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R Perazzo

Publications and source records attributed to R Perazzo.

5 recordsLinked to original sources
PubMed2001

A model for the interaction of learning and evolution.

We present a simple model in order to discuss the interaction of the genetic and behavioral systems throughout evolution. This considers a set of adaptive perceptrons in which some of their synapses can be updated through a learning process. This framework provides an extension of the well-known Hinton and Nowlan model by blending together some learning capability and other (rigid) genetic effects that contribute to the fitness. We find a halting effect in the evolutionary dynamics, in which the transcription of environmental data into genetic information is hindered by learning, instead of stimulated as is usually understood by the so-called Baldwin effect. The present results are discussed and compared with those reported in the literature. An interpretation is provided of the halting effect.

Algorithms↗
PubMed2000

Fault tolerance in noise-enhanced propagation.

As a mock-up of synaptic transmission between neurons, we revisit a problem that has recently risen the interest of several authors: the propagation of a low-frequency periodic signal through a chain of one-way coupled bistable oscillators, subject to uncorrelated additive noise. On a numerical study performed in the optimal range of noise intensity for which essentially undamped transmission along the chain has been reported, we focus on the outcome of feeding with noise all the nodes but the central one. A (moderate) critical value of the coupling between oscillators is found such that whereas below it the propagation can be considered to be interrupted at the "dead neuron," it is reestablished above it. Thus, one of the distinguishing features of synaptic transmission, namely, a fault-tolerant behavior that enhances reliability at the expense of efficiency, arises here as an emergent property of the system.

Models, Neurological↗
PubMedDate not supplied

[Neuroendocrine cell tumor of the stomach (carcinoid). Clinico-pathological experience with 4 patients and demonstration of its ultrastructure].

Neuroendocrine cell tumours of the stomach (carcinoid) are uncommon, low potential for malignancy, lesions grow slowly and produce hormonal substances in contrast with others malignant neoplasias of the gastrointestinal tract. Early diagnosis is important because the curative treatment could not be done in advanced stage with disseminated metastases. In small lesions less than 2 cm without invasion to lymph node, the local wedge resection is reasonable and definitive curative treatment. Neuroendocrine differentiation, in doubtful cases, becomes established by a characteristic silver affinity, by the ultrastructurally observed presence of "endocrine" secretion granules, and by immunohistochemically detectable biogenic amines, neurohormonal peptides and "panNE markers".

Adult↗