11 research outputs found
Current and fluctuation in a two-state stochastic system under non-adiabatic periodic perturbation
We calculate a current and its fluctuation in a two-state stochastic system
under a periodic perturbation. The system could be interpreted as a channel on
a cell surface or a single Michaelis-Menten catalyzing enzyme. It has been
shown that the periodic perturbation induces so-called pump current, and the
pump current and its fluctuation are calculated with the aid of the geometrical
phase interpretation. We give a simple calculation recipe for the statistics of
the current, especially in a non-adiabatic case. The calculation scheme is
based on the non-adiabatic geometrical phase interpretation. Using the Floquet
theory, the total current and its fluctuation are calculated, and it is
revealed that the average of the current shows a stochastic-resonance-like
behavior. In contrast, the fluctuation of the current does not show such
behavior.Comment: 7 pages, 1 figur
The stochastic pump current and the non-adiabatic geometrical phase
We calculate a pump current in a classical two-state stochastic chemical
kinetics by means of the non-adiabatic geometrical phase interpretation. The
two-state system is attached to two particle reservoirs, and under a periodic
perturbation of the kinetic rates, it gives rise to a pump current between the
two-state system and the absorbing states. In order to calculate the pump
current, the Floquet theory for the non-adiabatic geometrical phase is extended
from a Hermitian case to a non-Hermitian case. The dependence of the pump
current on the frequency of the perturbative kinetic rates is explicitly
derived, and a stochastic resonance-like behavior is obtained.Comment: 11 page
Fermionic coherent states for pseudo-Hermitian two-level systems
We introduce creation and annihilation operators of pseudo-Hermitian fermions
for two-level systems described by pseudo-Hermitian Hamiltonian with real
eigenvalues. This allows the generalization of the fermionic coherent states
approach to such systems. Pseudo-fermionic coherent states are constructed as
eigenstates of two pseudo-fermion annihilation operators. These coherent states
form a bi-normal and bi-overcomplete system, and their evolution governed by
the pseudo-Hermitian Hamiltonian is temporally stable. In terms of the
introduced pseudo-fermion operators the two-level system' Hamiltonian takes a
factorized form similar to that of a harmonic oscillator.Comment: 13 pages (Latex, article class), no figures; v2: some amendments in
section 2, seven new refs adde
Stochastic pump effect and geometric phases in dissipative and stochastic systems
The success of Berry phases in quantum mechanics stimulated the study of
similar phenomena in other areas of physics, including the theory of living
cell locomotion and motion of patterns in nonlinear media. More recently,
geometric phases have been applied to systems operating in a strongly
stochastic environment, such as molecular motors. We discuss such geometric
effects in purely classical dissipative stochastic systems and their role in
the theory of the stochastic pump effect (SPE).Comment: Review. 35 pages. J. Phys. A: Math, Theor. (in press
ANALYSIS OF INTERFACE REACTION BETWEEN CELL AND GRAIN BOUNDARY DURING CELLULAR PRECIPITATION
La précipitation discontinue dans l'alliage Cu-15% en poids In se fait essentiellement par décomposition cellulaire. Il a été établi que la réaction de précipitation discontinue peut avoir lieu en un joint de grain pré-existant (statique) seulement si la structure de ce joint est convertie en une structure de haute mobilité par une transformation structurale. Il est connu que la déformation plastique provoque le déplacement du joint de grain sous l'effet d'une force motrice en plus de la force chimique. Suivant le taux de déformation plastique la vitesse de précipitation cellulaire peut croître ou décroître. L'analyse de l'intéraction joint de grain-lamelles dans les cellules peut expliquer ces résultats.Discontinuous precipitation in Cu-15 wt% In is found to occur predominatly by cellular decomposition. It has been established that a discontinuous precipitation reaction can occur only at pre-existing (static) grain boundary if the structure of the static boundary is converted into a structure of high mobility by a structural transformation. It is known that plastic deformation causes grain boundary motion due to a driving force in addition to the chemical force. It depends on the amount of plastic deformation whether the reaction rate is incrensed or decreased. The analysis of the interaction between grain boundary and lamella in the cells interface can explain these results
Earthquake Ground Motion Matching on a Small Electric Shaking Table Using a Combined NN-PDFF Controller
Replicating acceleration time histories with high accuracy on shaking table platforms is still a challenging task. The complex interference between the components of the system, the inherent nonlinearities, and the coupling effect between the specimen and the shaking table are among other reasons that most affect the control performance. In this paper, a neural network- (NN-) based controller has been developed and experimentally implemented to improve the acceleration tracking performance of an electric shaking table. The latter is a biaxial shaking table driven by linear motors and controlled by a proportional-derivative-feedforward (PDFF) controller that is very efficient in reproducing displacement waveforms on the detriment of the simulation of the prescribed acceleration ground motions. In order to bypass this shortcoming, a control scheme combining the PDFF as a basic control function with a NN controller which filters the shaking table feedback signal and acts on the drive signal by compensating for acceleration distortions is proposed in this study. Several experimental tests have been carried out to build a database for offline training, validating, and testing of the proposed NN control model. Subsequently, the well-trained NN is implemented in the inner control loop of the shaking table to compensate, in parallel with the PDFF controller, the distortions during the replication of acceleration signals. Results of tests using earthquake records showed an enhancement in signal matching when integrating the NN model for both bare and loaded conditions of the shaking table. The tracking errors, estimated using the relative root-mean-square error, between the measured and the desired signal, are significantly reduced in time and frequency domains with the additional NN online controller