scholarly journals Heterogeneous materials: metastable and non-ergodic internal structures

2019 ◽  
Vol 377 (2143) ◽  
pp. 20180353 ◽  
Author(s):  
Dmitri V. Alexandrov ◽  
Andrey Yu. Zubarev
Keyword(s):  
Magnetic Fields ◽  
Heterogeneous Media ◽  
Heterogeneous Materials ◽  
Computer Methods ◽  
Atomistic Modelling ◽  
Internal Structures ◽  
Long Time ◽  
Biological Polymers ◽  
Physical Mechanics ◽  
Non Equilibrium

This issue is concerned with structural and phase transitions in heterogeneous and composite materials, the effects of external magnetic fields on these phenomena and the macroscopic properties and behaviour of materials with isotropic and anisotropic internal structures. Using experimental, theoretical and computer methods, these transitions are studied at the atomic and mesoscopic levels. The fundamental specific feature of structural transitions in many heterogeneous media consists of the fact that these transitions are stacked for a long time in non-equilibrium states that appear due to either macroscopic dissipative processes (an alternating magnetic field or hydrodynamic flow, for instance) or system lifetime in a metastable state. It is important to explain and describe these transitional states using the general approach of non-equilibrium physical mechanics. The review and research articles in the issue will cover the whole spectrum of scales (from nano to macro) and materials (from metastable liquids to biological polymers) in order to exhibit recently developed trends in the field of heterogeneous materials. Atomistic modelling, structuring induced by external magnetic fields and hydrodynamic flows, metastable and non-ergodic states, mechanical properties and phenomena in heterogeneous materials—all these are covered. This article is part of the theme issue ‘Heterogeneous materials: metastable and non-ergodic internal structures’.

Anomalous Behavior of Heterogeneous Materials at Microwaves Frequencies: Introduction to Fractional Derivatives in Electromagnetism

1990 ◽  
Vol 189 ◽  
Author(s):  
F. Heliodore ◽  
D. Cottevieille ◽  
A. Le Mehaute
Keyword(s):  
Electromagnetic Wave ◽  
Physical Meaning ◽  
Fractional Derivatives ◽  
Heterogeneous Media ◽  
Present Note ◽  
Heterogeneous Materials ◽  
Anomalous Behavior ◽  
Point Of View ◽  
Unique Point ◽  
Validity Range

ABSTRACTThe present note introduces new trends in electromagnetic spectroscopy in complex media.When an electromagnetic wave propagates in heterogeneous media, some questions arise about both physical meaning and validity range of the traditional analysis. The aim of our advanced research is related to the generalisation of Maxwell's equations able todescribe both homogeneous and heterogeneous media from an unique point of view.

A Survey of Models of Ultraslow Diffusion in Heterogeneous Materials

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Yingjie Liang ◽  
Shuhong Wang ◽  
Wen Chen ◽  
Zhifang Zhou ◽  
Richard L. Magin
Keyword(s):  
Process Model ◽  
Heterogeneous Media ◽  
Heterogeneous Materials ◽  
Aging Effect ◽  
Macroscopic Models ◽  
Ergodic Properties ◽  
Velocity Autocorrelation ◽  
Mechanical Models ◽  
Many Body Systems ◽  
Distributed Order

Ultraslow diffusion is characterized by a logarithmic growth of the mean squared displacement (MSD) as a function of time. It occurs in complex arrangements of molecules, microbes, and many-body systems. This paper reviews mechanical models for ultraslow diffusion in heterogeneous media from both macroscopic and microscopic perspectives. Macroscopic models are typically formulated in terms of a diffusion equation that employs noninteger order derivatives (distributed order, structural, and comb models (CM)) or employs a diffusion coefficient that is a function of space or time. Microscopic models are usually based on the continuous time random walk (CTRW) theory, but use a weighted logarithmic function as the limiting formula of the waiting time density. The similarities and differences between these models are analyzed and compared with each other. The corresponding MSD in each case is tabulated and discussed from the perspectives of the underlying assumptions and of real-world applications in heterogeneous materials. It is noted that the CMs can be considered as a type of two-dimensional distributed order fractional derivative model (DFDM), and that the structural derivative models (SDMs) generalize the DFDMs. The heterogeneous diffusion process model (HDPM) with time-dependent diffusivity can be rewritten to a local structural derivative diffusion model mathematically. The ergodic properties, aging effect, and velocity autocorrelation for the ultraslow diffusion models are also briefly discussed.

scholarly journals Multiscale structures and noise in magnetized plasmas line-tied at conducting surfaces

2019 ◽  
Vol 85 (2) ◽  
Author(s):  
A. B. Hassam ◽  
Yi-Min Huang
Keyword(s):  
Magnetic Fields ◽  
Boundary Conditions ◽  
Numerical Simulations ◽  
Magnetized Plasma ◽  
Long Wavelength ◽  
Numerical Noise ◽  
Long Time ◽  
Multiscale Structures ◽  
Ideal Magnetohydrodynamic ◽  
Numerical And Analytical Methods

In magnetized plasma situations where magnetic fields intersect massive conducting boundaries, ‘line-tied’ boundary conditions are often used, analytically and in numerical simulations. For ideal magnetohydrodynamic (MHD) plasmas, these conditions are arrived at given the relatively long time scales for magnetic fields penetrating resistively into good conductors. Under line-tied boundary conditions, numerical simulations often exhibit what could be construed as numerical ‘noise’ emanating from the boundaries. We show here that this ‘noise’ is real. By combining numerical and analytical methods, we highlight the existence of sharp spatial structures near the conductors and confirm the appearance of short wavelength structures riding on long wavelength modes. We conclude that, for numerical fidelity, the short multiscale structures need to be resolved. Generally, the short structure widths scale as the square root of the plasma $\unicode[STIX]{x1D6FD}$.

New results of the spectral observations of CP stars

2009 ◽  
Vol 5 (S268) ◽  
pp. 351-354
Author(s):  
N. S. Polosukhina ◽  
A. V. Shavrina ◽  
N. A. Drake ◽  
D. O. Kudryavtsev ◽  
M. A. Smirnova
Keyword(s):  
Magnetic Fields ◽  
Chemical Elements ◽  
Individual Characteristics ◽  
Physical Origin ◽  
Surface Distribution ◽  
Lithium Abundance ◽  
Phase Rotation ◽  
Long Time ◽  
Resonance Doublet

AbstractThe lithium problem in Ap-CP stars has been, for a long time, a subject of debate. Individual characteristics of CP stars, such as high abundance of the rare-earth elements presence of magnetic fields, complicate structure of the surface distribution of chemical elements, rapid oscillations of some CP-stars, make the detection of the lithium lines and the determination of the lithium abundance, a difficult task. During the International Meeting in Slovakia in 1996, the lithium problem in Ap-CP stars was discussed. The results of the Li study carried out in CrAO Polosukhina (1973–1976), the works of Hack & Faraggiana (1963), Wallerstein & Hack (1964), Faraggiana et al. (1992–1996) formed the basis of the International project ‘Lithium in the cool CP-stars with magnetic fields’. The main goal of the project was, using systematical observations of Ap-CP stars with phase rotation in the spectral regions of the resonance doublet Li I 6708 Å and subordinate 6104 Å lithium lines with different telescopes, to create a database, which will permit to explain the physical origin of anomalous Li abundance in the atmospheres of these stars.

scholarly journals Effective models for the multidimensional wave equation in heterogeneous media over long time and numerical homogenization

2016 ◽  
Vol 26 (14) ◽  
pp. 2651-2684 ◽  
Author(s):  
Assyr Abdulle ◽  
Timothée Pouchon
Keyword(s):  
Wave Equation ◽  
Wave Equations ◽  
Heterogeneous Media ◽  
Multiscale Model ◽  
Bloch Wave ◽  
Time Interval ◽  
Numerical Homogenization ◽  
Effective Equation ◽  
Long Time ◽  
Effective Models

A family of effective equations that capture the long time dispersive effects of wave propagation in heterogeneous media in an arbitrary large periodic spatial domain [Formula: see text] is proposed and analyzed. For a wave equation with highly oscillatory periodic spatial tensors of characteristic length [Formula: see text], we prove that the solution of any member of our family of effective equations is [Formula: see text]-close to the true oscillatory wave over a time interval of length [Formula: see text] in a norm equivalent to the [Formula: see text] norm. We show that the previously derived effective equation in [T. Dohnal, A. Lamacz and B. Schweizer, Bloch-wave homogenization on large time scales and dispersive effective wave equations, Multiscale Model. Simulat. 12 (2014) 488–513] belongs to our family of effective equations. Moreover, while Bloch wave techniques were previously used, we show that asymptotic expansion techniques give an alternative way to derive such effective equations. An algorithm to compute the tensors involved in the dispersive equation and allowing for efficient numerical homogenization methods over long time is proposed.

scholarly journals Magnetic fields in O-type stars measured with FORS 1 at the VLT

2008 ◽  
Vol 4 (S259) ◽  
pp. 381-382
Author(s):  
Swetlana Hubrig ◽  
M. Schöller ◽  
R. S. Schnerr ◽  
I. Ilyin ◽  
H. F. Henrichs ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Massive Stars ◽  
Emission Lines ◽  
X Ray ◽  
Wind Variability ◽  
Thermal Radio ◽  
Wide Range ◽  
Long Time ◽  
Hα Emission ◽  
Chemical Peculiarity

AbstractThe presence of magnetic fields in O-type stars has been suspected for a long time. The discovery of such fields would explain a wide range of well documented enigmatic phenomena in massive stars, in particular cyclical wind variability, Hα emission variations, chemical peculiarity, narrow X-ray emission lines and non-thermal radio/X-ray emission. Here we present the results of our studies of magnetic fields in O-type stars, carried out over the last years.

scholarly journals Non-equilibrium evolution of Bose-Einstein condensate deformation in temporally controlled weak disorder

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Milan Radonjic ◽  
Axel Pelster
Keyword(s):  
Mean Field ◽  
Einstein Condensate ◽  
Weak Disorder ◽  
Field Approach ◽  
Bose Einstein Condensate ◽  
Adiabatic Switching ◽  
Long Time ◽  
Disorder Potential ◽  
Bose Einstein ◽  
Non Equilibrium

We consider a time-dependent extension of a perturbative mean-field approach to the homogeneous dirty boson problem by considering how switching on and off a weak disorder potential affects the stationary state of an initially {equilibrated} Bose-Einstein condensate by the emergence of a disorder-induced condensate deformation. We find that in the switch on scenario the stationary condensate deformation turns out to be a sum of an equilibrium part{, that actually corresponds to adiabatic switching on the disorder,} and a dynamically-induced part, where the latter depends on the particular driving protocol. If the disorder is switched off afterwards, the resulting condensate deformation acquires an additional dynamically-induced part in the long-time limit, while the equilibrium part vanishes. {We also present an appropriate generalization to inhomogeneous trapped condensates.} Our results demonstrate that the condensate deformation represents an indicator of the generically non-equilibrium nature of steady states of a Bose gas in a temporally controlled weak disorder.

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