Paolo Allegrini - Academia.edu (original) (raw)

Papers by Paolo Allegrini

We address the issue of criticality that is attracting the attention of an increasing num-ber of ... more We address the issue of criticality that is attracting the attention of an increasing num-ber of neurophysiologists. Our main purpose is to establish the specific nature of some dynamical processes that although physically different, are usually termed as “critical,” and we focus on those characterized by the cooperative interaction of many units. We notice that the term “criticality ” has been adopted to denote both noise-induced phase transitions and Self-Organized Criticality (SOC) with no clear connection with the traditional phase transitions, namely the transformation of a thermodynamic system from one state of matter to another. We notice the recent attractive proposal of extended criticality advo-cated by Bailly and Longo, which is realized through a wide set of critical points rather than emerging as a singularity from a unique value of the control parameter. We study a set of cooperatively firing neurons and we show that for an extended set of interaction couplings the sys...

We study the long-range correlations of heartbeat fluctuations with the method of diffusion entro... more We study the long-range correlations of heartbeat fluctuations with the method of diffusion entropy. We show that this method of analysis yields a scaling parameter delta\deltadelta that apparently conflicts with the direct evaluation of the distribution of times of sojourn in states with a given heartbeat frequency. The strength of the memory responsible for this discrepancy is given by a parameter epsilon2\epsilon^{2}epsilon2, which is derived from real data. The distribution of patients in the ($\delta$, epsilon2\epsilon^{2}epsilon2)-plane yields a neat separation of the healthy from the congestive heart failure subjects.

AIP Conference Proceedings, 2002

We show that the derivation of Lévy statistics from a Liouville-like approach is still an unresol... more We show that the derivation of Lévy statistics from a Liouville-like approach is still an unresolved problem, even though a satisfactory derivation resting on the Generalized Central Limit Theorem (GCLT) has been obtained. We discuss a quantum relaxation that according to the supposed equivalence between decoherence theory and wave function collapses is expected to be equivalent to the characteristic function

Eprint Arxiv Cond Mat 0309350, Sep 1, 2003

Eprint Arxiv Cond Mat 0212614, Dec 27, 2002

We study an idealized version of intermittent process leading the fluctuations of a stochastic di... more We study an idealized version of intermittent process leading the fluctuations of a stochastic dichotomous variable ξ. It consists of an overdamped and symmetric potential well with a cusplike minimum. The right-hand and left-hand portions of the potential corresponds to ξ = W and ξ = −W , respectively. When the particle reaches this minimum is injected back to a different and randomly chosen position, still within the potential well. We build up the corresponding Frobenius-Perron equation and we evaluate the correlation function of the stochastic variable ξ, called Φ ξ (t). We assign to the potential well a form yielding Φ ξ (t) = (T /(t + T )) β , with β > 0. Thanks to the symmetry of the potential, there are no biases, and we limit ourselves to considering correlation functions with an even number of times, indicated for concision, by 12 , 1234 and, more, in general, by 1...2n . The adoption of a formal treatment, based on density, and thus of the operator driving the density time evolution, establishes a prescription for the evaluation of the correlation functions, yielding 1...2n = 12 ... (2n − 1)2n . We study the same dynamic problem using trajectories, and we establish that the resulting two-time correlation function coincides with that afforded by the density picture, as it should. We then study the four-times correlation function and we prove that in the non-Poisson case it departs from the density prescription, namely, from 1234 = 12 34 . We conclude that this is the main reason why the two pictures yield two different diffusion processes, as noticed in an earlier work [M. Bologna, P. Grigolini, B.

Matematicas Y Tratamiento De Corpus Actas Del Segundo Seminario De La Escuela Interlatina De Altos Estudios En Linguistica Aplicada San Millan De La Cogolla 19 23 De Septiembre De 2000 2002 Isbn 84 607 4688 7 Pags 245 268, 2002

What is the role of the linguistic context in shaping up our mental representations of word meani... more What is the role of the linguistic context in shaping up our mental representations of word meanings and what does this tell us about the way we learn, memorise and use these representations? The dynamic, context-based approach to word meaning (as opposed to the more established "representational" approach) has nowadays left the circles of associative and cognitive psychology to become a vividly discussed and intensely investigated topic in the field of machine language learning. In this paper we deal with some of the theoretical and empirical implications of this shift of conceptual paradigm and describe an analogy-based approach to the automatic acquisition and representation of word similarity from pre-annotated contexts.

2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2015

Sea-diving operations for monitoring or intervention are carried out by highly-specialized divers... more Sea-diving operations for monitoring or intervention are carried out by highly-specialized divers called Certified Commercial Divers (CCD). CCDs operate under highly demanding working conditions in extreme and hazardous environments. Every day consists of an 8 hours' shift. To avoid decompression problems the remaining 16 hours are spent in a hyperbaric environment located aboard the surface vessel or on the platform. These operating conditions require the design of a technologically-advanced device for tele-monitoring, to maximize CCDs' safety. Here we describe a proposal for monitoring and supporting CCDs during operations. We design a dedicated Life Support System (LSS), that captures real-time, vital (heart rate, respiratory rate, accelerometry, etc) and stress-related (heart-rate variability) signals from operators to transmit them to dedicated servers via telematic protocols. LSS is equipped with protocols for tele-medicine/tele-consultation. Our system is being developed within the research project SUONO (Safe Underwater OperatioNs in Oceans).

Physical Review E, 2015

Criticality reportedly describes brain dynamics. The main critical feature is the presence of sca... more Criticality reportedly describes brain dynamics. The main critical feature is the presence of scale-free neural avalanches, whose auto-organization is determined by a critical branching ratio of neural-excitation spreading. Other features, directly associated to second-order phase transitions, are: (i) scale-free-network topology of functional connectivity, stemming from suprathreshold pairwise correlations, superimposable, in waking brain activity, with that of ferromagnets at Curie temperature; (ii) temporal long-range memory associated to renewal intermittency driven by abrupt fluctuations in the order parameters, detectable in human brain via spatially distributed phase or amplitude changes in EEG activity. Herein we study intermittent events, extracted from 29 night EEG recordings, including presleep wakefulness and all phases of sleep, where different levels of mentation and consciousness are present. We show that while critical avalanching is unchanged, at least qualitatively, intermittency and functional connectivity, present during conscious phases (wakefulness and REM sleep), break down during both shallow and deep non-REM sleep. We provide a theory for fragmentation-induced intermittency breakdown and suggest that the main difference between conscious and unconscious states resides in the backwards causation, namely on the constraints that the emerging properties at large scale induce to the lower scales. In particular, while in conscious states this backwards causation induces a critical slowing down, preserving spatiotemporal correlations, in dreamless sleep we see a self-organized maintenance of moduli working in parallel. Critical avalanches are still present, and establish transient auto-organization, whose enhanced fluctuations are able to trigger sleep-protecting mechanisms that reinstate parallel activity. The plausible role of critical avalanches in dreamless sleep is to provide a rapid recovery of consciousness, if stimuli are highly arousing.

Chaos Solitons & Fractals

We argue that complex systems, defined as non-Poisson renewal process, with complexity index µ, e... more We argue that complex systems, defined as non-Poisson renewal process, with complexity index µ, exchange information through complexity matching. We illustrate this property with detailed theoretical and numerical calculations describing a system with complexity index µS perturbed by a signal with complexity index µP . We focus our attention on the case 1.5 ≤ µS ≤ 2 and 1 ≤ µP ≤ 2. We show that for µS ≥ µP , the system S reproduces the perturbation, and the response intensity increases with increasing µP . The maximum intensity is realized by the matching condition µP = µS. For µP > µS the response intensity dies out as 1/t µ P −µ S .

Fractals in Biology and Medicine, 1998

ABSTRACT

BMC Systems Biology, 2015

A fundamental evolutionary step in the onset of living cells is thought to be the spontaneous for... more A fundamental evolutionary step in the onset of living cells is thought to be the spontaneous formation of lipid vesicles (liposomes) in the pre-biotic mixture. Even though it is well known that hydrophobic forces drive spontaneous liposome formation in aqueous solutions, how the components of the earliest biochemical pathways were trapped and concentrated in the forming vesicles is an issue that still needs to be clarified. In recent years, some authors carried out a set of experiments where a unexpectedly high amount of solutes were found in a small number of liposomes, spontaneously formed in aqueous solution. A great number of empty liposomes were found in the same experiments and the global observed behavior was that of a distribution of solute particles into liposomes in agreement with a inverse power-law function rather than with the expected Poisson distribution. The chemical and physical mechanisms leading to the observed "anomalous solute crowding" are still unclear, but the non-Poisson power-law behavior is associated with some cooperative behavior with strong non-linear interactions in the biochemical processes occurring in the solution. For tackling this issue we propose a model grounding on the Cox's theory of renewal point processes, which many authors consider to play a central role in the description of complex cooperative systems. Starting from two very basic hypotheses and the renewal assumption, we derive a model reproducing the behavior outlined above. In particular, we show that the assumption of a "cooperative" interaction between the solute molecules and the forming liposomes is sufficient for the emergence of the observed power-law behavior. Even though our approach does not provide experimental evidences of the chemical and physical bases of the solute crowding, it suggests promising directions for experimental research and it also provide a first theoretical prediction that could possibly be tested in future experimental investigations.

International Journal of Environment and Pollution, 2014

Back-trajectory techniques are extensively used to identify the most probable source locations, s... more Back-trajectory techniques are extensively used to identify the most probable source locations, starting from the known pollutants concentration data at some receptor sites. In this paper, we review the trajectory statistical methods (TSMs) that are most used in literature for source identification, which are essentially based on the concept of residence time (RT), and we introduce a novel statistical method. To validate this method, artificial receptor data at two receptor sites are derived from numerical simulations with a given aerial source, using the Lagrangian dispersion model (LSM) FLEXPART in forward mode. Then the RTs are computed using again the model FLEXPART, but in backward mode. Then, the new statistical methodology, which is based on the use of peak concentration events, is applied to reconstruct the spatial distribution of emission sources. Our approach requires simulation times shorter than those required in other methods and could overcome the problem of ghost sources.

DECISION MAKING - A Psychophysics Application of Network Science, 2011

International Journal of Psychophysiology, 2015

Sleep Slow Oscillations (SSOs), paradigmatic EEG markers of cortical bistability (alternation bet... more Sleep Slow Oscillations (SSOs), paradigmatic EEG markers of cortical bistability (alternation between cellular downstates and upstates), and sleep spindles, paradigmatic EEG markers of thalamic rhythm, are two hallmarks of sleeping brain. Selective thalamic lesions are reportedly associated to reductions of spindle activity and its spectrum ~14Hz (sigma), and to alterations of SSO features. This apparent, parallel behavior suggests that thalamo-cortical entrainment favors cortical bistability. Here we investigate temporally-causal associations between thalamic sigma activity and shape, topology, and dynamics of SSOs. We recorded sleep EEG and studied whether spatio-temporal variability of SSO amplitude, negative slope (synchronization in downstate falling) and detection rate are driven by cortical-sigma-activity expression (12-18Hz), in 3 consecutive 1s-EEG-epochs preceding each SSO event (Baselines). We analyzed: (i) spatial variability, comparing maps of baseline sigma power and of SSO features, averaged over the first sleep cycle; (ii) event-by-event shape variability, computing for each electrode correlations between baseline sigma power and amplitude/slope of related SSOs; (iii) event-by-event spreading variability, comparing baseline sigma power in electrodes showing an SSO event with the homologous ones, spared by the event. The scalp distribution of baseline sigma power mirrored those of SSO amplitude and slope; event-by-event variability in baseline sigma power was associated with that in SSO amplitude in fronto-central areas; within each SSO event, electrodes involved in cortical bistability presented higher baseline sigma activity than those free of SSO. In conclusion, spatio-temporal variability of thalamocortical entrainment, measured by background sigma activity, is a reliable estimate of the cortical proneness to bistability.

Proceedings of the 18th conference on Computational linguistics -, 2000

The paper illustrates a linguistic knowledge acquisition model making use of data types, innite m... more The paper illustrates a linguistic knowledge acquisition model making use of data types, innite memory, and an inferential mechanism for inducing new information from known data. The model is compared with standard stochastic methods applied to data tokens, and tested on a task of lexico semantic classi cation.

We address the issue of criticality that is attracting the attention of an increasing num-ber of ... more We address the issue of criticality that is attracting the attention of an increasing num-ber of neurophysiologists. Our main purpose is to establish the specific nature of some dynamical processes that although physically different, are usually termed as “critical,” and we focus on those characterized by the cooperative interaction of many units. We notice that the term “criticality ” has been adopted to denote both noise-induced phase transitions and Self-Organized Criticality (SOC) with no clear connection with the traditional phase transitions, namely the transformation of a thermodynamic system from one state of matter to another. We notice the recent attractive proposal of extended criticality advo-cated by Bailly and Longo, which is realized through a wide set of critical points rather than emerging as a singularity from a unique value of the control parameter. We study a set of cooperatively firing neurons and we show that for an extended set of interaction couplings the sys...

We study the long-range correlations of heartbeat fluctuations with the method of diffusion entro... more We study the long-range correlations of heartbeat fluctuations with the method of diffusion entropy. We show that this method of analysis yields a scaling parameter delta\deltadelta that apparently conflicts with the direct evaluation of the distribution of times of sojourn in states with a given heartbeat frequency. The strength of the memory responsible for this discrepancy is given by a parameter epsilon2\epsilon^{2}epsilon2, which is derived from real data. The distribution of patients in the ($\delta$, epsilon2\epsilon^{2}epsilon2)-plane yields a neat separation of the healthy from the congestive heart failure subjects.

AIP Conference Proceedings, 2002

We show that the derivation of Lévy statistics from a Liouville-like approach is still an unresol... more We show that the derivation of Lévy statistics from a Liouville-like approach is still an unresolved problem, even though a satisfactory derivation resting on the Generalized Central Limit Theorem (GCLT) has been obtained. We discuss a quantum relaxation that according to the supposed equivalence between decoherence theory and wave function collapses is expected to be equivalent to the characteristic function

Eprint Arxiv Cond Mat 0309350, Sep 1, 2003

Eprint Arxiv Cond Mat 0212614, Dec 27, 2002

We study an idealized version of intermittent process leading the fluctuations of a stochastic di... more We study an idealized version of intermittent process leading the fluctuations of a stochastic dichotomous variable ξ. It consists of an overdamped and symmetric potential well with a cusplike minimum. The right-hand and left-hand portions of the potential corresponds to ξ = W and ξ = −W , respectively. When the particle reaches this minimum is injected back to a different and randomly chosen position, still within the potential well. We build up the corresponding Frobenius-Perron equation and we evaluate the correlation function of the stochastic variable ξ, called Φ ξ (t). We assign to the potential well a form yielding Φ ξ (t) = (T /(t + T )) β , with β > 0. Thanks to the symmetry of the potential, there are no biases, and we limit ourselves to considering correlation functions with an even number of times, indicated for concision, by 12 , 1234 and, more, in general, by 1...2n . The adoption of a formal treatment, based on density, and thus of the operator driving the density time evolution, establishes a prescription for the evaluation of the correlation functions, yielding 1...2n = 12 ... (2n − 1)2n . We study the same dynamic problem using trajectories, and we establish that the resulting two-time correlation function coincides with that afforded by the density picture, as it should. We then study the four-times correlation function and we prove that in the non-Poisson case it departs from the density prescription, namely, from 1234 = 12 34 . We conclude that this is the main reason why the two pictures yield two different diffusion processes, as noticed in an earlier work [M. Bologna, P. Grigolini, B.

Matematicas Y Tratamiento De Corpus Actas Del Segundo Seminario De La Escuela Interlatina De Altos Estudios En Linguistica Aplicada San Millan De La Cogolla 19 23 De Septiembre De 2000 2002 Isbn 84 607 4688 7 Pags 245 268, 2002

What is the role of the linguistic context in shaping up our mental representations of word meani... more What is the role of the linguistic context in shaping up our mental representations of word meanings and what does this tell us about the way we learn, memorise and use these representations? The dynamic, context-based approach to word meaning (as opposed to the more established "representational" approach) has nowadays left the circles of associative and cognitive psychology to become a vividly discussed and intensely investigated topic in the field of machine language learning. In this paper we deal with some of the theoretical and empirical implications of this shift of conceptual paradigm and describe an analogy-based approach to the automatic acquisition and representation of word similarity from pre-annotated contexts.

2015 37th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), 2015

Sea-diving operations for monitoring or intervention are carried out by highly-specialized divers... more Sea-diving operations for monitoring or intervention are carried out by highly-specialized divers called Certified Commercial Divers (CCD). CCDs operate under highly demanding working conditions in extreme and hazardous environments. Every day consists of an 8 hours' shift. To avoid decompression problems the remaining 16 hours are spent in a hyperbaric environment located aboard the surface vessel or on the platform. These operating conditions require the design of a technologically-advanced device for tele-monitoring, to maximize CCDs' safety. Here we describe a proposal for monitoring and supporting CCDs during operations. We design a dedicated Life Support System (LSS), that captures real-time, vital (heart rate, respiratory rate, accelerometry, etc) and stress-related (heart-rate variability) signals from operators to transmit them to dedicated servers via telematic protocols. LSS is equipped with protocols for tele-medicine/tele-consultation. Our system is being developed within the research project SUONO (Safe Underwater OperatioNs in Oceans).

Physical Review E, 2015

Criticality reportedly describes brain dynamics. The main critical feature is the presence of sca... more Criticality reportedly describes brain dynamics. The main critical feature is the presence of scale-free neural avalanches, whose auto-organization is determined by a critical branching ratio of neural-excitation spreading. Other features, directly associated to second-order phase transitions, are: (i) scale-free-network topology of functional connectivity, stemming from suprathreshold pairwise correlations, superimposable, in waking brain activity, with that of ferromagnets at Curie temperature; (ii) temporal long-range memory associated to renewal intermittency driven by abrupt fluctuations in the order parameters, detectable in human brain via spatially distributed phase or amplitude changes in EEG activity. Herein we study intermittent events, extracted from 29 night EEG recordings, including presleep wakefulness and all phases of sleep, where different levels of mentation and consciousness are present. We show that while critical avalanching is unchanged, at least qualitatively, intermittency and functional connectivity, present during conscious phases (wakefulness and REM sleep), break down during both shallow and deep non-REM sleep. We provide a theory for fragmentation-induced intermittency breakdown and suggest that the main difference between conscious and unconscious states resides in the backwards causation, namely on the constraints that the emerging properties at large scale induce to the lower scales. In particular, while in conscious states this backwards causation induces a critical slowing down, preserving spatiotemporal correlations, in dreamless sleep we see a self-organized maintenance of moduli working in parallel. Critical avalanches are still present, and establish transient auto-organization, whose enhanced fluctuations are able to trigger sleep-protecting mechanisms that reinstate parallel activity. The plausible role of critical avalanches in dreamless sleep is to provide a rapid recovery of consciousness, if stimuli are highly arousing.

Chaos Solitons & Fractals

We argue that complex systems, defined as non-Poisson renewal process, with complexity index µ, e... more We argue that complex systems, defined as non-Poisson renewal process, with complexity index µ, exchange information through complexity matching. We illustrate this property with detailed theoretical and numerical calculations describing a system with complexity index µS perturbed by a signal with complexity index µP . We focus our attention on the case 1.5 ≤ µS ≤ 2 and 1 ≤ µP ≤ 2. We show that for µS ≥ µP , the system S reproduces the perturbation, and the response intensity increases with increasing µP . The maximum intensity is realized by the matching condition µP = µS. For µP > µS the response intensity dies out as 1/t µ P −µ S .

Fractals in Biology and Medicine, 1998

ABSTRACT

BMC Systems Biology, 2015

A fundamental evolutionary step in the onset of living cells is thought to be the spontaneous for... more A fundamental evolutionary step in the onset of living cells is thought to be the spontaneous formation of lipid vesicles (liposomes) in the pre-biotic mixture. Even though it is well known that hydrophobic forces drive spontaneous liposome formation in aqueous solutions, how the components of the earliest biochemical pathways were trapped and concentrated in the forming vesicles is an issue that still needs to be clarified. In recent years, some authors carried out a set of experiments where a unexpectedly high amount of solutes were found in a small number of liposomes, spontaneously formed in aqueous solution. A great number of empty liposomes were found in the same experiments and the global observed behavior was that of a distribution of solute particles into liposomes in agreement with a inverse power-law function rather than with the expected Poisson distribution. The chemical and physical mechanisms leading to the observed "anomalous solute crowding" are still unclear, but the non-Poisson power-law behavior is associated with some cooperative behavior with strong non-linear interactions in the biochemical processes occurring in the solution. For tackling this issue we propose a model grounding on the Cox's theory of renewal point processes, which many authors consider to play a central role in the description of complex cooperative systems. Starting from two very basic hypotheses and the renewal assumption, we derive a model reproducing the behavior outlined above. In particular, we show that the assumption of a "cooperative" interaction between the solute molecules and the forming liposomes is sufficient for the emergence of the observed power-law behavior. Even though our approach does not provide experimental evidences of the chemical and physical bases of the solute crowding, it suggests promising directions for experimental research and it also provide a first theoretical prediction that could possibly be tested in future experimental investigations.

International Journal of Environment and Pollution, 2014

Back-trajectory techniques are extensively used to identify the most probable source locations, s... more Back-trajectory techniques are extensively used to identify the most probable source locations, starting from the known pollutants concentration data at some receptor sites. In this paper, we review the trajectory statistical methods (TSMs) that are most used in literature for source identification, which are essentially based on the concept of residence time (RT), and we introduce a novel statistical method. To validate this method, artificial receptor data at two receptor sites are derived from numerical simulations with a given aerial source, using the Lagrangian dispersion model (LSM) FLEXPART in forward mode. Then the RTs are computed using again the model FLEXPART, but in backward mode. Then, the new statistical methodology, which is based on the use of peak concentration events, is applied to reconstruct the spatial distribution of emission sources. Our approach requires simulation times shorter than those required in other methods and could overcome the problem of ghost sources.

DECISION MAKING - A Psychophysics Application of Network Science, 2011

International Journal of Psychophysiology, 2015

Sleep Slow Oscillations (SSOs), paradigmatic EEG markers of cortical bistability (alternation bet... more Sleep Slow Oscillations (SSOs), paradigmatic EEG markers of cortical bistability (alternation between cellular downstates and upstates), and sleep spindles, paradigmatic EEG markers of thalamic rhythm, are two hallmarks of sleeping brain. Selective thalamic lesions are reportedly associated to reductions of spindle activity and its spectrum ~14Hz (sigma), and to alterations of SSO features. This apparent, parallel behavior suggests that thalamo-cortical entrainment favors cortical bistability. Here we investigate temporally-causal associations between thalamic sigma activity and shape, topology, and dynamics of SSOs. We recorded sleep EEG and studied whether spatio-temporal variability of SSO amplitude, negative slope (synchronization in downstate falling) and detection rate are driven by cortical-sigma-activity expression (12-18Hz), in 3 consecutive 1s-EEG-epochs preceding each SSO event (Baselines). We analyzed: (i) spatial variability, comparing maps of baseline sigma power and of SSO features, averaged over the first sleep cycle; (ii) event-by-event shape variability, computing for each electrode correlations between baseline sigma power and amplitude/slope of related SSOs; (iii) event-by-event spreading variability, comparing baseline sigma power in electrodes showing an SSO event with the homologous ones, spared by the event. The scalp distribution of baseline sigma power mirrored those of SSO amplitude and slope; event-by-event variability in baseline sigma power was associated with that in SSO amplitude in fronto-central areas; within each SSO event, electrodes involved in cortical bistability presented higher baseline sigma activity than those free of SSO. In conclusion, spatio-temporal variability of thalamocortical entrainment, measured by background sigma activity, is a reliable estimate of the cortical proneness to bistability.

Proceedings of the 18th conference on Computational linguistics -, 2000

The paper illustrates a linguistic knowledge acquisition model making use of data types, innite m... more The paper illustrates a linguistic knowledge acquisition model making use of data types, innite memory, and an inferential mechanism for inducing new information from known data. The model is compared with standard stochastic methods applied to data tokens, and tested on a task of lexico semantic classi cation.