scholarly journals Hot Spots in Compact Sources

1984 ◽  
Vol 110 ◽  
pp. 45-46 ◽  
Author(s):  
T. K. Menon
Keyword(s):  
Hot Spots ◽  
Low Frequency ◽  
Physical Parameters ◽  
Strongly Correlated ◽  
Physical Conditions ◽  
Compact Sources

The low-frequency turnover of a selected sample of quasars is found to be strongly correlated with their redshift (Menon 1983)). Assuming that the components which produce the low-frequency turnover are hot spots in the quasars I have derived the physical parameters of the hot spots and show that there is a continuity in the various parameters as the angular sizes of the hot spots vary from subarcseconds to milliarcseconds. Hence the low-frequency turnover can be used as a probe into the physical conditions at the earliest phases of quasar activity.

scholarly journals The UTR-2 Very Low Frequency Sky Survey and Its Main Results

1998 ◽  
Vol 179 ◽  
pp. 100-102
Author(s):  
K.P. Sokolov
Keyword(s):  
High Frequency ◽  
Surface Brightness ◽  
Low Frequency ◽  
Source Population ◽  
Low Frequencies ◽  
Physical Conditions ◽  
The Past ◽  
Sky Survey ◽  
Low Surface Brightness ◽  
Compact Sources

During the past decade there has been a dramatic increase in the amount of high-frequency (v > 1000 MHz) data currently underlying the studies of bright compact sources (Tb ∼ 1011–12K, l ≤ 1 kpc) with flat spectra. But in order to determine physical conditions inside extragalactic radio sources at different stages of their evolution the studies of old extended (l ∼ 100 kpc) sources with low surface brightness and steep spectra which constitute the dominant radio source population at very low frequencies (v ≪ 100 MHz) are also needed. These sources are known to represent the final stage in the evolution of extragalactic objects.

Numerical simulation of seismic waves in porous media components

2021 ◽  
Vol 9 (1) ◽  
pp. 4-30
Author(s):  
M. Azeredo ◽  
◽  
V. Priimenko ◽  
Keyword(s):  
Numerical Simulation ◽  
Porous Medium ◽  
High Frequency ◽  
Seismic Waves ◽  
Computational Algorithm ◽  
Low Frequency ◽  
Physical Parameters ◽  
Mathematical Algorithm ◽  
Biot Equations ◽  
Attenuation And Dispersion

This work presents a mathematical algorithm for modeling the propagation of poroelastic waves. We have shown how the classical Biot equations can be put into Ursin’s form in a plane-layered 3D porous medium. Using this form, we have derived explicit for- mulas that can be used as the basis of an efficient computational algorithm. To validate the algorithm, numerical simulations were performed using both the poroelastic and equivalent elastic models. The results obtained confirmed the proposed algorithm’s reliability, identify- ing the main wave events in both low-frequency and high-frequency regimes in the reservoir and laboratory scales, respectively. We have also illustrated the influence of some physical parameters on the attenuation and dispersion of the slow wave.

scholarly journals The broad line region of AGN: Kinematics and physics

2006 ◽  
pp. 1-11 ◽  
Author(s):  
L.C. Popovic
Keyword(s):  
Electron Temperature ◽  
Accretion Disk ◽  
Emission Lines ◽  
Physical Parameters ◽  
Broad Line ◽  
Physical Conditions ◽  
Broad Line Region ◽  
Broad Emission ◽  
Line Region

In this paper a discussion of kinematics and physics of the Broad Line Region (BLR) is given. The possible physical conditions in the BLR and problems in determination of the physical parameters (electron temperature and density) are considered. Moreover, one analyses the geometry of the BLR and the probability that (at least) a fraction of the radiation in the Broad Emission Lines (BELs) originates from a relativistic accretion disk.

scholarly journals INTERSTELLAR MEDIUM AND DECAMETER RADIO SPECTROSCOPY

2021 ◽  
Vol 26 (4) ◽  
pp. 314-325
Author(s):  
S. V. Stepkin ◽  
◽  
O. O. Konovalenko ◽  
Y. V. Vasylkivskyi ◽  
D. V. Mukha ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Radio Telescope ◽  
Radio Astronomy ◽  
Low Frequency ◽  
Spectral Lines ◽  
Physical Parameters ◽  
Recombination Mechanism ◽  
Radio Recombination Lines ◽  
Radio Spectroscopy ◽  
Correlation Spectrum

Purpose: The analytical review of the main results of research in the new direction of the low-frequency radio astronomy, the interstellar medium radio spectroscopy at decameter waves, which had led to astrophysical discovery, recording of the radio recombination lines in absorption for highly excited states of interstellar carbon atoms (more than 600). Design/methodology/approach: The UTR-2 world-largest broadband radio telescope of decameter waves optimally connected with the digital correlation spectrum analyzers has been used. Continuous modernization of antenna system and devices allowed increasing the analysis band from 100 kHzto 24 MHz and a number of channels from 32 to 8192. The radio telescope and receiving equipment with appropriate software allowed to have a long efficient integration time enough for a large line series simultaneously with high resolution, noise immunity and relative sensitivity. Findings: A new type of interstellar spectral lines has been discovered and studied, the interstellar carbon radio recombination lines in absorption for the record high excited atoms with principal quantum numbers greater than 1000. The line parameters (intensity, shape, width, radial velocity) and their relation ship with the interstellar medium physical parameters have been determined. The temperature of line forming regions is about 100 K, the electron concentration up to 0.1 cm–3 and the size of a line forming region is about 10 pc. For the first time, radio recombination lines were observed in absorption. They have significant broadening and are amplified by the dielectronic-like recombination mechanism and are also the lowest frequency lines in atomic spectroscopy. Conclusions: The detected low-frequency carbon radio recombination lines and their observations have become a new highly effective tool for the cold partially ionized interstellar plasma diagnostics. Using them allows obtaining the information which is not available with the other astrophysical methods. For almost half a century of their research, a large amount of hardware-methodical and astrophysical results have been obtained including a record number of Galaxy objects, where there levant lines have been recorded. The domestic achievements have stimulated many theoretical and experimental studies in other countries, but the scientific achievements of Ukrainian scientists prove the best prospects for further development of this very important area of astronomical science. Key words: low-frequency radio astronomy; radio telescope; interstellar medium; radio recombination lines; carbon; hydrogen; spectral analyzer

scholarly journals Effect of Variable Viscosity and Gravity Modulation on Linear and Non-Linear Rayleigh-Benard Convection in Viscoelastic Ferromagnetic Liquids

2020 ◽  
Vol 9 (3) ◽  
pp. 3482-3488
Keyword(s):  
Stability Analysis ◽  
Heat Transport ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Variable Viscosity ◽  
Low Frequency ◽  
Physical Parameters ◽  
Gravity Modulation ◽  
Non Linear ◽  
The Individual

The combined effect of various parameters of gravity modulation on the onset of ferroconvection is studied for both linear and non-linear stability. The effect of various parameters of ferroconvection is studied for linear stability analysis. The resulting seven-mode generalized Lorenz model obtained in non-linear stability analysis is solved using Runge -Kutta-Felberg 45 method to analyze the heat transfer. Consequently the individual effect of gravity modulation on heat transport has been investigated. Further, the effect of physical parameters on heat transport has been analyzed and depicted graphically. The low-frequency gravity modulation is observed to get an effective influence on the stability of the system. Therefore ferro convection can be advanced or delayed by controlling different governing parameters. It shows that the influence of gravity modulation stabilizes system.

Non-Linear Dynamic Magneto Electric Effects in Ferromagnetic-Ferroelectric Layered Composites

2013 ◽  
Author(s):  
Satenik Harutyunyan ◽  
Davresh Hasanyan
Keyword(s):  
Vibration Frequency ◽  
Strain Distribution ◽  
Longitudinal Vibration ◽  
Three Dimensional ◽  
Low Frequency ◽  
Structure Design ◽  
Experimental Results ◽  
Physical Parameters ◽  
Wide Range ◽  
Non Linear

A non-linear theoretical model including bending and longitudinal vibration effects was developed for predicting the magneto electric (ME) effects in a laminate bar composite structure consisting of magnetostrictive and piezoelectric multi-layers. If the magnitude of the applied field increases, the deflection rapidly increases and the difference between experimental results and linear predictions becomes large. However, the nonlinear predictions based on the present model well agree with the experimental results within a wide range of applied electric field. The results of the analysis are believed to be useful for materials selection and actuator structure design of actuator in actuator fabrication. It is shown that the problem for bars of symmetrical structure is not divided into a plane problem and a bending problem. A way of simplifying the solution of the problem is found by an asymptotic method. After solving the problem for a laminated bar, formula that enable one to change from one-dimensional required quantities to three dimensional quantities are obtained. The derived analytical expression for ME coefficients depend on vibration frequency and other geometrical and physical parameters of laminated composites. Parametric studies are presented to evaluate the influences of material properties and geometries on strain distribution and the ME coefficient. Analytical expressions indicate that the vibration frequency strongly influences the strain distribution in the laminates, and that these effects strongly influence the ME coefficients. It is shown that for certain values of vibration frequency (resonance frequency), the ME coefficient becomes infinity; as a particular case, low frequency ME coefficient were derived as well.

Physical Parameters for Four Seabed Geoacoustic Models from Low-Frequency Measurements

2010 ◽  
Author(s):  
Ji-Xun Zhou ◽  
Xue-Zhen Zhang ◽  
Jeffrey Simmen ◽  
Ellen S. Livingston ◽  
Ji-Xun Zhou ◽  
...  
Keyword(s):  
Low Frequency ◽  
Physical Parameters ◽  
Frequency Measurements

Optimization of space-constrained micro-perforated absorbers by causality criteria

2021 ◽  
Vol 263 (6) ◽  
pp. 275-286
Author(s):  
Teresa Bravo ◽  
Cedric Maury
Keyword(s):  
Absorption Coefficient ◽  
Low Frequency ◽  
Single Layer ◽  
Optimization Procedure ◽  
Separation Distance ◽  
Physical Parameters ◽  
Total Absorption ◽  
Causality Criterion ◽  
Selection Of ◽  
Total Absorption Coefficient

The problem of space-constrained absorbers in the low frequency range constitutes an area of continuous research. Micro-perforated panels are advantageous because they can be tuned by a proper selection of their constitutive physical parameters including the diameter of the perforations and their separation distance, their thickness and the length of the backing cavity. However, such optimal selection is not straightforward, especially when considering multi-layer partitions. Current optimization algorithms are based on the maximization of the total absorption coefficient averaged over a frequency band, that requires a compromise between the bandwidth and the thickness of the control device. In this work, the problem is analysed on the basis of a causality criterion. This principle is generalized from its formulation in the field of electromagnetism to obtain a relation that correlates the thickness-to-bandwidth performance of a micro-perforated absorber to its total absorption coefficient. Using this relation, an optimization procedure is presented for the sequential selection of the optimal physical parameters for single-layer partitions. An excellent agreement has been found between the optimal values obtained by the causality criterion and those achieved by critical coupling conditions.

scholarly journals A Complexity-Entropy Based Approach for the Detection of Fish Choruses

Entropy ◽  
2019 ◽  
Vol 21 (10) ◽  
pp. 977 ◽  
Author(s):  
Shashidhar Siddagangaiah ◽  
Chi-Fang Chen ◽  
Wei-Chun Hu ◽  
Nadia Pieretti
Keyword(s):  
Diversity Index ◽  
Pearson Correlation ◽  
Low Frequency ◽  
Strongly Correlated ◽  
Marine Environments ◽  
Sound Sources ◽  
Efficient Detection ◽  
Acoustic Diversity ◽  
User Friendly ◽  
Robust To Noise

Automated acoustic indices to infer biological sounds from marine recordings have produced mixed levels of success. The use of such indices in complex marine environments, dominated by several anthropogenic and geophonic sources, have yet to be understood fully. In this study, we introduce a noise resilient method based on complexity-entropy (hereafter named C-H) for the detection of biophonic sounds originating from fish choruses. The C-H method was tested on data collected in Changhua and Miaoli (Taiwan) during the spring in both 2016 and 2017. Miaoli was exposed to continual shipping activity, which led to an increase of ~10 dB in low frequency ambient noise levels (5–500 Hz). The acoustic dataset was successively analyzed via the acoustic complexity index, the acoustic diversity index and the bioacoustic index. The C-H method was found to be strongly correlated with fish chorusing (Pearson correlation: rH < −0.9; rC > 0.89), and robust to noise originating from shipping activity or natural sources, such as wind and tides (rH and rC were between 0.22 and −0.19). Other indices produced lower or null correlations with fish chorusing due to missed identification of the choruses or sensitivity to other sound sources. In contrast to most acoustic indices, the C-H method does not require a prior setting of frequency and amplitude thresholds, and is therefore, more user friendly to untrained technicians. We conclude that the use of the C-H method has potential implications in the efficient detection of fish choruses for management or conservation purposes and could help with overcoming the limitations of acoustic indices in noisy marine environments.

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