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Non-equilibrium State (non-equilibrium + state)

Distribution by Scientific Domains
Physics and Astronomy60%

Selected Abstracts

Neutron Reflectometry: A Tool to Investigate Diffusion Processes in Solids on the Nanometer Scale,

ADVANCED ENGINEERING MATERIALS, Issue 6 2009
Harald Schmidt
Abstract The investigation of self-diffusion for the characterization of kinetic process in solids is one of the most fundamental tasks in materials science. We present the method of neutron reflectometry (NR), which allows the detection of extremely short diffusion lengths in the order of 1,nm and below at corresponding low self-diffusivities between 10,25 and 10,20,m2 s,1. Such a combination of values cannot be achieved by conventional methods of diffusivity determination, like the radiotracer method, secondary ion mass spectrometry, quasielastic neutron scattering, or nuclear magnetic resonance. Using our method, the extensive characterization of materials which are in a non-equilibrium state, like amorphous or nanocrystalline solids becomes possible. Due to the small experimentally accessible diffusion length microstructural changes (grain growth and crystallization) taking place simultaneously during the actual diffusion experiment can be avoided. For diffusion experiments with NR isotope multilayers are necessary, which are chemical homogeneous but isotope modulated films. We illustrate the basic aspects and potential of this technique using model systems of different classes of materials: single crystalline germanium, amorphous silicon nitride, and nanocrystalline iron. [source]

The role of phonons in establishing a non-equilibrium quasiparticle state in small gap multiple tunnelling superconducting tunnel junctions

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004
A. G. Kozorezov
Abstract We derive expressions for phonon escape times from a thin superconducting film. The escape time is determined by the rate of scattering conversion for phonons propagating beyond the critical cone for total internal reflection. The conversion is due to different scattering processes for the groups of Cooper pair breaking and sub-gap phonons. For pair breaking phonons the most efficient conversion mechanism is through the interaction with the condensate. For sub-gap phonons the conversion rate is much slower and for plane parallel films is due to elastic scattering at surface or interface roughness resulting in significantly slower escape times. We discuss implications of slow escape time for sub-gap phonons for the properties of the recently observed new non-equilibrium state in small gap multiple tunnelling superconducting tunnel junctions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ultra-fast dynamics in solids: non-equilibrium behaviour of magnetism and atomic structure

ANNALEN DER PHYSIK, Issue 7-8 2009
K.H. Bennemann
Abstract Non-equilibrium physics is of fundamental interest, for example, for extensions of statistical mechanics and thermodynamics. In particular, it is important to understand how conservation laws like energy conservation and angular-momentum conservation in magnetic solids control the time scale of the dynamics. Laser irradiation may cause intense electronic excitations and thus a strong non-equilibrium state. Results are presented for the ultra-fast response of magnetism in ferromagnetic transition metals like Ni, Co, Fe, and Gd and furthermore of the atomic structure in semiconductors like Si, Ge, and InSb. Non-thermal melting is a most spectacular example of ultra-fast bond breaking. Time-resolved magnetooptical experiments yielding sub-picosecond spin dynamics are discussed. The spin dynamics is accompanied by THz light emission. The structural changes in semiconductors, bond changes sp3 , s2p2, and phase transitions occur within about 100 fs. The results also shed light on electron-transfer processes, on ionization, and on molecular dissociation dynamics, which may occur during fs and as times. We discuss the application of time-resolved analysis to tunnelling problems and the phase diagram of high-Tc superconductivity. [source]

Ultra-fast dynamics in solids: non-equilibrium behaviour of magnetism and atomic structure

ANNALEN DER PHYSIK, Issue 7-8 2009
K.H. Bennemann
Abstract Non-equilibrium physics is of fundamental interest, for example, for extensions of statistical mechanics and thermodynamics. In particular, it is important to understand how conservation laws like energy conservation and angular-momentum conservation in magnetic solids control the time scale of the dynamics. Laser irradiation may cause intense electronic excitations and thus a strong non-equilibrium state. Results are presented for the ultra-fast response of magnetism in ferromagnetic transition metals like Ni, Co, Fe, and Gd and furthermore of the atomic structure in semiconductors like Si, Ge, and InSb. Non-thermal melting is a most spectacular example of ultra-fast bond breaking. Time-resolved magnetooptical experiments yielding sub-picosecond spin dynamics are discussed. The spin dynamics is accompanied by THz light emission. The structural changes in semiconductors, bond changes sp3 , s2p2, and phase transitions occur within about 100 fs. The results also shed light on electron-transfer processes, on ionization, and on molecular dissociation dynamics, which may occur during fs and as times. We discuss the application of time-resolved analysis to tunnelling problems and the phase diagram of high-Tc superconductivity. [source]

Metabolic systems maintain stable non-equilibrium via thermodynamic buffering

BIOESSAYS, Issue 10 2009
Abir U. Igamberdiev
Abstract Here, we analyze how the set of nucleotides in the cell is equilibrated and how this generates simple rules that help the cell to organize itself via maintenance of a stable non-equilibrium state. A major mechanism operating to achieve this state is thermodynamic buffering via high activities of equilibrating enzymes such as adenylate kinase. Under stable non-equilibrium, the ratios of free and Mg-bound adenylates, Mg2+ and membrane potentials are interdependent and can be computed. The adenylate status is balanced with the levels of reduced and oxidized pyridine nucleotides through regulated uncoupling of the pyridine nucleotide pool from ATP production in mitochondria, and through oxidation of substrates non-coupled to NAD+ reduction in peroxisomes. The set of adenylates and pyridine nucleotides constitutes a generalized cell energy status and determines rates of major metabolic fluxes. As the result, fluxes of energy and information become organized spatially and temporally, providing conditions for self-maintenance of metabolism. [source]