We study the behavior of the string tension in the SU(3) lattice pure-gauge theory close to the deconfining critical point. We find very large correlation lengths, increasing with the lattice size. This result is strongly suggestive of a second-order phase transition, and excludes the presence of a strong first-order transition.

We present the results of a high statistics lattice calculation of hadronic form factors relevant for D- and B-meson semileptonic decays into light pseudoscalar and vector mesons. The results have been obtained by averaging over 170 gauge held configurations, generated in the quenched approximation, at beta = 6.0, on a 18(3) x 64 lattice, using the O(a)-improved SW-Clover action. From the study of the matrix element < K-\J(mu)\D-0>, we obtain f(+)(0) = 0.78+/-0.08 and from the matrix element < ($) over bar K*(0)\J(mu)\D+ > we obtain V(0) = 1.08+/-0.22, A(1)(0) = 0.67+/-0.11 and A(2)(0) = 0.49+/-0.34. We also obtain the ratios V(0)/A(1)(0) = 1.6+/-0.3 and A(2)(0)/A(1)(0) = 0.7+/-0.4. Our predictions for the different form factors are in good agreement with the experimental data, although, in the case of Az(O),the errors are still too large to draw any firm conclusion. With the help of the Heavy Quark Effective Theory (HQET) we have also extrapolated the lattice results to B-meson decays. The form factors follow a behaviour compatible with the HQET predictions. Our results are in agreement with a previous lattice calculation, performed at beta = 6.4, using the standard Wilson action

The occurrence of sleep passed through the evolutionary sieve and is widespread in animal species. Sleep is known to be beneficial to cognitive and mnemonic tasks, while chronic sleep deprivation is detrimental. Despite the importance of the phenomenon, a complete understanding of its functions and underlying mechanisms is still lacking. In this paper, we show interesting effects of deep-sleep-like slow oscillation activity on a simplified thalamo-cortical model which is trained to encode, retrieve and classify images of handwritten digits. During slow oscillations, spike-timing-dependent-plasticity (STDP) produces a differential homeostatic process. It is characterized by both a specific unsupervised enhancement of connections among groups of neurons associated to instances of the same class (digit) and a simultaneous down-regulation of stronger synapses created by the training. This hierarchical organization of post-sleep internal representations favours higher performances in retrieval and classification tasks. The mechanism is based on the interaction between top-down cortico-thalamic predictions and bottom-up thalamo-cortical projections during deep-sleep-like slow oscillations. Indeed, when learned patterns are replayed during sleep, cortico-thalamo-cortical connections favour the activation of other neurons coding for similar thalamic inputs, promoting their association. Such mechanism hints at possible applications to artificial learning systems.