Search results for "Time evolution"
showing 10 items of 155 documents
Dependence of two-proton radioactivity on nuclear pairing models
2017
Sensitivity of two-proton emitting decay to nuclear pairing correlation is discussed within a time-dependent three-body model. We focus on the $^6$Be nucleus assuming $\alpha + p + p$ configuration, and its decay process is described as a time-evolution of the three-body resonance state. For a proton-proton subsystem, a schematic density-dependent contact (SDDC) pairing model is employed. From the time-dependent calculation, we observed the exponential decay rule of a two-proton emission. It is shown that the density dependence does not play a major role in determining the decay width, which can be controlled only by the asymptotic strength of the pairing interaction. This asymptotic pairin…
Microstructure Design for Fast Lifetime Measurements of Magnetic Tunneling Junctions
2019
The estimation of the reliability of magnetic field sensors against failure is a critical point concerning their application for industrial purposes. Due to the physical stochastic nature of the failure events, this can only be done by means of a statistical approach which is extremely time consuming and prevents a continuous observation of the production. Here, we present a novel microstructure design for a parallel measurement of the lifetime characteristics of a sensor population. By making use of two alternative designs and the Weibull statistical distribution function, we are able to measure the lifetime characteristics of a CoFeB/MgO/CoFeB tunneling junction population. The main param…
A micro-mechanical model for grain-boundary cavitation in polycrystalline materials
2015
In this work, the grain-boundary cavitation in polycrystalline aggregates is investigated by means of a grain-scale model. Polycrystalline aggregates are generated using Voronoi tessellations, which have been extensively shown to retain the statistical features of real microstructures. Nucleation, thickening and sliding of cavities at grain boundaries are represented by specific cohesive laws embodying the damage parameters, whose time evolution equations are coupled to the mechanical model. The formulation is presented within the framework of a grain-boundary formulation, which only requires the discretization of the grain surfaces. Some numerical tests are presented to demonstrate the fea…
Time evolution of size and polydispersity of an ensemble of nanoparticles growing in the confined space of AOT reversed micelles by computer simulati…
2005
The time dependence of size and polydispersity of an ensemble of nanoparticles growing in the confined space of water-containing AOT reversed micelles has been investigated by computer simulations. It has been found that, in a wide time range, the mean nanoparticle size can be described by power laws whose exponent is critically dependent on the efficiency of the intermicellar material exchange process while the nanoparticle polydispersity increases with time. From the analysis of all the disentangled effects arising from the variation of internal and external parameters provided by simulations, useful suggestions for a better and rationale control of the nanoparticle synthetic procedure ar…
Amorphous polymorphis in ice investigated by inelastic neutron scattering
1997
Abstract High-density Ilda and low-density Ilda amorphous have been investigated by inelastic neutron scattering (INS) with emphasis on the energy window from 0.5 to 20 meV. At variance with earlier measurements the spectra in the Ilda phase show a simple ω2 behaviour in the acoustic region and the temperature dependence is found to be harmonic. Ilda converts with a strongly temperature-dependent rate towards Ilda ice. We have investigated in detail the time evolution of both the static and dynamic response functions at several temperatures. Elastic small-angle signals indicate the presence of strong heterogeneties at the early stages of the conversion process. At least two different time s…
Scaling properties of magnetic domain walls in Pt/Co/Pt trilayers on MgO (111)
2002
Abstract We present a scaling analysis of the time evolution of domain walls in ultrathin magnetic films that are subject to different forms of uncorrelated and correlated disorder caused by the microstructure of the underlying template. The study is performed on ultrafine modulated Pt/Co/Pt trilayers grown on as-supplied and structured MgO (1 1 1) substrates employing polar Kerr microscopy for the imaging of the magnetic domains.
Thermodiffusion of sodium polystyrene sulfonate in a supporting electrolyte
2019
Thermodiffusion, or the Soret phenomenon, is well understood in simple systems, but in multicomponent and polyvalent electrolyte systems the process becomes more complicated due to the coupling of fluxes. We experimentally investigate the time evolution of a concentration gradient generated by thermodiffusion of a polyelectrolyte (poly(sodium 4-styrene sulfonate), NaPSS) in a 1:1 supporting electrolyte. We also derive and solve the transport equations that are used to extract the Soret coefficient from the experimental observations. It is shown that NaPSS thermodiffusion in NaCl is strongly dependent on concentration, with almost 100% thermal separation in concentrations below 15 nmol L−1. …
Femtosecond Raman time-resolved molecular spectroscopy
2004
Abstract The applicability of several femtosecond time resolved non-linear coherent techniques such as Raman induced polarization spectroscopy (RIPS), degenerate four-wave mixing (DFWM) and coherent anti-Stokes Raman spectroscopy (CARS) for molecular spectroscopy is presented. All methods rely on the initial coherent excitation of molecular states producing wavepackets, whose time evolution is then measured. In the case of RIPS and DFWM only pure rotational transitions are involved, whereas in CARS vibrational states can be excited. First the methodology of concentration and temperature measurements using RIPS in gas mixtures involving N2, CO2, O2, and N2O is shown. In addition some applica…
Iterative momentum relaxation for fast lattice-Boltzmann simulations
2001
Abstract Lattice-Boltzmann simulations are often used for studying steady-state hydrodynamics. In these simulations, however, the complete time evolution starting from some initial condition is redundantly computed due to the transient nature of the scheme. In this article we present a refinement of body-force driven lattice-Boltzmann simulations that may reduce the simulation time significantly. This new technique is based on an iterative adjustment of the local body-force. We validate this technique on three test cases, namely fluid flow around a spherical obstacle, flow in random fiber mats and flow in a static mixer reactor.
Wait-and-switch relaxation model: Relationship between nonexponential relaxation patterns and random local properties of a complex system
2006
The wait-and-switch stochastic model of relaxation is presented. Using the ``random-variable'' formalism of limit theorems of probability theory we explain the universality of the short- and long-time fractional-power laws in relaxation responses of complex systems. We show that the time evolution of the nonequilibrium state of a macroscopic system depends on two stochastic mechanisms: one, which determines the local statistical properties of the relaxing entities, and the other one, which determines the number (random or deterministic) of the microscopic and mesoscopic relaxation contributions. Within the proposed framework we derive the Havriliak-Negami and Kohlrausch-Williams-Watts funct…