scholarly journals Strong influence of solar X-ray flares on low-frequency electromagnetic signals in middle latitudes

2019 ◽  
Author(s):  
Alexandr Rozhnoi ◽  
Mariya Solovieva ◽  
Viktor Fedun ◽  
Peter Gallagher ◽  
Joseph McCauley ◽  
...  
Keyword(s):  
Solar Flares ◽  
Low Frequency ◽  
Signal Frequency ◽  
Frequency Range ◽  
Effective Height ◽  
X Ray ◽  
Middle Latitudes ◽  
Burst Data ◽  
Path Lengths ◽  
Electromagnetic Signals

Abstract. In this paper we analysed Sudden Phase Anomalies (SPAs) of VLF/LF signals recorded at Graz (Austria), Birr (Ireland) and Moscow (Russia) stations during two strong solar flares in September 2017. The first X-class 9.3 flare occurred on 6 September at 12:02 UT and the second X-class 8.2 flare was observed on 10 September 2017 at 16:06 UT. Data from seven transmitters in a frequency range between 20–45 kHz are used for the analysis. The SPAs were observed in all middle-latitudes paths (differently orientated) with path lengths from 350 km to 7000 km. Solar X-ray burst data were taken from GOES satellite observations in the wavelength band of 0.05–0.4 nm. If was found that (i) the amplitude of SPAs in different paths varies from 10 to 282 degrees, and (ii) the correlation between the amplitudes of SPAs, the lengths of paths and the signal frequency is weak. The change in effective height of reflection due to lowering of the reflecting layer during the flares was found to be about 12 km for the first event and about 9 km for the second event. Spectral analysis of the X-ray and LF data, filtered in the range between 5 s and 16 min, showed that the LF signal spectra are very similar to X-ray spectra. Maxima of both X-ray and LF spectra are in 2–16 min interval.

scholarly journals Strong influence of solar X-ray flares on low-frequency electromagnetic signals in middle latitudes

2019 ◽  
Vol 37 (5) ◽  
pp. 843-850
Author(s):  
Alexander Rozhnoi ◽  
Maria Solovieva ◽  
Viktor Fedun ◽  
Peter Gallagher ◽  
Joseph McCauley ◽  
...  
Keyword(s):  
Solar Flares ◽  
Low Frequency ◽  
Middle Latitude ◽  
Signal Frequency ◽  
Effective Height ◽  
X Ray ◽  
Middle Latitudes ◽  
Burst Data ◽  
Path Lengths ◽  
Electromagnetic Signals

Abstract. In this paper we analysed sudden phase anomalies (SPAs) of VLF–LF signals recorded at Graz (Austria), Birr (Ireland) and Moscow (Russia) stations during two strong solar flares in September 2017. The first X-class 9.3 flare occurred on 6 September at 12:02 UT, and the second X-class 8.2 flare was observed on 10 September 2017 at 16:06 UT. Data from seven transmitters in a frequency range between 20 and 45 kHz are used for the analysis. The SPAs were observed in all middle-latitude paths (differently orientated) with path lengths from 350 to 7000 km. Solar X-ray burst data were taken from GOES satellite observations in the wavelength band of 0.05–0.4 nm. It was found that (i) the amplitude of SPAs in different paths varies from 10 to 282∘, and (ii) the correlation between the amplitudes of SPAs, the lengths of paths and the signal frequency is weak. The change in effective height of reflection due to lowering of the reflecting layer during the flares was found to be about 12 km for the first event and about 9 km for the second event. Spectral analysis of the X-ray and LF data, filtered in the range between 5 s and 16 min, showed that the LF signal spectra are very similar to X-ray spectra. Maxima of both X-ray and LF spectra are in 2–16 min interval.

scholarly journals Classification of X-ray solar flares regarding their effects on the lower ionosphere electron density profile

2008 ◽  
Vol 26 (7) ◽  
pp. 1731-1740 ◽  
Author(s):  
D. P. Grubor ◽  
D. M. Šulić ◽  
V. Žigman
Keyword(s):  
Electron Density ◽  
Solar Flares ◽  
Low Frequency ◽  
Lower Ionosphere ◽  
Electron Density Profile ◽  
Height Range ◽  
X Ray ◽  
Reflection Height ◽  
Single Trace

Abstract. The classification of X-ray solar flares is performed regarding their effects on the Very Low Frequency (VLF) wave propagation along the Earth-ionosphere waveguide. The changes in propagation are detected from an observed VLF signal phase and amplitude perturbations, taking place during X-ray solar flares. All flare effects chosen for the analysis are recorded by the Absolute Phase and Amplitude Logger (AbsPal), during the summer months of 2004–2007, on the single trace, Skelton (54.72 N, 2.88 W) to Belgrade (44.85 N, 20.38 E) with a distance along the Great Circle Path (GCP) D≈2000 km in length. The observed VLF amplitude and phase perturbations are simulated by the computer program Long-Wavelength Propagation Capability (LWPC), using Wait's model of the lower ionosphere, as determined by two parameters: the sharpness (β in 1/km) and reflection height (H' in km). By varying the values of β and H' so as to match the observed amplitude and phase perturbations, the variation of the D-region electron density height profile Ne(z) was reconstructed, throughout flare duration. The procedure is illustrated as applied to a series of flares, from class C to M5 (5×10−5 W/m2 at 0.1–0.8 nm), each giving rise to a different time development of signal perturbation. The corresponding change in electron density from the unperturbed value at the unperturbed reflection height, i.e. Ne(74 km)=2.16×108 m−3 to the value induced by an M5 class flare, up to Ne(74 km)=4×1010 m−3 is obtained. The β parameter is found to range from 0.30–0.49 1/km and the reflection height H' to vary from 74–63 km. The changes in Ne(z) during the flares, within height range z=60 to 90 km are determined, as well.

Masking of Tinnitus Compared to Masking of Pure Tones

1984 ◽  
Vol 27 (1) ◽  
pp. 106-111 ◽  
Author(s):  
Richard S. Tyler ◽  
David Conrad-Armes
Keyword(s):  
Tuning Curve ◽  
Low Frequency ◽  
Frequency Resolution ◽  
Signal Frequency ◽  
Frequency Range ◽  
Apparent Relationship ◽  
Pure Tones ◽  
Frequency Threshold ◽  
High Level ◽  
Tinnitus Masking

In 10 subjects with sensorineural tinnitus (associated with a sensorineural hearing loss and no apparent source for a tinnitus originating elsewhere), the minimum level required to mask the tinnitus was determined for tonal maskers at several masker frequencies. This tinnitus masking pattern was compared to a psychoacoustical tuning curve (PTC) in which the signal frequency and level were determined from tinnitus pitch and loudness matching. Different patterns emerged. One subject showed a near-normal PTC but required high-level maskers across the frequency range to mask the tinnitus. Another subject showed some frequency resolution in the PTC but required low-level maskers across the frequency range to mask the tinnitus. For the remaining eight subjects, the masker levels required to mask the tone were generally higher than those levels required to mask the tinnitus. In addition, it was noted that the tinnitus pitch-match frequency was sometimes associated with an increase or a decrease in threshold sensitivity, or it was found at the low-frequency edge of a steep high-frequency threshold loss. In other subjects there was no apparent relationship between the tinnitus pitch and the audiogram shape.

Nature of Low-Frequency Excess Noise in n-Type Gallium Nitride

2000 ◽  
Vol 622 ◽  
Author(s):  
C. F. Zhu ◽  
W. K. Fong ◽  
B. H. Leung ◽  
C. C. Cheng ◽  
C. Surya
Keyword(s):  
Flicker Noise ◽  
Power Spectra ◽  
Low Frequency ◽  
Excess Noise ◽  
Rf Plasma ◽  
Frequency Noise ◽  
Noise Power ◽  
Frequency Range ◽  
X Ray Diffraction ◽  
X Ray

ABSTRACTLow-frequency noise is investigated in n-type GaN film grown by rf-plasma assisted molecular beam epitaxy. The temperature dependence of the voltage noise power spectra, SV(f), was examined from 400K to 80K in the frequency range between 30Hz and 100KHz, which can be modeled as the superposition of 1/f (flicker) noise G-R noise. At f > 500 Hz the noise is dominated by G-R noise with activation energies of 360meV and 65meV from the conduct band. The results clearly demonstrate the trap origin for both the 1/f noise and G-R noise. At the low-frequency range the fluctuation was dominated by 1/f noise. To determine the origin of the noise we considered both the bulk mobility fluctuation and the trap fluctuation models. Our experimental results showed that rapid thermal annealing (RTA) at 800°C resulted in over one order of magnitude decrease in the Hooge parameter. Annealing at temperatures in excess of 1000°C resulted in significant increase in the noise. Photoluminescence and x-ray diffraction measurements also showed that the crystallinity of the films improved with RTA at 800°C with an accompanying reduction in deep levels. Annealing at 900°C and 1000°C resulted in an increase in the FWHM of the x-ray diffraction indicative of thermal decomposition of the materials. The results are in excellent agreement with the trend of Hooge parameters as a function of annealing temperature, strongly indicating trap origin of the observed 1/f noise.

Effects of Ba and Ti Codoping on Stoichiometric and Nonstoichiometric BiFeO3 Multiferroic Ceramics

2015 ◽  
Vol 815 ◽  
pp. 154-158 ◽  
Author(s):  
Xi Zhou ◽  
Yao Xiong ◽  
Yu Chong Pei ◽  
Wan Ping Chen
Keyword(s):  
Perovskite Phase ◽  
Magnetic Hysteresis ◽  
Low Frequency ◽  
Magnetic Hysteresis Loop ◽  
Solid State Reactions ◽  
Frequency Range ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electrical And Dielectric Properties ◽  
Loop Measurement

Bi0.9Ba0.1Fe0.95O3 and Bi0.9Ba0.1FexTi0.05O3 (x=0.95, 0.925, 0.90) ceramics were prepared through conventional solid state reactions. X-ray diffraction analyses indicated that a high content of perovskite phase was obtained for all the four compositions. While the three (Ba,Ti)-codoped compositions all showed a higher resistivity than Bi0.9Ba0.1Fe0.95O3, and Bi0.9Ba0.1Fe0.925Ti0.05O3 had the best electrical and dielectric properties among the three (Ba,Ti)-codoped compositions, including the largest dielectric constant, the smallest dielectric loss at low frequency range, and the highest electrical resistivity. Magnetic hysteresis loop measurement revealed that the four compositions had similarly enhanced magnetic properties. It is concluded that much attention should be paid to fine composition adjustment when multiple elements are co-doped to BiFeO3 system.

scholarly journals A comparative study of measured amplitude and phase perturbations of VLF and LF radio signals induced by solar flares

2014 ◽  
pp. 45-54 ◽  
Author(s):  
D.M. Sulic ◽  
V.A. Sreckovic
Keyword(s):  
Solar Flares ◽  
Low Frequency ◽  
Geographic Location ◽  
Electron Density Profile ◽  
Great Circle ◽  
Direct Result ◽  
Ionospheric Disturbances ◽  
X Ray ◽  
Radio Signals ◽  
Middle Europe

Very Low Frequency (VLF) and Low Frequency (LF) signal perturbations were examined to study ionospheric disturbances induced by solar X-ray flares in order to understand processes involved in propagation of VLF/LF radio signals over short paths and to estimate specific characteristics of each short path. The receiver at the Belgrade station is constantly monitoring the amplitude and phase of a coherent and subionospherically propagating LF signal operated in Sicily NSC at 45.90 kHz, and a VLF signal operated in Isola di Tavolara ICV at 20.27 kHz, with the great circle distances of 953 km and 976 km, respectively. A significant number of similarities between these short paths is a direct result of both transmitters and the receiver?s geographic location. The main difference is in transmitter frequencies. From July 2008 to February 2014 there were about 200 events that were chosen for further examination. All selected examples showed that the amplitude and phase of VLF and LF signals were perturbed by solar X-ray flares occurrence. This six-year period covers both minimum and maximum of solar activity. Simultaneous measurement of amplitude and phase of the VLF/LF signals during a solar flare occurrence was applied to evaluate the electron density profile versus altitude, to carry out the function of time over the middle Europe.

scholarly journals Ba\(_{1-x}\)Ca\(_{x}\)TiO\(_{3}\) and the Dielectric Properties

2014 ◽  
Vol 24 (2) ◽  
pp. 170
Author(s):  
Nguyen Van Khien ◽  
Vu Dinh Lam ◽  
Le Van Hong
Keyword(s):  
Dielectric Constant ◽  
Frequency Dependence ◽  
Low Frequency ◽  
Solid State Reaction Method ◽  
Ambient Atmosphere ◽  
Frequency Range ◽  
X Ray Diffraction ◽  
Impedance Analyzer ◽  
X Ray ◽  
Ray Patterns

Ba1-xCaxTiO3 material samples with x changing from zero to 1 were fabricated by the solid state reaction method at a temperature of 1200 oC in the ambient atmosphere. Crystalline structure of the material samples was recorded and identified by X-ray diffraction and Raman scattering. Analyzing the X-ray patterns found that Ba can be completely substituted by Ca with the concentration lower than 11 at%. The frequency dependence of the impedance (C) and AC conductance (G) of all the samples were recorded in a frequency range lower than 10 MHz by using an impedance analyzer HP 4192A. It was found that in the low frequency range lower than 1 MHz the dielectric constant and its loss decrease as Ca substituted for Ba. Besides an abnormal in the frequency dependence of the dielectric constant was observed for all samples in the higher frequency range up to 10 MHz.

Problems in Thin-Film X-ray Quantification

1990 ◽  
Vol 48 (2) ◽  
pp. 458-459
Author(s):  
J N Chapman ◽  
W A P Nicholson
Keyword(s):  
Thin Film ◽  
Specimen Thickness ◽  
X Rays ◽  
Characteristic Peak ◽  
Local Composition ◽  
X Ray ◽  
Measured Ratio ◽  
Path Lengths ◽  
Composition Changes

Energy dispersive x-ray microanalysis (EDX) is widely used for the quantitative determination of local composition in thin film specimens. Extraction of quantitative data is usually accomplished by relating the ratio of the number of atoms of two species A and B in the volume excited by the electron beam (nA/nB) to the corresponding ratio of detected characteristic photons (NA/NB) through the use of a k-factor. This leads to an expression of the form nA/nB = kAB NA/NB where kAB is a measure of the relative efficiency with which x-rays are generated and detected from the two species.Errors in thin film x-ray quantification can arise from uncertainties in both NA/NB and kAB. In addition to the inevitable statistical errors, particularly severe problems arise in accurately determining the former if (i) mass loss occurs during spectrum acquisition so that the composition changes as irradiation proceeds, (ii) the characteristic peak from one of the minority components of interest is overlapped by the much larger peak from a majority component, (iii) the measured ratio varies significantly with specimen thickness as a result of electron channeling, or (iv) varying absorption corrections are required due to photons generated at different points having to traverse different path lengths through specimens of irregular and unknown topography on their way to the detector.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

The occurrence of single hard x-ray sources in solar flares

2003 ◽  
Vol 32 (12) ◽  
pp. 2483-2488
Author(s):  
C GOFF ◽  
S MATTHEWS ◽  
L HARRA
Keyword(s):  
Solar Flares ◽  
X Ray
Sign in / Sign up

Export Citation Format

Share Document