scholarly journals Frequency and plasma condition dependent spatial structure of low frequency global potential oscillations in the TJ-II stellarator

2019 ◽  
Vol 59 (4) ◽  
pp. 044006 ◽  
Author(s):  
T. Kobayashi ◽  
U. Losada ◽  
B. Liu ◽  
T. Estrada ◽  
B.Ph. van Milligen ◽  
...  
Keyword(s):  
Spatial Structure ◽  
Low Frequency ◽  
Plasma Condition ◽  
Potential Oscillations

Spatial structure of long‐range, low‐frequency seafloor reverberation in the Canary Basin

1990 ◽  
Vol 88 (S1) ◽  
pp. S106-S106
Author(s):  
Jonathan M. Berkson ◽  
Fredrick R. Facemire ◽  
Jay A. Wallmark
Keyword(s):  
Spatial Structure ◽  
Long Range ◽  
Low Frequency

Spatial structure of low-frequency wind noise

2007 ◽  
Vol 122 (6) ◽  
pp. EL223-EL228 ◽  
Author(s):  
D. Keith Wilson ◽  
Roy J. Greenfield ◽  
Michael J. White
Keyword(s):  
Spatial Structure ◽  
Low Frequency ◽  
Wind Noise

scholarly journals Modulation of radio frequency signals by ULF waves

2007 ◽  
Vol 25 (5) ◽  
pp. 1113-1124 ◽  
Author(s):  
C. L. Waters ◽  
T. K. Yeoman ◽  
M. D. Sciffer ◽  
P. Ponomarenko ◽  
D. M. Wright
Keyword(s):  
Spatial Structure ◽  
Radio Frequency ◽  
Wave Energy ◽  
Ionospheric Plasma ◽  
Low Frequency ◽  
Radar Data ◽  
Hf Radar ◽  
Ulf Waves ◽  
Ulf Wave ◽  
Magnetometer Arrays

Abstract. The ionospheric plasma is continually perturbed by ultra-low frequency (ULF; 1–100 mHz) plasma waves that are incident from the magnetosphere. In this paper we present a combined experimental and modeling study of the variation in radio frequency of signals propagating in the ionosphere due to the interaction of ULF wave energy with the ionospheric plasma. Modeling the interaction shows that the magnitude of the ULF wave electric field, e, and the geomagnetic field, B0, giving an e×B0 drift, is the dominant mechanism for changing the radio frequency. We also show how data from high frequency (HF) Doppler sounders can be combined with HF radar data to provide details of the spatial structure of ULF wave energy in the ionosphere. Due to spatial averaging effects, the spatial structure of ULF waves measured in the ionosphere may be quite different to that obtained using ground based magnetometer arrays. The ULF wave spatial structure is shown to be a critical parameter that determines how ULF wave effects alter the frequency of HF signals propagating through the ionosphere.

Generation of magnetic and particle Pc5 pulsations during the recovery phase of strong magnetic storms

2010 ◽  
Vol 466 (2123) ◽  
pp. 3363-3390 ◽  
Author(s):  
V. Pilipenko ◽  
O. Kozyreva ◽  
V. Belakhovsky ◽  
M. J. Engebretson ◽  
S. Samsonov
Keyword(s):  
Solar Wind ◽  
Spatial Structure ◽  
Stable State ◽  
Low Frequency ◽  
Solar Wind Plasma ◽  
Recovery Phase ◽  
Magnetic Storms ◽  
Relativistic Electrons ◽  
Oscillatory Systems ◽  
Using Data

The dynamics of intense ultra-low-frequency (ULF) activity during three successive strong magnetic storms during 29–31 October 2003 are considered in detail. The spatial structure of Pc5 waves during the recovery phases of these storms is considered not only from the perspective of possible physical mechanisms, but as an important parameter of the ULF driver of relativistic electrons. The global structure of these disturbances is studied using data from a worldwide array of magnetometers and riometers augmented with data from particle detectors and magnetometers on board magnetospheric satellites (GOES, LANL). The local spatial structure is examined using the IMAGE magnetometers and Finnish riometer array. Though a general similarity between the quasi-periodic magnetic and riometer variations is observed, their local propagation patterns turn out to be different. To interpret the observations, we suggest a hypothesis of coupling between two oscillatory systems—a magnetospheric magnetohydrodynamic (MHD) waveguide/resonator and a system consisting of turbulence + electrons. We propose that the observed Pc5 oscillations are the result of MHD waveguide excitation along the dawn and dusk flanks of the magnetosphere. The magnetospheric waveguide turns out to be in a meta-stable state under high solar wind velocities, and quasi-periodic fluctuations of the solar wind plasma density stimulate the waveguide excitation.

Intrinsic NMDA-Induced Oscillations in Motoneurons of an Adult Vertebrate Spinal Cord Are Masked by Inhibition

1997 ◽  
Vol 77 (2) ◽  
pp. 717-730 ◽  
Author(s):  
Mengia-Seraina Rioult-Pedotti
Keyword(s):  
Spinal Cord ◽  
Membrane Potential ◽  
Nmda Receptor ◽  
Low Frequency ◽  
Receptor Activation ◽  
Intracellular Recordings ◽  
Potential Oscillations ◽  
Frog Spinal Cord ◽  
Nmda Receptor Activation ◽  
Membrane Potential Oscillations

Rioult-Pedotti, Mengia-Seraina. Intrinsic NMDA induced oscillations in motoneurons of an adult vertebrate spinal cord are masked by inhibition. J. Neurophysiol. 77: 717–730, 1997. Low-frequency membrane potential oscillations were induced in motoneurons (MNs) of isolated hemisected frog spinal cords during N-methyl-d-aspartate (NMDA) application. Oscillations required the presence of physiological Mg2+ and preincubation with strychnine, whereas incubation with bicuculline or phaclofen was not effective. Oscillations were evident in intracellular recordings from single MNs and simultaneous extracellular recordings from lumbar ventral roots. In Mg2+-free solution, MNs exhibited irregular transient membrane potential depolarizations that were blocked by d,l-2-amino-5-phosphonopentanoic acid (APV) but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Generation and maintenance of membrane potential oscillations required specific NMDA receptor activation. Oscillations were antagonized by APV but not by CNQX. Strychnine preincubation was required for NMDA to induce oscillations, but was not critical in maintaining them, because oscillations persisted after removal of strychnine. Therefore oscillations are suggested to be an inherent property of the spinal neuronal circuitry. Tetrodotoxin (TTX) blocked spike activity and had a bimodal effect on membrane potential oscillations. Oscillations initially were blocked by TTX, but reappeared spontaneously after 10–40 min. This suggests that maintenance of oscillations, once evoked, does not involve MN firing. Na+ entry through TTX-insensitive Na+ channels and/or NMDA receptor channels, transmembrane Ca2+ flux, Ca2+ release from intracellular stores, and Ca2+ activated K+ channels were critical in controlling the amplitude and frequency of membrane potential oscillations. It is hypothesized that these unmasked intrinsic oscillations in adult frog spinal cord MNs may represent a premetamorphic spinal oscillator involved in tadpole swimming that becomes suppressed during metamorphosis as strychnine-sensitive inhibition becomes more pronounced.

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