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.

scholarly journals Kepler eclipsing binaries with δ Scuti components and tidally induced heartbeat stars

2015 ◽  
Vol 11 (A29B) ◽  
pp. 648-652
Author(s):  
Zhao Guo ◽  
Douglas R. Gies ◽  
Rachel A. Matson
Keyword(s):  
Binary Stars ◽  
High Frequency ◽  
Eclipsing Binaries ◽  
Frequency Separation ◽  
High Frequency Oscillations ◽  
Orbital Frequency ◽  
Scuti Stars ◽  
Large Frequency ◽  
Δ Scuti Stars ◽  
Stellar Density

Abstractδ Scuti stars are generally fast rotators and their pulsations are not in the asymptotic regime, so the interpretation of their pulsation spectra is a very difficult task. Binary stars, especially eclipsing systems, offer us the opportunity to constrain the space of fundamental stellar parameters. Firstly, we show the results of KIC9851944 and KIC4851217 as two case studies. We found the signature of the large frequency separation in the pulsational spectrum of both stars. The observed mean stellar density and the large frequency separation obey the linear relation in the log-log space as found by Suarez et al. (2014) and García Hernández et al. (2015). Second, we apply the simple ‘one-layer model’ of Moreno & Koenigsberger (1999) to the prototype heartbeat star KOI-54. The model naturally reproduces the tidally induced high frequency oscillations and their frequencies are very close to the observed frequency at 90 and 91 times the orbital frequency.

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.

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.

A Driving Mechanism for High Frequency Combustion Instability in Liquid Fuel Rocket Engines

1964 ◽  
Vol 68 (645) ◽  
pp. 633-637 ◽  
Author(s):  
P. D. McCormack
Keyword(s):  
High Frequency ◽  
Liquid Fuel ◽  
Low Frequency ◽  
Pressure Oscillation ◽  
Experimental Investigations ◽  
Driving Mechanism ◽  
Rocket Engines ◽  
High Frequency Oscillations ◽  
The Subject ◽  
Motor Operation

The problem of combustion pressure oscillation in liquid-fuel rocket motor operation has long been the subject of theoretical and experimental investigations.The low frequency (less than 200 cps) type of oscillation, known as “chugging”, has been thoroughly analysed and the problem solved (see Crocco, 5th Combustion Symposium, p. 164).This Note is concerned with the more complex (and more destructive) high frequency oscillations, covering a range from about 1000 to 6000 cps. Such oscillations can resonate with the acoustical modes of the combustion chamber. Longitudinal, tangential and radial oscillating modes have been observed.

scholarly journals Rapidly varying A-type stars in the SuperWASP archive

2013 ◽  
Vol 9 (S301) ◽  
pp. 423-424
Author(s):  
Daniel L. Holdsworth ◽  
Barry Smalley
Keyword(s):  
High Frequency ◽  
Broad Band ◽  
Photometric Data ◽  
Time Resolved ◽  
Vast Amount ◽  
Ap Stars ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Initial Results ◽  
Existing Data

AbstractThe searches for transiting exoplanets have produced a vast amount of time-resolved photometric data of many millions of stars. One of the leading ground-based surveys is the SuperWASP project. We present the initial results of a survey of over 1.5 million A-type stars in the search for high frequency pulsations using SuperWASP photometry. We are able to detect pulsations down to the 0.5 mmag level in the broad-band photometry. This has enabled the discovery of several rapidly oscillating Ap stars and over 200 δ Scuti stars with frequencies above 50 d−1, and at least one pulsating sdB star. Such a large number of results allows us to statistically study the frequency overlap between roAp and δ Scuti stars and probe to higher frequency regimes with existing data.

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
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