Generalized Lamb Modes in Fluid-Saturated Porous Plate

Since analysis by Rayleigh [1] and Lamb [2], the vibration modes for an elastic homogeneous infinite solid thin plate are well understood. These so-called “Lamb modes” result from a pure compressional wave and pure shear wave. Similarly, excitation of “leaky Lamb modes” in elastic plates immersed in a fluid, caused by incident acoustic waves, has been extensively described theoretically [3–7] and experimentally [8,9]. Results are generally presented as dispersion curves which relate the phase velocity of the mode to the product of frequency and plate thickness

Modeling Brain Resonance Phenomena Using a Neural Mass Model

Stimulation with rhythmic light flicker (photic driving) plays an important role in the diagnosis of schizophrenia, mood disorder, migraine, and epilepsy. In particular, the adjustment of spontaneous brain rhythms to the stimulus frequency (entrainment) is used to assess the functional flexibility of the brain. We aim to gain deeper understanding of the mechanisms underlying this technique and to predict the effects of stimulus frequency and intensity. For this purpose, a modified Jansen and Rit neural mass model (NMM) of a cortical circuit is used. This mean field model has been designed to strike a balance between mathematical simplicity and biological plausibility. We reproduced the entrainment phenomenon observed in EEG during a photic driving experiment. More generally, we demonstrate that such a single area model can already yield very complex dynamics, including chaos, for biologically plausible parameter ranges. We chart the entire parameter space by means of characteristic Lyapunov spectra and Kaplan-Yorke dimension as well as time series and power spectra. Rhythmic and chaotic brain states were found virtually next to each other, such that small parameter changes can give rise to switching from one to another. Strikingly, this characteristic pattern of unpredictability generated by the model was matched to the experimental data with reasonable accuracy. These findings confirm that the NMM is a useful model of brain dynamics during photic driving. In this context, it can be used to study the mechanisms of, for example, perception and epileptic seizure generation. In particular, it enabled us to make predictions regarding the stimulus amplitude in further experiments for improving the entrainment effect

Inhibition of enamel demineralization by glass ionomer cements

Composite materials find a number of applications nowadays in various engineering domains. The heterogeneous and anisotropic properties of the composite materials call for specific non-destructive evaluation methods and ultrasonic ones appear very suitable [ 1–3 ]