High frequency fluctuations in an active ionospheric experiment

2021 ◽  
Author(s):  
Irina Kovaleva ◽  
Alexey Kovalev
Keyword(s):  
High Frequency ◽  
Frequency Fluctuations

High-frequency fluctuations in the IGS'92 polar series

1995 ◽  
Vol 19 (3) ◽  
pp. 391-398
Author(s):  
Cheng-li Huang ◽  
Wen-jing Jin ◽  
De-chun Liao ◽  
Wen-yao Zhu ◽  
Jie-xian Wang
Keyword(s):  
High Frequency ◽  
Frequency Fluctuations

Exploring High Frequency Temporal Fluctuations in the Terminal Aneurysm of the Basilar Bifurcation

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Matthew D. Ford ◽  
Ugo Piomelli
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
High Frequency ◽  
Cerebral Aneurysms ◽  
Patient Specific ◽  
Disturbed Flow ◽  
Frequency Fluctuations ◽  
Wall Shear ◽  
Inflow Jet

Cerebral aneurysms are a common cause of death and disability. Of all the cardiovascular diseases, aneurysms are perhaps the most strongly linked with the local fluid mechanic environment. Aside from early in vivo clinical work that hinted at the possibility of high-frequency intra-aneurysmal velocity oscillations, flow in cerebral aneurysms is most often assumed to be laminar. This work investigates, through the use of numerical simulations, the potential for disturbed flow to exist in the terminal aneurysm of the basilar bifurcation. The nature of the disturbed flow is explored using a series of four idealized basilar tip models, and the results supported by four patient specific terminal basilar tip aneurysms. All four idealized models demonstrated instability in the inflow jet through high frequency fluctuations in the velocity and the pressure at approximately 120 Hz. The instability arises through a breakdown of the inflow jet, which begins to oscillate upon entering the aneurysm. The wall shear stress undergoes similar high-frequency oscillations in both magnitude and direction. The neck and dome regions of the aneurysm present 180 deg changes in the direction of the wall shear stress, due to the formation of small recirculation zones near the shear layer of the jet (at the frequency of the inflow jet oscillation) and the oscillation of the impingement zone on the dome of the aneurysm, respectively. Similar results were observed in the patient-specific models, which showed high frequency fluctuations at approximately 112 Hz in two of the four models and oscillations in the magnitude and direction of the wall shear stress. These results demonstrate that there is potential for disturbed laminar unsteady flow in the terminal aneurysm of the basilar bifurcation. The instabilities appear similar to the first instability mode of a free round jet.

High-frequency fluctuations of surface temperatures in an urban environment

2011 ◽  
Vol 108 (1-2) ◽  
pp. 301-324 ◽  
Author(s):  
Andreas Christen ◽  
Fred Meier ◽  
Dieter Scherer
Keyword(s):  
Urban Environment ◽  
High Frequency ◽  
Surface Temperatures ◽  
Frequency Fluctuations

ON ANALYSIS AND SYNTHESIS OF ELEMENTARY AND COMPLEX INFORMATIONAL BISPECTRAL STRUCTURES

2008 ◽  
Vol 18 (09) ◽  
pp. 2753-2763 ◽  
Author(s):  
GERMAN N. BOCHKOV ◽  
KONSTANTIN V. GOROKHOV
Keyword(s):  
Spectral Line ◽  
High Frequency ◽  
Frequency Synthesizer ◽  
Realistic Model ◽  
Sectional Area ◽  
The Real ◽  
Analysis And Synthesis ◽  
Frequency Fluctuations

The problem regarding shapes of bispectral peak of the triplet representing the triharmonic signal is discussed. This triplet can be used as both standard diagnostic signal for a bispectral analyzers and a simplest element of complex informational patterns of bispectrally organized signals. The problem of analyzing and measuring the parameters of bispectral peak is equally fundamental as the well-known problem concerning the shape and width of spectral line of quasi-monochromatic oscillations. The sectional area of bispectral peak restricts the limiting informational volume of complex bispectral patterns. Two models of an actual triplet with frequency fluctuations are analyzed. Universal bispectral-peak shapes are found for a triplet with proportional frequencies for the limiting cases of extremely slow and extremely fast frequency fluctuations. The phenomenon of bispectral-peak superlocalization is discovered for quasi-static fluctuations and analyzed for the most realistic model of 1/f frequency fluctuations. The experiment investigating the bispectral peak of the real high-frequency synthesizer is presented.

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