Radio Flux Flicker of Extragalactic Sources

ABSTRACT The University of Tasmania Ceduna radio telescope has been used to investigate rapid variability in the radio flux density of the BL Lac object PKS B1144−379 at 6.7 GHz. High-cadence monitoring of this extreme scintillator was carried out over a period of approximately 9 yr, between 2003 and 2011. We have used structure functions created from the intensity time-series to determine the characteristic time-scale of the variability. The characteristic time-scale is consistently observed to increase during certain periods of each year, demonstrating the annual cycle expected for scintillation through an interstellar scattering screen. The best-fitting annual cycle model for each year suggests that the scintillation pattern has an anisotropic structure and that the upper limit of its scattering screen is at a distance of ∼0.84 kpc. Higher anisotropy in some of the annual cycle fits suggests that changes in the intrinsic source structure might be influencing the variability time-scale. We found a prominent annual cycle is only present in the variability time-scale for certain years, where other evidence suggests that the core is compact. From our measurements, we calculated that the core angular size varied between 5.65 and 15.90 μas (0.05–0.13 pc). The core component was found to be at its most compact during two flares in the total flux density, which were observed in 2005 and 2008. We conclude that the long-term variability in the radio flux density of PKS B1144−379 is due to intrinsic changes in the source and that these affect our ability to measure an annual cycle in its variability time-scale.

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Effect of Particle Residence Time on Particle Dispersion in a Plane Mixing Layer

Journal of Fluids Engineering ◽

10.1115/1.2910208 ◽

1993 ◽

Vol 115 (4) ◽

pp. 751-759 ◽

Cited By ~ 22

Author(s):

Tsuneaki Ishima ◽

Koichi Hishida ◽

Masanobu Maeda

Keyword(s):

Gas Phase ◽

Residence Time ◽

Time Scale ◽

Characteristic Time ◽

Mixing Layer ◽

Particle Dispersion ◽

Laser Doppler Velocimeter ◽

Characteristic Time Scale ◽

Two Phase ◽

Particle Residence Time

A particle dispersion has been experimentally investigated in a two-dimensional mixing layer with a large relative velocity between particle and gas-phase in order to clarify the effect of particle residence time on particle dispersion. Spherical glass particles 42, 72, and 135 μm in diameter were loaded directly into the origin of the shear layer. Particle number density and the velocities of both particle and gas phase were measured by a laser Doppler velocimeter with modified signal processing for two-phase flow. The results confirmed that the characteristic time scale of the coherent eddy apparently became equivalent to a shorter characteristic time scale due to a less residence time. The particle dispersion coefficients were well correlated to the extended Stokes number defined as the ratio of the particle relaxation time to the substantial eddy characteristic time scale which was evaluated by taking account of the particle residence time.

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UNIVERSAL MULTIFRACTAL CHARACTERIZATION AND SIMULATION OF SPEECH

International Journal of Bifurcation and Chaos ◽

10.1142/s0218127492000835 ◽

1992 ◽

Vol 02 (03) ◽

pp. 715-719

Author(s):

CHRIS LARNDER ◽

NICOLAS DESAULNIERS-SOUCY ◽

SHAUN LOVEJOY ◽

DANIEL SCHERTZER ◽

CLAUDE BRAUN ◽

...

Keyword(s):

Time Scale ◽

Scale Invariance ◽

Characteristic Time ◽

Low Frequency ◽

Characteristic Time Scale ◽

Low Frequencies ◽

Universal Behavior ◽

Nonlinear Mixing

In the 1970's it was found that; for low frequencies (<10 Hz), speech is scaling: it has no characteristic time scale. Now such scale invariance is associated with multiscaling statistics, and multifractal structures. Just as Gaussian noises frequently arise because they are generically produced by sums of many independent noise processes, scaling noises have an analogous universal behavior arising from nonlinear mixing of processes. We show that low frequency speech is consistent with these ideas, and use the measured parameters to produce stochastic speech simulations which are strikingly similar to real speech.

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Daytime efficiency and characteristic time scale of interplanetary electric fields penetration to equatorial latitude ionosphere

Journal of Atmospheric and Solar-Terrestrial Physics ◽

10.1016/j.jastp.2010.09.003 ◽

2011 ◽

Vol 73 (11-12) ◽

pp. 1555-1559 ◽

Cited By ~ 11

Author(s):

C.M. Denardini ◽

H.C. Aveiro ◽

P.D.S.C. Almeida ◽

L.C.A. Resende ◽

L.M. Guizelli ◽

...

Keyword(s):

Electric Fields ◽

Time Scale ◽

Characteristic Time ◽

Characteristic Time Scale ◽

Equatorial Latitude

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A characteristic time scale of tick quotes on foreign currency markets

Practical Fruits of Econophysics ◽

10.1007/4-431-28915-1_14 ◽

2006 ◽

pp. 82-86 ◽

Cited By ~ 1

Author(s):

Aki-Hiro Sato

Keyword(s):

Time Scale ◽

Characteristic Time ◽

Foreign Currency ◽

Characteristic Time Scale ◽

Currency Markets

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Does the Radio Luminosity of Pulsar Grow up in its Later Stage?

Symposium - International Astronomical Union ◽

10.1017/s007418090016036x ◽

1987 ◽

Vol 125 ◽

pp. 50-50

Author(s):

T. Lu ◽

P. C. Zhu ◽

J. S. Kui

Keyword(s):

Time Scale ◽

Characteristic Time ◽

Statistical Analyses ◽

Striking Feature ◽

Characteristic Time Scale ◽

Radio Luminosity ◽

Mean Values ◽

The Mean

In usual statistical analyses, because of diversities of proper parameters of pulsars, some interesting features might be smeared. In order to remove these diversities, we use the mean values for all quantities of pulsars, instead of values of individual pulsar, to do statistical analyses. logP/P3 - log τ and logL - logτ have been plotted, here τ P/2P and L denote the characteristic time scale and the radio luminosity of pulsars respectively. The most striking feature is that after its initial dropping to a dip at about τ∼106 yrs, the radio luminosity of pulsar appears to grow up evidently and then redrop again. This feature is difficult to be understood in usual models. However, two tentative interpretations have been given in this paper.

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The characteristic time scale for basin hydrological response using radar data

Journal of Hydrology ◽

10.1016/s0022-1694(01)00451-6 ◽

2001 ◽

Vol 252 (1-4) ◽

pp. 85-99 ◽

Cited By ~ 35

Author(s):

Efrat Morin ◽

Yehouda Enzel ◽

Uri Shamir ◽

Rami Garti

Keyword(s):

Time Scale ◽

Characteristic Time ◽

Radar Data ◽

Characteristic Time Scale ◽

Hydrological Response

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Role of thermal conduction in the expansion of a plasma from a vacuum interface

Canadian Journal of Physics ◽

10.1139/p88-111 ◽

1988 ◽

Vol 66 (8) ◽

pp. 662-673 ◽

Cited By ~ 1

Author(s):

D. Parfeniuk ◽

A. Ng ◽

P. Celliers

Keyword(s):

Time Scale ◽

Thermal Conduction ◽

Characteristic Time ◽

Characteristic Time Scale ◽

Rarefaction Waves ◽

Vacuum Interface ◽

Aluminum Plasma ◽

Self Similar ◽

Expansion Model ◽

Isotropic Expansion

The effects of thermal conduction are examined for the expansion of a plasma from a vacuum interface using an analytic model based on well-known self-similar models of rarefaction waves. Conventional analysis of shock-unloading experiments uses an isotropic expansion model. However, thermal conduction introduces a characteristic time scale during which the flow is not self-similar. The significance of this time scale for experimental measurements is also discussed. The characteristic time is calculated for an aluminum plasma using theoretical equation-of-state and conductivity models.

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The ‘Hurst phenomenon’ in grid turbulence

Journal of Fluid Mechanics ◽

10.1017/s0022112078000798 ◽

1978 ◽

Vol 85 (3) ◽

pp. 573-589 ◽

Cited By ~ 10

Author(s):

K. N. Helland ◽

C. W. Van Atta

Keyword(s):

Wind Tunnel ◽

Time Scale ◽

Characteristic Time ◽

Time Interval ◽

Characteristic Time Scale ◽

Grid Turbulence ◽

Mean Velocity ◽

Statistical Tool ◽

Rescaled Range ◽

Rescaled Range Analysis

Measurements of the statistical property called the ‘rescaled range’ in grid-generated turbulence exhibit a Hurst coefficient H = 0·5 for 43 < UT/M < 1850, where M/U is a characteristic time scale associated with the grid size M and mean velocity U. Theory predicts that H = 0·5 for independence of two observations separated by a time interval T, and the deviation from H = 0·5 is referred to as the ‘Hurst phenomenon’. The rescaled range obtained for grid turbulence contains an initial region UT/M < 43 of large H, approaching 1·0, corresponding approximately to the usual region of a finite non-zero autocorrelation of turbulent velocity fluctuations. For UT/M > 1850 the rescaled range breaks from H = 0·5 and rises at a significantly faster rate, H = 0·7-0·8, implying a long-term dependence or possibly non-stationarity at long times. The measured autocorrelations remain indistinguishable from zero for UT/M > 20. The break in the trend H = 0·5 is probably caused by motions on scales comparable to characteristic time scales of the wind-tunnel circulation. Rescaled-range analysis is a powerful statistical tool for determining the time scale separating the grid turbulence from the background wind-tunnel motions.

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