scholarly journals Exploring short period oscillations in filaments

2007 ◽  
Vol 3 (S247) ◽  
pp. 178-181 ◽  
Author(s):  
D. Y. Kolobov ◽  
N. I. Kobanov ◽  
S. A. Chupin
Keyword(s):  
Data Reduction ◽  
High Frequency ◽  
Entrance Slit ◽  
Doppler Velocity ◽  
High Frequencies ◽  
Spectrograph Slit ◽  
High Frequency Oscillations ◽  
Short Period ◽  
False Signal ◽  
Image Shifting

AbstractThe authors analyse sources of false Doppler velocity signals of high frequencies (10 mHz and higher) in observations of filaments. In ground-based observations, spectrograph noise and image shifting at the spectrograph entrance slit are the main causes of the false signal. It is shown that using differential methods and telluric lines as reference lines significantly reduces the influence of the first factor. Periodical image shifting along the spectrograph slit can be compensated for during data reduction. In some cases detected high-frequency oscillations appear to be real.

Neocortical pathological high-frequency oscillations are associated with frequency-dependent alterations in functional network topology

2013 ◽  
Vol 110 (10) ◽  
pp. 2475-2483 ◽  
Author(s):  
George M. Ibrahim ◽  
Ryan Anderson ◽  
Tomoyuki Akiyama ◽  
Ayako Ochi ◽  
Hiroshi Otsubo ◽  
...  
Keyword(s):  
Functional Connectivity ◽  
High Frequency ◽  
Phase Locking ◽  
Critical Role ◽  
Intractable Epilepsy ◽  
Network Connectivity ◽  
Relative Increase ◽  
High Frequencies ◽  
High Frequency Oscillations ◽  
Cortical Regions

Synchronization of neural oscillations is thought to integrate distributed neural populations into functional cell assemblies. Epilepsy is widely regarded as a disorder of neural synchrony. Knowledge is scant, however, regarding whether ictal changes in synchrony involving epileptogenic cortex are expressed similarly across various frequency ranges. Cortical regions involved in epileptic networks also exhibit pathological high-frequency oscillations (pHFOs, >80 Hz), which are increasingly utilized as biomarkers of epileptogenic tissue. It is uncertain how pHFO amplitudes are related to epileptic network connectivity. By calculating phase-locking values among intracranial electrodes implanted in children with intractable epilepsy, we constructed ictal connectivity networks and performed graph theoretical analysis to characterize their network properties at distinct frequency bands. Ictal data from 17 children were analyzed with a hierarchical mixed-effects model adjusting for patient-level covariates. Epileptogenic cortex was defined in two ways: 1) a hypothesis-driven method using the visually defined seizure-onset zone and 2) a data-agnostic method using the high-frequency amplitude of each electrode. Epileptogenic cortex exhibited a logarithmic decrease in interregional functional connectivity at high frequencies (>30 Hz) during seizure initiation and propagation but not at termination. At slower frequencies, conversely, epileptogenic cortex expressed a relative increase in functional connectivity. Our findings suggest that pHFOs reflect epileptogenic network interactions, yielding theoretical support for their utility in the presurgical evaluation of intractable epilepsy. The view that abnormal network synchronization plays a critical role in ictogenesis and seizure dynamics is supported by the observation that functional isolation of epileptogenic cortex at high frequencies is absent at seizure termination.

Instrumental group delay for high-frequency and teleseismic P waves

1987 ◽  
Vol 77 (5) ◽  
pp. 1854-1861
Author(s):  
Goetz G. R. Buchbinder
Keyword(s):  
High Frequency ◽  
Group Delay ◽  
P Waves ◽  
High Frequencies ◽  
Long Period ◽  
Short Period ◽  
The World ◽  
Seismograph Station ◽  
Group Delays ◽  
Seismograph Network

Abstract The instrumental group delay dθ/dω is considered here. First, these delays were calculated for three different recording systems that were used in a precise travel-time monitoring experiment where the delays varied between 10 and 40 msec for the high frequencies of the seismograms involved. A technique is demonstrated by which these delays may be readily accounted for and by which instrumental malfunctions can be readily detected. Second, two of these systems are also currently used for the recording of short-period teleseisms; at the 1-sec period, the group delays are from 0.3 to 0.4 sec, which is significant and must be accounted for. This is particularly important when these systems are used in connection with data from other systems that have different delays, such as the World-Wide Seismograph Station Network and Canadian Seismograph Network stations. Neglecting these delays will create serious problems in seismological tomography and earthquake catalogs. Third, for long-period phases recorded by the SRO-type instruments, the delays for the 10- to 20-sec periods are 6 to 12 sec; again, these are significant and must be accounted for.

scholarly journals High frequencies in TESS A–F main-sequence stars

2019 ◽  
Vol 487 (2) ◽  
pp. 2117-2132 ◽  
Author(s):  
L A Balona ◽  
D L Holdsworth ◽  
M S Cunha
Keyword(s):  
High Frequency ◽  
Driving Mechanism ◽  
Rotational Axis ◽  
Satellite Mission ◽  
High Frequencies ◽  
High Frequency Oscillations ◽  
Photometric Observations ◽  
F Stars ◽  
Ap Stars ◽  
Scuti Stars

Abstract The driving mechanism for high-frequency oscillations in some chemically peculiar Ap stars, the rapidly oscillating Ap stars (roAp stars), is not understood. The Transiting Exoplanet Survey Satellite mission (TESS) data provide an ideal opportunity to extend the number of roAp stars that might provide further clues to address this problem. From an examination of over 18 000 stars in TESS sectors 1–7, we have discovered high-frequency pulsations in 14 A–F stars, of which only 3 are classified as Ap stars. In addition to these new discoveries, we discuss the frequencies in nine previously known roAp stars. In one of these stars, HD 60435, we confirm a previous finding that the pulsations have lifetimes of only a few days. In another known roAp star, HD 6532, the relative amplitudes of the rotationally modulated sidelobes, which are generally used to estimate the inclination of the magnetic axis relative to the rotational axis, are significantly different from those found in ground-based B-band photometric observations. We also discuss four δ Scuti stars that appear to have independent frequencies similar to those of roAp stars.

Quasi-Periodic Oscillations in Dwarf Novae

1979 ◽  
Vol 46 ◽  
pp. 77-88
Author(s):  
Edward L. Robinson
Keyword(s):  
Binary Systems ◽  
Outer Edge ◽  
Light Curves ◽  
Close Binary ◽  
Bright Spot ◽  
Dwarf Novae ◽  
Periodic Oscillations ◽  
High Frequencies ◽  
Short Period ◽  
Typical Time

Three distinct kinds of rapid variations have been detected in the light curves of dwarf novae: rapid flickering, short period coherent oscillations, and quasi-periodic oscillations. The rapid flickering is seen in the light curves of most, if not all, dwarf novae, and is especially apparent during minimum light between eruptions. The flickering has a typical time scale of a few minutes or less and a typical amplitude of about .1 mag. The flickering is completely random and unpredictable; the power spectrum of flickering shows only a slow decrease from low to high frequencies. The observations of U Gem by Warner and Nather (1971) showed conclusively that most of the flickering is produced by variations in the luminosity of the bright spot near the outer edge of the accretion disk around the white dwarf in these close binary systems.

HIGH FREQUENCY OSCILLATIONS AND ELECTRON BEAM RELAXATION IN HOMOGENEOUS GAS-DISCHARGE PLASMA

1979 ◽  
Vol 40 (C7) ◽  
pp. C7-619-C7-620
Author(s):  
L. L. Pasechnik ◽  
L. I. Romanyuk ◽  
N. Ye. Svavil'ny
Keyword(s):  
Electron Beam ◽  
High Frequency ◽  
Discharge Plasma ◽  
Gas Discharge ◽  
Gas Discharge Plasma ◽  
High Frequency Oscillations

scholarly journals Can we use intraoperative high‐frequency oscillations to guide tumor‐related epilepsy surgery?

Epilepsia ◽  
2021 ◽  
Author(s):  
Nicole E. C. Klink ◽  
Willemiek J. E. M. Zweiphenning ◽  
Cyrille H. Ferrier ◽  
Peter H. Gosselaar ◽  
Kai J. Miller ◽  
...  
Keyword(s):  
Epilepsy Surgery ◽  
High Frequency ◽  
High Frequency Oscillations

scholarly journals Rheology of rounded mammalian cells over continuous high-frequencies

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Gotthold Fläschner ◽  
Cosmin I. Roman ◽  
Nico Strohmeyer ◽  
David Martinez-Martin ◽  
Daniel J. Müller
Keyword(s):  
High Frequency ◽  
Mammalian Cells ◽  
Mechanical Response ◽  
Cell Mass ◽  
Low Frequency ◽  
Mass Measurements ◽  
High Frequencies ◽  
Polymer Relaxation ◽  
Continuous Frequency ◽  
Rheological Experiments

AbstractUnderstanding the viscoelastic properties of living cells and their relation to cell state and morphology remains challenging. Low-frequency mechanical perturbations have contributed considerably to the understanding, yet higher frequencies promise to elucidate the link between cellular and molecular properties, such as polymer relaxation and monomer reaction kinetics. Here, we introduce an assay, that uses an actuated microcantilever to confine a single, rounded cell on a second microcantilever, which measures the cell mechanical response across a continuous frequency range ≈ 1–40 kHz. Cell mass measurements and optical microscopy are co-implemented. The fast, high-frequency measurements are applied to rheologically monitor cellular stiffening. We find that the rheology of rounded HeLa cells obeys a cytoskeleton-dependent power-law, similar to spread cells. Cell size and viscoelasticity are uncorrelated, which contrasts an assumption based on the Laplace law. Together with the presented theory of mechanical de-embedding, our assay is generally applicable to other rheological experiments.

scholarly journals High-frequency oscillations recorded with surface EEG in neonates with seizures

2021 ◽  
Author(s):  
Lotte Noorlag ◽  
Maryse A. van 't Klooster ◽  
Alexander C. van Huffelen ◽  
Nicole E.C. van Klink ◽  
Manon J.N.L. Benders ◽  
...  
Keyword(s):  
High Frequency ◽  
High Frequency Oscillations ◽  
Surface Eeg
Sign in / Sign up

Export Citation Format

Share Document