Optical limiting, nonlinear refraction and nonlinear absorption of the associates of Cd0.5Zn0.5S quantum dots and dyes.

The optical limiting properties of alloyed Cd0.5Zn0.5S quantum dots associated with erythrosine dye are analyzed using 532 nm, 40 ps pulses. We show that joint influence of saturable absorption, reverse saturable absorption and two-photon absorption cause the optical limiting of 532 nm radiation at the pulse energies exceeding 1 mJ. The nonlinear refraction and nonlinear absorption of these quantum dots associated with different organic dyes were studied using 1064 nm and 532 nm radiation. The nonlinear refraction index and nonlinear absorption coefficient of Cd0.5Zn0.5S quantum dots were measured at λ = 1064 nm to be 2 × 10-13 cm2 W-1 and 1.2 × 10-8 cm W-1, while the reverse saturable absorption of Cd0.5Zn0.5S quantum dots and erythrosine at λ = 532 nm was almost two orders larger. The potential applications of these quantum dots for high-order harmonic generation are discussed.

Substrate clamping effects on irreversible domain wall dynamics in lead zirconate titanate thin films.

The role of long-range strain interactions on domain wall dynamics is explored through macroscopic and local measurements of nonlinear behavior in mechanically clamped and released polycrystalline lead zirconate-titanate (PZT) films. Released films show a dramatic change in the global dielectric nonlinearity and its frequency dependence as a function of mechanical clamping. Furthermore, we observe a transition from strong clustering of the nonlinear response for the clamped case to almost uniform nonlinearity for the released film. This behavior is ascribed to increased mobility of domain walls. These results suggest the dominant role of collective strain interactions mediated by the local and global mechanical boundary conditions on the domain wall dynamics. The work presented in this Letter demonstrates that measurements on clamped films may considerably underestimate the piezoelectric coefficients and coupling constants of released structures used in microelectromechanical systems, energy harvesting systems, and microrobots.

Disorder identification in hysteresis data: recognition analysis of the random-bond-random-field Ising model.

An approach for the direct identification of disorder type and strength in physical systems based on recognition analysis of hysteresis loop shape is developed. A large number of theoretical examples uniformly distributed in the parameter space of the system is generated and is decorrelated using principal component analysis (PCA). The PCA components are used to train a feed-forward neural network using the model parameters as targets. The trained network is used to analyze hysteresis loops for the investigated system. The approach is demonstrated using a 2D random-bond-random-field Ising model, and polarization switching in polycrystalline ferroelectric capacitors.

[Estimation of the excitation reduction following spike generation in the frog central auditory neurons]. / Otsenka stepeni snizheniia vozbudimosti posle generatsii spaika dlia tsentral'nykh slukhovykh neironov liagushki.

A method for the estimation of the spike probability reduction caused by a preceding spike is proposed for central auditory neurons. The method is based upon a comparison of the normalized poststimulus time histogram with the normalized latency histogram and the expected probability function. For the solution of the superfluous system of linear equations, the least-squares fit was used. The result (temporal course of discharge history effect) was then approximated by a function that included several initial zero points (absolute refractory period). Three points were approximated by the error function (short relative refractory period) and all following points were equal to one. The only variable parameter was the number of zero points, the duration of refractoriness. This method was tested on a descriptive model of an auditory neuron in which each interspike interval consists of an absolute refractory period and a random-length waiting time to the next spike. The estimation of the model absolute refractory period by the proposed method was in reasonable coincidence with input data after several thousands of stimulus presentations. The same method was used for the estimation of dead-time in 87 single units of the midbrain auditory region of the frog. A great variability of refractory time (from less than 2 ms to more than 18 ms) was shown. The duration of refractoriness correlated with the latency period of neurons.