scholarly journals New type of ensemble of quasi-periodic, long-lasting VLF emissions at the auroral zone

2012 ◽  
Vol 30 (12) ◽  
pp. 1655-1660 ◽  
Author(s):  
J. Manninen ◽  
N. G. Kleimenova ◽  
O. V. Kozyreva
Keyword(s):  
Temporal Dynamics ◽  
Low Frequency ◽  
Auroral Zone ◽  
Spectral Structure ◽  
Geomagnetic Pulsations ◽  
Frequency Range ◽  
Theoretical Investigations ◽  
New Type ◽  
Periodic Signals ◽  
Vlf Emissions

Abstract. A new type of the series of quasi-periodic (QP) very low frequency (VLF) emissions in frequency range of 1–5 kHz, and not associated with geomagnetic pulsations, has been discovered at auroral latitudes (L = 5.3) during the Finnish VLF campaign (held in December 2011). At least five unusually spectacular events, each with a duration of several hours, have been observed during the night under conditions of quiet geomagnetic activity (Kp = 0–1), although QPs usually occur during the daytime. Contrary to the QP emissions typically occurring during the day, the spectral structure of these QP events represented an extended, complicated sequence of repeated discrete rising VLF signals. Their duration was about 2–3 min each, with the repetition periods ranging from ~1 min to ~10 min. Two such nighttime non-typical events are reported in this paper. The fine structure of the separated QP elements may represent a mixture of the different frequency band signals, which seem to have independent origins. It was found that the periodic signals with lower frequency appear to trigger the strong dispersive upper frequency signals. The temporal dynamics of the spectral structure of the QPs studied were significantly controlled by some disturbances in the solar wind and interplanetary magnetic field (IMF). This finding is very important for future theoretical investigations because the generation mechanism of this new type of QP emissions is not yet understood.

scholarly journals New high-frequency (7–12 kHz) quasi-periodic VLF emissions observed on the ground at <i>L</i>  ∼  5.5

2018 ◽  
Vol 36 (3) ◽  
pp. 915-923 ◽  
Author(s):  
Jyrki Manninen ◽  
Natalia Kleimenova ◽  
Tauno Turunen ◽  
Liudmila Gromova
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Digital Filtering ◽  
Spectral Shape ◽  
Geomagnetic Pulsations ◽  
High Frequency Band ◽  
Polarized Waves ◽  
Electron Gyrofrequency ◽  
Vlf Emissions ◽  
The Waves

Abstract. We reveal previously unknown quasi-periodic (QP) very low frequency (VLF) emissions at the unusually high-frequency band of ∼ 7–12 kHz by applying the digital filtering of strong atmospherics to the ground-based VLF data recorded at Kannuslehto station (KAN). It is located in northern Finland at L ∼ 5.5. The frequencies of QP emissions are much higher than the equatorial electron gyrofrequency at L ∼ 5.5. Thus, these emissions must have been generated at much lower L shells than KAN. Two high-frequency QP emission events have been studied in detail. The emissions were right-hand polarized waves indicating an overhead location of the exit area of waves in the ionosphere. In one event, the spectral–temporal forms of the emissions looked like a series of giant “bullets” due to the very abrupt cessation. Unfortunately, we could not explain such a strange dynamic spectral shape of the waves. In the second event, the modulation period was about 3 min under the absence of simultaneous geomagnetic pulsations. The studied emissions lasted about 4 h and were observed under the very quiet geomagnetic activity. The adequate mechanisms of the generation and propagation of the revealed high-frequency QP emissions have not yet been established. We speculate that studied QP emissions can be attributed to the auto-oscillations of the cyclotron instability in the magnetospheric plasma maser.

Correlations between very low frequency chorus bursts and impulsive magnetic variations at L ~ 4.5

1981 ◽  
Vol 59 (8) ◽  
pp. 1034-1041 ◽  
Author(s):  
S. Kokubun ◽  
K. Hayashi ◽  
T. Oguti ◽  
K. Tsuruda ◽  
S. Machida ◽  
...  
Keyword(s):  
Low Frequency ◽  
Frequency Range ◽  
Conductivity Enhancement ◽  
Very Low Frequency ◽  
Close Relationship ◽  
Magnetic Pulsations ◽  
Whistler Mode Waves ◽  
Short Time ◽  
Vlf Emissions ◽  
Vlf Waves

Coordinated observations of aurora, ULF, and VLF waves were made at 13 stations in Canada in January and February, 1980. The analysis of simultaneous ULF and VLF data obtained at Park Site (L = 4.4) revealed a close relationship between irregular magnetic pulsations and VLF emissions in the frequency range of 1.5–5 kHz. One-to-one correlations were observed between VLF chorus bursts and impulsive magnetic variations, called magnetic impulses, during sub-storms of Kp ≥ 4+ on the local morning-to-noon side. VLF chorus bursts consist of discrete risers of 0.1–0.3 s duration. It is found that magnetic impulses with a rise time of 0.5–1 s and with a duration of ~2 s coincide with the occurrence of VLF riser groups of a similar duration within ~2 s. This short time difference strongly suggests that magnetic impulses are caused by a conductivity enhancement due to electron precipitation induced by whistler mode waves.

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.

Theoretical and experimental research on slip and uplift of the timber-concrete composite beam

BioResources ◽  
2020 ◽  
Vol 15 (3) ◽  
pp. 7079-7099
Author(s):  
Jianying Chen ◽  
Guojing He ◽  
Xiaodong (Alice) Wang ◽  
Jiejun Wang ◽  
Jin Yi ◽  
...  
Keyword(s):  
Differential Equations ◽  
Deformation Theory ◽  
Concrete Slab ◽  
Theoretical Calculations ◽  
Structural Element ◽  
Structural Efficiency ◽  
Theoretical Investigations ◽  
New Type ◽  
Interlayer Slip ◽  
Good Agreement

Timber-concrete composite beams are a new type of structural element that is environmentally friendly. The structural efficiency of this kind of beam highly depends on the stiffness of the interlayer connection. The structural efficiency of the composite was evaluated by experimental and theoretical investigations performed on the relative horizontal slip and vertical uplift along the interlayer between composite’s timber and concrete slab. Differential equations were established based on a theoretical analysis of combination effects of interlayer slip and vertical uplift, by using deformation theory of elastics. Subsequently, the differential equations were solved and the magnitude of uplift force at the interlayer was obtained. It was concluded that the theoretical calculations were in good agreement with the results of experimentation.

Dynamic Damping and Stiffness Characteristics of the Rolling Tire

2001 ◽  
Vol 29 (4) ◽  
pp. 258-268 ◽  
Author(s):  
G. Jianmin ◽  
R. Gall ◽  
W. Zuomin
Keyword(s):  
Dynamic Behavior ◽  
Variable Parameter ◽  
Low Frequency ◽  
Vertical Load ◽  
Frequency Range ◽  
Inflation Pressure ◽  
Vehicle Simulation ◽  
Dynamic Damping ◽  
Speed Range ◽  
Stiffness Characteristics

Abstract A variable parameter model to study dynamic tire responses is presented. A modified device to measure terrain roughness is used to measure dynamic damping and stiffness characteristics of rolling tires. The device was used to examine the dynamic behavior of a tire in the speed range from 0 to 10 km/h. The inflation pressure during the tests was adjusted to 160, 240, and 320 kPa. The vertical load was 5.2 kN. The results indicate that the damping and stiffness decrease with velocity. Regression formulas for the non-linear experimental damping and stiffness are obtained. These results can be used as input parameters for vehicle simulation to evaluate the vehicle's driving and comfort performance in the medium-low frequency range (0–100 Hz). This way it can be important for tire design and the forecasting of the dynamic behavior of tires.

scholarly journals An Improved Time Integration Method Based on Galerkin Weak Form with Controllable Numerical Dissipation

2021 ◽  
Vol 11 (4) ◽  
pp. 1932
Author(s):  
Weixuan Wang ◽  
Qinyan Xing ◽  
Qinghao Yang
Keyword(s):  
High Frequency ◽  
Integration Method ◽  
Time Integration ◽  
Low Frequency ◽  
Weak Form ◽  
High Accuracy ◽  
Numerical Dissipation ◽  
Frequency Range ◽  
Time Integration Method ◽  
Numerical Damping

Based on the newly proposed generalized Galerkin weak form (GGW) method, a two-step time integration method with controllable numerical dissipation is presented. In the first sub-step, the GGW method is used, and in the second sub-step, a new parameter is introduced by using the idea of a trapezoidal integral. According to the numerical analysis, it can be concluded that this method is unconditionally stable and its numerical damping is controllable with the change in introduced parameters. Compared with the GGW method, this two-step scheme avoids the fast numerical dissipation in a low-frequency range. To highlight the performance of the proposed method, some numerical problems are presented and illustrated which show that this method possesses superior accuracy, stability and efficiency compared with conventional trapezoidal rule, the Wilson method, and the Bathe method. High accuracy in a low-frequency range and controllable numerical dissipation in a high-frequency range are both the merits of the method.

scholarly journals Extended High Frequencies Provide Both Spectral and Temporal Information to Improve Speech-in-Speech Recognition

2020 ◽  
Vol 24 ◽  
pp. 233121652098029
Author(s):  
Allison Trine ◽  
Brian B. Monson
Keyword(s):  
Speech Recognition ◽  
Pure Tone ◽  
Recognition Performance ◽  
Low Frequency ◽  
Exploratory Analysis ◽  
Temporal Information ◽  
Significant Benefit ◽  
Head Orientation ◽  
Spectral Structure ◽  
High Frequencies

Several studies have demonstrated that extended high frequencies (EHFs; >8 kHz) in speech are not only audible but also have some utility for speech recognition, including for speech-in-speech recognition when maskers are facing away from the listener. However, the contribution of EHF spectral versus temporal information to speech recognition is unknown. Here, we show that access to EHF temporal information improved speech-in-speech recognition relative to speech bandlimited at 8 kHz but that additional access to EHF spectral detail provided an additional small but significant benefit. Results suggest that both EHF spectral structure and the temporal envelope contribute to the observed EHF benefit. Speech recognition performance was quite sensitive to masker head orientation, with a rotation of only 15° providing a highly significant benefit. An exploratory analysis indicated that pure-tone thresholds at EHFs are better predictors of speech recognition performance than low-frequency pure-tone thresholds.

A waveform inversion technique for measuring elastic wave attenuation in cylindrical bars

Geophysics ◽  
1992 ◽  
Vol 57 (6) ◽  
pp. 854-859 ◽  
Author(s):  
Xiao Ming Tang
Keyword(s):  
Elastic Wave ◽  
Wave Attenuation ◽  
Waveform Inversion ◽  
Finite Size ◽  
Low Frequency ◽  
Frequency Range ◽  
Multiple Reflections ◽  
Low Frequencies ◽  
The Time Domain ◽  
Attenuation Values

A new technique for measuring elastic wave attenuation in the frequency range of 10–150 kHz consists of measuring low‐frequency waveforms using two cylindrical bars of the same material but of different lengths. The attenuation is obtained through two steps. In the first, the waveform measured within the shorter bar is propagated to the length of the longer bar, and the distortion of the waveform due to the dispersion effect of the cylindrical waveguide is compensated. The second step is the inversion for the attenuation or Q of the bar material by minimizing the difference between the waveform propagated from the shorter bar and the waveform measured within the longer bar. The waveform inversion is performed in the time domain, and the waveforms can be appropriately truncated to avoid multiple reflections due to the finite size of the (shorter) sample, allowing attenuation to be measured at long wavelengths or low frequencies. The frequency range in which this technique operates fills the gap between the resonant bar measurement (∼10 kHz) and ultrasonic measurement (∼100–1000 kHz). By using the technique, attenuation values in a PVC (a highly attenuative) material and in Sierra White granite were measured in the frequency range of 40–140 kHz. The obtained attenuation values for the two materials are found to be reliable and consistent.

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