scholarly journals Searching for energy-resolved quasi-periodic oscillations in AGN

2021 ◽  
Author(s):  
Dominic I Ashton ◽  
Matthew J Middleton
Keyword(s):  
Power Law ◽  
Spectral Component ◽  
Broad Band ◽  
Initial Study ◽  
Periodic Oscillations ◽  
Single Observation ◽  
Curved Space ◽  
Multiple Observations ◽  
Band Noise ◽  
The Impact

Abstract X-ray quasi-periodic oscillations (QPOs) in AGN allow us to probe and understand the nature of accretion in highly curved space-time, yet the most robust form of detection (i.e. repeat detections over multiple observations) has been limited to a single source to-date, with only tentative claims of single observation detections in several others. The association of those established AGN QPOs with a specific spectral component has motivated us to search the XMM-Newton archive and analyse the energy-resolved lightcurves of 38 bright AGN. We apply a conservative false alarm testing routine folding in the uncertainty and covariance of the underlying broad-band noise. We also explore the impact of red-noise leak and the assumption of various different forms (power-law, broken power-law and lorentzians) for the underlying broad-band noise. In this initial study, we report QPO candidates in 6 AGN (7 including one tentative detection in MRK 766) from our sample of 38, which tend to be found at characteristic energies and, in four cases, at the same frequency across at least two observations, indicating they are highly unlikely to be spurious in nature.

scholarly journals X-ray spectral and timing evolution of MAXI J1727–203 with NICER

2020 ◽  
Vol 497 (3) ◽  
pp. 3896-3910
Author(s):  
K Alabarta ◽  
D Altamirano ◽  
M Méndez ◽  
V A Cúneo ◽  
L Zhang ◽  
...  
Keyword(s):  
Broad Band ◽  
Periodic Oscillations ◽  
X Ray ◽  
Band Noise ◽  
Intermediate States ◽  
Hard State ◽  
The Moment ◽  
Variability Study ◽  
Spectral States ◽  
Rule Out

ABSTRACT We present a detailed X-ray spectral and variability study of the full 2018 outburst of MAXI J1727–203 using NICER observations. The outburst lasted approximately four months. Spectral modelling in the 0.3–10 keV band shows the presence of both a soft thermal and a hard Comptonised component. The analysis of these components shows that MAXI J1727–203 evolved through the soft, intermediate, and hard spectral states during the outburst. We find that the soft (disc) component was detected throughout almost the entire outburst, with temperatures ranging from ∼0.4 keV, at the moment of maximum luminosity, to ∼0.1 keV near the end of the outburst. The power spectrum in the hard and intermediate states shows broad-band noise up to 20 Hz, with no evidence of quasi-periodic oscillations. We also study the rms spectra of the broad-band noise at 0.3−10 keV of this source. We find that the fractional rms increases with energy in most of the outburst except during the hard state, where the fractional rms remains approximately constant with energy. We also find that, below 3 keV, the fractional rms follows the same trend generally observed at energies >3 keV, a behaviour known from previous studies of black holes and neutron stars. The spectral and timing evolution of MAXI J1727–203, as parametrised by the hardness–intensity, hardness–rms, and rms–intensity diagrams, suggest that the system hosts a black hole, although we could not rule out a neutron star.

The Multilevel p2 Model

Methodology ◽  
2006 ◽  
Vol 2 (1) ◽  
pp. 42-47 ◽  
Author(s):  
Bonne J. H. Zijlstra ◽  
Marijtje A. J. van Duijn ◽  
Tom A. B. Snijders
Keyword(s):  
Social Network ◽  
Network Data ◽  
Mcmc Algorithm ◽  
Independent Observation ◽  
Single Observation ◽  
Multiple Networks ◽  
Social Network Data ◽  
Multiple Observations ◽  
Practical Support ◽  
The Social

The p 2 model is a random effects model with covariates for the analysis of binary directed social network data coming from a single observation of a social network. Here, a multilevel variant of the p 2 model is proposed for the case of multiple observations of social networks, for example, in a sample of schools. The multilevel p 2 model defines an identical p 2 model for each independent observation of the social network, where parameters are allowed to vary across the multiple networks. The multilevel p 2 model is estimated with a Bayesian Markov Chain Monte Carlo (MCMC) algorithm that was implemented in free software for the statistical analysis of complete social network data, called StOCNET. The new model is illustrated with a study on the received practical support by Dutch high school pupils of different ethnic backgrounds.

scholarly journals Qualitative and quantitative assessment of magnetic vestibular stimulation in humans

2020 ◽  
Vol 30 (6) ◽  
pp. 353-361
Author(s):  
Rebecca S. Dewey ◽  
Rachel Gomez ◽  
Chris Degg ◽  
David M. Baguley ◽  
Paul M. Glover
Keyword(s):  
Magnetic Field ◽  
Objective Measure ◽  
Quantitative Measure ◽  
Vestibular Stimulation ◽  
Initial Study ◽  
Clinical Test ◽  
Healthy Control ◽  
Student’S T ◽  
The Impact ◽  
The Magnetic Field

The sensation of phantom motion or exhibition of bodily sway is often reported in the proximity of an MR scanner. It is proposed that the magnetic field stimulates the vestibular system. There are a number of possible mechanisms responsible, and the relative contributions of susceptibility on the otolithic receptors and the Lorentz force on the cupulae have not yet been explored. This exploratory study aims to investigate the impact of being in the proximity of a 7.0 T MR scanner. The modified clinical test of sensory interaction on balance (mCTSIB) was used to qualitatively ascertain whether or not healthy control subjects who passed the mCTSIB in normal conditions 1) experienced subjective sensations of dizziness, vertigo or of leaning or shifting in gravity when in the magnetic field and 2) exhibited visibly increased bodily sway whilst in the magnetic field compared to outside the magnetic field. Condition IV of the mCTSIB was video recorded outside and inside the magnetic field, providing a semi-quantitative measure of sway. For condition IV of the mCTSIB (visual and proprioceptive cues compromised), all seven locations/orientations around the scanner yielded significantly more sway than at baseline (p < 0.01 FDR). A Student’s t-test comparing the RMS velocity of a motion marker on the upper arm during mCTSIB condition IV showed a significant increase in the amount of motion exhibited in the field (T = 2.59; d.f. = 9; p = 0.029) compared to outside the field. This initial study using qualitative measures of sway demonstrates that there is evidence for MR-naïve individuals exhibiting greater sway while performing the mCTSIB in the magnetic field compared to outside the field. Directional polarity of sway was not significant. Future studies of vestibular stimulation by magnetic fields would benefit from the development of a sensitive, objective measure of balance function, which can be performed inside a magnetic field.

Acceptable Levels of Tonal and Broad-Band Repetitive and Continuous Sounds during the Performance of Nonauditory Tasks

1995 ◽  
Vol 81 (3) ◽  
pp. 803-816 ◽  
Author(s):  
Ulf Landström ◽  
Anders Kjellberg ◽  
Marianne Byström
Keyword(s):  
Reaction Time ◽  
Sound Pressure ◽  
Broad Band ◽  
Reaction Time Task ◽  
Simple Reaction Time Task ◽  
Reasoning Test ◽  
Band Noise ◽  
Time Test ◽  
The Difference ◽  
Reaction Time Test

Three groups of 24 subjects were exposed to a 1000–Hz tone or broad band noise in a sound chamber. During the exposures subjects were engaged in an easy reaction time test or a difficult grammatical reasoning test. For each exposure and work subjects adjusted the noise to a tolerance level defined by its interference with task performance. During the simple reaction-time task significantly higher sound-pressure levels were accepted than during the reasoning test. At the tonal exposure, much lower levels were accepted than during the exposure to broad-band noise. For continuous sound exposures much higher levels were accepted than for noncontinuous exposures. For tonal exposures the difference was approximately 5 dB, for the broad-band exposures approximately 9 dB. In a separate study the effects of the noncontinuity of the noise and pauses were analysed. The raised annoying effect of the noncontinuous noise was not more affected by the noncontinuity of the noise periods than by the noncontinuity of the pauses. The results imply that the annoying reactions to the sound will be increased for repetitive noise and that the reaction is highly influenced by the over-all noncontinuity of the exposure.

A NONLINEAR STRAIN-DEPENDENT VARIABLE-ORDER FRACTIONAL MODEL WITH APPLICATIONS TO ALUMINUM FOAMS

Fractals ◽  
2021 ◽  
Author(s):  
WEI CAI ◽  
PING WANG
Keyword(s):  
Power Law ◽  
Variable Order ◽  
Aluminum Foams ◽  
Static Compression ◽  
Fractional Model ◽  
Comparative Results ◽  
The Impact ◽  
Strain Responses ◽  
Strain Dependent ◽  
Quasi Static Compression

In this paper, a power-law strain-dependent variable order is first incorporated into the fractional constitutive model and employed to describe mechanical behaviors of aluminum foams under quasi-static compression and tension. Comparative results illustrate that power-law strain-dependent variable order is capable of better describing stress–strain responses compared with the traditional linear one. The evolution of fractional order along with the porosities or relative densities can be well qualitatively interpreted by its physical meaning. Furthermore, the model is also extended to characterize the impact behaviors under large constant strain rates. It is observed that fractional model with sinusoidal variable order agrees well with the experimental data of aluminum foams with impact and non-impact surfaces.

scholarly journals Breakdown Degradation Associated With Elementary Screw Dislocations In 4H-SiC P+N Junction Rectifiers

1997 ◽  
Vol 483 ◽  
Author(s):  
P. G. Neudeck ◽  
W. Huang ◽  
M. Dudley
Keyword(s):  
Video Camera ◽  
Initial Study ◽  
Hollow Core ◽  
Power Devices ◽  
Screw Dislocations ◽  
Burgers Vector ◽  
X Ray ◽  
Current Voltage ◽  
The Impact ◽  
Sic Wafer

AbstractIt is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = Ic with no hollow core) in densities on the order of thousands per cm2, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p+n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p+n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.

The Prediction of Hearing Loss in Persons With Cerebral Palsy Using Contralateral Acoustic Reflex Threshold for Broad-Band Noise

2003 ◽  
Vol 12 (2) ◽  
pp. 91-95
Author(s):  
Michele B. Emmer ◽  
Shlomo Silman
Keyword(s):  
Hearing Loss ◽  
Cerebral Palsy ◽  
Broad Band ◽  
Screening Method ◽  
Accurate Method ◽  
Normal Hearing ◽  
Acoustic Reflex ◽  
Band Noise ◽  
Reflex Threshold ◽  
Acoustic Reflex Threshold

The utility of R. Keith’s (1977) method of screening for hearing sensitivity using the contralateral acoustic-reflex threshold (ART) for broad-band noise (BBN) was tested in persons with cerebral palsy (CP). Three groups of participants were included in this prospective study. The first group comprised 20 normal-hearing individuals without CP whose results were used as normative data. The second group comprised 16 participants with normal hearing and CP. The third group comprised 22 participants with sensorineural hearing loss and CP. The results of this study indicate that Keith’s screening method employing ART for BBN can be used successfully in a population with multiple handicaps where a quick, inexpensive, readily available, and accurate method is needed.

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