Variable G and Λ\Lambda: scalar-tensor versus RG-improved cosmology

We study the consequences due to time varying $G$ and $\Lambda$ in scalar-tensor theories of gravity for cosmology, inspired by the modifications introduced by the Renormalization Group (RG) equations in the Quantum Einstein Gravity. We assume a power-law scale factor in presence contemporarily of both the scalar field and the matter components of the cosmic fluid, and analyze a special case and its generalization, also showing the possibility of a phantom cosmology. In both such situations we find a negative kinetic term for the scalar field $Q$ and, possibly, an equation-of-state parameter $w_Q<-1$. A violation of dominant energy condition (DEC) for $Q$ is also possible in both of them; but, while in the first special case the $Q$-energy density then remains positive, in the second one we find it negative.Comment: 25 pages, to be published in Gen. Rel. Grav. 200

An electrophoretic coupling mechanism between efficiency modification of spine synapses and their stimulation

Abstract. Changes in e ciency of dendritic excitable spine synapses are interpreted as a result of the electrophoretic movement of particles transferring new membrane material into spines. Restoring membrane particles migrate through cytoplasm along spine axes in endogenous electric eld caused by the stimulation of the synapses themselves. During such an electrophoretically controlled spine membrane renewal, the restoring particles are distributed into individual spines proportionally to the stimulation level of the corresponding synapses. Fusion of restoring particles with the spine membrane is facilitated by in ux of calcium ions. Degradation of postsynaptic regulatory protein complexes is also supposed to be initiated by an increase of the intracellular calcium concentration. Thus, more stimulated spine synapses than neighbouring ones are restored during calcium in ux, whereas those disused are silenced. The proposed short-term memory mechanism is theoretically examined and discussed from the viewpoint of new experimental ndings concerning plastic changes in the cerebellar cortex. 1 Introduction and biological background Recently, Gray [10] and Crick [6]putforward the idea that the change of the dendritic spine geometry could be in a sophisticated manner involved in the neuron memory mechanism. The hypertrophy, branching and elimination of dendritic spines have already been interpreted by Eccles [7] as a morphologically observabl