PubMed · 930556
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A Ehrenberg. 1977. Environmental biophysics.. https://pubmed.ncbi.nlm.nih.gov/930556/
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Small deformation dynamic oscillation was used to develop an index of physical significance for the rationalisation of the mechanical properties of high co-solute/biopolymer systems during vitrification. The index is based on the combined framework of Williams-Landel-Ferry equation with the free volume theory and is called the 'rheological glass transition temperature, T(g)' thus differentiating it from the empirical calorimetric T(g) used in thermal analysis. The rheological T(g) is located at the conjunction of two distinct molecular processes, namely: free-volume effects in the glass transition region and the predictions of the reaction-rate theory in the glassy state. The method of reduced variables was used to shift the mechanical spectra of shear moduli to composite curves. The temperature dependence of shift factors for all materials was identical provided that they were normalised at suitably different reference temperatures, which reflect iso-free-volume states. The treatment makes free volume the overriding parameter governing the mechanical relaxation times during vitrification of high co-solute/biopolymer systems regardless of physicochemical characteristics. We believe that potential applications resulting from this fundamental work are numerous for the food and pharmaceutical industries.
We analyze the learning of noisy teacher-generated examples by nonlinear and differentiable student perceptrons using the cavity method. The generic activation of an example is a function of the cavity activation of the example, which is its activation in the perceptron that learns without the example. Mean-field equations for the macroscopic parameters and the stability condition yield results consistent with the replica method. When a single value of the cavity activation maps to multiple values of the generic activation, there is a competition in learning strategy between preferentially learning an example and sacrificing it in favor of the background adjustment. We find parameter regimes in which examples are learned preferentially or sacrificially, leading to a gap in the activation distribution. Full phase diagrams of this complex system are presented, and the theory predicts the existence of a phase transition from poor to good generalization states in the system. Simulation results confirm the theoretical predictions.
In physiological and pathological conditions, many biological oscillators, such as pacemaker cells, operate under the influence of feedbacks. Fixed delay stimulation is a standard preparation to evaluate the effects of such influences. Through the study of the Hodgkin-Huxley model, we show that such recurrent excitation can lead to regular and irregular discharge trains with interdischarge intervals that are up to several multiples of the period of the oscillator. In other words, we show that recurrent excitation can considerably slow down the firings of the pacemaker. This result contrasts with previous studies of similar preparations that have reported that fixed delay stimulation leads to a bursting pattern in which regimes of high-frequency firing alternate with periods of quiescence. We elucidate the mechanisms underlying the behavior of the oscillator under fixed delay perturbation through the analysis of the dynamics of a well-known two-dimensional oscillator, namely, the Poincaré oscillator.