L Bellomonte

Analysis of the human a-wave ERG component

The a-wave is one of the main issues of research in the field of ocular electrophysiology, since it is strictly connected with early photoreceptoral activities. The present study proposes mathematical methods that analyse this component in human subjects, and supports experimental evidence relating to possible correlations among the responses of photoreceptoral units under a light stimulus. The investigation is organized in two parts: the first part concerns the onset and the initial slope, up to the first minimum (about 10-15 ms), the second part deals with the main portion of the wave, up to about 30 ms. In both cases, the a-waves, recorded at various levels of luminance, have been fitted with a set of appropriate functions representing possible models of physiological behaviour which would take place in the early stages of phototransduction. The statistical nature of the underlying processes is also discussed. The results indicate that correlations occur in the early stages, whereas random processes are set up later.

Student knowledge and learning skill modeling in the learning environment 'forces'

Abstract In this paper we present a student module modeling knowledge states and learning skills of students in the field of Newtonian dynamics. Student data recorded during the exploratory activity in microworlds are used to infer mental representations concerning the concept of force. A fuzzy algorithm able to follow the cognitive states the student goes through in solving a task and to interpret the monitored changes is discussed.

Empirical mode decomposition and neural network for the classification of electroretinographic data.

Abstract The processing of biosignals is increasingly being utilized in ambulatory situations in order to extract significant signals’ features that can help in clinical diagnosis. However, this task is hampered by the fact that biomedical signals exhibit a complex behavior characterized by strong nonlinear and non-stationary properties that cannot always be perceived by simple visual examination. New processing methods need be considered. In this context, we propose a signal processing method, based on empirical mode decomposition and artificial neural networks, to analyze electroretinograms, i.e., the retinal response to a light flash, with the aim to detect and classify retinal diseases. The present application focuses on two retinal pathologies: achromatopsia, which is a cone disease, and congenital stationary night blindness, which affects the photoreceptoral signal transmission. The results indicate that, under suitable conditions, the method proposed here has the potential to provide a powerful tool for routine clinical examinations, since it is able to recognize with high level of confidence the eventual presence of one of the two pathologies.

A study of the human rod and cone electroretinogram a-wave component

The study of the electrical response of the retina to a luminous stimulus is one of the main fields of research in ocular electrophysiology. The features of the first component (a-wave) of the retinal response reflect the functional integrity of the two populations of photoreceptors: rods and cones. We fit the a-wave for pathological subjects with functions that account for possible mechanisms governing the kinetics of the photoreceptors. The paper extends a previous analysis, carried out for normal subjects, in which both populations are active, to patients affected by two particular diseases that reduce the working populations to only one. The pathologies investigated are Achromatopsia, a cone disease, and Congenital Stationary Night Blindness, a rod problem. We present evidence that the analysis of a pathological a-wave can be employed to quantitatively measure either cone or rod activities and to test hypotheses about their responses. The results show that the photoreceptoral responses differ in the two cases and functions implying a different number of photocascade stages are necessary to achieve a correct modeling of the early phototransduction process. Numerical values of the parameters characterizing the best-fit functions are given and discussed.

A stochastic approach to quantum statistics distributions: theoretical derivation and Monte Carlo modelling

We present a method aimed at a stochastic derivation of the equilibrium distribution of a classical/quantum ideal gas in the framework of the canonical ensemble. The time evolution of these ideal systems is modelled as a series of transitions from one system microstate to another one and thermal equilibrium is reached via a random walk in the single-particle state space. We look at this dynamic process as a Markov chain satisfying the condition of detailed balance and propose a variant of the Monte Carlo Metropolis algorithm able to take into account indistinguishability of identical quantum particles. Simulations performed on different two-dimensional (2D) systems are revealed to be capable of reproducing the correct trends of the distribution functions and other thermodynamic properties. The simulations allow us to show that, away from the thermodynamic limit, a pseudo-Bose–Einstein condensation occurs for a 2D ideal gas of bosons.

Mechanical models of amplitude and frequency modulation

This paper presents some mechanical models for amplitude and frequency modulation. The equations governing both modulations are deduced alongside some necessary approximations. Computer simulations of the models are carried out by using available educational software. Amplitude modulation is achieved by using a system of two weakly coupled pendulums, whereas the frequency modulation is obtained by using a pendulum of variable length. Under suitable conditions (small oscillations, appropriate initial conditions, etc) both types of modulation result in significantly accurate and visualized simulations.

Functional analysis of Normal and CSNB a-wave ERG component

The features of a-wave of the human electroretinogram are one of the more debated problems in electrophysiology since the a-wave reflects the functional integrity of the two photoreceptoral populations (rods and cones). Although different models concerning the contributions of the early photoreceptoral response are available in current literature, a fully comprehensive theory is difficult to formulate because of the large amount of individual photoreceptors. We study the kinetics of the photoreceptoral response through the analysis of the a-wave shape both in healthy and in patients affected by the Congenital Stationary Night Blindness, that interests the rod population only. The physiological behavior has been explored by modeling the a-waves with a set of appropriate statistical functions, representing all possible mechanisms governing the interactions occurring in the phototransduction process. The results indicate that in healthy subjects, correlations between photoreceptoral populations take place, as a consequence of direct cell-to-cell interactions among rods and/or cones and a sum of Gaussian-Lorentzian functions is appropriate. In pathological subjects the best fit is obtained using the Symon-Vavilov function, that is suitable to simulate coherent responses in situations affected by fluctuations.

Time-Frequency behaviour of the a-wave of the human electroretinogram

The electroretinogram is the record of the electrical response of the retina to a light stimulus. The two main components are the a-wave and the b-wave, the former is related to the early photoreceptoral activity. Aim of this paper is to acquire useful information about the time-frequency features of the human a-wave, by means of the wavelet analysis. This represents a proper approach in dealing with nonstationary signals. We have used the Mexican Hat as mother wavelet. The analysis, carried out for four representative values of the luminance, comprehends the frequency dependence of the variance and the skeleton. The results indicate a predominance of low frequency components, their time distribution depends on the luminance whereas that of the high frequency components is little affected by the luminance.

Electronic Properties of Graphene: A Learning Path for Undergraduate Students

The purpose of this work is to present a learning path aimed at deepening student understanding of the fundamental concepts underlying the electronic properties of new materials, graphene in particular. To achieve this task, we propose a five-week long workshop where students may be introduced to fundamental concepts of advanced physics, rarely used in learning paths, such as the symmetry properties of the crystal lattice, the group theory , the features of the free electron wave functions and energy levels, the relativistic Dirac equation. Particular emphasis is given to the manner of introducing these concepts, since an essential knowledge of solid state physics, quantum physics and relativity is first necessary. We here present and discuss these concepts as preliminary steps towards a learning sequence that may guide physics/engineering undergraduates to reach a deeper understanding of the physics underlying the complex world of graphene and its properties. The conceptual framework might support both instructors and students toward further scientific investigations.

Analysis of the Electroretinogram in normals and pathological subjects

The Electroretinogram (ERG) is a composite signal reflecting the complex response of the retinal different parts. It is known that the rod and cone systems contribute to this response. The most used method to analyze the data is the study of the b-wave amplitude and peak time change against the intensity of the stimulus theoretically investigated by an approach based on a simplified picture of a single responding photoreceptorial population in scotopic or photopic condition. The aim of the present paper is to investigate the dependence of the amplitude and the implicit time of the a- and b-wave of the ERG on the input luminance level to obtain hints devoted to recognize the different contribution to the response of the two systems, rods and cones, in normals and pathological subjects.