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A Borsellino

Publications and source records attributed to A Borsellino.

16 recordsLinked to original sources
PubMed1987

Statistical properties of flip-flop processes associated to the chaotic behavior of systems with strange attractors.

The chaotic behavior of systems with strange attractors can be discussed by examining the flip-flop process associated to the system dynamics. This was already shown by Lorenz (1963) in his first seminal paper. A somewhat surprising result was obtained by Aizawa (1982), who, studying the same Lorenz attractor at the parameter value r = 28, reached the conclusion that the associated flip-flop was a typical Markov process. Since the process is generated in a deterministic way, one may wonder if the Aizawa result is accidental, depending on the particular parameter value, or if a similar conclusion can be extended to other systems, with different attractors. Our conclusions are that the Aizawa result is mostly accidental, because for other parameter values and for other attractors there are sharp deviations from the Markovian process.

Animals↗
PubMed1986

Perceptual ambiguity and stability of reversible figures.

In this work, the results of two experiments on ambiguous patterns are reported, which have been obtained by presenting a series of stimuli designed, in both cases, to reduce gradually the ambiguity of the patterns. Such reduction has been performed by respectively increasing or decreasing the amount of graphic details in the experiments. Data of both experiments show a lengthening of mean reversal time. The increase in the stability of one percept can be regarded as associated with the increasing difficulties encountered by an observer in organizing and restating the alternative "hypothesis" through the perceptual mechanisms. The loss of balance in the durations of percepts is discussed in terms of their different informational contents. Finally, in Exp. 1 an analysis is made to evaluate to what extent an addition of perceptual cues, designed to reinforce a three-dimensional interpretation of a pattern, can influence its figure-ground alternation.

Adult↗
PubMed1982

Effects of visual angle on perspective reversal for ambiguous patterns.

Reversal rates of an ambiguous figure (the Necker cube) were studied for different pattern sizes covering a range of visual angles theta from approximately 1 to 62 deg. A large number of reversals was obtained for each observer and each pattern in order to examine the statistical distributions of reversal times. A pronounced flattening of the statistical distributions (represented throughout by a gamma distribution) and a growth of the mean duration of each percept, with increasing pattern size was found. A plateau in the range of theta between 5 and 20-30 deg was observed. For larger values of theta two kinds of observers have been identified: for 'fast' observers the inversion rate is little affected by theta, whilst for 'slow' observers, the mean reversal time increases strongly with theta. A tentative model, based on three different contributions to the duration of the alternation process, is proposed: a constant term, independent of theta, and two terms dependent on theta--a retinal term, and a cortical one. The last term is interpreted as due to the spreading of excitation with the characteristic of a filling-in process.

Adult↗
PubMed1981

Diffusion and consumption of oxygen in the superfused retina of the drone (Apis mellifera) in darkness.

Double-barreled O2 microelectrodes were used to study O2 diffusion and consumption in the superfused drone (Apis mellifera) retina in darkness at 22 degrees C. Po2 was measured at different sites in the bath and retinas. It was found that diffusion was essentially in one dimension and that the rate of O2 consumption (Q) was practically constant (on the macroscale) down to Po2 s less than 20 mm Hg, a situation that greatly simplified the analysis. The value obtained for Q was 18 +/- 0.7 (SEM) microliter O2/cm3 tissue . min (n = 10), and Krogh's permeation coefficient (alpha D) was 3.24 +/- 0.18 (SEM) X 10(-5) ml O1/min . atm . cm (n = 10). Calculations indicate that only a small fraction of this Q in darkness is necessary for the energy requirements of the sodium pump. the diffusion coefficient (D) in the retina was measured by abruptly cutting off diffusion from the bath and analyzing the time-course of the fall in Po2 at the surface of the tissue. The mean value of D was 1.03 +/- 0.08 (SEM) X 10(-5) cm2/s (n = 10). From alpha D and D, the solubility coefficient alpha was calculated to be 54 +/- 4.0 (SEM) microliter O2 STP/cm3 . atm (n = 10), approximately 1.8 times that for water.

Animals↗
PubMed1975

Regulation of antibody formation in chickens escaping from tolerance to human serum albumin.

The immune capacity of chickens made tolerant to human serum albumin just after hatching was studied after a primary and secondary challenge at 7--14 weeks of age, of either 1 mg/kg or 100 mg/kg. The class and avidity of antibody produced by birds "escaping" from tolerance was similar to normal controls. The escaping chickens made a normal peak antibody response to a high dose but not to a low dose (except that the response to a low secondary dose after priming with a high dose was normal); but the decline of the antibody titer was abrupt, indicating inability to maintain the response. It is concluded that the antibody-forming capacity of B cells is normal, but regulation of antibody formation is impaired in previously tolerant chickens.

Animals↗
PubMed1968

Responses to single photons in virual cells of limulus.

1. A system proposed in a previous article as a model of responses of visual cells has been analysed with the purpose of predicting the features of responses to single absorbed photons.2. As a result of this analysis, the stochastic variability of responses has been expressed as a function of the amplification of the system.3. The theoretical predictions have been compared to the results obtained by recording electrical responses of visual cells of Limulus to flashes delivering only few photons.4. Experimental responses to single photons have been tentatively identified and it was shown that the stochastic variability of these responses is similar to that predicted for a model with a multiplication factor of at least twenty-five.5. These results lead to the conclusion that the processes responsible for visual responses incorporate some form of amplification. This conclusion may prove useful for identifying the physical mechanisms underlying the transducer action of visual cells.

Animals↗