Effect of surface nonradiative recombination on kinetics and total yield of the interband photoluminescence (PL) of c-Si wafers excited at room temperature by short laser pulses is studied. Numerical simulations show that a correlation of the PL quenching with the surface defect density takes place even at the high excitation level in spite of Auger recombination in the bulk. The quantum yield of PL reaches some percent for Si wafers with low bulk and surface defect concentrations. The calculations are confirmed by the experimental correlation between the PL quenching with the density of interface states (Dit) at the Si/SiO2 interface which has been obtained by conventional capacitance–voltage measurements. The express characterization of the Dit of Si surfaces by the pulsed PL can be carried out for the defect density in the range from 108 to 1014 cm−2 at room temperature.
We analyzed bifurcations of periodic regimes generated in the systems of two identical relaxation oscillators under strong coupling through a ''slow'' ͑inhibitory͒ variable. It was numerically shown that complex spatiotemporal behavior is observed near the boundaries of stability of the known antiphase periodic attractor and inhomogeneous steady states. Specifically, the following attractors were found: ͑i͒ a set of cycles of the antiphase type, each of which consists of one full-amplitude excursion and of the different number of smallamplitude high-frequency oscillations ͑the period of antiphase mixed-mode regimes is much greater than that of simple antiphase oscillations͒, ͑ii͒ inhomogeneous regimes of the above described type ͑out-of-phase mixed mode͒ with unequal numbers of small oscillations for different oscillators, ͑iii͒ period doubling cascades of the out-of-phase mixed mode that lead to the appearance of chaotic attractors. We showed that the modes found are not specific for our particular model; however, they are common for several classes of models and sensitive to the stiffness of oscillators. We discuss also conditions for the generation of such regimes. ͓S1063-651X͑96͒06806-7͔
Cell proliferation is considered a periodic process governed by a relaxation timer. The collective behavior of a system composed of three identical relaxation oscillators in numerically studied under the condition that diffusion of the slow mode dominates. We demonstrate: (1) the existence of three periodic regimes with different periods and phase relations and an unsymmetrical, stable steady-state (USSS); (2) the coexistence of in-phase oscillations and USSS; (3) the coexistence of periodic attractors; and (4) the emergence of a two-loop limit cycle coexisting with both in-phase oscillations and a stable steady-state. The qualitative reasons for such a diversity and its possible role in the generation of cell cycle variability are discussed.
We have analyzed the firing activity of two and three excitable FitzHugh-Nagumo oscillators, coupled via slow variable diffusion and under the action of an external noise. We find a different form of coherence resonance in this system, which is, in contrast to previous studies, intrinsically based on the antiphase behavior of coupled elements. Additionally, we show that an exchange, performed by this form of coupling, is remarkably rhythmogenic and results in polymodal interspike distributions without any external periodic stimuli. The dependence of these distributions on the noise amplitude and the coupling strength is studied.
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