Electrojet-independent ionospheric extremely low frequency/very low frequency wave generation by powerful high frequency waves

ABSTRACT We estimated the areas exhibiting high-frequency (1∼10 Hz) wave radiation on the fault plane of the 2008 Wenchuan earthquake, by applying envelope inversion to strong-motion acceleration records. The corrected records of two small earthquakes are adopted as the empirical Green’s functions. Considering the change in the rupture pattern of the Wenchuan earthquake from southwest to northeast, the records of small earthquakes dominated by thrust and strike-slip are utilized as the empirical Green’s function for the southwestern and northeastern fault sections, respectively. The results are as follows: (1) According to the high-frequency wave radiation, the rupture process is complex. High-frequency waves radiated strongly in six areas: around the initial rupture point, along the north and south edges of the fault plane, near the area of intersection with the cross-cutting Xiaoyudong fault, south of Nanba, and near the area of Qingchuan. In total, these areas can be divided into three cases. In the first situation, high-frequency waves radiated strongly around the initial rupture area, which may be associated with the initiation of rupture and a high stress drop. The second location is near the periphery of the fault, which is associated with the termination of rupture. The third condition comprises high-frequency waves near the intersection with the cross-cutting Xiaoyudong fault. This area as a geometric barrier, and the surface rupture is observed. (2) The distribution patterns of the high- and low-frequency radiation intensity differ on the fault plane. From the hypocenter to the point of intersection with the Xiaoyudong fault, the high-frequency wave is located around the area with large slip value. In other areas, the distribution of the high- and low-frequency radiation is no obvious relationship. This different characteristic indicates the complexity of the rupture process.

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Preferential acceleration of heavy ions from thermal velocities

Canadian Journal of Physics ◽

10.1139/p68-314 ◽

1968 ◽

Vol 46 (10) ◽

pp. S638-S641 ◽

Cited By ~ 1

Author(s):

D. B. Melrose

Keyword(s):

Frequency Spectrum ◽

High Frequency ◽

Heavy Ions ◽

Crab Nebula ◽

Low Frequency ◽

High Frequency Waves ◽

Hydromagnetic Waves ◽

The Crab Nebula ◽

Low Frequency Waves

The acceleration of ions from thermal velocities is analyzed to determine conditions under which heavy ions can be preferentially accelerated. Two accelerating mechanisms involving high-and low-frequency hydromagnetic waves respectively are considered. Preferential acceleration of heavy ions occurs for high-frequency waves if the frequency spectrum falls off faster than (frequency)−1. For the low-frequency waves heavy ions are less effectively accelerated than lighter ions. However, very heavy ions can be preferentially accelerated, the abundances of the very heavy ions being enhanced by a factor Ai over the thermal abundances. Acceleration of ions in the envelope of the Crab nebula is considered as an example.

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Generation of extra and very low-frequency (ELF/VLF) radiation by ionospheric electrojet modulation using high-frequency (HF) heating waves

Journal of Plasma Physics ◽

10.1017/s0022377802001964 ◽

2002 ◽

Vol 68 (4) ◽

pp. 267-284 ◽

Cited By ~ 2

Author(s):

S. P. KUO

Keyword(s):

High Frequency ◽

Thermal Instability ◽

Loss Rate ◽

Inelastic Collision ◽

Modulation Frequency ◽

Low Frequency ◽

Heating Power ◽

Very Low Frequency ◽

Hf Heating ◽

Heating Wave

Extra and very low-frequency (ELF/VLF) wave generation by modulated polar electrojet currents is studied numerically. Through Ohmic heating by the amplitude-modulated high-frequency heating wave, the conductivity and thus the current of the electrojet are modulated accordingly to set up the ionospheric antenna current. Stimulated thermal instability, which can further enhance the electrojet current modulation, is studied. It is first analysed analytically to determine the threshold heating power for its excitation. The nonlinear evolutions of the generated ELF/VLF waves enhanced by the instability are then studied numerically. Their spectra are also evaluated. The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency in agreement with the Tromso observations. The efficiency enhancement by the stimulated thermal instability is hampered by inelastic collisions of electrons with neutral particles (mainly due to vibration excitation of N2), which cause this instability to saturate at low levels. However, the electron inelastic collision loss rate drops rapidly to a low value in the energy regime from 3.5 to 6 eV. As the heating power exceeds a threshold level, significant electron heating enhanced by the instability is shown, which indeed causes a steep drop in the electron inelastic collision loss rate. Consequently, this instability saturates at a much higher level, resulting to a near step increase (of about 10–13 dB depending on the modulation wave form) in the spectral intensity of ELF radiation. The dependence of the threshold power of the HF heating wave on the modulation frequency is determined.

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Strange VLF bursts in northern Scandinavia: case study of the afternoon "mushroom-like" hiss on 8 December 2013

Annales Geophysicae ◽

10.5194/angeo-33-991-2015 ◽

2015 ◽

Vol 33 (8) ◽

pp. 991-995 ◽

Cited By ~ 4

Author(s):

J. Manninen ◽

N. G. Kleimenova ◽

A. Kozlovsky ◽

I. A. Kornilov ◽

L. I. Gromova ◽

...

Keyword(s):

Low Frequency ◽

Mutual Effect ◽

Time History ◽

Lower Ionosphere ◽

Wave Interaction ◽

Recovery Phase ◽

Frequency Wave ◽

Left Hand ◽

Very Low Frequency ◽

The Right

Abstract. We investigate a non-typical very low frequency (VLF) 1–4 kHz hiss representing a sequence of separated noise bursts with a strange "mushroom-like" shape in the frequency–time domain, each one lasting several minutes. These strange afternoon VLF emissions were recorded at Kannuslehto (KAN, &varphi; = 67.74° N, λ = 26.27° E; L ∼ 5.5) in northern Finland during the late recovery phase of the small magnetic storm on 8 December 2013. The left-hand (LH) polarized 2–3 kHz "mushroom caps" were clearly separated from the right-hand (RH) polarized "mushroom stems" at the frequency of about 1.8–1.9 kHz, which could match the lower ionosphere waveguide cutoff (the first transverse resonance of the Earth–ionosphere cavity). We hypothesize that this VLF burst sequence could be a result of the modulation of the VLF hiss electron–cyclotron instability from the strong Pc5 geomagnetic pulsations observed simultaneously at ground-based stations as well as in the inner magnetosphere by the Time History of Events and Macroscale Interactions during Substorms mission probe (THEMIS-E; ThE). This assumption is confirmed by a similar modulation of the intensity of the energetic (1–10 keV) electrons simultaneously observed by the same ThE spacecraft. In addition, the data of the European Incoherent Scatter Scientific Association (EISCAT) radar at Tromsø show a similar quasi-periodicity in the ratio of the Hall-to-Pedersen conductance, which may be used as a proxy for the energetic particle precipitation enhancement. Our findings suggest that this strange mushroom-like shape of the considered VLF hiss could be a combined mutual effect of the magnetospheric ULF–VLF (ultra low frequency–very low frequency) wave interaction and the ionosphere waveguide propagation.

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Review on the Millimeter-Wave Generation Techniques Based on Photon Assisted for the RoF Network System

Advances in Condensed Matter Physics ◽

10.1155/2020/6692941 ◽

2020 ◽

Vol 2020 ◽

pp. 1-14

Author(s):

Jiangnan Xiao ◽

Chuang Zhao ◽

Xingxing Feng ◽

Xu Dong ◽

Jiangli Zuo ◽

...

Keyword(s):

High Frequency ◽

Low Cost ◽

Electronic Devices ◽

Low Frequency ◽

Digital Signal ◽

Development Trend ◽

Wave Generation ◽

Communication Link ◽

Network System ◽

High Frequency Microwave

With the development trend of wireless and broadband in the communication link and even the whole information industry, the demand of high-frequency microwave bandwidth has been increasing. The RoF network system solves the problem of spectrum congestion in low-frequency band by providing an effective technology for the distribution of high-frequency microwave signals over optical fiber links. However, the traditional mm-wave generation technique is limited by the bandwidth of electronic devices. It is difficult to generate high-frequency and low-phase noise mm-wave signals with pure electrical components. The mm-wave communication technology based on photon assisted can overcome the bandwidth bottleneck of electronic devices and provide the potential for developing the low-cost infrastructure demand of broadband mobile services. This paper will briefly explain the characteristics of the RoF network system and the advantages of high-frequency mm-wave. Then we, respectively, introduce the modulation schemes of RoF mm-wave generation based on photon assisted including directly modulated laser (DML), external modulation, and optical heterodyne. The review mainly focuses on a variety of different mm-wave generation technologies including multifrequency vector mm-wave. Furthermore, we list several approaches to realize the large capacity data transmission techniques and describe the digital signal processing (DSP) algorithm flow in the receiver. In the end, we summarize the RoF network system and look forward to the future.

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Investigation of Native Speaker and Second Language Learner Intuition of Collocation Frequency

10.26686/wgtn.13670635 ◽

2021 ◽

Author(s):

Anna Siyanova ◽

S Spina

Keyword(s):

Language Learning ◽

High Frequency ◽

Native Speakers ◽

Native Speaker ◽

Low Frequency ◽

Language Learner ◽

Very Low Frequency ◽

Second Language Learner ◽

L2 Learners ◽

L1 And L2

© 2015 Language Learning Research Club, University of Michigan. Research into frequency intuition has focused primarily on native (L1) and, to a lesser degree, nonnative (L2) speaker intuitions about single word frequency. What remains a largely unexplored area is L1 and L2 intuitions about collocation (i.e., phrasal) frequency. To bridge this gap, the present study aimed to answer the following question: How do L2 learners and native speakers compare against each other and corpora in their subjective judgments of collocation frequency? Native speakers and learners of Italian were asked to judge 80 noun-adjective pairings as one of the following: high frequency, medium frequency, low frequency, very low frequency. Both L1 and L2 intuitions of high frequency collocations correlated strongly with corpus frequency. Neither of the two groups of participants exhibited accurate intuitions of medium and low frequency collocations. With regard to very low frequency pairings, L1 but not L2 intuitions were found to correlate with corpora for the majority of the items. Further, mixed-effects modeling revealed that L2 learners were comparable to native speakers in their judgments of the four frequency bands, although some differences did emerge. Taken together, the study provides new insights into the nature of L1 and L2 intuitions about phrasal frequency.

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Impact of Catheter Ablation on Sleep Quality and Relationship Between Sleep Stability and Recurrence of Paroxysmal Atrial Fibrillation After Successful Ablation: 24‐Hour Holter‐Based Cardiopulmonary Coupling Analysis

Journal of the American Heart Association ◽

10.1161/jaha.120.017016 ◽

2020 ◽

Vol 9 (23) ◽

Author(s):

Woohyeun Kim ◽

Jin Oh Na ◽

Robert J. Thomas ◽

Won Young Jang ◽

Dong Oh Kang ◽

...

Keyword(s):

Atrial Fibrillation ◽

Catheter Ablation ◽

Sleep Quality ◽

High Frequency ◽

Low Frequency ◽

Coupling Analysis ◽

Very Low Frequency ◽

Cardiopulmonary Coupling ◽

Frequency Coupling ◽

Af Recurrence

Background Sleep fragmentation and sleep apnea are common in patients with atrial fibrillation (AF). We investigated the impact of radio‐frequency catheter ablation (RFCA) on sleep quality in patients with paroxysmal AF and the effect of a change in sleep quality on recurrence of AF. Methods and Results Of 445 patients who underwent RFCA for paroxysmal AF between October 2007 and January 2017, we analyzed 225 patients who had a 24‐hour Holter test within 6 months before RFCA. Sleep quality was assessed by cardiopulmonary coupling analysis using 24‐hour Holter data. We compared cardiopulmonary coupling parameters (high‐frequency coupling, low‐frequency coupling, very‐low‐frequency coupling) before and after RFCA. Six months after RFCA, the high‐frequency coupling (marker of stable sleep) and very‐low‐frequency coupling (rapid eye movement/wake marker) was significantly increased (29.84%–36.15%; P <0.001; and 26.20%–28.76%; P =0.002, respectively) while low‐frequency coupling (unstable sleep marker) was decreased (41.25%–32.13%; P <0.001). We divided patients into 3 tertiles according to sleep quality before RFCA, and the risk of AF recurrence in each group was compared. The second tertile was used as a reference; patients with unstable sleep (Tertile 3) had a significantly lower risk of AF recurrence (hazard ratio [HR], 0.32; 95% CI, 0.12–0.83 for high‐frequency coupling; and HR, 0.22; 95% CI, 0.09–0.58 for low‐frequency coupling). Conclusions Sleep quality improved after RFCA in patients with paroxysmal AF. The recurrence rate was significantly lower in patients who had unstable sleep before RFCA. These results suggest that RFCA can influence sleep quality, and sleep quality assessment before RFCA may provide a risk marker for recurrence after RFCA in patients with paroxysmal AF.

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