IMT Institutional Repository: No conditions. Results ordered -Date Deposited. 2019-06-17T23:26:29ZEPrintshttp://eprints.imtlucca.it/images/logowhite.pnghttp://eprints.imtlucca.it/2016-04-12T08:23:27Z2016-04-12T08:23:27Zhttp://eprints.imtlucca.it/id/eprint/3406This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/34062016-04-12T08:23:27ZDifferential amygdala responses to winning and losing: a functional magnetic resonance imaging study in humansThe amygdala has been shown to respond to many distinct types of affective stimuli, including reward and punishment feedback in animals. In humans, winning and losing situations can be considered as reward and punishment experiences, respectively. In this study, we used functional magnetic resonance imaging (fMRI) to measure regional brain activity when human subjects were given feedback on their performance during a simple response time task in a fictitious competitive tournament. Lexical stimuli were used to convey positive ‘win’ or negative ‘lose’ feedback. The frequency of positive and negative trials was parametrically varied by the experimenters independently from the subjects' actual performance and unbeknownst to them. The results showed that the parametric increase of winning was associated with left amygdala activation whereas the parametric increase of losing was associated with right amygdala activation. These findings provide functional evidence that the human amygdala differentially responds to changes in magnitude of positive or negative reinforcement conveyed by lexical stimuli.Tiziana ZallaEtienne KoechlinPietro Pietrinipietro.pietrini@imtlucca.itGianpaolo BassoPatrick AquinoAngela SiriguJordan Grafman2016-04-11T09:33:52Z2016-04-11T09:33:52Zhttp://eprints.imtlucca.it/id/eprint/3401This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/34012016-04-11T09:33:52ZFunctional brain studies of the neurometabolic bases of cognitive and behavioral changes in Alzheimer's diseasePietro Pietrinipietro.pietrini@imtlucca.itMaura L. FureyMario GuazzelliGene E. Alexander2016-04-08T09:40:31Z2016-04-08T09:40:31Zhttp://eprints.imtlucca.it/id/eprint/3400This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/34002016-04-08T09:40:31ZPositron Emission Tomography in Evaluation of DementiaContext Deficits in cerebral glucose utilization have been identified in patients with cognitive dysfunction attributed to various disease processes, but their prognostic and diagnostic value remains to be defined.
Objective To assess the sensitivity and specificity with which cerebral metabolic patterns at a single point in time forecast subsequent documentation of progressive dementia.
Design, Setting, and Patients Positron emission tomography (PET) studies of [18F]fluorodeoxyglucose in 146 patients undergoing evaluation for dementia with at least 2 years' follow-up for disease progression at the University of California, Los Angeles, from 1991 to 2000, and PET studies in 138 patients undergoing evaluation for dementia at an international consortium of facilities, with histopathological diagnoses an average of 2.9 years later, conducted from 1984 to 2000.
Main Outcome Measures Regional distribution of [18F]fluorodeoxyglucose in each patient, classified by criteria established a priori as positive or negative for presence of a progressive neurodegenerative disease in general and of Alzheimer disease (AD) specifically, compared with results of longitudinal or neuropathologic analyses.
Results Progressive dementia was detected by PET with a sensitivity of 93% (191/206) and a specificity of 76% (59/78). Among patients with neuropathologically based diagnoses, PET identified patients with AD and patients with any neurodegenerative disease with a sensitivity of 94% and specificities of 73% and 78%, respectively. The negative likelihood ratio of experiencing a progressive vs nonprogressive course over the several years following a single negative brain PET scan was 0.10 (95% confidence interval, 0.06-0.16), and the initial pattern of cerebral metabolism was significantly associated with the subsequent course of progression overall (P<.001).Daniel H. S. SilvermanGary W. SmallCarol Y. ChangCarolyn S. LuMichelle A. Kung de AburtoWei ChenJohannes CzerninStanley I. RapoportPietro Pietrinipietro.pietrini@imtlucca.itGene E. AlexanderMark B. SchapiroWilliam J. JagustJohn M. HoffmanKathleen A. Welsh-BohmerAbass AlaviChristopher M. ClarkEric SalmonMony J. de LeonRuediger MielkeJeffrey L. CummingsArthur P. KowellSanjiv S. GambhirCarl K. HohMichael E. Phelps2016-04-08T09:26:44Z2016-04-08T09:26:44Zhttp://eprints.imtlucca.it/id/eprint/3399This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33992016-04-08T09:26:44ZConjoint and extended neural networks for the computation of speech codes: the neural basis of selective impairment in reading words and pseudowordsThe computation of speech codes (i.e. phonology) is an important aspect of word reading. Understanding the neural systems and mech- anisms underlying phonological processes provides a foundation for the investigation of language in the brain. We used high-resolution three-dimensional positron emission tomography (PET) to investigate neural systems essential for phonological processes. The burden of neural activities on the computation of speech codes was maximized by three rhyming tasks (rhyming words, pseudowords and words printed in mixed letter cases). Brain activation patterns associated with these tasks were compared with those of two baseline tasks involving visual feature detection. Results suggest strong left lateralized epicenters of neural activity in rhyming irrespective of gender. Word rhyming activated the same brain regions engaged in pseudoword rhyming, suggesting conjoint neural networks for phonological processing of words and pseudowords. However, pseudoword rhyming induced the largest change in cerebral blood flow and activated more voxels in the left posterior prefrontal regions and the left inferior occipital–temporal junction. In addition, pseudoword rhyming activated the left supramarginal gyrus, which was not apparent in word rhyming. These results suggest that rhyming pseudowords requires active participation of extended neural systems and networks not observed for rhyming words. The implications of the results on theories and models of visual word reading and on selective reading dysfunctions after brain lesions are discussed.Benjamin XuJordan GrafmanWilliam D. GaillardKenji IshiiFrancisco Vega-BermudezPietro Pietrinipietro.pietrini@imtlucca.itPatricia Reeves-TyerPaul DiCamilloWilliam Theodore2016-04-07T10:04:42Z2016-04-07T10:04:42Zhttp://eprints.imtlucca.it/id/eprint/3398This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33982016-04-07T10:04:42ZThe effect of brain atrophy on cerebral hypometabolism in the visual variant of Alzheimer diseaseBackground Brain glucose metabolic rates measured by positron emission tomography can be more affected by partial volume effects in Alzheimer disease (AD) than in healthy aging because of disease-associated brain atrophy.
Objective To determine whether the distinct distribution of cerebral metabolic lesions in patients with the visual variant of AD (AD + VS) represents a true index of neuronal/synaptic dysfunction or is the consequence of brain atrophy.
Setting Government research hospital.
Design Resting cerebral metabolic rate for glucose was measured with positron emission tomography in a cross-sectional study of AD and AD + VS groups and in healthy control subjects. Segmented magnetic resonance images were used to correct for brain atrophy.
Patients Patients with AD + VS had prominent visual and visuospatial symptoms. There were 15 patients with AD, 10 with AD + VS, and 37 age-matched control subjects.
Main Outcome Measure Measurement of the rate of cerebral glucose metabolism.
Results Before atrophy correction, the AD + VS group, compared with the control subjects, showed hypometabolism in primary and extrastriate visual areas and in parietal and superior temporal cortical areas. Compared with the AD group, the AD + VS group showed hypometabolism in visual association areas. After atrophy correction, hypometabolism remained significantly different between patients and controls and between the 2 AD groups.
Conclusions The reductions in cerebral hypometabolism represent a true loss of functional activity and are not simply an artifact caused by brain atrophy. The different patterns of hypometabolism indicate the differential development of the lesions between the AD and AD + VS groups.Arun L. W. BokdePietro Pietrinipietro.pietrini@imtlucca.itVicente IbáñezMaura L. FureyGene E. AlexanderNeill R. Graff-RadfordStanley I. RapoportMark B. SchapiroBarry Horwitz2016-04-07T09:54:43Z2016-09-13T10:20:16Zhttp://eprints.imtlucca.it/id/eprint/3397This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33972016-04-07T09:54:43ZBasi neurometaboliche degli effetti della modulazione colinergica: studi PET e fMRI nell'uomoPietro Pietrinipietro.pietrini@imtlucca.itEmiliano Ricciardiemiliano.ricciardi@imtlucca.itMario GuazzelliMaura L. Furey2016-04-07T09:51:50Z2016-04-08T09:28:16Zhttp://eprints.imtlucca.it/id/eprint/3396This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33962016-04-07T09:51:50ZAltered brain functional connectivity and impaired short-term memory in Alzheimer's diseaseTo examine functional interactions between prefrontal and medial temporal brain areas during face memory, blood flow was measured in patients with Alzheimer's disease and healthy controls using PET. We hypothesized that controls would show correlated activity between frontal and posterior brain areas, including the medial temporal cortex, whereas patients would not, although frontal activity per se might be spared or even increased compared with controls. We used a delayed match to sample paradigm with delays from 1 to 16 s. There was no change in recognition accuracy with increasing delay in controls, whereas patients showed impaired recognition over all delays that worsened as delay increased. Controls showed increased activity in the bilateral prefrontal and parietal cortex with increasing delay, whereas the patients had increased activity in the right prefrontal, anterior cingulate and left amygdala. Increased activity in the right prefrontal cortex was associated with better memory performance in both groups and activity in the left amygdala was correlated with better performance in the patients. Based on these task and behavioural effects, we examined functional connectivity of the right prefrontal cortex and left amygdala in both groups by determining those areas whose activity was correlated with activity in these regions. In controls, activity in the right prefrontal cortex was positively correlated with blood flow in the left prefrontal cortex, bilateral extrastriate and parietal areas and the right hippocampus. In patients, activity in the right prefrontal cortex was correlated mainly with other prefrontal regions. Areas where activity was correlated with the left amygdala in patients included the bilateral posterior parahippocampal gyri, a number of left prefrontal regions, anterior and posterior cingulate, thalamus, and insula. Controls had a relatively restricted set of regions where activity correlated with the left amygdala, mainly temporal and occipital areas. These results support the idea of a functional disconnection between the prefrontal cortex and the hippocampus in Alzheimer's disease and suggest that memory breakdown in early Alzheimer's disease is related to a reduction in the integrated activity within a distributed network that includes these two areas. The unexpected finding of increased involvement of the amygdala suggests that the patients may have processed the emotional content of the faces to a greater degree than did the controls. Furthermore, the positive association between amygdala activity and memory performance in the patients suggests a possible compensatory role for an emotion-related network of regions.Cheryl L. GradyMaura L. FureyPietro Pietrinipietro.pietrini@imtlucca.itBarry HorwitzStanley I. Rapoport2016-04-07T09:46:32Z2016-04-07T09:46:32Zhttp://eprints.imtlucca.it/id/eprint/3395This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33952016-04-07T09:46:32ZDistributed and overlapping representations of faces and objects in ventral temporal cortexThe functional architecture of the object vision pathway in the human brain was investigated using functional magnetic resonance imaging to measure patterns of response in ventral temporal cortex while subjects viewed faces, cats, five categories of man-made objects, and nonsense pictures. A distinct pattern of response was found for each stimulus category. The distinctiveness of the response to a given category was not due simply to the regions that responded maximally to that category, because the category being viewed also could be identified on the basis of the pattern of response when those regions were excluded from the analysis. Patterns of response that discriminated among all categories were found even within cortical regions that responded maximally to only one category. These results indicate that the representations of faces and objects in ventral temporal cortex are widely distributed and overlapping.James V. HaxbyMaria Ida GobbiniMaura L. FureyAlumit IshaiJennifer L. SchoutenPietro Pietrinipietro.pietrini@imtlucca.it2016-04-07T09:35:27Z2016-09-13T10:19:50Zhttp://eprints.imtlucca.it/id/eprint/3394This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33942016-04-07T09:35:27ZBasi neuronali degli effetti della modulazione farmacologica del sistema colinergico: studi PET e FMRI nell'uomoMaura L. FureyEmiliano Ricciardiemiliano.ricciardi@imtlucca.itMario GuazzelliPietro Pietrinipietro.pietrini@imtlucca.it2016-04-07T09:19:29Z2016-04-07T09:19:29Zhttp://eprints.imtlucca.it/id/eprint/3389This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33892016-04-07T09:19:29ZAdvance image processing in clinical and research applicationsDavide CaramellaEmanuele NeriM. LombardiLuigi LandiniVincenzo PositanoS. La MannaA. StaritaPietro Pietrinipietro.pietrini@imtlucca.itMario GuazzelliJames V. HaxbyCarlo Bartolozzi2016-04-07T08:29:37Z2016-04-07T08:29:37Zhttp://eprints.imtlucca.it/id/eprint/3387This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33872016-04-07T08:29:37ZDistinct, overlapping representations of faces and multiple categories of objects in ventral temporal cortexJames V. HaxbyMaria Ida GobbiniMaura L. FureyAlumit IshaiPietro Pietrinipietro.pietrini@imtlucca.it2016-04-07T08:21:06Z2016-04-07T08:21:06Zhttp://eprints.imtlucca.it/id/eprint/3386This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33862016-04-07T08:21:06ZLe basi biologiche del decadimento cognitivo nella malattia di Alzheimer: lo studio del metabolismo cerebrale del glucosio mediante tomografia ad emissione di positroniG. GiovacchiniMario GuazzelliPietro Pietrinipietro.pietrini@imtlucca.it2016-04-07T08:13:30Z2016-09-13T10:20:04Zhttp://eprints.imtlucca.it/id/eprint/3385This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33852016-04-07T08:13:30ZCorrelati neurometabolici del decadimento cognitivo nella malattia di Alzheimer: implicazioni per la terapiaMario GuazzelliEmiliano Ricciardiemiliano.ricciardi@imtlucca.itPietro Pietrinipietro.pietrini@imtlucca.it2016-04-07T08:04:23Z2016-04-07T08:04:23Zhttp://eprints.imtlucca.it/id/eprint/3384This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/33842016-04-07T08:04:23ZNeuroradiological Investigation: Functional Neuroimaging: SPECT/PETGene E. AlexanderPietro Pietrinipietro.pietrini@imtlucca.it2016-01-13T12:28:31Z2016-09-14T10:21:18Zhttp://eprints.imtlucca.it/id/eprint/2987This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/29872016-01-13T12:28:31ZLa valorizzazione dei beni culturaliLorenzo Casinilorenzo.casini@imtlucca.it2016-01-13T12:26:08Z2016-09-14T10:21:18Zhttp://eprints.imtlucca.it/id/eprint/2986This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/29862016-01-13T12:26:08ZAmministratori locali: attività professionale ed obbligo di astensione. Commento a Corte di Appello di Salerno 3-11 agosto 2000, n. 270Lorenzo Casinilorenzo.casini@imtlucca.it2013-12-19T13:33:57Z2014-10-09T09:20:26Zhttp://eprints.imtlucca.it/id/eprint/2078This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/20782013-12-19T13:33:57ZModelli micromeccanici di contatto: analisi critica comparativaMarco Paggimarco.paggi@imtlucca.it2013-11-06T12:10:36Z2013-11-20T09:03:02Zhttp://eprints.imtlucca.it/id/eprint/1877This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/18772013-11-06T12:10:36ZFrom Minority Games to real markets We address the question of market efficiency using the Minority Game (MG) model. First we show that removing unrealistic features of the MG leads to models which reproduce a scaling behaviour close to what is observed in real markets. In particular we find that (i) fat tails and clustered volatility arise at the phase transition point and that (ii) the crossover to random walk behaviour of prices is a finite-size effect. This, on one hand, suggests that markets operate close to criticality, where the market is marginally efficient. On the other it allows one to measure the distance from criticality of real markets, using cross-over times. The artificial market described by the MG is then studied as an ecosystem with different species of traders. This clarifies the nature of the interaction and the particular role played by the various populations. Damien ChalletAlessandro Chessaalessandro.chessa@imtlucca.itMatteo MarsiliYi-Cheng Zhang2013-11-06T11:50:13Z2016-04-06T09:55:08Zhttp://eprints.imtlucca.it/id/eprint/1876This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/18762013-11-06T11:50:13ZTime evolution of stochastic processes with correlations in the variance: stability in power-law tails of distributions We model the time series of the S&P500 index by a combined process, the AR+GARCH process, where {AR} denotes the autoregressive process which we use to account for the short-range correlations in the index changes and {GARCH} denotes the generalized autoregressive conditional heteroskedastic process which takes into account the long-range correlations in the variance. We study the AR+GARCH process with an initial distribution of truncated Lévy form. We find that this process generates a new probability distribution with a crossover from a Lévy stable power law to a power law with an exponent outside the Lévy range, beyond the truncation cutoff. We analyze the sum of n variables of the AR+GARCH process, and find that due to the correlations the AR+GARCH process generates a probability distribution which exhibits stable behavior in the tails for a broad range of values n—a feature which is observed in the probability distribution of the S&P500 index. We find that this power-law stability depends on the characteristic scale in the correlations. We also find that inclusion of short-range correlations through the {AR} process is needed to obtain convergence to a limiting Gaussian distribution for large n as observed in the data. Boris PodobnikKaushik MatiaAlessandro Chessaalessandro.chessa@imtlucca.itPlamen Ch. IvanovYoungki LeeH. Eugene Stanley2012-08-10T08:02:12Z2012-08-10T08:02:12Zhttp://eprints.imtlucca.it/id/eprint/1332This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/13322012-08-10T08:02:12ZTomas Bjork, A geometric view of the term structure of interest rates, Cattedra Galileiana 2000 (Lecture notes written by Irene Crimaldi)This set of lecture notes is the outcome of a lecture series, given in April 2000 by Prof. Tomas Bjork while holding the "Cattedra Galileiana" at Scuola Normale Superiore in Pisa. The purpose of the lectures was to give an overview of some recent work concerning structural properties of the evolution of the forward rate curve in an arbitrage free bond market.Irene Crimaldiirene.crimaldi@imtlucca.it2012-02-27T11:58:34Z2012-02-27T11:58:34Zhttp://eprints.imtlucca.it/id/eprint/1194This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11942012-02-27T11:58:34ZThe fractal properties of internetIn this paper we show that the Internet web, from a user’s perspective, manifests robust scaling properties of the type P(n)∝n−r where n is the size of the basin connected to a given point, P represents the density of probability of finding a basin of size n connected and τ = 1.9±0.1 is a characteristic universal exponent. The connection between users and providers are studied and modeled as branches of a world spanning tree. This scale-free structure is the result of the spontaneous growth of the web, but is not necessarily the optimal one for efficient transport. We introduce an appropriate figure of merit and suggest that a planning of few big links, acting as information highways, may noticeably increase the efficiency of the net without affecting its robustness.Riccardo MarchettiGuido Caldarelliguido.caldarelli@imtlucca.itLuciano Pietronero2012-02-23T10:16:47Z2013-11-20T14:18:23Zhttp://eprints.imtlucca.it/id/eprint/1155This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11552012-02-23T10:16:47ZCellular models for river networksA cellular model introduced for the evolution of the fluvial landscape is revisited using extensive numerical and scaling analyses. The basic network shapes and their recurrence especially in the aggregation structure are then addressed. The roles of boundary and initial conditions are carefully analyzed as well as the key effect of quenched disorder embedded in random pinning of the landscape surface. It is found that the above features strongly affect the scaling behavior of key morphological quantities. In particular, we conclude that randomly pinned regions (whose structural disorder bears much physical meaning mimicking uneven landscape-forming rainfall events, geological diversity or heterogeneity in surficial properties like vegetation, soil cover or type) play a key role for the robust emergence of aggregation patterns bearing much resemblance to real river networks.Guido Caldarelliguido.caldarelli@imtlucca.it2012-02-23T10:12:18Z2012-02-23T10:12:18Zhttp://eprints.imtlucca.it/id/eprint/1154This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11542012-02-23T10:12:18ZCold and warm swelling of hydrophobic polymersWe introduce a polymer model where the transition from swollen to compact configurations is due to interactions between the monomers and the solvent. These interactions are the origin of the effective attractive interactions between hydrophobic amino acids in proteins. We find that in the low and high temperature phases polymers are swollen, and there is an intermediate phase where the most favorable configurations are compact. We argue that such a model captures in a single framework both the cold and the warm denaturation experimentally detected for thermosensitive polymers and for proteins.Paolo De Los RiosGuido Caldarelliguido.caldarelli@imtlucca.it2012-02-23T10:07:06Z2012-02-23T10:07:06Zhttp://eprints.imtlucca.it/id/eprint/1153This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11532012-02-23T10:07:06ZSex-oriented stable matchings of the marriage problem with correlated and incomplete informationIn the stable marriage problem two sets of agents must be paired according to mutual preferences, which may happen to conflict. We present two generalizations of its sex-oriented version, aiming to take into account correlations between the preferences of agents and costly information. Their effects are investigated both numerically and analytically.Guido Caldarelliguido.caldarelli@imtlucca.itAndrea CapocciPaolo Laureti2012-02-22T16:33:38Z2013-11-20T14:03:00Zhttp://eprints.imtlucca.it/id/eprint/1152This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11522012-02-22T16:33:38ZBeauty and distance in the stable marriage problemThe stable marriage problem has been introduced in order to describe a complex system where individuals attempt to optimise their own satisfaction, subject to mutually conflicting constraints. Due to the potential large applicability of such model to describe all the situation where different objects has to be matched pairwise, the statistical properties of this model have been extensively studied. In this paper, we present a generalisation of this model, introduced in order to take into account the presence of correlations in the lists and the effects of distance when the players are supposed to be represented by a position in space.Guido Caldarelliguido.caldarelli@imtlucca.itAndrea Capocci2012-02-22T16:18:26Z2014-12-05T09:31:58Zhttp://eprints.imtlucca.it/id/eprint/1151This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11512012-02-22T16:18:26ZPerturbative approach to the Bak-Sneppen modelWe study the Bak-Sneppen model in the probabilistic framework of the run time statistics (RTS). This model has attracted a large interest for its simplicity being a prototype for the whole class of models showing self-organized criticality. The dynamics is characterized by a self-organization of almost all the species fitnesses above a nontrivial threshold value, and by a lack of spatial and temporal characteristic scales. This results in avalanches of activity power law distributed. In this Letter we use the RTS approach to compute the value of xc, the value of the avalanche exponent τ, and the asymptotic distribution of minimal fitnesses.Maddalena FeliciGuido Caldarelliguido.caldarelli@imtlucca.itAndrea GabrielliLuciano Pietronero2012-02-22T10:59:34Z2012-02-22T10:59:34Zhttp://eprints.imtlucca.it/id/eprint/1145This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11452012-02-22T10:59:34ZGrowing dynamics of Internet providersIn this paper we present a model for the growth and evolution of Internet providers. The model reproduces the data observed for the Internet connection as probed by tracing routes from different computers. This problem represents a paramount case of study for growth processes in general, but can also help in the understanding the properties of the Internet. Our main result is that this network can be reproduced by a self-organized interaction between users and providers that can rearrange in time. This model can then be considered as a prototype model for the class of phenomena of aggregation processes in social networks.Andrea CapocciGuido Caldarelliguido.caldarelli@imtlucca.itRiccardo MarchettiLuciano Pietronero2012-02-22T10:36:35Z2013-11-20T14:15:03Zhttp://eprints.imtlucca.it/id/eprint/1144This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11442012-02-22T10:36:35ZFractal growth from local instabilitiesWe study, both with numerical simulations and theoretical methods, a cellular automata model for surface growth in the presence of a local instability, driven by an external flux of particles. The growing tip is selected with probability proportional to the local curvature. A probability p of developing overhangs through lateral growth is also introduced. For small external fluxes, we find a fractal regime of growth. The value of p determines the fractal dimension of the aggregate. Furthermore, for each value of p a crossover between two different fractal dimensions is observed. The roughness exponent χ of the aggregates, instead, does not depend on p (χ simeq 0.5). A Fixed Scale Transformation (FST) approach is applied to compute theoretically the fractal dimension for one of the branches of the structure.Raffaele CafieroGuido Caldarelliguido.caldarelli@imtlucca.it2012-02-21T13:36:05Z2013-11-20T14:23:53Zhttp://eprints.imtlucca.it/id/eprint/1143This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11432012-02-21T13:36:05ZPercolation in real wildfiresThis paper focuses on the statistical properties of wild-land fires and, in particular, investigates if spread dynamics relates to simple invasion model. The fractal dimension and lacunarity of three fire scars classified from satellite imagery are analysed. Results indicate that the burned clusters behave similarly to percolation clusters on boundaries and look denser in their core. We show that Dynamical Percolation reproduces this behaviour and can help to describe the fire evolution. By mapping fire dynamics onto the percolation models, the strategies for fire control might be improved.Guido Caldarelliguido.caldarelli@imtlucca.itRaffaella FrondoniAndrea GabrielliMarco MontuoriRebecca RetzlaffCarlo Ricotta2012-02-21T13:08:49Z2013-11-20T14:27:32Zhttp://eprints.imtlucca.it/id/eprint/1142This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/11422012-02-21T13:08:49ZCold and warm denaturation of proteins We introduce a simplified protein model where the water degrees of freedom appear explicitly (although in an extremely simplified fashion). Using this model we are able to recover both the warm and the cold protein denaturation within a single framework, while addressing important issues about the structure of model proteins.Guido Caldarelliguido.caldarelli@imtlucca.itPaolo De Los Rios2011-11-22T12:19:23Z2011-12-20T12:00:25Zhttp://eprints.imtlucca.it/id/eprint/1016This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/10162011-11-22T12:19:23ZProtocol verification with heuristic searchWe present an approach to reconcile explicit state model checking and heuristic directed search and provide experimental evidence that the model checking problem for concurrent systems, such as communications protocols, can be solved more efficiently, since finding a state violating a property can be understood as a directed search problem. In our work we combine the expressive power and implementation efficiency of the SPIN model checker with the HSF heuristic search workbench, yielding the HSF-SPIN tool that we have implemented. We start off from the A* algorithm and some of its derivatives and define heuristics for various system properties that guide the search so that it finds error states faster. In this paper we focus on safety properties and provide heuristics for invariant and assertion violation and deadlock detection. We provide experimental results for applying HSF-SPIN to two toy protocols and one real world protocol, the CORBA GIOP protocol.Stefan EdelkampAlberto Lluch-Lafuentealberto.lluch@imtlucca.itStefan Leue2011-10-18T09:12:06Z2011-10-18T09:12:06Zhttp://eprints.imtlucca.it/id/eprint/947This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/9472011-10-18T09:12:06ZPer Pescia ma non più a Pescia, una serie di opere d’arte perduteEmanuele Pellegriniemanuele.pellegrini@imtlucca.it2011-08-11T13:04:07Z2013-03-05T15:51:08Zhttp://eprints.imtlucca.it/id/eprint/805This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/8052011-08-11T13:04:07ZFast compressed domain watermarking of MPEG multiplexed streamsIn this paper, a new technique for watermarking of
MPEG compressed video streams is proposed. The watermarking scheme operates directly in the domain of MPEG multiplexed streams. Perceptual models are used during the embedding process in order to preserve the quality of the video. The watermark is embedded in the compressed domain and is detected without the use of the original video sequence. Experimental evaluation demonstrates that the proposed scheme is able to withstand a variety of attacks. The resulting watermarking system is very fast and reliable, and is suitable for copyright protection and real-time content authentication applications.Dimitrios SimitopoulosSotirios A. Tsaftarissotirios.tsaftaris@imtlucca.itNikolaos BoulgourisMichael Strintzis2011-08-11T12:39:52Z2013-03-05T15:50:56Zhttp://eprints.imtlucca.it/id/eprint/804This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/8042011-08-11T12:39:52ZDigital watermarking of MPEG-1 and MPEG-2 multiplexed streams for copyright protectionA new technique for watermarking of MPEG-1/2 compressed video streams is proposed. The watermarking scheme operates directly in the domain of MPEG-1/2 program streams. Perceptual models are used during the embedding process in order to preserve the quality of the video. The detection of the watermark is performed in the compressed domain without requiring the original video. The resulting watermarking system is very fast and reliable and is suitable for copyright protection and real-time content authentication applicationsDimitrios SimitopoulosSotirios A. Tsaftarissotirios.tsaftaris@imtlucca.itNikolaos BoulgourisMichael Strintzis2011-08-09T10:28:36Z2011-08-12T15:18:50Zhttp://eprints.imtlucca.it/id/eprint/779This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/7792011-08-09T10:28:36ZIncertezza e investimenti The paper proposes a dynamic partial equilibrium model where competitive firms with constant return to scale technology are risk averse. Firms are subject to output price uncertainty. We show that it is possible that the investment-uncertainty relationship is positive even when firms have a high degree of risk aversion. Indeed, the paper shows that risk aversion can explain the negative relationship between investment and uncertainty only in a static context. In a dynamic framework, the linkage between periods can lead risk aversion to have a positive effect on investment when uncertainty increases. Moreover, the paper shows that investment should be positively correlated with uncertainty for reasonable values of the preference and technological parameters.Enrico SaltariDavide Ticchidavide.ticchi@imtlucca.it2011-07-27T09:32:44Z2014-07-17T12:39:20Zhttp://eprints.imtlucca.it/id/eprint/468This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4682011-07-27T09:32:44ZConvexity recognition of the union of polyhedraIn this paper we consider the following basic problem in polyhedral computation: Given two polyhedra in Rd, P and Q, decide whether their union is convex, and, if so, compute it. We consider the three natural specializations of the problem: 1) when the polyhedra are given by halfspaces (H-polyhedra), 2) when they are given by vertices and extreme rays (V-polyhedra), and 3) when both H- and V-polyhedral representations are available. Both the bounded (polytopes) and the unbounded case are considered. We show that the first two problems are polynomially solvable, and that the third problem is strongly-polynomially solvable.Alberto Bemporadalberto.bemporad@imtlucca.itKomei FukudaFabio Danilo Torrisi2011-07-27T09:11:10Z2014-07-17T12:48:08Zhttp://eprints.imtlucca.it/id/eprint/519This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5192011-07-27T09:11:10ZA hybrid approach to traction controlIn this paper we describe a hybrid model and an optimization-based control strategy for solving a traction control prob- lem currently under investigation at Ford Research Laboratories. We show through simulations on a model and a realistic set of parameters that good and robust performance is achieved. Furthermore, the result- ing optimal controller is a piecewise linear function of the measurements that can be implemented on low cost control hardware. Francesco BorrelliAlberto Bemporadalberto.bemporad@imtlucca.itMichael FodorDavor Hrovat2011-07-27T09:11:08Z2014-07-17T12:49:10Zhttp://eprints.imtlucca.it/id/eprint/582This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5822011-07-27T09:11:08ZDiscrete-time hybrid modeling and verificationFor hybrid systems described by interconnections of linear dynamical systems and logic devices, we recently (A. Bemporad et al., 2000, 2001) proposed mixed logical-dynamical (MLD) systems and the language HYSDEL (HYbrid System DEscription Language) as a modeling tool. For MLD models, we developed a reachability analysis algorithm which combines forward reach-set computation and feasibility analysis of trajectories by linear and mixed-integer linear programming. In this paper, the versatility of the overall analysis tool is illustrated in the verification of an automotive cruise control system for a car with a robotized manual gear shiftFabio Danilo TorrisiAlberto Bemporadalberto.bemporad@imtlucca.it2011-07-27T09:11:06Z2014-07-17T12:48:51Zhttp://eprints.imtlucca.it/id/eprint/581This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5812011-07-27T09:11:06ZAn algorithm for multi-parametric quadratic programming and explicit MPC solutionsExplicit solutions to constrained linear model-predictive control (MPC) problems can be obtained by solving multi-parametric quadratic programs (mp-QP) where the parameters are the components of the state vector. We study the properties of the polyhedral partition of the state space induced by the multi-parametric piecewise linear solution and propose a new mp-QP solver. Compared to existing algorithms, our approach adopts a different exploration strategy for subdividing the parameter space, avoiding unnecessary partitioning and QP problem solving, with a significant improvement in efficiencyPetter TondelTor Arne JohansenAlberto Bemporadalberto.bemporad@imtlucca.it2011-07-27T09:09:10Z2014-07-17T12:47:36Zhttp://eprints.imtlucca.it/id/eprint/585This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5852011-07-27T09:09:10ZIdentification of hybrid systems via mixed-integer programmingAddresses the problem of identification of hybrid dynamical systems, by focusing the attention on hinging hyperplanes and Wiener piecewise affine autoregressive exogenous models. In particular, we provide algorithms based on mixed-integer linear or quadratic programming which are guaranteed to converge to a global optimumAlberto Bemporadalberto.bemporad@imtlucca.itJacob RollLennart Ljung2011-07-27T09:09:07Z2014-07-17T12:47:14Zhttp://eprints.imtlucca.it/id/eprint/577This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5772011-07-27T09:09:07ZOptimization-based hybrid control toolsThe paper discusses a framework for modeling, analyzing and controlling systems whose behavior is governed by interdependent physical laws, logic rules, and operating constraints, denoted as Mixed Logical Dynamical (MLD) systems. They are described by linear dynamic equations subject to linear inequalities involving real and integer variables. MLD models are equivalent to various other system descriptions like Piecewise Affine (PWA) systems and Linear Complementarity (LC) systems. They have the advantage, however, that many problems of system analysis (like reachability/controllability, observability, and verification) and many problems of synthesis (like controller design and filter design) can be readily expressed as mixed integer linear or quadratic programs, for which many commercial software packages exist. In this paper we first recall MLD models and the modeling language HYSDEL (HYbrid Systems DEscription Language). Subsequently, we illustrate the use of Model Predictive Control (MPC) based on mixed-integer programming for hybrid MLD models, and the use of multiparametric programming for obtaining explicitly the equivalent piecewise linear control form of MPC. The eventual practical success of these methods will depend on progress in the development of the various optimization algorithms and tools so that problems of realistic size can be tackledAlberto Bemporadalberto.bemporad@imtlucca.itManfred Morari2011-07-27T09:09:04Z2014-07-17T12:48:28Zhttp://eprints.imtlucca.it/id/eprint/583This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5832011-07-27T09:09:04ZOn the equivalence of classes of hybrid dynamical modelsWe establish equivalences among five classes of hybrid systems, that we have encountered in previous research: mixed logical dynamical systems, linear complementarity systems, extended linear complementarity systems, piecewise affine systems, and max-min-plus-scaling systems. These results are of paramount importance for transferring properties and tools from one class to anotherW.P.M.H. HeemelsBart De SchutterAlberto Bemporadalberto.bemporad@imtlucca.it2011-07-27T09:09:02Z2014-07-17T12:46:56Zhttp://eprints.imtlucca.it/id/eprint/584This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5842011-07-27T09:09:02ZOn hybrid systems and closed-loop MPC systemsThe following five classes of hybrid systems were proved by W.P.M.H. Heemels et al. (2001) to be equivalent: linear complementarity (LC) systems, extended linear complementarity (ELC) systems, mixed logical-dynamical (MLD) systems, piecewise affine (PWA) systems and max-min-plus-scaling (MMPS) systems. Some of the equivalences were obtained under additional assumptions, such as boundedness of system variables. In this paper, for closed-loop linear or hybrid plants with model-predictive control (MPC) based on a linear model and fulfilling linear constraints on the input and state variables, we provide a simple and direct proof that the closed-loop system (cl-MPC) is a subclass of any of the former five classes of hybrid systems. This result opens up the use of tools developed for hybrid systems (such as stability, robust stability and safety analysis tools) to study the closed-loop properties of MPCAlberto Bemporadalberto.bemporad@imtlucca.itW.P.M.H. HeemelsBart De Schutter2011-07-27T09:08:58Z2014-07-17T12:46:26Zhttp://eprints.imtlucca.it/id/eprint/586This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5862011-07-27T09:08:58ZSuboptimal explicit MPC via approximate multiparametric quadratic programmingAlgorithms for solving multiparametric quadratic programming (mp-QP) were proposed in Bemporad et al. (2001) and Tondel et al. (2001) for computing explicit model predictive control (MPC) laws. The reason for this interest is that the solution to mp-QP is a piecewise affine function of the state vector and thus it is easily implementable on-line. The main drawback of solving mp-QP exactly is that whenever the number of linear constraints involved in the optimization problem increases, the number of polyhedral cells in the piecewise affine partition of the parameter space may increase exponentially. We address the problem of finding approximate solutions to mp-QP, where the degree of approximation is arbitrary and allows a trade off between optimality and a smaller number of cells in the piecewise affine solutionAlberto Bemporadalberto.bemporad@imtlucca.itCarlo Filippi2011-07-27T09:08:55Z2014-07-09T14:43:59Zhttp://eprints.imtlucca.it/id/eprint/580This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5802011-07-27T09:08:55ZEfficient on-line computation of constrained optimal control For discrete-time linear time-invariant systems with constraints on inputs and outputs, the constrained finite-time optimal controller can be obtained explicitly as a piecewise-affine function of the initial state via multi-parametric programming. By exploiting the properties of the value function, we present two algorithms that efficiently perform the online evaluation of the explicit optimal control law both in terms of storage demands and computational complexity. The algorithms are particularly effective when used for model-predictive control (MPC) where an open-loop constrained finite-time optimal control problem has to be solved at each sampling timeFrancesco BorrelliMato BaoticAlberto Bemporadalberto.bemporad@imtlucca.itManfred Morari2011-07-27T09:08:53Z2014-07-17T12:46:08Zhttp://eprints.imtlucca.it/id/eprint/578This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5782011-07-27T09:08:53ZPiecewise linear robust model predictive controlFor discrete-time linear time-invariant systems with input disturbances and constraints on inputs and states, we develop an algorithm to determine explicitly, as a function of the initial state, the solution to robust optimal control problems based on min-max optimization. We show that the optimal control sequence is a piecewise linear function of the initial state. Thus, when the optimal control problem is solved at each time step according to a moving horizon scheme, the on-line computation of the resulting MPC controller is reduced to a simple linear function evaluation. In this paper the uncertainty is modeled as an additive norm-bounded input disturbance vector. The technique can be also extended to robust control of constrained systems affected by polyhedral parametric uncertainty.Alberto Bemporadalberto.bemporad@imtlucca.itFrancesco BorrelliManfred Morari2011-07-27T09:08:51Z2014-07-17T12:40:36Zhttp://eprints.imtlucca.it/id/eprint/576This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5762011-07-27T09:08:51ZOptimal piecewise-linear control of dry clutch engagementBased on a discrete-time second order state-space dynamic model of the powertrain system, a piecewise feedback control for the dry clutch engagement process is proposed. The engine speed and the clutch disk speed are assumed to be measurable and the control input is the normal engaging force applied to the disks. The controller is designed by minimizing a quadratic performance index subject to constraints on the normal force, normal force derivative, and engine speed. The resulting Model Predictive Controller (MPC) is shown to consist of a piecewise linear feedback control: the state space can be divided into several regions, such that in each region an off-line computed linear controller must be implemented. The explicit piecewise linear form of the MPC law is obtained by using a multiparametric programming solver and can be tuned so that fast engagement, small friction losses and smooth lock-up are achieved. The paper reports numerical results, carried out by a Simulink/MPC Toolbox simulation scheme and a realistic set of parameters, showing the good performance of the closed-loop system.Alberto Bemporadalberto.bemporad@imtlucca.itFrancesco BorrelliLuigi GlielmoFrancesco Vasca2011-07-27T09:08:49Z2014-07-17T12:40:08Zhttp://eprints.imtlucca.it/id/eprint/579This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/5792011-07-27T09:08:49ZHybrid control of dry clutch engagementThis paper proposes a novel piecewise linear feedback control strategy for the automotive dry clutch engagement process. Based on a dynamic model of the powertrain system, the controller is designed by minimizing a quadratic performance index subject to constraints on the inputs and on the states. The resulting model predictive controller is shown to consist of a piecewise linear feedback control and can be tuned so that fast engagement, small friction losses and smooth lock-up are achieved. Numerical results show the good performance of the closed-loop system.Alberto Bemporadalberto.bemporad@imtlucca.itFrancesco BorrelliLuigi GlielmoFrancesco Vasca2011-07-27T09:08:46Z2014-07-17T12:39:43Zhttp://eprints.imtlucca.it/id/eprint/458This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4582011-07-27T09:08:46ZDiscrete-time hybrid modeling and verification of the batch evaporator process benchmarkFor hybrid systems described by interconnections of linear discrete-time dynamical systems, automata, and propositional logic rules, we recently proposed the Mixed Logical Dynamical (MLD) systems formalism and the language HYSDEL (Hybrid System Descrip- tion Language) as a modeling tool. For MLD models, we developed a reachability analysis algorithm which combines forward reach set computation and feasibility analysis of trajectories by linear and mixed-integer linear programming. In this paper the versatility of the overall analysis tool is illustrated on the batch evaporator benchmark process. Alberto Bemporadalberto.bemporad@imtlucca.itFabio Danilo TorrisiManfred Morari2011-07-27T09:08:06Z2014-07-17T12:38:20Zhttp://eprints.imtlucca.it/id/eprint/457This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/4572011-07-27T09:08:06ZEquivalence of hybrid dynamical modelsThis paper establishes equivalences among five classes of hybrid systems: mixed logical dynamical (MLD) systems, linear complementarity (LC) systems, extended linear complementarity (ELC) systems, piecewise affine (PWA) systems, and max-min-plus-scaling (MMPS) systems. Some of the equivalences are established under (rather mild) additional assumptions. These results are of paramount importance for transferring theoretical properties and tools from one class to another, with the consequence that for the study of a particular hybrid system that belongs to any of these classes, one can choose the most convenient hybrid modeling framework.W.P.M.H. HeemelsBart De SchutterAlberto Bemporadalberto.bemporad@imtlucca.it2011-07-05T11:10:24Z2011-08-31T14:40:40Zhttp://eprints.imtlucca.it/id/eprint/703This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/7032011-07-05T11:10:24ZGlobal Competitiveness in Pharmaceuticals: A European PerspectiveFabio Pammollif.pammolli@imtlucca.itAlfonso GambardellaLuigi Orsenigo2011-06-30T14:28:11Z2011-10-07T08:27:21Zhttp://eprints.imtlucca.it/id/eprint/629This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/6292011-06-30T14:28:11ZTechnological change and network dynamics: Lessons from the pharmaceutical industryIn this paper, we investigate how underlying relevant technological conditions induce distinguishable patterns of change in industry structure and evolution. A mapping is detected between the specific nature of problem decompositions and research techniques at the micro level of knowledge bases, and patterns of structural evolution at the macro level of the industry network. The graph-theoretic techniques we introduce map major technological discontinuities on changes observed at the level of dominant organization forms. They might have applications in other domains, whenever the identification of structural breaks and homological relationships between technological and industrial spaces are important issues.Fabio Pammollif.pammolli@imtlucca.itLuigi OrsenigoMassimo Riccabonimassimo.riccaboni@imtlucca.it2011-06-30T14:25:58Z2011-08-31T14:40:39Zhttp://eprints.imtlucca.it/id/eprint/649This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/6492011-06-30T14:25:58ZInnovation and corporate growth in the evolution of the drug industryThis work studies the processes of growth of the worlds top 150 pharmaceutical firms, on the grounds of an original database which also allows disaggregate analysis at the level of single therapeutical classes and chemical entities. Our findings show that the industry -- whose long-term evolution is driven by innovation, imitation and permanent creation of new markets -- displays (i) "fat tails" in the distribution of growth shocks, present at all levels of aggregation, with (relatively rare) big "spurs of growth", (ii) a significant autocorrelation of growth rates, (iii) a fall of variance of growth rates with size entirely dependent on corporate diversification patterns, in turn plausibly shaped by the "competence scope" of each firm, and (iv) different "lifecycles" of diverse types of products, and persistent forms of heterogeneity across firms in terms of innovative output, which, however, do not not seem to affect comparative growth performances.Fabio Pammollif.pammolli@imtlucca.itGiulio BottazziGiovanni DosiMarco LippiMassimo Riccabonimassimo.riccaboni@imtlucca.it2011-06-30T14:25:20Z2011-08-31T14:40:40Zhttp://eprints.imtlucca.it/id/eprint/656This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/6562011-06-30T14:25:20ZVariety and Irreversibility in Scientific and Technological Systems: the Evolution of an Industry NetworkFabio Pammollif.pammolli@imtlucca.itLuigi OrsenigoMassimo Riccabonimassimo.riccaboni@imtlucca.it2011-06-30T14:24:14Z2011-08-31T14:40:39Zhttp://eprints.imtlucca.it/id/eprint/665This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/6652011-06-30T14:24:14ZThe Nature and the Extent of Markets for TechnologyFabio Pammollif.pammolli@imtlucca.itAshish AroraAlfonso GambardellaMassimo Riccabonimassimo.riccaboni@imtlucca.it2011-06-09T08:19:03Z2011-07-11T14:36:26Zhttp://eprints.imtlucca.it/id/eprint/331This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3312011-06-09T08:19:03ZDivergence in testing and readiness semanticsMany variants of must-testing semantics have been put forward that are equally sensitive to deadlock, but differ for the stress they put on divergence, i.e. on the possibility for systems of getting involved in infinite internal computations. Safe-testing is one such variant, that naturally pops up when studying the behavioural pre-congruences induced by certain basic observables. Here, we study the relationship between safe-testing and Olderog's readiness semantics, a semantics induced by a natural process logic. We show that safe-testing is finer than readiness, and coincides with a refinement of readiness obtained by tuning Olderog's definition. For both safe-testing and the original readiness semantics we propose simple complete axiomatizations, which permit a fuller appreciation of their similarities and differences.Michele BorealeRocco De Nicolar.denicola@imtlucca.itRosario Pugliese2011-06-06T09:50:50Z2011-07-11T14:36:26Zhttp://eprints.imtlucca.it/id/eprint/327This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3272011-06-06T09:50:50ZTranslating Strong Mobility into Weak MobilityMobile agents are software objects that can be transmitted over the net together with data and code, or can autonomously migrate to a remote computer and execute automatically on arrival. However many frameworks and languages for mobile agents only provide weak mobility: agents do not resume their execution from the instruction following the migration action, instead they are always restarted from a given point. In this paper we present a purely syntactic translation process for transforming programs that use strong mobility into programs that rely only on weak mobility, while preserving the original semantics.This transformation applies to programs written in a procedural language and can be adapted to other languages, like Java, that provide means to send data and code, but not the execution state.It has actually been exploited for implementing our language for mobile agents X-Klaim, that has linguistic constructs for strong mobility.
Lorenzo BettiniRocco De Nicolar.denicola@imtlucca.it2011-06-06T08:45:50Z2011-07-11T14:36:26Zhttp://eprints.imtlucca.it/id/eprint/329This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3292011-06-06T08:45:50ZProof Techniques for Cryptographic ProcessesContextual equivalences for cryptographic process calculi, like the spi-calculus, can be used to reason about correctness of protocols, but their definition suffers from quantification over all possible contexts. Here, we focus on two such equivalences, namely may-testing and barbed equivalence, and investigate tractable proof methods for them. To this aim, we design an enriched labelled transition system, where transitions are constrained by the knowledge the environment has of names and keys. The new transition system is then used to define a trace equivalence and a weak bisimulation equivalence that avoid quantification over contexts. Our main results are soundness and completeness of trace and weak bisimulation equivalence with respect to may-testing and barbed equivalence, respectively. They lead to more direct proof methods for equivalence checking. The use of these methods is illustrated with a few examples concerning implementation of secure channels and verification of protocol correctness.Michele BorealeRocco De Nicolar.denicola@imtlucca.itRosario Pugliese2011-05-31T12:34:16Z2011-07-11T14:36:26Zhttp://eprints.imtlucca.it/id/eprint/330This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/3302011-05-31T12:34:16ZAlgebraic characterizations of trace and decorated trace equivalences over tree-like structuresBehavioural equivalences of labelled transition systems are characterized in terms of homomorphic transformations. This permits relying on algebraic techniques for proving systems properties and reduces equivalence checking of two systems to studying the relationships among the elements of their structures. Different algebraic characterizations of bisimulation-based equivalences in terms of particular transition system homomorphisms have been proposed in the literature. Here, it is shown that trace and decorated trace equivalences can neither be characterized in terms of transition system homomorphisms, nor be defined locally, i.e., only in terms of action sequences of bounded length and of root-preserving maps. However, results similar to those for bisimulation can be obtained for restricted classes of transition systems. For tree-like systems, we present the algebraic characterizations of trace equivalence and of three well-known decorated trace equivalences, namely ready, ready trace equivalence and failure.Xiao Jun ChenRocco De Nicolar.denicola@imtlucca.it2011-05-18T08:54:26Z2014-10-07T14:41:43Zhttp://eprints.imtlucca.it/id/eprint/171This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1712011-05-18T08:54:26ZTrail-directed model checkingHSF-SPIN is a Promela model checker based on heuristic search strategies. It utilizes heuristic estimates in order to direct the search for finding software bugs in concurrent systems. As a consequence, HSF-SPIN is able to find shorter trails than blind depth-first search.
This paper contributes an extension to the paradigm of directed model checking to shorten already established unacceptable long error trails. This approach has been implemented in HSF-SPIN. For selected benchmark and industrial communication protocols experimental evidence is given that trail-directed model-checking effectively shortcuts existing witness paths.
Stefan EdelkampAlberto Lluch-Lafuentealberto.lluch@imtlucca.itStefan Leue2011-05-17T14:37:17Z2011-07-11T14:34:35Zhttp://eprints.imtlucca.it/id/eprint/170This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1702011-05-17T14:37:17ZDirected Explicit Model Checking with HSF-SPINWe present the explicit state model checker HSF-SPIN which is based on the model checker SPIN and its Promela modeling language. HSF-SPIN incorporates directed search algorithms for checking safety and a large class of LTL-specified liveness properties. We start off from the A* algorithm and define heuristics to accelerate the search into the direction of a specified failure situation. Next we propose an improved nested depth-first search algorithm that exploits the structure of Promela Never-Claims. As a result of both improvements, counterexamples will be shorter and the explored part of the state space will be smaller than with classical approaches, allowing to analyze larger state spaces. We evaluate the impact of the new heuristics and algorithms on a set of protocol models, some of which are real-world industrial protocols.
Stefan EdelkampAlberto Lluch-Lafuentealberto.lluch@imtlucca.itStefan Leue2011-03-10T11:08:53Z2011-07-11T14:27:37Zhttp://eprints.imtlucca.it/id/eprint/200This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/2002011-03-10T11:08:53ZBruno Leoni Filosofo della politicaAn examination of the University lectures delivered by Bruno Leoni in Pavia suggests that it is fair to claim that Leoni had been studying the judicial thought of the Greek and Roman period in order to understand whether it was possible to single out a connection between the process by which Law comes about and the natural feeling of justice, which belongs to every individual and not just to the legislator. In this regard, Leoni captures meaningful elements by observing both the distinction made by the Greeks between nomos, physis and thesis (which Hayek developed later), and the Aristotelian theory of commutative equality (which is considered as the first attempt to study both law and economics) and, above all, the Roman " science of Law ", which aimed to discover the law rather than to produce it (an idea developed in Freedom and the Law). After discovering Austrian marginalism Leoni realised the importance of comparing economic method with the study of law and politics. By reflecting on such a comparison and the idea of power, which Leoni considered as resources shared amongst all individuals, he achieved, by the end of the Fifties, some original definitions for the concepts of Law, Policy and State, which place him in a pivotal position within the politological studies of that period. A few years later, through his portrayal of the process of Law-making, which starts with each individual and with the exchange of his own powers and claims with other individuals, Leoni reached his well-known theory of " Law as Individual Claim ". This implied a significant shift from the former predominant legal perspective — a shift that is comparable to the " marginalistic revolution " which took place in economic methodology. Moreover, according to Leoni, the starting point in the study of the Law should involve a weighing of the common individual claims as something that paves the way for Law. This theory may be considered a new philosophical vision of the social order, in which the idea of exchange lies at the heart of every single aspect of society, and which led Leoni to give a lesser role to the concept of coercion within society. Antonio Masalaa.masala@imtlucca.it2011-03-10T10:43:48Z2011-07-11T14:27:37Zhttp://eprints.imtlucca.it/id/eprint/199This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1992011-03-10T10:43:48ZNatural Right, Providence, and Order: Frédéric Bastiat's Laissez-FaireThe paper suggests that Bastiat’s theory of interests, harmony, and the State is rooted in a particular conception of Natural Right, in which the Lockeans and thomistic streams of thought meet. But it also suggests that Bastiat’s interpretation of the role that Providence plays in human events is not able to give a sustainable theory of liberal order. The paper also considers the criticisms to Bastiat’s economic and political theory coming from exponents of classical liberalism, from the Austrians, and from Catholic thinkers of that time, such as L. Taparelli d’Azeglio and M. Liberatore.
The conclusion is that although the economic theory of Bastiat is by now obsolete from the conceptual point of view, his political theory and his criticism of the state do remain extraordinarily topical.
Cet article suggère que les théories des intérêts, de l’harmonie et de l’Etat de Bastiat sont ancrées dans une conception particulière du droit naturel au confluent des pensées lockéenne et thomiste. Cependant, il suggère aussi que l’interprétation que donne Bastiat du rôle de la Providence dans les affaires humaines ne débouche pas sur une théorie recevable de l’ordre libéral. L’article examine aussi les critiques qu’adressent les partisans du libéralisme classique-tels que les économistes autrichiens, les penseurs catholiques de l’époque comme L. Taparelli d’Azeglio et M. Liberatore-à l’égard des théories économiques et politiques de Bastiat. L’article conclut que le caractère obsolète des théories de Bastiat d’un point de vue conceptuel ne remet pas en cause la singulière actualité de sa théorie politique et de sa critique de l’Etat.Raimondo CubedduAntonio Masalaa.masala@imtlucca.it2011-03-01T11:14:20Z2011-07-11T14:33:43Zhttp://eprints.imtlucca.it/id/eprint/134This item is in the repository with the URL: http://eprints.imtlucca.it/id/eprint/1342011-03-01T11:14:20ZHigh-Level Petri Nets as Type Theories in the Join CalculusWe study the expressiveness of the join calculus by comparison with (generalised, coloured) Petri nets and using tools from type theory. More precisely, we consider four classes of nets of increasing expressiveness, ∏ i , introduce a hierarchy of type systems of decreasing strictness, Δ i , i = 0,..., 3, and we prove that a join process is typeable according to Δ i if and only if it is (strictly equivalent to) a net of class ∏ i . In the details, ∏ 0 and ∏ 1 contain, resp., usual place/transition and coloured Petri nets, while ∏ 2 and ∏ 3 propose two natural notions of high-level net accounting for dynamic reconfiguration and process creation and called reconfigurable and dynamic Petri nets, respectively.
Maria Grazia Buscemim.buscemi@imtlucca.itVladimiro Sassone