Search results for "Complex system"
showing 10 items of 226 documents
Statistics of reversible bond dynamics observed in force-clamp spectroscopy
2010
We present a detailed analysis of two-state trajectories obtained from force-clamp spectroscopy (FCS) of reversibly bonded systems. FCS offers the unique possibility to vary the equilibrium constant in two-state kinetics, for instance the unfolding and refolding of biomolecules, over many orders of magnitude due to the force dependency of the respective rates. We discuss two different kinds of counting statistics, the event-counting usually employed in the statistical analysis of two-state kinetics and additionally the so-called cycle-counting. While in the former case all transitions are counted, cycle-counting means that we focus on one type of transitions. This might be advantageous in p…
On the interpretation of optical illusions.
1973
If excited by stimuli adjacent in space and time, the optical system frequently perceives illusions in the form of apparent movements. These effects may be attributed to the dynamic properties of the retinal nerve nets. On the basis of a specific psychophysical experiment the mechanism underlying the generation of optical illusions is interpreted by the methods of systems theory and its use in systems analysis is discussed. It is shown that for the perception of apparent movements the transit times of the signals in the dendrites are particularly important.
Diffusive thermal dynamics for the spin-S Ising ferromagnet
2008
We introduce an alternative thermal diffusive dynamics for the spin-S Ising ferromagnet realized by means of a random walker. The latter hops across the sites of the lattice and flips the relevant spins according to a probability depending on both the local magnetic arrangement and the temperature. The random walker, intended to model a diffusing excitation, interacts with the lattice so that it is biased towards those sites where it can achieve an energy gain. In order to adapt our algorithm to systems made up of arbitrary spins, some non trivial generalizations are implied. In particular, we will apply the new dynamics to two-dimensional spin-1/2 and spin-1 systems analyzing their relaxat…
Debye representation of dispersive focused waves
2006
We report on a matrix-based diffraction integral that evaluates the focal field of any diffraction-limited axisymmetric complex system. This diffraction formula is a generalization of the Debye integral applied to apertured focused beams, which may be accommodated to broadband problems. Longitudinal chromatic aberration may limit the convenience of the Debye formulation and, additionally, spatial boundaries of validity around the focal point are provided. Fresnel number is reformulated in order to guarantee that the focal region is entirely into the region of validity of the Debye approximation when the Fresnel number of the focusing geometry largely exceeds unity. We have applied the matri…
Electrodynamics in complex systems
1996
This paper discusses recent theoretical efforts to develop a general and flexible method for the calculation of the field distributions around and inside complex optical systems involving both dielectric and metallic materials. Starting from the usual light-matter coupling Hamiltonian, we derive a self-consistent equation for the optical field in arbitrary optical systems composed of N different subdomains. We show that an appropriate solving procedure based on the real-space discretization of each subdomain raises the present approach to the rank of an accurate predictive numerical scheme. In order to illustrate its applicability, we use this formalism to address challenging problems relat…
Nonresonant holeburning in the Terahertz range: Brownian oscillator model
2003
The response to the field sequence of nonresonant hole burning, a pump-wait-probe experiment originally designed to investigate slow relaxation in complex systems, is calculated for a model of Brownian oscillators, thus including inertial effects. In the overdamped regime the model predictions are very similar to those of the purely dissipative stochastic models investigated earlier, including the possibility to discriminate between dynamic homogeneous and heterogeneous relaxation. The case of underdamped oscillations is of particular interest when low-frequency excitations in glassy systems are considered. We show that also in this situation a frequency selective modification of the respon…
Modulated magnetic structures of ErPb3, HoPb3, ErTl3 and HoTl3
1981
Neutron diffraction experiments have been carried out on the magnetically ordered phases of ErPb3, HoPb3, ErTl3 and HoTl3. The magnetic moments were found to be sinusoidally modulated with a propagation vector of (0, 0.2, 0.5) for the Pb-compounds and (0.38, 0.38, 0.16) for the Tl-compounds.
Dynamical precursor of nematic order in a dense fluid of hard ellipsoids of revolution
2004
We investigate hard ellipsoids of revolution in a parameter regime where no long range nematic order is present but already finite size domains are formed which show orientational order. Domain formation leads to a substantial slowing down of a collective rotational mode which separates well from the usual microscopic frequency regime. A dynamic coupling of this particular mode into all other modes provides a general mechanism which explains an excess peak in spectra of molecular fluids. Using molecular dynamics simulation on up to 4096 particles and on solving the molecular mode coupling equation we investigate dynamic properties of the peak and prove its orientational origin.
Effective bias and potentials in steady-state quantum transport: A NEGF reverse-engineering study
2016
Using non-equilibrium Green’s functions combined with many-body perturbation theory, we have calculated steady-state densities and currents through short interacting chains subject to a finite electric bias. By using a steady-state reverse-engineering procedure, the effective potential and bias which reproduce such densities and currents in a non-interacting system have been determined. The role of the effective bias is characterised with the aid of the so-called exchange-correlation bias, recently introduced in a steady-state density-functionaltheory formulation for partitioned systems. We find that the effective bias (or, equivalently, the exchange-correlation bias) depends strongly on th…
One-dimensional Ising-like systems: an analytical investigation of the static and dynamic properties, applied to spin-crossover relaxation
2000
We investigate the dynamical properties of the 1-D Ising-like Hamiltonian taking into account short and long range interactions, in order to predict the static and dynamic behavior of spin crossover systems. The stochastic treatment is carried out within the frame of the local equilibrium method [1]. The calculations yield, at thermodynamic equilibrium, the exact analytic expression previously obtained by the transfer matrix technique [2]. We mainly discuss the shape of the relaxation curves: (i) for large (positive) values of the short range interaction parameter, a saturation of the relaxation curves is observed, reminiscent of the behavior of the width of the static hysteresis loop [3]; …