Criticality in epidemic spread: An application in the case of COVID19 infected population.

Recently, it has been successfully shown that the temporal evolution of the fraction of COVID-19 infected people possesses the same dynamics as the ones demonstrated by a self-organizing diffusion model over a lattice, in the frame of universality. In this brief, the relevant emerging dynamics are further investigated. Evidence that this nonlinear model demonstrates critical dynamics is scrutinized within the frame of the physics of critical phenomena. Additionally, the concept of criticality over the infected population fraction in epidemics (or a pandemic) is introduced and its importance is discussed, highlighting the emergence of the critical slowdown phenomenon. A simple method is proposed for estimating how far away a population is from this "singular" state, by utilizing the theory of critical phenomena. Finally, a dynamic approach applying the self-organized diffusion model is proposed, resulting in more accurate simulations, which can verify the effectiveness of restrictive measures. All the above are supported by real epidemic data case studies.

Perceptual stability during dramatic changes in olfactory bulb activation maps and dramatic declines in activation amplitudes.

We compared the concentration dependence of the ability of rats to identify odorants with the calcium signals in the nerve terminals of the olfactory receptor neurons. Although identification performance decreased with concentrations both above and below the training stimuli it remained well above random at all concentrations tested (between 0.0006% and 35% of saturated vapor). In contrast, the calcium signals in the same awake animals were much smaller than their maximum values at odorant concentrations <1% of saturated vapor. In addition, maps of activated glomeruli changed dramatically as odorant concentration was reduced. Thus perceptual stability exists in the face of dramatic changes in both the amplitude and the maps of the input to the olfactory bulb. The data for the concentration dependence of the response of the most sensitive glomeruli for each of five odorants was fitted with a Michaelis-Menten (Hill) equation. The fitted curves were extrapolated to odorant concentrations several orders of magnitude lower the smallest observed signals and suggest that the calcium response at low odorant concentrations is > 1000 times smaller than the response at saturating odorant concentrations. We speculate that only a few spikes in olfactory sensory neurons may be sufficient for correct odorant identification.

Assessing the effects of three dental impression materials on the isolated sciatic nerve of rat and frog.

The effects on nerve tissue of three dental impression pastes were compared in this study. Two of the impression pastes, Examix and Express 3M, contained vinyl polysiloxane while the other, Xanthopren, did not. An in vitro model based on the isolated sciatic nerve of the frog and rat was used. As an indication of the proper functioning of the fibres in the nerve, the amplitude of evoked compound action potential (CAP) was monitored continuously. The results clearly showed that the number of active nerve fibres in the isolated sciatic nerves of either rat or frog exposed directly to impression pastes containing vinyl polysiloxane, decreased much faster than those of the nerves in contact to impression material without vinyl polysiloxane. When the nerve of the frog was exposed to Xanthopren there was a decrease in the CAP to 50% of the control values within 56.87+/-2.42 h (n=6). This value was called inhibition time to 50%, IT(50) and for Examix it was found to be 9.97+/-1.53 h. When the nerve of the rat was exposed to Xanthopren, the IT(50) was 15.34+/-2.97 h (n=6) for the Xanthopren and only 2.86+/-1.20 h for Examix and 2.76+/-0.48 h for Express 3M (n=6). There was no significant difference between the action of the last two compounds (P=0.85). This fast nerve fibre inactivation could be caused either by the chemical used for the synthesis of the two impression pastes, Examix and Express 3M, or by the unusual constriction of the nerve when it is embedded in the materials with vinyl polysiloxane. There is strong evidence to support the first case, since the incubation of the nerve in the presence of Examix, Express 3M and Xantopren in a way so the nerve was not in contact with the impression pastes, shows a much faster decrease of the CAP in the presence of the first two pastes. The decrease is caused by the death of nerve fibres, since there is no recovery in the CAP after the removal of Examix from the incubating saline.

Three fluorescent protein voltage sensors exhibit low plasma membrane expression in mammalian cells.

Three first-generation fluorescent protein voltage sensitive probes (FP-voltage sensors) were characterized in mammalian cells. Flare, a Kv1.4 variant of FlaSh [Siegel MS, Isacoff EY. Neuron 1997;19(October (4)):735-41], SPARC [Ataka K, Pieribone VA. Biophys J 2002;82(January (1 Pt 1)):509-16], and VSFP-1 [Sakai R, Repunte-Canonigo V, Raj CD, Knopfel T. Eur J Neurosci 2001;13(June (12)):2314-18] were expressed, imaged and voltage clamped in HEK 293 cells and in dissociated hippocampal neurons. We were unable to detect a signal in response to changes in membrane potential after averaging16 trials with any of the three constructs. Using the hydrophobic voltage sensitive dye, di8-ANEPPS, as a surface marker, confocal analyses demonstrated poor plasma membrane expression for Flare, SPARC and VSFP-1 in both HEK 293 cells and dissociated hippocampal neurons. Almost all of the expressed FP-voltage sensors reside in internal membranes in both cell types. This internal expression generates a background fluorescence that increases the noise in the optical measurement.