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Showing papers on "Very low frequency published in 2009"


Journal ArticleDOI
TL;DR: In this paper, a very low frequency (VLF) seismic signals observed in southwestern Japan are evidently radiated from shear slips on the upper surface of the subducting Philippine Sea Plate.
Abstract: [1] Very low frequency (VLF) seismic signals observed in southwestern Japan are evidently radiated from shear slips on the upper surface of the subducting Philippine Sea Plate We used grid moment tensor inversion and centroid moment tensor inversion to calculate 242 moment tensor solutions with moment magnitudes between 31 and 38 from continuous seismograms recorded over a 5 year period by using a very dense broadband seismic network At least 5–10 sequences of repetitive activity were observed during the 5 years The VLF events formed clustered distributions along the 35 km isodepth contour of the subducting plate surface The nodal planes (which dip landward) of moment tensor solutions of the VLF events reflected the configuration of the subducting plate interface The slip vectors were consistent with the direction of movement of the subducting plate; the dip and strike of the slip vectors clearly reflected the configuration of the upper surface of the subducting plate We found that the rates of seismic moment release per unit area associated with five major VLF clusters were very similar, although both the seismic magnitudes and sizes of the clusters varied considerably The rate of seismic moment released from detectable VLF sources was 01% of the rates of short-term slow slip events, suggesting that the source areas occupied only 01% of the fault segment on which the short-term slow slip events occurred

70 citations


Patent
15 Dec 2009
TL;DR: In this paper, a ground-based Horizontal Electric Dipole (HED) antenna is used to send electromagnetic pulses upward in the E-region of the ionosphere to form an oscillatory or pulsed electric field.
Abstract: A method for generating electromagnetic waves in the ELF/ULF comprising the steps of using a ground-based Horizontal Electric Dipole (HED) antenna to send electromagnetic pulses upwardly in the E-region of the ionosphere to form an oscillatory or pulsed electric field; allowing said pulsed electric field to interact with magnetized plasma of the lower ionosphere to generate a pulsed horizontal and vertical current which have associated Horizontal and Vertical Electric Dipole moment; and allowing them to radiate.

57 citations


Journal ArticleDOI
TL;DR: In this paper, a model for very low frequency and low-frequency lightning signal propagation over ranges of hundreds to a couple of thousand kilometers is presented, which is a composite of ground and ionospheric-reflected waves.
Abstract: A model simulation for very low-frequency and low-frequency lightning signal propagation over ranges of hundreds to a couple of thousand kilometers is presented in this paper. The model is a composite of ground and ionospheric-reflected waves. The ground wave is modeled over a spherical earth that has a finite conductivity. The ionospheric-wave simulation is based on a recently developed full-wave model that treats the lower portion of the ionosphere as a magnetized, anisotropic, collisional, and cold-electron medium. In this paper, only the first-hop ionosphere reflection is presented, although higher order reflections can be readily implemented by the model. For the purpose of demonstration, the modeled results are compared to actual observations of negative cloud-to-ground strokes at various distances for day and nighttime. The model itself, however, can be used for any type of lightning discharge event, including the incloud events that occur above the ground. This model, together with multistation Los Alamos Sferic Array measurements of lightning discharges, might provide an alternate means for monitoring the temporal and spatial variations of the lower portion of the ionosphere.

49 citations


Journal ArticleDOI
TL;DR: In this paper, the authors analyzed night-side measurements of the DEMETER spacecraft related to lightning activity and found that the penetration into the ionosphere occurs at nearly vertical wave vector angles (as was expected from coupling conditions) at distances of 100-900 km from the source lightning.
Abstract: (1) We analyze nightside measurements of the DEMETER spacecraft related to lightning activity. At the 707 km altitude of DEMETER, we observe 3-D electric and magnetic field waveforms of fractional-hop whistlers. At the same time, the corresponding atmospherics are recorded by a very low frequency (VLF) ground-based station located in Nancay (France). The source lightning strokes are identified by the METEORAGE lightning detection network. We perform multidimensional analysis of the DEMETER measurements and obtain detailed information on wave polarization characteristics and propagation directions. This allows us for the first time to combine these measurements with ray-tracing simulation in order to directly characterize how the radiation penetrates upward through the ionosphere. We find that penetration into the ionosphere occurs at nearly vertical wave vector angles (as was expected from coupling conditions) at distances of 100-900 km from the source lightning. The same distance is traveled by the simultaneously observed atmospherics to the VLF ground station. The measured dispersion of fractional-hop whistlers, combined with the ionosonde measurements at the Ebro observatory in Spain, allows us to derive the density profile in the topside ionosphere.

46 citations


Journal ArticleDOI
TL;DR: In this article, the precipitated flux of >100 keV electrons induced by the NPM transmitter peaks at L ≃ 1.9 and, in the rare cases of detection, may be at higher energies than the ∼100 kV peak predicted by the model.
Abstract: [1] Near loss cone energetic electron flux increases induced by ground-based very low frequency (VLF) transmissions are observed directly via satellite-based detection. In 2 years of experiments ranging from 27 March 2006 through 2 April 2008 with the 21.4-kHz transmitter NPM in Lualualei, Hawaii, and the French satellite DEMETER (detection of electromagnetic emissions transmitted from earthquake regions), only a few cases of detection of individual pulses of transmitter-induced precipitation of inner radiation belt electrons have been realized. Analysis of the specific cases of detection allow comparison of precipitating flux with predictions based on ray-tracing analyses of wave propagation and test particle modeling of the wave-particle interaction. Results indicate that the precipitated flux of >100 keV electrons induced by the NPM transmitter peaks at L ≃ 1.9 and, in the rare cases of detection, may be at higher energies than the ∼100 keV peak predicted by the model. The low detection rate is attributed to the orientation of the DEMETER particle detector, which is mostly overwhelmed by the trapped population at the location of detection.

38 citations


Patent
20 May 2009
TL;DR: In this paper, a very low frequency test generator for generating a high voltage having a low frequency in order to test the insulation of capacitive loads, in particular power cables, is described.
Abstract: Disclosed is a very low frequency test generator for generating a high voltage having a low frequency in order to test the insulation of capacitive loads, in particular power cables. Said VLF test generator comprises two oscillators, the frequencies of which differ from one another by twice said low frequency, a resonance circuit which is fed in an interfering manner by the oscillators, is adjusted to the oscillator frequencies and causes a voltage rise of the interfering oscillator frequencies, and a demodulator for disconnecting the low-frequency high voltage generated by the interference from the resonance circuit and applying the same to the load.

32 citations


Journal ArticleDOI
TL;DR: In this paper, very low frequency electromagnetic (VLF) survey was carried out across Fethiye-Burdur Fault Zone (FBFZ) to locate subsurface faults covered by basin fills.

27 citations


Journal ArticleDOI
TL;DR: The development of a triaxial ldquoVLF gaussmeter,rdquo which can be made portable and can be used to monitor VLF electromagnetic radiation in residential and occupational environments is described.
Abstract: Naturally occurring electromagnetic oscillating fields in the very-low-frequency (VLF) range of the spectrum, i.e., from 1 to 200 kHz, are weak and difficult to detect under normal conditions. These naturally occurring VLF electromagnetic events are observed during thunderstorms, in certain mountain winds, and during earthquakes. On the other hand, man-made VLF electromagnetic fields are stronger and have been suspected of causing negative health effects. Typical sources of these VLF emissions include television sets, video display terminals (VDTs), certain medical devices, some radio stations, and the ground-wave emergency network (GWEN) used for military communications. This paper describes the development of a triaxial ldquoVLF gaussmeter,rdquo which can be made portable. This electronic system can be used to monitor VLF electromagnetic radiation in residential and occupational environments. The ldquoVLF gaussmeterrdquo is based on a microcontroller with a built-in 10-bit A/D converter and has been designed to measure the magnetic flux density and frequency across the wide VLF bandwidth (BW). A digitized resolution of 0.2 mG is used for the 0-200-mG range, and 2-mG resolution is used for the range of 2-2000 mG. The meter has been designed to include the following features: 1) automatic or manual range selection; 2) data logging; 3) single-axis mode; 4) peak hold; 5) RS-232 communication port; and 6) analog recorder output.

22 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a three-dimensional wave propagation code to predict the incidence and frequency offset of Doppler-shifted signals resulting from non-ducted interhemispheric propagation paths through the plasmasphere.
Abstract: Observations of signals from a terrestrial very low frequency (VLF) transmitter made by the DEMETER spacecraft inside the plasmasphere are modeled using a three-dimensional wave propagation code. The simulation results agree well with the satellite measurements, predicting both the incidence and frequency offset of Doppler-shifted signals resulting from non-ducted interhemispheric propagation paths through the plasmasphere. The observed Doppler shifts are similar to those which can result from linear mode coupling as VLF transmitter signals scatter from small-scale plasma density irregularities. Thus care must be taken to differentiate the two effects when studying the power loss of VLF waves through the ionosphere. The agreement shown between predictions and observation demonstrates the utility of the models used for understanding the wave energy distribution in the plasmasphere from terrestrial transmitters.

21 citations


Journal ArticleDOI
TL;DR: In this article, the role of humidity and frequency on the electrical breakdown of air in uniform field gaps was investigated and a correction factor to calculate breakdown voltage as a function of humidity for VLF was presented.
Abstract: The paper reports about the role of humidity and frequency on the electrical breakdown of air in uniform field gaps. Experiments were conducted on Rogowski-profile electrodes with gap lengths ranging from 5 to 53 mm at power frequency (60 Hz) and frequencies in the range of 18-50 kHz, corresponding to the VLF/LF bands used for long-range communication. The results show that breakdown voltage at VLF decreases with humidity, opposite to that observed at 60 Hz. Breakdown mechanisms for explaining this important phenomenon are proposed. A correction factor to calculate breakdown voltage as a function of humidity for VLF is presented.

15 citations


Journal ArticleDOI
TL;DR: In this article, the authors identify the signature of the sprite-producing lightning discharges in the ELF and VLF electromagnetic frequency bands, to qualify and compare their parameters, and study the influence of the thunderstorm-activated region on its overlaying ionosphere.

Journal ArticleDOI
TL;DR: In this paper, a robust indicator of the 27-day rotation of the Sun was discovered from measurements of VLF radio signals produced by lightning around the globe, and the solar rotation signal was found only at VlF frequencies close to the Earth-ionosphere waveguide cutoff frequency (∼2 kHz).
Abstract: [1] Typical solar parameters such as sunspot number, Lyman alpha radiation, and 10.7 cm radio flux exhibit 27-day variations associated with the rotation of the Sun. We have discovered a robust indicator of this 27-day rotation from measurements of VLF radio signals produced by lightning around the globe. The solar rotation signal is found only at VLF frequencies close to the Earth-ionosphere waveguide cutoff frequency (∼2 kHz). Furthermore, the 27-day solar rotation is detected only during daylight hours, implying a 27-day periodicity in the daytime collision frequency between free electrons and neutral air molecules in the lower ionosphere (∼80 km). We propose that continuous monitoring of VLF radio noise at frequencies close to the waveguide cutoff could provide a new method of continuously monitoring changes in the solar rotation rate.

Journal ArticleDOI
TL;DR: In this article, a case study has been performed on the lower ionospheric perturbations as seen from the Japanese subionospheric VLF/LF propagation network for a recent powerful earthquake, i.e., the Miyagi-oki earthquake on 16 August 2005 (magnitude 7.2, and depth 36.km).
Abstract: A case study has been performed on the lower ionospheric perturbations as seen from the Japanese subionospheric VLF (very low frequency, 3–30 kHz) /LF (low frequency, 30–300 kHz) propagation network for a recent powerful earthquake, i.e., the Miyagi-oki earthquake on 16 August 2005 (magnitude 7.2, and depth 36 km). Different propagation paths were examined and the two paths from a transmitter with call sign of JJY ( f = 40 kHz, in Fukushima prefecture) to both receiving stations of Kamachatka, Russia and Moshiri, Hokkaido, exhibit clear signatures of ionospheric perturbations a few days before and a few days after the earthquake. We have detected a clear nighttime amplitude decrease and an enhancement in nighttime fluctuation, both exceeding the corresponding three standard deviations from the mean. We discuss other seismogenic phenomena in order to study the lithosphere–ionosphere coupling.

Journal ArticleDOI
TL;DR: The mechanism of the Q-burst is investigated in the time and frequency domains in this paper, and it is found that the Qburst is produced by combination of direct and antipodal pulses from a source lightning stroke occurring all over the world.

Journal ArticleDOI
TL;DR: In this paper, measurements of very low frequency electric fields were performed onboard a stratospheric balloon launched on 7 August 2006 from Niamey, Niger, where numerous sferics were observed associated to lightning from active convective cells a few hundred kilometers from the balloon.
Abstract: In the frame of the African Monsoon Multidisciplinary Analyses campaign, measurements of very low frequency electric fields were performed onboard a stratospheric balloon launched on 7 August 2006 from Niamey, Niger. During flight, numerous sferics were observed associated to lightning from active convective cells a few hundred kilometers from the balloon. Lightning data analysis shows the transverse mode mean frequency of the Earth-ionosphere cavity decreasing from ∼2.4 to 2 kHz over a period of 1 h about sunset. The observed change of the transverse resonance near dusk can be fairly reproduced by an electromagnetic wave propagation model, which takes into account the D-region electron density variation predicted by the International Reference Ionosphere model.

Journal ArticleDOI
TL;DR: In this article, the authors studied the VLF (very low frequency) signal transmitted from the radio-navigation station in Komsomolsk-na-Amure at frequencies 11.9 and 14.8 kHz during seismic activity in Japan.
Abstract: The paper is related to the study of the VLF (very low frequency) signal transmitted from the radio-navigation station in Komsomolsk-na-Amure at frequencies 11.9 kHz and 14.8 kHz during seismic activity in Japan. First, using data collected with the electric field experiment on board the DEMETER satellite, global maps of electromagnetic signal at the frequencies of the transmitter have been obtained. Second, particular analysis of the VLF signals have been done at the time of two powerful earthquakes which took place in the region of Honshu Island on 2005/08/16 and on 2007/07/16. Comparison with averaged background data revealed disturbances in the signal intensity transmitted from the Komsomolsk-na-Amure station and received by the satellite. Discussions to understand why such changes can be associated with seismic activity are developed.

Journal Article
TL;DR: Based on the observing data of electro-magnetic field and other plasma parameters on DEMETER satellite of France, the anomalous variations in ion temperature, ion density, very low frequency (VLF)magnetic spectral values and so on were analyzed before Yutian 7.2 earthquake in Xinjiang as mentioned in this paper.
Abstract: Based on the observing data of electro-magnetic field and other plasma parameters on DEMETER satellite of France,the anomalous variations in ion temperature(T_i),ion density(N_i), Very Low Frequency(VLF)magnetic spectral values and so on were analyzed before Yutian 7.2 earthquake in Xinjiang.The analysis on Ti shows that the abrupt abnormal signals above epicentral area occur frequently in a much wider space,so they are with lower reliability as seismic precursors. Using revisited orbit method to compare the shapes of the density of H~+,it is found that all curves in a year are with consistent shape,but the peak amplitude in summer and autumn is 1 times of that in spring and winter.Compared the curves of N_i in 2008 with those in 2007 and 2006,apparent increases were exhibited at peak value regions in one month prior to Yutian earthquake with the amplitude rising to more than a magnitude relative to the other two years since February,and it continued to the earthquake occurrence.As for the magnetic spectrum data,orbits were selected in the distance of 2000 km and single frequency(400 Hz)values were extracted and arranged to a time series according to their record date and common latitude scale(0~60°N).The results show that during 2 days before the earthquake,the spectrum values at 400 Hz increased approximately by an order of magnitude,reflecting an obvious electro-magnetic emission occurred in ionosphere before the earthquake.It is illustrated after processing the three components of ELF electric and magnetic field on March 20 by vector analysis that,some left-rotated polarization electro-magnetic signals existing at the observing period reflect that the variation of ion density in ionosphere was accompanied by the emission of ELF electro-magnetic signals.Summing up,the variation process of these ionospheric parameters is consistent to the coupling mechanism of earthquake preparation and ionosphere at present.

Journal ArticleDOI
TL;DR: In this article, the STEREO/WAVES experiment at high radio frequencies is used to measure interplanetary radio emission and in situ plasma waves in the solar wind using three orthogonal monopole electric antennas in pseudodipole and monopole mode.
Abstract: [1] The STEREO/WAVES instrument is designed to measure interplanetary radio emission and in situ plasma waves in the solar wind. The instrument uses three orthogonal monopole electric antennas as its sensor system in both a pseudodipole and monopole mode. At high radio frequencies, the capacitance of the antennas determines the system gain. Here we estimate the stray capacitance in the antenna system by comparing the measured voltage spectrum with a model of the galactic continuum spectrum, which is the instrument background at high frequencies. Together with the antenna free-space capacitance, these measurements provide an absolute calibration of the STEREO/WAVES experiment at radio frequencies, a prerequisite for quantitative studies of solar and astrophysical radio emission.

27 Nov 2009
TL;DR: This paper presents the novel concept of OLFAR, the orbiting low frequency antennas for radio astronomy in space, and proposes an autonomous distributed sensor system in space to explore this new low-frequency band forRadio astronomy.
Abstract: New interesting astronomical science drivers for very low frequency radio astronomy have emerged, ranging from studies of the astronomical dark ages, the epoch of reionization, exoplanets, to ultra-high energy cosmic rays. Huge efforts are currently made to establish low frequency Earthbound instruments, since today’s technology is able to support this. However, astronomical observations with Earth-bound radio telescopes at very low frequencies are hampered by the ionospheric plasma, which scatters impinging celestial radio waves. This effect is larger at lower frequencies. Below about 5 MHz at night or about 10 MHz during daytime, the ionosphere is even opaque for radio waves. That means that Earth-bound radio astronomy observations in those bands would be severely limited in sensitivity and spatial resolution, or would be entirely impossible. A radio telescope in space would not be hampered by the Earths ionosphere, but up to now such a telescope was technologically and financially not feasible. However, extrapolation of current technological advancements in signal processing and small satellite systems imply that distributed low frequency radio telescopes in space could be feasible. We propose an autonomous distributed sensor system in space to explore this new low-frequency band for radio astronomy. The array will have identical elements (satellites), and ideally no central processing system. An advantage of such a system is that it is highly scalable and, due to the distributed nature, virtually insensitive to failure or non-availability of a fraction of its components. In this paper we present this novel concept of OLFAR, the orbiting low frequency antennas for radio astronomy in space.

01 Jan 2009
TL;DR: In this article, correlations between VLF signatures and optical events are used to show that these Early VlF events may be the signature of ionospheric modification by in-cloud (IC) lightning discharges.
Abstract: Lightning discharges emit intense optical and acoustic energy, in the form of lightning and thunder, respectively, but a large amount of energy is emitted as radio-frequency electromagnetic pulses (EMP). These pulses can be detected thousands of kilometers away, thanks to efficient propagation in the waveguide formed by the conducting Earth and the overlying ionosphere. In addition, intense discharges interact with the overlying ionosphere at 80-100 km altitude. The EMP-ionosphere interaction is directly observed in one manifestation as the bright transient optical emissions known as “elves”, but in addition, the interaction can directly modify the free electron density in the nighttime lower ionosphere. Modifications of the ionospheric electron density can be detected via subionospheric Very Low Frequency (VLF) remote sensing. In this method, coherent signals from powerful VLF transmitters, built for submarine communication and operated by the Navy, are monitored and their amplitude and phase are tracked in time. The variations of these signals are used to sense ionospheric modifications through rapid changes in the received amplitude and/or phase when the transmitted signal propagates through an ionospheric perturbation. When these perturbations are caused by lightning, they are known as “Early VLF” perturbations, due to the negligible delay between the lightning discharge and the appearance of the VLF signal change, whereas lightning-induced electron precipitation (LEP) events have a delay of 1–2 seconds. In this work, correlations between VLF signatures and optical events are used to show that these Early VLF events may be the signature of ionospheric modification by in-cloud (IC) lightning discharges. While the more impressive cloud-to-ground

01 Aug 2009
TL;DR: In this paper, a borehole antenna has been installed at Agra (latitude 27.2N, longitude 78E), India since 1 June 2006 and the subsurface very low frequency (VLF) electric field emissions (f = 3.042 kHz) data has been recorded round the clock for a period of nineteen months from 01 June 2006 to 31 December 2007.
Abstract: A borehole antenna has been installed at Agra (latitude 27.2N, longitude 78E), India since 01 June 2006. The subsurface very low frequency (VLF) electric field emissions (f = 3.042 kHz) data has been recorded round the clock for a period of nineteen months from 01 June 2006 to 31 December 2007. This statistical analysis of data is presented in the paper. The occasional amplitude enhancement is observed in the data and examined in the light of magnetic storms, earthquakes, and lightning activities. It is found that in majority of the cases, amplitude anomalies are correlated with moderate seismic activities occurred during the period in the region. The propagation mechanism of VLF signals from the hypocenters of earthquakes to the observing station is discussed in the paper.

Patent
04 Sep 2009
TL;DR: In this article, a signal processor (104) separates a signal space associated with the at least one signal in the one radio frequency band and a background space associated to interference and noise in the other radio band.
Abstract: A receiver receives at least one radio frequency band. A signal processor (104) separates a signal space associated with the at least one signal in the at least one radio frequency band and a background space associated with interference and noise in the at least one radio frequency band. For a simulation, a memory (106) stores the environment data of the at least one radio system based on the background space under control of the signal processor (104).

Proceedings ArticleDOI
13 Apr 2009
TL;DR: A radio interferometric technique is used to transform the useful phase information from the high frequency radio signal to a low frequency signal that can be processed on low-cost hardware.
Abstract: The paper introduces a novel technique for the bearing estimation of radio sources that can be used for the precise localization and/or tracking of RF tags such as wireless sensor nodes. It is well known that the bearing to a radio source can be estimated by an array of antennas typically arranged in a circular manner. The method is often referred to as Quasi-Doppler measurement. The disadvantage of the existing method is that the receiver is relatively large because of the multiple antennas (typically 8 or 16) and it is computationally intensive to process the high frequency radio signals. Thus, it cannot be done on small, inexpensive radio tags. Instead, we propose to use the array on the transmitter side utilizing as few as three antennas. We use a radio interferometric technique to transform the useful phase information from the high frequency radio signal to a low frequency signal (≪ 1 kHz) that can be processed on low-cost hardware. Utilizing three anchors nodes with small antenna arrays, any number of low cost wireless nodes with single antennas can be accurately localized.

Proceedings ArticleDOI
TL;DR: In this paper, the loss cone imager (LCI) was used to sample the energetic-particle pitch-angle distributions relative to the local geomagnetic field vector in the magnetosphere as a part of the DSX satellite.
Abstract: The Loss Cone Imager (LCI) will sample the energetic-particle pitch-angle distributions relative to the local geomagnetic field vector in the magnetosphere as a part of the Demonstration and Science Experiment (DSX) satellite. A description of the LCI electrical interfaces and data flow will be presented. The pitch angle and energy of energetic particles are recorded by the FSH (Fixed Sensor Head) and HST (High Sensitivity Telescope) sensor electronics using solid state detectors. Energetic particle data must be extracted from the FSH and HST by the DPU (Data Processing Unit) and stored in a format that is practical for ground data analysis. The DPU must generate a data packet that is sent to the experiment computer containing science and housekeeping data, as well as receive ground and time commands from the experiment computer. The commands are used to configure the sensor electronics and change the data acquisition periods of the science data. The instrument works in conjunction with the WIPER (Wave-Induced Precipitation of Electron Radiation) VLF (Very Low Frequency) transmitter on the DSX satellite to view the effects of VLF waves injected in the Earth's magnetic field on the precipitation of electrons into the Loss Cone. The system is designed to operate autonomously with the changing state of the transmitter to provide more appropriate data for examining the effects of the VLF transmitter.

Proceedings ArticleDOI
28 Apr 2009
TL;DR: In this paper, the passage of the day-night terminator across the transmitter-receiver path has a characteristic signature in the amplitude and phase of the signal and principal component analysis (PCA) was applied to distinguish between this regular diurnal pattern and exogenous perturbations.
Abstract: Very Low Frequency (VLF) waves propagate with insignificant attenuation in the Earth-ionosphere waveguide. Attenuation is, however, relatively higher on illuminated paths due to the presence of the ionospheric D region. Sub-ionospheric propagation conditions may be monitored using a narrowband receiver tuned to the stable signals from numerous VLF transmitters distributed across the surface of the Earth. The passage of the day-night terminator across the transmitter-receiver path has a characteristic signature in the amplitude and phase of the signal. Principal Component Analysis (PCA) was applied to distinguish between this regular diurnal pattern and exogenous perturbations.

Proceedings ArticleDOI
15 Dec 2009
TL;DR: The receivers developed will contribute to the research of D-layer ionospheric activities and natural radio receiver which is used to detect natural radio signals such as sferics, whistlers emitted by the activities of lightning discharges.
Abstract: VLF (very low frequency) can be used to probe lower atmospheric activities. To detect lower atmospheric activities, two types of VLF receiver were developed in this project. The first type is called SID (sudden ionospheric disturbances) receiver which is used to detect the solar flares activities that affect communication systems. The second one is called natural radio receiver which is used to detect natural radio signals such as sferics, whistlers emitted by the activities of lightning discharges. A wire loop antena was developed to receive VLF signals from outer space for the receivers that has been developed. In the process of developing the VLF receiver, MULTISIM software. It was used to simulate the receiver's circuit developed for this purpose. The simulation results was adopted to design a prototype for the circuit for experiments carried out to measure the performance and the ability of the receivers in receiving VLF signals. Lab equipment, such as signal generators and oscilloscopes, were used to test the performance of the receivers. The receivers developed will contribute to the research of D-layer ionospheric activities.

Journal ArticleDOI
TL;DR: In this article, the effect of the initial pump wave on the generation of whistlers by a weakly unstable background distribution was studied. But the model was not applied to the case of a very low-frequency (VLF) signal.

Proceedings ArticleDOI
20 May 2009
TL;DR: The band analysis of Very Low Frequency (VLF) is performed using Wavelet Packet Transform (WPT) on VTA (Ventricular Tachyarrhythmia) Patients and the performance of Daubechies Wavelets is compared in VLF band.
Abstract: Heart rate variability is an important tool for cardiac diagnosis. In this work, the band analysis of Very Low Frequency (VLF) is performed using Wavelet Packet Transform (WPT) on VTA (Ventricular Tachyarrhythmia) Patients. In order to determine the performance of Daubechies Wavelets, the energy value of each nodes is computed using db4, db8, db12, db16 and db20 WPTs. The energy characteristic of main VLF band is estimated from sub-bands using Multilayer Perceptron Neural Network and dominant sub-bands of VLF are obtained. The dominant band is determined and the performance of Daubechies Wavelets is compared in VLF band.

Journal ArticleDOI
TL;DR: The variability of the following spectral parameters was studied in apparently healthy adult subjects: heart rate, stroke volume, left ventricular ejection fraction, amplitude of aortal pulsing, Amplitude of peripheral vessel pulsation in the first toe, and systolic blood pressure.
Abstract: The variability of the following spectral parameters was studied in apparently healthy adult subjects: heart rate, stroke volume, left ventricular ejection fraction, amplitude of aortal pulsing, amplitude of peripheral vessel pulsation in the first toe, and systolic blood pressure. The average values of the parameter of blood circulation per 500 heart beats (M), total power of variation spectrum of blood circulation parameter (TP), and absolute and relative powers of the oscillations of blood circulation parameter were estimated in the following spectral bands: ultralow frequency (ULF, % ULF), very low frequency (VLF, % VLF), low frequency (LF, % LF), and high frequency (HF, % HF). The variability of each blood circulation parameter proved to be characterized by a specific ratio of slow oscillations of different frequencies, which was a result of the specific regulation of this parameter. The parameters of central hymodynamics were relatively similar in oscillation structure. The oscillation spectra of the parameters of central and peripheral hemodynamics differed significantly. In adulthood, sex-related differences were determined in spectral parameters of the heart rate variability (ULF and VLF were higher in women), in the ejection fraction (% ULF was higher in women), in the amplitude of aortal pulsation (TP, ULF, VLF, LF and HF were higher in women), in the amplitude of pulsation of the peripheral vessels in the first toe (TP, ULF, VLF, LF and HF were higher in men), and in the blood pressure (% ULF was higher in women).