scholarly journals 1/fNoise from Glauber Dynamics: Self-Consistent Interaction and Temperature Dependent Correlations

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Amrit De
Keyword(s):  
Flicker Noise ◽  
A Priori ◽  
Low Frequency ◽  
Glauber Dynamics ◽  
Glauber Model ◽  
Temperature Dependent ◽  
Spatially Extended ◽  
Two Level Systems ◽  
Ferromagnetic Interactions ◽  
Log Normal

Low frequency flicker noise has been argued to occur in spatially extended metastable systems near a critical point (Bak et al., 1987). An Ising-Glauber model based method is suggested here to systematically obtain temperature dependentnth-order correlation functions forNarbitrary interacting two-level systems (TLSs). This model is fully consistent with existing methods to calculate1/fnoise spectra from TLSs and complements them. However, with as such noa prioriassumptions on the typical log normal distribution of fluctuation rates, it is shown that1/fαnoise manifests in two different cases: first in the thermodynamic limit on a 2D lattice with long range antiferromagnetic interactions at low temperatures and second in the case of a statistical ensemble of finite-sized spin clusters representing disorder, but where each cluster is ordered due to ferromagnetic interactions.

Interpretation of temperature-dependent low frequency vibrational spectrum of solid-state benzoic acid dimer

2009 ◽  
Vol 479 (4-6) ◽  
pp. 211-217 ◽  
Author(s):  
Masae Takahashi ◽  
Yoshiyuki Kawazoe ◽  
Yoichi Ishikawa ◽  
Hiromasa Ito
Keyword(s):  
Solid State ◽  
Vibrational Spectrum ◽  
Benzoic Acid ◽  
Low Frequency ◽  
Temperature Dependent

Temperature Dependent Raman Scattering in CsTiOAsO4 Single Crystal

1995 ◽  
Vol 398 ◽  
Author(s):  
A.R. Guo ◽  
C.-S. Tu ◽  
Ruiwu Tao ◽  
R.S. Katiyar ◽  
Ruyan Guo ◽  
...  
Keyword(s):  
Soft Mode ◽  
Low Frequency ◽  
High Mobility ◽  
Vibrational Modes ◽  
Frequency Range ◽  
Temperature Dependent ◽  
Higher Symmetry ◽  
Phonon Spectra ◽  
Symmetry Structure ◽  
Increasing Temperature

ABSTRACTThe longitudinal (LO) and transverse (TO) A1 vibrational modes have been measured between 30-1200 cm−1 as a function of temperature (30–1240 K) for CsTiOAsO4 (CTA). The frequencies for all corresponding Raman components shifted to lower frequencies on increasing the temperature, however, there is no typical soft-mode like behavior observed in the measured frequency range. The relative intensities of the low frequency bands increase dramatically with increasing temperature due to high mobility of Cs+ ion. A higher symmetry structure taking place above 940K has been confirmed by changes in the phonon spectra.

A theory for Langmuir solitons

1982 ◽  
Vol 27 (1) ◽  
pp. 95-120 ◽  
Author(s):  
N. Nagesha Rao ◽  
Ram K. Varma
Keyword(s):  
Mach Number ◽  
A Priori ◽  
Low Frequency ◽  
Analytic Solutions ◽  
Smooth Transition ◽  
Langmuir Waves ◽  
Method Of Solution ◽  
Mach Numbers ◽  
Ion Waves ◽  
Langmuir Solitons

A systematic and self-consistent analysis of the problem of Langmuir solitons in the entire range of Mach numbers (0 < M < 1) has been presented. A coupled set of nonlinear equations for the amplitude of the modulated, high-frequency Langmuir waves and the associated low-frequency ion waves is derived without using the charge neutrality condition or any a priori ordering schemes. A technique has been developed for obtaining analytic solutions of these equations where any arbitrary degree of ion nonlinearity consistent with the nonlinearity retained in the Langmuir field can be taken into account self-consistently. A class of solutions with non-zero Langmuir field intensity at the centre (ξ = 0) are found for intermediate values of the Mach number. Using these solutions, a smooth transition from single-hump solitons to the double-hump solitons with respect to the Mach number has been established through the definitions of critical and cut-off Mach numbers. Further, under appropriate limiting conditions, various solutions discussed by other authors are obtained. Sagdeev potential analyses of the solutions for the Langmuir field as well as the ion field are carried out. These analyses confirm the transition from single-hump solitons to the double-hump solitons with respect to the Mach number. The existence of many-hump solitons for higher-order nonlinearities in the low-frequency ion wave potential has been conjectured. The method of solution developed here can be applied to similar equations in other fields.

Source-independent extended waveform inversion based on space-time source extension: Frequency-domain implementation

Geophysics ◽  
2018 ◽  
Vol 83 (5) ◽  
pp. R449-R461 ◽  
Author(s):  
Guanghui Huang ◽  
Rami Nammour ◽  
William W. Symes
Keyword(s):  
Source Function ◽  
Random Noise ◽  
A Priori ◽  
Waveform Inversion ◽  
Low Frequency ◽  
Inversion Method ◽  
Target Velocity ◽  
Extended Source ◽  
Full Waveform ◽  
Time Variables

Source signature estimation from seismic data is a crucial ingredient for successful application of seismic migration and full-waveform inversion (FWI). If the starting velocity deviates from the target velocity, FWI method with on-the-fly source estimation may fail due to the cycle-skipping problem. We have developed a source-based extended waveform inversion method, by introducing additional parameters in the source function, to solve the FWI problem without the source signature as a priori. Specifically, we allow the point source function to be dependent on spatial and time variables. In this way, we can easily construct an extended source function to fit the recorded data by solving a source matching subproblem; hence, it is less prone to cycle skipping. A novel source focusing annihilator, defined as the distance function from the real source position, is used for penalizing the defocused energy in the extended source function. A close data fit avoiding the cycle-skipping problem effectively makes the new method less likely to suffer from local minima, which does not require extreme low-frequency signals in the data. Numerical experiments confirm that our method can mitigate cycle skipping in FWI and is robust against random noise.

A new Co(II) coordination polymer with the 2-(4-pyridyl)-terephthalate ligand: synthesis, crystal structure and magnetic properties

2019 ◽  
Vol 74 (7-8) ◽  
pp. 619-622
Author(s):  
Danian Tian ◽  
Runmei Ding ◽  
Bingbing Chen ◽  
Peipei Cen
Keyword(s):  
Magnetic Measurements ◽  
Layer Structure ◽  
Octahedral Geometry ◽  
Supramolecular Network ◽  
Asymmetric Unit ◽  
Temperature Dependent ◽  
X Ray ◽  
Hydrogen Bonding Interactions ◽  
Bimetallic Layer ◽  
Ferromagnetic Interactions

AbstractA new Co(II) complex, [Co(pta)(H2O)2]n (1), with the 2-(4-pyridyl)-terephthalate ligand (pta2−) has been synthesized and structurally and magnetically characterized. Single crystal X-ray analysis indicates that the unique Co(II) ion in the asymmetric unit of 1 displays stretched octahedral geometry. Compound 1 presents a bimetallic layer structure which is further expanded to a 3D supramolecular network through hydrogen bonding interactions. Magnetic measurements have revealed the temperature-dependent existence of antiferromagnetic and ferromagnetic interactions in compound 1.

Friction Induced Brake Vibrations at Low Speeds: Experiments, State-Space Reconstruction and Implications on Modeling

2006 ◽  
Author(s):  
Hartmut Hetzler ◽  
Wolfgang Seemann
Keyword(s):  
Classical Model ◽  
A Priori ◽  
Experimental Studies ◽  
Low Frequency ◽  
Disc Brake ◽  
Minimal Models ◽  
Stick Slip ◽  
Cast Doubt ◽  
Vibration Pattern ◽  
Embedding Methods

Today, low frequency disc-brake noises are commonly explained as self-sustained stick-slip oscillations. Although, at a first glance this explanation seems reasonable, there are indices that cast doubt on it. For instance, the basic frequency of the observed oscillations does not scale with the disc-speed as it is with stick-slip oscillations and the classical model does not explain the observed ending of the vibrations beyond a certain speed. Indeed, our experimental studies on groaning noises reveal two different vibration patterns: stick-slip vibrations at almost vanishing relative speed and a second, differing vibration pattern at low to moderate relative speeds. Yet, these two patterns produce a very similar acoustic impression. While the experiment provides a vast amount of data, the dimension and structure of the underlying oscillation is not known a priori – hence, constructing phenomenological minimal models usually must rely on assumptions, e.g. about the number of DOF, etc. Due to noise and complexity, the measured raw data did only allow for a first straight forward insight, rendering further analysis necessary. Hence, time-delay embedding methods together with a principle component analysis were used to reconstruct a pseudo-phase space together with the embedded attractor to analyse for the system's dimension and to separate signal from noise.

scholarly journals Evaluating quasi-periodic variations in the γ-ray light curves of Fermi-LAT blazars

2020 ◽  
Vol 634 ◽  
pp. A120 ◽  
Author(s):  
F. Ait Benkhali ◽  
W. Hofmann ◽  
F. M. Rieger ◽  
N. Chakraborty
Keyword(s):  
Flicker Noise ◽  
Timing Analysis ◽  
Statistical Significance ◽  
Light Curves ◽  
Noise Power ◽  
Care Needs ◽  
Radiation Physics ◽  
Power Spectral ◽  
Timing Properties ◽  
Log Normal

Context. The detection of periodicities in the light curves of active galactic nuclei (AGNs) could have profound consequences for our understanding of the nature and radiation physics of these objects. At high energies (HE; E >  100 MeV), five blazars (PG 1553+113, PKS 2155−304, PKS 0426−380, PKS 0537−441 and PKS 0301−243) have been reported to show year-like quasi-periodic variations (QPVs) with significance > 3σ. As these findings are based on only a few cycles, care needs to be taken to properly account for random variations that can produce intervals of seemingly periodic behavior. Aims. We present results of an updated timing analysis for six blazars (adding PKS 0447−439 to the above), using suitable methods to evaluate their long-term variability properties and to search for QPVs in their light curves. Methods. We generate γ-ray light curves covering almost ten years, study their timing properties, and search for QPVs using the Lomb-Scargle Periodogram and the Wavelet Z-transform. Extended Monte Carlo simulations are used to evaluate the statistical significance. Results. (1) Comparing their probability density functions, all sources (except PG 1553+113) exhibit a clear deviation from a Gaussian distribution, but are consistent with being log-normal, suggesting that the underlying variability is of a nonlinear, multiplicative nature. (2) Apart from PKS 0301−243, the power spectral density for all investigated blazars is close to flicker noise (power-law slope −1). (3) Possible QPVs with a local significance ≳3σ are found in all light curves (apart from PKS 0426−380 and PKS 0537−441), with observed periods in the range (1.7 − 2.8) yr. The evidence is strongly reduced however if evaluated in terms of a global significance. Conclusions. Our results advise caution as to the significance of reported year-like HE QPVs in blazars. Somewhat surprisingly, the putative redhift-corrected period all cluster around ∼1.6 yr. We speculate on possible implications for QPV generation.

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