Time Dependence Of Excitation Research Articles

Universal Regimes in Long-Time Asymptotic of Multilevel Quantum System Under Time-Dependent Perturbation.

In the framework of an exactly soluble model, one considers a typical problem of the interaction between radiation and matter: the dynamics of population in a multilevel quantum system subject to a time dependent perturbation. The algebraic structure of the model is taken richly enough, such that there exists a strong argument in favor of the fact that the behavior of the system in the asymptotic of long time has a universal character, which is system-independent and governed by the functional property of the time dependence exclusively. Functional properties of the excitation time dependence, resulting in the regimes of resonant excitation, random walks, and dynamic localization, are identified. Moreover, an intermediate regime between the random walks and the localization is identified for the polyharmonic excitation at frequencies given by the Liouville numbers.

Large fluctuations of radiation in stochastically activated two-level systems

We study large fluctuations of emitted radiation in the system of N non-interacting two-level atoms. Two methods are used to calculate the probability of large fluctuations and the time dependence of excitation and emission. The first method is based on the large deviation principle for Markov processes. The second one uses an analogue of the quantum formalism for classical probability problems.Particularly we prove that in a large fluctuation limit approximately half of the atoms are excited. This fact is independent on the fraction of the excited atoms in equilibrium.

Excitation Time Dependence of Luminescence Decay in Thermally Oxidized Porous Si

ABSTRACTThermally oxidized porous silicon shows stable visible luminescence under laser irradiation. The photoluminescence decay has been measured in the temporal range from microsecond to millisecond. The decay curve is well fitted to a stretched exponential function. The mean lifetime of the luminescence increases with increasing the excitation pulse width. It is also found that the higher energy emission exhibits a faster decay compared with the lower energy emission at 293K, while at 18K it is reversed. The results are explained by a model in which photogenerated carriers are captured by localized radiative centers through a thermally assisted tunneling mechanism

Microwave Ionization and Excitation of Rydberg Atoms

A classical theory gives excellent agreement with the Bayfield-Koch experiment on microwave ionization of Rydberg hydrogen atoms. The time dependence of excitation and ionization is presented, and classical trajectories are divided into four significant categories. The results suggest that nonresonant laser ionization of atoms in states of low quantum number can also take place as a result of extremely high-order processes with large numbers of intermediate states of excitation.

Tuning between Central Auditory Pathways and the Ear

Emphasis in research on auditory signal reception has shifted in recent years from studies of the peripheral area alone to include more and more the central portion of the auditory pathways. The findings are characterized by timing mechanisms well balanced between excitatory and inhibitory processes on the one hand and both the selection of auditory information and the concept of two channels of the auditory transmission system on the other. Data on two types of optimizing processes will be presented: the process involved in selecting auditory information and the system responsible for the synergism of frequency (pitch)-and periodicity-analysis. The human CNS selects the 100 bits/sec processed for conscious perception from the 109 bits/sec offered from all sensory receptors in two principal ways: 1) "Specific auditory information" is modulated by "unspecific" information processed through the recticular formation of the brain stem; 2) The descending fiber systems alter selectively the information-flow on every level of the auditory pathway. The filtered information perceived in turn triggers a set of inborn and learned behavioral responses such as speech, mimicry and motor, altogether representing approximately 107 bits/sec. The system for frequency-and periodicity-analysis of the sensory excitation uses space and time attributes, respectively. Psychophysiological as well as electrophysiological data allow the relating of these two attributes to the two sets of sensory sources, the space on the basilar membrane (inner hair cells) and the time dependence of excitation (predominantly outer hair cells).