Showing papers on "Radio wave published in 2008"

Nanometre-scale germanium photodetector enhanced by a near-infrared dipole antenna

Abstract: A critical challenge for the convergence of optics and electronics is that the micrometre scale of optics is significantly larger than the nanometre scale of modern electronic devices. In the conversion from photons to electrons by photodetectors, this size incompatibility often leads to substantial penalties in power dissipation, area, latency and noise1,2,3,4. A photodetector can be made smaller by using a subwavelength active region; however, this can result in very low responsivity because of the diffraction limit of the light. Here we exploit the idea of a half-wave Hertz dipole antenna (length ∼ 380 nm) from radio waves, but at near-infrared wavelengths (length ∼ 1.3 µm), to concentrate radiation into a nanometre-scale germanium photodetector. This gives a polarization contrast of a factor of 20 in the resulting photocurrent in the subwavelength germanium element, which has an active volume of 0.00072 µm3, a size that is two orders of magnitude smaller than previously demonstrated detectors at such wavelengths. By scaling down device size, the principles of radio antennas can be used in the optical regime. These optical antennas act as a bridge between optics and electronics, collecting and enhancing light to enable the creation of tiny semiconductor photodetectors.

S/WAVES: The radio and plasma wave investigation on the STEREO Mission

Abstract: This paper introduces and describes the radio and plasma wave investigation on the STEREO Mission: STEREO/WAVES or S/WAVES. The S/WAVES instrument includes a suite of state-of-the-art experiments that provide comprehensive measurements of the three components of the fluctuating electric field from a fraction of a hertz up to 16 MHz, plus a single frequency channel near 30 MHz. The instrument has a direction finding or goniopolarimetry capability to perform 3D localization and tracking of radio emissions associated with streams of energetic electrons and shock waves associated with Coronal Mass Ejections (CMEs). The scientific objectives include: (i) remote observation and measurement of radio waves excited by energetic particles throughout the 3D heliosphere that are associated with the CMEs and with solar flare phenomena, and (ii) in-situ measurement of the properties of CMEs and interplanetary shocks, such as their electron density and temperature and the associated plasma waves near 1 Astronomical Unit (AU). Two companion papers provide details on specific aspects of the S/WAVES instrument, namely the electric antenna system (Bale et al., Space Sci. Rev., 2007) and the direction finding technique (Cecconi et al., Space Sci. Rev., 2007).

Learning Adaptive Temporal Radio Maps for Signal-Strength-Based Location Estimation

Abstract: In wireless networks, a client's locations can be estimated using the signals received from various signal transmitters. Static fingerprint-based techniques are commonly used for location estimation, in which a radio map is built by calibrating signal-strength values in the offline phase. These values, compiled into deterministic or probabilistic models, are used for online localization. However, the radio map can be outdated when the signal-strength values change with time due to environmental dynamics, and repeated data calibration is infeasible or expensive. In this paper, we present a novel algorithm, known as LEMT (Location Estimation using Model Trees), to reconstruct a radio map using real-time signal- strength readings received at the reference points. This algorithm can take into account real-time signal-strength values at each time point and make use of the dependency between the estimated locations and reference points. We show that this technique can effectively accommodate the variations of signal strength over different time periods without the need to rebuild the radio maps repeatedly. We demonstrate the effectiveness of our proposed technique on realistic data sets collected from an 802.11b wireless network and a RFID-based network.

Radio Wave Characterization and Modeling in Underground Mine Tunnels

Abstract: Results are presented on wideband radio propagation measurements and statistical modeling at 2.4 GHz and 5.8 GHz in real underground mine tunnels. This peculiar type of confined environment is characterized by very rough surfaces and a frequent absence of a line-of-sight between transmitting and receiving antennas. The resulting propagation characteristics differ from those frequently encountered in more typical indoor environments such as offices and corridors. Indeed, the rms delay spread shows little or no correlation with respect to transmitter-receiver distance and, in addition, no impulse response path arrival clustering effect is observed. However, the path amplitude distribution does tend to follow a Rice distribution in the line-of-sight case, and a Rayleigh distribution otherwise.

Electromagnetic Reduction of Plasma Density During Atmospheric Reentry and Hypersonic Flights

Abstract: As a vehicle reenters or travels through the atmosphere at hypersonic velocities, the shock-heated air surrounding the vehicle becomes weakly ionized. This plasma layer causes an important systems operation problem known as communications blackout or radio blackout. At sufficiently high plasma density, the plasma layer either reflects or attenuates radiowave communications to and from the vehicle. In this paper, we study the application of electric and magnetic fields to reduce the plasma density. Specifically, an E ? B crossed-field configuration is proposed. Both analytical and numerical results suggest that significant reduction of the plasma density is possible at large altitudes. For instance, plasma density reduction by a factor of 10 is predicted in the case of 81 km and a magnetic field of about 0.1 T. Theoretical results suggest that significant reduction of the plasma density is possible, enabling radio communication across the plasma layer. The benefit of the reduced plasma density in terms of electromagnetic wave absorption across the plasma layer is estimated.

The Electric Antennas for the STEREO/WAVES Experiment

Abstract: The STEREO/WAVES experiment is designed to measure the electric component of radio emission from interplanetary radio bursts and in situ plasma waves and fluctuations in the solar wind. Interplanetary radio bursts are generated from electron beams at interplanetary shocks and solar flares and are observed from near the Sun to 1 AU, corresponding to frequencies of approximately 16 MHz to 10 kHz. In situ plasma waves occur in a range of wavelengths larger than the Debye length in the solar wind plasma λ D ≈10 m and appear Doppler-shifted into the frequency regime down to a fraction of a Hertz. These phenomena are measured by STEREO/WAVES with a set of three orthogonal electric monopole antennas. This paper describes the electrical and mechanical design of the antenna system and discusses efforts to model the antenna pattern and response and methods for in-flight calibration.

Analysis of an Electromagnetic Mitigation Scheme for Reentry Telemetry Through Plasma

Abstract: During hypersonic reentry flight, the shock heated air generates a weakly ionized plasma layer. Because the weakly ionized plasma layer has a high plasma number density, it causes an important systems operation problem that is known as a communication, or radio, blackout. The radio blackout occurs when the plasma frequency of the plasma layer is higher than a radio wave frequency. In this case, the radio wave signals to and from the vehicle are reflected or attenuated so that the vehicle loses voice communication, data telemetry, and Global Positioning System navigation. The radio blackout problem can be solved by reducing the plasma number density of the plasma layer because the plasma frequency is mainly related to the plasma number density of the plasma layer. To reduce the plasma number density of the plasma layer, an electromagnetic E ? B layer approach is proposed. The proposed ExB layer is analyzed by a two-dimensional model. It suggests that an E ? B layer can be used to allow transmission of the communication signals through the plasma layer. We also propose an alternative to reduce the plasma density, based on an electrostatic plasma sheath.

Positioning system, positioning method, and positioning program

Abstract: An object of the present invention is to implement accurate positioning of a mobile communication terminal even in an environment in which delay waves are included in radio waves arriving at the mobile communication terminal from radio wave sources A positioning server 10 forming a positioning system for estimating a location of a cellular terminal 20 has a distance information acquisition unit 13 for acquiring information indicating distances calculated based on radio waves transmitted and received between a plurality of cellular base stations 30 and the cellular terminal 20; a direction information acquisition unit 14 for acquiring a plurality of pieces of information indicating directions of radio waves received by the cellular terminal 20; a virtual sector calculation unit 15 for calculating for each of the cellular base stations, a range of directions from the cellular base station 30 to the cellular terminal 20 from the information indicating the directions of the radio waves, based on a range calculation rule stored in advance; and a location calculation unit 16 for calculating the location of the cellular terminal 20, based on the distances and the range of directions

Modeling of Io‐Jupiter decameter arcs, emission beaming and energy source

Abstract: [1] The electrodynamic interaction between Io and Jupiter causes electron acceleration in/near the Io flux tube (IFT), which in turn produces intense radio emissions in the hecto-decameter range, displaying arc shapes in the time-frequency plane. The shapes depend on the hemisphere of origin of the emission and on the Io-Jupiter-observer geometry. Assuming radio wave generation by the cyclotron-maser instability, we simulate t-f arc shapes as a function of emission beaming, lead angle between the radio emitting field line and the instantaneous Io field line, and electron energy. A good fit of arcs t-f location and shape is obtained for loss-cone driven (oblique) emission beamed in a hollow cone of half-angle ≥80° around the source magnetic field, closing at high frequencies, and of cone thickness ≤1°. The lead angle is found between a few degrees and ∼40° in both hemispheres. Resonant electron energies are about a few keV. Implications on the absence of a plasma cavity at IFT footprints and on Jupiter's internal magnetic field model are discussed.

Global mapping of ionospheric HF/VHF radio wave absorption due to solar energetic protons

Abstract: [1] Simple, one-parameter algorithms are applied to the observed energetic proton flux as provided by instruments aboard the GOES series of satellites to yield estimates of the high-latitude HF and VHF radio wave absorption for day and night, respectively. These results are extended to full daily coverage by treating the effects of solar illumination, geomagnetic cutoff variation, and frequency dependence over the entire earth. Validation calculations of the polar cap absorption of HF radio waves have been performed for 11 larger solar energetic particle events during the period from 1992 to 2002 and the results are compared to observations of 30 MHz riometers operated by the Air Force Geophysics Laboratory and located at Thule, Greenland. Prediction of the minimum event duration from current flux level is also obtained, and a specimen presentation of the north and south polar caps illustrates the graphical output of the model for the peak of the 6 December 2006 solar proton event.

Recent results for plasma antennasa)

Abstract: Plasma antennas are just as effective as metal antennas. They can transmit, receive, and reflect radio waves just as well as metal antennas. In addition, plasma generated noise does not appear to be a problem.

Amplitude calibration of a digital radio antenna array for measuring cosmic ray air showers

Abstract: Radio pulses are emitted during the development of air showers, where air showers are generated by ultra-high energy cosmic rays entering the Earth’s atmosphere. These nano­ second short pulses are presently investigated by various experiments for the purpose of using them as a new detection technique for cosmic particles. For an array of 30 digital radio antennas (LOPES experiment) an absolute amplitude calibration of the radio antennas including the full electronic chain of the data acquisition system is performed, in order to estimate absolute values of the electric field strength for these short radio pulses. This is mandatory, because the measured radio signals in the MHz frequency range have to be compared with theoretical estimates and with predictions from Monte Carlo simulations to reconstruct features of the primary cosmic particle. A commercial reference radio emitter is used to estimate frequency dependent correction factors for each single antenna of the radio antenna array. The expected received power is related to the power recorded by the full electronic chain. Systematic uncertainties due to different environmental conditions and the described calibration procedure are of order 20 %.

Method for detecting interference in radar system and radar using the same

Abstract: A method for detecting an occurrence of interference between a return of a radar wave which has been transmitted by a radar and has an oscillating amplitude in time and a radio wave transmitted by some other radar, Includes steps of: detecting extremal points of an incident radio wave in which the radio wave transmitted by the other radar is superposed on the return of the radar wave, extracting, sequentially in time, an emerging pattern of the extremal points of the incident radio wave within each of periods of time to obtain a series of emerging patterns of the extremal points, detecting a period during which the emerging pattern of the extremal points is irregular among the series of the emerging patterns of the extremal points, and determining that the interference occurs during the detected period of time.

A 5GHz Double-Sideband Radar Sensor Chip in 0.18 $\mu$ m CMOS for Non-Contact Vital Sign Detection

Abstract: A 5 GHz double-sideband radar sensor chip for non-contact vital sign detection was designed and fabricated in UMC 0.18 mum mixed-mode/radio frequency CMOS process. The transceiver was designed with a differential architecture. Measurements show that it has over 1 GHz tuning range, and can successfully detect both the respiration and the heartbeat signals of a human subject. It is also shown that the differential architecture has the advantage of reducing local oscillation leakage. The 5 GHz double-sideband system can avoid null detection point by frequency tuning.

Minimal size FSS for long wavelength operation

Abstract: The properties of small finite size frequency selective structures (FSS) for use particularly at long wavelengths are summarised. The intended application is the modification of the EM architecture of buildings at mobile radio frequencies, for improved efficiency of radio spectrum use.

The interdependence of wavelength, redundancy and dose in sulfur SAD experiments.

Abstract: In the last decade, the popularity of sulfur SAD anomalous dispersion experiments has spread rapidly among synchrotron users as a quick and streamlined way of solving the phase problem in macromolecular crystallography. On beamline 10 at SRS (Daresbury Laboratory, UK), a versatile design has allowed test data sets to be collected at six wavelengths between 0.979 and 2.290 A in order to evaluate the importance and the interdependence of experimental variables such as the Bijvoet ratio, wavelength, resolution limit, data redundancy and absorbed X-ray dose in the sample per data set. All the samples used in the experiments were high-quality hen egg-white lysozyme crystals. X-radiation damage was found to affect disulfide bridges after the crystals had been given a total dose of 0.20 x 10(7) Gy. However, with such a total dose, it was still possible in all cases to find a strategy to collect data sets to determine the sulfur substructure and produce good-quality phases by choosing an optimum combination of wavelength, exposure time and redundancy. A |Delta(ano)|/sigma(Delta(ano)) greater than 1.5 for all resolution shells was a necessary requirement for successful sulfur SAD substructure location. Provided this is achieved, it seems possible to find an optimum compromise between wavelength, redundancy and dose to provide phasing information. The choice of the wavelength should then follow the sample composition and the diffracting properties of the crystal. For strongly diffracting crystals, wavelengths equal or shorter than 1.540 A can be selected to capture the available data (provided the Bijvoet ratio is reasonable), while a longer wavelength, to gain as high a Bijvoet ratio as possible, must be used for more weakly diffracting crystals. These results suggest that an approach to a sulfur SAD experiment based on a complete description of the crystal system and the instrument for data collection is useful.

STEREO/Waves Goniopolarimetry

Abstract: The STEREO/Waves experiment is dedicated to the study of inner heliosphere radio emissions. This experiment is composed of a set of two identical receivers placed on each of the two STEREO spacecraft. The STEREO/Waves receivers have instantaneous Goniopolarimetric (GP) capabilities (also referred to as direction-finding capabilities). This means that it is possible to retrieve the direction of arrival of an incoming electromagnetic radio wave, its flux and its polarization. We review the state of the art of GP-capable radio receivers and available GP techniques. We then present the GP capabilities of the STEREO/Waves experiment. We finally show some GP results on solar Type III radio bursts, using data recorded with the Cassini/RPWS/HFR, which are very similar to the STEREO/Waves data.

Energetic electron precipitation during substorm injection events: High-latitude fluxes and an unexpected midlatitude signature

Abstract: [1] Geosynchronous Los Alamos National Laboratory (LANL-97A) satellite particle data, riometer data, and radio wave data recorded at high geomagnetic latitudes in the region south of Australia and New Zealand are used to perform the first complete modeling study of the effect of substorm electron precipitation fluxes on low-frequency radio wave propagation conditions associated with dispersionless substorm injection events. We find that the precipitated electron energy spectrum is consistent with an e-folding energy of 50 keV for energies <400 keV but also contains higher fluxes of electrons from 400 to 2000 keV. To reproduce the peak subionospheric radio wave absorption signatures seen at Casey (Australian Antarctic Division), and the peak riometer absorption observed at Macquarie Island, requires the precipitation of 50–90% of the peak fluxes observed by LANL-97A. Additionally, there is a concurrent and previously unreported substorm signature at L < 2.8, observed as a substorm-associated phase advance on radio waves propagating between Australia and New Zealand. Two mechanisms are discussed to explain the phase advances. We find that the most likely mechanism is the triggering of wave-induced electron precipitation caused by waves enhanced in the plasmasphere during the substorm and that either plasmaspheric hiss waves or electromagnetic ion cyclotron waves are a potential source capable of precipitating the type of high-energy electron spectrum required. However, the presence of these waves at such low L shells has not been confirmed in this study.

Ionosphere and Applied Aspects of Radio Communication and Radar

Abstract: The Regular Ionosphere: Main Characteristics and Processes Ionosphere Content Major Characteristics of the Ionospheric Plasma Transport Processes of Plasma in the Ionosphere Ionization-Recombination Balance in the Ionosphere Nonlinear Phenomena and Plasma Instabilities in the Disturbed Irregular Ionosphere Physical Aspects of Nonlinear Phenomena in the Artificially Heated Ionospheric Plasma Interaction of Probing Radio Waves with Heating-Induced Plasma Instabilities Generated by Strong Radio Waves Plasma Instabilities of Natural Origin Generated in the Irregular Ionosphere Natural Thermal-Induced Instabilities: Recombination Kinetic Kinetic Drift-Dissipative Current-Induced Natural Plasma Instabilities: The Current-Convective Gradient-Drift Two-Stream Convergence Dissipative Drift-Dissipative Rayleigh-Taylor Hydrodynamic Theoretical Aspects of Generation of Nonlinear Plasma Instabilities Nonlinear Wave-Wave Interactions in the Ionospheric Plasma Particle-Wave Interactions in the Ionospheric Plasma: Nonlinear Saturation of Electrostatic Instabilities in the Ionosphere Numerical Analysis of Nonlinear Effects of Instabilities Generation Radio Signal Presentation in the Ionospheric Communication Channel Bandpath and Baseband Signal Presentation Narrowband Signal Presentation Wideband Signal Presentation Fading Phenomena in Ionospheric communication Channels Path Loss: A Mathematical Description Slow Fading of Radio Signal: A Mathematical Description Fast Fading: A Mathematical Description Definition of Fading Phenomena in Static and Dynamic Ionospheric Channel Evolution of Plasma Irregularities in the Ionosphere Diffusion of Plasma Irregularities in the Ionosphere Classical Description of the Diffusion Process in Plasma Diffusion of Small Plasma Disturbance in Weakly Ionized Plasma Diffusion of Plasma Disturbances with an Arbitrary Degree of Ionization Diffusion Spreading of Plasma Irregularities in the Middle-Latitude Ionosphere Drift of Plasma Irregularities in the Ionosphere A Classical Description of Drift in Unbounded Homogeneous Plasma Dynamics and Spreading of Arbitrary Irregularity in the Ionosphere Thermodiffusion of Plasma Irregularities in the Ionosphere General Problem Statement: Functions and Parameters One-Dimensional Heating of the E and F Layers of the Ionosphere Evolution of 3-D Heating-Induced Irregularity in the Ionosphere Modern Radiophysical Methods of Investigation of Ionospheric Irregularities Radio and Optical Methods of Studying Artificially Induced Irregularities in the Ionosphere Radio Methods for Diagnostics of Heating-Induced Irregularities Methods of Investigations of Dynamics of Plasma Clouds in the Ionosphere by Rocket Injection Natural Ionospheric Irregularities and Methods of Their Parameters' Diagnostics Radio Methods of Diagnostics of Meteor-Induced and HE Irregularities in the Middle-Latitude Ionosphere Radio Sounding of Sporadic Inhomogeneities and Bubbles in the Equatorial Ionosphere Observations of Irregularities in the High-Latitude Ionosphere Performance of Radio Communication in Ionospheric Channels Absorption of Radio Waves in the Regular Ionosphere Radio Scattering Caused by Plasma Irregularities of Various Origins in the Ionosphere Experimental Investigations of Backscattering and Forward Scattering in Region E of the Ionosphere Theory of Backscattering of Radio Waves from Anisotropic Plasma Irregularities Forward Scattering of Radio Waves from Anisotropic Irregularities Power of HE-Scatter Radio Signals Forward and Backscattering from Irregularities of the F Region of the Ionosphere Long-Distance Radio Propagation through the Ionospheric Channels Wave Propagation in the Ionosphere Disturbed by Powerful Radio Waves Capturing of Radio Waves into the Ionospheric Layered Waveguides Partial Scattering of Radio Waves in the D Region of the Ionosphere Methods of Design of Ionospheric Radio Propagation Channels Optical and Radio Systems for Investigation of the Ionosphere and Ionospheric Communication Channels Devices and Systems for Diagnostics of Ionospheric Phenomena Optical Devices Incoherent Scatter Radars SuperDARN The Global Positioning System in Investigations of the Ionosphere Diagnostics of the Nonregular Ionosphere by LFM-Ionosondes Developments of LFM Ionosondes in the Historical Perspective Operating Principles of LFM Ionosondes Monitoring of Ionospheric Communication Channels Performance of Land-Satellite Communication Links Passing through the Irregular Ionosphere Refraction of Radio Waves in Quasi-Regular Ionospheric Plasma Propagation Effects of Large- and Moderate-Scale Ionospheric Irregularities Effects of Large-Scale Irregularities on Radio Propagation Effects of Moderate-Scale Irregularities on Radio Propagation Fading Effects Caused by Small-Scale Ionospheric Irregularities Effects of Magnetic Storm on Land-Satellite Communication Parameters of Data Signals in the Land-Satellite Communication Links with Fading Main Parameters of the Information Data Stream Data Stream Parameters for Channels with Fading Caused by Magnetic Storm

Mean Effective Gain of Mobile Antennas in Line-of-Sight Street Microcells With Low Base Station Antennas

Abstract: A method for evaluating the mean effective gain (MEG) of mobile antennas in line-of-sight (LOS) street microcells with low base station antennas is investigated. The received power patterns of incident radio waves along typical streets measured in actual street microcells in urban areas of Tokyo are presented to clarify the proper distribution model for the incident radio waves. A two-dimensional statistical distribution model is proposed based on the measured received power patterns for the incident radio waves that follow a Gaussian distribution in the azimuth angle, but are concentrated in the horizontal plane in the elevation angle. The two-dimensional theoretical expression of the MEG that consists of the incident distribution model function and the radiation patterns in the horizontal plane of the mobile antennas is derived to evaluate easily the MEG. We show that the MEG values in street microcells are not defined as only one value and form the MEG pattern because the MEG values are changed by the relative direction of the radio waves arriving at the mobile station antennas. The measured and calculated MEG values (MEG patterns) of the whip antennas used in the experiments are in good agreement. The average error between the measured and calculated MEG values is within approximately 4.5 dB at maximum. The results show that the MEG degradation of the mobile station antennas due to the effect of the human body is properly evaluated by the proposed distribution model. The proposed statistical distribution model is valid and effective in both estimating the MEG values of mobile antennas and designing the LOS street microcell systems with low base station antennas.

Geometric modulation : A more effective method of steerable ELF/VLF wave generation with continuous HF heating of the lower ionosphere

Abstract: [1] ELF/VLF radio waves (300 Hz–30 kHz) are difficult to generate with practical antennae, because of their extraordinarily long (10–1000 km) wavelengths, and the lossy nature of the Earth's surface at these frequencies. ELF/VLF waves have been successfully generated via amplitude modulated (AM) HF (2–10 MHz) heating of the lower ionosphere. Through the temperature-dependent conductivity of the lower ionospheric plasma, a patch of the ionospheric current becomes a large radiating ‘antenna’. We implement a new method of ELF/VLF wave generation, herein named ‘geometric modulation’, involving scanning the HF heating beam in a geometric pattern without modulating its power. Utilizing results from the upgraded 3.6 MW radiated HAARP HF antenna array, we show that geometric modulation can enhance ELF/VLF wave generation by up to ∼11 dB over the conventional AM method. Geometric modulation also allows directional launching of the signal into the Earth-ionosphere waveguide, forming an unprecedented steerable large-element ELF/VLF ionospheric phased array.

Wireless tag reader/writer

Abstract: In a wireless reader/writer according to one example of the present invention, a reader/writer main body 120 emits a radio wave with a different output power from an antenna 121 when a base unit 140 is detected to be mounted on an enclosure In addition, when a base unit 140 A is detected to be mounted on the enclosure, a reader/writer main body 120 A controls a switching device 132 to emit radio waves simultaneously or alternately from a first antenna and a second antenna

Direction identification in radio images of cosmic-ray air showers detected with LOPES and KASCADE

Abstract: Aims. We want to understand the emission mechanism of radio emission from air showers to determine the origin of high-energy cosmic rays. Therefore, we study the geometry of the air shower radio emission measured with LOPES and search for systematic e! ects between the direction determined on the radio signal and the direction provided by the particle detector array KASCADE. Methods. We produce 4D radio images on time-scales of nanoseconds using digital beam-forming. Each pixel of the image is calculated for three spatial dimensions and as a function of time. The third spatial dimension is obtained by calculating the beam focus for a range of curvature radii fitted to the signal wave front. We search this multi-dimensional parameter space for the direction of maximum coherence of the air shower radio signal and compare it to the direction provided by KASCADE. Results. The maximum radio emission of air showers is obtained for curvature radii being larger than 3 km. We find that the direction of the emission maximum can change when optimizing the curvature radius. This dependence dominates the statistical uncertainty for the direction determination with LOPES. Furthermore, we find a tentative increase of the curvature radius to lower elevations, where the air showers pass through a larger atmospheric depth. The distribution of the o! sets between the directions of both experiments is found to decrease linearly with increasing signal-to-noise ratio. Significantly increased o! sets and enhanced signal strengths are found in events which were modified by strong electric fields in thunderstorm clouds. Conclusions. We conclude that the angular resolution of LOPES is su" cient to determine the direction which maximizes the observed electric field amplitude. However, the statistical uncertainty of the directions is not determined by the resolution of LOPES, but by the uncertainty of the curvature radius. We do not find any systematic deviation between the directions determined from the radio signal and from the detected particles. This result places a strong supportive argument for the use of the radio technique to study the origin of high-energy cosmic rays.

HF radio wave acceleration of ionospheric electrons: Analysis of HF‐induced optical enhancements

Abstract: The shape of the HF-pump modified electron energy distribution has long been a central question in the field of ionospheric high-frequency radio wave modification experiments. Here we present estimates of the enhanced differential electron flux, from 1.9 to 100 eV based on optical multiwavelength (6300, 5577, 8446, and 4278 A) data and 930 MHz incoherent scatter radar measurements of ion temperature, electron temperature and concentration. According to our estimate, the electron energy distribution is depleted in the energy range of 2 to approximately 4 eV, probably caused by electron excitation of vibrational states in N2. At the higher energies the electron energy distribution has a nonthermal tail. Further we show that the altitude variations of the four optical emissions should differ both in altitude coverage and center altitude.

Radio wave propagation characteristic estimation system, its method, and program

Abstract: [PROBLEMS] To prevent the estimation accuracy of a radio wave propagation estimation system from being degraded significantly and to reduce computation complexity. [MEANS FOR SOLVING PROBLEMS] A radio wave propagation characteristic estimation system for estimating the radio wave characteristic in deterministic consideration of a structure such as a building or a piece of indoor furniture. The system comprises object selecting means for selecting an object having a less degree of influence on the estimation accuracy from the objects within an analysis region by using transmission point position data, number-of-constituting-planes reducingmeans for reducing the number of constituting planes of the selected object, and radio wave propagation estimating means for performing radio wave propagation estimation by using an object included in the analysis region and not selected by the object selecting means and the object the number of constituting-planes of which is reduced.

Determination of GPS Total Electron Content using Single Layer Model (SLM) Ionospheric Mapping Function

Abstract: Summary The ionosphere layer is very important to the communication system. The ions produced from the striking process of the ultra violet light have an active role in reflecting and observing the earth radio waves. This layer also is an unstable medium because it is vulnerable to several distortions which affect its physical condition. Studies of Total Electron Content (TEC) have given important relationship to the ionospheric layers due to high density of electron concentration at F region. Total Electron Content (TEC) measurements from ground stations to Global Positioning System (GPS) satellite provide a rich source of information about the Earth’s ionosphere. This research involves the determination of TEC content in ionosphere based on single layer model in order to determine the appropriate TEC value for Malaysia. This research assessing the errors translated from the code-delay to the carrier-phase ionospheric observable by the socalled “Levelling Process” which is applied to reduce carrier phase ambiguities from the data.

Schumann Resonances as a Means of Investigating the Electromagnetic Environment in the Solar System

Abstract: The propagation of extremely low frequency (ELF, 3 Hz to 3 kHz) radio waves and resonant phenomena in the spherical Earth-ionosphere cavity has been studied for almost fifty years. When such a cavity is excited by naturally occurring broadband electromagnetic radiation, resonances can develop if the equatorial circumference is approximately equal to an integral number of wavelengths of the propagating electromagnetic waves; these are termed Schumann resonances. They provide information not only about thunderstorm and lightning activity on the Earth, and their relation to climate, but also on the properties of the low ionosphere. Similar investigations can be performed for any other planet or satellite, provided that it has an ionosphere.

Polarization transfer for sensitivity-enhanced MRS using a single radio frequency transmit channel

Abstract: Polarization transfer techniques are used to enhance sensitivity and improve localization in multinuclear MRS, by transferring polarization from highly polarized or even hyperpolarized nuclei to less sensitive spin systems. Clinical MR scanners are in general not equipped with a second radio frequency (RF) transmit channel, making the conventional implementation of polarization transfer techniques such as distortionless enhanced polarization transfer (DEPT) impossible. Here we present a DEPT sequence using pulses sequentially that can be used on a single RF transmit channel (SC-DEPT). Theoretical simulations, phantom measurements, and in vivo results from human brain at 3 T show that the SC-DEPT method performs as well as the conventional DEPT method. The results indicate that an independent second RF transmit channel for simultaneous pulsing at different nuclear frequencies is not needed for polarization transfer, facilitating the use of these methods with common clinical systems with minor modifications in the RF architecture.