instrumentation that is implemented in the Deep Space Network. The deep space communication complexes along with the telecommunications subsystem on board the spacecraft constitute the major elements of the radio science instrumentation. Investigators examine small changes in the phase and\\/or amplitude of the radio signal propagating from a spacecraft to

S. W. Asmar; N. A. Renzetti

1993-01-01

284

An Interference Cancellation Scheme for Mobile Communication Radio Repeaters  

NASA Astrophysics Data System (ADS)

An interference cancellation (ICAN) scheme for mobile communication radio repeaters is presented. When a radio repeater has a gain that is larger than the isolation between its transmit and receive antennas, it oscillates due to feedback interference signals. To prevent feedback oscillation of a radio repeater, we first formulate a feedback oscillation model of the radio repeater and then derive an ICAN model from that model. From the derived ICAN model, we show that the stability and the signal quality of the repeater depend on the repeater's gain and delay, the propagation delay on feedback paths, feedback channel characteristics, and the capability of the feedback channel estimation algorithm. It is also shown that the stability condition of the repeater does not guarantee the quality of the repeater's output signal. To guarantee repeater's stability and signal quality, an ICAN scheme based on an iterative algorithm is subsequently proposed. The simulation results confirm the relationship between the stability and signal quality of the repeater and the impact of the aforementioned factors. Using the proposed ICAN scheme, a mean error vector magnitude (quality indicator) of about 6.3% for the repeater's output signal was achieved.

Lee, Moohong; Keum, Byungjik; Shim, Young Serk; Lee, Hwang Soo

285

From Millihertz to Tetrahertz: Radio Waves in Marine Communication and Navigation.  

National Technical Information Service (NTIS)

Classification of radio waves by their manner of propagation is discussed including the influence of the earth's magnetic field on this process. Radio waves of specific frequency ranges are also examined with special attention to the applications of ultra...

M. P. Dolukhanov

1971-01-01

286

Characteristics of nighttime West-to-East VLF waves propagation using the South America VLF Network (SAVNET): Application of the Terminator Time method to Earthquake detection  

NASA Astrophysics Data System (ADS)

We present the monitoring of ~5 years of daily VLF amplitude curves using two parallel propagation paths from the South America VLF Network (SAVNET). During this period, the time of occurrence (Teminator Times) of deep amplitude minima were measured. We discuss typical properties of West-to-East VLF subionospheric propagation like the seasonal effect on the temporal evolution of Terminator Times, the fact that they are simultaneously detected on parallel propagation paths, and the derivation of the undisturbed nighttime ionospheric height. We will also show that he method known as the Terminator Time is also a promising way of looking for possible seismic-electromagnetic effects.

Raulin, Jean Pierre; Samanes Cardenas, Jorge

2012-07-01

287

Track Telemetering Propagation Study.  

National Technical Information Service (NTIS)

The report describes the telemetry propagation characteristics of the AFMDC test track when operated at L and S-band frequencies, and based on this data, an estimate of the cost of changing to these bands from the present 800 MHz band is presented. The re...

D. B. Davis N. C. MacLeod

1966-01-01

288

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

289

Analysis of the effects of a resistively coated upper dielectric layer on the propagation characteristics of hybrid modes in a waveguide-shielded microstrip using the method of lines  

Microsoft Academic Search

In this paper, propagation characteristics of even-symmetric hybrid modes in a waveguide-shielded microstrip in the presence of a resistively coated dielectric layer affixed to the top cover of the housing is analyzed with the method of lines. The resistive boundary condition is employed to model the resistive film. A shielded microstrip line having a unity strip-width-to-substrate-thickness ratio (i.e., w\\/h 1=1)

Shyh-Jong Chung; Lin-Kun Wu

1993-01-01

290

A database for propagation models  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

291

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

PubMed

The paper presents a subject-specific radio propagation study and system modeling in wireless body area networks using a simulation tool based on the parallel finite-difference time-domain technique. This technique is well suited to model the radio propagation around complex, inhomogeneous objects such as the human body. The impact of different digital phantoms in on-body radio channel and system performance was studied. Simulations were performed at the frequency of 3-10 GHz considering a typical hospital environment, and were validated by on-site measurements with reasonably good agreement. The analysis demonstrated that the characteristics of the on-body radio channel and system performance are subject-specific and are associated with human genders, height, and body mass index. Maximum variations of almost 18.51% are observed in path loss exponent due to change of subject, which gives variations of above 50% in system bit error rate performance. Therefore, careful consideration of subject-specific parameters are necessary for achieving energy efficient and reliable radio links and system performance for body-centric wireless network. PMID:22147331

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

2012-03-01

292

Phenomenology of magnetospheric radio emissions  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

293

Analysis of the defocusing of radio waves in the inosphere due to the influence of an intense radio-frequency radiation field  

Microsoft Academic Search

This paper reports on strong attenuation of probe radio waves that have been observed when the waves propagate through the ionosphere as it is being disturbed by an intense radio wave. Experimental results are compared with theory. The effect observed is shown to be due to the defocusing of the probe wave propagating through an artificial ionospheric lens which is

G. N. Boiko; Y. S. Dimant; S. F. Golyan; A. V. Gurevich; V. Y. Kim; V. V. Vaskov; V. A. Zyuzin

1986-01-01

294

Spacecraft Radio Scintillation and Solar System Exploration  

NASA Technical Reports Server (NTRS)

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

Woo, Richard

1993-01-01

295

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

296

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

297

UHF Radio Wave Attenuation Factor Database  

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

298

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

NASA Technical Reports Server (NTRS)

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

Davarian, Faramaz (editor)

1993-01-01

299

Investigation of the time characteristics of fluctuations of the phases of optical waves propagating in the bottom layer of the atmosphere  

Microsoft Academic Search

It is shown that heterodyning by means of a reference signal that is phase modulated by a harmonic wave allows the amplitude and phase fluctuations of optical radiation propagating in a turbulent atmosphere to be separated. The performed experiments show that the phase fluctuations actually are governed by a Gaussian law; a correlation hmction of the phase fluctuations exists having

V. P. Lukin; V. V. Pokasov; S. S. Khmelevtsov

1972-01-01

300

Surface elastic-wave propagation and amplification  

Microsoft Academic Search

Surface elastic-wave propagation, transduction, and amplification (in a piezoelectric semiconductor) are discussed with emphasis on characteristics useful in electronic devices. Computed curves show the dependence on distance from the surface of the elastic and the electric fields associated with surface elastic-wave propagation in cadmium sulfide. The interaction impedance, relating the external electric field to power flow, is computed for propagation

RICHARD M. WHITE

1967-01-01

301

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

302

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

303

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

304

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

SciTech Connect

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. (NSF, Washington, DC); Price, R.M. (New Mexico, University, Albuquerque, NM)

1981-08-01

305

Plane wave pulse propagation through random media  

Microsoft Academic Search

The theory of plane wave pulse propagation through a random medium, under the forward-scattering assumption is presented. Since pulse propagation characteristics are determined by two-frequency mutual coherence functionGamma, a set of normalized curves is given forGammafor different propagation parameters (operating frequency, propagation distance, turbulence strength or density of scatterers, etc.). From the curves one can obtain the coherence bandwidth of

Shin Hong; I. Sreenivashiah; A. Ishimaru

1977-01-01

306

A New Method for SNR and Doppler Shift Estimation in Wireless Propagations  

Microsoft Academic Search

Recently, thanks to the development of wireless communications, radio propagation plays an important role in the research of electromagnetic wave. Furthermore, signal-to-noise ratio (SNR) and Doppler shift of radio propagations receive many attentions due to their comprehensive use in adaptive reception. Hence with the help of double sampling rate (DSR) technique, this paper presents a new estimator to estimate the

J. Hua; L. Meng; Z. Xu; D. Wang

2007-01-01

307

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

308

The occurrence and propagation characteristics of large-scale atmospheric gravity waves observed by OH and OI airglow and GPS TEC during the substorms  

NASA Astrophysics Data System (ADS)

Using the data of hydroxyl OH and atomic oxygen OI airglow observations of three-field photometer from the University of Adelaide s Buckland Park and the data of GPS global position system total electronic content TEC employed by IGS web site we report the statistical study of propagation of TIDs and atmospheric gravity waves AGWs over Adelaide 34 5 r S 138 5 r E Australia Both of the airglow and TEC data are selected over the years from 1995 to 2002 and the observations of 557 7 nm airglow intensity emitted by OI at heights about 97km while the 730 0 nm airglow intensity emitted by OH about 87 km The propagation and variation features of TIDs and AGWs associated with substorms is analyzed This paper also presents a preliminary analysis of the coupling relation between the TIDs and AGWs

Jiang, Kui; Ding, Feng; Wan, Weixing; Reid, I. M.; Woith, J. M.

309

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

Microsoft Academic Search

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

Kai Wang; Aitao Zhou; Jianfang Zhang; Pin Zhang

310

Ground Wave Propagation over Arctic Sea Ice.  

National Technical Information Service (NTIS)

Radio ground wave propagation in the Arctic Ocean occurs over mixed paths. The mixed paths include layered or homogeneous sea ice and sea water. Amplitude and phase variations occurring as 'dropoff' or 'recovery' effects at the ice-sea water boundaries pr...

A. W. Biggs

1970-01-01

311

Recent progress in duct propagation predictions  

Microsoft Academic Search

Attention is given to enhanced radio fields that are encountered in the presence of trapping or ducting atmospheric refractivity gradients either aloft or at or near the surface. Recent progress in the theoretical formulation of ducted fields is summarized, covering topics such as, propagation via the atmospheric layers, duct geometry and ray theory, duct-theory relationships, and occurrences. Some resulting expressions

H. T. Dougherty; B. A. Hart

1979-01-01

312

A New Approach to Performance analysis of Point-To-Point Radio Links at Frequencies above 70 GHz  

NASA Astrophysics Data System (ADS)

In this paper we discuss high throughput fixed point-to-point radio links in frequency bands above 70 GHz. These links are interesting as a commercial alternative to fiber connections in IP computer networks. Characteristics of equipment used for radio transmission above 70 GHz are presented. As rain is being the predominant propagation effect that causes link outages, standard rain model is described. Performance analysis in the case of adaptive radio equipment is presented. A new approach to point-to-point radio link performance analysis, that uses two dimensional rain cell models and performance criterion based on end-user experience, is proposed. This approach is compared with the standard point-to-point radio link performance analysis procedure, based on calculation of percentage of time when link is unavailable and percentage of time when link has reduced capacity. It is shown on characteristic examples that proposed performance analysis gives better insight into how rain event would really affect end-user.

Peri?, Miroslav V.; Peri?, Dragana B.; Todorovi?, Branislav M.

2012-01-01

313

Cassini/RPWS: A low frequency radio imager at Saturn  

NASA Astrophysics Data System (ADS)

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

Cecconi, Baptiste; Lamy, Laurent; Zarka, Philippe

2014-05-01

314

Decision Feedback Equalization of Dispersive Radio Channels  

Microsoft Academic Search

The performance of adaptive decision feedback equalization applied to high bit rate digital radio systems in the presence of multipath propagation is analytically investigated. Minimum phase (MP) and nonminimum phase (NMP) type fades as well as the transition periods between these two states are considered. Insight is given into the IF recovered timing epoch and its consequences on the decision

ALNN LECLERT; P. Vandamme

1985-01-01

315

Distributed Antennas for Indoor Radio Communications  

Microsoft Academic Search

The idea of implementing an indoor radio communications system serving an entire building from a single central antenna appears to be an attractive proposition. However, based on various indoor propagation measurements of the signal attenuation and the multipath delay spread, such a centralized approach appears to be limited to small buildings and to narrow-band FDMA-type systems with limited reliability and

A. Saleh; A. Rustako; R. Roman

1987-01-01

316

Comparative statistical analysis of indoor positioning using empirical data and indoor radio channel models  

Microsoft Academic Search

Indoor geolocation using maximum likelihood algorithms applied to the measured reference radio map of the received signal strength (RSS) in indoor areas has attracted tremendous attention in the recent published literature. In this paper we examine generation of reference radio maps using two different radio propagation models to replace on site measurements for calibration of these indoor geolocation systems. The

Ahmad Hatami; Kaveh Pahlavan

2006-01-01

317

Radio tracking system  

Microsoft Academic Search

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

J. C. Breidenthal; T. A. Komarek

1982-01-01

318

Global morphology of infrasound propagation  

Microsoft Academic Search

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

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

2003-01-01

319

Radio Continuum Emission from FS CMa Stars  

NASA Astrophysics Data System (ADS)

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

Rodríguez, L. F.; Báez-Rubio, A.; Miroshnichenko, A. S.

2012-04-01

320

Effects of magneto-ionic propagation on the polarization scattering matrix  

Microsoft Academic Search

Magneto-ionic propagation effects are considered at radio frequencies that are sufficiently high so that there is negligible physical separation between the ordinary and extraordinary propagation paths. It is recognized that the sensible magneto-ionic propagation effects are birefringence and Faraday rotation. A matrix representation for magneto-ionic propagation is employed in order to facilitate the determination of the effects of magneto-ionic propagation

S. H. Bickel; R. H. T. Bates

1965-01-01

321

Multiple Scientific Uses of Radio Occultation  

NASA Astrophysics Data System (ADS)

Global Navigation Satellite System Radio Occultation Workshop; Pasadena, California, 7-9 April 2009; There is a clear need for observing systems that characterize decadal-scale changes of the climate system. A National Research Council (NRC) report, “Earth science and applications from space” (2007); recommends the radio occultation (RO) technique to monitor climate change. Radio occultation establishes a global climate benchmark by measuring the effect of atmospheric temperature, pressure, and water vapor on radio signals propagating above the outer edge of Earth's surface, known as the limb. The atmospherically induced delays are tied to atomic clock standards via the Global Positioning System (GPS). Measurements obtained decades apart can be intercompared without concern for intersatellite bias or calibration drift.

Mannucci, Anthony J.; Rocken, Christian

2009-07-01

322

Experimental determination of the propagation pressure of circular pipes  

Microsoft Academic Search

Local geometric imperfections on pipes under external pressure can lead to local buckling which under the ''right'' conditions can cause the initiation of a propagating buckle. This buckle, driven by the pressure, propagates up and down the pipe flattening it. The lowest pressure which can sustain a propagating buckle is called the propagation pressure and is a characteristic pressure of

S. Kyriakides; C. D. Babcock

1981-01-01

323

Cutting line determination for plant propagation  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

324

Measurement of radio emission from extensive air showers with LOPES  

NASA Astrophysics Data System (ADS)

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

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

2011-02-01

325

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

326

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

327

Radio Controlled Clocks  

Microsoft Academic Search

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

Michael A. Lombardi

328

The Frequency Spectrum Radio.  

ERIC Educational Resources Information Center

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

Howkins, John, Ed.

1979-01-01

329

CLEA: Radio Astronomy of Pulsars  

NSDL National Science Digital Library

The software for this exercise presents students with a radio telescope whose default operating characteristics (beam width, receiver noise, steerability) can be set by the instructor. Students can point the telescope at a source in the sky, viewing the output of the radio receiver on a graphic display that resembles a digital oscilloscope. The student manual describes an exercise in which students first acquaint themselves with the operation of the radio telescope. They then measure the signals from several pulsars at various frequencies, learning about the appearance of pulsar signals, the strength and period of the signal as a function of frequency, and the relation between pulsar period and age of the pulsar. Finally they view the signal from a pulsar at three different frequencies, using the delay in arrival times due to interstellar dispersion to estimate the distance to the pulsar.

Marschall, Laurence; Snyder, Glenn; Cooper, P. R.; Hayden, Michael; Good, Rhonda

2005-11-03

330

HIGH AMPLITUDE PROPAGATED CONTRACTIONS  

PubMed Central

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

Bharucha, Adil E.

2012-01-01

331

Application of radio channel modelling to a planning tool in a mobile radio indoor communication system  

Microsoft Academic Search

For mobile radio systems, it is very important to know how the propagation medium performs at the right frequency and within the given geographical environment. When this environment is an indoor one, that is, when a mobile system is being deployed within a building, a number of new issues appear that pose a number of constraints and restrictions to the

Gema Vallejo-Cabrejas; P. Batolome-Pascual

1993-01-01

332

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

333

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

334

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

335

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

336

Investigation of Seismic Wave Propagation in Eastern North America.  

National Technical Information Service (NTIS)

Seismic waves propagated and recorded at regional distances in eastern North America are being studies for possible use in discriminating between explosion and earthquake sources. This report deals with (a) the propagation characteristics of the regional ...

P. W. Pomeroy T. A. Nowak

1978-01-01

337

Radio halo sources in clusters of galaxies  

SciTech Connect

A series of observations have been made of clusters of galaxies in search of radio halo emission. The observations are of several types; (1) a survey at 430 MHz using the 305-meter telescope at Arecibo of 72 rich clusters, (2) a survey at 50 to 120 MHz using the high frequency array of the University of Tasmania in Llanherne of 30 rich, x-ray emitting clusters, (3) detailed maps of the Coma cluster, Abell 1367, and Abell 399/401 at 430 and 1400 MHz, again using the Arecibo telescope, and (4) low-frequency fan-beam maps of several clusters (Coma, Perseus, Virgo, Abell 1367, and Abell 399/401) made at the University of Maryland's Clark Lake Radio Observatory. The surveys had two goals: first, to determine just how common or uncommon radio halo sources are, and second, to determine if radio halo sources occur preferentially in one type of cluster. The more detailed mapping was intended to determine the extent and size-frequency dependence of the radio halo sources and thereby to learn more about particle propagation rates and modes of diffusion in astrophysical plasmas. The observations corroborate previous indications that radio halo sources similar to the one in the Coma cluster are quite uncommon. The results indicate that this is not because it requires some unusual history of radio frequency activity to produce a radio halo, but rather because ratio halos can exist only in clusters that are highly evolved dynamically, i.e., that have a deep and wide central potential capable of containing a large amount of hot gas. This type of cluster, which is also characterized by a high degree of central concentration and an unusually low fraction of spiral galaxies, is itself rather uncommon and thus can account for the rarity of radio halo sources.

Hanisch, R.J.

1981-01-01

338

Propagation of Nonideal Blast Waves.  

National Technical Information Service (NTIS)

The propagation of non-ideal blast waves initiated by finite power density sources has been classified into three regimes. The early-time motion of a non-ideal blast reflects the characteristics of the energy-time profile of the particular initiation ener...

C. M. Guirao G. G. Bach J. H. Lee

1974-01-01

339

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

340

S-Band propagation measurements  

NASA Astrophysics Data System (ADS)

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

Briskman, Robert D.

1994-08-01

341

Forecasting The Radio Effects of Space Weather (substorms) On Network of Hf Radio Paths  

NASA Astrophysics Data System (ADS)

The emergence of active solar processes results certain disturbances in the near-Earth environment. The disturbances manifest themselves first of all in the high-latitude ionosphere. Therefore the latter may serve as an object of studies in order to predict its state by means of radiophysical methods of investigation. Among them, one should specially single out the method of prediction with the help of a system of HF paths. The system represents a set of several paths of length up to 3000 km and of different directions but with one reception center located at a geomagnetic latitude L = 60-65°. The decameter waves pass through the ionosphere, hence they are an effective tool to predict its state. The network of HF paths makes it possible to obtain and carry out an analysis of a complex of statistical characteristics of the SW signal envelope at the receiver output. The envelope characteristics of the signal are evaluated by a computer in on-line mode and include: m ­ the Nakagami law parameter, - the time correlation radius, X ­ the signal average, L1, L2, L3 ­ parameters of the process non-stationarity and so on. Their variations at different phases of a substorm reveal certain regularities. By our studies, two-three hours before the start of the decrease of the H-component of the Earth magnetic field, there is observed the growth of absolute values of all parameters. At about one hour before the substorm intensification there begins a sharp decrease in magnitudes of the characteristics considered, which reach their minimum at the expansion phase of substorm. Hence the forecasting of the substorm onset may be made about two hours before the breakup begins. At the recovery phase there is a gradual growth of the parameters back to their original values. Thus the suggested method of forecasting the geomagnetic substorm by the characteristics of propagating radio waves is important for investigation of potentially-damaging space weather events.

Blagoveshchensky, D. V.

342

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

NASA Technical Reports Server (NTRS)

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

Davarian, Faramaz (editor)

1992-01-01

343

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

NASA Technical Reports Server (NTRS)

The NASA Propagation Experimenters Meeting (NAPEX), supported by the NASA Propagation Program, is convened annually to discuss studies made on radio wave propagation by investigators from domestic and international organizations. Participants included representatives from Canada, the Netherlands, England, and the United States, including researchers from universities, government agencies, and private industry. The meeting was organized into two technical sessions. The first session was dedicated to slant path propagation studies and experiments. The second session focused on propagation studies for mobile, personal, and sound broadcast systems. In total, 14 technical papers and some informal contributions were presented. Preceding NAPEX_17, the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop was held to review ACTS propagation activities.

Davarian, Faramaz (editor)

1994-01-01

344

Radio frequency picosecond phototube  

SciTech Connect

We propose a photon detector for recording low-level and ultra-fast optical signals, based on radio frequency (RF) analysis of low-energy photoelectrons (PEs). By using currently developed 500 MHz RF deflector, it is possible to scan circularly and detect single PEs, amplified in multi-channel plates (MCPs). The operation of the tube is investigated by means of thermionic electron source. It is demonstrated that the signals generated in the MCP can be processed event by event; by using available nanosecond electronics and that time resolution better than 20 ps can be achieved. Timing characteristics of the Cherenkov detector with RF phototube in a ''head-on'' geometry is investigated by means of Monte Carlo simulation.

A. Margaryan; R. Carlini; R. Ent; N. Grigoryan; K. Gyunashyan; O. Hashimoto; K. Hovater; M. Ispiryan; S. Knyazyan; B. Kross; S. Majewski; G. Marikyan; M. Mkrtchyan; L. Parlakyan; V. Popov; L. Tang; H. Vardanyan; C. Yan; S. Zhamkochyan; C. Zorn

2006-10-01

345

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

346

Surface Elastic-Wave Propagation and Amplification.  

National Technical Information Service (NTIS)

Surface elastic-wave propagation, transduction, and amplification (in a piezoelectric semiconductor) are discussed with emphasis on characteristics useful in electronic devices. Computed curves show the dependence on distance from the surface of the elast...

R. M. White

1967-01-01

347

Studies in Flame Propagation and Blowout.  

National Technical Information Service (NTIS)

This report outlines our most recent research work on the topic of upstream flame propagation and blowout in hydrocarbon jet flames. Outlined specifically are the recent elements of the research for the study of fundamental structural characteristics of j...

K. M. Lyons

2006-01-01

348

Resonance and Radio  

ERIC Educational Resources Information Center

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

Starrett, Malin J.

2008-01-01

349

Recommended Radio Terms.  

National Technical Information Service (NTIS)

The report contains the draft of a compilation of 188 radio terms recommended by the USSR Scientific Commission created by the Interdepartmental Commission on Radio Frequencies for use in scientific and technical literature, education, standards, and in t...

A. L. Badalov N. I. Chistyakov V. F. Pchelkin

1972-01-01

350

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

351

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

352

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

353

Radio studies of cosmic rays in nearby galaxies  

Microsoft Academic Search

The study reviews the constraints on cosmic-ray electron sources and propagation as derived from radio continuum observations of galaxies. Special attention is given to the inferences which can be obtained from the radio continuum properties of spiral galaxies seen edge-on. It is found that a large fraction of the cosmic-ray electrons leave the source distribution, presumably associated with the thin

E. Hummel

1991-01-01

354

Extragalactic Radio Sources  

ERIC Educational Resources Information Center

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

Kellerman, Kenneth I.

1973-01-01

355

The software radio architecture  

Microsoft Academic Search

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

J. Mitola

1995-01-01

356

Electromagnetic Wave Propagation from Dipole Sources in Lossy Media (Elektromagnetisk Vagutbredning Fran Dipolkaellor i Dissipativa Media).  

National Technical Information Service (NTIS)

Computational electromagnetics as a rule requires high performance computers, especially in real-time applications. In this MSc thesis, a theoretical model for propagation of extremely low frequency radio waves in the sea is studied. The source is modeled...

M. Liefvendahl

1997-01-01

357

Results on VLF long-distance propagation received at Brazil and at Antarctic Peninsula  

NASA Astrophysics Data System (ADS)

Recent results are presented of VLF long-distance propagation obtained at Itapetinga Radio Observatory, Atibaia, Brazil, and at Antarctic Station Commandante Ferraz, King George Island, Antarctic Peninsula. The signals originated in North West Cape, Australia.

Piazza, L. R.; Mendesdacosta, A.; Kaufmann, P.; Kuntz, V. L. R.; Paesleme, N. M.; Macedomoura, M. S. S.

1987-03-01

358

Radio frequency interference mitigation in radio astronomy  

NASA Astrophysics Data System (ADS)

The next generation of radio telescopes is expected to be one to two orders of magnitude more sensitive than the current generation. Examples of such new telescopes are the Low Frequency Array (LOFAR), currently under construction in the Netherlands, and the Square Kilometer Array (SKA), currently in a concept study phase. Another trend is that technological advances in the fields of electronics and communications systems have led to a vast increase in radio communication applications and systems, and also to an increasing demand for radio spectrum. These two trends, more sensitive telescopes and a much denser spectrum use, imply that radio astronomy will become more vulnerable to interference from radio transmitters. Although protection criteria exist for radio astronomy, it becomes increasingly difficult to keep the radio astronomy frequency bands free from interference. In order to mitigate interference in radio astronomical data, filtering techniques can be used. In this thesis, modern array signal processing techniques have been applied to narrow-band multichannel interference detection and excision, and to narrow-band spatial interference filtering. By investigating the subspace structure of the telescope array output covariance matrices, new results were found, such as upper limits on interference residuals after excision and spatial filtering. The effect of bandwidth, extendedness of the interfering sources, and multipath effects on the detection and spatial filter effectiveness were studied as well. The advantage of a multichannel approach over a single telescope approach was demonstrated by using experimental data from the Westerbork Synthesis Radio Telescope (WSRT). As the performance of mitigation algorithms can be improved by calibration of the telescope gains and noise powers, calibration algorithms were developed. These algorithms were verified both for single and dual polarised arrays. Finally, a LOFAR interference mitigation strategy was developed.

Boonstra, Albert-Jan

2005-12-01

359

Intelligent systems control and multipath protection for next generation digital radios  

NASA Astrophysics Data System (ADS)

It is pointed out that technology has advanced to the stage where both the 16 QAM (quadrature amplitude modulation) and 64 QAM high-level modulation techniques are used in digital microwave radios. This new generation of digital radios attains spectral efficiency that is comparable to or better than conventional FM/FDM. Attention is given here to the intelligent system monitor built into a new family of 16-QAM digital radios and to the various propagation protection schemes available for use against multipath fading. Together they make digital radios easy to operate and maintain while providing for the transmission objectives of a digital microwave radio system.

Wallace, R. L.; Huang, J. C. Y.

1984-01-01

360

Characterizing Cosmic-Ray Propagation in Massive Star-forming Regions: The Case of 30 Doradus and the Large Magellanic Cloud  

NASA Astrophysics Data System (ADS)

Using infrared, radio, and ?-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 ~100-140 pc for ~3 GeV CR electrons resident in 30 Dor from consideration of the radio and infrared data. Assuming that the observed ?-ray emission toward 30 Dor is associated with the star-forming region, and applying the same methodology to the infrared and ?-ray data, we estimate a ~20 GeV propagation length of 200-320 pc for the CR nuclei. This is approximately twice as large as for ~3 GeV CR electrons, corresponding to a spatial diffusion coefficient that is ~4 times higher, scaling as (R/GV)? with ? ? 0.7-0.8 depending on the smearing kernel used in the correlation analysis. This value is in agreement with the results found by extending the correlation analysis to include ~70 GeV CR nuclei traced by the 3-10 GeV ?-ray data (? ? 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 DR ? (0.9-1.0) × 1027(R/GV)0.7 cm2 s-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.; Porter, T. A.; Moskalenko, I. V.; Helou, G.; Strong, A. W.

2012-05-01

361

A statistical comparison of interplanetary shock and CME propagation models  

Microsoft Academic Search

We have compared the prediction capability of two types of Sun-Earth connection models: (1) ensemble of physics-based shock propagation models (STOA, STOA-2, ISPM, and HAFv.2) and (2) empirical CME propagation (CME-ICME and CME-IP shock) models. For this purpose, we have selected 38 near-simultaneous pairs of coronal mass ejections (CMEs) and metric type II radio bursts. By applying the adopted models

K.-S. Cho; Y.-J. Moon; M. Dryer; C. D. Fry; Y.-D. Park; K.-S. Kim

2003-01-01

362

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

363

Wave propagation in pulsar magnetospheres - Dispersion relations and normal modes of plasmas in superstrong magnetic fields  

NASA Astrophysics Data System (ADS)

We derive the dispersion relations and polarization characteristics of the normal modes of radiation in superstrong magnetic fields, with particular attention to those attributes of importance to the transfer of radiation in the relativistic electron-positron plasmas expected to occur in the magnetospheres of radio pulsars. We restrict ourselves to the regions where the proper frequency of cyclotron resonance greatly exceeds the proper frequencies of the radiative normal modes. The normal modes are derived when the plasma has no momentum dispersion across the magnetic field but has arbitrary momentum dispersion along the field. The contribution of displacement current to the propagation of these "hydromagnetic" waves is consistently included. The distinction between superluminous and subluminous modes is made in the superstrong regime, where drift motions across the field are negligible, and useful formulae for the Landau damping of the subluminous branch of ordinary mode (the Alfven wave) are derived. These are used to set observational constraints on the geometry of the emission zone in radio pulsars, if the emission mechanism generates radiation in the form of subluminous waves. A brief discussion is given of the relevance of nonvacuum propagation to Razin suppression of bunched coherent curvature emission.

Arons, J.; Barnard, J. J.

1986-03-01

364

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

NASA Technical Reports Server (NTRS)

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

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

1971-01-01

365

Radio Frequency Interference Mitigation in Radio Astronomy.  

National Technical Information Service (NTIS)

The next generation of radio telescopes is expected to be one to two orders of magnitude more sensitive than the current generation. Examples of such new telescopes are the Low Frequency Array (LOFAR), currently under construction in the Netherlands, and ...

A. J. Boonstra

2005-01-01

366

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

367

Low-frequency radio emissions at Neptune  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

368

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

369

Routing metrics for multi-radio wireless mesh networks  

Microsoft Academic Search

Multi-radio wireless mesh networks provide a great improvement over traditional mobile ad-hoc networks and are able to provide increased capacity and scalability. Routing metrics for multi-radio wireless mesh networks must cater to the specific characteristics that these networks exhibit and attempt to exploit these to maximize performance. Many routing metrics were designed for single-radio ad-hoc networks and hence do not

Jonathan Guerin; Marius Portmann; Asad Pirzada

2007-01-01

370

The Giant Metrewave Radio Telescope  

NASA Astrophysics Data System (ADS)

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

Nityananda, R.

2003-05-01

371

Auroral ionospheric electron gyroharmonic radio emissions: Observation and theory  

NASA Astrophysics Data System (ADS)

Since 1992 Dartmouth College researchers have observed natural radio emissions on the ground in the Earth's auroral regions. Auroral roar, a relatively narrowband (?f/f < 0.1) emission near 3 MHz and 4.5 MHz and believed to occur at harmonics of the ionospheric electron cyclotron frequency (2fce and 3fce), is commonly detected with receivers located at sites located in these regions. A satisfactory mechanism for generating auroral roar emissions has eluded researchers since the first auroral roar observations in 1978. Several experiments designed to elicit characteristics of these emissions in order to refine existing generation theories are discussed in detail. Specifically, polarization measurements reveal that auroral roar must propagate in the O mode, contrary to the predictions of several theories. High time and frequency measurements show that auroral roar is often comprised of extremely narrow (~6 Hz) tonal features which drift in a complicated manner. Ionospheric electron density profiles from the Sondrestrom incoherent scatter radar (ISR) during auroral roar emissions often exhibit significant F region horizontal n e gradient scale lengths and localized F region auroral ionospheric cavities. The ISR profiles also show that the relationship between the electron plasma frequency (fpe) and the electron gyrofrequency (fce) f2pe=(n2-1) f2ce , where n is the harmonic number of the emission (2 or 3), holds somewhere in the ionosphere during nearly all the ISR scans that were studied. Auroral roar observed with a meridional chain of radio receivers spanning 67° to 79° invariant latitude is compared to the latitudinal location of current systems measured by a similar magnetometer chain. The strongest emissions most often occur poleward, up to 8°, of the inferred poleward boundary of the auroral electrojet and often track movements of this boundary. Finally, ray tracing simulations show that Z mode waves at f = 2fce are contained by cavity- like density structures similar to those seen in ISR profiles. The waves refract in these structures, some in such a manner that they access the Ellis radio window, presumably convert to O mode radiation, and propagate to the ground as 2fce auroral roar.

Shepherd, Simon George

372

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

373

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

374

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

Microsoft Academic Search

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

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

375

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

Microsoft Academic Search

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

J. Ralph Johler; Richard L. Lewis

1969-01-01

376

Parameters of a forward scatter radio meteor set-up: Preliminary calculations for the MSR radio meteor project in Argentina  

NASA Astrophysics Data System (ADS)

The MSR set-up was developed considering several parameters related to radio astronomy calculations for the observing system, neighborhood environmental characteristics, and many conditions related to the placement of the instrument. In the present work a forward scatter radio meteor link is analyzed to obtain the required parameters for a meteor radio astronomy dedicated set-up. The analysis is illustrated by calculating the parameters for the MSRV2 system employed at the Instituto Argentino de Radioastronoma (IAR).

Semegone, Juan Martin; Sanz, Juan A.

2006-08-01

377

Turbofan Duct Propagation Model.  

National Technical Information Service (NTIS)

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 marc...

J. H. Lan

2001-01-01

378

Tropospheric Propagation Assessment.  

National Technical Information Service (NTIS)

It is well known that microwave propagation in a marine environment frequently exhibits unexpected behavior. The deviation from 4/3 earth propagation calculations is due to the fact that the vertical refractivity distribution of the troposphere rarely fol...

H. V. Hitney J. H. Richter K. D. Anderson

1984-01-01

379

The Sardinia Radio Telescope  

NASA Astrophysics Data System (ADS)

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

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

380

American RadioWorks  

NSDL National Science Digital Library

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

381

US Radio Broadcasting Past  

NSDL National Science Digital Library

Thomas H. White discusses the history of United States radio in detail from the late 1800�s to the 1940�s in this informative site featuring a compilation of materials and articles. The site features 24 different sections arranged by title and year for users to browse, each section allows the user to discover the beginnings of radio in the United States. Sections include some that outline the changes of radio in relation to U.S. history, including but not limited to the World Wars, as well as discussions of big business and radio, and early government regulation to name only a few. For anyone interested in the history of radio and how radio got to where it is today, this site is an excellent resource.

White, Thomas W.

2007-02-11

382

HF propagation characteristics of artificial ionospheric layers  

Microsoft Academic Search

Artificial ionospheric layers descending from the background F-region ionosphere can be produced by highpower HF transmissions with effective radiated powers of 10 5 ->10 6 W, especially near harmonics of the electron gyrofrequency. Multiple high-speed DPS-4D ionosondes were utilized to obtain direct and oblique ionospheric soundings from a large number of artificial layers during an experimental campaign at the High

Todd Pedersen; Bodo Reinisch; Vadym Paznukhov; Ryan Hamel

2011-01-01

383

Characteristics of Electromagnetic Pulse Propagation in Metal.  

National Technical Information Service (NTIS)

It is well known that the solution of the diffusion equation for an electromagnetic field with a time harmonic term, e(sup iax), is in the form of a traveling wave whose amplitude attenuates over distance into a conducting medium. As the attenuation is an...

M. Namkung B. Wincheski S. Nath

2004-01-01

384

Radio Link Frequency Assignment  

Microsoft Academic Search

Abstract: The problem of radio frequency assignment is to provide communication channelsfrom limited spectral resources whilst keeping to a minimum the interference suered by thosewhishing to communicate in a given radio communication network. This problem is a combinatorial(NP-hard) optimization problem. In 1993, the CELAR (the French \\\\Centre d'Electronique del'Armement") built a suite of simplied versions of Radio Link Frequency Assignment

Bertrand Cabon; Simon De Givry; Lionel Lobjois; Thomas Schiex; Joost P. Warners

1999-01-01

385

Dominion Radio Astrophysical Observatory  

NASA Astrophysics Data System (ADS)

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

Murdin, P.

2000-11-01

386

Radio-Locator  

NSDL National Science Digital Library

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

2006-11-14

387

National Radio Observatory  

NSDL National Science Digital Library

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

388

The universal propagator  

NASA Technical Reports Server (NTRS)

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

Klauder, John R.

1993-01-01

389

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

390

Experimental radio frequency link for Ka-band communications applications  

NASA Technical Reports Server (NTRS)

An experimental radio frequency link has been demonstrated to provide two-way communication between a remote user ground terminal and a ground-based Ka-band transponder. Bit-error-rate performance and radio frequency characteristics of the communication link were investigated.

Fujikawa, Gene; Conray, Martin J.; Saunders, Alan L.; Pope, Dale E.

1988-01-01

391

Report from the Symposia on Antennas and Propagation  

NASA Astrophysics Data System (ADS)

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

Mattsson, S.

1985-12-01

392

A prediction model for personal radio frequency electromagnetic field exposure.  

PubMed

Radio frequency electromagnetic fields (RF-EMF) in our daily life are caused by numerous sources such as fixed site transmitters (e.g. mobile phone base stations) or indoor devices (e.g. cordless phones). The objective of this study was to develop a prediction model which can be used to predict mean RF-EMF exposure from different sources for a large study population in epidemiological research. We collected personal RF-EMF exposure measurements of 166 volunteers from Basel, Switzerland, by means of portable exposure meters, which were carried during one week. For a validation study we repeated exposure measurements of 31 study participants 21 weeks after the measurements of the first week on average. These second measurements were not used for the model development. We used two data sources as exposure predictors: 1) a questionnaire on potentially exposure relevant characteristics and behaviors and 2) modeled RF-EMF from fixed site transmitters (mobile phone base stations, broadcast transmitters) at the participants' place of residence using a geospatial propagation model. Relevant exposure predictors, which were identified by means of multiple regression analysis, were the modeled RF-EMF at the participants' home from the propagation model, housing characteristics, ownership of communication devices (wireless LAN, mobile and cordless phones) and behavioral aspects such as amount of time spent in public transports. The proportion of variance explained (R2) by the final model was 0.52. The analysis of the agreement between calculated and measured RF-EMF showed a sensitivity of 0.56 and a specificity of 0.95 (cut-off: 90th percentile). In the validation study, the sensitivity and specificity of the model were 0.67 and 0.96, respectively. We could demonstrate that it is feasible to model personal RF-EMF exposure. Most importantly, our validation study suggests that the model can be used to assess average exposure over several months. PMID:19819523

Frei, Patrizia; Mohler, Evelyn; Bürgi, Alfred; Fröhlich, Jürg; Neubauer, Georg; Braun-Fahrländer, Charlotte; Röösli, Martin

2009-12-15

393

75 FR 10439 - Cognitive Radio Technologies and Software Defined Radios  

Federal Register 2010, 2011, 2012, 2013

...10-12] Cognitive Radio Technologies and Software Defined Radios AGENCY: Federal Communications...proceeding concerning the use of open source software to implement security features in software defined radios (SDRs). While, the...

2010-03-08

394

Ionospheric Error Contribution To GPS Radio Occultation Temperature Retrievals  

Microsoft Academic Search

The NRC Decadal Survey calls for long-term climate records. GPS radio occultation (GPS RO) is viewed as a promising measurement technique that fulfills the need for high accuracy measurements of upper atmospheric temperature and pressure with robust systematic error bounds known on orbit. Geophysical observables are derived by measuring propagation delay induced by the atmosphere, a measurement whose fundamental unit--the

A. J. Mannucci; C. O. Ao; X. Pi; B. A. Iijima

2007-01-01

395

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

396

ACTS propagation program  

NASA Astrophysics Data System (ADS)

The Advanced Communications Technology Satellite (ACTS) Propagation Program is organized to fulfill certain needs and requirements of the ACTS community. It is hoped that issues related to propagation effects in the context of ACTS experiments can be addressed and resolved by this program. The objectives of the ACTS Propagation Program are included in but not limited to planning for propagation measurements and studies using ACTS; organizing propagation experimenters who want to use ACTS into one group; developing observation stations for ACTS propagation measurements; supervising data collection, analysis, and ensure uniformity of data recording among various experimenters; and assisting the ACTS Program Office to carry out its objectives. This program is organized and managed by the NASA Propagation Program at the Jet Propulsion Laboratory. Financial support for this program is provided by NASA.

Davarian, Faramaz

1990-07-01

397

Effect of Spatial Node Distribution on Performance of Frequency-Hop Spread Spectrum Packet Radio Networks  

Microsoft Academic Search

We study the effect of spatially distributed terminals on the link error probabilities for fiequencyhop spread spectrum packet radio networks where the propagation loss factor comes into play. There have been two quite different approaches in research in multihop spread spectrum networks. One where propagation power loss is explicitly accounted for by adopting a “soft” interference model and is more

Thomas D. Papavassiliou; Andreas Polydoros; John A. Silvester

1990-01-01

398

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

399

The Sardinia Radio Telescope  

Microsoft Academic Search

We describe the Sardinia Radio Telescope (SRT), a new general purpose, fully steerable antenna of the National Institute for Astrophysics. The radio telescope is under construction near Cagliari (Sardinia). With its large aperture (64m diameter) and its active surface, SRT is capable of operations up to ˜100GHz, it will contribute significantly to VLBI networks and will represent a powerful single-dish

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

2004-01-01

400

The Sardinia Radio Telescope  

Microsoft Academic Search

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

Nichi D’Amico

2011-01-01

401

Deterministic Radio Broadcasting  

Microsoft Academic Search

. We consider broadcasting in radio networks: one node of thenetwork knows a message that needs to be learned by all the remainingnodes. We seek distributed deterministic algorithms to perform this task.Radio networks are modeled as directed graphs. They are unknown, inthe sense that nodes are not assumed to know their neighbors, nor thesize of the network, they are aware

Bogdan S. Chlebus; Leszek Gçasieniec; Anna Östlin; John Michael Robson

2000-01-01

402

Lunar Farside Radio Lab  

Microsoft Academic Search

It is proposed that the Farside of the Moon should be protected legally against man-made radio pollution and uncontrolled exploitation. In fact, only by establishing a radiotelescope on the Farside of the Moon it will finally be possible to cope with the Radio Frequency Interference (RFI) that is now increasingly plaguing all of Radioastronomy, Bioastronomy and Search for Extraterrestrial Intelligence

Claudio Maccone

2005-01-01

403

Radio astronomy receivers  

Microsoft Academic Search

A general survey of the principles of radio astronomy receivers is presented. System noise temperature, the sensitivity of different receiver types, and the calibration of receivers are studied. A total-power receiver is analyzed as a basic radio telescope receiver and the results are used to obtain the performance of other receiver types such as the Dicke receiver, Graham's receiver, correlation

M. Tiuri

1964-01-01

404

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

405

Switched ultrawideband antenna array for radio tomography  

NASA Astrophysics Data System (ADS)

The characteristics of the ultrawideband (UWB) timed antenna array developed by the authors are described. The efficiency of the system is confirmed by experiments processed with the use of focusing and aperture synthesis methods. Technical solutions used in this work allow us to proceed to the development of the UWB radio tomograph operating in real time.

Satarov, R. N.; Kuz'menko, I. Yu.; Muksunov, T. R.; Klokov, A. V.; Balzovskii, E. V.; Buyanov, Yu. I.; Shipilov, S. É.; Yakubov, V. P.

2013-01-01

406

Correlation of radio and gamma emissions in lightning initiation.  

PubMed

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

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

2013-10-18

407

Implementation of Physical Layer Authentication Using Software Radio.  

National Technical Information Service (NTIS)

Authentication is the process where claims of identity are verified and is a critical first step for sensitive communications. We propose a physical layer authentication technique that identifies radios based on their unique signal characteristics. The tr...

B. Sadler J. Baras P. Yu

2009-01-01

408

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

409

Tracking of Interplanetary CME/Shocks Using Type II Radio Observations  

NASA Astrophysics Data System (ADS)

Interplanetary Type II radio burst radiation results from the excitation of plasma waves in the ambient medium by shock waves driven by coronal mass ejections (CMEs). These radio emissions provide a means of remotely tracking CME/shocks. The aim of this work is to combine, by using WIND/WAVES and STEREO/SWAVES radio data, different techniques to estimate the speed evolution of CME/shocks associated with Type II radio bursts. Moreover, in order to illuminate the CME/shock propagation, it is included an analysis of coronographic and heliospheric images, in situ data, and an analytical model of CME/shock propagation, which provide complementary information on CME/shocks propagating through the entire Sun-Earth connected space.

Aguilar-Rodriguez, E.; Ontiveros-Hernandez, V.; Manuel-Hernandez, T.; Corona-Romero, P.; Gonzalez-Esparza, A.

2012-12-01

410

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

411

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

NASA Technical Reports Server (NTRS)

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

Ho, Christian

2005-01-01

412

Low frequency radio observations of five rich clusters of galaxies  

SciTech Connect

Observations have been made at 43.0 and 73.8 MHz of five rich x-ray emitting clusters of galaxies: Abell 399/401, Abell 426 (the Perseus cluster), Abell 1367, Abell 1656 (the Coma cluster), and the Virgo cluster. A fan beam synthesis system has been used to search for extended radio emission, i.e., radio halos, in these clusters. Radio halos were detected in the Coma and Virgo clusters. No evidence was found for the existence of 3C84B, the halo source previously thought to exist in the Perseus cluster. If halo sources exist in Abell 399/401 or Abell 1367, they must be quite weak at frequencies less than 100 MHz. The observed sizes of the extended sources in Coma and Virgo imply that the rate of particle propagation away from strong radio galaxies greatly exceeds the Alfven velocity and is probably independent of particle energy.

Hanisch, R.J.; Erickson, W.C.

1980-03-01

413

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

414

Simultaneous Observations of Multi-mode Echoes on IMAGE: Propagation, Reflection, and Scattering of Whistler-, Slow Z-, Fast Z-, LO-, and RX-mode Waves at Low Altitude (<5,000 km)  

NASA Astrophysics Data System (ADS)

RPI on IMAGE designed to sweep from 3 kHz to 3 MHz permitted sounding in all five cold plasma wave modes including whistler- , slow Z-, fast Z-, LO- and RX-mode. Previous studies presented simultaneous observations of two or three echoes on IMAGE each propagating in distinct plasma wave mode (e.g. Reinisch et al. [2001], Carpenter et al. [2003], Sonwalkar et al. [2004]). We define multimode echoes to be simultaneously occurring echoes that have each propagated in distinctive plasma wave mode. We present here first simultaneous observations of multimode echoes containing four or five echoes. These echoes were typically observed below 5000 km in the middle to high geomagnetic latitude region. From the ~10,000 RPI transmissions in 20 kHz to 1000 kHz frequency range, during 2003-05 period, multimode echoes containing up to two echoes were found in ~2500 cases, up to three echoes in ~1000 cases, up to four echoes in ~200 cases, and up to five in ~20 cases. Because different wave modes have unique propagation characteristics (e.g. frequency, wave length, cut offs, refractive index surface), they propagate along different paths, undergo distinctive reflections, and are affected differently by field aligned irregularities of various scale sizes. With the help of ray tracing analysis of one case, 27 July 2003, when whistler-, fast Z- , slow Z- , LO- and RX-mode echoes were observed, we illustrate propagation of echoes in each mode. At this time IMAGE was at 43°S geomagnetic latitude, 2045 km altitude, L=2.5, and 5 MLT. We found that whistler mode waves propagated in a nonducted mode and reflected at the Earth-ionosphere boundary; fast Z-mode waves propagated in a duct, both above and below the satellite, and reflected at an altitude where fZ=f, where f is the transmission frequency and fZ is the fast Z-mode cutoff; the slow Z-mode waves propagated obliquely with respect to magnetic field and were scattered back by field aligned irregularities; LO mode waves propagated in a ducted mode and reflected from the conjugate hemisphere; RX mode waves propagated in a nonducted mode and reflected below the satellite at an altitude where fX=f, where fX is the RX-mode cutoff frequency. This example demonstrates the potential of multimode echoes for radio sounding and the advantages that it presents over single mode radio sounding. Propagation analysis of multimode echoes should provide us with better understanding of the propagation, reflection, and scattering of naturally occurring plasma waves.

Sonwalkar, V. S.; Mayank, K.; Reddy, A.; Hazra, S.; Proddaturi, R.; Carpenter, D. L.; Reinisch, B. W.

2010-12-01

415

OneWorldRadio  

NSDL National Science Digital Library

A number of media commentators have been complaining lately about the lack of ideological viewpoints within the vast sea of radio programming, something that has not been lost on the people at OneWorldRadio. Funded by the Department for International Development, OneWorld Radio is part of an international network of over 1200 partner organizations that are utilizing the internet "to promote human rights and sustainable development worldwide." With online audio content from member organizations (such as radio stations) available in French, Spanish, and a number of other languages, visitors can listen or download any one of hundreds of programs archived here. Additionally, visitors can elect to search their impressive archive by language, region, or topic. Persons interested in the use of radio for development and human rights will want to examine the news and events section as it contains important updates about events dealing with conferences on media freedom throughout the world and links to important radio broadcasts of note. Finally, visitors (and all who sign up for the free membership) can elect to receive the helpful OneWorldRadio e-newsletter.

416

Plants 2: Plant Propagation  

NSDL National Science Digital Library

This is the second (and final) Science NetLinks lesson in a series on plants. In this lesson, students will do a project in which they choose a plant and try to propagate it. The project will take about 6 to 8 weeks to complete. During this time, students will research propagation, attempt to propagate a plant, keep a journal, and write a summary when the project is finished.

Science Netlinks;

2001-10-20

417

The threat to radio astronomy from radio pollution  

Microsoft Academic Search

The interference of man-made signals to radio astronomy is discussed and changes to the international radio regulations are proposed to protect the future of radio astronomy. The benefits of radio astronomy are outlined and the problem of shared frequency bands is described. The interference caused by the Soviet Glonass satellite is used to illustrate the problems caused by interference.

R. J. Cohen

1989-01-01

418

Radio studies of relativistic SN 2009bb  

NASA Astrophysics Data System (ADS)

A local sub-population of type Ib/c supernovae (stripped envelope SNe) with mildly relativistic outflows have been detected as sub-energetic Gamma Ray Bursts (GRBs) or X-ray Flashes (XRFs) and as radio afterglows without detected GRB counterpart. SN 2009bb belongs to the last class of objects. The long term radio observations with (J)VLA and GMRT of this SN map the dynamics of the relativistic ejecta characteristic of Central Engines associated with GRBs. We present here GMRT observations of this SN from October 2009 onwards.

Ray, Alak; Yadav, Naveen; Chakraborti, Sayan; Soderberg, Alicia; Chandra, Poonam

2014-01-01

419

Results on VLF (Very Low Frequencies) Long-Distance Propagation Received at Brazil and at Antarctic Peninsula.  

National Technical Information Service (NTIS)

Recent results are presented of VLF long-distance propagation obtained at Itapetinga Radio Observatory, Atibaia, Brazil, and at Antarctic Station Commandante Ferraz, King George Island, Antarctic Peninsula. The signals originated in North West Cape, Austr...

L. R. Piazza A. Mendesdacosta P. Kaufmann V. L. R. Kuntz N. M. Paesleme

1987-01-01

420

Riding the Radio Waves  

NSDL National Science Digital Library

Through this lesson students learn how AM radios work through basic concepts about waves and magnetic fields. Waves are first introduced by establishing the difference between transverse and longitudinal waves, as well as identifying the amplitude and frequency of a given waveform. Then students learn general concepts about magnetic fields, leading into how radio waves are created and transmitted. Several demonstrations are performed to help students better understand these concepts. The lesson goal is for students to comprehend how the AM radios they will build during the associated activity function.

Techtronics Program

421

Modeling of radio meteors  

SciTech Connect

A modified version of a computer model of radio meteors, based on empirical data for the arrival of meteoric material in circumterrestrial space, is presented. Good agreement with the experimental data for the Moscow-Kazan radio link is obtained. Results of calculations of the angular sizes of the reflection area for the St. Petersburg-Kazan radio link are presented. The reflection area is shown to be a sufficiently compact object with angular sizes 34.6{degrees}{+-}2.1{degrees} in the azimuthal plane and 12.7{degrees}{+-}1.2{degrees} in the vertical plane.

Karpov, A.V.; Sidorov, V.V.; Tereshin, S.N. [Kazan State Univ., Tatarstan (Russian Federation)

1995-11-01

422

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

423

HF propagation through actively modified ionospheres  

NASA Astrophysics Data System (ADS)

A computer modeling capability was developed to predict the effect of localized electron density perturbations created by chemical releases or high power radio frequency heating upon oblique, one-hop hf propagation paths. Three dimensional deterministic descriptions of the depleted or enhanced ionization, including formation, evolution, and drift are included. A homing ray trace code was developed to calculate the path of energy propagation through the modified ionosphere in order to predict multipath effects. Also considered is the effect of random index of refraction variations using a formalism to calculate the mutual coherence functions for spatial and frequency separations based upon a path integral solution of the parabolic wave equation for a single refracted path through an ionosphere which contains random electron density fluctuations.

Argo, Paul E.; Fitzgerald, T. Joseph; Wolcott, John H.; Simons, David J.; Warshaw, Steve; Carlson, Ralph

424

Radio emission altitudes in the pulsar magnetosphere  

NASA Astrophysics Data System (ADS)

Multifrequency timing measurements of four pulsars are used to search for propagation delays predicted by the 'radius-to-frequency mapping' (RFM) model of pulsar radio emission. The RFM model specifies that emissions at different frequencies are produced at different altitudes in the pulsar magnetosphere. An analysis including aberration, retardation, and magnetic sweepback effects showed that the 47 and 4800 MHz emission zones were separated by no more than 200 km. Assuming a dipolar form for the pulsar magnetic field, the data indicate that 4800 MHz emission was produced less than about 100 km above the surface of the neutron star.

Phillips, J. A.

1992-01-01

425

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

426

Radio-optical alignments in a low radio luminosity sample  

Microsoft Academic Search

We present an optically based study of the alignment between the radio axes and the optical major axes of eight z~0.7 radio galaxies in a 7C sample. The radio galaxies in this sample are ~20 times less radio-luminous than 3C galaxies at the same redshift, and are significantly less radio-luminous than any other well-defined samples studied to date. Using Nordic

Mark Lacy; Susan E. Ridgway; Margrethe Wold; Per B. Lilje; Steve Rawlings

1999-01-01

427

Inexpensive Megabit Packet Radio System.  

National Technical Information Service (NTIS)

Although packet radio is relatively new to the amateur radio community, there are now over 10,000 amateur packet radio units in service. These units cost between $500 and $800, including the controller and radio, and generally operate at 1200 baud. An eff...

R. Bisbey R. Parker R. Cole

1986-01-01

428

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

429

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

430

Broadcast Radio Service.  

National Technical Information Service (NTIS)

The tape contains data for applicants and licensees operating radio equipment approved by the Federal Communications Commission. Data records include station and license identification, location, radiofrequency, mailing address (all items do not contain c...

J. J. Sharkey

1974-01-01

431

General Radio Service.  

National Technical Information Service (NTIS)

The tape contains data for applicants and licensees operating radio equipment approved by the Federal Communications Commission. Data records include station and license identification, location, radiofrequency, mailing address (all items do not contain c...

J. J. Sharkey

1974-01-01

432

Broadcast Auxiliary Radio Service.  

National Technical Information Service (NTIS)

The tape contains data for applicants and licensees operating radio equipment approved by the Federal Communications Commission. Data records include station and license identification, location, radiofrequency, mailing address (all items do not contain c...

J. J. Sharkey

1974-01-01

433

Radio Telescope Design  

Microsoft Academic Search

\\u000a This is an important chapter concerning radio telescope design. In the first part of this chapter, all the major design issues\\u000a of radio telescopes are discussed, which include the reflector surface transmission loss, the antenna tolerance theory, the\\u000a antenna homology design, the antenna surface best fitting, the antenna component positional tolerance, the antenna aperture\\u000a blockage, the ground radiation pick-up, and

Jingquan Cheng

434

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

435

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

436

Transionospheric Propagation Code (TIPC)  

Microsoft Academic Search

The Transionospheric Propagation Code is a computer program developed at Los Alamos National Lab to perform certain tasks related to the detection of VHF signals following propagation through the ionosphere. The code is written in FORTRAN 77, runs interactively and was designed to be as machine independent as possible. A menu format in which the user is prompted to supply

Robert Roussel-Dupre; Thomas A. Kelley

1990-01-01

437

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

438

Uncertainties and Error Propagation  

NSDL National Science Digital Library

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

Lindberg, Vern

2008-07-22

439

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

440

Polarization Characteristics of Low-Frequency Resonances in the Earth-Ionosphere Cavity  

NASA Astrophysics Data System (ADS)

We present the results of measurements and model calculations of the polarization characteristics of ULF-ELF fields in the Earth - ionosphere cavity. It is shown that the horizontal magnetic field in the cavity is elliptically polarized. The ellipticity sign remains constant in the vicinity of the first Schumann resonance. This is explained by the fact that the first resonance frequency splits into a triplet, and one side-band wave of this triplet plays the dominant role in the radio-wave propagation. It is also shown that occasional degeneracy may occur in the cavity within the framework of the hedgehog model of the geomagnetic field.

Nickolaenko, A. P.; Rabinovich, L. M.; Shvets, A. V.; Shchekotov, A. Yu.

2004-04-01

441

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

442

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

443

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.

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

2013-01-01

444

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

Microsoft Academic Search

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

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

2010-01-01

445

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